CA2317438C - Method for maximizing water removal in a press nip - Google Patents
Method for maximizing water removal in a press nip Download PDFInfo
- Publication number
- CA2317438C CA2317438C CA002317438A CA2317438A CA2317438C CA 2317438 C CA2317438 C CA 2317438C CA 002317438 A CA002317438 A CA 002317438A CA 2317438 A CA2317438 A CA 2317438A CA 2317438 C CA2317438 C CA 2317438C
- Authority
- CA
- Canada
- Prior art keywords
- blanket
- web
- nip
- endless fabric
- pressing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000000034 method Methods 0.000 title claims abstract description 77
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title abstract description 51
- 238000003825 pressing Methods 0.000 claims abstract description 144
- 230000002745 absorbent Effects 0.000 claims abstract description 55
- 239000002250 absorbent Substances 0.000 claims abstract description 55
- 238000009826 distribution Methods 0.000 claims abstract description 26
- 239000011800 void material Substances 0.000 claims abstract description 24
- 239000004744 fabric Substances 0.000 claims description 137
- 238000012546 transfer Methods 0.000 claims description 51
- 238000001035 drying Methods 0.000 claims description 27
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- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 3
- NJSSICCENMLTKO-HRCBOCMUSA-N [(1r,2s,4r,5r)-3-hydroxy-4-(4-methylphenyl)sulfonyloxy-6,8-dioxabicyclo[3.2.1]octan-2-yl] 4-methylbenzenesulfonate Chemical compound C1=CC(C)=CC=C1S(=O)(=O)O[C@H]1C(O)[C@@H](OS(=O)(=O)C=2C=CC(C)=CC=2)[C@@H]2OC[C@H]1O2 NJSSICCENMLTKO-HRCBOCMUSA-N 0.000 description 3
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- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 description 2
- 230000002708 enhancing effect Effects 0.000 description 2
- 230000001815 facial effect Effects 0.000 description 2
- ZNNLBTZKUZBEKO-UHFFFAOYSA-N glyburide Chemical compound COC1=CC=C(Cl)C=C1C(=O)NCCC1=CC=C(S(=O)(=O)NC(=O)NC2CCCCC2)C=C1 ZNNLBTZKUZBEKO-UHFFFAOYSA-N 0.000 description 2
- 239000011121 hardwood Substances 0.000 description 2
- 230000002706 hydrostatic effect Effects 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
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- 230000000704 physical effect Effects 0.000 description 2
- 229920002451 polyvinyl alcohol Polymers 0.000 description 2
- 150000003856 quaternary ammonium compounds Chemical class 0.000 description 2
- 230000002787 reinforcement Effects 0.000 description 2
- 238000012827 research and development Methods 0.000 description 2
- 210000004872 soft tissue Anatomy 0.000 description 2
- 239000011122 softwood Substances 0.000 description 2
- 229920001187 thermosetting polymer Polymers 0.000 description 2
- YSGSDAIMSCVPHG-UHFFFAOYSA-N valyl-methionine Chemical compound CSCCC(C(O)=O)NC(=O)C(N)C(C)C YSGSDAIMSCVPHG-UHFFFAOYSA-N 0.000 description 2
- WRIDQFICGBMAFQ-UHFFFAOYSA-N (E)-8-Octadecenoic acid Natural products CCCCCCCCCC=CCCCCCCC(O)=O WRIDQFICGBMAFQ-UHFFFAOYSA-N 0.000 description 1
- LQJBNNIYVWPHFW-UHFFFAOYSA-N 20:1omega9c fatty acid Natural products CCCCCCCCCCC=CCCCCCCCC(O)=O LQJBNNIYVWPHFW-UHFFFAOYSA-N 0.000 description 1
- QSBYPNXLFMSGKH-UHFFFAOYSA-N 9-Heptadecensaeure Natural products CCCCCCCC=CCCCCCCCC(O)=O QSBYPNXLFMSGKH-UHFFFAOYSA-N 0.000 description 1
- 241000609240 Ambelania acida Species 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical group N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 244000099147 Ananas comosus Species 0.000 description 1
- 235000007119 Ananas comosus Nutrition 0.000 description 1
- 240000006248 Broussonetia kazinoki Species 0.000 description 1
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 239000004155 Chlorine dioxide Substances 0.000 description 1
- 241000218631 Coniferophyta Species 0.000 description 1
- RPNUMPOLZDHAAY-UHFFFAOYSA-N Diethylenetriamine Chemical compound NCCNCCN RPNUMPOLZDHAAY-UHFFFAOYSA-N 0.000 description 1
- 229920001875 Ebonite Polymers 0.000 description 1
- BRLQWZUYTZBJKN-UHFFFAOYSA-N Epichlorohydrin Chemical compound ClCC1CO1 BRLQWZUYTZBJKN-UHFFFAOYSA-N 0.000 description 1
- 241000945868 Eulaliopsis Species 0.000 description 1
- 229920002907 Guar gum Polymers 0.000 description 1
- 241001531995 Hesperaloe Species 0.000 description 1
- 241001148717 Lygeum spartum Species 0.000 description 1
- 241000218922 Magnoliophyta Species 0.000 description 1
- 229920000877 Melamine resin Polymers 0.000 description 1
- 240000000907 Musa textilis Species 0.000 description 1
- 240000008790 Musa x paradisiaca Species 0.000 description 1
- 235000018290 Musa x paradisiaca Nutrition 0.000 description 1
- ZQPPMHVWECSIRJ-UHFFFAOYSA-N Oleic acid Natural products CCCCCCCCC=CCCCCCCCC(O)=O ZQPPMHVWECSIRJ-UHFFFAOYSA-N 0.000 description 1
- 239000005642 Oleic acid Substances 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
- 235000007164 Oryza sativa Nutrition 0.000 description 1
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- 240000000111 Saccharum officinarum Species 0.000 description 1
- 235000007201 Saccharum officinarum Nutrition 0.000 description 1
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 1
- 229920002472 Starch Polymers 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 description 1
- 229920001807 Urea-formaldehyde Polymers 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 125000000217 alkyl group Chemical group 0.000 description 1
- 230000029936 alkylation Effects 0.000 description 1
- 238000005804 alkylation reaction Methods 0.000 description 1
- 150000001412 amines Chemical class 0.000 description 1
- 235000019270 ammonium chloride Nutrition 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000010905 bagasse Substances 0.000 description 1
- 238000003490 calendering Methods 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000002752 cationic softener Substances 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 235000019398 chlorine dioxide Nutrition 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000007859 condensation product Substances 0.000 description 1
- 230000001143 conditioned effect Effects 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- DENRZWYUOJLTMF-UHFFFAOYSA-N diethyl sulfate Chemical compound CCOS(=O)(=O)OCC DENRZWYUOJLTMF-UHFFFAOYSA-N 0.000 description 1
- 229940008406 diethyl sulfate Drugs 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000009408 flooring Methods 0.000 description 1
- 238000009432 framing Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000000665 guar gum Substances 0.000 description 1
- 229960002154 guar gum Drugs 0.000 description 1
- 235000010417 guar gum Nutrition 0.000 description 1
- MTNDZQHUAFNZQY-UHFFFAOYSA-N imidazoline Chemical compound C1CN=CN1 MTNDZQHUAFNZQY-UHFFFAOYSA-N 0.000 description 1
- 150000002462 imidazolines Chemical class 0.000 description 1
- QXJSBBXBKPUZAA-UHFFFAOYSA-N isooleic acid Natural products CCCCCCCC=CCCCCCCCCC(O)=O QXJSBBXBKPUZAA-UHFFFAOYSA-N 0.000 description 1
- 239000002655 kraft paper Substances 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000010147 laser engraving Methods 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 238000007620 mathematical function Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- ZQPPMHVWECSIRJ-KTKRTIGZSA-N oleic acid Chemical compound CCCCCCCC\C=C/CCCCCCCC(O)=O ZQPPMHVWECSIRJ-KTKRTIGZSA-N 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 239000010893 paper waste Substances 0.000 description 1
- 239000011087 paperboard Substances 0.000 description 1
- 150000002978 peroxides Chemical class 0.000 description 1
- 230000002085 persistent effect Effects 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 239000005077 polysulfide Substances 0.000 description 1
- 229920001021 polysulfide Polymers 0.000 description 1
- 150000008117 polysulfides Polymers 0.000 description 1
- 235000020004 porter Nutrition 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 235000009566 rice Nutrition 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- GCLGEJMYGQKIIW-UHFFFAOYSA-H sodium hexametaphosphate Chemical compound [Na]OP1(=O)OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])O1 GCLGEJMYGQKIIW-UHFFFAOYSA-H 0.000 description 1
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F3/00—Press section of machines for making continuous webs of paper
- D21F3/02—Wet presses
- D21F3/0209—Wet presses with extended press nip
- D21F3/0218—Shoe presses
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
- D21F11/14—Making cellulose wadding, filter or blotting paper
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
- D21F11/14—Making cellulose wadding, filter or blotting paper
- D21F11/145—Making cellulose wadding, filter or blotting paper including a through-drying process
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F3/00—Press section of machines for making continuous webs of paper
- D21F3/02—Wet presses
- D21F3/0209—Wet presses with extended press nip
- D21F3/0218—Shoe presses
- D21F3/0227—Belts or sleeves therefor
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F3/00—Press section of machines for making continuous webs of paper
- D21F3/02—Wet presses
- D21F3/0281—Wet presses in combination with a dryer roll
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F3/00—Press section of machines for making continuous webs of paper
- D21F3/02—Wet presses
- D21F3/029—Wet presses using special water-receiving belts
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
- D21H25/08—Rearranging applied substances, e.g. metering, smoothing; Removing excess material
- D21H25/12—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with an essentially cylindrical body, e.g. roll or rod
- D21H25/14—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with an essentially cylindrical body, e.g. roll or rod the body being a casting drum, a heated roll or a calender
Abstract
The present invention is a method for maximizing water removal from an absorbent web in a press nip, thus improving the efficiency of a papermaking machine. The present invention uses a pressing unit having a blanket with a void volume and with a pressure profile that maximizes water removal in the press section or on the Yankee dryer of a paper machine. The pressure profile of the pressing unit according to the present invention has a very steep pressure drop at and/or following the exit of a pressure distribution curve in order to maximize water removal by minimizing rewet of the web.
The improved pressure profile according to the present invention results in increased water removal and/or improved line speed, thus improving efficiency. The configuration and low void volume of the pressing unit blank may further increase water removal and/or improve line speed, which also improves efficiency.
The improved pressure profile according to the present invention results in increased water removal and/or improved line speed, thus improving efficiency. The configuration and low void volume of the pressing unit blank may further increase water removal and/or improve line speed, which also improves efficiency.
Description
METHOD FOR MAXIMIZING WATER REMOVAL IN A PRESS NIP
FIELD OF INVENTION
The invention relates to a method for maximizing water removal from an absorbent paper web in a press nip. More particularly, the present invention relates to the use of a shoe press on the Yankee dryer with a pressure profile that maximizes water removal. Still more particularly, the present invention relates to a method for utilizing a very steep pressure drop at and/or foi(owing the exit of a nip curve in order to maximize water removal by minimizing rewet. Finally, the present invention relates to a method for increasing paper machine speed by utilizing a press section that maximizes water removal.
BACKGROUND OF THE INVENTION
In modern society, bath tissue, paper towels, facial tissue, and paper napkins (hereinafter referred to as packaged paper products) have been remarkably successfully consumer products. The success of these paper products stems from the ability of manufacturers to consistently enhance product attributes at lower cost and to meet volume demands on a timely basis. Packaged paper products offer consumers an array of attributes necessary to such jobs as performing the daily tasks of wiping up spills, personal cleansing, and cleaning household goods. For example, paper towels are engineered to be absorbent and strong while wet whereas bath tissue products are expected to be soft to the touch yet strong while in use.
Absorbency and softness are inversely related to strength, often making it difficult to obtain the right balance of attributes. Accordingly, significant research and development efforts are routinely expended to enhance the quality of these products while continuing to reduce cost by, for example, improving the production of these products. Although numerous schemes have been developed and patented, the search by R&D departments continues to seek out new and innovative methods for improving.these products.
There are numerous methods described in the patent literature for improving the quality of packaged paper products. One of the earliest known methods to enhance the quality of consumer paper products is described in U.S. Patent No. 3,301,746 by Sanford and Sisson, assigned to Procter and Gamble Corporation.
This patent describes a papermaking scheme for enhancing product quality by avoiding overall web compression and by using a pattem array of densified regions in the xy plane of the sheet to enhance product strength.
Other early methods for improving the quality of packaged paper products are described in U.S. Patent No. 3,812,000 by Saivucci and Yiannos and U.S. Patent No. 3,821,068 by Shaw. These patents are assigned to Scott Paper Company. Shaw discloses a papermaking scheme for producting soft tissue by avoiding mechanical compression until the sheet has been dried to at least 80% solids. Salvucci and Yiannos disclose a technique for producing a soft tissue structure by avoiding mechanical compression of an elastomeric containing fiber furnish until the consistency of the web is at least 80%
solids.
Thicker more absorbent structures can be made using a low batting papermaking felt as described in U.S. Patent No. 4,533,457 by Curran et al., assigned to Scott Paper Company. U.S. Patent Nos. 5,591,305 and 5,569,358 by Cameron, assigned to James River Corporation disclose a low-batting, high-bulk-generating felt with improved dewatering capabilities.
A more recent method for improving the quality of a through-air-dried sheet is described in U.S. Patent No. 41,440,597 by Wells and Hensler, assigned to Procter and Gamble Company. This patent describes a method for increasing the stretch of a paper web by operating the forming section of a paper machine faster than the through air dryer section of the paper machine. As a result of
FIELD OF INVENTION
The invention relates to a method for maximizing water removal from an absorbent paper web in a press nip. More particularly, the present invention relates to the use of a shoe press on the Yankee dryer with a pressure profile that maximizes water removal. Still more particularly, the present invention relates to a method for utilizing a very steep pressure drop at and/or foi(owing the exit of a nip curve in order to maximize water removal by minimizing rewet. Finally, the present invention relates to a method for increasing paper machine speed by utilizing a press section that maximizes water removal.
BACKGROUND OF THE INVENTION
In modern society, bath tissue, paper towels, facial tissue, and paper napkins (hereinafter referred to as packaged paper products) have been remarkably successfully consumer products. The success of these paper products stems from the ability of manufacturers to consistently enhance product attributes at lower cost and to meet volume demands on a timely basis. Packaged paper products offer consumers an array of attributes necessary to such jobs as performing the daily tasks of wiping up spills, personal cleansing, and cleaning household goods. For example, paper towels are engineered to be absorbent and strong while wet whereas bath tissue products are expected to be soft to the touch yet strong while in use.
Absorbency and softness are inversely related to strength, often making it difficult to obtain the right balance of attributes. Accordingly, significant research and development efforts are routinely expended to enhance the quality of these products while continuing to reduce cost by, for example, improving the production of these products. Although numerous schemes have been developed and patented, the search by R&D departments continues to seek out new and innovative methods for improving.these products.
There are numerous methods described in the patent literature for improving the quality of packaged paper products. One of the earliest known methods to enhance the quality of consumer paper products is described in U.S. Patent No. 3,301,746 by Sanford and Sisson, assigned to Procter and Gamble Corporation.
This patent describes a papermaking scheme for enhancing product quality by avoiding overall web compression and by using a pattem array of densified regions in the xy plane of the sheet to enhance product strength.
Other early methods for improving the quality of packaged paper products are described in U.S. Patent No. 3,812,000 by Saivucci and Yiannos and U.S. Patent No. 3,821,068 by Shaw. These patents are assigned to Scott Paper Company. Shaw discloses a papermaking scheme for producting soft tissue by avoiding mechanical compression until the sheet has been dried to at least 80% solids. Salvucci and Yiannos disclose a technique for producing a soft tissue structure by avoiding mechanical compression of an elastomeric containing fiber furnish until the consistency of the web is at least 80%
solids.
Thicker more absorbent structures can be made using a low batting papermaking felt as described in U.S. Patent No. 4,533,457 by Curran et al., assigned to Scott Paper Company. U.S. Patent Nos. 5,591,305 and 5,569,358 by Cameron, assigned to James River Corporation disclose a low-batting, high-bulk-generating felt with improved dewatering capabilities.
A more recent method for improving the quality of a through-air-dried sheet is described in U.S. Patent No. 41,440,597 by Wells and Hensler, assigned to Procter and Gamble Company. This patent describes a method for increasing the stretch of a paper web by operating the forming section of a paper machine faster than the through air dryer section of the paper machine. As a result of
2 the speed differential, the paper web is inundated into the through air-dryer-fabric leading to enhanced stretch and absorbency properties in the base sheet and resulting product.
Fibers and chemicals can be used to enhance the quality of packaged paper products. For example, U.S. Patent No. 5,320,710 by Reeves et al., assigned to Fort James Corporation describes a new furnish combination extracted from the species Funifera of the genus Hesporaloe in the Agavaceae family. This furnish has fibers which are very long and which have very fine-geometrical attributes known to enhance tissue and towel performance. U.S. Patent No. 3,755,220 by Freimark and Schaftlein, assigned to Scott Paper Company describes a debonding scheme for maintaining wet strength while reducing product dry strength-a method known to enhance the handfeel of towel products.
The use of bulking fibers can improve the quality of the final end product. U.S. Patent No. 3,434,918 by Bernardin, U.S. Patent No. 4,204,504 by Lesas et al., U.S. Patent No. 4,431,481 by Drach et al., U.S. Patent No.
Fibers and chemicals can be used to enhance the quality of packaged paper products. For example, U.S. Patent No. 5,320,710 by Reeves et al., assigned to Fort James Corporation describes a new furnish combination extracted from the species Funifera of the genus Hesporaloe in the Agavaceae family. This furnish has fibers which are very long and which have very fine-geometrical attributes known to enhance tissue and towel performance. U.S. Patent No. 3,755,220 by Freimark and Schaftlein, assigned to Scott Paper Company describes a debonding scheme for maintaining wet strength while reducing product dry strength-a method known to enhance the handfeel of towel products.
The use of bulking fibers can improve the quality of the final end product. U.S. Patent No. 3,434,918 by Bernardin, U.S. Patent No. 4,204,504 by Lesas et al., U.S. Patent No. 4,431,481 by Drach et al., U.S. Patent No.
3,819,470 by Shaw et al., and U.S. Patent No. 5,087,324 by Awofeso et al.
disclose the use of bulking fibers in papermaking webs to improve product attributes like thickness, absorbency, and softness.
U.S. Patent No. 5,348,620 by Hermans et al., assigned to Kimberly-Clark Worldwide Inc. discusses a high consistency/high temperature fiber-treaiment-process using a disperser to improve product attributes. To improvel tissue softness, several approaches are available to the papermaker such al using certain species of hardwood like eucalyptus in stratified webs as disclosed in U.S. Patent No. 4,300,981 by Carstens and U.S. Patent No. 3,994,771 by Morgan et al. These aforementioned patents describe just a few of the many methods developed over the last thirty years to enhance the quality of packaged paper products.
WO 00JS9667 PCT/us99n7097 There are also numerous schemes for enhancing the productivity of paper machines. For example, gap formers have been developed to enhance sheet drainage ultimately leading to increased machine speed. New developments in Yankee hood design and Yankee cylinder design have allowed improvements in heat transfer coefficients and mass transfer coefficients, ultimately leading to enhanced machine speeds. New developments in forming fabrics, e.g., multi-layer and triple-layer forming fabrics, have resulted in improved drainage, better fabric life, and enhanced fiber support. These factors translate into enhanced machine speed and productivity. lmprovements in press felts, e.g. Scapa's SPECTRA TM' felt concept of using a soft polyurethane sandwich near the base of the felt or the use of stratified batting, have led to improvements in felt life, reductions in break-in time, and improvements in water removal at wet presses. These improved press-felt developments have ultimately translated into improved machine speed and productivity. Improvements in Yankee creping adhesives have been helpful to enhance blade wear and reduce sheet plugging.
Continuos creping doctors have alleviated the need to frequently change doctor blades. The last two aforementioned developments have led to improvements in machine speed, reductions in down time, and reductions in paper waste. In spite of all these advances, methods are sought to enhance productivity.
The present invention improves the efficiency of known water removal methods by adding one or more pressing units to the production paper machine, in place of or in conjunction with a suction pressure roll. "Pressing units" according to the present invention include those unrts that physically engage a belt or pressing blanket, which contacts the impression fabric or felt upon which the web travels. "Foraminous endless fabric" as defined in accordance with the present invention includes either an impression fabric or felt. "Pressing unit" as defined in accordance with the present invention includes any press members allowing deformation of the pressing blanket/impression fabric and/or felt/web sandwich to result in asymmetric
disclose the use of bulking fibers in papermaking webs to improve product attributes like thickness, absorbency, and softness.
U.S. Patent No. 5,348,620 by Hermans et al., assigned to Kimberly-Clark Worldwide Inc. discusses a high consistency/high temperature fiber-treaiment-process using a disperser to improve product attributes. To improvel tissue softness, several approaches are available to the papermaker such al using certain species of hardwood like eucalyptus in stratified webs as disclosed in U.S. Patent No. 4,300,981 by Carstens and U.S. Patent No. 3,994,771 by Morgan et al. These aforementioned patents describe just a few of the many methods developed over the last thirty years to enhance the quality of packaged paper products.
WO 00JS9667 PCT/us99n7097 There are also numerous schemes for enhancing the productivity of paper machines. For example, gap formers have been developed to enhance sheet drainage ultimately leading to increased machine speed. New developments in Yankee hood design and Yankee cylinder design have allowed improvements in heat transfer coefficients and mass transfer coefficients, ultimately leading to enhanced machine speeds. New developments in forming fabrics, e.g., multi-layer and triple-layer forming fabrics, have resulted in improved drainage, better fabric life, and enhanced fiber support. These factors translate into enhanced machine speed and productivity. lmprovements in press felts, e.g. Scapa's SPECTRA TM' felt concept of using a soft polyurethane sandwich near the base of the felt or the use of stratified batting, have led to improvements in felt life, reductions in break-in time, and improvements in water removal at wet presses. These improved press-felt developments have ultimately translated into improved machine speed and productivity. Improvements in Yankee creping adhesives have been helpful to enhance blade wear and reduce sheet plugging.
Continuos creping doctors have alleviated the need to frequently change doctor blades. The last two aforementioned developments have led to improvements in machine speed, reductions in down time, and reductions in paper waste. In spite of all these advances, methods are sought to enhance productivity.
The present invention improves the efficiency of known water removal methods by adding one or more pressing units to the production paper machine, in place of or in conjunction with a suction pressure roll. "Pressing units" according to the present invention include those unrts that physically engage a belt or pressing blanket, which contacts the impression fabric or felt upon which the web travels. "Foraminous endless fabric" as defined in accordance with the present invention includes either an impression fabric or felt. "Pressing unit" as defined in accordance with the present invention includes any press members allowing deformation of the pressing blanket/impression fabric and/or felt/web sandwich to result in asymmetric
4 pressure profiles. These pressing'units including pressing blankets are generally discussed in the literature as "shoe presses." Pressing units according to the present invention do not include suction pressure rolls since they lead to symmetrical pressure distributions frequently mathematically described by sine or haversine functions.
Shoe presses have been used to increase water removal at wet presses, ultimately leading to increased machine speed for linerboard grades and more recently, newsprint and fine paper grades. The idea of extending the time in a press nip as a means to enhance water removal is not a new idea. Nissan in 1954 published a paper in Tappi, Vol. 37, No.12, p.597 (1954) suggesting that the use of extended time in a press nip would enhance the water removal performance of a press. Over twenty-five years, ago Busker published an early paper in Tappi, Vol. 54, No.3, p.373 (1971) on the use of extended nip times, as a means to enhance water removal. Beloit Corporation commercialized the first open belt wide shoe press on a linerboard machine in 1980 as described in an article by J. Blackledge presented during the 2"d International Pira Conference, entitled 'Modern Technologies in Pressing and Drying', Nov 6-8, 1990, p. 1.
Figure 1 shows a typical closed belt wide shoe press (see Figure 2 in an article entitled "New Pressing Tecthnologies for Multiply Board" by J.
Breiten in 81s' Annual Meeting, Techdical Section, CPPA, p. A137 for a more detailed drawing). A wide shoe press as described in the literature is essentially a controlled crown roll with a flexible shell and a concave shoe hydrodynamically loaded against each other. The belt or blanket is usually a fabric reinforced polyurethane-coated structure that can be grooved or blind drilled for more efficient water removal. The inside of the belt is generally lubricated with oil, which develops a hydrodynamic film as it passes over the shoe and reduces wear/friction in both surfaces. Wide shoe press nips are on average 5 to 10 times longer than conventional roll press nips (generally, 5" -
Shoe presses have been used to increase water removal at wet presses, ultimately leading to increased machine speed for linerboard grades and more recently, newsprint and fine paper grades. The idea of extending the time in a press nip as a means to enhance water removal is not a new idea. Nissan in 1954 published a paper in Tappi, Vol. 37, No.12, p.597 (1954) suggesting that the use of extended time in a press nip would enhance the water removal performance of a press. Over twenty-five years, ago Busker published an early paper in Tappi, Vol. 54, No.3, p.373 (1971) on the use of extended nip times, as a means to enhance water removal. Beloit Corporation commercialized the first open belt wide shoe press on a linerboard machine in 1980 as described in an article by J. Blackledge presented during the 2"d International Pira Conference, entitled 'Modern Technologies in Pressing and Drying', Nov 6-8, 1990, p. 1.
Figure 1 shows a typical closed belt wide shoe press (see Figure 2 in an article entitled "New Pressing Tecthnologies for Multiply Board" by J.
Breiten in 81s' Annual Meeting, Techdical Section, CPPA, p. A137 for a more detailed drawing). A wide shoe press as described in the literature is essentially a controlled crown roll with a flexible shell and a concave shoe hydrodynamically loaded against each other. The belt or blanket is usually a fabric reinforced polyurethane-coated structure that can be grooved or blind drilled for more efficient water removal. The inside of the belt is generally lubricated with oil, which develops a hydrodynamic film as it passes over the shoe and reduces wear/friction in both surfaces. Wide shoe press nips are on average 5 to 10 times longer than conventional roll press nips (generally, 5" -
5 10" versus 1" - 2"). Water deflectors (not shown) on the outside surface will dewater the blanket. By utilizing such a wide nip, loads up to 10,000 pli are possible without the risk of damaging blankets and felts or crushing the sheet.
The exit side of the shoe features a sharply curved nose designed to pull the sheet directly out of the nip and away from the felt, thus reducing rewet and improving sheet dryness. U.S. Patent No. 4,931,142 describes certain advantages to this type of take off angle in conjunction with long press riips.
Rolls do not normally support the belt loop of the wide shoe press. The loop generally is closed off with special head assemblies for containing the oil.
Numerous schemes for improving the operation of shoe presses have been developed over the years. For example, in U.S. Patent No. 5,043,046 by Laapotti and assigned to Valmet Corporation, U.S. Patent No. 4,625,376 by Schiel et al. and assigned to Voith Corporation, and U.S. Patent No.
4,673,461 by Roerig and assigned to Beloit Corporation, methods are described to enclose the shoe press in order to contain the oil within the unit. U.S. Patent No. 5,167,768 by Cronin and Roerig and assigned to Beloit Corporation and U.S. Patent No. 5,582,689 by Rolf Van Haag and Hans-Rolf Conard and assigned to Voith Corporation describe methods for varying the pressure distribution in a shoe press. This capability avoids the need to offset the center of loading or reshape the shoe to change the pressure distribution.
U.S. Patent No. 5,693,186 by Vallius, assigned to Valmet Corporation describes a tension link scheme for containing the loading within the framing of the shoe press apparatus. This scheme ultimately avoids the need to fortify flooring when operating at high line loads. These are just a few of the many developments that have led to improved operating shoe presses.
In the art of pressing linerboard, newsprint, and fine paper webs with a shoe press, a long shoe with a gradual pressure rise is desirable for good dewatering and enhanced bulk properties. This is especially true for flow
The exit side of the shoe features a sharply curved nose designed to pull the sheet directly out of the nip and away from the felt, thus reducing rewet and improving sheet dryness. U.S. Patent No. 4,931,142 describes certain advantages to this type of take off angle in conjunction with long press riips.
Rolls do not normally support the belt loop of the wide shoe press. The loop generally is closed off with special head assemblies for containing the oil.
Numerous schemes for improving the operation of shoe presses have been developed over the years. For example, in U.S. Patent No. 5,043,046 by Laapotti and assigned to Valmet Corporation, U.S. Patent No. 4,625,376 by Schiel et al. and assigned to Voith Corporation, and U.S. Patent No.
4,673,461 by Roerig and assigned to Beloit Corporation, methods are described to enclose the shoe press in order to contain the oil within the unit. U.S. Patent No. 5,167,768 by Cronin and Roerig and assigned to Beloit Corporation and U.S. Patent No. 5,582,689 by Rolf Van Haag and Hans-Rolf Conard and assigned to Voith Corporation describe methods for varying the pressure distribution in a shoe press. This capability avoids the need to offset the center of loading or reshape the shoe to change the pressure distribution.
U.S. Patent No. 5,693,186 by Vallius, assigned to Valmet Corporation describes a tension link scheme for containing the loading within the framing of the shoe press apparatus. This scheme ultimately avoids the need to fortify flooring when operating at high line loads. These are just a few of the many developments that have led to improved operating shoe presses.
In the art of pressing linerboard, newsprint, and fine paper webs with a shoe press, a long shoe with a gradual pressure rise is desirable for good dewatering and enhanced bulk properties. This is especially true for flow
6
7 PCT/US99/27097 controlled webs. Linerboard and to a certain extent newsprint and fine paper have flow controlled pressing conditions. Flow controlled pressing conditions occur when the time in the nip becomes an important factor determining the amount of water removed from the web: High pressure can be attained with these long shoes but it requires high line loads. Figure 2 shows the relationship between peak pressure (i.e., the maximum pressure in the nip) and line load (i.e., the total force divided by linear width) for shoe press nips compiled from an extensive but not exhaustive search of the literature. Table I describes the literature references used to develop Figure 2.
Table i: References Used to Generate Figure 2.
Reference Source Number 1 U.S. Patent No. 5,167,768 2 W. Schuwerk, Paper Age, September, 1997, p:18.
3 N. Anderson, Joumai of Tappik, Vol. 21, No. 1, 1998, p.52.
4 J. Kinnunen and A. Kiviranta, Paperi Ja Puu-Paper and Timber Vol. 74, No. 4, 1992, p. 314.
5 J. Kivimaa, M. Laurikainen, and K. Pansu, PITA
Water Removal Conference 1997 York, Paper Technology, April, 1998.
6 J. Blacklege and D. Lange, 2nd Intemational Pira Conference, "Modem Technologies in Pressing and D in ", Nov. 6-8, 1990, p.1.
7 M. Radtke, 79th Annual Meeting, Technical Section, CPPA, p. A221.
Table i: References Used to Generate Figure 2.
Reference Source Number 1 U.S. Patent No. 5,167,768 2 W. Schuwerk, Paper Age, September, 1997, p:18.
3 N. Anderson, Joumai of Tappik, Vol. 21, No. 1, 1998, p.52.
4 J. Kinnunen and A. Kiviranta, Paperi Ja Puu-Paper and Timber Vol. 74, No. 4, 1992, p. 314.
5 J. Kivimaa, M. Laurikainen, and K. Pansu, PITA
Water Removal Conference 1997 York, Paper Technology, April, 1998.
6 J. Blacklege and D. Lange, 2nd Intemational Pira Conference, "Modem Technologies in Pressing and D in ", Nov. 6-8, 1990, p.1.
7 M. Radtke, 79th Annual Meeting, Technical Section, CPPA, p. A221.
8 J. Breiten, 811 Annual Meeting, Technical Section, CPPA, p. A137.
9 E. Tenfalt, J. Wilmenius, and 0. Swanberg, Nordic Pulp and Paper Research Joumal, 1998, p.16:
10 D. Lange and M. Radtke, Papermaker, July 1996, p. 16.
11 "Chemical Systems Boost Dry Content", PPI, February, 1989, p. 41.
The graph in Figure 2 shows that shoe presses normally operate at high line load conditions, usually greater than 270kN/m and at high peak WO 00/24667 PC'T/US99R7097 pressures. It also shows that shoe presses are not operated at low line loads and at high peak pressures (e.g., see the crosshatched region in Figure 2).
In the art of making tissue by the conventional wet pressing operation, Yankee dryers are loaded with suction pressure rolls to remove water from the tissue web and attach the web to the dryer for further processing by the creping operation. The pressure distribution in the suction pressure roll nip is symmetrical in shape and is described mathematically by a sine or a haversine curve. Suction pressure rolls loaded to a Yankee dryer are routinely run at line loads less than 100 kN/m and at peak pressures of less than 4500 kN/ml. In the lower left-hand comer of Figure 2 some typical peak pressure versus line load data for suction pressure rolls are shown. The deflection of large, conventional Yankee dryers due to hoop stress levels limits the line load to less than about 100 kN/m. As a result, it is very difficult to attain high peak pressures in the nip at these low line loads, since the pressure distribution cannot be altered. This limitation has extreme consequences for tissue grades since they are pressure controlled, i.e., the flow resistance in the web is low due to the use of high freeness fumishes and low basis weight webs, thus it is believed that peak pressure, not time in the nip, controls press dewatering. These suction pressure rolls suffer from other disadvantages. For example, since the nip diverges after the maximum pressure is achieved, rewet can occur for a large part of the press nip. A
typical suction pressure roll curve appears in Figure 3, where nip divergence is apparent. Also, the suction pressure roll unit is not flexible so that the line load needs to be fixed and matched to a given Yankee crown condition in order to obtain a uniform nip profile across the machine. Furthermore, since the loading cylinders are located at each end of the pressure roll, profiling capabilities are very limited.
The use of conventional shoe presses on a Yankee dryer at the maximum hoop stress limit of 100kN/m would lead to very low peak pressures as Figures 2 and 3 demonstrate. For example, with a 120 mm shoe at 100 kN/m, the typical peak pressure is on the order of 1700 kN/m as Figure 3 demonstrates. Since the press nip for low weight tissue and towel grades is pressure controlled, the very low peak pressure could cause a decrease in post press dryness, ultimately causing a loss in production. The counter roll in a conventional shoe press is small by comparison to the diameter of a Yankee dryer. As a result, the use of a conventional shoe shape would make it very difficult to remove the felt/fabric from the sheet at the nip exit.
Therefore, conventional shoe shapes and conventional felt/fabric takeoff angles would exacerbate rewet for low weight absorbent products.
Currently, there are no commercial uses of shoe press technology in the production of absorbent paper products. U.S. Patent No. 5,795,440 by Ampulski et al., and U.S. Patent No. 5,776,307 by Ampulski et al.-both assigned to Procter and Gamble Corporation describe a scheme for making a shaped web by pressing an embryonic web into an imprinting fabric between two felts. These patents use a shoe press assembly in the preparation of a wet pressed paper web.
Ampulski et al., like others using pressing units, teaches the use of longer conventional press nips. Ampulski et al. discioses that the nip length is greater than 3.0 inches and may be as long as 20.0 inches. Ampuiski et al.
achieves this extended nip length through the use of a shoe press. Ampulski et al., like all previous users of shoe presses, fails to consider the use of increased peak pressure.
International patent application WO 97/43483 by Hermans and Friedbaurer, assigned to Kimberly-Clark Worldwide, Inc.
discloses that extended nip presses, while having been successfully used for making paperboard, have not been used to make low density paper products such as tissue because the high pressure and longer dwell times in an extended nip press serve to densify the sheet beyond that experienced by conventional tissue wet pressing methods. Hermans and Friedbaurer overcome the increased density due to extended nip pressing by incorporating modified resilient fibers (e.g., chemically cross-linked cellulosic fibers) in the web and by wet micro-shaping the web. They also disclose shoe lengths typically in the range of 5 to 10 inches. Like Ampulski et al., Hermans and Friedbaurer do not consider critical peak pressures or line loads as important.
U.S. Patent No. 5,393,384 by Steiner et al., and assigned to J.M.
Voith, GmbH (hereinafter "the '384 patent") generally describes the use of a shoe press in the production of a tissue web. The '384 patent describes the use of a shoe press preceding or contacting a Yankee drying cylinder. The shoe press is used in conjunction with an impermeable belt to reduce remoistening of the sheet by the felt. These authors used the impermeable belt since they state: "the prevailing opinion in selecting suitable drying presses in contingence on the web thickness so far has been that for drying thin webs there areonly simple roll presses suited which generate a sufficiently high contact pressure for a short time, thus optimally removing the water from a thin web (tissue web) due to the short path, whereas shoe type presses are suited essentially for drying thick, heavy webs, since they generate a persistent pressure which allows the water sufficient time for the considerable longer path in leaving the web." Critical peak pressure and line loads are not discussed in the disclosure. Since the shoe press described in this disclosure is conventional, a pressure curve for this type of shoe press is most likely similar to the "typical shoe press curve" illustrated in Figure 3.
Voith, the assignee of the '384 patent, continues to develop the use of a shoe press for the production of paper products. U.S. Patent No. 5,500,092 by Schiel describes a tissue making machine using a triple press nip where the second nip is a shoe press nip. The criticality of pressure distribution shape and peak pressure/line load magnitudes are not disclosed in the '092 patent. In the September 1997 article W. Schuwerk, "Shoe Presses and Sleeves for Newsprint-Concepts and Initial Operating Experience," PaperAge, Pp. 18-23, Voith described the advantages of their NIPCOFLEX shoe press.
According to that article, "(Tjo obtain optimum product characteristics, dewatering in the press must [therefore] show as flat a pressure gradient as possible." In fact, the shoe press described in the article refers to the third section of a newsprint paper machine operating at a line loading of 850 kN/m and a peak pressure of -5.6 MPa, typical of standard conventional shoe designs and well outside the range of the present invention.
U.S. Patent No. 4,931,142-by Steiner, Muller, Schiel, and Flamig, assigned to Vodh Corporation describes a method of eccentrically arranging a press blanket wih respect to the press plane. This arrangement enables the blanket upon leaving the press nip to immediately move steeply downward and away from the sheet in order to reduce remoistening of the web. Methods of varying the felt angle with respect to the traveling web in a double felted press nip were disclosed to avoid remoistening the sheet and for quick release of the sheet from the felt. Steiner et al. also discloses that the joint path of travel of the paper web, felt, and blanket can be made substantially shorter than prior art.
By utilizing the Steiner et al. invention, the joint travel of the felt, web, and blanket can be made equal to zero, i.e., the web can detach itself from the felt directly at the emergence from the press nip. Steiner et al. does not address low line loads and high peak pressures needed for optimum shoe press performance on Yankee dryers. It also does not disclose the need to taper the press shoe to achieve minimized rewet.
U.S. Patent No. 5,556,511 by Bluhm and Gotz, assigned to Suizer-Escher Wyss describes a process for making toilet tissue webs whereby a web is wet pressed in a heated pressing
The graph in Figure 2 shows that shoe presses normally operate at high line load conditions, usually greater than 270kN/m and at high peak WO 00/24667 PC'T/US99R7097 pressures. It also shows that shoe presses are not operated at low line loads and at high peak pressures (e.g., see the crosshatched region in Figure 2).
In the art of making tissue by the conventional wet pressing operation, Yankee dryers are loaded with suction pressure rolls to remove water from the tissue web and attach the web to the dryer for further processing by the creping operation. The pressure distribution in the suction pressure roll nip is symmetrical in shape and is described mathematically by a sine or a haversine curve. Suction pressure rolls loaded to a Yankee dryer are routinely run at line loads less than 100 kN/m and at peak pressures of less than 4500 kN/ml. In the lower left-hand comer of Figure 2 some typical peak pressure versus line load data for suction pressure rolls are shown. The deflection of large, conventional Yankee dryers due to hoop stress levels limits the line load to less than about 100 kN/m. As a result, it is very difficult to attain high peak pressures in the nip at these low line loads, since the pressure distribution cannot be altered. This limitation has extreme consequences for tissue grades since they are pressure controlled, i.e., the flow resistance in the web is low due to the use of high freeness fumishes and low basis weight webs, thus it is believed that peak pressure, not time in the nip, controls press dewatering. These suction pressure rolls suffer from other disadvantages. For example, since the nip diverges after the maximum pressure is achieved, rewet can occur for a large part of the press nip. A
typical suction pressure roll curve appears in Figure 3, where nip divergence is apparent. Also, the suction pressure roll unit is not flexible so that the line load needs to be fixed and matched to a given Yankee crown condition in order to obtain a uniform nip profile across the machine. Furthermore, since the loading cylinders are located at each end of the pressure roll, profiling capabilities are very limited.
The use of conventional shoe presses on a Yankee dryer at the maximum hoop stress limit of 100kN/m would lead to very low peak pressures as Figures 2 and 3 demonstrate. For example, with a 120 mm shoe at 100 kN/m, the typical peak pressure is on the order of 1700 kN/m as Figure 3 demonstrates. Since the press nip for low weight tissue and towel grades is pressure controlled, the very low peak pressure could cause a decrease in post press dryness, ultimately causing a loss in production. The counter roll in a conventional shoe press is small by comparison to the diameter of a Yankee dryer. As a result, the use of a conventional shoe shape would make it very difficult to remove the felt/fabric from the sheet at the nip exit.
Therefore, conventional shoe shapes and conventional felt/fabric takeoff angles would exacerbate rewet for low weight absorbent products.
Currently, there are no commercial uses of shoe press technology in the production of absorbent paper products. U.S. Patent No. 5,795,440 by Ampulski et al., and U.S. Patent No. 5,776,307 by Ampulski et al.-both assigned to Procter and Gamble Corporation describe a scheme for making a shaped web by pressing an embryonic web into an imprinting fabric between two felts. These patents use a shoe press assembly in the preparation of a wet pressed paper web.
Ampulski et al., like others using pressing units, teaches the use of longer conventional press nips. Ampulski et al. discioses that the nip length is greater than 3.0 inches and may be as long as 20.0 inches. Ampuiski et al.
achieves this extended nip length through the use of a shoe press. Ampulski et al., like all previous users of shoe presses, fails to consider the use of increased peak pressure.
International patent application WO 97/43483 by Hermans and Friedbaurer, assigned to Kimberly-Clark Worldwide, Inc.
discloses that extended nip presses, while having been successfully used for making paperboard, have not been used to make low density paper products such as tissue because the high pressure and longer dwell times in an extended nip press serve to densify the sheet beyond that experienced by conventional tissue wet pressing methods. Hermans and Friedbaurer overcome the increased density due to extended nip pressing by incorporating modified resilient fibers (e.g., chemically cross-linked cellulosic fibers) in the web and by wet micro-shaping the web. They also disclose shoe lengths typically in the range of 5 to 10 inches. Like Ampulski et al., Hermans and Friedbaurer do not consider critical peak pressures or line loads as important.
U.S. Patent No. 5,393,384 by Steiner et al., and assigned to J.M.
Voith, GmbH (hereinafter "the '384 patent") generally describes the use of a shoe press in the production of a tissue web. The '384 patent describes the use of a shoe press preceding or contacting a Yankee drying cylinder. The shoe press is used in conjunction with an impermeable belt to reduce remoistening of the sheet by the felt. These authors used the impermeable belt since they state: "the prevailing opinion in selecting suitable drying presses in contingence on the web thickness so far has been that for drying thin webs there areonly simple roll presses suited which generate a sufficiently high contact pressure for a short time, thus optimally removing the water from a thin web (tissue web) due to the short path, whereas shoe type presses are suited essentially for drying thick, heavy webs, since they generate a persistent pressure which allows the water sufficient time for the considerable longer path in leaving the web." Critical peak pressure and line loads are not discussed in the disclosure. Since the shoe press described in this disclosure is conventional, a pressure curve for this type of shoe press is most likely similar to the "typical shoe press curve" illustrated in Figure 3.
Voith, the assignee of the '384 patent, continues to develop the use of a shoe press for the production of paper products. U.S. Patent No. 5,500,092 by Schiel describes a tissue making machine using a triple press nip where the second nip is a shoe press nip. The criticality of pressure distribution shape and peak pressure/line load magnitudes are not disclosed in the '092 patent. In the September 1997 article W. Schuwerk, "Shoe Presses and Sleeves for Newsprint-Concepts and Initial Operating Experience," PaperAge, Pp. 18-23, Voith described the advantages of their NIPCOFLEX shoe press.
According to that article, "(Tjo obtain optimum product characteristics, dewatering in the press must [therefore] show as flat a pressure gradient as possible." In fact, the shoe press described in the article refers to the third section of a newsprint paper machine operating at a line loading of 850 kN/m and a peak pressure of -5.6 MPa, typical of standard conventional shoe designs and well outside the range of the present invention.
U.S. Patent No. 4,931,142-by Steiner, Muller, Schiel, and Flamig, assigned to Vodh Corporation describes a method of eccentrically arranging a press blanket wih respect to the press plane. This arrangement enables the blanket upon leaving the press nip to immediately move steeply downward and away from the sheet in order to reduce remoistening of the web. Methods of varying the felt angle with respect to the traveling web in a double felted press nip were disclosed to avoid remoistening the sheet and for quick release of the sheet from the felt. Steiner et al. also discloses that the joint path of travel of the paper web, felt, and blanket can be made substantially shorter than prior art.
By utilizing the Steiner et al. invention, the joint travel of the felt, web, and blanket can be made equal to zero, i.e., the web can detach itself from the felt directly at the emergence from the press nip. Steiner et al. does not address low line loads and high peak pressures needed for optimum shoe press performance on Yankee dryers. It also does not disclose the need to taper the press shoe to achieve minimized rewet.
U.S. Patent No. 5,556,511 by Bluhm and Gotz, assigned to Suizer-Escher Wyss describes a process for making toilet tissue webs whereby a web is wet pressed in a heated pressing
12 arrangement. The heated pressing arrangement can be a shoe press. This disclosure does not address the importance of proper choice of peak pressure, line load, and shoe shape for making absorbent products at high speeds. In fact, the critically of line ioads and peak pressures is not discussed. Bluhm and Gotz like all previous users of shoe presses, fails to consider the use of increased peak pressure at low line loads as a means to improve water removal.
U.S. Patent No. 4,973,384 by Crouse, Pulkowski, and Porter, assigned to Beloit Corporation describes a process for using a heated extended nip press for optimizing sheet properties without lamination. To accomplish the aforementioned task Crouse et a(.
found that by application of pressure for an increased period of time, the increased residence time enables the removal of more water from the formed web. As a result, these authors teach toward the use of a conventional long shoe design. They also found that for a heated extended nip press by "gradually decreasing pressure in machine direction toward the trailing edge of the shoe, rapid flashing of steam from the emerging pressed web was avoided." As a result these authors teach away from the use of a heavy peaked pressure distribution at the exit side of a shoe press nip.
WO 97/16593 by Wedel and Worcester discloses an impulse drying method for tissue structures using a shoe press and an induction heater. This disclosed impulse-drying method is intended to replace the Yankee dryer with its associated problems. These
U.S. Patent No. 4,973,384 by Crouse, Pulkowski, and Porter, assigned to Beloit Corporation describes a process for using a heated extended nip press for optimizing sheet properties without lamination. To accomplish the aforementioned task Crouse et a(.
found that by application of pressure for an increased period of time, the increased residence time enables the removal of more water from the formed web. As a result, these authors teach toward the use of a conventional long shoe design. They also found that for a heated extended nip press by "gradually decreasing pressure in machine direction toward the trailing edge of the shoe, rapid flashing of steam from the emerging pressed web was avoided." As a result these authors teach away from the use of a heavy peaked pressure distribution at the exit side of a shoe press nip.
WO 97/16593 by Wedel and Worcester discloses an impulse drying method for tissue structures using a shoe press and an induction heater. This disclosed impulse-drying method is intended to replace the Yankee dryer with its associated problems. These
13 WO OOfZ4667 PCT/US99/27097 authors list the issues with Yankee dryers as being limited in surface temperature to 185 F, as being limited in line load to 500 pli due to shell thickness limitations, and as being limited in roll diameter. These authors state that shoe length is typicaliy ten inches for the impulse drying unit.
The line loads disclosed are 1000 pli to10,000 pli. As a result, this application teaches away from the combined use of a low line load with a substantial peak pressure.
Contrary to the current state of the art, the present inventors have, quite unexpectedly, found that in the production of absorbent paper products, the use of a steep, sharp pressure gradient and controlled separation when producing absorbent paper can improve dewatering efficiency without adversely affecting product properties. An example of the pressure profile of the, new shoe design for absorbent paper production according to the present invention is illustrated in Figure 3.
The present inventors unexpectedly discovered that good sheet dewatering and appropriate bulk/strength properties for low weight absorbent products could be attained with this pressure optimized shoe press. The optimized pressure conditions can be achieved according to the present invention by shaping the shoe, tilting the shoe in the shoe press, reducing the length of the shoe in the shoe press, and/or tapering the exit side of the shoe.
In addition, these conditions can also be achieved by deflecting the pressing blanket from the web carrying foraminous-endless-fabric at a point nearly simultaneous with separation of the foraminous-endless-fabric from the
The line loads disclosed are 1000 pli to10,000 pli. As a result, this application teaches away from the combined use of a low line load with a substantial peak pressure.
Contrary to the current state of the art, the present inventors have, quite unexpectedly, found that in the production of absorbent paper products, the use of a steep, sharp pressure gradient and controlled separation when producing absorbent paper can improve dewatering efficiency without adversely affecting product properties. An example of the pressure profile of the, new shoe design for absorbent paper production according to the present invention is illustrated in Figure 3.
The present inventors unexpectedly discovered that good sheet dewatering and appropriate bulk/strength properties for low weight absorbent products could be attained with this pressure optimized shoe press. The optimized pressure conditions can be achieved according to the present invention by shaping the shoe, tilting the shoe in the shoe press, reducing the length of the shoe in the shoe press, and/or tapering the exit side of the shoe.
In addition, these conditions can also be achieved by deflecting the pressing blanket from the web carrying foraminous-endless-fabric at a point nearly simultaneous with separation of the foraminous-endless-fabric from the
14 nascent web, thereby reducing rewet. These techniques enable the pressure optimized shoe press according to the present invention to achieve improved dewatering while maintaining bulk with line loads less than about 240kN/m and peak pressures greater than about 2000 kN/m2.
SUMMARY OF THE INVENTION
Further advantages of the invention will be set forth in part in the description, which follows and in part will be apparent from the description.
The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particulariy pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is disclosed:
An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric; a moving endless pressing blanket; a transfer cylinder, wherein said nascent web is located between said fpraminous endless fabric and said transfer cylinder; and a pressing unit engaging said pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, said pressing unit being configured to impose an asymmetrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless to fabric; a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a transfer cylinder wherein said nascent web is located between said foraminous endless fabric and said transfer cylinder, and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric; a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a backing roll wherein said nascent web is located between said foraminous endless fabric and said backing roll; and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said backing roll thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric;
means for depositing a nascent web for the absorbent paper sheet on the foraminous endless fabric;
a moving endless pressing blanket;
a transfer cylinder; and a pressing unit engaging the pressing blanket adapted to urge the WO Oen9669 PCT/US99/27097 nascent web for the absorbent paper sheet on the foraminous endless fabric into engagement with the transfer cylinder thereby forming a nip, the pressing unit being configured to create a peak engagement pressure of at least about 2000 kN/mz at an overall line load of less than about 240 kN/m.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric;
means for depositing a nascent web for the absorbent paper sheet on the foraminous endless fabric;
a moving endless pressing blanket;
a transfer cylinder, and a pressing unit engaging the pressing blanket adapted to urge the nascent web for the absorbent paper sheet on the foraminous endless fabric into engagement with the transfer cylinder thereby forming a nip, the pressing unit being configured to create a peak engagement pressure of at least about 2000 kN/m2.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric;
means for depositing a nascent web for the absorbent paper sheet on the foraminous endless fabric;
a moving endless pressing blanket;
a backing roll; and a pressing unit engaging the pressing blanket adapted to urge the nascent web for the absorbent paper sheet on the foraminous endless fabric into engagement with the backing roll thereby forming a nip, the pressing unit being configured to create a peak engagement pressure of at least about 2000 kN/m2 at an overall line load of less than about 240 kN/m.
There is still further disclosed:
A method of making an absorbent paper sheet product comprising:
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless pressing blanket engaged with a pressing unit thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmotrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by'said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
There is still further disclosed:
A method of making an absorbent paper sheet product comprising:
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless void volume s containing pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket engaged with a pressing unit, thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less io than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
19a There is finally disclosed:
A method of making an absorbent paper sheet product comprising:
depositing a nascent web for the absorbent paper sheet product on a moving foraminous endless fabric;
contacting the moving foraminous endless fabric bearing the deposited nascent web with a shoe press thereby forming a nip between the shoe press and a Yankee drying cylinder, the shoe press being configured to create a peak engagement pressure of at least about 2000 kN/m2 at an overall line load of less than about 240 kN/m;
disengaging the web from the foraminous endless fabric in the nip onto a Yankee drying cylinder;
drying the web on the Yankee drying cylinder; and creping the web from the Yankee drying cylinder.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a side view of a typical stand alone shoe press.
WO 00d29667 PCT/US99R7097 Figure 2 illustrates the relationship between peak pressure and line load for a variety of shoe press arrangements found in the literature, as well as for Yankee suction pressure rolls.
Figure 3 illustrates nip pressure profiies for a suction pressure roll, a typical shoe press, and a shoe press made according to the present invention.
Figure 4 illustrates one conventional wet press processing apparatus.
Figure 5 illustrates one conventional through-air-drying processing apparatus.
Figure 6 illustrates a typical pressure profile in the nip of a suction pressure roll, backing roll, or transfer cylinder according to the prior art.
Figure 7 illustrates a pressure profiie in the nip of a shoe press.
Figure 8 illustrates a preferred pressure profile in the nip of a shoe press where the negative pressure corresponds to the vacuum level in the feit.
Figure 9 illustrates a shoe press with a large diameter transfer cylinder where the felt rides the web causing rewet after the press nip.
Figure 10 illustrates a tapered shoe in a shoe press with a large diameter transfer cylinder where the felt is rapidly separated from the web but not from the pressing blanket.
Figure 11 iiiustrates a tapered shoe in a shoe press with a large diameter transfer cylinder where the felt is simultaneously stripped from the sheet and from the pressing blanket on the exit side of the nip.
I III
WO 00n9667 PCT/US99n7097 Figure 12 shows a plot of cold Yankee press solids versus line loading for a conventional 120 mm shoe, for a 50 mm shoe made according to the present invention, and for a suction pressure roll.
Figure 13 illustrates a side view of a typical stand alone shoe press with a blanket having void space.
Figure 14 illustrates a blind drilled blanket or belt.
Figure 15 illustrates a grooved blanket or belt.
ipETAI LED DESCRI PTI ON
In the production of absorbent paper products, paper web drying efficiency and paper web moisture removal directly affect machine speed, and therefore have a significant effect on the productivity that can be attained on a papermachine. The present invention improves paper web moisture removal through the controlled use of a pressing unit in conjunction with a backing roll andlor a transfer cylinder or Yankee drying cylinder. An absorbent paper web as defined herein includes bath tissue, paper towels, paper napkins, wipers, and facial tissue. The basis weight of such products and their base sheets are in the range of about 8 Ib/3000ft2to about 50 lbJ3000ft~.
According to the present invention, absorbent paper may be produced using any known method or papermaking scheme. The most common papermaking methods are (I) conventional wet pressing (CWP) and (il) through-air-drying (TAD). In a conventional wet press process, i.e., apparatus (10), as exemplified in Figure 4, a fumish is fed by means not shown through conduits (40,41) to headbox chambers (20, 20'). A web (W) is formed on a conventional wire former on fabric (12), supported by rolis (18, 19), from a liquid slurry of pulp, water and other chemicals. Materials removed from the web through fabric (12) in the forming zone are returned to silo (50), from saveall (22) through conduit (24). The web is then transferred to a moving felt (14), supported by roll (11) for pressing and drying. Materials removed from the web during pressing or from the Uhle box (29) are collected in saveall (44) and fed to white water conduit (45). The web is pressed by suction pressure roll (16) against the surface of a rotating Yankee dryer cylinder (26), which is heated to cause the paper to substantially dry on the cylinder surface. The moisture within the web as it is laid on the Yankee surface causes the web to transfer to the surface. Liquid adhesive may be applied to the surface of the dryer to provide substantial adherence of the web to the creping surface. The web is then creped from the surface with a creping blade (27). The creped web is then usually passed between calender rollers (not shown) and rolled up on reel (28) prior to further converting operations, for example, embossing.
A web may alternatively be subjected to vacuum deformation on an impression fabric, alone or in conjunction with other physical deformation processes, and a dewatering step which removes water from the web to a solids content of at least about 30% without the need for overall physical compression. This type of process is conventionally referred to as a through-air-drying process or TAD process. This process is generally described in U.S. Patent Nos. 3,301,746 to Sanford et al. and 3,905,863 to Ayers.
As an example, one conventional TAD process is illustrated in Figure 5. In this process, fibers are fed from a headbox (10) to a converging set of forming wires (20,30). In this twin wire forming arrangement water is removed from the web by centrifugal forces and by vacuum means. The wet nascent web is cleanly transferred to forming wire (30) via Uhie box (40). The web 10can be optionally processed to remove water by vacuum box (50) and steam shroud (60). The web is carried along forming fabric (30) until it is transferred to a TAD fabric (70) at junction (80) by means of a vacuum pickup shoe (90).
The web is further dewatered at dewatering box (100) to increase web solids.
Besides removing water from the web, vacuum, pickup shoe (90) and dewatering box (100) inundate the web into TAD fabric (70) causing bulk and absorbency improvements.
Further enhancements in bulk and absorbency can be obtained by operating the speed of the forming section (i.e., the speeds of forming fabrics and 30) faster than the speed of TAD fabric (70). This is referred to as 20 fabricJfabric creping. In this manner the web is inundated and wet shaped into the fabric creating bulk and absorbency. Thickness created by wet shaping is more effective in generating absorbency (i.e. less structural collapse) than thickness created in the dry state, e.g., by conventional embossing. The web is. then carried on TAD fabric (70) to drying unit (110) where heated air is passed through both the web and the fabric to increase the solids content of the web. Generally, the web is 30 to 95% dry after exiting drying unit (110). In one process, the web may be removed directly ...... . . ..... . .._. . . i Ili from TAD fabric (70) in an uncreped state. In the embodiment shown in Figure 5, the web is transferred from TAD fabric (70) to Yankee dryer cy(inder (130) and is creped from dryer cylinder (130) via creping blade (150). The creped web is then usually passed between calender roilers (160) and roNed up on reel (170) prior to further converting operations, for example, embossing to make roll products.
According to the present invention, an absorbent paper web can be made by dispersing fibers into aqueous slurry and depositing the aqueous slurry onto the forming wire of a paper making machine. Any art recognized forming scheme might be used. For example,an extensive but non-exhaustive list includes a crescent former, a C-wrap.twin wire former, an S-wrap twin wire former, a suction breast roll former, a fourdrinier former, or any art recognized forming configuration. The particular forming apparatus is not critical to the success of the present invention. The forming fabric can be any art recognized foraminous member including single layer fabrics, double layer fabrics, triple layer fabrics, photopolymer fabrics, and the like. Non-exhaustive background art in the forming fabric area include U.S. Patent Nos.
4,157,276; 4,605,585; 4,161,195; 3,545,705; 3,549,742; 3,858,623;
4,041,989; 4,071,050; 4,112,982; 4,149,571; 4,182,381; 4,184,519; ' 4,314,589; 4,359,069; 4,376,455; 4,379,735; 4,453,573; 4,564,052; 4592, 395; 4,611,639; 4,640,741; 4,709,732; 4,759,391; 4,759,976; 4,942,077;
4,967,085; 4,998,568; 5,016,678; 5,054,525; 5,066,532; 5,098,519;
5,103,874; 5,114,777; 5,167,261; 5,199,467; 5,211,815; 5,219,004;
5,245,025; 5,277,761; 5,328,565; and 5,379,808. The par6cular forming fabric is not critical to the success of the present invention. One forming fabric found particularly useful with the present invention is Appleton Mills Forming Fabric 2184 made by Appleton Mills Forming Fabric Corporation, Florence, MS.
Papermaking fibers used to form the absorbent products of the present invention include cellulosic fibers commonly referred to as wood pulp fibers, liberated in the pulping process from softwood (gymnosperms or coniferous trees) and hardwoods (angiosperms or deciduous trees).
Cellulosic fibers from diverse material origins rnay be used to form the web of the present invention. These fibers include non-woody fibers liberated from sugar cane, bagasse, sabai grass, rice straw, banana leaves, paper mulberry (i.e., bast fiber), abaca leaves, pineapple leaves, esparto grass leaves, and fibers from the genus Hesperaloe in the family Agavaceae. Also recycled fibers which may contain any of the above fiber sources in different percentages, can be used in the present invention. Suitable fibers are disclosed in U.S. Patent Nos., 5,320,710 and 3,620,911.
Papermaking fibers can be liberated from their source material by any one of the number of chemical pulping processes familiar to one experienced in the art including sulfate, sulfite, polysulfide, soda pulping, etc. The pulp can be bleached if desired by chemical means including the use of chlorine, chlorine dioxide, oxygen, etc. Furthermore, papermaking fibers can be liberated from source material by any one of a number of mechanical/chemical pulping processes familiar to anyone experienced in the art inciuding mechanical pulping, thermomechanical pulping, and chemi-thermomechanical pulping. These mechanical pulps can be bleached, if, necessary, by a number of familiar bleaching schemes including alkaline peroxide and ozone bleaching.
The suspension of fibers or fumish may contain chemical additives to alter the physical properties of the paper produced. These chemistries are well understood by the skilled artisan and may be used in any known combination.
The pulp can be mixed with strength adjusting agents such as wet strength agents, dry strength agents and debonders/softeners. Suitable wet strength agents will be readily apparent to the skilled artisan. A
comprehensive but non-exhaustive list of useful wet strength aids include urea-formaldehyde resins, melamine formaldehyde resins, glyoxylated polyacrylamide resins, polyamide-epichlorhydrin resins and the like.
Thermosetting polyacrylamides are produced by reacting acrylamide with diallyl dimethyl ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which is ultimately reacted with glyoxal to produce a cationic cross-linking wet strength resin, glyoxylated polyacrylamide. These materials are generally described in U.S. Patent Nos. 3,556,932 to Coscia et al. and 3,556,933 to Williams et al. Resins of this type are commercially available under the trademark of PAREZ 631 NC by Cytec Industries. -Different mole ratios of acrylarnide/DADMAC/glyoxal can be used to produce cross-linking resins, which are useful as wet strength agents. Furthermore, other dialdehydes can be substituted for glyoxal to produce thermosetting wet strength characteristics. Of particular utility are the poiyamide-epichlorhydrin resins, an example of which is sold under the trademarks Kymene 557LX
and Kymene 557H by Hercules Incorporated of Wilmington, Delaware and CASCAMIDO from Borden Chemical Inc. These resins and the process for making the resins are described in U.S. Patent No. 3,700,623 and U.S.
Patent No. 3,772,076. An extensive description of polymeric-epihalohydrin resins is given in Chapter 2: Alkaline -Curing Polymeric Amine-Epichlorohydrin by Espy in Wet-Strength Resins and Their Application (L.
Chan, Editor, 1994). A reasonably comprehensive list of wet strength resins is described by Westfelt in Cellulose Chemistry and Technoloqy, Volume 13, p. 813, 1979. The pulp, when making towel grades according to the present invention, preferably contains up to about 30 lbs/ton, more preferably from 10 to 20 lbs/ton of wet strength aids. Wet strength resins are not normally added to tissue grades.
Suitable dry strength agents will be readily apparent to one skilled in the art. A comprehensive but non-exhaustive list of useful dry strength aids includes starch, guar gum, polyacrylamides, carboxymethyl cellulose and the = 5 like. Of particular utility is carboxymethyl cellulose, an example of which is sold under the trademark Hercules CMC by Hercules Incorporated of Wilmington, Delaware. The pulp preferably contains from 0 tolO lbs/ton, more preferably from 1 to 5 lbs/ton of dry strength aid.
Suitable debonders will be readily apparent to the skilled artisan.
Debonders or softeners may also be incorporated into the pulp or sprayed upon the web after its formation. The pulp preferably contains from 0 to 10 lbs/ton, more preferably from 1 to 5 lbs/ton of debonder/softener.
The present invention may be used with a particular class of softener materials - amido amine salts derived from partially acid neutralized amines.
Such materials are disclosed in U.S. Patent No. 4,720,383. Evans, Chemistry and Industry, 5 July 1969, Pp. 893-903; Egan, J. Am. Oil Chemist's Soc., Vol.
55 (1978), Pp. 118-121; and Trivedi et al., J. Am. Oil Chemist's Soc., June 1981 , Pp. 754-756, indicate that softeners are often available commercially only as complex mixtures rather than as single compounds. While the following discussion will focus on the predominant species, it should be understood that commercially available mixtures would generally be used in practice.
QuasoftTM 202-JR is a suitable softener material, which may be derived by alkylating a condensation product of oleic acid and diethylenetriamine.
Synthesis conditions using a deficiency of alkylation agent (e.g., diethyl sulfate) and only one alkylating step, followed by pH adjustment to protonate the non-ethylated species, result in a mixture consisting of cationic ethylated = 5 and cationic non-ethylated species. A minor proportion (e.g., about 10%) of the resulting amido amine cyclize to imidazoline compounds. Since only the imidazoline portions of these material are quaternary ammonium compounds, the compositions as a whole are pH-sensitive. Therefore, in the practice of the present invention with this class of chemicals, the pH in the headbox should be approximately 6 to 8, more preferably 6 to 7 and most preferably 6.5 to 7.
Quaternary ammonium compounds, such as dialkyl dimethyl quaternary ammonium salts are also suitable particularly when the alkyl groups contain from about 14 to 20 carbon atoms. These compounds have the advantage of being relatively insensitive to pH.
Biodegradable softeners can be utilized. Representative biodegradable cationic softeners/debonders are disclosed in U.S. Patent Nos.
5,312,522; 5,415,737; 5,262,007; 5,264,082; and 5,223,096. These compounds are biodegradable diesters of quaternary ammonia compounds, quaternized amine-esters, and biodegradable vegetable oil based esters functional with quaternary ammonium chloride and diester dierucyldimethyl ammonium chloride and are representative biodegradable softeners.
The fibrous web is then either deposited on an impression drying fabric, in the case of the TAD process or on a dewatering felt for the CWP
process. Any art recognized fabrics or felts could be used with the present invention. For example, a non-exhaustive list of impression fabrics would include plain weave fabrics described in U.S. Patent No. 3,301,746; semitwill fabrics described in U.S. Patent Nos. 3,974,025 and 3,905,863; bilaterally-staggered-wicker-basket-cavity type fabrics described in U.S. Patent Nos.
4,239,065 and 4,191,609; sculptured/load bearing layer type fabrics described in U.S. Patent No. 5,429,686; photopolymer fabrics described in U.S. Patent Nos. 4,529,480, 4,637,859, 4,514,345, 4,528,339, 5,364,504, 5,334,289, 5,275,799, and 5,260,171; and fabrics containing diagonal pockets described in U.S. Patent No. 5,456,293. Any art-recognized-felt can be used with the present invention. For example, felts can have double-layer base weaves, triple-layer base weaves, or laminated base weaves.
Preferred felts according to the present invention are those having the laminated base weave design. A wet-press-felt found particularly useful with the present invention isAMFIexTM3 madeby Appleton Mills Corporation. Non-exhaustive background art in the press felt area includes U.S. Patent Nos.
5,657,797; 5,368,696; 4,973,512; 5,023,132; 5,225,269; 5,182,164;
5,372,876; and 5,618,612. After the web made by the conventional wet press process has reached a solids content of about 15 %, more preferably about 20 %, the web/foraminous fabric sandwich is contacted with a pressing blanket engaged with a=pressing unit, one embodiment in the art referred to as a shoe press.
In a similar web made by through air drying, the web/foraminous fabric sandwich is preferably contacted with the pressing blanket engaged with a pressing unk after the web has reached a solids content of at least about 20%, more preferably at ieast about 25%.
The pressing unit including a pressing blanket according to the present invention can have any art-recognized configu.ration. The nip can be created between the pressing unit and a backing. roll, in the case of a stand-atone pressing unit, or can be created betvveen the pressing unit and a transfer cylinder. As used in the present invention, backing roll refers to a roll that contacts the web but does not remove the fibrous web from the carrier fabric or fett. Backing rolls for use according to the present inventon may be . heated or cold. The backing roll can be made of hard rubber or metal. When the rolls are heated with an induction heater the roH is preferably constructed or coated with high diffusivity material, such as copper, to aid in Increasing heat transfer.
As used in the present invention, transfer cylinder refers to a roll that picks up the fibrous web thereby transferring the fibrous web from the foraminous carrier fabric upon which it had been carried. Typical transfer cylinders according to the present invention can include a steel roll, a metal coated roll, a granite roll, a Yankee drying cylinder, and a gas fired drying cylinder. Transfer cylinders for use according to the present method may be heated or cold. When the transfer cylinder is heated with an induction heater the cylinder is preferably constructed or coated with high diffusivity material, such as copper, to aid in increasing heat transfer. One or more transfer cylinders may be used in the process according to the present invention.
I I~l CA 02317438 2000-07-10 ' Heat is preferably applied to, the transfer cylinder and/or backing roil.
Heat can be applied by any art-known scheme including induction heating, oil heating and steam heating. Commercial available induction heaters can generate very high energy-transfer rates. An induction heater induces electrical current to the conducc#ing roll surface. Since the induced current can be quite large, this factor produces a substantial-amount of resistive heating in the conducting roll. Backing roll or transfer cylinder temperature can be anywhere from ambient to 700 F but are more preferably from 180 F to 500 F. Preferred heating schemes according to the present invention are induction heating and steam-heating.
Increased temperature in the backing roli or transfer cylinder decreases the viscosity of the water and makes the sheet more deformable hence improving water removal. Also, increased temperature and operating pressure bring the sheet into intimate contact with the transfer cylinder or backing roll, which improves heat transfer to the web. Furthermore, high steam pressure in the web within the nip can aid in rapidly displacing water from the sheet to the felt.
The pressing unit inciuding.a pressing blanket according to the present invention is preferably a shoe press. A shoe press includes a shoe element(s), which is pressed against the backing roll or transfer cylinder.
The shoe element is loaded hydrodynamically against the backing roll or transfer cytinder causing a nip to be-f.ormed. A pressing belt or blanket traverses the shoe press nip with the fibrous web in contact with the foraminous fabric.
Pressing blankets can be smooth, or to enhance water removal at the press they can be grooved or blind drilled. Conventional pressing blanket designs contain a fabric coated with polyurethane where the fabric is used as reinforcement. Other pressing blanket designs use yarns embedded in the polyurethane to provide reinforcement. One preferred pressing blanket according to the present invention is a yam reinforced blanket design under the tradename QualiFlex B, which is supplied by Voith Sulzer Corporation.
The shoe element length can be less than about 7 inches but is'more preferably less than about 3 inches for the present invention. According to the present invention the shoe element will also be referred to as a hydraulic engagement member. Shoe designs can be hydrodynamic, hydrodynamic pocket, or hydrostatic. In the hydrodynamic shoe design, the oil- lubricant forms a wedge at the ingoing side of the nip ultimately causing the formation of a thin oil film that protects the blanket and the shoe. The hydrodynamic pocket design incorporates a machined full width pocket in the shoe used for emptying the oil in the pressurized zone of the shoe. The fnal designis the hydrostatic design where oil is fed into the center region of the shoe. The preferred shoe design according to the present invention is hydrodynamic.
Shoe presses for use according to the present invention can be open or closed. Early shoe press designs were the open belt confngurations where an impermeable pressing blanket encircled a series of rollers similar to that of a fabric or felt run. These open designs suffered from papermachine system contamination by oil. The oil loss was at one time, up to 20 liters per day on 34.
wo'00/29667 PCT/US99n7097 some systems. The open shoe design is also inferior to a closed design since it cannot be operated in the inverted mode. The closed shoe design alleviates the.oil contamination issue and is therefore preferred for use in the present invention.
According to one embodiment of the present invention, the peak pressure in the shoe press is preferably greater than about 2000 kNlm2, with a line load of preferably less than about 240 kN/m. In another embodiment of the present invention, for conventionally made wide-Yankee-dryers the peak pressure is preferably greater than about 2000 kN/m2, while the line load is preferably less than about 175 kN/m and more preferably 1ess than about 100 kN/m. For the purposes of the present invention, kN/m is an abbreviation for kilonewtons per meter and kN/m2 is an abbreviation for kilonewtons-per square meter.
The sheet can be creped from the transfer cylinder by any art-recognized methods using any art recognized creping aid.
The maximum line iaad a current standard Yankee can sustain is on the order of 100kN/m. When a Yankee is used in conjunction with a suction pressure roll, the Yankee needs to be precisely crowned at the prevailing load to. obtain a uniform nip. This procedure is necessary due to the inflexibility of the suction pressure roll arrangement and also due to loading at only the ends of the suction pressure roll. For the case of a shoe press, loading occurs at multiple points across the cross machine direction; individual shoe elements can be installed across the machine to give. more precise cross WO 60/29667 PCTNS99l27097 machine direction pressing flexibility; and the shoe press is flexible and capable of conforming to the Yankee dryer surface. As a result, the precision to which the Yankee is ground for crowning wiil be iess.
Figure 6 shows a schematic sketch of a typical pressure distribution curve for a suction pressure roll described by symmetricai mathematical functions like the sine and haversine curves. Since the nip pressure is relieved when the nip diverges, rewet is exacerbated for the suction pressure roll. Figure 7 shows a schematic sketch of a pressure distribution curve for a shoe press with a steep drop off where the felt is stripped from the sheet and later from the peessing bianket. Such a steep drop-off in pressure reduces the amount of rewet. Figure 8 shows'a schematic sketch of a.pressure distribution curve for a shoe press with a steeper drop off and where suction occurs in the felt at the point of simultaneous separation of the felt, sheet, and blanket when the nip pressure reaches about zero. The negative pressure in the felt, when the blanket and felt are stripped apart, is caused by capillary forces -and should aid in holding water in the felt and should help further dewater the web.
Previous shoe, bett or blanket, and felt designs in wide nip presses do not permit optimum separation of these members. For instance, present designs allow for quick separation of the felt and blanket since the felt cannot "wrap" the unsupported blanket. But the drawback is that the felt stays in contact with the sheet allowing capillary flow back into the sheet, i.e., rewet (see Figure 9). Figure 9 is a schematic sketch of a shoe press nip showing III
sheet, felt, and btanket. Point A in Figure 9 is the point of zero pressure on the pressure distribution curve at the exit side of the nip.
Rewet is detennined in the literature by plotting moisture ratio versus the reciprocal of the basis weight using the following equation:
Kp = Ko + R/W
where.Kp is the moisture ratio of the paper after the wet press in grams of water per gram of ftber, Ko is the moisture ratio of paper for 1/W = 0; W is the basis weight in g/m2; and R is the magnitude of the rewet of paper in g/m2,and corresponds to the slope of the straight line used to fit moisture ratio versus reciprocal basis weight data. The aforementioned equation was first established by John Sweet. Data plotted according to the above equation is frequently referred to in the litenature as a Sweet plot. The original work can be found in Sweet, J.S., Pulp and Paper Mag. Can., 62, No. 7: T267 (1961) and a review article can be found in Heller, H., MacGregor, M., and Biiesner, W., Paper Technology and Industry, p.154, June, 1975. Rewet is much more significant for lightweight tissue grades than heavy weight linerboard grades.
Rewet has been estimated to be from 5 to 50 g/rn2 of water, depending on the felt, fumish, etc. Rewet for a conventional shoe press can be determined from the above equation. The amount of rewet for the optimum shoe press is preferably less than about 50 % of the amount determined from Sweet's theory using a conventional shoe press system. Rewet is preferably from 0 to 10 g/m2 of water, more preferably from 0 to 5 g/m2 of water.
According to another embodiment of the present invention, a pressing WO 00R9667 PCT/US99l27097 felt wraps the blanket and, therefore, pulls awayquickly from the sheet reducing the time for possible rewetting.. This design, as depicted in Figure 10, can be achieved by altering the take-away angle of the felt from the nip and tapering the exit side of the- shoe. To aid in blanket deflection from the felt at the exit side of the shoe, the blanket diameter can be reduced; the blanket can be eccentrically arranged with respects to the press plane; or a roll (not shown in Figure 10) positioned against the blanket can deflect the belt further.
Figure 11 shows another embodiment according to the present invention. In Figure 11, a schematic sketch of a shoe press showing a sheet, fe1t, and blanket is displayed. This shoe press utilizes a very steep pressure drop at and following the exit of a nip-curve of the press while simultaneously, separating the felt from the blanket and from the sheet. In this manner, the negative pressure generated bysurface tension forces as the felt and blanket separate are effective in reducing the flow of water back into the sheet as the felt and sheet are separated. The drawing shows a sharp drop off of the blanket near the shoe which in tum permits a quick separation of the felt from both the blanket and the sheet. The outgoing felt would be_ pulled at an angle that equally bisected the Yankee and blanket surfaces. Then by adjusting the tension on the felt, the exact point of separation can be controlled to affect the minimum in rewet. A felt drive roll located immediately following the shoe press can control the tension level on the felt. The objective of this embodiment according to the present invention is to affect the transfer of the III
sheet from the felt at the sarne time that the negative pulse.caused by the separation of the felt and blanket occurs. This design not only minimizes the.
time the felt is in contact with the sheet; the added vacuum pulse will significantly reduce the amount of water that can flow, even over the shoit time. Point A in Figure 11 is the point of zero pressure on the pressure distribution. curve at the exit side of the:nip. The nip pressure curve for the sheet/felt in Figure 11 would most likely approach that shown in Figure 8.
The web is preferably either adhered to the Yankee dryer by nip transfer with a pressing unit including a pressing blanket or is after pressing adhered to the Yankee dryer. The web is dried by steam and hot air impingement hoods. Any suitable art recognized adhesive might be used on the Yankee dryer. Preferred adhesives include polyvinyl alcohol with suitable plasticizers, glyoxylated polyacrylamide with or without polyvinyl alcohol, and polyamide epichlorohydrin resins such 'as Quacoat A-252 (QA252), Betzcreplus 97 (Betz+97) and Calgon 675 B. Suitable adhesives are widely described in the patent literature. A comprehensive but non-exhaustive list includes U.S. Patent Nos. 5,246,544; 4,304,625; "4,064,213; 3,926,716;
4,501,640; 4,528,316; 4,788,243; 4,883,564; 4,684,439; 5,326,434;
4,886,579; 5,374,334; 4,440,898; 5,382,323; 4,094,718; 5,025,046; and 5,281,307. Typical release agents can be used in accordance with the present invention.
The final product may be calendered or uncalendered and is usually reeled to await further converting processes. The products according to the, wo:00/29667 PCT/US99/27097 present invention may be subjected to. any art recognized, converting operations, including embossing, printing, etc.
The following ezample is illustrative of the invention embodied herein.
A nascent web was formed on a Crescent-forming machine using a blend of 50/50 long fiber/short fiber refined to 23 SR freeness. Chemicals like wet strength agents or dry strength agents were not added to the stock.
The basis weight of the sheet on the Yankee dryer was 8.5 Ibs/3000 W. Two pressing an-angements were used on the paper machine. In the first pressing arrangement, the sheet was pressed onto a Yankee dryer with a suctioR
pressure roll. The vacuum in the suction roA\was nominally 0.22 bar. In the second pressing arrangement, the suction pressure roll was replaced by a Yankee shoe press. The sheet was conditioned before the shoe press with a suction turning roll having the same size and open area as the suction pressure roll. The suction tuming roll vacuum was nominally equivalent to the level used during the suction pressure roll experiments. After sheet conditioning, the web was pressed onto the Yankee with a shoe press. In order to obtain precise sheet solids data after the shoe press or the suction pressure roll, the Yankee dryer was run cold. Blotters were used to coltect flatsheets for physical property determination. Two types of shoes were run:
a typical 120 mm shoe and a 50 mm shoe. Figure 3 shows the pressure distribution of the shoes and the suction pressure roll. Figure 12 depicts a plot of sheet solids versus line loading. The typical 120 mm shoe shows no WO 00129667 PCT/US99f27097 solids benefit versus the suction pressure roll at present operating line load limits of current Yankee dryers (i.e., approximately, 87.5 kN/m), while the 50 mm pressure optimized shoe press shows an advantage of several percentage points of solids. Furthermore, the strength and specific volume properties of a web made with the 50 mm pressure optimized shoe press were equivalent to the strength and specific volume properties of a web made by the suction pressure roll.
Figures 13-15 illustrate a method for maximizing water removal in a press nip in accordance with another embodiment of the present invention.
The present embodiment involves a conventional wet pressing (CWP) process. For consistency, like numbers have been used to=indicate the corresponding portions of the apparatus depicted in Figures 13-15 with those, of Figures 1-12. The description of the apparatus of Figures 1-12 thus applies equally to this embodiment, unless stated otherwise.
Referring to Figure 13, the present embodiment uses a shoe press, preferably a controlled crown roll with a flexible shell and a concave shoe hydrodynamically loaded against one another. The present embodiment further includes a belt or, blanket (100) having a void volume that enhances sheet solids after the shoe press to further improve water removal in the press nip. Appropriate void volume can be achieved by a number of blanket configurations, including, but not limited to, those made by grooving, blind drilling and the like. The total void volume of the belt or blanket for use according to the present invention is preferably about 50 to about 3000 cmI/m2, more preferably about 100 to about 1000 cm'/mZ, most preferably from about 200 to about 500 cm'/m3.
Blankets for use according to the present invention can include any art recognized blanket having, or which can be modified to have, the required void volume.
For example, blankets disclosed by E.J. Justus and D. Cronin in Tappi, August 1964, Vol. 47, No. 8, p.493 include grooved belts that improve water removal in a press nip where the groove width is about 0.01 to about 0.03 in., the land width is about 2 to about 20 times the groove width and the groove depth is about 2 to about 10 times the groove width.
For another example, blankets disclosed by Bo-Christer Aberg in Das Papier No. 6, 1996 include grooved belts that work at higher line loads and machine speeds than smooth belts. The belts have groove widths of about 0.5 to about 1 mm and a void volume of about 100 cc/rn2 to about 500 cc/mz.
For yet another example, blankets disclosed by P. Slater and K.
Fitzpatrick in the 84" Annual Meeting of the Technical Section, CPPA, January 1998 include grooved belts that provide a press dryness about 1 % to about 3% greater than the press dryness obtained with a similar smooth belt. The belts have groove widths of about 0.58 to about 0.79 mm and a void volume of about 200 cc/mz to about 365 cc/m2.
For still another example, blankets disclosed by D. Madden et al. in the Tappi 1998 Engineering Conference include grooved belts that provide a press dryness about 1%
greater than the dryness obtained with a blind drilled belt. The grooved belt has an open area of about a 20.3% and a void volume of about 260 cc/mZ, and the blind drilled belt has an open area of about 21 % and a void volume of about 380 cc/mZ void volume.
Referring to Figure 14, blind drilling involves drilling holes into a smooth blanket, as will be understood by one of skill in the art. Nip compression between a blind drilled blanket and the felt causes a hydraulic pressure gradient between the holes in the blanket and the felt which improves water flow and removal.
The blind drilled blanket preferably has a plurality of holes sequentially arranged in the machine direction and a plurality of rows sequentially arranged in the cross-machine direction to cause a hydraulic pressure gradient. The blind drilled blanket can take a variety of configurations. For example, the hole depth, hole diameter, hole spacing, hole angle, hole geometry, row spacing and/or row pattern can be varied.
In particular, the hole depth can range from about 0.2 to about 10 mm, more preferably about 0.5 to about 5 mm, most preferably from about 0.5 to about 3 mm. Also, the hole depth can extend partially or completely through the blanket.
The hole diameter can range from about 0.2 to about 10 mm, more . . . y . . . . _ . . . CA 02317438 2000-07-10 WO 00n9667 PCT/US99n7097 preferably about 0.5 to about 5 mm, most preferably from about 1 to about 3 mm.
The hole spacing can range from about I to about 20 mm between holes arranged within the samerow, more preferably about 1 to about 10 mm, most preferably from about I to about 5 mm.
The hole angle C.e., the angle measured from the. surface of the belt material counterclockwise to the side of the hole) can range from about 45 to about 135 degrees along any wall in either the machine or cross-machine, more preferably about 70 to about 110 degrees, most preferably from about 80 "to about 100 degrees.
The row spacing can range from about 1 to about 20 mm, more preferably about 1 to about 10 mm, most preferably from about 1 to about 5 mm.
The hole geometry can be curved, linear or curvilinear, e.g. round, square, elliptical, polygonal, and the row pattem can be such that the holes in each row are aligned in the cross-machine direction, offset in the cross-machine direction, aligned in the machine direction, offset in the machine direction and the like.
There is no requirement that all holes have the same configuration, rather, each of the holes can have a different configuration, or one or more individual or set of holes can have the same configuration as one or more other individual or set of holes. Further, there is no requirement that the hole pattem form any type of geometric or other pattem, for example, the pattern WO 9on9667 PCT/US99J27097 can be random.
Referring to Figure,15, forming.grooves in the blanket involves removing elongated sections, as will be understood by one of skill in the art.
G . . . . . . . . . . _ _ _ Nip compression of the grooved blanket and the press felt causes a hydraulic pressure gradient in the machine 'direction, which improves water flow and removal.
The grooved blanket preferably has a pluratity of grooved sections sequentially arranged in the cross-machine direction that circumscribe the blanket to cause machine direction water movement. The grooved blanket can take a variety of configurations. For example, the groove depth, groove width, groove bevel, groove angle, land width, open area and groove patterrrn can all be varied.
In particular, the groove depth can range from about 0.1 to about 8 mm, more preferably about 0.2 to about 5 mm, most preferably from about 0.4 to about 3mm.
The groove width can range from about 0.1 to about 6 mm, more preferably about 0.2 to about 4 mm; most preferably from about 0.4 to about 3 mm.
The groove bevel (i.e., the angle measured from the surface of the belt material counterclockwise to the side of the groove minus 90 ) can range from about 0 to about 45 0, more preferably about 0 to about 30 , most preferably from about 0 to about 20 .
The groove angle can range from about 45 to about 135 degrees (with . . . . . r ~ . ~ . . .
WO 00129b67 PCT/US99/27097 90 degrees being orthogonal to the, cross-machine direction), more preferably about 65 to about 1150, most preferably from about 80 to about 100 .
The land width can range from about 0.2 to about 25 mm, more preferably about 0.4 to about 10 mm, most preferably from about 0.6 to about 4 mm.
The open area can range up to 80% of the total blanket area, more preferably about 15 to about 50%, most preferably from about 20 to about 40%.
The groove pattem can be such that the grooves in each row are aligned in the cross-machine direction, offset in the cross-machine direction, aligned in the machine direction, offset in the machine direction and the iike.
Also, for blankets-for use in the present invention, grooves need not have the same configuration, rather, all the grooves can have a different configuration, or one or more individuai or'set of grooves can have the same configuration as one or more other individuai or set of grooves. Further, there is no requirement that the groove pattem form any type of geometric or other pattem, for example, the groove placement can also be random.
Blankets having the disclosed void voiume will be readily apparent to the skilled artisan. Such biankets can include any physidal arrangement as long as the void space requirements are satisfied. Blankets for use in the present invention may be manufactured by any art recognized process, including but not limited to, casting molding, laser engraving, etc.
. . , . . . - . .
A punch press was used to perform dewatering experiments with different belt structures. An AMFIex 3S. felt manufactured by Appleton Mills Corporation was used to dewater the paper web. The web basis weight was 8.9 lbs/m1. The felt dryness was controlled to 69.3% dryness by using'blotters and a couch roll to remove excess water. Web moisture was controlled to 19.3% dryness by rewetting moist webs using a water spray. The webs were made from a 50/50 blend of northem softwood kraft and eucalyptus refined in a PFI mill to 510 ml CSF.
A smooth belt, a blind drilled belt and a grooved bett were used in the punch press experiment. The blind drilled belt had a bore area of. 3.82 mm2, a bore depth of 1.76 mm, an open area of 22.73% and a void volume of 402.9 cc/m2 The grooved belt had a groove width of 0.66 mm, a groove depth of 1.41 mm, a pitch of 0.33 grooves/mm, an open area of 21.78%, and a void volume of 270.6 cc/m2.
The punch press was operated such that the average nip pressure was fixed at 400 psi and the average nip dwell time was fixed at 1.8 ms. The experimental post press dryness results for the experiment were.:
smooth belt 31.0 +/- 0.30%
blind drilled belt 39.2 +/- 0.28%
grooved belt 40.3 +/- 0.42%
with the +/- percentage being the 95% confidence limit for the test.
These results indicate that pressing with either a blind drilled or grooved belt leads to enhanced sheet solids when compared to a smooth belt. These results also indicate that pressing with a grooved beit leads to enhanced sheet solids over a blind drilied belt.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification- and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.
SUMMARY OF THE INVENTION
Further advantages of the invention will be set forth in part in the description, which follows and in part will be apparent from the description.
The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particulariy pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is disclosed:
An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric; a moving endless pressing blanket; a transfer cylinder, wherein said nascent web is located between said fpraminous endless fabric and said transfer cylinder; and a pressing unit engaging said pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, said pressing unit being configured to impose an asymmetrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless to fabric; a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a transfer cylinder wherein said nascent web is located between said foraminous endless fabric and said transfer cylinder, and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric; a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a backing roll wherein said nascent web is located between said foraminous endless fabric and said backing roll; and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said backing roll thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric;
means for depositing a nascent web for the absorbent paper sheet on the foraminous endless fabric;
a moving endless pressing blanket;
a transfer cylinder; and a pressing unit engaging the pressing blanket adapted to urge the WO Oen9669 PCT/US99/27097 nascent web for the absorbent paper sheet on the foraminous endless fabric into engagement with the transfer cylinder thereby forming a nip, the pressing unit being configured to create a peak engagement pressure of at least about 2000 kN/mz at an overall line load of less than about 240 kN/m.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric;
means for depositing a nascent web for the absorbent paper sheet on the foraminous endless fabric;
a moving endless pressing blanket;
a transfer cylinder, and a pressing unit engaging the pressing blanket adapted to urge the nascent web for the absorbent paper sheet on the foraminous endless fabric into engagement with the transfer cylinder thereby forming a nip, the pressing unit being configured to create a peak engagement pressure of at least about 2000 kN/m2.
There is still further disclosed:
An apparatus for forming an absorbent paper sheet product comprising:
a moving foraminous endless fabric;
means for depositing a nascent web for the absorbent paper sheet on the foraminous endless fabric;
a moving endless pressing blanket;
a backing roll; and a pressing unit engaging the pressing blanket adapted to urge the nascent web for the absorbent paper sheet on the foraminous endless fabric into engagement with the backing roll thereby forming a nip, the pressing unit being configured to create a peak engagement pressure of at least about 2000 kN/m2 at an overall line load of less than about 240 kN/m.
There is still further disclosed:
A method of making an absorbent paper sheet product comprising:
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless pressing blanket engaged with a pressing unit thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmotrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by'said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
There is still further disclosed:
A method of making an absorbent paper sheet product comprising:
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless void volume s containing pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket engaged with a pressing unit, thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less io than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
19a There is finally disclosed:
A method of making an absorbent paper sheet product comprising:
depositing a nascent web for the absorbent paper sheet product on a moving foraminous endless fabric;
contacting the moving foraminous endless fabric bearing the deposited nascent web with a shoe press thereby forming a nip between the shoe press and a Yankee drying cylinder, the shoe press being configured to create a peak engagement pressure of at least about 2000 kN/m2 at an overall line load of less than about 240 kN/m;
disengaging the web from the foraminous endless fabric in the nip onto a Yankee drying cylinder;
drying the web on the Yankee drying cylinder; and creping the web from the Yankee drying cylinder.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a side view of a typical stand alone shoe press.
WO 00d29667 PCT/US99R7097 Figure 2 illustrates the relationship between peak pressure and line load for a variety of shoe press arrangements found in the literature, as well as for Yankee suction pressure rolls.
Figure 3 illustrates nip pressure profiies for a suction pressure roll, a typical shoe press, and a shoe press made according to the present invention.
Figure 4 illustrates one conventional wet press processing apparatus.
Figure 5 illustrates one conventional through-air-drying processing apparatus.
Figure 6 illustrates a typical pressure profile in the nip of a suction pressure roll, backing roll, or transfer cylinder according to the prior art.
Figure 7 illustrates a pressure profiie in the nip of a shoe press.
Figure 8 illustrates a preferred pressure profile in the nip of a shoe press where the negative pressure corresponds to the vacuum level in the feit.
Figure 9 illustrates a shoe press with a large diameter transfer cylinder where the felt rides the web causing rewet after the press nip.
Figure 10 illustrates a tapered shoe in a shoe press with a large diameter transfer cylinder where the felt is rapidly separated from the web but not from the pressing blanket.
Figure 11 iiiustrates a tapered shoe in a shoe press with a large diameter transfer cylinder where the felt is simultaneously stripped from the sheet and from the pressing blanket on the exit side of the nip.
I III
WO 00n9667 PCT/US99n7097 Figure 12 shows a plot of cold Yankee press solids versus line loading for a conventional 120 mm shoe, for a 50 mm shoe made according to the present invention, and for a suction pressure roll.
Figure 13 illustrates a side view of a typical stand alone shoe press with a blanket having void space.
Figure 14 illustrates a blind drilled blanket or belt.
Figure 15 illustrates a grooved blanket or belt.
ipETAI LED DESCRI PTI ON
In the production of absorbent paper products, paper web drying efficiency and paper web moisture removal directly affect machine speed, and therefore have a significant effect on the productivity that can be attained on a papermachine. The present invention improves paper web moisture removal through the controlled use of a pressing unit in conjunction with a backing roll andlor a transfer cylinder or Yankee drying cylinder. An absorbent paper web as defined herein includes bath tissue, paper towels, paper napkins, wipers, and facial tissue. The basis weight of such products and their base sheets are in the range of about 8 Ib/3000ft2to about 50 lbJ3000ft~.
According to the present invention, absorbent paper may be produced using any known method or papermaking scheme. The most common papermaking methods are (I) conventional wet pressing (CWP) and (il) through-air-drying (TAD). In a conventional wet press process, i.e., apparatus (10), as exemplified in Figure 4, a fumish is fed by means not shown through conduits (40,41) to headbox chambers (20, 20'). A web (W) is formed on a conventional wire former on fabric (12), supported by rolis (18, 19), from a liquid slurry of pulp, water and other chemicals. Materials removed from the web through fabric (12) in the forming zone are returned to silo (50), from saveall (22) through conduit (24). The web is then transferred to a moving felt (14), supported by roll (11) for pressing and drying. Materials removed from the web during pressing or from the Uhle box (29) are collected in saveall (44) and fed to white water conduit (45). The web is pressed by suction pressure roll (16) against the surface of a rotating Yankee dryer cylinder (26), which is heated to cause the paper to substantially dry on the cylinder surface. The moisture within the web as it is laid on the Yankee surface causes the web to transfer to the surface. Liquid adhesive may be applied to the surface of the dryer to provide substantial adherence of the web to the creping surface. The web is then creped from the surface with a creping blade (27). The creped web is then usually passed between calender rollers (not shown) and rolled up on reel (28) prior to further converting operations, for example, embossing.
A web may alternatively be subjected to vacuum deformation on an impression fabric, alone or in conjunction with other physical deformation processes, and a dewatering step which removes water from the web to a solids content of at least about 30% without the need for overall physical compression. This type of process is conventionally referred to as a through-air-drying process or TAD process. This process is generally described in U.S. Patent Nos. 3,301,746 to Sanford et al. and 3,905,863 to Ayers.
As an example, one conventional TAD process is illustrated in Figure 5. In this process, fibers are fed from a headbox (10) to a converging set of forming wires (20,30). In this twin wire forming arrangement water is removed from the web by centrifugal forces and by vacuum means. The wet nascent web is cleanly transferred to forming wire (30) via Uhie box (40). The web 10can be optionally processed to remove water by vacuum box (50) and steam shroud (60). The web is carried along forming fabric (30) until it is transferred to a TAD fabric (70) at junction (80) by means of a vacuum pickup shoe (90).
The web is further dewatered at dewatering box (100) to increase web solids.
Besides removing water from the web, vacuum, pickup shoe (90) and dewatering box (100) inundate the web into TAD fabric (70) causing bulk and absorbency improvements.
Further enhancements in bulk and absorbency can be obtained by operating the speed of the forming section (i.e., the speeds of forming fabrics and 30) faster than the speed of TAD fabric (70). This is referred to as 20 fabricJfabric creping. In this manner the web is inundated and wet shaped into the fabric creating bulk and absorbency. Thickness created by wet shaping is more effective in generating absorbency (i.e. less structural collapse) than thickness created in the dry state, e.g., by conventional embossing. The web is. then carried on TAD fabric (70) to drying unit (110) where heated air is passed through both the web and the fabric to increase the solids content of the web. Generally, the web is 30 to 95% dry after exiting drying unit (110). In one process, the web may be removed directly ...... . . ..... . .._. . . i Ili from TAD fabric (70) in an uncreped state. In the embodiment shown in Figure 5, the web is transferred from TAD fabric (70) to Yankee dryer cy(inder (130) and is creped from dryer cylinder (130) via creping blade (150). The creped web is then usually passed between calender roilers (160) and roNed up on reel (170) prior to further converting operations, for example, embossing to make roll products.
According to the present invention, an absorbent paper web can be made by dispersing fibers into aqueous slurry and depositing the aqueous slurry onto the forming wire of a paper making machine. Any art recognized forming scheme might be used. For example,an extensive but non-exhaustive list includes a crescent former, a C-wrap.twin wire former, an S-wrap twin wire former, a suction breast roll former, a fourdrinier former, or any art recognized forming configuration. The particular forming apparatus is not critical to the success of the present invention. The forming fabric can be any art recognized foraminous member including single layer fabrics, double layer fabrics, triple layer fabrics, photopolymer fabrics, and the like. Non-exhaustive background art in the forming fabric area include U.S. Patent Nos.
4,157,276; 4,605,585; 4,161,195; 3,545,705; 3,549,742; 3,858,623;
4,041,989; 4,071,050; 4,112,982; 4,149,571; 4,182,381; 4,184,519; ' 4,314,589; 4,359,069; 4,376,455; 4,379,735; 4,453,573; 4,564,052; 4592, 395; 4,611,639; 4,640,741; 4,709,732; 4,759,391; 4,759,976; 4,942,077;
4,967,085; 4,998,568; 5,016,678; 5,054,525; 5,066,532; 5,098,519;
5,103,874; 5,114,777; 5,167,261; 5,199,467; 5,211,815; 5,219,004;
5,245,025; 5,277,761; 5,328,565; and 5,379,808. The par6cular forming fabric is not critical to the success of the present invention. One forming fabric found particularly useful with the present invention is Appleton Mills Forming Fabric 2184 made by Appleton Mills Forming Fabric Corporation, Florence, MS.
Papermaking fibers used to form the absorbent products of the present invention include cellulosic fibers commonly referred to as wood pulp fibers, liberated in the pulping process from softwood (gymnosperms or coniferous trees) and hardwoods (angiosperms or deciduous trees).
Cellulosic fibers from diverse material origins rnay be used to form the web of the present invention. These fibers include non-woody fibers liberated from sugar cane, bagasse, sabai grass, rice straw, banana leaves, paper mulberry (i.e., bast fiber), abaca leaves, pineapple leaves, esparto grass leaves, and fibers from the genus Hesperaloe in the family Agavaceae. Also recycled fibers which may contain any of the above fiber sources in different percentages, can be used in the present invention. Suitable fibers are disclosed in U.S. Patent Nos., 5,320,710 and 3,620,911.
Papermaking fibers can be liberated from their source material by any one of the number of chemical pulping processes familiar to one experienced in the art including sulfate, sulfite, polysulfide, soda pulping, etc. The pulp can be bleached if desired by chemical means including the use of chlorine, chlorine dioxide, oxygen, etc. Furthermore, papermaking fibers can be liberated from source material by any one of a number of mechanical/chemical pulping processes familiar to anyone experienced in the art inciuding mechanical pulping, thermomechanical pulping, and chemi-thermomechanical pulping. These mechanical pulps can be bleached, if, necessary, by a number of familiar bleaching schemes including alkaline peroxide and ozone bleaching.
The suspension of fibers or fumish may contain chemical additives to alter the physical properties of the paper produced. These chemistries are well understood by the skilled artisan and may be used in any known combination.
The pulp can be mixed with strength adjusting agents such as wet strength agents, dry strength agents and debonders/softeners. Suitable wet strength agents will be readily apparent to the skilled artisan. A
comprehensive but non-exhaustive list of useful wet strength aids include urea-formaldehyde resins, melamine formaldehyde resins, glyoxylated polyacrylamide resins, polyamide-epichlorhydrin resins and the like.
Thermosetting polyacrylamides are produced by reacting acrylamide with diallyl dimethyl ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which is ultimately reacted with glyoxal to produce a cationic cross-linking wet strength resin, glyoxylated polyacrylamide. These materials are generally described in U.S. Patent Nos. 3,556,932 to Coscia et al. and 3,556,933 to Williams et al. Resins of this type are commercially available under the trademark of PAREZ 631 NC by Cytec Industries. -Different mole ratios of acrylarnide/DADMAC/glyoxal can be used to produce cross-linking resins, which are useful as wet strength agents. Furthermore, other dialdehydes can be substituted for glyoxal to produce thermosetting wet strength characteristics. Of particular utility are the poiyamide-epichlorhydrin resins, an example of which is sold under the trademarks Kymene 557LX
and Kymene 557H by Hercules Incorporated of Wilmington, Delaware and CASCAMIDO from Borden Chemical Inc. These resins and the process for making the resins are described in U.S. Patent No. 3,700,623 and U.S.
Patent No. 3,772,076. An extensive description of polymeric-epihalohydrin resins is given in Chapter 2: Alkaline -Curing Polymeric Amine-Epichlorohydrin by Espy in Wet-Strength Resins and Their Application (L.
Chan, Editor, 1994). A reasonably comprehensive list of wet strength resins is described by Westfelt in Cellulose Chemistry and Technoloqy, Volume 13, p. 813, 1979. The pulp, when making towel grades according to the present invention, preferably contains up to about 30 lbs/ton, more preferably from 10 to 20 lbs/ton of wet strength aids. Wet strength resins are not normally added to tissue grades.
Suitable dry strength agents will be readily apparent to one skilled in the art. A comprehensive but non-exhaustive list of useful dry strength aids includes starch, guar gum, polyacrylamides, carboxymethyl cellulose and the = 5 like. Of particular utility is carboxymethyl cellulose, an example of which is sold under the trademark Hercules CMC by Hercules Incorporated of Wilmington, Delaware. The pulp preferably contains from 0 tolO lbs/ton, more preferably from 1 to 5 lbs/ton of dry strength aid.
Suitable debonders will be readily apparent to the skilled artisan.
Debonders or softeners may also be incorporated into the pulp or sprayed upon the web after its formation. The pulp preferably contains from 0 to 10 lbs/ton, more preferably from 1 to 5 lbs/ton of debonder/softener.
The present invention may be used with a particular class of softener materials - amido amine salts derived from partially acid neutralized amines.
Such materials are disclosed in U.S. Patent No. 4,720,383. Evans, Chemistry and Industry, 5 July 1969, Pp. 893-903; Egan, J. Am. Oil Chemist's Soc., Vol.
55 (1978), Pp. 118-121; and Trivedi et al., J. Am. Oil Chemist's Soc., June 1981 , Pp. 754-756, indicate that softeners are often available commercially only as complex mixtures rather than as single compounds. While the following discussion will focus on the predominant species, it should be understood that commercially available mixtures would generally be used in practice.
QuasoftTM 202-JR is a suitable softener material, which may be derived by alkylating a condensation product of oleic acid and diethylenetriamine.
Synthesis conditions using a deficiency of alkylation agent (e.g., diethyl sulfate) and only one alkylating step, followed by pH adjustment to protonate the non-ethylated species, result in a mixture consisting of cationic ethylated = 5 and cationic non-ethylated species. A minor proportion (e.g., about 10%) of the resulting amido amine cyclize to imidazoline compounds. Since only the imidazoline portions of these material are quaternary ammonium compounds, the compositions as a whole are pH-sensitive. Therefore, in the practice of the present invention with this class of chemicals, the pH in the headbox should be approximately 6 to 8, more preferably 6 to 7 and most preferably 6.5 to 7.
Quaternary ammonium compounds, such as dialkyl dimethyl quaternary ammonium salts are also suitable particularly when the alkyl groups contain from about 14 to 20 carbon atoms. These compounds have the advantage of being relatively insensitive to pH.
Biodegradable softeners can be utilized. Representative biodegradable cationic softeners/debonders are disclosed in U.S. Patent Nos.
5,312,522; 5,415,737; 5,262,007; 5,264,082; and 5,223,096. These compounds are biodegradable diesters of quaternary ammonia compounds, quaternized amine-esters, and biodegradable vegetable oil based esters functional with quaternary ammonium chloride and diester dierucyldimethyl ammonium chloride and are representative biodegradable softeners.
The fibrous web is then either deposited on an impression drying fabric, in the case of the TAD process or on a dewatering felt for the CWP
process. Any art recognized fabrics or felts could be used with the present invention. For example, a non-exhaustive list of impression fabrics would include plain weave fabrics described in U.S. Patent No. 3,301,746; semitwill fabrics described in U.S. Patent Nos. 3,974,025 and 3,905,863; bilaterally-staggered-wicker-basket-cavity type fabrics described in U.S. Patent Nos.
4,239,065 and 4,191,609; sculptured/load bearing layer type fabrics described in U.S. Patent No. 5,429,686; photopolymer fabrics described in U.S. Patent Nos. 4,529,480, 4,637,859, 4,514,345, 4,528,339, 5,364,504, 5,334,289, 5,275,799, and 5,260,171; and fabrics containing diagonal pockets described in U.S. Patent No. 5,456,293. Any art-recognized-felt can be used with the present invention. For example, felts can have double-layer base weaves, triple-layer base weaves, or laminated base weaves.
Preferred felts according to the present invention are those having the laminated base weave design. A wet-press-felt found particularly useful with the present invention isAMFIexTM3 madeby Appleton Mills Corporation. Non-exhaustive background art in the press felt area includes U.S. Patent Nos.
5,657,797; 5,368,696; 4,973,512; 5,023,132; 5,225,269; 5,182,164;
5,372,876; and 5,618,612. After the web made by the conventional wet press process has reached a solids content of about 15 %, more preferably about 20 %, the web/foraminous fabric sandwich is contacted with a pressing blanket engaged with a=pressing unit, one embodiment in the art referred to as a shoe press.
In a similar web made by through air drying, the web/foraminous fabric sandwich is preferably contacted with the pressing blanket engaged with a pressing unk after the web has reached a solids content of at least about 20%, more preferably at ieast about 25%.
The pressing unit including a pressing blanket according to the present invention can have any art-recognized configu.ration. The nip can be created between the pressing unit and a backing. roll, in the case of a stand-atone pressing unit, or can be created betvveen the pressing unit and a transfer cylinder. As used in the present invention, backing roll refers to a roll that contacts the web but does not remove the fibrous web from the carrier fabric or fett. Backing rolls for use according to the present inventon may be . heated or cold. The backing roll can be made of hard rubber or metal. When the rolls are heated with an induction heater the roH is preferably constructed or coated with high diffusivity material, such as copper, to aid in Increasing heat transfer.
As used in the present invention, transfer cylinder refers to a roll that picks up the fibrous web thereby transferring the fibrous web from the foraminous carrier fabric upon which it had been carried. Typical transfer cylinders according to the present invention can include a steel roll, a metal coated roll, a granite roll, a Yankee drying cylinder, and a gas fired drying cylinder. Transfer cylinders for use according to the present method may be heated or cold. When the transfer cylinder is heated with an induction heater the cylinder is preferably constructed or coated with high diffusivity material, such as copper, to aid in increasing heat transfer. One or more transfer cylinders may be used in the process according to the present invention.
I I~l CA 02317438 2000-07-10 ' Heat is preferably applied to, the transfer cylinder and/or backing roil.
Heat can be applied by any art-known scheme including induction heating, oil heating and steam heating. Commercial available induction heaters can generate very high energy-transfer rates. An induction heater induces electrical current to the conducc#ing roll surface. Since the induced current can be quite large, this factor produces a substantial-amount of resistive heating in the conducting roll. Backing roll or transfer cylinder temperature can be anywhere from ambient to 700 F but are more preferably from 180 F to 500 F. Preferred heating schemes according to the present invention are induction heating and steam-heating.
Increased temperature in the backing roli or transfer cylinder decreases the viscosity of the water and makes the sheet more deformable hence improving water removal. Also, increased temperature and operating pressure bring the sheet into intimate contact with the transfer cylinder or backing roll, which improves heat transfer to the web. Furthermore, high steam pressure in the web within the nip can aid in rapidly displacing water from the sheet to the felt.
The pressing unit inciuding.a pressing blanket according to the present invention is preferably a shoe press. A shoe press includes a shoe element(s), which is pressed against the backing roll or transfer cylinder.
The shoe element is loaded hydrodynamically against the backing roll or transfer cytinder causing a nip to be-f.ormed. A pressing belt or blanket traverses the shoe press nip with the fibrous web in contact with the foraminous fabric.
Pressing blankets can be smooth, or to enhance water removal at the press they can be grooved or blind drilled. Conventional pressing blanket designs contain a fabric coated with polyurethane where the fabric is used as reinforcement. Other pressing blanket designs use yarns embedded in the polyurethane to provide reinforcement. One preferred pressing blanket according to the present invention is a yam reinforced blanket design under the tradename QualiFlex B, which is supplied by Voith Sulzer Corporation.
The shoe element length can be less than about 7 inches but is'more preferably less than about 3 inches for the present invention. According to the present invention the shoe element will also be referred to as a hydraulic engagement member. Shoe designs can be hydrodynamic, hydrodynamic pocket, or hydrostatic. In the hydrodynamic shoe design, the oil- lubricant forms a wedge at the ingoing side of the nip ultimately causing the formation of a thin oil film that protects the blanket and the shoe. The hydrodynamic pocket design incorporates a machined full width pocket in the shoe used for emptying the oil in the pressurized zone of the shoe. The fnal designis the hydrostatic design where oil is fed into the center region of the shoe. The preferred shoe design according to the present invention is hydrodynamic.
Shoe presses for use according to the present invention can be open or closed. Early shoe press designs were the open belt confngurations where an impermeable pressing blanket encircled a series of rollers similar to that of a fabric or felt run. These open designs suffered from papermachine system contamination by oil. The oil loss was at one time, up to 20 liters per day on 34.
wo'00/29667 PCT/US99n7097 some systems. The open shoe design is also inferior to a closed design since it cannot be operated in the inverted mode. The closed shoe design alleviates the.oil contamination issue and is therefore preferred for use in the present invention.
According to one embodiment of the present invention, the peak pressure in the shoe press is preferably greater than about 2000 kNlm2, with a line load of preferably less than about 240 kN/m. In another embodiment of the present invention, for conventionally made wide-Yankee-dryers the peak pressure is preferably greater than about 2000 kN/m2, while the line load is preferably less than about 175 kN/m and more preferably 1ess than about 100 kN/m. For the purposes of the present invention, kN/m is an abbreviation for kilonewtons per meter and kN/m2 is an abbreviation for kilonewtons-per square meter.
The sheet can be creped from the transfer cylinder by any art-recognized methods using any art recognized creping aid.
The maximum line iaad a current standard Yankee can sustain is on the order of 100kN/m. When a Yankee is used in conjunction with a suction pressure roll, the Yankee needs to be precisely crowned at the prevailing load to. obtain a uniform nip. This procedure is necessary due to the inflexibility of the suction pressure roll arrangement and also due to loading at only the ends of the suction pressure roll. For the case of a shoe press, loading occurs at multiple points across the cross machine direction; individual shoe elements can be installed across the machine to give. more precise cross WO 60/29667 PCTNS99l27097 machine direction pressing flexibility; and the shoe press is flexible and capable of conforming to the Yankee dryer surface. As a result, the precision to which the Yankee is ground for crowning wiil be iess.
Figure 6 shows a schematic sketch of a typical pressure distribution curve for a suction pressure roll described by symmetricai mathematical functions like the sine and haversine curves. Since the nip pressure is relieved when the nip diverges, rewet is exacerbated for the suction pressure roll. Figure 7 shows a schematic sketch of a pressure distribution curve for a shoe press with a steep drop off where the felt is stripped from the sheet and later from the peessing bianket. Such a steep drop-off in pressure reduces the amount of rewet. Figure 8 shows'a schematic sketch of a.pressure distribution curve for a shoe press with a steeper drop off and where suction occurs in the felt at the point of simultaneous separation of the felt, sheet, and blanket when the nip pressure reaches about zero. The negative pressure in the felt, when the blanket and felt are stripped apart, is caused by capillary forces -and should aid in holding water in the felt and should help further dewater the web.
Previous shoe, bett or blanket, and felt designs in wide nip presses do not permit optimum separation of these members. For instance, present designs allow for quick separation of the felt and blanket since the felt cannot "wrap" the unsupported blanket. But the drawback is that the felt stays in contact with the sheet allowing capillary flow back into the sheet, i.e., rewet (see Figure 9). Figure 9 is a schematic sketch of a shoe press nip showing III
sheet, felt, and btanket. Point A in Figure 9 is the point of zero pressure on the pressure distribution curve at the exit side of the nip.
Rewet is detennined in the literature by plotting moisture ratio versus the reciprocal of the basis weight using the following equation:
Kp = Ko + R/W
where.Kp is the moisture ratio of the paper after the wet press in grams of water per gram of ftber, Ko is the moisture ratio of paper for 1/W = 0; W is the basis weight in g/m2; and R is the magnitude of the rewet of paper in g/m2,and corresponds to the slope of the straight line used to fit moisture ratio versus reciprocal basis weight data. The aforementioned equation was first established by John Sweet. Data plotted according to the above equation is frequently referred to in the litenature as a Sweet plot. The original work can be found in Sweet, J.S., Pulp and Paper Mag. Can., 62, No. 7: T267 (1961) and a review article can be found in Heller, H., MacGregor, M., and Biiesner, W., Paper Technology and Industry, p.154, June, 1975. Rewet is much more significant for lightweight tissue grades than heavy weight linerboard grades.
Rewet has been estimated to be from 5 to 50 g/rn2 of water, depending on the felt, fumish, etc. Rewet for a conventional shoe press can be determined from the above equation. The amount of rewet for the optimum shoe press is preferably less than about 50 % of the amount determined from Sweet's theory using a conventional shoe press system. Rewet is preferably from 0 to 10 g/m2 of water, more preferably from 0 to 5 g/m2 of water.
According to another embodiment of the present invention, a pressing WO 00R9667 PCT/US99l27097 felt wraps the blanket and, therefore, pulls awayquickly from the sheet reducing the time for possible rewetting.. This design, as depicted in Figure 10, can be achieved by altering the take-away angle of the felt from the nip and tapering the exit side of the- shoe. To aid in blanket deflection from the felt at the exit side of the shoe, the blanket diameter can be reduced; the blanket can be eccentrically arranged with respects to the press plane; or a roll (not shown in Figure 10) positioned against the blanket can deflect the belt further.
Figure 11 shows another embodiment according to the present invention. In Figure 11, a schematic sketch of a shoe press showing a sheet, fe1t, and blanket is displayed. This shoe press utilizes a very steep pressure drop at and following the exit of a nip-curve of the press while simultaneously, separating the felt from the blanket and from the sheet. In this manner, the negative pressure generated bysurface tension forces as the felt and blanket separate are effective in reducing the flow of water back into the sheet as the felt and sheet are separated. The drawing shows a sharp drop off of the blanket near the shoe which in tum permits a quick separation of the felt from both the blanket and the sheet. The outgoing felt would be_ pulled at an angle that equally bisected the Yankee and blanket surfaces. Then by adjusting the tension on the felt, the exact point of separation can be controlled to affect the minimum in rewet. A felt drive roll located immediately following the shoe press can control the tension level on the felt. The objective of this embodiment according to the present invention is to affect the transfer of the III
sheet from the felt at the sarne time that the negative pulse.caused by the separation of the felt and blanket occurs. This design not only minimizes the.
time the felt is in contact with the sheet; the added vacuum pulse will significantly reduce the amount of water that can flow, even over the shoit time. Point A in Figure 11 is the point of zero pressure on the pressure distribution. curve at the exit side of the:nip. The nip pressure curve for the sheet/felt in Figure 11 would most likely approach that shown in Figure 8.
The web is preferably either adhered to the Yankee dryer by nip transfer with a pressing unit including a pressing blanket or is after pressing adhered to the Yankee dryer. The web is dried by steam and hot air impingement hoods. Any suitable art recognized adhesive might be used on the Yankee dryer. Preferred adhesives include polyvinyl alcohol with suitable plasticizers, glyoxylated polyacrylamide with or without polyvinyl alcohol, and polyamide epichlorohydrin resins such 'as Quacoat A-252 (QA252), Betzcreplus 97 (Betz+97) and Calgon 675 B. Suitable adhesives are widely described in the patent literature. A comprehensive but non-exhaustive list includes U.S. Patent Nos. 5,246,544; 4,304,625; "4,064,213; 3,926,716;
4,501,640; 4,528,316; 4,788,243; 4,883,564; 4,684,439; 5,326,434;
4,886,579; 5,374,334; 4,440,898; 5,382,323; 4,094,718; 5,025,046; and 5,281,307. Typical release agents can be used in accordance with the present invention.
The final product may be calendered or uncalendered and is usually reeled to await further converting processes. The products according to the, wo:00/29667 PCT/US99/27097 present invention may be subjected to. any art recognized, converting operations, including embossing, printing, etc.
The following ezample is illustrative of the invention embodied herein.
A nascent web was formed on a Crescent-forming machine using a blend of 50/50 long fiber/short fiber refined to 23 SR freeness. Chemicals like wet strength agents or dry strength agents were not added to the stock.
The basis weight of the sheet on the Yankee dryer was 8.5 Ibs/3000 W. Two pressing an-angements were used on the paper machine. In the first pressing arrangement, the sheet was pressed onto a Yankee dryer with a suctioR
pressure roll. The vacuum in the suction roA\was nominally 0.22 bar. In the second pressing arrangement, the suction pressure roll was replaced by a Yankee shoe press. The sheet was conditioned before the shoe press with a suction turning roll having the same size and open area as the suction pressure roll. The suction tuming roll vacuum was nominally equivalent to the level used during the suction pressure roll experiments. After sheet conditioning, the web was pressed onto the Yankee with a shoe press. In order to obtain precise sheet solids data after the shoe press or the suction pressure roll, the Yankee dryer was run cold. Blotters were used to coltect flatsheets for physical property determination. Two types of shoes were run:
a typical 120 mm shoe and a 50 mm shoe. Figure 3 shows the pressure distribution of the shoes and the suction pressure roll. Figure 12 depicts a plot of sheet solids versus line loading. The typical 120 mm shoe shows no WO 00129667 PCT/US99f27097 solids benefit versus the suction pressure roll at present operating line load limits of current Yankee dryers (i.e., approximately, 87.5 kN/m), while the 50 mm pressure optimized shoe press shows an advantage of several percentage points of solids. Furthermore, the strength and specific volume properties of a web made with the 50 mm pressure optimized shoe press were equivalent to the strength and specific volume properties of a web made by the suction pressure roll.
Figures 13-15 illustrate a method for maximizing water removal in a press nip in accordance with another embodiment of the present invention.
The present embodiment involves a conventional wet pressing (CWP) process. For consistency, like numbers have been used to=indicate the corresponding portions of the apparatus depicted in Figures 13-15 with those, of Figures 1-12. The description of the apparatus of Figures 1-12 thus applies equally to this embodiment, unless stated otherwise.
Referring to Figure 13, the present embodiment uses a shoe press, preferably a controlled crown roll with a flexible shell and a concave shoe hydrodynamically loaded against one another. The present embodiment further includes a belt or, blanket (100) having a void volume that enhances sheet solids after the shoe press to further improve water removal in the press nip. Appropriate void volume can be achieved by a number of blanket configurations, including, but not limited to, those made by grooving, blind drilling and the like. The total void volume of the belt or blanket for use according to the present invention is preferably about 50 to about 3000 cmI/m2, more preferably about 100 to about 1000 cm'/mZ, most preferably from about 200 to about 500 cm'/m3.
Blankets for use according to the present invention can include any art recognized blanket having, or which can be modified to have, the required void volume.
For example, blankets disclosed by E.J. Justus and D. Cronin in Tappi, August 1964, Vol. 47, No. 8, p.493 include grooved belts that improve water removal in a press nip where the groove width is about 0.01 to about 0.03 in., the land width is about 2 to about 20 times the groove width and the groove depth is about 2 to about 10 times the groove width.
For another example, blankets disclosed by Bo-Christer Aberg in Das Papier No. 6, 1996 include grooved belts that work at higher line loads and machine speeds than smooth belts. The belts have groove widths of about 0.5 to about 1 mm and a void volume of about 100 cc/rn2 to about 500 cc/mz.
For yet another example, blankets disclosed by P. Slater and K.
Fitzpatrick in the 84" Annual Meeting of the Technical Section, CPPA, January 1998 include grooved belts that provide a press dryness about 1 % to about 3% greater than the press dryness obtained with a similar smooth belt. The belts have groove widths of about 0.58 to about 0.79 mm and a void volume of about 200 cc/mz to about 365 cc/m2.
For still another example, blankets disclosed by D. Madden et al. in the Tappi 1998 Engineering Conference include grooved belts that provide a press dryness about 1%
greater than the dryness obtained with a blind drilled belt. The grooved belt has an open area of about a 20.3% and a void volume of about 260 cc/mZ, and the blind drilled belt has an open area of about 21 % and a void volume of about 380 cc/mZ void volume.
Referring to Figure 14, blind drilling involves drilling holes into a smooth blanket, as will be understood by one of skill in the art. Nip compression between a blind drilled blanket and the felt causes a hydraulic pressure gradient between the holes in the blanket and the felt which improves water flow and removal.
The blind drilled blanket preferably has a plurality of holes sequentially arranged in the machine direction and a plurality of rows sequentially arranged in the cross-machine direction to cause a hydraulic pressure gradient. The blind drilled blanket can take a variety of configurations. For example, the hole depth, hole diameter, hole spacing, hole angle, hole geometry, row spacing and/or row pattern can be varied.
In particular, the hole depth can range from about 0.2 to about 10 mm, more preferably about 0.5 to about 5 mm, most preferably from about 0.5 to about 3 mm. Also, the hole depth can extend partially or completely through the blanket.
The hole diameter can range from about 0.2 to about 10 mm, more . . . y . . . . _ . . . CA 02317438 2000-07-10 WO 00n9667 PCT/US99n7097 preferably about 0.5 to about 5 mm, most preferably from about 1 to about 3 mm.
The hole spacing can range from about I to about 20 mm between holes arranged within the samerow, more preferably about 1 to about 10 mm, most preferably from about I to about 5 mm.
The hole angle C.e., the angle measured from the. surface of the belt material counterclockwise to the side of the hole) can range from about 45 to about 135 degrees along any wall in either the machine or cross-machine, more preferably about 70 to about 110 degrees, most preferably from about 80 "to about 100 degrees.
The row spacing can range from about 1 to about 20 mm, more preferably about 1 to about 10 mm, most preferably from about 1 to about 5 mm.
The hole geometry can be curved, linear or curvilinear, e.g. round, square, elliptical, polygonal, and the row pattem can be such that the holes in each row are aligned in the cross-machine direction, offset in the cross-machine direction, aligned in the machine direction, offset in the machine direction and the like.
There is no requirement that all holes have the same configuration, rather, each of the holes can have a different configuration, or one or more individual or set of holes can have the same configuration as one or more other individual or set of holes. Further, there is no requirement that the hole pattem form any type of geometric or other pattem, for example, the pattern WO 9on9667 PCT/US99J27097 can be random.
Referring to Figure,15, forming.grooves in the blanket involves removing elongated sections, as will be understood by one of skill in the art.
G . . . . . . . . . . _ _ _ Nip compression of the grooved blanket and the press felt causes a hydraulic pressure gradient in the machine 'direction, which improves water flow and removal.
The grooved blanket preferably has a pluratity of grooved sections sequentially arranged in the cross-machine direction that circumscribe the blanket to cause machine direction water movement. The grooved blanket can take a variety of configurations. For example, the groove depth, groove width, groove bevel, groove angle, land width, open area and groove patterrrn can all be varied.
In particular, the groove depth can range from about 0.1 to about 8 mm, more preferably about 0.2 to about 5 mm, most preferably from about 0.4 to about 3mm.
The groove width can range from about 0.1 to about 6 mm, more preferably about 0.2 to about 4 mm; most preferably from about 0.4 to about 3 mm.
The groove bevel (i.e., the angle measured from the surface of the belt material counterclockwise to the side of the groove minus 90 ) can range from about 0 to about 45 0, more preferably about 0 to about 30 , most preferably from about 0 to about 20 .
The groove angle can range from about 45 to about 135 degrees (with . . . . . r ~ . ~ . . .
WO 00129b67 PCT/US99/27097 90 degrees being orthogonal to the, cross-machine direction), more preferably about 65 to about 1150, most preferably from about 80 to about 100 .
The land width can range from about 0.2 to about 25 mm, more preferably about 0.4 to about 10 mm, most preferably from about 0.6 to about 4 mm.
The open area can range up to 80% of the total blanket area, more preferably about 15 to about 50%, most preferably from about 20 to about 40%.
The groove pattem can be such that the grooves in each row are aligned in the cross-machine direction, offset in the cross-machine direction, aligned in the machine direction, offset in the machine direction and the iike.
Also, for blankets-for use in the present invention, grooves need not have the same configuration, rather, all the grooves can have a different configuration, or one or more individuai or'set of grooves can have the same configuration as one or more other individuai or set of grooves. Further, there is no requirement that the groove pattem form any type of geometric or other pattem, for example, the groove placement can also be random.
Blankets having the disclosed void voiume will be readily apparent to the skilled artisan. Such biankets can include any physidal arrangement as long as the void space requirements are satisfied. Blankets for use in the present invention may be manufactured by any art recognized process, including but not limited to, casting molding, laser engraving, etc.
. . , . . . - . .
A punch press was used to perform dewatering experiments with different belt structures. An AMFIex 3S. felt manufactured by Appleton Mills Corporation was used to dewater the paper web. The web basis weight was 8.9 lbs/m1. The felt dryness was controlled to 69.3% dryness by using'blotters and a couch roll to remove excess water. Web moisture was controlled to 19.3% dryness by rewetting moist webs using a water spray. The webs were made from a 50/50 blend of northem softwood kraft and eucalyptus refined in a PFI mill to 510 ml CSF.
A smooth belt, a blind drilled belt and a grooved bett were used in the punch press experiment. The blind drilled belt had a bore area of. 3.82 mm2, a bore depth of 1.76 mm, an open area of 22.73% and a void volume of 402.9 cc/m2 The grooved belt had a groove width of 0.66 mm, a groove depth of 1.41 mm, a pitch of 0.33 grooves/mm, an open area of 21.78%, and a void volume of 270.6 cc/m2.
The punch press was operated such that the average nip pressure was fixed at 400 psi and the average nip dwell time was fixed at 1.8 ms. The experimental post press dryness results for the experiment were.:
smooth belt 31.0 +/- 0.30%
blind drilled belt 39.2 +/- 0.28%
grooved belt 40.3 +/- 0.42%
with the +/- percentage being the 95% confidence limit for the test.
These results indicate that pressing with either a blind drilled or grooved belt leads to enhanced sheet solids when compared to a smooth belt. These results also indicate that pressing with a grooved beit leads to enhanced sheet solids over a blind drilied belt.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification- and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.
Claims (72)
1. An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric;
a moving endless pressing blanket; a transfer cylinder, wherein said nascent web is located between said foraminous endless fabric and said transfer cylinder; and a pressing unit engaging said pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, said pressing unit being configured to impose an asymmetrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
a moving endless pressing blanket; a transfer cylinder, wherein said nascent web is located between said foraminous endless fabric and said transfer cylinder; and a pressing unit engaging said pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, said pressing unit being configured to impose an asymmetrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
2. An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric; a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a transfer cylinder wherein said nascent web is located between said foraminous endless fabric and said transfer cylinder, and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said transfer cylinder thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
3. An apparatus for forming an absorbent paper sheet product comprising: a moving foraminous endless fabric; means for depositing a nascent web for said absorbent paper sheet on said foraminous endless fabric;
a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a backing roll wherein said nascent web is located between said foraminous endless fabric and said backing roll; and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said backing roll thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
a moving endless grooved pressing blanket for pressing said nascent web on said foraminous endless fabric, said moving endless grooved pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket; a backing roll wherein said nascent web is located between said foraminous endless fabric and said backing roll; and a pressing unit engaging said grooved pressing blanket adapted to urge said nascent web for said absorbent paper sheet on said foraminous endless fabric into engagement with said backing roll thereby forming a nip, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
4. The apparatus of claim 1, 2, or 3, wherein said asymmetrical pressure distribution is skewed such that the pressure declines from a peak pressure to a value of 20% of said peak pressure over a nip length which is no more than about half of the nip length over which it rose to said peak pressure from 20%
of said peak pressure.
of said peak pressure.
5. The apparatus of claim 1, 2, or 3, wherein said pressing unit comprises at least one hydraulic engagement member.
6. The apparatus of claim 5, wherein said at least one hydraulic engagement member has a length of less than 3 inches.
7. The apparatus of claim 6, wherein said at least one hydraulic engagement member has a length of less than 2 inches.
8. The apparatus of claim 1, 2, or 3, wherein said foraminous endless fabric is a press felt or an impression fabric.
9. The apparatus of claim 1, 2, or 3, wherein the means for forming a nascent web is selected from a crescent former, a twin wire former, a suction breast roll former, or a fourdrinier former.
10. The apparatus of claim 1, 2, or 3, wherein said pressing unit is configured to have a line load of less than 175 kN/m.
11. The apparatus of claim 10, wherein said pressing unit is configured to have a line load of less than 100 kN/m.
12. The apparatus of claim 1, 2, or 3, wherein the peak pressure in said nip is at least 2500 kN/m2.
13. The apparatus of claim 12, wherein the peak pressure in said nip is at least 3000 kN/m2.
14. The apparatus of claim 13, wherein the peak pressure in said nip is at least 3150 kN/m2.
15. The apparatus of claim 2, wherein said pressing unit is configured to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
16. The apparatus of claim 1 or 15, wherein said pressing unit is configured to disengage said web from said foraminous endless fabric at a nip length of less than one inch from the point the nip pressure reaches zero.
17. The apparatus of claim 1 or 15, wherein said pressing unit is configured to both disengage said web from said foraminous endless fabric and disengage said foraminous endless fabric from said pressing blanket at a nip length of less than one inch from the point the nip pressure reaches zero.
18. The apparatus of claim 1, wherein the pressing blanket is a blind drilled blanket.
19. The apparatus of claim 18, wherein the blind drilled blanket has a plurality of holes formed thereon.
20. The apparatus of claim 19, wherein the diameter of the holes is about 0.2 to about 10 mm.
21. The apparatus of claim 19, wherein the holes extend into but not through the blanket.
22. The apparatus of claim 19, wherein a plurality of rows of holes are sequentially arranged in the cross-machine direction.
23. The apparatus of claim 22, wherein the rows of holes are arranged in a geometric pattern.
24. The apparatus of claim 1, wherein the blanket is a grooved blanket.
25. The apparatus of claim 2, 3, or 24, wherein the grooved blanket has at least one groove that extends in the machine direction.
26. The apparatus of claim 25, wherein the groove extends into but not through the blanket and has a depth of about 0.1 to about 8 mm.
27. The apparatus of claim 25, wherein the groove bevel is about 0 to about 45 degrees.
28. The apparatus of claim 25, wherein the groove angle is about 45 to about 135 degrees, with 90 degrees being orthogonal to the cross-machine direction.
29. The apparatus of claim 25, wherein a plurality of grooves are sequentially arranged in the cross-machine direction of the blanket.
30. The apparatus of claim 29, wherein the rows of grooves are arranged in a geometric pattern.
31. The apparatus of claim 29, wherein one or more individual groove has the same configuration as one or more other individual groove.
32. The apparatus of claim 29, wherein each of the plurality of grooves circumscribe the blanket.
33. The apparatus of claim 32 wherein the width of the widest portion of a groove is about 0.1 to about 6 mm.
34. The apparatus of claim 32, wherein the groove width is about 0.4 to about 3 mm.
35. The apparatus of claim 32, wherein the land width is about 0.2 to about 25 mm.
36. The apparatus of claim 32, wherein the open area is up to about 80% of the total blanket area.
37. The apparatus of claim 1 or 2, wherein said transfer cylinder is heated.
38. The apparatus of claim 37, wherein said transfer cylinder is heated by an induction heater.
39. The apparatus of claim 1 or 2, wherein said transfer cylinder is selected from a granite roll, a cold steel roll, a gas fired heater, or a Yankee drying cylinder.
40. The apparatus of claim 39, wherein said transfer cylinder is a Yankee drying cylinder.
41. The apparatus of claim 40, further comprising a creping blade for removing said absorbent paper sheet from said Yankee-drying cylinder:
42. The apparatus of claim 3, wherein said backing roll is heated.
43. The apparatus of claim 42, wherein said backing roll is heated by steam.
44. The apparatus of claim 42, wherein said backing roll is heated by an induction heater.
45. A method of making an absorbent paper sheet product comprising:
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless pressing blanket engaged with a pressing unit thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50%
of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless pressing blanket engaged with a pressing unit thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web and to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50%
of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
46. A method of making an absorbent paper sheet product comprising:
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless void volume containing pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket engaged with a pressing unit, thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
depositing a nascent web for said absorbent paper sheet product on a moving foraminous endless fabric; and contacting said moving foraminous endless fabric bearing said deposited nascent web with a moving endless void volume containing pressing blanket having a void volume of less than 1500 cm3/m2 and grooves that circumscribe the blanket engaged with a pressing unit, thereby forming a nip between said foraminous endless fabric and an impervious member, said pressing unit being configured to create a peak engagement pressure of at least 2000 kN/m2 at an overall line load of less than 240 kN/m, and wherein said pressing unit is configured to impose an asymmetrical pressure distribution upon said nascent web.
47. The method of claim 45 or 46, wherein said asymmetrical pressure distribution is skewed such that the pressure declines from a peak pressure to a value of 20% of said peak pressure over a nip length which is no more than about half of the nip length over which it rose to said peak pressure from 20%
of said peak pressure.
of said peak pressure.
48. The method of claim 45 or 46, wherein said pressing unit comprises at least one hydraulic engagement member.
49. The method of claim 48, wherein said at least one hydraulic engagement member has a length of less than 3 inches.
50. The method of claim 49, wherein said at least one hydraulic engagement member has a length of less than 2 inches.
51. The method of claim 45 or 46, wherein said foraminous endless fabric is a press felt or an impression fabric.
52. The method of claim 45 or 46, wherein said pressing unit is configured to have a line load of less than 175 kN/m.
53. The method of claim 52, wherein said pressing unit is configured to have a line load of less than 100 kN/m.
54. The method of claim 45 or 46, wherein the peak pressure in said nip is at least 2500 kN/m2.
55. The method of claim 54, wherein the peak pressure in said nip is at least 3000 kN/m2.
56. The method of claim 55, wherein the peak pressure in said nip is at least 3150 kN/m2.
57. The method of claim 46, wherein said pressing unit is configured to disengage said web from said foraminous endless fabric such that rewet of said nascent web by said foraminous endless fabric is less than 50% of the rewet predicted by the Sweet equations based upon the properties of said foraminous endless fabric and said nascent web.
58. The method of claim 45 or 56, wherein said pressing unit is configured to disengage said web from said foraminous endless fabric at a nip length of less than one inch from the point the nip pressure reaches zero.
59. The method of claim 45 or 56, wherein said pressing unit is configured to both disengage said web from said foraminous endless fabric and disengage said foraminous endless fabric from said pressing blanket at a nip length of less than one inch from the dint the nip pressure reaches zero.
60. The method of claim 45 or 46, wherein said nascent web contacts a transfer cylinder.
61. The method of claim 60, wherein said transfer cylinder is heated.
62. The method of claim 61, wherein said transfer cylinder is heated by an induction heater.
63. The method of claim 60, further comprising a creping blade for removing said absorbent sheet from said transfer cylinder.
64. The method of claim 45 or 46, wherein said nascent web contacts a backing roll.
65. The method of claim 64, wherein said backing roll is heated.
66. The method of claim 65, wherein said backing roll is heated by an induction heater.
67. The method of claim 45 or 46, wherein said moving endless blanket engaged with said pressing unit forms said nip with a Yankee drying cylinder.
68. The method of claim 67, wherein said web is dried on said Yankee drying cylinder.
69. The method of claim 68, wherein said dried web is creped from said Yankee drying cylinder.
70. The method of claim 45 or 46, wherein said pressing unit is a shoe press.
71. The method of claim 45 or 46, wherein said nascent web is compactively dewatered on said foraminous endless fabric prior to entering said nip.
72. The method of claim 45 or 46, wherein said pressing unit includes a hydraulic engagement member and said hydraulic engagement member is shaped and positioned to substantially align the separation of said foraminous endless fabric from said nascent web and the separation of said foraminous endless fabric from said endless pressing blanket.
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US09/191,376 US6248210B1 (en) | 1998-11-13 | 1998-11-13 | Method for maximizing water removal in a press nip |
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US6248210B1 (en) | 1998-11-13 | 2001-06-19 | Fort James Corporation | Method for maximizing water removal in a press nip |
DE10032251A1 (en) * | 2000-07-03 | 2002-01-17 | Voith Paper Patent Gmbh | Water extraction station for a web of tissue/toilet paper has a shoe press unit at the drying cylinder with an extended press gap and a suction unit within an overpressure hood at the carrier belt |
US6610173B1 (en) * | 2000-11-03 | 2003-08-26 | Kimberly-Clark Worldwide, Inc. | Three-dimensional tissue and methods for making the same |
US6752907B2 (en) * | 2001-01-12 | 2004-06-22 | Georgia-Pacific Corporation | Wet crepe throughdry process for making absorbent sheet and novel fibrous product |
US7494563B2 (en) * | 2002-10-07 | 2009-02-24 | Georgia-Pacific Consumer Products Lp | Fabric creped absorbent sheet with variable local basis weight |
US7442278B2 (en) * | 2002-10-07 | 2008-10-28 | Georgia-Pacific Consumer Products Lp | Fabric crepe and in fabric drying process for producing absorbent sheet |
-
1998
- 1998-11-13 US US09/191,376 patent/US6248210B1/en not_active Expired - Lifetime
-
1999
- 1999-11-12 TR TR2000/02032T patent/TR200002032T1/en unknown
- 1999-11-12 EP EP99960375A patent/EP1047830A1/en not_active Withdrawn
- 1999-11-12 US US09/439,610 patent/US6387217B1/en not_active Expired - Lifetime
- 1999-11-12 WO PCT/US1999/027097 patent/WO2000029667A1/en not_active Application Discontinuation
- 1999-11-12 CA CA002317438A patent/CA2317438C/en not_active Expired - Lifetime
-
2000
- 2000-03-17 US US09/528,184 patent/US6458248B1/en not_active Expired - Lifetime
-
2001
- 2001-07-16 US US09/904,540 patent/US6517672B2/en not_active Expired - Lifetime
- 2001-11-14 US US09/987,248 patent/US6669821B2/en not_active Expired - Lifetime
-
2003
- 2003-03-03 US US10/376,319 patent/US7300552B2/en not_active Expired - Fee Related
-
2007
- 2007-10-18 US US11/874,251 patent/US7754049B2/en not_active Expired - Fee Related
Also Published As
Publication number | Publication date |
---|---|
US6458248B1 (en) | 2002-10-01 |
US7300552B2 (en) | 2007-11-27 |
US20020088595A1 (en) | 2002-07-11 |
US7754049B2 (en) | 2010-07-13 |
US6387217B1 (en) | 2002-05-14 |
US6248210B1 (en) | 2001-06-19 |
TR200002032T1 (en) | 2001-01-22 |
US6669821B2 (en) | 2003-12-30 |
EP1047830A1 (en) | 2000-11-02 |
US6517672B2 (en) | 2003-02-11 |
US20030226650A1 (en) | 2003-12-11 |
US20080035289A1 (en) | 2008-02-14 |
CA2317438A1 (en) | 2000-05-25 |
US20020088594A1 (en) | 2002-07-11 |
WO2000029667A1 (en) | 2000-05-25 |
WO2000029667A9 (en) | 2000-11-02 |
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