CA2250851A1 - A process for including a fine particulate filler into tissue paper using starch - Google Patents

Abstract

A process for incorporating a fine particulate filler such as kaolin clay into tissue paper is disclosed. The process results in strong, soft, and low dusting tissue paper webs useful in the manufacture of soft, absorbent sanitary products such as bath tissue, facial tissue, and absorbent towels.

Description

CA 022~08~1 1998-10-01 wo 97/37080 PCT/US97/05~96 A PROCESS FOR INCLUDING A FINE PARTICUI,ATE FILLER INTO
TISSUE PAPER USING STARCH
-This invention relates, in general, to creped tissue paper products and processes. More specifically, it relates to a process for incorporating a fine particulate filler into creped tissue paper products.

BACKGROUND OF THE rNVENTION
Sanitary paper tissue products are widely used. Such items are commercially offered in forrnats tailored for a variety of uses such as facial tissues, toilet tissues and absorbent towels. The formats, i.e. basis weight, thickness, strength, sheet size, dispensing mediurn, etc. of these products often differ widely, but they are linked by 5 the common process by which they originate, the so-called creped papenn~king process.
Creping is a means of mechanically compacting paper in the machine direction. The result is an increase in basis weight (mass per unit area) as well as dramatic changes in many physical plop~llies, particularly when measured in the 20 m~rhin~ direction. Creping is generally accomplished with a flexible blade~ a so-called doctor blade, against a Yankee dryer in an on m~rhine operation.
A Yankee dryer is a large ~i~metP~ generally 8-20 foot drurn which is desi~ d to be pressurized with steam to provide a hot surface for completing thedrying of pap~ kin~ webs at the end of the papermaking process. The paper web 2s which is first formed on a foraminous forming carrier, such as a Fourdrinier wire.
where it is freed of the copious water needed to disperse the fibrous slurry is generally transferred to a felt or fabric in a so-called press section where de-watering is continued either by mechanically compacting the paper or by some other de-watering method such as through-drving with hot air. before finally being transferred 30 in the semi-dry condition to the surface of the Yankee for the drying to be completed.
The various creped tissue paper products are further linked by comrnon CA 022~08~1 1998-10-01 consumer demand for a generally conflicting set of physical properties: A pleasing tactile impression, i.e. soRness while~ at the same time having a high strength and a resistance to linting and dusting.
Softness is the tactile sensation perceived by the consumer as helshe holds a 5 particular product, rubs it across his/her skin, or crumples it within his/her hand.
This tactile sensation is provided by a combination of several physical properties.
One of the most important physical properties related to softness is generally considered by those skilled in the art to be the stiffness of the paper web from which the product is made. Stiffness, in turn, is usually considered to be directly dependent 10 on the strength ofthe web.
Strength is the ability of the product, and its constituent webs, to m~int~in physical integrity and to resist tearing, bursting, and shredding under use conditions.
Linting and dusting refers to the ten-len~y of a web to release unbound or loosely bound fibers or particulate fillers during h~n~ling or use.
Creped tissue papers are generally comprised essentially of papenn~kin~
fibers. Small amounts of chemical functional agents such as wet strength or dry strength binders, retention aids, surf~ct~nt~, size, chemical softeners, crepe facilitating compositions are fre~uently included but these are typically only used in minor amounts. The papermaking fibers most frequently used in creped tissue papers are virgin chemical wood pulps.
As the world's supply of natural resources comes under increasing economic and environmental scrutiny, pressure is mounting to reduce consumption of forestproducts such as virgin chemical wood pulps in products such as sanitary tissues.
One way to extend a given supply of wood pulp without sacrificing product mass is to replace virgin chemical pulp fibers with high yield fibers such as mechanical or chemi-mech~nical pulps or to use fibers which have been recycled. Unfortunately,comparatively severe deterioration in performance usually accompanies such changes. Such fibers are prone to have a high coarseness and this contributes to the loss of the velvety feel which is imparted by prime fibers selected because of their flaccidness. In the case of the mechanical or chemi-mechanical liberated fiber, high coarseness is due to the retention of the non-cellulosic components of the original wood substance. such components including lignin and so-called hemicelluloses.
This makes each fiber weigh more without increasing its length. Recycled paper can also tend to have a high mechanical pulp content, but, even when all due care is CA 022~08~1 1998-10-01 exercised in selecting the wastepaper grade to rninimi7e this, a high coarseness still often occurs. This is thought to be due to the impure mixture of fiber morphologies which naturally occurs when paper from many sources is blended to make a recycled pulp. For example, a certain wastepaper might be selected because it is primarily North American hardwood in nature; however, one will often find extensive ~ cont~min~fion from coarser softwood fibers, even of the most deleterious species such as variations of Southern U.S. pine. U.S. Patent 4,300,981, Carstens, issued November 17, 1981, and incorporated herein by reference, explains the textural and surface qualities which are imparted by prime fibers. U.S. Patent 5,228,954, o Vinson, issued July 20, 1993, and U.S. Patent 5,405,499, Vinson issued April 11, 1995, both incorporated herein by reference, disclose methods for upgrading suchfiber sources so that they have less deleterious effects, but still the level ofreplacement is limited and the new fiber sources themselves are in limited supply and this often limits their use.
Applicants have discovered that another method of limiting the use of wood pulp in sanitary tissue paper is to replace part of it with a lower cost, readily available filling material such as kaolin clay or calciurn carbonate. While those skilled in the art will recognize that this practice has been common in some parts of the paper industry for many years, they will also appreciate that e~ctendin~ this approach to sanitary tissue products has involved particular difficulties which have prevented it from being practiced up to now.
One major restriction is the retention of the filling agent during the papern~king process. Among paper products, sanitary tissues occupy an extreme oflow basis weight. The basis weight of a tissue web as it is wound on a reel from a Yankee m~hine is typically only about 15 g/m2 and because of the crepe, or foreshortening, introduced at the creping blade, the dry fiber basis weight in the forming, press, and drying sections of the machine is actually lower than the finished dry basis weight by from about 10% to about 20%. To compound the difficulties in retention caused by the low basis weight, tissue webs occupy an extreme of low density, often having an apparent density as wound on the reel ofonly about 0.1 g/cm3 or less. While it is recognized that some of this loft is introduced at the creping blade, those skilled in the art will recognize that tissue webs are generally formed from relatively free stock which means that the fibers of which they are comprised are not rendered flaccid from beating. Tissue machines are required to operate at very high speeds to be practical; thus free stock is needed to prevent excessive forming pressures and drying load. The relatively stiff fibers CA 022~08~1 1998-10-01 WO 97137~80 PCT/US97/05596 comprising the free stock retain their ability to prop open the embryonic web as it is forming. Those skilled in the art will at once recognize that such light weight, low density structures do not afford any significant opportunity to filter fine particulates as the web is forming. Filler particles not substantively affixed to fiber surfaces will 5 be torn away by the torrent of the high speed approach flow systems, hurled into the liquid phase, and driven through the embryonic web into the water drained from the forming web. Only with repeated recycling of the water used to form the web doesthe concentration of particulate build to a point where the filler begins to exit with the paper. Such concentrations of solids in water effluent are impractical.
o A second major limitation is the general failure of particulate fillers to naturally bond to papermaking fibers in the fashion that pap~ king fibers tend to bond to each other as the formed web is dried. This reduces the strength of the product. Filler inclusion causes a reduction in strength, which if left uncorrected, severely limits products which are already quite weak. Steps required to restorestrength such as increased fiber beating or the use of chemical strengthening agents is often restricted as well.
The deleterious effects of filler on sheet integrity also often cause hygiene problems by plugging press felts or by transferring poorly from the press section to the Yankee dryer.
Finally, tissue products containing fillers are prone to lint or dust. This is not only because the fillers themselves can be poorly trapped within the web, but also because they have the aforementioned bond inhibiting effect which causes a localized weakening of fiber anchoring into the structure. This tendency can cause operational difficulties in the creped paperrn~kin~ processes and in subsequent 2s converting operations, because of excessive dust created when the paper is handled.
Another consideration is that the users of the sanitary tissue products made from the filled tissue c~m~n~i that they be relatively free of lint and dust.
Consequently, the use of fillers in papers made on Yankee machines has been severely limited. United States Patent 2,216,143, issued to Thiele on October 1, 1940, and incorporated herein by reference discusses the limitations of fillers on Yankee machines and discloses a method of incorporation which overcomes those limitations. Unfortunately, the method requires a cumbersome unit operation to coat a layer of adhesively bound particles onto the felt side of the sheet while it is in contact with the Yankee dryer. This operation is not practical for modern high CA 022~08~1 1998-10-01 speed Yankee machines and, those skilled in the art will recognize that the Thiele method would produce a coated rather than filled tissue product. A "filled tissue paper" is distinguished from "coated tissue paper" essentially by the methods - practiced to produce them, i.e. a "filled tissue paper" is one which has the particulate 5 matter added to the fibers prior to their assembly into a web while a "coated tissue ~ paper" is one which has the particulate matter added after the web has been e~senti~lly assembled. As a result of this difference, a filled tissue paper product can be described as a relatively lightweight, low density creped tissue paper made on a Yankee machine which contains a filler dispersed throughout the thickness of at 0 least one layer of a multi-layer tissue paper, or throughout the entire thickness of a single-layered tissue paper. The term "dispersed throughout" means that essentially all portions of a particular layer of a filled tissue product contain filler particles, but, it specifically does not imply that such dispersion necPssQrily be uniform in that layer. In fact, certain advantages can be anticipated by achieving a difference in 5 filler concentration as a function of thickness in a filled layer of tissue.
Therefore, it is the object of the present invention to provide a process for incorporating a fine particulate filler into a creped tissue paper such as to overcome the aforellle,l~ioned limitations of the prior art. The process disclosed herein enables the m~nllf~cture of creped tissue paper at high levels of retention of the filler; the 20 resultant tissue is soft, has a high level of tensile strength, and is low in dust.
This and other objects are obtained using the present invention as will be taught in the following disclosure.
SUMMARY OF THE INVENTION
The invention is a process for incorporating a non-cellulosic fine particulate filler 25 into a creped tissue paper. The process comprises the steps of:
a) cont~ting an aqueous dispersion of a non-cellulosic particulate filler with an aqueous dispersion of starch, b) mixing the aqueous dispersion of starch-contacted filler with papermaking fibers forming an aqueous papermaking furnish comprising starch-contacted filler and 30 paperrnaking fibers, c) contacting said aqueous paperrn~king furnish with a flocculant, d) forming an embryonic paper web from the aqueous paperrnaking furnish on CA 022~08~1 1998-10-01 forarninous paperm~king clothing, e) removing water from said embryonic web to form a semi-dry papermaking web, f) adhering the semi-dry papermaking web to a Yankee dryer and drying said web to a substantially dry condition, 5 g) creping the subst~nti~lly dry web from the Yankee dryer by means of a flexible creping blade, thereby forming a creped tissue paper.
In its preferred embodiment, the invention incorporates non-cellulosic particulate filler such that said filler comprises at least about 1% and up to about 50%, but, more preferably from about 8% to about 20% by weight of said tissue.
o Unexpected combinations of softness, strength, and resi~t~nce to dusting have been obtained by filling creped tissue paper with these levels of particulate fillers by the process of the present invention.
In its preferred embodiment, the filled tissue paper of the present invention has a basis weight between about 10 g/m2 and about S0 glm2 and, more preferably,between about 10 glm2 and about 30 g/m2. It has a density between about 0.03 g/cm3 and about 0.6 g/cm3 and, more preferably, between about O.OS g/cm3 and 0.2g/cm3.
The ~lefelled embodiment further comprises ~ king fibers of both hardwood and softwood types wherein at least about 50% of the papçnn~king fibers20 are hardwood and at least about 10% are softwood. The hardwood and softwood fibers are most preferably isolated by relegating each to separate layers wherein the tissue comprises an inner layer and at least one outer layer.
The ~,Çe~cd practice of the process of the present invention utilizes a starch of minimllm water solubility while it contacts the particulate filler of the present 2s invention. Most preferably the starch possesses an electrostatic charge opposite that of the particulate filler such that it is attracted to the surface of the filler, so that the starch and filler tend to agglomerate when the two are brought into contact with one another in an aqueous dispersion.
The ple~l,ed flocculant used in the process of the present invention is a 30 cationic polyelectrolyte; most preferred is a cationic polyacrylamide.
The ~lef~ d creped tissue papermaking process of the present invention CA 022~08~1 1998-10-01 uses pattern densification wherein water removal and transfer to the Yankee dryer is effected while the embryonic tissue web is supported by a drying fabric having an array of supports. This results in a creped tissue product having zones of relatively high density dispersed within a high bulk field. Such processes include pattern s densification methods wherein zones of relatively high density are formed in continuous pattern while the high bulk field is formed in a discrete pattern. Most preferably, the tissue paper is through air dried.
In its preferred embodiment, the process of the present invention utilizes a particulate filler selected from the group coniictin~ of clay, calcium carbonate, 10 titanium dioxide, talc, al-lminl~m silicate, calcium silicate, alumina trihydrate, activated carbon, pearl starch, calcium sulfate, glass microspheres, diatomaceous earth, and mixtures thereof. When selecting a filler from the above group several factors need to be evaluated. These include cost, availability, ease of ret~ining into the tissue paper, color, scattering potential, refractive index, and chemical s compatibility with the selected papenn~king environrnent.
It has now been found that a particularly suitable filler is kaolin clay. Most preferably the so called "hydrous alllminl~m silicate" form of kaolin clay is preferred as contrasted to the kaolins which are further processed by calcining.
The morphology of kaolin is naturally platy or blocky, but it is preferable to 20 use clays which have not been subjected to mechanical del~min~tion treatm~nt~ as this tends to reduce the mean particle size. It is common to refer to the mean particle size in terms of equivalent spherical ~ met~r. An average equivalent spherical diameter greater than about 0.2 micron, more preferably greater than about 0.5 micron is l,lefe..ed in the practice of the present invention. Most preferably, an 2s equivalent spherical diameter greater than about 1.0 micron is prer~ d.
All percentages, ratios and proportions herein are by weight unless otherwise specified.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure I is a scll~m~tic representation illustrating the steps for pre~ua~ g the30 aqueous papermaking furnish for the creped paperrn~king process, according to the present invention.
Figure 2 is a sr~em~tic representation illustrating a creped papermaking CA 022~08~1 1998-10-01 process according to the present invention for producing a strong, soft, and low lint creped tissue paper comprising papermaking fibers and particulate fillers.
DETAILED DESCRlPTION OF T~E INVENTION
While this specification concludes with claims particularly pointing out and 5 distinctly cl~iming the subject matter regarded as the invention, it is believed that the invention can be better understood from a reading of the following detailed description and of the appended examples.
As used herein, the term "comprising" means that the various components, ingredients, or steps, can be conjointly employed in practicing the present invention.
o Accordingly, the term "comprising" encompasses the more restrictive terms "consisting essenti~lly of" and "consisting of."
As used herein, the term "water soluble" refers to materials that are soluble in water to at least 3%, by weight, at 25 ~C.
As used herein, the terms "tissue paper web, paper web, web, paper sheet and 5 paper product" all refer to sheets of paper made by a process comprising the steps of forming an aqueous pdlJc.~..Akin~ furnish, depositing this furnish on a foraminous surface, such as a ~ourdrinier wire, and removing the water from the furnish as by gravity or vacuum-Assi~t~cl drainage, with or without pressing, and by evaporation, comprising the final steps of adhering the sheet in a semi-dry condition to the 20 surface of a Yankee dryer, completing the water removal by evaporation to an essPnti~lly dry condition, removal of the web from the Yankee dryer by means of a flexible creping blade, and winding the resultant sheet onto a reel.
As used herein, the term "filled tissue paper" means a paper product that can be described as a relatively lightweight, low densit,v creped tissue paper made on a 25 Yankee m~ine which contains a filler dispersed throughout the thickness of atleast one layer of a multi-layer tissue paper, or throughout the entire thickness of a single-layered tissue paper. The term "dispersed throughout" means that essenti~lly all portions of a particular layer of a filled tissue product contain filler particles, but, it specifically does not imply that such dispersion n~cçss~rily be uniform in that 30 layer. In fact, certain advantages can be anticipated by achieving a difference in filler concentration as a function of thickness in a filled layer of tissue.
The terms "multi-layered tissue paper web, multi-layered paper web, multi-CA 022~08~1 1998-10-01 layered web, multi-layered paper sheet and multi-layered paper product" are all used interchangeably in the art to refer to sheets of paper prepared from two or morelayers of aqueous paper making furnish which are preferably comprised of different - fiber types, the fibers typically being relatively long softwood and relatively short s hardwood fibers as used in tissue paper making. The layers are preferably formed from the deposition of separate streams of dilute fiber slurries upon one or more endless foraminous surfaces. If the individual layers are initially formed on separate foraminous surfaces, the layers can be subsequently combined when wet to form a multi-layered tissue paper web.
o As used herein, the term "single-ply tissue product" means that it is comprised of one ply of creped tissue; the ply can be substantially homogeneous in nature or it can be a multi-layered tissue paper web. As used herein, the term "multi-ply tissue product" means that it is comprised of more than one ply of creped tissue. The plies of a multi-ply tissue product can be subst~nti:llly homogeneous in nature or they can be multi-layered tissue paper webs.
The invention is a process for incorporating a fine particulate filler into a creped tissue paper said process comprising the steps of:
a) contacting an aqueous dispersion of a non-cellulosic particulate filler with an aqueous dispersion of starch, b) mixing the aqueous dispersion of starch-contacted filler with pal,~ ",~king fibers forming an aqueous papc.~ king furnish comprising starch-contacted filler and paperrn~kin~ fibers, c) contacting said aqueous pap~ aking furnish with a flocculant, d) forming an embryonic paper web from the aqueous papermaking furnish on foraminous paperrn~kin~ clothing, e) removing water from said embryonic web to form a semi-dry paperrnAking web, f) adhering the semi-dry paperrn~king web to a Yankee dryer and drying said web to a substantially dry condition, g) creping the substantially dry web from the Yankee dryer by means of a flexible creping blade, thereby forrning a creped tissue paper.

CA 022~08~l l998-lO-Ol WO 97/37~80 PCT/US97/05596 Alternatively, the invention is a process for incorporating a fine non-cellulosic particulate filler into a multi-layered creped tissue paper, said process comprising the steps of:
a) contacting an aqueous dispersion of a non-cellulosic particulate filler with an s aqueous dispersion of starch, b) mixing the aqueous dispersion of starch-contacted filler with paperm~king fibers, thereby forming a filler-cont~ining aqueous paperrn~king furnish comprising starch-contacted filler and paperrn~king fibers, c) contacting said aqueous paperrnaking furnish with an aqueous dispersion of a 10 flocc~ nt, d) providing at least one additional papermaking furnish, e) directing said paperrn~king furnishes onto foraminous paperrn~ing clothing;
thereby forming an embryonic multi-layered paper web from the filler-cont~ininE~aqueous papermaking furnish and the additional pal.~ .n~in~ furnish in a manner 5 to create a multi-layered paper web wherein at least one layer is forrned from the filler-cont~ining aqueous paperrn~king filrnish and at least one layer is formedfrom said additional p~ellllaking furnish, f) removing water from said multi-layered embryonic web to form a semi-dry multi-layered ~l.e. ",~king web, 20 g) adhering the semi-dry multi-layered paperrn~king web to a Yankee dryer and drying said multi-layered web to a subst~nti~lly dry condition, h) creping the snbst~nti~lly dry multi-layered web from the Yankee dryer by means of a flexible creping blade, thereby forming a multi-layered creped tissue paper.
The following part of the specification details each of these steps of the 2s process of the present invention.
Contacting Parti~lqt~ Filler with Starch The Particulate Filler In its preferred embodiment, the invention incorporates non-cellulosic particulate filler such that said filler comprises at least about 1% and up to about CA 022~08~1 1998-10-01 50%, but, more preferably from about 8% to about 20% by weight of said tissue.
Unexpected combinations of softness, strength, and resistance to dusting have been obtained by filling creped tissue paper with these levels of particulate fillers by the process of the present invention.
The invention provides for a creped tissue paper comprising paperm~king fibers and a particulate filler. In its preferred embodiment, the particulate filler is selected from the group consisting of clay, calcium carbonate, titanium dioxide, talc, al-lmin~m silicate, calcium silicate, alumina trihydrate, activated carbon, pearl starch, calcium sulfate, glass microspheres, diatomaceous earth, and mixtures o thereof. When selecting a filler from the above group several factors need to be evaluated. These include cost, availability, ease of ret~ining into the tissue paper, color, scattering potential, refractive index, and chemical compatibility with the selected papermaking environment.
It has now been found that a particularly suitable particulate filler is kaolin s clay. Kaolin clay is the common name for a class of naturally occurring alurninum silicate mineral beneficiated as a particulate.
With respect to terminology, it is noted that it is common in the industry, as well as in the prior art patent literature, when referring to kaolin products orprocessin~, to use the term "hydrous" to refer to kaolin which has not been subject to calcination. Calcination subjects the clay to temperatures above 450~C, whichtemperatures serve to alter the basic crystal structure of kaolin. The so-called"hydrous" kaolins may have been produced from crude kaolins, which have been subjected to beneficiation, as, for example, to froth flotation, to magnetic separation, to mech~nical del~min~tion~ grinding, or similar comminution, but not to the mentioned heating as would impair the crystal structure.
To be accurate in a technical sense, the description of these materials as "hydrous" is in~plopl;ate. More specifically, there is no molecular water actually present in the kaolinite structure. Thus although the composition can be, and often is, ~ ;ly written in the forrn 2H~o-Al2o3.2sio2~ it has long been known that kaolinite is an aluminum hydroxide silicate of approximate composition A12(OH)4Si2Os, which equates to the hydrated formula just cited. Once kaolin is subjected to calcination, which for the purposes of this specification refers tosubjecting a kaolin to temperatures excee~ g 450~C, for a period sufficient to elimin~te the hydroxyl groups, the original crystalline structure of the kaolinite is CA 022~08~l l998-lO-Ol destroyed. Therefore, although technically such calcined clays are no longer '~kaolin", it is common in the industry to refer to these as calcined kaolin, and, for the purposes of this specification, the calcined materials are included when the class of materials "kaolin" is cited. Accordingly, the terrn "hydrous aluminum silicate"
5 refers to natural kaolin, which has not been subjected to calcination Hydrous aluminum silicate is the kaolin form most preferred in the practice of the present invention. It is therefore characterized by the before mentioned approximate 13% by weight loss as water vapor at tempeldlurCs excee~ling 450~C.
The morphology of kaolin is naturally platy or blocky, because it naturally o occurs in the forrn of thin platelets which adhere together to form "stacks" or "books". The stacks separate to some degree into the individual platelets duringprocessing, but it is preferable to use clays which have not been subjected to extensive mechanical .~el~min~tion treatments as this tends to reduce the mean particle size. It is common to refer to the mean particle size in terrns of equivalent 5 spherical diameter. An average equivalent spherical diarneter greater than about 0.2~, more preferably greater than about 0.5~1 is plefell~d in the practice of the present invention. Most preferably, an equivalent spherical diameter greater than about 1~1, but less than about 5'~1.
Most mined clay is subjected to wet processing. Aqueous s~spen~ling of the 20 crude clay allows the coarse impurities to be removed by centrifugation and provides a media for chemical ble~t~hing. A polyacrylate polymer or phosphate salt is sometimes added to such slurries to reduce viscosity and slow settling. Resultant clays are normally shipped without drying at about 70% solids suspen~ions, or they can be spray dried.
Treatments to the clay, such as air floating, froth flotation, washing, ble~ching, spray drying, the addition of agents as slurry stabilizers and viscosity modifiers, are generally acceptable and should be selected based upon the specific commercial considerations at hand in a particular circ~m.ct~nce.
Each clay platelet is itself a multi-layered structure of al--min--m polysilicates. A continuous array of oxygen atoms forms one face of each basic layer. The polysilicate sheet structure edges are united by these oxygen atoms. A
continuous array of hydroxyl groups of joined octahedral alumina structures forms the other face forrning a two-dimensional polyaluminum oxide structure. The oxygen atoms sharing the tetrahedral and octahedral structures bind the aluminum CA 022~08~1 1998-10-01 atoms to the silicon atoms.
Imperfections in the assembly are primarily responsible for the natural clay - particles posses~ing an anionic charge in suspension. This happens because other di-, tri-, and tetra-valent cations substitute for al-lminllm The consequence is that s some of the oxygen atoms on the surface become anionic and become weakly dissociable hydroxyl groups.
Natural clay also has a cationic character capable of exrh~nging their anions for others that are preferred. This happens because aluminum atoms lacking a full complement of bonds occur at some frequency around the peripheral edge of the o platelet. They must satisfy their r~m~inin~ valencies by attracting anions from the aqueous suspension that they occupy. If these cationic sites are not satisfied with anions from solutions, the clay can satisfy its own charge balance by orienting itself edge to face assembling a "card house" structure which forms thick dispersions.
Polyacrylate dispersants ion exchange with the cationic sites providing a repulsive 5 character to the clay preventing these assemblies and simplifying the production, shipping, and use of the clay.
A kaolin grade WW Filg) is a kaolin marketed by Dry Branch Kaolin Company of Dry Branch, Georgia suitable to make creped tissue paper webs of the present invention. It is available in either spray dried or in slurry (70% solids) form.
20 Starch The present invention utilizes starch, added in amounts of about 0.1% to about 5%, but most preferably from about 0.25% to about 0.75%, by weight based on the weight of the particulate filler.
A starch that has limited solubility in water in the presence of particulate 2s fillers and fibers is particularly useful in the present invention. A particularly ~fefe.led means of achieving this is to use a starch which possesses a charge opposite to that of the particulate filler so that, when the filler and the starch are suspended in aqueous medium, they tend to agglomerate. Since most particulate fillers possess a net anionic charge under practical papermaking conditions, the most 30 preferred form of starch for the present invention is a so called "cationic starch".
As used herein the ter~n "cationic starch" is defined as starch, as naturally derived, which has been further chemically modified to impart a cationic constituent CA 022~08~1 1998-10-01 moiety. Preferably the starch is derived from corn or potatoes, but can be derived from other sources such as rice, wheat, or tapioca. Starch from waxy maize also known industrially as amioca starch is particularly preferred. Amioca starch differs from common dent corn starch in that it is entirely amylopectin, whereas common 5 corn starch contains both amylopectin and amylose. Various unique characteristics of amioca starch are further described in "Amioca - The Starch from Waxy Corn", H. H. Schopmeyer, Food Industries, December 1945, pp. 106-108.
Cationic starches can be divided into the following general classifications:
(1) tertiary aminoalkyl ethers, (2) onium starch ethers including quaternary ~mines, 0 phosphonium, and sulfonium derivatives, (3) primary and secondary ~mino~lkyl starches, and (4) miscellaneous (e.g., imino starches). New cationic products continue to be developed, but the tertiary aminoalkyl ethers and quaternary ammonium alkyl ethers are the main commercial types. Preferably, the cationic starch has a degree of substitution ranging from about 0.01 to about 0.1 cationic 5 substituent per anhydroglucose units of starch; the substituents preferably chosen from the above mentioned types. Suitable starches are produced by National Starch and Chemical Company, (Bridgewater, New Jersey) under the tr~d~n~me, RediBOND~. Grades with cationic moieties only such as RediBOND 5320~) and RediBOND 5327~) are suitable, and grades with additional anionic functionality 20 such as RediBOND 2005~) are also suitable.
Contactin~ the Particulate Filler with the Starch The selected particulate filler is first prepared by also dispersing it into an aqueous slurry. Dilution generally favors the absorption of polymers and retention aids onto solids ~u~rdces; consequently, the slurry or slurries of particulate fillers at ~s this point in the p~e~ dlion is no more than about 10% and preferably from about 1-5% solids by weight.
Similarly, the starch is preferably properly dispersed in water prior to contacting the particulate filler. The raw starch can be in gr~nnl~r forrn, pre-gel~tini7Pcl granular form, or dispersed form. While the dispersed form is preferred 30 for ease of use, any form of raw starch can be used and none are disclaimed. If the raw starch is in granular pre-gel~tini~Pcl form, it need only be dispersed in cold water prior to its use, with the only precaution being to use equipment which overcomes any tendency to gel-block in forming the dispersion. Suitable dispersers known as eductors are cornmon in the industry. If the starch is in granular forrn and has not CA 022~08~1 1998-10-01 been pre-gel~tini7Pd it is necessary to cook the starch to induce swelling of the granules. Preferably, such starch granules are swollen, as by cooking, to a point just prior to dispersion of the starch granule. Such highly swollen starch granules shall - be referred to as being "fully cooked". The conditions for dispersion in general can 5 vary depending upon the size of the starch granules, the degree of crystallinity of the - granules, and the amount of amylose present. Fully cooked amioca starch, for example, can be prepared by heating an aqueous slurry of about 4% consistency ofstarch granules at about 190 ~F (about 88 ~C) for between about 30 and about 40 minutes.
lo After re~c~ling a properly water dispersed starch, it need only be further diluted to the proper consistency for use. The preferred dilutions are below about 10% solids, but above about 0.1% solids. Most preferred dilutions are about 1%
solids.
When both the particulate filler and the starch are brought to this condition, s the two dispersions can be mixed. With cationic starch and anionic filler, thereaction between the starch and the particulate filler is relatively fast, and the minimum amount of time required to thoroughly mix the two is sufficient time forthe reaction between the materials to occur as well.
While not wishing to be bound by theory, it is believed that the cationic 20 starch which is initially dissolved in water, becomes insoluble in the presence of filler because of its attraction for the anionic sites on the filler surface. This causes the filler to be covered with the bushy starch molecules which provide an attractive surface for more filler particles, ultimately resulting in agglomeration of the filler.
While the charge characteristics of the starch are important to aid in the formation of 25 the agglomerates, the essen~i~l characteristic of the starch is believed to be related to the size and shape of the starch molecule rather than wholly its charge characteristics. For example, inferior results would be expected by substituting a charge biasing species such as synthetic linear polyelectrolyte for the cationic starch.
Mixing the Starch and Filler with Papermaking Fibers 30 The Papermakin~ Fibers It is anticipated that wood pulp in all its varieties will normally comprise thepap~....~king fibers used in this invention. However, other cellulose fibrous pulps, such as cotton linters, bagasse, rayon, etc., can be used and none are disclaimed.

CA 022~08~l l998-lO-Ol Wood pulps useful herein include chemical pulps such as, sulfite and sulfate (sometimes called Kraft) pulps as well as mechanical pulps including for example, ground wood, ThermoMechanical Pulp (TMP) and Chemi-ThermoMechanical Pulp (CTMP). Pulps derived from both deciduous and coniferous trees can be used.
Both hardwood pulps and softwood pulps as well as combinations of the two may be employed as papelm~kin~ fibers for the tissue paper of the present invention.
The terrn "hardwood pulps" as used herein refers to fibrous pulp derived from the woody substance of deciduous trees (angiosperms), whereas "softwood pulps" are fibrous pulps derived from the woody substance of coniferous trees (gymnosperms).
o Blends of hardwood Kraft pulps, especially eucalyptus, and northern softwood Kraft (NSK) pulps are particularly suitable for making the tissue webs of the present invention. A preferred embodiment of the present invention comprises forming layered tissue webs wherein, most preferably, hardwood pulps such as eucalyptus are used for outer layer(s) and wherein northern softwood Kraft pulps are used for the inner layer(s). Also applicable to the present invention are fibers derived from recycled paper, which may contain any or all of the above categories of fibers.
Paperrn~king fibers are first prepared by liberating the individual fibers into a aqueous slurry by any of the corn~non pulping methods adequately described in the prior art. Refining, if n~cess~ry, is then carried out on the selected parts of the paperrnaking furnish. It has been found that there are advantages in retention and in reducing lint, if the aqueous slurry of paperm~kin~ fibers which will later be used to adsorb the particulate filler is refined at least to the equivalent of a C~n~ n Standard Freeness of about 600 ml, but, more preferably about 550 ml or below.
In one ~.ef~ ,d embo~limPnt of the present invention, which utilizes multiple ~ell,laking filmichPs, the furnish cont~ining the paperrn~kin& fibers which will be con~tetl by the particulate filler is predo~ l~llly of the hardwood type, preferably of content of at least about 80% hardwood.
Dilution generally favors the absorption of polymers and retention aids;
consequently, the slurry or slurries of paperln~kin~ fibers at this point in thepreparation is preferably no more than from about 3-5% solids by weight.
Mixin~ the Starch and Filler with Papermakin~ Fibers In pr~ pdldlion to be used in the present invention, it is only necessary to prepare the p~perrn~king fibers by forming an aqueous slurry with them in a CA 022~08~l l998-lO-Ol conventional repulper. In this form, it is most convenient to slurry the fibers at less than about 15%, and more preferably from about 3% to about 5% in water.
After forming an aqueous slurry of the papermaking fibers, they can be mixed by any conventional batch or continuous processes with the combined starch5 and particulate filler composition previously formed.
The resultant aqueous paperrn~king furnish is now prepared for contacting with the cationic flocculant.
Contacting the Aqueous Papermaking Furnish with the Fl~cc~ t Floccul~nt 0 Flocculants are part of a class of materials marketed by the trade as so-called "retention aids" a term, as used herein, referring to additives used to increase the retention of the fine furnish solids in the web during the papermaking process.
Without adequate retention of the fine solids, they are either lost to the process effluent or accumulate to excessively high concentrations in the recirculating white s water loop and cause production difficulties including deposit build-up and impaired drainage. Chapter 17 entitled "Retention Chemistry" of "Pulp and Paper, Chemistry and Chemical Technology", 3rd ed. Vol. 3, by J. E. Unbehend and K. W. Britt, A
Wiley Interscience Publication, incorporated herein by reference, provides the essçnti~l underst~n~ling of the types and merh~ni~mx by which polymeric retention aids function. A flocculant agglomerates suspended particles generally by a bridging mech~ni.sm While certain multivalent cations are considered common flocculants, they are generally being replaced in practice by superior acting polymers which carry many charge along the polymer chain.
The process of the present invention uses as a retention aid a "flocc~ nt", a 2s terrn which, as used herein, refers to a chemical species having a plurality of charges of either the anionic or cationic type or a combination of the two, so that it is capable of bridging together charged particles in aqueous suspensions. It is well known in the papenn~king field that shear stages break down the flocs formed by flocculating agents, and hence it is preferred practice to add the floccul~ting agent after as many shear stages encountered by the aqueous papermaking slurry as feasible.
One type of flocculant acceptable for use in the present invention is an "anionic polyelectrolyte polymer", a term which, as used herein, refers to a high CA 022~08~l l998-lO-Ol molecular weight polymer having pendant anionic groups.
Anionic polymers often have a carboxylic acid (-COOH) moiety. These can be immediately pendant to the polymer backbone or pendant through typically, an alkalene group, particularly an alkalene group of a few carbons. In aqueous 5 mediurn, except at low pH, such carboxylic acid groups ionize to provide to the polymer a negative charge.
Anionic polymers suitable for anionic flocculants do not wholly or essentially consist of monomeric units prone to yield a carboxylic acid group upon polymerization, instead they are comprised of a combination of monomers yielding0 both nonionic and anionic functionality. Monomers yielding nonionic functionality, especially if po~escing a polar character, often exhibit the same flocculating tendencies as ionic functionality. The incorporation of such monomers is often practiced for this reason. An often used nonionic unit is (meth) acrylamide.
Anionic polyacrylamides having relatively high molecular weights are satisfactory flocc~ ting agents. Such anionic polyacrylamides contain a combination of (meth) acrylamide and (meth) acrylic acid, the latter of which can be derived from the incorporation of (meth)acrylic acid monomer during the polymerization step or by the hydrolysis of some (meth) acrylamide units after the polymerization, or combined methods.
The polymer is preferably subst~nti~lly linear in comparison to the globular structure of anionic starch.
A wide range of charge densities is s~ticf~ctory for the present invention, although a medium density is plcr~ ed. Polymers useful to make products of the present invention contain cationic functional groups at a frequency ranging from as low as about 0.2 to as high as about 7 or higher, but more preferably in a range of about 2 to about 4 milliequivalents per gram of polymer.
Polymers useful for the process according to the present invention should have a molecular weight of at least about 500,000, and preferably a molecular weight above about 1,000,000, and may advantageously have a molecular weight above 5,000,000.
An example of an acceptable material is RETEN 235~, which is delivered as a solid granule; a product of Hercules, Inc. of Wilmington, Delaware. Other CA 022~08~1 1998-10-01 WO 97/37080 PCT/US97/0~596 acceptable anionic polyelectrolyte are Accurac 62 $' and Accurac 171 RS g)~ products of Cytec, Inc. of Starnford, CT. All of these products are polyacrylamides, specifically, copolymers of acrylamide and acrylic acid.
An even more preferred type of flocculant for use in the present invention is s an "cationic polyelectrolyte polymer", a term which, as used herein, refers to a high molecular weight polymer having pendant cationic groups.
A "cationic flocculant", a term as used herein, refers to a class of polyelectrolyte which generally originate from copolymerization of one or more ethylenically unsaturated monomers, generally acrylic monomers, that consist of or 0 include cationic monomer.
Suitable cationic monomers are dialkyl amino alkyl-(meth) acrylates or -(meth) acrylamides, either as acid salts or quaternary amrnonium salts. Suitablealkyl groups include dialkylaminoethyl (meth) acrylates, dialkylaminoethyl (meth) acrylamides and dialkylaminomethyl (meth) acrylamides and dialkylamino -1,3-5 propyl (meth) acrylamides. These cationic monomers are preferably copolymerizedwith a nonionic monom~r, preferably acrylamide. Other suitable polymers are polyethylene imines, polyamide epichlorohydrin polymers, and homopolymers or copolymers, generally with acrylamide, of monomers such as diallyl dimethyl ammonium chloride.
The flocculant is preferably a sl~bst~nti~lly linear polymer in comparison, for example, to the globular structure of cationized starches.
A wide range of charge densities is useful, although a medium density is preferred. Polymers useful to make products of the present invention contain cationic functional groups at a frequency ranging from as low as about 0.2 to as high 2S as 2.5, but more preferably in a range of about 1 to about 1.5 milliequivalents per gram of polymer.
Polymers useful to make tissue products according to the present invention should have a molecular weight of at least about 500,000, and preferably a molecular weight above about l,000,000, and, may advantageously have a molecularweight above 5,000,000.
Examples of acceptable materials are RETEN 1232(~) and Microform 2321~), both emulsion polymerized cationic polyacrylamides and RETEN 157~), which is CA 022~08~1 1998-10-01 WO 97/37080 rCT/US97105596 delivered as a solid granule; all are products of Hercules, Inc. of Wilmington, Delaware. Another acceptable cationic flocculant is Accurac 91, a product of Cytec, Inc. of Stamford~ CT.

5 Contactin~ the Aqueous Furnish and the Flocculant The flocculant is added to the aqueous paperrn~king furnish which is comprised of a mixture of paperm~kin~ fibers and a starch-treated particulate filler composition. It can be added at any suitable point in the approach flow of the stock ,ulepala~ion system of the paperrn~king process. It is particularly preferred to add the lo cationic flocculant after the fan pump in which the final dilution with the recycled m~hine water returned from the process is made. It is well known in the papermaking field that shear stages break down bridges formed by flocculating agents, and hence it is preferred practice to add the flocculating agent after as many shear stages encountered by the aqueous p~ aking slurry as feasible.
The dilution which takes place at the fan pump preferably reduces the consistency to a point below about 0.5% solids, and most preferably between about 0.05% - 0.2%.
The flocculant is delivered as an aqueous dispersion. Because of the relatively high molecular weight of the flocculant, the solids content of the aqueous dispersion needs to be low. Preferably, the solids content of the aqueous dispersion of the cationic flocculant is less than about 0.3% solids.
Whether the polymer chosen for this application is of the anionic or cationic type, they will be delivered as aqueous solutions at comparable conc~ntrations and overall usage rates. It is preferred that the concentration of these polymers be below about 0.3% solids and more preferably below about 0.1% prior to contacting them with aqueous paperrn~kin~ filrni~hes. Those skilled in the art will recognize that the desired usage rates of these polymers will vary widely. Amounts as low as about 0.005% polymer by weight based on the dry weight of the polymer and the dry fini~h.od weight of tissue paper will deliver useful results, but normally the usage rate would be expected to be higher; even higher for the purposes of the presentinvention than commonly practiced as application of these materials. Amounts as high as about 0.5% might be employed, but normally about 0.1% is optimum.

CA 022~08~l l998-lO-Ol In the present invention, it is possible to utilize multiple aqueous papermaking slurries, one or more of the slurries can be used to adsorb particulate fibers in accordance with the present invention. Even if one or more aqueous slurries of papermaking fibers in the paperrn~king process is m~int~ine(~ relatively 5 free of particulate fillers prior to reaching its fan pump, it is preferred to add a flocculant after the fan pump of such slurries. This is because the recycled water used in that fan pump contains filler agglomerates which failed to retain in previous passes over the foraminous screen. When multiple dilute fiber slurries are used in the creped paperm~king process, the flow of cationic or anionic flocculant is 0 preferably added to all dilute fiber slurries and it should be added in a manner which approximately proportions it to the flow of solids in the aqueous paperm~king furnish of each dilute fiber slurry.
Additional Furnishes In one aspect of the present invention, multiple pap~ . "~AkinE furnishes are 5 provided. In this case, it is desirable for the paperrn~king fibers used to contact the fine particulate filler be of the hardwood type, preferably at least about 80%
hardwood. In this aspect, at least one additional furnish would be provided, preferably predominantly of longer, and coarser fibered softwood type, preferably of greater than 80% softwood content. This latter furnish, preferably of softwood 20 type, is preferably m~int~inecl relatively free of the fine particulate filler.
In a most plef~ ,d aspect of the present invention, these furnishes would be discharged onto foraminous papermaking clothing in such a manner so that they are m~int~ined in separate layers thorough the paper forming process. One specifically desirable practice, is to relegate the particulate-filler contacted papermaking fibers 25 into a multi-layered tissue paper web wherein three layers are provided. The three layers comprise two outer layers formed from the particulate filler contacted papermaking fibers surrounding an inner layer formed from a furnish relatively free of fine particulate fillers.
Forming an Embryonic Paper Web In its simplest form, the present invention prescribes forming an embryonic paper web by directing a dilute slurry from a fan pump and discharging it onto aforaminous surface such as a papermaking wire as is well known in the art. The equipment and methods to accomplish this are well known to those skilled in the art.
In a typical process, a low consistency pulp furnish is provided in a pressurized CA 022~08~1 1998-10-01 headbox. The headbox has an opening for delivering a thin deposit of pulp furnish onto the Fourdrinier wire to form a embryonic web.
To aid in this process, a headbox is used to m~int~in a uniform flow of the dilute slurry onto the papermaking surface. More elaborate arrangements can alsos be used, as, for example, when multiple paperm~king slurries are used to make a layered paper web. In such a case, the headbox is preferably charnbered so as tom~int~in the multiple slurries separate as long as possible. This allows the maximum arnount of layer purity.
In one plcr~ d arrangement, a slurry of relatively short papenn~kin~ fibers, o comprising hardwood pulp, is prepared and used to adsorb fine particulate fibers, while a slurry of relatively long papermaking fibers, comprising softwood pulp, is pr~p~red and left essenti~lly free of fine particulates. The fate of the resultant short fibered slurry is to be directed to the outer chambers of a three chambered headbox to form outer layers of a three layered tissue in which a long fibered inner layer is s formed out of a inner chamber in the headbox in which the slurry of relatively long paperm~king fibers is directed. The resultant three-layered web with predomin~ntly short, hardwood fibers and filler in its outer layers, and longer-fibered, predomin~n~ly softwood fibers in its inner layers yields a filled tissue web which is particularly suitable for converting into a single-ply tissue product.
In an alternate preferred arrangement, a slurry of relatively short p~el,l,aking fibers, comprising hardwood pulp, is prepared and used to adsorb fine particulate fibers, while a slurry of relatively long ~ap.l.n~king fibers, comprising softwood pulp, is ~ ed and left Pc.senti~lly free of fine particulates. ~he fate of the resultant short fibered slurry is to be directed to one chamber of a two chambered ~5 headbox to form one layer of a two layered tissue in which a long fibered alternate layer is for~ned out of the second chamber in the headbox in which the slurry ofrelatively long pa~ ll,aking fibers is directed. The resultant filled tissue web is particularly suitable for converting into a multi-ply tissue product comprising two plies in which each ply is oriented so that the layer comprised of relatively short paperm~king fibers is on the surface of the two-ply tissue product.
Those skilled in the art will also recognize that the appalel~t number of chambers of a headbox can be reduced by directing the same type of aqueous paperrn~kin~ furnish to adjacPnt chambers. For example, the aforementioned threechambered headbox could be used as a two chambered headbox simply by directing CA 022~08~1 1998-10-01 WO 97/37080 PCT/US97/05~;96 essentially the sarne aqueous papermaking furnish to either of two adjacent charnbers.
Water Removal to Form a Semi-Dry Web Upon depositing the dilute fiber slurry onto the foraminous surface, it begins 5 to dewater by gravity, aided by vacuum as needed, by mechanical means conventional in the art to increase the solids content to about 7-25% thereby completing the conversion of the slurry into a wet paper web.
The scope of the present invention also includes processes which form multiple paper layers in which two or more layers of furnish are preferably formed o from the deposition of separate strearns of dilute fiber slurries for example in a multi-channeled headbox. The layers are preferably comprised of different fiber types, the fibers typically being relatively long softwood and relatively short hardwood fibers as used in multi-layered tissue paper m~king. If the individual layers are initially formed on separate wires, the layers are subsequently combined 5 when wet to form a multi-layered tissue paper web. The paperrn~king fibers arepreferably comprised of different fiber types, the fibers typically being relatively long softwood and relatively short hardwood fibers. More preferably, the hardwood fibers comprise at least about 50% and said softwood fibers comprise at least about 10% of said papenn~ing fibers.
In the paperrnaking process of the present invention, the water removal step preferably comprises the transfer of the web to a felt or fabric, e.g., conventionally felt pressing tissue paper, well known in the art, is expressly included within the scope of this invention. In this process step, the web is dewatered by transferring to a dewatering felt and pressing the web so that water is removed from the web into the felt by pressing operations wherein the web is subjected to pressure developed by opposing mechanical members, for example, cylindrical rolls. Because of the substantial pressures needed to de-water the web in this fashion, the resultant webs made by conventional felt pressing are relatively high in density and are characterized by having a uniform density throughout the web structure.
More preferable variations of the paperrn~king process incorporated into the present invention include the so-called pattern densification process methods wherein water removal and transfer to the Yankee dryer is effected while the embryonic tissue web is supported by a drying fabric having an array of supports.
This results in a creped tissue product having zones of relatively high density CA 022~08~1 1998-10-01 dispersed within a high bulk field. The high bulk field is alternatively characterized as a field of pillow regions. The densifled zones are alternatively referred to as knuckle regions. The densified zones may be discretely spaced within the high bulk field or may be interconnected, either fully or partially, within the high bulk field.
Preferably, the zones of relatively high density are continuous and the high bulk field is discrete. Preferred processes for making pattern densified tissue webs are disclosed in U.S. Patent No. 3,301,746, issued to Sanford and Sisson on January 31, 1967, U.S. Patent No. 3,974,025, issued to Peter G. Ayers on August 10, 1976, and U.S. Patent No. 4,191,609, issued to Paul D. Trokhan on March 4, 1980, and U.S.
o Patent 4,637,859, issued to Paul D. Tro~han on January 20, 1987, U.S. Patent 4,942,077 issued to Wendt et al. on July 17, 1990, European Patent Publication No.
0 617 164 A1, Hyland et al., published September 28, 1994, European Patent Publication No. 0 616 074 A1, Herrnans et al., published September 21, 1994; all of which are incorporated herein by reference.
To forrn pattern densified webs, the web transfer step imme~ tp~ly after forming the web is to a forming fabric rather than a felt. The web is juxtaposedagainst an array of supports comprising the forming fabric. The web is pressed against the array of supports, thereby resulting in densified zones in the web at the locations geographically corresponding to the points of contact between the array of supports and the wet web. The rem~in~ler of the web not co.l.plessed during thisoperation is referred to as the high bulk field. This high bulk field can be further tlp~lpn~ified by application of fluid p~s~u-e, such as with a vacuum type device or a blow-through dryer. The web is dewatered, and optionally predried, in such a manner so as to subst~nti~lly avoid compression of the high bulk field. This is preferably accomplished by fluid pressure, such as with a vacuum type device or blow-through dryer, or alternately by meçh~nically pressing the web against an array of supports wherein the high bulk field is not col.lpressed. The operations of dewatering, optional predrying and forrnation of the densified zones may be integrated or partially integrated to reduce the total number of processing steps performed. The moisture content of the semi-dry web at the point of transfer to the Yankee surface is less than about 40% and the hot air is forced through said semi-dry web while the semi-dry web is on said forming fabric to form a low density structure.
The array of supports is preferably an i~ ,fil~ g carrier fabric having a patterned displ~cem~nt of knuckles which operate as the array of supports which facilitate the formation of the densified zones upon application of ~res~ . The CA 022~08~1 1998-10-01 pattern of knuckles constitutes the array of supports previously referred to.
Imprinting carrier fabrics are disclosed in U.S. Patent No. 3,301,746, Sanford and Sisson, issued January 31, 1967, U.S. Patent No. 3,821,068, Salvucci, Jr. et al., issued May 21, 1974, U.S. Patent No. 3,974,025, Ayers, issued August 10, 1976, s U.S. Patent No. 37573,164, Friedberg et al., issued March 307 1971, U.S. Patent No.
3,473,576, Amneus, issued October 21, 1969, U.S. Patent No. 4,239,065, Trokhan, issued December 16, 1980, and U.S. Patent No. 4,528,239, Trokhan, issued July 9,1985, all of which are incorporated herein by reference.
Most preferably, the embryonic web is caused to conform to the surface of an 0 open mesh drying/im~ ling fabric by the application of a fluid force to the web and thereafter thPrm~lly predried on said fabric as part of a low density paper making process.
Another variation of the processing steps included within the present invention includes the formation of, so-called uncomp~te~l non panern-densified multi-layered tissue paper structures such as are described in U.S. Patent No.
3,812,000 issued to Joseph L. Salvucci, Jr. and Peter N. Yiannos on May 21, 1974and U.S. Patent No. 4,208,459, issued to Henry E. Becker, Albert L. McConnell, and Richard Schune on June 17, 1980, both of which are incorporated herein by reference. In general uncomr~cte~ non pattern densified multi-layered tissue paper structures are p~p~d by depositing a paper making furnish on a foraminous forrning wire such as a Fourdrinier wire to form a wet web as described earlier herein. The processes differ from the aforementioned felt pressed and pattern densified processes however in that the draining of the web and removing additional water is effected without mechanical c~,l.,plcs~ion. Water removal is accomplished from the web by vacuum dewatering and thermal drying. The web has a fiber con.cictçncy of at least 80%, prior to creping the web, said subsequent Yankee drying and creping steps therein carried out in a manner as is described hereinafter as applying to similarly to conventionally felt pressed and pattern densifing processes. The resulting high bulk sheet of relatively uncompacted fibers structure is soft but weak; therefore bonding material is preferably applied to portions of the web prior to creping.
Yankee Dlying Regardless of the method chosen to effect the dewatering of the wet paper web, the creped paperm~kin~. process as described herein utilizes a cylindrical stearn CA 022~08~1 1998-10-01 drurn ~)paldLlls known in the art as a Yankee dryer to effect completion of the drying. This step is effected by pressing the semi-dry papermaking web in order to adhere it to the Yankee dryer and drying said web to a subst~nti~lly dry condition.
The transfer is effected by mechanical means such as an opposing cylindrical drum 5 pressing against the web. Vacuurn may also be applied to the web as it is pressed against the Yankee surface. Multiple Yankee dryer drums can be employed in the process of the present invention.
The consistency of the semi-dry web at the point at which it is transferred to the Yankee dryer can vary considerably. In general, felt pressed paper structures can o be delivered to the Yankee dryer at a higher moisture content owing to the fact that the web has a uniforrn contact with the dryer surface. The consistency of the web at transfer in such as case typically is about 20% - 40%.
For Yankee drying a pattern densified web, the consistency at the point of transfer is at least about 40% and is typically from about 50% to about 80%. is transferred to the Yankee dryer and dried to completion, preferably still avoiding meçh~nical pressing. In the present invention, preferably from about 8% to about55% of the creped tissue paper surface co~ ,.lses densified knuckles having a relative density of at least 125% of the density of the high bulk field.
.

Crepmg In the final step of the present invention, the s~lbst~rlti~lly dry web is creped from the Yankee dyer surface by means of a flexible creping blade, forming a creped tissue paper, such means being well known to those skilled in the art.
In order to aid in adhering the web to the Yankee dryer, any of a number of adhesives and co~tineC can optionally be used preferably by praying them onto the 2s surface of the web or onto the Yankee dryer. Many such products design~d for controlling adhesion to the Yankee dryer are known in the art. For exarnple, U S.
Patent 3,926,716, Bates, incorporated here by reference, discloses a process using an aqueous dispersion of polyvinyl alcohol of certain degree of hydrolysis and viscosity for improving the adhesion of paper webs to Yankee dryers. Such polyvinyl alcohols, sold under the tradenarne Airvol~' by Air Products and Chemicals, lnc. of Allentown, PA can be used in conjunction with the present invention. Other Yankee coatings similarly recommen~1ed for use directly on the Yankee or on the surface of the sheet are cationic polyamide or polyarnine resins such as those made under the tr~d~n~me Rezosol'~' and Unisoft(~ by Houghton International of Valley CA 022~08~1 1998-10-01 Forge, PA and the Crepetrol(Z~' tradenarne by Hercules, Inc. of Wilmington, Delaware. These can also be used with the present invention. Preferably the web is secured to the Yankee dryer by means of an adhesive selected from the group consisting of partially hydrolyzed polyvinyl alcohol resin, polyamide resin, s polyamine resin, mineral oil, and mixtures thereof.
Optional Chemical Additives Other materials can be added to the aqueous paperrn~king furnish or the embryonic web to impart other characteristics to the product or improve the paperrn~kin~ process so long as they are compatible with the chl-mi.ctry of the o selected particulate filler and do not significantly and adversely affect the softness, strength, or low dusting character of the present invention. The following materials are expressly included, but their inclusion is not offered to be all-inclusive. Other materials can be included as well so long as they do not interfere or counteract the advantages of the present invention.
It is comrnon to add a cationic charge biasing species to the pap~rrn~king process to control the zeta potential of the aqueous papc...~ing furnish as it is delivered to the p~perrn~king process. These materials are used because most of the solids in nature have negative surface charges, including the surfaces of cellulosic fibers and fines and most inorganic fillers. Many experts in the field believe that a cationic charge biasing species is desirable as it partially neutralizes these solids, making them more easily flocculated by cationic flocculants such as the before mentioned cationic starch and cationic polyelectrolyte. One traditionally used cationic charge biasing species is alum. More recently in the art, charge biasing is done by use of relatively low molecular weight cationic synthetic polyrners preferably having a molecular weight of no more than about 500,000 and more preferably no more than about 200,000, or even about 100,000. The charge densities of such low molecular weight cationic synthetic polymers are relatively high. These charge densities range from about 4 to about 8 equivalents of cationic nitrogen per kilograrn of polymer. One suitable material is Cypro 514~), a product of Cytec, Inc. of Stamford, CT. The use of such materials is expressly allowed within the practice of the present invention. Caution should be used in their application, however. It is well known that while a small amount of such agents can actually aid retention by neutralizing anionic centers in~cessible to the largerflocculant molecules and thereby lowering the particle repulsion; however, sincesuch materials can compete with cationic flocculants for anionic anchoring sites, CA 022~08~l l998-lO-Ol they can actually have an effect opposite to the intended one by negatively impacting retention when anionic sites are limited.
The use of high surface area, high anionic charge microparticles for the purposes of improving formation, drainage, strength, and retention is well taught in s the art. See, for example, U. S. Patent, 5,221,435, issued to Smith on June 22, 1993, incorporated herein by reference. Common materials for this purpose are silica colloid, or bentonite clay. The incorporation of such materials is expressly included within the scope of the present invention.
If permanent wet strength is desired, the group of chemicals: including 0 polyamide-epichlorohydrin, polyacrylarnides, styrene-but~-lien~ latices;
insolubilized polyvinyl alcohol; urea-forrna}dehyde; polyethyleneimine; chitosanpolymers and mixtures thereof can be added to the papermaking furnish or to the embryonic web. Polyamide-epichlorohydrin resins are cationic wet strength resinswhich have been found to be of particular utility. Suitable types of such resins are described in U.S. Patent No. 3,700,623, issued on October 24, 1972, and 3,772,076, issued on November 13, 1973, both issued to Keim and both being hereby incorporated by lefel, nce. One commercial source of a useful polyamide-epichlorohydrin resins is Hercules, Inc. of Wilmington, Delaware, which markets such resin under the mark Kymene 557H~'.
Many creped paper products must have limited strength when wet because of the need to dispose of them through toilets into septic or sewer systems. If wetstrength is imparted to these products, it is preferred to be fugitive wet strength characterized by a decay of part or all of its potency upon standing in presence of water. If fugitive wet strength is desired, the binder materials can be chosen from the group comi~tin~ of dialdehyde starch or other resins with aldehyde functionality such as Co-Bond 1000(~) offered by National Starch and Chemical Company, Parez 750'~) offered by Cytec of Stamford, CT and the resin described in U.S. Patent No.
4,981,557 issued on January 1, 1991, to Bjork~uist and incorporated herein by reference.
If enhanced absorbency is needed, surfactants may be used to treat the creped tissue paper webs of the present invention. The level of surfactant, if used, ispreferably from about 0.01% to about 2.0% by weight, based on the dry fiber weight of the tissue paper. The surfactants preferably have alkyl chains with eight or more carbon atoms. Exemplary anionic surfactants are linear alkyl sulfonates, and CA 022~08~1 1998-10-01 alkylbenzene sulfonates. Exemplary nonionic surfactants are alkylglycosides including alkylglycoside esters such as Crodesta SL-40(~' which is available from Croda, Inc. (New York, NY); alkylglycoside ethers as described in U.S. Patent 4.011,389, issued to W. K. Langdon, et al. on March 8, 1977; and 5 alkylpolyethoxylated esters such as Pegosperse 200 ML available from Glyco Chemicals, Inc. (Greenwich, CT) and IGEPAL RC-520~) available from Rhone Poulenc Corporation (Cranbury, NJ).
Chemic~l softening agents are expressly included as optional ingredients.
Acceptable chemical softening agents comprise the well k~own o dialkyldimethylammonium salts such as ditallowdimethylammonium chloride, ditallowdimethylammonium methyl sulfate, di(hydrogenated) tallow dimethyl ammonium chloride; with di(hydrogenated) tallow dimethyl ammonium methyl sulfate being ~le~,lcd. This particular material is available commercially from Witco Chemical Company Inc. of Dublin, Ohio under the tr~(lPn~me Varisoft 137~.
Biodegradable mono and di-ester variations of the quaternary ammonium compound can also be used and are within the scope of the present invention.
The above listings of optional chemical additives is intçn~lç~l to be merely exemplary in nature, and are not meant to limit the scope of the invention.
Detailed D~ ,tion of the D. ..~
Further insight into the process of the present invention can be gained by reference to Figure 1, which is a sçhPm~tic r~lcs~ ion illustrating a p.~p~lion of the aqueous papPrm~king furnish for the creped pape~n~king operation, and to Figure 2, which is a schPrn~tic le~.leselltalion of the creped papçrm~king operation.
The following description makes lefer~nce to Figure 1:
A storage vessel 1 is provided for staging an aqueous slurry of relatively long papçrm~king fibers. The slurry is conveyed by means of a pump 2 and optionally through a refiner 3 to fully develop the strength potential of the long papermaking fibers. Additive pipe 4 conveys a resin to provide for wet or dry strength, as desired in the fini.che~ product. The slurry is then further conditioned in mixer 5 to aid in absorption of the resin. The suitably conditioned slurry is then diluted with white water 7 in a fan pump 6 forrning a dilute long paperrnaking fiber slurry 15. Pipe 20 adds a flocculant to the slurry 15, producing a flocc~ t~l long fibered slurry 22.

CA 022~08~1 1998-10-01 WO 97137080 PCTIUS97/0~596 Still referring to Figure 1, a storage vessel 8 is a repository for a fine particulate filler slurry. Additive pipe 9 conveys an aqueous dispersion of a cationic starch additive. Pump 10 acts to convey the fine particulate slurry as well as provide for dispersion of the starch. The slurry is conditioned in a mixer 12 to aid in 5 absorption of the additives. Resultant slurry 13 is conveyed to a point where it is mixed with an aqueous dispersion of refined short fiber paperm~king fibers.
Still referring to Figure 1, short paperm~king fiber slurry originates from a repository 11, from which it is conveyed through pipe 49 by pump 14 through a refiner 15 where it becomes a refined slurry of short paperm~king fibers 16. After o mixing with the conditioned slurry of fine particulate filler 13, it becomes the short fiber based aqueous papc..naking slurry 17. White water 7 is mixed with slurry 17 in a fan pump 18 at which point the slurry becomes a dilute aqueous papermaking slurry 19. Pipe 21 directs a flocculant into slurry 19, after which the slurry becomes a flocculated aqueous papermaking slurry 23.
Preferably, the flocc~ te~l short-fiber based aqueous paperm~king slurry 23 is directed to the creped papermaking process illustrated in Figure 2 and is divided into two approximately equal strearns which are then directed into headbox charnbers 82 and 83 ultimately evolving into off-Yankee-side-layer 75 and Yankee-side-layer 71, respectively of the strong, soft, low ~l~stin~, filled creped tissue paper.
Similarly, the aqueous flocculated long papenn~king fiber slurry 22, referring to Figure 1, is preferably directed into headbox charnber 82b ultimately evolving into center layer 73 of the strong, soft, low dusting, filled creped tissue paper.
The following description makes reference to Figure 2:
Figure 2 is a schPm~tic repres~nt~tion illustrating a creped papermaking process for producing a strong, soft, and low dust filled creped tissue paper.
Preferred embo~liment~ are described in the following discussion. Figure 2 is a side elevational view of a preferred papermaking n~chin~ 80 for m~nllf~rturing paper according to the present invention. Referring to Figure 2, papermaking machine 80 comprises a layered headbox 81 having a top chamber 82 a center charnber 82b, and a bottom chamber 83, a slice roof 84, and a Fourdrinier wire 85 which is looped over and about breast roll 86, deflector 90, vacuurn suction boxes 91, couch roll 92, and a plurality of turning rolls 94. In operation, one p~penn~king furnish is pumped through top chamber 82 a second paperrn~king furnish is pumped through center chamber 82b, while a third furnish is pumped through bottom chamber 83 and CA 022~08~l l998-lO-Ol thence out of the slice roof 84 in over and under relation onto Fourdrinier wire 85 to form thereon an embryonic web 88 comprising layers 88a, and 88b, and 88c.
Dewatering occurs through the Fourdrinier wire 85 and is assisted by deflector 90 and vacuum boxes 91. As the Fourdrinier wire makes its return run in the direction 5 shown by the arrow, showers 95 clean it prior to its commencing another pass over ~ breast roll 86. At web transfer zone 93, the embryonic web 88 is transferred to a forarninous carrier fabric 96 by the action of vacuum transfer box 97. Carrier fabric 96 carries the web from the transfer zone 93 past vacuum dewatering box 98, through blow-through predryers 100 and past two turning rolls 101 after which the o web is transferred to a Yankee dryer 108 by the action of pressure roll 102. The carrier fabric 96 is then cleaned and dewatered as it completes its loop by passing over and around additional turning rolls 101, showers 103, and vacuum dewateringbox 105. The predried paper web is a&esively secured to the cylindrical surface of Yankee dryer 108 aided by adhesive applied by spray applicator 109. Drying is completed on the steam heated Yankee dryer 108 and by hot air which is heated and circulated through drying hood 110 by means not shown. The web is then dry creped from the Yankee dryer 108 by doctor blade 111 after which it is rlPcign~tpfl paper sheet 70 comprising a Yankee-side layer 71 a center layer 73, and an off-Yankee-side layer 75. Paper sheet 70 then passes between calendar rolls 112 and 113, about a circumferential portion of reel 115, and thence is wound into a roll 116 on a core 117 disposed on shaft 118.
Still referring to Figure 2, the genesis of Yankee-side layer 71 of paper sheet 70 is the furnish pumped through bottom chamber 83 of headbox 81, and which furnish is applied directly to the Fourdrinier wire 85 whereupon it becomes layer 88c of embryonic web 88. The genesis of the center layer 73 of paper sheet 70 is the furnish delivered through charnber 82.5 of headbox 81, and which furnish forms layer 88b on top of layer 88c. The genesis of the off-Yankee-side layer 75 of paper sheet 70 is the furnish delivered through top chamber 82 of headbox 81, and which furnish forms layer 88a on top of layer 88b of embryonic web 88. Although Figure2 shows pape~ rhine 80 having headbox 81 adapted to make a three-layer web, headbox 81 may alternatively be adapted to make unlayered, two layer or other multi-layer webs.
Further, with respect to making paper sheet 70 embodying the present invention on papermaking machine 80, Figure 2, the Fourdrinier wire 85 must be of a fine mesh having relatively small spans with respect to the average lengths of the fibers con~liluling the short fiber fi~rnish so that good formation will occur; and the CA 022~08~1 1998-10-01 WO 97/37080 PCT/US97/0~596 forarninous carrier fabric 96 should have a fine mesh having relatively small opening spans with respect to the average lengths of the fibers constituting the long fiber furnish to substantially obviate bulking the fabric side of the embryonic web into the inter-filamentary spaces of the fabric 96. Also, with respect to the process 5 conditions for m~king exemplary paper sheet 70, the paper web is preferably dried to about 80% fiber consistency, and more preferably to about 95% fiber consistency prior to creping.
The present invention is applicable to creped tissue paper in general, including but not limited to conventionally felt-pressed creped tissue paper; high o bulk pattern densified creped tissue paper; and high bulk, uncompacted creped tissue paper.
The filled creped tissue paper webs of the present invention have a basis weight of bet~,veen 10 g/m2 and about 100 g/m2. In its preferred embodiment, thefilled tissue paper of the present invention has a basis weight between about 10 g/m2 and about 50 g/m2 and, most preferably, between about 10 g/m2 and about 30 g/m2.Creped tissue paper webs suitable for the present invention possess a density ofabout 0.60 g/cm3 or less. In its preferred embodiment, the filled tissue paper of the present invention has a density between about 0.03 g/cm3 and about 0.6 g/cm3 and, most preferably, bet~veen about 0.05 g/cm3 and 0.2 g/cm3.
The present invention is further applicable to multi-layered tissue paper webs~ Tissue structures forrned from layered paper webs are described in U.S.
Patent 3,994,771, Morgan, Jr. et al. issued November 30, 1976, U.S. Patent No.
4,300,981, Carstens, issued November 17, 1981, U.S. Patent No. 4,166,001, Dunning et al., issued August 28, 1979, and European Patent Publication No. 0 613 979 Al, Edwards et al., published September 7, 1994, all of which are incorporated herein by reference. The layers are preferably comprised of different fiber types, the fibers typically being relatively long softwood and relatively short hardwood fibers as used in multi-layered tissue paper m~kin~. Multi-layered tissue paper webs suitable for the present invention comprise at least two superposed layers, an inner layer and at least one outer layer contiguous with the inner layer. Preferably, the multi-layered tissue papers comprise three superposed layers, an inner or centerlayer, and two outer layers, with the inner layer located between the two outer layers.
The two outer layers preferably comprise a primary filarnentary constituent of relatively short paper m~king fibers having an average fiber length between about 0.5 and about 1.5 mm, preferably less than about 1.0 rnm. These short paper making CA 022~08~1 1998-10-01 fibers typically comprise hardwood fibers, preferably hardwood Kraft fibers, andmost preferably derived from eucalyptus. The inner layer preferably comprises a primary filamentary constituent of relatively long paper making fibers having anaverage fiber length of least about 2.0 mm. These long paper m~king fibers are 5 typically softwood fibers, preferably, northern softwood Kraft fibers. Preferably, the majority of the particulate filler of the present invention is contained in at least one of the outer layers of the multi-layered tissue paper web of the present invention.
More preferably, the majority of the particulate filler of the present invention is contained in both of the outer layers.
o The creped tissue paper products made from single-layered or multi-layered creped tissue paper webs can be single-ply tissue products or multi-ply tissue products.
The advantages related to the practice of the present invention include the ability to reduce the amount of papenn~king fibers required to produce a given amount of tissue paper product. Further, the optical ~ p~,.lies, particularly the opacity, of the tissue product are improved. These advantages are realized in a tissue paper web which has a high level of strength and is low ~ ting The term "opacity" as used herein refers to the recict~nce of a tissue paper web from transmitting light of a wavelength corresponding to the visible portion of the electromagnetic spectrum. The "specific opacity" is the measure of the degree of opacity imparted for each 1 g/m2 unit of basis weight of a tissue paper web. The method of measuring opacity and calc~ ting specific opacity are detailed in a later section of this specifi~tion. Tissue paper webs according to the present invention preferably have more than about 5%, more preferably more than about 5.5%, and 2s most preferably more than about 6% specific opacity.
The term "strength" as used herein refers to the specific total tensile strength, the detPnnin~tion method for this measure is included in a later section of thisspecification. The tissue paper webs according to the present invention are strong.
This generally means that their specific total tensile strength is at least about 0.25 meters, more preferably more than about 0.40 meters.
The terms "lint" and "dust" are used interchangeably herein and refer to the tendency of a tissue paper web to release fibers or particulate fillers as measured in a controlled abrasion test, the methodology for which is detailed in a later section of this specification. Lint and dust are related to strength since the tendency to release CA 022~08~1 1998-10-01 fibers or particles is directly related to the degree to which such fibers or particles are anchored into the structure. As the overall level of anchoring is increased, the strength will be increased. However, it is possible to have a level of strength which is regarded as acceptable but have an unacceptable level of linting or dusting. This 5 is because linting or dusting can be localized. For example, the surface of a tissue paper web can be prone to linting or dusting, while the degree of bonding beneath the surface can be sufficient to raise the overall level of strength to quite acceptable levels. In another case, the strength can be derived from a skeleton of relatively long papermaking fibers, while fiber fines or the particulate filler can be o insufficiently bound within the structure. The filled tissue paper webs according to the present invention are relatively low in lint. Levels of lint below about 12 are preferable, below about 10 are more preferable, and below 8 are most preferable.
The multi-layered tissue paper web of this invention can be used in any application where soft, absorbent multi-layered tissue paper webs are required.
5 Particularly advantageous uses of the multi-layered tissue paper web of this invention are in toilet tissue and facial tissue products. Both single-ply and multi-ply tissue paper products can be produced from the webs of the present invention.
Analytical and Testing Procedures A. Density The density of multi-layered tissue paper, as that term is used herein, is the average density calculated as the basis weight of that paper divided by the caliper, with the approl,l;ate unit conversions incorporated therein. Caliper of the multi-layered tissue paper, as used herein, is the thickness of the paper when subjected to a con,~les~ive load of 95 g/in2 (15.5 g/cm2).
B. M~lE~I9r Weight Determination The es.~nti~l distinguishing characteristic of polymeric materials is their molecular size. The prop~.lies which have enabled polyrners to be used in a diversity of applications derive almost entirely from their macro-molecular nature. In order to characterize fully these materials it is escelltial to have some means of 30 defining and determining their molecular weights and molecular weight distributions. It is more correct to use the term relative molecular mass rather the molecular weight, but the latter is used more generally in polymer technology. lt is not always practical to determine molecular weight distributions. However, this is CA 022~08~1 1998-10-01 becoming more cornmon practice using chromatographic techniques. Rather, recourse is made to expressing molecular size in terrns of molecular weight averages.
Molecular Weight Averages If we consider a simple molecular weight distribution which represents the weight fraction (wi) of molecules having relative molecular mass (Mi), it is possible to define several useful average values. Averaging carried out on the basis of the number of molecules (Ni) of a particular size (Mi) gives the Number Average Molecular Weight o Mn = ~NiMi ~ Ni An important consequence of this definition is that the Number Average Molecular Weight in grarns contains Avogadro's Number of molecules. This definition of molecular weight is con~iitel-t with that of monodisperse molecular species, i.e. molecules having the same molecular weight. Of more significance is the recognition that if the number of molecules in a given mass of a polydisperse polymer can be deterlnine(l in some way then n, can be calculated readily. This is the basis of colligative p~ y measurements.
Averaging on the basis of the weight fractions (Wi) of molecules of a given mass (Mi) leads to the definition of Weight Average Molecular Weights M w = ~ Wj Nj_= ~ Ni Mj2 ~ Wj ~ Nj Mj w is a more useful means for expressing polymer molecular weights than n since it reflects more accurately such properties as melt viscosity and mech~ical properties of polymers and is therefor used in the present invention.
C. Filler Particle Size Determination Particle size is an important determinant of performance of filler, especially as it relates to the ability to retain it in a paper sheet. Clay particles, in particular, are platy or blocky, not spherical, but a measure referred to as "equivalent spherical diameter" can be used as a relative measure of odd shaped particles and this is one CA 022~08~1 1998-10-01 WO 97/37(180 PCT/US97/05596 of the main methods that the industry uses to measure the particle size of clays and other particulate fillers. Equivalent spherical diameter determinations of fillers can be made using TAPPI Useful Method 655, which is based on the Sedigraph(~) analysis, i.e., by the instrurnent of such type available from the Micromeritics5 Instrument Corporation of Norcross, Georgia. The instrument uses soft x-rays to determine gravity sedimentation rate of a dispersed slurry of particulate filler and employs Stokes Law to calculate the equivalent spherical diameter.
D. Filler Quantitative Analysis in Paper Those skilled in the art will recognize that there are many methods for o quantitative analysis of non-cellulosic filler materials in paper. To aid in the practice of this invention, two methods will be detailed applicable to the most preferred inorganic type fillers. The first method, ashing, is applicable to inorganic fillers in general. The second method, cletçrrnin~tion of kaolin by XRF, is tailored specifically to the filler found particularly suitable in the practice of the present 5 invention, i.e. kaolin.
Ashing Ashing is performed by use of a muffle furnace. In this method, a four place balance is first cleaned, calibrated and tarred. Next, a clean and empty platinum dish is weighed on the pan of the four place balance. Record the weight of the 20 empty pl~timlm dish in units of grams to the ten-thom~n.1th~ place. Without re-tarring the balance, approximately 10 grams of the filled tissue paper sample iscarefully folded into the pl~tinnm dish. The weight of the platinum boat and paper is recorded in units of grams to the ten-thol.s~nflth~ place.
The paper in the pl~tinl~m dish is then pre-ashed at low telllp~ldlu~es with a 25 Bunsen burner flame. Care must be taken to do this slowly to avoid the formation of air-borne ash. If air-borne ash is observed, a new sarnple must be p~ ed. After the flarne from this pre-ashing step has subsided, place the sample in the muffle furnace. The muffle furnace should be at a temperature of 575 C. Allow the sample to completely ash in the muffle furnace for approximately 4 hours. After this time, 30 remove the sample with thongs and place on a clean, flame ~ ant surface. Allow the sample to cool for 30 minllte~. After cooling, weigh the platinum dish/ash combination in units of grams to the ten-tho~ ntlth.c place. Record this weight.
The ash content in the filled tissue paper is calculated by subtracting the CA 022~08~1 1998-10-01 weight of the clean, empty platinum dish from the weight of the platinum dish/ash combination. Record this ash content weight in units of grams to the ten-tholls~ndthc place.
The ash content weight may be converted to a filler weight by knowledge of ~ 5 the filler loss on ashing (due for example to water vapor loss in kaolin). To determine this, first weigh a clean and empty platinum dish on the pan of a fourplace balance. Record the weight of the empty platinum dish in units of grams tothe ten-thol1c~n~lth~ place. Without re-tarring the balance, approximately 3 grams of the filler is carefully poured into the platinum dish. The weight of the platinum o dish/filler combination is recorded in units of grarns to the ten-thol~s~n~thc place.
This sarnple is then carefully placed in the muffle furnace at 575 C. Allow the sample to completely ash in the muffle furnace for approximately 4 hours. After this time, remove the sarnple with thongs and place on a clean, flarne retardantsurface. Allow the sarnple to cool for 30 minutes. After cooling, weigh the platinum dish/ash combination in units of grams to the ten-tho~c~n-lthc place.
Record this weight.
Calculate the percent loss on ashing in the original filler sample using the following equation:
% Loss on ashing= j(Wt. of Ori~inai Filler ~~ rle.~~rt dish)- (Wt. of Filler Ash&Dt dish)l x 100 [(Wt. of Original Filler c , '- ~~pt dish) - (Wt of pt dish~]
The % loss on ashing in kaolin is 10 to 15%. The original ash weight in units of CA 022~08~1 1998-10-01 grams can then be converted to a filler weight in units of grams with the following equation:
Weight of Filler (g) = Weight of Ash (~
[1 - (% Loss on Ashing/100)]
s The percent filler in the original filled tissue paper can then be calculated as follows:
% Filler in Tissue Paper = Wei~ht of Filler (~) x 100 [(Weight of Platinum Dish&Paper~ - (Weight of Platinum Dish)]
Determination of Kaolin Clay by XRF
0 The main advantage of the XRF technique over the muffle furnace ashingtechnique is speed, but it is not as universally applicable. The XRF spectrometer can qual~ital~ the level of kaolin clay in a paper sample within 5 minl1tec compared to the hours it takes in the muffle furnace ashing method.
The X-ray Fluorescence technique is based on the bombardment of the sample of interest with X-ray photons from a X-ray tube source. This bombardmentby high energy photons causes core level electrons to be photoemitted by the elements present in the sample. These empty core levels are then filled by outershell electrons. This filling by the outer shell electrons results in the fluorescence process such that additional X-ray photons are emitted by the elements present in the sample. Each element has distinct '~finge~ energies for these X-ray fluorescent transitions. The energy and thus the identity of the element of interest of these emitted X-ray fluoresclon~e photons is deterrnined with a lithium doped silicon semiconductor detector. This detector makes it possible to det~rrnine the energy of the impin~in~ photons and thus the identify the elements present in the sample. The elements from sodium to uranium may be identified in most sample matrices.
In the case of the clay fillers, the detected elements are both silicon and ah-minltm The particular X-ray Fluorescence instrument used in this clay analysis is a Spectrace 5000 made by Baker-Hughes Inc. of Mountain View, California. The first step in the quantitative analysis of clay is to calibrate the instrument with a set of known clay filled tissue standards, using clay inclusions ranging from 8% to 20%, for example.
The exact clay level in these standard paper samples is determined with the muffle furnace ashing technique described above. A blank paper sample is also CA 022So8S1 1998-10-01 included as one of the standards. At least 5 standards bracketing the desired target clay level should be used to calibrate the instrument.
Before the actual calibration process, the X-ray tube is powered to settings of 13 kilovolts and 0.20 mi11i~mps. The instrument is also set up to integrate the s detected signals for the aluminurn and silicon contained in the clay. The paper sample is prepared by first cutting a 2" by 4" strip. This strip is then folded to make a 2" X 2" with the off-Yankee side facing out. This sample is placed on top of the sample cup and held in place with a ret~inin~ ring. During sample p~p~dlion, care must be taken to keep the sample flat on top of the sample cup. The instrument is o then calibrated using this set of known standards.
After calibrating the instruxnent with the set of known standards, the linear calibration curve is stored in the co~ uulel system's memory. This linear calibration curve is used to calculate clay levels in the unkno~vns. To insure the X-ray Fluorescence system is stable and working l..op~,.ly, a check sample of known clay 1S content is run with every set of unknowns. If the analysis of the check sample results in an inaccurate result (10 to 15% off from its known clay content), theinstrument is subjected to trouble-shooting and/or re-calibrated.
For every paper-making condition, the clay content in at least 3 unknown samples is determine~ The average and standard deviation is taken for these 3 20 samples. If the clay application procedure is suspected or intentionally set up to vary the clay content in either the cross direction (CD) or m~chin~- direction (~D) of the paper, more samples should be measured in these CD and MD directions.
E. Measuremeot of Tissue Paper Lint The amount of lint generated from a tissue product is determined with a 2s Sutherland Rub Tester. This tester uses a motor to rub a weighted felt 5 times over the stationary toilet tissue. The Hunter Color L value is measured before and after the rub test. The difference between these two Hunter Color L values is calculated as lint.
SAMPLE PREPARATION:
Prior to the lint rub testing, the paper sarnples to be tested should be conditioned according to Tappi Method #T4020M-88. Here, sarnples are preconditioned for 24 hours at a relative humidity level of 10 to 35% and within a CA 022~08~1 1998-10-01 temperature range of 22 to 40 ~C. After this preconditioning step, sarnples should be conditioned for 24 hours at a relative humidity of 48 to 52% and within a temperature range of 22 to 24 ~C. This rub testing should also take place within the confines of the constant temperature and humidity room.
The Sutherland Rub Tester may be obtained from Testing ~chinec, Inc.
(Amityville, NY, 11701). The tissue is first prepared by removing and discardingany product which might have been abraded in handling, e.g. on the outside of the roll. For multi-ply finished product, three sections with each cont~ining two sheets of multi-ply product are removed and set on the bench-top. For single-ply product, 0 six sections with each cont~inin~ two sheets of single-ply product are removed and set on the bench-top. Each sarnple is then folded in half such that the crease is running along the cross direction (CD) of the tissue sarnple. For the multi-ply product, make sure one of the sides facing out is the same side facing out after the sample is folded. In other words, do not tear the plies apart from one another and rub test the sides facing one another on the inside of the product. For the single-ply product, make up 3 samples with the off-Yankee side out and 3 with the Yankee side out. Keep track of which samples are Yankee side out and which are off-Yankee side out.
Obtain a 30" X 40" piece of Crescent #300 cardboard from Cordage Inc.
(800 E. Ross Road, Cincinn~ti Ohio, 45217). Using a paper cutter, cut out six pieces of cardboard of llimencions of 2.5" X 6". Puncture t~,vo holes into each of the six cards by forcing the cardboard onto the hold down pins of the Sutherland Rubtester.
If working with single-ply finiche~ product, center and carefully place each of the 2.5" X 6" cardboard pieces on top of the six previously folded samples. Make sure the 6" ~limen.cion of the cardboard is running parallel to the m~chine direction (MD) of each of the tissue samples. If working with multi-ply finich~l product, only three pieces of the 2.5" X 6" cardboard will be required. Center and carefully place each of the cardboard pieces on top of the three previousiy folded samples.
Once again, make sure the 6" /limeneion of the cardboard is running parallel to the m~rhine direction (MD) of each of the tissue sarnples.
Fold one edge of the exposed portion of tissue sample onto the back of the cardboard. Secure this edge to the cardboard with adhesive tape obtained from 3MInc. (3/4" wide Scotch Brand, St. Paul, MN). Carefully grasp the other over-CA 022~08~l l998-lO-Ol PCTtUS97/05596 h~nEing tissue edge and snugly fold it over onto the back of the cardboard. While m~int~ininE a snug fit of the paper onto the board, tape this second edge to the back of the cardboard. Repeat this procedure for each sample.
Turn over each sarnple and tape the cross direction edge of the tissue paper 5 to the cardboard. One half of the adhesive tape should contact the tissue paper while the other half is adhering to the cardboard. Repeat this procedure for each of the sarnples. If the tissue sarnple breaks, tears, or becomes frayed at any time during the course of this sample pl~pd~dtion procedure, discard and make up a new sarnple with a new tissue sample strip.
o If working with multi-ply converted product, there will now be 3 samples on the cardboard. For single-ply finich~d product, there will now be 3 off-Yankee side out samples on cardboard and 3 Yankee side out samples on cardboard.
FELT PREPARATION:
Obtain a 30" X 40" piece of Crescent #300 cardboard from Cordage Inc.
(800 E. Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut out six pieces of cardboard of ~lim~cions of 2.25" X 7.25". Draw two lines parallel to the short dimension and down 1.125" from the top and bottom most edges on the white side of the cardboard. Carefully score the length of the line with a razor blade using a straight edge as a guide. Score it to a depth about half way through the thickness of the sheet. This scoring allows the cardboard/felt combination to fit tightly around the weight of the Sutherland Rub tester. Draw an arrow running parallel to the long dimension of the cardboard on this scored side of the cardboard.
Cut the six pieces of black felt (F-55 or equivalent from New F.nEI~nd Gasket, 550 Broad Street, Bristol, CT 06010) to the dimensions of 2.25" X 8.5" X0.0625." Place the felt on top of the unscored, green side of the cardboard such that the long edges of both the felt and cardboard are parallel and in alignment. Make sure the fluffy side of the felt is facing up. Also allow about 0.5" to overhang the top and bottom most edges of the cardboard. Snugly fold over both overh~nging felt edges onto the backside of the cardboard with Scotch brand tape. Prepare a total of six of these feltlcardboard combinations.
For best reproducibility, all samples should be run with the same lot of felt.
Obviously, there are occasions where a single lot of felt becomes completely depleted. In those cases where a new lot of felt must be obtained, a correction factor CA 022~08~1 1998-10-01 should be deterrnined for the new lot of felt. To determine the correction factor, obtain a representative single tissue sample of interest, and enough felt to make up 24 cardboard/felt sa~nples for the new and old lots.
As described below and before any rubbing has taken place, obtain Hunter L
5 readings for each of the 24 cardboard/felt samples of the new and old lots of felt.
Ca}culate the averages for both the 24 cardboard/felt satnples of the old lot and the 24 cardboard/felt samples of the new lot.
Next, rub test the 24 cardboard/felt boards of the new lot and the 24 cardboard/felt boards of the old lot as described below. Make sure the same tissue 0 lot number is used for each of the 24 satnples for the old and new lots. In addition, sarnpling of the paper in the p~ Lion of the cardboard/tissue samples must be done so the new lot of felt and the old lot of felt are exposed to as representative as possible of a tissue sample. For the case of I -ply tissue product, discard any product which might have been darnaged or abraded. Next, obtain 48 strips of tissue eachtwo usable units (also termed sheets) long. Place the first two usable unit strip on the far left of the lab bench and the last of the 48 satnples on the far right of the bench. Mark the sample to the far left with the number " I " in a 1 cm by I cm area of the corner of the sample. Continue to mark the samples consecutively up to 48such that the last sample to the far right is numbered 48.
Use the 24 odd numbered samples for the new felt and the 24 even numbered sarnples for the old felt. Order the odd number samples from lowest to highest. Order the even nurnbered samples from lowest to highest. Now, mark the lowest nurnber for each set with a letter "Y." Mark the next highest nurnber with the letter "O." Continue m~rking the samples in this altçrn~ting "Y"/"O" pattern. Use the "Y" samples for Yankee side out lint analyses and the "O" samples for off-Yankee side lint analyses. For l-ply product, there are now a total of 24 samples for the new lot of felt and the old lot of felt. Of this 24, twelve are for Yankee side out lint analysis and 12 are for off-Yankee side lint analysis.
Rub and measure the Hunter Color L values for all 24 samples of the old felt as described below. Record the 12 Yankee side Hunter Color L values for the old felt. Average the 12 values. Record the 12 off-Yankee side Hunter Color L valuesfor the old felt. Average the 12 values. Subtract the average initial un-rubbed Hunter Color L felt reading from the average Hunter Color L reading for the Yankee side rubbed samples. This is the delta average difference for the Yankee side CA 022~08~1 1998-10-01 samples. Subtract the average initial un-rubbed Hunter Color L felt reading fromthe average Hunter Color L reading for the off-Yankee side rubbed samples. This is the delta average difference for the off-Yankee side samples. Calculate the sum of the delta average difference for the Yankee-side and the delta average difference for 5 the off-Yankee side and divide this surn by 2. This is the uncorrected lint value for the old felt. If there is a current felt correction factor for the old felt, add it to the uncorrected lint value for the old felt. This value is the corrected Lint Value for the old felt.
Rub and measure the Hunter Color L values for all 24 samples of the new 0 felt as described below. Record the 12 Yankee side Hunter Color L values for the new felt. Average the 12 values. Record the 12 off-Yankee side Hunter Color L
values for the new felt. Average the 12 values. Subtract the average initial un-rubbed Hunter Color L felt reading from the average Hunter Color L reading for the Yankee side rubbed samples. This is the delta average difference for the Yankee 15 side sa,nples. Subtract the average initial un-rubbed Hunter Color L felt reading from the average Hunter Color L reading for the off-Yankee side rubbed samples.
This is the delta average difference for the off-Yankee side samples. Calculate the sum of the delta average difference for the Yankee-side and the delta average difference for the off-Yankee side and divide this sum by 2. This is the uncorrected 20 lint value for the new felt.
Take the difference between the corrected Lint Value from the old felt and the uncorrected lint value for the new felt. This difference is the felt correction factor for the new lot of felt.
Adding this felt correction factor to the uncorrected lint value for the new 2s felt should be identical to the corrected Lint Value for the old felt.
The same type procedure is applied to two-ply tissue product with 24 samples run for the old felt and 24 run for the new felt. But, only the consurner used outside layers of the plies are rub tested. As noted above, make sure the samples are prepared such that a represent~tive sample is obtained for the old and new felts.
30 CARE OF 4 POUND WEIGHT:
The four pound weight has four s~uare inches of effective contact area providing a contact pressure of one pound per square inch. Since the contact pressure can be changed by alteration of the rubber pads mounted on the face of the CA 022~08~1 1998-10-01 weight, it is important to use only the rubber pads supplied by the manufacturer(Brown Inc., Mechanical Services Department, K~l~m~7oo, MI). These pads must be replaced if they become hard, abraded or chipped off.
When not in use, the weight must be positioned such that the pads are not 5 supporting the full weight of the weight. It is best to store the weight on its side.
RUB TESTER INSTRUMENT CALIBRATION:
The Sutherland Rub Tester must first be calibrated prior to use. First, turn on the Sutherland Rub Tester by moving the tester switch to the "cont" position.When the tester arm is in its position closest to the user, turn the tester's switch to 0 the "auto" position. Set the tester to run 5 strokes by moving the pointer arm on the large dial to the "five" position setting. One stroke is a single and complete forward and reverse motion of the weight. The end of the rubbing block should be in the position closest to the OpC~tOl at the beginning and at the end of each test.
Prepare a tissue paper on cardboard sample as described above. In addition, 5 prepare a felt on cardboard sarnple as described above. Both of these samples will be used for calibration of the instrument and will not be used in the acquisition of data for the actual samples.
Place this calibration tissue sample on the base plate of the tester by slippingthe holes in the board over the hold-down pins. The hold-down pins prevent the 20 sample from moving during the test. Clip the calibration felt/cardboard sample onto the four pound weight ~,vith the cardboard side cont~ctin~ the pads of the weight.
Make sure the cardboard/felt combination is resting flat against the weight. Hook this weight onto the tester arrn and gently place the tissue sample underneath the weight/felt combination. The end of the weight closest to the operator must be over 25 the cardboard of the tissue sample and not the tissue sarnple itself. The felt must rest flat on the tissue sarnple and must be in 100% contact with the tissue surface.
Activate the tester by depressing the "push" button.
Keep a count of the number of strokes and observe and make a mental note of the starting and stopping position of the felt covered weight in relationship to the 30 sample. If the total number of strokes is five and if the end of the felt covered weight closest to the operator is over the cardboard of the tissue sample at thebeginning and end of this test, the tester is calibrated and ready to use. If the total number of strokes is not five or if the end of the felt covered weight closest to the CA 022~08~1 1998-10-01 operator is over the actual paper tissue sample either at the beginning or end of the test, repeat this calibration procedure until 5 strokes are counted the end of the felt covered weight closest to the operator is situated over the cardboard at the both the start and end of the test.
During the actual testing of samples, monitor and observe the stroke count and the starting and stopping point of the felt covered weight. Recalibrate whennecessary.
HUNTER COLOR METER CALIBRATION:
Adjust the Hunter Color Difference Meter for the black and white standard o plates according to the procedures outlined in the operation manual of the instrument. Also run the stability check for standardization as well as the daily color stability check if this has not been done during the past eight hours. In addition, the zero reflectance must be checkl-~ and readjusted if neceSs~ry Place the white standard plate on the sample stage under the instrument port.
Release the sample stage and allow the sample plate to be raised beneath the sample port.
Using the "L-Y", "a-X", and "b-Z" standardizing knobs, adjust the instrument to read the Standard White Plate Values of "L", "a", and "b" when the"L", "a", and "b" push buttons are depressed in turn.
MEASUREMENT OF SAMPLES:
The first step in the measurement of lint is to measure the Hunter color values of the black feltlcardboard samples prior to being rubbed on the toilet tissue.
The first step in this measurement is to lower the standard white plate from under the instrument port of the Hunter color instrument. Center a felt covered cardboard, with the arrow pointing to the back of the color meter, on top of the standard plate.
Release the sample stage, allowing the felt covered cardboard to be raised under the sample port.
Since the felt width is only slightly larger than the viewing area diameter, make sure the felt completely covers the viewing area. After confirming completecoverage, depress the L push button and wait for the reading to stabilize. Read and record this L value to the nearest 0.1 unit.

CA 022~08~1 1998-10-01 If a D25D2A head is in use, lower the felt covered cardboard and plate, rotate the felt covered cardboard 90 degrees so the arrow points to the right side of the meter. Next, release the sample stage and check once more to make sure the viewing area is completely covered with felt. Depress the L push button. Read and 5 record this value to the nearest 0.1 unit. For the D25D2M unit, the recorded value is the Hunter Color L value. For the D25D2A head where a rotated sample reading is also recorded, the Hunter Color L value is the average of the two recorded values.
Measure the Hunter Color L values for all of the felt covered cardboards using this technique. If the Hunter Color L values are all within 0.3 units of one o another, take the average to obtain the initial L reading. If the Hunter Color L
values are not within the 0.3 units, discard those felt/cardboard combinations outside the limit. Prepare new samples and repeat the Hunter Color L measurementuntil all samples are within 0.3 units of one another.
For the measurement of the actual tissue paper/cardboard combinations, 5 place the tissue sample/cardboard combination on the base plate of the tester by slipping the holes in the board over the hold-down pins. The hold-down pins prevent the sample from moving during the test. Clip the calibration felt/cardboard sample onto the four pound weight with the cardboard side contacting the pads ofthe weight. Make sure the cardboard/felt combination is resting flat against the20 weight. Hook this weight onto the tester arm and gently place the tissue sample llnlle~ne~th the weight/felt combination. The end of the weight closest to the operator must be over the cardboard of the tissue sample and not the tissue sample itself. The felt must rest flat on the tissue sample and must be in 100% contact with the tissue surface.
Next, activate the tester by de~ ssing the "push" button. At the end of the five strokes the tester will automatically stop. Note the stopping position of the felt covered weight in relation to the sample. If the end of the felt covered weight toward the operator is over cardboard, the tester is ol~eldting properly. If the end of the felt covered weight toward the operator is over sample, disregard this measurement and recalibrate as directed above in the Sutherland Rub Tester Calibration section.
Remove the weight with the felt covered cardboard. Inspect the tissue sample. If torn, discard the felt and tissue and start over. If the tissue sample is intact, remove the felt covered cardboard from the weight. Determine the Hunter CA 022~08~1 1998-10-01 Color L value on the felt covered cardboard as described above for the blank felts.
Record the Hunter Color L readings for the felt after rubbing. Rub, measure, andrecord the Hunter Color L values for all rem~ining sarnples.
After all tissues have been measured, remove and discard all felt. Felts strips s are not used again. Cardboards are used until they are bent, torn, limp, or no longer have a smooth surface.
CALCULATIONS:
Determine the delta L values by subtracting the average initial L reading found for the unused felts from each of the measured values for the off-Yankee and o Yankee sides of the sarnple. Recall, multi-ply-ply product will only rub one side of the paper. Thus, three delta L values will be obtained for the multi-ply productAverage the three delta L values and subtract the felt factor from this final average This final result is terrned the lint for the fabric side of the 2-ply product.
For the single-ply product where both Yankee side and off-Yankee side measurements are obtained, subtract the average initial L reading found for the unused felts from each of the three Yankee side L readings and each of the three off-Yankee side L re~tlin~c. Calculate the average delta for the three Yankee side values. Calculate the average delta for the three fabric side values. Subtract the felt factor from each of these averages. The final results are terrned a lint for the fabric ~o side and a lint for the Yankee side of the single-ply product. By taking the average of these two values, an ultimate lint is obtained for the entire single-ply product.
F. Measurement of Panel Softness of Tissue Papers Ideally, prior to softness testing, the paper samples to be tested should be conditioned according to Tappi Method #T4020M-88. Here~ samples are preconditioned for 24 hours at a relative humidity level of 10 to 35% and within a t~nlp~ldlllre range of 22 to 40 ~C. After this preconditioning step, sarnples should be conditioned for 24 hours at a relative humidity of 48 to 52% and within a t~lllp~.d~llre range of 22 to 24 ~C.
Ideally, the softness panel testing should take place within the confines of a constant telllpe.dlLlre and humidity room. If this is not feasible, all samples,including the controls, should experience identical environmental exposure conditions.

CA 022~08~1 1998-10-01 Softness testing is performed as a paired comparison in a form similar to that described in "Manual on Sensory Testing Methods", ASTM Special Technical Publication 434, published by the American Society For Testing and Materials 1968 and is incorporated herein by reference. Softness is evaluated by subjective testing using what is referred to as a Paired Difference Test. The method employs a standard external to the test material itself. For tactile perceived softness two samples are presented such that the subject cannot see the samples, and the subject is required to choose one of them on the basis of tactile softness. The result of the test is reported in what is referred to as Panel Score Unit (PSU). With respect to o softness testing to obtain the softness data reported herein in PSU, a number of softness panel tests are l~clru~med. In each test ten practiced softness judges are asked to rate the relative softness of three sets of paired sarnples. The pairs of samples are judged one pair at a time by each judge: one sample of each pair being ~esign~te(~ X and the other Y. Briefly, each X sarnple is graded against its paired Y
sample as follows:
1. A grade of plus one is given if X is judged to may be a little softer than Y, and a grade of minus one is given if Y is judged to may be a little softer than X;

2. A grade of plus two is given if X is judged to surely be a little softer than Y, and a grade of minus two is given if Y is judged to surely be a little softer than X;

3. A grade of plus three is given to X if it is judged to be a lot softer than Y, and a grade of minus three is given if Y is judged to be a lot softer than X; and, lastly:

4. A grade of plus four is given to X if it is judged to be a whole lot softer than Y, and a grade of minus 4 is given if Y is judged to be a whole lot softer than X.
The grades are averaged and the resultant value is in units of PSU. The resulting data are considered the results of one panel test. If more than one sample 30 pair is evaluated then all sample pairs are rank ordered according to their grades by paired statistical analysis. Then, the rank is shifted up or down in value as required to give a zero PSU value to which ever sample is chosen to be the zero-base standard. The other samples then have plus or minus values as determined by their relative grades with respect to the zero base standard. The number of panel tests CA 022~0851 1998-10-01 W O 97/37080 PCT~US97/05596 performed and averaged is such that about 0.2 PSU represents a significant difference in subjectively perceived softness.
G. Measurement of Opacity of Tissue Papers The percent opacity is measured using a Colorquest DP-9000 s Spectrocolorimeter. Locate the on/off switch on the back of the processor and turn it on. Allow the instrument to warm up for two hours. If the system has gone into standby mode, press any key on the key pad and allow the instru~nent 30 minutes of additional warrn-up time.
Standardize the instrurnent using the black glass and white tile. Make sure o the standardization is done in the read mode and according to the instructions given in the standardization section of the DP9000 instrurnent m~nl-~l. To standardize the DP-9000, press the CAL key on the processor and follow the prompts as shown on the screen. You are then prompted to read the black glass and the white tile.
The DP-9000 must also be zeroed according the instructions given in the s DP-9000 instrurnent manual. Press the setup key to get into the setup mode. Define the following para~neters:
UF filter: OUT
Display: ABSOLUTE
Read Interval: SINGLE
20 Sample ID: ON or OFF
Average: OFF
Statistics: SKIP
Color Scale: XYZ
Color Index: SKIP
25 Color Difference Scale: SKIP
Color Difference Index: SKIP
CMC Ratio: SKIP
CMC Commercial Factor: SKIP
Observer: 10 degrees 30 Illllmin~nt D
M l 2nd illnmin~nt- SK~P
Standard: WORKING
Target Values: SKIP
Tolerances: SKIP

CA 022~08~1 1998-10-01 Confirm the color scale is set to XYZ, the observer set to 10 degrees, and the illumin~rlt set to D. Place the one ply sample on the white uncalibrated tile. The white calibrated tile can also be used. Raise the sarnple and tile into place under the sample port and determine the Y value.
s Lower the sarnple and tile. Without rotating the sample itself, remove the white tile and replace with the black glass. Again, raise the sarnple and black glass and deterrnine the Y value. Make sure the l-ply tissue sample is not rotated between the white tile and black glass readings.
The percent opacity is calculated by taking the ratio of the Y reading on the o black glass to the Y reading on the white tile. This value is then multiplied by 100 to obtain the percent opacity value.
For the purposes of this specification, the measure of opacity is converted into a "specific opacity", which, in effect, corrects the opacity for variations in basis weight. The forrnula to convert opacity % into specific opacity % is as follows:
SPeCific Opacity = ( 1 - (Opacity/ l oo)( 1 /Basis Weight)) X 10 where the specific opacity unit is per cent for each g/m2, opacity is in units of per cent, and basis weight is in units of g/m2.
Specific opacity should be reported to 0.01%.

G. Measurement of Strength of Tissue Papers DRY TENSILE STRENGTH:
The tensile strength is determined on one inch wide strips of sample using a Thwing-Albert Intelect II Standard Tensile Tester (Thwing-Albert Instrument Co.,2s 10960 Dutton Rd., Philadelphia, PA, 19154). This method is intended for use on finished paper products, reel samples, and unconverted stocks.
SAMPLE CONDITIONING AND PREPARATION:
Prior to tensile testing, the paper samples to be tested should be conditioned CA 022~08~l l998-lO-Ol according to Tappi Method #T4020M-88. All plastic and paper board p~r~gjng materials must be carefully removed from the paper sarnples prior to testing. The paper sarnples should be conditioned for at least 2 hours at a relative humidity of 48 to 52% and within a temperature range of 22 to 24 ~C. Sarnple preparation and all 5 aspects of the tensile testing should also take place within the confines of the constant temperature and humidity room.
For finished product, discard any damaged product. Next, remove 5 strips of four usable units (also termed sheets) and stack one on top to the other to form a long stack with the perforations between the sheets coincident. Identify sheets 1 and o 3 for machine direction tensile measurements and sheets 2 and 4 for cross direction tensile measurements. Next, cut through the p~lroldlion line using a paper cutter (JDC-l-10 or JDC-1-12 with safety shield from Thwing-Albert Instrument Co., 10960 Dutton Road, Philadelphia, PA, 19154) to make 4 separate stocks. Make sure stacks 1 and 3 are still identified for m~rhine direction testing and stacks 2 and 5 4 are identified for cross direction testing.
Cut two 1" wide strips in the m~rhin~ direction from stacks 1 and 3. Cut two 1 " wide strips in the cross direction from stacks 2 and 4. There are now four 1 "
wide strips for m~rhinP direction tensile testing and four 1" wide strips for cross direction tensile testing. For these fini~hPd product samples, all eight 1" wide strips 20 are five usable units (also termed sheets) thick.
For unconverted stock and/or reel samples, cut a 15" by 15" sarnple which is 8 plies thick from a region of interest of the sample using a paper cutter (JDC-1-10 or JDC-1-12 with safety shield from Thwing-Albert Instrument Co., 10960 Dutton Road, Philadelphia, PA, 19154) . Make sure one 15" cut runs parallel to the 25 m~r.hin.o direction while the other runs parakeet to the cross direction. Make sure the sample is conditioned for at least 2 hours at a relative humidity of 48 to 52% and within a te-llp~,dl lre range of 22 to 24 ~C. Sample l rep~dlion and all aspects of the tensile testing should also take place within the confines of the constant temperature and humidity room.
From this preconditioned 15" by 15" sarnple which is 8 plies thick, cut four strips 1" by 7" with the long 7" dimension running parallel to the m~cl~ine direction.
Note these samples as machine direction reel or unconverted stock samples. Cut an additional four strips 1" by 7" with the long 7" ~lim~n~jon running parallel to the cross direction. Note these samples as cross direction reel or unconverted stock CA 022~08~1 1998-10-01 samples. Make sure all previous cuts are made using a paper cutter (JDC-1-10 or JDC-1-12 with safety shield from Thwing-Albert Instrument Co., 10960 Dutton Road, Philadelphia, PA, 19154). There are now a total of eight samples: four 1" by 7" strips which are 8 plies thick with the 7" dimension running parallel to the s machine direction and four 1" by 7" strips which are 8 plies thick with the 7"
dimension running parallel to the cross direction.
OPERATION OF TENSILE TESTER:
For the actual measurement of the tensile strength, use a Thwing-Albert Intelect II Standard Tensile Tester (Thwing-Albert Instrument Co., 10960 Dutton 0 Rd., Philadelphia, PA, 19154). Insert the flat face clamps into the unit and calibrate the tester according to the instructions given in the operation manual of the Thwing-Albert Intelect II. Set the instrument crosshead speed to 4.00 in/min and the 1st and 2nd gauge lengths to 2.00 inches. The break sensitivity should be set to 20.0 grams and the sample width should be set to 1.00" and the sample thickness at 0.025".
A load cell is selected such that the predicted tensile result for the sarnple to be tested lies between 25% and 75% of the range in use. For example, a 5000 gramload cell may be used for samples with a predicted tensile range of 1250 grams (25% of 5000 grams) and 3750 grarns (75% of 5000 grarns). The tensile tester canalso be set up in the 10% range with the 5000 gram load cell such that samples with predicted tensiles of 125 grams to 37S grams could be tested.
Take one of the tensile strips and place one end of it in one clamp of the tensile tester. Place the other end of the paper strip in the other cla~np. Make sure the long dimension of the strip is running parallel to the sides of the tensile tester.
Also make sure the strips are not overh~nping to the either side of the two clamps.
25 In addition, the pressure of each of the clamps must be in full contact with the paper sample.
After inserting the paper test strip into the two clamps, the instrument tension can be monitored. If it shows a value of 5 grams or more, the sample is too taut. Conversely, if a period of 2-3 seconds passes after starting the test before any 30 value is recorded, the tensile strip is too slack.
Start the tensile tester as described in the tensile tester instrurnent manual.
The test is complete after the crosshead a~ltt~m~tically returns to its initial starting position. Read and record the tensile load in units of grarns from the instrument CA 022~08~1 1998-10-01 scale or the digital panel meter to the nearest unit.
If the reset condition is not performed automatically by the instrument, perform the necessary adjustment to set the instrument clamps to their initial starting positions. Insert the next paper strip into the two clamps as described above and s obtain a tensile reading in units of grams. Obtain tensile readings from all the paper test strips. It should be noted that readings should be rejected if the strip slips or breaks in or at the edge of the clarnps while performing the test.
CALCULATIONS:
For the four machine direction 1" wide finished product strips, sum the four o individual recorded tensile rea(ling~ Divide this sum by the number of strips tested.
This number should normally be four. Also divide the surn of recorded tensiles by the number of usable units per tensile strip. This is normally five for both l-ply and 2-ply products.
Repeat this calculation for the cross direction fini~h~ product strips.
For the unconverted stock or reel samples cut in the m~rhine direction, sum the four individual recorded tensile re~ling~ Divide this sum by the number of strips tested. This number should normally be four. Also divide the sum of recorded tensiles by the nurnber of usable units per tensile strip. This is normally eight.
Repeat this calculation for the cross direction unconverted or reel sample paper strips.
All results are in units of grams/inch.
For purposes of this specification, the tensile strength should be converted into a "specific total tensile strength" defined as the sum of the tensile strength 2s measured in the m~f hin~ and cross machine directions, divided by the basis weight, and corrected in units to a value in meters.
EXAMPLE
The following example is offered to illustrate the practice of the present invention. These examples are intended to aid in the description of the present invention, but, in no way, should be interpreted as limiting the scope thereof. The . _ . .

CA 022~08~1 1998-10-01 present invention is bounded only by the appended claims.
Reference Process This following discussion illustrates a reference process not incorporating the features of the present invention.
5First, an aqueous slurry of Northern Softwood Kraft of about 3% consistency is made up using a conventional pulper and is passed through a stock pipe towardthe headbox of the Fourdrinier.
In order to impart a temporary wet strength to the fini~h.od product, a 1%
dispersion of National Starch Co-BOND 1000 g) is prepared and is added to the NSK
10stock pipe at a rate sufficient to deliver 1% Co-BOND 1000~ based on the dry weight of the NSK fibers. The absorption of the temporary wet strength resin is enhanced by passing the treated slurry through an in-line mixer.
The NSK slurry is diluted with white water to about 0.2% consistency at the fan pump.
5An aqueous slurry of eucalyptus fibers of about 3% by weight is made up using a conventional repulper.
The eucalyptus is passed through a stock pipe to another fan pump where it is diluted with white water to a consistency of about 0.2%.
The slurries of NSK and eucalyptus are directed into a multi-channeled 20headbox suitably equipped with layering leaves to m~int~in the streams as separate layers until discharge onto a traveling Fourdrinier wire. A three-charnbered headbox is used. The eucalyptus slurry cont~ining 80% of the dry weight of the ultimate paper is directed to chambers leading to each of the two outer layers, while the NSK
slurry comprising 20% of the dry weight of the ultimate paper is directed to a 25chamber leading to a layer between the two eucalyptus layers. The NSK and eucalyptus slurries are combined at the discharge of the headbox into a composite slurry.
The composite slurry is discharged onto the traveling Fourdrinier wire and is dewatered assisted by a deflector and vacuum boxes.
30The embryonic wet web is transferred from the Fourdrinier wire, at a fiber CA 022~08~1 1998-10-01 consistency of about 15% at the point of transfer, to a pattemed forming fabric of a 5-shed, satin weave configuration having 84 machine-direction and 76 cross-machine-direction monofilaments per inch, respectively, and about 36 % knuckle area.
Further de-watering is accomplished by vacuum ~ccicted drainage until the web has a fiber con~i~tency of about 28%.
While rem~inin~ in contact with the pattemed forming fabric, the patterned web is pre-dried by air blow-through to a fiber consistency of about 62% by weight.
The semi-dry web is then adhered to the surface of a Yankee dryer with a o sprayed creping adhesive comprising a 0.125% aqueous solution of polyvinyl alcohol. The creping adhesive is delivered to the Yankee surface at a rate of 0.1%
adhesive solids based on the dry weight of the web.
The fiber con~i~tency is increased to about 96% before the web is dry creped from the Yankee with a doctor blade.
The doctor blade has a bevel angle of about 25 degrees and is positioned with respect to the Yankee dryer to provide an impact angle of about 81 degrees.
The percent crepe is adjusted to about 18% by operating the Yankee dryer at about 800 fpm (feet per minute) (about 244 meters per minute), while the dry web is formed into roll at a speed of 656 fpm (201 meters per min~teS).
The web is converted into a three-layer, single-ply creped patterned densified tissue paper product of about 18 lb per 3000 ft2 basis weight.
Pr~c~ss Accordin~ to the Present Invention This discussion illustrates preparation of a filled tissue paper exhibiting one embodiment of the present invention.
~5 An aqueous slurry of eucalyptus fibers of about 3% by weight is made up using a conventional repulper. The eucalyptus is passed through a refiner where its freeness is decreased from about 640 CSF to about 500 CSF. It then is carried through a stock pipe toward the paperrnachine.
The particulate filler is kaolin clay, grade WW Fil SD~), made by Dry Branch Kaolin of Dry Branch, GA. It is first made down to an aqueous slurrv by CA 022~08~1 1998-10-01 mixing it with water to a consistency of about 1% solids. It is then carried through a stock pipe where it is mixed with a cationic starch, RediBOND 5327'~), which is delivered as a 1% dispersion in water. RediBOND 5327(~ is a pre-dispersed form of waxy maize corn starch. It is added at a rate equivalent to about 0.5% based on the 5 arnount of solid weight of the starch per solid weisht of the filler. The adsorption of the cationic starch is promoted by passing the mixture through an in-line mixer.This forms an agglomerated suspension of filler particles.
The agglomerated suspension of filler particles is then mixed into the stock pipe carrying the refined eucalyptus fibers and the final mixture is diluted with white 0 water at the inlet of a fan purnp to a consistency of about 0.2% based on the weight of the solid filler particles and eucalyptus fibers. ARer the fan pump carrying the combination of agglomerated filler particles and eucalyptus fibers, Reten 1232, a cationic flocculant is added to the mixture at a rate corresponding to 0.067% based on the solids weight of the filler and eucalyptus fiber.
An aqueous slurry of NSK of about 3% con~i~tency is made up using a conventional pulper and is passed through a stoclc pipe toward the headbox of the Fourdrinier.
In order to impart a temporary wet strength to the fini~he~l product, a 1%
dispersion of National Starch Co-BOND 1000(~) is prepared and is added to the NSK
stock pipe at a rate sufficient to deliver 1% Co-BOND 1000~ based on the dry weight of the NSK fibers. The absorption of the temporary wet strength resin is enhanced by passing the treated slurry through an in-line mixer.
The NSK slurry is diluted with white water to about 0.2% consistency at the fan pump. After the fan pump, RETEN 1232(~, a cationic flocculant is added at a rate corresponding to 0.067% based on the dry weight of the NSK fiber.
The slurries of NSK and eucalyptus are directed into a multi-channeled headbox suitably equipped with layering leaves to m~int~in the streams as separate layers until discharge onto a traveling Fourdrinier wire. A three-chambered headbox is used. The combined eucalyptus and particulate filler slurry contain sufficient solids flow to achieve 80% of the dry weight of the ultimate paper. This combined slurry is directed to chambers leading to each of the two outer layers, while the NSK
slurry comprising sufficient solids flow to achieve 20% of the dry weight of theultimate paper is directed to a chamber leading to a layer between the two eucalyptus layers. The NSK and eucalyptus slurries are combined at the discharge of the CA 022~0851 1998-10-01 W O 97137080 PCTrUS97/05596 ~7 headbox into a composite slurry.
The composite slurry is discharged onto the traveling Fourdrinier wire and is dewatered assisted by a deflector and vacuum boxes.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber consistency of about 15% at the point of transfer, to a patterned forming fabric of a S-shed, satin weave configuration having 84 machine-direction and 76 cross-machine-direction monofilaments per inch, respectively, and about 36% knuckle area.
Further de-watering is accomplished by vacuum assisted drainage until the o web has a fiber consistency of about 28%.
While rem~ininE in contact with the pattemed forrning fabric, the p~ttemP~l web is pre-dried by air blow-through to a fiber con~ict~ncy of about 62% by weight.
The semi-dry web is then a&ered to the surface of a Yankee dryer with a sprayed creping adhesive comprising a 0.125% aqueous solution of polyvinyl alcohol. The creping adhesive is delivered to the Yankee surface at a rate of 0.1%
adhesive solids based on the dry weight of the web.
The fiber consistency is increased to about 96% before the web is dry creped from the Yankee with a doctor blade.
The doctor blade has a bevel angle of about 20 degrees and is positioned with respect to the Yankee dryer to provide an impact angle of about 76 degrees.
The percent crepe is adjusted to about 18% by operating the Yankee dryer at about 800 fpm (feet per minute) (about 244 meters per minute), while the dry web is formed into roll at a speed of 656 fpm (200 meters per minutes).
The web is converted into a three-layer, single-ply creped patterned densified tissue paper product of about 18 Ib per 3000 ft2 basis weight.

Reference Present Invention Kaolin content % None 13.3 Kaolin Retention NA 74 (Overall) %

Tensile Strength (g/in) 400 396 Specific Opacity %5.2 5.8 Ultimate Lint Number 7.0 6.0 Softness score 0.0 -0.03 What is claimed is:

Claims (10)

1. A process for incorporating a fine non-cellulosic particulate filler into a creped tissue paper, said process characterized in that it comprises the steps of:
a) contacting an aqueous dispersion of a non-cellulosic particulate filler with an aqueous dispersion of starch, b) mixing the aqueous dispersion of starch-contacted filler with papermaking fibers forming an aqueous papermaking furnish comprising starch-contacted filler and papermaking fibers, c) contacting said aqueous papermaking furnish with a flocculant, d) forming an embryonic paper web from the aqueous papermaking furnish on foraminous papermaking clothing, e) removing water from said embryonic web to form a semi-dry papermaking web, f) adhering the semi-dry papermaking web to a Yankee dryer and drying said web to a substantially dry condition, g) creping the substantially dry web from the Yankee dryer by means of a flexible creping blade, thereby forming a creped tissue paper.

2. A process for incorporating a fine non-cellulosic particulate filler into a multi-layered creped tissue paper, said process characterized in that it comprises the steps of:
a) contacting an aqueous dispersion of a non-cellulosic particulate filler with an aqueous dispersion of starch, b) mixing the aqueous dispersion of starch-contacted filler with papermaking fibers, thereby forming a filler-containing aqueous papermaking furnish comprising starch-contacted filler and papermaking fibers, c) contacting said aqueous papermaking furnish with an aqueous dispersion of a flocculant, d) providing at least one additional papermaking furnish, e) directing said papermaking furnishes onto foraminous papermaking clothing; thereby forming an embryonic multi-layered paper web from the filler-containing aqueous papermaking furnish and the additional papermaking furnish in a manner to create a multi-layered paper web wherein at least one layer is formed from the filler-containing aqueous papermaking furnish and at least one layer is formed from said additional papermaking furnish, f) removing water from said multi-layered embryonic web to form a semi-dry multi-layered papermaking web, g) adhering the semi-dry multi-layered papermaking web to a Yankee dryer and drying said multi-layered web to a substantially dry condition, h) creping the substantially dry multi-layered web from the Yankee dryer by means of a flexible creping blade, thereby forming a multi-layered creped tissue paper.

3. The process of Claim 2 wherein the papermaking fibers of step (b) contain at least 80% by weight of hardwood fibers, and the papermaking fibers comprising said additional papermaking furnish of step (d) contain at least 80%
by weight of softwood fibers.

4. The process of Claim 2 or 3 wherein the multi-layered embryonic paper web formation of step (e) comprises a three-layered tissue paper web having two outer layers and an inner layer, said inner layer being located between said twoouter layers, wherein the filler-containing aqueous papermaking furnish comprises said two outer layers and said additional papermaking furnish comprises said inner layer.

5. The process of any of Claims 1 - 4 wherein said particulate filler comprises from 1% to 50% of the total weight of said creped tissue paper, said particulatefiller selected from clay, calcium carbonate, titanium dioxide, talc, aluminum silicate, calcium silicate, alumina trihydrate, activated carbon, pearl starch, calcium sulfate, glass microspheres, diatomaceous earth, and mixtures thereof, preferably kaolin clay, wherein said kaolin clay has an average equivalent spherical diameter between 0.5 microns and 5 microns.

6. The process of any of Claims 1 - 5 wherein said starch has a degree of substitution ranging from 0.01 to 0.1 cationic substituent per anhydroglucose units of starch, and wherein said cationic substituent is preferably selected from tertiary aminoalkyl ethers, quaternary ammonium alkyl ethers and mixtures thereof.

7. The process of Claims 1 - 6 wherein said starch comprises from 0.1% to 5% by weight based on the weight of said particulate filler, and wherein in step(a), said aqueous dispersion of particulate filler contains between 0.1% and 5%
solids and said aqueous dispersion of starch contains between 0.1% and 10%
solids.

8. The process of any of Claims 1 - 7 wherein said flocculant is a cationic polyacrylamide containing from 0.2 to 2.5 milliequivalents of cationic substituent per gram of polyacrylamide and having a molecular weight of at least 1,000,000.

9. The process of any of Claims 1 - 8 comprising the additional step of refining the papermaking fibers to a freeness less than 600 ml Canadian Standard Freeness prior to contact with said particulate filler in step (b).

10. The process of any of Claims 1 - 9 wherein said water removal step comprises a pattern densified process wherein the water removal is effected while the embryonic web is supported on a drying fabric comprising an array of supports, wherein said water removal is preferably accomplished at least partially by means of thermal transfer using air forced through the web while it is in contact with said fabric.