CA1204613A

CA1204613A - Apparatus and process for treating web material

Info

Publication number: CA1204613A
Application number: CA000425475A
Authority: CA
Inventors: Scott B. Weldon
Original assignee: Crown Zellerbach Corp
Current assignee: James River Corp of Nevada
Priority date: 1982-07-01
Filing date: 1983-04-08
Publication date: 1986-05-20
Also published as: FI832144L; DE3368091D1; EP0098683B1; FI832144A0; ATE24024T1; JPS597651A; FI71803C; FI71803B; US4551199A; EP0098683A2; EP0098683A3

Abstract

ABSTRACT OF THE DISCLOSURE

A system of treating web material wherein the web is transported within a differential relative velocity nip defined by a web support surface and a pick-up member having voids therein and having a relative velocity differing from that of the support surface at the nip location. Substantially simultaneously with the web treatment the web is applied to the pick-up member with the web impressed into the voids to lock the web against movement relative to the pick-up member.

Description

~ 3 1 APPARATUS AND PROCESS FOR TREATING WEB ~1ATERI~L

6 1. Field of Invent-lon 7 This invention relates to a system for treating web materlal such as paper sheets~ and in particular, to a system 8 that substantlally simultaneously bulks, crepes, embosses and 10 provides extensibility thereto and locks said characteri ~ ics 11 into the web material.

13 2. _scription oE the Prior Art 14 A number of systems have been employed in the past for 15 bulking, creping and embossing paper webs and similar web 16 material to attain desirable characteristics in the end product 17 such as extensibility, greater absorbency and strength and 1~ higher bulko Such prior art approaches are generally characterized by their complexity and high expense and the process steps are often carried out sequentially through the

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21 use of separate equipment between which the web must be 22 conveyed across open draws. Open draws lead to web control 23 problems which may place unnecessary speed limitations on the 24 production equipment to avoid web breakage or other undesirable 25 consequences. It is often desirable to perform such treatment 26 on paper webs still sufficiently ~et so that the cellulosic 27 fibers thereof have not yet been completely bonded together or 28 set and the problem of potential weh breakage becomes even more 29 acute. Also, when conveying a web in moist condition between 30 the various operating stages there 1s always some loss of the 31 characteristics imparted to the web at the previous stage or 32 stages. For example, in a wet web loss of crepe is Erequently encountered after the wet creping stage because of the weakness '~

lZ04~3.3 1 thereof, particularly when the sheet is passed throu~h an open

3 draw as is often the case in convemtional wet creplng

4 operations.

BRIEF SU~AP~Y OF THE INVENTION
7 Accordlng to the teachings of the present invention a web 8 is bulked, creped and embossed in a single operation under 9 conditions of continuous web support and control. In addition, 10 the desired characteristics inparted to the web by such treatment are "locked" into the web as the operation ls carried 12 According to the present invention web material such as a paper web is transported on a transport surface through a 35 differential relfltive velocity nip deflned by the transport 16 surface and the surface of a pick-up member having a relative velocity differing from that of the transport surface at the 17 nip location. The pick-up member includes web locking elements 19 defining voids and selected portions of the web are impressed 20 into the voids during web passage between the pick-up member 21 and the transport surface. The differential relative velocity 22 nip results in the simultaneous bulking, creping~ and 23 embossment of the web as well as transfer of the web to the 24 pick-up member. Due to the faet that the web is impressed into 2~ the voids of the pick-up member the web will be mechanically 26 locked into position thereon by the lock;ng elements and w;ll retain the desired characteristics just imparted to it. In the 2~
28 preferred embodiment the pick-up member is an open mesh fabric 29 woven or otherwise formed by filaments with the filaments 30 comprising the locking elements and the voids being defined by 3~ the filaments. The filaments may be made Erom a single strand 32 ~f material (monofilament) or comprised of a plurality of strands (multifilament). The fabric can be readily replaced ~nd adjusted as necessary.
__ , 1;2~4~6~

3 Fig~ l is a schematic side view of one form of apparatus 4 constructed in accordance with the teachings of the present

5 inventlon and for carrying out the method thereof;

6 Fig. 2 is an enlarged plan vlew of an open ~esh fabrlc

7 sui~able for use in connection wlth the present inventloo;

8 Fig. 3 is an enlarged side view of the fabric o~ Flg. 2

9 with a paper web impressed thereon;

Fig. 4 is a view similar to Fig. l but showlng an 11 alternate form of apparatus, and 12 Fig. 5 ls an enlarged cross sectional side view showing 13 passage of an alternate form of fabric and a web between a 14 transport surEace and back-up rollO

17 Referring now to Fig. l) ~ preferred form of apparatus 18 constructed in accordance with the teachings of the present 19 invention is illustrated. For purposes of illustration, the 20 web to be treated ls a paper web. The apparatus includes a 21 transport member l0 which in the dlsclosed embodiment comprises 22 a Yankee dryer having an outer support surface 12 for 23 supporting and transporting a web 14. It will be appreciated 24 ~hat a cylinder, belt or other member havin~ a suitable web 25 support surface may be substituted for the Yankee. The we~ is 26 formed by any suitable conventional web forming equ;pment (not shown) such as a Fourdrinier machine, twin wire former, dry 28 former, etc. and delivered and applied to the support surface 12 by any suitable expedient such as carrier felt 16 disposed about roll 18.

31 Transport member l0 ls rotated counter clock~ise as viewed 32 in Fig. l so that the support surface thereof moves at a predeter~ined speed. The web is delivered to a nip formed 2 between the support surface 12 and the outer surface of a 3 pic~-up member 22 disposed about ~ back-up device such as back-up or press roll 24 ~hich may, if des~red, be a vacuum 4 rollO Alternatlvely, a shoe may be employed as the back-up device. Pick-up member 22 is preferably in the form of a 6 continuous loop (only the pertinent port~on of whlch is 7 illustrated~ and preferably comprlses an open mesh fabric 8 formed of woven filaments and defining voids between the filaments. As will be seen, the filaments function as web

10 locking elements which serve to lock and retain the web therein

11 in creped, bulked and embossed condition. The strlcture of a 1 representative open mesh fabric is shown in detail in Figs. 2 13 and 3 wherein it may be seen that f~bri~ 22 comprises warp and 15 woof filaments defining volds 30 therebetween. Pick-up member 16 22 is driven in a clockwise manner as viewed in Fig. 1 through 17 any suitable mechanism. The plck-up member is driven so that the outer surface thereof has a surface speed less than the 1~ surface speed of the transport member support surface 12. This differential relative velocity nip arrangement results in the 20 accumulation and bulking of the web at the nip location as well 22 as the creping thereof. Also, substantially simultaneously 23 with occurrence of the aforesaid treatment the web is impressed 24 into the voids 30 of the open mesh fabric 22 with the fllaments 25 embossing the web. This action is illustrated in Fig. 5 where 26 the accumulation of the web and extrusion of portions thereof 27 into the voids of an open mesh fabric are illustrated. In this 28 par~icular figure an alternative form of fabric 22a, a double 29 layer fabric, is illustrated and lt will be understood that the 30 principles of the present invention are not to be restricted to 31 any particular type of picl~-up member or fabric of any particular type as long as it has sufficient vo:~ds, locking elements3 and other characteristics enablin~ it to at~ain ~he desired objectives of this invention.

2 Insofar as t~e theory of operation of the present 3 invention is concerned, as the web approaches the polnt of convergence between the fabric and support surface of the 4 Yankee dryer or other support member a deceleration of the web 5 occurs. This is caused by the impact of the web against the 6 slower moving fabric filaments. On impact, the pick-up web 8 collapses on itself one or more times to form crepe folds. The 9 succeeding folds in the web press agsinst the earlier folds, pushing th~m into the voids of the fabric, the size and number 10 of folds being determined among other things by the flexibility

12 of the web and the magnitude of the relative velocity differential between the fabrlc and the support surEace of

13 transport member l0.

~ Because the we~ is impressed into the voids the web will be locked into position by the filaments which function ~s 16 locking elements and be retained on the open mesh fabric as 18 such member diverges from the support surface 12. Thus, the 19 web will be locked into position by the locking elements and 20 retained on the pick-up member with the crepe folds, 21 embossments (formed by the Eilaments) and other desirable 22 features of the web being maintained. The web will then be 23 conveyed by pick-up member 22 to a downstream station for 24 subsequent additional drying or other desired treatment before 25 removal therefrom.
2G ~hen ~ back-up roll such as roll 24 is employed it is 27 desirable to provide some means whereby it may be readily 28 adjusted relative to transport member lO. Fig. l illustrates a 29 simple adjustment arrangement. Specifically a framework 32 of 30 structural steel or the like is provided. Pivota]ly connected 31 to framework 32 as by means of a connector pin are roll support 32 arms 36 (only one of which is shown3 having centrally disposed bearings 38 whlch freely rotatably accomodate the shaf~ en~s of ~LZ514~ 13 2 back-up roll 24. One or more hydraulic or Air cylinders 40 are employed to selectively pivot roll support arms 36 and hence 3 ad~ust the position of back-up roll 24 relative to transport member 10. In the arrangement o Fig. l the back-up roll 24 5 preferably has a resilient outer cover forrned of rubber or the 6 llke which will serve to distribute forces evenly across the full width of pick-up member 22 and accomodate any dimensional 8 variations therein.
9 Fig. 4 illustrates an alternative embodiment of the present invention. Whereas the embodiment of Fig. l relies ll solely on pressure between pick-up member 22 and the faster 13 transport member support surface 12 to treat the web and adhere

14 it to the piclc-up member, in the arrangement of Fig. 4

15 supplemental means for accomplishing this end is provided.

16 Specifically, a doctor blade 50 is positioned in engagement

17 with transport surface 12 with the working edge thereof 38 positioned in the nip formed between back-up roll 24a and the support surface. This arrangement is particularly useful when a gap is maintained between the pick-up member 22 and support 2] surface 12 and compression of the web by these elements alone 22 might not be sufficient to effect transfer of the wet web to 23 the pick-up member. In addition to at least partially 24 assisting in making such transfer the doctor blade 50 25 contributes to the creping and bulking of the web by 26 interrupting movement of the web. The arrangement of Fig. 4 27 also differs from that of Fig. 1 by virtue of the fact that the 28 back-up device employed is a hard vacuum roll 24a with the 29 vacuum being applied to the backside of pick-up member 22 to assist in movement of the web into the voids thereof ~hereat 31 the filament locking elements lock the web for retenti~n on the 32 pick-up member aEter the vacuum section is p~ssed.

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2 It will be appreclated that the operatlng parameters of the present invention will depend upon many factors such aa the 4 basis weight and otller physical characteristlcs of the web, the moisture content thereof, the differential relative velocity 5 between the pick-up member and transport meMber, nip loading 6 pressures and the natures of the pick-up members and back-up devices employed. To illustrate the present invention, 8 experiments were conducted employing the general arrangement of 10 Fig. 1. A furnish of 100% bleached kraft hemlock pulp was used without refining or additives to provide flat sheets that 11 varied from 9 to 28 lbs/3000 sq.ft. At each weight, the 12 diferential speed, web dryness and nip loading were varled.

13 Samples of the creped papers were obtained by stopping the 14 fabric and air-drying the sheet on the fabrlc. These dried 15 sheets were removed and submitted for analysis. Successful 16 creping occurred within the following range of machine conditions:

18Variable UnitsOperating Range 19Basis Weight lbs/3000 sq. ft. 9 to 28 20Web Dryness % o.d. 37 to 62 Differential Fabric 21Speed % 13 to 51 22Nip Loading pli 40 to 75 The dried sheets were tested for basis weight and Lobb caliper 23 tthickness when loaded to 1.35 lb/in2) and values for Lobb 25 density were calculated. At a glven weight the densities ~re 26 consistently less than would be expected for a conventionally 27 wet-creped sheet:

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~9Basis Weight Lobb BulkLobb Density _lbs/3000 sq.ft. mils/24 sheetsgrams/cc 10.1 116 0.133 3212.3 159 0.119 13.8 144 0.147

18.5 200 0.142 - ~Z~ 3 24.2 274 0.13~
l 25.6 296 0.133 2~.5 295 0.138 2 33.6 282 0.183 38.8 300 0.199 3 41.7 295 0.217 4 During the planning phase of these runs, it was believed that a 5 1~ed clearance between the fabric surface and the Yankee would 6 be necessary. For this reason stops we,re inst~lled against 7 which the air cylinders 40 were loaded. In early experiments 8 this gap was adJusted to 0.002 to 0.004 in. It was later 9 discovered that a more positive transfer occurred by loading 10 directly against the paper with adjustments in the air pressure ll ts the cylinders.
12 The influence of fabric design was evaluated by comparing 13 both sides o a double-layer Style 8;0 monofilament fabric made 14 available by The Albany Felt Company, the warp and woof 15 characteristics of which are shown in Fig. 5. One side of this 16 fabric was sanded to increase its surface area. the other side 17 rema~ned unsanded. In the experiments `the s~nded surface 18 permitted easier tranfer and creping. However~ the non-sanded l9 side could be made to work successfully by selecting a higher 20 nip loading (75 vs. ~0 pli).
21 As previously stated, the present invention encompasses 22 the transporting of a paper web on a transport surface through 23 a differential relative velocity nip defined by the transport 24 surface and the surface of a pick-up member havlng a relative 25 velocity differing from that of the transport surface. As 26 described above, this differential relative velocity nip was 27 defined by a pick-up member and a support surface moving in the 28 same direction but at different speeds at the nip location.
~9 That is, the faster moving web on the transport surface 30 impacted on either a slower moving pick-up member directly or 31 agalnst a creping blade operatively associated ~ith a slower 32 moving pick-up member to efect subst~ntially simultaneous a;~

1 bulking3 creping, embossment and transfer of the web. Rather thAn operating the apparatus in this manner it is consldered 3 w~thin the scope of the present invention to run the pick-up 5 member in a direction opposlte to the direction of motion of the transport surface at the nip location to define the 6 differential relative velocity nip. In other words, 8 substantially simultaneously with the crepe and transfer 9 functions the web would be subjected to an essent;ally 180 10 degree reversal in direction of movement. Wlth this latter 11 approach a differential relative velocity nip would be created 12 even if the pick-up member and transport surface were driven at 13 the same speeds.
14 While the present invention is believed to have particular 15 benefit when utilized with a wet web wherein the cellulosic 16 fibers have not yet completely bonded together'or set, the 17 advantcage of maintaining complete web control is equ'ally 13 applicable when utilizing the teachings thereof to treat a dryer web.

19 As stated above, any -form oE pick-up member may be 21 employed when practicing this invention as long as it has 22 sufficient voids, locking 'elements9 and other characteristics 23 enabling it to attain the desired objectives of this 24 invention. For example, it is possible that the pick-up 25 member, rather than comprising a fabric, ~ay be in the form of 26 a rotating roll or drum suitably machined or otherwise forming 27 on the outer periphery thereof voids into which the web is 28 impressed and locking elements for retaining the web thereon.
29 A fabric, however, is considered to be the preferred form of 30 pick-up member since such an element can be readily employed ~s 31 ~ continuous support for the web as it proceeds through one or 32 more additional stages of the manufacturing process such as a through dryer stage. A1SOJ such fabric may to be used as an 1~

1 imprinting fabric to directly apply the web to a Yankee dryer 2 or other dryer device as taught, for example, in Un~ted States Patent No. 4,309,246 lssued to Hulit, et al. on January 5, 4 1982. Xt will be appreciated tlat the web may be sub~ected to 5 any desirable treatment after passing through the diferential 6 velocity nip. For example, the web may be subjected to 8 supplemental pressing by a press roll and/or supplemental ]2 v uum box treatment d~wns~ream rom tho nip ]3 l6 19 .

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process of treating web material comprising the steps of:
transporting said web on a transport surface moving at a predetermined surface speed, said transport surface comprising the outer surface of a rotating roll;
positioning an open mesh fabric pick-up member formed of filaments comprising web locking elements defining voids at a predetermined location whereat a surface of said pick-up member is adjacent to said trans-port surface;
driving said pick-up member so that it has a relative velocity differing from that of said transport surface and continuously urging said fabric toward said roll whereby a differential relative velocity nip is defined thereby;
passing said web between said pick-up member and said transport surface through said differential relative velocity nip to impress portions of said web into said voids whereby said web portions are lockingly engaged by said locking elements;
transferring said web to said pick-up member substantially simultaneously with passage of said web between the pick-up member and transport surface;
retaining said web on said pick-up member positioned in the voids thereof and in locking engagement with said locking elements after the web has passed between the pick-up member and transport surface; and transporting said web on said pick-up member away from said transport surface.

2. The process of claim 1, wherein web transfer is at least partially accomplished by doctoring the web from the roll.

3. The process of claim 1, wherein the step of trans-ferring said web to said pick-up member is at least partially accomplished by engaging the fibers of said web with the locking elements defining said voids and sub-sequently effecting divergent movement between said locking elements and said transport surface.

4. The process of claim 3, wherein a vacuum is applied to the pick-up member through said locking elements to draw the web into engagement therewith with web portions positioned in said voids.

5. The process of claim 1, including the step of forming crepe folds in said web during transfer of the web to the pick-up member.

6. The process of claim 1, wherein the pick-up member comprises an open mesh fabric formed of filaments and wherein said web is embossed by said fabric filaments during passage of the web between the fabric and transport surfaces.

7. The process of claim 1, wherein the web decelerates on said transport surface during passage thereof between the pick-up member and transport surface to accumulate and bulk said web prior to completion of web transfer to said pick-up member.

8. The process of claim 1, wherein said pick-up member is driven at a predetermined surface speed less than the predetermined speed of said transport surface.

9. The process of claim 8, wherein said pick-up member and transport surface are moving in the same direction at the location of said nip.

10. The process of claim 1, wherein said pick-up member and transport surface move in opposite directions at the location of said nip whereby the web is subjected to a substantially 180 degree change of direction during transfer.

11. A process of treating web material comprising the steps of:
transporting said web along a predtermined path of movement on a surface of a transport member having a predetermined surface speed, said predetermined path of movement leading to a differential relative velocity nip between said transport member surface and a surface of a moving pick-up member including web locking elements defining voids therebetween;

during said web transport through said dif-ferential relative velocity nip applying forces thereto to form crepe folds in said web;
transferring said creped web to said pick-up member substantially simultaneously with application of said forces to said web, said transfer being at least partially accomplished by doctoring the web from the transport member surface toward the pick-up member; and impressing portions of the web into locking engagement with said locking elements and into the voids of the pick-up member substantially simultaneously with said transfer and application of said forces to form embossments in said web and to lock the web against move-ment relative to the pick-up member so that the crepe folds and embossments are retained therein.

12. The process of claim 11, wherein the web is at least partially formed of fibers and wherein the step of transferring the web to the pick-up member is at least partially accomplished by engaging the fibers of the web with said locking elements at said voids.

13. The process of claim 11, wherein the forces are imparted to the web by said transport member surface and said pick-up member on opposed sides of said web to accumulate and bulk the web prior to completion of web transfer to said pick-up member.

14. The process of claim 11, wherein said web is continuously supported during transfer thereof to said pick-up member.

15. The process of claim 11, wherein said dif-ferential relative velocity nip is defined by said trans-port member surface moving at a predetermined speed and the pick-up member moving at a lesser speed through the nip than the transport member surface predetermined speed.

16. The process of claim 15, wherein the pick-up member and transport member surface are moving in the same direction at the nip.

17. The process of claim 11, wherein the transport member surface and pick-up member move in opposite directions at the nip.

18. A process of treating web material comprising the steps of:
attaching the web to a surface rotating at a predetermined surface speed;
driving an open mesh fabric having locking elements defining voids so that said fabric has a relative speed differing from the speed of said rotating surface whereby a differential relative velocity nip is formed there-between;
creping said web at the location of said dif-ferential relative velocity nip;
transferring said creped web to said fabric while continuously supporting said web; and lockingly engaging said creped web with said lock-ing elements so that the web is locked against movement relative to said fabric and crepe retained therein.

19. The process of claim 18, including the step of heating said web on said rotating surface.

20. Apparatus for treating a web, comprising:
a transport member comprising a hard roll having a support surface for supporting and transporting said web at a predetermined speed;
a pick-up member having web locking elements defining voids;
positioning means for positioning said pick-up member at a predetermined location whereat said pick-up member forms a differential relative velocity nip with said transport member surface; and means for effecting transfer of said web from said transport member surface to said pick-up member surface at said differential relative velocity nip, said locking elements locking said web on said pick-up member so that said web is conveyed thereby in essentially undisturbed condition after transfer.

21. The apparatus of claim 20, wherein said pick-up member comprises an open mesh fabric formed of filaments defining said voids and wherein said filaments comprise the web locking elements.

22. The apparatus of claim 21, additionally comprising a resilient back-up roll for biasing said open mesh fabric toward said transport member.

23. The apparatus of claim 20, additionally comprising a doctor blade at said differential relative velocity nip for doctoring said web from said transport member support surface and assisting in the transfer of said web to said pick-up member.

24. Apparatus for treating a web, comprising:
a roll having an outer transport surface and adapted to be rotated at a predetermined rate of surface speed; and an open mesh fabric formed of woven filaments and defining voids between the filaments at the outer surface thereof, said fabric being positioned adjacent to the roll and adapted to be driven at a speed and direction defining a differential relative velocity nip between the roll outer transfer surface and the fabric outer surface, said roll and fabric cooperable to effect working of said web at said differential relative velocity speed nip and sub-stantially simultaneously effect transfer of said web from said roll to said fabric with portions of the web impressed into the voids thereof whereby the web will be locked into position on the fabric with said portions between the filaments thereof.