CA1107109A - Ply-separable paper - Google Patents

Abstract

PLY-SEPARABLE PAPER

Abstract of the Disclosure An improved process to produce a novel tissue which becomes ply-separable during the papermaking process.
In a first embodiment of the invention a two-layered stratified web is formed, having a first layer comprised of a relatively low consistency slurry of long papermaking fibers and a second layer comprised of a high consistency slurry of relatively short papermaking fibers. In a second embodiment of the invention, a stratified web having three layers is formed, comprised of well-bonded layers separated by an interior barrier layer. These improved tissue products need not be creped from a creping roll with a doctor blade in order to exhibit ply-separability, and they may be creped in a single step to form a finished product which is creped all the way through.

Description

Field o~ the In~ention The present inventio;l rela~es to improveme;lts in wet-laid web manufacturing operations, ~specially thosP
~0 utilized :Eor p~oducing soft, bulky, absorbent paper shee~s sui~able for use in tissue, to~eling, and sa~itary produc~s.
In particular, ~he present invention rela~es to the provislon of a ply-separable stratified web formed froTn more than one - ~ibe~ s~r~ said stratified web being subsequen~ly conformed ~5 to the surfac~ oi~ an open mesh drying fabric by ~he application of a Dartial vacuum to the web and then the:rmally predried on the ~ora~Linous in~ermediate drying ~abric (hereina~ter - "intermediate drying fabric") as par~ o~ a low density papenQaking proces s O

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Unexpec~edly, the process disclosed herein allows the use o a variety of creping techniques to ~orm a ply-separable strati~ied web, and permits the web to be creped throughout in a single creping operation. The impressions of the intermediate drying fabric on the web influence the ereping pattern. The resulting finished pruduc~ is a single s~ratified web which is capable of separation into individual plies, and wh~ch in its unseparated sta~e is characterized by creping which is substantially equal in frequency and simulta~eous in phase in the several layers of the we~.

Background of the Invention Ply-separability is desir~ble in a tissue produo~
. because a ply-separable web is believed by applicants to be : more flexible than a conventional web o the same basis .
weight which isln'otlply-separable. The source of this hypothe.sis is the rela-tion between thickness a~d flexural : rigidity in a given ma~erial. The flexural rigidity o~ a ~ember is proportional to the cube of its thickness in the .
direction in which a flexing force is applied. Thus, where a one-pl~ member has a thickness h, and thus a ~lexural rigidity proportionaL to h3, a two-ply member with a combined thiclmess of h (each pl~ is hl~ thic~) has a flexural rigidi~y propor~ional to 2(h~2)3, or h3~4~ Thus, in the case where he ~wo plles of a ~wo-ply mem~er do no~ subs~antially in~eract at their interace, the ~lexuraL rigidity of the ~wo-ply member is I/4 that of a one-ply member of equal thickness. This~illustra~es that to reduce ~he bonding .b~twe~n wel~-bonded~layers o a web, forming ~istinct plies :: ~ which resemble~:plural no~inter~acting members, i5 ~0 increase: 30 ~he ~l xibility of~a pap~x web o a given ~hic~ness.

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Laminate paper and paper-like s-tructures exhibiting ply-separability are well known in the art. For example, United States Patent Nos. 514,059, issued to Bird on February 6, 1894;
1,606,428, issued to Kirschbraun on No~ember 9, 1926; 1,964,793, issued to Richter on July 3, 1934; and 2,234,457, issued to Strovir~ on October 9, 1937 demonstrate that a nonadhesive material applied between two outer layers of paper or the like can be used to produce a ply-separabIe structure. However, none of this early work is believed by applicants to disclose the crea*ion of a ply-separable web which is useful in the manu-facture of absorbent paper products.
British Patent Specification No. 1,504,374 of Charles H.
Dunning et al, entitled "Creped Laminar Tissue and Process of Manufacture", said British Patent Specification having been pub-lished on March 22, 1978, and German Offenlegungsschrift 25 28 311, laid open on January 8, 1976, which is a counterpart of said British Patent Specification, describe various methods for producing a three-layered ply-separable tissue web. The essence of the disclosure is that a web may be formed having outer layers of strongly bonded fibers separated by an intermediate zone wherein intralayer bonding is reduced. When the web is subjected to creping from a creping roll using a doctor blade, this ref-erence teaches that only the layer of the tissue adjacent the creping roll is creped, and a second operation is be]ieved to be necessary to crepe the other side of the web in order to create a finished pxoduct. This application also discloses that ply-separability is imparted to the web as a result of the creping operations which shear the two outer layers ~rom each other.
The result of this process ~is said to be a tissue product having two ply-separable laye~rs, formed such that the crepe in one`well-bonded layer is independent in both frequency and phase of the :
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crepe in the other well-bonded layer. The applicants believe that this pxocess would be: much more expensive to produce soft webs than the process disclosed h.ereina.~ter, since an additional creping step is required to crepe both exterior surfaces of the web.: Furthermore, the Dunning, et al. sritish paten-~ specifica~.ly requires creping with a doctor blade as an essential element to produce a ply-separabIe product, while the applicants have found that unique aspects of the process disclosed hereinafter permit the use of many creping techniques.
The applicants are not aware of any prior art respecting the use of differential consistency in a paper web foxmed in two ~-layers to crea-te a ply-separable product.
U.S. Patent No. 3,994,771, issued to Morgan et al. on Nov-; ember 30, 1976 and commonly ownecl with this application, dis-closes the general type of papermaking machinery which may be used to produce paper according to the present invention. This reference, as well as others, can be distinguished from the present invention ln that there is no teaching that this process ~ ~ can be used to make:ply-separable products. Such a result is . 20 ~ unexpected when using this process because, accordlng to the teachings of Morgan et al, small isolated areas of the web strata are compressed together to ~orm discrete densified areas corres-ponding to the knuckle patt~rn in the foraminous intermediate : drying fabric, which would be expected to cause the two layers to adhere together rather than to separate. This reference does disclose, however, that the knuckle impression imparted by the drying fabric creates sites at which the web is predisposed to buckle, so:that the~mesh of the dxying fabric influences the : : fineness of creping. This prior ar~ re~erence discloses that a -strati~ied web~may be~ creped all the way through, although this , teaching would not be expe~ted t~ ~ppl~ to the creping o~ a web to which ply-se~a~abilit~v is imparted prlor to creping.
Summary o~ the In~entio~
Tissue of the present invention is formed by wet-laying a strati~ied web.
In a first embodiment o~ the in~ention a web is formed in one or more forming sections of a papermaking machine, and com~
prlses at least a ~irst layer of short papermaking fibers and a second layer of long papermaking fibers. The first and second layers may be deposited from a single divided headbox of a single forming section, in which case the consistency of the first layer as it leaves the headbox is about 0.25 to 0.6 percent fiber by weight, and the consistency of the second layer as it lea~es the headbox throat is ahout 0.1 to 0.3 percent fiber by weight. Alternatively, the first and second layers may be deposited from separate headboxes of separate forming sections, dewatered so that one layer, pre~erably the short-fiber fabric side layer, has a much lower consistency than that of the second layer. ~ The layers are then combined into a sinyle stratified web while still in the wet end of the paperma]cing machine.
In a second embodiment of the invention a three-layered stratified web is formed in one or more forming sections, comprised of two well bonded layers separated by a barrier layer which isolates the bonding within one well-bonded layer from the bonding within the other well-bonded layer.

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~ ~ ~ - 5 -In eit~er embodiment of the inven~ion, the web is rendered ply-separable by t~ansferring i~ to a for~minous intermediate drying fabric having a mio-sh of such a ~ineness that the machine direction distance between adj acent row:s of knuckles in the drying fabric is approximately O . 2 to 1. 0, or more preferably about 0. 3 times the length of the long papermaking fibers in the well-bonded layers of the strati~ied web. Transfer is effected by applying a partial ~acuula to the opposing sides of the web. This partial vacu~L~
is imporl:ant because it tends to isola~e I:he ply-separable areas of the web from each other, and thus it enables the web to become ply~separable ~hen it is dried. I the web is dried comple~ely at this point, it will be ply-separable.
However, after the web is dried it is desirably creped, using any one o a number o known methods in a single creping operation to produce a finished tissue web. The creping of the several layers of the web is equal in frequency and simultaneous in phase, the crepe ~requency depPndîn~
upon ~hf~ distance measured in the machir~e direct~on be~een ~0 successive cross -machine direction rows of ~uckle imp~es sions in t~e webJ and depending also on the draw o~ the ta~e-up reel. The finished tissue web is ply-separable~ ~hich means that ~ although the web normall~ exists as a single sheet, the two separable layers o~ the web can be.pee~ed apart into two plies wiehout subs~antia~ly destroying the bonds with;n he respective separable la~ers.

More particularly, the present invention provides a method to produce a:ply-separable web, cQmprisi~g the steps of:
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(a~ ~orm.ing a wire side web l~yer of long papermaking fibers on a ~irst forming wire,: said wire side ~eb layer having a consistency of about 10 to 25 percent fiber by weight at the point of juxtaposition wi.th a ~abric side web;
(b) forming said fabric side web :layer of short paper-making fibers on a second forming wire, said fabric side web layer having a consistency of from about 5 to 15 percent fibre by weig.ht, whereby the consistency of said wire side web layer is about 5 to 10 percent by weight greater than the consistency of the fabric side web layer at the point of juxtaposition with the wire side wèb;
~c) juxtaposing said ~irst and second forming wires with : said fabric side web and wire side web layers disposed there- :
between, bringing said first and second wires into contacting relat.ion to form a comhined web;
(d) applying a sufficient differential pressure to said combined web to unify it into a stratified web having first and second strata which are weakly bound together by papermkaing bonds;
(e~ ~pplying a partial vacuum to said stratified web adjacent said fabric side of the web, whereby to transfer said stratified web to an intermediate drying fabric and to reduce the adherence of said wire side web and fabric side web layers ~ to ~ach other;
- 25 (f) drying said strat.iEied web while it is on said inter-mediate drying fabric, to a consistency of about 85 to 100 per-cent fibers by weight; and (g) creping said stratified web in a single operation to produce a web with~creping which:is e~ual in frequency and :~
slmultaneous in phase in each layer of said stratified web.

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~lso~ then, in anothex aspect, the present inVention resides in an absorbent ply-separabIe paper web which has creping which is substantially equal in frequency and simultan~
eous in phase in each separable layer.
A web having ply-separable layers which are creped as a unit, so that the creping pattern in all layers of the web is equal in frequency and simultaneous in phase and the plies nest together, exhibits properties which are advantageous compared with the webs disclosed in the prior art. Specifically, the tissue of this lnvention has very good wicking properties and absorbency, as well as an outstanding subjective impression of softness compared with prior art tissue products.

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; - 6b -Brief DescriPtion of the Drawin~s Figu-e 1 is a schema~ic side elevational view of a papermaking machine used ~o practice the inven~ion, having a single forming section and a divided headbox.
Figure 2 is a schema~ic side elevational view o~ a second type of papermaking machine, having two forming sections. Two headboxes, which may each be single or divided, are used.
- Figure 3 is a schematic side elevational view of an inter~ediate drying section of a p~permaking machine wherein the web is wound directly from ~he intermedia~e drying fabric so that creping may be perfor~ed, i desired, i~ a separa~e opera~ion.
Figure 4 is a schematic side eleva~ional view o a two-~hannel fixed-roof headbox used in one embodimen~ o~ ~he ;n-vcntion .
; ~ Figure 5 is a schematic side elevational view o a~hree-channel ~ixed-roof headbox used in a~other embodi~ent . of thc invention.
:: 20 Figure 6 is a schema~ic s;de elevational enlarged . ~iew.of a web of: the ~present in~en~ion as it resides on the : in~ermediate~drying fabric.
Fi~ure 7 is a ~iew identieal to Figure 6, except that a machi~e direction filament is removed so tha~ the ~S entire web is visible~
; Figure 8 is a schematic side elevational view of : buckli~g si~es created in the web by passing it through a nip between a pressure roll and the Yankee dryer :~ Figure ~ is a view identical to Figure 8, excep~
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3:0 that~:a machine direction ~ilamen~ is removed so tha~ ~he ~;~: . entire web is visible.

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Fi~ure 10 is a schematic side elevational vi~w of a longitudinal sec~ion of a finished produc~ wi~h nesting separable plies, made according to the invention.
While several embodimerlts of the present invention are described with great particularity hereinbfter to enable persons skilled in the art to make and use the invention, the applicants do not in~end thereby to limit the scope o~
~heir invention, which is defined by ~he claims eoncluding this specification.

Definitions A stratified web as used herein is a single paper web made up of plu:eal ~;ayers with distinct proper~:ies.
While a s~all degree of mixi:ng be~ween strata a~ their interaees is inevi~able, such mixing is desirably held t:o a mirlimum in accordance wit~. the presen~ invcrl~on.
, A ~ond as used herein is an electros~atic bond, includin~; bu~ not limiLed co hydrogen, ion-dipole, . and dipole-dipole bonds. This includes bonds occurr~ng directly between~ ibers, as welL as bonds occurrin~; indirec~ly be~:ween ~ ~iber~ through an electrost0tically bondable non-cellulosic ma-~erial.

A barrier la~er as used herein is a layer o:E material interposed between layers which are to be ply-separable : ~ in order to pre~en~ those layers from substantially interacting with, or becoming substantially ~ound ~o each other while the barrier is maintained.

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The fabric side of the web as used herein is the -layer or major face thereof which is in conforming contact wi~h the inter~ediate drying fabric at that stage of the papermaking process, The wire side of the web as used herein is the 12yer or major ace thereof OppO5 ite the fabric side of ~he web.
Lon aPermakin fibers as used h~rein are fibers, ~ Y . ~ .
o the types cus~om~rily used for paperma~ingS ~Aypically cellulosic fibers having a length in the range o abou~ .08 to about ~12 inches or more.
Shor~aperm~ no ibers as used herein are fibers, of the types customarily used for paper~naking, typical].y cellulosic fibers having a length in the range of abou~ . 01 ...
to about ~ 08 inches.
A knuckle as used herein is a point in the in~ermediate drying fabric where woof and warp ilaments overlap.
Cre ~.ff as usPd herein is broadly defined to mean any paper web processing technique which longitudinally compresses the web in order to improve its bulk, softness, and other qualities. Examples o creping are the MICRF~ alld CLUPAK proprie~ary proce~ses described hereina~er, as well as Yankee creping.
The mpact an~e as used herein is the plane angle 2S defined by the beveled ace of a doctor blade and by the down-stream segment of a plane tangent to the surace o:E a Yankee dryer at the point o intersectivn of the dryer and b~ade.
.~ ~ The impact-. angle defines the angle on which a paper sheet - is deflected when in con~acts ~he doc~or blade during Yankee .
~30 creping.

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.. , _ 9 _ ' MICREX cr~ as use~ herein is a proprietary method ~or creping a web by conveying it between a drivinO
roll and a s~ationary surface in~o a retarding zone so that the speed or the web as it en~ers the retarding zone e~ceeds the speed of the ~eb as it leaves the reta~ding zone.

CLUPAK creping as used herein is a prop~ietary method ~or ereping a web by applying a eompressive force parallel to the respective faees of a paper web in a longi~udinal direc~ion while si~ul~aneously applying a force pe~pendic~lar to said faces.

Ply separabili~y as used herein is a property o~
lS webs made according to the present invention. Such webs - ordinariLy exist as a single stratified web, and are not intended to delaminate while in nonmal use, but are separable int~ twv plies (or more) wî ~out destroyis~g the 1 avers ~mediately adiacen~ the plane of separation.

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.' ' ~:~y~ of the invention as used herein are those embodimPnts of the invention having no distinct layer interposed be~cween the two ply-separable layers. It should be noted, however, that a ~o-l~yer S embodiment may have additional layers on either or both sides of the ply-separable portions of the web.
Three-layer embodiments of the invention have a sandwich construction comprising two ply-separable layers, separated during at least part of the papermaking process by 1~ a barrier l.ayer o~ material which isolates t~e ply-sPparable layers to prevent them frorn bonding to each other. 0 course, the cen~ral layer mus~ either be non-cohesive> or non-adhesive to the ply-separable layer~, ~o allow l:he layers ~o separat:e.
Again, the three-layer embodime~t may have addi~ional layers on eithe~ or bo~h sides of the ply-separable poxt:ions o~ the web .
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Description of the Pre~erred EmbodiFIents Referx ing to Fîgure 1, there is shown an e.~ample ; ~ of a papermaking m~chine ~apab~e of producing paper accordin~
; 2~0 ~ ~ ~ t;o the~ pr~sent in~ention~ ~e papermaking fu~ish is delivexed from a~ closed headbox lG to a Fourdrinier wire 11~ support:ed by a: breast roll 1;~ mcompac~ed pape~ web 13 comprising at leas~ a wire side la~er 13a and a fabric side la~.er l~b is fonned, and the Fourd:r~nier wire. passes over onning boa~ds 14, which are des~rable but no~ necessary. Toward he dry end of ~he forming sectîon ~he Fourdrinier wire 11 with the we~ paper web 13 suppar~ed thereon passes over a p7urality o vacuuun boxes 15. Five such vacuum boxes are shown in the illua~ration.: After passing over ~he vacuuas 30 ;~ boxes~ 15~ the ~Fourdr}nier~ wire and the moist web pass around a Fourdrînier wir roll 17J and;dowr~ward~y adJacen~ a pick-up~ shoe 19. ~Pick-up shoe 19 draws a sufficient ~ac~um with resp~ct to ~he embient pressure to create a pressure diferen~ial across web 13 which reduces the adherence between wire side layer 13a and fabric side Layer 13b, thus rendering layers 13a and 13b of ~he web ply-separable. Also as a result o~ the pressure differen~ial crea~ed by pick-up shoe 19, the paper web 13 is transferred without compac~ion ~a the intermediate drying fabric 20. At the same time, Fourdrinier wire 11~ which is now free of ~eb 13, passes around wire return roll 21d and is cleaned by wa~er sprays 18 before returning around breast roll 12 to complete its cyc~e.

The web on the drying fabric is first carried over roller 21e to the vicinity of a hot air dryer 22. The intermediate drying abric and the ~he~mally pre-~ried paper web ~hen pass over a s~raigh~ening roll 23, which pxPven~s t~e formation of wrinkles in the intermediate drying ~abric, an~ over ~n~her i~te~mediate dr,~.$ ~abric r~ll . 21f ~or trans~er onto the sur:Eace of a Yankee dryer drum 2h~ The pressure roll 2S causes the knuckles o ~he intermediate drying ~abric 20 to be impressed into the pre-dried paper sheet 13 during transfer to the Yankee surace. The intermedia~e drying fabric ~O~then raturns to the. vîcinity of Fourdrinier .
: wire 11 over ~everal return rolls 21g, h, a~d i, being washed free o~ clinging fibers by sprays 26 and dried by vacuus~ bo~ 27 d~lring i~s return. The paper sheet 13 is carri~d a~ound ~he periphery o the Yankee dryer dn~m. 24 for drying and is desirab~y creped f~om the Yankee dryer surace by a doctor blade 28. Typically, the ~urface o~ the Yankee dryer is ~prayed with a small amoun~ o~ a~ adhesive rom spray , .
head 29 to ;mprove the bond between the knuckle imprin~s of 30 :: the paper sheet and l:he ~ankee dryer suxfacè during drying Fi~ure :2 illustrates ano~her papex~2aking mac~lne which may be used~ to~practice the present invention. A ~ .
first :papermaking furnish i~ delivered ~rom closed headbox : ~
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llOa to a Fourdrinier wire llla supported by breast roll 112a. An uncompacted web 113a is formed and Fourdrinier wire llla passes over ~orming boards 114a, which are desirable but not necessary. The web 113a passes over vacuum boxes 115a to increase its consistency. Simultaneously, a second papermaking furnish is delivered from closed headbox llOb ~o a second Fourdrinier wire lllb suppor~ed by breast roll 112b. A se~ond uncompacted paper web 113b is ~ormed, and Fourdrinier wire lllb passes over the forming boards 114b, which again are desirable bu~ not ~ecessary; vacuum boxes 115b serve to increase the consistency of web 113b, Webs 113a and 113~ are dried at this early stage to di.~feren~
consistencies,.~as further described hereina~er. Webs 113a and 113b are combined into a single stra~i~ied web by the : 15 ac~ion o~ vacuum box 116 which creates a pressure differen~
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DetWeen ~he wire side o~ web 113a and the wire ~ide of web . 113b, so that thereater webs 113a and 113b orm a s~ngle stra~ified web 113. Toward tke d~y end of th~ ~or~ing section the Fourdrinier wire llla, wi~h.the we~ paper web 113 ~upported thereon, passes over additional vacuum bo~es 115c to ur~her dry and ~ify stra~ified web 113. After pas~ing :over vacuum boxes ll5c, Fourdrinier wire 11.1~ and ~he moist w~b 113 pass around a Fourdrinier wîre roll 11 t and dows~wardly adjacent a pick-up shoe :119. At this point ~5 the paper web ~13 is transferred wl~hou~ co~pac~ion ~o intexmediate drying ~abric 120 by a pressure di~eréntial between opposing sides o the web crea~et by pi~k-up shoe 119, whieh again contribul:es substan~ially ~: to the :ply-separabili~y o~ the resulting web ~y t:ending ~o :30. : ~draw webs 113a and 113b apart.

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-A~ter webs 113a and b have been removed ~rom Fourdrinier wi~es llla and b, respectively, wire llla passes around return roll 121d and is washed by showers ll~a before returning to breast roll 112a to complete its cycle.
w~ile wire lllb passes over return rolls 121~; 121j, 121kJ
121 1, and is was'ned by wate~ shower 118b before re~urning to breas~ roll 112b ~o comple~e its cycle.

Meanwhile, web 113 on intermed~ate drying abric 120 passes over roll 121e to a ho~ ~ir predrier ~22. The lQ in~ermPdiate d~ying fabri and the thermaLly predried paper web then pass over a straightening roll 123 which preven~s the formation ~f wrinkles in the intermediate drying ~bric, a~d over another ~ntermediat~ drying fabric roll 121f for transfer on~o the surface of a Yankee dryer drum 124. The pressure roll 12S causes the knuclcles of ~he~intennedia~e drying fabric 120 to be impressed in~o the predrled paper web 113 during transer to the Yar.lcee su~~ . T~.e inte~med~at~
drying fabric 120 then passes over several re~urn rolls ; ~ 121g, l~lh, and 121i, being washed fre~ of clinging fibers by~a discharge ~rom spray heads 126 and dried by .~acuum box 127 during its return. The paper sbe~ 113 is carried a~ound the periphery oE the Yankee dryer drum 1~4 and may be creped from t:h~ Yarlk~e dryer surace by a doc~or blade 128, al~hou~L
the Yank~e drg~ing and creping with a doctor bl~de a~e no~
: 25 e~sen~ial to the in~rention, as will become apparen~ a Yankee dryer is used, its surace is. ~ypically sprayed wi~
a small amount of adhesive solu~ion rom spray head 129 t~o improve the~ bond~ between t~e knuclkle imprints of 1:he p~per sheet and the~ Yankee dryer surface during the dryi~g period~
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~, In a ~referxed embodiment of the invention, as seen in ~igure 2, a ply-separabIe paper is formed by nlaking a wire side web layer 113a of long papermaking fibers on a first forming wire llla and dewatering the web to a consistency of from about 10 to 25 percent fiber by we'ight. A ~abric side web laiyer 113b of short papermaking fibers is formed on a second forming wire lllb and dewa-tered to a consistency of from about 5 to 15 percent iber by weight, where the consistency of the wire side web layer is from about 5 to 10 percent by weight greater than the consistency o~ the fabric side web layer. The fabric side web layer 113b and the wire side web layer 113a are superimposed by juxtapositioning the first and second forming wires that form a combined web. SuE~icient differential pressures are applied to the combined web by a vlacuum box 116 to unify it into a strati-fied web 113 having a first and second adjacent strata which are weakly bound together by papermaking bonds. The stratified web 113 is then transferred to an intermediate drying fabric 120 through the application of a partial vacuum by pick-up shoe 119 to the stratified web 113 adjacent the fabric side layer which simultaneously reduces the adhierence of the wire side and the ~, fabric side layers~to each other. The stratif'ied web 113 is predried to~a conisistency of about 50 to 90 percent fiber by , weight. The stratiied web 113 is then imprinted on a Yankee dryer 124 by a pressure roll 125 acting through the intermediate drying :Eabric 120 to orm a multiplicity of d:iscrete densiied areas def'ining a pattern of' spaced lines having a substantial ~ i :
orientation predisposed to buckle during creping. The stratified web 113 is then dried to a consistency of from ~:

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~ 15 -about 85 to 100 percent iber by weight. The strati~ied web is then creped along each o the creping lines t~o orm creping which is equal in frequency and simultaneous in phase in all layers of the web.

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In another pre~erred embodi~nen~ o the inven~ion ~
': a ply-separable paper web is formed on two forming wires ~s seen in Figure 2. The first headbox llOa. deposits a irs~
~urnish on a first FourdriIlier wire llla orming a wire side web layer 113a ~ade of ibl~rs capable o~ ~onning subst:antial p~perT~aking bonds. A fabric s;de web layer 113b is ormed ~n a second Fourdrinier wire lllb from urnish deposi~ed from headbox llOb made of fibers capable of pex~orming subs~antial p~permak~ng bonds. ~ barrier layer is superimposed lp~n on~ o~ er thc wire side web 113a or tE~e fa~ic ~ide 1~ web 113b, The fabric side ~eb layex 113b is dewatered to a consist~ncy o abou~ 5 co 15 percent fiber by weigh~ by ~rming boa~ds 114b and ~vacuu~n box 115~. The wire side web layer 113a is dewatered to a consis tency o~ abou~ 10 ~o 25 percen~ fiber by weight, w~ereby the consistency o~ ~he wire side web :layer is .a~ least as high as the consist:ency o the lCabric side ~eb layer, by orrning board~; 114a and vacuum boxes 115a. The first and second FourdriTlier wires a:re juxtaposed wi'ch ~he~ fabric and wire side layers disposed therebetween oxming a combined web ha~ g a barrier layer ~disposed ~etween the fabric side and wire side layers.
differential press~re::is ~applied to the s~ratiie~ web by - . . . .
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vacuum boxes 115c to form it into a unified web~ The stratified web is then -trans.~erred to the intermediate drying fabric 120 by di~erential pressure applied by vacuum pick-up shoe 119.
The strati~ied web 113 is predried on the intermediate drying fabric to a consistency oE about 65 to about 90 percent Eibers by weight. The web 113 is imprinted on a Yankee dryer roll 124 by pressure roll 125 ac~ing through the intermediate drying fabric 120, which'forms a multiplicity of discrete densified areas in the web defining a pattern of spaced lines having a substantial orientation predisposed to buckle during creping.
The stratif'ied web 113 is dried to a consistency of 85 to about 100 percent fibers by weight on the Yankee dryer roll 124. The ' web 113 is then creped along the plural creping lines to form a creping pattern which is substantially equal in frequency and simultaneous in phase in all layers of the web.
Figure 3 shows a modification of the intermediate drying fabric section of the machines shown in Figures 1 and 2 in order to bypass the Yankee dryer, permitting creping to be delayed and , aLlowing the use of alternate creping methods. The unitary web ''' 213 is transferred to the intermediate drying fabric 220 by the pressure differential caused by pick-up shoe 219, as described , ~ ,. .
~ above. Paper web 213, which has been trans~erred to intermed-; iate drying fabric 220 without compaction, con-tinues over roll 221e to a hot air dryer 222. Since the web will not he trans-ferred to a Yan]cee dryer to complete the drying of the web, it is deslrabLe that hot~air dryer 222 should apply a greater volume of air~ apply hotter air, or should dry the web for a longer period of time'than is ; 30 :: . ': . . .

the case when a Yankee dryer is used. When drying on the intermediate drying fabric, the stratifi~d web is preferably dried to a consistency of from about 85 to about 100 percent fibers by weight. The intermediate drying fabric and the thermally dried paper web then pass over a straightening roll 223, which prevents the formation of wrinkles in the intermediate drying f~bric , over drum roll 232, and then away from the intermediate drying ~abric l220, whereupon the web is wound onto parent roll 231 to be processed ~ur~her. Of course, i~ will be obvious .that winding and interim storage o the web on parent roll ~31 ¦could be eliminated, provided ~ha~ after the web leaves intermediate drying abric 220 it is conveyed to creping me~ns or other urther processing. Intermedia~e dr~ling fabric 22Q ~hen passes over ~abric return rolls 221g, h, and i, and the web is cleaned by showers 226 znd dr-ed by ~acuum box 227 be~ore re~u~ling to the vicini.ty of pick-up shoe 219 to complete its cycle. In any of the methods dis-: closed herein~ the stratified web may alternatively be dried : ~ 20 on the intermediate drying fabric as disclosed immadiately . . ~ .
above or on ~he Yankee dryer roll.

~ ~ .
.

:
.~ "' ' Figures 4 and 5 schematically illu~rate ~he type of construction of divided headboxes which may be used to prac~ice some embodiments o~ this invention.
Re~erring to Figure 4, a headbox 40 having irst and second slurry depositing channels 41 and 42 may be used to simultaneously deposit a slurry comprising ~wo super-imposed layers in the practice of the t~o-layered embodiment of th~ in~rention. Supply pipes 45, 46 convPy slurries from supply means (not shown) ~o supply cham~ers 47 and 48 of the headbox. The slurries flow past fixed separator S3 which divldes the~headbox in~o separate chambers. Fle~ible separator 54, at~ached to fixed separa~o~ 53 a~ pivo~:ed lcnuckle joint 95, dîvides~ the two chambers i~rom i~s point Olc attachmen~ to ~ixed separator 53 ~o the outlet 44 of ~he headbox. The slurries are channeled by conver~ g fixed ~: pla~e~ 51, S~, while ~e~n~g m.a~r~t:2~ned ~s eep~rate slurrles .
by flexi~le separator 54, and are deposited from ou~le~ 44 ~: onto a ~orming wire (not showrl). In the single wire embodiment described here~in~ a fixed roof 53, attached by p~vot:ed knuckle 0 -:joine ~9 to fi~ed plate 51, is employed.
:
!In another prefe~red embodimen~ o the invention, a di~rided headbox havir~g irs~ and seeond slurry depositing channels depos;ts a first sluxry o s~or~ papermaking ibexs having a consistency o about 0 . 25 to 0 . 6 percen~ ibers by 2S weight on a siDgle orming wire 11 as seen in Figure 1. A
se~ond slurry depositing channel deposits a second slu~:~y o ~ long papermakirlg ~i~ers on ~he forming wixe, superimpGsed on : ~ the ~first slurry.~ having a consistency of û.l ~c~ 0. 3 perc~nt::
: ib rs~ by wei~ht an:l an average ~ er ~eng~h o about: ~hre times the average fiber len~th o~ the fibers in the ~irst slurry and a glow rate of about two to three times the ~low rate of the first slurry. The first and second slurries combine to form a stratified web. The stratified web formed by the first slurry and the second slurry is transferred to an intermediate drying fabric 20 by the partial vacuum applied by pick-up shoe 19. The partial vacuum transfers the stratified web to the intermediate dryiny fabric 20 as well as reducing the adherence of -the fabric side layer to the wire side layer. While on the intermediate drying fabric, the stratified web is predried to a consistency of about 50 to 90 percent fiber by weight by hot air dryer 22.
The stratified web is imprinted on a Yankee dryer roll 24 by pressure roll 25 acting through the intermediate drying fabric to impress the stratified web on the Yankee dryer roll 24 and thereby form a multiplicity of discrete densifie,d areas defining a pattern of spaced lines having a substantial orientation pre-disposed to buckle during creping. The Yankee dryer roll 24 dries the stratified web to a consistency of about 85 to 100 percent fiber by weight. The stratified web is then creped 20 along ach of the creping lines to form creping which is equal in frequency and slmultaneous in phase in all the layers of the web.
In another preferred emhodi.ment of the invention a ply-separable web having a barrier layer is created on two forming sections on apparatus similar to that shown in Figure 2. A
first furnish of fibers~capable of forming ' .
~: :
, :
i ~ 30 ~ ~ - 2G -::
: ~:
: : :, : , : ' :. -: :

substantial papermaking bonds is applied ~co a ~irst forming wire llla rom the first outlet of a irs~c head~ox havin~
mul~iple outlets to ~orm a wire side web layer 1~3a. A
barrier layer is deposited on the firs~: urnish by a second ou'clet in the first headboY.. A second urnis~ of fibers capable o forming substantial paperTnakin~ bonds i5 deposited on a second forming wire lllb by a seeond headbox havlng a single outlet to form a fabric side web layer 113bo The wire side forming wire llla passes over orming boaxds 114a and vacuum boxes lL5a which dewater the ~7ire side ~eb 113a to abo.ut 5 ~o 25 percent iber by weight. l'he abric side orming wire lllb passes o~Ter forming l~oards 114b and vacuum boxes llSb and is dewatered to about S l:o 25 percen'c ~ber by weight~ The fabrxc side forming ~ire lllb an~ the ~ire side formîng wire llla are then juxtaposed with the ~abric side web layer 113b contac~ing the .~arrier layer overiying the wire.side web layer 113a, the two webs combinin~ into a - stra~ified web 113. A diffcr2ni:ial pressure is applied ac~oss ~he orrn~ng wires by vacuurn box llG su~icient to ~o create a sin~le str~ ied ~cb 113 o a ~irs~ ~nd second , .

. ~ ' :

:

2 1 , ' : :

layer of papermal;ing fibers s~par~d by a barrier layer.
The stratificd web is ~urther dried ~nd uni~1e~ while passin~
over vacuum bo;.es 115c. The fonning wire l~la and moist web 113 pass around a I~our~rinier wire roll 117 and downwar.dly adjacent inter~.edia~e drying ~abric 120. A~ this point, the paper web 113 is transferred, without compac~ion, ~o inte~-mediate drying fab~ic 120 by a pressure di~ferential be~ween opposin~
sides of the ~Jeb created by pick-up shoe 119 adjaoent drying fabric 120, ~hich again contributes subs~antially to the 0 ply-separability of the resulting web by ~ending to draw webs 113a and 113b apart . Web 113 then pl: oceeds ~chrough the dry end of the papermaking process in ~he mallner describecl hereinabove, Similarly, to produce a three 1ayered embodimen~
15 o~ the invention a headbox such as tha~ shown in Figure S
:~ may be uti1ized. In this headbox, supply pipes 55, 56, and : 57 supply separate slurries to portions 59, 60, and 61 of the headbox 62. In ~his embodiment, manifold 58 supplies a single slurr~ to inle~ pipes 55:and 57, which will resul~ in ; 20 ~ identi~al outer layers in the web when it is laid~ It wi~1 be understoQd, however, that three diferent s1urries could be ~upplied or that ~ore ~han ~hree la~ers could be laid ' within the scope of this invention. The ~hree slurries are : ~ :::

.

~' ~

~ 22 -, - . : , ..... . . .. .
. . . . . . . . . . . . . ... . . . .. .. , : . ,.. . . . :, .. . . .

kepc separate by fixed separatc~rs 64 and 65, and by ~lexible separa~ors 68 and 69 (which again may be pivotally attached to achieve flexibili~y), and the three slur~ies are guided by converging Eixed plates 66 and 67 to ou~let 70. The composite slurry is then deposi~ced on the Fourdrinier wire ~or~ing sec~ion as described above. Again, in a single wire embodiment of the invention3 a fixed roof 97, a~tached by pivoted knuckle join~ 98 to converging fixed pla~e 66, is employed .

~n another preferred embodiment of the invention, i . a strati~ied ~eb of three lay~rs is made on one.Xo~ming section ~rom a mul~i-outlet head~ox. R~ferring ~o Figure 1, headbox 10 has a~ least ~hree outlets depositing papermaking furnish on Fourdrinier wire 11. The furnishes or a wire side j . 15 w~b layer 13a and fab~ic side web layer 13b are o~ fibers capable ¦~ of ~orming substan~ial interl~yer bcnds and a bar~iPr lay~ i.s - interposed between the wîre side web layer 13a and the abric side ws~b layers from becoming bound to each other. The I "-; str~tiie~ wel) 13 is de~ater~d by fo~ing boards 14 and vacuum : ~
2Q boxes lS~ The ~tratifi~d web 13 is transerred to in~ermediat:e I dx~ing abric 20 by the applîcation o~ a p~tial ~acuum through ¦ pi~ up shoe 19. Th~ application o~ th~ partial vacu~ reduc~s I ~he ~herence o the wire side web layer ~o ~he ~ab~ic side web ¦ laye~ The strati~ied wcb 13 is predried ~n the intermedi~t~
: 25 ~ dryin~:abric ~O by ho~ air drycr ~2 ~o a consis~ency o rom , ~ abou~ 65 to about 90 percent ibcrs by wei~h~. The s~ra~i~ied .

.., ..: . . . . . .
., -: :

web 13 is imprin-ted on a Yan~e.e dryer roll 24 b~ p~es:sure roll 25 acting -through the intermediate drying fabric 20, which forms a multiplicity of discrete densi~ied areas defining a pattern of spaced lines having a substantial orientation predisposed to buckle duriny creping. The stratified web 13 is dried to a con-sistency of from about 85 to about 100 percent fibers by weight on the Yankee dryer roll 24. The stratified web 13 is then creped along the plural creping lines to form a creping pattern which is substantially equal in frequency and simultaneous in phase in all layers of the web.
A conventional headbox which does not have fixed or flex- ~.
ible saparators may be used when depositing a single layer of :Eurnish according to some of the examp1es set forth hereinafter.
Commercial embodiments of each of these headboxes are available from a number o sources and are well known in the art. Especially preerred headboxes used to practi.ce the pre.sent invention are described at length .in U. S. Patent No. 3,923,593, issued to Verseput on December 2, 1975, and U. S. Patent No.

3,939,037, 1ssued to Hill on February 17, 1976.
The forming sections used to practice the embodiments o this lnvention may be of the single wire variety employing a fixed roof headbox, as shown in the figures and descriptions ~ :
herein, or an analogous twin wire forming section may be used : instead within the scope o this invention.
: 25 In a particularly preferred e~odiment of the present invention, the intermediate drying fabric is characterized by a : :diagonal free =pan, i.e., the planar distance as measured from one corner of a projected fabric mesh opening to its , - .30 , , .
.:
~ 24 -~, .

diagonall~T opposite corne-, between about . 01 inches and about .1 inches, most preferably be~ween about .015 inches and about ~ 04 inches, and a fabric mesh couIlt of between about 100 and ~, 600 openin~s per square inch I i. e., said fabric having between about 10 and about 60 filaments per inch in both the machine and cross-machine di;:ections~
In a long fiber/short fiber stratified wPb o the type referred to herein as the two-layered embvdiment of the inven~ion1 it is preferable tha~ the dîagon21 ree span o~
the intermediate drying fabric be less ~han the average fiber length of the short iber stra~um of the web. I~ the diagonal free span is greater than ~he aver~ge :Eiber lengt:h in the short-~ibered strat-um of the web, the ibers are too easily pulled through the fabric mesh openings when su~jected to ~luid pressure~ thereby detracting from the bulk and caliper of .he fini;,h~d ;,hee~Ls. ~L~ the other harlcl, t:h~
diagonal ~ree span of the fa~ric is preferably greater ~han about ~/3, and most preXerably greater than about 1/2 of t~e average ~iber length in the short fiber stratum o~ ~e web 2Q in order to minimize bridging of the shor~ fibers across the abric~ filaments. In addition, the diagonal free span o~
the~ fabr;c is preferably less than about 1/3 o the average iber }ength o the long fiber strat~ o~ the web in order to encourage bridging of the long fibers across at lea~ one ~5 pair af fabric ~ilamen~s. Accordingly, the sho~t: fibers tend ~o reorient themsel~es and p~ne~ra~e ~he abrie mesh ~ ~ ~: openings ~uring transfer of the moist stratified web ~o the : ;nterrnediate drying fabric, while the long ibers tend t:o bridge ~he openings :in the mesh, and thus the long :f~îber 3 0~ stra~um remains substantially:planar.: The patterned discrete areas of the web ~hich correspond to the~ fabr:tc mesh openings ~; and which ~e~tend outwardly ~ront the abric side o:~ a web o :
~:: : , :
2 5 - ~

. ~ : :. .. . .

~ ~ 7~
the type generally ~hown in Figure 6 typically assume the form of to~ally enclosed pillows, conically grouped arrays of fibers, or a combina~ion ~hereof.
The inventors believe tha~ the quality of ply~
separability, particularly in ~he two-layer one headbox embodiment o:f the invention, results from maintenance of the distinct fiber compositions in the several layers of the strati:Eied web, particularly as the layers come toge~her to fonn a unitary web. This main~:enance of distinctness among layers deposited from a single headbox in the for~ ng section of the paper~aking; machine ~llows production o~ layers in ~he completed produet which have fil~er compositions similar to the ~iber cornpositions in ~he slurries suppli~d to the headbox. It is impor~ant in realizing th~
L5 ~bject of ply-separability, ~herefore, to utilize a headbo~
design which minimizes flow turbulence and which equalizes .... . .... .. ~ . . .. . ... . _ __ _ _ __ __ as nearly as possible ~he relative veloci~ies o~ flow for the respeetive furnishes as ~hey 1P~TP the di~7~ded h~d~o~. u~ ec in some embodimen~s o~ this invention.
. ,~ .
~0 In the two-12y~r embodi~ent of ~he inven~ion in which ~wo orming sections are employed, the distincl:ness o the layers wh~ch are fo~med separately is more easily maintained because no two layers are joined ~til they have Tnuch greater consistenc7 than the headbox throa~ consistency~ and equal !5 velc)city of layers is main~ained by running the respe~'cive forming wires-a~:substantially equal velocities. ~`

Axl especially preferred predrying appa~atus for : use in the pape~making processes disclosed herein is described ~ :~ in U.S. Patent No. 3,~3039576, issued to Sisson on February :~! 14, 1967 and.commonLy owned with this application.

: , :

: . . . ;

(Dry bulb iIlpU-. te~pe~atures for each predryer st:age are ~eas~r~d -the air input plenum o:E the predryer, and dry bulb output temperatures for e2ch stage are measured i~m~ediately adj acent the side of the web which is downstream with respe-t to t:he S direction of air travel through the predryer. ) The web of the pres en~ invention may be creped using any of a number of known techniques. While several types of creping are discussed hereinafter, the applicants do n~ limi~ themselves to thes e techniques, as chey envision L0 that many techniques will be useful to crepe pl y-separable webs of the presen~c in~ention.
First, the web may be crep~d by adhering i~ ~o a creping roll and then shearing it from the roll with a doctor blade, as is well knowr. in the ar~. ~s indica~e~l ~5 hereinbefore, this particular type of creping is not essen~ial to the present invention, and ply-separability is not imparted to the web by this step, since the web is already ply~
separable on the intermediate drying fabric.
Second, creping may be i~parted to the web b~ a process kno~l he~einafter as MICRE~ creping. (MI~R~X is a trademal-k o Bird Machine Co., Micrex Division, Walpole, Massachusetts.) This ~echnique is illustrated and described :~ in U.S. Patent 3,260,778, issued to Walton on July 12, 1966;
Patene No. 3,416,19~, issued to Packard on December 17~ . 1 1968; and Paten~ No. 3,4~6,405~ issued ~o Walton on February :
11, lg69.

Third9 a web made according ~o this inven~ion may be creped by confi~ing it between a rubber belt and a J pulley face at vary~ng tensions to produce micro-creping. ::his: creping~ tec~inique;l known as CLUPAK ~reatmen'c in ~he ar~ .
~CLUPA~ is a trademark of Clupak, Inc. of New Yor~c.)" is ::
disclosed in U~S. Pa~en~ ~o. 2,624,245~ issued to Cluet~ on : J~nuary 6, l9S3,, : : : .

27- 1 .

7 ~ ~

Example 1: ~wo-layered Ply-Separable Web Formed in a Sinzle Forminc~ Section In ~his embodiment of the invention, a two-layered web is formed from a single di~ided headbox, and has a first layer (disposed nearest the forming wire) co;nprised o:E a relatively concentrated slurry of sho~t papermaking fibers, overlaid by a second layer of furnish having a somewhat lower consistency of longer papermaking fibers. Thus, a papermaking machine such as that sho~rl in Figure 1 and a h~adbox of the type shown in Figure 4 is used. What fol lows is ~ specifi example of the production of a ply-separable web according ~o ~his em~odiment.

. A first furnish, to be laid adjacen~ the orming wire, was c:ompris ed of 100 percent krai~ eucalyptus pulp .
S The fiber was combined with 4~7 po~nds of a 2 percent solutio~ (by weight) o~ PAREZ 631NC wet strength resin per . ton of fiber, and was unrefined. (PAREZ 631NC is a modi~ied polyacrylamide wet strengtn resin available ~rom the Amerit~an Cyanamid Company. ) The basis weight of the firs~
~ furnish was~10.8 pounds per 3,000 sq. ft., and it was supplied ~: to :the:headbox at a fl;ow rate o~ 111 gallons per minute .
~ : and at a consistency at the headbox o~ 0.26 percent fiber : ~y weight.
.

An unrefined second papermaking furnish, to be superimposed ~5 on said first ~urnish, was comprised of 70 percent northern so~wcsod kraft and 30 percent northern har~700d sulfi~e pulps, along with 7.S pounds of a 1 perc~nt solu~ion (by weight) ACCOST~ENGTH*~8 d~y strength additive per ton.

:: * :T.rad~k ;
~: ** Tr~demark of fiber, (ACCOSTRENGTH 98 is the trademark o~ a dry strength additi~e comprised o~ a modified pol~acrylamide material, a~ail-able from the American C~anamid Company.)~ and 14 pounds per ton of fiber of a 4 percent solution (by weight) of ACCOSTRENGTH 514 promoter (ACCOSI'RENGTH 514 is the trademark for a linear ~uater-nary ammonium compound available from the American Cyanamid Company,) This furnish was supplied to the headbox at a Elow rate of 272 gallons per minute and at a consistency at the head-box of 0.107 percent fiber by weight. When laid on the Fourd-rinier wire, this furnish had a basis weight of 10.8 pounds per3,000 square feet.
The first and second furnishes were deposited in super-imposed reIation on a 78 mesh Fourdrinier wire (a style 78(s) wire r available from Appleton Wire Corporation). The headbox throat opening was set at 0.75 inches. The rate of travel oE
the Fourdrinier wire was 503 feet per minute. The ratio oE the Elow rate of the wire side furnish to the Elow rate oE the ~ab-ric side furnish was approximately 2.45 to 1.
; I'he stratified web was then dried to a consistency of about 23 percent fiber by weight, and the breast roll vacuum setting was 1.5 inches Hg. The web was then transferred to a second Fourdrinier wire by a vacuum box vacuum o,E 11.5 inches Hg., so that the :Eirst :Eurnish above formed the :Eabric side layer and the second furnish formed the wire side layer. The pickup shoe had a vacuum oE 15.5 inches Hg., and in the course of transferriny the web to the intermediate drying fabric the :
consistency of the web was incxeased to about 24 percent Eiber by weight.
.:

;~ 30 9 _ The .intermediate drying ~abric for this run was an 18 by 16 mesh semi-twill ~abric, available from Hermann Wangner GmbH of the Federal Republic of Germany. The fabric was run at a speed of 501 feet per minu~e, resulting in a draw with respect to the Fourdrinier wire of minus 2 feet per minute. The inpu~ dry bulb air tempera~ure o~ the firs~
stage of the pre-dryer was about 360F, and the output dry bulb air temperature in ~he ~irst stage was abou~ 135F.
The input dry bulb air tempera~ure of the second stagP was about 350F, and the output dry bulb air tempera~ure of ~he second stage was about 7~5 . As a resul~ of pre~drying ~he web consistenc~ was 80 percent fiber by weigh~
; In this run, the web was adhered to a Yankee dryer and creped therefrom using a doctor blade. A 0.5 percen~ :
~y w~ight) ~olution o polyvinyl alcohol adhesive sold under the trademark OE LVATOL by The Monsanto Company was sprayed on the Yankee dryer in an a~ount of abQut 7 ~ ~n ~
fiber to facilitate Yankee dryin~ and creping. The web was pressed against the Yankee dryer and imprinted b~ the :~
p~essure r~ll at a nip loading o~ 365 pounds per linear ::
înch. The steam pressure supplîed to the Yankee dryer was 122 psig. The surface speed o the Yankee dryer was S01 fee~ per minute~ As a res~l~ of Yankee dryin~, the web was dried ~a a consistency o about 99.6 percent fiber b~
5 . weight.
: . me web was creped from the Yankee dryer usin~
doctor blade se~ at an ~mpac~ ,angle of ~ ut 90 degrees, As a result of creping, t~e web ~7a~ longi~udinally compressed al~d j: ` : :
wound at~a web speed of abou~ 373 feet per minute. The ~ . ~
j `

, ` ~ .

resul~ing web had net creping of about 25.5 percen~cl a ina basis weigh~ of about 29 pounds per 3, 000 square feet, and a crepe :Erequency of abc:ut 21-22 cycles per inch.

Example ~: l~o-layered Ply-sepa~able Web, :Each I.ayer Formed in a_ePar~te Formin~ Section In this embodiment of the in~Jen~ion, a first w~
is formed by wet laying a urTlish comprised o long paperTnakir1g fibers in a first formirlg section; and a second web is formed by wet-laying a furni5h comprised o short:er paperma}cing :Eibers in a second forming sec~ion. The webs ar~ par~ially dewatered, then brollgh~ toge~her t:o orm a single stra~i~ied web while each is still in the formlng sec~:ion. The short fiber layer has a mu~h lower consis~ency than ~hat of the - long :~iber l~y~r at th~ point ~here ~he two web~ ar~ allowc~
to eon~act each othe~. After the webs are combined, the further trea~men~ of the web is essentia.lly iden~ical ~o ~h~
treatmen~ described above for the two layered ply sep~rable w~ ormed in: a s~in~le forming section~ Wha~ ~ollows is a :speclfic example ~of the ~praetice of ~his embodimen~ of the invention~
The wire side layer wa~ comprised of 100 percent nort:hern sotwood kra~t pulp to which ~as added 7.5 pounds of a 2 percen~ solution o.~ PAREZ 631NC wet streng~h resin per ton o ~Eiber. The wire side o~ the furnish was re~ined 25 ~ : at ~no load in ~ a disc refiner to increase its ~ry ~ensile strength. The headbox throat was set a~ 0.50 inehes, ~he breast roll had a ~racuum o l.O inches H~., and a single a:cuum box set~ at; a vacuum o 3. 5 inches Hg~ was used ~o , 31- .

, ~, . ~ . , . . , . : , .

beqin the dewatering of the wire side la~er~ ~t the point where the wire side layer and *he fabric side layer were combined, the wire side layer had a consistency of about 17 percent fiber by weight, and the basis weight of the wire side layer was about 11.1 pounds per 3,000 sq. ~t.
The fabric side of the furnish was comprised of 100 per-cent northern hardwood sulfite pulp, laid at a basis weight of 11.1 pounds per 3,000 square feet and having a consistency of 10.4 percent fiber by weight at the time the fabric side and wixe side layers were combined into a single stratified web.
The level of P~EZ 631NC wet strength resin solution applied to this layer was again 7.5 pounds per ton of fiber. The headbox throat setting was 0.775 inches. The breast roll vacuum for this layer was 0.75 inches Hg. and a single vacuum box maintain-ing a vacuum of 3 inches Hg. was used to dewater the web. The speeds of each Fourdrinier wire were approximately equal to the speed cited in the two-layer single wire embodiments described above.
At the point where -the wire side and fabric side webs were combined, combination was facilitated by a vacuum box applying a vacuum of about 5 inches Hg.l creating a pressure differential between the respective sides of the web to unify them into a unitary web. The consistency of the combined stratified web at the point of transfer to the :Lntermediate drying fabric was 18~1 percent fiber by weight, increased to about 26.7 percent fiber by weight as the result of dewatering resulting from the pressure differential applied at the pickup shoe. The first stage pre-dryer input dry bulb air temperature was about 460F and output dry bulb ., ~

' ~ 32 -.

~ 7~

air tempera~ure was 150F; the second stage predryer inpu~
dry bulb air temperature was about 470F and output dry bulb air te~perature was about 270F. Consistency o~ the web after predrying was 95.1 percent fiber by weight. In this run, the web was again finally dried and creped by adhering ~.
it ~o a Yankee dryer and shearing i~ therefrom with a doctor blade. The operating parameters for the Yankee dryer and creping were comparable ~o ~hose measured in the first example abo~e.
.
Ex~mple 3: Three-layered Ply-separ~blP Web Formed in a Single Formin~ Section n ~his embodiment of the invention, three d;stinc~
: . layers of furnish are laid by a divided headbox onto a single Fourdrinier wire ormi~g section and further processed to ~orm a ply-separable paper web comprised o two dis~inct~
well-bonded layers of tissue, separated by an in~ermedia~e barrier layer. ~It will be noted, however, that tne finished prvduct is separable into two pLies, rather than three : plies, for when the plies are separat~d the barri~r adheres ~ to one of the well-bonded ~ayers, or fragments o~ the .
bar~ier each adhere ~o one or the o~her of the well-bonded layers. ) , ' ' ' ' .
To practice this embodiment, a we~ is ormed ~rom a three-cha~nel:headbox which deposits identical layers :
~5 comprised of 50 percent northe~n sof~wood kra~t pulp and 50 perccnt northern har~woo~ sulite pulp, each layer having a : - ~ b is weight of abou~ 7.5 pounds per 3,000 square ee~p and :~ , : . . .

: - 33~

:
~: :

a central layer th~rebetween comprised o~ 100 per ::ent mercerized sulfite pulp having a basis weight of abou~ 7 . 5 pounds per 3,000 square feet. The web is dried on the Fourdrinier wire to a consis~ency of about 20 percent: ~iber by weigh~, transferred to an intermedia~e drying fabric, predried to a consistency of abou~ 95 percent ~iber by weight, and found ~o be ply-separable upon removal from ~he intermed~te d~yi~g fabric. In this exæmple, the pickup shoe vacuum is about 15 inches Hg. The web is then ro~led up without being creped. The resulting web is ply-separable a~ this poin~. Ultimately the web i.s creped to produce a finished product.
Example 4: Three-layered Ply separable l~eb, _F'ormed in Two Forming Sections In this embodi~ent of the invention, a stratified first web is formed by depositing on a Fourdrinier wirc a first furnish adap~ed to form strong internal papermaking bonds and a superimposed furnish which ~orms ~he barrier ~ layer o a three-layered embodimen~ of the invention. On a : :20 separate Fourdri~ier wire, a second ~eb adapted to form ~ strong internal papermaking bonds is laid and partially .
dewatered be:~ore i~ is superimposed ad~aeen~ the barrier layer of the stratified ~irst: web. The ~wo webs are then combined into a ~ingle stratified web having three layers -~wo ply-separable layers having s~rong papermaking bonds, and a barrie~ ~ layer separating ~hem. (When superimposed, the second web defines the fabric side of ~he assembled web, while the first ~urnish of ~he first web defines ~he wixe side of the ~ssembled web.) . ~ :
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As an example of this embodiment of the invention, furnishes capable of forming well-bonded layers were formed from 50 percent northern softwood kraf~ and 50 percent no~thern hard~ood sulfite PU1PSJ while the furnish which ultimately would comprise ~he barr~ er layer OI' the assembled web was comprised of 100 percent mercerized sulfite pulp.
Each well-bonded layer had a basis weight o 5.5 pounds per 3,000 square ee~, ~nd th~ barrier layer had a ba~is weight o~ 10.9 pounds per 3,000 square eet. The to~al throa~
setting for each headbox was 0.60 inch~s.
A dry str~ngth addi~i~e was included in the w~
bonded layers, consisting o 18 poun~s o a 1 percent solu~ion of ACCOSTRENGTH 98 per ton of iber and 65 pouuLds o:E a 4 percellt solution ACCOSTRENGTH 5~L4 per (:on of ~iber.
For ~he web deposited ~rom the d~Yided headbox, the irst furnish was supplied at a ~ate o 171 gallons per minute and t~e su~erimposed furn.ish was supplied a~.a ra~e o 175: gallons :~ per minute . The cons is tency at ~le headbox .
~: : throat for ~he fi~s~ urnish, which would ~orm t:he ~ahric ~o side layer in the as~embled web, was 0.17 percen~ :Eiber ~y weigh~ and the headbox throat consistency ~or ~he superimposed furnish wa~ 0.36 percent iber by weight. In the la~er deposited f~rom the single channel headbox, the furnish was sup~lied at 5I7 gallons per minute; and thE consistency the headbo~ throat was 0.06 pe~cen~ fiber by weigh~. The : vacuum boxes, which uni~ the separate webs into a single ~: ~ stratified web when the webs are 3uxtaposed by cxeating a pressure difere~eial between~th respec~i~e sid~s o~ the :combined webs~,~;were main~ained a~ v cuum levels of I0 inches ~: :
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Hg. and 7 inches H,,., respectively. No vacuum was applied a~ the breast rolls in this embodimen~. The vacuum box for the wire-side layer was maintained at a vacuu~L o 5 inches Hg .
When the unified web was transferxed l:o the intermediate drying fabric, which was the same type o fabric described hereinbefore, ~he pickup shoe was maintained at a ~acuum of 15 inches Hg.9 and the vacuum boxes were maîntained at a vacuum of~ 13 inches Hg. Be~or.e the web was transferred to the in~enmedia~e drying fabric> i~s consis~ency was 20.1 percent ~iber by weigh~, and af~er passing over ~e vacuum boxes ~re consîstency was 27.5 percen~ iber by weîgh~. The web was passed through ~he ~wo-stage predrier at a ~irst stage dry bulb air inpu~ ~emperature o~ abou~
lS 380F, a ~irst stage dry bulb air output temperature of `~ abou~ 160F, a second stage dry bulb air inpu~ ~empera~ure of about 380F and a second stage dry bulb air ou~pu~
temperature o~ about 230F. After predrying, the fiber ` consistency was 87.9 percent fiber by~weight, and the web 20~ was ply_separable at this poin~. GELV~TOL adhes~ve was.
applied a~ a level of 2 pounds ~er ton of. fîbex ~o the Yankee dryer, and th~ web was imprinted thereon by the presqure roll operating at a nip loading o~ 325 pounds : per lin~a~ inch. The ~ankee dryer steam pressure was 122 ~ pslg. ~The consi~tency o~ the ~eb at the time of creping was : 99.2 percent fiber by weigh~.
As a result o this procedure, a final web was ~:~ ormed ha~ing a basis weight of 28. 7 pound~ per 3~000 sauarefeet,~hàving~a caliper o~ .0268 inches. In this embodiment :~ , ~ 3 6 .

7~

the speed of the surace of the Yallkee dryer was 601 feet per minute and the speed at which the web was wound after creping was 458 feet per minute, resulting in a net creping of 23. 8 percPnt.
The Barr ier Lav er It will be understood that any of a number of barrier layer configura~ions can be used to achieve the ply-separability of the three layer embodiment this invention.
By way of example, ~ibers which do not form paper~aking bonds, or (like merceriæed pulp) form papermakin~ bonds at r2duced stren~th, or do not adhere as a layer to the separable layers, may be~interposed between well-bonded layers to produce a ply-separable paper. M~ny synthe~ic ibers such as polyester or the like fit into this ca~egory. Chemical debonding agerl~s may be added to ~he barrier layer in order to selectively prevent the formation of papermaking bonds.
Examples of suitable debondin~ agents ar~' ~uaker 2000", *
manufac~ured by Ouaker Chemical Co., Conshohoc~;en, Pennsylvania, as well as the debonding ;3gents referred to in Column 8 oi~ :
U. S . Patent No. 3, 812, 000 issued May 21, 1~74 to Salvucci, Jr. et al., and in references cited thereinJ
A :eluid such as ~but not limited ~o~ :water may be in~roduced through ~he central charmel of a three-channel divided headbox> and thus be :
interposed between two urnishes to inltially separate them and reduce in~e~ningling o :Eibers until the wacer is remo~red during the papermaking process. C1ther fluids which can be used to separate the well-bonded layers ~til ~hey no .
lon~ser will interlink with strong papermaking bonds are air or another gas which may be introduced be~ween the oul:er .

, ~ * Trademark ~ 37~

layers of furnish ~o keep them physically separated to reduce intermingling of fibers. A solid or powdered material capable of sublimation may also be interposed between the separable plies ~o ~emporarily isolate them during ~he S papermaking process. In all of these varia~ions, it will be noted that it is not necessary to incorporate materials in ~he web whis~h will substantially inhibi~ ~he absorp~ive properties o the finished tissue produced.

Product D~s cri~tion Figures 6 through 10 illus~rate schema~ical] ~ ~he attributes o a paper web made accordingly ~o~ any o~ he processes described above.
Referring first to Figure 6, intermedia~e dr~ing ~a~ric o '~ is ~d~ up ~f machine direction rilsmen~s ol and cross-machine direction filaments 91. Knuclcles such as 83 and 90 are formed in areas of fabric 84 where a machine direction filament and a cross machine direc~ion fil~men~
overlap. Refexring to Figure 7, which shows the view o:E
- Figure 6 with machine direction filamen~ 91 cut away, web 80 2û is comprised o~ fabric side la~er 85 and wire side layer 86 which are ~he outside l~yers o the three~layer embodiments o the inverltion, or both lay~rs of ~he two-la~er embodiment:s of the il~vention. I)ensified areas such as 82 and void spaces such as 87 are evident in the web a~ ~his s1:age of the papermaking process, although they are accentuated by ~urther trea~me~.
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Figures 8 and 9 show ~he treatment o so~ne embodlmen~s of the lnvell~ion wherein the intermediate drying fabric and , 38 - ( :
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the attached web are passed through a nip be~ween pressure roll 8~ and another roll 89, which may be a Yankee dryer drum. The result of this treatment is the compaction of densified areas 82 by knuckles 83. However, this treatment does not substan~ially c:ompact void I spaces 87. As a result of this ~reatment, densified areas 82 become buckling sites which influence crepe ~r~quen y and cause the creping o~ ~he ~espective layers to be in phase.
Figure 10 illustrates the web ~hich results from the papermaking processes described by ~he applican~s hexein.
Fabric and wire side layers 85 an-d 86 are dis~inct, and are separa~ed a~ intervals by ~oid spaces 87. C~eping causes the ~70id spaces 87 to open up, thus increasing ~he absorbency and bulk o the final product. The creping of the web is e~ident o~ ~ither oid2 t~ereof, although only one crepi~g step is employed, and the creping is equal in frequency and simultaneous in phase in each layer of the finisned web.

: Product Test Procedu~es :Tests conduc~ed on ~he products of the exa~ples .
d:escribed abo~e were carried out as ~ollows:

Dry Callper Thi~ was obtained on a Model 549M motorized microme~er such as is a~railable from Tes~ing Machines~ Inc, of AmityviLle, Long Island, New York. Product samples were sub; ected to a loadi~g of 80 gm. per sq. in. under a 2 in .
: diameter anvil. T~e micrometer was zeroed to assure that no foreign matter was present beneath the anv~l prior ~o :

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inserting the-samples for measurement and calibrated to assure proper readings. Measurements were read direc~ly from the dial on ~he micrometer and are expressed in mils.
Calculated Dens ity Th.o density of each sample sheet was calculated according to the followillg equa~ion:

(Calculated Density, g. /cc. ~= (. 064) (8asis weight, lb . /3000 sq . t . ' (~ry Ca lper, ml s where . 064 i~ a conversion factor.
` 10 ~9~
This was obtaiiled on a Inteles:~ 500 ~ensile tes~er such as is available from the Thwing~ ert Inst~ument Comp~ny o Philadelphia, Pennsyl~ania. Product samples measuring l inch wide were cut in both the machine and c~oss-machine direc~ions. For each run r a sample s~rip was p~aced in the jaws of ~he tester, se~ at ~ 2 in. gauge . length. l~e ~rosshead speed during the test was 4 in. per minuce.~ Readings were ~akPn directly from a digital readout on the tester at ~he point o~ r~tpture to obtain th~ tensile 2~ strength of an individual sample. Results are expressed in grams per inch o~ sample width.
Stretch ~ .
::- Stretch is the percent mac~ine direction c~
cross-machi~e dir~ction elongation o the sheet, as measured at rupture, and is read directly from a second digital readou~ on the Intelect SOO tensile tester. Stre~ch readings .
~ wer taken concurren~ly with tensile strength readings.

::
_ 40 Tearin~ Kesis tance This was obtained on a 200-gram capaci~y Elmendorf Midel 60-5-2 tearing tester such as is available from the Thwing-~lbert Instrument Company of Philadelphia, Pennsylv~nia.
S The test is designed to measure the t:earing resistance in the machina direction of sheets in which a tear has been started. Product samples were cu~ to a size of 2 1/2 in. by 3 in., wi~h the 2 lJ2 in. dimension aligned parallel t:o ~he machîne ~lirection o~ the samples. Eight product samples were stacked one upon ~he othar and clamped in ~e jaws O:e the ~es~er so as ~o aligrL the direc~ion o:E ~ear pa~allel ~o the 2 1/2 în. dimensîon. A 1/2 in~ long cut was ~hen made at the lowermost edge of the stack o samples in a direc~ion parallel to the direc~ion o tear. A model 65-1 digital read-out unit, also availabie from ~he 'l~wing-~lbert ~nstrument Compan~, was zeroed and calibrated using an Elmendo~ No. 60 calibra~ion weight prior to initiating th~ test:. Readings : were taken directly ~xom the digital read-ou~ unit and inserted in:to ~he following equation:

20 ~ ~ ~ Tear: Resis~ance= (. 01~ (TTC) tDR) ~ ~ num er or p ies ~este ~
Where TTC ~.9 tearing tester cap;3city in grams, and :)R is ~he r~ading from the digi~al readout uni~. Results are expressed in terTns o gram~ per ply of produc~.
2S ~ ~ :Burs~_Stren~
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This ~est is used to determine how much force can be exer~ed by a plunger driven ~erpend:icularl~7 against: a clam7ed~}aoer~ ample~ befor- the sl~pLe will burst and a~lov :~ : :: : ; :

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the plunger to pass through it.
The test is performed using a burst tester ~abricated by the Thwing-Albert Instrument Co. The instrument is calibra~ed, then a sample of a pxoduct to be tested is clamped between the upper and lower rings of the burst tester and the plunger drive is actuated. The machine will read out the burs~ str~ng~h direetly in grams a~ the time of sæmple rupture.
9~B~ . , . This ~est is per:~ormed to measure wicking, which is the ability of a paper sample to absorb ligui.d and rapidly distribute it o~eX a wide area.. Such a property i5 desi~:able in absorbent products of all kinds becaus~ a produc~ with good wicking more e:Efec~ively uti~izes i~s entire absorptive ~ )ac-tv b~ avoiding l~calized wet spo~s.
The machine used to perform tbis test (whic~ is not: commerciaïly a~ail ble) co~prises an ~pstar~ding Poly-tetrafluoroethylene tube having an inside diameter of 0. 31~5 , inches, co~nected with reservoi~ means to main~ain a constan~
water level at the tip o the tube very slightly above its lip while a test is in progress, and to supply water to the : lip as it is demanded during the tes~.
A 5 inch diam!ter sample o~ known dry ~eight is suspended in a horizontal plane with the center o its lower ace ad3acen~ the ups~andîng tube, and a ~ype 6005B04COX
weighing cell:(available from Au~omatic Timing and Con~rols, Inc. o~ ~ing of Prussia, Pennsyl~ania~ a~tached to the : samp~e continuously records the weigh~ o~ ~he sample as i~
becomes laden with:water.
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~ - 42 -To ini~iate the tes~, the water in the ups~anding tube is raised to its operative level, forming a meniscus at or above the lip of the tube. Contact between the sample and ~eniscus occurs and is maintained as water is absorbed from the tube. The test con~inues for 60 seconds, and the weight of water absorbed by the sample is recorded Resul~s are expressed as grams of water abs~rbed per gram o~ dry sample weight. A high result indicates rapid wicking, and ~ice versa.
Peel Test A~ Instron ~odel ~S tensile testing machine available rom Ins~ron CO~JQra~iOn, C~n~on, Massachuse~s is used to conduc~ this test. Sa~ples al~e cut 1 inch wide a 6 inehes long for the test. t'Cellophana" tape is attached to opposing sides of ~he sample adjaeen~ a common edge and a "T-shaped" peel is started acro~s the entire width o~ ~e sample by hand. (~hen the peel test i5 carried out, neither of the plies is backed by tape at the site o~ ply separation.3 The respective tapes are clamped în the top and ~ot~o~ jaws o~ the tensile testing machine, and the load which mus~ be applied to ~ur~her peel ~e layers apart in the machine direetion is measurPd in grams. I~ the sample tested is no~
ply-separable, peeling will not occur. Rather, one or both of the tapes will pull a~ay ro~ the sample, carrying only a small amoun~ o~ ~ibrous material pulled ~rom khe s~r~aces o~
the sheet. ~ ¦ _ ,, ~k~ , This test is performed using an Ins~ron Model TMS
tensil~ tes ~ing machine ~r its equivalen~. In t~is ~est, ~the en~ire ~ur~ace of each side of a circular sample wi~h a * Trademark for a brand of regenerated ceIlulose film producPd from ~lscose by treatment with suluxic a~id :~~3 ,. . . ' , ' . ' ~ . ~.,' '' . '' : . ' ' .. ' ' ' ' . . ~

diameter of 1~ 25 inches is adhered to the opposing generally planar pu1 ling surfaces of the machirle, which lie in plarles perpendicular to the directioII of pull to be exerted by the tester. (Adherance is effectPd by applying 1.125 inch discs S af two-sided tape between the machine jaws and che respe~r.ive sides of the samp~e.) A pulling force is ~hen applied ~Q
the sampLe unti1 the plies separate--unlike ~he peel testJ
in this test the en~ire sample delamin?~es simu1 ~neously, or nea3~ly so. The load needed to effect sepa~cation o ~he plies is ~herL ~ecorded, measured in grams.
Gontrol Samples To ~e~re~oy a standard fo~ coTnparison o: ply-separable paper webs of the present inven~ion wi~h a s~rat:i:Eied non-ply-separab~e paper web (hereina~ter: "reversed s~rat:~
web") and with a homogeneous paper web, examples of .~,h~
lat:ter webs were produced on ~he same ma~hine used in Example b, above. Process condi~-.olls ~or these runs are summarized i~ Table I, alignQd adj acent the same data o: .
Example 4 for comparison. In Table I, Layer W is ~he second ueb of Example 4 or îts equi~ralent, layer F is ~he iayer fo~ed from the firs~ furnish of the :Eirs~ web o~ Example. 4 or .its ~qu~ivalent, and layer C is the layer which becomes the barrier layer of the web. The homogeneous paper web w~s ormed entirely Erom ~he headbox which deposi~ed layer W in ~he other ~s . ~lso in Tal~le I, "N . S, K. " is nor~hern ~so~wood ~raft pulp "`N.H.S." is northern hard~ood suli~e pulp, and i'M.S." is mercerized sulfi~e pulp.
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71~
~ABLE I
Homogeneous Reversed Stra~a Parame ~er ExamD le 4 Web Web Composition:
5Layer F 50~/O M . S .K. ~ % M. S.
50% N.H.S. - _ Layer W 50% N.S.K. 25% N~S.K. 100% M.5.
50% N.H. S .25% N.H. S .
- 50% M.S.
Layer C 100% M, S . - 50% N. H. S .
- - 50% N.S.K.
Basis Wei~ht (Frac~ion o~ sample):
Layer F . 25 - . 25 I.ayer W 25 1.0 .25 L~er C _50 ~ 50 Throat Settings~ J- * *
Headbox f lows; gall~ns/min .:
Layer F 171 - 1~1 IJayer W 517 51~ 510 2~ .,ayer C L7~ ~ 184 Headbox Consistencies, % iber;
Layer F 0.17 - 0. 15 Layer W O . 06 0 . 24 û . 06 Layer C 0.36 - 0. 34 Vacuurn Box Vacuum Level ~ *
Breast Roll Va~uum .Level . * * *
Pickup Shoe Vacuum 30~ . ~ Lev.el ~ ~ * * *
:
Webs Consistencies, % Fiber:
Be~ore trans~e3:
to fab~ic:20 .1 22, 2 20 . 0 Be;~ore predryer ~7 . 5 26 . 2 26 . ~ ~
~:fter predrye~ 87 . 9 72 . 2 %2 . 4 At ~creping~99.2 9~.7 .9g.2 Pred~yer Temp~e~atures:~

Ist stage input 380 380 . ` 415 1st stage: Outpul: 1:65: : 150 170 : ~~ :2nd~ :s~age ~inpu~ : 380 :~ 380 4L0 2nt~s~age output~ ~ 230 220 ~ ~ 240 J'; - Indicates ~identical ~Talues for eac~ run, as per example 4.

.

Test Results . .~ .
Tabl~ II indicates the results o 'che above ~ests LCor the examples and control samples previously de s crib ed:

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-a co C;~ ~ ~ ~ u~
~ ~ oo cr~ ~ ~o ~ u~
~ . C~
h D:;
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C~

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a) " r~
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C~ I ~
fd I ~ ~0 0 ~ ~ , _I ~ co ~n co ~ c~l . u~

K r- o ~ ~ o~ co~ oo ~ o~ ~I h u~ o ~ 1~
~ . ~ ~ ~1 . . ,~ co C~ , r` '~.
.~', W ~ r~ O ~1 ~

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b.O ~o E-l~1 J-l .

~rl QJ ~ O ~ ~ O ~
V ~ O ~
rl Q~ 5~ O
~ a 5~ ~ n ~ ~
a~ ra ~ ,~ ~ ~ a~

~ a, ,l ~a ~ ~a P ~ oc~
~ ~ a) a ~ ~ h 6-' h~ C `' 4 7 ~

A comparison in Table II o the daca :for Example 4 versus the concrol data illustrates the presence of` ply separation as a func tion of ~he type of fiber used in the central layer o:f ~he three-layer embodimen1: o the invention.
This data illustra~es ~hat while the tensile strength, stretch, and burst parameters for the ply-separable web of E;xample 4 are not optimal (although they are acceptable) ~
nevertheless ply-separation is present in ~he Exampl 4 da~a and absent in the control da~a.
The center point wicking ~est also illus~:a~es a significan~ improvement in ra~e of absorbency ~or the Exa~ple -4 w~b as compared ~o ~che con~rol webs which have similar basis weights.
Data is not reported for Example 3, as tbat ls a hypo~he~ical example. However, the in~Tentors predic~ t:ha~
the product of Example 3 is ply-separable.
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Claims (17)

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

1. A method to produce a ply-separable web, comprising the steps of:
(a) forming a wire side web layer of long paper-making fibers on a first forming wire, said wire side web layer having a consistency of about 10 to 25 percent fiber by weight at the point of juxtaposition with a fabric side web;
(b) forming said fabric side web layer of short papermaking fibers on a second forming wire, said fabric side web layer having a consistency of from about 5 to 15 percent fiber by weight, whereby the consistency of said wire side web layer is about 5 to 10 percent by weight greater than the consistency of the fabric side web layer at the point of juxtaposition with the wire side web;
(c) juxtaposing said first and second forming wires with said fabric side web and wire side web layers disposed therebetween, bringing said first and second wires into contacting relation to form a combined web;
(d) applying a sufficient differential pressure to said combined web to unify it into a stratified web having first and second strata which are weakly bound together by papermaking bonds;
(e) applying a partial vacuum to said stratified web adjacent said fabric side of the web, whereby to transfer said stratified web to an intermediate drying fabric and to reduce the adherence of said wire side web and fabric side web layers to each other;
(f) drying said stratified web while it is on said intermediate drying fabric, to a consistency of about 85 to 100 percent fibers by weight; and (g) creping said stratified web in a single operation to produce a web with creping which is equal in frequency and simultaneous in phase in each layer of said stratified web.

2. The method of claim 1, wherein said fabric side and wire side webs are unified by passing said juxtaposed first and second forming wires over a vacuum source situated adjacent one of said forming wires on the side thereof opposite said combined web.

3. The method of claim 1, wherein said intermediate drying fabric has a mesh size of about 100 to 3,600 openings per square inch.

4. The method of claim 1, wherein said stratified web is adhered to a creping roll and then creped therefrom using a doctor blade.

5. The method of claim 1, wherein said stratified web is creped by conveying it between a driving roll and a stationary surface into a retarding zone so that the speed of the web as it enters the retarding zone exceeds the speed of the web as it leaves the retarding zone.

6. The method of claim 1, wherein said stratified web is creped by applying a compressive force parallel to its respective surfaces in a longitudinal direction while simultaneously applying a force perpendicular to said faces.

7. A method to produce a ply-separable paper web, comprising the steps of:
(a) forming a wire side web layer of long papermaking fibers on a first forming section, and dewatering said wire side web layer to a consistency of from about 10 to 25 percent fiber by weight a the point of juxtaposition with a fabric side web;

(b) forming said fabric side web layer of short papermaking fibers on a second forming wire and dewatering said fabric side web layer to a consistency of from about 5 to 15 percent fiber by weight, whereby the consistency of said wire side web layer is from about 5 to 10 percent by weight greater than the consistency of the fabric side web layer at the point of juxtaposition with the wire side web;
(c) juxtaposing said first and second forming wires with said wire side web and fabric side web layer disposed therebetween to bring said wire side web and said fabric side web layers into contacting relation to form a combined web;
(d) applying a sufficient differential pressure to the respective sides of said combined web to unify it into a stratified web having at least first and second adjacent strata which are weakly bound together by papermaking bonds;
(e) applying a partial vacuum to said stratified web adjacent said fabric side layer whereby to transfer said stratified web to an intermediate drying fabric and to reduce the adherence of said wire side and fabric side layers to each other;
(f) predrying said stratified web to a consistency of about 50 to 95 percent fiber by weight;
(g) imprinting said stratified web on a drying roll means through a pressure roll means acting on said intermediate drying fabric, wherein said stratified web is disposed between said intermediate drying fabric and drying roll means, to form a multiplicity of discrete densified areas defining a pattern of spaced lines having a substantial orientation predisposed to buckle during creping;

(h) drying said stratified web to a consistency of from about 85 to 100 percent fiber by weight; and (i) creping said stratified web along each of said creping lines to form creping which is equal in frequency and simultaneous in phase in all the layers of the web.

8. The method of claim 7, wherein said fabric side and wire side webs are unified by passing said juxtaposed adjacent one of said forming wires on the side thereof opposite said combined web.

9. The method of claim 7, wherein said intermediate drying fabric has a mesh size of about 100 to 3,600 openings per square inch.

10. The method of claim 7, wherein said stratified web is adhered to a creping roll, and creped therefrom using a doctor blade.

11. The method of claim 7, wherein said stratified web is adhered to a Yankee dryer, and creped therefrom using a doctor blade.

12. An absorbent ply-separable paper web comprised of at least two separable plies, wherein the improvement comprises creping which is substantially equal in frequency and simultaneous in phase in each separable layer.

13. The absorbent ply-separable paper web of claim 12 wherein said at least two separable plies are maintained in spaced relation by a barrier layer.

14. The absorbent ply-separable paper web of Claim 13, wherein said barrier layer is comprised of mercerized pulp fibers.

15. The absorbent ply-separable paper web of Claim 13 wherein said barrier layer is comprised of synthetic fibers.

16. The absorbent ply-separable paper web of Claim 13 wherein said barrier layer is comprised of partially debonded papermaking fibers.

17. The absorbent ply-separable paper web of Claim 13 wherein said at least two separable plies have relatively strong intra-ply bonds and relatively weaker inter-ply bonds.