CA2063947A1

CA2063947A1 - Liquid absorbant composite laminate

Info

Publication number: CA2063947A1
Application number: CA002063947A
Authority: CA
Inventors: Kambiz B. Makoui; David H. Hollenberg; Ralph H. Reeves
Original assignee: Kambiz B. Makoui; David H. Hollenberg; Ralph H. Reeves; James River Corporation Of Virginia
Current assignee: Fort James Corp
Priority date: 1991-03-27
Filing date: 1992-03-25
Publication date: 1992-09-28
Also published as: US5139841A; EP0506336A1

Abstract

Abstract A disposable, cloth-like towel of superior wet strength and absorbency comprises a scrim at least one face of which is coated with a superabsorbent material and a nonwoven cellulosic web which is bonded to the coated scrim. The superabsorbent coating preferably is formed by wetting the scrim with water or an aqueous adhesive, applying a solid hydrophilic polymer to the scrim, then applying a nonwoven absorbent cellulosic web to the coated scrim and drying the resulting composite web.
Bonding of the scrim to the cellulosic web can be achieved by applying an adhesive to the side of the cellulosic web which is brought into contact with the coated scrim.
Alternatively, both the hydrophilic coating and bonding can be effected by sandwiching the scrim, coated with an unreacted mixture of hydrophilic polymer and crosslinking compound, between two cellulosic layers and then subjecting the multi-ply sheet to crosslinking reaction conditions to form the superabsorbent on the scrim as well as to cause adhesion of the cellulosic webs thereto.

Description

2~63~

? ~ ~23.~ '~S
LT.QUID ABSORBANT COMPOSIT~: LAMINATE

~his inven~ion -elases ~o a superabsor~er.t c~o-n.- -:~e ~ la.~ina~e strucsure and o its merhcd o- orepar~ior.. In oee o. i.s more specific aspec~s, ~his inven~ on rela~es ~o a scrim-reinforced, cloth-like, composlte ilcuid absorbe.n-lamlnate structure comprising a superabsorben~ ma~eria1 associated wlth scrim and covered on at least one side wi.h a nonwoven ~elluLosic web. In another of irs more speci ic aspects, tne Lnvention lncludes a scrim-reinforced composl_e laminate ln w~ich the scrim is coated with solid absorben~
and sandwiched between layers of non-woven cellulosic webs.
Other aspects of this invention relate to the ~e~hod of manufacture of the structure and to consumer produccs lS incorporating such structures as an element thereof. The resul~ing structures are both highly absorbent and reslstan.
to tear.

Backaround of the rnvention The noveL cloth-like fibrous l~minate is useful as disposable towelLn~, ~ed pads, diaper liners, sani~ar~
napkins, wipes, wound drsssings, and f ilter materLa~s which are capable of remaving m~isture from non-a~ueous ~iltrates.
In one of i~s pre~erred em~odimerlts, a cQmposi~e ~abric comprising a superabsorbent scrim layer sandwiched between layers o~ dry laid n~nwoven cellulosic fibers ls produced as a strong laminate structure of high liquid-absorbency which is soft to the touch.
Numerous proposals have ~een made for the manufactur3 of cellulosic composite products useful as dlsposable towels and similar products. ~wo desirable ~roper-ies of absorbent paper produccs, namely, high-liquid absorbenc~ and superior wet strength are virtuaily anclthetlcal. ~lsh absorbency is 9~7 ~___, -aavc ~ a~ ~~ _ 5 ~- :~ ~.. ,o~-s_-, ~ U = _ ^ ~ _ ~ r 5 ~ ~ _ _ ~ r. ~ ~ . ~ ";~G-Q5 a '~ e r a~~Q~.~ _ nvol~es -he us- c- -~ e~s o- -C..,-2C-'~ ' _e-s -.
e~v ~ow -~av~3er.c~, -:~ ~.e-ho- -3r =:-~ ma.r.~a_-c=~a-- c- a c!- '.,-l_',ce cer.--s =e l2.~~-.2._~ is cisc ose~ ~~. U.s. ?-_~n,_ ~o, ~ ~ ~; A. ~ ~ ~ _ _3 .~lar.ning er 1 r W;~lCh SC~~ ~ co2_ed wi_'n a ='~.em.o?ias_ic 'vinde- ls ir.ser~ec oerweer. .wo nor.-wover. 12yers '^,onced wi~n a la~e.Y aches ve a..c 'ne comr~osa _e he__~d ~o a ~-mpera-!a~e su_~lc er._ ~o ac-iv2!ts ~'ne ~'nermo?'as~ c blnder. ,~. sc-i~
-elr._orced, c'o~ e comr~osi t9 1 2~n.2.~Q iS ?roducsd .~avi ?.5 both excel1en~ c-~ cn.d we~ st-er.gth pro?er_ies.

; ~ numDer o- ?aten~s sre direc.Q~ .3 mer'.nods ~or ir.c3.pora~ing su~e~sDsor~er._ ma~erials, commonly ~er'er-ed ~o ~?. c'n9 arc as S~M~s, lnco cellulosic com?osi=es co -'o-~
?roduc_s or s_ea~l~ enhanced acsor_en.cy -or li nics, ~or e~æ~ple, '~or?m2r:, U.s. 4,A.13,~3~ dlscloses ar. absv3~_er..
~,, .
?anel s~ruc~u_e use_ul i n, various n~sien.~c ?roduc_s i-. whi-:.
c ?a~er or ~aDric su~s~~ate is c3aCQ~ wi~n a ~e2c~_ve com?osi~ion o_ a l~cuid ?oLyr.yd_ox-~ orcanic compQun.d -nc a ?ar_icula~e wacer-l nsolu31e~ wzcer s~el123Ls aDsor3en.
?ol~fmer. ~ac~, in U.S. ?a-e,n~ 4,oO0,402, disc1os2s a 'aee.~
2~ bonded, air lsid weD o~ enhanced a'csorberc-~ co w'r.ich J Wc~er soLuble 'nydr3?'n11s Ls addsd a~.d dried on t'ne web. An a~sorDent pad assemoly in which 2 '~.yd-oo'nlllc ?ol~,rmer coatin~ ls applied ~o one sur-ace o~ one p2d and cover~d with ano~ner r?ad adjacen~ the coa~ed sur-~cs ~s dlsclosec n.
~.s. 4,46l,o2L to :~a~aml et al.

_n accordancs wi.h ;his ~n-~en~ion, - s~rong dis~csaDie absor~en~ lamina~e o~ improved wa~er absor~ency ~s -o~ed 3Y
incorporating a superabsorbent material on a scrim, e.g.
a polyester or ~iberglass scrim, and covering the scrim with a layer of celluloslc fibers. In one specific embodiment of the invention, the scrlm is coated with an adhesive, e.g. a polyvinyl alcohol latex, to which superabsorbent powder is added to form a coatlng on one or both sides of the scrim, S and the thus formed superabsorbent scrim is covered with a web of cellulose fibers. The resultant product is a s~ron~
laminate structure with superior water absorbency and a cloth-like appearance and feel.

Summary of the Invention In accordance with a preferred embodiment o~ this invention, a cloth-like composite laminate is formed which comprises two nonwoven layers of ceLlulosic fibers attached to the opposite sides of a scrim or screen which has been coated or impregnated with a superabsorbent hydrophilic polymer.

A number of superabsorbent polymers are known in the art. U.S. Patent No. 4,600,458 to ~ramer et ai., for example, includes a Long list of patents disclosing superabsorbent polymers useful in absorbent structures in which the superabsorbent polymers are incorpcrated into an absorbent fibrous web or laminate. Among the polymers disclosed for this purpose are saponi~Led starch-polyacrylonitrile graft copolymers, crosslinked/grafted cellulose, saponiEled vinyl acetate-acrylic acld copolymers, starch gra~ted polyvinyl acetate, acrylic acid polymers, crosslinked polyethylene oxide, and the like. In the method of this paten~, superabsorben~ solid par~icles are layered between webs of fibrous Material and the layered stacks of webs crimped to retain the solid absorbent ln place.
McFarland et al., U.S. Patent No. 4,655,757 incorporates solid particles of superabsorbent material into a coformed layer of meltblown fibers containing wood fibers for ~0~3~

mproved a~sorbency- Among the superabsorbents mentioned therein are those ~ormed from hydrolyzed cross-linked polyacrylamides, polyacrylates, polymers of acrylic polymers or their copolymers. Sodium polyacrylate hydrocolloid particles are preferred as superabsorbents.

Fibrous slivers and absorbent structures having superabsorbents or hydrocolloids distribut?~d there~hrough are disclosed in U.S Patent No. 4,340,556 to Ciencewicki and U.S. Patent No. 4,596,567 to Iskra wherein some superabsorbents are described as having a backbone of natural or synthetic polymers with hydrophilic groups, or polymers containing hydrophilic groups, chemically bonded thereto or in intimate admixture therewith. Among the superabsorbents mentioned therein are modified natural and regenerated polymers, such as polysaccharides including cellulose, and starch and regenerated cellulose which are modified by being carhoxylate?~, phosphonoalkylated, sulfoalkylated, or phosphorylated to render them highly hydrophilic. These polymers may be cross-linked to render them water insoluble, all as described in U.S. Patent No.
4,105,033 to Chatterjee et al.

The superabsorbent pol~mer and cross linker ma~ be any of those already known in the chemical litera~ure as well as those resul~ing ~rom con~lnued research and developmen~ to produce water insoluble cross linked polymer products o~
enhanced hydrophilic propensity. Currently, superabsorbents suitable for application to the scrim used in the toweling of this invention include the metal ion crosslinked polymers described in U.S. Patent 4,090,013 and a polyacrylate absorbent containing both amide and carboxylate gro?lps prepared by radiation polynerization and crosslin~ing as described in U.S. Patent 4,192,727. Hydrophilic polymers that are reacted wi~h organic crosslinkers as described in ~, , 9~7 ~he U.s. Paten~ ~,310,~93 are further examples o.
superabsorbents that may be applied to ~he scrim.

The scrim is formed o~ a continuous filament of nonwoven ~aterial such as rayon, nylon, polyester, polypropylene, aramids, and glass. A polyes~er scrim or screen sold under the trademark Bayex by Bay Mills, Ltd., of Canada is illustrative of a desirable rein~orcement for production of the novel toweling of high wet strength and superior water absorbency. The scrim will in most cases have a mesh opening of 2 to 5 mm between fibers and will contribute a weight in the range of a . 2 to 2.0 ounces per square yard to the total weight of the multi-ply towel.

The two layers of nonwoven cellulosic fibers which are attached to the opposite sides of the supera~sorbent coated scrim or screen may be produced by any of the many known procedures. For example, previously mentioned U.S. Patent No. 4,634,621, incorporated herein by reference, discloses an operation in which dry fibers are laid on two separate belts and bonded with a latex adhesive forming two separate air laid bonded cellulosic webs which are then brought into contact wlth the opposite sides o~ a scrim coated with a thermoplastic resin. In the process of this patent, the scrim has a thermoplastic polymer binder applied as a coating to each o~ its two sides. The nonwoven cellulosic layers and th~ i.ntermediate binder~coated scrim are finally passed through a heated lamination s~a~ivn to cause adhesion of the cellulosic layers to the scrim.
In accordance with a preferred embodiment of this invention, each of the cellulosic webs which is brought into contact with the scrim is given a coating of binder on its surface nearest the scrim so that surface fibers of each 3S nonwoven layer become attached on contact with the _ 5 _ ' .

206~l77 su~er-~oso _en~ s~- m ~nd ~ clrin~ o _:-e 'o ~der, ~:~.e cel~u_os c ~ayers Ars oon_ed _o ~,e sc m c~ _r~v ~e -un.~carr ~roauce of n~sn we~ se-sr.gc:n ~.nd 5-e~ en.:--~r.-~r a'Dsoroenc~ .
-Ai.err.a~1vely, i~ ls in ;~any casqs ?re~er-bl~ -o bri-.g .he nonwoven celluloslc layers ir.co con~ace wieh ~ e sc~ m i~mediately a~ter tne hydrophilic solymer has Deen ps1ed ehereon. In such cases, the wet sur-ace coatlng on ehe scrim contaces the cellulosic layers and durinq ~e drying or curing reaction creates a bonding o~ ~he cellul OSlC
layers to the scrim.

8rief Descri~tion Of The Drawin~
To facilLtate the further description and understanding of c~e invention, rererence will be made to the accompany_n.g drawings ln wnlch:

FIG.l i~ a fragmen~ar~ sectio~lal view of a rnultl~-ply cloth like laminate according to the invention, FIG. 2 is a schematic diagram showing the assaracus used in che method of making the product illus~ratsd ln -IG.
2S l; and FIG. 3 is a schematic di.agram showlng alternaei~re apparatus for the manu~ac~ure o~ a superabsor~ent product by che me~hod o~ this invention.
Description of ~rererred Embodiments A ~ypical cross section of the product of the invenctar.
is il}ustrated in Fig. l wherein scrim lO coated on boeh 3S sides with superabsorbent material ll is sandwiched ~e~ween., ~39~7 ar.c. ~o nced - e ~ o nc n ~ o v e r. c ~ i o s i~ we ~ s ~ ~ ~ a ~
~o~.c ~ a~e~a'~ 13. ~he su-e~-bsorser.t ma~ Cn -, Q
coposi~e sices o~ sc_im 10 anc -'ne bondin~ mat_r~ ?.
~ne in~er sur aces o~ c~llulasLc 1ayers 12 con~ig~aus ~o sc m 10 'nold the muiti-?l~ shee~ ~oge~her to ~rov de a d~sposable, cloth-li~e towel of su~erio_ assor~e~c~r ~.d ~er s~~ength. 3cr.ding material 13 may ta,ke differen; -or~s and di_ferent methods or ap~llcation as illustrated ir. ~s. 2 and 3.
The nonwoven cellulosic webs 11 may be formed from air laid cellulose fibers ~y methods well known in the art, for example, by t'ne method and apparatus disclosed in U.S.
Patent No. 3,797,074 U.~. ~atent Z,008,638~; or U.S. Patents iS 4,014,635; 4,193,751; and 4,285,647, incorpora~ed by reference herein.
Wi~h -eference ~o Fig. 2, scr,m lO from roll lOA is ~ assed between s~rays 14 which ap~ly water or a sui.able adhesive, e.g. a solution of carboxyme~hyl cellulose to bo~h sides of ~he scrim. The coated scrim 10 then passes ~hrougn s~ation 15 where ~owdered superabsorbent ma~erial ~s added to the scrlm ar.d held in place by the adhesive as the sc-im passes over a ~elt lSA wh.ich presses solid absorben~
material passing through op~nings in the s~rim agains~ the side opposite the powder appLicator li, ~hus coating bo~h sides of the scrim with superabsorbent powder which is held in place by the, water or adhesive on the scrim.

Simultaneously, two nonwoven air laid cellulQsic webs 12 and 12' are supplied ~rom a suitable source 12A; 12A' over rollers ~6 and 16' into ehe nip of opposed rcilers 17 and 17' ~nere they meet and sandwlch scrim lO laden with supera~sorben~ 11 between them. ~efore entering the nip between rolLers 17 and li', each of ceilulQsic layers 12 and ~2~ ~s sprayed ~63~3~7 -h ~ ~cn ~ ; a~;e.n ad:-.osl vo bl jers 13 ;nd ' 3 ~ on. -.,o s- _o a~ eacn layer ra~ is :o b~ou~nc in~~ c_r.~ac~ ~ -. sc- .
;0. ~he mult ~ sr.eet cnen ~asses ~hrough drying S~3r ~ ~.n whic:~ has~ns che ~ondinq o- csLlulosic ~ayers L2 an.d L~' ~o aDsor~en.t-co~to~ sc~im '0.

In FLg. 3, illuscraring apparatus similar eo c.ha~ --Fig. 1, sc_im 10 passes over roller 20 and ur.der rollers 21 which are par~ially immersed in water or adhesive solucior.
in tank 22. ~he thus impregnated sc~im 10 is then drawn -rom tank 2~ over raller 23, dusced with superabsorbent powcer from discribucor 15 and ir.~o the nip or opposed rollers 17 and 17'. Thence, the multl-ply sheet passes throuqh drying station 24 bondLnq che ce!lulosic layers 12 to the opposite sides of scrim 10.

~ he weight of the cellulosic fibers forming each nor.woven layer is wic~.in the rar.~e of 20 ~ounds/ream to ~0 Dounds/ream. ~he separate layers containing ~e celLulosic ribers can be ~ormed by ai_ laying or foam laying .he cellulosic ri~ers onto various belts knawn in the art. One ty~e of apparacus far air rorming each layer a~ csllulosic -ibers is shown in U.S. ~atent No. 4,193,751 to Miller.
Other techni~ues known in tne ar~ c3n also ~e used such as 2; foam forminq as described ln ~.S. ~atent ~a. 3,~337,999 ~o Chung or air emulsion as discL~sed in u.s. Pa~ent Na.
4,049,491 to ~randon et aL.

The latex adhesi~re, used ta blnd tagether the ~hree dimensional cellulosic flbers in each nonwo~e~ layer, can be selected fram various late.~ adhesives known in the art.
~cceptable latex adhesives include acrylate emulsians, butadiene-styrene emulsions~ acetate-e~hylene emulsi~ns, and acrylonitriLe-butadiene emulsians. An especially ef-ec-ive latex adhesive is aceta~e-ethylene which is s~ld under ~he - a 2~639~7 ~-~dema~k .~ r_X A-106 Dy Air ?raducrs, ~~c, 3_ ~e~nsy~anl~ The skilled arcisan can sele~ ~he ?~r- ~ C'l ' ~ -latex adheslve depending upon t;ne ~ype ~ c~llulosi G ~ t DerS
th2t are ~o ~e bonded. The latex adhesive i~ applied 3V
known techniques, e.g., by spraying or ~oaming. The ~maun~
of solids deposited from the latex adhesive de?ends, Ln~er alia, on the welght of the cellulosic fibers in eacn layer.
Generally, la~ex adheslves having from l; to 2i% solids are used.
After the latex adhesive is applied to the celluLosic fibers, the latex adhesive is dried by conventionai technlques. As a result, two separate nonwoven layers of cellulosic fibers are formed.
1~ .
The scrim is prefera~ly a continuous filament scrim composed of a nonwoven material, such as nylon, ravon, polyester, polypropylene, glass, and ar~mids, such as ~evlar and Nomex which are trademarks of the E.I. DuPo~t de ~emours & Co. ~n example of a bonded polyester nonwoven material useful as scrim is Bayex, which is a trademark of Bay Mi.lls, Ltd. Such a scrim can have dimensions o~ 4 thr~ads per inch of LS0 denier in the cross machine directian ~CD) and 12 threads per inch o 70 denier in the machine directlon (~D).
2i The weight o~ the scrim is pre~erably within the range o 0.2 ounce per square yard to 2.0 ounces pex square ~ard.
other scrims, such as a mesh scrim, can also ~e used in the present invention.

The preferred nonwoven rnaterial for the scrim has a set or spaced machine direction threads with a second set o~
spaced threads lying cross-directionall~ with respect to the first set of threads. The two sets of threads are bound o~
adhered together at the points where the threads of one set 3; cross the threads of another set. The threads maklng up the _ g _ . . . .

~63~1~7 scrim can be in an over and under configuration, as shown in U.S. Patent No. 3,885,279 to Darnell et al, or a one side pattern, as shswn in U.S. Paten~ No. 2,902,39i to Hirschy e~
al. Other scrim configurations known in the art, such as extended netting described in U.S. Patent No. 4 ,1~2, 479 to Larsen, can also be used.

The scrim is coated with a thermoplastic binder so tha~
the two nonwoven layers of cellulosic fibers adhere to the scrim, when the scrim is inserted between the two nonwoven layers. Examples of acceptable thermoplastic polymer binders include polyvinyl chloride plastisol, polyvinyl chloride, polyvinyl acetate, ethylene acrylic acid and ethylene vinyl acetate. Other known thermoplastic binders can also be used. ~n especially effective polyvinyl chloride plastisol is sold under the trademark BAYEX F-50 by the Bay Mills, Ltd. of Canada.

The skilled artisan can select the particular therm~plastic polymer binder depending upon the type of celLulosic fibers and the scrim that are to be bound together. The scrim can be coated with the thermoplastic polymer binder by various known techniques.
Af~er the scrim is inserted between the two nonwoven layers of cellulosic ~ibers, the scrim and the two nonwoven layers are heated to a tempera~ure sufficient to actlvate the thermoplastic binder so as to laminate together the scrim and the nonwoven layers. The heating of the scrim and the nonwoven layers is performed without pressing the scrim and the nonwoven layers together.

The heating pro~edure is preferably performed by passing hot air through the two nonwoven layers and the scrim, in a manner shown in FIG. 2, or by passing the ~wo .

~0~3~7 nonwoven layers and the scrim over a large diameter, hea~ed drum, as shown in FIG. 3. Other heatin~ ~echniques, however, kno~n in the art can also be used to bind the two separate nonwoven la~ers of cellulosic fibers onto opposite sides of the scrim.

Those skilled in the art know that there are numerous hydrophilic polymers which may be crosslinked with or without crosslinking agents and which are suitable for use to provide the superabsorbent coating on the scrim pursuant to this invention. U.s. Patent No. 4,461,621 lists several patents which teach the formation of superabsorbent coatings that are useful in the present invention. Ionizing radiation may be used to accelerate the cross-linking lS reaction with or without the appli~ation of heat from an external source.

The embodiments of the invention which have been described are exemplary of others which will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Accordinyly, only such limitations should be imposed on the invention as are set forth in the appended claims.

,,, .. , . , . ",, .. , ,.. ,.. . . . , . . ,.. , , . , ... .. . .. ..... , .. . .. ~ . . . . . . ... .

Claims

1. A method of making a liquid absorbent composite laminate having high wet strength and enhanced absorbency which comprises:

(a) coating a scrim with a superabsorbent hydrophilic polymer, and (b) bonding the coated scrim to an absorbent nonwoven cellulosic web.

2. A method as claimed in Claim 1 characterised in that bonding is effected by applying an adhesive to the side the cellulosic web which is brought into contact with the coated scrim and then heating said cellulosic web and the coated scrim to bond the web to the coated scrim.

3. A method as claimed in Claim 1 or Claim 2 characterised in that the scrim is wet with water and then coated with a powdered solid hydrophilic polymer prior to bonding the coated scrim to the cellulosic web.

4. A method as claimed in Claim 3 characterised in that the water contains a water soluble adhesive.

5. A method as claimed in Claim 1 characterised in that the superabsorbent coating and bonding is effected by coating the scrim with a liquid hydrophilic polymer, covering both sides of the coated scrim with absorbent cellulosic webs and the hydrophilic polymer coating on said scrim is crosslinked in situ by heat or ionizing radiation causing crosslinking of the polymer and bonding of the scrim to the cellulosic webs.

6. A liquid absorbent composite laminate having high wet strength and enhanced absorbency which comprises a scrim, a superabsorbent coating on said scrim, and a nonwoven cellulosic layer bonded to the said scrim.

7. A liquid absorbent laminate as claimed in Claim 6 wherein both sides of the scrim are coated with solid superabsorbent and bonded to nonwoven cellulose webs.

8. A liquid absorbent composite laminate which comprises a scrim, a solid superabsorbent coating on at least one side of the scrim, and an absorbent nonwoven cellulosic web bonded to the scrim and covering the superabsorbent on the coated side of the scrim.

9. A liquid absorbent laminate as claimed in claim 8 wherein both sides of the scrim are coated with a solid superabsorbent and an absorbent nonwoven cellulosic fibrous web is bonded to each side of the scrim.

10. A liquid absorbent laminate as claimed in Claim 8 or Claim 9 wherein the scrim is a woven polyester screen and the cellulosic fibrous web is an air laid cellulose sheet bonded with latex on the side adjacent the scrim.