CA2012652A1

CA2012652A1 - Manufacture of composite web having absorbent properties

Info

Publication number: CA2012652A1
Application number: CA002012652A
Authority: CA
Inventors: Thomas W. Piantek; Larry H. Witte; Michael J. Iskra
Original assignee: Individual
Current assignee: Weyerhaeuser Co
Priority date: 1989-04-10
Filing date: 1990-03-21
Publication date: 1990-10-10
Also published as: EP0396920A1; JPH0382875A

Abstract

ABSTRACT OF THE DISCLOSURE
A method of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web, in which the material is to be polymerized and cross-linked, as a part of a method of manufacturing a composite web, which comprises the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked.
Droplets of the material are dispersed within the fibrous web by moving the fibrous web through a droplet-flicking zone and flicking droplets of the material, in the liquid carrier, onto opposite sides of the fibrous web as the fibrous web is moved through the droplet-flicking zone. On each of opposite sides of the fibrous web, a rotating brush has bristles, picking up the material, in the liquid carrier, and flicking droplets thereof as the brush rotates. Each brush picks up the material, in the liquid carrier, from a rotating roller wiped by the bristles of such brush. Each brush and the roller wiped by the bristles of such brush rotate, in opposite rotational senses, about parallel axes. The material is polymerized and cross-linked in situ, so as to form the composite web.

Description

2 ~ ~ 2 ~ 2 ~ ~

MANUFACTURE OF COMPO,SITE WE~
~AVING ABSORBENT PROPERTIES ~ .
Technical Field of the Invention -i -This invention pertains to an improved - - -method of-dispersing droplets of a polymerizable, cross-linkable material, in a liquifl carrier, within a fibrous web. The improved method, which effects dispersion of the droplets through the use of a brush roller, may be advantaaeously employed as a part of a method of manufacturing a composite web. If the material, as polymerized and cross-linked, has absorbent or superabsorbent properties, so that the material is capable of absorbing liauid human excreta, such as urine, menses, or wound excreta, the -15 composite web may be advantaqeously employed in or as `
an absorbent article, such as a disposable diaper, tampon, sanitary napkin, wound dressina, or similar product reauiring such properties. -~
Background of the Invention Detailed discussions of absorbent articles employing superabsorbent materials in disposable diapers and other products are included in Pieniak et al. U.S. Patents No. 4,500,315, No. 4,54n,4s4, No. ::
4,537,5~0, and No. 4,573,9~8, which collectivelv 25 provide useful background for this invention. -~
As discussed in the Pieniak et al. patents noted above, absorbent articles can be advantaaeously made with absorbing layers and wickina layers. ~he absorbing layers can be advantageously made from polyester fibers, within which particles of a superabsorbent material are dispersed. The wicking layers can be advantageously made from cellulosic `~
fibers, such as wood pulp, and can include or take the form of a densified, paper-like layer, such as is disclosed in Burqeni U.S. Patent No. 3,017,~04, on 20~ 26a2 one side or each side. See, also, Mesek et al. U.S.
Patent No. 3,612,055 and Repke U.S. Patent No.

3,~38,522.
As also discussed in the Pieniak et al.
patents noted above, the superabsorbent material can be advantageously formed from a polymeriza~le, cross-linkable material, e.g., a water-soluble monomer exemplified by sodium, potassium, or ammcnium acrylate, which is coate~, in a liquid carrier, e.q., -10 in an a~ueous solution, onto a fibrous web, and which ~-is polymerized and cross-linked in situ, so as to form a hydroPhyllic polymer having superahsorbent properties.
Conventional coatina techniaues involve lS flooding the fibrous web with the material, in the liquid carrier, while the fibrous web is supported on a screen, so as to saturate the fibrous weh, and exposing the saturated web to a partial vacuum, which removes excess amounts of the material, in the li~uid -~
20 carrier. Typically, there is about a 7 to 1 ratio ~ -~
between the weight of liquid retained by the fibrous web and the weight of the fibrous web, and the retained liquid is Aistrihuted as fragments of `~
continuous film bridging adjacent fibers, and bein held by fiber-to-fiber capillaries. It has ~een heretofore known to remove excess amounts of liquid by means of a padder or a squeeze roll, after the fibrous web has been saturated, with similar results.
It has been heretofore known that polymerization and cross-linkinq in situ can be advanta~eously effected by electron beam, chemical, or heat initiation. Chemical initiation may require a catalyst or initiator of a known type. `
As polymerized and cross-linked in situ, the -material tends to retain whatever morpholo~y, i.e., , ,., - . .
`'.'''''~'.' ~'~' ' ~.~.'`";; ''':~
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size and shape, the material has as retained, in the liquid carrier, within the fibrous web before the material is polymerized and cross-linke~. As an example, if the material is retained by the fibrous web in fragments of continuous film includinq the `
liquid carrier, the material tends to occur as -fragments of continuous film after the material has been polymerized and cross-linked.
Conventional techniaues for coatina a -ln fibrous web with a polymerizable, cross-linkable material, in a liquid carrier, so that the material -~
can be then polymerized and cross-linked in situ, tend to result in polymerized, cross-linked particles ~ : -that do not have optimal morphologies for absorbencY. - `
Smaller, nearly spherical particles have preferred morphologies, since such particles have higher surface-to-volume ratios, as compared to fragments of continuous film, and since such particles may have lower internal stresses when ~ m -~
swollen with absorbed liquids, as compared to such fragments. Small diameter particles, with optimal ;;~
spatial distribution, give minimal interference with adjacent, swollen particles. The spheres of swollen gel also create a capillary infrastructure which is effective in immobilizina additional free liquid.
Smaller, nearly spherical particles are also ~ `
preferred because such particles are less ~rone to cause gel blocking when swollen with a liqui~ beina absorbed, e.g., urine being absorbed in a fliaper.
Gel blocking occurs if particles of a superabsorbent material tending to form a gel when swelling with absorbed liquid are too densely distributed within an absorbent article, so that the swellinq particles ~ -tend to form a gel layer, which bloc~s additional liquid from penetratina.

:'`'' ;~ ~

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2~2~2 It also has been heretofore known to sprav the aqueous solution by means of nozzles, which _ typically spray globules of the aqueous solution in circular or oval patterns. Althouah such alohules ~
tend to be more nearly spherical, such sprayinq -~ -techniques employing nozzles have not been entirely satisfactory alternatives to conventional coatinq techniques discussed above, since nozzles used in --such spraying techniques tend to provide nonuniform 10 coverage and to plug or clo~ intermittently. ~ -Although the Pieniak et al. patents noted -;
above disclose useful products and useful methods of manufacturing such products, there has been a n~ed, heretofore, for an improved method o~ dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web. Moreover, ;~
there has been a need, heretofore, for such an ~-$mproved method as a part of a method for manufacturing a composite web comprising such a ~ ~-20 fibrous web and dispersed inclusions of such a -~
material, as polymerized and cross-linked.
Summary of the Invention This invention provides an improved method ji of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a f!ibrous web, in which the material is to be ~ ~ ;
polymerized and cross-linked in situ. The method contemplates u~e of a brush and roller combination, which is operated so that its brush bristles flick ;~
such material, in the liquid carrier, on and penetratingly into the fibrous web. The improved `; ~;
method may be advantaqeously emPloyed as a part of a ~ -method of manufacturing a composite web, which comprises the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked. If -; . . :..:
.: .

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2 ~ 2 ~ -..,... -, :, , ~.-, . , the polymerized, cross-linkea material has absorbent - ~ -or superabsorbent properties, the composite web mav ~-_ be further processed, e.q., com~ressed and cut down to a useful size, and employed as or in an absorbent /
article useful in a disposable diaper, tampon, ~ -sanitary napkin, wound dressing, or similar or ;
dissimilar product requiring such Properties.
The improved method tends to produce from the material, as polymerized and cross-linke~, smaller inclusions, which tend to be more nearly spherical, as compared with fraqments of continuous film produced by conventional coating techniaues discussed above. If the polymerized, cross-linke~
material has absorbent or superabsorhent properties, -~
15 such smaller inclusions have more preferable ;~ ;
morphologies for absorbency or superabsorbency, as compared to such fragments. Moreover, the imProved method tends to provide more uniform coveraqe an~
eliminates plug~ing and clogqing, as compared to spraying techniques employinq no~zles.
Pursuant to the improved method, droplets of -the material, in the liauid carrier, are dispersed within the fibrous web by moving the fibrous web Y ;
through a zone wherein droplets of the material, in 25 the liquid carrier, are flicked onto the fibrous web ;~ as the fibrous web is moved through the zone, which may be conveniently called a droplet-flicking zone. -~Droplets flicked onto the fibrous web tend to become ~;
dispersed within the fibrous web, as dispersed inclusions, which tend to be nearly spherical, as retained by the fibrous web. Such inclusions tend to ~
be more nearly spherical, as compared to fra~ments of- `
continuous film resultinq from conventional coatina techniques.

;~
,, ' 2~2~2 ~:

Pursuant to the improved method, droplets of the material, in the liquid carrier, are flicked onto the fibrous web as the fibrous web is moved throuqh the droplet-flicking zone, by means of a rotating el~ment picking up the material, in the liquid carrier, and flicking droplets of the material, in the li~uid carrier, onto the fibrous web as the element rotates. Preferably, the rotatinq element is a brush with bristles ~icking up the material, in the ~-liquid carrier, and flicking droplets of the material, ln the liquid carrier, as the brush rotates. Preferably, the bristles pick up the -~
material, in the liquid carrier, from a rotatina roller wiped by the bristles as the brush and the roller rotate. The brush and the roller maY rotate, in opposite rotational senses ~i.e., counter-rotate), ~;
about parallel axes.
Being resilient, the bristles are deflected, ;
or deformed, from their normal orientation as they wipe the associated roller and receive the polymerizable, cross-linkable material, in the li~uid carrier. As the bristles leave the roller, they return to their normal orientation, whereby their resiliency and centrifuaal forces combine to cause the liquid on the bristles to be enerqetically flicked, i.e., flung or pro3ected, onto the movin~
fibrous web.
It is desirable, particularly if the flbrous web is thick, for droplets of the material, in the liquid carrier, to penetrate from oPposite sides of the fibrous web. ~ence, droplets of the material, in the liauid carrier, may be so flicked onto opposite sides of the fibrous web as the fibrous web is moved -through the droplet-flickina zones, by rotating ;
elements picking up the material, in the liquid '`~: ~'` ` ' 2 ~1 2 !~ !; 2 carrier, and flickinq droplets of the material, in the liquid carrier, onto opposite si~es of the _ fibrous web as the elements rotate. At least one of the rotating elements may be then adapted to flick droplets onto a respective si~e of the fibrous web as the fibrous web is moved throuqh the ;
droplet-receiving zone. Each of the rotatina elements may be a brush, which may have bristles ~ '!' , wiping a rotating roller, as aescribed above.
Ry var~ing the rotational speed of such a brush, the nominal diameter of the droplets (i.e., the largest cross-sectional dimension of such a droplet, regardless of its shape) flicked by its bristles can be readily controlled within useful 15 ranqes, e.a., nominal diameters ranqina from less -~
than 0.1 mm to greater than 1 mm. The resultinq inclusions, which tend to be nearly spherical, tenn to have nearly uniform diameters. It is possible, - ~ -therefore, to disperse droplets tendinq to have -~
smaller nominal diameters and droplets tendina to have larger nominal diameters respectively onto the fibrous web, either onto a qiven side or onto opposite sides, in two successive passes of the fibrous web through the droplet-fllckinq zone. It is ~ -25 possible, moreover, to disperse droplets tendina to ` - ;
have smaller nominal diameters and droPlets tendina to have larger nominal diameters respectively onto ~ -~
opposite sides of the fibrous web in a sinqle pass of the fibrous web throuqh the droPlet-flickinq zone. -~
It is possible, furthermore, to disperse ;
droplets of two different materials, in liquid carriers, one on each side of the fibrous web, either in two successive passes of the fibrous web through the droplet-flicking zone or in a sinqle pass throuah such zone. Conseauently, after such materials have ' - 2 ~ 2 been polymerized and cross-linked, the respective sides of the resultant, composite web can have - different characteristics, such as different rates of absorbency or different capacities to absorb liquids.
When the improved method is employed as a part of a method of manufacturing a composite web, ;
which comprises the fibrous web and dispersed ~ : -inclusions of the material, as polymerized and cross-linked, the manufacturinq method further ;:~
10 involves polymerizing and cross-linking the material : :
in situ, so as to form the composite web. If the polymerized, cross-linked material has superabsorbent- :
properties, the composite web may be advantaqeouslY
employed with superior results, possiblY in a compressed and cut-down form, in or as an absorbent article useful in a tampon, sanitarv napkin, wound dressing, or similar or dissimilar product reauirinq absorbent properties. If used in such an article, ..
the composite web can be also Provided with a wickinq ~0 layer or wicking layers, as discussed ahove, one or more densified, paper-like layers, as discussed above, or both.
Herein, each reference to a polymerizable, .
cross-linkable material, in a liquid carrier, is 25 intended to refer to any suitable monomer, oligomer, :~
or,polymer of low molecular weight, as exemplified bv but not limited to a sodium, potassium, or ammonium .
salt of acrylic or methacrylic acid, together with a sufficient quantity of any catalyst or initiator 30 needed to catalyze or initiate polymerizina and i cross-linking of the monomer, oligomer, or polymer of ` :~
low molecular weight, in a solution or susPension in a liquid carrier, as exemplified by not limited to water. Moreover, as and where apPropriate, each ~'` `',~'' ,.'' ~, `, : :'` `'"

2 ~ 2 reference to a polymer is intended to refer to a heteropolymer or a polymer of a usual structure.
~ erein, each reference to a material havina absorbent properties is intended to refer to a material capable of absorbinq liquid human excreta, such as urine, menses, or wound excreta. Moreover, ~-each reference to a material havinq su~erabsorbent properties is intended to refer to a material capahle of absorbing many times its own weiaht of such human 10 excreta. `
These and other ohjects, features, and advantaqes of this invention are evident from the following description of a preferred mode of carrvinq out this invention with reference to the accompanying drawing.
Brief Description of the Drawing FIGURE 1 is a schematic diagram of a fibrous web being moved upwardlY throuah a lower zone, -wherein droplets of a polymerizable, cross-linkable material, in a liquid carrier, are being disPersed onto the fihrous web, and throuqh an upper zone, wherein the material, as retained by the fibrous web,~;~
i8 beinq polymerized and cross-linked. An edqe of the fibrous web is shown. - ;~
Detailed Description of the Preferred Embodiment ~ While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment, with the understanding that the pre~ent disclosure is to be considered as an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.
As shown in the schematic diaqram, a fibrous~ ~ ;
35 web W is being moved upwardly through a lower zone -2 ~ ~ ~ ?J ?~ 2 Zl' wherein droplets D of a polymerizable, cross-linkable material M are being flicked onto opposite sides of the fibrous web W, and throuah an upper zone 22, wherein the material is beinq polymerized and cross-linke?~ in situ. The lower zone Zl may be conveniently called a droplet-flickina zone. The upper zone Z2 may be conveniently called a polymerizing and cross-linking zone. Any suita~le means (not shown) may be use~ to move the fibrous weh n W upwardly through the successive zones. Althouah it is preferred for the fibrous web W to be moved upwardly because the droplets D tend to be better retained by the fibrous web W when the fibrous web is ~ . . ~ -: .
moved upwardlv, the fibrous web W may be move~
downwardly, or in any other direction, so lonq as the fibrous web W is moved throuah such droplet-flickina zone before the fi?brous web W is moved throuah such a polymerizing and cross-linking zone.
As an example of one tvpe of fibrous web useful with this invention, the fibrous web W maY
comprise (a) 80~ by weight of a fiber blend beina a blend of rl~ 75% by weight of poly(ethylene -~
terephthalate) fiber ~5.5 denier x 1.5 inches~ an~
(2) 25~ of a first composite fiber (4.1 denier x 1.
inches) having a soli~ core of ?~oly(ethylene terephthalate) and a sheath of a polv(ethvlene terephthalate) copolymer, as available commercially under the trade designation DuPont D-28nW from E.I.
DuPont de Nemours and Company, Wilminqton, Delaware, and ~b) 20% by weiqht of a second composite fiber (3.0 denier x 2 inches) havinq a solid core of poly~ethylene terephthalate) and a sheath of a copolymer of poly(ethylene terephthalate) and -polyethylene, as available commerciallv under the 35 trade desiqnation Enka ~ico from BA~F ?~orporation, `~
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' ~

-'' - 2~26~2 Parsippany, New Jersey, as carded into a nonwoven web having a basis weight of about 1.~5 oz/yd~ and -- thermally bonded by subjecting the nonwoven web to air heated to about 350 F as the nonwoven web is pulled through a forced air oven while the nonwoven web is supported on a screen (not shown~ in a known manner. This invention, however, is not limited to the type of fibrous web given as an example.
As an example of one type of polymerizable, 10 cross-linkable material useful with this invention, -in a liquid carrier useful therewith, an a~ueous solution of ~0% concentration of fiS% neutralized (on --~
a weight basis) potassium acrylate, as neutralized -~
with potassium hydroxide, may constitute the polymerizable, cross-linkable material, in the liquid carrier, i.e., in water. When such material is polymerized and cross-linked, a ma~ority, e.q., approximately 80%, of the liquid carrier, i.e., water, is evolved. This invention, however, is not 2D limited to the polymerizable, cross-linkable material given as an example, or to the liquid carrier aiven as an example. Other examples of a polymerizable, cross-linkable material useful with this invention, in a liquid carrier useful therewith, are disclosed in Pieniak et al. U.S. Patents No. 4,500,~15, No.

4,540,454, No. 4,537,590, and No. 4,573,~, the disclosures of which patents are incorporated herein -by reference. ~ -In the droplet-flickinq zone Zl' droplets D of the material M in the liquid carrier are flicked onto a given side of the fibrous web W, i.e., its left side as shown, by a rotating brush 2, which is at least as wide as the fibrous web W, and which has bristles 4 picking up the material M, in the liquid carrier, and flicking droplets D of the material M in 2~ ~$~2 the liquid carrier onto the qiven or left side of the fibrous web W as the brush 2 rotates. The brush ~ is _ rotated in a counterclockwise sense, a~ shown, hv anY
suitable means (not shown~ so as to rotate about a horizontal axis parallel to the fibrous web W movina -~
through the droplet-flickinq zone Zl- .~imilarly, droplets D of the material M, in the liaui~ carrier, are flicked onto the other side of the fibrous weh W, i.e., its riqht side as shown, by a rotatina brush which is at least as wide as the fibrous web W, and which has bristles 8 picking up the material M, in the liquid carrier, and flicking droplets D of the material M, in the liquid carrier, onto the other or right side of the fibrous web W as the brush 6 ;-15 rotates. The brush 6 is rotated in a clockwise `~
sense, as shown, by any suitable means ~not shown) so -~
as to rotate about a horizontal axis parallel to the fibrous web W movinq through the droplet-flicking zone ~1- The horizontal axes of the brushes ~
respectively are at similar elevations, as shown, but may be at different elevations.
. ` ~ , .
In the droplet-flickinq zone Zl~ the ~M~
bristles 4 of the brush 2 pick up the material M, in the liquid carrier, by wipinq a rotatina roller ln as -the brush 2 and the roller 10 rotate. The roller ln picks up the material M, in the liquid carrier, from a pan 1~ containing a supply of the material M, in the liquid carrier, as the roller 10 rotates. The roller 10 is rotate~ in a clockwise sense, as shown, ^`~
by any suitable means (not shown~ so as to rotate about a horizontal axis parallel to and disposed vertically beneath the horizontal axis of the brush `; ;~
~. Similarly, the bristles 8 of the brush ~ pick u~
the material M, in the liquid carrier, by wiping a rotating roller 14 as the brush ~ and the roller 14 .''~ '~ ".~", . -.; ~ ~.. .
~, ':-~- :.,';
, ,. ~."~ .- -..... .

-- 2~ 2~2 rotate. The roller 14 picks up the material M, in the liquid carrier, from a pan 16 containina a SUpplY ~ ;
of the material M, in the liquid carrier, as the roller 14 rotates. The roller 14 is rotated in a counterclockwise sense, as shown, bv any suitable ~ -means (not shown) so as to rotate about a horizontal axis parallel to and disposed vertically heneath the horizontal axis of the brush 6. The horizontal axes of the rollers 10, 14, respectively are at similar -~
elevations.
The aforesaid means rotatinq the brush ~ maY
be also used to rotate the roller 10 via wiping action of the bristles 4 of the hrush 2 aaainst the roller 10. The aforesaid means rotatinq the brush h may be also used to rotate the roller 14 via wipina action of the bristles R of the brush ~ against the roller 14. Any suitable, level-controlled or other means (not shownl may be also provided for replenishinq the supplies of the material M, in the ~ ;
20 liquid carrier, in the pans 12, 16, respectively. ~ -Droplets D flicked by the bristles of the brushes 2, fi, onto opposite sides of the fibrous web W tend to be nearly spherical, to penetrate the fibrous web W from opposite sides, and to be well 25 dispersed within and among the fibers of the fibrous -~
weh W, as dispersed inclusions, which tend to be nearly spherical. Such inclusions tend to be more nearly spherical when compared to fra~ments of continuous film, as produced by conventional coatinq techniques noted above.
Typically, the rotational speeds of the brushes 2, ~, are at least 20n rpm. Typically, the rotational speeds of the rollers 10, 14, are from about 50 rpm to about 20n rPm dependinq on throughput, preferably about 125 rpm. R~ varvina the :'`:~' ' 2 ~ ~ h ~ ~ 2 ~ ~ :

--14-- ~ ~ :
rotational speeds of the brushes 2, 6, the nominal diameters of droplets D fli~ked by the bristles of the brushes 2, 6, onto opposite sides of the fibrous web W can be readily controlled within useful ranges, e.g., nominal diameters ranginq from less than n.l mm to greater than 1 mm. `~
Each brush can have a bristle diameter (thickness) from about o.on4 inch to ahout o.n inch, a bristle diameter ~thickness) of ahout n.n~
inch being preferred, an~ a bristle lenath from ahout 0.5 inch to about 3 inches, a bristle lenath of ahoat 1.~75 inches being preferred. Depen~ing on the overall diameter of the brush, each brush can have a rotational speed from about 200 rpm to about ?nnn rpm, a rotational spee~ of about 900 rpm beinq preferred. Preferably, as supplied to the brushes ?, . . .~ ,.
~, the polymerizable, cross-linkahle material, in the liqu~d carrier, has a water-like viscosity, i.e., a viscosity from about one centipoise to about ln 20 centipoise. `~
If the material M, when polymerized and cross-linked, results in a su~erabsorbent nolymer tending to form a gel as such polvmer becomes swollen w~th a li~uid bein~ absorbed, iudicious selection of 25 the rotational speeds of the brushes 2, 6, entails ` ~--that droplets D of the material M, in the liauid carrier, do not tend to be too denselv d~stribute~
within the fibrous web W. This invention, therefore, enables qel blocking to be largelY avoided or minimized.
Care is taken to avoid aqglomeration or ~`~
smearing of droplets D of the material M, in the ;~
liquid carrier, as retained by the fibrous web W.
Therefore, spacinq hetween each of the brushes ~
and the fibrous web W is suitably selected for the ~ ' ''i' ~ ~' : . ,:, ,- . :. ,.
~ ,,.',.`, '`',', ;'-;

2 ~ 2 rotational speeas of the brushes ~ ~, so as to avoid agglomeration of droplets D as droplets D are flicked _ onto the fibrous web W. ~iqher rotational speeds require greater spacin~s. ~ower rotational speeds permit lesser spacinqs. Suitable spacinas for aiven rotational speeds may be readily selected by trial and error. Care is taken, moreover, to avoi~
touching the fibrous web W retaininq droplets D of the material M, in the liquid carrier, before the material M is polymerized and cross-linked.
In the polymerizinq and cross-linking zone Z2~ the material M, as retained in the liauid :
carrier by the fibrous web W, in dispersed inclusions, is polymerized an~ cross-linked in situ, whereby the liquid carrier is evolved, so as to for~
a composite web W', which comprises the fibrous weh W
and dispersed inclusions of the Polvmerized, cross-linke~ material. Anv suitahle means rnot shown) for electron beam irradiation is ~referred as 2n a means for polymerizinq and cross-linkin~ the material M; an example is an Enerqv SciencesT~
(Model? C~300 accelerator, as available from Fnerqv Sciences, Inc. If electron beam irra~iation is used, -the fibrous web W retaining the material M, in the liquid carrier, in dispersed inclusions mav be initially exposed to 2 MRAD of such radiation on each side of the fibrous web W, and finally exposed to a curing dose of ~ MRAD on each side of the fibrous web W. Any other suitable techni~ue for electron beam irradiation may be instead used.
The composite web W' resultinq from electron beam irradiation of the fibrous web W retaining dispersed inclusions of the material M, in the liquid carrier, contains dispersed inclusions of the ~ -polymerized, cross-linked material, from which , J ~ 2 . ~ .

substantially all of the liquid carrier has evolved. ~- -If the polymerizable, cross-linkable material, in the liquid carrier, is an aqueous solution of fi concentration of 65~ neutralized ~on a weight basis~
potassium acrylate, as neutralized with potassium hydroxide, as in the example given above, such ~ -inclusions in the composite web W' are inclusions of a potassium polyacrylate, from which a substantial part of the liquid carrier, i.e., water, has evolve~
If the inclusions of the polvmerized, cross-linked material have superahsorbent pro~erties, the composite web W' may be further processed in known ways, e.g., compressed and cut-down to a useful ~ -size, whereupon the composite web W, as furt~er ~-processed, may be advantaqeouslv emploved in or as an absorbent article useful in a disposable diaper, tampon, sanitary napkin, wound dressinq, or similar of dissimilar product requirinq absorbent properties. The composite web W' may be also ~ ~
20 provided with one or more densified, paper-like ; ~ ~;
layers (not shown) in a manner disclosed in the Burgeni, Mesek et al., and Re~ke patents notefl above.
EXAMPLE 1 ;~
Two comparative samPles were made ;~
respectively by the improved method described above and by one of the conventional techniques dis~ussed above.
For each comparative sample, the fihrous weh `~
comprised 80% by wei~ht of the first composite fiber ~
30 noted above, and ~0~ by weight of the second - -composite fiber noted above, as carded into a ~ -nonwoven web havina a basis wei~ht of about 1.25 oz/yd2 and thermally bonded by subjectinq the nonwoven web to air heated to about ~sno F as the 35 nonwoven web was pulled throuqh a forced-air oven ~ --while the nonwoven web was supported on a screen.
..... : :
, . , ~. ~, ,~
: ,: : - ,.: ': ., - 2~2~2 For each comparative sample, the polymerizable, cross-linkable material, in a liquid _ carrier, was an aqueous solution of hn~ concentration of 65~ neutralize~ (on a wei~ht basis~ potass~um acrylate, as neutralized with potassium hv~roxi~e.
For one such sample, ~he aqueous solution was flooded onto the fibrous web while the fibrous web was supported on a screen, which served as a carrier, until the fibrous web was saturated. The saturated web, while supported on the screen servin~
as a carrier, was passed over a slot so as to be there exposed to a partial vacuum, which removed excess amounts of liquid until there was about a 7 to 1 ratio between the volume of liquid retained by the fibrous web and the weight of the fibrous web.
For the other sample, the fibrous web was moved through a zone wherein droplets of the aqueous solution were flicked onto opposite sides of the fibrous web, as the fihrous web was moved throuqh the zone, by the improved method described above. ~wo rotating brushes were used, one at each side of the fibrous web. Each brush had a diameter of about ln.~
inches at the tips of its bristles, which were made ---of nylon, as noted above, each havin~ an exposed 2S length of about l.R75 inches an~ a diameter of about 0.012 inch. Each brush was rotated, in the rotational senses described above, so that its ;
bristles picked up the aqueous solution from a rotating roller wiped by the bristles. Each roller 30 had a diameter of about 6.5 inches and a rotational ;
speed of about ~0 rpm. Each brush was above its `
associated roller. There was interference of about 0.2 inch between each brush and its associated roller. Each brush was rotated at a rotational speed 35 of about 600 rpm. The fibrous web W was moved ~-upwardly at a linear speed of about 6n fpm.

2 ~

For each comparative sample, the fibrous web retaining the aqueous solution was subiected to electron beam irradiation with an initial exposure of 2 MRAD on each side of the fibrous web, and wth a curing dose of P MRAD on each side of the fibrous web.
Demand absorbency of each comparative sample and free swell absorbency of each com~arative sam~le were determined, in each instance with a test liauid, which was an aaueous solution of 1~ sodium chlorid~
Demand absorbency of each comparative sample was determined under a sample pressure of n .5 psig and a 1~ cm negative head of the test liaui~ for thirtv minutes, after which the absorbed volume was measured. Free swell absorbency of each com~arative 15 sample was determined by allowina such comparative -sample to swell to its absorbent caPacitv for two ~;
hours, after which the swollen sam~le was drained , . , ; .: :v:: r . .. .
throuah filter paper until no more liauid ~raine~
from the swollen sam~le, whereu~on absorbed vo~ume `;:
was measured.
The following results were o~tained~

Web Demand Free Swell ~ -: .: ... .
Preparation Absorbency Absorbency Improved Method 13.7 ml/qm 27.0 ml~am ~;
Conventional Technique 1~.6 ml/qm 2n.6 ml/qm . ! . ' ~ Improvement 8.7~
-EXAMPLE ? ~ -Two comparative samples were maAe bv takina webs made per Example 1 and ~r$ndina them into powder.
Each comparative sample was ~around into a 3~ powder, wh$ch passed through a 2n mesh tU.~. mesh~
screen.

. .: .
.. . .... .
.... ..

2 ~ L ~ iP3 ~ ~ ~

Demand absorbency and free swell absorbencv of each comparative sample were determined, as in _ Example 1 discussed above.
The followina results were obtained:
Web Demand ~ree ~well Preparation Absorbencv AbsorbencY

Improved Method lP. n ml/gm ~ mJ/qm Conventional Technique 14.R ml/qm lq.q ml/gm n % Improvement , As given above, examples 1 and ~ are --believed to indicate that, if physical differences --tend to be largely nullified as by grindinq, a polymer having a given composition and resultina from ~ ;
the improved method used in each examPle has a molecular structure providing better absorbencv, as ;-compared to a polymer having the same comPosition but resulting from the conventional techniaue used in each example.
These examples demonstrate that the improved method is superior to the conventional coating technique used in these examples. The improved method is believed to be similarly superior to conventional coatinq techniaues emplovinq padders or s~ueeze rolls.
Moreover, the improved method is believed to ;~
be also superior to known spra~ing techni~ues 30 employing nozzles, particularly nozzles spraving in ~ -circular or oval patterns. As mentioned above, ;i nozzles used in such techniaues tend to provide non-uniform coverage, whereas the improved method can be readily controlled so as to provide more uniform coverage. Moreover, nozzles used in such sPrayin~

~ 2~2 techniques tend to plua or clo~ intermittently, whereas the improvea method does not reauire anv element capable of pluagin~ or clottinq.
From the foreqoinq, it will be observed that numerous modifications and variations can be effected without departing from the true sPirit and sco~e of the novel concept of the present invention. It is to be understood that no limitation with res~ect to the ;
specific embodiment illustrated herein is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.
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Claims

1. A method of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web, in which the material is to be polymerized and cross-linked, comprising the steps of:
(a) moving the fibrous web through a droplet-flicking zone; and (b) flicking droplets of the material, in the liquid carrier, onto the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of a rotating element picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, onto the fibrous web as the element rotates.

2. The method of claim 1 wherein the rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

3. The method of claim 2 wherein the bristles pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles as the brush and the roller rotate.

4. The method of claim 3 wherein the brush and the roller rotate about parallel axes.

5. The method of claim 4 wherein the brush and the roller rotate in opposite rotational senses.

6. The method of claim 1 wherein the flicking step comprises flicking droplets of the material, in the liquid carrier, onto opposite sides of the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of rotating elements picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, onto opposite sides of the fibrous web as the elements rotate, at least one of the rotating elements being adapted to flick droplets onto a respective one of opposite sides of the fibrous web as the fibrous web is moved through the droplet-flicking zone.

7. The method of claim 6, wherein each rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

8. The method of claim 7 wherein the bristles of each brush pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles of such brush as such brush and the roller wiped by the bristles of such brush rotate.

9. The method of claim 8 wherein each brush and the roller wiped by the bristles of such brush rotate about parallel axes.

10. The method of claim 9 wherein each brush and the roller wiped by the bristles of such brush rotate in opposite rotational senses.

11. A method of forming a composite web from a fibrous web and a polymerizable, cross-linkable material, in a liquid carrier, comprising the steps of:
(a) dispensing droplets of the material, in the liquid carrier, within the fibrous web, by the method of claim 1; and (b) polymerizing and cross-linking the material in situ, so as to form a composite web comprising the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked.

12. The method of claim 11 wherein the rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

13. The method of claim 12 wherein the bristles pick up the material in the liquid carrier, from a rotating roller wiped by the bristles as the brush and the roller rotate.

14. The method of claim 13 wherein the brush and the roller rotate about parallel axes.

15. The method of claim 14 wherein the brush and the roller rotate in opposite rotational senses.

16. The method of forming a composite web from a fibrous web and a polymerizable, cross-linkable material, in a liquid carrier, comprising the steps of:
(a) dispensing droplets of the material, in the liquid carrier, within the fibrous web, by the method of claim 6; and (b) polymerizing and cross-linking the material in situ, so as to form a composite web comprising the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked.

17. The method of claim 15 wherein each rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

18. The method of claim 17 wherein the bristles of each brush pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles of such brush as such brush and the roller wiped by the bristles of such brush rotate.

19. The method of claim 18 wherein each brush and the roller wiped by the bristles of such brush rotate about parallel axes.

20. The method of claim 19 wherein each brush and the roller wiped by the bristles of such brush rotate in opposite rotational senses.

21. A method of dispersing droplets of two different, polymerizable, cross-linkable materials, each material in a liquid carrier for such material, within a fibrous web, in which said materials are to be polymerized and cross-linked, comprising the steps of (a) moving the fibrous web through a droplet-flicking zone; and (b) flicking droplets of a different one of said materials, in the liquid carrier therefor, onto each side of the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of a rotating element picking up the said one of said materials, in the liquid carrier therefor, onto such side of the fibrous web as the element rotates.

22. The method of claim 21 wherein each rotating element is a brush with bristles picking up a different one of said materials, in the liquid carrier therefor, as the brush rotates.

23. The method of claim 22 wherein the bristles of each brush pick up a different one of said materials, in the liquid carrier therefor, from a rotating roller wiped by the bristles of such brush as such brush and the roller wiped by the bristles of such brush rotate.