CA1104782A

CA1104782A - Absorbent films and laminates

Info

Publication number: CA1104782A
Application number: CA279,440A
Authority: CA
Inventors: Robert E. Erickson; Richard M. Krajewski
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1976-06-07
Filing date: 1977-05-30
Publication date: 1981-07-14
Also published as: DE2725736A1; AU516746B2; FR2354184B1; GB1589431A; FR2354184A1; JPS6140693B2; SE427278B; AU2579177A; SE7706634L; US4117184A; JPS52150463A

Abstract

Abstract of the Disclosure This invention is directed to water swellable films of a lightly crosslinked polyelectrolyte and to a method for their preparation. Films of this invention are characterized by having a density of 0.3 to 1.1 grams per cubic centimeter and a water absorbence rate of not greater than 60 seconds. The films are useful wherever aqueous solutions such as, for example, urine and blood, need to be absorbed. Examples of the diverse utilities include catamenial tampons, diapers/ paper towels, disposable door mats, disposable bath mats, and disposable litter mats for household pets.

18,045-F

Description

llf3'~7~32 Water swellable films of lightly crosslinked polyelectro-lytes and methods for their preparation are known in the art. It is also known to employ crosslinked polymeric sorbents between flexible supports in such items as disposable diapers and dress-ings. The known water swellable films oE lightly crosslinked polyelectrolytes are not able to rapidly absorb a deluge of an aqueous fluid so as to prevent the fluid from flowing off to the water swellable film.
The present invention provides a water swellable film of a lightly crosslinked alkali metal carboxylic polyelectrolyte wherein the film has a density of from 0.3 to 1.1 grams per cubic centimeter and a water absorbency rate of not greater than 60 seconds.
In a second embodiment the present invention provides a method of making a water swellable film of a lightly crosslink-ed alkali metal carboxylic polyelectrolyte which comprises:
(1) mixing the polyelectrolyte with the crosslinking agent in a water and/or lower alcohol solution;

(2) mechanically aerating the solution of the polyelec-trolyte and the crosslinking agent;

(3) casting a wet film of the solution on an impervioussupport; and

(4) heating the film to a temperature of from 30C to 175C to crosslink the polyelectrolyte and to remove substanti-ally all of the solvent.
In a third embodiment the present invention provides a method of making a water swellable laminate which comprises:
(1) mixing an alkali metal carboxylic polyelectrolyte with a crosslinking agent in a water and/or lower alcohol solu-tion, (2) mechanically aerating the solution of the polyelectro-lyte and the crosslinking agent, , .~_-r ' 1 ~.

'. .

~1~}47~2 (3) casting a wet film of the solution on an impervious support, (4) heating the film to a temperature from 30 to 175 C
to crosslink the polyelectrolyte and remove substantially all of the solvent,

(5) contacting the film while it is still wet with wick-ing substrate to form a laminate, and

(6) completing the drying of the laminate.
In a fourth embodiment the present invention provides a water swellable laminate comprising a wicking substrate and a water swellable film of a lightly crosslinked alkali metal carboxylic polyelectrolyte wherein the film has a density of from 0.3 to 1.1 grams per cubic centimeter and a water absorbency rate of not greater than 60 seconds. Preferably during heating and crosslinking, forced hot air .~ ~
-la-,

7~2 at a temperature of from 100 to 200C is impinged on the surface of the film. After the film is dried, it is stripped off the support as an intact film. The films of this invention usually have a thickness of from 0.1 to 10 mils (2.5 to 254 micrometers), preferably 1 to 3.5 mils (25 to 89 micrometers).
Polyelectrolytes useful in this in~ention must be essentially water soluble in the salt form. Examples of useful polyelectrolytes include ammonium or alkali metal salts of homopolymers of acrylic or methacrylic acid and copolymers with one or more ethylenically unsaturated comonomers.
Preferably the polyelectrolyte is a partially saponified polyacrylate polymer. The polymer before saponification is the result of reacting together a mixture of monomers which comprises (1) 30 to 92 percent by weight of an alkyl acrylate wherein the alkyl group has from 1 to 10 carbon atoms, an alkyl methacrylate wherein the alkyl group has from 4 to 10 carbon atoms, or mixtures thereof; (2~ 8 to 70 percent by weight of an olefinically unsaturated carboxylic acid; and (3) 0 to 15 percent by weight of an omega hydroxyalkyl acrylate wherein the hydroxyalkyl groups has from 1 to 4 carbon atoms.
Examples of useful alkyl acrylates include methyl acrylate, ethyl acrylate, propyl acrylate and hexyl acrylate. Examples of useful alkyl methacrylates include butyl methacrylate, hexyl methacrylate, octyl methacrylate and decyI methacrylate. Example of useful omega hydroxy-alkyl acrylates include 2-hydroxyethyl acrylate, hydroxy-methyl acrylate, 3-hydroxypropyl acrylate and 4-hydroxy-butyl acrylate.

18,045-F -2-~4782 The olefinically unsaturated carboxylic acids !
useful in this invention are mono or polycarboxylic acids.
Examples of monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, and isocrotonic acid.
Examples of polycarboxylic acids include maleic acid, fumaric acid, and itaconic acid.
The foregoing polyacrylates are then dissolved in an aqueous alkali metal hydroxide solution. The amount of hydroxide solution employed is sufficient to saponify some of the acrylate esters to alkali metal - carboxylates and to neutralize the carboxylic groups of the polyacrylate to alkali metal carboxylates so that the saponified polyacrylate polymer has from 30 to 70 weight percent alkali metal carboxylates.
The partially saponified polyacrylate polymer is employed as a solution containing from 5 to 60 percent by weight of the polymer. It is preferred to use alkali--soluble latices having from 15 to 60 weight percent non-volatile polymer solids.
Crosslinking agents useful in this invention are di- or polyfunctional compounds that are reactive with carboxylate groups. Examples of suitable crosslinking agents include polyhaloa~lkanols such as 1,3-dichloroiso-propanol; 1,3-dibromoisopropanol; sulfonium zwitterions such as the tetrahydrothiophene adduct of novolac resins and bisphenol A; haloepoxyalkanes such as epichlorohydrin, epibromohydrin, 2-methyl epichlorohydrin and epiiodohydrin;
polyglycidyl ethers such as 1,4-butanediol diglycidyl ether, glycerine-1,3-diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 18,045-F -3-~04~8~

diethylene glycol diglycidyl ether, neopentyl glycol ~iglycidyl ether, polypropylene glycol diglycidyl ethers having an epoxy equivalent weight range from about 175 to about 380, bisphenol A-epichlorohydrin epoxy resins having an epoxy equivalent weight range from about 182 to about 975 and mixtures of the above.
Also useful as crosslinking agents are mono-meric amino~epihalohydrin adducts prepared by reacting at least two moles of an epihalohydrin with one mole of various monoamines, diamines and triamines at a tempera-ture in the range from 0 to 90C for a time period of 0.5 to 8 hours. The reaction is carried out in a reaction media containing 20 to 90 percent water, lower alcohols such as methanol or ethanol, or in aqueous solutions of the lower alcohols. The amine-epihalohydrin adducts are used directly as made without separation or concentration.
The amino-epihalohydrin adducts used herein are known to have a plurality of 3-halo-2-hydroxy-propyl and azetidinium groups as is shown by Ross, et al. J. Organic Chemistry 29:824-6 (1964).
Examples of useful monoamines are ammonia, ethyl amine, methyl amine, and propyl amine.
Examples of useful diamines are triethylene diamine, bis-2-aminoethyl ether, N,N-dimethyl ethylene diamine, piperazine, and ethylenediamine.
Examples of useful triamines are N-aminoethyl piperazine, and diethylene triamine.
The epihalohydrins used herein can be epichloro-hydrin, epibromohydrin and epiiodohydrin. Epichlorohydrin is preferred because of its lower cost and availability.

18,045-F _4_ Preferably the crosslinking agents are polyamide--polyamine/epichlorohydrin adducts. They are produced commercially by Hercules Incorporated under U.S. Patent 2,926,154. They are prepared by reacting a polyalkylene polyamine with a saturated dicarboxylic acid having from 3 to 10 carbon atoms. The molar ratio of the polyalkylene polyamine to dicarbo~ylic acid is from 0.8:1 to 1.4:1. The reaction temperature i5 from 110C to 250C and the reaction time is from 0.25 to 2 hours. The polyamide so produced is reacted with epichlorohydrin. The molar ratio of epichlorohydrin to secondary amine groups of the polyamide is from 0.5:1 to 1.8:1. The reaction temperature is from 45C to 100C. The pH of aqueous solutions of the adduct is reduced to such an extent that 10 percent and 25 percent aqueous solutions thereof have a pH not in excess of 6 and 4, respectively. The structure of these adducts has been discussed in an article by M. E. Carr et al., Journal of Applied Polymeric Science, Volume 17, pages 721-735 (1973).
For the purpose of this invention, a water swellable polyelectrolyte is defined as one which adsorbs greater than 15 times its weight of synthetic or natural urine. Preferably the absorbency should be in the range from 20-40 gram of urine per gram of polyelectrolyte or in the range of 90-250 grams of deionized water per gram of polyelectrolyte. The level of crosslinking agent used is a variable factor which is dependent upon the particular polyelectrolyte used and the molecular weight of the polyelectrolyte. In general, the amount used varies from 0.5 to 5.0 percent based on the weight of the polyelectro-18,045-F -5-~L~1q34~8;~

lyte. However, this range varies for each polyelectrolyte in order to adjust the absorbency of the final crosslinked gel.
In order to obtain very high production rates of the absorbent films, it may be desirable to replace part or nearly all of the water in the polyelectrolyte solution with a lower alcohol such as methanol or ethanol.
This substitution results in lower solution viscosities at a given percent solids and promotes rapid drying.
It is sometimes desirable to add a small amount of a surfactant to the polyelecttolyte composition to aid in flowing on and removing the continuous film from the water impervious substrate. A secondary bene-fit of using a surfactant is to increase the wettability of the final dry absorbent film. Either nonionic or cationic surfactants may be used. Examples of useful surfactants include polyoxyethylene sorbitan monolaurate, sorbitan monolaurate, nonylphenoxy polyoxyethylene (C6-10), polyglycerol ester of fatty acids, polyethylene (5) glycol cocoate, and lauric alkylaolamine.
The water swellable films of this invention may be combined into laminates with wicking or non-wicking substrates. Examples of wicking substrates include woven fabrices, non-woven fiber mats, polymeric foams, tissue paper, crepe paper and toweling. Examples of non-wicking substrates include polymer films such as polyethylene, polypropylene and polystyrene; and hard surface papers such as Kraft and writing paper.
An absorbent laminate may be prepared by coating a suitable substrate with the composition of the poly-18,045-F _~_ ~`4782 electrolyte which is air frothed or blown with air and t:hen the coating is crosslinked. It is to be understood 1;hat for the purposes of this invention the coating step :implies a complete coating or a discontinuous coating, thus when a fiberous substrate such as, for example, cellulose batting, paper, woven or non-woven cloth, and polyurethane foam are used as the substrate, the composition can be applied in a discontinuous manner, i.e., in a pattern of large dots, strips, squares, or grid lines to retain the inherent flexibility of the fiberous substrate and at the same time vastly improve its water absorbency.
The final products of the present invention are thus rapidly water swellable and are useful wherever aqueous solutions such as, for example, urine and blood need to be absorbed. Examples of the diverse utilities include catamenial tampons, diapers, paper towels, dispos-able door mats, disposable bath mats and disposable litter mats for household pets.
Examples 1 through 5 and _omparative Runs A through E
Polyelectrolyte A employed in ~xamples 1 through 5 and Comparative Runs A through E was prepared from a polymeric latex that contained 83 mole percent ethyl acrylate and 17 mole percent methacrylic acid. The latex `
was saponified with sodium hydroxide to the extent that the polymer of polyelectrolyte A contained 50 mole percent ethyl acrylate, 33 mole percent sodium acrylate and 17 mole percent sodium methacrylate. Polyelectrolyte A
contains 25.8 weight percent solids.
Crosslinking Agent B employed in Examples 1 and 2 and Comparative Runs A and B was a liquid adduct of 18,045-F -7-epichlorohydrin and a polyamide-polyamine. Crosslinking agent B contains 4.2 weight percent solids, 4.3 weight percent nitrogen and has a pH between 4.6 and 4.9.
Crosslinking Agent C employed in Example 3 and Comparative ~un C was a methanol solution containing 5 weight percent of an polyglycol diepoxide having an EEW
of 181.
Crosslinking Agent D employed in Example 4 and Comparative Run D was a 5 percent by weight solution of an epichlorohydrin adduct of piperazine prepared by reacting 2 moles of epichlorohydrin with one mole of piperazine.
Crosslinking Agent E employed in Example 5 and Comparative Run E was a 24 weight percent solution of a cyclic sulfonium zwitterion of bisphenol A in water. The cyclic sulfonium zwitterion was prepared by reacting 2 moles of tetrahydrothiophene with one mole of bisphenol A.
Surfactant F employed in Examples 1, 3, 4, and 5 and Comparative Runs A, C, D, and E is polyoxy-ethylene sorbitan monolaurate.
In Example 1, Polyelectrolyte A, Crosslinking Agent B, Surfactant D, and additional water were mixed in a high speed blender for one minute. During the mixing air was entrapped in the formulation increasing the volume of the formulation by about 50 percent. The mixed formula-tion was cast on a commercial release coated paper employing a 15 mil (.38 mm) gap casting bar. The wet film was dried in an air circulating oven at 250F (121C) for 20 minutes.
The film was allowed to condition at 50% relative humidity for 1 hour and was then removed from the release coated paper.

18,045-F -8-~V47~2 In Comparative Run A, the same formulation was prepared but it was only mixed in the normal manner of ~paddle mixing with a minimum amount of air entrapped in the mixed formulation. The mixed formulation was cast on a commercial release coated paper with a 20 mil (.51 mm) gap casting bar.
In Example 2 and Comparative Run B, the same procedures were followed as in Example 1 and Comparative Run A, respectively, except that the formulations did not contain Surfactant D.
In Example 3 and Comparative Run C, the same procedures were followed as in Example 1 and Comparative Run A, respectively, except that Crosslinking Agent C was employed in place of Crosslinking Agent B, and the films were dried at 347F (175C).
In Example 4 and Comparative Run D, the same procedures were followed as in Example 1 and Comparative Run A, respectively, except that Crosslinking Agent D
was employed in place of Crosslinking Agent B and the mixed formulation was cast on a glass plate that con-tained a release coating. The glass plate was heated to 250F (121C) before the formulation was cast. The wet film was dried in an air circulating oven at 250F
(121C) for 20 minutes.
In Example 5 and Comparative Run E, the same procedures were followed as in Example 4 and Comparative Run D, respectively, except that Crosslinking Agent E
was employed in place of Crosslinking Agent D and the films were dried at 250F (121C) for 30 minutes.

18,045-F _g_ ~4~2 Water absorbency rates were determined for all films from Examples 1 through 5 and Comparative Runs A through E. The water absorbency rate was measured by placing a 1 by 3 inch (2.5 by 7.6 cm) sample of a water swellable film on the 4.5 by 8 inch (11.4 by 20.3 cm) glass plate base of a stereoscopic microscop~. One drop of deionized water was gently placed on the surface of the film and observed through the microscope at 20X
magnification. The number of seconds required for the drop of water to be completely absorbed by the film was the absorbency rate. Complete absorption means all motion and/or swelling of the film ceases.
The formulations and properties of the films produced in Examples 1 through 5 and Comparative Runs A through E are shown in Table 1.

18,045-F -10-, ~47~3Z
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t~oO In O~ O _I
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~4P U UU U u~ 3 p~ ~ E4 1¢

18, 045--F --12--~47~

The mixing of the formulation in Examples 1 through 5 in a blender entraps air in the formulation.
When the formulation was dried to a film, the film was observed to have small air bubbles in the film and craters from opened air bubbles on the surface of the film.
The examples of aerated films show markedly improved absorbency rates over the Comparative Runs of unaerated films.
~xamples 6, 7, 8, 9, and 10 In Example 6, the formulation of Example 1 was mixed in a blender by first adding Polyelectrolyte A, Surfactant D and the water and then slowly adding Cross-linking Agent B. The mixed formulation was placed in a paint pressure pot and pressure fed to a metering pipe in front of a casting bar on the top surface of a heated steel drum coated with polytetrafluoroethylene at a rate sufficient to minimize puddle formation in front of the casting bar.
The steel drum was 12 inches (30.5 cm) in diameter and 21 inches (53.3 cm) long. The drum was heated to 215F (102C) and rotated at a surface speed of 2.2 feet per minute (.67 meters per minute). The cast wet film had a thickness of 15 mils (0~38 mm).
The film was allowed to dry on the drum for 1.5 minutes and then removed from the surface of the drum dryer.
The film, containing between 8 and 10 weight percent moisture, was wound on a cardboard core and packaged in a polyethylene bag to retain the moisture in the film and thus maintain the flexibility of the film.

18,045-F -13-~4~

In Example 7, the procedure of Example 6 was repeated with the addition that after the film had rotated 6 inches (15.2 cm), it then passed under a forced hot air blower where the air at about 400F (204C) impinged directly on the surface of the wet film. This additional step facilitated more rapid drying of the film and caused a surface blistering or roughening which resulted in a fast absorbency rate.
In Example 8, the procedure of Example 6 was repeated with the additional step of having a crimped paper tissue, 25 pounds (11.3 kilograms) per reem, fed onto the outside of the wet film within the first 6 inches (15.2 cm) of drum travel. Two hot air blowers held the tissue against the film surface during drying.
The laminate was removed from the drum and wound on a cardboard core.
In Example 9, the procedure of Example 8 was repeated with the variation that the film was dried to about 8 weight percent moisture. Next the surface of the film was moistened with a water mist. Then the tissue was pressed against the moistened surface of the film.
The film and tissue were passed under a pressure roll (about 1.2 psi) so that the tissue was lightly bonded to the surface of the film. The laminate was wound on a cardboard core.
In Example 10, the same procedure of Example 6 was repeated with the variation that the formulation was cast by reverse roll on a 46 inch (117 cm) wide stainless steel endless belt coated with a silicone release agent and traveled at a rate of 20 feet per 18,045-F -14-' :., .

1~4782 minute (6 meters per minute). The endless belt containing the wet film was passed through a hot air oven at 200F
(93C) where the film was cured and dried in a residence time of 1.85 minutes. After leaving the oven, the film was removed from the endless belt, wound on a cardboard core and stored.
The thicknesses, densities and absorbency rates for the films of Examples 6, 7, 8, 9, and 10 are reported in Table II.

18,045-F -15-478~:
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P~ ~ ~ ~

18, 045-F --16--, .: : ~ i -

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A water swellable film of a lightly crosslinked alkali metal carboxylic polyelectrolyte wherein the film has a density of from 0.3 to 1.1 grams per cubic centimeter and a water absorb-ency rate of not greater than 60 seconds.

2. The film of claim 1 wherein the film has a density of from 0.5 to 0.9 grams per cubic centimeter.

3. The film of claim 2 wherein the film has a water absorb-ency rate of not greater than 50 seconds.

4. The film of claim 1 wherein the lightly crosslinked alkali metal carboxylic polyelectrolyte is a lightly crosslinked saponified alkyl acrylate copolymer obtained by saponifying a polymer derived from:
(a) 30 to 92 percent by weight of an alkyl acrylate wherein the alkyl group has from 1 to 10 carbon atoms; or of an alkyl methacrylate wherein the alkyl group has from 4 to 10 carbon atoms; or of a mixture thereof;
(b) 8 to 70 percent by weight of an olefinically unsatur-ated carboxylic acid; and (c) O to 15 percent by weight of an omega-hydroxyalkyl acrylate, wherein the alkyl group has from 1 to 4 carbon atoms;
and which contains from 30 to 70 weight percent of alkali metal carboxylates.

5. The film of claim 1 wherein the lightly crosslinked alkali metal carboxylic polyelectrolyte is a saponified ethyl-acrylate/methacrylic acid copolymer containing 50 mole percent ethyl acrylate units; 33 mole percent sodium acrylate units, and 17 mole percent sodium methacrylate.

6. A method of making a water swellable film of a lightly crosslinked alkali metal carboxylic polyelectrolyte which com-prises:
(1) mixing the polyelectrolyte with the crosslinking agent: in a water and/or lower alcohol solution;
(2) mechanically aerating the solution of the polyelec-trolyte and the crosslinking agent;
(3) casting a wet film of the solution on an impervious support; and (4) heating the film to a temperature of from 30°C to 175°C to crosslink the polyelectrolyte and to remove substantial-ly all of the solvent.

7. The method of claim 6 wherein during step (4) hot air at a temperature of from 100°C to 200°C is impinged on the sur-face of the film.

8. The method of claim 6 wherein the alkali metal carboxylic polyelectrolyte is a polymer derived from:
(a) 30 to 92 percent by weight of an alkyl acrylate wherein the alkyl group has from 1 to 10 carbon atoms; or of an alkyl methacrylate wherein the alkyl group has from 4 to 10 carbon atoms; or of a mixture thereof;
(b) 8 to 70 percent by weight of an olefinically unsatur-ated carboxylic acid; and (c) 0 to 15 percent by weight of an omega-hydroxyalkyl-acrylate, wherein the alkyl group has from 1 to 4 carbon atoms;
and which contains from 30 to 70 weight percent of alkali metal carboxylates.

9. The method of claim 6 wherein the alkali metal carboxy-lic polyelectrolyte is a saponified ethyl acrylate/methacrylic acid copolymer containing 50 mole percent ethyl acrylate units;
33 mole percent sodium acrylate units, and 17 mole percent sodium methacrylate.

10. The method of claim 6 wherein the crosslinking agent is a di- or polyfunctional compound reactive with carboxylate groups.

11. The method of claim 6 wherein the crosslinking agent is chosen from the group comprising liquid adducts of epichlorhydrin with a polyamide-polyamine; a polyglycol diepoxide; an adduct obtained by reacting 2 moles of epichlorhydrin and 1 mole of piperazine; and a cyclic sulfonium zwitterion obtained by reacting 2 moles of tetrahydrothiophene and one mole of 2,2-(4'-hydroxy-phenyl)-propane.

12. A method of making a water swellable laminate which comprises (1) mixing an alkali metal carboxylic polyelectrolyte with a crosslinking agent in a water and/or lower alcohol solu-tion, (2) mechanically aerating the solution of the polyelec-trolyte and the crosslinking agent, (3) casting a wet film of the solution on an impervious support, (4) heating the film to a temperature from 30 to 175°C
to crosslink the polyelectrolyte and remove substantially all of the solvent, (5) contacting the film while it is still wet with wick-ing substrate to form a laminate, and (6) completing the drying of the laminate.

13. The method of claim 12 including the further step of moistening the surface of the film with water after completing the heating of step (4) and before the contacting of step (5).

14. The method of claim 8 or 9 wherein the wicking substrate is a crimped paper tissue.

15. The method of claim 8 or 9 wherein during step (4) hot air at a temperature of from 100°C to 200°C is impinged on the surface of the film.

16. The method of claim 8 or 9 wherein the alkali metal carboxylic polyelectrolyte is a polymer derived from:
(a) 30 to 92 percent by weight of an alkyl acrylate wherein the alkyl group has from 1 to 10 carbon atoms; or of an alkyl methacrylate wherein the alkyl group has from 4 to 10 carbon atoms; or of a mixture thereof;
(b) 8 to 70 percent by weight of an olefinically unsatur-ated carboxylic acid; and (c) 0 to 15 percent by weight of an omega-hydroxyalkyl-acrylate, wherein the alkyl group has from 1 to 4 carbon atoms;
and which contains from 30 to 70 weight percent of alkali metal carboxylates.

17. The method of claim 8 or 9 wherein the alkali metal car-boxylic polyelectrolyte is a saponified ethylacrylate/methacrylic acid copolymer containing 50 mole percent ethylacrylate units;
33 mole percent sodium acrylate units, and 17 mole percent sodium methacrylate.

18. The method of claim 8 or 9 wherein the crosslinking agent is a di- or polyfunctional compound reactive with carboxylate groups.

19. The method of claim 8 or 9 wherein the crosslinking agent is chosen from the group comprising liquid adducts of epichlor-hydrin with a polyamide-polyamine; a polyglycol diepoxide; an adduct obtained by reacting 2 moles of epichlorhydrin and 1 mole of piperazine; and a cyclic sulfonium zwitterion obtained by re-acting 2 moles of tetrahydrothiophene and one mole of 2,2-(4'-hydroxyphenyl)-propane.

20. A water swellable laminate comprising a wicking substrate and a water swellable film of a lightly crosslinked alkali metal carboxylic polyelectrolyte wherein the film has a density of from 0.3 to 1.1 grams per cubic centimeter and a water absorb-ency rate of not greater than 60 seconds.

21. The water swellable laminate of claim 20 wherein the film has a density of from 0.5 to 0.9 grams per cubic centimeter.

22. The water swellable laminate of claim 20 wherein the film has a water absorbency rate of not greater than 50 seconds.

23. The water swellable laminate of claim 20 wherein the lightly crosslinked alkali metal carboxylic polyelectrolyte is a lightly crosslinked saponified alkyl acrylate copolymer obtained by saponifying a polymer derived from:
(a) 30 to 92 percent by weight of an alkyl acrylate wherein the alkyl group has from 1 to 10 carbon atoms; or of an alkyl methacrylate wherein the alkyl group has from 4 to 10 car-bon atoms; or of a mixture thereof;
(b) 8 to 70 percent by weight of an olefinically unsatur-ated carboxylic acid; and (c) 0 to 15 percent by weight of an omega-hydroxyalkyl acrylate, wherein the alkyl group has from 1 to 4 carbon atoms;
and which contains from 30 to 70 weight percent of alkali metal carboxylates.

24. The water swellable laminate of claim 20 wherein the lightly crosslinked alkali metal carboxylic polyelectrolyte is a saponified ethylacrylate/methacrylic acid copolymer containing 50 mole percent ethyl acrylate units; 33 mole percent sodium acrylate units, and 17 mole percent sodium methacrylate.

25. The water swellable laminate of claim 20 wherein the wick-ing substrate is a crimped paper tissue.