CA1318655C

CA1318655C - Immobilizing particulate absorbents by conversion to hydrates

Info

Publication number: CA1318655C
Application number: CA000577822A
Authority: CA
Inventors: John M. Lesniak; Franklin Boardman; Wayne G. Koci; James E. Mccann
Original assignee: Johnson and Johnson
Current assignee: Johnson and Johnson
Priority date: 1987-09-21
Filing date: 1988-09-19
Publication date: 1993-06-01
Anticipated expiration: 2010-06-01
Also published as: EP0309187B1; DE3856353D1; EP0309187A2; PT88560B; GR880100616A; ZA887023B; PT88560A; US4826880B1; ES2133267T3; BR8804860A; GR1000150B; DE3856353T2; PH24708A; EP0309187A3; MX165440B; ATE182471T1; AR247751A1; US4826880A; AU2223788A; JPH01230671A

Abstract

ABSTRACT OF THE DISCLOSURE

The invention provides absorbent compositions, a method for handling and immobilizing particulate absorbents and absorbent articles produced therefrom.
Absorbent materials such as cross-linked, water-soluble and water-swellable particulate polymers are immobilized and safely handled by adding thereto an aqueous liquid such as water or saline in amounts sufficient to form hydrates in which the water comprises from 20% to 80% by weight of the total hydrate. The hydrates may be extruded, sprinkled, or sprayed and can be incorporated into absorbent articles such as diaper and tampons by conventional means. The hydrates unexpectedly increase the total water absorbency of the absorbent on a dry basis.

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Description

1 ~1 8655 IMMOBILIZING PARTICULATE
ABSO BENTS BY CONVERSION TO HYDRATES

BACRGROUND OF THE INVENTION

The present invention relates to absorbent compo~itions, a method for handling and immobilizing particulate absorbents and absorbent articles produced therefrom.
~ bsorption of mobile aqueous liquids have conventionally been accompli~hed by the ~se of sponge or batting. ~ore recently, water-insoluble but water-swellable polymers having high absorptive capacity have been developed for immobilizing water and aqueous fluids.
These polymers are particula~e, i.e., pulverulent or granular and have no structural integrity. They are frequently referred to in the art as ~superabsorbents~, ~hydrogelsU or ~hydrocolloids~ and have been incorporated in the cellulosic absorbent structure of diapers, sanitary napkins and other absorbent articles to increase their absorptive efficiency. The expected advantage of incorporating these particulate materials is diminished by the shifting of the particulate materials generally requiring special construction to immobilize them within the structure of the articles.
These particulate absorbents also present a health hazard to both the manufacturers and users because the particulates can be inhaled and swell inside the respiratory passages on contact with water vapor or liquid.
In an effort to overcome these disadvantages methods of treating such parSiculate polymer6 with liquids to immobilize them have been described in the art.
For example, in U.S. Patent No. 4,410,571 immobilized superabsorbent compositions are de6cribed which are prepared by mixlng a water-insoluble, water-swellable polymer absorbent and a liquid polyhydroxy J&J 1227 organic compound auch as glycerol or ethylene glycol. In this manner the superabsorbent is converted to a non-particulate immobilized form which can be foamed and is rendered self-supporting.
In U.S. Patent No. 4,605,401, an absorption ~aterial is provided consisting of an absorbent permanently fixed on or in a support material obtained by treating the support material with a partially water-softened absorbent followed by drying. The preferred absorption material is an absorbent softened with an organic solvent containing up to 60~ water.
U.S. Patent No. 4,444,830 deals with an aqueous polymer solution containing from 5~ to 60% by weight of polymer which is formulated into an absorbent composition.
The aqueous polymer solution is coated on a base fluffing material, dried and the dried coated substrate iB
disintegrated into an absorbent hydrophilic fluff.

SUMMARY OF THE INVENTION

The present invention provides a method of safely handling or immobilizing water insoluble, water 6wellable absorbents by employing an aqueous liquid such as water as the treating medium to form an absorbent hydrate.
It has been found that water alone is an excellent adjunct for the ab~orbent rendering it safe to handle, and significantly reducing the cost of treatment of the absorbent in relation to organic liquids herein-b~fore described. It has also been found that absorbent hydrates comprising water and absorbent according to the present invention can be formed which increase the water absorbency or retention capacity of the ~uper-absorbent under pressure rather than reducing such absorbency or retention as might be expected.
The hydrates are formed by merely adding an aqueous liquid 6uch as water or saline to the super-absorbent with mixing in amounts sufficient to comprise J&J 1227 from 20~ to ~0% by weight of total composition. Theresulting hydrates may be e~trudable and can be incorpoeated into absorbent articles by conventional extrusion techniques, or ~ay be sprinkled or sprayed onto absorbent articles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, the addition of water to an absorbent ~aterial immobilizes the absorbent material rendering it safe to handle. When the absorbent material iB mixed with water it can be incorporated into absorbent products such as diapers, tampons and the like.
The hydrates are themselves absorbent and based on the dry superabsorbent content of the hydrate may absorb more water than dry absorbent alone. When incorporated into absorbent material such as fluffy wood pulp they retain ~ore water than the fluffly wood pulp alone and almost as much as dry absorbent incorporated into the pulp.
The hydrates can be extruded without expanding to a uniform consistency and can be applied to a temporary or ultimate surface. The ultimate surface is hereinafter referred to as the substrate. For making a film, sheet, or coated substrate, any method of application conventionally employed for coating or preparing films, e.g. knife-coating, spray-coating, reverse-roll coating, gravure-coating, cold extrusion coating or casting, sprinkling and the l$ke, may be employed. Preferred methods are cold extrusion coating and 6prinkling.
~ hen use as a coating on a substrate is contemplated, the substrate is of materials generally employed for absorbent articles, such as cellulose, vinyl films, polypeopylene, polyester, polyethylene, nylon, metal foils, elastomers, cloth, nonwovens of various fibers, and the like. Coating on a substrate may be of the entire surface of the substrate, in ~trips, in rows, or in any other predetermined pattern.

J~J 1227 I 3 1 ~655 The amount of water used in forming the hydrates of the invention may vary from about 20~ to 80~ by weight of the total weight of the composition and pre~erably from about 30~ t~ 50% by weight of the composition, the remainder being absorbent.
The hydrates are prepared quite easi~y by merely co~bining the absorbent and wa~er with mixing until a tacky, agglo~erate is formed.
The actual amounts of absorbent in the hydrate6 within the scope previously indicated i8 dependent on the level of absorption required in ~he ultimate environment.
Thus, if the absorption is to be accomplished by a diaper, and the subctrate is a diaper pad, the hydrate will contain absorbent sufficient to supply the desired lS absorptive capacit, in the pad substrate. The hydrates are useful in the manufacture of numerous absorbent articles. They are especially useful where high capaci~y is desirable, such as in articles to be worn. Thus, they are particularly useful for diapers and incontinence pads, and also for sanitary napkins, bandages and the like. In diapers, the absorbent hydrates may be used as the sole absorbent or as a component improving the quality of the existing absorbent. In the manufacture of diapers in which the hydrate is incorporated as an improvement to the li~uid receiving portion of the diaper, the hydrate is applied to the Rurface of the aqueous liguid receiving portion of the article, namely batting, and the resulting modified batting provided with moisture impermeable backing and a moisture permeable top sheet. Alternative-ly, the absorbent hydrate may be coated on a conventionalnon-ab30rbent moisture impermeable diaper backing without batting and thereafter laminated with a conventional moisture permeable top sheet to provide a thin diaper.
In the case of sanitary napkins, the hydrates ~ay be applied to the cellulosic absorbent surface and wrapped in a conventional manner to produce a napkin of improved absorbent capacity.

J~J 1227 1 3 1 ~655 , . , In the case of bandages, the hydrates may be coated onto an aqueous liquid permeable but gel impervious ~aterial, e.g. non woven fabrics such as rayon or polyester fabrics, and then inserted in the gauze bandage.
The e~pression ~absorbent~ r~fers to ~ater-insoluble, water-swellable polymers as hereinafter described having an enhanced capacity for removing water or aqueou~ fluids. The water-insoluble, water-swellable polymers are lightly cro6s-linked polymers containing a plurality of hydrophilic groups, such as carboxyl, carboxamide, sulfonate salt or hydroxyl groups, along the polymer chain in sufficient porportions so tha~ the polymer would be water-soluble if it were not for the crosa-linking thereof. ln these polymers, the hydrophilic qroups constitute at least 25% and up to 72~ of the molecular 6tructure. The materials are of sufficient molecular weight or degree of cross-linking to be water insoluble while being water-swellable. Many of the suitable materials are those which have been reported to have an average molecular weight per cross-linkage in the range of from about 13,000 to about 300,000 but are not limited thereto. The most common and best known of such materials are polyacrylate modified polysaccharides, cross-linked ~ynthetic polyacrylates such as sodium and potas~ium poly(methacrylates), cross-linked carboxymethyl-celluloses or cross-linked poly(alkylene oxides) as hereinafter defined. Other graft polymers of poly-saccharides and natural gums such as xantham gum, locust gu~, guar gum and the like or blends thereof are al60 suitable provided they meet the requirements of water insolubility and water ~wellability. One such polymer is a 6tarch grafted polyacryla~e. The water-insoluble, water-swellable polymers have a gel capacity of at least about 10. 8y ~gel capacity~ i8 meant the weight of aqueou~ fluid which can be imbibed and held per unit weight of polymer, i.e., grams of fluid per gram of polymer. Stated another way, the absorbent polymers have J&J 1227 an ~bsorbent capacity of at least 10 times the weight of the material 1n dry form. The capacity may be up to 1500 times or more of the weight of the material in dry form;
commonly it i5 about lS to 70 times the dry weight. The materials are frequently spoken of in the art as ~hydrogels~, ~hydrocolloids~ or ~superabsorbents~. Many of the water-6wellable polymers are available commercially.
The polymers are used 1n particulate form. By ~particulate form~ i8 ~eant a ~ub6tance in the form of fine discrete particles. They may be variously shaped such as spherical, rounded, angular, acicular, irregular, or fibrous. The particles generally range in ~ize from about 1 micron to 2 x 104 microns in diameter or cross-section (largest dimension when not spherical). Theparticles are preferably of finely divided powder of particle size of from about 1 to about 103 microns.
The preferred synthetic acrylate polymer absorbents are those which have a salt group, an acid group, or which have both an amide group and a salt or acid group. These have been represented in the literature, e.g. U.S. Patent No. 3,686,024.

The invention i9 not limited to the use of water or saline alone as a treatment medium for the absorbents.
Absorbencies of hydrates made according to the invention are not significantly different if water used to wet the superabsorbent is replaced by saline. Other aqueous solutions containing dyes as urine wetness indicators or preservatives to prevent microbiological growth in the aqueous composition may be employed.
In addition to the foregoing components, the composition may have included therein minor amounts of other additives which may impart desirable properties to the absorbent product. Thus, a surface active wetting agent, particularly a non-ionic surface active agent may be included to enhance liquid uptake. A surface active J&J 1227 :'~

agent i6 of particular advantage in a~sisting vertical transport of liquids. Repre~entative surface active agentQ are those commonly described such as alkyl aryl polyether alcohols or alkyphenyl ethers of polyethylene glycol, e.g. reaction product of l-oc~ylphenol or nonylphenol with ethylene oxide. Fine fibrous cellulose such as cellulose flour, silicates and the like also have similar effect. Activated charcoal or other adsorbent may be included for odor uptake. Fragrance, coloring, etc.
~ may be included for a pleasing effect. Inert materials containing bound water such as silicates, aluminum hydrate and the like may be employed to modify the texture of the sheet. Similar results may be achieved employing slightly wet ethylene glycol or glycerol, e.g. commercial glycerine. If the absorbent immobilizing composition contains a low level of pulverulent absorbent, there i~ a slight tendency for the absorbent to settle. The composition may be modified to include small quantities of materials to af~ect its spreading properties. Suitable viscosity modifiers include silicated powders, clays, zinc oxide, inert fillers and like materials. Generally, the additives, if employed, do not constitute more than about 25~ of the total hydrate.
In order to more completely describe the present invention the following Examples are given.

Examples 1-3 In these Examplec absorbent hydrates were prepared by adding water or a 1~ aqueous sodium chloride solution (sa1ine) in separate experiments to each of three superabsorbents with stirring. Each hydrate contained about 33% by weight of superab~orbent and 67~ by weight of water. The hydrates comprised agglomerated particles of superabsorbent having a slightly tacky texture.
Teabag absorbencies of the hydrates were measured by placing 0.2 - 0.4 9 of hydrate in a teabag, stapling J&J 1227 the open end of the bag, immer~ing the bag in the saline for 10 second6, recording the uptake in weight of the bag, and also recording uptakes of the same bag at 30 seconds, and 60 ~econds. After the 60 second uptake each bag was squeezed by hand until the bag ruptured, and the new uptake recorded in order to determine the capacity of the hydrate to retain absorbed water.
As a control, dry superabsorbent was also subjected to the teabag absorbency test in each case.
Table 1 below summarizes teabag absorbencies of each dry superabsorbent, each superabsorbent hydrate and each superabsorbent hydrate calculated on the basis of the dry powder alone in the hydrate.

J&J 1227 N
C
C) .Q ~ O O O ~ c~
~1-~ ~ ~ ~ ~ ~ ~ ~D
e o ~ c~
U E~ u~
.,~ ~ ~ .,., E
O ~ 3~
U~ 5o ,~ o o c~ ~r C~D ~ ~ ~ ~ O~
O
~ ~ -~t)o ~ 0 X O U ~ O
~aa u~
O
_I ~ _I

N
~ a ~ .
.,4 co a~ ~ ~ tr P u~
~- ~q o O
~ ~ ~ ^ ~ ~ O
.cl a) o J~ ~ U7 ~ ~1 0 O ~ _ ,~ C O o~ ~ CD ~ O~
-I U ~ ~r ~ o ~C ~ O U tl; ~ ~ o o a~
_ :~
~ ¦ E E U ~ c 8~1 ,., .~ 8~ ~ o ,~
e m ~ ~ O v ~q ~ O ~ o o~
O _I ~ ~ ~ ~ ~ ~ ~ ~ o ~n ~ _,, o ~ ~ c D El ~ ~ U oO 11 \ --I ~ ~D
~ a~ ~ u D 1~3 ~ u~ o o ,~
E~ C C
~1 C ~

P ~D dP ~ ,, C
8 n ~ ~ ~
~q 8 ~n ~n o .Q ,~
a~
R
!1~ N
~ o In As Table l 6hows, in each Example, the superabsorbent in hydrate form, i.e., ba~ed on dry superabsorbent, absorb more water or saline than the dry superab60rbent alone and retains at least a~ much liquid after squeezing.

Examples 4 to 8 In the following Examples four composites each comprising an absorbent hydrate according to the inven~ion were placed between two-one gram layers of fluffed wood pulp and ~easured for absorbency on a TEF0 tester.
(Marketing/~echnology Service, Inc., Kalamazoo, Michigan).
Fluffed wood pulp i8 used as an absorbent for articles Quch as diapers. A layer of fluffy wood pulp containing no hydrate (Ex. 4) and a composite containing 0.3 9 of dry superabsorbent (Ex. 8) were used as controls. In u6ing the TEF0 tester, the composite is subjected to passage of a saline solution under pressure, and the amount of leakage of saline through the composite is determined as a measure of the composite's ability to retain the saline solution. In these Examples, 50 ml of saline solution at 7 ml/sec was poured over each composite on the tester, at pressures of lO0 pascals, (pa), 3 Kpa after 5 minutes and 5 Rpa after lO minutes.
The hydrates of the composites of Examples 5, 6 &
7 contained 0.3 9 of superabsorbent and 0~6 g of water prepared as in Examples 1-3. In the case of Example 5, the hydrate was placed in rows between the layers of fluffed wood pulp (Placed in Rows). In Example 6, the hydrate was sprinkled between the layers (Sprinkled). In Example 7, the hydrate was sprinkled between the pulp layer and allowed to stand overnight at room temperature ~Sprinkled, Stand). This allows water vapor to either combine with the superabsorbent or escape from it depending on the rel~tive humidity in the room simulating the treatment a commercial diaper would receive in which J~J 1227 1 31 ~3655 no att~ampt is made to seal th~ diape!,r ~nd preven'c water 1088 from the diaper durir,$ mainten~nce, di~tribution or storage . The super~b~orbent used in all compositea was a 3~ poly~po~a~ium ~crylate). Arasorb 720 i~ ~Arakawa Chet!n., S Inc.) ~ , Tabl~ 2 summari2es the results o the testing in terms o~ overflow and fluid re~ai~ed by the aompo~ite at the three pr~sure~.

T~ble 2 Ex. 4 ~X~ 5 Ex~ 6 Ex. 7 Ex. 8 Wood Pulp None Hyd~a~e ~ydra~e ~drate Dry Filler S::ontent Placed Sprinkled Sprinkled ~;uper-In ~ows . S~and ~b~ bent _ _ .. .
@lOQ pa Overflow O n ~.6 0.13 1.3 Fluid Retalned 4~ 45 45 43 47 ~ 3 Kpa FlUid Retained 22 ~9 ~8 30 31 5 E~pa ~0 ~lUid Re~ained . 20 :~5 2g ~6 ~7 As Ta~le 2 5hOW~, ~ll of the abo~r~ aonpo~1te~
containir~g ~uperab~o~bent hydrate hold more fluid ~der pre~sure than pUlp ~lone ~nd hold nearly a~3 m~ch f lu~d a~
the dry superabsorbent.

e /~ K

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

Claims

1. An absorbent hydrate comprising a mixture of (a) a particulate water-insoluble, water-swellable absorbent polymer; and (b) an aqueous liquid.

2. The absorbent hydrate of claim 1 wherein said aqueous liquid is water.

3. The absorbent past of claim 1 wherein said aqueous liquid is saline.

4. The absorbent hydrate of claim 1 wherein said absorbent polymer is a cross-linked polymer containing a plurality of hydrophilic groups selected from the group consisting of carboxyl, carboxamide, sulfonate salt and hydroxyl.

5. The absorbent hydrate of claim 1 wherein said absorbent polymer is a polysodium acrylate or polysodium meth-acrylate.

6. The absorbent hydrate of claim 1 wherein said absorbent polymer is a polypotassium acrylate or polypotassium methacrylate.

7. The absorbent hydrate of claim 1 wherein said absorbent polymer is a starch grafted polyacrylate or polymeth-acrylate.

8. The Absorbent hydrate of claim 1 wherein said absorbent polymer is a cross-linked carboxy methyl cellulose.

9. An absorbent hydrate comprising a mixture of (a) a cross-linked particulate water-insoluble, water-swellable absorbent polymer selected from the group consisting of a polysodium acrylate, a polysodium J&J 1227 methacrylate, polypotassium acrylate, polypotassium methacrylate, a starch grafted polyacrylate, a starch grafted polymethacrylate, and carboxy methyl cellulose;
and (b) from 20% to 80% by weight of the total weight of said hydrate of an aqueous liquid.

10. The absorbent hydrate of claim 9 wherein said aqueous liquid is selected from the group consisting of water and saline.

11. The absorbent hydrate of claim 9 wherein said aqueous liquid comprises from 30% to 50% by weight of the total weight of said hydrate.

12. An absorbent article containg the absorbent hydrate of claim 1.

13. An absorbent article containing the absorbent hydrate of claim 9.

14. A method for immobilizing a particulate water-insoluble, water swellable absorbent polymer comprising combining an aqueous liquid with said polymer to form a hydrate.

15. The method of claim 14 wherein said aqueous liquid is water.

16. The method of claim 14 wherein said aqueous liquid is saline.

17. The method of claim 14 wherein said absorbent polymer is a cross-linked polymer containing a plurality of hydrophilic groups selected from the group consisting of carboxyl, carboxamide, sulfonate salt and hydroxyl.
J&J 1227

18. The method of claim 14 wherein said absorbent polymer is a polysodium acrylate or polysodium methacrylate.

19. The method of claim 14 wherein said absorbent polymer is a polypotassium acrylate or polypotassium methacrylate.

20. The method of claim 14 wherein said absorbent polymer is a starch grafted polyacrylate or polymethacrylate.

21. The method of claim 14 wherein said absorbent polymer is a cross-linked carboxy methyl cellulose.

22. A method for immobilizinq a cross-linked particulate water-insoluble water-swellable absorbent polymer selected from the group consisting of a polysodium acrylate, a polysodium methacrylate, polypotassium acrylate, polypotassium methacrylate, a starch grafted polyacrylate, a starch grafted polymethacrylate, and carboxy methyl cellulose comprising combining an aqueous liquid with said polymer to form a hydrate wherein the aqueous liquid comprises from 20% to 80% by weight of the total hydrate.

23. The method of claim 22 wherein said aqueous liquid is selected from the group consisting of water and saline.

24. The method of claim 22 wherein said aqueous liquid comprises from 30% to 50% by weight of the total weight of said hydrate.
J&J 1227