CA1180154A

CA1180154A - Highly absorbent materials having good wicking characteristics which comprise hydrogel particles and surfactant treated filler

Info

Publication number: CA1180154A
Application number: CA000400447A
Authority: CA
Inventors: Peter A. Mazurak; Donald M. Fries
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 1981-04-21
Filing date: 1982-04-05
Publication date: 1985-01-02
Also published as: EP0063331B1; US4381782A; IE53058B1; DE3265750D1; BR8202280A; AU8268382A; PH17860A; ZA822542B; JPS5812652A; AU548248B2; EP0063331A3; EP0063331A2; KR830009765A; DK176782A; IE820922L

Abstract

ABSTRACT OF THE DISCLOSURE
Highly absorbent low density fibrous struc-tures such as webs or batts formed from mixtures of powdered or microcrystalline hydrogel pre-parations with surfactant treated filler materials having a particle size equal to or greater than the hydrogel particle size. Absorbent materials of the invention exhibit good wicking properties and result in more efficient use of hydrogels by minimizing gel blocking. Additional improvements include reduced dusting, improved stabilization and somewhat higher absorbency when compared with hydrogel materials alone. Uses for these materials include, by way of example and not limitation, disposable diapers, incontinent pads, sanitary napkins, wipes, surgical sponges and the like.

Description

54~

This invention relates to highly absorbent fibrous structures such as webs and batts as well as to methods and compositions for making them.
~ore specifically, it pertains to such fibrous structures including hydrogel or, so-called "superabsorbent" materials. These materials exhibit the ability to absorb many times their weight in aqueous and other liquids making them extremely useful for applications such as dis-posable diapers, catamenial devices, wipes, surgical sponges and the like. ~hen used alone or in combination with other materials, such hydro-gels may permit the absorbing device to be re-duced in size for a given application or increase its capacity in use. In most cases, however, to effectively utilize such hydrog~ls, it is nec-essary for some means or treatment to be provided to increase contact with the liquid being absorbed by improving distribution of the liquid throughout the absorbing medium. ~his invention is directed to improvements in achieving such distribution and effective utilization of hydrogel absorbing materials.
Hydrogel materials or so-called "super-absorbents" have been known for many years.

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Examples include lightly crosslinked polymers as described in ~.S. Pat~nt 3,669,103 to Harper et al; starch grafted materials such as polyacry-lonitrile grafted starch copolymers described in U.S. Patent 3,661,815 to Smith; and a wide variety of chemically treated cellulose materials. In general the cellulose materials may be treated by chemical substitution, etherization or esterifi-cation with or without crosslinking and by poly-meric grafting~ Such materials are described in further detail in U.S. Patent 3,997,647 to ~assen and others. These matexials are manufactured in various forms including powders, granules, fibers, and paperlike sheets. Webs may be formed from these materials and are also described in U.S.
Patent 3,997,647 to Lassen as well as U.S. Patent 4,174 r 417 to Rydell.
Effec~ive utilizatLon of such materials has been hindered however, by a phenomenon referred to commonly as "gel-blocking". This describes the tendency of hydrogel materials to swell in place when wetted and produce gelatinous material which blocks further transfer of the liquid being absorbed. Thus, in many cases contact of ab-sorbent material with the liquid being absorbed is highly localized and much of the absorbent 5~

medium is not utilized at all. In addition, such hydrogels have proved extremely difficult to handle in bulk form (due to blocking, caking, or dusting) or are otherwise unable to be eYenly distributed in a free-flowing manner.
Attempts in the past to solve these problems have been successful only to a limited degree.
For example, U.S. Patent 3,932,322 to Duchane relates to mixtures of such hydrogels with fumed silica or alumina fillers to provide increased absorbency. The presence of these fillers in products such as sanitary napkins may be ob-jectionable, and handling during processing results in increased problems of dusting and the like.
Mixtures of hydrogels with other materials in-cluding cotton, cellulose fibers, and synthetic fibers has been taught. For example, U.S. Paten~
3,055,369 to Grahm, Jr. discloses such mixtures for applications including tampon devices. However, such mixtures have not demonstrated satisfactory wicking properties for effectiva use in connection with fluids such as urine.
The present invention provides improved highly absorbent hydrogel materials having good wicking properties which are also more stable and easily handled with xeduced problems of dusting and ~180~59~

bloc~ing. In accordance with the invention the hydrogel materizls are mixed with up to 95 ~er cent by weight of a surfactant treated filler material. The resulting material has a reduced tendency to create dusting and is free flcwing and easily incorporated into an absorbent device such as a disposable diaper, catamenial device or wi~er. Preferred hydrogel materials include car~
box~me~hyl cellulose, polyacrylonitrile gxafted st~arch~s, as well as entirely synthetic Permasor~ -10 (National Starch and Chemical Company). Pxe-ferred filler malerials include sh_edded poly-styrene, polyethylene, polypropylene or blends of such synthetic materials each o, which is trea~ed with a surfactant, preferably Aerosol CT
(American Cyanamid) up to a level ol about 0.5 per cent by weight. ~he filler material ~as a re-latively large average particle size in the range generally of l to 10,000, preferably 1 to 1,000, and, most preferred 10 to 100 times the hydrogel particle si7e. The resulting material may be incorporated into products by spreading the mixture directly or by forming a ~eb or batt of the mixture and combining the web or batt as a component of the product.
Absorbenc~ and wicking properties of materials *trade mark I

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of the invention may be controlled within wide limits by varying the composition and relative ~mounts of hydrogel and filler materials. In general, however, when compared with other hydrogel compositions, materials of the present invention demonstrate impxoved wicking and absorbency pro-perties. Also, materials of t~e invention have improved integrity and better mechanical properties which also improve overall in-use absorbent per-formance.
FIG. 1 is a graph illustrating improved absorbency results obtained by means of the present invention; and FIGS. 2, 3 and 4 illustrate the present invention in the form o~ a disposable diaper.

As used herein the term "hydrogel" refers to dry, solid, water swellable, water insoluble absorbent compositions of polymeric materials capable of absorbing at least 15 times their own weight of body exudate or 1% saline solution. More particularly, such compositions provide gelatinous agglomerates of liquid swollen, particulate members in the presence of body exudate or 1% saline solution. Hydrogels may be initially in powdered or microcrystalline form and prepared by known pro-cesses, such as described in U.S. Patent 3,929,741 ~3l80~54 to ~askey, and U.S. Patent 3,900,378 to Yen et al, for exampleO
. The "filler materials" include a wide variety of materials in--powder, fiber, or particulate form which are normally hydrophilic or hydrophobic but may be treated with a surfactant to improve surface wettability. Examples include polyolerins such as polyethylene, polypropylene, and polystyrene, as well as natural, s~ightly absorbent clays, micas or ve~table (e.g. corn ccb) debris, as well as blends of these materials.
Surfactants which may be utilized in accor-dance with the invention include ionic and nonionic mater als such zs Aersol O.T. (American Cyanamid), Teepol 610 (Partiole Data Laboratories, Ltd.~, Neodol -27 (Shell Chemical Company3, and ~uomeen*-361 (Armour Industrial Chemical Company~.
To prepare the material of the present in-~ention the filler material is first uniformly wetted with up to about 20 per cen' by weight of surfactant solution containing surfactant in the range of from about 0.5% to 2.5% by weight. The hydrogel powder is then added and the admixture thoroughly ~lended to provide an intimate mixture and integration throughout of the components. T~e hydrogel particles will swell slightly and adhere *trade mark ~' .

~30~54 to the filler material. After drying, the admixture is preferably sub~ected to slight mechanical action destroying lumps. In use the filler material acts to rapidly wick liquid throughout the mixture and substantially eliminate the tendency to ~orm gel blocks. While it is no~ desired to limit the in~ention to any particular theory, i~ is believed that th~ surfactant_liquid slightly swells the dry hydrogel making it sticky and allowing it to adhere to filler particles. For this reason it is pre-ferred ~hat the iller be damp, ir.cluding, up to 10% by weight of water~prior to mixing with sur-factant solutionu The ~inal admixture may be dried or zllowed to retain up to 10% by weight of water. Retainea moisture preve~ts formation of hard lumps and also reduces dxying costs.
Preferred amounts of filler material are in the range of 5~ to 95% and, more pr~ferably, 25% to 75%, based on the total weight of material including the hydrogel, with a 50-50 mixture being most preferred. The sur-factant is preferably added to filler material in an amount of about 0.05~ to 0.5% and, more pre-fe~.ably, 0.1~ to 0~2~ by weight based on the amourt o nonabsoroent filler. The filler material is of relatively large average particle diameter, in the ~18()~5~

range of from 1 to 10,000 preferably 1 to 1,000, and, most preferred, 10 to 100 times the average ~ydrogel particle diameter.
The mixture may be collected into a batt prior to drying in which case it is preferably mainta ned in a uncompressed state with a density in the range of from about 0.05 to 0.25 g/cc, or it may be stored as a particulate mixture having a density of about 0.05 to 0.50 g/cc. As a web or batt of course, it may be used directly as a component of an absorbent productO
Th~ following examples are pr~vided as Illus-trations of the present invention. Absorbency test results were determined by total immersion of absorbent in test fluid for a period of 2 minutes, allowing nonabsorbed fluid to drain off for a period of 5 minutes, and weightng. Wicking tests were determined by a demand absorbency device as described by Lichstein in pages 129-142 of The INDA
Technological Symposium proceedings, March 1974.
This equipment was modified by application of a Mettler PL1200 electronic balance which provided a continuous plot of amount of fluid wicked. Density was measured by weight and volume.
Example 1 ~ ive hydrogel compositions were ob~ained and tested individuallv for absorbency: Polymer 35_A_ * *
10~ and 35-A-200 (both polyacrylonitrile gra~ted starch - Grain Processing Corporatio~, Permasorb 10 (100% synthetic material from acrylic acid precursors - National Starch and Chemical Company~, Sanwet IM-300 (polyacrylic acid grafted s.arcn -Sanyo Chemical Corporation), and Stasor~*-372 (polyacrylic acid grafted sta~ch - A. E. Staley Chemical Corporation).
Example 2 Four of the hydrogels of Example 1 were mixed 50-50 with ground mixture (60/40 weight ~) of shredded polye'hylene sheet and polypropylene fibers, average particle diameter 1.5 mm, including O.5~ by weight of Aerosoi-OT` surfactant and tested ~o~r- absoxbency with synthetic urine (1.6~ urea in water, surLace tension adjusted with surractant to 55 dynes/cm).
Example 3 Using Permaso b*10 and Polymer 35-A-700 as the hydrogel materials, Example 2 was repeated sub-stituting the following as filler materials~
shredded polyethylene (average paxticle diameter 10 mm), ground corn cobs (average par~icle diameter

2.5 mm), filler OL Example 2 (including 50% pul~
fibers ~verage particle size 3.0 x 0.1 mm), and skredded polystyrene packing material ~average *trade mark ..~

~80~54 particle diameter 1.5 mm).
Example 4 Using Permasor~ 10 and Polymer 35-A-lO0 as the hydrogel materials, Example 2 was repeated sub-stituting the following as sur~actants: Teepol -610 (anionic secondary aklyl sulfate), Duome~.~ tcat-ionic N-Tallow-proplyenediamine), Neodol 25-7-(nonionic primary alcohol exthoxylaie)-~ ' . ,~ ' "Example 5 Using Permasorb*10 and Polymer 35-A-100 as the hydrogel materials, Example 2 was repeated at the following levels of surfactant (Aerosc:*O.T.) add-on: 0%, 0.1%, 0.2~, 0.3~j 0.4%, and 0.5%.
Example 6 ~ ~Using Permas~rb~10 and Polyme~ 35-A-100 as the hydrogeI materials, ~xample 2 was repeated at a surfactant addition level of 0.25% (Aerosol -OT) based on filler weight and fiIler to hydrogel ratios as follows: 1~0, 3/1, 1/1, 1/3, 0/1.
Example 7 ~ Using Permasorb 10 and Pol,vmer 35-A-100 as the hydrogel materials, Example 2 was repeated at a surfactant (Aerosol -OT) addition level of 0.~5~
bzsed on filler weight and testea in the following fluids: 0.9% saline, synthetic urine OL Example 2, *trade:mark :.: .

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synthetic urine ~2 (urea plus mixture of salts includins NaC1, CaC12, MgC12, Na2SO4 and Na3PO4;, distilled water and tap water.
Example ~
Example 2 was repeated using Polymer 35-A-100 and Perm~sorb*-lC as hydrogels, with 0.25% Aerosol*-OT`surfactant. Ground corn cob material of sev ral different particle diameter ranges was used as filler material. The Table demonstrates that, as the filler particle diameter increased, absorbency was increased 2S was bulk. For these reasons, filler particle diameters o 1 .o 10,000 are preferred with part cular preference for diameters within the range o 1 to 1,000 and, especially, 10 to 100 times the hydrogel particle diameter which is generally in the ranse of from 0.01 mm to 1.0 ~n.
The results obtained are illustrated in ~he Table which shows a marked increase in absorbency obtained by means of the present invention.

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FIG. 1 is a graph of automated demand ab-sorbency test results showing increased wicking performance resulting from th~ present invention.
As shown, the wicking performance of hydrogel absoxbents is increased greatly through incor-poration with fillers~
Turning to FIGS. 2 through 4, a preferred disposable sanitary garment application for the material of the present invention will be des-cribed. FIGS. 2 and 3 show the absorbent layer, lO, prior to incorporation into the diaper. Cut-out areas 12 provide for folding along lines 14.
Prior to folding, hydrogel material 16 is incor-porated by placement at 18 near the front edge 20 of batt 10. After folding, the batt 10 may be incorporated into diaper 22 as shown in FIG. 4.
Diaper 22 also includes liquid impermeable backing 24 and permeable liner 26 as well as fastening means 28. Elastic means 29 are provided to aid in rluid retention within the diaper structure. While the amount of hydrogel material 16 may vary within a wide range, useful results have been obtained with amounts in the range of from about 1 gm to 10 gm distribu~ed evenly in area ~8 as illustrated.
The liner 26 may be a nonwoven material such as spunbonded polypropylene, carded webs, or the like . ~18()lS4 or a spl'it or ribrillated film. The backing 24 may -be any of a wide variety of films such as matt embossed polyethylene, for example~ Fastening means 28 may be adhesive tabs, for example. Other variations will also be useful and suggest them-selves to those skilled in the art such as shape modi`fications, reinrorcement of stress areas, and incorporation of~elastic. These varia~ions can also take advantage~of the hydrogel configuration ~of thc~pr~sent int~ention. An advantage wi~.l be in r d ùced~fluff requirements. ~ ~
~ In a~specifLc~example~,~a~diaper was prepared ~~ ~as in~FIGS~ 2~through 4 using 22 grams OL ~fIuff ' instead of the normal 36 grams~used for tha~ size of standard product. To 'tha~-fluff was~added 3 `grams~of~the hydrogel-;admix~ture of Example~,2,`as shown'~in~F}GS~ Z~and;3~ The;resul ~ing~product ~
performed'~as~well~as~ the~standard;~diaper~in terms ,of~leakage~res~istance.~ n , As~demonstra:ted~above,;'~,the~;present inve~tion provides~a~more effective~use~f~highly absorbent matèrials~that`~can~be more`easily incorporated into end~uses such as;~catamenl;al~devices, disposable di~apers,~ incontinent'~pads, wipes and the like.
While-the intrention~has been described in con-;junct~on~with~specific embodiments thereof, ~t is :: ~ 1 7--:
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~1~30~i4 evident that many alternatives, modifications and variations would be apparent ta those skilled in the art in light of the foregoing description.
Accordingly, it is intended to e~brace all such alternatives, modifications and variations as fall within the spirit and broad scope of the append~d claims.

Claims

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

1. A low density highly absorbent material having improved wicking characteristics comprising an inti-mate mixture of particulate hydrogel material with 5 to 95 percent by weight of a filler material, said filler material having an average particle diameter 1 to 10,000 times the average hydrogel particle diameter and having been treated with a surfactant.

2. The material of claim 1 wherein the surfac-tant is anionic dioctyl sulfosuccinate.

3. The material of claim 2 wherein the average filler particle diameter is 1 to 1,000 times the average hydrogel particle diameter.

4. The material of claim 2 wherein the average filler particle diameter is 10 to 100 times the average hydrogel particle diameter.

5. The material of claim 2 wherein the filler is selected from the group consisting of mixtures of poly-ethylene sheet and polypropylene fibers, ground vegetable debries, mixtures of polypropylene fibers and pulp fibers, and shredded polystyrene.

6. The material of claim 2 wherein the amount of filler is in the range of 25 to 75% based on the total weight of material including the hydrogel.

7. The material of claim 2 in batt form having a density in the range of from 0.05 to 0.50 g/cc.

8. A disposable sanitary garment comprising, in combination:
a) a liquid impermeable backing, b) a liquid permeable liner, and c) between said backing and said liner an absorbent layer comprising a low density, highly absorbent material having improved wicking characteristics comprising an intimate mixture of particulate hydrogel material with 5 to 95% by weight of a filler material, said filler material having an average particle diameter 1 to 10,000 times the average hydrogel particle diameter and having been treated with a surfactant.

9. The disposable sanitary garment of claim 8 in the form of a disposable diaper wherein the absorbent layer includes said low density material placed near the front edge thereof and the sides of the absorbent layer are folded over covering said low density material.

10. The disposable diaper of claim 9 wherein the hydrogel material contains filler having an average particle diameter 10 to 100 times the average hydrogel particle diameter and wherein said surfactant is anionic dioctyl sulfosuccinate.

11. The disposable diaper of claim 10 further including elastic means to aid in fluid retention.

12. The material of claim 1 wherein the surfactant is added at a level of up to about 1.0 percent by weight remaining on the material after drying.

13. The garment of claim 8 wherein the surfactant is added at a level of up to about 1.0 percent by weight remaining on the material after drying.