CA2049861C

CA2049861C - Absorbent body and absorbent article

Info

Publication number: CA2049861C
Application number: CA 2049861
Authority: CA
Inventors: Nobuyuki Harada; Kazumasa Kimura; Tadao Shimomura
Original assignee: Nippon Shokubai Co Ltd
Current assignee: Nippon Shokubai Co Ltd
Priority date: 1990-08-30
Filing date: 1991-08-26
Publication date: 1996-09-17
Anticipated expiration: 2011-08-26
Also published as: DE69130754T2; EP0474443B1; DE69130754D1; ES2129402T3; MX174266B; CA2049861A1; US5195999A; EP0474443A2; EP0474443A3; BR9103755A

Abstract

An absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof, characterized by the fact that the density of said absorbent body is in the range of from 0.1 to 0.5 g/cm3 or a ratio of wet swelling is not less than 200%, a capacity of said absorbent body for absorption of physiological saline solution under pressure is in the range of from 11 to 25 g/g, and the ratio of exfoliation of said absorbent polymer is not more than 45%, and an absorbent article comprising a liquid-pervious surface material, a liquid-impervious lining material, and the absorbent body layer interposed therebetween.

Description

- BAC~GROUND OF THE INVENTION
Field of the Invention:
This inYention relate9 to a novel thin absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof and an absorbent article using the absorbent body.
Description of the Prior Art:
Most of the ab90rbent bodies in such absorbent articles as disposable diapers and sanitary napkins which are currently in the ~arket have been changing to composites of such hydrophilic fibers as fluffy pulp and paper with absorbent polymers. The require~ent~ which an ab~orbent body using an absorbent polymer in a relatively large amount i3 expected to ful~il include capacity for abAorption, small thickness and light weight, and shape-retaining property, for example. It is necessary that these functions should be wholly qatisfied.
The absorbent bodies which are now in use are nearly satisfactory in terms of capacity Por absorption but are not satisfactory in terms of small thickness and light weight and shape-retaining property. Thus, the manufacture of an absorbent article which has small thickness and light weight, possesses a large capacity for absorption, suffers from no serious leakage, and therefore fully satisf'ies producers and c~ alike has not been materialized to date .
An object of an aspect of this invention, therefore, is to provide a novel absorbent body and an absorbent article.
An object of an aspect of this invention is to provide an absorbent body which has small thickness and light weight, posses~es a large capacity for absorption, and suffers from no serious leakage and an AhsQrh~t article using the Ahssrh~nt body.
~UMMARY OF T~:E INV~ ~ N

.~

20498~ 1 Various aspects of the invention are as follow~:
An absorbent body having an absorbent polymer and hydrophilic fiber9 as main ccmponent9 thereof, characterized by the ~act that a density of 9aid absorbent body is in the range oî from 0.1 to 0.5 g/cm3, a capacity of said absorbent body f or absorption of physiological saline solution under pressure is in the range of ~rom 11 to 25 g/g, and a ratio o~ ex~oliation of said absorbent polymer is not more than 45S .
An absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof', characterized by the fact that the capacity of said absorbent body f`or absorption of physiological saline solution under pressure is in the range of 11 to 25 g/g, a ratio of exfoliation of said absorbent polymer is not more than 45~, and a ratio of wet swelling is not less than 200,~.
An absorbent article comprising a liquid-pervious surfaoe material, a liquid-impervious lining material, and an absorbent layer interposed therebetween, characterized by the i'act that said absorbent layer at least partly comprises of an absorbent body having an absorbent polymer and hydrophilic ribers as main components thereof and exhibiting absorption characteristics such that the density is in the range of f'rom 0.1 to 0.5 g/cm3, a capacity for absorption o~
physiological saline solution under pressure is in the range OI from 11 to 25 g/g, and a ratio of exfoliation of said absorbent polymer is not more than 45~.

. ~

2~9~ 1 An absorbent article compri~ing a liquid-perviou3 ~urPace material, a liquid-impervious lining material, and an ab~orbent layer interpoqed therebetween, characterized by the Pact that said ab~orbent layer at least partly comprises of an ab~orbent body having an ab~orbent polymer and hydrophilic Piber~ aq main componentq thereoP and exhibiting absorption characteriqtics ~uch that a capacity fcr ab~orption of physiological saline solutLon 19 in the range of Prom 11 to 25 g/g, a ratio of exPoliation of ~aid absorbent polymer i~ not more than 45~, and a ratio of wet qwelling iq not les~ than 200,~.
The inventorq continued a dillgent ~tudy on abqorbent bodie~ with a view to developing an absorbent article having ~mall thickne~ and light weight, poqse~ing a large capacity Por abqorption, and ~ufPering from no qeriouq leakage. Aq a reqult, they have succeeded in perfecting thi~ invention by the u~e oP an abqorbent body - 2a -- ~c whose density, amount oP absorption under pre~ure, and ratio of exfoliation of absorbent polymer are 3everally controlled in prescribed ranges.
Since the absorbent body obtained in the present invention has such a construction as described above, it serves as an ideal absorbent for various absorbent articles in the medical and sanitary fields such as sanitary napkins, disposable diapers, pads for children and adults ~uffering from incontinence, pads for excessively secreting brea3ts, and medical pads. It is al30 useful for various applications requiring to retain and absorb water 3uch as, ~'or example, freshness-retaining materials, agricultural-horticultural water-retaining materials, and industrial water-retaining materials.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a schematic cross section illustrating an apparatus to be used in this invention for the determination of an amount of absorption under pressure.
EXPLANATION OF THE PREFERRED EMBODIMENT
For this invention, it is important that since the absorbent body 19 made mainly of an absorbent polymer, it should excel in ability to absorb liquid and possess satisfactorily small thickness and avoid exfoliation of the absorbent polymer after absorption of liquid. It is further important that the absorbent body should be capable of absorbing and diffusing liquid without inducing the phenomenon of gel blocking and incapable of inducing exfoliation of the absorbent polymer after absorption of liquid .
The absorbent body is not disintegrated even af ter absorbing liquid because it has a small ratio of exfoliation of absorbent polymer. Even when it is used in absorbing liquid for the second time or the third time, therefore, it i~ capable of quickly ab~orbing urine and menstruation without a sacrifice of its wicking speed. Thus, it warrants production of an absorbent article which suffers from no ~ ,;

conspicuous leakage and enables the wearer to en~oy a sensation of drynes~. Further, the amount of absorption under pressure of the ab30rbent body constitutes it~elf an important factor for the production of an ab30rbent article because an unduly small or large amount of absorption under pressure prevents the absorbent body from acquiring a desired reduction in weight, cau~es breakage in the absorbent body, and compels the absorbent body to suffer from leakage. If the density is unduly small, since the absorption and diffusion of liquid are retarded and the leakage of lLquid i9 suffered to occur conspicucusly, the absorbent body is not allowed a substantial reduction in thickness and consequently is prevented from finding practical utility. It is only by the use of an absorbent exhibiting density, amount of absorption under pressure, and ratio of exfoliation of absorbent polymer in balanced magnitudes that the production of an absorbent article en~oying freedom from objectionable feeling and possessing small thickness and light welght is rendered possible.
If the ratio of wet swelling is unduly small, since the absorption and diffusion of liquid are retarded and the leakage of liquid i9 suffered to occur con~picuously, the absorbent body is not allowed a substantial reduction in thickness and consequently is prevented from finding practical utility. It is, therefore, only by the use of an absorbent body exhibiting ratio of wet swelling, amount of absorption under pressure, and ratio of exfoliation in balanced magnitudes that the production of an absorbent article enjoying freedom from unpleasantness and possessing sufficiently small thickness and light weight is materialized .
For this invention, it i~ further important that the absorbent body mentioned above should be produced by mixing the mixture of an absoroent polymer with synthetic pulp (gravimetric ratio of 100: 1 - 30) in the presence of water with hydrophilic fibers in a gravlmetric ratio in the range of 100: 5 - 500, preferably 100: 10 - 200, based on the absorbent polymer and thermally compressing the resultant mixture to a density in the range of from 0.1 to 0.5 g/cm3, preferably from 0.15 - 0.4 g/cm3.
For the purpose of restraining the ratio of exfoliation of absorbent polymer, a method for solidifying the absorbent polymer by the use of a varying binder and a method for enclosing the absorbent polymer with a fibrous matrix have been proposed, for example. In the absorbent bodies which are produced by these methods, there generally exists the relation of contradiction between the ratio of exfoliation and the amount of ab30rption under pressure.
None of the currently commercially available absorbent bodies ~atisfies all of the aforementioned physical properties, i.e. the density in the range of from 0 .1 to 0 . 5 g/cm3, the amount of absorption of physiological saline solution under pressure in the range of from 11 to 25 g/g, and the ratio of defoliation of absorbent polymer of not more than 45%.
None of the currently commercially available absorbent bodies satisfies all of the aforementioned physical properties; i.e. the amount of absorption of physiological saline water under pressure in the range of from 11 to 25 g/g, the ratio of exfoliation of absorbed polymer of not more than 45%, and the ratio of wet swelling of not less than 200%.
To satisfy all of these physlcal properties, the absorbent body should be what is produced by mixing the mixture of an absorbent polymer with synthetic pulp (gravimetric ratio 100: 1 - 30) in the pre3ence of water with hydrophilic fibers in a gravimetric ratio in the range of 100: 5 - 500, based on the absorbent polymer and thermally compressing the resultant mixture to a density in the range of from 0 .1 to 0 . 5 g/cm3 .

204986~
The absorbent polymer for use in the present invention generally i~ only required to possess absorbency.
The absorbent polymers which an~wer this description include, in addition to (cross-linked) polymers oP water-~oluble ethylenically unsaturated monomers having (meth)acrylic acid~ or salts thereof a~ main components and optionally incorporating a cross-linking agent therein, cross-linked derivatives of polyethylene oxide, polyvinyl pyrrolidone, sulfonated polystyrene, and polyvinyl pyridine, ~aponified starch-poly(meth)acrylonitrile graft polymer~, starch-poly(meth)acrylic acid (and ~alt~ thereof) graft copolymer3 (and cross-linked derivatives thereof ), starch-poly(meth)acrylic e~ter graft copolymers (and cross-linked derivatives thereof ), and hydrolyzed ~tarch-poly(meth)acrylic ester graft copolymers, for example.
Among other absorbent polymers cited above, the (cross-linked) polymers of water-soluble ethylenically unsaturated monomers having acrylic acid or an acrylate as a main component prove to be preferable and cro~s-linked polymers of acrylLc acid (salt~ thereof) to be more preferable. This invention does not discriminate the absorbent polymer on account of the method to be used ~or the production thereof.
Optionally two or more of these absorbent polymers may be jointly used. The absorbent polymer to be used consists of substantially dry particles which are capable of ab~orbing physiological saline solution in a ratio exceeding 5 g/g, preferably falling in the range of from 20 to 80 g/g and more preferably in the range of from 35 to 60 g/g. The absorbent polymer by nature generally contains water to a certain extent. The expre~ion "~ubstantially dry" a3 u~ed herein means the state in which the individual particle~ are incapa~le o~ mutually adhering in the normal atmo3phere.
The shapes which the particles are required to as3ume in order to en~ure effective use herein include various forms of powder such as spheres, granules, randomly shaped particles, and foamed particle~ and fibrillar particles.

.

These partlcle3 may be simple particles or pelletlzed part1cles. These part1cles are allowed to have a cros~-11nk degree gradient near their surface regions. In the case of a powder, the agglomerates thereof are pref erable to have diameters 3uch that the weight average particle diameter is in the range of from 10 to 1,000 microns, preferably 100 to 700 micrcns.
The hydrophilic f1bers whlch are effectlvely used ln the present lnventlon lnclude wood pulp f 1bers such as mechanlcal pulp, chemlcal pulp, and d1ssolved pulp and man-made cellulos1c f1bers such as rayon and acetate, for example. In the present invention, the hydrophilic fibers may partly incorporate therein additlonally 3uch synthet1c fibers as nylon, polyesters, and polyolefins. Preferable hydrophilic fibers are represented by wood pulp fibers. The amount of the hydrophilic fiber3 to be used herein is in the range of from 5 to 500 parts by weight, preferably from 10 to 200 parts by weight, based on 100 parts by weight of the absorbent polymer.
In the present invention, the hydrophlllc f1bers may be used jolntly w1th synthet1c pulp. The amount of the synthet1c pulp to be used addltlonally 19 ln the range of from 1 to 30 parts by weight, preferably from 2 to 25 parts by weight, based on 100 parts by weight of the ab~orbent polymer. The synthetic pulp to be used in the present invention is known in the art. For example, see "Pulp, Synthetic, " Rirk-Othmer, Encyclopedla of Chemlcal Technology, 3rd Ed.(New york:1982), Vol. 19, pp. 420-1~35.
The pulps are very flne, hlghly branched, d1scontinuous fibrils made from thermoplastic resins. Their visual appearance and dimensions closely resemble those of wood pulp. The thermoplastic re~ins which are effectively usable herein for the production of the synthetic pulp include polyolefins, polyesters, polyacrylonitrile, and other hydrophobic thermoplastic resins, for example. Among other thermoplastic resins cited above, polyolefins formed of one 204986~
or more c~-olefins such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, and ethylene-4-methyl-1-pentene copolymer prove to be particularly preferable because they are capable of notably improving the hydrophilicity of the hydrophilic fibers. Methods for the production of synthetic pulp from thermopla31tic resin are disclosed in JP-B-47-2 1, 898 ( 1972 ), JP-B-47-32, 133 ( 1972), JP-A-3-180,504( 1991 ), JP-A-3-180,505( 19g1 ), and JP-B-52-47,049(1977). The products o~ ~uch methods are aYailable under trademark designations such as, for example, SWP
(Mitsui Petrochemical Industries, Ltd.) PULPLUS (E.I. du Pont de Nemours & Company), and PULPEX (Hercules Incorporated). The ab~orbent body oP the present invention i~ produced by the following method~, for example.
( 1 ) A method which produce~ an absorbent body having density in the range of from 0.1 to 0.5 g/cm3 by mixing 100 parts by weight of an ab~orbent polymer with 1 to 30 part~
by weight oP synthetic pulp during addition thereto o~ 1 to 40 parts by weight of water, dry mixing the resultant mixture with 5 to 500 parts by weight of hydrophilic Pibers such as ground pulp, based on 100 parts by weight of the absorbent polymer, molding the produced mixture in the Porm of web, and thermally compressing the web to the density mentioned above.
(2) A method which produces an ab~orbent body having density in the range of from 0.1 to 0.5 g/cm3 by mixing 100 part~ by weight oP an absorbent polymer with 1 to 30 part~
by weight of synthetic pulp wetted with 1 to 40 part~ by weight of water, dry mixing the resultant mixture with 5 to 500 parts by weight of hydrophilic fibers such as ground pulp, ba3ed on 100 part:3 by weight of the ab~orbent polymer, molding the produced mixture in the Porm of web, and thermally compre~lng the web to the density mentioned above .

20~98Gl The absorbent body which is produced as described above po3sesses speciflc physical properties, i.e. density in the range of from 0.1 to 0.5 g/cm3, preferably from 0.15 to 0.4 g/cm3, amount of absorption of physiological saline solution under pressure in the range of from 11 to 25 g/g, preferably from 12 to 20 g/g, and ratio of exfoliation of absorbent polymer of not more than 45%, preferably not more than 30%.
The absorbent body which is produced as described above possesses physical properties such as amount of ab30rption of physiological saline solution under pressure in the range of from 11 to 25 g/g, preferably from 12 to 20 g/g, ratio of exfoliation of absorbent polymer of not more than 45%, preferably not more than 30%, and ratio of wet ~welling of not less than 200%, preferably in the range of from 220 to 600,~.
The absorbent body could be made to acquire an amount of absorption of even not less than 30 g/g by suitably varying the mixing ratio of the component materials. For the reason given above, the absorbent body having this large amount of absorption is deficient in stability to resist the influence of wetness and in efficiency of absorption and, therefore, is unpreferable.
If the absorbent body has a ratio of exfoliation of absorbent polymer of not less than 45%, a disposable diaper, for example, which uses this absorbent body has the disadvantage that the diaper worn by an infant sustains leakage when the absorbent body used therein is fractured by the motion of the infants body. If the absorbent body has an amount of absorption under pressure of less than 11 g/g, it has the disadvantage that the absorbent body is def icient in ability of absorption and, therefore, is not allowed a preferred reduction in thickness or weight. In view of the various factors described above, it may well be concluded that the most preferable absorption properties to be possessed by the absorbent body are density in the range of 0 .1 to 0 . 5 g/cm3 , amount of ab~orption under pressure in the range of 11 to 25 g/g, and ratio of exfoliation of absorbent polymer of not more than 45%.
In view of the various factors described above, it may well be concluded that the most preferable absorption properties to be possessed by the absorbent body are amount of absorption under pressure in the range of from 11 to 25 g/g, ratio of exfoliation of absorbent polymer of not more than 45,~, and ratio of wet swelling of not less than 200,~.
The application to an absorbent article of the absorbent body of this invention which satisfies all of the absorption properties may be effected by simply interposing the absorbent body of the present invention between a liquid-pervious qheet and a liquid-imperviou~ sheet which are other indispensable component parts of the absorbent article or by jointly using the absorbent body of this invention and a known absorbent body such as of fluffy pulp as an absorbent layer.
The liquid-impervious sheets which are effectively usable in the present invention include sheetlike substances of such sof t synthetic resins as polyethylene, polypropylene, vinyl chloride resin, nylon, and vinylon, for example. The liquid-pervious surface materials which are effectively usable herein include non-woven fabrics of natural fibers (such as, for example, wood or cottom fibers), synthetic fibers (such as, for example, polyester or polyolefin fibers), or combinations of natural fibers and synthetic fibers, perforated pla~tic film~, porous foamed materials, and reticular foamed articles, for example.
The absorbent body and absorbent article as embodiments of the present invention have been described.
It should be noted that this invention need not be limited to these embodiments but may be practi~ed otherwise without departing from the spirit of the invention.

Now, the present inventlon will be described below with reference to working examples. Wherever the term "part~" iq mentioned Ln the following referential example~, working examples, and controls, it shall be construed a~
"part~ by weight" unless otherwise specif ied.
(Test for quality) The absorbent bodies produced were evaluated by the following method~:
1. Amount of ab~orption under pre~ure An apparatus which, as illu~trated in Fig. 1, comprised a container 4 for an aqueous O.9,q~ physiological saline solution 3 mounted on a balance 1 and provided with an ambient air inlet pipe 2, an inver~e funnel 6 communicating via a conduit 5 with the container 4, and a glas~ filter 7 attached to the top part of the inverse funnel 6 was used. The capacity of a given absorbent body ô
for absorption (g/g) was determined by mounting the absorbent body ô on the filter 7, ~uperposing a weight 9 on the ab~orbent body 8, allowing the ab~orbent body to ~tand under a load of 30 g/cm2 for 30 minutes, and mea~uring the amount of the saline ~olution absorbed by the absorbent body during this standing. In thi~ test, a circular sample 5.5 cm in diameter from the absorbent body 8 wa~ used.
2. Density of absorbent body The den~ity of a given ab~orbent body wa~ determined by placing a 10 cm ~quare sample from the ab30rbent body under a load of 7 g/cm2, measuring the height, z (mm), of the ~quare sample in the pressed state, dividing the weight, x (g), of the sample by the volume, 10z (cm3), and reporting the quotient.
3. Ratio of exfoliation of ab~orbent polymer This property of a given absorbent body wa~
determined by placing a 2 cm x 4 cm rectangular sample from a given ab30rbent body into 100 cc of phy~iological saline solution kept ~tirred (at a rate of 100 rpm by the use of a stirrer) in a 100-cc beaker, keeping the ~ample in the qtirred 3aline 301ution for 10 minute~, removing the 3ample from the saline 301ution, weighing the ab30rbent polymer fallen from the 3ample into the 3aline 301ution during the 3tanding in the ~tirred 3aline solution, and calculating the ratio oP exPoliation oP the ab30rbent polymer in accordance with the Pollowing Pormula.
Ratio oP exPoliation ~%) = {(Amount of exfoliated polymer (g))/(Amount of polymer in original 3ample (g)) x Referential Example 1 In an atmo3phere of nitrogen, 4,000 parts of an aqueou3 301ution oP 37S an acrylic monomer compo3ed of 74 . 98 mol% of 30dium acrylate, 25 mol7~ of acrylic acid, and 0.02 mol% of trimethylolpropane triacrylate wa3 polymerized by being 3tirred with 2.0 part3 oP 30dium per3ulPate and 0.08 part of ~-a3corbic acid, to produce a gel hydrated polymer finely divided in a particle diameter of about 5 mm. The gel hydrated polymer wa3 dried with a hot air drier at 150 C, pulverized with a hammer type pulverizing device, and 3ifted with a 20-me3h metallic gauze to 3eparate a 20-me3h pa33 powder (having an average particle diameter of 405 micron3). Then, 100 part3 of the 3eparated powder wa3 mixed with 0.5 part oP glycerol, 2 part3 oP water, and 2 part3 of ethyl alcohol and the re3ultant mixture wa3 heat-treated at 210 C, to produce an ab30rbent polymer A having the 3urface region thereoP 3econdarily croqq-linked. The capacity oP
thi3 polymer for ab30rption oP phy3iological 3aline 301ution wa3 found to be 50 g/g.
RePerential Example 2 In an atmo3phere of nitrogen, 4,000 part3 of an aqueou3 301ution of 37% acrylic monomer compo3ed of 74 . 95 mol,~ of 30dium acrylate, 25 mol% of acrylic acid, and 0.05 mol% oP trimethylolpropane triacrylate was polymerized by being 3tirred with 2.0 parts of 30dium per3ulfate and o.o8 part of Q-aqcorbic acid, to produce a gel hydrated polymer f inely divided in a particle diameter of about 5 mm. The gel hydrated polymer was dried with a hot air drier at 150 C, pulverized with a hammer type pulverizing device, and sifted with a 20-mesh metallic gauze to separate a 20-mesh pass powder as an absorbent polymer B (having an average particle diameter of 350 microns). The capacity of this absorbent polymer for absorption of physiological saline solution was Pound to be 46 g/g.
Referential Example 3 By mixing 100 parts of the absorbent polymer B
produced in Referential Example 2 with 0.5 part of glycerol, 2 parts of water, and 2 parts of ethyl alcohol and then heat-treating the resultant mixture at 210 C, an absorbent polymer C having the surface region thereof secondarily cross liked was obtained. The capacity of this absorbent polymer for absorption of physiological saline solution was found to be 43 g/g.
Referential Example 4 An absorbent polymer D (having particle diameters of 250 to 149 microns) was separated by classifying the absorbent polymer C produced in Referential Example 3 with 60- to 100-mesh sieves. The capacity of the absorbent polymer 3 for absorption of physiological saline solution was found to be 42 g/g.
Examp l e One hundred ( 100) parts by weight of the absorbent polymer A and 25 parts by weight Or synthetic pulp (produced by Mitsui Petrochemical Industries, Ltd. and marketed under product code of "SWP UL-415n) were mixed while the addition of 25 parts by weight of water thereto was continued. In a mixer, the resultant mixture wa3 dry mixed with 125 parts by weight of ground pulp. The produced mixture was pneumatically molded in the form Or sheet on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area and having a basiA weight of 0.047 g/cm2. The produced web was compressed and heated at 150 ~C ror 10 minutes, to produce ~ 20498~
an ab30rbent body ( 1 ) of this invention having a density of 0.16 g/cm3. The capacity of the absorbent body ( 1 ) for absorption under pressure was found to be 16.5 g/g, the ratio of exfoliation of absorbent polymer to be 19%, and the ratio of wet swelling to be 256,~.
Examp l e 2 An absorbent body (2) of this invention having a basis weight of 0.051 g/cm2 and a density of 0.13 g/cm3 was produced by following the procedure of Example 1, except that the amount of water was changed to 32 part3 by weight, that of the synthetic pulp to 17 parts by weight, and that of the ground pulp to 133 parts by weight. The capacity of the ab30rbent body (2) for absorption under pres3ure was found to be 16.0 g/g, the ratio of exfoliation of ab30rbent polymer to be 22,~, and the ratio of wet swelling to be 210%.
Examp l e 3 One hundred ( 100) parts by weight of the absorbent polymer A was mixed with 7 part3 by weight of synthetic pulp wetted in advance with 5 parts by weight of water. In a mixer, the re3ultant mixture was dry mixed with 67 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area and having a ba3i3 weight of 0.042 g/cm2. The web was compressed and heated at 150 C
for 10 minute3, to produce an ab30rbent body (3) of thi3 invention having a density of O . 20 g/cm3 . The capacity of the absorbent body (3) for ab30rption under pre3sure was found to be 15.8 g/g, the ratio of exfoliation of absorbent polymer to be 20%, and the ratio of wet swelling to be 270%.
Example 4 One hundred ( 100) part3 by weight of the ab30rbent polymer C wa3 mixed with 13 part3 by weight of 3ynthetic pulp (produced by ~itsui Petrochemical Indu3trie3, Ltd. and marketed under product code of "SWP UL-415") while the addition of 20 parts by weight of water thereto was ~ 2049861 continued. In a mixer, the resultant mixture was dry mixed with 100 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid oP a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interposed between two opposed ti~que paper~ haYing a basi~ weight of 0.0013 g/cm2 and then embo~q pressed at 150 C for one minute, to produce an absorbent body (4) of this invention having a basis weight of 0.054 g/cm2 and a density of 0.27 g/cm3. The capacity of the abqorbent body (4) for ab~orption was found to be 14.4 g/g, the ratio of exfoliation of absorbent polymer to be 6,~, and the ratio of wet swelling to be 300,~.
Example 5 An ab~orbent body (5) of this invention having a basis weight of 0.044 g/cm2 and a density of 0.22 g/cm3 was obtained by following the procedure of Example 4, except that the amount of the ground pulp wa~ changed to 66 parts by weight. The capacity of this ab~orbent body (5) for absorption under pre~ure was found to be 17.3 g/g, the ratio of exfoliation of absorbent polymer to be 7%, and the ratio of wet swelling to be 325%.
Examp l e 6 An absorbent body (6) of this invention having a basis weight of 0.029 g/cm2 and a density of 0.30 g/cm3 was obtalned by following the procedure of Example 4, except that the amount of the ~ynthetic pulp was changed to 15 parts by weight and that of the ground pulp to 34 partq by weight. The capacity of the produced absorbent body (6) for absorption under presqure was found to be 16.3 g/g, the ratio of exfoliation of absorbent polymer to be 19%, and the ratio of wet swelling to be 300%.
Examp l e 7 One hundred ( 100) parts by weight of the absorbent polymer C was mixed with 12 parts by weight of synthetic pulp (produced by Mit~ui Petrochemical Industries, Ltd. and ~ 2049861 marketed under product code of "SWP UL-4 15 n ) during continued additlon of 20 parts by weight of water thereto.
Then, in a mixer, the resultant mixture was dry mixed with 131 parts by weight oP ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interpo~ed between two opposed tissue papers having a basis weight of 0.0013 g/cm2 and then emboss preAsed at 150 C for one minute, to produce an absorbent body (7) of this invention having a basis weight of 0.047 g/cm2 and a density of 0.24 g/cm3. The capacity of the absorbent body (7) for ab30rption under pres~ure was found to be 12.5 g/g, the ratio of exfoliation of absorbent polymer to be 8%, and the ratio of wet swelling to be 275%.
Examp 1 e 8 An absorbent body (8) of thi~ invention having a basis weight of 0.050 g/cm2 and a density of 0.25 g/cm3 was produced by following the procedure of Example 7, except that the amount of the synthetic pulp was changed to 5 parts by weight and that of the ground pulp to 100 parts by weight. The capacity Or the absorbent body (8) for absorption under pressure wa~ Pound to be 15.3 g/g, the ratio of exfoliation of absorbent polymer to be 13%, and the ratio of wet ~welling to be 225%.
Examp 1 e 9 An absorbent body (9) of this invention having a ba~is weight of 0 . 060 g/cm2 and a density of 0 . 30 g/cm3 was produced by following the procedure of Example 7, except that the amount of the synthetic pulp was changed to 23 parts by weight and that of the ground pulp to 133 parts by weight. The capacity of the absorbent body (9) for absorption under pre~ure wa~ found to be 13.5 g/g, the ratio of exfoliation of absorbent polymer to be 12%, and the ratio of wet swelling to be 400%.
Examp 1 e 10 .
An absorbent body ( 10) of this invention having a basis weight of 0.070 g/cm2 and a density of 0.35 g/cm3 was produced by following the procedure of Example 7, except that the amount of the synthetic pulp was changed to 24 parts by weight and that of the ground pulp to 167 parts by weight. The capacity of the absorbent body ( 10) for absorption under pressure was found to be 12.3 g/g, the ratio of exfoliation of absorbent polymer to be 15%, and the ratio of wet sNelling to be 400%.
Example 1 1 An absorbent body ( 11 ) of this invention having a basis weight oP O . 044 g/cm2 and a density of O . 33 g/cm3 was produced by following the procedure of Example 9, except that the amount of the ground pulp was changed to 67 parts by weight . The capacity of the absorbent body ( 11 ) for absorption under pressure was found to be 14.2 g/g and the ratio of defoliation of absorbent polymer to be 10%, and the ratio of wet swelling to be 333,~.
Example 12 One hundred ( 100) parts by weight of the absorbent polymer D was mixed with 13 parts by weight of synthetic pulp (produced by Mitsui Petrochemical Industrie~, Ltd. and marketed under product code of "SWP UL-415n) during continued addition of 20 parts by weight of an aqueous 30 wt% aluminum polychloride solution thereto. Then, in a mixer, the resultant mixture was dry mixed with 100 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The produced web was interposed between two opposed tis~ue papers having a basi~
weight of 0.0013 g/cm2 and then emboss pressed at 150 C for one minute, to produce an absorbent body ( 12) of thls invention having a ba~is weight of 0.042 g/cm2 and a density of 0.21 g/cm3. The capacity of the absorbent body ( 12) for absorption under pressure wa~ found to be 13.2 g/g, the ~ 20498~1 ratio of exfoliation of absorbent polymer to be 5%, and the ratio of wet swelling to be 350%.
Example 1 3 One hundred ( 100) part~ by weight of the absorbent polymer B and 13 parts by weight of synthetic pulp ( produced by Mitsui Petrochemical Industries, Ltd. and marketed under product code of "SNP UL-415n) were mixed while the addition oP 20 parts by weight of 1% by weight aqueous solution of ethyleneglyool diglycidyl ether (product of Nagase Easei K.K. and marketed under Denacol EX-810) thereto was continued. In a mixer, the resultant nixture was dry mixed with 67 parts by weight of ground pulp. The produced mixture was pneumatically molded in the form of sheet on a wire screen with the aid of a batch type pneumatic molding device, to produce a web mea9urin~ 14 cm x 40 cm in area.
The web was interposed between two opposed tissue papers having a basis weight of 0.0013 g/cm2 and then emboss pressed at 150 C for 1 minute, to produce an absorbent body ( 13) of this invention having a basis weight of 0.047 g/cm2 and a density of 0.23 g/cm3. The oapacity of the absorbent body ( 13) for absorption under pres3ure was found to be 13.7 g/g, the ratio of exfoliation of absorbent polymer to be 3%, and the ratio of wet swelling to be 250%.
Example 1 4 An absorbent body ( 14 ) of this invention having a basis weight of O . 043 g/om2 and a density of O . 22 g/om3 was produced by following the procedure of Example 8, except that the amount of synthetic pulp was changed to 7 parts by weight. The capacity of the absorbent body ( 14) for absorption under pressure was found to be 15.3 g/g, the ratio of exfoliation of absorbent polymer to be 14%, and the ratio of wet swelling to be 300%.
Example 1 5 One hundred (100) parts by weight of the absorbent polymer C and 13 parts by weight of synthetio pulp (produced by Mitsui Petrochemical Industries, Ltd. and marketed under ~ 20~9861 product code of "SWP UL-415n) were mlxed while the addition of 20 parts by weight of water thereto was continued. In a mixer, the resultant mixture wa3 dry mixed with 100 parts by weight of ground pulp. The produced mixture was pneumatically molded in the form of sheet on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interpo3ed between two opposed tis3ue papers having a basis weight of 0.002 g/cm2 and then emboss pressed at 200 C for 10 seconds, to produce an absorbent body (15) of this invention having a basis weight of 0.052 g/cm2 and a density of 0.26 g/cm3. The capacity of the absorbent body (15) for ab30rption under pressure was found to be 14.5 g/g, the ratio of exfoliation of absorbent polymer to be 11,~, and the ratio of wet swelling to be 300%.
Example 16 One hundred ( 100) part~ by weight of the absorbent polymer C and 10 parts by weight of synthetic pulp (produced by Mitsui Petrochemical Industries, Ltd. and marketed under product code of "SWP UL-415n) were mixed while the addition of 20 part3 by weight of water thereto was continued. In a mixer, the resultant mixture wa~ dry mixed with 133 parts by weight of ground pulp. The produced mixture was pneumatically molded in the form of 3heet on a wire ~creen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interposed between two opposed tis3ue papers having a basis weight of 0.002 gicm2 and then embo33 pres3ed at 150 C for 10 minutes, to produce an absorbent body ( 16) of this invention having a basis weight of 0.092 g/cm2 and a density of 0.23 g/cm3. The capacity of the absorbent body ( 16) for ab30rption under pre33ure wa3 found to be 13.5 g/g, the ratio of exfoliation of ab30rbent polymer to be 29~, and the ratio of wet 3welling to be 350,~.
Example 17 ~ 2049861 One hundred ( 100) parts by weight of the absorbent polymer A was mixed with 8 parts by weight of synthetic pulp, while the addition of 20 parts by weight of water thereto was continued. In a mixer, the resultant mixture was dry mixed with 70 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web. On one hand, another web comprising 35 parts by weight of ground pulp and O . 7 parts by weight of synthetic pulp were prepared, and a web measuring 14 cm x 40 cm in area and having a basis weight of 0.046 g/cm2 was prepared by interposing the former web with these two latter webs. The web was compressed and heated at 150 C for 1 minute, to produce an absorbent body ( 17) of this invention having a density of 0.23 g/cm3. The capacity of the absorbent body ( 17) for absorption under pressure was found to be 13.5 g/g, the ratio of exfoliation of absorbent polymer to be 20%, and the ratio of wet ~welling to be 352%.
Examp l e 18 One hundred ( 100) parts by weight of the absorbent polymer D was mixed with 20 parts by weight of synthetic pulp while the addition of 20 parts by weight of water thereto was continued. In a mixer, the re~ultant mixture was dry mixed with 18 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire 3creen with the ald of a pneumatic molding device, to produce a web. The web was interposed between two opposed tissue papers having a basis weight oP 0.0013 g/cm2 and then emboss pressed at 150 C for 1 minute, to produce an absorbent body (18) of this invention having a basis weight of 0.019 g/cm2 and a density of 0.25 g/cm3. The capacity of the absorbent body ( 18) for absorption was round to be 18.0 g/g, the ratio of exfoliation of absorbent polymer to be 35%, and the ratio of wet swelling to be 375%.
Example 1 9 One hundred ( 100) parts by weight of the absorbent polyner A and 13 parts by weight of synthetic pulp (produced by Mit~ui Petrochemical Industries, Ltd. and marketed under product code of "SWP UL-415n~ were mLxed while the addition of 10 parts by weight of water thereto was continued. The produced mixture was interposed between two webs comprising 33 parts by weight of ground pulp to produce a web mea~uring 14 cm x 40 cm in area and having a ba~i~ weight oP 0.052 g/cm2. The produced web was embos~ compres3ed and heated at 150 C for 1 minute, to produce an absorbent body ( 19) of this invention having a density of 0.17 g/cm3. The capacity of the ab~orbent body ( 19~ for absorption under pressure wa~
found to be 12.5 g/g, the ratio of exfoliation of absorbent polymer to be 33%, and the ratio of wet ~welling to be 233%.
Example 20 One hundred ( 100) parts by weight of the ab~orbent polymer C and 20 parts by weight of synthetic pulp ( produced by Mitsui Petrochemical Industries, Ltd. and marketed under product code Or "SWP UL-415n) were mixed while the addition of 20 part~ by weight of water thereto was continued. In a mixer, the re3ultant mixture was dry mixed with 60 parts by weight of ground pulp. The produced mixture wa~
pneumatically molded in the form of sheet on a wire screen with the aid of a batch type pneumatic molding device, to produce a web mea3uring 14 cm x 40 cm in area. A web compri~ing 30 parts by weight group pulp was put on one ~urface of the produced web, and the web thus obtained was interposed between two oppo~ed tis3ue papers having a basis weight of 0.0013 g/cm2 and then passed between hot rollers to heat at 200 C for 20 ~econd~ and to obtain an absorbent body (20) of this invention having a basis weight of 0.048 g/cm2 and a denqity of 0.16 g/cm3. The capacity of the absorbent body (20) for absorption under pre~sure wa~q found to be 12.2 g/g, the ratio of exfoliation of absorbent polymer to be 14%, and the ratio of wet ~welling to be 210%.
Control 1 One hundred ( 100) parts by weight of the absorbent polymer C was mixed with 33 parts by weight of synthetLc pulp (produced by Mitsui Petrochemical Industries, Ltd. and marketed under product code of "SWP UL-4 15 n ) during continued addition of 20 parts by weight of water thereto.
Then, in a mixer, the resultant mixture was dry mixed with 100 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interposed between two opposed tissue papers having a basis welght of 0.0013 g/cm2 and then emboss pressed at 150 C for one minute to produce an absorbent body ( 1 ) for comparison having a basis weight of 0.048 g/cm2 and a density of 0.24 g/cm3. The capacity of the absorbent body ( 1 ) for comparison was found to be 10.2 g/g, the ratio of exfoliation of absorbent polymer to be 17%, and the ratio of wet swelling to be 250%.
Control 2 One hundred ( 100) parts by weight of the absorbent polymer C was mixed with 66 parts by weight of synthetic pulp (produced by Mitsui Petrochemical Industries, Ltd. and marketed under product code of "SWP UL-415n) during continued addition of 20 parts by weight of water thereto.
Then, in a mixer, the resultant mixture was dry mixed with 100 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The produced web was interposed between two opposed tissue papers having a basis weight of 0.0013 g/cm2 and then emboss pressed at 150 C for one minute, to produce an ab30rbent body (2) for comparison having a basis weight of 0.056 g/cm2 and a density of 0.28 g/cm3. The capacity of the absorbent body (2) for comparison for absorption under pressure was found to be 8.8 ~ 204986~
g/g, the ratio of exfoliation of absorbent polymer to be 5,q~, and the ratio of wet swelling to be 275,S.
Control 3 In a mixer, 100 parts by weight of the absorbent polymer C was dry mixed with 100 parts by weight of ground pulp. Then, the resultant mixture wa3 pneumatically molded on a wire 3creen with the aid of a batch type pneumatic molding device, to produ¢e a web mea3uring 14 cm x 40 cm in area. The web was interposed between two opposed tissue papers haYing a basis weight of 0.0013 g/cm2 and then emboss pressed at 150 C for one minute, to produce an absorbent body (3) Por comparison having a basi~ weight of 0.043 g/cm2 and a density of 0.17 g/cm3. The capacity of the absorbent body (3) for comparison for absorption under pressure was found to be 12.3 g/g, the ratio of exfoliation oP absorbent polymer to be 76S, and the ratio of wet swelling to be 240%.
Control 4 In a mixer, 100 parts by weight of the absorbent polymer C wa3 dry mixed with 13 parts by weight of synthetic pulp (produced by Mitsui Petrochemical Indu~tries, Ltd. and marketed under product code of "SWP UL-415") and 100 parts by weight of ground pulp. The resultant mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interpo3ed between two oppo3ed ti33ue paper3 having a basis weight of 0.0013 g/cm2 and then embos3 pre3sed at 150 C for one minute, to produce an ab30rbent body (4) for compari30n having a basis weight of 0.049 g/cm2 and a density of 0.25 g/cm3. The capacity of the ab30rbent body (4) for comparison for absorption under pressure was found to be 10.9 g/g, the ratio of exfoliation of absorbent polymer to be 53,~, and the ratio of wet 3welling to be 250,~.
Control 5 One hundred ( 100) parts by weight of the absorbent polymer C was mixed with 13 part3 by weight of 3ynthetic 2n4sg6l pulp (produced by Mitsui Petrochemical Industrie3, Ltd. and marketed under product code of "SWP UL-415") during continued addition of 20 parts by weight of water thereto.
Then, in a mixer, the resultant mixture was dry mixed with 100 parts by weight of ground pulp. The produced mixture was pneumatically molded on a wire screen with the aid of a batch type pneumatic molding device, to produce a web measuring 14 cm x 40 cm in area. The web was interposed between two opposed tissue papers having a basis weight of 13 g/m2 and then heated at 150 C for 10 minute3, to produce an absorbent body (5) for comparison having a basis weight of 0.050 g/cm2 and a den~ity of 0.08 g/cm3. The capacity of the absorbent body (5) for comparison for absorption under pressure was found to be 13.9 g/g, the ratio of exfoliation of absorbent polymer to be 56%, and the ratio of wet swelling to be 100%.
Example 21 A disposable diaper comprising a liquid-pervious polypropylene top sheet, two tis3ue papers, a 9 cm x 35 cm rectangular sample of the absorbent body ( 1 ) of this invention (weighing 15 g), a liquid-impervious polyethylene back sheet containing leg gathers, and two tape fasteners was manually assembled by tying the component parts with a double-face adhesive tape. The total weight of the diaper was 33 g.
The diaper was tried on a one-year old infant (having 10 kg of body weight) in comparison with a diaper (having a total weight of 50 g) currently available in the market. The diaper using the absorbent body of this invention was found to excel preeminently in shape-retaining property after absorption of urine and suffered only sparingly from leakage.
Example 22 Disposable diapers using absorbent bodies of varying properties were manufactured by following the procedure of Example 21. These diapers were tested for one month by a ~ 2~48~1 panel of ~even mother~. Each paneli~t randomly reoelved 30 diapers and tried them on her child. After the te~t, the diaper~ were tested for ratio OI test diaper leaked and shape-retaining property of abAorbent body. The re~ult~ are shown in Table 1. It iY clearly noted from the table that the absorbent article~ u~ing the ab~orbent bodies of thi~
invention pos~e~ed out~tanding ab~orption characteri~tlc~.

-~ 20~3861 o o ' .
O ~ O L_ r_ ~ t~ ~
.
O;
O ~
E-' I O
q~
~- ' ~ 5 ~ 5 ~ O
o C ' ~
P. _ ~-1 E ~ ~ ~ ~ ~ ~ o .
~ Z C ~
~ .

Claims

1. An absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof, characterized by the fact that a density of said absorbent body is in the range of from 0.1 to 0.5 g/cm3, a capacity of said absorbent body for absorption of physiological saline solution under pressure is in the range of from 11 to 25 g/g, and a ratio of exfoliation of said absorbent polymer is not more than 45%.

2. An absorbent body according to claim 1, wherein said absorbent polymer is a cross-linked polymer of a water-soluble ethylenic monomer having acrylic acid or an acrylate as a main component thereof.

3. An absorbent body according to claim 1, wherein the amount of said hydrophilic fibers is in the range of from 5 to 500 parts by weight, based on 100 parts by weight of said absorbent polymer.

4. An absorbent body according to claim 3, which further comprises 1 to 30 parts by weight of synthetic pulp, based on 100 parts by weight of said absorbent polymer.

5. An absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof, characterized by the fact that the capacity of said absorbent body for absorption of physiological saline solution under pressure is in the range of 11 to 25 g/g, a ratio of exfoliation of said absorbent polymer is not more than 45%, and a ratio of wet swelling is not less than 200%.

6. An absorbent body according to claim 5, wherein said absorbent polymer is a cross-linked polymer of a water-soluble ethylenic monomer having acrylic acid or an acrylate as a main component thereof.

7. An absorbent body according to claim 5, wherein the amount of said hydrophilic fibers is in the range of from 5 to 500 parts by weight, based on 100 parts by weight of said absorbent polymer.

8. An absorbent body according to claim 7, which further comprises 1 to 30 parts by weight of synthetic pulp, based on 100 parts by weight of said absorbent polymer.

9. An absorbent article comprising a liquid-pervious surface material, a liquid-impervious lining material, and an absorbent layer interposed therebetween, characterized by the fact that said absorbent layer at least partly comprises of an absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof and exhibiting absorption characteristics such that the density is in the range of from 0.1 to 0.5 g/cm3, a capacity for absorption of physiological saline solution under pressure is in the range of from 11 to 25 g/g, and a ratio of exfoliation of said absorbent polymer is not more than 45%.

10. An absorbent article according to claim 9, wherein said absorbent polymer is a cross-linked polymer of a water-soluble ethylenic monomer having acrylic acid or an acrylate as a main component thereof.

11. An absorbent article according to claim 9, wherein the amount of said hydrophilic fibers is in the range of from 5 to 500 parts by weight, based on 100 parts by weight of said absorbent polymer.

12. An absorbent article according to claim 11, wherein said absorbent body further comprises 1 to 30 parts by weight of synthetic pulp, based on 100 parts by weight of said absorbent polymer.

13. An absorbent article comprising a liquid-pervious surface material, a liquid-impervious lining material, and an absorbent layer interposed therebetween, characterized by the fact that said absorbent layer at least partly comprises of an absorbent body having an absorbent polymer and hydrophilic fibers as main components thereof and exhibiting absorption characteristics such that a capacity for absorption of physiological saline solution is in the range of from 11 to 25 g/g, a ratio of exfoliation of said absorbent polymer is not more than 45%, and a ratio of wet swelling is not less than 200%.

14. An absorbent article according to claim 13, wherein said absorbent polymer is a cross-linked polymer of a water-soluble ethylenic monomer having acrylic acid or an acrylate as a main component thereof.

15. An absorbent article according to claim 13, wherein the amount of said hydrophilic fibers is in the range of from 5 to 500 parts by weight, based on 100 parts by weight of said absorbent polymer.

16. An absorbent article according to claim 15, wherein said absorbent body further comprises 1 to 30 parts by weight of synthetic pulp, based on 100 parts by weight of said absorbent polymer.