Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1996-08-02
1999-11-16
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
604358, 604369, C08J 928
Patent
active
059859440
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to water-absorbent resins suitable for use in absorbent articles, for example, sanitary materials (body fluid absorbent articles) such as paper diapers (disposable diapers), sanitary napkins, so-called incontinence pads (articles for incontinent person), wound protecting material and wound healing material, building material, water retentive material for soil, drip absorbing and freshness retentive materials for food, and waterproof material. The present invention also relates to a process for producing such water-absorbent resins, and water-absorbent resin compositions using the water-absorbent resins.
BACKGROUND OF THE INVENTION
In recent years, water-absorbent resins for absorbing body fluids such as urine, sweat, and blood are widely used as a constituent element of sanitary materials such as paper diapers, sanitary napkins, incontinence pads, wound protecting material, and wound healing material. Such water-absorbent resins are utilized not only as sanitary materials, but also applied to various uses to absorb and retain water and absorb moisture, for example, building material, water retentive material for soil, drip absorbing and freshness retentive materials for food, and waterproof material.
Known water absorbing resins include partially neutralized and cross-linked acrylic acid (Japanese Publication for Unexamined Patent Applications No. (Tokukaisho) 55-84304, 55-108407, and 55-133413, and U.S. Pat. No. 4,654,039), hydrolyzed starch-acrylonitrile graft polymer (Japanese Publication for Examined Patent Application No. (Tokukosho) 49-43995, neutralized starch-acrylic acid graft polymer (Japanese Publication for Unexamined Patent Application No. (Tokukaisho) 51-125468), saponified vinyl acetate-acrylate copolymer (Japanese Publication for Unexamined Patent Application No. (Tokukaisho) 52-14689), hydrolyzed acrylonitrile copolymer or acrylamide copolymer, or cross-linked acrylonitrile copolymer and acrylamide copolymer (Japanese Publication for Unexamined Patent Application No. (Tokukaisho) 53-15959), cross-linked carboxymethyl cellulose, and cross-linked cationic monomer (Japanese Publication for Unexamined Patent Applications No. (Tokukaisho) 58-154709 and 58-154710), cross-linked isobutylene-maleic anhydrid copolymer material, cross-linked copolymer of 2-acrylamido-2-methylpropane sulfonic acid and acrylic acid, cross-linked polyethyleneoxide, and cross-linked copolymer of methoxypolyethylene glycol and acrylic acid.
All of the water-absorbent resins are in the form of particles or powder having a particle diameter of around 0.01 mm to 5 mm. The absorption rate of the water-absorbent resin is generally determined by the particle diameter. There is a tendency that the absorption rate of each particle increases as the particle diameter becomes smaller ("Polymers" Vol. 36, page 614, Polymer Association, 1987).
However, in actual, as the particle diameter becomes smaller, the liquid permeability for allowing aqueous fluids, for example, body fluids, to flow between the particles, is lowered. Namely, a so-called gel blocking phenomenon occurs. Therefore, when using the water-absorbent resin, it is necessary to select an optimum particle diameter by considering the absorption rate and the liquid permeability. The tendency of causing a gel blocking phenomenon becomes higher as the absorption rate of the water-absorbent resin increases. The main causes of the gel blocking phenomenon are a decrease in the void space and an increase in tack between particles after being swelled, under pressure.
In order to improve the water absorption characteristics of the water-absorbent resin, particularly, the absorption rate, various production methods and modification methods of water-absorbent resins have been proposed as shown below. More specifically, as the production and modification methods of water-absorbent resins, for example, the following two methods have been proposed. 1 Application of secondary cross-linking treatment, i.e., improving the cross-link
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Harada Nobuyuki
Ishizaki Kunihiko
Miyake Koji
Motono Yoshihiro
Obara Hisanobu
Foelak Morton
Nippon Shokubai Co. , Ltd.
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