Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-08-11
2001-12-25
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C521S028000, C525S057000, C525S058000, C524S599000, C524S602000, C428S500000
Reexamination Certificate
active
06333109
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a water-swellable crosslinked polymer composition.
More specifically, the present invention relates to a novel water-swellable crosslinked polymer composition which comprises and exhibits an excellent saltwater absorption speed and has a greatly enhanced absorption capacity under a load.
BACKGROUND ART
In recent years, so-called water-absorbent polymers are widely used as constituent materials of sanitary materials, such as disposable diapers, sanitary napkins, and so-called incontinent pads, for the purpose of causing the water-absorbent polymers to absorb body fluids.
Known examples of the above water-absorbent polymers include: crosslinked products of partially neutralized polyacrylic acids; hydrolyzed products of starch-acrylic acid graft polymers; saponified products of vinyl acetate-acrylic acid ester copolymers; and hydrolyzed products of acrylonitrile- or acrylamide copolymers, and their crosslinked products. However, almost all of these conventionally known water-absorbent polymers are products by neutralizing their acid groups with compounds of alkaline metals. Therefore, in the case where the surface neighborhood of particles of the polymers is not secondarily crosslinked, their absorption capacity under a load for a physiological salt solution is below 10 g/g, and further, even if the surface neighborhood of particles of the polymers is secondarily crosslinked, their absorption capacity under a load for a physiological salt solution is merely 25 g/g at the highest, and is therefore still insufficient to the use for disposable diapers or sanitary articles. In addition, because those conventional water-absorbent polymers merely exhibit a remarkably low absorption capacity for aqueous liquids containing electrolytes, their application range is limited. Thus, it is desired to develop a novel salt-water-absorbing agent which can rapidly absorb salt water to swell therewith even under loaded conditions.
To solve such problems, WO 96/15162, WO 96/15180, WO 96/17681, WO 98/24832, and WO 98/37149 propose water-absorbing agents which comprise water-swellable crosslinked polymers of acidity in water and compounds of basicity in water and utilize the ion-exchanging function and desalting mechanism due to interactions between the acid and the base. However, processes as described in these patents have problems in that: because the compound of basicity in water and the water-swellable crosslinked polymer of acidity in water are allowed to exist separately from each other, the saltwater absorption speed under a load is slow, and further, the absorption capacity under a load is low.
DISCLOSURE OF THE INVENTION
OBJECT OF THE INVENTION
An object of the present invention is to provide: a novel water-swellable crosslinked polymer composition which can rapidly absorb salt water to swell therewith even under loaded conditions; and a production process therefor. Accordingly, if the water-swellable crosslinked polymer composition according to the present invention is used as a water-absorbing agent for absorbent articles such as disposable diapers, the leakage can be remarkably decreased and their surfaces can be kept in a rustling dry state, even in the case of a long-term use.
SUMMARY OF THE INVENTION
The present inventors diligently studied to provide the novel water-swellable crosslinked polymer composition which can achieve the above object. As a result, the inventors attained to the present invention.
That is to say, the following inventions are described herein:
(First invention): A water-swellable crosslinked polymer composition, which comprises a blend of a water-swellable crosslinked polymer of acidity in water and a water-swellable crosslinked polymer of basicity in water, with the composition being characterized by exhibiting a saltwater absorption capacity of at least 50 g/g under a load of 3.5 g/cm
2
in 10 hours, and absorbing 60% of the 10-hour saltwater absorption capacity under the load of 3.5 g/cm
2
in less than 5 minutes.
(Second invention): A water-swellable crosslinked polymer composition, which comprises a blend of a water-swellable crosslinked polymer of acidity in water and a water-swellable crosslinked polymer of basicity in water, with the composition being characterized by exhibiting a saltwater absorption capacity of at least 40 g/g under a load of 21 g/cm
2
in 10 hours, and absorbing 60% of the 10-hour saltwater absorption capacity under the load of 21 g/cm
2
in less than 5 minutes.
(Third invention): A water-swellable crosslinked polymer composition, which comprises a blend of water-swellable crosslinked polymer particles of acidity in water and water-swellable crosslinked polymer particles of basicity in water, with the composition being characterized in that the water-swellable crosslinked polymer particles of acidity in water are unified with the water-swellable crosslinked polymer particles of basicity in water through ionic bondings in a state where water is present between the particles, and further characterized by exhibiting a saltwater absorption capacity of not less than 33 g/g in 60 minutes.
(Fourth invention): A water-swellable crosslinked polymer composition, which comprises a blend of water-swellable crosslinked polymer particles of acidity in water and water-swellable crosslinked polymer particles of basicity in water, with the composition being characterized in that ionic bondings are formed in a state where water is present between the particles by neutralization of at least part of acid groups of the water-swellable crosslinked polymer particles of acidity in water with the water-swellable crosslinked polymer particles of basicity in water, and further characterized by exhibiting an absorption capacity of not less than 25 g/g under a load.
(Fifth invention): A water-swellable crosslinked polymer composition, which comprises a blend of a water-swellable crosslinked polymer of acidity in water and a water-swellable crosslinked polymer of basicity in water, with the composition being characterized in that the water-swellable crosslinked polymer of acidity in water is a crosslinked polyacrylic acid, and in that the water-swellable crosslinked polymer of basicity in water is a crosslinked polyethylenimine and/or a crosslinked polyallylamine, and further characterized by exhibiting a desalting amount of not less than 0.35 g/g.
(Sixth invention): A production process for a water-swellable crosslinked polymer composition including a blend of water-swellable crosslinked polymer particles of acidity in water and water-swellable crosslinked polymer particles of basicity in water, with the process being characterized by comprising the step of adding the water-swellable crosslinked polymer particles of basicity in water to the water-swellable crosslinked polymer particles of acidity in water, thereby neutralizing at least part of acid groups of the water-swellable crosslinked polymer particles of acidity in water to form ionic bondings in a state where water is present between the particles.
(Seventh invention): A production process for a water-swellable crosslinked polymer composition including a blend of a water-swellable crosslinked polymer of acidity in water and a water-swellable crosslinked polymer of basicity in water, with the process being characterized by comprising the step of blending the water-swellable crosslinked polymer of acidity in water and the water-swellable crosslinked polymer of basicity in water under conditions where at least one of the water-swellable crosslinked polymer of acidity in water and the water-swellable crosslinked polymer of basicity in water is in a hydrogelled state, and further characterized in that both the water-swellable crosslinked polymer of acidity in water and the water-swellable crosslinked polymer of basicity in water have an extractable content of not more than 10 weight % before blending.
(Eighth invention): A production process for a water-swellable crosslinked polymer of acidity in water, comprising the steps of: carrying out aqueous solution polym
Adachi Yoshifumi
Harada Nobuyuki
Kitayama Toshimasa
Sakamoto Shigeru
Acquah Samuel A.
Nippon Shokubai Co. , Ltd.
Roylance Abrams Berdo & Goodman L.L.P.
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