Particulate water absorbing agent with water-absorbing resin as main component

Abstract

The present invention provides a water absorbing agent which maintains excellent water absorbing properties for a long time, even when urine composition of human urine varies depending. A particulate water absorbing agent comprising a water-absorbing resin obtained by crosslinking polymerization of an unsaturated monomer, which exhibits Centrifuge retention capacity in a physiological saline solution of not lower than 32 g / g, mass median particle size (D50) of 200 to 400 μm, ratio of particles with diameter of smaller than 150 μm of 0 to 2% by weight, and increased extractables by deterioration of 0 to 15% by weight and extractables for one hour in deterioration test liquid of 0.1 to 30% by weight.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a particulate water absorbing agent including a water-absorbing resin as a main component. In particular, it relates to a particulate water absorbing agent fulfilling superior absorption ability conventionally not obtained in practical applications as absorbing articles such as a diaper. [0003] 2. Description of Related Art [0004] At present, as component materials in sanitary goods such as a paper diaper, a sanitary napkin, an incontinence pad, and the like, a water-absorbing resin to absorb body fluid and hydrophilic fibers such as pulp are widely used. As the water-absorbing resin, for example, partially neutralized and crosslinked polyacrylic acid, hydrolysates of starch-acrylic acid graft polymer, saponified vinyl acetate-acrylic acid ester copolymers, hydrolysates of acrylonitrile copolymers or acrylamide copolymers or crosslinked polymers thereof, crosslinked polymers of catio...

AI Technical Summary

Benefits of technology

[0062] Using the particulate water absorbing agent of the present invention, due to having specific absorption capacity and specific particle size distribution, in practical application as absorbing articles such as a diaper, particularly in absorbing ability in short period, not conventionally obtained performance can be attained. In particular, rewet amount can be reduced and improvement effect of dry feeling at diaper surface is significant.

[0063] Further, due to inhibition of deterioration caused by urine, it provides superior gel stability and maintains absorbing performance over long period, therefore it reduces discomfort for persons wearing absorbing articles.

[0064] In the present invention, because deterioration caused by urine can be inhibited and simultaneously specific particle size distribution is provided, size segregation is less and in powder transfer to produce the particulate water absorbing agent and produce absorbing articles such as a diaper, superior piston-flow property is provided and pulsation which is periodical change in powder feed amount is inhibited. In addition to this, in production of absorbing articles such as a diaper, mixing is easy between the particulate water absorbing agent of the present invention and hydrophilic fibers such as wood crushed pulp, which conveniently provides homogeneous composition. Best Embodiments to Practice the Invention

[0065] Raw materials used for the water-absorbing resin and the water absorbing agent of the present invention and reaction conditions will be explained below. In the present invention, the followings are values obtained by methods described in Examples shown later: (a) centrifuge retention capacity (CRC) in a physiological saline solution, (b) mass median particle size (D50), (d) increased extractables by deterioration, (e) increased ratio of extractables by deterioration, (f) extractables for 16 hours in a physiological saline solution, (g) absorbency against pressure at 4.8 kPa (AAP4.8 kPa) in a physiological saline solution, (i) absorbency against pressure at 1.9 kPa (AAP1.9 kPa) in a physiological saline solution, (j) absorption speed with vortex method in a physiological saline solution, (k) fluidity after moisture absorption, (l) logarithmic standard deviation of particle size distribution and extractables for one hour in deterioration test liquid.

[0067] A water-absorbing resin of the present invention means a crosslinked polymer which can form hydrogel and is water swelling and non-dissolving in water, for example, water swelling indicates one absorbing large quantity of water in ion exchanged water, such as essentially 5 times or more own weight and preferably 50 to 1000 times. Non-dissolving in water means one with extractables in water in 1 hour of not higher than 50% by weight and in the range described later. Measurement methods thereof are specified in Examples.

[0068] As the water-absorbing resin in the present invention, to attain objectives of the present invention, a water-absorbing resin obtained by crosslinking polymerization of an unsaturated monomer containing an acid group and / or salts thereof is essentially used and preferably (partially) neutralized polymer of polyacrylic acid obtained by polymerizing and crosslinking of an unsaturated monomer mainly composed of acrylic acid and / or salts thereof is used. Any water-absorbing resin may be used as long as it has crosslinked polymerized structure and it may be the water-absorbing resin obtained by crosslinking reaction with a crosslinking agent after polymerization of an unsaturated monomer containing an acid group and / or salts thereof.

Problems solved by technology

Among water-absorbing resins or water absorbing agents which have been developed based on many properties, as described above, those targeted to or with specifications of these properties have also been produced, however, there was a problem that they have not yet satisfactorily fulfilled performance in practical use such as a paper diaper, and the like, even if these properties are controlled.

Practically sufficient performance has not yet attained even by controlling or designing such properties as water-absorption speed, centrifuge retention capacity, absorbency against pressure, gel strength, durability, extractables and particle size whereas many water-absorbing resins or water absorbing agents have been developed and used.