Sumitomo Seika Chemicals Co., Ltd.

Sumitomo Seika Singapore Pte. Ltd.

Tetsuhiro Hinayama

Masayoshi Handa

Hideki Yokoyama

Hiroki Yabuguchi

Masahiro Murakami

Junichi Takatori

Shinya Fukudome

Maoki Hama

Koji Ueda

Kenta Kumazawa

Haruka Inaba

Noriko Honda

Hideki Matsushita

Sok Kiat Cheng

Syuji Tsuno

Junichi Maruo

Yohei Yamamoto

A water-absorbent resin that can reduce the amount of backflow of an absorbed liquid even when the water-absorbent resin is used at a low content in an absorbent material is provided. An absorbent article comprising an absorbent material containing the resin is also provided. The resin is a crosslinked polymer of a water-soluble ethylenically unsaturated monomer and has a dry-up index of 1.85 or more, as represented by equation (1):dry-up index=overall absorption capacity term α×water absorption rate term β  (1)where the overall absorption capacity term α and the water absorption rate term β are determined according to equations (2) and (3): water absorption rate term β=dynamic water absorption rate/static water absorption rate  (3).

Water-absorbing resin

Provided is a water-absorbent resin which is capable of giving an absorbent material improved gel-shape stability and which has excellent water-absorption capacity. A water-absorbent resin of the present invention is a polymer of a water-soluble ethylenically unsaturated monomer, and has the following properties (1) and (2): (1) A disintegration amount at 20-fold swelling is 30% by mass or less; and (2) a solubility in physiological saline is 25% by mass or less. (Determination Method for Disintegration Amount at 20-Fold Swelling) 5 g of the water-absorbent resin is added to 100 g of physiological saline to allow the water-absorbent resin to absorb the physiological saline, thereby obtaining a gel. The obtained gel is divided approximately equally into five portions, and these portions are introduced respectively into cylindrical molds having a length of 3.6 cm and a radius of 2.8 cm and molded. The masses of the five molded cylindrical gels are measured. The heaviest and the lightest of the five gels are removed, and the remaining three gels are used as samples. A mass Wa (g) of each sample is measured. Each weighed sample is placed on the uppermost sieve of a combination of JIS standard sieves having a mesh size of 5.6 mm and a receptacle in this order and shaken for 10 minutes using a Ro-Tap shaker (rotation speed, 290 rpm; number of taps, 165 rpm). A mass Wb (g) of the gel which has passed through the sieves is measured. The disintegration amount of each sample is calculated using the following equation: Disintegration amount of sample (%)=Wb (g)/Wa (g)&#xd7;100. An average of the disintegration amounts for three samples to be measured is regarded as the disintegration amount at 20-fold swelling of the water-absorbent resin.

Provided is a method of producing a water-absorbent resin comprising a step of polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal-crosslinking agent, and a step of performing post-crosslinking, wherein:

Water-absorbent resin and method of producing water-absorbent resin

Provided is: a water-absorbent resin which has a better water absorption performance and with which it is possible to improve absorption performance under a load when used in an absorbent material. This water-absorbent resin, obtained by polymerising a water soluble ethylenically unsaturated monomer in the presence of an internal-crosslinking agent and by post-crosslinking using a post-crosslinking agent, has a water-absorption capacity of physiological saline under a load of 4.14 kPa of 16 mL/g or more, has a mass proportion of particles from 150 to 850 &#x3bc;m relative to the whole proportion of 85 mass % or more, moreover has a mass proportion of particles from 300 to 400 &#x3bc;m relative to the whole proportion of 20 mass % or more, and has an absorption capacity elasticity index represented by formula (I) of 68,000 or more. Absorption capacity elasticity index=storage elastic modulus [Pa]&#xd7;centrifugal retention rate [g/g] . . . (I).

Water-absorbent resin and absorbent article

Provided are: a water-absorbent resin which, when used as an absorbent material, retains a high water-absorption performance, increases the diffusivity of a to-be-absorbed liquid and makes it possible to effectively decrease the amount of re-wet; and an absorbent article formed using an absorbent material including the water-absorbent resin. The water-absorbent resin according to the present invention is a water-absorbent resin obtained by polymerizing a water-soluble ethylenically monomer in the presence of an internal-crosslinking agent and thereafter post-crosslinking the polymer with a post-crosslinking agent, characterized in that when subjected to a liquid flow test, the water-absorbent resin has an effective absorbent material index (K) indicated by equation (I) of 250 or greater.Effective absorbent material index ()=[(the amount of liquid flow) (g)]&#xd7;[(artificial-urine absorption ratio) (g/g)]&#x2003;&#x2003;(I)

The present invention provides a process for producing a water-absorbent resin, characterized in that a reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer is carried out in a hydrocarbon dispersion medium comprising a dispersion stabilizer while an azo-based compound and a peroxide are combined in the presence of an internal-crosslinking agent, in that the following formulae are satisfied,0.10&#x2264;/()&#x2003;&#x2003;(1), and0.055&#x2264;+9&#xd7;&#x2264;0.120&#x2003;&#x2003;(2),

Process for producing water-absorbent resin

The following are provided: a water-absorbent resin in which, in the formation of an absorbent material forming an absorbent article, dispersion is satisfactory even in a moisture absorption state, which prevents the occurrence of troubles at the time of manufacturing of the absorbent article and which allows efficient manufacturing; and an absorbent article using an absorbent material containing the water-absorbent resin. The water-absorbent resin according to the present invention is obtained by polymerizing a water-soluble ethylenically unsaturated monomer and performing post-crosslinking thereon with a post-crosslinking agent, and the water-absorbent resin satisfies the requirements below:

Provided are a water-absorbent resin having better water-absorption performance and being prevented from discoloring before and after storage for a long time under high temperature and high humidity, and an absorbent article including the absorbent resin. The water-absorbent resin according to the present invention is prepared by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal-crosslinking agent and performing post-crosslinking with a post-crosslinking agent, wherein the water-absorbent resin satisfies the following properties: (A) a water-absorption capacity of physiological saline of 55 g/g or more, a water-absorption capacity of physiological saline under a load of 4.14 kPa of 15 mL/g or more, and a residual monomer content of 300 ppm or less; and (B) a yellow index of 5.0 or less and a yellow index change ratio (&#x394;YI) after leaving for 10 days under 70&#xb0; C. and 90% RH of 10 or less.

With respect to water-absorbent resins, there are provided a method of manufacturing a water-absorbent resin having an appropriate BET specific surface and a water-absorption rate and a water-absorbing agent and an absorbent article that are formed by using the water-absorbent resin. In a first aspect of the present invention, when reverse phase suspension polymerization of two steps or more is performed on a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium in the presence of at least an azo compound, a peroxide and an internal-crosslinking agent, the used amount of the internal-crosslinking agent at the time of the polymerization of a first step is adjusted to fall within a range of 0.015 to 0.150 mmol per mole of the water-soluble ethylenically unsaturated monomer used at the time of the polymerization of the first step and he polymerization is performed such that, the BET specific surface area of secondary particles formed by agglomeration of primary particles obtained is controlled.

Method of manufacturing water-absorbent resin, water-absorbent resin, water-absorbing agent and absorbent article

The invention provides a novel method for producing a water-absorbent resin comprising: subjecting at least one water-soluble ethylenic unsaturated monomer to reversed-phase suspension polymerization in a petroleum hydrocarbon dispersion medium, the reversed-phase suspension polymerization being conducted using a 0.00005 to 0.00016 mole of water-soluble azo initiator for radical polymerization per mole of the water-soluble ethylenic unsaturated monomer in the presence of 0.000015 to 0.00015 mole of hypophosphorous compound per mole of the water-soluble ethylenic unsaturated monomer. According to the method, the environmental impact can be lessened by reducing the amount of petroleum hydrocarbon dispersion medium released to the outside of the system, and the method makes it possible to obtain a water-absorbent resin having a high water-retention capacity and water-absorption capacity under a load, and a small content of water soluble component at the same time.

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Himeji, Japan

Tetsuhiro Hinayama