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  Particulate water absorbing agent with water-absorbing resin as main componentUSPTO Application #: 20070066167Title: 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. (end of abstract) Agent: Fish & Richardson PC - Minneapolis, MN, US Inventors: Katsuyuki Wada, Kazuki Kimura, Hiroko Ueda, Teruyuki Kanto, Hirotama Fujimaru USPTO Applicaton #: 20070066167 - Class: 442101000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Coated Or Impregnated Woven, Knit, Or Nonwoven Fabric Which Is Not (a) Associated With Another Preformed Layer Or Fiber Layer Or, (b) With Respect To Woven And Knit, Characterized, Respectively, By A Particular Or Differential Weave Or Knit, Wherein The Coating Or Impregnation Is Neither A Foamed Material Nor A Free Metal Or Alloy Layer, Coating Or Impregnation Is Anti-slip Or Friction-increasing Other Than Specified As An Abrasive The Patent Description & Claims data below is from USPTO Patent Application 20070066167. Brief Patent Description - Full Patent Description - Patent Application Claims
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 cationic monomers, and the like are used as main raw materials. [0005] The water-absorbing resin has conventionally been required to have superior property such as superior liquid absorption amount or water absorption speed, gel strength and gel permeability in contact with aqueous liquid such as body fluid, along with water suction force to suck water from a substrate containing aqueous liquid. Further, as recent trends, a water-absorbing resin powder with very narrow particle size distribution or a water-absorbing resin with high absorption capacity and low water-extractables has been required and high absorbency against pressure or liquid permeability under pressure has essentially been required. In addition to the above needs, such characteristics of gel has also been required as not to be deteriorated for long term and to retain absorbing performance even in swollen and gelled state by absorption of body fluid or urine. [0006] For example, there are many patent applications on many parameters specifying various properties of these water-absorbing resins or water absorbing agents with a water-absorbing resin as a main component, or on measurement methods thereof (U.S. Reissued 32,649, UK2267094B, U.S. Pat. No. 5,051,259, U.S. Pat. No. 5,419,956, U.S. Pat. No. 6,087,002, EP0629441, EP0707603, EP0712659, EP1029886, U.S. Pat. No. 5,462,972, U.S. Pat. No. 5,453,323, U.S. Pat. No. 5,797,893, U.S. Pat. No. 6,127,454, U.S. Pat. No. 6,184,433, U.S. Pat. No. 6,297,335, U.S. Reissued 37,021, U.S. Pat. No. 5,140,076, U.S. Pat. No. 6,414,214B1, U.S. Pat. No. 5,994,440, U.S. Pat. No. 6,444,744, U.S. Pat. No. 6,194,531, EP0940148, EP1153656, EP0605215, U.S. Pat. No. 5,147,343, U.S. Pat. No. 5,149,335, EP0532002, U.S. Pat. No. 5,601,452, U.S. Pat. No. 5,562,646, U.S. Pat. No. 5,669,894, U.S. Pat. No. 6,150,582, WO02/053198, EP0937739). [0007] Water-absorbing resins superior in gel strength, extractables and absorption capacity are proposed in U.S. Reissued 32,649. A water-absorbing resin superior in liquid permeability under no pressure, absorption speed and absorption capacity is proposed in UK2267094B. Technology specifying specific particle size distribution is also proposed in U.S. Pat. No. 5,051,259, U.S. Pat. No. 5,419,956, U.S. Pat. No. 6,087,002 and EP0629441. Further, a water-absorbing resin superior in absorbency against pressure under various loads or many measurement methods therefore are also proposed and water-absorbing resins with superior absorbency against pressure alone or in combination with other property are proposed in EP0707603, EP0712659, EP1029886, U.S. Pat. No. 5,462,972, U.S. Pat. No. 5,453,323, U.S. Pat. No. 5,797,893, U.S. Pat. No. 6,127,454, U.S. Pat. No. 6,184,433, U.S. Pat. No. 6,297,335 and U.S. Reissued 37,021. [0008] Water-absorbing resins with little property decrease by impact are proposed in U.S. Pat. No. 5,140,076 and U.S. Pat. No. 6,414,214B1. A water-absorbing resin with specific powdery dust amount is proposed in U.S. Pat. No. 5,994,440, and a water-absorbing resin with less coloring is proposed in U.S. Pat. No. 6,444,744. Water-absorbing resins superior in gel durability in an aqueous L-ascorbic acid solution as index of urine resistance or superior in water absorption ability are proposed in U.S. Pat. No. 6,194,531 and EP0940148. A water-absorbing resin with superior air permeability is proposed in EP1153656. A water-absorbing resin with less residual monomers is proposed in EP0605215. [0009] Further, in U.S. Pat. No. 5,147,343, U.S. Pat. No. 5,149,335, EP0532002, U.S. Pat. No. 5,601,452, U.S. Pat. No. 5,562,646, U.S. Pat. No. 5,669,894, U.S. Pat. No. 6,150,582, WO02/053198, water-absorbing resins with specific property are proposed as suitable to water-absorbing articles such as a diaper having specific property, composition or polymer concentration. Further, a method for surface crosslinking, while pulverizing at least a part of resin particles is proposed in EP0937739. SUMMARY OF THE INVENTION [0010] 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. [0011] 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. Therefore, it is an object of the present invention to provide a water absorbing agent suitable to practical use in conventional water absorbing agent substrate. DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0012] After studying to solve the problems, it was found that in a water absorbing agent of the present invention having specific particle size distribution and absorption capacity, components contained in urine gradually destruct crosslinked structure of a water-absorbing resin to make labile to deterioration of the water absorbing agent and such deterioration caused by urine increases extractables and changes water-absorption properties. Conventionally, properties of the water-absorbing resin or the water absorbing agent measured by a physiological saline solution (an aqueous solution of 0.9% by weight of NaCl) or various artificial urine solutions have been proposed, however, urine components in artificial urine are different in each patent and composition of practical urine solution itself is not constant but changes depending on living environment, food practice, age or seasons and furthermore largely changes every time or by physical conditions even in the same person. Because absorption properties of a conventional water-absorbing resin or a water absorbing agent have been evaluated using single kind of specific absorption liquid such as a specific physiological saline solution or artificial urine solution as a urine model, evaluation of the water absorbing agent responsive to change in urine composition could not suitably be carried out and thus it was clarified that a conventional water absorbing agent could not exert sufficient performance in practical use when extractables of the water absorbing agent changed due to change in urine composition. [0013] Therefore, the present invention defined "deterioration caused by urine" as deterioration of a water absorbing agent generated by personal difference in urine, or urine compositional change by seasons or physical conditions of even the same person, and as indexes of degree of deterioration caused by urine, "increased extractables by deterioration" and "increased ratio of extractables by deterioration" were introduced. In the present invention, increased extractables by deterioration and increased ratio of extractables by deterioration are defined by the following formulas. In the present invention, deterioration test liquid means a physiological saline solution containing 0.05% by weight of L-ascorbic acid and a physiological saline solution means an aqueous solution of 0.9% by weight of NaCl, which is used at room temperature (25.degree. C..+-.2.degree. C.) unless otherwise specified especially. Measurement methods thereof are as described in Examples shown later. Increased extractables by deterioration (% by weight)=extractables for one hour in deterioration test liquid (% by weight)-extractables for one hour in a physiological saline solution (% by weight) Increased ratio of extractables by deterioration=extractables for one hour in deterioration test liquid (% by weight)/extractables for one hour in a physiological saline solution (% by weight) [0014] When extractables increases from the amount before deterioration, in deterioration test liquid, the extractables tends to be more easily exuded from an absorbing substrate, which in turn obstructs diffusion of liquid such as blood and urine into an absorbing substrate and thus lowers absorption properties. In addition, significant increase in extractables suggests destruction of crosslinked structure of the water absorbing agent, making retention difficult of body fluid such as urine absorbed by the water absorbing agent and thus absorption performance is lowered. Such decrease in absorption performance appears as increase in rewet amount in an absorbing substrate or absorbing articles. It is thus preferable for "increased extractables by deterioration" and "increased ratio of extractables by deterioration" to be limited within specific range to inhibits increase in rewet amount. [0015] It is also clarified by detailed study on deterioration due to urine that the deterioration degree tends to depend on surface area of the water absorbing agent and extractables by the deterioration significantly increases in the water absorbing agent with particle size distribution of smaller mass median particle size, for example, the water absorbing agent with mass median particle size D50 not larger than 400 .mu.m. Mass median particle size is an important factor influencing absorption behavior of the water-absorbing resin or the water absorbing agent and finishing of absorbing articles such as a diaper, and thus problems cannot be solved merely by increasing mass median particle size to inhibit deterioration caused by urine. [0016] Further, deterioration of the water absorbing agent caused by urine also correlates to absorption capacity and higher absorbency significantly increases extractables due to deterioration caused by urine. Therefore, it is not enough to increase only absorption capacity of the water-absorbing resin aiming at improving absorption amount of absorbing articles such as a diaper, to attain long term durability in practical use. [0017] This indicates that, in a present day with favor of thinner type absorbing articles, such the water absorbing agent as having small mass median particle size D50 of not larger than 400 .mu.m, high absorption capacity and certain limited range of extractables irrespective of change in urine can be a more superior water absorbing agent than conventional ones, however, further indicates that such the water absorbing agent as having small mass median particle size D50 of not larger than 400 .mu.m, high absorption capacity and low extractables irrespective of change in urine is difficult to prepare practically and has thus not been present before. [0018] By consideration of the above, the inventors thought of that the problems could be solved, in the present invention, by making the water absorbing agent with also superior stability to urine in specific mass median particle size, by furnishing crosslinked structure, specific centrifuge retention capacity, specific particle size distribution and mass median particle size and further specific ranges of "increased extractables by deterioration" and "increased ratio of extractables by deterioration" as a water absorbing agent. [0019] A first particulate water absorbing agent of the present invention is: [0020] a particulate water absorbing agent comprising a water-absorbing resin obtained by crosslinking polymerization of an unsaturated monomer containing an acid group and/or a salt thereof as a main component, and said water absorbing agent satisfies the following (a) to (d): [0021] (a) centrifuge retention capacity (CRC) in a physiological saline solution being in the range of not lower than 32 g/g; Continue reading... Full patent description for Particulate water absorbing agent with water-absorbing resin as main component Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Particulate water absorbing agent with water-absorbing resin as main component patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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