AU739387B2

AU739387B2 - Absorbent composition, method for producing thereof and absorbent products

Info

Publication number: AU739387B2
Application number: AU82440/98A
Authority: AU
Inventors: Shingo Mukaida; Daisuke Tagawa; Hitoshi Takai; Kenji Tanaka; Tsuyoshi Yuki
Original assignee: Sanyo Chemical Industries Ltd
Current assignee: Sanyo Chemical Industries Ltd
Priority date: 1997-07-18
Filing date: 1998-07-17
Publication date: 2001-10-11
Anticipated expiration: 2018-07-17
Also published as: AU8244098A; DE19882553T1; WO1999003577A1

Description

Specification Absorbent Composition, Method for Producing Thereof and Absorbent Products Field of the Invention This invention relates to absorbent compositions, method for producing the absorbent compositions and absorbent products. More specifically, the present invention relates to absorbent compositions having a micro-filler built in a water absorptive resin so as to increase a surface area and improve an absorption speed, to absorbent compositions in which an absorption speed for absorbing blood and an amount of retention an amount of liquid held) are further improved, to processes for manufacturing these absorbent compositions, and to absorbent products using the compositions.

Background Technology An absorption speed of a water absorptive resin is influenced by a surface area size of the water absorptive resin. That is, in the case of a water absorptive resin of a particle type having a constant mass, an absorption speed of the water absorptive resin becomes slower as a particle size becomes greater since a surface area of particles becomes smaller and an area contacting water as well becomes smaller. Conversely, the absorption speed becomes faster as the particle size becomes smaller since the surface area increases accordingly. However, if the particle size is too small, fine particles of the water absorptive resin adhere with each other via water (This phenomenon is often called "undissolved lump".) when the water absorptive resin contacts water, and as a result, the apparent absorption speed slows down.

In order to improve an absorption speed of a water absorptive resin, methods as those described in to below have been proposed: A method in which a surface active agent or water soluble polymer is added to a surface of a water absorptive resin which is in the form of small particles, to thereby prevent "undissolved lump" (Japanese Patent Application Laid-Open Gazette No.2-30333); A method which requires to add a volatile solvent which boils at a low temperature to a polymerization solution which is used in manufacturing of a water absorptive resin and to vaporize the volatile solvent by polymerization heat, to thereby obtain a porous resin (Japanese Patent Application Laid-Open Gazette No.59-18712); A method which requires to add a crosslinking agent and a pyrolytic foaming agent to a mixture of a water absorptive resin which contains a carboxyl group and a polyolefin resin which contains a glycidyl group and to cause the mixture to foam up under heat, to thereby obtain a foam SRT Le resin (Japanese Patent Application Laid-Open Gazette No.63-251437); -2- A method which requires to disperse a foaming agent of an azo compound containing an amino group within an aqueous monomer solution which contains an unsaturated monomer and a crosslinking agent and to polymerize the monomer with the azo compound, to thereby obtain a porous water absorptive resin by (Japanese PCT Application Re-Publication No.WO96-17884); and A method in which particles are granulated using water or a heat melting resin binder.

Although the above methods to realize improvements to a certain extent in the case that a liquid to be absorbed is a less viscous liquid such as urine or saline, these methods are not necessarily satisfactory in terms of production and quality as described below.

When applied as an absorbent to a paper diaper after mixed with a fibrous material such as pulp, a water absorptive resin obtained by the method causes a problem that excessively fine resin particles tend to separated from the fibrous material. Further, the water absorptive resin obtained by the method may cause a problem that a powder fluidity decreases because of processing using a surface active agent or a water soluble polymer, a working environment deteriorates as the fine particles creates dust, etc.

While improving an absorption speed to a certain extent, the method which requires to make a resin porous needs equipment of a special type such as an explosion proof type since it is necessary to use a volatile solvent whose boiling point is low.

In the method which uses a pyrolytic foaming agent, since the materials used, a water absorptive resin and a polyolefin resin, have no flexibility and hence discharge gases at once when a gas pressure reaches a certain level, and as a result, an uneven foam of a large diameter is created, it is difficult to obtain a constant absorption speed and absorption performance.

In the method of producing a porous resin, since a radical is generated at the same time when an azo compound containing an amino group decomposes and generates nitrogen gas, an absorption performance deteriorates due to a decrease in a molecular weight of the water absorptive resin, an amount of a water soluble component increases, etc.

In the method which uses a binder to granulate particles, an absorption speed fails to improve sufficiently if adhesion force of the binder is increased. On the contrary, if the adhesion force of the binder is decreased, a mechanical strength of the granulated substance drops and may be destroyed to return to powder again by mechanical shear or mechanical abrasion during powder transfer process such as screw feeder or wind pressure.

Further, when blood is a liquid to be absorbed, the above mentioned methods to do not give necessarily satisfactory results since the viscosity of blood is relatively high and contains high molecular organic components such as blood corpuscle, hemoglobin, cytoplasm, and proteins.

NAccordingly, a water absorptive resin which satisfies an absorption efficiency for blood and -3both amount of retention and absorption speed, and is suitable for blood absorbent products such as menstrual products has been strongly awaited. In order to improve an absorption performance of a water absorptive resin for blood, methods such as following to have been proposed: A method for adding salts of an inorganic acid or an organic acid to a water absorptive resin (Japanese Patent Application Laid-Open Gazette No. 58-501107); A method for using potassium salt or lithium salt as a part of neutralizing salt for a water absorptive resin (Japanese Patent Application Laid-Open Gazette No. 6-25543); A method for adding a polyamino acid (salt) aqueous solution to a water absorptive resin, or polymerizing a water soluble unsaturated monomer in the presence of a polyamino acid (salt) and a crosslinking agent (Japanese Patent Application Laid-Open Gazette No. 7-310021).

According to the method although a blood absorption speed may somewhat improve, an absorption efficiency and an amount of retention fall since a large amount of inorganic salt or organic salt must be used.

According to the method although an absorption efficiency for blood improves to some extent, the level of the blood absorption speed is not satisfactory.

According to the method although an absorption performance for physiological saline is good, an absorption efficiency for blood is low and between 6 and 11 times, and the level of the absorption speed is unsatisfactory.

Accordingly, a first purpose of the present invention is to provide an absorbent composition comprising a water absorptive resin having an increased surface area size and an improved absorption speed.

A second purpose of the present invention is to provide an absorbent composition which solves the problems associated with the above-mentioned methods to A third purpose of the present invention is to provide an absorbent composition whose absorption efficiency for blood is improved and both an amount of retention and an absorption speed are improved.

A fourth purpose of the present invention is to provide an absorbent products using the abovementioned absorbent composition.

Summary of the Invention The present invention is the following absorbent compositions methods for producing the absorbent compositions and absorbent products Absorbent composition An absorbent composition having a structure in which a water absorptive resin contains a built-in micro-filler the micro-filler being mixed under a condition of hydrate gelling after polymerisation of the resin or in the first stages of polymerisation of the resin, wherein the surface area size of such an absorbent composition is at least 10% larger than the surface area of an absorbent composition having a structure in which the water absorptive resin does not contain the built-in micro-filler Absorbent composition An absorbent composition in which a surface active agent is further added to a surface of the absorbent composition described in above Method for producing absorbent composition A method for producing an absorbent composition in which a micro-filler whose density measured by PYCNOMETER is 0.1 g/cm 3 or smaller and particle size is between 1 and 20091 m, is mixed prior to drying of hydrogel polymer, arid the mixture is dried.

Method for producing absorbent composition A method for producing an absorbent composition containing a built-in micro-filler in which thermally expansive hollow filler having a particle size of between 1 and 150/Um is mixed before drying hydrogel polymer and the mixture is dried under heat so that which is formed when thermally expands, is contained within the water absorption resin Method for producing absorbent composition A method for producing an absorbent composition in which a surface active agent is "****added to a surface of the composition which is obtained by the method or Absorbent Products 20 An absorbent product in which an absorption layer comprising the absorbent composition [1] or described above and a fibrous material is covered by a surface protection sheet which comprises a water permeable portion.

Best Mode for Achieving the Invention S 25 [Embodiment of water absorptive resin A representative example of the water absorptive resin in the absorbent composition [1] according to the present invention is a water absorptive resin described in below. Besides the "resin water absorptive resins to below are also included as examples.

A water absorptive resin of a water insoluble, water expansive polymer having a crosslinked structure and/or a graft structure, which is obtained by polymerizing a water soluble or solubilizable by hydrolysis radical polymerizable monomer or a radical polymerizable monomer which becomes water soluble as a result of hydrolysis with a polyfunctional compound (b) selected from a group consisting of a crosslinking agent (bl) and a grafting base and thereafter S'RA/ bjecting and to hydrolysis if necessary.

A resin having a water insoluble, water expansive structure which is obtained by crosslinking surfaces of polysaccharide of a particle type (for instance, a resin obtained by crosslinking a surface of water soluble polysaccharide particles, such as gua gum, xanthan gum, cellulose, methylcellulose, ethylcellulose, carboxylmethylcellulose and denaturation thereof, using a polyfunctional crosslinking agent).

A water insoluble, water expansile polymer which is obtained by selfcrosslinking of water-soluble radical polymerizable monomer (for example, self crosslinked polyacrylate).

A water insoluble, water expansile polymer which is obtained by polymerizing a water-soluble radical polymerizable monomer, and thermally crosslinking a resultant substance in the presence of a crosslinking agent if necessary (for instance, a resin obtained by thermally crosslinking a copolymer of acrylamide and an acrylic acid (acrylate)).

In the water absorptive resin examples of a water-soluble radical polymerizable monomer (a 1) of the monomer include a water-soluble radical polymerizable monomer having an acid group such as a carboxlic acid group, a sulfonic acid group or a phosphoric acid group (a 11); salt of a water-soluble radical polymerizable monomer having these acid groups (a 12); and a nonionic watersoluble radical polymerizable monomer (a 13).

Among (a 11), examples of a water-soluble radical polymerizable monomer having a carboxylic acid group include, for instance, an unsaturated mono or polycarboxylic acid [(meth)acryl acid (This refers to an acryl acid and/or a methacryl acid. Hereinafter the same definition will apply.) a crotonic acid, a sorbic acid, a maleic acid, an itaconic acid, a cinnamic acid, and salts thereof, etc.], and anhydride thereof [for instance, maleic anhydride].

Among (a 11), examples of a water-soluble radical polymerizable monomer having a sulfonic acid group include, for instance, a fatty acid or an aromatic vinylsulfonic acid (a vinylsulfonic acid, an acrylsulfonic acid, a vinyltoluene sulfonic acid, a sterene sulfonic acid and the like), a (meth)acryl alkylsulfonic acid, [(meth) sulfoethylacrylate, (meth)sulfopropylacrylate, a (meth)acrylamidalkylsulfonic acid [a 2-acrylamid-2-methylpropanesulfonic acid], and salts thereof.

Among (a 11), examples of a water-soluble radical polymerizable monomer having a phosphoric acid group include, for instance, a (meth)acryloyloxyalkylphosporic acid monoester [(meth)acryloyloxy 2-hydroxyethylphosphate, phenyl-2-acryloyloxyethylphospate and so forth].

Types of salts among (a 12) include alkali metal salts, ammonium salts, amine salts and so forth, preferably the alkali metal salts, and especially preferably sodium salts.

Examples of a nonionic water-soluble radical polymerizable monomer (a 13) include (meth)acrylamide, vinylpyrrolidone, 2-hydroxyethyl(meth)acrylate and so forth.

_R Among monomers examples of a radical polymerizable monomer (a2) capable of -6becoming water soluble as a result of hydrolysis include (meth)acrylonitrile, lower alkyl(meth)acrylate (The number of carbon atoms of alkyl group is 1 to lower alkylmaleate (The number of carbon atoms of alkyl group is 1 to vinylacetate and so forth.

As for the monomer described above, it is possible to use two or more of them together.

Further, when the water absorptive resin is a resin having a acid group and/or salt thereof, the neutralization degree of the acid group of the resin is preferably 50 to 90 mol%, especially 60 to mol%. The neutralization may be carried out at a monomer stage prior to the polymerization, or alternatively, it is possible to perform the neutralization after the polymerization.

Examples of the crosslinking agents (bl) include a crosslinking agent having two or more of ethylenic unsaturated group (bll), a crosslinking agent having at least one of an ethylenic unsatuarted group and a reactive functional group (b 12), a crosslinking agent having two or more of functional groups (b 13), and the like.

Examples of the crosslinking agents (bll) include N, N'-methylene bis-(meth)acrylamide, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, glycerol (di or tri)acrylate, trimethylolpropane triacrylate, triallylamine, triallylcyanurate, triallylisocyanurate, tetraallyloxyethane, pentaerythritol triallyether and so forth.

Examples of the crosslinking agent (b12) include glycidyl (meth)acrylate, N-methylol (meth)acryl amide and so forth.

Examples of the crosslinking agents (b 13) include ethylene glycol, diethylene glycol, glycerol, propylene glycol, diethanol amine, trimethylol propane, polyethylene imine, ethyleneglycol diglycidyl ether, glycerol diglycidyl ether, polyglycerol polyglycidyl ether and so forth.

Two or more of these crosslinking agents may be used together. Among these the crosslinking agent (b 11), inter alia N, N'-methylene bis-acrylamide, ethylene glycol diacrylate, trimethylolpropane triacrylate, tetraallyloxy ethane, pentaerythritol triallyether and triallylamine are preferable.

Examples of the grafting base (b2) include starch, gua gum, xanthan gum, cellulose, methylcellulose, ethylcellulose, carboxylmethylcellulose, water soluble polysaccharide such as denaturation thereof, polyvinyl alcohol, polyester resin and so forth.

In order to form a crosslinking structure and/or a graft structure, one or more types of the polyfunctional compounds selected from the group consisting of the crosslinking agents (bl) and the grafting bases (b2) is used for the water absorptive resin The amount of the crosslinking agent (bl) used for forming a crosslinking structure is generally 0.001 to preferably 0.05 to and more preferably 0.1 to 1% of the total mass of the omer and the crosslinking agent (bl).

-7- If the amount of the crosslinking agent (bl) is less than 0.001%, the resin becomes sol when it absorbs water and its water absorbing/holding function, which is a function of a water absorptive resin, is decreased. In addition, an apparent absorption speed of the resin is also reduced since "undissolved lump" tends to occur when the resin contacts a aqueous solution. Moreover, the resin dries very slowly and manufacturing of the resin is not efficient. On the other hand, if the amount of the crosslinking agent exceeds crosslinking becomes too strong and an absorbent composition cannot exhibit a sufficient water absorbing/holding function.

The amount of the grafting structure (b2) used for forming a graft structure does not generally exceed 30 by mass, is preferably 0.1 to 20 by mass, and more preferably 1 to 10 by mass of the total mass of the monomer, the crosslinking agent (bl) and the grafting base Examples of the water absorptive resin include a saponificated starch-acrylonitrile copolymer, a crosslinked starchacrylate copolymer, crosslinked polyacrylate, a saponificated crosslinked (meth)acrylatevinylacetate copolymer, a crosslinked isobutylene/maleic anhydride copolymer, a crosslinked polysulfonate, a crosslinked polyacrylate/polysulfonatecopolymer, a crosslinked polyacrylate/polyacrylamide copolymer, crosslinked polyacrylamide and hydrolyzed products thereof, crosslinked polyvinylpyrrolidone, crosslinked cellulose derivatives and so forth.

The water absorptive resin is preferably a water absorptive resin whose main component is a polymerizable monomer having a carboxylate group and/or a carboxyl group, which is capable of absorbing/holding a large amount of a liquid and discharges only a little amount of water because of an ion osmotic pressure even when a load or external force is applied. The water absorptive resin (A) is more preferably a crosslinked starchacrylate copolymer and crosslinked polyacrylate.

In the above-mentioned water absorptive resin as for the type of salts and the degree of neutralization when it is a form of a neutralization salt, alkali salt is preferable and sodium salt and potassium salt are more preferable, and the degree of neutralization for acid group is preferably 50 to 90 mol%, and more preferably 60 to 80 mol%.

In order to obtain the water absorptive resin it is possible to add, if necessary, various additives, chain transfer agents (for instance, thiol compounds), surface active agents and so forth, to polymerization system which polymerizes the monomer and the polyfunctional compound Methods for polymerization used for manufacturing the water absorptive resin are not limited and include an aqueous solution polymerization method, a suspension polymerization method, reverse phase suspension polymerization, spray polymerization, photo polymerization, radiation polymerization and so forth. A preferred polymerization method is aqueous solution polymerization using a radical polymerization catalysts. In this case, a type of a radical polymerization catalysts and ,a condition for radical polymerization are not limited and may be conventional.

-8- [Examples of micro-filler The absorbent composition according to the present invention is an absorbent composition having a structure in which a micro-filler is built in the water absorptive resin Examples of the micro-filler include a micro-filler (B1) whose density measured by PYCNOMETER is 0.1 g/cm 3 or less and particle size is between 1 and 200/m and a micro-filler (B2) comprising thermally expanded thermally expansive hollow filler having a particle size of between 1 and 150/ m. The micro-filler together with the micro-filler with an arbitrary ratio, may be contained in the water absorptive resin The density measured by PYCNOMETER of the micro-filler (B1) is generally 0.1 g/cm 3 or less, preferably 0.08 g/cm 3 or less, and more preferably 0.01 to 0.06 g/cm 3 If the density measured by PYCNOMETER of is greater than 0.1 g/cm 3 a volume, and hence, a surface area of the absorbent composition does not increase much and the absorption speed of a resulting absorbent composition is little improved.

The term "density measured by PYCNOMETER" refers to a value measured using, for instance, ACCUPYC 1330 PYCNOMETER An example of the practical measuring operation is as follow.

Two chambers, a cell chamber and an expansion chamber which are connected by a valve are present in the PYCNOMETER and volumes of the chambers are indicated by V(c) and V(e), respectively. The mass of a sample is measured in the cell chamber (the volume of the sample is indicated by and the valve connecting to the expansion chamber is closed to obtain a constant pressure P(1) inside the cell chamber. The pressure inside the expansion chamber at that time is P(a).

Then, the valve connecting to the expansion chamber is opened and the pressure P(2) across the two chambers is measured. The volume of the sample may be calculated from the volume and a pressure change of the two chambers, and the density measured by PYCNOMETER is obtained using the following equation: Density measured by PYCNOMETER W/V The particle size of (B1) is generally 1 to 200/ m, preferably 1 to 150 Um, and more preferably 5 to 100 m. It is not preferable that the particle size of is greater than 2009 m, since uniformity, which is obtained when is dispersed in hydrogel of in accordance with the manufacturing method of the present invention, becomes poor and the absorption speed of the resulting absorbent composition may not be effectively enhanced. On the other hand, if the particle size of is less than 1/ m, coagulation among (B1) tends to occur when (B1) is dispersed in the R /,hydrogel of and its uniformity becomes insufficient.

-9- Materials forming (Bl) are not limited and may be an organic or inorganic material.

Examples of organic materials include polyethylene, polypropylene, polystyrene, poly-pxylylene, polyacrylate, polymethacrylate, poly(vinyl chloride), poly(vinylidene chloride), poly(vinyl acetate), fluorine-contained resin, polyacrylonitrile, poly(vinyl ether), polybutadiene, polyamide, thermoplastic polyester, polycarbonate, poly(phenylene oxide), polysulfone, thermoplastic polyurethane, poly(ethylene oxide), poly(propylene oxide), poly(tetramethylene oxide), polyacetal, cellulose derivatives and so forth. One which may be obtained by copolymerizing two or more of monomers comprising these resin is also included in the examples.

Examples of inorganic material include silicon oxide, aluminum oxide, iron oxide, titanium oxide, magnesium oxide, zirconium oxide and so forth.

Two or more of these in the examples may be used together. Among those, the organic materials are preferable and, inter alia, polyacrylate, polymethacrylate, polyvinylidene chloride, polyvinyl acetate and polyacrylonitrile are more preferable.

The shape of (Bl) is not limited and may be hollow, porous and so forth. The hollow shape is preferable.

Practical examples of the micro-filler (Bl) according to the present invention include, for instance, Matsumoto Microsphere F-50E of Matsumoto Yushi Co., Expansel 551DE, 461DE, and 091DE of Japan Ferrite Co. and so forth. Two or more of these may be used in combination.

On the other hand, (B2) in the absorbent composition having a structure in which the microfiller (B2) is contained in the water absorption resin is a micro-filler that is obtained when the thermally expansive hollow filler of a particle size 1 to 150/. m is thermally expanded.

An example of the thermally expansive hollow filler is, for instance, a hollow fine resin having a gas or volatile compound in the pore.

Examples of the kind of a resin which forms an outer surface of the hollow fine resin include, for instance, polyethylene, polypropylene, polystyrene, poly-p-xylyene, polyacrylate, polymethacrylate, poly(vinyl chloride), poly(vinylidene chloride), poly(vinyl acetate), a fluorinecontained resin, polyacrylonitrile, poly(vinyl ether), polybutadiene, polyamide, thermal plastic polyester, polycarbonate, poly(phenylene oxide), polysulfone, thermoplastic polyurethane, poly(ethylene oxide), poly(propylene oxide), poly(tetramethylene glycol), polyacetal and so forth.

Two or more of these may be used in combination.

Among these resins, polyacrylate, polyvinylidene chloride, and polyacrylonitrile are preferable.

A temperature at which starts to expand may be varied according to a softening temperature of the resin, types of gases present in the pore, or the kind of the volatile compound, and is preferably between 60 and 150 0 C. On the other hand, the maximum expansion temperature is preferably between 80 and 180"C. It is more preferable that a temperature at which expansion starts is between 70 and 120°C and a maximum expansion temperature is between 90 and 150 °C.

If the expansion-starting tempereture is lower than 60"C, it may be necessary, according to the present invention, to cool down the hydrogel and, hence, it is inefficient. On the other hand, if the temperature at which expansion starts is higher than 150C, then the expansion efficiency may be lowered since the evaporation of water component of of hydrogel state proceeds during a heat dry step and flexibility of the hydrogel may be lowered when starts expanding.

In cases where the maximum expansion temperature is less than 80°C, or more than 180*C, the same phenomenon as described above may be generated and is not preferable.

Examples of the gases or volatile compounds which are contained in the pore portion of the filler include compounds having a boiling point, at normal pressure, of 150C or less, preferably 120°C or less, and more preferably 100°C or less. If the boiling point is higher than 150'C, it is economically inefficient since the temperature at which starts to expand becomes high and a high temperature is required for a heating process. Further, it may be possible that the degree of enhancement of the absorption speed of the resulting absorbent composition is lowered due to insufficient thermal expansion.

Examples of the gases or volatile compounds which may be contained in the pore of (B2') include, for instance, isobutane, isopentane, petroleum ether, n-butane, n-pentane, n-hexane, cyclopentane, cyclohexane, trichlorofluoromethane, dichlorofluoromethane, butylene, methylene chloride and so forth. These may be used in combination.

Among them, isobutane, isopentane, n-butane, n-pentane, and petroleum ether are preferable.

The particle size of is not limited, however, it is generally 1 to 150/ m, and preferably 1 to 100 t m. If the particle size of is greater than 150/m or less than 1/ m, the degree of uniformity of the mixture comprising the hydrogel of and is lowered and the degree of improvement in the absorption speed of the resulting absorbent composition may become insufficient and, hence, it is not preferable.

A a volumetric swelling factor of is preferably 10 times or more, and more preferably times or more. If the magnitude at which the volume of expands is less than 10 times, a lower degree of enhancement of the absorption speed of the resulting absorbent composition may be realized since the expansion rate of is low.

Examples of the thernally expansive hollow filler used in the present invention include "^iatsumoto microsphere F-20, F-30, F-40, F-50, F-80S, F-82, F-85, F-100, F-30VS, F-80GS, 11 F-100SS, F-1300, F-1400 and so forth of Matsumoto Yushi Co., and Expansel 820, 642, 551, 461, 051, 091DE and so forth. Two or more of these may be used in combination.

[Ratio between and A mass ratio of to in the absorbent composition of the present invention is preferably 100 (0.05 to 10), more preferably 100 (0.1 to and further preferably 100 (0.5 to If is less than 0.05, a lower degree of enhancement of the absorption speed is realized. On the other hand, if it is more than 10, although the absorption speed may improve, the mechanical strength of particles of the resulting absorbent composition tends to be weakened since its volume becomes too large. In addition, a lower degree of improvement in the absorption speed of the resulting absorbent composition under an applied pressure tends to be realized.

[Process for manufacturing the absorbent composition The absorbent composition according to the present invention may be obtained by, for instance, the manufacturing method using the micro-filler (B1) or the manufacturing method [4] using the thermal extensile hollowed filler In the manufacturing method the micro-filler (B1) is built in resin prior to drying hydrogel polymer and then the mixture is dried to obtain an absorbent composition.

In the embodiment of the manufacturing method a hydrogel form of the water absorptive resin containing the built-in micro-filler (B1) is dried and an absorbent composition is obtained.

Although the water absorptive resin is formed prior to the drying in this embodiment, the water absorptive resin may be formed, in other embodiments, during drying or after the drying by using a thermal crosslinking or a surface crosslinking method.

In the manufacturing method according to the present invention, the micro-filler (B1) may be added during any step which is carried out between prior to the polymerization step and the drying step of the water absorptive resin It is preferable that the filler (B1) is added, after the polymerization of to hydrogel polymer prior to the drying step. This is because a larger degree of enhancement of the absorption speed is realized when (B1) is added to hydrogel of since (B1) is contained inside the particles of the water absorptive resin.

(B1) may be added in the form of aqueous slurry or aqueous dispersion, however, it is preferable to add as aqueous slurry or aqueous dispersion, to hydrogel homogeneously in order to realize a larger degree of enhancement of the uniformity and the absorption speed of the absorbent composition.

Further, a percentage of the water content in the mixture of the hydrogel of and (B1) is -12preferably 2 to 10 times of solid components of If the percentage is less than 2 times, then a lower degree of uniformity is obtained during a mixing step and a lower degree of enhancement of the absorption speed of the resulting absorbent composition may result. If the percentage is more than times, a longer time is required for drying, which is not economical.

A conventional kneader may be used for homogeneously dispersing (Bl) in hydrogel of Examples of such an apparatus include a double arm kneader, an internal mixer (banbury mixer), a self-cleaning type mixer, a gear compounder, a screw type extruder, a screw type kneader, mincer and so forth. These may be used in combination.

A temperature for drying the hydrogel type mixture, to which (B1) has been added, is generally 60 to 230°C, preferably 100 to 200"C, and more preferably 105 to 180°C. If the drying temperature is lower than 60°C, it is not economical since it takes very long time for drying the mixture. On the other hand, if the temperature is higher than 230*C, the absorption performance and the absorption speed may be lowered due to a possible side reaction and decomposition of the resin.

Conventional apparatuses may be used for drying the mixture comprising the hydrogel state of and Examples of such an apparatus include, for instance, a drum dryer, a parallel current flow band dryer (tunnel dryer), a through-flow band dryer, a blow current (nozzle jet) dryer, a box type hot air dryer, an infrared dryer and so forth. A heat source is not limited. A plurality of these dryers may be used in combination.

The absorbent composition according to the present invention may be obtained by surface crosslinking the proximity of surfaces of the absorbent composition, which contains (Bl) and has been obtained by grinding and adjusting the particle size after the drying, using a crosslinking agent having at least two functional groups which may be reacted with an acid group such as a carboxyl group and/or its base.

Such a surface crosslinked type absorbent composition is suitable for the present invention since it has an excellent absorption performance and an excellent absorption speed under not only a normal pressure but an applied pressure as well and exhibits a larger gel strength.

Examples of crosslinking agents used for surface crosslinking include, for instance, polyglycidyl ether compounds (ethylene glycol diglycidyl ether, glycerol 1,3-diglycidyl ether, glycerol triglycidyl ether, poly(ethylene glycol) diglycidyl ether, polyglycerol polyglycidyl ether and so forth); polyol compounds (glycerol, ethylene glycol, poly(ethylene glycol) and so forth); polyamine compounds (ethylene diamine, diethylene triamine and so forth); polyamine type resins (polyamide polyamine epichlorohydrin resins, polyamine epichlorohydrin resins and so forth), alkylene carbonate, aziridine compounds, polyimine compounds and so forth. Polyglycidyl ether compounds and polyamine type resins are preferable since surface crosslinking may be carried out at -13a relatively low temperature.

An amount of a crosslinking agent used for surface crosslinking is not limited and may be varied in accordance with the type of the crosslinking agent used, a condition for crosslinking, a performance to be obtained and so forth. However, the amount is generally 0.001 to 3 by mass, preferably 0.01 to 2 by mass, and more preferably 0.05 to 1 by mass of the absorbent composition. If the amount of the crosslinking agent is less than 0.001% by mass, the resulting water absorptive resin has substantially the same performance as a water absorptive resin which is not subjected to crosslinking. On the other hand, if the amount is greater than 3 by mass, the magnitude of absorption and water retention tend to be lowered, which is not preferable.

An additive and an extending agent, if necessary, may be added to the mixture of the hydrogel state of and (B1) and examples of such include a residual monomer reducer (for instance, sodium sulfite, hydrogen peroxide and so forth), an antibacterial agent (for instance, quaternary ammonium salt, chlorohexizin compounds, metallic salt type antibacterial agent and so forth), a preservative, a fragrant, a deodorant, a colorant, an antioxidant, silica, zeolite and so forth. These additives may be added during or after the drying step of the hydrogel state mixture.

The apparent density of the absorbent composition may be decreased, depending on the amount of (B1) added, to one third of that of a composition containing no (B1) since the density measured by PYCNOMETER of (B1) is low. Because of this, the surface area size per unit area of the composition increases significantly and the absorption speed thereof improves.

On the other hand, the manufacturing method is a method in which the thermally expansive hollow filler is built in the water absorptive resin prior to a drying step for manufacturing the water absorptive resin via hydrogel polymer and then they are dried by heat so that is thermally expanded to produce the water absorptive resin containing the micro-filler (B2).

In practice, according to the manufacturing method hydrogel of the water absorptive resin which contains the thermally expansive hollow filler is dried by heat and an absorbent composition is obtained comprising the water absorptive resin and the micro-filler (B2) contained therein. Although the water absorptive resin is formed prior to the drying step by heat in this embodiment, it is possible to form the water absorptive resin during or after the drying step by using a thermal crosslinking method or a surface crosslinking method.

In the manufacturing method according to the present invention, may be added at any step between prior to the polymerization of the water absorptive resin a preparatory step for mixing materials used for the polymerization and so forth, and prior to the drying step. It is preferable that it is added to and mixed with hydrogel polymer after the polymerization step of (A) -14and before the drying step thereof. This is because the hydrogel of has a flexibility suitable for expansion and it is possible to increase the surface area by thermal volume expansion during the drying step carried out thereafter. In addition, the volume expansion may be achieved in more uniform manner by using a crosslinking agent (for instance, polyglycidyl ether compounds) when (B) is added to the hydrogel polymer between after the polymerization step of and before the drying step.

may be added in any form such as powder, an aqueous slurry, and aqueous dispersion.

However, it is preferable that an aqueous slurry or aqueous dispersion form of is added homogeneously to the hydrogel in order to improve the uniformity in expansion and the absorption speed of the resulting absorbent composition.

Further, a percentage of the-water content in the mixture of the hydrogel of and is preferably 2 to 10 times with respect to the solid components of If the percentage is less than 2 times, then the magnitude of expansion is lowered and a lower degree of enhancement of the absorption speed of the resulting absorbent composition may be realized. If the percentage is more than 10 times, then, a longer time is required for drying and it is not economical.

As a kneader device for mixing and homogeneously dispersing with the hydrogel of the same apparatuses used for mixing and homogeneously dispersing (B1) with in the manufacturing method according to the present invention may be employed.

A temperature for drying the hydrogel state compound, to which has been added, is generally 60 to 230°C, preferably 100 to 200C, and more preferably 105 to 180C. If the drying temperature is lower than 60C, it is not economical since it takes very long time for drying the mixture. On the other hand, if the temperature is higher than 230C, the absorption performance and the absorption speed may be lowered due to a possible side reaction and decomposition of the resin.

Conventional apparatuses may be used for heat drying the mixture comprising the hydrogel of and Examples of such apparatuses include, for instance, a drum dryer, a parallel current flow band dryer (tunnel dryer), a through-flow band dryer, a blow current (nozzle jet) dryer, a box type hot air dryer, an infrared dryer and so forth.

If inflammable compounds are contained in the pore portion of a direct fire type heat source is not preferable. However, if the compound is non-inflammable, types of heat source are not limited. A plurality of these dryers may be used in combination.

If necessary, the absorbent composition according to the present invention may be obtained by surface crosslinking the proximity of surfaces of the absorbent composition, which has been obtained by grinding and adjusting the particle size after the drying, using a crosslinking agent having at least two functional groups which may be reacted with a carboxyl group and/or its base. Such a surface crosslinked type absorbent composition is suitable for the present invention since it has an excellent absorption performance and an excellent absorption speed under not only a normal pressure but also an applied pressure and exhibits a larger gel strength.

The same crosslinking agents used for surface crosslinking in the aforementioned manufacturing method according to the present invention may be employed and the amount to be used is also the same.

Additives and extending agents, if necessary, may be added to the mixture of the hydrogel of and and examples of such include residual monomer reducer (for instance, sodium sulfite, hydrogen peroxide and so forth), antibacterial agents (for instance, quaternary ammonium salt, chlorohexizin compounds, metallic salt type antibacterial agent and so forth), preservatives, fragrants, deodorants, colorants, antioxidants, silica, zeolite and so forth. These additives may be added during or after the drying step of the hydrogel state mixture.

[Shape and Particle Size Distribution] A suitable form for the absorbent composition of the present invention is a grain form and, for example, it may be a crushed grain which is obtained via a dry-grinding process after performing the polymerization of the aqueous solution, or it may be a spherical type which is obtained by using a reverse phase suspension polymerization method.

The average particle size of the absorbent composition of the present invention is generally 200 to 600gm, and preferably 250 to 550g.m. Further, the particle size distribution between 1000gItm and 100gm is generally 90 by mass or more and preferably 95 by mass or more.

If the average particle size is more than 600/tm, or the content of particle having size of 1000 gam or more is 10 by mass or greater, the absorption speed tends to be lowered. On the other hand, if the average particle size is less than 200g.m, or the content of particle having size of less than 100 g.m is 10 by mass or greater, then the amount supplied may become inconstant due to a difficulty in particle handling or the performance of a disseminating machine, or the operation environment may be deteriorated due to the generation of dusts.

[Specific Surface Area] The absorbent composition of the present invention is characterized by an improvement by 10% or more of the specific surface area as compared with not containing the built-in Here, the specific surface area is a value which is measured by using the BET method and, hence, the 7T57 pecific surface area of the absorbent composition of the present invention measured by the BET -16method is improved by 10% or more with respect to the specific surface area of not containing the built-in measured by the BET method.

In addition, the specific surface area, measured by the BET method, of the absorbent composition of the present invention whose particle size is 150 to 5009m is preferably 0.1 m 2 /g or more, and more preferable 0.15 m 2 /g or more.

[Bulk Density] The bulk density of the absorbent composition of the present invention is generally 0.1 to 0.7 g/cm 3 preferably 0.1 to 0.55 g/cm 3 and more preferably 0.2 to 0.5 g/cm 3 If it is more than 0.7 g/cm 3 the effect of increasing the surface area per unit mass becomes insufficient. Note that the bulk density is a value measured based on JIS K3362.

[Absorption Speed, Absorption Amount under Applied Pressure] Since the specific surface area of the absorbent composition of the present invention is improved as described above, its absorption speed (time required for absorbing certain fixed amount) for physiological saline is improved as compared with that of not containing the built-in and the degree of the improvement in the absorption speed is preferably 80% or less in terms of time.

That is, the absorption speed (a time required for absorbing a certain fixed amount) for physiological saline of the absorbent composition of the present invention is preferably reduced to 80% or less of the absorption speed (a time required for absorbing a certain fixed amount) for physiological saline of not containing the built-in Absorption speed of the absorbent composition of the present invention is preferably seconds or less, and more preferably 20 seconds or less. When the composition having such absorption speed is applied to sanitary products such as a paper diaper, it is effective to increase a dry feeling and reduce leaking.

Particularly, the absorbent composition of the present invention which is obtained by a surface crosslinking has an improved absorption amount under an applied pressure and is capable of achieving the absorption speed of 25 seconds or less, preferably 20 seconds or less, for physiological saline and the absorption amount under an applied pressure of 25 g/g or more, preferably 28 g/g or more, for physiological saline under the condition of 20 g/cm 2 It is, therefore, effective to further increase a dry feeling and further reduce leaking when applied to sanitary products such as a paper diaper.

Note that the absorption speed and the absorption amountunder an applied pressure are values measured using methods which will be described later.

0-17o0 [Surface Active Agent Treatment] The absorbent composition of the present invention comprises the above-mentioned absorbent composition and the surface active agent which is added to the surface thereof.

Accordingly, properties such as the shape, a particle size distribution, a specific surface area, a bulk density and so forth of the absorbent composition of the present invention is basically the same as those of the absorbent composition and the quick absorption speed characteristic to the composition is maintained in the composition as well.

Types of the surface active agent are not particularly limited and any of nonionic surface active agents, anionic surface active agents, cationic surface active agents, and ampholytic surface active agents may be employed.

Examples of the nonionic surface active agents include alkyl phenols, aliphatic alcohols, carboxylic acids, aliphatic amines, aliphatic amides, compounds of which ethylene oxide and/or propylene oxide is added (in case both ethylene oxide and propylene oxide are used, it is random or block addition) to an active hydrogen containing compound such as hydroxy denatured or amine denatured polysiloxane, polyalcohols which are partially esterified by fatty acids and so forth. One or more of these may be used in combination.

Specific examples of the nonionic surface active agents include the followings: C8-C24 alkyl phenols which have been alkoxylified by ethylene oxide and/or propylene oxide; C10-C24 aliphatic alcohols which have been alkoxylified in the same manner; C10-C24 fatty acids which have been alkoxylified in the same manner; C10-C24 aliphatic amines which have been alkoxylified in the same manner; C10-C24 aliphatic amides which have been alkoxylified in the same manner; polyoxyethylene denatured silicone oils; and C3-C6 polyalcohols which have been partially esterified by C10-C24 fatty acids, or compounds thereof further comprising 2-20 mole of ethylene oxide and/or propylene oxide on the partially esterified portion.

Examples of the anionic surface active agents include alkali metal salts of (C8-C24)alkylsulfonic acid, alkali metal salts or trialchanol amine salts of (C8-C24)-alkylsulfate, diesters of sulfosuccinic acid, monoesters of sulfosuccinic acid, (C8-C24)-alkylaryl sulfonic acids, sulfuric halfesters of products of which ethylene oxide is added to alkylphenol or aliphatic alcohol and so forth. Two or more of these anionic surface active agents may be used in together or may be used with the nonionic surface active agents described above.

SExamples of cationic surface active agents include an inorganic acid (chloric acid and so -18forth) salt or an organic acid (acetic acid, formic acid and so forth) salt of aliphatic higher amine (lauryl amine, stearyl amine and so forth), higher fatty acid (stearic acid, oleic acid and so forth) of lower amines, solomin A type cationic surface active agent, sapamin A type cationic surface active agent, quaternary ammonium salt having long chain (C10-C22) alkyl (long chain alkylbenzyldimethyl ammonium chloride and so forth), inorganic acid salt or organic acid salt of aliphatic amine to which alkyleneoxide (ethylene oxide and so forth) is added and so forth. Examples of the ampholytic surface active agents include compounds having at least one cationic group (for instance, quaternary ammonium group) and anionic group (for instance, carboxylate group, sulfate group) on the same molecule, more specifically, dimethylcarboxymethyl-fatty acid-alkylamideammonium betaines, 3-(3fatty acid amid-propyl)dimethylammonium-2-hydroxypropane sulfonates and so forth.

Among these surface active agents, nonionic surface active agents having HLB (Griffin) of 3 or more, preferably between 8 and 14, are preferable. Here, HLB is an index which indicates the balance of a surface active agents in terms of hydrophilic property and lipophilic property, and it may be controlled by the kind and the number of functional groups, or mole number or molecular weight of added alkyleneoxide.

The absorbent composition of the present invention may be obtained by further adding the surface active agent on the surface of the absorbent composition which is obtained by the manufacturing methods described in or above.

The amount of the surface active agent based on the mass, is generally 0.1 to preferably 0.1 to more preferably 0.2 to with respect to the absorbent composition If the amount of is less than a composition that has an excellent absorption speed for blood may not be obtained because the effect of treating with is insufficient and the improvement in affinity between the resulting composition and blood is hardly obtained. On the other hand, if the amount of is larger than although the absorption speed may be improved, a powder fluidity of the resulting composition may be lowered and problems may be caused in terms of particle handling.

Hence, it in not preferable.

The surface active agent is attached to the surface of the absorbent composition when it is applied to the surface and, if the surface active agent has permeability, it further permeates into the composition.

Methods for adding the surface active agent to the absorbent composition are not particularly limited and, for example, the surface active agent is mixed with the absorbent composition using a conventional mixing apparatus. The surface active agent may be undiluted or diluted using water or an aqueous solution.

Examples of the mixing apparatuses include a V-type mixer, ribbon blender, turbulizer, -19almighty mixer, nauter mixer, fluidized mixer, spray mixer, line blender, continuous mixer, banbury mixer, mortar mixer and so forth. These may be used in combination.

[Absorption Speed for Sheep Blood] The composition of the present invention has an absorption speed for sheep blood of generally 30 seconds or less, preferably 25 seconds or less, and a retention amount, after swelling in sheep blood for 30 minutes, of generally 20 g/g or more, preferably 23 g/g or more.

Since the composition of the present invention possesses the balance for the absorption properties (the absorption speed and the amount of retention), it is effective, as compared with a conventional water absorptive resin, to improve a surface dry feeling and the amount of retention, and decrease leaking when it is applied to various absorption products (such as sanitary napkins, panty liners, tampons, under-pads for operation, mats for delivery beds, dressing materials for protecting a cut portion and so forth), especially sanitary napkins.

Further, if the composition of the present invention is surface crosslinked, the amount the composition retains sheep blood under an applied pressure may be further improved to 20 g/g under a load of 20 g/cm 2 The absorption speed for sheep blood, the amount of retention after swelling in the sheep blood for 30 minutes, the amount of retention for the sheep blood an under applied pressure, and surface dryness of napkins and the amount of retention of napkins, are values measured by using methods which will be described later.

Note that although artificial blood (for instance, an aqueous solution containing about 0.9% of sodium chloride, about 0.4% of sodium bicarbonate, about 30% of glycerol, and about 0.18% of sodium carboxymethylcellulose, and if necessary, surface active agents and coloring agents are added) has been conventionally used for evaluating the absorption properties of the water absorptive resin, there is a large difference in the absorption property when the artificial blood is used and when real blood (human blood, menstrual flow, cattle blood, sheep blood and so forth) is used. Hence, it is necessary to use real blood for examining absorption properties for blood.

This is because about 45 mol% of high molecular weight organic substances such as hemocytes, hemoglobin, cytoplasm, and protein components are contained in real blood.

[Absorbent Products] The absorbent products of the present invention include an absorption layer comprising the absorbent composition or of the present invention and a fibrous material, and a surface protection sheet having a water permeability portion to cover the absorption layer. The surface protection sheet, in the case of a diaper for adults or infants or sanitary products, comprises, from the view point of usage, a non-water permeable sheet which is normally located outside and a water permeable sheet which is located inside. The absorption layer is located between the two sheets and end portions of the two sheets are joined to form an absorbent product. Inaddition to such an absorption layer disposed between the two sheets, a water absorption sheet, a liquid diffusion sheet and so forth maybe used together if necessary.

Examples The present invention will be further explained by using the following examples. However, the present invention is not limited to these particular examples by any means. Percentage values herein used indicate by mass unless otherwise described.

Methods for measuring the following items 1) to 10) for water absorptive resins, absorbent compositions, and napkins are shown below.

[Items] Water absorptive resins and absorbent compositions: 1) Specific surface area Absorbent composition: 2) Absorption speed for 0.9% saline 3) Amount of absorption under load for 0.9% saline 4) Amount of retention for 0.9% saline Absorption speed for sheep blood 6) Amount of retention for sheep blood 7) Amount of absorption under load for sheep blood Napkins 8) Absorption speed for sheep blood 9) Diffusion area of sheep blood Surface dryness after the diffusion of sheep blood 11) Amount of retention for sheep blood [Measuring methods] 1) Method for measuring specific surface area: A specific surface area was measured by B.E.T 1 point method using (Kansoubu QS-19) of Yuasa Ionisc Co. Conditions used for the measurement were measurement gas of He/Kr 99.1/0.1 -21vo measuring gas of N 2 and a standard cell was used. Water absorptive resin or absorbent sample was pre-adjusted to 30 to 100 mesh.

2) Method for measuring absorption speed of absorbent composition: Absorbent composition (2.00 g) which had been adjusted to particle size of 30 to 60 mesh using a JIS standard strainer was prepared as a sample.

Saline (0.9 by mass, 50 g) was added to a beaker (100 ml, flat bottom) which contains a magnet (diameter 0 at central portion of 8 mm, diameter 0 at both ends of 7 mm, length of 30 mm, coated by fluorine-contained resin to be thick in the center) and the beaker was placed on the center portion of a magnetic stirrer. The rotation of the magnetic stirrer was adjusted to be 600 30 per minute and it was confirmed that a stable swirl of saline was formed.

Time was measured using a timer after the sample was added to saline of a position as close as, but not contacting, the inner surface of the beaker. The procedures so far according to JIS K7224.

The end point was defined as when the swirl was disappeared and the liquid surface became horizontal. The absorption speed was defined as time in second unit required from the start to the end point.

3) Method for measuring amount of absorption under load of absorbent composition: Sample of absorbent composition (0.10 g) whose particle size had been adjusted to 30 to mesh using a JIS standard strainer was put in a cylindrical plastic tube (inner diameter 9 of 30 mm, height of 60 mm) having a nylon mesh of 250 mesh at the bottom, and flattened.

A weight of outer diameter 0 30 mm was put on the absorbent composition so that it applied a load of 20 g/cm 2 The plastic tube containing the absorbent composition was placed, with the nylon mesh side thereof faces downward, in a Petri dish (diameter q5of 12 cm) containing 60 ml of 0.9 by mass saline. After 5 minutes and 60 minutes, mass of the absorbent composition increased by absorbing 0.9% saline was measured. A value obtained by multiplying the measured value after minutes by 10 is used as an initial amount of absorption under applied pressure for 0.9 saline, and a value obtained by multiplying the measured value after 60 minutes by 10 is used as the amount of absorption under applied pressure.

4) Method for measuring amount of retention of the absorbent composition: Sample of absorbent composition (1.00 g) which had been adjusted to particle size of 30 to mesh using a JIS standard strainer was put in a tea bag (20 cm in length, 10 cm in width) made of nylon mesh of 250 mesh and immersed in saline (0.9 by mass, 500 ml) for 60 minutes to absorb saline. The tea bag was hanged for 15 minutes to drain water and then centrifuged (150G, 90 sec.) to measure mass increase. This increased mass is used as the amount of retention for 0.9 by mass n,saline.

-22- Method for measuring absorption speed of absorbent composition for sheep blood: Sample of absorbent composition (10 g) which had been adjusted to particle size of 30 to mesh using a JIS standard strainer was prepared. The sample (20 g) was put in a Petri dish (diameter qof 12 cm) and flattened. Then, sheep blood (5 g, containing 3.8% citric acid, Towa Jyunyaku Co.) was poured onto the center of the sample and time was measured from the start of pouring to the complete absorption of sheep blood by the sample. This value is used as the absorption speed.

6) Method for measuring amount of retention of absorbent composition for sheep blood: Sample of absorbent composition (1.0 g) which had been adjusted to particle size of 30 to mesh using a JIS standard strainer was put in a tea bag (20 cm in length, 10 cm in width) made of nylon mesh of 250 mesh and immersed in sheep blood for 30 minutes to absorb and expand. The tea bag was hanged for 15 minutes to drain liquid and then centrifuged (250G, 2 min.) to measure mass increase. This increased mass is used as the amount of retention for sheep blood.

7) Method for measuring amount of absorption under load of absorbent composition for sheep blood: Sample of absorbent composition (0.1 g) whose particle size had been adjusted to 30 to mesh using a JIS standard strainer was put in a cylindrical plastic tube (inner diameter 5 of 30 mm, height of 60 mm) having a nylon mesh of 250 mesh at the bottom, and flattened.

A weight of outer diameter 0 30 mm was put on the sample so that it applied a load of g/cm 2 The plastic tube containing the sample was placed, with the nylon mesh side thereof faces downward, in a Petri dish (diameter 0 of 12 cm) containing 50 g of sheep blood. After 30 minutes, mass of the sample increased by absorbing sheep blood was measured and a value which is obtained by multiplying the measured value by 10 is used as the amount of absorption under applied load.

8) Method for measuring absorption speed of napkin: A fluff pulp layer of 100 g/m 2 was cut to the size of 6 cm X 15 cm and absorbent composition sample (0.4 g) was uniformly applied on it. Another fluff pulp layer of the same mass and size was put on top of that and they were pressed (10 kg/cm 2 30 sec.) on a wire netting to form an absorption layer.

A model napkin was made by using a leak-prevention film, size of which is a little larger than the absorption layer and placed underneath the absorption layer, and non-woven fabric made of rayon, which is placed on the absorption layer, and heat sealing their edges along with the absorption layer.

A hole of diameter 12 mm was made on the center of an acryl plate whose area was the same as the area of the absorption layer, and a pouring plate was prepared by fixing a circular cylinder of inner diameter 12 mm (length of 10 cm) on the hole. This pouring plate was placed on the model T7 2apkin and a load of 20 g was placed so as to uniformly apply the load. Sheep blood (5 g) was poured -23from the circular cylinder and time was measured until all of blood (5 g) was absorbed. This measurement was repeated three times and the average value thereof is used as the absorption speed.

9) Method for measuring diffusion area of napkin: After each measurement of the absorption speed, diffusion area of sheep blood on the absorption layer was obtained. This was repeated three times and the average value thereof is used as the diffusion area.

Method for measuring surface dryness of napkin: After each measurement of the diffusion area, feeling of dryness on the surface of the model napkin was judged based on the tactile measurements on five panellers. This was repeated three times and the average thereof was evaluated using the following criteria: excellent dry feeling; O: somewhat damp but practically no problem; A: a little seepage with a feeling of tackiness; and X a lot of seepage with accompanying tackiness.

11) Method for measuring amount of retention of napkin: Model napkin was soaked in excess of sheep blood for five minutes to absorb the blood.

After that, it was centrifuged (250G, 2min.), with the non-woven fabric side facing the outside, to obtain the mass increase. The first number after the decimal point of the obtained value was rounded and this value is used as the amount of retention.

(Example 1) Sodium acrylate (77g), acrylic acid (22.8 N,N'-methylene bisacrylamide (0.2 g) and deionized water (295 g) was put in a reaction container (1 litter) made of glass and the temperature of the mixture was maintained at 3 'C with stirring.

After nitrogen gas was purged in the mixture in order to decrease the amount of dissolved oxygen to 1 ppm or less, an aqueous solution of hydrogen peroxide 1 an aqueous solution of ascorbic acid 1.2 and an aqueous solution of 2,2'-azobisamidinopropane dihydrochloride 2.8 g) were added and mixed to initiate a polymerization reaction. After five hours of polymerization, hydrogel polymer (A1G) was obtained.

After cutting the hydrogel polymer (A1G) to the size of 3 to 7 mm using an internal mixer, 100 g of 2% aqueous dispersion (B11) of Expansel 091DE (density measured by PYCNOMETER 0.03 g/cm 3 particle size of 50 to 80/m) was added and mixed to be homogeneous using the internal mixer. After that the mixture was dried using a through-flow band dryer (150C, air flow speed of STIRe sec. Inoue Kinzoku Kogyo The resulting dried substance was ground so as to adjust the -24particle size to 20 to 100 mesh and absorbent composition was obtained.

On the other hand, after cutting the hydrogel polymer (A1G) to the size of 3 to 7 mm using an internal mixer, it was dried using a through-flow band dryer (150C, air flow speed of 2.0 m/sec.).

The resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh and water absorptive resin (Al) was obtained.

Specific surface area of the water absorptive resin (Al) and that of the absorbent composition were measured and its increasing rate were calculated. The results are shown in Table 1. Further, results of the evaluation on the performance of the absorbent composition are shown in Table 2.

(Example 2) 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the absorbent composition which had been stirred at high speed.

After that the composition was subjected to thermal crosslinking (140"C, 30 min.) to obtain an absorbent composition of surface crosslinked type.

On the other hand, 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the water absorptive resin (Al) prepared in Example 1 which had been stirred at high speed and the composition was subjected to thermal crosslinking (140"C, 30 min.) to obtain a water absorptive resin (A2) of surface crosslinked type.

Specific surface area of the water absorptive resin (A2) and that of the absorbent composition were measured and its increasing rate were calculated. The results are shown in Table 1. Further, results of the evaluation on the performance of the absorbent composition are shown in Table 2.

(Examples 3 and 4) Dried substance of particle size 20 to 100 mesh (100 which was obtained by using the same procedure in Example 1 except that the amount of the dispersion (Bl) added was changed to g or 250 g, was thermally crosslinked in the same manner as in Example 2 and an absorbent composition and an absorbent composition were obtained.

Specific surface area of the absorbent compositions and was measured and their increasing rates relative to the water absorptive resin (A2) were calculated. The results are shown in Table 1. Further, results of the evaluation on the performance of the absorbent compositions and are shown in Table 2.

(Examples 5 and 6) Absorbent composition and absorbent composition were obtained by using the same procedure as in Example 1, except that the following dispersion (B12) or (B13) was used instead of the dispersion (Bl) (the amount used was the same), and the same surface crosslinking method as in Example 2: Dispersion (B12): 2% aqueous dispersion of Expansel 461DE (density measured by PYCNOMETER 0.06 g/cm 3 particle size of 20 to 40g and Dispersion (B13): 2% aqueous dispersion of Expansel 551DE (density measured by PYCNOMETER 0.04 g/cm 3 particle size of 30 to 50/ m).

(Example 7) Sodium acrylate (77 acrylic acid (22.8 N,N'-methylene bisacrylamide (0.2 g) and deionized water (293 g) was put in a reaction container (1 litter) made of glass and "Expansel 091DE" (2 g) was added with stirring. The temperature of the mixture was maintained at 3 "C.

After nitrogen gas was purged in the mixture in order to decrease the amount of dissolved oxygen to 1 ppm or less, an aqueous solution of hydrogen peroxide 1 an aqueous solution of ascorbic acid 1.2 and an aqueous solution of 2,2'-azobisamidinopropane dihydrochloride 2.8 g) were added and mixed to initiate a polymerization reaction. After five hours of polymerization, hydrogel polymer mixture (AB1G) was obtained.

After cutting the hydrogel polymer mixture (AB1G) using an internal mixer, they were dried using a through-flow band dryer (150°C, air flow speed of 2.0 m/sec.).

After the resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh, 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the ground dried substance being stirred at high speed and the composition was subjected to thermal crosslinking (140'C, 30 min.) to obtain an absorbent composition of surface crosslinked type.

Specific surface area of the absorbent composition was measured and an its increasing rate of the specific surface area relative to the water absorptive resin (A2) was calculated. The results are shown in Table 1. Further, results of the evaluation on the performance of the absorbent composition are shown in Table 2.

(Example 8) Acrylic acid (81.8 N,N'-methylene bisacrylamide (0.2 g) and deionized water (241 g) was put in a reaction container (1 litter) made of glass and the temperature of the mixture was maintained at 3 °C with stirring.

After nitrogen gas was purged in the mixture in order to decrease the amount of dissolved -26oxygen to 1 ppm or less, an aqueous solution of hydrogen peroxide 1 an aqueous solution of ascorbic acid 1.2 and an aqueous solution of 2,2'-azobisamidinopropane dihydrochloride 2.8 g) were added and mixed to initiate a polymerization reaction. After five hours of polymerization, hydrogel polymer was obtained.

During cutting of the hydrogel polymer using an internal mixer, 30% sodium hydroxide aqueous solution (109.1 g) was added and mixed to obtain hydrogel polymer (A3G) in which 72 mol% of carboxylic acid was neutralized.

The same 2% aqueous dispersion (B11) (100 g) used in Example 1 was added to the hydrogel polymer (A3G) and, after homogeneously mixed using an internal mixer, it was dried using a throughflow band dryer (150"C, air flow speed of 2.0 m/sec.).

After the resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh, 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the ground dried substance being stirred at high speed and the composition was subjected to thermal crosslinking (140"C, 30 min.) to obtain an absorbent composition of surface crosslinked type.

On the other hand, after the hydrogel polymer (A3G) was homogeneously mixed using an internal mixer, it was dried using a through-flow band dryer (150"C, air flow speed of 2.0 m/sec.).

After the resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh, ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the ground dried substance being stirred at high speed. The composition was subjected to thermal crosslinking (140C, 30 min.) to obtain water absorptive resin (A3) of surface crosslinked type.

Specific surface area of the water absorptive resin (A3) and the absorbent composition (8) were measured and increasing rates of the specific surface area were calculated. The results are shown in Table 1. Further, results of the evaluation on the performance of the absorbent composition are shown in Table 2.

(Comparative Example 1) Water absorptive resin (Al) obtained in Example 1 is considered as a comparative absorbent composition (cl) and its results of the evaluation on the performance are shown in Table 2.

(Comparative Example 2) Water absorptive resin (A2) obtained in Example 2 is considered as a comparative absorbent composition (c2) and its results of the evaluation on the performance are shown in Table 2.

(Comparative Examples 3 and 4) Comparative absorbent composition (c3) and comparative absorbent composition were -27- Sobtained by surface crosslinking, in the same manner as in Example 2, 100 g of dried substance having particle size of 20 to 100 mesh, which had been obtained using the same procedure as in Example 1 except that the amount of the dispersion (B11) added was changed to 2 g or 600 g.

Specific surface area of the comparative absorbent compositions (c3) and (c4) were measured and its increasing rate of the specific surface area relative to the water absorptive resin (A2) were calculated. The results are shown in Table 1. Further, results of the evaluation on the performance of the comparative absorbent compositions (c3) and (c4) are shown in Table 2.

(Comparative Example Comparative absorbent composition (c5) was obtained by surface crosslinking, in the same manner as in Example 2, 100 g of dried substance having particle size of 20 to 100 mesh, which had been obtained using the same procedure as in Example 1 except that the following dispersion (B14) of the same amount was used instead of the dispersion (B11).

Specific surface area of the comparative absorbent composition (c5) was measured and an increasing rate of the specific surface area relative to the water absorptive resin (A2) was calculated.

The results are shown in Table 1. Further, results of the evaluation on the performance of the comparative absorbent composition (c5) are shown in Table 2.

Aqueous dispersion (B14): 2% aqueous dispersion of Matsumoto Microsphere (density measured by PYCNOMETER 0.2 g/cm3; particle size of 20/m, Matsumoto Yushi Seiyaku Co.).

(Comparative Example 6) After cutting the hydrogel polymer (A1G) which was obtained in Example 1 using an internal mixer to the size of 3 to 7 mm, with respect to solid components of (A1G), of "Binihole AZ-S" (decomposition temperature of 100C, main components: azobisisobutylonitrile, Eiwa Kasei Kogyo Co.) which is a pyrolytic foaming agent was added. After they were mixed homogeneously using an internal mixer, the mixture was dried using a through-flow band dryer (150'C, air flow speed of m/sec.). After the resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh, 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the ground dried substance being stirred at high speed and the composition was subjected to thermal crosslinking (140 0 C, 30 min.) to obtain a comparative absorbent composition (c6) of surface crosslinked type.

Specific surface area of the comparative absorbent composition (c6) was measured and an its increasing rate of the specific surface area relative to the water absorptive resin (A2) was calculated.

The results are shown in Table 1. Further, results of the evaluation on the performance of the comparative absorbent composition (c6) are shown in Table 2.

-28- (Table 1) Water absorptive resin Absorbent composition Increasing rate of Specific surface area Mark Specific surface area Mark Specific surface (s2-sl)/sl X 100 S1 area S2 Ex.1 (Al) 0.44 0.53 20.5 Ex.2 (A2) 0.42 0.51 21.4 Ex.3 (A2) 0.42 0.48 14.3 Ex.4 (A2) 0.42 0.71 69.0 (A2) 0.42 0.50 19.0 Ex.6 (A2) 0.42 0.52 23.8 Ex.7 (A2) 0.42 0.49 16.7 Ex.8 (A3) 0.43 0.53 23.3 C. Ex.3 (A2) 0.42 (c3) 0.43 2.4 C. Ex.4 (A2) 0.42 (c4) 1.12 166.7 C. Ex.5 (A2) 0.42 (c5) 0.44 4.8 C. Ex.6 (A2) 0.42 (c6) 0.46 (Table 2) Absorbent Absorption Initial absorbency Absorbency under Retention (g/g) composition speed (sec) under load load (g/g) Ex.1 17 14 17 53 Ex.2 15 24 33 41 Ex.3 19 23 34 41 Ex.4 11 27 33 41 18 23 34 41 Ex.6 17 25 33 41 Ex.7 16 24 33 41 Ex.8 16 26 36 44 C. Ex.1 (cl) 35 5 16 53 C. Ex.2 (c2) 34 18 33 41 C. Ex.3 (c3) 34 18 32 41 C. Ex.4 (c4) 23 14 26 39 -29- C. Ex.5 (c5) 30 18 32 41 C.Ex.6 (c6) 27 16 24 34 (Example 9) After cutting the hydrogel polymer (A1G) using an internal mixer to the size of 3 to 7 mm, g of 20% aqueous dispersion of (B21) "Matsumoto Microsphere F-30 (initial expansion temperature of 85 to 90C, maximum expansion temperature of 130 to 140°C, expansion rate of about 72 times) was added. After they were mixed homogeneously using an internal mixer, the mixture was dried using a through-flow band dryer (150*C, air flow speed of 2.0 mrn/sec., Inoue Kinzoku Kogyo Co.).

The resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh and an absorbent composition was obtained.

Specific surface area of the absorbent composition was measured and an increasing rate of the specific surface area relative to the water absorptive resin (A2) was calculated. The results are shown in Table 3. Further, results of the evaluation on the performance of the comparative absorbent composition are shown in Table 4.

(Example After 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the absorbent composition being siirred at high speed, the composition was subjected to thermal crosslinking (140C, 30 min.) to obtain an absorbent composition (10) of surface crosslinked type.

Specific surface area of the absorbent composition (10) was measured and an increasing rate of the specific surface area relative to the water absorptive resin (A2) of surface crosslinked type was calculated. The results are shown in Table 3. Further, results of the evaluation on the performance of the absorbent composition (10) are shown in Table 4.

(Examples 11 and 12) Absorbent composition (11) and absorbent composition (12) were obtained by surface crosslinking, in the same manner as in Example 10, 100 g of dried substance having particle size of to 100 mesh, which had been obtained using the same procedure as in Example 9 except that the amount of the dispersion (B21) added was changed to 2.5 g and 25 g, respectively.

Specific surface area of the absorbent compositions (11) and (12) were measured and its increasing rate of the specific surface area relative to the water absorptive resin (A2) of surface crosslinked type were calculated. The results are shown in Table 3. Further, results of the evaluation on the performance of the absorbent compositions (11) and (12) are shown in Table 4.

(Examples 13 and 14) Absorbent composition (13) and absorbent composition (14) were obtained by using the same procedure as in Example 9 except that the following respective dispersion (B22) or (B23) of the same amount was used instead of the dispersion (B21), and surface crosslinking in the same manner as in Example Aqueous dispersion (B23): 20% aqueous dispersion of "Matsumoto Microsphere (initial expansion temperature of 100 to 105°C, maximum expansion temperature of 130 to 140°C, expansion rate of 46 times).

Aqueous dispersion (B24): 20% aqueous dispersion of "Matsumoto Microsphere (initial expansion temperature of 80 to 85°C, maximum expansion temperature of 105 to 115 0

C,

expansion rate of about 43 times).

Specific surface area of the absorbent compositions (13) and (14) were measured and their increasing rates of the specific surface area relative to the water absorptive resin (A2) were calculated.

The results are shown in Table 3. Further, results of the evaluation on the performance of the absorbent compositions (13) and (14) are shown in Table 2.

(Example Sodium acrylate (77 acrylic acid (22.8 N,N'-methylene bisacrylamide (0.2 g) and deionized water (293 g) was put in a reaction container (1 litter) made of glass and "Matsumoto Microsphere F-30" (2 g) was added with stirring. The temperature of the mixture was maintained at 3 C.

After nitrogen gas was purged in the mixture in order to decrease the amount of dissolved oxygen to 1 ppm or less, an aqueous solution of hydrogen peroxide 1 an aqueous solution of ascorbic acid 1.2 and an aqueous solution of 2,2'-azobisamidinopropane dihydrochloride.

2.8 g) were added and mixed to initiate a polymerization reaction. After five hours of polymerization, hydrogel polymer mixture (AB2G) was obtained.

After cutting the hydrogel polymer mixture (AB2G) using an internal mixer, they were dried using a through-flow band dryer (150°C, air flow speed of 2.0 m/sec.).

After the resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh, 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the ground dried substance being stirred at high speed and the composition was subjected to thermal crosslinking (140 0 C, 30 min.) to obtain an absorbent composition (15) of surface crosslinked type.

Specific surface area of the absorbent composition (15) was measured and an increasing rate of the specific surface area relative to the water absorptive resin (A2) was calculated. The results are -31shown in Table 3. Further, results of the evaluation on the performance of the absorbent composition are shown in Table 4.

(Example 16) Using the same procedure as in Example 8, hydrogel polymer (A3G) in which 72 mol% of carboxylic acid had been neutralized was obtained.

After the same dispersion (B21, 10 g) used in Example 9 was added to the hydrogel polymer (A3G) and homogeneously mixed, it was dried using a through-flow band dryer (150C, air flow speed of 2.0 m/sec.).

After the resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh, 10% ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol 70/30) (2 g) was added to 100 g of the ground dried substance being stirred at high speed and the composition was subjected to thermal crosslinking (140TC, 30 min.) to obtain an absorbent composition (16) of surface crosslinked type.

Specific surface area of the absorbent composition (16) was measured and an increasing rate of the specific surface area relative to the water absorptive resin (A3) of surface crosslinked type was calculated. The results are shown in Table 3. Further, results of the evaluation on the performance of the absorbent composition (16) are shown in Table 4.

(Comparative Examples 7 and 8) Comparative absorbent composition (c7) and comparative absorbent composition (c8) were obtained by surface crosslinking, in the same manner as in Example 10, 100 g of dried substance having particle size of 20 to 100 mesh, which had been obtained using the same procedure as in Example 9 except that the amount of the dispersion (B21) added was changed to 0.2 g or 60 g, respectively.

Specific surface area of the comparative absorbent compositions (c7) and (c8) were measured and increasing rates of the specific surface area relative to the water absorptive resin (A2) of surface crosslinked type were calculated. The results are shown in Table 3. Further, results of the evaluation on the performance of the comparative absorbent compositions (c7) and (c8) are shown in Table 4.

(Table 3) Water absorptive resin Absorbent composition Increasing rate of specific surface area Mark Specific surface area Mark Specific surface (s2-sl)/sl X 100 sl area s2 Ex.9 (Al) 0.44 0.58 31.8 0 -32k 0 14, 0%- (A2) 0.42 (10) 0.57 35.7 Ex.11 (A2) 0.42 (11) 0.50 19.0 Ex.12 (A2) 0.42 (12) 0.72 60.0 Ex.13 (A2) 0.42 (13) 0.53 26.2 Ex.14 (A2) 0.42 (14) 0.54 28.6 (A2) 0.42 (15) 0.51 21.4 Ex.16 (A3) 0.43 (16) 0.60 39.5 C. Ex.7 (A2) 0.42 (c7) 0.44 4.8 C. Ex.8 (A2) 0.42 (c8) 1.10 162.2 (Table 4) Absorbent Absorption Initial absorbency Absorbency under Retention (g/g) composition speed (sec) under load load (g/g) Ex.9 16 13 18 53 (10) 14 25 34 41 Ex.11 (11) 19 23 34 41 Ex.12 (12) 11 28 33 41 Ex.13 (13) 17 24 34 41 Ex.14 (14) 16 26 34 41 (15) 15 25 34 44 Ex.16 (16) 15 27 37 44 C. Ex.7 (c7) 34 19 32 41 C. Ex.8 (c8) 21 15 27 38 (Example 17) Absorbent composition was obtained using the same procedure as in Example 9.

The absorbent composition (100 g) was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil ("Shinetsu Silicone KF-618", Shinetsu Kagaku Co.; HLB 14) was added and mixed to obtain absorbent composition (17) of the present invention. Results of the evaluation on the performance of the absorbent composition (17) are shown in Table (Example 18) ethylene glycol diglycidyl ether in water/methanol mixed solution (water/methanol -33- 70/30) (2.5 g) was added to 100 g of the absorbent composition being stirred at high speed and the composition was subjected to thermal crosslinking (140"C, 30 min.) to obtain an absorbent composition of surface crosslinked type.

The absorbent composition (100 g) was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil used in Example 17 was added and mixed to obtain absorbent composition (18) of the present invention. Results of the evaluation on the performance of the absorbent composition (18) are shown in Table (Examples 19 and Absorbent composition (11) and absorbent composition (12) were obtained using the same procedure as in Examples 11 and 12.

Each of the absorbent composition (11) (100 g) and absorbent composition (12) (100 g) was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil used in Example 17 was added and mixed to obtain absorbent composition (19) and absorbent composition (20) of the present invention. Results of the evaluation on the performance of these absorbent compositions are shown in Table (Examples 21 to 24) Absorbent composition and absorbent composition were obtained using the same procedure as in Examples 2 and 5. Further, absorbent composition (13) and absorbent composition (14) were obtained using the same procedure as in Examples 13 and 14.

Each of these absorbent compositions (13) and (14) (100 g each) was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil used in Example 17 was added and mixed to obtain absorbent compositions (21) to (24) of the present invention. Results of the evaluation on the performance of these absorbent compositions are shown in Table (Examples 25 to 28) Absorbent compositions (25) to (28) were obtained using the same procedure as in Example 18 except that the respective following surface active agents of the same amount was used instead of the polyoxyethylene denatured silicone oil. Results of the evaluation on the performance of these absorbent compositions are shown in Table Used for the absorbent composition Mixture of polyoxyethylene lauryl ether and polyoxyethylene myristyl ether ("Nonipol soft SS-50" Sanyo Kasei Kogyo Co.; HLB 10.6).

Used for the absorbent composition Polyoxyethylene nonylphenyl ether ("Nonipol Sanyo Kasei Kogyo Co.; HLB 8.9).

Used for the absorbent composition Sodium sulfate of polyoxyethylene lauryl ether -34- ("Sandet EN" Sanyo Kasei Kogyo Co.; an anionic surface active agent).

Used for the absorbent composition Disodium lauroyl ethanolamide polyoxyethylene sulfosuccinate ("Beaulight A-5000" Sanyo Kasei Kogyo Co.; an amphoteric surface active agent).

(Example 29) Absorbent composition (15) was obtained using the same procedure as in Example The absorbent composition (15) (100 g) was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil used in Example 17 was added and mixed to obtain absorbent composition (29) of the present invention. Results of the evaluation on the performance of the absorbent composition (29) are shown in Table (Example Absorbent composition (16) was obtained using the same procedure as in Example 16.

The absorbent composition (16) (100 g) was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil used in Example 17 was added and mixed to obtain absorbent composition (30) of the present invention. Results of the evaluation on the performance of the absorbent composition (30) are shown in Table (Table 5) Bulk density of the absorbent composition and results of the evaluation of the absorbent composition using sheep blood Absorbent Bulk density Absorption Retention after Absorbency for Examples composition (g/cm 3 speed for swelling in sheep sheep blood under sheep blood blood for 30 min. load (g/g) (sec) (g/g) 17 (17) 0.44 28 31 12 18 (18) 0.42 10 29 27 19 (19) 0.55 18 30 28 (20) 0.28 9 29 21 (21) 0.49 12 30 27 22 (22) 0.48 15 29 27 23 (23) 0.46 21 28 26 24 (24) 0.54 23 28 26 (25) 0.44 12 29 28 26 (26) 0.45 15 28 27 27 (27) 0.46 13 27 26 28 (28) 0.44 10 27 28 0 :FE~ 29 (29) 0.48 10 29 27 (30) 0.43 8 30 (Comparative Example 9) The comparative absorbent composition (cl) obtained in Comparative Example 1 was used as a comparative absorbent composition (c9) and results of a measurement of bulk density and the evaluation using sheep blood are shown in Table 6.

(Comparative Example The comparative absorbent composition (c2) obtained in Comparative Example 2 was used as a comparative absorbent composition (c10) and results of a measurement of bulk density and the evaluation using sheep blood are shown in Table 6.

(Comparative Examples 11 to 16) Each of the absorbent composition obtained in Example 9, the absorbent composition of surface crosslinked type obtained in Example 18, the absorbent compositions and obtained in the same manner as in Examples 2 and 5, and the absorbent compositions (13) and (14) obtained in the same manner as in Examples 13 and 14 is used as a comparative absorbent composition (cll) to (c16), respectively. Results of these compositions are shown in Table 6.

(Comparative Example 17) The comparative absorbent composition (c9) obtained in Comparative Example 9 was put in a V-type mixer (300 ml capacity) and, while it was rotated, 0.1 g of polyoxyethylene denatured silicone oil used in Example 17 was added and mixed to obtain comparative absorbent composition (c17).

Results of the evaluation on the performance of the comparative absorbent composition (c17) are shown in Table 6.

(Comparative Example 18) After cutting the hydrogel polymer (AB2G) obtained in Example 15 using an internal mixer to a size of 3 to 7 mm, they were dried using a through-flow band dryer (150°C, air flow speed of m/sec.). The resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh.

This dried substance having adjusted particle size was surface crosslinked, in the same manner as in Example 2, to obtain a comparative absorbent composition (cl8). Results of the evaluation of the comparative absorbent composition (c18) are shown in Table 6.

(Comparative Example 19) After cutting the hydrogel polymer (A1G) obtained in Example 1 using an internal mixer to a size of 3 to 7 mm, with respect to solid components of (A1G), of "Binihole AZ-S" (decomposition temperature of 100°C, main components: azobisisobutylonitrile, Eiwa Kasei Kogyo Co.) which is a pyrolytic foaming agent was added. After they were mixed homogeneously using an -36internal mixer, the mixture was dried using a through-flow band dryer (150C, air flow speed of m/sec.). The resulting dried substance was ground so as to adjust the particle size to 20 to 100 mesh to obtain a comparative absorbent composition (c19). Results of the evaluation of the comparative absorbent composition (c19) are shown in Table 6.

(Table 6) Bulk density of the comparative absorbent and results of the evaluation of the absorbent composition using sheep blood Compar- Comparat- Bulk density Absorption Retention after Absorbency for ative ive (g/cm 3 speed for sheep swelling in sheep sheep blood under Example absorbent blood (sec) blood for 30 min. load (g/g) (g/g) 9 (c9) 0.71 180 18 7 (c10) 0.68 72 23 22 11 (e11) 0.44 96 19 9 12 (c12) 0.43 47 25 26 13 (c13) 0.51 51 25 14 (c14) 0.48 60 25 (c15) 0.47 66 24 24 16 (c16) 0.53 68 24 24 17 (c17) 0.69 85 20 18 (c18) 0.47 50 24 19 (c19) 0.62 63 21 11 (Examples 31 to 37) Model napkins were made using the absorbent compositions (17) to (20) obtained in Examples 17 to 20, the absorbent composition (23) obtained in Example 23, the absorbent composition (25) obtained in Example 25, and the absorbent composition (29) obtained in Example 29. Results of the evaluation on the performance of these are shown in Table 7.

(Comparative Examples 20 to Comparative model napkins were made using the comparative absorbent composition (c9) obtained in Comparative Example 9, the comparative absorbent composition (cll) obtained in Comparative Example 11, the comparative absorbent composition (c15) obtained in Comparative Example -37and the comparative absorbent compositions (c17) to (c19) obtained in Comparative Examples 17 to 19.

Results of the evaluation on the performance of these are shown in Table 7.

(Table 7) Results of the evaluation of model napkins Absorbent Absorption Retention Diffusion area Surface dryness used speed (sec) (cm 2 Ex.31 (17) 38 15 37 O Ex.32 (18) 19 15 44 Ex.33 (19) 24 16 41 0~@ Ex.34 (20) 18 16 45 (23) 23 15 42 O~@ Ex.36 (25) 20 15 44 Ex.37 (29) 18 17 45 C. Ex.20 (c9) 66 8 26 x C. Ex.21 (cll) 60 9 29 x C. Ex.22 (c15) 53 12 35 x -A C. Ex.23 (c17) 58 10 28 x C. Ex.24 (c18) 49 12 36 A C. Ex.25 (c19) 57 10 30 X Industrial utility The absorbent compositions and the manufacturing methods of the present invention possess the following characteristics and effects: Since the absorption speed under pressure free state free state is quick and the initial absorbency under load the absorption speed under load) is excellent, effects such as an improvement in initial surface dryness and a decrease in leaking may be realized when used as, for instance, absorbent for sanitary products; In addition to that they have an excellent retention and absorbency under load; Since the effects set forth in the above and are realized even if they are in normal particle size, they are excellent in particle handling. Further, almost no fine particles are generated by mechanical shear or abrasion as in the case of fine particles or granulates; -38- Since the effects set forth in the above and are realized even if they are in normal particle size, when used as an absorbent being mixed with fibrous material such as pulp, almost none of them are separated from the fibrous material if external force such as vibration is applied; Unlike the improvement of absorption speed using a pyrolytic foaming agent, since no radicals, etc., are generated during heat-drying, absorbent compositions having an excellent absorption ability and a small amount of water soluble components are obtained; The absorption speed may be improved by a simple method in which micro-filler is added to hydrogel at any stage between prior to polymerization of water absorptive resin and prior to drying and then dried by heat; Since the absorption speed of compositions treated with a surface active agent, is quick for blood and menstrual flow and their retention is excellent, effects such as an improvement in surface dryness and a decrease in leaking may be realized when used as, for instance, absorbent for sanitary products (especially sanitary napkin). Further, excellent absorption performance and absorption speed are realized for other bodily fluids (urine, breast milk, amniotic fluid at giving birth, etc.); and By applying the composition treated with a surface active agent to absorbent products such as sanitary napkin, a napkin which is excellent in the absorption speed, diffusion area, surface dryness, retention and so forth, as compared with ones using conventional water absorptive resin, may be obtained.

Since the absorptive composition according to the present invention have the abovementioned effects, they are particularly suitable for various absorbent products, for example, sanitary products and medical products such as disposable paper diaper (paper diaper for baby and for adults), sanitary napkin, pad for incontinence, pad for breast milk, under-pad for operation, mat for a delivery bed, dressing materials for protecting a cut and so forth. Further, they are suitable for use in various absorption sheets (for instance, absorption sheet for pet urine, sheet for maintaining freshness, drip absorption sheet, rice plant raising sheet, sheet used for concrete production, water-running protection sheet for cables and so forth). Moreover, the present invention may be suitably employed for a use in which powder of the absorbent composition is applied (for instance, soil water retention agent, sludge solidifying agent, solidifying agent for damped blood or aqueous waste liquid, urine gelling agent, gelling agent for battery electrolyte and so forth).

39 P:\OPERlAxd\8244I-98 spe.doc4)l/Am)I -39A- Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

*o **go go

Claims

1. An absorbent composition which has a structure in which a water absorptive resin contains a built-in micro-filler said micro-filler being mixed under a condition of hydrate gelling after polymerisation of the resin or in the first stages of polymerisation of the resin, wherein the surface area size of such an absorbent composition is at least larger than the surface area of an absorbent composition having a structure in which the water absorptive resin does not contain the built-in micro-filler wherein the surface area of said absorbent composition is at least 10% larger than the surface area of an absorbent composition which has a structure in which said water absorptive resin does 10 not contain said micro-filler

2. An absorbent composition according to claim 1, wherein the absorption speed a time required for absorbing a certain amount) to absorb physiological saline of said absorbent composition is 80% or less than the absorption speed to absorb physiological saline of an absorbent composition in which said water absorptive resin does not 15 contain said micro-filler

3. An absorbent composition according to claim 1 or 2, which is a particle type absorbent composition having an average particle size of 200 to 600 pgm, the specific :surface area of particles having sizes of 150 to 500 gm being 0.1 m 2 /g or larger when measured by the BET method.

4. An absorbent composition according to any one of claims 1 to 3, wherein the absorption speed of said absorbent composition to absorb physiological saline is seconds or shorter. An absorbent composition according to any one of claims 1 through 4, wherein a mass ratio of said water absorptive resin to said micro-filler is 100:(0.05 to

6. An absorbent composition according to any one of claims 1 through 5, wherein said micro-filler is a micro-filler (B1) having a density measured by PYCNOMETER of 0.1 g/cm 3 or smaller and a particle size of 1 to 200 m. P:\OPER\Axd\82440-98 spc.doc-011001 40A

7. An absorbent composition according to claim 6, wherein said micro-filler (Bl) is a hollow filler made of at least one resin selected from a group consisting of polyacrylate, polymethcrylate, poly(vinylidene chloride), poly(vinyl acetate) and polyacrylonitrile.

8. An absorbent composition according to claim 6 or 7, which is obtained by drying hydrogel of said water absorptive resin containing said built-in micro-filler (B1). o* -41-

9. An absorbent composition according to any one of claims 6 through 8, which is obtained by drying and granulating said hydrogel of said water absorptive resin containing said built- in micro-filler (Bi) and surface crosslinking particles which are generated by said drying and granulating. An absorbent composition according to any one of claims 1 through 5, wherein said micro- filler is a micro filler (B2) which is obtained by thermally expanding a thermally expansive hollowed filler which has a particle size of 1 to 150/tm.

11. An absorbent composition according to claim 10, wherein said thermally expansive hollow filler is a hollow fine resin containing a gas or a volatile substance in pores.

12. An absorbent composition according to claim 10, wherein a volumetric swelling factor of said thermally expansive hollow filler by heat is 10 or larger.

13. An absorbent composition according to any one of claims 10 through 12, wherein said thermally expansive hollow filler is a thermally expansive hollow filler whose initial thermal expansion temperature is 60 to 150°C and maximum expansion temperature is 80 to 180C. 20 14. An absorbent composition according to any one of claims 10 through 13, which is obtained by heating and drying said hydrogel of said water absorptive resin containing said built-in thermally expansive hollow filler

15. An absorbent composition according to any one of claims 10 through 14, which is obtained 25 by drying and granulating said hydrogel of said water absorptive resin containing said built-in 0. and surface crosslinking particles which are generated by said drying and granulating.

16. An absorbent composition which has a structure in which a water absorptive resin o contains a built-in micro-filler said micro-filler being mixed under a condition of hydrate gelling after polymerisation of the resin or in the first stages of polymerisation of the resin, wherein an absorption speed of said absorbent composition to absorb physiological saline is 25 seconds or shorter.

17. An absorbent composition according to claim 16, whose bulk density is 0.1 to 0.55 Lj g/cm 3 and average particle size is 200 to 600 tm. P:UOPER\Axd\S2440-98 sp.doc-O I0501 -42-

18. An absorbent composition according to claim 16 or 17, wherein said water absorptive resin is a water absorptive resin having a surface crosslinked structure, and said absorbent composition absorbs 25 g/g or more of physiological saline under an applied pressure of 20 g/cm 2

19. An absorbent composition which is obtained by further attaching a surface active agent to a surface of an absorbent composition according to any one of claims 1 through 18. An absorbent composition according to claim 19, wherein said surface active agent is a nonionic surface active agent having HLB of 8 to 14.

21. An absorbent composition which is obtained by attaching a surface active agent (C) to a surface of absorptive particles of a water absorptive resin containing a built-in micro-filler the bulk density of said resin being 0.1 to 0.55 g/cm 3 and average particle size of resin being 200 to 600 uim, wherein an absorption speed of said absorbent composition to absorb sheep blood is 30 seconds or shorter and an amount of the sheep blood which said absorbent composition holds after swelled in the sheep blood for 15 30 minutes is 20 g/g or more.

22. An absorbent composition substantially as hereinbefore described with reference to the Examples, but excluding the Comparative Examples. 20 23. A method for producing an absorbent composition, wherein prior to drying of hydrogel polymer of said water absorptive resin a micro-filler (Bl) whose density measured by PYCNOMETER is 0.lg/ cm 3 or smaller and particle size is 1 to 200um is built within a water absorptive resin and dried.

24. A method for producing an absorbent composition, wherein prior to drying of hydrogel polymer of a water absorptive resin a thermally expansive hollow filler having a particle size of 1 to 150 m is built within said water absorptive resin and dried under heat so that a micro-filler (B2) which is obtained as said thermally expansive hollow filler thermally expands is built within said water absorptive resin P:\OPER\Axd\82440-98 spc.docOI-01A0 -43- A method for producing an absorbent composition, comprising a step of surface crosslinking particles of an absorbent composition which is obtained by a method according to claim 23 or 24.

26. A method for producing an absorbent composition, comprising a step of adding a surface active agent to a surface of a composition which is obtained by a method according to any one of claims 23 through

27. A method for producing an absorbent composition substantially as hereinbefore described with reference to the Examples, but excluding the Comparative Examples. S28. An absorbent product wherein an absorption layer which comprises an absorbent composition according to any one of claims 1 through 22 and a fibrous material is covered with a surface protection sheet which comprises a water permeable portion. DATED this 1st day of May, 2001 S Sanyo Chemical Industries, Ltd. by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s)