JPH11286611A - Water-absorbing resin composition and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition having excellent liquid permeability and a high absorption rate under pressure by mixing a water-absorbing resin with microparticles being monodisperse or having a specified sphericity. SOLUTION: It requires that the microparticles should be monodisperse or have a sphericity of 1-1.1, and it is desirable that they are ones being monodisperse and having a sphericity of 1-1.1. The phrase 'being monodisperse' means that the particles have a sharp particle size distribution and are not agglomerated each other. More particularly, microparticles having a particle size distribution index (d25 /d75 ) of 3 or below and a mean particle diameter of 0.01-10 μm are desirable. The microparticles are particularly desirably silica microparticles and are used in an amount of, desirably, 0.01-10 pts.wt. per 100 pts.wt. water-absorbing resin. The water-absorbing resin is desirably one with its surface and proximity being crosslinked. Thus, a composition having an absorption rate under pressure of 30 g/g or above can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a water-absorbent resin composition containing a water-absorbent resin and fine particles. More specifically, the present invention relates to a water-absorbent resin composition preferably used in various industrial fields such as civil engineering, agricultural and horticultural fields, such as sanitary materials such as disposable diapers, sanitary napkins and incontinence pads.

[0002]

2. Description of the Related Art In recent years, in the field of sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, water-absorbing resins have been widely used for the purpose of absorbing body fluids. Examples of the water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, and vinyl acetate-acrylate. Saponified polymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or cross-linked thereof,
Crosslinked products of cationic monomers and the like are known.

The properties that the water-absorbent resin should have include various properties such as excellent absorption capacity, absorption rate, and liquid permeability when coming into contact with an aqueous liquid such as a body fluid. Furthermore,
In recent years, absorbent articles in sanitary articles which use a large amount of a water-absorbent resin and are thinner, which are in recent years, have been described under "under a high load (for example, 50 g / cm ² ) (hereinafter sometimes referred to as absorption capacity under pressure). However, the relationship between these various properties does not always show a positive correlation, and for example, the higher the absorption capacity, the lower the physical properties such as liquid permeability and absorption rate.

As a method for improving the water absorbing properties of such a water-absorbent resin in a well-balanced manner, there has been proposed a technique of cross-linking the surface of the water-absorbent resin in the vicinity of the surface with a crosslinking agent such as a polyhydric alcohol. Further, at the time of the crosslinking reaction, the crosslinking agent is more evenly distributed on the surface of the water-absorbent resin, and when adding the crosslinking agent in an attempt to perform uniform surface crosslinking, a method in which an inert inorganic powder is present, a method in which a dihydric alcohol is present, A method in which an ether compound is present, a method in which a water-soluble polymer is present, an alkylene oxide adduct of a monohydric alcohol,
A method in which an organic acid salt, a lactam or the like is present is also known.

However, even with these methods, a water-absorbing resin which satisfies all of the above-mentioned characteristics at a high level has not been obtained at the same time. For example, inorganic fine particles were added to the water-absorbing resin for the purpose of improving liquid permeability. In this case, the effect of the surface cross-linking treatment is significantly impaired, and the absorption capacity under pressure is greatly reduced. That is, a water-absorbing resin excellent in both the absorption capacity under pressure and the liquid permeability has not been obtained.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water-absorbent resin composition having excellent liquid permeability and high absorption capacity under pressure.

[0007]

In order to solve the above problems, the present invention has the following arrangement. (1) A water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the fine particles include monodisperse fine particles. (2) The monodisperse fine particles have a particle size distribution index (d ₂₅
/ D ₇₅ ) is 3 or less and are not agglomerated with each other. (3) A water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the fine particles include fine particles having a sphericity of 1 to 1.1. (4) A water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the fine particles include fine particles having a monodispersity and a sphericity of 1 to 1.1. Resin composition. (5) The fine particles have an average particle size of 0.01 to 10 μm.
The water absorbent resin composition according to any one of the above (1) to (4). (6) A water-absorbent resin composition containing a water-absorbent resin and inorganic fine particles and having an absorption capacity under pressure of 30 g / g or more. (7) A method for producing a water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the water-absorbent resin and the monodisperse fine particles are mixed. (8) A method for producing a water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the water-absorbent resin and the sphericity are 1 to 1.
A method for producing a water-absorbent resin, comprising mixing the fine particles of (1).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the fine particles contained in the water-absorbent resin composition are monodisperse or have a sphericity of 1 to 1.
It is necessary to be 1, and it is preferable to contain fine particles which are monodisperse and have a sphericity of 1 to 1.1. In the present invention, being monodisperse means that the particle size distribution is sharp and the particles are not aggregated with each other. The particle size distribution and the degree of aggregation can be measured not in the state of powder but in the state of slurry in which fine particles are dispersed in a hydrophilic solvent (water, ethanol, isopropanol, acetone, methyl ethyl ketone, ethylene glycol, etc.). . Therefore, the present invention also includes a case where particles are loosely aggregated in a powder state. For the fine particles contained in the water-absorbent resin composition, the shape and the particle diameter can be confirmed by first observing the water-absorbent resin composition with an electron microscope, and then saturating the water-absorbent resin composition with water. After swelling, the swollen gel was filtered through a 50 μm wire mesh using a large amount of water, and the fine particles contained in the filtrate were subjected to the above-mentioned centrifugal sedimentation type particle size distribution analyzer (SA-CP3 manufactured by Shimadzu Corporation).
) Can be used to measure the particle size distribution. Specifically, the particle size distribution of the fine particles is preferably those having a particle size distribution index (d ₂₅ / d ₇₅ ) of 3 or less, more preferably 2 or less, and still more preferably 1.5 or less. . When the particles are aggregated, the aggregate of the aggregated particles is measured as one particle. In addition, the phrase “the particles are not aggregated with each other” means that the fine particles do not substantially form secondary particles, and it is preferable that 50% or more of the fine particles do not form secondary particles. By containing the above-mentioned monodisperse fine particles as the fine particles, the fine particles are uniformly present on the surface of the water-absorbent resin, so that the aggregation of the water-absorbent resins is prevented, so that the liquid permeability is improved, and the water-absorbent resin is improved. Since the effect of the surface cross-linking treatment is not impaired, it is possible to obtain a water-absorbent resin composition having excellent absorption capacity under pressure.

The sphericity of the fine particles is the value of the longest diameter / shortest diameter of the fine particles, and the value of 1 to 1.1 means that the fine particles are substantially spherical. When the particles are aggregated, the sphericity of the fine particles is measured as a single aggregate of the aggregated particles. The reason why the particles are preferably substantially spherical is as follows. Surface cross-linking effect of water-absorbent resin (improvement of absorption capacity under pressure, etc.)
It is preferable that the surface of the water-absorbent resin is not completely covered with the fine particles so as not to damage the water-absorbent resin, and in order to improve the liquid permeability, the fine particles are uniformly present on the entire surface of the water-absorbent resin. This is because it is preferable to prevent aggregation between them. The sphericity is more preferably 1 to 1.01.

The fine particles have an average particle size of 0.01 to 10
μm, more preferably 0.1 to 5 μm, and even more preferably 0.2 to 1.5 μm. If the average particle diameter is smaller than 0.01 μm, the effect of the surface cross-linking treatment is impaired probably because the water-absorbent resin is easily buried in the pores, and the absorption capacity under pressure is apt to decrease. When it is larger than 10 μm, it is difficult to uniformly exist on the surface of the water-absorbing resin, so that the effect of improving the liquid permeability is reduced. Alternatively, in order to improve the liquid permeability, it is necessary to add a considerable amount of fine particles, so that the absorption capacity decreases.

The fine particles include silicon dioxide, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, calcium phosphate, barium phosphate, clay,
Inorganic particulate powders such as diatomaceous earth, zeolite, bentonite, kaolin, hydrosaltite, activated clay, cellulose powder, pulp powder, ethyl cellulose, ethyl hydroxyethyl cellulose, cellulose acetate butyrate, modified starch, chitin, rayon, polyester, polyethylene , Polypropylene, polyvinyl chloride, polystyrene, nylon, polymethyl methacrylate, melamine resin, melamine-benzoguanamine resin,
Examples thereof include organic fine particles such as activated carbon and tea leaves, and one or more of these can be used. Further, among these fine particles, inorganic fine particles are preferable, and among them, silicon dioxide,
Titanium dioxide, aluminum oxide, zeolite, kaolin and hydrosaltite are preferred. Among them, Seahorster KE-P (silica fine particle powder) and Seahorster KE-E (ethylene glycol dispersion of silica fine particles) (all trade names) manufactured by Nippon Shokubai Co., Ltd. are particularly preferable.

The method for producing fine particles having the above-mentioned monodispersity and a sphericity of 1 to 1.1 is not particularly limited. For example, a raw material slurry of fine particles containing water and a solvent may be used. One end of the tube that can be externally heated is a raw material slurry supply port, and the other end is depressurized (about 20 to 500 Torr).
And a method of powdering using a powdering device in which a powder collecting chamber is connected to the separating device.

The raw material slurry is obtained by wet grinding of coarse particles in a solvent containing water, classification of fine particles in a solvent containing water, and collection of powder obtained by a dry synthesis method with a solvent containing water. And a wet synthesis method in which a metal compound (silica or the like) is hydrolyzed or added with a precipitant in a solvent in which water is present, and a fine particle slurry is produced by ion exchange or the like. Among them, the wet synthesis method is preferable in that the fine particles in the slurry are highly dispersed and particles having a uniform particle diameter are easily obtained.

As the solvent contained in the raw material slurry,
The solubility of water in methanol or an organic compound at 20 ° C. is 1.0% by weight or more, and the azeotrope of a binary azeotrope of water and an organic compound is azeotropic with water. Organic compounds having a composition of 40% by weight or more are exemplified. By using these solvents, generation of aggregated particles can be suppressed during powderization. Examples of the organic compound include aliphatic lower alcohols having 2 or more carbon atoms such as ethanol, n-propanol and isopropanol; alicyclic alcohols; ketones such as methyl ethyl ketone; lower carboxylic esters such as methyl acetate and ethyl acetate. Cyclic ethers such as tetrahydrofuran and dioxane; nitriles such as acetonitrile; amines such as cyclohexylamine; organic acids such as formic acid and propionic acid.

When the solvent is methanol, the amount of the solvent in the raw material slurry is at least 1 time by weight of the amount of water, and when the solvent is other than methanol, the amount of the azeotrope is 0% with respect to the amount of water. It is preferably at least 0.6 times by weight. The amount of the fine particles is 0.01 to 100 parts by weight of the water absorbent resin.
It is preferable to use 10 parts by weight, more preferably 0.1 to 5 parts by weight. If the amount is less than 0.01 part by weight, the effect of improving the liquid permeability may be small, and if the amount is more than 10 parts by weight, it may be difficult to obtain the effect corresponding to the added amount, and the absorption capacity may be reduced. .

The water absorbing resin used in the water absorbing resin composition of the present invention includes those having a carboxyl group. For example, a crosslinked product of partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylate copolymer, and an acrylonitrile copolymer Examples include a hydrolyzate of a polymer or acrylamide copolymer or a crosslinked product thereof, and a crosslinked product of a cationic monomer. Among these, a crosslinked product of a partially neutralized polyacrylic acid is most preferred.

In order to obtain a crosslinked product of partially neutralized polyacrylic acid, a hydrophilic monomer having acrylic acid and / or a salt thereof as a main component may be polymerized, and a simple monomer other than acrylic acid and / or a salt thereof may be used. The amount of the monomer is preferably 30 mol% or less in the monomer component. The neutralization rate is 50 to 9 of the acid groups.
Preferably, 5 mol% is neutralized,
More preferably, the mole% is neutralized. Examples of the salt include an alkali metal salt, an ammonium salt, an amine salt and the like. As the polymerization method, it is preferable to carry out aqueous solution polymerization or reverse phase suspension polymerization.

In order to make the partially neutralized product of polyacrylic acid obtained by polymerization into a crosslinked product, a self-crosslinking type which does not use a crosslinking agent may be used, but two or more polymerizable compounds in one molecule may be used. It is preferable to copolymerize or react with an unsaturated group or an internal crosslinking agent having two or more reactive groups. Specific examples of the internal crosslinking agent include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylolpropane tri (meth) acrylate. ) Acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine , Poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol Examples thereof include coal, propylene glycol, glycerin, pentaerythritol, ethylene diamine, ethylene carbonate, propylene carbonate, polyethylene imine, and glycidyl (meth) acrylate. These internal crosslinking agents may be used alone or in combination of two or more.

The amount of the internal crosslinking agent to be used is 0.005 to 3 mol%, more preferably 0.1 to 3 mol%, based on the monomer components.
01 to 1.5 mol%. If the amount of the internal crosslinking agent is too small, the liquid permeability and the absorption rate tend to decrease, while if the amount of the internal crosslinking agent is too large, the absorption capacity tends to decrease.
When the polymer obtained by the above polymerization is a gel, the gel polymer is dried and crushed if necessary, so that the water-absorbent resin powder having an average particle size of about 10 to 1000 μm can be obtained. it can.

By subjecting the vicinity of the surface of the water-absorbing resin powder to a cross-linking treatment, the water-absorbing properties of the water-absorbing resin, particularly the absorption capacity under pressure, can be further increased. The surface cross-linking agent may be any one having two or more functional groups capable of reacting with the functional group on the surface of the water-absorbing resin. Examples thereof include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene. Glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4
-Diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, poly Polyhydric alcohol compounds such as oxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl Polyepoxy compounds such as ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol; Polyamine compounds such as diamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine, and inorganic or organic salts thereof (e.g., aditinium salt); 2,4-tolylenediisocyanate; Polyvalent isocyanate compounds such as hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one; 4-methyl-1,3-dioxolan-2-one; 5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-
On, 4-hydroxymethyl-1,3-dioxolane-
2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-
Alkylene carbonate compounds such as 1,3-dioxan-2-one and 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and the like Polyvalent amine adducts (for example, Kaimen manufactured by Hercules: registered trademark); hydroxides such as zinc, calcium, magnesium, aluminum, iron, and zirconium; and polyvalent metal compounds such as chlorides. Among these, polyhydric alcohol compounds, polyepoxy compounds, polyamine compounds and salts thereof, and alkylene carbonate compounds are preferred. These surface cross-linking agents may be used alone or in combination of two or more.

The amount of the surface cross-linking agent may be selected from water-absorbent resin 10
It is preferably used in an amount of 0.01 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 0 parts by weight. When the amount of the surface cross-linking agent is less than 0.01 part by weight, the liquid permeability may decrease. If you use more than 10 parts by weight,
Absorption capacity may be extremely reduced. An ordinary dryer or heating furnace can be used for the heat treatment. For example, a thin stirring dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, a flash dryer, an infrared dryer, and the like. In that case, the heat treatment temperature is preferably 40 to 250 ° C, more preferably 90 to 230 ° C, and still more preferably 120 to 220 ° C.
It is. When the heat treatment temperature is lower than 40 ° C., the fine powder retention may decrease, while the heat treatment temperature is lower than 250 ° C.
When the temperature exceeds ℃, there is a risk of causing thermal degradation depending on the type of the water-absorbing resin used. The heat treatment time is usually preferably from 1 to 120 minutes, more preferably from 10 to 60 minutes.

The method for producing the water-absorbent resin composition of the present invention is not particularly limited, and the fine particles may be added to and mixed with the water-absorbent resin. For example, the fine particles may be added to the surface-crosslinked water-absorbent resin. Examples of the method include a method of mixing, a method of adding the fine particles to the water-absorbent resin and then performing a surface crosslinking treatment, and a method of adding and mixing the fine particles in a slurry state with the water-absorbent resin.

Since the water-absorbent resin composition of the present invention contains specific fine particles as described above, it is excellent in both liquid permeability and absorbency against pressure. Conventionally, since the decrease in absorption capacity under pressure due to the addition of inorganic fine particles was remarkable,
For the first time in the present invention, a water-absorbent resin composition containing inorganic fine particles, which has a high absorption capacity under pressure, can be provided. Specifically, a water-absorbent resin composition having an absorption capacity under pressure of 30 g / g or more can be provided.

The water-absorbent resin composition of the present invention absorbs not only water but also various liquids including water such as body fluids, physiological saline, urine, blood, cement water, and fertilizer-containing water. And sanitary materials such as sanitary napkins and incontinence pads, as well as in various industrial fields such as civil engineering and agricultural and horticultural. Furthermore, a new function is provided by interposing a deodorant, a fragrance, a drug, a plant growth aid, a bactericide, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a fertilizer, and the like in the water-absorbent resin composition of the present invention. Can also be given.

[0025]

The present invention will be described below in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples, “parts” means “parts by weight” unless otherwise specified. Various properties of the water absorbent resin composition and the fine particles were measured by the following methods. (A) Absorption capacity under normal pressure (under no load) 0.2 g of a water-absorbent resin composition was applied to a nonwoven bag (60 mm ×
60 mm), and immersed in physiological saline (0.9% by weight aqueous sodium chloride solution) at room temperature. After 60 minutes, the bag was taken out, and after draining at 250 G for 3 minutes using a centrifuge, the weight W ₁ (g) of the bag was measured. The same operation was performed without using the water-absorbing resin composition, and the weight W ₀ (g) at that time was measured. These W ₁ and W ₀
From the following formula, absorption capacity under normal pressure (g / g) = (weight W ₁ (g) −weight W ₀
(G)) / weight (g) -1 of water-absorbent resin composition, the absorption capacity (g / g) under normal pressure was calculated. (A) Absorption capacity under pressure (under load) First, a measuring apparatus used for measuring absorption capacity under pressure will be briefly described below with reference to FIG.

As shown in FIG. 1, the measuring device comprises a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have. The container 2 has an opening 2a at the top and an opening 2b at the side surface thereof.
The outside air suction pipe 3 is fitted into the opening a, and the conduit 4 is attached to the opening 2b. The container 2 contains a predetermined amount of physiological saline 12.

The lower end of the outside air suction pipe 3 is
Submerged in physiological saline 12. The outside air suction pipe 3
Is provided to keep the pressure in the container 2 at substantially normal pressure (atmospheric pressure). The above glass filter 6 has a diameter of 70 m
m. The container 2 and the glass filter 6 communicate with each other by a conduit 4 made of a silicone resin. Further, the position and the height of the glass filter 6 with respect to the container 2 are kept constant. Further, the glass filter 6 is fixed such that the upper surface thereof is at a position slightly higher than the lower end surface 3 a of the outside air suction pipe 3.

The measuring section 5 includes a filter paper 7 and a support cylinder 9.
And a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11. In the measuring section 5, the filter paper 7 and the support cylinder 9 (that is, the wire mesh 10) are placed on the glass filter 6 in this order, and the weight 11 is placed inside the support cylinder 9, that is, on the wire mesh 10. Has become. The support cylinder 9 is formed to have an inner diameter of 60 mm, and the wire mesh 10 is made of stainless steel.
m). Then, a predetermined amount of the water-absorbing resin composition 15 is evenly spread on the wire mesh 10. The weight 11 can uniformly apply a load to the wire netting 10, that is, the water-absorbent resin composition 15.

The absorption capacity under pressure was measured using the measuring apparatus having the above-mentioned configuration. The measuring method will be described below. First, predetermined preparation operations such as putting a predetermined amount of physiological saline 12 into the container 2 and fitting the outside air suction pipe 3 into the container 2 were performed. Next, the filter paper 7 was placed on the glass filter 6. On the other hand, in parallel with these mounting operations, the support cylinder 9
0.9 g of the water-absorbent resin composition 15 was evenly dispersed inside, that is, on the wire mesh 10, and the weight 11 was placed on the water-absorbent resin composition 15.

Next, a wire mesh 10, that is,
The support cylinder 9 on which the water-absorbent resin composition 15 and the weight 11 were placed was placed so that the center of the support cylinder 9 coincided with the center of the glass filter 6. Then, from the time when the support cylinder 9 is placed on the filter paper 7, the physiological saline 12
Weight W ₂ (g) of the, obtained from the measured values of the balance 1.

From the above weight W ₂ (g) and the weight of the water-absorbent resin composition 15 (0.9 g), the following formula, absorption capacity under pressure (g / g) = weight W ₂ (g) According to the weight (g) of the water-absorbent resin composition, 6% from the start of water absorption under pressure
The absorption capacity (g / g) after 0 minute was calculated. In addition, for the measurement,
A weight 11 having a load of 20 g / cm ² was used. (C) Liquid Permeability Glass column 11 with a cock as shown in FIG. 2 (“Bio Column CF-30K” Co., Ltd. Catalog code 22-635-07, Inoui Seieido, lower filter # G2, inner diameter 1)
Inches, length 400 mm), water-absorbent resin composition 0.5
g, and the water-absorbent resin composition is equilibrium-swelled with an excess of physiological saline (about 1 hour). Next, after the swollen water-absorbent resin composition 12 has sufficiently settled, the liquid surface is raised to a liquid height of 2.
The cock was opened at the position of 00 ml, and the physiological saline 13 was filled with two standard lines C (liquid level of 150 ml) and D
(Liquid level of 100 ml liquid level)
ml), and the average value of the three measurements is taken as the liquid permeability (sec).

The value measured using this apparatus in the absence of the water-absorbent resin composition was 10 seconds. (D) Particle Size Distribution of Fine Particles After 5 g of fine particle powder was added to 100 ml of methyl ethyl ketone, a slurry dispersed for 20 minutes using an ultrasonic homogenizer was used, and a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 manufactured by Shimadzu Corporation) was used. It measured using. (E) Shape and average particle size of the fine particles For the slurry used for the measurement in the above (d), the shape of the fine particles was observed from an image of a transmission electron microscope at a magnification of 50,000, and individual particles were obtained for 100 or more particles. Measure the diameter,
The average was determined. Here, each particle diameter was an average of the longest diameter and the shortest diameter of the particles. When the particles were aggregated, the aggregate of the aggregated particles was regarded as one particle. (F) Sphericity The average value of the longest diameter and the average value of the shortest diameter of the fine particles measured in (e) were determined, and the sphericity of the fine particles was calculated according to the following equation.

The sphericity of the fine particles = (average value of the longest diameter of the fine particles) / (average value of the shortest diameter of the fine particles) Reference Example 1 In the production of the water-absorbing resin having a carboxyl group, 2.72 parts of trimethylolpropane triacrylate as an internal cross-linking agent was dissolved in 4400 parts of a 37% by weight aqueous solution of sodium acrylate (neutralization ratio: 75 mol%) to prepare a reaction solution. Next, the reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere.

Next, the reaction solution was supplied to a reactor equipped with a jacketed stainless steel double-armed kneader having two sigma-type blades and the reaction solution was maintained at 30 ° C. while flowing nitrogen gas into the reactor. Replaced. Subsequently, while stirring the reaction solution, sodium persulfate as a polymerization initiator was added.
When 1 part and 1.1 parts of sodium sulfite as a reducing agent for accelerating the decomposition of the polymerization initiator were added, polymerization started about 1 minute later. Then, polymerization was carried out at 30 ° C. to 80 ° C., and the hydrogel polymer was taken out 40 minutes after the initiation of the polymerization.

The obtained hydrogel polymer was spread on a wire net and dried with hot air at 150 ° C. for 2 hours. Next, the dried product is pulverized using a hammer mill, and classified with a 20-mesh wire mesh (opening: 850 μm) to obtain an average particle diameter of 350 μm.
An irregularly crushed water-absorbent resin (1) having a size of μm was obtained. Next, 1 part of propylene glycol as a first surface cross-linking agent, 0.05 parts of ethylene glycol diglycidyl ether as a second surface cross-linking agent, and 3 parts of water with respect to 100 parts of the obtained water-absorbent resin (1). And an aqueous solution consisting of 0.75 parts of isopropyl alcohol was added and mixed, and the resulting mixture was heated at 175 ° C. for 40 minutes to obtain a water-absorbent resin (2). [Example 1] 100 parts of the obtained water-absorbent resin (2) was coated with Seahorster KE-P100 (manufactured by Nippon Shokubai Co., Ltd .: monodispersed silica spherical fine particles, average particle diameter 1.00 µm, d ₂₅ /
(d ₇₅ <1.5, sphericity: 1.00) 1 part was added and mixed to obtain a water-absorbent resin composition (1). Table 1 shows the results of measuring various properties of the water absorbent resin composition (1) by the above-described methods. Example 2 100 parts of the obtained water-absorbent resin (2) was coated with Seahorster KE-P30 (manufactured by Nippon Shokubai Co., Ltd .: monodispersed silica spherical fine particles, average particle diameter 0.28 μm, d ₂₅ / d).
₇₅ <1.5, sphericity 1.01) 1 part was added and mixed to obtain a water-absorbent resin composition (2). Table 1 shows the results of measuring various properties of the water absorbent resin composition (2) by the methods described above. [Example 3] 100 parts of the obtained water-absorbent resin (2) was coated with Seahorster KE-P50 (manufactured by Nippon Shokubai Co., Ltd .: monodisperse silica spherical fine particles, average particle diameter 0.53 µm, d ₂₅ / d).
₇₅ <1.5, sphericity: 1.00) 1 part was added and mixed to obtain a water-absorbent resin composition (3). Table 1 shows the results obtained by measuring various properties of the water absorbent resin composition (3) by the above-described methods. Example 4 100 parts of the obtained water-absorbent resin (2) was coated with Seahorster KE-P150 (manufactured by Nippon Shokubai Co., Ltd .: monodisperse silica fine particles, average particle size 1.50 μm, d ₂₅ /
(d ₇₅ <1.5, sphericity: 1.00) 1 part was added and mixed to obtain a water absorbent resin composition (4). Table 1 shows the results of measuring the performance of the water-absorbent resin composition (4) by the methods described above. [Comparative Example 1] Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd .: silica fine particles, average particle size 0.012 µm, usually agglomerated to several µm, 100 spheres) in 100 parts of the obtained water-absorbent resin (2), sphericity 1 .89) 1 part was added and mixed to obtain a comparative water absorbent resin composition (1). Table 1 shows the results obtained by measuring various properties of the comparative water-absorbent resin composition (1) by the methods described above. [Comparative Example 2] Carplex # 100 (manufactured by Shionogi Pharmaceutical Co., Ltd .: silica fine particles) was added to 100 parts of the obtained water-absorbent resin (2).
Average particle diameter of single particles 0.023 μm, average particle diameter of aggregated particles 2.2 μm, d ₂₅ / d ₇₅ > 4, sphericity 1.72) 1
Parts were added and mixed to obtain a comparative water-absorbent resin composition (2). Table 1 shows the results of measuring the various properties of this comparative water-absorbent resin composition (2) by the methods described above.

[0036]

[Table 1]

Table 1 shows that the comparative water absorbent resin compositions (1) and (2) of the comparative example were compared with the water absorbent resin (2) of the reference example. It can be seen that although the liquid permeability was improved, the absorption capacity under normal pressure was reduced, and the absorption capacity under pressure was greatly reduced. On the other hand, when specific fine particles are added and mixed as in the water-absorbent resin compositions (1) to (4) of the examples, the liquid permeability is improved, and the absorption capacity and the addition capacity under normal pressure are improved. It can be seen that the absorption capacity under rolling is hardly reduced or improved, and that the absorption capacity is 30 g / g or more.

[0038]

Since the water-absorbent resin composition of the present invention contains specific fine particles, the water-absorbent resin composition is excellent in liquid permeability and also excellent in absorption capacity under normal pressure and under pressure.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method of measuring an absorption capacity under pressure in an example.

FIG. 2 is a diagram for explaining a method for measuring liquid permeability in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance 2 Container 3 External air suction pipe 4 Pipe 5 Measurement part 6 Glass filter 7 Filter paper 9 Support cylinder 10 Wire net 11 Weight 12 Physiological saline

Claims (8)

[Claims] 1. A water-absorbent resin composition comprising a water-absorbent resin and fine particles, wherein the fine particles include monodisperse fine particles. 2. The water-absorbent resin composition according to claim 1, wherein the monodisperse fine particles have a particle size distribution index (d ₂₅ / d ₇₅ ) of 3 or less and are not aggregated with each other. 3. A water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the fine particles have a sphericity of 1 to 3.
A water-absorbent resin composition comprising the fine particles of 1.1. 4. A water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the fine particles include fine particles having a monodispersity and a sphericity of 1 to 1.1. Water-absorbent resin composition. 5. The fine particles having an average particle size of 0.01 to 1
The water-absorbent resin composition according to any one of claims 1 to 4, which has a thickness of 0 µm. 6. A water-absorbent resin composition comprising a water-absorbent resin and inorganic fine particles and having an absorption capacity under pressure of 30 g / g or more. 7. A method for producing a water-absorbent resin composition containing a water-absorbent resin and fine particles, the method comprising mixing the water-absorbent resin and monodisperse fine particles. 8. A method for producing a water-absorbent resin composition containing a water-absorbent resin and fine particles, wherein the sphericity is 1%.
A method for producing a water-absorbent resin, which comprises mixing the fine particles of 1.1 to 1.1.