JP2007314794A - Water-absorbing resin composition, and water-absorbing article containing the same and preparation process of water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-absorbing resin composition which is excellent in water absorbing characteristics such as diffusivity of an aqueous liquid, water-absorbing rate, water retainability, and dry touch property and has decreased values in the amount of water-soluble component and the amount of remained monomers and to provide a water-absorbing article containing it and a preparation process of a water-absorbing resin. <P>SOLUTION: This water-absorbing resin is prepared by dispersing a solid blowing agent whose mean particle size is in the range of 1-100 μm into an aqueous monomer solution containing an unsaturated monomer and a crosslinking agent and then polymerizing the unsaturated monomer. This water-absorbing resin is excellent in water absorbing properties such as diffusivity of an aqueous liquid, water-absorbing rate, water retainability, and dry touch property and has decreased values in the amount of water-soluble component and the amount of remained monomers. If a water-absorbing resin composition using this water-absorbing resin is used as a sanitary material, for example, leak from this sanitary material can be avoided since its water-absorbing rate, water retainability, and the like are improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention is, for example, a paper diaper (disposable diaper), a sanitary napkin, a so-called incontinence pad (jig for incontinence), a sanitary material (body fluid absorbing article) such as a wound protection material, a wound healing material, or a building material. Water- absorbing resin composition suitably used for absorbent articles such as drip-absorbing materials such as water retaining materials for soil, foodstuffs, freshness-keeping materials, water-stopping materials, absorbent articles containing the same, and methods for producing water-absorbing resins is there.

  In recent years, hygiene materials such as paper diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials, water absorption for the purpose of absorbing bodily fluids such as urine, sweat and menstrual blood as their constituent materials Resins are widely used. The water-absorbing resin is not only used as a sanitary material but also for building materials, water retaining materials for soil, drip absorbent materials for foods, freshness retaining materials, water-stopping materials, water absorption (absorption), water retention, moisture absorption, etc. It is widely used for various applications.

Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product ( Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 ), and a hydrolyzate of starch-acrylonitrile graft polymer ( Patent Document). 5 ), neutralized product of starch-acrylic acid graft polymer ( Patent Document 6 ), saponified product of vinyl acetate-acrylic acid ester copolymer ( Patent Document 7 ), hydrolysis of acrylonitrile copolymer or acrylamide copolymer Or cross-linked products thereof ( Patent Document 8 ), cross-linked carboxymethyl cellulose, cross-linked cationic monomers ( Patent Document 9 and Patent Document 10 ), isobutylene-maleic anhydride copolymer cross-linked product, 2-acrylamide-2- Copolymerized crosslinked product of methylpropanesulfonic acid and acrylic acid, crosslinked polyethylene oxide, methoxypolyethylene Copolymer crosslinked body and the like of the call and acrylic acid are known.

Any of these water-absorbent resins is in the form of particles or powder having a particle diameter of about 0.01 mm to 5 mm. In general, the water absorption rate of a water absorbent resin is determined by the particle size, and the water absorption rate of individual particles tends to increase as the particle size decreases ( Non-Patent Document 1 ).

  However, in practice, as the particle diameter decreases, the liquid permeability when an aqueous liquid such as a body fluid passes between the particles decreases. That is, a so-called gel block is generated. Therefore, when using the water-absorbent resin, it is necessary to select the optimum particle size in consideration of the water absorption speed and the liquid permeability. In addition, the water-absorbent resin tends to cause gel block as the water absorption speed increases. The main cause of the gel block includes a decrease in voids under pressure and an increase in tackiness between the particles after swelling.

In view of this, for the purpose of improving the water absorption characteristics of the water absorbent resin, in particular, improving the water absorption speed, various methods for producing and modifying water absorbent resins as described below have been proposed. That is, as a method for producing or modifying a water-absorbing resin, for example, (1) a method of secondary crosslinking treatment, that is, a method of increasing the crosslinking density near the surface of the particle, (2) granulation, foaming, porous A method for increasing the surface area of particles by qualification or the like has been proposed.

As the method of (1) above, as a surface crosslinking agent, for example, a method using a polyhydric alcohol, a method using a polyvalent glycidyl compound, a polyvalent aziridine compound, a polyvalent amine compound, a polyvalent isocyanate compound, or a method using glyoxal , A method using a polyvalent metal salt, a method using a silane coupling agent, a method using a monoepoxy compound, a method using an epoxy group-containing polymer, a method using an epoxy compound and a hydroxy compound, a method using an alkylene carbonate, etc. It is done.

Further, at the time of the crosslinking reaction, for example, a method in which an inert inorganic powder is present ( Patent Document 11 ), a method in which a dihydric alcohol is present, a method in which water and an ether compound are present, an alkylene oxide adduct of a monohydric alcohol, A method of causing an organic acid salt, lactam or the like to exist, a method of using two or more kinds of crosslinking agents having different solubility parameters, and the like have also been proposed. Further, methods for increasing the cross-linking density near the surface of the particles are also disclosed in Patent Document 12, Patent Document 13, Patent Document 14, Patent Document 15, Patent Document 16, and the like.

As the method (2) , for example, a method using a foaming agent during polymerization or crosslinking is proposed. As a method using a foaming agent, for example, a method of introducing a crosslinked structure into a linear water-soluble polymer while neutralizing with a foaming agent such as carbonate ( Patent Document 17, Patent Document 18 and the like), carbonic acid A method of adding a salt to a monomer ( Patent Document 19, Patent Document 20, Patent Document 21, Patent Document 22, Patent Document 23, Patent Document 24 ), a method of polymerizing a monomer using microwaves in the presence of a carbonate ( Patent Document 25 ), a method of polymerizing by adding an organic solvent having a boiling point of 40 ° C. to 150 ° C. to a specific monomer ( Patent Document 26, Patent Document 27, Patent Document 28, Patent Document 29 ), adding a hydrophobic organic solvent And a method of polymerizing under a specific pressure ( Patent Document 30, Patent Document 31 ) and the like. Furthermore, a method of adding a foaming agent after polymerizing monomers ( Patent Document 32, Patent Document 33, Patent Document 34 ) has also been proposed.

Further, a method of imparting polarity (porous) to particles using a microwave ( Patent Document 35 ), a method of granulating fine particles into secondary particles ( Patent Document 36, Patent Document 37, Patent Document 38, Patent Document) 39, Patent Document 40 ) and the like have been proposed.

By the methods (1) and (2) , the water absorption speed of the water absorbent resin can be improved to some extent.
JP 55-84304 A JP-A-55-108407 JP 55-133413 A US Pat. No. 4,654,039 Japanese Patent Publication No.49-43995 Japanese Patent Laid-Open No. 51-125468 JP-A-52-14689 Japanese Patent Laid-Open No. 53-15959 JP 58-154709 A JP 58-154710 A US Pat. No. 4,587,308 U.S. Pat. No. 4,666,983 US Pat. No. 5,140,076 US Pat. No. 5,229,466 JP 59-62665 A JP-A-5-508425 U.S. Pat. No. 4,529,739 U.S. Pat. No. 4,649,164 Japanese Patent Publication No.62-34042 Japanese Patent Publication No. 2-60681 Japanese Examined Patent Publication No. 2-54362 US Pat. No. 5,118,719 US Pat. No. 5,154,713 US Pat. No. 5,314,420 U.S. Pat. No. 4,808,637 JP 59-18712 A US Pat. No. 4,552,938 U.S. Pat. No. 4,654,393 US Pat. No. 4,703,067 US Pat. No. 5,328,935 US Pat. No. 5,338,766 JP-A-56-13906 JP-A-57-182331 JP-A-57-208236 WO91 / 02552 WO93 / 24153 US Pat. No. 5,002,986 US Pat. No. 5,300,565 US Pat. No. 5,140,076 U.S. Pat. No. 4,732,968 Published by The Society of Polymer Science, Japan, “Polymer” Vol. 36, 614, 1987

  However, the water-absorbing resin formed by the secondary cross-linking treatment cannot achieve a quick water absorption speed required when used for, for example, sanitary materials. In addition, a water-absorbent resin obtained by crosslinking a foamed linear polymer has an insufficient amount of water absorption (water retention amount) and is expensive. Furthermore, a porous water-absorbent resin that is foamed while polymerizing monomers is excellent in water absorption speed and does not cost much, but it is difficult to control the timing of the foaming, and a constant pore diameter is obtained. I can't. For this reason, the water-absorbent resin is insufficient in improving various properties such as the diffusibility of the aqueous liquid, the amount of water-soluble components, the amount of residual monomer, and the dry touch property (all will be described later).

  That is, the water-absorbent resin obtained by the above production method or modification method is insufficient in the mutual balance of conflicting characteristics such as the diffusibility of the aqueous liquid, the amount of water-soluble components, and the dry touch property. That is, the conventional water-absorbent resin has insufficient improvement in water absorption characteristics, and therefore cannot achieve the high water absorption characteristics required when used for, for example, sanitary materials.

  In addition, the above-described production method and modification method are intended to design a water-absorbing resin so that the water-absorbing resin can be quickly absorbed when the water-absorbing resin comes into contact with the aqueous liquid. Therefore, with respect to sanitary materials, particularly sanitary materials that use a large amount of water-absorbing resin to reduce the thickness, little consideration has been given to the water-absorbing properties required for the water-absorbing resin.

  In a sanitary material using a large amount of water-absorbent resin, it is necessary to improve the water absorption speed, but if the water absorption speed is increased, gel blocks are likely to be formed. Then, in order to make a gel block hard to produce, the trial which improves the gel elasticity of a water absorbing resin particle, for example is also made | formed. However, when the gel elasticity is improved, the water retention capacity of the water-absorbent resin is lowered. For this reason, even if a water-absorbent resin with improved water absorption speed and gel elasticity is used as a sanitary material, it is difficult to say that the sanitary material can be prevented from leaking. Therefore, a water-absorbing resin with improved diffusibility of the aqueous liquid between the water-absorbing particles, which is contrary to these various characteristics while maintaining various characteristics such as the water absorption speed and water retention capacity, is desired. .

The present invention has been made in view of the above-described conventional problems, and the purpose thereof is excellent in water absorption characteristics such as diffusibility and water absorption speed, water retention ability, and dry touch property of an aqueous liquid, An object of the present invention is to provide a water-absorbent resin composition having a reduced amount of residual monomer , an absorbent article containing the same, and a method for producing the water-absorbent resin .

  In order to achieve the above object, the inventors of the present application have made extensive studies on a water absorbent resin, a method for producing the same, and a water absorbent resin composition. As a result, a solid foaming agent having an average particle size in the range of 1 μm to 100 μm is dispersed in an aqueous monomer solution containing an unsaturated monomer and a crosslinking agent, and then the unsaturated monomer is polymerized. It is found that the water-absorbing resin obtained by this method has excellent water-absorbing properties such as diffusibility of water-based liquids, water absorption speed, water retention ability, and dry touch properties, and also reduces the amount of water-soluble components and residual monomers. It was. Then, when the water-absorbent resin composition using the water-absorbent resin is used as, for example, a sanitary material, the water absorption speed and water retention ability are improved, and the leakage of the sanitary material can be avoided, and the present invention is completed. It came to do.

That is, the water-absorbent resin composition of the present invention crosslinks an unsaturated monomer containing, as a main component, at least one acrylate monomer selected from the group consisting of acrylic acid and water-soluble salts of acrylic acid. A water-absorbent resin composition comprising a water-absorbent resin polymerized in the presence of an agent and an inorganic powder, wherein the water-absorbent resin composition comprises 60% of physiological saline (0.9 wt% sodium chloride aqueous solution). The water retention capacity per minute is 20 g / g or more, the water absorption rate for physiological saline is 120 seconds or less, and the liquid passing rate under pressure is 200 seconds or less.

According to the above water-absorbing resin composition, the water-absorbing properties such as diffusibility, water absorption speed, water retention ability, and dry touch property of the aqueous liquid are excellent, and the water-soluble component amount and the residual monomer amount are reduced. Articles can be obtained industrially inexpensively and easily.

Moreover, in the water absorbing resin composition of this invention, it is preferable to contain 0.001 weight part-10 weight part of inorganic powder with respect to 100 weight part of the said water absorbing resin.

Moreover, in the water absorbent resin composition of the present invention, the amount of the inorganic powder used relative to 100 parts by weight of the water absorbent resin is preferably 0.001 part by weight or more and 10 parts by weight or less.

In the water absorbent resin composition of the present invention, the bulk specific gravity of the water absorbent resin is 0.01 g / cm. ³ Or more, 0.5 g / cm ³ The following is preferable.

In the water absorbent resin composition of the present invention, the inorganic powder contains at least one selected from silicon dioxide, silicic acid, and silicate, and the average particle diameter of the inorganic powder measured by a Coulter counter method Is preferably 200 μm or less.

Moreover, in the water absorbent resin composition of the present invention, it is preferable that the surface of the water absorbent resin is crosslinked by a covalent bond.

Moreover, in the water absorbent resin composition of the present invention, it is preferable that the surface of the water absorbent resin is crosslinked with a covalent bond and an ionic bond.

Moreover, the absorbent article of this invention contains the water absorbing resin composition.

In the method for producing a water-absorbing resin of the present invention, a solid foaming agent having an average particle diameter of 1 μm to 1000 μm is uniformly dispersed in an aqueous monomer solution containing acrylic acid and a water-soluble salt of acrylic acid and a crosslinking agent. Thereafter, the method includes a step of polymerizing the aqueous monomer solution and a step of crosslinking the surface of the water-absorbent resin after the step.

According to the above method for producing a water-absorbent resin, the water-soluble component amount and the residual monomer amount are reduced while being excellent in water-absorbing characteristics such as diffusibility of water-based liquid, water absorption speed, water retention ability, and dry touch property. Absorbent articles can be obtained industrially inexpensively and easily.

In the method for producing a water absorbent resin of the present invention, it is preferable that the step of crosslinking the surface is a step of forming a covalent bond.

Moreover, in the manufacturing method of the water absorbing resin of this invention, it is preferable that it is a step which forms the ionic bond on the surface of a water absorbing resin further using the cationic compound after the step of bridge | crosslinking the surface.

Moreover, in the manufacturing method of the water absorbing resin of this invention, it is preferable to mix the said water absorbing resin and inorganic powder.

The water-absorbent resin composition of the present invention comprises an unsaturated monomer containing as a main component at least one acrylate monomer selected from the group consisting of acrylic acid and water-soluble salts of acrylic acid. A water-absorbent resin composition comprising a water-absorbent resin that is polymerized in the presence, having a water retention capacity of 20 g / g or more with respect to physiological saline, a water absorption rate with respect to physiological saline of 120 seconds or less, and physiological saline 24.5 g / cm for water ² The liquid passing speed under pressure in is 200 seconds or less.

  Moreover, the manufacturing method of the water-absorbent resin of the present invention uniformly disperses a solid foaming agent having an average particle diameter of 1 μm to 1000 μm in a monomer aqueous solution containing acrylic acid and a water-soluble salt of acrylic acid and a crosslinking agent. And a step of polymerizing the aqueous monomer solution, and a step of crosslinking the surface of the water-absorbent resin after the step.

Therefore, it is easy to industrially manufacture absorbent articles with excellent water absorption characteristics such as diffusibility, water absorption speed, water retention capacity, and dry touch properties of aqueous liquids, and with reduced amounts of water-soluble components and residual monomers. The effect that it can be obtained is produced.

  The present invention is described in detail below.

  The unsaturated monomer used as a raw material in the present invention has water solubility. Specific examples of the unsaturated monomer include acrylic acid, β-acryloyloxypropionic acid, methacrylic acid, crotonic acid, (anhydrous) maleic acid, fumaric acid, itaconic acid, cinnamic acid, sorbic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, vinylphosphonic acid, Acid group-containing monomers such as 2- (meth) acryloyloxyethyl phosphoric acid, and alkali metal salts, alkaline earth metal salts, ammonium salts, alkylamine salts thereof; N, N-dimethylaminoethyl (meth) Dialkylamino such as acrylate, N, N-dimethylaminopropyl (meth) acrylate Rualkyl (meth) acrylates and quaternized products thereof (for example, reactants with alkyl halides, reactants with dialkyl sulfuric acid, etc.); dialkylaminohydroxyalkyl (meth) acrylates and quaternized products thereof N-alkylvinylpyridinium halides; hydroxyalkyl (meth) acrylates such as hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate; acrylamide, methacrylamide, N-ethyl ( (Meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Acrylate), methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; vinyl acetate; methyl (meth) acrylate, ethyl (meth) ) Alkyl (meth) acrylates such as acrylate; These monomers may be used alone or in combination of two or more.

  Of the above-exemplified monomers, an unsaturated monomer containing an acrylate monomer as a main component is preferable because the water absorption property of the resulting water absorbent resin is further improved. Here, the acrylate monomer refers to acrylic acid and / or water-soluble salts of acrylic acid. The water-soluble salts of acrylic acid are alkali metal salts and alkaline earths of acrylic acid having a neutralization rate in the range of 30 mol% to 100 mol%, preferably in the range of 50 mol% to 99 mol%. Metal salt, ammonium salt, hydroxyammonium salt, amine salt, alkylamine salt are shown. Of the water-soluble salts exemplified above, sodium salts and potassium salts are more preferable. These acrylate monomers may be used alone or in combination of two or more.

  When the unsaturated monomer contains an acrylate monomer as a main component, the amount of the monomer other than the acrylate monomer is less than 40% by weight of the entire unsaturated monomer Is more preferable, less than 30% by weight is more preferable, and less than 10% by weight is particularly preferable. By using a monomer other than the acrylate monomer in the above ratio, the water absorbing property of the resulting water absorbent resin can be further improved, and the water absorbent resin can be obtained at a lower cost.

  Examples of the crosslinking agent used when polymerizing the unsaturated monomer in the present invention include a compound having a plurality of vinyl groups in the molecule; an unsaturated monomer having at least one vinyl group in the molecule; A compound having at least one functional group capable of reacting with the carboxyl group; a compound having a plurality of functional groups capable of reacting with the carboxyl group in the molecule. These crosslinking agents may be used alone or in combination of two or more.

Specific examples of the compound having a plurality of vinyl groups in the molecule include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol di (meth). Acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate , Dipentaerythritol hexa (meth) acrylate, N, N-diallylacrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallyl And poly (meth) allyloxyalkanes such as amine, diallyloxyacetic acid, N-methyl-N-vinylacrylamide, bis (N-vinylcarboxylic acid amide), and tetraallyloxyethane.

  Examples of the compound having at least one vinyl group in the molecule and at least one functional group capable of reacting with a carboxyl group include, for example, ethylenically unsaturated group having at least one hydroxyl group, epoxy group, cationic group, etc. Compounds. Specific examples of the compound include glycidyl (meth) acrylate, N-methylolacrylamide, dimethylaminoethyl (meth) acrylate, and the like.

  Examples of the compound having a plurality of functional groups capable of reacting with a carboxyl group in the molecule include compounds having at least two hydroxyl groups, epoxy groups, cationic groups, isocyanate groups, and the like. Specific examples of the compound include (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, ethylene carbonate, polyethyleneimine, and aluminum sulfate. Etc.

  Among the crosslinking agents exemplified above, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, tri Multiple vinyl groups in the molecule such as allyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, etc. Compounds of soluble are more preferred.

  The amount of the crosslinking agent used with respect to the unsaturated monomer depends on the combination of the unsaturated monomer and the crosslinking agent, but is 0.0001 to 10 parts by weight with respect to 100 parts by weight of the unsaturated monomer. Within the range, preferably within the range of 0.001 to 5 parts by weight, more preferably within the range of 0.01 to 2 parts by weight. When the amount of the crosslinking agent used exceeds 10 parts by weight, the amount of water absorption of the resulting water-absorbent resin is lowered, and foaming by the foaming agent described later is insufficient, which is not preferable. On the other hand, when the amount of the crosslinking agent used is less than 0.0001 parts by weight, the water absorption rate and gel strength of the resulting water-absorbent resin are decreased, the amount of water-soluble components is increased, and foaming by the foaming agent is performed. Since it becomes difficult to control, it is not preferable. In addition, when an unsaturated monomer is polymerized without using a crosslinking agent, the water-absorbing properties of the water-absorbing resin obtained and the properties after water absorption of the water-absorbing resin are insufficient.

  When the unsaturated monomer is polymerized in the presence of a crosslinking agent, in order to improve the water absorption characteristics of the resulting water absorbent resin and efficiently perform foaming with the foaming agent, the unsaturated monomer and The cross-linking agent is preferably an aqueous solution. That is, it is preferable to use water as a solvent. The concentration of the unsaturated monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) is more preferably in the range of 20% by weight to 65% by weight, and further preferably in the range of 25% by weight to 60% by weight. A range of 30% to 45% by weight is particularly preferable. When the concentration of the unsaturated monomer is less than 20% by weight, the amount of water-soluble components in the resulting water-absorbent resin may increase, and foaming by the foaming agent may be insufficient to improve the water absorption rate. There is a risk that it will not be possible. On the other hand, when the concentration of the unsaturated monomer exceeds 65% by weight, it may be difficult to control the reaction temperature and foaming by the foaming agent.

  Moreover, water and the organic solvent soluble in water can also be used together as a solvent of monomer aqueous solution. Specific examples of the organic solvent include methyl alcohol, ethyl alcohol, acetone, dimethyl sulfoxide, ethylene glycol monomethyl ether, glycerin, (poly) ethylene glycol, (poly) propylene glycol, and alkylene carbonate. These organic solvents may be used alone or in combination of two or more.

  When the organic solvent is used in combination, the amount of the organic solvent used may be within a range in which the average particle diameter of the foaming agent can be controlled within a range of 1 μm to 100 μm in a dispersed state. Specifically, it may be 40% by weight or less, more preferably 20% by weight or less, still more preferably 10% by weight or less based on water.

In the present invention, the foaming agent used when the unsaturated monomer is polymerized is particulate, and is a solid compound at room temperature that is hardly soluble in water and the organic solvent. Specific examples of the foaming agent include azodicarbonamide, azobisisobutyronitrile, barium azodicarboxylate, dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydrazide), para Toluenesulfonyl hydrazide, diazoaminobenzene, N, N′-dimethyl-N, N′-dinitrosotephthalamide, nitrourea, acetone-p-toluenesulfonyl hydrazone, p-toluenesulfonyl azide, 2,4-toluenedisulfonyl hydrazide , P-methylurethanebenzenesulfonyl hydrazide, trinitroso trimethylene triamine, p-toluenesulfonyl semicarbazide, oxalyl hydrazide, nitroguanidine, hydrazodicarbonamide, trihydrazinotriamine, Zobisformamide, benzenesulfonylhydrazide, benzene-1,3-disulfonylhydrazide, diphenylsulfone-3,3′-disulfonylhydrazide, 4,4′-oxybis (benzenesulfonylhydrazide), sulfonylhydrazide, malonic acid and its Organic compounds such as salts, carbamic acid and salts thereof;
General formula (1)

(Wherein X ₁ and X ₂ each independently represents an alkylene group having 1 to 4 carbon atoms, and R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ are each independently , Represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an aryl group, an allyl group, or a benzyl group)
Or general formula (2)

(Wherein X ₃ and X ₄ each independently represent an alkylene group having 1 to 4 carbon atoms, X ₅ and X ₆ each independently represent an alkylene group having 2 to 4 carbon atoms, R ₇ and R ₈ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
Acrylates of amino group-containing azo compounds represented by: Inorganic compounds such as carbonates such as sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, basic magnesium carbonate, and calcium carbonate; These foaming agents may be used alone or in combination of two or more. Among the foaming agents exemplified above, an acrylate salt of an amino group-containing azo compound is more preferable. The acrylate of the amino group-containing azo compound has an average particle size without using a dispersion stabilizer (described later) such as a surfactant or a water-soluble polymer, or without stirring the monomer aqueous solution. While maintaining the diameter at a predetermined value, it can be uniformly dispersed in the monomer aqueous solution in a stationary state without causing sedimentation, floating or separation. Acrylates of amino group-containing azo compounds are particularly excellent in dispersibility with respect to acrylate monomers.

  Specific examples of the acrylate salt of the amino group-containing azo compound represented by the general formula (1) or the general formula (2) include 2,2′-azobis (2-methyl-N-phenylpropion). Amidine) diacrylate, 2,2′-azobis [N- (4-chlorophenyl) -2-methyl-propionamidine] diacrylate, 2,2′-azobis [N- (4-hydroxyphenyl)- 2-methylpropionamidine] diacrylate, 2,2′-azobis [2-methyl-N- (phenylmethyl) -propionamidine] diacrylate, 2,2′-azobis [2-methyl-N— (2-propenyl) propionamidine] diacrylate, 2,2′-azobis (2-methylpropionamidine) diacrylate, 2,2′-azobis [N- (2-hydride) Xylethyl) -2-methyl-propionamidine] diacrylate, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] diacrylate, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] diacrylate, 2,2′-azobis- [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2- Yl) propane] diacrylate, 2,2′azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] diacrylate, 2,2′-azobis [2- ( 5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] diacrylate, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazoline-2 -Il] propane Two acrylate and the like although not limited in particular. Of the acrylates of the amino group-containing azo compounds exemplified above, 2,2'-azobis (2-methylpropionamidine) diacrylate is particularly preferred.

  The acrylate of the amino group-containing azo compound can be isolated by, for example, using a method such as filtration after precipitation in an aqueous monomer solution. In addition, when the acrylate of the amino group-containing azo compound is precipitated in the monomer aqueous solution, a poor solvent may be added to the monomer aqueous solution, if necessary, You may go.

  The foaming agent prepared above may be used by adding it to the monomer aqueous solution, and the foaming agent precursor (hereinafter referred to as the foaming agent precursor) is dissolved in the monomer aqueous solution. Then, if necessary, it can be prepared in the monomer aqueous solution by adding carbon dioxide gas or acrylate to the monomer aqueous solution. That is, the foaming agent can be precipitated by reacting the foaming agent precursor with carbon dioxide gas or acrylate in an aqueous monomer solution. As the acrylate, sodium acrylate is preferred. When the unsaturated monomer is an acrylate monomer, the unsaturated monomer can act as an acrylate.

  The acrylate of the amino group-containing azo compound has a function as a foaming agent and a function as a radical polymerization initiator. Then, by polymerizing the unsaturated monomer in the presence of the acrylate salt of the amino group-containing azo compound, a water-absorbing resin in which the amount of water-soluble components and the amount of residual monomer are further reduced can be obtained. it can. That is, by using an acrylate salt of an amino group-containing azo compound, the amount of water-soluble components is 15% by weight or less, preferably 1% by weight to 10% by weight, and the residual monomer amount is 500 ppm. Hereinafter, it is possible to obtain a water-absorbent resin preferably reduced to 300 ppm or less, more preferably 100 ppm or less.

  The amount of the blowing agent used with respect to the unsaturated monomer may be set according to the combination of the unsaturated monomer and the blowing agent, and is not particularly limited, but is 100 parts by weight of the unsaturated monomer. Is more preferably in the range of 0.005 to 25 parts by weight, still more preferably in the range of 0.01 to 5 parts by weight, and in the range of 0.05 to 2.5 parts by weight. Particularly preferred. When the amount of the foaming agent used is out of the above range, the resulting water-absorbent resin may have insufficient water absorption characteristics.

  The average particle diameter of the foaming agent present in a dispersed state during polymerization in the aqueous monomer solution is preferably within the range of 1 μm to 100 μm, more preferably within the range of 2 μm to 50 μm, and further within the range of 3 μm to 40 μm. preferable. By setting the average particle diameter of the blowing agent within the above range, the average pore diameter of the water absorbent resin is within the range of 10 μm to 500 μm, more preferably within the range of 20 μm to 400 μm, and even more preferably within the range of 30 μm to 300 μm. Most preferably, it can be adjusted within the range of 50 μm to 200 μm, and the water absorption characteristics (for example, the diffusibility of the aqueous liquid and the water absorption speed) of the water absorbent resin can be improved. That is, by setting the average particle diameter of the foaming agent, the average pore diameter of the water absorbent resin can be set within a desired range.

  When the average particle diameter of the foaming agent is smaller than 1 μm, or when the foaming agent is dissolved in the monomer aqueous solution, foaming becomes insufficient, and the average pore diameter of the water absorbent resin is adjusted within a desired range. It is not preferable because it cannot be performed. On the other hand, when the average particle diameter of the foaming agent is larger than 100 μm, the average pore diameter of the water absorbent resin cannot be adjusted within a desired range. Moreover, since the gel strength of the water-absorbent resin obtained falls and the amount of water-soluble components increases, it is not preferable. In addition, the average particle diameter of the foaming agent in the monomer aqueous solution can be easily measured by using a laser type particle size distribution meter.

  Specific examples of the foaming agent precursor when the foaming agent is an inorganic compound include calcium hydroxide and magnesium hydroxide.

  The foaming agent precursor when the foaming agent is an acrylate salt of an amino group-containing azo compound is a hydrochloride salt of an amino group-containing azo compound, and specifically, for example, 2,2′-azobis (2- Methyl-N-phenylpropionamidine) dihydrochloride, 2,2′-azobis [N- (4-chlorophenyl) -2-methyl-propionamidine] dihydrochloride, 2,2′-azobis [N- (4- Hydroxyphenyl) -2-methylpropionamidine] dihydrochloride, 2,2′-azobis [2-methyl-N- (phenylmethyl) -propionamidine] dihydrochloride, 2,2′-azobis [2-methyl- N- (2-propenyl) propionamidine] dihydrochloride, 2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-hydroxyethyl) -2-methyl-propionamidine] dihydrochloride, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- ( 2-Imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis- [2- (4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl) propane] 2 Hydrochloride, 2,2′azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (5-hydroxy-3,4) , 5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride Etc. The hydrochlorides of these amino group-containing azo compounds are thermal decomposition azo polymerization initiators.

  In addition, the hydrochloride of an amino group-containing azo compound causes sedimentation, floating, and separation when the solubility in an aqueous monomer solution is low. Therefore, if the hydrochloride of the amino group-containing azo compound is used as a foaming agent as it is, a water-absorbing resin having excellent water absorption characteristics cannot be obtained.

  The conditions for preparing the acrylate of the amino group-containing azo compound by reacting the hydrochloride of the amino group-containing azo compound with the acrylate are not particularly limited, but the following conditions are preferred. And these conditions are set arbitrarily, and the pore diameter of the resulting water-absorbent resin may be adjusted to a desired size by appropriately adjusting the particle diameter at the time of dispersion of the acrylate of the amino group-containing azo compound. .

  That is, the preparation temperature is preferably −10 ° C. to 50 ° C., and more preferably 0 ° C. to 40 ° C. Further, the acrylate is more preferably an alkali metal acrylate, and more preferably sodium acrylate. The neutralization rate of the acrylate is preferably 50 mol% or more, more preferably 70 mol% or more. And the density | concentration of the acrylate in monomer aqueous solution has the preferable inside of the range of 20 weight%-saturation concentration, and the inside of the range of 25 weight%-saturation concentration is more preferable.

  Moreover, when preparing the acrylic acid salt of an amino group-containing azo compound, it is preferable to stir the aqueous monomer solution. Then, by stirring the monomer aqueous solution preferably at 10 rpm or more, more preferably 20 rpm to 10,000 rpm, an acrylate salt of an amino group-containing azo compound having a substantially uniform particle size can be prepared in a short time. it can. The prepared acrylate of an amino group-containing azo compound may be used as it is for the polymerization of the unsaturated monomer, and does not need to be isolated once.

  Examples of a method for preparing an amino group-containing azo compound acrylate salt in an aqueous monomer solution, that is, a method for dispersing the amino group-containing azo compound acrylate salt in an aqueous monomer solution include, for example, the following methods: Can be mentioned. That is, after preparing an acrylate salt of an amino group-containing azo compound by adding a hydrochloride salt of an amino group-containing azo compound to an acrylate salt with a neutralization rate of 100%, A method of obtaining an aqueous monomer solution by mixing an unsaturated monomer such as a crosslinking agent and, if necessary, a solvent; a hydrochloride of an amino group-containing azo compound in an aqueous monomer solution prepared in advance; In addition, a method of preparing an aqueous monomer solution in which an acrylic acid salt of an amino group-containing azo compound is dispersed by adding an acrylic acid salt as necessary is included. Among these methods, the latter method is preferable because an acrylate of an amino group-containing azo compound can be obtained more efficiently and the particle diameter becomes more uniform. After preparing an acrylate salt of an amino group-containing azo compound, the unsaturated monomer in the aqueous monomer solution is adjusted to a desired concentration by adding a solvent such as water to the aqueous monomer solution. May be.

  Next, the manufacturing method of the water absorbing resin concerning this invention is demonstrated.

  The water-absorbent resin according to the present invention is obtained by dispersing a foaming agent in an aqueous monomer solution and then polymerizing an unsaturated monomer (aqueous solution polymerization).

  The method for dispersing the foaming agent in the aqueous monomer solution is not particularly limited. For example, a method in which a foaming agent is added and dispersed in an aqueous monomer solution; a method in which a foaming agent precursor is added in an aqueous monomer solution, and then a foaming agent is prepared and dispersed in the aqueous monomer solution; Examples include a method of preparing a monomer aqueous solution by adding a monomer, a crosslinking agent, and a foaming agent to a solvent such as water and dispersing the foaming agent. Among these methods, after adding the foaming agent precursor to the aqueous monomer solution, the method of preparing and dispersing the foaming agent in the aqueous monomer solution provides a water-absorbing resin with even better water absorption properties. Is more preferable. In addition, when dispersing the foaming agent, the monomer aqueous solution may be stirred or may not be stirred.

  However, when the foaming agent is an inorganic compound such as carbonate and the unsaturated monomer contains an acrylate monomer as a main component, the reaction between the inorganic compound and the acrylate monomer Since the properties are relatively high, it is difficult to disperse the inorganic compound in the monomer aqueous solution and to control the particle size. Therefore, in this case, it is desirable to disperse the inorganic compound in the monomer aqueous solution using a dispersion stabilizer such as a surfactant or a water-soluble polymer.

  Specific examples of the dispersion stabilizer suitable when the foaming agent is carbonate include, for example, hydrophilic organic solvents such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, acetonitrile, and dimethylformamide; polyvinyl alcohol, Water-soluble polymers such as starch and derivatives thereof, polygalactomannan, methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose, and derivatives thereof, polyalkylene oxide, polyacrylic acid, polyacrylate, sodium oleate, castor oil potash, etc. Fatty acid salts, alkyl sulfates such as sodium lauryl sulfate and ammonium lauryl sulfate, alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate, alkyl naphthalene Anionic surfactants such as phonate, dialkylsulfosuccinate, alkyl phosphate ester salt, naphthalene sulfonate formalin condensate, polyoxyethylene alkyl sulfate ester salt; polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, poly Nonionic surfactants such as oxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxysorbitan fatty acid esters, polyoxyethylene alkylamines, fatty acid esters, oxyethylene-oxypropylene block polymers; alkylamines such as laurylamine acetate and stearylamine acetate Cations such as salts, quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride Surfactants; zwitterionic surfactants such as lauryl dimethylamine oxide; but like, but is not particularly limited. These dispersion stabilizers may be used alone or in combination of two or more.

  Among the above exemplified dispersion stabilizers, at least one selected from the group consisting of a water-soluble polymer and a surfactant is more preferable, and it is more preferable to use a water-soluble polymer and a surfactant in combination. Of the water-soluble polymers, polyvinyl alcohol, starch and derivatives thereof, cellulose and derivatives thereof are more preferable, and polyvinyl alcohol and hydroxyethyl cellulose are particularly preferable. The polyvinyl alcohol is more preferably partially saponified. Of the surfactants, anionic surfactants and nonionic surfactants are more preferable, and nonionic surfactants having an HLB of 7 or more are particularly preferable.

  By adding the above dispersion stabilizer to the monomer aqueous solution, an inorganic compound such as carbonate (foaming agent) is uniformly dispersed in the monomer aqueous solution, and the average particle size of the inorganic compound is 1 μm to 100 μm. Can be controlled within the range. The amount of the dispersion stabilizer used relative to the foaming agent may be set according to the combination of the foaming agent and the dispersion stabilizer, and is not particularly limited, but is 5 weights with respect to 100 parts by weight of the unsaturated monomer. And not more than 500 parts by weight, more preferably not more than 100 parts by weight, still more preferably not more than 50 parts by weight, particularly preferably not more than 10 parts by weight based on 100 parts by weight of the foaming agent. Specifically, within the range of 0.01 parts by weight to 500 parts by weight, more preferably within the range of 0.05 parts by weight to 100 parts by weight, still more preferably within the range of 0.5 parts by weight to 50 parts by weight, Particularly preferably, it may be in the range of 0.5 to 10 parts by weight.

  The unsaturated monomer in the monomer aqueous solution in which the foaming agent is dispersed can be polymerized by a known method. As the polymerization method, for example, various methods such as a radical polymerization method using a radical polymerization initiator, a radiation polymerization method, an electron beam polymerization method, an ultraviolet polymerization method using a photosensitizer can be adopted, and the polymerization method is particularly limited. It is not a thing. Of the above methods, the radical polymerization method is more preferable because the polymerization of the unsaturated monomer can be carried out quantitatively and completely.

  Examples of the radical polymerization method include aqueous solution polymerization, casting polymerization performed in a mold, thin layer polymerization performed on a belt conveyor, polymerization performed while subdividing the produced hydrogel polymer, reverse phase suspension polymerization, and reverse polymerization. Various polymerization forms such as phase emulsion polymerization, precipitation polymerization, and bulk polymerization can be employed. Of these, aqueous polymerization in which an unsaturated monomer is polymerized in the state of an aqueous solution is more preferable because the polymerization temperature can be easily controlled.

  When the unsaturated monomer is polymerized in an aqueous solution, any of continuous polymerization and batch polymerization may be employed, and it may be carried out under any pressure of reduced pressure, increased pressure, or atmospheric pressure. Good. The polymerization is preferably carried out under an inert gas stream such as nitrogen, helium, argon, carbon dioxide.

  In the case of aqueous solution polymerization, it is more preferable to previously dissolve or disperse the radical polymerization initiator in the monomer aqueous solution. Specific examples of the radical polymerization initiator include peroxides such as ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, and di-t-butyl peroxide. A redox initiator comprising a combination of the above peroxide and a reducing agent such as sulfite, bisulfite, thiosulfate, formamidinesulfinic acid, ascorbic acid; the general formula (1) or the general formula (2); An acrylate polymerization initiator of an amino group-containing azo compound represented by the formula; an azo polymerization initiator such as a hydrochloride of the amino group-containing azo compound; These radical polymerization initiators may be used alone or in combination of two or more. In addition, when using the acrylic acid salt of an amino group containing azo compound as a radical polymerization initiator, it is more preferable to use a redox initiator together.

  The amount of the radical polymerization initiator used for the unsaturated monomer depends on the combination of the unsaturated monomer and the radical polymerization initiator, but is 0.0005 parts by weight to 100 parts by weight of the unsaturated monomer. It is preferably within the range of 5 parts by weight, and more preferably within the range of 0.005 to 2.5 parts by weight. When the amount of the radical polymerization initiator used is less than 0.0005 parts by weight, the amount of unreacted unsaturated monomer increases, and therefore the amount of residual monomer in the resulting water-absorbent resin increases, which is preferable. Absent. On the other hand, when the usage-amount of a radical polymerization initiator exceeds 5 weight part, since the amount of water-soluble components in the water-absorbing resin obtained increases, it is not preferable.

  The temperature at the start of polymerization depends on the type of radical polymerization initiator used, but is more preferably in the range of 0 ° C to 40 ° C, and more preferably in the range of 10 ° C to 30 ° C. The polymerization temperature during the reaction depends on the type of radical polymerization initiator used, but is preferably in the range of 40 ° C to 120 ° C, more preferably in the range of 50 ° C to 110 ° C. If the temperature at the start of polymerization or the polymerization temperature during the reaction is out of the above range, the amount of residual monomer in the resulting water-absorbent resin increases; it is difficult to control foaming by the foaming agent; The self-crosslinking reaction proceeds and the water absorption amount of the water absorbent resin is decreased;

  The reaction time may be set according to reaction conditions such as a combination of an unsaturated monomer, a crosslinking agent and a radical polymerization initiator, or a reaction temperature, and is not particularly limited. Further, the time from the dispersion of the foaming agent to the start of polymerization of the unsaturated monomer is not particularly limited, but a relatively short time is preferable.

  When the aqueous solution polymerization is performed, the aqueous monomer solution may or may not be stirred. However, the foaming agent may be allowed to stand for at least a predetermined time during the reaction. This is preferable for efficiently performing foaming. The time from the start of polymerization until the polymerization rate becomes 10% or more, more preferably the time until it becomes 30% or more, more preferably the time until it becomes 50% or more, particularly preferably until the end of the polymerization. By allowing the monomer aqueous solution to stand still for this time, foaming with the foaming agent can be performed more efficiently. When the acrylate of the amino group-containing azo compound represented by the general formula (1) or (2) is used as a foaming agent, the time from the start of polymerization to the end of polymerization, that is, polymerization Can also be carried out under stirring.

  By the above polymerization, a bubble-containing hydrogel that is a (co) polymer of unsaturated monomers is generated. That is, as the unsaturated monomer is (co) polymerized, the crosslinking reaction by the crosslinking agent and the foaming by the foaming agent proceed to form pores (voids) in the (co) polymer, and the bubble-containing hydrogel It becomes.

  The bubble-containing hydrogel is crushed into pieces of about 0.1 mm to about 50 mm by a predetermined method during or after the reaction, as necessary. Next, the foam-containing hydrogel is dried in order to foam more efficiently. In addition, foaming by a foaming agent can be performed not at the time of reaction but at the time of drying.

  The drying temperature is not particularly limited, but may be set, for example, in the range of 100 ° C. to 300 ° C., more preferably in the range of 120 ° C. to 220 ° C., in order to foam more efficiently. Moreover, although drying time is not specifically limited, About 10 second-about 3 hours are suitable. In addition, before making it dry, a bubble containing water-containing gel may be neutralized, and you may crush and subdivide further.

  Various drying methods such as heat drying, hot air drying, vacuum drying, infrared drying, microwave drying, drum dryer drying, dehydration by azeotropy with a hydrophobic organic solvent, and high humidity drying using high temperature steam Is not particularly limited. Of the drying methods exemplified above, hot air drying and microwave drying are more preferable, and microwave drying is more preferable. When the bubble-containing hydrogel is irradiated with microwaves, the bubbles expand several times to several tens of times, so that a water-absorbent resin with a further improved water absorption rate can be obtained.

  When the bubble-containing hydrogel is microwave-dried, the thickness of the crushed bubble-containing hydrogel is preferably 3 mm or more, more preferably 5 mm or more, and further preferably 10 mm or more. preferable. In addition, when the bubble-containing hydrated gel is microwave-dried, it is particularly preferable that the bubble-containing hydrated gel is formed into a sheet having the above thickness.

By the above polymerization, that is, by the above production method, the water absorbent resin according to the present invention can be easily obtained at low cost. The above water-absorbent resin has pores uniformly formed throughout, has a relatively large molecular weight, and has an average pore diameter in the range of 10 μm to 500 μm, more preferably in the range of 20 μm to 400 μm, still more preferably in the range of 30 μm to 300 μm. Of these, a porous cross-linked polymer is most preferably in the range of 50 μm to 200 μm. The sheet-like water absorbent resin obtained by microwave drying a bubble-containing hydrogel has a bulk specific gravity of ^{0.01g / cm 3 ~0.5g / cm 3} .

  Said average hole diameter is calculated | required by performing the image analysis of the cross section of the dried water absorbing resin with an electron microscope. That is, a histogram representing the distribution of pore diameters of the water-absorbent resin is created by performing image analysis, and the average pore diameter is obtained by calculating the number average of pore diameters from the histogram.

  Since the water-absorbent resin is porous having the above average pore diameter, a liquid introduction space necessary for the aqueous liquid to move inside the water-absorbent resin is sufficiently secured under no pressure and under pressure. . Therefore, the water permeability and diffusibility of the aqueous liquid are excellent, and the water absorption speed and the water retention ability can be improved by the capillary phenomenon. Further, since the water-absorbent resin is porous, even when the shape of the water-absorbent resin is particulate, it is possible to maintain liquid permeability when the aqueous liquid passes between the particles. It will not cause a block. When the average pore diameter is smaller than 10 μm, the liquid permeability and diffusibility of the aqueous liquid are inferior. Further, when the average pore diameter is larger than 500 μm, the water absorption rate is inferior, which is not preferable.

  The shape and size (particle diameter) of the water absorbent resin may be appropriately set according to the use of the water absorbent resin, and are not particularly limited. The water-absorbent resin can be formed into various shapes such as a sheet shape and a block shape, but when the water-absorbent resin is used as a sanitary material, the average particle is obtained by performing a process such as pulverization and classification. What is necessary is just to adjust to the particle form in which the diameter is in the range of 50 μm to 1,000 μm, more preferably in the range of 150 μm to 800 μm, and still more preferably in the range of 200 μm to 600 μm. Moreover, granulation operation can be performed and water-absorbing resin can also be formed in a particulate form.

  The water-absorbing resin having the above structure may be further treated with a surface crosslinking agent to form a covalent bond (secondary crosslinking), thereby further increasing the crosslink density in the vicinity of the surface. The surface cross-linking agent is not particularly limited as long as it is a compound having a plurality of functional groups that can react with the carboxyl group of the water-absorbent resin to form a covalent bond. By treating the water absorbent resin with a surface cross-linking agent, the liquid permeability, water absorption speed, water absorption amount under pressure and liquid permeability (described later) of the water absorbent resin are further improved.

  Specific examples of the surface crosslinking agent include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, dipropylene glycol, 2,2, and the like. 4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, Polyhydric alcohol compounds such as enterythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl Epoxy compounds such as ether and glycidol; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and polyamidepolyamine; epichlorohydrin, epibromohydrin, α-methyl Haloepoxy compounds such as epichlorohydrin; the above polyamine compounds Condensation product of haloepoxy compound and polyvalent isocyanate compound such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; Multivalent oxazoline compound such as 1,2-ethylenebisoxazoline; γ-glycidoxypropyltrimethoxysilane Silane coupling agents such as γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolane -2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3- Alkylene carbonate compounds such as dioxane-2-one and 1,3-dioxopan-2-one; and the like, but are not particularly limited. Of the surface crosslinking agents exemplified above, polyhydric alcohol compounds, epoxy compounds, polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, and alkylene carbonate compounds are more preferred.

  These surface cross-linking agents may be used alone or in combination of two or more. When two or more types of surface cross-linking agents are used in combination, the water absorption characteristics are further improved by combining the first surface cross-linking agent and the second surface cross-linking agent having different solubility parameters (SP values). A resin can be obtained. The solubility parameter is a value generally used as a factor representing the polarity of a compound.

Said 1st surface crosslinking agent is a compound with the solubility parameter of 12.5 (cal / cm < ³ >) ^<1/2 > or more which can react with the carboxyl group which water absorbing resin has, for example, glycerol etc. correspond. The second surface cross-linking agent is a compound having a solubility parameter of less than 12.5 (cal / cm ³ ) ^1/2 that can react with the carboxyl group of the water-absorbent resin, such as ethylene glycol diglycidyl ether. Applicable.

  The amount of the surface cross-linking agent used for the water-absorbent resin is in the range of 0.01 to 5 parts by weight with respect to 100 parts by weight of the water-absorbent resin in a dry state, although it depends on the combination of the water-absorbent resin and the surface cross-linker. Of these, more preferably 0.05 to 3 parts by weight. By using the surface cross-linking agent within the above range, it is possible to further improve the water absorption characteristics for body fluids (aqueous liquids) such as urine, sweat and menstrual blood. When the amount of the surface cross-linking agent used is less than 0.01 parts by weight, the cross-linking density in the vicinity of the surface of the water absorbent resin can hardly be increased. Further, when the amount of the surface cross-linking agent used is more than 5 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and it may be difficult to control the cross-linking density to an appropriate value. .

The processing method at the time of processing a water absorbing resin using a surface crosslinking agent is not specifically limited. For example, (1) a method of mixing the water-absorbent resin and the surface cross-linking agent without solvent, (2) a method of mixing the surface cross-linking agent after dispersing the water-absorbent resin in a hydrophobic solvent such as cyclohexane or pentane, (3) A method in which a surface crosslinking agent is dissolved or dispersed in a hydrophilic solvent, and then the solution or dispersion is sprayed or dropped onto a water-absorbent resin and mixed. Of these treatment methods, the method (3) is more preferred. As the hydrophilic solvent, water or a mixture of water and an organic solvent soluble in water is preferable.

  Specific examples of the organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, and t-butyl alcohol; Ketones such as acetone; Dioxane, ethylene oxide (EO) adducts of monohydric alcohols, ethers such as tetrahydrofuran; Amides such as N, N-dimethylformamide and ε-caprolactam; Sulfoxides such as dimethyl sulfoxide . These organic solvents may be used alone or in combination of two or more.

  The amount of the hydrophilic solvent used for the water-absorbing resin and the surface cross-linking agent depends on the combination of the water-absorbing resin, the surface cross-linking agent and the hydrophilic solvent, but is 200 parts by weight or less with respect to 100 parts by weight of the water-absorbing resin. Preferably, it may be within the range of 0.01 to 50 parts by weight, more preferably within the range of 0.1 to 50 parts by weight, and particularly preferably within the range of 0.5 to 20 parts by weight. .

  It is preferable that the mixing apparatus used when mixing the water-absorbent resin and the surface cross-linking agent has a large mixing force in order to mix both uniformly and reliably. Examples of the mixing apparatus include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidized furnace rotary desk type. A mixer, an airflow type mixer, a double arm type kneader, an internal mixer, a pulverizing type kneader, a rotary mixer, a screw type extruder and the like are suitable.

  The treatment temperature and treatment time when treating the water-absorbent resin with the surface cross-linking agent may be appropriately set according to the combination of the water-absorbent resin and the surface cross-linking agent, the desired cross-linking density, etc., and are particularly limited. For example, the processing temperature is preferably in the range of 0 ° C to 250 ° C.

  And when processing a water absorbing resin using a surface crosslinking agent, you may add a mixing adjuvant further as needed. Examples of the mixing aid include fine powders insoluble in water, surfactants, organic acids, inorganic acids, polyamino acids and the like. Examples of the organic acid include saturated carboxylic acids such as citric acid, lactic acid, and succinic acid. Examples of the inorganic acid include phosphoric acid, sulfuric acid, hydrochloric acid and the like. These mixing aids may be used alone or in combination of two or more. What is necessary is just to use a mixing adjuvant within the range of 0.01 weight part-5 weight part with respect to 100 weight part of water absorbing resin. The mixing method of the water absorbent resin and the surface cross-linking agent and the mixing aid is not particularly limited.

  The water-absorbing resin whose crosslink density near the surface is increased by the formation of a covalent bond, that is, the water-absorbing resin subjected to the above-described treatment is treated with a cationic compound and has an ionic bond (secondary cross-linking). By being formed, the crosslink density in the vicinity of the surface may be further increased. The cationic compound is not particularly limited as long as it is a compound that can react with a carboxyl group (that is, a carboxyl group that has not reacted with the surface cross-linking agent) of the water-absorbent resin to form an ionic bond. Absent. By treating the water-absorbing resin with a cationic compound, the water-absorbing properties of the water-absorbing resin, such as water absorption rate, diffusibility, water retention ability, dry touch property, and water absorption under pressure, are further improved.

  Specific examples of the cationic compound include low molecular weight polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; polyethyleneimine, and epihalohydrin so as to be water-soluble. Modified polyethyleneimine modified, polyamine, polyamidoamine modified by grafting of ethyleneimine, protonated polyamidoamine, polyetheramine, polyvinylamine, polyalkylamine, polyvinylimidazole, polyvinylpyridine, polyvinylimidazoline, polyvinyltetrahydropyridine, poly Cation such as dialkylaminoalkyl vinyl ether, polydialkylaminoalkyl (meth) acrylate, polyallylamine And the like; and polyvalent metal compounds such as hydroxides, chlorides, sulfates and carbonates of polyvalent metals such as zinc, calcium, magnesium, aluminum, iron and zirconium; However, it is not particularly limited. These cationic compounds may be used alone or in combination of two or more. Of the above-exemplified cationic compounds, cationic polymer electrolytes and salts thereof are more preferable.

  The amount of the cationic compound used relative to the water-absorbent resin depends on the combination of the water-absorbent resin and the cationic compound, but ranges from 0.01 to 5 parts by weight with respect to 100 parts by weight of the water-absorbent resin in the dry state. Of these, more preferably within the range of 0.1 to 3 parts by weight. By using a cationic compound within the above-mentioned range, a water-absorbing resin with further improved water absorption characteristics such as water absorption rate, diffusibility, water retention ability, dry touch property, and water absorption under pressure can be obtained. The treatment method for treating the water absorbent resin with the cationic compound is the same as the treatment method for treating with the surface cross-linking agent. The treatment temperature and treatment time when treating the water-absorbent resin with the cationic compound may be appropriately set according to the combination of the water-absorbent resin and the cationic compound, the desired crosslinking density, etc., and are particularly limited. Although not intended, for example, the treatment temperature is preferably room temperature, and may be heated to about 50 ° C. to 100 ° C. as necessary.

  By the above production method, the water-absorbing resin can be industrially obtained at a low cost. The obtained water-absorbent resin is porous having an average pore diameter in the range of 10 μm to 500 μm. The water-absorbent resin has a water absorption amount of 25 g / g or more, more preferably 30 g / g or more under pressure 60 minutes after the start of water absorption. Further, the water-absorbent resin has a water-soluble component amount of 15% by weight or less, more preferably 1% by weight to 10% by weight. Furthermore, the water-absorbing resin has a residual monomer amount of 500 ppm or less, more preferably 300 ppm or less, and still more preferably 100 ppm or less. Since the water-absorbent resin is excellent in these various physical properties and has a good balance between the physical properties, the water-absorbent resin is excellent in water absorption properties such as liquid permeability under pressure.

  In addition to the above water-absorbent resin, if necessary, deodorant, fragrance, various inorganic powders, foaming agent, pigment, dye, hydrophilic short fiber, plasticizer, adhesive, surfactant, fertilizer, oxidation An agent, a reducing agent, water, salts, and the like may be added to thereby impart various functions to the water absorbent resin.

  The water-absorbent resin composition according to the present invention has a water-absorbent resin having the above-described configuration, that is, an average particle diameter in the range of 50 μm to 1,000 μm, more preferably in the range of 150 μm to 800 μm, depending on processes such as pulverization and classification. Among them, it is obtained by mixing water-absorbing resin particles adjusted to a range of 200 μm to 600 μm and fine inorganic powder. The water absorbent resin composition preferably comprises a water absorbent resin composed of an unsaturated monomer containing an acrylate monomer as a main component.

  Examples of the inorganic powder include substances that are inert to aqueous liquids, such as fine particles of various inorganic compounds, fine particles of clay minerals, and the like. The inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water. Specific examples include metal oxides such as silicon dioxide and titanium oxide, silicic acid (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay, bentonite and the like. Among these, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter measured by a Coulter counter method of 200 μm or less are more preferable.

  The amount of inorganic powder used for the water-absorbent resin depends on the combination of the water-absorbent resin and the inorganic powder, but is preferably in the range of 0.001 to 10 parts by weight with respect to 100 parts by weight of the water-absorbent resin. May be in the range of 0.01 to 5 parts by weight. The mixing method of the water-absorbent resin and the inorganic powder is not particularly limited, and for example, a dry blend method, a wet mixing method, or the like can be employed, but it is preferable to employ the dry blend method.

  The water-absorbing resin composition having the above structure has a water retention capacity of 20 g / g or more, a water absorption speed of 120 seconds or less, and a liquid passing speed under pressure of 200 seconds or less. The water absorbent resin composition is made into an absorbent article by, for example, combining (combining) with a fibrous material such as pulp.

  Examples of absorbent articles include sanitary materials (body fluid absorbent articles) such as paper diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials; absorbent articles such as pet urine; building materials and soil water retention materials, Civil engineering and construction materials such as water-stopping materials, packing materials, gel water sacs; food articles such as drip absorbers, freshness-keeping materials, and cold insulation materials; various industrial products such as oil-water separators, anti-condensation materials, and solidification materials; Agricultural and horticultural articles such as water-retaining materials such as plants and soils; For example, a paper diaper is formed by laminating a back sheet (back material) made of a liquid-impermeable material, the above water-absorbent resin composition, and a top sheet (surface material) made of a liquid-permeable material in this order. Then, they are fixed together and formed by attaching a gather (elastic portion) or a so-called tape fastener to the laminate. Paper diapers also include pants with paper diapers that are used when urinating or defecation is performed on infants.

  The water-absorbent resin composition may be used in so-called high concentration conditions, that is, when the ratio of the water-absorbent resin composition to the total amount of the water-absorbent resin composition and the fibrous material is 50% by weight or more. The liquid introduction space necessary for the aqueous liquid to move into the water-absorbent resin is sufficiently secured under pressure. Therefore, it is excellent in liquid permeability and diffusibility under pressure of an aqueous liquid, does not produce a gel block, and can improve the water absorption speed and water retention ability by capillary action. Thereby, even in applications where it is required to absorb the aqueous liquid a plurality of times, for example, when the absorbent article is a sanitary material, leakage of the sanitary material can be avoided. In addition, the sanitary material can be thinned.

  Other objects, features, and advantages of the present invention will be fully understood from the following description. The benefits of the present invention will become apparent from the following description with reference to the accompanying drawings.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these. In the following description, “part” indicates “part by weight” and “%” indicates “% by weight” unless otherwise specified.

  Various performances of the water absorbent resin or the water absorbent resin composition were measured by the following methods. In the performance measurement, a particulate water-absorbing resin was used, and the particle size distribution was 100% as a whole, and particles in the range of 850 μm to 500 μm were 25% to 35%, 500 μm to 150 μm. The particles in the range were adjusted to 65% to 75%, and the particles in the range of 150 μm to 10 μm were adjusted to 0% to 10%.

  In addition, a method for preparing 2,2′-azobis (2-methylpropionamidine) diacrylate as an acrylate (foaming agent) of the amino group-containing azo compound represented by the general formula (1) will be described below. Show.

(1) Water-retaining amount of water-absorbing resin 0.2 g of water-absorbing resin was uniformly placed in a tea bag-type bag (6 cm × 6 cm), the opening was heat sealed, and then a 0.9% sodium chloride aqueous solution (saline) Soaked in. After 60 minutes, the tea bag type bag was pulled up, drained using a centrifuge at 1,300 rpm for 3 minutes, and the weight W _1a (g) of the bag was measured. Moreover, the same operation was performed without using a water absorbent resin, and the weight W _0a (g) at that time was measured. And from these weights W _1a · W _0a ,
Water retention (g / g)
= (Weight W _1a (g) _−weight W _0a (g)) / weight of water absorbent resin (g)
The water retention amount (g / g) was calculated according to

(2) Residual monomer amount of water-absorbing resin After adding 100 ml of deionized water to a beaker having a capacity of 200 ml, 1.0 g of the water-absorbing resin was added with stirring, whereby the deionized water was all gelled. . After 1 hour, the gel was contracted by adding 5 ml of phosphoric acid aqueous solution to the obtained gel. The shrunken gel was filtered through a filter paper with stirring, and the filtrate, that is, the water generated by the shrinkage was analyzed using high performance liquid chromatography.

  On the other hand, the same analysis was performed using a monomer aqueous solution having a known concentration as a standard solution, and a calibration curve was obtained. Then, this calibration curve was set as an external standard, and the residual monomer amount (ppm) of the water absorbent resin was determined in consideration of the dilution rate of the filtrate. The residual monomer amount is a conversion value with respect to the solid content of the water absorbent resin.

(3) Water-soluble resin content of water-absorbing resin 0.5 g of water-absorbing resin was dispersed in 1,000 ml of deionized water, stirred for 16 hours, and then filtered through filter paper. And the amount (%) of water-soluble components was calculated | required by colloid titrating the obtained filtrate.

(4) Diffusion rate of water absorbent resin (diffusivity)
First, by dissolving various reagents in water, 600 ppm to 700 ppm sodium cation, 65 ppm to 75 ppm calcium cation, 55 ppm to 65 ppm magnesium cation, 1,100 ppm to 1,200 ppm potassium cation, 240 ppm to 280 ppm phosphorus, An aqueous solution containing 450 ppm to 500 ppm of sulfur, 1,100 ppm to 1,300 ppm of chlorine, and 1,300 ppm to 1,400 ppm of sulfate radical was prepared and used as artificial urine.

  Next, 1.0 g of a water-absorbing resin was uniformly spread in a petri dish having an inner diameter of 58 mm and a depth of 12 mm. Thereafter, 20 g of the artificial urine set at a temperature of 25 ° C. was poured into the central portion of the petri dish at once and gently. Then, the time from the time when the artificial urine was poured to the time when the artificial urine was completely confirmed to be absorbed by the water-absorbent resin was measured, and this time was defined as the diffusion rate (seconds).

(5) Dry touch property of water-absorbent resin 20 sheets of filter paper having a diameter of 55 mm previously measured on the water-absorbent resin after measuring the diffusion rate, that is, the water-absorbent resin swollen by absorbing artificial urine. And a 500 g weight (load) was placed on the filter paper and left for 1 minute. After standing, the weight (g) of the filter paper was measured, and the increase in weight (g) was determined to evaluate the dry touch property. That is, the smaller the amount of artificial urine transferred from the swollen water absorbent resin to the filter paper, the smaller the increase in the weight of the filter paper. And the touch to the swollen water-absorbent resin becomes dry the smaller the increase in weight. That is, it can be evaluated that the dry touch property is good.

(6) Water absorption amount under pressure of water-absorbing resin First, a measurement apparatus used for measuring the water absorption amount under pressure will be briefly described below with reference to FIG.

  As shown in FIG. 1, the measuring device includes a balance 1, a container 2 having a predetermined capacity placed on the balance 1, an outside air suction pipe 3, a conduit 4 made of silicone resin, a glass filter 6, The measuring unit 5 is placed on the glass filter 6. The container 2 has an opening 2a at the top and an opening 2b at the side, and the outside air intake pipe 3 is fitted into the opening 2a, while the conduit 4 is attached to the opening 2b. It has been. The container 2 contains a predetermined amount of artificial urine 12. The lower end of the outside air intake pipe 3 is submerged in the artificial urine 12. The outside air suction pipe 3 is provided in order to keep the pressure in the container 2 at almost atmospheric pressure. The glass filter 6 is formed with a diameter of 55 mm. The container 2 and the glass filter 6 are communicated with each other by a conduit 4. Further, the glass filter 6 is fixed in position and height with respect to the container 2.

The measurement unit 5 includes a filter paper 7, a support cylinder 9, a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11. In the measuring unit 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. It has become. The metal mesh 10 is made of stainless steel and is formed to 400 mesh (mesh size 38 μm). At the time of measurement, a predetermined amount and a predetermined particle diameter of the water-absorbing resin 15 are uniformly distributed on the wire mesh 10. Further, the height of the upper surface of the wire mesh 10, that is, the contact surface between the wire mesh 10 and the water absorbent resin 15 is set to be equal to the height of the lower end surface 3 a of the outside air intake pipe 3. The weight of the weight 11 is adjusted so that a load of 50 g / cm ² can be uniformly applied to the wire mesh 10, that is, the water absorbent resin 15.

  The amount of water absorption under pressure was measured using the measuring apparatus having the above configuration. The measurement method will be described below.

  First, predetermined preparatory operations such as putting a predetermined amount of artificial urine 12 into the container 2; inserting the outside air suction pipe 3 into the container 2; Next, the filter paper 7 was placed on the glass filter 6. In parallel with this placing operation, 0.9 g of water-absorbing resin was uniformly distributed inside the support cylinder 9, that is, on the wire net 10, and the weight 11 was placed on the water-absorbing resin 15.

  Subsequently, the metal mesh 10, that is, the support cylinder 9 on which the water absorbent resin 15 and the weight 11 were placed was placed on the filter paper 7 so that the center portion thereof coincided with the center portion of the glass filter 6.

Then, the weight W ₂ (g) of the artificial urine 12 absorbed by the water absorbent resin 15 over time from the time when the support cylinder 9 was placed on the filter paper 7 was measured using the balance 1. The same operation is performed without using the water absorbent resin 15, and the weight at that time, that is, the weight of the artificial urine 12 absorbed by, for example, the filter paper 7 other than the water absorbent resin 15 is measured using the balance 1. And a blank weight W ₃ (g). And from these weights W ₂ · W ₃ ,
Water absorption under pressure (g / g)
= (Weight W ₂ (g) −weight W ₃ (g)) / weight of water-absorbent resin (g)
The water absorption amount under pressure (g / g) was calculated.

(7) Water-retaining ability of water-absorbent resin composition 0.2 g of water-absorbent resin composition was uniformly placed in a tea bag bag (6 cm × 6 cm), and the opening was heat-sealed. It was immersed in physiological saline. After 60 minutes, the tea bag-type bag was pulled up, drained at 250 G for 3 minutes using a centrifuge, and then the weight W _1b (g) of the bag was measured. The same operation was performed without using the water absorbent resin composition, and the weight W _0b (g) at that time was measured. And from these weights W _1b · W _0b ,
Water retention capacity (g / g)
= (Weight W _1b (g) _−weight W _0b (g)) / weight of water absorbent resin composition (g)
The water retention capacity (g / g) was calculated according to

(8) Water absorption rate of water absorbent resin composition 1.0 g of the water absorbent resin composition was put into a bottomed cylindrical polypropylene cup having an inner diameter of 50 mm and a height of 70 mm. Next, 28 g of physiological saline was poured into the cup. Then, the time from when the physiological saline was poured until the physiological saline was completely absorbed by the water-absorbent resin composition and became invisible was measured. The measurement was repeated three times, and the average value of these was taken as the water absorption rate (second).

(9) Flow rate under pressure of the water-absorbent resin composition (liquid permeability)
First, a measuring apparatus used for measuring the liquid flow rate under pressure will be briefly described below with reference to FIG.

  As shown in FIG. 2, the measuring device includes a glass column 20, a pressure rod 21, and a weight 22. The glass column 20 is formed in a cylindrical shape having an inner diameter of 1 inch and a height of 400 mm. An openable / closable cock 25 is provided at the bottom of the glass column 20. Further, a glass filter 27 is inserted into the glass column 20 so that the water absorbent resin composition 30 can be filled. The coarseness of the glass filter 27 is # G2. Furthermore, standard lines L and M are written on the glass column 20. The standard line L is written at a height of 150 mm from the upper surface of the glass filter 27, and the standard line M is written at a height of 100 mm from the upper surface of the glass filter 27. A predetermined amount of physiological saline 29 is contained in the glass column 20. As the glass column 20, a biocolumn CF-30K (trade name: manufactured by Inei Seieido Co., Ltd., catalog code 22-635-07) was used.

  A mounting plate 23 on which the weight 22 can be mounted is fixed to the upper end of the pressure bar 21. The mounting plate 23 is formed in a disc shape having a diameter slightly smaller than the inner diameter of the glass column 20. The pressurizing rod 21 is formed to have such a length that the mounting plate 23 is not submerged in the physiological saline 29.

  A pressure plate 24 is fixed to the lower end portion of the pressure rod 21. The pressure plate 24 is formed in a disc shape having a diameter of about 1 inch and a thickness of 10 mm, and 64 holes 24a penetrating from the upper surface to the lower surface are formed. The holes 24a have a diameter of 1 mm and are provided with an interval of about 2 mm. Accordingly, the physiological saline 29 can flow from the upper surface side to the lower surface side of the pressure plate 24 through the holes 24a.

  The pressure bar 21, that is, the pressure plate 24 is movable in the glass column 20 in the vertical direction. A glass filter 26 is attached to the lower surface of the pressure plate 24. The coarseness of the glass filter 26 is # G0.

The weight of the weight 22 is adjusted so that a load of 24.5 g / cm ² can be uniformly applied to the swollen water absorbent resin composition 30.

  Using the measuring apparatus having the above-described configuration, the flow rate under pressure was measured. The measurement method will be described below.

  First, the cock 25 was closed and the glass filter 27 was inserted into the glass column 20, and then 0.5 g of the water absorbent resin composition was filled into the glass column 20. Next, an amount of physiological saline 29 that could not be absorbed by the water-absorbent resin composition 30 (that is, excess) was placed in the glass column 20 to swell the water-absorbent resin composition 30.

  After about 1 hour, when the water-absorbent resin composition 30 was sufficiently settled and the swelling was in an equilibrium state, the pressure rod 21 was inserted into the glass column 20. That is, the pressure plate 24 was placed on the water-absorbent resin composition 30 while removing air so as not to accumulate between the swollen water-absorbent resin composition 30 and the glass filter 26. Subsequently, the weight 22 was mounted on the mounting plate 23, and the water absorbent resin composition 30 was pressurized.

  Subsequently, physiological saline 29 was added, and the height (liquid depth) H from the upper surface of the glass filter 27 (the lowermost part of the water absorbent resin composition 30) to the liquid level was adjusted to 200 mm.

  Then, the cock 25 was opened and the physiological saline 29 was poured out, and the time from when the liquid level of the physiological saline 29 passed through the standard line L to the time when it passed through the standard line M was measured. In addition, the amount of the physiological saline 29 that flows from the time when it passes through the standard line L to the time when it passes through the standard line M is about 25 ml (actual measurement value).

  The above measurement was repeated three times, and the average value thereof was defined as the liquid passing speed (second) under pressure. In addition, when the same measurement was performed without using the water-absorbent resin composition 30, the liquid passing speed was 10 seconds.

(10) Preparation of 2,2′-azobis (2-methylpropionamidine) diacrylate 10% aqueous solution of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as a blowing agent precursor 36 While maintaining the temperature at 20 ° C. with stirring at 1,200 rpm, 6.7 parts of a 37% aqueous solution of sodium acrylate as an acrylate was added. Several seconds after the addition, the aqueous solution became cloudy, and a white fine particle solid having an average particle diameter of 10 μm was formed. The particulate solid was uniformly dispersed in the aqueous solution.

By filtering the aqueous solution, about 2.2 parts of the particulate solid was isolated, then washed with water and purified. When the ultraviolet absorption spectrum (UV) of the obtained particulate solid was measured, absorption specific to the azo group was observed at 365 nm. In addition, elemental analysis of the particulate solid was performed, and ¹ H-NMR (nuclear magnetic resonance) and infrared absorption spectrum (IR) were measured. Heavy water was used as a solvent for the above ¹ H-NMR measurement.

As a result, 2,2′-azobis (2-methylpropionamidine) diacrylic acid as the acrylate (foaming agent) of the amino group-containing azo compound represented by the general formula (1) is obtained as a result of the above-mentioned fine particulate solid. It was confirmed to be a salt. ^{The 1} H-NMR chart is shown in FIG. An IR chart is shown in FIG.

[Example 1]
First, 38.6 parts of acrylic acid as an unsaturated monomer and 409 parts of a 37% aqueous solution of sodium acrylate, 0.48 part of trimethylolpropane triacrylate as a crosslinking agent, and 53 parts of deionized water are mixed. Thus, an aqueous monomer solution was prepared. That is, the monomer aqueous solution is a 38% aqueous solution of an acrylate monomer having a neutralization rate of 75 mol%.

  While maintaining the above monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid (bubbling) to expel dissolved oxygen. Next, while stirring, 4.3 parts of a 10% aqueous solution of 2,2'-azobis (2-methylpropionamidine) dihydrochloride as a blowing agent precursor was added to the aqueous monomer solution. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 7 minutes after the start of stirring, the aqueous solution became cloudy, and a white fine-particle solid having an average particle size of 9 μm was formed. The particulate solid was 2,2'-azobis (2-methylpropionamidine) diacrylate as a blowing agent. And 10 minutes after the start of stirring, the solid content of the monomer aqueous solution, that is, the amount of 2,2′-azobis (2-methylpropionamidine) diacrylate generated with respect to the acrylate monomer Was 0.29%. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this time (10 minutes after the start of stirring), while stirring the aqueous monomer solution, 2.6 parts of a 10% aqueous solution of sodium persulfate as a redox initiator (radical polymerization initiator) and L-ascorbine 1 part of an acid 1% aqueous solution was added. And after fully stirring, this monomer aqueous solution was left still.

  About 10 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 89 ° C. Thereafter, while maintaining the temperature at 70 ° C. to 80 ° C., the monomer aqueous solution was allowed to stand for 10 minutes to polymerize the acrylate monomer. As a result, a water-containing gel containing bubbles, which is a porous crosslinked polymer, was obtained.

  The obtained air-containing hydrogel was taken out and subdivided into sizes of about 20 mm to 1 mm, and then hot-air dried at 150 ° C. using a hot-air dryer. Next, the dried product was pulverized using a roll mill, and further classified with a JIS standard sieve (850 μm) to obtain a water-absorbent resin according to the present invention.

  It was confirmed with an electron micrograph that the water-absorbent resin was porous. The average pore diameter of the water absorbent resin was 60 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 29 g / g, the residual monomer amount was 200 ppm, the water soluble component amount was 9%, the diffusion rate was 33 seconds, and the dry touch property was The water absorption amount under pressure was 4.3 g and 11 g / g. The results are shown in Table 1.

[Example 2]
First, an aqueous monomer solution was prepared by mixing 38.6 parts of acrylic acid, 409 parts of a 37% aqueous solution of sodium acrylate, 1.08 parts of polyethylene glycol diacrylate as a crosslinking agent, and 53 parts of deionized water. did. That is, the monomer aqueous solution is a 38% aqueous solution of an acrylate monomer having a neutralization rate of 75 mol%.

  While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 4.3 parts of 2,2'-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 7 minutes after the start of stirring, the aqueous solution became cloudy, and 2,2′-azobis (2-methylpropionamidine) diacrylate having an average particle size of 9 μm and white fine particles was formed. Then, 10 minutes after the start of stirring, the amount of 2,2′-azobis (2-methylpropionamidine) diacrylate produced with respect to the acrylate monomer was 0.29%. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this point, 2.6 parts of a 10% aqueous solution of sodium persulfate and 1 part of a 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. After the addition, the aqueous monomer solution was kept stirring.

  About 10 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 79 ° C. Thereafter, the monomer aqueous solution was stirred for 10 minutes while maintaining the temperature at 70 ° C. to 80 ° C. to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 70 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 33 g / g, the residual monomer amount was 170 ppm, the water soluble component amount was 6%, the diffusion rate was 30 seconds, and the dry touch property was 3.9 g, the water absorption under pressure was 12 g / g. The results are shown in Table 1.

Example 3
First, an aqueous monomer solution was prepared in the same manner as in Example 2. While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Subsequently, 21 parts of a 10% aqueous solution of 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 1 minute after the start of stirring, the aqueous solution became cloudy, and 2,2'-azobis (2-methylpropionamidine) diacrylic acid salt in the form of white fine particles having an average particle diameter of 10 µm was formed. And 5 minutes after starting stirring, the production amount of 2,2'-azobis (2-methylpropionamidine) diacrylate with respect to the acrylate monomer was 1.4%. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this point, 2.6 parts of a 10% aqueous solution of sodium persulfate and 1 part of a 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. After the addition, the aqueous monomer solution was kept stirring.

  About 7 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 82 ° C. Thereafter, the monomer aqueous solution was stirred for 10 minutes while maintaining the temperature at 70 ° C. to 80 ° C. to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 70 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 27 g / g, the residual monomer amount was 120 ppm, the water-soluble component amount was 5%, the diffusion rate was 37 seconds, and the dry touch property was The water absorption amount under pressure was 4.1 g and 11 g / g. The results are shown in Table 1.

Example 4
First, a monomer aqueous solution was prepared by mixing 18 parts of acrylic acid, 190 parts of a 37% aqueous solution of sodium acrylate, 0.154 part of N, N′-methylenebisacrylamide as a crosslinking agent, and 21 parts of deionized water. Was prepared. That is, the monomer aqueous solution is a 38% aqueous solution of an acrylate monomer having a neutralization rate of 75 mol%.

  While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 1.34 parts of powdery 2,2′-azobis (2-methylpropionamidine) diacrylate prepared by the above preparation method was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  Next, 1.2 parts of a 10% aqueous solution of sodium persulfate and 0.5 part of an 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. After the addition, the aqueous monomer solution was kept stirring.

  About 13 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 92 ° C. Thereafter, while maintaining the temperature at 60 ° C. to 80 ° C., the monomer aqueous solution was further stirred for 1 hour to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 65 μm. Moreover, as a result of measuring various performances of the water-absorbent resin by the above methods, the water retention amount was 27 g / g, the residual monomer amount was 220 ppm, the water-soluble component amount was 9%, the diffusion rate was 25 seconds, and the dry touch property was The amount of water absorption under pressure was 4.3 g and 9 g / g. The results are shown in Table 1.

Example 5
First, 21.6 parts of acrylic acid, 178 parts of a 37% aqueous solution of sodium acrylate, 0.046 part of N, N′-methylenebisacrylamide, 0.18 part of hydroxylethyl cellulose as a water-soluble polymer (dispersion stabilizer), and A monomer aqueous solution was prepared by mixing 50 parts of deionized water. That is, the monomer aqueous solution is a 38% aqueous solution of an acrylate monomer having a neutralization rate of 70 mol%.

  While maintaining the above monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid (bubbling) to expel dissolved oxygen. Next, with stirring, 0.18 part of polyoxyethylene sorbitan monostearate as a surfactant (dispersion stabilizer) and 2.63 parts of heavy calcium carbonate as a foaming agent are added to the aqueous monomer solution. did. The average particle size of calcium carbonate was 3 μm and was uniformly dispersed in the monomer aqueous solution.

  Thereafter, 1.2 parts of 10% aqueous solution of sodium persulfate and 0.5 part of 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous solution at a temperature of 25 ° C. under a nitrogen stream. And after fully stirring, this monomer aqueous solution was left still.

  About 10 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 99 ° C. Thereafter, while maintaining the temperature at 60 ° C. to 80 ° C., the aqueous monomer solution was allowed to stand for 10 minutes to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 250 μm. Moreover, as a result of measuring various performances of the water-absorbent resin by the above methods, the water retention amount was 45 g / g, the residual monomer amount was 520 ppm, the water-soluble component amount was 13%, the diffusion rate was 24 seconds, and the dry touch property was 4.5 g, the water absorption under pressure was 8 g / g. The results are shown in Table 1.

[Comparative Example 1]
First, a monomer aqueous solution was prepared in the same manner as in Example 1. While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, while stirring, 4.3 parts of a 10% aqueous solution of 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution and dissolved. Immediately thereafter, 2.6 parts of 10% aqueous solution of sodium persulfate and 1 part of 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. After the addition, the aqueous monomer solution was stirred, and then the aqueous monomer solution was allowed to stand when polymerization started. That is, the acrylate monomer was polymerized without generating the foaming agent according to the present invention.

  About 10 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 95 ° C. Thereafter, the monomer aqueous solution was stirred for another 10 minutes while maintaining the temperature at 70 ° C. to 85 ° C. to polymerize the acrylate monomer. Thereby, a hydrogel having substantially no bubbles was obtained. The water-containing gel had a slight amount of bubbles having a size of about 2 mm to 4 mm.

  The obtained hydrogel was taken out and the same operation as that of Example 1 was performed to obtain a comparative water-absorbent resin. The comparative water absorbent resin did not have pores. Moreover, as a result of measuring various performances of the comparative water-absorbent resin by the above method, the water retention amount was 29 g / g, the residual monomer amount was 540 ppm, the water-soluble component amount was 14%, the diffusion rate was 63 seconds, Touchability was 6.1 g, and water absorption under pressure was 7 g / g. Therefore, the comparative water-absorbent resin was inferior in diffusion rate and dry touch property. The results are shown in Table 1. Further, FIG. 7 shows an electron micrograph showing the particle structure of a comparative water-absorbent resin having a particle diameter in the range of 300 μm to 600 μm.

[Comparative Example 2]
First, an aqueous monomer solution was prepared by mixing 21.6 parts of acrylic acid, 178 parts of a 37% aqueous solution of sodium acrylate, 0.046 part of N, N′-methylenebisacrylamide, and 50 parts of deionized water. did. While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 2.63 parts of sodium carbonate as a foaming agent was added to the aqueous monomer solution while stirring.

  Then, since carbon dioxide gas began to be generated, 1.2 parts of 10% aqueous solution of sodium persulfate and 0.5 part of 1% aqueous solution of L-ascorbic acid were immediately added while stirring the aqueous monomer solution. After the addition, the aqueous monomer solution was kept stirring. Calcium carbonate was not dispersed in the monomer aqueous solution.

  About 10 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 97 ° C. Thereafter, the monomer aqueous solution was further stirred for 10 minutes while maintaining the temperature at 60 ° C. to 80 ° C. to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a comparative water-absorbent resin. The average pore diameter of the comparative water-absorbent resin was about 600 μm. Moreover, as a result of measuring various performances of the comparative water-absorbent resin by the above method, the water retention amount was 40 g / g, the residual monomer amount was 3,400 ppm, the water-soluble component amount was 17%, and the diffusion rate was 47 seconds. The dry touch property was 6.5 g, and the water absorption under pressure was 7 g / g. Therefore, the comparative water-absorbent resin has a large amount of residual monomers and water-soluble components, and is inferior in diffusion rate and dry touch properties. The results are shown in Table 1.

Example 6
The water-absorbent resin obtained in Example 1 was subjected to secondary crosslinking treatment. First, 0.05 part of ethylene glycol diglycidyl ether and 0.75 part of glycerin as a surface cross-linking agent, 0.5 part of lactic acid as a mixing aid, 3 parts of water as a hydrophilic solvent and 0.75 of isopropyl alcohol The liquid mixture was prepared by mixing the part.

  Next, 100 parts of the water-absorbent resin obtained in Example 1 and the above mixed solution were mixed, and the resulting mixture was heat-treated at 195 ° C. for 20 minutes. As a result, a water-absorbing resin in which a covalent bond was formed in the vicinity of the surface and the cross-linking density was increased, that is, a water-absorbing resin subjected to secondary cross-linking treatment was obtained. The average pore diameter of the water absorbent resin was 60 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 27 g / g, the residual monomer amount was 180 ppm, the water soluble component amount was 9%, the diffusion rate was 28 seconds, and the dry touch property was The amount of water absorption under pressure was 3.4 g and 30 g / g. The results are shown in Table 1.

Example 7
The water-absorbent resin obtained in Example 2 was subjected to secondary crosslinking treatment. First, 1 part of glycerin, 3 parts of water, and 1.75 parts of isopropyl alcohol were mixed to prepare a mixed solution.

  Next, 100 parts of the water-absorbent resin obtained in Example 2 and the above mixed solution were mixed, and the obtained mixture was heat-treated at 195 ° C. for 25 minutes. As a result, a water-absorbing resin in which a covalent bond was formed in the vicinity of the surface and the cross-linking density was increased, that is, a water-absorbing resin subjected to secondary cross-linking treatment was obtained. The average pore diameter of the water absorbent resin was 70 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 30 g / g, the residual monomer amount was 160 ppm, the water-soluble component amount was 6%, the diffusion rate was 30 seconds, and the dry touch property was The amount of water absorption under pressure was 2.9 g and 31 g / g. The results are shown in Table 1.

Example 8
The water-absorbent resin obtained in Example 3 was subjected to secondary crosslinking treatment. First, by mixing 0.05 part of ethylene glycol diglycidyl ether, 0.75 part of glycerin, 0.5 part of polyaspartic acid as a mixing aid, 3 parts of water, and 5 parts of isopropyl alcohol, Prepared.

  Next, 100 parts of the water-absorbent resin obtained in Example 3 and the above mixed solution were mixed, and the resulting mixture was heat-treated at 195 ° C. for 15 minutes. As a result, a water-absorbing resin in which a covalent bond was formed in the vicinity of the surface and the cross-linking density was increased, that is, a water-absorbing resin subjected to secondary cross-linking treatment was obtained. The average pore diameter of the water absorbent resin was 70 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 26 g / g, the residual monomer amount was 120 ppm, the water soluble component amount was 5%, the diffusion rate was 35 seconds, and the dry touch property was 3.3 g, the water absorption under pressure was 29 g / g. The results are shown in Table 1.

Example 9
The water-absorbent resin obtained in Example 6 was further subjected to a crosslinking treatment. That is, 100 parts of the water absorbent resin obtained in Example 6 and 5 parts of a 30% aqueous solution of polyethyleneimine having a weight average molecular weight of 70,000 were mixed, and the resulting mixture was heat-treated. As a result, a water-absorbing resin in which ionic bonds were formed in the vicinity of the surface and the crosslinking density was further increased was obtained. Various performances of the obtained water-absorbing resin were further improved over various performances of the water-absorbing resin before the treatment.

  Further, the water-absorbent resin obtained in Example 7 and Example 8 was subjected to the same treatment as the above treatment. Various performances of the obtained water-absorbing resin were further improved over various performances of the water-absorbing resin before the treatment.

[Comparative Example 3]
The comparative water-absorbent resin obtained in Comparative Example 2 was subjected to secondary crosslinking treatment. First, a mixed liquid was prepared by mixing 0.05 part of ethylene glycol diglycidyl ether, 0.75 part of glycerin, 0.5 part of lactic acid, 3 parts of water, and 0.75 part of isopropyl alcohol.

Next, 100 parts of the comparative water-absorbent resin obtained in Comparative Example 2 and the above mixed solution were mixed, and the resulting mixture was heat-treated at 195 ° C. for 20 minutes. As a result, a comparative water-absorbing resin in which a covalent bond was formed in the vicinity of the surface and the cross-linking density was increased, that is, a comparative water-absorbing resin subjected to secondary cross-linking treatment was obtained. The average pore diameter of the comparative water-absorbent resin was about 600 μm. Further, the performance of the comparative water-absorbent resin was measured by the above method. As a result, the water retention amount was 35 g / g, the residual monomer amount was 3,400 ppm, the water-soluble component amount was 17%, and the diffusion rate was 40 seconds. The dry touch property was 5.5 g, and the water absorption under pressure was 23 g / g. Therefore, the comparative water-absorbent resin has a large amount of residual monomers and water-soluble components, and is inferior in diffusion rate and dry touch properties. The results are shown in Table 1.

Example 10
While maintaining 166 parts of a 37% aqueous solution of sodium acrylate at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 47 parts of a 10% aqueous solution of 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added to the above aqueous solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 1 minute after the start of stirring, the aqueous solution became cloudy, and 2,2'-azobis (2-methylpropionamidine) diacrylic acid salt in the form of white fine particles having an average particle diameter of 15 µm was formed. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the aqueous solution.

  At this point (1 minute after the start of stirring), while stirring the aqueous solution, 425 parts of acrylic acid and 5.23 parts of trimethylolpropane triacrylate were mixed and dissolved to obtain 2,2 ′ -A monomer aqueous solution in which azobis (2-methylpropionamidine) diacrylate was dispersed (hereinafter simply referred to as a monomer aqueous solution) was prepared. That is, the monomer aqueous solution is a 38% aqueous solution of an acrylate monomer having a neutralization rate of 75 mol%.

  On the other hand, a 2 L separable flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas introduction tube was used as a reaction vessel. In this reaction container, 4 g of sucrose fatty acid ester (trade name: DK-ester F-50, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a dispersion stabilizer and 2 L of cyclohexane as a solvent were charged. Further, 300 g of the above monomer aqueous solution was placed in a dropping funnel.

  Then, the monomer aqueous solution was dropped while stirring the cyclohexane solution at 230 rpm to disperse and suspend the monomer aqueous solution. Next, the cyclohexane solution was stirred at 60 ° C. for 2 hours to carry out reverse phase suspension polymerization of the acrylate monomer. Thereafter, water generated by the reaction was removed by azeotropic distillation with cyclohexane (azeotropic dehydration). By filtering the cyclohexane solution, a spherical water-absorbing resin having an average particle diameter of several hundreds of μm, that is, a water-absorbing resin according to the present invention was obtained.

  The average pore diameter of the water absorbent resin was 50 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 30 g / g, the residual monomer amount was 70 ppm, the water-soluble component amount was 9%, the diffusion rate was 40 seconds, and the dry touch property was The water absorption under pressure was 4.5 g and 10 g / g. The results are shown in Table 2.

Example 11
First, a monomer aqueous solution was prepared by mixing 216 parts of acrylic acid, 4321 parts of 37% aqueous solution of sodium acrylate, 5.8 parts of polyethylene glycol diacrylate, and 887 parts of water. That is, the aqueous monomer solution is an aqueous solution of about 33% acrylate monomer having a neutralization rate of 85 mol%.

  While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 40 parts of a 10% aqueous solution of 2,2'-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 6 minutes after the start of stirring, the aqueous solution became cloudy, and 2,2'-azobis (2-methylpropionamidine) diacrylic acid salt in the form of white fine particles having an average particle diameter of 7 µm was formed. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this time, 28 parts of sodium persulfate 10% aqueous solution and 1.3 parts of L-ascorbic acid 1% aqueous solution were added while stirring the monomer aqueous solution. After the addition, the aqueous monomer solution was kept stirring.

  About 30 seconds after the addition of the sodium persulfate aqueous solution, polymerization of the acrylate monomer started. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 150 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 39 g / g, the residual monomer amount was 240 ppm, the water soluble component amount was 8%, the diffusion rate was 21 seconds, and the dry touch property was The water absorption amount under pressure was 4.0 g and 11 g / g. The results are shown in Table 2. Moreover, the electron micrograph which shows the particle structure of the water absorbing resin whose particle diameter is in the range of 300 micrometers-600 micrometers is shown in FIG.

Example 12
First, a monomer aqueous solution was prepared by mixing 375 parts of acrylic acid, 5290 parts of a 37% aqueous solution of sodium acrylate, 6.3 parts of polyethylene glycol diacrylate, and 808 parts of water. That is, the monomer aqueous solution is an aqueous solution of about 35.5% acrylate monomer having a neutralization rate of 85 mol%.

  While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 52 parts of a 10% aqueous solution of 2,2'-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 2.5 minutes after the start of stirring, the aqueous solution became cloudy, and 2,2'-azobis (2-methylpropionamidine) diacrylic acid salt in the form of white fine particles having an average particle diameter of 9 µm was formed. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this point, 36 parts of sodium persulfate 10% aqueous solution and 1.7 parts of L-ascorbic acid 1% aqueous solution were added while stirring the monomer aqueous solution. After the addition, the aqueous monomer solution was kept stirring.

  About 30 seconds after the addition of the sodium persulfate aqueous solution, polymerization of the acrylate monomer started. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 100 μm. In addition, as a result of measuring various performances of the water-absorbent resin by the above methods, the water retention amount was 38 g / g, the residual monomer amount was 270 ppm, the water-soluble component amount was 9%, the diffusion rate was 24 seconds, and the dry touch property was The water absorption amount under pressure was 4.0 g and 10 g / g. The results are shown in Table 2.

Example 13
First, a monomer aqueous solution was prepared by mixing 375 parts of acrylic acid, 5290 parts of a 37% aqueous solution of sodium acrylate, and 6.3 parts of polyethylene glycol diacrylate. That is, the monomer aqueous solution is an aqueous solution of about 42% acrylate monomer having a neutralization rate of 85 mol%.

  While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 52 parts of a 10% aqueous solution of 2,2'-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 2.5 minutes after the start of stirring, the aqueous solution became cloudy, and 2,2'-azobis (2-methylpropionamidine) diacrylic acid salt in the form of white fine particles having an average particle diameter of 9 µm was formed. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this point, 808 parts of water was added to the aqueous monomer solution to dilute the acrylate monomer concentration from about 42% to about 35.5%. Then, 36 parts of sodium persulfate 10% aqueous solution and 1.7 parts of L-ascorbic acid 1% aqueous solution were added while stirring the monomer aqueous solution. After the addition, the aqueous monomer solution was kept stirring.

  About 30 seconds after the addition of the sodium persulfate aqueous solution, polymerization of the acrylate monomer started. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a water absorbent resin. The average pore diameter of the water absorbent resin was 100 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 38 g / g, the residual monomer amount was 270 ppm, the water soluble component amount was 9%, the diffusion rate was 23 seconds, and the dry touch property was The water absorption amount under pressure was 4.1 g and 10 g / g. The results are shown in Table 2.

Example 14
First, a bubble-containing hydrated gel was obtained by carrying out a polymerization method similar to the polymerization method of Example 1. That is, by standing the aqueous monomer solution and polymerizing the acrylate monomer, a bubble-containing hydrogel as a porous cross-linked polymer was obtained.

  The obtained water-containing gel containing air bubbles was taken out and cut into a sheet having a thickness of about 5 mm, and then microscopically using a home microwave oven (trade name: NE-A460, Matsushita Electric Industrial Co., Ltd., frequency 2,450 MHz). Irradiated with waves. About 30 seconds after the start of irradiation, the water-containing hydrogel was dried in an expanded state about 10 times. Thereby, the sheet-like water absorbing resin concerning this invention was obtained.

  The average pore diameter of the water absorbent resin was about 500 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 31 g / g, the residual monomer amount was 170 ppm, the water soluble component amount was 10%, the diffusion rate was 19 seconds, and the dry touch property was The amount of water absorption under pressure was 4.3 g and 9 g / g. The results are shown in Table 2. Moreover, the electron micrograph which shows the cross-section of the said sheet-like water absorbing resin is shown in FIG.

Example 15
First, a bubble-containing hydrated gel was obtained by carrying out a polymerization method similar to the polymerization method of Example 1. That is, by standing the aqueous monomer solution and polymerizing the acrylate monomer, a bubble-containing hydrogel as a porous cross-linked polymer was obtained.

  The obtained air-containing hydrogel was taken out, cut into a sheet having a thickness of about 5 mm, and then hot-air dried at 170 ° C. using a hot-air dryer. The foam-containing hydrogel was dried in a state of swelling about 1.5 times. Thereby, the sheet-like water absorbing resin concerning this invention was obtained.

  The average pore diameter of the water absorbent resin was 250 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 30 g / g, the residual monomer amount was 200 ppm, the water-soluble component amount was 9%, the diffusion rate was 24 seconds, and the dry touch property was The water absorption under pressure was 4.5 g and 9 g / g. The results are shown in Table 2.

Example 16
The water-absorbent resin obtained in Example 13 was subjected to secondary crosslinking treatment. First, a mixed liquid was prepared by mixing 0.05 part of ethylene glycol diglycidyl ether, 0.75 part of glycerin, 0.5 part of lactic acid, 3 parts of water, and 0.75 part of isopropyl alcohol.

Next, 100 parts of the water absorbent resin obtained in Example 13 and the above mixed solution were mixed, and the obtained mixture was heat-treated at 195 ° C. for 20 minutes. As a result, a water-absorbing resin in which a covalent bond was formed in the vicinity of the surface and the cross-linking density was increased, that is, a water-absorbing resin subjected to secondary cross-linking treatment was obtained. The average pore diameter of the water absorbent resin was about 600 μm. Moreover, as a result of measuring various performances of the water absorbent resin by the above methods, the water retention amount was 35 g / g, the residual monomer amount was 250 ppm, the water-soluble component amount was 9%, the diffusion rate was 14 seconds, and the dry touch property was The water absorption amount under pressure was 3.5 g and 33 g / g. The results are shown in Table 2.

[Comparative Example 4]
First, the same polymerization method as that of Comparative Example 1 was carried out to obtain a hydrous gel. That is, the aqueous gel was obtained by allowing the monomer aqueous solution to stand and polymerizing the acrylate monomer.

  The obtained water-containing gel was taken out, cut into a sheet having a thickness of about 5 mm, and then dried by irradiation with microwaves using a household microwave oven. Thereby, a sheet-like water-absorbing resin for comparison was obtained. However, during drying, a discharge phenomenon occurred on a part of the surface of the hydrogel, and the part was burnt black.

  The comparative water absorbent resin did not have pores. In addition, as a result of measuring various performances of the comparative water-absorbent resin by the above method, the water retention amount was 27 g / g, the residual monomer amount was 640 ppm, the water-soluble component amount was 15%, the diffusion rate was 83 seconds, Touchability was 7.1 g, and water absorption under pressure was 6 g / g. Therefore, the comparative water-absorbent resin was inferior in diffusion rate and dry touch property. The results are shown in Table 2.

[Comparative Example 5]
First, an aqueous monomer solution was prepared in the same manner as in Example 11. While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, after stirring, 40 parts of a 10% aqueous solution of 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring, Further, 1.3 parts of a 1% aqueous solution of L-ascorbic acid was further added. After the addition, the aqueous monomer solution was stirred to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained. That is, the acrylate monomer was polymerized without generating the foaming agent according to the present invention. The bubble-containing water-containing gel had bubbles having a size of about 1 mm to 3 mm.

  The obtained water-containing gel was taken out and the same operation as in Example 1 was performed to obtain a comparative water-absorbent resin. The comparative water-absorbent resin had a particle size of 850 μm to 10 μm and had almost no pores. Further, as a result of measuring various performances of the comparative water-absorbent resin by the above method, the water retention amount was 39 g / g, the residual monomer amount was 940 ppm, the water-soluble component amount was 12%, the diffusion rate was 42 seconds, Touchability was 6.0 g, and water absorption under pressure was 8 g / g. Therefore, the comparative water-absorbent resin has a large amount of residual monomer and is inferior in diffusion rate and dry touch property. The results are shown in Table 2.

[Comparative Example 6]
First, a monomer aqueous solution was prepared in the same manner as in Example 1. While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, with stirring, sorbitan monostearate, which is a surfactant, is added to the monomer aqueous solution so that it becomes 0.2%, and then cyclohexane, which is a liquid foaming agent, is added so that it becomes 23%. did. Thereby, cyclohexane was uniformly dispersed in the monomer aqueous solution with an average particle diameter of about 50 μm.

  Thereafter, 2.6 parts of a 10% aqueous solution of sodium persulfate and 1 part of a 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. And after fully stirring, this monomer aqueous solution was left still and the acrylate monomer was polymerized. Thereby, a hydrogel was obtained. That is, the acrylate monomer was polymerized without using the foaming agent according to the present invention. The hydrogel had bubbles with a size of about 2 mm to 3 mm.

  The obtained hydrogel was taken out and the same operation as that of Example 1 was performed to obtain a comparative water-absorbent resin. The comparative water-absorbent resin had a particle size of 850 μm to 10 μm and had almost no pores. Moreover, the comparative water absorbent resin had a cyclohexane odor.

  As a result of measuring the performance of the comparative water-absorbing resin by the above method, the water retention amount was 27 g / g, the residual monomer amount was 540 ppm, the water-soluble component amount was 12%, the diffusion rate was 63 seconds, and dry touch. The property was 7.4 g, and the water absorption under pressure was 7 g / g. Therefore, the comparative water-absorbent resin was inferior in diffusion rate and dry touch property. The results are shown in Table 2.

[Comparative Example 7]
First, a monomer aqueous solution was prepared in the same manner as in Example 1. While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, while stirring, ethylene carbonate, which is a liquid foaming agent, was dissolved in the monomer aqueous solution so as to be 1%.

  Thereafter, 2.6 parts of a 10% aqueous solution of sodium persulfate and 1 part of a 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. And after fully stirring, this monomer aqueous solution was left still and the acrylate monomer was polymerized. Thereby, a hydrogel was obtained. That is, the acrylate monomer was polymerized without using the foaming agent according to the present invention. The hydrogel had bubbles with a size of about 2 mm to 3 mm.

  The obtained hydrogel was taken out and the same operation as that of Example 1 was performed to obtain a comparative water-absorbent resin. The comparative water-absorbent resin had a particle size of 850 μm to 10 μm and had almost no pores.

  As a result of measuring the performance of the comparative water-absorbing resin by the above method, the water retention amount was 23 g / g, the residual monomer amount was 740 ppm, the water-soluble component amount was 7%, the diffusion rate was 73 seconds, and the dry touch. The property was 8.4 g, and the water absorption under pressure was 9 g / g. Therefore, the comparative water-absorbent resin was inferior in diffusion rate and dry touch property. The results are shown in Table 2.

Example 17
First, a bubble-containing hydrated gel was obtained by carrying out a polymerization method similar to the polymerization method of Example 1. That is, by standing the aqueous monomer solution and polymerizing the acrylate monomer, a bubble-containing hydrogel as a porous cross-linked polymer was obtained.

  The obtained air-containing hydrogel was taken out and subdivided into sizes of about 20 mm to 1 mm, and then hot-air dried at 150 ° C. using a hot-air dryer. Next, the dried product was pulverized using a roll mill and further classified with a 20-mesh sieve to obtain a water-absorbent resin according to the present invention.

  It was confirmed with an electron micrograph that the water-absorbent resin was porous. The average pore diameter of the water absorbent resin was 60 μm. Next, 0.3 part of inorganic powder (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) is added to 100 parts of the water-absorbent resin, and the mixture is thoroughly mixed, whereby the water-absorbent resin composition according to the present invention. Got. As a result of measuring various performances of the obtained water-absorbent resin composition by the above methods, the water retention capacity was 33 g / g, the water absorption speed was 77 seconds, and the liquid passing speed under pressure was 112 seconds. The results are shown in Table 3.

Example 18
First, a bubble-containing hydrated gel was obtained by carrying out the same polymerization method as in Example 2. That is, by standing the aqueous monomer solution and polymerizing the acrylate monomer, a bubble-containing hydrogel as a porous cross-linked polymer was obtained.

  The obtained air-containing hydrogel was taken out and subdivided into sizes of about 20 mm to 1 mm, and then hot-air dried at 150 ° C. using a hot-air dryer. Next, the dried product was pulverized using a roll mill and further classified with a 20-mesh sieve to obtain a water-absorbent resin according to the present invention.

Next, secondary crosslinking treatment was performed on the water-absorbent resin. First, a mixed liquid was prepared by mixing 1 part of glycerin, 3 parts of water, and 1 part of isopropyl alcohol. Next, 100 parts of the above water-absorbent resin and the above mixed solution were mixed, and the resulting mixture was heat-treated at 195 ° C. for 25 minutes. As a result, a water-absorbing resin in which a covalent bond was formed in the vicinity of the surface and the cross-linking density was increased, that is, a water-absorbing resin subjected to secondary cross-linking treatment was obtained. The average pore diameter of the water-absorbent resin subjected to the secondary crosslinking treatment was 70 μm, the residual monomer amount was 150 ppm, the water-soluble component amount was 5%, and the water absorption amount under pressure was 31 g / g.

  Next, 0.3 part of inorganic powder (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) is added to 100 parts of this water-absorbent resin, and mixed sufficiently, whereby the water-absorbent resin composition according to the present invention. I got a thing. As a result of measuring various performances of the obtained water-absorbent resin composition by the above methods, the water retention capacity was 31 g / g, the water absorption speed was 66 seconds, and the liquid passing speed under pressure was 32 seconds. The results are shown in Table 3.

Example 19
First, a monomer aqueous solution was prepared by mixing 38.6 parts of acrylic acid, 409 parts of a 37% aqueous solution of sodium acrylate, 0.45 part of trimethylolpropane triacrylate, and 53 parts of deionized water.

  While maintaining the monomer aqueous solution at a temperature of 25 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen. Next, 4.3 parts of 2,2'-azobis (2-methylpropionamidine) dihydrochloride was added to the aqueous monomer solution while stirring. Thereafter, the aqueous solution was stirred at a temperature of 25 ° C. under a nitrogen stream.

  About 7 minutes after the start of stirring, the aqueous solution became cloudy, and 2,2′-azobis (2-methylpropionamidine) diacrylate having an average particle size of 9 μm and white fine particles was formed. Then, 11 minutes after the start of stirring, the amount of 2,2′-azobis (2-methylpropionamidine) diacrylate produced with respect to the acrylate monomer was 0.32%. 2,2'-azobis (2-methylpropionamidine) diacrylate was uniformly dispersed in the monomer aqueous solution.

  At this point, 2.6 parts of a 10% aqueous solution of sodium persulfate and 1 part of a 1% aqueous solution of L-ascorbic acid were added while stirring the aqueous monomer solution. After the addition, the aqueous monomer solution was kept stirring.

  About 10 minutes after the addition of the aqueous sodium persulfate solution, the temperature of the aqueous monomer solution reached about 88 ° C. Thereafter, the monomer aqueous solution was stirred for another 12 minutes while maintaining the temperature at 70 ° C. to 80 ° C. to polymerize the acrylate monomer. Thereby, a bubble-containing water-containing gel was obtained.

  The obtained air-containing hydrogel was taken out and subdivided into sizes of about 20 mm to 1 mm, and then hot-air dried at 150 ° C. using a hot-air dryer. Next, the dried product was pulverized using a roll mill and further classified with a 20-mesh sieve to obtain a water-absorbent resin according to the present invention.

Next, secondary crosslinking treatment was performed on the water-absorbent resin. First, a mixed liquid was prepared by mixing 0.05 part of ethylene glycol diglycidyl ether, 0.75 part of glycerin, 0.5 part of lactic acid, 3 parts of water, and 0.75 part of isopropyl alcohol. Next, 100 parts of the above water-absorbing resin and the above mixed solution were mixed, and the resulting mixture was mixed at 195 ° C.
For 20 minutes. Further, 5 parts of a 30% aqueous solution of polyethyleneimine having a weight average molecular weight of 70,000 was mixed with the mixture, and the resulting mixture was heat-treated. As a result, a water-absorbing resin in which covalent bonds and ionic bonds were formed in the vicinity of the surface and the cross-linking density was increased, that is, a water-absorbing resin subjected to secondary cross-linking treatment was obtained.

  Next, 0.3 part of inorganic powder (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) is added to 100 parts of this water-absorbent resin, and mixed sufficiently, whereby the water-absorbent resin composition according to the present invention. I got a thing. As a result of measuring various performances of the obtained water-absorbent resin composition by the above methods, the water retention capacity was 28 g / g, the water absorption speed was 56 seconds, and the liquid passing speed under pressure was 23 seconds. The results are shown in Table 3.

[Comparative Example 8]
First, 800 parts of acrylic acid, 4 parts of tetraallyloxyethane, and 3166 parts of water were charged into a reaction vessel to prepare a monomer aqueous solution. Nitrogen gas was blown into the monomer aqueous solution to drive out dissolved oxygen, and the temperature of the monomer aqueous solution was set to 10 ° C.

  An aqueous solution obtained by dissolving 2.4 parts of 2,2′-azobisamidinopropane dihydrochloride in 10 parts of water as a catalyst when the dissolved oxygen in the monomer aqueous solution becomes 1 ppm or less, ascorbine An aqueous solution prepared by dissolving 0.2 parts of acid in 10 parts of water and an aqueous solution prepared by diluting 2.29 parts of a 35% aqueous hydrogen peroxide solution with 10 parts of water were added in this order.

  Polymerization started some time after the addition, and about 2 hours later, the temperature of the aqueous monomer solution reached a maximum of about 65 ° C to 70 ° C. Thereby, a hydrogel was obtained. Then, the amount of residual monomers was reduced to 1,000 ppm or less by putting the hydrogel in a heat insulating container and holding it for 3 hours.

  The above hydrogel was taken out and subdivided using a minced meat machine. The temperature of this finely divided hydrous gel was about 66 ° C. Next, 640 parts of a 50% aqueous solution of sodium hydroxide was added to this hydrous gel. The temperature of the 50% sodium hydroxide aqueous solution was 38 ° C. Then, the aqueous solution was stirred while the hydrogel was further subdivided in the aqueous solution so that neutralization was performed uniformly. The aqueous solution generated heat due to neutralization, and its temperature rose to 88 ° C to 93 ° C.

  Next, an aqueous solution prepared by dissolving 2.4 parts of ethylene glycol diglycidyl ether as a crosslinking agent in 50 parts of water was added to the above aqueous solution. The temperature of the aqueous ethylene glycol diglycidyl ether solution was 24 ° C. Then, the aqueous solution was stirred while the hydrogel was further subdivided in the aqueous solution so that the ethylene glycol diglycidyl ether was uniformly dispersed and surface crosslinking was performed uniformly.

  The above hydrogel subjected to neutralization and surface cross-linking was taken out and dried at 105 ° C. using a rotary drum dryer, so that the water content of the hydrogel was 10%. As a result, a flaky dried product was obtained. Next, the dried product was pulverized and further classified using a 20 mesh sieve and a 325 mesh sieve to obtain a comparative water absorbent resin composition.

  As a result of measuring various performances of the obtained water-absorbing resin composition for comparison, the water retention capacity was 31 g / g, the water absorption rate was 87 seconds, and the liquid passing rate under pressure was 600 seconds. Therefore, the comparative water-absorbent resin composition was inferior in water absorption speed and liquid passing speed under pressure. The results are shown in Table 3.

[Comparative Example 9]
First, while cooling an aqueous solution obtained by diluting 72.1 g of acrylic acid with 18.0 g of water, 98.9 g of a 30% aqueous solution of sodium hydroxide was added for neutralization. Thereafter, 10.7 g of a 2.8% aqueous solution of potassium persulfate was added to the aqueous solution to obtain a uniform solution. Thereby, the monomer aqueous solution to which the radical polymerization initiator was added was prepared.

  On the other hand, a 500 ml flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas introduction tube was used as a reaction vessel. In this reaction vessel, 283 ml of cyclohexane and 2.2 g of 25% aqueous solution of polyoxyethylene dodecyl ether sulfate sodium salt were charged and stirred at 300 rpm to disperse the polyoxyethylene dodecyl ether sulfate sodium salt. The flask was purged with nitrogen and then heated to 75 ° C. Moreover, said monomer aqueous solution was put into the dropping funnel.

  Then, while stirring the cyclohexane solution, the monomer aqueous solution was dropped over 30 minutes to disperse and suspend the monomer aqueous solution. After completion of the dropping, the cyclohexane solution was stirred at 75 ° C. for 1.5 hours, and further stirred at 80 ° C. for 4 hours to carry out reverse phase suspension polymerization of the acrylate monomer. During the polymerization, water in the reaction vessel was continuously removed by azeotropy with cyclohexane (azeotropic dehydration).

  When the amount of water in the reaction vessel reached 30% of the amount of water added before polymerization, 0.18 g of ethylene glycol diglycidyl ether was added to the reaction vessel and reacted for another 30 minutes.

  After completion of the reaction, the cyclohexane solution was filtered, and the resulting hydrogel was dried under reduced pressure to obtain 88.0 g of an acrylic acid (sodium) polymer. Next, the polymer was pulverized and further classified using a 20-mesh sieve to obtain a comparative water-absorbent resin composition.

  As a result of measuring various performances of the obtained water-absorbing resin composition for comparison, the water retention capacity was 30 g / g, the water absorption speed was 81 seconds, and the liquid passing speed under pressure was 670 seconds. Therefore, the comparative water-absorbent resin composition was inferior in water absorption speed and liquid passing speed under pressure. The results are shown in Table 3.

[Comparative Example 10]
The water absorbent resin was taken out by decomposing commercially available paper diapers. As the above-mentioned paper diapers, Mooney Power Slim (trade name, manufactured by Unicharm Corporation, hereinafter referred to as commercial product A), Doremi (trade name, manufactured by Shin Oji Paper Co., Ltd., hereinafter referred to as commercial product B), Mary's pants (trade name, manufactured by Kao Corporation, hereinafter referred to as commercial product C) and Mooney Man (trade name, manufactured by Unicharm Corporation, hereinafter referred to as commercial product D) were used. And various performances of these comparative water-absorbing resins, that is, commercial products A to D were measured by the above-described methods.

  Further, Sunwet IM-5000 (trade name, manufactured by Sanyo Chemical Industries, Ltd., hereinafter referred to as a commercial product E), which is a commercially available water-absorbing resin, and Arasov 720 (trade name, manufactured by Arakawa Chemical Co., Ltd.) Hereinafter, various performances of the commercially available product F) were also measured by the above method.

  The results are shown in Table 3. The commercial products A to F were inferior in at least one of the water absorption speed and the liquid passing speed under pressure.

  It should be noted that the specific embodiments or examples made in the best mode for carrying out the invention are merely to clarify the technical contents of the present invention, and are limited to such specific examples. The present invention should not be construed as narrowly defined but can be implemented with various modifications within the spirit of the present invention and the scope of the following claims.

  According to the above method, the water-absorbing resin having excellent water-absorbing properties such as diffusibility of water-based liquid, water-absorbing speed, water-holding ability, and dry touch property, and water-soluble resin and water-reducing monomer amount are reduced. And can be easily obtained industrially.

  Further, according to the above configuration, the water-absorbing resin and the water-absorbing resin that are excellent in liquid permeability and diffusibility under pressure of an aqueous liquid, do not cause gel block, and have improved water absorption speed, water retention ability, and the like. A resin composition can be provided.

  Water-absorbing resin and water-absorbing resin composition include, for example, paper diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials, and other hygiene materials (body fluid absorbing articles); pet urine absorbing articles; building materials Civil engineering and construction materials such as water retention materials, water-stopping materials, packing materials, gel water sacs, etc .; food articles such as drip absorbers, freshness retention materials, cold insulation materials; oil-water separators, anti-condensation materials, coagulants, etc. Various industrial articles; agricultural and horticultural articles such as water-retaining materials such as plants and soil; and absorbent articles in various fields. Thereby, the absorbent article which shows the outstanding performance mentioned above can be provided.

FIG. 1 is a schematic cross-sectional view of a measuring device used for measuring the amount of water absorption under pressure, which is one of the performances of the water-absorbent resin in the present invention. FIG. 2 is a schematic cross-sectional view of a measuring apparatus used for measuring a liquid passing velocity under pressure, which is one of the performances exhibited by the water absorbent resin composition in the present invention. FIG. 3 is a ¹ H-NMR chart of 2,2′-azobis (2-methylpropionamidine) diacrylate which is one of the foaming agents in the present invention. FIG. 4 is a chart of an infrared absorption spectrum (IR) of the 2,2′-azobis (2-methylpropionamidine) diacrylate. FIG. 5 is a drawing-substituting photograph showing the particle structure of the water-absorbent resin obtained in Example 11. FIG. 6 is a drawing-substituting photograph as a micrograph showing the cross-sectional structure of the water-absorbent resin obtained in Example 14. FIG. 7 is a drawing-substituting photograph showing the particle structure of the water-absorbent resin obtained in Comparative Example 1.

Explanation of symbols

15 Water Absorbent Resin 30 Water Absorbent Resin Composition

Claims (12)

Water-absorbent resin obtained by polymerizing an unsaturated monomer containing at least one acrylate monomer selected from the group consisting of acrylic acid and water-soluble salts of acrylic acid as a main component in the presence of a crosslinking agent And a water-absorbent resin composition comprising an inorganic powder,
The water retention capacity in 60 minutes with respect to physiological saline (0.9 wt% sodium chloride aqueous solution) is 20 g / g or more, the water absorption rate with respect to physiological saline is 120 seconds or less, and the liquid passing rate under pressure is 200 seconds. A water-absorbent resin composition characterized by the following. 2. The water absorbent resin composition according to claim 1, wherein the water absorbent resin has an average particle diameter in the range of 200 μm to 600 μm. The water-absorbent resin composition according to claim 1 or 2, wherein the inorganic powder is used in an amount of 0.001 to 10 parts by weight with respect to 100 parts by weight of the water-absorbent resin. The bulk specific gravity of the water absorbent resin is 0.01 g / cm. ³ Or more, 0.5 g / cm ³ The water-absorbent resin composition according to any one of claims 1 to 3, wherein: The inorganic powder contains at least one selected from silicon dioxide, silicic acid, and silicate, and the average particle size of the inorganic powder measured by a Coulter counter method is 200 μm or less. 5. The water absorbent resin composition according to any one of 1 to 4. The water absorbent resin composition according to any one of claims 1 to 5, wherein the surface of the water absorbent resin is crosslinked by a covalent bond. The water-absorbent resin composition according to any one of claims 1 to 6, wherein the surface of the water-absorbent resin is crosslinked with a covalent bond and an ionic bond. An absorbent article comprising the water absorbent resin composition according to any one of claims 1 to 7. A step of polymerizing the aqueous monomer solution after uniformly dispersing a solid foaming agent having an average particle size in the range of 1 μm to 1000 μm in the aqueous monomer solution containing acrylic acid and a water-soluble salt of acrylic acid and a crosslinking agent And a step of crosslinking the surface of the water-absorbent resin after the above steps. The method for producing a water absorbent resin according to claim 9, wherein the step of crosslinking the surface is a step of forming a covalent bond. Furthermore, the manufacturing method of the water absorbing resin of Claims 9-10 which is a step of forming an ionic bond on the surface of a water absorbing resin using a cationic compound after the step of bridge | crosslinking the surface. A method for producing a water-absorbent resin composition, comprising mixing the water-absorbent resin obtained in claims 9 to 11 and an inorganic powder.

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