JP5014607B2 - Particulate water-absorbing agent mainly composed of water-absorbing resin - Google Patents

Description

  The present invention relates to a particulate water-absorbing agent mainly composed of a water-absorbing resin. More specifically, it is a particulate water-absorbing agent for absorbers used in absorbent articles such as paper diapers, which is unprecedented and does not generate odors or ethylene glycol during actual use, and exhibits excellent absorption capacity. It relates to the agent.

  Currently, sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, as constituent materials, water-absorbing resins (or particulate water-absorbing agents containing water-absorbing resins) and pulp intended to absorb body fluids Such hydrophilic fibers are widely used. Examples of the water-absorbing resin include a crosslinked polyacrylic acid partial neutralized product, a hydrolyzate of starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic acid ester copolymer, and a hydrolysis of acrylonitrile copolymer. Products or cross-linked products, hydrolysates or cross-linked products of acrylamide copolymers, cross-linked polymers of cationic monomers, and the like are used as main raw materials.

  The water-absorbing characteristics desired for the water-absorbent resin include conventionally high absorption capacity when contacting with an aqueous liquid such as body fluid, excellent absorption rate, liquid permeability, gel strength of swollen gel, and a group containing an aqueous liquid. The amount of water sucked up from the material is advocated, and a particulate water-absorbing agent adjusted to specific physical properties is provided.

  Furthermore, in recent years, water-absorbing resin powders having a very narrow particle size distribution and water-absorbing resin powders having a high absorption capacity and a low water-soluble content have been demanded, and the absorption capacity under pressure and liquid permeability under pressure are high. It has come to be required. And many patent patents and measurement methods that define various physical properties of these water-absorbent resins have been filed, as in Patent Documents 1 to 39 below.

  Patent Document 1 proposes a water absorbent resin excellent in gel strength, soluble content, and water absorption magnification. Patent Document 2 proposes a water absorbent resin excellent in non-pressurized liquid permeability, water absorption speed, and water absorption magnification. Patent Documents 3 to 6 and the like have also been proposed as techniques for defining a specific particle size distribution. In addition, many water-absorbing resins excellent in absorption capacity under pressure under various loads and methods for measuring the same are proposed, and water-absorbing resins excellent in absorption capacity under pressure alone or in combination with other physical properties are disclosed in Patent Documents 7 to 16, 38, 39, etc.

  Further, water-absorbing resins having excellent impact resistance have been proposed in Patent Documents 17 and 18 and the like. Further, a water-absorbing resin that defines the amount of dust is proposed in Patent Document 19 and the like, and a water-absorbing resin with less coloring is proposed in Patent Document 20 and the like. Patent Literatures 21 and 22 propose water-absorbing resins excellent in gel durability and water-absorbing ability to L-ascorbic acid aqueous solutions that regulate urine resistance, and Patent Literature 23 proposes a water-absorbing resin excellent in air permeability. Has been. Further, Patent Document 24 proposes a water-absorbing resin with little residual monomer.

  Further, Patent Documents 25 to 32 propose that a water-absorbing resin having specific physical properties is suitable for a water-absorbing article (paper diaper) having specific physical properties, constitution, and polymer concentration. Further, Patent Document 33 proposes a method of performing surface cross-linking while pulverizing at least a part of resin particles.

In recent years, sanitary materials such as paper diapers are becoming thinner, that is, the concentration of the water-absorbing resin tends to increase, and there is an increasing demand for improvement of odors generated from the water-absorbing resin. For odor, in order to impart deodorizing performance to the water absorbent resin, combinations of the water absorbent resin with various deodorants and antibacterial agents have been proposed so far. For example, a water absorbent resin composition comprising a water absorbent resin and a leaf extract of a camellia plant (see, for example, Patent Document 34), a coniferous tree extract and a water absorbent resin having a specific performance. Compositions (see, for example, Patent Document 35) are known. In recent years, a technique (for example, see Patent Document 36) that focuses attention on acetic acid and propionic acid, which are impurities in acrylic acid, has been proposed as the odor of the water-absorbent resin. Furthermore, a technique (for example, see Patent Document 37) that focuses on β-hydroxypropionic acid, which is an impurity in acrylate, has been proposed in relation to the residual monomer.
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  As described above, many technologies have been proposed to satisfy various characteristics of the water-absorbent resin, but in recent years, the amount of water-absorbent resin used in absorbent bodies such as paper diapers has increased, and the water absorption capacity of the absorbent body has increased. However, the conventional water-absorbent resin cannot be said to exhibit sufficient performance for use at a high concentration (high weight ratio of the water-absorbent resin). In addition, as the amount of water-absorbent resin used for absorbents such as paper diapers increases (higher concentration), the deodorizing performance, which has become an important factor, is also given to the water-absorbing agent itself. Even if various deodorants are studied, sufficient deodorizing performance has not been obtained.

  Furthermore, in recent years, water-absorbent resin particles with a narrow particle size distribution have been used to reduce the lumpy feeling of water-absorbent particles in absorbent bodies such as paper diapers, and to reduce particle size segregation and reduce particle size fluctuations during the production of the absorber. Is required.

  However, there has been no water-absorbing resin that has all of the characteristics that it has less unpleasant odor during actual use, exhibits excellent absorption capacity, and has a narrow particle size distribution and little particle size segregation.

  That is, the problem of the present application is to realize a water-absorbing resin that has all of the characteristics that there are few unpleasant odors during actual use, an excellent absorption rate, and a narrow particle size distribution and little particle size segregation. An object of the present invention is to provide a water-absorbing agent that not only has high physical properties and safety during actual use, but also has a less unpleasant odor generated after swelling and can be used comfortably.

  In order to solve the above-mentioned problems, the present inventors unexpectedly discovered the water-absorbing resin itself in the process of examining the deodorizing performance (for example, the addition of a deodorant) as an additional function of the water-absorbing resin (water-absorbing agent). Found that the water-absorbent resin itself has a specific odor when swollen, and the odor of the water-absorbent resin itself decreases the deodorizing performance, resulting in a decrease in the deodorizing performance in actual use in paper diapers and the like. I found it.

  As a result of diligent investigation of the cause of the specific odor of the water-absorbent resin itself, a specific surface cross-linking agent (surface cross-linking agent capable of ester-bonding with a carboxyl group) was used, and the absorption under high pressure and high absorption under no pressure were used. Even when the raw material of the water-absorbent resin itself does not have an odor when it has a magnification, a problem of odor occurs specifically during actual use of the obtained product, and the water-absorbing agent in the absorbent such as paper diapers The fact that the performance in actual use is deteriorated was found. In addition, by eliminating the problem of odor of the water-absorbent resin itself, a surface cross-linking agent capable of ester-bonding with a carboxyl group is used, and for the first time, it has the opposite characteristics of having a high absorption capacity and improving odor. The present inventors have found that water-absorbing articles such as paper diapers with high physical properties can be obtained.

  Furthermore, the present inventors have studied specific surface cross-linking agents with low odors, and that residual ethylene glycol may be contained even in water-absorbing resins that do not use ethylene glycol as a monomer or cross-linking agent at all. The headline, as described above, even when no odor-causing monomer or cross-linking agent is used, depending on the type of surface cross-linking agent to be selected, ethylene glycol is present as a by-product in the water-absorbent resin. It was found to cause problems. As a result of pursuing the origin of such ethylene glycol, it was found that it is an impurity or decomposition product of the surface cross-linking agent of the raw material (especially ethylene glycol derivatives; eg, ethylene carbonate and polyethylene glycol). In addition, when alkylene carbonate (especially ethylene carbonate) is used as a surface cross-linking agent to improve physical properties (especially absorption capacity under pressure or liquid permeability under pressure), a large amount of surface cross-linking agent or reaction at high temperature is required. Therefore, it was found that even in a water-absorbing resin that does not contain ethylene glycol at all as a raw material, even if alkylene carbonate such as ethylene carbonate does not contain substantial ethylene glycol, ethylene glycol is produced as a by-product in the absorbent product that is the final product. . By eliminating such safety problems due to ethylene glycol, using alkylene carbonate as a surface cross-linking agent to improve physical properties (especially absorption capacity under pressure and liquid permeability under pressure), and improving safety The present inventors have found that a water-absorbing article such as a paper diaper having high physical properties that has the contradictory characteristics for the first time can be obtained.

  Furthermore, focusing on the problem of increasing the amount of fine powder generated when finely pulverized in order to obtain water-absorbent resin particles with a narrow particle size distribution and little particle size segregation, By finding the fact that the particle size distribution is an important factor for water-absorbing articles such as paper diapers with high physical properties, and by setting the values of the contradictory properties, such as the average particle size and particle size distribution, and the amount of fine powder, within a predetermined range It was found that water-absorbing resin particles having a narrow particle size distribution and little particle size segregation can be obtained.

  Such new findings (specific surface cross-linking agent and specific physical properties and odor are contradictory, high physical properties due to alkylene carbonate as a surface cross-linking agent and ethylene glycol by-product residual are contradictory, average particle diameter and fine powder amount are contradictory, 5 Three properties (absorption capacity under no pressure (CRC), absorption capacity under pressure (AAP), mass average particle diameter, proportion of particles less than 150 μm in particulate water-absorbing agent, logarithmic standard deviation of particle size distribution) On the basis of practical use), the present inventors have found that at least five particulate water-absorbing agents controlled to specific physical properties are suitable for practical use, and have completed the present invention.

That is, the particulate water-absorbing agent (first water-absorbing agent) of the present invention is a particulate water-absorbing material mainly composed of polycarboxylic acid-based water-absorbing resin particles surface-crosslinked with a surface-crosslinking agent capable of ester-bonding with a carboxyl group. It is an agent and is characterized by satisfying the following (a), (b), (c), (d), (e) and (f).
(A) Absorption capacity without load (CRC) of 27 g / g or more in physiological saline (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa of physiological saline is 20 g / g or more (c) Mass Average particle size (D50) is 200 to 450 μm
(D) 0-5 mass% of particles less than 150 μm in the particulate water-absorbing agent
(E) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.40.
(F) The content of the alcohol-based volatile substance volatilized from the particulate water-absorbing agent, defined as the atmospheric concentration determined by the gas detector tube, is 0 to 10 ppm.

Further, the particulate water-absorbing agent (second water-absorbing agent) of the present invention is a particulate water-absorbing material composed mainly of polycarboxylic acid-based water-absorbing resin particles surface-crosslinked with a surface-crosslinking agent capable of ester-bonding with a carboxyl group. The surface cross-linking agent is an alkylene carbonate-containing surface cross-linking agent and satisfies the following (a), (b), (c), (d), (e) and (g): Yes.
(A) Absorption capacity without load (CRC) of 27 g / g or more in physiological saline (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa of physiological saline is 20 g / g or more (c) Mass Average particle size (D50) is 200 to 450 μm
(D) 0-5 mass% of particles less than 150 μm in the particulate water-absorbing agent
(E) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.40.
(G) The residual ethylene glycol content (HPLC determination) in the particulate water-absorbing agent is 0 to 40 ppm.

  The particulate water-absorbing agent of the present invention preferably further contains an alcohol compound selected from amino alcohol, alkylene carbonate and polyhydric alcohol (excluding ethylene glycol).

  Moreover, the particulate water-absorbing agent of the present invention may further contain a component selected from the group consisting of a chelating agent, a deodorant, a polyvalent metal salt, and inorganic fine particles.

  The surface cross-linking agent is preferably one or more compounds selected from the group consisting of glycerin, 1,3-propanediol, ethylene carbonate, 3-ethyl-3-hydroxymethyloxetane, and ethanolamine.

  In the particulate water-absorbing agent of the present invention, the amount of sulfur-based volatile substances volatilized from the particulate water-absorbing agent is further defined as (h) the atmospheric concentration determined by the gas detector tube. preferable.

  The particulate water-absorbing agent of the present invention preferably further has (i) a total content of acrylic acid, acetic acid and propionic acid (HPLC determination) in the particulate water-absorbing agent of 0 to 1000 ppm.

  The particulate water-absorbing agent of the present invention further has (j) a brightness index L value indicated by a Hunter colorimetric color difference meter of 80 or more as whiteness, and an a value indicating a chromaticness index is -2 to 2. And the b value is preferably 0-4.

  The high-concentration absorber of the present invention is an absorber molded from the particulate water-absorbing agent of the present invention and hydrophilic fibers, and the particulate water-absorbing agent is contained in the total mass of the particulate water-absorbing agent and hydrophilic fibers. 30 to 100% by mass (100% by mass is the particulate water-absorbing agent alone).

The method for producing a particulate water-absorbing agent according to the present invention comprises crosslinking an unsaturated monomer aqueous solution comprising unneutralized acrylic acid and / or a salt thereof as a main component of a monomer in the presence of an internal crosslinking agent. A step of obtaining a polymer, a step of drying the obtained crosslinked polymer and sizing to obtain a water-absorbing resin satisfying the following (a), (b), (c) and (d);
(A) Absorption capacity (CRC) under no pressure to physiological saline is 30 g / g or more (b) Mass average particle diameter (D50) is 200 to 450 μm
(C) 0 to 8% by mass of particles less than 150 μm
(D) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.50.
The surface vicinity of the water-absorbent resin is further subjected to a heat treatment after adding a surface cross-linking agent that forms an ester bond, and the water-absorbent resin during and / or after the heat treatment is subjected to an air flow at an ambient temperature of 60 ° C. or higher. And a step of exposing to.

  In the method for producing a particulate water-absorbing agent according to the present invention, the unneutralized acrylic acid is 10 to 200 ppm of methoxyphenol, 0 to 10,000 ppm of acetic acid and propionic acid based on the mass of the acrylic acid, and acrylic acid dimer. One or more compounds selected from an amount of 0 to 1000 ppm, furfural 0 to 10 ppm, and protoanemonin 0 to 10 ppm are preferably acrylic acid within the applicable range. The surface cross-linking agent is preferably a surface cross-linking agent containing alkylene carbonate.

  The amount of ethylene glycol contained in the alkylene carbonate is preferably 0.1% by mass or less based on the mass of the alkylene carbonate.

  According to the particulate water-absorbing agent and the method for producing the same of the present invention, the particles satisfying all the characteristics that there are few unpleasant odors and safety problems at the time of actual use, an excellent absorption ratio, and a narrow particle size distribution and a small particle size segregation. A water-absorbing agent is realized. Therefore, the obtained particulate water-absorbing agent has high physical properties and safety in actual use in absorbent articles such as high-concentration paper diapers (a large amount of water-absorbent resin is used in one sheet), which has been a particularly problematic odor. In addition to its high performance, it has an unpleasant odor and can be used comfortably, and exhibits excellent absorption.

  Hereinafter, the particulate water-absorbing agent of the present invention, the water-absorbing resin used for the particulate water-absorbing agent, and the raw materials and reaction conditions thereof will be described. Further, in the present invention, (a) Absorption capacity without load (CRC) into physiological saline, (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa physiological saline, (c) Mass average Particle diameter (D50), (d) ratio of particles less than 150 μm, (e) logarithmic standard deviation of particle size distribution (σζ), (f) content of alcohol-based volatile material volatilized from particulate water-absorbing agent, (g ) Residual ethylene glycol content in particulate water-absorbing agent, (h) Amount of sulfur-based volatile substances volatilized from particulate water-absorbing agent (content of sulfur-based volatile components), (i) Acrylic acid in particulate water-absorbing agent , Acetic acid and propionic acid total content, (j) whiteness is a value measured by the method described in the examples described later. In the present specification, “parts by weight” and “% by weight” may be read as “parts by mass” and “% by mass”, respectively.

(1) Water-absorbing resin In the present invention, the water-absorbing resin is a water-swellable water-insoluble cross-linked polymer that can form a hydrogel. For example, water-swelling property is essential weight of 5 in ion-exchanged water. It is one that absorbs a large amount of water, preferably 50 times to 1000 times, and water-insoluble means one having a water-soluble content of 50% by weight or less. In addition, these measuring methods should just be based on the Example of this invention, ERT (EDENA Recommended Test Method) 441.1-99 of EDANA (Europian Disposables And Nonwovens Association), and 470.1-99.

  In the present invention, the water-absorbing resin may be any water-absorbing resin obtained by drying a crosslinked polymer obtained by crosslinking polymerization of an acid group and / or a salt-containing unsaturated monomer thereof for achieving the present invention. Polycarboxylic acid water-absorbing resins can be used more suitably. Among them, a partially neutralized polyacrylic acid polymer obtained by polymerizing / crosslinking an unsaturated monomer containing acrylic acid and / or a salt thereof (neutralized product) as a main component is more preferably used.

  Further, the water-absorbent resin used in the present invention is not limited to those produced by the production method disclosed in the present application, and may be any one obtained by drying a crosslinked polymer containing a constituent unit derived from an unsaturated monomer described later. Good. The structural unit derived from an unsaturated monomer described later is, for example, a structure in which a polymerizable double bond of each monomer is opened by a polymerization reaction (double bond (—C═C—) is a single bond (—C— This corresponds to the structure (C-).

(2) Particulate water-absorbing agent and production method thereof In the present invention, the particulate water-absorbing agent is a water-absorbing solidifying agent containing a water-absorbing resin as a main component, and optionally containing a small amount of additives and / or water. That is, the content of the water-absorbing resin is 70 to 100% by mass, more preferably 80 to 100% by mass, and still more preferably 90 to 100% when the total amount of the water-absorbing resin is 100% by mass. It is the range of mass%. As components other than the water-absorbing resin in the particulate water-absorbing agent, water is usually the main component, and the additives described later are used. The above-mentioned aqueous liquid is not limited to water, but is specified as long as it includes water, such as urine, blood, feces, waste liquid, moisture and steam, ice, a mixture of water and organic solvent and / or inorganic solvent, rainwater, and groundwater. Preferably, urine, particularly human urine can be mentioned.

  The method for producing the particulate water-absorbing agent of the present invention is not particularly limited as long as the physical properties of the present invention are controlled. As such a production method, for example, a production method in which surface crosslinking is performed by controlling to a specific particle size before surface crosslinking, more preferably, the following <Production Method Example 1> can be used. In addition to <Production Method 1>, for example, the following <Production Method 2>, <Production Example 3>, or <Production Example 4> may be used.

<Production Example 1>
After obtaining a water-absorbent resin controlled to a specific particle size and absorption rate, the surface of the obtained water-absorbent resin is subjected to heat treatment after adding a surface cross-linking agent that forms an ester bond, and / or during the heat treatment and / or A method of exposing the water-absorbent resin after heat treatment to an air current having an atmospheric temperature of 60 ° C. or higher. Preferably, the purity of the raw acrylic acid is further controlled within the range described later.

<Production Example 2>
An unsaturated monomer aqueous solution containing unneutralized acrylic acid and / or a salt thereof as a main component of the monomer was subjected to cross-linking polymerization in the presence of an internal cross-linking agent and, if necessary, a chain transfer agent, and the specific absorption ratio was controlled. A method comprising the steps of, after obtaining a water-absorbing resin, adjusting to a specific particle size and surface-crosslinking the obtained crosslinked polymer having a specific particle size and absorption capacity.

<Production Example 3>
Cross-linking polymerization of an unsaturated monomer aqueous solution with a specific concentration of unneutralized acrylic acid in the presence of an internal cross-linking agent to obtain a water-absorbing resin controlled to a specific absorption ratio, followed by further neutralization A method comprising the steps of surface-crosslinking a crosslinked polymer having a specific particle size and an absorption capacity obtained by adjusting to a specific particle size.

<Production Example 4>
An unsaturated monomer aqueous solution containing unneutralized acrylic acid and / or a salt thereof as a main component of the monomer was subjected to cross-linking polymerization in the presence of an internal cross-linking agent to obtain a water-absorbing resin controlled to a specific absorption ratio. After that, it includes a step of surface-crosslinking the obtained crosslinked polymer having a specific particle size and absorption capacity, and if necessary, adding a chelating agent at the time of the polymerization, before or after or simultaneously with the surface crosslinking. Method.

  Hereinafter, the manufacturing method of the particulate water-absorbing agent of the present invention and further the particulate water-absorbing agent of the present invention will be described in order.

(3) Unsaturated monomer <Acrylic acid>
As an unsaturated monomer (hereinafter abbreviated as a monomer as appropriate) constituting the water-absorbent resin, it is preferable to use acrylic acid and / or a salt thereof as a main component. In order to obtain the particulate water-absorbing agent of the present invention, it is preferable to use acrylic acid having a specific purity, that is, acrylic acid containing a specific content of a specific compound. As such acrylic acid, specifically, from methoxyphenol 10-200 ppm, acetic acid and propionic acid total content 0-10000 ppm, acrylic acid dimer amount 0-1000 ppm, furfural 0-10 ppm, and protoanemonin 0-10 ppm It is preferable that one or more selected compounds is acrylic acid within the applicable range.

  Among them, the acrylic acid preferably has a total content of acetic acid and propionic acid in acrylic acid of 1000 ppm to 0 ppm and an acrylic acid dimer amount of 1000 ppm to 0 ppm. Further, the total content of acetic acid and propionic acid in acrylic acid and the content of the acrylic acid dimer amount are more preferably 500 ppm or less, further preferably 300 ppm or less, and more preferably 100 ppm or less. Particularly preferred. The furfural is more preferably 5 ppm or less, and further preferably 1 ppm or less. Protoanemonin is more preferably 5 ppm or less, and further preferably 1 ppm or less. When the total content of acetic acid and propionic acid in acrylic acid and the amount of acrylic acid dimer is large, it becomes a factor of odor or residual monomer, and the particulate form of the present invention is low in volatile organic substances such as alcohol-based volatile substances (in terms of alcohol) It is difficult to obtain a water-absorbing agent. Moreover, when there is much furfural and protoanemonin, it is hard to become a high magnification water-absorbing agent. p-methoxyphenol is usually 200 ppm or less, preferably 20 to 160 ppm, more preferably 30 to 100 ppm, and is effective for controlling and promoting polymerization.

  As a method for obtaining such acrylic acid, the oxidation conditions of acrylic acid may be controlled, or the conditions for distillation and crystallization may be strictly controlled so as to be in the above range. When the distillation method is used as a purification method, the number of theoretical plates is increased (for example, by 6 to 20 plates) or the reflux ratio is increased. When the crystallization method is used as a purification method, the number of crystallizations is increased. (For example, increase 3-10 times) etc., respectively, can raise rectification degree and can obtain acrylic acid of the said range. The distillation method and the crystallization method may be used in combination. Moreover, what is necessary is just to control the preservation | save of this acrylic acid after refinement | purification to low temperature (10-25 degreeC).

<Other monomers>
As the monomer constituting the water-absorbing resin used in the present invention, “other monomers” other than acrylic acid may be used in combination as a copolymerization component, or only from “other monomers”. A resin may be obtained. Examples of such “other monomers” include methacrylic acid, (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, vinyl sulfonic acid, 2- (meth) acrylamido-2-methylpropane sulfonic acid, ( (Meth) acryloxyalkanesulfonic acid, alkali metal salts thereof, ammonium salts thereof, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl Water-soluble or hydrophobic unsaturated monomers such as (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, isobutylene, lauryl (meth) acrylate, etc. To mention That. In the present invention, the term “water-soluble” means that 1 g or more is dissolved in 100 g of water at room temperature.

  In addition, the polycarboxylic acid-based water-absorbing resin may be a polyamino acid cross-linked product (eg, polyaspartic acid) or a carboxylated polymer cross-linked product (eg, carboxymethylcellulose, carboxymethyl) other than the above-mentioned crosslinked polymer of unsaturated monomer. A water-absorbing resin such as starch) may be used.

  When a monomer other than acrylic acid (salt) is used in the present invention, in order to achieve the present invention, a monomer other than acrylic acid (salt) is used with acrylic acid and / or a salt thereof used as a main component. Preferably it is 0-30 mol% with respect to the total amount, More preferably, it is 0-10 mol%, Most preferably, it is a ratio of 0-5 mol%.

  In addition, when an acid group-containing unsaturated monomer is used as the monomer, examples of the salt include alkali metal salts, alkaline earth metal salts, and ammonium salts. Sodium salts and potassium salts are preferred from the standpoints of availability and safety.

  The acid group-containing unsaturated monomer such as acrylic acid is preferably neutralized in terms of physical properties and pH, and the acid group neutralization rate is usually 20 to 100 mol%, more preferably 30 to 95 mol%, more preferably 40 to 80 mol%. The neutralization of the acid group may be performed with a monomer, may be performed with a polymer as in <Production Example 3>, or may be used in combination.

(4) Crosslinkable monomer (internal crosslinking agent)
The water-absorbent resin used in the present invention is obtained by drying a cross-linked polymer obtained by polymerizing the unsaturated monomer, but the cross-linked polymer is self-crosslinked without using a cross-linkable monomer. In terms of physical properties, a crosslinkable monomer having two or more polymerizable unsaturated groups and two or more reactive groups in one molecule (inside the water absorbent resin) It is also obtained by copolymerizing or reacting a crosslinking agent). In addition, being a crosslinked polymer is also defined by being insoluble in water.

  Specific examples of the internal cross-linking agent include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, tri Allylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene Glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylenimine, and glycidyl (meth) acrylate.

  These internal cross-linking agents may be used alone or in combination of two or more. These internal cross-linking agents may be added to the reaction system all at once or in divided portions. In the case of using at least one type or two or more types of internal crosslinking agents, two or more polymerizable unsaturated groups are added in consideration of the absorption characteristics of the finally obtained water-absorbing resin and particulate water-absorbing agent. It is preferable to use the compound which has it at the time of superposition | polymerization.

  The amount of these internal crosslinking agents to be used is preferably 0.001 to 2 mol%, more preferably 0.005 to 0.5 mol%, still more preferably 0, based on the above monomers (excluding the internal crosslinking agent). 0.01 to 0.2 mol%, particularly preferably 0.03 to 0.15 mol%. When the amount of the internal cross-linking agent used is less than 0.001 mol% and more than 2 mol%, sufficient absorption characteristics may not be obtained. When the amount of the internal cross-linking agent used is less than the above range, the cross-linked structure is not sufficiently formed and the water-swellable water-insoluble cross-linked polymer as described in the above (1) cannot be obtained. If the amount of the internal cross-linking agent used is larger than the above range, the water-soluble content and the like are reduced, but the absorption capacity of the water-absorbent resin and water-absorbing agent is reduced, and the absorption of absorbent articles such as paper diapers is reduced. This is not preferable because the amount is reduced.

  When the crosslinked structure is introduced into the polymer using the internal crosslinking agent, the internal crosslinking agent is added to the reaction system before or during the polymerization of the unsaturated monomer, after the polymerization, or after the neutralization. What is necessary is just to add.

(5) Polymerization initiator As the initiator used for polymerizing the above-mentioned monomers to obtain the water-absorbent resin used in the present invention, potassium persulfate, ammonium persulfate, sodium persulfate, potassium peracetate, Radical polymerization initiators such as sodium acetate, potassium percarbonate, sodium percarbonate, t-butyl hydroperoxide, hydrogen peroxide, 2,2'-azobis (2-amidinopropane) dihydrochloride; 2-hydroxy-2- Photopolymerization initiators such as methyl-1-phenyl-propan-1-one can be used. The amount of these polymerization initiators used is 0.001 to 2 mol%, preferably 0.01 to 0.1 mol% (based on the total monomers) in view of physical properties. When these polymerization initiators are less than 0.001 mol%, the amount of unreacted residual monomers increases, whereas when the polymerization initiator exceeds 2 mol%, it is difficult to control the polymerization. .

(6) Polymerization method and polymerization solution When the unsaturated monomer is polymerized in order to produce the water-absorbent resin used in the present invention, bulk polymerization or precipitation polymerization can be performed. It is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization by making the monomer into an aqueous solution. When the monomer is an aqueous solution, the concentration of the monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) is determined by the temperature of the aqueous solution and the monomer, and is not particularly limited. Production Example 1> + <Production Example 2>, <Production Example 1> + <Production Example 4> When polymerization is performed with a neutralized acid group-containing unsaturated monomer (neutralization polymerization method) in advance Is preferably 10 to 70% by mass, more preferably 20 to 60% by mass. Moreover, when performing the said aqueous solution polymerization, you may use together solvents other than water as needed, and the kind of solvent used together is not specifically limited.

  When starting the above polymerization, it can be started using the above polymerization initiator. In addition to the polymerization initiator, active energy rays such as ultraviolet rays, electron beams, and γ rays may be used alone or in combination with the polymerization initiator. The temperature at the start of polymerization depends on the type of polymerization initiator used, but the upper and lower limits are preferably in the range of 15 to 130 ° C, and more preferably in the range of 20 to 120 ° C.

  The reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735. It is described in. Aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, US Pat. Nos. 4,462,001, 4,873,299, 4,286,082, 4,973,632, 4,985,518, 5,124,416, 5,250,640 are used. No. 5264495, No. 5145906, No. 5380808, European Patent No. 081636, No. 09555086, No. 0922717, and the like. The monomers and initiators exemplified in these can also be applied in the present invention.

(7) Other polymerization method (a) Polymerization of monomer whose main component is unneutralized carboxylic acid group (acrylic acid) The polymerization method of (6) above usually contains a previously neutralized acid group. Polymerized with an unsaturated monomer (neutralization polymerization method), for example, as in <Production Example 3> above, as a polymerization method, an unneutralized acid group-containing unsaturated monomer, particularly an unneutralized monomer A so-called acid polymerization & post-neutralization method may be used in which polymerization is performed using acrylic acid as a main component and acid groups are neutralized after polymerization.

  For example, in <Production Example 3>, an unsaturated monomer aqueous solution having a specific concentration mainly composed of unneutralized acrylic acid is subjected to cross-linking polymerization in the presence of an internal cross-linking agent, and then neutralized, adjusted to a specific particle size, The obtained crosslinked polymer having a specific particle size and absorption capacity is further subjected to surface crosslinking.

  In such an acid polymerization & post-neutralization method, unneutralized acrylic acid is polymerized as a main component, particularly 30 to 100 mol%, more preferably 90 to 100 mol%, and particularly 100 mol% of an unsaturated monomer. A monovalent salt, particularly an alkali metal salt, is added to the resulting crosslinked polymer, and the carboxyl group of the crosslinked polymer is partially neutralized to obtain an alkali metal salt. Can be obtained. When the water-absorbent resin obtained by the acid polymerization & post-neutralization method is used as the particulate water-absorbing agent of the present invention, it becomes possible to obtain a particulate absorber having high absorbability and excellent stability to urine. .

  In addition, in the acid polymerization & post-neutralization method, “other monomer” can be used together with acrylic acid as necessary, similarly to the above-described polymerization method (6). In addition, the details of “other monomer”, “crosslinkable monomer (internal crosslinking agent)”, “polymerization initiator”, addition amount, and the like are described in (3), (4), and (5) above. It is the same as the contents of. In addition, in the acid polymerization & post-neutralization method, the concentration of the whole unsaturated monomer (acrylic acid + other monomer) when using a solvent is not particularly limited, but is usually 5 to 40%. The concentration is as low as mass%, preferably 10 to 30 mass%. Moreover, the polymerization start temperature is low temperature and it is set as 10-25 degreeC aqueous solution.

In the acid polymerization & post-neutralization method, the cross-linked polymer after polymerization is essentially neutralized. Alkali metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide) are used as alkali metal compounds used to neutralize the acid groups in the resulting crosslinked polymer and partially convert them to alkali metal bases. Etc.), alkali metal carbonates (sodium carbonate, sodium bicarbonate, etc.). In addition, amines such as ammonia, alkanolamine, and ammonium carbonate may be used. Sodium salt and potassium salt are preferable from the viewpoint of the performance of the water-absorbing resin to be obtained, industrial availability, safety and the like. In the present acid polymerization & post-neutralization method, 50 to 90 mol%, preferably 60 to 80 mol% of the acid groups in the crosslinked polymer are converted into alkali metal salts by a neutralization reaction with an alkali metal compound. As a method for neutralizing the cross-linked polymer obtained by polymerization with an alkali metal compound, an aqueous solution of an alkali metal compound is obtained while polymerizing using a solvent while cutting the obtained gel polymer into pieces of about 1 cm ³ or less. And the gel is further kneaded with a kneader or meat chopper. Further, in obtaining the particulate water-absorbing agent of the present invention, the neutralization temperature is preferably 50 to 100 ° C., more preferably 60 to 90 ° C., and neutralization is performed according to claim 1 of US Pat. No. 6,187,872. Preferably, the neutralization index (specified by the degree of neutralization of 200 particles) is 10 or less, indicating uniformity.

(B) A method of adding a chain transfer agent (for example, <Production Example 2>)
In the method for producing a particulate water-absorbing agent of the present invention, a chain transfer agent may be used as necessary during polymerization. The water-absorbing resin produced from the crosslinked polymer obtained by polymerizing in the presence of the water-soluble chain transfer agent in addition to the unsaturated monomer, the internal cross-linking agent, and the polymerization initiator is used as the particles of the present invention. When used as a water-absorbing agent, it is possible to obtain an absorbent body having high absorbability and excellent urine stability.

  The water-soluble chain transfer agent used for polymerization in the present invention is not particularly limited as long as it dissolves in water or a water-soluble ethylenically unsaturated monomer, and thiols, thiolic acids, secondary alcohols, Examples include amines and hypophosphites. Specifically, one or two selected from the group consisting of mercaptoethanol, mercaptopropanol, dodecyl mercaptan, thioglycols, thiomalic acid, 3-mercaptopropionic acid, isopropanol, sodium hypophosphite, formic acid, and salts thereof. Although more than one kind is used, it is more preferable to use a hypophosphite such as sodium hypophosphite because of its effect.

  The amount of the water-soluble chain transfer agent used depends on the type of water-soluble chain transfer agent and the monomer concentration of the aqueous monomer solution, but is 0.001 to 1 mol% with respect to the total monomer, preferably 0. 0.005 to 0.3 mol%. When the amount used is less than 0.001 mol%, the amount of the internal crosslinking agent used in the present invention is not preferable because the crosslinking density is high and the absorption capacity is too low. On the other hand, if it exceeds 1 mol%, the amount of water-soluble components increases, and on the contrary, the stability of the gel decreases, which is not preferable.

(8) Drying The crosslinked polymer obtained by the polymerization method described above is obtained as a hydrogel crosslinked polymer. The obtained cross-linked polymer is pulverized, for example, in a gel state having a water content of 10% or more and less than 70% as necessary, and further dried. Drying is usually performed in a temperature range of 60 ° C to 250 ° C, preferably 100 ° C to 220 ° C, more preferably 120 ° C to 200 ° C. The drying time depends on the surface area of the polymer, the moisture content, and the type of dryer, and is selected to achieve the desired moisture content. In the present invention, the crosslinked polymer after drying is referred to as a water absorbent resin.

  The water content of the water-absorbent resin that can be used in the present invention is not particularly limited, but is a particle (powder) that exhibits fluidity even at room temperature, more preferably the water content is 0.2 to 30% by mass, and even more preferably 0. .3 to 15% by mass, particularly preferably 0.5 to 10% by mass. If the moisture content is higher than the upper limit of the above range, the water-absorbent resin will not be fluid and the production will be hindered, and the water-absorbent resin cannot be pulverized or controlled to a specific particle size distribution. There is a fear. The water content of the water-absorbent resin is defined by the amount of water contained in the water-absorbent resin, and 1 g of the water-absorbent resin is spread on an aluminum cup with a diameter of 52 mm and is subjected to airless drying at 180 ° C. for 3 hours before drying. It is defined by the ratio (%) to the mass of.

  The drying method used includes heat drying, hot air drying, vacuum drying, infrared drying, microwave drying, dehydration by azeotropy with a hydrophobic organic solvent, and high moisture content using high-temperature steam. As described above, various methods can be employed, and the method is not particularly limited.

  If the shape of the water-absorbent resin used in the present invention obtained by the above-described manufacturing method can be handled as a powder, it is spherical, fibrous, rod-like, substantially spherical, flat, irregular, granulated particle, Although it does not specifically limit etc., the particle | grains which have a porous structure, The thing of the irregular-shaped crush form obtained through the grinding | pulverization process can be used preferably.

(9) Grinding / classification, particle size control, and absorption ratio The water absorbent resin obtained in the step (8) is preferably adjusted to a specific particle size as a powder in order to obtain the particulate water absorbing agent of the present invention. The

  The water-absorbent resin preferably used for the particulate water-absorbing agent of the present invention has a mass average particle diameter of usually 150 to 600 μm, preferably 180 to 500 μm, more preferably 200 to 450 μm, and particularly preferably 220 to 430 μm. The proportion of particles less than 150 μm is controlled to 0 to 8% by mass, preferably 0 to 5% by mass, more preferably 0 to 3% by mass, and particularly preferably 0 to 1% by mass. .

  The bulk specific gravity (specified in JIS K-3362-1998) of the above water-absorbing tree, which is preferable for obtaining the particulate water-absorbing agent of the present invention, is preferably 0.40 to 0.90 g / ml, more preferably 0.8. It is adjusted in the range of 50 to 0.80 g / ml. Moreover, the particle | grains between 600-150 micrometers are preferably 90-100 mass% of the whole, More preferably, it is 95-100 mass%, More preferably, it is set as 98-100 mass%. The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.20 to 0.45, and particularly preferably 0.20 to 0.40.

  When the cross-linked polymer is produced by reverse phase suspension polymerization, the particle size may be adjusted by dispersion polymerization and dispersion drying in the form of particles. Usually, particularly in the case of aqueous solution polymerization, The particle size is adjusted to a specific particle size while controlling the mass average particle diameter D50 and the ratio of particles having a particle diameter of less than 150 μm, which are classified and contradictory. For example, in the preparation to a specific particle size in which the amount of fine particles of less than 150 μm is reduced while the mass average particle diameter D50 is reduced to 400 μm or less, a general classification such as sieving coarse particles and fine particles after pulverization is necessary. It may be removed with a device. The coarse particles removed at this time are preferably particles having a particle size of 5000 μm to 400 μm, more preferably particles having a particle size of 2000 μm to 400 μm, and still more preferably particles having a particle size of 1000 μm to 400 μm. . The fine particles removed by adjusting the particle size are preferably particles having a particle size of less than 200 μm, more preferably particles having a particle size of less than 150 μm. Although the removed coarse particles may be discarded as they are, they are generally pulverized again in the above pulverization step. Further, the removed fine particles can be reduced in loss by performing the step of enlarging the fine particles in the next item (10). Thus, the shape of the water-absorbing resin obtained by adjusting to a specific particle size through the pulverization step shows an irregularly crushed shape.

  The water-absorbent resin obtained in the step (8) is adjusted to the above particle size, but preferably has a non-pressure absorption capacity (CRC) of 30 g / g or more to physiological saline before surface crosslinking, More preferably, it is 32-70 g / g, More preferably, it is 35-65 g / g, Most preferably, it is 40-60 g / g. The absorption capacity without pressure (CRC) may be controlled by controlling the aforementioned polymerization conditions and drying conditions such as an internal cross-linking agent. In addition, since the water-absorbent resin is subjected to surface cross-linking treatment described later in order to obtain the particulate water-absorbing agent of the present invention, the absorption capacity under no pressure of the particulate water-absorbing agent of the present invention is 27 g / g or more. For this purpose, it is usually essential that the absorption capacity without pressure of the water-absorbing resin before the surface crosslinking treatment is 27 g / g or more. In the case of using an internal crosslinking agent (see US Pat. No. 5,389,722, US Pat. No. 5,532,323, etc.) in which the absorption capacity of the water-absorbent resin itself is improved by heating, it may be less than 27 g / g.

(10) Increasing the particle size of fine particles The fine particles removed by pulverization / classification and particle size control in (9) above are regenerated into larger particles or particulate aggregates and used as the water-absorbent resin used in the present invention. Can do. As a method for increasing the particle size of such fine particles, methods described in US Pat. Nos. 6,228,930, 5,264,495, 4,950,692, 5,478,879 and European Patent 844270 can be used. The regenerated water absorbent resin regenerated in this way has a substantially porous structure.

  The ratio of the regenerated water absorbent resin regenerated by this step contained in the water absorbent resin used in the present invention is preferably 0 to 50% by mass, more preferably 5 to 40% by mass, and further preferably 10 to 30% by mass. %. The regenerated water-absorbing resin regenerated by this process has the same particle size and has a larger surface area than that of non-regenerated, so that the finally obtained particulate water-absorbing agent can obtain a faster absorption rate. This is advantageous in terms of performance. As described above, generally, the recycled water-absorbing resin having a large particle size is mixed with the water-absorbing resin obtained in the above (8) drying step, and then pulverization / classification and particle size control are performed.

(11) Surface cross-linking treatment The particulate water-absorbing agent of the present invention is preferably controlled to a specific particle size and absorptivity as represented by <Production Method 1> and <Production Examples 2 to 4>, for example. The water-absorbing resin after surface crosslinking treatment obtained by further surface-crosslinking the obtained water-absorbing resin having a specific particle size and absorption capacity is included. The particulate water-absorbing agent of the present invention, for example, decreases its absorption capacity without pressure (CRC) by such surface crosslinking, preferably 95-50% of the absorption capacity without pressure (CRC) before surface crosslinking, and further 90 It is obtained by reducing it to ˜60%. In addition, what is necessary is just to adjust suitably the fall of absorption capacity | capacitance (CRC) under no pressure with the kind and quantity of a crosslinking agent, reaction temperature, time, etc.

<Surface cross-linking agent>
As the surface crosslinking agent that can be used in the surface crosslinking treatment step, a surface crosslinking agent that forms an ester bond with a carboxyl group is used. When such a cross-linking agent is not used, the following specific physical properties (absorption capacity under no pressure, absorption capacity under pressure) are difficult to achieve, and surface cross-linking agents that form generally highly safe ester bonds (preferably polyhydric alcohols) , Alkylene carbonate, oxetane compound, amino alcohol compound), depending on the other crosslinking agent, there may be a problem of the safety of the remaining crosslinking agent.

  As a surface cross-linking agent that forms an ester bond (preferably a dehydrated ester bond) with a functional group (carboxyl group) of the polycarboxylic acid-based water-absorbing resin, a cross-linking agent having a hydroxyl group in the molecule such as polyhydric alcohol or amino alcohol; Examples thereof include surface crosslinking agents that generate hydroxyl groups by ring opening such as alkylene carbonates, oxazolidinones, and oxetanes.

  Examples of such surface cross-linking agents include mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, 1,3-propanediol, 1-methyl-1,3-propanediol, 2-methyl-1,3- Propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,3 -Polyhydric alcohol compounds such as butanediol, 1,5-pentanediol, 1,6-hexanediol, meso-erythritol, D-sorbitol, 1,2-cyclohexanedimethanol; N-acyloxazolidinone, 2-oxazolidinone, etc. Oxazolidinone compounds (US Pat. No. 6,559) 239); 1,3-dioxolan-2-one (also known as ethylene carbonate), 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3 dioxolane-2- ON, 4,4-dimethyl-1,3 dioxolan-2-one, 4-ethyl-1,3 dioxolan-2-one, 4-hydroxymethyl-1,3 dioxolan-2-one, 1,3-dioxane- Alkylene carbonate compounds such as 2-one, 4-methyl-1,3-dioxan-2-one, 4,6 dimethyl-1,3-dioxan-2-one, 1,3-dioxespan-2-one (US Patent) 5409771); cyclic ureas such as 2-imidazolidinone and oxetane compounds such as 3-ethyl-3-hydroxymethyloxetane (US Patent Publication 2002/0072471); etano Triethanolamine, diethanolamine, amino alcohols compounds such as triethanolamine and the like, may be used only these one kind or in combination of two or more.

  In particular, in order to sufficiently exhibit the surface cross-linking effect while suppressing the generation of the odor component that is a feature of the present invention, the surface cross-linking agent has 3 to 6 carbon atoms and 2 hydroxyl groups contained in the molecule. It is more preferable that it is 1 or more types of surface crosslinking agents chosen from the group which consists of -3 polyhydric alcohol, amino alcohol, C3-C5 alkylene carbonate, and C2-C10 oxetane compound, More preferably, it is at least one surface cross-linking agent selected from the group consisting of 1,3-propanediol, polyethylene glycol, ethylene carbonate, 3-ethyl-3-hydroxymethyloxetane, and ethanolamine.

  The amount of the surface cross-linking agent used depends on the compounds used as the surface cross-linking agent and combinations thereof, but is preferably in the range of 0.001 to 10% by mass with respect to the water-absorbent resin, and 0.01 to 5 More preferably within the range of mass%.

  The surface cross-linking agent may further contain “other cross-linking agent”. Examples of the “other crosslinking agent” include epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamidepolyamine; Examples thereof include haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin; condensates of the polyvalent amine compounds and the haloepoxy compounds. The “other crosslinking agent” may be used in an amount of 0 to 10% by mass, further 0 to 5% by mass, and particularly 0 to 1% by mass with respect to the entire surface crosslinking agent.

<Mixing of surface cross-linking agent and heat treatment>
When performing surface crosslinking in the present invention, it is preferable to use water. At this time, although the amount of water used depends on the water content of the water-absorbing resin to be used, it is preferably in the range of 0.5 to 20% by mass, more preferably 0.5 to It is in the range of 10% by mass.

  In addition to water and the surface cross-linking agent, a hydrophilic organic solvent may be used. However, in order to avoid causing the odor of the obtained particulate water-absorbing agent, the amount used is preferably as small as possible. The amount used is preferably in the range of 0 to 10% by weight, more preferably in the range of 0 to 5% by weight, still more preferably 0 to 3% by weight, particularly preferably 0% by weight (with respect to the water-absorbent resin. It is within the range of (not substantially used). In addition, the hydrophilic organic solvent as used in this application means the organic solvent which melt | dissolves in 100 g of room temperature water 1g or more, Preferably it is 10g or more, More preferably, it is 100g or more. The boiling point of the hydrophilic organic solvent is preferably 150 ° C. or lower.

  Furthermore, in addition to the surface cross-linking agent, acid substances such as organic acids (lactic acid, citric acid, p-toluenesulfonic acid) and inorganic acids (phosphoric acid, sulfuric acid, sulfurous acid), basic substances such as caustic soda and sodium carbonate, sulfuric acid If a polyvalent metal such as aluminum is within the range where the odor level particulate water-absorbing agent of the present invention is obtained, it is 0 to 10% by weight, more preferably 0 to 5% by weight, particularly 0% to the water-absorbing resin. You may use together at about 1%.

  In the case of performing surface crosslinking in the present invention, it is preferable to mix water and / or a hydrophilic organic solvent and a surface crosslinking agent in advance, and then spray or drop-mix the aqueous solution onto the water-absorbent resin. The method is more preferred. The size of the droplets to be sprayed is preferably in the range of 0.1 to 300 μm, more preferably in the range of 0.1 to 200 μm, in terms of average particle diameter.

  The mixing device used when mixing the water-absorbent resin of the present invention and the surface cross-linking agent, water or a hydrophilic organic solvent should have a large mixing force in order to mix both uniformly and reliably. preferable. Examples of the mixing apparatus include a cylindrical mixer, a double-wall cone mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a double-arm kneader, and a pulverizing kneader. Rotating mixers, airflow mixers, turbulators, batch-type Redige mixers, continuous-type Redige mixers, and the like are suitable.

  It is preferable that the water-absorbent resin after mixing the surface cross-linking agent is heat-treated. The heating temperature (heating medium temperature or material temperature) is preferably in the range of 120 to 250 ° C, more preferably in the range of 150 to 250 ° C, and the heating time is preferably in the range of 1 minute to 2 hours. Preferable examples of the combination of the heating temperature and the heating time are 0.1 to 1.5 hours at 180 ° C. and 0.1 to 1 hour at 200 ° C.

  The apparatus for performing the heat treatment is not particularly limited as long as the apparatus can perform heat treatment so that heat is uniformly transmitted to the mixture of the surface cross-linking agent and the water absorbent resin. In order to carry out reliably, it is preferable to provide a large mixing device. Examples of the heat treatment apparatus include belt type, groove type stirring type, screw type, rotary type, disk type, kneading type, fluidized bed type, airflow type, infrared type, electron beam type dryer or heating furnace.

<Exposure to airflow>
A preferred production method of the present invention is characterized by exposure to an air stream. That is, it is preferable that the water-absorbent resin is exposed to air current during and / or after the heat treatment of the water-absorbent resin after mixing the surface crosslinking agent. The exposure of the water-absorbing resin under the airflow means circulation and replacement of the gas filled inside the heat-absorbing resin or the particulate water-absorbing agent in the heat treatment machine and / or other processes. By performing this operation, it becomes possible to remove volatile components that cause unpleasant odors generated by heat treatment at high temperatures. Examples of the gas used in the air flow include water vapor, air, nitrogen, and one or more kinds of mixed gases thereof. The supply amount of the gas is appropriately determined. Usually, a water absorbent resin or a particulate water absorbent exists. heat treatment machine and / or unit volume 1 m ³ per in other processes, 0.001~100m ³ / hr, further in the range of 0.01~10m ³ / hr. Moreover, if expressed with the linear velocity of the airflow which is another index, the linear velocity of the airflow is preferably in the range of 0.01 to 100 m / s, more preferably in the range of 0.1 to 50 m / s. Further, the exposure time is preferably in the range of 1 minute to 120 minutes, more preferably 10 minutes to 90 minutes. The airflow may be generated by blowing air or may be generated by suction. In this case, the pressure may be reduced or increased within 10%, preferably within 1%.

  When the exposure under the airflow is performed simultaneously with the heat treatment of the water absorbent resin after mixing the surface cross-linking agent, it is preferable to use the dryer or heating furnace provided with the gas supply device or the gas exhaust device. As long as the temperature setting (preferably 120 ° C. to 250 ° C.) of the hour is remarkably lowered and does not adversely affect the energy, the gas (steam, air, nitrogen, and one of these) occupying the space of the dryer or heating furnace It is preferable to replace more than one kind of mixed gas).

  In the case where the exposure under the airflow is performed in a step after the heat treatment, it is preferable that the water-absorbent resin after surface cross-linking is ventilated in the transport line or the pipe during transport. The temperature of the gas in this case may be appropriately heated or cooled, but is usually such a temperature that the volatile component causing unpleasant odor is likely to volatilize from the water absorbent resin or the particulate water absorbent. Is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, and even more preferably 70 ° C. or higher. In addition, when the temperature of the airflow to be exposed is less than 50 ° C., it is not preferable because removal of the volatile components may be difficult. Moreover, since it is performed in a step after the heat treatment, it should be set lower than 120 ° C., which is a heat treatment temperature for performing surface crosslinking.

  In addition to the effect of reducing unpleasant odor, the step of exposing to an air stream at a specific temperature is a by-product of high-temperature treatment when an alkylene carbonate compound, particularly 1,3-dioxolan-2-one, is used as a surface cross-linking agent. There is also an effect of removing ethylene glycol. Although details will be described later, since ethylene glycol is a substance that may adversely affect the human body, it is preferably reduced or removed in this step as much as possible.

  Furthermore, as another method for removing unpleasant odor, ethylene glycol, and the like, in addition to the above-described method of exposing to an air stream at a specific temperature, a method of washing the obtained water-absorbing resin or particulate water-absorbing agent after the surface crosslinking treatment Can be mentioned. For example, in order to reduce or remove substances that cause unpleasant odors, washing may be performed with a low boiling point solvent. As such a low boiling point solvent, for example, those having a boiling point of 0 ° C. or more and less than 70 ° C., more preferably 30 ° C. or more and less than 50 ° C. are preferable, and among these, acetone, dimethyl ether, methylene chloride and the like are preferable. Further, since ethylene glycol is water-soluble, water may be used in combination as long as the water absorbent resin does not swell. In addition, when washing | cleaning by this solvent is performed, the odor derived from the used solvent may remain. Therefore, it is necessary to sufficiently remove the low-boiling solvent so that the content of the alcohol-based volatile substance described later falls within a predetermined range. Examples of the method for removing the low boiling point solvent include a method of drying these with hot air as long as the performance of the obtained water absorbent resin or particulate water absorbent is not impaired.

(12) Granulation In order to obtain the particulate water-absorbing agent of the present invention, the water-absorbent resin after the surface cross-linking treatment is adjusted to a specific particle size as a powder by adding water as necessary. Further, the water to be added may contain a chelating agent, a plant component, an antibacterial agent, a water-soluble polymer, an inorganic salt, etc., which will be described later. The content of these chelating agents, plant components, antibacterial agents, water-soluble polymers and inorganic salts is such that the concentration of the aqueous solution is in the range of 0.001 to 50% by mass. Suitable granulation methods and granulation characteristics are exemplified in Japanese Patent Application No. 2004-21856.

(13) Addition of chelating agent The particulate water-absorbing agent of the present invention can contain a chelating agent, particularly a polyvalent carboxylic acid and a salt thereof.

  In particular, the above production method example 4 has a specific particle size after cross-linking polymerization of an unsaturated monomer aqueous solution containing unneutralized acrylic acid and / or a salt thereof as a main component in the presence of an internal cross-linking agent. The cross-linked polymer particles having a specific absorption capacity are further surface-cross-linked, and a chelating agent is added at the time of polymerization, before or after or simultaneously with the surface cross-linking. It can also be obtained by adding a chelating agent using Example 4.

  The chelating agent that can be used in the particulate water-absorbing agent of the present invention is preferably a rate agent having a high ion sequestering ability and chelating ability for Fe and Cu, specifically, a stability constant for Fe ions of 10 or more, preferably Is preferably 20 or more chelating agents, more preferably aminopolycarboxylic acids and salts thereof, particularly preferably aminocarboxylic acids having 3 or more carboxyl groups and salts thereof.

  Specific examples of these polycarboxylic acids include diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl etherdiaminetetraacetic acid, ethylenediaminetetraacetic acid. Examples include propionacetic acid, N-alkyl-N′-carboxymethylaspartic acid, N-alkenyl-N′-carboxymethylaspartic acid, and alkali metal salts, alkaline earth metal salts, ammonium salts, or amine salts thereof. Of these, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, N-hydroxyethylethylenediaminetriacetic acid and salts thereof are most preferable.

  In the present invention, the amount of the chelating agent, particularly the amino polyvalent carboxylic acid, is a minor component, usually 0.00001 to 10 parts by weight, preferably 0.0001 to 1 part by weight, based on 100 parts by weight of the water-absorbent resin as the main component. Part. When the amount used exceeds 10 parts by weight, not only an effect commensurate with the use cannot be obtained, but it becomes uneconomical, and problems such as a decrease in the amount of absorption occur. On the other hand, when the amount is less than 0.00001 part by weight, a sufficient addition effect cannot be obtained.

(14) Other additives In the present invention, in addition to the chelating agent described above, the following (A) plant component, (B) polyvalent metal salt of organic acid, (C) inorganic fine particles ((D) complex hydrous oxide) And (E) reducing substances and the like can be added as trace components, thereby imparting various functions to the particulate water-absorbing agent of the present invention.

  The amount of these additives (A) to (E) and (F) to be used varies depending on the purpose and additional function, but is usually 0 to 100 parts by weight per 100 parts by weight of the water-absorbent resin. The range is 10 parts by weight, preferably 0.001 to 5 parts by weight, and more preferably 0.002 to 3 parts by weight. Usually, if it is less than 0.001 part by weight, sufficient effects and additional functions cannot be obtained, and if it is 10 parts by weight or more, an effect corresponding to the amount added may not be obtained, or the absorption performance may be lowered.

(A) Plant component The particulate water-absorbing agent according to the present invention can be blended with a plant component in the above amount in order to exhibit deodorant properties. The plant component that can be used in the present invention is preferably at least one compound selected from polyphenols, flavones and the like, caffeine; at least one compound selected from tannin, tannic acid, pentaploid, gallic acid and gallic acid. Compounds and the like. Suitable plant components are exemplified in US Pat. No. 6,469,080, WO2002 / 423479, International Application No. PCT2003 / JP6751, and the like.

(B) Polyvalent metal salt The particulate water-absorbing agent according to the present invention contains a polyvalent metal salt, particularly a polyvalent metal salt of an organic acid, in the above amount in order to improve powder flowability and prevent blocking during moisture absorption. I can do it.
The polyvalent metal salt of organic acid used and the mixing method are exemplified in PCT / JP2004 / 1355, PCT / JP2004 / 1007, PCT / JP2004 / 1294, PCT / JP2004 / 9242, etc. with international application numbers, for example. Has been. The organic acid polyvalent metal salt (PCT / JP2004 / 1355) having 7 or more carbon atoms in the molecule that can be used in the present invention is preferably other than alkali metal salts such as fatty acids, petroleum acids, and polymer acids. It consists of a metal salt.

(C) Inorganic fine particles The particulate water-absorbing agent according to the present invention can be blended with inorganic fine particles, particularly water-insoluble inorganic fine particles, in order to prevent blocking during moisture absorption. Specific examples of the inorganic powder used in the present invention 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. It is done. 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 the Coulter counter method of 0.001 to 200 μm are more preferable.

(D) Composite Hydrous Oxide The particulate water-absorbing agent according to the present invention exhibits excellent moisture-absorbing fluidity (powder fluidity after the water-absorbing resin or particulate water-absorbing agent absorbs moisture), and further exhibits excellent quenching properties. In order to exhibit odor performance, a composite hydrous oxide containing zinc and silicon, or zinc and aluminum (for example, exemplified in Japanese Patent Application Nos. 2003-280373 and PCT / JP2004 / 10896) can be blended.

(E) Reducing substance The water-absorbing agent according to the present invention preferably uses a reducing substance, particularly an inorganic reducing substance, and further a sulfur-containing or oxygen-containing reducing substance in order to prevent odor and coloring. . Examples of the reducing substance used include sulfurous acid (salt) and sulfurous acid (hydrogen salt) exemplified in US Pat. Nos. 4,863,889 and 4,863,889.

(F) Others Other additives such as antibacterial agents, water-soluble polymers, water-insoluble polymers, water, and organic fine particles can be arbitrarily added as long as the particulate water-absorbing agent of the present invention is obtained.

(15) Particulate water-absorbing agent of the present invention The particulate water-absorbing agent of the present invention having the above-mentioned production method, further, production examples 1 to 4 as an example of the production method, It is. That is, the present invention is based on new findings (average particle size and fine powder amount are contradictory, specific surface cross-linking agent and specific physical properties and odor are conflicting, and five physical properties are important for actual use of absorbent articles such as paper diapers). Based on this, the particulate water-absorbing agent of the present invention is a water-absorbing agent designed and manufactured by finding that a water-absorbing agent controlled to at least 5 specific physical properties is suitable for practical use.

The particulate water-absorbing agent (first water-absorbing agent) of the present invention is a particulate water-absorbing agent mainly composed of polycarboxylic acid-based water-absorbing resin particles that are further surface-crosslinked with a surface-crosslinking agent capable of ester-bonding with a carboxyl group. And
The following (a), (b), (c), (d), (e) and (f) are satisfied.
(A) Absorption capacity without load (CRC) of 27 g / g or more in physiological saline (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa of physiological saline is 20 g / g or more (c) Mass Average particle size (D50) is 200 to 450 μm
(D) 0 to 5% by mass of particles less than 150 μm
(E) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.40.
(F) The content of the alcohol-based volatile substance volatilized from the particulate water-absorbing agent, defined as the atmospheric concentration determined by the gas detector tube, is 0 to 10 ppm.

  Hereinafter, the particulate water-absorbing agent of the present invention will be further described.

<Alcohol-based volatile substances>
The alcohol-based volatile substance referred to in the present invention is the amount of alcohol volatile substance (atmospheric concentration determined by a gas detector tube) detected by the measurement method defined in the embodiment of the present application. In particular, it is a volatile component quantified by a methanol gas detector tube.

  Alcohol-based volatile substances are volatile components that are detected and quantified with a methanol gas detector tube, and therefore are not necessarily limited to alcohols. In this application, they are defined by the total amount of volatile components in terms of alcohol. . Therefore, in some cases, volatile substances other than alcohol such as the aforementioned acetic acid, propionic acid, and residual monomer (acrylic acid) may be counted as alcohol-based volatile substances.

  In the process of examining the deodorizing performance (for example, provision of a deodorant) as an additional function of the water absorbent resin (particulate water absorbent), the present inventors surprisingly have a specific characteristic when the water absorbent resin itself swells. It has been found that it has an odor, and the odor generated when the water-absorbent resin itself swells reduces the deodorization performance, and as a result, the fact that the deodorization performance in actual use such as in a paper diaper is reduced. . And, as a result of examining and analyzing the odor of the water absorbent resin itself and the deodorizing performance in actual use in paper diapers by various methods, the odor of the water absorbent resin itself, paper diapers, etc. The present invention was completed by finding the fact that the deodorizing performance in actual use correlates very well with the atmospheric concentration measured with an alcohol detector tube, and found the critical range of such new parameters.

  The content of the (f) alcohol-based volatile substance in the particulate water-absorbing agent of the present invention is 0 to 10 ppm, preferably 0 to 8 ppm, more preferably 0 to 5 ppm, and particularly preferably 0 ppm (not detectable). Outside this range, the amount of volatilization of odorous substances causing unpleasant odors increases and the effects of the present invention are not exhibited.

<Absorption magnification>
In the conventional water-absorbing agent, the present inventor has specified a specific surface cross-linking agent (surface cross-linking agent capable of ester-bonding with a carboxyl group) and specific physical properties (high absorption capacity under pressure, high absorption capacity under no pressure) and odor (extinction). The odor performance was found to be a contradictory characteristic, but the fact that water-absorbing articles such as paper diapers with high physical properties could be obtained by solving them was found.

  That is, the absorption capacity (CRC) of the particulate water-absorbing agent of the present invention under pressure-free (a) physiological saline is 27 g / g or more, preferably 28 g / g or more, 29 g / g or more, 30 g / g or more, 33 g / g. g or more and 36 g / g or more. When the absorption capacity under no pressure is less than 27 g / g, there is a possibility that high physical properties are not exhibited when used for paper diapers and the like. Moreover, although an upper limit is not ask | required in particular, about 60 g / g is enough from the cost increase by the difficulty on manufacture.

  (B) Absorption capacity under pressure (AAP) under a load of 4.8 kPa of the particulate water-absorbing agent of the present invention is 20 g / g or more, more preferably 22 g / g or more, further preferably 24 g / g or more, particularly preferably. It is set to 26 g / g or more. When the absorption capacity under pressure is less than 20 g / g, there is a possibility that high physical properties are not exhibited when used for paper diapers and the like. Moreover, although an upper limit is not ask | required in particular, about 35 g / g is enough from the cost increase by the difficulty on manufacture.

<Particle size distribution>
In addition to the specific surface cross-linking agent, specific physical properties and odor, the average particle size and fine powder amount of the water-absorbing agent (water-absorbing resin) are also important factors for water-absorbing articles such as paper diapers with high physical properties. In addition, in the process of controlling them, it was found that the average particle size and the amount of fine powder are also contradictory properties, and it was found that water-absorbing articles such as paper diapers with high physical properties could be obtained by solving them.

  That is, the particulate water-absorbing agent of the present invention has a (c) mass-average particle diameter (D50) of 200 to 450 μm, preferably 220 to 430 μm, more preferably 250 to 400 μm, and (d) less than 150 μm. The ratio of the particles is controlled to 0 to 5% by mass, preferably 0 to 3% by mass, more preferably 0 to 1% by mass, and (e) logarithmic standard deviation (σζ) is 0.20 to 0.40. , Preferably 0.20 to 0.38, particularly preferably 0.20 to 0.35.

  In the particle size adjustment, the particle size is controlled before surface cross-linking, and after surface cross-linking, pulverization, classification and granulation are performed to obtain a specific particle size. When the particle size is out of these ranges, the effect of the present invention is not exhibited when used for a paper diaper or the like.

<Residual ethylene glycol content>
The residual ethylene glycol content (HPLC determination) of the particulate water-absorbing agent of the present invention is 0 to 40 ppm, preferably 0 to 30 ppm, more preferably 0 to 20 ppm, and particularly preferably 0 ppm (not detected). If the content of residual ethylene glycol exceeds the above range, it is not preferable because it not only causes odor but also may adversely affect the human body.

  The present inventors have found that ethylene glycol may be contained even in a water-absorbing resin that does not use ethyne glycol as a monomer or a crosslinking agent, and found that there is a safety problem due to ethylene glycol. It was. As a result of pursuing the origin of such ethylene glycol, it has been found that it is an impurity or decomposition product of the surface cross-linking agent of the raw material (particularly ethylene glycol derivative; eg, ethylene carbonate or polyethylene glycol), and in particular, the decomposition product. In addition, when alkylene carbonate (especially ethylene carbonate) is used as a surface cross-linking agent to improve physical properties (especially absorption capacity under pressure or liquid permeability under pressure), a large amount of surface cross-linking agent or reaction at high temperature is required. Therefore, even if it is a water-absorbing resin that does not use ethylene glycol as a raw material at all, or even if it uses a high-purity resin that contains substantially no ethylene glycol or ethylene glycol impurities contained in alkylene carbonate such as ethylene carbonate, It was found that ethylene glycol was produced as a by-product in the product.

  Therefore, as a preferred production method of the particulate water-absorbing agent of the present invention, not only ethylene glycol is not used at all, but also ethylene glycol and ethylene glycol impurities contained in ethylene carbonate and polyethylene glycol are reduced (for example, a purity of 98% or more, Preferably 99% or more, more preferably 99.9% or more), and by-produced ethylene glycol is removed during the production of the water-absorbent resin, preferably washing or volatilization, specifically the above-mentioned ambient temperature of 60 ° C. What is necessary is just to expose in the above airflow.

  Thus, the present invention not only increases the purity of the raw material and reduces the ethylene glycol content in the particulate water-absorbing agent, but in order to achieve high physical properties, ethylene glycol and ethylene glycol-based materials are substantially used. This is based on the finding that ethylene glycol is produced as a by-product even when a high-purity raw material (especially ethylene carbonate) having no impurities is used.

That is, the particulate water-absorbing agent (second water-absorbing agent) of the present invention is a particulate water-absorbing agent mainly composed of polycarboxylic acid-based water-absorbing resin particles that are further surface-crosslinked with a surface-crosslinking agent capable of ester-bonding with a carboxyl group. Because
The surface crosslinking agent capable of ester bonding is a surface crosslinking agent containing alkylene carbonate,
The following (a), (b), (c), (d), (e) and (g) are satisfied.
(A) Absorption capacity without load (CRC) of 27 g / g or more in physiological saline (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa of physiological saline is 20 g / g or more (c) Mass Average particle size (D50) is 200 to 450 μm
(D) 0 to 5% by mass of particles less than 150 μm
(E) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.40.
And (g) the residual ethylene glycol content (HPLC determination) in the water-absorbing agent is 0 to 40 ppm
The second water-absorbing agent preferably further satisfies the content (f) of the alcohol-based volatile substance (0 to 10 ppm) and further satisfies the physical properties (h) to (j) described later. Contains additives.

  Conventionally, when using alkylene carbonate (particularly ethylene carbonate) as a surface cross-linking agent to improve physical properties (especially absorption capacity under pressure or liquid permeability under pressure), a water-absorbing resin that does not use ethylene glycol as a raw material, The present inventor has found that even in a water-absorbent resin using a high-purity raw material having substantially no ethylene glycol, an amount of ethylene glycol far exceeding the amount of ethylene glycol as a raw material or impurities is by-produced in the final product. . Although such ethylene glycol has caused various problems as well as safety, the present invention provides a novel water-absorbing agent having no such problems.

Such a particulate water-absorbing agent is, for example, the aforementioned production method, that is, a production method of a particulate water-absorbing agent,
A step of crosslinking polymerization of an unsaturated monomer aqueous solution containing unneutralized acrylic acid and / or a salt thereof as a main component in the presence of a crosslinking agent to obtain a crosslinked polymer;
Drying the obtained cross-linked polymer, further sizing to obtain a water-absorbing resin satisfying the following (a), (b), (c) and (d);
(A) Absorption capacity (CRC) under no pressure to physiological saline is 30 g / g or more (b) Mass average particle diameter (D50) is 200 to 450 μm
(C) 0 to 8% by mass of particles less than 150 μm
(D) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.50.
A step of further heat-treating the vicinity of the surface of the water-absorbent resin with a surface cross-linking agent that forms an ester bond;
Exposing the water-absorbent resin during and / or after the heat treatment to an air flow having an atmospheric temperature of 60 ° C. or higher;
It is obtained by the manufacturing method of a particulate water absorbing agent containing. Furthermore, in this production method, it is preferable to use a surface cross-linking agent containing alkylene carbonate (particularly in the case of the second water-absorbing agent) as the surface cross-linking agent capable of ester bonding.

(16) Other characteristics of the particulate water-absorbing agent of the present invention <Second component>
The water-absorbing agent of the present invention preferably further contains an alcohol compound selected from amino alcohols, alkylene carbonates and polyhydric alcohols (excluding ethylene glycol) in addition to the main component water-absorbing resin. Since alkylene carbonate is an alcohol derivative (for example, ethylene carbonate is ethylene glycol and carbon dioxide), in the present invention, alkylene carbonate is also referred to as an alcohol compound regardless of the presence or absence of a hydroxyl group.

  By containing such an alcohol compound, the fixing property to paper diapers and the like is improved, dust of the water-absorbing agent is also prevented, and the water absorption speed is also improved. The content of the alcohol compound is 10 to 10000 ppm, preferably 20 to 5000 ppm, more preferably 30 to 3000 ppm based on the weight of the water-absorbent resin. The alcohol-based compound may be used as a surface cross-linking agent to leave a specific amount, or may be added separately. However, even if it is within the above range, if the alcohol volatile substance exceeds the range of (f), there is a risk of causing odor during swelling. It is set to be within the content range.

<Third component>
In addition to the water-absorbent resin as the main component, it is preferable to further contain a trace component selected from the above-described chelating agent, deodorant, polyvalent metal salt, and inorganic fine particles.

<Surface cross-linking agent>
The ester bondable surface crosslinking agent is preferably at least one compound selected from the group consisting of glycerin, 1,3-propanediol, ethylene carbonate, 3-ethyl-3-hydroxymethyloxetane, and ethanolamine. . The purity is preferably high in order to avoid mixing of impurities that cause odor, more preferably 93% or more, still more preferably 95% or more, and most preferably 97% or more.

<Sulfur-based volatile components>
The amount of sulfur-based volatile substances volatilized from the particulate water-absorbing agent, which is defined as the atmospheric concentration determined by the gas detector tube (h) of the particulate water-absorbing agent of the present invention, is usually 0 to 10 ppm, preferably 0 to 5 ppm. More preferably, it is 0-2 ppm, More preferably, it is 0-0.3 ppm, Especially preferably, it is 0 ppm (it cannot detect).

  When the content of the sulfur-based volatile component exceeds 10 ppm, the deodorizing action is critically lowered, which is not preferable. Such sulfur-based volatile components are presumed to be derived from decomposition or impurities of the raw material sulfur-based compounds (eg, persulfate, bisulfite), and do not use any sulfur-based compounds or reduce impurities in sulfur-based compounds (for example, (Purity 99.99% or more).

<Residual monomer>
The total content (HPLC determination) of acrylic acid, acetic acid and propionic acid in (i) the particulate water-absorbing agent of the present invention is 0 to 1000 ppm, more preferably 0 to 500 ppm, preferably 0 to 300 ppm, more preferably 0 to 200 ppm. Especially preferably, it is 0-100. When the total content exceeds 500 pm, the deodorizing action is critically lowered, which is not preferable. For this purpose, for example, the above-described polymerization may be performed using the above-described high-purity acrylic acid.

<Whiteness>
The (j) whiteness of the particulate water-absorbing agent of the present invention is represented by a lightness index L value shown by a Hunter type colorimetric color difference meter, and a value and b value showing a chromaticness index. The L value is 80 or more, the a value is preferably −3 to 3, and the b value is preferably −5 to 15. The L value is 83 or more, the a value is −2.5 to 2.5, b The value is more preferably −3 to 13, particularly preferably L value is 85 or more, a value is −2 to 2, and b value is 0 to 10.

  When the whiteness is not satisfied, it is not only unsuitable for practical use as a water-absorbing article such as a paper diaper, but it may be particularly problematic when used at a high concentration. For this purpose, for example, the above-described polymerization may be performed using the above-described high-purity acrylic acid.

<600-150 μm particles>
The particulate water-absorbing agent of the present invention has a bulk specific gravity (specified in JIS K-3362) of preferably 0.40 to 0.90 g / ml, more preferably 0.50 to 0.80 g / ml. Further, the particles (defined by standard sieve classification) existing between 600 to 150 μm particles are preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and particularly preferably 90 to 100% by mass. The When the above particle size is deviated, not only is it unsuitable for actual use as a water-absorbing article such as a paper diaper, but the deodorizing performance is also lowered. For this purpose, the above particle size control before surface cross-linking, granulation and classification after surface cross-linking are achieved.

<Vortex water absorption speed>
The absorption rate of the particulate water-absorbing agent of the present invention is 60 seconds or less, preferably 1 to 55 seconds, more preferably 2 to 50 seconds, as a vortex water absorption rate into physiological saline. When the absorption speed exceeds 60 seconds, there are cases where sufficient absorption capacity is not exhibited when a water absorbent resin or a particulate absorbent is used as the absorbent such as a paper diaper.

<Soluble content, soluble content degradation increase amount and soluble content degradation increase rate>
The hourly soluble amount of the particulate water-absorbing agent of the present invention is essentially 40% by mass or less, preferably 0.1 to 30% by mass, more preferably 0.2 to 25% by mass, and further preferably 0.3 to 20%. % By mass, particularly preferably 0.4 to 15% by mass, most preferably 0.5 to 10% by mass. When the amount of the soluble component exceeds the above upper limit range, the soluble component is eluted into the absorber at the time of water absorption, which is not preferable because the diffusibility of the liquid to the absorber such as blood or urine may be inhibited. In general, it is difficult to achieve the lower limit or less, and it is not worth the cost.

  The amount of increase in soluble matter deterioration of the particulate water-absorbing agent of the present invention is usually 0 to 15% by mass, more preferably 0 to 10% by mass, further preferably 0 to 8% by mass, and particularly preferably 0 to 5% by mass. is there. When the amount of increase in deterioration exceeds 15% by mass, the stability of the water-absorbent resin with respect to urine is insufficient, and it becomes difficult to maintain the structure as a crosslinked polymer when actually used in an absorber for a long time. There is a possibility that it is not possible to demonstrate a sufficient absorption capacity.

  The soluble component deterioration increasing ratio of the particulate water-absorbing agent of the present invention is usually 1 to 4 times, preferably 1 to 2 times, more preferably 1 to 1.5 times. When the deterioration increasing ratio exceeds 4 times, the stability of the water-absorbent resin against urine is insufficient, and it becomes difficult to maintain the structure as a crosslinked polymer when actually used in an absorbent for a long time. There is a possibility that absorption ability cannot be demonstrated. In addition, about these parameters, the measuring method is described in Japanese Patent Application No. 2004-96083.

(17) Absorber and Absorbent Article The use of the particulate water-absorbing agent of the present invention is not particularly limited, but it is preferably used in an absorber and an absorbent article, and particularly high-concentration paper in which conventional odor has been particularly problematic. The diaper (uses a large amount of water-absorbing resin per sheet) exhibits excellent absorbency.

  The absorber of the present invention is obtained using the particulate water-absorbing agent. In the present invention, the absorber is an absorbent material (for example, a sheet) molded with a particulate water-absorbing agent and, if necessary, hydrophilic fibers. When the hydrophilic fibers are zero, particles are formed on paper or nonwoven fabric. It is obtained by fixing the water-absorbing agent.

In the absorbent body of the present invention, the content (core concentration) of the particulate water-absorbing agent with respect to the total mass of the particulate water-absorbing agent and the hydrophilic fiber is high, that is, 30 to 100% by mass, preferably 40 to 100 mass. %, More preferably 50 to 100% by weight, still more preferably 60 to 100% by weight, particularly preferably 70 to 100% by weight. Such an absorber is compression-molded to a density of 0.05 to 0.50 g / cm ² and a basis weight of 10 to 1000 g / m ² . Examples of the fiber base used include hydrophilic fibers such as pulverized wood pulp, cotton linters and cross-linked cellulose fibers, rayon, cotton, wool, acetate, and vinylon. Preferably, they are airlaid.

  In the method for producing an absorbent article of the present invention, for example, an absorbent body (core) is prepared by blending or sandwiching a fiber base material and a particulate water-absorbing agent, and the core is a base material (surface sheet) having liquid permeability. ) And a liquid-impermeable base material (back sheet), and if necessary equipped with an elastic member, diffusion layer, adhesive tape, etc., absorbent articles, especially children's paper diapers, adult paper A diaper or sanitary napkin may be used.

  The particulate water-absorbing agent of the present invention exhibits excellent absorption characteristics. Specific examples of such absorbent articles include hygiene materials such as children's disposable diapers and adult disposable diapers, which have been growing rapidly in recent years, as well as children's diapers and sanitary napkins, so-called incontinence pads. Although not particularly limited, the particulate water-absorbing agent present in the absorbent article is excellent in deodorizing performance, has a small amount of leakage, has a remarkable feeling of use and dryness, and the wearer and the caregiver The burden on people can be greatly reduced.

  EXAMPLES Examples and comparative examples of the present invention will be specifically described below, but the present invention is not limited to the following examples.

  The various performances of the particulate water-absorbing agent (or water-absorbing resin) and the absorbent article were measured by the following methods. In addition, all electric devices used in the examples were used under conditions of 200 V or 100 V, 60 Hz. Further, the water-absorbing resin, the particulate water-absorbing agent and the absorbent article were used under the conditions of 25 ° C. ± 2 ° C. and relative humidity of 50% RH unless otherwise specified. Moreover, 0.90 mass% sodium chloride aqueous solution was used as physiological saline.

  In addition, as a comparison, when a comparative test is performed with a commercially available water-absorbent resin, paper diaper, or paper diaper water-absorbent resin, if moisture is absorbed in the distribution process, it is appropriately dried under reduced pressure (eg, 60 to 80 ° C. for about 16 hours). ) And the water content of the water-absorbent resin (specified by the ratio (%) of weight loss to the weight before drying when 1 g of water-absorbent resin is spread on an aluminum cup with a diameter of 52 mm and air-dried at 180 ° C. for 3 hours) What is necessary is just to compare after drying to equilibrium (around 5 mass%, 2-8 mass%). Furthermore, the reagents and instruments exemplified in the following measurement methods and examples may be appropriately replaced with equivalent products.

(A) Absorption capacity under non-pressurization with respect to physiological saline (0.90 mass% sodium chloride aqueous solution) (CRC / Cenrifuge Retention Capacity)
Particulate water-absorbing agent (or water-absorbing resin) W (g) (approx. 0.20 g) obtained in Examples and Comparative Examples described later is a non-woven bag (60 mm × 85 mm, material conforms to EDANA ERT 441.1-99) ) And then immersed in physiological saline adjusted to 25 ± 2 ° C. After 30 minutes, the bag was pulled up, drained at 250 G (250 × 9.81 m / s ² ) for 3 minutes using a centrifuge (manufactured by Kokusan Co., Ltd., model H-122 small centrifuge), Mass W ₂ (g) was measured. Moreover, the same operation was performed without using the particulate water-absorbing agent (or water-absorbing resin), and the mass W ₁ (g) at that time was measured. And from these masses W ₁ and W ₂ , the absorption capacity (g / g) was calculated according to the following formula.
Absorption capacity under no pressure (g / g) = ((mass W ₂ (g) −mass W ₁ (g)) / W (g)) − 1
(B) Absorption capacity under pressure at 4.8 kPa against physiological saline (AAP / Absorbency Against Pressure)
It was obtained in Examples and Comparative Examples described later on a metal mesh at the bottom of a plastic support cylinder having an inner diameter of 60 mm in which a 400-mesh stainless steel mesh (mesh size: 38 μm) was welded to one side (bottom) of a cylindrical section. Particulate water-absorbing agent (or water-absorbing resin) W (g) (approx. 0.90 g) is sprayed uniformly, and the outer diameter is slightly smaller than 60 mm on the wall, and no gap is formed on the wall surface with the support cylinder. A piston that does not hinder the movement was placed, and the support cylinder, the particulate water-absorbing agent (or water-absorbing resin), and the mass W ₃ (g) of the piston were measured. On this piston, a load adjusted so that a 4.8 kPa load including the piston can be uniformly applied to the particulate water-absorbing agent (or water-absorbing resin) is placed, and a complete measuring device is completed. I let you. A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a petri dish having a diameter of 150 mm, and physiological saline adjusted to 25 ± 2 ° C. was added so as to be at the same level as the upper surface of the glass filter. On top of that, a sheet of 9 cm diameter filter paper (Toyo Filter Paper Co., Ltd., No. 2) was placed so that the entire surface was wetted, and excess liquid was removed.

The set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. When the liquid level dropped from the top of the glass filter, the liquid was added to keep the liquid level constant. After 1 hour, the set of measuring devices was lifted, and the mass W ₄ (g) (the mass of the support cylinder, the swollen particulate water-absorbing agent (or water-absorbing resin), and the piston) after removing the load was measured again. And from these masses W ₃ and W ₄ , the absorption capacity under pressure (g / g) was calculated according to the following formula.

Absorption capacity under pressure (g / g) = (mass W ₄ (g) −mass W ₃ (g)) / W (g)
(C) Mass (weight) average particle diameter (D50), weight percentage of particle diameter less than 150 μm, and logarithmic standard deviation (σζ)
The water-absorbing resin or particulate water-absorbing agent obtained in Reference Examples, Examples and Comparative Examples described later is classified using JIS standard sieves of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm and 45 μm. In addition, the percentage by weight with a particle diameter of less than 150 μm was measured, and the residual percentage R of each particle size was plotted on a logarithmic probability paper. Thereby, the particle size corresponding to R = 50% by weight was read as the mass average particle size (D50). In addition, the logarithmic standard deviation (σζ) is expressed by the following equation, and the smaller the value of σζ, the narrower the particle size distribution.
σζ = 0.5 × ln (X2 / X1)
(X1 is R = 84.1% by mass, X2 is the respective particle size when 15.9% by mass)
In the classification screening, 10.00 g of a water-absorbing resin or a particulate water-absorbing agent was charged into the above-mentioned JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm), and a low-tap type sieve shaker (manufactured by Iida Seisakusho Co., Ltd.). , ES-65 type sieve shaker) for 5 minutes.

  The mass average particle diameter (D50) is a particle diameter of a standard sieve corresponding to 50% by mass of the whole particle with a standard sieve having a constant mesh as described in US Pat. No. 5,051,259.

(D) Content of alcohol-based volatile substance (ppm)
Examples and comparative examples described later in a glass petri dish (described in GENERAL CATALLOGUE A-1000 (issued in 2003) issued by Mutual Science Glass Co., Ltd., code: 305-07, outer diameter × height = 120 mm × 25 mm) 6.00 g of the obtained particulate water-absorbing agent (or water-absorbing resin) was uniformly distributed. Next, the particulate water-absorbing agent (or water-absorbing resin) is covered with one sheet of breathable and liquid-permeable heatron paper (Nangoku Pulp Co., Ltd., varieties: GSP-22) cut into a circle (diameter 116 mm) (heat In the case of non-ron paper, a non-woven fabric was used as a substitute), and the three circumferences of heatlon paper (or non-woven fabric) were fixed to the inner wall of the glass petri dish with tape (10 mm × 10 mm). Open one side of a 3L odor bag (Omi Odo Air Service Co., Ltd.), put a glass petri dish coated with particulate water absorbent (or water absorbent resin), and then open the odor bag opening with adhesive tape Closed so that there is no. After depressurizing the inside of the odor bag from the glass tube portion provided in the odor bag, 1.2 L of odorless air is injected, and subsequently, Teflon (registered trademark) is applied to the petri dish in the odor bag while preventing outside air from being mixed. Using a glass funnel equipped with a tube, 30 ml of 0.90 mass% aqueous sodium chloride solution (physiological saline) adjusted to 25 ± 2 ° C. is poured all at once, and the particulate water-absorbing agent (or water-absorbing resin) is uniformly swollen. And sealed with a silicone rubber stopper. It was swollen and allowed to stand at 37 ° C., taken out after 60 minutes, and left at room temperature. 10 minutes after standing at room temperature, the silicon rubber stopper is removed to prevent the outside air from being mixed, while the gas sampling device (manufactured by Gastec, GV-100S) and the gas detector tube (manufactured by Gastech, No. 111LL). ) Was used to measure the atmospheric concentration. And this atmospheric concentration was made into content (ppm) of the alcohol-type volatile substance which volatilizes from a water absorbing agent. In this measurement method, the gas detection tube may be discolored even if the same operation is performed using only physiological saline without using the particulate water-absorbing agent. In such a case, correction was made by subtracting the blank test detection value detected from the discolored region using only physiological saline (detection limit 2 ppm).

(E) Content of sulfur-based volatile substances (amount of sulfur-based volatile substances) (ppm)
The atmosphere concentration was measured by repeating the same operation as the measurement of (f) alcohol-based volatile substances except that (No. 4LT, manufactured by Gastec Co., Ltd.) was used as the gas detection tube. And this atmospheric concentration was made into the amount (ppm) of sulfur type volatile substances which volatilize from a water absorbing agent. In this measurement method, the gas detection tube may be discolored even if the same operation is performed using only physiological saline without using the particulate water-absorbing agent. In such a case, correction was made by subtracting the blank test detection value detected from the discoloration region using only physiological saline (detection limit 0.1 ppm).

(F) Residual monomer content (ppm)
500 mg of a particulate water-absorbing agent (or water-absorbing resin) obtained in Examples and Comparative Examples described later is dispersed in 1 L of ion-exchanged water and is 1 hour with a cylindrical rotor having a length of 40 mm and a diameter of 8 mm (8 mmφ). The swollen gel was filtered after stirring. By analyzing the residual monomer of the obtained filtrate by liquid chromatography, the residual monomer of the particulate water-absorbing agent (or water-absorbing resin) was quantified.

(G) Residual ethylene glycol content 2 g of the particulate water-absorbing agent was added to 2 ml of methanol aqueous solution (water: methanol = 1: 2 mixing ratio) and allowed to stand for 10 minutes, and then 48 ml of methanol was added to the ultrasonic generator. Rinse with vibration using After rinsing, the methanol solution was separated by filtration, and 30 ml of the solution was evaporated to dryness with an evaporator. The obtained dried product was dissolved again in 3 ml of an aqueous phosphoric acid carrier solution to obtain a residual ethylene glycol measurement sample. The obtained measurement sample was analyzed by liquid chromatography to quantify the residual ethylene glycol content of the particulate water-absorbing agent.

(H) Whiteness The brightness index L value, chromaticness index a value, and b value were determined using a Hunter-type colorimetric color difference meter.

(I) Absorption rate evaluation (Vortex method)
To 1000 parts by weight of physiological saline prepared in advance, Food Blue No. 1 Brilliant Blue = 0.02 part by weight of FCF as a food additive was added, and the liquid temperature was adjusted to 30 ° C. While measuring 50 ml of the physiological saline in a 100 ml beaker and stirring at 600 rpm with a cylindrical rotor having a length of 40 mm and a diameter of 8 mm (8 mmφ), the particulate water-absorbing agent obtained in Examples and Comparative Examples described later ( Alternatively, 2.0 g of water-absorbing resin) was added and the absorption rate (seconds) was measured. The end point is in accordance with the standard described in JIS K 7224 (1996) “Explanation of Water Absorption Rate Test Method for Highly Water Absorbent Resin” when the particulate water absorbent (or water absorbent resin) absorbs physiological saline. The time until the stirrer chip was covered with the test solution was measured as the absorption rate (seconds).

(J) Moisture absorption blocking rate (% by mass)
2 g of the particulate water-absorbing agent (or water-absorbing resin) obtained in the examples and comparative examples described later are uniformly sprayed on the bottom of an aluminum cup having a bottom diameter of 52 mm and a height of 22 mm, and 25 ° C. and a relative humidity of 90% in advance. It was quickly put in a thermo-hygrostat (PLATIOUS LUCIFER PL-2G manufactured by Tabai Espec) adjusted to 1 and left for 60 minutes. Thereafter, the moisture-absorbing particulate water-absorbing agent (or water-absorbing resin) is transferred to a JIS standard sieve having a diameter of 7.5 cm and an opening of 2000 μm. At this time, when the water-absorbed particulate water-absorbing agent (or water-absorbing resin) is firmly attached to the aluminum cup and cannot be transferred to a sieve, the particulate water-absorbing agent (or water-absorbing resin) in a state of moisture absorption and blocking is used. Take care not to break as much as possible, peel off and transfer to a sieve. This was immediately sieved for 8 seconds with a vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65 type, SER. No. 0501), and the weight W _{5 of the} particulate water-absorbing agent (or water-absorbing resin) remaining on the sieve. The weight W ₆ (g) of the particulate water-absorbing agent (or water-absorbing resin) that passed through (g) and the sieve was measured.
Moisture absorption blocking rate (mass%) = weight W ₅ (g) / (weight W ₅ (g) + weight W ₆ (g)) × 100
Was used to calculate the moisture absorption blocking rate (mass%). The lower the moisture absorption blocking rate, the better the moisture absorption fluidity, and the handleability of the powder is improved.

(K) Soluble component amount, soluble component deterioration increase amount and soluble component deterioration increase ratio According to the method of water soluble component and urine resistance evaluation described in the examples of Japanese Patent Application No. 2004-96083 The amount of soluble matter, the amount of increase in soluble content deterioration, and the rate of increase in soluble content deterioration were determined.

(L) Absorber performance evaluation In order to evaluate the performance of the particulate water-absorbing agent (or water-absorbing resin) obtained in Examples and Comparative Examples described later as an absorbent body (core), an absorbent body was prepared and subjected to pressure (4 (8 kPa), the core absorption was evaluated.

  First, a method for producing an absorber for evaluation was shown below.

1 part by mass of a particulate water-absorbing agent (or a water-absorbing resin) described later and 1 part by mass of pulverized wood pulp were dry-mixed using a mixer. Next, the obtained mixture was spread on a wire screen formed in 400 mesh (mesh size: 38 μm) and formed into a web having a diameter of 60 mmφ. Further, this web was pressed at a pressure of 196.14 kPa (2 kgf / cm ² ) for 1 minute to obtain an evaluation absorbent having a basis weight of about 520 g / m ² .

  Subsequently, a method for evaluating the absorption amount of the core under pressure (4.8 kPa) is shown below.

  The measurement procedure was as follows. (B) In the evaluation method of the absorption capacity under pressure (AAP) at 4.8 kPa against physiological saline, the evaluation absorbent prepared above was supported by plastic instead of the particulate water-absorbing agent. Placed on the wire mesh at the bottom of the cylinder and performed the same procedure except that the physiological saline absorption time was 10 minutes. The absorption amount after 10 minutes was the absorption amount of the core under pressure (4.8 kPa). (G).

[Production example of acrylic acid]
A commercially available acrylic acid (acrylic acid dimer 2000 ppm, acetic acid 500 ppm, propionic acid 500 ppm, p-methoxyphenol 200 ppm) acid is supplied to the bottom of a high-boiling-point impurity separation column having 50 stages of non-weired perforated plates, and the reflux ratio is adjusted. Distillation as 1, dimer composed of maleic acid and acrylic acid (acrylic acid dimer), etc., and then crystallization is carried out to further crystallize acrylic acid (acrylic acid dimer 20 ppm, acetic acid 50 ppm, propionic acid 50 ppm, furfural 1 ppm. Hereinafter, protoanemonin 1 ppm or less) was obtained, and 50 ppm of p-methoxyphenol was further added after distillation.

[Production method of aqueous solution of sodium acrylate]
According to Example 9 of US Pat. No. 5,210,298, 1390 g of the acrylic acid was neutralized at 20 to 40 ° C. using 48% caustic soda to obtain a 100% neutralized sodium acrylate aqueous solution at a concentration of 37%.

[Reference Example 1]
75 mol% obtained by mixing acrylic acid obtained in the above-mentioned acrylic acid production example, sodium acrylate aqueous solution obtained by the above-mentioned method for producing sodium acrylate aqueous solution, and deionized water using the acrylic acid 4.3 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide 9) was dissolved in 5500 g of an aqueous solution of sodium acrylate having a neutralization rate (monomer concentration 38% by mass) to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma-shaped blades, and the system was nitrogenated while maintaining the reaction solution at 30 ° C. The gas was replaced, and dissolved oxygen in the reaction solution was removed. Subsequently, while stirring the reaction solution, 28.3 g of a 10% by mass aqueous solution of sodium persulfate and 1.5 g of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. A polymerization peak temperature of 86 ° C. was exhibited 17 minutes after the start of the polymerization, and a hydrogel polymer was taken out 40 minutes after the start of the polymerization. The obtained hydrogel polymer was fragmented into particles of about 1 to 4 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried with hot air at 160 ° C. for 60 minutes. Next, the dried product was pulverized using a roll mill, and further classified and prepared with a wire mesh having an opening of 600 μm to obtain an irregularly crushed water-absorbing resin (a). Table 2 shows the particle size distribution of the water-absorbent resin (a) obtained.

[Reference Example 2]
In Reference Example 1, the dried product was pulverized using a roll mill, and further classified with a wire mesh having an opening of 850 μm to obtain an irregularly crushed water-absorbent resin (b). Table 2 shows the particle size distribution of the water-absorbent resin (b) obtained.

[Reference Example 3]
75 mol% obtained by mixing acrylic acid obtained in the above-mentioned acrylic acid production example, sodium acrylate aqueous solution obtained by the above-mentioned method for producing sodium acrylate aqueous solution, and deionized water using the acrylic acid 7.5 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide 9) was dissolved in 5500 g of an aqueous solution of sodium acrylate having a neutralization rate (monomer concentration 38% by mass) to prepare a reaction solution. Next, after degassing this reaction solution in the same manner as in Reference Example 1, the above reaction solution was supplied to the reactor of Reference Example 1, and the system was replaced with nitrogen gas while keeping the reaction solution at 30 ° C. Subsequently, while stirring the reaction solution, 28.3 g of a 10% by mass aqueous solution of sodium persulfate and 1.5 g of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. A polymerization peak temperature of 86 ° C. was exhibited 17 minutes after the start of the polymerization, and a hydrogel polymer was taken out 40 minutes after the start of the polymerization. The obtained hydrogel polymer was fragmented into particles of about 1 to 4 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried with hot air at 160 ° C. for 60 minutes. Subsequently, the dried product was pulverized using a roll mill, and further classified and prepared with a wire mesh having an opening of 600 μm, whereby an irregularly shaped water-absorbing resin (c) was obtained. Table 2 shows the particle size distribution of the water-absorbent resin (c) obtained.

[Example 1]
To 100 parts by mass of the water-absorbent resin (a) obtained in Reference Example 1, 3.4 parts by mass of an aqueous surface-crosslinking agent solution consisting of 0.2 parts by mass of ethylene carbonate, 0.2 parts by mass of glycerin and 3 parts by mass of water is sprayed. Mixed. The above mixture is heat-treated at a powder temperature of 195 ° C. for 45 minutes while replacing the gas in the upper space with outside air using a paddle type mixed heat treatment machine to obtain a surface-crosslinked water-absorbent resin (1). It was. The obtained surface-crosslinked water-absorbing resin (1) was further passed through a sieve having an aperture of 710 μm to obtain a particulate water-absorbing agent (1). Absorption capacity under pressure of particulate water-absorbing agent (1), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatile substance Tables 1 and 2 show the content, the amount of sulfur-based volatile substances, the amount of residual monomer, and the content of residual ethylene glycol.

[Example 2]
Surface cross-linking agent aqueous solution consisting of 0.2 parts by mass of ethylene carbonate, 0.3 parts by mass of 1,3-propanediol and 3 parts by mass of water to 100 parts by mass of the water absorbent resin (a) obtained in Reference Example 1. 3.5 parts by mass were spray mixed. The above mixture is heat-treated at a powder temperature of 195 ° C. for 45 minutes while replacing the gas in the upper space with outside air by using a paddle type mixed heat treatment machine to obtain a surface-crosslinked water-absorbent resin (2). It was. The obtained surface-crosslinked water-absorbing resin (2) was spray-mixed so that 2 parts by mass of the aqueous solution and 50 ppm of diethylenetriaminepentaacetic acid sodium salt were 50 ppm with respect to the surface-crosslinked water-absorbing resin (2). The obtained mixture was cured at 60 ° C. for 1 hour, and further passed through a sieve having an aperture of 710 μm to obtain a particulate water-absorbing agent (2). Absorption capacity under pressure of particulate water-absorbing agent (2), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatile substance Tables 1 and 2 show the content, the content of sulfur-based volatile components, the amount of residual monomer, and the content of residual ethylene glycol. The soluble content was 8% by mass, and the 1 hour soluble content after deterioration was 10% by mass.

[Comparative Example 1]
100 parts by mass of the water-absorbent resin (a) obtained in Reference Example 1, 0.05 part by mass of ethylene glycol diglycidyl ether, 0.3 part by mass of 1,4-butanediol, 0.5 part by mass of propylene glycol, 3 water 3.85 parts by mass of a surface crosslinking agent aqueous solution consisting of parts by mass was spray mixed. A water-absorbing resin for comparison (1) whose surface was cross-linked by heat-treating the above mixture for 45 minutes at a powder temperature of 195 ° C. while replacing the gas in the upper space with outside air using a paddle type mixed heat treatment machine Got. The obtained surface-crosslinked comparative water-absorbing resin (1) was further passed through a sieve having an aperture of 710 μm to obtain a comparative particulate water-absorbing agent (1). Absorption capacity under pressure of the particulate water absorbing agent for comparison (1), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatility Tables 1 and 2 show the substance content, sulfur-based volatile substance quantity, residual monomer quantity, and residual ethylene glycol content.

[Comparative Example 2]
To 100 parts by mass of the water-absorbent resin (a) obtained in Reference Example 1, 4.5 parts by mass of a surface cross-linking agent consisting of 0.5 parts by mass of ethylene carbonate, 2 parts by mass of water, and 2 parts by mass of ethanol were spray mixed. A comparative water-absorbent resin (2) which was subjected to surface crosslinking by heat-treating the above mixture for 45 minutes at a powder temperature of 195 ° C. in a state where the gas in the upper space was not replaced with outside air using a closed heating furnace. Got. The obtained surface-crosslinked comparative water-absorbing resin (2) was further passed through a sieve having an aperture of 710 μm to obtain a comparative particulate water-absorbing agent (2). Absorption capacity under pressure of the particulate water-absorbing agent (2) for comparison, absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcoholic volatility Tables 1 and 2 show the substance content, sulfur-based volatile substance quantity, residual monomer quantity, and residual ethylene glycol content.

[Comparative Example 3]
To 100 parts by mass of the water-absorbent resin (b) obtained in Reference Example 2, 3.4 parts by mass of an aqueous surface-crosslinking agent solution consisting of 0.2 parts by mass of ethylene carbonate, 0.2 parts by mass of glycerin and 3 parts by mass of water is sprayed. Mixed. A water-absorbing resin for comparison (3), which was subjected to a heat treatment for 45 minutes at a powder temperature of 195 ° C. while the gas in the upper space was replaced with the outside air by using a paddle type mixed heat treatment machine (3) Got. The obtained surface-crosslinked comparative water-absorbing resin (3) was further passed through a sieve having an aperture of 850 μm to obtain a comparative particulate water-absorbing agent (3). Absorption capacity under pressure of the particulate water-absorbing agent (3) for comparison, absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatility Tables 1 and 2 show the substance content, sulfur-based volatile substance quantity, residual monomer quantity, and residual ethylene glycol content.

Example 3
A surface cross-linking agent comprising 100 parts by mass of the water-absorbent resin (c) obtained in Reference Example 3, 0.2 parts by mass of ethylene carbonate, 0.3 parts by mass of 1,3-propanediol, and 3 parts by mass of water. 3.5 parts by mass of the aqueous solution was spray mixed. The above mixture is heat-treated at a powder temperature of 200 ° C. for 45 minutes while replacing the gas in the upper space with outside air using a paddle type mixed heat treatment machine to obtain a surface-crosslinked water-absorbent resin (3). It was. The obtained surface-crosslinked water-absorbent resin (3) is spray-mixed with 2 parts by weight of water, the resulting mixture is cured at 60 ° C. for 1 hour, and further passed through a sieve having an aperture of 710 μm to form a particulate form. A water absorbing agent (3) was obtained. Absorption capacity under pressure of particulate water-absorbing agent (3), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatile substance Tables 1 and 2 show the content, the amount of sulfur-based volatile substances, the amount of residual monomer, and the content of residual ethylene glycol.

Example 4
To 100 parts by mass of the water-absorbent resin (c) obtained in Reference Example 3, 3.4 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.2 parts by mass of ethylene carbonate, 0.2 parts by mass of glycerin, and 3 parts by mass of water. Spray mixed. The above mixture is heat-treated at a powder temperature of 200 ° C. for 45 minutes while replacing the gas in the upper space with outside air using a paddle type mixed heat treatment machine to obtain a surface-crosslinked water-absorbent resin (4). It was. The obtained surface-crosslinked water-absorbing resin (4) was further passed through a sieve having an aperture of 710 μm to obtain a particulate water-absorbing agent (4). Absorption capacity under pressure of particulate water-absorbing agent (4), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatile substance Tables 1 and 2 show the content, the amount of sulfur-based volatile substances, the amount of residual monomer, and the content of residual ethylene glycol.

[Comparative Example 4]
Surface cross-linking agent aqueous solution 3 comprising 100 parts by mass of the water absorbent resin (c) obtained in Reference Example 3, 0.3 parts by mass of 1,4 butanediol, 0.5 parts by mass of propylene glycol, and 3 parts by mass of water. 8 parts by mass were spray mixed. A water-absorbing resin for comparison (4) whose surface was cross-linked by heat-treating the above mixture for 45 minutes at a powder temperature of 200 ° C. while replacing the gas in the upper space with outside air using a paddle type mixed heat treatment machine. Got. The obtained surface-crosslinked water-absorbing resin (4) was further passed through a sieve having an aperture of 710 μm to obtain a particulate water-absorbing agent (4). Absorption capacity without pressure of the particulate water absorbing agent for comparison (4), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcoholic volatility Tables 1 and 2 show the substance content, sulfur-based volatile substance quantity, residual monomer quantity, and residual ethylene glycol content.

Example 5
Particulate water-absorbing agent (5) obtained by adding and mixing (dry blending) 0.1 parts by mass of particulate calcium stearate (manufactured by Kanto Chemical Co., Inc.) to the particulate water-absorbing agent (2) obtained in Example 2 Was obtained. Table 3 shows the results obtained by evaluating the absorption capacity without load of the particulate water-absorbing agent (5) obtained, the absorption capacity under pressure at 4.8 kPa, the absorption rate evaluation, and the moisture absorption blocking rate. Note that the particle size distribution, L value indicating whiteness, a value and b value, alcohol volatile substance content, sulfur volatile substance content, residual monomer content, and residual ethylene glycol content are in the form of particles before addition. It was the same as the water absorbing agent (2).

Example 6
To the particulate water-absorbing agent (3) obtained in Example 3, 0.3 part by mass of fine-particle silicon dioxide / Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.) was added and mixed (dry blended) to form a particulate water-absorbing agent ( 6) was obtained. Table 3 shows the results obtained by evaluating the absorption capacity without load of the obtained particulate water-absorbing agent (6), the absorption capacity under pressure at 4.8 kPa, the absorption rate evaluation, and the moisture absorption blocking rate. Note that the particle size distribution, L value indicating whiteness, a value and b value, alcohol volatile substance content, sulfur volatile substance content, residual monomer content, and residual ethylene glycol content are in the form of particles before addition. It was the same as the water absorbing agent (3).

  For comparison, the comparative particulate water-absorbing agents (1) and (4) were also measured in the same manner and shown in Table 3.

Example 7
In order to evaluate the performance of the particulate water-absorbing agent (1) obtained in Example 1 as an absorbent, an absorbent for evaluation (1) was prepared according to the method for evaluating the performance of (1) absorbent. The absorption amount of the core under pressure (4.8 kPa) of the obtained absorbent body for evaluation (1) was measured and shown in Table 4.

  Moreover, the odor sensory test by 10 adult test subjects was done for the absorber after evaluation. In the evaluation method, scores were reported according to the subject's degree of discomfort from no unpleasant odor (0 points) to unpleasant odors (5 points), and the average was taken as the odor point. The lower the odor point, the less unpleasant odor. The results are also shown in Table 4.

[Examples 8 to 10]
In Example 7, instead of the particulate water-absorbing agent (1), the same operation was performed except that the particulate water-absorbing agents (3), (5) and (6) were used, and the evaluation absorbers (2) to ( 4) was obtained. The obtained absorber for evaluation was evaluated in the same manner as in Example 7, and the results are shown in Table 4.

Example 11
To 100 parts by mass of the water absorbent resin (c) obtained in Reference Example 3, 0.2 parts by mass of 3-ethyl-3-hydroxymethyloxetane, 0.3 parts by mass of 1,3-propanediol, and 3 parts by mass of water 3.5 parts by mass of a surface cross-linking agent aqueous solution consisting of The resulting mixture was heat-treated for 45 minutes at a powder temperature of 200 ° C. while replacing the gas in the upper space with the outside air using a paddle type mixed heat treatment machine to obtain a surface-crosslinked water-absorbent resin (7). Obtained. The surface-crosslinked water-absorbing resin (7) was further passed through a sieve having an aperture of 710 μm to obtain a particulate water-absorbing agent (7). Absorption capacity under pressure of particulate water-absorbing agent (7), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatile substance Tables 1 and 2 show the content, the amount of sulfur-based volatile substances, the amount of residual monomer, and the content of residual ethylene glycol.

Example 12
In Comparative Example 2, using a paddle type mixed heat treatment machine instead of a closed heating furnace, after heat treatment for 45 minutes at a powder temperature of 195 ° C. while replacing the gas in the upper space with the outside, The heat-treated product was exposed for 60 minutes in a stream of heated air at a linear velocity of 1 m / s and 90 ° C. to obtain a water absorbent resin (8). Absorption capacity under pressure of the surface-crosslinked water absorbent resin (8) obtained, absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, Tables 1 and 2 show the contents of alcohol-based volatile substances, sulfur-based volatile substances, residual monomers, and residual ethylene glycol contents.

Example 13
An aqueous solution composed of 0.1 parts by mass of ethanolamine and 1.9 parts by mass of water was spray mixed with the water absorbent resin (4) obtained in Example 4. The obtained mixture was cured by exposure for 60 minutes in a stream of heated air at a linear speed of 1 m / s and 90 ° C., and further passed through a sieve having an aperture of 710 μm to obtain a particulate water-absorbing agent (9). . Absorption capacity under pressure of particulate water-absorbing agent (9), absorption capacity under pressure at 4.8 kPa, absorption rate evaluation, particle size distribution, L value indicating whiteness, a value and b value, alcohol-based volatile substance Tables 1 and 2 show the content, the amount of sulfur-based volatile substances, the amount of residual monomer, and the content of residual ethylene glycol.

[Comparative Examples 5 to 8]
In place of the particulate water-absorbing agent (1) used in Example 7, the same operation was performed except that the comparative particulate water-absorbing agents (1) to (4) were used, and the comparative absorbers (1) to ( 4) was obtained. The obtained absorber for evaluation was evaluated in the same manner as in Example 7, and the results are shown in Table 4.

  As shown in Tables 1 and 2, the particulate water-absorbing agent of the present invention does not contain alcohol-based volatile components or sulfur-based volatile components, and has no odor from gel in a swollen state, absorption capacity under no pressure, absorption under pressure It has excellent magnification and absorption rate, and if necessary, by adding inorganic fine particles, polyvalent metal salts, deodorants, etc., it has high caking resistance (low blocking rate, described in Table 3), urine resistance, Also shows odor performance.

  In the absorbent article (Paper diaper in Table 4) using the particulate water-absorbing agent of the present invention, a high-performance absorbent article (paper diaper) with a small return amount is provided.

  The present invention relates to a particulate water-absorbing agent mainly composed of a water-absorbing resin. More specifically, the present invention relates to a particulate water-absorbing agent that does not generate an odor during actual use in an absorbent article such as a paper diaper and exhibits an excellent absorption capacity.

  When the particulate water-absorbing agent obtained according to the present invention is used in a thin absorbent body such as a paper diaper, it is possible to provide an absorbent body having a very excellent absorption performance and less unpleasant odor compared to a conventional absorbent body. There is an effect that you can.

Claims (13)

A particulate water-absorbing agent mainly composed of polycarboxylic acid-based water-absorbing resin particles surface-crosslinked with a surface cross-linking agent capable of ester bonding with a carboxyl group,
The polycarboxylic acid-based water-absorbent resin particles are partially neutralized polyacrylic acid polymers obtained by cross-linking an unsaturated monomer having acrylic acid and / or a salt thereof (neutralized product) as a main component. And
A particulate water-absorbing agent satisfying the following (a), (b), (c), (d), (e) and (f),
(A) Absorption capacity without load (CRC) of 27 g / g or more in physiological saline (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa of physiological saline is 20 g / g or more (c) Mass Average particle size (D50) is 200 to 450 μm
(D) 0-5 mass% of particles less than 150 μm in the particulate water-absorbing agent
(E) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.40.
(F) The content of the alcohol-based volatile substance volatilized from the particulate water-absorbing agent, defined as the atmospheric concentration determined by the alcohol detector tube, is 0 to 10 ppm. A particulate water-absorbing agent mainly composed of polycarboxylic acid-based water-absorbing resin particles surface-crosslinked with a surface cross-linking agent capable of ester bonding with a carboxyl group,
The polycarboxylic acid-based water-absorbent resin particles are partially neutralized polyacrylic acid polymers obtained by cross-linking an unsaturated monomer having acrylic acid and / or a salt thereof (neutralized product) as a main component. And
The surface cross-linking agent is a surface cross-linking agent containing alkylene carbonate,
A particulate water-absorbing agent satisfying the following (a), (b), (c), (d), (e) and (g),
(A) Absorption capacity without load (CRC) of 27 g / g or more in physiological saline (b) Absorption capacity under pressure (AAP) under load of 4.8 kPa of physiological saline is 20 g / g or more (c) Mass Average particle size (D50) is 200 to 450 μm
(D) 0-5 mass% of particles less than 150 μm in the particulate water-absorbing agent
(E) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.40.
(G) The residual ethylene glycol content (HPLC determination) in the particulate water-absorbing agent is 0 to 40 ppm.   The particulate water-absorbing agent according to claim 1 or 2, further comprising an alcohol compound selected from amino alcohol, alkylene carbonate and polyhydric alcohol (excluding ethylene glycol).   The particulate water-absorbing agent according to any one of claims 1 to 3, further comprising a component selected from the group consisting of a chelating agent, a deodorant, a polyvalent metal salt, and inorganic fine particles.   The surface crosslinking agent is at least one compound selected from the group consisting of glycerin, 1,3-propanediol, ethylene carbonate, 3-ethyl-3-hydroxymethyloxetane, and ethanolamine. 5. The particulate water-absorbing agent according to any one of 4 above.   Furthermore, (h) The sulfur-type volatile substance amount volatilized from a particulate water-absorbing agent prescribed | regulated as atmospheric concentration quantified with a gas detector tube is 0-10 ppm, The any one of Claims 1-5. Particulate water-absorbing agent.   Furthermore, (i) The particulate water absorbing agent of any one of Claims 1-6 whose total content (HPLC fixed_quantity | quantitative_assay) of acrylic acid, an acetic acid, and propionic acid in a particulate water absorbing agent is 0-1000 ppm. .   Furthermore, (j) the brightness index L value indicated by a Hunter-type colorimetric color difference meter as whiteness is 80 or more, the a value indicating the chromaticness index is -2 to 2.5, and the b value is 0 to 0. The particulate water-absorbing agent according to any one of claims 1 to 7, which is 4.   It is an absorber shape | molded from the particulate water absorbing agent and hydrophilic fiber of any one of Claims 1-8, Comprising: This particulate water absorbing agent with respect to the total mass of a particulate water absorbing agent and a hydrophilic fiber Is a high-concentration absorber having 30 to 100% by mass (100% by mass is a particulate water-absorbing agent alone). A method for producing the particulate water-absorbing agent according to any one of claims 1 to 8,
A step of obtaining a crosslinked polymer by crosslinking polymerization of an unsaturated monomer aqueous solution containing unneutralized acrylic acid and / or a salt thereof as a main component in the presence of an internal crosslinking agent;
Drying the obtained crosslinked polymer, sizing and obtaining a water-absorbing resin satisfying the following (a), (b), (c) and (d);
(A) Absorption capacity without load (CRC) in physiological saline is 30 g / g or more (b) Mass average particle diameter (D50) is 200 to 450 μm
(C) 0 to 8% by mass of particles less than 150 μm
(D) Logarithmic standard deviation (σζ) of particle size distribution is 0.20 to 0.50.
A step of further heat-treating the vicinity of the surface of the water-absorbent resin after adding a surface cross-linking agent that forms an ester bond;
Exposing the water-absorbent resin during and / or after the heat treatment to an air flow having an atmospheric temperature of 60 ° C. or higher;
A method for producing a particulate water-absorbing agent.   The unneutralized acrylic acid is 10 to 200 ppm of methoxyphenol, 0 to 10,000 ppm of total acetic acid and propionic acid, 0 to 1000 ppm of acrylic acid dimer, 0 to 10 ppm of furfural, and protoanemo based on the mass of the acrylic acid. The method for producing a particulate water-absorbing agent according to claim 10, wherein one or more compounds selected from 0 to 10 ppm of nin are acrylic acid within a corresponding range.   The method for producing a particulate water absorbing agent according to claim 10 or 11, wherein the surface crosslinking agent is a surface crosslinking agent containing an alkylene carbonate.   The method according to claim 12, wherein the amount of ethylene glycol contained in the alkylene carbonate is 0.1% by mass or less based on the mass of the alkylene carbonate.