WO2017200085A1 - Water-absorbing resin particles, process for producing same, and absorbent object and absorbent article both comprising or including same - Google Patents

Abstract

Provided are water-absorbing resin particles which retain the intact water-absorbing performance and can attain both absorption rate and liquid permeation through swelled gel particles. The present invention is: water-absorbing resin particles which comprise a crosslinked polymer (A) of a monomer composition that comprises an internal crosslinking agent (b) and a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) upon hydrolysis, and which further include an inorganic acid (c) containing one or more protons and having a pKa of 4.5-10, and which have a water-soluble content of 20% or less; a process for producing the water-absorbing resin particles which includes a step in which the surface of resin particles (B) that comprise the crosslinked polymer (A) and the inorganic acid (c) and that have a water content of 3-8 wt% is crosslinked with a surface-crosslinking agent (d); and an absorbent object comprising the water-absorbing resin particles.

Description

Water-absorbent resin particles, method for producing the same, absorbent body containing the same, and absorbent article

The present invention relates to water-absorbent resin particles, a method for producing the same, an absorbent body containing the same, and an absorbent article.

For sanitary materials such as disposable diapers, sanitary napkins and incontinence pads, absorbent polymers (mainly absorbent fibers such as pulp and acrylic acid (salt)) as absorbents (Super Absorbent Polymer is also abbreviated as SAP) )) Is widely used. From the viewpoint of improving QOL (Quality Of Life) in recent years, the demand for these sanitary materials is shifting to lighter and thinner ones. Along with this, it has been desired to reduce the amount of hydrophilic fibers used. Therefore, SAP itself is required to fulfill the role that hydrophilic fibers have played in the absorber. For example, an important function of diapers is leakage reduction due to high-speed absorption of urine. The conventional absorbent has a high urine absorption rate due to the presence of a physical space (called “Void”) between the bulky hydrophilic fibers. However, in the above-described absorbent with a high SAP ratio, the SAP particles are not spaced apart. In order to form a filling structure with a small amount of voids, there is a problem that the absorption rate of urine is low with little Void.

In addition, conventional absorbent bodies have high urine diffusibility due to capillary action due to hydrophilic fibers, and can diffuse urine throughout the absorbent body, whereas absorbent bodies with a high SAP ratio have a capillary force. In addition to the low urine diffusion inhibition of urine by swelling gel, the urine diffusibility in the absorber is significantly reduced. This decrease in diffusibility is a serious cause of diaper leakage coupled with the decrease in the absorption rate described above.

As a method for preventing a decrease in diffusibility, the surface of the water-absorbent resin particles obtained by polymerization is cross-linked with an aqueous solution containing a specific organic cross-linking agent compound and an aqueous solution containing a specific cation to deform the surface of the swollen gel. There is known a method of efficiently forming a gel gap by suppressing (for example, see Patent Document 1).

However, in the method described in Patent Document 1, although the absorption rate of the absorbent body and the liquid permeability between the swollen gels are improved, the water-absorbing performance of the water-absorbent resin is lowered due to the increase in the cross-linking density. This may interfere with long-term use of the product and prevention of fog during use.

International Publication No. 00/53664 Pamphlet

An object of the present invention is to provide water-absorbing resin particles capable of achieving both absorption speed and liquid permeability between swollen gels without reducing water-absorbing performance, and a method for producing the same.

The first aspect of the present invention is the crosslinking of a monomer composition comprising a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal crosslinking agent (b). A water-absorbing resin particle containing a polymer (A) and an inorganic acid (c) having a proton of pKa 4.5 to 10 and having a water-soluble content of 20% by weight or less; and the water-absorbing resin particle An absorbent body comprising the water-absorbent resin particles and a fibrous material; an absorbent article comprising the absorbent body.
The second aspect of the present invention is a method for producing the water-absorbent resin particles of the first aspect of the present invention, which comprises the crosslinked polymer (A) and an inorganic acid (c) having a proton of pKa 4.5 to 10 In this production method, the resin particles (B) are subjected to surface crosslinking with a surface crosslinking agent (d) at a water content of 3 to 8% by weight.
The third aspect of the present invention is the crosslinking of a monomer composition comprising a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal crosslinking agent (b). A water-absorbent resin comprising a step of surface-crosslinking the surface of a resin particle (B) containing a polymer (A) and phosphoric acid (c1) and / or phosphate (c2) with a surface-crosslinking agent (d) A method for producing particles. In the above production method, the centrifugal retention amount of physiological saline is 29 to 40 g / g, the gel bed permeability at 0 psi swelling pressure is 40 darcies or more, and the absorption rate under no load measured by the Demand Wettability test method Is 15 seconds or less, and it is suitable as a method for producing water-absorbent resin particles having an absorption rate measured by the Vortex test method of 50 seconds or less.

The water-absorbent resin particles produced by the water-absorbent resin particles of the present invention and the production method of the present invention (also referred to as the production method of the present invention without distinguishing the second invention and the third invention), The above-described configuration solves the above-described problems and has excellent characteristics described in detail below. Among them, thin hygienic materials and absorbent articles with a high water-absorbing resin ratio because they have a high absorption rate despite having a high absorption rate and excellent liquid permeability between swollen gels. When applied to, it exhibits stable and excellent absorption performance (for example, liquid diffusibility, absorption speed, and amount of absorption) in any state, and is less prone to fog.

In the water-absorbent resin particles of the present invention and the production method of the present invention (hereinafter also referred to as the present invention), the water-soluble vinyl monomer (a1) is not particularly limited and is publicly known (for example, Japanese Patent No. 3648553). No. 0007-0023, vinyl monomers having at least one water-soluble substituent and an ethylenically unsaturated group (for example, anionic vinyl monomers, nonionic vinyl monomers, cationic vinyl monomers), JP, Anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers disclosed in paragraphs 0009 to 0024 of 2003-16583, and carboxy groups disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982 , Sulfo group, phosphono group, hydroxyl group, carbamoyl group, amino And vinyl monomers such as vinyl monomers) may be used with at least one selected from the group consisting of ammonio group.

The vinyl monomer (a2) (hereinafter also referred to as a hydrolyzable vinyl monomer (a2)) that becomes a water-soluble vinyl monomer (a2) by hydrolysis is not particularly limited, and is publicly known (for example, Patent No. 3648553, 0024- A vinyl monomer having at least one hydrolyzable substituent which becomes a water-soluble substituent by hydrolysis as disclosed in paragraph 0025, at least one of those disclosed in paragraphs 0052 to 0055 of JP-A-2005-75982; Vinyl monomers of hydrolyzable substituents (vinyl monomers having 1,3-oxo-2-oxapropylene (—CO—O—CO—) group, acyl group, cyano group, etc.) can be used. The water-soluble vinyl monomer is a concept well known to those skilled in the art, but when expressed using numerical values, for example, it means a vinyl monomer that dissolves at least 100 g in 100 g of water at 25 ° C. Hydrolysis is a concept well-known to those skilled in the art. More specifically, hydrolysis means, for example, hydrolysis by the action of water and, if necessary, a catalyst (an acid or a base). Hydrolysis of the hydrolyzable vinyl monomer (a2) may be performed either during polymerization, after polymerization, or both of them, but from the viewpoint of the absorption performance of the resulting water-absorbent resin composition, it is preferably after polymerization.

Of these, the water-soluble vinyl monomer (a1) is preferable from the viewpoint of absorption characteristics. The water-soluble vinyl monomer (a1) is preferably an anionic vinyl monomer, more preferably a carboxy (salt) group, a sulfo (salt) group, an amino group, a carbamoyl group, an ammonio group, or a mono-, di- or tri-alkyl. It is a vinyl monomer having an ammonio group. Among these, a vinyl monomer having a carboxy (salt) group or a carbamoyl group is more preferable, (meth) acrylic acid (salt) and (meth) acrylamide, more preferably (meth) acrylic acid (salt), Most preferred is acrylic acid (salt).

The “carboxy (salt) group” means “carboxy group” or “carboxylate group”, and the “sulfo (salt) group” means “sulfo group” or “sulfonate group”. Moreover, (meth) acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylate, and (meth) acrylamide means acrylamide or methacrylamide. Examples of the salt include an alkali metal (such as lithium, sodium and potassium) salt, an alkaline earth metal (such as magnesium and calcium) salt or an ammonium (NH ₄ ) salt. Among these salts, alkali metal salts and ammonium salts are preferable from the viewpoint of absorption characteristics and the like, more preferably alkali metal salts, and particularly preferably sodium salts.

When the monomer composition contains either the water-soluble vinyl monomer (a1) or the hydrolyzable vinyl monomer (a2) as a constituent component, one type may be used alone, or two or more types as necessary. May be a component. The same applies when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent components. In the case where the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent components, the molar ratio (a1 / a2) of these is preferably 75/25 to 99/1, more preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, and most preferably 91/9 to 92/8. Within this range, the absorption performance is further improved.

The monomer composition may contain, in addition to the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), other vinyl monomers (a3) copolymerizable therewith. it can.

Other vinyl monomers (a3) that can be copolymerized are not particularly limited, and are known (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, Japanese Patent Laid-Open No. 2003-165883, Hydrophobic vinyl monomers (vinyl monomers disclosed in paragraph 0058 of JP-A-2005-75982) can be used, and the following vinyl monomers (i) to (iii) can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted products of styrene such as vinylnaphthalene and dichlorostyrene.
(Ii) C2-C20 aliphatic ethylene monomer Alkene [ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.]; and alkadiene [butadiene, isoprene, etc.], etc.
(Iii) Cycloaliphatic ethylene monomer having 5 to 15 carbon atoms Monoethylenically unsaturated monomer [pinene, limonene, indene and the like]; Polyethylene vinyl polymerizable monomer [cyclopentadiene, bicyclopentadiene, ethylidene norbornene and the like] and the like.

When the other vinyl monomer (a3) is used as a constituent component, the content (mol%) of the other vinyl monomer (a3) unit is that of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. Based on the number of moles, it is preferably 0.01 to 5, more preferably 0.05 to 3, then preferably 0.08 to 2, particularly preferably 0.1 to 1.5. In spite of the above, it is most preferable that the content of other vinyl monomer (a3) units is 0 mol% from the viewpoint of absorption characteristics and the like.

The internal cross-linking agent (b) is not particularly limited, and is known (for example, a cross-linking agent having two or more ethylenically unsaturated groups disclosed in Japanese Patent No. 3648553, paragraphs 0031 to 0034, a water-soluble substituent, Cross-linking agent having at least one functional group capable of reacting and having at least one ethylenically unsaturated group, cross-linking agent having at least two functional groups capable of reacting with a water-soluble substituent, and JP-A-2003-165883 The crosslinking agent having two or more ethylenically unsaturated groups, the crosslinking agent having an ethylenically unsaturated group and a reactive functional group, and two or more reactive substituents disclosed in paragraphs 0028 to 0031 of the publication Cross-linking agent, cross-linkable vinyl monomer disclosed in paragraph 0059 of JP-A-2005-75982, stages 0015 to 0016 of JP-A-2005-95759 Crosslinking agent of the crosslinkable vinyl monomer) as disclosed in can be used. Of these, from the viewpoint of absorption characteristics, a crosslinking agent having two or more ethylenically unsaturated groups is preferable, more preferably a poly (meth) allyl ether of a polyol having 2 to 10 carbon atoms, particularly preferably triallyl cyanide. Nurate, triallyl isocyanurate, tetraallyloxyethane, trimethylolpropane diallyl ether and pentaerythritol triallyl ether, most preferably pentaerythritol triallyl ether.

The content (% by weight) of the internal crosslinking agent (b) contained in the monomer composition is such that other vinyl monomers (a3) of the water-soluble vinyl monomer (a1) and hydrolyzable vinyl monomer (a2) are also used. In this case, the total weight of (a1) to (a3) is preferably 0.05 to 0.7, more preferably 0.1 to 0.6, and particularly preferably 0.15 to 0.5. is there. Within this range, the water-soluble content is reduced and the absorption characteristics are further improved.

As a method for producing the crosslinked polymer (A), a known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization method and the like; JP-A-55-133413, etc.) using the monomer composition described above, It can be produced in the same manner as known reverse phase suspension polymerization (Japanese Patent Publication No. 54-30710, Japanese Patent Application Laid-Open No. 56-26909, Japanese Patent Application Laid-Open No. 1-5808, etc.). Among the polymerization methods, the solution polymerization method is preferable, and an aqueous solution polymerization method is particularly preferable because it is not necessary to use an organic solvent and is advantageous in terms of production cost.

At the time of polymerization, a polymerization control agent represented by a chain transfer agent may be used in combination as necessary. Specific examples thereof include sodium hypophosphite, sodium phosphite, alkyl mercaptan, alkyl halide, thiol. Examples include carbonyl compounds. These polymerization control agents may be used alone or in combination of two or more thereof. The amount (% by weight) of the polymerization control agent used is that of the water-soluble vinyl monomer (a1) and hydrolyzable vinyl monomer (a2), and when other vinyl monomers (a3) are also used (a1) to (a3). Based on the total weight, 0.0005 to 5 is preferable, and 0.001 to 2 is more preferable.

When a solvent (organic solvent, water, etc.) is used for the polymerization, it is preferable to distill off the solvent after the polymerization. When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably based on the weight of the crosslinked polymer (A). Is 0-3, most preferably 0-1. Within this range, the absorption performance of the water-absorbent resin particles is further improved.

When water is contained in the solvent, the water content (% by weight) after the distillation is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, based on the weight of the crosslinked polymer (A). Most preferably, it is 3-8. Within this range, the absorption performance and the breakability of the crosslinked polymer (A) after drying are further improved.

A water-containing gel composed of the crosslinked polymer (A) and water is obtained by an aqueous solution polymerization method. The obtained water-containing gel can be chopped and used as necessary. The size (longest diameter) of the gel after chopping is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the later-described solvent (including water) can be easily distilled off, which is preferable.

Shredding can be performed by a known method, and can be performed using a shredding device (for example, a bex mill, rubber chopper, pharma mill, mincing machine, impact crusher, and roll crusher).

In addition, the content of the organic solvent and the water content are infrared moisture measuring devices (JE400 manufactured by KETT Co., Ltd.): 120 ± 5 ° C., 30 minutes, atmospheric humidity before heating 50 ± 10% RH, lamp specification 100V, 40W) is obtained from the weight loss of the measurement sample before and after heating.

As a method of distilling off the solvent (including water), a method of distilling (drying) with hot air at a temperature of 80 to 230 ° C., a thin film drying method using a drum dryer heated to 100 to 230 ° C., (heating ) Vacuum drying, freeze drying, infrared drying, decantation, filtration, etc. can be applied.

In the present invention, the crosslinked polymer (A) may be one kind or a mixture of two or more kinds.

In the first invention, the inorganic acid (c) has a proton with a pKa of 4.5 to 10, and from the viewpoint of absorption characteristics, the pKa of the proton is preferably 5.5 to 8.5, more preferably 6.5 to 7.5.
Examples of the inorganic acid (c) include phosphoric acid, phosphorous acid, tungstophosphoric acid, polyphosphoric acid, triphosphoric acid, cyclophosphoric acid, carbonic acid, sulfuric acid, sulfurous acid, hypochlorous acid, silicic acid and the like and salts thereof.
The salt is not particularly limited, and specific examples include salts with metals, ammonium, alkylammonium and the like. Specific examples of the metal include metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these metals, metals belonging to Group 1A, 3A or 3B are more preferable, and sodium and potassium belonging to Group 1A are most preferable from the viewpoint of absorption characteristics and the like.

The inorganic acid (c) is preferably an inorganic acid that is difficult to function as a chain transfer agent or a salt thereof from the viewpoint of uniformity of surface cross-linking, absorption characteristics, and the like, and the inorganic acid (c) is strong as a chain transfer agent. When functioning, the molecular weight decreases and the water-soluble component increases, which is not preferable from the viewpoint of uniformity of surface cross-linking and absorption characteristics. As preferred agents, phosphoric acid (c1), phosphorous acid, tungstophosphoric acid, polyphosphoric acid, triphosphoric acid, cyclophosphoric acid and salts thereof are more preferred, and phosphoric acid (c1), phosphorous acid and their salts are particularly preferred. A salt, most preferably phosphoric acid (c1) and a salt thereof (c2). Phosphoric acid (c1) is orthophosphoric acid, and phosphate (c2) includes alkali metal phosphates (trilithium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, phosphoric acid Potassium dihydrogen, dipotassium hydrogen phosphate and tripotassium phosphate), alkaline earth metal phosphates (monomagnesium phosphate, dimagnesium phosphate, trimagnesium phosphate, calcium dihydrogen phosphate, monohydrogen phosphate) Calcium, tricalcium phosphate, etc.), ammonium phosphate (NH ₄ ) salts (ammonium dihydrogen phosphate, diammonium hydrogen phosphate, etc.) and the like. From the viewpoint of absorption characteristics, alkali metal phosphates and phosphoric acid An ammonium salt is preferable, an alkali metal phosphate is more preferable, and a sodium phosphate is particularly preferable.

The content (% by weight) of the inorganic acid (c) contained in the water-absorbent resin particles of the first present invention is such that the water-soluble vinyl monomer (a1) and the vinyl monomer (a1) by hydrolysis become a water-soluble vinyl monomer (a1) ( a2), when other vinyl monomer (a3) is also used, it is 0.004 to 2.4 based on the total weight of (a1) to (a3) and the internal crosslinking agent (b), more preferably 0.01 to 1.2. Within this range, the absorption characteristics are further improved.
The content (% by weight) of the inorganic acid (c) contained in the water-absorbent resin particles of the first invention is the total weight of the inorganic acid (c) used and the weight of the crosslinked polymer (A) or the crosslinked polymer. It can be calculated using the weight of the monomer composition used to obtain (A).
In addition, when the hydrate of inorganic acid (c) is used, the weight of inorganic acid (c) shall not contain hydration water.

When the water-absorbent resin particles contain phosphoric acid (c1) and phosphate (c2), the content (% by weight) of phosphoric acid (c1) and phosphate (c2) depends on the cross-linked polymer (A). When the water-soluble vinyl monomer (a1), hydrolyzable vinyl monomer (a2), and other vinyl monomer (a3) used are also used, the total weight of (a1) to (a3) and the internal crosslinking agent (b) Based on this, 0.008 to 1.4 is preferable, and 0.01 to 1.2 is more preferable. Within this range, the absorption characteristics are further improved.
The contents (wt%) of phosphoric acid (c1) and phosphate (c2) contained in the water-absorbent resin particles can be calculated in the same manner as described above. Similarly to the above, when a hydrate is used, the weight of phosphoric acid (c1) and phosphate (c2) does not include hydration water.

The water-absorbent resin particles of the first present invention are not limited as long as the crosslinked polymer (A) and the inorganic acid (c) are contained, and a preferable method for obtaining the water-absorbent resin particles is a water-soluble resin particle. A monomer composition comprising, as essential constituents, a water-soluble vinyl monomer (a1) by hydrolysis and a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) and an internal cross-linking agent (b) as inorganic constituents (c) (Hereinafter also referred to as a polymerization method), a method of mixing a hydrogel containing the crosslinked polymer (A) and an inorganic acid (c) (hereinafter also referred to as a mixing method). ).
The water-absorbent resin particles obtained by the polymerization method and the mixing method are preferable from the viewpoint of absorption characteristics because the inorganic acid (c) exists without being unevenly distributed inside the crosslinked polymer (A).

The said polymerization method can be performed by superposing | polymerizing by the said method coexisting the inorganic acid (c) with the said monomer composition. In particular, a method of performing aqueous solution polymerization in the presence of the inorganic acid (c) is preferable.
When the inorganic acid (c) is polymerized by the above-mentioned method in the presence of the monomer composition, the hydrate can be used as the inorganic acid (c).

The mixing method can be performed by mixing an inorganic acid (c) with the water-containing gel obtained by aqueous polymerization of the monomer composition.
The water-containing gel and the inorganic acid (c) can be mixed by mixing the water-containing gel and the inorganic acid (c) with a known stirring and mixing device (Henschel mixer, planetary mixer, universal mixer, etc.). Moreover, when cutting a water-containing gel with a cutting device, it can also carry out by putting a water-containing gel and an inorganic acid (c) into a cutting device simultaneously.
When the inorganic acid (c) is mixed with the hydrated gel, the hydrate can be used as the inorganic acid (c).

The product (hydrogel) obtained by the polymerization method or the mixing method can be used for the production of water-absorbent resin particles by pulverization after drying. The pulverization method is not particularly limited, and a pulverizer (for example, a hammer pulverizer, an impact pulverizer, a roll pulverizer, and a shet airflow pulverizer) can be used. After pulverization, if necessary, the particle size can be adjusted by sieving or the like.

When the particle size is adjusted by sieving, the weight average particle diameter (μm) of the water-absorbent resin particles obtained after sieving is preferably 100 to 800, more preferably 200 to 700, and then preferably 250. To 600, particularly preferably 300 to 500, most preferably 350 to 450. Within this range, the absorption performance is further improved.

The weight average particle size was measured using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook, 6th edition (Mac Glow Hill Book, 1984). , Page 21). That is, JIS standard sieves are combined in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 m and 45 μm, and a tray from the top. About 50 g of the measured particles are put in the uppermost screen and shaken for 5 minutes with a low-tap test sieve shaker. Weigh the measured particles on each sieve and the pan, and calculate the weight fraction of the particles on each sieve with the total as 100% by weight. This value is logarithmic probability paper (the horizontal axis is the sieve aperture (particle size ), The vertical axis is plotted in terms of weight fraction), and then a line connecting the points is drawn to determine the particle diameter corresponding to the weight fraction of 50% by weight, which is defined as the weight average particle diameter.

In addition, the content of the fine particles contained in the water absorbent resin particles is 106 μm or less (preferably 150 μm or less) of the fine particles contained in the water absorbent resin particles from the viewpoint of absorption performance. Based on this, it is preferably 3% by weight or less, more preferably 1% by weight or less. The content of the fine particles can be determined using a plot created when determining the above weight average particle diameter.

The apparent density (unit: g / ml, the same applies hereinafter) of the water-absorbent resin particles is preferably 0.54 to 0.70, more preferably 0.56 to 0.65, and particularly preferably 0.58 to 0.00. 60. Within this range, the absorption performance is further improved. The apparent density is measured at 25 ° C. according to JIS K7365: 1999.

The shape of the water-absorbent resin particles is not particularly limited, and examples thereof include an irregularly crushed shape, a flake shape, a pearl shape, and a rice grain shape. Among these, from the viewpoint of good entanglement with the fibrous material in the use of paper diapers and the like and no fear of dropping off from the fibrous material, an irregular crushed shape is preferable.

The water-absorbent resin particles of the first present invention preferably have a surface cross-linked structure with a surface cross-linking agent (d).

As the surface cross-linking agent (d), known ones (polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridines, polyvalent isocyanates and the like described in JP-A No. 59-189103) can be used. Of these surface cross-linking agents (d), a polyvalent glycidyl compound is preferred from the viewpoint of economy and absorption characteristics, and ethylene glycol diglycidyl ether is most preferred.

The amount (% by weight) of the surface cross-linking agent (d) is not particularly limited because it can be variously changed depending on the type of the surface cross-linking agent (d), the cross-linking conditions, the target performance, etc. When using other vinyl monomers (a3) of the water-soluble vinyl monomer (a1), hydrolyzable vinyl monomer (a2) and internal cross-linking agent (b) used in the crosslinked polymer (A) from the viewpoint, etc. Based on the total weight of (a1) to (a3), 0.03 to 0.5 is preferable, more preferably 0.05 to 0.3, and particularly preferably 0.08 to 0.2.

In the present invention, the water-absorbent resin particles are reduced in the amount of water-soluble polymer that is a water-soluble polymer by adjusting the amount of internal cross-linking agent added and, if applicable, the amount of water before surface cross-linking. It is desirable. In the first invention, the water-absorbent resin particles have a water-soluble content reduced to 20% or less. In the first aspect of the present invention, if the water-soluble content exceeds 20%, the soluble content is not eluted at the time of water absorption, gel blocking occurs, and the liquid permeability and water absorption capacity are adversely affected. From the viewpoint of liquid permeability, it is preferably 10% or less, more preferably 5% or less. The water-soluble component can be measured by the following method.

<Water-soluble content>
In a 300 ml plastic container, 100 g of 0.9 wt% saline is weighed, 1.2 g of the water-absorbent resin composition is added to the saline, sealed with a wrap, and stirred for 3 hours by rotating a stirrer at 500 rpm. A water-soluble extract from which the water-soluble component of the water-absorbent resin composition is extracted is prepared. And this water-soluble extract is filtered using the filter paper made from ADVANTEC Toyo Co., Ltd. (product name; JIS P 3801, No. 2, thickness 0.26 mm, reserved particle diameter 5 μm). Then, 20 g of the obtained filtrate is weighed, and 30 g of ion exchange water is added to obtain a measurement solution. Hereinafter, a method for measuring the water-soluble content of the water-absorbent resin composition for the measurement solution will be described.

First, a N / 50 KOH aqueous solution is titrated with respect to a blank test solution obtained by adding 30 g of ion-exchanged water to 20 g of 0.9 wt% saline until the pH of the saline becomes 10. Then, a titration amount ([W _{KOH, b} ] ml) of an N / 50 aqueous KOH solution necessary for the pH of the 0.9 wt% saline solution to be 10 is obtained. Then, titration of N / 20 HCl aqueous solution is performed until the pH of the saline solution becomes 2.7. Then, a titration amount of N / 10 HCl aqueous solution ([W _{HCl, b} ] ml) necessary for the pH of the 0.9 wt% saline solution to be 2.7 is obtained.

Next, the above measurement solution is subjected to the same operation as the above titration operation, and a titration amount of N / 50 KOH aqueous solution necessary for the measurement solution to have a pH of 10 ([W _{KOH, S} ] ml). A method for obtaining a titration amount ([W _{HCl, S} ] ml) of an HCl aqueous solution of N / 10 necessary for the measurement solution to have a pH of 2.7 will be described in detail.

For example, in the case of a water absorbent resin composition comprising acrylic acid and its sodium salt, the amount of _{unneutralized} acrylic acid substance n _COOH is
n _COOH (mol) = (W _{KOH, S} −W _{KOH, b} ) × (1/50) / 1000 × 5
In addition, the total acrylic acid substance amount n _tot is
n _tot (mol) = (W _{HCl, S} −W _{HCl, b} ) × (1/10) / 1000 × 5
In addition, the amount of neutralized acrylic acid substance n _COONa is
n _COONa (mol) = n _tot −n _COOH
Furthermore, the weight of _{unneutralized} acrylic acid m _COOH is
m _COOH (g) = n _COOH × 72
Further, the neutralized acrylic acid material amount m _COONa is
m _COONa (g) = n _COONa x 94
Based on the above and the water content of the water-absorbent resin composition used as a sample ([W _H2O ] wt%), the water-soluble content of the water-absorbent resin composition can be calculated by the following calculation formula.
Water-soluble amount (% by weight) = {(m _COOH + m _COONa ) × 100} / {1.2 × (100−W _H2O )}

In the water-absorbent resin particles of the present invention, the centrifugal retention amount (centrifugal retention capacity: hereinafter also referred to as CRC) (g / g) is 25 or more from the viewpoint of water absorption characteristics and other physical properties. Is preferable, 27 or more is more preferable, and 29 or more is further more preferable. Further, the upper limit is preferably 40 or less, and more preferably 38 or less. CRC (g / g) can be measured by the method described later.

In the water absorbent resin particles of the present invention, the gel bed permeability (hereinafter also referred to as GBP) (darcies) at 0 psi swelling pressure of the absorbent resin particles is 5 or more from the viewpoint of water absorption characteristics and other physical properties. Is more preferable, 30 or more is more preferable, and 40 or more is still more preferable. GBP (darcies) can be measured by the method described later.

In the water-absorbent resin particles of the present invention, an absorption rate under no load (hereinafter also referred to as an absorption rate (T1)) measured by a demand wettability test method (hereinafter also referred to as a DW test) of the absorbent resin particles. Is 15 seconds or less from the viewpoint of water absorption characteristics and other physical properties. The absorption rate (T1) can be measured by the method described later.

In the water-absorbent resin particles of the present invention, the absorption rate of the absorbent resin particles measured by the Vortex test method (hereinafter also referred to as absorption rate (Vortex)) can be measured by the method described later. From the viewpoint of the relationship with other physical properties, it is 50 seconds or less.

In the method for producing resin particles according to the second aspect of the present invention, the resin particles (B) containing the crosslinked polymer (A) and the inorganic acid (c) are contained at a water content of 3 to 8% by weight. And a step of surface cross-linking with the surface cross-linking agent (d). The surface crosslinking with the surface crosslinking agent (d) preferably contains, for example, a crosslinked polymer (A) and an inorganic acid (c), for example, phosphoric acid (c1) and / or phosphate (c2). The resin particles (B) to be subjected to surface cross-linking with the surface cross-linking agent (d) can be performed. If the inorganic acid (c) is added at the time of surface cross-linking, absorption characteristics such as liquid permeability and blocking properties are inferior.

The surface cross-linking step can be performed by mixing the resin particles (B) and the surface cross-linking agent (d) and further heating, and is known (for example, Japanese Patent No. 3648553, Japanese Patent Application Laid-Open No. 2003-165883). , Surface crosslinking treatment methods described in JP-A-2005-75982 and JP-A-2005-95759.

As a preferable method for the surface cross-linking step, an aqueous solution of the surface cross-linking agent (d) is sprayed on the surface of the resin particles (B) while stirring the resin particles (B), and then in a stirred state or a stationary state. A method of heating to 100 to 200 ° C. (preferably 120 ° C. to 160 ° C.) can be mentioned.
When the aqueous solution of the surface cross-linking agent (d) is sprayed on the surface of the resin particles (B), the concentration of the surface cross-linking agent (d) contained in the aqueous solution to be sprayed can be adjusted depending on the type of the surface cross-linking agent (d). However, it is preferably 0.1 to 10% by weight from the viewpoint of absorption characteristics.
The amount of the aqueous solution to be sprayed is preferably 0.5 to 15% by weight based on the weight of the resin particles (B) from the viewpoint of the uniformity of surface crosslinking.
In the step of surface cross-linking, spraying an aqueous solution of the surface cross-linking agent (d) onto the resin particles (B) under stirring is carried out by using a known fluid humidifying and mixing granulator [Flexomix (manufactured by Hosokawa Micron) and Shugi Flexomix (manufactured by Paulek Co., Ltd.) etc.] and a known powder mixer [V-type mixer, Henschel mixer and turbulizer (manufactured by Hosokawa Micron Co., Ltd.), etc.] Can be used.

Of the steps of surface cross-linking, heating to 100 to 200 ° C. in a stirred state means that the resin particles (B) sprayed with the surface cross-linking agent are mixed with a known stirrer equipped with a heating device (such as a two-arm kneader). It can carry out by stirring while heating using.
Of the step of surface cross-linking, heating to 100 to 200 ° C. in a stationary state can be performed using a known heat drying apparatus (such as a circulating dryer).
When heating to 100 to 200 ° C., the heating time is usually 3 to 60 minutes, preferably 10 to 40 minutes.

In addition, as a method of mixing the resin particles (B) and the surface crosslinking agent (d), in addition to the method of spraying an aqueous solution of the surface crosslinking agent (d), the resin particles (B) are mixed with the surface crosslinking agent (d). A method of immersing in an aqueous solution can also be used. When the resin particles (B) are immersed in an aqueous solution of the surface cross-linking agent (d), the surface cross-linking can be performed by a method of heating with stirring thereafter.

In the production method of the present invention, after the surface cross-linking step, the particle size may be adjusted by further sieving. The average particle size of the particles obtained by adjusting the particle size is preferably 100 to 600 μm, more preferably 200 to 500 μm. The content of fine particles is preferably small, the content of particles of 100 μm or less is preferably 3% by weight or less, and the content of particles of 150 μm or less is more preferably 3% by weight or less.

In the production method of the present invention, a step of adjusting the water content of the resin particles (B) containing the crosslinked polymer (A) and the inorganic acid (c) to 3 to 8% by weight before the surface crosslinking step. Can have. By subjecting the resin particles having an appropriate amount of water to surface crosslinking in the presence of the inorganic acid (c), water-absorbing resin particles exhibiting high water absorption characteristics can be obtained. The water content of the resin particles after the moisture adjustment step is preferably 4 to 8% by weight, particularly preferably 6 to 8% by weight, from the viewpoint of water absorption characteristics, based on the weight of the resin particles (B).

It is preferable to adjust the moisture content by adjusting temperature conditions and process time during the drying process and the pulverization process. More preferably, from the viewpoint of productivity, by adjusting the drying temperature and the drying speed in the drying step, the target moisture content is adjusted.

The water-absorbent resin particles of the present invention may further contain a polyvalent metal salt (e). For this reason, the production method of the present invention may further include a step of mixing with the polyvalent metal salt (e). good. By containing the polyvalent metal salt (e), the blocking resistance and liquid permeability of the water-absorbent resin particles are improved. Examples of the polyvalent metal salt (e) include salts of at least one metal selected from the group consisting of magnesium, calcium, zirconium, aluminum, and titanium with the above inorganic acid or organic acid.
As the polyvalent metal salt (e), an inorganic acid salt of aluminum and an inorganic acid salt of titanium are preferable from the viewpoint of availability and solubility, and aluminum sulfate, aluminum chloride, potassium aluminum sulfate and sulfuric acid are more preferable. Sodium aluminum, particularly preferred are aluminum sulfate and sodium aluminum sulfate, and most preferred is sodium aluminum sulfate. These may be used alone or in combination of two or more.

The use amount (% by weight) of the polyvalent metal salt (e) is preferably 0.05 to 5, more preferably 0.1 to 100 parts by weight with respect to 100 parts by weight of the water-absorbent resin from the viewpoints of absorption performance and blocking resistance. 3, particularly preferably 0.2 to 2.

When the production method of the present invention includes a step of mixing with the polyvalent metal salt (e), the step of mixing with the polyvalent metal salt (e) is performed before the surface cross-linking step, after the surface cross-linking step, And at the same time as the surface cross-linking step.

The mixing method of the polyvalent metal salt (e) includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulator, a nauter mixer, a double-arm kneader, a fluid mixer, and a V mixer. And a uniform mixing method using a known mixing device such as a machine, a minced mixer, a ribbon mixer, a fluid mixer, an airflow mixer, a rotating disk mixer, a conical blender and a roll mixer.
When mixing before or after the surface cross-linking step, the temperature during mixing is not particularly limited, but is preferably 10 to 150 ° C, more preferably 20 to 100 ° C, and particularly preferably 25 to 80 ° C.
When mixing at the same time as the surface cross-linking step, the temperature at the time of mixing is not particularly limited, but can be performed under the same conditions as the step of surface cross-linking with the surface cross-linking agent (d).
In the production method of the present invention, the particle size may be further adjusted after the step of mixing with the polyvalent metal salt (e).

The water-absorbing resin particles of the present invention may further contain water-insoluble inorganic particles (f). For this reason, the production method of the present invention further mixes the water-insoluble inorganic particles (f) and the water-absorbing resin particles. The process of carrying out may be included. By mixing the water-insoluble inorganic particles (f), the surface of the water-absorbent resin particles is surface-treated with the water-insoluble inorganic particles (f), thereby improving the blocking resistance and liquid permeability of the water-absorbent resin particles.

Examples of the water-insoluble inorganic particles (f) include colloidal silica, fumed silica, clay and talc. Colloidal silica and silica are preferable and more preferable from the viewpoints of availability, ease of handling, and absorption performance. Is colloidal silica. One type of water-insoluble inorganic particles (f) may be used alone, or two or more types may be used in combination.

The amount (% by weight) of the water-insoluble inorganic particles (f) used is preferably from 0.01 to 5, more preferably from 0.05 to 1, particularly preferably from 100 parts by weight of the water-absorbent resin from the viewpoint of absorption performance. Is 0.1 to 0.5.

When the water-insoluble inorganic particles (f) are contained, it is preferable to mix the water-absorbing resin particles and the water-insoluble inorganic particles (f), and the mixing is performed in the same manner as the mixing of the polyvalent metal salt (e). The conditions are the same.

After the step of mixing the water-insoluble inorganic particles (f), a step of adjusting the particle size of the water-absorbent resin particles may be performed. The particle size adjustment can be performed in the same manner as the particle size adjustment of the resin particles (B), and the particle size after the particle size adjustment is also the same.

The production method of the present invention has a centrifugal retention amount (centrifugation retention capacity: hereinafter referred to as CRC) of 29 to 40 g / g, and gel bed permeability (hereinafter also referred to as GBP) at 0 psi swelling pressure. ) Is 40 darcies or more, the absorption rate under no load (hereinafter, also referred to as absorption rate (T1)) measured by the demand wettability test method (hereinafter also referred to as DW test) is 15 seconds or less, Water-absorbing resin particles having an absorption rate (hereinafter also referred to as absorption rate (Vortex)) measured by the Vortex test method of 50 seconds or less can be produced.

Centrifugal holding capacity, gel bed permeability at 0 psi swelling pressure, absorption rate under no load measured by Demand Wettability test method and absorption rate measured by Vortex test method are 25 ± 2 ° C., humidity 50 ± 10% Each of the rooms is measured by the following method. The temperature of the physiological saline used is adjusted to 25 ° C. ± 2 ° C. in advance.

<Amount of centrifugal saline retained>
Measured according to the CRC test method described in Japanese Patent No. 5236668, and 0.200 g of water-absorbent resin particles were freely added to physiological saline (0.9 mass% sodium chloride aqueous solution) for 30 minutes under no pressure. Swell, then drain with a centrifuge and measure the amount of saline (unit: [g / g]) retained by the water-absorbent resin particles after draining. In addition, it means that the water absorption performance of a water absorbing resin particle is so high that CRC is high.

<Gel bed permeability test at swelling pressure at 0 psi>
Measured according to the GBP test method at 0 psi swelling pressure described in Japanese Patent No. 5236668 (unit: [darcies]). In addition, it means that it is excellent in the absorption rate of a water absorbing resin particle, and the liquid permeability between swelling gel, so that GBP is high.

<Absorption rate under no load measured in Demand Wettability test>
When measured by the DW method described in JP-A-2014-005472 using 0.50 g of water-absorbent resin particles and physiological saline, the amount of absorption (ml / g) from the start of water absorption is 2.0. The time required to become the absorption rate under no load measured in the Demand Wettability test. Note that the DW test is to determine the ability to suck up the water-absorbent resin under no load on a measurement table connected to a burette and a conduit.

<Absorption rate measured by Vortex test>
Necessary until 2.000 g of water-absorbent resin particles have absorbed 50 g of physiological saline stirred at 600 rpm in a 100 ml tall beaker with a flat bottom as defined in JIS R 3503. The time (unit: second) is measured according to JIS K7224-1996, and the absorption rate is measured by the Vortex test.

The water-absorbent resin particles of the present invention may contain, as necessary, additives (for example, known preservatives, fungicides, antibacterial agents, oxidation agents (described in JP-A No. 2003-225565 and JP-A No. 2006-131767, etc.)) Inhibitors, ultraviolet absorbers, colorants, fragrances, deodorants, liquid permeability improvers, organic fibrous materials, etc.) can also be used. When these additives are used, the content (% by weight) of the additive is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably based on the weight of the resin particles (B). Is 0.05 to 1, most preferably 0.1 to 0.5.

The water-absorbent resin particles of the present invention may have a physiological saline pH of 5.80 to 7.20 when the water-absorbent resin particles are contained at 0.5% by weight based on the weight of the physiological saline. Preferably, it is 5.80 to 6.50. Within this range, it is preferable because it becomes weakly acidic and is less prone to fog.

The water-absorbent resin particles, which are the water-absorbent resin particles of the present invention, exhibit stable and excellent absorption performance (liquid diffusivity, absorption speed, and amount of absorption) in any state regardless of load or non-load. In addition, the anti-fogging property of the absorbent article is improved.

The apparent density (g / ml) of the water absorbent resin particles of the present invention is preferably 0.54 to 0.70, more preferably 0.56 to 0.65, and particularly preferably 0.58 to 0.60. . Within this range, the anti-fogging property of the absorbent article is further improved. The apparent density can be measured in the same manner as in the case of the resin particles (B).

The shape of the water-absorbent resin particles is not particularly limited, and examples thereof include an irregularly crushed shape, a flake shape, a pearl shape, and a rice grain shape. Among these, from the viewpoint of good entanglement with the fibrous material in the use of paper diapers and the like and no fear of dropping off from the fibrous material, an irregular crushed shape is preferable.

The water-absorbent resin particles obtained by the method for producing the water-absorbent resin particles of the present invention or the water-absorbent resin particles of the present invention (hereinafter also referred to simply as the water-absorbent resin particles or the water-absorbent resin particles of the present invention, without distinguishing both). ) May be used alone as an absorber, or may be used together with other materials as an absorber.
The other material is preferably a fibrous material. The structure and production method of the absorbent when used together with the fibrous material are the same as those known (JP 2003-225565 A, JP 2006-131767 A, JP 2005-097569 A, etc.). is there.

Preferred as the fibrous material are cellulose fibers, organic synthetic fibers, and a mixture of cellulose fibers and organic synthetic fibers.

Examples of the cellulosic fibers include natural fibers such as fluff pulp, and cellulosic chemical fibers such as viscose rayon, acetate, and cupra. There are no particular restrictions on the raw materials (conifers, hardwoods, etc.), production methods (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching methods, etc. of this cellulose-based natural fiber.

Examples of organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and heat-fusible composite fibers (the above fibers having different melting points). And a fiber obtained by compounding at least two of the above into a sheath core type, an eccentric type, a parallel type, and the like, a fiber obtained by blending at least two kinds of the above fibers, and a fiber obtained by modifying the surface layer of the above fibers).

Among these fibrous materials, preferred are cellulose-based natural fibers, polypropylene-based fibers, polyethylene-based fibers, polyester-based fibers, heat-fusible conjugate fibers, and mixed fibers thereof, and more preferable are obtained. The fluff pulp, the heat-fusible conjugate fiber, and the mixed fiber thereof are preferable in that the water-absorbing agent has excellent shape retention after water absorption.

The length and thickness of the fibrous material are not particularly limited and can be suitably used as long as the length is 1 to 200 mm and the thickness is in the range of 0.1 to 100 denier. The shape is not particularly limited as long as it is fibrous, and examples thereof include a thin cylindrical shape, a split yarn shape, a staple shape, a filament shape, and a web shape.

In the case of the absorbent body containing the water absorbent resin particles and the fibrous material, the weight ratio of the water absorbent resin particles to the fibrous material (weight of the water absorbent resin particles / weight of the fibrous material) is 40/60. Is preferably 90/10, more preferably 70 / 30-80 / 20.

The absorber of the present invention contains the water-absorbing resin particles described above. The absorber of the present invention may be an absorber containing water-absorbing resin particles alone, or may be an absorber containing water-absorbing resin particles and a fibrous material. The absorbent body of the present invention can be used as an absorbent article. Absorbent articles include not only sanitary articles such as disposable diapers and sanitary napkins, but also various uses such as absorption and retention of various aqueous liquids, gelling agents (eg, pet urine absorbent, urine gel for portable toilets) Fresheners for fruits and vegetables, drip absorbent for meat and seafood, cold insulation, disposable warmers, gelling agents for batteries, water retention agents for plants and soil, anti-condensation agents, water-stopping materials, packing materials, artificial snow Etc.). The manufacturing method and the like of the absorbent article are the same as known ones (described in JP 2003-225565 A, JP 2006-131767 A, JP 2005-097569 A, etc.).

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<Example 1>
Acrylic acid (manufactured by Mitsubishi Chemical Corporation, purity 100%, the same shall apply hereinafter) 135 parts, pentaerythritol triallyl ether (manufactured by Daiso Corporation, the same shall apply hereinafter) 0.68 parts, sodium bisulfite (Wako Pure Chemical Industries, Ltd.) 0.02 part (manufactured by Co., Ltd., the same applies hereinafter) and 363 parts deionized water were kept at 3 ° C. with stirring and mixing. After flowing nitrogen into this mixture to reduce the dissolved oxygen amount to 1 ppm or less, 0.5 part of 1% aqueous hydrogen peroxide solution, 1 part of 2% aqueous ascorbic acid solution and 2% 2,2′-azobisamidinopropane Polymerization was initiated by adding and mixing 0.3 parts of a dihydrochloride aqueous solution. After the temperature of the mixture reached 80 ° C., polymerization was carried out at 80 ± 2 ° C. for about 5 hours to obtain a hydrogel (1).

Next, while chopping the entire amount of the obtained hydrogel (1) with a mincing machine (12VR-400K manufactured by ROYAL), adding and mixing and neutralizing 180 parts of a 30% aqueous sodium hydroxide solution, Obtained. Further, the chopped gel was dried with a ventilation band dryer (140 ° C., wind speed 2 m / sec) to obtain a dried product. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster Co., Ltd.) and sieved to adjust the particle size to a particle size range of 710 to 150 μm to obtain resin particles (B1) having a moisture content of 6%. .

2 parts aqueous solution of ethylene glycol diglycidyl ether (manufactured by Nagase Kasei Kogyo Co., Ltd., Denacol EX-810) while stirring 100 parts of the obtained resin particles (B1) at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm) 4 parts are added while being sprayed and mixed, and the mixture is allowed to stand at 140 ° C. for 30 minutes in an air circulation dryer (manufactured by Tabai Espec Co., Ltd.) for surface cross-linking so that the water-absorbent resin particles (1) of the present invention Got.

<Example 2>
“Pentaerythritol triallyl ether 0.68 part” was changed to “Pentaerythritol 0.2 part” and “Sodium hydrogen sulfite 0.02 part” was changed to “Phosphoric acid (manufactured by Kanto Chemical Co., Inc., purity 85%, and so on) ”1.9 parts”, “water content 6%” is changed to “water content 8%”, and “ethylene glycol diglycidyl ether 4% 2% aqueous solution” is changed to “ethylene glycol diglycidyl”. The water-absorbent resin particles (2) of the present invention were obtained in the same manner as in Example 1 except for changing to "6.6 parts of a 3% aqueous solution of ether".

<Example 3>
“Pentaerythritol triallyl ether 0.68 parts” was changed to “Pentaerythritol triallyl ether 0.82 parts”, “Sodium hydrogen sulfite 0.02 parts” was changed to “Sodium hydrogen sulfite 0.008 parts”, “Moisture amount 6%” was changed to “Moisture amount 4%” and “2 parts aqueous solution of ethylene glycol diglycidyl ether 4 parts” was changed to “5 parts 1% aqueous solution of ethylene glycol diglycidyl ether” Except for the above, water-absorbent resin particles (3) of the present invention were obtained in the same manner as Example 1.

<Example 4>
“Pentaerythritol triallyl ether 0.68 parts” was changed to “pentaerythritol triallyl ether 0.14 parts”, “1.9 parts phosphoric acid” was changed to “3.8 parts phosphoric acid”, “ “6%” was changed to “3% moisture” and “4 parts 2% aqueous solution of ethylene glycol diglycidyl ether” was changed to “7.4 parts 4% aqueous solution of ethylene glycol diglycidyl ether”. Except for the above, water-absorbent resin particles (4) of the present invention were obtained in the same manner as Example 2.

<Example 5>
In the same manner as in Example 1 except that “pentaerythritol triallyl ether 0.68 part” was changed to “pentaerythritol 0.95 part” and “sodium bisulfite 0.02 part” was not added. Gel (2) was obtained.

Next, the water-containing gel (2) is shredded with a mincing machine (12VR-400K manufactured by ROYAL), mixed and neutralized by adding 180 parts of a 30% aqueous sodium hydroxide solution, followed by fluorophosphoric acid (Sigma) -1.9 parts of 1% aqueous solution (Aldrich, 70% purity, the same applies hereinafter) was added and mixed to obtain a chopped gel. Further, the chopped gel was dried with a ventilation band dryer (140 ° C., wind speed 2 m / sec) to obtain a dried product. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster) and then sieved to adjust the particle size to a particle size range of 710 to 150 μm to obtain resin particles (B2) having a moisture content of 6%. .

0.7% of polyglycerol polyglycidyl ether (Nagase Kasei Kogyo Co., Ltd., Denacol EX-512) while 100 parts of the obtained resin particles (B2) were stirred at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). 4.3 parts of the aqueous solution was added while being sprayed and mixed, and the mixture was allowed to stand at 140 ° C. for 30 minutes in a circulating air dryer (manufactured by Tabai Espec Co., Ltd.) for surface cross-linking, and the water-absorbent resin particles of the present invention (5) was obtained.

<Example 6>
“0.95 parts of pentaerythritol triallyl ether” was changed to “0.068 parts of pentaerythritol triallyl ether” and “1% aqueous solution of fluorophosphoric acid (manufactured by Sigma-Aldrich, purity 70%, the same shall apply hereinafter) "1.9 parts" was changed to "1.3 parts of 1% aqueous solution of silicic acid (manufactured by Sigma-Aldrich, the same shall apply hereinafter)" and "4.3 parts of 0.7% aqueous solution of polyglycerol polyglycidyl ether" Was changed to “9.1 parts of a 5.5% aqueous solution of polyglycerol polyglycidyl ether” in the same manner as in Example 5 to obtain water absorbent resin particles (6) of the present invention.

<Example 7>
“Pentaerythritol triallyl ether 0.68 parts” was changed to “pentaerythritol triallyl ether 0.4 parts” and “sodium hydrogen sulfite 0.02 parts” was changed to “sodium dihydrogen phosphate dihydrate (Tohoku Chemical) Changed to "0.088 parts" manufactured by Kogyo Co., Ltd., and "Moisture amount 6%" was changed to "Moisture amount 7%". "Ethylene glycol diglycidyl ether 2% aqueous solution 4 parts Was changed to “5.6 parts of a 2.5% aqueous solution of ethylene glycol diglycidyl ether” in the same manner as in Example 1 to obtain water absorbent resin particles (7) of the present invention.

<Example 8>
Water-absorbent resin particles (8) of the present invention were obtained in the same manner as in Example 3 except that "sodium bisulfite 0.08 part" was changed to "sodium hydrogen sulfite 0.05 part".

<Example 9>
Water-absorbing resin particles (9) of the present invention were obtained in the same manner as in Example 3 except that “3.8 parts of phosphoric acid” was changed to “4.0 parts of phosphoric acid”.

<Comparative Example 1>
Resin particles (B3) were obtained in the same manner as in Example 1 except that 0.02 part of sodium hydrogen sulfite was not added.

1 part of phosphoric acid (c1) (phosphoric acid, manufactured by Kanto Chemical Co., Inc., purity 85%) while stirring 100 parts of the obtained resin particles (B3) at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm) Add 1.2 parts of a 2% aqueous solution while spraying and mix, and then add and mix 4 parts of a 2% aqueous solution of ethylene glycol diglycidyl ether (Nagase Chemical Industries, Denacol EX-810) while spraying. Then, it was allowed to stand at 140 ° C. for 30 minutes in a circulating air dryer (manufactured by Tabai Espec Co., Ltd.) for surface crosslinking to obtain comparative water-absorbent resin particles (1).

<Comparative Example 2>
Ethylene containing 2% of sodium alum (manufactured by Showa Chemical Co., Ltd.) with 100 parts of the resin particles (B3) obtained in the same manner as in Comparative Example 1 while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm) 5 parts of a 2% aqueous solution of glycol diglycidyl ether (Nagase Kasei Kogyo Co., Ltd., Denacol EX-810) was added while being sprayed and mixed, and the mixture was mixed at 140 ° C. in a circulating air dryer (manufactured by Tabai Espec Co., Ltd.) for 30 minutes. The mixture was allowed to stand still for surface crosslinking to obtain comparative water absorbent resin particles (2).

<Comparative Example 3>
“Pentaerythritol triallyl ether 0.68 parts” was changed to “pentaerythritol triallyl ether 0.068 parts” and “2 parts aqueous solution of ethylene glycol diglycidyl ether 4 parts” changed to “ethylene glycol diglycidyl ether 4% Comparative water-absorbent resin particles (3) were obtained in the same manner as in Comparative Example 1 except that the amount was changed to “0.75 part of aqueous solution”.

<Example 10>
Acrylic acid (manufactured by Mitsubishi Chemical Corporation, purity 100%, the same shall apply hereinafter) 135 parts, pentaerythritol triallyl ether (manufactured by Daiso Corporation, the same shall apply hereinafter) 0.68 parts, phosphoric acid (Kanto Chemical Co., Ltd.) Manufactured, purity 85%, the same applies hereinafter) 0.016 part and 363 parts deionized water were kept at 3 ° C. with stirring and mixing. After flowing nitrogen into this mixture to reduce the dissolved oxygen amount to 1 ppm or less, 0.5 part of 1% aqueous hydrogen peroxide solution, 1 part of 2% aqueous ascorbic acid solution and 2% 2,2′-azobisamidinopropane Polymerization was initiated by adding and mixing 0.3 parts of a dihydrochloride aqueous solution. After the temperature of the mixture reached 80 ° C., polymerization was carried out at 80 ± 2 ° C. for about 5 hours to obtain a hydrogel (3).

Next, while shredding the entire amount of the obtained hydrogel (3) with a mincing machine (12VR-400K, manufactured by ROYAL), adding and mixing and neutralizing 180 parts of a 30% aqueous sodium hydroxide solution, Obtained. Further, the chopped gel was dried with a ventilation band dryer (140 ° C., wind speed 2 m / sec) to obtain a dried product. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster) and then sieved to adjust the particle size to a particle size range of 710 to 150 μm to obtain resin particles (B4).

2 parts aqueous solution of ethylene glycol diglycidyl ether (manufactured by Nagase Kasei Kogyo Co., Ltd., Denacol EX-810) while stirring 100 parts of the obtained resin particles (B4) at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm) 4 parts are added while being sprayed and mixed, and the mixture is allowed to stand at 140 ° C. for 30 minutes in an air circulation dryer (manufactured by Tabai Espec Co., Ltd.) for surface cross-linking to obtain the water absorbent resin particles (10) of the present invention. Got.

<Example 11>
“Pentaerythritol triallyl ether 0.68 part” is changed to “Pentaerythritol 0.2 part” and “Phosphoric acid (manufactured by Kanto Chemical Co., Inc., purity 85% 0.016 part)” is changed to “Sodium dihydrogen phosphate” "Dihydrate (manufactured by Tohoku Chemical Co., Ltd., the same shall apply hereinafter)" is changed to 2.1 parts ". Except having changed to "6.6 parts", it carried out similarly to Example 10, and obtained the water absorbing resin particle (11) of this invention.

<Example 12>
“Pentaerythritol triallyl ether 0.68 parts” was changed from “pentaerythritol triallyl ether 0.82 parts”, “0.016 parts phosphoric acid” to “0.013 parts phosphoric acid”, “ The water-absorbent resin particles (12) of the present invention were the same as in Example 10 except that “4 parts of 2% aqueous solution of ethylene glycol diglycidyl ether” was changed to “5 parts of 1% aqueous solution of ethylene glycol diglycidyl ether”. Got.

<Example 13>
“Pentaerythritol triallyl ether 0.2 part” was changed to “pentaerythritol triallyl ether 0.14 part” and “sodium dihydrogen phosphate dihydrate 2.1 parts” changed to “sodium dihydrogen phosphate 2 parts”. Except for changing to "2.5 parts hydrate" and changing "6.6 parts of 3% aqueous solution of ethylene glycol diglycidyl ether" to "7.4 parts of 4% aqueous solution of ethylene glycol diglycidyl ether" In the same manner as in Example 11, water absorbent resin particles (13) of the present invention were obtained.

<Example 14>
Hydrous gel in the same manner as in Example 10 except that "pentaerythritol triallyl ether 0.68 part" was changed to "pentaerythritol 0.95 part" and "phosphoric acid 0.016 part" was not added. (4) was obtained.

Next, this hydrogel (4) is shredded with a mincing machine (12 VR-400K manufactured by ROYAL), mixed and neutralized by adding 180 parts of 30% aqueous sodium hydroxide, followed by 1% of phosphoric acid. 1.6 parts of an aqueous solution was added and mixed to obtain a chopped gel. Further, the chopped gel was dried with a ventilation band dryer (140 ° C., wind speed 2 m / sec) to obtain a dried product. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster), and then sieved to adjust the particle size to a particle size range of 710 to 150 μm to obtain resin particles (B5).

0.7% of polyglycerol polyglycidyl ether (Nagase Kasei Kogyo Co., Ltd., Denacol EX-512) while stirring 100 parts of the obtained resin particles (B5) at a high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). 4.3 parts of the aqueous solution was added while being sprayed and mixed, and the mixture was allowed to stand at 140 ° C. for 30 minutes in a circulating air dryer (manufactured by Tabai Espec Co., Ltd.) for surface cross-linking, and the water-absorbent resin particles of the present invention (14) was obtained.

<Example 15>
“Pentaerythritol triallyl ether 0.95 part” was changed to “pentaerythritol triallyl ether 0.068 part” and “0.7% aqueous solution of polyglycerol polyglycidyl ether 4.3 parts” changed to “polyglycerol polyglycidyl A water absorbent resin particle (15) of the present invention was obtained in the same manner as in Example 14 except that it was changed to 9.1 parts of a 5.5% aqueous solution of ether.

<Example 16>
“Pentaerythritol triallyl ether 0.2 part” was changed to “pentaerythritol triallyl ether 0.4 part” and “sodium dihydrogen phosphate dihydrate 2.1 parts” changed to “sodium dihydrogen phosphate 2 parts”. Except that it was changed to “0.88 parts of hydrate” and “6.6 parts of 3% aqueous solution of ethylene glycol diglycidyl ether” was changed to “5.6 parts of 2.5% aqueous solution of ethylene glycol diglycidyl ether”. Were the same as in Example 11 to obtain water-absorbent resin particles (16) of the present invention.

<Comparative Example 4>
Resin particles (B6) were obtained in the same manner as in Example 10 except that 0.016 part of phosphoric acid was not added.

1 part of phosphoric acid (c1) (phosphoric acid, manufactured by Kanto Chemical Co., Inc., purity: 85%) while stirring 100 parts of the obtained resin particles (B6) at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm) Add 1.2 parts of a 2% aqueous solution while spraying and mix, and then add and mix 4 parts of a 2% aqueous solution of ethylene glycol diglycidyl ether (Nagase Chemical Industries, Denacol EX-810) while spraying. Then, it was allowed to stand at 140 ° C. for 30 minutes in an air circulation dryer (manufactured by Tabai Espec Co., Ltd.) for surface crosslinking to obtain comparative water-absorbent resin particles (4).

<Comparative Example 5>
Ethylene containing 2% of sodium alum (manufactured by Showa Chemical Co., Ltd.) while stirring 100 parts of the resin particles (B6) obtained in the same manner as in Comparative Example 4 at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm) 5 parts of a 2% aqueous solution of glycol diglycidyl ether (Nagase Kasei Kogyo Co., Ltd., Denacol EX-810) was added while being sprayed and mixed, and the mixture was mixed at 140 ° C. in a circulating air dryer (manufactured by Tabai Espec Co., Ltd.) for 30 minutes. The mixture was allowed to stand still for surface crosslinking to obtain comparative water absorbent resin particles (5).

For each water-absorbent resin particle obtained in Examples 1 to 16 and Comparative Examples 1 to 5, the physiological saline centrifugal retention capacity (CRC), gel bed permeability at 0 psi swelling pressure [GBP (0 psi swelling pressure)], The absorption rate under the no load [absorption rate (T1)] measured by the DW test method and the absorption rate [absorption rate (Vortex)] measured by the Vortex test method were measured by the following methods. It was described in. The water-soluble resin particles obtained in Examples 1 to 9 and Comparative Examples 1 to 3 were measured for water-soluble content by the method described above and are shown in Table 1.

<Centrifuged retention capacity of physiological saline>
Using 0.200 g of the water-absorbing resin particles obtained in Examples 1 to 16 and Comparative Examples 1 to 5, the measurement was performed by the method described above. The higher this value, the higher the water absorption performance of the water absorbent resin.

<Gel bed permeability test at swelling pressure at 0 psi>
Using the water-absorbent resin particles obtained in Examples 1 to 16 and Comparative Examples 1 to 5, measurement was performed by the method described above. The higher this value, the better the absorption rate of the absorber and the liquid permeability between the swollen gels.

<Absorption rate under no load measured by DW test>
Measurement was performed by the above-described method using 0.50 g of each water-absorbent resin particle obtained in Examples 1 to 16 and Comparative Examples 1 to 5 and physiological saline. The DW test is to determine the ability to suck up the water-absorbent resin under no load on a measurement table connected to a burette and a conduit.

<Absorption rate measured by Vortex test>
Using the water-absorbent resin particles obtained in Examples 1 to 16 and Comparative Examples 1 to 5, measurement was performed by the method described above.

 

From Tables 1 and 2, the water-absorbent resin particles in the present invention have a high centrifugal retention amount of physiological saline, a gel bed permeability at 0 psi swelling pressure of 40 darcies or more, and under no load as measured by the Demand Wettability test method. The absorption rate was 15 seconds or less, and the absorption rate measured by the Vortex test method was 50 seconds or less. And even if there is no significant difference in the centrifugal retention amount (CRC) of physiological saline and the absorption rate of the Vortex test compared to the resin particles of the comparative example, in the liquid permeability (GBP) between the swollen gels. It was significantly better. Moreover, according to Comparative Example 3, when the water-soluble content exceeds 20%, the liquid permeability and the water absorption capacity are adversely affected and the absorption performance is poor. The absorption rate in the DW test (the smaller the value, the better the absorption performance) was shown to be high. Therefore, it was found that the absorption speed is high and the liquid permeability between the swollen gels is very excellent, but at the same time it has high water absorption performance.

The water-absorbent resin composition of the present invention has the characteristics that it is possible to achieve both liquid permeability between swollen gels and absorption performance under load, and blocking and discoloration during storage are unlikely to occur. Because of the above effects, the water-absorbent resin composition of the present invention can be used for absorbent articles having a large absorption amount and excellent reversibility and surface dryness when applied to various absorbers. It is suitably used for articles.

Claims (26)

1. A crosslinked polymer (A) of a monomer composition comprising a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal crosslinking agent (b); Water-absorbent resin particles containing an inorganic acid (c) having a proton of pKa 4.5 to 10 and having a water-soluble content of 20% or less.
2. The inorganic acid (c) is at least one selected from the group consisting of phosphoric acid, phosphorous acid, tungstophosphoric acid, polyphosphoric acid, triphosphoric acid, cyclophosphoric acid, carbonic acid, sulfurous acid, hypochlorous acid, silicic acid, and salts thereof The water-absorbent resin particle according to claim 1, which is an inorganic acid.
3. The water-absorbent resin particles according to claim 1 or 2, wherein the inorganic acid (c) is at least one selected from the group consisting of phosphoric acid, phosphorous acid, tungstophosphoric acid, polyphosphoric acid, triphosphoric acid, and salts thereof. .
4. The total content of the inorganic acid (c) is based on the total weight of the water-soluble vinyl monomer (a1), the vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and the internal crosslinking agent (b). The water-absorbent resin particle according to any one of claims 1 to 3, which is 0.004 to 2.4% by weight.
5. The water-absorbent resin particles according to any one of claims 1 to 4, wherein the physiological saline has a centrifugal retention amount of 29 to 40 g / g.
6. 6. The water-absorbent resin particles according to claim 1, wherein the gel bed permeability at 0 psi swelling pressure is 40 darcies or more.
7. The water-absorbent resin particles according to any one of claims 1 to 6, wherein the absorption rate under no load as measured by the Demand Wettability test method is 15 seconds or less.
8. The water-absorbent resin particles according to any one of claims 1 to 7, wherein the absorption rate measured by the Vortex test method is 50 seconds or less.
9. Based on the total weight of the water-soluble vinyl monomer (a1), the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis, and the internal crosslinking agent (b), The water-absorbent resin particle according to any one of claims 1 to 8, which is 0.05 to 0.7% by weight.
10. An absorbent comprising the water-absorbent resin particles according to any one of claims 1 to 9.
11. The absorbent body according to claim 10, further comprising a fibrous material.
12. An absorbent article comprising the absorber according to claim 10 or 11.
13. The method for producing resin particles according to any one of claims 1 to 9, wherein the water-soluble vinyl monomer (a1) and / or the vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and internal crosslinking Resin particles (B) containing a cross-linked polymer (A) of a monomer composition containing an agent (b) and an inorganic acid (c) having a proton of pKa 4.5 to 10 are mixed with a water content of 3 to 8 A method for producing water-absorbing resin particles having a step of surface cross-linking with a surface cross-linking agent (d) at a weight percent.
14. Based on the total weight of the water-soluble vinyl monomer (a1), the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis, and the internal crosslinking agent (b), the weight ratio of the surface cross-linking agent (d) The method for producing water-absorbent resin particles according to claim 13, wherein the content is 0.03 to 0.5% by weight.
15. Based on the total weight of the water-soluble vinyl monomer (a1), the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis, and the internal crosslinking agent (b), The method for producing water-absorbent resin particles according to claim 13 or 14, wherein the content is 0.05 to 0.7% by weight.
16. The physiological saline centrifugal retention is 29-40 g / g, the gel bed permeability at 0 psi swelling pressure is 40 darcies or more, and the absorption rate under no load measured by the Demand Wettability test method is 15 seconds or less. The method for producing water-absorbent resin particles according to any one of claims 13 to 15, which is a method for producing water-absorbent resin particles having an absorption rate measured by the Vortex test method of 50 seconds or less.
17. Water-soluble vinyl monomer (a1) and / or cross-linked polymer (A) and phosphorus of monomer composition containing vinyl monomer (a2) which becomes water-soluble vinyl monomer (a1) by hydrolysis and internal cross-linking agent (b) A method for producing water-absorbing resin particles, comprising a step of surface-crosslinking the surfaces of resin particles (B) containing an acid (c1) and / or a phosphate (c2) with a surface-crosslinking agent (d).
18. The method for producing water-absorbent resin particles according to claim 17, wherein the surface cross-linking agent (d) is a polyvalent glycidyl compound.
19. The total content of phosphoric acid (c1) and phosphate (c2) is a water-soluble vinyl monomer (a1), a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and an internal crosslinking agent (b) The method for producing water-absorbent resin particles according to claim 17 or 18, wherein the water-absorbent resin particle content is 0.008 to 1.4% by weight based on the total weight of the water.
20. Based on the total weight of the water-soluble vinyl monomer (a1), the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis, and the internal crosslinking agent (b), the weight ratio of the surface cross-linking agent (d) The method for producing water-absorbent resin particles according to any one of claims 17 to 19, wherein the content is 0.03 to 0.5% by weight.
21. Based on the total weight of the water-soluble vinyl monomer (a1), the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis, and the internal crosslinking agent (b), The method for producing water-absorbent resin particles according to any one of claims 17 to 20, wherein the content is 0.05 to 0.7% by weight.
22. The method for producing water-absorbent resin particles according to any one of claims 17 to 21, wherein the water-soluble vinyl monomer (a1) is (meth) acrylic acid.
23. The physiological saline centrifugal retention is 29-40 g / g, the gel bed permeability at 0 psi swelling pressure is 40 darcies or more, and the absorption rate under no load measured by the Demand Wettability test method is 15 seconds or less. The method for producing water-absorbent resin particles according to any one of claims 17 to 22, which is a method for producing water-absorbent resin particles having an absorption rate measured by the Vortex test method of 50 seconds or less.
24. The physiological saline centrifugal retention is 29-40 g / g, the gel bed permeability at 0 psi swelling pressure is 40 darcies or more, and the absorption rate under no load measured by the Demand Wettability test method is 15 seconds or less. An absorbent comprising the water-absorbent resin particles according to any one of claims 1 to 4, wherein the absorption rate measured by the Vortex test method is 50 seconds or less.
25. The absorbent body according to claim 24, further comprising a fibrous material.
26. An absorbent article comprising the absorber according to claim 24 or 25.