JP7234101B2 - Water-absorbing resin particles easily dehydrated and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to water-absorbing resin particles that can be easily dehydrated and a method for producing the same.

In recent years, as the amount of sanitary goods used has increased, waste disposal of used sanitary goods has become a serious problem. Sanitary goods, especially disposable diapers, have rapidly spread as essential goods in an age of declining birthrate and aging population, and their consumption is increasing rapidly. Disposal of sanitary goods after use is usually incinerated, but since the percentage of moisture in diapers is nearly 80%, incineration requires a large amount of combustion energy. This treatment method puts a heavy load on the incinerator itself, which not only leads to shortening the life of the incinerator, but also leads to air pollution and global warming, which is a factor that places a burden on the environment. is strongly desired.

Several measures have been proposed in the past to solve the disposal problem of sanitary products after use. For example, by using lime, technology related to a system for separating and collecting water-absorbent resin particles and other members of sanitary goods (Patent Document 1), water-absorbent resin particles are dehydrated and aggregated by using an aqueous calcium chloride solution, A technique for reducing the cohesive force by adding a salt of a strong acid and a nitrogen-containing basic compound and facilitating subsequent drying (Patent Document 2), dehydrating the used superabsorbent polymer with an aqueous polyvalent metal salt solution. After that, by treating with an aqueous alkali metal salt solution, a technique for recovering the water absorption capacity of the superabsorbent polymer (Patent Document 3), recovering pulp fibers from used sanitary products containing pulp fibers and superabsorbent polymers, A technique for producing recycled pulp that can be reused for sanitary goods by decomposing a superabsorbent polymer by ozone treatment has been proposed (Patent Document 4).

JP 2009-183893 A JP 2015-120834 A JP 2013-198862 A JP 2017-193819 A

To solve the problem of waste disposal of used sanitary products, if the moisture contained in used sanitary products can be efficiently removed, combustion efficiency during incineration and productivity during recycling will be improved, and the environmental impact will be greatly reduced. can be expected to be reduced. An object of the present invention is to provide water-absorbent resin particles that have good absorption properties during normal use and that facilitate dehydration of water contained in used sanitary goods, and a method for producing the same.

The present invention provides a crosslinked polymer (A) comprising a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal cross-linking agent (b) as essential structural units. and has a water separation rate of 70% or more represented by the following formula (1) and is easily dehydrated, and sanitary goods containing the same.
Syneresis rate [%] = {1-(Water retention amount after treatment with 1.0% by weight calcium chloride aqueous solution [g/g])/(Water retention amount in physiological saline [g/g])} x 100 (1)
The present invention also provides a method for producing the water-absorbing resin particles, wherein the water-soluble vinyl monomer (a1) and/or the vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis and the internal cross-linking agent (b) ) to obtain a hydrogel containing the crosslinked polymer (A) by polymerizing a monomer composition having essential constituent units, a step of subdividing the hydrous gel of the crosslinked polymer (A), and a subdivided hydrous Production of the water-absorbing resin particles, comprising a step of further kneading and shredding the gel at a gel temperature of 40° C. to 120° C., and a step of drying the kneaded and shredded hydrous gel and then pulverizing it to obtain water-absorbing resin particles. The method.

The water-absorbing resin particles of the present invention, which are easily dehydrated (hereinafter also simply referred to as the water-absorbing resin particles of the present invention), exhibit excellent water repellency when treated with a dehydrating agent. In addition, sanitary goods such as paper diapers containing the water-absorbing resin particles of the present invention satisfy the absorption performance necessary for paper diapers during use, and after use, by adding a dehydrating agent such as an aqueous solution of a polyvalent metal salt, the water-absorbing resin particles are reduced. The moisture content can be greatly reduced, and dehydration can be easily carried out. Therefore, the combustion efficiency during incineration and the productivity during recycling are improved, and the environmental load can be reduced.

FIG. 3 is a cross-sectional view schematically showing a filtration cylindrical tube for measuring gel permeation speed. FIG. 4 is a perspective view schematically showing a pressurizing shaft and a weight for measuring gel permeation speed.

The water-absorbing resin particles of the present invention are crosslinked with water-soluble vinyl monomer (a1) and/or vinyl monomer (a2) that becomes water-soluble vinyl monomer (a1) by hydrolysis and internal cross-linking agent (b) as essential structural units. It is a water absorbent resin particle containing a polymer (A).

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited. vinyl monomers having saturated groups (e.g., anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers), anionic vinyl monomers disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883, nonionic a carboxy group, a sulfo group, a phosphono group, a hydroxyl group, a carbamoyl group, an amino group and an ammonio group disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982; Any vinyl monomer having at least one of the following can be used.

The vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a2) by hydrolysis (hereinafter also referred to as hydrolyzable vinyl monomer (a2)) is not particularly limited and is known (for example, 0024 to 0025 of Japanese Patent No. 3648553). A vinyl monomer having at least one hydrolyzable substituent that becomes a water-soluble substituent by hydrolysis disclosed in paragraph, and at least one hydrolyzate disclosed in paragraphs 0052 to 0055 of JP-A-2005-75982. A vinyl monomer such as a vinyl monomer having a decomposable substituent (a 1,3-oxo-2-oxapropylene (--CO--O--CO--) group, an acyl group, a cyano group, etc.) can be used. The water-soluble vinyl monomer means a vinyl monomer having a property of dissolving at least 100 g in 100 g of water at 25°C. Moreover, hydrolyzability means the property of being hydrolyzed by the action of water at 50° C. and, if necessary, a catalyst (acid, base, etc.) to become water-soluble. The hydrolysis (a2) of the hydrolyzable vinyl monomer may be carried out during polymerization, after polymerization, or both, but preferably after polymerization from the viewpoint of the molecular weight of the resulting water-absorbing resin particles.

Among these, the water-soluble vinyl monomer (a1) is preferable from the viewpoint of absorption properties. 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, more preferably a vinyl monomer having a carboxy (salt) group or a carbamoyl group, more preferably (meth)acrylic acid (salt) and (meth)acrylamide, particularly preferably (meth)acrylic acid (salt), Acrylic acid (salt) is most preferred.

In addition, "carboxy (salt) group" means "carboxy group" or "carboxylate group", and "sulfo (salt) group" means "sulfo group" or "sulfonate group". (Meth)acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylate, and (meth)acrylamide means acrylamide or methacrylamide. The salts include alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts, ammonium (NH ₄ ) salts, and the like. Among these salts, alkali metal salts and ammonium salts are preferred, alkali metal salts are more preferred, and sodium salts are particularly preferred, from the viewpoint of absorption properties and the like.

When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the water-soluble vinyl monomer (a1), it is preferred that a portion of the acid group-containing monomer is neutralized with a base from the viewpoint of water absorption performance and residual monomers. . As the neutralizing base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium hydrogencarbonate and potassium carbonate can be used. Neutralization may be performed before, during, or after polymerization in the production of water-absorbent resin particles. A preferred example is a method of neutralizing an acid group-containing polymer in the state of a hydrous gel.

Further, when the acid group-containing monomer is used, the neutralization degree of the acid group is preferably 50 to 80 mol %. If the degree of neutralization is less than 50 mol %, the resulting hydrous gel polymer will have high adhesiveness, and workability during production and use may deteriorate. Furthermore, the water-retaining capacity of the obtained water-absorbent resin particles may decrease. On the other hand, if the degree of neutralization exceeds 80%, the resulting resin will have a high pH and may be unsafe for human skin.

When either the water-soluble vinyl monomer (a1) or the hydrolyzable vinyl monomer (a2) is used as a structural unit, each of them may be used alone as a structural unit, or two or more of them may be used as a structural unit, if necessary. The same applies to the case where the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as structural units. Further, when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as structural units, the molar ratio (a1/a2) of these contained is preferably 75/25 to 99/1, more preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, most preferably 91/9 to 92/8. Within this range, the absorption performance is further improved.

In addition to the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), other vinyl monomers (a3) copolymerizable therewith are used as structural units of the crosslinked polymer (A). can be done.

Other copolymerizable vinyl monomers (a3) are not particularly limited and are known (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553; (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 styrene such as vinylnaphthalene and dichlorostyrene.
(ii) C2-C20 Aliphatic Ethylene Monomer Alkenes [ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.]; and alkadienes [butadiene, isoprene, etc.] and the like.
(iii) Alicyclic ethylene monomers having 5 to 15 carbon atoms, monoethylenically unsaturated monomers [pinene, limonene, indene, etc.];

When the other vinyl monomer (a3) is used as a structural unit, the content (mol%) of the other vinyl monomer (a3) unit is 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, even more preferably 0.08 to 2, particularly preferably 0.1 to 1.5. In spite of the above, the content of other vinyl monomer (a3) units is most preferably 0 mol % from the viewpoint of absorption properties.

The internal cross-linking agent (b) (hereinafter also simply referred to as cross-linking agent (b)) is not particularly limited and is known (for example, two ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553 a cross-linking agent having at least one functional group capable of reacting with a water-soluble substituent and having at least one ethylenically unsaturated group; and at least a functional group capable of reacting with a water-soluble substituent. Cross-linking agents having two, cross-linking agents having two or more ethylenically unsaturated groups disclosed in paragraphs 0028 to 0031 of JP-A-2003-165883, cross-linking having an ethylenically unsaturated group and a reactive functional group and a crosslinking agent having two or more reactive substituents, a crosslinkable vinyl monomer disclosed in paragraph 0059 of JP-A-2005-75982 and JP-A-2005-95759 disclosed in paragraphs 0015 to 0016 A cross-linking agent such as a cross-linking vinyl monomer) can be used. Among these, from the viewpoint of absorption performance and the like, cross-linking agents having two or more ethylenically unsaturated groups are preferable, and more preferable are triallyl cyanurate, triallyl isocyanurate and polyols having 2 to 10 carbon atoms ( Meta)allyl ethers, particularly preferred are triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane and pentaerythritol triallyl ether, most preferred is pentaerythritol triallyl ether. The crosslinking agent (b) may be used alone or in combination of two or more.

The content (mol %) of the cross-linking agent (b) unit is the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit, and when other vinyl monomers (a3) are used, (a1) to Based on the total number of moles of (a3), it is preferably 0.001 to 5, more preferably 0.005 to 3, and particularly preferably 0.01 to 1. Within this range, the absorption performance is further improved.

The method for producing water-absorbing resin particles of the present invention comprises a monomer composition comprising the water-soluble vinyl monomer (a1) and/or the hydrolyzable vinyl monomer (a2) and the internal cross-linking agent (b) as essential structural units. is polymerized to obtain a hydrogel containing the crosslinked polymer (A), a step of finely dividing the hydrogel of the crosslinked polymer (A), and the finely divided hydrogel is further kneaded at a gel temperature of 40 ° C. to 120 ° C. and a step of drying and pulverizing the kneaded and chopped water-containing gel to obtain water-absorbing resin particles.

Examples of the method for producing the crosslinked polymer (A) include known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc.; JP-A-55-133413, etc.), known suspension polymerization and reverse phase suspension. A water-containing gel (consisting of a crosslinked polymer and water .) can be obtained. The crosslinked polymer (A) may be used alone or as a mixture of two or more.

Among the polymerization methods, the solution polymerization method is preferred, and the aqueous solution polymerization method is particularly preferred because it does not require the use of an organic solvent and is advantageous in terms of production cost, and has a large water retention capacity and is water soluble. The aqueous solution adiabatic polymerization method is most preferable because a water-absorbing resin with a small amount of components can be obtained and temperature control during polymerization is unnecessary.

When aqueous solution polymerization is carried out, the concentration of the monomer composition in the aqueous solution is preferably 10-60% by weight, more preferably 15-50% by weight, still more preferably 20-40% by weight. A mixed solvent containing water and an organic solvent can be used as the solvent, and examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, dimethyl sulfoxide and mixtures of two or more thereof. can be mentioned. When aqueous solution polymerization is carried out, the amount (% by weight) of the organic solvent used is preferably 40 or less, more preferably 30 or less, based on the weight of water.

When an initiator is used for polymerization, conventionally known initiators for radical polymerization can be used. hydrochloride, etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinate acid peroxides and di(2-ethoxyethyl)peroxydicarbonate, etc.] and redox catalysts (alkali metal sulfites or bisulfites, reducing agents such as ammonium sulfite, ammonium bisulfite and ascorbic acid and alkali metal persulfates salts, ammonium persulfate, hydrogen peroxide, organic peroxides, etc.). These catalysts may be used alone, or two or more of them may be used in combination.
The amount (% by weight) of the radical polymerization initiator used is the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), and when the other vinyl monomer (a3) is used, (a1) to (a3). , preferably 0.0005 to 5, more preferably 0.001 to 2, based on the total weight.

When the polymerization method is a suspension polymerization method or a reverse-phase suspension polymerization method, polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. In the case of the reversed-phase suspension polymerization method, the polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, normal hexane and normal heptane.

The polymerization initiation temperature can be appropriately adjusted depending on the type of initiator used, but is preferably 0 to 100°C, more preferably 5 to 80°C.

A crosslinked polymer (A) can be obtained by kneading and shredding the hydrous gel polymer obtained by polymerization, followed by drying and pulverization. In the present invention, kneading and shredding is a process of making the hydrous gel fine while repeating cutting of the hydrous gel and coalescence of the cut hydrous gel particles by shearing force (shear). A water-containing gel in which gel particles are aggregated can be obtained, and unevenness can be formed on the surface of the water-absorbing resin particles. The size (maximum diameter) of the gel after kneading and shredding is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying process is further improved.

The size (longest diameter) of the gel particles after kneading and pulverization is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying step is further improved, and the miscibility with the additive hydrophobic substance (c) is improved, resulting in a syneresis rate and 1.0% by weight calcium chloride. The gel permeation speed of the aqueous solution is improved.

Kneading and shredding can be performed by a known method, and kneading and shredding is performed using a kneading and shredding device (e.g., kneader, universal mixer, single-screw or twin-screw kneading extruder, mincing machine, meat chopper, etc.). can. It is 40 to 120°C, preferably 50 to 110°C from the viewpoint of dehydration efficiency and performance balance with other physical properties. The number of times of kneading and shredding is not particularly limited as long as the size of the gel particles is within the above range, and may be one or more times. Further, when kneading and shredding are performed a plurality of times, it may be performed a plurality of times with one pulverizer, or may be performed continuously with a plurality of pulverizers.

In the present invention, the hydrous gel polymer obtained by polymerization is finely divided before being kneaded and chopped. In the present invention, the subdivision is a step of cutting the hydrogel into fine pieces while maintaining the internal structure of the hydrogel, and is different from the kneading and shredding described above from the viewpoint of the internal structure. By subdividing before the kneading and shredding process, the excessive stress applied to the hydrous gel during the kneading and shredding process can be alleviated, and deterioration of the hydrous gel polymer can be suppressed, so that the absorption performance is improved and the water absorption is improved. It becomes possible to prevent an extreme increase in the degree of particle defect of the resin particles.

The method of subdivision is not particularly limited, and for example, it may be subdivided with scissors, or the frozen hydrous gel may be pulverized by a pulverizer (for example, a hammer pulverizer, an impact pulverizer, a roll pulverizer, and a jet pulverizer. ).

The size (maximum diameter) of the gel after fragmentation is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 500 μm to 1 cm. Within this range, the subsequent kneading and shredding step can be carried out smoothly, and the absorption performance of the water-absorbent resin particles may be improved.

Further, as described above, the water-containing gel of the acid group-containing polymer obtained after polymerization can be neutralized by mixing with a base before or during the kneading and chopping step. The preferred range of the degree of neutralization of the acid group when neutralizing the acid group-containing polymer is also the same as described above.

The water-containing gel particles containing the crosslinked polymer (A) obtained by the kneading and shredding step are dried and then pulverized to obtain water absorbent resin particles.

Methods for drying (including distillation) the solvent (including water) in the hydrous gel particles include a method of drying with hot air at a temperature of 80 to 300 ° C., and a thin film using a drum dryer heated to 100 to 300 ° C. A drying method, vacuum drying method, freeze-drying method, infrared drying method, decantation, filtration, and the like can be applied.

When water is contained in the solvent of the hydrous gel particles, the water content (% by weight) after drying is preferably 0 to 20, more preferably 1 to 10, particularly preferably 1 to 10, based on the weight of the crosslinked polymer (A). 2-9, most preferably 3-8. Within this range, the pulverizability is improved in the subsequent pulverization step, and the absorption performance is further improved.

Further, when the solvent (organic solvent, water, etc.) of the hydrous gel particles contains an organic solvent, the content (% by weight) of the organic solvent after drying is 0 to 10 based on the weight of the crosslinked polymer (A). is preferred, more preferably 0-5, particularly preferably 0-3, and most preferably 0-1. Within this range, the absorption performance of the water absorbent resin particles is further improved.

The content and water content of the organic solvent were measured using an infrared moisture meter [JE400 manufactured by KETT Co., Ltd., etc.: 120 ± 5 ° C., 30 minutes, atmospheric humidity before heating 50 ± 10% RH, lamp specification 100 V, 40 W].

The method of pulverizing the hydrous gel particles after drying is not particularly limited, and known pulverizers (for example, hammer pulverizers, impact pulverizers, roll pulverizers, jet stream pulverizers, etc.) can be used. . The resulting water absorbent resin particles can be classified by sieving or the like, if necessary, to adjust the particle size.

The weight-average particle diameter (μm) of the water-absorbent resin particles classified by sieving or the like after pulverization is preferably 150-500, more preferably 250-500, and most preferably 350-450. Within this range, the absorption performance, the water separation rate, and the gel permeation rate of a 1.0% by weight calcium chloride aqueous solution are further improved.

In addition, the weight average particle size was measured using a low-tap test sieve shaker and standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook 6th Edition (McGraw Hill Book Company, 1984). , page 21). That is, JIS standard sieves of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm and a saucer are combined in this order from the top. About 50 g of the particles to be measured are placed in the top sieve and shaken for 5 minutes with a Rotap test sieve shaker. The weight of the particles to be measured on each sieve and the tray is weighed, the total is 100% by weight, and the weight fraction of the particles on each sieve is obtained. ) and the weight fraction on the vertical axis], draw a line connecting the points, determine the particle diameter corresponding to a weight fraction of 50% by weight, and take this as the weight average particle diameter.

In addition, since the smaller the content of fine particles contained in the water-absorbent resin particles, the better the absorption performance, the content ratio (weight %) is preferably 3 or less, more preferably 1 or less. The content of fine particles can be determined using the graph created when determining the weight-average particle size.

The shape of the water-absorbent resin particles is not particularly limited, and examples thereof include irregularly pulverized shape, scaly shape, pearl shape, rice grain shape, and the like. Of these, irregularly pulverized powders are preferred from the viewpoints of good entanglement with fibrous materials for use in paper diapers and the like, and the fact that they do not fall off from fibrous materials.

The water absorbent resin particles of the present invention can contain a hydrophobic substance (c). (c) includes a hydrophobic substance (c1) containing a hydrocarbon group, a hydrophobic substance (c2) containing a hydrocarbon group having a fluorine atom, a hydrophobic substance (c3) having a polysiloxane structure, and the like. be

Hydrophobic substances (c1) containing hydrocarbon groups include polyolefin resins, polyolefin resin derivatives, polystyrene resins, polystyrene resin derivatives, waxes, long-chain fatty acid esters, long-chain fatty acids and their salts, long-chain aliphatic alcohols, long-chain Chain fatty amides and mixtures of two or more thereof are included.

As the polyolefin resin, the weight of an olefin having 2 to 4 carbon atoms {ethylene, propylene, isobutylene, isoprene, etc.} as an essential constituent monomer (the content of the olefin is at least 50% by weight based on the weight of the polyolefin resin). Polymers having an average molecular weight of 1,000 to 1,000,000 {eg, polyethylene, polypropylene, polyisobutylene, poly(ethylene-isobutylene), isoprene, etc.} can be mentioned.

Polyolefin resin derivatives include polymers with a weight average molecular weight of 1,000 to 1,000,000 obtained by introducing a carboxy group (-COOH) or 1,3-oxo-2-oxapropylene (-COOCO-) into a polyolefin resin {for example, polyethylene heat Degraded product, polypropylene heat degraded product, maleic acid-modified polyethylene, chlorinated polyethylene, maleic acid-modified polypropylene, ethylene-acrylic acid copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, maleated polybutadiene, ethylene-vinyl acetate copolymer, maleated ethylene-vinyl acetate copolymer, etc.}.

A polymer having a weight average molecular weight of 1,000 to 1,000,000 can be used as the polystyrene resin.

As the polystyrene resin derivative, a polymer having a weight average molecular weight of 1,000 to 1,000,000 containing styrene as an essential constituent monomer (the styrene content is at least 50% by weight based on the weight of the polystyrene derivative) {for example, styrene- maleic anhydride copolymer, styrene-butadiene copolymer, styrene-isobutylene copolymer, etc.}.

Waxes include waxes having a melting point of 50 to 200° C. {eg, paraffin wax, beeswax, carnauba wax, beef tallow, etc.}.

Examples of long-chain fatty acid esters include esters of fatty acids having 8 to 30 carbon atoms and alcohols having 1 to 12 carbon atoms {for example, methyl laurate, ethyl laurate, methyl stearate, ethyl stearate, methyl oleate, oleic acid, Ethyl, glycerol monolaurate, glycerine monostearate, monoglycerol oleate, pentaerythrityl monolaurate, pentaerythrityl monostearate, pentaerythrityl monooleate, sorbitol monolaurate, Sorbit monostearate, sorbitol monooleate, sucrose palmitate monoester, sucrose palmitate diester, sucrose palmitate triester, sucrose stearate monoester, sucrose stearate diester, sucrose tristearate ester and beef tallow, etc.].

Examples of long-chain fatty acids and salts thereof include fatty acids having 8 to 30 carbon atoms {eg, lauric acid, palmitic acid, stearic acid, oleic acid, dimer acid, behenic acid, etc.}, and salts thereof include zinc, calcium, Salts with magnesium or aluminum (hereinafter abbreviated as Zn, Ca, Mg, Al, respectively) {eg, Ca palmitate, Al palmitate, Ca stearate, Mg stearate, Al stearate, etc.}.

Long-chain fatty alcohols include fatty alcohols having 8 to 30 carbon atoms {eg, lauryl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol, etc.}. Palmityl alcohol, stearyl alcohol, and oleyl alcohol are preferable, and stearyl alcohol is more preferable, from the viewpoint of anti-leakage property of the absorbent article.

Examples of long-chain aliphatic amides include amidates of long-chain aliphatic primary amines with 8 to 30 carbon atoms and carboxylic acids having a hydrocarbon group with 1 to 30 carbon atoms, ammonia, or primary amines with 1 to 7 carbon atoms. and an amide of a long-chain fatty acid having 8 to 30 carbon atoms, an amide of a long-chain aliphatic secondary amine having at least one aliphatic chain of 8 to 30 carbon atoms and a carboxylic acid having 1 to 30 carbon atoms, and Amidates of secondary amines having two aliphatic hydrocarbon groups of 1 to 7 carbon atoms and long-chain fatty acids of 8 to 30 carbon atoms can be mentioned.

As an amidated product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms, a product obtained by reacting the primary amine and carboxylic acid in a ratio of 1:1 and 1 : It is divided into the reacted products in 2. Examples of the 1:1 reaction product include N-octylamide acetate, N-hexacosylamide acetate, N-octylamide heptacosanoate and N-hexacosylamide heptacosanoate. Those reacted at 1:2 include N-octylamide diacetate, N-hexacosylamide diacetate, N-octylamide diheptacosanoate and N-hexacosylamide diheptacosanoate. In the case of a product obtained by reacting a primary amine and a carboxylic acid at a ratio of 1:2, the carboxylic acids used may be the same or different.

As an amidation product of ammonia or a primary amine having 1 to 7 carbon atoms and a long-chain fatty acid having 8 to 30 carbon atoms, a product obtained by reacting ammonia or a primary amine with a carboxylic acid at a ratio of 1:1 and a 1:2 It is divided into reactants. Nonanoic acid amide, nonanoic acid methylamide, nonanoic acid N-heptylamide, heptacosanoic acid amide, heptacosanoic acid N-methylamide, heptacosanoic acid N-heptylamide and heptacosanoic acid N-hexacosylamide etc. Dinonanoic acid amide, dinonanoic acid N-methylamide, dinonanoic acid N-heptylamide, dioctadecanoic acid amide, dioctadecanoic acid N-ethylamide, dioctadecanoic acid N-heptylamide, diheptacosanoic acid amide , diheptacosanoic acid N-methylamide, diheptacosanoic acid N-heptylamide and diheptacosanoic acid N-hexacosylamide. In addition, as a product obtained by reacting ammonia or a primary amine with a carboxylic acid at a ratio of 1:2, the carboxylic acids used may be the same or different.

Examples of the amidated product of a long-chain aliphatic secondary amine having at least one aliphatic chain having 8 to 30 carbon atoms and a carboxylic acid having 1 to 30 carbon atoms include N-methyloctylamide acetate and N-methylhexacosylate acetate. Acetate N-octylhexacosylamide, Acetate N-dihexacosylamide, Heptacosanoic acid N-methyloctylamide, Heptacosanoic acid N-methylhexacosylamide, Heptacosanoic acid N-octylhexacosylamide and Heptacosane and acid N-dihexacosylamide.

Examples of amidates of secondary amines having two aliphatic hydrocarbon groups of 1 to 7 carbon atoms and long-chain fatty acids of 8 to 30 carbon atoms include nonanoic acid N-dimethylamide, nonanoic acid N-methylheptylamide, nonanoic acid N-diheptylamide, heptacosanoic acid N-dimethylamide, heptacosanoic acid N-methylheptylamide, heptacosanoic acid N-diheptylamide and the like.

As the hydrophobic substance (c1), long-chain fatty acid esters, long-chain fatty acids and their salts, long-chain fatty alcohols and long-chain fatty amides are preferable from the viewpoint of dehydration efficiency and anti-leak property of the absorbent article. Preferred are sorbitol stearate, sucrose stearate, stearic acid, Mg stearate, Ca stearate, Zn stearate and Al stearate, particularly preferred are sucrose stearate and Mg stearate.

Hydrophobic substances (c2) containing a hydrocarbon group having a fluorine atom include perfluoroalkanes, perfluoroalkenes, perfluoroaryls, perfluoroalkyl ethers, perfluoroalkylcarboxylic acids, perfluoroalkyl alcohols and two of these. A mixture of more than one species is included.

Hydrophobic substances (c3) having a polysiloxane structure include polydimethylsiloxane, polyether-modified polysiloxane {polyoxyethylene-modified polysiloxane and poly(oxyethylene/oxypropylene)-modified polysiloxane, etc.}, carboxy-modified polysiloxane, Epoxy-modified polysiloxane, amino-modified polysiloxane, alkoxy-modified polysiloxane, etc. and mixtures thereof and the like are included.

Carboxy-modified polysiloxanes include, for example, X-22-3701E, X-22-3710 (both manufactured by Shin-Etsu Chemical Co., Ltd.), DOWSIL (model number BY16-880 Fluid), DOWSIL (model number BY16-880) (Dow Toray Industries, Inc.) manufactured by the company). The position of the carboxyl group relative to the polysiloxane backbone is side chain and/or terminal.

Examples of epoxy-modified polysiloxane include X-22-343 (manufactured by Shin-Etsu Chemical Co., Ltd.), KF-101, KF-1001, X-22-2000, X-22-2046, KF-102, X-22- 4741, KF-1002, KF-1005 (all manufactured by Shin-Etsu Chemical Co., Ltd.), DOWSIL (model number BY 16-839 Fluid), DOWSIL (model number BY8411 Fluid), DOWSIL (model number BY 8413 Fluid), DOWSIL (model number BY8421 Fluid) (both Dow · manufactured by Toray Industries, Inc.), SF8411, SF8413, BY16-839, BY16-876, FZ-3736, SF8421 (all manufactured by Dow Corning Toray). The position of the epoxy group relative to the polysiloxane backbone is side chain and/or terminal.

Examples of amino-modified polysiloxanes include monoamine-modified type in which the modifying group is a primary amine and diamine-modified type in which the modifying group is a secondary amine.
Examples of monoamino-modified types include KF-868, KF-865, KF-864, PAM-E, KF-8010, X-22-161A, X-22-161B, KF-8012, KF-8008, X- 22-1660B-3, X-22-9409 (both manufactured by Shin-Etsu Chemical Co., Ltd.), DOWSIL (model number BY16-205), DOWSIL (model number BY16-213), DOWSIL (model number BY16-849Fluid), DOWSIL (model number BY16- 853U), DOWSIL (model number BY16-871), DOWSIL (model number BY16-872), DOWSIL (model number BY16-879B), DOWSIL (model number BY16-892), DOWSIL (model number FZ-3705), DOWSIL (model number FZ-3710Fluid) , DOWSIL (model number FZ-3760), DOWSIL (model number FZ-3785), DOWSIL (model number SF8417Fluid) (all manufactured by Dow Toray Co., Ltd.), and the like. Examples of diamino-modified types include KF-859, KF-393, KF-860, KF-860, KF-8004, KF-8002, KF-8005, KF-867, KF-8021, KF-869, KF- 861 (both manufactured by Shin-Etsu Chemical Co., Ltd.) and the like. The position of the diamino group relative to the polysiloxane backbone is side chain and/or terminal.

Examples of alkoxy-modified polysiloxanes include X-22-4952, X-22-4272, KF-6123, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF -945, KF-640, KF-642, KF-643, KF-644, KF-6020, KF-6204, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017, DOWSIL (Model number 501W Additive), DOWSIL (Model number FZ-2110), DOWSIL (Model number FZ-2123), DOWSIL (Model number L-7001), DOWSIL (Model number SF8410Fluid), DOWSIL (Model number SH3746Fluid), DOWSIL (Model number SH3746Fluid) model number SH8700 Fluid) (both manufactured by Dow Toray Co., Ltd.). The position of the alkoxy groups relative to the polysiloxane backbone is side chain and/or terminal.

As the hydrophobic substance (c3), carboxy-modified polysiloxane, epoxy-modified polysiloxane, amino-modified polysiloxane, and alkoxy-modified polysiloxane are preferable, and carboxy-modified polysiloxane is more preferable, from the viewpoint of dehydration efficiency and leakage resistance of the absorbent article. Polysiloxane.

The HLB value of the hydrophobic substance (c) is preferably 1-10, more preferably 1-8, and particularly preferably 1-7. Within this range, the anti-leak property of the absorbent article is further improved. The HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is determined by the Oda method (Introduction to Surfactants, p. 212, Takehiko Fujimoto, published by Sanyo Chemical Industry Co., Ltd., published in 2007).

Of the hydrophobic substances (c), the hydrophobic substance (c1) containing a hydrocarbon group or the hydrophobic substance (c3) having a polysiloxane structure is preferable from the viewpoint of the dehydration efficiency and the anti-leak property of the absorbent article. . More preferably, it is a hydrophobic substance (c3).

The content (% by weight) of the hydrophobic substance (c) is 0.001 to 2.0, based on the weight of the crosslinked polymer (A), from the viewpoint of water absorption properties (particularly water absorption rate and liquid permeation rate). % by weight, preferably 0.01 to 1.0% by weight, particularly preferably 0.02 to 0.3% by weight.

The hydrophobic substance (c) may be present anywhere in the water-absorbent resin particles, but from the viewpoint of water absorption characteristics (particularly, water absorption rate) and water separation rate, it should be present inside the water-absorbent resin particles. is preferred.

Hydrophobic substance (c) should only contain (c) in the hydrous gel containing the crosslinked polymer (A) during the kneading and shredding step described above. ) is preferably contained. As a method of adding (c), a method of adding to the polymerization liquid after the polymerization process is started and before the polymerization process is completed, a method of adding to the hydrous gel before the kneading and shredding process after the polymerization process is completed, and a method of kneading and shredding. There is a method of adding to the hydrogel particles during the process, but from the viewpoint of improving the water separation rate, a method of adding to the hydrogel before the kneading and shredding process after the completion of the polymerization process, or a method of adding to the hydrogel particles during the kneading and shredding process is preferably added to the water-containing gel particles during the kneading and shredding step. The hydrophobic substance (c) can also be added in the form of being dissolved and/or dispersed in water and/or an organic solvent.

It is preferable that the surface of the water absorbent resin particles is further crosslinked. Therefore, the production method of the present invention may include a step of drying and pulverizing the aforementioned hydrous gel particles, followed by surface cross-linking. By surface cross-linking, the gel strength can be further improved, and the desired water retention capacity and absorption capacity under load can be satisfied in actual use. In addition, the step of surface-crosslinking the hydrous gel particles is also simply referred to as a cross-linking step.

As a method for surface-crosslinking the water-absorbent resin particles, a conventionally known method, for example, a method in which a mixed solution of the surface-crosslinking agent (e), water and a solvent is mixed with the water-absorbent resin in the form of particles, and heated to react. is mentioned. Examples of the mixing method include a method of spraying the mixed solution onto the water absorbent resin particles and a method of dipping the water absorbent resin particles into the mixed solution. Preferably, the mixed solution is sprayed onto the water absorbent resin particles. It is a method of mixing

Examples of the surface cross-linking agent (e) include polyglycidyl compounds such as ethylene glycol diglycidyl ether, glycerol diglycidyl ether and polyglycerol polyglycidyl ether; polyhydric alcohols such as glycerin and ethylene glycol; ethylene carbonate; A metal compound etc. are mentioned. Among these, polyglycidyl compounds are preferable in that the cross-linking reaction can be performed at a relatively low temperature. These surface cross-linking agents may be used alone or in combination of two or more.

The amount of the surface cross-linking agent (e) used is preferably 0.001 to 5% by weight, more preferably 0.005 to 2% by weight, based on the weight of the water-absorbent resin particles before cross-linking. If the amount of the surface cross-linking agent (e) used is less than 0.001% by weight, the degree of surface cross-linking may be insufficient, and the effect of improving the absorption under load may be insufficient. On the other hand, if the amount of the surface cross-linking agent (e) used exceeds 5% by weight, the degree of surface cross-linking may become excessive and the water retention may decrease.

The amount of water used during surface crosslinking is preferably 0.5 to 10% by weight, more preferably 1 to 7% by weight, based on the weight of the water-absorbing resin particles before crosslinking. If the amount of water used is less than 0.5% by weight, the degree of penetration of the surface cross-linking agent (e) into the inside of the water-absorbent resin particles may be insufficient, and the effect of improving the absorption under load may be poor. On the other hand, if the amount of water used exceeds 10% by weight, the penetration of the surface cross-linking agent (e) into the inside becomes excessive, and although the absorption under load is improved, the water retention capacity may decrease.

Conventionally known solvents can be used as the solvent used in combination with water for surface cross-linking. In consideration of the above, it can be appropriately selected and used, but hydrophilic organic solvents that are soluble in water, such as methanol, diethylene glycol, and propylene glycol, are preferred. A solvent may be used individually and may use 2 or more types together.

The amount of the solvent used can be appropriately adjusted depending on the type of solvent, but is preferably 1 to 10% by weight based on the weight of the water-absorbing resin particles before surface cross-linking. Also, the ratio of solvent to water can be arbitrarily adjusted, but is preferably 20 to 80% by weight, more preferably 30 to 70% by weight.

For surface cross-linking, a mixed solution of the surface cross-linking agent (e), water and solvent is mixed with the water-absorbing resin particles by a conventionally known method, followed by heating reaction. The reaction temperature is preferably 100-230°C, more preferably 120-180°C. The reaction time can be appropriately adjusted depending on the reaction temperature, preferably 3 to 60 minutes, more preferably 10 to 45 minutes. The water absorbent resin particles obtained by surface cross-linking can be further surface cross-linked using a surface cross-linking agent that is the same as or different from the surface cross-linking agent used first.

After surface cross-linking, if necessary, the particles may be sieved to adjust the particle size. The weight-average particle diameter of the particles obtained after the particle size adjustment and the preferred range of the fine particle content are the same as described above. In addition, the particle size adjustment step after surface cross-linking of the hydrous gel particles is also referred to as a post-step after the cross-linking step, or simply a post-step.

In the cross-linking step and/or in the post-step after the cross-linking step, the hydrophobic substance (c) can be added to water and/or an organic solvent in the form of being dissolved and/or dispersed. By adding in the cross-linking step and/or in a post-step after the cross-linking step, the dehydration efficiency can be improved because it can be uniformly added to the particle surface.

The water absorbent resin particles of the present invention may further contain a polyvalent metal salt (f), and for this reason, the production method of the present invention may further include a step of mixing with the polyvalent metal salt (f). good. By containing the polyvalent metal salt (f), the blocking resistance and liquid permeability of the water absorbent resin particles are improved. Examples of the polyvalent metal salt (f) include salts of at least one metal selected from the group consisting of magnesium, calcium, zirconium, aluminum and titanium and the aforementioned inorganic or organic acids.

As the polyvalent metal salt (f), from the viewpoint of availability and solubility, inorganic acid salts of aluminum and inorganic acid salts of titanium are preferable, and aluminum sulfate, aluminum chloride, potassium aluminum sulfate and sulfuric acid are more preferable. Sodium aluminum, particularly preferred are aluminum sulphate and sodium aluminum sulphate, most preferred is sodium aluminum sulphate. These may be used individually by 1 type, and may use 2 or more types together.

The amount (% by weight) of the polyvalent metal salt (f) used is preferably 0.01 to 5, more preferably 0.01 to 5, based on the weight of the crosslinked polymer (A) from the viewpoint of absorption performance and blocking resistance. 05 to 4, particularly preferably 0.1 to 3.

The timing of mixing with the polyvalent metal salt (f) is not particularly limited, but mixing after drying the hydrous gel to obtain water-absorbing resin particles is preferable from the viewpoint of absorption performance and blocking resistance. .

The surface of the water absorbent resin particles of the present invention may be coated with inorganic powder. The inorganic powder includes hydrophilic inorganic particles and hydrophobic inorganic particles. Hydrophilic inorganic particles include particles such as glass, silica gel, silica and clay. Examples of hydrophobic inorganic particles include particles of carbon fiber, kaolin, talc, mica, bentonite, sericite, asbestos and shirasu. Among these, hydrophilic inorganic particles are preferred, and silica is most preferred.

The shape of the hydrophilic inorganic particles and the hydrophobic inorganic particles may be amorphous (crushed), spherical, film-like, rod-like, fibrous, etc., preferably amorphous (crushed) or spherical. It is more preferably spherical.

The content (% by weight) of the inorganic powder is preferably 0.01 to 3.0, more preferably 0.05 to 1.0, and most preferably 0.1 to 3.0, based on the weight of the water-absorbing resin particles. 0.8, particularly preferably 0.2 to 0.7, most preferably 0.3 to 0.6. Within this range, the gel permeation rate of the absorbent article is further improved.

The water-absorbent resin particles of the present invention may contain other additives {for example, known antiseptic agents (Japanese Unexamined Patent Publication No. 2003-225565, Japanese Unexamined Patent Publication No. 2006-131767, etc.), antifungal agents, antibacterial agents, antioxidants, ultraviolet Absorbents, coloring agents, fragrances, deodorants, organic fibrous materials, etc.} may also be included. When these additives are contained, the content (% by weight) of the additives is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably 0.01 to 5, based on the weight of the water-absorbing resin particles. 0.05 to 1, most preferably 0.1 to 0.5.

The apparent density (g/ml) of the water absorbent resin particles of the present invention is preferably 0.40 to 0.62, more preferably 0.45 to 0.60, and particularly preferably 0.48 to 0.58. . Within this range, the syneresis rate and the gel permeation rate are further improved. The apparent density of water absorbent resin particles is measured at 25° C. in accordance with JIS K7365:1999.

The water retention capacity (g/g) of the water-absorbing resin particles of the present invention with respect to physiological saline is preferably 30 to 50, more preferably 33 to 49, still more preferably 36 to 48, particularly 39 to 47. preferable. If it is less than 30, leakage tends to occur during repeated use, which is not preferable. On the other hand, if it exceeds 50, blocking tends to occur, which is not preferable. The amount of water retention can be appropriately adjusted by the types and amounts of the cross-linking agent (b) and the surface cross-linking agent (e). Therefore, for example, when it is necessary to increase the water retention capacity, it can be easily achieved by reducing the amount of the cross-linking agent (b) and the surface cross-linking agent (e) used.

The water-absorbing resin particles of the present invention preferably have a gel permeation rate (ml/min) of physiological saline of 5-250, more preferably 10-230, particularly preferably 30-210. If the gel permeation rate (ml/min) of physiological saline is less than 5, the diffusibility of the liquid may decrease, and as a result, there is a concern that it may lead to leakage or rash. , there is a concern that the water may leak from the absorbent before the water is absorbed by the water-absorbent resin particles.

The water syneresis rate in the present invention is a value represented by the following formula (1), and the water retention amount with respect to physiological saline and the water retention amount after treating the swollen gel after measuring the water retention amount with a 1.0 wt% calcium chloride aqueous solution. calculated from the ratio of That is, it shows the weight ratio of the separated water after treatment to the weight of the swollen gel before treatment with a dehydrating agent. Therefore, the higher the syneresis rate, the better the dehydration efficiency by a given dehydrating agent treatment.
Syneresis rate [%] = {1-(Water retention amount after treatment with 1.0% by weight calcium chloride aqueous solution [g/g])/(Water retention amount in physiological saline [g/g])} x 100 (1)
A specific measuring method will be described later.

The water-separation rate (%) of the water-absorbing resin particles of the present invention is 70 or more, more preferably 73 or more, and particularly preferably 75 or more, from the viewpoint of efficiency of dehydration treatment. The upper limit is preferably as high as possible and is not particularly limited, but is preferably 95 or less, more preferably 90 or less, from the viewpoint of performance balance with other physical properties and productivity. As a means for improving the water syneresis rate, it is conceivable to increase the specific surface area of the particles or to adjust the balance between hydrophilicity and hydrophobicity within the particles or on the surface of the particles. As a means for achieving this, for example, a hydrophobic substance is used in combination in the polymerization step, the kneading and shredding step, the crosslinking step, and/or the post-crosslinking step, or the gel temperature in the step of kneading the hydrous gel is increased. adjustment, increasing the heating temperature during drying when dehydrating the hydrous gel, increasing the heating temperature in the cross-linking step, decreasing the weight average particle size, and the like. The gel temperature in the step of kneading the hydrous gel is preferably 40 to 120°C, more preferably 50 to 110°C from the viewpoint of dehydration efficiency and performance balance with other physical properties. The heating temperature during dehydration from the hydrous gel is preferably 100 to 300° C., more preferably 110 to 280° C., from the viewpoint of performance balance with other physical properties and productivity. Heating over 300° C. is not preferable because the water-absorbing resin particles undergo thermal deterioration. The heating temperature in the cross-linking step is preferably 100 to 230°C, more preferably 120 to 180°C. Within this range, the hydrophobic substance melts or the viscosity decreases to cover the surface of the absorbent resin particles. be done. The weight-average particle size is preferably 150 μm to 500 μm, more preferably 200 μm to 400 μm, from the viewpoint of the performance balance between dehydration and other physical properties.

The reswelling ratio (%) of the water absorbent resin particles of the present invention with ion-exchanged water is a value shown by the following formula (2), and the swollen gel after measuring the water retention amount is dehydrated with a 1.0% by weight aqueous calcium chloride solution. After the treatment, it is calculated from the ratio of the water retention amount after swelling again with ion-exchanged water and the water retention amount with respect to the physiological saline. Therefore, the lower the reswelling ratio with ion-exchanged water, the more the dehydrating effect of the dehydrating agent is maintained under dilution with water.
Re-swelling ratio with ion-exchanged water [%] = (water retention amount in ion-exchanged water after treatment with 1.0% by weight calcium chloride aqueous solution [g/g])/(water retention amount in physiological saline [g/g] × 100 (2)
A specific measuring method will be described later.

The reswelling ratio (%) of the water absorbent resin particles of the present invention with ion-exchanged water is 110 or less, more preferably 105 or less, from the viewpoint of efficiency of dehydration treatment. The lower limit is preferably as low as possible and is not particularly limited, but is preferably 80 or more from the viewpoint of balance with absorption performance and productivity. Means for reducing the reswelling ratio include increasing the specific surface area of the particles, adjusting the balance between hydrophilicity and hydrophobicity within the particles or on the surface of the particles, increasing the anion concentration inside the particles, and adding a dehydrating agent. It is conceivable to keep the surface area of the water absorbent resin particles after treatment small. Specifically, in the polymerization step, the kneading and shredding step, the crosslinking step, or the post-crosslinking step, a hydrophobic substance is used in combination, and the heating temperature during drying when dehydrating the hydrous gel is increased. For example, the average particle size can be reduced. It is assumed that the presence of the hydrophobic substance on the surface of the absorbent resin particles prevents contact between the water absorbent resin particles and the water present around them, and as a result, it is thought that re-swelling of the gel is suppressed.

The gel permeation rate of the 1.0% by weight calcium chloride aqueous solution of the present invention is the value shown by the following formula. 1.0% by weight aqueous solution of calcium chloride, and the mixed aqueous solution of 20 ml of physiological saline and calcium chloride is allowed to flow down between the swollen gels (T3; seconds). It is calculated from the value obtained by subtracting the time (T4; seconds) for the aqueous solution to flow down without the sample to be measured. Therefore, the higher the gel permeation rate of the 0.1% by weight calcium chloride aqueous solution, the more the dehydrating agent swells and easily permeates between the aggregated water-absorbent resin particles, which means that the dehydration efficiency is excellent.
Gel permeation rate of 1.0 wt% calcium chloride aqueous solution (ml/min) = 20ml x 60/(T3-T4)
A specific measuring method will be described later.

The water-absorbing resin particles of the present invention have a gel permeation rate (ml/min) of a 1.0% by weight calcium chloride aqueous solution of 200 or more, more preferably 300 or more, and particularly preferably 300 or more, from the viewpoint of efficiency of dehydration treatment. 500 or more. The upper limit is preferably as high as possible and is not particularly limited, but is preferably 2300 or less, more preferably 2000 or less, from the viewpoint of performance balance with other physical properties and productivity. The gel permeation rate of an aqueous solution of 1.0% by weight of calcium chloride is controlled by increasing the specific surface area of the particles and adjusting the balance between hydrophilicity and hydrophobicity within the particles or on the surface of the particles.

The water absorbent resin particles of the present invention preferably have an absorption under load (g/g) of 19 or more. If it is less than 19, leakage tends to occur during repeated use, which is not preferable. The upper limit is preferably as high as possible and is not particularly limited, but is preferably 27 or less, more preferably 25 or less, from the viewpoint of performance balance with other physical properties and productivity. The absorption under load can be appropriately adjusted by the types and amounts of the cross-linking agent (b) and the surface cross-linking agent (e). Therefore, for example, when it is necessary to increase the absorption under load, it can be easily achieved by increasing the amount of the cross-linking agent (b) and the surface cross-linking agent (e) used.

The sanitary goods of the present invention contain the water-absorbent resin particles of the present invention, and are easy to dehydrate from used articles. Sanitary products include, for example, paper diapers and sanitary napkins, but not only sanitary products but also various applications such as absorbents and retention agents for various aqueous liquids, and gelling agents. It is possible. The method for producing the sanitary goods is the same as the known ones (described in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, etc.).

In the sanitary goods of the present invention, the water-absorbing resin particles may be used alone as the absorbent, or may be used together with other materials to form the absorbent. Other materials include fibrous materials and the like. The structure and manufacturing method of the absorbent when used with fibrous materials are the same as those of known ones (Japanese Patent Laid-Open Nos. 2003-225565, 2006-131767 and 2005-097569). be.

When the water-absorbing resin particles are used as an absorber together with fibrous material, the weight ratio of the water-absorbing resin particles to the fibers (weight of water-absorbing resin particles/weight of fibers) is preferably 30/70 to 90/10, more preferably. is 40/60 to 70/30. Examples of the fibrous materials include cellulosic fibers, organic synthetic fibers, mixtures of cellulosic fibers and organic synthetic fibers, and the like.

Next, the method for treating sanitary goods of the present invention will be described. The method for treating sanitary products of the present invention is a method for treating used sanitary products containing water-absorbing resin particles, which comprises a step of pulverizing the used sanitary products (hereinafter referred to as a “pulverization step”). a step of dehydrating the water-absorbent resin particles contained in the sanitary goods or the pulverized sanitary goods with a dehydrating agent (hereinafter referred to as a dehydration step), and mixing the pulverized and dehydrated sanitary goods with water. A step of transporting to a solid-liquid processing apparatus (hereinafter referred to as a “transporting step”) is included. The sanitary article may further comprise pulp fibers.

The pulverization step is a step of pulverizing sanitary products to obtain pulverized products. For pulverization, a known pulverizer or crusher can be used, for example, a disposer-type crusher used in a kitchen garbage crusher (a turntable that rotates at high speed throws the sanitary product on the wall surface, and the peripheral edge of the turntable Crushing with a fixed or variable hammer and a fixed blade on the wall), cutter mill, single shaft crusher, twin shaft crusher, coaxial crusher, hammer crusher, ball mill, etc. Since materials for sanitary products include plastic sheets, non-woven fabrics, and stretchable materials, a disposer-type crusher or cutter mill that cuts with a blade while rotating at high speed is particularly suitable.

The sanitary product pulverized material may be an aqueous suspension. Methods for obtaining an aqueous suspension include adding water to swell sanitary products and then pulverizing, pulverizing by adding water while pulverizing, and adding water after pulverizing. From the viewpoint of reducing the load, it is preferable to add water to swell the sanitary goods and then pulverize them.

The preferred range of the size of the pulverized product of the sanitary product after pulverization depends on the separation and recovery method using a solid-liquid separator to be described later, but from the viewpoint of transportability with water flow, the size of one piece of sanitary product is preferably is 100 mm or less. The size of the pulverized product can be appropriately adjusted depending on the type of pulverizer or crusher described above, processing conditions, and the like.

The sanitary goods to be pulverized may be pulverized as they are, or may be pulverized after removing the absorbent containing the water-absorbent resin particles from the sanitary goods.

The dehydration step is a step of dehydrating the water absorbent resin particles contained in the sanitary goods or pulverized sanitary goods with a dehydrating agent. Due to this dehydration treatment, the water absorbing capacity of the water absorbent resin particles is lowered, and the water content and volume of the water absorbent resin particles are lowered. As a result, the gel elasticity of the water-absorbing resin particles is improved, and the separation and recovery efficiency is improved. The dehydration step in the present invention includes not only the step of dehydrating the water absorbent resin particles with a dehydrating agent, but also the step of simply adding a dehydrating agent without actually causing the dehydration phenomenon.

The dehydrating agent in the present invention is not particularly limited as long as it is a compound having dehydrating performance, and known dehydrating agents include water-soluble polyvalent metal compounds, acidic substances, and the like. The water-soluble polyvalent metal compound forms a chelate salt with a carboxyl group or a carboxyl group ion, or converts a carboxyl group ion into a carboxyl group by an acidic substance, so that the inside of the water-absorbing resin particles and the surrounding water As the difference in ion concentration between the particles decreases, the difference in osmotic pressure also decreases, resulting in dehydration from inside the water-absorbing resin particles.

The water-soluble polyvalent metal compound is an element having a valence of 2 or more in the periodic table, and is a water-soluble polyvalent metal compound that forms a carboxyl group or a carboxyl group ion and a chelate salt after dissolving in water or reacting with water. If so, it is not particularly limited. Examples of divalent metal compounds include polyvalent metal compounds containing alkaline earth metals such as magnesium, calcium, strontium and barium, and polyvalent metal compounds containing transition metals such as iron, nickel, copper and zinc. Examples of trivalent metals include polyvalent metal compounds containing metals such as boron, aluminum, and gallium. The polyvalent metal compounds, even if they are nonhydrates, are monohydrate, dihydrate, trihydrate, tetrahydrate, pentahydrate, hexahydrate, heptahydrate. hydrates such as monohydrates, octahydrates and nonahydrates. These dehydrating agents may be used alone or in combination of two or more. In the present invention, the term "water-soluble polyvalent metal compound" refers to a polyvalent metal compound having a solubility in water at 20°C of 1 mg/ml or more, preferably 10 mg/ml or more.

Water-soluble polyvalent metal compounds containing magnesium include magnesium sulfate, magnesium nitrate, magnesium chloride, magnesium acetate, magnesium bromide, magnesium iodide, magnesium perchlorate, magnesium permanganate, and magnesium acetate.

Water-soluble polyvalent metal compounds containing calcium include calcium oxide, calcium peroxide, calcium hydroxide, calcium fluoride, calcium chloride, calcium bromide, calcium iodide, calcium hydride, calcium carbide, calcium phosphide, carbonate Calcium, calcium nitrate, calcium sulfite, calcium silicate, calcium phosphate, calcium pyrophosphate, calcium hypochlorite, calcium chlorate, calcium perchlorate, calcium bromate, calcium iodate, calcium chromate, calcium acetate, calcium gluconate , calcium benzoate, calcium stearate and the like.

The acidic substance is a substance having acidity capable of converting carboxyl group ions in the crosslinked polymer (A) into carboxyl groups. More specifically, it is a compound having an acid dissociation constant of 3.5 or less. When the acidic substance is a polyvalent acid, the dissociation constant in at least the first step is 3.5 or less, and part of the polyvalent acid may be in the form of a neutralized salt.

The acidic substance is at least one acidic compound selected from the group consisting of inorganic acids and organic acids, and two or more of them may be used in combination.

Inorganic acids include sulfuric acid, sulfamic acid, hydrochloric acid, nitric acid, phosphoric acid, metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid and hexametaphosphoric acid.

Examples of organic acids include organic acids having a sulfonic acid group in the molecule, organic acids having a carboxylic acid group in the molecule, and organic acids having a phosphonic group or a phosphoric acid group in the molecule.

Organic acids having a carboxylic acid group in the molecule include halogen-containing carboxylic acids, hydroxycarboxylic acids, amino acids, ketocarboxylic acids, and the like.

Halogen-containing carboxylic acids include monohalogencarboxylic acids, dihalogencarboxylic acids, and trihalogencarboxylic acids, depending on the number of substituents in which hydrogen atoms in the molecule are replaced with fluorine atoms, chlorine atoms, bromine atoms, and/or iodine atoms. , pentahalogencarboxylic acid, and the like.

Monohalogen carboxylic acids include monofluoroacetic acid, monochloroacetic acid, monobromoacetic acid, monoiodoacetic acid, 2-fluoropropionic acid, 2-chloropropionic acid, 2-bromopropionic acid, 2-iodopropionic acid, 2-fluorobutyric acid, 2 -chlorobutyric acid, 2-bromobutyric acid, 2-iodobutyric acid, ortho-fluorobenzoic acid, ortho-chlorobenzoic acid, ortho-bromobenzoic acid, ortho-iodobenzoic acid, 3-chloromandelic acid, and the like.

Dihalogencarboxylic acids include difluoroacetic acid, dichloroacetic acid, dibromoacetic acid, diiodoacetic acid, 2,2-difluoropropionic acid, 2,2-dichloropropionic acid, 2,3-dichloropropionic acid, 2,2-dibromopropionic acid, 2,3-dibromopropionic acid, 2,2-diiodopropionic acid, 2,2-difluorobutyric acid, 2,2-dichlorobutyric acid, 2,2-dibromobutyric acid, 2,2-diiodobutyric acid, and the like.

Trihalogencarboxylic acids include trifluoroacetic acid, trichloroacetic acid, tribromoacetic acid, triiodoacetic acid, 3,3,3-trifluoropropionic acid, and the like.

Examples of pentahalogencarboxylic acids include pentafluorolopionic acid and the like.

A hydroxycarboxylic acid is a compound having a carboxyl group and a hydroxyl group in one molecule. , 2,5-dihydroxybenzoic acid, 3,5-dibromosalicylic acid, 4-methylsalicylic acid, and the like.

An amino acid is a compound having a carboxyl group and an amino group in one molecule, and examples thereof include glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, asparagine, aspartic acid, histidine, and glutamine. , glutamic acid, phenylalanine, tryptophan, arginine, tyrosine, 3-aminohexadioic acid, and the like.

A ketocarboxylic acid is a compound having a carboxyl group and a ketone group in one molecule. , etc.

Examples of organic acids having a phosphonic group or a phosphoric acid group in the molecule include methyldiphosphonic acid, aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotrismethylenephosphonic acid, ethylenediaminetetra(methylenephosphonic acid), ethylenediaminetetramethylenephosphonic acid, hexamethylenediaminetetra(methylenephosphonic acid), propylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), triethylenetetraminehexa(methylenephosphonic acid), triaminotriethylaminehexa (methylene phosphonic acid), trans-1,2-cyclohexanediamine tetra(methylene phosphonic acid), glycol ether diamine, tetramethylene phosphonic acid, and tetraethylenepentamine hepta(methylene phosphonic acid).

Among these dehydrating agents, from the viewpoint of improving dehydration properties, divalent water-soluble polyvalent metal compounds and acidic substances are preferred, and water-soluble polyvalent metal compounds containing magnesium and water-soluble polyvalent metals containing calcium are more preferred. Compounds, inorganic acids, and organic acids having a carboxylic acid group in the molecule, more preferably calcium chloride, calcium oxide, calcium acetate, calcium hypochlorite, hydrochloric acid, nitric acid, and hydroxycarboxylic acid.

The method of treatment with a dehydrating agent is not particularly limited as long as the water-absorbing resin particles in the sanitary product and the dehydrating agent are in contact with each other. Aqueous solutions may be added. As for sanitary goods treated with a dehydrating agent, the dehydrating agent may be added after swelling with water in advance, or water may be added after adding the dehydrating agent. The device for treatment with the dehydrating agent may be any device that can mix the sanitary goods and the dehydrating agent, and may be treated with the above-mentioned pulverizer and crusher, or may be performed in a separate agitable treatment tank. may

The amount of the dehydrating agent used in the dehydrating step depends on the type of dehydrating agent used, but is preferably 0.1% or more, more preferably 1.0% or more, relative to the dry weight of the water-absorbing resin particles. , more preferably 3.0% or more. When the amount of the dehydrating agent is small, the water separation rate of the water-absorbing resin particles is lowered, and the separation and recovery efficiency is lowered.

Regarding the order of the pulverization step and the dehydration step described above, the step of pulverizing the sanitary product and the step of dehydrating the sanitary product or the water-absorbent particles contained in the pulverized sanitary product with a dehydrating agent can be performed sequentially or simultaneously. . The order of specific processing steps is shown below. Arrows indicate order.
(1) Process of pulverizing sanitary products → Process of dehydrating the water-absorbing resin particles contained in the pulverized sanitary products with a dehydrating agent → Mixing the pulverized and dehydrated sanitary products with water and transferring them to a solid-liquid treatment device. The process of transporting.
(2) Step of dehydrating the water absorbent resin particles contained in the sanitary goods with a dehydrating agent→Process of pulverizing the sanitary goods→Step of mixing the pulverized and dehydrated sanitary goods with water and transporting them to a solid-liquid treatment apparatus. .
(3) A step of dehydrating the water-absorbent resin particles contained in the sanitary goods or pulverized sanitary goods with a dehydrating agent and a process of pulverizing the sanitary goods at the same time. A step of mixing with and transporting to a solid-liquid processing apparatus.

The transportation step is a step of mixing the pulverized and dehydrated sanitary goods with water and transporting the mixture to a downstream solid-liquid processing device. The sanitary article pulverized material, preferably an aqueous suspension, is transported in a stream of water to the solid-liquid treatment apparatus by means of a water supply.

The transportation means in the transportation process can be transported to the solid-liquid processing equipment by a pump type or a gravity flow system. Transport is preferred. Types of pipes or hoses include copper pipes, lead pipes, iron pipes, rigid polyvinyl chloride pipes, polyethylene pipes, rigid vinyl chloride lined pipes, stainless steel pipes, white pipes, earthen pipes, fireproof two-layer pipes, and the like.

A known solid-liquid separation processing device can be used as the solid-liquid processing device. For example, screen separation, sedimentation separation, membrane separation, centrifugation and the like can be mentioned.

One preferred embodiment of the method for treating sanitary products of the present invention is a disposal wastewater treatment system. Disposer wastewater treatment is a system in which raw garbage is usually pulverized by a disposer attached to the drain of a kitchen sink and discharged into a sewage system or a septic tank together with wastewater from water supply. This is a wastewater treatment system, and it is widely used especially in collective housing. In order to expand the wastewater treatment system to sanitary products, it is important to reduce the water swelling of the water-absorbing resin particles and prevent poor drainage and clogging of pipes due to deposition and adhesion in drainpipes. The treatment method of the invention is preferable because it can solve such problems.

In the method for treating sanitary products of the present invention, after the sanitary products that have been pulverized and dehydrated are transported to the solid-liquid treatment device, the sanitary products containing water-absorbing resin particles that have been pulverized and dehydrated by the solid-liquid separator are recovered. be done. Since the recovered sanitary products obtained by the method for treating sanitary products of the present invention are characterized by having a low water content, they not only have excellent combustion efficiency during incineration, but can also be recycled as solid fuel or the like. . Accordingly, the present invention includes a method for producing a sanitary article collected material and a solid fuel obtained by the sanitary article processing method. When the solid fuel is recycled, it is preferable to further dry the collected sanitary goods.

EXAMPLES The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these. In addition, unless otherwise specified, parts indicate parts by weight and % indicates weight %. The water retention capacity of the water-absorbing resin particles in physiological saline, the syneresis rate, the absorption under load, the gel permeation rate of physiological saline, and the gel permeation rate of 1.0% by weight calcium chloride aqueous solution are measured by the following methods. bottom.

<Method for measuring water retention in physiological saline>
Put 1.00 g of the measurement sample in a tea bag (20 cm long, 10 cm wide) made of nylon mesh with an opening of 63 μm (JIS Z8801-1: 2006), and put it in 1,000 ml of physiological saline (salt concentration 0.9%). After being immersed for 1 hour without stirring, it was taken out and hung for 15 minutes to drain. After that, the whole tea bag was placed in a centrifuge and dehydrated by centrifugation at 150 G for 90 seconds to remove excess physiological saline. The physiological saline used and the temperature of the measurement atmosphere were set to 25°C ± 2°C. (h2) is the weight of the tea bag measured in the same manner as above without the measurement sample.
Water retention amount (g/g) = (h1) - (h2)

<Method for measuring separation rate>
After the measurement of the water retention amount, the following operations were continuously performed. That is, after centrifugation, the tea bag was immersed in 500 ml of a 1.0% by weight calcium chloride aqueous solution for 5 minutes without stirring, then pulled out, placed in a centrifuge together with the tea bag, and centrifuged at 150 G for 90 seconds. Excess calcium chloride aqueous solution was removed by dehydration, the weight (h3) including the tea bag was measured, and the water retention capacity after treatment with 1.0% by weight calcium chloride aqueous solution was obtained from the following equation. (h4) is the weight of the tea bag measured in the same manner as above without the measurement sample.
Water retention after treatment with 1.0% calcium chloride aqueous solution (g/g) = (h3) - (h4)
After that, the syneresis rate was determined by the following formula.
Syneresis rate (%) = (1-1.0% by weight water retention after treatment with calcium chloride solution)/(water retention with respect to physiological saline) x 100

<Method for measuring reswelling ratio with ion-exchanged water>
After the measurement of the syneresis rate, the following operations were continuously performed. That is, the tea bag after centrifugal dehydration is immersed in 500 ml of an ion-exchanged aqueous solution for 5 minutes without agitation, then taken out, placed in a centrifuge together with the tea bag, and dehydrated by centrifugation at 150 G for 90 seconds to remove excessive ion exchange. The aqueous solution was removed, the weight (h5) including the tea bag was measured, and the water retention amount after treatment with ion-exchanged water was calculated from the following equation. (h6) is the weight of the tea bag measured in the same manner as above without the measurement sample.
Water retention amount [g/g] for deionized water after treatment with 1.0 wt% calcium chloride aqueous solution = (h5) - (h6)
After that, the reswelling ratio with ion-exchanged water was determined by the following formula.
Re-swelling ratio with ion-exchanged water [%] = (Water retention amount in ion-exchanged water after treatment with 1.0% by weight calcium chloride aqueous solution [g/g])/(Water retention amount in physiological saline [g/g])} ×100

<Method for measuring absorption under load>
Measured by sieving into a range of 250 to 500 μm using a standard sieve in a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh of 63 μm (JIS Z8801-1: 2006) attached to the bottom. A 0.16 g sample was weighed, and the cylindrical plastic tube was set vertically so that the sample to be measured had a uniform thickness on the nylon net. Diameter: 24.5 mm,) was placed. After measuring the weight (M1) of the entire cylindrical plastic tube, a cylindrical plastic tube containing a measurement sample and a weight in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%) The tube was placed vertically, immersed with the nylon mesh side down, and allowed to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, tilted to collect the water adhering to the bottom in one place, and dripped down to remove excess water. The weight (M2) of the entire cylindrical plastic tube was weighed, and the absorption under load was obtained from the following formula. The physiological saline used and the temperature of the measurement atmosphere were set to 25°C ± 2°C.
Absorption under load (g/g) = {(M2) - (M1)}/0.16

<Method for measuring gel permeation rate of physiological saline>
It was measured by the following operation using the instrument shown in FIGS.
Swollen gel particles 2 were prepared by immersing 0.32 g of the measurement sample in 150 ml of physiological saline 1 (salt concentration: 0.9%) for 30 minutes. A vertical cylinder 3 (diameter (inner diameter) 25.4 mm, length 40 cm) has scale lines 4 and 5 at positions 60 ml and 40 ml from the bottom, respectively. } at the bottom of the filtration cylindrical tube having a wire mesh 6 (opening 106 μm, JIS Z8801-1: 2006) and a freely openable and closable cock 7 (inner diameter of the liquid passing part 5 mm), with the cock 7 closed, After transferring the prepared swollen gel particles 2 together with physiological saline, a circular wire mesh having a pressurizing shaft 9 (weight 22 g, length 47 cm) connected perpendicularly to the surface of the wire mesh is placed on the swollen gel particles 2. 8 (opening 150 μm, diameter 25 mm) was placed so that the wire mesh and the swollen gel particles were in contact, and a weight 10 (88.5 g) was placed on the pressure shaft 9 and allowed to stand for 1 minute. Subsequently, open the cock 7, measure the time (T1; seconds) required for the liquid level in the filtration cylindrical tube to change from the 60 ml scale line 4 to the 40 ml scale line 5, and use the following formula to calculate the gel permeation rate (ml / min). asked for
Gel permeation rate (ml / min) = 20ml × 60 / (T1-T2)
The physiological saline used and the temperature of the measurement atmosphere were set at 25° C.±2° C., and T2 is the time measured by the same operation as above without the measurement sample.

<Method for measuring gel permeation rate of 1.0% by weight calcium chloride aqueous solution>
It was measured by the following operation using the instrument shown in FIGS.
Swollen gel particles 2 were prepared by immersing 0.32 g of the measurement sample in 150 ml of physiological saline 1 (salt concentration: 0.9%) for 30 minutes. A vertical cylinder 3 (diameter (inner diameter) 25.4 mm, length 40 cm) has scale lines 4 and 5 at positions 60 ml and 40 ml from the bottom, respectively. }, a wire mesh 6 (opening 106 μm, JIS Z8801-1: 2006) and a freely openable and closable cock 7 (internal diameter of the liquid passing part 5 mm) are placed in the filtration cylindrical tube, and the cock 7 is closed. . Of the physiological saline solution used for the preparation of the measurement sample, 80 ml of the supernatant was discarded, and the remaining swollen gel particles 2 were transferred together with the physiological saline solution. A circular wire mesh 8 (opening 150 μm, diameter 25 mm) having a pressure axis 9 (weight 22 g, length 47 cm) connected perpendicularly to the surface of the wire mesh is placed on the particle 2, and the wire mesh and the swollen gel particles are brought into contact with each other. Further, a weight 10 (88.5 g) was placed on the pressurizing shaft 9 and left to stand for 1 minute. Subsequently, open the cock 7, measure the time (T3; seconds) required for the liquid level in the filtration cylindrical tube to change from the 60 ml scale line 4 to the 40 ml scale line 5, and use the following formula to calculate the gel permeation rate (ml / min). asked for
Gel permeation rate of 1.0 wt% calcium chloride aqueous solution (ml/min) = 20ml x 60/(T3-T4)
The physiological saline solution, 1.0% by weight calcium chloride aqueous solution, and temperature of the measurement atmosphere were set at 25° C.±2° C. T4 is the time measured by the same operation as above without the measurement sample.

<Example 1> Water-soluble vinyl monomer (a1) {acrylic acid} 157 parts (2.18 mol parts), internal cross-linking agent (b) {pentaerythritol triallyl ether} 0.6305 parts (0.0024 mol parts) and 344.65 parts of deionized water were kept at 3° C. while stirring and mixing. After nitrogen was introduced into this mixture to make the dissolved oxygen content 1 ppm or less, 0.63 parts of a 1% aqueous hydrogen peroxide solution, 1.1774 parts of a 2% ascorbic acid aqueous solution and 2% 2,2'-azobis [ 2-Methyl-N-(2-hydroxyethyl)-propionamide] aqueous solution (2.355 parts) was added and mixed to initiate polymerization. After the temperature of the mixture reached 90° C., the mixture was polymerized at 90±2° C. for about 5 hours to obtain hydrous gel (1).

Next, 502.27 parts of this hydrous gel (1) was finely divided into approximately 1 mm squares with scissors, and 128.42 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed. Subsequently, using a mincing machine with a perforated plate diameter of 16 mm (12VR-400K manufactured by ROYAL), 4 times while adding 0.10 parts of the hydrophobic substance (c-1) {Mg stearate} to the gel at a gel temperature of 80 ° C. After kneading and shredding, the mixture was dried with a ventilation band dryer {150° C., wind speed 2 m/sec} to obtain a dry product. The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), and then adjusted to a particle size range of 710 to 150 μm in opening to obtain dried product particles. The weight-average particle size of the dry particles at this time was 392 μm. 5.00 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio = 70/30) was added to 100 parts of the dried particles while being stirred at high speed and mixed. , at 150° C. for 30 minutes for surface cross-linking to obtain water absorbent resin particles (P-1).

<Example 2>
Water absorbent resin particles (P-2) were obtained in the same manner as in Example 1, except that the gel temperature was changed from 80°C to 120°C.

<Example 3>
Water absorbent resin particles (P-3) were obtained in the same manner as in Example 1, except that the gel temperature was changed from 80°C to 40°C.

<Example 4>
Water absorbent resin particles (P-4) were obtained in the same manner as in Example 1, except that the weight average particle size of the dry particles was changed from 392 μm to 200 μm.

<Example 5>
502.27 parts of hydrous gel (1) was finely divided into approximately 1 mm squares with scissors, and 128.42 parts of 48.5% sodium hydroxide aqueous solution was added and mixed. Subsequently, using a mincing machine with a perforated plate diameter of 16 mm (12VR-400K manufactured by ROYAL), after kneading and shredding four times, it was dried with a ventilated band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried body. . The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), and then adjusted to a particle size range of 710 to 150 μm in opening to obtain dried product particles. 7.30 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio = 70/30) and a hydrophobic substance (c-2) were added to 100 parts of the dried particles while stirring at high speed. {Carboxy-modified polysiloxane Model No. X-22-3701E, manufactured by Shin-Etsu Chemical Co., Ltd.} 0.02 part was added while spraying and mixed, and allowed to stand at 150° C. for 30 minutes for surface cross-linking to obtain composite particles. . 100 parts of these composite particles and 0.4 parts of inorganic powder (silicon dioxide, Tokusil, volume average particle size 2.5 μm, specific surface area 120 m ² /g, manufactured by Tokuyama Corporation) are uniformly mixed in a conical blender (manufactured by Hosokawa Micron Corporation). Thus, absorbent resin particles (P-5) were obtained.

<Example 6>
502.27 parts of hydrous gel (1) was finely divided into approximately 1 mm squares with scissors, and 128.42 parts of 48.5% sodium hydroxide aqueous solution was added and mixed. Subsequently, using a mincing machine with a perforated plate diameter of 16 mm (12VR-400K manufactured by ROYAL), after kneading and shredding four times, it was dried with a ventilated band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried body. . The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), and then adjusted to a particle size range of 710 to 150 μm in opening to obtain dried product particles. 7.30 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio = 70/30) was added to 100 parts of the dried particles while being stirred at high speed and mixed. , and 150° C. for 30 minutes for surface cross-linking to obtain composite particles. 100 parts of the composite particles, 1.0 parts of methanol, and 0.02 parts of the hydrophobic substance (c-2) are uniformly mixed in a conical blender (manufactured by Hosokawa Micron Corporation) to obtain absorbent resin particles (P-6). rice field.

<Example 7>
Water absorbent resin particles (P-7) were obtained in the same manner as in Example 5, except that 0.4 part of the inorganic powder was not added.

<Example 8>
Water-absorbing resin particles (P-8) were obtained in the same manner as in Example 5, except that the hydrophobic substance (c-2) was changed from 0.02 parts to 0.04 parts.

<Example 9>
Water absorbent resin particles (P-9) were obtained in the same manner as in Example 5, except that the hydrophobic substance (c-2) was changed from 0.02 parts to 0.10 parts.

<Example 10>
Hydrophobic substance (c-1) 0.10 parts was changed to hydrophobic substance (c-3) {sucrose stearic acid monoester} 0.15 parts, except for changing 4 times kneading to 2 times kneading Water absorbent resin particles (P-10) were obtained in the same manner as in Example 1.

<Example 11>
Except for changing the subdivision to about 1 mm square with scissors to about 5 mm square and changing 0.10 parts of the hydrophobic substance (c-1) to 0.15 parts of the hydrophobic substance (c-3), Water absorbent resin particles (P-11) were obtained in the same manner as in Example 1.

<Example 12>
In the same manner as in Example 1, except that the perforated plate diameter was changed to 8 mm and 0.10 parts of the hydrophobic substance (c-1) was changed to 0.15 parts of the hydrophobic substance (c-3). Water absorbent resin particles (P-12) were obtained.

<Examples 13 to 15>
For Examples 13 to 15, the water absorbent resin particles (P-5) obtained in Example 5 were added with 1,000 ml of a 1.0% by weight aqueous calcium chloride solution as a dehydrating agent, and 1 part of an aqueous 1 N hydrochloric acid solution was added. ,000 ml, 1,000 ml of 1.0% by weight glyceric acid aqueous solution, and 1,000 ml of 1 N sulfuric acid aqueous solution, but the same operation was carried out for evaluation.

<Comparative Example 1>
Comparative water absorbent resin particles (H-1) were obtained in the same manner as in Example 1, except that the hydrophobic substance (c-1) was not added.

<Comparative Example 2> A water-containing gel finely divided into about 1 mm squares is kneaded with a mincing machine (12VR-400K manufactured by ROYAL) without being kneaded and shredded. Comparative water-absorbing resin particles (H-2) were obtained in the same manner as in Example 1, except that the solid particles were obtained.

<Comparative Example 3> Water-absorbing resin particles (H-3) were prepared in the same manner as in Example 1, except that the particle size range of the opening of 710 to 150 µm was changed to the particle size of the opening of 710 to 300 µm. got

<Comparative Example 4>
Water absorbent resin particles (H-4) were obtained in the same manner as in Example 1 except that the gel temperature was changed from 80°C to 20°C.

<Comparative Example 5>
Water-absorbent resin particles (H-5) were obtained in the same manner as in Example 1, except that the drying temperature was changed from 150°C to 300°C.

<Comparative Example 6>
Water absorbent resin particles (H-6) were obtained in the same manner as in Example 1, except that the surface cross-linking temperature was changed from 150°C to 90°C.

<Comparative Example 7>
Water absorbent resin particles (H-7) were obtained in the same manner as in Example 1 except that the surface cross-linking temperature was changed from 150°C to 210°C.

<Comparative Example 8> A commercially available diaper GOO. N (pants L size, manufactured by Daio Paper Co., Ltd., May 2018, Japan) is crushed by hand, and the crushed water-absorbing resin particles contained in the absorber are taken out together with the pulp, and then separated. Crushed water absorbent resin particles (H-8) were obtained.

<Comparative Example 9>
The commercially available diaper GOO. N (pants S size, manufactured by Daio Paper Co., Ltd., May 2018, Japan) is crushed by hand, and the spherical water-absorbing resin particles contained in the absorbent body are taken out together with the pulp, and then each is separated. Spherical water absorbent resin particles (H-9) were obtained.

Regarding the water-absorbent resin particles obtained in Examples 1 to 15 and Comparative Examples 1 to 9, the water retention amount against physiological saline, the absorption under load, the gel permeation rate of physiological saline, the apparent density, the weight average particle diameter, Tables 1 and 2 show the results of the gel permeation rate of the 1.0% by weight calcium chloride aqueous solution, the syneresis rate, and the reswelling ratio with ion-exchanged water.

Tables 1 and 2 also show the dehydration evaluation results of absorbent bodies prepared by the following method using the water absorbent resin particles obtained in Examples 1 to 15 and Comparative Examples 1 to 9.
In the table, dehydrating agent A is a 1.0% by weight calcium chloride aqueous solution, dehydrating agent B is a 1N hydrochloric acid aqueous solution, dehydrating agent C is a 1.0% by weight glyceric acid aqueous solution, and dehydrating agent D is a 1N sulfuric acid solution. Aqueous solutions, respectively.

<Preparation of hygiene products>
100 parts of hydrophilic fiber (fluff pulp) and 100 parts of water-absorbing resin particles (each water-absorbing resin particles obtained in Examples and Comparative Examples) are mixed in an airflow mixing device (pad former) to form a mixture. After obtaining, this mixture was uniformly laminated on an acrylic plate (thickness 4 mm) so as to have a weight per unit area of 500 g/m ² and pressed at a pressure of 5 kg/cm ² for 30 seconds to obtain an absorber. This absorber was cut into 10 cm×10 cm squares, and water-permeable sheets of the same size as the absorber (15.5 g/m ² basis weight, manufactured by Advantech, filter paper No. 2) were placed above and below each, and further A sanitary product was prepared by placing a polyethylene sheet (S-1) (polyethylene film UB-1 manufactured by Tamapoly Co., Ltd.) as an impermeable sheet on the back side and a nonwoven fabric (S-2) as a nonwoven fabric layer on the front side.

<Evaluation of dehydration property of absorber>
The prepared sanitary product is placed on a metal bat so that the nonwoven fabric (S-2) side faces upward, and 150 ml of physiological saline (salt concentration: 0.9%) in a 300 ml beaker is evenly applied to the sanitary product. After the nonwoven fabrics (S-1) and (S-2) were removed from the sanitary goods, the weight (h5; g) of the swollen absorbent body was measured. Next, put the swollen absorber in a tea bag (15 cm long, 15 cm wide) made of nylon mesh with an opening of 63 μm (JIS Z8801-1: 2006), and put it in 1,000 ml of a 1.0 wt% calcium chloride aqueous solution. After being immersed for 5 minutes without stirring, take it out, put it in a centrifuge, spin-dry it at 150 G for 90 seconds to remove excess calcium chloride aqueous solution, and measure the weight (h6; g) including the tea bag using the following formula. Calculate the absorber dehydration rate from The temperatures of the physiological saline solution, the calcium chloride aqueous solution, and the measurement atmosphere used are 25°C ± 2°C. In (h7; g), an absorber was prepared in the same manner and allowed to stand for 5 hours, then the nonwoven fabrics (S-1) and (S-2) were removed from the sanitary goods, and the weight of the swollen absorber (h7; g ) is the weight when measuring.
Absorbent dehydration rate (%) = [1-{(h6)-(h7)}/(h5)] × 100

As is clear from the results shown in Tables 1 and 2, the water absorbent resin particles of the present invention, which can be easily dehydrated, have an improved water separation rate compared to the water absorbent resin particles of the comparative examples. In addition, in the evaluation of the water separation rate of the absorbent using the present water absorbent resin particles, it can be seen that the higher the water separation rate of the water absorbent resin particles, the more the water separation rate of the absorbent is improved. From this result, it can be said that the absorber using water-absorbent resin particles with a high water syneresis rate can reduce the total weight per sheet of absorber because the water content of the swollen absorber after dehydration treatment is reduced. Therefore, for example, by performing the same treatment operation with an aqueous calcium chloride solution after urinating, the labor during transportation can be reduced, and when incinerating, the energy used for incineration can be reduced, so the environmental load can be reduced.

By applying the water absorbent resin particles of the present invention, which can be easily dehydrated, to various absorbent articles including sanitary goods, the absorbent article can be improved by a predetermined dehydration treatment after use while satisfying the required absorption performance during use. Since the moisture content can be easily reduced, it is used in disposable diapers (child diapers, adult diapers, etc.), napkins (sanitary napkins, etc.), paper towels, pads (pads for incontinent persons, surgical underpads, etc.), and pets. It is suitable for sanitary products such as sheets (pet urine absorbing sheets), and is particularly suitable for disposable diapers.

1 Physiological saline solution 2 Water-containing gel particles 3 Cylinder 4 Scale line 5 at 60 ml from the bottom Scale line 4 at 40 ml from the bottom 6 Wire mesh 7 Cock 8 Circular wire mesh 9 Pressure shaft 10 Weight

Claims (12)

Containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a crosslinked polymer (A) having an internal cross-linking agent (b) as essential structural units, Water-absorbent resin particles that can be easily dehydrated and have a water separation rate represented by the following formula (1) of 70% or more , wherein the water-absorbent resin particles include long-chain fatty acid esters, long-chain fatty acids and salts thereof, long-chain Contains at least one hydrophobic substance (c) selected from the group consisting of aliphatic alcohols, long-chain aliphatic amides, carboxy-modified polysiloxanes, epoxy-modified polysiloxanes, amino-modified polysiloxanes and alkoxy-modified polysiloxanes. , water absorbent resin particles .
Syneresis rate [%] = {1-(Water retention amount after treatment with 1.0% by weight calcium chloride aqueous solution [g/g])/(Water retention amount in physiological saline [g/g])} x 100 (1)
However, in the above formula (1), the water retention amount [g / g] for physiological saline is immersed in physiological saline (salt concentration 0.9%) without stirring for 1 hour, and then centrifuged at 150 G for 90 seconds. It is the water retention amount for the physiological saline obtained by dehydration,
The water retention capacity [g/g] after treatment with a 1.0 wt% calcium chloride aqueous solution was obtained by immersing the specimen in a 1.0 wt% calcium chloride aqueous solution for 5 minutes without stirring after measuring the water retention capacity with respect to physiological saline, and measuring 150 G. is the amount of retained water after treatment with a 1.0% by weight calcium chloride aqueous solution obtained by centrifugal dehydration for 90 seconds at . 2. The water absorbent resin particles according to claim 1, wherein the water separation rate is 75% or more. 3. The water absorbent resin particles according to claim 1 or 2, wherein the re-swelling ratio with ion-exchanged water represented by the following formula (2) is 110% or less.
Re-swelling ratio with ion-exchanged water [%] = (water retention amount in ion-exchanged water after treatment with 1.0 wt% calcium chloride aqueous solution [g/g])/(water retention amount in physiological saline [g/g]) x 100 (2)
However, in the above formula (2), the water retention amount [g/g] for ion-exchanged water after treatment with a 1.0 wt% calcium chloride aqueous solution) is 5 It is the amount of water retained in ion-exchanged water after treatment with a 1.0% by weight calcium chloride aqueous solution, obtained by immersing for 10 minutes and centrifugal dehydration at 150 G for 90 seconds. 4. The water absorbent resin particles according to any one of claims 1 to 3, having a water retention capacity of 30 to 50 g/g in physiological saline. 5. The water absorbent resin particles according to any one of claims 1 to 4, having an apparent density of 0.40 to 0.62 g/ml. The water absorbent resin particles according to any one of claims 1 to 5, having a weight average particle diameter of 150 to 500 µm. 7. The water-absorbent resin particles according to any one of claims 1 to 6, which have an irregular crushed shape. 8. The method for producing water-absorbent resin particles according to any one of claims 1 to 7 , wherein the water-soluble vinyl monomer (a1) and/or the vinyl monomer that becomes the water-soluble vinyl monomer (a1) by hydrolysis ( A polymerization step of obtaining a hydrous gel containing the crosslinked polymer (A) by polymerizing a monomer composition containing a2) and the internal cross-linking agent (b) as essential constituent units, a hydrous gel of the crosslinked polymer (A) , further kneading and shredding the finely divided hydrous gel at a gel temperature of 40 ° C. to 120 ° C., and drying and pulverizing the kneaded and shredded hydrous gel to obtain water-absorbent resin particles. and a method for producing the water absorbent resin particles. 9. The production method according to claim 8 , comprising a surface cross-linking step. 10. The production method according to claim 9 , comprising a step of adjusting the particle size after the surface cross-linking step. Sanitary goods containing the water-absorbing resin particles according to any one of claims 1 to 7 , and facilitating dehydration of water from used goods. used sanitary goods,
Containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a crosslinked polymer (A) having an internal cross-linking agent (b) as essential structural units, Treatment of used sanitary products that contain water-absorbing resin particles that are easily dehydrated and whose water separation rate represented by the following formula (1) is 70% or more, and whose moisture is easily dehydrated. A method comprising a step of pulverizing used sanitary products, a step of dehydrating water absorbent resin particles contained in the sanitary products or the pulverized sanitary products with a dehydrating agent, and pulverized and dehydrated sanitary products. is mixed with water and treated by a sanitary product treatment method including a step of transporting to a solid-liquid treatment apparatus , wherein the water-absorbing resin particles that can be easily dehydrated are a long-chain fatty acid ester, At least one hydrophobic selected from the group consisting of long-chain fatty acids and salts thereof, long-chain fatty alcohols, long-chain fatty amides, carboxy-modified polysiloxanes, epoxy-modified polysiloxanes, amino-modified polysiloxanes and alkoxy-modified polysiloxanes A manufacturing method containing substance (c) .
Syneresis rate [%] = {1-(Water retention amount after treatment with 1.0% by weight calcium chloride aqueous solution [g/g])/(Water retention amount in physiological saline [g/g])} x 100 (1)
However, in the above formula (1), the water retention amount [g / g] for physiological saline is immersed in physiological saline (salt concentration 0.9%) without stirring for 1 hour, and then centrifuged at 150 G for 90 seconds. It is the water retention amount for the physiological saline obtained by dehydration,
The water retention capacity [g/g] after treatment with a 1.0 wt% calcium chloride aqueous solution was obtained by immersing the specimen in a 1.0 wt% calcium chloride aqueous solution for 5 minutes without stirring after measuring the water retention capacity with respect to physiological saline, and measuring 150 G. is the amount of retained water after treatment with a 1.0% by weight calcium chloride aqueous solution obtained by centrifugal dehydration for 90 seconds at .

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