JP2021181507A - Water absorbent resin particle easy in dehydration treatment and manufacturing method thereof - Google Patents

Abstract

To provide a water absorbent resin particle that has excellent absorption characteristics during normal usage and is easy in dehydration treatment after usage, its manufacturing method and a treatment method of hygiene products.SOLUTION: A water absorbent resin particle that contains a crosslinked polymer (A) having an aqueous vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes the aqueous vinyl monomer (a1) due to hydrolysis as well as an internal crosslinking agent (b) as the necessary constituent, and has a syneresis ratio represented by the following formula of 70% or larger and hygiene product containing the same, as well as, a treatment method of hygiene products comprising a step of dehydrating the water absorbent resin particle contained in the crashed dehydration agent, and a step of transporting the crashed and dehydrated hygiene product to a solid liquid treatment apparatus by mixing with water. The syneresis ratio [%]={1-(water capacity [g/g] after treatment with 1.0 wt.% calcium chloride aqueous solution/(water capacity [g/g] relative to physiological saline)} × 100.SELECTED DRAWING: None

Description

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

In recent years, as the amount of hygiene products used has increased, waste disposal of hygiene products after use has become a serious problem. Hygiene products, especially disposable diapers, are rapidly becoming widespread as indispensable items in the age of declining birthrate and aging population, and their consumption is increasing rapidly. Regarding waste disposal of sanitary goods after use, disposable diapers and the like are usually incinerated, but since the proportion of water in diapers is close to 80%, incineration requires a large amount of combustion energy. This treatment method puts a heavy load on the incinerator itself, which not only shortens the life of the incinerator, but also leads to air pollution and global warming, which is a factor that puts a load on the environment. Is strongly desired.

Several means have been proposed to solve the problem of waste disposal of hygiene products after use. For example, a technique relating to a system for separating and recovering superabsorbent polymer particles and other members of sanitary products by using lime (Patent Document 1), after dehydration and aggregation of superabsorbent polymer particles by using an aqueous solution of calcium chloride. A technique of adding a salt of a strong acid and a nitrogen-containing basic compound to reduce the cohesive force and facilitating subsequent drying (Patent Document 2), a used superabsorbent polymer is dehydrated with a polyvalent metal salt aqueous solution. After that, a technique for recovering the water absorption capacity of the superabsorbent polymer by treating with an aqueous alkali metal salt solution (Patent Document 3), recovering the pulp fiber from the used sanitary goods containing the superabsorbent polymer and the superabsorbent polymer, and recovering the pulp fiber. A technique for producing recycled pulp that can be reused for sanitary products by decomposing a superabsorbent polymer by ozone treatment (Patent Document 4) has been proposed.

Japanese Unexamined Patent Publication No. 2009-183893 JP-A-2015-120834 Japanese Unexamined Patent Publication No. 2013-198862 Japanese Unexamined Patent Publication No. 2017-193819

If the water contained in used hygiene products can be efficiently removed to deal with the problem of waste disposal of hygiene products after use, the combustion efficiency during incineration and the productivity during recycling will improve, and the environmental load will be significantly increased. It can be expected to be reduced. An object of the present invention is to provide water-absorbent resin particles having good absorption characteristics during normal use and easy to dehydrate water contained in used sanitary goods, and a method for producing the same.

In the present invention, a crosslinked polymer (A) containing a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal cross-linking agent (b) as essential constituent units. It is a water-absorbent resin particle which contains, and has a water separation rate of 70% or more, which is represented by the following formula (1), and is easy to dehydrate, and a sanitary product containing the same.
Water separation rate [%] = {1- (Water retention amount after treatment with 1.0 wt% calcium chloride aqueous solution [g / g]) / (Water retention amount for physiological saline [g / g])} × 100 (1)
The present invention is also a method for producing the water-absorbent resin particles, wherein the water-soluble vinyl monomer (a1) and / or the vinyl monomer (a2) which becomes the water-soluble vinyl monomer (a1) by hydrolysis and the internal cross-linking agent (b). ) Is polymerized to obtain a water-containing gel containing the crosslinked polymer (A), a step of subdividing the water-containing gel of the crosslinked polymer (A), and subdivided water content. Production of the water-absorbent resin particles, which comprises a step of further kneading and shredding the gel at a gel temperature of 40 ° C. to 120 ° C., and a step of drying and then pulverizing the kneaded and shredded water-containing gel to obtain water-absorbent resin particles. The method.

The water-absorbent resin particles of the present invention, which are easy to dehydrate (hereinafter, also simply referred to as the water-absorbent resin particles of the present invention), show excellent water release when treated with a dehydrating agent. Further, the sanitary products such as disposable diapers containing the water-absorbent resin particles of the present invention satisfy the absorption performance required for disposable diapers at the time of use, and after use, by adding a dehydrating agent such as a polyvalent metal salt aqueous solution, the water-absorbent resin particles can be obtained. The water content can be significantly reduced and dehydration can be easily performed. Therefore, the combustion efficiency at the time of incineration and the productivity at the time of recycling can be improved, and the environmental load can be reduced.

It is sectional drawing which represented typically the filtration cylinder tube for measuring the gel liquid passing rate. It is a perspective view schematically showing a pressure shaft and a weight for measuring a gel liquid passing rate.

The water-absorbent resin particles of the present invention are crosslinked with a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and an internal cross-linking agent (b) as essential constituent units. Water-absorbent resin particles containing the polymer (A).

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and is a known monomer, for example, at least one water-soluble substituent disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 36485553 and ethylenia-free. Vinyl monomers having a saturated group (for example, anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers), anionic vinyl monomers and nonionic vinyl monomers disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883. Select from the group consisting of a sex vinyl monomer, a cationic vinyl monomer, and 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. A vinyl monomer having at least one of these can be used.

The vinyl monomer (a2) (hereinafter, also referred to as hydrolyzable vinyl monomer (a2)) which becomes a water-soluble vinyl monomer (a2) by hydrolysis is not particularly limited and is known (for example, 0024 to 0025 of Japanese Patent No. 36485553). A vinyl monomer having at least one hydrolyzable substituent that becomes a water-soluble substituent by hydrolysis disclosed in the paragraph, at least one hydrate disclosed in paragraphs 0052 to 0055 of JP-A-2005-75982. A vinyl monomer having a degradable substituent (a vinyl monomer having 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. Further, the hydrolyzable property means a 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 during polymerization, after polymerization, or both, but is preferably after polymerization from the viewpoint of the molecular weight of the obtained water-absorbent resin particles.

Of these, the water-soluble vinyl monomer (a1) is preferable from the viewpoint of absorption characteristics and the like. 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, vinyl monomers having a carboxy (salt) group or a carbamoyl group are more preferable, (meth) acrylic acid (salt) and (meth) acrylamide are more preferable, and (meth) acrylic acid (salt) is particularly preferable. The most preferable is acrylic acid (salt).

In addition, "carboxy (salt) group" means "carboxy group" or "carboxylate group", and "sulfo (salt) group" means "sulfo group" or "sulfonate group". Further, (meth) acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylamide, and (meth) acrylamide means acrylamide or methacrylamide. The salt includes an alkali metal (lithium, sodium, potassium, etc.) salt, an alkaline earth metal (magnesium, calcium, etc.) salt, an ammonium (NH ₄ ) salt, and the like. Of these salts, alkali metal salts and ammonium salts are preferable, and alkali metal salts are more preferable, and sodium salts are particularly preferable, from the viewpoint of absorption characteristics 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 preferable that a part of the acid group-containing monomer is neutralized with a base from the viewpoint of water absorption performance and residual monomer. .. As the base to be neutralized, 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 the water-absorbent resin particles, and for example, a method for neutralizing the acid group-containing monomer before polymerization or after polymerization. A method such as neutralizing the acid group-containing polymer in the state of a water-containing gel is exemplified as a preferable example.

When the acid group-containing monomer is used, the degree of neutralization of the acid group is preferably 50 to 80 mol%. When the degree of neutralization is less than 50 mol%, the adhesiveness of the obtained hydrogel polymer may be high, and the workability during production and use may be deteriorated. Further, the amount of water retention of the obtained water-absorbent resin particles may decrease. On the other hand, when the degree of neutralization exceeds 80%, the pH of the obtained resin becomes high, and there may be a concern about the safety of the obtained resin on the skin of the human body.

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

As a constituent unit of the crosslinked polymer (A), in addition to the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), another vinyl monomer (a3) copolymerizable with these shall be a constituent unit. Can be done.

The other copolymerizable vinyl monomer (a3) is not particularly limited and is known (for example, the hydrophobic vinyl monomer disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, JP-A-2003-165883, Japanese Patent Laid-Open No. 2003-165883. The hydrophobic vinyl monomer (vinyl monomer) 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, halogen substituted styrene such as vinylnaphthalene and dichlorostyrene and the like.
(Ii) Alkene, an aliphatic ethylene monomer having 2 to 20 carbon atoms [ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.]; and alkaziene [butadiene and isoprene, etc.] and the like.
(Iii) Alicyclic ethylene monomer having 5 to 15 carbon atoms Monoethylene unsaturated monomer [pinene, limonene, indene, etc.]; and polyethylene vinyl polymerizable monomer [cyclopentadiene, bicyclopentadiene, ethylidene norbornene, etc.] and the like.

When the other vinyl monomer (a3) is used as a constituent 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, still more preferably 0.08 to 2, and particularly preferably 0.1 to 1.5. In spite of the above, it is most preferable that the content of the other vinyl monomer (a3) unit is 0 mol% from the viewpoint of absorption characteristics and the like.

The internal cross-linking agent (b) (hereinafter, also simply referred to as the cross-linking agent (b)) is not particularly limited and is known (for example, the ethylenically unsaturated group disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 36485553 is 2 At least a cross-linking agent having at least one, 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 a functional group capable of reacting with a water-soluble substituent. A cross-linking agent having two, a cross-linking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0028 to 0031 of JP-A-2003-165883, a cross-linking having an ethylenically unsaturated group and a reactive functional group. Agents and cross-linking agents having two or more reactive substituents, cross-linking vinyl monomers disclosed in paragraph 0059 of JP-A-2005-75982 and paragraphs 0015-0016 of JP-A-2005-95759. A cross-linking agent or the like of a cross-linking vinyl monomer) can be used. Of these, a cross-linking agent having two or more ethylenically unsaturated groups is preferable from the viewpoint of absorption performance and the like, and more preferable is a poly (triallyl cyanurate, triallyl isosocyanurate, and a polyol having 2 to 10 carbon atoms). Meta) Allyl ethers, particularly preferred are triallyl cyanurate, triallyl isocyanurate, tetraallyloxyetane and pentaerythritol triallyl ethers, most preferably pentaerythritol triallyl ethers. The cross-linking agent (b) may be used alone or in combination of two or more.

The content (mol%) of the cross-linking agent (b) unit is (a1) to that of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit, when other vinyl monomers (a3) are used. Based on the total number of moles of (a3), 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-absorbent resin particles of the present invention is a monomer composition containing the above-mentioned water-soluble vinyl monomer (a1) and / or hydrolyzable vinyl monomer (a2) and an internal cross-linking agent (b) as essential constituent units. A polymerization step of obtaining a water-containing gel containing the crosslinked polymer (A), a step of subdividing the water-containing gel of the crosslinked polymer (A), and further kneading the subdivided water-containing gel at a gel temperature of 40 ° C to 120 ° C. It includes a step of shredding and a step of drying and then pulverizing the kneaded shredded water-containing gel to obtain water-absorbent resin particles.

As a method for producing the crosslinked polymer (A), known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc.; JP-A-55-133413, etc.), known suspension polymerization method, reverse phase polymerization, etc. A water-containing gel (composed of a crosslinked polymer and water) containing the crosslinked polymer (A) by turbid polymerization (Japanese Patent Laid-Open No. 54-30710, JP-A-56-26909, JP-A-1-5808, etc.). .) Can be obtained. The crosslinked polymer (A) may be one kind alone or a mixture of two or more kinds.

Of the polymerization methods, the solution polymerization method is preferable, and since it is not necessary to use an organic solvent and is advantageous in terms of production cost, the aqueous solution polymerization method is particularly preferable because it has a large water retention capacity and is water soluble. The aqueous solution adiabatic polymerization method is most preferable because a water-absorbent resin having a small amount of components can be obtained and temperature control during polymerization is not required.

In the case of aqueous solution polymerization, the concentration of the monomer composition in the aqueous solution is preferably 10 to 60% by weight, more preferably 15 to 50% by weight, still more preferably 20 to 40% by weight. As the solvent, a mixed solvent containing water and an organic solvent can be used, and as the organic solvent, methanol, ethanol, acetone, methyl ethyl ketone, N, N-dimethylformamide, dimethyl sulfoxide and a mixture of two or more thereof can be used. Can be mentioned. In the case of aqueous solution polymerization, 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. For example, azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2'-azobis (2-amidinopropane)) can be used. Hydrochloride, etc.], Inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, dit-butyl peroxide, cumene hydroperoxide, succinic acid, etc.] Acid peroxides and di (2-ethoxyethyl) peroxydicarbonates, etc.] and redox catalysts (alkali metal sulfites or persulfates, ammonium sulfite, reducing agents such as ammonium bicarbonate and ascorbic acid, and alkali metal persulfates. (Combined with an oxidizing agent such as salt, ammonium persulfate, hydrogen peroxide and organic peroxide) and the like. These catalysts may be used alone or in combination of two or more of them.
The amount (% by weight) of the radical polymerization initiator used is the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), and the other vinyl monomers (a3) are (a1) to (a3). , 0.0005-5, more preferably 0.001-2, based on the total weight.

When the polymerization method is a suspension polymerization method or a reverse phase suspension polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. Further, in the case of the reverse 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 the initiator used, but is preferably 0 to 100 ° C, more preferably 5 to 80 ° C.

The crosslinked polymer (A) can be obtained by kneading and shredding the hydrogel polymer obtained by the polymerization, drying the polymer, and then pulverizing the polymer. In the present invention, the kneading shredding is a step of finely dividing the water-containing gel by repeating cutting of the water-containing gel by a shearing force (shear) and coalescence of the cut water-containing gel particles, and fine water content by the present kneading shredding step. A hydrous gel in which gel particles are aggregated can be obtained, and irregularities can be formed on the surface of the water-absorbent resin particles. The size (longest diameter) of the gel after kneading and shredding is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying step is further improved.

The size (maximum diameter) of the gel particles after kneading and pulverizing is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying step is further improved, and the mixing property with the hydrophobic substance (c) which is an additive is improved. As a result, the water separation rate and 1.0% by weight calcium chloride are obtained. The gel passage rate 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 (for example, a kneader, a universal mixer, a uniaxial or biaxial kneading extruder, a minced machine, a meat chopper, etc.). can. From the viewpoint of dehydration efficiency and performance balance with other physical characteristics, the temperature is 40 to 120 ° C, preferably 50 to 110 ° C. 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 once or a plurality of times. Further, when the kneading and shredding is performed a plurality of times, one crushing device may be used a plurality of times, or a plurality of crushing devices may be used continuously.

In the present invention, the hydrogel polymer obtained by polymerization is subdivided before kneading and shredding. In the present invention, the subdivision is a step of cutting the hydrous gel into small pieces while maintaining the internal structure of the hydrous gel, and is different from the above-mentioned kneading shredding from the viewpoint of the internal structure. By subdividing before the kneading and shredding process, excessive stress applied to the water-containing gel during the kneading and shredding process can be alleviated and deterioration of the water-containing gel polymer can be suppressed, so that the absorption performance is improved and the water absorption is improved. It is 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 may be subdivided with scissors, for example, or the frozen hydrogel is crushed by a crusher (for example, a hammer type crusher, an impact type crusher, a roll type crusher, and a shet airflow type crusher). ) May be crushed.

The size (longest diameter) of the gel after subdivision is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 500 μm to 1 cm. Within this range, the subsequent kneading and shredding step can be smoothly performed, 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 the polymerization can be neutralized by mixing a base before the kneading and shredding step or during the kneading and shredding step. The preferred range of the degree of neutralization of the acid group when neutralizing the acid group-containing polymer is 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.

As a method of drying (including distilling) the solvent (including water) in the hydrogel particles, a method of drying with hot air at a temperature of 80 to 300 ° C., a thin film by a drum dryer heated to 100 to 300 ° C., etc. A drying method, a vacuum drying method, a freeze-drying method, an infrared drying method, decantation, filtration and the like can be applied.

When water is contained in the solvent of the water-containing gel particles, the water content (% by weight) after drying is preferably 0 to 20, more preferably 1 to 10, and 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 becomes good in the subsequent pulverization step, and the absorption performance becomes further improved.

When the solvent of the hydrogel particles (organic solvent, water, etc.) 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 preferable, more preferably 0 to 5, particularly preferably 0 to 3, and most preferably 0 to 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 are determined by an infrared moisture measuring instrument [JE400 manufactured by KETT Co., Ltd .: 120 ± 5 ° C., 30 minutes, atmospheric humidity before heating 50 ± 10% RH, lamp specification 100 V, It is obtained from the weight loss of the measurement sample when heated by [40 W].

The method of crushing the water-containing gel particles after drying is not particularly limited, and a known crushing device (for example, a hammer type crusher, an impact type crusher, a roll type crusher, a shet airflow type crusher, etc.) can be used. .. The obtained 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 to 500, more preferably 250 to 500, and most preferably 350 to 450. Within this range, the absorption performance, the water separation rate, and the gel flow rate of the 1.0 wt% calcium chloride aqueous solution are further improved.

The weight average particle size was determined by using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook 6th Edition (McGlow Hill Book Company, 1984). , Page 21). That is, the JIS standard sieves are combined in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and the saucer from the top. Place about 50 g of the measurement particles in the uppermost sieve and shake with a low-tap test sieve shaker for 5 minutes. Weigh the measured particles on each sieve and saucer, and set the total to 100% by weight to obtain the weight fraction of the particles on each sieve. ), The vertical axis is the weight fraction], then draw a line connecting each point to obtain the particle size corresponding to the weight fraction of 50% by weight, and use this as the weight average particle diameter.

In addition, the smaller the content of the fine particles contained in the water-absorbent resin particles, the better the absorption performance. Therefore, the content (weight) of the fine particles of 106 μm or less (preferably 150 μm or less) in the total weight of the water-absorbent resin particles. %) Is preferably 3 or less, more preferably 1 or less. The content of the fine particles can be determined by using the graph created when determining the weight average particle diameter described above.

The shape of the water-absorbent resin particles is not particularly limited, and examples thereof include amorphous crushed particles, phosphorus flakes, pearl particles, and rice granules. Of these, the amorphous crushed form is preferable from the viewpoint that it is easily entangled with the fibrous material for use in disposable diapers and the like and there is no concern that it will fall off from the fibrous material.

The water-absorbent resin particles of the present invention can contain the hydrophobic substance (c). The (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. Is done.

Examples of the hydrophobic substance (c1) containing a hydrocarbon group include polyolefin resins, polyolefin resin derivatives, polystyrene resins, polystyrene resin derivatives, waxes, long-chain fatty acid esters, long-chain fatty acids and salts thereof, long-chain aliphatic alcohols, and long chains. Includes chain aliphatic amides and mixtures of two or more of these.

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 10 to 1,000,000 {for example, polyethylene, polypropylene, polyisobutylene, poly (ethylene-isobutylene), isoprene, etc.} can be mentioned.

As the polyolefin resin derivative, a polymer having a weight average molecular weight of 10 to 1,000,000 in which a carboxy group (-COOH), 1,3-oxo-2-oxapropylene (-COOCO-), etc. are introduced into a polyolefin resin {for example, polyethylene heat Amenity, Polypropylene Heat Attenuated, Maleic Acid Modified Polyethylene, Chlorinated Polyethylene, Maleic Acid Modified Polypropylene, Ethylene-Acrylic Acid Copolymer, Ethylene-Moleic Anhydrous Polymeric Polymer, Isobutylene-Maleic Anhydrous Maleic Acid Copolymer, Maleinized Polybutadiene, ethylene-vinyl acetate copolymer, maleinate of ethylene-vinyl acetate copolymer, etc.} can be mentioned.

As the polystyrene resin, a polymer having a weight average molecular weight of 10 to 1,000,000 can be used.

As the polystyrene resin derivative, a polymer having a weight average molecular weight of 10 to 1,000,000 containing styrene as an essential constituent monomer (the content of styrene 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.} can be mentioned.

Examples of the wax include waxes having a melting point of 50 to 200 ° C. {for example, 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, glycerin lauric acid monoester, glycerin stearate monoester, glycerin oleic acid monoester, pentaerythlit lauric acid monoester, pentaerythlit lauric acid monoester, pentaerythlit oleic acid monoester, sorbit lauric acid monoester, Solbit stearate monoester, sorbit oleic acid monoester, sucrose palmitic acid monoester, sucrose palmitate diester, sucrose palmitate triester, sucrose stearate monoester, sucrose stearate diester, sucrose stearate tori Esters, beef fat, etc.} can be mentioned.

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

Examples of the long-chain fatty alcohol include fatty alcohols having 8 to 30 carbon atoms {for example, lauryl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol, etc.}. From the viewpoint of leakage resistance of the absorbent article, palmityl alcohol, stearyl alcohol, and oleyl alcohol are preferable, and stearyl alcohol is more preferable.

The long-chain aliphatic amide is an amidate 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, ammonia or a primary amine having 1 to 7 carbon atoms. And an amidate of a long-chain fatty acid having 8 to 30 carbon atoms, an amidate 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, and Examples thereof include amidates of a secondary amine having two aliphatic hydrocarbon groups having 1 to 7 carbon atoms and a long chain fatty acid having 8 to 30 carbon atoms.

As an amidate 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 reaction of a primary amine and a carboxylic acid in a ratio of 1: 1 and 1 : Divided into those that reacted in 2. Examples of the 1: 1 reaction include acetic acid N-octylamide, acetate N-hexacosylamide, heptacosane acid N-octylamide, and heptacosane acid N-hexacosylamide. Examples of the 1: 2 reaction include diacetic acid N-octylamide, diacetic acid N-hexacosylamide, diheptacosanoic acid N-octylamide and diheptacosanoic acid N-hexacosylamide. When the primary amine and the carboxylic acid are reacted in a ratio of 1: 2, the carboxylic acid used may be the same or different.

As an amidate of ammonia or a primary amine having 1 to 7 carbon atoms and a long-chain fatty acid having 8 to 30 carbon atoms, it is 1: 2 with a product obtained by reacting ammonia or a primary amine with a carboxylic acid in a ratio of 1: 1. It is divided into those that have reacted. The 1: 1 reaction products include 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. And so on. The 1: 2 reaction was dinonanoic acid amide, dinonanoic acid N-methylamide, dinonanoic acid N-heptylamide, dioctadecanoic acid amide, dioctadecanic acid N-ethylamide, dioctadecanic acid N-heptylamide, diheptacosanoic acid amide. , Diheptacosanoic acid N-methylamide, diheptacosanoic acid N-heptylamide, diheptacosanoic acid N-hexacosylamide and the like. As for the product obtained by reacting ammonia or a primary amine with a carboxylic acid in a ratio of 1: 2, the carboxylic acid used may be the same or different.

Examples of the amidate 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-methylhexakoshi acetate. Luamide, N-octylhexacosylamide acetate, N-dihexacosylamide acetate, N-methyloctylamide heptacosanoic acid, N-methylhexacosylamide heptacosanoic acid, N-octylhexacosylamide heptacosanoate and heptacosane Acid N-dihexacosylamide and the like can be mentioned.

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

As the hydrophobic substance (c1), long-chain fatty acid esters, long-chain fatty acids and salts thereof, long-chain aliphatic alcohols and long-chain aliphatic amides are preferable from the viewpoint of dehydration efficiency and leakage resistance of absorbent articles. It is preferably sorbit stearic acid ester, sucrose stearic acid ester, stearic acid, stearic acid Mg, stearic acid Ca, stearic acid Zn and stearic acid Al, and particularly preferably sucrose stearic acid ester and stearic acid Mg.

Hydrophobic substances (c2) containing a hydrocarbon group having a fluorine atom include perfluoroalkane, perfluoroalkene, perfluoroaryl, perfluoroalkyl ether, perfluoroalkylcarboxylic acid, perfluoroalkyl alcohol and 2 of these. Contains mixtures of seeds and above.

Examples of the hydrophobic substance (c3) having a polysiloxane structure include polydimethylsiloxane, polyether-modified polysiloxane {polyoxyethylene-modified polysiloxane and poly (oxyethylene / oxypropylene) -modified polysiloxane}, carboxy-modified polysiloxane, and the like. Includes epoxy-modified polysiloxanes, amino-modified polysiloxanes, alkoxy-modified polysiloxanes and the like, and mixtures thereof.

Examples of the carboxy-modified polysiloxane include X-22-3701E, X-22-3710 (all manufactured by Shin-Etsu Chemical Co., Ltd.), DOWNSIL (model number BY16-880Fluid), DOWNSIL (model number BY16-880) (Dow Toray Co., Ltd.). (Made by company) and so on. The position of the carboxyl group with respect to the polysiloxane backbone is the side chain and / or the terminal.

Examples of the 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.), DOWNSIL (model number BY 16-839 Fluid), DOWNSIL (model number BY8411 Fluid), DOWNSIL (model number BY 8413 Fluid), DOWNSIL (model number BY8421 Fluid) (Toray Industries, Inc.), SF8411, SF8413, BY16-839, BY16-876, FZ-3736, SF8421 (all manufactured by Toray Dow Corning) and the like. The position of the epoxy group with respect to the polysiloxane backbone is the side chain and / or the terminal.

Examples of the amino-modified polysiloxane include a monoamine-modified type in which the modifying group is a primary amine and a diamine-modified type in which the modifying group is a secondary amine.
Examples of the monoamino modified type 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 (all manufactured by Shin-Etsu Chemical Co., Ltd.), DOWNSIL (model number BY16-205), DOWNSIL (model number BY16-213), DOWNSIL (model number BY16-849Fluid), DOWNSIL (model number BY16- 853U), DOWNSIL (model number BY16-871), DOWNSIL (model number BY16-872), DOWNSIL (model number BY16-879B), DOWNSIL (model number BY16-892), DOWNSIL (model number FZ-3705), DOWNSIL (model number FZ-3710Flid). , DOWNSIL (model number FZ-3760), DOWNSIL (model number FZ-3785), DOWNSIL (model number SF8417 Fluid) (all manufactured by Toray Dow Co., Ltd.) and the like. Examples of the diamino-modified type 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 can be mentioned. The position of the diamino group with respect to the polysiloxane backbone is the side chain and / or the terminal.

Examples of the alkoxy-modified polysiloxane include X-22-4952, X-22-4272, KF-6123, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, and 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, DOWNSIL (Model number 501W Adaptive), DOWNSIL (model number FZ-2110), DOWNSIL (model number FZ-2123), DOWNSIL (model number L-7001), DOWNSIL (model number SF8410Fluid), DOWNSIL (model number SH3746 Fluid), DOWNSIL (model number SIL) Model number SH8700Fluid) (both manufactured by Toray Dow Co., Ltd.) and the like. The position of the alkoxy group with respect to the polysiloxane backbone is the side chain and / or the 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. It is a polysiloxane.

The HLB value of the hydrophobic substance (c) is preferably 1 to 10, more preferably 1 to 8, and particularly preferably 1 to 7. Within this range, the leak resistance of the absorbent article becomes even better. The HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is obtained by the Oda method (Introduction to Surfactants, page 212, Takehiko Fujimoto, published by Sanyo Chemical Industries, Ltd., published in 2007).

Among 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 dehydration efficiency and leakage resistance 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 characteristics (particularly, water absorption rate and liquid passage rate). It is% by weight, preferably 0.01 to 1.0% by weight, and particularly preferably 0.02 to 0.3% by weight.

The hydrophobic substance (c) may be present at any position of the water-absorbent resin particles, but is present inside the water-absorbent resin particles from the viewpoint of water absorption characteristics (particularly, water absorption rate) and water separation rate. Is preferable.

The hydrophobic substance (c) may contain (c) in the water-containing gel containing the crosslinked polymer (A) at the time of the above-mentioned kneading and shredding step, and is (c) in the polymerization step or the kneading and shredding step. ) Is preferably contained. Examples of the method of adding (c) include a method of adding to the polymerization solution after the start of the polymerization step and before the completion of the polymerization step, a method of adding to the hydrogel after the completion of the kneading and shredding step, and a method of adding to the water-containing gel. Examples thereof include a method of adding to the water-containing gel particles during the step, but from the viewpoint of improving the water separation rate, a method of adding to the water-containing gel after the completion of the polymerization step and before the kneading and shredding step, or a method of adding to the water-containing gel particles during the kneading and shredding step. It is preferable to add it to the water-containing gel particles during the kneading and shredding step. The hydrophobic substance (c) can be added to water and / or an organic solvent in a dissolved and / or dispersed form.

It is preferable that the surface of the water-absorbent resin particles is further cross-linked. Therefore, the production method of the present invention may include a step of drying, pulverizing, and then surface-crosslinking the above-mentioned hydrogel particles. By surface cross-linking, the gel strength can be further improved, and the desired water retention amount in actual use and the absorption amount under load can be satisfied. The step of surface cross-linking the hydrogel particles is also simply referred to as a cross-linking step.

As a method of surface-crosslinking the water-absorbent resin particles, a conventionally known method, for example, a method of forming the water-absorbent resin into particles, mixing the surface cross-linking agent (e), a mixed solution of water and a solvent, and heat-reacting the particles. Can be mentioned. Examples of the mixing method include spraying the mixed solution on the water-absorbent resin particles, dipping the water-absorbent resin particles in the mixed solution, and the like, preferably spraying the mixed solution on 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, polyamine and polyvalent. Examples include metal compounds. Of these, the polyglycidyl compound is preferable in that the crosslinking reaction can be carried out 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 amount under load may be insufficient. On the other hand, when the amount of the surface cross-linking agent (e) used exceeds 5% by weight, the degree of cross-linking of the surface becomes excessive and the amount of water retention may decrease.

The amount of water used during surface cross-linking is preferably 0.5 to 10% by weight, more preferably 1 to 7% by weight, based on the weight of the water-absorbent resin particles before cross-linking. When 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 water-absorbent resin particles becomes insufficient, and the effect of improving the absorption amount under a load may be poor. On the other hand, when the amount of water used exceeds 10% by weight, the surface cross-linking agent (e) permeates into the inside excessively, and although the absorption amount under load is improved, the water retention amount may decrease.

Conventionally known solvents can be used as the solvent used in combination with water during surface cross-linking, and the degree of penetration of the surface cross-linking agent (e) into the water-absorbent resin particles and the reactivity of the surface cross-linking agent (e). It can be appropriately selected and used in consideration of the above, but is preferably a hydrophilic organic solvent such as methanol, diethylene glycol and propylene glycol which can be dissolved in water. The solvent may be used alone or in combination of two or more.

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

In order to carry out surface cross-linking, a mixed solution of the surface cross-linking agent (e), water and a solvent is mixed with the water-absorbent resin particles by a conventionally known method, and a heating reaction is carried out. The reaction temperature is preferably 100 to 230 ° C, more preferably 120 to 180 ° C. The reaction time can be appropriately adjusted depending on the reaction temperature, but is preferably 3 to 60 minutes, more preferably 10 to 45 minutes. It is also possible to further surface-crosslink the water-absorbent resin particles obtained by surface-crosslinking with a surface-crosslinking agent of the same type or different type as the surface-crosslinking agent used first.

After surface cross-linking, the particle size may be adjusted by sieving if necessary. The preferred ranges of the weight average particle size of the particles obtained after adjusting the particle size and the content of the fine particles are the same as described above. Further, the particle size adjusting step after surface cross-linking of the hydrogel 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 the post-step after the cross-linking step, the hydrophobic substance (c) can be added to water and / or an organic solvent in a dissolved and / or dispersed form. By adding the particles in the cross-linking step and / or in the post-step after the cross-linking step, the particles can be uniformly added to the particle surface, so that the dehydration efficiency can be improved.

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 above-mentioned inorganic acid or organic acid.

As the polyvalent metal salt (f), an inorganic acid salt of aluminum and an inorganic acid salt of titanium are preferable from the viewpoint of availability and solubility, and aluminum sulfate, aluminum chloride, potassium aluminum sulfate and sulfate are more preferable. Aluminum sulphate, particularly preferred are aluminum sulphate and sulphate aluminum sulphate, most preferably sulphate aluminum sulphate. One of these may be used alone, or two or more thereof may be used in combination.

The amount (% by weight) of the polyvalent metal salt (f) used is preferably 0.01 to 5, more preferably 0, based on the weight of the crosslinked polymer (A) from the viewpoint of absorption performance and blocking resistance. 05-4, particularly preferably 0.1-3.

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

The surface of the water-absorbent resin particles of the present invention can be further coated with an inorganic powder. The inorganic powder includes hydrophilic inorganic particles, hydrophobic inorganic particles and the like. Examples of the hydrophilic inorganic particles include particles such as glass, silica gel, silica and clay. Examples of the hydrophobic inorganic particles include particles such as carbon fiber, kaolin, talc, mica, bentonite, sericite, asbestos and shirasu. Of these, hydrophilic inorganic particles are preferable, and silica is most preferable.

The shape of the hydrophilic inorganic particles and the hydrophobic inorganic particles may be any of amorphous (crushed), spherical, film, rod and fibrous, but amorphous (crushed) or spherical is preferable. More preferably, it is a true sphere.

The content (% by weight) of the inorganic powder is preferably 0.01 to 3.0, more preferably 0.05 to 1.0, and then preferably 0.1 to 0, based on the weight of the water-absorbent resin particles. It is 0.8, particularly preferably 0.2 to 0.7, and most preferably 0.3 to 0.6. Within this range, the gel flow rate of the absorbent article becomes even better.

The water-absorbent resin particles of the present invention include other additives {for example, known (for example, JP-A-2003-225565, JP-A-2006-131767, etc.) preservatives, antifungal agents, antibacterial agents, antioxidants, ultraviolet rays. It can also contain absorbents, colorants, fragrances, deodorants, organic fibrous materials, etc.}. When these additives are contained, the content (% by weight) of the additives is preferably 0.001 to 10, more preferably 0.01 to 5, and particularly preferably 0.01 to 5, based on the weight of the water-absorbent resin particles. It is 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 water separation rate and the gel flow rate are further improved. The apparent density of the water-absorbent resin particles is measured at 25 ° C. according to JIS K7365: 1999.

The water retention amount (g / g) of the water-absorbent resin particles of the present invention with respect to physiological saline is preferably 30 to 50, more preferably 33 to 49, further preferably 36 to 48, and particularly preferably 39 to 47. preferable. If it is less than 30, leakage is likely to occur during repeated use, which is not preferable. Further, if it exceeds 50, blocking is likely to occur, which is not preferable. The amount of water retention can be appropriately adjusted depending on the type and amount 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 amount, it can be easily realized by reducing the amounts of the cross-linking agent (b) and the surface cross-linking agent (e).

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

The water separation rate in the present invention is a value represented by the following formula (1), and is the amount of water retained in physiological saline and the amount of water retained after the swollen gel after measuring the amount of water retained is treated with a 1.0 wt% calcium chloride aqueous solution. It is calculated from the ratio of. That is, the weight ratio of the separated water after the treatment to the weight of the swollen gel before the dehydrating agent treatment is shown. Therefore, the higher the water separation rate, the better the dehydration efficiency by the predetermined dehydrating agent treatment.
Water separation rate [%] = {1- (Water retention amount after treatment with 1.0 wt% calcium chloride aqueous solution [g / g]) / (Water retention amount for physiological saline [g / g])} × 100 (1)
The specific measurement method will be described later.

The water separation rate (%) of the water-absorbent 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 higher the upper limit is, the more preferable and not particularly limited, but from the viewpoint of performance balance with other physical characteristics and productivity, it is preferably 95 or less, more preferably 90 or less. As a means for improving the water separation rate, it is conceivable to increase the specific surface area of the particles or to adjust the balance between hydrophilicity and hydrophobicity in the particles or on the surface of the particles. As a means for achieving this, for example, a hydrophobic substance may be used in combination in a polymerization step, a kneading shredding step, a crosslinking step, and / or a post-step after the crosslinking step, or a gel temperature in a step of kneading a hydrogel. These include adjusting, raising the heating temperature during drying when dehydrating from a hydrogel, raising the heating temperature in the crosslinking step, and lowering the weight average particle size. 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 characteristics. The heating temperature during drying when dehydrating from a hydrogel is preferably 100 to 300 ° C, more preferably 110 to 280 ° C from the viewpoint of performance balance with other physical characteristics and productivity. When heated above 300 ° C., the water-absorbent resin particles are thermally deteriorated, which is not preferable. The heating temperature in the crosslinking step is preferably 100 to 230 ° C, more preferably 120 to 180 ° C. Within this range, it is considered that the hydrophobic substance melts or the viscosity decreases to cover the surface of the absorbent resin particles, so that the gels can be prevented from coalescing and the reaction point with the dehydrating agent can be increased. 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 characteristics.

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

The reswelling ratio (%) of the water-absorbent resin particles of the present invention by ion-exchanged water is 110 or less, more preferably 105 or less, from the viewpoint of the efficiency of dehydration treatment. The lower the lower limit value is, the more preferable it is, and it is not particularly limited, but it is preferably 80 or more from the viewpoint of balance with absorption performance and productivity. As a means for reducing the re-swelling ratio, the specific surface area of the particles is increased, the balance between hydrophilicity and hydrophobicity in the particles or on the surface of the particles is adjusted, the anion concentration inside the particles is increased, and the dehydrating agent is used. It is conceivable to keep the surface area of the water-absorbent resin particles after the treatment small. Specifically, a hydrophobic substance may be used in combination in a polymerization step, a kneading shredding step, a cross-linking step, or a post-step after the cross-linking step, or the heating temperature at the time of drying when dehydrating from a hydrogel is increased by weight. For example, reducing the average particle size. It is assumed that the presence of the hydrophobic substance on the surface of the absorbent resin particles prevents the water-absorbing resin particles from coming into contact with the water existing around them, and as a result, it is considered that the re-swelling of the gel is suppressed.

The gel passage rate of the 1.0 wt% calcium chloride aqueous solution of the present invention is a value represented by the following formula, and the gel of the measurement sample swollen with physiological saline is 80 ml together with a part of the liquid used for swelling. 20 ml of physiological saline and calcium chloride mixed solution from the time (T3; sec) that the mixed aqueous solution of 20 ml of physiological saline and calcium chloride flowed down between the swollen gels. It is calculated from the value obtained by subtracting the time (T4; sec) at which the aqueous solution flows down in the absence of the measurement sample. Therefore, the higher the gel flow rate of the 0.1 wt% calcium chloride aqueous solution, the more the dehydrating agent swells and easily permeates between the particles of the aggregated water-absorbent resin, which means that the dehydration efficiency is excellent.
Gel passage rate of 1.0 wt% calcium chloride aqueous solution (ml / min) = 20 ml x 60 / (T3-T4)
The specific measurement method will be described later.

The gel passage rate (ml / min) of the 1.0 wt% calcium chloride aqueous solution of the water-absorbent resin particles of the present invention is 200 or more, more preferably 300 or more, and particularly preferably 300 or more, from the viewpoint of the efficiency of dehydration treatment. It is more than 500. The higher the upper limit is, the more preferable and not particularly limited, but from the viewpoint of performance balance with other physical characteristics and productivity, it is preferably 2300 or less, more preferably 2000 or less. The aqueous gel passage rate of 1.0 wt% calcium chloride is controlled by increasing the specific surface area of the particles and adjusting the balance between hydrophilicity and hydrophobicity in or on the surface of the particles.

The amount of water-absorbent resin particles of the present invention absorbed under load (g / g) is preferably 19 or more. If it is less than 19, leakage is likely to occur during repeated use, which is not preferable. The higher the upper limit is, the more preferable it is, but it is not particularly limited, but it is preferably 27 or less, more preferably 25 or less, from the viewpoint of performance balance with other physical characteristics and productivity. The amount of absorption under load can be appropriately adjusted depending on the type and amount of the cross-linking agent (b) and the surface cross-linking agent (e). Therefore, for example, when it is necessary to increase the absorption amount under load, it can be easily realized by increasing the amount of the cross-linking agent (b) and the surface cross-linking agent (e).

The hygienic product of the present invention contains the water-absorbent resin particles of the present invention, and dehydration treatment of water from the used product is easy. Examples of hygienic products include disposable diapers, sanitary napkins, etc., but they are applied not only to sanitary products but also to various uses such as absorbents and preservatives for various aqueous liquids and gelling agents. It is possible. The method for manufacturing hygienic products is the same as that known (described in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, etc.).

The hygienic product of the present invention may use the water-absorbent resin particles alone as an absorber, or may be used together with other materials to form an absorber. Examples of other materials include fibrous materials. The structure and manufacturing method of the absorber when used together with the fibrous material are the same as those known (Japanese Patent Laid-Open Nos. 2003-225565, 2006-131767, 2005-097569, etc.). be.

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

Next, a method for treating the hygienic product of the present invention will be described. The method for treating hygiene products of the present invention is a method for treating used hygiene products containing water-absorbent resin particles, and is a step of crushing used hygiene products (hereinafter referred to as "crushing step"). (Referred to as), a step of dehydrating the water-absorbent resin particles contained in the sanitary goods or the crushed sanitary goods with a dehydrating agent (hereinafter referred to as a dehydration step), and mixing the crushed and dehydrated sanitary goods with water. It includes a step of transporting to a solid-liquid processing apparatus (hereinafter referred to as “transporting step”). The hygiene product may further contain pulp fiber.

The crushing step is a step of crushing sanitary goods to obtain a crushed product. For crushing, a known crusher or crusher can be used. Crushing with a fixed or variable hammer and a fixed blade on the wall surface), cutter mill, uniaxial crusher, biaxial crusher, coaxial core crusher, hammer crusher, ball mill, etc. Since the materials for sanitary goods include plastic sheets, non-woven fabrics, and elastic materials, a disposer type crusher or cutter mill that cuts with a blade while rotating at high speed is particularly suitable.

The crushed product of hygiene products may be an aqueous suspension. As a method of obtaining an aqueous suspension, there are a method of adding water to swell the sanitary goods and then crushing, a method of adding water while crushing and crushing, and a method of adding water after crushing. From the viewpoint of load reduction, a method of adding water to swell the sanitary goods and then crushing them is preferable.

The suitable range of the size of the crushed product of the sanitary product after crushing depends on the separation / recovery method by the solid-liquid separator described later, but from the viewpoint of transportability in a water stream, the length of a piece of the sanitary product is preferable. The size is 100 mm or less. The size of the crushed material can be appropriately adjusted depending on the type of the crusher or the crusher described above, the processing conditions, and the like.

As the hygiene product to be crushed, the hygiene product may be crushed as it is, or the absorber containing the water-absorbent resin particles may be taken out from the hygiene product and crushed.

The dehydration step is a step of dehydrating the water-absorbent resin particles contained in the sanitary goods or the crushed sanitary goods with a dehydrating agent. By this dehydration treatment, the water absorption 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-absorbent resin particles is improved, and the separation and recovery efficiency is improved. The dehydration step in the present invention includes not only a step of dehydrating the water-absorbent resin particles with a dehydrating agent but also a step of simply adding a dehydrating agent without actually causing a dehydration phenomenon.

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

A 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 chelate salt with a carboxyl group ion after being dissolved in water or reacting with water. If so, there is no particular limitation. Examples of the divalent metal compound 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 the trivalent metal include polyvalent metal compounds containing metals such as boron, aluminum and gallium. Even if the polyvalent metal compound is a non-hydrate, monohydrate, dihydrate, trihydrate, tetrahydrate, pentahydrate, hexahydrate, and heptahydrate It may be a hydrate such as a substance, octahydrate or nine hydrate. These dehydrating agents may be used alone or in combination of two or more. In the present invention, the "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.

Examples of the water-soluble polyvalent metal compound containing magnesium include magnesium sulfate, magnesium nitrate, magnesium chloride, magnesium acetate, magnesium bromide, magnesium iodide, magnesium perchlorate, magnesium permanganate, magnesium acetate and the like.

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 phosphate, and carbonic acid. Calcium, calcium nitrate, calcium sulfite, calcium silicate, calcium phosphate, calcium pyrophosphate, calcium hypochlorite, calcium chlorate, calcium perchlorate, calcium bromide, calcium iodide, calcium chromate, calcium acetate, calcium gluconate , Calcium benzoate, calcium stearate, etc. are included.

The acidic substance is a substance having an acidity capable of converting a carboxyl group ion in the crosslinked polymer (A) into a carboxyl group. 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 at least in the first step may be 3.5 or less, and a part of the polyvalent acid may be in a neutralized salt state.

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 can be used in combination.

Examples of the inorganic acid include sulfuric acid, sulfamic acid, hydrochloric acid, nitric acid, phosphoric acid, metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, hexametaphosphoric acid and the like.

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

Examples of the organic acid having a carboxylic acid group in the molecule include halogen-containing carboxylic acid, hydroxycarboxylic acid, amino acid, ketocarboxylic acid and the like.

The halogen-containing carboxylic acid is a monohalogen carboxylic acid, a dihalogen carboxylic acid, or a trihalogen carboxylic acid, depending on the number of substituents in which the hydrogen atom in the molecule is replaced with a fluorine atom, a chlorine atom, a bromine atom, and / or an iodine atom. , Pentahalohexylcarboxylic acid, and the like.

Examples of the monohalogen carboxylic acid include monofluoroacetic acid, monochloroacetic acid, monobromoacetic acid, monoiodoacetic acid, 2-fluoropropionic acid, 2-chloropropionic acid, 2-bromopropionic acid, 2-iodopropionic acid, 2-fluorobutyric acid, and 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 can be mentioned.

Examples of the dihalogen carboxylic acid include difluoroacetic acid, dichloroacetic acid, dibromoacetic acid, diiodoacetic acid, 2,2-difluoropropionic acid, 2,2-dichloropropionic acid, 2,3-dichloropropionic acid, and 2,2-dibromopropionic acid. Examples thereof include 2,3-dibromopropionic acid, 2,2-diiodopropionic acid, 2,2-difluorobutyric acid, 2,2-dichlorobutyric acid, 2,2-dibromobutyric acid, and 2,2-diiodobutyric acid.

Examples of the trihalogen carboxylic acid include trifluoroacetic acid, trichloroacetic acid, tribromoacetic acid, triiodoacetic acid, 3,3,3-trifluoropropionic acid and the like.

Examples of the pentahalogen carboxylic acid include pentafluorolopionic acid and the like.

The hydroxycarboxylic acid is a compound having a carboxyl group and a hydroxyl group in one molecule, and is, for example, tartronic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicylic acid, 4-chlorosalicylic acid 5-chlorosalicylic acid. , 2,5-Dihydroxybenzoic acid, 3,5-dibromosalicylic acid, 4-methylsalicylic acid, and the like.

Amino acids are compounds having a carboxyl group and an amino group in one molecule, and are, for example, glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, aspartic acid, aspartic acid, histidine, and glutamic acid. , Glutamic acid, phenylalanine, tryptophan, arginine, tyrosine, 3-aminohexadiic acid, and the like.

Ketocarboxylic acid is a compound having a carboxyl group and a ketone group in one molecule, and is, for example, pyruvic acid, oxaloacetate, α-ketobutyric acid, α-ketoglutaric acid, acetoacetic acid, oxaloacetate, acetonedicarboxylic acid. , Etc. can be mentioned.

Examples of organic acids having a phosphon group or a phosphoric acid group in the molecule include methyldiphosphonic acid, aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotrismethylenephosphonic acid, and ethylenediaminetetra (methylenephosphone). Acid), ethylenediaminetetramethylenephosphonic acid, hexamethylenediaminetetra (methylenephosphonic acid), propylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), triethylenetetraminehexa (methylenephosphonic acid), triaminotriethylaminehexa (Methylenephosphonic acid), trans-1,2-cyclohexanediaminetetra (methylenephosphonic acid), glycol etherdiamine, tetramethylenephosphonic acid, tetraethylenepentaminehepta (methylenephosphonic acid) and the like can be mentioned.

Among these dehydrating agents, a divalent water-soluble polyvalent metal compound and an acidic substance are preferable, and more preferably, a water-soluble polyvalent metal compound containing magnesium and a water-soluble polyvalent metal containing calcium are preferable from the viewpoint of improving dehydration. It is an organic acid having a compound, an inorganic acid, and a carboxylic acid group in the molecule, and more preferably calcium chloride, calcium oxide, calcium acetate, calcium hypochlorite, hydrochloric acid, nitrate, and hydroxycarboxylic acid.

The method of treating with a dehydrating agent is not particularly limited as long as it is a method in which the water-absorbent resin particles in the sanitary product come into contact with the dehydrating agent, but a solid dehydrating agent may be added to the sanitary product, or the dehydrating agent may be treated. An aqueous solution may be added. Further, for hygienic products treated with a dehydrating agent, the dehydrating agent may be added after being swollen with water in advance, or water may be added after the dehydrating agent is added. The device for treating with a dehydrating agent may be any device that can mix sanitary goods and a dehydrating agent, may be treated with the above-mentioned crusher and crusher, or may be treated in a separately stirable treatment tank. You may.

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

In the process order of the above-mentioned crushing step and dehydration step, the step of crushing the sanitary goods and the step of dehydrating the water-absorbent particles contained in the sanitary goods or the crushed sanitary goods with a dehydrating agent can be sequentially or simultaneously carried out. .. The specific order of the processing steps is shown below. Arrows indicate the order.
(1) Step of crushing sanitary goods → Step of dehydrating water-absorbent resin particles contained in crushed sanitary goods with dehydrating agent → Mixing crushed and dehydrated sanitary goods with water to make a solid-liquid treatment device The process of transporting.
(2) Step of dehydrating water-absorbent resin particles contained in sanitary goods with dehydrating agent → Step of crushing sanitary goods → Step of mixing crushed and dehydrated sanitary goods with water and transporting to solid-liquid treatment equipment ..
(3) A step of simultaneously performing a step of dehydrating the water-absorbent resin particles contained in the sanitary goods or the crushed sanitary goods with a dehydrating agent and a step of crushing the sanitary goods → Watering the crushed and dehydrated sanitary goods The process of mixing with and transporting to a solid-liquid processing device.

The transportation step is a step of mixing crushed and dehydrated sanitary goods with water and transporting them to a downstream solid-liquid treatment device. The sanitary pulverized product, preferably an aqueous suspension, is transported by a water supply means to a solid-liquid treatment apparatus by a water stream.

The transportation means in the transportation process can be transported to the solid-liquid treatment device by a pump type or a natural flow type, but the sanitary goods that have been crushed and dehydrated are sent to the solid-liquid separation device by a water flow via a pipe or a hose. It is preferable to transport it. Types of pipes or hoses include copper pipes, lead pipes, iron pipes, rigid polyvinyl chloride pipes, polyethylene pipes, hard vinyl chloride lining pipes, stainless steel pipes, white pipes, clay pipes, fireproof double-layer pipes and the like.

As the solid-liquid processing apparatus, a known solid-liquid separation processing apparatus can be used. For example, screen separation, precipitation separation, membrane separation, centrifugation and the like can be mentioned.

One of the preferred embodiments of the sanitary goods treatment method of the present invention is a disposer wastewater treatment system. Disposer wastewater treatment is a system that normally crushes swill with a disposer attached to the sink drainage port of the kitchen and discharges it to the sewer or septic tank together with the wastewater from the water supply. It is a wastewater treatment system, and is widely used especially in apartment houses. In order to develop the wastewater treatment system in sanitary goods, it is important to reduce the water swelling property of the water-absorbent resin particles and prevent poor drainage and pipe blockage due to accumulation and adhesion in the drainage pipe. The processing method of the present invention is preferable because it can solve such a problem.

In the method for treating hygiene products of the present invention, after the crushed and dehydrated sanitary articles are transported to the solid-liquid processing device, the sanitary products containing the water-absorbent resin particles crushed and dehydrated by the solid-liquid separation device are collected. Will be done. Since the recovered product of the sanitary goods obtained by the sanitary goods treatment method of the present invention has a feature of low water content, not only the combustion efficiency at the time of incineration is excellent, but also it can be recycled as solid fuel or the like. .. Therefore, the present invention includes a method for producing a sanitary article recovered product and a solid fuel obtained by the method for treating sanitary goods. When recycled as the solid fuel, it is preferable to further dry the recovered material of the sanitary goods.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, parts indicate parts by weight and% indicates weight%. The amount of water-absorbent resin particles retained in the saline solution, the water separation rate, the amount absorbed under load, the gel flow rate of the physiological saline solution, and the gel flow rate of the 1.0 wt% calcium chloride aqueous solution are measured by the following methods. bottom.

<Measurement method of water retention for physiological saline>
Put 1.00 g of the measurement sample in a tea bag (length 20 cm, width 10 cm) made of a nylon net 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 soaking for 1 hour without stirring, the sample was pulled up and hung for 15 minutes to drain water. Then, each tea bag was placed in a centrifuge and dehydrated at 150 G for 90 seconds to remove excess physiological saline, and the weight (h1) including the tea bag was measured to determine the amount of water retained by the following formula. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C. (H2) is the weight of the tea bag measured by the same operation as above when there is no measurement sample.
Water retention (g / g) = (h1)-(h2)

<Measurement method of water separation rate>
After measuring the water retention amount, the following operations were continued. That is, the tea bag measured by the centrifuge is immersed in 500 ml of 1.0 wt% calcium chloride aqueous solution without stirring for 5 minutes, then pulled up, put into the centrifuge together with the tea bag, and centrifuged at 150 G for 90 seconds. The excess calcium chloride aqueous solution was removed by dehydration, the weight (h3) including the tea bag was measured, and the water retention amount after the 1.0 wt% calcium chloride aqueous solution treatment was determined from the following formula. (H4) is the weight of the tea bag measured by the same operation as above when there is no measurement sample.
Water retention amount after treatment with 1.0% calcium chloride aqueous solution (g / g) = (h3)-(h4)
After that, the water separation rate was calculated by the following formula.
Water separation rate (%) = (Amount of water retained after treatment with 1-1.0 wt% calcium chloride aqueous solution) / (Amount of water retained for physiological saline) x 100

<Measurement method of re-swelling ratio with ion-exchanged water>
After the measurement of the water separation rate, the following operations were continued. That is, the tea bag after centrifugal dehydration is immersed in 500 ml of an ion exchange aqueous solution without stirring for 5 minutes, then pulled up, put into a centrifuge together with the tea bag, and centrifugally dehydrated at 150 G for 90 seconds to exchange excess ions. The aqueous solution was removed, the weight (h5) including the tea bag was measured, and the amount of water retained after the ion-exchanged water treatment was determined from the following formula. (H6) is the weight of the tea bag measured by the same operation as above when there is no measurement sample.
Amount of water retained in ion-exchanged water after treatment with 1.0 wt% calcium chloride aqueous solution [g / g] = (h5)-(h6)
Then, the re-swelling ratio by ion-exchanged water was determined by the following formula.
Reswelling ratio by ion-exchanged water [%] = (Water retention amount for ion-exchanged water after treatment with 1.0 wt% calcium chloride aqueous solution [g / g]) / (Water retention amount for physiological saline [g / g])} × 100

<Measurement method of absorption under load>
Measurements were performed by sieving into a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh with a mesh opening of 63 μm (JIS Z8801-1: 2006) attached to the bottom, in the range of 250 to 500 μm using a standard sieve. Weigh 0.16 g of the sample, set the cylindrical plastic tube vertically and arrange it on a nylon net so that the measurement sample has almost uniform thickness, and then put a weight (weight: 310.6 g, outside) on this measurement sample. Diameter: 24.5 mm,) was placed. After weighing the entire weight (M1) of this cylindrical plastic tube, a cylindrical plastic containing a measurement sample and a weight is placed in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%). The tube was erected vertically and immersed with the nylon mesh side facing down, and allowed to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, tilted diagonally, and the water adhering to the bottom was collected in one place and dropped as water droplets to remove excess water, and then the measurement sample and weight were contained. The weight (M2) of the entire cylindrical plastic tube was weighed, and the amount of absorption under load was calculated from the following equation. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C.
Absorption amount under load (g / g) = {(M2)-(M1)} /0.16

<Measurement method of gel flow rate of physiological saline>
The measurement was performed by the following operation using the instruments shown in FIGS. 1 and 2.
The swollen gel particles 2 were prepared by immersing 0.32 g of the measurement sample in 150 ml physiological saline 1 (salt concentration 0.9%) for 30 minutes. A vertically erect cylinder 3 {diameter (inner diameter) 25.4 mm, length 40 cm, and a scale line 4 and a scale line 5 are provided at a position 60 ml and a position 40 ml from the bottom, respectively. } In a filtration cylindrical tube having a wire mesh 6 (opening 106 μm, JIS Z8801-1: 2006) and a cock 7 that can be opened and closed (inner diameter of the liquid passage portion 5 mm) at the bottom of the filter, with the cock 7 closed. After transferring the prepared swollen gel particles 2 together with physiological saline, a circular wire mesh having a pressure shaft 9 (weight 22 g, length 47 cm) that binds perpendicularly to the wire mesh surface on the swollen gel particles 2. No. 8 (opening 150 μm, diameter 25 mm) was placed so that the wire mesh and the swollen gel particles were in contact with each other, and a weight 10 (88.5 g) was further placed on the pressure shaft 9 and allowed to stand for 1 minute. Subsequently, the cock 7 was opened, the time (T1; sec) 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 was measured, and the gel liquid passing speed (ml / min) was measured from the following equation. Asked.
Gel passage rate (ml / min) = 20 ml x 60 / (T1-T2)
The temperature of the physiological saline used and the measurement atmosphere was 25 ° C. ± 2 ° C., and T2 was the time measured by the same operation as above when there was no measurement sample.

<Measurement method of gel flow rate of 1.0 wt% calcium chloride aqueous solution>
The measurement was performed by the following operation using the instruments shown in FIGS. 1 and 2.
The swollen gel particles 2 were prepared by immersing 0.32 g of the measurement sample in 150 ml physiological saline 1 (salt concentration 0.9%) for 30 minutes. A vertically erect cylinder 3 {diameter (inner diameter) 25.4 mm, length 40 cm, and a scale line 4 and a scale line 5 are provided at a position 60 ml and a position 40 ml from the bottom, respectively. }, The cock 7 is closed in a filtration cylindrical tube having a wire mesh 6 (opening 106 μm, JIS Z8801-1: 2006) and a cock 7 that can be opened and closed (inner diameter of the liquid passage portion is 5 mm). .. Of the physiological saline used for preparing the measurement sample, 80 ml of the supernatant liquid was discarded, the remaining swelling gel particles 2 were transferred together with the physiological saline, and then 80 ml of calcium chloride solution was injected into the cylinder 3 to inject the swelling gel. The wire mesh and the swollen gel particles come into contact with a circular wire mesh 8 (opening 150 μm, diameter 25 mm) having a pressure shaft 9 (weight 22 g, length 47 cm) that is vertically coupled to the wire mesh surface on the particles 2. The weight 10 (88.5 g) was further placed on the pressurizing shaft 9 and allowed to stand for 1 minute. Subsequently, the cock 7 was opened, the time (T3; sec) 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 was measured, and the gel flow rate (ml / min) was measured from the following equation. Asked.
Gel passage rate of 1.0 wt% calcium chloride aqueous solution (ml / min) = 20 ml x 60 / (T3-T4)
The temperature of the physiological saline solution used, the 1.0 wt% calcium chloride aqueous solution and the measurement atmosphere was 25 ° C. ± 2 ° C., and T4 was the time measured by the same operation as above when there was no 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 was kept at 3 ° C. while stirring and mixing. After inflowing nitrogen into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.63 parts of a 1% hydrogen peroxide solution and 1.1774 parts of a 2% ascorbic acid solution and 2% of 2,2'-azobis [ 2-355 parts of a 2-methyl-N- (2-hydroxyethyl) -propionamide] aqueous solution 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 a hydrogel (1).

Next, 502.27 parts of this hydrogel (1) was subdivided into about 1 mm squares with scissors, and 128.42 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed. Then, using a minced machine with a perforated diameter of 16 mm (12VR-400K manufactured by ROYAL), add 0.10 part of the hydrophobic substance (c-1) {Mg stearate} to the gel 4 times 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 dried 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 opening to obtain dried product particles. The weight average particle size of the dried particles at this time was 392 μm. While stirring 100 parts of the dried body particles at high speed, 5.00 parts of a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30) is added while spraying and mixed. , The surface was crosslinked by allowing to stand at 150 ° C. for 30 minutes 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 of 80 ° C. was changed 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 of 80 ° C. was changed 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 dried particles was changed from 392 μm to 200 μm.

<Example 5>
502.27 parts of the water-containing gel (1) was subdivided into about 1 mm squares with scissors, and 128.42 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed. Subsequently, a minced machine with a perforated diameter of 16 mm (12VR-400K manufactured by ROYAL) was used to knead and shred four times, and then dried with a ventilation type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. .. The dried product was pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then adjusted to a particle size range of 710 to 150 μm opening to obtain dried product particles. While stirring 100 parts of the dried body particles at high speed, 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). {Carboxy-modified polysiloxane model number X-22-3701E manufactured by Shin-Etsu Chemical Industry Co., Ltd.} 0.02 parts were 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 this composite particle and 0.4 part of inorganic powder (silicon dioxide, Tokseal, volume average particle diameter 2.5 μm, specific surface area 120 m ² / g manufactured by Tokuyama Co., Ltd.) are uniformly mixed with a conical blender {manufactured by Hosokawa Micron Co., Ltd.}. Then, absorbent resin particles (P-5) were obtained.

<Example 6>
502.27 parts of the water-containing gel (1) was subdivided into about 1 mm squares with scissors, and 128.42 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed. Subsequently, a minced machine with a perforated diameter of 16 mm (12VR-400K manufactured by ROYAL) was used to knead and shred four times, and then dried with a ventilation type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. .. The dried product was pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then adjusted to a particle size range of 710 to 150 μm opening to obtain dried product particles. While stirring 100 parts of the dried body particles at high speed, 7.30 parts of a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30) is added while spraying and mixed. , The mixture was allowed to stand at 150 ° C. for 30 minutes for surface cross-linking to obtain composite particles. 100 parts of the composite particles, 1.0 part of methanol, and 0.02 parts of the hydrophobic substance (c-2) are uniformly mixed with a conical blender {manufactured by Hosokawa Micron Co., Ltd.} 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-absorbent 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 part to 0.04 part.

<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 part to 0.10 part.

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

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

<Example 12>
The same as in Example 1 except that the perforated diameter of 16 mm was changed to 8 mm and 0.10 part of the hydrophobic substance (c-1) was changed to 0.15 part of the hydrophobic substance (c-3). Water-absorbent resin particles (P-12) were obtained.

<Examples 13 to 15>
For Examples 13 to 15, 1,000 ml of a 1.0 wt% calcium chloride aqueous solution was added as a dehydrating agent to the water-absorbent resin particles (P-5) obtained in Example 5, respectively, with respect to 1N hydrochloric acid aqueous solution 1 The evaluation was performed by performing the same operation except that the solution was changed to 1,000 ml, 1.0 wt% glyceric acid aqueous solution 1,000 ml, and 1 specified sulfuric acid aqueous solution 1,000 ml.

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

<Comparative Example 2> The water-containing gel subdivided into approximately 1 mm squares is not kneaded and shredded with a mincing machine (ROYAL 12VR-400K), but dried with a ventilation dryer {150 ° C., wind speed 2 m / sec}. Water-absorbent resin particles (H-2) for comparison were obtained in the same manner as in Example 1 except that the body was obtained.

<Comparative Example 3> The same operation as in Example 1 was performed except that the particle size range of the mesh size of 710 to 150 μm was changed to the particle size range of the mesh size of 710 to 300 μm, and the water-absorbent resin particles (H-3) were subjected to the same operation. Got

<Comparative Example 4>
The same operation as in Example 1 was carried out except that the gel temperature was changed from 80 ° C. to 20 ° C. to obtain water-absorbent resin particles (H-4).

<Comparative Example 5>
The same operation as in Example 1 was carried out except that the drying temperature was changed from 150 ° C. to 300 ° C. to obtain water-absorbent resin particles (H-5).

<Comparative Example 6>
The same operation as in Example 1 was carried out except that the surface cross-linking temperature of 150 ° C. was changed to 90 ° C. to obtain water-absorbent resin particles (H-6).

<Comparative Example 7>
The same operation as in Example 1 was carried out except that the surface cross-linking temperature of 150 ° C. was changed to 210 ° C. to obtain water-absorbent resin particles (H-7).

<Comparative Example 8> Commercially available diapers GOO. N (Pants L size, manufactured by Daio Paper Corporation, May 2018, Japan) is crushed by hand, and the crushed water-absorbent 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>
Commercially available diapers GOO. N (pants S size, manufactured by Daio Paper Corporation, May 2018, Japan) is crushed by hand, and the spherical water-absorbent resin particles contained in the absorber are taken out together with the pulp and then 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 with respect to the physiological saline solution, the absorption amount under load, the gel flow rate of the physiological saline solution, the apparent density, the weight average particle diameter, and the like. Tables 1 and 2 show the results of the gel passage rate of the 1.0 wt% calcium chloride aqueous solution, the water separation rate, and the re-swelling ratio by ion-exchanged water.

Tables 1 and 2 also show the results of dehydration evaluation of the absorber 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, the dehydrating agent A is a 1.0% by weight calcium chloride aqueous solution, the dehydrating agent B is a 1-standard hydrochloric acid aqueous solution, the dehydrating agent C is a 1.0% by weight glyceric acid aqueous solution, and the dehydrating agent D is 1-defined sulfuric acid. Represents each aqueous solution.

<Preparation of hygiene products>
100 parts of hydrophilic fibers (fluff pulp) and 100 parts of water-absorbent resin particles (each water-absorbent resin particles obtained in Examples and Comparative Examples) are mixed by an air flow type mixing device (pad former) to prepare a mixture. After obtaining the mixture, the mixture was uniformly laminated on an acrylic plate (thickness 4 mm) so as to have a grain ^{size of 500 g / m 2, and pressed at a pressure of 5 kg / cm 2} for 30 seconds to obtain an absorber. This absorber is cut into a square of 10 cm x 10 cm, and a water-permeable sheet (meshing 15.5 g / m ² , manufactured by Advantech, filter paper No. 2) of the same size as the absorber is placed above and below each. Hygienic products were prepared by arranging a polyethylene sheet (S-1) (polyethylene film UB-1 manufactured by Tamapoli) on the back surface as an impermeable sheet and a nonwoven fabric (S-2) on the front surface as a nonwoven fabric layer.

<Evaluation of dehydration of absorber>
Place the prepared hygiene product on a metallic vat with the non-woven fabric (S-2) side facing up, and uniformly add 150 ml of physiological saline (salt concentration 0.9%) in a 300 ml beaker to the hygiene product. After gently pouring and allowing to stand for 20 minutes, the nonwoven fabrics (S-1) and (S-2) were removed from the sanitary ware, and the weight of the swollen absorber (h5; g) was measured. Next, a swollen absorber was placed in a tea bag (length 15 cm, width 15 cm) made of a nylon net having an opening of 63 μm (JIS Z8801-1: 2006) and placed in 1,000 ml of a 1.0 wt% calcium chloride aqueous solution. After immersing for 5 minutes without stirring, pull up, put in a centrifuge, centrifuge at 150 G for 90 seconds to remove excess calcium chloride aqueous solution, measure the weight (h6; g) including the tea bag, and measure the formula below. The absorber dehydration rate is obtained from. The temperature of the physiological saline solution, calcium chloride aqueous solution and measurement atmosphere used is 25 ° C ± 2 ° C. For (h7; g), an absorber was similarly prepared 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 measured.
Absorber 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 as compared with the water-absorbent resin particles of the comparative example. Further, in the evaluation of the water separation rate of the absorber using the 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 absorber is improved. From this result, it can be said that the absorber using the water-absorbent resin particles having a high water separation rate can reduce the water content of the swollen absorber after the dehydration treatment and reduce the total weight per absorber. Therefore, for example, by performing the same treatment operation with an aqueous solution of calcium chloride after urination, the labor during transportation can be reduced, and the energy used for incineration during the incineration can be suppressed, so that the environmental load can be reduced.

By applying the water-absorbent resin particles of the present invention, which are easy to dehydrate, to various absorbent articles including sanitary products, the absorbent articles can be subjected to a predetermined dehydration treatment after use while satisfying the absorption performance required at the time of use. Since the water content can be easily reduced, paper diapers (children's disposable diapers and adult disposable diapers, etc.), napkins (sanitary napkins, etc.), paper towels, pads (pads for incontinence and surgical underpads, etc.) and pets. It is suitably used for sanitary products such as sheets (pet urine absorbing sheets), and is particularly suitable for disposable diapers.

1 Saline 2 Hydrous gel particles 3 Cylinder 4 Scale line 60 ml from the bottom 5 Scale line 40 ml from the bottom 6 Wire mesh 7 Cock 8 Circular wire mesh 9 Pressurized shaft 10 Weight

Claims (21)

It contains a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis and a cross-linked polymer (A) containing an internal cross-linking agent (b) as an essential constituent unit. Water-absorbent resin particles easily dehydrated and having a water separation rate of 70% or more represented by the following formula (1).
Water separation rate [%] = {1- (Water retention amount after treatment with 1.0 wt% calcium chloride aqueous solution [g / g]) / (Water retention amount for physiological saline [g / g])} × 100 (1) The water-absorbent resin particle according to claim 1, wherein the water separation rate is 75% or more. The water-absorbent resin particle according to claim 1 or 2, wherein the re-swelling ratio by ion-exchanged water represented by the following formula (2) is 110% or less.
Reswelling ratio by ion-exchanged water [%] = (Water retention amount for ion-exchanged water after treatment with 1.0 wt% calcium chloride aqueous solution [g / g]) / (Water retention amount for physiological saline [g / g]) × 100 (2) The water-absorbent resin particles are composed of long-chain fatty acid esters, long-chain fatty acids and salts thereof, long-chain aliphatic alcohols, long-chain aliphatic amides, carboxy-modified polysiloxanes, epoxy-modified polysiloxanes, amino-modified polysiloxanes, and alkoxy-modified polysiloxanes. The water-absorbent resin particle according to any one of claims 1 to 3, which contains at least one hydrophobic substance (c) selected from the group. The water-absorbent resin particle according to any one of claims 1 to 4, wherein the water retention amount with respect to the physiological saline is 30 to 50 g / g. The water-absorbent resin particle according to any one of claims 1 to 5, which has an apparent density of 0.40 to 0.62 g / ml. The water-absorbent resin particle according to any one of claims 1 to 6, wherein the weight average particle size is 150 to 500 μm. The water-absorbent resin particle according to any one of claims 1 to 7, wherein the particle shape is amorphous and crushed. The method for producing a water-absorbent resin particle according to any one of claims 1 to 8, wherein the water-soluble vinyl monomer (a1) and / or the vinyl monomer (a1) becomes a water-soluble vinyl monomer (a1) by hydrolysis. A polymerization step of polymerizing a 2) and a monomer composition containing an internal cross-linking agent (b) as an essential constituent unit to obtain a water-containing gel containing the cross-linked polymer (A), a water-containing gel of the cross-linked polymer (A). The steps include a step of further kneading and shredding the subdivided water-containing gel at a gel temperature of 40 ° C. to 120 ° C., and a step of drying and then pulverizing the kneaded and shredded water-containing gel to obtain water-absorbent resin particles. , The method for producing the water-absorbent resin particles. The production method according to claim 9, further comprising a surface cross-linking step. The manufacturing method according to claim 10, further comprising a step of adjusting the particle size after the surface cross-linking step. A sanitary product containing the water-absorbent resin particles according to any one of claims 1 to 8 and easily dehydrating water from a used product. The method for treating a used hygiene product according to claim 12, wherein the step of crushing the used hygiene product and the water-absorbent resin particles contained in the hygiene product or the crushed hygiene product are dehydrated. A method for treating sanitary products, which comprises a step of dehydrating with water, a step of mixing crushed and dehydrated sanitary products with water, and transporting the sanitary products to a solid-liquid processing apparatus. The method for treating a sanitary product according to claim 13, wherein the dehydrating agent is a 2- to 3-valent water-soluble polyvalent metal compound and / or an acidic substance. The method for treating a sanitary product according to claim 14, wherein the acidic substance is at least one acid selected from the group consisting of an inorganic acid having an acid dissociation constant of 3.5 or less and an organic acid. The method for treating a sanitary product according to claim 14 or 15, wherein the acidic substance is at least one acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydroxycarboxylic acid, and methanesulfonic acid. 13. Claim 14, wherein the water-soluble polyvalent metal compound is at least one water-soluble polyvalent metal compound selected from the group consisting of magnesium chloride, magnesium acetate, calcium chloride, calcium oxide, calcium acetate and calcium hypochlorite. How to dispose of sanitary products. The process according to any one of claims 13 to 17, wherein the step of crushing the sanitary goods and the step of dehydrating the water-absorbent resin particles contained in the sanitary goods or the crushed sanitary goods with a dehydrating agent are sequentially or simultaneously performed. Method. The treatment method according to any one of claims 13 to 18, wherein the crushed and dehydrated sanitary goods are transported to the solid-liquid treatment apparatus by a water stream via a pipe or a hose. The treatment method according to any one of claims 13 to 19, wherein the hygiene product is a hygiene product containing pulp fibers and water-absorbent resin particles. A method for producing solid fuel, wherein the used sanitary goods are treated by the treatment method according to any one of claims 13 to 20.

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