1. A method for treating a used article of a sanitary article which is easy to dehydrate the used article to remove water therefrom, the sanitary article comprising water-absorbent resin particles which are easy to dehydrate and which contain a crosslinked polymer (A) having a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which is hydrolyzed to a water-soluble vinyl monomer (a1) and an internal crosslinking agent (b) as essential constituent units, the dehydration ratio represented by the following formula (1) being 70% or more,

the dehydration rate [% ], {1- (water retention amount [ g/g ] after treatment with 1.0 wt% calcium chloride aqueous solution)/(water retention amount [ g/g ] for physiological saline) } × 100(1),

in the method for treating the sanitary product,

comprises the following steps: a step of crushing the used sanitary article; a step of dehydrating the water-absorbent resin particles contained in the sanitary article or the crushed sanitary article with a dehydrating agent; mixing the crushed and dehydrated sanitary product with water, and conveying the mixture to a solid-liquid treatment device.

2. The method for treating sanitary goods according to claim 1, wherein the dehydrating agent is a water-soluble polyvalent metal compound containing magnesium and/or a water-soluble polyvalent metal compound containing calcium.

3. The method for treating sanitary materials according to claim 1 or 2, wherein the dehydrating agent is at least one water-soluble polyvalent metal compound selected from the group consisting of calcium chloride, calcium oxide, calcium acetate and calcium hypochlorite.

4. The treatment method according to any one of claims 1 to 3, wherein the step of pulverizing the sanitary article and the step of dehydrating the water-absorbent resin particles contained in the sanitary article or the pulverized sanitary article with a dehydrating agent are performed sequentially or simultaneously.

5. The treatment method according to any one of claims 1 to 4, wherein the crushed and dehydrated sanitary products are conveyed to the solid-liquid treatment apparatus by a water flow through a pipe or a hose.

6. The treatment method according to any one of claims 1 to 5, wherein the sanitary article is a sanitary article comprising pulp fibers and water-absorbent resin particles.

7. The method for treating a sanitary product according to any one of claims 1 to 6, wherein the dehydration ratio of the water-absorbent resin particles is 75% or more.

8. The method for treating a sanitary article according to any one of claims 1 to 7, wherein the water-absorbent resin particles have a re-swelling capacity based on ion-exchanged water represented by the following formula (2) of 110% or less,

the reswelling rate [% ] based on ion-exchanged water is (water retention [ g/g ] for ion-exchanged water after treatment with a 1.0 wt% calcium chloride aqueous solution)/(water retention [ g/g ] for physiological saline) x 100 (2).

9. The method for treating a sanitary material according to any one of claims 1 to 8, wherein a gel passing speed of the 1.0 wt% calcium chloride aqueous solution of the water-absorbent resin particles is 200 ml/min or more.

10. The method for treating a sanitary article according to any one of claims 1 to 9, wherein the water-absorbent resin particles contain at least one hydrophobic substance (c) selected from the group consisting of long-chain fatty acid esters, long-chain fatty acids and salts thereof, long-chain fatty alcohols, long-chain fatty amides, carboxyl-modified polysiloxanes, epoxy-modified polysiloxanes, amino-modified polysiloxanes, and alkoxy-modified polysiloxanes.

11. The method for treating a sanitary material according to any one of claims 1 to 10, wherein the water-absorbent resin particles have a water retention capacity of 30 to 50g/g with respect to physiological saline.

12. The method for treating a sanitary article according to any one of claims 1 to 11, wherein the water-absorbent resin particles have an apparent density of 0.40g/ml to 0.62 g/ml.

13. The method for treating a sanitary material according to any one of claims 1 to 12, wherein the water-absorbent resin particles have a weight-average particle diameter of 150 to 500 μm.

14. The method for treating a sanitary material according to any one of claims 1 to 13, wherein the water-absorbent resin particles have an amorphous crushed shape.

15. A method for producing a solid fuel, wherein a used sanitary product is treated by the treatment method according to any one of claims 1 to 14.

Background

In recent years, as the amount of sanitary goods used increases, waste disposal of the sanitary goods after use has become a serious problem. Sanitary articles, especially disposable diapers, are rapidly becoming popular as indispensable articles for the age-old age of children, and their consumption is rapidly increasing. In the waste disposal of used sanitary products, disposable diapers and the like are generally subjected to incineration treatment, but since the proportion of moisture in the diapers is approximately 8, a large amount of combustion energy is required for incineration. This treatment method imposes a large load on the incinerator itself, and as a result, not only does it shorten the life of the incinerator, but it also causes air pollution, global warming, and also becomes a factor of imposing a load on the environment, and therefore improvement is strongly desired.

Several solutions have been proposed so far for solving the waste disposal problem of the used sanitary articles. For example, the following techniques are proposed: a system related to a system for separating and recovering water-absorbent resin particles from other components of a sanitary article by using lime (patent document 1); a technique of causing water-absorbent resin particles to undergo dehydration coagulation by using an aqueous calcium chloride solution, and then adding a salt of a strong acid and a nitrogen-containing basic compound to reduce the coagulation force and facilitate subsequent drying (patent document 2); a technique of recovering the water absorption capacity of a super absorbent polymer by subjecting a used super absorbent polymer to dehydration treatment with an aqueous solution of a polyvalent metal salt and then treatment with an aqueous solution of an alkali metal salt (patent document 3); a technique of producing recycled pulp that can be reused in a sanitary product by recovering pulp fibers from a used sanitary product containing the pulp fibers and a super absorbent polymer and decomposing the super absorbent polymer by ozone treatment (patent document 4); and so on.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2009-183893

Patent document 2: japanese patent laid-open publication No. 2015-120834

Patent document 3: japanese patent laid-open publication No. 2013-198862

Patent document 4: japanese patent laid-open publication No. 2017-193819

Disclosure of Invention

Problems to be solved by the invention

In order to solve the waste disposal problem of used sanitary products, if moisture contained in the used sanitary products can be effectively removed, the combustion efficiency in the incineration treatment and the productivity in the recycling are improved, and it is expected that the environmental load can be greatly reduced. The purpose of the present invention is to provide water-absorbent resin particles which have good absorption characteristics during normal use and which are easy to dehydrate water contained in used sanitary articles, and a method for producing the same.

Means for solving the problems

The present invention relates to water-absorbent resin particles which are easily dehydrated and contain a crosslinked polymer (a) having a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which is hydrolyzed into a water-soluble vinyl monomer (a1) and an internal crosslinking agent (b) as essential constituent units, and which have a dehydration rate represented by the following formula (1) of 70% or more, and a sanitary article comprising the same.

Dehydration rate [% ], {1- (water retention amount [ g/g ] after treatment with 1.0 wt% calcium chloride aqueous solution)/(water retention amount [ g/g ] for physiological saline) } × 100(1)

The present invention also relates to a method for producing the water-absorbent resin particles, which comprises the steps of: a polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) hydrolyzed to a water-soluble vinyl monomer (a1) and an internal crosslinking agent (b) as essential constituent units to obtain a hydrogel containing a crosslinked polymer (a); a step of finely dividing the aqueous gel of the crosslinked polymer (A); further kneading and chopping the finely divided hydrous gel at a gel temperature of 40 to 120 ℃; and a step of drying and then pulverizing the kneaded and chopped hydrogel to obtain water-absorbent resin particles.

ADVANTAGEOUS EFFECTS OF INVENTION

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

Drawings

FIG. 1 is a sectional view schematically showing a filtration cylinder tube for measuring the flow rate of a gel.

FIG. 2 is a perspective view schematically showing a pressurizing shaft and a weight for measuring the liquid passing speed of the gel.

Detailed Description

The water-absorbent resin particles of the present invention are water-absorbent resin particles containing a crosslinked polymer (A) having a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which is hydrolyzed into a water-soluble vinyl monomer (a1) and an internal crosslinking agent (b) as essential constituent units.

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and known monomers such as vinyl monomers having at least 1 water-soluble substituent and an ethylenically unsaturated group (for example, anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers) disclosed in paragraphs 0007 to 0023 of japanese patent No. 3648553; anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers disclosed in paragraphs 0009 to 0024 of Japanese patent application laid-open No. 2003-165883; and a vinyl monomer having at least one member selected from the group consisting of a carboxyl group, a sulfo group, a phosphono group, a hydroxyl group, a carbamoyl group, an amino group and an ammonium group, disclosed in paragraphs 0041 to 0051 of Japanese patent application laid-open No. 2005-75982.

The vinyl monomer (a2) (hereinafter also referred to as hydrolyzable vinyl monomer (a2)) which is hydrolyzed to water-soluble vinyl monomer (a1) is not particularly limited, and known vinyl monomers (for example, vinyl monomers having at least 1 hydrolyzable substituent which is hydrolyzed to a water-soluble substituent as disclosed in paragraphs 0024 to 0025 of Japanese patent No. 3648553, and vinyl monomers having at least 1 hydrolyzable substituent (1, 3-oxo-2-oxapropene (-CO-O-CO-) group, acyl group, cyano group, etc.) as disclosed in paragraphs 0052 to 0055 of Japanese patent laid-open publication No. 2005-75982) and the like can be used. The water-soluble vinyl monomer is a vinyl monomer having a property of dissolving at least 100g in 100g of water at 25 ℃. The term "hydrolyzability" refers to a property of being hydrolyzed by water at 50 ℃ and, if necessary, a catalyst (such as an acid or an alkali) to become water-soluble. The hydrolysis of the hydrolyzable vinyl monomer (a2) may be carried out at any of the following stages: during, after, and after the polymerization, the polymerization is preferably performed after the polymerization from the viewpoint of the molecular weight of the water-absorbent resin particles obtained.

Among these, the water-soluble vinyl monomer (a1) is preferable in view of absorption characteristics and the like. The water-soluble vinyl monomer (a1) is preferably an anionic vinyl monomer, and more preferably a vinyl monomer having a carboxylate group, a sulfonate group, an amino group, a carbamoyl group, an ammonium group, or a monoalkylammonium group, a dialkylammonium group, or a trialkylammonium group. Among these, vinyl monomers having a carboxylate group or a carbamoyl group are more preferable, and (meth) acrylic acid (salt) and (meth) acrylamide are further preferable, and (meth) acrylic acid (salt) is particularly preferable, and acrylic acid (salt) is most preferable.

The "carboxylate group" means "carboxyl group" or "carboxylate group", and the "sulfonate group" means "sulfo group" or "sulfonate group". The term (meth) acrylic acid (salt) means acrylic acid, acrylic acid salt, methacrylic acid or methacrylic acid salt, and the term (meth) acrylamide means acrylamide or methacrylamide. Examples of the salt include an alkali metal (lithium, sodium, potassium, and the like), an alkaline earth metal (magnesium, calcium, and the like), and ammonium (NH)₄) Salts and the like. Among these salts, alkali metal salts and ammonium salts are preferable, 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 monomers. 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 hydrogen carbonate and potassium carbonate can be used. The neutralization may be carried out at any of the following stages in the production of the water-absorbent resin particles: before, during, after and during the polymerization, for example, a method of neutralizing an acid group-containing monomer before the polymerization, a method of neutralizing an acid group-containing polymer in a state of a hydrogel after the polymerization, and the like are exemplified as preferable examples.

In addition, when the acid group-containing monomer is used, the degree of neutralization of the acid group is preferably 50 to 80 mol%. When the neutralization degree is less than 50 mol%, the tackiness of the resulting hydrogel polymer increases, and workability during production and use may deteriorate. And further, the water-retention capacity of the resulting water-absorbent resin particles may be reduced. On the other hand, in the case where the neutralization degree is more than 80%, the pH of the resulting resin is increased, and there may be a fear of safety to human skin.

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

As the structural unit of the crosslinked polymer (a), other vinyl monomer (a3) copolymerizable with the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) may be used as the structural unit.

The other copolymerizable vinyl monomer (a3) is not particularly limited, and known hydrophobic vinyl monomers (e.g., the hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese patent No. 3648553, the vinyl monomers disclosed in paragraphs 0058 of Japanese patent laid-open Nos. 2003-165883 and 2005-75982) and the like can be used, and the following vinyl monomers (i) to (iii) and the like can be used.

(i) An aromatic ethylenic monomer having 8 to 30 carbon atoms

And halogen-substituted compounds of styrene, such as styrene, α -methylstyrene, vinyltoluene and hydroxystyrene, and styrene, such as vinylnaphthalene and dichlorostyrene.

(ii) Aliphatic ethylene monomer having 2 to 20 carbon atoms

Olefins [ ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc. ]; and dienes [ butadiene and isoprene, etc. ], and the like.

(iii) Alicyclic vinyl monomer having 5-15 carbon atoms

Monoethylenically unsaturated monomers [ pinene, limonene, indene, and the like ]; and a polyethylenic vinyl polymerizable monomer [ cyclopentadiene, dicyclopentadiene, ethylidene norbornene, etc. ].

When the other vinyl monomer (a3) is used as a structural unit, the content (mol%) of the other vinyl monomer (a3) unit 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 based on the number of moles of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. However, from the viewpoint of absorption characteristics, it is most preferable that the content of the other vinyl monomer (a3) unit is 0 mol%.

The internal crosslinking agent (b) (hereinafter also simply referred to as crosslinking agent (b)) is not particularly limited, and known crosslinking agents (for example, crosslinking agents having 2 or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese patent No. 3648553, crosslinking agents having at least 1 functional group reactive with a water-soluble substituent and having at least 1 ethylenically unsaturated group and crosslinking agents having at least 2 functional groups reactive with a water-soluble substituent, crosslinking agents having 2 or more ethylenically unsaturated groups disclosed in paragraphs 0028 to 0031 of Japanese patent laid-open No. 2003-165883, crosslinking agents having an ethylenically unsaturated group and a reactive functional group and crosslinking agents having 2 or more reactive substituents, crosslinking vinyl monomers disclosed in paragraph 0059 of Japanese patent laid-open No. 2005-75982, and crosslinking vinyl monomers disclosed in paragraphs 0015 to 0016 of Japanese patent laid-open No. 2005-95759) and the like can be used. Among these, from the viewpoint of absorption performance and the like, a crosslinking agent having 2 or more ethylenically unsaturated groups is preferable, triallyl cyanurate, triallyl isocyanurate, and poly (meth) allyl ether of a polyol having 2 to 10 carbon atoms are more preferable, triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane, and pentaerythritol triallyl ether are particularly preferable, and pentaerythritol triallyl ether is most preferable. One crosslinking agent (b) may be used alone, or two or more crosslinking agents may be used in combination.

The content (mol%) of the unit of the crosslinking agent (b) is preferably 0.001 to 5, more preferably 0.005 to 3, and particularly preferably 0.01 to 1 based on the total mol number of the units of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) (when another vinyl monomer (a3) is used, based on the total mol number of the units of (a1) to (a 3). When the content of the unit of the crosslinking agent (b) is in this range, the absorption performance becomes better.

The method for producing water-absorbent resin particles of the present invention comprises the steps of: a polymerization step of polymerizing a monomer composition containing the water-soluble vinyl monomer (a1) and/or the vinyl monomer (a2) hydrolyzed to the water-soluble vinyl monomer (a1) and the internal crosslinking agent (b) as essential constituent units to obtain a hydrogel containing the crosslinked polymer (a); a step of finely dividing the aqueous gel of the crosslinked polymer (A); further kneading and chopping the finely divided hydrous gel at a gel temperature of 40 to 120 ℃; and a step of drying and then pulverizing the kneaded and chopped hydrogel to obtain water-absorbent resin particles.

As a method for producing the crosslinked polymer (A), a water-containing gel (containing a crosslinked polymer and water) containing the crosslinked polymer (A) can be obtained by a known solution polymerization (adiabatic polymerization, film polymerization, spray polymerization, etc.; Japanese patent application laid-open No. 55-133413, etc.), a known suspension polymerization method, or a known reversed-phase suspension polymerization (Japanese patent application laid-open Nos. 54-30710, 56-26909, and 1-5808, etc.). The crosslinked polymer (a) may be a single polymer or a mixture of two or more polymers.

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

When aqueous solution polymerization is carried out, the concentration of the monomer composition in the aqueous solution is preferably 10 to 60% by weight, more preferably 15 to 50% by weight, and still more preferably 20 to 40% by weight. The solvent may be a mixed solvent containing water and an organic solvent, and examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N-dimethylformamide, dimethyl sulfoxide, and a mixture of two or more of these. In the case of aqueous solution polymerization, the amount (wt%) of the organic solvent is preferably 40 or less, more preferably 30 or less, based on the weight of water.

When an initiator is used in the polymerization, a conventionally known radical polymerization initiator can be used, examples thereof include azo compounds [ azobisisobutyronitrile, azobiscyanovaleric acid, 2' -azobis (2-amidinopropane) hydrochloride, etc. ], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [ benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide, di (2-ethoxyethyl) peroxydicarbonate, etc. ], redox catalysts (catalysts composed of a combination of a reducing agent such as alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite, and ascorbic acid, and an oxidizing agent such as alkali metal persulfate, ammonium persulfate, hydrogen peroxide, and organic peroxide), and the like. These catalysts may be used alone, or two or more of them may be used in combination.

The amount (% by weight) of the radical polymerization initiator is preferably 0.0005 to 5, more preferably 0.001 to 2, based on the total weight of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) (when another vinyl monomer (a3) is used, based on the total weight of (a1) to (a 3).

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

The polymerization initiation temperature may be suitably adjusted depending on the kind of the initiator used, and is preferably 0 to 100 ℃, and more preferably 5 to 80 ℃.

The hydrogel polymer obtained by polymerization may be kneaded, chopped, dried, and then pulverized to obtain the crosslinked polymer (A). The kneading and chopping in the present invention means a step of refining the hydrogel while repeating the cutting of the hydrogel by a shear force (shear) and the fusion (bonding) of the cut hydrogel particles, and the kneading and chopping step can provide a hydrogel in which fine hydrogel particles are aggregated, and can form irregularities on the surface of the water-absorbent resin particles. The size (longest diameter) of the gel after kneading and chopping is preferably 50 μm to 10cm, more preferably 100 μm to 2cm, and particularly preferably 1mm to 1 cm. When the size of the gel is within this range, the drying property in the drying step becomes better.

The size (longest diameter) of the gel particles after kneading and pulverization is preferably 50 μm to 10cm, more preferably 100 μm to 2cm, and particularly preferably 1mm to 1 cm. When the particle size is within this range, the drying property in the drying step becomes better and the mixing property with the hydrophobic substance (c) as an additive is good, so that the dehydration rate and the gel passing speed of the 1.0 wt% calcium chloride aqueous solution can be improved as a result.

The kneading and chopping can be carried out by a known method, and kneading and chopping can be carried out by using a kneading and chopping apparatus (for example, a kneader, a universal mixer, a single-shaft or double-shaft kneading extruder, a chopper, a meat chopper, and the like). The dehydration efficiency and the balance of other properties are 40 to 120 ℃, preferably 50 to 110 ℃. The number of kneading and chopping is not particularly limited as long as the size of the gel particles is within the above range, and may be one or more. In the case of kneading and chopping at least two times, the kneading and chopping may be performed a plurality of times by one pulverizer, or may be performed continuously by a plurality of pulverizers.

In the present invention, the hydrogel polymer obtained by polymerization is finely divided before kneading and chopping. The subdivision in the present invention is a step of cutting the hydrogel to be fine while maintaining the internal structure of the hydrogel, and is different from the kneading and chopping described above in view of the internal structure. By finely dividing the water-absorbent resin particles before the kneading and chopping steps, excessive stress applied to the hydrogel during the kneading and chopping steps can be relaxed, and deterioration of the hydrogel polymer can be suppressed, so that the water-absorbent resin particles can have good absorption properties and the water-absorbent resin particles can be prevented from having an extremely high particle defect degree.

The method of the fine-dividing is not particularly limited, and for example, the fine-dividing may be performed by using scissors, or the frozen hydrogel may be pulverized by a pulverizing device (for example, a hammer mill, an impact mill, a roll mill, and a jet mill).

The size (longest diameter) of the gel after the fine division is preferably 50 μm to 10cm, more preferably 100 μm to 2cm, and particularly preferably 500 μm to 1 cm. When the gel size is within this range, the subsequent kneading and chopping steps can be smoothly performed, and the absorption performance of the water-absorbent resin particles may be improved.

As described above, the aqueous gel containing an acid group polymer obtained after polymerization may be neutralized by mixing an alkali before or during the kneading and chopping step. The preferable range of the degree of neutralization of the acid group when the acid group-containing polymer is neutralized is also the same as described above.

The water-absorbent resin particles are obtained by drying and then pulverizing the hydrogel particles containing the crosslinked polymer (A) obtained in the kneading and chopping step.

As a method for drying (including distilling off) the solvent (including water) in the water-containing gel particles, a method of drying with hot air at a temperature of 80 to 300 ℃, a thin film drying method with a rotary dryer or the like heated to 100 to 300 ℃, a reduced pressure drying method, a freeze drying method, a drying method with infrared rays, decantation, filtration, or the like can be applied.

When the solvent containing the water-containing gel particles contains water, the water content (wt%) after drying is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, and most preferably 3 to 8 based on the weight of the crosslinked polymer (a). When the water content is in this range, the grindability in the subsequent grinding step is good, and the absorption performance is further improved.

When the solvent (organic solvent, water, etc.) for the hydrogel particles contains an organic solvent, the content (% by weight) of the organic solvent after drying is preferably 0 to 10, more preferably 0 to 5, particularly preferably 0 to 3, and most preferably 0 to 1 based on the weight of the crosslinked polymer (a). When the content of the organic solvent is in this range, the water-absorbent resin particles have better absorption performance.

The content and the water content of the organic solvent may be determined by a method using an infrared moisture meter (JE 400 manufactured by KETT corporation, ltd.): 120. + -. 5 ℃ for 30 minutes, an atmospheric humidity before heating of 50. + -. 10% RH, a lamp specification of 100V, 40W.

The method for drying and then pulverizing the hydrogel particles is not particularly limited, and a known pulverizing apparatus (for example, hammer mill, impact mill, roll mill, jet mill, and the like) can be used. The particle size of the water-absorbent resin particles obtained can be adjusted by classifying the particles by sieving or the like as necessary.

The water-absorbent resin particles classified by sieving or the like as necessary after the pulverization preferably have a weight average particle diameter (μm) of 150 to 500, more preferably 250 to 500, and most preferably 350 to 450. When the weight average particle diameter is within this range, the absorption performance, dehydration rate, and gel passing speed of a 1.0 wt% calcium chloride aqueous solution are more improved.

The weight average particle size was measured by a method described in the Peltier Chemical Engineers manual (Perry's Chemical Engineers' Handbook) 6 th edition (Mgelo-Hill book Co., Ltd., 1984, page 21) using a Ro-Tap type laboratory shaker and a standard sieve (JIS Z8801-1: 2006). That is, the JIS standard sieves were combined in the order of 1000. mu.m, 850. mu.m, 710. mu.m, 500. mu.m, 425. mu.m, 355. mu.m, 250. mu.m, 150. mu.m, 125. mu.m, 75. mu.m, and 45 μm from above and a tray. About 50g of the test particles were put on the uppermost stage sieve and vibrated for 5 minutes by an experimental sieve shaker of the Ro-Tap type. The weight of the particles measured on each sieve and tray was weighed, and the total weight was taken as 100% by weight, the weight fraction of the particles on each sieve was obtained, and the value was plotted on a logarithmic probability paper (the horizontal axis represents the mesh (particle diameter) of the sieve, and the vertical axis represents the weight fraction), and then the points were connected in a line, and the particle diameter corresponding to the weight fraction of 50% by weight was obtained as the weight-average particle diameter.

Further, since the absorption performance is better as the content of the fine particles contained in the water-absorbent resin particles is smaller, the content (% by weight) of the fine particles having a particle size 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, and more preferably 1 or less. The content of the fine particles can be determined using a map prepared when the weight average particle diameter is determined.

The shape of the water-absorbent resin particles is not particularly limited, and examples thereof include an amorphous crushed shape, a flake shape, a pearl shape, a rice grain shape, and the like. Among these, the amorphous crushed form is preferable because the fiber is well entangled with the fibrous material and the fibrous material is not likely to be separated therefrom in the use of a disposable diaper.

The water-absorbent resin particles of the present invention may contain a hydrophobic substance (c). Examples of the (c) include a hydrophobic substance containing a hydrocarbon group (c1), a hydrophobic substance containing a hydrocarbon group having a fluorine atom (c2), and a hydrophobic substance having a polysiloxane structure (c 3).

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 fatty alcohols, long-chain fatty amides, and mixtures of two or more of these.

Examples of the polyolefin resin include polymers { for example, polyethylene, polypropylene, polyisobutylene, poly (ethylene-isobutylene), isoprene and the like } having a weight average molecular weight of 1000 to 100 ten thousand, which are composed of an olefin having 2 to 4 carbon atoms { for example, ethylene, propylene, isobutylene, isoprene and the like } as an essential constituent monomer (the content of the olefin is at least 50% by weight based on the weight of the polyolefin resin).

Examples of the polyolefin resin derivative include polymers having a weight average molecular weight of 1000 to 100 ten thousand obtained by introducing a carboxyl group (-COOH), 1, 3-oxo-2-oxapropene (-COOCO-) and the like into a polyolefin resin { for example, polyethylene thermal degradation products, polypropylene thermal degradation products, maleic acid-modified polyethylene, chlorinated polyethylene, maleic acid-modified polypropylene, ethylene-acrylic acid copolymers, ethylene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, maleated polybutadiene, ethylene-vinyl acetate copolymers, and maleated products of ethylene-vinyl acetate copolymers }.

As the polystyrene resin, a polymer having a weight average molecular weight of 1000 to 100 ten thousand, or the like can be used.

Examples of the polystyrene resin derivative include polymers { for example, a styrene-maleic anhydride copolymer, a styrene-butadiene copolymer, a styrene-isobutylene copolymer, and the like } having a weight average molecular weight of 1000 to 100 ten thousand, which are composed of styrene as an essential constituent monomer (the content of styrene is at least 50% by weight based on the weight of the polystyrene derivative).

Examples of the wax include waxes having a melting point of 50 to 200 ℃ { for example, paraffin wax, beeswax, carnauba wax, tallow, and the like }.

Examples of the long-chain fatty acid ester 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, ethyl oleate, monolaurin, pentaerythritol monostearate, pentaerythritol oleate, monolaurin, sorbitol monostearate, sorbitol stearate monoester, sorbitol oleate monoester, sucrose palmitate, sucrose stearate monoester, sucrose stearate triester, tallow, etc. }.

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

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

Examples of the long-chain aliphatic amide include an amidation product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms, an amidation product of ammonia or a primary amine having 1 to 7 carbon atoms and a long-chain fatty acid having 8 to 30 carbon atoms, an amidation product of a long-chain aliphatic secondary amine having at least 1 aliphatic chain having 8 to 30 carbon atoms and a carboxylic acid having 1 to 30 carbon atoms, and an amidation product of a secondary amine having 2 aliphatic hydrocarbon groups having 1 to 7 carbon atoms and a long-chain fatty acid having 8 to 30 carbon atoms.

The amidation product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms can be classified into a product obtained by reacting a primary amine with a carboxylic acid in a 1:1 ratio and a product obtained by reacting a primary amine with a carboxylic acid in a 1:2 ratio. Examples of the substance obtained by the 1:1 reaction include N-octylamide acetate, N-hexacosanylamide acetate, N-octylamide heptacosanoic acid, and N-hexacosanylamide heptacosanoic acid. Examples of the substance obtained by the 1:2 reaction include diacetic acid N-octylamide, diacetic acid N-hexacosanylamide, di (heptacosanoic) N-octylamide, and di (heptacosanoic) N-hexacosanylamide. In the case of a product obtained by reacting a primary amine with a carboxylic acid in a 1:2 ratio, the carboxylic acids used may be the same or different. ]

The amidation product of ammonia or a primary amine having 1 to 7 carbon atoms and a long-chain fatty acid having 8 to 30 carbon atoms can be classified into a product obtained by reacting ammonia or a primary amine with a carboxylic acid in a ratio of 1:1 and a product obtained by reacting ammonia or a primary amine with a carboxylic acid in a ratio of 1: 2. Examples of the 1:1 reaction product include nonanamide, nonanoic acid methylamide, nonanoic acid N-heptylamide, heptacosamide, and heptacosamide. Examples of the substance obtained by the 1:2 reaction include dinonylamide, N-methylamide dinonylamide, N-heptylamide dinonylamide, dioctadecylamide, N-ethylamide dioctadecylamide, N-heptylamide dioctadecylamide, heptacosamide, N-methylamide dioctadecylamide, N-heptylamide and N-hexacosanamide. The carboxylic acids used in the reaction of ammonia or a primary amine with a carboxylic acid in a 1:2 ratio may be the same or different.

Examples of the amidation product of a long-chain aliphatic secondary amine having an aliphatic chain of at least 1 carbon number 8 to 30 and a carboxylic acid having 1 to 30 carbon numbers include N-methyloctylamide acetate, N-methylhexacosanamide acetate, N-octylhexacosanamide acetate, N-dicosanamide acetate, N-methyloctylamide heptacosanoate, N-methylhexacosanamide heptacosanoate, N-octylhexacosanamide heptacosanoate, and N-dicosanamide heptacosanoate.

Examples of amidation products of aliphatic hydrocarbon groups having 2 carbon atoms and having 1 to 7 carbon atoms, such as secondary amine and long-chain fatty acid having 8 to 30 carbon atoms, include N-dimethylamide nonanoate, N-methylheptylamide nonanoate, N-diheptylamide nonanoate, N-dimethylamide heptacosanoate, N-methylheptylamide heptacosanoate, and N-diheptylamide heptacosanoate.

The hydrophobic substance (c1) is preferably a long-chain fatty acid ester, a long-chain fatty acid and a salt thereof, a long-chain fatty alcohol, and a long-chain fatty amide, more preferably sorbitol stearate, sucrose stearate, stearic acid, Mg stearate, Ca stearate, Zn stearate, and Al stearate, and particularly preferably sucrose stearate and Mg stearate, from the viewpoints of dehydration efficiency and leakage resistance of the absorbent article.

Examples of the hydrophobic substance (c2) containing a hydrocarbon group having a fluorine atom include perfluoroalkanes, perfluoroolefins, perfluoroaromatics, perfluoroalkyl ethers, perfluoroalkyl carboxylic acids, perfluoroalkyl alcohols, and mixtures of two or more of these.

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

Examples of the carboxyl-modified polysiloxane include X-22-3701E, X-22-3710 (both manufactured BY shin-Etsu chemical industries, Ltd.), DOWSIL (model BY16-880Fluid), DOWSIL (model BY16-880) (manufactured BY Dow-Toray Co., Ltd.), and the like. The position of the carboxyl groups relative to the polysiloxane backbone is pendant and/or terminal.

Examples of the epoxy-modified polysiloxane include X-22-343 (manufactured BY shin-Etsu chemical industries, Ltd.), KF-101, KF-1001, X-22-2000, X-22-2046, KF-102, X-22-4741, KF-1002, KF-1005 (manufactured BY shin-Etsu chemical industries, Ltd.), DOWSIL (model BY16-839 Fluid), DOWSIL (model BY8411Fluid), DOWSIL (model BY 8413Fluid), DOWS (model BY8421Fluid) (manufactured BY Dow-Toray Corp.), SF8411, SF8413, BY16-839, BY16-876, FZ-3736, and SF8421 (manufactured BY Toray Dow Corn.). The position of the epoxy groups relative to the polysiloxane backbone is pendant and/or terminal.

Examples of the amino-modified polysiloxane include a monoamine-modified polysiloxane in which the modifying group is a primary amine, and a diamine-modified polysiloxane in which the modifying group is a secondary amine.

Examples of the single amino group-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 (manufactured BY shin-Etsu chemical industries, Ltd.), DOWSIL (model number BY16-205), DOWSIL (model BY16-213), DOWSIL (model BY16-849Fluid), DOWSIL (model BY16-853U), DOWSIL (model BY16-871), DOWSIL (model BY16-872), DOWSIL (model BY16-879B), DOWSIL (model BY16-892), DOWSIL (model FZ-3705), DOWSIL (model FZ-3710Fluid), DOWSIL (model FZ-3760), DOWSIL (model FZ-3785), DOWSIL (model SF8417Fluid) (all made BY Toray Dow corporation) and the like. Examples of the diamino-modified type include KF-859, KF-393, KF-860, KF-8004, KF-8002, KF-8005, KF-867, KF-8021, KF-869 and KF-861 (each manufactured by shin-Etsu chemical industries). The position of the diamino groups relative to the polysiloxane backbone is pendant and/or terminal.

Examples of the alkoxy-modified polysiloxane include X-22-4952, X-22-4272, KF-6123, KF-351A, KF-352-353, KF-354L, KF-355A, KF-615-A, 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, DOWFIL (model 501W Additive), DOWFIL (model FZ-2110), DOWF (model FZ-2123), DOWF SIL (model L-7001), DOWFSIL (model SF8410Fluid), DOWF (model SH3746Fluid), DOWF 8400Fluid, and SIL (model SH8700Fluid) (manufactured by Dowfl corporation). The position of the alkoxy groups relative to the polysiloxane backbone is pendant and/or terminal.

The hydrophobic substance (c3) is preferably a carboxyl-modified polysiloxane, an epoxy-modified polysiloxane, an amino-modified polysiloxane, or an alkoxy-modified polysiloxane, and more preferably a carboxyl-modified polysiloxane, from the viewpoints of dehydration efficiency and leakage resistance of the absorbent article.

The HLB value of the hydrophobic substance (c) is preferably 1 to 10, more preferably 1 to 8, and particularly preferably 1 to 7. When the HLB value is within this range, the absorbent article can have better leakage resistance. The HLB value is a hydrophilic-hydrophobic balance (HLB) value, and is obtained by the microtia method (surfactant entry, page 212, liangban wuyan, sanyo chemical industry co., 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 viewpoints of the dehydration efficiency and the leakage resistance of the absorbent article. Further preferred is the hydrophobic substance (c 3).

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

The hydrophobic substance (c) may be present at any position of the water-absorbent resin particles, and is preferably present inside the water-absorbent resin particles from the viewpoints of water absorption characteristics (particularly, water absorption rate) and dehydration ratio.

The hydrophobic substance (c) may be contained in the aqueous gel containing the crosslinked polymer (a) in the kneading and chopping step, and is preferably contained in the polymerization step or the kneading and chopping step. Examples of the method of adding (c) include a method of adding to the polymerization solution after the polymerization step is started and before the polymerization step is completed; a method of adding the aqueous gel to the aqueous gel before the kneading and chopping step after completion of the polymerization step; the method of adding the water-containing gel particles to the water-containing gel particles in the kneading and chopping step is preferably a method of adding the water-containing gel particles to the water-containing gel before the kneading and chopping step after the completion of the polymerization step or a method of adding the water-containing gel particles to the water-containing gel particles in the kneading and chopping step, and more preferably a method of adding the water-containing gel particles to the water-containing gel particles in the kneading and chopping step, from the viewpoint of improving the dehydration rate. The hydrophobic substance (c) may be added to water and/or an organic solvent in a dissolved and/or dispersed form.

In the water-absorbent resin particles, the particle surfaces are preferably further surface-crosslinked. Therefore, the production method of the present invention may include a step of drying and pulverizing the hydrogel particles and then surface-crosslinking the resultant particles. By performing surface crosslinking, the gel strength can be further improved, and the water retention amount and the absorption amount under load expected in actual use can be satisfied. The step of surface-crosslinking the hydrogel particles is also simply referred to as a crosslinking step.

As a method for surface-crosslinking the water-absorbent resin particles, there can be mentioned a conventionally known method, for example, a method in which the water-absorbent resin is made into particles, and then a mixed solution of the surface-crosslinking agent (e), water and a solvent is mixed and subjected to a heat reaction. Examples of the method of mixing include a method of spraying the above-mentioned mixed solution to the water-absorbent resin particles or a method of immersing the water-absorbent resin particles in the above-mentioned mixed solution, and a method of spraying the above-mentioned mixed solution to the water-absorbent resin particles and mixing them is preferable.

Examples of the surface cross-linking agent (e) include polyglycidyl compounds such as ethylene glycol diglycidyl ether, glycerol diglycidyl ether, and polyglycerol polyglycidyl ether, polyols such as glycerol and ethylene glycol, ethylene carbonate, polyamines, and polyvalent metal compounds. Among these, the polyglycidyl compounds are preferred because they allow the crosslinking reaction to proceed at a relatively low temperature. These surface-crosslinking agents may be used alone or in combination of two or more.

The amount of the surface-crosslinking agent (e) to be 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 crosslinking. When the amount of the surface cross-linking agent (e) is less than 0.001% by weight, the surface cross-linking degree is 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) is more than 5% by weight, the degree of cross-linking of the surface is too excessive, and the water retention may be lowered.

The amount of water used in the surface crosslinking 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 crosslinking. When the amount of water used is less than 0.5% by weight, the degree of penetration of the surface-crosslinking agent (e) into the water-absorbent resin particles may be insufficient, and the effect of improving the absorption under load may be insufficient. On the other hand, when the amount of water is more than 10% by weight, the surface-crosslinking agent (e) penetrates into the interior, and although an increase in the absorption under load is observed, the water retention may decrease.

The solvent to be used for the hydration at the time of surface crosslinking may be any conventionally known solvent, and may be suitably selected and used in consideration of the degree of penetration of the surface crosslinking agent (e) into the water-absorbent resin particles, the reactivity of the surface crosslinking agent (e), and the like, and is preferably a hydrophilic organic solvent soluble in water such as methanol, diethylene glycol, propylene glycol, and the like. The solvent may be used alone or in combination of two or more.

The amount of the solvent to be used may be suitably adjusted depending on the kind of the solvent, and is preferably 1 to 10% by weight based on the weight of the water-absorbent resin particles before surface crosslinking. The ratio of the solvent to water may be arbitrarily adjusted, and is preferably 20 to 80 wt%, more preferably 30 to 70 wt% on a weight basis.

For the surface crosslinking, a mixed solution of the surface crosslinking 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 ℃, and more preferably 120 to 180 ℃. The reaction time may be appropriately adjusted depending on the reaction temperature, and is preferably 3 to 60 minutes, and more preferably 10 to 45 minutes. The water-absorbent resin particles obtained by surface-crosslinking may be further surface-crosslinked using a surface-crosslinking agent that is the same as or different from the surface-crosslinking agent used initially.

After surface crosslinking, particle size adjustment can be performed by screening as needed. The preferable ranges of the weight average particle diameter and the fine particle content of the particles obtained by the particle size adjustment are the same as those described above. The particle size adjusting step after the surface crosslinking of the hydrogel particles is also referred to as a post-step after the crosslinking step or simply as a post-step.

In the crosslinking step and/or the post-step after the crosslinking step, the hydrophobic substance (c) may be added to water and/or an organic solvent in a dissolved and/or dispersed form. By adding the surfactant in the crosslinking step and/or a post-step after the crosslinking step, the surfactant can be uniformly added to the particle surface, and thus the dehydration efficiency can be improved.

The water-absorbent resin particles of the present invention may further contain a polyvalent metal salt (f), and therefore, the production method of the present invention may further comprise a step of mixing with the polyvalent metal salt (f). By containing the polyvalent metal salt (f), the water-absorbent resin particles are improved in blocking resistance and liquid permeability. 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 with the above-mentioned inorganic acid or organic acid.

The polyvalent metal salt (f) is preferably an inorganic acid salt of aluminum and an inorganic acid salt of titanium, more preferably aluminum sulfate, aluminum chloride, potassium aluminum sulfate and aluminum sodium sulfate, particularly preferably aluminum sulfate and aluminum sodium sulfate, and most preferably aluminum sodium sulfate, from the viewpoint of availability and solubility. These polyvalent metal salts may be used singly or in combination of two or more.

The amount (wt%) of the polyvalent metal salt (f) is preferably 0.01 to 5, more preferably 0.05 to 4, and particularly preferably 0.1 to 3 based on the weight of the crosslinked polymer (A) from the viewpoints of absorption performance and blocking resistance.

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

The water-absorbent resin particles of the present invention may be further coated with an inorganic powder on the surface. As the inorganic powder, hydrophilic inorganic particles, hydrophobic inorganic particles, and the like are included. Examples of the hydrophilic inorganic particles include particles of glass, silica gel, silica, clay, and the like. Examples of the hydrophobic inorganic particles include particles of carbon fibers, kaolin, talc, mica, bentonite, sericite, asbestos, volcanic ash, and the like. Among 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), regular spherical, film-like, rod-like, fibrous, and the like, and is preferably amorphous (crushed) or regular spherical, and more preferably regular spherical.

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

The water-absorbent resin particles of the present invention may contain other additives { for example, a known preservative (e.g., jp 2003-225565 a, jp 2006-131767 a, etc.), a fungicide, an antibacterial agent, an antioxidant, an ultraviolet absorber, a coloring agent, a fragrance, a deodorant, an organic fiber, etc. }. When these additives are contained, the content (% by weight) of the additive is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably 0.05 to 1, and most preferably 0.1 to 0.5 based on the weight of the water-absorbent resin particles.

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. When the apparent density is in this range, the dehydration rate and gel flow rate become better. The apparent density of the water-absorbent resin particles was measured in accordance with JIS K7365: 1999 at 25 ℃.

The water-absorbent resin particles of the present invention have a water retention capacity (g/g) for physiological saline of preferably 30 to 50, more preferably 33 to 49, still more preferably 36 to 48, and particularly preferably 39 to 47. If the amount is less than 30, leakage is likely to occur during repeated use, which is not preferable. Further, if it exceeds 50, blocking tends to occur, which is not preferable. The water retention amount can be suitably adjusted by the kind and amount of the crosslinking agent (b) and the surface crosslinking agent (e). Therefore, for example, in the case where the water retention needs to be increased, it can be easily achieved by reducing the amounts of the crosslinking agent (b) and the surface crosslinking agent (e).

The water-absorbent resin particles of the present invention preferably have a gel permeation rate (ml/min) of physiological saline of 5 to 250, more preferably 10 to 230, and particularly preferably 30 to 210. When the gel permeation rate (ml/min) of the physiological saline is less than 5, the liquid diffusibility decreases, and as a result, leakage or rash may occur; if the amount is more than 250, the liquid diffusibility is too large, and therefore the liquid may leak from the absorbent body before being absorbed by the water-absorbent resin particles.

The dehydration ratio in the present invention is a value represented by the following formula (1) and is calculated from the ratio of the water retention amount with respect to physiological saline and the water retention amount of the swollen gel after the water retention amount is measured after treatment with a 1.0 wt% calcium chloride aqueous solution. That is, it represents the ratio of the weight of water separated after the treatment to the weight of the swollen gel before the treatment with the dehydrating agent. Therefore, the higher the dehydration rate, the more excellent the dehydration efficiency based on the specific dehydrating agent treatment.

Dehydration rate [% ], {1- (water retention amount [ g/g ] after treatment with 1.0 wt% calcium chloride aqueous solution)/(water retention amount [ g/g ] for physiological saline) } × 100(1)

Specific measurement methods are described below.

From the viewpoint of efficiency of dehydration treatment, the water-absorbent resin particles of the present invention have a dehydration ratio (%) of 70 or more, more preferably 73 or more, and particularly preferably 75 or more. The higher the upper limit value is, the more preferable is, the higher is the upper limit value, and the higher is the upper limit value, but the upper is not particularly limited, and from the viewpoint of balance between performance and productivity with other properties, the upper is preferably 95 or less, and more preferably 90 or less. As means for increasing the dehydration rate, means for enlarging the specific surface area of the particles and adjusting the balance between hydrophilicity and hydrophobicity in the particles or on the particle surface may be considered. Examples of means for achieving this include: the use of hydrophobic materials in the polymerization step, kneading and chopping step, crosslinking step and/or post-step after the crosslinking step; adjusting the gel temperature in the step of kneading the water-containing gel; increasing the heating temperature during drying when dehydrating from the aqueous gel; increasing the heating temperature in the crosslinking process; reducing the weight average particle size; and so on. The gel temperature in the step of kneading the water-containing gel is preferably 40 to 120 ℃, more preferably 50 to 110 ℃ from the viewpoint of the balance between the dehydration efficiency and the performance with other physical properties. The heating temperature during drying in the dehydration of the hydrogel is preferably 100 to 300 ℃ and more preferably 110 to 280 ℃ from the viewpoint of the balance between the performance and other properties and the productivity. When the heating is carried out at a temperature higher than 300 ℃, the water-absorbent resin particles are not preferable because they are thermally deteriorated. The heating temperature in the crosslinking step is preferably 100 to 230 ℃, and more preferably 120 to 180 ℃. When the heating temperature is within this range, the hydrophobic substance melts or the viscosity decreases to coat the surface of the absorbent resin particles, and therefore, it is considered that fusion of the gels with each other can be prevented and the reaction point with the dehydrating agent can be increased. From the viewpoint of the balance between the dehydration property and other physical properties, the weight-average particle diameter is preferably from 150 to 500 μm, more preferably from 200 to 400 μm.

The reswelling ratio (%) of the water-absorbent resin particles of the present invention based on ion-exchanged water is a value represented by the following formula (2), and is calculated from the ratio of the water retention amount of the swollen gel obtained by measuring the water retention amount after dehydration treatment with a 1.0 wt% calcium chloride aqueous solution and re-swelling with ion-exchanged water to the water retention amount with respect to physiological saline. Therefore, the lower the re-swelling ratio by ion-exchanged water, the more the dehydrating effect of the dehydrating agent can be maintained when diluted with water.

Re-swelling ratio based on ion-exchanged water [% ] (water retention [ g/g ] for ion-exchanged water after treatment with a 1.0 wt% calcium chloride aqueous solution)/(water retention [ g/g ] for physiological saline × 100 (2))

Specific measurement methods are described below.

From the viewpoint of efficiency of the dehydration treatment, the water-absorbent resin particles of the present invention have a re-swelling ratio (%) of 110 or less, more preferably 105 or less, based on ion-exchanged water. The lower limit is preferably lower, and is not particularly limited, but is preferably 80 or more in view of balance with absorption performance and productivity. As means for reducing the re-swelling ratio, it is conceivable to enlarge the specific surface area of the particles, adjust the balance between hydrophilicity and hydrophobicity in the particles or on the particle surface, increase the anion concentration in the particles, and keep the surface area of the water-absorbent resin particles after the treatment with the dehydrating agent small. Specifically, the following means can be mentioned: the use of hydrophobic materials in the polymerization step, kneading and chopping step, crosslinking step or post-step after the crosslinking step; increasing the heating temperature during drying when dehydrating from the aqueous gel; reducing the weight average particle size; and so on. It is conceivable that the contact of the water absorbent resin particles with the water present in the surroundings thereof is hindered by the presence of the hydrophobic substance on the surface of the absorbent resin particles, and as a result, it is considered that the re-swelling of the gel is suppressed.

The gel permeation rate of the 1.0 wt% calcium chloride aqueous solution of the present invention was a value represented by the following formula, and the gel permeation rate was calculated from the value obtained by adding the gel of the measurement sample swollen with physiological saline to 80ml of a 1.0 wt% calcium chloride aqueous solution together with a part of the liquid used for swelling, and subtracting the time (T4; second) for 20ml of the mixed aqueous solution of physiological saline and calcium chloride to flow between the swollen gels from the time (T3; second) for 20ml of the mixed aqueous solution of physiological saline and calcium chloride to flow between the swollen gels without the measurement sample. Therefore, the higher the gel flow rate of the 0.1 wt% calcium chloride aqueous solution, the more likely the dehydrating agent penetrates into the particles of the swollen and aggregated water-absorbent resin, and the more excellent the dehydration efficiency.

Gel permeation rate (ml/min) of 1.0 wt% calcium chloride aqueous solution 20ml × 60/(T3-T4)

Specific measurement methods are described below.

From the viewpoint of efficiency of the dehydration treatment, the water-absorbent resin particles of the present invention have a gel permeation rate (ml/min) of a 1.0 wt% calcium chloride aqueous solution of 200 or more, more preferably 300 or more, and particularly preferably 500 or more. The higher the upper limit value is, the more preferable is, without particular limitation, 2300 or less, and more preferably 2000 or less, from the viewpoint of balance between performance and productivity with other properties. The gel permeation rate of the aqueous solution of 1.0 wt% calcium chloride was controlled by enlarging the specific surface area of the particles and adjusting the balance between hydrophilicity and hydrophobicity in the particles or on the particle surface.

The water-absorbent resin particles of the present invention preferably have an absorbency under load (g/g) of 19 or more. When the amount is less than 19, leakage is likely to occur during repeated use, which is not preferable. The higher the upper limit value is, the more preferable it is not particularly limited, but from the viewpoint of balance between performance and productivity with other properties, it is preferably 27 or less, and more preferably 25 or less. The absorption amount under load can be suitably adjusted by the kind and amount of the crosslinking agent (b) and the surface crosslinking agent (e). Thus, for example, in the case where it is desired to increase the absorption under load, this can be easily achieved by increasing the amounts of the crosslinking agent (b) and the surface crosslinking agent (e).

The sanitary article of the present invention comprises the water-absorbent resin particles of the present invention, and can be easily dehydrated from a used article. Examples of the sanitary products include disposable diapers and sanitary napkins, but they are used not only for sanitary products but also for various purposes such as absorbent and retention agents for various aqueous liquids and gelling agents. The method for producing a sanitary product is the same as a known method (the methods described in Japanese patent laid-open Nos. 2003-225565, 2006-131767, and 2005-097569).

In the sanitary article of the present invention, the water-absorbent resin particles may be used alone as the absorbent material, or may be used together with other materials as the absorbent material. As other materials, fibrous materials and the like can be cited. The structure, production method, and the like of the absorber when used together with a fibrous material are the same as those of known methods (e.g., japanese patent laid-open nos. 2003-225565, 2006-131767, and 2005-097569).

When the water-absorbent resin particles and the fibrous material are used together as an absorbent body, 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, and more preferably 40/60 to 70/30. Examples of the fibrous material include cellulose fibers, organic synthetic fibers, and a mixture of cellulose fibers and organic synthetic fibers.

Next, a method for treating a sanitary product of the present invention will be described. The method for treating a used sanitary article containing water-absorbent resin particles according to the present invention comprises the steps of: a step of crushing the used sanitary product (hereinafter referred to as "crushing step"); a step of dehydrating the water-absorbent resin particles contained in the sanitary article or the crushed sanitary article with a dehydrating agent (hereinafter referred to as a dehydrating step); a step of mixing the crushed and dehydrated sanitary product with water and transferring the mixture to a solid-liquid treatment apparatus (hereinafter referred to as "transfer step"). The sanitary article may further comprise pulp fibers.

The pulverization step is a step of pulverizing the sanitary product to obtain a pulverized product. As the pulverization, a publicly known pulverizer or a crusher can be used, and examples thereof include a shredder (dispower) type crusher (a fixed type in which the hygienic article is flown to a wall surface by a rotating disc rotating at a high speed and attached to a peripheral portion of the rotating disc, or a crusher in which the hygienic article is crushed by a variable hammer, a fixed blade on the wall surface, or the like), a cutter mill, a single shaft type crusher, a double shaft type crusher, a coaxial core type crusher, a hammer crusher, a ball mill, and the like, and a shredder type crusher or a cutter mill in which a material of the hygienic article contains a plastic sheet, a nonwoven fabric, a material having elasticity and is cut by a blade while rotating at a high speed is particularly suitable.

The pulverized material of the sanitary product can be made into aqueous suspension. As a method for obtaining the aqueous suspension, there are a method of adding water to swell the sanitary article and then pulverizing the article, a method of adding water to pulverize the article while pulverizing the article, and a method of adding water to pulverize the article, and from the viewpoint of reducing the load on the pulverizer, a method of adding water to swell the sanitary article and then pulverizing the article is preferable.

The appropriate range of the size of the pulverized material of the pulverized sanitary product depends on the separation and collection method by a solid-liquid separator described later, but from the viewpoint of transportability in a water flow, it is preferable that the sanitary product has a length of one sheet of 100mm or less. The size of the pulverized material can be appropriately adjusted by the type of the above-mentioned pulverizer or crusher, the treatment conditions, and the like.

In the sanitary article to be crushed, the sanitary article may be directly crushed, or the absorbent material containing the water-absorbent resin particles may be taken out from the sanitary article and crushed.

The dehydration step is a step of dehydrating the water-absorbent resin particles contained in the sanitary article or the crushed sanitary article with a dehydrating agent. By this dehydration treatment, the water absorption performance 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 the dehydrating agent but also a step of simply adding the dehydrating agent without actually causing a dehydration phenomenon.

The dehydrating agent in the present invention is not particularly limited as long as it has a dehydrating performance, and known dehydrating agents include water-soluble polyvalent metal compounds, strong acids, and the like. The water-soluble polyvalent metal compound reduces the difference in ion concentration between the inside of the water-absorbent resin particle and the surrounding water by forming a chelate salt with a carboxyl group or a carboxyl group ion or by converting a carboxyl group ion into a carboxyl group with a strong acid, thereby reducing the osmotic pressure difference and consequently causing dehydration from the inside of the water-absorbent resin particle. As the dehydrating agent, a water-soluble polyvalent metal compound is preferable in terms of dehydration efficiency and handling.

The water-soluble polyvalent metal compound is not particularly limited as long as it is an element having a valence of 2 or more in the periodic table and forms a chelate salt with a carboxyl group or a carboxyl group ion after dissolving in water or reacting with water. Examples of the 2-valent 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, and examples of the 3-valent metal include polyvalent metal compounds containing metals such as boron, aluminum, and gallium. The polyvalent metal compound may be a non-hydrate, or a hydrate such as a monohydrate, a dihydrate, a trihydrate, a tetrahydrate, a pentahydrate, a hexahydrate, a heptahydrate, an octahydrate, or a nonahydrate. These dehydrating agents may be used alone, or two or more kinds may be used in combination. The term "water-soluble polyvalent metal compound" in the present invention means a polyvalent metal compound having a solubility in water at 20 ℃ of 1mg/ml or more, preferably 10mg/ml or more.

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

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

Among these dehydrating agents, from the viewpoint of improving the dehydrating performance, a water-soluble polyvalent metal compound having a valence of 2 is preferable, a water-soluble polyvalent metal compound containing magnesium and a water-soluble polyvalent metal compound containing calcium are more preferable, and calcium chloride, calcium oxide, calcium acetate and calcium hypochlorite are further preferable.

The method for treating with the dehydrating agent is not particularly limited as long as the dehydrating agent is brought into contact with the water-absorbent resin particles in the sanitary article, and the dehydrating agent in a solid form may be added to the sanitary article or an aqueous solution of the dehydrating agent may be added. In the sanitary article treated with the dehydrating agent, the dehydrating agent may be added after swelling with water, or the dehydrating agent may be added after adding water. The device for treating with the dehydrating agent may be any device as long as it can mix the hygienic product and the dehydrating agent, and may be treated with the above-mentioned crusher and crusher, or may be separately carried out using a treatment tank capable of stirring.

The amount of the dehydrating agent used in the dehydration step depends on the type of the dehydrating agent used, and is preferably 0.1% or more, more preferably 1.0% or more, and still more preferably 3.0% or more, based on the dry weight of the water-absorbent resin particles. If the amount of the dehydrating agent is small, the dehydration rate of the water-absorbent resin particles decreases, and the separation and recovery efficiency decreases.

The step sequence of the pulverization step and the dehydration step may be a step of pulverizing the sanitary article and a step of dehydrating the water-absorbent particles contained in the sanitary article or the pulverized sanitary article with the dehydrating agent, sequentially or simultaneously. The sequence of the specific treatment steps is shown below. The arrows indicate the order.

(1) A step of pulverizing the sanitary product → a step of dehydrating the water-absorbent resin particles contained in the pulverized sanitary product with a dehydrating agent → a step of mixing the pulverized and dehydrated sanitary product with water and transferring the mixture to a solid-liquid treatment apparatus.

(2) The step of dehydrating the water-absorbent resin particles contained in the sanitary goods with the dehydrating agent → the step of pulverizing the sanitary goods → the step of mixing the pulverized and dehydrated sanitary goods with water and transferring the mixed goods to the solid-liquid treatment device.

(3) Simultaneously, the step of dehydrating the water-absorbent resin particles contained in the sanitary article or the crushed sanitary article with the dehydrating agent, and the step of crushing the sanitary article → the step of mixing the crushed and dehydrated sanitary article with water and transferring the mixture to the solid-liquid treatment device are performed.

The transport step is a step of mixing the crushed and dehydrated hygienic product with water and transporting the mixture to a downstream solid-liquid treatment apparatus. The pulverized sanitary product, preferably an aqueous suspension, is fed to a solid-liquid treatment apparatus by a water flow by means of a water feed means.

The transport means in the transport step may be a pump type or a natural flow type transport to the solid-liquid separation apparatus, but it is preferable that the hygienic articles after the pulverization and dehydration treatment are transported to the solid-liquid separation apparatus by a water flow through a pipe or a hose. The types of piping or hoses include copper pipes, lead pipes, iron pipes, rigid polyvinyl chloride pipes, polyethylene pipes, rigid vinyl chloride liner pipes, stainless steel pipes, white pipes, soil pipes, and fire-resistant double-walled pipes.

As the solid-liquid treatment apparatus, a known solid-liquid separation treatment apparatus can be used. Examples thereof include sieving, precipitation separation, membrane separation, and centrifugal separation.

One of preferred embodiments of the method for treating a sanitary product according to the present invention is a system for treating waste water from a slag crusher. In general, a slag crusher drainage treatment is a system in which kitchen waste is crushed by a slag crusher attached to a sink drain port of a kitchen and discharged to a sewer or a septic tank together with drainage water generated by water supply, and is a drainage treatment system which can reduce waste and is excellent in hygiene and convenience, and is widely used particularly in collective housing and the like. In order to apply the above-described drainage treatment system to sanitary goods, it is important to reduce the water swelling property of the water-absorbent resin particles and to prevent poor drainage or clogging of pipes due to accumulation and adhesion in the drainage pipes.

In the method for treating a sanitary article of the present invention, the sanitary article after the pulverization and dehydration treatment is conveyed to a solid-liquid treatment device, and then the sanitary article containing the water-absorbent resin particles after the pulverization and dehydration treatment is recovered by a solid-liquid separation device. The collected material of the sanitary goods obtained by the method for treating sanitary goods of the present invention has a characteristic of low water content, and therefore, not only is the combustion efficiency during incineration excellent, but also the collected material can be recycled as solid fuel or the like. Therefore, the present invention includes a method for producing a hygienic article recycle and a solid fuel obtained by the method for treating a hygienic article. When the solid fuel is recycled, it is preferable to further dry the recovered material of the sanitary goods.

Examples

The present invention will be further illustrated by the following examples and comparative examples, but the present invention is not limited thereto. Unless otherwise specified, parts means parts by weight and% means% by weight. The water retention capacity of the water-absorbent resin particles with respect to physiological saline, the dehydration ratio, the absorption capacity under load, the gel permeation rate of physiological saline, and the gel permeation rate of a 1.0 wt% calcium chloride aqueous solution were measured by the following methods.

< method for measuring Water Retention amount of physiological saline >

A measurement sample (1.00 g) was added to a tea bag (length: 20cm, width: 10cm) made of a nylon net having mesh openings of 63 μm (JIS Z8801-1: 2006), and the bag was immersed in 1,000ml of physiological saline (salt concentration: 0.9%) for 1 hour without stirring, pulled up, and suspended for 15 minutes to remove water. Then, the tea bag was put into a centrifugal separator together with the tea bag, and the centrifugal separator was centrifuged at 150G for 90 seconds to remove the remaining physiological saline, and the weight including the tea bag was measured (h1), and the water retention was determined by the following equation. The temperature of the physiological saline used and the temperature of the measurement atmosphere were 25 ℃. + -. 2 ℃. (h2) The weight of the tea bag was measured by the same procedure as described above without the measurement sample.

Water retention (g/g) ═ h1 (h2)

< method for measuring dehydration Rate >

After the measurement of the water retention amount, the following operations were continued. That is, the tea bag measured by the centrifugal separator was immersed in 500ml of 1.0 wt% calcium chloride aqueous solution without stirring for 5 minutes, pulled up, put into the centrifugal separator together with the tea bag, and subjected to centrifugal dehydration at 150G for 90 seconds to remove the remaining calcium chloride aqueous solution, and the weight including the tea bag was measured (h3), and the water retention after treatment with the 1.0 wt% calcium chloride aqueous solution was determined by the following formula. (h4) The weight of the tea bag was measured by the same procedure as described above without the measurement sample.

Water retention (g/g) after treatment with 1.0% calcium chloride aqueous solution (h3) - (h4)

The dehydration rate was then determined by the following equation.

Dehydration rate (%) (water retention after treatment with 1 to 1.0 wt.% calcium chloride aqueous solution)/(water retention for physiological saline) × 100

< method for measuring restol Rate Using ion exchanged Water >

After the above-described measurement of the dehydration rate, the following operation was continued. That is, the centrifugally dehydrated tea bag was immersed in 500ml of an ion-exchanged aqueous solution for 5 minutes without stirring, pulled up, put into a centrifugal separator together with the tea bag, centrifugally dehydrated at 150G for 90 seconds to remove the remaining ion-exchanged aqueous solution, and the weight of the tea bag including the ion-exchanged aqueous solution was measured (h5), and the water retention after ion-exchanged water treatment was determined by the following equation. (h6) The weight of the tea bag was measured by the same procedure as described above without the measurement sample.

Water retention [ g/g ] ═ h5 (g) to h6 for ion exchanged water after 1.0% by weight treatment with an aqueous calcium chloride solution

Then, the reswelling ratio by ion-exchanged water was determined by the following equation.

The re-swelling ratio [% ] based on ion-exchanged water is (water retention [ g/g ] for ion-exchanged water after treatment with 1.0 wt% calcium chloride aqueous solution)/(water retention [ g/g ] for physiological saline) x 100 }

< method for measuring absorption under load >

A measurement sample obtained by sieving a nylon mesh having a mesh opening of 63 μm (JIS Z8801-1: 2006) with a standard sieve was weighed in a cylindrical plastic tube (inner diameter: 25mm, height: 34mm) having a bottom surface to which a nylon mesh was attached at 250 to 500 μm, 0.16g was weighed so that the cylindrical plastic tube was perpendicular to the cylindrical plastic tube, and a weight (weight: 310.6g, outer diameter: 24.5mm) was placed on the measurement sample after adjustment so that the measurement sample had a substantially uniform thickness on the nylon mesh. The weight of the entire cylindrical plastic tube was measured (M1), and the cylindrical plastic tube containing the measurement sample and the weight was vertically placed in a dish (diameter: 12cm) containing 60ml of physiological saline (salt concentration: 0.9%), and the nylon net side was immersed in the dish for 60 minutes while the dish was kept still. After 60 minutes, the cylindrical plastic tube was pulled up from the plate and tilted, and water adhering to the bottom was concentrated at one point and dropped as water droplets to remove excess water, and then the weight of the entire cylindrical plastic tube to which the measurement sample and the weight were added was measured (M2), and the absorption under load was determined by the following equation. The temperature of the physiological saline used and the temperature of the measurement atmosphere were 25 ℃. + -. 2 ℃.

Absorption capacity under load (g/g) { (M2) - (M1) }/0.16

< method for measuring gel permeation speed of physiological saline >

The measurement was performed by the following procedure using the instrument shown in fig. 1 and 2.

The measurement sample (0.32 g) was immersed in 150ml of physiological saline 1 (common salt concentration: 0.9%) for 30 minutes to prepare swollen gel particles (2). Then, a filtration cylinder tube having a metal mesh 6 (mesh 106 μm, JIS Z8801-1: 2006) and a freely openable/closable cock 7 (inner diameter of liquid passing portion 5mm) at the bottom of a vertically standing cylinder 3{ diameter (inner diameter) 25.4mm, length 40cm, and scale marks 4 and 5 provided at positions 60ml and 40ml from the bottom part, respectively }, the prepared swollen gel particles 2 were transferred into the above-mentioned filtration cylinder tube together with physiological saline with the cock 7 closed, then a circular metal mesh 8 (mesh 150 μm, diameter 25mm) having a pressing shaft 9 (weight 22g, length 47cm) perpendicularly bonded to the metal mesh surface was placed on the swollen gel particles 2 so that the metal mesh and the swollen gel particles were in contact with each other, and a weight 10(88.5g) was further placed on the pressing shaft 9 and allowed to stand for 1 minute. Then, the cock 7 was opened, and the time (T1; sec) required for the liquid level in the filtration cylinder tube to reach from 60ml mark 4 to 40ml mark 5 was measured, and the gel permeation rate (ml/min) was determined by the following equation.

Gel infusion speed (ml/min) ═ 20ml × 60/(T1-T2)

The temperature of the physiological saline used and the temperature of the measurement atmosphere were measured at 25 ℃. + -. 2 ℃ and T2 was the time measured by the same procedure as described above in the case where no measurement sample was present.

< method for measuring gel permeation speed of 1.0 wt.% calcium chloride aqueous solution >

The measurement was performed by the following procedure using the instrument shown in fig. 1 and 2.

The measurement sample (0.32 g) was immersed in 150ml of physiological saline 1 (common salt concentration: 0.9%) for 30 minutes to prepare swollen gel particles (2). Then, a filtration cylinder tube having a metal mesh 6 (mesh 106 μm, JIS Z8801-1: 2006) and a cock 7 (inner diameter of liquid passing portion 5mm) which can be freely opened and closed was used in a bottom part of a vertically erected cylinder 3{ diameter (inner diameter) 25.4mm, length 40cm, and scale marks 4 and 5 provided at positions 60ml and 40ml from the bottom part, respectively }, so that the cock 7 was closed. 80ml of the supernatant was discarded from the physiological saline used for the preparation of the measurement sample, the remaining swollen gel particles 2 were transferred to the above-mentioned filtration cylinder tube together with the physiological saline, 80ml of the calcium chloride solution was poured into the cylinder 3, a circular metal net 8 (mesh 150 μm, diameter 25mm) (having a pressing shaft 9 (weight 22g, length 47cm)) perpendicularly bonded to the metal net surface was placed on the swollen gel particles 2 so that the metal net was in contact with the swollen gel particles, a weight 10(88.5g) was further placed on the pressing shaft 9, and the resultant was allowed to stand for 1 minute. Then, the cock 7 was opened, and the time (T3; sec) required for the liquid level in the filtration cylinder tube to reach from 60ml mark 4 to 40ml mark 5 was measured, and the gel permeation rate (ml/min) was determined by the following equation.

Gel permeation rate (ml/min) of 1.0 wt% calcium chloride aqueous solution 20ml × 60/(T3-T4)

The temperature of the physiological saline solution, the 1.0 wt% calcium chloride aqueous solution and the measurement atmosphere used were measured at 25 ℃. + -. 2 ℃, and T4 is the time measured by the same procedure as described above in the case where no measurement sample was present.

< example 1>

Water-soluble vinyl monomer (a1) { acrylic acid }157 parts (2.18 parts by mole), internal crosslinking agent (b) { pentaerythritol triallyl ether }0.6305 parts (0.0024 parts by mole), and deionized water 344.65 parts were stirred and mixed while being maintained at 3 ℃. After nitrogen gas was introduced into the mixture to reduce the dissolved oxygen amount to 1ppm or less, 0.63 parts of a 1% aqueous hydrogen peroxide solution, 1.1774 parts of a 2% aqueous ascorbic acid solution, and 2.355 parts of a 2% aqueous 2, 2' -azobis [ 2-methyl-N- (2-hydroxyethyl) -propionamide ] solution were added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ℃, polymerization was carried out at 90 ± 2 ℃ for about 5 hours, thereby obtaining an aqueous gel (1).

Next, 502.27 parts of this aqueous gel (1) was finely divided with scissors into pieces of about 1mm square, and 128.42 parts of a 48.5% aqueous sodium hydroxide solution was added and mixed. Subsequently, 0.10 part of hydrophobic substance (c-1) { Mg stearate } was added to the gel at a gel temperature of 80 ℃ for 4 kneading and chopping operations using a chopper (12 VR-400K, manufactured by ROYAL) having a discharge hole (mesh dish) diameter of 16mm, and then dried with an aeration type belt dryer {150 ℃ at an air speed of 2 m/s }, thereby obtaining a dried product. The dried material is pulverized by a juicer mixer (Oster corporation, OSTERIZER BLENDER), and then adjusted to a particle size range of 710 to 150 μm in mesh, thereby obtaining dried material particles. The weight average particle size of the dried granules was 392 μm. 100 parts of the dried particles were stirred at a high speed, and 5.00 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio: 70/30) were added and mixed while being atomized by spraying, and the mixture was allowed to stand at 150 ℃ for 30 minutes to crosslink the surface, thereby obtaining water-absorbent resin particles (P-1).

< example 2>

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

< example 3>

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

< example 4>

Water-absorbent resin particles (P-4) were obtained in the same manner as in example 1, except that the weight-average particle diameter of the dried particles was changed from 392 μm to 200. mu.m.

< example 5>

502.27 parts of hydrogel (1) was finely divided with scissors into pieces of about 1mm square, and 128.42 parts of a 48.5% aqueous sodium hydroxide solution was added and mixed. Subsequently, the mixture was kneaded and chopped 4 times using a chopper (12 VR-400K manufactured by ROYAL Co.) having a discharge hole (mesh dish) diameter of 16mm, and then dried by means of an aeration type belt dryer {150 ℃ C., air speed 2 m/s }, to obtain a dried product. The dried material is pulverized by a juicer mixer (Oster corporation, Osterizer BLENDER), and then adjusted to a particle size range of 710 to 150 μm in mesh, thereby obtaining dried material particles. 100 parts of the dried pellets were stirred at a high speed, and 7.30 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio: 70/30) and 0.02 part of a hydrophobic substance (c-2) { carboxy-modified polysiloxane type X-22-3701E shin-Etsu chemical Co., Ltd. } were added and mixed while being atomized by spraying, and the mixture was allowed to stand at 150 ℃ for 30 minutes to effect surface crosslinking, thereby obtaining composite pellets. 100 parts of the composite particles were mixed with an inorganic powder (silica, TOKUSIL, volume average particle diameter 2.5 μm, specific surface area 120 m)²0.4 part of water-soluble resin particles (P-5) was uniformly mixed in a conical mixer (manufactured by Hosokawa Micron Co., Ltd.).

< example 6>

502.27 parts of hydrogel (1) was finely divided with scissors into pieces of about 1mm square, and 128.42 parts of a 48.5% aqueous sodium hydroxide solution was added and mixed. Subsequently, the mixture was kneaded and chopped 4 times using a chopper (12 VR-400K manufactured by ROYAL Co.) having a discharge hole (mesh dish) diameter of 16mm, and then dried by means of an aeration type belt dryer {150 ℃ C., air speed 2 m/s }, to obtain a dried product. The dried material is pulverized by a juicer mixer (Oster corporation, Osterizer BLENDER), and then adjusted to a particle size range of 710 to 150 μm in mesh, thereby obtaining dried material particles. While stirring 100 parts of the dried particles at a high speed, 7.30 parts of a 2% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol weight ratio: 70/30) was added and mixed by spray atomization, and the mixture was allowed to stand at 150 ℃ for 30 minutes to perform surface crosslinking, thereby obtaining composite particles. 100 parts of the composite particles, 1.0 part of methanol, and 0.02 part of a hydrophobic substance (c-2) were uniformly mixed by means of a conical mixer (manufactured by Hosokawa Micron Co., Ltd.) to obtain absorbent resin particles (P-6).

< 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 amount of 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 amount of the hydrophobic substance (c-2) was changed from 0.02 part to 0.10 part.

< example 10>

Water-absorbent resin particles (P-10) were obtained in the same manner as in example 1, except that 0.10 part of the hydrophobic substance (c-1) was changed to 0.15 part of the hydrophobic substance (c-3) { sucrose stearate monoester } and that 4 kneading cycles were changed to 2 kneading cycles.

< example 11>

Water-absorbent resin particles (P-11) were obtained in the same manner as in example 1, except that the particles were subdivided into about 1mm square by scissors, about 5mm square by scissors, and 0.10 part of the hydrophobic substance (c-1) was changed to 0.15 part of the hydrophobic substance (c-3).

< example 12>

Water-absorbent resin particles (P-12) were obtained in the same manner as in example 1, except that the diameter of the discharge hole (cell) was changed to 8mm, and 0.10 part of the hydrophobic substance (c-1) was changed to 0.15 part of the hydrophobic substance (c-3).

< 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>

Water-absorbent resin particles (H-2) for comparison were obtained in the same manner as in example 1, except that a dried product was obtained by drying a water-containing gel finely divided to about 1mm square in terms of size by means of an aeration dryer {150 ℃ C., wind speed 2 m/s } without kneading and chopping the gel by means of a chopper (12 VR-400K manufactured by ROYAL Co.).

< comparative example 3>

Water-absorbent resin particles (H-3) were obtained in the same manner as in example 1, except that the particle diameter range of the mesh openings 710 to 150 μm was changed to the particle diameter range of the mesh openings 710 to 300. mu.m.

< comparative example 4>

Water-absorbent resin particles (H-4) were obtained in the same manner as in example 1, except that the gel temperature was changed from 80 ℃ to 20 ℃.

< comparative example 5>

Water-absorbent resin particles (H-5) were obtained in the same manner as in example 1, except that the drying temperature was changed from 150 ℃ to 300 ℃.

< comparative example 6>

Water-absorbent resin particles (H-6) were obtained in the same manner as in example 1, except that the surface crosslinking temperature was changed from 150 ℃ to 90 ℃.

< comparative example 7>

Water-absorbent resin particles (H-7) were obtained in the same manner as in example 1, except that the surface crosslinking temperature was changed from 150 ℃ to 210 ℃.

< comparative example 8>

Commercially available diapers goo.n (manufactured by diaper L-code kao paper corporation, japan 5 months 2018) were crushed by hand, and the crushed water-absorbent resin particles contained in the absorber were taken out together with pulp and separated from each other to obtain crushed water-absorbent resin particles (H-8).

< comparative example 9>

Commercially available diapers GOO.N (made by S-size Kao paper-making Kabushiki Kaisha, 5-month Japan 2018) were crushed by hand, and spherical water-absorbent resin particles contained in the absorber were taken out together with pulp and separated from each other to obtain spherical water-absorbent resin particles (H-9).

< preparation of sanitary articles >

100 parts of hydrophilic fibers (fluff pulp) and 100 parts of water-absorbent resin particles (each of the water-absorbent resin particles obtained in examples and comparative examples) were mixed by an air-flow type mixing device (Pad Former) to obtain a mixture, and the mixture was mixed so that the basis weight thereof was 500g/m²Uniformly laminated on an acrylic resin plate (thickness: 4mm) at a rate of 5kg/cm²Was pressed for 30 seconds to obtain an absorbent body. The absorbent body was cut into a 10cm × 10cm square, and water-permeable sheets (basis weight 15.5 g/m) having the same size as the absorbent body were placed above and below each sample²And filter paper No. 2) manufactured by ADVANTEC corporation, and further a polyethylene sheet (S-1) as an impermeable sheet (polyethylene film UB-1 manufactured by TAMAPOLY corporation) was disposed on the back surface, and a nonwoven fabric (S-2) as a nonwoven fabric layer was disposed on the front surface, thereby preparing a sanitary product.

< evaluation of dehydration Property of absorbent body >

The produced sanitary article was placed on a metallic tray so that the nonwoven fabric (S-2) side was the upper side, 150ml of physiological saline (salt concentration 0.9%) contained in a 300ml beaker was gently poured onto the sanitary article in a uniform manner, and after standing for 20 minutes, the nonwoven fabrics (S-1) and (S-2) were removed from the sanitary article, and the weight (h 5; g) of the swollen absorbent body was measured. Then, the swollen absorbent was put into a tea bag (length 15cm, width 15cm) made of a nylon net having a mesh opening of 63 μm (JIS Z8801-1: 2006), immersed in 1,000ml of a 1.0 wt% aqueous calcium chloride solution for 5 minutes without stirring, pulled up, put into a centrifugal separator, centrifuged at 150G for 90 seconds to remove the remaining aqueous calcium chloride solution, and the weight (h 6; G) including the tea bag was measured to determine the dehydration rate of the absorbent according to the following formula. The temperature of the physiological saline, the aqueous calcium chloride solution and the measurement atmosphere used was 25 ℃. + -. 2 ℃. (h 7; g) is the weight obtained when the absorbent body was similarly prepared, left to stand for 5 hours, the nonwoven fabrics (S-1) and (S-2) were removed from the sanitary article, and the weight of the swollen absorbent body (h 7; g) was measured.

Absorbent dehydration rate (%) [1- { (h6) - (h7) }/(h5) ] × 100

The water-absorbent resins obtained in examples and comparative examples were shown in tables 1 and 2, in terms of water retention capacity for physiological saline, absorption capacity under load, gel permeation rate for physiological saline, apparent density, weight-average particle diameter, gel permeation rate for 1.0 wt% calcium chloride aqueous solution, dehydration rate, and re-swelling ratio by ion-exchanged water. The results of evaluation of the dewatering property of the absorbent body produced using each water-absorbent resin are also shown.

From the results shown in tables 1 and 2, it is understood that the water-absorbent resin particles of the present invention, which are easy to be dehydrated, have a higher dehydration rate than the water-absorbent resin particles of the comparative examples. In addition, in the evaluation of the dehydration rate of the absorbent material using the water-absorbent resin particles, it is found that the higher the dehydration rate of the water-absorbent resin particles is, the more the dehydration rate of the absorbent material is improved. From the results, it can be said that the absorbent material using the water-absorbent resin particles having a high dehydration rate has a low water content after dehydration treatment of the swollen absorbent material, and the total weight of 1 absorbent material can be reduced. Therefore, for example, by performing the same treatment operation using a calcium chloride aqueous solution after urination, labor at the time of transportation can be reduced, and energy used for incineration can be suppressed at the time of incineration treatment, so that the environmental load can be reduced.

Industrial applicability

The water-absorbent resin particles which are easily subjected to dehydration treatment according to the present invention are applied to various absorbent articles including sanitary products, and can satisfy required absorption performance at the time of use, and the water content of the absorbent article can be easily reduced by a predetermined dehydration treatment after use, and therefore, the water-absorbent resin particles are suitably used in sanitary products such as disposable diapers (e.g., child disposable diapers and adult disposable diapers), sanitary napkins (e.g., sanitary napkins for menstrual use), paper towels, pads (e.g., incontinence pads and surgical pads), and pet diapers (e.g., pet diapers), and particularly, are most suitably used in disposable diapers.

Description of the symbols

1 physiological saline

2 aqueous gel particles

3 cylinders

4 graduation mark at 60ml position from bottom

5 Scale lines at 40ml from the bottom

6 Metal mesh

7 cock

8 round metal net

9 pressurized shaft

10 weight