WO2022080342A1

WO2022080342A1 - Method for producing water-absorbing resin particles

Info

Publication number: WO2022080342A1
Application number: PCT/JP2021/037650
Authority: WO
Inventors: 英二森田; 真平長谷川; 一充鈴木
Original assignee: 三洋化成工業株式会社
Priority date: 2020-10-15
Filing date: 2021-10-12
Publication date: 2022-04-21
Also published as: JPWO2022080342A1; CN116194208A

Abstract

Provided is a method for efficiently producing recycled water-absorbing resin particles having little reduced absorbing properties and various excellent properties, using, as a raw material, waste water-absorbing resin particles derived from used sanitary supplies, etc. This method for producing water-absorbing resin particles comprises a polymerization step (I) in which a monomer composition is polymerized to obtain an aqueous gel containing a crosslinked polymer (A), a gel chopping step (II) in which the aqueous gel is chopped, a drying step (III) in which the aqueous-gel particles obtained in the step (II) are dried, and a pulverization/classification step (IV) in which the dried particles obtained in the step (III) are pulverized and classified, wherein a product (B) of decomposition of water-absorbing resin particles obtained from sanitary supplies is added in at least one step among the steps (I), (II), (III), and (IV), the decomposition product (B) having a content of water solubles of 1.0-30.0 wt%.

Description

Method for manufacturing water-absorbent resin particles

The present invention relates to a method for producing water-absorbent resin particles. More specifically, the present invention relates to a method for producing water-absorbent resin particles that enables reuse of water-absorbent resin particles in used sanitary goods. More specifically, the present invention relates to a method for producing water-absorbent resin particles capable of reusing the water-absorbent resin particles contained in sanitary products, particularly used sanitary products.

As the amount of hygiene products used has increased, the problem of waste disposal of hygiene products after use is becoming a serious problem. Hygiene products, especially disposable diapers, are rapidly becoming widespread as indispensable products in an era of declining birthrate and aging society, and their consumption is rapidly increasing. Regarding waste disposal of sanitary goods after use, disposable diapers and the like are usually incinerated, but since the proportion of water in the diapers is close to 80%, incineration requires a large amount of combustion energy. For this reason, the treatment puts a heavy load on the incinerator itself, and as a result, it leads to a cause of shortening the life of the incinerator. In addition, incineration leads to air pollution and global warming, and is a factor that puts a burden on the environment, so improvement is strongly desired.

For the above issues, studies are underway to collect and reuse parts from used hygiene products. Normally, sanitary goods include an absorber composed of pulp fibers and water-absorbent resin particles, and it is necessary to separate the pulp fibers and water-absorbent resin particles in order to reuse them as members. However, since the water-absorbent resin particles in the absorber of the used hygiene product absorb water and become a swelled gel state, it is difficult to separate them as they are. Therefore, a technique has been proposed in which water-absorbent resin particles are decomposed and solubilized to separate solubilized components of pulp fibers and water-absorbent resin particles. For example, sanitary goods containing pulp fibers and water-absorbent resin particles are treated with ozone. There are techniques (Patent Documents 1 and 2) for recovering pulp fibers after decomposing and solubilizing water-absorbent resin particles by treating with a contained aqueous solution. Further, as a technique for decomposing and solubilizing water-absorbent resin particles, a technique using an oxidizing agent such as hydrogen peroxide as a decomposition method (Patent Documents 3 to 5) is known.

Japanese Unexamined Patent Publication No. 2016-881 Japanese Unexamined Patent Publication No. 2017-209675 Japanese Unexamined Patent Publication No. 4-317784 Japanese Unexamined Patent Publication No. 6-313008 Japanese Patent Application Laid-Open No. 2003-321574

All of the above-mentioned reuse techniques for used sanitary goods are aimed at recovering pulp fibers and using them as recycled pulp, and the decomposition / solubilization components of water-absorbent resin particles are either discarded or solid fuel, etc. It is hard to say that it is sufficient from the viewpoint of resource saving and reduction of environmental load. Further, the conventional technique of decomposing and solubilizing water-absorbent resin particles has an object of providing a disposal method having a small environmental load, and there is room for improvement from the viewpoint of reuse.

The present invention is a method for efficiently producing recycled water-absorbent resin particles having excellent various properties by using waste of water-absorbent resin particles derived from sanitary goods or the like as a raw material and having a small decrease in absorption characteristics. The purpose is to provide.

The present invention comprises a polymerization step (I) of polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and a cross-linking agent (b) to obtain a water-containing gel containing the cross-linking polymer (A), and the water-containing gel. A gel shredding step (II) for shredding the water-containing gel particles to obtain water-containing gel particles, a drying step (III) for drying the water-containing gel particles obtained in the gel cutting step (II), and a drying step (III). A method for producing water-absorbent resin particles, which comprises a crushing and classifying step (IV) for crushing and classifying a substance, wherein the polymerization step (I), the gel shredding step (II), the drying step (III), and the above. A method for producing water-absorbent resin particles, wherein the decomposition product (B) of the water-absorbent resin particles obtained from sanitary products is added in at least one step selected from the group consisting of the pulverization classification step (IV). This is a method for producing water-absorbent resin particles having a water-soluble content of the decomposition product (B) of 1.0 to 30.0% by weight.

In the method for producing water-absorbent resin particles of the present invention, even if the waste of water-absorbent resin particles discharged when the sanitary goods are reused is used, the absorption characteristics are hardly deteriorated and the water absorption is excellent in various characteristics. Resin particles can be manufactured, which contributes to resource saving and reduction of environmental load.

The method for producing water-absorbent resin particles of the present invention may have each of the above-mentioned essential steps, and may further include other steps as long as the gist of the present invention is not deviated. Further, the process of the present invention may include a transportation stage and a storage stage without departing from the spirit.

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and is a known monomer, for example, at least one water-soluble substituent disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 36485553 and ethylenia-free. Vinyl monomers having a saturated group (for example, anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers), anionic vinyl monomers and nonionic vinyl monomers disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883. Select from the group consisting of a sex vinyl monomer, a cationic vinyl monomer, and a carboxy group, a sulfo group, a phosphono group, a hydroxyl group, a carbamoyl group, an amino group, and an ammonio group disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982. A vinyl monomer having at least one of these can be used.

The water-soluble vinyl monomer (a1) is preferably an anionic vinyl monomer, more preferably a carboxy (salt) group, a sulfo (salt) group, an amino group, a carbamoyl group, an ammonio group or a mono-, di- or tri-alkyl. It is a vinyl monomer having an ammonio group. Among these, vinyl monomers having a carboxy (salt) group or a carbamoyl group are more preferable, (meth) acrylic acid (salt) and (meth) acrylamide are more preferable, and (meth) acrylic acid (salt) is particularly preferable. The most preferable is acrylic acid (salt).

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

When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the water-soluble vinyl monomer (a1), a part of the acid group-containing monomer can be neutralized with a base. As the base to be neutralized, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium hydrogencarbonate and potassium carbonate can be usually used. Neutralization may be performed either before or during the polymerization of the acid group-containing monomer in the process of producing the water-absorbent resin particles, and after the polymerization, the acid group is in the state of a water-containing gel containing the crosslinked polymer (A) described later. It is also possible to neutralize the contained polymer.

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

As the constituent unit of the crosslinked polymer (A), in addition to the water-soluble vinyl monomer (a1), another vinyl monomer (a2) copolymerizable with these can be used as the constituent unit. As the other vinyl monomer (a2), one type may be used alone, or two or more types may be used in combination.

The other copolymerizable vinyl monomer (a2) is not particularly limited, and is known (for example, the hydrophobic vinyl monomer disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 36485553, JP-A-2003-165883). Hydrophobic vinyl monomers (such as the vinyl monomers disclosed in paragraph 0025 and paragraph 0058 of JP-A-2005-75982) can be used, and specifically, for example, the following vinyl monomers (i) to (iii) and the like can be used. Can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, vinylnaphthalene, halogen-substituted styrene such as dichlorostyrene and the like.
(Ii) Alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkaziene (butadiene and isoprene, etc.) having 2 to 20 carbon atoms.
(Iii) Alicyclic ethylenic monomer having 5 to 15 carbon atoms Monoethylene unsaturated monomer (pinene, limonene, indene, etc.); and polyethylene vinyl monomer [cyclopentadiene, bicyclopentadiene, etylidene norbornene, etc.] and the like.

The content of the other vinyl monomer (a2) unit is preferably 0 to 5 mol%, more preferably 0 to 3 mol, based on the number of moles of the water-soluble vinyl monomer (a1) unit from the viewpoint of absorption performance and the like. %, Particularly preferably 0 to 2 mol%, particularly preferably 0 to 1.5 mol%, and the content of the other vinyl monomer (a2) unit is 0 mol% from the viewpoint of absorption performance and the like. Most preferred.

The cross-linking agent (b) is not particularly limited and reacts with a cross-linking agent having two or more ethylenically unsaturated groups and a water-soluble substituent disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553 (for example). JP-A-2003-165883, a cross-linking agent having at least one functional group to be obtained and having at least one ethylenically unsaturated group and a cross-linking agent having at least two functional groups capable of reacting with a water-soluble substituent. A cross-linking agent having two or more ethylenically unsaturated groups, a cross-linking agent having an ethylenically unsaturated group and a reactive functional group, and a cross-linking agent having two or more reactive substituents disclosed in paragraphs 0028 to 0031. , A cross-linking agent of the cross-linking vinyl monomer disclosed in paragraph 0059 of JP-A-2005-75982 and the cross-linking vinyl monomer disclosed in paragraphs 0015 to 0016 of JP-A-2005-59559) can be used. .. Of these, a cross-linking agent having two or more ethylenically unsaturated groups is preferable from the viewpoint of absorption performance and the like, and more preferably, a poly (meth) allyl ether of a polyhydric alcohol having 2 to 40 carbon atoms and a carbon number of carbon atoms. (Meta) acrylates of 2-40 polyhydric alcohols, (meth) acrylamides of polyhydric alcohols with 2-40 carbon atoms, particularly preferred are polyallyl ethers of polyhydric alcohols with 2-40 carbon atoms, most preferred. Pentaerythritol triallyl ether. The cross-linking agent (b) may be used alone or in combination of two or more.

In order to make the molecule less susceptible to cleavage, it is desirable to use the cross-linking agent (b1) having a polyether chain as an essential component in the molecule among the cross-linking agents (b). Since the flexibility is improved by having the polyether chain in the molecule, it is presumed that the force applied to the water-absorbent resin particles at the time of shearing is not locally applied and is relaxed to the particles or the entire gel. As for (b1), one type may be used alone, two or more types may be used in combination, or a cross-linking agent (b) other than (b1) may be used in combination.

Examples of the polyether chain include a polyoxyethylene chain, a polyoxypropylene chain, a polyoxytetramethylene chain, and a copolymerized polyether chain thereof. Of these, a polyether chain containing a polyoxyethylene chain is preferable from the viewpoint of improving the efficiency of decomposition and solubilization of the water-absorbent resin. In the case of a polyether chain containing a polyoxyethylene chain, the content of the oxyethylene chain in the polyether chain is preferably 50% by weight or more, and the polyoxyethylene polyoxypropylene chain is more preferable. Here, the polyoxyethylene polyoxypropylene chain is not particularly limited as long as it is a chain composed of oxyethylene units and oxypropylene units.

The cross-linking agent (b1) is selected from the group consisting of a hydroxyl group, an allyl group, an acryloyl group, an alkoxysilyl group, a carboxyl group, an epoxy group, an isocyano group, an N-methylol group, and an N-alkoxymethyl group in the molecule. It is preferable to have two or more crosslinkable functional groups per molecule.
The crosslinkable functional group is preferably an allyl group, an acryloyl group, a vinyl ether group, an alkoxysilyl group, a carboxyl group or an epoxy group, and more preferably an allyl group or an acryloyl group, from the viewpoint of improving the efficiency of decomposition and solubilization of the water-absorbent resin. Group, vinyl ether group.
Specific examples of the cross-linking agent (b1) include Alcox CP-A1H, Alcox CP-A2H (both manufactured by Meisei Chemical Industry Co., Ltd.), A-1000 (polyethylene glycol diacrylate, number average molecular weight 1108), A-. BPE-30 (diacrylate of 30 mol of ethylene oxide adduct of bisphenol A, number average molecular weight is 1133) (both by Shin-Nakamura Chemical Industry Co., Ltd.) and the like can be mentioned. From the viewpoint of degradability, Alcox CP-A1H and Alcox CP-A2H are preferable.

The cross-linking agent (b1) has a polyether chain as an essential component in the molecule, but has a number average molecular weight of 100 to 150,000 from the viewpoint of improving the efficiency of decomposition and solubilization and the water absorption performance of the water-absorbent resin particles. It is preferable, more preferably 200 to 100,000.

The number average molecular weight (hereinafter abbreviated as Mn) in the present invention is measured by gel permeation chromatography (hereinafter abbreviated as GPC). The measurement shall be in accordance with the following measurement conditions.
<GPC measurement conditions>
GPC model: HLC-8120GPC, Tosoh Corporation column: TSKgel GMHXL 2 bottles + TSKgel Multipole HXL-M, Tosoh Corporation solvent: Tetrahydrofuran (THF)
Detection device: Refractive index detector Reference material: Standard polystyrene (TSKstandardPOLYSTYRENE), manufactured by Tosoh Corporation

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

In the method for producing water-absorbent resin particles of the present invention, the above-mentioned monomer composition containing the water-soluble vinyl monomer (a1) and the cross-linking agent (b) is polymerized to obtain a water-containing gel containing the cross-linked polymer (A). The polymerization step (I) is included. A decomposition product (B) of water-absorbent resin particles obtained from a sanitary product described later may be added to the main polymerization step (I).

As the polymerization step (I), known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc .; JP-A-55-133413, etc.), known suspension polymerization method, reverse phase suspension polymerization (specially A water-containing gel containing the crosslinked polymer (A) according to JP-A-54-30710, JP-A-56-26909, JP-A-1-5808, etc. (a water-containing gel in which the crosslinked polymer contains water). Can be obtained. The crosslinked polymer (A) may be one kind alone or a mixture of two or more kinds.

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

When performing aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used, and the organic solvent includes methanol, ethanol, acetone, methyl ethyl ketone, N, N-dimethylformamide, dimethyl sulfoxide, and two or more of these. Can be mentioned as a mixture of. In the case of aqueous solution polymerization, the amount (% by weight) of the organic solvent used is preferably 40 or less, more preferably 30 or less, based on the weight of water.

When an initiator is used for polymerization, conventionally known initiators for radical polymerization can be used. For example, azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2'-azobis (2-amidinopropane)) can be used. Hydrochloride, etc.], Inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, dit-butyl peroxide, cumene hydroperoxide, succinic acid, etc.] Acid peroxide and di (2-ethoxyethyl) peroxydicarbonate, etc.] and redox catalyst (alkali metal sulfite or bicarbonate, ammonium sulfite, ammonium peroxide, ascorbic acid, and other oxidation-reducing agents and alkali metal peroxides. (Combined with oxidizing agents such as sulfate, ammonium persulfate, hydrogen peroxide and organic peroxide) and the like. These catalysts may be used alone or in combination of two or more of them.
The amount (% by weight) of the polymerization initiator used is preferably 0.0005 to 5 based on the total weight of the water-soluble vinyl monomer (a1) and, when other vinyl monomers (a2) are also used. More preferably, it is 0.001 to 2.

At the time of polymerization, a polymerization control agent typified by a chain transfer agent may be used in combination, and specific examples thereof include sodium hypophosphite, sodium phosphite, alkyl mercaptans, and alkyl halides. , Thiocarbonyl compounds and the like. These polymerization control agents may be used alone or in combination of two or more of them.
The amount (% by weight) of the polymerization control agent used is preferably 0.0005 to 5 based on the total weight of the water-soluble vinyl monomer (a1) and other vinyl monomers (a2) when they are also used. More preferably, it is 0.001 to 2.

When a suspension polymerization method or a reverse phase suspension polymerization method is used as the polymerization method, the polymerization may be carried out in the presence of a dispersant or a surfactant, if necessary. Further, in the case of the reverse phase suspension polymerization method, the polymerization can be carried out using a hydrocarbon solvent such as xylene, normal hexane and normal heptane.

The polymerization start temperature can be appropriately adjusted depending on the type of catalyst used, but is preferably 0 to 100 ° C, more preferably 2 to 80 ° C.

The gel shredding step (II) is a step of shredding the water-containing gel containing the crosslinked polymer (A) obtained by the above-mentioned polymerization step to obtain water-containing gel particles. A decomposition product (B) of water-absorbent resin particles obtained from a sanitary product described later may be added.
The size (maximum diameter) of the hydrous gel particles after the gel shredding step is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 500 μm to 1 cm. Within these ranges, the drying property in the drying step is further improved.

Gel shredding can be performed by a known method, and can be shredded using a crushing device (for example, a kneader, a universal mixer, a uniaxial or biaxial kneading extruder, a minced machine, a meat chopper, etc.).

Further, as described above, the water-containing gel of the acid group-containing polymer obtained after the polymerization can be neutralized by mixing a base during the gel shredding step. The base used when neutralizing the acid group-containing polymer and the preferable range of the degree of neutralization are the same as when the acid group-containing monomer is used.

The hydrogel particles obtained in the gel shredding step (II) are dried (including distilling off the solvent). As a method applied to the drying step (III), the hydrogel particles are dried with hot air at a temperature of 80 to 300 ° C. A method, a thin film drying method using a drum dryer heated to 100 to 230 ° C., a (heating) vacuum drying method, a freeze drying method, an infrared drying method, decantation, filtration, etc. can be applied, and these are used in combination. You can also do it. Further, the heat source (steam, heat medium, etc.) of these dryers is not particularly limited. Further, the drying method is not particularly limited to a batch drying method or a continuous drying method. A decomposition product (B) of water-absorbent resin particles obtained from a sanitary product described later may be added to the main drying step (III).

When water is contained in the solvent, the water content (% by weight) after drying is preferably 0 to 20, more preferably 1 to 10, based on the weight of the crosslinked polymer (A). Within these ranges, the absorption performance is further improved.

The water content in the present invention was heated by an infrared moisture meter (JE400 manufactured by KETT Co., Ltd .: 120 ± 5 ° C., 30 minutes, atmospheric humidity 50 ± 10% RH before heating, lamp specification 100 V, 40 W). It is obtained from the weight loss of the measurement sample before and after heating.

The crushing method in the crushing classification step (IV) for crushing and classifying the dried product that has undergone the drying step (III) is not particularly limited, and is a crushing device (for example, a hammer type crusher, an impact type crusher, a roll type crusher). And a shet airflow type crusher) can be used. A decomposition product (B) of water-absorbent resin particles obtained from a sanitary product described later in this pulverization classification step (IV) may be added.

The classification in the pulverization classification step (IV) is performed in order to control the weight average particle size and particle size distribution of the pulverized resin particles. The classification device is not particularly limited, but known methods such as a vibrating sieve, an in-plane moving sieve, a movable net type sieve, a forced stirring sieve, and a sonic sieve are used, and a vibrating sieve and an in-plane moving sieve are preferably used. Depending on the case, the resin particles after classification may contain some other components such as a residual solvent and a residual cross-linking component.

The method for producing water-absorbent resin particles of the present invention is obtained by obtaining a polymerization step (I), a gel shredding step (II), a drying step (III), and a pulverization classification step (IV), and contains a crosslinked polymer (A). The water-absorbent resin particles are obtained, but other steps may be further included as long as the gist of the production method of the present invention is not deviated.

The method for producing water-absorbent resin particles of the present invention may include, as another step, a surface cross-linking step (V) in which the resin particles containing the cross-linked polymer (A) are surface-crosslinked with a surface cross-linking agent. The surface cross-linking step (V) may include a step (Va) of mixing the resin particles and the surface cross-linking agent (d) and a reaction step (Vb) of the surface cross-linking agent (d) as essential steps. good.

Examples of the surface cross-linking agent (d) include polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridine compounds and polyhydric isocyanate compounds described in JP-A-59-189103, and JP-A-58-180233. And the polyhydric alcohol of JP-A-61-16903, the silane coupling agent described in JP-A-61-21305 and JP-A-61-252212, and described in JP-A-5-508425. Uses alkylene carbonates, polyvalent oxazoline compounds described in JP-A-11-240959, and surface cross-linking agents of JP-A-51-136588 and JP-A-61-257235 (polyvalent metals, etc.). can. Among these surface cross-linking agents, polyhydric glycidyl compounds, polyhydric alcohols and polyhydric amines are preferable, and polyhydric glycidyl compounds and polyhydric alcohols are more preferable, and polyhydric alcohols are particularly preferable, from the viewpoint of economic efficiency and absorption characteristics. Valuable glycidyl compounds, most preferably ethylene glycol diglycidyl ethers. One type of surface cross-linking agent may be used alone, or two or more types may be used in combination.

The amount (part by weight) of the surface cross-linking agent used is not particularly limited because it can be variously changed depending on the type of the surface cross-linking agent, the conditions for cross-linking, the target performance, etc. It is preferably 0.001 to 3, more preferably 0.005 to 2, and particularly preferably 0.01 to 1.5 with respect to 100 parts by weight of the resin particles containing the coalescence (A).

The surface cross-linking of the cross-linked polymer (A) has a step (Va) of mixing the resin particles containing the cross-linked polymer (A) and the surface cross-linking agent (d), and is performed by heating as necessary. be able to. As a mixing method, a cylindrical mixer, a screw type mixer, a screw type extruder, a turbulizer, a nauter type mixer, a double arm type kneader, a fluid type mixer, a V type mixer, a minced mixer, and a ribbon type are used. Examples thereof include a method of uniformly mixing using a mixing device such as a mixer, an air flow type mixer, a rotary disk type mixer, a conical blender and a roll mixer. At this time, the surface cross-linking agent (d) may be diluted with water and / or any solvent before use.

After mixing the resin particles containing the crosslinked polymer (A) and the surface crosslinking agent (d), the vicinity of the surface of the resin particles is reacted with (d) in the reaction step (Vb). The water-absorbent resin particles obtained by the production method of the present invention preferably have a structure in which the surface of the resin particles containing the crosslinked polymer (A) is surface-crosslinked with the surface cross-linking agent (d). By having a structure cross-linked with a surface cross-linking agent, gel blocking can be suppressed and necessary absorption characteristics (balance between water retention amount and absorption amount under load) can be controlled. Further, in this reaction step, the decomposition product (B) reacts with the surface cross-linking agent (d) to form a chemical bond, so that the cross-linking density is increased and sufficient strength can be given to the resin particles. The temperature of the resin particles in the reaction step is preferably room temperature or higher from the viewpoint of the reaction rate. Further, the powder temperature of (A) may be set to room temperature or higher by the step before that, but is preferably 100 ° C. or lower.

The heating temperature is preferably 100 to 180 ° C. Indirect heating using steam is possible if the heating is 180 ° C or lower, which is advantageous in terms of equipment, and if the heating temperature is lower than 100 ° C, the absorption performance may deteriorate. The heating time can be appropriately set depending on the heating temperature, but is preferably 5 to 60 minutes from the viewpoint of absorption performance. It is also possible to further surface-crosslink the water-absorbent resin particles obtained by surface-crosslinking with a surface-crosslinking agent of the same type or different type as the surface-crosslinking agent used first.

After the surface of the resin particles containing the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (d), the particle size is adjusted by sieving as necessary.

The water-absorbent resin particles of the present invention may contain a polyvalent metal salt (e). By containing the polyvalent metal salt (e), the absorption performance of the water-absorbent resin particles containing the decomposition product (B) can be dramatically improved. It is presumed that the polyvalent metal salt (e) has a plurality of polyvalent metal atoms and thus interacts with the water-absorbent resin particles containing the decomposition product (B) at multiple points to improve the absorption performance.

Examples of the polyvalent metal salt (e) include inorganic acid salts of zirconium, aluminum or titanium, and examples of the inorganic acid forming the polyvalent metal salt (e) include sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid and iodine. Examples thereof include hydride and phosphoric acid. Examples of the inorganic acid salt of zirconium include zirconium sulfate and zirconium chloride, and examples of the inorganic acid salt of aluminum include aluminum sulfate, aluminum chloride, aluminum nitrate, ammonium aluminum sulfate, potassium aluminum sulfate, sodium aluminum sulfate and the like. Examples of the inorganic acid salt of titanium include titanium sulfate, titanium chloride and titanium nitrate.

Of these, an inorganic acid salt of aluminum is preferable, and aluminum sulfate, aluminum chloride, potassium aluminum sulfate, and sodium aluminum sulfate are more preferable from the viewpoint of improving the absorption performance under pressure.

The amount (% by weight) of the polyvalent metal salt (e) used is preferably 0.05 to 5.0, more preferably 0.05 to 5.0, based on the weight of the crosslinked polymer (A) from the viewpoint of absorption performance under pressure. It is 0.2 to 2.0, particularly preferably 0.35 to 1.5. Here, when the polyvalent metal salt (e) is a hydrate, the mass excluding the hydrated water is used as a reference.

The polyvalent metal salt (e) may be added in any of the steps such as the polymerization step (I), the gel shredding step (II), and the surface cross-linking step, but the absorption performance under pressure may be obtained. From the viewpoint of improvement, it is preferably present on the surface of the resin particles, and it is preferable to add it in the surface cross-linking step. Further, in the case of surface treatment with the above-mentioned surface cross-linking agent, it can be added at any of the mixing step before the reaction step of surface-treating by surface cross-linking, after the reaction step, and at the same time as the reaction step. The equipment and temperature for mixing the polyvalent metal salt (e) can be the same as the above-mentioned surface cross-linking step.

The water-absorbent resin particles can contain a liquid-permeable improver, if necessary. The liquid flow improving agent means a material that treats the surface of water-absorbent resin particles by non-covalent bond interaction (ionic bond, hydrogen bond, hydrophobic interaction, etc.), and is distinguished from the above-mentioned surface cross-linking agent. To. The liquid-permeable improver is contained on the surface of the water-absorbent resin particles and has an effect of preventing inter-particle blocking during gel swelling and improving the liquid-permeable property.

Examples of the liquid passage improving agent include the above-mentioned polyvalent metal salt (e) in addition to cationic organic polymers and inorganic particles. These can be used alone or in combination.

The cationic organic polymer is not particularly limited, but a known cationic organic polymer exemplified in International Publication No. 2017-57709 can be used.

Inorganic particles include hydrophilic inorganic particles, hydrophobic inorganic particles and the like. Examples of the hydrophilic inorganic particles include particles such as glass, silica gel, silica (coloidal silica, fumed silica, etc.) and clay. Examples of the hydrophobic inorganic particles include particles such as carbon fiber, kaolin, talc, mica, bentonite, sericite, asbestos and silas. Of these, hydrophilic inorganic particles are preferable, and silica (coloidal silica, fumed silica, etc.) is most preferable.

The amount (parts by weight) of the liquid-permeable improver used is preferably 0.05 to 5 and more preferably 0.2 to 2.0 with respect to 100 parts by weight of the water-absorbent resin particles from the viewpoint of absorption performance.

The water-absorbent resin particles include additives {for example, known (for example, JP-A-2003-225565, JP-A-2006-131767, etc.) preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, colorants, etc. It can also contain fragrances, deodorants, organic fibrous substances, etc.}. When these additives are contained, the content (% by weight) of the additives is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably 0.01 to 5, based on the weight of the crosslinked polymer (A). It is preferably 0.05 to 1, most preferably 0.1 to 0.5.

The method for producing the water-absorbent resin particles of the present invention is at least selected from the group consisting of the polymerization step (I), the gel shredding step (II), the drying step (III) and the pulverization classification step (IV). In one step, the decomposition product (B) of the water-absorbent resin particles obtained from the sanitary goods is added.
The decomposition product (B) of the water-absorbent resin particles obtained from the sanitary ware is the polymerization step (I), the gel shredding step (II), the drying step (III) and / or the crushing classification step (IV). When added in, the decomposition product (B) becomes a part of the water-absorbent resin particles obtained by the production method of the present invention.

The water-absorbent resin particles contained in the sanitary products are obtained by polymerizing the above-mentioned monomer composition containing the water-soluble vinyl monomer (a1) and the cross-linking agent (b) to obtain the water-absorbent resin particles containing the cross-linked polymer (A). It can be manufactured by the same method as the manufacturing method.
The decomposition product (B) is a decomposition product of water-absorbent resin particles contained in sanitary products, and may be a decomposition product having a water-soluble content of 1.0 to 30.0% by weight, and is an unused sanitary product. It may be a decomposition product obtained from the water-absorbent resin particles contained in the above, or it may be a decomposition product obtained from the swollen water-absorbent resin particles contained in the used sanitary goods.

The water-absorbent resin particles to be decomposed preferably have a cross-linked polymer (A') containing a water-soluble vinyl monomer (a1') and a cross-linking agent (b') as essential constituent units.
The water-soluble vinyl monomer (a1') and the cross-linking agent (b') may be the same as or different from the above-mentioned (a1) and (b), respectively, but from the viewpoint of stability of absorption characteristics. , It is preferable that they are the same.
The properties of the water-absorbent resin particles to be decomposed are not particularly limited, but include powder, granules, gels that have absorbed liquids, and the like.

Examples of the decomposition product (B) include those obtained by subjecting water-absorbent resin particles contained in sanitary products to chemical treatment, mechanical treatment, or both. When the water-absorbent resin particles are chemically or mechanically treated, at least a part of the bonds of the molecules constituting the crosslinked polymer (A') of the water-absorbent resin particles is broken, so that the decomposition product (B) is contained. The decomposed product (Z) to be decomposed is obtained.
Chemical treatment of the water-absorbent resin particles includes a method of heating the crosslinked polymer (A') above the thermal decomposition temperature, a method of irradiating an active energy ray such as ultraviolet rays, and an oxidizing agent (hydrogen peroxide and hypochlorite). Etc.) to oxidatively decompose.
As the mechanical treatment of water-absorbent resin particles, known stirrers [minced machine (meat chopper), jaw crusher, hammer crusher, roll crusher, self-made crusher, stamp mill, stone mill type crusher, raft machine, ring mill, etc. A method of stirring water-absorbent resin particles using a roller mill, a jet mill, a pin mill, a vibration mill, a planetary mill, a bead mill, an attritor, a mixing device with a crusher, a cutter mill, etc.] can be mentioned. The shearing force generated by stirring the water-absorbent resin particles breaks at least a part of the bonds of the molecules constituting the crosslinked polymer (A'), so that the decomposed product (Z) containing the decomposed product (B) is produced. can get.

The decomposition product (B) added by the production method of the present invention has a water-soluble content of 1.0 to 30.0% by weight. The decomposition product (B) may be a product obtained by washing and / or drying the decomposition product (Z) obtained by chemically treating or mechanically treating the water-absorbent resin particles, or may be a decomposition treatment. The product (Z) itself may be used, or the decomposed product (Z) obtained by chemical treatment or mechanical treatment may be used as a known dehydrator (centrifugal dehydrator, roller dehydrator, etc.) and / or dehydration. It may be dehydrated with an agent.
Among them, those that have been chemically or mechanically treated can be used as they are, and those that have been chemically or mechanically treated can be used as known dehydrators (centrifugal dehydrators, roller dehydrators, etc.) and /. Alternatively, it is preferable to use one dehydrated with a dehydrating agent.
The properties of the decomposition product (B) used in the production method of the present invention are not particularly limited, and examples thereof include powder, granules, and gels.

Examples of the dehydrating agent used when dehydrating the decomposed product (Z) obtained by performing a chemical treatment and / or a mechanical treatment include a water-soluble polyvalent metal compound and the like.
A water-soluble polyvalent metal compound is an element having a valence of 2 or more in a periodic table, and is a water-soluble polyvalent metal compound that forms a carboxyl group or a chelate salt with a carboxyl group ion after being dissolved in water or reacting with water. If so, there is no particular limitation. For example, polyvalent metal compounds containing alkaline earth metals such as magnesium, calcium, strontium and barium, polyvalent metal compounds containing transition metals such as iron, nickel, copper and zinc, and trivalent or higher such as boron, aluminum and gallium. Examples thereof include polyvalent metal compounds containing the above metals. Even if the polyvalent metal compound is a non-hydrate, monohydrate, dihydrate, trihydrate, tetrahydrate, pentahydrate, hexahydrate, and heptahydrate It may be a hydrate such as a substance, octahydrate or nine hydrate.
These dehydrating agents may be used alone or in combination of two or more.
In the present invention, the "water-soluble polyvalent metal compound" refers to a polyvalent metal compound having a solubility in water at 20 ° C. of 1 mg / ml or more, preferably 10 mg / ml or more.

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

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

Among the dehydrating agents, from the viewpoint of dehydration efficiency and the like, a water-soluble polyvalent metal compound containing calcium is preferable, and calcium chloride, calcium oxide, calcium acetate and calcium hypochlorite are more preferable. These can be used alone or in combination of two or more. This purpose is the same in other parts of the specification of the present application.

When a dehydrating agent is used, the amount of the dehydrating agent added is preferably 0.01 to 10% by weight, more preferably 0.03 to 8% by weight, based on the weight of the decomposed product (Z) before the dehydration treatment. It is% by weight, most preferably 0.1 to 7% by weight. Within these ranges, dehydration proceeds efficiently from the decomposition-treated product (Z), and handling becomes easy.

The decomposition product (B) is a decomposition product of water-absorbent resin particles contained in sanitary products from the viewpoint of reducing the environmental load by reusing waste as a resource, and the water-absorbent resin particles contained in used sanitary products. It is preferably a decomposition product of.
The hygienic product is not particularly limited as long as it is a hygienic product containing water-absorbent resin particles. Hygiene products include disposable diapers (children's disposable diapers and adult disposable diapers, etc.), napkins (physiological napkins, etc.), paper towels, pads (pads for incontinence and surgical underpads, etc.) and pet sheets (pet urine absorption sheets). Etc., and the hygienic product may be a final product, an intermediate product, or the like.

When using water-absorbent resin particles contained in sanitary products, mince machines (meat choppers), jaw crushers, hammer crushers, roll crushers, and self-crushing machines are used for absorbers that are included in sanitary products and contain water-absorbent resin particles as constituent members. , Stamp mill, stone mill type crusher, crusher, ring mill, roller mill, jet mill, pin mill, vibration mill, planetary mill, bead mill, attritor, rigid stirrer, cutter mill, etc., JP-A-2020-11158 By crushing the particles using the crushing apparatus described in the above, decomposition products of water-absorbent resin particles can be obtained.
In the process of crushing the absorber using a crusher, shearing force is applied to the water-absorbent resin particles, which breaks at least a part of the bonds of the molecules constituting the crosslinked polymer (A'), thereby breaking the decomposition product (B). ) Is obtained. At that time, basically, the water content of the water-absorbent resin particles contained in the sanitary goods tends to be higher than that at the time of production of the water-absorbent resin particles. This includes the addition of water-absorbent resin particles while adding water during the process of manufacturing sanitary goods, and the period of exposure to air while stored as sanitary goods and before being processed by a crusher. In the meantime, it absorbs moisture in the atmosphere. Since the water content of the water-absorbent resin particles subjected to decomposition is high, the bond of the molecule constituting the crosslinked polymer (A') is more likely to proceed due to the shearing force applied from the crusher.

The step of sterilizing the water-absorbent resin particles may be performed before the decomposition treatment of the water-absorbent resin particles contained in the sanitary goods described above, or may be performed at the same time as the decomposition treatment.
The steps for sterilizing the water-absorbent resin particles include a high-temperature treatment step of heat-treating to 100 ° C. or higher, a step of irradiating with ultraviolet rays, a step of using a sterilizing agent, and a gas of an alkylating agent such as ethylene oxide or formaldehyde in the presence of ozone. Examples include the process used in. Examples of the bactericidal agent include an aqueous solution in which ozone is dissolved and hypochlorite (salt).
From the viewpoint of safety, the step of sterilizing the water-absorbent resin particles is preferably a step of using a bactericidal agent, and more preferably a step of using hypochlorite (salt).
When the water-absorbent resin particles are sterilized by irradiating with ultraviolet rays or by using a bactericidal agent, the decomposition of the crosslinked polymer proceeds at the same time. Therefore, the sterilization treatment step may be performed as a step that also serves as a decomposition treatment, or the decomposition treatment may be performed separately.

The water-soluble content (% by weight) of the decomposition product (B) is 1.0 to 30.0, preferably 1.0 to 25, from the viewpoint of the absorption characteristics of the water-absorbent resin particles obtained by the present production method. It is 0.0, more preferably 2.0 to 20.0, and particularly preferably 2.0 to 10.0. If it exceeds 30.0, various low molecular weight bodies will be produced by breaking a plurality of bonds. Therefore, it is not easy to obtain water-absorbent resin particles having stable absorption performance even when added to the manufacturing process. For example, when it is added in the polymerization step, radical polymerization does not proceed, and when it is added in the gel shredding step, it reacts with the surface cross-linking agent in the subsequent surface cross-linking step, so that the cross-linking agent is wasted. Not only that, but also the reaction with the main chain portion that the cross-linking agent originally wants to react with does not proceed, which lowers the gel strength and leads to a decrease in the amount of absorption under load. Further, if the amount of water-soluble content is large, a large amount is lost when the decomposition product (B) is obtained, and as a result, the recycling efficiency is deteriorated and it is difficult to obtain the effect of reducing the environmental load.

Further, the decomposition product of the water-absorbent resin particles is composed of a mixture of a water-soluble component and a water-insoluble component. A method of removing the insoluble component and using only the soluble component is also possible, but one of them should be removed. It is preferable to use all of them for reuse from the viewpoint of reuse of decomposition products.
The water-soluble component includes a constituent monomer of the polymer generated by the decomposition of the crosslinked polymer (A') and a non-crosslinked polymer generated by the decomposition.
The water-soluble content, which means the weight ratio of the water-soluble component to the total solid content, contained in the decomposition product of the crosslinked polymer is measured by the following method.

<Amount of soluble water>
1. Decomposition product (Z) obtained by weighing 100 g of physiological saline (salt concentration 0.9% by weight) in a 300 ml plastic container and subjecting the physiological saline to chemical treatment and / or mechanical treatment. Add 2 g, seal with a wrap, rotate the stirrer at 500 rpm for 3 hours, and stir to prepare a water-soluble component extract from which the water-soluble component of the water-absorbent resin particles has been extracted. Then, this water-soluble component extract is filtered using a filter paper manufactured by ADVANTEC Toyo Co., Ltd. (product name; JIS P 3801, No. 2, thickness 0.26 mm, reserved particle diameter 5 μm). Then, 10 g of the obtained filtrate is weighed, and 40 g of ion-exchanged water is added to prepare a measurement solution (G) for measuring the water-soluble content contained in the decomposition product of the water-absorbent resin particles.

Next, for the measurement solution (G), titration ([W _{KOH, S} ] ml) of N / 50 KOH aqueous solution required for the pH of the measurement solution (G) to reach 10, and the measurement solution. The titration amount ([W _{HCl, S} ] ml) of the N / 10 HCl aqueous solution required for the pH of the solution after the pH of (G) to be adjusted to 2.7 is obtained by the following method.

When the constituent monomer of the water-absorbent resin is acrylic acid and its sodium salt, the amount of unneutralized acrylic acid substance n _COOH contained in the decomposition product of the water-absorbent resin particles is calculated by the following formula.
n _COOH (mol) = (W _KOH, SW _{KOH, b} ) × (1/50) / 1000 × 5
Further, the total amount of acrylic acid substance n _tot is calculated by the following formula.
n _tot (mol) = (W _HCl, SW _{HCl, b} ) × (1/10) / 1000 × 5
The amount of neutralized acrylic acid substance _nCOONa is calculated by the following mathematical formula.
n _COONa (mol) = n _tot -n _COOH
Further, the unneutralized acrylic acid weight _mCOOH is calculated by the following formula.
m _COOH (g) = n _COOH × 72
The amount of neutralized acrylic acid substance _mCOONa is calculated by the following formula.
m _COONa (g) = n _COONa × 94
Based on the above values and the amount of water contained in the decomposition product of the water-absorbent resin particles used as the sample ([ _WH2O ]% by weight), the water-soluble content of the water-absorbent resin particles is calculated by the following formula. can do.
Water-soluble content (% by weight) = {(m _COOH + m _COONa ) x 100} / {1.2 x (100- _WH2O )}

[W _{KOH, b} ] in the formula is a titration amount of N / 50 KOH aqueous solution in a blank test conducted using 50 g of physiological saline (saline concentration 0.9% by weight) as a test solution, and is a titration. It is a value ([W _{KOH, b} ] ml) obtained by titrating an aqueous KOH solution of N / 50 until the pH of water reaches 10. For [W _{HCl, b} ], a blank test solution titrated with an N / 50 KOH aqueous solution until the pH reached 10, and then a N / 10 HCl aqueous solution was titrated until the pH reached 2.7. The obtained value ([W _{HCl, b} ] ml).

If the water-absorbent resin particles before the decomposition treatment contain water-soluble components (inorganic acid, organic acid having a carboxylic acid group, sulfonic acid group, etc.), the water-absorbent resin particles before the decomposition treatment By subtracting the water-soluble content measured and quantified by the above method from the water-soluble content measurement value measured for the decomposition product (B), the water-soluble content generated by the decomposition in the decomposition product (B) can be obtained. You can ask.

In the method for producing water-absorbent resin particles of the present invention, the decomposition product (B) comprises the polymerization step (I), the gel shredding step (II), the drying step (III), and the pulverization classification step (IV). It is added in at least one step selected from the group. By adding it during these steps, it is possible to efficiently produce a water-absorbent resin having excellent various properties such as absorption properties.
Above all, from the viewpoint of improving water absorption performance and stabilizing quality, the method of adding to the polymerization step (I) and / or the gel shredding step (II) is preferable, and it is more preferable to add to the gel shredding step (II). ..
Here, the gel shredding step means a series of steps of putting the water-containing gel into the crushing device and operating the crushing device to obtain the shredded gel.
Then, in the method of adding the decomposition product (B) to the gel shredding step (II), the decomposition product (B) is put into the crushing device in advance in the crushing device in which the operation of cutting the hydrous gel is not performed. The method of adding the hydrogel after leaving it, the method of adding the decomposition product (B) into the crusher in which the operation of cutting the hydrogel is performed, and the method of adding the hydrogel and the decomposition product into the operating crusher. A method of simultaneously inputting (B) and (B) is included.

When the decomposition product (B) is added to the polymerization step (I) using an acid group-containing monomer such as acrylic acid or methacrylic acid as the water-soluble vinyl monomer (a1), the decomposition product (B) is uniformly dissolved in the aqueous acrylic acid solution. It may be dispersed in an aqueous solution of acrylic acid.
The property of (B) added to the polymerization step (I) is preferably gel-like.

When the decomposition product (B) is added to the polymerization step (I), the weight ratio of the decomposition product (B) of the water-absorbent resin particles to the water-soluble vinyl monomer (a1) is 5/95 to 95/5. It is more preferably 5/95 to 80/20, and even more preferably 10/90 to 70/30. Within these ranges, the absorption performance of the water-absorbent resin particles obtained by this production method becomes good.
When the decomposition product (B) is added to the polymerization step (I), the decomposition product (B) is preferably 1 to 50 (% by weight) based on the total weight of the monomer composition in the polymerization step (I). ), More preferably 1 to 40, and particularly preferably 1 to 30.

When the decomposition product (B) is added to the gel shredding step (II), the properties of the decomposition product (B) may be powdery or gel. Further, the number of shredding may be increased or decreased as necessary, or the number of additions may be divided into two or more times, but the absorption performance of the water-absorbent resin particles after recycling containing (B) may be improved. From the viewpoint, it is preferable that the water-containing gel containing the crosslinked polymer (A) and (B) are kneaded while being shredded.

When the decomposition product (B) is added to the gel shredding step (II), the range of the mixed weight ratio of the water-containing gel containing the crosslinked polymer (A) and the decomposition product (B) is preferably 99/1 to 10 /. It is 90, more preferably 97/3 to 20/80. Within these ranges, the drying property is not impaired and the required water absorption performance can be satisfied.

When the decomposition product (B) is added to the drying step (III), the decomposition product (B) is added in the method described above as a method applied to the drying step (III).

When the decomposition product (B) is added to the pulverization classification step (IV), the decomposition product (B) is added to the pulverization apparatus described above as the pulverization method in the pulverization classification step (IV).

When the decomposition product (B) is added to either the drying step (III) or the pulverization classification step (IV), the content (% by weight) of the decomposition product (B) to be added is the crosslinked polymer. It is preferably 1 to 45, more preferably 1 to 40, and particularly preferably 1 to 30 with respect to the total weight of (A).

For the decomposed product (B) to be added, an operation of removing metal ions remaining in the decomposed product (B) may be performed in advance by using an ion exchange resin or a complex ion, if necessary. The metal content remaining in the decomposition product (B) can be measured by ICP emission spectroscopic analysis measurement or the like.

The weight average particle diameter (μm) of the water-absorbent resin particles obtained by the production method of the present invention is preferably 150 to 600, more preferably 200 to 500, from the viewpoint of absorption performance and handleability.

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

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

The apparent density (g / ml) of the water-absorbent resin particles obtained by the production method of the present invention is preferably 0.40 to 0.80, more preferably 0.50 to 0., From the viewpoint of the absorption performance of sanitary products. 75, particularly preferably 0.50 to 0.70. Within this range, the water absorption rate when the water-absorbent resin particles swell becomes good. The apparent density is measured at 25 ° C. in accordance with JIS K7365: 1999.

The amount of water-absorbing resin particles obtained by the production method of the present invention with respect to physiological saline is preferably 50 g / g or more and 70 g / g or less, and more preferably 53 g / g or more and 67 g when surface cross-linking is not performed. It is less than / g. When surface cross-linking is performed, it is preferably 30 g / g or more and 60 g / g or less, and more preferably 30 g / g or more and 55 g / g or less. If the water retention amount is low, the absorption amount of the diaper is small, and if the water retention amount is too high, the water-soluble content is large, which is not preferable. The amount of water retained in the present invention is measured by the following method.

<Measurement method of water retention>
Put 1.00 g of the measurement sample in a tea bag (length 20 cm, width 10 cm) made of a nylon net with an opening of 63 μm (JIS Z8801-1: 2006), and put it in 1,000 ml of physiological saline (salt concentration 0.9%). After soaking for 1 hour without stirring, the sample was pulled up and hung for 15 minutes to drain water. Then, the whole tea bag was placed in a centrifuge and dehydrated at 150 G for 90 seconds to remove excess physiological saline, and the weight (h1) including the tea bag was measured to determine the water retention amount from the following formula. (H2) is the weight of the tea bag measured by the same operation as above when there is no measurement sample. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C.
Water retention (g / g) = (h1)-(h2)

The amount of water-absorbent resin particles obtained by the production method of the present invention absorbed under load (g / g) is preferably 19 or more, more preferably 23 or more. If it is less than 19, leakage is likely to occur during repeated use, which is not preferable. Further, the higher the upper limit value is, the more preferably it is not particularly limited, but from the viewpoint of performance balance with other physical characteristics and productivity, it is preferably 28 or less, more preferably 26 or less. The amount of absorption under load can be appropriately adjusted depending on the type and amount of the cross-linking agent (b) and the surface cross-linking agent (e). Therefore, for example, when it is necessary to increase the absorption amount under load, it can be easily realized by increasing the amount of the cross-linking agent (b) and the surface cross-linking agent (e). The amount of absorption under load in the present invention is measured by the following method.

<Measurement method of absorption under load>
Measurements were performed by sieving into a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh with a mesh opening of 63 μm (JIS Z8801-1: 2006) attached to the bottom, in the range of 250 to 500 μm using a standard sieve. Weigh 0.16 g of the sample, set the cylindrical plastic tube vertically and arrange it on a nylon net so that the measurement sample has almost uniform thickness, and then put a weight (weight: 210.6 g, outside) on this measurement sample. Diameter: 24.5 mm,) was placed. After weighing the entire weight (M1) of this cylindrical plastic tube, a cylindrical plastic containing a measurement sample and a weight is placed in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%). The tube was erected vertically and immersed with the nylon mesh side facing down, and allowed to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, tilted diagonally, and the water adhering to the bottom was collected in one place and dropped as water droplets to remove excess water, and then the measurement sample and weight were contained. The weight (M2) of the entire cylindrical plastic tube was weighed, and the amount of absorption under load was calculated from the following equation. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C.
Absorption amount under load (g / g) = {(M2)-(M1)} /0.16

The absorption amount of the water-absorbent resin particles obtained by the production method of the present invention under no load measured by the Demand Wetability test is preferably 5 g / g to 30 g / g, more preferably 10 g / g to 30 g / g. It is less than or equal to g. Within this range, water can be absorbed without causing liquid leakage in the absorber, and if it is less than 5 g / g, the amount of water absorption is too small and there is a concern that leakage will occur. If it exceeds 30 g / g, the liquid will be absorbed. Since it does not diffuse in the absorber, it absorbs water locally, so it is not economical because there is a concern about leakage and the water absorption area of the absorber cannot be used efficiently. The "absorption amount under no load measured in the Demand Wetability test" in the present invention is measured by the following method.

<Absorption amount under no load measured by Demand Wetability test>
When measured by the DW method described in JP-A-2014-005472 using 0.50 g of absorbent resin particles and physiological saline, the amount of absorption (ml / g) 1 minute after the start of water absorption is determined. It is the amount of absorption under no load measured in the Demand Wetability test. The DW test determines the suction capacity of the absorbent resin under no load on a measuring table connected to the burette and the conduit.

The content of the polyvalent metal element of the water-absorbent resin particles obtained by the production method of the present invention is preferably 0.1 to 10% by weight, more preferably 0, based on the weight of the crosslinked polymer (A). .1 to 8% by weight, particularly preferably 0.1 to 5% by weight. The polyvalent metal element is contained in a surface cross-linking agent for water-absorbent resin particles, a dehydrating agent used for dehydrating decomposition products, and drainage absorbed by used sanitary goods. The content of the polyvalent metal element derived from the dehydrating agent of the water-absorbent resin particles is preferably 0.1 to 8% by weight, more preferably 0.1 to 7% by weight, based on the weight of the crosslinked polymer (A). It is 5.5% by weight, particularly preferably 0.1 to 4.5% by weight. The content of the polyvalent metal element of the water-absorbent resin particles in the present invention is measured by the following method.

<Method of measuring the content of multivalent metal elements by fluorescent X-ray measurement>
Take 5.000 g of the measurement sample into a sample container for loose powder (film is made of polypropylene, diameter 27 mm), and use a wavelength dispersive fluorescent X-ray analyzer (Axios, manufactured by Spectris Co., Ltd.) at 100 mA and 24 kV under a helium atmosphere. The setting was performed, the measurement was carried out, and the quantitative analysis software Uniquant was used.

The distribution index of the polyvalent metal element of the water-absorbent resin particles obtained by the production method of the present invention is preferably 0.1 to 3.0, more preferably 0.1 to 2.5, and most preferably. It is 0.1 to 2.0. Within this range, the variation in the distribution state of the multivalent metal element is small, so that the water absorption performance is good. The distribution index of the polyvalent metal element derived from the dehydrating agent is preferably 0.1 to 3.0, more preferably 0.1 to 2.5, and most preferably 0.1 to 2.0. ..
The smaller the value of the distribution index, the more the polyvalent metal element is evenly distributed in the water-absorbent resin particles. For example, since the polyvalent metal element derived from the dehydrating agent is also contained in the decomposition product (B) added in the present production method, the small distribution index is found in the water-absorbent resin particles obtained by the production method of the present invention. It means that the components derived from the decomposition product (B) are uniformly distributed on the surface and inside. When the distribution of the component derived from the decomposition product (B) in the water-absorbent resin particles is uniform, the water-absorbent resin particles swell uniformly at the time of water absorption, so that the water absorption performance is good.

For the distribution of the polyvalent metal element in the water-absorbent resin particles obtained by the production method of the present invention, the position of the polyvalent metal element in the water-absorbent resin particles is measured by using electron beam measurement (EDX, WDX) or the like. The image obtained by the measurement can be analyzed by processing it with image processing software (for example, WinROOF, etc.).
The distribution index of the polyvalent metal element in the present invention is measured by the following method.

<Distribution index of multivalent metal elements>
The water-absorbent resin particles were allowed to stand and dried at 140 ° C. for 30 minutes, and the particle size was adjusted to 500-300 μm particles by sieving in the order of JIS standard sieve 500 μm, 300 μm, and saucer. Got Next, the measurement sample (U) was embedded with Aronix D-800 (acrylic resin) manufactured by JEOL Ltd., and LUXSPOT (using a halogen lamp) manufactured by JEOL Ltd. was irradiated for 1 minute to cure the resin and embed it. The resin is cut with a microtome (LEICA EM UC7, manufactured by Leica) to expose the measurement surface, and the processed embedded resin is fixed to the sample table with carbon tape and a thin-film deposition device manufactured by JEOL Ltd. (JEC-300FC). ), Platinum was vapor-deposited under the conditions of 20 kV and 70 seconds. The obtained platinum vapor deposition material was put into a scanning electron microscope measurement (QUANTA FEG, manufactured by FEI), and energy dispersion type X-ray spectroscopy (Octane Elite, manufactured by Ametec) was applied to an acceleration voltage of 15 kV and a spot 4 (irradiation diameter). ), Arbitrary 10 points where the water-absorbent resin particles were exposed on the measurement surface of the platinum vapor deposition were selected under the measurement conditions of WD 10 mm, and the measurement was carried out by point analysis (point analysis) for each of them.
The average value of the 10 measurement values is [the average value of the polyvalent metal content by SEM-EDX], and the 10 measurement value is [the standard deviation value of the metal content by SEM-EDX]. Regarding the distribution state of the contained polyvalent metal elements, the distribution index of the polyvalent metal elements was obtained from the following calculated values.
Distribution index of polyvalent metal elements = [standard deviation value of metal content by SEM-EDX] / [average value of polyvalent metal content by SEM-EDX]

The water-absorbent resin particles obtained by the method of the present invention can be used for various applications requiring the water-absorbing action of the water-absorbing resin particles and the swelling action due to the water-absorbing resin particles, and are used for sanitary goods, pet-sheets, soil water-retaining materials, and batteries. It can be used as a gelling agent, agricultural materials such as seedling raising sheets and granulated fertilizers, dew condensation inhibitor, water retaining material for cold storage material, and building material such as water blocking agent.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, parts indicate parts by weight and% indicates weight%.

<Manufacturing example 1>
Commercially available diapers GOO. N (Pants L size, product name: Smooth ventilation, manufactured by Daio Paper Corporation, May 2021, Japan) is crushed by hand, and the crushed water-absorbent resin particles contained in the absorber are combined with pulp. After taking out, each was separated by a sieve to obtain crushed water-absorbent resin particles (Q-1).

<Manufacturing example 2>
10.00 g of the water-absorbent resin particles (Q-1) obtained in Production Example 1 were weighed and placed in a 2 L poly bucket (height 19 cm, bottom diameter 13 cm, top surface diameter 16 cm). Next, 400 ml of physiological saline (salt concentration 0.9% by weight) was placed in the above 2L poly bucket, and a stirring blade (propeller diameter 10.0 cm, propeller diameter 10.0 cm) of four paddles attached to a three-one motor (trade name: High Power Model No. BLh600) was added. The angle of the wing: 30 degrees with respect to the vertical direction and the wing width of 3.0 cm) was fixed at a height of 0.5 cm from the bottom surface of the poly bucket, and the mixture was stirred at a rotation speed of 600 rpm for 10 minutes. After stopping the stirring blade, all the gel in the poly bucket was taken out.
The gel (Z-1) taken out is a crosslinked polymer by applying a shearing force to the swollen water-absorbent resin particles (Q-1) by stirring using a three-one motor, so that the water-absorbent resin particles (Q-1) are also crosslinked polymers. -1) is a gel containing a decomposition product produced by decomposition treatment.
41.00 g of the removed gel (Z-1) was weighed, transferred to a SUS vat (length 20 cm, width 20 cm, height 4 cm) and spread uniformly on the vat. Next, the entire SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess physiological saline. Next, the entire amount of (Z-1) remaining on the vat was placed in a tea bag (length 20 cm, width 10 cm) made of a nylon net having an opening of 63 μm (JIS Z8801-1: 2006), and 500 ml of a 1 wt% calcium chloride aqueous solution was placed. Place in a 500 ml conical beaker containing calcium chloride, soak for 1 hour without stirring, then transfer all the contents of the tea bag to a SUS vat (length 20 cm, width 20 cm, height 4 cm) and evenly on the vat. I spread it out. Next, the whole SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess water, and the decomposition product (B-1) used in Example 1 was removed. ) Was obtained. The water-soluble content of (B-1) was 7.7% by weight, and the water content measured with an infrared moisture meter was 62.2% by weight.

<Manufacturing example 3>
10.00 g of the water-absorbent resin particles (Q-1) obtained in Production Example 1 were weighed and placed in a 2 L poly bucket (height 19 cm, bottom diameter 13 cm, top surface diameter 16 cm). Next, 400 ml of physiological saline (salt concentration 0.9% by weight) was placed in the 2 L poly bucket, and the stirring blades were further fixed in the same manner as in Production Example 2, and the mixture was stirred at a rotation speed of 400 rpm for 10 minutes. After stopping the stirring blade, the entire amount of gel (Z-2) in the poly bucket was taken out. The gel (Z-2) taken out is a crosslinked polymer by applying a shearing force to the swollen water-absorbent resin particles (Q-1) by stirring using a three-one motor, so that the water-absorbent resin particles (Q-1) are also crosslinked polymers. -1) is a gel containing a decomposition product produced by decomposition treatment.
Weigh 41.00 g of the removed gel (Z-2), put it in a tea bag (length 20 cm, width 10 cm) made of a nylon net with an opening of 63 μm (JIS Z8801-1: 2006), and then put it in a centrifuge. Then, the mixture was centrifuged at 150 G for 90 seconds to remove excess physiological saline. Next, the tea bag was placed in a 500 ml conical beaker containing 500 ml of a 1 wt% calcium chloride aqueous solution, soaked for 1 hour without stirring, and then the contents of the tea bag were all SUS bats (length 20 cm, width 20 cm, height). It was transferred to 4 cm) and spread evenly on the bat. Next, the whole SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess water, and the decomposition product (B-2) used in Example 2 was removed. ) Was obtained. The water-soluble content of (B-2) was 4.5% by weight, and the water content measured by an infrared moisture meter was 61.1% by weight.

<Manufacturing example 4>
The decomposition product (B-2) of the water-absorbent resin particles obtained in Production Example 3 was further statically dried for 3 hours in a circulating air dryer set at 150 ° C., and the decomposition product (B-3) used in Example 3 was obtained. Obtained. The water-soluble content of (B-3) was 3.2% by weight, and the water content measured by an infrared moisture meter was 1.2% by weight.

<Manufacturing example 5>
In Production Example 2, the same operation was performed except that 500 ml of a 1 wt% calcium hypochlorite aqueous solution was used instead of 500 ml of a 1 wt% calcium chloride aqueous solution, and the decomposition product (B-4) used in Example 4 was obtained. Obtained. The water-soluble content of (B-4) was 6.3% by weight, and the water content measured by an infrared moisture meter was 60.2% by weight.

<Manufacturing example 6>
100 parts of the fluff pulp and 100 parts of the water-absorbent resin particles (Q-1) obtained in Production Example 1 are mixed with an air flow type mixer {Padformer manufactured by Otec Co., Ltd.} to obtain a mixture, and then this The mixture was uniformly laminated on an acrylic plate (thickness 4 mm) so as to have a basis weight of about 500 g / m ² , and pressed at a pressure of 5 kg / cm ² for 30 seconds to obtain an absorber. A 10 cm x 10 cm test piece of this absorber [the weight of the water-absorbent resin particles (Q-1) contained in the test piece is 5 g] is cut out and a 2 L poly bucket (height 19 cm, bottom diameter 13 cm, top surface diameter 16 cm). After that, 300 ml of physiological saline (salt concentration 0.9% by weight) was added, and the mixture was allowed to stand for 1 hour.
A test piece absorbed in physiological saline was used as a substitute for used sanitary products.
Sanitary goods with 4 paddle stirring blades (propeller diameter 10.0 cm, blade angle: 30 degrees with respect to the vertical direction, blade width 3.0 cm) attached to the Three-One Motor (trade name: High Power Model No. BLh600) The 2L poly bucket containing the substitute was fixed at a height of 0.5 cm from the bottom surface of the poly bucket and operated at a rotation speed of 600 rpm for 10 minutes to stir the used sanitary substitute. After stirring for 10 minutes, the fluff pulp was removed by a decantation operation and a sieving operation, and swelled to obtain a gel-like substance (Z-3). The gel-like product is decomposed by applying a shearing force by stirring using a three-one motor to the gel in which the water-absorbent resin particles (Q-1) contained in the substitute for used sanitary products are swollen. It is a gel containing decomposition products.
After removing the fluff pulp, 41.00 g of the contained gel (Z-3) was weighed and placed in a tea bag (length 20 cm, width 10 cm) made of a nylon net having an opening of 63 μm (JIS Z8801-1: 2006). After that, it was placed in a centrifuge and dehydrated by centrifugation at 150 G for 90 seconds to remove excess physiological saline. Next, put the tea bag) in a 500 ml conical beaker containing 500 ml of a 1 wt% calcium chloride aqueous solution, soak it for 1 hour without stirring, and then fill the contents of the tea bag with a SUS bat (length 20 cm, width 20 cm, 20 cm). It was transferred to a height of 4 cm) and spread evenly on a bat. Next, the whole SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess water, and the decomposition product (B-5) used in Example 5 was removed. ) Was obtained. The water content of (B-5) was 64.4% by weight, and the water-soluble content was 10.2% by weight.

<Manufacturing example 7>
5. Put 30.0 g of the water-absorbent resin particles (Q-1) obtained in Production Example 1 into a PE wide-mouthed bottle 10 L (manufactured by Sampler Tech Co., Ltd.), and further ascorbic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.). Add 1500 ml of ion-exchanged water in which 0 g and 0.7 g of iron (II) sulfate / heptahydrate (manufactured by Fuji Film Wako Junyaku Co., Ltd.) are dissolved and let stand for 20 minutes to swell the water-absorbent resin particles. I let you. Then, using a homogenizer (product name: Excel Auto Homogenizer, manufactured by Nissei Tokyo Office Co., Ltd.), the water-absorbent resin particles in a swollen state were dispersed and homogenized at 1500 rpm for 10 minutes. After removing the homogenizer while collecting the swollen water-absorbent resin particles adhering to the homogenizer, cover the upper part of the PE wide-mouthed bottle with PVCA film (Saran film), fix it with a rubber band so that the PVCA film does not come off, and seal it. It was in a state. Subsequently, this was allowed to stand for 10 hours in a thermostat (model: IG401, manufactured by Yamato Scientific Co., Ltd.) set at 70 ° C. to decompose the water-absorbent resin particles. After the decomposition treatment, the obtained treatment liquid (Z-4) was transferred to a SUS vat (length 20 cm, width 20 cm, height 4 cm) and spread uniformly on the vat. Next, the entire SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess water and decompose the water-absorbent resin particles used in Comparative Example 2. The thing (B-6) was obtained. The water content of (B-6) was 75.1% by weight, and the water-soluble content was 82.0% by weight.

<Manufacturing example 8>
3. Put 30.0 g of the water-absorbent resin particles (Q-1) obtained in Production Example 1 into a PE wide-mouthed bottle 10 L (manufactured by Sampler Tech Co., Ltd.), and further ascorbic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.). Add 1500 ml of ion-exchanged water in which 0 g and 0.7 g of iron (II) sulfate / heptahydrate (manufactured by Fuji Film Wako Junyaku Co., Ltd.) are dissolved and let stand for 20 minutes to swell the water-absorbent resin particles. I let you. Then, using a homogenizer (product name: Excel Auto Homogenizer, manufactured by Nissei Tokyo Office Co., Ltd.), the water-absorbent resin particles in a swollen state were dispersed and homogenized at 1500 rpm for 3 minutes. After removing the homogenizer while collecting the swollen water-absorbent resin particles adhering to the homogenizer, cover the upper part of the PE wide-mouthed bottle with PVCA film (Saran film), fix it with a rubber band so that the PVCA film does not come off, and seal it. It was in a state. Subsequently, this was allowed to stand for 10 hours in a thermostat (model: IG401, manufactured by Yamato Scientific Co., Ltd.) set at 70 ° C. to decompose the water-absorbent resin particles. After the decomposition treatment, the obtained treatment liquid (Z-5) was transferred to a SUS vat (length 20 cm, width 20 cm, height 4 cm) and spread uniformly on the vat. Next, the entire SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess water and decompose the water-absorbent resin particles used in Comparative Example 3. The thing (B-7) was obtained. The water content of (B-7) was 42.4% by weight, and the water-soluble content was 35.0% by weight.

<Manufacturing example 9>
In Production Example 2, 500 ml of a 1 wt% calcium chloride aqueous solution was changed to 500 ml of a 1 wt% calcium acetate aqueous solution, and the same operation as in Production Example 2 was carried out to obtain a decomposition product (B-8). The water-soluble content of (B-8) was 8.0% by weight, and the water content measured with an infrared moisture meter was 62.9% by weight.

<Manufacturing example 10>
10.00 g of the water-absorbent resin particles (Q-1) obtained in Production Example 1 were weighed and placed in a 2 L poly bucket (height 19 cm, bottom diameter 13 cm, top surface diameter 16 cm). Next, 400 ml of physiological saline (salt concentration 0.9% by weight) was placed in the above 2L poly bucket, and a stirring blade (propeller diameter 10.0 cm, propeller diameter 10.0 cm) of four paddles attached to a three-one motor (trade name: High Power Model No. BLh600) was added. The angle of the wing: 30 degrees with respect to the vertical direction and the wing width of 3.0 cm) was fixed at a height of 0.5 cm from the bottom surface of the poly bucket, and the mixture was stirred at a rotation speed of 600 rpm for 10 minutes. After stopping the stirring blade, all the gel in the poly bucket was taken out.
In the gel (Z-6) taken out, the swollen water-absorbent resin particles (Q-1) are subjected to shearing force by stirring using a three-one motor, so that the water-absorbent resin particles (Q-1) which are also crosslinked polymers are applied. -1) is a gel containing a decomposition product produced by decomposition treatment.
Weigh 41.00 g of the removed gel, put it in a tea bag (length 20 cm, width 10 cm) made of a nylon net with an opening of 63 μm (JIS Z8801-1: 2006), put it in a centrifuge, and 90 at 150 G. Excess saline was removed by centrifugation for a second. Next, all the contents of the tea bag were transferred to a SUS vat (length 20 cm, width 20 cm, height 4 cm) and spread uniformly on the vat. Next, the whole SUS vat was placed in a vacuum constant temperature dryer (model number: VOS-210C manufactured by Tokyo Rika Kikai Co., Ltd.) and allowed to stand at 50 ° C. for 24 hours to remove excess water to obtain a decomposed product (B-9). The water-soluble content of (B-9) was 7.7% by weight, and the water content measured with an infrared moisture meter was 95.2% by weight.

<Example 1>
The hydrous gel (1) 452.04 parts and the decomposition product (B-1) 14.1 parts obtained in Production Example 1 were simultaneously put into a minced machine used in the gel cutting step, and the mixture was mixed and finely mixed with the minced machine. I refused. Further, while mixing and cutting, 115.58 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed to obtain hydrogel particles. The obtained hydrogel particles were dried with an aeration type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. Next, 5.00 parts of a 2% water / methanol mixed solution (water / methanol weight ratio = 70/30) of ethylene glycol diglycidyl ether was mixed with the dried product while spraying, and allowed to stand at 150 ° C. for 30 minutes. The surface was crosslinked to obtain water-absorbent resin particles (P-1).

<Example 2>
The hydrous gel (1) 452.04 parts and the decomposition product (B-2) 42.7 parts obtained in Production Example 1 were simultaneously put into a minced machine used for the gel cutting step, and the mixture was mixed and finely mixed with the minced machine. I refused. Further, while mixing and cutting, 115.58 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed to obtain hydrogel particles. The obtained hydrogel particles were dried with an aeration type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. Next, 5.00 parts of a 2% water / methanol mixed solution (water / methanol weight ratio = 70/30) of ethylene glycol diglycidyl ether was mixed with the dried product while spraying, and allowed to stand at 150 ° C. for 30 minutes. The surface was crosslinked to obtain water-absorbent resin particles (P-2).

<Example 3>
In Example 2, the same operation was performed except that 14.2 parts of the decomposition product (B-3) was used instead of 42.7 parts of the decomposition product (B-2), and the water-absorbent resin particles (P-3) were used. Got

<Example 4>
In Example 2, the same operation was performed except that 42.7 parts of the decomposition product (B-4) was used instead of 42.7 parts of the decomposition product (B-2), and the water-absorbent resin particles (P-4) were used. Got

<Example 5>
In Example 2, the same operation was performed except that 42.7 parts of the decomposition product (B-5) was used instead of 42.7 parts of the decomposition product (B-2), and the water-absorbent resin particles (P-5) were used. Got

<Example 6>
147 parts (2.04 mol) of acrylic acid, crosslinker (b) {pentaerythritol triallyl ether} 0.6305 parts (0.0024 mol part), 10 parts of decomposition product (B-1) and 344 parts of deionized water. .65 parts were kept at 3 ° C. while stirring and mixing. After inflowing nitrogen into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.63 parts of a 1% hydrogen peroxide solution and 1.1774 parts of a 2% ascorbic acid solution and 2% of 2,2'-azobis [ 2-355 parts of a 2-methyl-N- (2-hydroxyethyl) -propionamide] aqueous solution was added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ° C., the mixture was polymerized at 90 ± 2 ° C. for about 5 hours to obtain a hydrogel (1). Next, while 502.27 parts of this hydrogel (1) was shredded with a minced machine, 128.42 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed to obtain hydrogel particles. Further, the hydrogel particles were dried with an aeration type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. The dried product was pulverized with a juicer mixer and then adjusted to a particle size range of 710 to 150 μm, whereby the dried product particles (1) were obtained. While stirring 100 parts of the dried body particles (1) at high speed, 5.00 parts of a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30) is spray-sprayed. The mixture was mixed and allowed to stand at 150 ° C. for 30 minutes for surface cross-linking to obtain water-absorbent resin particles (P-6) which are also crosslinked polymers of acrylic acid.

<Example 7>
In Example 6, the same operation was carried out except that 10 parts of the decomposition product (B-3) was used instead of 10 parts of the decomposition product (B-1) to obtain water-absorbent resin particles (P-7).

<Example 8>
The hydrous gel (1) 452.04 parts and the decomposition product (B-2) 14.1 parts obtained in Production Example 1 were simultaneously put into a minced machine used in the gel cutting step, and the mixture was mixed and finely mixed with the minced machine. I refused. Further, while mixing and cutting, 115.58 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed to obtain hydrogel particles. The obtained hydrogel particles were dried with an aeration type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. Next, 5.00 parts of a 2% water / methanol mixed solution (water / methanol weight ratio = 70/30) of ethylene glycol diglycidyl ether was added to the dried product, and 12 water of sodium aluminum sulfate as the polyvalent metal salt (e). 1.2 parts of Japanese product was mixed while spraying and allowed to stand at 150 ° C. for 30 minutes for surface cross-linking to obtain water-absorbent resin particles (P-8).

<Example 9>
In Example 2, the same operation is performed except that 5.00 parts of a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30) is changed to 2.00 parts. Was carried out to obtain water-absorbent resin particles (P-9).

<Example 10>
In Example 2, the same operation is performed except that 5.00 parts of a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30) is changed to 7.50 parts. Was carried out to obtain water-absorbent resin particles (P-10).

<Example 11>
In Example 2, the same operation was performed except that 42.7 parts of the decomposition product (B-9) was used instead of 42.7 parts of the decomposition product (B-2), and the water-absorbent resin particles (P-11) were used. Got

<Example 12>
In Example 2, the same operation was performed except that 42.7 parts of the decomposition product (B-8) was used instead of 42.7 parts of the decomposition product (B-2), and the water-absorbent resin particles (P-12) were used. Got

<Comparative Example 1>
The water-absorbent resin particles (Q-1) obtained in Production Example 1 and the decomposition product (B-2) obtained in Production Example 3 were mixed in a weight ratio of 90/10 with Unipack (manufactured by Nippon Co., Ltd., L-). (4 sizes), and this unipack was shaken up and down by hand to sufficiently mix (Q-1) and (B-2) to obtain water-absorbent resin particles (H-1).

<Comparative Example 2>
The water-absorbent resin particles (Q-1) obtained in Production Example 1 and the decomposition product (B-5) obtained in Production Example 6 are mixed in a weight ratio of 90/10 to Unipack (L- manufactured by Nippon Seisakusho Co., Ltd.). (4 sizes), and this unipack was shaken up and down by hand to sufficiently mix (Q-1) and (B-2) to obtain water-absorbent resin particles (H-2).

<Comparative Example 3>
In Example 6, the same operation was carried out except that 10 parts of the decomposed product (B-6) was used instead of 10 parts of the decomposed product (B-1) to obtain water-absorbent resin particles (H-3).

<Comparative Example 4>
In Example 6, the same operation was carried out except that 10 parts of the decomposed product (B-7) was used instead of 10 parts of the decomposed product (B-1) to obtain water-absorbent resin particles (H-4).

<Comparative Example 5>
In Example 2, the same operation was carried out except that 10 parts of the decomposed product (B-6) was used instead of 10 parts of the decomposed product (B-2) to obtain water-absorbent resin particles (H-5).

<Comparative Example 6>
In Example 2, the same operation was carried out except that 10 parts of the decomposed product (B-7) was used instead of 10 parts of the decomposed product (B-2) to obtain water-absorbent resin particles (H-6).

Regarding the water-absorbent resins obtained in Examples and Comparative Examples, the amount of water retained in physiological saline, the amount absorbed under load, apparent density, weight average particle size, content of polyvalent metal elements, distribution index of polyvalent metal elements, Demand. The results of the absorption amount under no load measured by the Wetability test are shown in Tables 1 and 2.

As is clear from the results shown in Tables 1 and 2, the water-absorbent resin particles of the present invention obtained the water retention amount, the absorption amount under load, and the absorption amount under no load measured by the Demand Wetability test as comparative examples. It can be seen that it is superior to the water-absorbent resin particles. Further, according to the production method of the present invention, the required water absorption rate can be set in an appropriate range, so that the required absorption performance can be exhibited even when the absorber is used. From this result, by using the production method of the present invention, the decomposition product of the water-absorbent resin particles, which is the waste of the water-absorbent resin particles, can be reused as a raw material, and the obtained water-absorbent resin particles are good. It can be seen that it exhibits absorption characteristics. Therefore, the manufacturing method of the present invention can be said to be an excellent manufacturing method from the viewpoint of resource saving and reduction of environmental load.

The method for producing water-absorbent resin particles of the present invention includes paper diapers (children's disposable diapers, adult disposable diapers, etc.), napkins (physiological napkins, etc.), paper towels, pads (pads for incontinence and surgical underpads, etc.) and pets. It can be suitably used for recycling waste of water-absorbent resin particles discharged when reusing sanitary products such as sheets (pet urine absorbing sheets).

Claims

A polymerization step (I) of polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and a cross-linking agent (b) to obtain a water-containing gel containing the cross-linking polymer (A).
In the gel shredding step (II) of shredding the water-containing gel to obtain water-containing gel particles,
A drying step (III) of drying the hydrogel particles obtained in the gel cutting step (II), and a drying step (III).
A method for producing water-absorbent resin particles, which comprises a pulverization classification step (IV) for pulverizing and classifying a dried product that has undergone the drying step (III).
Water absorption obtained from sanitary products in at least one step selected from the group consisting of the polymerization step (I), the gel shredding step (II), the drying step (III) and the pulverization classification step (IV). A method for producing water-absorbent resin particles by adding the decomposition product (B) of the sex resin particles, wherein the water-soluble content of the decomposition product (B) is 1.0 to 30.0% by weight. How to make particles.
The method for producing water-absorbent resin particles according to claim 1, wherein the decomposition product (B) is added in the polymerization step (I) and / or the gel shredding step (II).
The method for producing water-absorbent resin particles according to claim 1 or 2, wherein the decomposition product (B) is added in an amount of 1 to 50% by weight based on the total weight of the monomer composition in the polymerization step (I).
The decomposition product (B) is a decomposition product obtained by dehydrating the decomposition product (Z) before the dehydration treatment by adding 0.01 to 10% by weight of the dehydrating agent (a) to the weight of the decomposition product (Z). The method for producing water-absorbent resin particles according to any one of claims 1 to 3.
The water-absorbent resin particles according to claim 4, wherein the dehydrating agent (a) is at least one water-soluble polyvalent metal compound selected from the group consisting of calcium chloride, calcium oxide, calcium acetate and calcium hypochlorite. Manufacturing method.
The method for producing water-absorbent resin particles according to any one of claims 1 to 5, wherein the decomposition product (B) is a decomposition product obtained from water-absorbent resin particles contained in used sanitary goods.