Coated resin particles and production method therefor

Abstract

One aspect of the present invention relates to coated resin particles which comprise water-absorbing resin particles and covering parts that cover at least some of the water-absorbing resin particles, wherein the covering parts are made of a coating material which has a breaking energy of 0.2 J / mm3 or greater, the breaking energy being obtained from a stress-strain curve determined by a tensile test conducted at a pulling speed of 200 mm / min, and which has a water absorption for physiological saline, as measured in accordance with JIS P 8140 under the conditions of a temperature of 25°C and a contact time of 120 seconds, exceeding 0 g / m2 but not exceeding 300 g / m2.

Description

Coated resin particles and method for producing same

[0001] The present invention relates to coated resin particles, a method for producing the same, and the like.

[0002] Water-absorbent resin particles are widely used in various fields, such as sanitary materials such as disposable diapers, sanitary products, and portable toilets; agricultural and horticultural materials such as water retention agents and soil conditioners; and industrial materials such as waterproofing agents and anti-condensation agents. The water-absorbent resin particles are required to have high performance such as a high water absorption capacity and gel strength, as well as control of the water absorption rate (see, for example, Patent Document 1 listed below).

[0003] JP 2016-28117 A

[0004] Upon contact with a liquid to be absorbed (aqueous liquid containing water), water-absorbent resin particles begin absorbing water immediately and reach a swollen state (a state in which they can no longer absorb any more water) in a short time. Therefore, water-absorbent resin particles may not be effectively utilized in fields where it is required that they begin absorbing water after a certain time has passed since contact with the liquid, or that they do not immediately absorb a large amount of liquid. For example, in sanitary materials such as disposable diapers, sanitary products, and portable toilets, when a liquid to be absorbed comes into contact with an absorbent core containing water-absorbent resin particles, the absorbent core may immediately begin absorbing a large amount of liquid, resulting in gel blocking (a phenomenon in which voids existing between water-absorbent resin particles are filled with water-absorbent resin particles that have become gel-like due to water absorption, thereby worsening the permeability of the liquid), and the liquid may not be sufficiently diffused within the absorbent core. In this case, liquid may pool at the point of contact with the liquid, and the sanitary material may be discarded with a large number of water-absorbent resin particles that have not sufficiently absorbed water present in areas other than the point of contact with the liquid. Therefore, if the water-absorption behavior of the water-absorbent resin particles can be adjusted, the occurrence of gel blocking may be suppressed. In this case, the liquid is sufficiently dispersed within the absorbent body, and the water-absorbent resin particles can be effectively utilized.

[0005] An object of one aspect of the present invention is to provide coated resin particles capable of delaying water absorption.An object of another aspect of the present invention is to provide a method for producing coated resin particles capable of delaying water absorption.

[0006] In some aspects, the present invention relates to the following [1] to [7], etc. [1] A water-absorbent resin composition comprising water-absorbent resin particles and a coating portion that coats at least a part of the water-absorbent resin particles, wherein a breaking energy calculated from a stress-strain curve in a tensile test at a tensile speed of 200 mm / min is 0.2 J / mm ３ or more, and the water absorbency of physiological saline measured in accordance with JIS P 8140 at a temperature of 25°C and a contact time of 120 seconds is 0 g / m ２ More than 300 g / m ２ [2] The coated resin particles according to [1], wherein the content of the coating portion is 0.50 to 20.00 parts by mass relative to 100 parts by mass of the water-absorbing resin particles. [3] The breaking energy is 80 J / mm ３ or more, and the water absorbency is 5 to 300 g / m ２ [4] The coated resin particles according to [1] or [2], wherein the breaking energy is 250 to 400 J / mm ３ and the water absorbency is 25 to 100 g / m ２ [5] The coated resin particle according to any one of [1] to [4], wherein the coating material comprises a copolymer of an olefin and an ethylenically unsaturated monomer. [6] The coated resin particle according to any one of [1] to [5], wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer. [7] A coated resin particle according to any one of [1] to [5], wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer. [8] A coated resin particle according to any one of [1] to [5], wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer. [9] A coated resin particle according to any one of [1] to [5], wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer.

[10] A coated resin particle according to any one of [1] to [5], wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer.

[11] A coated resin particle according to any one of [1] to

[12] , wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer.

[12] A coated resin particle according to any one of [1] to

[13] , wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer.

[13] A coated resin particle according to any one of [1] to

[14] , wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer.

[14] A coated resin particle according to any one of [1] to

[15] , wherein the coating material comprises a copolymer of a styrene and an ethylenically unsaturated monomer. ２ wherein the ratio Er / σ of the product Er of the Young's modulus E [MPa] of the coating material, obtained from a stress-strain curve in a tensile test at a tensile speed of 200 mm / min, to the median particle diameter r [nm] of the coating material, is greater than 0 and not greater than 40.00.

[0007] According to one aspect of the present invention, there is provided coated resin particles capable of delaying water absorption. According to another aspect of the present invention, there is provided a method for producing coated resin particles capable of delaying water absorption.

[0008] 1 is a schematic cross-sectional view showing a treatment device for bringing water-absorbent resin particles and a coating material into contact with each other.

[0009] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

[0010] As used herein, "(meth)acrylic" refers to at least one of acrylic and its corresponding methacrylic. The same applies to other similar expressions such as "(meth)acrylate." "(Poly)" refers to both cases with and without the "poly" prefix. A numerical range of "A or greater" refers to a range exceeding A and A. A numerical range of "A or less" refers to a range of A and less than A. In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of a numerical range of another stage. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with the value shown in the experimental examples. The materials exemplified in this specification may be used alone or in combination of two or more. "A or B" may include either A or B, or may include both. When multiple substances corresponding to each component are present in a composition, the content of each component refers to the total amount of those multiple substances present in the composition unless otherwise specified. "Room temperature" means 25°C ± 2°C. "Sieve" refers to a test sieve (metal mesh sieve) as specified in JIS Z 8801-1:2019. The term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended function of the process is achieved. "Physiological saline" means a 0.9% by mass aqueous sodium chloride solution. The phrase "A contains B" includes all forms in which A contains B, and also forms in which A contains only B (i.e., forms in which A consists only of B) as well as forms in which B constitutes only a part of A.

[0011] The coated resin particles according to this embodiment have water-absorbent resin particles and a coating portion that coats at least a part of the water-absorbent resin particles. In the coated resin particles according to this embodiment, the coating material that constitutes the coating portion has a fracture energy of 0.2 J / mm2 calculated from a stress-strain curve in a tensile test at a tensile speed of 200 mm / min. ３ or more, and the water absorbency of physiological saline measured in accordance with JIS P 8140 at a temperature of 25°C and a contact time of 120 seconds is 0 g / m ２More than 300 g / m ２ The following is the result.

[0012] The method for producing coated resin particles according to the present embodiment includes a coating step of bringing water-absorbent resin particles and a coating material into contact with each other to obtain coated resin particles having a coating portion that coats at least a part of the water-absorbent resin particles. In the method for producing coated resin particles according to the present embodiment, the surface free energy σ [mJ / m ２ The ratio Er / σ of the product Er of the Young's modulus E [MPa] of the coating material, obtained from a stress-strain curve in a tensile test at a tensile speed of 200 mm / min, and the median particle diameter r [nm] of the coating material, is greater than 0 and not more than 40.00. The coated resin particles according to this embodiment may be obtained by the method for producing coated resin particles according to this embodiment, or may be obtained by another production method.

[0013] The coated resin particles according to this embodiment can delay the water absorption of the coated resin particles. The method for producing coated resin particles according to this embodiment can produce coated resin particles capable of delaying water absorption. The coated resin particles and the method for producing the same according to this embodiment can increase the speed adjustment parameter, which is the product of the water absorption delay rate R1 calculated based on the lock-up height, which indicates the degree of effect of preventing contact between the water-absorbent resin particles in the coating portion and an aqueous liquid, and the water absorption delay rate R2 calculated based on the water absorption rate (Vortex method), which indicates the degree of suppression of swelling of the water-absorbent resin particles in the coating portion. This speed adjustment parameter makes it possible to evaluate both the suppression effect up to water absorption and the suppression effect after the start of water absorption, thereby enabling the evaluation of the overall effect of water absorption delay. The coated resin particles and the method for producing the same according to this embodiment can obtain the speed adjustment parameter, for example, 1 or more, 10 or more, 50 or more, 100 or more, 500 or more, 1000 or more, etc., in the evaluation described in the Examples below. The upper limit of the speed adjustment parameter is not particularly limited, but may be, for example, 10,000 or less, 5,000 or less, or the like.

[0014] The reason why the coated resin particles according to this embodiment can delay water absorption is presumed to be as follows. However, the reason is not limited to the following. If the fracture energy of the coating material is too low, the expansion of the water-absorbent resin particles due to water absorption cannot be sufficiently suppressed, and cracks or micropores are likely to form on the surface of the coating portion. As a result, water is more likely to come into contact with the water-absorbent resin particles through the cracks or micropores, which may make it difficult to achieve the water absorption delay effect. In contrast, if the fracture energy of the coating material is within the above-mentioned range, even if the water-absorbent resin particles expand to a certain extent, cracks or micropores are less likely to form in the coating portion, and as a result, water absorption is more likely to be sufficiently delayed. Furthermore, if the water absorbency of the coating material is within the above-mentioned range, water is prevented from penetrating the coating portion and causing the water-absorbent resin particles to start absorbing water, thereby making it easier to sufficiently delay water absorption. These effects enable the coated resin particles according to this embodiment to delay water absorption.

[0015] In the method for producing coated resin particles according to the present embodiment, since the ratio Er / σ is in the above-mentioned range, the formation of the coating portion is easy, and coated resin particles capable of delaying water absorption can be obtained. However, the reason for obtaining such coated resin particles is not limited to the above.

[0016] Usually, in order to delay the water absorption of coated resin particles, it is necessary to increase the amount of coating material used in the coating process. However, using a large amount of coating material may deteriorate productivity due to an increase in coating time, etc. On the other hand, according to one aspect of the coated resin particles and the method for producing the same according to the present embodiment, even if the coating portion is made thin, defects are unlikely to occur, so that the water absorption of coated resin particles can be sufficiently delayed without increasing the amount of coating material used.

[0017] The coated resin particles according to this embodiment can be used, for example, by mixing them with water-absorbent resin particles that do not have a coating portion. By using a mixture (mixed particles) of coated resin particles and water-absorbent resin particles that do not have a coating portion in an absorbent body of a sanitary material (such as disposable diapers, sanitary products, and portable toilets), gel blocking is likely to occur when the absorbent body comes into contact with a liquid to be absorbed. Specifically, when the mixed particles come into contact with a liquid, the water-absorbent resin particles that do not have a coating portion gel upon absorption, but because the absorption of the coated resin particles is suppressed (i.e., the coated resin particles do not gel immediately), the voids between the particles are not filled for a predetermined time, thereby ensuring liquid permeability. This allows for sufficient diffusion of liquid within the absorbent body, facilitating effective use of the water-absorbent resin particles throughout the absorbent body. The time during which gel blocking can be suppressed can be adjusted by appropriately changing the type or amount of the constituent material of the coating portion; the type of water-absorbent resin particles that constitute the coated resin particles; the type of water-absorbent resin particles that do not have a coating portion; the mixing ratio of the coated resin particles and the water-absorbent resin particles that do not have a coating portion, etc.

[0018] The water-absorbent resin particles constituting the coated resin particles may be polymer particles. The polymer particles may have an ethylenically unsaturated monomer (a compound having an ethylenically unsaturated bond) as a monomer unit (a monomer unit derived from an ethylenically unsaturated monomer), or may have only an ethylenically unsaturated monomer as a monomer unit. The polymer particles may be polymer particles having a crosslinked structure (crosslinked polymer particles). The method for producing coated resin particles according to this embodiment may include a polymerization step of obtaining water-absorbent resin particles by polymerizing an ethylenically unsaturated monomer before the coating step. Examples of polymerization methods for the ethylenically unsaturated monomer to obtain polymer particles include reverse-phase suspension polymerization, aqueous solution polymerization, bulk polymerization, and precipitation polymerization.

[0019] The ethylenically unsaturated monomer is a compound having at least one carbon-carbon double bond in the molecule and having radical polymerizability, preferably a compound having one carbon-carbon double bond in the molecule and having radical polymerizability. The ethylenically unsaturated monomer may be a water-soluble ethylenically unsaturated monomer (an ethylenically unsaturated monomer having a solubility of 1.0 g or more in 100 g of ion-exchanged water at 25°C). The solubility of the water-soluble ethylenically unsaturated monomer in 100 g of ion-exchanged water at 25°C may be 5.0 g or more, 10 g or more, 50 g or more, or 100 g or more. Examples of the ethylenically unsaturated monomer include (meth)acrylic acid and salts thereof, 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more.

[0020] When the ethylenically unsaturated monomer has an acidic group (e.g., a carboxy group), the acidic group may be neutralized with an alkaline neutralizing agent before being used in the polymerization reaction. The degree of neutralization of the ethylenically unsaturated monomer (neutralization degree with the alkaline neutralizing agent) may be 10 to 100 mol %, 50 to 90 mol %, or 60 to 80 mol % of the acidic group in the ethylenically unsaturated monomer.

[0021] From the viewpoint of industrial availability, the ethylenically unsaturated monomer may include at least one compound selected from the group consisting of (meth)acrylic acid, (meth)acrylates, (meth)acrylamide, and N,N-dimethylacrylamide, or may include at least one compound selected from the group consisting of (meth)acrylic acid, (meth)acrylates, and (meth)acrylamide.

[0022] Monomers other than the above-mentioned ethylenically unsaturated monomers may be used as monomers for obtaining water-absorbent resin particles. Such monomers can be used, for example, by mixing them with an aqueous solution containing the ethylenically unsaturated monomer. The proportion of the amount of the ethylenically unsaturated monomer used may be 70 to 100 mol%, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or 99.5 to 100 mol% relative to the total amount of monomers (total amount of monomers for obtaining water-absorbent resin particles). The proportion of the total amount of (meth)acrylic acid and (meth)acrylate salts may be 70 to 100 mol%, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or 99.5 to 100 mol% relative to the total amount of monomers (total amount of monomers for obtaining water-absorbent resin particles).

[0023] The water-absorbent resin particles may be crosslinked polymer particles. Crosslinking may occur due to self-crosslinking during polymerization, but crosslinking may be promoted by using an internal crosslinking agent. The use of an internal crosslinking agent makes it easy to control the water absorption properties (water retention capacity, etc.) of the water-absorbent resin particles. The polymerization step may be a step of obtaining water-absorbent resin particles by polymerizing an ethylenically unsaturated monomer in the presence of an internal crosslinking agent.

[0024] Examples of the internal crosslinking agent include compounds having two or more reactive functional groups (for example, polymerizable unsaturated groups). Examples of the internal crosslinking agent include di- or tri(meth)acrylic acid esters of polyols (polyethylene glycol di(meth)acrylate, etc.), unsaturated polyesters obtained by reacting polyols with unsaturated acids, glycidyl group-containing compounds ((poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, etc.), bisacrylamides, di- or tri(meth)acrylic acid esters obtained by reacting polyepoxides with (meth)acrylic acid, and hydroxy groups of polyisocyanates and (meth)acrylic acid.

[0123] Examples of the internal crosslinking agent include di(meth)acrylic acid carbamyl esters obtained by reacting di(meth)acrylic acid with diethyl, allylated starch, allylated cellulose, diallyl phthalate, N,N',N"-triallyl isocyanurate, divinylbenzene, pentaerythritol, ethylenediamine, polyethyleneimine, and the like. From the viewpoint of easily adjusting the water absorption properties of the water absorbent resin particles, the internal crosslinking agent may contain at least one selected from the group consisting of (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin diglycidyl ether.

[0025] The amount of the internal crosslinking agent can be appropriately adjusted in order to adjust the water absorption properties of the water absorbent resin particles, and may be, for example, within the following ranges relative to 1 mole of the ethylenically unsaturated monomer (for example, 1 mole of (meth)acrylic acid and a salt thereof in total). The amount of the internal crosslinking agent may be 0.001 mmol or more, 0.005 mmol or more, 0.010 mmol or more, 0.015 mmol or more, 0.020 mmol or more, 0.025 mmol or more, 0.030 mmol or more, 0.035 mmol or more, 0.040 mmol or more, 0.045 mmol or more, or 0.050 mmol or more. The amount of internal crosslinker may be 0.300 mmol or less, 0.200 mmol or less, 0.100 mmol or less, 0.090 mmol or less, 0.080 mmol or less, 0.070 mmol or less, 0.060 mmol or less, 0.055 mmol or less, 0.050 mmol or less, 0.045 mmol or less, or 0.040 mmol or less. From these viewpoints, the amount of the internal crosslinking agent may be 0.001 to 0.300 mmol, 0.001 to 0.100 mmol, 0.001 to 0.080 mmol, 0.001 to 0.045 mmol, 0.030 to 0.300 mmol, 0.030 to 0.100 mmol, 0.030 to 0.080 mmol, 0.030 to 0.045 mmol, 0.045 to 0.300 mmol, 0.045 to 0.100 mmol, or 0.045 to 0.080 mmol.

[0026] In the water-absorbent resin particles, the crosslink density in the vicinity of the surface of the polymer particle may be increased (surface crosslinking may be performed). The water absorption properties (water retention capacity, etc.) of the water-absorbent resin particles can be easily adjusted by surface crosslinking. Specifically, the water absorption properties can be adjusted by adjusting the crosslink density in the vicinity of the surface of the polymer particle depending on the moisture content of the polymer particle subjected to surface crosslinking, the type or amount of the surface crosslinking agent used in surface crosslinking, etc.

[0027] The water-absorbent resin particles may contain components such as gel stabilizers, metal chelating agents, flow improvers (lubricants), etc. These components may be located inside the water-absorbent resin particles, on the surface of the water-absorbent resin particles, or both.

[0028] The shape of the water-absorbent resin particles or coated resin particles may be, for example, substantially spherical, crushed, or granular, or may be a shape formed by aggregation of primary particles having these shapes. The particle diameter (median particle diameter determined by the measurement method described in Patent Document 1) of the water-absorbent resin particles or coated resin particles may be 100 to 800 μm, 150 to 700 μm, 200 to 600 μm, 250 to 500 μm, 300 to 400 μm, or 250 to 850 μm.

[0029] The coating portion of the coated resin particle coats at least a part (part or all) of the water-absorbent resin particle, and can coat at least a part (part or all) of the surface of the water-absorbent resin particle. The coating portion may be a layered coating layer. The coating layer may have a single-layer structure or a multi-layer structure having two or more layers. When the coating portion is composed of two or more coating layers, it is sufficient that the coating material constituting the coating layer in at least one layer satisfies the conditions such as various physical properties described below.

[0030] The coating portion can be obtained by contacting a coating material with the water-absorbent resin particles. The coating material may contain a polymer component. The coating material may be water-soluble, water-insoluble, or poorly water-soluble. The coating material may contain a water-soluble component or a poorly water-soluble component. "Water-soluble" means a solubility of 1 g or more (e.g., 1 to 150 g) in 100 g of ion-exchanged water at 25°C. "Poorly water-soluble" means a solubility of more than 0 g but less than 1 g in 100 g of ion-exchanged water at 25°C.

[0031] The water-soluble component may contain a compound having a hydrophilic group. Examples of the hydrophilic group include an anionic group, a cationic group, an amphoteric group, and a nonionic group. Examples of the anionic group include a carboxyl group, a sulfonic acid group, and a phosphate group. Examples of the cationic group include an amino group, an imino group, and a quaternary ammonium group. Examples of the amphoteric group include a carbobetaine group, a sulfobetaine group, and a phosphobetaine group. Examples of the nonionic group include a hydroxyl group, an amide group, a pyrrolidone group, a lactam group, an alkoxy group, and a (poly)oxyalkylene group.

[0032] The water-soluble component may contain at least one selected from the group consisting of compounds having a hydroxyl group, compounds having an amide group, compounds having a quaternary ammonium group, and compounds having a (poly)oxyalkylene group. Examples of compounds having a hydroxyl group include polyvinyl alcohol, monosaccharides, polysaccharides, phenyl diglycol, etc. Examples of compounds having an amide group include polyacrylamide, polyvinylpyrrolidone, etc. Examples of compounds having a quaternary ammonium group include ammonium chloride, etc. Examples of compounds having a (poly)oxyalkylene group include polyalkylene oxides (e.g., polyethylene oxide), polyalkylene glycols (e.g., polyethylene glycol), etc.

[0033] Examples of poorly water-soluble components include polyoxyalkylene alkyl ethers such as polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, and polyoxyethylene stearyl ether; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate; polyamides such as nylon (e.g., nylon 6 and nylon 66); polyolefins such as polyurethane, polyethylene, polypropylene, polyisoprene, ethylene / butene copolymer, and ethylene / propylene copolymer; poly-α-methylstyrene, and syndiotactic polystyrene. Examples of the poorly water-soluble component include polystyrenes such as polyhexamethylene carbonate; polycarbonates such as polyhexamethylene carbonate; poly(meth)acrylates such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; poly(alkyl(meth)acrylates) such as polymethyl(meth)acrylate; polyacetals such as polyoxymethylene, polyacetaldehyde, polypropionaldehyde, and polybutyraldehyde; halogenated vinyl polymers such as polyvinyl chloride, polyvinyl acetate, and polyvinyl fluoride; polyvinylidene fluoride; and polysiloxanes. The poorly water-soluble component may be acid-modified. The poorly water-soluble component may be acid-modified with, for example, an acid anhydride (maleic anhydride, succinic anhydride, phthalic anhydride, etc.).

[0034] The coating material may contain a polymer having an ethylenically unsaturated monomer as a monomer unit (a polymer having a monomer unit derived from an ethylenically unsaturated monomer). The ethylenically unsaturated monomer is a compound having at least one carbon-carbon double bond in the molecule and having radical polymerizability, and preferably a compound having one carbon-carbon double bond in the molecule and having radical polymerizability. Examples of the ethylenically unsaturated monomer include (meth)acrylic acid and salts thereof, (meth)acrylic acid esters (methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, 2-(diethylamino)propyl (meth)acrylate, etc.), (meth)acrylamide-based monomers ((meth)acrylamide, N-isopropyl(meth)acrylamide, 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, diethylaminopropyl(meth)acrylamide, etc.), polyethylene glycol mono(meth)acrylate, styrene, α-alkylstyrene, and butadiene. From the viewpoint of easily delaying the water absorption of the coated resin particles, the ethylenically unsaturated monomer may contain a (meth)acrylic compound (a compound having a (meth)acryloyl group), may contain at least one selected from the group consisting of (meth)acrylic acid and salts thereof, may contain styrene, may contain a (meth)acrylic compound and styrene, or may contain at least one selected from the group consisting of (meth)acrylic acid and salts thereof and styrene.

[0035] Examples of coating materials that can be used include chain polymerization products such as poly(meth)acrylic acid, poly(meth)acrylamide, polyvinyl alcohol, polyalkylene oxide, and polyalkylene glycol; and step-growth polymerization products such as urethane resins (e.g., condensates of polyol and polyisocyanate), phenolic resins (e.g., condensates of phenolic compounds and aldehydes), polyesters, polyamides, and polycarbonates.

[0036] From the viewpoint of easily delaying the water absorption of the coated resin particles, the coating material may be selected from polyvinyl alcohol, polyacrylamide, polyalkylene oxide, polyalkylene glycol, phenyl diglycol, polyoxyalkylene alkyl ether, poly(alkyl meth)acrylate, polyamide, polyolefin, olefin / ethylenically unsaturated monomer copolymer (copolymer having olefin and ethylenically unsaturated monomer as monomer units), styrene / ethylenically unsaturated monomer copolymer (copolymer having styrene and ethylenically unsaturated monomer as monomer units), and siloxane compound (siloxane bond). the copolymer may comprise at least one selected from the group consisting of a copolymer of an olefin / ethylenically unsaturated monomer, a copolymer of a styrene / ethylenically unsaturated monomer, and a copolymer of a siloxane compound / ethylenically unsaturated monomer; the copolymer may comprise at least one selected from the group consisting of a copolymer of an olefin / ethylenically unsaturated monomer, a copolymer of a styrene / ethylenically unsaturated monomer, and a copolymer of a siloxane compound / ethylenically unsaturated monomer; the copolymer may comprise an olefin / ethylenically unsaturated monomer, or a copolymer of a styrene / ethylenically unsaturated monomer. From the viewpoint of easily delaying the water absorption of the coated resin particles, the polymer component contained in the coating material may be composed of only at least one selected from the group consisting of polyvinyl alcohol, polyacrylamide, polyalkylene oxide, polyalkylene glycol, phenyl diglycol, polyoxyalkylene alkyl ether, polyalkyl(meth)acrylate, polyamide, polyolefin, olefin / ethylenically unsaturated monomer copolymer, styrene / ethylenically unsaturated monomer copolymer, and siloxane compound / ethylenically unsaturated monomer copolymer, or may be composed of only at least one selected from the group consisting of polyalkylene glycol, phenyl diglycol, polyamide, olefin / ethylenically unsaturated monomer copolymer, styrene / ethylenically unsaturated monomer copolymer, and siloxane compound / ethylenically unsaturated monomer copolymer, or may be composed of only an olefin / ethylenically unsaturated monomer copolymer, or may be composed of only a styrene / ethylenically unsaturated monomer copolymer.The coating material may contain an olefin / ethylenically unsaturated monomer copolymer and a polyalkylene glycol, or may contain an olefin / ethylenically unsaturated monomer copolymer and polyethylene glycol, from the viewpoint of easily delaying water absorption by the coated resin particles. The polymer component contained in the coating material may be composed solely of an olefin / ethylenically unsaturated monomer copolymer and a polyalkylene glycol, or may be composed solely of an olefin / ethylenically unsaturated monomer copolymer and polyethylene glycol, from the viewpoint of easily delaying water absorption by the coated resin particles. The ethylenically unsaturated monomer in the olefin / ethylenically unsaturated monomer copolymer, styrene / ethylenically unsaturated monomer copolymer, or siloxane compound / ethylenically unsaturated monomer copolymer may contain a (meth)acrylic compound, may contain at least one selected from the group consisting of (meth)acrylic acid and salts thereof, or may contain butadiene, from the viewpoint of easily delaying water absorption by the coated resin particles.

[0037] When the ethylenically unsaturated monomer constituting the polymer component contained in the coating material has an acidic group (e.g., a carboxy group), the acidic group may be neutralized with an alkaline neutralizing agent. In this case, the degree of neutralization of the ethylenically unsaturated monomer may be greater than 0 mol% to 100 mol%, 5 to 100 mol%, 10 to 100 mol%, 20 to 100 mol%, 30 to 100 mol%, 40 to 100 mol%, or 50 to 100 mol% of the acidic groups in the ethylenically unsaturated monomer. Increasing the degree of neutralization facilitates stabilization of the coating liquid (e.g., emulsion) described below, making it easier to obtain uniformly coated resin particles. From this perspective, the degree of neutralization of the ethylenically unsaturated monomer may be 10 to 100 mol%, 20 to 100 mol%, 30 to 100 mol%, 40 to 100 mol%, or 50 to 100 mol%. Examples of the ethylenically unsaturated monomers whose acidic groups have been neutralized in this way include sodium acrylate, ammonium acrylate, etc., with a degree of neutralization of 5 to 100 mol %.

[0038] The olefin, which is a monomer unit of a polyolefin, or the olefin, which is a monomer unit of an olefin / ethylenically unsaturated monomer copolymer, may contain at least one selected from the group consisting of ethylene, propylene, and butene, and may contain ethylene, from the viewpoint of easily delaying the water absorption of the coated resin particles. The ethylenically unsaturated monomer in the olefin / ethylenically unsaturated monomer copolymer may contain the ethylenically unsaturated monomer listed as a constituent material of the water-absorbent resin particles described above, may contain a (meth)acrylic compound, or may contain at least one selected from the group consisting of (meth)acrylic acid and its salts, from the viewpoint of easily delaying the water absorption of the coated resin particles. In the olefin / ethylenically unsaturated monomer copolymer, increasing the proportion of the ethylenically unsaturated monomer, which tends to be more hydrophilic than the olefin, tends to increase the water absorbency. Furthermore, increasing the proportion of the ethylenically unsaturated monomer tends to increase the breaking energy.

[0039] In an olefin / ethylenically unsaturated monomer copolymer, the water absorption behavior of the coated resin particles can be easily adjusted by adjusting the ratio of olefin monomer units (monomer units derived from an olefin) to ethylenically unsaturated monomer units (monomer units derived from an ethylenically unsaturated monomer). That is, by increasing the ratio of highly hydrophobic monomer units, the water absorption of the coated resin particles can be adjusted to be slower. For example, in an olefin / ethylenically unsaturated monomer copolymer, the ratio of olefin monomer units may be 72.0 to 98.0 mol% or 80.0 to 97.0 mol%.

[0040] The coating material may be used alone or in combination of two or more. The main component of the coating material is the component used in the largest amount (mass) of the coating material. When a single coating material is used, the single coating material is the main component of the coating material. When two or more coating materials are used in combination, the component used in the largest amount of the multiple coating materials is the main component of the coating material. From the viewpoint of easily delaying water absorption of the coated resin particles, the main component of the coating material may be at least one selected from the group consisting of an olefin / ethylenically unsaturated monomer copolymer (e.g., an ethylene / ethylenically unsaturated monomer copolymer), a styrene / ethylenically unsaturated monomer copolymer, and a siloxane compound / ethylenically unsaturated monomer copolymer, or may be an ethylene / ethylenically unsaturated monomer copolymer. The ethylenically unsaturated monomer in at least one selected from the group consisting of an olefin / ethylenically unsaturated monomer copolymer, a styrene / ethylenically unsaturated monomer copolymer, and a siloxane compound / ethylenically unsaturated monomer copolymer may contain a (meth)acrylic compound, may contain at least one selected from the group consisting of (meth)acrylic acid and its salts, and may contain butadiene, from the viewpoint of easily delaying the water absorption of the coated resin particles. When two or more main coating materials are present (when the amounts (mass) of the two or more coating materials used are the same and each of them is used in the largest amount), it is sufficient that at least one of the two or more main components is the above-mentioned coating material.

[0041] The proportion of the main component of the coating material may be in the following ranges based on the total mass of the coating material. From the viewpoint of easily delaying the water absorption of the coated resin particles, the proportion of the main component of the coating material may be 50% by mass or more, more than 50% by mass, 60% by mass or more, 70% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 91% by mass or more, 92% by mass or more, 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, or 99% by mass or more. From the viewpoint of easily adjusting the water absorption behavior of the coated resin particles, the proportion of the main component of the coating material may be 100% by mass or less, less than 100% by mass, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass or less, 95% by mass or less, 92% by mass or less, 91% by mass or less, or 90% by mass or less. From these viewpoints, the proportion of the main component in the coating material may be 50 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, or 90 to 100 mass%. When two or more main coating materials are present (when the amounts (mass) of two or more coating materials used are the same and each of them is used in the largest amount), the content of the main component in the coating material is the total amount of those two or more coating materials.

[0042] The content of the coating portion in the coated resin particles according to the present embodiment, the proportion of the coating material in the coating step, or the proportion of the main component of the coating material in the coating step (when two or more types of main component coating materials are present, the proportion of the total amount) may be within the following ranges relative to 100 parts by mass of the water-absorbent resin particles. From the viewpoint of easily delaying the water absorption of the coated resin particles, the content of the coating portion, the proportion of the coating material, or the proportion of the main component of the coating material may be 0.10 parts by mass or more, 0.50 parts by mass or more, 1.00 parts by mass or more, or 2.00 parts by mass or more. From the viewpoint of easily adjusting the water absorption behavior of the coated resin particles, the content of the coating portion, the proportion of the coating material, or the proportion of the main component of the coating material may be 3.00 parts by mass or more, 4.00 parts by mass or more, 5.00 parts by mass or more, 6.00 parts by mass or more, 7.00 parts by mass or more, 7.50 parts by mass or more, 8.00 parts by mass or more, 9.00 parts by mass or more, 10.00 parts by mass or more, 11.00 parts by mass or more, or 12.00 parts by mass or more. From the viewpoint of improving productivity, such as shortening the coating time, the content of the coating portion, the proportion of the coating material, or the proportion of the main component of the coating material may be 50.00 parts by mass or less, 40.00 parts by mass or less, 30.00 parts by mass or less, 25.00 parts by mass or less, 20.00 parts by mass or less, 18.00 parts by mass or less, 15.00 parts by mass or less, 12.00 parts by mass or less, 11.00 parts by mass or less, 10.00 parts by mass or less, less than 10.00 parts by mass, 9.00 parts by mass or less, 8.00 parts by mass or less, 7.50 parts by mass or less, 7.00 parts by mass or less, 6.00 parts by mass or less, or 5.00 parts by mass or less. From these viewpoints, the content of the coating portion, the proportion of the coating material, or the proportion of the main component of the coating material is preferably 0.10 to 50.00 parts by mass, 0.10 to 20.00 parts by mass, 0.10 to 15.00 parts by mass, 0.10 to 10.00 parts by mass, 0.50 to 50.00 parts by mass, 0.50 to 20.00 parts by mass, 0.50 to 10.00 parts by mass, 1.00 to 50.00 parts by mass. 00 parts by mass, 1.00 to 20.00 parts by mass, 1.00 to 15.00 parts by mass, 1.00 to 10.00 parts by mass, 1.00 to 9.00 parts by mass, 3.00 to 50.00 parts by mass, 3.00 to 20.00 parts by mass, 3.00 to 10.00 parts by mass, 5.00 to 50.00 parts by mass, 5.00 to 20.00 parts by mass, or 5.00 to 10.00 parts by mass.

[0043] In the coating material constituting the coating portion or the coating material that comes into contact with the water-absorbent resin particles in the coating process, the fracture energy (25°C) determined from the stress-strain curve in a tensile test at a tensile speed of 200 mm / min is set to be within the following range (unit: J / mm ３ " may be omitted). The fracture energy may be 0.2 or more, 0.4 or more, 0.5 or more, 1 or more, 5 or more, 10 or more, 20 or more, 30 or more, 40 or more, 50 or more, 80 or more, 90 or more, 100 or more, 150 or more, 200 or more, 250 or more, 300 or more, 330 or more, 340 or more, or 350 or more. The fracture energy may be 3000 or less, 2500 or less, 2000 or less, 1500 or less, 1000 or less, 800 or less, 700 or less, 600 or less, 500 or less, 400 or less, 360 or less, or 350 or less. From these viewpoints, the fracture energy may be 0.2 to 3000, 0.2 to 1000, 0.2 to 700, 0.2 to 400, 10 to 3000, 10 to 1000, 10 to 700, 10 to 400, 100 to 3000, 100 to 1000, 100 to 700, 100 to 400, 250 to 3000, 250 to 1000, 250 to 700, or 250 to 400.

[0044] The fracture energy is obtained by cutting a test piece from a film obtained by forming a coating material using a dumbbell cutter, and then performing a tensile test using the test piece at a tensile speed of 200 mm / min. The fracture energy is calculated as the integral of the stress-strain curve (vertical axis: stress, horizontal axis: strain). When multiple coating materials are used, the fracture energy described above refers to the fracture energy of a film obtained by forming a mixture of all the components of the coating materials that make up the coating portion. However, when the coating portion consists of two or more coating layers, the fracture energy ranges described above refer to the fracture energy of a film obtained by forming a coating material that makes up one layer (when multiple coating materials are used in one layer, a mixture of all the components of the coating materials that make up that layer). In at least one layer, the fracture energy of a film obtained by forming a coating material that makes up the coating layer may fall within the respective fracture energy ranges described above. The fracture energy can be adjusted by the type or usage ratio of the coating material. For example, the fracture energy varies depending on the type of polymer; for the same type of polymer, the higher the molecular weight, the higher the fracture energy.

[0045] In the coating material constituting the coating portion or the coating material that comes into contact with the water-absorbent resin particles in the coating process, the water absorbency of physiological saline measured under the conditions of a temperature of 25°C and a contact time of 120 seconds in accordance with JIS P 8140 is set to be within the following range (unit: g / m) from the viewpoint of easily delaying the water absorption of the coated resin particles. ２" may be omitted). The water absorbency may exceed 0, and from the viewpoint of improving the affinity between the water-absorbent resin particles and the coating material to improve coverage and easily obtaining a sufficient water absorption suppression effect, the water absorbency may be 1 or more, 3 or more, 5 or more, 6 or more, 10 or more, 15 or more, 20 or more, 25 or more, or 30 or more. From the viewpoint of easily obtaining a sufficient function of inhibiting contact between the water-absorbent resin particles and an aqueous liquid and easily obtaining a sufficient water absorption suppression effect, the water absorbency may be 300 or less, 250 or less, 240 or less, 230 or less, 200 or less, 150 or less, 100 or less, 80 or less, 60 or less, 50 or less, 40 or less, 35 or less, 34 or less, 33 or less, 32 or less, or 31 or less. From these viewpoints, the water absorbency may be greater than 0 and less than 300, greater than 0 and less than 100, greater than 0 and less than 40, greater than 0 and less than 33, 5 to 300, 5 to 100, 5 to 40, 5 to 33, 10 to 300, 10 to 100, 10 to 40, 10 to 33, 25 to 300, 25 to 100, 25 to 40, or 25 to 33. The water absorbency is measured by the Cobb method in accordance with JIS P 8140 (1998) using physiological saline as water. When multiple coating materials are used, the above-mentioned water absorbency refers to the water absorbency of a mixture consisting of all components of the coating materials that make up the covering portion. However, when the coating portion consists of two or more coating layers, the above-mentioned water absorbency ranges refer to the water absorbency of the coating material constituting one layer (when multiple coating materials are used in one layer, the mixture of all components of the coating materials constituting that layer), and the water absorbency of the coating material constituting at least one of the coating layers may be within the above-mentioned water absorbency ranges. The water absorbency can be adjusted by the type or ratio of the coating material, and is easily increased by using or increasing the ratio of a more hydrophilic monomer. It can also be adjusted by using a water-soluble polymer (e.g., polyethylene glycol, phenyl diglycol, etc.).

[0046] The above-mentioned breaking energy and water absorbency can be combined arbitrarily. For example, the coated resin particles according to this embodiment have a breaking energy of 80 J / mm ３ or more and the water absorption is 5 to 300 g / m ２and the fracture energy is 250 to 400 J / mm ３ and the water absorption is 25 to 100 g / m ２ The embodiment may be:

[0047] In the coating material constituting the coating portion or the coating material that comes into contact with the water-absorbent resin particles in the coating step, the Young's modulus E (25°C) obtained from the stress-strain curve in a tensile test at a tensile speed of 200 mm / min may be in the following range (the unit "MPa" is omitted) from the viewpoint of easily delaying the water absorption of the coated resin particles. The Young's modulus E is 0.10 × 10 －２ That's it, 0.50 x 10 －２ That's it, 0.10 x 10 －１ That's it, 0.50 x 10 －１ The Young's modulus E may be 5.00 or less, 4.00 or less, 3.00 or less, 2.50 or less, 2.30 or less, 2.00 or less, 1.50 or less, 1.30 or less, 1.20 or less, 1.00 or less, 0.90 or less, or 0.85 or less. From these viewpoints, the Young's modulus E may be 0.10×10 or less, 0.10 or more, 0.30 or more, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, or 0.85 or more. －２ ~5.00, 0.10~5.00, 0.70~5.00, 0.10x10 －２ Up to 3.00, 0.10 to 3.00, 0.70 to 3.00, 0.10 x 10 －２ It may be 0.10 to 1.00, 0.10 to 1.00, or 0.70 to 1.00.

[0048] Young's modulus E is obtained by cutting a test piece from a film obtained by depositing a coating material with a dumbbell cutter, and then performing a tensile test using the test piece at a tensile speed of 200 mm / min. The Young's modulus E is obtained as the initial slope of the plot of a stress-strain curve (vertical axis: stress, horizontal axis: strain). When multiple coating materials are used, the Young's modulus E described above refers to the Young's modulus of a mixture consisting of all the components of the coating materials that make up the coating portion. However, when the coating portion consists of two or more coating layers, the above-mentioned ranges of Young's modulus E refer to the Young's modulus E of a film obtained by depositing the coating materials that make up one layer (when multiple coating materials are used in one layer, the mixture consisting of all the components of the coating materials that make up that layer). In at least one layer, the Young's modulus E of a film obtained by depositing the coating materials that make up the coating layer may fall within the above-mentioned ranges of Young's modulus E. The Young's modulus E can be adjusted by the type or usage ratio of the coating materials, etc.

[0049] The surface free energy σ (25° C.) of a film (for example, a film having a thickness of 5 μm) obtained by forming the coating material constituting the coating portion or the coating material that comes into contact with the water-absorbent resin particles in the coating step is set to the following range (unit: mJ / m) from the viewpoint of easily delaying the water absorption of the coated resin particles. ２ " may be omitted). The surface free energy σ may be 5.0 or more, 10.0 or more, 15.0 or more, 17.0 or more, 20.0 or more, 22.0 or more, 24.0 or more, 25.0 or more, or 26.0 or more. The surface free energy σ may be 100.0 or less, 80.0 or less, 60.0 or less, 50.0 or less, 45.0 or less, 40.0 or less, 35.0 or less, 30.0 or less, 28.0 or less, or 26.5 or less. From these viewpoints, the surface free energy σ may be 5.0 to 100.0, 5.0 to 60.0, 5.0 to 30.0, 15.0 to 100.0, 15.0 to 60.0, 15.0 to 30.0, 20.0 to 100.0, 20.0 to 60.0, or 20.0 to 30.0.

[0050] The surface free energy σ is calculated by the Kaelble-Uy method based on the contact angles (25°C) with ion-exchanged water and formamide obtained using a contact angle meter. When multiple coating materials are used, the above-mentioned surface free energy σ refers to the surface free energy σ of a mixture consisting of all the components of the coating materials that make up the coating portion. However, when the coating portion consists of two or more coating layers, each of the above-mentioned ranges of surface free energy σ refers to the surface free energy σ of the coating materials that make up one layer (when multiple coating materials are used in one layer, it refers to the mixture consisting of all the components of the coating materials that make up that one layer), and the surface free energy σ of the coating materials that make up at least one of the coating layers may fall within each of the above-mentioned ranges of surface free energy σ. The surface free energy σ can be adjusted by the type or usage ratio of the coating materials, etc.

[0051] In the coating step of the method for producing coated resin particles according to this embodiment, water-absorbent resin particles (subject to be coated) and a coating material are brought into contact with each other to obtain coated resin particles having a coating portion that covers at least a part of the water-absorbent resin particles. That is, the coating step is a step in which the coating material is supplied to the water-absorbent resin particles all at once, continuously, or intermittently to bring the water-absorbent resin particles and the coating material into a state in which they can come into contact with each other. The coating step ends when the water-absorbent resin particles and the coating material reach a state in which they cannot come into contact with each other (typically, when the entire amount of the planned coating material has been supplied).

[0052] The atmospheric temperature in the coating step may be in the following ranges from the viewpoint of easily adjusting the water absorption behavior of the coated resin particles. The atmospheric temperature in the coating step may be 20°C or higher, 23°C or higher, 25°C or higher, 30°C or higher, 35°C or higher, 40°C or higher, 45°C or higher, 50°C or higher, 55°C or higher, 60°C or higher, 65°C or higher, 70°C or higher, 75°C or higher, 80°C or higher, 85°C or higher, 90°C or higher, 95°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, or 130°C or higher. The atmospheric temperature in the coating step may be 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, 95°C or lower, 90°C or lower, 85°C or lower, 80°C or lower, 75°C or lower, 70°C or lower, 65°C or lower, 60°C or lower, 55°C or lower, or 50°C or lower. From these viewpoints, the atmospheric temperature in the coating step may be 20 to 150°C, 20 to 140°C, 20 to 130°C, 50 to 150°C, 50 to 140°C, 50 to 130°C, 100 to 150°C, 100 to 140°C, or 100 to 130°C.

[0053] In the coating step, for example, a coating material can be brought into contact with water-absorbent resin particles present in an atmosphere of air, an inert gas (e.g., nitrogen gas), a mixed gas thereof, etc. The coating material brought into contact with the water-absorbent resin particles may be a dry coating material, a liquid or gel-like coating material (e.g., a molten coating material), or a coating material in a coating liquid (a solution of the coating material, a dispersion of the coating material (e.g., an emulsion), etc.) containing the coating material and a liquid medium (e.g., water).

[0054] The coating material may be brought into contact with the water-absorbent resin particles by bringing a coating liquid containing the coating material and a liquid medium (e.g., water) into contact with the water-absorbent resin particles. This makes it easier to obtain a coating portion with a uniform thickness. The liquid medium may be a solvent or a dispersion medium. The coating liquid containing the coating material and the liquid medium may be obtained by dissolving the coating material in a solvent or by dispersing the coating material in a dispersion medium.

[0055] Examples of solvents or dispersion media include water, hydrophilic compounds, and hydrocarbon compounds. A single solvent or dispersion medium may be used, or a mixture of two or more solvents or dispersion media (e.g., a mixture of water and a hydrophilic compound) may be used. A hydrophilic compound is a compound that dissolves substantially uniformly in water. Examples of hydrophilic compounds include alcohols such as methanol and isopropyl alcohol; glycols such as ethylene glycol; cellosolves such as methyl cellosolve and ethyl cellosolve; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; and ethers such as tetrahydrofuran. Examples of hydrocarbon compounds include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons such as toluene and xylene.

[0056] The content of the coating material in the coating liquid may be in the following ranges based on the total mass of the coating liquid, from the viewpoint of easily delaying water absorption by the coated resin particles. The content of the coating material may be 1.00% by mass or more, 3.00% by mass or more, 5.00% by mass or more, 8.00% by mass or more, or 10.00% by mass or more. The content of the coating material may be 50.00% by mass or less, 40.00% by mass or less, 30.00% by mass or less, 20.00% by mass or less, 15.00% by mass or less, 12.00% by mass or less, 11.00% by mass or less, 10.50% by mass or less, or 10.00% by mass or less. From these viewpoints, the content of the coating material may be 1.00 to 50.00 mass%, 1.00 to 20.00 mass%, 1.00 to 15.00 mass%, 5.00 to 50.00 mass%, 5.00 to 20.00 mass%, 5.00 to 15.00 mass%, 10.00 to 50.00 mass%, 10.00 to 20.00 mass%, or 10.00 to 15.00 mass%.

[0057] The content of the liquid medium in the coating liquid may be in the following ranges based on the total mass of the coating liquid, from the viewpoint of easily delaying water absorption by the coated resin particles. The content of the liquid medium may be 10.00 mass% or more, 30.00 mass% or more, 50.00 mass% or more, 60.00 mass% or more, 70.00 mass% or more, 80.00 mass% or more, 85.00 mass% or more, 88.00 mass% or more, 89.00 mass% or more, 89.50 mass% or more, or 90.00 mass% or more. The content of the liquid medium may be 99.00 mass% or less, 97.00 mass% or less, 95.00 mass% or less, 92.00 mass% or less, or 90.00 mass% or less. From these viewpoints, the content of the liquid medium may be 10.00 to 99.00 mass%, 30.00 to 99.00 mass%, 50.00 to 99.00 mass%, 80.00 to 99.00 mass%, 85.00 to 99.00 mass%, 50.00 to 95.00 mass%, 80.00 to 95.00 mass%, 85.00 to 95.00 mass%, 50.00 to 90.00 mass%, 80.00 to 90.00 mass%, or 85.00 to 90.00 mass%.

[0058] The water content in the coating liquid may be in the following ranges based on the total mass of the coating liquid, from the viewpoint of easily delaying water absorption by the coated resin particles. The water content may be 10.00 mass% or more, 30.00 mass% or more, 50.00 mass% or more, 60.00 mass% or more, 70.00 mass% or more, 80.00 mass% or more, 85.00 mass% or more, 88.00 mass% or more, 89.00 mass% or more, 89.50 mass% or more, or 90.00 mass% or more. The water content may be 99.00 mass% or less, 97.00 mass% or less, 95.00 mass% or less, 92.00 mass% or less, or 90.00 mass% or less. From these viewpoints, the water content may be 10.00 to 99.00 mass%, 30.00 to 99.00 mass%, 50.00 to 99.00 mass%, 80.00 to 99.00 mass%, 85.00 to 99.00 mass%, 50.00 to 95.00 mass%, 80.00 to 95.00 mass%, 85.00 to 95.00 mass%, 50.00 to 90.00 mass%, 80.00 to 90.00 mass%, or 85.00 to 90.00 mass%.

[0059] The median particle diameter r (25°C: for example, the median particle diameter of the coating material in the coating liquid) of the coating material that comes into contact with the water-absorbent resin particles in the coating step may be in the following ranges, from the viewpoint of easily improving the formability of the coating portion. The median particle diameter r may be 1 nm or more, 3 nm or more, 5 nm or more, 8 nm or more, 10 nm or more, or 13 nm or more. The median particle diameter r may be 1000 nm or less, 700 nm or less, 500 nm or less, 300 nm or less, 200 nm or less, 150 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 80 nm or less, 50 nm or less, 30 nm or less, or 20 nm or less. From these viewpoints, the median particle diameter r may be 1 to 1000 nm, 1 to 300 nm, 1 to 50 nm, 5 to 1000 nm, 5 to 300 nm, 5 to 50 nm, 10 to 1000 nm, 10 to 300 nm, or 10 to 50 nm. The median particle diameter r may be a particle diameter based on mass. The median particle diameter r is measured by the method described in [Examples] below. When multiple components are used as the coating material, the above-mentioned median particle diameter r refers to the median particle diameter of a mixture consisting of all components of the coating material.

[0060] Surface free energy σ [unit: mJ / m ２The ratio Er / σ (25°C) of the product Er of Young's modulus E [unit: MPa] and median particle diameter r [unit: nm] to the average particle diameter E (unit: MPa) may be in the following range from the viewpoint of easily delaying the water absorption of the coated resin particles. The ratio Er / σ may be 40.00 or less, 35.00 or less, 30.00 or less, 25.00 or less, 20.00 or less, 15.00 or less, 10.00 or less, 8.00 or less, 5.00 or less, 3.00 or less, 2.00 or less, 1.00 or less, 0.80 or less, 0.60 or less, or 0.50 or less. The ratio Er / σ may exceed 0, and may be 0.01 or more, 0.05 or more, 0.08 or more, 0.10 or more, 0.15 or more, 0.20 or more, 0.30 or more, or 0.40 or more. From these viewpoints, the ratio Er / σ may be greater than 0 and equal to or less than 40.00, greater than 0 and equal to or less than 10.00, greater than 0 and equal to or less than 1.00, 0.10 to 40.00, 0.10 to 10.00, 0.10 to 1.00, 0.30 to 40.00, 0.30 to 10.00, or 0.30 to 1.00. When a plurality of components are used as the coating material, the above-mentioned ratio Er / σ refers to the ratio Er / σ of a mixture consisting of all the components of the coating material.

[0061] The method for bringing the water-absorbent resin particles and the coating material into contact with each other in the coating step is not particularly limited, and various methods can be used. For example, in the coating step, the water-absorbent resin particles and the coating material (e.g., the coating material of a coating liquid) may be mixed in a container such as a flask to bring the water-absorbent resin particles and the coating material into contact with each other. In the coating step, the coating material may be brought into contact with the water-absorbent resin particles in an airflow, or the water-absorbent resin particles blown up by the airflow may be brought into contact with the coating material, or the water-absorbent resin particles and the coating material may be brought into contact with each other by supplying the coating material to a fluidized bed of the water-absorbent resin particles. The gas constituting the airflow may be air, an inert gas (e.g., nitrogen gas), a mixed gas thereof, or the like. The temperature of the airflow may exceed 25°C. In the coating step, the coating material may be brought into contact with the water-absorbent resin particles in a state of being stirred using a stirring means. The stirring means may be a stirring means having a stirring blade, or may be an air supply means capable of supplying an airflow different from the airflow for blowing up the water-absorbent resin particles. In the coating step, the water-absorbent resin particles may be agitated only by an airflow for blowing the water-absorbent resin particles upward, and no agitation means other than the airflow for blowing the water-absorbent resin particles upward may be used. In the coating step, the water-absorbent resin particles and the coating material may be brought into contact with each other by spraying a coating liquid onto the water-absorbent resin particles. The nozzle for spraying the coating liquid is not particularly limited, and, for example, a tangential spray or a two-fluid nozzle (e.g., a nozzle for spraying the coating liquid and an inert gas) may be used. In the coating step, the water-absorbent resin particles and the coating material may be brought into contact with each other using various devices such as a tumbling granulator, an agitation granulator, or a fluidized bed granulator.

[0062] The method for producing coated resin particles according to this embodiment may include a step of adjusting the atmospheric temperature of the space in which the water-absorbent resin particles and the coating material are brought into contact with each other before the coating step. The atmospheric temperature before the coating step in the space in which the water-absorbent resin particles and the coating material are brought into contact with each other may be 25°C or higher, 35°C or higher, 45°C or higher, or 55°C or higher, from the viewpoint of easily delaying the water absorption of the coated resin particles. The atmospheric temperature may be 140°C or lower, 120°C or lower, 100°C or lower, or 80°C or lower. From these viewpoints, the atmospheric temperature may be 25 to 140°C, 25 to 120°C, 25 to 100°C, or 25 to 80°C.

[0063] The method for producing coated resin particles according to this embodiment may include a drying step of drying the coated resin particles after the coating step. The ambient temperature and time of the drying step are appropriately adjusted depending on the type and amount of coating material, etc. The ambient temperature of the drying step may be 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher, from the viewpoint of easily delaying water absorption by the coated resin particles. The ambient temperature of the drying step may be 140°C or lower, 120°C or lower, 100°C or lower, or 80°C or lower. From these viewpoints, the ambient temperature of the drying step may be 20 to 140°C, 30 to 120°C, 40 to 100°C, or 50 to 80°C. The duration of the drying step may be 10 minutes or more, 20 minutes or more, or 30 minutes or more. The duration of the drying step may be 180 minutes or less, 120 minutes or less, or 60 minutes or less. From these viewpoints, the drying time may be 10 to 180 minutes, 20 to 120 minutes, or 30 to 60 minutes.

[0064] In the method for producing coated resin particles according to the present embodiment, in the coating step, the water-absorbent resin particles and the coating material may be brought into contact with each other while supplying an airflow from a vertically downward side into the internal space of an apparatus (e.g., a fluidized bed granulator) having an internal space in which the water-absorbent resin particles are accommodated. The internal space is a space into which the coating material is supplied and into which the water-absorbent resin particles and the coating material can come into contact with each other. The airflow may be supplied vertically from a vertically downward side, or may be supplied vertically from a vertically downward side in a direction intersecting the vertical direction.

[0065] 1 is a schematic cross-sectional view showing a treatment apparatus for bringing water-absorbent resin particles and a coating material into contact with each other. The treatment apparatus 1 includes a treatment section 10 and an air supply section (not shown) that supplies an air flow G to the treatment section 10.

[0066] The processing unit 10 is a substantially cylindrical member extending in the vertical direction (height direction of the processing device 1; the same applies below). The processing unit 10 has a substantially cylindrical internal space 11 in which the water-absorbent resin particles 20 are accommodated. The internal space 11 has a cylindrical space 11a, a space 11b located vertically above the space 11a, and a cylindrical space 11c located vertically above the space 11b. The spaces 11a, 11b, and 11c are continuous from below to above in the vertical direction, thereby constituting the internal space 11. The space 11a has the narrowest cross section (narrowest cross section) in the internal space 11. The space 11b tapers upward in the vertical direction.

[0067] An air inlet 12 is formed in the center of the bottom surface of the processing section 10. The air inlet 12 is connected to the air supply section, and an air flow G is supplied to the internal space 11 through the air inlet 12. The ambient temperature of the internal space 11 can be adjusted by adjusting the temperature of the air flow G.

[0068] The processing unit 10 includes an agitation means 13 (e.g., a rotor blade) for the water-absorbent resin particles 20. The agitation means 13 includes a disk-shaped disk portion 13a whose center protrudes vertically upward and a support portion 13b that supports the disk portion 13a. The disk portion 13a extends horizontally below the vertical direction in the space 11a, and an annular opening 14 is formed in the space 11a at a position on the outer periphery of the disk portion 13a. The disk portion 13a has an annular upper surface around the central protrusion, and horizontally extending blades (not shown: for example, three blades extending radially from the center of the disk portion 13a and arranged at equal intervals) are formed on the upper surface. The support portion 13b extends vertically and extends from the outside of the internal space 11 into the interior of the internal space 11 via the air inlet 12. The support portion 13b rotates in the horizontal direction (rotates around the axis of the support portion 13b), thereby allowing the disk portion 13a to rotate in the horizontal direction.

[0069] The air flow G supplied from the air intake port 12 to the internal space 11 is blocked by the disk portion 13a of the stirring means 13 and supplied to the outer periphery of the processing section 10, and then supplied vertically upward through the opening 14 located on the outer periphery of the space 11a.

[0070] The water-absorbent resin particles 20 are deposited on the upper surface of the disk portion 13a, etc., and are agitated as the disk portion 13a rotates, and are blown vertically upward by the airflow G supplied through the opening 14. After being blown vertically upward by the airflow G, the water-absorbent resin particles 20 fall vertically downward by gravity. An exhaust filter (e.g., a bag filter) 15 is disposed in the space 11c of the internal space 11, and the airflow G supplied to the internal space 11 is discharged from the exhaust filter 15 to the outside of the processing device 1.

[0071] The processing unit 10 includes a liquid supply unit 16 (e.g., a nozzle) that supplies the coating liquid L to the space 11a. The liquid supply unit 16 supplies the coating liquid L from the outer periphery to the inner periphery of the space 11a at a position vertically above the disk unit 13a of the stirring means 13 in the space 11a. The coating liquid L supplied from the liquid supply unit 16 is blown up by the airflow G and comes into contact with the water-absorbent resin particles 20 that are descending due to gravity. The water-absorbent resin particles 20 and the coating material of the coating liquid L come into contact with each other to form a coating portion, thereby obtaining coated resin particles. Volatile components (water, etc.) in the coating liquid L are volatilized by the airflow G, heat in the internal space 11, etc.

[0072] The processing unit 10 is provided with a thermometer (not shown) that measures the atmospheric temperature of the internal space 11. The thermometer may be arranged at a position in the internal space 11 where the water-absorbent resin particles 20 and the coating liquid L come into contact with each other, or may be arranged in the vicinity of the liquid supply unit 16 at a height equivalent to that of the liquid supply unit 16.

[0073] The configuration of the treatment device for bringing the water-absorbent resin particles and the coating material into contact with each other is not limited to the configuration of the treatment device 1. For example, the treatment device may be provided with an agitation device that supplies an airflow from the side of the treatment device 10 to agitate the water-absorbent resin particles 20, instead of or in addition to the agitation device of the treatment device 1. The treatment device may be provided with a means (e.g., a heater) for heating the treatment device 10 as a means for adjusting the atmospheric temperature of the internal space 11 of the treatment device 10 in the treatment device 1.

[0074] The amount of airflow supplied to the internal space can be adjusted appropriately depending on the volume of the internal space, etc. The amount of airflow supplied is set within the following range (unit: m ３ / min" may be omitted). The supply rate may be 0.1 or more, 0.3 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, or 1.0 or more. The supply rate may be 1000 or less, 500 or less, 300 or less, 100 or less, 75 or less, 50 or less, 25 or less, 10 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.5 or less, 1.2 or less, 1.0 or less, 0.9 or less, or 0.8 or less. From these viewpoints, the supply rate may be 0.1 to 1000, 0.3 to 500, 0.5 to 300, 0.6 to 100, 0.7 to 75, 0.8 to 50, 0.9 to 25, or 1.0 to 10.

[0075] The amount of coating liquid supplied to the internal space can be appropriately adjusted depending on the amount of water-absorbent resin particles supplied to the processing section, etc. The supply amount may be within the following ranges (the unit "g / min" is omitted) from the viewpoint of easily adjusting the water absorption behavior of the coated resin particles. The supply amount may be 1.0 or more, 2.0 or more, 3.0 or more, 4.0 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, 10.0 or more, 12.0 or more, 15.0 or more, 18.0 or more, 20.0 or more, or 21.0 or more. The supply amount may be 10,000 or less, 1,000 or less, 100 or less, 50.0 or less, 30.0 or less, 25.0 or less, 21.0 or less, 20.0 or less, 18.0 or less, 15.0 or less, 12.0 or less, 10.0 or less, 8.0 or less, 7.0 or less, or 6.0 or less. From these viewpoints, the supply amount may be 1.0 to 10,000, 1.0 to 1,000, 1.0 to 1000, 1.0 to 100, 1.0 to 50.0, 1.0 to 30.0, 1.0 to 20.0, 1.0 to 10.0, 1.0 to 5.0, 5.0 to 30.0, 5.0 to 20.0, 5.0 to 10.0, 10.0 to 30.0, or 10.0 to 20.0.

[0076] The absorbent body according to the present embodiment contains the coated resin particles according to the present embodiment, may contain the coated resin particles according to the present embodiment and water-absorbent resin particles without a coating portion, may contain the coated resin particles according to the present embodiment and fibrous material, or may contain the coated resin particles according to the present embodiment, water-absorbent resin particles without a coating portion, and fibrous material. Examples of fibrous material include finely pulverized wood pulp; cotton; cotton linters; rayon; cellulosic fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester, and polyolefin; and mixtures of these fibers. The absorbent article according to the present embodiment includes the absorbent body according to the present embodiment and may also include the absorbent body according to the present embodiment and other components. Examples of other components include a core wrap (e.g., a core wrap that maintains the shape of the absorbent body), a liquid-permeable sheet (e.g., a liquid-permeable sheet arranged at the outermost side on the side where the liquid to be absorbed penetrates), and a liquid-impermeable sheet (e.g., a liquid-impermeable sheet arranged at the outermost side opposite the side where the liquid to be absorbed penetrates).

[0077] The present invention will be explained in more detail below with reference to experimental examples. However, the present invention is not limited to these experimental examples. In the following, unless the temperature during the experimental procedure is specified, the experimental procedure was carried out at room temperature.

[0078] <Preparation of Water-Absorbent Resin Particles> (Water-Absorbent Resin Particles A) A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer (a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm). 293 g of n-heptane (hydrocarbon dispersion medium) and 0.736 g of maleic anhydride-modified ethylene / propylene copolymer (polymer dispersant, manufactured by Mitsui Chemicals, Inc., Hiwax 1105A) were added to the separable flask to obtain a mixture. While stirring this mixture at a rotation speed of 300 rpm, the separable flask was immersed in an 85 ° C water bath and heated to 80 ° C to dissolve the polymer dispersant. Thereafter, the water bath was removed, and the mixture was allowed to cool to 55 ° C at room temperature.

[0079] Next, 92.0 g of an 80.5% by mass acrylic acid aqueous solution (acrylic acid: 1.03 mol) and a stirrer chip were placed in a 500 mL Erlenmeyer flask, and stirring was initiated. Subsequently, while cooling externally, 102.2 g of a 30% by mass aqueous sodium hydroxide solution was added dropwise to the Erlenmeyer flask to neutralize the 75 mol% acrylic acid. Thereafter, 0.092 g of hydroxyethyl cellulose (thickener, manufactured by Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F), 0.0736 g (0.272 mmol) of potassium persulfate (water-soluble radical polymerization initiator), 0.0101 g (0.0580 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 34.66 g of ion-exchanged water were added, and the mixture was stirred until all components other than water were fully dissolved to prepare a first-stage monomer aqueous solution.

[0080] The first-stage aqueous monomer solution was added to the separable flask and stirred for 10 minutes. A surfactant solution was obtained by dissolving 0.736 g of sucrose stearate (surfactant, manufactured by Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370, HLB: 3) in 6.62 g of n-heptane under heating. 7.356 g of this surfactant solution was added to the separable flask to obtain a reaction solution. The rotation speed was then changed to 550 rpm, and the atmosphere inside the separable flask was thoroughly purged with nitrogen while stirring the reaction solution. The separable flask was then immersed in a 70°C water bath to heat the reaction solution. As the polymerization reaction progressed, heating was continued for another 10 minutes from the point at which the internal temperature reached its maximum (maximum temperature of 82°C), yielding a first-stage polymerization product.

[0081] Next, 128.8 g of an 80.5% by mass acrylic acid aqueous solution (1.44 mol of acrylic acid) and a stirrer chip were placed in a separate 500 mL Erlenmeyer flask, and stirring was initiated. Subsequently, while cooling externally, 143.1 g of a 30% by mass aqueous sodium hydroxide solution was added dropwise to the Erlenmeyer flask to neutralize the 75 mol% acrylic acid. Subsequently, 0.1030 g (0.3810 mmol) of potassium persulfate, 0.0116 g (0.0666 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 3.13 g of ion-exchanged water were added, and the mixture was stirred until all components other than water were fully dissolved, to prepare a second-stage monomer aqueous solution.

[0082] The rotation speed was changed to 1000 rpm, and the first-stage polymerization product was cooled to 25°C while stirring. The entire second-stage aqueous monomer solution was then added to the first-stage polymerization product to obtain a reaction mixture. The atmosphere in the separable flask was thoroughly purged with nitrogen while stirring the reaction mixture. The separable flask was then immersed in a 70°C water bath to heat the reaction mixture. Once the polymerization reaction had progressed and the internal temperature had reached its maximum (maximum temperature of 82°C), heating was continued for an additional 5 minutes to obtain a second-stage polymerization product (a slurry of polymer particles before surface crosslinking).

[0083] After the second-stage polymerization, the temperature of the second-stage polymerization product was increased in an oil bath at 125°C, and 252 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Subsequently, 0.0884 g (0.5075 mmol) of ethylene glycol diglycidyl ether was added as a surface cross-linking agent, and the mixture was maintained at 83°C for 2 hours to obtain a slurry of surface-cross-linked polymer particles.

[0084] Thereafter, the slurry of the polymer particles after the surface crosslinking described above was heated in an oil bath at 125°C, and n-heptane was evaporated and dried to obtain a dried product. Of this dried product, the polymer particles that had passed through a sieve with an opening of 850µm and remained on the surface of a sieve with an opening of 250µm were collected to obtain 210.1g of water-absorbent resin particles A in the form of agglomerated spherical particles (particles in a state where no coating portion was formed: particle diameter 250 to 850µm). Further, the same operation was performed to prepare a total of 500.0g or more of water-absorbent resin particles A.

[0085] (Water absorbent resin particles B) Except for changing the amount of ethylene glycol diglycidyl ether (internal crosslinking agent) added in the preparation of the first-stage aqueous monomer solution to 0.00534 g (0.0306 mmol), the same procedure as for the water absorbent resin particles A was carried out to obtain 211.1 g of water absorbent resin particles B. Furthermore, the same procedure was carried out to prepare 500.0 g or more of water absorbent resin particles B in total.

[0086] (Water-absorbent resin particles C) 227.2 g of water-absorbent resin particles C were obtained in the same manner as in the water-absorbent resin particles A, except that the amount of ethylene glycol diglycidyl ether (internal crosslinking agent) used when preparing the first-stage aqueous monomer solution was changed to 0.0046 g (0.026 mmol); the radical polymerization initiator added when preparing the first-stage aqueous monomer solution was changed to 0.092 g (0.339 mmol) of 2,2'-azobis(2-amidinopropane) dihydrochloride and 0.028 g (0.102 mmol) of potassium persulfate; the radical polymerization initiator added when preparing the second-stage aqueous monomer solution was changed to 0.129 g (0.475 mmol) of 2,2'-azobis(2-amidinopropane) dihydrochloride and 0.039 g (0.143 mmol) of potassium persulfate; and the amount of water extracted from the system was changed to 234.2 g. Furthermore, the same procedure was carried out to prepare 500.0 g or more of water-absorbent resin particles C in total.

[0087] <Preparation of Ethylene / Acrylic Acid Copolymer Partially Neutralized Emulsion> An ice bath at 3°C ​​was prepared by adding water and ice to a plastic tray measuring 27 cm in length, 38 cm in width, and 7 cm in depth. A glass beaker with an internal volume of 1 L was placed in the ice bath, and 545.78 g of ion-exchanged water was then added to the beaker. The ice bath was placed on a magnetic stirrer, and a stirrer tip was placed in the beaker, and stirring was initiated.

[0088] 10.55 g (0.264 mol) of sodium hydroxide (granules, manufactured by Nacalai Tesque, Inc.) was added little by little to the above beaker to prepare a 1.9% by mass aqueous sodium hydroxide solution.

[0089] A round-bottomed, cylindrical, separable flask with an inner diameter of 11 cm and an internal volume of 2 L was prepared. It was equipped with a reflux condenser, a thermometer, and a stirrer (a stirring blade with four inclined paddle blades and a blade diameter of 5 cm). 100 g of ethylene / acrylic acid copolymer (ethylene monomer: acrylic acid monomer molar ratio = 10:1, Primacol 5980i, manufactured by SK Global Chemical) was added to the separable flask. Subsequently, the entire amount of the 1.9% by mass sodium hydroxide aqueous solution was added. The beaker used to prepare the sodium hydroxide aqueous solution was then washed with 50.0 g of ion-exchanged water, and the wash water was added to the separable flask to obtain a reaction solution.

[0090] While stirring the reaction solution with a stirrer at a rotation speed of 500 rpm, the separable flask was immersed in an oil bath at 103° C., and the internal temperature of the separable flask was raised to 95° C. Thereafter, the internal temperature of the separable flask was maintained at 95 to 97° C. for 4 hours while appropriately adjusting the temperature of the oil bath.

[0091] Thereafter, the separable flask was removed from the oil bath and allowed to cool at room temperature until the internal temperature of the separable flask reached 35°C. After confirming that the internal temperature of the separable flask had reached 35°C or lower, the product in the separable flask was filtered through a nylon mesh with a mesh size of 108 µm. The filtrate was collected to obtain an emulsion of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), an aqueous dispersion of a partially neutralized ethylene / acrylic acid copolymer, nonvolatile content 15% by mass, degree of neutralization 90%; hereinafter referred to as "aqueous dispersion (A)").

[0092] <Preparation of Coated Resin Particles> (Experimental Example 1) In a 1 L beaker (made of polypropylene), 66.67 g of the above-mentioned aqueous dispersion (A) was mixed with 33.33 g of ion-exchanged water to prepare 100.00 g of a coating liquid. The content of the coating material in the 100.00 g coating liquid was 10.00 g (10.00 mass %) of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%).

[0093] A fluidized bed granulator having the configuration shown in Figure 1 was prepared. The area of ​​the narrowest cross section perpendicular to the vertical direction of the internal space in the processing section of the fluidized bed granulator was 0.011 m ２ It was.

[0094] 500.0 g of the water-absorbent resin particles A were introduced into the processing section of the fluidized bed granulator. Next, the processing section was stirred with a stirring means (rotor blade, rotation speed: 250 rpm), and the supply air temperature was 130° C. and the supply amount was 1.0 m ３ An airflow (air) supplied to the fluidized bed granulator at a rate of 1.0 g / min was supplied to the processing section from the air inlet. Then, the entire amount of the above-mentioned coating liquid was sprayed onto the water-absorbent resin particles being blown up by the airflow using a tangential spray at a supply rate of 21.0 g / min, thereby bringing the water-absorbent resin particles into contact with the coating material of the coating liquid. At this time, the supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 2.00 parts by mass. Thereafter, the coating material was sprayed at room temperature at a supply rate of 1.0 m ３ An air current (air) supplied to the fluidized bed granulator at a rate of 1 / min was supplied from the air inlet to the processing section for 30 minutes to dry the particles, thereby obtaining particles (A).

[0095] 50.0 g of the particles (A) were spread on a metal tray measuring 26 cm in length and 20 cm in width, and then covered with aluminum foil. After holes were perforated in the aluminum foil, the particles (A) were heated for 90 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 100°C to obtain 50.0 g of coated resin particles.

[0096] (Experimental Example 2) The same procedure as in Experimental Example 1 was carried out to obtain 50.0 g of coated resin particles, except that 200.00 g of a coating liquid was prepared by mixing 133.33 g of the above-mentioned aqueous dispersion (A) as the coating material with 66.67 g of ion-exchanged water, and the total supply rate of the coating liquid was changed to 18.0 g / min. As the content of the coating material in the 200.00 g coating liquid, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 20.00 g (10.00 mass%). The supply amount of the coating material per 100 mass parts of the water-absorbent resin particles was 4.00 mass parts.

[0097] (Experimental Example 3) 250.00 g of a coating liquid was prepared by mixing 166.67 g of the above-mentioned aqueous dispersion (A) with 83.33 g of ion-exchanged water as the coating material, the total supply rate of the coating liquid was changed to 18.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (manufactured by ADVANTEC, FV-320) set at 120°C. The same procedure as in Experimental Example 1 was carried out to obtain 50.0 g of coated resin particles. As the content of the coating material in the 250.00 g coating liquid, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 25.00 g (10.00 mass%). The amount of the coating material supplied per 100 parts by mass of the water-absorbent resin particles was 5.00 parts by mass.

[0098] Experimental Example 4 50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that 250.00 g of the above-mentioned aqueous dispersion (A) was mixed with 125.00 g of ion-exchanged water to prepare 375.00 g of a coating liquid as a coating material, the total supply rate of the coating liquid was changed to 15.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (manufactured by ADVANTEC, FV-320) set at 120°C. As the content of the coating material in the 375.00 g of coating liquid, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 37.50 g (10.00 mass%). The amount of coating material supplied per 100 parts by mass of the water-absorbent resin particles was 7.50 parts by mass.

[0099] (Experimental Example 5) 250.00 g of the above-mentioned aqueous dispersion (A) and 1.25 g of polyethylene glycol (PEG6000, manufactured by Tokyo Chemical Industry Co., Ltd., number average molecular weight: 7300 to 9300) were mixed with 123.75 g of ion-exchanged water to prepare 375.00 g of a coating liquid. The temperature of the airflow supply was changed to 90°C, and the airflow supply volume was 0.8 m ３50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 120°C. As the content of the coating material in 375.00 g of the coating liquid, the content of partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 37.50 g (10.00 mass%), and the content of polyethylene glycol was 1.25 g (0.33 mass%). The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 7.75 parts by mass.

[0100] Experimental Example 6 400.75 g of a coating solution was prepared by mixing 400.00 g of the above-mentioned aqueous dispersion (A) and 0.75 g of polyethylene glycol (PEG 6000, manufactured by Tokyo Chemical Industry Co., Ltd., number average molecular weight: 7300 to 9300) as the coating material, the total supply rate of the coating solution was changed to 18.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 120°C. The same procedure as in Experimental Example 1 was repeated to obtain 50.0 g of coated resin particles. The coating material contents in the 400.75 g of coating solution were 60.00 g (14.97% by mass) of partially neutralized ethylene / acrylic acid copolymer (P(E / AA), degree of neutralization 90%) and 0.75 g (0.19% by mass) of polyethylene glycol. The amount of the coating material supplied was 12.15 parts by mass per 100 parts by mass of the water-absorbent resin particles.

[0101] Experimental Example 7 50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that 400.00 g of the above-mentioned aqueous dispersion (A) and 10.00 g of polyethylene glycol (PEG 6000, manufactured by Tokyo Chemical Industry Co., Ltd., number average molecular weight: 7300 to 9300) were mixed with 190.00 g of ion-exchanged water to prepare 600.00 g of a coating solution, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 120° C. The coating material content in the 600.00 g coating solution was 60.00 g (10.00 mass%) of partially neutralized ethylene / acrylic acid copolymer (P(E / AA), degree of neutralization 90%) and 10.00 g (1.67 mass%) of polyethylene glycol. The amount of the coating material supplied was 14.00 parts by mass per 100 parts by mass of the water-absorbent resin particles.

[0102] (Experimental Example 8) 56.18 g of an aqueous dispersion of a partially neutralized styrene / acrylic acid copolymer (Neocryl XK-188, manufactured by DSM Resins & Functional Materials, non-volatile content: 44.5% by mass) was mixed with 193.82 g of ion-exchanged water to prepare 250.00 g of a coating solution, and the particles (A) were heated for 60 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 100°C. The same procedure as in Experimental Example 1 was carried out to obtain 50.0 g of coated resin particles. The content of the partially neutralized styrene / acrylic acid copolymer in the 250.00 g of coating solution was 25.00 g (10.00% by mass). The amount of coating material supplied per 100 parts by mass of water-absorbent resin particles was 5.00 parts by mass.

[0103] (Experimental Example 9) 53.19 g of an aqueous dispersion of a partially neutralized styrene / acrylic acid copolymer (Neocryl A-2092, manufactured by DSM Resins & Functional Materials, non-volatile content: 47% by mass) was mixed with 196.81 g of ion-exchanged water to prepare 250.00 g of a coating solution, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 130°C. The same procedure as in Experimental Example 1 was carried out to obtain 50.0 g of coated resin particles. The content of the partially neutralized styrene / acrylic acid copolymer in the 250.00 g of coating solution was 25.00 g (10.00% by mass). The amount of coating material supplied per 100 parts by mass of water-absorbent resin particles was 5.00 parts by mass.

[0104] (Experimental Example 10) 62.50 g of an aqueous dispersion of copolymerized nylon (Sepolsion PA200, manufactured by Sumitomo Seika Chemicals Co., Ltd., non-volatile content: 40% by mass) was mixed with 187.50 g of ion-exchanged water to prepare 250.00 g of a coating solution. The temperature of the airflow supply was changed to 50°C, and the airflow supply volume was 0.8 m ３ 50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 15 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 130°C. As the content of the coating material in 250.00 g of the coating liquid, the content of copolymerized nylon was 25.00 g (10.00 mass%). The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 5.00 parts by mass.

[0105] (Experimental Example 11) 98.04 g of a water dispersion of a styrene / (meth)acrylic compound copolymer (AQUENCE EPIX BC910F, manufactured by Henkel, non-volatile content: 51% by mass) was mixed with 401.96 g of ion-exchanged water to prepare 500.00 g of a coating liquid. The temperature of the airflow supply was changed to 110°C, and the airflow supply volume was changed to 0.8 m ３50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 120°C. As the content of the coating material in 500.00 g of the coating liquid, the content of the styrene / (meth)acrylic compound copolymer was 50.00 g (10.00 mass%). The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 10.00 parts by mass.

[0106] (Experimental Example 12) 98.04 g of a water dispersion of a (meth)acrylic compound polymer (Henkel, AQUEENCE EPIX BC9240A, non-volatile content: 51% by mass) was mixed with 401.96 g of ion-exchanged water to prepare 500.00 g of a coating liquid. The temperature of the airflow supply was changed to 110°C, and the airflow supply volume was changed to 0.8 m ３ 50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 110°C. As the content of the coating material in 500.00 g of the coating liquid, the content of the (meth)acrylic compound polymer was 50.00 g (10.00 mass%). The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 10.00 parts by mass.

[0107] (Experimental Example 13) 161.29 g of a water dispersion of a silicone / (meth)acrylic compound copolymer (manufactured by Nissin Chemical Industry Co., Ltd., Chaline FE-230N, emulsion of polyalkylsiloxane and (meth)acrylic acid alkyl ester copolymer, non-volatile content: 31% by mass) was mixed with 338.71 g of ion-exchanged water to prepare 500.00 g of a coating liquid. The inlet air temperature of the airflow was changed to 50°C, and the supply volume of the airflow was increased to 0.8 m. ３50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 70°C. As the content of the coating material in 500.00 g of the coating liquid, the content of the silicone / (meth)acrylic compound copolymer was 50.00 g (10.00 mass%). The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 10.00 parts by mass.

[0108] (Experimental Example 14) 103.73 g of an aqueous dispersion of styrene / butadiene copolymer (Narstar SR-115, manufactured by Nippon A&L Co., Ltd., non-volatile content: 48.2% by mass) and 5.00 g of phenyl diglycol (manufactured by Nippon Nyukazai Co., Ltd.) were mixed with 391.27 g of ion-exchanged water to prepare 500.00 g of a coating liquid. The temperature of the inlet airflow was changed to 60°C, and the supply volume of the airflow was increased to 0.8 m. ３ 50.0 g of coated resin particles were obtained by the same procedure as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 70°C. The content of the coating material in 500.00 g of the coating liquid was 50.00 g (10.00 mass%) of styrene / butadiene copolymer and 5.00 g (1.00 mass%) of phenyl diglycol. The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 11.00 parts by mass.

[0109] (Experimental Example 15) The same procedure as in Experimental Example 1 was carried out to obtain 50.0 g of coated resin particles, except that the water-absorbent resin particles A were changed to water-absorbent resin particles B, 250.00 g of a coating liquid was prepared by mixing 166.67 g of the above-mentioned aqueous dispersion (A) as the coating material with 83.33 g of ion-exchanged water, the total supply rate of the coating liquid was changed to 18.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (manufactured by ADVANTEC, FV-320) set at 100°C. As the content of the coating material in the 250.00 g coating liquid, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 25.00 g (10.00 mass%). The amount of the coating material supplied per 100 parts by mass of the water-absorbent resin particles was 5.00 parts by mass.

[0110] (Experimental Example 16) The water-absorbent resin particles A were changed to the water-absorbent resin particles B, 250.00 g of the above-mentioned aqueous dispersion (A) and 1.25 g of polyethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd., PEG6000, number average molecular weight: 7300 to 9300) were mixed with 123.75 g of ion-exchanged water to prepare 375.00 g of a coating liquid, the supply air temperature of the airflow was changed to 90°C, and the supply amount of the airflow was increased to 0.8 m ３ 50.0 g of coated resin particles were obtained in the same manner as in Experimental Example 1, except that the supply rate was changed to 6.0 g / min, the total supply rate of the coating liquid was changed to 6.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 120°C. As the content of the coating material in 375.00 g of the coating liquid, the content of partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 37.50 g (10.00 mass%), and the content of polyethylene glycol was 1.25 g (0.33 mass%). The supply amount of the coating material per 100 parts by mass of the water-absorbent resin particles was 7.75 parts by mass.

[0111] Experimental Example 17 The same procedure as in Experimental Example 1 was carried out, except that the water-absorbent resin particles A were changed to water-absorbent resin particles B, 600.00 g of a coating solution was prepared by mixing 400.00 g of the above-mentioned aqueous dispersion (A) with 200.00 g of ion-exchanged water as the coating material, and the particles (A) were heated for 30 minutes in a hot air dryer (manufactured by ADVANTEC, FV-320) set at 120°C, to obtain 50.0 g of coated resin particles. As the content of the coating material in the 600.00 g coating solution, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 60.00 g (10.00 mass%). The amount of coating material supplied per 100 parts by mass of the water-absorbent resin particles was 12.00 parts by mass.

[0112] (Experimental Example 18) The water-absorbent resin particles A were changed to water-absorbent resin particles B, 400.75 g of a coating liquid was prepared by mixing 400.00 g of the above-mentioned aqueous dispersion (A) and 0.75 g of polyethylene glycol (PEG6000, manufactured by Tokyo Chemical Industry Co., Ltd., number average molecular weight: 7300 to 9300) as the coating material, the supply rate of the total amount of the coating liquid was changed to 18.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 120 ° C. The same procedure as in Experimental Example 1 was carried out to obtain 50.0 g of coated resin particles. As the content of the coating material in 400.75 g of the coating liquid, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 60.00 g (14.97 mass%), and the content of polyethylene glycol was 0.75 g (0.19 mass%). The amount of the coating material supplied was 12.15 parts by mass per 100 parts by mass of the water-absorbent resin particles.

[0113] Experimental Example 19 The same procedure as in Experimental Example 1 was carried out, except that the water-absorbent resin particles A were changed to water-absorbent resin particles C, 600.00 g of a coating solution was prepared by mixing 400.00 g of the above-mentioned aqueous dispersion (A) with 200.00 g of ion-exchanged water as the coating material, and the particles (A) were heated for 60 minutes in a hot air dryer (manufactured by ADVANTEC, FV-320) set at 90°C, to obtain 50.0 g of coated resin particles. As the content of the coating material in the 600.00 g coating solution, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 60.00 g (10.00 mass%). The amount of the coating material supplied per 100 parts by mass of the water-absorbent resin particles was 12.00 parts by mass.

[0114] (Experimental Example 20) The same procedure as in Experimental Example 1 was carried out, except that the water-absorbent resin particles A were changed to water-absorbent resin particles C, 400.75 g of a coating liquid was prepared by mixing 400.00 g of the above-mentioned aqueous dispersion (A) and 0.75 g of polyethylene glycol (PEG 6000, manufactured by Tokyo Chemical Industry Co., Ltd., number average molecular weight: 7300 to 9300) as the coating material, the total supply rate of the coating liquid was changed to 18.0 g / min, and the particles (A) were heated for 30 minutes in a hot air dryer (FV-320, manufactured by ADVANTEC) set at 100°C. 50.0 g of coated resin particles was obtained. As the content of the coating material in 400.75 g of the coating liquid, the content of a partially neutralized ethylene / acrylic acid copolymer (P(E / AA), neutralization degree 90%) was 60.00 g (14.97% by mass), and the content of polyethylene glycol was 0.75 g (0.19% by mass). The amount of the coating material supplied was 12.15 parts by mass per 100 parts by mass of the water-absorbent resin particles.

[0115] <Measurement of Physical Properties of Coating Materials> (Median Particle Diameter r of Coating Material in Coating Liquid) Each of the above coating liquids was added to a 200 mL plastic beaker containing 100 mL of ion-exchanged water to obtain a mixture, which was then stirred at 600 rpm for 1 minute using a magnetic stirrer. The mixture was then degassed for 10 minutes using an ultrasonic cleaner (manufactured by Yamato Scientific Co., Ltd., CPX2800H-J) to obtain a sample liquid. The particle size distribution of the sample liquid was measured using a dynamic light scattering measurement device (manufactured by Malvern, ZETA SIZER Nano series) to calculate the median particle diameter r (volume average diameter, 25°C) of the coating material. The volume average measurement mode was selected. The results are shown in Table 2.

[0116] (Young's Modulus E and Fracture Energy) Each of the above coating solutions was added to a Teflon-coated metal tray (200 mm long, 260 mm wide, 50 mm deep) so that the nonvolatile components were 10 g, and then dried at 105°C using a heating dryer (manufactured by ADVANTEC, DRE320DR) until the weight no longer changed, thereby obtaining a solid. This solid was then shredded with scissors to 10 mm long and 10 mm wide to obtain resin pieces.

[0117] Using a 68-ton press (manufactured by Futanaikoki Co., Ltd.) and a Teflon-coated SUS frame (internal space: length 100 mm, width 100 mm, thickness 1 mm), the resin pieces were pressed under the following conditions: press temperature 140°C, pre-press melting time 3 minutes, bumping pressure 20 MPa, bumping number 8 times, press pressure 21 MPa, pressing number 1 time, and pressing time 30 seconds. After pressing, the resin film was obtained by quenching at 10°C for 1 minute.

[0118] Using a dumbbell cutter (SDMP-1000, manufactured by Dumbbell Co., Ltd.), test pieces having dimensions conforming to JIS K 6251-7 were cut from the resin film. The test pieces had one end and the other end each 6 mm wide, and a linear middle section (length: 12 mm) 2 mm wide connecting the one end and the other end, and the total length of the test piece was 35 mm. The thickness of the middle section of the test piece was measured using a film thickness meter (Thickness Gauge SM112, manufactured by Teclock Corporation), and the cross-sectional area of ​​the middle section was calculated as the product of the width 2 mm and the thickness at the middle section of the test piece.

[0119] A tensile test (JIS K 6251, jig: SCG-1kNA, tensile speed: 200 mm / min, gauge length: 12 mm, grip distance: 12 mm) was performed on this test piece using a bench-top precision universal testing machine (Shimadzu Corporation, Autograph AGS-X), and the stress [MPa] and strain [%] were calculated using the following formula. The force generated when the test piece was pulled at a tensile speed of 200 mm / min was taken as the test force at break. The changes in stress and strain over time were plotted to obtain a stress-strain curve (vertical axis: stress, horizontal axis: strain) up to the break point. The initial slope of the plot was taken as Young's modulus E [MPa, 25°C], and the integral value of the stress-strain curve was taken as the fracture energy [J / mm ３ , 25°C]. The results are shown in Table 2. Stress [MPa] = Test force [N] until breakage / (Width [mm] of the middle part of the sample piece × Thickness [mm] of the middle part of the sample piece) = Test force [N] until breakage / Cross-sectional area of ​​the middle part of the sample piece [mm ２ Strain [%] = (total length of intermediate portion until fracture / initial total length of intermediate portion (12 mm)) × 100

[0120] (Surface Free Energy) Using an automatic applicator (manufactured by TQC Sheen), each of the above-mentioned coating solutions was applied to aluminum foil (antibacterial Sunfoil, manufactured by Toyo Aluminum Echo Products Co., Ltd.) at a speed of 10 mm / sec so that the thickness when dried would be 5 μm, and then the coating was heated and dried at 100° C. for 5 minutes in a heating dryer (DRE320DR, manufactured by ADVANTEC) to obtain a laminate having a coating film disposed on the aluminum foil.

[0121] A test piece measuring 10 mm x 50 mm was cut out from the laminate. This test piece was attached to a stainless steel plate measuring 30 mm in length, 70 mm in width, and 1 mm in thickness using double-sided tape (No. 5000NS, manufactured by Nitto Denko CS Systems Corporation). The contact angle (25°C) with ion-exchanged water and formamide (manufactured by Tokyo Chemical Industry Co., Ltd.) was measured using a contact angle meter (DMo-601, manufactured by Kyowa Interface Science Co., Ltd.). The surface free energy σ [mJ / m ２ ] (25°C) was calculated. In addition, the ratio Er / σ of the product Er of the Young's modulus E and the median particle diameter r to the surface free energy σ was calculated. The results are shown in Table 2.

[0122] (Water Absorbency) Using an automatic applicator (manufactured by TQC Sheen), each of the above-mentioned coating liquids was applied to a substrate having a basis weight of 208 g / m2 so as to give a dry thickness of 5 μm. ２ The coating was applied to a sheet of high-quality paper at a speed of 10 mm / sec, and then heated and dried at 100°C for 5 minutes in a heating dryer (manufactured by ADVANTEC, DRE320DR) to obtain a laminate comprising a coating film disposed on the high-quality paper.

[0123] As an index of the water resistance of the coating film, the water absorbency (25°C) of the coating film of the above-mentioned laminate was measured using a water absorbency tester (Gurley type water absorbency tester, manufactured by Yasuda Seiki Seisakusho Co., Ltd.) by the Cobb method in accordance with JIS P 8140 (1998). The contact time between the coating film and water was 120 seconds, and physiological saline was used as the water. The results are shown in Table 2.

[0124] <Evaluation> (Lock-up height) 0.200 g of the above-mentioned coated resin particles was precisely weighed. Next, the coated resin particles were spread in a layer on the bottom of an acrylic cylinder with an inner diameter of 2.0 cm and a depth of 8.0 cm to form a particle layer with a flat upper surface, and then the height H0 from the upper surface of the bottom of the acrylic cylinder to the top of the particle layer was measured. Thereafter, 20 g of physiological saline at 25°C was poured into the acrylic cylinder from the top all at once. Measurement was started when the entire amount of physiological saline was poured, and after 2 minutes, the height H2 from the upper surface of the bottom of the acrylic cylinder to the top of the absorbed particle layer was measured. From the equation "2-minute lock-up height [cm] = H2 - H0", the lock-up height LU of the coated resin particles was calculated. １ The 2-minute value was calculated. If the upper surface of the particle layer after water absorption was not flat, the height of the highest part was taken as H2. The results are shown in Table 3.

[0125] The same procedure as for the coated resin particles was carried out except that the above-mentioned water-absorbent resin particles A to C were used instead of the coated resin particles, and the lock-up height LU of the water-absorbent resin particles was measured. ０ (2-minute value) was obtained. Lock-up height LU of water-absorbent resin particles ０ was 4.2 cm for the water-absorbent resin particles A, 3.9 cm for the water-absorbent resin particles B, and 3.2 cm for the water-absorbent resin particles C.

[0126] In addition, the reference value LU of the lockup height is calculated from the following formula: Ｓ The results are shown in Table 3. LU Ｓ [cm] = LU ０ [cm] × {(supplied amount of water-absorbent resin particles) / (supplied amount of water-absorbent resin particles + supplied amount of coating material)}

[0127] The water absorption retardation rate R1 [%] per 1 part by mass of the coating material was then calculated using the following formula. The results are shown in Table 3. Water absorption retardation rate R1 [%] per 1 part by mass of the coating material = {(LU Ｓ [cm]-LU １ [cm]) / LU Ｓ [cm]}×(100 / supply amount of coating material [parts by mass])

[0128] (Water absorption rate: Vortex method) After adding 50.0 g of saline to a 100 mL beaker, the saline was kept at 25°C in a thermostatic bath. A stirring bar (8 mmφ x 30 mm, without ring) was used to stir the saline at a rotation speed of 600 rpm to generate a vortex. 2.00 g of the above-mentioned coated resin particles were added to the vortex of the saline, and simultaneously measurement was started with a stopwatch. The time until the end point was determined as the time when the vortex disappeared and the liquid level became horizontal, and the water absorption rate AR of the coated resin particles was calculated. １ The time was obtained as [seconds].

[0129] The water absorption rate AR of the water absorbent resin particles was measured in the same manner as for the coated resin particles, except that the above-mentioned water absorbent resin particles A to C were used instead of the coated resin particles. ０ The water absorption rate AR of the water-absorbent resin particles was calculated in seconds. ０ was 42 seconds for the water-absorbent resin particles A, 45 seconds for the water-absorbent resin particles B, and 54 seconds for the water-absorbent resin particles C.

[0130] In addition, the reference value AR of the water absorption rate is calculated using the following formula: Ｓ The results are shown in Table 3. AR Ｓ [Seconds] = AR ０ [seconds] × {(supplied amount of water-absorbent resin particles + supplied amount of coating material) / supplied amount of water-absorbent resin particles}

[0131] The water absorption retardation rate R2 [%] per 1 part by mass of the coating material was then calculated using the following formula. The results are shown in Table 3. Water absorption retardation rate R2 [%] per 1 part by mass of the coating material = {(AR １ [Seconds]-AR Ｓ [seconds]) / AR Ｓ [seconds]}×(100 / supply amount of coating material [parts by mass])

[0132] (Speed ​​adjustment parameter) The speed adjustment parameter was obtained from the following formula. The results are shown in Table 3. It can be determined that the larger the speed adjustment parameter, the better the effect of delaying water absorption. Speed ​​adjustment parameter = (water absorption retardation rate R1 [%] per 1 part by mass of coating material) x (water absorption retardation rate R2 [%] per 1 part by mass of coating material)

[0133]

[0134]

[0135]

[0136] DESCRIPTION OF SYMBOLS 1... processing device, 10... processing section, 11... internal space, 11a, 11b, 11c... space, 12... air inlet, 13... stirring means, 13a... disk section, 13b... support section, 14... opening, 15... exhaust filter, 16... liquid supply section, 20... water-absorbent resin particles, G... air flow, L... coating liquid

Claims

1. It has water-absorbing resin particles and a coating portion that coats at least a part of the water-absorbing resin particles. In the coating material that constitutes the coating portion, the fracture energy obtained from the stress-strain curve in a tensile test at a tensile speed of 200 mm / min is 0.2 J / mm ３ or more, and the water absorption of physiological saline measured under the conditions of a temperature of 25°C and a contact time of 120 seconds in accordance with JIS P 8140 is more than 0 g / m ２ and not more than 300 g / m ２ The coated resin particles.

2. The coated resin particles according to claim 1, wherein the content of the coating portion is 0.50 to 20.00 parts by mass with respect to 100 parts by mass of the water-absorbing resin particles.

3. The breaking energy is 80 J / mm ３ or more, and the water absorption degree is 5 to 300 g / m ２ The coated resin particles according to claim 1, wherein the coated resin particles are as described above.

4. The breaking energy is 250 to 400 J / mm ３ and the water absorption degree is 25 to 100 g / m ２ The coated resin particles according to claim 1, wherein the coated resin particles have the above properties.

5. The coated resin particles according to any one of claims 1 to 4, wherein the coating material contains a copolymer of an olefin and an ethylenically unsaturated monomer.

6. The coated resin particles according to any one of claims 1 to 4, wherein the coating material contains a copolymer of styrene and an ethylenically unsaturated monomer.

7. A step of obtaining coated resin particles having a coating portion that coats at least a part of the water-absorbing resin particles by bringing the water-absorbing resin particles and a coating material into contact with each other, and the surface free energy σ [mJ / m ２ of the film obtained by forming the coating material, the ratio Er / σ of the product Er of the Young's modulus E [MPa] of the coating material and the median particle diameter r [nm] of the coating material obtained from the stress-strain curve in a tensile test at a tensile speed of 200 mm / min exceeds 0 and is 40.00 or less. A method for producing coated resin particles.

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