Method for producing coated resin particles

Abstract

One aspect of the present application relates to a method for producing coated resin particles, including a coating step of obtaining coated resin particles having a coating portion that coats at least a part of water-absorbent resin particles by bringing the water-absorbent resin particles and a coating material into contact with each other, in which the proportion of the time during which the water-absorbent resin particles and the coating material are brought into contact with each other at an atmospheric temperature of 27°C or higher than the glass transition temperature of the main component of the coating material and 4°C or lower than the melting point of the main component of the coating material is 30% or more.

Description

Technical Field

[0001] This invention relates to a method for manufacturing coated resin particles, etc. Background Technology

[0002] Water-absorbing resin particles are widely used in various fields, including diapers, hygiene products, portable toilets and other hygiene materials, water-retaining agents, soil conditioners and other agricultural and horticultural materials, water-stopping agents, anti-condensation agents and other industrial materials. In addition to high water absorption and gel strength, water-absorbing resin particles also require controlled water absorption rate (for example, refer to Patent Document 1 below).

[0003] Previous technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2016-28117 Summary of the Invention

[0004] The technical problem to be solved by the invention Superabsorbent polymer (SAP) particles begin absorbing water upon contact with the liquid they are meant to absorb (aqueous liquids containing water), and quickly reach a swollen state (a state where they cannot absorb further water). Therefore, in applications where absorption requires a certain time after contact with the liquid or where large amounts of liquid are not immediately absorbed, SAP particles cannot always be used effectively. For example, in hygiene materials such as diapers, sanitary products, and portable toilets, when the liquid comes into contact with the absorbent containing SAP particles, it immediately begins to absorb a large amount of liquid, resulting in gel blockage (the gaps between SAP particles are filled by the gel-like SAP particles due to water absorption, thus worsening the liquid's permeability). Consequently, the liquid cannot diffuse sufficiently within the absorbent. In such cases, liquid accumulation may occur at the contact points, leading to the disposal of the hygiene material with a large number of insufficiently absorbed SAP particles remaining outside the contact areas. Therefore, adjusting the water absorption behavior of SAP particles can suppress gel blockage. In this case, the water-absorbing resin particles can be effectively utilized by the sufficient diffusion of the liquid within the absorbent.

[0005] One aspect of the present invention is to provide a method for manufacturing coated resin particles that can be adjusted to slow down the water absorption rate.

[0006] means for solving technical problems The present invention relates to the following [1] to

[10] in several aspects.

[0007] [1] A method for manufacturing coated resin particles, comprising a coating step of obtaining coated resin particles having a coated portion having at least a portion of the coated resin particles by contacting the water-absorbing resin particles with a coating material, wherein the proportion of time during which the water-absorbing resin particles are in contact with the coating material is 30% or more at an atmosphere temperature that is 27°C or lower than the glass transition temperature of the main component of the coating material and 4°C or lower than the melting point of the main component of the coating material.

[0008] [2] According to the method for manufacturing coated resin particles described in [1], wherein, The glass transition temperature of the main component of the coating material is 20–140°C.

[0009] [3] The method for manufacturing coated resin particles according to [1] or [2], wherein, The melting point of the main component of the coating material is 30–150°C.

[0010] [4] The method for manufacturing coated resin particles according to any one of [1] to [3], wherein, The main component of the coating material is a copolymer of olefin / ethylene unsaturated monomers.

[0011] [5] The method for manufacturing coated resin particles according to any one of [1] to [4], wherein, An airflow is supplied from the vertically downward side to the internal space of the device having an internal space containing the absorbent resin particles, and the absorbent resin particles come into contact with the coating material.

[0012] [6] According to the method for manufacturing coated resin particles described in [5], wherein, In at least a portion of the coating process, the heat X, expressed by the following formula (1), is 1.000 [MJ / (min·m]. 2 In the above state, the water-absorbing resin particles are brought into contact with the coating material.

[0013] X=(AG×SG×SH×TD) / (NA×1000)...(1) AG: The amount of airflow supplied to the interior space [m 3 / min] SG: Specific gravity of the gas constituting the airflow [kg / m³] 3 ] SH: Specific heat of the gas constituting the airflow [kJ / (kg·K)] TD: The temperature difference between the airflow supplied to the device and 25°C [K] NA: The area of ​​the narrowest cross-section of the internal space perpendicular to the vertical direction [m²] 2 ] [7] According to the method for manufacturing coated resin particles described in [6], wherein, The heat X is 3.000 [MJ / (min·m 2 )]above.

[0014] [8] The method for manufacturing coated resin particles according to [6] or [7], wherein, In at least a portion of the coating process, the heat X [MJ / (min·m 2 The water content Y[kg / (min·m)] is expressed by the following formula (2). 2 When the ratio X / Y is 2.00 to 35.00 [MJ / kg], the water-absorbing resin particles are brought into contact with a coating liquid containing the coating material and water.

[0015] Y=[(AL×RW) / 100] / (NA×1000)...(2) AL: Amount of coating liquid supplied to the internal space [g / min] RW: Water content [mass %] in the coating solution NA: The area of ​​the narrowest cross-section of the internal space perpendicular to the vertical direction [m²] 2 ] [9] According to the method for manufacturing coated resin particles described in [8], wherein, The ratio X / Y is 7.00 to 30.00 [MJ / kg].

[0016]

[10] The method for manufacturing coated resin particles according to [8] or [9], wherein, The water content Y is 0.200 kg / (min·m 2 )]above.

[0017] Invention Effects According to one aspect of the present invention, a method for manufacturing coated resin particles that can be adjusted to slow down the water absorption rate can be provided. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view of a treatment apparatus used to bring absorbent resin particles into contact with a coating material. Detailed Implementation

[0019] The embodiments of the present invention will now be described. However, the present invention is not limited to the following embodiments and can be implemented in various ways within the scope of its spirit.

[0020] In this specification, "(meth)acrylic acid" refers to at least one of acrylic acid and its corresponding methacrylic acid. The same applies to other similar expressions such as "(meth)acrylate". "(poly)" refers to both cases with and without the prefix "poly". "Above A" in a numerical range means A and above A. "Below A" in a numerical range means A and below A. In the numerical ranges described in this specification, the upper or lower limit of a particular range can be arbitrarily combined with the upper or lower limits of other ranges. The upper or lower limit of the numerical ranges described in this specification can be replaced with the values ​​shown in the examples. The materials exemplified in this specification can be used alone or in combination of two or more. Regarding "A or B", it is sufficient to include either A or B, or both. When multiple substances conforming to each component are present in the composition, unless otherwise stated, the content of each component in the composition refers to the total amount of the multiple substances present in the composition. "Room temperature" means 25°C ± 2°C. “Sieve” refers to the test sieve (metal mesh sieve) specified in JIS Z 8801-1:2019. The term “process” includes not only independent processes, but also processes that cannot be clearly distinguished from others, as long as the intended function of the process is achieved. “Physiological saline” refers to a 0.9% by mass aqueous solution of sodium chloride. The term “A contains B” includes all ways in which A contains B, except for the way in which B constitutes only a part of A, and also the way in which A contains only B (A is composed solely of B).

[0021] The method for manufacturing coated resin particles according to this embodiment includes a coating step in which coated resin particles are obtained by contacting water-absorbing resin particles with a coating material to obtain a coated portion having at least a portion of the water-absorbing resin particles. In the method for manufacturing coated resin particles according to this embodiment, in the coating step, the proportion of time during which the water-absorbing resin particles are in contact with the coating material is 30% or more at an atmosphere temperature that is at least 27°C lower than the glass transition temperature of the main component of the coating material and at least 4°C higher than the melting point of the main component of the coating material. The atmosphere temperature is the temperature of the space in which the water-absorbing resin particles and the coating material are in contact.

[0022] According to the method for manufacturing coated resin particles according to this embodiment, coated resin particles that can be adjusted to slow down the water absorption rate can be obtained. According to the method for manufacturing coated resin particles according to this embodiment, in the evaluation described in the embodiments described later, the 5-minute value of the locking height can be reduced to, for example, 2.1 cm or less (preferably 1.9 cm or less, 1.5 cm or less, 1.2 cm or less, 1.0 cm or less, etc.).

[0023] The reasons for obtaining coated resin particles that can be adjusted to slow down the water absorption rate are speculated as follows. However, the reasons for obtaining such coated resin particles are not limited to the following.

[0024] That is, the coated portion of the resin particles obtained by contacting the absorbent resin particles with the coating material can prevent the absorbent resin particles from contacting the liquid of the object to be absorbed. However, if the contact time between the absorbent resin particles and the coating material is prolonged at a temperature that is too low for the glass transition temperature of the main component of the coating material, defects (exposed portions of the absorbent resin particles) are easily generated in the coated portion of the resin particles due to insufficient softening of the coating material, making it difficult to adjust to slow down the water absorption rate. Furthermore, if the contact time between the absorbent resin particles and the coating material is prolonged at a temperature that is too high for the melting point of the main component of the coating material, the coating material will over-melt, and the absorbent resin particles will adhere to each other through the coating material, making it difficult to obtain coated resin particles.

[0025] On the other hand, in the method for manufacturing coated resin particles according to this embodiment, during the coating process, the proportion of time in which the water-absorbing resin particles are in contact with the coating material is 30% or more at an atmosphere temperature that is at least 27°C lower than the glass transition temperature of the main component of the coating material and at least 4°C higher than the melting point of the main component of the coating material. As a result, the coating material softens easily, thus preventing defects (exposed portions of the water-absorbing resin particles) from forming in the coated portion of the coated resin particles. Furthermore, the coating material does not easily over-melt, thus easily suppressing the adhesion of the water-absorbing resin particles to each other through the coating material. In summary, the method for manufacturing coated resin particles according to this embodiment yields coated resin particles that are adjusted to slow down the water absorption rate.

[0026] Typically, to slow down the water absorption rate 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 can sometimes degrade productivity due to increased coating time. On the other hand, according to one aspect of the method for manufacturing coated resin particles according to this embodiment, even when the coated portion is thinned, defects are less likely to occur, and therefore, the water absorption rate of the coated resin particles can be slowed down without increasing the amount of coating material used.

[0027] The coated resin particles obtained by the manufacturing method of the coated resin particles according to this embodiment can be used, for example, in combination with absorbent resin particles without a coating. By using a mixture of coated resin particles and absorbent resin particles without a coating (mixed particles) in the absorbent body of sanitary materials (diapers, sanitary products, portable toilets, etc.), gel blockage upon contact with the liquid of the absorbent material is easily suppressed. Specifically, when the mixed particles come into contact with a liquid, the absorbent resin particles without a coating will gel due to water absorption, but the water absorption of the coated resin particles is suppressed (i.e., the coated resin particles do not gel immediately). Therefore, the gaps between the particles are not filled within a specified time, ensuring liquid permeability. As a result, the liquid can easily diffuse sufficiently within the absorbent body, thus allowing for effective utilization of the absorbent resin particles throughout the absorbent body. In addition, the time required to suppress gel blockage can be adjusted by appropriately changing the type or amount of the constituent material of the coating, the type of absorbent resin particles constituting the coating resin particles, the type of absorbent resin particles without the coating, and the mixing ratio of the coating resin particles and the absorbent resin particles without the coating.

[0028] The absorbent resin particles constituting the coated resin particles can be polymer particles. Polymer particles can be obtained by polymerizing monomers containing ethylene unsaturated monomers (compounds having ethylene unsaturated bonds), or by polymerizing only ethylene unsaturated monomers. They can have ethylene unsaturated monomers as monomer units (monomer units derived from ethylene unsaturated monomers) or only ethylene unsaturated monomers as monomer units. Polymer particles can be polymer particles with a cross-linked structure (cross-linked polymer particles). The method for manufacturing coated resin particles according to this embodiment can include a polymerization step of obtaining absorbent resin particles by polymerizing ethylene unsaturated monomers before the coating step. Examples of polymerization methods for obtaining ethylene unsaturated monomers for polymer particles include reverse suspension polymerization, aqueous solution polymerization, bulk polymerization, and precipitation polymerization.

[0029] Ethylene unsaturated monomers are compounds having at least one carbon-carbon double bond within the molecule and exhibiting free radical polymerization properties, preferably compounds having one carbon-carbon double bond within the molecule and exhibiting free radical polymerization properties. Ethylene unsaturated monomers can be water-soluble (their solubility in 100g of ion-exchanged water at 25°C is 1.0g or more). The solubility of water-soluble ethylene unsaturated monomers in 100g of ion-exchanged water at 25°C can be 5.0g or more, 10g or more, 50g or more, or 100g or more. Examples of vinyl unsaturated monomers include (meth)acrylic acid and its salts, 2-(meth)acrylamide-2-methylpropanesulfonic acid and its salts, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-hydroxymethyl(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. When the vinyl unsaturated monomer has an amino group, that amino group can also be quaternized. A single vinyl unsaturated monomer can be used alone, or two or more monomers can be used in combination.

[0030] When an ethylene-unsaturated monomer has an acidic group (e.g., a carboxyl group), this acidic group can be neutralized with a basic neutralizing agent before being used in the polymerization reaction. The degree of neutralization in the ethylene-unsaturated monomer (based on the degree of neutralization of the basic neutralizing agent) can be 10–100 mol%, 50–90 mol%, or 60–80 mol% of the acidic group in the ethylene-unsaturated monomer.

[0031] From an industrially readily available point of view, the vinyl unsaturated monomer may comprise at least one compound selected from the group consisting of (meth)acrylic acid, (meth)acrylate, (meth)acrylamide and N,N-dimethylacrylamide, or at least one compound selected from the group consisting of (meth)acrylic acid, (meth)acrylate and (meth)acrylamide.

[0032] Monomers other than the aforementioned vinyl unsaturated monomers can also be used as monomers for obtaining the superabsorbent resin particles. Such monomers can be used, for example, by mixing with an aqueous solution containing vinyl unsaturated monomers. The ratio of the amount of vinyl unsaturated monomer used relative to the total amount of monomers (the total amount of monomers used to obtain the superabsorbent resin particles) can be 70–100 mol%, 80–100 mol%, 90–100 mol%, 95–100 mol%, or 99.5–100 mol%. The ratio of the total amount of (meth)acrylic acid and (meth)acrylate relative to the total amount of monomers (the total amount of monomers used to obtain the superabsorbent resin particles) can also be 70–100 mol%, 80–100 mol%, 90–100 mol%, 95–100 mol%, or 99.5–100 mol.

[0033] Hygroscopic resin particles can be cross-linked polymer particles. While self-crosslinking can occur during polymerization, crosslinking can also be promoted by using an internal crosslinking agent. Using an internal crosslinking agent makes it easier to control the water absorption properties (water retention, etc.) of the hygroscopic resin particles. The polymerization process can be a process of obtaining hygroscopic resin particles by polymerizing ethylene-based unsaturated monomers in the presence of an internal crosslinking agent.

[0034] Examples of internal crosslinking agents include compounds having two or more reactive functional groups (e.g., polymerizable unsaturated groups). Examples of internal crosslinking agents include di or tri(meth)acrylates of polyols (such as polyethylene glycol di(meth)acrylate), unsaturated polyesters obtained by reacting polyols with unsaturated acids, compounds containing glycidyl groups (such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyglycerol diglycidyl ether), bisacrylamides, di or tri(meth)acrylates obtained by reacting polyepoxides with (meth)acrylic acid, and compounds obtained by reacting polyisocyanates with (meth)acrylic acid. The reactions of hydroxyethyl esters with di(meth)acrylate carbamates, allyl starch, allyl cellulose, diallyl phthalate, N,N',N”-triallyl isocyanurate, divinylbenzene, pentaerythritol, ethylenediamine, polyethyleneimine, etc., can yield these products. From the viewpoint of easily adjusting the water absorption properties of the absorbent resin particles, the internal crosslinking agent may include at least one selected from the group consisting of (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether.

[0035] The amount of internal crosslinking agent can be appropriately adjusted to modify the water absorption characteristics of the water-absorbing resin particles. For example, relative to 1 mole of vinyl unsaturated monomer (e.g., 1 mole of (meth)acrylic acid and its salts), the amount can be within the following ranges: 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 the internal crosslinking agent can be less than 0.300 mmol, less than 0.200 mmol, less than 0.100 mmol, less than 0.090 mmol, less than 0.080 mmol, less than 0.070 mmol, less than 0.060 mmol, less than 0.055 mmol, less than 0.050 mmol, less than 0.045 mmol, or less than 0.040 mmol. According to the above viewpoint, the amount of the internal crosslinking agent can be 0.001–0.300 mmol, 0.001–0.100 mmol, 0.001–0.080 mmol, 0.001–0.045 mmol, 0.030–0.300 mmol, 0.030–0.100 mmol, 0.030–0.080 mmol, 0.030–0.045 mmol, 0.045–0.300 mmol, 0.045–0.100 mmol, or 0.045–0.080 mmol.

[0036] In water-absorbing resin particles, the crosslinking density near the surface of the polymer particles can be increased (surface crosslinking can be implemented). Through surface crosslinking, the water absorption characteristics (water retention, etc.) of the water-absorbing resin particles can be easily adjusted. Specifically, the crosslinking density near the surface of the polymer particles can be adjusted by factors such as the moisture content of the polymer particles supplied for surface crosslinking and the type or amount of surface crosslinking agent used in surface crosslinking, thereby adjusting the water absorption characteristics.

[0037] Superabsorbent polymer (SAP) particles may contain components such as gel stabilizers, metal chelators, and flow improvers (lubricants). These components can be disposed within the SAP particles, on the surface of the SAP particles, or both.

[0038] The shape of the absorbent resin particles or coated resin particles can be, for example, generally spherical, fragmented, or granular, or it can be a shape formed by the aggregation of primary particles having these shapes. The particle size of the absorbent resin particles or coated resin particles (the median particle size determined by the measurement method described in Patent Document 1) can be 100–800 μm, 150–700 μm, 200–600 μm, 250–500 μm, 300–400 μm, or 250–850 μm.

[0039] The coated portion of the coated resin particles is coated with at least a portion (partially or entirely) of the water-absorbing resin particles, and is capable of coating at least a portion (partially or entirely) of the surface of the water-absorbing resin particles. The coated portion can be a layered coating layer. The coating layer can be a single-layer structure or a multi-layer structure having two or more layers.

[0040] The coating can be obtained by contacting the coating material with water-absorbing resin particles. The coating material may contain a polymer component. The coating material may be water-soluble, water-insoluble, or water-poorly soluble. "Water-soluble" means a solubility of 1 g or more (e.g., 1–150 g) in 100 g of ion-exchanged water at 25°C. "Water-poorly soluble" means a solubility of more than 0 g and less than 1 g in 100 g of ion-exchanged water at 25°C.

[0041] Water-soluble components can contain compounds with hydrophilic groups. Examples of hydrophilic groups include anionic, cationic, amphoteric, and nonionic groups. Examples of anionic groups include carboxyl, sulfonic acid, and phosphate groups. Examples of cationic groups include amino, imino, and quaternary ammonium groups. Examples of amphoteric groups include carboxy-betaine, sulfobetaine, and phosphate betaine. Examples of nonionic groups include hydroxyl, amide, pyrrolidone, lactam, alkoxy, and (poly)oxyalkylene groups.

[0042] The water-soluble component may include at least one compound selected from the group consisting of compounds having hydroxyl groups, compounds having amide groups, compounds having quaternary ammonium groups, and compounds having (poly)oxyalkylene groups. Examples of compounds having hydroxyl groups include polyvinyl alcohol, monosaccharides, polysaccharides, and phenyl diethylene glycol. Examples of compounds having amide groups include polyacrylamide and polyvinylpyrrolidone. Examples of compounds having quaternary ammonium groups include ammonium chloride. Examples of compounds having (poly)oxyalkylene groups include polyepoxides (e.g., polyethylene oxide) and polyalkylene glycols (e.g., polyethylene glycol).

[0043] Examples of water-insoluble components include polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and other polyoxyethylene alkylene ethers; 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; and poly-α-methylstyrene, syndiotactic polyols, etc. Polystyrene and other polystyrene; polycarbonate and other polyhexamethylene carbonate; poly(meth)acrylates such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; poly(alkyl)methacrylates such as poly(meth)acrylate; polyacetals such as polyoxymethylene, polyacetaldehyde, polypropionaldehyde, and polybutyraldehyde; halogenated vinyl polymers such as polyvinyl chloride, polyvinyl acetate, and polyvinyl fluoride; polyvinylidene fluoride; polysiloxanes, etc. Water-insoluble components can be acid-modified. For example, water-insoluble components can be acid-modified using acid anhydrides (maleic anhydride, succinic anhydride, phthalic anhydride, etc.).

[0044] The coating material may comprise a polymer having an vinyl unsaturated monomer as a monomer unit (a polymer having a monomer unit derived from an vinyl unsaturated monomer). The vinyl unsaturated monomer is a compound having at least one carbon-carbon double bond in the molecule and exhibiting free radical polymerization, preferably a compound having one carbon-carbon double bond in the molecule and exhibiting free radical polymerization. Examples of vinyl unsaturated monomers include (meth)acrylic acid and its salts, (meth)acrylates (methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, 2-(diethylamino)propyl (meth)acrylate, etc.), (meth)acrylamide monomers ((meth)acrylamide, N-isopropyl (meth)acrylamide, 2-(meth)acrylamide-2-methylpropanesulfonic acid and its salts, N,N-dimethyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, etc.), polyethylene glycol mono(meth)acrylate, styrene, α-alkylstyrene, butadiene, etc. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, vinyl unsaturated monomers may include (meth)acrylic acid compounds (compounds having (meth)acryloyl groups), or at least one selected from the group consisting of (meth)acrylic acid and its salts.

[0045] As coating materials, chain polymerization reactants such as poly(meth)acrylic acid, poly(meth)acrylamide, polyvinyl alcohol, polyepoxide, and polyalkylene glycol can be used; step-polymerization reactants such as urethane resins (e.g., condensates of polyols and polyisocyanates), phenolic resins (e.g., condensates of phenolic compounds and aldehydes), polyesters, polyamides, and polycarbonates can be used.

[0046] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the coating material may include at least one selected from the group consisting of polyvinyl alcohol, polyacrylamide, polyepoxide, polyalkylene glycol, phenylene glycol, polyoxyalkylene ether, poly(meth)acrylate, polyamide, polyolefin and copolymers of olefin / vinyl unsaturated monomers (copolymers having olefin and vinyl unsaturated monomers as monomer units), or may include at least one selected from the group consisting of polyvinyl alcohol, polyalkylene glycol, poly(meth)acrylate and copolymers of olefin / vinyl unsaturated monomers. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the polymer component contained in the coating material may consist only of at least one selected from the group consisting of polyvinyl alcohol, polyacrylamide, polyepoxide, polyalkylene glycol, phenyl diethylene glycol, polyoxyalkylene ether, poly(meth)acrylate, polyamide, polyolefin, and copolymers of olefins / vinyl unsaturated monomers, or it may consist only of at least one selected from the group consisting of polyvinyl alcohol, polyalkylene glycol, poly(meth)acrylate, and copolymers of olefins / vinyl unsaturated monomers. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the coating material may contain copolymers of olefins / vinyl unsaturated monomers and polyalkylene glycol, or it may contain copolymers of olefins / vinyl unsaturated monomers and polyethylene glycol. From the viewpoint that it is easy to adjust to slow down the water absorption rate of the coated resin particles, the polymer component contained in the coating material can be composed only of copolymers of olefins / vinyl unsaturated monomers and polyalkylene glycols, or it can be composed only of copolymers of olefins / vinyl unsaturated monomers and polyethylene glycols.

[0047] When the vinyl unsaturated monomers constituting the polymer components in a coating material have acidic groups (e.g., carboxyl groups), these acidic groups can be neutralized by an alkaline neutralizing agent. In this case, the degree of neutralization of the vinyl unsaturated monomer can exceed 0 mol% and less than 100 mol%, 5–100 mol%, 10–100 mol%, 20–100 mol%, 30–100 mol%, 40–100 mol%, or 50–100 mol% of the acidic groups in the vinyl unsaturated monomer. By increasing the degree of neutralization, the coating liquid (e.g., emulsion) described later is easily stabilized, and uniform coated resin particles are easily obtained. From this perspective, the degree of neutralization of the vinyl unsaturated monomer can be 10–100 mol%, 20–100 mol%, 30–100 mol%, 40–100 mol%, or 50–100 mol%. Examples of vinyl unsaturated monomers with such neutralized acidic groups include sodium acrylate and ammonium acrylate, with a degree of neutralization of 5–100 mol%.

[0048] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the olefin as a monomer unit of the polyolefin or the olefin as a monomer unit of the copolymer of olefin / vinyl unsaturated monomers may include at least one selected from the group consisting of ethylene, propylene, and butene, or may include ethylene. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the vinyl unsaturated monomer in the copolymer of olefin / vinyl unsaturated monomers may include the vinyl unsaturated monomers listed above as constituent materials of water-absorbing resin particles, or may include (meth)acrylic acid compounds, or may include at least one selected from the group consisting of (meth)acrylic acid and its salts.

[0049] In copolymers of olefins and vinyl unsaturated monomers, the water absorption rate of the coated resin particles can be easily adjusted by changing the ratio of olefin monomer units (derived from olefin monomer units) to vinyl unsaturated monomer units (derived from vinyl unsaturated monomer units). That is, by increasing the ratio of highly hydrophobic monomer units, the water absorption rate of the coated resin particles can be slowed down. For example, in copolymers of olefins and vinyl unsaturated monomers, the proportion of olefin monomer units can be 72.0–98.0 mol% or 80.0–97.0 mol%.

[0050] The coating material can be used alone or in combination of two or more. The main component of the coating material is the component used in the largest quantity (by mass) of the coating material. When using a single coating material, that single coating material is the main component of the coating material. When using two or more coating materials in combination, the component used in the largest quantity of each coating material is the main component of the coating material. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the main component of the coating material can be a copolymer of olefin / vinyl unsaturated monomers or a copolymer of ethylene / vinyl unsaturated monomers. The vinyl unsaturated monomers in these copolymers can include (meth)acrylic acid compounds or at least one selected from the group consisting of (meth)acrylic acid and its salts.

[0051] From the perspective of easily adjusting to slow down the water absorption rate of the coated resin particles, the proportion of the main component of the coating material, based on the total mass of the coating material, can be within the following ranges: The proportion of the main component of the coating material can be 50% by mass or more, exceeding 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, or 96% by mass or more. The proportion of the main component of the coating material can be 100% by mass or less, less than 100% by mass, less than 99% by mass, less than 98% by mass, less than 97% by mass, less than 96% by mass, less than 95% by mass, less than 92% by mass, or less than 91% by mass. From the above perspective, the proportion of the main component of the coating material can be 50-100% by mass, 70% by mass or more but less than 100% by mass, 80-98% by mass, or 85-97% by mass. When there are two or more main components of the coating material (the two or more coating materials are used in the same amount (mass) and each of them is used in the largest amount), the content of the main component of the coating material is the total amount of these two or more coating materials.

[0052] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the glass transition temperature (Tg) of the main component of the coating material can be within the following ranges: Glass transition temperature can be above 20°C, above 30°C, above 40°C, above 45°C, above 50°C, above 52°C, above 55°C, above 56°C, above 58°C, above 60°C, above 62°C, or above 63°C. Glass transition temperature can be below 140°C, below 120°C, below 100°C, below 90°C, below 80°C, below 75°C, below 70°C, below 65°C, below 63°C, below 62°C, below 60°C, below 58°C, or below 56°C. From the above perspective, the glass transition temperature can be 20–140°C, 30–120°C, 40–100°C, 50–100°C, 55–100°C, 60–100°C, 40–70°C, 50–70°C, 55–70°C, 60–70°C, 40–60°C, 50–60°C, or 55–60°C. When there are two or more coating materials as the main component, the glass transition temperature of each coating material can be within the above ranges. The glass transition temperature is determined by the method described in the examples below.

[0053] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the melting point (MP) of the main component of the coating material can be within the following ranges: Melting point can be above 30°C, above 40°C, above 50°C, above 60°C, above 65°C, above 70°C, above 75°C, above 80°C, above 85°C, above 88°C, above 90°C, above 95°C, or above 99°C. Melting point can be below 150°C, below 140°C, below 130°C, below 120°C, below 110°C, below 105°C, below 100°C, below 99°C, below 95°C, below 90°C, or below 88°C. For the purposes of the above, the melting point can be 30–150°C, 40–140°C, 50–130°C, 60–120°C, 60–100°C, 60–95°C, 80–130°C, 80–100°C, 80–95°C, 85–130°C, 85–100°C, 85–95°C, 95–130°C, or 95–100°C. When there are two or more main components in the coating material, the melting point of each coating material can be within the above ranges. The melting point is determined by the method described in the examples below.

[0054] The ratio of the coating material to 100 parts by weight of the water-absorbing resin particles in the coating process can be within the following range. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the ratio of the coating material can be 0.10 parts by weight or more, 0.50 parts by weight or more, 1.00 parts by weight or more, 2.00 parts by weight or more, 3.00 parts by weight or more, 4.00 parts by weight or more, 5.00 parts by weight or more, 6.00 parts by weight or more, 7.00 parts by weight or more, 8.00 parts by weight or more, 9.00 parts by weight or more, 10.00 parts by weight or more, or 11.00 parts by weight or more. From the perspective of improving productivity, such as shortening coating time, the proportion of coating material can be less than 50.00 parts by weight, less than 40.00 parts by weight, less than 30.00 parts by weight, less than 25.00 parts by weight, less than 20.00 parts by weight, less than 18.00 parts by weight, less than 15.00 parts by weight, less than 12.00 parts by weight, less than 11.00 parts by weight, less than 10.00 parts by weight, less than 9.00 parts by weight, less than 8.00 parts by weight, less than 7.00 parts by weight, less than 6.00 parts by weight, or less than 5.00 parts by weight. According to the above viewpoint, the proportion of the coating material can be 0.10–50.00 parts by weight, 0.10–15.00 parts by weight, 0.10–10.00 parts by weight, 4.00–50.00 parts by weight, 4.00–15.00 parts by weight, 4.00–10.00 parts by weight, 6.00–50.00 parts by weight, 6.00–15.00 parts by weight, 6.00–10.00 parts by weight, 10.00–50.00 parts by weight, or 10.00–15.00 parts by weight.

[0055] The proportion of the main component of the coating material in the coating process (or the proportion of its total amount if there are two or more main components of the coating material) relative to 100 parts by weight of the water-absorbing resin particles can be within the following range. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the proportion of the main component of the coating material can be 0.10 parts by weight or more, 0.50 parts by weight or more, 1.00 parts by weight or more, 2.00 parts by weight or more, 3.00 parts by weight or more, 4.00 parts by weight or more, 5.00 parts by weight or more, 6.00 parts by weight or more, 7.00 parts by weight or more, 8.00 parts by weight or more, 9.00 parts by weight or more, or 10.00 parts by weight or more. The proportion of the main component of the coating material can be less than 50.00 parts by weight, less than 40.00 parts by weight, less than 30.00 parts by weight, less than 25.00 parts by weight, less than 20.00 parts by weight, less than 18.00 parts by weight, less than 15.00 parts by weight, less than 12.00 parts by weight, less than 11.00 parts by weight, or less than 10.00 parts by weight. Alternatively, the proportion of the main component of the coating material can be less than 9.00 parts by weight, less than 8.00 parts by weight, less than 7.00 parts by weight, less than 6.00 parts by weight, or less than 5.00 parts by weight. According to the above viewpoint, the proportion of the main component of the coating material can be 0.10–50.00 parts by weight, 0.10–15.00 parts by weight, 0.10–10.00 parts by weight, 0.10–8.00 parts by weight, 4.00–50.00 parts by weight, 4.00–15.00 parts by weight, 4.00–10.00 parts by weight, 4.00–8.00 parts by weight, 6.00–50.00 parts by weight, 6.00–15.00 parts by weight, 6.00–10.00 parts by weight, 6.00–8.00 parts by weight, 8.00–50.00 parts by weight, 8.00–15.00 parts by weight, or 8.00–10.00 parts by weight.

[0056] In the coating process of the method for manufacturing coated resin particles according to this embodiment, coated resin particles having at least a portion of the coated absorbent resin particles are obtained by contacting the absorbent resin particles (coated body) with the coating material. That is, the coating process is a process in which the absorbent resin particles are supplied with the coating material one-time, continuously, or intermittently, so that the absorbent resin particles and the coating material can be in contact with each other. The coating process ends when the absorbent resin particles and the coating material cannot be in contact (typically, when the entire predetermined amount of coating material has been supplied). In this specification, the time of the coating process is referred to as the "coating time," and this interval is not included in the coating time when the coating process is performed in multiple sessions (for example, when the supply of the coating material is temporarily stopped midway through the coating process to set an interval, and then the supply of the coating material is resumed). The coating process includes a step X in which the absorbent resin particles and the coating material are contacted at an atmospheric temperature of "a certain temperature A1 or higher and a certain temperature A2 or lower". That is, process X is a process in which the water-absorbing resin particles come into contact with the coating material under an atmosphere temperature that satisfies the condition that "temperature A1 ≤ atmosphere temperature ≤ temperature A2".

[0057] In process X, from the viewpoint of obtaining coating resin particles that can be adjusted to slow down the water absorption rate, the water-absorbing resin particles are brought into contact with the coating material at an atmosphere temperature of at least 27°C lower than the glass transition temperature of the main component of the coating material, which is above temperature A1. Conversely, the water-absorbing resin particles are brought into contact with the coating material at an atmosphere temperature of at least 4°C higher than the melting point of the main component of the coating material, which is below temperature A2. When there are two or more main components in the coating material, temperature A1 and temperature A2 are set based on the main component with the highest glass transition temperature among the two or more main components.

[0058] From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, temperature A1 can be a temperature that is 25°C, 20°C, 15°C, 10°C, 5°C, 3°C, or 1°C lower than the glass transition temperature of the main component of the coating material, or it can be the same as the glass transition temperature of the main component of the coating material, or it can be a temperature that is 1°C, 2°C, 3°C, 4°C, 5°C, 10°C, 15°C, 20°C, or 25°C higher than the glass transition temperature of the main component of the coating material.

[0059] From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, temperature A2 can be a temperature 3°C, 2°C, or 1°C higher than the melting point of the main component of the coating material, or a temperature equal to the melting point of the main component of the coating material, or a temperature 1°C, 2°C, 3°C, 4°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or 55°C lower than the melting point of the main component of the coating material.

[0060] From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, the atmosphere temperature at which the water-absorbing resin particles come into contact with the coating material in process X can be an atmosphere temperature that is 26°C or higher below the glass transition temperature of the main component of the coating material and lower than the melting point of the main component of the coating material; it can also be an atmosphere temperature that is 10°C or higher below the glass transition temperature of the main component of the coating material and lower than the melting point of the main component of the coating material; it can also be an atmosphere temperature that is 5°C or higher than the glass transition temperature of the main component of the coating material and lower than the melting point of the main component of the coating material; it can also be an atmosphere temperature that is 20°C or higher than the glass transition temperature of the main component of the coating material and lower than the melting point of the main component of the coating material; it can also be an atmosphere temperature that is 20°C or higher than the glass transition temperature of the main component of the coating material and lower than the melting point of the main component of the coating material; it can also be an atmosphere temperature that is 26 ...

[0061] From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, the atmosphere temperature of process X can be within the following ranges: The atmosphere temperature of process X can 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, or 80°C or higher. The atmosphere temperature of process X can 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, 50°C or lower, 45°C or lower, 40°C or lower, 35°C or lower. According to the above viewpoint, the atmosphere temperature of process X can be 20-150℃, 20-140℃, 23-130℃, 30-120℃, 30-90℃, 30-60℃, 40-120℃, 40-90℃, 40-60℃, 60-120℃, or 60-90℃.

[0062] In addition to step X, the coating process may include step Y, in which the absorbent resin particles come into contact with the coating material at an atmospheric temperature below temperature A1, and / or step Z, in which the absorbent resin particles come into contact with the coating material at an atmospheric temperature above temperature A2. For example, step Y may be a step that raises the temperature to the atmospheric temperature of step X before step X, and step Z may be a step that is performed after step X. The coating process may include multiple steps X, multiple steps Y, multiple steps Z, or may alternate between steps X and Y, or alternate between steps X and Z. The atmospheric temperature of the coating process (steps X, Y, and Z) may be a constant temperature or may vary over time.

[0063] In the coating process, from the viewpoint of slowing down the water absorption rate of the coating resin particles, the ratio TR (total time of multiple coating processes) for the contact time between the water-absorbing resin particles and the coating material (based on the overall coating time) is 30% or more, at an atmosphere temperature that is at least 27°C lower than the glass transition temperature of the main component of the coating material and at least 4°C higher than the melting point of the main component of the coating material. From the viewpoint of easily adjusting to slow down the water absorption rate of the coating resin particles, the ratio TR can be 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more. The ratio TR can be 100% or less, 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 65% or less. In view of the above, the ratio TR can be 30-100%, 50-100%, 60-100%, 65-100%, 70-100%, 80-100%, 85-100%, 90-100%, or 95-100%.

[0064] In the coating process, for example, the coating material can be brought into contact with water-absorbing resin particles present in an atmosphere such as air, inert gases (e.g., nitrogen), or mixtures thereof. The coating material in contact with the water-absorbing resin particles can be a dry coating material, a liquid coating material, a gel 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) containing the coating material and a liquid medium (e.g., water).

[0065] The coating material can be brought into contact with the absorbent resin particles by contacting a coating solution containing the coating material and a liquid medium (e.g., water). This readily yields a coating of uniform thickness. The liquid medium can be a solvent or a dispersion medium. The coating solution containing the coating material and the liquid medium can be obtained by dissolving the coating material in a solvent or by dispersing the coating material in a dispersion medium.

[0066] Examples of solvents or dispersion media include water, hydrophilic compounds, and hydrocarbon compounds. A single solvent or dispersion medium can be used, or it can be a mixture of two or more (e.g., a mixture of water and a hydrophilic compound). Hydrophilic compounds are compounds that are substantially homogeneously soluble in water. Examples of hydrophilic compounds include alcohols such as methanol and isopropanol; diols 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.

[0067] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the content of the coating material in the coating solution, based on the total mass of the coating solution, can be within the following ranges: The content of the coating material can 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, 10.00% by mass or more, 10.50% by mass or more, 11.00% by mass or more, 12.00% by mass or more, or 15.00% by mass or more. The content of the coating material can 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. According to the above viewpoint, the content of the coating material can be 1.00–50.00% by mass, 1.00–20.00% by mass, 1.00–15.00% by mass, 5.00–50.00% by mass, 5.00–20.00% by mass, 5.00–15.00% by mass, 10.00–50.00% by mass, 10.00–20.00% by mass, 10.00–15.00% by mass, 12.00–50.00% by mass, or 12.00–20.00% by mass.

[0068] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the content of the liquid medium in the coating solution, based on the total mass of the coating solution, can be within the following ranges: The content of the liquid medium can be 10.00% by mass or more, 30.00% by mass or more, 50.00% by mass or more, 60.00% by mass or more, 70.00% by mass or more, 80.00% by mass or more, 85.00% by mass or more, 88.00% by mass or more, 89.00% by mass or more, 89.50% by mass or more, or 90.00% by mass or more. The content of the liquid medium can be 99.00% by mass or less, 97.00% by mass or less, 95.00% by mass or less, 92.00% by mass or less, 90.00% by mass or less, 89.50% by mass or less, 89.00% by mass or less, 88.00% by mass or less, or 85.00% by mass or less. According to the above viewpoint, the content of the liquid medium can be 10.00–99.00% by mass, 30.00–99.00% by mass, 50.00–99.00% by mass, 80.00–99.00% by mass, 85.00–99.00% by mass, 50.00–95.00% by mass, 85.00–95.00% by mass, 50.00–90.00% by mass, 80.00–90.00% by mass, 85.00–90.00% by mass, 50.00–88.00% by mass, or 80.00–88.00% by mass.

[0069] From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the water content in the coating solution (hereinafter referred to as water content RW) can be within the following ranges based on the total mass of the coating solution. The water content can be 10.00% by mass or more, 30.00% by mass or more, 50.00% by mass or more, 60.00% by mass or more, 70.00% by mass or more, 80.00% by mass or more, 85.00% by mass or more, 88.00% by mass or more, 89.00% by mass or more, 89.50% by mass or more, or 90.00% by mass or more. The water content can be 99.00% by mass or less, 97.00% by mass or less, 95.00% by mass or less, 92.00% by mass or less, 90.00% by mass or less, 89.50% by mass or less, 89.00% by mass or less, 88.00% by mass or less, or 85.00% by mass or less. According to the above viewpoint, the water content can be 10.00–99.00% by mass, 30.00–99.00% by mass, 50.00–99.00% by mass, 80.00–99.00% by mass, 85.00–99.00% by mass, 50.00–95.00% by mass, 80.00–95.00% by mass, 85.00–95.00% by mass, 50.00–90.00% by mass, 80.00–90.00% by mass, 85.00–90.00% by mass, 50.00–88.00% by mass, or 80.00–88.00% by mass.

[0070] There are no particular limitations on the method used to bring the absorbent resin particles into contact with the coating material during the coating process; various methods can be used. For example, in the coating process, the absorbent resin particles and the coating material (e.g., the coating material of a coating liquid) can be brought into contact in a container such as a flask. In the coating process, the coating material can be brought into contact with absorbent resin particles in an airflow, or with absorbent resin particles blown up by the airflow, or by supplying the coating material to a flow layer of absorbent resin particles. The gas constituting the airflow can be air, an inert gas (e.g., nitrogen), or a mixture thereof. The temperature of the airflow can exceed 25°C. In the coating process, the coating material can be brought into contact with absorbent resin particles that are being stirred using a stirring mechanism. The stirring mechanism can be a stirring mechanism with stirring blades, or a gas supply mechanism capable of supplying an airflow different from the airflow used to blow up the absorbent resin particles. In the coating process, the absorbent resin particles can be agitated solely by an airflow used to agitate them, without employing a different agitation mechanism. In the coating process, the absorbent resin particles can be brought into contact with the coating material by spraying a coating liquid onto them. The nozzle used for spraying the coating liquid is not particularly limited; for example, a tangential sprayer or a two-fluid nozzle (e.g., a nozzle that sprays both the coating liquid and an inert gas) can be used. In the coating process, various devices such as rotary granulators, agitated granulators, and fluidized bed granulators can be used to bring the absorbent resin particles into contact with the coating material.

[0071] The method for manufacturing coated resin particles according to this embodiment can include a step before the coating process to adjust the temperature of the atmosphere in the space where the absorbent resin particles and the coating material come into contact. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the temperature of the atmosphere in the space where the absorbent resin particles and the coating material come into contact before the coating process can be 25°C or higher, 35°C or higher, 45°C or higher, or 55°C or higher. The atmosphere temperature can be 140°C or lower, 120°C or lower, 100°C or lower, or 80°C or lower. From the above viewpoint, the atmosphere temperature can be 25–140°C, 25–120°C, 25–100°C, or 25–80°C.

[0072] The method for manufacturing coated resin particles according to this embodiment can include a drying step after the coating step to dry the coated resin particles. The atmosphere temperature and time of the drying step can be appropriately adjusted according to the type and amount of coating material. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the atmosphere temperature of the drying step can be 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher. The atmosphere temperature of the drying step can be 140°C or lower, 120°C or lower, 100°C or lower, or 80°C or lower. From the above viewpoint, the atmosphere temperature of the drying step can be 20–140°C, 30–120°C, 40–100°C, or 50–80°C. The drying time can be 10 minutes or more, 20 minutes or more, or 30 minutes or more. The drying time can be 180 minutes or less, 120 minutes or less, or 60 minutes or less. From the above viewpoint, the drying time can be 10–180 minutes, 20–120 minutes, or 30–60 minutes.

[0073] In the method for manufacturing coated resin particles according to this embodiment, during the coating process, an airflow can be supplied from the vertically downward side to the internal space of an apparatus (e.g., a flow layer granulator) that contains the internal space of the absorbent resin particles, thereby bringing the absorbent resin particles into contact with the coating material. The internal space is the space for supplying the coating material and is the space where the absorbent resin particles and the coating material can come into contact with each other. The airflow can be supplied from the vertically downward side along the vertical direction, or it can be supplied from the vertically downward side in a direction intersecting the vertical direction.

[0074] Figure 1 This is a schematic cross-sectional view of a treatment apparatus for bringing absorbent resin particles into contact with a coating material. The treatment apparatus 1 includes a treatment section 10 and an air supply section (not shown) for supplying airflow G to the treatment section 10.

[0075] The processing unit 10 is a generally cylindrical component extending in the vertical direction (the height direction of the processing device 1: the same below). The processing unit 10 has a generally cylindrical internal space 11 that contains absorbent resin particles 20. The internal space 11 has a cylindrical space 11a, a space 11b located vertically above space 11a, and a cylindrical space 11c located vertically above space 11b. Spaces 11a, 11b, and 11c are formed by continuous movement from below to above in the vertical direction to constitute the internal space 11. Space 11a has the narrowest cross-section (narrowest section) in the internal space 11. Space 11b extends in a conical shape towards the vertical direction.

[0076] An air supply port 12 is formed at the center of the bottom surface of the processing unit 10. The air supply port 12 is connected to the air supply unit, and airflow G is supplied to the internal space 11 through the air supply port 12. By adjusting the temperature of the airflow G, the atmosphere temperature of the internal space 11 can be adjusted.

[0077] The processing unit 10 includes a stirring mechanism 13 (e.g., rotor blades) for the agitation of absorbent resin particles 20. The stirring mechanism 13 has a disc-shaped portion 13a protruding vertically from its center and a support portion 13b supporting the disc portion 13a. The disc portion 13a extends horizontally downwards in the vertical direction within the space 11a, and an annular opening 14 is formed at a position on the outer periphery of the space 11a compared to the disc portion 13a. The disc portion 13a has an annular upper surface around its central protrusion, and blades extending horizontally are formed on the upper surface (not shown: for example, three blades extending radially from the center of the disc portion 13a and arranged at equal intervals). The support portion 13b extends vertically from the outside of the internal space 11 to the inside of the internal space 11 via an air supply port 12. The disc portion 13a can rotate horizontally by rotating the support portion 13b horizontally (rotating about the axis of the support portion 13b).

[0078] The airflow G supplied from the air supply port 12 to the internal space 11 is blocked by the disc portion 13a of the stirring mechanism 13 and supplied to the outer periphery of the processing unit 10, and then supplied to the vertical direction through the opening 14 located on the outer periphery of the space 11a.

[0079] The absorbent resin particles 20 accumulate on the upper surface of the disc portion 13a, etc., and are stirred as the disc portion 13a rotates. They are then blown upward in the vertical direction by the airflow G supplied through the opening 14. After being blown upward in the vertical direction by the airflow G, the absorbent resin particles 20 fall downward in the vertical direction due to 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 to the outside of the processing device 1 through the exhaust filter 15.

[0080] The processing unit 10 includes a liquid supply unit 16 (e.g., a nozzle) for supplying coating liquid L to the space 11a. The liquid supply unit 16 is located vertically above the disc portion 13a of the stirring mechanism 13 within the space 11a, supplying the coating liquid L from the outer periphery to the inner periphery of the space 11a. The coating liquid L supplied from the liquid supply unit 16 comes into contact with absorbent resin particles 20 that are blown up by the airflow G and fall due to gravity. Coated resin particles are obtained by forming a coating layer through contact between the absorbent resin particles 20 and the coating material of the coating liquid L. Volatile components (such as water) in the coating liquid L evaporate due to the airflow G, heat in the internal space 11, etc.

[0081] The processing unit 10 is equipped with a thermometer (not shown) for measuring the temperature of the atmosphere in the internal space 11. The thermometer can be positioned in the internal space 11 at a location where the absorbent resin particles 20 and the coating liquid L are in contact, or it can be positioned near the liquid supply unit 16 at the same height as the liquid supply unit 16.

[0082] The structure of the processing apparatus for bringing the absorbent resin particles into contact with the coating material is not limited to the structure of the processing apparatus 1 described above. For example, the processing apparatus may replace the stirring mechanism described above in the processing apparatus 1, or in addition to the stirring mechanism described above in the processing apparatus 1, it may include a stirring mechanism that supplies airflow from the side of the processing section 10 to stir the absorbent resin particles 20. The processing apparatus may include a mechanism (e.g., a heater) for heating the processing section 10 as a mechanism for adjusting the atmospheric temperature of the internal space 11 of the processing section 10 in the processing apparatus 1.

[0083] In the method for manufacturing coated resin particles according to this embodiment, in at least a part (partial or all) of the coating process or at least a part (partial or all) of process X, the heat X expressed by the following formula (1) [unit: MJ / (min·m 2 [Under a specific range of conditions, an airflow is supplied from the vertically downward side to the internal space of the device, which contains the internal space of the absorbent resin particles, and the absorbent resin particles come into contact with the coating material. By adjusting the heat X, the coating material is easily softened, the uniformity of the coating is easily adjusted, and thus the water absorption rate of the coated resin particles can be adjusted. The temperature of the airflow can exceed 25°C. The area of ​​the narrowest cross-section of the internal space is the area of ​​the narrowest cross-section in the horizontal direction of the internal space. The area occupied by the device (e.g., stirring mechanism 13) disposed in the internal space is included in the area of ​​the narrowest cross-section.]

[0084] X=(AG×SG×SH×TD) / (NA×1000)...(1) AG: Airflow supply to the interior space [m] 3 / min] SG: Specific gravity of the gas constituting the airflow [kg / m³] 3 ] SH: Specific heat of the gas constituting the airflow [kJ / (kg·K)] TD: The temperature difference between the airflow supplied to the device and 25°C [K] NA: The area of ​​the narrowest cross-section of the interior space perpendicular to the vertical direction [m²] 2 ] Heat X can be within the following range (unit omitted: MJ / (min·m)). 2(represented by ")"). From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the heat value X can be 1.000 or more, 2.000 or more, 3.000 or more, 4.000 or more, 5.000 or more, 6.000 or more, 7.000 or more, 8.000 or more, 9.000 or more, 10.000 or more, or 11.000 or more. From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, the heat value X can be 15.000 or less, 14.000 or less, 13.000 or less, 12.000 or less, or 11. Below 0.000, below 10.000, below 9.000, below 8.000, below 7.000, below 6.000, below 5.000, below 4.000, below 3.000, or below 2.000. In the above context, the calorie X can be 1.000–15.000, 1.000–10.000, 1.000–7.000, 5.000–15.000, 5.000–10.000, 5.000–7.000, 7.000–15.000, or 7.000–10.000.

[0085] The airflow supply AG to the internal space can be appropriately adjusted according to the volume of the internal space. From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, the supply amount AG can be within the following range (unit omitted in m). 3 (represented as " / min"). The supply quantity AG can 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 quantity AG can be less than 1000, less than 500, less than 300, less than 100, less than 75, less than 50, less than 25, less than 10, less than 3.0, less than 2.5, less than 2.0, less than 1.5, less than 1.2, less than 1.0, less than 0.9, or less than 0.8. From the above perspective, the supply quantity AG can 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.

[0086] In the method for manufacturing coated resin particles according to this embodiment, the water content Y [unit: kg / (min·m)] expressed by the following formula (2) may be used in at least a part (partial or all) of the coating process or at least a part (partial or all) of process X. 2 [Under specific conditions, water-absorbing resin particles are brought into contact with a coating liquid containing coating material and water. By adjusting the water content Y, the coating material is easily softened, which improves the uniformity of the coating and thus makes it easy to adjust the water absorption rate of the coated resin particles.]

[0087] Y=[(AL×RW) / 100] / (NA×1000)...(2) AL: Supply rate of coating liquid to the interior space [g / min] RW: Water content in the coating solution [mass %] NA: The area of ​​the narrowest cross-section of the interior space perpendicular to the vertical direction [m²] 2 ] The water content Y can be within the following range (unit omitted: kg / (min·m)). 2 (The text appears to be incomplete and contains errors. A more accurate translation would require the full context.) The water content Y can be 0.200 or less, 1.000 or less, 0.800 or less, 0.600 or less, or 0.500 or less. From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, the water content Y can be 0.400 or less, 0.300 or less, or 0.200 or less. From the above viewpoint, the water content Y can be 0.100–2.000, 0.100–1.500, 0.100–0.600, 0.200–2.000, 0.200–1.500, 0.200–0.600, 0.400–2.000, 0.400–1.500, or 0.400–0.600.

[0088] The supply amount AL of the coating liquid to the internal space can be appropriately adjusted by the amount of water-absorbing resin particles supplied to the processing unit. From the viewpoint of easily adjusting the water absorption rate of the coating resin particles, the supply amount AL can be within the following ranges (the unit "g / min" is omitted). The supply amount AL can 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, or 18.0 or more. The supply amount AL can be 10000 or less, 1000 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, 6.0 or less, 5.0 or less, 4.0 or less, or 3.0 or less. According to the above viewpoint, the supply quantity AL can be 1.0~10000, 1.0~1000, 1.0~100, 1.0~50.0, 1.0~30.0, 1.0~20.0, 1.0~10.0, 1.0~5.0, 5.0~30.0, 5.0~20.0, 5.0~10.0, 10.0~30.0 or 10.0~20.0.

[0089] In the method for manufacturing coated resin particles according to this embodiment, the heat X [MJ / (min·m]] can be applied in at least a part (partial or all) of the coating process or at least a part (partial or all) of process X. 2 The above water content Y [kg / (min·m)] 2 The ratio X / Y [unit: MJ / kg] is used to bring the absorbent resin particles into contact with a coating liquid containing coating material and water within a specific range. By adjusting the ratio X / Y, the softening degree of the coating material can be easily adjusted to a more suitable level, thereby improving the uniformity of the coating and making it easier to adjust the water absorption rate of the coated resin particles.

[0090] The ratio X / Y can be within the following range (the expression for the unit "MJ / kg" is omitted). From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the ratio X / Y can be 1.000 or higher, 2.000 or higher, 3.000 or higher, 4.000 or higher, 5.000 or higher, 6.000 or higher, 7.000 or higher, 8.000 or higher, 9.000 or higher, 10.000 or higher, 11.000 or higher, 12.000 or higher, 15.000 or higher, 17.000 or higher, or 19.000 or higher. From the viewpoint of easily adjusting to slow down the water absorption rate of the coated resin particles, the ratio X / Y can be 40.000 or less, 35.000 or less, 30.000 or less, 25.000 or less, 20.000 or less, 19.000 or less, 17.000 or less, 15.000 or less, or 12.000 or less. From the viewpoint of easily adjusting the water absorption rate of the coated resin particles, the ratio X / Y can be 11.000 or less, 10.000 or less, 9.000 or less, 8.000 or less, 7.000 or less, 6.000 or less, 5.000 or less, or 4.000 or less. Based on the above viewpoint, the ratio X / Y can be 1.000–40.000, 1.000–30.000, 1.000–20.000, 1.000–15.000, 2.000–40.000, 2.000–35.000, 2.000–30.000, 2.000–20.000, 2.000–15.000, 7.000–40. .000, 7.000~30.000, 7.000~20.000, 7.000~15.000, 10.000~40.000, 10.000~30.000, 10.000~20.000, 10.000~15.000, 15.000~40.000, 15.000~30.000 or 15.000~20.000.

[0091] The coated resin particles involved in this embodiment are coated resin particles obtained by the manufacturing method of the coated resin particles involved in this embodiment. The coated resin particles involved in this embodiment have a coating portion consisting of absorbent resin particles and at least a portion (partial or complete) of the absorbent resin particles. The absorbent body involved in this embodiment contains the coated resin particles involved in this embodiment, or it may contain the coated resin particles involved in this embodiment and absorbent resin particles without a coating portion, or it may contain the coated resin particles involved in this embodiment and fibrous material, or it may contain the coated resin particles involved in this embodiment, absorbent resin particles without a coating portion and fibrous material. Examples of fibrous material include finely ground wood pulp; cotton cloth; cotton linters; rayon; cellulose fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester, and polyolefin; and mixtures of these fibers. The absorbent article involved in this embodiment includes the absorbent body involved in this embodiment, or it may include the absorbent body involved in this embodiment and other components. Other components include core-covering layers (e.g., core-covering layers that maintain the shape of the absorbent), liquid-permeable sheets (e.g., liquid-permeable sheets disposed on the outermost side of the absorbent object where liquid seeps in), and liquid-impermeable sheets (e.g., liquid-impermeable sheets disposed on the outermost side opposite to the side of the absorbent object where liquid seeps in).

[0092] Example The present invention will be further described in detail below with reference to specific embodiments. However, the present invention is not limited to these embodiments. The following experiments were conducted at room temperature without specifying the temperature during the experimental operation.

[0093] <Preparation of Water-Absorbent Resin Particles> (Water-absorbing resin particles (1)) A round-bottomed cylindrical 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 inlet tube, and a stirrer (with four inclined blades of two sections each with a blade diameter of 5 cm). A mixture was obtained by adding 293 g of n-heptane (hydrocarbon dispersion medium) and 0.736 g of maleic anhydride-modified ethylene / propylene copolymer (polymeric dispersant, Mitsui Chemicals, Inc., Hi-WAX 1105A) to the flask. While stirring the mixture at 300 rpm, the flask was immersed in an 85°C water bath, thereby heating it to 80°C to dissolve the polymeric dispersant. The water bath was then removed, and the mixture was allowed to cool naturally to 55°C at room temperature.

[0094] Next, 92.0 g of an 80.5% by mass aqueous solution of acrylic acid (acrylic acid: 1.03 mol) and a stir bar were added to a 500 mL Erlenmeyer flask, and stirring was started. Then, while cooling from the outside, 102.2 g of a 30% by mass aqueous solution of sodium hydroxide was added dropwise to the Erlenmeyer flask, thereby neutralizing 75 mol% of the acrylic acid. Then, 0.092 g of hydroxyethyl cellulose (thickener, manufactured by Sumitomo Seika Chemicals Company, Limited, HEC AW-15F), 0.0736 g (0.272 mmol) of potassium persulfate (water-soluble free radical polymerization initiator), 0.0101 g (0.0580 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 34.66 g of deionized water were added, and the mixture was stirred until all components except water were fully dissolved, thus preparing the monomer aqueous solution for the first stage.

[0095] The monomer aqueous solution from stage 1 was added to the separated 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 SUGARESTER S-370, HLB: 3) in 6.62 g of n-heptane by heating. A reaction solution was obtained by adding 7.356 g of this surfactant solution to the separated flask. The reaction mixture was then stirred at 550 rpm while the flask was thoroughly purged with nitrogen. The flask was then immersed in a 70°C water bath to raise the temperature of the reaction mixture. Heating was continued for another 10 minutes from the point when the internal temperature reached its maximum during polymerization (reaching a maximum temperature of 82°C), thereby obtaining the polymerization product from stage 1.

[0096] Next, 128.8 g of an 80.5% (w / w) aqueous solution of acrylic acid (acrylic acid: 1.44 mol) and a stir bar were added to another 500 mL Erlenmeyer flask, and stirring was started. Then, while cooling from the outside, 143.1 g of a 30% (w / w) aqueous solution of sodium hydroxide was added dropwise to the Erlenmeyer flask, thereby neutralizing 75 mol% of the acrylic acid. Then, 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 deionized water were added, and the mixture was stirred until all components except water were fully dissolved, thus preparing the monomer aqueous solution for the second stage.

[0097] The rotation speed was changed to 1000 rpm, and the polymerization product of the first stage was stirred while cooling to 25°C. Then, the entire amount of the monomer aqueous solution of the second stage was added to the polymerization product of the first stage, thereby obtaining a reaction mixture. While stirring the reaction mixture, the interior of the separating flask was thoroughly purged with nitrogen. Then, the separating flask was immersed in a water bath at 70°C to raise the temperature of the reaction mixture. The mixture was further heated for 5 minutes from the point when the internal temperature reached its maximum during the polymerization reaction (reaching a maximum temperature of 82°C), thereby obtaining the polymerization product of the second stage (a slurry of polymer particles before surface crosslinking).

[0098] Following the polymerization in the second stage described above, the polymerization product from the second stage was heated in an oil bath at 125°C, and 252 g of water was removed from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. Next, 0.0884 g (0.5075 mmol) of ethylene glycol diglycidyl ether was added as a surface crosslinking agent, and the mixture was maintained at 83°C for 2 hours, thereby obtaining a dispersion of surface-crosslinked polymer particles.

[0099] Then, the slurry of the surface-crosslinked polymer particles was heated in an oil bath at 125°C to vaporize n-heptane and dry it, thereby obtaining a dried product. In this dried product, polymer particles that passed through an 850 μm sieve and remained on the surface of a 250 μm sieve were recovered, thereby obtaining 210.1 g of water-absorbing resin particles (1) in the form of spherical aggregates (particles without a coating: particle size 250–850 μm). Furthermore, the same operation was performed to prepare a total of 500.0 g or more of water-absorbing resin particles (1).

[0100] (Water-absorbing resin particles (2)) The amount of ethylene glycol diglycidyl ether (internal crosslinking agent) added during the preparation of the monomer aqueous solution in the first stage was changed to 0.00534 g (0.0306 mmol). Otherwise, the same procedure as for the water-absorbing resin particles (1) was followed to obtain 211.1 g of water-absorbing resin particles (2). Furthermore, the same procedure was performed to prepare a total of more than 500.0 g of water-absorbing resin particles (2).

[0101] <Preparation of Partially Neutralized Emulsion of Ethylene / Acrylic Acid Copolymer> An ice bath at 3°C ​​was prepared by adding water and ice to a plastic tray measuring 27cm in length, 38cm in width, and 7cm in depth. A 1L glass beaker was placed inside the ice bath, and 545.78g of ion-exchanged water was added to the beaker. The ice bath was then placed on a magnetic stirrer, and a stir bar was placed inside the beaker, and stirring began.

[0102] 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 solution of sodium hydroxide.

[0103] A round-bottomed cylindrical flask with an inner diameter of 11 cm and an internal volume of 2 L was prepared, equipped with a reflux condenser, a thermometer, and a stirrer (with four inclined blades of 5 cm diameter). 100 g of ethylene / acrylic acid copolymer (mol ratio of ethylene monomer to acrylic monomer = 10:1, manufactured by SK global chemical, PRIMACOR 5980i) was added to the flask. Next, the entire amount of the aforementioned 1.9% by mass sodium hydroxide aqueous solution was added. Then, the beaker used in preparing the sodium hydroxide aqueous solution was rinsed with 50.0 g of deionized water, and the rinsing water was added to the flask, thus obtaining the reaction solution.

[0104] While stirring the reaction solution at 500 rpm, the aforementioned split flask was immersed in an oil bath at 103°C, raising the internal temperature of the split flask to 95°C. Then, while adjusting the temperature of the oil bath as needed, the internal temperature of the split flask was maintained at 95–97°C for 4 hours.

[0105] Then, the separated flask was removed from the oil bath and allowed to cool naturally at room temperature until the internal temperature of the separated flask reached 35°C. Once the internal temperature of the separated flask was confirmed to be below 35°C, the product in the separated flask was filtered through a nylon mesh with a mesh size of 108 μm. The filtrate was recovered, thus yielding a partially neutralized ethylene / acrylic acid copolymer emulsion (P(E / AA), partially neutralized ethylene / acrylic acid copolymer aqueous dispersion, 15% by mass of non-volatile components, 90% degree of neutralization: hereinafter referred to as "aqueous dispersion (A)").

[0106] <Preparation of Partially Neutralized Emulsion of Ethylene / Methacrylic Acid Copolymer> An ice bath at 3°C ​​was created by adding water and ice to a plastic tray measuring 27cm in length, 38cm in width, and 7cm in depth. A 1L glass beaker was placed inside the ice bath, and 889.8g of ion-exchanged water was added to the beaker. The ice bath was then placed on a magnetic stirrer, and a stir bar was placed inside the beaker to stir the ion-exchanged water.

[0107] 8.83 g (0.221 mol) of sodium hydroxide (granules, manufactured by Nacalai Tesque, Inc.) was added little by little to the above beaker, thereby preparing a 0.98% by mass aqueous solution of sodium hydroxide.

[0108] A round-bottomed cylindrical flask with an inner diameter of 11 cm and an internal volume of 2 L was prepared, equipped with a reflux condenser, a thermometer, and a stirrer (with four inclined blades of 5 cm diameter). 100 g of ethylene / methacrylic acid copolymer (molar ratio of ethylene monomer to methacrylic acid monomer = 12.3:1, manufactured by DOW-MITSUIPOLYCHEMICALS CO.,LTD., NUCREL 2060) was added to the flask. Next, the entire volume of the aforementioned 0.98% by mass sodium hydroxide aqueous solution was added. Then, the beaker used in preparing the sodium hydroxide aqueous solution was rinsed with 50.0 g of deionized water, and the rinsing water was added to the flask, thus obtaining the reaction solution.

[0109] While stirring the reaction solution at 500 rpm, the aforementioned split flask was immersed in an oil bath at 103°C, raising the internal temperature of the split flask to 95°C. Then, while adjusting the temperature of the oil bath as needed, the internal temperature of the split flask was maintained at 95–97°C for 4 hours.

[0110] Then, the separated flask was removed from the oil bath and allowed to cool naturally at room temperature until the internal temperature of the separated flask reached 35°C. Once the internal temperature of the separated flask was confirmed to be below 35°C, the product in the separated flask was filtered through a nylon mesh with a mesh size of 108 μm. The filtrate was recovered, thus yielding an ethylene / methacrylic acid copolymer partially neutralized emulsion (P(E / MAA), ethylene / methacrylic acid copolymer partially neutralized aqueous dispersion, non-volatile components 10% by mass, degree of neutralization 92%: hereinafter referred to as "aqueous dispersion (B)").

[0111] <Determination of the glass transition temperature and melting point of the main components of the coating material> 7.00 g of the above-described aqueous dispersion (A) was added to a beaker (inner diameter: 6.2 cm) having an inner surface coated with fluororesin, and the beaker was then covered and sealed with aluminum foil. After perforating the aluminum foil, the beaker was dried using a hot air dryer at 40°C, thereby obtaining 1.08 g of polymer film (A). Furthermore, the 7.00 g of aqueous dispersion (A) was replaced with 10.0 g of the above-described aqueous dispersion (B), and the same procedure was performed to obtain 1.04 g of polymer film (B).

[0112] 3.0 mg of the polymer film (polymer film (A) or polymer film (B)) was sealed in an Al-sealed sample container (manufactured by Hitachi High-Tech Science Corporation, GCA-0017), and the glass transition temperature (Tg) and melting point (MP) of the polymer film were determined using a high-sensitivity differential scanning calorimeter (manufactured by Yamato Scientific Co., Ltd., DSC7020). An empty Al-sealed sample container was used as a reference. Two cycles of heating and cooling from -20°C to 150°C were performed, and differential scanning calorimetry (DSC) was conducted (heating and cooling rates: 20°C / min, nitrogen flow rate: 40 mL / min). The glass transition temperature and melting point were calculated based on the baseline change during the second heating cycle. The glass transition temperature of the partially neutralized ethylene / acrylic acid copolymer (neutralization degree 90 mol%) obtained from the aqueous dispersion (A) was 56°C, and the melting point was 88°C. The glass transition temperature of the partially neutralized ethylene / methacrylic acid copolymer (neutralization degree 92 mol%) obtained from the aqueous dispersion (B) is 63 °C, and the melting point is 99 °C.

[0113] <Preparation of Coated Resin Particles> (Comparative Example 1) In a 1L beaker (made of polypropylene), 333.33g of the above-mentioned aqueous dispersion (A) used as the coating material, 5.00g of polyethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd., PEG6000, number average molecular weight: 7300-9300), and 161.67g of deionized water were mixed to prepare a coating solution of 500.00g. The coating material content in the 500.00g coating solution consisted of 50.00g (10.00% by mass) of partially neutralized ethylene / acrylic acid copolymer (P(E / AA), degree of neutralization 90%) and 5.00g (1.00% by mass) of polyethylene glycol.

[0114] Prepared with Figure 1 A flow-layer granulator with a specific structure. The narrowest cross-sectional area perpendicular to the vertical direction within the processing section of the flow-layer granulator is 0.011 m². 2 .

[0115] 500.0 g of the aforementioned water-absorbing resin particles (1) were fed into the processing section of the aforementioned fluidized bed granulator. Then, while stirring the processing section using a stirring mechanism (rotor blades, speed: 250 rpm), gas was supplied at a temperature of 27°C and a flow rate of 0.8 m³ / kg. 3An airflow (air) supplied to the fluidized bed granulator at a rate of 6.0 g / min is introduced into the processing section from the air inlet. Then, the absorbent resin particles agitated by the airflow are sprayed with the entire amount of the coating liquid using a tangential sprayer at a supply rate of 6.0 g / min, thereby bringing the absorbent resin particles into contact with the coating material of the coating liquid. At this time, the supply amount of coating material is 11.00 parts by weight relative to 100 parts by weight of the absorbent resin particles. Then, the mixture is processed at room temperature with a supply rate of 0.8 m... 3 The airflow (air) supplied to the flow layer granulator is supplied from the air inlet to the processing section for 30 minutes for drying, thereby obtaining particles (A).

[0116] After spreading 50.0g of the particle (A) on a metal tray measuring 26cm in length and 20cm in width, it was covered with aluminum foil. After perforating the aluminum foil, the particle (A) was heated for 30 minutes using a hot air dryer (manufactured by ADVANTEC, FV-320) set to 120°C, thus obtaining 50.0g of coated resin particles.

[0117] (Example 1) The gas supply temperature was changed to 45°C, and the operation was carried out in the same manner as in Comparative Example 1 to obtain 50.0g of coated resin particles.

[0118] (Example 2) The gas supply temperature was changed to 50°C, and the operation was carried out in the same manner as in Comparative Example 1 to obtain 50.0g of coated resin particles.

[0119] (Example 3) The gas supply temperature was changed to 90°C, and the gas supply was changed to spray coating liquid until the atmosphere temperature dropped below 50°C. Otherwise, the operation was carried out in the same manner as in Comparative Example 1, and 50.0g of coated resin particles were obtained.

[0120] (Comparative Example 2) A coating solution of 375.00 g was prepared by mixing 250.00 g of the above-mentioned aqueous dispersion (A) used as the coating material, 1.25 g of polyethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd., PEG6000, number average molecular weight: 7300-9300), and 123.75 g of deionized water. The gas supply temperature was changed to 130°C, and the gas supply rate was changed to 1.0 m³ / min. 3The supply rate of the coating liquid was changed to 3.0 g / min, and the airflow was changed to continue supplying the airflow after spraying the coating liquid until the atmosphere temperature dropped below 50°C. Otherwise, the operation was carried out in the same manner as Comparative Example 1. The content of coating material in 375.00 g of coating liquid was 37.50 g (10.00% by mass) of ethylene / acrylic acid copolymer partially neutralized (P(E / AA), degree of neutralization 90%) and 1.25 g (0.33% by mass) of polyethylene glycol. The supply amount of coating material was 7.75 parts by mass relative to 100 parts by mass of water-absorbing resin particles. During the spraying of the coating liquid, the water-absorbing resin particles adhered to the inner wall and bottom surface of the processing section of the fluidized bed granulator and became lumpy, thus failing to obtain coated resin particles.

[0121] (Example 4) Change the air supply temperature to 50℃ and the air supply rate to 0.8m³. 3 / min, otherwise the operation was carried out in the same manner as in Comparative Example 2, and 50.0g of coated resin particles were obtained.

[0122] (Example 5) The supply rate of the coating solution was changed to 4.5 g / min, and the operation was otherwise performed in the same manner as in Comparative Example 2, resulting in 50.0 g of coated resin particles.

[0123] (Example 6) Change the air supply temperature to 90℃ and the air supply rate to 0.8m³. 3 The supply rate of the coating liquid was changed to 6.0 g / min, and the entire supply rate of the coating liquid was changed to 6.0 g / min. Otherwise, the operation was carried out in the same manner as in Comparative Example 2, and 50.0 g of coated resin particles were obtained.

[0124] (Example 7) 251.25 g of coating solution was prepared without mixing with ion-exchanged water, and the gas flow rate was changed to 0.8 m³ / h. 3 The supply rate of the coating solution was changed to 6.0 g / min, and the operation was performed in the same manner as in Comparative Example 2, yielding 50.0 g of coated resin particles. The content of the coating material in the 251.25 g coating solution was 37.50 g (14.93% by mass) of the partially neutralized ethylene / acrylic acid copolymer (P(E / AA), degree of neutralization 90%) and 1.25 g (0.50% by mass) of polyethylene glycol. The supply amount of the coating material was 7.75 parts by mass relative to 100 parts by mass of the absorbent resin particles.

[0125] (Example 8) The supply rate of the coating solution was changed to 18.0 g / min, and otherwise the operation was carried out in the same manner as in Comparative Example 2, resulting in 50.0 g of coated resin particles.

[0126] (Example 9) Change the airflow supply to 0.8m 3 The supply rate of the coating solution was changed to 18.0 g / min, and the operation was carried out in the same manner as in Comparative Example 2, otherwise 50.0 g of coated resin particles were obtained.

[0127] (Example 10) Without using polyethylene glycol, 166.70 g of the above-mentioned aqueous dispersion (A) used as the coating material was mixed with 83.30 g of deionized water to prepare 250.00 g of coating solution. The total supply rate of the coating solution was changed to 18.0 g / min. Otherwise, the operation was carried out in the same manner as in Comparative Example 2, and 50.0 g of coated resin particles were obtained. The content of coating material in the 250.00 g coating solution was 25.00 g (10.00% by mass) of the partially neutralized ethylene / acrylic acid copolymer (P(E / AA), degree of neutralization 90%). The supply amount of coating material was 5.00 parts by mass relative to 100 parts by mass of the water-absorbing resin particles.

[0128] (Comparative Example 3) A coating solution of 376.25 g was prepared by dissolving 1.25 g of polyethylene glycol in 375.00 g of the above-mentioned aqueous dispersion (B). Otherwise, the procedure was performed in the same manner as in Comparative Example 1, and 50.0 g of coated resin particles were obtained. The content of coating material in the 376.25 g coating solution was as follows: 37.50 g (9.97% by mass) of the partially neutralized ethylene / methacrylic acid copolymer (P(E / MAA), degree of neutralization 92%) and 1.25 g (0.33% by mass) of polyethylene glycol. The amount of coating material supplied was 7.75 parts by mass relative to 100 parts by mass of the absorbent resin particles.

[0129] (Example 11) The gas supply temperature was changed to 90°C, and the gas supply was changed to spray coating liquid until the atmosphere temperature dropped below 50°C. Otherwise, the operation was carried out in the same manner as in Comparative Example 3, and 50.0g of coated resin particles were obtained.

[0130] (Comparative Example 4) Change the air supply temperature to 140℃ and the air supply rate to 1.0m³. 3The supply rate of the coating liquid was changed to 3.0 g / min, and the airflow was changed to continue supplying the airflow after spraying the coating liquid until the atmosphere temperature dropped below 50°C. Otherwise, the operation was carried out in the same manner as in Comparative Example 3. During the spraying of the coating liquid, the water-absorbing resin particles adhered to the inner wall and bottom surface of the processing section of the fluidized bed granulator and became lumpy, thus failing to obtain coated resin particles.

[0131] (Example 12) The absorbent resin particles (1) were replaced with absorbent resin particles (2), and otherwise the operation was carried out in the same manner as in Example 2, resulting in 50.0 g of coated resin particles.

[0132] (Example 13) The absorbent resin particles (1) were replaced with absorbent resin particles (2), and otherwise the operation was carried out in the same manner as in Example 3, resulting in 50.0 g of coated resin particles.

[0133] <Measurement of Atmosphere Temperature> Inside the processing section of the aforementioned fluidized bed granulator, a thermometer was placed at the point where the absorbent resin particles came into contact with the coating liquid, and at the point where the absorbent resin particles were blown up by the airflow, to measure the atmosphere temperature. The atmosphere temperature rose after the coating liquid spraying began and remained at a certain value after a certain period of time. Table 2 shows the proportion of time during which the absorbent resin particles came into contact with the coating material at an atmosphere temperature that was at least 27°C lower than the glass transition temperature of the main component of the coating material and at least 4°C higher than the melting point of the main component of the coating material (the proportion of time within a specific temperature range) during the spraying period of the coating liquid (from the start to the end of spraying). Furthermore, Table 2 shows the difference between the atmosphere temperature at the end of the spraying of the coating liquid (the temperature at the point when all the coating liquid was sprayed) and the difference between the atmosphere temperature at the end of the spraying and the glass transition temperature (Tg) or melting point (MP) of the coating material (the main component of the coating material).

[0134] <Calculation of heat X, water content Y, and ratio X / Y> The heat X [MJ / (min·m)] was calculated according to the above formula (1). 2 As the specific gravity SG, the specific gravity of air, 1.1845 [kg / m³], was used. 3 The specific heat SH was calculated using air at 1.0063 kJ / (kg·K). The results of the heat calculation X are shown in Table 2.

[0135] The water content Y [kg / (min·m)] was calculated according to the above formula (2). 2The difference between the total amount of the coating solution and the total amount of the coating material (non-volatile components) was calculated, with the water content RW in the coating solution as the metric. Furthermore, the ratio X / Y [MJ / kg] of heat X to water content Y was calculated. The calculation results for water content Y and ratio X / Y are shown in Table 2.

[0136] <Determination of Locking Height> 0.200 g of the coated resin particles (excluding Comparative Examples 2 and 4) were accurately weighed. Next, the coated resin particles were layered at the bottom of an acrylic container with an inner diameter of 2.0 cm and a depth of 8.0 cm, forming a particle layer with a flat upper surface. The height H0 from the upper surface of the bottom of the acrylic container to the top of the particle layer was measured. Then, 20 g of physiological saline at 25°C was injected into the top of the acrylic container in one go. Starting from the moment all the physiological saline was added, the height H5 from the upper surface of the bottom of the acrylic container to the top of the absorbent particle layer was measured 5 minutes later. The 5-minute value of the locked height of the coated resin particles was calculated according to the formula “5-minute value of locked height [cm] = H5 - H0”. In the case where the upper surface of the absorbent particle layer was not flat, the height of the highest part was obtained as H5. The results are shown in Table 2.

[0137] [Table 1]

[0138] [Table 2]

[0139] Explanation of reference numerals in the attached figures 1-Processing device, 10-Processing section, 11-Internal space, 11a, 11b, 11c-Space, 12-Air supply port, 13-Stirring mechanism, 13a-Disc section, 13b-Support section, 14-Opening, 15-Exhaust filter, 16-Liquid supply section, 20-Water-absorbing resin particles, G-Airflow, L-Coating liquid.

Claims

1. A method for manufacturing coated resin particles, comprising a coating step of obtaining coated resin particles having a coated portion having at least a portion of the water-absorbing resin particles coated by contacting the water-absorbing resin particles with a coating material. In the coating process, the proportion of time during which the water-absorbing resin particles are in contact with the coating material is 30% or more, at an atmosphere temperature that is at least 27°C lower than the glass transition temperature of the main component of the coating material and at least 4°C higher than the melting point of the main component of the coating material.

2. The method for manufacturing coated resin particles according to claim 1, wherein, The glass transition temperature of the main component of the coating material is 20–140°C.

3. The method for manufacturing coated resin particles according to claim 1, wherein, The melting point of the main component of the coating material is 30–150°C.

4. The method for manufacturing coated resin particles according to claim 1, wherein, The main component of the coating material is a copolymer of olefin / ethylene unsaturated monomers.

5. The method for manufacturing coated resin particles according to any one of claims 1 to 4, wherein, An airflow is supplied from the vertically downward side to the internal space of the device having an internal space containing the absorbent resin particles, and the absorbent resin particles come into contact with the coating material.

6. The method for manufacturing coated resin particles according to claim 5, wherein, In at least a portion of the coating process, the heat X, expressed by the following formula (1), is 1.000 [MJ / (min·m]. 2 In the above state, the water-absorbing resin particles are brought into contact with the coating material. X=(AG×SG×SH×TD) / (NA×1000)...(1) AG: The amount of airflow supplied to the interior space [m 3 / min] SG: Specific gravity of the gas constituting the airflow [kg / m³] 3 ] SH: Specific heat of the gas constituting the airflow [kJ / (kg·K)] TD: The temperature difference between the airflow supplied to the device and 25°C [K] NA: The area of ​​the narrowest cross-section of the internal space perpendicular to the vertical direction [m²] 2 ].

7. The method for manufacturing coated resin particles according to claim 6, wherein, The heat X is 3.000 [MJ / (min·m 2 )]above.

8. The method for manufacturing coated resin particles according to claim 6, wherein, In at least a portion of the coating process, the heat X [MJ / (min·m 2 The water content Y[kg / (min·m)] is expressed by the following formula (2). 2 When the ratio X / Y is 2.00 to 35.00 [MJ / kg], the water-absorbing resin particles are brought into contact with a coating liquid containing the coating material and water. Y=[(AL×RW) / 100] / (NA×1000)...(2) AL: Amount of coating liquid supplied to the internal space [g / min] RW: Water content [mass %] in the coating solution NA: The area of ​​the narrowest cross-section of the internal space perpendicular to the vertical direction [m²] 2 ].

9. The method for manufacturing coated resin particles according to claim 8, wherein, The ratio X / Y is 7.00 to 30.00 [MJ / kg].

10. The method for manufacturing coated resin particles according to claim 8, wherein, The water content Y is 0.200 kg / (min·m 2 )]above.

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