Resin particle composition

Abstract

This resin particle composition has water-absorbing resin particles and a fixing member layer, and is configured such that, when a caking test is performed in the order of (1) through (5), at least a portion of the particles remain on a sieve used, the sieve having an aperture of 850 μm.

Description

Technical Field

[0001] The present invention relates to a resin particle composition.

Background Art

[0002] Among resin particles, water-absorbing resin particles having the property of absorbing and retaining water, which is an essential element in life, are widely used in fields such as sanitary materials such as disposable diapers and sanitary products, agro-horticultural materials such as water retention agents and soil conditioners, and industrial materials such as water stop agents and dew prevention agents. Since water-absorbing resin particles are usually powders without adhesive force, in the above applications, they are used as absorbers formed in a sandwich shape by spraying water-absorbing resin particles on a fibrous substrate such as a non-woven fabric. At this time, in order to fix the water-absorbing resin particles to the substrate, a method of spraying water-absorbing resin particles on a fibrous substrate coated with an adhesive has been carried out (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method of fixing water-absorbing resin particles to a fibrous substrate with an adhesive, only the water-absorbing resin particles in contact with the adhesive applied to the substrate are fixed, and the other particles are not fixed and are free in the absorber. Therefore, they may fall off from the edge of the absorber during the absorber manufacturing process and transportation.

[0005] An object of the present invention is to provide a resin particle composition that is difficult to fall off from an absorber.

Means for Solving the Problems

[0006] The resin particle composition of the present invention comprises water-absorbing resin particles and a fixing member layer, and at least a portion of the particles remain on the sieve with a mesh size of 850 μm after a caking test performed in the order of (1) to (5) below. (1) Place a circular release paper with a diameter of 50 mm on the bottom of a circular stainless steel petri dish with an inner diameter of 52 mm, and sprinkle 2.0 g of a resin particle composition with a particle size of less than 850 μm on top of the release paper. (2) A sample for measurement is obtained by stacking a circular release paper with a diameter of 50 mm, a circular stainless steel petri dish with an outer diameter of 50 mm and a mass of 20 g, and a cylindrical weight of 780 g with a diameter of 45 mm on top of the scattered resin particle composition in this order. (3) Dry the sample in a hot air dryer at 80°C for 1 hour, then allow it to cool to room temperature. (4) After cooling, the resin particle composition is removed from the release paper and recovered, and the entire amount of the recovered resin particle composition is placed on a sieve with a mesh size of 850 μm. (5) After shaking the sieve for 5 seconds using a rotary sieve shaker, check whether any resin particle composition remains on the sieve.

[0007] The above resin particle composition preferably has a caking index of 20% or more, as measured by the above caking test and represented by the following formula. Caking index (%) = [Mass of resin particle composition remaining on an 850 μm sieve / (Total mass of resin particle composition remaining on an 850 μm sieve and resin particle composition that passed through an 850 μm sieve)] × 100

[0008] The fixing member layer may contain at least one selected from the group consisting of ethylene polymers, polyether polymers, polyamide polymers, polyurethane polymers, and polyester polymers.

[0009] The amount of the fixing member may be 0.01 to 10 parts by mass per 100 parts by mass of water-absorbing resin particles.

[0010] The above resin particle composition may have a saline solution water retention capacity of 30 g / g or more. [Effects of the Invention]

[0011] The present invention provides a resin particle composition that is less likely to fall off the absorbent. [Modes for carrying out the invention]

[0012] Several embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0013] In this specification, "acrylic" and "methacrylic" are collectively referred to as "(meth)acrylic." Similarly, "acrylate" and "methacrylate" are referred to as "(meth)acrylate." "(poly)" means both with and without the prefix "poly." In the numerical ranges described stepwise in this specification, the upper or lower limit of one step in the numerical range can be arbitrarily combined with the upper or lower limit of another step in the numerical range. In the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. The materials exemplified in this specification may be used individually or in combination of two or more. The content of each component in a composition means the total amount of multiple substances present in the composition if there are multiple substances corresponding to each component, unless otherwise specified. "Water-soluble" means solubility of 5% by mass or more in water at 25°C. "Room temperature" means 25±2°C. The term "layer" encompasses not only structural shapes that are formed across the entire surface when observed as a plan view, but also structural shapes that are formed in only a portion of the surface.

[0014] The resin particle composition according to this embodiment comprises water-absorbing resin particles and a fixing member layer. The resin particle composition has caking properties as measured in a caking test performed in the order of (1) to (5) below. Having caking properties means that at least a portion of the particles remain on the sieve with a mesh size of 850 μm after step (5) of the caking test below. (1) Place a circular release paper with a diameter of 50 mm on the bottom of a circular stainless steel petri dish with an inner diameter of 52 mm, and sprinkle 2.0 g of a resin particle composition with a particle size of less than 850 μm on top of the release paper. (2) A measurement sample is obtained by stacking a circular release paper with a diameter of 50 mm, a circular stainless steel petri dish with an outer diameter of 50 mm and a mass of 20 g, and a cylindrical weight of 780 g with a diameter of 45 mm on top of the scattered resin particle composition in this order. This applies a pressure of 4000 Pa to the resin particle composition. (3) Dry the sample in a hot air dryer at 80°C for 1 hour, then allow it to cool to room temperature. (4) After cooling, the resin particle composition is removed from the release paper and recovered, and the entire amount of the recovered resin particle composition is placed on a sieve with a mesh size of 850 μm. (5) After shaking the sieve for 5 seconds using a rotary sieve shaker, check whether any resin particle composition remains on the sieve.

[0015] The resin particle composition according to this embodiment has the caking properties measured in the above caking test. For example, when preparing an absorbent, the resin particle composition can be fixed to the fibrous substrate by stacking the resin particle composition and the fibrous substrate and applying pressure and heating, without the need for a separate adhesive. While the above caking test is directly an indicator of the bonding properties between resin particle compositions, a resin particle composition having such caking properties can also be bonded to a fibrous substrate by applying pressure and heating.

[0016] The resin particle composition according to this embodiment preferably has a caking index of 20% or more, as shown by the following formula. The caking index can be calculated by measuring the mass of the resin particle composition remaining on a sieve with an opening of 850 μm and the mass of the resin particle composition that passed through the sieve with an opening of 850 μm after step (5) of the caking test described above. Caking index (%) = [Mass of resin particle composition remaining on an 850 μm sieve / (Total mass of resin particle composition remaining on an 850 μm sieve and resin particle composition that passed through an 850 μm sieve)] × 100

[0017] The caking index of the resin particle composition according to this embodiment may be 20% or more, 25% or more, 30% or more, 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, 78% or more, 80% or more, 85% or more, 90% or more, or 95% or more. The caking index of the resin particle composition according to this embodiment may be 100% or less, 99% or less, 98% or less, 97% or less, or 95% or less.

[0018] The resin particle composition according to this embodiment has water-absorbing resin particles and a fixing member layer. The fixing member layer may be provided on at least a part of the surface of the water-absorbing resin particles. It is preferable that the fixing member layer is fixed to at least a part of the surface of the water-absorbing resin particles.

[0019] The resin particle composition according to this embodiment can maintain high the water absorption performance that the water-absorbing resin particles originally have while having the ability to be fixed to a fibrous substrate used for an absorber or the like.

[0020] The amount of physiological saline retained by the resin particle composition according to this embodiment (hereinafter, may be simply referred to as "water retention amount") may be, for example, 30 g / g or more, 35 g / g or more, 38 g / g or more, or 40 g / g or more, and may be 50 g / g or less, 48 g / g or less, 45 g / g or less, or 43 g / g or less.

[0021] The amount of physiological saline retained by the water-absorbing resin particles used in the resin particle composition according to this embodiment may be, for example, 33 g / g or more, 35 g / g or more, 38 g / g or more, 40 g / g or more, or 42 g / g or more, and may be 55 g / g or less, 52 g / g or less, 50 g / g or less, 48 g / g or less, 45 g / g or less, or 43 g / g or less.

[0022] The ratio of the water-retaining capacity of the water-absorbing resin particles to the water-retaining capacity of the resin particle composition according to this embodiment (i.e., water-retaining capacity of the resin particle composition ÷ water-retaining capacity of the water-absorbing resin particles × 100) may be, for example, 60% or more, 70% or more, 75% or more, 80% or more, or 85% or more, and may be 110% or less, 105% or less, 100% or less, 98% or less, 95% or less, or 90% or less.

[0023] The median particle size of the resin particle composition according to this embodiment may be, for example, 20 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, or 250 μm or more, and may be 800 μm or less, 700 μm or less, 600 μm or less, 500 μm or less, 450 μm or less, 400 μm or less, or 380 μm or less.

[0024] [Fixing member layer] The fixing member layer preferably contains a heat-meltable resin. The fixing member may contain 80% by mass, 90% or more by mass, 95% or more by mass, 98% or more by mass, 99% or more by mass, or 100% by mass of a heat-meltable resin. The glass transition temperature of the heat-meltable resin forming the fixing member layer may be, for example, 20°C or higher, 25°C or higher, 30°C or higher, 35°C or higher, 40°C or higher, or 50°C or higher, and may be 90°C or lower, 80°C or lower, 75°C or lower, 70°C or lower, 65°C or lower, 60°C or lower, 55°C or lower, or 50°C or lower. The melting point of the heat-meltable resin forming the fixing member layer may be, for example, 70 to 175°C, 70 to 140°C, or 75 to 100°C.

[0025] Examples of resins that form the fixing member layer (i.e., fixing members) include ethylene polymers such as polyethylene, polypropylene, ethylene-butene copolymer, ethylene-propylene copolymer, and ethylene-acrylic acid copolymer; polyether polymers such as polyethylene glycol and polypropylene glycol; polyamide polymers such as nylon 6 and nylon 66; polyurethane polymers such as ether polyurethane, ester polyurethane, and carbonate polyurethane; polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate; polyacetals such as polyoxymethylene, polyacetaldehyde, polypropionaldehyde, and polybutyraldehyde; polyvinyl fluoride; polyvinylidene fluoride; and polysiloxane. These resins may be used individually or in combination of multiple types.

[0026] Polyurethane is a reaction product of polyols and polyisocyanates. Examples of polyols include polyether polyols, polyester polyols, polybutadiene polyols, and hydrogenated polybutadiene polyols. Examples of polyisocyanates include aromatic isocyanates such as diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and p-phenylene diisocyanate; alicyclic isocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate.

[0027] The fixing member layer is preferably chemically and / or physically bonded to the surface of the water-absorbing resin particles in their pre-water-absorbing state so as not to easily detach from them. Physical bonding is achieved, for example, by an anchoring effect resulting from the fixing member layer penetrating into microscopic depressions on the surface of the water-absorbing resin particles. The fixing member layer may be contained not only on the surface of the water-absorbing resin particles but also inside them. From the viewpoint of facilitating the expression of the present invention, it is preferable that the majority of the fixing member layer is exposed and fixed near the surface. The amount of the fixing member layer fixed near the surface may be 70% by mass or more, or 90% by mass or more, of the total amount of the fixing member layer contained in the resin particle composition.

[0028] The heat-meltable resin of the fixing member layer may have a peel-off adhesive strength of 1 to 500 N / 25 mm or 5 to 300 N / 25 mm as measured according to JIS Z0237.

[0029] The percentage of the surface area of ​​the water-absorbing resin particles occupied by the fixing material layer (i.e., the coverage rate) may be 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, 98% or more, or 99% or more, and may be 100% or less, 99% or less, 98% or less, 95% or less, 90% or less, or 80% or less. The coverage rate is calculated using RAMAN touch (manufactured by Nanophoton Inc.).

[0030] The thickness of the fixing member layer of the resin particle composition may be 0.001 to 100 μm, 0.01 to 50 μm, or 0.1 to 30 μm.

[0031] In the resin particle composition, the amount of the fixing member layer may be 0.01 parts by mass or more, 0.05 parts by mass or more, 0.1 parts by mass or more, 0.5 parts by mass or more, 1 part by mass or more, 1.5 parts by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more, per 100 parts by mass of water-absorbing resin particles, and may be 10 parts by mass or less, 8 parts by mass or less, or 6 parts by mass or less.

[0032] [Water-absorbing resin particles] The water-absorbing polymer particles may contain, for example, a crosslinked polymer formed by the polymerization of monomers including an ethylenically unsaturated monomer. The crosslinked polymer may have monomer units derived from the ethylenically unsaturated monomer. The water-absorbing polymer particles can be produced, for example, by a method that includes a step of polymerizing monomers including an ethylenically unsaturated monomer. Examples of polymerization methods include reverse-phase suspension polymerization, aqueous solution polymerization, bulk polymerization, and precipitation polymerization.

[0033] The ethylenically unsaturated monomer may be a water-soluble ethylenically unsaturated monomer. Examples of water-soluble ethylenically 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-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. If the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more types.

[0034] If the ethylenically unsaturated monomer has acidic groups, these acidic groups may be neutralized with an alkaline neutralizing agent before being used in the polymerization reaction. The degree of neutralization by the alkaline neutralizing agent in the ethylenically unsaturated monomer may be, for example, 10 to 100 mol%, 50 to 90 mol%, or 60 to 80 mol% of the acidic groups in the ethylenically unsaturated monomer.

[0035] From the viewpoint of industrial availability, the ethylenically unsaturated monomer may contain at least one compound selected from the group consisting of (meth)acrylic acid and its salts, acrylamide, methacrylamide, and N,N-dimethylacrylamide.

[0036] Other monomers besides the ethylenically unsaturated monomers described above may be used as monomers to obtain water-absorbent resin particles. Such monomers can be used, for example, by mixing them with an aqueous solution containing the ethylenically unsaturated monomers described above. The amount of ethylenically unsaturated monomers used may be 70 to 100 mol% of the total amount of monomers. The proportion of (meth)acrylic acid and its salts may also be 70 to 100 mol% of the total amount of monomers.

[0037] While self-crosslinking may occur during polymerization, crosslinking can also be induced by using an internal crosslinking agent. Using an internal crosslinking agent makes it easier to control the water absorption properties (water retention capacity, etc.) of the water-absorbing resin particles. Internal crosslinking agents are usually added to the reaction solution during the polymerization reaction.

[0038] The water-absorbing resin particles may be cross-linked near their surface (surface cross-linking). Furthermore, the water-absorbing resin particles may consist solely of polymer particles (cross-linked polymers), but may also contain various additional components selected from, for example, gel stabilizers, metal chelating agents, and fluidity enhancers (lubricants). The additional components may be located inside the polymer particles, on the surface of the polymer particles, or both. The additional components may be fluidity enhancers (lubricants). Fluidity enhancers may include inorganic particles. Examples of inorganic particles include silica particles such as amorphous silica.

[0039] The shape of the water-absorbing resin particles may be, for example, approximately spherical, crushed, or porous, or they may be aggregated primary particles having these shapes. Among these, from the viewpoint of ease of dispersion of the resin particles during the production of the absorbent material, it is preferable that they be approximately spherical or aggregated therein.

[0040] [Method for producing resin particle composition] The resin particle composition according to this embodiment may include, for example, a step of mixing water-absorbing resin particles with a fixing member to form a fixing member layer on at least a portion of the surface of the water-absorbing resin particles.

[0041] The amount of fixing material used in mixing may be 0.1 parts by mass or more, 0.5 parts by mass or more, 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more per 100 parts by mass of water-absorbing resin particles, and may also be 10 parts by mass or less, 8 parts by mass or less, or 6 parts by mass or less.

[0042] The fixing member is, for example, a heat-meltable resin capable of forming the aforementioned fixing member layer. The resin typically includes a polymer composed of repeating units. The fixing member may include not only the heat-meltable polymer itself, but also its monomers, precursors, and other forming materials.

[0043] For example, if the fixing member layer contains polyurethane, the fixing member may contain polyurethane itself, or it may contain polyol and polyisocyanate, which are materials that form the polyurethane.

[0044] If the fixing member contains polymer-forming materials (other than precursors), the method for producing the resin particle composition according to this embodiment preferably further comprises the step of mixing the water-absorbing resin particles with the fixing member and then polymerizing the fixing member. The specific methods for producing the resin particle composition will be described below according to the state of the fixing member.

[0045] <When using a solid fixing member> In this case, a particle compounding device can be used to fix a fixing member to the surface of water-absorbent resin particles, thereby forming a fixing member layer. Specifically, a predetermined amount of water-absorbent resin particles and a solid (e.g., powder) fixing member are introduced into the particle compounding device. Subsequently, stress (compressive stress and shear stress) is applied to the water-absorbent resin particles and the fixing member by the rotation of a stirring blade provided in the device, and the fixing member is pressed onto the surface of the water-absorbent resin particles by this stress, thereby producing a resin particle composition.

[0046] In this case, the thickness of the fixing member layer and the coverage rate can be arbitrarily adjusted by appropriately adjusting the amount of water-absorbing resin particles and fixing member introduced into the particle compounding device. Although the water-absorbing resin particles and fixing member may be introduced into the particle compounding device separately, it is preferable to introduce them into the device in a pre-mixed state, as this can lead to more uniform dispersion and coverage. When using a particle compounding device, it is easy to obtain a resin particle composition in which the fixing member layer is fixed to at least a portion of the surface of the water-absorbing resin particles. As a particle compounding device, for example, the particle compounding device NOBIRUTA MINI (manufactured by Sugino Machine Co., Ltd.) can be used.

[0047] <When using a liquid fixing agent> Liquid fixing material (hereinafter simply referred to as "fixing material liquid") can be obtained, for example, by melting the fixing material, or by dissolving or dispersing the fixing material in any solvent or dispersion medium. It is preferable to obtain the fixing material liquid by dissolving or dispersing the fixing material in any solvent or dispersion medium because it facilitates the formation of a fixing material layer of uniform thickness. Whether the fixing material liquid is a solution or a dispersion depends on the properties of the fixing material and the medium used.

[0048] Examples of solvents or dispersion media include water, hydrophilic compounds, mixtures of water and hydrophilic compounds, and hydrocarbon compounds. Hydrophilic compounds are compounds that dissolve almost uniformly in water. Examples of hydrophilic compounds include alcohols such as methanol and isopropyl alcohol; glycols such as ethylene glycol; cellosolves such as methyl cellosolve and ethyl cellosolve; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; and ethers such as tetrahydrofuran. Examples of hydrocarbon compounds include linear 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 benzene, toluene, and xylene. These may be used individually or in combination of two or more.

[0049] The concentration of the fixing agent in the fixing agent liquid is not particularly limited and can be adjusted as appropriate considering the amount of water-absorbing resin particles in order to obtain a fixing agent layer of the desired thickness. For example, it may be 1 to 50% by mass, 3 to 30% by mass, or 5 to 20% by mass.

[0050] When using a fixing agent liquid, the fixing agent layer can be formed by, for example, (1) adding the fixing agent liquid to a hydrocarbon dispersion medium in which water-absorbent resin particles are dispersed, (2) adding the fixing agent liquid and water-absorbent resin particles to the hydrocarbon dispersion medium almost simultaneously, (3) contacting the fixing agent liquid with water-absorbent resin particles in a dry state, (4) polymerizing the fixing agent in the presence of water-absorbent resin particles, or (5) crosslinking the fixing agent (including the precursor) using a crosslinking agent in the presence of water-absorbent resin particles. Each method will be described in detail below.

[0051] An example of the method described in (1) above will be explained. First, a separable flask equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer is prepared. Next, the hydrocarbon dispersion medium and water-absorbing resin particles are added to the flask and stirred thoroughly while maintaining a high temperature (e.g., 60-80°C). Meanwhile, the solvent or dispersion medium and the fixing member are added to a beaker and mixed to prepare a fixing member solution. After adding the fixing member solution to the flask and stirring thoroughly, the flask is immersed in an oil bath set to a high temperature (e.g., 100-125°C), and water that may be present in the reaction system is removed from the system by azeotropic distillation of the hydrocarbon dispersion medium and water while refluxing the hydrocarbon dispersion medium. After that, the hydrocarbon dispersion medium is evaporated to obtain a resin particle composition in which the fixing member is fixed to the surface of the water-absorbing resin particles.

[0052] An example of the method described in (2) above will be explained. First, a separable flask equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer is prepared. Next, a hydrocarbon dispersion medium, water-absorbent resin particles, and a fixing member liquid are added to the flask and stirred thoroughly while maintaining a high temperature (for example, 60-80°C). After that, the hydrocarbon dispersion medium is evaporated to obtain a resin particle composition in which the fixing member is fixed to the surface of the water-absorbent resin particles.

[0053] Although there are various methods for (3) above, the following will describe representative examples: (3-1) the method using a round-bottom flask, (3-2) the method using a sprayer, and (3-3) the method using various granulators.

[0054] (3-1) The fixing material solution is poured into a round-bottom flask, followed by the addition of water-absorbing resin particles. The round-bottom flask is attached to an evaporator and heated while rotating, and the solvent or dispersion medium contained in the fixing material solution is removed by distillation under reduced pressure. This yields a resin particle composition in which the fixing material is fixed to the surface of the water-absorbing resin particles.

[0055] (3-2) Absorbent resin particles are added to a separable flask equipped with a stirring blade and stirred. The fixing agent liquid is sprayed onto the absorbent resin particles that have been stirred up by the stirring blade. The fixing agent liquid can be sprayed using, for example, a two-fluid nozzle. It is desirable that the fixing agent liquid be sprayed in a mist form using an inert gas such as nitrogen, as uniform dispersion and coating can be expected. After that, the contents of the flask are removed, heated in a hot air dryer, and then cooled to room temperature to obtain the resin particle composition.

[0056] (3-3) Examples of granulators used in the production of resin particle compositions include rolling granulators, agitated granulators, and fluidized bed granulators.

[0057] When using a rolling granulator, a shallow, inclined circular container attached to the rolling granulator is rotated, and water-absorbing resin particles are supplied to the circular container, along with an appropriate amount of fixing agent liquid. As a result, some of the water-absorbing resin particles agglomerate during rolling due to the solvent or dispersion medium contained in the fixing agent liquid, and a fixing agent layer is formed on their surface. The process of adding water-absorbing resin particles and fixing agent liquid can be repeated multiple times as necessary.

[0058] When using a stirring granulator, the water-absorbent resin particles are placed in the mixer attached to the stirring granulator, mixed by stirring, and then a fixing agent liquid is added. As a result, some of the water-absorbent resin particles agglomerate due to the solvent or dispersion medium contained in the fixing agent liquid, and a fixing agent layer is formed on their surface. The process of adding water-absorbent resin particles and the fixing agent liquid can be repeated multiple times as needed. Excessive agglomeration of the water-absorbent resin particles can be suppressed by controlling the shear force of the mixer.

[0059] When using a fluidized bed granulator, first, the water-absorbent resin particles are placed in a container attached to the fluidized bed granulator that can blow hot air from the bottom, thereby pre-fluidizing the water-absorbent resin particles. Then, when a fixing agent liquid is sprayed from a nozzle attached to the container, some of the water-absorbent resin particles agglomerate due to the solvent or dispersion medium contained in the fixing agent liquid, and a fixing agent layer is formed on their surface. The fixing agent liquid can be sprayed multiple times as needed. Excessive agglomeration of the water-absorbent resin particles can be suppressed by adjusting the amount and frequency of spraying the fixing agent liquid. As a fluidized bed granulator, for example, the FBD / SG fluidized bed granulator (manufactured by Mutual Co., Ltd.) can be used.

[0060] An example of the method described in (4) above will be explained. First, water-containing gel-like superabsorbent resin particles are prepared in a separable flask by a known reverse-phase suspension polymerization method. The superabsorbent resin particles may be obtained by single-step polymerization or by multi-step polymerization of two or more steps. On the other hand, an aqueous monomer solution of the fixing member containing a fixing member, a polymerization initiator, and an internal crosslinking agent as needed is prepared. The fixing member, for example, contains a polyol and a polyisocyanate when the fixing member layer contains polyurethane.

[0061] Next, after removing some of the water from the separable flask by refluxing the hydrocarbon dispersion medium through azeotropic distillation, an aqueous monomer solution of the fixing member is added to the flask to initiate the polymerization reaction. Subsequently, by evaporating the hydrocarbon dispersion medium in the flask, a resin particle composition is obtained in which the fixing member layer (polymer of the fixing member) is fixed to the surface of the water-absorbing resin particles.

[0062] (5-1) An example of the method described in (5) above will be explained. First, water-containing gel-like superabsorbent resin particles are prepared in a separable flask by a known reverse-phase suspension polymerization method. The superabsorbent resin particles may be obtained by single-step polymerization or by multi-step polymerization of two or more steps. On the other hand, a fixing member (including a precursor) and an aqueous precursor solution containing a crosslinking agent are prepared.

[0063] Next, the hydrocarbon dispersion medium is refluxed from the separable flask by azeotropic distillation to remove some of the water, and then the aqueous precursor solution is added to the flask to initiate the crosslinking reaction. Subsequently, the hydrocarbon dispersion medium in the flask is evaporated to obtain a resin particle composition in which the fixing member layer (a polymer of the fixing member, which is a crosslinked product of the fixing member) is fixed to the surface of the water-absorbing resin particles.

[0064] (5-2) Another example of the method described in (5) above will be explained. First, water-containing gel-like superabsorbent resin particles are prepared in the same manner as in 5-1 above. Next, these particles are dehydrated to obtain dried superabsorbent resin particles. The dried superabsorbent resin particles are dispersed in a suitable dispersion medium (e.g., n-heptane), and fixing member A (e.g., polyol) and fixing member B (e.g., polyisocyanate) are added in sequence. By heating as necessary, a resin particle composition is obtained in which a polymer (fixing member layer) produced by the polymerization reaction of fixing member A and fixing member B is fixed to the surface of the superabsorbent resin particles.

[0065] When a fixing member layer is formed using a fixing member liquid, the fixing member can easily come into uniform contact with the water-absorbing resin particles, so the resulting resin particle composition is thought to exhibit good resistance to shedding in the absorbent. In particular, the methods using a fluid bed granulator described in (1), (2), and (3) above, as well as methods (4) and (5), are thought to be more likely to produce a fixing member layer of uniform thickness compared to other methods.

[0066] The resin particle composition according to this embodiment is suitable for use in fields such as sanitary materials like disposable diapers and sanitary products, agricultural and horticultural materials such as water-retaining agents and soil conditioners, and industrial materials such as water-stopping agents and condensation-preventing agents. [Examples]

[0067] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0068] [Example 1] (Preparation of water-absorbent resin particles) A reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a round-bottom cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L, equipped with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm, were prepared. 293 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Highwax 1105A) was added as a polymeric dispersant. The mixture in the flask was heated to 80°C while stirring to dissolve the dispersant, and then cooled to 50°C.

[0069] In a 300 mL beaker, 92.0 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution was added as a water-soluble ethylenically unsaturated monomer. While cooling from the outside, 147.7 g of a 20.9% by mass sodium hydroxide aqueous solution was added dropwise to neutralize to 75 mol%. Subsequently, 0.092 g of hydroxyethylcellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickening agent, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare the first stage monomer aqueous solution.

[0070] A surfactant solution was prepared by heating and dissolving 0.736 g of sucrose stearate (HLB:3, Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370) as a surfactant in 6.62 g of n-heptane. The first monomer aqueous solution was added to a flask and stirred for 10 minutes. Then, the surfactant solution was added, and the system was thoroughly purged with nitrogen while stirring at a stirrer speed of 500 rpm. After that, the flask was immersed in a 70°C water bath and the temperature was raised, and polymerization was carried out for 60 minutes to obtain the first stage polymerization slurry.

[0071] Next, 128.8 g (1.44 mol) of an 80.5% by mass acrylic acid aqueous solution was placed in another 500 mL beaker as a water-soluble ethylenically unsaturated monomer. While cooling from the outside, 159.0 g of a 27% by mass sodium hydroxide aqueous solution was added dropwise to neutralize to 75 mol%. Subsequently, 0.090 g (0.333 mmol) of potassium persulfate was added as a water-soluble radical polymerization initiator, and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was added as an internal crosslinking agent and dissolved to prepare the second monomer aqueous solution.

[0072] The flask system was cooled to 25°C while stirring at a stirrer speed of 1000 rpm. Then, the entire volume of the second stage monomer aqueous solution was added to the first stage polymerization slurry, and the system was purged with nitrogen for 30 minutes. After that, the flask was immersed again in a 70°C water bath to raise the temperature, and the polymerization reaction was carried out for 60 minutes to obtain a hydrated gel polymer.

[0073] To the obtained hydrated gel polymer, 0.589 g of a 45% by mass aqueous solution of sodium pentasodium diethylenetriaminepentaacetate was added under stirring. Then, the flask was immersed in an oil bath set at 125°C, and 257.2 g of water was removed from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. Subsequently, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was held at 83°C for 2 hours.

[0074] Subsequently, the polymer particles were dried by heating and evaporating n-heptane and water in an oil bath at 125°C. The polymer particles were passed through a sieve with a mesh size of 850 μm to obtain 231.2 g of superabsorbent resin particles.

[0075] The above procedure was repeated, and the resulting superabsorbent resin particles were classified using a sieve with a mesh size of 250 μm to obtain more than 500 g of superabsorbent resin particles (A) with a particle size of 250 to 850 μm. The water retention capacity of superabsorbent resin particles (A) was 41 g / g.

[0076] (Preparation of resin particle composition) In a 1L poly beaker, 20.0g of a 25% aqueous emulsion of ethylene-sodium acrylate copolymer (Sumitomo Seika Co., Ltd., Zychsen N) and 30.0g of deionized water were added and mixed to obtain a fixing agent solution.

[0077] 500.0 g of superabsorbent polymer particles (A) were placed in the container of a fluid bed granulator (Pawrec Co., Ltd., FD-MP-01), and hot air at 50°C was blown in from the bottom of the container. Next, 50.0 g of fixing agent liquid was sprayed onto the superabsorbent polymer particles being blown up by the airflow, while drying them. After spraying the fixing agent liquid, the particles were dried at 50°C for 30 minutes. After drying, 504.5 g of a resin particle composition with a medium particle size of 362 μm was obtained.

[0078] [Example 2] The procedure was carried out in the same manner as in Example 1, except that the fixing agent liquid was changed to 57.1 g of a 35% aqueous dispersion emulsion of polyurethane (Daiichi Kogyo Seiyaku Co., Ltd., Superflex 210) diluted with 342.9 g of ion-exchanged water, and 508.1 g of a resin particle composition with a medium particle size of 345 μm was obtained.

[0079] [Example 3] The procedure was carried out in the same manner as in Example 1, except that the fixing material liquid was changed to 62.5 g of a 40% aqueous dispersion emulsion of nylon copolymer (Sumitomo Seika Co., Ltd., Sepolsion PA200) diluted with 187.5 g of ion-exchanged water, and 502.3 g of a resin particle composition with a medium particle size of 336 μm was obtained.

[0080] [Example 4] Except for changing the fixing agent liquid to 20.0 g of polyethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd., Polyethylene Glycol 6,000) dissolved in 180.0 g of deionized water, and changing the hot air temperature and drying temperature in the fluid bed granulator to 60°C, the procedure was carried out in the same manner as in Example 1, and 508.3 g of a resin particle composition with a medium particle size of 347 μm was obtained.

[0081] [Example 5] Except for changing the fixing agent liquid to a solution of 25.0 g of ethylene-sodium acrylate copolymer (SK global chemical, Primacol) dissolved in 225.0 g of tetrahydrofuran, and changing the hot air temperature and drying temperature in the fluid bed granulator to 40°C, the procedure was carried out in the same manner as in Example 1, and 502.0 g of a resin particle composition with a medium particle size of 337 μm was obtained.

[0082] [Example 6] (Preparation of water-absorbent resin particles)

[0083] A reflux condenser, dropping funnel, nitrogen gas inlet tube, and a round-bottom cylindrical separable flask with four side baffles (baffle length: 10 cm, baffle width: 7 mm) with an inner diameter of 11 cm and a capacity of 2 L, equipped with a stirring blade consisting of two stages of four inclined paddle blades (surface-treated with fluororesin) with a blade diameter of 5 cm (baffle length: 10 cm, baffle width: 7 mm), were prepared. 451.4 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 1.288 g of sorbitan monolaurate (nonionic LP-20R, HLB value: 8.6, manufactured by NOF Corporation) was added as a surfactant. The mixture in the flask was heated to 50°C while being stirred at 300 rpm to dissolve the surfactant, and then cooled to 40°C.

[0084] In a 500 mL Erlenmeyer flask, 92.0 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution was placed, and while cooling from the outside, 147.7 g of a 20.9% by mass sodium hydroxide aqueous solution was added dropwise to neutralize to 75 mol%. Subsequently, 0.1012 g (0.374 mmol) of potassium persulfate was added as a water-soluble radical polymerization initiator and dissolved to prepare an aqueous monomer solution.

[0085] The prepared monomer aqueous solution was added to the separable flask described above, and the system was thoroughly purged with nitrogen. Then, while stirring the contents of the flask at a stirrer speed of 700 rpm, the flask was immersed in a 70°C water bath. By holding it in this state for 60 minutes to complete polymerization, a hydrated gel-like polymer was obtained.

[0086] Subsequently, the polymerization solution containing the generated hydrated gel polymer, n-heptane, and surfactant was mixed for 10 minutes while stirring at a stirrer speed of 1000 rpm. Then, the flask containing the reaction solution was immersed in an oil bath at 125°C, and 97.0 g of water was removed from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. After that, 4.14 g of 2% by mass aqueous solution of ethylene glycol diglycidyl ether (ethylene glycol diglycidyl ether: 0.475 mmol) was added as a surface crosslinking agent, and the mixture was maintained at an internal temperature of 83°C for 2 hours.

[0087] A surfactant solution was prepared by dissolving 0.074 g of sorbitan monolaurate (product name: Nonion LP-20R, HLB value 8.6, manufactured by NOF Corporation) in 6.62 g of n-heptane. This surfactant solution was added to the flask.

[0088] Subsequently, water and n-heptane were evaporated at 120°C, and the system was dried until almost no more evaporated products were distilled out to obtain a dried product. This dried product was passed through a sieve with a mesh size of 850 μm to obtain 91.2 g of water-absorbing resin particles.

[0089] The above procedure was repeated to obtain more than 500g of superabsorbent polymer particles (B). The water retention capacity of superabsorbent polymer particles (B) was 38g / g, and the median particle size was 205μm.

[0090] (Preparation of resin particle composition) Except for changing the fixing material liquid to 100.0 g of a 25% aqueous dispersion emulsion of ethylene-sodium acrylate copolymer (Sumitomo Seika Co., Ltd., Zychsen N) diluted with 150.0 g of ion-exchanged water, and using water-absorbent resin particles (B) instead of water-absorbent resin particles (A), the same procedure as in Example 1 was carried out to obtain 506.3 g of a resin particle composition with a medium particle size of 213 μm.

[0091] [Example 7] (Preparation of water-absorbent resin particles) A reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a round-bottom cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L, equipped with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm, were prepared. 293 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Highwax 1105A) was added as a polymeric dispersant. The mixture in the flask was heated to 80°C while stirring to dissolve the dispersant, and then cooled to 50°C.

[0092] In a 300 mL beaker, 92.0 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution was added as a water-soluble ethylenically unsaturated monomer. While cooling from the outside, 147.7 g of a 20.9% by mass sodium hydroxide aqueous solution was added dropwise to neutralize to 75 mol%. Subsequently, 0.092 g of hydroxyethylcellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickening agent, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare the first stage monomer aqueous solution.

[0093] A surfactant solution was prepared by heating and dissolving 0.736 g of sucrose stearate (HLB:3, Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370) as a surfactant in 6.62 g of n-heptane. The first monomer aqueous solution was added to a flask and stirred for 10 minutes. Then, the surfactant solution was added to the flask, and the system was thoroughly purged with nitrogen while stirring at a stirrer speed of 500 rpm. After that, the flask was immersed in a 70°C water bath and the temperature was raised, and polymerization was carried out for 60 minutes to obtain the first stage polymerization slurry.

[0094] Next, 128.8 g (1.44 mol) of an 80.5% by mass acrylic acid aqueous solution was placed in another 500 mL beaker as a water-soluble ethylenically unsaturated monomer. While cooling from the outside, 159.0 g of a 27% by mass sodium hydroxide aqueous solution was added dropwise to neutralize to 75 mol%. Subsequently, 0.090 g (0.333 mmol) of potassium persulfate was added as a water-soluble radical polymerization initiator, and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was added as an internal crosslinking agent and dissolved to prepare the second stage monomer aqueous solution.

[0095] The flask system was cooled to 44°C while stirring at a stirrer speed of 1000 rpm. Then, the entire volume of the second stage aqueous solution was added to the first stage polymerization slurry, and the system was purged with nitrogen for 30 minutes. After that, the flask was again immersed in a 70°C water bath to raise the temperature, and the polymerization reaction was carried out for 60 minutes to obtain a hydrated gel polymer.

[0096] Subsequently, the flask was immersed in an oil bath set at 125°C, and 260.1 g of water was removed from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was held at 83°C for 2 hours.

[0097] Subsequently, the polymer particles (dried product) were obtained by evaporating water and n-heptane at 125°C and drying the mixture. These polymer particles were passed through a sieve with a mesh size of 850 μm to obtain 229.8 g of superabsorbent resin particles.

[0098] The above procedure was repeated to obtain more than 500g of superabsorbent polymer particles (C). The water retention capacity of the superabsorbent polymer particles (C) was 43g / g, and the median particle size was 72μm.

[0099] (Preparation of resin particle composition) Except for changing the fixing material liquid to 100.0 g of a 25% aqueous dispersion emulsion of ethylene-sodium acrylate copolymer (Sumitomo Seika Co., Ltd., Zychsen N) diluted with 150.0 g of ion-exchanged water, and using water-absorbent resin particles (C) instead of water-absorbent resin particles (A), the procedure was carried out in the same manner as in Example 1, and 504.8 g of a resin particle composition with a medium particle size of 86 μm was obtained.

[0100] [Comparative Example 1] The procedure was carried out in the same manner as in Example 1, except that the fixing material liquid was changed to a mixture of 25.0 g of polyvinyl alcohol (Kuraray Co., Ltd., Kuraray Poval 3-80) dissolved in 332.5 g of ion-exchanged water and 142.5 g of ethanol, yielding 504.4 g of a resin particle composition with a medium particle size of 345 μm.

[0101] [Comparative Example 2] Except for changing the fixing agent liquid to a solution of 25.0 g of methyl methacrylate (Fujifilm Wako Pure Chemical Industries, Ltd., methyl methacrylate polymer) dissolved in 475.0 g of acetone, and changing the hot air temperature and drying temperature in the fluid bed granulator to 30°C, the procedure was carried out in the same manner as in Example 1, and 505.3 g of a resin particle composition with a medium particle size of 339 μm was obtained.

[0102] The obtained resin particle composition was evaluated based on the following criteria. Unless otherwise specified, measurements were performed under conditions of 25±2°C and 50±10% humidity.

[0103] [Measurement of the caking index] A circular piece of release paper (Lintec Corporation, KA-4G ShiroBD) with one side coated with silicone was cut to a diameter of 50 mm. The circular piece of release paper was placed in a circular stainless steel petri dish with an inner diameter of 52 mm, with the silicone-coated surface facing upwards. 2.0 ± 0.002 g of a resin particle composition, from which particles larger than 850 μm had been pre-removed, was uniformly sprinkled on top of the release paper. Another piece of release paper, similar to the one described above, was placed on top of the resin particle composition, with the silicone-coated surface in contact with the resin particle composition. A circular stainless steel petri dish with an outer diameter of 50 mm and a mass of 20 g, and a cylindrical weight of 780 g with a diameter of 45 mm were then placed on top of this in order to prepare a measurement sample.

[0104] The measurement sample was placed in a hot air dryer set to an internal temperature of 80°C and left to stand for 1 hour. The measurement sample was removed from the hot air dryer and allowed to cool to room temperature. Then, the resin particle composition was removed from the measurement sample along with the release paper, and the resin particle composition was carefully removed from the release paper on a sieve with a mesh opening of 850 μm (inner diameter 200 mm) with a receiving tray at the bottom, and the entire amount of resin particle composition was placed on the sieve. The sieve was vibrated for 5 seconds using a rotap-type shaker (manufactured by Iida Seisakusho Co., Ltd., rotap-type sieve shaker), and the mass Wa [g] of the resin particle composition remaining on the sieve and the mass Wb [g] of the resin particle composition that passed through the sieve were measured, respectively. The caking index, which is the ratio of the amount of resin particle composition remaining on the sieve to the total amount of resin particle composition, was calculated using the following formula. The results are shown in Table 1. Caking index [%] = [Wa / (Wa+Wb)] × 100

[0105] [Measurement of saline solution retention] The water retention capacity of superabsorbent polymer particles and resin particle compositions in physiological saline was measured using the following procedure. First, a cotton bag (membrane no. 60, 100 mm wide x 200 mm long) containing 2.0 ± 0.002 g of the measurement particles was placed in a 500 mL beaker. 500 g of physiological saline was poured into the cotton bag containing the measurement particles in one go, taking care not to cause spillage. The top of the cotton bag was then tied with a rubber band and left to stand for 30 minutes to allow the measurement particles to swell. After 30 minutes, the cotton bag was dewatered for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., model number: H-122) set to a centrifugal force of 167 G. The mass Wc [g] of the cotton bag containing the swollen gel after dewatering was then measured. The same procedure was performed without adding superabsorbent polymer particles or resin particle compositions, and the empty mass Wd [g] of the cotton bag when wet was measured. The water retention capacity of superabsorbent polymer particles and resin particle compositions in physiological saline was calculated using the following formula. The results are shown in Table 1. Water retention amount [g / g]=(Wc-Wd) / 2.0

[0106] [Measurement of medium particle size] The median particle size of the resin particle composition was measured using the following procedure. Specifically, JIS standard sieves were arranged in the following order from top to bottom: a sieve with a mesh size of 600 μm, a sieve with a mesh size of 500 μm, a sieve with a mesh size of 425 μm, a sieve with a mesh size of 300 μm, a sieve with a mesh size of 250 μm, a sieve with a mesh size of 180 μm, a sieve with a mesh size of 150 μm, and a receiving tray. 50 g of the resin particle composition was placed in the top sieve and classified by shaking for 10 minutes using a rotary shaker. After classification, the mass of the particles remaining on each sieve was calculated as a mass percentage of the total amount to determine the particle size distribution. The relationship between the sieve mesh size and the cumulative mass percentage of the particles remaining on the sieve was plotted on logarithmic probability paper by accumulating the mass on the sieves in order from the largest particle size. By connecting the plots on probability paper with straight lines, the particle size corresponding to a cumulative mass percentage of 50% was obtained as the median particle size.

[0107] [Table 1]

[0108] In the examples, a resin particle composition having a caking index above a certain level was obtained. By incorporating such a resin particle composition under pressure and heat during the production of an absorbent, it is possible to manufacture an absorbent in which particles are less likely to fall off.

Claims

1. It comprises water-absorbing resin particles and a fixing member layer provided on at least a portion of the surface of the water-absorbing resin particles, After the caking test performed in the order of (1) to (5) below, at least a portion of the particles remain on the sieve with a mesh size of 850 μm used, and the caking index, as measured by the caking test and shown by the following formula, is 20% or more. The fixing member comprises at least one selected from the group consisting of ethylene-sodium acrylate copolymer, polyamide polymer, and polyester polymer, in a resin particle composition. (1) Place a circular release paper with a diameter of 50 mm on the bottom of a circular stainless steel petri dish with an inner diameter of 52 mm, and sprinkle 2.0 g of a resin particle composition with a particle size of less than 850 μm on top of the release paper. (2) A sample for measurement is obtained by stacking a circular release paper with a diameter of 50 mm, a circular stainless steel petri dish with an outer diameter of 50 mm and a mass of 20 g, and a cylindrical weight of 780 g with a diameter of 45 mm on top of the scattered resin particle composition in this order. (3) Dry the sample in a hot air dryer at 80°C for 1 hour, then allow it to cool to room temperature. (4) After cooling, the resin particle composition is removed from the release paper and recovered, and the entire amount of the recovered resin particle composition is placed on a sieve with a mesh size of 850 μm. (5) After shaking the sieve in a rotary sieve shaker for 5 seconds, check whether any resin particle composition remains on the sieve. Caking index (%) = [Mass of resin particle composition remaining on an 850 μm sieve / (Total mass of resin particle composition remaining on an 850 μm sieve and resin particle composition that passed through an 850 μm sieve)] × 100

2. The resin particle composition according to claim 1, wherein the medium particle size is 20 to 600 μm.

3. The resin particle composition according to claim 1 or 2, wherein the fixing member comprises an ethylene-sodium acrylate copolymer.

4. The resin particle composition according to any one of claims 1 to 3, wherein the amount of the fixing member is 0.01 to 10 parts by mass per 100 parts by mass of the water-absorbing resin particles.

5. A resin particle composition according to any one of claims 1 to 4, wherein the saline solution water retention capacity is 30 g / g or more.

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