Water absorbent and method for manufacturing water absorbent

Abstract

Provided is a water absorbent comprising: a continuous skeleton that is formed from a crosslinked polymer having, as a main component, a structural unit derived from a (meth)acrylic acid (salt); and continuous pores. The water absorbent has a centrifuge retention capacity (CRC) of 5-25 g / g and a bulk specific gravity of less than 0.3 g / ml. The neutralization rate of the crosslinked polymer is less than 70 mol%. Said water absorbent can better reduce skin roughness and the like of a user in comparison to conventional water absorbents, and is excellent in water absorption speed and water separation rate.

Description

Water-absorbent material and method for producing the same

[0001] The present invention relates to a water-absorbent material and a method for producing the same.

[0002] Currently, mixtures containing water-absorbent resins and hydrophilic fibers such as pulp for the purpose of absorbing body fluids are widely used as constituent materials for sanitary materials such as disposable diapers, sanitary napkins, and so-called incontinence pads. Meanwhile, in recent years, in order to further improve the water absorption performance of sanitary materials, technology has been developed to use water-absorbent materials with superior water absorption speed as constituent materials for such sanitary materials.

[0003] Here, a known example of the water-absorbing material is a monolithic organic porous ion exchanger (water-absorbing material) having a continuous skeleton and continuous pores, as described in Patent Document 1. The monolithic organic porous ion exchanger is a hydrolyzate produced by hydrolyzing a crosslinked polymer of a (meth)acrylic acid ester and a compound having two or more vinyl groups in one molecule.

[0004] Furthermore, as a water-absorbing material having a continuous skeleton and continuous pores produced by a method other than the hydrolysis, for example, water-absorbing polymer particles described in Patent Document 2 are known. Specifically, the water-absorbing polymer particles are produced by a method including the following steps (a) and (b):

[0005] (a) a step of incorporating a first solvent into an aqueous solution of a water-soluble ethylenically unsaturated monomer in the presence of a first surfactant to obtain an O / W emulsion; and (b) a step of dispersing the O / W emulsion obtained in step (a) in a second solvent containing a second surfactant to obtain an O / W / O emulsion.

[0006] Japanese Patent Publication No. 2021-007900 Japanese Patent Publication No. 2006-342306

[0007] On the other hand, the monolithic organic porous ion exchanger described in Patent Document 1 is a hydrolyzate, and an excess amount of an alkaline component is used during production, resulting in 100% neutralization of the (meth)acrylic acid component by the alkaline component. Therefore, the alkaline component remains in the pores of the monolithic organic porous ion exchanger even after washing. Therefore, the pH value of the monolithic organic porous ion exchanger exceeds 8, which may cause, for example, rough skin in the user.

[0008] Furthermore, the water-absorbing polymer particles described in Patent Document 2 have room for improvement in terms of water absorption rate. Furthermore, water-absorbing materials that can be used as constituent materials for sanitary materials are required to have an excellent water-separation rate in addition to an excellent water-absorption rate. Here, excellent water-separation rate means that when pressure is applied to a water-absorbing material that has absorbed an aqueous liquid and is in a swollen state, the absorbed aqueous liquid is released more easily and in greater amounts.

[0009] An embodiment of the present invention aims to solve the above-mentioned problems and provide a water-absorbent material that can reduce skin irritation and other problems in users more than conventional water-absorbent materials and has excellent water absorption speed and water separation rate.

[0010] The present inventors have found that the above problems can be solved by a water-absorbing material comprising an organic porous body formed from a crosslinked polymer whose neutralization rate is controlled to be lower than that of conventional water-absorbing materials and which has a specific internal pore structure such that the water-retention capacity and bulk density fall within specific ranges.Furthermore, the present inventors have found that in the manufacturing method described in Patent Document 2, a water-absorbing material comprising an organic porous body having the specific internal pore structure can be obtained by controlling the volume ratio of the first solvent to the unsaturated monomer aqueous solution (O / W volume ratio) to 2.5 or more.

[0011] That is, one embodiment of the present invention is a water-absorbing material comprising an organic porous material having a continuous skeleton and continuous pores formed by a crosslinked polymer containing structural units derived from (meth)acrylic acid (salt) as a main component, wherein the water-absorbing material has a centrifuge retention capacity (CRC) of 5 to 25 g / g, a bulk specific gravity of less than 0.3 g / ml, and a neutralization rate of the crosslinked polymer of less than 70 mol%.

[0012] Another embodiment of the present invention is a method for producing a water-absorbing material comprising an organic porous body having a continuous skeleton and continuous pores formed by a crosslinked polymer containing as a main component structural units derived from (meth)acrylic acid (salt), the method comprising: an O / W emulsion preparation step of incorporating a first solvent into an aqueous monomer solution having a neutralization rate of less than 70 mol% in the presence of a first surfactant so that the volume ratio of the first solvent to the aqueous monomer solution is 2.5 or more to obtain an O / W emulsion; an O / W / O emulsion preparation step of dispersing the O / W emulsion in a second solvent to obtain an O / W / O emulsion; and a polymerization step of polymerizing the monomers contained in the aqueous monomer solution in the O / W / O emulsion to prepare an organic porous body.

[0013] The water-absorbent material according to one embodiment of the present invention can reduce skin roughness and the like of the user more than conventional water-absorbent materials, and is excellent in both water absorption speed and water separation rate. Furthermore, the method for producing a water-absorbent material according to one embodiment of the present invention has the effect of being able to produce the water-absorbent material.

[0014] FIG. 1 is a schematic diagram showing one embodiment of an O / W / O emulsion preparation step and a polymerization step in a method for producing a water-absorbent material according to one embodiment of the present invention.

[0015] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[0016] [1. Definition of Terms] [1-1. Crosslinked Polymer] In this specification, the term "crosslinked polymer" specifically refers to a polymer gelling agent having a water swelling capacity (CRC) as defined by NWSP 241.0.R2(15) of 5 g / g or more and a water-soluble component (Ext) as defined by NWSP 270.0.R2(15) of 70 mass% or less.

[0017] It should be noted that "NWSP" stands for "Non-Woven Standard Procedures - Edition 2015." NWSP was jointly published by EDANA (European Disposables And Nonwovens Association) and INDA (Association of the Nonwoven Fabrics Industry) to standardize evaluation methods for nonwoven fabrics and their products in the United States and Europe, and includes standard measurement methods for water-absorbent resins. Unless otherwise specified, in this specification, the physical properties of crosslinked polymers and water-absorbent materials are measured in accordance with NWSP.

[0018] In this specification, the term "crosslinked polymer" is not limited to an embodiment in which the total amount (100 mass%) is the crosslinked polymer alone, but may also be a composition generally referred to as a "water-absorbent resin composition" which contains additives, etc. Furthermore, in this specification, the term "crosslinked polymer" may also include a crosslinked polymer in a state of a hydrous gel in which water has been taken in.

[0019] [1-2. Water-Absorbent Material] In this specification, the term "water-absorbent material" refers to a material that has a continuous skeleton formed primarily of a crosslinked polymer and continuous pores, and that has the ability to absorb and retain a solution (liquid). In particular, it can be used as an absorbent body in combination with a particulate superabsorbent polymer, generally known as a water-absorbent resin, which has excellent water-absorbing properties. The water-absorbent material of the present invention is characterized by temporarily retaining the liquid and transferring the liquid to the superabsorbent polymer. Here, the solution (liquid) is not limited to water, but may be any liquid. Liquids that can be absorbed by the water-absorbent material according to one embodiment of the present invention include, for example, urine, menstrual blood, sweat, physiological saline, oil, organic solvents, and waste liquid.

[0020] The water absorbent material described herein may be a particulate (powdered) water absorbent material, i.e., a water absorbent material generally referred to as a "particulate water absorbent material." The particulate water absorbent material contains a crosslinked polymer as a main component, and therefore corresponds to a particulate crosslinked polymer. The concept of "particulate water absorbent material" encompasses both a single particle of particulate water absorbent material and an aggregate of multiple particulate water absorbents. In this specification, "particulate" means having a particle shape. In this specification, "particle" refers to a relatively small divided body of a substance, having a size of several angstroms to several mm (see "Particle," McGraw-Hill Scientific and Technical Dictionary, Third Edition, edited by the McGraw-Hill Scientific and Technical Dictionary Editorial Committee, Nikkan Kogyo Shimbun, 1996, p. 1929). In this specification, "particulate water absorbent material" may be simply referred to as "water absorbent material."

[0021] The water-absorbing material contains a cross-linked polymer (also referred to as a particulate cross-linked polymer) as a main component. The water-absorbing material contains 60 to 100% by mass, preferably 70 to 95% by mass, and more preferably 75 to 90% by mass of the cross-linked polymer. The remainder of the water-absorbing material may optionally contain water and / or additives (inorganic fine particles, polyvalent metal cations, etc.).

[0022] That is, the upper limit of the crosslinked polymer content in the water-absorbing material is, for example, 100 mass %, 90 mass %, 80 mass %, or 70 mass %. Preferably, the water-absorbing material further contains 5 to 30 mass % of components other than the crosslinked polymer, particularly water and / or additives (inorganic fine particles, polyvalent metal cations, etc.).

[0023] The preferred moisture content of the water-absorbing material is 0.2 to 30% by mass. As mentioned above, a composition containing a crosslinked polymer in which components such as water and / or additives are integrated with and / or mixed with the crosslinked polymer is also encompassed in the "particulate water-absorbing material." In this specification, the "moisture content" is a numerical value indicating the ratio of the mass of water contained in the measurement object to the mass of the entire measurement object, more specifically, the mass of the entire measurement object in a water-containing state, and can be calculated based on the following formula (2). Examples of the measurement object include the water-absorbing material, the organic porous material described below, the crosslinked polymer described below, and the hydrogel described below, and the moisture content can be calculated in the same manner. [Moisture content (mass%) of measurement object] = [(mass of water in measurement object) ÷ (mass of the entire measurement object)] × 100 ... (2) [2. Water-absorbent material] A water-absorbent material according to one embodiment of the present invention (hereinafter referred to as "water-absorbent material of the present invention") is a water-absorbent material comprising an organic porous material having a continuous skeleton formed by a crosslinked polymer containing as a main component structural units derived from (meth)acrylic acid (salt) and continuous pores, and has a centrifuge retention capacity (CRC) of 5 to 25 g / g, a bulk specific gravity of less than 0.3 g / ml, and a neutralization rate of the crosslinked polymer of less than 70 mol%.

[0024] In the water-absorbing material of the present invention, the neutralization rate of the crosslinked polymer is less than 70 mol %. Therefore, the water-absorbing material of the present invention is controlled to be weakly acidic, and can, for example, reduce skin roughness and the like in users of the water-absorbing material compared to conventional water-absorbing materials.

[0025] The water-absorbing material of the present invention comprises an organic porous material having a continuous skeleton formed by a crosslinked polymer and continuous pores, and therefore, when absorbing a liquid such as water, the liquid is retained inside the crosslinked polymer and the continuous pores.

[0026] Furthermore, the CRC refers to the amount of liquid remaining in the water-absorbent material after a specific centrifugal force (pressure) is applied to the water-absorbent material in a swollen state after absorbing the liquid and releasing a portion of the liquid. When the centrifugal force is applied, the liquid held within the interconnected pores is mainly released from the water-absorbent material in a swollen state. Therefore, the CRC is mainly the amount of liquid held in the cross-linked polymer of the water-absorbent material in a swollen state.

[0027] The bulk density is a parameter that represents the mass per unit volume of the water-absorbent material. This mass is mainly the mass of the cross-linked polymer that constitutes the water-absorbent material per unit volume. Therefore, the bulk density is a parameter that represents the ratio of the portion of the water-absorbent material that is occupied by the continuous skeleton to the portion of the water-absorbent material that is occupied by the continuous pores. In other words, a small bulk density means that the portion of the water-absorbent material that is occupied by the continuous skeleton is small and the portion of the water-absorbent material that is occupied by the continuous pores is large.

[0028] The water-absorbent material of the present invention has a CRC of 25 g / g or less and a bulk density controlled to less than 0.3 g / ml. Therefore, the water-absorbent material of the present invention has a structure in which a large proportion of the interconnected pores is occupied. This structure more easily absorbs the liquid and more easily releases the liquid when centrifugal force (pressure) is applied. Therefore, the water-absorbent material of the present invention is excellent in both water absorption rate and water syneresis rate.

[0029] The water-absorbing material of the present invention has a CRC of 5 g / g or more. This means that the water-absorbing material of the present invention contains a predetermined amount of the continuous skeleton. Therefore, the water-absorbing material of the present invention has a predetermined water-absorbing performance.

[0030] From the above, the water-absorbent material of the present invention can reduce the skin roughness of the user compared to conventional water-absorbent materials, and is excellent in both water absorption rate and water separation rate.

[0031] Patent Document 2 describes that water-absorbing materials containing organic porous materials with low bulk specific gravity lack mechanical strength. On the other hand, when the mechanical strength of the water-absorbing material of the present invention was confirmed by a method (damage test) in which the water-absorbing material and glass beads were placed in a glass container and then shaken, it was confirmed that the water-absorbing material of the present invention has sufficient mechanical strength for use as a water-absorbing material. Note that this method is a technique for simulating mechanical damage that occurs during the manufacturing process in a chemical plant, etc.

[0032] The components constituting the water-absorbent material of the present invention and the properties of the water-absorbent material of the present invention will be described in detail below.

[0033] [2-1. Crosslinked Polymer] The crosslinked polymer contained in the water-absorbing material of the present invention is a crosslinked polymer whose main component is a structural unit derived from (meth)acrylic acid (salt). In detail, the crosslinked polymer is a hydrophilic crosslinked polymer obtained by crosslinking a monomer composition containing a (meth)acrylic acid (salt)-based monomer, i.e., a poly(meth)acrylic (acid)-based crosslinked polymer.

[0034] In this specification, "(meth)acrylic acid (salt)" means (meth)acrylic acid and / or its salt. Furthermore, "a monomer composition containing a (meth)acrylic acid (salt)-based monomer" means a monomer composition containing 50 mol % or more of (meth)acrylic acid (salt) based on the total amount of monomers excluding the crosslinking agent.

[0035] The crosslinked polymer contained in the water-absorbing material of the present invention is a crosslinked polymer that contains 50 mol% or more of structural units derived from (meth)acrylic acid (salt) relative to all structural units constituting the poly(meth)acrylic acid (salt)-based crosslinked polymer, and is a crosslinked polymer that has structural units derived from an internal crosslinking agent as an optional component.

[0036] The crosslinked polymer is a crosslinked polymer in which 50 mol % or more, preferably 70 mol % or more, more preferably 90 mol % or more of the constituent monomers excluding the internal crosslinking agent is (meth)acrylic acid (salt). Also, the crosslinked polymer is a crosslinked polymer in which 100 mol % or less, more preferably substantially 100 mol % of the constituent monomers excluding the internal crosslinking agent is (meth)acrylic acid (salt).

[0037] The crosslinked polymer of the water-absorbing material of the present invention may have, for example, a particulate shape. The particulate crosslinked polymer may have, for example, one or more shapes selected from the group consisting of irregularly pulverized (irregular), spherical, fibrous, rod-like, approximately spherical, and flat. Among these, it is preferable that at least a portion of the crosslinked polymer be spherical particles. Considering damage during the manufacturing process and reduced productivity due to the generation of fine powder, among the above-mentioned particle shapes, it is more preferable that the crosslinked polymer be spherical particles. The particulate crosslinked polymer is referred to as a particulate crosslinked polymer whether it is a single particle or an aggregate of multiple particles. Furthermore, the crosslinked polymer is porous.

[0038] <Monomer, Monomer Composition> In this specification, the term "monomer composition" refers to raw material components that form the crosslinked polymer, and refers to a composition that contains (meth)acrylic acid (salt) as the main monomer component, as well as a monomer other than (meth)acrylic acid (salt), and an internal crosslinking agent as an optional component. In other words, the raw material components that form the crosslinked polymer are referred to as the monomer composition.

[0039] As the monomer other than (meth)acrylic acid (salt), a monomer containing an acid group is preferred among monomers having an unsaturated double bond (ethylenically unsaturated monomers). Specific examples of such monomers include anionic unsaturated monomers and / or salts thereof, such as maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and 2-hydroxyethyl (meth)acryloyl phosphate. One or more of these monomers may be used as needed.

[0040] The salt may be one or more salts selected from the group consisting of alkali metal salts, ammonium salts, and amine salts, with sodium salts, potassium salts, lithium salts, and ammonium salts being more preferred, and sodium salts being particularly preferred.

[0041] The neutralization ratio of the crosslinked polymer in the water-absorbing material of the present invention can be controlled by the neutralization ratio of the monomer composition. Alternatively, the neutralization ratio may be adjusted by adding a neutralizing agent to the crosslinked polymer or the water-absorbing material after the polymerization step. The neutralization ratio is the ratio (unit: mol%) of the number of moles of neutralized monomers to the number of moles of all monomers (excluding the internal crosslinking agent) constituting the crosslinked polymer.

[0042] The water-absorbent material of the present invention has a low neutralization rate of less than 70 mol%, and as a result, as described above, can reduce skin roughness and other problems in users of the water-absorbent material compared to conventional water-absorbent materials. From this perspective, the neutralization rate is preferably 65 mol% or less.

[0043] Furthermore, by ensuring that the neutralization rate is equal to or greater than a predetermined value, the water absorption performance of the water-absorbent material of the present invention, such as the water absorption capacity and water absorption rate, can be improved. From this perspective, the neutralization rate is preferably equal to or greater than 30 mol%, and more preferably equal to or greater than 40 mol%.

[0044] Furthermore, the monomer composition may contain, as necessary, a "hydrophilic or hydrophobic unsaturated monomer (hereinafter referred to as "other monomer")" in addition to the above-mentioned "(meth)acrylic acid (salt)" and "monomer other than (meth)acrylic acid (salt)".

[0045] Examples of the other monomer include mercaptan group-containing unsaturated monomers, phenolic hydroxyl group-containing unsaturated monomers, amide group-containing unsaturated monomers such as N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth)acrylamide, N-isopropyl(meth)acrylamide, N-ethyl(meth)acrylamide, and N,N-dimethyl(meth)acrylamide, and amino group-containing unsaturated monomers such as N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, and N,N-dimethylaminopropyl(meth)acrylamide. One or more of the other monomers can be used.

[0046] The amount of other monomers used may be such that the physical properties of the resulting water-absorbing material are not impaired, and specifically, the amount is 50 mol % or less, more preferably 20 mol % or less, based on the portion of the monomer composition excluding the internal crosslinking agent.

[0047] <Internal Crosslinking Agent> The crosslinked polymer is crosslinked. The crosslinking may be a self-crosslinking type that does not use a crosslinking monomer. On the other hand, from the viewpoint of physical properties, the crosslinked polymer is preferably internally crosslinked by an internal crosslinking agent.

[0048] The internal crosslinking agent is preferably at least one selected from the group consisting of polyfunctional acrylate crosslinking agents, acrylamide crosslinking agents, and glycidyl ether crosslinking agents.

[0049] Specific examples of the internal crosslinking agent include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth)acrylate. At least one type of internal crosslinking agent is selected from these internal crosslinking agents in consideration of reactivity and the like.

[0050] In the present invention, from the viewpoint of the water absorption performance of the crosslinked polymer and the water absorbent material of the present invention, an internal crosslinking agent having two or more polymerizable unsaturated groups is preferably selected.

[0051] Specific examples of the polymerizable unsaturated group include an allyl group and a (meth)acrylate group. Among the polymerizable unsaturated groups, a (meth)acrylate group is preferred. Among them, an internal crosslinking agent having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure can be used, for example, polyethylene glycol di(meth)acrylate. The number of alkylene glycol units in the internal crosslinking agent is preferably 1 or more, more preferably 2 or more, even more preferably 4 or more, and particularly preferably 6 or more. The number of alkylene glycol units is preferably 100 or less, more preferably 50 or less, even more preferably 20 or less, and particularly preferably 10 or less.

[0052] The content of the internal crosslinking agent is preferably 0.001 mol % or more, more preferably 0.01 mol % or more, and even more preferably 0.1 mol % or more, based on the portion of the monomer composition excluding the internal crosslinking agent, and is preferably 10 mol % or less, more preferably 7 mol % or less, and even more preferably 5 mol % or less, based on the portion of the monomer composition excluding the internal crosslinking agent.

[0053] When the content of the internal crosslinking agent is within the above range, the water absorption performance of the crosslinked polymer and the water absorbent material of the present invention can be controlled within a desired range. On the other hand, when the content of the internal crosslinking agent is outside the above range, the gel strength of the crosslinked polymer decreases, and the water-soluble content of the crosslinked polymer increases, or the absorption capacity of the crosslinked polymer and the water absorbent material of the present invention decreases.

[0054] <Surface Crosslinking Agent> The crosslinked polymer may be surface-crosslinked to provide a surface crosslinked layer. The surface crosslinked layer may be formed on the surface of the crosslinked polymer by surface crosslinking using a surface crosslinking agent described in U.S. Pat. No. 7,183,456, for example. At least one surface crosslinking agent is selected from these surface crosslinking agents, taking into consideration reactivity and the like. In addition, from the viewpoints of the handleability of the surface crosslinking agent and the water absorption performance of the water-absorbing material, a surface crosslinking agent having two or more functional groups that react with a carboxyl group and that form a covalent bond is preferably selected.

[0055] Examples of the surface cross-linking agent include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, and 2,4-pentanediol. polyhydric alcohol compounds such as 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,3-hexanediol, 2,4-hexanediol, glycerin, polyglycerin, diethanolamine, and triethanolamine; polyhydric amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine, and polyethyleneimine; haloepoxy compounds; polyhydric amine compounds condensation products of compounds with haloepoxy compounds; oxazoline compounds such as 1,2-ethylenebisoxazoline; oxazolidinone compounds; 1,3-dioxolan-2-one (ethylene carbonate), 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-di Examples thereof include alkylene carbonate compounds such as methyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one; polyhydric glycidyl compounds such as ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and glycidol; oxetane compounds; vinyl ether compounds; cyclic urea compounds; and the like.These may be used alone or in combination of two or more.

[0056] [2-2. Organic Porous Material] The organic porous material of the present invention has a continuous skeleton formed by the crosslinked polymer and continuous pores. In other words, the organic porous material is an organic porous material formed from the crosslinked polymer, and may be in the form of particles. Therefore, the organic porous material may be the crosslinked polymer in the form of particles.

[0057] The thickness of the continuous skeleton of the organic porous material in a dry state is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. When the thickness is equal to or greater than the lower limit, the strength of the organic porous material and the water-absorbing material of the present invention itself can be improved.

[0058] Furthermore, the thickness is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. When the thickness is equal to or less than the upper limit, the speed at which the water-absorbing material of the present invention absorbs liquids such as water can be improved.

[0059] In addition, when measuring the thickness of the continuous skeleton of the organic porous material in a dry state, the cross section of the skeleton that appears on a test piece for electron microscope measurement of the water-absorbing material of the present invention is used as the evaluation point, since the pore structure of the organic porous material is an open-cell structure. The open-cell structure is a structure in which cellular macropores overlap each other.

[0060] The average diameter of the interconnected pores of the organic porous material in a dry state is preferably 0.1 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. When the average diameter is equal to or greater than the lower limit, the rate at which the water-absorbing material of the present invention absorbs liquids such as water can be improved.

[0061] Furthermore, the average diameter of the interconnected pores of the organic porous material in a dry state is preferably 1,000 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. When the average diameter is equal to or less than the upper limit, the strength of the organic porous material and the water-absorbing material of the present invention itself can be improved.

[0062] The sample for measuring the thickness of the continuous skeleton and the average diameter of the continuous pores is prepared by drying the water-absorbing material of the present invention in a reduced pressure dryer at 50° C. for 18 hours or more, with the final pressure being 0 Torr.

[0063] [2-3. Surfactant] The water-absorbent material of the present invention can be produced by a method for producing a water-absorbent material according to one embodiment of the present invention, which will be described later. Therefore, the surfactant used in the production method remains, and the water-absorbent material can contain a surfactant.

[0064] The surfactant may be, for example, the surfactants exemplified below as "first surfactant" and "second surfactant." The surfactant may be one type or a mixture of two or more types.

[0065] The upper limit of the surfactant content is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the crosslinked polymer. When the upper limit of the surfactant content is the above-mentioned value or less, a decrease in water absorption performance due to the surfactant remaining in the water absorbent material of the present invention can be prevented, and water absorption performance such as water absorption rate can be improved. The lower limit of the surfactant content is not particularly limited, but can be, for example, 0.045 parts by mass or more, preferably 0.090 parts by mass or more, relative to 100 parts by mass of the crosslinked polymer.

[0066] [2-4. Chelating Agent] The water-absorbing material of the present invention may contain a chelating agent. The chelating agent may be, for example, a polycarboxylic acid and a salt thereof. The chelating agent is preferably a chelating agent having high ion-sequestering and chelating ability for Fe or Cu. Specifically, the chelating agent is a chelating agent having a stability constant for Fe ions of 10 or more, preferably 20 or more, and more preferably an aminopolycarboxylic acid and a salt thereof. The aminopolycarboxylic acid and a salt thereof may be a polymer. Particularly preferred as the aminopolycarboxylic acid and a salt thereof are aminocarboxylic acids and salts thereof having a lower limit of 3 or more, preferably 4 or more, more preferably 5 or more, and an upper limit of usually 100 or less, more preferably 20 or less, of carboxyl groups.

[0067] Examples of the polycarboxylic acid include diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl ether diaminetetraacetic acid, ethylenediaminetetrapropionic acid, N-alkyl-N'-carboxymethylaspartic acid, and N-alkenyl-N'-carboxymethylaspartic acid, as well as alkali metal salts, alkaline earth metal salts, ammonium salts, and amine salts thereof. Among these polycarboxylic acids, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, N-hydroxyethylethylenediaminetriacetic acid, and salts thereof are most preferred. One or more polycarboxylic acids can be used.

[0068] The content of the chelating agent, particularly the amino polycarboxylic acid, is a trace component, typically 0.00001 to 10 parts by mass, preferably 0.0001 to 1 part by mass, and more preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of the crosslinked polymer.

[0069] In this case, sufficient effects and / or additional functions can be obtained by including a chelating agent, and the absorption performance of the water-absorbing material can be maintained.

[0070] [2-5. Inorganic Fine Particles] The water-absorbing material of the present invention may contain inorganic fine particles, particularly water-insoluble inorganic fine particles, to prevent blocking during moisture absorption. Examples of the inorganic fine particles include one or more particles selected from the group consisting of metal oxides such as silicon dioxide and titanium oxide, silicic acid (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay, and bentonite. Of these inorganic fine particles, silicon dioxide and silicic acid (salts) are more preferred, and silicon dioxide and silicic acid (salts) having an average particle size of 0.001 to 200 μm as measured by the Coulter Counter method are even more preferred. Furthermore, the water-absorbing material of the present invention may be imparted with a deodorizing function by incorporating zeolite, and SiO ２ :Al ２ O ３ The preferred zeolite has a blending ratio of 1:1 to 100, preferably 1:2 to 10.

[0071] The content of the inorganic fine particles is usually in the range of 0 to 10 parts by mass, preferably 0.001 to 5 parts by mass, and more preferably 0.002 to 3 parts by mass, per 100 parts by mass of the crosslinked polymer.

[0072] In this case, sufficient effects and / or additional functions can be obtained by incorporating inorganic fine particles, and the absorption performance of the water-absorbing material can be maintained.

[0073] 2-6. Other Additives The water-absorbing material of the present invention may contain other additives in addition to the surfactant, the chelating agent, and the inorganic fine particles, to the extent that the object of the present invention is not impaired.

[0074] Examples of the other additives include plant components, polyvalent metal salts of organic acids, composite hydrous oxides, reducing substances, antibacterial agents, deodorants, water-soluble polymers, water-insoluble polymers, water, organic fine particles, reducing agents, oxidizing agents, and inorganic salts.

[0075] The content of the other additives varies depending on the purpose and additional function. For example, the content of each additive is usually in the range of 0 to 10 parts by mass, preferably 0.001 to 5 parts by mass, more preferably 0.002 to 3 parts by mass, per 100 parts by mass of the crosslinked polymer. One or more of the additives can be used.

[0076] In this case, it is possible to obtain sufficient effects and / or additional functions due to the inclusion of the additive, and also to maintain the absorption performance of the water-absorbent material.

[0077] 2-7. Physical Properties of Water Absorbent Material Centrifuge Retention Capacity (CRC) (NWSP241.0.R2(15)) CRC is generally an abbreviation for Centrifuge Retention Capacity, and is a parameter known as water absorption capacity without load.

[0078] Specifically, the CRC means the water absorption capacity (unit: g / g) after 0.2 g of the water-absorbing material is placed in a nonwoven bag, immersed in a large excess of 0.9% by mass sodium chloride aqueous solution for 30 minutes to allow free swelling, and then drained using a centrifuge (250 G). The CRC can be measured, for example, by the method shown in the Examples.

[0079] The CRC of the water absorbent material of the present invention is 25 g / g or less, preferably 23 g / g or less, and more preferably 20 g / g or less.

[0080] The CRC is 5 g / g or more, preferably 7 g / g or more, and more preferably 10 g / g or more. It is preferable that the CRC is equal to or more than the lower limit from the viewpoint of maintaining the water absorption performance, such as the water absorption rate, of the water-absorbing material of the present invention. The CRC value can be controlled by adjusting the water absorption capacity of the crosslinked polymer by changing the types and amounts of the internal crosslinking agent and surface crosslinking agent, etc.

[0081] <Bulk specific gravity> The bulk specific gravity of the water-absorbent material of the present invention is a parameter representing the mass per unit volume. The bulk specific gravity is the mass (unit: [g / mL]) of the water-absorbent material when the water-absorbent material is allowed to fall freely into a 10 mL container and filled therewith.

[0082] The bulk density is less than 0.3 g / mL, preferably 0.27 g / mL or less, more preferably 0.25 g / mL or less, even more preferably 0.20 g / mL or less, and even more preferably 0.17 g / mL or less. As described above, the bulk density being equal to or less than the upper limit means that the water-absorbing material of the present invention has a structure in which the interconnected pores are large and / or have a large number of interconnected pores, and as a result, both the water absorption rate and the water syneresis rate of the water-absorbing agent are improved.

[0083] The bulk density is preferably 0.05 g / mL or more, more preferably 0.07 g / mL or more. The bulk density being equal to or greater than the lower limit is preferable from the viewpoint of maintaining the water absorption performance such as CRC of the water-absorbent material of the present invention.

[0084] <Water absorption rate (vortex)> The water absorption rate of the water absorbent material of the present invention is expressed, for example, as a value measured by a method generally called the Vortex method (water absorption rate (vortex): unit [seconds]). The smaller the water absorption rate (vortex) value, the faster and more excellent the water absorption rate. The water absorption rate (vortex) value of the water absorbent material of the present invention is preferably a small value, specifically, preferably 10 seconds or less, more preferably 7 seconds or less, even more preferably 5 seconds or less, and particularly preferably 2 seconds or less. The water absorption rate (vortex) value can be measured, for example, by the method described in the examples.

[0085] <Free Swell Capacity (FSC) (NWSP 240.0.R2(15))> The free swell capacity (FSC) of the water absorbent material of the present invention is an abbreviation for Free Swell Capacity, and means the water absorption capacity of the water absorbent material when suspended under no pressure. In this specification, FSC is measured in accordance with NWSP 240.0.R2(15). The FSC value of the water absorbent material can be controlled by changing the types and amounts of the internal crosslinking agent and surface crosslinking agent, etc., to adjust the water absorption capacity of the crosslinked polymer.

[0086] The FSC value is preferably 35 g / g or more, more preferably 40 g / g or more, and even more preferably 50 g / g or more. The FSC value is preferably 150 g / g or less, more preferably 120 g / g or less, and even more preferably 100 g / g or less. When the FSC value is within the above range, the water absorption rate and syneresis rate of the water-absorbent material of the present invention can be further improved.

[0087] <Syneresis Rate> The syneresis rate of the water-absorbent material of the present invention is a parameter that indicates the ease with which a liquid such as water is released when a certain pressure (centrifugal force) is applied to the water-absorbent material in a swollen state after absorbing the liquid, and is expressed by the following formula (1): Syneresis rate [%] = {(FSC [g / g] - CRC [g / g]) / FSC [g / g]} × 100 (1) A high value of the syneresis rate means that the water-absorbent material in a swollen state is more likely to release the absorbed liquid, and has a high syneresis rate. A high value of the syneresis rate is preferable, and specifically, it is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. The value of the syneresis rate can usually be 95% or less.

[0088] <pH> The pH of the water-absorbing material of the present invention is controlled to a range showing weak acidity, specifically, it may be in the range of 4.5 to 6.5, and preferably in the range of 5.0 to 6.0. The pH can be controlled by adjusting the neutralization rate of the monomer composition, which is the raw material, to be within the above-mentioned range. The pH can be measured by the method described in the examples.

[0089] <Mass median particle diameter (D50)> The water-absorbing material of the present invention is a porous body and may be particulate. The mass median particle diameter (D50) is preferably 100 μm or more and 1000 μm or less, more preferably 300 μm or more and 800 μm or less, and even more preferably 400 μm or more and 700 μm or less. The mass median particle diameter (D50) refers to the particle diameter of a standard sieve with a fixed mesh size, corresponding to 50% by mass of the total particles, as described in U.S. Patent No. 5,051,259. The D50 can be measured, for example, by the method described in the Examples.

[0090] 2-8. Manufacturing Method The water-absorbent material of the present invention can be manufactured, for example, by a manufacturing method for a water-absorbent material according to one embodiment of the present invention, which will be described later.

[0091] [2-9. Uses of Water-Absorbent Material] The water-absorbent material of the present invention is an organic porous material having a continuous skeleton formed primarily from a crosslinked polymer and continuous pores, and therefore has the ability to absorb and retain solutions (liquids). Therefore, it can be used in absorbents for sanitary materials, and as mentioned above, it can be used in combination with existing superabsorbent polymers with excellent water-absorbing performance, such as water-absorbent resins. Furthermore, since the water-absorbent material of the present invention is a particulate porous material, it can be easily mixed with a particulate superabsorbent polymer (water-absorbent resin) to form a composition and used in absorbents, etc. Such a composite absorbent material containing the water-absorbent material of the present invention and water-absorbent resin particles is also included in the present invention.

[0092] 3. Method for producing water-absorbent material A method for producing a water-absorbent material according to one embodiment of the present invention (hereinafter referred to as "the production method of the present invention") is a method for producing a water-absorbent material comprising an organic porous material having a continuous skeleton formed by a crosslinked polymer mainly composed of structural units derived from (meth)acrylic acid (salt) and continuous pores, and includes the steps of: preparing an O / W emulsion by incorporating a first solvent into an aqueous monomer solution having a neutralization rate of less than 70 mol% in the presence of a first surfactant so that the volume ratio of the first solvent to the aqueous monomer solution is 2.5 or more; preparing an O / W / O emulsion by dispersing the O / W emulsion in a second solvent to obtain an O / W / O emulsion; and polymerizing the monomers contained in the aqueous monomer solution in the O / W / O emulsion to prepare the organic porous material.

[0093] In the production method of the present invention, the descriptions in the above section [2. Water-absorbing material] are used for the "crosslinked polymer," "organic porous material," and "water-absorbing material."

[0094] The present invention aims to provide a water-absorbent material that can reduce skin roughness and other issues in users compared to conventional water-absorbent materials and that has excellent water absorption rate and water syneresis rate. The inventors have discovered that the water-retention capacity and bulk density of the water-absorbent material produced by the production method of the present invention are controlled within specific ranges, and that the water-absorbent material can solve the above-mentioned problems. Furthermore, the inventors have discovered that by setting the neutralization rate of the monomer lower than that of conventional monomers, it is possible to prepare an O / W emulsion having an O / W volume ratio of 2.5 or more, and to produce a water-absorbent material that can solve the above-mentioned problems. Here, the neutralization rate of the monomer corresponds to the neutralization rate of the crosslinked polymer that constitutes the water-absorbent material to be produced.

[0095] Here, it will be explained that the production method of the present invention can provide a water-absorbent material that can solve the above-mentioned problems, with reference to Fig. 1. Fig. 1 is a schematic diagram showing one embodiment of the O / W / O emulsion preparation step and polymerization step of the production method of the present invention.

[0096] The leftmost diagram in Fig. 1 shows an O / W emulsion prepared in the O / W emulsion preparation step of the production method of the present invention. As shown in the leftmost diagram in Fig. 1, the O / W emulsion has a first solvent 1 dispersed in an aqueous monomer solution 2, and the volume ratio of first solvent 1 to aqueous monomer solution 2 (O / W volume ratio) is 2.5 or more.

[0097] In the O / W / O emulsion preparation step of the production method of the present invention, as shown from the left to the center of Figure 1, the O / W emulsion prepared in the O / W emulsion preparation step is added to a second solvent 3 and emulsified. This results in the preparation of an O / W / O emulsion in which an O / W emulsion 4 is dispersed in the second solvent 3.

[0098] Here, the first solvent is dispersed in the aqueous monomer solution in the O / W emulsion 4. The O / W volume ratio in the O / W emulsion 4 is the same as the O / W volume ratio in the O / W emulsion prepared in the O / W emulsion preparation step.

[0099] In the polymerization step of the production method of the present invention, as shown on the right side of FIG. 1 , the monomers contained in the aqueous monomer solution in the O / W emulsion 4 are polymerized to form a crosslinked polymer. The crosslinked polymer then forms a continuous skeleton that constitutes the organic porous material 5 prepared by the polymerization step. Furthermore, because no crosslinked polymer is formed in the first solvent dispersed in the O / W emulsion 4, the area where the first solvent is present becomes the continuous pores that constitute the organic porous material 5. Thus, as shown in the rightmost drawing of FIG. 1 , the polymerization step produces an organic porous material that has a continuous skeleton formed by the crosslinked polymer and a structure in which continuous pores are dispersed within. That is, the production method of the present invention produces a water-absorbing material that includes an organic porous material having the continuous skeleton and the continuous pores. The organic porous material 5 in FIG. 1 can be a water-absorbing material.

[0100] In the production method of the present invention, a monomer aqueous solution having a neutralization rate of less than 70 mol% is used as a raw material. Here, the neutralization rate of the monomer aqueous solution refers to the ratio (unit: mol%) of the number of moles of neutralized monomers to the number of moles of all monomers (excluding the internal crosslinking agent) in the monomer aqueous solution containing the monomer composition, and is the neutralization rate of the crosslinked polymer obtained from the monomer aqueous solution. Therefore, the water-absorbing material produced by the production method of the present invention is controlled to be weakly acidic, and can, for example, reduce skin roughness and the like in users of the water-absorbing material compared to conventional water-absorbing materials.

[0101] Unlike the manufacturing method described in Patent Document 1, the manufacturing method of the present invention can manufacture a water-absorbing material containing an organic porous material without undergoing hydrolysis. Therefore, the manufacturing method of the present invention does not require the use of excess alkali, which is essential for hydrolysis. Therefore, according to the manufacturing method of the present invention, a water-absorbing material containing an organic porous material can be manufactured while arbitrarily adjusting the neutralization rate to a small value of less than 70 mol%, and as a result, as described above, it is possible to reduce skin roughness and the like in users of the water-absorbing material.

[0102] Furthermore, the continuous pores of the organic porous material 5 are formed in areas where the first solvent dispersed in the O / W emulsion 4 is present. In the production method of the present invention, the O / W volume ratio in the O / W emulsion 4 is 2.5 or more. Therefore, the proportion of continuous pores in the organic porous material 5 is large. In other words, in the organic porous material 5, the portion of the entire water-absorbent material occupied by the continuous skeleton is small, and the portion occupied by the continuous pores is large.

[0103] As shown in the section [2. Water-absorbent material], when the proportion of the interconnected pores is large, the liquid can be more easily absorbed therein and can be more easily released when centrifugal force (pressure) is applied. Therefore, the water-absorbent material containing the organic porous material 5 has improved water absorption rate and water separation rate.

[0104] From the above, the manufacturing method of the present invention can reduce skin roughness and the like of the user of the water-absorbent material compared to conventional water-absorbent materials, and can produce a water-absorbent material that is excellent in water absorption speed and water-separation rate.

[0105] Furthermore, in the production method of the present invention, an O / W emulsion having an O / W volume ratio adjusted to 2.5 or more is prepared by using an aqueous monomer solution having a neutralization rate of less than 70 mol% as a raw material. Then, the O / W emulsion is dispersed in a second solvent to form an O / W / O emulsion, and the monomers contained in the aqueous monomer solution are polymerized in the emulsion to produce a water-absorbing material containing an organic porous material. Furthermore, in the production method of the present invention, particle size is controlled at the O / W / O emulsion stage to produce a water-absorbing material containing an organic porous material. As a result, the production method of the present invention can produce a water-absorbing material having a predetermined particle size without pulverizing the resulting organic porous material. It is known that pulverizing an organic porous material produces a large amount of fine powder as a by-product, reducing productivity. Therefore, the production method of the present invention can produce a water-absorbing material having a predetermined particle size while avoiding the reduction in productivity due to the by-production of a large amount of fine powder.

[0106] Each step constituting the production method of the present invention will be described in detail below.

[0107] [3-1. O / W emulsion preparation step] The O / W emulsion preparation step of the production method of the present invention is a step of obtaining an O / W emulsion by incorporating a first solvent into an aqueous monomer solution having a neutralization rate of less than 70 mol % in the presence of a first surfactant so that the volume ratio of the first solvent to the aqueous monomer solution is 2.5 or more.

[0108] <Aqueous monomer solution> The aqueous monomer solution is an aqueous solution containing monomers that are raw materials for the water-absorbing material to be produced, and optionally an internal cross-linking agent, etc. The concentration of the monomer in the aqueous monomer solution is usually preferably 30% by mass to the saturated concentration, more preferably 35 to 45% by mass, based on the total mass of the aqueous monomer solution. The water used in the aqueous monomer solution is not particularly limited, and examples thereof include tap water, distilled water, and ion-exchanged water.

[0109] The production method of the present invention may also include a monomer aqueous solution preparation step of preparing the monomer aqueous solution prior to the O / W emulsion preparation step. This step involves dissolving the monomer and, optionally, an internal crosslinking agent, etc., in water to prepare the monomer aqueous solution. This step may also include adjusting the neutralization rate of the monomer aqueous solution. Known methods can be used to adjust the neutralization rate. For example, one method may be to neutralize the acid group of (meth)acrylic acid (salt), which is the main component of the monomer in the production method of the present invention, using a compound containing an alkali metal. Examples of the alkali metal include lithium, sodium, and potassium. Among these alkali metals, sodium and potassium are preferred. One or more of the alkali metals may be used.

[0110] The acid groups can be neutralized by, for example, adding dropwise an aqueous solution of a compound containing an alkali metal such as sodium hydroxide and / or potassium hydroxide to the monomer or an aqueous solution containing the monomer, and mixing them together. The concentration of the compound containing an alkali metal in the aqueous solution is not particularly limited, but is usually about 20 to 50 mass %.

[0111] (Monomer, Internal Crosslinking Agent) The monomer and internal crosslinking agent of the aqueous monomer solution can be found in the <Monomer> and <Internal Crosslinking Agent> sections of [2-1. Crosslinked Polymer] in [2. Water Absorbent Material]. Note that the "neutralization rate of crosslinked polymer" in the <Monomer> section corresponds to the "neutralization rate of aqueous monomer solution," and the "content" corresponds to the "amount used" in the production method of the present invention.

[0112] A preferred example of the aqueous monomer solution is an aqueous monomer solution containing an internal crosslinking agent, wherein the internal crosslinking agent is at least one selected from a polyfunctional acrylate-based crosslinking agent, an acrylamide-based crosslinking agent, and a glycidyl ether-based crosslinking agent.

[0113] (Polymerization initiator) When a polymerization initiator is used in the production method of the present invention, the polymerization initiator can be added to one or more of the aqueous monomer solution, the O / W emulsion, and the O / W / O emulsion at any time before the polymerization step is carried out. The polymerization initiator is preferably added to the aqueous monomer solution in advance to disperse it uniformly.

[0114] A water-soluble radical polymerization initiator can be used as the polymerization initiator. Examples include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; azo polymerization initiators such as 2,2'-azobis(2-amidinopropane) dihydrochloride and 2,2'-azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride; and hydrogen peroxide. The polymerization initiator that can be used in the production method of the present invention is not limited to the exemplified polymerization initiators. The polymerization initiator is preferably an azo initiator and / or a persulfate. One or more polymerization initiators can be used.

[0115] The amount of the polymerization initiator used is usually preferably 0.05 to 10 millimoles per mole of the total monomers contained in the aqueous monomer solution.

[0116] <First Surfactant> The first surfactant used in the O / W emulsion preparation step is not particularly limited as long as it can prepare the O / W emulsion. Examples of the first surfactant include nonionic surfactants such as polyoxyethylene-polyoxypropylene copolymer, polyoxyethylene alkyl ether, polyoxypropylene alkyl ether, hydrophobically modified polyether urethane, hydrophobically modified polyester urethane, polyoxyethylene glycerin monostearate, polyoxyethylene glycerin monoisostearate, rosin ester, and polyoxyethylene rosin ester; and anionic surfactants such as sodium lauryl sulfate and polyoxyethylene sodium lauryl sulfate. Among the aforementioned compounds, the first surfactant is preferably a polyoxyethylene-polyoxypropylene copolymer. One or more types of first surfactants can be used.

[0117] The use of a polyoxyethylene-polyoxypropylene copolymer as the first surfactant is preferable because it has the advantage of improving the stability during polymerization in the polymerization step described below and enabling the formation of a large number of interconnected pores. As the polyoxyethylene-polyoxypropylene copolymer, for example, a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer can be used.

[0118] The mass average molecular weight of the polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer is preferably 3,000 or more, more preferably 5,000 or more, from the viewpoints of improving stability during polymerization in the polymerization step described below and forming a large number of continuous pores. Furthermore, from the viewpoints of increasing water solubility and improving workability, the mass average molecular weight is preferably 100,000 or less, more preferably 30,000 or less. From these viewpoints, the mass average molecular weight is preferably 3,000 to 100,000, more preferably 5,000 to 30,000.

[0119] The polyoxyethylene content of the polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer is preferably 40% by mass or more, more preferably 45% by mass or more, which makes it possible to maintain a good emulsified state of the O / W / O emulsion and to facilitate the formation of interconnected pores inside the particles when the monomers are polymerized in the O / W / O emulsion in the polymerization step described below.

[0120] The content is preferably 90% by mass or less, more preferably 85% by mass or less, from the viewpoint of stabilizing the O / W emulsion dispersed in the O / W / O emulsion in the polymerization step described below. From these viewpoints, the content is preferably 40 to 90% by mass, more preferably 45 to 85% by mass.

[0121] Polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymers are easily available industrially. Representative examples include the "ADEKA PLURONIC" (registered trademark) series manufactured by Asahi Denka Kogyo Co., Ltd., the "PLURONIC" (registered trademark) series manufactured by BASF, and the "NEUPOL" (registered trademark) series manufactured by Sanyo Chemical Industries, Ltd. These polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymers may be used alone or in combination of two or more.

[0122] The amount of the first surfactant used is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the aqueous monomer solution, from the viewpoint of facilitating dispersion of the first solvent in the aqueous monomer solution. Furthermore, adding an excessive amount of the first surfactant tends to result in a commensurate effect being unsatisfactory and to be uneconomical. Therefore, the amount of the first surfactant used is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the aqueous monomer solution. From these viewpoints, the amount of the first surfactant used is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the aqueous monomer solution. The destination and timing of addition of the first surfactant are not particularly limited, as long as it is used during the preparation of the O / W emulsion.

[0123] <First Solvent> The first solvent used in the O / W emulsion preparation step is not particularly limited as long as it is a hydrophobic organic solvent that can be dispersed in the aqueous monomer solution to obtain an O / W emulsion. The phrase "the first solvent is dispersed in the aqueous monomer solution" means that the first solvent is encapsulated in the aqueous monomer solution.

[0124] The first solvent is preferably a hydrocarbon organic solvent, such as one or more solvents selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, cyclohexane, and methylcyclohexane. Among these, one or more solvents selected from the group consisting of n-hexane, n-heptane, and cyclohexane are more preferred because they are easily available industrially, have stable quality, and are relatively inexpensive.

[0125] <Characteristics of aqueous monomer solution and O / W emulsion> In the production method of the present invention, the O / W volume ratio in the O / W emulsion preparation step is 2.5 or more. The O / W volume ratio is the volume (mL) of the first solvent / volume (mL) of the aqueous monomer solution in the O / W emulsion.

[0126] As described above, when the O / W volume ratio is 2.5 or more, it is possible to improve both the water absorption rate and the water syneresis rate of the water-absorbent material produced by the production method of the present invention. The O / W volume ratio can be controlled, for example, by adjusting the amount of the first solvent used in the O / W emulsion preparation step.

[0127] From the viewpoint of improving both the water absorption rate and the water syneresis rate of the water absorbent material, the O / W volume ratio is preferably 2.5 or more, more preferably 2.8 or more, even more preferably 3.0 or more, even more preferably 3.2 or more, and even more preferably 5.0 or more. Furthermore, when the O / W volume ratio is a specific value or less, the emulsification is stabilized, the aqueous monomer solution can sufficiently encapsulate the first solvent, and the O / W emulsion can be successfully prepared. From this viewpoint, the O / W volume ratio is preferably 15.0 or less, more preferably 10.0 or less.

[0128] The viscosity of the aqueous monomer solution at 25°C is preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, from the viewpoint of stabilizing the O / W emulsion and thereby increasing the porosity of the particles obtained.

[0129] The viscosity of the aqueous monomer solution can be adjusted, for example, by using a polymer thickener.

[0130] Preferred examples of the polymeric thickener include hydroxyethyl cellulose, carboxymethyl cellulose, guar gum, gum arabic, glucomannan, dextrin, polyvinyl alcohol, polyethylene oxide, and partially neutralized polyacrylic acid. This is because these polymeric thickeners can impart a relatively high viscosity to the aqueous monomer solution even when used in small amounts. One or more of the polymeric thickeners can be used.

[0131] <Conditions for the O / W emulsion preparation step> The method for preparing the O / W emulsion in the O / W emulsion preparation step is not particularly limited. For example, the method may include mixing a first surfactant with the aqueous monomer solution, and gradually adding a first solvent to the resulting mixture while stirring.

[0132] The liquid temperature of the aqueous monomer solution when preparing the O / W emulsion is preferably 30° C. or lower, more preferably 15 to 25° C., from the viewpoint of the stability of the O / W emulsion.

[0133] A stirring device or the like may be used when preparing the O / W emulsion. The stirring device is not particularly limited, and may be, for example, a device capable of finely emulsifying, such as a homomixer, or a general stirring blade such as a paddle type, propeller type, or screw type. In either stirring device, the number and size of pores in the resulting particles can be appropriately adjusted by adjusting the stirring speed, etc.

[0134] [3-2. O / W / O Emulsion Preparation Step] The O / W / O emulsion preparation step of the production method of the present invention is a step of dispersing the O / W emulsion prepared in the O / W emulsion preparation step in a second solvent to obtain an O / W / O emulsion. Note that, from the viewpoint of obtaining a good O / W / O emulsion, it is preferable that the second solvent contains a second surfactant.

[0135] <Second Solvent> The second solvent used in the O / W / O emulsion preparation step is a dispersion medium for the O / W emulsion. The second solvent is a hydrophobic organic solvent and is not particularly limited as long as it can disperse the O / W emulsion to obtain an O / W / O emulsion. The second solvent is preferably a hydrocarbon organic solvent such as one or more solvents selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, cyclohexane, and methylcyclohexane. Of these, one or more solvents selected from the group consisting of n-hexane, n-heptane, and cyclohexane are more preferred because they are easily available industrially, have stable quality, and are relatively inexpensive.

[0136] The first solvent and the second solvent may be the same or different from each other, and it is preferable that the first solvent and the second solvent are the same from the viewpoint of facilitating reuse of the solvent recovered in the drying step described below.

[0137] <Second Surfactant> Examples of the second surfactant include sucrose fatty acid esters, (poly)glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkyl allyl ethers. These may be used alone or in combination of two or more.

[0138] The second surfactant is preferably at least one selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, sorbitol fatty acid esters, and polyglycerin fatty acid esters, and sucrose fatty acid esters are more preferred because of their excellent safety.

[0139] In this specification, "(poly)" refers to both the case where the prefix "poly" is used and the case where it is not used.

[0140] The amount of the second surfactant used is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the aqueous monomer solution, from the viewpoint of ensuring stability during polymerization in the polymerization step described below. Furthermore, the amount of the second surfactant used is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the aqueous monomer solution. Adding an excessive amount of the second surfactant tends to result in a commensurate effect being insufficient and is therefore uneconomical. From these viewpoints, the amount of the second surfactant is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the aqueous monomer solution.

[0141] <Conditions for the O / W / O emulsion preparation step> The method for preparing the O / W / O emulsion in the O / W / O emulsion preparation step is not particularly limited. For example, the method may include a method in which the O / W emulsion is delivered to the second solvent using a delivery device such as a tube pump and added while stirring. The device used for stirring is not particularly limited, and for example, a paddle-type stirring blade used for stirring in a flask can be used.

[0142] [3-3. Polymerization Step] The polymerization step in the production method of the present invention is a step of preparing an organic porous material by polymerizing the monomers contained in the aqueous monomer solution in the O / W / O emulsion prepared in the O / W / O emulsion preparation step.

[0143] The reaction temperature when the polymerization reaction of the monomers is carried out in the polymerization step cannot be determined in general because it differs depending on the type of polymerization initiator used, etc. The reaction temperature is preferably 40 to 100°C, more preferably 50 to 80°C, from the viewpoint of rapidly progressing the polymerization reaction and shortening the polymerization time to thereby improve economic efficiency, while also carrying out the polymerization reaction so as not to boil the first or second organic solvent.

[0144] When the reaction temperature is 60° C. or higher, it is preferable to use a polymer dispersion stabilizer from the viewpoint of maintaining the stability of the O / W / O emulsion during the polymerization reaction of the monomers. Suitable polymer dispersion stabilizers include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified ethylene-propylene-diene terpolymer (EPDM), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethyl cellulose, and hydroxyethyl cellulose.

[0145] Among these, from the viewpoint of dispersion stability of the aqueous monomer solution, more preferred polymer dispersion stabilizers include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymer. The polymer dispersion stabilizer may be one type or a mixture of two or more types. Furthermore, these polymer dispersion stabilizers may be used in combination with the second surfactant.

[0146] From the viewpoint of sufficiently stabilizing the O / W / O emulsion, the amount of the polymer dispersion stabilizer used is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the aqueous monomer solution. Furthermore, the amount of the polymer dispersion stabilizer used is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the aqueous monomer solution. Adding an excessive amount of the polymer dispersion stabilizer may result in a commensurate effect not being obtained, and may even be uneconomical.

[0147] The reaction time for the polymerization reaction is not particularly limited, and is usually about 0.5 to 3 hours.

[0148] [3-4. Post-Crosslinking Step] The organic porous material is usually obtained in the form of hydrogel particles by the polymerization step. Here, from the viewpoint of increasing the water absorption rate and gel strength of the organic porous material and a water-absorbing material containing the organic porous material, the production method of the present invention may include a post-crosslinking step in which a post-crosslinking reaction is performed on the organic porous material obtained by the polymerization step. The post-crosslinking step post-crosslinks, i.e., surface-crosslinks, the crosslinked polymer constituting the organic porous material. The post-crosslinking step obtains the surface-crosslinked crosslinked polymer and an organic porous material formed from the continuous pores. Hereinafter, the organic porous material obtained by the post-crosslinking step will also be referred to as the "surface-crosslinked organic porous material."

[0149] <Post-Crosslinking Agent> As the post-crosslinking agent, a crosslinking agent capable of reacting with the reactive group in the crosslinked polymer can be used.

[0150] Specific examples of the post-crosslinking agent include polyols such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, (poly)oxyethylene glycol, polyoxypropylene glycol, and polyglycerin; ether compounds having two or more glycidyl groups such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin triglycidyl ether; and compounds having two or more reactive functional groups such as haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin. These can be used alone or in combination of two or more. Among the post-crosslinking agents, (poly)ethylene glycol diglycidyl ether is preferred.

[0151] The amount of the post-crosslinking agent used cannot be determined in general because it varies depending on the water content of the crosslinked polymer, the treatment temperature, etc. The water content of the crosslinked polymer is the same as the water content of the organic porous material.

[0152] The post-crosslinking agent may be added at any time after the polymerization reaction is completed. For example, from the viewpoint of sufficiently progressing the post-crosslinking reaction and increasing the water absorption rate of the water absorbent material, the addition time is preferably when the water content of the crosslinked polymer is 10% by mass or more, more preferably when it is 20% by mass or more. Furthermore, from the viewpoint of preventing the water retention capacity of the water absorbent material from becoming too low, the addition time is preferably when the water content of the crosslinked polymer is 80% by mass or less, more preferably when it is 65% by mass or less. From these viewpoints, the post-crosslinking agent is added preferably when the water content of the crosslinked polymer is 10 to 80% by mass, more preferably when it is 20 to 65% by mass.

[0153] <Dehydration Treatment> The post-crosslinking step may include a dehydration treatment for removing water from the crosslinked polymer to adjust its water content before adding the post-crosslinking agent to the crosslinked polymer. As the dehydration method, a known method may be adopted. For example, the method may include a method of distilling off water and a hydrophobic organic solvent using an azeotropic distillation column.

[0154] The water content in the hydrogel and the solid content in the hydrogel, i.e., the solid content of the crosslinked polymer, can be calculated from the amounts of raw material compounds such as monomers charged in the polymerization reaction and the amounts of water removed in the dehydration treatment and drying steps described below.

[0155] <Post-crosslinking method, conditions, etc.> The post-crosslinking reaction in the post-crosslinking step can be carried out, for example, by adding a solution of a post-crosslinking agent to a hydrogel adjusted to a predetermined water content obtained by subjecting a hydrogel after completion of the polymerization reaction to the dehydration treatment.

[0156] The solution of the post-crosslinking agent is, for example, a solution in which the post-crosslinking agent is dissolved in water or alcohol, and the concentration of the post-crosslinking agent is 0.5 to 50% by mass. When the post-crosslinking reaction is carried out, drying may be carried out immediately after the addition of the solution of the post-crosslinking agent, and it is more preferable to maintain the internal temperature at 50 to 90°C for 0.5 to 6 hours to promote the post-crosslinking reaction. The internal temperature refers to the temperature of the hydrogel after the addition of the solution of the post-crosslinking agent, i.e., the temperature of the mixture of the solution of the post-crosslinking agent and the hydrogel.

[0157] [3-5. Drying Step] The production method of the present invention may include a drying step of removing water and the hydrophobic organic solvent from the organic porous material obtained by the polymerization step or the surface-crosslinked organic porous material obtained by the post-crosslinking step.

[0158] The method for removing the water and hydrophobic organic solvent can be a known method. Examples of the method include distilling off the water and hydrophobic organic solvent using an azeotropic distillation column, filtration, and drying under reduced pressure. Only one method may be used, or two or more methods may be combined. By carrying out the drying step, a water-absorbing material having a low moisture content and in a dry state can be successfully produced.

[0159] [3-6. Chelating agent mixing step] The production method of the present invention may include a chelating agent mixing step of mixing the aqueous monomer solution or the organic porous material with a chelating agent. The organic porous material may be the organic porous material obtained in the polymerization step, or may be a surface-crosslinked organic porous material obtained after the post-crosslinking step.

[0160] The type and amount of the chelating agent used in the chelating agent mixing step are not particularly limited, and the description regarding the type and content of the chelating agent shown in the section [2-4. Chelating agent] in [2. Water-absorbing material] above can be used.

[0161] [3-7. Inorganic fine particle mixing step] The production method of the present invention may include an inorganic fine particle mixing step of mixing the organic porous material with inorganic fine particles. The organic porous material may be the organic porous material obtained in the polymerization step, or may be a surface-crosslinked organic porous material obtained after the post-crosslinking step.

[0162] The type and amount of inorganic fine particles used in the inorganic fine particle addition step are not particularly limited, and the description regarding the type and content of inorganic fine particles shown in the section [2-5. Inorganic fine particles] of [2. Water absorbent material] above can be used.

[0163] [3-8. Mixing step of other additives] The production method of the present invention may include a step of mixing the organic porous material with other additives. The organic porous material may be the organic porous material obtained in the polymerization step, or may be a surface-crosslinked organic porous material obtained after the post-crosslinking step.

[0164] The types and amounts of other additives used in this step are not particularly limited, and the descriptions regarding the types and contents of other additives shown in the section [2-6. Other additives] in [2. Water-absorbing material] above can be used.

[0165] [3-9. Recovery Step] The production method of the present invention may include a recovery step of separating and recovering fine powder from the produced organic porous material. The separated fine powder may be added to each step, such as the O / W emulsion preparation step and the O / W / O emulsion preparation step, for reuse.

[0166] An embodiment of the present invention may include the following inventions [1] to

[13] .

[0167] [1] A water-absorbing material comprising an organic porous material having a continuous skeleton formed by a crosslinked polymer whose main component is a structural unit derived from (meth)acrylic acid (salt) and continuous pores, wherein the water-absorbing material has a centrifuge retention capacity (CRC) of 5 to 25 g / g, a bulk specific gravity of less than 0.3 g / ml, and a neutralization rate of the crosslinked polymer of less than 70 mol%.

[0168] [2] The water-absorbing material according to [1], having a water-absorbing speed (Vortex) of physiological saline solution of 10 seconds or less.

[0169] [3] The water-absorbing material according to [1] or [2], having a free swelling capacity (FSC) of 35 g / g or more.

[0170] [4] The water-absorbing material according to any one of [1] to [3], wherein the water-separation rate represented by the following formula (1) is 40% or more.

[0171] Syneresis rate [%] = {(FSC [g / g] - CRC [g / g]) / FSC [g / g]} × 100 (1) [5] The water-absorbing material according to any one of [1] to [4], wherein the water-absorbing material contains a chelating agent.

[0172] [6] The water-absorbing material according to any one of [1] to [5], wherein the water-absorbing material contains inorganic fine particles.

[0173] [7] A method for producing a water-absorbing material comprising an organic porous body having a continuous skeleton formed by a crosslinked polymer mainly composed of structural units derived from (meth)acrylic acid (salt) and continuous pores, the method comprising: an O / W emulsion preparation step of incorporating a first solvent into an aqueous monomer solution having a neutralization rate of less than 70 mol% in the presence of a first surfactant so that the volume ratio of the first solvent to the aqueous monomer solution is 2.5 or more to obtain an O / W emulsion; an O / W / O emulsion preparation step of dispersing the O / W emulsion in a second solvent to obtain an O / W / O emulsion; and a polymerization step of polymerizing the monomers contained in the aqueous monomer solution in the O / W / O emulsion to prepare an organic porous body.

[0174] [8] The method for producing a water-absorbing material according to [7], wherein the aqueous monomer solution contains a polymerization initiator, and the polymerization initiator is an azo-based initiator and / or a persulfate.

[0175] [9] The method for producing a water-absorbing material according to [7] or [8], wherein the aqueous monomer solution contains an internal crosslinking agent, and the internal crosslinking agent is at least one selected from the group consisting of a polyfunctional acrylate-based crosslinking agent, an acrylamide-based crosslinking agent, and a glycidyl ether-based crosslinking agent.

[0176]

[10] The method for producing a water-absorbing material according to any one of [7] to [9], wherein the first surfactant is a block copolymer of polyoxyethylene-polyoxypropylene-polyoxyethylene.

[0177]

[11] The method for producing a water-absorbing material according to any one of [7] to

[10] , wherein the second solvent contains a second surfactant.

[0178]

[12] The method for producing a water-absorbent material according to

[11] , wherein the second surfactant is at least one selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, sorbitol fatty acid esters, and polyglycerin fatty acid esters.

[0179]

[13] The method for producing a water-absorbing material according to any one of [7] to

[12] , wherein the first solvent and the second solvent are the same type.

[0180]

[14] A composite absorbent body comprising the water-absorbing material according to any one of [1] to [6] and water-absorbent resin particles.

[0181] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0182] [Measurement and Calculation of Physical Properties] The physical properties of the water absorbent materials 1 to 6 produced in Examples 1 to 6 and Comparative Example 2, and the comparative water absorbent material 1, were measured and calculated by the following methods.

[0183] <Centrifuge Retention Capacity (CRC)> The CRC of the water-absorbing material was measured in accordance with NWSP 241.0. R2 (15). Specifically, 0.2 g of the water-absorbing material was placed in a nonwoven bag, and then immersed in a large excess of 0.9% by mass sodium chloride aqueous solution for 30 minutes to allow the water-absorbing material to freely swell. Thereafter, the bag was dehydrated for 3 minutes using a centrifuge (250 G), and the CRC (unit: g / g) was measured.

[0184] <Bulk specific gravity> The water-absorbing material was poured into a cylindrical plastic container with a volume of 10 mL (inner diameter 2.5 cm) until it was piled high and spilled outside the container, and then the water-absorbing material was leveled off at the top of the container using a flat leveling rod. During this process, the container was worked on with as little vibration as possible to prevent the water-absorbing material from being packed tightly inside the container. Thereafter, the weight of the water-absorbing material packed in the container was calculated from the change (difference) in the weight of the container before and after filling it with the water-absorbing material. The bulk specific gravity (unit: g / mL) of the water-absorbing material was calculated by dividing the weight by the volume (10 mL) of the container.

[0185] <Water absorption rate (vortex)> 0.02 parts by weight of Food Blue No. 1, a food additive, was added to 1,000 parts by weight of a 0.90 wt % aqueous sodium chloride solution (physiological saline), and the liquid temperature was adjusted to 30° C. 50 ml of the physiological saline was measured and placed in a 100 ml beaker, and 2.0 g of a water-absorbing material was added while stirring at 600 rpm with a cylindrical stirrer having a length of 40 mm and a thickness (diameter of the cross section perpendicular to the length direction of the cylinder) of 8 mm, and the vortex (water absorption rate: seconds) of the water-absorbing material was measured.

[0186] The end point of the measurement of the water absorption rate was determined in accordance with the standard described in JIS K 7224-1996 "Explanation of Test Method for Water Absorption Rate of Super Absorbent Resin," and the time (Vortex: seconds) until the sample absorbed the physiological saline solution and the stirrer tip was covered with the test liquid was measured as the water absorption rate (seconds).

[0187] <Free Swelling Capacity (FSC)> The FSC of the water-absorbent material was measured in accordance with NWSP 240.0. R2 (15). Specifically, 0.2 g of the water-absorbent material was placed in a nonwoven bag and then immersed in a large excess of 0.90% by mass sodium chloride aqueous solution for 30 minutes to allow free swelling. The bag was then removed and hung for 10 minutes to drain, after which the water absorption capacity (unit: g / g) was determined.

[0188] <Syneresis Rate> Using the CRC and FSC of the water-absorbing material, the water-syneresis rate of the water-absorbing material was calculated based on the following formula (1). Syneresis Rate [%] = {(FSC [g / g] - CRC [g / g]) / FSC [g / g]} × 100 (1) <pH> The pH of the water-absorbing material was measured in accordance with NWSP 200.0. R2 (15). Specifically, 100 ml of a 0.90% by mass sodium chloride aqueous solution at 23°C was weighed into a beaker. Next, 0.5 g of water-absorbing material was added to the sodium chloride aqueous solution while stirring the sodium chloride aqueous solution in the beaker at 150 rpm using a cylindrical stirrer having a length of 40 mm and a diameter (diameter of the cross section perpendicular to the length of the cylinder) of 8 mm. Subsequently, the sodium chloride aqueous solution was stirred for 10 minutes to swell the water-absorbing material. Thereafter, a pH electrode was inserted into the aqueous sodium chloride solution, and the pH was read when the value became stable.

[0189] <Mass-average particle diameter (D50)> The mass-average particle diameter (D50) of the water-absorbing material was measured in accordance with "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution" described in columns 27 and 28 of U.S. Pat. No. 7,638,570.

[0190] <Increase in Fine Powder (Damage Test)> The increase in fine powder of the water absorbent material was measured as follows.

[0191] 10 g of glass beads (soda-lime glass beads for precision fractional distillation filling) and 3 g of water-absorbing agent were placed in a glass container (a mayonnaise bottle manufactured by Yamamura Glass Co., Ltd., diameter 6 cm, height 11 cm) with a capacity of 242 ml (capacity with inner lid 225 ml). After a resin inner lid (material: polyethylene) and an outer lid (material: polypropylene) for the container were attached, the container was attached to a paint shaker (Toyo Seiki Seisakusho, product No. 488) and shaken at 800 cycles / min (CPM) for 10 minutes to impart mechanical damage to the water-absorbing material.

[0192] Next, the samples before and after the damage test were sieved with a JIS standard sieve with a mesh size of 150 μm, and the ratio of the fine powder that passed through the sieve to the test sample was taken as the amount of fine powder (% by weight), and the increase in the amount before and after the test (amount of fine powder after the test - amount of fine powder before the test) was calculated.

[0193] Example 1 (1) Preparation of O / W Emulsion A 1000 mL four-neck separable flask (1) (hereinafter referred to as "flask (1)") equipped with a stirrer, a dropping funnel, a fluororesin tube for nitrogen gas injection, and a thermometer was prepared. 16.85 g of acrylic acid, 39.63 g of a 37% by mass aqueous solution of sodium acrylate, and 2.00 g of methylenebisacrylamide were charged into the flask (1). The neutralization rate of the acrylic acid (salt) was 40 mol%. Subsequently, 0.64 g of hydroxyethyl cellulose was added to the flask (1) and stirred.

[0194] Furthermore, 2.27 g of polyoxyethylene-polyoxypropylene copolymer (manufactured by Asahi Denka Kogyo Co., Ltd., trade name: Adeka Pluronic F-108, mass average molecular weight: 15500) was dissolved in 21.61 g of ion-exchanged water to prepare aqueous solution A. Furthermore, 0.05 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was dissolved in 2.59 g of ion-exchanged water to prepare aqueous solution B.

[0195] Aqueous solution A and Aqueous solution B were added to the flask (1) and mixed and dissolved to prepare an aqueous monomer solution. Next, while stirring this aqueous monomer solution at a rotation speed of 600 rpm, 433.3 g (646 mL) of n-heptane was added dropwise to the aqueous monomer solution at a flow rate of 11 mL / min. As a result, an O / W emulsion in which the n-heptane was dispersed in the aqueous monomer solution was obtained. The O / W volume ratio of the O / W emulsion was 88 / 12 = 7.3.

[0196] (2) Preparation of O / W / O Emulsion A 2000 mL four-neck separable flask (2) (hereinafter referred to as "flask (2)") equipped with a stirrer, a reflux condenser, a fluororesin tube for nitrogen gas injection, and a thermometer was prepared, and 670 g (1000 mL) of n-heptane was poured into the flask (2). Subsequently, 3.11 g of sucrose fatty acid ester (manufactured by Mitsubishi Chemical Foods Corporation, product name: S-370) and 3.11 g of maleic anhydride-modified polyethylene (manufactured by Mitsui Chemicals, Inc., product name: HI-WAX1105A) were added to the flask (2).

[0197] Next, the flask (2) was immersed in a water bath at 80°C while stirring while nitrogen gas was blown into the flask (2) at a flow rate of 100 mL / min, and the contents of the flask were stirred until they became uniform. Thereafter, the rotation speed of the stirrer was set to 700 rpm, and the contents of the flask (2) were allowed to cool to 60°C while stirring. Thereafter, the O / W emulsion prepared in (1) was added dropwise to the flask (2) at a flow rate of 60 mL / min to prepare an O / W / O emulsion.

[0198] (3) Polymerization and Drying The flask (2) containing the O / W / O emulsion prepared in (2) above was immersed in a water bath at 70°C to raise the temperature of the O / W / O emulsion, and a polymerization reaction was carried out for 1.5 hours while stirring at a rotation speed of the stirrer of 700 rpm. Subsequently, the O / W / O emulsion after the polymerization reaction was dehydrated by azeotropic distillation at 100°C to obtain a slurry.

[0199] The solvent was removed from the slurry by filtration using a sieve with 125 μm openings to obtain a filtrate. The filtrate was dried under reduced pressure at 60° C. for 2 hours to produce 35 g of an organic porous material having a mass average particle size of 554 μm. This organic porous material was designated as water-absorbent material 1.

[0200] [Example 2] Except for the changes shown in (i) and (ii) below, an organic porous material was produced by the same method as in Example 1. The neutralization rate of the acrylic acid (salt) used in Example 2 was 50 mol %.

[0201] (i) The amount of acrylic acid used was changed to 13.67 g.

[0202] (ii) The amount of the 37% by mass aqueous sodium acrylate solution used was changed to 48.23 g.

[0203] The produced organic porous material had a mass average particle diameter of 524 μm and a mass of 34 g. This organic porous material was designated as water absorbent material 2.

[0204] [Example 3] An organic porous material was produced by the same method as in Example 2, except for the changes shown in (iii) and (iv) below. The neutralization rate of the acrylic acid (salt) used in Example 3 was 50 mol %, the same as in Example 2.

[0205] (iii) 2.00 g of methylenebisacrylamide was changed to 6.59 g of polyethylene glycol diacrylate (n-9).

[0206] (iv) The aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was changed to an aqueous solution prepared by dissolving 0.05 g of sodium persulfate in 0.4 g of ion-exchanged water.

[0207] The produced organic porous material had a mass average particle diameter of 542 μm and a mass of 34 g. This organic porous material was designated as water absorbent material 3.

[0208] [Example 4] An organic porous material was produced by the same method as in Example 2, except for the changes shown in (v) and (vi) below. The neutralization rate of the acrylic acid (salt) used in Example 4 was 50 mol%, the same as in Example 2. The O / W volume ratio of the O / W emulsion in Example 4 was 76 / 24 = 3.2.

[0209] (v) The amount of n-heptane used in preparing the O / W emulsion was changed to 216.7 g (323 mL).

[0210] (vi) The rotation speed of the stirrer during preparation of the O / W / O emulsion was changed to 350 rpm.

[0211] The produced organic porous material had a mass average particle diameter of 478 μm and a mass of 33 g. This organic porous material was designated as water absorbent material 4.

[0212] [Example 5] An organic porous material was produced by the same method as in Example 1, except for the changes shown in the following (vii) and (viii). The neutralization rate of the acrylic acid (salt) used in Example 5 was 60 mol %.

[0213] (vii) The amount of acrylic acid used was changed to 10.66 g.

[0214] (viii) The amount of 37% by mass aqueous sodium acrylate solution used was changed to 56.36 g.

[0215] The produced organic porous material had a mass average particle diameter of 488 μm and a mass of 35 g. This organic porous material was designated as water absorbent material 5.

[0216] Example 6 The organic porous material obtained in Example 2 was subjected to the following steps (ix) and (x) to produce an organic porous material. (ix) 100 parts by mass of the organic porous material obtained in Example 2 were uniformly mixed with 1.0 part by mass of pure water and 0.01 part by mass of diethylenetriaminepentaacetic acid trisodium (DTPA 3Na). The mixture was then heat-treated at 60°C for 45 minutes in a windless environment and crushed until it passed through a JIS standard sieve with an opening of 850 µm.

[0217] (x) 100 parts by mass of the organic porous material obtained through steps (ix) was mixed with 1.0 part by mass of silica (product name: Aerosil 200CF, manufactured by Nippon Aerosil Co., Ltd.) The mixing was carried out by placing 6 g of the organic porous material together with the silica in a mayonnaise bottle manufactured by Yamamura Glass Co., Ltd., which was used in the damage test, and then tightening the inner and outer lids, followed by applying vibration (at room temperature for 1 minute) using a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.).

[0218] The produced organic porous material had a mass average particle diameter of 520 μm. This organic porous material was designated as water absorbent material 6.

[0219] Comparative Example 1 The same method as in Example 1 was carried out, except for the changes shown in (xi) and (xii) below. The neutralization rate of the acrylic acid (salt) used in Comparative Example 1 was 75 mol %.

[0220] (xi) The amount of acrylic acid used was changed to 6.41 g.

[0221] (xii) The amount of the 37% by mass aqueous sodium acrylate solution used was changed to 67.85 g.

[0222] As a result, the aqueous monomer solution and n-heptane did not emulsify during the preparation of the O / W emulsion, resulting in phase separation, making it impossible to produce an organic porous material.

[0223] Comparative Example 2 An organic porous material was produced by the same method as in Example 1 of Patent Document 1, specifically by the method described below.

[0224] 9.2 g of t-butyl methacrylate, 0.28 g of divinylbenzene, 1.0 g of sorbitan monooleate, and 0.4 g of 2,2'-azobis(isobutyronitrile) were mixed and dissolved uniformly to obtain a mixture.

[0225] While stirring the mixture, 180 g of purified water was added to the mixture to obtain a water-in-oil emulsion having an O / W volume ratio of 8 / 92 = 0.087.

[0226] The resulting emulsion was quickly transferred to a reaction vessel, which was then sealed and left to stand at 60° C. for 24 hours to polymerize the monomers in the emulsion.

[0227] After the polymerization was completed, the contents of the reaction vessel were removed and crushed into 1 cm cubes, and then the contents were subjected to extraction with methanol to obtain an extract, which was then dried under reduced pressure to obtain a dried product.

[0228] The obtained dried material was immersed in dichloroethane containing zinc bromide, and then stirred at 40°C for 24 hours. After that, the dried material was contacted with methanol, 4% hydrochloric acid, 4% aqueous sodium hydroxide solution, and water, in that order, to hydrolyze the dried material. The obtained hydrolyzed material was dried, pulverized, and classified to obtain an organic porous material having a mass average particle size in the range of 500 to 850 μm. This organic porous material was designated Comparative Water-Absorbent Material 1.

[0229] [Conclusion] The manufacturing conditions of Examples 1 to 6 and Comparative Examples 1 and 2, as well as the physical properties of Water Absorbent Materials 1 to 6 and Comparative Water Absorbent Material 1 measured and calculated by the above-mentioned methods, are shown in Tables 1 and 2 below.

[0230]

[0231]

[0232] As shown in Table 1, the methods for producing the water-absorbing materials of Examples 1 to 6 satisfy the requirements of the production method of the present invention, in that the neutralization rate of the aqueous monomer solution is less than 70 mol % and the O / W volume ratio of the O / W emulsion is 2.5 or more. Therefore, the methods for producing the water-absorbing materials of Examples 1 to 6 correspond to the production method of the present invention.

[0233] Furthermore, since the neutralization rates of the aqueous monomer solutions in Examples 1 to 6 were less than 70 mol%, it is clear that the neutralization rates of the crosslinked polymers in Water Absorbent Materials 1 to 6 were also less than 70 mol%. Furthermore, as shown in Table 2, Water Absorbent Materials 1 to 6 have a CRC of 5 to 25 g / g and a bulk specific gravity of less than 0.3 g / ml. Therefore, Water Absorbent Materials 1 to 6 fall under the category of water absorbent materials of the present invention.

[0234] Therefore, it is clear that the water-absorbent material of the present invention can be produced by the production method of the present invention.

[0235] As shown in Table 2, Water Absorbent Materials 1 to 6 have a pH of 4.7 to 5.6, making them weakly acidic. This shows that Water Absorbent Materials 1 to 6 can reduce skin irritation and other problems in users more effectively than conventional water absorbent materials. Furthermore, Water Absorbent Materials 1 to 6 have sufficiently small Vortex values ​​and sufficiently high water syneresis rates, and therefore can be said to be excellent in both water absorption speed and water syneresis rate.

[0236] From the above, it was found that the water-absorbent material of the present invention can reduce the skin roughness of the user compared to conventional water-absorbent materials, and is excellent in both water absorption speed and water separation rate. It was also found that the manufacturing method of the present invention can manufacture the water-absorbent material.

[0237] In the conventional manufacturing method shown in Comparative Example 1, it was not possible to manufacture a water-absorbing material when the O / W volume ratio was 2.5 or more. On the other hand, a comparison between Examples 1 to 6 and Comparative Example 1 showed that the manufacturing method of the present invention can manufacture a water-absorbing material even when the O / W volume ratio is 2.5 or more by adjusting the neutralization rate of the aqueous monomer solution to less than 70 mol%.

[0238] The present invention can be preferably used in applications that require less skin roughness and the like in users than conventional water-absorbent materials, and that also require a high water absorption rate and a high water release rate. Examples of such applications include use as a substitute for hydrophilic fibers such as pulp that have been conventionally used in hygiene materials such as disposable diapers and sanitary napkins, pads for preventing urinary incontinence such as absorbent shorts / pads, and breast-feeding pads, or use as a water-absorbent polymer in the above-mentioned hygiene materials. Other uses include, for example, soil water retention agents, seedling sheets, seed coating materials, anti-condensation sheets, drip absorbents, freshness-preserving materials, disposable hand warmers, cooling bandanas, ice packs, medical waste liquid solidifying agents, soil surplus solidifying materials, water-damage preventing waste liquid gelling agents, water-absorbing sandbags, portable toilets for disasters, compresses, thickeners for cosmetics, water-stopping materials for electrical and electronic materials and communication cables, gasket packing, sustained-release agents for fertilizers, various sustained-release agents (space disinfectants, air fresheners, etc.), pet sheets, cat litter, wound protection dressings, anti-condensation building materials, and oil moisture removers.

[0239] 1 First solvent 2 Monomer aqueous solution 3 Second solvent 4 O / W emulsion 5 Organic porous material

Claims

1. A water-absorbing material comprising an organic porous body having a continuous skeleton formed by a cross-linked polymer whose main component is a structural unit derived from (meth)acrylic acid (salt) and continuous pores, the water-absorbing material having a centrifuge retention capacity (CRC) of 5 to 25 g / g, a bulk specific gravity of less than 0.3 g / ml, and a neutralization rate of the cross-linked polymer of less than 70 mol%.

2. The water-absorbent material according to claim 1, which has a water-absorption rate (Vortex) for physiological saline solution of 10 seconds or less.

3. The water-absorbent material according to claim 1 or 2, having a free swelling capacity (FSC) of 35 g / g or more.

4. The water-absorbent material according to any one of claims 1 to 3, wherein the water-separation rate, expressed by the following formula (1), is 40% or more: Water-separation rate [%] = {(FSC [g / g] - CRC [g / g]) / FSC [g / g]} × 100 (1) 5. The water-absorbing material according to any one of claims 1 to 4, wherein the water-absorbing material contains a chelating agent.

6. The water-absorbing material according to any one of claims 1 to 5, wherein the water-absorbing material contains inorganic fine particles.

7. A method for producing a water-absorbing material containing an organic porous body having a continuous skeleton formed by a crosslinked polymer whose main component is a structural unit derived from (meth)acrylic acid (salt) and continuous pores, the method comprising: an O / W emulsion preparation step of incorporating a first solvent into an aqueous monomer solution having a neutralization rate of less than 70 mol% in the presence of a first surfactant so that the volume ratio of the first solvent to the aqueous monomer solution is 2.5 or more to obtain an O / W emulsion; an O / W / O emulsion preparation step of dispersing the O / W emulsion in a second solvent to obtain an O / W / O emulsion; and a polymerization step of polymerizing the monomers contained in the aqueous monomer solution in the O / W / O emulsion to prepare an organic porous body.

8. The method for producing a water-absorbing material according to claim 7, wherein the aqueous monomer solution contains a polymerization initiator, and the polymerization initiator is an azo-based initiator and / or a persulfate.

9. The method for producing a water-absorbing material according to claim 7 or 8, wherein the aqueous monomer solution contains an internal crosslinking agent, and the internal crosslinking agent is at least one selected from the group consisting of polyfunctional acrylate-based crosslinking agents, acrylamide-based crosslinking agents, and glycidyl ether-based crosslinking agents.

10. A method for producing a water-absorbent material according to any one of claims 7 to 9, wherein the first surfactant is a block copolymer of polyoxyethylene-polyoxypropylene-polyoxyethylene.

11. A method for producing a water-absorbent material according to any one of claims 7 to 10, wherein the second solvent contains a second surfactant.

12. The method for producing a water-absorbent material according to claim 11, wherein the second surfactant is at least one selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, sorbitol fatty acid esters, and polyglycerin fatty acid esters.

13. The method for producing a water-absorbent material according to any one of claims 7 to 12, wherein the first solvent and the second solvent are of the same type.

14. A composite absorbent comprising the water-absorbent material according to any one of claims 1 to 6 and water-absorbent resin particles.

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