JP6257392B2 - Water absorbent resin foam and method for producing the same - Google Patents

Description

  The present invention relates to a water absorbent resin foam and a method for producing the same.

  Of the foams obtained by foaming by the gas mixing method using water-dispersible resin in which fine particles of polymer are dispersed in water as the main raw material, a wide range of water-stopping materials, wipes, etc. There are many methods for manufacturing the same.

  For example, Patent Document 1 discloses a water absorbent resin foam produced by applying a liquid mixture obtained by mixing a water absorbent polymer to an acrylic or urethane binder to a polyurethane foam. Has been.

JP 2007-008126 A

  However, in the method described in Patent Document 1, the water-absorbing polymer is not penetrated to the inside of the foam, so that the water-absorbing polymer is low. There was a problem.

  Then, an object of this invention is to provide the water absorbing resin foam which has high water absorption, and also water absorption is hard to fall, and its manufacturing method.

Means for Solving the Invention

  As a result of intensive studies to solve the above problems, the present inventors have found an aqueous liquid medium made from a water-dispersible resin as a dispersoid, a specific foaming agent, and water as a dispersion medium. In the method of producing a resin foam by foaming, it was found that a water-absorbing resin foam having excellent water absorption can be formed by including a specific hydrophilization step, and the present invention was completed. .

That is, the present invention (1) provides an aqueous liquid medium containing a water-dispersible resin as a dispersoid, an anionic surfactant as a foaming agent, and water or a mixture of water and a water-soluble solvent as a dispersion medium. A method of producing a water-absorbent resin foam by foaming the aqueous liquid medium by mixing and stirring the gas to obtain a foamed aqueous liquid medium, and heating the foamed aqueous liquid medium to evaporate the dispersion medium The water-based liquid medium further comprises a water-soluble polymer that dissolves in the dispersion medium.
This invention (2) is a manufacturing method of the water absorbing resin foam of this invention (1) whose weight average molecular weights of the said water-soluble polymer are 500 or more.
This invention (3) is a manufacturing method of the water-absorbent resin foam of this invention (1) or (2) whose said water-soluble polymer is a sulfonyl group containing polymer.
This invention (4) is a manufacturing method of the water absorbing resin foam of this invention (1) or (2) whose said water-soluble polymer is a carboxyl group containing polymer.
The present invention (5) is the method for producing a water-absorbent resin foam according to the present invention (1) or (2), wherein the water-soluble polymer is a copolymer of a sulfonyl group-containing polymer and a carboxyl group-containing polymer. .
The water-absorbent resin according to any one of the present inventions (1) to (5), wherein the aqueous liquid medium includes a cross-linking agent for cross-linking the water-dispersible resin and the water-soluble polymer. It is a manufacturing method of a foam.
Here, in the present invention, “water absorption” widely indicates the property of absorbing water (liquid) and can be evaluated by the water absorption speed, the water absorption rate, the water absorption amount, and the like.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the water absorbing resin foam which has high water absorption, and also water absorption is hard to fall, and its manufacturing method.

It is a cross-sectional SEM photograph of the resin foam based on the reference example 1. It is a cross-sectional SEM photograph of the resin foam based on Reference Example 19. It is a cross-sectional SEM photograph of the resin foam based on the reference comparative example 1. It is a figure which shows the calculation method of the cell diameter of the resin foam based on the reference example 1. FIG. It is a figure which shows the calculation method of the cell diameter of the resin foam based on the reference example 1. FIG. It is a figure which shows the calculation method of the cell diameter of the resin foam based on the reference example 1. FIG. It is a figure which shows the calculation method of the cell diameter of the resin foam based on the reference example 1. FIG. It is a figure which shows the calculation method of the cell diameter of the resin foam based on the reference example 1. FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, these are merely examples, and the present invention is not limited to the following aspects.

In addition, the water absorbent resin foam according to the present embodiment and the manufacturing method thereof will be described in the following order.
DESCRIPTION OF SYMBOLS 1 Manufacturing method of water absorbent resin foam 2 Structure of water absorbent foam 3 Properties of water absorbent foam 4 Use of water absorbent resin foam

≪Method for producing water absorbent resin foam≫
A method for producing a water-absorbent resin foam according to the present embodiment includes a water-dispersible resin as a dispersoid, an anionic surfactant as a foaming agent, water as a dispersion medium, and a water-soluble polymer dissolved in the dispersion medium. The foamed aqueous liquid medium is obtained by mixing and stirring the gas in the aqueous liquid medium containing, to obtain the foamed aqueous liquid medium, and the foamed aqueous liquid medium is heated to evaporate the dispersion medium to obtain the resin foam. It is a manufacturing method, and further contains a water-soluble polymer dissolved in the dispersion medium as a raw material. The raw material, composition (blending amount), liquidity (aqueous liquid medium or liquidity of the foamed aqueous liquid medium), and process (specific production steps) will be described in detail as a method for producing the water absorbent resin foam.

  In addition, in the manufacturing method of the water absorbing resin foam which concerns on this form, in order to prevent the coalescence of the bubble in a foaming aqueous liquid medium, the thixotropy provision process which reduces the fluidity | liquidity of the said aqueous liquid medium is included. Here, the thixotropy imparting step may be a known means, but in an aqueous liquid medium (foamed aqueous liquid medium), an anionic surfactant (not limited to a foaming anionic surfactant) The anionic surfactant present in the solvent may be insolubilized in some form in the dispersion medium. More specifically, it may be a step of insolubilizing the foaming anionic surfactant dissolved in the dispersion medium with respect to the dispersion medium. Hereinafter, the case where the foaming anionic surfactant dissolved in the dispersion medium is insolubilized in the dispersion medium is particularly referred to as “insolubilization of the anionic surfactant” or “insolubilization step”.

<Raw material>
The resin foam according to this embodiment includes a water-dispersible resin, an anionic surfactant as a raw material, water as a dispersion medium, a water-soluble polymer, a water-soluble polymer cross-linking agent, a gelling component (gelling agent), and other additions. (The foaming gas used in the foaming process is described in the foaming process). In the present invention, the water dispersible resin may be an aqueous dispersion in which the resin is dispersed in water.

(Water dispersible resin)
The manufacturing method of the resin foam which concerns on this form contains water-dispersible resin as a main ingredient. The structure and production method of the water dispersible resin are not limited at all, and any water dispersible resin may be used.

  Here, when the water-dispersible resin according to the present embodiment is insolubilized with an anionic surfactant, the preferred use form differs depending on whether it is a stable dispersion type or an unstable dispersion type. Next, a stable dispersion type water-dispersible resin and an unstable dispersion type water-dispersible resin will be described in detail. Note that a stable dispersion type water-dispersible resin means a water-dispersible resin having a precipitation rate (following the following method for a specific calculation method of the precipitation rate) of less than 10%, an unstable dispersion type water-dispersibility resin. The resin refers to a water dispersible resin having a precipitation rate of 10% or more.

・ Calculation method of precipitation rate In order to evaluate the dispersion stability of the water-dispersible resin, a coagulant aqueous solution (0.5 mass% calcium nitrate aqueous solution) is added to the water-dispersible resin, and the amount of the precipitate produced The precipitation rate was calculated. The specific precipitation rate is determined by the following formula (1) {wherein, in formula (1), A is the dry mass (g) of the precipitate, B is the mass (g) of the water-dispersible resin, and C is water-dispersed. It is the solid content concentration (mass%) of the conductive resin}.
Precipitation rate (%) = A / {B × (C / 100)} × 100 (1)

  More specifically, 10 g of a water-dispersible resin is placed in a resin container having a capacity of 100 ml in a room at 23 ° C., and 10 g of a calcium nitrate aqueous solution having a concentration of 0.5 mass% is dropped as a coagulant aqueous solution while stirring. After dropping the entire amount of the coagulant aqueous solution, it is allowed to stand for 1 hour. Next, the entire amount was filtered through a glass filter (Shibata Kagaku Co., Ltd., suction filter bottle 1L, Shibata Kagaku Co., Ltd., glass filter base φ47 mm, Kiriyama Seisakusho, Kiriyama Separot 55Z) and 40 mesh filter (Yamamani Co., Ltd.) Manufactured, T230LY-40), and filtered under reduced pressure to collect the precipitate. Further, after washing with water until the filtrate becomes transparent, it is dried at 110 ° C. for 3 hours. The dry mass of the precipitate is measured, the precipitation rate is calculated based on the above formula (1), and the dispersion stability of the water-dispersible resin is evaluated from the precipitation rate. That is, when the deposition rate is less than 10%, it means that the resin particles are difficult to aggregate. Therefore, it is evaluated as a “stable dispersion type water-dispersible resin”. When the deposition rate is 10% or more, the resin particles are aggregated. Therefore, it is evaluated as “unstable dispersion type water dispersible resin”.

  The water-dispersible resin according to this embodiment is not limited to one type of water-dispersible resin, and a plurality of types of water-dispersible resins may be used in combination. Thus, even when the water-dispersible resin is composed of a plurality of water-dispersible resins, the precipitation rate is calculated for the entire water-dispersible resin, whether it is a stable dispersion type or an unstable dispersion type, Is determined.

Stable dispersion type water-dispersible resin The stable dispersion type water-dispersible resin is not particularly limited, and examples thereof include urethane emulsions, acrylic emulsions, vinyl acetate emulsions, vinyl chloride emulsions, and epoxy emulsions. Of these, particularly preferred urethane emulsions and acrylic emulsions will be described in detail. Use of a urethane emulsion is preferred because the resulting urethane resin foam has excellent flexibility and lower compression residual strain. Moreover, since it is excellent in intensity | strength, and it is excellent in lightweight property and heat insulation, it is also suitable to use an acrylic emulsion.

Examples of the method for producing an aqueous dispersion of urethane resin (urethane emulsion) include the following methods (I) to (III).
(I) An active hydrogen-containing compound, a compound having a hydrophilic group, and an organic solvent solution or an organic solvent dispersion of a urethane resin having a hydrophilic group obtained by reacting a polyisocyanate are neutralized as necessary. The method of mixing the aqueous solution containing an agent and obtaining a urethane resin water dispersion.
(II) Whether an active hydrogen-containing compound, a compound having a hydrophilic group, and a terminal isocyanate group-containing urethane prepolymer having a hydrophilic group obtained by reacting a polyisocyanate are mixed with an aqueous solution containing a neutralizing agent. Alternatively, a method of obtaining a urethane resin aqueous dispersion by adding a neutralizing agent to a prepolymer in advance, mixing water and dispersing in water, and then reacting with polyamine.
(III) An active hydrogen-containing compound, a compound having a hydrophilic group, and a terminal isocyanate group-containing urethane prepolymer having a hydrophilic group obtained by reacting a polyisocyanate are mixed with an aqueous solution containing a neutralizing agent and a polyamine. Or a method in which a neutralizing agent is added to the prepolymer in advance, and then an aqueous solution containing a polyamine is added and mixed to obtain a urethane resin aqueous dispersion.

  Polyisocyanates used in the production of the urethane resin include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phphenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4. '-Diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro- 4,4′-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate Dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4,4 Examples include '-dicyclohexylmethane diisocyanate and 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate. Moreover, you may use together polyisocyanate more than trivalence in the range which does not impair the effect of invention.

  Examples of the compound having a hydrophilic group include polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyester amide polyols, polythioether polyols, polybutadiene-based polyolefin polyols, and the like. Two or more of these high molecular weight compounds may be used in combination. Known polyester polyols may be used.

  In the above methods (I) to (III), an emulsifier may be further used as long as the effects of the invention are not impaired. Examples of such emulsifiers include nonionic emulsifiers such as polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene sorbitol tetraoleate; fatty acid salts such as sodium oleate, alkyl Anionic emulsifiers such as sulfate esters, alkylbenzene sulfonates, alkyl sulfosuccinates, naphthalene sulfonates, alkane sulfonate sodium salts, sodium alkyl diphenyl ether sulfonates; polyoxyethylene alkyl sulfates, polyoxyethylene alkylphenyl sulfates Nonionic anionic emulsifiers such as

  As a method for producing an aqueous dispersion (acrylic emulsion) of an acrylic resin, a (meth) acrylic acid ester monomer is an essential polymerizable monomer in the presence of a polymerization initiator, and if necessary, an emulsifier and a dispersion stabilizer. It can be obtained by copolymerizing a mixture of other polymerizable monomers copolymerizable with these monomers as necessary.

  Examples of polymerizable monomers that can be used in the production of the acrylic resin emulsion include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) allylate, (meth ) Hexyl acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, octadecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, nonyl (meth) acrylate, ( (Meth) acrylic acid such as dodecyl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate Ester monomers; acrylic acid, methacrylic acid, β-carboxyethyl Unsaturation having carboxyl group such as (meth) acrylate, 2- (meth) acryloylpropionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, itaconic acid half ester, maleic acid half ester, maleic anhydride, itaconic anhydride Bond-containing monomers: Glycidyl group-containing polymerizable monomers such as glycidyl (meth) acrylate and allyl glycidyl ether; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) Hydroxyl group-containing polymerizable monomers such as acrylate and glycerol mono (meth) acrylate; ethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethyl Examples thereof include roll propane tri (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, diallyl phthalate, divinylbenzene, and allyl (meth) acrylate.

  In addition, what is necessary is just to use the above-mentioned emulsifier etc. when using an emulsifier at the time of manufacture of an acrylic emulsion.

Unstable dispersion type water-dispersible resin The unstable dispersion type water-dispersible resin is not particularly limited, and examples thereof include rubber latex. Rubber latex is preferred because it has a good foam feel and excellent elasticity. Next, the rubber latex will be described in detail.

  The rubber aqueous dispersion (rubber latex) according to this embodiment may be natural rubber latex or synthetic rubber latex. The synthetic rubber latex can be obtained by emulsion polymerization of an aliphatic conjugated diene monomer and another polymerizable monomer that can be copolymerized. Here, examples of the aliphatic conjugated diene monomer include 1,2-butadiene, 1,3-butadiene, isoprene, chloroprene and the like.

  Other polymerizable monomers that can be copolymerized include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) arylate, hexyl (meth) acrylate, ( (Meth) acrylic acid ester monomers such as heptyl (meth) acrylate, octyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylic acid, crotonic acid, maleic acid and its anhydride, fumaric acid , Itaconic acid, unsaturated dicarboxylic acid monoalkyl ester (for example, monomethyl maleate, monoethyl fumarate, mononormal butyl itaconate) and other unsaturated bond-containing monomers having a carboxyl group; styrene, α-methylstyrene, vinyltoluene Ethylenically unsaturated aromatic monomers such as chlorostyrene, 2,4-dibromostyrene; Unsaturated nitriles such as rilonitrile and methacrylonitrile; vinyl esters such as vinyl acetate and vinyl propionate; vinylidene halides such as vinylidene chloride and vinylidene bromide; (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid-2 -Hydroxyalkyl esters of ethylenically unsaturated carboxylic acids such as hydroxypropyl; glycidyl esters of ethylenically unsaturated carboxylic acids such as glycidyl (meth) acrylate; (meth) acrylamide, N-methylol (meth) acrylamide, butoxymethyl (meta ) Examples include acrylamide and diacetone acrylimide.

  A rubber latex (synthetic rubber latex) that can be used as a water-dispersible resin can be obtained by emulsion polymerization of the above monomers in an aqueous medium in the presence of an emulsifier, a free radical generating catalyst, and the like. In this case, a two-stage polymerization method can also be employed. As an emulsifier, various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants and the like can be used.

  In addition, in the classification related to the unstable dispersion type or the stable dispersion type of the water-dispersible resin of the present embodiment, the classification by the above materials is approximate {the water-dispersible resin is an unstable dispersion type or a stable dispersion Whether it is a type is classified according to the above formula (1) to the last}. For example, in the above formula (1), the urethane emulsion having a precipitation rate of 10% or more is classified as an unstable dispersion type water-dispersible resin, and the rubber latex having a precipitation rate of less than 10% is a stable dispersion type. It is classified as a water-dispersible resin.

(Dispersion medium)
In this embodiment, the dispersion medium of the aqueous liquid medium contains water as an essential component, but may be a mixture of water and a water-soluble solvent. Examples of the water-soluble solvent include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, and butyl cellosolve, polar solvents such as N-methylpyrrolidone, and the like, one or more of these. A mixture of the above may be used.

(Anionic surfactant)
The anionic surfactant (foaming anionic surfactant) functions as a foaming agent for the aqueous liquid medium. Moreover, when insolubilizing an anionic surfactant, it insolubilizes with respect to a dispersion medium by reaction with the below-mentioned metal cation, for example (this is mentioned later).

  Specific examples of anionic surfactants include sodium laurate, sodium myristate, sodium stearate, ammonium stearate, sodium oleate, potassium oleate soap, castor oil potassium soap, palm oil potassium soap, lauroyl sarcosine sodium, Myristoyl sarcosine sodium, oleyl sarcosine sodium, cocoyl sarcosine sodium, sodium palm oil alcohol sulfate, polyoxyethylene lauryl ether sodium sulfate, sodium alkylsulfosuccinate, sodium lauryl sulfoacetate, sodium dodecylbenzenesulfonate, sodium α-olefin sulfonate, etc. In particular, sodium alkylsulfosuccinate is preferable.

  Here, the anionic surfactant used in this embodiment is preferably 10 or more, more preferably 20 or more, in order to facilitate dispersion in an aqueous liquid medium. The above is particularly preferable.

・ HLB
In the present invention, the HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is determined by the Oda method. The method of obtaining HLB by the Oda method is “Introduction to New Surfactants”, pages 195 to 196, published by Sakai Shoten on March 20, 1957, “Synthetics and Applications of Surfactants” 492 It is described on page 502 and can be obtained by HLB = (inorganic / organic) × 10.

  Here, the anionic surfactant according to this embodiment is a component that is initially dissolved in the dispersion medium when insolubilizing the anionic surfactant, but is insolubilized in the dispersion medium (for example, , A component that is insolubilized in the dispersion medium by reaction with a metal cation. The insolubilizing means of such an anionic surfactant is not particularly limited, but together with the anionic surfactant, a metal cation source, an acid colloid solution of a melamine-formaldehyde condensate, a coagulant such as a vinyl phenol polymer, etc. Can be exemplified. By insolubilizing the anionic surfactant, it is possible to form a resin foam having a fine and uniform cell structure without limiting the type of water-dispersible resin or dispersant as the main agent. Furthermore, since the anionic surfactant is insolubilized, it is difficult to extract with water or the like (that is, bleeding can be prevented). In addition, since the gel strength is strong, the coalescence of the bubbles in the foaming stage is strongly suppressed, so that the bubbles are stabilized and it is possible to form a thick foam ( High speed is possible). Here, a particularly preferable insolubilization of the anionic surfactant by blending a metal cation source will be described in detail.

(Metal cation source)
The metal cation source according to the present embodiment is a component capable of releasing into the water a metal cation that can be combined with an anionic surfactant to form a water-insoluble salt. When such a component is present in the system, it binds to the anionic surfactant to form a water-insoluble salt. As a result, the coalescence of bubbles can be suppressed even during heating by imparting thixotropy to the foam raw material mixture mixed with gas and reducing fluidity. Such a metal cation source is not particularly limited as long as it is a component that dissolves in water and generates metal ions, such as a metal salt such as an inorganic metal salt or an organic metal salt, such as calcium nitrate; an alkali such as water. Examples include calcium oxide and calcium oxide; simple metal, for example, calcium. Of these, metal salts are preferred because of their relatively high ionization constant in water.

  Examples of the components include alkali metal ions such as lithium ions, sodium ions, and potassium ions, and aluminum ions, barium ions, calcium ions, copper ions, iron ions, magnesium ions, manganese ions, nickel ions, tin ions, titanium ions, Polyvalent metal ions such as zinc ions, inorganic acids (for example, hydrochloric acid, odorous acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, thiocyanic acid, etc.) and organic acids (for example, acetic acid, oxalic acid, lactic acid, And salts thereof with organic carboxylic acids such as fumaric acid, fumaric acid, citric acid, salicylic acid and benzoic acid, and organic sulfonic acids).

  Specific examples include lithium chloride, sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, potassium iodide, sodium sulfate, potassium nitrate, sodium acetate, potassium oxalate, sodium citrate, potassium benzoate and the like. Alkali metal salts and aluminum chloride, aluminum bromide, aluminum sulfate, aluminum nitrate, sodium aluminum sulfate, potassium aluminum sulfate, aluminum acetate, barium chloride, barium bromide, barium iodide, barium oxide, barium nitrate, thiocyanate Barium acid, calcium chloride, calcium bromide, calcium iodide, calcium nitrite, calcium nitrate, calcium dihydrogen phosphate, calcium thiocyanate, calcium benzoate, calcium acetate, salicylic acid Lucium, calcium tartrate, calcium lactate, calcium fumarate, calcium citrate, copper chloride, copper bromide, copper sulfate, copper nitrate, copper acetate, iron chloride, iron bromide, iron iodide, iron sulfate, iron nitrate, oxalic acid Iron, iron lactate, iron fumarate, iron citrate, magnesium chloride, magnesium bromide, magnesium iodide, magnesium sulfate, magnesium nitrate, magnesium acetate, magnesium lactate, manganese chloride, manganese sulfate, manganese nitrate, manganese dihydrogen phosphate , Manganese acetate, manganese salicylate, manganese benzoate, manganese lactate, nickel chloride, nickel bromide, nickel sulfate, nickel nitrate, nickel acetate, tin sulfate, titanium chloride, zinc chloride, zinc bromide, zinc sulfate, zinc nitrate, thiocyanate Examples thereof include salts of polyvalent metals such as zinc acid and zinc acetate.

  In a system in which a stable dispersion type water-dispersible resin is present, among components in which the metal cation source of the metal cation is a water-soluble metal salt, the gel strength is strong and the gel time is short, so the solubility is 10 g / It is preferably 100 g water or more, more preferably 30 g / 100 g water or more, and particularly preferably 100 g / 100 g water or more. Examples of the electrolyte as such a component include calcium nitrate (solubility 138 g / 100 g water), aluminum sulfate (solubility 38.6 g / 100 g water), magnesium sulfate (solubility 36.3 g / 100 g water), and the like. .

  In a system in which an unstable dispersion type water-dispersible resin is present, a component that is a metal cation source of a metal cation is a poorly water-soluble metal salt, so that foreign matter such as aggregates is difficult to be generated, so the solubility is 10 g / 100 g. It is preferably less than water, more preferably less than 3 g / 100 g water, and particularly preferably less than 1 g / 100 g water. In addition, although a lower limit is not specifically limited, it is 0.0001 g / 100g water or more. Examples of the electrolyte as such a component include calcium citrate (solubility 25.9 mg / 100 g water), calcium carbonate (solubility 0.81 g / 100 g water), primary calcium phosphate (solubility 1.8 g / 100 g water), Etc.

(Water-soluble polymer)
The water-soluble polymer used in this embodiment is a polymer having a solubility of 1 g / 100 g water or more. As the water-soluble polymer, -COOM group, -SO ₃ M group, (M represents a hydrogen atom, the periodic table I, II, III group element, amine, _ammonium) -NH 2, hydrophilicity such as -OH Examples thereof include a polymer having a group. As the water-soluble polymer, a sulfonyl group-containing polymer and a carboxyl group-containing polymer are suitable, but compared to the carboxyl group, the functional groups are less likely to crosslink with respect to the polyvalent electrolyte aqueous solution, so that it is difficult to lose water absorption. Since a high acid dissociation constant increases the difference in ion concentration and high water absorption can be expected, a sulfonyl group-containing polymer is more preferable. In addition, the water-soluble polymer is particularly preferably a copolymer of a sulfonyl group-containing polymer and a carboxyl group-containing polymer.

Specific examples of such water-soluble polymers include diene rubbers obtained by copolymerizing (meth) acrylic acid and diene compounds in addition to general-purpose resins such as polyvinyl alcohol (PVA) and carboxymethylcellulose, and maleic anhydride. 50 to 50,000 are liquid polybutadiene modified with the above, and -COOM, -SO ₃ M (M represents a hydrogen atom, Group I, II, Group III element, amine, ammonium) as a particularly effective skeleton. was equivalent / 10 6 ^g with polymer, the periodic table I, as a group II element, sodium, potassium, alkali metals such as lithium, calcium, alkaline earth metals such as magnesium, boron, and aluminum.

Further, as the water-soluble polymer, specifically, —COOM group or —SO ₃ M group-containing polyurethane, —COOM group or —SO ₃ M group-containing polyurethane, —COOM group or —SO ₃ M group-containing polyester, —COOM group Or -SO ₃ M group-containing epoxy compound, -COOM group or -SO ₃ M group-containing polyamic acid, -COOM group or -SO ₃ M group-containing acrylonitrile-butadiene copolymer, -COOM group or -SO ₃ M group-containing styrene- Butadiene copolymer, -COOM group or -SO ₃ M group-containing polybutadiene, polyacrylamide, sodium polyacrylate, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (MRC), methyl cellulose (MC), polyethylene oxide , Polyethyleneimine, and compound derivatives thereof can be used, but are not limited thereto.

  The compounds used to neutralize at least a part of the carboxyl group or sulfonic acid group contained in the water-soluble polymer include alkali metal hydroxides such as sodium hydroxide, lithium carbonate, and potassium carbonate. Alkali metal carbonates such as sodium carbonate, alkali metal alkoxides such as potassium t-butoxide and sodium methoxide, hydroxides of polyvalent metals such as calcium hydroxide, magnesium hydroxide and aluminum hydroxide, aluminum isopropoxide And other polyvalent metal alkoxides, tertiary amines such as triethylamine and tri-n-propylamine, secondary amines such as diethylamine and di-n-propylamine, ethylamines such as n-propylamine, primary amines such as morpholine, etc. Cyclic amine, N, N-dimethylamino Chill (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate such as an amino group-containing (meth) acrylate, ammonium carbonate, ammonium salts, and the like. These may be used alone or in combination.

In addition to the —COOM group or —SO ₃ M group, the water-soluble polymer may have a polyoxyalkylene chain as a hydrophilic portion, and contains an ethylenically unsaturated group so that it can act as a crosslinking agent. May be. In this embodiment, in addition to the water-soluble polymer, for example, a polymer having a hydrophilic group such as a hydroxyl group or an amine group and / or a polyoxyalkylene chain may be used in combination.

  The water-soluble polymer has a solubility of preferably 1 g / 100 g water or more, and more preferably 10 g / 100 g water or more in order to exhibit high water absorption. In addition, although it does not specifically limit as an upper limit, For example, it is 500 g / 100g water or less. The water-soluble polymer preferably has a weight average molecular weight of 500 or more and 1000000 or less, more preferably 1000 or more and 100000 or less, further preferably 1000 or more and 10,000 or less, and 3000 It is particularly preferable that it is 5,000 or more. By setting it as such a range, high water absorption will express and the liquid viscosity raise at the time of foaming can be suppressed.

Here, in this embodiment, “weight average molecular weight” indicates a numerical value obtained by a gel permeation chromatograph (GPC) method. Specifically, the molecular weight distribution of the water-dispersible resin was measured with a GPC measuring device (HLC-8320GPC EcoSEC, manufactured by Tosoh Corporation). TSKgel SuperMultipore HZ-M (manufactured by Tosoh Corporation) was used for the column. The column was stabilized in a heat chamber at 40 ° C., and THF (tetrahydrofuran) as a solvent was passed through the column at this temperature at a flow rate of 1 ml / min. Measurement was performed by injecting 50 to 200 μl of the sample solution. In measuring the weight average molecular weight Mw and the number average molecular weight Mn, the molecular weight distribution of the sample was calculated from the relationship between the logarithmic value of the calibration curve prepared from several types of monodisperse polystyrene standard samples and the number of counts. As a standard polystyrene sample for preparing a calibration curve, for example, Pressure Chemical Co. Or a molecular weight of 6 × 10 ² , 2.1 × 10 ² , 4 × 10 ² , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ , 1.1 × 10 ⁵ , 1.1 × 10 ⁵ , manufactured by Toyo Soda Kogyo Co., Ltd. 9 × 10 ⁵ , 8.6 × 10 ⁵ , 2 × 10 ⁶ , 4.48 × 10 ⁶ were used. An RI (refractive index) detector was used as the detector.

(Crosslinking agent for water-soluble polymer)
By using the cross-linking agent for the water-soluble polymer, the water-soluble polymer is grafted onto the water-dispersible resin, so that the water-absorbing agent is prevented from dropping and the repeated resistance is improved.

  Such a water-soluble polymer cross-linking agent is not particularly limited, and can be appropriately changed according to the water-soluble polymer to be used. Organic zirconium compounds, organic titanium compounds, and formaldehyde resins that cross-link oxygen atoms such as carboxyl groups (formalin) And water-soluble epoxy resins that crosslink nitrogen atoms such as amino groups.

(Gel component)
You may mix | blend the gelling component of the resin foam which concerns on this form (The component which gelatinizes an aqueous liquid medium in order to prevent the cell integration of the foamed aqueous liquid medium in the foaming process mentioned later). Such a gelling component may be appropriately added depending on the gelation method, for example, hexafluorosilicate such as sodium silicofluoride, potassium silicofluoride, calcium silicofluoride; or cyclohexylamine acetate, A cyclohexylamine salt such as a sulfamate can be used, and generally a liquid in which these compounds are in an aqueous solution is used. For example, by using sodium silicofluoride, reaction control such as control of gelation start time becomes easy.

(Other additives)
As other additives, a water dispersible resin dispersing surfactant (emulsifier), a curing agent and the like may be added.

-Water-dispersible resin-dispersing surfactant The water-dispersible resin-dispersing surfactant according to this embodiment is a surfactant for dispersing a water-dispersible resin (unlike an anionic surfactant, It may not have an effect as a foaming agent). Such a surfactant may be appropriately selected according to the water-dispersible resin to be selected. For example, when the water-dispersible resin is a urethane emulsion, an acrylic emulsion, or a rubber latex, the specific surfactant for dispersing the water-dispersible resin is as described above.

-Curing agent The hardening | curing agent which concerns on this form is a crosslinking agent for water-dispersible resin, and what is necessary is just to add required amount according to a use etc. Examples of the curing method using a curing agent include physical crosslinking, ionic crosslinking, and chemical crosslinking, and the crosslinking method can be selected according to the type of the water-dispersible resin.

  As the curing agent, epoxy resin curing agent, melamine curing agent, isocyanate curing agent, carbodiimide curing agent, oxazoline curing agent, etc. Appropriate amount can be used accordingly.

  When a rubber latex is used as the water-dispersible resin, a crosslinking agent (additive for crosslinking rubber polymers, for example, a vulcanizing agent), a crosslinking accelerator ( It is an additive for accelerating the crosslinking reaction by the crosslinking agent. For example, a vulcanization accelerator), an antiaging agent, or the like may be added.

  As the crosslinking agent, sulfur, an organic peroxide, a phenol compound, or the like is used depending on the type of rubber polymer and the crosslinking reaction mechanism. In the case of crosslinking by sulfur, in addition to colloidal sulfur and fine powder sulfur, sulfur compounds such as sulfur dichloride and dipentamethylene thiuram tetrasulfide can be used. In the case of crosslinking with an organic peroxide, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide; acyl peroxides such as benzoyl peroxide and m-toluyl peroxide; t-butylcumyl peroxide, dicumyl peroxide, 2,5- Alkyl peroxides such as dimethyl-2,5-bis (t-butoxyperoxy) hexane; peroxyesters such as t-butoxyperoxy-3,3,5-trimethylcyclohexanoate, t-butoxyperoxybenzoate; 1,1- Peroxyketals such as bis (t-butoxyperoxy) cyclohexane and 1,1-bis (t-butoxyperoxy) -3,3,5-trimethylcyclohexa; t-butoxyperoxyisopropyl carbonate, t-butoxyper Organic peroxides peroxycarbonate such as carboxymethyl-2-ethylhexyl carbonate can be used. Organic peroxides can be blended as they are, and are stable when adsorbed on inorganic powders such as molecular sieves, dissolved in hydrocarbons and plasticizers, and mixed with inert liquids such as polydimethylsiloxane. What was converted may be used for a mixing | blending. In the case of crosslinking with a phenol compound, an alkylphenol / formaldehyde resin, a sulfurized p-tert-butylphenol resin, an alkylphenol / sulfide resin, or the like can be used. The blending amount of the crosslinking agent varies depending on the type of the rubber polymer, the crosslinking mechanism, and the crosslinking agent, but is preferably 0.02 to 20 parts by mass with respect to 100 parts by mass of the rubber polymer in the rubber latex mixture. 1-10 mass parts is more preferable.

  Various substances can be used as the crosslinking accelerator, but since the swelling property against polar oil is lowered, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zinc dibenzyldithiocarbamate, ethylphenyl Zinc dithiocarbamates such as zinc dithiocarbamate and zinc N-pentamethylenedithiocarbamate; tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, N, N′-dimethyl-N, N ′ -Thiurams such as diphenyl thiuram disulfide and dipentamethylene thiuram tetrasulfide; N, N-diisopropyl-2-benzothialylsulfenamide, Nt-butyl- -Benzothialylsulfenamide, N-cyclohexyl-2-benzothiazylsulfenamide, N, N-dicyclohexyl-2-benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide 2-mercaptobenzothiazole and its salts (sodium salt, zinc salt, cyclohexylamine salt, dicyclohexylamine salt, etc.), 2- (4′-morpholinodithio) benzothiazole, 4-morpholinyl-2-benzo Preferred are thiazyl disulfide, benzothiazoles such as 2- (N, N-diethylthiocarbamoylthio) benzothiazole; and mixtures thereof. Of these, zinc dithiocarbamates are more preferred, and zinc dibutyldithiocarbamate is particularly preferred. The blending amount of the crosslinking accelerator is preferably 0.02 to 20 parts by mass and more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber polymer in the rubber latex mixture.

  Examples of the antioxidant include diphenylamine compounds such as N-phenyl-N ′-(p-toluenesulfonyl) -p-phenylenediamine; condensates of aromatic amines and aliphatic ketones; 2-mercaptobenzimidazole and the like Examples thereof include imidazole compounds such as zinc salts; mono-phenol compounds such as 2,6-di-t-butyl-4-methylphenol; bis-, tris, and polyphenol compounds. 1.0-10 mass parts is preferable with respect to 100 mass parts of rubber polymers in the mixture of rubber latex, and, as for the compounding quantity of anti-aging agent, 2.0-6.0 mass parts is more preferable.

  In addition, in order to improve the dispersibility in the rubber latex, the cross-linking agent, the cross-linking accelerator and the anti-aging agent are prepared by previously dispersing these auxiliary materials in water using a dispersant or the like ( A vulcanizing paste) may be prepared and this vulcanizing paste may be added to the rubber latex.

(Suitable combination of raw materials)
Here, as described above, when using a gelation technique by insolubilization of an anionic surfactant and using a stably dispersed water-dispersible resin as the water-dispersible resin, a water-soluble metal salt is used as the metal cation source of the metal cation. Is preferably used. By such a combination, the effect that gelation strength is strong and gelation time is short is acquired. Similarly, when an unstable dispersion type water dispersible resin is used as the water dispersible resin, it is preferable to use a poorly water-soluble metal salt as the metal cation source of the metal cation. By using such a combination, it is possible to obtain an effect that foreign matters such as aggregates are hardly generated.

<Composition>
(Blending amount and blending ratio of each raw material)
As a compounding quantity of water-dispersible resin (solid content) with respect to a liquid medium, 30-70 mass parts is preferable with respect to 100 mass parts of liquid media. By setting it as such a range, the effect that a stable foam can be shape | molded is acquired.

  The compounding amount of the anionic surfactant is preferably 1.0 to 10 parts by mass with respect to 100 parts by mass of the water-dispersible resin (solid content) in the water-dispersible resin mixture (aqueous liquid medium). 10 mass parts is more preferable. By setting it as such a range, it is easy to make it suitable foaming, and the effect that a fine cell structure can be shape | molded is acquired.

  As a compounding quantity of a water-soluble polymer, 0.5-10 mass parts is preferable with respect to 100 mass parts of water-dispersible resin (solid content) in the mixture of water-dispersible resin, and 2-5 mass parts is more preferable. . By setting it as such a range, the effect that high water absorption can be expressed is acquired.

  In the water-dispersible resin mixture, the mass part ratio of the water-soluble polymer crosslinking agent / water-soluble polymer is preferably 0.02 to 5, and more preferably 0.1 to 2 or more.

  As a compounding quantity of a crosslinking agent (curing agent), 0.1-20 mass parts is preferable with respect to 100 mass parts of water-dispersible resin (solid content) in the mixture of water-dispersible resin, and 1-10 mass parts. Is more preferable. In addition, when using a vulcanization | cure paste as a hardening | curing agent, 1-20 mass parts is preferable with respect to 100 mass parts of water-dispersible resin (solid content) in the mixture of water-dispersible resin, and 5-15. Part by mass is more preferable. By setting it as such a range, the effect that a foam with a small compression residual strain can be shape | molded is acquired.

  When the gelling component (gelling agent) is blended, the blending amount is not particularly limited, but is preferably about 1 to 10 parts by mass with respect to 100 parts by mass of the polymer in the mixture of the water-dispersible resin. When the blending amount of the gelling agent is out of the above range, suitable gelation cannot be expressed, that is, it does not gel in a liquid state even after a long time, or gelation proceeds in a short time to a desired shape. It may be difficult to mold. As a result, specifically, the time required for completion of gelation (gelation time) becomes too long or too short, so that a suitable resin foam cannot be obtained.

  In addition, when an anionic surfactant is insolubilized with a metal cation (metal cation source) and an electrolyte is used as the metal cation source, the amount of the electrolyte blended in the water-dispersible resin mixture is: The solid content is preferably 1.0 to 10 parts by mass, more preferably 2 to 5 parts by mass with respect to 100 parts by mass. By setting it as such a range, since it becomes suitable gelatinization intensity | strength and gelatinization time, the effect that a fine cell structure can be shape | molded is acquired.

  In the case where the anionic surfactant is insolubilized with a metal cation (metal cation source), the valence of the metal cation which is the target constituent to be insolubilized / the target constituent to be insolubilized in the water-dispersible resin mixture. The valence of the anionic surfactant that is {the abbreviation is omitted in the table and the like described later, and is also referred to as "metal cation (metal cation source) / anionic surfactant] etc.}" is 0 0.1 or more is preferable, 0.5 or more is more preferable, and 1.0 or more which is a molar equivalent of the valence is particularly preferable. By setting it as such a range, since it becomes suitable gelatinization intensity | strength and gelatinization time, the effect that a fine cell structure can be shape | molded is acquired.

<Process>
The manufacturing process of the resin foam according to the present embodiment includes a raw material preparation step, a stirring / foaming step, a thixotropy imparting step, and a heating step. Hereinafter, each step will be described in detail.
(Raw material preparation process)
In the raw material preparation step, an aqueous liquid medium that is a raw material mixture of the water absorbent resin foam is prepared by mixing the raw materials as described above. The mixing method at this time is not particularly limited, and for example, mixing may be performed while stirring in a container such as a mixing tank for mixing the components.

(Stirring / foaming process)
In the agitation / foaming step, a predetermined foaming gas is added to the aqueous liquid medium obtained in the raw material preparation step, and these are sufficiently mixed to produce a state in which many bubbles exist in the aqueous liquid medium (foamed aqueous liquid medium ). This stirring / foaming step is usually carried out by sufficiently mixing the raw material mixture of the liquid water-absorbent resin foam obtained in the raw material preparation step and the foaming gas with a mixing device such as a mixing head. .

-Foaming gas The foaming gas mixed with the aqueous liquid medium in the stirring / foaming process forms bubbles (cells) in the water-absorbent resin foam, and is obtained depending on the amount of the foaming gas mixed in. The expansion ratio and density of the water absorbent resin foam are determined. In order to adjust the density of the water absorbent resin foam, the density of the desired water absorbent resin foam and the volume of the raw material of the water absorbent resin foam (for example, a mold into which the raw material of the water absorbent resin foam is injected) The volume of the foaming gas may be determined so as to obtain a desired volume at this weight. As the type of foaming gas, air is mainly used, but in addition, inert gases such as nitrogen, carbon dioxide, helium, and argon can also be used.

-Foaming method and foaming conditions The foaming method used in the method for producing a water-absorbent resin foam according to the present invention is not particularly limited as long as it is a method generally used in the production of foams. A floss (mechanical foaming) method can be used. The mechanical floss method is a method in which air in the atmosphere is mixed into an aqueous liquid medium and foamed by stirring the aqueous liquid medium with a stirring blade or the like. As the stirring device, a stirring device generally used in the mechanical floss method can be used without particular limitation, and for example, a homogenizer, a dissolver, a mechanical floss foaming machine, or the like can be used. According to this mechanical floss method, by adjusting the mixing ratio of the aqueous liquid medium and air, it is possible to obtain water absorbent resin foams having a density suitable for various applications.

  The mixing time of the aqueous liquid medium and air is not particularly limited, but is usually 1 to 10 minutes, preferably 2 to 6 minutes. The mixing temperature is not particularly limited, but is usually room temperature. Further, the stirring speed in the above mixing is preferably 200 rpm or more in order to make the bubbles fine (more preferably 500 rpm or more), and 2000 rpm or less is preferable (800 rpm or less is preferable) in order to smoothly discharge the foam from the foaming machine. More preferred).

-Molding The aqueous liquid medium (foamed aqueous liquid medium) foamed as described above is formed into a sheet or the like that matches the thickness of the desired water-absorbent resin foam by known means such as a doctor knife or a doctor roll. Molded.

(Thixotropic process)
In the thixotropy imparting step, a gelled aqueous liquid medium is obtained by using a predetermined gelation method for the aqueous liquid medium obtained in the raw material preparation step. In this thixotropic imparting step, when a gelling agent is used, the liquid aqueous liquid medium obtained in the raw material preparation step, the foaming gas, and the gelling agent are sufficiently mixed by a mixing device such as a mixing head. It is carried out by doing. The gelled aqueous liquid medium here refers not only to an aqueous liquid medium that has been completely gelled, but can be obtained in the raw material preparation step by a gelling agent added in the thixotropy imparting step. It refers to both an aqueous liquid medium in the middle of gelation from a liquid aqueous liquid medium and a completely gelled aqueous liquid medium.

  Moreover, the foaming gas which exists in the gelatinized aqueous liquid medium will be hold | maintained as a bubble by completion of gelation. Since the bubbles become cells of the resin foam finally obtained as they are, the size of the bubbles determines the cell diameter.

  The gelation method and foaming method of the aqueous liquid medium are not limited at all, and may be appropriately selected according to the application. For example, room temperature gelation method using gelling agent (Dunlop method), freezing solidification method without using gelling agent (Tararay method), gelation method with ammine complex (caysam method), heat sensitive gelation using heat sensitive agent A known method such as a method may be used. In addition, as described above, a gelation method may be used in which an anionic surfactant is insolubilized by blending a metal cation source together with the anionic surfactant.

  In addition, when adding a metal cation source to the raw material of the resin foam, the timing of addition may be any time, especially when gelation time is short or when using a water-soluble salt with high solubility, Since the amount of gas that can be mixed by thickening due to gelation is reduced and a high-density foam is formed, it is preferably added to the foamed aqueous liquid medium after foaming. In addition, when the gelation time is long or when a sustained-release sparingly water-soluble salt is used, if it is added after foaming, a fine cell structure cannot be formed due to coalescence of bubbles, so it may be added to the aqueous liquid medium before foaming. preferable. On the other hand, by adding the metal cation source to the aqueous liquid medium in advance (before foaming), the process can be simplified.

  The insolubilization of the anionic surfactant detailed above is mainly to impart thixotropy to the system by insolubilizing the foaming anionic surfactant (foaming anionic surfactant) after foaming. However, as the insolubilizing step of the anionic surfactant, a different method may be considered. As an example, a water-soluble component existing in the system after foaming (for example, a metal cation derived from a foaming anionic surfactant, a component contained in a water-soluble resin, previously added) A method for insolubilizing the water-soluble component) can be mentioned. For example, a technique for forming a water-insoluble component using a metal cation derived from a foaming anionic surfactant can be realized by adding another component that binds to and insolubilizes the metal cation. A more preferred example is a method of adding an anionic surfactant other than the anionic surfactant that is a foaming agent. The solubility of anionic surfactants in water is generally determined by the multivalent metal salt {eg, alkaline earth metal salt (eg, calcium salt)} <alkali metal salt (eg, sodium salt) <ammonium or amine salt. In order. Utilizing this property, for example, by using a highly water-soluble salt as the foaming anionic surfactant (for example, the sodium salt of the first anionic surfactant), the foaming anionic surfactant Water-soluble cations derived from the foaming anionic surfactant are allowed to exist in the system while dissolving and ensuring foamability. Then, after foaming, a second anionic surfactant (for example, an ammonium salt) that forms a poorly soluble salt with the water-soluble cation is added to the system. Here, for example, in the case of the above example, the second anionic surfactant is soluble in water as an ammonium salt, but is insoluble in water as an alkali metal salt. By adding such a second anionic surfactant to the system, the second anionic surfactant undergoes cation exchange (for example, ammonium → sodium ion) and changes from a water-soluble type to a water-insoluble type. To do. Thereby, the fluidity | liquidity of a system falls and it becomes possible to manufacture the foam which has a low cell diameter etc. similarly to the aspect which insolubilizes the foaming anionic surfactant explained in full detail above.

  For example, it is assumed that at least an alkali metal salt (for example, sodium salt) is used as the foaming anionic surfactant (other surfactant may be used in combination). In this case, when long-chain fatty acid (for example, C16-22) ammonium (for example, ammonium stearate) is used as the second anionic surfactant, alkali metal ions derived from the foaming anionic surfactant ( For example, sodium ions) and a long-chain fatty acid derived from the second anionic surfactant react to precipitate a fatty acid alkali metal salt (for example, sodium salt) as a water-insoluble salt. In addition, it is assumed that a medium chain fatty acid (for example, C8-15) alkali metal salt (for example, sodium dodecanoate) is used as the foaming anionic surfactant (in this case, detailed above). This corresponds to an embodiment in which the foaming anionic surfactant is insolubilized). In this case, polyvalent metal ions (for example, calcium ions) are added to the foamed system. Thereby, the said polyvalent metal ion and the short chain fatty acid derived from a foaming anionic surfactant react, and it becomes possible to precipitate a fatty acid polyvalent metal salt (for example, calcium salt) as a water-insoluble salt.

  In addition, as an insolubilization process of an anionic surfactant, you may combine the method mentioned above suitably.

(Heating process)
In the heating step, the dispersion medium in the formed foamed aqueous liquid medium is evaporated. The drying method at this time is not particularly limited, and for example, hot air drying or the like may be used. Also, the drying temperature and the drying time are not particularly limited, but may be, for example, about 80 ° C. and about 1 to 3 hours.

  Further, in this heating step, the dispersion medium evaporates from the foamed aqueous liquid medium, but the path through which the vapor escapes communicates from the inside to the outside of the water absorbent resin foam. Therefore, in the water absorbent resin foam according to the present invention, the path when the water vapor escapes remains as open cells, so that at least some of the bubbles present in the water absorbent resin foam become open cells. Here, when the foaming gas mixed in the stirring / foaming process remains as it is, it becomes closed cells in the obtained water absorbent resin foam, and the mixed foaming gas is vaporized in this process. When the bubbles are communicated when they are removed, they become open cells in the obtained water-absorbent resin foam. In the present invention, some of the bubbles in the resin foam may be open cells, and the remaining bubbles may be closed cells, or all the bubbles may be open cells.

  When a curing agent / crosslinking agent is added, in the heating step, the crosslinking (curing) reaction of the raw material proceeds and is completed. Specifically, raw materials are cross-linked by the above-described curing agent / crosslinking agent, and a cured water-absorbent resin foam is formed. The heating means in this case is not particularly limited as long as the raw material can be sufficiently heated and the raw material can be crosslinked (cured). For example, a tunnel heating furnace or the like can be used. Also, the heating temperature and the heating time may be any temperature and time that can crosslink (harden) the raw material. .

≪Structure of water absorbent resin foam≫
<Structure>
The resin foam according to this embodiment is preferably a hole-in-hole type foam. By adopting such a structure, when the pores present in the membrane of each cell exhibit a capillary phenomenon and are used for hydrophilic purposes, the effect of improving water absorption can be achieved. The “hole-in-hole type foam” means that in each cell of the foam, a plurality of holes (openings) having a diameter smaller than the cell diameter of the cell exist in the film portion corresponding to the cell wall surface. It is a foam.

(Average cell diameter)
The average cell diameter (average cross-sectional cell diameter) of the cross section of the resin foam is preferably 5 μm or more (for example, 10 μm or more) and 300 μm or less, more preferably 5 μm or more and 200 μm or less, and 5 μm or more and 100 μm or less. Is particularly preferred. In addition, as a measuring method of an average cell diameter, the following method shall be followed.

  First, a cell photograph of a cross section of the resin foam is taken using a scanning electron microscope (SEM, manufactured by Keyence Corporation, VHXD-500). Then, each cell diameter is measured using image processing software Image-Pro PLUS (Media Cybernetics, 6.3 ver). More specifically, the contrast is adjusted in order to read the SEM image and recognize the cell with the contrast. Next, the shape of the cell is read by image processing (not a perfect circle, but the shape is recognized as it is). Next, “diameter (average)” is selected as the measurement item. Next, each cell diameter is calculated as a value obtained by measuring the diameter passing through the center of gravity of the object in increments of 2 degrees and averaging the measured values.

(Cell diameter distribution)
In the cross-sectional cell photograph, for each cell in the cross-section of the foam, Sx / S ≧ in the total value S of the cell cross-sectional areas of all the cells and the total value Sx of the cell areas having a cross-sectional cell diameter of 1 to 100 μm. 0.1 is preferable, Sx / S ≧ 0.2 is more preferable, and Sx / S ≧ 0.3 is particularly preferable. Although it does not specifically limit as an upper limit of Sx / S, For example, it is 1. It is more preferable that Sy / S ≧ 0.05 in the total value S of the cell cross-sectional areas of all the cells and the total value Sy of the cell area having a cross-sectional cell diameter of 50 to 125 μm. Yes, Sy / S ≧ 0.1 is more preferable, and Sy / S ≧ 0.15 is particularly preferable. The upper limit of Sy / S is not particularly limited, but for example, by setting the cross-sectional cell diameter and the cross-sectional cell diameter distribution of 1 to such a range, water absorption due to the capillary phenomenon can be expected more.

≪Properties≫
According to the water-absorbent resin foam according to the present embodiment, the foam is formed in such a way that the water-soluble polymer penetrates to the inside of the foam, so that the water-absorbing power (water absorption speed) is excellent. Furthermore, since the water-soluble polymer is partially embedded in the polymer matrix, it has excellent repeated resistance.

≪Use of water absorbent resin foam≫
The water absorbent resin foam according to the present invention includes a water absorbent roll, a cosmetic puff, a polishing pad such as various semiconductors or optical materials, a poultice, an ink retaining material, artificial leather, synthetic leather, a diaper, a sanitary product, It can be widely used in applications intended to absorb water.

  Here, in the present invention, “insolubilization” is synonymous with “insolubilization” generally understood in the art, and dissolution is suppressed by changing a water-soluble component to a water-insoluble component. For example, preferably 10% by mass or more (more preferably 50% by mass or more) of the water-soluble component before being insolubilized is precipitated as a water-insoluble component (for example, preferably an anionic surfactant, 10% by mass or more, more preferably 50% by mass or more is a water-insoluble component root); “water-insoluble salt” means a salt having a solubility of 1 g / 100 g or less of water; “Salt” refers to a metal salt with a solubility of 10 g / 100 g or more of water; “Slightly water-soluble metal salt” refers to a metal salt with a solubility of less than 10 g / 100 g of water; Water 10 at 25 ° C. g grams of saturated compounds against a (g / 100 g water) is shown.

  Next, although an example and a comparative example explain the present invention still more concretely, the present invention is not limited at all by these examples.

≪Raw material≫
First, in the examples and comparative examples, the following raw materials were used. In the following description, the method for determining the stable dispersion type or the unstable dispersion type of water-dispersible resin (calculation method for the precipitation rate) and the method for measuring the HLB value are the same as those described above. The tensile strength at break was measured by punching the test piece into a No. 2 dumbbell shape according to JIS K6400. The tensile elongation at break was measured by punching a test piece into a No. 2 dumbbell shape according to JIS K6400. The softening point was measured according to JIS K2207. The viscosity was measured using a single cylindrical rotational viscometer (B-type viscometer) according to JIS K7117. The surface tension was measured by a Wilhelmy method using a surface tension meter (Kyowa Kagaku Co., Ltd., ESB-V type). The polymer glass transition temperature (Tg) was measured using differential scanning calorimetry (DSC) according to JIS K7121.
<Water dispersible resin>
・ Water dispersible resin 1
Carbonate urethane emulsion (stable dispersion type water-dispersible resin; precipitation rate 0.8%), pH 8, hydrophilic group; sulfonic acid group, solid content 40%, tensile breaking strength 50 MPa, tensile breaking elongation 600%, softening point 200- 220 ° C
・ Water dispersible resin 2
{Acrylonitrile-butadiene rubber latex (unstable dispersion type water-dispersible resin; precipitation rate 33%), pH 11, solid content 40%, medium-high nitrile, viscosity 300 mPa · s, surface tension 34 mN / m, Tg-12 ° C
<Anionic surfactant>
Anionic surfactant 1 (sodium alkylsulfosuccinate)
Dispersion medium: water, pH 9.4, solid content 30%, HLB39.7
・ Anionic surfactant 2 (ammonium stearate)
Dispersion medium: water, pH 11, solid content 30%, HLB 25.5
<Metal cation source>
・ Metal cation source 1 (calcium nitrate)
(Solubility 138 g / 100 g water <water-soluble polymer>
・ Water-soluble polymer 1
Acrylic acid / sulfonic acid copolymer, molecular weight 3000, solid content 40%
・ Water-soluble polymer 2
Non-sulfonyl group-containing polymer, molecular weight 5000, solid content 40%
・ Water-soluble polymer 3
Acrylic acid / sulfonic acid copolymer, molecular weight 8000, solid content 40%
・ Water-soluble polymer 4
Acrylic acid / sulfonic acid copolymer, molecular weight 60000, solid content 40%
<Crosslinking agent for water-soluble polymer>
Zirconium ammonium carbonate <curing agent>
・ Hardening agent Hydrophobic HDI isocyanurate (functional group number 3.5, trimer)
<Vulcanization paste>
・ Vulcanized paste 1
10 parts by mass of vulcanizing agent such as sulfur, zinc oxide, thiazole vulcanization accelerator, anti-aging agent, 6 parts by mass of Noxeller MZ, 18 parts by mass of zinc oxide, 13 parts by mass of anti-aging agent, and 3 A vulcanizing paste was prepared by adding 50 parts by mass of a dispersant to 50 parts by mass of ion-exchanged water and dispersing for 48 hours in a ball mill.
<Gelling agent>
-Gelling agent 1
Polyether-modified silicone oil and gelling agent 2
Sodium silicofluoride

≪Formation of water absorbent resin foam≫
<Example 1>
(Raw material preparation process)
Using urethane emulsion of water-dispersible resin 1 as the main agent, 8.6 parts by mass of the anionic surfactant 1, 2.4 parts by mass of the inorganic electrolyte 1, 6.0 parts by mass with respect to 100 parts by mass of the main agent. A curing agent, 5.0 parts by mass of a water-soluble polymer 1, and 1.0 part by mass of a crosslinking agent for a water-soluble polymer were mixed to obtain a resin foam raw material.
(Stirring process)
An inert gas such as air or nitrogen gas was added to the resin foam raw material to cause foaming (at a foaming condition of 100 to 1000 rpm).
(Metal cation source addition process)
8.6 parts by mass of metal cation source 1 was blended with 100 parts by mass of the main agent.
(Heating process)
A resin foam was prepared by heat treatment (in a processing condition oven or a drying furnace).
<Preparation of Examples 2-3, 5-11 and Modification 4 >
Resin foams were prepared in the same manner as in Example 1 except that the raw materials shown in Tables 1 and 2 were blended.
<Adjustment of Examples 12-13>
A resin foam was prepared in the same manner as in Example 1 except that the gelling agent (gelling agent 1, gelling agent 2) was added and the metal cation source was not added.

<Comparative Example 1>
As shown in Table 3, a foam was prepared in the same manner except that the water-soluble polymer and the water-soluble polymer crosslinking agent were not added to Example 12, and the water-soluble polymer 1 was sprayed with an air gun. Thus, a water absorbent resin foam was obtained.
<Comparative example 2>
Except that the water-soluble polymer and the water-soluble polymer cross-linking agent were not added to Example 12, a foam was prepared in the same manner, and further impregnated with the water-soluble polymer 1 to obtain a water-absorbent resin foam. .

≪Water absorption test≫
The water absorption time was measured according to the method shown below, and the water absorption speed and water absorption were evaluated from the measurement results.
<Test method 1>
One drop (0.033 ml) of ion-exchanged water was dropped on the test piece, and the time until complete penetration was measured. Measurement points were measured at a total of five points at the four corners and the center of a 5 cm × 5 cm resin foam, and the water absorption rate was evaluated according to the following criteria. In the following evaluations, the evaluations of ◎, ○, △, and ▲ are good as the evaluation of the water absorption rate in the present invention, the water absorption is judged to be good, and the evaluation of × is in the present invention. It was judged that the water absorption rate was poor and no water absorption was obtained.
If the water absorption time at all five measurement points is within 10 seconds, “◎”
“○” when the water absorption time is within 10 seconds at 1 to 4 points out of 5 points to be measured.
If the water absorption time is more than 10 seconds and less than 30 seconds at 1 to 4 points out of 5 measurement points, “△”
If the water absorption time is more than 30 seconds and less than 60 seconds at 1 to 4 points out of 5 points, “▲”
If the water absorption time at all five measurement points is more than 60 seconds, “×”
<Test method 2>
Further, a water absorption test was repeatedly performed. A fully automatic washing machine (manufactured by Toshiba Corporation, AW-421S) was prepared, the amount of washing water was set to 45 L , and the test pieces prepared above (Examples 1 to 3 , 5 to 13, Modification Example 4, Comparative Example 1) ~ 2) was added. After washing for 13 minutes and dehydration for 7 minutes, the test piece was dried. In order to evaluate the durability of the test piece (whether the water absorption can be maintained), the water absorption was evaluated by repeating the washing step once. The obtained results are shown in Table 1. The method for evaluating water absorption is as described above.
Moreover, the durability of the test pieces (Examples 1, 7, 9, 11 and Comparative Examples 1 and 2) was evaluated by repeatedly performing the washing test. The results before and after washing were evaluated 1 to 3 times and the water absorption was evaluated. The results obtained are shown in Table 4. The method for evaluating water absorption is as described above.

  As shown in Table 4, the resin foam of Example 1 containing an appropriate amount of the water-soluble polymer crosslinking agent maintained very good water absorption even after three washing steps. From this, it was found that by adding an appropriate amount of the crosslinking agent, the binding force between the water-soluble polymer and the resin polymer was strengthened, the drop-off of the water-soluble polymer was suppressed, and the resin foam could maintain high water absorption for a long time. Moreover, the water absorption rate of the resin foam of Example 9 having a small amount of the water-soluble polymer cross-linking agent slightly decreased after one washing step. Further, the resin foam of Example 11 with a small amount of the water-soluble polymer crosslinking agent added had a slight decrease in water absorption after one washing step, and the water absorption decreased after two washing steps. From this, it was found that the addition of the water-soluble polymer cross-linking agent is suppressed to a certain extent by adding the water-soluble polymer crosslinking agent, but the effect is inferior to that in the case of adding an appropriate amount. On the other hand, in Comparative Example 1 in which the water-soluble polymer was sprayed and in Comparative Example 2 in which the water-soluble polymer was impregnated, the water absorption was greatly reduced after one washing step. For this reason, when the water-soluble polymer crosslinking agent is not added, the water-soluble polymer is likely to fall off and maintain high water absorption for a long period of time compared to the case where the water-soluble polymer crosslinking agent is added. Found it difficult. Similarly, in Example 7 in which the crosslinking agent for the water-soluble polymer was not added, the water absorption decreased after the washing process, but it had a certain degree of water absorption after the three washing processes.

[Reference example]
Next, reference examples and reference comparative examples will be described, but the present invention is not limited to these examples.

≪Raw material≫
First, in the reference example and the reference comparative example, the following raw materials were used. In the following description, the method for determining the stable dispersion type or the unstable dispersion type of water-dispersible resin (calculation method for the precipitation rate) and the method for measuring the HLB value are the same as those described above. The tensile strength at break was measured by punching the test piece into a No. 2 dumbbell shape according to JIS K6400. The tensile elongation at break was measured by punching a test piece into a No. 2 dumbbell shape according to JIS K6400. The softening point was measured according to JIS K2207. The viscosity was measured using a single cylindrical rotational viscometer (B-type viscometer) according to JIS K7117. The surface tension was measured by a Wilhelmy method using a surface tension meter (Kyowa Kagaku Co., Ltd., ESB-V type). The polymer glass transition temperature (Tg) was measured using differential scanning calorimetry (DSC) according to JIS K7121.
<Water dispersible resin>
・ Water dispersible resin 1
Carbonate urethane emulsion (stable dispersion type water-dispersible resin; precipitation rate 0.8%), pH 8, hydrophilic group; sulfonic acid group, solid content 40%, tensile breaking strength 50 MPa, tensile breaking elongation 600%, softening point 200- 220 ° C
・ Water dispersible resin 2
Acrylic emulsion (stable dispersion type water-dispersible resin; precipitation rate 4.9%), pH 610, solid content 40%, tensile breaking strength 25 MPa, tensile breaking elongation 300%, softening point 100-120 ° C.
・ Water-dispersible resin 3
Carbonate urethane emulsion (stable dispersion type water dispersible resin; precipitation rate 0.8%), pH 8, hydrophilic group; carboxyl group, solid content 40%, tensile breaking strength 20 MPa, tensile breaking elongation 700%, softening point 170-200 ℃
・ Water dispersible resin 4
Ether urethane emulsion (stable dispersion type water-dispersible resin; precipitation rate 1.1%), pH 8, solid content 40%, tensile breaking strength 20 MPa, tensile breaking elongation 500%, softening point 200-220 ° C.
・ Water dispersible resin 5
Acrylonitrile-butadiene rubber latex (unstable dispersion type water-dispersible resin; precipitation rate 33%), pH 11, solid content 40%, medium-high nitrile, viscosity 300 mPa · s, surface tension 34 mN / m, Tg-12 ° C.
・ Water dispersible resin 6
Styrene-butadiene rubber latex (unstable dispersion type water-dispersible resin; precipitation rate 38%), pH 10, solid content 40%, viscosity 440 mPa · s, surface tension 32 mN / m, Tg-63 ° C.
・ Water dispersible resin 7
Natural rubber latex (unstable dispersion type water-dispersible resin; precipitation rate 35%), pH 10, solid content 40%, viscosity 300 mPa · s, surface tension 34 mN / m, Tg-75 ° C.
<Anionic surfactant>
・ Anionic surfactant 1 (sodium alkylsulfosuccinate derived from beef tallow)
Dispersion medium: water, pH 9.4, solid content 30%, HLB39.7
・ Anionic surfactant 2 (ammonium stearate)
Dispersion medium: water, pH 11, solid content 30%, HLB 25.5
・ Anionic surfactant 3 (potassium oleate soap)
Dispersion medium: water, pH 11.2, solid content 30%, HLB18.3
・ Anionic surfactant 4 (sodium alkyldiphenyl ether sulfonate)
Dispersion medium: water, pH 8.5, solid content 30%, HLB 9.0
<Metal cation source>
・ Metal cation source 1 (calcium nitrate)
Solubility 138g / 100g Water / Metal Cation Source 2 (Aluminum Sulfate)
Solubility 38.6 g / 100 g Water / metal cation source 3 (magnesium sulfate)
Solubility 36.3g / 100g Water / Metal Cation Source 4 (Calcium Citrate)
Solubility 0.0259g / 100g Water / Metal Cation Source 5 (Calcium Carbonate)
Solubility 0.81g / 100g Water / Metal Cation Source 6 (Primary Calcium Phosphate)
Solubility 1.8 g / 100 g water <curing agent>
・ Hardening agent Hydrophobic HDI isocyanurate (functional group number 3.5, trimer)
<Vulcanization paste>
・ Vulcanization paste 50 parts of 10 parts by weight of vulcanizing agent, 6 parts by weight of thiazole vulcanization accelerator, 18 parts by weight of zinc oxide, 13 parts by weight of anti-aging agent, and 3 parts by weight of dispersant. Prepared by dispersing in a ball mill for 48 hours in addition to parts by mass of ion-exchanged water <Gelating agent>
-Gelling agent 1
Sodium silicofluoride gelling agent 2
Polyether-modified silicone oil <water-soluble polymer>
Water-soluble polymer Acrylic acid / sulfonic acid copolymer, molecular weight 3000, solid content 40%

<< Formation of foam >>
<Reference Example 1>
(Raw material preparation process)
The urethane emulsion of polymer water dispersion 1 is used as a main agent, and 8.6 parts by mass of anionic surfactant 1, 2.4 parts by mass of metal cation source 1, 6.0 parts by mass with respect to 100 parts by mass of the main agent. The curing agent 1 was mixed to obtain a resin foam raw material.
(Stirring process)
An inert gas such as air or nitrogen gas was added to the resin foam raw material to cause foaming (at a foaming condition of 100 to 1000 rpm).
(Heating process)
A resin foam having a thickness of 1 mm was obtained by heat treatment in an oven or a drying furnace.
(Liquid viscosity after foaming)
When the liquid viscosity after foaming was measured at room temperature using a single cylindrical rotational viscometer (B-type viscometer) according to JIS K7117-1, it was 3000 mPa · s.

<Preparation of Reference Example 2-38 and Reference Comparative Example 1-8>
Resin foams were obtained in the same manner as in Reference Example 1 according to the formulations shown in Tables 5-9. In addition, about liquid viscosity, it became comparable as the reference example 1 also about the reference examples 2-38 and the reference comparative examples 1-8.

≪Method for evaluating resin foam≫
Next, the resin foam according to Reference Example 1-38 and Reference Comparative Example 1-8 was evaluated in accordance with the following. The results (particularly the appearance and cell diameter distribution) are shown in Tables 5-9.
<Appearance>
The state of the cell and the surface of the resin foam were evaluated visually. When the cell was uniform, it was evaluated as “◯”, when the cell was rough, “Δ”, when the cell was very rough, and when the cell was not formed (not foamed), it was evaluated as “x”. 1 is a SEM photograph of the resin foam according to Reference Example 1, FIG. 2 is a SEM photograph of the resin foam according to Reference Example 19, and FIG. 3 is a resin foam according to Reference Comparative Example 1. It is a SEM photograph of.
<Density>
According to JIS K6400, the apparent density was measured at room temperature. The test result of Reference Example 1 was 150 kg / m ³ . It became the same grade also about the reference examples 2-38 and the reference comparative examples 1-8.
<Average cell diameter and cell diameter distribution>
Using a scanning electron microscope (SEM, manufactured by Keyence Corporation, VHXD-500), a cell photograph of a cross section of the resin foam was taken. Then, each cell diameter was measured using image processing software Image-Pro PLUS (Media Cybernetics company make, 6.3 ver). A cell photograph (200 times) of a cross section of the resin foam of the resin foam (thickness 1 mm) obtained in Reference Example 1 was taken, and each cell diameter was measured with image processing software Image-Pro PLUS. More specifically, first, using a scanning electron microscope (SEM, manufactured by Keyence Corporation, VHXD-500), a cell photograph (200 times) of a cross section of the resin foam is taken (FIG. 1). Thereafter, using the image processing software Image-Pro PLUS (Media Cybernetics, 6.3 ver), the SEM image is read and spatial calibration is performed (FIG. 4). Next, in order to recognize the cell by contrast, the contrast is adjusted (FIG. 5). Next, the shape of the cell is read by image processing {not a perfect circle but the shape is recognized as it is (FIG. 6)}. Next, “diameter (average)” is selected as a measurement item (FIG. 7). Next, the diameter passing through the center of gravity of the object is measured in increments of 2 degrees, and each cell diameter is calculated as an average value (FIG. 8). As a measurement result, the average cell diameter was 69.8 μm, and the number of cells was 295. Next, when the distribution of the cell diameter was measured from the obtained value, the total cell area S of all the cells and the total cell area Sx having a cell diameter of 1 to 100 μm, Sx / S = It was 0.52. The same measurement was performed for the other reference examples and the reference comparative example, “O” when Sx / S ≧ 0.3, “Δ” when 0.3> Sx / S ≧ 0.1, 1> Sx / S was evaluated as “x”. In Reference Example 19 (FIG. 2), the average cell size was 71.8 μm, the number of cells was 175, and Sx / S = 0.18. In Reference Comparative Example 1 (FIG. 3), the average cell size was 91.2 μm, the number of cells was 37, and Sx / S = 0.06.

Claims (4)

Mixing and stirring a gas in an aqueous liquid medium containing a water-dispersible resin as a dispersoid, an anionic surfactant as a foaming agent, and water or a mixture of water and a water-soluble solvent as a dispersion medium The aqueous liquid medium is foamed to obtain a foamed aqueous liquid medium, and the foamed aqueous liquid medium is heated to evaporate the dispersion medium to produce a water absorbent resin foam, wherein the aqueous liquid medium is A method for producing a water-absorbent resin foam, further comprising a water-soluble polymer dissolved in the dispersion medium , wherein the water-soluble polymer is a sulfonyl group-containing polymer . Mixing and stirring a gas in an aqueous liquid medium containing a water-dispersible resin as a dispersoid, an anionic surfactant as a foaming agent, and water or a mixture of water and a water-soluble solvent as a dispersion medium The aqueous liquid medium is foamed to obtain a foamed aqueous liquid medium, and the foamed aqueous liquid medium is heated to evaporate the dispersion medium to produce a water absorbent resin foam, wherein the aqueous liquid medium is And a water-soluble polymer that is soluble in the dispersion medium, wherein the water-soluble polymer is a copolymer of a sulfonyl group-containing polymer and a carboxyl group-containing polymer. . The method for producing a water-absorbent resin foam according to claim 1 or 2 , wherein the water-soluble polymer has a weight average molecular weight of 500 or more and 1000000 or less. The method for producing a water-absorbent resin foam according to any one of claims 1 to 3 , wherein the aqueous liquid medium contains a crosslinking agent for crosslinking the water-dispersible resin and the water-soluble polymer.