TWI806958B - Latex and foam rubber for foam rubber - Google Patents

Abstract

Provided is a latex for foam rubber, which is a latex for foam rubber containing particles of a nitrile-group-containing conjugated diene copolymer, wherein the nitrile-group-containing conjugated diene copolymer contains ethylenically unsaturated nitrile monomer units and conjugated diene monomer units, the proportion of the above-mentioned ethylenically unsaturated nitrile monomer units is 40 to 60% by weight, and the volume-cumulative particle diameter d10 of the above-mentioned particles in the volume-based particle size distribution is 130 nm or more.

Description

Latex and foam rubber for foam rubber

The present invention relates to latex for foam rubber used in the manufacture of foam rubber.

Foam rubber (rubber foam) manufactured using latex for foam rubber is used in various applications such as mattresses, powder puffs (cosmetic sponges), rollers, and shock absorbers. Among the uses of such foam rubber, especially as foam rubber used for powder puffs, good oil resistance and soft touch are required.

For example, Patent Document 1 discloses a copolymer rubber latex composition for foam rubber, which is a latex (A) of copolymer (a) formed by 30-45% by weight of cyano group-containing ethylenically unsaturated monomer units (a1), 55-70% by weight of conjugated diene monomer units (a2), and 0-15% by weight of units (a3) of other ethylenically unsaturated monomers that can be copolymerized with cyano-group-containing ethylenically unsaturated monomers and conjugated diene monomers; Ethylenically unsaturated monomer unit (b1) 45 to 65% by weight, conjugated diene monomer unit (b2) 35 to 55% by weight, and other ethylenically unsaturated monomer units (b3) that can be copolymerized with cyano group-containing ethylenically unsaturated monomers and conjugated diene monomers. Copolymer (b) latex (B) (wherein the amount of cyano group-containing ethylenically unsaturated monomer units (b1) is 5% by weight greater than the amount of cyano group-containing ethylenically unsaturated monomer units (a1) % or more.); mixed in a ratio of 20/80 to 80/20 in the weight ratio of the copolymer (a) to the copolymer (b) (copolymer (a)/copolymer (b)).

"Patent Documents" "Patent Document 1": International Patent Publication No. 2009/145009

However, there has been demanded a technique for further improving the handleability and formability, and at the same time, the swelling resistance of the obtained foam rubber to cosmetics and the abrasion resistance when cosmetics are contained.

The present invention was made in view of this fact, and an object of the present invention is to provide a latex for foam rubber that can produce foam rubber that is "excellent in handleability and formability, and is resistant to deformation and less abrasion even when it is made to contain cosmetics."

As a result of intensive research to achieve the above object, the present inventors found that by using particles of a nitrile-group-containing conjugated diene copolymer containing a relatively large amount of ethylenically unsaturated nitrile monomer units, and then appropriately adjusting the volume cumulative particle diameter d10 of the particles, the above object can be achieved, and the present invention has been completed.

That is, according to the present invention, there is provided a latex for foam rubber, which is a latex for foam rubber containing particles of a nitrile-group-containing conjugated diene copolymer, wherein the nitrile-group-containing conjugated diene copolymer contains ethylenically unsaturated nitrile monomer units and conjugated diene monomer units, the content ratio of the above-mentioned ethylenically unsaturated nitrile monomer units is 40 to 60% by weight, and the volume-cumulative particle diameter d10 of the particle size distribution on a volume basis is 130 nm or more.

In the latex for foam rubber of the present invention, the content ratio of the aforementioned ethylenically unsaturated nitrile monomer unit is preferably 45 to 55% by weight.

In the latex for foam rubber of the present invention, it is preferable that the volume-cumulative particle diameter d50 of the aforementioned particles in the volume-based particle diameter distribution is 420 to 1500 nm.

The latex for foam rubber of the present invention preferably has a solid content concentration of 60% by weight or more.

The latex for foam rubber of the present invention preferably has a viscosity of 3200 mPa·s or less when measured with a B-type viscometer at a temperature of 25°C, a rotation speed of 60 rpm, and a rotation time of 60 seconds.

The latex for foam rubber of the present invention preferably further contains a crosslinking agent.

Furthermore, according to the present invention, a foam rubber obtained from the aforementioned latex for foam rubber can be provided.

According to the present invention, it is possible to provide a latex for foam rubber that can produce a foam rubber that is "excellent in handleability and formability, and is hardly deformed when it is made to contain cosmetics, and has little abrasion."

<Latex for foam rubber>

The latex for foam rubber of the present invention contains particles of a nitrile group-containing conjugated diene copolymer.

[Nitrile group-containing conjugated diene copolymer]

The nitrile group-containing conjugated diene copolymer is a copolymer containing ethylenically unsaturated nitrile monomer units and conjugated diene monomer units. In addition to these, it may also contain other ethylenically unsaturated monomer units formed from other ethylenically unsaturated monomers that can be copolymerized with ethylenically unsaturated nitrile monomers and conjugated diene monomers.

The ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a nitrile group, and examples thereof include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, and α-cyanoethylacrylonitrile. Among them, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is more preferable. These ethylenically unsaturated nitrile monomers can be used individually or in combination of 2 or more types.

In the nitrile group-containing conjugated diene copolymer, the content ratio of the ethylenically unsaturated nitrile monomer unit formed from the ethylenically unsaturated nitrile monomer is 40 to 60% by weight, preferably 45 to 55% by weight. By setting the content ratio of the ethylenically unsaturated nitrile monomer unit within the above range, excellent handling properties and moldability can be obtained, and the obtained foam rubber can be made to be hard to deform even when cosmetics are contained therein, and to have less abrasion. If the content ratio of the ethylenically unsaturated nitrile monomer unit is too small, the obtained foam rubber is likely to be deformed and easily abraded when cosmetics are contained. If the content ratio of the ethylenically unsaturated nitrile monomer unit is too high, the obtained foam rubber will become too hard, and the touch of the skin will tend to deteriorate.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. Among these, 1,3-butadiene and isoprene are preferable. These conjugated diene monomers can be used individually or in combination of 2 or more types.

In the nitrile group-containing conjugated diene copolymer, the content ratio of the conjugated diene monomer unit formed from the conjugated diene monomer is preferably 40 to less than 60% by weight, more preferably 45 to 55% by weight. By setting the content ratio of the conjugated diene monomer unit in the above range, more excellent handling properties and formability can be obtained, and the obtained foam rubber can be made to be less deformable and wear less even when cosmetics are contained therein.

Other ethylenically unsaturated monomers that can be copolymerized with ethylenically unsaturated nitrile monomers and conjugated diene monomers include, for example, ethylenically unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid (anhydride), fumaric acid, and itaconic acid; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, mono- or dimethyl-maleate, mono- or diethyl-fumarate Mono- or di-alkyl esters of ethylenically unsaturated carboxylic acids such as mono- or di-n-butyl fumarate, mono- or di-n-butyl itacon; alkoxyalkyl esters of ethylenically unsaturated carboxylic acids such as methoxy acrylate, ethoxy acrylate, and (methoxyethoxy) ethyl acrylate; -Hydroxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide and other (meth)acrylamides and their derivatives; acrylates with amino groups such as dimethylaminomethyl acrylate and diethylaminomethyl acrylate; aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and chlorostyrene; α-olefins such as ethylene and propylene; These monomers can be used individually or in combination of 2 or more types. In the nitrile group-containing conjugated diene copolymer, the proportion of other monomer units formed from other ethylenically unsaturated monomers is preferably at most 40% by weight, more preferably at most 30% by weight, more preferably at most 20% by weight. By setting the content ratio of other monomer units in the above range, more excellent handling properties and formability can be obtained, and the obtained foam rubber can be made more resistant to deformation and less abrasion even when cosmetics are contained therein.

The particles contained in latex for foam rubber have a cumulative volume particle diameter d10 (a particle diameter at which the cumulative volume calculated from the small diameter side of the volume-based particle diameter distribution is 10%) of 130 nm or more, preferably 140 nm or more, more preferably 150 nm or more, and may be 250 nm or less. By setting the volume-cumulative particle size d10 of the particles within the above range, excellent handling properties and formability can be obtained, and the obtained foam rubber can be made difficult to deform even when cosmetics are contained therein, and has little abrasion. If the volume cumulative particle diameter d10 is too small, the latex for foam rubber will be poor in handling and formability.

In addition, the particles contained in latex for foam rubber have a cumulative volume particle diameter d50 (a particle diameter at which the cumulative volume accounts for 50% of the volume-based particle diameter distribution) of preferably 420 to 1500 nm, more preferably 460 to 1250 nm, and more preferably 500 to 1000 nm. By setting the volume cumulative particle diameter d50 within the above range, more excellent handling properties and formability can be obtained, and the obtained foam rubber can be made to be less deformable and less abrasive even when cosmetics are contained therein.

The solid content concentration of the latex for foam rubber is preferably 50 to 70% by weight or more, more preferably 57% by weight or more, and more preferably 60% by weight or more. By setting the solid content concentration within the above range, more excellent handling and formability can be obtained, and the obtained foam rubber can be made to be less deformable and less abrasive even when cosmetics are contained therein. The method of controlling the solid content concentration of the latex for foam rubber to the above-mentioned range is not particularly limited, and examples thereof include a method of concentrating the latex for foam rubber so that the latex for foam rubber has a desired solid content concentration.

The viscosity of latex for foam rubber when measured with a B-type viscometer at a temperature of 25°C, a rotation speed of 60 rpm, and a rotation time of 60 seconds is preferably below 3200 mPa·s, more preferably 100 to 2500 mPa·s, and more preferably 130 to 2000 mPa·s. By setting the viscosity within the above-mentioned range, more excellent properties and formability can be obtained, and the obtained foam rubber can be made to be less deformable and wear less even when cosmetics are contained therein.

The latex for foam rubber, for example, can be produced by copolymerizing the monomers constituting the nitrile group-containing conjugated diene copolymer contained in the latex for foam rubber through emulsion polymerization, and then performing the treatment and concentration of the obtained emulsion to adjust the volume-cumulative particle size of the particles.

As the emulsion polymerization method, conventionally well-known methods can be employed. For example, when emulsifying and polymerizing a monomer mixture containing the above-mentioned monomers, commonly used emulsifiers (surfactants), polymerization initiators, chelating agents, oxygen scavengers, molecular weight regulators and other auxiliary polymerization materials can be used. The method of adding these polymerization auxiliary materials is not particularly limited, and may be any method such as an initial batch addition method, a batch addition method, or a continuous addition method.

The emulsifier is not particularly limited, and examples thereof include anionic emulsifiers, nonionic emulsifiers, and the like. Examples of the anionic emulsifier include fatty acid salts such as potassium tallow fatty acid, potassium partially hydrogenated tallow fatty acid, potassium oleate, and sodium oleate; resinates such as potassium rosinate, potassium rosinate, potassium hydrogenated rosinate, and sodium hydrogenated rosinate; and alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate. Examples of the nonionic emulsifier include polyethylene glycol ester type and Pluronic® type emulsifiers such as block copolymers of ethylene oxide and propylene oxide. Among them, anionic emulsifiers are preferred, fatty acid salts are preferred, and potassium oleate and sodium oleate are particularly preferred. And these emulsifiers can be used individually or in combination of 2 or more types. The usage-amount of an emulsifier is preferably 0.5-5 weight part with respect to 100 weight part of monomer mixtures.

The polymerization initiator is not particularly limited, but examples thereof include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium superphosphate, and hydrogen peroxide; Organic peroxides such as acyl, isobutyryl peroxide, benzoyl peroxide, octyl peroxide, and 3,5,5-trimethylhexyl peroxide; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, methyl azobisisobutyrate, etc. These polymerization initiators can be used individually or in combination of 2 or more types, respectively. The usage-amount of a polymerization initiator is preferably 0.01-10 weight part with respect to 100 weight part of monomer mixtures, More preferably, it is 0.01-2 weight part.

Also, a peroxide initiator can be used in combination with a reducing agent as a redox system polymerization initiator. The reducing agent is not particularly limited, but examples include: compounds containing metal ions in a reduced state, such as ferrous sulfate and cuprous naphthenate; sulfurous acid compounds such as sodium hydroxymethanesulfinate; sulfonic acid compounds such as sodium methanesulfonate; amine compounds such as dimethylaniline; and the like. These reducing agents can be used alone or in combination of two or more. The usage-amount of a reducing agent is preferably 3-1000 weight part with respect to 100 weight part of peroxides.

As a molecular weight adjustment agent, it can be listed for examples: positive sulfurnol, sulfurnol, tertiary sulfur, sulfurnol, tertiary tiriol, ectoprotanol and other alkoliol; dyscopylite, diopylopylopylopylopylopylopylopate, etc.; Actuamonal sulfurbonium-thymeluminumin compounds; 2,6-two (three-t-orbetyl) -4-toloenols, lycolizol and other phenolin compounds; alcohol alcohol and other hydrocarbon; halogenic hydrocarbons such as dichlogenide, di bromide, tetravitromed carbonized; Aramine, triaxyl ether, pentahylene, acrylics, titocholin, chilitic acid, acetic acid-2-ethylbenate, alpha-meal pyrology diocyrin, pyrine olene, etc. These molecular weight modifiers can be used individually or in combination of 2 or more types, respectively. The amount of the molecular weight modifier used is preferably 0.1-3 parts by weight, more preferably 0.2-2 parts by weight, and most preferably 0.3-1.5 parts by weight relative to 100 parts by weight of the monomer mixture.

The amount of water used in the emulsion polymerization is preferably 80 to 600 parts by weight, more preferably 100 to 300 parts by weight, based on 100 parts by weight of all the monomers used.

The emulsion polymerization reaction may be either continuous or fractional, and the polymerization time and the like are not particularly limited. The method of adding monomers includes, for example, a method of adding monomers used in a reaction vessel at one go, a method of continuously or intermittently adding following polymerization, a method of adding a part of monomers and reacting them to a specific conversion rate, and then continuously or intermittently adding the remaining monomers to perform polymerization. Any method may be used. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be fixed or changed. In addition, each monomer may be added to the reaction container after mixing the various monomers used in advance, or may be added to the reaction container individually. In the case of using the method of "adding a part of the monomers to the reaction vessel after the initiation of the polymerization reaction to continue the polymerization", for example, a method in which "the ethylenically unsaturated nitrile monomer and a part of the conjugated diene monomer" are added to the reaction vessel to initiate the polymerization reaction, while the polymerization reaction rate in the reaction vessel is 20 to 65%, the remaining part of the conjugated diene monomer is added to the reaction vessel at once or in batches, and then the polymerization reaction is continued. At this time, the proportion of the conjugated diene monomer added after the initial polymerization reaction is preferably set at 20 to 60% by weight of the total amount of the conjugated diene monomer used in the polymerization.

Furthermore, during emulsion polymerization, polymerization auxiliary materials such as chelating agents, dispersants, pH regulators, deoxidizers, and particle size regulators may be used as required, and the types and usage amounts of these are not particularly limited.

The monomer mixture is emulsified and polymerized as above, and the polymerization reaction is terminated by cooling the polymerization system or adding a polymerization terminator when the specified polymerization conversion rate is reached. The polymerization conversion rate at the time of terminating the polymerization is not particularly limited, but is preferably 70% or higher, more preferably 80% or higher, more preferably 90% or higher. When the polymerization conversion rate is too low, productivity tends to decrease. The polymerization temperature is not particularly limited, but is preferably 0 to 50°C, more preferably 2 to 35°C.

The polymerization terminator is not particularly limited, but examples thereof include carbama, carbamate sulfate, diethylpoietin, carbamesulfonic acid and alkali metal salts thereof, sodium dimethyldithiocarbamate, hydroquinone derivatives, catechol derivatives, and aromatic hydroxydithiocarboxylic acids such as hydroxydimethyldithiobenzoic acid, hydroxydiethyldithiobenzoic acid, and hydroxydibutyldithiobenzoic acid, and alkali metal salts thereof. The usage-amount of a polymerization terminator is preferably 0.05-2 weight part with respect to 100 weight part of monomer mixtures.

By carrying out the polymerization reaction as described above, an emulsion can be obtained. In addition, after the polymerization reaction is terminated to obtain an emulsion, unreacted monomers may also be removed from the emulsion if necessary.

After the polymerization reaction is terminated, the cumulative volume particle size of the particles of the nitrile group-containing conjugated diene copolymer contained in the obtained emulsion is further adjusted, whereby the cumulative volume particle size d10 and the cumulative volume particle size d50 can be adjusted within the above range.

Examples of methods for adjusting the cumulative particle size include: (i) a method of enlarging the particles in the emulsion by unifying them, (ii) obtaining an aggregate by aggregating the particles contained in the emulsion, dissolving the aggregate in an organic solvent to obtain a solution, emulsifying the obtained solution in water in the presence of a surfactant, and removing the organic solvent if necessary, (iii) emulsifying two or more types of particles having different cumulative particle sizes. liquid mixing method, etc.

In the method (i), the method of enlarging the particle size is not particularly limited, but examples include (1) a method of adding a conjugated diene compound such as 1,3-butadiene or toluene as a solvent to the emulsion after the polymerization is terminated, and vigorously stirring, (2) a method of adding a particle diameter enlarging agent such as carboxyl group-containing polymer latex to the emulsion, and then vigorously stirring.

When the particle size enlargement treatment is carried out by the method (1) above, the amount of solvent added is preferably 30 to 300 parts by weight relative to 100 parts by weight of the nitrile group-containing conjugated diene copolymer in the emulsion. In addition, in the case where the particle size enlargement treatment is carried out by the method of (1) above, the stirring conditions are not particularly limited, but for example, a stirring device such as a paddle-type stirring impeller is used, the rotation speed is preferably set at 50 to 2,500 rpm, and the stirring time is preferably set at 0.5 to 12.0 hours.

In addition, when performing the particle diameter enlargement treatment, it is preferable to add an antifoaming agent to the emulsion and perform the particle diameter enlargement treatment in the presence of the antifoaming agent from the viewpoint of suppressing foaming accompanied by stirring.

Furthermore, it is preferable to adjust the solid content concentration of the latex for foam rubber by performing a concentration treatment on the latex for foam rubber after the particle size enlargement treatment is performed to obtain the latex for foam rubber. The method of concentration treatment is not particularly limited, but examples include methods such as vacuum distillation, atmospheric distillation, centrifugation, and membrane concentration. Among them, vacuum distillation is preferable.

In the case of concentrating foam rubber latex by vacuum distillation, as the conditions for concentration treatment, the pressure (gauge pressure) is preferably 0.0 MPa to -0.1 MPa, more preferably -0.05 MPa to -0.099 MPa, and the temperature is preferably 30 to 100°C, more preferably 40 to 95°C.

From the viewpoint of suppressing foaming during concentration even when concentration treatment is performed, it is preferable to add an antifoaming agent to the latex for foam rubber and perform concentration treatment in the presence of the antifoaming agent.

The antifoaming agent used during the particle size enlargement treatment and the concentration treatment is not particularly limited, but examples thereof include oil-based antifoaming agents, mineral oil-based antifoaming agents such as modified hydrocarbon oils with mineral oil as a base, silicone-based antifoaming agents such as silicone oil, and polymer-based antifoaming agents. Among them, mineral oil-based antifoaming agents and silicone-based antifoaming agents are preferred. These antifoaming agents can be used individually by 1 type or in combination of 2 or more types. In addition, the antifoaming agent may be added only in either one of the particle size enlargement treatment and the concentration treatment, or it may be added in the two treatments by adding the same defoamer or a different defoamer, but by adding the defoamer at least during the particle size enlargement treatment, it becomes not only the particle size enlargement treatment, but also the antifoamer suppresses foaming in the concentration treatment performed after the particle size enlargement treatment, so it is preferable.

The total amount of the antifoaming agent added during the particle size enlargement treatment and concentration treatment is preferably 0.001 to 1.0 parts by weight, more preferably 0.005 to 0.8 parts by weight, more preferably 0.005 to 0.6 parts by weight, based on 100 parts by weight of the nitrile group-containing conjugated diene-based copolymer in the latex for foam rubber obtained. If the added amount of the antifoaming agent is less than 0.001 parts by weight, the foaming will become severe during the particle size enlargement treatment, and the particle size enlargement will not be properly performed, and the desired particle size distribution may not be obtained, or the foaming will become severe during the concentration treatment, and the productivity of the latex for foam rubber may decrease. On the other hand, if the added amount of the antifoaming agent is more than 1.0 parts by weight, the content of the antifoaming agent in the finally obtained foam rubber latex will become too much, and the Young's modulus of the obtained foam rubber will become too low, resulting in poor elasticity.

In the method (ii), examples of the method of aggregating the particles contained in the emulsion include a method of mixing the emulsion with a water-soluble organic solvent, a method of mixing the emulsion with an acid, and a method of mixing the emulsion with a salt.

As the water-soluble organic solvent, it is better to choose a solvent in which the polymer in the latex will not dissolve. As such an organic solvent, methanol, ethanol, isopropanol, ethylene glycol, etc. are mentioned, for example. Examples of the acid include acetic acid, formic acid, phosphoric acid, hydrochloric acid and the like. Examples of the salt include calcium chloride, sodium chloride, aluminum sulfate, potassium chloride and the like.

As the organic solvent used in the method of (ii), for example: aromatic hydrocarbon solvents such as benzene, toluene, and xylene; alicyclic hydrocarbon solvents such as cyclopentane, cyclopentene, cyclohexane, and cyclohexene; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; Propyl acetate, butyl acetate, amyl acetate, ethyl propionate, ethyl isobutyrate, butyl butyrate and other ester solvents; dimethyl ether, dihexyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether and other ether solvents; etc.

In the method (ii), in order to emulsify the obtained solution in water in the presence of a surfactant, an emulsifier or a disperser can be used. Furthermore, the method of adding the surfactant is not particularly limited, and may be added to the solution in advance, or may be added to the solution during the emulsification operation, and may be added at one stroke or in batches.

Examples of emulsifiers include batch-type emulsifiers such as "Homomixer" (manufactured by IKA), brand name: Polytron (manufactured by Kinematica), and TK Autohomomixer (manufactured by Tokuki Kagaku Kogyo Co., Ltd.); ppon Coke & Engineering), brand name: Trigonal wet fine pulverizer (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), product name: CABITRON (manufactured by EUROTEC), product name: MILDER (manufactured by Pacific Kiko Co., Ltd.), brand name: Fine Flow Mill (manufactured by Pacific Kiko Co., Ltd.) and other continuous emulsifiers; NOMIZER Co., Ltd.), product name: high-pressure emulsifier such as APV-Gaulin (manufactured by Gaulin Co., Ltd.); membrane emulsifier such as membrane emulsifier (manufactured by Ryoka Kogyo Co., Ltd.); product name: vibration emulsifier such as VibroMixer (manufactured by Ryoka Kogyo Co., Ltd.); The conditions of the emulsification operation by the emulsifier are not particularly limited, as long as the treatment temperature, treatment time, etc. are appropriately selected so as to obtain a desired dispersion state. Furthermore, by adjusting the applied shear force by adjusting the stirring speed, etc., the cumulative volume particle size can be adjusted to a desired range.

As a surfactant used by the method of (ii), an anionic emulsifier, a nonionic emulsifier, etc. are mentioned. Examples of the anionic emulsifier include fatty acid salts such as potassium tallow fatty acid, potassium partially hydrogenated tallow fatty acid, potassium oleate, and sodium oleate; resinates such as potassium rosinate, potassium rosinate, potassium hydrogenated rosinate, and sodium hydrogenated rosinate; and alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate. Examples of the nonionic emulsifier include polyethylene glycol ester type and Pluronic® type emulsifiers such as block copolymers of ethylene oxide and propylene oxide. Among them, anionic emulsifiers are preferable, and fatty acid salts and alkylbenzenesulfonates are more preferable. The amount of the surfactant used is preferably 0.5-50 parts by weight, more preferably 0.5-30 parts by weight, and more preferably 5-25 parts by weight relative to 100 parts by weight of the particles. By properly adjusting the amount of surfactant used, the cumulative volume particle size can be adjusted within the desired range.

In the method of (ii), examples of methods for removing the organic solvent include methods such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation.

In the method (iii), as long as two or more types of emulsions are mixed so as to obtain a desired volume cumulative particle size, the mixing method is not particularly limited. The combination of the emulsions is also not limited. For example, two emulsions obtained by the method (i) with different cumulative particle diameters may be mixed, or two emulsions obtained by the method (ii) with different cumulative particle diameters may be mixed. Furthermore, the emulsion obtained by the polymerization and the emulsion obtained by the methods (i) and/or (ii) may be mixed by a known method, or the emulsion obtained by the method (i) may be mixed with the emulsion obtained by the method (ii).

<Latex composition for foam rubber>

As latex for foam rubber, it is preferable to use what has been blended with an admixture such as a crosslinking agent. That is, it is preferable to use it as a latex composition for foam rubber.

Examples of the crosslinking agent include sulfur powder, sulfur flower, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and other sulfur; sulfur-containing compounds such as sulfur chloride, sulfur dichloride, thioline disulfide, alkylphenol disulfide, N,N'-dithiobis(hexahydro-2H-acridine-2-one), phosphorus-containing polysulfides, polymer polysulfides, and 2-(4'-thiolinyldithio)benzothiazole. Among these, sulfur can be preferably used. A crosslinking agent can be used individually by 1 type or in combination of 2 or more types.

The content of the crosslinking agent is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 3 parts by weight relative to 100 parts by weight of the nitrile group-containing conjugated diene copolymer in the latex for foam rubber. By making content of a crosslinking agent into the said range, the intensity|strength of the obtained foam rubber can be improved more.

Furthermore, the latex for foam rubber used in the present invention preferably further contains a crosslinking accelerator.

As the cross-linking accelerator, those commonly used in the manufacture of foam rubber can be used, for example: diethylene dithiocarbamic acid, dibutyldithiocarbamic acid, di(2-ethylhexyl) dithiocarbamic acid, dicyclohexyl dithiocarbamic acid, dibenzyl dithiocarbamic acid and other dithiocarbamic acids and their zinc salts; (2,4-Dinitrophenylsulfanyl)benzothiazole, 2-(2,6-dimethyl-4-thiolinylthio)benzothiazole, disulfide-4-thiolinyl-2-benzothiazole, 1,3-bis(2-benzothiazolylthiomethyl)urea, etc., but zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, and 2-mercaptobenzothiazole zinc are preferred. A crosslinking accelerator can be used individually by 1 type or in combination of 2 or more types.

The content of the crosslinking accelerator is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 4 parts by weight, based on 100 parts by weight of the nitrile group-containing conjugated diene-based copolymer in the latex for foam rubber. By making content of a crosslinking accelerator into the said range, the intensity|strength of the obtained foam rubber can be improved more.

Furthermore, the latex for foam rubber used in the present invention preferably contains zinc oxide.

The content of zinc oxide is not particularly limited, but is preferably 0.5 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the nitrile group-containing conjugated diene copolymer in the latex for foam rubber. By making content of zinc oxide into the said range, while making emulsification stability favorable, the intensity|strength of the foam rubber obtained can be improved more.

In the latex for foam rubber used in the present invention, anti-aging agents, colorants, foam stabilizers, etc. can be further blended as required, or dispersants (such as: NASF (sodium salt of naphthalenesulfonic acid formaldehyde condensate), etc.), thickeners (such as: polyacrylic acid and its sodium salts, sodium alginate, polyvinyl alcohol, etc.), surfactants used as foaming agents (such as aliphatic alkali soaps such as potassium oleate, sulfates of higher alcohols such as sodium lauryl sulfate, etc.) that can be used to stably disperse the above-mentioned various admixtures in the latex. ).

The method of mixing various admixtures with the latex for foam rubber is not particularly limited, but examples include a method of mixing various admixtures that are blended as necessary with the latex for foam rubber using a disperser such as a ball mill, kneader, or disperser after obtaining the latex for foam rubber as described above, or a method of mixing the aqueous dispersion into the latex for foam rubber after preparing an aqueous dispersion of blending components other than the latex for foam rubber using the above-mentioned disperser.

<foam rubber>

A foam rubber can be obtained by foaming and solidifying the above latex for foam rubber at a desired expansion ratio. Air is usually used for foaming, but carbonates such as ammonium carbonate and sodium bicarbonate; azo compounds such as azodicarbonamide and azobisisobutyronitrile; substances that generate gas such as benzenesulfonylhydrazine can also be used. In the case of using air, the latex for foam rubber can be stirred to entrain air to form foam. In this case, for example, an OAKES foam machine, an ultrasonic foam machine, a stand mixer, etc. can be used.

After foaming the latex for foam rubber, the foamed latex for rubber foam is solidified in order to fix the foamed state. As long as the coagulation method is a method that can gel the latex and make it solidify, well-known methods can be used in the past. For example, adding room temperature coagulants such as sodium hexafluorosilicate (sodium silicofluoride), potassium hexafluorosilicate (potassium silicofluoride), titanium fluoride sodium silicofluoride and other silicon fluoride compounds to the foamed latex for foam rubber. The heat-sensitive coagulation method of foamed latex for foam rubber; the freezing coagulation method, etc. have been used by people. The amount of coagulants such as room temperature coagulants and heat-sensitive coagulants is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of the nitrile group-containing conjugated diene copolymer in the latex for foam rubber.

Then, after adding a coagulant to the foamed latex for foam rubber, it is moved to a mold having a desired shape and solidified to obtain foam rubber. When a crosslinking agent is blended in the latex for foam rubber, it is preferable to heat and crosslink after coagulation. The conditions for cross-linking can be determined as follows: at a temperature preferably of 100-160° C., heat treatment for preferably 15-120 minutes is applied.

For the obtained foam rubber, it is preferable to wash it after taking it out from the mold. The washing method is not particularly limited, and for example, a washing machine or the like is used to agitate washing with water at about 20 to 70° C. for about 5 to 15 minutes. After cleaning, it is better to drain the water and dry at a temperature of about 30-90°C in a way that does not damage the touch of the foam rubber. The foam rubber obtained in this way, for example, can be sliced into a specified thickness, cut into a specified shape, and then ground with a grinding wheel to use as a powder puff (cosmetic sponge).

The foam rubber obtained by using the latex for foam rubber of the present invention can be used in various applications such as mattresses, powder puffs (cosmetic sponges), rollers, and shock absorbers. In particular, the foam rubber obtained by using the latex for foam rubber of the present invention can be suitably used as a puff (cosmetic sponge) for impregnating liquid cosmetics, etc., because it is "hard to deform and has little abrasion even when it is made to store liquid cosmetics containing ultraviolet absorbers such as octyl p-methoxycinnamate (ethylhexyl methoxycinnamate).

"Example"

Examples and comparative examples are given below to specifically illustrate the present invention. The following "parts" are based on weight unless otherwise noted. In addition, tests and evaluations were performed as follows.

[Content ratio of ethylenically unsaturated nitrile monomer unit]

According to JIS K6384, the nitrogen content in the nitrile group-containing conjugated diene copolymer is measured by the Kjeldahl method, and calculated accordingly.

[Volume Cumulative Particle Size]

The volume-based particle size distribution of the latex for foam rubber was measured using a light scattering and diffraction particle size measuring device (model "LS-13320", manufactured by Beckman Coulter). Based on the obtained volume-based particle size distribution, the cumulative volume particle size d10 and the cumulative volume particle size d50 are determined.

[Concentration of solid content]

Precisely weigh 2 g of the sample (weight: X2) on an aluminum pan (weight: X1), and dry it in a hot air dryer at 105°C for 2 hours. Then, after cooling in a desiccator, measure the weight together with the aluminum pan (weight: X3), and calculate the solid content concentration according to the following calculation formula. Solid content concentration (weight %)=(X3-X1)×100/X2

[Viscosity]

Using a viscometer (BII type viscometer (model name: BLII), manufactured by Toki Sangyo Co., Ltd.), the viscosity of latex for foam rubber was measured at a temperature of 25°C, a rotation speed of 60 rpm, and a rotation time of 60 seconds.

[handling]

Filter 100 g of latex for foam rubber through an 80-mesh wire mesh (200 cm ² ), and measure the filtration amount (the amount of latex passing through the wire mesh) when filtering for 5 minutes without applying pressure, and then evaluate it by the following criteria. A large amount of filtration means excellent latex handling properties (handling properties when latex is conveyed or when additives are blended). A: The filtration amount is more than 90 g. B: Filtration amount is 20-90 g. C: The filtration amount is less than 20 g.

[Formability]

Observe the conditions of foaming and vulcanization, and evaluate according to the following criteria. A: It can be formed. B-1: Formable but will shrink during vulcanization. B-2: Moldable but difficult to foam. C: Unable to form.

[Difficulty of deformation when foam rubber contains liquid cosmetics]

The foam rubber was punched into a cylindrical shape with a diameter of 3.3 cm and a thickness of 0.8 cm, and immersed in a liquid cosmetic (ANESSA (registered trademark) Perfect UV Aqua Booster, manufactured by Shiseido Co., Ltd.) at 23°C for 7 days, and the ratio of the diameter of the foam rubber after dipping to the diameter of the foam rubber before dipping was calculated (swelling rate (%) = (diameter of foam rubber after dipping) / (diameter of foam rubber before dipping) × 100), And evaluated by the following criteria. A: The swelling ratio is less than 110%. B: The swelling rate is 110 to 115%. C: The swelling rate exceeds 115%.

[Abrasion resistance when foam rubber contains liquid cosmetics]

Foam rubber was impregnated in liquid cosmetics (ANESSA (registered trademark) Perfect UV Aqua Booster, manufactured by Shiseido Co., Ltd.), and using a Martindale abrasion tester (STM633, manufactured by SATRA Co., Ltd.), the amount of abrasion was measured at a test temperature of 23°C, a load of 9 kPa, and a grinding wheel rotation number of 1000 times, and then evaluated according to the following criteria. A: The abrasion amount is less than 30%. B: The amount of wear is 30 to 35%. C: The abrasion amount is more than 35%.

[Example 1]

[Manufacture of latex]

Add 200 parts of water, 1.5 parts of potassium oleate, 55 parts of acrylonitrile, 0.5 parts of tertiary dodecanethiol, 0.03 parts of sodium hydroxymethanesulfinate, 0.003 parts of ferrous sulfate, and 0.008 parts of sodium edetate to a pressure-resistant reaction vessel, and add 25 parts of 1,3-butadiene after fully degassing.

Then, 0.05 part of cumyl hydroperoxide was added as a polymerization initiator, and emulsion polymerization was started at reaction temperature 5 degreeC. When the polymerization conversion rate reached 40%, 10 parts of 1,3-butadiene was added to continue the polymerization reaction. Next, when the polymerization conversion rate reached 60%, 10 parts of 1,3-butadiene was added to continue the polymerization reaction. When the polymerization conversion rate became 80%, a polymerization terminator solution composed of 0.25 parts of diethylphenidate and 5 parts of water was added to terminate the polymerization reaction to obtain an emulsion.

Subsequently, 80 parts of 1,3-butadiene was added as a solvent to the emulsion, and the temperature in the system was set to 15°C. Using a paddle-type stirring impeller, the rotation speed was 1,000 rpm and the stirring time was 5 hours. Under the condition of strong stirring, the particle size enlargement treatment was carried out. Subsequently, after removing 1,3-butadiene, concentration treatment was performed at 70° C. under a reduced pressure condition of −0.05 MPa (gauge pressure) to obtain latex. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 65% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

[Preparation of Latex Composition]

To 100 parts of nitrile group-containing conjugated diene copolymer in latex, add 4 parts of vulcanization-based aqueous dispersion (colloidal sulfur/dithiamine formate-based vulcanization accelerator Nocceler EZ (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)/thiazole-based vulcanization accelerator Nocceler MZ (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) = 2/1/1 (weight ratio), solid content concentration 50%) 4 parts, zinc oxide aqueous dispersion (solid content concentration 50%) 3 parts, foam stabilizer (TRIMENE BASE: manufactured by Crompton Corp.) 1 part, and fully dispersed to obtain a latex composition.

［Manufacture of foam rubber］

The latex composition was stirred with a vertical mixer (model "ESM945", manufactured by Electrolux Co., Ltd.) and foamed so as to increase in volume by about 5 times, then 1.5 parts of sodium silicofluoride aqueous dispersion (solid content concentration: 20% by weight) was added, and further stirred for 1 minute to obtain a foamed product.

Next, the obtained foam was poured into a molding mold (7 cm in diameter, 8 cm in height) and solidified, then heated at 110°C for 1 hour to vulcanize it, then removed from the mold, washed with water at 40°C for 10 minutes, dried in an oven at 60°C for 4 hours, and cut to a thickness of 0.8 cm in the height direction to obtain a disc-shaped foam rubber. For the obtained foam rubber, the degree of deformation when the foam rubber contains liquid cosmetics and the abrasion resistance when the foam rubber contains liquid cosmetics were evaluated according to the above-mentioned methods. In addition, the conditions from foaming to the end of vulcanization were confirmed, and then the formability was confirmed in accordance with the above-mentioned method. The results are disclosed in Table 1.

[Example 2]

According to the operation of Example 1, the emulsion was obtained. 3,000 parts of methanol were prepared, and the obtained emulsion was dropped thereinto to aggregate the nitrile group-containing conjugated diene-based copolymer into crumbs. Subsequently, the obtained pellets were washed with water and dried at 50° C. under reduced pressure, thereby obtaining a nitrile group-containing conjugated diene copolymer.

Subsequently, the obtained nitrile group-containing conjugated diene copolymer was mixed with methyl isobutyl ketone, and the temperature was raised to 60° C. while stirring to dissolve it, thereby obtaining a solution of the nitrile group-containing conjugated diene copolymer.

On the other hand, potassium oleate was mixed with water to obtain an aqueous emulsifier solution having a concentration of 1.0% by weight.

Next, the solution of the above-mentioned nitrile group-containing conjugated diene-based copolymer and the above-mentioned emulsifier aqueous solution were mixed at a weight ratio of 1:1 using a trade name: Multiline Mixer MS26-MMR-5.5L (manufactured by Satake Chemical Machinery Industry Co., Ltd.), and then using a trade name: MILDER MDN310 (manufactured by Pacific Kiko Co., Ltd.) and mixed and emulsified at 1500 rpm to obtain an emulsion.

Subsequently, the emulsion was heated to 80°C under a reduced pressure of -0.01 to -0.09 MPa (gauge pressure), and methyl isobutyl ketone was distilled off to obtain latex. Subsequently, under reduced pressure conditions of -0.05 MPa (gauge pressure), concentration treatment was carried out at 70° C. to obtain latex. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 64% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

And, compare the operation of Example 1 to obtain latex composition and foam rubber, and compare it with Example 1 to evaluate it. The results are disclosed in Table 1.

[Comparative Example 1]

Add 200 parts of water, 1.5 parts of potassium oleate, 38 parts of acrylonitrile, 0.5 parts of tertiary dodecanethiol, 0.03 parts of sodium hydroxymethanesulfinate, 0.003 parts of ferrous sulfate, and 0.008 parts of sodium edetate into a pressure-resistant reaction vessel, and add 45 parts of 1,3-butadiene and 17 parts of isoprene after fully degassing.

Then, 0.05 part of cumyl hydroperoxide was added as a polymerization initiator, and emulsion polymerization was started at reaction temperature 5 degreeC. When the polymerization conversion rate became 95%, a polymerization terminator solution composed of 0.25 parts of diethylphenidate and 5 parts of water was added to terminate the polymerization reaction to obtain an emulsion. Subsequently, according to the operation of Example 1, particle size enlargement treatment and concentration treatment were carried out to obtain latex. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 65% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

And, compare the operation of Example 1 to obtain latex composition and foam rubber, and compare it with Example 1 to evaluate it. The results are disclosed in Table 1.

[Example 3]

The latex obtained in Example 2 and the latex obtained in Comparative Example 1 were mixed so that the weight ratio of the nitrile group-containing conjugated diene-based copolymer contained in each latex was 1:1, and latex was obtained. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 65% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

And, compare the operation of Example 1 to obtain latex composition and foam rubber, and compare it with Example 1 to evaluate it. The results are disclosed in Table 1.

[Example 4]

By adding water to the latex obtained in Example 2, the solid content concentration was adjusted to 55% by weight. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 55% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

And, compare the operation of Example 1 to obtain latex composition and foam rubber, and compare it with Example 1 to evaluate it. The results are disclosed in Table 1.

[Comparative Example 2]

Add 200 parts of water, 1.5 parts of potassium oleate, 60 parts of acrylonitrile, 0.6 parts of tertiary dodecanethiol, 0.03 parts of sodium hydroxymethanesulfinate, 0.003 parts of ferrous sulfate, and 0.008 parts of sodium edetate into a pressure-resistant reaction vessel, and add 20 parts of 1,3-butadiene after fully degassing.

Then, 0.05 part of cumyl hydroperoxide was added as a polymerization initiator, and emulsion polymerization was started at reaction temperature 5 degreeC. When the polymerization conversion rate reached 40%, 10 parts of 1,3-butadiene was added to continue the polymerization reaction. Next, when the polymerization conversion rate reached 60%, 10 parts of 1,3-butadiene was added to continue the polymerization reaction. When the polymerization conversion rate became 80%, a polymerization terminator solution composed of 0.25 parts of diethylphenidate and 5 parts of water was added to terminate the polymerization reaction to obtain an emulsion.

Thereafter, after removing unreacted monomers from the obtained emulsion, the content ratio and volume cumulative particle diameter of the ethylenically unsaturated nitrile monomer units were measured according to the above method. Concentration was then carried out to obtain latex with a solid content concentration of 63%. Then, the handleability of the latex was evaluated. The results are disclosed in Table 1. In addition, although the viscosity of latex (solid content concentration: 63% by weight) was to be measured, it could not be measured because the viscosity was too high.

And, although intending to compare the operation of Example 1 to obtain the latex composition and shape the foam rubber, it cannot be shaped because the viscosity is too high.

[Comparative Example 3]

Add 200 parts of water, 1.5 parts of potassium oleate, 40 parts of acrylonitrile, 0.5 parts of tertiary dodecanethiol, 0.03 parts of sodium hydroxymethanesulfinate, 0.003 parts of ferrous sulfate, and 0.008 parts of sodium edetate into a pressure-resistant reaction vessel, and add 60 parts of 1,3-butadiene after fully degassing.

Then, 0.05 part of cumyl hydroperoxide was added as a polymerization initiator, and emulsion polymerization was started at reaction temperature 5 degreeC. When the polymerization conversion rate reached 95%, a polymerization terminator solution composed of 0.25 parts of diethylphene and 5 parts of water was added to terminate the polymerization reaction to obtain an emulsion.

Thereafter, after removing unreacted monomers from the obtained emulsion, 80 parts of 1,3-butadiene was added as a solvent, and the temperature in the system was set to 15°C, and stirred at 1,000 rpm for 5 hours using a paddle-type stirring impeller to perform particle size enlargement treatment. Subsequently, after removing 1,3-butadiene, concentration was carried out to obtain latex with a solid content concentration of 63%.

The latex obtained above and the latex obtained in Comparative Example 2 were mixed so that the weight ratio of the nitrile group-containing conjugated diene copolymer contained in each latex became 1:1, and latex was obtained. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 63% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

And, compare the operation of Example 1 to obtain latex composition and foam rubber, and compare it with Example 1 to evaluate it. The results are disclosed in Table 1.

[Comparative Example 4]

Except that the concentration of the emulsifier aqueous solution used was changed to 4.0% by weight, and the rotation speed of trade name: MILDER MDN310 (manufactured by Pacific Machinery Co., Ltd.) was changed to 5000 rpm, the operation was carried out as in Example 2 to obtain latex. Then, for the obtained latex, the content ratio of the ethylenically unsaturated nitrile monomer unit, the volume cumulative particle size, and the viscosity of the latex (solid content concentration: 65% by weight) were measured according to the above method, and the handleability of the latex was evaluated. The results are disclosed in Table 1.

And, compare the operation of Example 1 to obtain latex composition and foam rubber, and compare it with Example 1 to evaluate it. The results are disclosed in Table 1.

"Table 1"

As shown in Table 1, the latex for foam rubber containing the particles of "a nitrile group-containing conjugated diene copolymer containing ethylenically unsaturated nitrile monomer units in a proportion of 40 to 60% by weight, and having a cumulative volume particle diameter d10 of 130 nm or more in the particle size distribution based on volume" can produce foam rubbers that are excellent in handleability and formability, and are resistant to deformation and less abrasion even when cosmetics are contained therein (Examples 1 to 4). In addition, when the solid content concentration of the latex for foam rubber is 60% by weight or more, the latex for foam rubber has more excellent formability (Examples 1 to 3).

On the other hand, as the latex disclosed in Production Example 1 of International Patent Publication No. 2009/145009, if the content ratio of the ethylenically unsaturated nitrile monomer unit in the nitrile group-containing conjugated diene copolymer contained in the latex for foam rubber is less than 40% by weight, it is impossible to manufacture a foam rubber that is difficult to deform and wears little even when it is made to store cosmetics (comparative example 1).

In addition, as the latex disclosed in Production Example 4 or Example 4 of International Patent Publication No. 2009/145009, the latex for foam rubber containing particles whose volume cumulative particle diameter d10 is less than 130 nm in the volume-based particle size distribution has poor formability, and it is impossible to produce foam rubber that is difficult to deform and wears little even when it is made to contain cosmetics (Comparative Examples 2 to 4).

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Claims (7)

A latex for foam rubber, which is a latex for foam rubber containing particles of a nitrile-group-containing conjugated diene copolymer, wherein the nitrile-group-containing conjugated diene copolymer contains ethylenically unsaturated nitrile monomer units and conjugated diene monomer units, the content of the ethylenically unsaturated nitrile monomer units is 50 to 60% by weight, and the volume-cumulative particle diameter d10 of the particle size distribution on a volume basis is not less than 130 nm and not more than 250 nm. The latex for foam rubber as described in Claim 1, wherein the content ratio of the ethylenically unsaturated nitrile monomer unit is 45 to 55% by weight. The latex for foam rubber as claimed in Claim 1 or 2, wherein the volume-cumulative particle size d50 of the particles in the volume-based particle size distribution is 420 to 1500 nm. The latex for foam rubber according to claim 1 or 2, which has a solid content concentration of 60% by weight or more and 70% by weight or less. The latex for foam rubber as described in claim 1 or 2, wherein the viscosity is 3200mPa when measured with a B-type viscometer at a temperature of 25°C, a rotation speed of 60rpm, and a rotation time of 60 seconds. below s. The latex for foam rubber as described in claim 1 or 2, which further contains a crosslinking agent. A foam rubber obtained from the latex for foam rubber as described in any one of claims 1 to 6.