JP2009263588A - Copolymer latex for foam rubber, copolymer latex composition for foam rubber and foam rubber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide foam rubber which is excellent in oil resistance and is suitable as a cosmetic sponge (puff) having a soft feel. <P>SOLUTION: The copolymer rubber latex for foam rubber is obtained by emulsion polymerization of a monomer mixture composed of 45-60 wt.% ethylenically unsaturated monomer having a cyano group, 15-52 wt.% 1,3-butadiene, 3-40 wt.% isoprene and 0-30 wt.% another ethylenically unsaturated monomer copolymerizable with these monomers. The gel content of the copolymer rubber latex is ≤65 wt.%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a foam rubber suitable as a cosmetic sponge (puff) having excellent oil resistance and a soft touch, a copolymer rubber latex for the foam rubber, and a foam rubber containing the copolymer rubber latex The present invention relates to a copolymer rubber latex composition.

  Foam rubber (rubber foam) produced using a polymer rubber latex is used in various applications as a mattress, puff, roll, impact absorber and the like. Among the applications of foam rubber, especially for puffs, there is a demand for sponges that have good oil resistance to cosmetics and have a soft feel.

In order to impart oil resistance to the puff, acrylonitrile-butadiene copolymer rubber (NBR) latex has been conventionally used (for example, Patent Document 1).
Patent Document 2 discloses 15 to 45% by weight of a cyano group-containing ethylenically unsaturated monomer, 55 to 85% by weight of a conjugated diene monomer, and an ethylenically unsaturated monomer 0 that can be copolymerized therewith. It is a copolymer rubber latex obtained by emulsion polymerization of a monomer mixture consisting of ˜30% by weight, the conjugated diene monomer unit has a microstructure within a specific range, and a gel content of 20˜65%. A copolymer rubber latex for foam rubber containing a copolymer rubber in the% range is disclosed.
Further, Patent Document 3 discloses 10 to 50% by weight of vinyl cyanated monomer, 50 to 90% by weight of aliphatic conjugated diene monomer, and 0 to 20% by weight of other monomers copolymerizable therewith. There is disclosed a copolymer latex obtained by emulsion polymerization of a monomer mixture comprising: a copolymer latex for puff having a solid content concentration of 60% or more and a Mooney viscosity of 60 to 150.
Furthermore, Patent Document 4 discloses a puff using a mixture of NBR latex and EPDM latex that defines the ratio of EPDM, which is suitable for powder cosmetics containing polar oil.

JP-A-6-14811 JP-A-11-263847 JP 2006-181051 A JP 2007-89965 A

In recent years, as disclosed in Patent Document 4, the puff has been required to have excellent oil resistance, as compared with the conventional case. In order to improve oil resistance in the NBR latex, it is usually performed to increase the amount of a cyano group-containing ethylenically unsaturated monomer typified by acrylonitrile. However, according to the study by the present inventors, it is possible to improve the oil resistance by increasing the amount of the cyano group-containing ethylenically unsaturated monomer. It was found that it was difficult to satisfy the characteristics required as a puff.
In view of the above circumstances, the present inventors have intensively studied to provide a foam rubber suitable as a puff having good oil resistance and a soft feel. As a result, a co-polymer which uses a relatively large amount of a cyano group-containing ethylenically unsaturated monomer and uses a specific amount of 1,3-butadiene and isoprene, respectively, and controls the gel content within a specific range. It has been found that the object of the present invention can be achieved by using a combined rubber latex, and the present invention has been completed based on this finding.

Thus, according to the present invention, the cyano group-containing ethylenically unsaturated monomer is 45-60% by weight, 1,3-butadiene 15-52% by weight, isoprene 3-40% by weight, and other copolymerizable with these. It is a copolymer rubber latex obtained by emulsion polymerization of a monomer mixture comprising 0 to 30% by weight of an ethylenically unsaturated monomer, and the gel content of the copolymer rubber is 65% by weight or less. A featured rubber rubber copolymer rubber latex is provided.
Moreover, according to this invention, the copolymer rubber latex composition for foam rubbers containing the said copolymer rubber latex for foam rubbers and a vulcanizing agent is provided.
Furthermore, according to the present invention, there is provided a foam rubber obtained by foaming, coagulating and vulcanizing the above copolymer rubber latex composition for foam rubber.

  The copolymer rubber latex for foam rubber of the present invention comprises 45 to 60% by weight of a cyano group-containing ethylenically unsaturated monomer, 15 to 52% by weight of 1,3-butadiene, 3 to 40% by weight of isoprene, and A copolymer rubber latex obtained by emulsion polymerization of a monomer mixture comprising 0 to 30% by weight of another copolymerizable ethylenically unsaturated monomer, and the gel content of the copolymer rubber is 65% by weight. % Or less.

  Examples of the cyano group-containing unsaturated monomer used in the present invention include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-cyanoethyl acrylate, and the like. These can be used alone or in combination of two or more. Particularly preferred are acrylonitrile and methacrylonitrile. The amount of the cyano group-containing ethylenically unsaturated monomer used is 45 to 60% by weight in the monomer mixture. When the amount of the cyano group-containing ethylenically unsaturated monomer is small, the oil resistance is insufficient, and when the amount is large, the puff feel becomes hard and the texture becomes worse. Preferably it is 46 to 58 weight%, More preferably, it is 47 to 55 weight%.

In the present invention, 1,3-butadiene is used in the monomer mixture in an amount of 15 to 52% by weight, preferably 24 to 49% by weight, more preferably 33 to 43% by weight. If the amount of 1,3-butadiene used is small, the puff feel will be hard and the texture will be poor, and conversely if it is large, the oil resistance will be insufficient.

  In the present invention, 3-40% by weight, preferably 5-30% by weight, more preferably 10-20% by weight of isoprene (2-methyl-1,3-butadiene) is used in the monomer mixture. If the amount of isoprene used is small, the texture of the puff becomes hard and the texture becomes poor, and conversely if it is large, the oil resistance becomes insufficient.

In the present invention, in addition to the cyano group-containing ethylenically unsaturated monomer, 1,3-butadiene and isoprene, other ethylenically unsaturated monomers copolymerizable with these can be used.
Examples of such ethylenically unsaturated monomers include 1,3-butadiene such as 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and the like. Conjugated diene monomers other than isoprene; ethylenically unsaturated carboxylic acids such as (meth) acrylic acid, (anhydrous) maleic acid, fumaric acid, 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-n-butyl fumarate, mono- or di-n-butyl itaconic acid, etc. Mono- or dialkyl esters of the ethylenically unsaturated carboxylic acids; methoxy acrylate, eth Alkoxyalkyl esters of ethylenically unsaturated carboxylic acids such as acrylate and methoxyethoxyethyl acrylate; having hydroxyalkyl groups such as 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxybutyl (meth) acrylate (Meth) acrylate; Glycidyl (meth) acrylate; (Meth) acrylamide, N-methylol (meth) acrylamide, (meth) acrylic amide and derivatives thereof such as N-butoxymethyl (meth) acrylamide; dimethylaminomethyl acrylate, diethylamino Acrylate having amino group such as methyl acrylate; Aromatic vinyl monomer such as styrene, α-methyl styrene, vinyl toluene, chlorostyrene; Ethylene, propylene And non-conjugated diene monomers such as dicyclopentadiene and vinylnorbornene. These monomers can be used alone or in combination of two or more.
The amount of other ethylenically unsaturated monomers used is 30% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less. If the amount used is too large, the balance of characteristics required as a puff deteriorates.

The gel content of the copolymer rubber in the copolymer rubber latex for farm rubber of the present invention is 65% by weight or less, preferably 5 to 60% by weight, more preferably 10 to 55% by weight. When the gel content is high, the flexibility of the foam rubber is lowered. When this gel content is too low, the strength of the foam rubber tends to decrease. If the strength of the foam rubber is too low, chipping may occur when a cosmetic material or the like is scraped off as a puff.
In addition, gel content is defined by the methyl ethyl ketone insoluble matter mentioned later.

The foam rubber copolymer rubber latex of the present invention having such characteristics can be obtained by a usual emulsion polymerization technique, the gel content is the polymerization temperature, the polymerization conversion rate, the usage amount of the molecular weight modifier, etc. Can be adjusted.
As the polymerization agent such as an emulsifier (surfactant), a polymerization initiator, a chelating agent, an oxygen scavenger and a molecular weight modifier used for emulsion polymerization, conventionally known respective agents can be used and are not particularly limited. For example, as the emulsifier, an anionic and / or nonionic (nonionic) emulsifier is usually used. The emulsifier is usually used in the range of 0.5 to 5 parts by weight with respect to 100 parts by weight of the total monomers.

  Examples of the anionic emulsifier include fatty acid salts such as potassium beef tallow fatty acid, partially hydrogenated beef tallow fatty acid potassium, potassium oleate, sodium oleate; potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate Resin acid salts such as alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate. Examples of the nonionic emulsifier include a polyethylene glycol ester type, a polyethylene glycol ester type, and a pluronic type emulsifier such as a block copolymer of ethylene oxide and propylene oxide.

  Examples of the polymerization initiator include pyrolytic initiators such as persulfates such as potassium persulfate and ammonium persulfate; t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, octanoyl peroxide, Organic peroxides such as 3,5,5-trimethylhexanoyl peroxide; azo compounds such as azobisisobutyronitrile; redox initiators composed of these and reducing agents such as divalent iron ions It is done. Of these, redox initiators are preferred. The amount of these initiators used is usually in the range of 0.01 to 10 parts by weight with respect to 100 parts by weight of the total monomers.

Examples of the molecular weight regulator include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide, diisopropylxanthogendi Xanthogen compounds such as sulfide; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide; phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; Allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; α-benzyloxystyrene, α-ben Examples include diloxyacrylonitrile, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, α-methylstyrene dimer, terpinolene, and the like. 1 type, or 2 or more types can be used.
The amount of the molecular weight modifier used is preferably 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight, and particularly preferably 0.3 to 1.5 parts by weight with respect to 100 parts by weight of the total monomers. Part. If the amount used is small, the gel content tends to be high, whereas if it is too large, the strength of the foam rubber tends to decrease.

The emulsion polymerization reaction may be either a continuous type or a batch type, and the polymerization time is not particularly limited.
The method for adding the monomer is not particularly limited, and for example, a batch addition method, a divided addition method, or the like can be used. However, the monomer is used for polymerization because it is excellent in the balance between oil resistance and flexibility of the obtained foam rubber. A method of adding a part of 1,3-butanediene and / or isoprene to the reactor after starting the polymerization reaction and continuing the polymerization can be preferably employed.
In this case, after adding a cyano group-containing ethylenically unsaturated monomer and a part of 1,3-butanediene and / or isoprene to the reactor and starting the polymerization reaction, the polymerization reaction rate in the reactor is It is preferable to add the remainder of 1,3-butanediene and / or isoprene to the reactor in a batch of 20 to 65% and further continue the polymerization reaction.

The polymerization conversion rate when the polymerization is stopped is not particularly limited, but is preferably 70 to 90% by weight, and more preferably 75 to 85% by weight. If the polymerization conversion is too low, the productivity tends to decrease, whereas if it is too high, the gel content tends to increase.
Although superposition | polymerization temperature is not specifically limited, Preferably it is 0-50 degreeC, More preferably, it is 5-35 degreeC. If the polymerization temperature is too high, the gel content tends to increase.
After the polymerization, if necessary, after removing the unreacted monomer, it is preferable to perform a particle size enlargement treatment by a known method. By performing this particle size enlargement treatment, the solid content concentration of the copolymer latex can be increased to a range suitable for foam rubber.

Examples of the method for enlarging the particle size include a method in which the reaction is stopped in the middle of the polymerization and strongly stirred; a method in which a conjugated diene monomer such as butadiene, toluene, or the like is added as a solvent after the polymerization is completed; Examples thereof include a method in which a particle size thickening agent such as a polymer latex is added to the copolymer rubber latex and stirred.
After the particle size enlargement treatment, the solid content concentration is adjusted to an optimum range by a concentration operation. The solid content concentration of the copolymer latex for foam rubber of the present invention is preferably in the range of 55 to 75% by weight, and preferably in the range of 60 to 70% by weight. If the solid content concentration is too low, bubble roughness tends to occur and the appearance tends to deteriorate, and it is difficult to increase the solid content concentration beyond the above range.
The weight average particle diameter of the copolymer latex for foam rubber is not particularly limited, but is usually about 300 to 3000 nm, preferably about 400 to 2000 nm.

The foam rubber copolymer rubber latex composition of the present invention comprises the foam rubber copolymer rubber latex and a vulcanizing agent.
As the vulcanizing agent, any vulcanizing system used for producing ordinary foam rubber using a polymer rubber latex can be used, and is not particularly limited. As the vulcanization system, for example, sulfur as a vulcanizing agent, particularly colloidal sulfur, zinc oxide / various vulcanization accelerators as a vulcanization aid are used. Examples of the vulcanization accelerator include 2-mercaptobenzothiazole and its zinc salt, a thiazole accelerator such as dibenzothiazyl disulfide, and a dithiocarbamate accelerator such as zinc diethyldithiocarbamate. The amount of these vulcanizing agents and vulcanizing aids used is not particularly limited, but usually 0.1 to 10 parts by weight of sulfur and 0. 10% of zinc oxide with respect to 100 parts by weight of copolymer rubber latex (solid content). It is about 5 to 10 parts by weight and about 0.1 to 5 parts by weight of the vulcanization accelerator. These usage amounts are determined so as to satisfy the required performance of the foam rubber.

  Examples of compounding agents used as necessary include anti-aging agents, colorants, foam stabilizers, and the like, and dispersants for stably dispersing the above-mentioned various compounding agents in latex, such as NASF (naphthalenesulfonic acid). Sodium salt of formalin condensate), etc .; thickeners such as polyacrylic acid and sodium salts thereof, sodium alginate, polyvinyl alcohol, etc .; surfactants as foaming agents such as aliphatic alkali soaps such as potassium oleate A necessary effective amount of sulfate of higher alcohol such as sodium dodecyl sulfate can be used. The following coagulants are used.

The foam rubber of the present invention can be obtained by foaming, coagulating and vulcanizing the above copolymer rubber latex composition for foam rubber.
Although air is usually used for foaming, carbonates such as ammonium carbonate and sodium bicarbonate; azo compounds such as azodicarboxylic acid amide and azobisisobutyronitrile; and gas generating substances such as benzenesulfonyl hydrazide can also be used. In the case of using air, the copolymer rubber latex is agitated, and air is entrained and foamed. At this time, for example, an Oaks foaming machine, an ultrasonic foaming machine or the like is used.
Foaming is performed at a predetermined foaming ratio, and then the foamed latex composition is coagulated in order to fix the foamed state. The coagulation method is not particularly limited as long as the latex can be gelled and solidified, and any conventionally known method can be used. For example, the Dunlop method (room temperature coagulation method) added to the latex composition obtained by foaming a silicon fluoride compound such as sodium hexafluorosilicate, potassium (sodium fluorosilicate, potassium), titanium silicofluoride, etc. as a coagulant ); A thermal coagulation method in which a thermal coagulant such as organopolysiloxane, polyvinyl methyl ether, zinc ammonium sulfate complex salt or the like is added to the foamed latex composition; a freeze coagulation method or the like is used. Although the usage-amount of a coagulant is not specifically limited, Usually, it is about 0.5-10 weight part with respect to 100 weight part of this latex composition (solid content).

  By transferring the foamed latex composition still having fluidity to which a coagulant has been added to a mold having a predetermined shape and coagulating, for example, by vulcanizing at a temperature of about 100 to 160 ° C. for about 15 to 60 minutes. Foam rubber is obtained. The foam rubber is taken out from the mold and washed with stirring at about 20 to 70 ° C. for about 5 to 15 minutes using, for example, a washing machine. After washing, drain water and dry at a temperature of about 30 to 90 ° C. so as not to impair the texture of the foam rubber. For example, the foam rubber thus obtained is sliced to a predetermined thickness, cut into a predetermined shape, and then the side surface is polished with a rotating grindstone to produce a cosmetic sponge, that is, a puff.

  The foam rubber of the present invention has excellent oil resistance and a good texture, and is particularly suitable for puffs. The oil resistance (according to the method described in Examples) of the foam rubber of the present invention is preferably 40% or less, more preferably 35% or less. The texture of the foam rubber of the present invention is related to the hardness (Asker F-type hardness). The lower the hardness is, the softer it is, and the preferable hardness is 65 (degrees) or less, more preferably 60 (degrees) or less. is there.

Next, the present invention will be described more specifically with reference to examples and comparative examples. Parts and% in the following examples are based on weight unless otherwise specified.
The evaluation method is shown below.

(Measurement of insoluble methyl ethyl ketone (%))
The copolymer latex was poured onto a glass plate kept horizontally and dried in a constant temperature and humidity chamber at a temperature of 23 ° C. and a humidity of 50% for 48 hours to prepare a dry film having a thickness of about 0.5 mm. A part of this was cut into a strip of about 2 mm × 2 mm, weighed about 0.25 g, placed in an 80 mesh wire net, and the weight of the test film was precisely weighed (WB). The wire mesh containing the test film is immersed in a beaker containing 80 ml of methyl ethyl ketone and left to stand for 48 hours in the temperature and humidity chamber. Thereafter, the wire mesh was taken out, dried, and precisely weighed to determine the weight (WA) of components insoluble in methyl ethyl ketone. From these, the methyl ethyl ketone insoluble matter is determined based on the following formula.
Methyl ethyl ketone insoluble matter (%) = (WA / WB) × 100

(Density of foam rubber (g / cm ³ ))
A plate-like foam rubber having a thickness of 0.8 cm is punched into a circle having a diameter of about 38 mm, its weight is measured, and the density is determined from the volume of the test piece and its weight.
(F hardness of foam rubber (degree))
The hardness of the foam rubber was measured using an Asker rubber hardness meter F type (manufactured by Kobunshi Keiki Co., Ltd.). The lower the value, the softer the foam rubber and the better the touch.
(Oil resistance of foam rubber (%))
A test piece obtained by punching a plate-like foam rubber having a thickness of 0.8 cm into a circle having a diameter of about 38 mm is immersed in 100 ml of toluene at 23 ° C. for 1 hour. Thereafter, the test piece was taken out, the diameter was measured, and the linear expansion degree (%) was determined by the following formula.
Linear expansion (%) = [(L′−L) / L] × 100
(L: Diameter before immersion L ′: Diameter after immersion)
The smaller the value of the linear expansion, the better the oil resistance of the foam rubber.

(Form rubber texture)
The texture of the foam rubber was inspected sensuously and evaluated in three stages.
○: The texture is soft and excellent in elasticity.
Δ: Soft texture but slightly inferior in elasticity.
X: The texture is hard and the elasticity is insufficient.
(Appearance of foam rubber)
Foam rubber foam uniformity was visually observed and evaluated in three stages.
○: Uniform.
Δ: There are non-uniform portions.
X: A nonuniform part is conspicuous.

Example 1
(Production of copolymer latex A)
In a pressure-resistant reaction vessel, water 200 parts, potassium oleate 1.5 parts, acrylonitrile 52 parts, t-dodecyl mercaptan 0.5 parts, sodium formaldehyde sulfoxylate 0.03 parts, ferrous sulfate 0.003 parts, Ethylenediaminetetraacetic acid / Natrilum 0.008 part was added, and after sufficient deaeration, 18 parts of 1,3-butadiene and 10 parts of isoprene were added.
Subsequently, 0.05 part of cumene hydroperoxide was added as a polymerization initiator, and emulsion polymerization was started at a reaction temperature of 5 ° C.
When the polymerization conversion rate reached 40%, 10 parts of 1,3-butadiene was added and the polymerization reaction was continued. Furthermore, when the polymerization conversion rate reached 60%, 10 parts of 1,3-butadiene was added and the polymerization reaction was continued.
When the polymerization conversion reached 80%, a polymerization stopper solution consisting of 0.25 part of diethylhydroxyamine and 5 parts of water was added to stop the polymerization reaction.
After removing the unreacted monomer, 80 parts of 1,3-butadiene was added, the temperature in the system was set to 15 ° C., and the mixture was stirred for 5 hours at a rotation speed of 1,000 rpm using a paddle type stirring blade. The particle size enlargement process was performed. Subsequently, 1,3-butadiene was removed and then concentrated to obtain a copolymer latex A having a solid concentration of 62%.
The methyl ethyl ketone insoluble content of copolymer latex A was measured, and the results are shown in Table 1.

(Production of foam rubber)
For 100 parts solids of copolymer latex A, vulcanized aqueous dispersion (colloidal sulfur / dithiocarbamate vulcanization accelerator Noxeller EZ (manufactured by Ouchi Shinsei Chemical Co., Ltd.) / Thiazole vulcanization acceleration Agent Noxeller MZ (Ouchi Shinsei Chemical Co., Ltd.) = 2/1/1 (weight ratio): solid content concentration 50%) 4 parts, zinc oxide aqueous dispersion (solid content concentration 50%) 3 parts, bubble stability 1 part of an agent (trimene base: manufactured by Crompton Corp) was added and sufficiently dispersed to obtain a copolymer latex composition for foam rubber.
The latex composition was stirred using a stand mixer (ESM945 manufactured by Electrolux Co., Ltd.) and foamed to a volume of about 5 times, and then an aqueous dispersion of sodium silicofluoride (solid content concentration 20%). 5 parts were added and further stirred for 1 minute.
The foamed product was poured into a molding form (diameter 7 cm, height 8 cm), solidified, and then vulcanized at 110 ° C. for 1 hour to obtain a foam rubber.
The foam rubber taken out from the mold was washed with hot water at 40 ° C. for 10 minutes, dried in an oven at 60 ° C. for 4 hours, and then cut into a disk shape so that the thickness was 0.8 cm in the length direction.
The properties of the foam rubber were measured and the results are shown in Table 1.

(Examples 2-3 and Comparative Examples 1-4)
Copolymer latexes B to G were obtained in the same manner as in Example 1 except that the polymerization recipe was changed as shown in Table 1. Methyl ethyl ketone insoluble matter was measured, and the results are shown in Table 1.
A farm rubber was produced in the same manner as in Example 1 except that the copolymer latexes B to G were used in place of the copolymer latex A. The properties of the obtained foam rubber were evaluated, and the results are shown in Table 1.

(Comparative Example 5)
Copolymer latex H was prepared in the same manner as in Example 1 except that the polymerization prescription (monomer composition and polymerization conversion rate when polymerization was stopped) shown in Table 1 was carried out so that the solid concentration was 65%. Got. Methyl ethyl ketone insoluble matter was measured, and the results are shown in Table 1.
A foam rubber was produced in the same manner as in Example 1 except that the copolymer latex H was used in place of the copolymer latex A. The properties of the obtained foam rubber were evaluated, and the results are shown in Table 1.

Table 1 shows the following.
Foam rubber produced from copolymer latexes D and E that do not use isoprene has high hardness and is slightly inferior in texture (Comparative Examples 1 and 2).
The foam rubber produced from the copolymer latex F having a large amount of acrylonitrile is high in hardness, inferior in its texture and in appearance (Comparative Example 3).
The foam rubber produced from the copolymer latex G having a high gel content has high hardness, is inferior in its texture, and is also deteriorated in appearance (Comparative Example 4).
The foam rubber produced from the copolymer latex H with a small amount of acrylonitrile used is inferior in oil resistance (Comparative Example 5).
The foam rubber produced from the copolymer latexes A to C in the range specified in the present invention is superior in oil resistance, has a low hardness, and has a soft feel as compared with the comparative example. ) Is a suitable foam rubber (Examples 1 to 3).

Claims (3)

Cyano group-containing ethylenically unsaturated monomer 45-60 wt%, 1,3-butadiene 15-52 wt%, isoprene 3-40 wt%, and other ethylenically unsaturated monomers copolymerizable therewith A copolymer rubber latex obtained by emulsion polymerization of a monomer mixture comprising 0 to 30% by weight, wherein the copolymer rubber has a gel content of 65% by weight or less. Polymer rubber latex. A copolymer rubber latex composition for foam rubber comprising the copolymer rubber latex for foam rubber according to claim 1 and a vulcanizing agent. A foam rubber obtained by foaming, solidifying and vulcanizing the copolymer rubber latex composition for foam rubber according to claim 2.