JP2014169404A - Method for producing copolymer latex, and copolymer latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing copolymer latex that can lower the production cost by recycling the oily mixture comprising unsaturated hydrocarbons when emulsion polymerizing 1,3-butadiene, acrylonitrile, and other monomers co-polymerizable therewith.SOLUTION: The method for producing copolymer latex includes emulsion polymerizing a monomer composition comprising 1,3-butadiene, acrylonitrile, and other monomers co-polymerizable therewith by feeding the oily mixture comprising unsaturated hydrocarbons obtained by distilling the copolymer latex finished with polymerization in the previous copolymer latex production, into the present emulsion polymerization system such that the proportion of 4-cyano cyclohexene coming from the oily mixture to the total amount of the monomer composition and the oily mixture comprising unused unsaturated hydrocarbons is 120 ppm or less.

Description

  The present invention relates to a method for producing a copolymer latex and a copolymer latex obtained by the method.

  Butadiene copolymer latex (copolymer latex based on 1,3-butadiene) is used as a binder in paper coating, carpet backsizing, wood adhesives, battery electrodes, tire cords, etc. Widely used.

  In the production of butadiene copolymer latex, hydrocarbons may be used in addition to monomers, emulsifiers, polymerization initiators, molecular weight modifiers, and the like.

  As a method for producing such a copolymer latex, for example, in JP-A No. 5-112604, in the emulsion polymerization of an aliphatic conjugated diene monomer and another monomer copolymerizable therewith, copolymerization is carried out. A method for polymerizing by adding a non-reactive branched alkane having 5 to 10 carbon atoms is disclosed.

  Japanese Patent No. 2961207 discloses a method of emulsion polymerization in the presence of a cyclic unsaturated hydrocarbon having an unsaturated bond in a ring selected from cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, and 1-methylcyclohexene. It is disclosed.

  Further, in Japanese Patent No. 2879121, an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, and other monomers copolymerizable therewith are chain-like having one unsaturated bond. A process for emulsion polymerization in the presence of an unsaturated hydrocarbon is disclosed.

Japanese Patent Laid-Open No. 5-112604 Japanese Patent No. 2961207 Japanese Patent No. 2879121

  In industrializing emulsion polymerization using hydrocarbons as described above, it is necessary to study methods for reducing production costs.

  Then, the objective of this invention is providing the manufacturing method of copolymer latex which can reduce manufacturing cost.

  The method for producing the copolymer latex of the present invention comprises a monomer composition containing 1,3-butadiene, acrylonitrile, and another monomer copolymerizable with 1,3-butadiene and acrylonitrile. A method for producing a copolymer latex in which emulsion polymerization is carried out in the presence of an unsaturated hydrocarbon having one saturated bond, obtained by distilling the copolymer latex after polymerization in the production of a previous copolymer latex. The ratio of 4-cyanocyclohexene derived from the oily mixture to the total amount of the monomer composition, the unused unsaturated hydrocarbon, and the oily mixture is determined as follows. It is characterized by blending in the emulsion polymerization system this time so that it becomes 120 ppm or less.

  The method for producing a copolymer latex of the present invention comprises a monomer composition containing 1,3-butadiene, acrylonitrile, and another monomer copolymerizable with 1,3-butadiene and acrylonitrile. A method for producing a copolymer latex in which emulsion polymerization is carried out in the presence of an unsaturated hydrocarbon having one unsaturated bond, wherein the post-polymerization copolymer latex is distilled in the previous production of the copolymer latex. The ratio of 4-cyanocyclohexene to the total amount of the monomer composition, the unused unsaturated hydrocarbon, and the oily mixture is 120 ppm or less. In addition, it is characterized by being blended in the emulsion polymerization system of this time.

  In the method for producing a copolymer latex of the present invention, it is preferable that the oily mixture is further distilled by being heated to a temperature at which the unsaturated hydrocarbon evaporates.

  In the method for producing a copolymer latex of the present invention, it is preferable that the unsaturated hydrocarbon is cyclohexene.

  The copolymer latex of the present invention is characterized by being produced by the above-described method for producing a copolymer latex.

  According to the method for producing a copolymer latex of the present invention, the production cost can be reduced by reusing unsaturated hydrocarbons as compared with the case where all of them use new unsaturated hydrocarbons.

  Moreover, according to the method for producing a copolymer latex of the present invention, a copolymer latex with few aggregates can be produced. In addition, the amount of unsaturated hydrocarbons discarded can be greatly reduced, and the environmental burden can be reduced.

  In the method for producing a copolymer latex of the present invention, a monomer composition containing 1,3-butadiene, acrylonitrile, and another monomer copolymerizable with 1,3-butadiene and acrylonitrile is used. Emulsion polymerization is performed in the presence of an unsaturated hydrocarbon having one saturated bond.

  1,3-butadiene is blended in the monomer composition in a proportion of, for example, 10% by mass or more, preferably 15% by mass or more, for example, 90% by mass or less, preferably 85% by mass or less. .

  The 1,3-butadiene may contain unreacted 1,3-butadiene recovered by distillation described later.

  Acrylonitrile is blended in the monomer composition in a proportion of, for example, 0.1% by mass or more, preferably 1% by mass or more, for example, 40% by mass or less, preferably 35% by mass or less.

  The acrylonitrile may include unreacted acrylonitrile recovered by distillation described later.

  Examples of other monomers copolymerizable with 1,3-butadiene and acrylonitrile (hereinafter referred to as other monomers) include, for example, alkenyl aromatic monomers, vinyl cyanide monomers other than acrylonitrile , Unsaturated carboxylic acid monomer, unsaturated carboxylic acid alkyl ester monomer, unsaturated monomer containing a hydroxyalkyl group, unsaturated carboxylic acid amide monomer, and the like.

  The other monomer is, for example, 9% by mass or more, preferably 14% by mass or more, for example, 89.9% by mass or less, preferably 84.9% by mass or less in the monomer composition. It is blended at a ratio of

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyl toluene, and divinylbenzene.

  Of these alkenyl aromatic monomers, styrene is preferable.

  Examples of the vinyl cyanide monomer include methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like.

  Examples of the unsaturated carboxylic acid monomer include monobasic acids such as acrylic acid, methacrylic acid, and crotonic acid, and dibasic acids (or anhydrides thereof) such as maleic acid, fumaric acid, and itaconic acid. It is done.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, Examples thereof include dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate and the like.

  Of these unsaturated carboxylic acid alkyl ester monomers, 2-ethylhexyl acrylate and methyl methacrylate are preferable.

  Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2- Examples include hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate and the like.

  Of these unsaturated monomers containing a hydroxyalkyl group, β-hydroxyethyl acrylate is preferable.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like.

  Of these unsaturated carboxylic acid amide monomers, acrylamide and methacrylamide are preferable.

  Furthermore, as other monomers, for example, monomers used in usual emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride can be used.

  These other monomers can be used alone (one type only) or in combination of two or more types. Of these other monomers, an unsaturated carboxylic acid monomer and an unsaturated carboxylic acid alkyl ester monomer are preferable.

  Examples of the unsaturated hydrocarbon having one unsaturated bond include cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, 1-methylcyclohexene, 1-pentene, 2-methyl-1-pentene, 1-hexene, 1-hexene, Examples include heptene, 2,4,4-trimethyl-1-pentene, and 1-octene.

  Of these unsaturated hydrocarbons, cyclohexene is preferable.

  These unsaturated hydrocarbons can be used alone (one kind only) or in combination of two or more kinds.

  Further, these unsaturated hydrocarbons can be recovered from the copolymer latex after the completion of the polymerization in the production of the copolymer latex and reused in the next and subsequent productions.

  In order to recover the unsaturated hydrocarbon after completion of the polymerization of the copolymer latex, it is recovered from the copolymer latex together with the remaining unreacted monomers and the like by a method such as distillation.

  The method for distilling the copolymer latex is not particularly limited, and a known method can be used. Preferably, steam distillation is performed at 50 to 100 ° C.

  Here, the oily mixture removed from the copolymer latex by distillation (hereinafter referred to as the oily mixture) is subjected to emulsion polymerization in addition to unsaturated hydrocarbons and volatile monomers. By-product 4-cyanocyclohexene (hereinafter abbreviated as 4CC) is included.

  To blend this oily mixture in the emulsion polymerization of 1,3-butadiene, acrylonitrile, and other monomers, the monomer composition and the unused unsaturated hydrocarbon (ie, the current unsaturated hydrocarbon) 4CC derived from the oily mixture with respect to the total amount of the unsaturated hydrocarbon (new unsaturated hydrocarbon) blended in the emulsion polymerization (excluding the unsaturated hydrocarbon in the oily mixture) and the oily mixture The proportion is blended so as to be, for example, 120 ppm or less, preferably 100 ppm or less, and more preferably 80 ppm or less.

  When 4CC exceeding the above upper limit is brought into the emulsion polymerization system, the amount of aggregates increases, the amount of deposits on the inner wall of the polymerization reactor increases, and the copolymer latex yield decreases. To do. Moreover, the tendency for the particle diameter of the obtained copolymer to become large is seen, and the reproducibility of superposition | polymerization deteriorates.

  As a method for controlling the amount of 4CC brought into the emulsion polymerization system in the polymerization for reusing the oily mixture, the amount of 4CC in the oily mixture is measured and the amount of 4CC brought into the emulsion polymerization system is calculated. It can be determined whether or not it can be reused as it is.

  At this time, the amount of 4CC contained in the unreacted 1,3-butadiene recovered by distillation used in the polymerization and the unreacted acrylonitrile recovered by distillation is also measured, and 4CC brought into the emulsion polymerization system. The amount is calculated and added to the 4CC amount brought into the emulsion polymerization system from the oily mixture.

  In addition, as a method of reducing 4CC brought into the emulsion polymerization system, for example, the oily mixture is further distilled by heating to a temperature at which the unsaturated hydrocarbon evaporates, and a distillate containing the unsaturated hydrocarbon (hereinafter, referred to as “an unsaturated hydrocarbon”). A method of using an oily mixture and a distillate, for example, a method of using a new unsaturated hydrocarbon in combination with at least one of an oily mixture and a distillate, etc. Can be mentioned. As for the distillate, similarly to the oily mixture described above, the amount of 4CC in the distillate is measured, the amount of 4CC brought into the polymerization system is calculated based on the amount used, and it is judged whether or not it can be reused.

  By reusing at least one of the oily mixture and the distillate, the amount of waste of the oily mixture containing unsaturated hydrocarbons can be greatly reduced.

  A known method can be applied as the emulsion polymerization method in the present invention. That is, the method for adding the monomer and other components is not particularly limited. In addition, any known method can be employed for the monomer addition method. In emulsion polymerization, known emulsifiers, polymerization initiators, chain transfer agents, electrolytes, chelating agents and the like can be used.

  Examples of the emulsifier include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalene sulfonic acid, Anionic surfactants such as sulfate ester salts of ionic surfactants, for example, nonionic surfactants such as alkyl ester type, alkyl phenyl ether type, and alkyl ether type of polyethylene glycol.

  These emulsifiers can be used alone (one kind only) or in combination of two or more kinds.

  Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, such as cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, and acetyl peroxide. Oil-soluble polymerization initiators such as oxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, for example, redox polymerization initiators can be used as appropriate.

  Of these polymerization initiators, potassium persulfate, sodium persulfate, cumene hydroperoxide, and t-butyl hydroperoxide are preferable.

  Examples of the chain transfer agent include alkyl mercaptans such as xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide, for example, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide, for example. 2,6-di-t-butyl-4-methylphenol, styrenated phenol and other phenolic compounds, for example, allyl compounds such as allyl alcohol, for example, halogenated carbonization such as dichloromethane, dibromomethane, carbon tetrabromide, etc. Hydrogen compounds such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, vinyl ethers such as α-benzyloxyacrylamide, such as triphenyl ether Emissions, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalate, 2-ethylhexyl thioglycolate, Tapinoren, such as α- methylstyrene dimer.

  These chain transfer agents can be used alone (one kind only) or in combination of two or more kinds.

  The particle diameter of the copolymer latex obtained by the method for producing the copolymer latex of the present invention is not particularly limited, and the average particle diameter by the photon correlation method is, for example, 50 nm or more, preferably 70 nm or more, for example, 300 nm. Hereinafter, it is preferably 270 nm or less. If the average particle diameter of the copolymer latex is less than the above lower limit, the viscosity of the copolymer latex becomes high and handling may be difficult, which is not preferable. When the average particle diameter of the copolymer latex is larger than the above upper limit, the surface area of the copolymer latex is decreased, and the adhesive force may be decreased, which is not preferable. The particle size of the copolymer latex can be adjusted by appropriately changing the various emulsifiers used in the polymerization of the copolymer latex, the type and amount of polymerization initiator used, the addition method, the proportion of polymerization water used, etc. is there.

  The gel content of the copolymer latex in the present invention is not particularly limited, but is, for example, 30% by mass or more, preferably 40% by mass or more, for example, 99% by mass or less, preferably 95% by mass or less. If the gel content is less than the above lower limit, the adhesive force tends to decrease, which is not preferable. The gel content is measured, for example, by the method of Examples described later.

  For the polymerization of the copolymer latex of the present invention, known oxygen scavengers, chelating agents, dispersants, antifoaming agents, anti-aging agents, preservatives, antibacterial agents, flame retardants, UV absorbers, etc., as necessary. These additives can also be used. These additives are not particularly limited in both types and amounts used, and can be used in appropriate amounts.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples. In the examples, parts and% indicating the mixing ratio are based on mass. Moreover, numerical values, such as a mixture ratio in an Example, can be substituted for the upper limit value or the lower limit value of the corresponding portion described in the above embodiment.

In this example, 1,3-butadiene and acrylonitrile, both containing no 4CC (less than 1 ppm) were used.
<Examples and Comparative Examples>
Example 1
As the first polymerization, in a pressure-resistant polymerization reactor equipped with a stirrer, 150 parts of polymerization water, 1.5 parts of sodium dodecylbenzenesulfonate, 1 part of potassium persulfate, monomers shown in the first stage of Table 1, t-Dodecyl mercaptan and cyclohexene were charged, and the temperature was raised to 70 ° C. Subsequently, the monomer shown in the second row of Table 1, t-dodecyl mercaptan, and cyclohexene were continuously added in 7 hours. Further, the polymerization was continued, and the polymerization was terminated when the polymerization conversion rate exceeded 98%.

  Next, the obtained polymer was adjusted to pH 7 with potassium hydroxide and subjected to steam distillation at 80 ° C. As a result, an oily mixture containing cyclohexene was separated from the obtained polymer to obtain a copolymer latex. Thereafter, a part of the separated oily mixture was distilled at 95 ° C. to obtain a distillate containing cyclohexene.

  The concentration of 4CC in the oily mixture and the concentration of 4CC in the distillate were measured by the following measuring method. Moreover, the average particle diameter and gel content of copolymer latex were measured by the following measuring method. The results are shown in Table 1.

  Thereafter, as the polymerization for reuse (reuse 1), a copolymer was prepared in the same manner as in the first polymerization except that the monomers shown in Table 1, t-dodecyl mercaptan, cyclohexene, oily mixture and distillate were charged. Latex was obtained.

  The average particle diameter and gel content of the obtained copolymer latex were measured by the following measuring method. The results are shown in Table 1.

  Separately, as the polymerization for reuse (reuse 2), the same procedure as in the first polymerization was carried out except that the monomers, t-dodecyl mercaptan, cyclohexene, oily mixture and distillate shown in Table 1 were charged. A polymer latex was obtained.

  The average particle diameter and gel content of the obtained copolymer latex were measured by the following measuring method. The results are shown in Table 1.

Examples 2-5 and Comparative Examples 1-3
As the first polymerization, the polymer obtained was treated with potassium hydroxide in the same manner as in Example 1 except that the blending amounts of the monomer, t-dodecyl mercaptan and cyclohexene were coated as shown in Table 1. The resulting mixture was adjusted to pH 7 and subjected to steam distillation at 80 ° C. to separate an oily mixture containing cyclohexene from the polymer to obtain a copolymer latex. A part of the separated oily mixture was distilled at 95 ° C. to obtain a distillate containing cyclohexene.

  The concentration of 4CC in the oily mixture and the concentration of 4CC in the distillate were measured by the following measuring method. Moreover, the average particle diameter and gel content of copolymer latex were measured by the following measuring method. The results are shown in Tables 1 and 2.

  Thereafter, a copolymer latex was obtained in the same manner as in the first polymerization, except that the monomers, t-dodecyl mercaptan, cyclohexene, oily mixture and distillate shown in Table 1 were charged as the polymerization for reuse.

The average particle size and gel content of the copolymer latex were measured by the following measuring methods. The results are shown in Tables 1 and 2.
<Evaluation methods for various physical properties>
1. Method for measuring 4CC content ratio of oily mixture or distillate As a gas chromatograph, GC-2014 type manufactured by Shimadzu Corporation was used.
(1) Preparation of sample The oily mixture or distillate of each Example and each comparative example was made into the measurement sample as it was.
(2) Gas chromatograph measurement conditions Sample volume: 1 μL
Detector: FID
Injection temperature: 170 ° C
Detector temperature: 250 ° C
Column: length / inner diameter / film thickness (liquid layer) = 30 m / 0.25 mm / 0.5 μm (DB-WAX)
Carrier gas: He 1 mL / min Split ratio: 1/40
Column temperature: After holding at 70 ° C. for 5 minutes, the temperature was raised to 170 ° C. at 10 ° C./minute, further raised to 230 ° C. at 20 ° C./minute, and held at 230 ° C. for 10 minutes.
(3) Quantitative method The retention time was confirmed using the sample which diluted 4CC with dimethylformamide. The sample was measured, and 4CC was quantified by the peak area appearing at the retention time of 4CC.

  In addition, also when measuring the 4CC content rate of the unreacted acrylonitrile recovered by distillation, the recovered acrylonitrile was quantified according to the above measurement conditions and the determination method using the recovered acrylonitrile as it was as a measurement sample.

The 4CC content ratio of unreacted butadiene recovered by distillation was quantified according to the same quantification method as described above using the recovered butadiene as it was as a measurement sample under the following gas chromatographic measurement conditions.
<Gas chromatographic measurement conditions for “1,3-butadiene”>
Sample volume: 0.5 μL
Detector: FID
Injection temperature: 250 ° C
Detector temperature: 250 ° C
Column: length / inner diameter / film thickness = 50 m / 0.53 mm / 50 μm (GS-ALUMINA 115-3552)
Carrier gas: He 6 mL / min Split ratio: 1/50
Column temperature: After holding at 45 ° C. for 3 minutes, the temperature was raised to 195 ° C. at 6 ° C./min and held at 195 ° C. for 15 minutes.
2. Method for Measuring Average Particle Diameter of Copolymer Latex The average particle diameter of the copolymer latex was measured as the average particle diameter by a photon correlation method by a dynamic light scattering method. In the measurement, FPAR-1000 (manufactured by Otsuka Electronics) was used.
3. Method for Measuring Gel Content of Copolymer Latex Copolymer latex is dried at 80 ° C. to produce a latex film. Thereafter, about 1 g of the latex film is weighed to obtain Xg. This is put into 400 ml of toluene and swelled and dissolved for 48 hours. Thereafter, this is filtered through a weighed 300-mesh stainless steel wire mesh, and then toluene is evaporated to dryness. After the drying, the mesh weight is subtracted, and the weight of the sample after drying is weighed to obtain Yg. The gel content was calculated from the following formula.

Gel content (%) = Y / X × 100
4). Method for Measuring Amount of Aggregate in Copolymer Latex After completion of polymerization and before steam distillation, 1 kg of copolymer latex was sampled and filtered through a 300 mesh wire mesh made of stainless steel. After drying the agglomerates remaining on the wire mesh, the weight was measured and the ratio to the sample (in terms of solid content) was determined to obtain the agglomerate generation rate. The incidence was evaluated in the following four stages.

    A: The aggregate generation rate is less than 0.01% (very small).

    ○: Aggregate generation rate is 0.01% or more and less than 0.02% (small).

    Δ: Aggregate generation rate is 0.02% or more and less than 0.05% (slightly more).

X: The aggregate generation rate is 0.05% or more (many).
5. Evaluation method of adhesion of coagulated substance on inner wall of polymerization reactor Polymer latex was polymerized in a 100 L pressure-resistant polymerization reactor, and the obtained copolymer latex was adjusted to pH 6 and then co-polymerized from the bottom of the polymerization reactor. The entire polymer latex was discharged.

  Thereafter, the polymerization reactor was filled with ion-exchanged water, and after stirring for 10 minutes, the entire amount of ion-exchanged water was discharged from the lower part of the polymerization reactor.

  After the ion-exchanged water discharge, the ratio of the solidified material to the inner wall of the polymerization reactor, that is, the area of the portion of the inner wall of the polymerization reactor to which the solidified material has adhered (S0) The ratio of S) was visually confirmed and evaluated based on the following evaluation criteria.

(Evaluation criteria)
○: S / S0 is less than 0.1.

    Δ: S / S0 is 0.1 or more and 0.3 or less.

    X: S / S0 is larger than 0.3.

Claims (5)

Presence of unsaturated hydrocarbon having one unsaturated bond, a monomer composition containing 1,3-butadiene, acrylonitrile, and other monomers copolymerizable with 1,3-butadiene and acrylonitrile A method for producing a copolymer latex that undergoes emulsion polymerization under
An oily mixture containing the unsaturated hydrocarbon obtained by distilling the copolymer latex after polymerization in the production of the copolymer latex is used as the monomer composition and the unused unsaturated hydrocarbon. And a mixture of the oily mixture and the oily mixture so that the ratio of 4-cyanocyclohexene derived from the oily mixture is 120 ppm or less. Method. Presence of unsaturated hydrocarbon having one unsaturated bond, a monomer composition containing 1,3-butadiene, acrylonitrile, and other monomers copolymerizable with 1,3-butadiene and acrylonitrile A method for producing a copolymer latex that undergoes emulsion polymerization under
An oily mixture containing the unsaturated hydrocarbon obtained by distilling the copolymer latex after polymerization in the production of the copolymer latex is used as the monomer composition and the unused unsaturated hydrocarbon. The method for producing a copolymer latex is characterized in that it is blended in the emulsion polymerization system so that the ratio of 4-cyanocyclohexene to the total amount of the oily mixture is 120 ppm or less.   The method for producing a copolymer latex according to claim 1 or 2, wherein the oily mixture is further distilled by being heated to a temperature at which the unsaturated hydrocarbon evaporates.   The method for producing a copolymer latex according to any one of claims 1 to 3, wherein the unsaturated hydrocarbon is cyclohexene.   A copolymer latex produced by the method for producing a copolymer latex according to any one of claims 1 to 4.