JPH03273005A - Production of copolymer latex - Google Patents

Abstract

PURPOSE:To obtain the title latex improved in the balance among pick strength and other properties, adhesiveness, etc., by emulsion-polymerizing a conjugated diene with an ethylenically unsaturated carboxylic acid and other copolymerizable monomers in the presence of a specified chain transfer agent. CONSTITUTION:100 pts.wt. monomer mixture comprising 20-90wt.% coujugated diene, 0.1-20wt.% ethylenically unsaturated monomer and 0-79.9wt.% other monomers copolymerizable therewith is emulsion-polymerized in the presence of 0.05-10.0 pts.wt. chain transfer agent comprising a thioalkylcarboxylic acid alkyl ester of the formula (wherein HS-R1 is 2-6C thioalkyl; and R2 is 1-18C alkyl), a surfactant, a radical polymerization initiator, etc., in water to obtain the title latex of a particle diameter of 0.05-1mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention provides a novel product for use in paper coating, carpet backing, fiber bonding, or adhesives. The present invention relates to a method for producing a combined latex.

[Conventional technology]

Conventionally, synthetic copolymer latex has been widely used, for example, as a binder for paper coating, a binder for carpet puncture sizing, a binder for binding fibers such as nonwoven fabrics and artificial leather, and adhesives for various materials. R7: When a copolymer latex is used for such purposes, it is required to have high adhesive strength and excellent water resistance, blistering resistance due to dry heating, and the like.

For example, coated paper uses pigments such as kaolin clay, calcium carbonate, satin white, talc, and titanium oxide on the surface of the base paper to improve the paper's printability and optical properties such as gloss. These coatings are coated with copolymer latex as a binder and paints containing water-soluble polymers such as starch, polyvinyl alcohol, and carboxymethyl cellulose as water-retaining agents or auxiliary binders, and conventionally styrene Styrene-butadiene copolymer latex, so-called SB latex, which is obtained by emulsion polymerization of and butadiene as main monomer components, is commonly used.

Incidentally, in recent years, the production of coated paper has increased significantly as demand for color-printed magazines, pamphlets, and advertisements has increased. In particular, with the trend toward higher speed printing in offset printing, the quality requirements for coated paper and pigment binders are becoming increasingly sophisticated. There is a strong need for improvement. Moreover, since this shock strength performance has a negative correlation with other print properties, such as wet shock strength, blister resistance, halftone dot reproducibility, etc., improvements are needed to balance these physical properties to a high level. is required even more.

Since these properties of coated paper are particularly strongly dependent on the design of the SB latex used as a pigment binder, various studies have been made on the performance of the SB latex.

For example, it has been confirmed that the proportion of the insoluble portion of the copolymer Latinx film in solvents such as benzene, toluene, and tetrahydrofuran is the controlling factor for pink strength and blister resistance. Specifically, it has been proposed that excellent performance can be achieved by adjusting the composition and gel fraction of the copolymer in latex to a specific range (Japanese Patent Publication No. 59-3598). Publication, Japanese Patent Publication No. 60-17879, Japanese Patent Publication No. 58-4894). The gel fraction of this latex changes depending on various polymerization factors such as monomer composition and polymerization temperature, but it is common and convenient to add a chain transfer agent to adjust it to the desired level. be. Conventionally, halogenated hydrocarbons such as carbon tetrachloride, t- or n-
Alkyl mercaptans such as dodecyl mercaptan, Sulfy-F, and the like have been used.

L7 However, in -tC, in SB latex, the coated paper's Bic strength is highest when its gel fraction is in the range of 75 to 95% by weight, whereas the blister resistance is determined by its gel fraction. It has been recognized that the lower the viscosity, the better the blister resistance, and none of the above-mentioned techniques have been fully satisfactory for simultaneously improving both pink strength and blister resistance to a high level.

Furthermore, since the optimal butadiene unit fraction for wet shock strength in offset printing is 34% by weight or less, which is different from the optimal butadiene unit fraction for dry shock strength, both of these physical properties must be at a high level at the same time. That was difficult.

As described above, as long as conventional chain transfer agents are used, there is a limit to how SB latex for offset printing paper can be improved in its blister resistance and shock strength balance, as well as its wet shock strength and dry shock strength balance.

On the other hand, for gravure printing paper, good halftone dot reproducibility and super calendar stain resistance during coated paper production are particularly important. Although binders with good reproducibility have been disclosed, they are designed with a high butadiene unit fraction, which inevitably leads to a decrease in supercalendar stain resistance. As long as conventional chain transfer agents are used, the appropriate balance between halftone dot reproducibility and resistance to spar calendar staining has not been improved to a sufficiently satisfactory level.

On the other hand, the adhesive for carpet bank sizing is a composition in which -C is blended with a copolymer latex, a filler such as calcium carbonate or aluminum hydroxide, and other additives such as a thickener. This adhesive composition is used in the manufacture of tufted carpets, needle punch carpets, etc., mainly to prevent piles from falling off and to bond with secondary base fabrics such as jute. Therefore, in this case, improving adhesive strength, which is the most important physical property of carpet, is one of the biggest technical challenges in this industry, and therefore improvements are being considered from the aspect of blending copolymer latex and compositions. However, since conventional chain transfer agents are still used, the reality is that products of a satisfactory level have not been obtained so far.

On the other hand, adhesives have traditionally been manufactured by dissolving natural rubber, synthetic rubber, etc. in an organic solvent, coating it on a base material, and then evaporating the organic solvent. Due to the above problems, there is increasing momentum to use polymer aqueous dispersions (latex) using water as a dispersion medium, and aqueous dispersions of rubber-tackifying resin combinations are being developed (Japanese Patent Publication No. 57-28545, JP-A-55-48270, JP-A-58-160378, JP-A-581.
83771). The aqueous dispersion containing this synthetic rubber latex and tackifier resin exhibits good adhesive properties at a measurement temperature of 20 to 23°C, but a satisfactory value for adhesive strength at a temperature of 0°C. It has not been done. In addition, it has been proposed that adhesive properties can be obtained only by using rubber latex polymers (Japanese Patent Laid-Open No. 1986-1999-1).
145909, Japanese Patent Application Laid-Open No. 57-57707)
. However, this material has the drawback of extremely low adhesion to polyethylene. As described above, as long as the chain transfer agent is used, it has been difficult to improve the balance between high-temperature cohesive strength, low-temperature adhesive strength, and polyethylene adhesiveness.

[Problem to be solved by the invention]

As described above, the conventional technology using conventional chain transfer agents cannot cope with the further increase in printing speed of coated paper, and it is necessary to use chain transfer agents as a binder to enable the production of high-quality coated paper. At present, there is a strong demand for the emergence of polymer latex. Furthermore, copolymer latexes with high adhesive strength are similarly desired for carpets and adhesives.

Furthermore, some conventional chain transfer agents remain in large amounts after the polymerization reaction, requiring troublesome recovery operations.

[Means to solve the problem]

Under these circumstances, the present inventors have developed a method to further improve the balance between bulk strength and other properties in coated printing paper, as well as the adhesive strength of carpent bank sizing and adhesives. As a result of various studies conducted in 2 with the aim of providing a high-performance copolymer latex, a copolymer latex obtained using a thioalkylcarboxylic acid alkyl ester as a chain transfer agent surprisingly met the above purpose. This was done after discovering that this could be achieved.

That is, the present invention relates to conjugated dienes, ethylenically unsaturated carboxylic acids, and the like! In a method of synthesizing a latex by emulsion polymerization from other monomers that can be synthesized and a chain transfer agent, the chain transfer agent is used as the following formula % (where HS-R is a thioalkyl group having 2 to 6 carbon atoms). R2 represents an alkyl group having 1 to 18 carbon atoms.

The present invention will be explained in detail below.

The method for adjusting the gel fraction of latex to the desired level is as follows:
Addition of a chain transfer agent is common and simple, but in the emulsion polymerization for preparing the copolymer latex of the present invention, the following formula % formula % [1 (However, HS-R, 2 to 6 carbon atoms) R2 represents an alkyl group having 1 to 18 carbon atoms. Examples include methyl thiopropionate, ethyl thiopropionate, propyl thiopropionate, butyl thiopropionate, pentyl thiopropionate, hexyl thiopropionate, hebutyl thiopropionate, octyl thiopropionate, and thiopropionate. Nonyl thiopropionate, decyl thiopropionate, thiopropionate tundane, dodecyl thiopropionate,
tridecyl thiopropionate, tetradecyl thiopropionate, pentadecyl thiopropionate, hexadecyl thiopropionate, heptadecyl thiopropionate, octadecyl thiopropionate, methyl thiobutanoate, ethyl thiobutanoate, propyl thiobutanoate, butyl thiobutanoate, pentyl thiobutanoate, Hexyl thiobutanoate, heptyl thiobutanoate, octyl thiobutanoate, nonyl thiobutanoate, decyl thiobutanoate, undecyl thiobutanoate, dodecyl thiobutanoate, tridecyl thiobutanoate, tetradecyl thiobutanoate, pentadecyl thiobutanoate, hexadecyl thiobutanoate, heptadecyl thiobutanoate, thiobutanoic acid Octadecyl, methyl thiopencunnate, ethyl thiopentanoate, propyl thiopentanoate, butyl thiopencunate, pentyl thiopentanoate, hexyl thiopencunate, heptyl thiopencunate,
Octyl thiopentanoate, nonyl thiopentanoate, decyl thiobencunate, undecyl thiopentanoate, dodecyl thiopencunate, tridecyl thiopencunate, tetradecyl thiobencunate, pentadecyl thiobencunate,
Hexadecyl thiobencunate, heptadecyl thiopencunate, octadecyl thiopencunate, methyl thiohexanoate, ethyl thiohexanoate, propyl thiohexanoate, butyl thiohexanoate, pentyl thiohexanoate, hexyl thiohexanoate, hebutyl thiohexanoate, octyl thiohexanoate, nonyl thiohexanoate, thiohexane Decyl thiohexanoate, undecyl thiohexanoate, dodecyl thiohexanoate, tridecyl thiohexanoate, tetradecyl thiohexanoate, pentadecyl thiohexanoate, hexadecyl thiohexanoate, heptadecyl thiohexanoate, octadecyl thiohexanoate, methyl thiohexanoate, ethyl thiohexanoate, thiohexanoate Propyl thiohebutanoate, butyl thiohebutanoate, pentyl thiohebutanoate, hexyl thiohebutanoate, hebutyl thiohebutanoate, octyl thiohebutanoate, nonyl thiohebutanoate, decyl thiohebutanoate, thiohebutanoic acid These include undecyl, dodecyl thiohetanoate, tridecyl thiohetanoate, tetradecyl thioheptanoate, pentadecyl thioheptanoate, hexadecyl thioheptanoate, heptadecyl thiohetanoate, octadecyl thioheptanoate, and the like. The thioalkyl carboxylic acid alkyl ester is preferably used in an amount of 0.05 to 10.0 parts by weight, more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the monomer! Department. Moreover, this thioalkyl carboxylic acid alkyl ester can also be used in combination with other well-known chain transfer agents. Examples of other chain transfer agents include t-dodecyl mercaptan,
Mention may be made of mercaptans such as n-dodecylmercaptan, mercaptoethanol, halogenated hydrocarbons such as terpinolene, dipentene, t-terpinene and carbon tetrachloride. Furthermore, any known method can be used for using the chain transfer agent. Namely, these include a pre-batch addition method, a continuous addition addition method, an intermittent addition addition method, and a concentration gradient addition method in which the addition rate is sequentially changed.

Latex polymers are obtained by emulsion polymerization of monomers composed of conjugated dienes, ethylenically unsaturated carboxylic acids, and other monomers copolymerizable with these.

The conjugated diene and L7 used in the present invention include butadiene, isoprene, 2-chloro-1,3-butadiene, etc., and the preferable amount used is 20 to 90 parts by weight based on the total monomers! % range. In the case of a copolymer latex for coated paper, a more preferable amount of this conjugated diene is 28 to 70 parts by weight! %.

As the ethylenically unsaturated carboxylic acid used in the present invention,
Examples include monobasic carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, dibasic carboxylic acids such as itaconic acid, maleic acid, and fumaric acid, and monoesters thereof.

The preferred amount of ethylenically unsaturated carboxylic acid used is 0.1
~20% by weight, more preferably used amount is 0.5~20% by weight
It is in the range of 10% by weight.

The most typical and effective other monomers used in the present invention are aromatic (di)vinyl compounds,
Next, there are (meth)acrylic acid esters, vinyl cyanide compounds, ethylenic amide monomers, and the like.

Examples of aromatic (di)vinyl compounds include styrene, α-methylstyrene, chlorostyrene, alkylstyrene, divinylhenzene, and the like.

As (meth)acrylic acid ester, methyl (meth)
Acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate,
Examples include 2-ethylhexyl (meth)acrylate, hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, and ethylene glycol di(meth)acrylate.

Examples of vinyl cyanide compounds include acrylonitrile and methacrylonitrile.

Examples of the ethylenic amide monomer include (meth)acrylamide and N-methylol (meth)acrylamide.

Furthermore, other monomers include vinyl esters such as vinyl acetate, vinyl chloride, vinyl halides such as vinylidene chloride, aminoethyl (meth)acrylate,
Ethylenic amine monomers such as dimethylamine ethyl (meth)acrylate and diethylaminoethyl (meth)acrylate, and sodium styrene sulfonate can also be used. The preferred usage amount of these is 0 to 79.9
Parts by weight.

The copolymer latex of the present invention can be produced by conventional emulsion polymerization methods. That is, the basic composition is a conjugated diene, an ethylenically unsaturated carboxylic acid, other monomers copolymerizable with these, a chain transfer agent, water, a surfactant, a radical polymerization initiator, and other raw materials if necessary. In the dispersion system, the monomer is a manufacturing method in which an aqueous dispersion of polymer particles is used, and the polymer concentration is in the range of 40 to 60% by weight. The particle size of the copolymer latex can be adjusted by the proportion of surfactant and/or seed latex used, and generally speaking, the higher the proportion used, the smaller the particle size of the produced copolymer latex.

Here, the preferred range of particle diameter is 0.05 to 1 μm, more preferably 0.07 to 0.5 μm.

As the surfactant used in the present invention, fatty acid soap,
Anionic surfactants such as rosin acid soaps, alkyl sulfonates, dialkylaryl sulfonates, alkyl sulfosuccinates, polyoxyethylene alkyl sulfates, polyoxyethylene alkylaryl sulfates,
Nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene sorbicun fatty acid ester, oxydiethylene oxypropylene block copolymer,
There are cationic surfactants. The surfactant is usually used as an anionic surfactant alone or in an anionic/nonionic mixed system, and the ratio of U7 to the monomer is in the range of 0.05 to 2%.

The polymerization initiator 52 used in the present invention is one that initiates addition polymerization of monomers by radical decomposition in the presence of heat or a reducing substance, and includes water-soluble or oil-soluble beroxonisulfate, peroxide, Azobis compounds and the like are commonly used. Examples include potassium peroxonisulfate, sodium peroxonisulfate, ammonium peroxonisulfate, hydrogen peroxide, t-butyl hydroperoxide,
Examples include hendiyl peroxide, 2,2-azobisisobutyronitrile, and cumenehytrobar oghisite, with beroxonisulfate being most preferably used. The proportion of the polymerization initiator used is 0.2 to 1.5% by weight based on the monomer. The polymerization temperature is generally in the range of 60 to 90'C, but if you want to accelerate the polymerization rate or polymerize at a lower temperature! Sodium sulfite, ascorbic acid or its salts, erythorbic acid or its salts,
A so-called redox polymerization method can be used in which a reducing agent such as longalint is used in combination with a polymerization initiator.

Furthermore, various polymerization regulators are often added as desired. For example, sodium hydroxide,
These include pH adjusters such as potassium hydroxide, sodium hydrogen carbonate, sodium carbonate, and disodium hydrogen phosphate, and various types of oxalter, such as sodium ethylenediaminetetraacetate.

The copolymer latex of the present invention can be used as a binder for paper coating materials in a conventional manner. That is, the copolymer latex is mixed with an inorganic pigment and/or an organic pigment, a water-soluble polymer, and various additives in water in which a dispersant is dissolved to form a uniform dispersion.

This paint can be applied to the base paper using a conventional method such as various blade coaters or roll coaters.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

In addition, each characteristic was calculated|required as follows.

(1) Properties of copolymer latex (a) Average particle size Light scattering particle size analyzer (manufactured by CN Wood, model 6.
The average particle diameter of the copolymer latex was measured using the following method.

([+) Gel fraction of copolymer The copolymer latex was uniformly coated on a polypropylene film using an N026 wire coater and dried for 1 hour in a dryer at 7.50°C to form a film.

Next, this copolymer latex film was peeled off, approximately 0.5 g was accurately weighed using an analytical balance, and the mixture was immersed in a container containing 300 mβ toluene and stirred at room temperature for 6 hours using a shaker. Afterwards, the contents were roughened and accurately weighed using a 45μ mesh.
Filter through M wire mesh. After that, it was dried in a dryer at 50°C for 2 hours, and the gel fraction was determined by the following formula.

Gel fraction (weight %) (2) Paper coating performance (a) Blister resistance Print both sides of coated paper using R1 printing tester (manufactured by Mei Seisakusho) Print 0.3mf all over. This printed coated paper is cut to an appropriate size, and the test piece is immersed in a silicone oil constant temperature bath adjusted to a predetermined temperature to observe whether or not blisters occur. This test is performed by varying the temperature of the thermostatic chamber, and the lowest temperature at which blistering is observed is determined. The higher the temperature, the better the frister resistance.

(a) Dry pink strength RI printing tester was used to test printing ink (SD Soo--Deluxe 50 Beni B; tack value 18, manufactured by Toka Shiki Co., Ltd.) 0.
4d Overprint 5 times, trace the pinking that appears on the rubber roll onto another mount, and observe the degree of pinking. Evaluation was performed using a 10-point evaluation method, and the fewer the picking phenomenon, the higher the score.

(c) Using a wet Bic strength R1 printing tester, moisten the surface of the coated paper with a water absorption roll, and then apply printing ink (SD Super Deluxe 50 Red B).
; tack value 18, manufactured by Toka Shiki Co., Ltd.) 0.4 mR printing is performed once, and the binking state that appears on the rubber roll is traced onto another mount and the extent of the binning is observed. The evaluation was carried out using a 10-point evaluation method, and the smaller the pinking phenomenon, the higher the score.

(d) Halftone dot reproducibility Printing was carried out using a Ministry of Finance graphia tester, and the missing halftone dot rate was counted. Evaluation was performed using a 10-point evaluation method, and the smaller the missing rate, the higher the score.

(n) Super calendar stain resistance Suitability The coated surface of coated paper before super calender treatment was overlaid with black rasha paper, using a super calender roll manufactured by Jiri Roll Co., Ltd., at 60°C and 200 kg/cm. 5
Process the paper again. Thereafter, the coated paper and the black rasha paper were peeled off, and the degree of transfer of the coating layer to the surface of the black rasha paper was observed. Evaluation was performed using a 10-point evaluation method, and the fewer metastases were given a higher score.

(3) Carpet back sizing performance Peel strength and thread removal strength were determined in accordance with JIS L-1021. The higher the average value, the better.

(4) Adhesive performance (a) High-temperature cohesive strength An adhesive sample with a size of 250 x 25 rMl is pasted on a stainless steel plate by making one reciprocation of a 2 kg roller, and the adhesive surface is parallel to the tensile direction of the tensile tester. Then, the shear force was measured at a speed of 2 m/min in an atmosphere of 40''C.

(II) Low-temperature adhesion A loop was made with the adhesive layer of an adhesive sample with a width of 25 mm and a length of 250 mm facing up, and the loop was formed for 500 m in an atmosphere of 0°C.
It is brought into contact with the corrugated pole surface at a speed of m/min with almost no pressure. 3 seconds after contact, same < 50
The peel adhesive strength was measured when peeling off at a speed of 0 mm/win.

(c) PE adhesive strength In an atmosphere of 23°C, 2 kg of an adhesive sample with a width of 25 mm was placed on a low-density polyethylene plate that did not contain any additives.
Go back and forth once with the roller and paste it together, then paste it and then
After 0 minutes, the 180° peel strength was measured at a speed of 500 mm/min.

Examples 1 to 20 and Comparative Examples 1 to 10 4 parts by weight of an aqueous dispersion of seed particles with a diameter of 0.04 μm (seed solid content concentration 25% by weight) was placed in a pressure-resistant reaction vessel equipped with a stirring device and a temperature control jacket. put in,
Further, add 70 parts by weight of water, 0.2 parts by weight of sodium lauryl sulfate, and 2.5 parts by weight of itaconic acid, and bring the internal temperature to 80''.
Then, an oily mixture consisting of the monomers and chain transfer agents shown in Table 1, 15 parts by weight of water, 1 part by weight of sodium beroxonisulfate, 0.2 parts by weight of sodium hydroxide, and 0.0 parts by weight of sodium lauryl sulfate were added. An aqueous solution consisting of 1 part by weight was added at a constant flow rate over 4 hours and 5 hours, respectively. After maintaining the temperature at 80°C for 1 hour, the resulting copolymer latex was adjusted to pH 7 with sodium hydroxide, and unreacted monomers and chain transfer were removed by steam stripping. The agent was removed, and the mixture was filtered through a filter cloth with a mesh size of 75 μm. In addition,
The final solid content concentration of all co-merged lattes was adjusted to 50% by weight.

Table 1 shows the average particle diameter and gel fraction of these copolymer latexes.

Application Example 1 The copolymer latexes prepared in Examples I to 12 and Comparative Examples 1 to 6 were evaluated for their performance as binders for paper coating. The results are shown in Table 4.

The coating material had the formulation shown in Table 2 and was prepared using a high-speed stirrer with an amount of water that gave a nonvolatile content concentration of 63% by weight. The pH of the paint was adjusted to 9.0 with aqueous ammonia. Table 3 shows the conditions for preparing coated paper using this paint.

Application Example 2 The copolymer latex prepared in Examples 13 to 16 and Comparative Examples 7 to 8 was evaluated for its performance as a binder for carpet bank sizing. The results are shown in Table 7.

The adhesive paint had the formulation shown in Table 5, and was prepared using a high-speed stirrer with an amount of water that gave a nonvolatile content concentration of 70% by weight. Table 6 shows the conditions for preparing force to vent using this paint.

Application Example 3 The copolymer latex prepared in Examples 17 to 20 and Comparative Examples 9 to 10 was evaluated for its performance as an adhesive. The results are shown in Table 8.

Adhesive samples were created by the method shown below.

Approximately 0.5 parts by weight of sodium polyacrylate was added to the obtained copolymer Latinx to adjust the viscosity to approximately 10.000c.
After adjusting the coating to a coating weight of approximately 45)·Lyg/'Po on release paper, it was dried for 2.5 minutes with hot air at 120°C. The resulting dried coating film on the release paper was pressed onto the corona discharge treated surface of a stretched polypropylene film (thickness: approximately 80 μm) →±, and the dried coating film was transferred to the polypropylene film to prepare an adhesive sample. Adhesive sample temperature is 23°
After curing for one week at a C2 relative temperature of 65%, the sticky properties were measured.

(Margin below) Table 2 Ultra White 90° manufactured by Engelhard; Ultra Coat manufactured by Engelhard; Niscalon #1500 manufactured by Sankyo Seifun; Aron T-40J manufactured by Toagosei; Sumiretz 636 manufactured by Sumitomo Chemical; Japan MS4600 manufactured by Shokuhin Kogyo Co., Ltd. (blank below) Table 5 Table 1) Grade 2 manufactured by Sankyo Seifun Co., Ltd. Aron T-404 manufactured by Toagosei Kagaku Co., Ltd. 3) rPVA-217 manufactured by Kuraray Co., Ltd. [Effects of the Invention] According to the present invention, (a) the balance between big strength and other performances in printed coated paper, and (b) curve.

It is possible to obtain a high-performance copolymer latex that can further improve the adhesive strength in tack sizing and pressure-sensitive adhesives, and (a) the operation for recovering residual chain transfer agents becomes unnecessary.

Claims (1)

[Claims] 1. In a method for synthesizing a latex by emulsion polymerization from a conjugated diene, an ethylenically unsaturated carboxylic acid, other monomers copolymerizable therewith, and a chain transfer agent, the following general chain transfer agents may be used as the chain transfer agent. Thioalkyl represented by the formula ▲ Numerical formulas, chemical formulas, tables, etc.▼ (However, HS-R_1 represents a thioalkyl group having 2 to 6 carbon atoms, and R_2 represents an alkyl group having 1 to 18 carbon atoms.) A method for producing a copolymer latex characterized by using a carboxylic acid alkyl ester