JP2022013975A - Method for producing copolymer latex, method for producing rubber composition for tire tread and method for producing pneumatic tire - Google Patents

Abstract

To provide a method for producing a copolymer latex capable of providing a rubber composition for a tire tread which can improve low fuel consumption, abrasion resistance and wet grip performance in good balance while obtaining good productivity, filler dispersibility and processability and a pneumatic tire having a tread prepared by using the rubber composition.SOLUTION: There is provided a method for producing a copolymer latex which completes the polymerization reaction with a polymer conversion rate of 85% or more, which comprises a step of adding a chain transfer agent in the course of the polymerization in subjecting a monomer component containing an aliphatic conjugated diene monomer and an itaconic acid ester monomer to emulsion polymerization.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a copolymer latex, a method for producing a rubber composition for a tire tread, and a method for producing a pneumatic tire.

Tire treads are mainly required to have high levels of performance such as fuel efficiency, wear resistance, and wet grip performance, and various studies have been conducted on methods for improving these performances.

In Patent Document 1, a rubber containing a conjugated diene-based rubber comprising a specific amount ratio of an olefinically unsaturated nitrile monomer unit, an aromatic vinyl monomer unit, and a conjugated diene monomer unit as a repeating unit. By preparing a rubber composition containing a component, an inorganic filler such as silica, and a compound having at least one polymerizable unsaturated group and a specific functional group such as an amino group, the rubber composition has excellent processability and rolls. It is disclosed that a vulnerable rubber having a small resistance and the like and having sufficient wear resistance and the like can be obtained.

Patent Document 2 uses a copolymer synthesized by copolymerizing a conjugated diene-based monomer and an itaconic acid diester in order to improve fuel efficiency, wear resistance, and wet grip performance in a well-balanced manner. Is disclosed.

Japanese Unexamined Patent Publication No. 2002-60437 International Publication No. 2015/075971

By the way, in recent years, further improvement of performance such as low fuel consumption, wear resistance and wet grip performance is required. Therefore, the present invention can provide a rubber composition for a tire tread that can improve fuel efficiency, wear resistance, and wet grip performance in a well-balanced manner while obtaining good productivity, filler dispersibility, and processability. , It is an object of the present invention to provide a method for producing a copolymer latex.

The present invention is a method for producing a copolymer latex used in a rubber composition for tire tread, in which a monomer component containing an aliphatic conjugated diene-based monomer and an itaconic acid ester monomer is emulsified and polymerized. To provide a method for producing a copolymer latex, which comprises a step of adding a chain transfer agent during polymerization and terminates the polymerization reaction at a polymer conversion rate of 85% or more.

In the method for producing a copolymer latex of the present invention, the Mooney viscosity ML1 + 4 (100 ° C.) of the copolymer latex is preferably 105 or less.

Further, the present invention provides a method for producing a rubber composition for a tire tread, which comprises a step of producing a rubber composition for a tire tread using the copolymer produced by the method for producing a copolymer latex of the present invention.

Further, the present invention provides a method for manufacturing a pneumatic tire, which comprises a step of manufacturing a pneumatic tire using the tire tread manufactured by the method for manufacturing a rubber composition for a tire tread of the present invention.

According to the present invention, it is possible to provide a rubber composition for a tire tread that can improve fuel efficiency, wear resistance and wet grip performance in a well-balanced manner while obtaining good productivity, filler dispersibility and processability. , A method for producing a copolymer latex can be provided.

The method for producing a copolymer latex according to the present embodiment is a method for producing a copolymer latex used in a rubber composition for tire tread, and is an aliphatic conjugated diene-based monomer and an itaconic acid ester monomer. In emulsifying and polymerizing the monomer component containing the above, there is a step of adding a chain transfer agent during the polymerization, and the polymerization reaction is terminated at a polymer conversion rate of 85% or more.

First, the monomer components constituting the copolymer latex will be described.

Examples of the aliphatic conjugated diene-based monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, and substitutions. Examples include straight chain conjugated pentadiene, as well as monomers such as substituted and side chain conjugated hexadiene. These can be used alone or in combination of two or more. Among them, 1,3-butadiene is preferably used from the viewpoint of easy industrial production, availability, and cost.

Examples of the itaconic acid ester monomer include itaconic acid monoester and itaconic acid diester, and specific examples thereof include itaconic acid 1-methyl, itaconic acid 4-methyl, itaconic acid dimethyl, itaconic acid 1-ethyl, and itaconic acid. Examples thereof include 4-ethyl acid, diethyl itaconic acid, 1-propyl itaconic acid, 4-propyl itaconic acid, dipropyl itaconic acid, 1-butyl itaconic acid, 4-butyl itaconic acid, and dibutyl itaconic acid. These monomers may be used alone or in combination of two or more. Among them, diethyl itaconic acid and dibutyl itaconate are preferable because they can improve the balance between fuel efficiency, wear resistance, and wet grip performance while obtaining good filler dispersibility and workability.

Further, in addition to the above-mentioned monomers, monomers used in ordinary emulsion polymerization such as styrene, ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride and vinylidene chloride can be used.

The content of the aliphatic conjugated diene-based monomer is preferably 20 to 95% by mass, more preferably 40 to 90% by mass, based on the total amount of the monomer components constituting the copolymer latex. .. By setting the content in the above range, it is possible to improve the balance between filler dispersibility, processability, fuel efficiency, wear resistance, and wet grip performance.

The content of the itaconic acid ester monomer is preferably 5 to 80% by mass, more preferably 10 to 60% by mass, based on the total amount of the monomer components constituting the copolymer latex. By setting the content in the above range, the balance between fuel efficiency, wear resistance and wet grip performance can be improved.

Further, the content of the aliphatic conjugated diene-based monomer and the other monomer copolymerizable with the itaconic acid ester monomer is 0 to 60 with respect to the total amount of the monomer components constituting the copolymer latex. It is preferably by mass%, more preferably 0 to 20% by mass.

Next, the emulsion polymerization according to this embodiment will be described.

The present embodiment includes a step of adding a chain transfer agent during the polymerization. The term "in the middle of polymerization" refers to the period from immediately after the start of the polymerization reaction to immediately before the end of the polymerization reaction. The start of the polymerization reaction refers to the time when the polymerization initiator is added to the reaction system and the polymerization is started. Further, in the present embodiment, the termination of the polymerization reaction means the time when the polymerization inhibitor is used when the polymerization inhibitor is used, and when the operation of removing the unreacted monomer is performed without using the polymerization inhibitor. , Refers to the time when the operation to remove the unreacted monomer is started, and if the operation to remove the unreacted monomer is not performed without using the polymerization inhibitor, open the reactor and take out the contents. Refers to the point in time when it started. By having a step of adding the chain transfer agent during the polymerization, it is possible to improve the balance between fuel efficiency, wear resistance and wet grip performance while obtaining good filler dispersibility and processability.

As the timing of adding the chain transfer agent, the polymer conversion rate of the reaction system is preferably between 10 and 90%, more preferably between 30 and 80%, and even more preferably between 50 and 70%. This makes it easy to adjust the gelation of the copolymer latex, and it becomes easy to improve the balance between filler dispersibility, processability, fuel efficiency, wear resistance, and wet grip performance. The polymer conversion rate can be measured by the method described later.

Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, tarcharied decyl mercaptan, and n-stearyl mercaptan; Xanthogen compounds such as sulphide; thiuram compounds such as tetramethylthium disulfide, tetraethylthium disulfide and tetramethylthium monosulfide; phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrylated phenol; Allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide; vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide; triphenylethane and penta Chain transfer agents such as phenylethane, achlorein, metaacrolein, thioglycolic acid, thioalinic acid, 2-ethylhexylthioglycolate, turpinolene, α-methylstyrene dimer and the like can be mentioned. Of these, Tasha Dodecyl mercaptan is preferred. These can be used alone or in combination of two or more.

The content of the chain transfer agent is preferably 0.01 to 0.50 parts by mass with respect to 100 parts by mass of the monomer component constituting the copolymer latex. When it is 0.01 part by mass or more, the balance between filler dispersibility, workability, fuel efficiency, wear resistance and wet grip performance can be improved, and when it is 0.50 part by mass or less, the machine. It is possible to improve the balance between target strength, fuel efficiency, wear resistance, and wet grip performance. It is more preferably 0.10 to 0.40 parts by mass, and further preferably 0.17 to 0.30 parts by mass.

The content of the chain transfer agent added during the polymerization is preferably 0.01 to 0.30 parts by mass with respect to 100 parts by mass of the monomer component constituting the copolymer latex. When it is 0.01 part by mass or more, the balance between filler dispersibility, workability, fuel efficiency, wear resistance, and wet grip performance can be improved, and when it is 0.30 part by mass or less, the machine. It is possible to improve the balance between target strength, fuel efficiency, wear resistance, and wet grip performance. It is more preferably 0.02 to 0.20 parts by mass, and even more preferably 0.03 to 0.15 parts by mass.

An emulsifier (surfactant), a polymerization initiator, and a reducing agent, if necessary, can be added to the reaction system of emulsion polymerization.

Examples of the emulsifier include sulfate ester salts of higher alcohols, alkylbenzene sulfonates, alkyldiphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroavietates, formalin condensates of naphthalene sulfonic acid, non-sulfuric acids. Examples thereof include anionic surfactants such as sulfate ester salts of ionic surfactants, alkyl ester type of polyethylene glycol, alkylphenyl ether type, and nonionic surfactants such as alkyl ether type. These can be used alone or in combination of two or more. The content of the emulsifier can be appropriately adjusted in consideration of the combination of other additives and the like. The emulsifier is preferably added at the start of polymerization and during the polymerization from the viewpoint of polymerization stability.

Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, paramenthane hydroperoxide, cumene hydroperoxide, benzoyl peroxide, and t-butyl hydroperoxide. , Acetyl peroxide, diisopropylbenzene hydroperoxide, and oil-soluble polymerization initiators such as 1,1,3,3-tetramethylbutylhydroperoxide. These can be used alone or in combination of two or more. Of these, potassium persulfate, sodium persulfate, paramenthane hydroperoxide, cumene hydroperoxide, or t-butyl hydroperoxide is preferably used. The blending amount of the polymerization initiator is appropriately adjusted in consideration of the combination of the monomer composition, the pH of the polymerization reaction system, other additives and the like.

Examples of the reducing agent include ferrous sulfate, sulfite, hydrogen sulfite, pyrosulfite, nitionate, nithionate, thiosulfate, formaldehyde sulfonate, benzaldehyde sulfonate; L-ascorbic acid. , Erythorbic acid, tartrate acid, citrate and other carboxylic acids and salts thereof; reducing saccharides such as dextrose and saccharose; amines such as dimethylaniline and triethanolamine. These can be used alone or in combination of two or more. Of these, formaldehyde sulfonate is preferred. The content of the reducing agent can be appropriately adjusted in consideration of the combination of other additives and the like.

Saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptene; penten, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methyl for the purpose of controlling the molecular weight and crosslinked structure of the copolymer. Unsaturated hydrocarbons such as cyclohexene and 1-methylcyclohexene; hydrocarbon compounds such as aromatic hydrocarbons such as benzene, toluene and xylene can be blended. These can be used alone or in combination of two or more.

Further, if necessary, additives such as an electrolyte, an oxygen supplement, a chelating agent, a dispersant, an antifoaming agent, an antiaging agent, a preservative, an antibacterial agent, a flame retardant, and an ultraviolet absorber may be added. These additives can be appropriately used in appropriate amounts in terms of both type and amount used.

From the viewpoint of pressure in the tank and productivity in consideration of safety, the reaction temperature is preferably set in the range of 0 to 100 ° C, more preferably in the range of 0 to 85 ° C.

As a method for adding the monomer component, for example, a batch addition method, a divided addition method, a continuous addition method, or a power feed method can be adopted. From the viewpoint of suppressing the monomer in the reaction system to a certain concentration or less to improve safety, a continuous addition method may be adopted. Further, continuous addition may be performed a plurality of times.

In the present embodiment, the polymerization reaction is terminated when the polymer conversion rate is 85% or more. By terminating the polymerization reaction with a polymer conversion rate of 85% or more, productivity can be improved by reducing the cost of disposing of unreacted substances and recovering them. In addition, the balance between fuel efficiency, wear resistance, and wet grip performance can be improved. It is preferably 87% or more, more preferably 89% or more.

The polymer conversion rate can be calculated from the following formula by weighing the reaction solution collected from the reaction vessel, drying at 150 ° C. for 1 hour, weighing again, and measuring the solid content C.
Polymer conversion rate (%) = [solid content C (g) -solid content other than the monomer contained in the reaction solution (g)] / amount of monomer component added to the reaction system (g) × 100
The polymer conversion rate can be set based on the data obtained in advance. For example, a reaction system similar to the emulsion polymerization to be carried out can be prepared and obtained in advance based on the transition of the polymer conversion rate of this reaction system.

From the viewpoint of dispersion stability, the copolymer latex preferably has a pH adjusted to 8 to 13, and more preferably adjusted to 8.5 to 12.

Further, it is preferable that the unreacted monomer and other low boiling point compounds are removed from the copolymer latex by a method such as hot vacuum distillation.

The Mooney viscosity ML1 + 4 (100 ° C.) of the copolymer latex is preferably 105 or less, and more preferably 100 or less. Further, it is preferably 40 or more, more preferably 50 or more, and further preferably 60 or more. When the Mooney viscosity ML1 + 4 (100 ° C.) of the copolymer latex is 105 or less, the dispersibility of the filler and the processability can be improved, and when it is 40 or more, the effect of the present invention can be fully exhibited. The Mooney viscosity ML1 + 4 (100 ° C.) is a value obtained by measuring the Mooney viscosity at 100 ° C. according to JISK6383.

If necessary, the copolymer latex may be blended with functional additives such as preservatives, antioxidants and surfactants. These additives can be appropriately used in appropriate amounts in terms of both type and amount used.

The method for producing a rubber composition for a tire tread according to the present embodiment includes a step of producing a rubber composition for a tire tread using a copolymer produced by the method for producing a copolymer latex according to the present embodiment. ..

The copolymer can be coagulated as a crumb by adding, for example, salts such as sodium chloride, calcium chloride and potassium chloride, alcohol, and in some cases hydrochloric acid, nitric acid, sulfuric acid and the like to the copolymer latex. It can be obtained by washing this crumb, dehydrating it, and then drying it with a dryer or the like.

The content of the copolymer is preferably 1% by mass or more, more preferably 50% by mass or more, still more preferably 70% by mass or more, particularly preferably 70% by mass or more, based on 100% by mass of the rubber component contained in the rubber composition for tire tread. Is 80% by mass or more, and may be 100% by mass. If it is less than 1% by mass, the content of the copolymer may be too small to obtain the effect of the present invention.

Other rubber components used with the copolymer include, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoplemme (SIR), styrene isoprene butadiene. Examples thereof include diene rubbers such as rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). These rubber components may be used alone or in combination of two or more.

The tire tread composition may contain a filler and, if desired, other formulations. Fillers include carbon black and / or silica.

The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 50 ml / 100 g or more, more preferably 100 ml / 100 g or more. The DBP is preferably 200 ml / 100 g or less and 150 ml / 100 g or less. If it is less than 50 ml / 100 g, sufficient reinforcing property may not be obtained and wear resistance may be lowered, and if it exceeds 200 ml / 100 g, the dispersibility of carbon black may be lowered and fuel efficiency may be deteriorated. There is. The carbon black DBP can be measured according to JIS K6217-4: 2001.

The content of carbon black is preferably 1 part by mass or more, and more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less. If it is less than 1 part by mass, the wear resistance may be deteriorated, and if it exceeds 50 parts by mass, the fuel efficiency may be deteriorated.

The silica is not particularly limited, and examples thereof include dry silica (silicic anhydride) and wet silica (hydrous silicic acid), but wet silica is preferable because it has many silanol groups.

The N2SA of silica is preferably 100 m2 / g or more, more preferably 150 m2 / g or more. The N2SA is preferably 300 m2 / g or less, more preferably 200 m2 / g or less. If the N2SA of silica is less than 100 m2 / g, the reinforcing effect is small and the wear resistance tends not to be sufficiently improved, and if it exceeds 300 m2 / g, the dispersibility of silica tends to deteriorate. The silica N2SA can be measured according to ASTMD3037-81.

The content of silica is preferably 1 part by mass or more, and more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. If it is less than 1 part by mass, fuel efficiency and wear resistance tend to be insufficient, and if it exceeds 150 parts by mass, the dispersibility of silica tends to deteriorate.

It is preferable to include a silane coupling agent together with silica. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, a sulfide system such as bis (3-triethoxysilylpropyl) tetrasulfide, 3 -Mercapto-based such as mercaptopropyltrimethoxysilane, vinyl-based such as vinyltriethoxysilane, amino-based such as 3-aminopropyltriethoxysilane, glycidoxy-based of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltri. Examples thereof include nitro type such as methoxysilane and chloro type such as 3-chloropropyltrimethoxysilane. Of these, a sulfide system is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable.

When the silane coupling agent is contained, the content thereof is preferably 1 part by mass or more, and more preferably 2 parts by mass or more with respect to 100 parts by mass of silica. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. If it is less than 1 part by mass, the effect such as improvement of dispersibility tends not to be sufficiently obtained, and if it exceeds 20 parts by mass, a sufficient coupling effect cannot be obtained and the reinforcing property tends to be lowered. ..

Examples of other formulations include formulations conventionally used in the rubber industry, such as other reinforcing fillers, anti-aging agents, vulcanizing agents such as oils, waxes and sulfur, vulcanization accelerators and the like.

The rubber composition for tire tread can be used for tire treads (cap treads, base treads), sidewalls and the like, and is particularly suitable for treads (particularly cap treads).

The method for manufacturing a pneumatic tire according to the present embodiment includes a step of manufacturing a pneumatic tire using the tire tread manufactured by the method for manufacturing a rubber composition for a tire tread according to the present embodiment.

Pneumatic tires are manufactured by conventional methods using rubber compositions for tire treads. That is, the rubber composition for a tire tread is extruded according to the shape of a tire member such as a tread at the unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. To form an unvulcanized tire. A tire is obtained by heating and pressurizing this unvulcanized tire in a vulcanizer.

Pneumatic tires are suitable for passenger car tires, large passenger car tires, large SUV tires, heavy load tires such as trucks and buses, and light truck tires, and can be used as winter tires and studless tires, respectively.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples. Unless otherwise specified,% and parts are based on mass.

(Manufacturing of copolymer latex)
<Manufacturing example 1>
In a pressure-resistant polymerization reaction vessel, 157.66 parts by mass of water, 83 parts by mass of 1,3-butadiene, 17 parts by mass of dibutyl itacone, and 0.1 parts by mass of tarchaleed decylmercaptan (hereinafter, TDM) as a chain transfer agent. 0.84 parts by mass of disproportionate sodium rosinate, 0.03 parts by mass of sardine, 0.5 parts by mass of tertiary sodium phosphate, 0.5 parts by mass of β-naphthalene sulfonate formarin condensate sodium salt, sodium hydrosulfite Add 0.004 part by mass, 0.05 part by mass of ferrous sulfate, 0.4 part by mass of sodium ethylenediamine tetraacetate, 0.01 part by mass of sodium formaldehyde sulfoxylate, and 0.15 part by mass of paramentan hydroperoxide. Polymerization was started at 10 ° C.

Emulsion polymerization was carried out while adjusting the polymerization stability by additionally adding sodium disproportionate, sodium formaldehyde sulfoxylate, and water into the reactor. When the polymer addition rate reaches 60%, 0.08 part by mass of TDM is added into the reactor, and when the polymer conversion rate sufficiently exceeds 85%, N, N-diethylhydroxylamine is added to carry out the polymerization. It was terminated to obtain a reaction product. The reaction product was subjected to thermal vacuum distillation to remove unreacted monomers and other low boiling point compounds to obtain a copolymer latex A.

<Manufacturing Examples 2 to 6>
Copolymer latexes B to F were obtained in the same manner as in Production Example 1 except that the amount of TDM added and the polymer conversion rate at the end of polymerization were changed as shown in Table 1.

(Measurement of polymer conversion rate)
The polymer conversion rate of the copolymer latex was calculated from the following formula by weighing the reaction solution collected from the inside of the reactor, drying at 150 ° C. for 1 hour, weighing again, and measuring the solid content.
Polymer conversion rate (%) = [(solid content (g) -solid content other than the monomer contained in the reaction solution (g)) / amount of monomer component added to the reaction system (g)] × 100
The higher the polymer conversion rate, the lower the cost of disposing of unreacted substances and the recovery, and the higher the productivity, so the polymer conversion rate is an index of productivity.

(Measurement of Mooney viscosity ML1 + 4 (100 ° C))
According to JISK6383, the measurement was performed at 100 ° C. using about 40 g of the copolymer latex.

Hereinafter, various chemicals used in Examples and Comparative Examples will be collectively described.
Rubber component:
NR: RSS # 3
SBR: NS116 manufactured by JSR Corporation (styrene content: 20% by mass)
BR: High cis BR (cis content: 97% by mass, Mw: 40 man)
Carbon Black: Show Black N220 manufactured by Cabot Japan Co., Ltd. (N2SA: 111m2 / g, DBP: 115ml / 100g)
Silica: Ultrasil VN3 manufactured by Degussa (N2SA: 175m2 / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa.
Process oil: Process X-140 (aroma oil) manufactured by Japan Energy Co., Ltd.
Resin: Copolymer of α-methylstyrene and styrene (softening point: 85 ° C, Tg: 107 ° C)
Zinc Hana: Zinc oxide type 2 stearic acid manufactured by Mitsui Metal Mining Co., Ltd .: Stearic acid "Tsubaki" manufactured by NOF CORPORATION
Anti-aging agent: Nocrack 6C (N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Wax: Sunknock wax manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. 1: Noxeller CZ (N-cyclohexyl-) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. 2-Benzothiazolyl vulcan amide)
Vulcanization accelerator 2: Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

<Examples and comparative examples>
According to the formulation shown in Tables 2 to 4, various chemicals excluding sulfur and the vulcanization accelerator were kneaded at 150 ° C. for 5 minutes with a Banbury mixer. Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded for 4 minutes to obtain an unvulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was press-vulcanized under the condition of 170 ° C. for 12 minutes to obtain a vulcanized rubber composition.

The following evaluation was performed using the obtained unvulcanized rubber composition and vulcanized rubber composition. The evaluation results are shown in Tables 2-4.

(Workability)
The Mooney viscosity ML (1 + 4) of the unvulcanized rubber composition at 130 ° C. was measured according to JIS K6300, and the burnability and flatness during sheet preparation were visually observed as sheet processability. These processability were comprehensively evaluated, and the standard comparative example was expressed as 100 as an exponential notation. When the index is smaller than 100, the thickness of the rubber at the time of molding becomes unstable, indicating that the molding processability is inferior.

(Silica dispersion)
The obtained vulcanized rubber composition was subjected to strain 0.5, 1, 2, 4, 8, 16, 32, 64 under the conditions of 100 ° C. and 1 Hz using an RPA2000 type tester manufactured by Alpha Technologies. % G * was measured, the pane effect of silica was obtained from the difference between the maximum value of G * and the minimum value of G *, and the result of the reciprocal of the standard comparative example was indexed as 100 and used as the dispersion index of silica.
The larger the index, the more dispersed the silica, indicating that the dispersibility of the silica is excellent.

(Fuel efficiency)
Using the viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), the tan δ of each vulcanized rubber composition was measured under the conditions of a temperature of 30 ° C., an initial strain of 10%, and a dynamic strain of 2%. The result of the reciprocal was indexed as 100 and used as an index of fuel efficiency.
The larger the index, the smaller the rolling resistance, indicating that the fuel efficiency is excellent.

(Wet grip performance)
The viscoelastic parameters of the test pieces prepared from each vulcanized rubber composition were measured in a torsion mode using a viscoelasticity tester (ARES) manufactured by Leometrics Scientific. Tan δ was measured at 0 ° C. at a frequency of 10 Hz and a strain of 1%, and the result of the standard comparative example was indexed as 100 and used as an index of wet grip performance.
The larger the index, the better the wet grip performance.

(Abrasion resistance)
Using a Ramborn type wear tester, the wear amount of the vulcanized rubber composition was measured under the conditions of room temperature, load load 1.0 kgf, and slip ratio 30%, and the index was indexed with the result of the standard comparative example as 100 by the following formula. displayed. The larger the value, the better the wear resistance.
(Abrasion resistance index) = (Abrasion amount of Comparative Example 1) / (Abrasion amount of each compound) × 100

Claims (4)

A method for producing a copolymer latex used in a rubber composition for a tire tread, which is a chain in emulsifying and polymerizing a monomer component containing an aliphatic conjugated diene-based monomer and an itaconic acid ester monomer. A method for producing a copolymer latex, which comprises a step of adding a transfer agent during polymerization and terminates the polymerization reaction at a polymer conversion rate of 85% or more. The method for producing a copolymer latex according to claim 1, wherein the Mooney viscosity ML1 + 4 (100 ° C.) of the copolymer latex is 105 or less. A method for producing a rubber composition for tire tread, which comprises a step of producing a rubber composition for tire tread using the copolymer produced by the method for producing the copolymer latex according to claim 1 or 2. A method for manufacturing a pneumatic tire, which comprises a step of manufacturing a pneumatic tire using the tire tread manufactured by the method for manufacturing a rubber composition for a tire tread according to claim 3.