JP2013133436A - Rubber composition for tire tread, and pneumatic tire - Google Patents

Abstract

A rubber composition for a tire tread capable of producing a tire excellent in dispersibility of a white filler and excellent in rolling resistance, and a pneumatic tire using the same.
A diene rubber, a white filler, a silane coupling agent, and a (meth) acrylate polymer having a reactive silyl group at a terminal,
20% by mass or more of the diene rubber is styrene-butadiene copolymer rubber,
The content of the white filler is 5 to 150 parts by mass with respect to 100 parts by mass of the diene rubber,
The content of the silane coupling agent is 0.5 to 20% by mass with respect to the mass of the white filler,
A rubber composition for a tire tread, wherein the content of the (meth) acrylate polymer is 1 to 30% by mass with respect to the mass of the white filler.
[Selection figure] None

Description

  The present invention relates to a rubber composition for a tire tread and a pneumatic tire.

  It is known to use a rubber composition containing silica as a technique for improving the wet performance of a tire and reducing rolling resistance. From the viewpoint of further improving the performance, a rubber composition using a silane coupling agent together with silica. Things are also known.

For example, Patent Document 1 discloses that “at least one filler selected from the group consisting of carbon black and white filler (B) with respect to 100 parts by mass of a rubber component (A) containing styrene / butadiene copolymer rubber (B ) 20-70 parts by mass, softening agent (C) 0-30 parts by mass, and (meth) acrylate-based (co) polymer (D) having a polystyrene-equivalent weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ 3 to 30 parts by weight of a rubber composition ”([Claim 1]), and when silica is used as a white filler, a silane coupling agent is used. Addition is described ([0045]).

JP 2006-274049 A

  However, when the inventor has repeatedly studied the rubber composition described in Patent Document 1, the rolling resistance of the tire is improved by blending the (meth) acrylate-based (co) polymer, but the improvement effect is not good. It has been found that this is sufficient, and the addition of the (meth) acrylate (co) polymer tends to inhibit the dispersion of the white filler (particularly silica).

  Accordingly, an object of the present invention is to provide a rubber composition for a tire tread capable of producing a tire excellent in dispersibility of a white filler and excellent in rolling resistance, and a pneumatic tire using the same. To do.

As a result of intensive studies to solve the above problems, the present inventor has formulated a specific amount of a silane coupling agent and a (meth) acrylate polymer having a reactive silyl group at the terminal with respect to the white filler. The present inventors have found that a tire excellent in dispersibility of white filler and excellent in rolling resistance can be produced.
That is, the present invention provides the following (1) to (3).

(1) A diene rubber, a white filler, a silane coupling agent, and a (meth) acrylate polymer having a reactive silyl group at the terminal,
20% by mass or more of the diene rubber is styrene-butadiene copolymer rubber,
The content of the white filler is 5 to 150 parts by mass with respect to 100 parts by mass of the diene rubber,
The content of the silane coupling agent is 0.5 to 20% by mass with respect to the mass of the white filler,
A rubber composition for a tire tread, wherein the content of the (meth) acrylate polymer is 1 to 30% by mass with respect to the mass of the white filler.

  (2) The rubber composition for a tire tread according to the above (1), wherein the (meth) acrylate polymer has a weight average molecular weight of 500 to 100,000.

  (3) A pneumatic tire using the tire tread rubber composition according to the above (1) or (2) as a tire tread.

  As shown below, according to the present invention, a rubber composition for a tire tread capable of producing a tire excellent in dispersibility of a white filler and excellent in rolling resistance, and a pneumatic tire using the same Can be provided.

It is a typical fragmentary sectional view of the tire showing an example of the embodiment of the pneumatic tire of the present invention.

[Rubber composition for tire]
The rubber composition for a tire tread of the present invention (hereinafter also simply referred to as “the rubber composition of the present invention”) has a diene rubber, a white filler, a silane coupling agent, and a reactive silyl group at the terminal. It contains a (meth) acrylate polymer, 20% by mass or more of the diene rubber is styrene-butadiene copolymer rubber, and the content of the white filler is 5 with respect to 100 parts by mass of the diene rubber. To 150 parts by mass, the content of the silane coupling agent is 0.5 to 20% by mass with respect to the mass of the white filler, and the content of the (meth) acrylate polymer is the white filling. The rubber composition for tire treads is 1 to 30% by mass with respect to the mass of the agent.
Below, each component which the rubber composition of this invention contains is demonstrated in detail.

<Diene rubber>
The diene rubber compounded in the rubber composition of the present invention is styrene-butadiene copolymer rubber (SBR) at 20% by mass or more.
Here, the terminal of the SBR may be modified with a hydroxy group, a polyorganosiloxane group, a carbonyl group, an amino group, or the like.
Further, the content (ratio) of the SBR is preferably 50 to 90% by mass of the diene rubber, and 60 to 80% by mass, because a tire excellent in rolling resistance can be produced. Is more preferable.

In the present invention, the SBR contains 30 to 50% by mass of aromatic vinyl (hereinafter referred to as “styrene amount”) for the reason that a tire excellent in rolling resistance can be produced, and vinyl in a conjugated diene. It is preferable to contain 30 to 65% by mass of the amount of bonds (hereinafter referred to as “amount of butadiene”).
The weight average molecular weight (Mw) of the SBR is not particularly limited, but is preferably 900,000 to 2,000,000, more preferably 1,000,000 to 1,800,000, because the effect of suppressing the increase in viscosity is increased. preferable. In addition, a weight average molecular weight shall be measured by gel permeation chromatography (GPC) by standard polystyrene conversion.

In the present invention, when a diene rubber other than the above SBR is contained, the diene rubber is not particularly limited as long as it has a double bond in the main chain. Specific examples thereof include natural rubber (NR ), Isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), ethylene-propylene-diene copolymer rubber (EPDM), styrene-isoprene rubber, isoprene-butadiene rubber, A nitrile rubber, hydrogenated nitrile rubber, etc. are mentioned, These may be used individually by 1 type and may use 2 or more types together.
Among these, it is preferable to use BR because the wear resistance is good and a tire excellent in rolling resistance can be produced.

<White filler>
The white filler compounded in the rubber composition of the present invention is not particularly limited, and any conventionally known white filler compounded in the rubber composition for use in tires or the like can be used.
Specific examples of the white filler include silica, aluminum hydroxide, and the like. Among these, silica is preferable.

Specific examples of the silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, fumed silica, calcined silica, precipitated silica, pulverized silica, and fused silica. Examples thereof include silica and colloidal silica, and these may be used alone or in combination of two or more.
Of these, wet silica is preferred because of its good wear resistance and the ability to produce tires with superior rolling resistance.

  In this invention, content of the said white filler is 5-150 mass parts with respect to 100 mass parts of said diene rubbers, and it is preferable that it is 40-120 mass parts.

<Silane coupling agent>
The silane coupling agent blended in the rubber composition of the present invention is not particularly limited, and any conventionally known silane coupling agent blended in a rubber composition for uses such as tires can be used.
Specific examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, Bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxy Silane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N- Methylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl Methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, Dimethoxymethylsilylpropylbenzothiazole tetrasulfide, trimethoxysilylpropyl-mercaptobenzo Include azole tetrasulfide and the like, may be used those either alone, or in combination of two or more.
Of these, a silane coupling agent containing a sulfur atom (a sulfur-containing silane coupling agent) is preferred, and a silane coupling agent containing a mercapto group is more preferred.

  In this invention, content of the said silane coupling agent is 0.5-20 mass% with respect to the mass of the said white filler, and it is preferable that it is 1-15 mass%.

<(Meth) acrylate polymer>
The (meth) acrylate polymer compounded in the rubber composition of the present invention has a reactive silyl group at least at the terminal, and the main chain is an acrylic acid alkyl ester monomer unit and / or a methacrylic acid alkyl ester monomer. It is a polymer containing a body unit.
Here, (meth) acrylate means one or both of acrylate and methacrylate.
The reactive silyl group is, for example, by using a catalyst or the like as necessary in the presence of moisture or a crosslinking agent such as a silicon-containing group or a silanol group having a hydrolyzable group bonded to a silicon atom. The group which can raise | generate a condensation reaction is said, and when a typical thing is shown, the group represented by following formula (1) will be mentioned, for example.

In the formula, R ¹ and R ² are each independently represented by an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or (R ³ ) ₃ SiO—. And when two or more R ¹ or R ² are present, they may be the same or different. Here, R ³ is a monovalent hydrocarbon group having 1 to 20 carbon atoms, and three R ^{3 s} may be the same or different.
Y represents a hydroxyl group or a hydrolyzable group, and when two or more Y exist, they may be the same or different.
A represents 0, 1, 2 or 3, and b represents 0, 1 or 2.
Moreover, b in t groups represented by the following formula (2) may be different. t shows the integer of 0-19. However, it is assumed that a + t × b ≧ 1 is satisfied. “A + t × b ≧ 1” means that a + t × b is 1 or more.

Specific examples of R ¹ and R ² in the above formula (1) include, for example, alkyl groups such as a methyl group and an ethyl group; alicyclic hydrocarbon groups such as a cyclohexyl group; aryl groups such as a phenyl group; And a triorganosiloxy group represented by (R ³ ) ₃ SiO— in which R ³ is a methyl group or a phenyl group. R ¹ , R ² and R ³ are particularly preferably methyl groups.

The hydrolyzable group represented by Y is not particularly limited as long as it is a conventionally known hydrolyzable group. Specific examples include a hydrogen atom, a halogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amide group, an acid amide group, an aminooxy group, a mercapto group, and an alkenyloxy group. Of these, a hydrogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amide group, an aminooxy group, a mercapto group, and an alkenyloxy group are preferable. Alkoxy groups such as groups are particularly preferred.
Among the crosslinkable silyl groups, a crosslinkable silyl group represented by the following formula (3) is preferable from the viewpoint of easy availability. In the following formula (3), R ² , Y and a have the same meanings as described in the above formula (1).

In the present invention, the reactive silyl group is excellent in reactivity with the white filler (especially silica) and can produce a tire having good wear resistance. A methylsilyl group is preferred.
Moreover, the said reactive silyl group has 1 or more at the terminal of the said (meth) acrylate type polymer, It is preferable to have 2 or more at both terminals, and it has 2-8. Is more preferable.

On the other hand, as the acrylic acid alkyl ester monomer unit forming the main chain of the (meth) acrylate polymer, specifically, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate , Isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-heptyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, Lauryl acrylate, tridecyl acrylate, myristyl acrylate, cetyl acrylate, stearyl acrylate, behenyl acrylate , Phenyl acrylate, toluyl acrylate, benzyl acrylate, biphenyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, glycidyl acrylate, 2-aminoethyl acrylate, trifluoromethyl Methyl acrylate, 2-trifluoromethyl ethyl acrylate, 2-perfluoroethyl ethyl acrylate, 2-perfluoroethyl-2-perfluorobutyl ethyl acrylate, perfluoroethyl acrylate, perfluoromethyl acrylate, diperfluoromethyl methyl acrylate, 2-perfluoromethyl-2-perfluoroethyl ethyl acrylate, 2-perfluorohexyl Chill acrylate, 2-perfluoro decyl ethyl acrylate, 2-perfluoro hexa acrylic or methacrylic acid esters corresponding thereto, such as decyl ethyl acrylate.
These may be used alone or in combination of two or more.

  The main chain of the (meth) acrylate polymer is not particularly limited as long as it contains an acrylic acid alkyl ester monomer unit and / or a methacrylic acid alkyl ester monomer unit, but is easy to handle. For these reasons, it is preferable that these monomer units exceed 50% by mass, and more preferably 70% by mass or more.

Further, the main chain of the (meth) acrylate-based polymer includes, in addition to the acrylic acid alkyl ester monomer unit and / or the methacrylic acid alkyl ester monomer unit, a monomer unit copolymerizable with these. May be included. For example, a monomer unit containing a carboxy group such as acrylic acid or methacrylic acid; a monomer unit containing an amide group such as acrylamide, methacrylamide, N-methylolacrylamide, or N-methylolmethacrylamide; glycidyl acrylate, glycidyl Monomer units containing an epoxy group such as methacrylate; and monomer units containing an amino group such as diethylaminoethyl acrylate, diethylaminoethyl methacrylate, and aminoethyl vinyl ether. Polyoxyethylene acrylate, polyoxyethylene methacrylate, and the like can be expected to have a copolymerization effect in terms of moisture curability and internal curability.
In addition, monomer units derived from acrylonitrile, styrene, α-methylstyrene, alkyl vinyl ether, vinyl chloride, vinyl acetate, vinyl propionate, ethylene and the like can be mentioned.

  As said (meth) acrylate type polymer, what is represented by following formula (4) is mentioned, for example.

In the formula, R ³ is a hydrogen atom or a methyl group, R ⁴ is an alkyl group, R ⁵ is an alkylene group, n is an integer of 3 to 100, and R ² , Y and a are each the above formulae. It is synonymous with what was demonstrated in (1).
Examples of the alkyl group include those having 1 to 20 carbon atoms, and specific examples thereof include a methyl group and an ethyl group.
Examples of the alkylene group include those having 1 to 20 carbon atoms, and specific examples thereof include a methylene group, a dimethylene group, a trimethylene group, a tetramethylene group, and the like.

Among the (meth) acrylate polymers represented by the above formula (4), a (meth) acrylate-based polymer represented by the following formula (5) is used because a tire having good wear resistance can be produced. Coalescence is preferred. In the following formula (5), R ³ and R ⁴ have the same meanings as described in the above formula (4).

In the present invention, the weight average molecular weight of the (meth) acrylate polymer is preferably 500 to 100,000 because it is excellent in handling viscosity and reactivity with white filler (particularly silica). More preferably, it is 10,000 to 40,000.
In addition, a weight average molecular weight shall be measured by gel permeation chromatography (GPC) by standard polystyrene conversion.

Further, the solution viscosity of the (meth) acrylate polymer is preferably 150 to 700 cps from the reason that a tire having excellent rubber composition handling properties and good wear resistance can be produced. More preferably, it is ˜600 cps.
In addition, melt viscosity shall be measured on 25 degreeC conditions in an E-type viscosity meter.

  As such a (meth) acrylate polymer, known commercial products can be used. Specific examples thereof include Kaneka Telechelic Polyacrylate-SA100S, SA100, SA110S, SA120S, SA310S, etc. manufactured by Kaneka Corporation. Can be mentioned.

  In this invention, content of the said (meth) acrylate type polymer is 1-30 mass% with respect to the mass of the said white filler, and it is preferable that it is 3-15 mass%.

The rubber composition of the present invention contains a specific amount of the silane coupling agent and the (meth) acrylate polymer with respect to the white filler, so that the dispersibility of the white filler is improved and obtained. The rolling resistance of the tire is also improved.
With respect to such an effect, the inventor presumes that it is due to the following mechanism.
First, it is considered that a part of the white filler causes an interaction (so-called silanization) with the silane coupling agent.
Next, since the (meth) acrylate-based polymer has a reactive silyl group at the terminal, it is caused by hydrogen bonding and / or hydrolysis condensation reaction on the particle surface of the remaining white filler (particularly silica). It is considered that a bond is formed and an association of the (meth) acrylate polymer and the white filler is formed.
And it is thought that the dispersibility of the white filler is improved by these interactions and aggregates, and the rolling resistance of the obtained tire is also improved.

  In addition to the components described above, the rubber composition of the present invention includes fillers other than white fillers (for example, carbon black), vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, zinc oxide, oil, anti-aging Various additives generally used in tire rubber compositions such as an agent and a plasticizer can be blended. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used.

The method for producing the rubber composition of the present invention is not particularly limited, and examples thereof include a method of kneading the above-described components using a known method and apparatus (for example, a Banbury mixer, a kneader, a roll, etc.). It is done.
The rubber composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

〔tire〕
The pneumatic tire of the present invention (hereinafter also simply referred to as “the tire of the present invention”) is a pneumatic tire using the rubber composition of the present invention described above.
FIG. 1 shows a schematic partial cross-sectional view of a tire representing an example of an embodiment of the tire of the present invention, but the tire of the present invention is not limited to the embodiment shown in FIG.

In FIG. 1, reference numeral 1 represents a bead portion, reference numeral 2 represents a sidewall portion, and reference numeral 3 represents a tire tread portion.
Further, a carcass layer 4 in which fiber cords are embedded is mounted between the pair of left and right bead portions 1, and the end of the carcass layer 4 extends from the inside of the tire to the outside around the bead core 5 and the bead filler 6. Wrapped and rolled up.
In the tire tread 3, a belt layer 7 is disposed over the circumference of the tire on the outside of the carcass layer 4.
Moreover, in the bead part 1, the rim cushion 8 is arrange | positioned in the part which touches a rim | limb.

  The tire of the present invention is vulcanized or cured at a temperature corresponding to, for example, the diene rubber, vulcanizing agent or crosslinking agent, vulcanization accelerator or crosslinking accelerator contained in the rubber composition of the present invention, and the blending ratio thereof. It can manufacture by bridge | crosslinking and forming a tread part, a side wall part, etc.

  Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to these.

(Examples 1-4 and Comparative Examples 1-2)
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in Table 1 below.
Specifically, when the components shown in Table 1 below, excluding sulfur and the vulcanization accelerator, were kneaded for 5 minutes with a 1.7 liter closed Banbury mixer and reached 150 ± 5 ° C. To obtain a master batch.
Next, sulfur and a vulcanization accelerator were kneaded with an open roll in the obtained master batch to obtain a rubber composition.

(Example 5)
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in Table 1 below.
Specifically, first, among the components shown in Table 1 below, a mixture in which a white filler and a (meth) acrylate polymer were mixed in advance was prepared.
Next, among the components shown in Table 1 below, components other than the white filler, (meth) acrylate polymer, sulfur and vulcanization accelerator, and the above mixture were mixed with a 1.7 liter closed Banbury mixer. The mixture was kneaded for 1 minute and discharged when the temperature reached 150 ± 5 ° C. to obtain a master batch.
Next, sulfur and a vulcanization accelerator were kneaded with an open roll in the obtained master batch to obtain a rubber composition.

<Mooney viscosity (index of workability)>
For the prepared rubber composition (unvulcanized), Mooney was used in accordance with JIS K6300-1: 2001, using an L-shaped rotor, with a preheating time of 1 minute, a rotor rotation time of 4 minutes, and a test temperature of 100 ° C. The viscosity was measured. The results are shown in Table 1 below.

<Pain effect (indicator of silica dispersibility)>
The prepared rubber composition (unvulcanized) was vulcanized at 160 ° C. for 20 minutes using a strain shear stress measuring machine (RPA2000, manufactured by α-Technology Co., Ltd.) and then strain shear stress G ′ having a strain of 0.28%. And a strain shear stress G ′ having a strain of 30.0% were measured, and the difference G′0.28 (MPa) −G′30.0 (MPa) was calculated as the Payne effect.
The calculated results were expressed as an index with Comparative Example 1 being 100, and are shown in Table 1 below. A smaller index means a smaller Pain effect and better dispersibility of the white filler.

<Tan δ (60 ° C.) (index of rolling resistance)>
The prepared rubber composition (unvulcanized) was vulcanized at 150 ° C. for 30 minutes in a mold (15 cm × 15 cm × 0.2 cm) to produce a vulcanized rubber sheet.
About the produced vulcanized rubber sheet, tan δ under the conditions of a temperature of 60 ° C., a frequency of 20 Hz, and a 1% twist was measured using a viscoelasticity tester (RDA-II type, manufactured by Rheometric Co., Ltd.).
The obtained results were expressed as an index with the value of Comparative Example 1 being 100, and are shown in Table 1 below. The smaller the index, the smaller the tan δ and the better (smaller) the rolling resistance.

The following components were used as the components in Table 1.
-Styrene-butadiene rubber: Nipol NS 460 [Oil extended amount with respect to 100 parts by mass of rubber: 37.5 parts by mass (the rubber content in 96.3 parts by mass is 70 parts by mass), Weight average molecular weight: 780,000, Amount of styrene : 25 mass%, butadiene content: 63 mass%, manufactured by Nippon Zeon Co., Ltd.]
-Butadiene rubber: Nippon BR 1220 (manufactured by Nippon Zeon)

White filler: silica (Zeosil 1165MP, N ₂ SA: 165 m ² / g, manufactured by Rhodia)
Carbon black: Seast 6 (N ₂ SA: 119 m ² / g, manufactured by Tokai Carbon Co., Ltd.)
Silane coupling agent 1: Si69 (Evonik Degussa)
Silane coupling agent 2: Si363 (Evonik Degussa)

-(Meth) acrylate-based polymer 1: silyl group-modified polyacrylate at both ends (SA100S, solution viscosity: 250 cps, weight average molecular weight: 38,000)
-(Meth) acrylate-based polymer 2: polyacrylates modified with silyl groups at both ends (SA120S, solution viscosity: 600 cps, weight average molecular weight: 16,000)
(Meth) acrylate polymer A: poly (styrene) -block-poly (acrylic acid) (weight average molecular weight: 7470-9130, manufactured by Aldrich)

・ Zinc oxide: 3 kinds of zinc white (made by Shodo Chemical Industry Co., Ltd.)
・ Stearic acid: Beads stearic acid (manufactured by NOF Corporation)
Anti-aging agent: N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine (Santflex 6PPD, manufactured by Flexis)
Aroma oil: Extract No. 4 S (manufactured by Showa Shell Sekiyu KK)
・ Sulfur: Fine sulfur with Jinhua stamp oil (manufactured by Tsurumi Chemical Co., Ltd.)
・ Vulcanization accelerator 1: N-cyclohexyl-2-benzothiazolylsulfenamide (Noxeller CZ-G, manufactured by Ouchi Shinsei Chemical Co., Ltd.)
・ Vulcanization accelerator 2: 1,3-diphenylguanidine (Soccinol DG, manufactured by Sumitomo Chemical Co., Ltd.)

From the results shown in Table 1 above, the rubber composition of Comparative Example 2 prepared by blending a (meth) acrylate polymer having no reactive silyl group does not blend a (meth) acrylate polymer. Although the rolling resistance of the tire was slightly improved as compared with the rubber composition of Comparative Example 1 prepared in the above, it was found that the dispersibility of the white filler was inferior.
In contrast, the rubber compositions of Examples 1 to 5 prepared by blending a white filler with a silane coupling agent and a (meth) acrylate polymer having a reactive silyl group at the terminal have low viscosity. It was found that the dispersibility of the white filler was excellent and the rolling resistance of the tire was also good.
In particular, it can be seen from the comparison between Example 2 and Example 4 that by using a silane coupling agent containing a mercapto group, the dispersibility of the white filler becomes better and the rolling resistance of the tire is further improved. It was.
Further, from the comparison between Example 3 and Example 5, Example 5 in which the white filler and the (meth) acrylate polymer were mixed in advance had better dispersibility of the white filler, and the tire It was found that rolling resistance was also improved. This is considered that in Example 5, the above-mentioned aggregate was easily formed, and this aggregate contributed to the dispersibility of the white filler.

1 Bead part 2 Side wall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims (3)

Contains a diene rubber, a white filler, a silane coupling agent, and a (meth) acrylate polymer having a reactive silyl group at the end,
20% by mass or more of the diene rubber is styrene-butadiene copolymer rubber,
The content of the white filler is 5 to 150 parts by mass with respect to 100 parts by mass of the diene rubber,
The content of the silane coupling agent is 0.5 to 20% by mass with respect to the mass of the white filler,
A rubber composition for a tire tread, wherein the content of the (meth) acrylate polymer is 1 to 30% by mass with respect to the mass of the white filler.   The rubber composition for a tire tread according to claim 1, wherein a weight average molecular weight of the (meth) acrylate polymer is 500 to 100,000.   A pneumatic tire using the tire tread rubber composition according to claim 1 or 2 as a tire tread.