阅读说明：本技术 轮胎用橡胶组合物和充气轮胎 (Rubber composition for tire and pneumatic tire ) 是由 北王彩加 富崎由佳理 三木尚之 中畑祥子 于 2019-03-04 设计创作，主要内容包括：本发明提供了具有良好的二氧化硅分散性和燃料经济性的橡胶组合物,以及包含该橡胶组合物的充气轮胎。本发明涉及轮胎用橡胶组合物,该橡胶组合物包含：橡胶组分,该橡胶组分包含30质量％以上的具有SiOR基团的丁苯橡胶,其中,R表示氢原子或烃基；二氧化硅,该二氧化硅的氮吸附比表面积为210m<Sup>2</Sup>/g以上,相对于100质量份的橡胶组分,该二氧化硅的量为50质量份以上；至少一种表面活性剂,该表面活性剂选自聚氧化烯烯基醚硫酸酯盐和聚氧化烯烷基醚硫酸酯盐。(The present invention provides a rubber composition having good silica dispersibility and fuel economy, and a pneumatic tire comprising the rubber composition. The present invention relates to a rubber composition for a tire, comprising: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m 2 (ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.)

1. A rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silicon dioxide having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

2. The rubber composition for a tire according to claim 1, wherein a ratio X/Y of an amount X (parts by mass) of the surfactant to an amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

3. The rubber composition for a tire according to claim 1 or 2, wherein a ratio Z/(X + Y) of an amount Z (parts by mass) of the silica to an amount X (parts by mass) of the surfactant and an amount Y (parts by mass) of the silane coupling agent is 3 to 30.

4. The rubber composition for a tire according to any one of claims 1 to 3, wherein the surfactant is a polyoxyalkylene alkenyl ether sulfate.

5. A pneumatic tire having a tire member formed of the rubber composition described in any one of claims 1 to 4.

6. A rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; a total content of styrene-butadiene rubber in the rubber component is 70 to 90 mass% and a content of polybutadiene rubber is 10 to 30 mass%, each based on 100 mass% of the rubber component;

silicon dioxide having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

7. The rubber composition for a tire according to claim 6, wherein a ratio X/Y of an amount X (parts by mass) of the surfactant to an amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

8. The rubber composition for a tire according to claim 6 or 7, wherein a ratio Z/(X + Y) of an amount Z (parts by mass) of the silica to an amount X (parts by mass) of the surfactant and an amount Y (parts by mass) of the silane coupling agent is 3 to 30.

9. The rubber composition for a tire according to any one of claims 6 to 8, wherein the surfactant is a polyoxyalkylene alkenyl ether sulfate.

10. A pneumatic tire having a tire component formed of the rubber composition according to any one of claims 6 to 9.

11. A rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silicon dioxide having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 70 to 130 parts by mass with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

12. The rubber composition for a tire according to claim 11, wherein a ratio X/Y of an amount X (parts by mass) of the surfactant to an amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

13. The rubber composition for a tire according to claim 11 or 12, wherein a ratio Z/(X + Y) of the amount Z (parts by mass) of the silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

14. The rubber composition for a tire according to any one of claims 11 to 13, wherein the surfactant is a polyoxyalkylene alkenyl ether sulfate.

15. A pneumatic tire having a tire component formed of the rubber composition described in any one of claims 11 to 14.

16. A rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silicon dioxide having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate,

the silica and the surfactant are kneaded simultaneously with the rubber.

17. The rubber composition for a tire according to claim 16, wherein a ratio X/Y of an amount X (parts by mass) of the surfactant to an amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

18. The rubber composition for a tire according to claim 16 or 17, wherein a ratio Z/(X + Y) of the amount Z (parts by mass) of the silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

19. The rubber composition for a tire according to any one of claims 16 to 18, wherein the surfactant is a polyoxyalkylene alkenyl ether sulfate.

20. A pneumatic tire having a tire component formed from the rubber composition of any one of claims 16 to 19.

21. A rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silicon dioxide having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component;

carbon black in an amount of 2 parts by mass or more per 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

22. The rubber composition for a tire according to claim 21, wherein a ratio X/Y of an amount X (parts by mass) of the surfactant to an amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

23. The rubber composition for a tire according to claim 21 or 22, wherein a ratio Z/(X + Y) of an amount Z (parts by mass) of the silica to an amount X (parts by mass) of the surfactant and an amount Y (parts by mass) of the silane coupling agent is 3 to 30.

24. The rubber composition for a tire according to any one of claims 21 to 23, wherein a ratio a/Z of an amount a (parts by mass) of the carbon black to an amount Z (parts by mass) of the silica is 0.01 to 120.

25. The rubber composition for a tire according to any one of claims 21 to 24, wherein the surfactant is a polyoxyalkylene alkenyl ether sulfate.

26. A pneumatic tire having a tire component formed from the rubber composition of any one of claims 21 to 25.

Technical Field

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

Background

To meet the existing demand for tires having good fuel economy, silica has been used as a filler.

For example, patent document 1 discloses that silica can be incorporated to improve fuel economy, but this technique still leaves room for improvement. In addition, the development of other technologies is awaited.

Reference list

Patent document

Patent document 1: JP 2007-177221A

Disclosure of Invention

Technical problem

Through extensive studies, the present inventors found that the conventional techniques leave room for improvement in silica dispersibility and fuel economy, particularly when the silica used is a fine-grained silica having a large nitrogen adsorption specific surface area.

Accordingly, the present invention aims to provide a rubber composition excellent in silica dispersibility and fuel economy, and a pneumatic tire comprising the rubber composition.

Technical scheme

The first aspect of the present invention relates to a rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

Preferably, the ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

Preferably, the ratio Z/(X + Y) of the amount Z (parts by mass) of silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

Preferably, the surfactant is a polyoxyalkylene alkenyl ether sulfate.

The first aspect of the invention also relates to a pneumatic tire having a tire member formed of the rubber composition.

A second aspect of the present invention relates to a rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; the total content of styrene-butadiene rubber is 70 to 90 mass% and the content of polybutadiene rubber is 10 to 30 mass%, each based on 100 mass% of the rubber component;

silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

Preferably, the ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

Preferably, the ratio Z/(X + Y) of the amount Z (parts by mass) of silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

Preferably, the surfactant is a polyoxyalkylene alkenyl ether sulfate.

The second aspect of the invention also relates to a pneumatic tire including a tire member formed of the rubber composition.

The third aspect of the present invention relates to a rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 70 to 130 parts by mass with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

Preferably, the ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

Preferably, the ratio Z/(X + Y) of the amount Z (parts by mass) of silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

Preferably, the surfactant is a polyoxyalkylene alkenyl ether sulfate.

The third aspect of the invention also relates to a pneumatic tire having a tire member formed of the rubber composition.

The fourth aspect of the present invention relates to a rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate,

the silica and the surfactant are kneaded simultaneously with the rubber.

Preferably, the ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

Preferably, the ratio Z/(X + Y) of the amount Z (parts by mass) of silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

Preferably, the surfactant is a polyoxyalkylene alkenyl ether sulfate.

The fourth aspect of the invention also relates to a pneumatic tire having a tire member formed of the rubber composition.

A fifth aspect of the present invention relates to a rubber composition for a tire, comprising:

a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group;

silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component;

carbon black in an amount of 2 parts by mass or more per 100 parts by mass of the rubber component; and

at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

Preferably, the ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is 0.05 to 20.

Preferably, the ratio Z/(X + Y) of the amount Z (parts by mass) of silica to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is 3 to 30.

Preferably, the ratio a/Z of the amount a (parts by mass) of carbon black to the amount Z (parts by mass) of silica is 0.01 to 120.

Preferably, the surfactant is a polyoxyalkylene alkenyl ether sulfate.

The fifth aspect of the invention also relates to a pneumatic tire having a tire member formed of a rubber composition.

Advantageous effects of the invention

The first aspect of the present invention provides a rubber composition for a tire, comprising: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate. Such rubber compositions have good silica dispersibility and fuel economy.

A second aspect of the present invention provides a rubber composition for a tire, the rubber composition comprising: a rubber component containing 30 mass% or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group, and the total content of the styrene-butadiene rubber is 70 to 90 mass% and the content of the polybutadiene rubber is 10 to 30 mass%, each based on 100 mass% of the rubber component; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate. Such rubber compositions have good silica dispersibility and fuel economy.

The third aspect of the present invention provides a rubber composition for a tire, comprising: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 70 to 130 parts by mass with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate. Such rubber compositions have good silica dispersibility and fuel economy.

A fourth aspect of the present invention provides a rubber composition for a tire, the rubber composition comprising: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate, wherein the silica and the surfactant are kneaded simultaneously with the rubber. The rubber composition hasGood silica dispersion and fuel economy.

A fifth aspect of the present invention provides a rubber composition for a tire, the rubber composition comprising: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; carbon black in an amount of 2 parts by mass or more per 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate. Such rubber compositions have good silica dispersibility and fuel economy.

Detailed Description

(first aspect of the invention)

The rubber composition for a tire of the first aspect of the present invention comprises: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

The reason why such a rubber composition provides good silica dispersibility and fuel economy is not clear, but can be explained as follows.

The SiOR group in a styrene-butadiene rubber having an SiOR group (referred to as "modified SBR") can interact with a hydroxyl group on the surface of silica. Thus, the modified SBR can reduce aggregation of silica particles to improve silica dispersibility. Further, due to the presence of the polyoxyalkylene moiety and the sulfate ester salt moiety, the above surfactant can be appropriately adsorbed on the hydrophilic silica surface, so that the silica surface has a hydrophobic alkenyl group or alkyl group at the molecular terminal. Therefore, the surfactant can reduce the silica particlesAggregation of the particles improves silica dispersibility, and also prevents the vulcanization accelerator from being adsorbed to the silica. Further, the combination of the modified SBR and the surfactant may provide a synergistic improvement in silica dispersibility, so that better silica dispersibility and fuel economy may be obtained as compared to the conventional art. It is believed that this is because the presence of the surfactant improves the affinity between the silica and the modified SBR. Further, when the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²At least/g, the amount of the silica is at least 50 parts by mass relative to 100 parts by mass of the rubber component). It is considered that this is because, although the fine particle silica is liable to aggregate due to its strong aggregating ability, the combination of the modified SBR and the surfactant can provide a greater synergistic improvement in dispersibility of the fine particle silica, so that the effect of improving the dispersibility can be more pronounced.

Probably for this reason, the present invention provides a rubber composition having good silica dispersibility and fuel economy even if the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component).

In addition to good silica dispersion and fuel economy, the present invention also provides good processability, abrasion resistance and grip performance.

Further, the combined use of styrene-butadiene rubber having an SiOR group (wherein, R represents a hydrogen atom or a hydrocarbon group) and a surfactant can synergistically improve silica dispersibility and fuel economy.

The rubber composition contains a rubber component containing a styrene-butadiene rubber (modified SBR) having SiOR groups, wherein R represents a hydrogen atom or a hydrocarbon group.

The modified SBR may be any SBR having SiOR groups. For example, the modified SBR may be a chain end-modified SBR obtained by modifying at least one chain end of an SBR with a compound (modifier) having an SiOR group (i.e., chain end-modified SBR terminated with an SiOR group); a main chain-modified SBR having an SiOR group in the main chain; or a main chain and chain end-modified SBR having an SiOR group at both the main chain and the chain end (for example, a main chain and chain end-modified SBR having an SiOR group at the main chain and at least one chain end modified with a modifier). The modified SBR can also be coupled with a polyfunctional compound (e.g., a tin compound). These modified SBR may be used alone or in combination of two or more.

The hydrocarbon group of R may be linear, branched, or cyclic, and may be an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof. Among them, an aliphatic hydrocarbon group is preferable. Also preferred are straight chains. In order to obtain the advantageous effects more favorably, the carbon number of the hydrocarbon group is preferably 1 or more, but is preferably 20 or less, more preferably 12 or less, still more preferably 6 or less, and particularly preferably 3 or less.

The aliphatic hydrocarbon group preferably has 1 or more carbon atoms, but preferably has 20 or less carbon atoms, more preferably 12 or less carbon atoms, still more preferably 6 or less carbon atoms, and particularly preferably 3 or less carbon atoms. Preferred examples of such groups include: an alkyl group having the above carbon number range. Specific examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl and octadecyl. Among them, methyl, ethyl, n-propyl and isopropyl groups are preferable, and methyl and/or ethyl groups are more preferable, for better obtaining the advantageous effects.

Examples of the alicyclic hydrocarbon group include: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, and cyclooctenyl.

Examples of the aromatic hydrocarbon group include: phenyl, benzyl, phenethyl, tolyl, xylyl, and naphthyl. The tolyl group or the xylyl group may have a methyl substituent at any of the ortho-, meta-, and para-positions of the benzene ring thereof.

In order to obtain the advantageous effects more preferably, R is preferably a hydrogen atom or an aliphatic hydrocarbon group having the above carbon number range, and more preferably a hydrogen atom or an alkyl group having the above carbon number range.

SiOR groups are generally represented by formula (A):

wherein R is¹And R²The same OR different from each other, each represents a hydrogen atom, a hydrocarbon group OR an OR group, wherein R represents a hydrogen atom OR a hydrocarbon group.

R¹Or R²Examples of the hydrocarbon group of (a) include those described for R, and suitable embodiments thereof are the same as described above. Examples of the OR group include those described with respect to the SiOR group (OR group in SiOR group), suitable embodiments of which are the same as described above.

To more suitably obtain the advantageous effects, R¹And R²Preferably both OR groups. In other words, the SiOR group is preferably Si (OR)₃A group.

In addition to the SiOR group, the modified SBR can also have other functional groups.

Examples of such functional groups include: amino, amide, isocyanate, imino, imidazole, urea, ether, carbonyl, oxycarbonyl, mercapto, sulfide, disulfide, sulfonyl, sulfinyl, thiocarbonyl, ammonium, imide, hydrazino, azo, diazo, carboxyl, nitrile, pyridyl, alkoxy, hydroxyl, oxy, and epoxy. These functional groups may be substituted. Among them, an amino group (preferably a hydrogen atom is substituted by C) is preferable for more suitably obtaining the advantageous effects₁-C₆Alkyl-substituted amino) and alkoxy (preferably C)₁-C₆Alkoxy groups).

The modified SBR may be emulsion polymerized styrene butadiene rubber (E-SBR) or solution polymerized styrene butadiene rubber (S-SBR). These rubbers may be used alone or in combination of two or more.

The weight average molecular weight (Mw) of the modified SBR is preferably 200,000 or more, more preferably 300,000 or more, and still more preferably 500,000 or more. The upper limit of Mw is not limited, but is preferably 2,000,000 or less, more preferably 1,500,000 or less, and further more preferably 1,000,000 or less. When the Mw is within the above range, the advantageous effects tend to be well obtained.

Here, the weight average molecular weight (Mw) of the rubber component can be determined by Gel Permeation Chromatography (GPC) (GPC-8000 series, available from Tosoh Corporation; detector: differential refractometer; chromatographic column: TSKGEL SUPERMULTIPORE HZ-M, available from Tosoh Corporation), which is calibrated with polystyrene standards.

The styrene content of the modified SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and further more preferably 20% by mass or more, but is preferably 50% by mass or less, more preferably 40% by mass or less, further more preferably 30% by mass or less, and particularly preferably 25% by mass or less. When the styrene content is within the above range, the advantageous effects tend to be well obtained.

Here, by H¹NMR analysis to determine the styrene content of the SBR.

The vinyl group content of the modified SBR is preferably 5% by mass or more, more preferably 10% by mass or more, further more preferably 20% by mass or more, particularly preferably 30% by mass or more, and most preferably 40% by mass or more, but preferably 70% by mass or less, and more preferably 60% by mass or less. When the vinyl content is within the above range, the advantageous effects tend to be well obtained.

Here, the vinyl group content (1, 2-butadiene unit content) can be measured by infrared absorption spectrometry.

For example, the modified SBR may be an SBR product manufactured or sold by Sumitomo Chemical co., ltd., JSR Corporation, asahi kasei Corporation, Zeon Corporation, or Dow.

The amount of the modified SBR is 30 mass% or more, preferably 50 mass% or more, and more preferably 60 mass% or more, based on 100 mass% of the rubber component. The upper limit may be 100 mass%, but when the rubber component contains any other rubber, the amount of modified SBR is preferably 90 mass% or less, more preferably 80 mass% or less. When the amount is within the above range, the advantageous effects tend to be well obtained.

Examples of materials other than the modified SBR that can be used in the rubber component of the rubber composition include SBR other than the modified SBR and diene rubber such as polybutadiene rubber (BR), isoprene-based rubber, nitrile rubber (NBR), Chloroprene Rubber (CR), butyl rubber (IIR) and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used alone or in combination of two or more.

The SBR other than the modified SBR (second SBR) is preferably an unmodified SBR having no functional group.

The preferred weight average molecular weight (Mw), styrene content, and vinyl content of the second SBR are as described for the modified SBR.

For example, the second SBR may be an SBR product manufactured or sold by Sumitomo Chemical co., ltd., JSR Corporation, asahi kasei Corporation, Zeon Corporation, or Dow.

The total content of the SBR (the total amount of the modified SBR and the second SBR) is preferably 30 mass% or more, more preferably 50 mass% or more, and further more preferably 70 mass% or more, based on 100 mass% of the rubber component. The upper limit may be 100 mass%, but when the rubber component contains any rubber other than SBR, the total content of SBR is preferably 90 mass% or less, more preferably 80 mass% or less. When the total content of SBR is within the above range, favorable effects tend to be obtained well.

Non-limiting examples of BR include: high cis BR, BR containing syndiotactic polybutadiene crystals, and polybutadiene rubber synthesized using rare earth catalysts (rare earth catalyzed BR). These may be used alone or in combination of two or more. Among them, high cis BR is preferable.

The BR can be unmodified BR or modified BR. These may be used alone or in combination of two or more.

Examples of the modified BR include those into which the listed functional groups for modified SBR have been introduced.

The cis content of BR is preferably 90 mass% or more, more preferably 93 mass% or more, and further more preferably 95 mass% or more. When the cis content is more than the lower limit, good abrasion resistance tends to be obtained.

Here, the cis content of the rubber component can be measured by infrared absorption spectroscopy.

For example, BR may be available from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation or Lanxess.

The amount of BR is preferably 5% by mass or more, more preferably 10% by mass or more, but preferably 50% by mass or less, more preferably 40% by mass or less, and further more preferably 30% by mass or less, based on 100% by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The total amount of the SBR (modified SBR and second SBR) and the BR is preferably 60 mass% or more, more preferably 80 mass% or more, further more preferably 90 mass% or more, and may be 100 mass% based on 100 mass% of the rubber component. When the total amount is within the above range, the advantageous effects tend to be well obtained.

Examples of the isoprene-based rubber include: natural Rubber (NR), polyisoprene rubber (IR), purified NR, modified NR and modified IR. Examples of NRs include those commonly used in the tire industry, such as SIR20, RSS #3, and TSR 20. Non-limiting examples of IR include those commonly used in the tire industry, such as IR 2200. Examples of the refined NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of modified NR include: epoxidized Natural Rubber (ENR), Hydrogenated Natural Rubber (HNR) and grafted natural rubber. Examples of modified IR include: epoxidized polyisoprene rubber, hydrogenated polyisoprene rubber and grafted polyisoprene rubber. These may be used alone or in combination of two or more. The amount of the isoprene-based rubber may be any amount that does not impair the beneficial effects, based on 100 mass% of the rubber component. The amount is preferably 5% by mass or more, but preferably 20% by mass or less.

The rubber composition contains silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component.

Examples of silica include dry silica (silicic anhydride) and wet silica (hydrous silicic acid). Wet silica is preferred because it has a large number of silanol groups. These may be used alone or in combination of two or more.

Nitrogen adsorption specific surface area (N) of silica₂SA) is preferably 220m²More preferably 230 m/g or more²(ii) at least g, more preferably 240m²More than g. N is a radical of₂SA is also preferably 300m²A value of 270m or less, more preferably 270m²The ratio of the carbon atoms to the carbon atoms is less than g. When N is present₂When SA is within the above range, the advantageous effect tends to be obtained well.

The nitrogen adsorption specific surface area of silica is measured by the BET method of ASTM D3037-81.

For example, the Silica may be a commercial product of Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan, or Tokuyama Corporation.

The amount of silica is 50 parts by mass or more, preferably 60 parts by mass or more, more preferably 70 parts by mass or more, but preferably 150 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 120 parts by mass or less, and particularly preferably 100 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

In addition to the above silica, the rubber composition may contain any silica (second silica) other than the silica. In this case, the total silica content may be the same as when silica is used alone.

The rubber composition contains at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate. These may be used alone or in combination of two or more.

The surfactant preferably has an ethylene oxide structure and/or a propylene oxide structure. The surfactant having an ethylene oxide structure and/or a propylene oxide structure as a hydrophilic group provides a higher affinity with silica, so that advantageous effects can be more suitably obtained. Among these structures, the surfactant preferably has an ethylene oxide structure. In the case of a surfactant having an ethylene oxide structure and/or a propylene oxide structure, the average number of moles of Ethylene Oxide (EO) and Propylene Oxide (PO) added (the sum of the average numbers of moles of EO and PO added) is preferably 10 or more, more preferably 13 or more, but is preferably 80 or less, more preferably 60 or less, and still more preferably 40 or less. In this case, the surfactant has a higher affinity with silica, so that a favorable effect can be more suitably obtained.

Further, the carbon number of each of the alkenyl group of the polyoxyalkylene alkenyl ether sulfate salt and the alkyl group of the polyoxyalkylene alkyl ether sulfate salt is preferably 8 or more, more preferably 10 or more, but preferably 20 or less, more preferably 18 or less, and even more preferably 15 or less. In this case, the silica dispersibility can be further improved, and thus advantageous effects can be more suitably obtained.

Non-limiting examples of surfactants in salt form include: alkali metal salts such as potassium and sodium salts; alkaline earth metal salts such as magnesium and calcium salts; amine salts such as monoethanolamine, diethanolamine, and triethanolamine salts; and ammonium salts. In order to more suitably obtain the advantageous effects, among them, alkali metal salts or ammonium salts are preferable, and sodium salts or ammonium salts are more preferable.

The HLB value (measured by the griffin method) of the surfactant is preferably 12 or more, more preferably 13 or more, but is preferably 19 or less, more preferably 17 or less. When the HLB value is within the above range, the beneficial effect tends to be well obtained.

Among polyoxyalkylene alkenyl ether sulfate ester salts and polyoxyalkylene alkyl ether sulfate ester salts, polyoxyalkylene alkenyl ether sulfate ester salts are preferable.

A preferred polyoxyalkylene alkenyl ether sulfate salt is a polyoxyalkylene alkenyl ether sulfate salt. More preferably ammonium polyoxyethylene alkenyl ether sulfate.

The preferred polyoxyalkylene alkyl ether sulfate salt is a polyoxyethylene alkyl ether sulfate salt. More preferably sodium polyoxyethylene alkyl ether sulfate.

For example, the surfactant may be a commercial product of Kao Corporation, Lion Corporation, or Lion specialty Chemicals Co., Ltd.

The amount of the surfactant is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, and further more preferably 2 parts by mass or more, but is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and further more preferably 10 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition may contain the above-mentioned surfactant and any surfactant (second surfactant) other than the surfactant. In this case, the total content of the surfactant may be the same as that when the surfactant is used alone.

The rubber composition preferably further contains a silane coupling agent.

Non-limiting examples of silane coupling agents include: sulfide-based silane coupling agents, for example, bis (3-triethoxysilylpropyl) disulfide, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylethyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (triethoxysilylpropyl) disulfide, bis (3-triethoxysilylpropyl) disulfide, bis (triethoxysil, Bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and NXT-Z (both available from Momentive); vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; aminosilane coupling agents such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silane coupling agents such as gamma-glycidoxypropyltriethoxysilane and gamma-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; chlorine-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. These may be used alone or in combination of two or more. Among them, sulfide-based silane coupling agents and mercapto-based silane coupling agents are preferable, and among them, mercapto-based silane coupling agents are more preferable because beneficial effects tend to be obtained well.

Here, the term "mercapto-based silane coupling agent" is not limited to a silane coupling agent having a mercapto group (-SH), and conceptually includes a silane coupling agent having a mercapto derivative group (for example, carbonylthio (-S-C (═ O) -)). The term "mercapto derivative group" is not limited to a group directly derived from a mercapto group (-SH) by a synthetic reaction, and conceptually includes a group in which a hydrogen atom of a mercapto group (-SH) is substituted with a different atom or group.

The mercapto-based silane coupling agent is preferably a silane coupling agent having a mercapto group (-SH), more preferably a compound represented by the following formula (1) and/or a compound containing the linking units a and B represented by the following formulae (2) and (3), respectively, and even more preferably a compound containing the linking units a and B of the formulae (2) and (3). The mercapto silane coupling agent can be used more suitably to obtain advantageous effects.

In the formula (1), R¹⁰¹To R¹⁰³Each represents a branched or unbranched C₁-C₁₂Alkyl, branched or unbranched C₁-C₁₂Alkoxy or from-O- (R)¹¹¹-O)_z-R¹¹²A group represented by (A) wherein R¹¹¹(number z) represents a branched or unbranched C₁-C₃₀A divalent hydrocarbon group, each R¹¹¹May be the same or different; r¹¹²Represents a branched or unbranched C₁-C₃₀Alkyl, branched or unbranched C₂-C₃₀An alkenyl group,C₆-C₃₀Aryl or C₇-C₃₀Aralkyl group; z represents an integer of 1 to 30; r¹⁰¹To R¹⁰³May be the same or different from each other; and R¹⁰⁴Represents a branched or unbranched C₁-C₆An alkylene group.

In the formulas (2) and (3), x represents an integer of 0 or more; y represents an integer of 1 or more; r²⁰¹Represents a hydrogen atom, a halogen atom, a branched or unbranched C₁-C₃₀Alkyl, branched or unbranched C₂-C₃₀Alkenyl, branched or unbranched C₂-C₃₀Alkynyl or alkyl with a terminal hydrogen atom substituted with hydroxyl or carboxyl; r²⁰²Represents a branched or unbranched C₁-C₃₀Alkylene, branched or unbranched C₂-C₃₀Alkenylene or branched or unbranched C₂-C₃₀Alkynylene with the proviso that R²⁰¹And R²⁰²May together form a ring structure.

The compounds of formula (1) are described below.

The use of the compound of formula (1) gives good silica dispersibility, so that advantageous effects can be obtained even better.

R¹⁰¹To R¹⁰³Each represents a branched or unbranched C₁-C₁₂Alkyl, branched or unbranched C₁-C₁₂Alkoxy or from-O- (R)¹¹¹-O)_z-R¹¹²The group shown. Based on the starting point that the beneficial effect is well obtained, R¹⁰¹To R¹⁰³At least one of them is preferably represented by-O- (R)¹¹¹-O)_z-R¹¹²A group represented by (a); more preferably, R¹⁰¹To R¹⁰³Two of them are represented by-O- (R)¹¹¹-O)_z-R¹¹²The radicals indicated and the other being branched or unbranched C₁-C₁₂An alkoxy group.

R¹⁰¹To R¹⁰³Branched or unbranched C of₁-C₁₂Examples of alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl and nonyl.

The upper limit of the carbon number is preferably 5.

R¹⁰¹To R¹⁰³Branched or unbranched C of₁-C₁₂Examples of alkoxy groups include: methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, hexoxy, heptoxy, 2-ethylhexoxy, octoxy and nonoxy.

The upper limit of the carbon number is preferably 5.

At R¹⁰¹To R¹⁰³Is composed of-O- (R)¹¹¹-O)_z-R¹¹²In the group represented, R¹¹¹Represents a branched or unbranched C₁-C₃₀(preferably C)₁-C₁₅More preferably C₁-C₃) A divalent hydrocarbon group.

Examples of hydrocarbyl groups include: c, branched or unbranched₁-C₃₀Alkylene, branched or unbranched C₂-C₃₀Alkenylene, branched or unbranched C₂-C₃₀Alkynylene and C₆-C₃₀An arylene group. Among them, a branched or unbranched C is preferable₁-C₃₀An alkylene group.

R¹¹¹Branched or unbranched C of₁-C₃₀Examples of alkylene groups include: methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecenyl, tridecylene, tetradecylene, pentadecenyl, hexadecylene, heptadecenyl, and octadecylene.

The upper limit of the carbon number is preferably 15, and more preferably 3.

R¹¹¹Branched or unbranched C of₂-C₃₀Examples of alkenylene groups include: vinylidene, 1-propenylene, 2-propenylene, 1-butenylene, 2-butenylene, 1-pentenylene, 2-butenylene-pentenylene, 1-hexenylene, 2-hexenylene and 1-octenylene.

The upper limit of the carbon number is preferably 15, and more preferably 3.

R¹¹¹Branched or unbranched C of₂-C₃₀Examples of alkynylene groups include: ethynylene, propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl, decynyl, undecylenyl and dodecylenyl.

The upper limit of the carbon number is preferably 15, and more preferably 3.

R¹¹¹C of (A)₆-C₃₀Examples of the arylene group include: phenylene, tolylene, xylylene, and naphthylene.

The upper limit of the carbon number is preferably 15.

The symbol z represents an integer of 1 to 30. The lower limit is preferably 2, more preferably 3, and still more preferably 5; the upper limit is preferably 20, more preferably 7, and still more preferably 6.

R¹¹²Represents a branched or unbranched C₁-C₃₀Alkyl, branched or unbranched C₂-C₃₀Alkenyl radical, C₆-C₃₀Aryl or C₇-C₃₀An aralkyl group. Wherein R is¹¹²Preferably branched or unbranched C₁-C₃₀An alkyl group.

R¹¹²Branched or unbranched C of₁-C₃₀Examples of alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl and octadecyl.

The lower limit of the carbon number is preferably 3, more preferably 10; the upper limit of the carbon number is preferably 25, more preferably 15.

R¹¹²Branched or unbranched C of₂-C₃₀Examples of alkenyl groups include: vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group,1-octenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, and octadecenyl.

The lower limit of the carbon number is preferably 3, more preferably 10; the upper limit of the carbon number is preferably 25, more preferably 15.

R¹¹²C of (A)₆-C₃₀Examples of the aromatic group include: phenyl, tolyl, xylyl, naphthyl, and biphenyl groups.

The lower limit of the carbon number is preferably 10; the upper limit of the carbon number is preferably 20.

R¹¹²C of (A)₇-C₃₀Examples of the aralkyl group include: benzyl and phenethyl.

The lower limit of the carbon number is preferably 10; the upper limit of the carbon number is preferably 20.

from-O- (R)¹¹¹-O)_z-R¹¹²Specific examples of the group represented include: -O- (C)₂H₄-O)₅-C₁₁H₂₃、-O-(C₂H₄-O)₅-C₁₂H₂₅、-O-(C₂H₄-O)₅-C₁₃H₂₇、-O-(C₂H₄-O)₅-C₁₄H₂₉、-O-(C₂H₄-O)₅-C₁₅H₃₁、-O-(C₂H₄-O)₃-C₁₃H₂₇、-O-(C₂H₄-O)₄-C₁₃H₂₇、-O-(C₂H₄-O)₆-C₁₃H₂₇and-O- (C)₂H₄-O)₇-C₁₃H₂₇. Among them, preferred is-O- (C)₂H₄-O)₅-C₁₁H₂₃、-O-(C₂H₄-O)₅-C₁₃H₂₇、-O-(C₂H₄-O)₅-C₁₅H₃₁and-O- (C)₂H₄-O)₆-C₁₃H₂₇。

R¹⁰⁴Branched or unbranched C of₁-C₆Examples of alkylene groups include those related to R¹¹¹Is branched chain ofOr unbranched C₁-C₃₀Alkylene or a group described above.

The upper limit of the carbon number is preferably 5.

Examples of the compound of formula (1) include: 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and a compound represented by the following formula (Si363, manufactured by EVONIK-DEGUSSA). Compounds of the formula are suitable. These compounds may be used alone or in combination of two or more.

Compounds comprising linking units a and B represented by formulas (2) and (3), respectively, are described below.

In order to better obtain the advantageous effects, the content of the linking unit a of the silane coupling agent having such a structure is preferably not less than 30 mol%, more preferably not less than 50 mol%, but preferably not more than 99 mol%, more preferably not more than 90 mol%. It is also preferable that the content of the linking unit B is not less than 1 mol%, more preferably not less than 5 mol%, further more preferably not less than 10 mol%, but preferably not more than 70 mol%, more preferably not more than 65 mol%, further more preferably not more than 55 mol%. Further, the total content of the linking units A and B is preferably not less than 95 mol%, more preferably not less than 98 mol%, particularly preferably 100 mol%.

The content of the linking unit A or B means the amount including the linking unit A or B present at the terminal of the silane coupling agent (if any). When the linking unit a or B is present at the terminal of the silane coupling agent, the form thereof is not particularly limited as long as it forms a unit corresponding to the linking unit a represented by formula (2) or the linking unit B represented by formula (3).

R²⁰¹Examples of the halogen atom of (a) include: chlorine, bromine and fluorine.

R²⁰¹Branched or unbranched C of₁-C₃₀Examples of alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, and mixtures thereof,2-ethylhexyl, octyl, nonyl and decyl. The carbon number of the alkyl group is preferably 1 to 12.

R²⁰¹Branched or unbranched C of₂-C₃₀Examples of alkenyl groups include: vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 1-hexenyl, 2-hexenyl and 1-octenyl. The carbon number of the alkenyl group is preferably 2 to 12.

R²⁰¹Branched or unbranched C of₂-C₃₀Examples of alkynyl groups include: ethynyl, propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl, decynyl, undecylynyl and dodecylynyl. The carbon number of the alkynyl group is preferably 2 to 12.

R²⁰²Branched or unbranched C of₁-C₃₀Examples of alkylene groups include: ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecenyl, tridecylene, tetradecylene, pentadecenyl, hexadecylene, heptadecenyl, and octadecylene. The carbon number of the alkylene group is preferably 1 to 12.

R²⁰²Branched or unbranched C of₂-C₃₀Examples of alkenylene groups include: vinylidene, 1-propenylene, 2-propenylene, 1-butenylene, 2-butenylene, 1-pentenylene, 2-pentenylene, 1-hexenylene, 2-hexenylene and 1-octenylene. The carbon number of the alkenylene group is preferably 2 to 12.

R²⁰²Branched or unbranched C of₂-C₃₀Examples of alkynylene groups include: ethynylene, propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl, decynyl, undecylenyl and dodecylenyl. The carbon number of the alkynylene group is preferably 2 to 12.

In the compound comprising the linking units a and B of the formulae (2) and (3), the sum (x + y) of the number of repetition (x) of the linking unit a and the number of repetition (y) of the linking unit B is preferably 3 to 300. When the sum is within the above range, the units A are linked to C₇H₁₅Partial coveringThe mercaptosilane of unit B is linked, so that the reduction in scorch time can be reduced and good reactivity with silica and rubber components is also ensured.

Examples of the compounds containing the linking units a and B of the formulae (2) and (3) include: NXT-Z30, NXT-Z45 and NXT-Z60, all available from Momentive. These may be used alone or in combination of two or more.

The silane coupling agent may be, for example, commercial products of Degussa, Momentive, Shin-Etsu Silicone, Tokyo chemical industry Co., Ltd., AZmax. Co., or Dow Corning Toray Co., Ltd.

The amount of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, but preferably 20 parts by mass or less, more preferably 15 parts by mass or less, relative to 100 parts by mass of silica. When the amount is within the above range, the advantageous effects tend to be well obtained.

The ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is preferably 0.05 to 20. When the ratio is within the above range, the advantageous effects tend to be well obtained. These amounts each refer to an amount relative to 100 parts by mass of the rubber component.

The lower limit of X/Y is preferably 0.1, more preferably 0.2, further more preferably 0.25; the upper limit of X/Y is preferably 10, more preferably 5, still more preferably 2, and most preferably 1.

The nitrogen adsorption specific surface area is 210m²The ratio Z/(X + Y) of the amount Z (parts by mass) of silica per g to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is preferably 3 to 30. When the ratio is within the above range, the advantageous effects tend to be well obtained. These amounts each refer to an amount relative to 100 parts by mass of the rubber component.

The lower limit of Z/(X + Y) is preferably 4, more preferably 5; the upper limit of Z/(X + Y) is preferably 20, more preferably 15, still more preferably 12, particularly preferably 10, most preferably 8.

The rubber composition preferably contains carbon black. In this case, favorable effects can be obtained appropriately.

Non-limiting examples of carbon blacks include: n134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. These may be used alone or in combination of two or more.

Nitrogen adsorption specific surface area (N) of carbon black₂SA) is preferably 70m²A value of 80m or more, more preferably 80m²(ii) at least g, more preferably 100m²More than g. N is a radical of₂SA is preferably 300m²A ratio of the total amount of the components to the total amount of the components is 250m or less²(ii) less than g, more preferably 200m²A specific ratio of 160m or less per gram²The ratio of the carbon atoms to the carbon atoms is less than g. When N is present₂When SA is within the above range, the advantageous effect tends to be obtained well.

Nitrogen adsorption specific surface area of carbon black according to JIS K6217-2: 2001.

For example, the Carbon black may be a commercial product of Asahi Carbon co., ltd., Cabot Japan k.k., Tokai Carbon co., ltd., Mitsubishi Chemical Corporation, Lion Corporation, NSCC Carbon co., ltd., or Columbia Carbon.

The amount of carbon black is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, but is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, further more preferably 30 parts by mass or less, particularly preferably 20 parts by mass or less, and most preferably 10 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The amount A (parts by mass) of carbon black and the nitrogen adsorption specific surface area were 210m²The ratio A/Z of the amount Z (parts by mass) of silica/g or more is preferably 0.01 to 120. When the ratio is within the above range, favorable effects tend to be obtained well. These amounts each refer to an amount relative to 100 parts by mass of the rubber component.

The lower limit of A/Z is preferably 0.02, more preferably 0.03; the upper limit of A/Z is preferably 20, more preferably 1, still more preferably 0.5, and particularly preferably 0.2.

The rubber composition may comprise an oil.

Examples of oils include: process oils, vegetable oils and mixtures thereof. Examples of process oils include: paraffinic process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include: castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower seed oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combination of two or more. Among them, aromatic process oils are preferable.

For example, the oil may be a commercial product of Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo K.K., Japan energy Corporation, Oliisoy, H & R, Hokoku Corporation, Showa Shell Sekiyu K.K., or Fuji Kosan Co., Ltd.

The amount of the oil is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and further more preferably 20 parts by mass or more, but is preferably 70 parts by mass or less, and more preferably 50 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The amount of oil includes the amount of oil (if present) in the rubber (oil-extended rubber).

The rubber composition preferably contains sulfur.

Examples of sulfur include: those commonly used in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. These may be used alone or in combination of two or more.

For example, the Sulfur may be a commercial product of Tsuumi Chemical Industry Co., Ltd., Karuizawa sulfurr Co., Ltd., Shikoku Chemicals Corporation, Flexsys, Nippon Kanryu Industry Co., Ltd., or Hosoi Chemical Industry Co., Ltd.

The sulfur content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, but preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and further more preferably 3 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition preferably contains a vulcanization accelerator.

Examples of the vulcanization accelerator include: thiazole-based vulcanization accelerators such as 2-Mercaptobenzothiazole (MBT) and dibenzothiazyl disulfide (MBTS); thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD) and tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-tert-butyl-2-benzothiazylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-oxyethylene-2-benzothiazylsulfenamide and N, N' -diisopropyl-2-benzothiazylsulfenamide; and guanidine-based vulcanization accelerators such as 1, 3-Diphenylguanidine (DPG), di-o-tolylguanidine and o-tolylbiguanide. These may be used alone or in combination of two or more. In order to more suitably obtain the advantageous effects, among them, thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferable. Also preferred is a combination of a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator or a combination of a thiazole-based vulcanization accelerator and a guanidine-based vulcanization accelerator.

Preferred thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are: MBT and MBTS; TBBS and CBS; and DPG.

The amount of the vulcanization accelerator is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, but preferably 10 parts by mass or less, more preferably 7 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition may comprise a resin.

Any resin commonly used in the tire industry can be used, and examples include: rosin resin, coumarone indene resin, α -methylstyrene resin, terpene resin, p-tert-butylphenol acetylene resin, acrylic resin, C5 resin and C9 resin. Examples of such commercially available resins include products of Maruzen Petrochemical co., ltd., Sumitomo Bakelite co., ltd., Yasuhara Chemical co., ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nitto Chemical co., ltd., Nippon Shokubai co., ltd., JX energy Corporation, Arakawa Chemical Industries, ltd., Taoka Chemical co., ltd., and Toagosei co. These may be used alone or in combination of two or more.

From the viewpoint of balance of properties, the amount of the resin is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, but is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, relative to 100 parts by mass of the rubber component.

The rubber composition may comprise an antioxidant.

Examples of antioxidants include: naphthylamine-based antioxidants, such as phenyl- α -naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4 '-bis (α, α' -dimethylbenzyl) diphenylamine; p-phenylenediamine antioxidants, such as N-isopropyl-N ' -phenyl-p-phenylenediamine, N- (1, 3-dimethylbutyl) -N ' -phenyl-p-phenylenediamine, and N, N ' -di-2-naphthyl-p-phenylenediamine; quinoline-based antioxidants, such as 2,2, 4-trimethyl-1, 2-dihydroquinoline polymers; monohydric phenol-based antioxidants such as 2, 6-di-t-butyl-4-methylphenol and styrenated phenol; and bisphenol, triphenol, or polyphenol antioxidants such as tetrakis [ methylene-3- (3 ', 5 ' -di-tert-butyl-4 ' -hydroxyphenyl) propionate ] methane. These may be used alone or in combination of two or more. Among them, a p-phenylenediamine-based antioxidant and a quinoline-based antioxidant are preferable, and a p-phenylenediamine-based antioxidant is more preferable.

For example, the antioxidant may be a commercial product of Seiko Chemical co.

The amount of the antioxidant is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, but preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition may comprise a wax.

Non-limiting examples of waxes include: petroleum waxes, such as paraffin wax and microcrystalline wax; natural waxes such as vegetable waxes and animal waxes; synthetic waxes, such as polymers of ethylene, propylene, or other similar monomers. These may be used alone or in combination of two or more. Among them, petroleum wax is preferable, and paraffin wax is more preferable.

For example, the wax may be a commercial product of Ouchi Shinko Chemical Industrial co.

From the viewpoint of balance of properties, the amount of the wax is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, but preferably 20 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the rubber component.

The rubber composition preferably comprises a fatty acid.

The fatty acid may be a conventional fatty acid, such as stearic acid, oleic acid or palmitic acid. Stearic acid is preferred because it is advantageous to achieve good results. These may be used alone or in combination of two or more.

For example, the Fatty Acid may be a commercial product of NOF Corporation, Kao Corporation, Wako Pure chemical industries Ltd, or Chiba Fatty Acid Co., Ltd.

The amount of the fatty acid is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, but preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition preferably comprises zinc oxide.

The Zinc oxide may be conventional Zinc oxide, and examples of such commercially available Zinc oxide include products of Mitsui Mining & smeltingco, ltd, Toho Zinc co, ltd, hakusui co, ltd, Seido Chemical Industry co, ltd, and Sakai Chemical Industry co, ltd.

The amount of zinc oxide is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, but preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be better obtained.

In addition to the above components, the rubber composition may contain additives commonly used in the tire industry, including, for example, organic peroxides and fillers (e.g., magnesium sulfate). The amount of each filler is preferably 0.1 part by mass or more, but preferably 200 parts by mass or less, relative to 100 parts by mass of the rubber component.

For example, the rubber composition can be prepared by the following method: by kneading the components using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanizing the kneaded mixture.

The kneading conditions were as follows. In the basic kneading step of kneading the additives other than the crosslinking agent (vulcanizing agent) and the vulcanization accelerator, the kneading temperature is usually 100 ℃ to 180 ℃, preferably 120 ℃ to 170 ℃. In the final kneading step of kneading the vulcanizing agent and the vulcanization accelerator, the kneading temperature is usually 120 ℃ or less, preferably 85 ℃ to 110 ℃. The composition obtained after kneading the vulcanizing agent and the vulcanization accelerator is usually vulcanized by, for example, press vulcanization. The vulcanization temperature is generally from 140 ℃ to 190 ℃, preferably from 150 ℃ to 185 ℃.

The rubber composition has good fuel economy and is therefore useful for tire components such as treads (cap treads), sidewalls, base treads, undertreads, clinchs, bead apexes, breaker rubbers, rubber for carcass cord topping, barrier rubbers, chafers, innerliners, and side reinforcements for run-flat tires (run-flat tires). Among them, the rubber composition is suitable for a tread.

(pneumatic tires)

The pneumatic tire of the present invention can be manufactured from the rubber composition by a conventional method. Specifically, an unvulcanized rubber composition containing the above components may be extruded into the shape of a tire member (e.g., a tread), and then assembled with other tire members on a tire building machine in a conventional manner to manufacture an unvulcanized tire, and then heated and pressurized in a vulcanizing machine, thereby producing a tire.

The pneumatic tire may be suitably used as, for example, a tire for passenger cars, large SUVs, or trucks and buses, or a racing tire, studless winter tire (winter tire), a tire for two-wheeled vehicles, a safety tire, an airplane tire, or a mining tire.

(second aspect of the invention)

Next, a second aspect of the present invention will be explained, but differences from the first aspect of the present invention will be mainly described. The above description of the first aspect of the invention applies unless otherwise indicated.

The rubber composition for a tire of the second aspect of the present invention comprises: a rubber component containing 30 mass% or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group, and the total content of the styrene-butadiene rubber is 70 to 90 mass% and the content of the polybutadiene rubber is 10 to 30 mass%, each based on 100 mass% of the rubber component; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

The reason why such rubber compositions provide good silica dispersibility and fuel economy is not completely clear, but can be explained as follows.

The SiOR group in a styrene-butadiene rubber having an SiOR group (referred to as "modified SBR") can interact with a hydroxyl group on the surface of silica. Thus, the modified SBR can reduce aggregation of silica particles to improve silica dispersibility. Further, due to the presence of the polyoxyalkylene moiety and the sulfate ester salt moiety, the above surfactant can be appropriately adsorbed on the hydrophilic silica surface, so that the silica surface has a hydrophobic alkenyl group or alkyl group at the molecular terminal. Therefore, the surfactant can reduce aggregation of silica particles to improve silica dispersibility, and can also prevent the vulcanization accelerator from adsorbing to silica. Further, the combination of the modified SBR and the surfactant may provide a synergistic improvement in silica dispersibility, so that better silica dispersibility and fuel economy may be obtained as compared to the conventional art. It is believed that this is because the presence of the surfactant improves the affinity between the silica and the modified SBR. Further, when the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²At least/g, the amount of the silica is at least 50 parts by mass relative to 100 parts by mass of the rubber component). It is believed that the first and second electrodes,this is because, although the fine particle silica is liable to aggregate due to its strong aggregating ability, the combination of the modified SBR and the surfactant can provide a greater synergistic improvement in dispersibility of the fine particle silica, so that the effect of improving the dispersibility can be more pronounced.

Probably for this reason, the present invention provides a rubber composition having good silica dispersibility and fuel economy even if the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component).

Further, in the present invention, the total content of the styrene-butadiene rubber is 70 to 90 mass% and the content of the polybutadiene rubber is 10 to 30 mass% based on 100 mass% of the rubber component. In other words, the rubber component is composed of rubbers highly compatible with each other. Therefore, the effect produced by the combination of the modified SBR and the surfactant can be sufficiently obtained, while the silica is well dispersed even in the polybutadiene rubber phase, thereby providing good abrasion resistance.

In addition to good silica dispersion and fuel economy, the present invention also provides good processability, abrasion resistance and grip performance.

Further, the combined use of styrene-butadiene rubber having an SiOR group (wherein, R represents a hydrogen atom or a hydrocarbon group) and a surfactant can synergistically improve silica dispersibility and fuel economy.

The amount of modified SBR is 30 mass% or more, preferably 50 mass% or more, and more preferably 60 mass% or more, but preferably 90 mass% or less, and more preferably 80 mass% or less, based on 100 mass% of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The total content of the SBR (the total amount of the modified SBR and the second SBR) is preferably 70% by mass or more, but preferably 90% by mass or less, more preferably 80% by mass or less, based on 100% by mass of the rubber component. When the total content of SBR is within the above range, favorable effects tend to be obtained well.

The amount of BR is preferably 10% by mass or more, more preferably 20% by mass or more, but preferably 30% by mass or less, based on 100% by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The total amount of the SBR (modified SBR and second SBR) and the BR is preferably 80 mass% or more, more preferably 90 mass% or more, and may be 100 mass% based on 100 mass% of the rubber component. When the total amount is within the above range, the advantageous effects tend to be well obtained.

The amount of the surfactant is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, and further more preferably 2 parts by mass or more, but is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, further more preferably 10 parts by mass or less, and particularly preferably 8 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The mercaptosilane coupling agent is preferably a silane coupling agent having a mercapto group (-SH), more preferably a compound of formula (1) and/or a compound comprising linking units a and B of formulae (2) and (3), and further more preferably a compound of formula (1). In this case, advantageous effects can be obtained more appropriately.

The amount of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, but is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and further more preferably 11 parts by mass or less, relative to 100 parts by mass of the silica. When the amount is within the above range, the advantageous effects tend to be well obtained.

The ratio X/Y of the amount X (parts by mass) of the surfactant to the amount Y (parts by mass) of the silane coupling agent is preferably 0.05 to 20. When the ratio is within the above range, the advantageous effects tend to be well obtained. These amounts each refer to an amount relative to 100 parts by mass of the rubber component.

The lower limit of X/Y is preferably 0.1, more preferably 0.2, further more preferably 0.25; the upper limit of X/Y is preferably 10, more preferably 5, further more preferably 2, most preferably 1, and even most preferably 0.8.

The nitrogen adsorption specific surface area is 210m²The ratio Z/(X + Y) of the amount Z (parts by mass) of silica per g to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is preferably 3 to 30. When the ratio is within the above range, the advantageous effects tend to be well obtained. These amounts each refer to an amount relative to 100 parts by mass of the rubber component.

The lower limit of Z/(X + Y) is preferably 4, more preferably 5; the upper limit of Z/(X + Y) is preferably 20, more preferably 15, still more preferably 12, and particularly preferably 10.

(third aspect of the invention)

Next, a third aspect of the present invention will be explained, but differences from the first aspect of the present invention will be mainly described. The above description of the first aspect of the invention applies unless otherwise indicated.

The rubber composition for a tire of the third aspect of the present invention comprises: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 70 to 130 parts by mass with respect to 100 parts by mass of the rubber component; and at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

The reason why such rubber compositions provide good silica dispersibility and fuel economy is not completely clear, but can be explained as follows.

The SiOR group (referred to as "modified SBR") in the styrene-butadiene rubber having the SiOR group can interact with the hydroxyl group on the surface of the silica. Thus, the modified SBR can reduce aggregation of silica particles to improve silica dispersibility. Further, due to the presence of the polyoxyalkylene moiety and the sulfate ester salt moiety, the above surfactant can be appropriately adsorbed on the hydrophilic silica surface, so that the silica surface has a hydrophobic alkenyl group or alkyl group at the molecular terminal. Therefore, the surfactant can reduce aggregation of silica particles to improve silica dispersibility, and also can preventThe vulcanization accelerator adsorbs to the silica. Further, the combination of the modified SBR and the surfactant may provide a synergistic improvement in silica dispersibility, so that better silica dispersibility and fuel economy may be obtained as compared to the conventional art. It is believed that this is because the presence of the surfactant improves the affinity between the silica and the modified SBR. Further, when the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²At least/g, the amount of the silica is at least 50 parts by mass relative to 100 parts by mass of the rubber component). It is considered that this is because, although the fine particle silica is liable to aggregate due to its strong aggregating ability, the combination of the modified SBR and the surfactant can provide a greater synergistic improvement in dispersibility of the fine particle silica, so that the effect of improving the dispersibility can be more pronounced.

Probably for this reason, the present invention provides a rubber composition having good silica dispersibility and fuel economy even if the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component).

Further, in the present invention, the nitrogen adsorption specific surface area is 210m²The amount of silica per g or more is 70 to 130 parts by mass, the effect produced by the combination of the modified SBR and the surfactant can be more remarkable.

In addition to good silica dispersion and fuel economy, the present invention also provides good processability, abrasion resistance and grip performance.

Further, the combined use of styrene-butadiene rubber having an SiOR group (wherein, R represents a hydrogen atom or a hydrocarbon group) and a surfactant can synergistically improve silica dispersibility and fuel economy.

The rubber composition contained a nitrogen-adsorbing specific surface area of 210m²(ii) more than g of silica.

Examples of the silica include: dry silica (silicic anhydride) and wet silica (hydrous silicic acid). Wet silica is preferred because it has a large number of silanol groups. These may be used alone or in combination of two or more.

The amount of silica is preferably 70 parts by mass or more, but preferably 130 parts by mass or less, more preferably 120 parts by mass or less, and particularly preferably 100 parts by mass or less, with respect to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition preferably further contains a silane coupling agent. Non-limiting examples of silane coupling agents include those described in relation to the first aspect of the invention. Among them, a sulfide-based silane coupling agent and a mercapto-based silane coupling agent are preferable, and among them, a sulfide-based silane coupling agent is more preferable because favorable effects tend to be obtained well.

The amount of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, but is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and further more preferably 11 parts by mass or less, relative to 100 parts by mass of the silica. When the amount is within the above range, the advantageous effects tend to be well obtained.

The nitrogen adsorption specific surface area is 210m²The ratio Z/(X + Y) of the amount Z (parts by mass) of silica per g to the amount X (parts by mass) of the surfactant and the amount Y (parts by mass) of the silane coupling agent is preferably 3 to 30. When the ratio is within the above range, the advantageous effects tend to be well obtained. These amounts each refer to an amount relative to 100 parts by mass of the rubber component.

The lower limit of Z/(X + Y) is preferably 4, more preferably 5; the upper limit of Z/(X + Y) is preferably 20, more preferably 15, still more preferably 12, and particularly preferably 10.

(fourth aspect of the invention)

Next, a fourth aspect of the present invention will be explained, but differences from the first aspect of the present invention will be mainly described. The above description of the first aspect of the invention applies unless otherwise indicated.

The rubber composition for a tire of the fourth aspect of the present invention comprises: a rubber component comprising 30 parts by massAn amount% or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; and at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate, wherein the silica and the surfactant are kneaded with the rubber at the same time.

The reason why such rubber compositions provide good silica dispersibility and fuel economy is not completely clear, but can be explained as follows.

The SiOR group in a styrene-butadiene rubber having an SiOR group (referred to as "modified SBR") can interact with a hydroxyl group on the surface of silica. Thus, the modified SBR can reduce aggregation of silica particles to improve silica dispersibility. Further, due to the presence of the polyoxyalkylene moiety and the sulfate ester salt moiety, the above surfactant can be appropriately adsorbed on the hydrophilic silica surface, so that the silica surface has a hydrophobic alkenyl group or alkyl group at the molecular terminal. Therefore, the surfactant can reduce aggregation of silica particles to improve silica dispersibility, and can also prevent the vulcanization accelerator from adsorbing to silica. Further, the combination of the modified SBR and the surfactant may provide a synergistic improvement in silica dispersibility, so that better silica dispersibility and fuel economy may be obtained as compared to the conventional art. It is believed that this is because the presence of the surfactant improves the affinity between the silica and the modified SBR. Further, when the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²At least/g, the amount of the silica is at least 50 parts by mass relative to 100 parts by mass of the rubber component). It is considered that this is because, although the fine particle silica is liable to aggregate due to its strong aggregating ability, the combination of the modified SBR and the surfactant can provide a greater synergistic improvement in dispersibility of the fine particle silica, so that the effect of improving the dispersibility can be more pronounced.

Probably for this reason, the present inventionIt is apparent that there is provided a rubber composition having good silica dispersibility and fuel economy even if the rubber composition contains a relatively large amount of fine-particle silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component).

Further, in the present invention where silica and a surfactant are kneaded together with rubber, the effect produced by the combination of the modified SBR and the surfactant can be more remarkable.

In addition to good silica dispersion and fuel economy, the present invention also provides good processability, abrasion resistance and grip performance.

Further, the combined use of styrene-butadiene rubber having an SiOR group (wherein, R represents a hydrogen atom or a hydrocarbon group) and a surfactant can synergistically improve silica dispersibility and fuel economy.

The rubber composition of the fourth aspect of the invention is prepared by a method in which silica and a surfactant are simultaneously kneaded with rubber. The term "simultaneously kneaded with rubber" means that silica and a surfactant are introduced into a kneader and kneaded in the same kneading step. For example, the two components may be introduced into a kneader and kneaded during basic kneading. In the case where the basic kneading process consists of a plurality of steps, both components may be introduced into the kneader and kneaded in one of the plurality of steps.

Preferably, the following total amounts of silica incorporated into the rubber composition are kneaded simultaneously with the rubber and the surfactant: preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably 100% by mass. In this case, the advantageous effects can be more effectively achieved.

Similarly, the following total amounts of surfactants incorporated into the rubber composition were kneaded simultaneously with the rubber and silica: preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably 100% by mass. In this case, the advantageous effects can be more effectively achieved.

(fifth aspect of the invention)

Next, a fifth aspect of the present invention will be explained, but differences from the first aspect of the present invention will be mainly described. The above description of the first aspect of the invention applies unless otherwise indicated.

The rubber composition for a tire of the fifth aspect of the present invention comprises: a rubber component containing 30% by mass or more of a styrene-butadiene rubber having an SiOR group, wherein R represents a hydrogen atom or a hydrocarbon group; silica having a nitrogen adsorption specific surface area of 210m²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component; carbon black in an amount of 2 parts by mass or more per 100 parts by mass of the rubber component; at least one surfactant selected from polyoxyalkylene alkenyl ether sulfate and polyoxyalkylene alkyl ether sulfate.

The reason why such rubber compositions provide good silica dispersibility and fuel economy is not completely clear, but can be explained as follows.

The SiOR group in a styrene-butadiene rubber having an SiOR group (referred to as "modified SBR") can interact with a hydroxyl group on the surface of silica. Thus, the modified SBR can reduce aggregation of silica particles to improve silica dispersibility. Further, due to the presence of the polyoxyalkylene moiety and the sulfate ester salt moiety, the above surfactant can be appropriately adsorbed on the hydrophilic silica surface, so that the silica surface has a hydrophobic alkenyl group or alkyl group at the molecular terminal. Therefore, the surfactant can reduce aggregation of silica particles to improve silica dispersibility, and can also prevent the vulcanization accelerator from adsorbing to silica. Further, the combination of the modified SBR and the surfactant may provide a synergistic improvement in silica dispersibility, so that better silica dispersibility and fuel economy may be obtained as compared to the conventional art. It is believed that this is because the presence of the surfactant improves the affinity between the silica and the modified SBR. Further, when the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²The ratio of the carbon atoms to the carbon atoms is more than g,the amount of the silica is 50 parts by mass or more with respect to 100 parts by mass of the rubber component), such an effect is particularly remarkable. It is considered that this is because, although the fine particle silica is liable to aggregate due to its strong aggregating ability, the combination of the modified SBR and the surfactant can provide a greater synergistic improvement in dispersibility of the fine particle silica, so that the effect of improving the dispersibility can be more pronounced.

Probably for this reason, the present invention provides a rubber composition having good silica dispersibility and fuel economy even if the rubber composition contains a relatively large amount of fine-particle silica (the silica having a nitrogen adsorption specific surface area of 210 m)²(ii)/g or more, the amount of the silica being 50 parts by mass or more with respect to 100 parts by mass of the rubber component).

Further, in the present invention in which a predetermined amount of carbon black is added, the effect produced by the combination of the modified SBR and the surfactant can be more remarkable.

In addition to good silica dispersion and fuel economy, the present invention also provides good processability, abrasion resistance and grip performance.

Further, the combined use of styrene-butadiene rubber having an SiOR group (wherein, R represents a hydrogen atom or a hydrocarbon group) and a surfactant can synergistically improve silica dispersibility and fuel economy.

The amount of silica is 50 parts by mass or more, preferably 60 parts by mass or more, and more preferably 70 parts by mass or more, but preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and further more preferably 120 parts by mass or less, relative to 100 parts by mass of the rubber component. When the amount is within the above range, the advantageous effects tend to be well obtained.

The rubber composition may comprise an antioxidant.

Non-limiting examples of antioxidants include those described above. Among them, p-phenylenediamine antioxidants and quinoline antioxidants are preferable, and p-phenylenediamine antioxidants are more preferable. Also preferred is a combination of a p-phenylenediamine antioxidant and a quinoline antioxidant.