JP5941353B2 - Rubber composition for tire and pneumatic tire using the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a tire rubber composition and a pneumatic tire using the tire rubber composition, and particularly, when used in a tread, excellent characteristics in wear resistance and other fracture resistance and wet grip performance. This relates to a rubber composition for a tire tread.

  A dread rubber composition for a high-performance wet tire has demands for contradictory performance such as wet grip performance and fracture resistance, and various devices have been conventionally made in order to ensure these performances. For example, in a rubber composition for a tire tread, as means for improving wet grip performance, it is known to compound silica, or to make the particle size of carbon black finer to make it highly filled. In this case, there is a problem that the wet grip performance is not improved on a slippery road surface (so-called low μ road) with a small friction coefficient. On the other hand, it is also known to improve wet grip performance by adding aluminum hydroxide, but there is a problem that wear performance is lowered.

  An object of the present invention is to provide a rubber composition for a tire that can improve fracture resistance such as wear resistance and wet grip performance, and a pneumatic tire using the rubber composition for a tire.

  As a result of intensive studies, the present inventors have found that the above-mentioned problem can be solved by blending a predetermined inorganic compound powder, silica, and a predetermined unsaturated carboxylic acid ester with a predetermined diene rubber component, Further studies were made to complete the present invention.

That is, the present invention
For 100 parts by mass of a diene rubber component containing at least styrene butadiene rubber,
5 to 30 parts by mass of an inorganic compound powder represented by the following general formula (1),
30 to 100 parts by mass of silica, and
The present invention relates to a tire rubber composition comprising 5 to 50 parts by weight of an unsaturated carboxylic acid ester.

_{mM-xSiO y -zH 2 O (} 1)

(Wherein M is at least one metal selected from the group consisting of aluminum, magnesium, titanium and calcium, an oxide of the metal, and at least one substance selected from the group consisting of a hydroxide of the metal) M is any integer from 1 to 5, x is any integer from 0 to 10, y is any integer from 2 to 5, and z is any integer from 0 to 10.)

  The average particle diameter of the inorganic compound powder is preferably 0.01 to 10 μm.

  The M is preferably alumina and / or aluminum hydroxide.

  The tire rubber composition preferably further comprises 0.02 to 5.0 parts by mass of a radical generator composed of an organic peroxide.

  The tire rubber composition preferably further comprises 0.02 to 5.0 parts by mass of an organic sulfur compound and / or 5 to 50 parts by mass of a styrene / α-methylstyrene copolymer resin.

The organic sulfur compound is preferably one or more selected from the group consisting of compounds represented by any of the following general formulas (2) to (5).
Formula (2): R ¹ -SH
Formula ^{(3): R 2 - (} S) n -R 3
Formula (4): R ⁴ —SM ¹
Formula (5): R ⁵ —SM ² —S—R ⁶
Wherein R ^{1 to} R ⁶ are each independently a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aralkyl. And M ¹ represents a monovalent metal atom, M ² represents a divalent metal atom, and n represents an integer of 1 or more.)

  The Mw of the styrene / α-methylstyrene copolymer resin is preferably 200 to 20000.

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

  According to the present invention, predetermined amounts of inorganic compound powder, silica, and predetermined unsaturated carboxylic acid ester are blended with predetermined diene rubbers in predetermined amounts, respectively, so that fracture resistance such as wear resistance and wet grip performance can be obtained. It is possible to provide a rubber composition for a tire that exhibits excellent characteristics.

  Further, by providing a predetermined amount of a radical generator composed of an organic peroxide to the rubber composition for tires, a rubber composition for tires having further improved characteristics such as fracture resistance and wet grip performance is provided. can do.

  In addition, various characteristics such as fracture resistance and wet grip performance are further improved by adding a predetermined amount of organic sulfur compound and / or a predetermined amount of styrene / α-methylstyrene copolymer resin to the rubber composition for tires. A tire rubber composition can be provided.

  Hereafter, each element which comprises this invention is demonstrated.

<Diene rubber component>
The diene rubber component according to the present invention contains at least styrene-butadiene rubber (SBR). Any of these SBRs can be suitably used, but a solution-polymerized styrene butadiene rubber (S-SBR) is preferred. The amount of bound styrene in SBR is preferably 10% by mass or more, and more preferably 15% by mass or more. If the amount of bound styrene is less than 10% by mass, there is a tendency that sufficient grip force cannot be obtained. On the other hand, the amount of bound styrene is preferably 80% by mass or less, and more preferably 75% by mass or less. When the amount of bound styrene exceeds 80% by mass, the hardness tends to increase.

  The SBR content in the diene rubber component is preferably 70% by mass or more, more preferably 80% by mass or more. If it is less than 70% by mass, there is a tendency that sufficient grip force cannot be obtained. In the most preferred embodiment, the SBR content is 100% by mass.

  As the rubber component other than SBR, which is included as the diene rubber component, any normal diene rubber can be used, for example, natural rubber (NR), butyl rubber (IIR), styrene-isoprene. Copolymers of conjugated diene compounds such as rubber (SIR) and aromatic vinyl compounds, homopolymers of conjugated diene compounds such as polyisoprene rubber (IR) and polybutadiene rubber (BR), ethylene-propylene copolymers, and Examples thereof include synthetic rubber, which is a mixture of these.

  In the present invention, a diene rubber having a branched structure in which a part thereof is modified with a polyfunctional modifier such as tin tetrachloride can be used.

  A diene rubber may be used individually by 1 type, and may use 2 or more types together.

<Inorganic compound powder>
In the inorganic compound powder represented by the general formula (1), M is at least one selected from the group consisting of aluminum, its oxide (for example, alumina) and its hydroxide (for example, aluminum hydroxide). Substance is preferable, m is preferably an integer of 1 to 5, x is preferably an integer of 0 to 8, y is preferably an integer of 2 to 5, and z is preferably an integer of 0 to 9.

Specific examples of the inorganic compound powder include alumina (Al ₂ O ₃ ), alumina hydrate (Al ₂ O ₃ .H ₂ O), aluminum hydroxide [Al (OH) ₃ ], magnesium hydroxide [Mg ( OH) _2], magnesium oxide (MgO), talc _{(MgO · 4SiO 2 · H 2} O), attapulgite _{(5MgO · 8SiO 2 · 9H 2} O), titanium white (TiO _2), titanium black (TiO _2n-1) , Calcium oxide (CaO), calcium hydroxide [Ca (OH) ₂ ], calcium carbonate (CaCO ₃ ), aluminum magnesium oxide (MgO · Al ₂ O ₃ ), clay (Al ₂ O ₃ · 2SiO ₂ ), kaolin ( Al ₂ O ₃ · 2SiO ₂ · 2H ₂ O), pyrophyllite (Al ₂ O ₃ · 4SiO ₂ · H ₂ O), bentonite (Al ₂ O ₃ · 4SiO ₂ · 2H ₂ O), aluminum silicate (Al ₂ SiO ₅ , Al ₄ .3SiO ₂ .5H ₂ O, etc.), magnesium silicate (Mg ₂ SiO ₄ , MgSiO ₃ etc.), calcium silicate (Ca ₂ SiO ₄ etc.), aluminum calcium silicate (Al ₂ O ₃₎ · CaO · 2SiO ₂ etc.), etc. magnesium calcium silicate (CaMgSiO ₄₎ can be mentioned. Among these, alumina, alumina hydrate, or aluminum hydroxide is particularly preferable from the viewpoint of improving the grip.

  The average particle size of the inorganic compound powder is preferably 0.01 or more, more preferably 0.02 μm or more, and further preferably 0.1 μm or more. When the average particle size of the inorganic compound powder is less than 0.01 μm, workability tends to be lowered. On the other hand, the average particle size is preferably 10 μm or less, more preferably 8 μm, and even more preferably 5 μm or less. If it exceeds 10 μm, the wear resistance tends to decrease. The average particle diameter of the inorganic compound powder is determined by measuring the long diameter of a predetermined number (5 or more) of inorganic compound powder with a transmission electron microscope (TEM), and averaging the obtained results. Is determined by

  The compounding quantity of inorganic compound powder is 5 or more with respect to 100 mass parts of diene rubbers, Preferably it is 7 mass parts or more. If the amount is less than 5 parts by mass, the effect of improving wet grip performance tends to be small. On the other hand, the amount is 30 parts by mass or less, preferably 25 parts by mass or less. When it exceeds 30 parts by mass, there is a tendency that sufficient wet grip performance cannot be obtained although wear resistance is lowered.

  An inorganic compound powder may be used individually by 1 type, and may use 2 or more types together.

<Silica>
As the silica to be blended in the present invention, any of those usually used in this field can be suitably used. As such silica, for example, silica prepared by a dry method (anhydrous silicic acid) And silica (hydrous silicic acid) prepared by a wet method. Of these, silica prepared by a wet method is preferred because of the large number of silanol groups on the surface and many reactive sites with the silane coupling agent.

Silica preferably has a cetyltrimethylammonium bromide (CTAB) adsorption amount of 100 m ² / g or more, more preferably 120 m ² / g or more. If the CTAB adsorption amount is less than 120 m ² / g, sufficient reinforcing properties tend not to be obtained. On the other hand, the amount of CTAB adsorption is not particularly limited, but is preferably, for example, 300 m ² / g or less. CTAB is measured according to JIS K6217-3: 2001.

  The compounding quantity of a silica is 30 mass parts or more with respect to 100 mass parts of said rubber components, Preferably it is 35 mass parts or more. If it is less than 30 parts by mass, the wet grip performance tends to be insufficient. On the other hand, the compounding quantity of a silica is 100 mass parts or less, Preferably it is 80 mass parts or less. If the blending amount exceeds 100 parts by mass, the fracture resistance, durability, workability and the like tend not to be sufficiently ensured.

In the present invention, a silane coupling agent can be blended in addition to silica.
As the silane coupling agent, any of those usually used in this field can be used. Specifically, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) Tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide Bis (3-triethoxysilylpropyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N -Dimethylthio Rubamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyltetra Sulfide systems such as sulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltri Mercapto series such as ethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; vinyltriethoxysilane, vinyl Vinyl bases such as rutrimethoxysilane; 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxy Amino systems such as silane; glycidoxy systems such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane Nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltri And the like, such as chloro-system, such as Tokishishiran. Among these, for example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide and the like are preferable.

  When the silane coupling agent is blended, the blending amount is preferably 5 parts by mass or more and more preferably 7 parts by mass or more with respect to 100 parts by mass of silica. When the content of the silane coupling agent is less than 5 parts by mass, effects such as improvement in dispersibility tend not to be obtained sufficiently. Moreover, it is preferable that it is 20 mass parts or less, and, as for content of a silane coupling agent, it is more preferable that it is 15 mass parts or less. When the content of the silane coupling agent exceeds 20 parts by mass, a sufficient coupling effect cannot be obtained and the reinforcing property tends to be lowered.

  A silane coupling agent may be used individually by 1 type, and may use 2 or more types together.

<Unsaturated carboxylic acid ester>
As unsaturated carboxylic acid of unsaturated carboxylic acid ester, C3-C8 alpha, beta-ethylenically unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, is mentioned. Of these, acrylic acid or methacrylic acid is preferred. Examples of the unsaturated carboxylic acid ester include alkyl esters, aryl esters, vinyl esters, and the like. Of these, alkyl esters are preferable. As the alkyl group constituting the alkyl ester, an alkyl group having 1 to 12 carbon atoms is preferable, an alkyl group having 1 to 8 carbon atoms is more preferable, and an alkyl group having 1 to 4 carbon atoms is more preferable. Examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an isobutyl group, and a tert-butyl group. Examples of the aryl group constituting the aryl ester include a phenyl group, a benzyl group, a tolyl group, o-, m- or p-xylyl group.

  Specific examples of the unsaturated carboxylic acid ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, isobutyl acrylate, tert-butyl acrylate, phenyl acrylate, benzyl acrylate, tolyl acrylate, o-, m- or p- Xylyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, phenyl methacrylate, benzyl methacrylate, tolyl methacrylate, o-, m- or p-xylyl methacrylate Etc.

  The compounding quantity of unsaturated carboxylic acid ester is 5 mass parts or more, Preferably it is 10 mass parts or more. When the blending amount is less than 5 parts by mass, the unsaturated carboxylic acid ester does not sufficiently graft onto the diene rubber component, and the desired physical properties of the present application tend not to be obtained. On the other hand, the blending amount is 50 parts by mass or less, preferably 35 parts by mass or less. If the amount exceeds 50 parts by mass, sufficient elasticity cannot be obtained and the rubber tends to be too hard.

  Unsaturated carboxylic acid may be used individually by 1 type, and may use 2 or more types together.

<Radical generator>
As the radical generator composed of an organic peroxide, any organic peroxide can be used as long as it generates a peroxy radical in the presence of heat or a redox system. Examples thereof include dicumyl peroxide (for example, Park Mill (registered trademark) D of Nippon Oil & Fat Co., Ltd.), 1,1-bis (t-butylperoxy) cyclohexane (for example, perhexa (of Nippon Oil & Fat Co., Ltd.) (Registered trademark) C), 1,1-bis (t-butylperoxy) -3,5,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t- Butyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, α α′-bis (t-butylperoxy) -p-diisopropylbenzene, 2,5-dimethyl-2,5-bis (t-butylperoxy) -3-hexyne (for example, perhexine from NOF Corporation) (Registered trademark) 25B), benzoyl peroxide, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxymaleic acid, t-butylperoxyisopropyl Examples include carbonate. Among them, dicumyl peroxide, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl- 2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-bis (t-butylperoxy) -3-hexyne, or t-butyl peroxide is preferred.

  Further, as the radical generator composed of an organic peroxide, those having a 10-hour half-life temperature (T10: a temperature at which the half-life of the organic peroxide is 10 hours) are preferably 110 ° C. or more. This is from the viewpoint of avoiding as much as possible that these organic peroxides cause a crosslinking reaction before the vulcanization step. Examples of such organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,5,5- Trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t-butylhydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl Peroxide, t-butylcumyl peroxide, α, α′-bis (t-butylperoxy) -p-diisopropylbenzene, 2,5-dimethyl-2,5-bis (t-butylperoxy) -3- Hexin, t-butyl peroxybenzoate, t-butyl peroxymaleic acid, t-butyl peroxyisopropyl carbonate, etc. The

  The amount of the radical generator composed of the organic peroxide is 0.02 parts by mass or more, preferably 0.2 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.02 parts by mass, the blending effect is small, and sufficient wet grip force tends to be not obtained. On the other hand, the amount is 5.0 parts by mass or less, preferably 3.0 parts by mass or less. If the blending amount exceeds 5 parts by mass, the breaking strength (breaking resistance) of the rubber composition tends to decrease.

  One radical generator composed of an organic peroxide may be used alone, or two or more kinds may be used in combination.

<Organic sulfur compounds>
The organic sulfur compounds used in the present invention include those represented by the general formula (2) (thiol type or SH type), those represented by the general formula (3) (sulfide type or Sn type), and And those represented by the general formulas (4) and (5) (metal salt type or SM type).

In the organic sulfur compounds represented by the general formulas (2) to (5), examples of the substituent for the aryl group, heteroaryl group, alkyl group, alkenyl group, or aralkyl group in R ^{1 to} R ⁶ include a halogen atom ( For example, fluorine atom, bromine atom, chlorine atom or iodine atom), C _1-4 alkyl group (for example, methyl group, ethyl group or t-butyl group), carboxyl group, amino group, C _1-4 alkoxy group (For example, a methoxy group, an ethoxy group, or a t-butoxy group), a benzoylamino group, a nitro group, a mercapto group, etc. are mentioned. Of these, a halogen atom, particularly a chlorine atom, is preferred. The number of substituents in each group (that is, aryl group, heteroaryl group, alkyl group, alkenyl group, or aralkyl group) is one or more, and all substitutable sites may be substituted.

In R ^{1 to} R ⁶ , the aryl group is, for example, a 6 to 10 membered aryl group, and is preferably a phenyl group or a naphthyl group, for example. The heteroaryl group is, for example, a 5- to 10-membered heteroaryl group containing N, S and / or O, and preferably a furyl group, a thienyl group, a pyridyl group or a benzothiazolyl group, for example. The alkyl group is, for example, a C _1-12 alkyl group, and is preferably, for example, a methyl group, an ethyl group, or a dodecyl group. The alkenyl group is, for example, a C _1-12 alkenyl group, and preferably an allyl group, for example. The aralkyl group is, for example, a C _1-12 alkyl group substituted with a 6 to 10-membered aryl group, and preferably a methyl group, ethyl group or dodecyl group substituted with a phenyl group or a naphthyl group, for example. It is. Among these, an aryl group, particularly a phenyl group is preferable.

Regarding M ¹ , examples of the monovalent metal atom include sodium, lithium, potassium, copper (I), silver (I) and the like, and among these, sodium or potassium is preferable.

Regarding M ² , examples of the divalent metal atom include zinc, magnesium, calcium, strontium, barium, titanium (II), manganese (II), iron (II), cobalt (II), nickel (II), and zirconium. (II), tin (II), etc. are mentioned, Among these, zinc or magnesium is preferable.

  n is an integer of 1 or more, but the upper limit is preferably 2. A preferred specific example of n is 1 or 2.

  Specific examples of the thiol-type organic sulfur compound represented by the general formula (2) include, for example, pentachlorothiophenol, pentafluorothiophenol, 4-chlorothiophenol, 4-bromothiophenol, 4-fluorothiophenol, 4 -T-butylthiophenol, 2,3-dichlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 3,4-dichlorothiophenol, 3,5 -Dichlorothiophenol, 2,4,5-trichlorothiophenol, thiosalicylic acid, methylthiosalicylic acid, o-toluenethiol, m-toluenethiol, p-toluenethiol, 3-aminothiophenol, 4-aminothiophenol, 3- Methoxythiophenol, 4-methoxy Oh phenol, or 2-benzamide thiophenol and the like.

  Specific examples of the sulfide-type organic sulfur compound represented by the general formula (3) include, for example, disulfide diphenyl disulfide, bis (2-aminophenyl) disulfide, bis (4-aminophenyl) disulfide, bis (4 -Hydroxyphenyl) disulfide, bis (4-methylphenyl) disulfide, bis (4-tert-butylphenyl) disulfide, bis (2-benzamidophenyl) disulfide, dixylyl disulfide, di (o-benzamidophenyl) disulfide, dimorpholino Disulfide, bis (4-chlorophenyl) disulfide, bis (fluorophenyl) disulfide, bis (iodophenyl) disulfide, bis (2,5-dichlorophenyl) disulfide, bis (3,5-dichlorophenyl) disulfide Bis (2,4,5-trichlorophenyl) disulfide, bis (2-cyanophenyl) disulfide, bis (2-nitrophenyl) disulfide, bis (4-nitrophenyl) disulfide, bis (2,4-dinitro Phenyl) disulfide, 2,2-dithiodibenzoic acid, 5,5-dithiobis (2-nitrobenzoic acid), bis (pentafluorophenyl) disulfide, dibenzyl disulfide, di-t-dodecyl disulfide, diallyl disulfide, difurfuryl disulfide 2,2′-dibenzothiazolyl disulfide, bis (2-naphthyl) disulfide, bis (4-mercaptophenyl) disulfide, 4- (2-benzothiazolyldithio) morpholine, 2,2-dipyridyldisulfide, 2, , 2-dithiobis (5-nitrate Pyridine), 2,2-dithiodianiline, 4,4-dithiodianiline, dithiodiglycolic acid, 4,4′-dithiomorpholine or L-cystine, or n in these disulfides (n = 2) Examples are those in which the number is changed to a number greater than 1 or 2 within the range that n can take. Specific examples of n = 1 include bis (4-mercaptophenyl) sulfide.

  Specific examples of the metal salt type organic sulfur compound represented by the general formula (4) include, for example, a salt of the above thiol type organic sulfur compound and a monovalent metal atom.

  Specific examples of the metal salt-type organic sulfur compound represented by the general formula (5) include, for example, a salt of the above-described thiol-type organic sulfur compound and a divalent metal atom.

  The compounding quantity of an organic sulfur compound is 0.02 mass part or more with respect to 100 mass parts of said rubber components, Preferably it is 0.05 mass part or more, More preferably, it is 0.1 mass part or more. If it is less than 0.02 parts by mass, the blending effect is small, and the tan δ of the rubber composition tends not to be sufficiently improved. On the other hand, a compounding quantity is 5.0 mass parts or less, Preferably it is 4.5 mass parts or less, More preferably, it is 4 mass parts or less. If it exceeds 5.0 parts by mass, the breaking strength (breaking resistance) of the rubber composition tends to decrease.

  An organic sulfur compound may be used individually by 1 type, and may use 2 or more types together.

<Styrene / α-methylstyrene copolymer resin>
The styrene / α-methylstyrene copolymer resin is a resin obtained by polymerizing styrene and α-methylstyrene. The polymerization ratio of styrene and α-methylstyrene is not particularly limited, but preferably comprises about 40 to about 70% by mass of styrene monomer and about 60 to 30% by mass of α-methylstyrene monomer. It is preferable.

  The softening point of the styrene / α-methylstyrene copolymer resin is 180 ° C. or lower, more preferably 150 ° C. or lower. When it exceeds 180 ° C., the hardness tends to increase. On the other hand, the lower limit of the softening point is not particularly limited, but is usually 30 ° C. or higher. In this specification, the softening point is a temperature at which a sphere descends when the softening point defined in JIS K 6220 is measured with a ring and ball softening point measuring device.

  The weight average molecular weight (Mw) of the styrene / α-methylstyrene copolymer resin is 20000 or less, preferably 10,000 or less, more preferably 5000 or less. When Mw exceeds 20000, the hardness tends to increase. On the other hand, the lower limit value of Mw is not particularly limited, but is usually about 200. In this specification, Mw is a gel permeation chromatograph (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation). Is obtained by standard polystyrene conversion on the basis of the measured value according to.

The amount of the styrene / α-methylstyrene copolymer resin used is 5 parts by mass or more, preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. Below 5 parts by weight
Unsaturated carboxylic acid esters may cause self-polymerization. On the other hand, a compounding quantity is 50 mass parts or less, Preferably it is 35 mass parts or less. If it exceeds 50 parts by mass, the hardness tends to be high and a sufficient grip force tends not to be obtained.

  The styrene / α-methylstyrene copolymer resin may be used alone or in combination of two or more.

<Other fillers>
In the present invention, other fillers can be blended in addition to the fillers described above, and examples of such fillers include carbon black. The type of carbon black is not particularly limited, and any carbon black that is commonly used in this field can be used. For example, those of FEF, SRF, HAF, ISAF, and SAF grades are preferable. Etc. Of these, HAF, ISAF, and SAF grades are more preferable from the viewpoint of improving wear resistance.

The carbon black preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 70 m ² / g or more, more preferably 80 m ² / g or more. If N ₂ SA is less than 70 m ² / g, sufficient reinforcing properties tend not to be obtained. On the other hand, N ₂ SA is not particularly limited, but is preferably 250 m ² / g or less, for example. Incidentally, N ₂ SA of the carbon black is determined by the measuring method of JIS K6217-2.

  The blending amount of carbon black is preferably 10 parts by mass or more, and more preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of reinforcing properties and the improvement efficiency of various physical properties thereby. If it is less than 10 parts by mass, the fracture characteristics and the like tend to be insufficient. On the other hand, about an upper limit, 50 mass parts or less are preferable, More preferably, it is 30 mass parts or less. If it exceeds 50 parts by mass, the processability of the rubber composition tends to deteriorate.

<Other ingredients>
In the rubber composition of the present invention, a general rubber crosslinking system can be used. For this purpose, a crosslinking agent and a vulcanization accelerator are usually used in combination. Here, as a crosslinking agent, sulfur is mentioned, for example. The compounding amount of the crosslinking agent is preferably 0.1 parts by mass or more, and more preferably 1 part by mass or more as a sulfur content with respect to 100 parts by mass of the rubber component. If the amount is less than 0.1 parts by mass, the fracture resistance and low heat build-up property of the vulcanized rubber tend to decrease. On the other hand, the blending amount of the crosslinking agent is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less. If it exceeds 10 parts by mass, rubber elasticity tends to be lost.

  On the other hand, the vulcanization accelerator is not particularly limited, but 2-mercaptobenzothiazole (M), dibenzothiazyl disulfide (DM), N-cyclohexyl-2-benzothiazylsulfenamide (CZ). ), Thiazole-based vulcanization accelerators such as Nt-butyl-2-benzothiazolylsulfenamide (NS), and guanidine-based vulcanization accelerators such as diphenylguanidine (DPG). Any of them can be preferably used.

  The compounding amount of the vulcanization accelerator is preferably 0.1 parts by mass or more, and more preferably 0.2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.1 parts by mass, a sufficient crosslinking density tends not to be obtained. On the other hand, the blending amount is preferably 5 parts by mass or less, and more preferably 4 parts by mass or less. If it exceeds 5 parts by mass, the hardness tends to increase.

  A vulcanization accelerator may be used individually by 1 type, and may use 2 or more types together.

  In the rubber composition of the present invention, process oil or the like can be blended as a softening agent. As the process oil, any of those usually used in this field can be suitably used, and examples thereof include paraffinic oil, naphthenic oil, and aromatic oil. Among these, aromatic oils are preferable from the viewpoint of tensile strength and wear resistance, and naphthenic oils and paraffinic oils are preferable from the viewpoint of hysteresis loss and low temperature characteristics.

  The amount of process oil used is preferably in the range of 0 to 100 parts by mass with respect to 100 parts by mass of the rubber component. When the amount of process oil used exceeds 100 parts by mass with respect to 100 parts by mass of the rubber component, the tensile strength and low heat build-up of the vulcanized rubber tend to deteriorate.

  Process oil may be used individually by 1 type, and may use 2 or more types together.

  In addition to the above, the rubber composition of the present invention includes additives usually used in this field such as anti-aging agent, zinc oxide, stearic acid, antioxidant, ozone degradation inhibitor, etc. Can be appropriately selected and blended within a range that does not harm the above.

  The rubber composition of the present invention thus obtained can be used for tire applications such as tire treads, undertreads, carcass, sidewalls, beads, and vibration-proof rubbers, belts, hoses, and other industrial products. However, it can be suitably used as a tread for a tire because of its characteristics. The rubber composition of the present invention can be suitably used for passenger cars, buses, and trucks, but can be suitably used as a high-performance wet tire particularly for racing vehicles.

<Tire>
The rubber composition of the present invention is used for manufacturing a tire and can be made into a tire by a usual method. That is, a mixture containing the above components as needed is kneaded using a kneader such as a roll or an internal mixer, and extruded in accordance with the shape of each part of the tire at an unvulcanized stage. Then, an unvulcanized tire is formed by molding by a usual method on a tire molding machine. A tire can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer, and ordinary air can be introduced into the tire as an injection gas to obtain a pneumatic tire. In addition to normal air, inert gas such as air with adjusted partial pressure of oxygen, nitrogen, argon, or helium can be used as the injection gas. In the rubber composition of this invention, since unsaturated carboxylic acid ester is included as a structural component, kneading is preferably performed in a temperature range where the unsaturated carboxylic acid ester does not volatilize. Such temperature is usually 80 to 100 ° C., for example, although it depends on the type of unsaturated carboxylic acid ester.

  Although not intended to be bound by theory, according to the present invention, an unsaturated carboxylic acid ester is used for the predetermined diene rubber component, the predetermined inorganic compound powder and silica, or the unsaturated A rubber composition for tires that is superior in fracture resistance such as wear resistance and wet grip performance by grafting to a diene rubber component during kneading using a carboxylic acid ester and a radical generator composed of an organic peroxide. It is thought that a thing is obtained. Further, when blending a predetermined organic sulfur compound and / or styrene / α-methylstyrene copolymer resin, these function as “molecular weight regulators for graft chains”, thereby further improving the above characteristics. It is thought that the obtained rubber composition can be obtained.

  The present invention will be described based on examples, but the present invention is not limited to the examples.

The various chemicals used in the production of the rubber compositions of Examples , Reference Examples and Comparative Examples are collectively shown below. Various chemicals were purified according to conventional methods as needed.
<Various chemicals used in the production of rubber composition>
SBR: styrene butadiene rubber “Toughden 4350” manufactured by Asahi Kasei Corporation (bound styrene content = 39% by mass)
Inorganic compound powder: Heidilite H-43 (aluminum hydroxide, average particle size: 0.75 μm) manufactured by Showa Denko K.K.
Silica: NIPSEAL VN3 manufactured by Tosoh Silica Co., Ltd.
Carbon black: Diamond Black A (N110) manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 142 m ² / g)
Unsaturated carboxylic acid ester: tert-butyl acrylate (boiling point: 127 ° C., density: 0.88)
Radical generator: Park Mill D manufactured by NOF Corporation (molecular weight: 270, specific gravity: 1.11, T10: 116.4 ° C.)
Organic sulfur compound: pentachlorothiophenol (molecular weight: 282.40) manufactured by Wako Pure Chemical Industries, Ltd.
STY-AMS resin (styrene / α-methylstyrene copolymer resin): Sylvares SA85 manufactured by Arizona Chemical Co. (softening point: 85 ° C., Mw: 700)
Oil: Process X-260 (Aroma Oil) manufactured by Japan Energy Co., Ltd.
Anti-aging agent 1: Santoflex 13 (N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine) manufactured by Flexis
Anti-aging agent 2: Nocrack 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Flexis
Stearic acid: Zinc stearate manufactured by Nippon Oil & Fats Co., Ltd .: Zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. 2 types of sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by

Reference example 1
According to the composition shown in Table 1, the rubber chemicals (excluding sulfur and vulcanization accelerator) were kneaded at 150 ° C. for 5 minutes in a Banbury mixer to obtain a kneaded product. To the obtained kneaded product, sulfur and a vulcanization accelerator were added, and kneaded at 120 ° C. for 5 minutes using an open roll to obtain an unvulcanized rubber composition. The unvulcanized rubber composition was press vulcanized at 170 ° C. for 20 minutes to obtain a vulcanized rubber composition.

Example 2 , Reference Examples 3-4, Example 5, Reference Examples 6-7, and Comparative Examples 1-6
According to the formulation shown in Table 1, the corresponding raw material compounds were treated in the same manner as in Reference Example 1 to obtain the corresponding unvulcanized rubber composition and vulcanized rubber composition, respectively.

<Evaluation>
(1) Abrasion resistance A tire of size 195 / 65R15 having a tread made of the rubber composition was prepared, and the actual tire was run for 20 km on a dry asphalt wet road test course. The remaining groove amount of the tire tread rubber at that time was measured (15 mm when new). The greater the remaining groove amount, the better the wear resistance. The amount of remaining grooves in Comparative Example 1 was taken as 100 and displayed as an index. The results are shown in Table 1. It shows that abrasion resistance is so high that a numerical value is large.

(2) Wet grip performance A tire of size 195 / 65R15 having a tread made of the rubber composition was produced. Using this tire, the vehicle traveled for 10 laps (1 lap: 2 km) on a dry asphalt wet road test course. At that time, the test driver evaluated the stability of the control at the time of steering in 10 stages with 5 points as a reference. The larger the value, the higher the grip performance on the wet road surface.

  According to the present invention, the predetermined unsaturated carboxylic acid ester and the predetermined radical generating agent are blended with the predetermined diene rubber, the predetermined inorganic compound powder and the silica, or the predetermined unsaturated carboxylic acid ester and the predetermined radical generator. By blending, it is possible to provide a rubber composition for tires with improved fracture resistance such as wear resistance and wet grip performance. Further, by providing the tire rubber composition with a predetermined organic sulfur compound and / or a predetermined styrene / α-methylstyrene copolymer resin, there is provided a tire rubber composition in which the above characteristics are further improved. be able to.

Claims (7)

For 100 parts by mass of a diene rubber component containing at least styrene butadiene rubber,
5 to 30 parts by mass of an inorganic compound powder represented by the following general formula (1),
30 to 100 parts by mass of silica ,
5-50 parts by weight unsaturated carboxylic acid ester, and,
A tire rubber composition comprising 0.02 to 5.0 parts by mass of a radical generator composed of an organic peroxide .

_{mM-xSiO y -zH 2 O (} 1)

(Wherein M is at least one metal selected from the group consisting of aluminum, magnesium, titanium and calcium, an oxide of the metal, and at least one substance selected from the group consisting of a hydroxide of the metal) M is any integer from 1 to 5, x is any integer from 0 to 10, y is any integer from 2 to 5, and z is any integer from 0 to 10.) The rubber composition for tires according to claim 1 whose average particle diameter of said inorganic compound powder is 0.01-10 micrometers. The rubber composition for tires according to claim 1 or 2, wherein M is alumina and / or aluminum hydroxide. The tire rubber according to any one of claims 1 to 3 , further comprising 0.02 to 5.0 parts by mass of an organic sulfur compound and / or 5 to 50 parts by mass of a styrene / α-methylstyrene copolymer resin. Composition. The tire rubber composition according to claim 4 , wherein the organic sulfur compound is one or more selected from the group consisting of compounds represented by any of the following general formulas (2) to (5).
Formula (2): R ¹ -SH
Formula ^{(3): R 2 - (} S) n -R 3
Formula (4): R ⁴ —SM ¹
Formula (5): R ⁵ —SM ² —S—R ⁶
Wherein R ^{1 to} R ⁶ are each independently a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aralkyl. And M ¹ represents a monovalent metal atom, M ² represents a divalent metal atom, and n represents an integer of 1 or more.) The tire rubber composition according to claim 4 or 5 , wherein Mw of the styrene / α-methylstyrene copolymer resin is 200 to 20000. A pneumatic tire obtained by using the tire rubber composition according to any one of claims 1 to 6 for a tread.