阅读说明：本技术 轮胎胎面用橡胶组合物和轮胎 (Rubber composition for tire tread and tire ) 是由 梶木亮 于 2018-06-06 设计创作，主要内容包括：一种轮胎胎面用橡胶组合物,其包括：100质量份的橡胶组分,所述橡胶组分包含60～80质量％的天然橡胶和20～40质量％的具有一种以上的具有除碳和氢以外的原子的官能团的改性共轭二烯系聚合物；35～70质量份的填料；和0.1～10质量份的甘油/脂肪酸酯组合物,其中：所述填料中的二氧化硅的含量为3～30质量％；和包括由该橡胶组合物形成的胎面的轮胎。使用该轮胎胎面用橡胶组合物获得的轮胎在滚动阻力的降低、耐摩耗性、耐撕裂性和耐切割性之间具有优异的平衡。(A rubber composition for a tire tread, comprising: 100 parts by mass of a rubber component containing 60 to 80% by mass of a natural rubber and 20 to 40% by mass of a modified conjugated diene polymer having one or more functional groups other than carbon and hydrogen; 35-70 parts by mass of a filler; and 0.1 to 10 parts by mass of a glycerin/fatty acid ester composition, wherein: the content of silica in the filler is 3-30 mass%; and a tire comprising a tread formed of the rubber composition. A tire obtained using the rubber composition for a tire tread has an excellent balance among reduction in rolling resistance, abrasion resistance, tear resistance and cut resistance.)

1. A rubber composition for a tire tread, comprising:

a rubber component containing 60 to 80 mass% of a natural rubber and 20 to 40 mass% of a modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen;

35 to 70 parts by mass of a filler per 100 parts by mass of the rubber component; and

0.1 to 10 parts by mass of a glycerin fatty acid ester composition per 100 parts by mass of the rubber component, wherein:

the content of silica in the filler is 3 to 30 mass%.

2. The rubber composition for a tire tread according to claim 1, further comprising 0.1 to 5 parts by mass of a fatty acid metal salt with respect to 100 parts by mass of the rubber component.

3. The rubber composition for a tire tread according to claim 1 or 2, wherein the filler contains dibutyl phthalate absorption amount (DBP absorption amount) of 40 to 180cm³100g, nitrogen adsorption specific surface area (N)₂SA) of 40 to 95m²A carbon black having a toluene extract light transmittance of 90% or more and a hydrogen release rate of 0.37 mass% or more.

4. The rubber composition for a tire tread according to any one of claims 1 to 3, wherein the glycerin fatty acid ester composition contains a glycerin fatty acid monoester and a glycerin fatty acid diester as an ester of glycerin and a fatty acid having 8 to 28 carbon atoms, and the content of the glycerin fatty acid monoester is 85 mass% or less.

5. The rubber composition for a tire tread according to any one of claims 1 to 3, wherein the glycerin fatty acid ester composition contains a glycerin fatty acid ester that is an ester of glycerin and two or more fatty acids, and of the fatty acid components of the fatty acid derivative sites of the glycerin fatty acid ester, the content of the fatty acid component occupying the largest amount among all the fatty acid components of all the glycerin fatty acid esters is 10 to 90 mass%, and the content of glycerin fatty acid monoester in the glycerin fatty acid ester composition is 50 to 100 mass%.

6. The rubber composition for a tire tread according to any one of claims 1 to 5, wherein the modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen is a modified conjugated diene polymer having one or more functional groups each having at least one of a nitrogen atom, an oxygen atom, and a silicon atom.

7. A tire using the rubber composition for a tire tread according to any one of claims 1 to 6 as a tread.

Technical Field

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

Background

In recent years, along with social demands for energy saving and natural resource saving, tires with small rolling resistance have become desired to improve fuel efficiency of automobiles. For such demands, as a means for reducing the rolling resistance of a tire, a method of using a rubber composition having a reduced hysteresis loss in which the amount of carbon black used is reduced or a low-grade carbon black is used, that is, a rubber composition having a low heat generating property, as a tire member, particularly as a tread rubber is known.

However, the mere loss of the carbon black used decreases the abrasion resistance of the rubber composition.

In contrast to this, PTLs 1 and 2 propose a rubber composition using a modified conjugated diene-based polymer having an amino group introduced into a polymerization active terminal as a rubber component and using carbon black as a filler to reduce rolling resistance thereof. PTLs 3 and 4 disclose a rubber composition capable of satisfying both abrasion resistance and rolling resistance of a tire, in which a terminal-modified polymer such as a terminal-modified polybutadiene rubber is used to improve dispersibility of carbon black therein.

Reference list

Patent document

PTL 1：JP 8-225604 A

PTL 2：JP 8-231658 A

PTL 3：JP 2005-041975 A

PTL 4：JP 2013-155256 A

Disclosure of Invention

Problems to be solved by the invention

In general, in order to improve the abrasion resistance of a tire, the particle diameter and structure of carbon black mixed in a rubber composition constituting the tire are considered to be the dominant factors, and it is known that reducing the particle diameter of carbon black can improve the abrasion resistance, but when the particle diameter of carbon black is very small, carbon black may undergo poor dispersion in rubber, so that the heat generating property of the rubber composition is thereby increased. When a tire using such a rubber composition as a tread is produced, its abrasion resistance may be excellent, but its fuel economy is poor. Specifically, regarding the particle diameter of carbon black, abrasion resistance and low heat build-up are in a two-bar relationship.

From the above-mentioned viewpoint, the above-mentioned rubber composition using a terminal-modified polymer as a rubber component reduces the heat generation property (hysteresis loss) of the terminal-modified polymer, and therefore, such a rubber composition is effective to some extent for the abrasion resistance and the rolling resistance, but still has a certain room for improvement in the above-mentioned two characteristics of the bar-shaped rubber.

The present invention has been made under the above-described circumstances, and an object thereof is to provide a rubber composition for a tire tread capable of providing a tread excellent in a balance of reduction in rolling resistance, abrasion resistance, tear resistance and cut resistance, and a tire excellent in a balance of reduction in rolling resistance, abrasion resistance, tear resistance and cut resistance.

Means for solving the problems

The present inventors have conducted intensive studies with the object of solving the above problems, and as a result, have found that a rubber composition for a tire tread comprising a rubber component containing a polymer having affinity for a filler, a small amount of silica and a glycerin fatty acid ester composition can solve the above problems. The present invention has been completed based on these findings. Specifically, the present invention is as follows.

<1> a rubber composition for a tire tread, comprising: a rubber component containing 60 to 80 mass% of a natural rubber and 20 to 40 mass% of a modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen; 35 to 70 parts by mass of a filler per 100 parts by mass of the rubber component; and 0.1 to 10 parts by mass of a glycerin fatty acid ester composition per 100 parts by mass of the rubber component, wherein: the content of silica in the filler is 3 to 30 mass%.

<2> the rubber composition for a tire tread according to <1>, which further comprises 0.1 to 5 parts by mass of a fatty acid metal salt with respect to 100 parts by mass of the rubber component.

<3>According to<1>Or<2>The rubber composition for a tire tread of (1), wherein the filler contains dibutyl phthalate absorption amount (DBP absorption amount) of 40 to 180cm³100g, nitrogen adsorption specific surface area (N)₂SA) of 40 to 95m²A carbon black having a toluene extract light transmittance of 90% or more and a hydrogen release rate of 0.37 mass% or more.

<4> the rubber composition for a tire tread according to any one of <1> to <3>, wherein the glycerin fatty acid ester composition contains a glycerin fatty acid monoester and a glycerin fatty acid diester as an ester of glycerin and a fatty acid having 8 to 28 carbon atoms, and a content of the glycerin fatty acid monoester is 85 mass% or less.

<5> the rubber composition for a tire tread according to any one of <1> to <3>, wherein the glycerin fatty acid ester composition contains a glycerin fatty acid ester that is an ester of glycerin and two or more fatty acids, and the content of the fatty acid component accounting for the maximum amount among all the fatty acid components of the entire glycerin fatty acid ester is 10 to 90% by mass among the fatty acid components of the fatty acid derivative sites of the glycerin fatty acid ester, and the content of the glycerin fatty acid monoester in the glycerin fatty acid ester composition is 50 to 100% by mass.

<6> the rubber composition for a tire tread according to any one of <1> to <5>, wherein the modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen is a modified conjugated diene polymer having one or more functional groups each having at least one of a nitrogen atom, an oxygen atom and a silicon atom.

<7> a tire using the rubber composition for a tire tread according to any one of <1> to <6> as a tread.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, there can be provided a rubber composition for a tire tread capable of providing a tread having an excellent balance among reduction in rolling resistance, abrasion resistance, tear resistance and cut resistance, and a tire having an excellent balance among reduction in rolling resistance, abrasion resistance, tear resistance and cut resistance.

Detailed Description

< rubber composition for tire Tread >

The rubber composition for a tire tread of the present invention comprises: a rubber component containing 60 to 80 mass% of a natural rubber and 20 to 40 mass% of a modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen; 35 to 70 parts by mass of a filler per 100 parts by mass of the rubber component; and 0.1 to 10 parts by mass of a glycerin fatty acid ester composition per 100 parts by mass of the rubber component, wherein: the content of silica in the filler is 3 to 30 mass%.

Generally, the glycerin fatty acid ester composition is used for a rubber composition containing a large amount of silica as a filler therein (for example, in an amount of 50 parts by mass or more relative to 100 parts by mass of the rubber component in the rubber composition). On the other hand, any other filler than silica, such as carbon black, interacts poorly with the glycerin fatty acid ester composition, and therefore, even when the rubber composition containing no silica contains carbon black and the glycerin fatty acid ester composition, the composition does not achieve the effect expected to be achieved by the system containing silica.

In the present invention, the amount of silica contained in the rubber composition for a tire tread is smaller than conventional. Specifically, the amount of silica in the filler is 3 to 30% by mass in 35 to 70 parts by mass of the filler per 100 parts by mass of the rubber component, and is at most 21 parts by mass per 100 parts by mass of the rubber component. In general, when a rubber composition contains only 21 parts by mass of silica therein relative to 100 parts by mass of a rubber component, the rubber component cannot be sufficiently reinforced and the composition cannot have various properties such as abrasion resistance.

However, the rubber composition for a tire tread of the present invention further includes a filler that does not interact well with the glycerin fatty acid ester composition and a specific rubber component together with a small amount of silica, and can provide a tread excellent in the balance of reduction in rolling resistance, abrasion resistance, tear resistance and cut resistance.

Although not clear, the reason is presumed as follows.

For example, in the case where carbon black is used as a filler other than silica, carbon black is generally contained as aggregates in the rubber composition, but silica dispersed by the glycerin fatty acid ester composition may be impregnated into the lumps of carbon black and the dispersed silica may be regarded as a dispersant for carbon black, and therefore, carbon black in the rubber composition may be easily dispersed therein. As a result, it is considered that a tread obtained from the rubber composition may be excellent in durability such as abrasion resistance, tear resistance, and cut resistance, and a tire produced using the tread may also be excellent in rolling resistance.

Hereinafter, details of the rubber composition for a tire tread and the tire of the present invention are described.

[ rubber component ]

The rubber composition for a tire tread of the present invention includes a rubber component containing 60 to 80 mass% of a natural rubber and 20 to 40 mass% of a modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen.

Hereinafter, the "modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen" may be referred to as "modified conjugated diene polymer in the present invention".

When the content of the natural rubber in the rubber component is less than 60 mass%, a tread produced from the rubber composition for a tire tread is poor in resilience and is not excellent in tear resistance and rolling resistance of a tire. On the other hand, when the content of the natural rubber in the rubber component is more than 80% by mass, the resulting tread may lose abrasion resistance and cut resistance.

The modified conjugated diene polymer in the present invention is excellent in affinity for the filler contained in the rubber composition for a tire tread of the present invention. When the content of the modified conjugated diene-based polymer in the rubber component is less than 20% by mass, the filler may be difficult to disperse in the rubber composition and the rubber component may not be reinforced, and therefore, the tread obtained from the rubber composition for a tire tread of the present invention may lose abrasion resistance and cut resistance. When the content of the modified conjugated diene-based polymer in the rubber component is more than 40% by mass, the tread is not excellent in tear resistance and rolling resistance of the tire.

The rubber component may contain any other rubber or polymer other than the natural rubber and the above-described modified conjugated diene-based polymer.

From the above viewpoint, the content of the natural rubber in the rubber component is preferably 62 to 80% by mass, more preferably 65 to 78% by mass. The content of the modified conjugated diene polymer of the present invention in the rubber component is preferably 20 to 38% by mass, and more preferably 22 to 35% by mass.

(Natural rubber)

The natural rubber used in the rubber component of the present invention is not particularly limited, and the natural rubber latex as a raw material is also not particularly limited. Natural rubber latex includes virgin latex and commercial latex.

The natural rubber used in the rubber component of the present invention is preferably a partially deproteinized natural rubber obtained from a partially deproteinized latex according to a mechanical separation method for removing proteins from a natural rubber latex, and the total nitrogen content in the partially deproteinized natural rubber is preferably more than 0.1% by mass and 0.4% by mass or less.

More preferably, the mechanical separation method for partial deproteinization is a centrifugal concentration method from the viewpoint of easy control of the total nitrogen content in the natural rubber.

This is because, in the case where deproteinization is performed according to a method different from the mechanical separation method, for example, according to a proteolysis method using a protease, or a method of repeatedly washing using a surfactant, or a method of simultaneously using an enzyme and a surfactant, proteins in the solid rubber can be reduced, but at the same time, active ingredients such as tocotrienol having an anti-aging effect are also lost, and thus, anti-aging properties inherent to natural rubber are lowered.

The total nitrogen content in the natural rubber in the present invention is an index of the protein content therein, and the content can be controlled by controlling the centrifugal separation conditions (e.g., rotation speed, time) of the raw natural rubber latex, preferably, the content is controlled so that the total nitrogen content in the resulting natural rubber product can be more than 0.1 mass% and 0.4 mass% or less. The conditions of the centrifugation are not particularly limited, but preferably, for example, the centrifugation is repeated several times at a rotation speed of about 7500 rpm. When the total nitrogen content is 0.1 mass% or less, the heat aging resistance is lowered, and when the total nitrogen content is more than 0.4 mass%, a sufficient low heat generating property (a sufficient heat generating property reducing effect) cannot be achieved. Specifically, controlling the total nitrogen content in the solid content in the centrifugally separated concentrated latex to be more than 0.1 mass% and 0.4 mass% or less followed by coagulation and drying gives a natural rubber having a reduced protein content and having improved low-heat-generation properties. More preferably, the total nitrogen content falls within the range of 0.25 to 0.38 mass%, even more preferably 0.25 to 0.35 mass%.

Under such partially deproteinized conditions, surprisingly, active ingredients such as tocotrienols as anti-aging agents are hardly lost, and thus the heat resistance of the thus deproteinized rubber can be almost at the same level as that of existing natural rubber.

The partially deproteinized natural rubber latex is coagulated and washed, and then dried using a conventional dryer such as a vacuum dryer, an air dryer or a drum dryer, to thereby obtain a preferred natural rubber for use in the present invention.

(modified conjugated diene Polymer)

The modified conjugated diene polymer in the present invention has one or more functional groups each having an atom other than carbon and hydrogen.

The atom other than carbon and hydrogen is preferably one or more atoms selected from the group consisting of a nitrogen atom, an oxygen atom, a sulfur atom, a semimetal atom and a metal atom. Here, the semimetal atom is preferably one or more atoms selected from boron, silicon, germanium, arsenic, antimony, and tellurium, more preferably one or more atoms selected from boron, silicon, and germanium, and particularly preferably silicon. The metal atom is preferably one or more atoms selected from tin, titanium, zirconium, bismuth and aluminum, more preferably one or more atoms selected from tin and titanium, and particularly preferably tin.

A functional group having atoms other than carbon and hydrogen is the residue of a compound having atoms other than carbon and hydrogen. A compound having an atom other than carbon and hydrogen may be reacted with the active terminal of the conjugated diene-based polymer as a modifier to form a modified conjugated diene-based polymer, or a nitrogen-containing compound as a compound having an atom other than carbon and hydrogen may be reacted with an alkali metal to form a polymerization initiator for anionic polymerization, thereby producing a modified conjugated diene-based polymer having a nitrogen-containing compound residue at the initiation terminal of the conjugated diene-based polymer.

The modifier which reacts with the active terminal of the conjugated diene polymer includes one or more modifiers selected from the group consisting of tin compounds, nitrogen-and silicon-containing compounds, oxygen-and silicon-containing compounds, sulfur-and silicon-containing compounds, and nitrogen-containing compounds, which will be described later.

Preferred examples of the tin compound include one or more tin compounds selected from tin tetrachloride and tributyltin chloride. Preferred examples of the nitrogen-and silicon-containing compound include silane compounds having a protected primary amino group selected from the group consisting of N, N-bis (trimethylsilyl) aminopropylmethyldimethoxysilane, 1-trimethylsilyl-2, 2-dimethoxy-1-aza-2-silacyclopentane, N-bis (trimethylsilyl) aminopropyltrimethoxysilane, N-bis (trimethylsilyl) aminopropyltriethoxysilane, N-bis (trimethylsilyl) aminopropylmethyldiethoxysilane, N-bis (trimethylsilyl) aminoethyltrimethoxysilane, N-bis (trimethylsilyl) aminoethyltriethoxysilane, N-bis (trimethylsilyl) aminoethylmethyldimethoxysilane and N, n-bis (trimethylsilyl) aminoethylmethyldiethoxysilane; and preferred examples thereof further include silane compounds having a protected secondary amino group selected from the group consisting of N-methyl-N-trimethylsilylaminopropyl (methyl) dimethoxysilane, N-methyl-N-trimethylsilylaminopropyl (methyl) diethoxysilane, N-trimethylsilyl (hexamethyleneimine-2-yl) propyl (methyl) dimethoxysilane, N-trimethylsilyl (hexamethyleneimine-2-yl) propyl (methyl) diethoxysilane, N-trimethylsilyl (pyrrolidin-2-yl) propyl (methyl) dimethoxysilane, N-trimethylsilyl (pyrrolidin-2-yl) propyl (methyl) diethoxysilane, N-trimethylsilyl (piperidin-2-yl) propyl (methyl) dimethoxysilane, N-trimethylsilyl (pyrrolidin-2-yl) dimethoxysilane, N-trimethylsilyl (methyl) dimethoxysilane, N-trimethylsilyl (piperidin-2-yl) propyl (methyl, N-trimethylsilyl (piperidin-2-yl) propyl (methyl) diethoxysilane, N-trimethylsilyl (imidazol-2-yl) propyl (methyl) dimethoxysilane, N-trimethylsilyl (imidazol-2-yl) propyl (methyl) diethoxysilane, N-trimethylsilyl (4, 5-dihydroimidazol-5-yl) propyl (methyl) dimethoxysilane, and N-trimethylsilyl (4, 5-dihydroimidazol-5-yl) propyl (methyl) diethoxysilane.

Preferred examples of the oxygen-and silicon-containing compound include one or more epoxy-containing hydrocarbyloxysilane compounds selected from the group consisting of 2-glycidoxyethyltrimethoxysilane, 2-glycidoxyethyltriethoxysilane, (2-glycidoxyethyl) methyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (3-glycidoxypropyl) methyldimethoxysilane, 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3, 4-epoxycyclohexyl) ethyltriethoxysilane and 2- (3, 4-epoxycyclohexyl) ethyl (methyl) dimethoxysilane; and preferable examples of the sulfur and silicon-containing compound include thioepoxy-containing hydrocarbyloxysilane compounds derived from the above-mentioned epoxy-containing hydrocarbyloxysilane compounds by substituting an epoxy group therein with a thioepoxy group. Preferred examples of the nitrogen-containing compound include one or more compounds selected from bis (diethylamino) benzophenone, dimethylimidazolidinone, N-methylpyrrolidone, and 4-dimethylaminobenzylideneaniline.

The modified conjugated diene polymer having one or more functional groups each having an atom other than carbon and hydrogen is preferably a modified conjugated diene polymer having one or more functional groups each having at least one of a nitrogen atom, an oxygen atom, and a silicon atom.

The unmodified conjugated diene polymer forming the modified conjugated diene polymer in the present invention may be a conjugated diene homopolymer prepared by polymerization of one conjugated diene monomer or a conjugated diene copolymer prepared by polymerization of two or more monomers. The conjugated diene copolymer may be one prepared by polymerizing two or more conjugated diene monomers or one prepared by copolymerizing one or more conjugated diene monomers and one or more aromatic vinyl compounds.

Examples of the conjugated diene monomer include 1, 3-butadiene, isoprene, 1, 3-pentadiene, 2, 3-dimethyl-1, 3-butadiene, 2-phenyl-1, 3-butadiene, 1, 3-hexadiene and the like. Among them, 1, 3-butadiene, isoprene and 2, 3-dimethyl-1, 3-butadiene are particularly preferable.

Examples of the aromatic vinyl compound include styrene, α -methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, 2,4, 6-trimethylstyrene and the like, of which styrene is particularly preferred.

The unmodified conjugated diene-based polymer forming the modified conjugated diene-based polymer in the invention is preferably polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), polyisoprene rubber (IR), isoprene-butadiene copolymer rubber (IBR), styrene-isoprene copolymer rubber (SIR), or the like, but from the viewpoint of improving the performance of a tire tread, polybutadiene rubber and polyisoprene rubber are more preferable, and polybutadiene rubber is particularly preferable.

The method for polymerizing the conjugated diene polymer in the present invention may be anionic polymerization or coordination polymerization.

In the case where the conjugated diene-based polymer is obtained by anionic polymerization, an alkali metal compound may be used as the polymerization initiator, and a lithium compound is preferable.

The lithium compound used for the polymerization initiator is not particularly limited, but it is preferable to use hydrocarbyl lithium and a lithium amide compound (lithium amide compound), and in the case where the former hydrocarbyl lithium is used, a conjugated diene-based polymer having a hydrocarbyl group at the polymerization initiation terminal and the other terminal being a polymerization active site is obtained. On the other hand, when the latter lithium amide compound is used, a conjugated diene-based polymer having a nitrogen-containing group at the polymerization initiating terminal and the other terminal being a polymerization active site is obtained.

The above-mentioned hydrocarbyl lithium is preferably one containing a hydrocarbyl group having 2 to 20 carbon atoms, and examples thereof include ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-octyllithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butylphenyl lithium, 4-phenylbutyllithium, cyclohexyllithium, cyclopentyllithium, a reaction product of diisopropenylbenzene and butyllithium, and the like. Among them, n-butyllithium is particularly preferable.

Examples of the lithium amide compound include lithium hexamethyleneimide, lithium pyrrolidine, lithium piperidine, lithium heptamethyleneimide, lithium dodecamethyleneimide, lithium dimethylamide, lithium diethylamide, lithium dibutylamide, lithium dipropylamide, lithium dihexylamide, lithium dioctylamide, lithium 2-ethylhexylamide, lithium didecylamide, lithium N-methylpiperazine, lithium ethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide, lithium methylphenethylamide, and the like. Among them, from the viewpoint of the interaction effect with carbon black and polymerization initiating property, for example, cyclic lithium amides such as lithium hexamethyleneimide, lithium pyrrolidine, lithium piperidine, lithium heptamethyleneimide and lithium dodecamethyleneimide are preferable, and lithium hexamethyleneimide and lithium pyrrolidine are more preferable.

The use of lithium hexamethyleneimide as a polymerization initiator is further more preferable because a modified conjugated diene polymer having hexamethyleneimide group which is a residue of a nitrogen-containing compound as a functional group having atoms other than carbon and hydrogen at the initiation terminal of the conjugated diene polymer can be obtained.

In the present invention, from the viewpoint of further reducing rolling resistance and further improving abrasion resistance, tear resistance (tear resistance) and cut resistance, a modified conjugated diene polymer having a nitrogen-containing compound residue at the initiating terminal end of the conjugated diene polymer and having at least one compound residue selected from a tin compound residue, a nitrogen-and silicon-containing compound residue, an oxygen-and silicon-containing compound residue, a sulfur-and silicon-containing compound residue and a nitrogen-containing compound residue at the active terminal end of the conjugated diene polymer is more preferred.

The method for producing the conjugated diene-based polymer by anionic polymerization using the above lithium compound as a polymerization initiator is not particularly limited, and any existing known method is available.

Specifically, in an organic solvent inert to the reaction, for example, in a hydrocarbon solvent such as an aliphatic compound, an alicyclic compound, or an aromatic compound, the conjugated diene compound, or the conjugated diene compound and the aromatic vinyl compound may undergo anionic polymerization using the above-described lithium compound as a polymerization initiator and in the presence of an optional randomizer to obtain a desired conjugated diene polymer.

The hydrocarbon solvent is preferably one having 3 to 8 carbon atoms, and examples thereof include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propylene, 1-butene, isobutene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, and ethylbenzene. One or two or more of these may be used alone or in combination.

The optional randomizer is a compound which controls the microstructure of the conjugated diene-based polymer, for example, increases the 1, 2-bond of the butadiene moiety in a butadiene-styrene copolymer or increases the 3, 4-bond in an isoprene polymer; or controlling the composition distribution of monomer units in the conjugated diene compound-aromatic vinyl compound copolymer, for example, randomizing butadiene units or styrene units in the butadiene-styrene copolymer.

The randomizer is not particularly limited, and may be appropriately selected from any known compounds heretofore generally used as randomizers. Specifically, ethers and tertiary amines are mentioned, such as dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, 2-bis (2-tetrahydrofuryl) -propane, triethylamine, pyridine, N-methylmorpholine, N' -tetramethylethylenediamine, and 1, 2-dipiperidinoethane. In addition, potassium salts such as potassium tert-amylate and potassium tert-butylate and sodium salts such as sodium tert-amylate are also useful.

One or two or more of these randomizers may be used alone or in combination. The amount of the lithium compound used is preferably selected from the range of 0.01 to 1,000 molar equivalents per mol of the lithium compound.

The polymerization temperature is preferably 0 to 150 ℃, more preferably 20 to 130 ℃. The polymerization reaction may be conducted under the generated pressure, but in general, it is desirable to operate the reaction at a sufficient pressure to maintain the monomers in a substantially liquid phase. In particular, high pressures may optionally be employed depending on the respective substances to be polymerized or the polymerization medium or the polymerization temperature, and such pressures may be achieved according to a suitable method of pressurizing the reactor with a gas inert to the polymerization reaction.

On the other hand, in the case where the modified conjugated diene-based polymer is produced by coordination polymerization using a rare earth metal compound as a polymerization initiator, it is more preferable to use the following component (a), component (B), and component (C) in combination.

The component (A) for coordination polymerization is selected from a rare earth metal compound and a complex of a rare earth metal compound and a Lewis base, etc. Here, the rare earth metal compound includes a carboxylate, alkoxide, β -diketone complex, phosphate, phosphite, etc. of a rare earth element, Lewis base includes acetylacetone, tetrahydrofuran, pyridine, N-dimethylformamide, thiophene, diphenyl ether, triethylamine, an organophosphorus compound, monoalcohol, diol, etc. the rare earth element of the rare earth metal compound is preferably lanthanum, neodymium, praseodymium, samarium or gadolinium, among which neodymium is particularly preferred, concretely, as the component (A), neodymium tri-2-ethylhexanoate, a complex thereof with acetylacetone, neodymium trineodecanoate, a complex thereof with acetylacetone, neodymium tri-N-butoxide, etc. these components (A) may be used singly or in combination.

The component (B) for coordination polymerization is selected from organoaluminum compounds. Specifically, as the organoaluminum compound, compounds represented by the formula: r¹² ₃A trihydrocarbylaluminum compound represented by Al, having the formula: r¹² ₂AlH or R¹²AlH₂A hydrocarbyl aluminum hydride of (wherein R)¹²Each independently represents a hydrocarbon group having 1 to 30 carbon atoms), a hydrocarbyl aluminoxane compound containing a hydrocarbon group having 1 to 30 carbon atoms, and the like. Specifically, the organoaluminum compound includes trialkylaluminum, dialkylaluminum hydride, alkylaluminum dihydride, alkylaluminoxane and the like. One or two or more of these compounds may be used alone or in combination. As component (B), preferably, an aluminoxane and any other organoaluminum compound are used in combination.

The component (C) for coordination polymerization is selected from a compound having a hydrolyzable halogen or a complex thereof with a Lewis base; organic halides including tertiary alkyl halides, benzyl halides or allyl halides; and ionic compounds composed of a non-coordinating anion and a counter cation. Specifically, as the component (C), alkyl aluminum dichloride, dialkyl aluminum chloride, complexes with lewis bases such as silicon tetrachloride, tin tetrachloride, zinc chloride and alcohols; complexes with Lewis bases such as magnesium chloride and alcohols; benzyl chloride, tert-butyl chloride, benzyl bromide, tert-butyl bromide, triphenylcarbenium tetrakis (pentafluorophenyl) borate, and the like. One or two or more of these components (C) may be used alone or in combination.

The above polymerization initiator may be optionally prepared in advance using the same conjugated diene compound and/or non-conjugated diene compound as the monomer for polymerization, in addition to the above components (A), (B) and (C). Part or all of component (A) or component (C) may be supported on an inert solid, as desired. The amount of each component may be appropriately defined, but generally, the amount of the component (A) is 0.001 to 0.5mmol relative to 100g of the monomer. Preferably, the ratio of component (B)/component (A) is 5 to 1,000 and the ratio of component (C)/component (A) is 0.5 to 10 in terms of a molar ratio.

The polymerization temperature in the above coordination polymerization is preferably in the range of-80 to 150 ℃, more preferably in the range of-20 to 120 ℃. As the solvent used for the coordination polymerization, a hydrocarbon solvent inert to the reaction as exemplified for the above-mentioned anionic polymerization can be used, and the monomer concentration in the reaction solution is the same as that in the anionic polymerization. Further, the reaction pressure in the coordination polymerization may also be the same as that in the anion polymerization, and the raw materials for the reaction are preferably those from which reaction-inhibiting substances such as water, oxygen, carbon dioxide and protic compounds have been substantially removed.

The modified conjugated diene polymer is preferably one prepared by anionic polymerization using an organic alkali metal compound, particularly an alkyllithium.

After the polymerization reaction in any case of anionic polymerization or coordination polymerization, the conjugated diene-based polymer in the invention may be subjected to a modification reaction with the above-mentioned modifier at the polymerization active terminal thereof to obtain a modified conjugated diene-based polymer.

The modification reaction temperature is preferably 20 ℃ or higher, but the polymerization temperature of the conjugated diene polymer may be used as it is, and a range of 30 to 120 ℃ is more preferable. When the reaction temperature is lowered, the viscosity of the polymer tends to increase too much or the dispersibility of the reaction product tends to deteriorate. On the other hand, when the reaction temperature is increased, the polymerization active site tends to be ineffective.

The amount of the modifier used is preferably in the range of 0.25 to 3.0mol, more preferably in the range of 0.5 to 1.5mol, based on 1mol of the polymerization initiator used in the production of the conjugated diene polymer.

Examples of other rubber components optionally blended into the rubber composition of the present invention in addition to the above-described natural rubber and modified conjugated diene-based polymer include unmodified styrene-butadiene copolymer (SBR), unmodified polybutadiene rubber (BR), polyisoprene rubber (IR), butyl rubber (IIR), ethylene-propylene-diene terpolymer, and the like. These other rubber components other than the natural rubber and the modified conjugated diene-based polymer may be used alone or as a blend of two or more.

[ Filler ]

The rubber composition for a tire tread of the present invention contains 35 to 70 parts by mass of a filler per 100 parts by mass of a rubber component, and the content of silica in the filler is 3 to 30% by mass.

When the content of the filler in the rubber composition for a tire tread is less than 35 parts by mass with respect to 100 parts by mass of the rubber component, the rubber component cannot be sufficiently reinforced and a tread obtained from the rubber composition for a tire tread is not excellent in wear resistance and cannot reduce rolling resistance. When the content of the filler is more than 70 parts by mass with respect to 100 parts by mass of the rubber component, the rigidity of the tread is too high, and thus the tear resistance and cut resistance thereof are deteriorated thereby.

The content of the filler in the rubber composition for a tire tread is preferably 40 to 70 parts by mass, and even more preferably 45 to 65 parts by mass, relative to 100 parts by mass of the rubber component.

(silica)

The filler contains at least silica, and the content of silica in the filler is 3 to 30 mass%.

As has been described above, the rubber composition for a tire tread of the present invention contains silica in an amount of at most 21 parts by mass relative to 100 parts by mass of the rubber component, but in general, when the filler contains such an amount of silica alone, it cannot reinforce the rubber component. However, a filler such as carbon black other than silica that has a poor interaction with the glycerin fatty acid ester composition is further contained together with the silica, and the rubber composition can form a tread having reduced rolling resistance and having improved abrasion resistance, tear resistance and cut resistance.

Even if the content of silica in the rubber composition for a tire tread of the present invention is 21 parts by mass or less with respect to 100 parts by mass of the rubber component, when the content of silica in the filler is not 30% by mass or less, the composition cannot improve rolling resistance, abrasion resistance, tear resistance and cut resistance. On the other hand, when the content of silica in the filler is less than 3% by mass, even if the rubber composition for a tire tread contains 0.1 to 10 parts by mass of the glycerin fatty acid ester composition relative to 100 parts by mass of the rubber component, the dispersibility of the filler other than silica therein cannot be improved.

The content of silica in the filler is preferably 12 to 30% by mass, more preferably 16 to 29% by mass, and even more preferably 19 to 25% by mass, from the viewpoint of improving rolling resistance, abrasion resistance, tear resistance, and cut resistance.

The content of silica in the rubber composition for a tire tread is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less, per 100 parts by mass of the rubber component.

In the present invention, silica is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), and colloidal silica.

Among the above silica, the adsorption specific surface area (CTAB adsorption specific surface area) measured by the cetyltrimethylammonium bromide adsorption method (CTAB) is preferably 50 to 350m²A concentration of 100 to 300m²In the range of/g.

The CTAB adsorption specific surface area can be measured according to the method of ASTM-D3765-80.

The CTAB adsorption specific surface area is 50-350 m²The Silica/g may be one commercially available, and is available, for example, as NIPSIL AQ (trade name) from Tosoh Silica Corporation, Zeosil1115MP (trade name) from Rhodia S.A., and VN-3 (trade name) from Evonik Degussa Corporation.

[ silane coupling agent ]

Since the rubber composition for a tire tread of the present invention contains silica, even in a small amount, the rubber composition preferably further contains a silane coupling agent for reinforcing the bonding between the silica-rubber component and additionally for further improving the reinforcing property and improving the dispersibility of silica.

The content of the silane coupling agent in the rubber composition for a tire tread of the present invention is preferably 5 to 15 mass% or less with respect to the content of silica. The content of the silane coupling agent of 15 mass% or less relative to the content of the silica ensures the effect of improving the reinforcing property and dispersibility of the rubber component and hardly hinders the economy. When the content of the silane coupling agent is 5% by mass or more with respect to the content of the silica, the dispersibility of the silica in the rubber composition for a tire tread can be improved.

The silane coupling agent is not particularly limited, and preferred examples thereof include bis (3-triethoxysilylpropyl) disulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) disulfide, bis (2-triethoxysilylethyl) trisulfide, bis (2-triethoxysilylethyl) tetrasulfide, 3-trimethoxysilylpropyl-benzothiazole disulfide, 3-trimethoxysilylpropyl-benzothiazole trisulfide and 3-trimethoxysilylpropyl-benzene trisulfide And thiazole tetrasulfide.

The filler contained in the rubber composition for a tire tread of the present invention includes, in addition to silica, metal oxides such as alumina and titanium dioxide, and carbon black, and particularly, carbon black is preferable from the viewpoint of improving the wear resistance and tensile characteristics of the tread.

(carbon Black)

The rubber composition for a tire tread of the present invention preferably contains carbon black from the viewpoint of improving the wear resistance and tensile characteristics of the tread.

Further, from the viewpoint of more increasing the affinity for the modified conjugated diene-based polymer in the present invention to thereby more effectively reduce the rolling resistance of a tire and more effectively improve the abrasion resistance, tear resistance and cut resistance of a tire, the filler is preferably coatedDibutyl phthalate-containing absorption (DBP absorption) of 40-180 cm³100g, nitrogen adsorption specific surface area (N)₂SA) of 40 to 95m²A carbon black having a toluene extract light transmittance of 90% or more and a hydrogen release rate of 0.37 mass% or more.

[ dibutyl phthalate absorption (DBP absorption) ]

The dibutyl phthalate absorption amount (DBP absorption amount) of the carbon black of the present invention is preferably 40 to 180cm³100g of the total weight. When the DBP absorption was 40cm³At 100g or more, the rubber composition for a tire tread can exhibit the minimum required tensile strength, and when it is 180cm³At a level of less than 100g, the rubber composition can ensure a minimum required elongation.

The DBP absorption of the carbon black of the present invention is more preferably 70 to 175cm³/100g。

The DBP absorption can be measured according to the method described in JIS K6217-4: 2008, and is expressed as a volume mL of dibutyl phthalate (DBP) absorbed by 100g of carbon black.

[ nitrogen adsorption specific surface area (N)₂SA)]

The carbon black of the present invention has a nitrogen adsorption specific surface area (N)₂SA) is preferably 40 to 95m²(ii) in terms of/g. When the nitrogen adsorption specific surface area of the carbon black is 40m²Above/g, the rubber composition for a tire tread can exhibit the minimum required tensile strength, and when it is 95m²At the time of/g or less, sufficient dispersibility in the rubber composition is ensured, so that the rubber composition is excellent in abrasion resistance.

More preferably, the carbon black of the present invention has a nitrogen adsorption specific surface area (N)₂SA) of 50 to 95m²(ii)/g, even more preferably 60 to 95m²/g。

Nitrogen adsorption specific surface area (N)₂SA) can be measured based on JIS K6217-2: 2001.

[ light transmittance of toluene extract ]

The light transmittance of the toluene extract of the carbon black in the present invention is preferably 90% or more.

When the toluene extract light transmittance of the carbon black is 90% or more, tar components, particularly aromatic components, which may be present in the surface of the carbon black, can be reduced, thereby increasing the interaction of the carbon black with the modified conjugated diene-based polymer in the present invention, and therefore, the rubber component can be sufficiently reinforced to improve the abrasion resistance of the rubber composition. The light transmittance of the toluene extract of carbon black is preferably 95% or more.

[ Hydrogen Release Rate ]

The hydrogen release rate of the carbon black in the present invention is preferably 0.37 mass% or more.

When the hydrogen release rate is 0.37 mass% or more, the interaction between the carbon black and the modified conjugated diene polymer in the present invention can be improved, and therefore, the rubber component can be sufficiently reinforced to improve the wear resistance of the tread.

The hydrogen release rate of the carbon black is preferably 0.40 mass% or more. The upper limit of the hydrogen release rate is not particularly limited, but from the viewpoint of ease of production due to the limitation of the apparatus, the upper limit of the hydrogen release rate is usually about 0.60 mass%.

For the hydrogen release rate of carbon black, (1) a carbon black sample was dried in a thermostatic dryer at 105 ℃ for 1 hour and cooled to room temperature (23 ℃) in a dryer, (2) about 10mg of the sample was precisely weighed in a tubular sample container made of tin and sealed under pressure, (3) it was heated in a stream of argon gas for 15 minutes using a gas chromatography analysis apparatus and the amount of hydrogen gas generated during this time was measured, and the value was expressed as mass%.

The carbon black having the above physical properties used in the present invention can be produced using a reaction system (carbon black-producing furnace) in which a combustion gas generation zone, a reaction zone and a reaction stop zone are arranged in series, wherein a high-temperature combustion gas is generated in the combustion gas generation zone, then a raw material is injected and introduced into the reaction zone to thereby form a reaction gas stream containing carbon black, and thereafter in the reaction stop zone, the reaction gas stream is rapidly cooled by a multi-stage rapid cooling medium introduction means to terminate the reaction, thereby obtaining carbon black. In a carbon black producing furnace, the amount of produced air (kg/hr), the air temperature (DEG C), the amount of fuel introduced (kg/hr), and the amount of raw material introduced (kg/h) are appropriately controlledr) and the raw material preheating temperature (. degree. C.), a desired nitrogen adsorption specific surface area (N) can be obtained₂SA), desired DBP absorption, desired toluene extract transmittance, and desired hydrogen release rate.

The content of carbon black in the rubber composition for a tire tread is preferably 40 to 60 parts by mass with respect to 100 parts by mass of the rubber component. The total amount of carbon black and silica is preferably 65 parts by mass or less with respect to 100 parts by mass of the rubber component.

When the content of the carbon black is 40 parts by mass or more with respect to 100 parts by mass of the rubber component, the rubber component can be sufficiently reinforced. On the other hand, when the content of carbon black is 60 parts by mass or less with respect to 100 parts by mass of the rubber component, carbon black can be easily dispersed in the rubber composition for a tire tread, and therefore the wear resistance and tear resistance of the tread obtained from the rubber composition for a tire tread can be improved and the rolling resistance of the tire can be more reduced.

[ Glycerol fatty acid ester composition ]

The rubber composition for a tire tread of the present invention contains 0.1 to 10 parts by mass of a glycerin fatty acid ester composition per 100 parts by mass of a rubber component.

The rubber composition for a tire tread of the present invention further contains 0.1 to 10 parts by mass of a glycerin fatty acid ester composition relative to 100 parts by mass of a rubber component together with a small amount of silica, and therefore, the filler dispersibility in the rubber composition for a tire tread is increased, and therefore, a tread capable of reducing the rolling resistance of a tire and improving the abrasion resistance, the tear resistance and the cut resistance thereof is provided.

The content of the glycerin fatty acid ester composition in the rubber composition for a tire tread of the present invention is preferably 0.5 to 7.0 parts by mass, and more preferably 0.8 to 4.5 parts by mass, per 100 parts by mass of the rubber component.

The glycerin fatty acid ester composition contains at least one glycerin fatty acid ester as an ester of glycerin and a fatty acid.

The glycerin fatty acid ester is as follows: fatty acids are bonded to at least one of three OH groups possessed by glycerin in a mode of an ester bond, and esters are classified into glycerin fatty acid monoesters, glycerin fatty acid diesters, and glycerin fatty acid triesters, depending on the number of bonding of fatty acids. Specifically, the ester includes a glycerin fatty acid monoester in which one molecule of glycerin is esterified with one molecule of fatty acid (monoester component), a glycerin fatty acid diester in which one molecule of glycerin is esterified with two molecules of fatty acid (diester component), and a glycerin fatty acid triester in which one molecule of glycerin is esterified with three molecules of fatty acid (triester component).

The two fatty acids constituting the glycerin fatty acid diester and the three fatty acids constituting the glycerin fatty acid triester may be the same or different, respectively.

The glycerin fatty acid ester composition preferably contains at least one selected from the group consisting of a glycerin fatty acid monoester, a glycerin fatty acid diester, and a glycerin fatty acid triester, and more preferably contains at least a glycerin fatty acid monoester (monoester component).

In the production of glycerin fatty acid esters, glycerin may remain as an unreacted raw material. The content of glycerin in the glycerin fatty acid ester composition is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less from the viewpoint of preventing a decrease in heat resistance of the rubber composition for a tire tread, and the content may be 0.3% by mass or more from the viewpoint of productivity.

(fatty acid)

The kind of the fatty acid as a raw material of the glycerin fatty acid ester is not particularly limited, and may be a monovalent fatty acid or a polyvalent fatty acid of divalent or more, and may be a saturated fatty acid or an unsaturated fatty acid.

The carbon number of the fatty acid is 8 or more, preferably 10 or more, more preferably 12 or more, even more preferably 16 or more from the viewpoint of reducing the viscosity of the unvulcanized rubber, and is 28 or less, preferably 22 or less, more preferably 18 or less from the viewpoint of improving the heat resistance.

The fatty acids may be saturated or unsaturated and are linear or branched, but linear saturated fatty acids are particularly preferred. Specific examples of the fatty acid include caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, arachidonic acid, and behenic acid. Among them, lauric acid, myristic acid, palmitic acid, and stearic acid are preferable, and palmitic acid and stearic acid are more preferable.

As for the fatty acid as a raw material of the glycerin fatty acid ester, each fatty acid, that is, each stereoisomer, which is the same in the steric configuration and the bonding state thereof except the number of carbons of the alkyl group is considered as one component. For example, the same carbon number 18 fatty acids include n-1-octadecanoic acid (typically linear stearic acid), 2-octyl-1-decanoic acid (2-branched stearic acid), cis-9-octadecenoic acid (typically oleic acid), and cis, cis-9, 12-octadecadienoic acid (typically linoleic acid), and these are considered to be different fatty acids.

Among the glycerin fatty acid ester compositions containing the above-described fatty acids and glycerin fatty acid esters of glycerin, preferred embodiments of the glycerin fatty acid ester composition used in the present invention are as follows:

1) a glycerin fatty acid ester composition comprising a glycerin fatty acid monoester and a glycerin fatty acid diester as an ester of glycerin and a fatty acid having 8 to 28 carbon atoms, wherein the content of the glycerin fatty acid monoester is 85 mass% or less (first embodiment); and

2) the glycerin fatty acid ester composition contains a glycerin fatty acid ester of an ester of glycerin and two or more fatty acids, wherein the content of the most abundant fatty acid component among all fatty acid components in the entire glycerin fatty acid ester is 10 to 90% by mass, and the content of the glycerin fatty acid monoester in the glycerin fatty acid ester composition is 50 to 100% by mass, among the fatty acid components that are fatty acid-derived sites in the glycerin fatty acid ester (second embodiment).

These two embodiments are described below.

(first embodiment)

The glycerin fatty acid ester composition of the first embodiment comprises a glycerin fatty acid monoester and a glycerin fatty acid diester as an ester of glycerin and a fatty acid having 8 to 28 carbon atoms, wherein the content of the glycerin fatty acid monoester is 85 mass% or less.

When the rubber composition for a tire tread of the present invention comprises the glycerin fatty acid ester composition of the first embodiment, the dispersibility of the filler other than silica therein can be improved, and in addition, the rubber composition can prevent shrinkage and scorching of the rubber without delaying the vulcanization rate of the rubber, the improvement of processability due to the reduction in viscosity of the unvulcanized rubber to which silica is added can be achieved and various properties such as heat resistance can be highly improved.

The glycerin fatty acid ester composition of the first embodiment contains at least two glycerin fatty acid esters of a glycerin fatty acid monoester and a glycerin fatty acid diester, wherein the content of the glycerin fatty acid monoester is 85 mass% or less. The glycerin fatty acid ester composition of the first embodiment may further contain glycerin fatty acid triester, glycerin, and the like.

When the content of the glycerin fatty acid monoester in the glycerin fatty acid ester composition of the first embodiment is 85 mass% or less, the rubber composition for a tire tread of the present invention can be prevented from shrinking, and the heat resistance of the vulcanized rubber is hardly deteriorated.

Therefore, in the glycerin fatty acid ester composition of the first embodiment, the content of the glycerin fatty acid monoester is preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and further more preferably 50% by mass or more from the viewpoint of reducing the viscosity of the unvulcanized rubber, and is 85% by mass or less, preferably 80% by mass or less, more preferably 75% by mass or less, and is preferably 35 to 85% by mass, more preferably 40 to 85% by mass, even more preferably 45 to 85% by mass, still more preferably 50 to 85% by mass, further more preferably 50 to 80% by mass, and still further more preferably 50 to 75% by mass from the viewpoint of delaying scorch, suppressing shrinkage, and maintaining heat resistance.

The content of the glycerin fatty acid diester in the glycerin fatty acid ester composition of the first embodiment is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more from the viewpoint of suppressing shrinkage, delaying scorch, and making the heat resistance better, and is preferably 65% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, and is preferably 10 to 65% by mass, more preferably 15 to 55% by mass, even more preferably 15 to 50% by mass, and still more preferably 20 to 50% by mass from the viewpoint of reducing the viscosity of the unvulcanized rubber.

The mass ratio of glycerin fatty acid monoester/glycerin fatty acid diester in the glycerin fatty acid ester composition of the first embodiment is preferably 0.5 or more, more preferably 0.8 or more, even more preferably 0.9 or more, and further more preferably 1.0 or more from the viewpoint of reducing the viscosity of the unvulcanized rubber, and is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, further more preferably 5 or less, further more preferably 4 or less, and further more preferably 3 or less from the viewpoint of suppressing shrinkage, delaying scorch, and making the heat resistance better.

The content of the glycerin fatty acid triester in the glycerin fatty acid ester composition of the first embodiment is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, from the viewpoint of preventing excessive deterioration of physical properties (for example, reduction in storage elastic modulus) of the vulcanized rubber, and may be 0.3% by mass or more from the viewpoint of productivity.

The total content of the glycerin fatty acid diester and the glycerin fatty acid triester in the glycerin fatty acid ester composition of the first embodiment is preferably 15 to 50% by mass, more preferably 17 to 50% by mass, from the viewpoint of reducing the viscosity of the unvulcanized rubber, suppressing shrinkage, and improving heat resistance.

In particular, in the glycerin fatty acid ester composition, from the viewpoints of reducing the viscosity of unvulcanized rubber, suppressing shrinkage, delaying scorch, and making heat resistance better, it is preferable that the content of glycerin fatty acid monoester is 50 to 85 mass% and the total content of glycerin fatty acid diester and triester is 15 to 50 mass%; in the glycerin fatty acid ester composition, more preferably, the content of glycerin fatty acid monoester is 50 to 80 mass% and the total content of glycerin fatty acid diester and triester is 17 to 50 mass%; preferably, the content of the glycerin fatty acid monoester is 50 to 85 mass% and the content of the glycerin fatty acid diester is 15 to 50 mass%; and even more preferably, the content of the glycerin fatty acid monoester is 50 to 80 mass% and the content of the glycerin fatty acid diester is 20 to 50 mass%.

Both the glycerin fatty acid monoester and the glycerin fatty acid diester contained in the glycerin fatty acid ester composition of the first embodiment are esters of fatty acid having 8 to 28 carbon atoms and glycerin.

When the fatty acid has 8 or more carbon atoms, the affinity between the rubber component and the glycerin fatty acid ester composition can be ensured and blooming hardly occurs. Blooming means precipitation of a glycerin fatty acid ester composition from a vulcanized rubber such as a tread. On the other hand, when the fatty acid has 28 or less carbon atoms, the rubber composition ensures the processability improving effect.

The carbon number of the fatty acid as the raw material of the glycerin fatty acid monoester and the glycerin fatty acid diester contained in the glycerin fatty acid ester composition of the first embodiment is preferably 8 to 22, more preferably 10 to 18, even more preferably 12 to 18, from the viewpoint of improving processability, suppressing shrinkage, and making heat resistance better due to a decrease in viscosity of the unvulcanized rubber.

The glycerin fatty acid ester composition of the first embodiment can be produced according to an esterification method using glycerin and fatty acid as a decomposition product of an oil or fat or a transesterification method using an oil or fat and glycerin as raw materials. For producing a glycerin fatty acid ester composition in which the amount of monoester is controlled, the following methods 1) to 3) are available.

1) In the esterification method and the transesterification method, the input ratio of fatty acid and glycerin is changed to control the esterification equilibrium composition. In this case, the glycerol can be removed by further distillation. However, in view of the reaction characteristics, the upper limit of the amount of the glycerin fatty acid monoester is considered to be about 65 mass%.

2) The reaction product obtained according to the esterification method or the transesterification method is further fractionated and distilled by molecular distillation to obtain a glycerin fatty acid monoester having high purity (usually 95% by mass or more).

3) The high-purity glycerin fatty acid monoester obtained according to the method 2) is mixed with the medium-purity glycerin fatty acid monoester obtained according to the method 1) in any desired ratio, thereby obtaining a glycerin fatty acid monoester in a relatively high-purity range (about 65 to 95 mass%).

Using fats and oils and fatty acids of natural products as raw materials, glycerin fatty acid esters contributing to a reduction in environmental load may be used herein. Further, the glycerin fatty acid ester composition used in the present invention may be a commercially available one in which the amount of monoester is controlled; and examples of commercially available products include glyceryl monostearate (Rheodol MS-60 and Excel S-95, both available from Kao Corporation).

In the present invention, the content of glycerin fatty acid monoester (content of monoglyceride) in the glycerin fatty acid ester composition is determined by GPC analysis (gel permeation chromatography) and according to the following equation (I), and means an area ratio of glycerin fatty acid monoester (monoglyceride) to the total of glycerin, glycerin fatty acid monoester, glycerin fatty acid diester (diglyceride), and glycerin fatty acid triester (triglyceride) in GPC analysis.

The same applies to the case of the glycerin fatty acid ester composition of the second embodiment.

In the above equation (I), G represents the glycerol area in GPC, MG means the glycerol fatty acid monoester area in GPC, DG means the glycerol fatty acid diester area in GPC, and TG means the glycerol fatty acid triester area in GPC.

The measurement conditions in GPC are as follows.

[ measurement conditions in GPC ]

The following measuring apparatus was used for GPC measurement, and as an eluent, THF (tetrahydrofuran) was made to flow at a flow rate of 0.6ml/min, and the column was stabilized in a constant temperature bath at 40 ℃. 10. mu.l of a 1 mass% sample solution dissolved in THF was injected into the measuring apparatus.

Standard substance: monodisperse polystyrene

A detector: RI-8022 (commercially available from Tosoh Corporation)

The measuring equipment comprises: HPLC-8220GPC (available from Tosoh Corporation)

And (3) analyzing the column: two columns of TSK-GEL SUPER H1000 and two columns of TSK-GEL SUPER H2000 in series (available from Tosoh Corporation)

Similarly, the content of the glycerin fatty acid diester (diglyceride) in the glycerin fatty acid ester composition means an area ratio of the glycerin fatty acid diester to the total of glycerin, the glycerin fatty acid monoester, the glycerin fatty acid diester, and the glycerin fatty acid triester in GPC analysis.

Examples of glycerin fatty acid ester compositions useful herein and having a controlled monoester content include glyceryl caprylate-containing compositions in which the fatty acids have 8 carbon atoms, glyceryl caprate-containing compositions in which the fatty acids have 10 carbon atoms, glyceryl laurate-containing compositions in which the fatty acids have 12 carbon atoms, glyceryl myristate-containing compositions in which the fatty acids have 14 carbon atoms, glyceryl palmitate-containing compositions in which the fatty acids have 16 carbon atoms, glyceryl stearate-containing compositions in which the fatty acids have 18 carbon atoms, glyceryl behenate-containing compositions in which the fatty acids have 22 carbon atoms, and glyceryl montanate-containing compositions in which the fatty acids have 28 carbon atoms. Among them, a lauric acid glyceride-containing composition, a palmitic acid glyceride-containing composition, and a stearic acid glyceride-containing composition are preferable. One or two or more of these glycerin fatty acid ester-containing compositions having a controlled monoester content may be used alone or in combination.

(second embodiment)

The glycerin fatty acid ester composition of the second embodiment comprises a glycerin fatty acid ester which is an ester of glycerin and two or more fatty acids, wherein the content of the fatty acid component having the largest amount among all fatty acid components of all glycerin fatty acid esters among the fatty acid components which are fatty acid derivative sites of the glycerin fatty acid ester is 10 to 90% by mass, and the content of glycerin fatty acid monoester in the glycerin fatty acid ester composition is 50 to 100% by mass.

When the rubber composition for a tire tread of the present invention contains the glycerin fatty acid ester composition of the first embodiment, the dispersibility of the filler other than silica therein can be improved, and in addition, the processability, low heat build-up property and fracture resistance property of the rubber composition can be well balanced at a high level.

The glycerin fatty acid ester constituting the glycerin fatty acid ester composition of the second embodiment is an ester of glycerin and two or more fatty acids.

The glycerin fatty acid ester may be a glycerin fatty acid diester or a glycerin fatty acid triester produced by esterification of two or more fatty acids with one molecule of glycerin, or may be a mixture of a glycerin fatty acid monoester produced by esterification of one molecule of glycerin and one molecule of one fatty acid of two or more fatty acids and a glycerin fatty acid monoester produced by esterification of one molecule of glycerin and one molecule of another kind of fatty acid.

In particular, from the viewpoint of improving processability, low heat build-up property and fracture resistance of the rubber composition for a tire tread of the present invention, a mixture of a glycerin fatty acid monoester produced by esterification of one molecule of glycerin and one molecule of one fatty acid of two or more fatty acids and a glycerin fatty acid monoester produced by esterification of one molecule of glycerin and one molecule of another kind of fatty acid is preferable.

From the same viewpoint, the content of the glycerin fatty acid monoester in the glycerin fatty acid ester composition of the second embodiment is 50 to 100% by mass, preferably 60 to 99% by mass, and more preferably 85 to 98% by mass.

The fatty acid constituting the glycerin fatty acid ester contained in the glycerin fatty acid ester composition of the second embodiment includes the aforementioned various fatty acids, and the carbon number of the fatty acid is preferably 8 to 22, more preferably 12 to 18, and even more preferably 14 to 18 from the viewpoints of processability, low heat build-up property, and fracture resistance of the rubber composition for a tire tread of the present invention.

The glycerin fatty acid ester composition of the second embodiment is as follows: the fatty acid component as a fatty acid derivative site in the glycerin fatty acid ester has a maximum content of 10 to 90% by mass of the total fatty acid components in the total glycerin fatty acid ester.

The glycerin fatty acid ester contains a glycerin component as a glycerin-derived site and a fatty acid component (a portion represented by "RCOO-" where R represents a hydrocarbon group of the fatty acid component) as a fatty acid-derived site. In each of the glycerin fatty acid esters of one molecule, the monoester of the glycerin fatty acid ester has one fatty acid component ("RCOO-"), the diester thereof has two such components, and the triester has three such components.

As described above, it is considered that each of the fatty acids, i.e., each of the stereoisomers, which are the same in the steric configuration and the bonding state thereof except the number of carbons of the alkyl group, is one component of the fatty acid as a raw material of the glycerin fatty acid ester. Therefore, fatty acids having the same carbon number but different molecular structures are considered to be different fatty acids.

In view of the above-described situation, the rubber composition for a tire tread of the present invention may have improved processability, low heat build-up property and fracture resistance property when the content of the fatty acid component in the largest amount among all the fatty acid components is 10 to 90% by mass, while classifying all the fatty acid components of the total glycerin fatty acid ester contained in the glycerin fatty acid ester composition of the second embodiment.

From the same viewpoint, the content of the most abundant fatty acid component among all the fatty acid components is preferably 15 to 80% by mass, more preferably 20 to 70% by mass, and even more preferably 30 to 60% by mass.

The kind and amount of the fatty acid component in the glycerin fatty acid ester contained in the glycerin fatty acid ester composition of the second embodiment can be confirmed by NMR measurement of the glycerin fatty acid ester composition.

The kind and amount of the fatty acid component in the glycerin fatty acid ester may also be calculated from the molecular weight of the fatty acid used for producing the glycerin fatty acid ester, and the calculation result using the molecular weight of the fatty acid component determined by measurement and the calculation result using the molecular weight of the fatty acid as a raw material are closely approximated to each other.

In all the fatty acid components in all the glycerin fatty acid esters contained in the glycerin fatty acid ester composition of the second embodiment, preferably, one of the most abundant fatty acid component and the second most abundant fatty acid component is a fatty acid component having 16 carbon atoms and the other is a fatty acid component having 18 carbon atoms. With such a constitution, the rubber composition for a tire tread of the present invention can secure improved processability, low heat build-up property and fracture resistance property.

Also from the same viewpoint, the mass ratio of the fatty acid component having 16 carbon atoms to the fatty acid component having 18 carbon atoms is preferably 90/10 to 10/90, more preferably 80/20 to 20/80, and even more preferably 75/25 to 25/75.

[ fatty acid metal salt ]

Preferably, the rubber composition for a tire tread of the present invention contains a fatty acid metal salt.

When the rubber composition for a tire tread contains a fatty acid metal salt, a tread produced from the rubber composition for a tire tread may have improved fracture resistance characteristics.

The melting point of the fatty acid metal salt is preferably 115 ℃ or less, more preferably 110 ℃ or less, and even more preferably 105 ℃ or less. When the melting point is 115 ℃ or less, the fatty acid metal salt can be dissolved in kneading and can be easily dispersed in the rubber composition, and therefore the fracture resistance of the tire tread can be more effectively improved.

The fatty acid metal salt is not particularly limited, and includes a fatty acid sodium salt, a fatty acid potassium salt, and a fatty acid zinc salt. The fatty acid constituting the fatty acid metal salt may be monovalent or divalent or more. The fatty acid of the fatty acid metal salt preferably includes oleic acid and palmitic acid, for example, the salt preferably includes zinc oleate and zinc palmitate.

The fatty acid metal salt may be a commercially available one, and examples thereof include "active PP" (trademark) available from LANXESSCorporation.

The content of the fatty acid metal salt in the rubber composition for a tire tread is preferably 0.1 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component, from the viewpoint of improving the fracture resistance of the tread.

(Components)

The rubber composition for a tire tread of the present invention may optionally contain various components commonly used in the rubber industry field, such as a vulcanizing agent, a vulcanization accelerator, zinc oxide, stearic acid, and an antioxidant, in addition to the rubber component comprising the natural rubber and the modified conjugated diene-based polymer specified in the present invention, silica, and the glycerin fatty acid ester composition, and mixed therein within a range not impairing the object of the present invention. Commercially available products can be used for such various components. The rubber composition may be prepared by: the rubber component, the filler and other optional various components are mixed, and then they are kneaded in a closed type kneading apparatus such as a Banbury mixer, an internal mixer or an intensive mixer or a non-closed type kneading apparatus such as a roll, after which the resultant mixture is heated and extruded.

< tire >

The tire of the present invention uses the rubber composition for a tire tread of the present invention as its tread.

The tire of the present invention is excellent in the balance among reduction of rolling resistance, abrasion resistance, tear resistance and cut resistance, and is therefore particularly useful as a heavy duty tire. Here, the heavy duty tires include truck and passenger tire, construction machine tire (building vehicle tire, mine vehicle tire), and small truck (light truck) tire.

The gas filled in the tire of the present invention may be conventional air or air with varying oxygen partial pressure, and further includes inert gases such as nitrogen, argon and helium.

The tire of the present invention is not particularly limited except for using the rubber composition for a tire tread of the present invention as a tread, and can be produced according to a conventional method. For example, the rubber composition for a tire tread of the present invention is extruded and processed into a member for a tread, and attached and shaped on a tire shaping machine according to a conventional method to obtain a green tire. The green tire is heated and pressurized in a vulcanizer to obtain a tire.