Rubber composition for tire treads, and tires using the same.

Abstract

To provide a rubber composition for a tire tread capable of improving rolling resistance and wear resistance, and a tire using the same.SOLUTION: The rubber composition for a tire tread contains: 100 pts.mass of a rubber component which contains 30 pts.mass or more of a solution-polymerized styrene-butadiene rubber and in which the content of a diene rubber other than a styrene-butadiene rubber is less than 50 pts.mass; 60 pts.mass or more of silica; and a trialkyl phosphate in an amount of 1.5-20 mass% of the silica content.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition for a tire tread and a tire using the same.

Background Art

[0002] In recent years, with the increasing interest in environmental issues, in rubber compositions used for tires, it has been required to reduce rolling resistance from the viewpoint of low fuel consumption. On the other hand, in order to obtain the required wet grip braking performance, high filling of silica may be carried out. However, when silica is highly filled, there is a risk that the wear resistance deteriorates or the rolling resistance deteriorates due to the aggregation of silica.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above points, an object of the present invention is to provide a rubber composition for a tire tread and a tire using the same, which can improve rolling resistance and wear resistance.

[0005] In Patent Document 1, as a tire excellent in wet grip performance and wear resistance, a tire containing a rubber composition containing an emulsion styrene / butadiene copolymer, an inorganic reinforcing filler, and a plasticizer is described. However, it does not use a solution-polymerized styrene-butadiene rubber as in the present invention.

[0006] Furthermore, while Patent Document 2 describes the use of glycerin fatty acid ester and silica in combination, it does not use a phosphate ester as in the present invention. [Means for solving the problem]

[0007] The present invention includes embodiments shown below. [1] A tread rubber composition comprising 100 parts by mass of a rubber component containing 30 parts by mass or more of solution-polymerized styrene-butadiene rubber and less than 50 parts by mass of diene rubber other than styrene-butadiene rubber, 60 parts by mass or more of silica, and a trialkyl phosphate in an amount of 1.5 to 20% by mass of the silica content. [2] The tread rubber composition according to [1], wherein the trialkyl phosphate has 3 to 30 carbon atoms. [3] The rubber composition for treads according to [1] or [2], wherein the solution polymerized styrene-butadiene rubber is a modified solution polymerized styrene-butadiene rubber. [4] A tread rubber composition according to any one of [1] to [3], further comprising a hydrocarbon resin. [5] A tire having a tread made of the rubber composition described in any one of items [1] to [4]. [Effects of the Invention]

[0008] The rubber composition for tire treads of the present invention can improve rolling resistance and wear resistance. [Modes for carrying out the invention]

[0009] The following describes in detail matters related to the implementation of the present invention.

[0010] The rubber composition for tire treads according to this embodiment contains 30 parts by mass or more of solution-polymerized styrene-butadiene rubber, 100 parts by mass of a rubber component having a content of less than 50 parts by mass of diene rubber other than styrene-butadiene rubber, 60 parts by mass or more of silica, and a trialkyl phosphate in an amount of 1.5 to 20% by mass of the silica content.

[0011] Generally, styrene-butadiene rubber is broadly classified into solution-polymerized styrene-butadiene rubber (hereinafter also called "S-SBR") and emulsion-polymerized styrene-butadiene rubber (hereinafter also called "E-SBR"). However, S-SBR has a narrower molecular weight distribution (Mw / Mn) compared to E-SBR.

[0012] S-SBR is generally obtained by anionic polymerization of raw material monomers in hydrocarbons, and is characterized by its ability to control both molecular weight distribution and vinyl content compared to E-SBR obtained by emulsion polymerization (suspension polymerization) in water.

[0013] In the present invention, it is preferable to include modified S-SBR as the S-SBR. Modified S-SBR contains a functional group containing a heteroatom. The functional group containing a heteroatom may be introduced at the end of the polymer chain or introduced within the polymer chain, but it is preferable to introduce it at the end. Examples of functional groups containing a heteroatom include amino groups, alkoxyl groups, hydroxyl groups, epoxy groups, carboxyl groups, cyano groups, halogen groups, etc. Modified S-SBR may contain at least one of the exemplified functional groups. Examples of amino groups include primary amino groups, secondary amino groups, tertiary amino groups, etc. Examples of alkoxyl groups include methoxy groups, ethoxy groups, propoxy groups, butoxy groups, etc. Examples of halogen groups include chlorine, bromine, etc. The exemplified functional groups interact with various functional groups of fillers, particularly carbon black, and with the silanol groups (Si-OH) of silica. Here, interaction means, for example, in the case of silica, chemical bonding or hydrogen bonding through chemical reactions with the silanol groups of silica. Furthermore, S-SBR may also use oil-based additives such as carbon black or silica to improve filler properties and processability.

[0014] The content of solution-polymerized styrene-butadiene rubber in 100 parts by mass of rubber component is 30 parts by mass or more, preferably 30 to 100 parts by mass, more preferably 35 to 100 parts by mass, and even more preferably 40 to 100 parts by mass.

[0015] The rubber component may contain emulsion polymerized styrene-butadiene rubber (E-SBR), but its content is preferably less than 60 parts by mass, more preferably less than 50 parts by mass, and even more preferably less than 40 parts by mass, per 100 parts by mass of the rubber component.

[0016] The rubber component may consist solely of styrene-butadiene rubber, but other diene rubbers such as natural rubber (NR), isoprene rubber (IR), nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber may be further blended in a range that does not impair the original effect. The content of these other rubbers is less than 50 parts by mass, preferably less than 40 parts by mass, and more preferably less than 30 parts by mass, per 100 parts by mass of the rubber component.

[0017] The rubber composition according to this embodiment contains silica as a reinforcing filler. The silica is not particularly limited, and for example, wet silica such as wet sedimentation silica or wet gel silica may be used.

[0018] The silica content is 60 parts by mass or more, preferably 60 to 140 parts by mass, more preferably 60 to 130 parts by mass, and even more preferably 65 to 120 parts by mass, per 100 parts by mass of rubber component. When the silica content is within the above range, excellent rolling resistance and wear resistance are easily obtained.

[0019] As the reinforcing filler, in addition to silica, carbon black may be used in combination. The content of the reinforcing filler (total amount of silica and carbon black) is preferably 60 to 150 parts by mass, more preferably 60 to 140 parts by mass, and even more preferably 60 to 130 parts by mass with respect to 100 parts by mass of the rubber component. The content of carbon black is preferably 0.1 to 40 parts by mass, more preferably 1 to 30 parts by mass, and even more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component.

[0020] The rubber composition according to the present embodiment preferably contains a silane coupling agent. In that case, the content of the silane coupling agent is preferably 1 to 20 parts by mass, more preferably 1 to 15 parts by mass with respect to 100 parts by mass of silica.

[0021] The rubber composition according to the present embodiment contains trialkyl phosphate, and its content is 1.5 to 20% by mass of the silica content. That is, it is contained at a ratio of 1.5 to 20 parts by mass with respect to 100 parts by mass of silica.

[0022] The number of carbon atoms of the trialkyl phosphate is preferably 3 to 30, and more preferably 3 to 24. Specifically, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri(2-ethylhexyl) phosphate, tricresyl phosphate, trixylenyl phosphate, tris(isopropylphenyl) phosphate, trinaphthyl phosphate, etc. can be mentioned.

[0023] The freezing point of the trialkyl phosphate is preferably -50°C or lower, and more preferably -55 to -90°C.

[0024] The rubber composition according to this embodiment may contain a hydrocarbon resin. The hydrocarbon resin content may be 1 to 20 parts by mass or 5 to 15 parts by mass per 100 parts by mass of the rubber component. When the hydrocarbon resin content is within the above range, excellent rolling resistance and wear resistance are easily obtained.

[0025] Examples of hydrocarbon resins include styrene resins, terpene resins, petroleum-based hydrocarbon resins, and rosin resins, with petroleum-based hydrocarbon resins and terpene resins being preferred among these.

[0026] The styrene-based resin can be any resin containing styrene and / or α-methylstyrene as constituent monomers, and examples include homopolymers obtained by polymerizing styrene or α-methylstyrene alone, copolymers obtained by copolymerizing styrene and α-methylstyrene, and copolymers of styrene and / or α-methylstyrene with other monomers. Examples of other monomers include terpene compounds (terpene monomers) such as α-pinene, β-pinene, dipentene, limonene, myrcene, allocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol, as well as non-conjugated olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene, and these may be used individually or in combination of two or more.

[0027] Examples of terpene resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers, as well as modified terpene resins obtained by modifying these terpene resins (phenol modification, aromatic modification, hydrocarbon modification, etc.) (for example, terpene phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, etc.).

[0028] Examples of petroleum-based hydrocarbon resins include C5 aliphatic hydrocarbon resins, C9 aromatic hydrocarbon resins, and C5 / C9 aliphatic / aromatic copolymer hydrocarbon resins. Aliphatic hydrocarbon resins are obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions (C5 fractions) with 4 to 5 carbon atoms, and may be partially hydrogenated. Aromatic hydrocarbon resins are obtained by cationic polymerization of monomers such as vinyltoluene, alkylstyrene, and indene, which are petroleum fractions (C9 fractions) with 8 to 10 carbon atoms, and may be partially hydrogenated. Aliphatic / aromatic copolymer hydrocarbon resins are obtained by copolymerizing the above C5 fraction and C9 fraction by cationic polymerization, and may be partially hydrogenated.

[0029] Examples of rosin-based resins include raw rosins such as gum rosin, wood rosin, and tall oil rosin, as well as rosins such as disproportionates of raw rosins and polymerized rosins, esterified rosins (rosin ester resins), phenol-modified rosins, unsaturated acid (such as maleic acid)-modified rosins, and formylated rosins obtained by reduction treatment of rosins.

[0030] In addition to the components mentioned above, the rubber composition according to this embodiment may contain various additives commonly used in rubber compositions, such as zinc oxide, stearic acid, antioxidants, waxes, oils, vulcanizing agents, and vulcanization accelerators.

[0031] Sulfur is preferably used as the vulcanizing agent. The content of the vulcanizing agent is not particularly limited, but is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component. Examples of the vulcanization accelerator include sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators, which can be used individually or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, but is preferably 0.1 to 7 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0032] The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixer such as a Banbury mixer, kneader, or roll. That is, for example, in the first mixing stage, other additives excluding the vulcanizing agent and vulcanization accelerator can be added and mixed with the rubber component, and then, in the final mixing stage, the vulcanizing agent and vulcanization accelerator can be added and mixed with the resulting mixture to prepare the rubber composition.

[0033] The rubber composition obtained in this way can be applied to the treads of pneumatic tires of various uses and sizes, such as passenger car tires and large tires for trucks and buses. Specifically, the rubber composition can be molded into a predetermined shape by conventional methods, for example by extrusion, and combined with other parts to produce a green tire. After that, a pneumatic tire can be manufactured by vulcanizing the green tire at, for example, 140 to 180°C. [Examples]

[0034] The following are examples of the present invention, but the present invention is not limited to these examples.

[0035] Using a lab mixer, the rubber components were first mixed in the first stage, with the addition of all compounding agents except sulfur and vulcanization accelerator, according to the formulations (parts by mass) shown in Tables 1-4 below (discharge temperature = 160°C). Then, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting mixture and mixed (discharge temperature = 90°C) to prepare the rubber composition. Details of each component in Tables 1-4 are as follows.

[0036] • SBR1: JSR Corporation's "HPR350," modified S-SBR (styrene content = 20.5% by mass, microstructure of butadiene portion: vinyl content = 55.5%) • SBR2: JSR Corporation's "SBR1502", E-SBR (styrene content = 23.5%) • SBR3: "Toughden 1834" manufactured by Asahi Kasei Corporation, unmodified S-SBR (Tg=-68℃, 37.5 parts by mass oil-distributed) • SBR4: JSR Corporation's "HPR840," modified S-SBR (styrene content = 10% by mass, microstructure of butadiene portion: vinyl content = 42%) • BR: "BR150B" manufactured by Ube Industries, Ltd., vinyl content 1% • NR: RSS#3 • Carbon Black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. • Silica: Evonik "Ultrasil VN3" • Silane coupling agent: Evonik's "Si-69", bis(3-triethoxysilylpropyl)tetrasulfide • Oil: ENEOS Corporation's "Process NC-140" • Zinc oxide: "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. • Stearic acid: "Lunaq S-20" manufactured by Kao Corporation • Anti-aging agent: "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. • Phosphate ester 1: Tris(2-ethylhexyl) phosphate (TOP), manufactured by Daihachi Chemical Industry Co., Ltd., freezing point below -70°C. • Phosphate ester 2: Triethyl phosphate (TEP), manufactured by Daihachi Chemical Industry Co., Ltd., freezing point -56°C • Ester plasticizer: Bis(2-ethylhexyl) phthalate (DOP) manufactured by Daihachi Chemical Industry Co., Ltd., freezing point -50°C • Hydrocarbon resin 1: C5 / C9 resin, "Petrotac 90" manufactured by Tosoh Corporation, softening point = 95°C • Hydrocarbon resin 2: β-pinene resin, DRT's "DERCOLYTE S 115", softening point = 114°C • Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries, Ltd. • Vulcanization accelerator 1: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. • Vulcanization accelerator 2: "Noxellar D" manufactured by Ouchi Shinko Chemical Co., Ltd.

[0037] For each rubber composition obtained, test pieces of a predetermined shape were prepared by vulcanization at 160°C for 20 minutes, and the rolling resistance and abrasion resistance were measured. The measurement method is as follows.

[0038] • Rolling resistance performance: Using a viscoelasticity testing machine manufactured by Toyo Seiki Co., Ltd., the loss coefficient tanδ was measured under the conditions of a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 60°C. The results are expressed as an index with the reciprocal of the value of the reference comparative example set to 100. A larger index indicates a smaller tanδ and superior rolling resistance performance.

[0039] • Abrasion resistance: In accordance with JIS K6264, abrasion loss was measured using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of a load of 40N and a slip ratio of 30%, and the result was expressed as an index with the reciprocal of the value of the reference comparative example set to 100. A higher index indicates less abrasion loss and superior abrasion resistance.

[0040] In Table 1, Examples 1-1 to 1-5 and Comparative Example 1-2 were based on Comparative Example 1-1, Examples 1-6 to 1-8 were based on Comparative Example 1-3, and Examples 1-9, 1-10, and Comparative Example 1-5 were based on Comparative Example 1-4. In Table 2, Examples 2-1 to 2-5, Comparative Example 2-2, and Comparative Example 2-3 were based on Comparative Example 2-1, and Examples 2-6 to 2-8 were based on Comparative Example 2-4. In Table 3, Examples 3-1 to 3-4 and Comparative Example 3-2 were based on Comparative Example 3-1, and Examples 3-5 to 3-9 and Comparative Example 3-4 were based on Comparative Example 3-3. In Table 4, Examples 4-1 to 4-4, Comparative Example 4-2, and Comparative Example 4-3 were based on Comparative Example 4-1, and Examples 4-5 to 4-9 and Comparative Example 4-5 were based on Comparative Example 4-4.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] [Table 4]

[0045] The results are shown in Tables 1-4. Compared to Comparative Example 1-1, Examples 1-1 to 1-5 exhibited superior rolling resistance and wear resistance. On the other hand, Comparative Example 1-2 was an example where the phosphate ester content exceeded the upper limit, resulting in inferior wear resistance compared to Comparative Example 1-1.

[0046] Examples 1-6 to 1-8 exhibited superior rolling resistance and wear resistance compared to Comparative Example 1-3.

[0047] Examples 1-9 exhibited superior rolling resistance and wear resistance compared to Comparative Example 1-4. Example 1-10 exhibited superior rolling resistance and wear resistance compared to Comparative Example 1-5.

[0048] Examples 2-1 to 2-4 showed superior rolling resistance and wear resistance compared to Comparative Example 2-1. Comparative Example 2-2 was an example using modified S-SBR, and while rolling resistance improved compared to Comparative Example 2-1, wear resistance deteriorated. On the other hand, Example 2-5 was an example using modified S-SBR and phosphate ester in combination, and showed superior rolling resistance and wear resistance compared to Comparative Example 2-1.

[0049] Examples 2-6 to 2-8 exhibited superior rolling resistance and wear resistance compared to Comparative Example 2-4.

[0050] Compared to Comparative Example 3-1, Examples 3-1 to 3-4 exhibited superior rolling resistance and wear resistance. On the other hand, Comparative Example 3-2 was an example where the phosphate ester content exceeded the upper limit, and no improvement in wear resistance was observed compared to Comparative Example 3-1.

[0051] Examples 3-5 and 3-6 showed superior rolling resistance and wear resistance compared to Comparative Example 3-3. Examples 3-7 to 3-9 showed superior rolling resistance and wear resistance compared to Comparative Example 3-4.

[0052] Compared to Comparative Example 4-1, Examples 4-1 to 4-4 exhibited superior rolling resistance and wear resistance. On the other hand, Comparative Example 4-2 was an example where the phosphate ester content exceeded the upper limit, and no improvement in wear resistance was observed compared to Comparative Example 4-1. Furthermore, Comparative Example 4-3 was an example where an ester plasticizer was used instead of phosphate ester, but the wear resistance deteriorated.

[0053] Examples 4-5 and 4-6 showed superior rolling resistance and wear resistance compared to Comparative Example 4-4. Examples 4-7 to 4-9 also showed superior rolling resistance and wear resistance compared to Comparative Example 4-5. [Industrial applicability]

[0054] The rubber composition of the present invention can be used in rubber compositions for various tires, such as those for passenger cars, light trucks, and buses.

Claims

1. A rubber component comprising 100 parts by mass containing 30 parts by mass or more of solution-polymerized styrene-butadiene rubber, and having a content of less than 30 parts by mass of diene-based rubbers other than styrene-butadiene rubber, 60 parts by mass or more of silica, A rubber composition for treads containing a trialkyl phosphate in an amount of 1.5 to 20% by mass of silica.

2. The tread rubber composition according to claim 1, wherein the trialkyl phosphate has 3 to 30 carbon atoms.

3. The rubber composition for treads according to claim 1, wherein the solution-polymerized styrene-butadiene rubber comprises a modified solution-polymerized styrene-butadiene rubber.

4. Furthermore, the tread rubber composition according to claim 1 further contains a hydrocarbon resin.

5. A tire having a tread made of the rubber composition described in any one of claims 1 to 4.

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