JP2014098065A - Tire tread rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire tread rubber composition which can improve rolling resistance performance without impairing wet grip performance, and can also improve workability when unvulcanized.SOLUTION: A tire tread rubber composition contains, with respect to 100 pts.mass of a diene rubber including a modified styrene-butadiene rubber, 0.1-30 pts.mass of an ethylene-vinyl acetate copolymer resin and 0.1-30 pts.mass of a petroleum-based hydrocarbon resin. A pneumatic tire is made using the rubber composition for a tread rubber constituting a tire contact area.

Description

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

  In recent tires, there is a high demand for low fuel consumption, and excellent rolling resistance performance, that is, low rolling resistance is required. On the other hand, tires are also required to have excellent grip performance on wet road surfaces, that is, wet grip performance. However, since these performances are contradictory, it is generally difficult to achieve both.

  In Patent Document 1, it is possible to achieve both wet grip performance and rolling resistance performance by blending an aromatic modified terpene resin together with specific carbon black and silica into a diene rubber containing a terminal-modified styrene butadiene rubber. It is disclosed. By using the modified rubber in this manner, the dispersibility of the filler can be improved and the rolling resistance performance can be improved. Moreover, wet grip performance can be improved by mix | blending adhesive resins, such as a terpene-type resin.

  However, at present, both wet grip performance and rolling resistance performance are required to be at a higher level, and the above-mentioned conventional method has reached a level where a balance between wet grip performance and rolling resistance performance is expected. Absent. Further, when a modified rubber is used as the diene rubber, the processability tends to deteriorate due to an increase in viscosity when not vulcanized.

  By the way, Patent Document 2 discloses blending an ethylene-vinyl acetate copolymer resin in order to suppress bleeding of the resin when an adhesive resin is blended with a diene rubber containing styrene butadiene rubber. ing. However, the point of combining the modified styrene butadiene rubber and the ethylene-vinyl acetate copolymer resin is not disclosed, and the specific effect by the combination is not suggested.

JP 2009-138157 A JP 2012-036229 A

  The present invention has been made in view of the above points. A tire tread that can improve rolling resistance performance without impairing wet grip performance and can improve workability during unvulcanization. It is an object of the present invention to provide a rubber composition for a vehicle and a pneumatic tire using the same.

  The rubber composition for tire treads according to the present invention comprises 0.1 to 30 parts by mass of an ethylene-vinyl acetate copolymer resin and 0.1% by mass of a petroleum hydrocarbon resin with respect to 100 parts by mass of a diene rubber containing a modified styrene butadiene rubber. 1-30 mass parts is contained.

  Moreover, the pneumatic tire according to the present invention is obtained by using the rubber composition as a tread rubber constituting a tire contact surface.

  According to the present invention, by adding an ethylene-vinyl acetate copolymer resin to a rubber composition containing a modified styrene butadiene rubber, the rolling resistance performance can be improved without impairing the wet grip performance, The processability during unvulcanized can be improved.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The rubber composition according to the present embodiment is obtained by blending a petroleum hydrocarbon resin and an ethylene-vinyl acetate copolymer resin with a diene rubber containing a modified styrene butadiene rubber (modified SBR).

  In the rubber composition of this embodiment, the rubber component is a diene rubber containing modified SBR. That is, the rubber component may be a modified SBR alone or a blend of the modified SBR and another diene rubber. The modified SBR can be used at 1 to 100 parts by mass of 100 parts by mass of the diene rubber, preferably 30 parts by mass or more, and more preferably 50 parts by mass or more.

  The modified SBR is a styrene butadiene copolymer rubber having a functional group containing a hetero atom introduced therein, and the functional group may be introduced at the molecular end or may be introduced into the molecular chain.

  Examples of the functional group of the modified SBR include an amino group, an alkoxy group, a hydroxyl group (—OH), an epoxy group, a cyano group (—CN), a carboxyl group (—COOH), a carboxylic acid derivative group, a halogen, and a thiol group ( -SH) and the like. Each of these may be introduced alone or in combination of two or more. These functional groups interact with the functional groups on the filler surface such as silica and carbon black (for example, silanol groups on the silica surface, carboxyl groups, phenolic hydroxyl groups, and quinone groups on the carbon black surface) (reactivity and affinity). ) And the dispersibility of the filler can be improved.

Specifically, the amino group may be not only a primary amino group but also a secondary or tertiary amino group. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like expressed as -OR (where R is an alkyl group). For example, a trialkoxysilyl group, an alkyl dialkoxysilyl group, a dialkylalkoxysilyl group. It may be included as an alkoxysilyl group such as a group (in which at least one of the three hydrogens of the silyl group is substituted with an alkoxy group). Examples of the carboxyl group include maleic acid, phthalic acid, acrylic acid, and methacrylic acid. Examples of the carboxylic acid derivative group include ester groups derived from these carboxylic acids (carboxylic acid ester groups) and acid anhydride groups composed of anhydrides of dicarboxylic acids such as maleic acid and phthalic acid. Examples of the carboxylic acid ester group include an acrylate group (—O—CO—CH═CH ₂ ) and / or a methacrylate group (—O—CO—C (CH ₃ ) ═CH ₂ ) (hereinafter referred to as a (meth) acrylate group. Said). Examples of the halogen include fluorine, chlorine, bromine and iodine.

  Modified SBR itself having such a functional group is known, and its production method and the like are not limited. For example, the functional group may be introduced by modifying a solution-polymerized styrene butadiene copolymer rubber synthesized by anionic polymerization with a modifier, or alternatively, the monomer having the functional group may be used as a base polymer. It may be introduced into the polymer chain by copolymerizing with styrene and butadiene, which are monomers constituting the.

The glass transition temperature (Tg) of the modified SBR is not particularly limited, but is preferably −70 to −10 ° C., more preferably −60 to −20 ° C. Furthermore, it is preferable that a styrene content (St) is 5-50 mass%, More preferably, it is 10-40 mass%. The glass transition temperature is a value measured by a differential scanning calorimetry (DSC) method in accordance with JIS K7121 at a rate of temperature increase of 20 ° C./minute (measurement temperature range: −150 ° C. to 50 ° C.). is there. The styrene content is a value calculated by an integration ratio of ¹ HNMR spectrum.

  The other diene rubber is not particularly limited. For example, natural rubber (NR), polyisoprene rubber (IR), unmodified styrene butadiene rubber (SBR), polybutadiene rubber (BR), acrylonitrile-butadiene rubber ( NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, and the like. These may be used alone or in combination of two or more. Of these, natural rubber is particularly preferable.

  Petroleum-type hydrocarbon resin is mix | blended with the rubber composition which concerns on this embodiment. The wet grip performance can be improved by blending the petroleum hydrocarbon resin. As the petroleum hydrocarbon resin, at least one selected from aliphatic petroleum resins and aliphatic / aromatic copolymer petroleum resins can be used. The softening point of the petroleum hydrocarbon resin is not particularly limited, but those of 80 to 120 ° C. are preferably used. Here, the softening point is a value measured according to JIS K2207 (ring and ball type).

  The aliphatic petroleum resin is a resin obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions corresponding to 4 to 5 carbon atoms (C5 fraction) (C5 petroleum resins). It may also be hydrogenated. In addition, the aliphatic / aromatic copolymer petroleum resin includes the C5 fraction and monomers such as vinyltoluene, alkylstyrene, and indene, which are petroleum fractions corresponding to 8 to 10 carbon atoms (C9 fraction). It is a resin obtained by copolymerization by cationic polymerization (also referred to as C5 / C9 petroleum resin), and may be hydrogenated.

  In order to improve wet grip performance, the amount of the petroleum hydrocarbon resin is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the diene rubber. More preferably, it is 2-10 mass parts.

  The rubber composition according to this embodiment is blended with an ethylene-vinyl acetate copolymer resin (EVA). EVA is a thermoplastic resin obtained by copolymerizing ethylene and vinyl acetate, and can be combined with the modified SBR to improve rolling resistance performance without impairing wet grip performance. The viscosity at the time can be reduced to improve processability.

  Although it does not specifically limit as EVA, It is preferable that vinyl acetate content (VA) is 10-30 mass%, More preferably, it is 10-20 mass%. Here, the vinyl acetate content is measured according to JIS K7192 (1999).

  The blending amount of EVA is preferably 0.1 to 30 parts by mass, and more preferably 1 to 25 parts by mass with respect to 100 parts by mass of the diene rubber.

  Carbon rubber and / or silica can be blended as a filler in the rubber composition according to this embodiment. In order to improve the balance between wet grip performance and rolling resistance performance, the filler is preferably silica alone or a combination of silica and carbon black, and silica is the main filler, and 50% by mass or more is used in the total amount of filler. Is preferred. Although the compounding quantity of a filler is not specifically limited, It is preferable that it is 30-200 mass parts with respect to 100 mass parts of said diene rubbers, More preferably, it is 40-120 mass parts.

The silica is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Among them, wet silica is preferable. Colloidal properties of the silica are not particularly limited, those which are nitrogen adsorption specific surface area (BET) 150~250m ² / g by BET method is preferably used, more preferably 180~230m ² / g. The BET of silica is measured according to the BET method described in ISO 5794.

  Carbon black is not particularly limited, and for example, SAF class (N100 series), ISAF class (N200 series), HAF (N300 series) (both are ASTM grades) and the like can be used.

  In addition, when mix | blending a silica as a filler, in order to improve the dispersibility of a silica, you may mix | blend a silane coupling agent. A silane coupling agent can be normally mix | blended in 2-25 mass parts with respect to 100 mass parts of silica. The silane coupling agent is not particularly limited. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis Sulfide silane coupling agents such as (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) disulfide; 3-mercaptopropyltrimethoxysilane, 3- Mercaptosilane coupling agents such as mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane; Examples thereof include protected mercaptosilane coupling agents such as tanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane. These can be used alone or in combination of two or more.

  The rubber composition according to the present embodiment includes a rubber composition such as a softener such as oil, zinc white, stearic acid, anti-aging agent, wax, vulcanizing agent, and vulcanization accelerator in addition to the above-described components. Various additives generally used in can be blended. Examples of the vulcanizing agent include sulfur and sulfur-containing compounds, and are not particularly limited. However, the blending amount is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. More preferably, it is 0.5-5 mass parts. Moreover, as a compounding quantity of a vulcanization accelerator, it is preferable that it is 0.1-7 mass parts with respect to 100 mass parts of diene rubbers, More preferably, it is 0.5-5 mass parts.

  The rubber composition can be prepared by kneading according to a conventional method using a rubber kneader such as a normal Banbury mixer or kneader. For example, in the first kneading stage, the diene rubber is kneaded with petroleum hydrocarbon resin and EVA and other additives excluding the vulcanizing agent and vulcanization accelerator, and then kneaded. In addition, a rubber composition can be obtained by adding and kneading a vulcanizing agent and a vulcanization accelerator in the final kneading step.

  The rubber composition thus obtained can be used for the tread rubber constituting the ground contact surface of the pneumatic tire. When used for tread rubber, a tread portion of a pneumatic tire can be formed by vulcanization molding at, for example, 140 to 180 ° C. according to a conventional method. The tread portion of the pneumatic tire includes a two-layer structure of a cap rubber and a base rubber and a single-layer structure in which both are integrated, and is preferably used for a rubber constituting the ground contact surface. That is, if the tread rubber has a single layer structure, the tread rubber is preferably made of the rubber composition. If the tread rubber has a two-layer structure, the cap rubber is preferably made of the rubber composition.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, a rubber composition for a tire tread was prepared according to a conventional method according to the formulation (parts by mass) shown in Table 1 below. Specifically, in the first mixing stage, other compounding agents excluding sulfur and a vulcanization accelerator are added to the diene rubber and kneaded (discharge temperature = 150 ° C.). In the final mixing stage, sulfur and a vulcanization accelerator were added and kneaded (discharge temperature = 110 ° C.) to prepare a rubber composition. Each component in the table is as follows.

Unmodified SBR: “Nipol 1502” manufactured by Zeon Corporation
Modified SBR: amino group and alkoxy group terminal modified solution polymerized styrene butadiene rubber, “HPR350” manufactured by JSR Corporation (Tg = −35 ° C., St = 20 mass%)
・ NR: Natural rubber, RSS No. 3 ・ Carbon black: “Seast 6” (ISAF) manufactured by Tokai Carbon Co., Ltd.
Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd. (BET = 205 m ² / g)
・ Oil: “Process NC140” manufactured by JOMO Sun Energy Co., Ltd.
Coupling agent: sulfide silane coupling agent, “Si75” manufactured by Evonik Degussa
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
・ Wax: “Sunknock N” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Petroleum hydrocarbon resin: Aliphatic / alicyclic copolymerized hydrocarbon resin, Mitsui Chemicals, Inc. “Hiretz T500X” (softening point: 97 ° C.)
EVA: “Evaflex V577” manufactured by Mitsui DuPont Chemical Co., Ltd. (vinyl acetate content = 19% by mass)
・ Vulcanization accelerator DM: Sanshin Chemical Industry Co., Ltd. “Sunseller DM-G”
・ Vulcanization accelerator CZ: “Soxinol CZ” manufactured by Sumitomo Chemical Co., Ltd.
・ Sulfur: "Sulfur powder" manufactured by Tsurumi Chemical Co., Ltd.

  For each rubber composition, while evaluating the processability in an unvulcanized state, using a test piece of a predetermined shape vulcanized at 160 ° C. for 30 minutes, rebound resilience (23 ° C.) as an index of wet grip performance, and Then, tan δ (60 ° C.) as an index of rolling resistance performance was measured and evaluated. Each measurement / evaluation method is as follows. The results are shown in Table 1.

Processability: Based on JIS K6300, using a rotorless Mooney measuring machine manufactured by Toyo Seiki Co., Ltd., pre-cured unvulcanized rubber at 100 ° C for 1 minute, and measured the torque value after 4 minutes in Mooney units. . The results are shown in Comparative Examples 1 to 4 using unmodified SBR as an index with the value of Comparative Example 1 (the value of ML (1 + 4)) being 100, and Examples 1 to 3 and Comparative Example using modified SBR. In 5-7, it showed with the index | exponent which set the value (value of ML (1 + 4)) of the comparative example 5 to 100. The smaller the index, the smaller the viscosity and the better the workability.

-Rebound resilience: A Rupke rebound resilience test was performed according to JIS K6255, and a resilience modulus at 23 ° C was measured. The results are shown as an index in Comparative Examples 1 to 4 using unmodified SBR, with the value of Comparative Example 1 being 100, and in Examples 1 to 3 and Comparative Examples 5 to 7 using modified SBR, Comparative Example 5 is used. It was shown as an index with the value of 100 as 100. A smaller index indicates a smaller impact resilience. It is well known to those skilled in the art that there is a correlation between the rebound resilience at 23 ° C. and the wet grip property, and the smaller the rebound resilience, the better the wet grip property. Therefore, it means that it is excellent in wet grip property, so that this index | exponent is small.

Exothermic property: tan δ was measured using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd. under conditions of initial strain 10%, dynamic strain 1%, frequency 10 Hz, and temperature 60 ° C. The results are shown as an index in Comparative Examples 1 to 4 using unmodified SBR, with the value of Comparative Example 1 being 100, and in Examples 1 to 3 and Comparative Examples 5 to 7 using modified SBR, Comparative Example 5 is used. It was shown as an index with the value of 100 as 100. The smaller the index is, the smaller the value of tan δ is, and the less heat is generated, which means that the rolling resistance performance is excellent.

  The results are as shown in Table 1. When unmodified SBR was used, as shown in Comparative Examples 1 to 4, by adding EVA, an improvement trend was recognized in workability and rolling resistance performance, but on the other hand, wet grip performance was greatly improved. It was getting worse.

  On the other hand, when modified SBR is used, as is apparent from comparison between Comparative Example 5 and Examples 1 to 3, the addition of EVA does not impair wet grip performance but rather slightly improves rolling. The resistance performance was improved, and the improvement effect was more remarkable than when unmodified SBR was used. Moreover, by adding EVA, the workability at the time of unvulcanization was improved, and the effect was more remarkable than when unmodified SBR was used. As described above, although the EVA was similarly added, the obtained effect was completely different between the case where the unmodified SBR was used and the case where the modified SBR was used, and an unexpectedly excellent effect was obtained. In Comparative Example 7 in which no petroleum hydrocarbon resin was added, although the rolling resistance performance was improved as compared with Comparative Example 5, the wet grip performance was significantly deteriorated. Further, in Comparative Example 6 in which no petroleum hydrocarbon resin was added and EVA was added, the processability was improved as compared with Comparative Example 7, but the effect of improving wet grip performance was not obtained.

Claims (3)

  Rubber for tire tread containing 0.1-30 parts by mass of ethylene-vinyl acetate copolymer resin and 0.1-30 parts by mass of petroleum hydrocarbon resin with respect to 100 parts by mass of diene rubber containing modified styrene-butadiene rubber Composition.   The modified styrene butadiene rubber has at least one functional group selected from an amino group, an alkoxy group, a hydroxyl group, an epoxy group, a cyano group, a carboxyl group, a carboxylic acid derivative group, a halogen, and a thiol group in the molecular end or molecular chain. The rubber composition for a tire tread according to claim 1, which is introduced into the tire tread.   A pneumatic tire obtained by using the rubber composition according to claim 1 or 2 for a tread rubber constituting a tire contact surface.