JP4583085B2 - Rubber composition for tread and pneumatic tire using the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a tread rubber composition and a pneumatic tire using the same, and more particularly to a tread rubber composition having improved workability and wear resistance without deteriorating rolling resistance characteristics and wet grip performance. The present invention relates to a pneumatic tire using a tire.

  In recent years, not only are there concerns about rising oil prices and depletion of oil due to supply problems, but natural materials are also being reconsidered from the perspective of environmental issues such as resource conservation and stricter regulations on carbon dioxide emission control. There is no exception in the tire industry, and natural rubber is attracting attention as an alternative to synthetic rubber. Since natural rubber has high mechanical strength and excellent wear resistance, it is often used for large tires such as truck / bus tires. However, natural rubber has only a methyl group with a small molecular weight in the side chain, and has a problem of poor grip performance because its glass transition temperature (Tg) is as low as -60 ° C. Moreover, since it is a natural material, there existed a problem that ozone resistance, heat aging resistance, a weather resistance, etc. were also inferior.

  In order to solve these problems, natural rubber derivatives such as cyclized natural rubber, chlorinated natural rubber, and epoxidized natural rubber are used. For example, Patent Documents 1 to 4 propose a method using epoxidized natural rubber as a tire material. Here, the epoxidized natural rubber is obtained by epoxidizing an unsaturated double bond of natural rubber. Since the molecular cohesive force is increased by an epoxy group which is a polar group, the glass transition temperature (Tg) is higher than that of natural rubber. ) And high mechanical strength, wear resistance, and gas permeation resistance. In particular, in rubber compositions containing silica, it is said that the silanol groups on the silica surface interact with the epoxy groups of the epoxidized natural rubber, so that the mechanical strength is comparable to that of carbon black-filled compounds. And wear resistance.

  However, the epoxidized natural rubber has a large hysteresis loss and excellent wet grip performance, but has a drawback that even when silica is used, the rolling resistance increases (the rolling resistance characteristic decreases). In addition, due to the strong interaction between silica and epoxidized natural rubber, in the blend compounding system of epoxidized natural rubber and other diene rubbers, a phenomenon occurs in which silica is unevenly distributed on the epoxidized natural rubber side, resulting in improved processability. In addition to being inferior, there were problems of increased hardness, wear resistance, and heat aging resistance.

  Patent Document 5 describes a method of blending a specific stearic acid derivative. By using a specific stearic acid derivative as a processing aid for rubber components such as natural rubber and isoprene rubber, the rubber is softened and the dispersibility of silica and other compounding agents improves, so that the processability and wear resistance are improved. The However, epoxidized natural rubber was not used as a rubber component, and it did not have sufficient processability and wear resistance.

JP-A-6-220254 JP-A-7-90123 JP-A-7-149955 Japanese Patent Laid-Open No. 2001-233959 Japanese Patent Laid-Open No. 11-71479

  An object of the present invention is to provide a rubber composition for a tread having improved workability and wear resistance without deteriorating rolling resistance characteristics and wet grip performance, and a pneumatic tire using the same.

The present invention relates to 1 to 10 parts by weight of a metal stearate and 100 to 300 m ² / g of silica having a nitrogen adsorption specific surface area based on 100 parts by weight of a rubber component containing 5 to 100% by weight of epoxidized natural rubber. 5 to 150 parts by weight, and 0.1 to 20 parts by weight of an anionic surfactant with respect to 100 parts by weight of the silica, and the following general formula (C _n H _{2n + 1} O) ₃ —Si— _{(CH 2) m -S l -} (CH 2) m -Si- (C n H 2n + 1 O) 3
(Wherein, l represents the number of sulfur in the polysulfide part, n is an integer of 1 to 3, m is an integer of 1 to 4, and the average value of l is 2.1 to 3.5)
It is related with the rubber composition for treads containing 1-20 weight part of silane coupling agents which satisfy | fill.

  The stearic acid metal salt is preferably an alkaline earth metal salt.

  Furthermore, the rubber composition preferably contains 1 to 50 parts by weight of plant-derived oil.

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

  According to the present invention, by blending a metal stearate salt and an anionic surfactant into a rubber composition containing epoxidized natural rubber and silica, the processability is reduced without deteriorating rolling resistance characteristics and wet grip performance. In addition, a rubber composition for a tread having improved wear resistance and a pneumatic tire using the same can be provided.

  The rubber composition for a tread of the present invention comprises a rubber component comprising an epoxidized natural rubber, a metal stearate, silica, an anionic surfactant and a silane coupling agent.

  As the epoxidized natural rubber used in the present invention, commercially available epoxidized natural rubber may be used, or natural rubber may be epoxidized. The method for epoxidizing natural rubber is not particularly limited, and can be carried out using a method such as a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, or a peracid method. Examples thereof include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid.

  The epoxidation rate of the epoxidized natural rubber is preferably 5 mol% or more, and more preferably 10 mol% or more. When the epoxidation rate is less than 5 mol%, the effect obtained by modifying the epoxidized natural rubber tends to be small. The epoxidation rate is preferably 80 mol% or less, and more preferably 60 mol% or less. If the epoxidation rate exceeds 80 mol%, the polymer gels, which is not preferable.

  The content of epoxidized natural rubber in the rubber component is 5% by weight or more, preferably 10% by weight or more. A content of less than 5% by weight is not preferable because sufficient grip performance cannot be obtained. The content of the epoxidized natural rubber is 100% by weight or less, preferably 95% by weight or less, more preferably 90% by weight or less.

  Examples of rubber components other than the epoxidized natural rubber used in the present invention include natural rubber and / or diene-based synthetic rubber. Specifically, styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), halogenated butyl rubber and the like. These rubbers may be used alone or in combination of two or more.

  Examples of the metal stearate used in the present invention include magnesium stearate, 12-hydroxy magnesium stearate, calcium stearate, 12-hydroxy calcium stearate, barium stearate, 12-hydroxy barium stearate, zinc stearate, 12-hydroxy Examples include zinc stearate. Among them, it is preferable to use an alkaline earth metal salt as the stearic acid metal salt from the viewpoint of heat resistance improvement effect and compatibility with the epoxidized natural rubber, and in particular, calcium stearate, 12-hydroxycalcium stearate or barium stearate. Is preferably used.

  The content of the stearic acid metal salt is 1 part by weight or more, preferably 1.5 parts by weight or more with respect to 100 parts by weight of the rubber component. When the stearic acid metal salt is less than 1 part by weight, a sufficient compatibility effect and heat resistance improvement effect cannot be obtained. The content of the stearic acid metal salt is 10 parts by weight or less, preferably 8 parts by weight or less. Exceeding 10 parts by weight is not preferable because hardness and modulus decrease and wear resistance deteriorates.

  As the silica used in the present invention, silica produced by a wet method or a dry method is preferably used, but there is no particular limitation.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 100 m ² / g or more, and more preferably 120 m ² / g or more. When N ₂ SA of silica is less than 100 m ² / g, the reinforcing effect obtained by blending silica tends to be small. It is preferable that the silica is of N ₂ SA is less than 300 meters ² / g, more preferably not more than 280m ² / g. When the N ₂ SA of silica exceeds 300 m ² / g, the dispersibility of the silica is lowered and the heat generation of the rubber composition is increased, which is not preferable.

  The content of silica is 5 parts by weight or more, preferably 10 parts by weight or more, more preferably 15 parts by weight or more with respect to 100 parts by weight of the rubber component. If the silica content is less than 5 parts by weight, sufficient low heat build-up and wet grip performance cannot be obtained. The silica content is 150 parts by weight or less, preferably 120 parts by weight or less, more preferably 100 parts by weight or less. Exceeding 150 parts by weight is not preferable because workability and workability deteriorate.

  There is no restriction | limiting in particular as an anionic surfactant used in this invention, It can be set as the anionic surfactant conventionally used as a dispersing agent of a filler or a pigment. For example, fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, naphthalene sulfonate formalin condensates, polycarboxylic acid type polymer surfactants, etc. can give. Of these, naphthalenesulfonic acid formalin condensate, polycarboxylic acid type polymer surfactant and the like are preferably used.

  The content of the anionic surfactant is 0.1 parts by weight or more, preferably 0.5 parts by weight or more with respect to 100 parts by weight of silica. If the anionic surfactant is less than 0.1 parts by weight, a sufficient compatibility effect cannot be obtained. The content of the anionic surfactant is 20 parts by weight or less, preferably 15 parts by weight or less. Exceeding 20 parts by weight is not preferable because the hardness and modulus are lowered and the reinforcement and wear resistance are deteriorated.

As the silane coupling agent used in the present invention, a silane coupling agent satisfying the following general formula is used.
_{(C n H 2n + 1 O} ) 3 -Si- (CH 2) m -S l - (CH 2) m -Si- (C n H 2n + 1 O) 3

  In the formula, l represents the number of sulfur in the polysulfide part, n is an integer of 1 to 3, m is an integer of 1 to 4, and an average value of l is 2.1 to 3.5. If the average value of l is less than 2.1, the reactivity between the silane coupling agent and the rubber component tends to be inferior, and if it exceeds 3.5, gelation may be promoted during processing. There is.

  Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) polysulfide, bis (2-triethoxysilylethyl) polysulfide, bis (4-triethoxysilylbutyl) polysulfide, and bis (3-trimethoxysilyl). Propyl) polysulfide, bis (2-trimethoxysilylethyl) polysulfide, bis (4-trimethoxysilylbutyl) polysulfide and the like. Of these, bis (3-triethoxysilylpropyl) disulfide is preferably used because of the addition effect of the coupling agent and cost. These silane coupling agents may be used alone or in combination of two or more.

  The content of the silane coupling agent is 1 part by weight or more, preferably 2 parts by weight or more with respect to 100 parts by weight of silica. When the content of the silane coupling agent is less than 1 part by weight, sufficient effects such as improving the dispersibility of silica cannot be obtained. The content of the silane coupling agent is 20 parts by weight or less, preferably 15 parts by weight or less. Exceeding 20 parts by weight is not preferable because a sufficient coupling effect cannot be obtained in spite of costs, and the reinforcement and wear resistance are lowered.

  The rubber composition for a tread of the present invention preferably contains plant-derived oil as a rubber softener. Here, plant-derived oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, wax, rosin, pine oil, dipentene, pineapple, and softeners Examples include tall oil. Among these plant-derived oils, cottonseed oil, rapeseed oil, and soybean oil are preferred because of their influence on workability and performance. Plant-derived oils usually have the effect that the epoxidized natural rubber has a greater softening effect than petroleum-derived oils such as aroma oils used as rubber softeners.

  The amount of plant-derived oil is preferably 1 to 50 parts by weight per 100 parts by weight of the rubber component. If the amount of plant-derived oil is less than 1 part by weight, the plasticizing effect of rubber tends to be small. On the other hand, when the amount exceeds 50 parts by weight, the compatibility is lowered, and the workability and the exudation property are deteriorated.

  In addition to the rubber component, stearic acid metal salt, silica, anionic surfactant, silane coupling agent and plant-derived oil, the rubber composition for tread of the present invention includes carbon black and the like, if necessary. The compounding agents used in normal rubber industry, such as fillers, softeners, anti-aging agents, vulcanizing agents, vulcanization accelerators, and vulcanization accelerating aids, can be appropriately blended.

  The tire of the present invention is produced by an ordinary method using the tread rubber composition of the present invention. That is, if necessary, the rubber composition for a tread of the present invention blended with the above-mentioned compounding agent is extruded according to the shape of each member of the tire at an unvulcanized stage, and is subjected to a normal method on a tire molding machine. An unvulcanized tire is formed by molding with. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these.

Below, the chemical | medical agent used in the Example is demonstrated in detail.
Natural rubber: RSS # 3
Epoxidized natural rubber: ENR-50 (epoxidation rate: 50 mol%) manufactured by Kumplan Guthrie Berhad (Malaysia)
Styrene butadiene rubber: SBR1502 from JSR Corporation (Styrene unit amount: 23.5% by weight)
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 210 m ² / g)
Silane coupling agent: Si266 manufactured by Degussa (average value of l: 2.2) (bis (3-triethoxysilylpropyl) disulfide)
Aroma oil: JOMO process X140 manufactured by Japan Energy Co., Ltd.
Vegetable oil: Soybean white squeezed oil aging inhibitor manufactured by Nisshin Oilio Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylene manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) Diamine)
Calcium stearate: GF200 manufactured by NOF Corporation
Barium stearate: Barium stearate anionic surfactant manufactured by Sakai Chemical Industry Co., Ltd.-1: Demol EP (special polycarboxylic acid type polymer surfactant) manufactured by Kao Corporation
Anionic surfactant-2: Demole MS (sodium salt of special aromatic sulfonic acid formalin condensate) manufactured by Kao Corporation
Stearic acid: Zinc stearate oxide manufactured by Nippon Oil & Fats Co., Ltd .: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. TBBS: Ouchi Shinsei Chemical Industry Noxeller NS (Nt-butyl-2-benzothiazylsulfenamide) manufactured by
Vulcanization accelerator DPG: Noxeller D (diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-4 and Comparative Examples 1-4
According to the blending contents shown in Table 1 below, they were kneaded and blended to obtain various test rubber compositions. These blends were press vulcanized at 160 ° C. for 20 minutes to obtain vulcanizates, which were subjected to the following characteristic tests. The test results for each characteristic are shown in Table 1.

(Processability)
It was measured at 130 ° C. according to the Mooney viscosity measurement method defined in JIS K6300. The Mooney viscosity (ML1 + 4) of Comparative Example 1 was set to 100, and each index was expressed by the following calculation formula. The larger the index, the lower the Mooney viscosity and the better the processability.
(Mooney viscosity index) = (ML1 + 4 of Comparative Example 1) / (ML1 + 4 of each formulation) × 100

(Abrasion test)
Using a Lambourn Abrasion Tester, measure the Lambourn wear amount under the conditions of a temperature of 20 ° C., a slip rate of 20%, and a test time of 5 minutes, and calculate the volume loss of each formulation. Expressed as an index using the formula. The higher the index, the better the wear resistance.
(Abrasion index) = (loss amount of Comparative Example 1) / (loss amount of each blend) × 100

(Rolling resistance index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each formulation was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The index was expressed by the following formula. The larger the index, the better the rolling resistance characteristics.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Wet skid test)
The measurement was performed according to the method of ASTM E303-83 using a portable skid tester manufactured by Stanley, and the measured value of Comparative Example 1 was set to 100 and indicated by the following formula. The larger the index, the better the wet grip performance.
(Wet skid index) = (Numerical value of each formulation) / (Numerical value of Comparative Example 1) × 100

  According to the results of Table 1, in a formulation containing epoxidized natural rubber and silica, by blending a metal stearate and an anionic surfactant, the workability, without reducing rolling resistance characteristics and wet grip performance, It can be seen that the wear resistance is improved and the balance of each property is improved.

Claims (4)

For 100 parts by weight of a rubber component containing 5 to 100% by weight of epoxidized natural rubber,
1 to 10 parts by weight of stearic acid metal salt and 5 to 150 parts by weight of silica having a nitrogen adsorption specific surface area of 100 to 300 m ² / g,
Furthermore, with respect to 100 parts by weight of the silica,
0.1 to 20 parts by weight of an anionic surfactant, and the following general formula _{(C n H 2n + 1 O} ) 3 -Si- (CH 2) m -S l - (CH 2) m -Si- (C _n H _{2n + 1} O) ₃
(Wherein, l represents the number of sulfur in the polysulfide part, n is an integer of 1 to 3, m is an integer of 1 to 4, and the average value of l is 2.1 to 3.5)
A tread rubber composition containing 1-20 parts by weight of a silane coupling agent satisfying,
The anionic surfactant is an alkyl sulfate ester salt, an alkylbenzene sulfonate, an alkyl naphthalene sulfonate, an alkyl sulfosuccinate, an alkyl diphenyl ether disulfonate, a naphthalene sulfonate formalin condensate, or a polycarboxylic acid type polymer surface activity. A rubber composition for a tread which is an agent . The rubber composition for a tread according to claim 1, wherein the metal stearate is an alkaline earth metal salt. Furthermore, the rubber composition for treads of Claim 1 or 2 which contains 1-50 weight part of plant-derived oils. A pneumatic tire using the tread rubber composition according to claim 1, 2 or 3.