JP4634181B2 - Rubber composition for tire tread and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread in which silica is blended, and a pneumatic tire using the rubber composition.

  Conventionally, a pneumatic tire, particularly a pneumatic tire called a so-called high-performance tire, has been required to have a high balance of grip performance, steering stability and heat generation characteristics.

  In general, in order to improve the grip performance on wet road surfaces and dry road surfaces, a method of increasing the blending amount of filler and oil is used, but heat generation and wear resistance are lowered. Moreover, since the viscosity in an unvulcanized state is increased and the dispersibility of the filler is deteriorated, workability such as an increase in the number of times of mixing is lowered in order to obtain sufficient performance.

  Silica is generally used to improve grip performance on wet road surfaces. However, when silica is used, workability is greatly inferior, such as an increase in the number of mixing times and a decrease in extrusion speed. In this case, it is possible to improve the workability by using a processing aid, but the rigidity decreases with an increase in the amount of use, leading to deterioration in steering stability.

  By the way, the following patent document 1 proposes a novel protected mercaptosilane as a silane coupling agent used together with silica in order to suppress unacceptable increase in viscosity during processing and improve early curing (scorch). .

Patent Document 2 below discloses that in a rubber composition for tires, resorcin, a phenol resin, hexamethylenetetramine, and a melamine derivative are blended for improving adhesion, etc. The present invention relates to a rubber composition used for peripheral rubber of a reinforcing member such as a tire cord, and there is no suggestion of blending it into a tire tread.
Special table 2001-505225 gazette JP 2002-327158 A

  When protected mercaptosilane as disclosed in Patent Document 1 is used as a silane coupling agent, silica incorporation into rubber during mixing and silica dispersibility can be maintained while maintaining grip performance on wet and dry road surfaces. Can be improved. Therefore, it is possible to improve workability and heat generation characteristics during rubber processing. However, in this case, since the rubber hardness after vulcanization and the dynamic elastic modulus E ′ are reduced due to the improvement of the dispersibility of silica, there is a concern that the steering stability on the dry road surface is deteriorated.

  The present invention has been made in view of the above points, and by eliminating the above problems when a protected mercaptosilane is used, workability and heat generation characteristics during rubber processing are maintained while maintaining grip performance. Further, it is an object to improve steering stability on a dry road surface.

  The present inventor can solve the above-mentioned problems by combining a specific protected mercaptosilane with a phenol-based component such as a novolac-type phenol resin or resorcin to a styrene-butadiene rubber having a high glass transition point. As a result, the present invention has been completed.

  That is, the tire tread rubber composition according to the present invention is a copolymer rubber obtained by copolymerization of 1,3-butadiene and styrene using an organolithium compound as an initiator, and has a glass transition point of − 100% by weight of a rubber component comprising a copolymer rubber alone having a styrene content of 30% by weight or more, or a blend of 50% by weight or more of the copolymer rubber and 50% by weight or less of another diene rubber. 20 parts by weight of silica and 0 to 100 parts by weight of carbon black are blended so that the total amount of both is 70 to 150 parts by weight, and the silane coupling represented by the following general formula (1) 2 to 25 parts by weight of the agent with respect to 100 parts by weight of silica, and at least one selected from the group consisting of novolac phenolic resin, resorcin and resorcin condensate The phenolic component is made by blending 0.5 to 10 parts by weight.

_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 (1)
In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9.

  In the tire tread rubber composition of the present invention, 5 to 30 parts by weight of at least one of hexamethylenetetramine and melamine derivatives may be blended with respect to 100 parts by weight of the phenol component.

  The pneumatic tire according to the present invention has a tread composed of these rubber compositions.

  According to the present invention, it is possible to improve workability and heat generation characteristics during rubber processing while maintaining grip performance, and further improve steering stability on a dry road surface.

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

  In the rubber composition for a tire tread of the present invention, the copolymer rubber used as a rubber component is a styrene-butadiene rubber obtained by copolymerization of 1,3-butadiene and styrene using an organolithium compound as an initiator. SBR). Such a copolymer rubber can be produced by a known solution polymerization method using an inert organic solvent such as pentane, hexane, heptane, benzene, toluene, diethyl ether and the like. Examples include alkyl lithium such as lithium, alkylene dilithium such as 1,4-dilithium butane, and phenyl lithium. The copolymer rubber may be one in which the end of the copolymer chain is treated with a tin-based, silicon-based or alkoxysilane-based coupling agent, and the terminal or main chain is a silanol group of silica. It may be modified with a functional group having interaction or chemical reactivity (for example, a hydroxyl group or an amino group).

  As the copolymer rubber, one having a glass transition point (Tg) of −40 ° C. or higher is used. By using such a copolymer rubber having a high glass transition point, grip performance on a wet road surface and a dry road surface can be improved. Although the upper limit of a glass transition point is not specifically limited, Usually, it is -10 degrees C or less. The glass transition point is a value measured by ASTM D3418.

  As the copolymer rubber, one having a styrene content of 30% by weight or more is used. When the styrene content is less than 30% by weight, it is difficult to obtain sufficient grip performance on both wet and dry road surfaces, and the influence of hardness reduction due to improved dispersibility of silica becomes large. Although the upper limit of styrene content is not specifically limited, It is preferable that it is 50 weight% or less. The styrene content is a value measured by infrared spectroscopy.

  The copolymer rubber is more preferably a high molecular weight copolymer rubber having a weight average molecular weight of 800,000 or more in order to increase rigidity and further improve grip performance on a dry road surface.

  The rubber component in the rubber composition of the present invention is composed of the above copolymer rubber alone or a blend rubber of 50% by weight or more of the copolymer rubber and 50% by weight or less of another diene rubber. When the ratio of the copolymer rubber is less than 50% by weight, the above-described effects of the present invention cannot be sufficiently exhibited. Here, the other diene rubber is not particularly limited, and other than natural rubber, isoprene rubber, butadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer. Examples include diene-based synthetic rubbers such as coalesced rubber and nitrile rubber, which may be used alone or in combination of two or more. Of these, natural rubber and butadiene rubber are more preferable.

  Silica used in the rubber composition of the present invention is not particularly limited, and examples thereof include wet silica, dry silica, colloidal silica, and precipitated silica. It is particularly preferable to use wet silica containing hydrous silicic acid as a main component. . Silica is blended in an amount of 20 to 100 parts by weight with respect to 100 parts by weight of the rubber component, and the more preferred blending amount is 40 parts by weight at the lower limit and 90 parts by weight at the upper limit. When the blending amount of silica is less than 20 parts by weight, a sufficient improvement in grip performance cannot be obtained.

  In the rubber composition of the present invention, the filler may be the above silica alone, or carbon black may be blended together with the silica. Carbon black is blended in an amount of 0 to 100 parts by weight with respect to 100 parts by weight of the rubber component. Silica and carbon black are blended in a total amount of 70 to 150 parts by weight. In the rubber composition of the present invention, other fillers such as titanium oxide, aluminum silicate, clay, and talc can be blended in addition to the silica and carbon black as fillers.

  The silane coupling agent used in the rubber composition of the present invention is a protected mercaptosilane represented by the general formula (1). Such protected mercaptosilane can be produced according to the method described in JP-T-2001-505225. The protected mercaptosilane is blended in an amount of 2 to 25 parts by weight with respect to 100 parts by weight of silica in order to sufficiently exhibit the effects of the present invention described above. The silane coupling agent may be preliminarily treated with silica, and the treated silica may be added and mixed with the rubber component.

  The rubber composition of the present invention is blended with a phenolic component comprising a novolac type phenol resin, resorcin, or resorcin condensate. Examples of the novolak type, that is, the thermoplastic phenol resin include an unmodified phenol resin (straight phenol resin) obtained by condensing phenol and formaldehyde, an alkyl-substituted phenol resin, and an oil-modified phenol resin. Examples of the alkyl-substituted phenol resin include a cresol-formaldehyde resin using cresol instead of phenol, and an alkyl phenol resin using another alkyl phenol such as xylenol or octylphenol instead of phenol. Examples of the oil-modified phenol resin include novolak-type modified phenol resins modified with various oils such as cashew nut oil, tall oil, and rosin oil. Examples of the resorcin condensate include resorcin / formaldehyde resin initial condensate and resorcin / formaldehyde co-condensed formaldehyde resin.

  These phenolic components are blended in an amount of 0.5 to 10 parts by weight with respect to 100 parts by weight of the rubber component. When the blending amount of the phenolic component is less than 0.5 parts by weight, the effects of the present invention described above cannot be achieved, and in particular, the decrease in hardness due to blending of the protected mercaptosilane can be eliminated. It is not possible, and the handling stability on the dry road surface is inferior. On the contrary, when the compounding amount of the phenol component exceeds 10 parts by weight, the grip performance on the wet road surface is greatly deteriorated. In general, methods for increasing the hardness of a rubber composition include methods such as increasing the amount of filler, decreasing the amount of oil, and increasing the amount of a vulcanizing agent such as sulfur. However, when the amount of filler is increased or the amount of oil is decreased, workability is also deteriorated. On the other hand, in the present invention using the above phenolic component, the hardness can be increased while maintaining the modulus, and the processability is also excellent.

  In the rubber composition of the present invention, it is preferable to add hexamethylenetetramine or a melamine derivative as a methylene donor together with these phenolic components to increase the hardness. Examples of the melamine derivative include hexamethoxymethyl melamine obtained by reacting melamine and formaldehyde, hexamethylol melamine pentamethyl ether, and polyvalent methylol melamine. The blending amount of these methylene donors is preferably 30 parts by weight or less, more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the phenol component. If this blending amount exceeds 30 parts by weight, it becomes excessive and has no effect.

  In addition to the components described above, the rubber composition of the present invention is generally used in rubber compositions for tire treads such as anti-aging agents, zinc white, stearic acid, softeners, vulcanizing agents, and vulcanization accelerators. Various additives can be blended. In addition, mixing of a rubber composition can be performed using a well-known mixer, In that case, the said rubber component, silica (it may contain carbon black depending on the case), and a silane coupling agent are 150-180 degreeC. Mixing is preferable in order to exhibit the effect of the present invention.

  By using a styrene-butadiene rubber having a high glass transition point as a rubber component and using the protected mercaptosilane as a silane coupling agent together with the phenol component, The silica dispersibility can be improved by improving the incorporation of silica into the rubber component. Therefore, it is excellent in workability of rubber processing. In addition, this unique combination does not impair grip performance on wet or dry road surfaces, and also has excellent heat generation characteristics, i.e., less heat generation, resulting in excellent fuel efficiency and high performance such as racing tires. When used in a tire, thermal degradation can be suppressed and the durability can be improved. Furthermore, it is possible to improve steering stability by suppressing a decrease in hardness due to an improvement in dispersibility of silica.

  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 was prepared according to the formulation shown in Table 1 below. At that time, the mixing temperature of the rubber composition was 160 ° C. The detail of each component of Table 1 is as follows.

SBR1: Solution polymerization SBR “TUFDENE E50” manufactured by Asahi Kasei (styrene content = 36% by weight, glass transition point Tg = −30 ° C., weight average molecular weight Mw = about 900,000)
SBR2: Solution polymerization SBR “SBR1502” manufactured by JSR (styrene content = 24 wt%, glass transition point Tg = −66 ° C., weight average molecular weight Mw = about 600,000).

Silica: “Ultrasil 7000GR” manufactured by Degussa (BET specific surface area = 170 m ² / g, CTAB specific surface area = 160 m ² / g)
Carbon black: ISAF, “Dia Black N234” manufactured by Mitsubishi Chemical Corporation.

General-purpose coupling agent: bis- (3-triethoxysilylpropyl) disulfide, “Si-75” manufactured by Degussa.

Protected mercaptosilane: coupling agent represented by the above formula (1) (n = 2, m = 3, k = 7), “NXT” manufactured by GE Silicones.

Oil modified phenolic resin: Novolak type oil modified phenolic resin “Sumilite Resin PR-133491” manufactured by Sumitomo Bakelite
Resorcin / alkylphenol resin: Resorcin / alkylphenol / formaldehyde copolymer “SUMIKANOL 620” manufactured by Sumitomo Chemical Co., Ltd.
・ Resorcin: “Resorcin” manufactured by Sumitomo Chemical
Melamine derivative: “Ciretz 964RPC” manufactured by Mitsui Cytec Co., Ltd. (hexamethoxymethylmelamine 65% + silica 35%)
Hexamethylenetetramine: “Noxeller H” manufactured by Ouchi Shinsei Chemical Industry.

  Moreover, in each rubber composition, 40 parts by weight of an aroma-based process oil (“JOMO Process X-140” manufactured by Japan Energy Co., Ltd.), 2 parts by weight of wax (“Ozoace 0355” manufactured by Nippon Seiki), 2 parts by weight of anti-aging agent ("Santflex 6PPD" manufactured by Flexis), 2 parts by weight of stearic acid ("Lunac S20" manufactured by Kao Soap), 2 parts by weight of zinc flower ("Zinc Flower No. 1" manufactured by Mitsui Kinzoku Co., Ltd.) Parts, 1.8 parts by weight of vulcanization accelerator CZ (“Noxeller CZ-G” manufactured by Ouchi Shinsei Chemical Industry) and 2.0 parts by weight of sulfur (“Powder Sulfur 150 Mesh” manufactured by Hosoi Chemical Co., Ltd.) were blended. .

  Each rubber composition obtained was evaluated for processability and heat generation characteristics, and a pneumatic tire was produced using each rubber composition. The tire was manufactured by applying each rubber composition to a cap tread of a radial tire for test of 185 / 70R14 having a tread having a cap / base structure, and vulcanizing and molding the rubber composition according to a conventional method. And about each obtained tire, the grip performance (wet grip performance) on the wet road surface and the steering stability on the dry road surface were evaluated. Each evaluation method is as follows.

Processability: Processability was evaluated by Mooney viscosity measured with a Mooney viscometer manufactured by Shimadzu Corporation. The test method was based on JIS K6300, and the value of the comparative example 1 was set to 100 and displayed as an inverse index. Larger numbers indicate lower viscosity, that is, better workability.

Exothermic characteristics: The exothermic characteristics were evaluated by the temperature rise measured by a constant stress flexometer manufactured by Ueshima Seisakusho. The test method was performed in accordance with JIS K6265, and the comparative example 1 was set to 100 and the inverse index was displayed. Larger numbers indicate better heat generation characteristics.

-Wet grip performance: Four pneumatic tires were mounted on a passenger car, and the vehicle was run on a water surface with a water depth of 2 to 3 mm. The friction coefficient was measured at 100 km / h to evaluate the wet grip performance. The value of Comparative Example 1 is displayed as an index, which is 100, and the larger the value, the better the grip performance.

-Steering stability: The above four pneumatic tires were mounted on a passenger car, and the driver in charge of sensory tests drove the test course at high speed while paying attention to steering response and running stability, and evaluated steering stability performance. The result is “+2” for excellent, “+1” for slightly superior, “± 0” for equivalent, and “−1” for slightly inferior compared with Comparative Example 1 of the control. "Inferior ones were set to" -2 ".

  As shown in Table 1, in Comparative Example 2 in which protected mercaptosilane was simply combined with Comparative Example 1 as a control, although the processability and heat generation characteristics were excellent, the steering stability was deteriorated. Further, in Comparative Examples 3 and 4 in which a phenolic component was simply blended with respect to Comparative Example 1, the steering stability on the dry road surface was excellent, but the wet grip property was deteriorated. In Comparative Example 5 in which SBR having a low glass transition point, protected mercaptosilane, and a phenolic component were combined, the workability and heat generation characteristics were improved, but the wet grip property and the handling stability on a dry road surface were deteriorated. Was. On the other hand, in Examples 1 to 4 used in combination with a specific SBR having a high glass transition point, a protected mercaptosilane, and a phenolic component, compared to Comparative Example 1, the rubber workability is excellent, It was excellent in heat generation characteristics and handling stability on dry roads without impairing wet grip.

  The rubber composition of the present invention is used as a rubber for forming a tread of a pneumatic tire, and particularly has a good balance between heat generation characteristics, grip performance, and handling stability as described above, so that it is a high performance tire such as a tire for racing. It is suitable as a tread.

Claims (3)

A copolymer rubber obtained by copolymerization of 1,3-butadiene and styrene using an organolithium compound as an initiator, having a glass transition point of -40 ° C or higher and a styrene content of 30% by weight or higher. With respect to 100 parts by weight of a rubber component consisting of a copolymer rubber alone or a blend of 50% by weight or more of the copolymer rubber and 50% by weight or less of another diene rubber,
20 to 100 parts by weight of silica and 0 to 100 parts by weight of carbon black are blended so that the total amount of both is 70 to 150 parts by weight,
2 to 25 parts by weight of a silane coupling agent represented by the following general formula (1) is blended with respect to 100 parts by weight of silica,
Furthermore, the rubber composition for tire treads which mix | blends 0.5-10 weight part of at least 1 sort (s) phenolic component selected from the group which consists of a novolak-type phenol resin, a resorcinol, and a resorcinol condensate.
_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 (1)
(In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9)   The rubber composition for a tire tread according to claim 1, wherein at least one of hexamethylenetetramine and a melamine derivative is blended in an amount of 5 to 30 parts by weight with respect to 100 parts by weight of the phenolic component.   A pneumatic tire having a tread made of the rubber composition according to claim 1.