JP2012031300A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire tread, which achieves improved driving stability, low rolling resistance, and wear resistance.SOLUTION: The rubber composition is obtained by blending 5-70 pts.wt of carbon black and 5-70 pts.wt of silica with 100 pts.wt of diene-based rubber containing 60-95 wt.% of styrene-butadiene rubber and 5-40 wt.% of butadiene rubber, wherein the total amount of the fillers containing the carbon black and silica is 50-80 pts.wt. The rubber composition is characterized in that the butadiene rubber has: a weight average molecular weight of 700,000 to 900,000; a molecular weight distribution (Mw/Mn) of 1.5 to 3.0, the molecular weight distribution (Mw/Mn) being obtained from the weight average molecular weight (Mw) and the number-average molecular weight (Mn); and a viscosity of a toluene solution at 25°C of 300 to 1,000 mPa s.

Description

  The present invention relates to a rubber composition for a tire tread in which handling stability, low rolling resistance, and wear resistance are improved.

  In general, pneumatic tires for passenger cars are required to have excellent low rolling resistance and wear resistance in addition to excellent steering stability. In order to reduce the rolling resistance of a pneumatic tire, it is known to reduce the heat build-up by adding silica to the rubber composition constituting the tread portion. However, when silica is blended, there is a problem that the effect of improving the wear resistance of the rubber composition cannot be sufficiently obtained as compared with the case where other fillers such as carbon black are blended.

  Further, when butadiene rubber is blended in the rubber composition in order to increase the wear resistance and the blending amount is increased, the hardness is lowered and the steering stability is lowered when used in a tire tread. In addition, by adopting carbon black with a small particle size as the rubber composition, it is possible to increase the reinforcement and improve the wear resistance. However, the heat generation of the rubber composition increases and the rolling resistance of the tire increases. Becomes larger. Therefore, it has been difficult to achieve both low rolling resistance (low heat generation), wear resistance, and steering stability.

  Here, Patent Document 1 proposes a rubber composition containing butadiene rubber having high linearity in order to improve both rolling resistance and wear resistance. However, this rubber composition does not always have a sufficient balance between rolling resistance and wear resistance, and there is still room for improvement.

JP 2007-106799 A

  An object of the present invention is to provide a rubber composition for a tire tread in which handling stability, low rolling resistance, and wear resistance are improved.

  The rubber composition for a tire tread of the present invention that achieves the above-mentioned object comprises carbon black in an amount of 5 to 70 wt% with respect to 100 parts by weight of a diene rubber containing 60 to 95 wt% of styrene butadiene rubber and 5 to 40 wt% of butadiene rubber. 5 to 70 parts by weight of silica, and the total of the filler containing carbon black and silica is 50 to 80 parts by weight, and the weight average molecular weight of the butadiene rubber is 700,000 to 900,000, and the weight average The molecular weight distribution (Mw / Mn) obtained from the molecular weight (Mw) and the number average molecular weight (Mn) is 1.5 to 3.0, and the viscosity of the toluene solution at 25 ° C. is 300 to 1000 mPa · s.

  The rubber composition for a tire tread of the present invention has a weight average molecular weight of 700,000 to 900,000, and a molecular weight distribution (Mw / Mn) determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn) of 1.5 to By using a butadiene rubber having a toluene solution viscosity at 3.0 and 25 ° C. of 300 to 1000 mPa · s, the hardness and wear resistance of the rubber composition are increased, and tan δ is decreased to reduce rolling resistance. I can do it. Also, by adding 5 to 70 parts by weight of carbon black and silica with respect to 100 parts by weight of the diene rubber, respectively, the total amount of fillers including carbon black and silica is 50 to 80 parts by weight. Since it improves further and rolling resistance is reduced more, both can be made compatible at a higher level.

  The diene rubber is preferably composed of 60 to 95% by weight of styrene butadiene rubber and 5 to 40% by weight of butadiene rubber.

  In the rubber composition for a tire tread of the present invention, the rubber component is a diene rubber containing styrene butadiene rubber and butadiene rubber. The butadiene rubber used in the present invention is characterized by a high molecular weight, a narrow molecular weight distribution, and few molecular chain branches. The molecular weight of the butadiene rubber is 700,000 to 900,000, preferably 750,000 to 850,000, and more preferably 750,000 to 800,000 in terms of weight average molecular weight (Mw). When the weight average molecular weight of the butadiene rubber is less than 700,000, the wear resistance and rubber strength of the rubber composition are insufficient. On the other hand, when the weight average molecular weight of the butadiene rubber exceeds 900,000, the mixing processability is deteriorated, the dispersion of carbon black and silica is deteriorated, and the wear resistance is lowered.

  The molecular weight distribution (Mw / Mn) of the butadiene rubber determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn) is 1.5 to 3.0, preferably 2.0 to 2.5. When the molecular weight distribution (Mw / Mn) of the butadiene rubber is less than 1.5, the mixing processability is deteriorated, the dispersion of carbon black and silica is deteriorated, and it is difficult to obtain industrially. On the other hand, when the molecular weight distribution (Mw / Mn) of butadiene rubber exceeds 3.0, hysteresis loss increases and rolling resistance increases.

  In the present invention, the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of butadiene rubber are measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  The viscosity of the butadiene rubber at 25 ° C. in toluene is 300 to 1000 mPa · s, preferably 500 to 800 mPa · s. The toluene solution viscosity is an index indicating the linearity (amount of branching) of the molecular chain of butadiene rubber. The higher the toluene solution viscosity, the less the molecular chain branching and the higher the proportion of linear chain, improving the breaking strength and wear resistance. can do. When the toluene solution viscosity of the butadiene rubber is less than 300 mPa · s, the wear resistance and fracture properties of the rubber composition are insufficient. Further, when the toluene solution viscosity of the butadiene rubber exceeds 1000 mPa · s, the mixing processability is deteriorated, whereby the wear resistance and the fracture property are deteriorated. In the present invention, the viscosity of a toluene solution of butadiene rubber at 25 ° C. was measured at 25 ° C. using a Canon Fenske type kinematic viscometer.

  The blending amount of butadiene rubber is 5 to 40% by weight, preferably 10 to 35% by weight, in 100% by weight of diene rubber. If the blending amount of butadiene rubber is less than 5% by weight, the effect of improving the wear resistance and rolling resistance is insufficient. Moreover, when the compounding quantity of butadiene rubber exceeds 40 weight%, the rigidity of rubber will fall and rolling resistance will rise.

  As the styrene butadiene rubber used in the present invention, those usually used in rubber compositions for tires can be used. The blending amount of the styrene butadiene rubber is 60 to 95% by weight, preferably 65 to 90% by weight, based on 100% by weight of the diene rubber. When the blending amount of the styrene butadiene rubber is less than 60% by weight, the hardness is lowered and steering stability is deteriorated. Moreover, when the compounding quantity of styrene butadiene rubber exceeds 95 weight%, abrasion resistance and rolling resistance will deteriorate.

  In the present invention, a diene rubber other than butadiene rubber and styrene butadiene rubber can be contained as long as the above-described composition is satisfied. Examples of other diene rubbers include natural rubber, isoprene rubber, acrylonitrile butadiene rubber, butyl rubber, and butadiene rubber excluding butadiene rubber having the above-described characteristics. These other diene rubbers can contain any one type. Two or more kinds of other diene rubbers can be contained in combination.

  The diene rubber is preferably composed of 60 to 95% by weight of styrene butadiene rubber and 5 to 40% by weight of butadiene rubber. By adopting such a rubber component composition, both wear resistance and rolling resistance can be achieved.

  The rubber composition for tire treads of the present invention increases the strength and hardness of the rubber composition for tire treads and improves the wear resistance and steering stability by blending carbon black. The compounding quantity of carbon black is 5-70 weight part with respect to 100 weight part of diene rubbers, Preferably it is 10-40 weight part. If the blending amount of carbon black is less than 5 parts by weight, the effect of improving the wear resistance and steering stability cannot be obtained sufficiently. Moreover, when the compounding quantity of carbon black exceeds 70 weight part, the viscosity of a rubber composition will become high and a moldability will deteriorate.

  The rubber composition for a tire tread of the present invention reduces rolling resistance by blending silica. The compounding quantity of a silica is 5-70 weight part with respect to 100 weight part of diene rubbers, Preferably it is 25-50 weight part. If the amount of silica is less than 5 parts by weight, the effect of reducing rolling resistance cannot be obtained sufficiently. On the other hand, when the amount of silica exceeds 70 parts by weight, mixing processability is deteriorated and silica dispersion is deteriorated, so that fracture characteristics and wear resistance are deteriorated. The silica may be any silica that is usually blended in a tire rubber composition. For example, wet method silica, dry method silica, or surface-treated silica can be used.

  In the present invention, a silica reinforcing effect can be obtained by blending a silane coupling agent with silica. The amount of the silane coupling agent is 1 to 12% by weight, preferably 3 to 10% by weight, based on the amount of silica. When the blending amount of the silane coupling agent is less than 1% by weight, a sufficient silica reinforcing effect cannot be obtained. On the other hand, if the silane coupling agent exceeds 12% by weight, rubber scorch is likely to occur during rubber kneading.

  Although it does not restrict | limit especially as a kind of silane coupling agent, A sulfur containing silane coupling agent is preferable. Examples of the sulfur-containing silane coupling agent include bis- (3-triethoxysilylpropyl) tetrasulfide, bis- (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, and γ-mercapto. Examples thereof include propyltriethoxysilane and 3-octanoylthiopropyltriethoxysilane.

  In the rubber composition for a tire tread of the present invention, the filler may be composed of carbon black and silica. In addition to carbon black and silica, other fillers may be blended. As other fillers, for example, clay, calcium carbonate, talc, mica, aluminum hydroxide, magnesium carbonate and the like can be blended as necessary.

  In the present invention, the total amount of fillers containing carbon black and silica is 50 to 80 parts by weight, preferably 55 to 75 parts by weight with respect to 100 parts by weight of the diene rubber. When the total amount of the filler is less than 50 parts by weight, the wear resistance is lowered, the hardness is lowered, and the steering stability is lowered. When the total amount of fillers exceeds 80 parts by weight, rolling resistance increases.

  The tire tread rubber composition includes various additives generally used in tire rubber compositions such as a vulcanization or crosslinking agent, a vulcanization accelerator, a processing aid, an anti-aging agent, an oil, and a plasticizer. These additives can be compounded and kneaded by a general method to obtain a rubber composition for a tire tread, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for a tire tread can be produced by mixing the above-described components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a tire tread of the present invention is suitable for constituting a tread portion of a pneumatic tire, particularly a passenger vehicle tire. A pneumatic tire having a tread portion made of this rubber composition can achieve both high rolling resistance and high wear resistance and further improve steering stability.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  Table 1 shows the characteristics of the butadiene rubber used in Examples and Comparative Examples. The weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and toluene solution viscosity at 25 ° C. were measured by the methods described above.

  12 types of rubber compositions for tire treads (Examples 1 to 5 and Comparative Examples 1 to 7) each having the composition shown in Tables 2 and 3 were weighed for the composition components except for the vulcanization accelerator and sulfur, respectively. The mixture was kneaded for 5 minutes with a 5 L closed Banbury mixer, and the master batch was discharged at a temperature of 150 ° C. and cooled at room temperature. Thereafter, this master batch was added with a roll with a vulcanization accelerator and sulfur and mixed for 2 minutes to prepare a rubber composition for a tire tread.

  Using the obtained 12 types of rubber compositions for tire treads, a vulcanized rubber test piece was prepared by press vulcanization at 160 ° C. for 20 minutes in a predetermined mold, and the hardness, tan δ ( 60 ° C.) and wear resistance.

Hardness According to JIS K6253, the hardness of the obtained vulcanized rubber test piece was measured with a durometer type A at a temperature of 20 ° C. The obtained results are shown in the column of “Hardness” in Tables 2 and 3, using Comparative Example 1 as an index of 100. The larger this index is, the higher the hardness is, and the better the steering stability when a pneumatic tire is made.

tan δ (60 ° C)
The dynamic viscoelasticity of the obtained vulcanized rubber test piece was measured at an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, and tan δ at a temperature of 60 ° C. was measured. Asked. The obtained results are shown in the column of “tan δ (60 ° C.)” in Tables 2 and 3, using the index of Comparative Example 1 as 100. The smaller this index, the smaller the tan δ (60 ° C.), which means that the rolling resistance is excellent when a pneumatic tire is made.

Abrasion resistance The obtained vulcanized rubber test piece was compliant with JIS K6264 using a lambone wear tester (manufactured by Iwamoto Seisakusho Co., Ltd.) at a temperature of 20 ° C., a test piece surface rotation speed of 80 m / min, a load of 40 N, The amount of wear was measured under the conditions of a slip rate of 30% and a time of 10 minutes. The obtained results are shown in the column of “Abrasion resistance” in Tables 2 and 3, with the reciprocal of the value of Comparative Example 1 as an index of 100. Higher index means better wear resistance.

The types of raw materials used in Tables 2 and 3 are shown below.
SBR: styrene butadiene rubber, Nipol 1502 manufactured by Nippon Zeon
NR: natural rubber, SIR20
BR-1 to BR-5: butadiene rubber CB shown in Table 1, CB: carbon black, Nitelon # 200 manufactured by Nippon Nihon Carbon Co., Ltd.
Silica: ULTRASIL 7000GR manufactured by EVONIK DEGUSSA
Coupling agent: Silane coupling agent, Si69 made by EVONIK DEGUSSA
Zinc Hana: Zinc Oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. Stearic Acid: Stearic Acid 50S manufactured by Chiba Fatty Acid Co.
Anti-aging agent: SANTOFLEX 6PPD manufactured by FLEXSYS
Vulcanization accelerator-1: PERKACIT DPG manufactured by FLEXSYS
Vulcanization accelerator-2: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical
Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd.

  As is clear from the results in Table 3, the rubber compositions for tire treads of Examples 1 to 5 both improved tan δ (rolling resistance) and wear resistance at 60 ° C. and hardness (steering) compared to Comparative Example 1. (Stability) can be increased.

  On the other hand, as is clear from the results in Table 2, the rubber composition of Comparative Example 2 has a butadiene rubber having a weight average molecular weight (Mw) of less than 700,000 and a toluene solution viscosity at 25 ° C. of less than 300. Abrasion cannot be improved sufficiently. In the rubber composition of Comparative Example 3, the molecular weight distribution (Mw / Mn) of the butadiene rubber exceeds 3.0, and thus tan δ (rolling resistance) and hardness (steering stability) at 60 ° C. are not sufficiently improved. In the rubber composition of Comparative Example 4, since the total amount of carbon black and silica is less than 50, the wear resistance is deteriorated and the hardness (steering stability) is lowered. In the rubber composition of Comparative Example 5, since the total amount of carbon black and silica exceeds 80 parts by weight, tan δ (rolling resistance) at 60 ° C. is deteriorated.

  Further, as is clear from the results in Table 3, the rubber composition of Comparative Example 6 is deteriorated in hardness (steering stability) because the styrene-butadiene rubber is less than 60% by weight and the butadiene rubber is more than 40% by weight. . Since the rubber composition of Comparative Example 7 was blended with natural rubber instead of styrene butadiene rubber, the hardness (steering stability) deteriorated.

Claims (3)

  5 to 70 parts by weight of carbon black and 5 to 70 parts by weight of silica are blended with 100 parts by weight of diene rubber containing 60 to 95% by weight of styrene butadiene rubber and 5 to 40% by weight of butadiene rubber. And a filler containing silica is 50 to 80 parts by weight, the weight average molecular weight of the butadiene rubber is 700,000 to 900,000, and the molecular weight distribution obtained from the weight average molecular weight (Mw) and the number average molecular weight (Mn) (Mw / Mn) 1.5-3.0, 25 degreeC toluene solution viscosity is 300-1000 mPa * s, The rubber composition for tire tread characterized by the above-mentioned.   The rubber composition for a tire tread according to claim 1, wherein the diene rubber is composed of 60 to 95% by weight of styrene butadiene rubber and 5 to 40% by weight of butadiene rubber.   A pneumatic tire using the rubber composition for a tire tread according to claim 1.