JP2012031299A - Rubber composition for tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire, suppressed in heat generation property and improved in bend fatigue resistance.SOLUTION: The rubber composition for the tire is characterized in that: 30 to 60 wt.pts. carbon black is compounded based on 100 wt.pts. dine-based rubber which contains 30 to 60 wt.% natural rubber and 40 to 70 wt.% butadiene rubber; the weight average molar weight of the butadiene rubber is 700,000 to 900,000; a molar weight distribution (Mw/Mn) acquired from the weight average molar weight (Mw) and a number average molar weight (Mn) is 1.5 to 3.0; toluene solution viscosity at a temperature of 25°C is 300 to 1,000mPa s; and a CTAB adsorption specific surface area of the carbon black is 30 to 100 m/g.

Description

  The present invention relates to a rubber composition for tires that reduces heat generation and improves resistance to bending fatigue.

  In recent years, pneumatic tires are strongly required to have excellent fuel efficiency. In order to increase the fuel efficiency of the pneumatic tire, it is necessary to reduce the rolling resistance. In order to reduce the rolling resistance of the tire, it is known that the members constituting the tire should be lightened or thinned, or the heat generation property of the rubber material should be reduced. For example, by reducing the heat build-up of the rubber composition that constitutes the tread portion that contacts the road surface, the fuel efficiency of the tire can be improved efficiently. However, there is a concern that reducing the heat build-up of the rubber composition for tread will reduce the wear resistance of the tread.

  On the other hand, the sidewall portion of the tire is a portion that easily generates heat due to repeated large deformation during traveling, and has a great influence on the fuel consumption performance of the tire. Therefore, it has been studied to reduce the heat generation or thin the rubber composition constituting the sidewall portion.

  For example, Patent Document 1 proposes to reduce the fuel consumption of a tire by arranging a low heat-generating rubber composition in a sidewall portion. However, since the sidewall portion repeatedly undergoes large deformation during traveling as described above, it is necessary to have high fatigue resistance against this deformation. Even if the rubber composition for a sidewall described in Patent Document 1 described above can reduce the heat build-up, the bending fatigue resistance is insufficient and there is still room for improvement.

Japanese Patent No. 4151629

  An object of the present invention is to provide a rubber composition for a tire that reduces heat generation and improves bending fatigue resistance.

In the tire rubber composition of the present invention that achieves the above object, 30 to 70 parts by weight of carbon black is blended with 100 parts by weight of diene rubber containing 30 to 60% by weight of natural rubber and 40 to 70% by weight of butadiene rubber. In addition, the weight average molecular weight of the butadiene rubber is 700,000 to 900,000, and the molecular weight distribution (Mw / Mn) obtained from the weight average molecular weight (Mw) and the number average molecular weight (Mn) is 1.5 to 3.0, 25. The toluene solution viscosity at 300 ° C. is 300 to 1000 mPa · s, and the CTAB adsorption specific surface area of the carbon black is 30 to 100 m ² / g.

  The rubber composition for tires 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 3 By using butadiene rubber whose toluene solution viscosity at 0.025 ° C. is 300 to 1000 mPa · s, the bending fatigue resistance of the rubber composition is increased, and tan δ at 60 ° C. is decreased to reduce heat generation. I can do it.

  The diene rubber is preferably composed of 30 to 60% by weight of natural rubber and 40 to 70% by weight of butadiene rubber.

  This tire rubber composition is suitable for use in the sidewall portion, and a tire having this tire rubber composition disposed in the sidewall portion reduces heat buildup and improves flex fatigue resistance. I can do it.

  In the rubber composition for tires of the present invention, the rubber component is a diene rubber containing natural 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 760,000 to 850,000, and more preferably 760,000 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 strength and wear resistance of the rubber composition are insufficient. Moreover, when the weight average molecular weight of butadiene rubber exceeds 900,000, the viscosity of a rubber composition will become high and workability will deteriorate. Moreover, the dispersibility of the filler containing carbon black is deteriorated.

  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 1.5 to 2.5. When the molecular weight distribution (Mw / Mn) of the butadiene rubber is less than 1.5, the dispersibility of the carbon black is deteriorated and it is difficult to obtain it industrially. If the molecular weight distribution (Mw / Mn) of the butadiene rubber exceeds 3.0, the hysteresis loss increases, the heat buildup of the rubber increases, and the bending fatigue resistance decreases.

  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, the rubber strength (tensile breaking strength and breaking elongation). ) Is excellent. At the same time, the bending fatigue resistance can be improved. If the toluene solution viscosity of the butadiene rubber is less than 300 mPa · s, the bending fatigue resistance of the rubber composition is insufficient. On the other hand, if the toluene solution viscosity of the butadiene rubber exceeds 1000 mPa · s, the viscosity of the rubber composition increases and the processability deteriorates. 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 40 to 70% by weight, preferably 50 to 60% by weight, based on 100% by weight of diene rubber. When the blending amount of butadiene rubber is less than 40% by weight, the heat buildup increases and the bending fatigue resistance decreases. Moreover, when the compounding quantity of butadiene rubber exceeds 70 weight%, the rigidity of rubber | gum will fall and exothermic property will fall.

  As the natural rubber used in the present invention, those usually used in tire rubber compositions can be used. Modified natural rubber or modified natural rubber may also be used. The blending amount of the natural rubber is 30 to 60% by weight, preferably 40 to 50% by weight, based on 100% by weight of the diene rubber. When the blending amount of the natural rubber is less than 30% by weight, the rigidity of the rubber is lowered and the exothermic property is lowered. Moreover, when the compounding quantity of natural rubber exceeds 60 weight%, exothermic property will raise and bending fatigue resistance will fall.

  In this invention, as long as the composition mentioned above is satisfy | filled, other diene rubbers other than natural rubber and butadiene rubber can be contained. Examples of other diene rubbers include isoprene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, butyl rubber, and butadiene rubber excluding the butadiene rubber having the characteristics described above. 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 30 to 60% by weight of natural rubber and 40 to 70% by weight of butadiene rubber. By using such a composition of the rubber component, both heat generation and bending fatigue resistance can be achieved.

The tire rubber composition of the present invention can increase the strength of the tire rubber composition and improve the bending fatigue resistance by blending carbon black. In particular, the bending fatigue resistance can be further improved by blending carbon black having a specific CTAB adsorption specific surface area. Carbon black has a CTAB adsorption specific surface area of 30 to 100 m ² / g, preferably 30 to 80 m ² / g. If the CTAB adsorption specific surface area of carbon black is less than 30 m ² / g, the effect of improving the bending fatigue resistance cannot be sufficiently obtained. On the other hand, if the CTAB adsorption specific surface area of carbon black exceeds 100 m ² / g, the heat generation becomes large and the bending fatigue resistance becomes insufficient. Moreover, the viscosity of a rubber composition becomes high and molding processability deteriorates. In the present invention, the CTAB adsorption specific surface area of carbon black is measured according to JIS K6217-3.

  The compounding amount of carbon black is 30 to 70 parts by weight, preferably 35 to 60 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of carbon black is less than 30 parts by weight, the reinforcing effect of the rubber composition cannot be obtained sufficiently and the bending fatigue resistance is insufficient. Moreover, when the compounding quantity of carbon black exceeds 70 weight part, the viscosity of a rubber composition will become high and molding processability will deteriorate.

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

  The tire rubber composition contains various additives commonly used in tire rubber compositions, such as vulcanization or crosslinking agents, vulcanization accelerators, processing aids, anti-aging agents, oils, and plasticizers. Such additives can be kneaded by a conventional method to obtain a rubber composition for tires, 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 tires can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for tires of the present invention is suitable for constituting the sidewall portion. A tire having a sidewall portion made of this rubber composition can reduce heat generation and improve bending fatigue resistance.

  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.

  11 types of tire rubber compositions (Examples 1 and 2 and Comparative Examples 1 to 9) each having the composition shown in Tables 2 and 3 were weighed with the composition components except the vulcanization accelerator and sulfur, and 1.7 L. The mixture was kneaded for 5 minutes in a 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 subjected to a 1.7 L hermetic banbury mixer, and a vulcanization accelerator and sulfur were added and mixed for 2 minutes to prepare a tire rubber composition.

  Using the 11 types of obtained rubber compositions for tires, a vulcanized rubber test piece was prepared by press vulcanization at 170 ° C. for 10 minutes in a predetermined mold. Fatigue was measured.

Exothermic; 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 Tables 2 and 3 as “exothermic properties” with the index of Comparative Example 1 being 100. A smaller index indicates a smaller tan δ (60 ° C.) and better heat generation.

Bending fatigue resistance The obtained vulcanized rubber test piece was bent 300 times per minute at room temperature according to JIS K6260, and the number of bending until the crack length reached 20 mm was determined. The obtained results are shown in Tables 2 and 3 as an index with the value of Comparative Example 1 as 100. The larger this value, the better the bending fatigue resistance.

The types of raw materials used in Tables 2 and 3 are shown below.
NR: Natural rubber, SIR20 made in Indonesia
BR-1 to BR-5: Butadiene rubber CB-1 shown in Table 1, respectively: Carbon black, Seast N made by Tokai Carbon Co., CTAB adsorption specific surface area 76 m ² / g
CB-2: carbon black, Cabot Japan Show Black N234, CTAB adsorption specific surface area 115 m ² / g
CB-3: carbon black, HTC # G manufactured by Nippon Kayaku Carbon, CTAB adsorption specific surface area 29 m ² / g
Oil: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Zinc flower: Zohua Chemical Industry Co., Ltd., Zinc flower type 3 Stearic acid: NOF Co., Ltd. Beads stearic acid vulcanization accelerator: FLEXSYS, SANTOCURE TBBS
Sulfur: Oil-treated sulfur manufactured by Tsurumi Chemical Co., Ltd.

  As is clear from the results in Table 3, the rubber compositions for tires of Examples 1 and 2 can both reduce heat generation and improve bending fatigue resistance as compared with Comparative Example 1.

  On the other hand, as is clear from the results in Table 2, the rubber composition of Comparative Example 2 has an exothermic property because the weight average molecular weight (Mw) of the butadiene rubber is less than 700,000 and the toluene solution viscosity at 25 ° C. is less than 300. Bending fatigue resistance cannot be improved sufficiently. In the rubber composition of Comparative Example 3, since the molecular weight distribution (Mw / Mn) of the butadiene rubber exceeds 3.0, the exothermic property and the bending fatigue resistance cannot be sufficiently improved. In the rubber composition of Comparative Example 4, since the blending amount of natural rubber exceeds 60% by weight and the blending amount of butadiene rubber is less than 40% by weight, the heat build-up increases and the bending fatigue resistance is insufficient. Although the rubber composition of Comparative Example 5 has a natural rubber compounding amount of less than 30% by weight and a butadiene rubber compounding amount of more than 70% by weight, the heat build-up decreases and the bending fatigue resistance increases, but the rubber composition Unsatisfactory due to insufficient strength.

Further, as is clear from the results in Table 3, the rubber composition of Comparative Example 6 has less heat generation because the compounding amount of carbon black is less than 30 parts by weight, but the flex fatigue resistance also decreases. In the rubber composition of Comparative Example 7, since the blending amount of carbon black exceeds 70 parts by weight, the heat buildup increases and the bending fatigue resistance decreases. In the rubber composition of Comparative Example 8, since the CTAB adsorption specific surface area of carbon black exceeds 100 m ² / g, the heat generation increases and the bending fatigue resistance is insufficient. Since the rubber composition of Comparative Example 9 has a CTAB adsorption specific surface area of carbon black of less than 30 m ² / g, heat generation is reduced, but strength as a rubber composition is insufficient.

Claims (3)

30 to 70 parts by weight of carbon black is blended with 100 parts by weight of diene rubber containing 30 to 60% by weight of natural rubber and 40 to 70% by weight of butadiene rubber, and the weight average molecular weight of the butadiene rubber is 700,000 to 90 parts. The molecular weight distribution (Mw / Mn) determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn) is 1.5 to 3.0, and the toluene solution viscosity at 25 ° C. is 300 to 1000 mPa · s. A rubber composition for tires, wherein the carbon black has a CTAB adsorption specific surface area of 30 to 100 m ² / g.   The tire rubber composition according to claim 1, wherein the diene rubber is composed of 30 to 60% by weight of natural rubber and 40 to 70% by weight of butadiene rubber.   The rubber composition for tires according to claim 1 or 2 used for a side wall part.