JP2009126966A - Rubber composition for base tread and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a base tread having excellent reinforcing properties and flex crack propagation resistance, and to provide a pneumatic tire having the base tread using the rubber composition. <P>SOLUTION: The rubber composition for the base tread comprises, based on 100 pts.wt. of a rubber component, 1-8 pts.wt. of ultrafine particulate zinc oxide having a 30-200 nm average particle diameter. The pneumatic tire has the base tread composed of the rubber composition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, various means have been taken up in order to reduce the rolling resistance of a tire (improve the rolling resistance) or improve the driving stability and riding comfort of a vehicle for the purpose of energy saving. As a means for this, the tread of the tire has a double structure (inner surface layer and surface layer), and a rubber composition showing excellent rolling resistance and steering stability is used for the base tread as the inner surface layer. It is done.

  In order to reduce heat generation and fuel consumption, conventional base tread rubber compositions have been incorporated with carbon black or silica having a large particle size to reduce the amount thereof. However, if the blending amount of carbon black or silica is reduced, even if a low heat generation is achieved, it is not always sufficient from the viewpoint of the reinforcing property of the rubber composition.

  Patent Document 1 describes that low rolling resistance and wear resistance can both be achieved by containing specific zinc oxide. However, the zinc oxide blended in Patent Document 1 has an average particle diameter of 1 μm or more, and the bending crack resistance performance is insufficient.

JP 2003-55505 A

  An object of the present invention is to provide a rubber composition for a base tread excellent in reinforcing properties and resistance to flex crack growth, and a pneumatic tire having a base tread using the same.

  The present invention relates to a rubber composition for a base tread containing 1 to 8 parts by weight of ultrafine zinc oxide having an average particle size of 30 to 200 nm with respect to 100 parts by weight of a rubber component.

  The base tread rubber composition preferably contains 25 to 60 parts by weight of carbon black with respect to 100 parts by weight of the rubber component.

  The present invention also relates to a pneumatic tire having a base tread comprising the rubber composition for base tread.

  According to the present invention, a rubber composition for a base tread excellent in reinforcement and bending crack growth resistance by blending ultrafine zinc oxide having an average particle diameter of 30 to 200 nm instead of ordinary zinc oxide, and A pneumatic tire having the base tread used can be provided.

  The rubber composition for base treads of the present invention contains a rubber component and ultrafine zinc oxide.

  Examples of the rubber component include natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), epoxidized natural rubber (ENR), acrylonitrile butadiene rubber (NBR), and ethylene propylene rubber. (EPM), butyl rubber (IIR), halogenated butyl rubber (X-IIR), and the like. These rubber components may be used alone or in combination of two or more. Of these, NR and BR are preferably used in combination because they are excellent in low heat build-up, bending crack resistance and workability.

  As NR, grade NR such as RSS # 3, TSR20 and the like conventionally used in the rubber industry can be used.

  When NR and BR are used in combination, NR is preferably contained in an amount of 20% by weight or more, more preferably 40% by weight or more, because of excellent workability and low heat build-up. Further, when NR and BR are used in combination, it is preferable to contain 90% by weight or less, and more preferably 80% by weight or less because of blending BR having excellent crack growth resistance.

  When NR and BR are used in combination, it is preferable that BR is contained in an amount of 10% by weight or more, and more preferably 20% by weight or more, because of excellent bending crack resistance. When NR and BR are used in combination, BR is preferably contained in an amount of 80% by weight or less, more preferably 60% by weight or less, because NR excellent in tensile properties is blended.

  The ultrafine zinc oxide used in the present invention has an average particle size smaller than that of normally used zinc oxide. By blending ultrafine zinc oxide, it is possible to improve flex crack growth resistance while improving reinforcement.

  The average particle size of the ultrafine zinc oxide is 200 nm or less, preferably 150 nm or less, because it has excellent resistance to flex crack growth and low heat build-up. The average particle diameter of the ultrafine zinc oxide is 30 nm or more, preferably 50 nm or more, because it is difficult to aggregate and is excellent in resistance to flex crack growth and tensile properties.

  The content of the ultrafine zinc oxide is 1 part by weight or more, preferably 1.5 parts by weight or more based on 100 parts by weight of the rubber component, because the reinforcing property is improved and the flex crack growth resistance is excellent. Further, the content of the ultrafine zinc oxide is 8 parts by weight or less, preferably 6 parts by weight or less, because aggregates cannot be formed and dispersion is easy.

  The rubber composition for a base tread of the present invention preferably further contains carbon black because it is excellent in rubber destructive properties.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, and more preferably 30 m ² / g or more, because it has excellent reinforcing properties. Also, N ₂ SA of carbon black is the reason that suppressed the pyrogenic, preferably not more than 100 m ² / g, more preferably at most 90m ² / g.

  The content of carbon black is preferably 25 parts by weight or more and more preferably 30 parts by weight or more with respect to 100 parts by weight of the rubber component because it has excellent fracture characteristics. Further, the content of carbon black is preferably 60 parts by weight or less, more preferably 50 parts by weight or less with respect to 100 parts by weight of the rubber component, because of its excellent low heat build-up.

  The rubber composition for a base tread of the present invention may further contain a reinforcing filler other than carbon black.

  Examples of reinforcing fillers other than carbon black include silica, calcium carbonate, clay, alumina, aluminum hydroxide, talc and the like, and silica is preferable because it is easy to obtain sufficient hardness and reinforcing properties.

  When a reinforcing filler other than carbon black is contained, the content of the reinforcing filler other than carbon black is preferably 25 parts by weight or more and more preferably 30 parts by weight or more with respect to 100 parts by weight of the rubber component. If the content of the reinforcing filler other than carbon black is less than 25 parts by weight, the hardness tends to decrease and the reinforcing property tends to be insufficient. Further, the content of the reinforcing filler other than carbon black is preferably 50 parts by weight or less, and more preferably 45 parts by weight or less. When the content of the reinforcing filler other than carbon black exceeds 50 parts by weight, the heat generation tends to be high.

  In addition to the rubber component, ultrafine zinc oxide and carbon black, the rubber composition for base tread of the present invention includes compounding agents conventionally used in the rubber industry, such as softeners, waxes, various anti-aging agents, stearin Vulcanizing agents such as acid and sulfur, various vulcanization accelerators, and the like can be appropriately blended as necessary.

  The tread portion of the pneumatic tire of the present invention has a two-layer structure including a cap tread and a base tread, not a one-layer structure. The rubber composition for a base tread of the present invention has a good breaking strength and does not need to consider wear resistance. Therefore, it is not a cap tread because it can achieve excellent low heat buildup. Used for base tread.

  The rubber composition for a base tread of the present invention is blended with the above-mentioned compounding agents as necessary, kneaded, extruded in accordance with the shape of the base tread of the tire at an unvulcanized stage, and placed on a tire molding machine. By bonding together with other tire members, an unvulcanized tire is formed, and further, the tire can be obtained by heating and pressing the unvulcanized tire in a vulcanizer.

  The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Next, various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber (NR): RSS # 3
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Carbon black: Dia Black H (N330, N ₂ SA: 79 m ² / g) manufactured by Mitsubishi Chemical Corporation
Aroma oil: Kronos KA10 manufactured by Titanium Industry Co., Ltd.
Zinc oxide: Silver candy R (average particle size: 290 nm) manufactured by Toho Zinc Co., Ltd.
Ultrafine zinc oxide: Zincox Super F-2 (average particle size: 130 nm) manufactured by Hakusui Tech Co., Ltd.
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Sulfur: Sulfur powder vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. CZ: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

Examples 1-3 and Comparative Examples 1-4
According to the formulation shown in Table 1, using a 1.7 L Lab Banbury mixer, chemicals other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes under a condition of 80 ° C. using a biaxial open roll to obtain an unvulcanized rubber composition. Furthermore, the vulcanized rubber composition of Examples 1-3 and Comparative Examples 1-4 was created by press-curing the obtained unvulcanized rubber composition for 12 minutes on 170 degreeC conditions.

(Bending crack growth test)
According to JIS K 6260 “Dematcher bending crack growth test method for vulcanized rubber and thermoplastic rubber”, a crack of 1 mm is generated in the vulcanized rubber composition at a room temperature of 25 ° C., and this crack grows by 1 mm. The number of bends up to was measured. In addition, this measurement was performed twice and the average value was computed. Moreover, the larger the value, the better the resistance to flex crack growth, and 70% and 110% indicate the elongation ratio with respect to the length of the original vulcanized rubber composition.

(Tensile test)
In accordance with JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber—How to Obtain Tensile Properties”, a tensile test was performed using a No. 3 dumbbell, and the breaking strength (TB (MPa)) of each compound was measured. In addition, it shows that it is excellent in rubber | gum strength, so that TB is large.

  The rubber compositions of Examples 1 and 2 containing ultrafine zinc oxide are superior in resistance to flex crack growth compared to the rubber compositions of Comparative Examples 1 and 2 containing the same amount of ordinary zinc oxide. .

  In Comparative Example 3 in which the blending amount of the ultrafine zinc oxide is less than 1 part by weight, sufficient bending crack growth resistance cannot be obtained.

  Further, in Comparative Example 4 in which the blending amount of ultrafine zinc oxide exceeds 8 parts by weight, sufficient bending crack growth resistance cannot be obtained.

Claims (3)

A rubber composition for a base tread containing 1 to 8 parts by weight of ultrafine zinc oxide having an average particle diameter of 30 to 200 nm with respect to 100 parts by weight of a rubber component. Furthermore, the rubber composition for base treads of Claim 1 which contains 25-60 weight part of carbon black with respect to 100 weight part of rubber components. A pneumatic tire having a base tread made of the rubber composition for a base tread according to claim 1.