JP5480699B2 - Sidewall rubber composition and pneumatic tire - Google Patents

Description

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

Natural rubber has excellent raw rubber strength (green strength) compared to synthetic rubber, and is excellent in processability. Also, vulcanized rubber is often used for sidewalls because of its high mechanical strength and excellent low heat build-up.

In addition to the performance of a general sidewall (for example, excellent tear strength), steering stability is required for the sidewall from the viewpoint of safety. In particular, racing tires are required to have steering stability rather than ride comfort and weather resistance. However, in general, the sidewall portion of the tire is likely to generate heat as the vehicle travels, and there is a problem that the rigidity is lowered and the steering stability is lowered due to a high temperature condition.

As a method for improving the steering stability, a method for increasing the rigidity of the sidewall is known. As a method of increasing the rigidity of the sidewall, a method of thickening the gauge of the sidewall and a method of increasing the amount of the filler component of the sidewall and making it harder are used. There is room for improvement in terms of blow resistance.

Patent Documents 1 and 2 disclose that the resistance to bending crack growth is improved by using finely divided zinc oxide and silica or titanium dioxide in combination. However, there is room for improvement in terms of low handling stability and compatibility between handling stability and blow resistance.

JP 2007-169431 A JP 2008-88381 A

An object of the present invention is to solve the above-mentioned problems, and to provide a rubber composition for a sidewall that can achieve both steering stability and blow resistance, and a pneumatic tire using the rubber composition.

Generally, in a rubber composition having high rigidity, the blow resistance is reduced. However, as a result of intensive studies, the present inventors have determined that a specific rubber component, zinc oxide having a specific average primary particle size, carbon It has been found that blow resistance can be improved even when a rubber composition having high rigidity is used in combination with black. That is, the present invention relates to a rubber composition for a side wall comprising a rubber component containing isoprene-based rubber, zinc oxide having an average primary particle size of 200 nm or less, and carbon black.

The rubber component preferably further contains butadiene rubber and / or styrene butadiene rubber.

It is preferable that the content of the zinc oxide is 0.1 to 10 parts by mass and the content of the carbon black is 20 to 70 parts by mass with respect to 100 parts by mass of the rubber component.

The present invention also relates to a pneumatic tire having a sidewall produced using the rubber composition. The pneumatic tire is preferably a competition tire.

According to the present invention, since it is a rubber composition for a sidewall containing a rubber component containing isoprene-based rubber, zinc oxide having a specific average primary particle diameter, and carbon black, both steering stability and blow resistance are achieved. It is possible to provide a pneumatic tire excellent in handling stability and blow resistance.
Blowing refers to damage such as tire surface rubber boils, becomes blisters, and rubber scatters. Such damage can be suppressed as the blow resistance is higher.

The rubber composition for a side wall of the present invention contains a rubber component containing isoprene-based rubber, zinc oxide having a specific average primary particle size, and carbon black.

In the present invention, isoprene-based rubber is included as a rubber component. By including isoprene-based rubber, the mechanical strength and low heat build-up required for the sidewall rubber can be obtained. Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. Moreover, as IR, what is common in the tire industry can be used. These may be used alone or in combination of two or more.

The content of isoprene-based rubber in 100% by mass of the rubber component is preferably 35% by mass or more, more preferably 40% by mass or more. If it is less than 35% by mass, the rubber strength tends to decrease, and there is a possibility that the steering stability and the blow resistance may not be sufficiently achieved. Further, the content of the isoprene-based rubber is preferably 60% by mass or less, more preferably 55% by mass or less. If it exceeds 60% by mass, sufficient bending fatigue resistance may not be obtained.

In addition to isoprene rubber, rubber components that can be used in the present invention include diene rubbers such as butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), and butyl rubber (IIR). Is mentioned. These diene rubbers may be used alone or in combination of two or more. Among these, NR, BR, and SBR are preferable because low exothermic property and durability can be obtained in a balanced manner, and it is more preferable to use NR and BR in combination.

It is not particularly limited as BR, for example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd., VCR617, etc. BR containing syndiotactic polybutadiene crystals can be used. Among them, the BR cis content is preferably 90% by mass or more because of its excellent bending fatigue resistance.

The content of BR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 45% by mass or more. If it is less than 40% by mass, sufficient bending fatigue resistance may not be obtained. The BR content is preferably 65% by mass or less, more preferably 60% by mass or less. If it exceeds 65% by mass, the mechanical strength may be insufficient and the workability may be deteriorated.

The SBR is not particularly limited, and for example, emulsion polymerization styrene butadiene rubber (E-SBR), solution polymerization styrene butadiene rubber (S-SBR) and the like can be used.

The styrene content of SBR is preferably 20% by mass or more, more preferably 30% by mass or more. If it is less than 20% by mass, the rigidity required for steering stability may not be obtained. The styrene content is preferably 45% by mass or less, more preferably 40% by mass or less. If it exceeds 45% by mass, the heat generation is too high and blow resistance may be reduced.

The content of SBR in 100% by mass of the rubber component is preferably 15% by mass or more, more preferably 20% by mass or more. If it is less than 15% by mass, the rigidity required for steering stability may not be obtained. The SBR content is preferably 40% by mass or less, more preferably 35% by mass or less. If it exceeds 40% by mass, the heat generation is too high and blow resistance may be reduced.

In the present invention, zinc oxide having a specific average primary particle size is used. By blending zinc oxide having a specific average primary particle size, the dispersibility of zinc oxide can be improved and blow resistance can be improved.

The average primary particle diameter of zinc oxide is 200 nm or less, preferably 150 nm or less, more preferably 120 nm or less, and still more preferably 90 nm or less. When it exceeds 200 nm, there is a possibility that sufficient improvement effect cannot be obtained in the dispersibility of zinc oxide and the physical properties of rubber as compared with normal zinc oxide. The average primary particle diameter of zinc oxide is preferably 20 nm or more, more preferably 50 nm or more. If it is less than 20 nm, the average particle size of zinc oxide becomes smaller than the primary particle size of carbon black, the dispersibility of zinc oxide cannot be sufficiently improved, and blow resistance may be deteriorated.
In addition, the average primary particle diameter of zinc oxide represents the average particle diameter (average primary particle diameter) converted from the specific surface area measured by the BET method by nitrogen adsorption.

The content of the zinc oxide is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and further preferably 1.0 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.1 parts by mass, sufficient physical properties of the vulcanized rubber tend not to be obtained. The zinc oxide content is preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and still more preferably 8 parts by mass or less. If it exceeds 10 parts by mass, sufficient blow resistance may not be obtained.

In the present invention, carbon black is used. Thereby, the rigidity required for mechanical strength and steering stability is obtained. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. Carbon black may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 35 m ² / g or more. If it is less than 30 m ² / g, sufficient mechanical strength may not be obtained. Further, the nitrogen adsorption specific surface area of the carbon black is preferably ^{80 m} 2 / g or less, ^{60 m} 2 / g or less is more preferable. If it exceeds 80 m ² / g, the heat generation is too high, and the blow resistance may be reduced.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

Carbon black has a dibutyl phthalate (DBP) oil absorption of preferably 100 ml / 100 g or more, more preferably 110 ml / 100 g or more. If it is less than 100 ml / 100 g, sufficient mechanical strength may not be obtained. The DBP oil absorption of carbon black is preferably 130 ml / 100 g or less, more preferably 120 ml / 100 g or less. If it exceeds 130 ml / 100 g, the heat generation is too high and blow resistance may be reduced.
In addition, the DBP oil absorption amount of carbon black is calculated | required by the measuring method of JISK6217-4.

The content of carbon black is preferably 20 parts by mass or more, more preferably 23 parts by mass or more, and further preferably 25 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 20 parts by mass, sufficient mechanical strength and rigidity may not be obtained. The carbon black content is preferably 70 parts by mass or less, more preferably 65 parts by mass or less, and still more preferably 60 parts by mass or less. If it exceeds 70 parts by mass, the heat generation is too high and blow resistance may be reduced.

In addition to the above components, the rubber composition of the present invention contains compounding agents generally used in the production of rubber compositions, such as reinforcing fillers such as silica, silane coupling agents, stearic acid, and various anti-aging agents. Oils, waxes, vulcanizing agents, vulcanization accelerators and the like can be appropriately blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, by extruding the rubber composition containing the above components in accordance with the shape of the sidewall at the unvulcanized stage, and molding the tire composition together with other tire members on a tire molding machine by a normal method, Form an unvulcanized tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The pneumatic tire of the present invention is preferably used as a tire for passenger cars, a tire for trucks and buses, a tire for motorcycles, a tire for competition, and the like, and particularly preferably used as a tire for competition. The pneumatic tire obtained by the present invention can achieve both steering stability and blow resistance.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: RSS # 3
BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 98% by mass)
SBR: Toughden 4350 manufactured by Asahi Kasei Corporation (styrene content: 39% by mass, containing 50 parts by mass of oil with respect to 100 parts by mass of rubber solid content)
Carbon black: N550 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 42 m ² / g, DBP oil absorption: 115 ml / 100 g)
Silica: Ultrasil VN3 (average primary particle size 15 nm) manufactured by Evonik Degussa
Oil: NC300S manufactured by JOMO
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Anti-aging agent: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Zinc stearate manufactured by NOF Corporation 1: Zinc Hana No. 1 (average primary particle size: 300 nm) manufactured by Mitsui Kinzoku Mining Co., Ltd.
Zinc oxide 2: Zincock Super F-2 (average primary particle size: 65 nm) manufactured by Hakusui Tech Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller NS (Nt-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-5 and Comparative Examples 1-4
According to the blending contents shown in Table 1, using a 1.7 L Banbury mixer, among the blended materials, materials other than sulfur and 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.
The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 12 minutes to obtain a vulcanized rubber sheet.
Further, the obtained unvulcanized rubber composition is molded into a sidewall shape, bonded to another tire member, molded into a tire, and vulcanized at 150 ° C. and 25 kgf for 35 minutes for a test cart tire (tire) Size: 11 × 7.10-5) was produced. In addition, the thickness of the side wall of Table 1 was measured by measuring the thickness of the thickest part of the side wall, and the comparative example 1 was set as 100 and indicated as an index. The larger the index, the thicker the sidewall.

The following evaluation was performed using the obtained vulcanized rubber sheet and test cart tire. Each test result is shown in Table 1.

(Tensile test)
In accordance with JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber-Determination of Tensile Properties”, using the test piece (dumbbell No. 3) obtained by cutting the vulcanized rubber sheet, the tensile strength at 100% elongation Stress M100 (MPa) was measured. The measurement conditions were a test temperature of 25 ° C. and a tensile speed of 500 mm / min. The results were expressed as an index according to the following formula, with the result of Comparative Example 1 being 100. The larger the index, the better the rigidity.
Tensile strength index = (M100 of each formulation) / (M100 of Comparative Example 1) × 100

(Maneuvering stability)
The test cart tire was attached to the test cart, and the test course of 1 km 2 km was run 8 times. The steering stability of the tire of Comparative Example 1 was 3 points, and the test driver made a sensory evaluation with 5 points. The larger the value, the better the steering stability.

(Blow resistance)
The obtained vulcanized rubber sheet was subjected to a flexo test at 100 ° C. in accordance with JIS K6265, and the degree of occurrence of blow inside the sample after the test was visually evaluated. In addition, according to the side wall thickness index of a table | surface, the test was implemented changing the thickness of the sample. The case where blow did not occur was assigned 5 points, and the case where blow occurred most was 1 point. That is, a larger score indicates better blow resistance.

The examples including a rubber component containing isoprene-based rubber, zinc oxide having a specific average primary particle size, and carbon black were able to achieve both steering stability and blow resistance. On the other hand, Comparative Examples 1 to 3 in which carbon black was blended and zinc oxide having a specific average primary particle size was not blended were inferior in blow resistance compared to the Examples, and it was impossible to achieve both steering stability and blow resistance. . On the other hand, in Comparative Example 4 in which silica and zinc oxide having a specific average primary particle size are blended and carbon black is not blended, sufficient mechanical strength and rigidity cannot be obtained, and the handling stability is significantly higher than that of the Examples. Although it was inferior, in the silica compounding system not containing carbon black, the heat generation itself was small, and thus the blow resistance was excellent. Thus, in Comparative Example 4, it was not possible to achieve both steering stability and blow resistance.

Claims (4)

A racing tire having a sidewall produced using a rubber composition for a sidewall including a rubber component containing isoprene-based rubber, zinc oxide having an average primary particle size of 200 nm or less, and carbon black. The racing tire according to claim 1, further comprising butadiene rubber and / or styrene butadiene rubber as the rubber component. The racing tire according to claim 2, wherein the cis content of the butadiene rubber is 90% by mass or more . Against 100 parts by mass of the rubber component, the content is 0.1 to 10 parts by weight of zinc oxide, the content of the carbon black according to any one of claims 1 to 3 which is 20 to 70 parts by weight Racing tire .