TREAD RUBBER COMPOSITION AND PNEUMATIC TIRE

Abstract

Provided are a tread rubber composition and a pneumatic tire, which exhibit excellent wet grip performance when thermally damaged. A tread rubber composition having acetone extractable contents before and after heat aging (denoted by AEf and AEo, respectively) that satisfy the following relationships 1) and 2):

1) AEf16.0%;
2) AEo/AEf10095%.

Claims

1. A pneumatic tire, comprising a tread comprising a tread rubber composition, the tread rubber composition having acetone extractable contents before and after heat aging (denoted by AEf and AEo, respectively) that satisfy the following relationships 1) and 2): 1) AEf16.0%; 2) AEo/AEf10095%.

2. The pneumatic tire according to claim 1, wherein the tread rubber composition comprises silica, and at least one of a liquid polymer or a resin.

3. The pneumatic tire according to claim 1, wherein the tread rubber composition has an acetone extractable content before heat aging AEf of 22.0% or higher.

Description

EXAMPLES

[0115] The present invention is specifically described with reference to examples, but the present invention is not limited to the examples.

[0116] The chemicals used in the examples and comparative examples are listed below.

[0117] SBR: Nipol 1502 available from Zeon Corporation (E-SBR, styrene content: 24% by mass, vinyl content: 16% by mass, unmodified SBR)

[0118] BR: BR150B available from Ube industries, Ltd. (cis content: 98% by mass)

[0119] Carbon black: SHOBLACK N110 available from Cabot Japan K.K. (N.sub.2SA: 145 m.sup.2/g)

[0120] Silica: Ultrasil VN3 available from Degussa (N.sub.2SA: 175 m.sup.2/g)

[0121] Silane coupling agent: Si69 (bis(3-triethoxysilyl-propyl)tetrasulfide) available from Evonik Degussa

[0122] Oil: Diana Process Oil NH-60 available from Idemitsu Kosan Co., Ltd.

[0123] Resin 1: SYLVARES SA85 available from Arizona Chemical (-methylstyrene resin (a copolymer of -methylstyrene and styrene), softening point: 85 C., Tg: 43 C.)

[0124] Resin 2: Sylvatraxx 4150 available from Arizona Chemical (-pinene resin, -pinene content: at least 98% by mass, Mw: 2350, Mn: 830)

[0125] Resin 3: YS resin TO125 available from Yasuhara Chemical Co., Ltd. (aromatic modified terpene resin, softening point: 125 C.)

[0126] Liquid polymer 1: RICON 100 available from Sartomer (liquid SBR, styrene content: 25% by mass, Mw: 4500)

[0127] Liquid polymer 2: FBR-746 available from Kuraray Co., Ltd. (farnesene-butadiene copolymer, Mw: 100,000, copolymerization ratio: farnesene/butadiene=60/40 by mass, melt viscosity: 603 Pa.Math.s, Tg: 78 C.)

[0128] Wax: Ozoace 0355 available from Nippon Seiro Co., Ltd.

[0129] Antioxidant: Antigene 6C (N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine) available from Sumitomo Chemical Co., Ltd.

[0130] Stearic acid: stearic acid TSUBAKI available from NOF Corporation

[0131] Zinc oxide: Ginrei R available from Toho Zinc Co., Ltd.

[0132] Sulfur: HK-200-5 available from Hosoi Chemical Industry Co., Ltd. (5% oil-containing powdered sulfur)

[0133] Vulcanization accelerator: NOCCELER CZ (N-cyclohexyl-2-benzothiazole sulfenamide) available from Ouchi Shinko Chemical Industrial Co., Ltd.

Examples and Comparative Examples

[0134] The chemicals other than the sulfur and vulcanization accelerator in the amounts shown in Table 1 or 2 were kneaded using a 1.7 L Banbury mixer (Kobe Steel, Ltd.) at 150 C. for 5 minutes to give a kneaded mixture. Then, the sulfur and vulcanization accelerator were added to the kneaded mixture, and they were kneaded using an open roll mill at 80 C. for 5 minutes to give an unvulcanized rubber composition.

[0135] The unvulcanized rubber composition was formed into a tread shape and assembled with other tire components to build an unvulcanized tire. The unvulcanized tire was press-vulcanized at 150 C. for 30 minutes to prepare a test tire (size: 215/45R17)

Heat Aging

[0136] The fresh test tires (before heat aging) were left at 80 C. for 168 hours in accordance with JIS K6257:2010 to obtain heat-aged test tires.

[0137] The test tires and the unvulcanized rubber compositions were evaluated as described below. Tables 1 and 2 show the results. Comparative Example 1-1 and Comparative Example 2-1 are used as standards of comparison in Tables 1 and 2, respectively.

Acetone Extractable Content Before Heat Aging or Initial Acetone Extractable Content (AEf)

[0138] Specimens of the rubber compositions (vulcanized rubber compositions) alone were cut out from the treads of the test tires before heat aging. The amount of material extractable with acetone (extractable content: % by mass) in the rubber composition specimens (before heat aging; was determined by a method for measuring acetone extractable content according to JIS K6229:2015 (the method A).

Acetone Extractable Content After Heat Aging (AEo)

[0139] Specimens of the rubber compositions (vulcanized rubber compositions) alone were cut out from the treads of the test tires after heat aging. The amount of material extractable with acetone (extractable content: % by mass) in the rubber composition specimens (after heat aging) was determined by a method for measuring acetone extractable content according to JIS K6229:2015 (the method A)

Wet Grip Performance

[0140] The test tire of each example, before and after heat aging, was mounted on each wheel of a front-engine, front-wheel-drive car of 2000cc displacement made in Japan. The breaking distance of the car with an initial speed of 100 km/h under wet asphalt conditions was determined and expressed as an index, with the standard comparative example before heat aging set equal to 100. A higher index indicates better wet grip performance.

Processability

[0141] The Mooney viscosity (ML.sub.1+4/130 C.) of the unvulcanized rubber compositions was determined in accordance with JIS K 6300-1 Rubber, unvulcanizedPhysical propertyPart 1: Determination, of Mooney viscosity and pre-vulcanization characteristics with Mooney viscometer using a Mooney viscosity tester as follows. After preheating for one minute up to 130 C., a small rotor was rotated at this temperature, and after a lapse of four minutes the Mooney viscosity was measured. The Mooney viscosity of each example was standardized by dividing by the Mooney viscosity of the standard comparative example and then multiplying by 100 to obtain an index. A higher index indicates a lower viscosity and better processability.

TABLE-US-00001 TABLE 1 Example Comparative Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-1 1-2 1-3 Amount SBR 80 80 80 80 80 80 80 80 80 80 (parts BR 20 20 20 20 20 20 20 20 20 20 by Carbon black 10 10 10 10 10 10 10 10 10 10 mass) Silica 100 100 100 100 100 100 100 100 100 100 Silane coupling agent 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 Oil 50 30 Resin 1 30 30 20 Resin 2 30 30 Resin 3 30 30 Liquid polymer 1 20 20 20 50 Liquid polymer 2 20 20 20 50 Wax 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Antioxidant 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Stearic acid 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Zinc oxide 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Sulfur 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 Vulcanization accelerator 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 Eval- Acetone extractable 22.8 22.8 22.8 20.6 17.2 17.2 17.2 24.4 6.4 24.4 uation content before heat aging AEf (% by mass) Acetone extractable 22.2 22.2 22.2 19.9 16.7 16.7 16.7 19.1 6.4 21.4 content after heat aging AEo (% by mass) AEo/AEf 100 (%) 97 97 97 97 97 97 97 78 100 88 Wet grip performance 115 115 115 110 112 112 112 100 95 102 (before heat aging) Wet grip performance 111 110 110 106 110 109 109 90 94 95 (after heat aging) Processability 98 98 98 98 97 97 97 100 97 99

TABLE-US-00002 TABLE 2 Example Comparative Example 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-1 2-2 2-3 Amount SBR 90 90 90 90 90 90 90 90 90 90 (parts BR 10 10 10 10 10 10 10 10 10 10 by Carbon black 30 30 30 30 30 30 30 30 30 30 mass) Silica 80 80 80 80 80 80 80 80 80 80 Silane coupling agent 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.4 Oil 50 30 Resin 1 30 30 20 Resin 2 30 30 Resin 3 30 30 Liquid polymer 1 20 20 20 50 Liquid polymer 2 20 20 20 50 Wax 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Antioxidant 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Stearic acid 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.02.0 2.0 2.0 Zinc oxide 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Sulfur 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 Vulcanization accelerator 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 Eval- Acetone extractable 22.3 22.3 22.3 20.1 16.8 16.8 16.8 23.8 6.5 23.8 uation content before heat aging AEf (% by mass) Acetone extractable 21.7 21.7 21.7 19.4 16.4 16.4 16.4 18.7 6.5 20.8 content after heat aging AEo (% by mass) AEo/AEf 100 (%) 97 97 97 97 98 98 98 79 100 87 Wet grip performance 115 115 115 110 112 112 112 100 95 102 (before heat aging) Wet grip performance 111 110 110 106 110 109 109 90 94 95 (after heat aging) Processability 98 98 98 98 97 97 97 100 97 99

[0142] As shown in Tables 1 and 2, the examples satisfying relationships 1) and 2) exhibited a slight degradation in wet grip performance after heat aging and an excellent ability to maintain yet grip performance. Moreover, good processability was also ensured in the examples. Furthermore, the examples had excellent wet grip performance before heat aging (initial wet grip performance). Thus, the examples were very excellent in the balance of initial wet grip performance, wet grip performance after thermal damage, and processability.