JP4964441B2 - Sidewall rubber composition and tire comprising the same - Google Patents

Description

  The present invention relates to a sidewall rubber composition and a tire comprising the same.

  Among tire components, particularly, the sidewall has a problem of aging due to external factors such as ozone because the contact portion with the outside air is large.

  In order to suppress aging of the sidewall due to ozone (in order to improve ozone resistance), generally, an antioxidant has been added to the rubber composition for the sidewall. However, by increasing the amount of the anti-aging agent, there is a problem that the obtained sidewall is likely to cause a poor appearance due to discoloration or a decrease in rubber strength due to running or aging.

  Patent Document 1 discloses that a silicone oil is blended in a tire tread for a tire roller, but the ozone resistance performance is improved without deteriorating the rubber strength and appearance of the sidewall portion of the tire. It wasn't.

JP-A-7-52608

  An object of the present invention is to provide a rubber composition for a sidewall and a tire comprising the same, which have improved ozone resistance without deteriorating rubber strength and appearance.

  The present invention relates to a rubber composition for a sidewall containing 2 to 15 parts by weight of dimethyl silicone oil with respect to 100 parts by weight of a diene rubber.

  The present invention also relates to a tire comprising the rubber composition for sidewalls.

  According to the present invention, by using a diene rubber and a specific amount of dimethyl silicone oil, the deterioration of the appearance is prevented without reducing the rubber strength, the ozone resistance performance is improved, and the generation of cracks is suppressed. A rubber composition for a wall and a tire comprising the same can be provided.

  The rubber composition for a side wall of the present invention comprises a diene rubber and dimethyl silicone oil.

  Diene rubbers include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), ethylene-propylene-diene rubber (EPDM), and acrylonitrile-butadiene copolymer rubber (NBR). And chloroprene rubber (CR). These diene rubbers may be used alone or in combination of two or more.

  Of these, NR, BR, IR, and EPDM are preferable as the diene rubber, and NR and BR are more preferable.

  When NR and BR are used in combination, the NR content in the diene rubber is preferably 20 to 80% by weight, and the BR content is preferably 80 to 20% by weight. If the NR content is less than 20% by weight and the BR content exceeds 80% by weight, the strength of the rubber tends to decrease, and the cut resistance and crack resistance tend to deteriorate. On the other hand, when the NR content is greater than 80% by weight and the BR content is less than 20% by weight, the amount of shrinkage increases in the unvulcanized rubber, and there is a tendency for negatives to occur in terms of workability.

  Dimethyl silicone oil is a linear polymer composed of siloxane bonds, and all of the side chains and terminals of polysiloxane are methyl groups.

  The weight average molecular weight of dimethyl silicone oil is preferably 100 to 10,000. If the weight average molecular weight is less than 100, bloom tends to occur and the appearance tends to deteriorate. Moreover, when the weight average molecular weight of dimethyl silicone oil exceeds 10,000, there exists a tendency for a viscosity to become high too much and for workability to deteriorate.

  The content of dimethyl silicone oil is 2 parts by weight or more, preferably 3 parts by weight or more with respect to 100 parts by weight of the diene rubber. If the content of dimethyl silicone oil is less than 2 parts by weight, the resistance to ozone cracking cannot be improved. The content of dimethyl silicone oil is 15 parts by weight or less, preferably 13 parts by weight or less with respect to 100 parts by weight of the diene rubber. When the content of dimethyl silicone oil exceeds 15 parts by weight, the rubber strength is lowered, which is not preferable.

  The rubber composition for a side wall of the present invention preferably further contains a softening agent. By using the softener in combination with dimethyl silicone oil, the strength of the rubber is not reduced.

  Examples of softeners include paraffinic oils, naphthenic oils, and aromatic (aromatic) oils. Among them, aromatic (aromatic) oils have good compatibility with rubber. This is advantageous in terms of rubber strength.

  The content of the softening agent is preferably 2 to 20 parts by weight with respect to 100 parts by weight of the diene rubber. If the content of the softening agent is less than 2 parts by weight, the hardness of the rubber tends to be too high. Moreover, when content of a softening agent exceeds 20 weight part, there exists a tendency for the intensity | strength of rubber | gum to fall too much.

  The rubber composition for a side wall of the present invention preferably further contains an antiaging agent. When used in combination with dimethyl silicone oil, the weather resistance, the anti-bending property and the like tend to be improved.

  Anti-aging agents include p-phenylenediamine derivatives such as N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer A quinoline-based anti-aging agent such as the above can be used, and among them, a p-phenylenediamine derivative is preferable because ozone resistance and bending cracking prevention tend to be excellent.

  The content of the antioxidant is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the diene rubber. When the content of the anti-aging agent is less than 0.5 parts by weight, the weather resistance and the anti-bending property tend to be insufficient. Moreover, when content of an anti-aging agent exceeds 10 weight part, there exists a tendency which causes bloom and an external appearance deteriorates.

  In addition to the diene rubber, dimethyl silicone oil, softener and anti-aging agent, the rubber composition for a sidewall of the present invention includes a reinforcing filler such as carbon black, a vulcanizing agent such as sulfur, and a vulcanization accelerator. Those generally used in the tire industry such as stearic acid and zinc oxide can be appropriately blended.

  The tire of the present invention has a sidewall made of the rubber composition for a sidewall of the present invention, and the tire is produced by a usual method. That is, the rubber composition is extruded according to the shape of the sidewall of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine to form an unvulcanized tire. This unvulcanized tire can be heated and pressed in a vulcanizer to produce a tire.

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

The various chemicals used in the examples and comparative examples are shown below.
NR: RSS # 3 grade BR: BR150B manufactured by Ube Industries, Ltd.
Carbon black: N550 manufactured by Showa Cabot Corporation
Process oil: Diana process PS32 (aromatic oil) manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sannoc Wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd .: Santoflex 13 (N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine) manufactured by Flexis Co., Ltd.
Stearic acid: Tung Zinc Hana made by Nippon Oil & Fats Co., Ltd .: Zinc oxide No. 2 made by Mitsui Kinzoku Mining Co., Ltd. NS
Dimethyl silicone oil: TSF451-50M (weight average molecular weight: 100-1000) manufactured by GE Toshiba Silicone

Examples 1-3 and Comparative Examples 1-3
100 parts by weight of a rubber component consisting of 50% by weight of NR and 50% by weight of BR, 50 parts by weight of carbon black, 10 parts by weight of process oil, 2 parts by weight of anti-aging agent, 2 parts by weight of stearic acid, 2 parts by weight of zinc oxide, And the dimethyl silicone oil of the compounding quantity shown in Table 1 was knead | mixed for 5 minutes at 140 degreeC using the Banbury mixer.

  Next, 1.5 parts by weight of sulfur and 1 part by weight of a vulcanization accelerator were added to the obtained kneaded product, and kneaded at 95 ° C. for 3 minutes with a biaxial roller.

  And the rubber composition of Examples 1-3 and Comparative Examples 1-3 was produced by vulcanizing the obtained kneaded material for 10 minutes at 175 degreeC, and it used for the following tests.

<Ozone test>
Vulcanized rubber samples (length 10 cm × width 1.5 cm × thickness 0.2 cm) composed of the rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were stretched 10%, temperature 30 ° C., ozone concentration 0 It was left under an atmosphere of 5 ppm. The sample evaluation after aging was visually performed according to the following criteria.

A: A few cracks occur B: A small number of cracks occur (a crack of about several mm is about 1/3 of the area of the sample)
C: Many occurrences (a crack of about several mm is about 2/3 of the area of the sample)
D: Cracks occurred on the entire sample surface

<Tensile test>
Using the dumbbell No. 3 type test pieces comprising the rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3, a tensile test was performed at room temperature based on JIS K6251, and the breaking stress TB (MPa) and the breaking time were The elongation EB (%) was measured. It shows that intensity | strength is so large that the value of TB and EB is large.

<Appearance evaluation>
Each of the samples after aging obtained in the ozone test was visually observed, and Examples 1-3 and Comparative Examples 1-2 were based on the appearance (color) of the sample after aging of Comparative Example 1 not containing dimethyl silicone oil. It was confirmed whether or not the appearance (color) of the sample after aging was different.

  Table 1 shows the test results.

  In Examples 1 to 3, in which the blending amount of dimethyl silicone oil is in the range of 2 to 15 parts by weight, the ozone resistance performance is improved as compared with Comparative Example 1, and the rubber strength (TB value, EB value) is also maintained. In addition, the appearance was at the same level as the standard, and it was possible to achieve both ozone resistance, strength and appearance.

  On the other hand, in Comparative Example 2 in which the amount of dimethyl silicone oil was 1 part by weight, ozone resistance could not be improved as compared with Comparative Example 1 that did not contain dimethyl silicone oil.

  Further, in Comparative Example 3 in which the blending amount of dimethyl silicone oil was 20 parts by weight, the ozone resistance performance was improved, but the TB was low, which was not preferable.

Claims (2)

Containing 5 to 15 parts by weight of a dimethyl silicone oil having a weight average molecular weight of 100 to 1000 and 2 to 20 parts by weight of a softening agent with respect to 100 parts by weight of a diene rubber;
A rubber composition for a sidewall which does not contain silica as a reinforcing filler. A tire comprising the sidewall rubber composition according to claim 1.