JP2010084057A - Rubber composition for sidewall - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a sidewall that can further improve both crack resistance and flex crack resistance without increasing hardness, as compared to another rubber composition for a sidewall whose main component is comprised of a raw material derived from petroleum resources, taking account of environmental problem and preparing for the reduced supply in petroleum resources in future. <P>SOLUTION: The rubber composition for a sidewall includes 10-50 pts.mass of surface treatment silica having a silica content of 95 mass% or more, based on 100 pts.mass of rubber component containing 20-80 mass% of natural rubber and 20-80 mass% of at least one type of rubber selected from the group consisting of epoxidized natural rubber, butadiene rubber and styrene-butadiene rubber. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rubber composition for a sidewall.

  Conventionally, rubber compositions for tire sidewalls are blended with butadiene rubber (BR) in order to improve flex crack growth resistance in addition to natural rubber (NR) exhibiting excellent tear strength, and weather resistance. And carbon black has been used to improve reinforcement.

However, in recent years, environmental issues have become more important, regulations on CO ₂ emission control have been strengthened, and oil resources are limited and the supply amount has been decreasing year by year. The price is expected to rise, and there is a limit to the use of raw materials derived from petroleum resources such as BR and carbon black. Therefore, assuming that the oil will be depleted in the future, it is necessary to use non-oil resources such as NR and silica. However, in that case, there is a problem that performance equal to or higher than the resistance to bending cracking and reinforcement obtained by the use of petroleum resources that have been conventionally used cannot be obtained.

  In Patent Documents 1 and 2, by having a rubber composition for a sidewall using a predetermined non-petroleum resource, the non-petroleum resource ratio in the tire is increased, and characteristics comparable to conventional tires are increased. An eco-tire having the same is disclosed.

  Patent Document 3 discloses a rubber composition for a sidewall that uses a white filler in place of carbon black made of petroleum resources as a reinforcing filler in order to improve the reinforcement and strength of the sidewall portion of the tire. ing.

However, for any of the inventions, further improvement in performance is required.
JP 2007-246710 A JP 2006-70093 A JP 2006-348222 A

  In consideration of the environment, the present invention prepares for the future reduction in the supply of petroleum resources, and without increasing the hardness, compared with a rubber composition for sidewalls mainly composed of raw materials derived from petroleum resources. Another object of the present invention is to provide a rubber composition for a sidewall that can improve both crack resistance and bending crack resistance.

  The present invention relates to 100 to 100 parts by mass of a rubber component containing 20 to 80% by mass of natural rubber and 20 to 80% by mass of at least one rubber selected from the group consisting of epoxidized natural rubber, butadiene rubber and styrene butadiene rubber. It is an unvulcanized rubber composition containing 10 to 50 parts by mass of surface-treated silica treated with a silane coupling agent having a silica content of 95% by mass or more.

  In the unvulcanized rubber composition of the present invention, the content of the silane coupling agent in the surface-treated silica is preferably 5 to 15% by mass.

  In the unvulcanized rubber composition of the present invention, the reaction rate of the rubber component with the surface-treated silica is preferably 50% or more.

  Furthermore, the present invention is a vulcanized rubber composition for a sidewall obtained by vulcanizing the unvulcanized rubber composition.

  According to the present invention, by containing a predetermined amount of a predetermined rubber component and surface-treated silica, it is environmentally friendly, and it is derived from petroleum resources without increasing hardness while preparing for a decrease in the supply amount of future petroleum resources. A vulcanized rubber composition for a sidewall which can improve both the crack resistance and the bending crack resistance can be provided as compared with the rubber composition for a sidewall mainly composed of the above raw materials.

  The unvulcanized rubber composition and the vulcanized rubber composition for sidewall of the present invention contain a rubber component and surface-treated silica.

(Rubber component)
The rubber component contains natural rubber (NR) and at least one rubber selected from the group consisting of epoxidized natural rubber (ENR), butadiene rubber (BR), and styrene butadiene rubber (SBR). It is preferable to include NR and ENR because it is environmentally friendly and uses non-oil resources to prepare for future reductions in the supply of petroleum resources. Moreover, it is preferable that NR and ENR are included also from the reason that the sea-island structure which causes two-layer separation can be produced using only raw materials derived from non-petroleum resources.

  Examples of rubber components include isoprene rubber (IR), butyl rubber (IIR), acrylonitrile butadiene rubber (NBR), ethylene propylene diene rubber (EPDM), halogenated butyl rubber (X-IIR), isomonoolefin and paraalkyl styrene. Rubbers other than NR, ENR, BR, and SBR such as copolymer halides are also listed. However, when these rubbers are used, they cannot be considered environmentally because they are derived from petroleum resources. For reasons of inferior performance, it is preferable not to include rubber other than NR, ENR, BR and SBR.

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

  The content of NR in the rubber component is 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. If the content of NR is less than 20% by mass, it is impossible to consider the environment and to prepare for a future reduction in the supply of petroleum resources, and it is impossible to obtain strength as rubber. Moreover, the content rate of NR is 80 mass% or less, Preferably it is 70 mass% or less. If the NR content exceeds 80% by mass, the island phase of the sea-island structure formed by phase separation with the rubber to be blended at the same time is reduced, and the effect of improving crack growth resistance by phase separation is insufficient. Become.

  As the ENR, a commercially available ENR may be used, or NR in the latex state may be epoxidized. The method for epoxidizing NR latex is not particularly limited, and examples thereof include a method of reacting NR latex with hydrogen peroxide water.

  The epoxidation rate of ENR is preferably 4 mol% or more, and more preferably 10 mol% or more. When the epoxidation ratio of ENR is less than 4 mol%, even if blended with NR, it is difficult to separate phases and to form a sea-island structure, so that the effect of improving crack growth resistance tends to be insufficient. The epoxidation rate of ENR is preferably 60 mol% or less, and more preferably 50 mol% or less. When the epoxidation rate of ENR exceeds 60 mol%, the embrittlement temperature becomes high and tends to be easily cracked in a low temperature range.

  When it contains ENR, the content of ENR in at least one rubber selected from the group consisting of ENR, BR and SBR is preferably 15% by mass or more, and more preferably 20% by mass or more. If the ENR content is less than 15% by mass, it is not possible to consider the environment or prepare for a future reduction in the supply of petroleum resources, and it is difficult to form a sea-island structure. There is an inadequate tendency. In particular, the content of ENR in at least one rubber selected from the group consisting of ENR, BR and SBR is most preferably 100% by mass.

  The content of at least one rubber selected from the group consisting of ENR, BR and SBR in the rubber component is 20% by mass or more, preferably 30% by mass or more. Further, the content of at least one rubber selected from the group consisting of ENR, BR and SBR is 80% by mass or less, preferably 70% by mass or less. When the content of at least one rubber selected from the group consisting of ENR, BR and SBR exceeds 80% by mass, the rubber strength decreases.

(Surface treatment silica)
As the silica, surface-treated silica in which the silica surface is pretreated with a silane coupling agent is used because the affinity between the silica surface and NR can be improved.

  The surface-treated silica means one obtained by previously treating silica with a silane coupling agent. In the present invention, the surface-treated silica is added to the rubber component during kneading. Since the present invention uses surface-treated silica, the reaction efficiency of the silane coupling agent is higher than that of a conventional method in which silica and a silane coupling agent are separately added to the rubber component and the silica is treated with the silane coupling agent during kneading. Thus, the flex cracking performance of the vulcanized rubber composition for sidewalls is improved.

  When silica is treated with a silane coupling agent, the silane coupling agent is usually used in an amount of 1 to 15%, more preferably 1 to 8% based on silica. If the ratio of the silane coupling agent to the silica is small, sufficient rubber reinforcing properties cannot be obtained. Conversely, if the amount is too large, the silane coupling agent is excessively used, which is uneconomical.

  The treatment method of silica with a silane coupling agent may be performed by attaching the silane coupling agent to silica and leaving it as it is to react the silica and the silane coupling agent. From the viewpoint of workability, it is preferable to promote the reaction and to easily evaporate the generated alcohol.

  The silica content of the hydrous silica conventionally used in the rubber industry is 80 to 95% by mass, but the silica content of the surface-treated silica contained in the rubber composition for a sidewall of the present invention is 95% by mass or more. Moreover, the content rate of the silane coupling agent in surface treatment silica is 5-15 mass%.

The BET specific surface area (BET) of the surface-treated silica is preferably 90 m ² / g or more, and more preferably 110 m ² / g or more. If the BET of the surface-treated silica is less than 90 m ² / g, the rubber strength tends to decrease. Further, the BET of the surface-treated silica is preferably 380 m ² / g or less, and more preferably 250 m ² / g or less. When the BET of the surface-treated silica exceeds 380 m ² / g, the hardness increases and the crack growth resistance tends to decrease.

  The content of the surface-treated silica is 10 parts by mass or more, preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of the surface-treated silica is less than 10 parts by mass, the rubber strength is lowered. Further, the content of the surface-treated silica is 50 parts by mass or less, preferably 40 parts by mass or less. When the content of the surface-treated silica exceeds 50 parts by mass, the hardness increases and the crack growth resistance decreases.

  When the surface-treated silica is blended, a sufficient reinforcing effect can be obtained without using a silane coupling agent in combination.

  Examples of the silica used for producing the surface-treated silica include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid) and the like. Of these, wet-process silica is preferred from the viewpoint of rubber reinforcement.

  There is no restriction | limiting in particular as a silane coupling agent used for the surface treatment of a silica, It can be used together with a silica conventionally in the rubber industry, for example, trimethoxyl silane, dimethylsilane, dimethylsiloxane, alkylsilane , Methacryloxysilane, bis (3-triethoxysilylpropyl) polysulfide, bis (2-triethoxysilylethyl) polysulfide, bis (3-trimethoxysilylpropyl) polysulfide, bis (2-trimethoxysilylethyl) polysulfide, bis (4-triethoxysilylbutyl) polysulfide, bis (4-trimethoxysilylbutyl) polysulfide and the like can be mentioned, and these silane coupling agents may be used alone or in combination of two or more.

(Other ingredients)
The unvulcanized rubber composition and the vulcanized rubber composition for sidewalls of the present invention are friendly to the earth by utilizing non-petroleum resources and are intended to prepare for a future reduction in the supply of petroleum. It is preferable not to use black, aroma oil or the like.

  In addition to the rubber component and silica (surface-treated silica), the side wall rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, such as waxes, resins, various anti-aging agents, stearic acid, Vulcanizing agents such as zinc oxide and sulfur, various vulcanization accelerators, and the like can be appropriately blended as necessary.

(Method for producing unvulcanized rubber composition)
Although the usual method can be used for the manufacturing method of the unvulcanized rubber composition of this invention, it is preferable that especially the following process 1 and 2 are included.

In step 1, NR and surface-treated silica are kneaded.
In step 2, the kneaded product discharged in step 1 and at least one rubber selected from the group consisting of ENR, BR and SBR are kneaded to obtain an unvulcanized rubber composition.

  In Step 1, a softener such as wax, various anti-aging agents, a compounding agent such as stearic acid and zinc oxide can be blended.

  Further, by kneading at least one rubber selected from the group consisting of ENR, BR and SBR in step 2 instead of step 1, the effect that the surface-treated silica is easily dispersed uniformly in NR is obtained. It is done.

  Since the unvulcanized rubber composition thus obtained uses surface-treated silica in which the silica surface is preliminarily thermally reacted with a silane coupling agent, the reaction efficiency of the silane coupling agent is improved. Therefore, the unvulcanized rubber composition of the present invention preferably has a reaction rate of the rubber component with the surface-treated silica of 50% or more. The reaction rate was determined by dissolving the unvulcanized rubber composition in toluene, and treating the portion not passing through the 50 mesh net as a reaction of the rubber component of the unvulcanized rubber composition and the surface-treated silica. Calculated.

Reaction rate (%) = (residual weight remaining in toluene (g)) × 100 / (initial unvulcanized rubber composition weight (g))
(Vulcanized rubber composition for sidewall and tire manufacturing method using the same)
A tire using the vulcanized rubber composition for a sidewall of the present invention can be produced by a usual method. That is, if necessary, the unvulcanized rubber composition of the present invention blended with the above compounding agent is extruded in accordance with the shape of the tire sidewall at the unvulcanized stage, and together with other members of the tire, the tire An unvulcanized tire is molded by molding on a molding machine by a normal method. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire using the vulcanized rubber composition for a sidewall of the present invention.

  Thus, by producing tires using the vulcanized rubber composition for sidewalls of the present invention, considering the environment and preparing for a decrease in the future supply of petroleum resources, without increasing the hardness, Even when compared with a conventional rubber composition for sidewalls mainly composed of raw materials derived from petroleum resources, an eco-tire that can improve both crack resistance and bending crack resistance can be obtained.

  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.
NR (natural rubber): TSR20
ENR (epoxidized natural rubber): ENR25 (epoxidation rate: 25 mol%) manufactured by Kunpu Langurs
BR (butadiene rubber): BR150B manufactured by Ube Industries, Ltd.
Carbon Black: Dia Black E (N ₂ SA: 41 m ² / g) manufactured by Mitsubishi Chemical Corporation
Surface-treated silica: RX200 manufactured by Nippon Aerosil Co., Ltd. (silane coupling agent: trimethylsilane, silica content: 95% by mass, BET: 200 m ² / g, (content of surface-treated silica: 8%)
Silica 1: Ultrazil VN3 manufactured by Degussa (silica content: 94% by mass, BET: 175 m ² / g)
Silica 2: 200 manufactured by Degussa (silica content: 99.5% by mass, BET: 200 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Petroleum resin: SP1068 resin manufactured by Nippon Shokubai Co., Ltd. Wax: Ozoace 0355 manufactured by Nippon Seiki
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Tsubaki stearic acid manufactured by Nippon Oil & Fats Co., Ltd.
Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noxeller CZ (N-cyclohexyl-2-made by Ouchi Shinko Kogyo Co., Ltd.) Benzothiazolylsulfenamide)
<Examples 1-3 and Comparative Examples 1-5>
In accordance with the formulation shown in Table 1, using a 1.7 L Banbury mixer, the chemical shown in Step 1 was filled so that the filling rate was 58%, and kneaded for 3 minutes until reaching 140 ° C. at 80 rpm. A kneaded product 1 was obtained. Subsequently, using a 1.7 L Banbury mixer, the chemical shown in Step 2 was filled so that the filling rate was 58%, and kneaded at 80 rpm for 2 minutes to obtain a kneaded product 2. Next, using the 8-inch roll, the chemicals shown in Step 3 were added to the obtained kneaded product 2 and kneaded for 5 minutes at 60 ° C. to obtain an unvulcanized rubber composition. Furthermore, the vulcanized rubber composition for side walls of Examples 1 to 3 and Comparative Examples 1 to 5 was prepared by vulcanizing the obtained unvulcanized rubber composition for 20 minutes at 160 ° C. Step 2 was performed only in Example 2. The following tests were conducted on the obtained unvulcanized rubber composition and the vulcanized rubber composition for sidewall.

(Reaction rate)
10 g of the unvulcanized rubber composition was dissolved in 100 ml of toluene, and the solution was filtered through a 50 mesh screen. The rate of reaction of the rubber component in the unvulcanized rubber composition with the surface-treated silica was calculated by the following formula, using the portion that could not be filtered as the residual weight.
Reaction rate (%) = (residual weight remaining in toluene (g)) × 100 / (initial unvulcanized rubber composition weight (g))
(hardness)
The hardness of the vulcanized rubber composition for the sidewall was measured with a spring type A according to JIS K 6253 “Method for testing hardness of vulcanized rubber and thermoplastic rubber”.

(Flexible crack growth test)
With respect to the vulcanized rubber composition for sidewalls, a vulcanized rubber composition sample having a thickness of 1 mm was measured under a condition of room temperature of 25 ° C. according to JIS K 6260 “Dematcher bending crack growth test method for vulcanized rubber and thermoplastic rubber”. The number of times until breakage occurred was measured, and the obtained number was expressed logarithmically. In addition, it shows that it is excellent in the bending crack-proof performance, so that a numerical value is large, and 70% and 110% show the elongation rate with respect to the length of the original vulcanized rubber composition sample.

  The evaluation results of the test are shown in Table 1.

(Evaluation results)
Examples 1 and 3 used surface-treated silica, and ENR was blended in step 1. The bending crack growth resistance test result was good.

  In Example 2, surface-treated silica was used, and ENR was blended in Step 2. The bending crack growth resistance test result was good.

  In Comparative Example 1, carbon black was used as a reinforcing agent. The bending crack growth test results were slightly inferior to the examples.

  In Comparative Example 2, wet method silica and a silane coupling agent were used. The results of the flex crack growth resistance test were inferior to those of the examples.

  In Comparative Example 3, the rubber component had an NR of 100% by mass, and wet-process silica and a silane coupling agent were used. The bending crack growth resistance test result was inferior.

  In Comparative Example 4, the rubber component had an NR of 100% by mass, and dry silica and a silane coupling agent were used. The results of the flex crack growth resistance test were inferior to those of the examples.

  In Comparative Example 5, the rubber component had an NR of 60% by mass and an ENR of 40% by mass, and dry silica and a silane coupling agent were used. The results of the flex crack growth resistance test were inferior to those of the examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (4)

  Silica content is 100 parts by mass of rubber component containing 20-80% by mass of natural rubber and 20-80% by mass of at least one rubber selected from the group consisting of epoxidized natural rubber, butadiene rubber and styrene butadiene rubber. An unvulcanized rubber composition containing 10 to 50 parts by mass of surface-treated silica treated with a silane coupling agent that is 95% by mass or more.   The unvulcanized rubber composition according to claim 1, wherein the content of the silane coupling agent in the surface-treated silica is 5 to 15% by mass.   The unvulcanized rubber composition according to claim 1 or 2, wherein a reaction rate of the rubber component with the surface-treated silica is 50% or more.   A vulcanized rubber composition for a sidewall obtained by vulcanizing the unvulcanized rubber composition according to any one of claims 1 to 3.