JP2009114255A - Rubber composition for tire sidewall - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire sidewall, which can reduce heat generation without impairing processability. <P>SOLUTION: The rubber composition for a tire sidewall is obtained by mixing a diene-based rubber containing ≥20 wt.% of a natural rubber with a chaff charcoal powder. The pneumatic tire includes a sidewall rubber composed of the rubber composition. The amount of the chaff charcoal powder mixed is 1-30 pts.wt. based on 100 pts.wt. of the diene-based rubber. The chaff charcoal powder includes preferably 30-90 wt.% of a silicon dioxide component and 60-5 wt.% of a carbon component. The diene-based rubber comprising the natural rubber and a polar group-containing modified natural rubber (e.g., epoxidized natural rubber) is preferably used as the diene-based rubber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire sidewall used for a sidewall portion of a pneumatic tire.

  Conventionally, as a sidewall rubber of a pneumatic tire, carbon black is generally blended as a filler in a diene rubber such as natural rubber or butadiene rubber. In recent pneumatic tires, silica particles are blended in the tread rubber as a filler in order to improve fuel efficiency, and the blending of silica particles in the sidewall rubber is also being studied.

  Silica particles can significantly reduce the heat build-up compared to carbon black, which can contribute to low fuel consumption, but on the other hand, aggregation of silica particles increases the viscosity of unvulcanized rubber. There is a drawback that the workability is remarkably deteriorated.

  By the way, the technique which mix | blends a rice husk with the rubber composition of a pneumatic tire has already been proposed for tread rubber in a studless tire (refer the following patent documents 1-3). The techniques disclosed in these documents focus on the cellulose component of rice husk and aim at the spike effect in which the rice husk scratches the ice surface. Therefore, rice husk is used as a powder processed product that is pulverized to a predetermined particle size without being carbonized, and rice husk charcoal obtained by carbonizing rice husk is not disclosed.

  In addition, it is also known to blend activated charcoal and porous carbide particles such as charcoal and bamboo charcoal for the tread rubber of studless tires (see Patent Documents 4 and 5 below), which are generated on the road surface on ice. It is added to absorb and remove the water film to increase the frictional force on ice. Moreover, the charcoal and bamboo charcoal disclosed in these documents are clearly distinguished from the rice husk charcoal used in the present invention in that the content ratio of the silicon dioxide component is low, and the effects peculiar to the present invention are not exhibited.

Patent Document 6 below discloses a flammable silicone rubber composition containing rice husk silica. However, this document focuses on only the silicon dioxide component of rice husk and uses silica obtained from the ash of the residue obtained by burning rice husk. It is not used.
Japanese Patent Laid-Open No. 02-167353 JP 11-255966 A JP 2000-351304 A JP 2000-21113 A JP 2005-162865 A Japanese Patent Laid-Open No. 11-43607

  The present invention has been made in view of the above, and an object of the present invention is to provide a rubber composition for a tire sidewall capable of reducing heat generation without impairing processability.

  The present inventor is intensively studying in view of the above problems, by blending the powder of rice husk charcoal obtained by carbonizing the rice husk as a part of the filler with respect to the specific diene rubber, As compared with carbon black, it was found that heat generation was reduced (that is, improved) while maintaining durability, and that the viscosity of the unvulcanized rubber was reduced, and the present invention was completed.

  That is, the rubber composition for a tire sidewall according to the present invention is obtained by blending rice husk charcoal powder with a diene rubber containing 20% by weight or more of natural rubber. Moreover, the pneumatic tire according to the present invention includes a sidewall rubber made of the rubber composition.

  According to the present invention, by adding rice husk charcoal powder to a rubber composition for a tire sidewall made of a diene rubber, exothermic property can be reduced without impairing workability, thus improving fuel efficiency. can do.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition according to the present invention, a diene rubber containing 20% by weight or more of natural rubber (NR) is used as the rubber component. That is, a rubber containing at least 20 parts by weight of natural rubber in 100 parts by weight of diene rubber is used. Thereby, fatigue resistance as a tire sidewall can be secured. The natural rubber here is an unmodified natural rubber that does not contain a modified natural rubber having the following polar group. The upper limit of the blending amount of the natural rubber is not particularly limited, but is preferably 60 parts by weight or less in 100 parts by weight of the diene rubber.

  As the diene rubber, those containing the natural rubber and a modified natural rubber having a polar group are particularly preferably used. The polar group includes epoxy group, hydroxyl group, carboxyl group, carbonyl group, oxycarbonyl group, oxy group, amino group, imino group, nitrile group, hydrazo group, azo group, diazo group, imide group, amide group, ammonium And groups having heteroatoms such as oxygen, nitrogen, sulfur, etc., such as a group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, and thiocarbonyl group. If it is such a polar group, it can contribute to a heat_generation | fever fall by interaction with the silicon dioxide component in rice husk charcoal powder.

  The modified natural rubber having these polar groups can be obtained by subjecting the natural rubber to a chemical treatment such as reacting the compound having the polar groups. Specific examples include epoxidized natural rubber, methyl methacrylate-modified natural rubber, maleic acid-modified natural rubber and the like, and it is particularly preferable to use epoxidized natural rubber (ENR).

  Epoxidized natural rubber is obtained by introducing an epoxy group into the double bond of the main chain of natural rubber, and can be obtained, for example, by reacting natural rubber latex with peracetic acid. The epoxidation rate of the epoxidized natural rubber is preferably 5 to 50 mol%, more preferably 15 to 40 mol%.

  As the diene rubber, other diene rubbers can be used in combination with the natural rubber and the modified natural rubber. Examples of such other diene rubbers include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), and ethylene propylene diene copolymer rubber (EPDM). And BR and SBR are preferable.

  The modified natural rubber is preferably blended in an amount of 2 to 40 parts by weight in 100 parts by weight of a diene rubber that is a rubber component. Accordingly, the diene rubber is preferably composed of 20 to 60 parts by weight of natural rubber, 2 to 40 parts by weight of modified natural rubber, and 0 to 70 parts by weight of other diene rubbers that are not essential. It is a blend of 20-50 parts by weight of natural rubber, 5-30 parts by weight of modified natural rubber, and 20-60 parts by weight of other diene rubbers. By blending 2 parts by weight or more of the modified natural rubber, the effect of reducing exothermic properties can be enhanced. If the modified natural rubber exceeds 40 parts by weight, the fatigue resistance tends to deteriorate.

The rice husk charcoal powder blended in the rubber composition is a powder of rice husk charcoal obtained by carbonizing rice husk by heating. Rice husk charcoal contains a larger amount of silicon dioxide (SiO ₂ ) component than charcoal, bamboo charcoal, etc., and this is considered to contribute to a decrease in heat generation. In particular, when a modified natural rubber having a polar group such as an epoxidized natural rubber is used as the rubber component, interaction between the silicon dioxide component in the rice husk charcoal powder and the polar group can be expected, It is considered that the exothermic property can be further reduced.

  Preferably, rice husk charcoal powder containing 30 to 90% by weight of the silicon dioxide component and 60 to 5% by weight of the carbon component is used. These component ratios can be adjusted by changing the degree of burning of the rice husk according to the carbonization conditions. By using the rice husk charcoal powder within the above range, the effect of the present invention can be further enhanced. In order to enhance the hybrid effect of the silicon dioxide component and the carbon component, the silicon dioxide component is more preferably 40 to 80% by weight and the carbon component is more preferably 40 to 15% by weight.

  The method for producing rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be pyrolyzed by steaming using a kiln to obtain rice husk charcoal. The rice husk charcoal powder can be obtained by pulverizing the rice husk charcoal obtained in this way using a known pulverizer (for example, a ball mill), selecting and classifying it into a predetermined particle size range. The particle size of the rice husk charcoal powder is not particularly limited, but the average particle size is preferably 100 μm or less, more preferably 0.1 to 50 μm. Here, the average particle diameter is a median diameter value measured using a laser diffraction particle size distribution analyzer “SALD-2000A” manufactured by Shimadzu Corporation.

  The rice husk charcoal powder is preferably blended in an amount of 1 to 30 parts by weight, more preferably 2 to 15 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of rice husk charcoal powder is too small, the effect of reducing the heat build-up will be insufficient. Conversely, if the blending amount is too large, the fatigue resistance tends to deteriorate.

  Rice husk charcoal powder is preferably used as part of the filler. That is, the rubber composition of the present invention can be used in combination with fillers such as carbon black and silica particles (wet silica, particularly precipitated silica) generally blended in tire rubber compositions. In particular, by replacing the same amount of rice husk charcoal powder with commonly used carbon black, exothermicity can be reduced without impairing durability such as ozone resistance and fatigue resistance. Processability can be improved by reducing the viscosity of the vulcanized rubber.

  When silica particles are used in combination as a filler, it is preferable to use a silane coupling agent. Any silane coupling agent may be used as long as it is conventionally used in rubber compositions together with silica particles. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, Examples thereof include bis (2-triethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-nitropropyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

  In addition to the above components, the rubber composition according to the present invention includes an anti-aging agent, wax, zinc white, stearic acid, softener, resin, sulfur and other vulcanizing agents, vulcanization accelerators, and vulcanization delays. Various additives usually blended in the rubber composition for a tire sidewall, such as an agent, can be blended.

  The rubber composition according to the present invention is obtained, for example, by kneading using a kneader such as a Banbury mixer, a kneader, or a roller. Can be configured.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(First embodiment)
Using a Banbury mixer, according to the formulation shown in Table 1 below, rubber compositions for tire sidewalls of Examples and Comparative Examples were prepared. Each component in the table is as follows.

・ NR: RSS 3
-BR: "BR01" manufactured by JSR Corporation
・ Carbon black: “Seast 3” manufactured by Tokai Carbon Co., Ltd.
Rice husk charcoal powder 1: Rice husk charcoal powder (silicon dioxide component = 60 wt%, carbon component = 38) obtained by pulverizing rice husk charcoal (“Bio charcoal” manufactured by Kansai Sangyo Co., Ltd.) with a ball mill. weight%),
Rice husk charcoal powder 2: Rice husk charcoal powder having an average particle size of 2.0 μm obtained by pulverizing rice husk charcoal (“Bio charcoal” manufactured by Kansai Sangyo Co., Ltd.) with a jet mill (silicon dioxide component = 60 wt%, carbon Component = 38% by weight),
Rice husk charcoal powder 3: Rice husk charcoal powder having an average particle size of 2.0 μm obtained by pulverizing rice husk charcoal (“Bio charcoal” manufactured by Kansai Sangyo Co., Ltd.) with a jet mill (silicon dioxide component = 75 wt%, carbon Component = 20% by weight),
Charcoal powder: charcoal powder (average particle size = 20 μm) obtained by pulverizing “minori carbon (powder)” manufactured by Nara Carbon Co., Ltd. with a ball mill,
In each rubber composition, 5 parts by weight of a petroleum hydrocarbon resin (“Quinton A100” manufactured by Nippon Zeon Co., Ltd.) and oil (Japan Energy Co., Ltd.) per 100 parts by weight of a rubber component (diene rubber) "Process X-140") 17 parts by weight, Zinc Hana (Mitsui Kinzoku Mining Co., Ltd. "Zinc Hana 1") 3 parts by weight, stearic acid (Kao Co., Ltd. "Lunac S-20") 2 parts by weight, 1 part by weight of wax (“Sannok” manufactured by Ouchi Shinsei Chemical Co., Ltd.), 4 parts by weight of an anti-aging agent (“Nocrack 6C” manufactured by Ouchi Shinsei Chemical Co., Ltd.), sulfur (“Rubber” by Hosoi Chemical Co., Ltd.) Powdered sulfur 150 mesh ") 2.1 parts by weight and a vulcanization accelerator (" Noxeller CZ "manufactured by Ouchi Shinsei Chemical Co., Ltd.) 0.7 parts by weight were blended.

  For each rubber composition, the Mooney viscosity of the unvulcanized rubber was measured, and vulcanized rubber pieces were prepared by vulcanizing at 160 ° C. for 20 minutes. For each vulcanized rubber piece, heat generation, fatigue resistance, The ozone property was evaluated. Each measurement and evaluation method is as follows.

Mooney viscosity: Measured at a temperature of 100 ° C. in accordance with JIS K6300 (L-shaped rotor), preheating 1 minute, measurement 4 minutes.

Exothermic property: Based on JIS K6265, the exothermic property of the vulcanized rubber piece was measured and displayed as an index with the value of Comparative Example 1 being 100. The smaller the index, the lower the heat generation and the better the fuel efficiency.

Fatigue resistance: The number of flexures until the occurrence of cracks was determined by a dematched flexure crack generation test in accordance with JIS K6260, and displayed as an index with the value of Comparative Example 1 being 100. It shows that it is excellent in fatigue resistance, so that an index | exponent is large.

・ Ozone resistance: Installed in an ozone weather meter device under the condition that the vulcanized rubber piece is stretched 25%, left in an environment with an ozone concentration of 100 pphm and a temperature of 50 ° C. for 24 hours, and then visually observed the occurrence of cracks The ozone resistance was evaluated according to the following criteria.
○: No cracking occurred
Δ: Cracks of 1 mm or less have occurred,
X: Cracks exceeding 1 mm are generated.

  As shown in Table 1, it can be seen that, in an example in which rice husk charcoal powder was blended, heat generation was reduced as compared with carbon black, and therefore fuel efficiency was improved. Moreover, the viscosity of the unvulcanized rubber was reduced, and the processability could be improved. In particular, in Examples 1 to 6 and 8 to 11 in which 1 to 30 parts by weight of carbon black as a filler was replaced with the same amount of rice husk charcoal powder, while maintaining ozone resistance and fatigue resistance, heat generation It was possible to reduce the viscosity of the unvulcanized rubber.

(Second embodiment)
According to the formulation shown in Table 2 below, rubber compositions for tire sidewalls of Examples and Comparative Examples were prepared in the same manner as in Example 1. ENR in Table 2 is an epoxidized natural rubber (“ENR-25” manufactured by MRB, Malaysia) having an epoxidation rate of 25 mol%, and other components are the same as those in the first example. Also, each rubber composition was added with the same common formulation as in the first example, and the Mooney viscosity, heat buildup, fatigue resistance, and ozone resistance of the unvulcanized rubber were measured in the same manner as in the first example. ,evaluated. The evaluation of exothermic property and fatigue resistance was expressed as an index with Comparative Example 3 taken as 100.

  As shown in Table 2, in the example in which rice husk charcoal powder was blended, the exothermic property was lowered as compared with carbon black, and the viscosity of unvulcanized rubber was reduced. In particular, in Examples 12 to 16 in which 30 parts by weight or less of carbon black as a filler was replaced with rice husk charcoal powder, heat resistance and unvulcanized rubber viscosity were reduced while maintaining ozone resistance and fatigue resistance. I was able to.

(Third embodiment)
According to the formulation shown in Table 3 below, rubber compositions for tire sidewalls were prepared in the same manner as in the second example, while changing the blend ratio of epoxidized natural rubber (ENR) and unmodified natural rubber (NR). Each component in Table 3 and the common formulation are the same as in the second example, and for each of the resulting rubber compositions, the Mooney viscosity, heat buildup, fatigue resistance, and ozone resistance of the unvulcanized rubber are the same. Was measured and evaluated. The evaluation of exothermicity and fatigue resistance was expressed as an index with Example 18 as 100.

  As shown in Table 3, the exothermic reduction effect could be enhanced by increasing the blend ratio of the epoxidized natural rubber. However, when the blending amount of natural rubber was less than 20 parts by weight as in Comparative Examples 4 and 5, the fatigue resistance was greatly deteriorated.

  The present invention can be used for various pneumatic tires including radial tires for passenger cars.

Claims (6)

  A rubber composition for tire sidewalls, in which rice husk charcoal powder is blended with diene rubber containing 20% by weight or more of natural rubber.   The rubber composition for a tire sidewall according to claim 1, wherein the rice husk charcoal powder is blended in an amount of 1 to 30 parts by weight with respect to 100 parts by weight of the diene rubber.   The rubber composition for a tire sidewall according to claim 1 or 2, wherein the rice husk charcoal powder contains 30 to 90% by weight of a silicon dioxide component and 60 to 5% by weight of a carbon component.   The rubber composition for a tire sidewall according to any one of claims 1 to 3, wherein the diene rubber includes a modified natural rubber having a polar group together with the natural rubber.   The rubber composition for a tire sidewall according to claim 4, wherein the modified natural rubber having a polar group is an epoxidized natural rubber.   A pneumatic tire comprising a sidewall rubber made of the rubber composition according to any one of claims 1 to 5.