JP2009114251A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread by which the balance of rolling resistance properties and wet properties can be improved while improving processability. <P>SOLUTION: The rubber composition for the tire tread contains a 1-80 pts.wt. chaff charcoal powder based on a 100 pts.wt. rubber component comprising a single modified natural rubber having a polar group (e.g., an epoxidized natural rubber) or a blend of the modified natural rubber with other diene rubbers. A pneumatic tire has the tread comprising the rubber composition. The chaff charcoal powder preferably contains a 30-90 wt.% silicon dioxide component and a 60-5 wt.% carbon component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Recent pneumatic tires are required to improve the balance between wet performance, which is grip performance on wet road surfaces, and rolling resistance performance, which contributes to low fuel consumption. Silica particles are blended as a filler in a rubber component made of rubber and / or a diene synthetic rubber.

  Compared with carbon black, silica particles can remarkably reduce the exothermic property that contributes to rolling resistance performance, but on the other hand, the aggregation of silica particles increases the viscosity of unvulcanized rubber, and the processability is remarkable. There is a drawback that it gets worse.

  By the way, the technique which mix | blends a rice husk with the rubber composition which comprises the tread of a pneumatic tire has already been proposed for studless tires (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, in the rubber composition for a tread of a studless tire, it is also known to incorporate activated carbon, porous carbide particles such as charcoal and bamboo charcoal (see Patent Documents 4 and 5 below). It is formulated to absorb and remove the water film generated on the surface to increase the frictional force on ice. In addition, 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 specific to the present invention are not exhibited. is there.

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

  This invention is made | formed in view of the above, and it aims at providing the rubber composition for tire treads which can improve the balance of rolling resistance performance and wet performance, improving workability.

  The present inventor has been diligently considering in view of the above problems, and rolling the powder by blending a powder of rice husk charcoal obtained by carbonizing rice husk as a filler into a modified natural rubber having a polar group. It has been found that the resistance performance is improved over that of an equivalent amount of silica particles and that the viscosity of the unvulcanized rubber is reduced, and the present invention has been completed.

  That is, the rubber composition for a tire tread according to the present invention comprises rice husk charcoal with respect to 100 weight of a rubber component composed of a modified natural rubber having a polar group alone or a blend of the modified natural rubber and another diene rubber. It contains 1 to 80 parts by weight of powder. Moreover, the pneumatic tire according to the present invention includes a tread made of the rubber composition.

  According to the present invention, by adding rice husk charcoal powder to a modified natural rubber having a polar group, it is possible to improve the balance between rolling resistance performance and wet performance over an equivalent amount of silica particles, and unvulcanized Processability can be improved because the viscosity of the rubber is lowered.

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

  In the rubber composition according to the present invention, the rubber component is composed of a modified natural rubber having a polar group alone or a blend of the modified natural rubber and another diene rubber.

  The polar groups include 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. With such a polar group, the balance between the rolling resistance performance and the wet performance can be improved by the interaction with the silicon dioxide component in the 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%.

  Examples of other diene rubbers include unmodified natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), and ethylene propylene diene copolymer rubber. Various diene rubbers such as (EPDM) can be used, and these may be used alone or in combination of two or more.

  The other diene rubber can be blended in 0 to 80 parts by weight in 100 parts by weight of the rubber component. That is, the rubber component is composed of a modified natural rubber having a polar group alone or a blend of 20 parts by weight or more of the modified natural rubber and 80 parts by weight or less of another diene rubber. When the modified natural rubber is less than 20 parts by weight, wet performance is impaired. More preferably, it is a blend of 100 to 50 parts by weight of the modified natural rubber and 0 to 50 parts by weight of another diene rubber.

  Further, as other diene rubbers, unmodified natural rubber is particularly suitable. Therefore, the rubber component is composed of epoxidized natural rubber alone or a blend of epoxidized natural rubber and unmodified natural rubber. Is preferred.

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 or bamboo charcoal, and this is considered to contribute to the improvement of rolling resistance performance. In particular, since a modified natural rubber having a polar group such as an epoxidized natural rubber is used as a rubber component, an interaction between the silicon dioxide component in the rice husk charcoal powder and the polar group can be expected. The balance between resistance performance and wet performance can be improved.

  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.

  Rice husk charcoal powder is blended in an amount of 1 to 80 parts by weight with respect to 100 parts by weight of the rubber component. When the blending amount of rice husk charcoal powder is too small, the effect of improving the rolling resistance performance is insufficient. Conversely, when the blending amount is too large, the physical properties decrease and the wet performance tends to decrease. In order to improve rolling resistance performance while maintaining reinforcement and wet performance, the amount of rice husk charcoal powder is more preferably 2 to 40 parts by weight, more preferably 100 parts by weight of rubber component. 4 to 20 parts by weight.

  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 silica particles, the rolling resistance performance can be improved without impairing the reinforcement and wet performance, and the viscosity of the unvulcanized rubber can be improved. As a result, the workability can be improved.

  When blending silica particles, 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.

  The rubber composition according to the present invention includes an anti-aging agent, wax, zinc white, stearic acid, softener, vulcanizing agent such as sulfur, vulcanization accelerator, vulcanization retarder, etc. Various additives usually blended in a rubber composition for a tire tread can be blended.

  The rubber composition according to the present invention can be obtained, for example, by kneading using a kneader such as a Banbury mixer, a kneader, or a roller, and vulcanized and molded according to a conventional method to obtain tread rubber for various pneumatic tires. Can be configured.

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

  Using a Banbury mixer, according to the formulations shown in Tables 1 and 2 below, rubber compositions for tire treads of Examples and Comparative Examples were prepared. Each component in the table is as follows.

ENR25: Epoxidized natural rubber (“ENR-25” manufactured by MRB, Malaysia) with an epoxidation rate of 25 mol%,
NR: unmodified natural rubber (RSS 3),
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,
・ Silica particles: “Nippal AQ” manufactured by Tosoh Silica Co., Ltd.
Silane coupling agent: “Si69” manufactured by Degussa
Carbon black: “Seast 3” manufactured by Tokai Carbon Co., Ltd.

  In each rubber composition, 15 parts by weight of oil (“Process X-140” manufactured by Japan Energy Co., Ltd.) and zinc white (“Zinc Hana 1” manufactured by Mitsui Mining & Smelting Co., Ltd.) are used as a common compound. No. "), 3 parts by weight, 2 parts by weight of stearic acid (" Lunac S-20 "manufactured by Kao Corporation), 2 parts by weight of anti-aging agent 6C (" NOCRACK 6C "manufactured by Ouchi Shinsei Chemical Co., Ltd.), wax (large 2 parts by weight of Uchisei Shin Chemical Co., Ltd. “Sannok”), 2 parts by weight of sulfur (“Powders sulfur 150 mesh for rubber” manufactured by Hosoi Chemical Co., Ltd.), CBS (Ouchi Shinsei Chemical Co., Ltd.) "Noxeller CZ") 1.5 parts by weight was blended.

  For each rubber composition, the Mooney viscosity of the unvulcanized rubber was measured and vulcanized at 160 ° C. for 20 minutes to produce a vulcanized rubber piece. The physical properties (hardness, 100%, 300% modulus, tensile strength, elongation at break, tear strength) were measured. In addition, each rubber composition is applied to a cap tread of a tire having a tread having a cap / base structure, and a 205 / 65R159H pneumatic radial tire is manufactured according to a conventional method, and rolling resistance, wet performance, and wear resistance are produced. 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.

Hardness: Based on JIS K6253, the hardness was measured at 23 ° C. using a type A durometer (A type).

Modulus, tensile strength, elongation at break: measured by a tensile test according to JIS K6251 (dumbbell shape No. 3).

-Tear strength: Measured according to JIS K6252 (Crescent test piece).

Rolling resistance performance: The rolling resistance was measured when running at 80 km / h at 23 ° C. with a single-axis drum tester for measuring rolling resistance at an air pressure of 230 kPa and a load of 450 kgf. The results were expressed as an index with the value of Comparative Example 1 as 100. The smaller the index, the smaller the rolling resistance and thus the better the fuel efficiency.

・ Wet performance: A 2000cc domestic FF car is equipped with four tires, runs on asphalt roads with water depth of 2-3mm, operates ABS at 90km / h, decelerates to 20km / h The braking distance was measured. The results were expressed as an index with the value of Comparative Example 1 as 100. A larger index indicates better wet performance.

-Abrasion resistance: Four tyres were mounted on a 2000cc domestic FF vehicle, and the amount of wear was determined from the tread remaining groove depth after running 20,000 km while rotating every 5000 km on the general road surface of dry asphalt. The results were expressed as an index with the value of Comparative Example 1 as 100. It shows that it is excellent in abrasion resistance, so that an index | exponent is small.

  As shown in Tables 1 and 2, the epoxidized natural rubber blended with rice husk charcoal powder as a filler can improve the balance between rolling resistance performance and wet performance over the equivalent amount of silica particles. In addition, the viscosity of the unvulcanized rubber was lowered and the processability was improved.

  In addition, when the amount of rice husk charcoal powder is 4 to 40 parts by weight, there is almost no adverse effect on the physical properties, the rolling resistance performance is good, but the wet performance is slightly reduced, and the wear resistance is also particularly reduced. It was not seen (see Examples 1-4 and 6-11). When the blended amount of rice husk charcoal powder is 80 parts by weight (Examples 5 and 12), although the rolling resistance performance is very excellent, the wet performance tends to decrease, and the physical properties are slightly decreased. Charcoal powder should be blended at 80 parts by weight or less.

  When the modified natural rubber is 20 parts by weight, the rolling resistance performance is excellent, but the wet performance is low (see Example 13). Therefore, the modified natural rubber is preferably blended at 20 parts by weight or more. Note that, as in Comparative Example 5, when the unmodified natural rubber was used alone, the wet performance was greatly reduced.

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

Claims (4)

  A rubber for tire tread containing 1 to 80 parts by weight of rice husk charcoal powder with respect to 100 parts by weight of a rubber component composed of a modified natural rubber having a polar group alone or a blend of the modified natural rubber and another diene rubber. Composition.   The rubber composition for a tire tread according to claim 1, wherein the modified natural rubber having a polar group is an epoxidized natural rubber.   The rubber composition for a tire tread according to claim 1, 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.   A pneumatic tire provided with the tread which consists of a rubber composition of any one of Claims 1-3.