JP2010265413A - Rubber composition for studless tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a studless tire which improves both frictional force on ice and wet frictional force more than the conventional level. <P>SOLUTION: The rubber composition for the studless tire comprises diene-based rubber including 80-97 wt.% of natural rubber and/or butadiene rubber and 3-20 wt.% of acrylonitrile butadiene rubber, and the acrylonitrile content in the acrylonitrile butadiene rubber is 25-42 wt.%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition for studless tires, and more particularly, to a rubber composition for studless tires in which the friction force on ice and the wet friction force are improved from the conventional level.

  Pneumatic tires (studless tires) for icy and snowy roads maintain the hardness of the tread rubber flexibly even at low temperatures, thereby improving adhesion to the ice surface and improving frictional force on ice. For this reason, the rubber composition for tread is made of a diene rubber having a low glass transition temperature (Tg) such as natural rubber and butadiene rubber (for example, see Patent Document 1).

  However, in recent years, studless tires are required to improve running performance on wet roads (wet road surfaces) that are not covered with ice and snow as well as running performance on ice and snow roads described above. For this purpose, it is necessary to increase the wet friction force, and generally a styrene butadiene rubber having a high glass transition temperature (Tg) is blended. However, when a styrene butadiene rubber having a high Tg is blended, the Tg of the entire rubber composition is increased, and the rubber hardness at low temperatures is increased, resulting in a problem that the frictional force on ice is deteriorated.

  Therefore, in the rubber composition for studless tires, the friction force on ice and the wet friction force are contradictory properties, and it has been difficult to improve both.

Japanese Patent No. 3955565

  An object of the present invention is to provide a rubber composition for a studless tire in which both the friction force on ice and the wet friction force are improved from the conventional level.

  The rubber composition for studless tires of the present invention that achieves the above object comprises a diene rubber containing 80 to 97% by weight of natural rubber and / or butadiene rubber and 3 to 20% by weight of acrylonitrile butadiene rubber. The acrylonitrile content of the butadiene rubber is 25 to 42% by weight.

  Moreover, the rubber composition of this invention is good to mix | blend 0.5-20 weight part of thermally expansible microcapsules with respect to 100 weight part of said diene rubbers.

  A studless tire using the rubber composition for a studless tire in a tread portion can improve the performance on ice as compared with the conventional level and also improve the wet performance.

  The rubber composition for studless tires of the present invention is a diene rubber containing 80 to 97% by weight of natural rubber and / or butadiene rubber and 3 to 20% by weight of acrylonitrile butadiene rubber having an acrylonitrile content of 25 to 42% by weight. Because it is composed of a rubber having a low glass transition temperature (Tg) made of natural rubber and butadiene rubber as a main component, an acrylonitrile butadiene rubber having an acrylonitrile content of 25 to 42% by weight is blended while ensuring frictional force on ice. As a result, the frictional force on ice is further improved and the hysteresis loss (tan δ) at 0 ° C. to 10 ° C. is increased, so that the wet frictional force can be improved.

  The diene rubber used in the present invention comprises natural rubber and / or butadiene rubber and acrylonitrile butadiene rubber. Only one of the natural rubber and the butadiene rubber may be blended, in which case natural rubber is preferred. Moreover, you may mix | blend both natural rubber and butadiene rubber together. Natural rubber and butadiene rubber are not particularly limited, and the glass transition temperature (Tg) may be −50 ° C. or lower, preferably −55 ° C. to −110 ° C., respectively. In the present invention, the Tg of the diene rubber was measured by a differential scanning calorimetry (DSC) under a temperature increase rate condition of 20 ° C./min, and was set as the temperature at the midpoint of the transition region.

  The amount of the diene rubber containing natural rubber and / or butadiene rubber is 80 to 97% by weight, preferably 80 to 95% by weight. If the content of natural rubber and butadiene rubber is less than 80% by weight, the frictional force on ice of the rubber composition cannot be ensured. If the content of natural rubber and butadiene rubber exceeds 97% by weight, the wet friction force of the rubber composition cannot be improved.

  By blending acrylonitrile butadiene rubber having an acrylonitrile content of 25 to 42% by weight in the present invention, the friction force on ice can be further improved and the wet friction force can be improved. The reason why the wet friction force is improved is that the acrylonitrile butadiene rubber having an acrylonitrile content of 25 to 42% by weight has a tan δ peak at 0 ° C. to 10 ° C., and thus the hysteresis loss (tan δ) of the rubber composition in this temperature region It is thought to increase. On the other hand, the reason why the frictional force on ice is improved is that the acrylonitrile butadiene rubber has polarity, so that it interacts with water molecules, and when the thermally expandable microcapsule described later is blended, Since the shell material is composed of polyacrylonitrile, etc., the affinity between this shell material and diene rubber will increase, and the lack of shell material during running will be suppressed, so it is assumed that the performance on ice will be higher Is done.

  The content of acrylonitrile in the acrylonitrile butadiene rubber is 25 to 42% by weight, preferably 26 to 42% by weight. When the acrylonitrile content is less than 25% by weight, the tan δ peak of the acrylonitrile butadiene rubber becomes lower than 0 ° C., and the tan δ around 0 ° C. of the rubber composition does not increase, so that the wet friction force cannot be improved. On the other hand, when the acrylonitrile content exceeds 42% by weight, the peak of tan δ is higher than 10 ° C., and the wet friction force of the rubber composition cannot be improved. Further, the Tg of the acrylonitrile butadiene rubber is increased, and the rubber hardness in the low temperature state is increased, so that the performance on ice is deteriorated.

  The acrylonitrile butadiene rubber described above is blended in the diene rubber so as to be 3 to 20% by weight, preferably 5 to 20% by weight. When the blending amount of acrylonitrile butadiene rubber is less than 3% by weight, the wet friction force and the friction force on ice cannot be improved. On the other hand, if the amount of acrylonitrile butadiene rubber exceeds 20% by weight, the low-temperature rubber hardness increases, and the frictional force on ice cannot be ensured.

  In the studless tire rubber composition, the total Tg of the diene rubber having the above-described composition is −50 ° C. or less, preferably −55 ° C. to −110 ° C. When the Tg of the diene rubber is higher than −50 ° C., the hardness of the rubber composition at a low temperature is increased, the adhesion to the ice surface is insufficient, and the frictional force on ice is deteriorated.

  It is preferable to mix thermally expandable microcapsules with the rubber composition of the present invention. The thermally expandable microcapsule expands during vulcanization molding of an unvulcanized tire and forms a large number of resin-coated bubbles in the tread rubber. The resin-coated bubbles efficiently absorb and remove the water film generated on the ice surface, and a micro edge effect is obtained, so that the frictional force on ice is improved. The thermally expandable microcapsule has a structure in which a thermally expandable substance is included in a shell material formed of a thermoplastic resin such as polyacrylonitrile. For this reason, when the microcapsules in the rubber composition are heated during vulcanization of the unvulcanized tire, the thermally expandable substance encapsulated in the shell material expands to form resin-coated bubbles with a larger particle size of the shell material. Form. Examples of such thermally expandable microcapsules include trade name “EXPANCEL 091DU-80” or “EXPANCEL 092DU-120” manufactured by EXPANSEL, Sweden, or trade name “Microsphere” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. F-85D "or" Microsphere F-100D "can be used.

  The amount of the thermally expandable microcapsule is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of the microcapsules is less than 0.5 parts by weight, the volume of the resin-coated bubbles in the tread rubber is insufficient, and the frictional force on ice cannot be further improved. On the contrary, when the compounding quantity of a microcapsule exceeds 20 weight part, the abrasion resistance of a tread rubber will deteriorate.

  In the rubber composition of the present invention, silica is preferably blended, and the flexibility of the rubber in the low temperature state can be maintained, the adhesion to the ice surface can be increased, and the frictional force on ice can be improved. The compounding amount of silica is preferably 10 parts by weight or more, more preferably 10 to 90 parts by weight, and further preferably 15 to 80 parts by weight with respect to 100 parts by weight of the diene rubber. When the amount of silica is less than 10 parts by weight, the effect of maintaining the flexibility of the rubber at low temperatures and increasing the adhesion to the ice surface cannot be obtained sufficiently. The type of silica is not particularly limited, and those usually blended with rubber compositions can be used. Examples thereof include wet method silica, dry method silica, and surface-treated silica.

  In the present invention, by adding a silane coupling agent together with silica, the dispersibility of silica is improved and the reinforcement with rubber is improved, so that the flexibility of rubber at low temperature is improved and the frictional force on ice is further increased. Can do. The amount of the silane coupling agent is 3 to 15% by weight, preferably 5 to 10% by weight, based on the amount of silica. When the silane coupling agent is less than 3% by weight of the silica content, the effect of improving the silica dispersion may not be sufficiently obtained, and the rubber flexibility at low temperatures may not be maintained. If the silane coupling agent exceeds 15% by weight, the silane coupling agents will aggregate and condense, making it impossible to obtain the desired effect.

  Any silane coupling agent may be used as long as it can be used in a rubber composition containing silica, and a sulfur-containing silane coupling agent is particularly preferable. Examples of the sulfur-containing silane coupling agent include bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, and γ-mercaptopropyl. Examples thereof include triethoxysilane and 3-octanoylthiopropyltriethoxysilane.

  The rubber composition for studless tires of the present invention includes ordinary vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, various oils, anti-aging agents, plasticizers (softening agents), and other general rubber compositions for tires. Various additives that are blended can be blended, and the blending amount of these additives can also be a conventional general blending amount as long as the object of the present invention is not violated. The rubber composition of the present invention can be produced by mixing the above components using a normal rubber kneading machine, such as a Banbury mixer, a kneader, or a roll.

  The rubber composition of the present invention is suitable as a studless tire because both the friction force on ice and the wet friction force are improved as compared with the conventional level. The studless tire using the rubber composition of the present invention for the tread portion has a high frictional force on ice and improves the running performance on ice from the conventional level, and also has a high wet frictional force and can improve the wet running performance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  In the formulation shown in Table 1, the components excluding the vulcanization accelerator, sulfur, and thermally expandable microcapsules were kneaded for 5 minutes with a 1.7 liter closed Banbury mixer and released when the temperature reached 150 ± 5 ° C. Cooled down. Vulcanization accelerator, sulfur, and microcapsules were blended into this and mixed with a 1.7 liter closed Banbury mixer, and nine types of rubber compositions for studless tires (Examples 1 to 5 and Comparative Examples 1 to 4). Prepared.

  Nine kinds of obtained rubber compositions (Examples 1 to 5, Comparative Examples 1 to 4) were press vulcanized at 170 ° C. for 15 minutes in a predetermined mold to prepare vulcanized rubber test pieces. The frictional force on ice and wet skid of the obtained vulcanized rubber test piece were evaluated by the following methods.

Friction force on ice The obtained vulcanized rubber specimen was attached to a flat cylindrical base rubber, and the friction coefficient on ice was measured using an inside drum type on-ice friction tester. The measurement conditions were a temperature of −1.5 ° C., a load of 0.54 MPa, and a drum rotation speed of 25 km / h. The obtained results are shown in Table 1 as “friction force on ice” with Comparative Example 1 as an index of 100. The larger this index, the better the frictional force on ice.

Wet skid The wet skid of the obtained vulcanized rubber test piece was measured according to the method of ASTM E-303-83 using a portable skid tester manufactured by Stanley under wet road conditions. The obtained results are shown in Table 1 as “wet skids” with Comparative Example 1 as an index of 100. It means that wet friction force is so excellent that this index | exponent is large.

In addition, the kind of raw material used in Table 1 is shown below.
NR: natural rubber, RSS # 3, glass transition temperature -65 ° C
BR: butadiene rubber, Nipol BR1220 manufactured by ZEON Corporation, glass transition temperature of −105 ° C.
NBR1: acrylonitrile butadiene rubber, acrylonitrile content 50% by weight, Nipol DN003 manufactured by Nippon Zeon Co., Ltd.
NBR2: acrylonitrile butadiene rubber, acrylonitrile content 41% by weight, Nipol 1041 manufactured by Nippon Zeon Co., Ltd.
NBR3: acrylonitrile butadiene rubber, acrylonitrile content 34% by weight, Nipol 1042 manufactured by Nippon Zeon Co., Ltd.
NBR4: acrylonitrile butadiene rubber, acrylonitrile content 29% by weight, Nipol 1043 manufactured by Nippon Zeon Co., Ltd.
NBR5: acrylonitrile butadiene rubber, acrylonitrile content 18% by weight, Nipol DN401 manufactured by Nippon Zeon
CB: Carbon black, Toast Carbon Co., Ltd. Seast 6
Silica: Niosil AQ manufactured by Nippon Silica Industry Co., Ltd.
Coupling agent: Silane coupling agent, Dexa Si69
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads manufactured by NOF Co., Ltd. Bead stearic acid anti-aging agent: SANTOFLEX 6PPD manufactured by Flexis
Aroma oil: Showa Shell Sekiyu Extract 4 S
Sulfur: Fine powder sulfur vulcanization accelerator with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd .: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
Microcapsule: Thermally expandable microcapsule, Microsphere F100 manufactured by Matsumoto Yushi Seiyaku Co., Ltd.

Claims (3)

  A studless tire comprising a diene rubber containing 80 to 97% by weight of natural rubber and / or butadiene rubber and 3 to 20% by weight of acrylonitrile butadiene rubber, wherein the acrylonitrile content of the acrylonitrile butadiene rubber is 25 to 42% by weight. Rubber composition.   The rubber composition for studless tires according to claim 1, wherein 0.5 to 20 parts by weight of thermally expandable microcapsules is blended with 100 parts by weight of the diene rubber.   The studless tire which used the rubber composition for studless tires of Claim 1 or 2 for the tread part.