JP2011148897A - Rubber composition for studless tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for studless tire which suppresses hardening due to aging with time. <P>SOLUTION: The rubber composition for studless tire is obtained by blending 0.5-20 pts.wt. thermally expandable microcapsule, 1-30 pts.wt. microcapsule in which vegetable oil and fat containing polyphenol originating in natural material is encapsulated and 10-120 pts.wt. silica in 100 pts.wt. diene based rubber and further blending 1-12 wt.% silane coupling agent to the blended amount of silica. <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 that suppresses curing associated with aging.

  The tread part of a studless tire (pneumatic tire for snowy roads) uses a rubber composition that is designed to optimize the rubber hardness at low temperatures to ensure excellent grip performance even when driving on snowy snowy roads. Has been. However, even if the rubber hardness is optimal at the start of use of the tire, there is a problem that the frictional force on ice is lowered because the rubber is cured by aging when used for a long time.

  As such an anti-aging measure, it is conceivable to increase the amount of the anti-aging agent blended in the rubber composition for studless tires. However, even if the amount of the anti-aging agent is increased, the rubber curing due to aging cannot be sufficiently suppressed, or the anti-aging agent is transferred to the tire surface, so that the tire surface turns brown and the appearance There was a problem that was damaged.

  As a countermeasure against this, Patent Document 1 proposes a tire rubber composition in which a thermally expandable microcapsule containing a thermally expandable substance and a nonpolar oil is blended. However, in this rubber composition, although the oil contained in the capsule gradually migrates into the rubber, an increase in rubber hardness can be suppressed. There was room for improvement.

JP 2009-138181 A

  An object of the present invention is to provide a rubber composition for studless tires that is capable of reducing the curing due to aging.

  The rubber composition for studless tires of the present invention that achieves the above-mentioned object is a microencapsulated product comprising 100 to 10 parts by weight of a diene rubber, 0.5 to 20 parts by weight of thermally expandable microcapsules, and vegetable oils and fats containing natural polyphenols. 1 to 30 parts by weight of capsules and 10 to 120 parts by weight of silica are blended, and 1 to 12% by weight of a silane coupling agent is blended with respect to the amount of silica blended.

The diene rubber may be at least one selected from natural rubber, butadiene rubber, and styrene-butadiene rubber. Moreover, it is preferable that the said vegetable oil and fat contains the said polyphenol 0.9x10 < ^-3 > weight% or more, and also it is good that it is grape seed oil.

  The rubber composition for studless tires of the present invention comprises 1 to 30 microcapsules containing 0.5 to 20 parts by weight of thermally expandable microcapsules and vegetable oils and fats containing natural polyphenols in 100 parts by weight of diene rubber. Since 10 parts by weight and 10 to 120 parts by weight of silica are blended, and 1 to 12% by weight of the silane coupling agent is blended with respect to silica, polyphenols are extracted from microcapsules containing vegetable oils and fats dispersed in rubber products. In order to prevent the rubber component from aging due to the gradual release of vegetable oils and fats and the antioxidant action of this polyphenol, curing due to aging can be suppressed. In addition, since vegetable oils and fats containing polyphenols are encapsulated in microcapsules, the consumption of polyphenols during the molding and vulcanization of the rubber composition for studless tires is suppressed, and the aging of rubber components is prevented. Can act selectively.

  In the rubber composition for studless tires of the present invention, the rubber component is a diene rubber. As the diene rubber, those having a glass transition temperature (hereinafter referred to as “Tg”) of preferably −50 ° C. or less, more preferably −120 ° C. to −55 ° C. may be used. By setting the Tg of the diene rubber to −50 ° C. or less, the frictional force on ice of the rubber composition can be secured at a high level. The Tg of the diene rubber is measured by a differential scanning calorimetry (DSC) under a heating rate condition of 10 ° C./min, and is defined as the temperature at the midpoint of the transition region. In addition, when diene rubber contains oil extended oil, it is set as the glass transition temperature of the state except oil extended oil.

  Such a diene rubber is not particularly limited, and examples thereof include natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and butyl rubber. Of these, natural rubber, butadiene rubber, and styrene-butadiene rubber are preferable. These diene rubbers can be used alone or as a blend of plural kinds. Of these, natural rubber (NR) and butadiene rubber (BR) are preferably blended as the diene rubber, and the weight ratio between the two is preferably NR: BR = 1: 9 to 9: 1, more preferably NR: BR =. It is good to use 3: 7-7: 3. By making the weight ratio of NR and BR within such a range, it is possible to make the rubber composition excellent in molding processability and wear resistance while taking advantage of the excellent low-temperature performance of BR.

  The rubber composition for studless tires of the present invention improves the frictional force on ice by blending thermally expandable microcapsules. That is, a rubber composition containing thermally expandable microcapsules is used in the tread portion to form an unvulcanized tire and heated in the vulcanization process, whereby the thermally expandable microcapsules expand to form resin-coated bubbles. By forming a large number of resin-coated bubbles in the tread rubber in this way, the water film on the icy road surface is absorbed and removed when the tread steps on the icy road surface. By repeatedly stepping on the road surface, it is possible to improve the frictional force on ice against the ice surface of the tread.

  The thermally expandable microcapsule used in the present invention has a structure in which a thermally expandable substance is encapsulated in a shell material formed of a thermoplastic resin such as polyacrylonitrile. For this reason, when the thermally expandable microcapsule is heated, the thermally expandable substance contained in the shell material expands to increase the particle size of the shell material, and a large number of resin-coated bubbles are formed in the tread rubber. These 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 increases. 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-85 "or" Microsphere F-100 "can be used.

  In this invention, the compounding quantity of a thermally expansible microcapsule is 0.5-20 weight part with respect to 100 weight part of diene rubbers, Preferably it is 1-15 weight part. When the amount of the thermally expandable microcapsule is less than 0.5 parts by weight, the volume of the resin-coated bubbles formed in the tread rubber is insufficient, and a sufficient frictional force on ice cannot be obtained. Moreover, when the compounding quantity of a thermally expansible microcapsule exceeds 20 weight part, the abrasion resistance of a tread rubber will deteriorate.

  The rubber composition for studless tires of the present invention is dispersed in a rubber composition by blending microcapsules enclosing vegetable oils and fats containing polyphenols as natural components (hereinafter referred to as “vegetable oil and fat-containing microcapsules”). The vegetable oil and fat are gradually released from the vegetable oil and fat-containing microcapsules, and the rubber component is prevented from aging due to the antioxidant action of the polyphenol contained in the vegetable oil and fat. In addition, since the vegetable oil containing polyphenol is encapsulated in the microcapsule, the polyphenol is prevented from being thermally decomposed or consumed in contact with oxygen during molding and vulcanization of the rubber composition. For this reason, polyphenol can be made to selectively act to prevent aging of the rubber component. Therefore, when the blending amount of the vegetable oil and fat containing polyphenols to the diene rubber is the same, it is better to encapsulate the vegetable oil and fat in the microcapsule than when the vegetable oil and fat are blended as they are. The effect of preventing is excellent and the curing of rubber can be further reduced.

  In the present invention, since vegetable oils and fats containing naturally derived polyphenols are encapsulated in microcapsules, they are characterized by excellent safety and hygiene. That is, the vegetable fats and oils used in the present invention do not contain natural polyphenols and / or chemically synthesized polyphenol antioxidants by artificial manipulation.

The naturally-derived polyphenol content in the vegetable oil is preferably 0.03 × 10 ⁻³ wt% or more, more preferably 0.9 × 10 ⁻³ wt% or more, and even more preferably 1.1 × 10 ⁻³ wt. % Or more. When the content of polyphenol in the vegetable oil is less than 0.03 × 10 ⁻³ wt%, the antioxidant action cannot be sufficiently obtained and the rubber component cannot be inhibited from curing. The polyphenol content in the vegetable oil was determined by the foreign-thiocult method. The foreign-thiocult method uses a foreign-thiocult reagent that develops a blue color under strong alkali against a reducing substance. Polyphenols in a sample (vegetable oil) are collectively collected by a colorimetric method (660 nm). It was measured as the amount of polyphenol. In addition, (+)-catechin was used as a standard sample, and the amount of polyphenol was determined from the calibration curve.

  Examples of vegetable oils and fats containing naturally derived polyphenols include grape seed oil, olive oil, safflower oil, sunflower oil, canola oil, walnut seed oil, sesame oil, and the like. These vegetable fats and oils can be used alone. A plurality of types may be blended and used.

As vegetable oils and fats, grape seed oil and olive oil are particularly preferable. Grape seed oil is produced all over the world, but chilean grape seed oil is particularly preferable because it has an extremely high polyphenol content of 1.1 × 10 ⁻³ wt% or more. However, in addition to Chilean grape seed oil, the same effect can be expected if it is a vegetable oil containing 0.9 × 10 ⁻³ wt% or more of polyphenol due to variety improvement or the like. Grape seed oil contains a large amount of naturally occurring polyphenols and also contains a lot of vitamin E. Since vitamin E has an antioxidant effect, it prevents aging of the rubber composition for studless tires together with polyphenols and suppresses curing.

  The shell material of the vegetable oil-and-fat microcapsule prevents the vegetable oil and fat containing polyphenol from coming into contact with oxygen during the molding process and vulcanization of the rubber composition, and prevents the polyphenol from being consumed by oxidation. In addition, after vulcanization, vegetable oil and fat containing polyphenol is gradually released into a rubber product such as a pneumatic tire so that the rubber component can be prevented from being cured by aging.

  Such shell material of vegetable oil-containing microcapsules can be formed of a thermoplastic resin useful as a normal microencapsulating agent. The thermoplastic resin is formed by polymerizing a polymerizable component in the presence of a polymerization initiator. The polymerizable component generally includes a monomer component called a (radical) polymerizable monomer having at least one polymerizable double bond. The monomer component is not particularly limited. For example, nitrile monomers such as acrylonitrile; carboxyl group-containing monomers such as acrylic acid and methacrylic acid; vinylidene chloride; vinyl halide monomers such as vinyl chloride Monomer; vinyl ester monomer such as vinyl acetate; (meth) acrylic acid ester monomer such as methyl (meth) acrylate and ethyl (meth) acrylate; styrene monomer such as styrene and α-methylstyrene Acrylamide monomers such as acrylamide; ethylenically unsaturated monoolefin monomers such as ethylene and propylene. These monomer components may be used alone or in combination of two or more.

  The polymerizable component may contain a polymerizable monomer (crosslinking agent) having two or more polymerizable double bonds in addition to the monomer component. By polymerizing using a cross-linking agent, the heat resistance and solvent resistance of the microcapsule shell material can be improved, and the release speed of vegetable oil and fat in the rubber product can be controlled.

  The crosslinking agent is not particularly limited. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; allyl methacrylate, triacryl formal, triallyl isocyanate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) Acrylate, triethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, PEG # 200 Di (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, Trimethylo Propane trimethacrylate, glycerin dimethacrylate, dimethylol-tricyclodecane diacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, neopentyl glycol acrylate benzoate, trimethylol propane benzoate Acid esters, 2-hydroxy-3-acryloyloxypropyl methacrylate, hydroxypivalate neopentyl glycol diacrylate, ditrimethylolpropane tetraacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate and the like ( Mention may be made of (meth) acrylate compounds. These crosslinking agents may be used alone or in combination of two or more. In the above, a series of compounds described as “PEG # OOXX di (meth) acrylate” means polyethylene glycol di (meth) acrylate.

  The method for producing vegetable oil-containing microcapsules of the present invention always includes a polymerizable component, vegetable oil and fat, an aqueous dispersion medium containing water as an essential component, and a polymerization aid such as an electrolyte and a water-soluble additive as necessary. It is carried out by mixing the components such as the dispersion stabilizer and the dispersion auxiliary stabilizer and polymerizing the polymerizable component. The order of blending these components is not particularly limited, and components that can be dissolved or dispersed in the aqueous dispersion medium may be blended in advance and blended with other components.

  In the method for producing vegetable oil-containing microcapsules, an oily mixture such as a polymerizable component and vegetable oil is emulsified and dispersed in an aqueous dispersion medium so that spherical oil droplets having a predetermined particle diameter are prepared. Examples of the method for emulsifying and dispersing the oily mixture include, for example, a method of stirring with a homomixer (for example, manufactured by Special Machine Engineering Co., Ltd.), a homodisper (for example, manufactured by Special Machine Engineering Co., Ltd.), or the like, or a static mixer (for example, manufactured by Noritake Engineering Co., Ltd.). And the like, a general dispersion method such as a method using a static dispersion apparatus such as a membrane emulsification method, an ultrasonic dispersion method, and a microchannel method.

  Next, suspension polymerization is started by heating the dispersion in which the oily mixture is dispersed as spherical oil droplets in the aqueous dispersion medium. Although superposition | polymerization temperature is freely set by the kind of polymerization initiator, Preferably it is 30-100 degreeC, More preferably, it is 40-90 degreeC, More preferably, it controls in the range of 50-85 degreeC. The time for maintaining the reaction temperature is preferably about 0.1 to 20 hours.

  After completion of the polymerization reaction, the dispersion stabilizer is decomposed with hydrochloric acid or the like, if desired, and the resulting product (microcapsule) is isolated from the dispersion by an operation such as suction filtration, centrifugation, or centrifugal filtration. Furthermore, the water-containing cake of the obtained microcapsule can be washed with water and dried to obtain a vegetable oil-and-fat-containing microcapsule.

  The content of vegetable oil in the vegetable oil-containing microcapsule is preferably 10 to 70% by weight, more preferably 20 to 50% by weight. When the vegetable oil content in the vegetable oil-containing microcapsule is less than 10% by weight, the period for suppressing the aging of the rubber composition for studless tires is shortened. On the other hand, if the content of vegetable oil exceeds 70% by weight, it becomes difficult to produce microcapsules, and it becomes fragile during molding and vulcanization.

  In the present invention, the size of the vegetable oil-and-fat-containing microcapsules is not particularly limited, but is preferably 1 to 100 μm in diameter, more preferably 5 to 50 μm in diameter. When the diameter of the microcapsule is less than 1 μm, the amount of the vegetable fat / oil is reduced. Moreover, when the diameter of a microcapsule exceeds 100 micrometers, it will become difficult to include vegetable fats and oils, and it will become easy to break during rubber molding or vulcanization.

  The amount of the vegetable oil-and-fat-containing microcapsules containing polyphenol is 1 to 30 parts by weight, preferably 2 to 25 parts by weight, per 100 parts by weight of the diene rubber. When the blending amount of the vegetable oil-and-fat microcapsules is less than 1 part by weight, the antioxidant effect of polyphenol cannot be sufficiently obtained, and the rubber component cannot be inhibited from curing due to aging. Moreover, even if it mix | blends vegetable oil and fat containing microcapsule more than 30 weight part, not only the further improvement effect will be acquired, but abrasion resistance will fall.

  The rubber composition for studless tires of the present invention, by adding silica, ensures rubber flexibility at low temperatures (softness at low temperatures), improves adhesion of treads to ice surfaces, and friction on ice. The power can be improved. Furthermore, by adding silica, the wet grip performance (0 ° C. tan δ) on a wet road surface (wet road surface) not covered with ice and snow is increased, and the exothermic property (60 ° C. tan δ) of the rubber composition is reduced. The rolling resistance of the tire can be reduced.

Silica having a BET specific surface area of 70 to 300 m ² / g, preferably 70 to 280 m ² / g is used. When the BET specific surface area of silica is less than 70 m ² / g, the reinforcing property for the rubber composition becomes insufficient. Further, if the BET specific surface area of silica exceeds 300 m ² / g, the dispersibility of silica is deteriorated and the processability of rubber is deteriorated, which is not preferable. In the present invention, the BET specific surface area of silica is measured according to ASTM-D-4820-93. The silica may be any silica that is usually blended in a tire rubber composition. For example, wet method silica, dry method silica, or surface-treated silica can be used.

The compounding quantity of a silica is 10-120 weight part with respect to 100 weight part of diene rubbers, Preferably it is 10-90 weight part. If the amount of silica is less than 10 parts by weight, the frictional force on ice (flexibility at low temperatures) and wet grip performance (tan δ at 0 ° C.) cannot be increased. Moreover, when the compounding quantity of a silica exceeds 120 weight part, the workability of rubber will deteriorate remarkably.

  In this invention, the dispersibility of the silica with respect to a diene rubber can be improved by mix | blending a silane coupling agent with a silica. The amount of the silane coupling agent is 1 to 12% by weight, preferably 3 to 10% by weight, based on the amount of silica. When the amount of the silane coupling agent is less than 1% by weight, the dispersibility of silica cannot be sufficiently improved. Moreover, when the compounding quantity of a silane coupling agent exceeds 12 weight%, silane coupling agents will aggregate and condense, and it will become impossible to acquire a desired effect.

  Although it does not restrict | limit especially as a kind of silane coupling agent, A sulfur containing silane coupling agent is 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.

  In the present invention, carbon black can be blended. By blending carbon black, the strength of the rubber composition for studless tires is increased and the wear resistance is improved. The compounding amount of carbon black is preferably 10 to 100 parts by weight, more preferably 20 to 90 parts by weight with respect to 100 parts by weight of the diene rubber. When the compounding amount of the carbon black is less than 10 parts by weight, the rubber composition cannot be sufficiently reinforced and hardened and wear resistance is insufficient. Moreover, when the compounding quantity of carbon black exceeds 100 weight part, the viscosity of a rubber composition will become high and molding processability will deteriorate.

  In addition to silica and carbon black, other inorganic fillers can be blended in the rubber composition for studless tires of the present invention. As other inorganic fillers, for example, clay, calcium carbonate, talc, mica, aluminum hydroxide, magnesium carbonate and the like can be blended as necessary.

  The studless tire rubber composition contains various additives generally used in tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, processing aids, anti-aging agents, oils, and plasticizers. These additives can be compounded and kneaded by a general method to obtain a rubber composition for studless tires, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for studless tires can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  Since the studless tire constituted by the rubber composition for studless tires of the present invention prevents aging and suppresses curing, the product life can be extended. In particular, this rubber composition is suitable for constituting the tread portion of a studless tire, and suppresses the curing due to aging of the tread portion and consumes polyphenols in the microcapsules containing vegetable oils and fats during molding and vulcanization. Therefore, since it is contained in a large amount in the tread, it can be made to selectively act to prevent aging of the tread rubber.

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

Manufacture of vegetable oil-and-fat-containing microcapsules (microcapsules encapsulating grape seed oil) As an aqueous system, add 40 g of colloidal silica with a solid content of 40%, 0.5 g of diethanolamine-adipic acid condensate, 150 g of sodium chloride, and 500 g of ion-exchanged water. After mixing, the pH was adjusted to 3.5 to prepare an aqueous dispersion medium. As an oil system, 100 g of acrylonitrile, 50 g of methacrylonitrile, 50 g of methacrylic acid, 1 g of ethylene glycol dimethacrylate, 3 g of azobis (2,4-dimethylvaleronitrile) are mixed, and grape seed oil (Grape Seed Oil from Chile, Catac 90 g of planner's edible grape oil) was further added to prepare an oily mixture.

  The aqueous dispersion medium and the oily mixture were mixed, and the resulting mixture was dispersed with a homomixer (TK homomixer manufactured by Tokushu Kika Kogyo Co., Ltd.) at a rotation speed of 9000 rpm for 5 minutes to prepare a suspension. This suspension was charged into an autoclave, purged with nitrogen, and reacted at a reaction temperature of 60 ° C. and a reaction pressure of 0.5 MPa for 8 hours to obtain vegetable oil-containing microcapsules. The vegetable oil and fat-containing microcapsules contained 30% by weight of grape seed oil, and the average particle size was 19 μm.

Production of oil-containing microcapsules (microcapsules encapsulating naphthenic oil) In the production of the above vegetable oil-and-fat microcapsules, oil-containing microcapsules were produced in the same procedure except that grape seed oil was changed to naphthenic oil. The oil-containing microcapsules contained 30% by weight of naphthenic oil, and the average particle size was 22 μm.

Preparation and Evaluation of Studless Tire Rubber Composition Eight types of studless tire rubber compositions (Examples 1 to 4 and Comparative Examples 1 to 4) having the formulations shown in Tables 1 and 2 were respectively used as a vulcanization accelerator and sulfur. In addition, the ingredients except for the microcapsules (vegetable oil-and-fat-containing microcapsules or oil-containing microcapsules, heat-expandable microcapsules) are weighed, kneaded for 5 minutes in a 1.7 L closed Banbury mixer, and a master batch is prepared at a temperature of 150 ° C. Release and cool to room temperature. Then, this master batch is subjected to a 1.7 L hermetic Banbury mixer, and a vulcanization accelerator, sulfur and various microcapsules (vegetable oil-containing microcapsules or oil-containing microcapsules, thermally expandable microcapsules) are added and mixed for 2 minutes. A rubber composition for a studless tire was prepared.

  By using the eight rubber compositions for studless tires obtained, the following methods were used to increase the rubber hardness (aging hardness increase rate) before and after the heat aging test, the frictional force on ice, and the friction on ice after the heat aging treatment. The force was measured.

Aging hardness increase rate Using the obtained rubber composition for studless tires, a test piece vulcanized into a shape of a Rupke sample (a cylindrical shape having a thickness of 12.5 mm and a diameter of 29 mm) was prepared. Each test piece was divided into two groups, and one of them was subjected to air heat aging treatment at 80 ° C. for 120 hours. Using the test specimens before and after the aging treatment, the rubber hardness at a temperature of 20 ° C. was measured by a durometer type A in accordance with JIS K6253, and each (rubber hardness after aging treatment / rubber hardness before aging treatment × 100) Was used to calculate the rate of increase in rubber hardness (%) accompanying heat aging. The obtained results are shown in Tables 1 and 2 as “aging hardness increase rate” with the index of Comparative Example 1 being 100 in Table 1 and the value of Comparative Example 4 being 100 in Table 2. It means that the smaller the index is, the more the curing of the rubber composition for studless tires accompanying heat aging is suppressed.

Friction force on ice Using the obtained rubber composition for studless tires, a test piece was prepared by press vulcanization at 170 ° C. for 10 minutes in a predetermined mold. The obtained test piece was attached to a flat cylindrical base rubber, and the coefficient of friction 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 Tables 1 and 2 as “friction force on ice” with an index in Table 1 where the value of Comparative Example 1 is 100 and in Table 2 the value of Comparative Example 4 is 100. The larger this index, the greater the frictional force on ice.

Friction force on ice after heat aging treatment Using the obtained rubber composition for studless tires, a test piece was prepared by press vulcanization at 170 ° C. for 10 minutes in a predetermined mold. The obtained test piece was subjected to air heat aging treatment at 80 ° C. for 120 hours. The frictional force on ice was measured by the method described above using the test piece subjected to the heat aging treatment. The obtained results are shown in Tables 1 and 2 as “friction force on ice after heat aging treatment” with the index of Comparative Example 1 being 100 in Table 1 and the value of Comparative Example 4 being 100 in Table 2. The larger this index is, the larger the frictional force on ice after heat aging treatment is, which means that the performance degradation accompanying aging is suppressed and excellent.

The types of raw materials used in Tables 1 and 2 are shown below.
NR: natural rubber, RSS # 3
BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon
Carbon black: Toast carbon carbon seast 6
Silica: Nipsil AQ manufactured by Tosoh Silica Co., BET specific surface area 200 m ² / g
Silane coupling agent: bis- (3-triethoxysilylpropyl) tetrasulfide, Si69 manufactured by Dexa Corporation
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
Wax: Paraffin wax process oil manufactured by Ouchi Shinsei Chemical Co., Ltd .: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
Grapeseed oil: Chilean grapeseed oil, edible grape oil manufactured by Catac Planners, natural polyphenol content 1.3 x 10 ^-3 wt% (polyphenol content measured by the method described above)
Vegetable oil-containing microcapsules: microcapsules encapsulating grape seed oil, manufactured by the method described above Oil-containing microcapsules: microcapsules encapsulating naphthenic oil, manufactured by the method described above Thermally expandable microcapsules: Matsumoto oil Pharmaceutical microsphere F100
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.

Claims (4)

  100 parts by weight of diene rubber, 0.5 to 20 parts by weight of thermally expandable microcapsules, 1 to 30 parts by weight of microcapsules containing vegetable oils and fats containing natural polyphenols, and 10 to 120 parts by weight of silica And a rubber composition for studless tires containing 1 to 12% by weight of a silane coupling agent based on the amount of silica.   The rubber composition for a studless tire according to claim 1, wherein the diene rubber is at least one selected from natural rubber, butadiene rubber, and styrene-butadiene rubber. The rubber composition for studless tires according to claim 1 or 2, wherein the vegetable oil contains 0.9 x 10 ^-3 wt% or more of the polyphenol.   The rubber composition for studless tire according to claim 1, wherein the vegetable oil is grape seed oil.