JP2015067745A - Tire rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire rubber composition comprising heat-expansible microcapsules, the rubber composition having an improved level of on-ice frictional performance.SOLUTION: The rubber composition is characterized in that 100 pts.wt. of a diene rubber is blended with 0.5-15 pts.wt. of surface-treated heat-expansible microcapsules in which the surfaces of heat-expansible microcapsules carry silica.

Description

  The present invention relates to a rubber composition for tires that includes a thermally expandable microcapsule and is improved in friction performance on ice from a conventional level.

  The structure of pneumatic tires for snow and snow (studless tires) is that many bubbles are formed in the tread rubber, and when the tread steps on the ice surface, these bubbles absorb and remove the water film on the ice surface, and the tread becomes the ice surface. It is known that the performance on ice is improved by repeatedly removing the absorbed water by centrifugal force when leaving the vehicle.

  Patent Document 1 proposes blending a thermally expandable microcapsule with a rubber composition for a tire tread as means for forming such bubbles. This thermally expandable microcapsule expands by heating in the vulcanization process of a pneumatic tire, and a large number of bubbles (resin-coated bubbles) covered by the expanded microcapsule shell are formed in the tread rubber of the vulcanized tire. The In such a studless tire, the size and number of the resin-coated bubbles affect the performance on ice.

  However, in the studless tire composed of the above-described tread rubber, the shell of the microcapsule exposed on the tire surface may fall off from the tread rubber. As a result, the water film removal effect on the ice surface may be reduced, and the performance on ice may not be sufficiently improved. On the other hand, the level demanded by the consumer for the performance on ice of the studless tire is higher, and it is required to further increase the friction performance on ice.

Japanese Patent Laid-Open No. 10-316801

  An object of the present invention is to provide a rubber composition for tires, which is a rubber composition containing thermally expandable microcapsules and whose friction performance on ice is improved from the conventional level.

  The rubber composition for a tire according to the present invention that achieves the above object comprises 0.5 to 15 parts by weight of a surface-treated thermally expandable microcapsule having silica supported on the surface of a thermally expandable microcapsule in 100 parts by weight of a diene rubber. It is characterized by blending.

  Since the rubber composition for tires of the present invention contains 0.5 to 15 parts by weight of the surface-treated thermally expandable microcapsules supporting silica on the surface of the thermally expandable microcapsules with respect to 100 parts by weight of the diene rubber, By strengthening the interface between the vulcanized tread rubber and the microcapsule shell, the microcapsule shell can be prevented from falling off, and the friction performance on ice can be further improved.

  The surface-treated thermally expandable microcapsule may support 1 to 20% by weight of silica based on the weight of the thermally expandable microcapsule.

  The pneumatic tire using the tire rubber composition of the present invention in the tread portion has excellent performance as a studless tire, and can particularly further improve the friction performance on ice.

  In the present invention, the diene rubber to be used may be any rubber that can be used for the tread portion of a pneumatic tire. For example, natural rubber, isoprene rubber, butadiene rubber, various styrene butadiene rubbers, butyl rubber, ethylene-propylene- Examples include diene rubber. In particular, natural rubber, butadiene rubber, and styrene butadiene rubber are preferable when used for a tread portion of a pneumatic tire for snow and snowy road (studless tire). These diene rubbers can be used alone. A plurality of types can be used in combination.

  In the present invention, the above-mentioned diene rubber has an average glass transition temperature of preferably −50 ° C. or lower, and more preferably −60 to −100 ° C. By setting the average glass transition temperature of diene rubber to -50 ° C or lower, the suppleness of the rubber compound is maintained at low temperatures and the adhesion to the ice surface is increased, making it suitable for the toled part of winter tires. Can be used. The glass transition temperature is determined by differential scanning calorimetry (DSC) with a thermogram measured at a rate of temperature increase of 20 ° C./min and set as the temperature at the midpoint of the transition region. When the diene rubber is an oil-extended product, the glass transition temperature of the diene rubber in a state not containing an oil-extended component (oil) is used. The average glass transition temperature is the sum of the glass transition temperature of each diene rubber multiplied by the weight fraction of each diene rubber (weight average value of glass transition temperature). The total weight fraction of all diene rubbers is 1.

  The rubber composition for tires of the present invention is blended with the above-described diene rubber and surface-treated thermally expandable microcapsules having silica supported on the surface thereof. The compounding amount of the surface-treated thermally expandable microcapsule is 0.5 to 15 parts by weight, preferably 2 to 10 parts by weight with respect to 100 parts by weight of the diene rubber. When the amount of the surface-treated thermally expandable microcapsule is less than 0.5 parts by weight, the volume of the resin-coated air bubbles (microcapsule shell) after vulcanization is insufficient, and the friction performance on ice cannot be improved sufficiently. . Moreover, when the compounding quantity of a surface treatment thermally expansible microcapsule exceeds 15 weight part, there exists a possibility that the abrasion resistance performance of a tread rubber may deteriorate.

  In the present invention, the thermally expandable microcapsule has a structure in which a thermally expandable substance is encapsulated in a shell material formed of a thermoplastic resin. For this reason, when the microcapsules dispersed in the rubber composition are heated at the time of vulcanization of the unvulcanized tire, the thermally expansible substance contained in the shell material expands to increase the particle size of the shell material, and the tread A large number of resin-coated bubbles are formed in the rubber. As a result, the water film generated on the surface of the ice is efficiently absorbed and removed, and a micro edge effect is obtained, thereby improving the performance on ice. In addition, since the shell material of the microcapsule is harder than the tread rubber, the wear resistance of the tread portion can be increased. The shell material of the thermally expandable microcapsule can be formed of a nitrile polymer.

  Further, the thermally expandable substance included in the shell material of the microcapsule has a property of being vaporized or expanded by heat, and examples thereof include at least one selected from the group consisting of hydrocarbons such as isoalkane and normal alkane. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, and examples of normal alkanes include n-butane, n-propane, n-hexane, Examples thereof include n-heptane and n-octane. These hydrocarbons may be used alone or in combination. As a preferable form of the thermally expandable substance, a substance obtained by dissolving a hydrocarbon which is gaseous at normal temperature in a hydrocarbon which is liquid at normal temperature is preferable. By using such a mixture of hydrocarbons, a sufficient expansion force can be obtained from the low temperature region to the high temperature region in the vulcanization molding temperature region (150 to 190 ° C.) of the unvulcanized tire.

  In the present invention, the surface-treated thermally expandable microcapsule is one in which silica is supported on the surface of the thermally expandable microcapsule. The silica supported on the surface of the thermally expandable microcapsule has a part of the silica particle embedded in the shell of the microcapsule even after expansion by heat treatment, and the remaining part of the silica particle not embedded in the shell is vulcanized rubber. It can be thought of as taking a form that bites into This is considered to strengthen the interface between the vulcanized rubber and the microcapsule shell. Silica is not particularly limited, and those usually used in tire rubber compositions can be used.

  The method of supporting silica on the surface of the thermally expandable microcapsule can be performed by a usual method. For example, a suspension in which silica is dispersed in water or alcohol is sprayed on the thermally expandable microcapsule by spraying or the like. Then, a dry method in which drying is performed, or a suspension in which silica is dispersed in water, alcohol, or the like is added to a slurry of a thermally expandable microcapsule or a wet cake (water content 10 to 95%), and after mixing, Examples thereof include a wet method for performing dehydration and drying. Preferably, in the process of producing the heat-expandable microcapsules, silica is supported on the surface of the heat-expandable microcapsules by mixing the water slurry or wet cake with silica and drying.

  The amount of silica supported on the surface-treated thermally expandable microcapsule is 1 to 20% by weight, preferably 2 to 15%, based on the weight of the thermally expandable microcapsule. If the supported amount of silica is less than 1% by weight, the effect of reinforcing the interface between the vulcanized rubber and the microcapsule shell cannot be obtained sufficiently. Further, if the supported amount of silica exceeds 20% by weight, there is a concern that the microcapsules are inhibited from thermal expansion.

  In the present invention, the tire rubber composition may contain a filler such as silica or carbon black. By blending the filler, the strength of the rubber can be increased and the wear resistance can be improved. The blending amount of the filler is preferably 10 to 80 parts by weight, more preferably 20 to 70 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of the filler is less than 10 parts by weight, the rubber strength cannot be increased and the wear resistance performance cannot be improved. When the blending amount of the filler is larger than 80 parts by weight, the rolling resistance of the tire rubber composition is deteriorated.

  As fillers other than silica and carbon black, any filler that can be used for pneumatic tires can be used, for example, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide. And calcium sulfate.

  The tire rubber composition of the present invention preferably contains silica. For example, any silica such as wet silica and dry silica can be used alone or in combination.

  When silica is blended with the rubber composition of the present invention, a silane coupling agent can be blended. By compounding a silane coupling agent, the dispersibility of silica in the diene rubber can be improved and the reinforcement with the rubber can be enhanced. At the same time, the effect of improving the affinity of the silica diene rubber supported on the thermally expandable microcapsule and strengthening the interface between the vulcanized rubber and the microcapsule shell cannot be sufficiently obtained.

  The blending amount of the silane coupling agent is preferably 3 to 15% by weight, more preferably 5 to 10% by weight based on the blending amount of silica in the rubber composition. If the amount of the silane coupling agent is less than 3% by weight of the amount of silica, the silica dispersion cannot be improved sufficiently. If the blending amount of the silane coupling agent exceeds 15 parts by weight of the blending amount of silica, desired hardness, strength and wear resistance cannot be obtained.

  The type of the silane coupling agent is not particularly limited as long as it can be used for the rubber composition containing silica. For example, bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3- Examples thereof include sulfur-containing silane coupling agents such as (triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane. .

  In addition to the fillers described above, tire rubber compositions are generally used for tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, anti-aging agents, plasticizers, and processing aids. Various additives can be blended, and such additives can be kneaded by a general method to obtain a rubber composition, 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. Such a rubber composition can be produced by mixing each of the above components using a known rubber kneading machine, for example, a Banbury mixer, a kneader, a roll or the like.

  In the tire rubber composition of the present invention, the surface-treated thermally expandable microcapsule supporting silica is blended on the surface of the thermally expandable microcapsule, so that the interface between the vulcanized tread rubber and the microcapsule shell is reinforced. As a result, the shell of the microcapsule can be prevented from falling off, and the friction performance on ice can be further improved. Also, by strengthening this interface, the rubber strength such as 100% modulus can be improved, the loss of rubber (tan δ at 60 ° C.) can be reduced, the heat generation can be reduced, and the fuel efficiency performance when used in a tire can be improved. it can.

  The rubber composition for tires of the present invention is suitable for constituting a tread portion of a studless tire. The tread portion configured as described above can improve the performance on ice to a level higher than the conventional level.

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

Production of thermally expandable microcapsules Thermally expandable microcapsules were prepared by the following steps. As an aqueous component, 45 g of colloidal silica having a solid content of 40%, 1 g of diethanolamine-adipic acid condensate, 150 g of sodium chloride and 500 g of ion-exchanged water were mixed and adjusted to pH 3.5 to produce an aqueous dispersion medium. Next, as an oil component, 70 g of acrylonitrile, 70 g of methacrylonitrile, 70 g of methacrylic acid, 3 g of ethylene glycol dimethacrylate and 1 g of azobis (2,4-dimethylylvaleronitrile) are mixed to obtain a monomer mixture in a uniform solution. Prepared. To this monomer mixture, 30 g of isopentane or 30 g of 2-methylpentane was added and charged into an autoclave, and an aqueous dispersion medium was further charged. After stirring the charged product at 700 rpm for 5 minutes, the inside of the autoclave was purged with nitrogen and reacted at a reaction temperature of 60 ° C. for 8 hours. The reaction pressure was 0.5 MPa and stirring was performed at 350 rpm. In the final process, in order to remove the water | moisture content of a thermally expansible microcapsule, it dried at 70 degreeC using the mixer dryer.

Manufacture of surface-treated thermally expandable microcapsules Thermally expandable microcapsules were prepared by the above-described method of manufacturing thermally expandable microcapsules, and in the final step, silica containing water was added so as to have the composition shown in Table 1. It was dispersed in water, added to the thermally expandable microcapsules, and dried at 70 ° C. using a mixer dryer. As a result, the surface-treated thermally expandable microcapsules (surface-treated microcapsules 1 and 2) shown in Table 1 were obtained.

  The surface-treated microcapsule 1 supported 5% by weight of silica with respect to the weight of the thermally expandable microcapsule. Further, the surface-treated microcapsule 2 supported 10% by weight of silica with respect to the weight of the thermally expandable microcapsule. Here, the supported amount of silica was measured by thermogravimetric analysis.

Preparation and Evaluation of Rubber Composition for Tires Using two kinds of surface-treated thermally expandable microcapsules (surface-treated microcapsules 1 to 2) and thermally expandable microcapsules having the composition shown in Table 1, the compositions shown in Table 5 12 types of tire rubber compositions (Examples 1 to 6 and Comparative Examples 1 to 6) having the formulations shown in Tables 2, 3 and 4 as sulfur, a vulcanization accelerator, and a thermal expansion property. The components excluding the microcapsule and the surface-treated thermally expandable microcapsule are kneaded with a 1.8 L closed mixer for 5 minutes and released, and then sulfur, vulcanization accelerator, thermally expandable microcapsule and surface-treated thermally expandable microcapsule are released. It was prepared by adding capsules and kneading with an open roll. The amounts of the compounding agents described in Table 5 are shown in parts by weight with respect to 100 parts by weight of the diene rubber described in Tables 2, 3, and 4.

  Twelve kinds of obtained rubber compositions for tires were press vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare vulcanized rubber test pieces. The obtained vulcanized rubber test piece was evaluated for its 100% modulus, exothermic property (tan δ at 60 ° C.), and friction performance on ice by the following methods.

100% modulus (M100)
A JIS No. 3 dumbbell-shaped test piece was cut out from the obtained vulcanized rubber test piece in accordance with JIS K6251. 100% deformation stress (100% modulus) was measured according to JIS K6251. The obtained 100% modulus was indexed with the value of Comparative Example 1 being 100 in Table 2, the value of Comparative Example 3 being 100 in Table 3, the value of Comparative Example 5 being 100 in Table 4, and each “M100” ”Column. A larger index value means a larger 100% modulus.

Exothermic (tan δ at 60 ° C)
Using the viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., the dynamic viscoelasticity of the obtained vulcanized rubber test piece was determined as follows. It was measured. The obtained results are shown in Table 2, with the value of Comparative Example 1 as 100, Table 3 as Comparative Example 3 as 100, and Table 4 as Comparative Example 5 as 100. ° C) "column. The smaller the index value, the smaller the tan δ at 60 ° C., and the smaller the exothermic property.

Friction performance on ice The obtained vulcanized rubber test piece was affixed to a flat columnar base rubber, and using an inside drum type on-ice friction tester, measurement temperature -1.5 ° C, load 5.5 kg / cm ³ , drum The friction coefficient on ice was measured under the condition of a rotational speed of 25 km / h. The obtained friction coefficient on ice is an index in which the value in Comparative Example 1 is 100 in Table 2, the value in Comparative Example 3 is 100 in Table 3, and the value in Comparative Example 5 is 100 in Table 4. It is shown in the column of “Friction performance”. A larger index value means a greater frictional force on ice and better performance on ice.

The types of raw materials used in Table 1 are shown below.
Silica: Nipsil AQ manufactured by Tosoh Silica

The types of raw materials used in Tables 2, 3, and 4 are shown below.
・ NR: Natural rubber, RSS # 3
BR: Butadiene rubber, Nippon Zeon BR1220
・ Carbon black: Seest 6 made by Tokai Carbon
Silica: Nipsil AQ manufactured by Tosoh Silica
Coupling agent: Sulfur-containing silane coupling agent, Si69 manufactured by Evonik Degussa
-Microcapsules: Thermally expandable microcapsules obtained by the above-described manufacturing method-Surface-treated microcapsules 1, 2: Surface-treated thermally expandable microcapsules described in Table 1 obtained by the above-described manufacturing method

The types of raw materials used in Table 5 are shown below.
-Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.-Stearic acid: Beads stearic acid manufactured by NOF Corporation-Anti-aging agent-1: Ozonon 6C manufactured by Seiko Chemical Co., Ltd.
Anti-aging agent-2: Seiko Chemical Co., Ltd. non-flex RD
・ Oil: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. ・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As is apparent from Tables 2 to 4, the rubber compositions for tires of Examples 1 to 6 maintain and improve 100% modulus (M100) and heat build-up (tan δ at 60 ° C.), and have a conventional level of friction performance on ice. It has been confirmed that this is improved.

  In the rubber composition of Comparative Example 2, the amount of silica and the amount of thermally expandable microcapsules in the rubber composition were the same as in Example 2, but the heat generation (tan δ at 60 ° C.) was large, and the friction performance on ice was further increased. Could not be improved.

  In the rubber composition of Comparative Example 4, the amount of silica and the amount of thermally expandable microcapsules in the rubber composition were the same as in Example 4, but the friction performance on ice could not be improved.

  In the rubber composition of Comparative Example 6, the amount of silica and the amount of thermally expandable microcapsules in the rubber composition were the same as in Example 6, but the exothermic property (tan δ at 60 ° C.) was large and the friction performance on ice was further increased. Could not be improved.

Claims (3)

  A tire rubber composition comprising 100 parts by weight of a diene rubber and 0.5 to 15 parts by weight of surface-treated thermally expandable microcapsules having silica supported on the surface of thermally expandable microcapsules.   The rubber composition for tire according to claim 1, wherein the surface-treated thermally expandable microcapsule carries 1 to 20% by weight of silica based on the weight of the thermally expandable microcapsule.   The pneumatic tire which formed the tread part with the rubber composition for tires of Claim 1 or 2.