JP6180948B2 - Vulcanized rubber composition for tires - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a vulcanized rubber composition for tires, which is a vulcanized rubber composition containing thermally expandable microcapsules and whose friction performance on ice is improved from the 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 (hollow particles) covered with the expanded microcapsule shell are formed in the tread rubber of the vulcanized tire. . In such a studless tire, the size and number of hollow particles influence the performance on ice.

  In Patent Document 2, in order to stably expand the thermally expandable microcapsules during vulcanization of the rubber composition, the ratio of the thermally expandable microcapsules having a particle diameter before expansion of 20 to 60 μm is set to 80% or more. Has proposed. 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 No. 40466678 JP 2004-91745 A

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

  The vulcanized rubber composition for tires of the present invention that achieves the above object is obtained by blending 1 to 15 parts by weight of thermally expandable microcapsules with 100 parts by weight of diene rubber containing natural rubber and / or butadiene rubber. Including hollow particles formed by expansion of the thermally expandable microcapsules at the time of molding, among the hollow particles, those having a particle size of 50 μm or less are 1 to 15%, those having a particle size of 140 μm or more are 10% or more It is characterized by that.

  The vulcanized rubber composition for tires of the present invention has a particle size distribution of hollow particles formed by expansion of thermally expandable microcapsules when vulcanized and molded, with particle sizes of 50 μm or less being 1 to 15% and particle sizes of 140 μm or more. Surprisingly, it is possible to further improve the frictional performance on ice.

  In the vulcanized rubber composition for tires of the present invention, 1 to 15 parts by weight of thermally expandable microcapsules are blended with 100 parts by weight of diene rubber containing natural rubber and / or butadiene rubber, and the thermally expandable microcapsules are It can be produced by blending 20 to 60% of microcapsules having a particle size of 40 μm or less and 10% or more of microcapsules having a particle size of 60 μm or more, and vulcanizing the mixture.

  In this production method, it is preferable that at least two types of thermally expandable microcapsules having different particle size distributions are combined as the thermally expandable microcapsules.

  The pneumatic tire using the vulcanized rubber composition for tires of the present invention in the tread portion has excellent performance as a studless tire, and in particular, the friction performance on ice can be further improved.

  In the present invention, the diene rubber used includes natural rubber and / or butadiene rubber. By including natural rubber and / or butadiene rubber, the friction performance on ice can be enhanced when a pneumatic tire is formed. In the present invention, diene rubbers other than natural rubber and butadiene rubber can be blended. Examples of other diene rubbers include isoprene rubber, various styrene butadiene rubbers, butyl rubber, and ethylene-propylene-diene rubber. Natural rubber, butadiene rubber, and styrene butadiene rubber are preferable as the diene rubber constituting the tread portion of the pneumatic tire of the present invention, particularly a pneumatic tire for snowy and snowy roads (studless tire).

  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.

  In the vulcanized rubber composition of the present invention, 1 to 15 parts by weight, preferably 2 to 10 parts by weight of thermally expandable microcapsules are blended with 100 parts by weight of the diene rubber described above. If the amount of the thermally expandable microcapsule is less than 1 part by weight, the volume of the hollow particles (microcapsule shell) in which the thermally expandable microcapsule expanded during vulcanization will be insufficient, and the friction performance on ice will be sufficiently improved. I can't. 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.

  The thermally expandable microcapsule has a configuration in which a thermally expandable substance is encapsulated in a shell formed of a thermoplastic resin. For this reason, when vulcanizing and molding an unvulcanized tire, if the microcapsules dispersed in the rubber composition are heated, the thermally expandable substance contained in the shell material expands to increase the particle size of the shell material. A large number of hollow particles are formed in the tread 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 thermally expandable microcapsule has a particle size distribution of hollow particles formed by the expansion of the thermally expandable microcapsule when the rubber composition is vulcanized, and the hollow particles having a particle size of 50 μm or less are 1 to The hollow particles having a particle size of 15% and a particle size of 140 μm or more are 10% or more. By making the particle size distribution of the hollow particles after vulcanization molding within such a range, the on-ice friction performance can be further improved.

  Generally, a vulcanized rubber composition containing hollow particles made of thermally expandable microcapsules has a higher frictional performance on ice as the average particle diameter of the hollow particles is larger, and a lower frictional performance on ice as the average particle diameter of the hollow particles is smaller. . On the other hand, the vulcanized rubber composition for tires of the present invention is surprisingly compounded only by hollow particles having a large particle size by combining hollow particles having a large particle size and hollow particles having a small particle size. The friction performance on ice can be made superior to the vulcanized rubber composition.

  The particle size distribution of the hollow particles is 10% or more of hollow particles having a particle size of 140 μm or more, preferably 10 to 40%, preferably 140 to 200 μm, more preferably 140 to 180 μm. 10 to 30% is good. Among hollow particles, those having a particle size of 50 μm or less are 1 to 15%, preferably those having a particle size of 20 to 50 μm are 1 to 5%, more preferably those having a particle size of 30 to 50 μm are 2 to 5%. It is good to be.

  In the present specification, the particle size distribution of the hollow particles in the vulcanized rubber composition obtained by vulcanization molding is determined by observing the cross section of the vulcanized rubber composition with a scanning electron microscope (SEM) and measuring 50 or more hollow particles. The particle size of the particles is measured, and the number average particle size and particle size distribution (ratio [%] based on the number) are obtained. As the vulcanized rubber composition, a rubber composition cut out from a tread portion of a vulcanized pneumatic tire can be used. Moreover, when it can discriminate | determine from the cross section which cut | disconnected the edge part of the hollow particle at the time of observation, the particle size of the particle | grain can be excluded.

  In the method for producing a vulcanized rubber composition for tires according to the present invention, 1 to 15 parts by weight of thermally expandable microcapsules are blended with 100 parts by weight of diene rubber containing natural rubber and / or butadiene rubber, and the heat expandability thereof. An unvulcanized rubber composition is prepared so that the microcapsules are composed of 20 to 60% of microcapsules having a particle size of 40 μm or less and 10% or more of microcapsules having a particle size of 60 μm or more, and this is vulcanized and molded. Can be manufactured.

  In the production method of the present invention, the thermally expandable microcapsules having a particle size before expansion of 40 μm or less are 20 to 60%, and the thermally expandable microcapsules having a particle size before expansion of 60 μm or more are 10% or more. One or more kinds of thermally expandable microcapsules are blended and mixed with the diene rubber. The heat-expandable microcapsules are compounded and mixed by mixing and mixing with fillers and various compounding agents in diene rubber and then cooling and compounding and mixing with vulcanizing compounding agents such as sulfur and vulcanization accelerators. Good. The obtained unvulcanized rubber composition is green-molded and vulcanized to produce a vulcanized rubber composition containing the hollow particles having the particle size distribution described above.

  The heat-expandable microcapsules before expansion have a particle size of 20 to 60%, preferably 20 to 60%, more preferably 30 to 40 μm, and more preferably 20 to 60%. Mix to 60%. Further, 10% or more of thermally expandable microcapsules having a particle size of 60 μm or more before expansion, preferably 10 to 50% of those having a particle size of 60 to 80 μm, more preferably 10 to 10 of those having a particle size of 60 to 80 μm. Mix to 40%.

  Thus, in order to adjust the particle size of the thermally expandable microcapsules, at least two types of thermally expandable microcapsules having different particle size distributions can be combined and blended. When two types of thermally expandable microcapsules are selected, the difference between the average particle diameters is preferably 25 μm or more, more preferably 25 to 50 μm. By using two types of thermally expandable microcapsules having such a difference in average particle diameter, the particle diameter of the thermally expandable microcapsules before expansion can be easily adjusted.

  The mixing ratio of the two types of thermally expandable microcapsules is preferably 30 to 95% by weight of thermally expandable microcapsules having a large average particle diameter, more preferably 40 to 90% by weight, and thermally expandable microcapsules having a small average particle diameter. The capsule is preferably 70 to 5% by weight, more preferably 60 to 10% by weight. By setting the blending ratio of the two types of thermally expandable microcapsules within such a range, the friction performance on ice can be improved to a level higher than the conventional level.

  In the present invention, the tire vulcanized rubber composition may contain a filler such as silica and 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 vulcanized rubber composition for tire 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 vulcanized rubber composition for tires 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 vulcanized 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 vulcanized 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, vulcanized rubber compositions for tires generally include tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, anti-aging agents, plasticizers, and processing aids. Various additives used can be blended. Such an additive can be kneaded by a general method to form an unvulcanized 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.

  The vulcanized 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.

  Eight types of rubber compositions (Examples 1 to 4, Standard Examples 1 to 2, Comparative Examples 1 to 2) having the composition shown in Tables 1 and 2 with the diene rubber, filler and compounding agent shown in Table 3 as a common compound. 2), components other than sulfur, vulcanization accelerator, and heat-expandable microcapsules are kneaded for 5 minutes in a 1.8 L closed mixer, discharged and cooled, and sulfur, vulcanization accelerator, and heat-expandable micro An unvulcanized rubber composition was prepared by adding capsules and mixing with an open roll. In addition, the compounding quantity of the thermally expansible microcapsule described in Table 1, 2 was shown by the weight part with respect to 100 weight part of diene rubbers described in Table 3.

  In Tables 1 and 2, the average particle size and particle size distribution of the thermally expandable microcapsules before expansion are determined by using a laser diffraction particle size distribution measuring device (HEROS & RODOS manufactured by SYMPATEC) and a dispersion pressure of 5 in the dry dispersion unit. It was determined by dry measurement under the conditions of 0.0 bar and a vacuum degree of 5.0 mbar.

  In addition, the particle size distribution of the hollow particles formed by the expansion of the thermally expandable microcapsule with the vulcanization of the rubber composition is the same as that of the vulcanized rubber test piece made of the vulcanized rubber composition. It observed with the scanning electron microscope (SEM), the particle size of 50 or more hollow particles was measured, and the number average particle size and the number distribution of the particle size were calculated | required.

  The obtained eight kinds of rubber compositions were press vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare test pieces made of a vulcanized rubber composition for tires. The friction performance on ice of the obtained vulcanized rubber test piece was evaluated by the following method.

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 shown in the column of “Friction performance on ice” in Table 1 with an index in which the value of Standard Example 1 is 100 in Table 1 and the value of Standard Example 2 is 100 in Table 2. A larger index value means a greater frictional force on ice and better performance on ice.

  In Tables 1 and 2, microcapsule-1 and microcapsule-2 are both thermally expandable microcapsules prepared by Matsumoto Yushi Seiyaku Co., Ltd.

Manufacturing method of microcapsule-1 A thermally expandable microcapsule was prepared by the following steps to obtain a microcapsule-2. As an aqueous component, 25 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, 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 as oil components to prepare a monomer mixture of a uniform solution. did. To this monomer mixture, 30 g of isopentane and 30 g of 2-methylpentane were added and charged in 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.

  Microcapsule-1 had an average particle size of 57 μm before expansion, 8% of microcapsules having a particle size of 40 μm or less, and 36% of microcapsules having a particle size of 60 μm or more. Further, the hollow particles after the expansion of the microcapsule-1 were 0% of hollow particles having a particle size of 50 μm or less and 40% having a particle size of 140 μm or more.

Manufacturing method of microcapsule-2 A thermally expandable microcapsule was prepared by the following steps to obtain a microcapsule-2. 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, 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 as oil components to prepare a monomer mixture of a uniform solution. did. To this monomer mixture, 30 g of isopentane and 30 g of 2-methylpentane were added and charged in 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.

  Microcapsule-2 had an average particle size of 25 μm before expansion, 94% of microcapsules with a particle size of 40 μm or less, and 0% of microcapsules with a particle size of 60 μm or more. The hollow particles after the expansion of the microcapsule-2 were 20% of hollow particles having a particle size of 50 μm or less, and 0% having a particle size of 140 μm or more.

In addition, the kind of raw material used in Table 3 is 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
Silane coupling agent: Sulfur-containing silane coupling agent, Si69 manufactured by Evonik Degussa
・ Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. ・ Stearic acid: Bead stearic acid manufactured by NOF Corporation ・ Anti-aging agent-1: Ozonon 6C manufactured by Seiko Chemical Co., Ltd.
Anti-aging agent-2: Seiko Chemical 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 clear from Tables 1 and 2, it was confirmed that the vulcanized rubber compositions for tires of Examples 1 to 4 improved the friction performance on ice to the conventional level (Standard Examples 1 and 2, Comparative Examples 1 and 2) or more. It was done.

  The vulcanized rubber composition of Comparative Example 1 has a smaller particle size of the hollow particles formed by expanding the blended microcapsule-2, compared to the hollow particles expanded by the microcapsule-1 blended in Standard Example 1, Frictional performance on ice decreased.

  The vulcanized rubber composition of Comparative Example 2 has a smaller particle size of the hollow particles formed by expanding the blended microcapsule-2, compared to the hollow particles expanded by the microcapsule-1 blended in Standard Example 2, Frictional performance on ice decreased.

Claims (4)

  Hollow particles formed by expanding 1 to 15 parts by weight of thermally expandable microcapsules in 100 parts by weight of diene rubber containing natural rubber and / or butadiene rubber, and expanding the thermally expandable microcapsules during vulcanization molding A vulcanized rubber composition for tires comprising 1 to 15% of hollow particles having a particle size of 50 μm or less and 10% or more of particles having a particle size of 140 μm or more.   1 to 15 parts by weight of thermally expandable microcapsules are blended with 100 parts by weight of diene rubber containing natural rubber and / or butadiene rubber, and the thermally expandable microcapsules have 20 to 20 μm of microcapsules having a particle size of 40 μm or less. The method for producing a vulcanized rubber composition for a tire according to claim 1, wherein 60% and microcapsules having a particle size of 60 µm or more are blended so as to consist of 10% or more and vulcanized. .   The method for producing a vulcanized rubber composition for tire according to claim 2, wherein at least two types of thermally expandable microcapsules having different particle size distributions are combined as the thermally expandable microcapsules.   A pneumatic tire having a tread portion formed of the vulcanized rubber composition for a tire according to claim 1.