JP5436954B2 - Rubber composition and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition, and more specifically, as an example, a rubber composition that can be suitably used for a tread of a winter tire (winter tire) such as a studless tire or a snow tire, and the rubber composition The present invention relates to a pneumatic tire used.

  On snowy and snowy roads, the friction coefficient is significantly lower than that on ordinary roads, making it easier to slip. Therefore, in rubber compositions used for winter tire treads such as studless tires, the use of butadiene rubber with a low glass transition point or blending of a softening agent at low temperatures in order to improve the ground contact on the road surface on ice. The rubber hardness is kept low. In addition, in order to increase the frictional force on ice, foamed rubber is used for the tread, or hard materials such as hollow particles, glass fibers, and vegetable granules are blended.

  For example, in Patent Document 1 below, particles having a scratching effect such as plant granules obtained by pulverizing seed shells or fruit nuclei are added to a rubber component, and the friction performance on ice is improved by the scratching effect. Is disclosed. In particular, in this document, the plant granule is surface-treated with a rubber adhesion improver mainly composed of a mixture of resorcin / formalin resin initial condensate and latex, thereby chemically bonding to the tread rubber and scratching effect. The point which improves is proposed.

  In Patent Document 2 below, in order to effectively remove a water film on ice, a fly pon obtained by supporting a unit layer of fine laminated plate-like crystals of aluminosilicate metal salt fly pontoite around silica particles. It has been proposed to incorporate a tight-silica composite into a rubber component.

  Patent Document 3 below proposes blending bamboo charcoal with a rubber component in order to more effectively remove the water film on ice.

  In Patent Document 4 below, heat-expanding thermoplastic resin particles that form cavities in rubber by heat during vulcanization are included in a thermoplastic resin that is not melted by heat during mixing but softened during vulcanization. It is disclosed that an expandable composite resin is blended with rubber, which allows a plurality of thermally expandable thermoplastic resin particles to expand in a chain form in a vulcanized rubber, and an independent cavity is not sufficient on ice. It is described that it is possible to greatly improve the water film removal effect of the water. Further, as the thermally expandable thermoplastic resin particles, there are disclosed particles in which a thermoplastic resin such as a polymer of (meth) acrylonitrile is used as an outer shell and a liquid or solid that generates a gas by heat is included.

JP-A-10-007841 JP 2001-123017 A JP 2005-162865 A JP 2004-043680 A

  As described above, various measures have been proposed in order to improve the performance on ice. However, it cannot be said that the level is sufficiently high to meet the increasingly demanding market demands recently.

  This invention is made | formed in view of the above point, and it aims at providing the rubber composition and pneumatic tire which can exhibit the outstanding performance on ice.

  In view of the above-mentioned problems, the present inventor has found that the performance on ice is remarkably improved by blending specially shaped fine particles into the rubber composition, and has completed the present invention.

That is, the rubber composition according to the present invention is obtained by polymerizing at least one polymerizable monomer selected from methacrylic acid ester, acrylic acid ester, vinyl acetate and acrylonitrile with respect to 100 parts by weight of the diene rubber. Resin particles having a mean particle size of 1 to 100 μm are blended in an amount of 0.3 to 20 parts by weight.

  Moreover, the pneumatic tire according to the present invention includes a tread made of such a rubber composition.

  According to the present invention, the performance on ice can be remarkably improved while suppressing a decrease in wear resistance.

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

  Examples of the diene rubber used as the rubber component in the rubber composition of the present invention include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and styrene-isoprene. Examples include various diene rubbers that are usually used in rubber compositions for tire treads such as polymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These diene rubbers can be used alone or in a blend of two or more.

  As the rubber component, a blend of natural rubber and another diene rubber is preferably used, and a blend rubber of natural rubber (NR) and butadiene rubber (BR) is particularly preferably used. In that case, if the ratio of BR is too small, it is difficult to obtain low temperature characteristics of the rubber composition. Conversely, if the ratio is too large, the processability tends to deteriorate and the tear resistance tends to decrease, so the ratio of NR / BR is The weight ratio is preferably about 30/70 to 80/20, more preferably about 40/60 to 70/30.

  In the rubber composition of the present invention, bowl-shaped fine particles are blended. The bowl-shaped fine particles are fine particles having a substantially hemispherical shape or a substantially semi-elliptical spherical shape and having a concave shape at the center. Such fine particles themselves are disclosed, for example, in JP-A-5-317688, and are conventionally used as cosmetic raw materials. In the present invention, such a bowl-shaped fine particle is blended with a rubber composition, and for example, it has been found that the performance on ice can be remarkably improved by using it for a tread rubber of a pneumatic tire such as a studless tire. The reason for this is not necessarily clear, but it is because the water film on the ice surface is effectively removed by the unique shape of the bowl shape, and the effect of scratching the ice surface by the edge effect of the bowl shape edge is demonstrated. Guessed.

  An example of those suitably used as the bowl-shaped fine particles will be described in detail based on JP-A-5-317688. The bowl-shaped fine particles are obtained, for example, by suspension polymerization of a polymerizable monomer in water in the presence of a crosslinking agent and a hydrophobic liquid, and the presence of a predetermined amount of the crosslinking agent and the hydrophobic liquid allows the hydrophobic liquid to be obtained. Are encapsulated in polymer fine particles, and the polymer is deformed during polymerization to form rod-like fine particles. Therefore, the obtained fine particles are formed in a shape as if the rubber balls were crushed by the escape of air, that is, in a substantially hemispherical or substantially semi-elliptical spherical shape having a large recess in the center. Therefore, the edge of the bowl corresponding to the opening of the recess has a rounded shape, and therefore, when blended in a rubber composition, it is not a sharp pointed edge, so the vulcanized rubber is cut resistant Can be improved.

  Examples of the polymerizable monomer include methacrylic acid esters, acrylic acid esters, styrene, vinyl acetate, acrylonitrile, and the like, and these can be used alone or in combination of two or more. Therefore, the bowl-shaped fine particles are preferably resin particles obtained by polymerizing at least one of these polymerizable monomers. In terms of further improving the water film removal effect, the bowl-shaped particles are preferably made of a hydrophilic resin that is easily compatible with water. Therefore, methacrylic acid esters such as methyl methacrylate and ethyl methacrylate, methyl acrylate and acrylic acid are preferred. It is preferably an acrylic acid ester such as ethyl, a homopolymer of vinyl acetate or acrylonitrile, or a copolymer containing these. Particularly preferred is a methacrylic resin such as polymethyl methacrylate (PMMA). Since the methacrylic resin has high chemical stability, impact resistance and hydrophilicity, it is excellent in the water film removal effect and scratching effect on the road surface on ice due to the synergistic effect with the bowl shape.

  Examples of the crosslinking agent include at least one of ethylene glycol dimethacrylate, divinylbenzene, ethylene dimethacrylate, triethylene glycol dimethacrylate, 1,3-butylene dimethacrylate, allyl methacrylate, trimethylolpropane trimethacrylate, and the like. Species are mentioned. Examples of the hydrophobic liquid include those having a boiling point of 100 ° C. or higher and a melting point of 0 ° C. or lower, such as hydrocarbons such as liquid paraffin, animal oils, vegetable oils, and silicones.

  As such bowl-shaped fine particles, “Matsumoto Microsphere M-310” (bowl-shaped) and “Matsumoto Microsphere M-311” (elliptical bowl-shaped) are commercially available from Matsumoto Yushi Seiyaku Co., Ltd. Can be suitably used.

  As the particle diameter of the bowl-shaped fine particles, the average particle diameter is preferably 100 μm or less, more preferably 20 μm or less. If the average particle size is increased, the wear resistance and cut resistance may be impaired, so the average particle size is preferably small. The lower limit of the average particle diameter is not particularly limited, but is preferably 1 μm or more. The average particle diameter is a value measured by a laser diffraction / scattering method. In the following examples, a laser diffraction particle size distribution measuring apparatus “SALD-” manufactured by Shimadzu Corporation using a red semiconductor laser (wavelength 680 nm) as a light source is used. 2200 ".

  The bowl-shaped fine particles can be blended in the range of 0.3 to 20 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount is less than 0.3 parts by weight, the effect of addition is insufficient, and when it exceeds 20 parts by weight, the wear resistance is deteriorated. The blending amount is more preferably 1 to 15 parts by weight.

  The rubber composition of the present invention may further contain plant particulates obtained by pulverizing seed shells or fruit nuclei, and / or a pulverized product of porous carbides of plants together with the bowl-shaped fine particles. Good. The performance on ice can be further improved by using these plant granules and porous carbide pulverized material in combination.

  As the plant granular material, a pulverized product obtained by pulverizing seed husks such as walnuts and persimmons or fruit nuclei such as peaches and plums by a known method can be used. Since these have a Mohs hardness of about 2 to 5 and are harder than ice, they can exhibit a scratching effect on the road surface on ice.

  In order to improve the familiarity with rubber and prevent dropping, it is preferable to use a plant granule that has been surface-treated with a rubber adhesion improver. As the rubber adhesion improver, for example, one having a mixture of resorcin / formalin resin initial condensate and latex as a main component (RFL solution) can be mentioned.

  The average particle size of the plant-based granular material is not particularly limited, but is preferably 100 to 600 μm in order to exhibit a scratching effect and prevent the flakes from falling off the tread. The average particle diameter is a value measured by the laser diffraction / scattering method, as described above.

  The pulverized product of the porous carbide is obtained by pulverizing a porous material composed of a solid product mainly composed of carbon obtained by carbonizing a plant such as wood or bamboo. Since the pulverized product (bamboo charcoal powder) exhibits excellent adsorptivity due to its unique porosity, the water film generated on the road surface on ice can be effectively absorbed and removed.

  Bamboo materials that are used as raw materials for bamboo charcoal include various kinds of bamboo such as 孟 mune bamboo, maitake, pale bamboo, and crested bamboo, as well as bamboo such as chidori and Sendai. The bamboo charcoal pulverized product can be obtained by pulverizing bamboo charcoal obtained by steaming and baking bamboo material using a kiln into a powder using a known pulverizer (for example, a ball mill).

  The average particle size of the pulverized product of the porous carbide is not particularly limited, but is preferably 10 to 500 μm. The average particle diameter is a value measured by a laser diffraction / scattering method as described above.

  When blending the pulverized product of these plant granules and porous carbide, the blending amount of both is preferably 0.3 to 20 parts by weight with respect to 100 parts by weight of the diene rubber. More preferably, it is 1 to 10 parts by weight.

  The rubber composition of the present invention comprises, in addition to the above-mentioned components, reinforcing agents and fillers such as carbon black and silica, process oil, zinc white, stearic acid, softener, and plasticizer that are used in ordinary rubber industry. , Anti-aging agent (amine-ketone, aromatic secondary amine, phenol, imidazole, etc.), vulcanizing agent, vulcanization accelerator (guanidine, thiazole, sulfenamide, thiuram, etc.), etc. These compounding chemicals can be appropriately blended within a normal range.

Here, as carbon black, when used in a tread portion of a studless tire, nitrogen adsorption specific surface area (N ₂ SA) (JIS K6217) is considered from the viewpoint of low temperature performance, abrasion resistance, rubber reinforcement, and the like of the rubber composition. -2) is 70 to 150 m ² / g and DBP oil absorption (JIS K6217-4) is preferably 100 to 150 ml / 100 g. Specifically, SAF, ISAF, and HAF grade carbon black are exemplified, and the blending amount is preferably in the range of about 10 to 80 parts by weight with respect to 100 parts by weight of the diene rubber.

  In addition, when silica is used, wet silica, dry silica, surface-treated silica or the like is used, and the blending amount is 50 with respect to 100 parts by weight of diene rubber from the viewpoint of balance of tan δ of rubber, reinforcing property, and electrical conductivity. The amount is preferably less than parts by weight, and is preferably about 10 to 120 parts by weight in total with carbon black. Moreover, when mix | blending a silica, it is preferable to use a silane coupling agent together.

  The rubber composition of the present invention can be prepared by kneading using a commonly used mixer such as a Banbury mixer or a kneader. The rubber composition is suitably used as a rubber composition for a tread portion of a winter tire (winter tire) such as a studless tire or a snow tire.

  The pneumatic tire of the present invention is manufactured by producing a tread portion of a tire using a rubber extruder or the like and molding an unvulcanized tire using the rubber composition, followed by a vulcanization process according to a conventional method. Can do. When applied to a studless tire having a cap base structure, the rubber composition of the present invention may be applied only to the cap tread on the ground contact surface side.

  The pneumatic tire thus obtained has a coefficient of friction between the tread rubber and the road surface due to the above-mentioned water film removing effect and scratching effect, etc., because the waxy fine particles blended in the tread rubber are exposed on the tread surface. It can be increased to improve the performance on ice. In addition, it is possible to suppress a decrease in wear resistance. Further, the use of vegetable granules such as pulverized walnut shells and porous carbide pulverized products such as bamboo charcoal pulverized products can further improve the performance on ice.

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

  Using a Banbury mixer, a tread rubber composition for studless tires was prepared according to the formulation shown in Table 1 below. Each component in Table 1 is as follows.

・ Natural rubber: RSS # 3
・ Butadiene rubber: High butadiene rubber “BR01” manufactured by JSR Corporation
Carbon black: “Seast KH” (N339, HAF) manufactured by Tokai Carbon Co., Ltd.
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
Silane coupling agent: “Si75” manufactured by Degussa
Paraffin oil: “JOMO Process P200” manufactured by Japan Energy Corporation.

・ Bow-like fine particles 1 (bowl-like): “Matsumoto Microsphere M-310” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. (methyl methacrylate crosspolymer (cross-linked PMMA), mineral oil, average particle size = 15 μm)
・ Vaginal fine particles 2 (elliptical vaginal shape): “Matsumoto Microsphere M-311” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. (methyl methacrylate crosspolymer (crosslinked PMMA), mineral oil, average particle size = 15 μm)
Hollow hollow spherical fine particles: “Matsumoto Microsphere M-600” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. (methyl methacrylate crosspolymer (crosslinked PMMA), average particle size = 30 μm)
・ Bamboo charcoal pulverized material: Bamboo charcoal powder obtained by crushing bamboo charcoal from Somune bamboo (“No. 1 charcoal” manufactured by Miyazaki Dogo Co., Ltd.) with a hammer mill and classifying the obtained pulverized material with a sieve (average particle size = 100 μm)
・ Plant granules: crushed walnut shell ("Soft Grip # 46" manufactured by Japan Walnut Co., Ltd.) subjected to surface treatment with an RFL treatment solution according to the method described in JP-A-10-7841 (Average particle size of the plant granule after treatment = 300 μm).

  In each rubber composition, 2 parts by weight of stearic acid ("Lunac S-20" manufactured by Kao Corporation) and zinc white ("Zinc Flower" manufactured by Mitsui Mining & Smelting Co., Ltd.) are used as a common compound. 1 type)) 2 parts by weight, anti-aging agent (“Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.) 2 parts by weight, wax (“OZOACE0355” manufactured by Nippon Seiki Co., Ltd.) 2 parts by weight, vulcanization accelerator (Sumitomo Chemical Co., Ltd.) 1.5 parts by weight of company "Soccinol CZ") and 2.1 parts by weight of sulfur ("powder sulfur" manufactured by Tsurumi Chemical Co., Ltd.) were blended.

  About each obtained rubber composition, hardness (23 degreeC) was measured. Also, studless tires were prepared using each rubber composition, and the wear resistance and braking performance on the road surface on ice (on-ice braking performance) were evaluated. The tire size was 185 / 65R14, and each rubber composition was applied to the tread and vulcanized and molded according to a conventional method. Each rim used was 14 × 5.5 JJ. Each measurement / evaluation method is as follows.

Hardness: Based on JIS K6253, the hardness at 23 ° C. of a sample vulcanized at 160 ° C. for 20 minutes (thickness of 12 mm or more) was measured using a type A durometer.

・ Abrasion resistance: The above tire was mounted on a 2000 cc 4WD vehicle, rotated left and right every 2500 km, and the remaining grooves after running 10,000 km (average value of remaining grooves of four tires) were measured. The value was expressed as an index with a value of 100. A larger index indicates better wear resistance.

-On-ice braking performance: The above tire is mounted on a 2000 cc 4WD vehicle, and the braking distance is measured by running an ABS from 40 km / h on an icing road at -3 ± 3 ° C (average value of n = 10). The reciprocal of the distance was displayed as an index with the value of Comparative Example 2 as 100. The larger the index, the shorter the braking distance and the better the braking performance.

  The results are as shown in Table 1, and in Examples 1 to 4 in which bowl-shaped fine particles were blended, the abrasion resistance was substantially compared to Comparative Examples 2 and 6 in which bamboo charcoal pulverized products and plant granules were blended. The braking performance on ice was greatly improved without any deterioration. In particular, braking performance on ice was greatly improved even in Comparative Example 3 in which hollow porous spherical fine particles having the same material as PMMA but having different shapes were blended.

  Further, in Example 5 in which the bowl-shaped fine particles and the plant granules are used in combination, and in Example 6 in which the bowl-shaped fine particles, the bamboo charcoal pulverized product and the plant granules are combined, the effect of further improving the braking performance on ice is obtained. Obtained.

  In Comparative Example 4 where the amount of bowl-shaped fine particles is too small, the effect of improving braking performance on ice is insufficient, and in Comparative Example 5 where the amount is too large, the wear resistance is greatly deteriorated. It was.

  The rubber composition according to the present invention is required to have anti-slip properties such as shoe soles, mats, floor materials, and the like, including various pneumatic tires such as winter tires such as studless tires and snow tires, and tires for industrial vehicles. Can be widely used for rubber products.

Claims (4)

Resin particles obtained by polymerizing at least one polymerizable monomer selected from methacrylic acid ester, acrylic acid ester, vinyl acetate and acrylonitrile with respect to 100 parts by weight of diene rubber and having an average particle size of 1 to 1 A rubber composition comprising 0.3 to 20 parts by weight of bowl-shaped fine particles of 100 μm . The rubber composition according to claim 1, wherein the bowl-shaped fine particles are made of a methacrylic resin. The rubber composition according to claim 1 or 2 , further comprising a plant granule obtained by pulverizing a seed shell or a fruit core and / or a pulverized product of a porous carbonaceous material of a plant. The pneumatic tire provided with the tread which consists of a rubber composition of any one of Claims 1-3 .