JP7640845B2 - Rubber composition for tires - Google Patents

Description

The present invention relates to a rubber composition for tires intended to be used primarily in the tread portion of winter tires.

In the rubber composition used in the tread of winter tires (e.g., studless tires, etc.) that are expected to run on snowy and icy roads, it is required to improve the running performance (performance on ice) on snowy and icy roads. For example, Patent Document 1 proposes blending powder obtained by crushing urethane foam into the rubber composition used in the tread of studless tires. That is, the powder of urethane foam maintains the elastic properties of the urethane foam, such as compression resistance and rebound elasticity, within the rubber composition, so by dispersing it in the rubber, the elastic properties of the rubber composition are improved, and the flexibility of the rubber composition is ensured, improving the ground contact with snowy and icy roads and improving the performance on ice. In addition, since water generated by melting snow and ice may be present on snowy and icy roads, in addition to the above-mentioned performance, it is also required to further improve wet performance. In order to achieve both of these performance characteristics (performance on ice, wet performance, and breaking elongation), the incorporation of various materials into the rubber composition (such as the urethane foam powder proposed in the aforementioned Patent Document 1) has been considered, and in particular, in recent years, the use of naturally derived ingredients has been considered from the perspective of environmental issues such as the depletion of petroleum resources and restrictions on carbon dioxide emissions.

JP 2007-31521 A

The object of the present invention is to provide a rubber composition for tires that improves performance on ice and in wet conditions and ensures good elongation at break.

The rubber composition for tires of the present invention that achieves the above-mentioned object is characterized in that, per 100 parts by mass of diene rubber, a total of 30 parts by mass to 100 parts by mass of carbon black and white filler, and 0.1 parts by mass to 30 parts by mass of a particle dispersion containing 10% by mass to 60% by mass of polyurethane-based fine particles are blended, the polyurethane-based fine particles being a synthetic product derived from a plant-based fatty acid ester containing a hydroxy group and having an average particle diameter of 1 μm to 100 μm.

The inventors of the present invention conducted extensive research into compounding agents for imparting excellent performance on ice to rubber compositions for tires, and discovered that by using a particle dispersion containing polyurethane-based microparticles (particularly synthetic substances derived from plant-based fatty acid esters containing hydroxyl groups and having an average particle size of 1 μm to 100 μm), it is possible to improve performance on ice and in wet conditions and ensure better elongation at break. Based on this discovery, the present invention provides a rubber composition for tires that is formulated as described above, and the amount of the particle dispersion and the proportion of the polyurethane-based microparticles in the particle dispersion are set within specific ranges, thereby improving performance on ice and in wet conditions and ensuring better elongation at break, and achieving a high level of compatibility between these performances in a well-balanced manner.

In the present invention, the particle dispersion is preferably a liquid diene polymer having a number average molecular weight of 1,000 to 100,000. It is also preferable that the polyurethane-based fine particles are surface-modified with a diene-based copolymer having an acid anhydride group or a carboxylic acid group. Furthermore, it is preferable that the vegetable fatty acid ester is a castor oil-based polyol. This is advantageous in improving the performance on ice and wet surfaces and in ensuring good breaking elongation.

In the present invention, it is preferable that the diene rubber contains natural rubber and polybutadiene rubber, and that the proportion of polybutadiene rubber in the diene rubber is 30 mass% or more. By using a diene rubber containing a moderate amount of polybutadiene rubber in this way, the rubber physical properties are improved, which is advantageous for improving performance on ice.

The above-mentioned rubber composition for tires of the present invention can be suitably used in the tread portion of studless tires. A tire using the rubber composition for tires of the present invention in the tread portion can improve performance on ice and wet surfaces and ensure good elongation at break due to the above-mentioned excellent rubber properties.

In the rubber composition for tires of the present invention, the rubber component is a diene rubber. As the diene rubber, rubbers generally used in rubber compositions for tires (particularly rubber compositions for winter tires) can be used. In the present invention, it is particularly preferable that the diene rubber contains natural rubber and polybutadiene rubber. When the diene rubber contains natural rubber and polybutadiene rubber, the amount of polybutadiene rubber is preferably 30% by mass or more, more preferably 30% to 70% by mass, in 100% by mass of the diene rubber. In addition, the amount of natural rubber is preferably 30% by mass or more, more preferably 30% to 70% by mass, in 100% by mass of the diene rubber. If the amount of polybutadiene rubber is less than 30% by mass, there is a risk of adversely affecting flexibility at low temperatures. In addition, the rubber composition of the present invention can also contain diene rubbers other than natural rubber and polybutadiene rubber. As the other diene rubbers, rubbers generally used in rubber compositions for tires, such as isoprene rubber and styrene-butadiene rubber, can be used. These other diene rubbers can be used alone or in any blend.

The rubber composition of the present invention is compounded with 30 to 100 parts by mass, preferably 35 to 90 parts by mass, of carbon black and/or white filler per 100 parts by mass of diene rubber. By compounding an appropriate amount of carbon black or white filler in this way, the flexibility of the rubber composition can be ensured and the performance on ice can be improved. If the amount of carbon black and/or white filler is less than 30 parts by mass, the mechanical properties of the rubber composition cannot be sufficiently ensured, and basic tire performance (e.g., hardness and abrasion resistance) may be reduced. If the amount of carbon black and/or white filler is more than 100 parts by mass, the flexibility of the rubber composition decreases and it becomes difficult to ensure good performance on ice. When carbon black and white filler are used in combination, the above-mentioned compounding amount is the total amount of these two.

Examples of carbon black include furnace carbon black such as SAF, ISAF, HAF, FEF, GPF, HMF, and SRF, which may be used alone or in combination of two or more. The nitrogen adsorption specific surface area N ₂ SA of carbon black is not particularly limited, but is preferably 40 m ² /g to 200 ^{m 2} /g, more preferably 50 m ² /g to 150 m ² /g. By making the nitrogen adsorption specific surface area of carbon black 40 m ² /g or more, the mechanical properties and abrasion resistance of the rubber composition can be ensured. In addition, by making the nitrogen adsorption specific surface area of carbon black 200 m ² /g or less, the performance on ice can be improved. In this specification, the nitrogen adsorption specific surface area N ₂ SA of carbon black is measured in accordance with JIS K6217-2.

Examples of white fillers include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These may be used alone or in combination of two or more. Among these, silica is preferred as it provides better performance on ice.

Examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate, which may be used alone or in combination of two or more. The CTAB adsorption specific surface area of silica is not particularly limited, but is preferably 80 m ² /g to 260 ^{m 2} /g, and more preferably 140 m ² /g to 200 m ² /g. By making the CTAB adsorption specific surface area of silica 80 m ² /g or more, the abrasion resistance of the rubber composition can be ensured. In addition, by making the CTAB adsorption specific surface area of silica 200 m ² /g or less, wet performance and low rolling resistance can be improved. In this specification, the CTAB specific surface area of silica is a value measured according to ISO 5794.

In the present invention, it is preferable to compound a silane coupling agent together with silica. By compounding a silane coupling agent, the dispersibility of silica in diene rubber can be improved, and the balance between wear resistance and performance on ice can be improved. The type of silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, but examples include sulfur-containing silane coupling agents such as bis-(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, γ-mercaptopropyl triethoxysilane, and 3-octanoylthiopropyl triethoxysilane. The amount of the silane coupling agent is preferably 3% to 15% by mass, more preferably 5% to 10% by mass, based on the weight of the silica. If the amount of the silane coupling agent is less than 3% by mass of the silica, there is a risk that the dispersion of the silica cannot be sufficiently improved. If the amount of silane coupling agent exceeds 15% by mass of the amount of silica, the silane coupling agents will condense with each other, making it impossible to obtain the desired hardness and strength in the rubber composition.

The rubber composition of the present invention contains a particle dispersion containing polyurethane-based microparticles, as described below. The inventors of the present invention have conducted extensive research into compounding agents for imparting excellent performance on ice to rubber compositions for tires, and have discovered that the use of a particle dispersion containing polyurethane-based microparticles having the properties described below improves performance on ice and wet surfaces, and also ensures good elongation at break.

The polyurethane-based microparticles used in the present invention are synthetic products derived from plant-based fatty acid esters containing hydroxyl groups. Examples of plant-based fatty acid esters containing hydroxyl groups include castor oil-based polyols, palm oil-based polyols, and peanut oil-based polyols. Of these, castor oil-based polyols are particularly suitable. By including the above-mentioned naturally derived polyurethane-based microparticles, the rubber composition can ensure appropriate flexibility and water absorption, which is advantageous for improving ice performance and wet performance while ensuring good breaking elongation. The term "polyurethane-based" refers to compounds having bonds such as urea bonds and urethane bonds that are generated by the reaction of isocyanate groups.

The polyurethane-based microparticles used in the present invention are preferably surface-modified with a diene-based copolymer having an acid anhydride group or a carboxylic acid group. By performing surface modification in this manner, the number of double bonds in the molecule increases, improving crosslinking with rubber and preventing the polyurethane-based microparticles from falling off. Examples of diene-based copolymers having an acid anhydride group or a carboxylic acid group include maleic anhydride-modified polyisoprene, maleic anhydride-modified polybutadiene, and maleic anhydride-modified polystyrene butadiene.

The polyurethane microparticles used in the present invention have an average particle size of 1 μm to 100 μm, preferably 10 μm to 50 μm. Having such an appropriate average particle size is advantageous for improving performance on ice and wet surfaces, and for ensuring good breaking elongation. If the average particle size is less than 1 μm, there is no effect of improving friction on ice, and if the average particle size exceeds 100 μm, breaking elongation decreases.

For example, a liquid diene-based polymer can be used as the particle dispersion used in the present invention. In particular, it is preferable that the polyurethane-based microparticles described above are compatible with the diene-based rubber that is the main component of the rubber composition of the present invention. In other words, it is preferable that the particle dispersion (liquid diene-based polymer) has a solubility parameter (SP value) close to that of the diene-based rubber that is the main component of the rubber composition of the present invention. In particular, it is preferable to use a liquid diene-based polymer that is composed of the same components as the diene-based rubber that is the main component of the rubber composition of the present invention.

When a liquid diene polymer is used as the particle dispersion, its number average molecular weight is preferably 1,000 to 100,000, more preferably 10,000 to 60,000. This is advantageous for improving ice performance and wet performance, and for ensuring better breaking elongation. If the number average molecular weight is less than 1,000, the fine particles cannot be retained, and the effect of improving friction on ice cannot be obtained. If the number average molecular weight exceeds 100,000, the fine particles cannot be dispersed, and the effect of improving friction on ice decreases. Examples of liquid diene polymers having a number average molecular weight of 1,000 to 100,000 include liquid isoprene polymer, liquid butadiene polymer, and liquid styrene butadiene polymer.

In the present invention, the polyurethane-based microparticles described above are dispersed in the particle dispersion described above. In this case, the proportion of the polyurethane-based microparticles contained in the particle dispersion is 10% by mass to 60% by mass, preferably 20% by mass to 50% by mass. In this way, by making the particle dispersion contain an appropriate amount of polyurethane-based microparticles, it is advantageous to improve the performance on ice and wet performance and to ensure good breaking elongation. If the proportion of the polyurethane-based microparticles contained in the particle dispersion is less than 10% by mass, the effect of improving friction on ice cannot be obtained. If the proportion of the polyurethane-based microparticles contained in the particle dispersion exceeds 60% by mass, the microparticles will aggregate and the breaking properties will deteriorate.

In the present invention, the above-mentioned particle dispersion containing the above-mentioned polyurethane-based fine particles is blended with the diene rubber, which is the main component of the rubber composition. In this case, the blending amount of the particle dispersion per 100 parts by mass of the diene rubber is 0.1 to 30 parts by mass, preferably 5 to 20 parts by mass. Blending the particle dispersion in this manner is advantageous for improving the performance on ice and in wet conditions, and for ensuring better breaking elongation. If the blending amount of the particle dispersion is less than 0.1 parts by mass, the particle dispersion (polyurethane-based fine particles) is too small, and the effect of blending it cannot be fully obtained. If the blending amount of the particle dispersion exceeds 30 parts by mass, the breaking elongation of the rubber composition decreases.

The rubber composition for tires of the present invention can be blended with various additives commonly used in rubber compositions for tires, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, plasticizers, processing aids, liquid polymers, terpene resins, and thermosetting resins, within the range that does not impair the object of the present invention. These additives can also be kneaded in a general manner to form a rubber composition, which can then be used for vulcanization or crosslinking. The amount of these additives blended can be a conventional amount, as long as it does not violate the object of the present invention. The rubber composition for tires can be produced by mixing the above-mentioned components using a general rubber kneading machine, such as a Banbury mixer, kneader, roll, etc.

The above-mentioned rubber composition for tires of the present invention can be suitably used in the tread portion of pneumatic tires (particularly winter tires such as studless tires that are expected to be driven on snowy and icy roads). A pneumatic tire using the rubber composition for tires of the present invention in the tread portion has excellent physical properties, which improves ice performance, wet performance, and breaking elongation beyond conventional levels, and can achieve a good balance between these performances.

The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

The compounding ingredients shown in Table 3 were used as a common compounding, and to prepare rubber compositions for tires (Standard Example 1, Comparative Examples 1-6, Examples 1-14) consisting of the compounds shown in Tables 1-2, the components except for sulfur and vulcanization accelerator were mixed in a 1.7 L Banbury mixer for 5 minutes, and when the temperature reached 145°C, they were released to form a master batch. Sulfur and vulcanization accelerator were added to the obtained master batch, and the mixture was mixed in an open roll at 70°C to obtain 21 types of rubber compositions for tires.

The resulting rubber composition for tires was evaluated for wet performance, ice performance, and elongation at break using the methods described below.

Wet Performance The obtained rubber composition for tires was vulcanized at 170°C for 10 minutes using a mold of a predetermined shape (inner dimensions: length 150 mm, width 150 mm, thickness 2 mm) to prepare a vulcanized rubber test piece. The dynamic viscoelasticity of the vulcanized rubber test piece was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of an elongation deformation strain rate of 10±2%, a vibration frequency of 20 Hz, and a temperature of 0°C, and tan δ (0°C) was obtained. The obtained results are shown in the "Wet Performance" column of Tables 1 and 2 as an index with the value of Standard Example 1 set to 100. The larger this index, the larger the tan δ (0°C) and the better the wet grip performance.

Performance on ice The obtained rubber composition for tires was vulcanized at 170°C for 10 minutes using a mold of a specified shape (inner dimensions: length 150 mm, width 150 mm, thickness 2 mm) to prepare a vulcanized rubber test piece. The vulcanized rubber test piece was attached to a flat cylindrical rubber base, and the coefficient of friction on ice was measured using an inside drum type ice friction tester under the following conditions: measurement temperature -3.0°C, load 5.5 kg/ ^cm2 , drum rotation speed 25 km/h. The obtained results are shown in the "Performance on ice" column in Tables 1 and 2 as an index, with the value of Standard Example 1 set to 100. The higher the index, the greater the frictional force on ice and the better the performance on ice. An index value of "105" or less means that the improvement in performance on ice is insufficient.

Breaking Elongation The obtained rubber composition for tires was vulcanized at 170°C for 10 minutes using a mold of a predetermined shape (inner dimensions: length 150 mm, width 150 mm, thickness 2 mm) to prepare a vulcanized rubber test piece. Using the vulcanized rubber test piece, a dumbbell JIS No. 3 test piece was prepared in accordance with JIS K6251, and a tensile test was performed at room temperature (20°C) at a pulling rate of 500 mm/min to measure the tensile breaking elongation when broken. The obtained results are shown in the "breaking elongation" column of Tables 1 and 2 as an index with the value of Standard Example 1 set to 100. The larger the index value, the larger the tensile breaking elongation (the better the tensile properties). Note that if the index value is "110" or less, the effect of improving the breaking elongation is insufficient.

The types of raw materials used in Tables 1 and 2 are shown below.
NR: Natural rubber, STR20 manufactured by Bonbandit (glass transition temperature: -65°C)
BR: Polybutadiene rubber, Nipol BR1220 manufactured by Zeon Corporation (glass transition temperature: -110°C)
CB: Carbon black, Cabot Japan's Show Black N339
Silica: ULTRASIL VN3 manufactured by Evonik Degussa
Silane coupling agent: Si69, bis(3-triethoxysilylpropyl)tetrasulfide manufactured by Evonik Degussa Particle dispersions 1 to 9: manufactured by the manufacturing method described below Urethane fine particles: Dimic Beads manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. (average particle size: 200 μm)

The types of raw materials used in Table 3 are shown below.
Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Co., Ltd. Stearic acid: Beads of stearic acid YR manufactured by Nippon Oil & Fats Co., Ltd.
Antiaging agent: Amine-based antiaging agent, Santoflex 6PPD manufactured by Flexis
Wax: Paraffin wax manufactured by Ouchi Shinko Chemical Co., Ltd. Oil: Aroma oil, Extract No. 4 S manufactured by Showa Shell Sekiyu Co., Ltd.
Sulfur: Hosoi Chemical Co., Ltd. oil-treated sulfur Vulcanization accelerator: Sulfenamide-based vulcanization accelerator, Sansera CM-G manufactured by Sanshin Chemical Co., Ltd.

Manufacturing method of particle dispersion 1 55.0 g of castor oil-based polyol A (HF-2009 manufactured by Ito Oil Mills, hydroxyl value 43.1 mgKOH/g), 14.5 g of dimethylthiotoluenediamine (Heartcure 30 manufactured by Kumiai Chemical Co., Ltd.), 79.5 g of liquid isoprene polymer (LIR-30 manufactured by Kuraray Co., Ltd., number average molecular weight 28000), and 1.1 g of sorbitan acid-based surfactant (TW-O320V manufactured by Kao Corporation) were stirred for 2 minutes with a planetary centrifugal mixer. Next, 11.0 g of polymeric MDI (Coronate 1331 manufactured by Tosoh Corporation, NCO% 32.4%) was added and stirred for 2 minutes. Next, maleic anhydride modified polyisoprene (LIR-403 manufactured by Kuraray Co., Ltd., number average molecular weight 34000, functional groups per molecule 3) was added thereto, and stirring was continued for 1 hour to obtain Particle Dispersion 1. When the obtained Particle Dispersion 1 was measured with a laser diffraction type particle size distribution measuring device, it was confirmed that particles having an average particle size of 10 μm were generated. In addition, the content of particles contained in Particle Dispersion 1 was 50 mass%.

Manufacturing method of particle dispersion 2 40.0 g of castor oil polyol A (HF-2009 manufactured by Ito Oil Milling Co., Ltd., hydroxyl value 43.1 mgKOH/g) and 9.6 g of 4,4'-diphenylmethane diisocyanate (Millionate MT manufactured by Tosoh Corporation, number average molecular weight 250) were reacted at 80 ° C. for 5 hours to obtain a terminal isocyanate castor oil urethane prepolymer (a castor oil-based urethane prepolymer having an isocyanate group at the end. It has a urethane bond.) 76.2 g of liquid isoprene polymer (LIR-30 manufactured by Kuraray Co., Ltd., number average molecular weight 28000) and 1.2 g of sorbitan acid surfactant (TW-O320V manufactured by Kao Corporation) were added to the terminal isocyanate castor oil urethane prepolymer prepared as described above, and the mixture was stirred for 2 minutes with a planetary centrifugal mixer. Then, 2.0 g of dimethylthiotoluenediamine (Heartcure 30 manufactured by Kumiai Chemical Co., Ltd.) and 7.4 g of polycarbonate diol (Duranol T5650J manufactured by Asahi Kasei Co., Ltd., hydroxyl value 139.6 mgKOH/g) were added thereto and stirred for 2 minutes. Then, 16.0 g of maleic anhydride modified polyisoprene (LIR-403 manufactured by Kuraray Co., Ltd., number average molecular weight 34000, number of functional groups per molecule 3) was added thereto and stirred for 1 hour to obtain particle dispersion 2. When the obtained particle dispersion 2 was measured with a laser diffraction type particle size distribution measuring device, it was confirmed that particles with an average particle size of 30 μm were generated. In addition, the content of particles contained in particle dispersion 2 was 50% by mass.

Manufacturing method of particle dispersion 3 Particle dispersion 3 was obtained according to the same procedure as the "manufacturing method of particle dispersion 1" described above, except that 50.0 g of castor oil-based polyol B (H-57 manufactured by Ito Oil Mills, hydroxyl value 92.9 mgKOH/g) was used instead of the above-mentioned castor oil-based polyol A, 2.2 g of dimethylthiotoluenediamine, 80.1 g of liquid isoprene polymer, 1.0 g of sorbitan acid surfactant, 16.9 g of polymeric MDI, and 10.0 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 3 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 30 μm were generated. In addition, the content of particles contained in particle dispersion 3 was 50 mass%.

Manufacturing method of particle dispersion 4 Particle dispersion 4 was obtained according to the same procedure as the above-mentioned "Manufacturing method of particle dispersion 2" except that 30.0 g of castor oil-based polyol B (H-57 manufactured by Ito Oil Mills, hydroxyl value 92.9 mgKOH/g) was used instead of the above-mentioned castor oil-based polyol A, 18.6 g of 4,4'-diphenylmethane diisocyanate, 81.8 g of liquid isoprene polymer, 0.9 g of sorbitan acid surfactant, 4.3 g of dimethylthiotoluenediamine, 16.0 g of polycarbonate diol, and 12.0 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 4 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 40 μm were generated. In addition, the content of particles contained in particle dispersion 4 was 50 mass%.

Manufacturing method of particle dispersion 5 Particle dispersion 5 was obtained according to the same procedure as the "manufacturing method of particle dispersion 1" described above, except that 37.0 g of castor oil-based polyol B (AC-009 manufactured by Ito Oil Mills, hydroxyl value 223.0 mgKOH/g) was used instead of the above-mentioned castor oil-based polyol A, 3.9 g of dimethylthiotoluenediamine, 79.0 g of liquid isoprene polymer, 0.7 g of sorbitan acid surfactant, 30.0 g of polymeric MDI, and 7.4 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 5 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 30 μm were generated. In addition, the content of particles contained in particle dispersion 5 was 50 mass%.

Manufacturing method of particle dispersion 6 Particle dispersion 6 was obtained according to the same procedure as in the above-mentioned "Manufacturing method of particle dispersion 2", except that 35.0 g of polycarbonate diol (Duranol T4692 manufactured by Asahi Kasei Corporation, hydroxyl value 56.1 mgKOH/g) was used instead of the above-mentioned castor oil-based polyol A, 13.1 g of 4,4'-diphenylmethane diisocyanate, 77.4 g of liquid isoprene polymer, 1.1 g of sorbitan acid surfactant, 3.0 g of dimethylthiotoluenediamine, and 14.0 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 6 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 150 μm were generated. In addition, the content of particles contained in particle dispersion 6 was 50 mass%.

Manufacturing method of particle dispersion 7 Particle dispersion 7 was obtained according to the same procedure as the "Manufacturing method of particle dispersion 1" described above, except that 11.0 g of the castor oil-based polyol A described above, 0.2 g of dimethylthiotoluenediamine, 138.3 g of liquid isoprene polymer, 0.2 g of sorbitan acid surfactant, 1.7 g of polymeric MDI, and 2.2 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 7 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 20 μm were generated. In addition, the content of particles contained in particle dispersion 7 was 10 mass%.

Manufacturing method of particle dispersion 8 Particle dispersion 8 was obtained according to the same procedure as the "Manufacturing method of particle dispersion 1" described above, except that 33.0 g of the castor oil-based polyol A, 0.7 g of dimethylthiotoluenediamine, 107.6 g of liquid isoprene polymer, 0.7 g of sorbitan acid surfactant, 5.2 g of polymeric MDI, and 6.6 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 8 was measured with a laser diffraction particle size distribution measuring device, and it was confirmed that particles with an average particle size of 20 μm were generated. In addition, the content of particles contained in particle dispersion 8 was 30 mass%.

Manufacturing method of particle dispersion 9 Particle dispersion 6 was obtained according to the same procedure as in the above-mentioned "Manufacturing method of particle dispersion 2", except that 33.0 g of polycarbonate diol (Duranol T5651 manufactured by Asahi Kasei Corporation, hydroxyl value 112 mgKOH/g) was used instead of the above-mentioned castor oil-based polyol A, 24.7 g of 4,4'-diphenylmethane diisocyanate, 88.7 g of liquid isoprene polymer, 0.9 g of sorbitan acid surfactant, 9.9 g of dimethylthiotoluenediamine, and 19.4 g of maleic anhydride-modified polyisoprene were used. The obtained particle dispersion 9 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 50 μm were generated. In addition, the content of particles contained in particle dispersion 9 was 50 mass%.

Manufacturing method of particle dispersion 10 Particle dispersion 10 was obtained according to the same procedure as in the "Manufacturing method of particle dispersion 1" described above, except that liquid isoprene polymer B (LIR-50 manufactured by Kuraray Co., Ltd., number average molecular weight 54,000) was used instead of the liquid isoprene polymer A described above. The obtained particle dispersion 11 was measured with a laser diffraction type particle size distribution measuring device, and it was confirmed that particles with an average particle size of 50 μm were produced. In addition, the content of particles contained in particle dispersion 10 was 50 mass%.

As is clear from Table 1, the tire rubber compositions of Examples 1 to 14 (using any of Particle Dispersions 1 to 5, 7, 8, and 10) improved wet performance, ice performance, and breaking elongation compared to Standard Example 1, and achieved a high degree of compatibility between these. On the other hand, in Comparative Example 1 (using Particle Dispersion 6), the particles contained in the particle dispersion were not a synthetic product derived from a plant-based fatty acid ester containing a hydroxyl group, and the average particle diameter was too large, so the breaking elongation was deteriorated. In Comparative Example 2 (using Particle Dispersion 9), the particles contained in the particle dispersion were not a synthetic product derived from a plant-based fatty acid ester containing a hydroxyl group, so the ice performance and breaking elongation could not be sufficiently improved. In Comparative Example 3, the breaking elongation was deteriorated because the particle dispersion contained urethane fine particles instead of a particle dispersion. In Comparative Example 4 (using Particle Dispersion 1), the amount of particle dispersion was too high, so the breaking elongation was deteriorated. In Comparative Example 5 (using Particle Dispersion 1), the amount of silica and carbon black (total of fillers) was low, so the wet performance was deteriorated. Comparative Example 6 (using Particle Dispersion 1) had a high amount of silica and carbon black (total of fillers), which resulted in poor performance on ice and poor elongation at break.

Claims (6)

A rubber composition for tires, comprising 100 parts by mass of diene rubber, a total of 30 to 100 parts by mass of carbon black and a white filler, and 0.1 to 30 parts by mass of a particle dispersion containing 10 to 60% by mass of polyurethane fine particles, wherein the polyurethane fine particles are a synthetic product derived from a plant-based fatty acid ester containing a hydroxy group and have an average particle size of 1 μm to 100 μm. The rubber composition for tires according to claim 1, characterized in that the particle dispersion is a liquid diene-based polymer having a number average molecular weight of 1,000 to 100,000. The rubber composition for tires according to claim 1 or 2, characterized in that the polyurethane-based fine particles are surface-modified with a diene-based copolymer having an acid anhydride group or a carboxylic acid group. The rubber composition for tires according to any one of claims 1 to 3, characterized in that the vegetable fatty acid ester is a castor oil-based polyol. The rubber composition for tires according to any one of claims 1 to 4, characterized in that the diene rubber contains natural rubber and polybutadiene rubber, and the proportion of the polybutadiene rubber in the diene rubber is 30 mass % or more. A studless tire characterized in that the rubber composition for tires according to any one of claims 1 to 5 is used in the tread portion.