Rubber composition for tires and studless tires using the same

Abstract

On icy and snowy roads, the coefficient of friction is lower than on normal roads, making them more slippery. Therefore, numerous methods have been proposed to improve the ice performance of studless tires, but there is a need to further enhance ice performance. [Solution] The above problem was solved by a tire rubber composition containing diene rubber, at least one filler selected from the group consisting of carbon black and white filler, and aggregated particles containing polyvinyl alcohol and inorganic fine particles with an average particle diameter of 1 to 300 μm, wherein the proportion of the inorganic fine particles in the aggregated particles exceeds 50% by mass, and the amount of aggregated particles blended is 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber.

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires and a studless tire using the same, and more particularly, to a rubber composition for tires having excellent ice performance and a studless tire using the same.

Background Art

[0002] On icy and snowy roads, the friction coefficient is lower than that on ordinary roads, making it easier to slip. Therefore, conventionally, many methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. For example, in Patent Document 1 below, a tread rubber composition containing 3 to 25 parts by weight of a powder of a water-soluble polymer having a melting point of 180°C or higher and a solubility in 100 g of water at 0°C of 5 g or more and having an average particle size of 20 to 600 μm with respect to 100 parts by weight of a base rubber is used for a studless tire. The studless tire described in Patent Document 1 is said to improve the ice grip performance by, for example, the crystals of the water-soluble polymer powder being exposed on the tire surface due to wear and scraping the ice surface on the road to exhibit a spike effect. Currently, there is a demand for a method to further improve the ice performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a rubber composition for tires having excellent ice performance and a studless tire using the same.

Means for Solving the Problems

[0005] As a result of diligent research, the inventors of the present invention have discovered that a tire rubber composition comprising a diene-based rubber blended with polyvinyl alcohol and inorganic fine particles having a specific average particle size in a specific amount can solve the above problems, and have completed the present invention.

[0006] In other words, the present invention contains diene rubber, at least one filler selected from the group consisting of carbon black and white fillers, and aggregated particles comprising polyvinyl alcohol and inorganic fine particles with an average particle size of 1 to 300 μm. The proportion of inorganic fine particles in the aggregated particles exceeds 50% by mass, The amount of aggregated particles blended is 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber. This invention provides a rubber composition for tires characterized by the following features.

[0007] Furthermore, the present invention provides a studless tire in which the above-mentioned tire rubber composition is used in the tread portion. [Effects of the Invention]

[0008] The rubber composition of the present invention contains a diene rubber, at least one filler selected from the group consisting of carbon black and a white filler, polyvinyl alcohol and inorganic fine particles having an average particle diameter of 1 to 300 μm, wherein the proportion of the inorganic fine particles in the aggregated particles exceeds 50% by mass, and the amount of aggregated particles blended is 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber. Therefore, it is possible to provide a rubber composition with excellent ice performance and a studless tire using the same.

[0009] The aggregated particles in this invention contain inorganic fine particles and polyvinyl alcohol having a binding function, with the polyvinyl alcohol binding the inorganic fine particles together, and have an average particle size of 1 to 300 μm. Aggregated particles having this configuration can improve the surface roughness of the tire and significantly increase the coefficient of friction on the tire surface, thereby improving performance on ice. [Brief explanation of the drawing]

[0010] [Figure 1] This is an electron microscope image of one form of aggregated particles used in the present invention. [Modes for carrying out the invention]

[0011] The present invention will be described in more detail below. (Diene-based rubber) The diene rubber used in this invention can be any diene rubber that can be incorporated into tire rubber compositions, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and ethylene-propylene-diene polymer (EPDM). These may be used individually or in combination of two or more. Furthermore, their molecular weight and microstructure are not particularly limited, and they may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or epoxidized. The weight-average molecular weight (Mw) of the above diene rubber is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000. In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are standard polystyrene equivalent values ​​obtained by gel permeation chromatography (GPC) measurement. Furthermore, from the viewpoint of improving ice performance, it is preferable that butadiene rubber accounts for 30% by mass or more, preferably 40% by mass or more, of the diene-based rubber. Furthermore, it is preferable that the diene-based rubber has a glass transition temperature (Tg) of -50°C or lower. By specifying the Tg in this way, the performance on ice is improved. When multiple types of diene rubber are included, the Tg as used herein is calculated based on the weighted average, which is the sum of the products obtained by multiplying the glass transition temperature of each rubber by the weight fraction of each rubber. For calculation purposes, the sum of the weight fractions of each component is assumed to be 1.0. In this invention, the glass transition temperature (Tg) refers to the temperature at the midpoint of the transition region, measured by differential scanning calorimetry (DSC) at a heating rate of 20°C / min using a thermogram. A more preferable average Tg is -60°C or lower.

[0012] (Filler) The rubber composition for tires of the present invention includes at least one filler selected from the group consisting of carbon black and white fillers. Specifically, examples of carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF. These may be used individually or in combination of two or more types. Furthermore, from the perspective of improving ice performance, the carbon black should have a nitrogen adsorption specific surface area (N2SA) of 10 to 300 m². 2 It is preferable that the amount is / g, and 50-150m 2 It is even more preferable that it be / g. The nitrogen adsorption specific surface area (N2SA) was measured according to JIS K 6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0013] Examples of white fillers used in the present invention include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium dioxide, calcium sulfate, etc. These may be used individually or in combination of two or more. Of these, silica is preferred because it provides better performance on ice. As the silica, specifically, for example, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. can be mentioned. These may be used alone or in combination of two or more. Also, silica may be silica made from biomass materials such as rice husks as a raw material.

[0014] From the viewpoint of improving the performance on ice, the silica preferably has a CTAB adsorption specific surface area of 50 to 300 m 2 / g, and more preferably 90 to 200 m 2 / g. The CTAB adsorption specific surface area is a value measured according to JIS K6217-3:2001 "Part 3: Method for determining specific surface area - CTAB adsorption method" for the adsorption amount of n-hexadecyltrimethylammonium bromide on the silica surface.

[0015] (Agglomerated particles) The agglomerated particles used in the present invention contain polyvinyl alcohol and inorganic fine particles. Polyvinyl alcohol has a role as a binder, and a plurality of inorganic fine particles are bound by polyvinyl alcohol. FIG. 1 is an electron micrograph of one form of the agglomerated particles used in the present invention. In FIG. 1, it can be seen that light-colored spherical inorganic fine particles are bound by dark-colored polyvinyl alcohol. The agglomerated particles of the present invention have an average particle diameter of 1 μm to 300 μm, and the proportion of inorganic fine particles in the agglomerated particles exceeds 50% by mass. The agglomerated particles satisfying these conditions exhibit a good scratching effect on the ice and snow road surface and can enhance the performance on ice. The average particle diameter can be measured according to a known measurement method. For example, from 100 samples, using an electron microscope, a laser microscope, a microscope, etc., image processing is performed to obtain the equivalent circle diameter, and the average particle diameter can be calculated.

[0016] The inorganic fine particles in the aggregated particles are preferably at least one selected from the group consisting of silica, aluminum hydroxide, calcium carbonate, and aluminum silicate. These inorganic fine particles in the aggregated particles are not included in the amount of the white filler.

[0017] Furthermore, from the viewpoint of improving the effects of the present invention, it is preferable that one or more of the following conditions be met. (1) The average particle size of the aggregated particles is more preferably 1 μm to 100 μm. (2) The proportion of inorganic fine particles in the aggregated particles is more preferably 70 to 94% by mass. (3) The melting point of the polyvinyl alcohol is preferably 150°C or higher, and more preferably 180 to 230°C. (4) The proportion of polyvinyl alcohol in the aggregated particles is preferably 5% by mass or more, and more preferably 7 to 30% by mass. (5) The maximum diameter of the primary particles of the inorganic fine particles is preferably less than 20 μm, and more preferably between 0.01 μm and 15 μm. (6) The degree of saponification of the polyvinyl alcohol is preferably 75 mol% or more, and more preferably 80 mol% or more.

[0018] The aggregated particles used in this invention can be produced, for example, as follows. First, polyvinyl alcohol is dissolved in water to obtain an aqueous solution of polyvinyl alcohol. Next, inorganic fine particles are added to the aqueous solution, for example, to satisfy the conditions in (2) above, and stirred for several minutes using, for example, a rotary-orbiting agitator. Then, oil is added and stirred for several more minutes. The amount of oil added is preferably 30% by mass or more, more preferably 35-80% by mass, relative to the total amount of polyvinyl alcohol, inorganic fine particles, water, and oil. The aggregated particles used in the present invention are obtained by dehydrating the resulting system, for example, in a vacuum oven.

[0019] (Compounding ratio of rubber composition for tires) The tire rubber composition of the present invention is characterized by containing 0.1 to 30 parts by mass of the aggregated particles with respect to 100 parts by mass of the diene rubber. If the amount of aggregated particles added to 100 parts by mass of the diene rubber is less than 0.1 parts by mass, the amount added is too small to achieve the effects of the present invention. Conversely, if it exceeds 30 parts by mass, the ice performance deteriorates.

[0020] The amount of aggregated particles is more preferably 1 to 20 parts by mass per 100 parts by mass of diene rubber. Furthermore, the amount of at least one filler selected from the group consisting of carbon black and white fillers is preferably 30 to 100 parts by mass per 100 parts by mass of the diene rubber. When using carbon black, the amount added is more preferably 1 to 80 parts by mass per 100 parts by mass of diene rubber. When using a white filler, the amount added is more preferably 1 to 80 parts by mass per 100 parts by mass of diene rubber.

[0021] (Other ingredients) In addition to the components mentioned above, the rubber composition of the present invention may contain various additives commonly used in rubber compositions, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; zinc oxide; antioxidants; plasticizers; and silane coupling agents. These additives can be mixed in a conventional manner to form a composition that can then be used for vulcanization or crosslinking. The amounts of these additives can also be the conventional amounts, as long as they do not contradict the purpose of the present invention.

[0022] Furthermore, the studless tire of the present invention can be prepared using the rubber composition of the present invention, and is preferably a pneumatic tire, and can be filled with air, nitrogen or other inert gases and other gases. Furthermore, the rubber composition of the present invention is used in the tread portion of the studless tire, particularly the cap tread portion. It is best to apply this to [the situation]. [Examples]

[0023] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0024] Method for producing aggregated particles 1 5.0 g of fully saponified polyvinyl alcohol (Kuraray POVA 28-98, manufactured by Kuraray Co., Ltd., melting point = 222°C, degree of saponification = 98 mol% or higher) was dissolved in 27.5 g of distilled water to obtain an aqueous solution of polyvinyl alcohol. 32.5 g of the aqueous solution of polyvinyl alcohol and 22.5 g of silica (AEROSIL R972, manufactured by Evonik, maximum primary particle diameter = 0.02 μm) were stirred in a rotary-orbiting stirrer for 3 minutes. Then, 110.0 g of oil (Extract No. 4 S, manufactured by Shell Lubricants Japan Co., Ltd.) was added and stirred in a rotary-orbiting stirrer for 3 minutes. The obtained system was dehydrated in a vacuum oven to obtain a dispersion in which aggregated particles were dispersed in oil. The content of aggregated particles in the dispersion was 20% by mass. The obtained aggregated particles are also referred to as aggregated particles 1, and the dispersion in which aggregated particles 1 were dispersed in oil is also referred to as aggregated particle dispersion 1. The average particle size of aggregated particle 1 was measured using a microscope and found to be 84 μm.

[0025] Manufacturing method for aggregated particles 2 10.0 g of fully saponified polyvinyl alcohol (Kuraray Poval 28-98, manufactured by Kuraray Co., Ltd., saponification degree = 98 mol% or higher) was dissolved in 55.0 g of distilled water to obtain an aqueous solution of polyvinyl alcohol. 65.0 g of the aqueous solution of polyvinyl alcohol and 45.0 g of aluminum hydroxide (BF013, manufactured by Nippon Light Metal Co., Ltd., maximum primary particle diameter = 1 μm) were stirred for 3 minutes in a rotary-orbiting agitator. 55.0 g of oil (Extract No. 4 S, manufactured by Shell Lubricants Japan Co., Ltd.) was then added and stirred for 3 minutes in the rotary-orbiting agitator. The obtained system was dehydrated in a vacuum oven to obtain a dispersion in which aggregated particles were dispersed in oil. The content of aggregated particles in the dispersion was 50% by mass. The obtained aggregated particles are also called aggregated particles 2, and the dispersion in which aggregated particles 2 were dispersed in oil is also called aggregated particle dispersion 2. The average particle size of aggregated particles 2 was measured using a microscope and found to be 13 μm.

[0026] Method for producing aggregated particles 3 In the method for producing aggregated particles 2 described above, a dispersion in which aggregated particles were dispersed in oil was obtained by following the same procedure as above, except that calcium carbonate (Calfoseal 15B, manufactured by Maruo Calcium Co., Ltd., with a maximum primary particle diameter of 0.07 μm) was used instead of aluminum hydroxide. The content of aggregated particles in the dispersion was 50% by mass. The obtained aggregated particles are also referred to as aggregated particles 3, and the dispersion in which aggregated particles 3 were dispersed in oil is also referred to as aggregated particle dispersion 3. The average particle size of aggregated particles 3 was measured using a microscope and found to be 62 μm.

[0027] Method for producing aggregated particles 4 In the method for producing aggregated particles 2 described above, aggregated particles dispersed in oil were obtained by following the same procedure as above, except that aluminum silicate (Dragonite HP-A, manufactured by APPLIED MINERALS, with a maximum primary particle diameter of 2 μm) was used instead of aluminum hydroxide. The particle content in the dispersion was 50% by mass. The obtained aggregated particles are also referred to as aggregated particles 4, and the dispersion of aggregated particles 4 in oil is also referred to as aggregated particle dispersion 4. The average particle size of aggregated particles 4 was measured using a microscope and found to be 42 μm.

[0028] Method for manufacturing aggregated particles 5 In the method for producing the aggregated particles 2 described above, aggregated particles dispersed in oil were obtained by following the same procedure except that mica (A-11, manufactured by Yamaguchi Mica Co., Ltd., with a maximum primary particle diameter of 3 μm) was used instead of aluminum hydroxide. The particle content in the dispersion was 50% by mass. The obtained aggregated particles are also referred to as aggregated particles 5, and the dispersion of aggregated particles 5 in oil is also referred to as aggregated particle dispersion 5. The average particle size of aggregated particles 5 was measured using a microscope and found to be 51 μm.

[0029] Method for producing aggregated particles 6 6.0 g of partially saponified polyvinyl alcohol (Kuraray Poval 22-88, manufactured by Kuraray Co., Ltd., degree of saponification = 88 mol%) was dissolved in 33.0 g of distilled water to obtain an aqueous solution of polyvinyl alcohol. 39.0 g of the aqueous solution of polyvinyl alcohol and 54.0 g of calcium carbonate (Snowlight S, manufactured by Maruo Calcium Co., Ltd., maximum primary particle diameter = 6 μm) were stirred for 3 minutes in a rotary-orbiting stirrer. 60.0 g of oil (Extract No. 4 S, manufactured by Shell Lubricants Japan Co., Ltd.) was then added and stirred for 3 minutes in the rotary-orbiting stirrer. The obtained system was dehydrated in a vacuum oven to obtain a dispersion in which aggregated particles were dispersed in oil. The content of aggregated particles in the dispersion was 50% by mass. The obtained aggregated particles are also called aggregated particles 6, and the dispersion in which aggregated particles 6 are dispersed in oil is also called aggregated particle dispersion 6. The average particle size of aggregated particles 6 was measured using a microscope and found to be 35 μm.

[0030] Method for producing aggregated particles 7 In the method for producing the aggregated particles 2 described above, aggregated particles dispersed in oil were obtained by following the same procedure as above, except that calcium carbonate (Whiscal, manufactured by Maruo Calcium Co., Ltd., with a maximum primary particle diameter of 20 μm) was used instead of aluminum hydroxide. The content of aggregated particles in the dispersion was 50% by mass. The obtained aggregated particles are also referred to as aggregated particles 7, and the dispersion of aggregated particles 7 dispersed in oil is also referred to as aggregated particle dispersion 7. The average particle size of aggregated particles 7 was measured using a microscope and found to be 76 μm.

[0031] Method for producing comparative aggregated particles 1 In the method for producing aggregated particles 3 described above, aggregated particles dispersed in oil were obtained by following the same procedure except that the amount of calcium carbonate was changed to 10 g and the amount of oil was changed to 20 g. The particle content in the dispersion was 50% by mass. The obtained aggregated particles are also called comparative aggregated particles 1, and the dispersion of comparative aggregated particles 1 dispersed in oil is also called comparative aggregated particle dispersion 1. The average particle size of comparative aggregated particle 1 was measured using a microscope and found to be 311 μm.

[0032] Standard Example 1, Examples 1-8, Comparative Examples 1-3 In the formulations (parts by mass) shown in Table 1, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then released from the mixer and cooled to room temperature. Subsequently, the composition was put back into the same Banbury mixer, the vulcanization system was added and kneaded to obtain a rubber composition.

[0033] Ice Performance: Using the rubber compositions manufactured as described above, a pneumatic tire (tire size: 215 / 60R16) was produced by vulcanization molding using each rubber composition in the tread. The pneumatic tire was mounted on a 16×7J rim, inflated to 220 [kPa] air pressure, and mounted on a test vehicle (Japanese 2-liter sedan FF vehicle). Subsequently, the test vehicle was subjected to emergency braking from an initial speed of 40 [km / h] on an icy test course, and the braking distance until a complete stop was measured. The braking distance results measured as described above are shown as an index with the reciprocal of Standard Example 1 set to 100. A larger index indicates better ice performance. The results are shown in Table 1.

[0034] [Table 1]

[0035] *1: NR (STR20 manufactured by Bombandit, glass transition temperature = -65°C) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., glass transition temperature = -110℃) *3: Silica (ULTRASIL VN3 manufactured by Evonik DeGussa) *4: Carbon black (Show Black N339 manufactured by Cabot Japan Co., Ltd.) *5: Silane coupling agent (Si69 manufactured by Evonik DeGussa) *6: Zinc oxide (3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd.) *7: Stearic acid (YR bead stearic acid manufactured by NOF Corporation) *8: Anti-aging agent (Santoflex 6PPD manufactured by Flexis, an amine-based anti-aging agent) *9: Wax (Paraffin wax manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *10: Oil (Shell Lubricants Japan Extract No. 4S, aroma oil) *11: Sulfur (5% oil-treated sulfur manufactured by Hosoi Chemical Industry Co., Ltd.) *12: Vulcanization accelerator (Sunceller CM-G, manufactured by Sanshin Chemical Industry Co., Ltd.) *13: Polyvinyl alcohol (JF-17S, manufactured by Nippon Vivaceae Co., Ltd., #100 pass grade) *14: Calcium carbonate (Snowlight S, manufactured by Maruo Calcium Co., Ltd.) *Agglutinated particle dispersions 1-7, comparative aggregated particle dispersion 1: Manufactured as described above.

[0036] From the results in Table 1, the rubber composition of each example contains diene rubber, at least one filler selected from the group consisting of carbon black and white filler, polyvinyl alcohol and inorganic fine particles with an average particle size of 1 to 300 μm, the proportion of the inorganic fine particles in the aggregated particles exceeds 50% by mass, and the amount of aggregated particles is 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber, thus improving ice performance compared to Standard Example 1. In contrast, Comparative Example 1 was simply an example in which polyvinyl alcohol was added, so the ice performance did not improve as much as in the examples. Comparative Example 2 was simply an example in which calcium carbonate was added, so the ice performance did not improve as much as in the other examples. Comparative Example 3 did not show as much improvement in ice performance as the other examples because the proportion of inorganic fine particles in the aggregated particles was 50% by mass or less, and the average particle size of the aggregated particles exceeded 300 μm.

[0037] This disclosure includes the following embodiments. Embodiment 1: It contains diene rubber, at least one filler selected from the group consisting of carbon black and white fillers, and aggregated particles containing polyvinyl alcohol and inorganic fine particles with an average particle size of 1 to 300 μm. The proportion of inorganic fine particles in the aggregated particles exceeds 50% by mass, The amount of aggregated particles blended is 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber. A rubber composition for tires characterized by the following features. Embodiment 2: The rubber composition according to Embodiment 1, characterized in that the melting point of the polyvinyl alcohol is 150°C or higher. Embodiment 3: The rubber composition according to Embodiment 1 or 2, characterized in that the inorganic fine particles include at least one selected from the group consisting of silica, aluminum hydroxide, calcium carbonate, and aluminum silicate. Embodiment 4: The tire rubber composition according to any one of Embodiments 1 to 3, characterized in that the proportion of polyvinyl alcohol in the aggregated particles is 5% by mass or more. Embodiment 5: The tire rubber composition according to any one of Embodiments 1 to 4, characterized in that the maximum diameter of the primary particles of the inorganic fine particles is less than 20 μm. Embodiment 6: The tire rubber composition according to any one of Embodiments 1 to 5, characterized in that the degree of saponification of the polyvinyl alcohol is 75 mol% or more. Embodiment 7: The tire rubber composition according to any one of Embodiments 1 to 6, characterized in that the diene rubber comprises natural rubber and butadiene rubber, the proportion of butadiene rubber to the total diene rubber is 30% by mass or more, and the filler is contained in an amount of 30 to 100 parts by mass per 100 parts by mass of the diene rubber. Embodiment 8: A studless tire using the tire rubber composition described in any of Embodiments 1 to 7 in the tread portion.

Claims

1. It contains diene rubber, at least one filler selected from the group consisting of carbon black and white fillers, and aggregated particles containing polyvinyl alcohol and inorganic fine particles with an average particle size of 1 to 300 μm. The proportion of inorganic fine particles in the aggregated particles exceeds 50% by mass, The amount of the aggregated particles is 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber. A rubber composition for tires characterized by the following features.

2. The tire rubber composition according to claim 1, characterized in that the melting point of the polyvinyl alcohol is 150°C or higher.

3. The tire rubber composition according to claim 1, characterized in that the inorganic fine particles include at least one selected from the group consisting of silica, aluminum hydroxide, calcium carbonate, and aluminum silicate.

4. The tire rubber composition according to claim 1, characterized in that the proportion of polyvinyl alcohol in the aggregated particles is 5% by mass or more.

5. The tire rubber composition according to claim 1, characterized in that the maximum diameter of the primary particles of the inorganic fine particles is less than 20 μm.

6. The tire rubber composition according to claim 1, characterized in that the degree of saponification of the polyvinyl alcohol is 75 mol% or more.

7. The tire rubber composition according to claim 1, characterized in that the diene rubber comprises natural rubber and butadiene rubber, the proportion of the butadiene rubber to the total diene rubber is 30% by mass or more, and the filler is contained in an amount of 30 to 100 parts by mass per 100 parts by mass of the diene rubber.

8. A studless tire using the tire rubber composition described in claim 1 in the tread portion.

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