JP2017031356A - Rubber composition for studless tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for studless tire for maintaining and enhancing abrasion resistance and on-ice performance while reducing heat generation property by blending carbon black having a specific colloidal property.SOLUTION: Thermal expansion microcapsule of 0.2 to 20 pts.mass and carbon black having nitrogen adsorption specific surface area NSA of 90 m/g or less and compression DBP absorption amount (24M4) of 95 to 120 ml/100 g of 30 to 70 pts.mass are blended with 100 pts.mass of a diene rubber containing a butadiene rubber of 30 to 50 mass% and a natural rubber of 50 to 70 mass% and a ratio of mode diameter Dst (nm) in a mass distribution curve of a Stokes diameter of an aggregate of the carbon black and half band width thereof ΔDst (nm), ΔDst/Dst is 0.65 or more and the NSA, (24M4) and Dst satisfy the following formula;(24M4)/Dst<0.0093×NSA-0.06.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a rubber composition for studless tires that maintains and improves wear resistance and performance on ice while reducing heat build-up by incorporating carbon black having specific colloidal characteristics.

  A structure that improves the performance on ice of a pneumatic tire (studless tire) for icy and snowy roads. By forming a large number of bubbles in the tread rubber, these bubbles form a water film on the ice surface when the tread steps on the ice surface. It is known that the water is absorbed and removed, and when the tread is separated from the ice surface, the absorbed water is repeatedly separated by centrifugal force. Patent Document 1 proposes blending thermally expandable microcapsules with a rubber composition for studless tires as a means for forming such bubbles. Since this thermally expandable microcapsule expands when heated in the vulcanization process, a large number of bubbles (resin-coated bubbles) covered with the shell of the expanded microcapsule are formed in the rubber compound of the vulcanized tire. However, a studless tire using such a rubber compound has a problem that wear resistance is deteriorated.

  On the other hand, with increasing interest in global environmental issues, fuel efficiency is required to be excellent, and studless tires are no exception as required performance for pneumatic tires. In order to improve fuel efficiency, it is necessary to reduce rolling resistance, and heat generation of the rubber composition constituting the tire is suppressed to reduce rolling resistance. Generally, 60 ° C. tan δ by dynamic viscoelasticity measurement is used as an index of exothermic property of the rubber composition. The smaller the tan δ (60 ° C.) of the rubber composition, the smaller the exothermic property.

  Examples of a method for reducing the tan δ (60 ° C.) of the rubber composition include increasing the particle size of carbon black, reducing the amount of compound, and compounding silica. However, in such a method, there is a problem that the wear resistance is greatly reduced when a pneumatic tire, particularly a studless tire having a tread rubber containing a thermally expandable microcapsule is used.

Japanese Patent Laid-Open No. 10-316801

  An object of the present invention is to provide a rubber composition for studless tires that maintains and improves wear resistance and on-ice performance while reducing heat build-up by incorporating carbon black having specific colloidal characteristics. is there.

The rubber composition for studless tires of the present invention that achieves the above-mentioned object has 0 thermal expansion microcapsules with respect to 100 parts by mass of diene rubber containing 30 to 50% by mass of butadiene rubber and 50 to 70% by mass of natural rubber. ² to 20 parts by mass, 30 to 70 parts by mass of carbon black having a nitrogen adsorption specific surface area N ₂ SA of 90 m ² / g or less and a compressed DBP absorption (24M4) of 95 to 120 ml / 100 g, and the carbon black The ratio ΔDst / Dst of the mode diameter Dst (nm) and its half-value width ΔDst (nm) in the mass distribution curve of the Stokes diameter of the aggregate is 0.65 or more, and the N ₂ SA, (24M4) and Dst are as follows: (1) is satisfied.
(24M4) / Dst <0.0093 × N ₂ SA−0.06 (1)
(Where Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and (24M4) is the compressed DBP absorption (ml / 100 g). is there.)

The rubber composition for studless tires of the present invention comprises 0.2 to 20 mass of thermally expandable microcapsules with respect to 100 mass parts of diene rubber containing 30 to 50 mass% of butadiene rubber and 50 to 70 mass% of natural rubber. Part, the nitrogen adsorption specific surface area N ₂ SA is 90 m ² / g or less, the compressed DBP absorption (24M4) is 95 to 120 ml / 100 g, and the ratio ΔDst / Dst in the Stokes diameter mass distribution curve of the carbon black aggregate is 0.65. As described above, since 30 to 70 parts by mass of carbon black satisfying the relationship of the above formula (1) is blended, the wear resistance and the performance on ice are maintained and improved while reducing the heat build-up of the rubber composition. Can do.

The Dst of the carbon black is preferably 160 nm or more. The N ₂ SA of carbon black is preferably not 50 m ² / g or more.

  The studless tire using the rubber composition for studless tires of the present invention in the tread portion has improved heat resistance and on-ice performance over conventional levels while reducing heat generation and rolling resistance to improve fuel efficiency. Can do.

The carbon black ASTM grade is a graph showing the relationship between (24M4) / Dst for N ₂ SA. For carbon black used in the rubber composition for a tire of the present invention, an example of a graph showing the relationship between (24M4) / Dst for N ₂ SA. It is a graph showing the carbon (24M4) for N ₂ SA of the black / Dst relationship used in Examples and Comparative Examples herein.

  In the rubber composition for studless tires of the present invention, the diene rubber necessarily contains butadiene rubber and natural rubber. By using natural rubber and butadiene rubber as main components, the performance on ice can be enhanced.

  The content of butadiene rubber is 30 to 50% by mass, preferably 35 to 45% by mass, in 100% by mass of the diene rubber. When the content of butadiene rubber is less than 30% by mass, the performance on ice is lowered. On the other hand, when the content of butadiene rubber exceeds 70% by mass, the mechanical properties deteriorate.

  The content of the natural rubber is 50 to 70% by mass, preferably 55 to 65% by mass in 100% by mass of the diene rubber. If the content of natural rubber is less than 50% by mass, the mechanical properties are deteriorated. On the other hand, when the content of natural rubber exceeds 70% by mass, the on-ice performance decreases.

  The rubber composition for studless tires of the present invention can be prepared such that the diene rubber is 100% by mass with natural rubber and butadiene rubber. Alternatively, other diene rubbers other than natural rubber and butadiene rubber can be blended as the diene rubber. Examples of other diene rubbers include isoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber, and halogenated butyl rubber. Of these, isoprene rubber, styrene-butadiene rubber, and halogenated butyl rubber are preferable. These diene rubbers can be used alone or as any blend. The content of the other diene rubber is within a range that does not hinder the achievement of the object of the present invention, and in 100% by mass of the diene rubber, preferably 0 to 10% by mass, more preferably 0 to 5% by mass. It is good to be.

  In the present invention, by adding thermally expandable microcapsules, the performance on ice when the tread portion of a pneumatic tire is configured is improved. The thermally expandable microcapsule has a configuration in which a thermally expandable substance is encapsulated in a shell formed of a thermoplastic resin. Therefore, when a non-vulcanized tire having a tread portion made of a rubber composition mixed with thermally expandable microcapsules is molded and the thermally expandable microcapsules in the rubber composition are heated during the vulcanization, the shell material The heat-expandable substance contained in the resin expands to increase the particle size of the shell material, and a large number of resin-coated bubbles are formed in the tread rubber. By forming a large number of resin-coated bubbles in the tread rubber in this way, the water film on the icy road surface is absorbed and removed when the tread steps on the icy road surface. By repeatedly stepping on the road surface, the water film is removed, and the friction force on ice on the ice road surface of the tread can be improved. Moreover, since a micro edge effect is obtained, the frictional force on ice is improved.

  The shell material of the thermally expandable microcapsule can be formed of a nitrile polymer. In addition, the thermally expandable substance encapsulated in the shell 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.

  Examples of such thermally expandable microcapsules include trade name “EXPANCEL 091DU-80” or “EXPANCEL 092DU-120” manufactured by EXPANSEL, Sweden, or trade name “Microsphere” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. F-85D "or" Microsphere F-100D "can be used.

  The compounding amount of the thermally expandable microcapsule is 0.2 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. When the compounding amount of the thermally expandable microcapsule is less than 0.2 parts by mass, the volume of the resin-coated bubbles in the tread rubber is insufficient, and sufficient performance on ice cannot be obtained. When the amount of the microcapsule exceeds 20 parts by mass, the wear resistance of the tread rubber is deteriorated.

  In the present invention, silica, clay, talc, mica, calcium carbonate and the like can be blended as inorganic fillers other than carbon black. In particular, exothermicity can be reduced by blending silica. In addition, wet grip performance can be improved.

  The amount of silica is preferably 5 to 25 parts by mass, more preferably 7 to 18 parts by mass with respect to 100 parts by mass of the diene rubber. By setting the blending amount of silica in such a range, the low exothermic property and wear resistance of the rubber composition can be compatible. If the amount of silica is less than 5 parts by mass, the exothermic property cannot be sufficiently reduced. When the amount of silica exceeds 25 parts by mass, the wear resistance decreases.

Silica preferably has a nitrogen adsorption specific surface area of 150 to 250 m ² / g. When the nitrogen adsorption specific surface area of silica is less than 150 m ² / g, the rubber composition has insufficient reinforcement and wear resistance is insufficient. On the other hand, when the nitrogen adsorption specific surface area of silica exceeds 250 m ² / g, the exothermic property increases. Note that the nitrogen adsorption specific surface area of silica is determined in accordance with ISO 9277.

  The silica used in the present invention is not limited as long as it has the above-described characteristics, and may be appropriately selected from those manufactured, or may be manufactured to have the above-described characteristics by a normal method. . As the type of silica, for example, wet method silica, dry method silica, or surface-treated silica can be used.

  In the rubber composition of the present invention, it is preferable to mix a silane coupling agent with silica, so that the dispersibility of silica can be improved and the reinforcement with the rubber component can be further enhanced. The silane coupling agent is preferably added in an amount of 3 to 20% by mass, more preferably 5 to 15% by mass, based on the amount of silica. When the compounding quantity of a silane coupling agent is less than 3 mass% of silica mass, the effect which improves the dispersibility of a silica is not fully acquired. Moreover, when the compounding quantity of a silane coupling agent exceeds 20 mass%, silane coupling agents will condense and it will become impossible to acquire a desired effect.

  Although it does not restrict | limit especially as a silane coupling agent, A sulfur containing silane coupling agent is preferable, for example, bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide. , 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like.

The rubber composition for studless tires of the present invention has a specific nitrogen adsorption specific surface area N ₂ SA and a compressed DBP absorption amount (24M4), and a mode diameter Dst and a half-value width thereof in a mass distribution curve of the Stokes diameter of the aggregate. By blending a new carbon black with a limited ΔDst ratio ΔDst / Dst and the relationship between Dst / (24M4) and N ₂ SA, the heat buildup of the rubber composition is reduced using carbon black having a large particle size. However, mechanical properties such as tensile strength at break, tensile elongation at break, and wear resistance are not deteriorated. The compounding amount of carbon black is 30 to 70 parts by mass, preferably 32 to 68 parts by mass, and more preferably 40 to 65 parts by mass with respect to 100 parts by mass of the diene rubber. When the blending amount of carbon black is less than 30 parts by mass, the tensile strength at break and the wear resistance of the rubber composition are deteriorated. On the other hand, if the blending amount of carbon black exceeds 70 parts by mass, the exothermic property increases. In addition, the performance on ice may be reduced.

Carbon black used in the present invention, the nitrogen adsorption specific surface area N ₂ SA is 90m ² / g or less, preferably 50~90m ² / g, more preferably 55~85m ² / g. When N ₂ SA exceeds 90 m ² / g, the exothermic property increases. In this specification, N ₂ SA of carbon black shall be measured according to JIS K6217-7.

  The compressed DBP absorption amount (24M4) of carbon black is 95 to 120 ml / 100 g, preferably 100 to 115 ml / 100 g. When the compressed DBP absorption amount is less than 95 ml / 100 g, the heat buildup increases and the wear resistance decreases. Further, since the molding processability of the rubber composition is lowered and the dispersibility of the carbon black is deteriorated, the reinforcing performance of the carbon black cannot be sufficiently obtained. When the compressed DBP absorption exceeds 120 ml / 100 g, the wear resistance deteriorates. In addition, workability deteriorates due to an increase in viscosity. The amount of compressed DBP absorption shall be measured using a compressed sample described in Appendix A according to JIS K6217-4.

The carbon black used in the present invention has the above-described nitrogen adsorption specific surface area N ₂ SA and compressed DBP absorption (24M4), and also relates to the mode diameter Dst and its half-value width ΔDst in the mass distribution curve of the Stokes diameter of the aggregate. Have the relationship.

  In the present invention, the ratio ΔDst / Dst of the half-value width ΔDst (nm) of the mass distribution curve to the mode diameter Dst (nm) in the mass distribution curve of Stokes diameter of the carbon black aggregate is 0.65 or more, preferably 0.8. 70 or more. Heat generation can be reduced by setting the ratio ΔDst / Dst to 0.65 or more. In the present specification, the mode diameter Dst in the mass distribution curve of the Stokes diameter of the aggregate refers to the mode diameter of the maximum frequency in the mass distribution curve of the Stokes diameter of the aggregate obtained by centrifugal sedimentation of carbon black. The half-value width ΔDst refers to the distribution width when the frequency is half the maximum point in the aggregate mass distribution curve. In the present invention, Dst and ΔDst are measured according to the method for obtaining the aggregate distribution by JIS K6217-6 disc centrifugal light sedimentation method.

In the rubber composition for studless tires of the present invention, the nitrogen adsorption specific surface area N ₂ SA, the compressed DBP absorption amount (24M4), and Dst satisfy the following formula (1).
(24M4) / Dst <0.0093 × N ₂ SA−0.06 (1)
(Where Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and (24M4) is the compressed DBP absorption (ml / 100 g). is there.)

Carbon black has N ₂ SA, compression DBP absorption and ratio ΔDst / Dst within the specified range as described above, and (24M4) / Dst and N ₂ SA satisfy the above formula (1), thereby providing rubber. Mechanical properties such as tensile strength at break, tensile elongation at break and wear resistance can be maintained and improved while reducing the exothermic properties of the composition.

FIG. 1 is a graph showing the relationship between (24M4) / Dst and N ₂ SA for an ASTM grade which is a representative carbon black having an ASTM standard number. In FIG. 1, the horizontal axis represents N ₂ SA (m ² / g), and the vertical axis represents (24M4) / Dst (ml / 100 g / nm). As shown in FIG. 1, (24M4) / Dst of conventional standardized carbon black black is approximately represented by a linear line (dashed line in FIG. 1) with respect to N ₂ SA, and its slope is about 0.0093, intercept Is 0.0133.

On the other hand, in the carbon black used in the present invention, the upper limit of the aggregate characteristic ratio (24M4) / Dst with respect to N ₂ SA is limited by the formula (1). This boundary line (primary straight line in which the inequality sign of the formula (1) is equal) is shown by a solid line in FIG. In addition, carbon black used in the examples of the present specification is plotted with ◯ marks. The broken line in FIG. 2 is a linear straight line obtained from ASTM grade carbon black. When the aggregate characteristic ratio (24M4) / Dst and N ₂ SA satisfy this relationship, the wear resistance can be improved.

In the present invention, when the carbon black specified by the formula (1) has N ₂ SA, compressed DBP absorption (24M4) and ratio ΔDst / Dst within the above-mentioned ranges, the exothermic property of the rubber composition is reduced. However, it is possible to maintain and improve mechanical properties such as tensile breaking strength and tensile breaking elongation, and to improve the wear resistance of the studless tire.

  The Dst of the carbon black used in the present invention is not particularly limited, but is preferably 160 nm or more, and preferably 170 nm or more. If Dst is less than 160 nm, the exothermic property of the rubber composition may increase.

  The carbon black having the above-described characteristics is, for example, feedstock introduction conditions in a carbon black production furnace, supply amount of all air, introduction amount of fuel oil and feedstock, reaction time (combustion from the last feedstock introduction position to reaction stoppage) The production conditions such as gas residence time) can be adjusted.

  In the present invention, as carbon black, both carbon black having the above-described characteristics and other carbon blacks can be used. At this time, the proportion of carbon black having a specific colloidal characteristic exceeds 50% by mass, and the total amount of carbon black is preferably 30 to 70 parts by mass with respect to 100 parts by mass of the diene rubber. Thus, by blending together with other carbon blacks, the balance between the heat build-up of the rubber composition, the wear resistance and the performance on ice can be adjusted.

  Various additives commonly used in tire rubber compositions, such as vulcanization or crosslinking agents, vulcanization accelerators, various inorganic fillers, various oils, anti-aging agents, and plasticizers, for tire rubber compositions These additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for tires of the present invention can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for studless tires of the present invention can be suitably used for a cap tread portion of a studless tire. The studless tire using the rubber composition of the present invention has excellent fuel efficiency, and can maintain and improve on-ice performance and wear resistance at or above conventional levels.

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

Using 11 types of carbon black (CB-1 to CB-11), 17 types of rubber compositions (Examples 1 to 5, Standard Example, Comparative Examples 1 to 11) were prepared. Of these, 3 types of carbon black (CB-1 to CB-3) are commercially available grades, 8 types of carbon black (CB-4 to CB-11) are prototypes, and their colloidal characteristics are shown in Table 1. . In FIG. 3, the relationship between (24M4) / Dst and N ₂ SA of each of the carbon blacks CB-1 to CB-11 is plotted, and numbers for referring to the respective carbon blacks are attached. In FIG. 3, the solid line is a straight line when the equation (1) is made equal, and the broken line is a primary straight line corresponding to the ASTM grade of carbon black.

In Table 1, each abbreviation represents the following colloidal characteristics.
N ₂ SA: Nitrogen adsorption specific surface area measured based on JIS K6217-7 24M4: Compressed DBP absorption measured based on JIS K6217-4 (compressed sample) Dst: Based on JIS K6217-6 Mode diameter which is the maximum value of the mass distribution curve of the Stokes diameter of the aggregate measured by the disc centrifugal light sedimentation method. ΔDst: Stokes diameter of the aggregate measured by the disc centrifugal photoprecipitation method measured based on JIS K6217-6 The distribution width when the mass frequency is half the maximum point in the mass distribution curve (half width)
ΔDst / Dst: ratio ΔDst / Dst value • left side of equation (1) (24M4) / calculated value of Dst • right side of equation (1) 0.0093 × N ₂ SA−0.06 Success or failure of formula (1): When the left side <right side is true, it is indicated by ◯, and when it is not true, it is indicated by ×.

Moreover, in Table 1, carbon black CB1-CB3 represents the following commercial grades, respectively.
CB1: Niteron Carbon Corporation Niteron # 200IS, N339
・ CB2: Tokai Carbon Co., Ltd. Seest 300, N326
CB3: Niteron Carbon Corporation Niteron # 10N, N550

Production of carbon blacks CB4 to CB11 Using a cylindrical reactor, carbon blacks CB4 to CB11 were produced by changing the total air supply amount, fuel oil introduction amount, raw material oil introduction amount, and reaction time as shown in Table 2. .

Preparation and Evaluation of Tire Rubber Composition 17 kinds of rubber compositions having the composition shown in Tables 3 and 4 in which the above 11 kinds of carbon blacks (CB1 to CB11) were added in common with the compounding ingredients in Table 5. In preparing the products (Examples 1 to 5, Standard Examples and Comparative Examples 1 to 11), the components excluding sulfur and the vulcanization accelerator were weighed and kneaded in a 55 L kneader for 15 minutes. Release and cool to room temperature. This master batch was subjected to a 55 L kneader, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for studless tires. In addition, the quantity of the compounding agent described in Table 5 was described in parts by mass with respect to 100 parts by mass of the diene rubber described in Tables 3 and 4.

  The 17 types of rubber compositions for studless tires obtained above (Examples 1 to 5, Standard Examples and Comparative Examples 1 to 11) were vulcanized in a predetermined mold at 160 ° C. for 20 minutes to obtain test pieces. The exothermic property, abrasion resistance and performance on ice were evaluated by the following methods.

Abrasion resistance For the test piece of the rubber composition for studless tires obtained, the amount of wear was measured under the conditions of a load of 4.0 kg (= 39 N) and a slip rate of 30% in accordance with JIS K6264 using a Lambourn abrasion tester. It was measured. The obtained results are shown in the column of “Abrasion resistance” in Tables 3 and 4 by calculating the reciprocal of the wear amount of each test piece and taking the value of the standard example as 100. A larger index of wear resistance means better wear resistance and better tire durability.

About the test piece of the rubber composition for the studless tire thus obtained, a tan δ of 60 ° C. was obtained using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under conditions of initial strain 10%, amplitude ± 2%, and frequency 20 Hz. It was measured. The obtained results are shown in the “low heat generation” column of Tables 3 and 4 as an index with the value of the standard example being 100. A smaller index of low heat generation means that the temperature rise of the studless tire can be suppressed.

Performance on ice About the test piece (sheet) of the obtained rubber composition for studless tires, the sheet was attached to a flat cylindrical base rubber, and measured with an inside drum type on-ice friction tester at −3.0 ° C. and −1. It was measured at 0.5 ° C., a load of 5.5 kg / cm ² (about 0.54 MPa), and a drum rotation speed of 25 km / h. The obtained results are shown in the column “Performance on ice” in Tables 3 and 4 as an index with the value of the standard example as 100. The larger the index on ice, the better the performance on ice of the studless tire.

The types of raw materials used in Tables 3 and 4 are shown below.
・ NR: Natural rubber, STR20
-BR: Polybutadiene, Nipol BR1220 manufactured by Nippon Zeon
Silica: 1165MP manufactured by Dexa Corporation, nitrogen adsorption specific surface area of 165 m ² / g
Coupling agent: Sulfur-containing silane coupling agent, bis (3-triethoxysilylpropyl) tetrasulfide, Dexa Si69
Microcapsule: Thermally expandable microcapsule, Matsumoto Yushi Seiyaku Microsphere F100D
CB1 to CB11: carbon black shown in Table 1 above

The types of raw materials used in Table 5 are shown below.
・ Stearic acid: Beads stearic acid manufactured by NOF Corporation ・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry ・ Vulcanization accelerator: SANTOCURE CBS manufactured by FLEXSYS
・ Sulfur: Fine powdered sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. (sulfur content 95.24% by mass)

  As is clear from Tables 3 and 4, it was confirmed that the rubber compositions for studless tires of Examples 1 to 5 maintained and improved the wear resistance, low heat build-up property, and performance on ice above the conventional levels.

  As is clear from Table 5, the rubber composition of Comparative Example 1 has a wear resistance because the compressed DBP absorption amount (24M4) of carbon black CB-2 is less than 95 ml / 100 g and does not satisfy the formula (1). Inferior.

  The rubber composition of Comparative Example 2 is inferior in wear resistance because the compressed DBP absorption amount (24M4) of carbon black CB-3 is less than 95 ml / 100 g and does not satisfy the formula (1).

  The rubber composition of Comparative Example 3 is inferior in wear resistance because the carbon black CB-4 does not satisfy the formula (1).

  The rubber composition of Comparative Example 4 is inferior in wear resistance because the compressed DBP absorption amount (24M4) of carbon black CB-9 is less than 95 ml / 100 g and does not satisfy the formula (1).

The rubber composition of Comparative Example 5 is inferior in low heat build-up because the nitrogen adsorption specific surface area N ₂ SA of carbon black CB-10 exceeds 90 m ² / g and does not satisfy the formula (1).

The rubber composition of Comparative Example 6 has poor wear resistance because the nitrogen adsorption specific surface area N ₂ SA of carbon black CB-11 exceeds 90 m ² / g.

  Since the rubber composition of Comparative Example 7 has a butadiene rubber content of less than 30 parts by mass and a natural rubber content of more than 70 parts by mass, the wear resistance and the performance on ice are inferior.

  The rubber composition of Comparative Example 8 has inferior wear resistance because the content of butadiene rubber exceeds 50 parts by mass and the content of natural rubber is less than 50 parts by mass.

  The rubber composition of Comparative Example 9 is inferior in wear resistance because the amount of carbon black is less than 30 parts by mass.

  The rubber composition of Comparative Example 10 is inferior in low heat build-up because the amount of carbon black exceeds 70 parts by mass.

  The rubber composition of Comparative Example 11 was inferior in performance on ice because it did not contain thermally expandable microcapsules.

Claims (4)

0.2 to 20 parts by mass of thermally expandable microcapsules and 90 m of nitrogen adsorption specific surface area N ₂ SA with respect to 100 parts by mass of diene rubber containing 30 to 50% by mass of butadiene rubber and 50 to 70% by mass of natural rubber ² / g or less, 30 to 70 parts by mass of carbon black having a compressed DBP absorption amount (24M4) of 95 to 120 ml / 100 g, and a mode diameter Dst (nm) in a Stokes diameter mass distribution curve of the carbon black aggregate ) And its half-value width ΔDst (nm) ratio ΔDst / Dst is 0.65 or more, and N ₂ SA, (24M4) and Dst satisfy the following formula (1): Composition.
(24M4) / Dst <0.0093 × N ₂ SA−0.06 (1)
(Where Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and (24M4) is the compressed DBP absorption (ml / 100 g). is there.)   The rubber composition for a studless tire according to claim 1, wherein the Dst is 160 nm or more. The rubber composition for studless tire according to claim 1 or 2, wherein the N ₂ SA is 50 m ² / g or more.   The studless tire which used the rubber composition for studless tires in any one of Claims 1-3 for the tread part.

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