JP5830950B2 - Rubber composition and studless tire using the same - Google Patents

Description

  The present invention relates to a rubber composition and a pneumatic tire using the same.

Conventionally, tan δ is high near 0 ° C. and 30 ° C., and the dynamic elastic modulus (G ′) is low near −20 ° C., so that the dry performance, wet performance and on-ice performance of a studless tire can be improved. Mainly natural rubber and / or polyisoprene rubber and polybutadiene rubber for the purpose of providing a rubber composition and a studless tire using such a rubber composition in a tread and having excellent dry performance, wet performance and on-ice performance. 20 to 70 parts by mass of at least one filler (B) selected from the group consisting of carbon black and white filler with respect to 100 parts by mass of the rubber component (A) as a component, and a weight average molecular weight in terms of polystyrene of 2 × a 10 ³ to 50 × 10 ³ (meth) acrylate (co) polymer (C) rubber, characterized in that by blending a 3-30 parts by weight Compositions, studless tire characterized by using the rubber composition in a tread has been proposed (Patent Document 1).

JP 2006-274051 A

However, the inventors of the present application have found that the friction on ice is not particularly increased and the wear resistance is lowered for the rubber composition containing the (meth) acrylate polymer.
Accordingly, an object of the present invention is to provide a rubber composition having large friction on ice and excellent wear resistance, and a pneumatic tire having large friction on ice and excellent wear resistance.

  As a result of intensive studies to solve the above problems, the present inventor has found that the white filler (A) is 5 to 60 parts by mass with respect to 100 parts by mass of the diene rubber, the white filler (A), hydrogen bonds and / or Or a (meth) acrylate-based polymer and / or a (meth) acrylamide-based polymer (B) having two or more functional groups capable of hydrolytic condensation reaction, with respect to the amount of the white filler (A) The ratio of the amount of the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) is 0.1 to 1.5, and the white filler (A) and the (meth) acrylate A rubber composition characterized by premixing a polymer and / or the (meth) acrylamide polymer (B), and a pneumatic tire having a tread portion obtained by using the rubber composition is on ice. High friction resistance It found that excellent 耗性, and completed the present invention.

That is, this invention provides the following 1-9.
1. 5-60 parts by weight of white filler (A) with respect to 100 parts by weight of diene rubber, and two or more functional groups capable of hydrogen bonding and / or hydrolysis condensation reaction with the white filler (A) ( A (meth) acrylate polymer and / or a (meth) acrylamide polymer (B), and the (meth) acrylate polymer and / or the (meth) acrylamide with respect to the amount of the white filler (A). The ratio of the amount of the polymer (B) is 0.1 to 1.5, and the white filler (A) and the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B ) In advance.
2. 2. The rubber composition according to 1 above, wherein the functional group is a reactive silyl group and / or an amide group.
3. The rubber according to the above 1 or 2, wherein the white filler (A) is at least one selected from the group consisting of silica, clay, mica, talc, shirasu, calcium carbonate, magnesium carbonate, aluminum hydroxide and barium sulfate. Composition.
4). 4. The rubber composition according to any one of 1 to 3, wherein the diene rubber contains natural rubber and butadiene rubber.
5. Furthermore, carbon black is contained, the amount of the carbon black is 10 to 65 parts by mass with respect to 100 parts by mass of the diene rubber, and the total amount of the white filler and the carbon black is 100 masses of the diene rubber. The rubber composition according to any one of 1 to 4 above, which is 15 to 125 parts by mass with respect to parts.
6). 6. The rubber composition according to any one of 1 to 5 above, wherein the diene rubber has an average glass transition temperature of −50 ° C. or lower.
7). Furthermore, the rubber composition in any one of said 1-6 which contains a silane coupling agent and the quantity of the said silane coupling agent is 3-15 mass% of the compounding quantity of the said white filler (A).
8). The rubber composition according to any one of 1 to 7 above, which is used for a tread portion of a pneumatic tire.
9. The pneumatic tire which has a tread part obtained using the rubber composition in any one of said 1-8.

The rubber composition of the present invention has large friction on ice and excellent wear resistance.
The pneumatic tire of the present invention has high friction on ice and excellent wear resistance.

FIG. 1 is a cross-sectional view schematically showing an example of the rubber composition of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of the aggregate. FIG. 3 is a cross-sectional view schematically showing another example of the rubber composition of the present invention.

The present invention will be described in detail below.
The rubber composition of the present invention is capable of 5 to 60 parts by weight of the white filler (A) with respect to 100 parts by weight of the diene rubber, and hydrogen bonding and / or hydrolysis condensation reaction with the white filler (A). A (meth) acrylate polymer having two or more functional groups and / or a (meth) acrylamide polymer (B), and the (meth) acrylate polymer relative to the amount of the white filler (A) And / or the ratio of the amount of the (meth) acrylamide polymer (B) is 0.1 to 1.5, and the white filler (A) and the (meth) acrylate polymer and / or ( A rubber composition characterized in that a (meth) acrylamide polymer (B) is mixed in advance.
In the present invention, the (meth) acrylate polymer as the component (B) has two or more functional groups capable of hydrogen bonding and / or hydrolysis condensation reaction with the white filler (A), and / or The (B) component has an affinity for the white filler (A) because the (meth) acrylamide polymer as the component (B) has an amide bond as a functional group capable of hydrogen bonding with the white filler (A). Excellent in properties and / or reactivity.
In the present invention, the white filler (A) and the component (B) are premixed in specific amounts. At this time, it is considered that an aggregate (complex) described later is formed in the mixture of the white fillers (A) and (B) due to the affinity and / or reactivity described above. The mixture (aggregate) of the white filler (A) and the component (B) obtained in this manner can effectively disperse the white filler in the diene rubber.
And, the rubber composition of the present invention has the above-mentioned requirements, so that the friction on ice is large and the wear resistance is excellent, that is, the friction on ice can be increased without decreasing the wear resistance or improving the wear resistance. it can.

The rubber composition of the present invention has two or more functional groups capable of hydrogen bonding and / or hydrolysis condensation reaction with a diene rubber, a white filler (A), and the white filler (A). ) Acrylate polymer (B).
The diene rubber will be described below. The diene rubber blended in the rubber composition of the present invention is not particularly limited as long as it is a rubber obtained from a monomer containing at least a diene compound. For example, natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile butadiene rubber, ethylene-propylene-diene copolymer rubber, styrene-isoprene copolymer Examples thereof include polymer rubber and isoprene-butadiene copolymer rubber.
The polybutadiene rubber preferably has a cis-1,4 bond content of 75% or more.
The diene rubbers can be used alone or in combination of two or more.

Examples of the combination of diene rubbers include a combination of natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR). Among these, it is preferable that the diene rubber contains natural rubber and butadiene rubber from the viewpoint that friction on ice is larger and wear resistance is more excellent.
From the viewpoint that friction on ice is larger and wear resistance is superior, the content of natural rubber and / or isoprene rubber in the diene rubber is preferably in the range of 20 to 70% by mass, and the content of butadiene rubber is 30 to 80% by mass. % Range is preferred.

The average glass transition temperature of the diene rubber is preferably −50 ° C. or less, and more preferably −55 ° C. or less, from the viewpoint that friction on ice is larger and wear resistance is superior. The average glass transition temperature of the diene rubber can be set to −70 ° C. or less.
The glass transition temperature is determined by differential scanning calorimetry (DSC) with a thermogram measured at a rate of temperature increase of 20 ° C./min and set as the temperature at the midpoint of the transition region. When the diene rubber is an oil-extended product, the glass transition temperature of the diene rubber in a state not containing an oil-extended component (oil) is used. The average glass transition temperature is the sum of the glass transition temperature of each diene rubber multiplied by the weight fraction of each diene rubber (weight average value of glass transition temperature). The total weight fraction of all the diene rubbers is 1.

The white filler (A) will be described below. The white filler (A) blended in the rubber composition of the present invention (hereinafter sometimes referred to as “white filler”) is generally limited as long as it can be blended as a filler in the rubber composition. Not. Especially, it is preferable that it has polarity from a viewpoint that friction on ice is larger and it is more excellent in wear resistance. Examples of the polar group that the white filler (A) can have include OH group, silanol group, amide group, carboxyl group, amino group, CO ₃ ²⁻ , and SO ₄ ²⁻ .
Examples of the white filler (A) include silica; clay minerals such as clay and talc and silicate minerals such as mica; shirasu; calcium carbonate (for example, extremely fine calcium carbonate, light calcium carbonate, heavy carbonate) Calcium), magnesium carbonate (for example, basic magnesium carbonate), carbonates such as potassium carbonate; alumina hydrate such as aluminum hydroxide (for example, hydrous aluminum hydroxide); and barium sulfate.
Among them, from the viewpoint of greater friction on ice and better wear resistance, from the group consisting of silicate minerals such as silica, clay, talc, mica, shirasu, calcium carbonate, magnesium carbonate, aluminum hydroxide, and barium sulfate. At least one selected from the above is preferable, and silica is more preferable.
The silica is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate and the like. Of these, wet silica is preferred because it has a higher friction on ice and is more excellent in wear resistance, and is excellent in the effect of improving fracture characteristics, and in the effect of achieving both wet grip properties and low rolling resistance.
Examples of the clay include smectite groups such as montmorillonite, beidellite, saponite and hectorite: kaolinites such as kaolinite and halosite: vermiculites such as dioctahedral vermiculite and trioctahedral vermiculite.
Examples of mica include teniolite, tetrasilicic mica, mascobite, illite, sericite, phologobite, and biotite.
Of these, silica, clay and mica are preferred from the viewpoint of higher friction on ice, and silica, montmorillonite clay and hectorite clay are more preferred.
The white fillers can be used alone or in combination of two or more.

  In the present invention, the amount of the white filler is 5 to 60 parts by mass with respect to 100 parts by mass of the diene rubber. The amount of the white filler is preferably 10 to 60 parts by mass and preferably 20 to 60 parts by mass with respect to 100 parts by mass of the diene rubber from the viewpoint that the friction on ice is larger and the wear resistance is superior. Is more preferable.

The rubber composition of the present invention is a (meth) acrylate polymer having two or more functional groups capable of hydrogen bonding and / or hydrolysis condensation reaction with the white filler (A) as the component (B) and / or Contains a (meth) acrylamide polymer.
The (meth) acrylate polymer and (meth) acrylamide polymer as the component (B) may be either a homopolymer or a copolymer.
The (meth) acrylate polymer as the component (B) will be described below. The (meth) acrylate polymer (hereinafter sometimes referred to as “(meth) acrylate polymer”) that can be blended in the rubber composition of the present invention is composed of a white filler (A), hydrogen bonds, and It is a polymer having two or more functional groups capable of hydrolytic condensation reaction, and the main chain containing an acrylic acid alkyl ester monomer unit and / or a methacrylic acid alkyl ester monomer unit. In the present invention, (meth) acrylate means one or both of acrylate and methacrylate. The same applies to (meth) acrylamide.
In addition to the ester bond derived from the (meth) acrylate monomer, the (meth) acrylate polymer as the component (B) can be further subjected to hydrogen bonding and / or hydrolysis condensation reaction with the white filler (A). It has a functional group.
Functional groups can be attached to one or more ends (eg, both ends) of the main chain and / or as side chains.
In the present invention, the number of functional groups contained in the (meth) acrylate polymer is 2 or more, and preferably 2 to 5 from the viewpoint that the friction on ice is greater and the wear resistance is superior.
Examples of the functional group include a reactive silyl group, an amide group, a hydroxyl group, a tetramethylammonium group, a silanol group, an epoxy group, a carboxyl group, and an amino group. Of these, the functional group is preferably a reactive silyl group and / or an amide group from the viewpoint that friction on ice is larger and wear resistance is more excellent.
In the present invention, the functional group does not include an ester bond [for example, an ester bond derived from a monomer included in a (meth) acrylate polymer].
The functional group is, for example, a monomer used when polymerizing the (meth) acrylate polymer and / or by modifying the main chain of the (meth) acrylate polymer, Can be introduced into the coalescence.
Here, the reactive silyl group means that, for example, a catalyst or the like is used in the presence of moisture or a crosslinking agent such as a silicon-containing group or a silanol group having a hydrolyzable group bonded to a silicon atom, if necessary. Refers to a group capable of causing a condensation reaction. Specific examples include a group represented by the following formula (1).

In the formula, R ⁶ and R ⁷ are each independently represented by an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or (R ⁸ ) ₃ SiO—. And when two or more R ⁶ or R ⁷ are present, they may be the same or different. R ⁸ is a monovalent hydrocarbon group having 1 to 20 carbon atoms, and three R ⁸ may be the same or different.
Y represents a hydroxy group or a hydrolyzable group, and when two or more Y are present, they may be the same or different. a represents 0, 1, 2 or 3, and b represents 0, 1 or 2.
Moreover, b in t groups represented by the following formula (2) may be different. t shows the integer of 0-19. However, it is assumed that a + t × b ≧ 1 is satisfied. Note that a + t × b ≧ 1 means that a + t × b is 1 or more.

Specific examples of R ⁶ and R ⁷ in the above formula (1) include, for example, alkyl groups such as methyl group and ethyl group; alicyclic hydrocarbon groups such as cyclohexyl group; aryl groups such as phenyl group; And a triorganosiloxy group represented by (R ⁸ ) ₃ SiO— in which R ⁸ is a methyl group or a phenyl group. R ⁶ , R ⁷ and R ⁸ are particularly preferably a methyl group.

The hydrolyzable group represented by Y is not particularly limited as long as it is a conventionally known hydrolyzable group. Specific examples include a hydrogen atom, a halogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amide group, an acid amide group, an aminooxy group, a mercapto group, and an alkenyloxy group. Of these, a hydrogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amide group, an aminooxy group, a mercapto group, and an alkenyloxy group are preferable. Alkoxy groups such as groups are particularly preferred.
Of the reactive silyl groups, a reactive silyl group represented by the following formula (3) is preferable from the viewpoint of easy availability. In the following formula (3), R ⁷ , Y and a have the same meanings as R ⁷ , Y and a described above.

The reactive silyl group is preferably a dimethoxymethylsilyl group or a diethoxymethylsilyl group from the viewpoint of excellent reactivity with a white filler (for example, silica), resulting in higher friction on ice and excellent wear resistance.
When the (meth) acrylate polymer has a reactive silyl group, it is preferable to have 2 to 8 reactive silyl groups in one molecule of the (meth) acrylate polymer.
The reactive silyl group can be bonded to at least the terminal of the (meth) acrylate polymer. The reactive silyl group can be bonded to both ends of the main chain, or can be bonded to the main chain as a side chain.

The (meth) acrylic acid ester monomer used when producing the (meth) acrylate polymer is not particularly limited. Examples of the (meth) acrylic acid alkyl ester monomer unit that forms the (meth) acrylate polymer (main chain) include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, and isobutyl acrylate. Tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-heptyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, lauryl acrylate, Tridecyl acrylate, myristyl acrylate, cetyl acrylate, stearyl acrylate, behenyl acrylate, phenol Acrylate, toluyl acrylate, benzyl acrylate, biphenyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, glycidyl acrylate, 2-aminoethyl acrylate, trifluoromethylmethyl acrylate 2-trifluoromethyl ethyl acrylate, 2-perfluoroethyl ethyl acrylate, 2-perfluoroethyl-2-perfluorobutyl ethyl acrylate, perfluoroethyl acrylate, perfluoromethyl acrylate, diperfluoromethyl methyl acrylate, 2- Perfluoromethyl-2-perfluoroethyl ethyl acrylate, 2-perfluorohexyl ethyl acetate Rate, 2-perfluorodecyl acrylate, 2-perfluoro acrylic or methacrylic acid esters corresponding thereto, such as hexadecyl ethyl acrylate.
These may be used alone or in combination of two or more.

Further, the (meth) acrylate polymer (main chain) is not only an acrylic acid alkyl ester monomer unit and / or a methacrylic acid alkyl ester monomer unit, but also a monomer unit copolymerizable therewith. May be included. For example, a monomer unit containing a carboxy group such as acrylic acid or methacrylic acid; a monomer unit containing an amide group such as acrylamide, methacrylamide, N-methylol acrylamide or N-methylol methacrylamide [(meth) acrylamide Compound units]; monomer units containing epoxy groups such as glycidyl acrylate and glycidyl methacrylate; and monomer units containing amino groups such as diethylaminoethyl acrylate, diethylaminoethyl methacrylate and aminoethyl vinyl ether. Polyoxyethylene acrylate, polyoxyethylene methacrylate, and the like can be expected to have a copolymerization effect in terms of moisture curability and internal curability.
In addition, monomer units derived from acrylonitrile, styrene, α-methylstyrene, alkyl vinyl ether, vinyl chloride, vinyl acetate, vinyl propionate, ethylene and the like can be mentioned.
In the present invention, the (meth) acrylate polymer may not use a (meth) acrylamide compound as a monomer.

Examples of the (meth) acrylate polymer having a reactive silyl group include those represented by the following formula (4).
In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is an alkyl group, R ⁵ is an alkylene group, n is an integer of 3 to 100, and R ⁷ , Y, and a are as defined above. It is. Examples of the alkyl group include those having 1 to 20 carbon atoms. Specific examples include a methyl group and an ethyl group. Examples of the alkylene group include those having 1 to 20 carbon atoms. Specific examples include a methylene group, a dimethylene group, a trimethylene group, and a tetramethylene group.

Especially, it is preferable that a (meth) acrylate type polymer is following formula (5) from a viewpoint that friction on ice is larger and it is excellent in abrasion resistance.
In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is an alkyl group, and n is an integer of 1 to 20. The alkyl group has the same meaning as described above.

The (meth) acrylamide polymer as the component (B) is not particularly limited as long as it is a polymer obtained by polymerizing a monomer containing at least a (meth) acrylamide compound. The (meth) acrylamide compound is not particularly limited as long as it is a compound having an ethylenically unsaturated bond and an amide group.
The (meth) acrylamide polymer as the component (B) is a general (meth) acrylate polymer and / or a (meth) acrylate polymer having no functional group capable of hydrolytic condensation reaction, Excellent affinity with the white filler (A).
The (meth) acrylamide polymer is, for example, (meth) acrylamide, N-substituted (meth) alkylamide, N, N-substituted (meth) alkylamide, N-alkylmethacrylamide, N, N-dialkylmethacrylamide. Such an amide group and a monomer containing an ethylenically unsaturated bond can be used.
Examples of the substituent that N-substituted (meth) acrylamide and N, N-substituted (meth) acrylamide have on the nitrogen atom include a hydrocarbon group and a hydrocarbon group having a functional group. As the hydrocarbon group, an aliphatic hydrocarbon group (which may be chain-like or branched and may have an unsaturated bond), an alicyclic hydrocarbon group (which may be branched, or an unsaturated bond). ), Aromatic hydrocarbon groups, and combinations thereof.
Examples of the N-substituted (meth) acrylamide include N-methylacrylamide, N-ethyl (meth) acrylamide, N-cyclopropylacrylamide, N-isopropyl (meth) acrylamide, N-methylmethacrylamide, and N-cyclopropylmethacrylate. Examples include amide and N-isopropylmethacrylamide.
Examples of the N, N-substituted (meth) acrylamide include N, N-diethyl (meth) acrylamide, N, N-dimethylaminopropyl acrylamide, N-ethyl-N-methyl (meth) acrylamide, and N-methyl-N. -Isopropylacrylamide, N-acryloylpyrrolidine, N-acryloylmethylhomopyrrolidine, N-acryloylmethylpiperazine, N-vinylacetamide.
The (meth) acrylamide polymer preferably has 3 to 4 amide groups in one molecule.

Furthermore, the (meth) acrylamide polymer may contain a monomer unit having copolymerizability with these in addition to the (meth) acrylamide compound as a monomer unit. For example, monomer units containing a carboxy group such as acrylic acid and methacrylic acid; monomer units containing an epoxy group such as glycidyl acrylate and glycidyl methacrylate; amino such as diethylaminoethyl acrylate, diethylaminoethyl methacrylate and aminoethyl vinyl ether And monomer units containing groups. Polyoxyethylene acrylate, polyoxyethylene methacrylate, and the like can be expected to have a copolymerization effect in terms of moisture curability and internal curability.
In addition, monomer units derived from acrylonitrile, styrene, α-methylstyrene, alkyl vinyl ether, vinyl chloride, vinyl acetate, vinyl propionate, ethylene and the like can be mentioned.

Examples of the (meth) acrylamide polymer include a compound represented by the following formula (6).
In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is an alkyl group, m is an integer of 2 to 100, n is an integer of 1 to 100, and R ³ and R ⁴ are hydrogen atoms. , A hydrocarbon group, and a hydrocarbon group having a functional group. Examples of the alkyl group include those having 1 to 4 carbon atoms. Specific examples include a methyl group and an ethyl group. A hydrocarbon group and a hydrocarbon group having a functional group are as defined above.

The (meth) acrylate polymer and / or (meth) acrylamide polymer is not particularly limited for the production thereof. For example, a conventionally well-known thing is mentioned.
The molecular weight of the (meth) acrylate polymer and / or the (meth) acrylamide polymer is in gel permeation chromatography (GPC) from the viewpoint of excellent handling viscosity and reactivity with a white filler (for example, silica). The weight average molecular weight in terms of polystyrene is preferably 500 to 30,000, and more preferably 2,000 to 30,000.

The (meth) acrylate polymer and / or (meth) acrylamide polymer is preferably in the form of a liquid from the viewpoint that the friction on ice is greater, the wear resistance is superior, and the handleability is excellent. When the (meth) acrylate polymer and / or (meth) acrylamide polymer is a solid, it is preferably used after being dissolved in a solvent (for example, water).
From the viewpoint that the solution viscosity of the (meth) acrylate polymer and / or the (meth) acrylamide polymer is higher on ice, more excellent in wear resistance, and excellent in handleability, the (meth) acrylate polymer is The solution viscosity measured under the condition of 25 ° C. in an E-type viscometer is preferably 1 to 300 cps, and more preferably 1 to 280 cps.
(B) A component is used individually or in mixture of 2 or more types.

  A well-known thing can be used as a (meth) acrylate type polymer. Specifically, for example, Kaneka Telechelic Polyacrylate-SA100S, SA100, SA110S, SA120S, SA310S manufactured by Kaneka Corporation are listed.

The amount of component (B) [(meth) acrylate polymer and / or (meth) acrylamide polymer] is the (meth) acrylate polymer as component (B) relative to the white filler (A). And / or ratio of (meth) acrylamide polymer [B / A: ratio of mass of the (meth) acrylate polymer and / or (meth) acrylamide polymer (B) to the white filler (A)] Value] is 0.1 to 1.5. In such a range, the friction on ice is large and the wear resistance is excellent.
The amount of the (meth) acrylate polymer and / or the (meth) acrylamide polymer is (meth) acrylate based on the amount of the white filler (A) from the viewpoint that the friction on ice is greater and the wear resistance is superior. The ratio (B / A) of the amount of the combined and / or (meth) acrylamide polymer (B) is preferably 0.1 to 1.3, more preferably 0.1 to 1.2. .
The amount of the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) is 3 with respect to 100 parts by mass of the white filler from the viewpoint that the friction on ice is greater and the wear resistance is superior. -120 mass parts, 10-120 mass parts, 40-120 mass parts.

When using the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B), the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) is dissolved in a solvent. It is mentioned as one of the preferable aspects to use.
Examples of the solvent used when dissolving the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) include polar solvents such as water, methanol, acetone, methyl ethyl ketone, and tetrahydrofuran. . A solvent can be used individually or in combination of 2 types or more, respectively.
The amount of the solvent is 5 to 10000 mass with respect to 100 parts by mass of the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) from the viewpoint that friction on ice is larger and wear resistance is superior. Part is preferable, and 10 to 1500 parts by weight is more preferable.

  The combination of the white filler (A) and the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) is reactive with silica from the viewpoint that friction on ice is greater and wear resistance is superior. A combination with a (meth) acrylate polymer having a silyl group, a combination of clay (for example, montmorillonite clay) and a (meth) acrylamide polymer is preferable.

The rubber composition of the present invention can further contain carbon black. From the viewpoint that the friction on ice is larger and the wear resistance is more excellent, it is preferable to blend carbon black and white filler as fillers.
Carbon black that can be further contained in the rubber composition of the present invention is not particularly limited. For example, FEF, SRF, HAF, ISAF, SAF grades and the like can be mentioned. From the viewpoint of further improving the wear resistance, carbon black is preferably of the HAF, ISAF, or SAF grade. Carbon blacks can be used alone or in combination of two or more.

The amount of carbon black is preferably 10 to 65 parts by mass and more preferably 15 to 50 parts by mass with respect to 100 parts by mass of the diene rubber from the viewpoint that the friction on ice is larger and the wear resistance is superior. preferable.
The total amount of the white filler and carbon black is preferably 15 to 125 parts by mass, and 40 to 90 parts by mass with respect to 100 parts by mass of the diene rubber, from the viewpoint that friction on ice is larger and wear resistance is superior. More preferably, it is part.

When blending carbon black and white filler as filler, the amount of carbon black is preferably 15 to 90% by mass in the total amount of filler from the viewpoint of greater friction on ice and better wear resistance, More preferably, it is 20-85 mass%.
When carbon black and white filler are blended as the filler, the amount of the white filler is preferably 10 to 85% by mass in the total amount of the filler from the viewpoint that friction on ice is larger and wear resistance is superior. More preferably, it is 15-80 mass%.

The rubber composition of the present invention can further contain a silane coupling agent.
When using a filler (especially silica), it is preferable to add a silane coupling agent at the time of blending from the viewpoint of further improving the reinforcing property.
Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxy). Silylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyl Trimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarb Moyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate Monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, dimethoxy And methylsilylpropylbenzothiazole tetrasulfide.
Of these, bis (3-triethoxysilylpropyl) tetrasulfide is preferable from the viewpoint of greater friction on ice and superior wear resistance, and the effect of improving reinforcing properties.
A silane coupling agent can be used individually or in combination of 2 types or more, respectively.

  The amount of the silane coupling agent is preferably 3 to 15% by mass (weight percent) of the amount of the white filler from the viewpoint of the effect of improving the reinforceability and having a higher friction on ice and better abrasion resistance. More preferably, it is -12 mass%.

In the rubber composition of the present invention, a general rubber crosslinking compound (for example, a crosslinking agent or a vulcanization accelerator) can be used. Among these, it is preferable to use a combination of a crosslinking agent and a vulcanization accelerator. Examples of the crosslinking agent include sulfur. It is preferable that the usage-amount of a crosslinking agent is 0.1-3.0 mass parts as a sulfur content with respect to 100 mass parts of diene rubbers.
The vulcanization accelerator is not particularly limited. For example, 2-mercaptobenzothiazole (M), dibenzothiazyl disulfide (DM), N-cyclohexyl-2-benzothiazylsulfenamide (CZ), Nt-butyl-2-benzothiazolylsulfenamide ( NS) and other thiazole vulcanization accelerators, and guanidine vulcanization accelerators such as diphenylguanidine (DPG).
It is preferable that the usage-amount of a vulcanization accelerator is 0.1-5 mass parts with respect to 100 mass parts of diene rubbers. A vulcanization accelerator may be used individually by 1 type, and may use 2 or more types together.

  The rubber composition of the present invention can contain process oil or the like as a softening agent. Examples of the process oil include paraffinic oil, naphthenic oil, and aromatic oil. Of these, aromatic oils are preferable from the viewpoint of tensile strength and wear resistance, and naphthenic oils and paraffinic oils are preferable from the viewpoint of hysteresis loss and low temperature characteristics. The amount of process oil used is preferably 0 to 100 parts by mass with respect to 100 parts by mass of the diene rubber.

  In addition to the above components, the rubber composition of the present invention includes, for example, white fillers and fillers other than carbon black, anti-aging agents, zinc oxide, stearic acid, antioxidants, waxes, ozone deterioration inhibitors, etc. Additives usually used in the rubber industry can be appropriately selected and blended within a range not impairing the object of the present invention.

The rubber composition of the present invention can be used as necessary using a kneading machine such as a roll or an internal mixer, if necessary, a diene rubber, a white filler, and a (meth) acrylate polymer. It can be produced by kneading carbon black, a softener, an additive and a crosslinking compound for rubber.
In the present invention, a white filler and a (meth) acrylate polymer and / or a (meth) acrylamide polymer are mixed in advance. In this case, it is mentioned as one of preferred embodiments that the (meth) acrylate polymer and / or (meth) acrylamide polymer is used as a solution dissolved in a solvent.
The mixing (kneading) temperature is preferably 120 to 160 ° C. from the viewpoint of excellent wear resistance. The rubber composition of the present invention can be vulcanized after being molded, for example.

  Applications of the rubber composition of the present invention include, for example, pneumatic tires (for example, for tread parts), anti-vibration rubbers, belts, hoses, and other industrial products. Specifically, for example, it can be used for a tread portion, an under tread, a carcass, a sidewall, and a bead of a pneumatic tire. Especially, it is suitable to use for the tread part of a studless tire.

The inventors of the present application infer the mechanism by which the rubber composition of the present invention has high friction on ice and excellent wear resistance as follows.
The rubber composition of the present invention comprises a hydrophobic diene rubber and a highly polar (meth) acrylate polymer and / or (meth) acrylamide polymer, and the diene rubber and (meth) acrylate polymer. Since the rubber composition of the present invention is diene rubber as a matrix, the (meth) acrylate polymer and / or (meth) acrylamide polymer is used as a domain. It is thought to form a sea-island structure. Due to such a morphology, the composition of the present invention allows the rubber to follow the unevenness of the ice by the domain of the (meth) acrylate polymer and / or (meth) acrylamide polymer softer than the rubber in the diene rubber. And the friction on ice is thought to increase.

In the rubber composition of the present invention, since the (meth) acrylate polymer and / or the (meth) acrylamide polymer has a functional group (for example, a reactive silyl group or an amide group), a white filler (particularly, (Silica, montmorillonite clay) forms a bond with a (meth) acrylate polymer and / or (meth) acrylamide polymer on the surface thereof by hydrogen bonding and / or hydrolysis condensation reaction, and (meth) acrylate polymer and It is considered that an aggregate of the (meth) acrylamide polymer and the white filler can be formed.
In this way, the (meth) acrylate polymer and / or (meth) acrylate polymer and / or (meth) acrylate polymer and / or (meth) acrylate polymer and / or (meth) acrylate are interacted and / or bonded together. It is considered that the acrylamide polymer is easily held in the diene rubber, and as a result, wear resistance and frictional force on ice are improved. Therefore, the rubber composition of the present invention does not have a functional group (for example, reactive silyl group, amide group, etc.), (meth) acrylate polymer, and / or has no amide bond (meth). It is considered that the frictional force on ice and the abrasion resistance are remarkably superior to the conventional rubber composition containing an acrylic polymer.

When the rubber composition of the present invention is blended with a silane coupling agent, the silane coupling agent forms a bond with the component (B) and / or the white filler by hydrogen bonding and / or hydrolysis condensation reaction. It is considered possible.
In this way, the silane coupling agent interacts and / or bonds with the component (B) and / or the white filler, so that the interface stress between the domain and / or aggregate of the component (B) and the diene rubber is reduced. It is considered that the rubber composition of the present invention is more excellent in wear resistance by being easily relaxed and improved in reinforcement.

The case where the rubber composition of this invention mix | blends a white filler as a filler is demonstrated below using attached drawing.
FIG. 1 is a cross-sectional view schematically showing an example of the rubber composition of the present invention.
In FIG. 1, a rubber composition 10 contains a diene rubber 1, a white filler 5, a (meth) acrylate polymer and / or a (meth) acrylamide polymer 3, and the rubber composition 10 is a diene rubber 1. And a (meth) acrylate polymer and / or (meth) acrylamide polymer 3 as a domain. Further, since the white filler has high general polarity and hydrophilicity, the white filler 5 is dispersed and / or (meth) around the (meth) acrylate polymer and / or the (meth) acrylamide polymer 3. The aggregate 7 can be formed by reacting with the acrylate polymer and / or the (meth) acrylamide polymer 3. In FIG. 1, the white filler 5 is shown covering the entire (meth) acrylate polymer and / or (meth) acrylamide polymer 3, but the white filler is a surface of the (meth) acrylate polymer. The part may be coated.

FIG. 2 is a cross-sectional view schematically showing an example of the aggregate.
2, the aggregate 7 has white filler particles 9 on the surface of the (meth) acrylate polymer and / or the (meth) acrylamide polymer 3, and the particles 9 are the white filler 5 in FIG. Indicates that a layer is formed.

FIG. 3 is a cross-sectional view schematically showing another example of the rubber composition of the present invention.
In FIG. 3, the rubber composition 30 contains a diene rubber 31, a white filler 35, a (meth) acrylate polymer and / or a (meth) acrylamide polymer 33, and the rubber composition 30 is a diene rubber 31. A matrix 37 formed by bonding a (meth) acrylate polymer and / or a (meth) acrylamide polymer 33 and a white filler 35 by a hydrogen bond and / or hydrolysis condensation reaction. The morphology is as follows.
In addition, the said mechanism is a guess of this inventor, and even if a mechanism is a thing other than the above, it is in the range of this invention.

The pneumatic tire of the present invention will be described below.
The pneumatic tire of the present invention is a pneumatic tire having a tread portion obtained using the rubber composition of the present invention.
The rubber composition used when forming the tread portion of the pneumatic tire of the present invention is not particularly limited as long as it is the rubber composition of the present invention.
The pneumatic tire of the present invention is not particularly limited except that the rubber composition of the present invention is used for the tread portion, and can be produced, for example, according to a conventionally known method. Moreover, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.
<Manufacture of rubber composition 1>
In Table 1, except for Standard Example 1 and Comparative Example 4, first, white filler 1 or white filler 4, silyl group-terminated (meth) acrylate polymers 1 to 4, and (meth) acrylamide shown in Table 1 The polymer 1 or the (meth) acrylate polymer 1 was mixed in advance in the amount (unit: part by mass) shown in the same table. Next, the components shown in Table 1 except for the vulcanization accelerator and other than sulfur are used in the amounts shown in the same table (unit: parts by mass), and the above-mentioned white filler 1 or white filler 4 and silyl are used. Add a mixture of base terminal (meth) acrylate polymers 1 to 4, (meth) acrylamide polymer 1 or (meth) acrylate polymer 1, and knead them in a 1.5 liter closed mixer for 6 minutes, When it reached 150 ° C., it was taken out from the mixer, and a vulcanization accelerator and sulfur were added to this mixture and kneaded with an open roll to obtain a rubber composition. In Table 1, B / A means the ratio (mass ratio) of the (meth) acrylate polymer and / or (meth) acrylamide polymer (B) to the white filler (A). For Standard Example 1 and Comparative Example 4, the components other than those other than the vulcanization accelerator and sulfur shown in Table 1 were used in the amounts (unit: parts by mass) shown in the same table, and these were mixed at the same time. A rubber composition was produced in the same manner as described above.

<Manufacture of rubber composition 2>
In Table 2, except for Standard Example 2 and Comparative Example 8, first, white fillers 2 and 3 and (meth) acrylamide polymers 1 to 3 or (meth) acrylamide polymer 1 shown in Table 2 were used. They were mixed in advance using the amounts shown in the table (unit: parts by mass). Next, the components shown in Table 2 except for the vulcanization accelerator and other than sulfur are used in the amounts shown in the same table (unit: parts by mass), and the above-mentioned white fillers 2 and 3 and (meth) acrylamide are used. Add a mixture of polymer 1 to 3 or (meth) acrylate polymer 1 and knead them in a 1.5 liter closed mixer for 6 minutes. When the temperature reaches 150 ° C., remove from the mixer and add to this mixture. A vulcanization accelerator and sulfur were added and kneaded with an open roll to obtain a rubber composition. In Table 2, B / A means the ratio (mass ratio) of the (meth) acrylamide polymer (B) to the white filler (A). For Standard Example 2 and Comparative Example 8, the components other than those other than the vulcanization accelerator and sulfur shown in Table 2 were used in the amounts shown in the same table (unit: parts by mass), and these were mixed at the same time. A rubber composition was produced in the same manner as described above.

<Vulcanization of rubber composition>
The obtained rubber composition was vulcanized in a predetermined mold at 160 ° C. for 20 minutes to produce a vulcanized rubber sheet.
<Test of vulcanized rubber>
The resulting vulcanized rubber was measured for the friction coefficient index on ice and the wear resistance index by the following test methods. The results are shown in Tables 1 and 2.
・ Friction coefficient index on ice The vulcanized rubber sheet (size: 30cm in length, 1.5cm in width, 2mm in thickness) was attached to a flat cylindrical base rubber, and the inside drum type on-ice friction test. The friction coefficient on ice was measured with a machine. The measurement temperature was −1.5 ° C., the load was 5.5 kg / cm ³ , and the drum rotation speed was 25 km / hr.
Table 1 shows the friction coefficient index (%) on ice of each example and comparative example based on the value of the friction coefficient on ice obtained in the standard example 1 being 100. In Table 2, Standard Example 2 is used as a reference.
The larger the friction index coefficient on ice, the higher the friction force on ice.

Abrasion resistance index The vulcanized rubber sheet obtained as described above was worn using a Lambone abrasion tester in accordance with JIS K6264, with a load of 4.0 kg (= 39 N) and a slip rate of 30%. Was measured.
In Table 1, the value of the amount of wear obtained in Standard Example 1 was taken as 100, and the index (%) was expressed as [(wear amount of Standard Example 1) / (wear amount of sample)] × 100. In Table 2, Standard Example 2 is used as a reference.
The larger the value of the wear resistance index, the better the wear resistance.

The details of each component shown in Tables 1 and 2 are as follows.
・ Diene rubber 1 (NR): Natural rubber RSS # 3
・ Diene rubber 2 (BR): manufactured by Nippon Zeon Co., Ltd., “Nipol BR1220”
Carbon black: “Seast 6” manufactured by Tokai Carbon Co., Ltd., grade HAF.
White filler 1: Silica, Rhodia, “Zeosil 1165MP, wet silica” White filler 2: Montmorillonite clay, Kunimine Kogyo Co., Ltd., trade name “Kunipia”
・ White filler 3 (clay other than montmorillonite): Kaolin clay, manufactured by Takehara Chemical Industry Co., Ltd., trade name “NN Kaolin clay”
White filler 4 (silica other than white filler 1): hydrophilic fumed silica, manufactured by Nippon Aerosil Co., Ltd., trade name “AEROSIL 130”
Silane coupling agent: bis (3-triethoxysilylpropyl) tetrasulfide, manufactured by Dexa, “SI69”
・ Zinc oxide: manufactured by Shodo Chemical Industry Co., Ltd., "Zinc oxide 3 types"
・ Stearic acid: manufactured by Nippon Oil & Fats, “Beadstearic acid”
Anti-aging agent: “6PPD”, manufactured by Flexis
・ Wax: Ouchi Shinsei, “paraffin wax”
・ Process oil: Showa Shell Sekiyu KK, “Extract No. 4 S”
Silyl group terminal (meth) acrylate polymer 1: SA100 manufactured by Kaneka Chemical Co., Ltd., solution viscosity 250 cps, oligomer type of methoxy terminal modified acrylate, liquid polymer having polystyrene equivalent molecular weight of 500 to 30,000 in GPC (Meth) acrylate polymer 2: SA310 manufactured by Kaneka Chemical Co., Ltd., oligomer type of methoxy terminal-modified acrylate, liquid polymer having a polystyrene equivalent molecular weight of 500 to 30,000 in GPC. Silyl group-terminated (meth) acrylate polymer 3: Kaneka SA310S manufactured by Kagaku Co., oligomer type of methoxy terminal modified acrylate, liquid polymer having a polystyrene equivalent molecular weight of 500 to 30,000 in GPC. Silyl group terminal (meth) acrylate polymer 4: The above silyl group terminal (meth) acrylate Polymer polymer 1: 100 parts by mass of (solvent) acetone: 10 parts by mass (meth) acrylamide polymer 1: manufactured by Arakawa Chemical Industries, trade name “Polytension”, solution viscosity 4, 000 to 15,000 cps, polymer of (meth) acrylamide compound, polymer having polystyrene equivalent molecular weight of 500 to 30,000 in GPC, (meth) acrylamide polymer 2: trade name “Polymerset” manufactured by Arakawa Chemical Industries, Ltd. ”, Solution viscosity of 1,000 to 4,000 cps, polymer of (meth) acrylamide compound, liquid polymer having polystyrene equivalent molecular weight of 500 to 30,000 in GPC. (Meth) acrylamide polymer 3: (meth) above Acrylamide polymer 1: 100 parts by mass dissolved in 10 parts by mass of (solvent) acetone - (meth) acrylate polymer 1: Aldrich Co. Poly (styrene) -block-poly (acrylic acid), mol wt Mn 1,890-2,310 (poly (acrylic acid))
Mn 5,580-6,820 (polystyrene)
Mn 7,470-9,130
Mw / Mn 1.1-1.3
・ Sulfur: manufactured by Tsurumi Chemical Industry Co., Ltd.
・ Vulcanization accelerator: “Noxeller CZ-G” manufactured by Ouchi Shinsei Chemical Industry
The average glass transition temperature of the diene rubber containing 50 parts by mass of the diene rubber 1 (NR) and 50 parts by mass of the diene rubber 2 (BR) was −84 ° C.

As is clear from the results shown in Table 1 (when the white filler is silica), Comparative Example 1 in which the ratio of the (meth) acrylate polymer (B) to the white filler (A) exceeds 1.5. The wear resistance was low. Comparative Example 2 containing a (meth) acrylate polymer having no functional group, Comparative Example 3 in which the ratio of the (meth) acrylate polymer (B) to the white filler (A) is less than 0.1, The frictional force on ice was small and the wear resistance was low. Particularly in Comparative Example 2, the wear resistance is lowered. In Comparative Example 2, since a (meth) acrylate polymer having no functional group is used, the (meth) acrylate polymer interacts with the white filler and the functional group (hydrogen bonding and / or hydrolysis condensation reaction). ) In Comparative Example 4 in which the white filler (A) and the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) were not mixed in advance, the friction force on ice was small and the wear resistance was low.
On the other hand, Examples 1-9 have a large frictional force on ice and excellent wear resistance. That is, Examples 1 to 9 can increase the friction on ice while improving the wear resistance without reducing the wear resistance. In particular, when the white filler is silica, the component (B) can increase friction on ice when it is a (meth) acrylate polymer having a functional group rather than a (meth) acrylamide polymer.

As is clear from the results shown in Table 2 (when the white filler is a silicate mineral), the wear resistance of Comparative Example 6 containing the (meth) acrylate polymer 1 decreased. Comparative Example 5 in which the ratio of the (meth) acrylamide polymer to the white filler (A) exceeded 1.5 had low wear resistance. In Comparative Example 7 in which the ratio of the (meth) acrylamide polymer to the white filler (A) was less than 0.1, the frictional force on ice was low. In Comparative Example 8 in which the white filler (A) and the (meth) acrylate polymer and / or the (meth) acrylamide polymer (B) were not mixed in advance, the frictional force on ice was small. In particular, the wear resistance of Comparative Example 6 is reduced. In Comparative Example 6, since a (meth) acrylate polymer having no functional group is used, the (meth) acrylate polymer interacts with the white filler and the functional group (hydrogen bonding and / or hydrolysis condensation reaction). ) Is inferior to (meth) acrylamide polymers.
In contrast, Examples 10 to 16 have a large frictional force on ice and excellent wear resistance. That is, Examples 10 to 16 can increase the friction on ice while improving the wear resistance without reducing the wear resistance.
In the present invention, even when a silicate mineral is used as a white filler, the component (B) is a (meth) acrylamide polymer, and the (meth) acrylamide polymer is diluted with a solvent. , The friction on ice can be higher.

10, 30 Rubber composition 1, 31 Diene rubber 3, 33 (meth) acrylate polymer and / or (meth) acrylamide polymer 5 White filler (layer)
35 White filler 7, 37 Aggregate 9 Particles of white filler

Claims (10)

White filler (A) 5-60 parts by mass with respect to 100 parts by mass of diene rubber containing natural rubber and butadiene rubber, and hydrogen bonding and / or hydrolysis condensation reaction with the white filler (A) are possible. A (meth) acrylate polymer having two or more functional groups and / or a (meth) acrylamide polymer (B), and the (meth) acrylate polymer relative to the amount of the white filler (A) And / or the ratio of the amount of the (meth) acrylamide polymer (B) is 0.1 to 1.5, and the white filler (A) and the (meth) acrylate polymer and / or ( A rubber composition, which is premixed with a (meth) acrylamide polymer (B) and used for a studless tire .   The rubber composition according to claim 1, wherein the functional group is a reactive silyl group and / or an amide group.   The white filler (A) is at least one selected from the group consisting of silica, clay, mica, talc, shirasu, calcium carbonate, magnesium carbonate, aluminum hydroxide, and barium sulfate. Rubber composition. The content of the natural rubber in the diene rubber is in the range of 20 to 70% by mass, and the content of the butadiene rubber is in the range of 30 to 80% by mass. The rubber composition as described.   Furthermore, carbon black is contained, the amount of the carbon black is 10 to 65 parts by mass with respect to 100 parts by mass of the diene rubber, and the total amount of the white filler and the carbon black is 100 masses of the diene rubber. It is 15-125 mass parts with respect to a part, The rubber composition in any one of Claims 1-4.   The rubber composition according to any one of claims 1 to 5, wherein the diene rubber has an average glass transition temperature of -50 ° C or lower.   The rubber composition according to any one of claims 1 to 6, further comprising a silane coupling agent, wherein the amount of the silane coupling agent is 3 to 15% by mass of the blending amount of the white filler (A). .   The rubber composition according to any one of claims 1 to 7, wherein the (meth) acrylamide polymer is a compound represented by the following formula (6).
  Where R ¹ Is a hydrogen atom or a methyl group, R ² Is an alkyl group, m is an integer from 2 to 100, n is an integer from 1 to 100, R ^Three , R ^Four Is a hydrogen atom or a hydrocarbon group. The rubber composition according to any one of claims 1 to 8 , which is used for a tread portion of the studless tire . Studless tire having a tread portion that is obtained by using the rubber composition according to any one of claims 1-9.