JP6287324B2 - Rubber composition for studless tire and studless tire - Google Patents

Description

  The present invention relates to a rubber composition for studless tires and a studless tire.

Conventionally, a rubber composition in which silica and a silane coupling agent are blended with a diene rubber containing natural rubber and butadiene rubber is known as a rubber composition (rubber composition for studless tire) used for a tire tread portion of a studless tire. (For example, see Patent Document 1).
In [Example] of Patent Document 1, bis (3-triethoxysilylpropyl) tetrasulfide (Si69: manufactured by Evonik Degussa) is used as a silane coupling agent.

JP 2012-007068 A

In recent years, there has been an increasing demand for improvement of various characteristics for studless tires.
The present inventor used a mercapto-based silane coupling agent (for example, Si363: manufactured by Evonik Degussa) as the silane coupling agent, and the silane coupling agent described in [Example] of Patent Document 1 was used. Compared with the case of using, although the wet performance and rolling resistance were improved, it was revealed that the performance on ice and the wear resistance were inferior.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a rubber composition for a studless tire that is excellent in wet performance, on-ice performance, and wear resistance, and can also reduce rolling resistance. To do.

  As a result of intensive studies to achieve the above object, the present inventors have added wet performance, on-ice performance, by adding silica and a specific silane coupling agent in combination to the rubber composition for studless tires. And it discovered that rolling resistance could be reduced while making both abrasion resistance favorable, and completed this invention.

That is, the present invention provides the following (I) to (VII).
(I) A diene rubber, silica, and a silane coupling agent are contained, and the diene rubber includes natural rubber and / or butadiene rubber, and the silica has a CTAB specific surface area of 50 to 300 m ² / g. It is a certain silica, The content is 3-100 mass parts with respect to 100 mass parts of said diene rubbers, The said silane coupling agent is represented by the average compositional formula of Formula (1) mentioned later. Polysiloxane, the content of which is 2 to 20% by mass with respect to the content of the silica, and the type A durometer hardness measured at 20 ° C. in accordance with JIS K6253 after vulcanization is less than 60 A rubber composition for studless tires.
(II) The rubber composition for studless tires according to (I), wherein the average glass transition temperature of the diene rubber is −70 ° C. or lower.
(III) The rubber composition for studless tires according to (I) or (II), wherein a is greater than 0 in formula (1) described later.
(IV) The rubber composition for tires according to any one of the above (I) to (III), wherein b is greater than 0 in formula (1) described later.
(V) The rubber composition for studless tires according to any one of (I) to (IV), further comprising a thermally expandable microcapsule.
(VI) The rubber composition for studless tires according to (V) above, wherein the content of the thermally expandable microcapsule is 0.1 to 30 parts by mass with respect to 100 parts by mass of the diene rubber.
(VII) A studless tire using the rubber composition for a studless tire according to any one of (I) to (VI) above in a tire tread portion.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for studless tires which is excellent in wet performance, on-ice performance, and abrasion resistance, and can also reduce rolling resistance can be provided.

1 is a schematic partial cross-sectional view of a tire that represents an example of an embodiment of a studless tire of the present invention.

  The studless tire using the rubber composition for studless tires of the present invention and the rubber composition for studless tires of the present invention will be described below.

[Rubber composition for studless tire]
The rubber composition for studless tires of the present invention (hereinafter also simply referred to as “the rubber composition of the present invention”) contains a diene rubber, silica, and a silane coupling agent. The silica contains rubber and / or butadiene rubber, and the silica has a CTAB specific surface area of 50 to 300 m ² / g, and the content thereof is 3 to 100 parts by mass with respect to 100 parts by mass of the diene rubber. The silane coupling agent is a polysiloxane represented by an average composition formula of formula (1) described later, and the content thereof is 2 to 20% by mass with respect to the content of the silica. A rubber composition for studless tires having a type A durometer hardness measured at 20 ° C. in accordance with JIS K6253 after vulcanization is less than 60.

According to the rubber composition of the present invention, the wet performance, the performance on ice, and the wear resistance are excellent, and the rolling resistance can be reduced. The reason is not clear, but is estimated as follows.
First, polysiloxane (hereinafter also referred to as specific polysiloxane) represented by an average composition formula of formula (1) described later has a hydrolyzable group and a mercapto group.
In the rubber composition of the present invention, by using the diene rubber, the mercapto group and the hydrolyzable group of the specific polysiloxane interact with both the network structure and the silica while improving the performance on ice. It is considered that the dispersibility of the silica in the rubber component is improved, and as a result, excellent wet performance, on-ice performance, and wear resistance are exhibited, and the rolling resistance is reduced due to low heat generation.

  Hereinafter, each component contained in the rubber composition of the present invention will be described in detail.

<Diene rubber>
The diene rubber contained in the rubber composition of the present invention includes natural rubber and / or butadiene rubber. Thereby, physical properties such as performance on ice and wear resistance are excellent.
The ratio of these rubber components in the diene rubber is not particularly limited, but from the viewpoint of maintaining on-ice performance and mechanical strength, the ratio of the natural rubber is preferably 70 to 30% by mass, and 40 to 60% by mass. Is more preferable. Moreover, 30-70 mass% is preferable and, as for the ratio of the said butadiene rubber, 40-60 mass% is more preferable.

The average glass transition temperature of the diene rubber is preferably −70 ° C. or lower, because the hardness of the tire can be kept low even at low temperatures and the performance on ice (particularly the frictional force on ice) is more excellent. More preferably, it is not higher than ° C.
Here, the glass transition temperature is a value measured at a heating rate of 10 ° C./min according to ASTM D3418-82 using a differential thermal analyzer (DSC) manufactured by DuPont.
The average glass transition temperature is an average value of the glass transition temperature. When only one diene rubber is used, the glass transition temperature of the diene rubber is used, but when two or more diene rubbers are used in combination. Means the glass transition temperature of the whole diene rubber (mixture of each diene rubber), and can be calculated as an average value from the glass transition temperature of each diene rubber and the blending ratio of each diene rubber.

The butadiene rubber may be a vinyl-cis butadiene rubber.
Vinyl-cis butadiene rubber is a polybutadiene rubber composite (hereinafter referred to as “polybutadiene rubber composite”) composed of cis-1,4-polymerization and syndiotactic-1,2 polymerization in an inert organic solvent mainly composed of C ₄ fraction. Also referred to as “VCR”.
Examples of the vinyl-cis butadiene rubber include 97-80% by mass of cis-1,4-polybutadiene rubber having a cis 1,4-bond content of 90% or more, and 3-20% by mass of syndiotactic-1,2-polybutadiene. And the like.
As such a vinyl-cis butadiene rubber, for example, commercially available products such as UBEPOL-VCR manufactured by Ube Industries, Ltd. can be used.
A commercially available product of vinyl-cis butadiene rubber (VCR) may contain a resin component (oil) other than the rubber component, but this resin is used as a reference for the content of each component such as silica described later. The whole including the components is regarded as “butadiene rubber”.

The butadiene rubber may be a modified butadiene rubber modified with a polysiloxane compound. Dispersibility of silica is improved by using a modified butadiene rubber modified with a polysiloxane compound having high affinity with silica, which will be described later.
Examples of the polysiloxane compound in the modified butadiene rubber include compounds described in JP-A-2009-84413.

  The diene rubber may further contain other rubber components. Other rubber components are not particularly limited, and general rubber components used in conventional tire rubber compositions can be used. Specifically, for example, styrene-butadiene rubber, isoprene rubber Butyl rubber, halogenated butyl rubber and the like, and these may be used alone or in combination of two or more.

  The diene rubber may contain the natural rubber and / or the butadiene rubber. For example, the diene rubber contains the butadiene rubber and styrene-butadiene rubber without containing the natural rubber. In some cases, performance on ice and wear resistance may deteriorate. Therefore, it is preferable to contain the natural rubber because it is more excellent in physical properties such as performance on ice and wear resistance, and it is preferable to contain both the natural rubber and the butadiene rubber.

<Silica>
CTAB specific surface area of the silica-containing rubber composition of the present invention is 50 to 300 m ² / g, preferably from ^{80~250m 2 / g, 110~230m 2 /} g is more preferable.
Here, the CTAB specific surface area is a surrogate property of the surface area that silica can use for adsorption with the silane coupling agent, and the amount of cetyltrimethylammonium bromide (CTAB) adsorbed on the silica surface is determined according to JIS K6217-3: 2001 “No. 3”. Part: How to obtain specific surface area-CTAB adsorption method ".
The type of 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, but wet performance and rolling resistance. From this viewpoint, wet silica is preferable.
Content of the said silica is 3-100 mass parts with respect to 100 mass parts of said diene rubbers, 10-90 mass parts is preferable, and 20-80 mass parts is more preferable.

<Silane coupling agent>
The silane coupling agent contained in the rubber composition of the present invention is a polysiloxane (specific polysiloxane) represented by an average composition formula of the following formula (1).
(A) _a (B) _b (C) _c (D) _d (E) _e SiO _{(4-2a-bcde) / 2} (1)

In the above formula (1), A represents a divalent organic group containing a sulfide group (hereinafter also referred to as a sulfide group-containing organic group). Of these, a group represented by the following formula (2) is preferable.
^{_{* - (CH 2) n -S}} x - (CH 2) n - * (2)
In said formula (2), n represents the integer of 1-10, and the integer of 2-4 is preferable especially.
In said formula (2), x represents the integer of 1-6, and the integer of 2-4 is preferable especially.
In the above formula (2), * indicates a bonding position.
Specific examples of the group represented by the formula (2) are, for ^{_{example, * -CH 2 -S 2 -CH 2}} - *, * -C 2 H 4 -S 2 -C 2 H 4 - *, * - _{C 3 H 6 -S 2 -C 3} H 6 - *, * -C 4 H 8 -S 2 -C 4 H 8 - *, * -CH 2 -S 4 -CH 2 - *, * -C 2 H _{4 -S 4 -C 2 H 4 -} *, * -C 3 H 6 -S 4 -C 3 H 6 - *, * -C 4 H 8 -S 4 -C 4 H 8 - * , and the like.

  In said formula (1), B represents a C1-C10 monovalent hydrocarbon group, As a specific example, a hexyl group, an octyl group, a decyl group etc. are mentioned, for example.

In the above formula (1), C represents a hydrolyzable group, and specific examples thereof include an alkoxy group, a phenoxy group, a carboxyl group, an alkenyloxy group, and the like. Of these, a group represented by the following formula (3) is preferable.
^* -OR ² (3)
In the above formula (3), R ² is an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group (aryl alkyl group) or an alkenyl group having 2 to 10 carbon atoms having from 6 to 10 carbon atoms Among them, an alkyl group having 1 to 5 carbon atoms is preferable. Specific examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a decyl group, and an octadecyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a tolyl group. Specific examples of the aralkyl group having 6 to 10 carbon atoms include a benzyl group and a phenylethyl group. Specific examples of the alkenyl group having 2 to 10 carbon atoms include a vinyl group, a propenyl group, and a pentenyl group.
In the above formula (3), * indicates a bonding position.

In said formula (1), D represents the organic group containing a mercapto group. Of these, a group represented by the following formula (4) is preferable.
^{_{* - (CH 2) m -SH}} (4)
In said formula (4), m represents the integer of 1-10, and the integer of 1-5 is preferable especially.
In the above formula (4), * indicates a bonding position.
Specific examples of the group represented by the formula _{^{(4), * -CH 2 SH}} , * -C 2 H 4 SH, * -C 3 H 6 SH, * -C 4 H 8 SH, * -C 5 ^{_{H 10 SH, * -C 6 H}} 12 SH, * -C 7 H 14 SH, * -C 8 H 16 SH, * -C 9 H 18 SH, include * -C ₁₀ H ₂₀ SH.

  In said formula (1), E represents a C1-C4 monovalent hydrocarbon group.

  In the above formula (1), a to e are relational expressions of 0 ≦ a <1, 0 ≦ b <1, 0 <c <3, 0 <d <1, 0 ≦ e <2, 0 <2a + b + c + d + e <4. Meet. However, one of a and b is not 0.

  In the specific polysiloxane, a is preferably larger than 0 (0 <a) because the performance on ice and the wet performance are more excellent and the workability is excellent while maintaining high-order wear performance. That is, it preferably has a sulfide group-containing organic group. Among them, 0 <a ≦ 0.50 is preferable because the performance on ice and the wet performance are further excellent, and the workability and rolling resistance are more excellent.

In the above formula (1), b is preferably 0 <b from the reason that the on-ice performance, the wet performance, and the rolling resistance are better and the workability is better while maintaining high-order wear performance. 0.10 ≦ b ≦ 0.89 is more preferable.
In the above formula (1), c has better dispersibility of silica, while maintaining high-order wear performance, on-ice performance, wet performance, and better rolling resistance and workability, It is preferable that 1.2 ≦ c ≦ 2.0.
In the above formula (1), d is 0.1 ≦ d ≦ 0.8 because the on-ice performance, wet performance, rolling resistance and workability are excellent while maintaining high-order wear performance. It is preferable that

  The specific polysiloxane is a group represented by the above formula (2) in the above formula (1) because the dispersibility of silica becomes better and the processability is excellent. It is preferable that C in (1) is a group represented by the above formula (3) and D in the above formula (1) is a polysiloxane which is a group represented by the above formula (4).

The weight average molecular weight of the specific polysiloxane is preferably from 500 to 2,300, because the performance on ice, the wet performance, and the rolling resistance are better and the workability is better while maintaining high-order wear performance. ˜1,500 is more preferred. The molecular weight of the specific polysiloxane in the present application is determined in terms of polystyrene by gel permeation chromatography (GPC) using toluene as a solvent.
The mercapto equivalent by the titration method of acetic acid / potassium iodide / potassium iodate-sodium thiosulfate solution of the specific polysiloxane is preferably 550 to 1900 g / mol from the viewpoint of excellent vulcanization reactivity, 600 to More preferably, it is 1800 g / mol.

  The specific polysiloxane preferably has 2 to 50 siloxane units (—Si—O—) because the performance on ice and the wet performance are more excellent while maintaining high-order wear performance.

  Note that no metal other than a silicon atom (for example, Sn, Ti, Al) exists in the skeleton of the specific polysiloxane.

The method for producing the specific polysiloxane is not particularly limited. As a first preferred embodiment, an organosilicon compound represented by the following formula (6), an organosilicon compound represented by the following formula (7), and The method of hydrolyzing and condensing can be mentioned. As a second preferred embodiment, an organosilicon compound represented by the following formula (5), an organosilicon compound represented by the following formula (6), and an organosilicon represented by the following formula (7) The method of hydrolyzing and condensing a compound is mentioned. Further, as a third preferred embodiment, an organosilicon compound represented by the following formula (5), an organosilicon compound represented by the following formula (6), and an organosilicon represented by the following formula (7) The method of hydrolyzing and condensing a compound and the organosilicon compound represented by following formula (8) is mentioned.
Especially, it is preferable that it is the said 2nd suitable aspect from the reason that performance on ice and wet performance are more excellent.

In the above formula (5), R ⁵¹ represents an alkyl group, an aryl group or an alkenyl group having 2 to 10 carbon atoms having 6 to 10 carbon atoms having 1 to 20 carbon atoms, among them, alkyl groups of 1 to 5 carbon atoms Is preferred. Specific examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a decyl group, and an octadecyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group, a tolyl group, and a naphthyl group. Specific examples of the alkenyl group having 2 to 10 carbon atoms include a vinyl group, a propenyl group, and a pentenyl group.
In the above formula (5), R ⁵² represents an alkyl group or an aryl group having 6 to 10 carbon atoms having 1 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, and a decyl group. Specific examples of the aryl group having 6 to 10 carbon atoms are the same as R ⁵¹ described above.
In the above formula (5), the definition and preferred embodiment of n are the same as those of n.
In the above formula (5), the definition and preferred embodiment of x are the same as the above x.
In said formula (5), y represents the integer of 1-3.

  Specific examples of the organosilicon compound represented by the above formula (5) include, for example, bis (trimethoxysilylpropyl) tetrasulfide, bis (triethoxysilylpropyl) tetrasulfide, bis (trimethoxysilylpropyl) disulfide, bis (Triethoxysilylpropyl) disulfide and the like.

In the above formula (6), the definition, specific examples and preferred embodiments of R ⁶¹ are the same as those of R ⁵¹ described above.
In the above formula (6), the definition, specific examples and preferred embodiments of R ⁶² are the same as those of R ⁵² described above.
In the above formula (6), the definition of z is the same as the above y.
In said formula (6), p represents the integer of 5-10.

  Specific examples of the organosilicon compound represented by the above formula (6) include, for example, pentyltrimethoxysilane, pentylmethyldimethoxysilane, pentyltriethoxysilane, pentylmethyldiethoxysilane, hexyltrimethoxysilane, and hexylmethyldimethoxysilane. , Hexyltriethoxysilane, hexylmethyldiethoxysilane, octyltrimethoxysilane, octylmethyldimethoxysilane, octyltriethoxysilane, octylmethyldiethoxysilane, decyltrimethoxysilane, decylmethyldimethoxysilane, decyltriethoxysilane, decylmethyl Examples include diethoxysilane.

In the above formula (7), the definition, specific examples and preferred embodiments of R ⁷¹ are the same as R ⁵¹ described above.
In the above formula (7), the definition, specific examples and preferred embodiments of R ⁷² are the same as those of R ⁵² described above.
In the above formula (7), the definition and preferred embodiment of m are the same as m.
In the above formula (7), the definition of w is the same as y.

  Specific examples of the organosilicon compound represented by the above formula (7) include, for example, α-mercaptomethyltrimethoxysilane, α-mercaptomethylmethyldimethoxysilane, α-mercaptomethyltriethoxysilane, α-mercaptomethylmethyldi Examples include ethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyldiethoxysilane.

In the above formula (8), the definition, specific examples and preferred embodiments of R ⁸¹ are the same as those of R ⁵¹ described above.
In the above formula (8), the definition, specific examples and preferred embodiments of R ⁸² are the same as R ⁵² described above.
In the above formula (8), the definition of v is the same as y above.
In said formula (8), q represents the integer of 1-4.

  Specific examples of the organosilicon compound represented by the above formula (8) include, for example, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, methylethyldiethoxysilane, propyltrimethoxysilane, propylmethyldimethoxysilane, Examples thereof include propylmethyldiethoxysilane.

  When manufacturing the said specific polysiloxane, you may use a solvent as needed. The solvent is not particularly limited, but specifically, aliphatic hydrocarbon solvents such as pentane, hexane, heptane, decane, ether solvents such as diethyl ether, tetrahydrofuran, 1,4-dioxane, formamide, dimethylformamide, N -Amide type solvents such as methylpyrrolidone, aromatic hydrocarbon type solvents such as benzene, toluene and xylene, and alcohol type solvents such as methanol, ethanol and propanol.

When manufacturing the said specific polysiloxane, you may use a catalyst as needed. Examples of the catalyst include acidic catalysts such as hydrochloric acid and acetic acid, Lewis acid catalysts such as ammonium fluoride, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium acetate, potassium acetate, sodium bicarbonate, potassium carbonate, potassium bicarbonate And alkali metal salts such as calcium carbonate, sodium methoxide and sodium ethoxide, and amine compounds such as triethylamine, tributylamine, pyridine and 4-dimethylaminopyridine.
The catalyst is preferably not an organometallic compound containing Sn, Ti or Al as a metal. When such an organometallic compound is used, a metal is introduced into the polysiloxane skeleton, and the specific polysiloxane (metal other than silicon atoms (for example, Sn, Ti, Al) is not present in the skeleton) is obtained. It may not be possible.

  As an organosilicon compound used in producing the specific polysiloxane, a silane coupling agent having a mercapto group [for example, an organosilicon compound represented by the formula (7)] and a silane cup having a sulfide group or a mercapto group When a silane coupling agent other than a ring agent [for example, an organosilicon compound represented by formula (6) or formula (8)] is used in combination, a silane coupling agent having a mercapto group and a silane having a sulfide group or a mercapto group Mixing ratio (molar ratio) with silane coupling agent other than coupling agent (silane coupling agent having mercapto group / silane coupling agent other than silane coupling agent having sulfide group or mercapto group) From the viewpoint of superior rolling resistance and excellent workability Preferably 1.1 / 8.9 to 6.7 / 3.3, more preferably 1.4 / 8.6 to 5.0 / 5.0.

  As the organosilicon compound used for producing the specific polysiloxane, a silane coupling agent having a mercapto group [for example, an organosilicon compound represented by the formula (7)] and a silane coupling agent having a sulfide group [ For example, when the organosilicon compound represented by formula (5) is used in combination, the mixing ratio (molar ratio) of the silane coupling agent having a mercapto group and the silane coupling agent having a sulfide group (a silane having a mercapto group) The coupling agent / silane coupling agent having a sulfide group) is preferably 2.0 / 8.0 to 8.9 / 1.1 from the viewpoints of better wet performance and rolling resistance and excellent workability. 2.5 / 7.5 to 8.0 / 2.0 is more preferable.

  As an organosilicon compound used in producing the specific polysiloxane, a silane coupling agent having a mercapto group [for example, an organosilicon compound represented by the formula (7)], a silane coupling agent having a sulfide group [ For example, an organosilicon compound represented by formula (5) and / or] and a silane coupling agent other than a silane coupling agent having a sulfide group or a mercapto group [for example, represented by formula (6) or formula (8) When the organosilicon compound] is used in combination, the amount of the silane coupling agent having a mercapto group is preferably 10.0 to 73.0% in the total amount (mol) of the former three. The amount of the silane coupling agent having a sulfide group is preferably 5.0 to 67.0% in the total amount of the former three. The amount of the silane coupling agent other than the silane coupling agent having a sulfide group or a mercapto group is preferably 16.0 to 85.0% in the total amount of the former three.

  The content of the silane coupling agent is 2 to 20% by mass with respect to the content of the silica, and reacts effectively and efficiently with the silica and the diene rubber to obtain optimum rubber physical properties. For the reason, 4 to 18% by mass is preferable, and 5 to 14% by mass is more preferable.

<Thermal expandable microcapsules>
The rubber composition of the present invention can further contain thermally expandable microcapsules. The thermally expandable microcapsule is a thermally expandable thermoplastic resin particle in which a liquid that is vaporized by heat to generate a gas is encapsulated in a thermoplastic resin, and the particle is at a temperature higher than its expansion start temperature, usually 130 to 190 ° C. It expands by heating at a temperature of 5 to form gas-encapsulated thermoplastic resin particles in which gas is encapsulated in an outer shell made of the thermoplastic resin.
The rubber composition of the present invention is more excellent in performance on ice by containing the thermally expandable microcapsules.

In the thermoplastic resin, the expansion start temperature is preferably 100 ° C. or higher, and more preferably 120 ° C. or higher. The maximum expansion temperature is preferably 150 ° C. or higher, and more preferably 160 ° C. or higher.
As the thermoplastic resin, for example, a polymer of (meth) acrylonitrile or a copolymer having a high (meth) acrylonitrile content is preferably used. As the other monomer (comonomer) in the case of the copolymer, monomers such as vinyl halide, vinylidene halide, styrene monomer, (meth) acrylate monomer, vinyl acetate, butadiene, vinylpyridine, chloroprene are used. .
The thermoplastic resin is divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, allyl. It may be made crosslinkable with a crosslinking agent such as (meth) acrylate, triacryl formal, triallyl isocyanurate or the like. The crosslinked form is preferably uncrosslinked, but may be partially crosslinked so as not to impair the properties as a thermoplastic resin.
Examples of the liquid that is vaporized by heat to generate gas include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, and petroleum ether; methyl chloride, methylene chloride, dichloroethylene, trichloroethane, Liquids such as chlorinated hydrocarbons such as trichloroethylene;

The heat-expandable microcapsule is not particularly limited as long as it is a heat-expandable microcapsule that expands by heat to become a gas-filled thermoplastic resin, and may be used alone or in combination of two or more. Good.
The particle size of the thermally expandable microcapsule before expansion is preferably 5 to 300 μm, more preferably 10 to 200 μm.

  As such thermally expandable microcapsules, commercially available products can be used. Specifically, for example, EXPANCEL 091DU-80, EXPANCEL 092DU-120 manufactured by EXPANCEL; Sphere F-85, Microsphere F-100;

  The content of the thermally expandable microcapsule is preferably 0.1 to 30 parts by mass and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber because the above-described effect is more excellent.

<Softener>
The rubber composition for studless tires of the present invention may contain a softening agent because a certain degree of flexibility is required as described later.
The softening agent is not particularly limited as long as it gives flexibility to the rubber composition to be blended. For example, oil such as process oil blended in tire manufacture can be suitably used.
Examples of such process oil (oil) include, for example, an extra with a large amount of aroma produced as a by-product when a lubricating base oil is produced by solvent refining from a debris oil obtained by removing a vacuum distillation residue of paraffinic crude oil. And a specific example thereof is Extract No. 4S (manufactured by Showa Shell Sekiyu K.K.).
In addition, although the mineral oil is mix | blended with respect to the said diene rubber from viewpoints of processing etc. (oil extension), in this invention, this compounded oil shall be contained in the said softener.
The content of the softening agent is preferably 10 to 50 parts by mass and more preferably 15 to 45 parts by mass with respect to 100 parts by mass of the diene rubber from the viewpoint of the hardness required for the tire tread part of the studless tire. preferable.

<Other additives>
The rubber composition of the present invention may further contain additives as long as necessary without departing from the effects and purposes.
Examples of the additive include silane coupling agents other than the silane coupling agent contained in the rubber composition of the present invention, fillers other than silica (for example, carbon black), vulcanization aids, anti-aging agents, additives Examples thereof include a vulcanizing agent and a vulcanization accelerator.

<Hardness>
Since the rubber composition of the present invention is used for a tire tread portion of a studless tire, flexibility is required. Therefore, a type A durometer hardness (hereinafter referred to as “a”) measured at 20 ° C. according to JIS K6253 after vulcanization. Simply called “durometer hardness”) is less than 60. When the durometer hardness is 60 or more, properties such as on-ice performance and wet performance are inferior.
On the other hand, the lower limit of durometer hardness is not particularly limited, but is preferably 40 or more.

<Method for producing rubber composition for studless tire>
The manufacturing method of the rubber composition for studless tires of the present invention is not particularly limited, and specific examples thereof include, for example, the above-described components using known methods and apparatuses (for example, Banbury mixers, kneaders, rolls, etc.). And a kneading method.
The rubber composition of the present invention can be vulcanized under conventionally known vulcanization conditions.

〔studless tire〕
The studless tire of the present invention (hereinafter, also simply referred to as “the tire of the present invention”) is a pneumatic tire, and is a pneumatic tire using the above-described rubber composition of the present invention for a tire tread portion.
FIG. 1 shows a schematic partial sectional view of a tire representing an example of an embodiment of the tire of the present invention, but the tire of the present invention is not limited to the embodiment shown in FIG.

The pneumatic tire includes a pair of left and right bead portions 1 and sidewall portions 2, and a tire tread portion 3 connected to both sidewall portions 2.
Between the pair of left and right bead portions 1, a carcass layer 4 in which fiber cords are embedded is mounted, and an end portion of the carcass layer 4 is folded around the bead core 5 and the bead filler 6 from the inside to the outside of the tire. Rolled up.
In the tire tread 3, a belt layer 7 is disposed over the circumference of the tire outside the carcass layer 4.
In the bead portion 1, a rim cushion 8 is disposed at a portion in contact with the rim.

  The tire of the present invention is not particularly limited except that the rubber composition of the present invention is used for a tire tread portion of a pneumatic tire, and can be produced, for example, according to a conventionally known method. As the gas filled in the tire, an inert gas such as nitrogen, argon, helium, etc. can be used in addition to normal or air with adjusted oxygen partial pressure.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

<Synthesis of polysiloxane 1>
A 2 L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 107.8 g (0.2 mol) of bis (triethoxysilylpropyl) tetrasulfide (KBE-846 manufactured by Shin-Etsu Chemical Co., Ltd.), γ-mercapto. Contains 190.8 g (0.8 mol) of propyltriethoxysilane (KBE-803, Shin-Etsu Chemical Co., Ltd.), 442.4 g (1.6 mol) of octyltriethoxysilane (KBE-3083, Shin-Etsu Chemical Co., Ltd.) and 190.0 g of ethanol. Thereafter, a mixed solution of 37.8 g (2.1 mol) of 0.5N hydrochloric acid and 75.6 g of ethanol was added dropwise at room temperature. Then, it stirred at 80 degreeC for 2 hours. Thereafter, filtration, 17.0 g of a 5% KOH / EtOH solution was added dropwise, and the mixture was stirred at 80 ° C. for 2 hours. Then, 480.1 g of polysiloxane of brown transparent liquid was obtained by concentration under reduced pressure and filtration. As a result of measurement by GPC, the average molecular weight was 840, and the average polymerization degree was 4.0 (set polymerization degree 4.0). Moreover, as a result of measuring mercapto equivalent by acetic acid / potassium iodide / potassium iodate addition-sodium thiosulfate solution titration method, it was 730 g / mol, and it was confirmed that it was the mercapto group content as set. From the above, it is shown by the following average composition formula.
_{(-C 3 H 6 -S 4 -C} 3 H 6 -) 0.071 (-C 8 H 17) 0.571 (-OC 2 H 5) 1.50 (-C 3 H 6 SH) 0.286 SiO 0.75
The obtained polysiloxane was designated as polysiloxane 1.

<Synthesis of polysiloxane 2>
In a 2 L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a thermometer, γ-mercaptopropyltriethoxysilane (KBE-803, Shin-Etsu Chemical Co., Ltd.) 190.8 g (0.8 mol), octyltriethoxysilane ( After putting 442.4 g (1.6 mol) and ethanol 162.0 g of Shin-Etsu Chemical KBE-3083), a mixed solution of 0.5N hydrochloric acid 32.4 g (1.8 mol) and ethanol 75.6 g at room temperature. It was dripped. Then, it stirred at 80 degreeC for 2 hours. Thereafter, filtration, 14.6 g of a 5% KOH / EtOH solution was added dropwise, and the mixture was stirred at 80 ° C. for 2 hours. Thereafter, 412.3 g of a colorless transparent liquid polysiloxane was obtained by concentration under reduced pressure and filtration. As a result of measurement by GPC, the average molecular weight was 850, and the average polymerization degree was 4.0 (set polymerization degree 4.0). Moreover, as a result of measuring a mercapto equivalent by the acetic acid / potassium iodide / potassium iodate addition-sodium thiosulfate solution titration method, it was 650 g / mol and it was confirmed that it is a mercapto group content as set. From the above, it is shown by the following average composition formula.
_{(-C 8 H 17) 0.667 (} -OC 2 H 5) 1.50 (-C 3 H 6 -SH) 0.333 SiO 0.75
The obtained polysiloxane was designated as polysiloxane 2.

<Synthesis of Comparative Polysiloxane 1>
3-mercaptopropyltrimethoxysilane (0.1 mol) was hydrolyzed with water and concentrated aqueous hydrochloric acid, and then ethoxymethyl polysiloxane (100 g) was added and condensed to obtain polysiloxane. The obtained polysiloxane is referred to as comparative polysiloxane 1.
The comparative polysiloxane 1 has a structure in which the methoxy group of 3-mercaptopropyltrimethoxysilane and the ethoxy group of ethoxymethyl polysiloxane are condensed. That is, the monovalent hydrocarbon group of the comparative polysiloxane 1 is only a methyl group. The comparative polysiloxane 1 does not have a divalent organic group containing a sulfide group.

<Synthesis of Comparative Polysiloxane 2>
Bis (3- (triethoxysilyl) propyl) tetrasulfide (0.1 mol) is hydrolyzed with water and concentrated aqueous hydrochloric acid, and then ethoxymethylpolysiloxane (100 g) is added and condensed to obtain polysiloxane. It was. The obtained polysiloxane is referred to as comparative polysiloxane 2.
The comparative polysiloxane 2 has a structure in which the ethoxy group of bis (3- (triethoxysilyl) propyl) tetrasulfide and the ethoxy group of ethoxymethyl polysiloxane are condensed. That is, the monovalent hydrocarbon group of the comparative polysiloxane 2 is only a methyl group. The comparative polysiloxane 2 does not have an organic group containing a mercapto group.

<Comparative Examples 1-7, Example 1 , Reference Example 2 and Examples 3-4>
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in Table 1 below.
Specifically, first, the components shown in Table 1 except for the vulcanizing agent and the vulcanization accelerator are mixed for 5 minutes with a 1.7 liter closed Banbury mixer, and then the rubber is released. A master batch was obtained by cooling at room temperature.
Next, a vulcanizing agent and a vulcanization accelerator were mixed with the obtained master batch with the above Banbury mixer to obtain a rubber composition for a studless tire (hereinafter also simply referred to as “rubber composition”).
Next, the obtained rubber composition was vulcanized at 170 ° C. for 15 minutes in a lamborn abrasion mold (diameter 63.5 mm, disk shape 5 mm thick) to produce a vulcanized rubber sheet.
In the following description, Reference Example 2 is referred to as Example 2.

<Durometer hardness>
For each vulcanized sheet, the type A durometer hardness was measured at 20 ° C. in accordance with JIS K6253. The results are shown in Table 1 below.

<Wet skid>
The wet skid of the vulcanized sheet of each example was measured according to the method of ASTM E-303-83 using a portable skid tester manufactured by Stanley under the condition of a wet road surface.
In Table 1 below, the result of Comparative Example 1 is represented as an index with the value “100”. The larger the index value, the greater the wet friction force and the better the wet performance.

<Tan δ (60 ° C.)>
With respect to the vulcanized sheet of each example, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), loss tangent tan δ (60 ° C.) at a temperature of 60 ° C. under conditions of initial strain 10%, amplitude ± 2%, frequency 20 Hz. ) Was measured.
In Table 1 below, the value of tan δ (60 ° C.) of Comparative Example 1 is set to “100” and is displayed as an index. It can be evaluated that the rolling resistance can be reduced with lower heat generation as the value of the index display is smaller (that is, as tan δ (60 ° C.) is smaller).

<Coefficient of friction on ice>
The vulcanized rubber sheet of each example was attached to a flat columnar base rubber and measured with an inside drum type on-ice friction tester: measurement temperature: −1.5 ° C., load: 5.5 kg / cm ³ , drum rotation speed: 25 km The friction coefficient on ice was measured under the conditions of / hour.
In Table 1 below, the index of friction according to the following equation is shown with the friction coefficient on ice of Comparative Example 1 as 100. The larger the displayed numerical value, the better the frictional force between rubber and ice, and the higher the performance on ice can be evaluated.
Friction coefficient index on ice = (Friction coefficient on ice of sample / Friction coefficient on ice of Comparative Example 1) × 100

<Abrasion resistance>
The vulcanized rubber sheet of each example was measured using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) according to JIS K6264, with a load of 4.0 kg and a slip rate of 30%. The amount was measured.
In Table 1 below, the wear amount of Comparative Example 1 was set to 100, and the index was calculated according to the following formula. The larger the displayed numerical value, the better the wear resistance.
Abrasion resistance = (Abrasion amount of Comparative Example 1 / Abrasion amount of sample) × 100

Details of each component shown in Table 1 are as follows.
-Diene rubber 1 (NR): STR20 (Tg: -65 ° C, manufactured by BON BUNDIT)
・ Diene rubber 2 (BR): Nipol BR1220 (Tg: −110 ° C., manufactured by Nippon Zeon Co., Ltd.)
-Diene rubber 3 (SBR): Nipol BR1502 (manufactured by Nippon Zeon)
・ Carbon black: Show Black N339 (Cabonet Japan)
Silica: ULTRASIL VN-3 (CTAB specific surface area: 155 m ² / g, manufactured by Evonik Degussa)
Silane coupling agent X1: Si69 (Evonik Degussa) (bis (3-triethoxysilylpropyl) tetrasulfide)
Silane coupling agent X2: Si363 (manufactured by Evonik Degussa) (mercapto silane coupling agent represented by the following formula (X))
Silane coupling agent X3: Comparative polysiloxane 1 synthesized as described above
Silane coupling agent X4: Comparative polysiloxane 2 synthesized as described above

Silane coupling agent 1: Polysiloxane 1 synthesized as described above
Silane coupling agent 2: Polysiloxane 2 synthesized as described above
-Thermally expandable microcapsules: Microsphere F100 (manufactured by Matsumoto Yushi Co., Ltd.)
・ Zinc oxide: 3 types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.)
・ Stearic acid: Bead stearic acid YR (manufactured by NOF Corporation)
Anti-aging agent: 6PPD (manufactured by Flexis) (N- (1,3-dimethylbutyl) -N'-phenyl-1,4-phenylenediamine)
・ Wax: Paraffin wax (Ouchi Shinsei Chemical Co., Ltd.)
・ Softener (oil): Extract No. 4 S (manufactured by Showa Shell Sekiyu KK)
・ Vulcanizing agent: Oil-treated sulfur (manufactured by Hosoi Chemical Co., Ltd.)
・ Vulcanization accelerator 1: Sunseller CM-G (manufactured by Sanshin Chemical Industry Co., Ltd.) (N-cyclohexyl-2-benzothiazolesulfenamide)
-Vulcanization accelerator 2: TBzTD (Evonik Degussa) (tetrabenzylthiuram disulfide)

As is apparent from the results shown in Table 1 above, the comparative example 2 using the mercapto-based silane coupling agent X2 has wet performance and rolling resistance as compared with the comparative example 1 using the silane coupling agent X1. Although the improvement was observed, the performance on ice and the wear resistance were inferior. Similarly, Comparative Examples 6 and 7 using silane coupling agents X3 and X4 made of polysiloxane that does not satisfy the predetermined average composition formula are inferior in wet performance and in on-ice performance to the same or lower than Comparative Example 1. It was.
On the other hand, Examples 1-4 using the silane coupling agent 1 or 2 have better wet performance, on-ice performance, and wear resistance than Comparative Example 1, and rolling resistance. It was also found that it can be reduced.
Moreover, when Example 1 and Example 2 are contrasted, Example 1 using the silane coupling agent 1 has better wet performance and on-ice performance than Example 2 using the silane coupling agent 2. It was.
Moreover, Example 4 which mix | blended the thermally expansible microcapsule had more excellent performance on ice.

In addition, even if it was a case where the silane coupling agent 1 or 2 was used, the comparative examples 3-5 were inferior in various characteristics.
For example, Comparative Example 3 containing only SBR as a diene rubber had poor performance on ice and wear resistance.
Further, Comparative Example 4 containing no silica had a high tan δ (60 ° C.) value, did not show the effect of reducing rolling resistance, and had poor performance on ice.
Moreover, the comparative example 5 whose durometer hardness is 60 or more was inferior in wet performance and on-ice performance.

Next, test tires of size 185 / 65R14 were produced using the rubber compositions of Comparative Example 1 and Examples 1 to 4 in the tire tread portion, and subjected to the following braking test. The test results are shown in Table 2 below.
<Wet braking test>
Using a domestic 1500cc FF vehicle, traveling on a flooded asphalt road surface at an initial speed of 40 km / h, the braking distance when braking was measured, and the value of Comparative Example 1 was displayed as an index. The larger the value, the better the wet performance.
<ABS braking test on ice>
Using a domestic 1500cc FF vehicle, ABS braking was performed when traveling at 40km / h on an icy road (test course), and the distance from the time of braking to the stop was displayed as a numerical value from 1 to 5. The larger the value, the better the performance on ice.

  As shown in Table 2 above, the tires using the rubber compositions of Examples 1 to 4 are superior in performance on ice while exhibiting wet performance equivalent to or better than that of the tire using the rubber composition of Comparative Example 1. It was.

1 Bead part 2 Side wall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims (6)

Containing a diene rubber, silica, and a silane coupling agent,
The diene rubber includes natural rubber and / or butadiene rubber,
The silica is a silica having a CTAB specific surface area of 50 to 300 m ² / g, and the content thereof is 3 to 100 parts by mass with respect to 100 parts by mass of the diene rubber.
The silane coupling agent is a polysiloxane represented by an average composition formula of the following formula (1), and the content thereof is 2 to 20% by mass with respect to the content of the silica.
A rubber composition for studless tires, having a type A durometer hardness of less than 60 measured at 20 ° C. in accordance with JIS K6253 after vulcanization.
(A) _a (B) _b (C) _c (D) _d (E) _e SiO _{(4-2a-bcde) / 2} (1)
(In formula (1), A represents a divalent organic group containing a sulfide group, B represents a monovalent hydrocarbon group having 5 to 10 carbon atoms, C represents a hydrolyzable group, and D represents Represents an organic group containing a mercapto group, E represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, a to e represent 0 <a <1, 0 ≦ b <1, 0 <c <3, (0 <d <1, 0 ≦ e <2, 0 <2a + b + c + d + e <4 is satisfied )   The rubber composition for studless tires according to claim 1 whose average glass transition temperature of said diene system rubber is -70 ° C or less. The rubber composition for studless tires according to claim 1 or 2 , wherein b is larger than 0 in the formula (1). Furthermore, the rubber composition for studless tires in any one of Claims 1-3 containing a thermally expansible microcapsule. The rubber composition for studless tires according to claim 4 , wherein the content of the thermally expandable microcapsule is 0.1 to 30 parts by mass with respect to 100 parts by mass of the diene rubber. The studless tire which used the rubber composition for studless tires in any one of Claims 1-5 for the tire tread part.