JP7271991B2 - Rubber composition for studless tire and studless tire using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition for a studless tire and a studless tire using the same, and more specifically, a rubber composition for a studless tire capable of improving performance on ice and wet performance as compared with the prior art, and a studless tire using the same. It is about.

The studless compound is designed to have a low glass transition temperature (Tg) in order to ensure flexibility at low temperatures. ) is inevitably low.
To compensate for this, it is known to use silica even in studless compounds. However, natural rubber, which is mainly used in studless compounds, tends to inhibit the reactivity between silane coupling agents and silica, and natural rubber itself does not have functional groups that can interact with silica. Therefore, there is a problem that the dispersibility of silica is not improved, and the effect of silica blending on wet performance cannot be fully exhibited.

On the other hand, in order to improve performance on ice (friction force on icy road surfaces), it is effective to increase the surface roughness of the tread rubber. Alternatively, a technique of containing a crosslinkable oligomer or polymer having a reactive functional group incompatible with diene rubber and three-dimensionally crosslinked fine particles having an average particle size of 1 to 200 μm is known (for example, Patent Document 1), this technology does not contribute to the improvement of wet performance, but rather reduces the strength of the compound, which may lead to deterioration of wet performance.

Japanese Unexamined Patent Application Publication No. 2014-62168

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rubber composition for a studless tire and a studless tire using the same, which can improve performance on ice and wet performance as compared with the prior art.

As a result of extensive research, the inventors of the present invention have found that the above problems can be solved by blending a specific amount of silica with a diene rubber, and further by adding specific amounts of a specific plasticizer and heat-expandable microcapsules. and was able to complete the present invention.
That is, the present invention is as follows.

1. 10 parts by mass or more of silica, 1 to 40 parts by mass of polyethylene glycol bis(2-ethylhexanoate), and 0.1 to 20 parts by mass of thermally expandable microcapsules are compounded with respect to 100 parts by mass of diene rubber. A rubber composition for studless tires characterized by:
2. For 100 parts by mass of the diene rubber, 0.3 to 30 parts by mass of a crosslinkable oligomer or polymer incompatible with the diene rubber and three-dimensionally crosslinked fine particles having an average particle size of 0.5 to 50 μm 1. The rubber composition for a studless tire according to 1 above, wherein 0.1 to 12 parts by mass of is blended.
3. 3. A studless tire using the rubber composition according to 1 or 2 for the tread.

The rubber composition of the present invention contains 10 parts by mass or more of silica per 100 parts by mass of diene rubber, 1 to 40 parts by mass of polyethylene glycol bis(2-ethylhexanoate) as a specific plasticizer, and thermal expansion Since 0.1 to 20 parts by mass of soluble microcapsules are blended, it is possible to provide a rubber composition for studless tires and a studless tire using the same that can improve performance on ice and wet performance compared to the prior art.

The present invention will now be described in more detail.

(Diene rubber)
The diene rubber used in the present invention includes, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber ( NBR), ethylene-propylene-diene terpolymer (EPDM), and the like. These may be used alone or in combination of two or more. Further, its molecular weight and microstructure are not particularly limited, and it may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or epoxidized.
Among these, from the viewpoint of improving performance on ice and wet performance, it is preferable to use NR and BR. It is preferable to use 30 to 75 parts by mass of NR and 25 to 70 parts by mass of BR in 100 parts by mass of diene rubber. preferable.

(silica)
As the silica used in the present invention, any silica conventionally known to be used in rubber compositions, such as dry silica, wet silica, and colloidal silica, can be used singly or in combination of two or more.
From the viewpoint of further improving performance on ice and wet performance, the nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 150 to 250 m ² /g.
The nitrogen adsorption specific surface area (N ₂ SA) shall be determined according to JIS K6217-2.

The amount of silica compounded is 10 parts by mass or more, preferably 20 to 120 parts by mass, more preferably 25 to 100 parts by mass, based on 100 parts by mass of the diene rubber.

(Specific plasticizer)
The present invention uses polyethylene glycol bis(2-ethylhexanoate) as a specific plasticizer.
Polyethylene glycol bis(2-ethylhexanoate) is presumed to have the effect of improving silica dispersion by preventing aggregation of silica, in addition to its effect as a plasticizer.

In polyethylene glycol bis(2-ethylhexanoate), the number of repeating polyoxyethylene units is, for example, 6-12, preferably 8-10.

Polyethylene glycol bis(2-ethylhexanoate) can be used as a commercial product, such as Lionon DEH-40 manufactured by Lion Specialty Chemicals Co., Ltd., and the like.

The blending amount of polyethylene glycol bis(2-ethylhexanoate) is 1 to 40 parts by mass, preferably 2 to 25 parts by mass, per 100 parts by mass of the diene rubber.
If the blending amount of polyethylene glycol bis(2-ethylhexanoate) is less than 1 part by mass, the effect of the present invention cannot be achieved because the blending amount is too small, and if it exceeds 40 parts by mass, the wet performance is lowered.

(Thermal expandable microcapsules)
The rubber composition of the present invention incorporates thermally expandable microcapsules from the viewpoint of enhancing performance on ice.
In the present invention, the thermally expandable microcapsules are constructed by enclosing a thermally expandable substance in a shell material made of a thermoplastic resin. The shell material of the thermally expandable microcapsules can be made of a nitrile polymer.
In addition, the thermally expandable substance contained in the shell material of the microcapsules has the property of being vaporized or expanded by heat, and is exemplified by at least one selected from the group consisting of hydrocarbons such as isoalkanes and normal alkanes. Isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, etc. Normal alkanes include n-butane, n-propane, n-hexane, Examples include n-heptane and n-octane. These hydrocarbons may be used alone or in combination. A preferred form of the thermally expandable substance is a hydrocarbon that is liquid at room temperature and a hydrocarbon that is gas at room temperature dissolved therein. By using such a mixture of hydrocarbons, it is possible to obtain a sufficient expansion force from a low temperature range to a high temperature range in the vulcanization molding temperature range (150° C. to 190° C.) of an unvulcanized tire.
Examples of such thermally expandable microcapsules include the trade name "EXPANCEL 091DU-80" or "EXPANCEL 092DU-120" manufactured by Expancel in Sweden, or the trade name "Matsumoto Micros" manufactured by Matsumoto Yushi Seiyaku Co., Ltd. Fair F-85D" or "Matsumoto Microsphere F-100D" or the like can be used.

The blending ratio of the thermally expandable microcapsules is 0.1 to 20 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass of the diene rubber.

Here, in the present invention, in order to further improve the performance on ice, 0.3 to 30 parts by mass of a crosslinkable oligomer or polymer incompatible with the diene rubber and an average particle size of It is preferable to blend 0.1 to 12 parts by mass of three-dimensionally crosslinked fine particles of 0.5 to 50 μm. These components are disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-62168) and are publicly known, and will be described below.

The cross-linkable oligomer or polymer used is incompatible with (A) the diene rubber.
The phrase "incompatible with the diene rubber" does not mean that it is incompatible with all rubber components included in the diene rubber. It means that specific components are incompatible with each other.

Examples of crosslinkable oligomers or polymers include polyether-, polyester-, polyolefin-, polycarbonate-, aliphatic-, saturated hydrocarbon-, acrylic-, plant-derived or siloxane-based polymers or copolymers. mentioned.

Among these, polyether-based, polycarbonate-based, acrylic-based or siloxane-based polymers or copolymers are used as the above-mentioned crosslinkable oligomer or polymer from the viewpoint of better performance on ice and wear resistance of studless tires. It is preferable to have

Here, examples of the polyether-based polymer or copolymer include polyethylene glycol, polypropylene glycol (PPG), polypropylene triol, ethylene oxide/propylene oxide copolymer, polytetramethylene ether glycol (PTMEG), sorbitol. system polyols, and the like.
Examples of the polycarbonate-based polymer or copolymer include an ester of a polyol compound (eg, 1,6-hexanediol, 1,4-butanediol, 1,5-pentanediol, etc.) and a dialkyl carbonate. Examples thereof include those obtained by an exchange reaction.
Examples of the acrylic polymer or copolymer include acrylic polyols; homopolymers of acrylates such as acrylate, methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate; and combinations of two or more of these acrylates. acrylate copolymers; and the like.
The siloxane-based polymer or copolymer is not particularly limited as long as it is a compound having an organopolysiloxane as a main chain, and specific examples thereof include polydimethylsiloxane, methylhydrogenpolysiloxane, methylphenylpolysiloxane, Examples include siloxane and diphenylpolysiloxane.

In the present invention, the above-mentioned crosslinkable oligomer or polymer has a hydroxyl group, a silane functional group, an isocyanate group, a (meth)acryloyl group, allyl It preferably has at least one or more reactive functional groups selected from the group consisting of groups, carboxyl groups, acid anhydride groups and epoxy groups.
Here, the silane functional group is also called a so-called crosslinkable silyl group, and specific examples thereof include a hydrolyzable silyl group; a silanol group; functional group substituted with; and the like.
Among these functional groups, the above-mentioned crosslinkable oligomer or polymer is appropriately crosslinked during processing of the rubber, and the performance on ice of the studless tire is further improved, and the wear resistance is also improved. , an acid anhydride group or an epoxy group, and more preferably a silane functional group (especially a hydrolyzable silyl group or a silanol group) and/or an isocyanate group.

Here, specific examples of the hydrolyzable silyl group include an alkoxysilyl group, an alkenyloxysilyl group, an acyloxysilyl group, an aminosilyl group, an aminooxysilyl group, an oximesilyl group, an amidosilyl group, and the like. be done.
Among these, an alkoxysilyl group is preferable, and specifically, a methoxysilyl group and an ethoxysilyl group are preferable because the balance between hydrolyzability and storage stability is improved.

Further, the isocyanate group is an isocyanate group that remains when a hydroxyl group of a polyol compound (for example, a polycarbonate-based polyol, etc.) is reacted with an isocyanate group of a polyisocyanate compound.
The polyisocyanate compound is not particularly limited as long as it has two or more isocyanate groups in the molecule. ), 2,6-tolylene diisocyanate (2,6-TDI)), MDI (e.g., 4,4′-diphenylmethane diisocyanate (4,4′-MDI), 2,4′-diphenylmethane diisocyanate (2,4′ -MDI)), 1,4-phenylene diisocyanate, polymethylene polyphenylene polyisocyanate, xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), tolidine diisocyanate (TODI), 1,5-naphthalene diisocyanate (NDI), aromatic polyisocyanates such as triphenylmethane triisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), lysine diisocyanate, norbornane diisocyanate (NBDI); transcyclohexane-1,4-diisocyanate , isophorone diisocyanate (IPDI), bis(isocyanatomethyl)cyclohexane (H6XDI), dicyclohexylmethane diisocyanate (H12MDI) and other alicyclic polyisocyanates; these carbodiimide-modified polyisocyanates; these isocyanurate-modified polyisocyanates; .

In the present invention, when a crosslinkable oligomer or polymer having a hydroxyl group as a reactive functional group is used, a part or all of the crosslinkable oligomer or polymer is preliminarily added with an isocyanate compound or the like before being blended with the diene rubber. It is preferable that the rubber is crosslinked or that a crosslinking agent such as an isocyanate compound is blended in advance with the rubber.

In the present invention, the reactive functional group preferably has at least the end of the main chain of the crosslinkable oligomer or polymer, and has 1.5 or more when the main chain is linear. preferably, more preferably two or more. On the other hand, when the main chain is branched, it preferably has 3 or more.

In the present invention, the weight-average molecular weight or number-average molecular weight of the crosslinkable oligomer or polymer provides good dispersibility in the diene rubber and kneading processability of the rubber composition. It is preferably from 300 to 30,000, more preferably from 500 to 25,000, because it facilitates adjustment of the particle size and shape during preparation in a polyoligomeric oligomer or polymer.
Here, both the weight average molecular weight and the number average molecular weight are measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

Furthermore, in the present invention, the content of the crosslinkable oligomer or polymer is 0.3 to 30 parts by mass, preferably 1 to 15 parts by mass, per 100 parts by mass of the diene rubber.

The microparticles used in the present invention are three-dimensionally crosslinked microparticles having an average particle diameter of 0.5 to 50 μm formed using a thermoplastic elastomer.
The average particle diameter of the fine particles is preferably 1 to 50 μm, more preferably 5 to 40 μm, because the surface of the studless tire becomes moderately rough and the performance on ice is better. .
Here, the average particle size refers to the average value of equivalent circle diameters measured using a laser microscope. 8710 (manufactured by KEYENCE CORPORATION) can be used for measurement.

In the present invention, the content of the fine particles is 0.1 to 12 parts by mass, preferably 0.3 to 10 parts by mass, more preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the diene rubber. Parts by mass are more preferred.
Further, the content of the fine particles is 1 to 50% by mass, preferably 3 to 30% by mass, and 5 to 20% by mass with respect to the total mass of the crosslinkable oligomer or polymer and the fine particles. is more preferred.
By containing a predetermined amount of the fine particles, the performance on ice and the wear resistance of the studless tire using the rubber composition for tires of the present invention in the tire tread are both improved.
This is probably because the elasticity of the fine particles disperses the locally applied strain and relieves the stress, thereby improving the performance on ice and the abrasion resistance.

Further, in the present invention, the fine particles are added to the cross-linkable oligomer or polymer in advance so as to improve the performance on ice and the wear resistance of the studless tire. Fine particles of plastic elastomer are preferred. This is because the crosslinkable oligomer or polymer functions as a solvent for the fine particles and the dispersibility and dispersibility of the crosslinkable oligomer or polymer and the fine particles in the rubber composition when the mixture thereof is blended into the rubber composition. This is thought to be due to the fact that the effect of improving the ductility can be expected.
Here, the term "incompatible (with the crosslinkable oligomer or polymer)" does not mean incompatible with all the components contained in the crosslinkable oligomer or polymer. and that each specific component used in the thermoplastic elastomer is incompatible with each other.

Examples of the thermoplastic elastomer include olefin-based elastomers, styrene-based elastomers, polyvinyl chloride-based elastomers, polyurethane-based elastomers, polyester-based elastomers, and polyamide-based elastomers. You may use 2 or more types together.
Specific examples of olefinic elastomers include ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), and ethylene-butene rubber (EBM).
Specific examples of styrene-based elastomers include styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), and styrene-ethylene-propylene-styrene block copolymer (SEPS). , styrene ethylene butylene styrene block copolymers (SEBS, hydrogenated SBS), styrene ethylene ethylene propylene styrene block copolymers (SEEPS), and the like.
Specific examples of polyvinyl chloride-based elastomers include highly polymerized polyvinyl chloride with a plasticizer added, modified polyvinyl chloride, blends of these with other resins, and the like. .
Specific examples of polyurethane elastomers include, for example, short-chain glycol diisocyanate as a hard segment and long-chain polyol as a soft segment; hard segments rich in urethane and urea bonds and polyether as main those consisting of a soft segment; and the like.
Specific examples of polyester-based elastomers include those having polybutylene terephthalate as a hard segment and a long-chain polyol or polyester as a soft segment; and the like.
Specific examples of polyamide-based elastomers include those having nylon as a hard segment and polytetramethylene glycol as a soft segment; and the like.

Commercially available products of such thermoplastic elastomers include, for example, polyamide elastomer (TPAE-12, number average molecular weight: 30000, manufactured by T&K Toka Co., Ltd.), polyamide elastomer (DAIAMID PAE, manufactured by Degussa Huls), and polyamide. Polyether elastomer (UBESTA (registered trademark) XTA, manufactured by Ube Industries, Ltd.), polyester thermoplastic elastomer (Grelax A, manufactured by Dainippon Ink and Chemicals), polyester thermoplastic elastomer (Hytrel (registered trademark), Toray DuPont Co., Ltd.), polyether block amide copolymer (PEBAX (registered trademark), manufactured by Atofina Japan), polyamide elastomer (NOVAMID (registered trademark), manufactured by Mitsubishi Engineering-Plastics Corporation), and the like.

In the present invention, since only the thermoplastic elastomer can be three-dimensionally crosslinked in the crosslinkable oligomer or polymer, a reactive functional group different from the above-described reactive functional group possessed by the crosslinkable oligomer or polymer is used. and at least one or more reactive functional groups selected from the group consisting of hydroxyl groups, mercapto groups, silane functional groups, isocyanate groups, (meth)acryloyl groups, allyl groups, carboxy groups, acid anhydride groups and epoxy groups It is preferred to have
Here, the silane functional group is also referred to as a so-called crosslinkable silyl group, and specific examples thereof include the same silane functional groups possessed by the crosslinkable oligomer or polymer, such as a hydrolyzable silyl group; a silanol group; a functional group substituted with an acetoxy group derivative, an enoxy group derivative, an oxime group derivative, an amine derivative, or the like;
After the thermoplastic elastomer is three-dimensionally crosslinked, the crosslinkable oligomer or polymer has the same reactive functional groups as the thermoplastic elastomer (for example, a carboxy group, a hydrolyzable silyl group, etc.). Alternatively, the existing functional groups may be modified into the same reactive functional groups as those of the thermoplastic elastomer.
Among these functional groups, silane functional groups (especially hydrolyzable silyl groups) or hydroxyl groups are more preferable because the three-dimensional cross-linking of the thermoplastic elastomer proceeds easily.
Commercially available thermoplastic elastomers having such reactive functional groups include, for example, silylated (hydrolyzable silyl group terminated) amorphous poly-α-olefin polymer (Bestplast 206, number average molecular weight: 10600, Evonik manufactured by Degussa) and the like.

In the present invention, the reactive functional group is preferably present at least at the end of the main chain of the thermoplastic elastomer, and when the main chain is linear, the reactive functional group is present at 1.5 or more. is preferred, and having two or more is more preferred. On the other hand, when the main chain is branched, it preferably has 3 or more.

In the present invention, the weight-average molecular weight or number-average molecular weight of the thermoplastic elastomer is not particularly limited. It is preferably from 1,000 to 100,000, more preferably from 3,000 to 60,000.
Here, both the weight average molecular weight and the number average molecular weight shall be measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

Examples of the method of preparing fine particles by micronizing the thermoplastic elastomer in the crosslinkable oligomer or polymer include a method of three-dimensional cross-linking using the reactive functional groups of the thermoplastic elastomer. .

Specifically, the method for three-dimensional cross-linking using a reactive functional group includes the thermoplastic elastomer having the reactive functional group, water, a catalyst, and a functional group that reacts with the reactive functional group. and a method of reacting with at least one component selected from the group consisting of compounds for three-dimensional cross-linking.

Here, water as the component can be suitably used when the thermoplastic elastomer has a hydrolyzable silyl group, an isocyanate group, or an acid anhydride group as a reactive functional group.

Further, examples of catalysts for the above components include condensation catalysts for silanol groups (silanol condensation catalysts).
Specific examples of the silanol condensation catalyst include dibutyltin dilaurate, dibutyltin dioleate, dibutyltin diacetate, tetrabutyl titanate, and stannous octoate.

Examples of the compound having a functional group that reacts with the reactive functional group of the component include polyisocyanate compounds and silanol compounds.

The polyisocyanate compound can be suitably used when the thermoplastic elastomer has a hydroxyl group as a reactive functional group.
Specific examples of the polyisocyanate compound include TDI (eg, 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI)), MDI (e.g. 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI)), 1,4-phenylene diisocyanate, polymethylene polyphenylene polyisocyanate, xyloxy aromatic polyisocyanates such as diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), tolidine diisocyanate (TODI), 1,5-naphthalene diisocyanate (NDI), triphenylmethane triisocyanate; hexamethylene diisocyanate (HDI), Aliphatic polyisocyanates such as trimethylhexamethylene diisocyanate (TMHDI), lysine diisocyanate, norbornane diisocyanate methyl (NBDI); Polyisocyanate having 3 or more isocyanate groups; and the like.

The silanol compound can be suitably used when the thermoplastic elastomer has a silane functional group as a reactive functional group.
Specific examples of the silanol compound include tert-butyldimethylsilanol, diphenylmethylsilanol, polydimethylsiloxane having a silanol group, and cyclic polysiloxane having a silanol group.

In the present invention, a solvent may be used, if necessary, when the thermoplastic elastomer is three-dimensionally crosslinked in the crosslinkable oligomer or polymer to prepare fine particles.
Examples of the mode of use of the solvent include a mode of using a plasticizer, a diluent, and a solvent that serve as a good solvent for the thermoplastic elastomer and a poor solvent for the crosslinkable oligomer or polymer, and/or the use of the crosslinkable oligomer or Examples include an embodiment in which a plasticizer, diluent, or solvent that is a good solvent for the polymer and a poor solvent for the thermoplastic elastomer is used.
Specific examples of such solvents include n-pentane, isopentane, neopentane, n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, n-heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2 , 3-trimethylbutane, n-octane, isooctane and other aliphatic hydrocarbons; cyclopentane, cyclohexane, methylcyclopentane and other cycloaliphatic hydrocarbons; xylene, benzene, toluene and other aromatic hydrocarbons; α-pinene, Terpene-based organic solvents such as β-pinene and limonene are included.

Further, in the present invention, additives such as surfactants, emulsifiers, dispersants, silane coupling agents and the like are added when preparing fine particles by three-dimensionally cross-linking the thermoplastic elastomer in the cross-linkable oligomer or polymer. It is preferably prepared using

(Other ingredients)
In the rubber composition of the present invention, in addition to the above components, vulcanizing or cross-linking agents; vulcanizing or cross-linking accelerators; various fillers such as zinc oxide, carbon black, clay, talc and calcium carbonate; Ringing agents; anti-aging agents; various additives that are generally blended in rubber compositions such as plasticizers can be blended; or can be used for cross-linking. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

Further, the rubber composition of the present invention is suitable for manufacturing a pneumatic tire according to a conventional pneumatic tire manufacturing method, and is preferably applied to a tread, particularly a cap tread, to form a studless tire.

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

Examples 1-5 and Comparative Examples 1-4
Sample preparation In the formulation (parts by mass) shown in Table 1, the components except the vulcanization accelerator and sulfur were kneaded in a 1.7-liter closed Banbury mixer for 5 minutes, then the kneaded product was discharged out of the mixer and allowed to cool to room temperature. Let cool. Thereafter, a vulcanization accelerator and sulfur were added and further kneaded in the same Banbury mixer to obtain a rubber composition. Next, the obtained rubber composition was press-vulcanized in a predetermined mold at 160° C. for 20 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were measured by the following test methods.

Performance on ice: The obtained vulcanized rubber test piece was attached to a flat columnar base rubber, and was measured using an inside drum type friction tester on ice at a temperature of -1.5°C, a load of 5.5 kg/cm ² , and a drum. The coefficient of friction on ice was measured at a rotation speed of 25 km/h. The coefficient of friction on ice thus obtained was indexed to the value of Comparative Example 1 as 100 and shown in the column of "performance on ice". The larger the index value, the greater the on-ice frictional force and the better the on-ice performance.

Wet performance: Using the obtained vulcanized rubber test piece, water was sprayed on the road surface using an outside friction tester, under the conditions of a measurement temperature of 25 ° C., a surface pressure of 180 kPa, and a drum rotation speed of 30 km / h. The maximum wet friction coefficient was measured. The obtained maximum value of the wet friction coefficient was indexed with the value of Comparative Example 1 being 100, and shown in the column of "Wet Performance". A larger index value means better wet performance.

Table 1 shows the results.

*1: NR (RSS#3)
*2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd.)
*3: Plasticizer 1 (glycerol monostearate manufactured by Sigma-Aldrich)
*4: Plasticizer 2 (Lionon DEH-40 manufactured by Lion Specialty Chemicals Co., Ltd., polyethylene glycol bis(2-ethylhexanoate))
*5: Aroma oil (Extract No. 4S manufactured by Showa Shell Sekiyu K.K.)
*6: Carbon black (Show Black N339 manufactured by Cabot Japan)
*7: Silica (1165MP manufactured by Rhodia, nitrogen adsorption specific surface area (N ₂ SA) = 160 m ² /g)
*8: Silane coupling agent 1 (Si69 manufactured by Evonik Degussa)
*9: Zinc white (Type 3 zinc oxide manufactured by Seido Chemical Industry Co., Ltd.)
* 10: Stearic acid (industrial stearic acid N manufactured by Chiba Fatty Acid Co., Ltd.)
* 11: Anti-aging agent (Ozonon 6C manufactured by Seiko Chemical Co., Ltd.)
* 12: Thermally expandable microcapsules (Matsumoto Microsphere F100 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)
*13: A crosslinkable oligomer or polymer incompatible with the diene rubber (a fine particle-containing crosslinkable polymer prepared according to the method described in paragraph 0074 of JP-A-2014-62168. The polymer has an isocyanate group-terminated hydroxyl group-terminated A polyolefin-based elastomer with an average particle size of 25 μm, which is three-dimensionally crosslinked by siloxane bonds, is dispersed in polyoxypropylene glycol at a rate of 11% by mass.)
*14: Sulfur (fine powdered sulfur with Kinkain oil manufactured by Tsurumi Chemical Industry Co., Ltd.)
* 15: Vulcanization accelerator 1 (Noccellar CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
*16: Vulcanization accelerator 2 (PERKACIT DPG manufactured by Flexis)

From the results in Table 1, the rubber compositions of the examples contain 10 parts by mass or more of silica per 100 parts by mass of diene rubber, and 1 to 1 part of polyethylene glycol bis(2-ethylhexanoate), which is a specific plasticizer. Since 40 parts by mass and 0.1 to 20 parts by mass of thermally expandable microcapsules are blended, performance on ice and wet performance are improved compared to the composition of Comparative Example 1 having a typical conventional composition. there is
On the other hand, in Comparative Example 2, the amount of plasticizer 1 was simply increased compared to the rubber composition of Comparative Example 1, so wet performance was deteriorated.
Compared to the rubber composition of Comparative Example 1, Comparative Example 3 simply increased the amount of heat-expandable microcapsules, resulting in poor wet performance.
In Comparative Example 4, the blending amount of polyethylene glycol bis(2-ethylhexanoate) exceeded the upper limit specified in the present invention, so the wet performance deteriorated.

Claims (3)

With respect to 100 parts by mass of diene rubber, 20 to 120 parts by mass of silica, 1 to 40 parts by mass of polyethylene glycol bis(2-ethylhexanoate) having a repeating number of polyoxyethylene units of 6 to 12, and thermal expansion 1. A rubber composition for studless tires, characterized by containing 0.1 to 20 parts by mass of soluble microcapsules. For 100 parts by mass of the diene rubber, 0.3 to 30 parts by mass of a crosslinkable oligomer or polymer incompatible with the diene rubber and three-dimensionally crosslinked fine particles having an average particle size of 0.5 to 50 μm The rubber composition for studless tires according to claim 1, wherein 0.1 to 12 parts by mass of is blended. A studless tire using the rubber composition according to claim 1 or 2 for a tread.