JP5259049B2 - Rubber composition and studless tire using the same - Google Patents

Description

  The present invention relates to a rubber composition and a studless tire using the rubber composition in a tread, and more particularly to a rubber composition for a studless tire capable of improving the dry performance, wet performance and on-ice performance of the tire.

  In general, in a studless tire, when the dynamic elastic modulus (G ′) of the tread at a low temperature (here, the low temperature is a temperature when traveling on ice, which is about −20 ° C.), the icing road surface of the tire increases. It is preferable to lower the elastic modulus of the tread at a low temperature because the adhesion to the tire is lowered and the braking performance on the ice of the tire is lowered.

  In addition, it is also required to improve performance (dry performance and wet performance) when a studless tire is used on a normal road surface other than an icing road surface, specifically, a dry road surface and a wet road surface. Here, in developing a tire tread rubber composition that directly contributes to the dry and wet performance of the tire, the index is the loss tangent (tanδ) near 0 ° C and the loss tangent (tanδ) near 30 ° C. In general, using a rubber composition having a high tan δ at around 0 ° C. for the tread increases the coefficient of friction (μ) on the wet road surface of the tire and improves the wet performance. On the other hand, by using a rubber composition having a high tan δ at around 30 ° C. for the tread, the friction coefficient (μ) on the dry road surface of the tire can be increased to improve the dry performance.

On the other hand, conventionally, as a technique for increasing the tan δ of the rubber composition, a technique of blending a C ₉ aromatic resin having a high glass transition point (Tg) into the rubber composition (see Patent Document 1), and a molecular weight. A technique (see Patent Document 2) in which tens of thousands of liquid styrene-butadiene copolymers are blended into a rubber composition is known.

However, in order to increase the tan δ of the rubber composition, when a C ₉ aromatic resin having a high glass transition point (Tg) or a liquid styrene-butadiene copolymer having a molecular weight of tens of thousands is added to the rubber composition, Since the dynamic elastic modulus near 20 ° C. increases, a studless tire in which such a rubber composition is applied to a tread has insufficient braking performance on ice.

JP-A-5-9338 JP-A-61-203145

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, with high tan δ around 0 ° C. and 30 ° C., low dynamic elastic modulus (G ′) around −20 ° C. The object is to provide a rubber composition capable of improving dry performance, wet performance and on-ice performance. Another object of the present invention is to provide a studless tire using such a rubber composition as a tread and having excellent dry performance, wet performance and on-ice performance.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have good compatibility with a rubber component with respect to a rubber component mainly composed of natural rubber and / or polyisoprene rubber and polybutadiene rubber. in, that the glass transition point to formulate high and relatively high molecular weight styrene copolymer, with the tanδ at around 0 ℃ and around 30 ° C. of the rubber composition increases, movement of around -20 ° C. As a result, it was found that the elastic modulus (G ′) was lowered, and the present invention was completed.

That is, the rubber composition of the present invention is
For 100 parts by mass of the rubber component (A) mainly composed of natural rubber and / or polyisoprene rubber and polybutadiene rubber,
20 to 70 parts by mass of at least one filler (B) selected from the group consisting of carbon black and white filler;
Styrene copolymer (C) 3 having a polystyrene-reduced weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ and comprising a copolymer of styrene and one or more styrene derivatives or two or more styrene derivatives. 30 parts by mass and
The styrene derivative is selected from methyl styrene, ethyl styrene, isobutyl styrene, tert-butyl styrene , 2,4,6-trimethyl styrene, 4-cyclohexyl styrene, and divinylbenzene.

In the rubber composition of the present invention, at least one of the styrene derivatives is preferably selected from methylstyrene , ethylstyrene, isobutylstyrene, tert-butylstyrene , 2,4,6-trimethylstyrene, and tert-butyl. More preferably, it is styrene.

  The rubber composition of the present invention preferably contains foamable bubbles in the rubber matrix after vulcanization, and the foaming ratio in the rubber matrix is preferably 3 to 50%.

  The rubber composition of the present invention preferably further contains organic short fibers. Here, it is further preferable that at least a part of the organic short fibers are fine particle-containing organic short fibers.

  The studless tire of the present invention is characterized in that the rubber composition is used for a tread.

  According to the present invention, the tan δ is high near 0 ° C. and 30 ° C., the dynamic elastic modulus (G ′) is low near −20 ° C., and the dry performance, wet performance and on-ice performance of the studless tire are improved. The rubber composition which can be provided can be provided. Moreover, the studless tire which was excellent in dry performance, wet performance, and on-ice performance using this rubber composition for a tread can be provided.

The present invention is described in detail below. The rubber composition of the present invention is selected from the group consisting of carbon black and white filler with respect to 100 parts by mass of the rubber component (A) mainly composed of natural rubber and / or polyisoprene rubber and polybutadiene rubber. 20 to 70 parts by mass of a filler (B) having a polystyrene-reduced weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ , and styrene and one or more styrene derivatives or two or more styrene derivatives And 3-30 parts by mass of a styrene copolymer (C) obtained by copolymerization of styrene, and the styrene derivative is methylstyrene, ethylstyrene, isobutylstyrene, tert-butylstyrene , 2 , 4 , 6 -Trimethylstyrene, 4-cyclohexylstyrene, divinylbenzene.

The styrene-based copolymer polymer (C), since the glass transition point is high, it is possible to increase the tanδ at around 0 ℃ and around 30 ° C. of the rubber composition. Moreover, the styrenic polymer (C) is relatively with the molecular weight is high, the natural rubber and / or polyisoprene rubber, compatibility with the rubber component consisting mainly of a polybutadiene rubber (A) is relatively Since it is favorable, the dynamic elastic modulus (G ′) around −20 ° C. of the rubber composition can be reduced. Therefore, the dry performance, wet performance and on-ice performance of the studless tire can be improved by applying the rubber composition of the present invention to the tread of the studless tire.

  The rubber component (A) of the rubber composition of the present invention contains natural rubber (NR) and / or polyisoprene rubber (IR) and polybutadiene rubber (BR) as main components. Here, the total content of natural rubber and / or polyisoprene rubber in the rubber component (A) is preferably in the range of 20 to 70% by mass, and the content of polybutadiene rubber in the rubber component (A) is 30 to 30%. A range of 80% by weight is preferred. The rubber component (A) can also contain rubber components other than natural rubber, polyisoprene rubber and polybutadiene rubber. The polybutadiene rubber preferably has a cis-1,4 bond content of 75% or more.

  The rubber composition of the present invention contains 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). When the blending amount of the filler (B) is less than 20 parts by mass, the wear resistance and fracture characteristics of the rubber composition are insufficient. On the other hand, when it exceeds 70 parts by mass, the low exothermic property of the rubber composition is deteriorated. There are things to do.

  The carbon black is not particularly limited, and examples thereof include FEF, SRF, HAF, ISAF, and SAF grades. The carbon black is preferably carbon black having an iodine adsorption amount (IA) of 60 mg / g or more and a dibutyl phthalate (DBP) oil absorption of 80 mL / 100 g or more. By blending carbon black, various physical properties of the rubber composition can be improved, but from the viewpoint of improving the wear resistance, those of HAF, ISAF, and SAF grade are more preferable.

  On the other hand, examples of the white filler include silica and aluminum hydroxide. Among these, silica is preferable. Examples of the silica include, but are not limited to, wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. Wet silica is preferred because it is excellent in the effect of achieving both wet grip properties and low rolling resistance. In addition, when using a silica as a filler (B), it is preferable to add a silane coupling agent at the time of a mixing | blending from a viewpoint of improving the reinforcement property further. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxysilyl). Ethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltri Methoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilyl Ethyl-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, dimethoxymethylsilylpropylbenzothiazole tetrasulfide, etc. Among these, bis (3-triethoxysilylpropyl) tetrasulfide and 3-trimethoxysilyl from the viewpoint of reinforcing effect Propyl benzothiazole tetrasulfide are preferable. These silane coupling agents may be used alone or in combination of two or more.

The rubber composition of the present invention has a polystyrene-equivalent weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ and is a styrene-based copolymer obtained by copolymerizing styrene and one or more styrene derivatives or two or more styrene derivatives. co-polymer (C) containing 3 to 30 parts by mass relative to the rubber component (a) 100 parts by mass of. When the amount of styrenic polymer (C) is less than 3 parts by mass, the effect of increasing the tanδ at around 0 ℃ and around 30 ° C. of the rubber composition, as well as dynamic modulus at around -20 ° C. (G ') Insufficient effect to reduce.

The styrene-based copolymer polymer (C) is a styrene copolymer obtained by copolymerization of styrene and one or more styrene derivatives, or styrene copolymerization obtained by copolymerizing two or more kinds of styrene derivatives It is a coalescence.

Moreover, the styrenic polymer (C) is required to be a polystyrene-reduced weight-average molecular weight of ^{2 × 10 3 ~50 × 10 3} . Here, the weight average molecular weight is less than 2 × 10 ³ of styrenic polymer (C), tend to fracture properties of the rubber composition is deteriorated, when it exceeds 50 × 10 ^3, processability of the rubber composition Tends to decrease. Also, depending on the purpose, and the polystyrene reduced weight average molecular weight of 5 × 10 ³ ~50 × 10 ³ of styrenic polymer and (C) were compounded in the rubber composition, by using the rubber composition in a tread The tread performance is the best.

The styrene-based copolymer polymer (C) preferably has a glass transition point of 70 ° C. or higher. By blending the rubber composition with a styrene copolymer having a glass transition point of 70 ° C. or higher, tan δ at about 0 ° C. and about 30 ° C. of the rubber composition can be sufficiently increased.

  As said styrene-type copolymer, what was random-copolymerized is preferable. The styrene content in the styrene copolymer is preferably 90% by mass or less, and more preferably 50% by mass or less.

The styrene derivative that is a raw material monomer of the styrene copolymer (C) is selected from methyl styrene, ethyl styrene, isobutyl styrene, tert-butyl styrene , 2,4,6-trimethyl styrene, 4-cyclohexyl styrene, and divinyl benzene. P-tert-butylstyrene is particularly preferred. In the styrene copolymer (C), it is necessary to use one or more styrene derivatives as monomers, and two or more kinds may be used.

The styrene-based copolymer polymer (C) is styrene and one or more styrene derivatives as monomers or by using two or more kinds of styrene derivatives, can be prepared by general polymerization method of olefins, for example, anionic It can be produced by polymerization. In the case of producing styrenic polymer (C) is in anionic polymerization, usually, by using an organolithium compound as a polymerization initiator, is copolymerized the monomers in an inert organic solvent. Further, as described above, since a styrene copolymer is preferably a random copolymer, it is preferable to use a randomizer if necessary.

  Examples of the organic lithium compound used as the polymerization initiator include alkyl lithium such as ethyl lithium, n-propyl lithium, i-propyl lithium, n-butyl lithium, sec-butyl lithium, tert-octyl lithium, and n-decyl lithium, phenyl Lithium, 2-naphthyllithium, aryllithium such as 2-butyl-phenyllithium, aralkyllithium such as 4-phenyl-butyllithium, cycloalkyllithium such as cyclohexyllithium and 4-cyclopentyllithium, lithium hexamethyleneimide, lithium pyrrolidide , Lithium piperidide, lithium heptamethylene imide, lithium dodecamethylene imide, lithium dimethylamide, lithium diethylamide, lithium dipropylamide, lithium dibutylamide, lithium dihexyl Amide, Lithium diheptylamide, Lithium dioctylamide, Lithymdi-2-ethylhexylamide, Lithium didecylamide, Lithium-N-methylpiperazide, Lithium ethylpropylamide, Lithium ethylbutyramide, Lithium methylbutyramide, Lithium ethylbenzylamide, Lithium Examples include lithium amide compounds such as methylphenethylamide, and among these, n-butyllithium is preferable. The amount of these organolithium compounds used is preferably in the range of 0.2 to 20 mmol per 100 g of monomer.

  Examples of the inert organic solvent include propane, n-butane, i-butane, n-pentane, i-pentane, n-hexane, propene, 1-butene, i-butene, trans-2-butene, and cis-2- Examples include aliphatic hydrocarbons such as butene, 1-pentene, 2-pentene, 1-hexene, and 2-hexene, aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, and alicyclic hydrocarbons such as cyclohexane. Of these, cyclohexane is preferred. Moreover, the said inert organic solvent may be used individually by 1 type, or may mix and use 2 or more types.

  Examples of the randomizer include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, bistetrahydrofurylpropane, triethylamine, pyridine, N-methylmorpholine, N, N, N ′, N′-tetramethylethylenediamine, 1 , 2-dipiperidinoethane, potassium-t-amylate, potassium-t-butoxide, sodium-t-amylate and the like. The amount of these randomizers used is preferably in the range of 0.01 to 20 mol with respect to 1 mol of the organic lithium compound as a polymerization initiator.

In the production of the styrenic polymer (C), the polymerization temperature is preferably in the range of about -80 to 150 ° C., more preferably in the range of -20 to 100 ° C.. The polymerization can be carried out under a generated pressure, but it is usually preferred to carry out the polymerization under a pressure sufficient to keep the monomer used in a substantially liquid phase. Although the pressure of the polymerization reaction depends on the raw materials such as monomers and initiators used and the polymerization temperature, the polymerization reaction can be carried out at a pressure higher than the generated pressure if desired. When carried out below, the reaction system is preferably pressurized with an inert gas. In addition, it is preferable to previously remove water, oxygen, carbon dioxide and other catalyst poisons from all the raw materials such as monomers, polymerization initiators and solvents used in the polymerization.

The rubber composition of the present invention preferably contains foamable bubbles in the rubber matrix after vulcanization, and the foaming ratio in the rubber matrix is preferably 3 to 50%. Here, the foaming rate (Vs) is expressed by the following formula:
Vs = (ρ ₀ / ρ ₁ −1) × 100 (%)
Wherein, [rho ₁ represents the density of the rubber composition after vulcanization ^{(g / cm 3), ρ} 0 represents the density of the solid phase portion in the rubber composition after vulcanization (g / cm ^3)] Can be calculated. If the foaming rate is less than 3%, the function of removing water by foaming bubbles is insufficient, and the performance of the vulcanized rubber on ice cannot be improved sufficiently. On the other hand, if the foaming rate exceeds 50%, the vulcanized rubber The amount of foamable bubbles in the inside becomes too large, and the destructive properties of the vulcanized rubber deteriorate.

  When the vulcanized rubber composition contains foamable bubbles, it is preferable to add a foaming agent to the rubber composition. Here, examples of the foaming agent include azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DNPT), dinitrosopentastyrenetetramine, benzenesulfonylhydrazide derivatives, p, p′-oxybisbenzenesulfonylhydrazide (OBSH), Ammonium bicarbonate that generates carbon dioxide, sodium bicarbonate, ammonium carbonate, nitrososulfonylazo compounds that generate nitrogen, N, N'-dimethyl-N, N'-dinitrosophthalamide, toluenesulfonylhydrazide, P-toluenesulfonyl Semicarbazide, P, P′-oxybisbenzenesulfonyl semicarbazide and the like can be mentioned. These foaming agents may be used individually by 1 type, and may use 2 or more types together. The foaming agent is preferably used in combination with urea, zinc stearate, zinc benzenesulfinate, zinc white or the like as a foaming aid.

  The rubber composition of the present invention preferably further contains organic short fibers made of a thermoplastic resin, and the matrix of the rubber composition until the temperature of the rubber composition reaches the maximum vulcanization temperature during vulcanization. It is further preferred to contain organic short fibers having thermal properties that melt or soften therein. The organic short fiber may be formed of a crystalline polymer, an amorphous polymer, or a crystalline polymer and an amorphous polymer. It is preferably formed from a functional polymer.

  Examples of the crystalline polymer include polyethylene (PE), polypropylene (PP), polybutylene, polybutylene succinate, polyethylene succinate, syndiotactic-1,2-polybutadiene (SPB), polyvinyl alcohol (PVA), Single-composition polymers such as polyvinyl chloride (PVC), those having a melting point controlled to an appropriate range by copolymerization, blending, or the like can be used, and those having additives added thereto can also be used. These may be used individually by 1 type and may use 2 or more types together. Among these crystalline polymers, polyolefins and polyolefin copolymers are preferable, polyethylene (PE) and polypropylene (PP) are more preferable in terms of general availability and availability, polyethylene (PE) in terms of low melting point and easy handling. Is particularly preferred. Examples of the non-crystalline polymer include polymethyl methacrylate (PMMA), acrylonitrile / butadiene / styrene copolymer (ABS), polystyrene (PS), polyacrylonitrile, copolymers thereof, and blends thereof. Etc. These may be used individually by 1 type and may use 2 or more types together.

  The average diameter of the organic short fibers is not particularly limited, but is preferably in the range of 10 to 100 μm, and more preferably in the range of 15 to 90 μm. The average length of the organic short fibers is not particularly limited, but is preferably in the range of 0.5 to 20 mm, and more preferably in the range of 1 to 10 mm. In this case, after vulcanization, elongated bubbles can be suitably formed in the rubber matrix, and the elongated bubbles can function as micro drainage grooves, improving the performance of vulcanized rubber on ice. Can be made. In addition, the compounding quantity of the said organic short fiber has the preferable range of 0.2-10 mass parts with respect to 100 mass parts of said rubber components (A).

  The organic short fibers are preferably fine particle-containing organic short fibers in which at least a part thereof contains fine particles. When the fine particle-containing organic short fibers are blended, the on-ice performance of the rubber composition is further improved by the scratching effect of the fine particles. Examples of the fine particles include inorganic fine particles such as glass fine particles, aluminum hydroxide fine particles, alumina fine particles, and iron fine particles, and organic fine particles such as (meth) acrylic resin fine particles and epoxy resin fine particles. These fine particles may be used individually by 1 type, and 2 or more types may be mixed and used for them. The particle diameter of the fine particles is not particularly limited, but the long diameter (the longest diameter of the fine particles) is preferably in the range of 0.1 to 500 μm, and 80% or more of the total fine particles are in the range of 0.1 to 500 μm. It is further preferable to have The content of the fine particles in the fine particle-containing organic short fibers is preferably in the range of 3 to 145 parts by mass with respect to 100 parts by mass of the organic short fibers made of a thermoplastic resin. If the content of the fine particles is less than 3 parts by mass, the scratch effect by the fine particles may be insufficient, and the performance on ice may not be sufficient.On the other hand, if the content exceeds 145 parts by mass, the spinning operability of the fine organic particles containing fine particles is poor. Tend to be.

  In the rubber composition of the present invention, a general rubber crosslinking system can be used, and it is preferable to use a combination of a crosslinking agent and a vulcanization accelerator. Here, as a crosslinking agent, sulfur etc. are mentioned, The usage-amount of a crosslinking agent has the preferable range of 0.1-10 mass parts as a sulfur content with respect to 100 mass parts of said rubber components (A), and 1-5 masses. A range of parts is more preferred. If the compounding amount of the crosslinking agent is less than 0.1 parts by mass as a sulfur component with respect to 100 parts by mass of the rubber component, the rupture strength, wear resistance and low heat build-up of the vulcanized rubber will decrease, and if it exceeds 10 parts by mass, the rubber elasticity Is lost.

  On the other hand, the vulcanization accelerator is not particularly limited, but 2-mercaptobenzothiazole (M), dibenzothiazyl disulfide (DM), N-cyclohexyl-2-benzothiazylsulfenamide (CZ). ), Thiazole vulcanization accelerators such as Nt-butyl-2-benzothiazolylsulfenamide (NS), and guanidine vulcanization accelerators such as diphenylguanidine (DPG). The amount of the vulcanization accelerator used is preferably in the range of 0.1 to 5 parts by mass and more preferably in the range of 0.2 to 3 parts by mass with respect to 100 parts by mass of the rubber component (A). These vulcanization accelerators may be used alone or in combination of two or more.

  In the rubber composition of the present invention, process oil or the like can be used as a softening agent, and examples of the process oil include paraffinic oil, naphthenic oil, and aromatic oil. Among 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 these process oils used is preferably in the range of 0 to 100 parts by mass with respect to 100 parts by mass of the rubber component (A). When the amount of process oil used exceeds 100 parts by mass with respect to 100 parts by mass of the rubber component (A), the tensile strength and low heat build-up of the vulcanized rubber tend to deteriorate.

In the rubber composition of the present invention, the rubber component (A), filler (B), styrenic polymers (C), foaming agent, foaming aid, an organic short fibers, a silane coupling agent, crosslinking agent, In addition to vulcanization accelerators and softeners, additives commonly used in the rubber industry, such as anti-aging agents, zinc oxide, stearic acid, antioxidants, ozone degradation inhibitors, etc., do not impair the purpose of the present invention. It can select suitably and mix | blend within the range.

  The rubber composition of the present invention is obtained by kneading using a kneading machine such as a roll or an internal mixer, and after molding, vulcanization is performed, and the tire tread, undertread, carcass, sidewall, It can be used for tire applications such as beads, anti-vibration rubber, belts, hoses, and other industrial products, but is particularly suitable as a tread for studless tires.

  The studless tire of the present invention is characterized by using the rubber composition in a tread. The tire is formed by applying a rubber composition having a high tan δ near 0 ° C. and 30 ° C. and a low dynamic elastic modulus (G ′) near −20 ° C. to the tread. Excellent wet performance and on-ice performance. The studless tire of the present invention is not particularly limited except that the above rubber composition is used for the tread, and can be produced according to a conventional method. Moreover, as gas with which this tire is filled, inert gas, such as nitrogen, argon, helium other than normal or the air which adjusted oxygen partial pressure, can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Synthesis of Styrene Copolymer A>
500 g of cyclohexane, 70 g of p-tert-butylstyrene, and 30 g of styrene were previously added to a 2 L stainless steel pressure-resistant reaction vessel with a temperature control jacket that was dried and purged with nitrogen. After adjusting the jacket temperature and adjusting the internal temperature to 40 ° C., 5 mmol of bistetrahydrofurylpropane was added, and further a hexane solution of n-butyllithium (n-BuLi) (n-BuLi: 10 mmol) was added to carry out the polymerization reaction. went. The polymerization reaction was carried out while adjusting the temperature so that the temperature of the polymerization system became 75 ° C. after 25 minutes. Further, after maintaining the temperature of the polymerization system for 15 minutes, 0.5 mL of an isopropanol solution (BHT concentration = 5%) of 2,6-di-tert-butylparacresol (BHT) was added to the polymerization system to stop the polymerization reaction. And styrenic copolymer A was obtained by drying according to a conventional method. The obtained polymer had 70% p-tert-butylstyrene units and 30% styrene units, and styrene was randomly connected. In addition, the molecular weight was measured based on monodisperse polystyrene by gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two in series), detector: differential refractometer (RI)]. As a result, it was found that the obtained styrene copolymer A had a polystyrene equivalent weight average molecular weight (Mw) of 10 × 10 ³ . Furthermore, the glass transition point of the styrene copolymer A was 120 ° C.

<Synthesis of Styrene Copolymer B>
p-Methylstyrene is used in place of p-tert-butylstyrene, and the mass ratio of p-methylstyrene / styrene and the total amount of monomer / n-BuLi are changed (the moles of bistetrahydrofurylpropane / n-BuLi). The ratio was fixed at 0.5), and the styrene copolymer B was obtained in the same manner as in the synthesis example of the styrene copolymer A. The obtained polymer had 50% by mass of p-methylstyrene units and 50% by mass of styrene units, and styrene was randomly connected. The styrene copolymer B had a polystyrene equivalent weight average molecular weight (Mw) of 10 × 10 ³ and a glass transition point of 105 ° C.

  Next, using the styrenic copolymer A or B, a rubber composition having a formulation shown in Table 1 was prepared, and the obtained rubber composition was applied to a tread to obtain a studless of size 185 / 70R13. A tire was prototyped. Moreover, the following method evaluated the on-ice performance, wet performance, and dry performance of the obtained studless tire. The results are shown in Table 1 and FIGS.

(1) Performance on ice The above test tires were mounted on a 1600cc displacement passenger car and the braking performance on ice at an ice temperature of -1 ° C was confirmed. Specifically, run on a flat surface on ice, step on the brake at a speed of 20 km / h to lock the tire, measure the distance to stop (braking distance), and use the following formula:
Performance on ice = braking distance of tire of Comparative Example 1 / braking distance of test tire × 100 (index)
According to the index. The larger the index value, the shorter the braking distance and the better the braking performance on ice.

(2) Wet and dry performance The above test tires are mounted on a 1600cc displacement passenger car, and the wet and dry performance of the tire is evaluated by the driver's feeling in the actual vehicle test on wet and dry road surfaces. expressed. The higher the score, the better the wet performance and the dry performance.

* 1 Ube Industries, UBEPOL 150L.
* 2 N134, the nitrogen adsorption specific surface area ^{_{(N 2 SA) = 146m 2}} / g.
* 3 Nippon Silica Co., Ltd., Nippon AQ.
* 4 Degussa, Si69, bis (3-triethoxysilylpropyl) tetrasulfide.
* 5 N-isopropyl-N'-phenyl-p-phenylenediamine.
* 6 Dibenzothiazyl disulfide.
* 7 N-cyclohexyl-2-benzothiazolesulfenamide.
* 8 Dinitrosopentamethylenetetramine.

  As is clear from Table 1 and FIGS. 1-2, the rubber composition which mix | blended the styrene-type copolymer (C) with the rubber component (A) which has a natural rubber and a polybutadiene rubber as a main component was applied to the tread. The studless tire of the example had improved wet performance and dry performance while maintaining braking performance on ice as compared with the tire of Comparative Example 1. On the other hand, the studless tires of Comparative Examples 2 to 6 in which the rubber composition not containing the styrene copolymer (C) was applied to the tread were inferior in wet performance and dry performance as compared with the tires of the Examples.

It is a graph which shows the relationship between the performance on ice and wet performance of the tire of an Example and a comparative example. It is a graph which shows the relationship between the performance on ice of the tire of an Example and a comparative example, and dry performance.

Claims (7)

For 100 parts by mass of the rubber component (A) mainly composed of natural rubber and / or polyisoprene rubber and polybutadiene rubber,
20 to 70 parts by mass of at least one filler (B) selected from the group consisting of carbon black and white filler;
Styrene copolymer (C) 3 having a polystyrene-reduced weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ and comprising a copolymer of styrene and one or more styrene derivatives or two or more styrene derivatives. 30 parts by mass and
The rubber composition, wherein the styrene derivative is selected from methylstyrene, ethylstyrene, isobutylstyrene, tert-butylstyrene , 2,4,6-trimethylstyrene, 4-cyclohexylstyrene, and divinylbenzene. 2. The rubber composition according to claim 1, wherein at least one of the styrene derivatives is selected from methyl styrene, ethyl styrene, isobutyl styrene, tert-butyl styrene , and 2,4,6-trimethyl styrene.   The rubber composition according to claim 2, wherein at least one of the styrene derivatives is tert-butylstyrene.   The rubber according to any one of claims 1 to 3, wherein the rubber composition contains foamable bubbles in the rubber matrix after vulcanization, and the foaming ratio in the rubber matrix is 3 to 50%. Composition.   The rubber composition according to any one of claims 1 to 4, further comprising organic short fibers made of a thermoplastic resin.   6. The rubber composition according to claim 5, wherein at least a part of the organic short fibers are fine particle-containing organic short fibers.   A studless tire, wherein the rubber composition according to any one of claims 1 to 6 is used for a tread.

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