JP2006274051A - Rubber composition and stud-less tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition which can improve the dry performance, wet performance and ice performance of studless tires. <P>SOLUTION: This rubber composition is characterized by comprising 100 pts.mass of (A) a rubber component consisting mainly of natural rubber and/or polyisoprene rubber, and polybutadiene rubber, 20 to 70 pts.mass of (B) at least one filler selected from the group consisting of carbon black and white fillers, and 3 to 30 pts.mass of (C) a (meth)acrylate-based (co)polymer having a weight-average mol.wt. of 2×10<SP>3</SP>to 50×10<SP>3</SP>converted into polystyrene. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 addition, by blending a (meth) acrylate (co) polymer having a high glass transition point and a relatively high molecular weight, tan δ increases around 0 ° C. and 30 ° C. of the rubber composition, and −20 The present inventors have found that the dynamic elastic modulus (G ′) in the vicinity of ° C. is lowered and have completed the present invention.

That is, 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. and at least one filler (B) 20 to 70 parts by weight is selected, and the polystyrene reduced weight average molecular weight of ^{2 × 10 3 ~50 × 10 3} ( meth) acrylate (co) polymer (C). 3 to 30 mass parts is mix | blended, It is characterized by the above-mentioned.

  In a preferred example of the rubber composition of the present invention, the (meth) acrylate-based (co) polymer (C) contains tert-butyl acrylate units and / or tert-butyl methacrylate units.

  In the rubber composition of the present invention, the (meth) acrylate-based (co) polymer (C) includes at least one alkyl (meth) acrylate containing tert-butyl acrylate and / or tert-butyl methacrylate and styrene. (Meth) acrylate copolymer obtained by copolymerization of (meth) acrylate copolymer, and (meth) acrylate copolymer obtained by copolymerization of two or more alkyl (meth) acrylates including tert-butyl acrylate and / or tert-butyl methacrylate. Polymers are preferred.

  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 weight of at least one filler (B) and (meth) acrylate (co) polymer (C) 3 to 30 parts by weight in terms of polystyrene equivalent weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ Part.

  Since the (meth) acrylate-based (co) polymer (C) has a high glass transition point, it is possible to increase the tan δ at around 0 ° C. and around 30 ° C. of the rubber composition. In addition, the (meth) acrylate-based (co) polymer (C) has a relatively high molecular weight, and a rubber component (A) mainly composed of natural rubber and / or polyisoprene rubber and polybutadiene rubber. Since the compatibility is also relatively good, the dynamic elastic modulus (G ′) of the rubber composition around −20 ° C. 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 is a (meth) acrylate-based (co) polymer (C) having a polystyrene-equivalent weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ with respect to 100 parts by mass of the rubber component (A). 3 to 30 parts by mass. Here, when the weight average molecular weight of the (meth) acrylate-based (co) polymer (C) is less than 2 × 10 ³ , the fracture characteristics of the rubber composition tend to be lowered, and when it exceeds 50 × 10 ³ There exists a tendency for the workability of a composition to fall. Further, although depending on the purpose, a (meth) acrylate-based (co) polymer (C) having a polystyrene-equivalent weight average molecular weight of 5 × 10 ³ to 50 × 10 ³ is blended in the rubber composition, By using it for the tread, the performance of the tread becomes the best. Further, if the blending amount of the (meth) acrylate-based (co) polymer (C) is less than 3 parts by mass, the effect of increasing tan δ at around 0 ° C. and around 30 ° C. of the rubber composition, and around −20 ° C. The effect of lowering the dynamic elastic modulus (G ′) is insufficient.

  The (meth) acrylate (co) polymer (C) preferably has a glass transition point of 70 ° C. or higher. By adding (meth) acrylate (co) polymer (C) having a glass transition point of 70 ° C. or higher to the rubber composition, the tan δ at 0 ° C. or 30 ° C. of the rubber composition is sufficiently increased. be able to.

  The (meth) acrylate-based (co) polymer (C) needs to contain one or more (meth) acrylate units, and preferably contains alkyl (meth) acrylate units, tert-butyl acrylate units and tert More preferably, it contains at least one of -butyl methacrylate units. Therefore, as the (meth) acrylate-based (co) polymer (C), a (meth) acrylate-based polymer obtained by homopolymerizing tert-butyl acrylate or tert-butyl methacrylate, tert-butyl acrylate and / or A (meth) acrylate copolymer obtained by copolymerizing two or more alkyl (meth) acrylates containing tert-butyl methacrylate is preferred.

  The raw material monomer of the (meth) acrylate-based (co) polymer (C) needs to contain (meth) acrylate, preferably contains alkyl (meth) acrylate, tert-butyl acrylate and / or tert- More preferably, it contains butyl methacrylate. Here, the alkyl group of the alkyl (meth) acrylate is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, specifically, a methyl group, an ethyl group, n -Propyl group, isopropyl group, isobutyl group, tert-butyl group and the like. Further, as the above alkyl (meth) acrylate, specifically, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate , Isobutyl acrylate, tert-butyl acrylate and the like.

  In addition, the raw material monomer of the (meth) acrylate-based (co) polymer (C) may contain styrene in addition to (meth) acrylate. Here, among (meth) acrylate (co) polymers containing styrene units, one or more alkyl (meth) acrylates containing tert-butyl acrylate and / or tert-butyl methacrylate are copolymerized with styrene. A (meth) acrylate copolymer is preferred. The (meth) acrylate copolymer is preferably a random copolymer. Here, the styrene content in the (meth) acrylate copolymer is preferably 90% by mass or less, and more preferably 50% by mass or less.

  The (meth) acrylate-based (co) polymer (C) can be produced by a general olefin polymerization method using (meth) acrylate and optionally styrene as monomers, for example, anionic polymerization. can do. When the (meth) acrylate-based (co) polymer (C) is produced by anionic polymerization, usually, an organic lithium compound is used as a polymerization initiator, and one or more monomers in an inert organic solvent ( Co) polymerization. In order to activate the polymerization initiator and suppress the termination reaction, it is preferable to add an organoaluminum compound as a ligand for the polymerization initiator to the polymerization system. Furthermore, as described above, the (meth) acrylate copolymer is preferably a random copolymer, and therefore, 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 organoaluminum compound used as the ligand for the polymerization initiator include triethylaluminum, tripropylaluminum, tributylaluminum, ethyldimethylaluminum, 2-ethylhexylaluminum, cyclohexylaluminum, and diphenylaluminum. Among these, triethylaluminum is used. preferable. The amount of these organoaluminum compounds 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.

  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 (meth) acrylate (co) 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, and the polymerization reaction is performed at a pressure higher than the generated pressure. 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. When the compounding amount of the crosslinking agent is less than 0.1 parts by mass with respect to 100 parts by mass of the rubber component (A), the breaking strength, wear resistance and low heat build-up of the vulcanized rubber are reduced, and when it exceeds 10 parts by mass. , 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 weight, more preferably in the range of 0 to 30 parts by weight with respect to 100 parts by weight 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.

  The rubber composition of the present invention includes the rubber component (A), filler (B), (meth) acrylate (co) polymer (C), foaming agent, foaming aid, organic short fiber, silane coupling. In addition to additives, crosslinking agents, vulcanization accelerators, and softeners, additives commonly used in the rubber industry, such as anti-aging agents, zinc oxide, stearic acid, antioxidants, and ozone degradation inhibitors, are used in the present invention. Can be appropriately selected and blended within a range that does not impair the purpose.

  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 poly t-butyl methacrylate (tBuMA polymer)>
500 g of cyclohexane and 100 g of tert-butyl methacrylate that had been dried in advance were added to a 2 L stainless steel pressure-resistant reaction vessel with a temperature control jacket that had been dried and purged with nitrogen, respectively. After adjusting the jacket temperature and adjusting the internal temperature to 40 ° C., 10 mmol of triethylaluminum was added, and further a hexane solution (n-BuLi: 10 mmol) of n-butyllithium (n-BuLi) was added to carry out a polymerization reaction. . 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. Poly t-butyl methacrylate (tBuMA polymer) was obtained by drying according to a conventional method. When the molecular weight is measured with gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two in series), detector: differential refractometer (RI)] based on monodisperse polystyrene. The obtained poly-t-butyl methacrylate was found to have a polystyrene-equivalent weight average molecular weight (Mw) of 10 × 10 ³ . The poly t-butyl methacrylate had a glass transition point of 120 ° C.

<Synthesis of Styrene / t-Butyl Methacrylate Copolymer (St / tBuMA Copolymer)>
500 g of cyclohexane, 80 g of tert-butyl methacrylate and 20 g of styrene, which had been dried in advance, were added to a 2 L stainless steel pressure-resistant reaction vessel with a temperature control jacket that had been dried and purged with nitrogen, respectively. After adjusting the jacket temperature and adjusting the internal temperature to 40 ° C., 10 mmol of triethylaluminum was added, and further a hexane solution (n-BuLi: 10 mmol) of n-butyllithium (n-BuLi) was added to carry out a polymerization reaction. . The polymerization reaction was carried out while adjusting the temperature so that the temperature of the polymerization system became 75 ° C. after 25 minutes. Furthermore, 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. The styrene / t-butyl methacrylate copolymer (St / tBuMA copolymer) was obtained by drying according to a conventional method. The obtained styrene / t-butyl methacrylate copolymer had 80% by mass of tert-butyl methacrylate units and 20% by mass of styrene units, and styrene was randomly connected. The styrene / t-butyl methacrylate copolymer had a polystyrene equivalent weight average molecular weight (Mw) of 10 × 10 ³ and a glass transition point of 115 ° C.

<Synthesis of poly t-butyl acrylate (tBuA polymer)>
500 g of cyclohexane and 100 g of tert-butyl acrylate that had been dried in advance were added to a 2 L stainless steel pressure-resistant reaction vessel with a temperature adjustment jacket that had been dried and purged with nitrogen, respectively. After adjusting the jacket temperature and adjusting the internal temperature to 40 ° C., 10 mmol of triethylaluminum was added, and further a hexane solution (n-BuLi: 10 mmol) of n-butyllithium (n-BuLi) was added to carry out a polymerization reaction. . 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 was dried according to a conventional method to obtain poly-t-butyl acrylate (tBuA polymer). The obtained poly t-butyl acrylate had a polystyrene equivalent weight average molecular weight (Mw) of 10 × 10 ³ and a glass transition point of 107 ° C.

<Synthesis of Styrene / t-Butyl Acrylate Copolymer (St / tBuA Copolymer)>
500 g of cyclohexane, 80 g of tert-butyl acrylate and 20 g of styrene, which had been dried in advance, were added to a 2 L stainless steel pressure-resistant reaction vessel with a temperature control jacket that had been dried and purged with nitrogen, respectively. After adjusting the jacket temperature and adjusting the internal temperature to 40 ° C., 10 mmol of triethylaluminum was added, and further a hexane solution of n-butyllithium (n-BuLi) (n-BuLi: 10 mmol) was added to carry out a polymerization reaction. . 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. The styrene / t-butyl acrylate copolymer (St / tBuA copolymer) was obtained by drying according to a conventional method. The obtained styrene / t-butyl acrylate copolymer had 80% by mass of tert-butyl acrylate units and 20% by mass of styrene units, and styrene was randomly connected. The styrene / t-butyl acrylate copolymer had a polystyrene equivalent weight average molecular weight (Mw) of 10 × 10 ³ and a glass transition point of 105 ° C.

  Next, using the (meth) acrylate-based (co) polymer, 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 size of 185 / 70R13. A prototype studless tire was made. 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 apparent from Table 1 and FIGS. 1 and 2, a rubber composition in which a (meth) acrylate copolymer (C) is blended with a rubber component (A) mainly composed of natural rubber and polybutadiene rubber is used as a tread. The studless tire of the applied 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 (meth) acrylate copolymer (C) was applied to the tread were inferior in wet performance and dry performance as compared with the tires of 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 (8)

At least one filler (B) selected from the group consisting of carbon black and white filler with respect to 100 parts by mass of a rubber component (A) mainly composed of natural rubber and / or polyisoprene rubber and polybutadiene rubber. ) 20 to 70 parts by mass and (meth) acrylate-based (co) polymer (C) 3 to 30 parts by mass having a polystyrene-equivalent weight average molecular weight of 2 × 10 ³ to 50 × 10 ³ A rubber composition characterized by the above.   The rubber composition according to claim 1, wherein the (meth) acrylate-based (co) polymer (C) contains a tert-butyl acrylate unit and / or a tert-butyl methacrylate unit.   The (meth) acrylate (co) polymer (C) is obtained by copolymerizing one or more alkyl (meth) acrylates containing tert-butyl acrylate and / or tert-butyl methacrylate with styrene (meth). The rubber composition according to claim 2, which is an acrylate copolymer.   The (meth) acrylate-based (co) polymer (C) is obtained by copolymerizing two or more alkyl (meth) acrylates containing tert-butyl acrylate and / or tert-butyl methacrylate. The rubber composition according to claim 2, wherein the rubber composition is a polymer.   The rubber according to any one of claims 1 to 4, 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 5, further comprising an organic short fiber made of a thermoplastic resin.   7. The rubber composition according to claim 6, 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 7 is used for a tread.

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