JP4881562B2 - Rubber composition and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition and a pneumatic tire using the rubber composition as a tread rubber, and in particular, by using the rubber composition as a tread rubber, steering stability on a dry road surface and a wet road surface without lowering the fracture characteristics of the tire. It is related with the rubber composition which can improve this.

  With the recent evolution of advanced power performance of automobiles, more excellent handling stability has been required as a tire characteristic. On the other hand, from the viewpoint of safety, it is also an important issue to sufficiently ensure the fracture characteristics of the tire. On the other hand, various techniques for improving the steering stability of tires have been developed so far. Here, it is known that loss characteristics (tan δ) are generally important as a development index of a rubber composition related to the steering stability of the tire, and in order to improve the steering stability on the dry road surface of the tire. It is effective to increase the hysteresis loss at room temperature or higher of the rubber composition used for the tire tread rubber, and to improve the steering stability on the wet road surface of the tire, the rubber composition used for the tire tread rubber It is effective to increase the hysteresis loss near 0 ℃.

  On the other hand, as a technique for increasing the hysteresis loss of the rubber composition at room temperature or higher, a technique using a liquid polymer having a weight average molecular weight of tens of thousands and excellent compatibility with the rubber component of the matrix is known. (See Patent Documents 1 and 2). However, although the liquid polymer increases the hysteresis loss of the rubber composition at room temperature or higher, it cannot increase the hysteresis loss near 0 ° C., so the liquid polymer-containing rubber composition was used for a tread rubber. In this case, there is a problem that the steering stability on the wet road surface of the tire cannot be improved.

JP-A-61-203145 JP 63-101440 A

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and improve handling stability on dry and wet road surfaces without deteriorating the fracture characteristics of the tires by using the tire tread rubber. It is to provide a possible rubber composition. Another object of the present invention is to provide a pneumatic tire using such a rubber composition for a tread rubber and having excellent fracture characteristics and excellent steering stability on a dry road surface and a wet road surface. is there.

  As a result of intensive studies to achieve the above object, the present inventor has obtained an aromatic vinyl compound-conjugated diene compound copolymer (A) having a specific molecular weight, a specific molecular weight and a bound styrene amount, A rubber composition comprising a hydrogenated styrene-butadiene copolymer (B) having a specific ratio within a specific range as a rubber component is used for a tread rubber of a tire, so that the tire can be dried without deteriorating the breaking characteristics of the tire. It has been found that the handling stability on the road surface and the wet road surface can be improved at the same time, and the present invention has been completed.

That is, the rubber composition of the present invention has a polystyrene-reduced weight average molecular weight of 3.0 × 10 ^{5 to} 3.0 × 10 ⁶ measured by gel permeation chromatography, and an aromatic vinyl compound-conjugated with a lithium polymerization initiator. For 100 parts by mass of diene compound copolymer (A),
The polystyrene-reduced weight average molecular weight measured by gel permeation chromatography is 5.0 × 10 ^{3 to} 2.0 × 10 ⁵ , the amount of bonded styrene is 10 to 70% by mass, and 55% or more and 60% or less of the double bonds in the butadiene part. The hydrogenated hydrogenated styrene-butadiene copolymer (B) is characterized by comprising a rubber component blended at a ratio of 10 to 200 parts by mass.

In the rubber composition of the present invention, 55% to 60% of the double bonds in the butadiene portion of the hydrogenated styrene-butadiene copolymer (B) are hydrogenated . In this case, since the copolymer (B) and the copolymer (A) can be surely made into a semi-compatible system, the hysteresis loss at 0 ° C. is maintained while maintaining the breaking strength of the rubber composition. It can be greatly improved.

  In a preferred example of the rubber composition of the present invention, the aromatic vinyl compound-conjugated diene compound copolymer (A) is a styrene-butadiene copolymer. Here, the amount of bound styrene of the aromatic vinyl compound-conjugated diene compound copolymer (A) is preferably in the range of 20 to 40% by mass, and in this case, wear resistance is ensured while ensuring the fracture characteristics of the rubber composition. Can be improved. The vinyl bond content in the butadiene portion of the aromatic vinyl compound-conjugated diene compound copolymer (A) is preferably in the range of 30 to 60%. In this case, wet skid resistance and wear resistance of the rubber composition Therefore, the steering stability and the wear resistance on the wet road surface of the tire can be sufficiently improved.

  In another preferable example of the rubber composition of the present invention, the hydrogenated styrene-butadiene copolymer (B) has a bound styrene content of 10 to 60% by mass. In this case, the wet skid resistance and dry grip property of the rubber composition are high, and the steering stability on the dry road surface and wet road surface of the tire can be sufficiently improved.

  In the rubber composition of the present invention, the hydrogenated styrene-butadiene copolymer (B) is 20 to 100 parts by mass with respect to 100 parts by mass of the aromatic vinyl compound-conjugated diene compound copolymer (A). It is preferable to mix | blend in the ratio. In this case, the steering stability on the dry road surface and wet road surface of the tire can be sufficiently improved while sufficiently ensuring the productivity of the rubber composition.

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

  According to the present invention, an aromatic vinyl compound-conjugated diene compound copolymer (A) having a specific molecular weight, and a hydrogenated styrene having a specific molecular weight and a bound styrene amount, and having a hydrogenation rate within a specific range. -Rubber that can improve steering stability on dry road surfaces and wet road surfaces without deteriorating the fracture characteristics of tires by using butadiene copolymer (B) as a rubber component and being used for tire tread rubber A composition can be provided. Further, it is possible to provide a pneumatic tire in which such a rubber composition is applied to a tread rubber and has excellent fracture characteristics and excellent handling stability on a dry road surface and a wet road surface.

The present invention is described in detail below. The rubber composition of the present invention is an aromatic vinyl compound-conjugated diene compound polymerized with a lithium-based polymerization initiator, having a polystyrene-equivalent weight average molecular weight of 3.0 × 10 ^{5 to} 3.0 × 10 ^{6 as} measured by gel permeation chromatography. The polystyrene-converted weight average molecular weight measured by gel permeation chromatography is 5.0 × 10 ^{3 to} 2.0 × 10 ⁵ with respect to 100 parts by mass of the copolymer (A), the amount of bound styrene is 10 to 70% by mass, and butadiene A hydrogenated styrene-butadiene copolymer (B) in which 55% to 60% of the double bonds in a part are hydrogenated contains a rubber component compounded in a proportion of 10 to 200 parts by mass. And

Since the rubber composition of the present invention contains the hydrogenated styrene-butadiene copolymer (B) having a weight average molecular weight of 5.0 × 10 ^{3 to} 2.0 × 10 ⁵ as a rubber component, the hysteresis loss (tan δ) at room temperature or higher is reduced. It has improved. Further, since the hydrogenated styrene-butadiene copolymer (B) has a hydrogenation rate of the double bond of the butadiene portion of 55% or more and 60% or less , the aromatic vinyl compound-conjugated diene compound copolymer ( A) and a semi-compatible system can be formed. As a result, it is possible to improve the hysteresis loss (tan δ) of the rubber composition near 0 ° C. while suppressing the deterioration of the fracture characteristics of the rubber composition. it can. Therefore, by using the rubber composition of the present invention for the tread rubber of a pneumatic tire, it is possible to improve steering stability on a dry road surface and a wet road surface while maintaining the fracture characteristics (safety) of the tire. Moreover, since the rubber composition of this invention has the above characteristics, it can be suitably applied to belts and various industrial rubber articles.

  The rubber component of the rubber composition of the present invention is required to contain at least the aromatic vinyl compound-conjugated diene compound copolymer (A) and the hydrogenated styrene-butadiene copolymer (B), and further natural rubber. (NR) and / or other synthetic rubbers may be included. Here, as other synthetic rubber, polyisoprene rubber (IR), polybutadiene rubber (BR), butyl rubber (IIR), styrene-butadiene copolymer rubber other than ethylene-propylene copolymer and copolymer (A) (SBR) and the like. In addition, a part of these rubber components modified with a polyfunctional modifier such as tin tetrachloride and the like and having a branched structure can be blended. However, the content of rubber components other than the aromatic vinyl compound-conjugated diene compound copolymer (A) and the hydrogenated styrene-butadiene copolymer (B) should be 60% by mass or less of the total rubber components. Is preferred.

The aromatic vinyl compound-conjugated diene compound copolymer (A) used in the rubber composition of the present invention has a polystyrene-equivalent weight average molecular weight of 3.0 × 10 ^{5 to} 3.0 × 10 as measured by gel permeation chromatography (GPC). ⁶ and preferably 7.0 × 10 ^{5 to} 2.5 × 10 ⁶ . The polystyrene reduced weight-average molecular weight of 3.0 × 10 under ⁵ above copolymer (A), reduces the fracture properties of the rubber composition, while when it exceeds 3.0 × 10 ^6, only the viscosity of the polymerization solution increases production Low.

  The aromatic vinyl compound-conjugated diene compound copolymer (A) is produced by copolymerizing an aromatic vinyl compound and a conjugated diene compound using a lithium polymerization initiator. Here, examples of the aromatic vinyl compound include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene and 2,4,6-trimethylstyrene. These aromatic vinyl compounds may be used alone or in combination of two or more. On the other hand, examples of the conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene, and the like. These conjugated diene compounds may be used alone or in combination of two or more. Among the aromatic vinyl compounds, styrene is particularly preferable, and among the conjugated diene compounds, 1,3-butadiene is particularly preferable. Accordingly, as the aromatic vinyl compound-conjugated diene compound copolymer (A), a styrene-butadiene copolymer (SBR) is particularly preferable.

  When the aromatic vinyl compound as the raw material of the aromatic vinyl compound-conjugated diene compound copolymer (A) is styrene, the copolymer (A) preferably has a bound styrene content of 20 to 40% by mass. . When the amount of bound styrene of the copolymer (A) is less than 20% by mass, the fracture characteristics of the rubber composition are deteriorated. On the other hand, when it exceeds 40% by mass, the wear resistance of the rubber composition is deteriorated.

  Further, when the conjugated diene compound as a raw material of the aromatic vinyl compound-conjugated diene compound copolymer (A) is 1,3-butadiene, the copolymer (A) has a vinyl bond amount of 30 to butadiene part. 60% is preferred. When the amount of vinyl bonds in the butadiene portion of the copolymer (A) is less than 30%, the wet skid resistance of the rubber composition is insufficient, so that the steering stability on the wet road surface of the tire can be sufficiently improved. On the other hand, if it exceeds 60%, the wear resistance of the rubber composition is lowered.

On the other hand, the hydrogenated styrene-butadiene copolymer (B) used in the rubber composition of the present invention has a polystyrene-equivalent weight average molecular weight of 5.0 × 10 ^{3 to} 2.0 × 10 ⁵ measured by gel permeation chromatography (GPC). It is necessary to be. If the copolymer (B) has a polystyrene-equivalent weight average molecular weight of less than 5.0 × 10 ³ , the rubber composition has insufficient fracture characteristics, wear resistance, wet skid resistance, and dry grip properties, so tire breakdown Characteristics, wear resistance, and handling stability on dry and wet road surfaces cannot be balanced to a high degree. On the other hand, if it exceeds 2.0 × 10 ⁵ , the wet skid resistance and dry grip properties of the rubber composition Since it is insufficient, the steering stability on the dry road surface and wet road surface of the tire cannot be improved.

  The hydrogenated styrene-butadiene copolymer (B) needs to have a bound styrene content of 10 to 70% by mass, and preferably 10 to 60% by mass. When the amount of bound styrene in the copolymer (B) is less than 10% by mass, the wet skid resistance and dry grip property of the rubber composition are insufficient, so that the steering stability on the dry road surface and wet road surface of the tire is improved. On the other hand, when the amount exceeds 70% by mass, the copolymer becomes resinous, so that the rubber composition becomes hard, wet skid resistance and dry grip properties deteriorate, and the dry road surface and wetness of the tire decrease. It becomes impossible to improve the handling stability on the road surface.

Furthermore, the hydrogenated styrene-butadiene copolymer (B) requires that 55% or more and 60% or less of the double bonds in the butadiene portion are hydrogenated. When the hydrogenation rate of the double bond in the butadiene portion of the copolymer (B) is 55% or more and 60% or less , the aromatic vinyl compound-conjugated diene compound copolymer (A) and the copolymer (B) Can form a semi-compatible system, and can improve hysteresis loss at the highest degree at 0 ° C. and room temperature or higher, while sufficiently suppressing the deterioration of fracture characteristics. Here, when the hydrogenation rate of the double bond of the butadiene part of the copolymer (B) is 50% or less, the copolymer (B) is compatible with the copolymer (A), and the rubber composition The improvement width of the hysteresis loss at 0 ° C. of the product is small, and the steering stability on the wet road surface of the tire cannot be sufficiently improved. On the other hand, when the hydrogenation rate exceeds 70%, the copolymer ( The compatibility with A) deteriorates too much, so that the fracture strength of the rubber composition is lowered and the hysteresis loss at 0 ° C. cannot be improved. Also, the hydrogenated styrene - butadiene copolymer (B), from the viewpoint of further improving the hysteresis loss at 0 ℃ of the rubber composition, the double bond hydrogenation ratio of butadiene portion is 55% or more 60% It is in the following range .

  In the rubber composition of the present invention, 10 to 200 parts by mass of the hydrogenated styrene-butadiene copolymer (B) with respect to 100 parts by mass of the aromatic vinyl compound-conjugated diene compound copolymer (A). It is necessary to mix | blend in a ratio, and it is preferable to mix | blend in the ratio of 20-100 mass parts. When the blending amount of the copolymer (B) is less than 10 parts by mass with respect to 100 parts by mass of the copolymer (A), the steering stability on the dry road surface and the wet road surface of the tire cannot be sufficiently improved, When the amount exceeds 200 parts by mass, the Mooney viscosity of the rubber composition becomes too low, and the productivity is deteriorated.

  In the aromatic vinyl compound-conjugated diene compound copolymer (A), for example, the above-described aromatic vinyl compound and conjugated diene compound are polymerized in the presence of ether or tertiary amine in a hydrocarbon solvent. It is obtained by copolymerizing by anionic polymerization using an agent. Here, the hydrocarbon solvent is not particularly limited, but cycloaliphatic hydrocarbons such as cyclohexane, methylcyclopentane, cyclooctane, propane, butane, pentane, hexane, heptane, octane, decane, etc. Aliphatic hydrocarbons, aromatic hydrocarbons such as benzene, toluene, and ethylbenzene can be used. These hydrocarbons may be used alone or in combination of two or more. Of these hydrocarbons, aliphatic hydrocarbons and alicyclic hydrocarbons are preferred.

  The lithium-based polymerization initiator is preferably an organic lithium compound. Examples of the organic lithium compound include alkyl lithium such as ethyl lithium, propyl lithium, n-butyl lithium, sec-butyl lithium, and t-butyl lithium; phenyl Aryl lithium such as lithium and tolyl lithium; Alkenyl lithium such as vinyl lithium and propenyl lithium; Alkylene dilithium such as tetramethylene dilithium, pentamethylene dilithium, hexamethylene dilithium and decamethylene dilithium; 1,3-dilithio In addition to arylene lithium such as benzene and 1,4-dilithiobenzene; 1,3,5-trilithiocyclohexane, 1,2,5-trilithionaphthalene, 1,3,5,8-tetralithiodecane, 1 , 2,3,5-tetralithio-4-hexyl-anthracene, etc. It is below. Among these, n-butyllithium, sec-butyllithium, t-butyllithium and tetramethylenedilithium are preferable, and n-butyllithium is particularly preferable. The amount of the lithium-based polymerization initiator used is determined by the polymerization rate in the reaction operation and the molecular weight of the copolymer to be produced, and is usually preferably in the range of 0.02 to 5 mg as a lithium atom per 100 g of monomer, and 0.05 to 2 mg. A range is more preferred.

  The polymerization reaction for obtaining the aromatic vinyl compound-conjugated diene compound copolymer (A) can be performed by either a batch polymerization method or a continuous polymerization method. The polymerization temperature in the polymerization reaction is preferably in the range of 0 to 130 ° C. The polymerization reaction can be carried out by any polymerization method such as isothermal polymerization, temperature rising polymerization and adiabatic polymerization. Furthermore, when performing the polymerization, an allene compound such as 1,2-butadiene may be added in order to prevent the formation of a gel in the reaction vessel.

  On the other hand, the hydrogenated styrene-butadiene copolymer (B) is a styrene-butadiene copolymer synthesized by the same method as the copolymer (A) using styrene and 1,3-butadiene as raw materials. It can be obtained by hydrogenation according to a conventional method in the presence of a hydrogenation catalyst. That is, the synthesized styrene-butadiene copolymer is a hydrogenation catalyst comprising an organic carboxylate nickel, an organic cobalt carboxylate, a group 1-3 organometallic compound; nickel supported on carbon, silica, diatomaceous earth, etc. Platinum, palladium, ruthenium, rhodium metal catalyst; obtained by hydrogenating under 1-100 atm of pressurized hydrogen using a catalyst selected from cobalt, nickel, rhodium, ruthenium complex and the like.

  The rubber composition of the present invention preferably contains a reinforcing filler, and is not particularly limited, but preferably contains silica and / or carbon black.

  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. The rubber composition of the present invention may contain only silica as a filler. In this case, the amount of silica is in the range of 10 to 250 parts by mass with respect to 100 parts by mass of the rubber component. From the viewpoint of reinforcing properties and the improvement efficiency of various physical properties thereby, a range of 20 to 150 parts by mass is preferable. When the compounding amount of silica is less than 10 parts by mass with respect to 100 parts by mass of the rubber component, the fracture characteristics and the like are not sufficient.

  In the rubber composition of the present invention, when silica is used as a filler, it is preferable to add a silane coupling agent at the time of blending from the viewpoint of further improving the reinforcing property. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-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.

  On the other hand, 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. The rubber composition of the present invention may contain only carbon black as a filler. In this case, the amount of carbon black is in the range of 10 to 250 parts by mass with respect to 100 parts by mass of the rubber component. From the viewpoint of reinforcing properties and efficiency of improving various physical properties thereby, a range of 20 to 150 parts by mass is preferable. When the compounding amount of carbon black is less than 10 parts by mass with respect to 100 parts by mass of the rubber component, the fracture characteristics and the like are not sufficient, and when it exceeds 250 parts by mass, the processability of the rubber composition decreases.

  Moreover, the rubber composition of this invention can use the general crosslinking system for rubber | gum, and it is preferable to use it combining 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, The range of 1-5 mass parts Is more preferable. 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 be reduced. 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, more preferably in the range of 0.2 to 3 parts by mass with respect to 100 parts by mass of the rubber component. 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. If the amount of process oil used exceeds 100 parts by mass with respect to 100 parts by mass of the rubber component, the tensile strength and low heat build-up of the vulcanized rubber tend to deteriorate.

  In the rubber composition of the present invention, in addition to the rubber component, filler, silane coupling agent, crosslinking agent, vulcanization accelerator, softener, for example, anti-aging agent, zinc oxide, stearic acid, antioxidant Additives usually used in the rubber industry such as an ozone deterioration inhibitor can be appropriately selected and blended within a range that does not impair the object of the present invention.

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

  The pneumatic tire of the present invention is characterized by using the rubber composition as a tread rubber. The tire has a high hysteresis loss (tan δ) at 0 ° C. and above room temperature, and is formed by applying a rubber composition having sufficient fracture characteristics to the tread rubber, so that it has sufficient fracture resistance, Excellent handling stability on dry and wet road surfaces. The tire of the present invention is not particularly limited except that the above rubber composition is used for the tread rubber, 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.

  Copolymers (B-1) to (B-4) were synthesized by the following method, and the styrene bond amount, vinyl bond amount, polystyrene equivalent weight average molecular weight and hydrogenation rate of the obtained copolymer were determined as follows. Measured with

(1) Styrene bond amount The styrene bond amount of the synthesized copolymer was calculated from the integral ratio of ¹ H-NMR spectrum.

(2) Vinyl bond amount The vinyl bond amount of the butadiene part of the synthesized copolymer was analyzed by an infrared method.

(3) Weight average molecular weight in terms of polystyrene (Mw)
The weight average molecular weight in terms of polystyrene of the synthesized copolymer was measured by GPC. Here, 244 type GPC manufactured by Waters is used as GPC, a differential refractometer is used as a detector, columns GMH-3, GMH-6, and G6000H-6 manufactured by Tosoh are used as columns, and tetrahydrofuran is used as a mobile phase. Was used. In addition, using a monodisperse styrene polymer manufactured by Waters as a standard substance, a calibration curve was prepared by previously obtaining the relationship between the molecular weight of the monodisperse styrene polymer peak by GPC and the GPC count number, and using this, The molecular weight in terms of polystyrene of the copolymer (B) was determined.

(4) Hydrogenation rate The hydrogenation rate of the butadiene part of the synthesized copolymer is the spectrum of the unsaturated bond part of 100 MHz ¹ H-NMR measured at a concentration of 15% by mass using carbon tetrachloride as a solvent. Calculated from the decrease.

<Synthesis of copolymer (B-1)>
Cyclohexane 3000 g, tetrahydrofuran (THF) 12 g, 1,3-butadiene 180 g and styrene 120 g were introduced into a 5 liter autoclave with a stirring blade sufficiently purged with nitrogen, and the temperature in the autoclave was adjusted to 21 ° C. Next, 1.50 g of n-butyllithium was added and polymerized for 60 minutes under elevated temperature conditions. After confirming that the monomer conversion rate was 99%, 4.68 g of tributylsilyl chloride was added to terminate the polymerization. Then, a catalyst solution of nickel naphthenate: triethylaluminum: butadiene = 1: 3: 3 (molar ratio) prepared in a separate container in advance was charged to 1 mol of nickel with respect to 1000 mol of butadiene in the copolymer. Thereafter, hydrogen was introduced into the reaction system at a hydrogen pressure of 30 atm and reacted at 80 ° C. The analytical values are shown in Table 1.

<Synthesis of Copolymers (B-2) to (B-4)>
Copolymers (B-2) to (B-4) were synthesized in the same manner as the copolymer (B-1) except that the monomer charge ratio, catalyst amount, hydrogen pressure, and the like were changed. The analytical values are shown in Table 1.

  Next, using the copolymers (B-1) to (B-4), a rubber composition having a formulation shown in Table 2 was prepared according to a conventional method, and the resulting rubber composition had fracture resistance. In addition, steering stability on dry road surfaces and wet road surfaces was evaluated by the following method. The results are shown in Tables 3 and 4.

(5) Fracture resistance A tensile test was performed in accordance with JIS K6301-1995, and the tensile strength (Tb) of the vulcanized rubber composition was measured. In Table 1, the tensile strength of Comparative Example 1 was taken as 100. An index is displayed, and in Table 2, the tensile strength of Comparative Example 5 is set to 100 and the index is displayed. The larger the index value, the better the fracture resistance.

(6) Steering stability on dry and wet road surfaces Using a rheometrics mechanical spectrometer, tan δ was measured at a shear strain of 5%, a temperature of 50 ° C or 0 ° C, and a frequency of 15 Hz. In Table 2, the tan δ of Comparative Example 5 was displayed as an index with 100 as an index. The larger the index value, the greater the hysteresis loss, and the better the steering stability on the dry or wet road surface.

* 1 SBR (A) [manufactured by JSR Corporation, SBR1500, bound styrene content = 23.5 mass%, vinyl bond content = 18%, polystyrene equivalent weight average molecular weight = 450 × 10 ³ ] or SBR (B) [in solution polymerization The synthesized SBR, bound styrene content = 38 mass%, vinyl bond content = 35%, polystyrene equivalent weight average molecular weight = 400 × 10 ³ ] are used, and the types of SBR used are shown in Tables 3 and 4.
* 2 ISAF, Tokai Carbon Co., Ltd., Seest 3H.
* 3 N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, "NOCRACK 6C" manufactured by Ouchi Shinsei Chemical Industry.
* 4 1,3-Diphenylguanidine, “Noxeller D” manufactured by Ouchi Shinsei Chemical Industry.
* 5 Nt-Butyl-2-benzothiazolylsulfenamide, “Noxeller NS” manufactured by Ouchi Shinsei Chemical Industry.
* 6 The types of additives used are shown in Tables 3 and 4.

As is apparent from the results of Examples in Tables 3 and 4, the molecular weight and the amount of bound styrene specified in the present invention are provided, and the hydrogenation rate of the double bond in the butadiene part is in the range of 55% to 60%. By blending a certain hydrogenated styrene-butadiene copolymer (B), tan δ at 50 ° C. and 0 ° C. can be improved without impairing the fracture resistance of the rubber composition.

On the other hand, from the results of Comparative Example 2 and Comparative Example 6, it can be seen that blending the aroma oil can increase the tan δ at 50 ° C. of the rubber composition, but greatly reduces the fracture resistance. As is clear from the results of Comparative Example 3 and Comparative Example 7, when a styrene-butadiene copolymer having a molecular weight and a bound styrene amount specified in the present invention but having no butadiene portion hydrogenated is blended. Further, the tan δ at 0 ° C. of the rubber composition cannot be sufficiently improved, and the improvement width of the steering stability on the wet road surface is greatly inferior to that of the example. Further, from the results of Comparative Example 4 and Comparative Example 8, a hydrogenated styrene-butadiene copolymer having a molecular weight and a bound styrene amount specified in the present invention but having a too high hydrogenation rate of double bonds in the butadiene portion is blended. In this case, the compatibility between the matrix rubber and the hydrogenated SBR is too bad, and it can be seen that the fracture resistance of the rubber composition is greatly reduced.

Claims (7)

100 mass of aromatic vinyl compound-conjugated diene compound copolymer (A) polymerized with a lithium-based polymerization initiator, having a polystyrene-reduced weight average molecular weight of 3.0 × 10 ^{5 to} 3.0 × 10 ⁶ measured by gel permeation chromatography Against
The polystyrene-reduced weight average molecular weight measured by gel permeation chromatography is 5.0 × 10 ^{3 to} 2.0 × 10 ⁵ , the amount of bonded styrene is 10 to 70% by mass, and 55% or more and 60% or less of the double bonds in the butadiene part. A rubber composition comprising a hydrogenated styrene-butadiene copolymer (B) hydrogenated with 10 to 200 parts by mass of a rubber component.   The rubber composition according to claim 1, wherein the aromatic vinyl compound-conjugated diene compound copolymer (A) is a styrene-butadiene copolymer. The rubber composition according to claim 2 , wherein the amount of bound styrene of the aromatic vinyl compound-conjugated diene compound copolymer (A) is 20 to 40% by mass. 3. The rubber composition according to claim 2 , wherein the vinyl bond content in the butadiene portion of the aromatic vinyl compound-conjugated diene compound copolymer (A) is 30 to 60%.   2. The rubber composition according to claim 1, wherein the hydrogenated styrene-butadiene copolymer (B) has a bound styrene content of 10 to 60 mass%.   The hydrogenated styrene-butadiene copolymer (B) is blended at a ratio of 20 to 100 parts by mass with respect to 100 parts by mass of the aromatic vinyl compound-conjugated diene compound copolymer (A). The rubber composition according to claim 1. A pneumatic tire using the rubber composition according to claim 1 for a tread rubber.