TW201406859A - Rubber composition - Google Patents

Abstract

The invention provides a rubber composition for obtaining a rubber elastomer with excellent crack resistance and good workability. The rubber composition is characterized in including a rubber component having (A) polybutadiene containing 60% or less of cis-1, 4 bonds and (B) conjugated diene-based polymer with a syndiotactic 1, 2-polybutadiene bond. Preferably, within the rubber component, a ratio of (A) polybutadiene is 10 mass% to 80 mass%, and a ratio of (B) conjugated diene-based polymer is 1 mass% to 30 mass%.

Description

Rubber composition

The present invention relates to a rubber composition. More specifically, the present invention relates to a rubber composition suitable as a material for a side wall or a chafer constituting a tire.

For example, the rubber elastomer used in the side wall of the tire or the chafer is required to have excellent crack resistance. As a rubber composition which can obtain such a rubber elastomer having crack resistance, polybutadiene having a cis 1,4 bond content of, for example, 92% or more is known (hereinafter, also referred to as "high" A rubber composition of cis 1,4-polybutadiene") with natural rubber or other diene rubber (for example, see Patent Document 1).

However, a rubber composition containing high cis 1,4-polybutadiene as a rubber component has a problem of low workability.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] International Publication No. 2007/094370

The present invention has been completed based on the above circumstances, and an object thereof is to provide an A rubber elastomer having excellent crack resistance is obtained, and a rubber composition having good processability can be obtained.

The rubber composition of the present invention is characterized in that it contains (A) a polybutadiene having a cis 1,4 bond content of less than 60%, and (B) a syndiotactic 1,2-polybutane The conjugated diene polymer other than the above (A) of the olefin chain is obtained as a rubber component.

In the rubber composition of the present invention, the ratio of the (A) polybutadiene is 10% by mass to 80% by mass, and the ratio of the (B) conjugated diene polymer is 1% by mass. ~30% by mass.

Further, it is preferred to further contain (C) natural rubber or polyisoprene as the rubber component.

The rubber composition is preferably the rubber component, and the ratio of the (C) natural rubber or polyisoprene is 10% by mass to 70% by mass.

Further, in the natural rubber composition of the present invention, the content of the 1,2-vinyl bond in the syndiotactic 1,2-polybutadiene chain in the (B) conjugated diene polymer is preferably 70% or more.

Further, the rubber composition of the present invention is preferably used for the side wall of a tire.

A rubber composition according to the present invention which comprises (A) a polybutadiene having a cis 1,4 bond content of less than 60%, and (B) a conjugate having a syndiotactic 1,2-polybutadiene chain Since the diene polymer is formed as a rubber component, a rubber elastomer having excellent crack resistance can be obtained, and good workability can be obtained.

Hereinafter, embodiments of the present invention will be described.

<Rubber component>

The rubber composition of the present invention contains the component (A) containing polybutadiene having a cis 1,4 bond content of less than 60% (hereinafter referred to as "low cis 1,4-polybutadiene"), and The component (B) containing a conjugated diene polymer having a syndiotactic 1,2-polybutadiene chain (hereinafter referred to as "syndiotactic diene polymer") is used as a rubber component.

"(A) Ingredients"

The low cis 1,4-polybutadiene as the component (A) may, for example, be a polybutadiene having a cis 1,4 bond amount of less than 60%, preferably less than 55%.

When the amount of the cis 1,4 bond of the polybutadiene is 60% or more, not only good workability but also compatibility with the syndiotactic diene polymer as the component (B) is lowered, and the compatibility cannot be obtained. Full resistance to crack growth. By the good affinity of the component (A) and the component (B), workability and crack growth resistance can be simultaneously achieved.

The amount of the cis 1,4 bond of the low-cis 1,4-polybutadiene can be easily controlled by a known method such as the type of the catalyst system to be used and the polymerization temperature. Specifically, the 1,3-butadiene can be polymerized in a hydrocarbon solvent using, for example, organolithium as a polymerization catalyst, and the obtained active polymer having an active terminal can be imparted by various specific compounds as necessary. It is obtained by modifying the base, or by coupling it.

Commercial products of low-cis 1,4-polybutadiene as the component (A) include "BR500" and "BR502" manufactured by JSR Corporation, and JAPAN ZEON Corporation. "BR1220" and "BR1250H" manufactured by the company, "HB25" manufactured by Karbochem.

The ratio of the component (A) in the rubber component of the rubber composition of the present invention is preferably 10% by mass to 80% by mass, and more preferably 40% by mass to 70% by mass. When the ratio of the component (A) is less than 10% by mass, the processability tends to be insufficient, and the molding appearance may be deteriorated. On the other hand, when the ratio of the component (A) exceeds 80% by mass, good crack growth resistance may not be obtained.

"(B) Ingredients"

As the syndiotactic diene polymer as the component (B), a syndiotactic 1,2-polybutadiene or a block copolymer having a syndiotactic 1,2-polybutadiene fragment can be used.

The content of the 1,2-vinyl bond in the 1,2-polybutadiene chain of the syndiotactic diene polymer intermediate is preferably 70% or more, more preferably 80% or more, still more preferably 90% or more. When the 1,2-vinyl bond is contained in an amount of less than 70%, the crystallinity of the syndiotactic diene polymer is lowered, and the workability of the obtained rubber composition is lowered.

In the present invention, the "1,2-vinyl bond content" is a value obtained by an infrared absorption spectrum method (Morero method).

Further, the crystallinity of the syndiotactic diene polymer is preferably from 15% to 50%, more preferably from 18% to 40%. When the degree of crystallinity is too small, there is a case where good crack growth resistance cannot be obtained. On the other hand, in the case where the degree of crystallinity is too large, it is necessary to carry out the preparation of the rubber composition at a high temperature, and thus there is a case where thermal deterioration or scorch occurs, thereby causing deterioration in workability. In the present invention, "crystallinity" is a 1,2-polybutadiene having a density of 0% of 1,2-polybutadiene of 0.892 g/cm ³ and a crystallinity of 100%. The density was set to 0.963 g/cm ³ , which was determined by the density gradient tube method.

Further, the melting point (Tm) of the syndiotactic diene polymer is preferably from 50 ° C to 150 ° C, more preferably from 60 ° C to 140 ° C. When the melting point (Tm) is from 50 ° C to 150 ° C, a rubber crosslinked body having more excellent balance of heat resistance, mechanical strength, and flexibility can be formed.

Further, the weight average molecular weight (Mw) of the syndiotactic diene polymer is preferably from 10,000 to 5,000,000, more preferably from 10,000 to 1,500,000, still more preferably from 50,000 to 1,000,000. When the weight average molecular weight (Mw) is less than 10,000, the fluidity tends to be too high at the time of heating and melting, and the workability tends to be lowered. On the other hand, when the weight average molecular weight (Mw) exceeds 5,000,000, the fluidity tends to be low during heating and melting, and the workability tends to be lowered.

Further, the syndiotactic diene polymer may contain a small amount of a structural unit derived from a conjugated diene other than butadiene in the syndiotactic 1,2-polybutadiene chain. As the conjugated diene other than butadiene, 1,3-pentadiene, a higher alkyl-substituted 1,3-butadiene derivative, a 2-alkyl-substituted-1,3-butadiene or the like can be used.

Specific examples of the higher alkyl-substituted 1,3-butadiene derivative include 1-pentyl-1,3-butadiene, 1-hexyl-1,3-butadiene, and 1-heptyl group. - 1,3-butadiene, 1-octyl-1,3-butadiene, and the like.

Further, specific examples of the 2-alkyl-substituted-1,3-butadiene include 2-methyl-1,3-butadiene (isoprene) and 2-ethyl-1,3-butylene. Diene, 2-propyl-1,3-butadiene, 2- Isopropyl-1,3-butadiene, 2-butyl-1,3-butadiene, 2-isobutyl-1,3-butadiene, 2-pentyl-1,3-butane Alkene, 2-isopentyl-1,3-butadiene, 2-hexyl-1,3-butadiene, 2-cyclohexyl-1,3-butadiene, 2-isohexyl-1,3- Butadiene, 2-heptyl-1,3-butadiene, 2-isoheptyl-1,3-butadiene, 2-octyl-1,3-butadiene, 2-isooctyl- 1,3-butadiene and the like.

Among the above conjugated dienes other than butadiene, isoprene and 1,3-pentadiene are preferred.

In the rubber component of the rubber composition of the present invention, the ratio of the component (B) is preferably from 1% by mass to 30% by mass, and more preferably from 5% by mass to 20% by mass. When the ratio of the component (B) is less than 1% by mass, there is a case where good crack growth resistance cannot be obtained. On the other hand, when the ratio of the component (B) exceeds 30% by mass, the material strength may be impaired.

Among the syndiotactic diene polymers as the component (B), the syndiotactic 1,2-polybutadiene can be polymerized by, for example, a butadiene in the presence of a polymerization catalyst containing a cobalt compound and an aluminoxane. And get.

As the cobalt compound constituting the above polymerization catalyst, an organic acid having a carbon number of 4 or more and an organic acid salt of cobalt can be preferably used.

Specific examples of such an organic acid salt include octanoate such as butyrate, hexanoate, heptanoate, and 2-ethylhexanoic acid; citrate, stearate, oleate, and erucic acid salt; Higher fatty acid salt; benzoate, or alkyl, aralkyl or allyl substituted benzoate, such as xylyl glycolate, dimethyl benzoate, ethyl benzoate, An alkyl, aralkyl or allyl substituted naphthoate. Among these, an octanoate such as 2-ethylhexanoic acid, or a stearate or a benzoate has excellent solubility to a hydrocarbon solvent. Better.

As the aluminoxane constituting the above polymerization catalyst, for example, an aluminoxane represented by the following formula (1) or the following formula (2) can be used.

In the above formula (1) and the above formula (2), R ^{1 is} independently a methyl group, an ethyl group, a propyl group or a butyl group, preferably a methyl group or an ethyl group, and particularly preferably a methyl group. Further, m is an integer of 2 or more, preferably an integer of 5 or more, and more preferably an integer of 10 to 100.

Specific examples of such an aluminoxane include methyl aluminoxane, ethyl aluminoxane, propyl aluminoxane, and butyl aluminoxane. Among these, methylaluminoxane is preferred.

It is preferred that the polymerization catalyst contains a phosphine compound in addition to the above cobalt compound and aluminoxane. The phosphine compound is a component effective for controlling the activation of a polymerization catalyst, a vinyl bond structure, and crystallinity. The phosphine compound can be used in the following formula (3) The organophosphorus compound is represented.

General formula (3) P(Ar) _n (R ² ) _3-n

In the above formula (3), R ² represents a cycloalkyl group or an alkyl group-substituted cycloalkyl group, n is an integer of 0 to 3, and Ar represents a group represented by the following formula (4).

In the above formula (4), R ³ , R ⁴ and R ⁵ each independently represent a hydrogen atom, an alkyl group, a halogen atom, an alkoxy group or an aryl group.

Among the groups represented by R ³ , R ⁴ and R ^{5 in} the above formula (4), the alkyl group is preferably an alkyl group having 1 to 6 carbon atoms. Further, among the groups represented by R ³ , R ⁴ and R ⁵ , the alkoxy group is preferably an alkoxy group having 1 to 6 carbon atoms. Further, among the groups represented by R ³ , R ⁴ and R ⁵ , the aryl group is preferably an aryl group having 6 to 12 carbon atoms.

Specific examples of the organophosphorus compound represented by the above formula (3) include tris(3-methylphenyl)phosphine, tris(3-ethylphenyl)phosphine, and tris(3,5-dimethylbenzene). Phosphine, tris(3,4-dimethylphenyl)phosphine, tris(3-isopropylphenyl)phosphine, tris(3-t-butylphenyl)phosphine, tris(3,5-di Ethylphenyl)phosphine, tris(3-methyl-5-ethylphenyl)phosphine, tris(3-phenyl Phenyl)phosphine, tris(3,4,5-trimethylphenyl)phosphine, tris(4-methoxy-3,5-dimethylphenyl)phosphine, tris(4-ethoxy-3) ,5-diethylphenyl)phosphine, tris(4-butoxy-3,5-dibutylphenyl)phosphine, tris(p-methoxyphenylphosphine), tricyclohexylphosphine, dicyclohexyl Phenylphosphine, tribenzylphosphine, tris(4-methylphenylphosphine), tris(4-ethylphenylphosphine), and the like. Among these, triphenylphosphine, tris(3-methylphenyl)phosphine, tris(4-methoxy-3,5-dimethylphenyl)phosphine, etc. are mentioned.

Further, as the polymerization catalyst, a cobalt compound represented by the following formula (5) can also be used.

In the above formula (5), R ³ , R ⁴ and R ⁵ each independently represent a hydrogen atom, an alkyl group, a halogen atom, an alkoxy group or an aryl group.

The compound represented by the above formula (5) is a complex compound having a phosphine compound in which n is 3 in the above formula (3) as a ligand in cobalt chloride. When the cobalt compound is used, a cobalt compound which has been synthesized in advance may be used, or a cobalt compound may be used in a polymerization system by contacting cobalt chloride with a phosphine compound. Control of the 1,2-vinyl bond content and crystallinity of the obtained syndiotactic 1,2-polybutadiene can be carried out by selecting a phosphine compound in various complexes.

Specific examples of the cobalt compound represented by the above formula (5) include bis (three) Phenylphosphine)cobalt dichloride, bis[tris(3-methylphenylphosphine)]cobalt dichloride, bis[tris(3,5-dimethylphenylphosphine)]cobalt dichloride, bis[ Tris(4-methoxy-3,5-dimethylphenylphosphine)]cobalt dichloride or the like.

Regarding the amount of the cobalt compound used, in the case of separately polymerizing butadiene, in the case of copolymerizing butadiene with other conjugated dienes with respect to butadiene 1 mole, with respect to butadiene and The total amount of the other conjugated diene is 1 mol, and is preferably 0.001 mmol to 1 mmol in terms of cobalt atom, and more preferably 0.01 mmol to 0.5 mmol.

Further, the phosphine compound is used in an amount such that the ratio (P/Co) of the phosphorus atom to the cobalt atom in the cobalt compound is usually 0.1 to 50, preferably 0.5 to 20, more preferably 1 to 20.

Further, the aluminoxane is used in an amount of usually 4 to 107, preferably 10 to 106, in terms of the ratio of aluminum atoms to cobalt atoms in the cobalt compound (Al/Co).

In the case where the compound represented by the above formula (5) is used as the polymerization catalyst, the ratio (P/Co) of the phosphorus atom to the cobalt atom is 2, and the amount of the aluminoxane used is in the above range.

As the polymerization solvent, an aromatic hydrocarbon solvent such as benzene, toluene, xylene or cumene, an aliphatic hydrocarbon solvent such as n-pentane, n-hexane or n-butane, cyclopentane, methylcyclopentane or cyclohexane can be used. An alicyclic hydrocarbon solvent, and a mixture of such solvents.

The polymerization temperature is preferably -50 ° C to 120 ° C, and more preferably -20 ° C to 100 ° C. The polymerization reaction can be batch or continuous. Further, the monomer concentration in the solvent is preferably from 5% by mass to 50% by mass, and more preferably from 10% by mass to 35% by mass. the amount%.

Further, in the production of a polymer, in order to prevent deactivation of the catalyst and the polymer, it is preferable to remove as much as possible the incorporation of a compound having deactivation such as oxygen, water, or carbon dioxide in the polymerization system. After the polymerization reaction is carried out to the desired stage, an alcohol, another polymerization terminator, an anti-aging agent, an antioxidant, an ultraviolet absorber or the like is added to the reaction mixture, and then the formed polymer is separated, washed, and dried according to a usual method. Thereby, the desired syndiotactic 1,2-polybutadiene can be obtained.

In the case where a block copolymer is used as the syndiotactic diene polymer, the polymer segment other than the syndiotactic 1,2-polybutadiene fragment preferably contains a source derived from butadiene, ethylene, propylene, A structural unit of one or more monomers of isoprene and styrene.

Further, the ratio of the syndiotactic 1,2-polybutadiene fragment in the syndiotactic diene polymer is preferably 50% by mass or more, and more preferably 60% by mass or more.

"VCR412" manufactured by Ube Industries Co., Ltd., "RB810", "RB820", "RB830", and "RB840" manufactured by JSR Corporation, may be mentioned as a commercial product of the syndiotactic diene polymer as the component (B). "VCR617", "VCR450", "VCR800", etc.

"(C) Ingredients"

The rubber composition of the present invention preferably contains a component (C) containing natural rubber or polyisoprene as a rubber component in addition to the components (A) and (B).

In the rubber component of the rubber composition of the present invention, the ratio of the component (C) is preferably 10% by mass to 70% by mass, and more preferably 30% by mass to 60% by mass.

Other Rubber Ingredients

The rubber composition of the present invention may contain other rubber components other than the above components (A) to (C).

Such other rubber component may be a styrene-butadiene copolymer rubber, a butyl rubber, an ethylene-α-olefin copolymer rubber, an ethylene-α-olefin-diene copolymer rubber, and an acrylonitrile-butadiene copolymerization. Rubber, chloroprene rubber and halogenated butyl rubber, and mixtures of these rubbers.

In the rubber component of the rubber composition of the present invention, the ratio of the other rubber component is preferably 30% by mass or less.

<filler>

The rubber composition of the present invention may contain a filler in addition to the above rubber component. As such a filler, cerium oxide and carbon black can be used.

Specific examples of the cerium oxide used as the filler include wet cerium oxide (aqueous ceric acid), dry cerium oxide (anhydrous ceric acid), calcium citrate, aluminum citrate, and the like. These cerium oxides may be used singly or in combination of two or more. Further, among these, wet cerium oxide is preferred.

Specific examples of the carbon black used as the filler include semi-reinforcing purpose furnace black (SRF), general purpose furnace black (GPF), and fast extrusion furnace black (fast extrusion furnace black). , FEF), high abrasion furnace black (HAF), medium super abrasion furnace black (ISAF), super abrasion furnace black (SAF), etc. Carbon black. These carbon blacks may be used singly or in combination of two or more. Further, among these, HAF, ISAF, and SAF are preferable in terms of obtaining excellent abrasion resistance.

Further, the carbon black preferably has a iodine adsorption amount (IA) of 60 mg/g or more and a dibutyl phthalate oil absorption (DBP) of 80 ml/100 g or more. By using such carbon black, the obtained rubber composition has improved grip performance and damage resistance.

The use ratio of the filler is from 10 parts by mass to 200 parts by mass, preferably from 25 parts by mass to 100 parts by mass, per 100 parts by mass of the rubber component.

Further, when cerium oxide is used as a filler, a decane coupling agent may be contained.

Specific examples of the decane coupling agent include bis(3-triethoxydecylpropyl)tetrasulfide, bis(3-triethoxydecylpropyl)trisulfide, and bis(3- Triethoxynonylpropyl)disulfide, bis(2-triethoxydecylethyl)tetrasulfide, bis(3-trimethoxydecylpropyl)tetrasulfide, bis(2- Trimethoxydecylethylethyl)tetrasulfide, 3-mercaptopropyltrimethoxydecane, 3-mercaptopropyltriethoxydecane, 2-mercaptoethyltrimethoxydecane, 2-mercaptoethyltriethyl Oxydecane;

3-trimethoxydecylpropyl-N,N-dimethylthioaminemethanyltetrasulfide, 3-triethoxydecylpropyl-N,N-dimethylthioaminemethine Tetrasulfide, 2-triethoxydecylethyl-N,N-dimethylthiocarbamoyltetrazole, 3-trimethoxydecylpropylbenzothiazolyl tetrasulfide, 3-triethoxydecyl propyl benzhydryl tetrasulfide, 3-triethoxydecyl propyl methacrylate monosulfide, 3-trimethoxydecyl propyl methacrylate Thioether, bis(3-diethoxymethyldecylpropyl) tetrasulfide Ether, 3-mercaptopropyl dimethoxymethyl decane, dimethoxymethyl decyl propyl-N, N-dimethyl thiocarbamyl thiocyanate, dimethoxymethyl decane Propyl benzothiazolyl tetrasulfide and the like. These decane coupling agents may be used singly or in combination of two or more. Further, among these, bis(3-triethoxydecylpropyl) polysulfide and 3-trimethoxydecylpropylbenzothiazolyl are preferred in terms of the effect of improving the reinforcing property and the like. Tetrasulfide.

The use ratio of the decane coupling agent is preferably 0.5 parts by mass to 20 parts by mass based on 100 parts by mass of the cerium oxide.

<Other ingredients>

The rubber composition of the present invention may contain various additives in addition to the rubber component and the filler. As such an additive, for example, a vulcanizing agent, a vulcanization aid, a processing aid, a vulcanization accelerator, a process oil, an anti-aging agent, an anti-coking agent, zinc white, stearic acid or the like can be used.

The vulcanizing agent usually uses sulfur. The use ratio of the vulcanizing agent is preferably 0.1 parts by mass to 3 parts by mass, more preferably 0.5 parts by mass to 2 parts by mass, per 100 parts by mass of the rubber component.

Stearic acid is usually used as the vulcanization aid and the processing aid, and the use ratio thereof is preferably 0.5 parts by mass to 5 parts by mass based on 100 parts by mass of the rubber component.

Further, the vulcanization accelerator is not particularly limited, and examples thereof include M (2-mercaptobenzothiazole), DM (dibenzothiazolyl disulfide), and CZ (N-cyclohexyl-2-benzothiazolylsulfenyl). A thiazole-based vulcanization accelerator such as an amine is preferred. The use ratio of the vulcanization accelerator is preferably 0.1 part by mass to 5 parts by mass based on 100 parts by mass of the rubber component. The portion is further preferably 0.2 parts by mass to 3 parts by mass.

<Preparation of rubber composition>

The rubber composition of the present invention can be prepared by kneading the rubber component and, if necessary, a filler and an additive, at a temperature equal to or higher than the melting point of the syndiotactic diene polymer as the component (B). Examples of the kneading machine used in the preparation of the rubber composition include open or closed such as a plast mill, a Banbury mixer, a roll, and an internal mixer. Type of mixing machine.

Such a rubber composition has good workability because it has a Mooney viscosity (ML ₁₊₄ , 100 ° C) in the range of, for example, 40 to 50.

<Rubber Elastomer>

In the present invention, a rubber elastic body is obtained by subjecting the above rubber composition to a crosslinking treatment.

Such a rubber elastic body is suitable as a rubber elastic body used in a side wall of a tire or a chafer because it has excellent crack resistance.

[Examples]

Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to the embodiments.

In addition, in the following Examples and Comparative Examples, the measurement methods of various physical property values are as follows.

[cis 1,4 bond content and 1,2-vinyl bond content]

Using an infrared spectrophotometer ("FT/IR-7300" manufactured by JASCO Corporation Infrared spectrophotometer" was determined by infrared absorption spectroscopy (Molero method).

[crystallinity]

The density of 1,2-polybutadiene having a crystallinity of 0% was set to 0.892 g/cm ³ , and the density of 1,2-polybutadiene having a crystallinity of 100% was set to 0.963 g/cm ³ . Determined by the density gradient tube method.

[melting point]

Determined according to American Society for Testing Material (ASTM) D3418.

[weight average molecular weight]

The weight average molecular weight in terms of polystyrene was calculated using Gel Permeation Chromatography (GPC) ("HLC-8120" manufactured by Tosoh Corporation).

<Example 1>

The rubber composition of the present invention was produced in the following manner using a plastic grinder equipped with a temperature control device.

Polybutadiene as component (A) ("HB25" manufactured by Karbochem Co., Ltd., cis 1,4 bond content = 34%, hereinafter referred to as "low cis BR (A1)"), 60 parts by mass, as B) Syndiotactic 1,2-polybutadiene ("RB840" manufactured by JSR Corporation, 1,2-vinyl bond content = 94%, crystallinity = 36%, melting point = 126 ° C, weight average molecular weight = 150,000 parts, hereinafter referred to as "syndiotactic BR (B1)"), 5 parts by mass, 40 parts by mass of natural rubber as component (C), 14 parts by mass of expanded oil, 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 3 parts by mass of anti-aging agent and 3 parts by mass of zinc white by rotation speed The mixing conditions of 60 rpm and a filling rate of 72% were mixed for 5 minutes.

Then, after the obtained kneaded material was cooled to room temperature, 1.5 parts by mass of a vulcanization accelerator and 1.5 parts by mass of sulfur were added to the kneaded product, and kneaded by the same kneading conditions as above to produce a rubber composition.

[Evaluation of rubber composition]

(1) Processability

For the obtained rubber composition, the L rotor (L rotor) was used for a preheating time of 1 minute, a rotor operating time of 4 minutes, and a temperature of 100 ° C according to Japanese Industrial Standards (JIS) K6300-1. The Mooney viscosity (ML ₁₊₄ , 100 ° C) was measured, and the case where the Mooney viscosity was less than 40 was evaluated as ×, and the case where the Mooney viscosity was 40 or more and less than 42 was evaluated as Δ, and the Mooney viscosity was evaluated. The case of 42 or more was evaluated as ○. The results are shown in Table 1 below.

(2) Crack resistance

The obtained rubber composition was molded into a sheet shape by calendering, and then subjected to a vulcanization treatment at 160 ° C for a predetermined time using a vulcanizing pressing machine, thereby producing a thickness of 2 mm. A sheet containing a rubber elastomer as a crosslinked rubber. The obtained sheet was subjected to punching processing to prepare a type IV test piece including a dumbbell shape as described in ASTM D638. At this time, the sheet is punched so that the longitudinal direction of the dumbbell shape becomes the grain direction of the sheet, and a through hole of 0.5 mm square extending in the reverse grain direction is formed at the center position in the longitudinal direction of the dumbbell shape.

For the obtained test piece, the elongation was 100%, the measurement temperature was 23 ° C, and the measurement was carried out. A constant elongation fatigue test was carried out under conditions of a speed of 300 cpm, and the number of cycles before the test piece was broken was measured. The case where the number of cycles was less than 18,000 was evaluated as ×, and the case where the number of cycles was 18,000 or more and less than 20,000 was evaluated as Δ, and the case where the number of cycles was 20,000 or more was evaluated as ○. The results are shown in Table 1 below. In addition, the number of cycles in Table 1 shows the values obtained by rounding off the last two digits.

<Example 2>

A rubber composition was prepared in the same manner as in Example 1 except that the amount of the syndiotactic BR (B1) was changed from 5 parts by mass to 10 parts by mass, and the processability and crack resistance of the rubber composition were carried out. evaluation of. The results are shown in Table 1 below.

<Example 3>

A rubber composition was prepared in the same manner as in Example 1 except that the amount of the syndiode BR (B1) was changed from 5 parts by mass to 20 parts by mass, and the rubber composition was processed and crack resistant. evaluation of. The results are shown in Table 1 below.

<Example 4>

The syndiotactic 1,2-polybutadiene ("RB820" manufactured by JSR Corporation, 1,2-vinyl bond content = 92%, crystallinity = 25%, melting point = 95 ° C, weight average molecular weight = 220,000, A rubber composition was prepared in the same manner as in Example 1 except that 5 parts by mass of "syndiotactic BR (B2)") was used instead of 5 parts by mass of the syndiode BR (B1), and the rubber composition was processed. Evaluation of sex and crack resistance. The results are shown in Table 1 below.

<Example 5>

20 parts by mass of the syndiotactic BR (B2) is used instead of the syndiotactic BR (B1) 5 parts by mass, A rubber composition was prepared in the same manner as in Example 1 except that the processability and crack resistance of the rubber composition were evaluated. The results are shown in Table 1 below.

<Comparative Example 1>

60 parts by mass of polybutadiene ("BR01" manufactured by JSR Corporation, cis 1,4 bond content = 96%, hereinafter referred to as "high-cis BR"), and 60 parts by mass of low-cis BR (A1) were used. A rubber composition was prepared in the same manner as in Example 1 except that the syndiometer BR (B1) was not used, and the processability and crack resistance of the rubber composition were evaluated. The results are shown in Table 1 below.

<Comparative Example 2>

60 parts by mass of polybutadiene ("BR01" manufactured by JSR Corporation, cis 1,4 bond content = 96%, hereinafter referred to as "high-cis BR"), and 60 parts by mass of low-cis BR (A1) were used. A rubber composition was prepared in the same manner as in Example 1 except that 5 parts by mass of the syndiode BR (B2) was used instead of 5 parts by mass of the syndiotactic BR (B1), and the rubber composition was processed and crack resistant. Sexual evaluation. The results are shown in Table 1 below.

<Comparative Example 3>

60 parts by mass of polybutadiene ("BR01" manufactured by JSR Corporation, cis 1,4 bond content = 96%, hereinafter referred to as "high-cis BR"), and 60 parts by mass of low-cis BR (A1) were used. A rubber composition was prepared in the same manner as in Example 1 except that 20 parts by mass of the syndiode BR (B2) was used instead of the syndiode BR (B1) in an amount of 5 parts by mass, and the rubber composition was processed and crack resistant. Sexual evaluation. The results are shown in Table 1 below.

<Comparative Example 4>

The same procedure as in the first embodiment is used except that the syntax BR (B1) is not used. A rubber composition was prepared, and the workability and crack resistance of the rubber composition were evaluated. The results are shown in Table 1 below.

As is clear from the results of Table 1, it was confirmed that the rubber compositions having excellent crack resistance can be obtained by the rubber compositions of Examples 1 to 5, and good workability can be obtained.

On the other hand, in the rubber compositions of Comparative Examples 1 to 3, since the low-cis 1,4-polybutadiene as the component (A) was not used, the workability was low. Further, since the rubber composition of Comparative Example 4 does not contain the syndiotactic diene polymer as the component (B), the obtained rubber elastic body has low crack resistance.

Claims (6)

A rubber composition characterized by comprising (A) a polybutadiene having a cis 1,4 bond content of less than 60%, and (B) having a syndiotactic 1,2-polybutadiene chain A conjugated diene polymer other than (A) is obtained as a rubber component. The rubber composition according to claim 1, wherein the ratio of the (A) polybutadiene to the rubber component is 10% by mass to 80% by mass, and the (B) conjugated diene polymer The ratio is 1% by mass to 30% by mass. The rubber composition according to claim 1 or 2, further comprising (C) natural rubber or polyisoprene as the rubber component. The rubber composition according to claim 3, wherein the ratio of the (C) natural rubber or polyisoprene in the rubber component is 10% by mass to 70% by mass. The rubber composition according to any one of claims 1 to 4, wherein the (1) syndiotactic 1,2-polybutadiene chain in the (B) conjugated diene polymer is 1, 2 The vinyl bond content is 70% or more. The rubber composition according to any one of claims 1 to 5, which is used for a side wall of a tire.