RUBBER COMPOSITION FOR TIRES AND PNEUMATIC TIRE

Abstract

Provided is a rubber composition for tires which contains: a rubber component including an aromatic vinyl-conjugated diene copolymer that contains aromatic vinyl units and conjugated diene units, a high-cis polybutadiene rubber having a cis microstructure content of 95% by mass or higher, and an isoprene-based rubber; carbon black; and a silica having a N.sub.2SA of 40 m.sup.2/g or more, the copolymer containing at least 80% of isolated aromatic vinyl units based on the total aromatic vinyl units, the copolymer having a Tg of more than 10 C. but less than 20 C. as determined by DSC, the rubber component including, based on 100% by mass thereof, 1-45% by mass of the copolymer, 20-64% by mass of the high-cis polybutadiene rubber, and 35-60% by mass of the isoprene-based rubber, the rubber composition containing 5 parts by mass or more of the silica per 100 parts by mass of the rubber component.

Claims

1. A pneumatic tire, comprising a cap tread formed from a rubber composition for tires, the rubber composition comprising: a rubber component including an aromatic vinyl-conjugated diene copolymer that comprises aromatic vinyl units derived from an aromatic vinyl compound and conjugated diene units derived from a conjugated diene compound, a high-cis polybutadiene rubber having a cis microstructure content of 95% by mass or higher, and an isoprene-based rubber; carbon black; and a silica having a nitrogen adsorption specific surface area of 40 m.sup.2/g or more, the copolymer comprising at least 80% of isolated aromatic vinyl units based on the total aromatic vinyl units, the copolymer having a glass transition temperature width of more than 10 C. but less than 20 C. as determined by differential scanning calorimetry, the rubber component including, based on 100% by mass thereof, 1 to 45% by mass of the copolymer, 20 to 64% by mass of the high-cis polybutadiene rubber, and 35 to 60% by mass of the isoprene-based rubber, the rubber composition comprising 5 parts by mass or more of the silica per 100 parts by mass of the rubber component.

2. The pneumatic tire according to claim 1, wherein the rubber composition comprises a particulate zinc carrier that comprises a silicate particle and finely divided zinc oxide or finely divided basic zinc carbonate supported on a surface of the silicate particle.

3. The pneumatic tire according to claim 1, wherein the silica has a nitrogen adsorption specific surface area of 160 m.sup.2/g or more.

4. The pneumatic tire according to claim 1, wherein the carbon black has an oil absorption number of compressed sample of 100 to 180 mL/100 g.

5. The pneumatic tire according to claim 1, wherein the rubber composition comprises 90 parts by mass or more of the silica per 100 parts by mass of the rubber component.

6. The pneumatic tire according to claim 1, wherein the rubber composition comprises a plasticizer in an amount of 50 parts by mass or more per 100 parts by mass of the rubber component.

7. The pneumatic tire according to claim 1, wherein the rubber composition comprises a resin.

8. The pneumatic tire according to claim 1, wherein the rubber component includes a modified polymer.

9. The pneumatic tire according to claim 1, wherein the rubber composition comprises a tetrazine compound represented by the following formula (1): ##STR00010## wherein R.sup.1 and R.sup.2 may be the same or different and each represent a hydrogen atom, COOR.sup.3 in which R.sup.3 represents either a hydrogen atom or an alkyl group, or a C1-C11 monovalent hydrocarbon group optionally containing a heteroatom, and R.sup.1 and R.sup.2 may each form a salt.

10. The pneumatic tire according to claim 1, wherein the rubber composition comprises a mercapto silane coupling agent.

11. The pneumatic tire according to claim 1, wherein the rubber composition comprises a farnesene resin produced by polymerizing farnesene.

Description

EXAMPLES

[0403] The present invention will be specifically described below with reference to, but not limited to, examples.

Production Example 1

[0404] <Production of Aromatic Vinyl-Conjugated diene Copolymer 1 (Copolymer 1)>

[0405] A stainless steel polymerization reactor having an inner volume of 20 L and equipped with a stirrer was cleaned and dried, and the atmosphere in the reactor was replaced by dry nitrogen.

[0406] The polymerization reactor was then charged with 7.65 kg of industrial hexane (trade name: hexane (general product), Sumitomo Chemical Co., Ltd., density: 0.68 g/mL), 2.93 kg of cyclohexane, 240 g of 1,3-butadiene, 510 g of styrene, 8.8 mL of tetrahydrofuran, and 0.9 mL of ethylene glycol dibutyl ether. Subsequently, a small amount of a solution of n-butyllithium (n-BuLi) in hexane was introduced as a scavenger into the polymerization reactor to preliminarily detoxify impurities which can act to deactivate the polymerization initiator. Then, an n-hexane solution containing 3.12 mmol of n-BuLi was introduced into the polymerization reactor to initiate a polymerization reaction.

[0407] The polymerization reaction was performed for 4 hours and 10 minutes. During the polymerization reaction, the temperature inside the polymerization reactor was adjusted to 65 C., and the solution in the polymerization reactor was stirred at 100 rpm. Twenty minutes after the start of the polymerization, 660 g of 1, 3-butadiene and 90 g of styrene were continuously fed into the polymerization reactor over a period of 3 hours and 20 minutes. Next, while maintaining the polymerization reactor temperature at 65 C., the resulting polymerization solution in the polymerization reactor was stirred at 100 rpm and 0.25 mmol of silicon tetrachloride was added to the polymerization solution, followed by stirring for 15 minutes. Thereafter, 5 mL of a hexane solution containing 0.8 mL of methanol was introduced into the polymerization reactor, and the resulting polymerization solution was stirred for five minutes.

[0408] The stirred contents in the polymerization reactor were sampled and analyzed for the Mw, vinyl bond content, styrene unit content, Tg, and proportion of isolated styrene units of the copolymer.

[0409] To the stirred contents were added 6.0 g of 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (trade name: Sumilizer GM, Sumitomo Chemical Co., Ltd.), 3.0 g of pentaerythrityl tetrakis(3-laurylthiopropionate) (trade name: Sumilizer TP-D, Sumitomo Chemical Co., Ltd.), and 562.5 g of an extender oil (trade name: JOMO process NC-140, JX Energy Corporation) to give a mixture. Then, the most volatile components of the mixture were evaporated at room temperature for 24 hours, followed by drying at 55 C. for 12 hours under reduced pressure to obtain an aromatic vinyl-conjugated diene copolymer 1 (Copolymer 1).

Production Example 2

<Production of Aromatic Vinyl-Conjugated Diene Copolymer 2 (Copolymer 2)>

[0410] A stainless steel polymerization reactor having an inner volume of 20 L and equipped with a stirrer was cleaned and dried, and the atmosphere in the reactor was replaced by dry nitrogen. The polymerization reactor was then charged with 7.65 kg of hexane (general product), 2.93 kg of cyclohexane, 298 g of 1,3-butadiene, 553 g of styrene, 8.8 mL of tetrahydrofuran, and 0.9 mL of ethylene glycol dibutyl ether. Subsequently, a solution of n-BuLi in hexane was introduced into the polymerization reactor, and then an n-hexane solution containing 3.06 mmol of n-BuLi was introduced into the polymerization reactor to initiate a polymerization reaction.

[0411] The polymerization reaction was performed for 4 hours and 10 minutes. During the polymerization reaction, the temperature inside the polymerization reactor was adjusted to 65 C., and the solution in the polymerization reactor was stirred at 130 rpm. Twenty minutes after the start of the polymerization, 630 g of 1,3-butadiene and 66 g of styrene were continuously fed into the polymerization reactor over a period of 3 hours and 20 minutes. Next, while maintaining the polymerization reactor temperature at 65 C., the resulting polymerization solution in the polymerization reactor was stirred at 130 rpm and 0.27 mmol of silicon tetrachloride was added to the polymerization solution, followed by stirring for 15 minutes. Thereafter, 5 mL of a hexane solution containing 0.8 mL of methanol was introduced into the polymerization reactor, and the resulting polymerization solution was stirred for five minutes.

[0412] The stirred contents in the polymerization reactor were sampled and analyzed for the Mw, vinyl bond content, styrene unit content, Tg, and proportion of isolated styrene units of the copolymer.

[0413] To the stirred contents were added 6.2 g of Sumilizer GM, 3.1 g of Sumilizer TP-D, and 580 g of JOMO process NC-140 to give a mixture. Then, the most volatile components of the mixture were evaporated at room temperature for 24 hours, followed by drying at 55 C. for 12 hours under reduced pressure to obtain an aromatic vinyl-conjugated diene copolymer 2 (Copolymer 2).

Production Example 3

<Production of Aromatic Vinyl-Conjugated Diene Copolymer 3 (Copolymer 3)>

[0414] A stainless steel polymerization reactor having an inner volume of 20 L and equipped with a stirrer was cleaned and dried, and the atmosphere in the reactor was replaced by dry nitrogen. The polymerization reactor was then charged with 7.65 kg of hexane (general product), 2.93 kg of cyclohexane, 240 g of 1,3-butadiene, 360 g of styrene, 8.8 mL of tetrahydrofuran, and 0.9 mL of ethylene glycol dibutyl ether. Subsequently, a solution of n-BuLi in hexane was introduced into the polymerization reactor, and then an n-hexane solution containing 2.64 mmol of n-BuLi was introduced into the polymerization reactor to initiate a polymerization reaction.

[0415] The polymerization reaction was performed for 4 hours and 10 minutes. During the polymerization reaction, the temperature inside the polymerization reactor was adjusted to 65 C., and the solution in the polymerization reactor was stirred. at 130 rpm. Twenty minutes after the start of the polymerization, 480 g of 1, 3-butadiene and 120 g of styrene were continuously fed into the polymerization reactor over a period of 3 hours and 20 minutes. Next, while maintaining the polymerization reactor temperature at 65 C., the resulting polymerization solution in the polymerization reactor was stirred at 130 rpm and 0.24 mmol of silicon tetrachloride was added to the polymerization solution, followed by stirring for 15 minutes. Thereafter, 5 mL of a hexane solution containing 0.8 mL of methanol was introduced into the polymerization reactor, and the resulting polymerization solution was stirred for five minutes.

[0416] The stirred contents in the polymerization reactor were sampled and analyzed for the Mw, vinyl bond content, styrene unit content, Tg, and proportion of isolated styrene units of the copolymer.

[0417] To the stirred contents were added 7.2 g of Sumilizer GM, 3.6 g of Sumilizer TP-D, and 450 g of JOMO process NC-140 to give a mixture. Then, the most volatile components of the mixture were evaporated at room temperature for 24 hours, followed by drying at 55 C. for 12 hours under reduced pressure to obtain an aromatic vinyl-conjugated diene copolymer 3 (Copolymer 3).

Production Example 4

<Production of Aromatic Vinyl-Conjugated Diene Copolymer 4 (Copolymer 4)>

[0418] A stainless steel polymerization reactor having an inner volume of 20 L and equipped with a stirrer was cleaned and dried, and the atmosphere in the reactor was replaced by dry nitrogen.

[0419] The polymerization reactor was then charged with 7.65 kg of hexane (general product), 2.93 kg of cyclohexane, 240 g of 1,3-butadiene, 360 g of styrene, 8.8 mL of tetrahydrofuran, and 0.9 mL of ethylene glycol dibutyl ether. Subsequently, a solution of n-BuLi in hexane was introduced into the polymerization reactor, and then an n-hexane solution containing 3.12 mmol of n-BuLi was introduced into the polymerization reactor to initiate a polymerization reaction.

[0420] The polymerization reaction was performed for 4 hours and 10 minutes. During the polymerization reaction, the temperature inside the polymerization reactor was adjusted to 65 C., and the solution in the polymerization reactor was stirred at 130 rpm, and 540 g of 1,3-butadiene and 360 g of styrene were continuously fed into the polymerization reactor over a period of 2 hours and 30 minutes. Next, while maintaining the polymerization reactor temperature at 65 C., the resulting polymerization solution in the polymerization reactor was stirred at 130 rpm and 0.25 mmol of silicon tetrachloride was added to the polymerization solution, followed by stirring for 15 minutes. Thereafter, 5 mL of a hexane solution containing 0.8 mL of methanol was introduced into the polymerization reactor, and the resulting polymerization solution was stirred for five minutes.

[0421] The stirred contents in the polymerization reactor were sampled and analyzed for the Mw, vinyl bond content, styrene unit content, Tg, and proportion of isolated styrene units of the copolymer.

[0422] To the stirred contents were added 8.0 g of Sumilizer GM, 4.0 g of Sumilizer TP-D, and 562.5 g of JOMO process NC-140 to give a mixture. Then, the most volatile components of the mixture were evaporated at room temperature for 24 hours, followed by drying at 55 C. for 12 hours under reduced pressure to obtain an aromatic vinyl-conjugated diene copolymer 4 (Copolymer 4).

[0423] Table 1 shows the results of analyses of Mw, vinyl bond content, styrene unit content, Tg before the addition of the extender oil, and proportion of isolated styrene units of Copolymers 1 to 4 obtained in Production Examples 1 to 4. The physical properties of Copolymers 1 to 4 were analyzed as described below.

1. Vinyl bond content (in mol %)

[0424] The vinyl bond content of the conjugated diene units of the copolymers was determined by infrared spectroscopy using the intensity of absorption around 910 cm.sup.1 which corresponds to the absorption peak for the vinyl group.

2. Styrene unit content (in % by mass)

[0425] The styrene unit content of the copolymers was determined from the refractive index in accordance with JIS K6383 (1995).

3. Weight average molecular weight (Mw)

[0426] The Mw was measured by gel permeation chromatography (GPC) under the following conditions (1) to (8). [0427] (1) Apparatus: Prominence available from Shimadzu Corporation [0428] (2) Separation column: one PLgel 5 m 10.sup.5 column and one PLgel 5 m 10.sup.6 A column connected to each other, both available from Agilent [0429] (3) Measurement temperature: 40 C. [0430] (4) Carrier: tetrahydrofuran [0431] (5) Flow rate: 1.0 mL/min [0432] (6) Injection volume: 100 L [0433] (7) Detector: differential refractometer [0434] (8) Molecular weight standards: polystyrene standards
4. Proportion of isolated styrene units (in %)

[0435] The structure of the copolymers was analyzed by measuring a .sup.1H-NMR (AL400 available from Jeol Ltd.) spectrum at 400 MHz using deuterochloroform solvent. The sequences of styrene units were determined from the integrals of the ranges indicated below in the NMR spectrum. The calculated value of the meta and para protons on the aromatic ring determined from the following integrals (b) and (c) was subtracted from the following integral (a), and the ratio of the resulting integral value to a total of integrals (a) to (c) was defined as the proportion of isolated styrene units.

[0436] (a) isolated styrene unit, two to three sequential styrene units, four or more sequential styrene units: peak integral between 7.6 and 7.0 ppm

[0437] (b) two to three sequential styrene units (ortho protons): peak integral between 7.0 and 6.9 ppm

[0438] (c) four or more sequential styrene units (ortho protons): peak integral between 6.9 and 6.0 ppm

5. Glass transition temperature width (Tg)

[0439] A heat flow curve of each copolymer was determined using a differential scanning calorimeter DSC7020 (Hitachi High-Tech Science Corporation) by cooling the copolymer to 100 C. in a nitrogen atmosphere, followed by heating to 100 C. at a rate of 10 C./min. The difference between the extrapolated onset and extrapolated end of the baseline shift associated with the transition in the heat flow curve was recorded as Tg.

TABLE-US-00001 TABLE 1 Copolymer Copolymer 1 Copolymer 2 Copolymer 3 Copolymer 4 Vinyl bond content (mol %) 24 24 24 24 Styrene unit content (% by mass) 40 40 40 40 Proportion of isolated styrene units (%) 82 83 82 76 Mw 1,250,000 1,100,000 1,300,000 1,130,000 Tg ( C.) 11 12 6 24

Production Example 5

<Production of Particulate Zinc Carrier>

[0440] An amount of 91.5 g of zinc oxide was added to 847 mL of a 5.5% by mass aqueous suspension of calcined clay, and they were sufficiently stirred. To the mixture were added 330 g of a 10% by mass aqueous solution of sodium carbonate and 340 g of a 10% by mass aqueous solution of zinc chloride, followed by stirring. Subsequently, 30% by mass carbon dioxide gas was injected into the resulting mixture until the pH reached 7 or lower so that basic zinc carbonate was precipitated on the surface of calcined clay, thereby synthesizing a particulate zinc carrier. The particulate zinc carrier was then subjected to dehydration, drying, and pulverization steps to obtain powder. A particulate zinc carrier was thus prepared.

[0441] The particulate zinc carrier had a BET specific surface area of 50 m.sup.2/g. In the particulate zinc carrier, 45% by mass, calculated as metallic zinc, of basic zinc carbonate was supported on calcined clay. The supported basic zinc carbonate thus had a BET specific surface area of 60 m.sup.2/g.

Production Examples 6 and 7

<Production of Carbon Blacks B and C>

[0442] Carbon blacks were produced under the conditions shown in Table 2 using D-heavy oil as fuel oil and creosote oil as feedstock hydrocarbon (feedstock oil) in a carbon black reaction furnace in which a combustion zone, a feedstock introduction zone, and a rear reaction zone were joined in sequence. The combustion zone had an inner diameter of 1,100 mm and a length of 1,700 mm and was provided with an air inlet duct and a combustion burner. The feedstock introduction zone was connected to the combustion zone and included a narrow portion having an inner diameter of 175 mm and a length of 1,050 mm and provided with a feedstock nozzle penetrating into the portion from the periphery. The rear reaction zone had an inner diameter of 400 mm and a length of 3,000 mm and was provided with a quenching device.

[0443] The carbon blacks were then heated under the conditions shown in Table 2 with no oxygen flow (in a nitrogen atmosphere).

[0444] Table 2 shows the properties of the carbon blacks obtained in the production examples. The properties were measured as described above.

TABLE-US-00002 TABLE 2 Production Example 6 7 Carbon black B C Combustion air (Nm.sup.3/H) 5800 5800 Fuel oil (kg/h) 330 330 Combustion gas temperature ( C.) 1700 1700 Air for fuel atomization (Nm.sup.3/H) 120 120 Feedstock oil (kg/h) 1300 1200 Heat treatment temperature ( C.) 1200 1200 Heat treatment time (h) 4 3 N.sub.2SA (m.sup.2/g) 103 177 DBP (mL/100 g) 143 170 Volatile matter content (900 C.) (% by mass) 0.38 0.45 Volatile matter content (1500 C.) (% by mass) 0.48 0.67 pH 10.4 9.7 Oil absorption number of compressed sample 113 126 (mL/100 g) CTAB (m.sup.2/g) 87 157

Production Example 8

<Production of Modified Conjugated Diene Polymer>

(Synthesis of Conjugated Diene Polymer)

[0445] A catalyst composition (molar ratio of iodine atom to lanthanoid-containing compound: 2.0) was previously prepared by reacting and aging 0.90 mmol of 1,3-butadiene with a cyclohexane solution containing 0.18 mmol of neodymium versatate, a toluene solution containing 3.6 mmol of methylalumoxane, a toluene solution containing 6.7 mmol of diisobutylaluminum hydride, and a toluene solution containing 0.36 mmol of trimethylsilyl iodide for 60 minutes at 30 C. Next, 2.4 kg of cyclohexane and 300 g of 1,3-butadiene were introduced into a 5 L autoclave purged with nitrogen. Then, the catalyst composition was introduced into the autoclave, and a polymerization reaction was performed for two hours at 30 C. to give a polymer solution. The conversion rate of the introduced 1,3-butadiene was almost 100%.

[0446] In order to measure the physical properties of the conjugated diene polymer (hereinafter, also referred to as polymer), i.e. the unmodified polymer, a 200 g portion of the polymer solution was taken, to which a methanol solution containing 1.5 g of 2,4-di-tert-butyl-p-cresol was added to stop the polymerization reaction. Thereafter, the solvent was removed by steam stripping, and the product was dried using a roll at 110 C. to obtain a dry product which was used as a polymer.

[0447] The polymer was measured for physical properties as described below and found to have a Mooney viscosity (ML.sub.1+4, 100 C.) of 12, a molecular weight distribution (Mw/Mn) of 1.6, a cis-1,4 bond content of 99.2% by mass, and a 1,2-vinyl bond content of 0.21% by mass.

[Mooney Viscosity (ML.SUB.1+4., 100 C.)]

[0448] The Mooney viscosity was measured at 100 C. in accordance with JIS K 6300 using an L-type rotor with a preheating time of 1 minute and a rotor operation time of 4 minutes.

[Molecular Weight Distribution (Mw/Mn)]

[0449] The molecular weight distribution was determined using a gel permeation chromatograph (trade name: HLC-8120GPC, Tosoh Corporation) and a differential refractometer as a detector under the following conditions and calibrated with polystyrene standards. [0450] Column: two columns of GMHHXL (trade name) available from Tosoh Corporation [0451] Column temperature: 40 C. [0452] Mobile phase: tetrahydrofuran [0453] Flow rate: 1.0 mL/min [0454] Sample concentration: 10 mg/20 mL
[Cis-1,4 bond content, 1,2-vinyl bond content]

[0455] The cis-1,4 bond content and 1,2-vinyl bond content were determined by .sup.1H-NMR and .sup.13C-NMR analyses. The NMR analyses were carried out using EX-270 (trade name) available from Jeol Ltd. Specifically, in the .sup.1H-NMR analysis, the ratio between 1,4-bonds and 1,2-bonds of the polymer was calculated from the signal intensities at 5.30-5.50 ppm (1,4-bond) and at 4.80-5.01 ppm (1,2-bond). Also, in the .sup.13C-NMR analysis, the ratio between cis-1,4 bonds and trans-1,4 bonds of the polymer was calculated from the signal intensities at 27.5 ppm (cis-1,4 bond) and at 32.8 ppm (trans-1,4 bond). These calculated ratios were used to determine the cis-1, 4 bond content (% by mass) and 1,2-vinyl bond content (% by mass).

(Synthesis of Modified Conjugated Diene Polymer)

[0456] A modified conjugated diene polymer (hereinafter, also referred to as modified polymer) was prepared by treating the polymer solution of the conjugated diene polymer prepared as above as follows. To the polymer solution maintained at 30 C. was added a toluene solution containing 1.71 mmol of 3-glycidoxypropyltrimethoxysilane, and they were reacted for 30 minutes to give a reaction solution. To the reaction solution was then added a toluene solution containing 1.71 mmol of 3-aminopropyltriethoxysilane, and they were stirred for 30 minutes. Subsequently, to the reaction solution was added a toluene solution containing 1.28 mmol of tetraisopropyl titanate, followed by stirring for 30 minutes. Then, the polymerization reaction was stopped by adding a methanol solution containing 1.5 g of 2,4-di-tert-butyl-p-cresol. The resulting solution was used as a modified polymer solution. The yield was 2.5 kg. To the modified polymer solution was then added 20 L of an aqueous solution with a pH of 10 adjusted with sodium hydroxide, followed by performing a condensation reaction at 110 C. for two hours while removing the solvent. Thereafter, the reaction product was dried using a roll at 110 C. to obtain a dry product which was used as a modified polymer.

[0457] The modified polymer was measured for physical properties as described below (but the molecular weight distribution (Mw/Mn) was measured under the same conditions as described for the polymer) and found to have a Mooney viscosity (ML.sub.1+4, 125 C.) of 46, a molecular weight distribution (Mw/Mn) of 2.4, a cold flow value of 0.3 mg/min, a temporal stability of 2, and a glass transition temperature of 106 C.

[Mooney Viscosity (ML.SUB.1+4., 125 C.)]

[0458] The Mooney viscosity was measured at 125 C. in accordance with JIS K 6300 using an L-type rotor with a preheating time of 1 minute and a rotor operation time of 4 minutes.

[Cold Flow Value]

[0459] The cold flow value was measured by extruding the polymer through a inch orifice at a pressure of 3.5 lb/in.sup.2 and a temperature of 50 C. After allowing 10 minutes for the polymer to reach steady state, the rate of extrusion was measured and reported in milligrams per minute (mg/min).

[Temporal Stability]

[0460] The temporal stability was determined by measuring Mooney viscosity (ML.sub.1+4, 125 C.) after storage in a thermostatic bath at 90 C. for two days, and using it in the expression below. A smaller value indicates better temporal stability.

Expression: [the Mooney viscosity (ML.sub.1+4, 125 C.) after storage in a thermostatic bath at 90 C. for two days][the Mooney viscosity (ML.sub.1+4, 125 C.) measured immediately after the synthesis]

[Glass Transition Temperature]

[0461] The glass transition temperature was defined as the glass transition onset temperature measured at a temperature increase rate of 10 C./min using a differential scanning calorimeter (Q200, TA Instruments Japan) in accordance with JIS K 7121.

[0462] The chemicals used in the examples and comparative examples were listed below.

[0463] Copolymers 1 to 4: the copolymers obtained in Production Examples 1 to 4

[0464] Modified conjugated diene polymer: the modified polymer obtained in Production Example 8

[0465] Natural rubber: TSR20

[0466] Polybutadiene rubber: Ubepol BR150B available from Ube Industries, Ltd. (cis content: 97% by mass)

[0467] Silica A: VN3 available from Evonik (N.sub.2SA: 175 m.sup.2/g)

[0468] Silica B: 9000GR available from Evonik (N.sub.2SA: 235 m.sup.2/g)

[0469] Silane coupling agent A: Si69 (bis(3-triethoxysilyl-propyl)tetrasulfide) available from Evonik

[0470] Silane coupling agent B: NXT (3-octanoylthio-1-propyl-triethoxysilane) available from Momentive

[0471] Silane coupling agent C: NXT-Z45 available from Momentive (copolymer of linking units A and B (linking unit A: 55 mol %, linking unit B: 45 mol %))

[0472] Carbon black A: DIABLACK N339 available from Mitsubishi Chemical Corporation (N.sub.2SA: 96 m.sup.2/g, DBP absorption: 124 mL/100 g)

[0473] Carbon black B: the carbon black obtained in Production Example 6

[0474] Carbon black C: the carbon black obtained in Production Example 7

[0475] Resin A: YS resin PX1150N available from Yasuhara Chemical Co., Ltd. (polyterpene (-pinene resin), softening point: 115 C.)

[0476] Resin B: YS POLYSTER T160 available from Yasuhara Chemical Co., Ltd. (terpene phenol resin, softening point: 160 C.)

[0477] Resin C: Marukarez M-890A available from Maruzen Petrochemical Co., Ltd. (dicyclopentadiene resin, softening point: 105 C.)

[0478] Resin D: PINECRYSTAL KR-85 available from Arakawa Chemical Industries, Ltd. (rosin resin, softening point: 80 to 87 C.)

[0479] Resin E: SYLVARES SA85 available from Arizona Chemical (copolymer of -methylstyrene and styrene, softening point: 85 C.)

[0480] Oil: X-140 available from JX Nippon Oil & Energy Corporation (aromatic process oil)

[0481] Farnesene resin A: KB-101 available from Kuraray Co., Ltd. (farnesene homopolymer, Mw: 10,000, melt viscosity: 0.7 Pa.Math.s, Tg: 72 C.)

[0482] Farnesene resin B:. FSR-221 available from Kuraray Co., Ltd. (farnesene-styrene copolymer, Mw: 10,000, copolymerization ratio (by mass): farnesene/styrene=77/23, melt viscosity: 5.7 Pa.Math.s, Tg: 54 C.)

[0483] Farnesene resin C: FBR-746 available from Kuraray Co., Ltd. (farnesene-butadiene copolymer, Mw: 100,000, copolymerization ratio (by mass): farnesene/butadiene=60/40, melt viscosity: 603 Pa.Math.s, Tg: 78 C.)

[0484] Antioxidant: Antigene 3C available from Sumitomo Chemical Co., Ltd.

[0485] Stearic acid: stearic acid beads TSUBAKI available from NOF Corporation

[0486] Zinc oxide: Zinc oxide #1 available from Mitsui Mining & Smelting Co., Ltd.

[0487] Particulate zinc carrier: the particulate zinc carrier obtained in Production Example 5

[0488] Wax: Sunnoc N available from Ouchi Shinko Chemical Industrial Co., Ltd.

[0489] Processing aid: WB16 available from STRUKTOL (mixture of fatty acid metal salt (fatty acid calcium salt, constituent fatty acids: C14-C20 saturated fatty acids) and fatty acid amide)

[0490] Sulfur: Sulfur powder available from Tsurumi Chemical Industry Co., Ltd.

[0491] Vulcanization accelerator 1: Soxinol CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) available from Sumitomo Chemical Co., Ltd.

[0492] Vulcanization accelerator 2: Soxinol D (1,3-diphenylguanidine) available from Sumitomo Chemical Co., Ltd.

[0493] Tetrazine compound A: a compound of formula (1-1-1)

[0494] Tetrazine compound B: a compound of formula (1-2-1)

Examples and Comparative Examples

[0495] According to each of the formulations shown in Tables 3 to 12, the materials other than the sulfur and vulcanization accelerators were kneaded for five minutes at 150 C. using a 1.7 L Banbury mixer (Kobe Steel, Ltd.) to give a kneaded mixture. Next, the sulfur and vulcanization accelerators were added to the kneaded mixture, followed by kneading for five minutes at 80 C. using an open roll mill to give an unvulcanized rubber composition. The unvulcanized rubber composition was press-vulcanized for 20 minutes at 170 C. in a 0.5 mm-thick die to obtain a vulcanized rubber composition.

[0496] Separately, the unvulcanized rubber composition prepared as above was formed into the shape of a cap tread and assembled with other tire components on a tire building machine to build an unvulcanized tire. The unvulcanized tire was vulcanized at 170 C. for 12 minutes to prepare a test tire (cold weather tire for passenger cars, size: 195/65R15, DS-2 pattern).

<Evaluations and Testing Methods>

[0497] In the following evaluations, Comparative Examples 1-1, 2-1, . . . , and 10-1 are regarded as reference comparative examples in Tables 3, 4, . . . , and 12, respectively.

<Abrasion Resistance>

[0498] The volume loss of the vulcanized rubber compositions was measured with a laboratory abrasion and skid tester (LAT tester) at a load of 50 N, a speed of 20 km/h, and a slip angle of 5 degrees. The volume losses are expressed as an index (abrasion resistance index), with the corresponding reference comparative example set equal to 100. A higher index indicates better abrasion resistance.

<Fuel Economy>

[0499] The tan of the vulcanized rubber compositions was determined using a spectrometer (Ueshima Seisakusho Co., Ltd.) at a dynamic strain amplitude of 1%, a frequency of 10 Hz, and a temperature of 50 C. The tan values are expressed as an index (fuel economy index), with the corresponding reference comparative example set equal to 100. A higher index indicates a lower rolling resistance and better fuel economy.

<Grip Performance on Ice>

[0500] The test tires of each formulation example were mounted on all wheels of a vehicle (front-engine, front-wheel-drive car of 2000 cc displacement made in Japan). The stopping distance required for the vehicle to stop after the brakes that lock up were applied at 30 km/h was measured. The stopping distances are expressed as an index (index of grip performance on ice), with the corresponding reference comparative example set equal to 100. A higher index indicates better grip performance on ice.

TABLE-US-00003 TABLE 3 Example Comparative Example 1-1 1-2 1-3 1-4 1-1 1-2 1-3 1-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 Oil 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide Particulate zinc carrier 1.6 0.8 1.6 0.8 1.6 0.8 1.6 0.8 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 115 113 115 111 100 103 96 94 Index of grip performance on ice 109 107 111 110 100 98 106 102 Fuel economy index 114 114 113 110 100 100 94 92

TABLE-US-00004 TABLE 4 Example Comparative Example 2-1 2-2 2-3 2-4 2-1 2-2 2-3 2-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 Silica B 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 Oil 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 112 110 111 114 100 98 94 101 Index of grip performance on ice 108 108 111 110 100 100 105 103 Fuel economy index 115 113 112 111 100 97 95 95

TABLE-US-00005 TABLE 5 Example Comparative Example 3-1 3-2 3-3 3-4 3-1 3-2 3-3 3-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 Carbon black A Carbon black B 5 5 5 5 Carbon black C 5 5 5 5 Oil 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 113 111 113 111 100 102 95 101 Index of grip performance on ice 109 110 114 114 100 99 107 105 Fuel economy index 110 110 108 107 100 100 92 95

TABLE-US-00006 TABLE 6 Example Comparative Example 4-1 4-2 4-3 4-4 4-1 4-2 4-3 4-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 160 130 160 130 160 130 160 130 Silane coupling agent A 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 Oil 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 113 113 114 114 100 98 104 104 Index of grip performance on ice 110 110 113 112 100 100 104 104 Fuel economy index 111 112 109 110 100 101 94 96

TABLE-US-00007 TABLE 7 Example Comparative Example 5-1 5-2 5-3 5-4 5-1 5-2 5-3 5-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 Oil 60 80 60 80 60 80 60 80 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 114 114 112 112 100 99 100 95 Index of grip performance on ice 109 109 113 112 100 99 103 105 Fuel economy index 114 110 109 107 100 99 94 95

TABLE-US-00008 TABLE 8 Example Comparative Example 6-1 6-2 6-3 6-4 6-5 6-6 6-1 6-2 6-3 6-4 6-5 6-6 Formulation Copolymer 1 20 20 20 20 20 (parts by Copolymer 2 20 mass) Copolymer 3 20 20 20 20 20 Copolymer 4 20 Natural rubber 40 40 40 40 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 5 5 5 5 Resin A 5 5 5 5 Resin B 5 5 Resin C 5 5 Resin D 5 5 Resin E 5 5 Oil 40 40 40 40 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 115 113 112 115 111 111 100 98 102 101 102 98 Index of grip performance on ice 111 108 110 109 109 114 100 100 99 98 100 105 Fuel economy index 110 111 108 110 109 107 100 101 102 101 100 94

TABLE-US-00009 TABLE 9 Comparative Example Example 7-1 7-2 7-1 7-2 Formulation Copolymer 1 20 (parts by mass) Copolymer 2 20 Copolymer 3 20 Copolymer 4 20 Modified conjugated 40 40 40 40 diene polymer Natural rubber 40 40 40 40 Polybutadiene rubber Silica A 75 75 75 75 Silane coupling agent A 6 6 6 6 Carbon black A 5 5 5 5 Oil 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 Wax 1 1 1 1 Processing aid 1 1 1 1 Sulfur 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 114 114 100 94 Index of grip performance 109 111 100 104 on ice Fuel economy index 112 109 100 94

TABLE-US-00010 TABLE 10 Example Comparative Example 8-1 8-2 8-3 8-4 8-1 8-2 8-3 8-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 Oil 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Tetrazine compound A 2 2 2 2 Tetrazine oompound B 2 2 2 2 Evaluation Abrasion resistance index 111 110 111 113 100 97 93 107 Index of grip performance on ice 110 110 112 111 100 100 104 106 Fuel economy index 111 113 110 108 100 99 97 94

TABLE-US-00011 TABLE 11 Example Comparative Example 9-1 9-2 9-3 9-4 9-1 9-2 9-3 9-4 Formulation Copolymer 1 20 20 (parts by Copolymer 2 20 20 mass) Copolymer 3 20 20 Copolymer 4 20 20 Natural rubber 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 Silane coupling agent A Silane coupling agent B 6 6 6 6 Silane coupling agent C 3.75 3.75 3.75 3.75 Carbon black A 5 5 5 5 5 5 5 5 Oil 40 40 40 40 40 40 40 40 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 114 114 115 111 100 103 95 104 Index of grip performance on ice 110 109 111 113 100 99 104 105 Fuel economy index 110 110 108 109 100 99 97 95

TABLE-US-00012 TABLE 12 Example Comparative Example 10-1 10-2 10-3 10-4 10-5 10-6 10-1 10-2 10-3 10-4 10-5 10-6 Formulation Copolymer 1 20 20 20 (parts by Copolymer 2 20 20 20 mass) Copolymer 3 20 20 20 Copolymer 4 20 20 20 Natural rubber 40 40 40 40 40 40 40 40 40 40 40 40 Polybutadiene rubber 40 40 40 40 40 40 40 40 40 40 40 40 Silica A 75 75 75 75 75 75 75 75 75 75 75 75 Silane coupling agent A 6 6 6 6 6 6 6 6 6 6 6 6 Carbon black A 5 5 5 5 5 5 5 5 5 5 5 5 Oil 30 30 30 30 30 30 30 30 30 30 30 30 Farnesene resin A 10 10 10 10 Farnesene resin B 10 10 10 10 Farnesene resin C 10 10 10 10 Antioxidant 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Wax 1 1 1 1 1 1 1 1 1 1 1 1 Processing aid 1 1 1 1 1 1 1 1 1 1 1 1 Sulfur 2 2 2 2 2 2 2 2 2 2 2 2 Vulcanization accelerator 1 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Vulcanization accelerator 2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Evaluation Abrasion resistance index 113 111 113 113 114 111 100 101 101 94 94 102 Index of grip performance on ice 110 109 110 111 112 112 100 100 99 103 105 105 Fuel economy index 113 112 112 109 109 110 100 100 100 96 95 94

[0501] As demonstrated in Tables 3 to 12, the examples which contained a rubber component including a specific aromatic vinyl-conjugated diene copolymer, a high-cis polybutadiene rubber, and an isoprene-based rubber, carbon black, and a specific silica achieved a balanced improvement of abrasion resistance, grip performance on ice, and fuel economy.