RUBBER COMPOSITION FOR TREAD, AND PNEUMATIC TIRE

Abstract

The present invention provides a tread rubber composition that is excellent in wet grip performance during the initial phase of running and tensile properties, and a pneumatic tire including the tread rubber composition. The present invention relates to a tread rubber composition containing: a diene rubber; silica; and sulfur and/or a sulfur-containing compound, the tread rubber composition satisfying the following relationships (1) to (3):

EB/M30050 (1);

M1001.7 MPa (2); and

EB500% (3).

Claims

1. A tread rubber composition, comprising: a diene rubber; silica; and at least one of sulfur or a sulfur-containing compound, the tread rubber composition satisfying the following relationships (1) to (3):
EB/M30050 (1);
M1001.7 MPa (2); and
EB500% (3).

2. The tread rubber composition according to claim 1, satisfying the following relationships (1A) to (3A):
EB/M30070 (1A);
M1002.0 MPa (2A); and
EB550% (3A).

3. The tread rubber composition according to claim 1, wherein the diene rubber comprises at least one of a modified styrene-butadiene rubber or a modified polybutadiene rubber.

4. The tread rubber composition according to claim 1, wherein the diene rubber comprises an alkoxysilyl-modified styrene-butadiene rubber.

5. The tread rubber composition according to claim 1, comprising at least one of a sulfur-containing oligomer or a rosin resin.

6. A tire, comprising a tread, at least part of the tread satisfying the following relationships (1) to (3):
EB/M30050 (1);
M1001.7 MPa (2); and
EB500% (3).

Description

EXAMPLES

[0166] The present invention is specifically described below with reference to, but not limited to, examples.

<Preparation of Chain End Modifier>

[0167] A chain end modifier was prepared by putting 20.8 g of 3-(N,N-dimethylamino)propyltrimethoxysilane (AZmax. Co.) in a 250 mL graduated flask in a nitrogen atmosphere, and then adding anhydrous hexane (Kanto Chemical Co., Inc.) to a total volume of 250 mL.

Copolymer Production Example 1

[0168] To a sufficiently nitrogen-purged 30 L pressure-proof vessel were added 18 L of cyclohexane (Kanto Chemical Co., Inc.), 2,000 g of butadiene (Takachiho Trading Co., Ltd.), and 53 mmol of diethyl ether (Kanto Chemical Co., Inc.), followed by heating to 60 C. Next, 16.6 mL of butyllithium (Kanto Chemical Co., Inc.) was added and then stirred for three hours. Subsequently, 12 mL of a 0.4 mol/L solution of silicon tetrachloride in hexane was added and stirred for 30 minutes. Thereafter, 13 mL of the chain end modifier was added and stirred for 30 minutes. To the reaction solution was added 2 mL of a solution of 0.2 g of 2,6-tert-butyl-p-cresol (Ouchi Shinko Chemical Industrial Co., Ltd.) in methanol (Kanto Chemical Co., Inc.). The resulting reaction solution was put in a stainless steel vessel containing 18 L of methanol, followed by collecting the aggregates. The aggregates were dried for 24 hours under reduced pressure to give a modified BR.

Copolymer Production Example 2

[0169] To a sufficiently nitrogen-purged 30 L pressure-proof vessel were added 18 L of n-hexane, 540 g of styrene (Kanto Chemical Co., Inc.), 1,460 g of butadiene, and 17 mmol of tetramethylethylenediamine, followed by heating to 40 C. Subsequently, 3.5 mL of a 0.4 mol/L solution of silicon tetrachloride in hexane was added and stirred for 30 minutes. Then, 10.5 mL of butyllithium was added, and the mixture was heated to 50 C. and stirred for three hours. Thereafter, 30 mL of the chain end modifier was added and stirred for 30 minutes. To the reaction solution was added 2 mL of a solution of 0.2 g of 2,6-tert-butyl-p-cresol (Ouchi Shinko Chemical Industrial Co., Ltd.) in methanol (Kanto Chemical Co., Inc.). The resulting reaction solution was put in a stainless steel vessel containing 18 L of methanol, followed by collecting the aggregates. The aggregates were dried for 24 hours under reduced pressure to give a modified SBR.

Production Example 1

Synthesis of Sulfur-Containing Oligomer 1 (Rubbery)

[0170] A flask completely purged with an inert gas such as nitrogen or argon gas was charged with 104.4 g of a 30% aqueous solution of sodium polysulfide (0.180 mol), 150 g of ion exchanged water, and 150 g of ethanol, and they were stirred and heated to 90 C. Thereafter, 25.0 g of bis(2-chloroethyl)ether (0.175 mol) diluted with 100 g of toluene was dropwise added to the mixture over two hours, and the reaction was further continued for three hours at the same temperature. Then, the organic phase was separated, followed by vacuum concentration and drying at 90 C. to give 27.3 g of a target oligomer.

[0171] The sulfur-containing oligomer 1 (rubbery) thus prepared had a Mw of 21,000, an elemental sulfur content of 55% by mass, and an SP value of 11.1 and contained a repeating unit of formula (I) wherein R=(CH.sub.2).sub.2O(CH.sub.2).sub.2 and x=4.0 on average.

Production Example 2

Synthesis of Sulfur-Containing Oligomer 2 (Liquid)

[0172] A flask completely purged with an inert gas such as nitrogen or argon gas was charged with 104.4 g of a 30% aqueous solution of sodium polysulfide (0.180 mol), 150 g of ion exchanged water, and further 1.25 g of tetrabutylammonium chloride (TBAB) as a reaction catalyst, and they were stirred and heated to 90 C. Thereafter, 25.0 g of bis(2-chloroethyl)ether (0.175 mol) diluted with 100 g of toluene was dropwise added to the mixture over two hours, and the reaction was further continued for three hours at the same temperature. Then, the organic phase was separated, followed by vacuum concentration and drying at 90 C. to give 25.5 g of a target oligomer.

[0173] The sulfur-containing oligomer 2 (liquid) thus prepared had a Mw of 2,670, an elemental sulfur content of 55% by mass, and an SP value of 11.1 and contained a repeating unit of formula (I) wherein R=(CH.sub.2).sub.2O(CH.sub.2).sub.2 and x=4.0 on average.

Production Example 3

Synthesis of Sulfur-Containing Oligomer 3 (Liquid)

[0174] A flask completely purged with an inert gas such as nitrogen or argon gas was charged with 104.4 g of a 30% aqueous solution of sodium polysulfide (0.180 mol) and 150 g of ion exchanged water, and they were stirred and heated to 90 C. Thereafter, 25.0 g of bis(2-chloroethyl)ether (0.175 mol) diluted with 100 g of toluene was dropwise added to the mixture over two hours, and the reaction was further continued for three hours at the same temperature. Then, the organic phase was separated, followed by vacuum concentration and drying at 90 C. to give 25.0 g of a target oligomer.

[0175] The sulfur-containing oligomer 3 (liquid) thus prepared had a Mw of 1,250, an elemental sulfur content of 55% by mass, and an SP value of 11.1 and contained a repeating unit of formula (I) wherein R=(CH.sub.2).sub.2O(CH.sub.2).sub.2 and x=4.0 on average.

Production Example 3

Synthesis of Sulfur-Containing Oligomer 4 (Rubbery)

[0176] A flask completely purged with an inert gas such as nitrogen or argon gas was charged with 104.4 g of a 30% aqueous solution of sodium polysulfide (0.180 mol) and 150 g of ion exchanged water, and they were stirred and heated to 90 C. Thereafter, 27.13 g of 1,6-dichlorohexane (0.175 mol) diluted with 100 g of toluene was dropwise added to the mixture over two hours, and the reaction was further continued for three hours at the same temperature. Then, the organic phase was separated, followed by vacuum concentration and drying at 90 C. to give 28.0 g of a target oligomer.

[0177] The sulfur-containing oligomer 4 (rubbery) thus prepared had a Mw of 16,000, an elemental sulfur content of 58% by mass, and an SP value of 11.1 and contained a repeating unit of formula (I) wherein R=(CH.sub.2).sub.5 and x=4.0 on average.

[0178] With regard to the structure of the sulfur-containing oligomer 1 used in the examples, the oligomer seems to be a compound containing a repeating unit represented by the following formula (Chem. X):

##STR00006##

[0179] With regard to the structure of the sulfur-containing oligomers 2 and 3, each oligomer seems to be a mixture of the compound of formula (Chem. X) and/or a compound represented by the following formula (Chem. XI) (a mixture of Chem. X and/or Chem. XI):

##STR00007##

[0180] With regard to the structure of the sulfur-containing oligomer 4, the oligomer seems to be a compound containing a repeating unit represented by the following formula (Chem.

[0181] XII):

##STR00008##

[0182] The polymers were analyzed as described below.

(Structural Identification)

[0183] The structure (styrene content, vinyl content) of the polymers was identified using a JNM-ECA series system available from Jeol Ltd. A solution of 0.1 g of the polymer in 15 mL of toluene was slowly poured into 30 mL of methanol for reprecipitation. The precipitate was dried under reduced pressure and then analyzed.

(Weight Average Molecular Weight (Mw) Measurement)

[0184] The weight average molecular weight (Mw) of the polymers was determined by gel permeation chromatography (GPC) (GPC-8000 series available from Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M available from Tosoh Corporation) calibrated with polystyrene standards.

[0185] The Mw measurement and structural identification of the sulfur-containing oligomers were performed as described below.

(Weight Average Molecular Weight (Mw), Structural Identification)

[0186] The Mw was determined by gel permeation chromatography (GPC) using the apparatus and conditions indicated below and calibrated with polystyrene standards.

[0187] Moreover, the fractions corresponding to the peaks in the chromatogram prepared by GPC were separated and then analyzed by gas chromatography-mass spectrometry (GC/MS) to determine the molecular weight of the peak fractions.

[0188] The sulfur-containing oligomers were also subjected to .sup.13C NMR analysis.

[0189] Then, the structure of the sulfur-containing oligomers was identified based on the .sup.13C NMR analysis results, the weight average molecular weight determined by GPC, and the molecular weights of the peak fractions determined by GC/MS.

(1) Pretreatment

[0190] Each sample was dissolved in a solvent and then filtered through a 0.45 m membrane filter to prepare a solution for analysis.

(2) Apparatus and Measurement Conditions

[0191] Apparatus: GPC-8000 series available from Tosoh Corporation

[0192] Column: TSKGel SuperAWM-H2+SuperAW25001 (6.0 mm i.d.150 mm, 3 columns) available from Tosoh Corporation

[0193] Solvent: chloroform

[0194] Flow rate: 0.6 mL/min

[0195] Detector: RI detector

[0196] Column temperature: 40 C.

[0197] Injection amount: 20 L

[0198] Molecular weight standards: polystyrene standards

[0199] The acid value of the rosin ester resins was measured as described below.

(Acid Value (mg KOH/g) Measurement)

[0200] In accordance with JIS K 5902 (2006), 0.5 to 0.7 g of a sample was weighed with an analytical balance and placed in a 100 mL Erlenmeyer flask. The sample was completely dissolved in a neutral solvent (toluene:methanol=2:1) with vigorous shaking. About five drops of 1% phenolphthalein were added to the solution, followed by titration with N/5 KOH to determine the acid value.

[0201] The end point of the titration was set at a point where the measurement liquid turned pale red that did not disappear within 30 seconds.

[0202] The chemicals used in examples and comparative examples are listed below.

[0203] Modified SBR 1 for silica: modified SBR (alkoxysilyl-modified, bound styrene content: 27% by mass, vinyl content: 53 mol%, Mw: 400,000) prepared in Copolymer

Production Example 2

[0204] Modified SBR 2 for silica: NS616 (non-oil extended, amine-modified, styrene content: 21% by mass, vinyl content: 66% by mass, Mw: 240,000) available from Zeon Corporation

[0205] High-cis BR 1: BUNA-CB25 (BR synthesized using Nd catalyst, cis content: 96 mol%) available from Lanxess

[0206] Modified low-cis BR 2 for silica: modified BR (vinyl content: 13% by mass, cis content: 38% by mass, trans content: 50% by mass, Mw/Mn: 1.19, Mw: 420,000) prepared in

Copolymer Production Example 1

[0207] Carbon black: SHOBLACK N220 (N.sub.2SA: 114 m.sup.2/g) available from Cabot Japan K.K.

[0208] Silica: Ultrasil VN3 (N.sub.2SA: 175 m.sup.2/g) available from Degussa

[0209] Silane coupling agent: Si75 (bis(3-triethoxysilylpropyl) disulfide) available from Evonik

[0210] Wax: Ozoace 0355 (paraffin wax, melting point: 70 C., normal alkane content: 85% by mass) available from Nippon Seiro Co., Ltd.

[0211] Stearic acid: stearic acid TSUBAKI available from NOF Corporation

[0212] Process oil: Diana Process AH-24 (aromatic process oil) available from Idemitsu Kosan Co., Ltd.

[0213] Antioxidant: Antigene 6C (N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine) available from Sumitomo Chemical Co., Ltd.

[0214] Zinc oxide: zinc oxide #2 available from Mitsui Mining & Smelting Co., Ltd.

[0215] TO-125: YS resin TO-125 (aromatic modified terpene resin, softening point: 125 C., Tg: 64 C.) available from Yasuhara Chemical Co., Ltd.

[0216] T160: YS polystar T160 (terpene phenol resin, softening point: 160 C., Tg: 100 C.) available from Yasuhara Chemical Co., Ltd.

[0217] Sylvares 4401: Sylvares 4401 (copolymer of -methylstyrene and styrene, softening point: 85 C., Tg: 43 C.) available from Arizona Chemical

[0218] C10: NOVARES C10 (liquid coumarone-indene resin, softening point: 10 C., Tg: -30 C.) available from Rutgers Chemicals

[0219] Rosin P: HARIESTER P (rosin ester resin, softening point: 102 C., acid value: 9 mg KOH/g) available from Harima Chemicals Group, Inc.

[0220] Rosin TF: HARIESTER TF (rosin ester resin, softening point: 80 C., acid value: 10 mg KOH/g) available from Harima Chemicals Group, Inc.

[0221] Sulfur-containing oligomer 1: the sulfur-containing oligomer in Production Example 1

[0222] Sulfur-containing oligomer 2 (liquid): the sulfur-containing oligomer in Production Example 2

[0223] Sulfur-containing oligomer 3 (liquid): the sulfur-containing oligomer in Production Example 3

[0224] Sulfur-containing oligomer 4: the sulfur-containing oligomer in Production Example 4

[0225] Hybrid crosslinking agent 1: PERKALINK 900 (1,3-bis(citraconimidomethyl)benzene) available from Flexsys

[0226] Hybrid crosslinking agent 2: Vulcuren VP KA9188 (1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane) available from Lanxess

[0227] Sulfur: 5% oil-containing powder sulfur available from Hosoi Chemical Industry Co., Ltd.

[0228] Vulcanization accelerator 1: NOCCELER NS (N-tert-butyl-2-benzothiazolylsulfenamide, melting point: 103 C.) available from Ouchi Shinko Chemical Industrial Co., Ltd.

[0229] Vulcanization accelerator 2: NOCCELER D (N,N-diphenylguanidine, melting point: 145 C.) available from Ouchi Shinko Chemical Industrial Co., Ltd.

(Examples and Comparative Examples)

[0230] The chemicals other than sulfur and vulcanization accelerators in the amounts indicated in Table 1 were kneaded for five minutes at 150 C. using a 1.7 L Banbury mixer (Kobe Steel, Ltd.) to give a kneaded mixture. To the kneaded mixture were added the sulfur and vulcanization accelerators, and they were kneaded for five minutes at 80 C. using an open roll mill to give an unvulcanized rubber composition. The unvulcanized rubber composition was formed into the shape of a tread and assembled with other tire components to build an unvulcanized tire. The unvulcanized tire was press-vulcanized at 170 C. for 10 minutes to prepare a test tire (size: 195/65R15). For evaluation of rubber specimens, they were cut out of the tread of the test tire.

[0231] The test tires and rubber specimens were evaluated as described below. Table 1 shows the results.

(Initial Wet Grip Performance)

[0232] The test tires were mounted on a front-engine, rear-wheel-drive car of 2,000 cc displacement made in Japan. A test driver drove the car 10 laps around a test track with wet asphalt conditions and then evaluated control stability during steering on the second lap. The results are expressed as an index (initial wet grip performance index), with Comparative Example 1 taken as 100. A higher index indicates higher initial wet grip performance. Tires with an index of 105 or higher are considered good.

(EB, M300, M100)

[0233] In accordance with JIS K6251:2010, No. 6 dumbbell-shaped test pieces were prepared from the rubber specimens cut out of the tread of the test tires, and then subjected to tensile testing at room temperature (25 C.) to determine the elongation at break (EB, %), stress at 300% elongation (M300, MPa), and stress at 100% elongation (M100, MPa).

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 Amount Modified SBR 1 for 80 80 100 (parts silica (alkoxysilyl- by mass) modified) Modified SBR 2 for 80 80 80 80 80 80 80 80 silica (amine-modified) High-cis BR 1 (Nd 20 20 20 20 20 20 20 20 20 catalyst) Modified BR for 20 silica (low cis) Carbon black (N220) 5 5 5 5 5 5 5 5 5 5 5 Silica (VN3) 75 75 75 75 75 95 115 75 75 75 75 Silane coupling 6 6 6 6 6 7.6 9.2 6 6 6 6 agent (Si75) Wax 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 Process oil 17 17 7 7 27 17 7 7 7 7 Antioxidant 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 TO-125 (softening 20 20 20 20 20 20 point: 125 C., Tg: 64 C.) T160 (softening point: 160 C., Tg 100 C.) Sylvares 4401 10 10 (softening point: 85 C., Tg: 43 C.) C10 (softening point: 7 15 10 C., Tg 30 C.) Rosin P (rosin ester 20 20 resin, acid value: 9) Rosin TF (rosin ester 20 resin, acid value: 10) Sulfur-containing 3.0 oligomer 1 (sulfur content: 55%, Mw: 21,000) Sulfur-containing 3.0 oligomer 2 (liquid, sulfur content: 55%, Mw: 2,670) Sulfur-containing oligomer 3 (liquid, sulfur content: 55%, Mw: 1,250) Sulfur-containing oligomer 4 (sulfur content: 58%, Mw: 16,000) Hybrid crosslinking agent 1 Hybrid crosslinking agent 2 Sulfur 1.50 1.50 1.50 1.30 1.20 1.50 1.50 1.50 1.50 Vulcanization 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 accelerator 1 Vulcanization 2.2 2.2 2.2 2.2 2.2 2.5 2.7 2.2 2.2 2.2 2.2 accelerator 2 Total amount 227.9 227.9 226.4 226.4 226.4 268.1 294.8 226.4 226.4 226.4 226.4 Evaluation Tensile M100 2.2 2.3 2.3 2.3 2.3 2.1 1.9 2.2 2.2 2.3 2.2 properties M300 7.8 8.1 9.4 9.5 8.4 7.3 6.7 8.9 9.7 8.4 8.4 EB 615 580 535 530 560 690 675 625 560 585 575 EB/M300 79 72 57 56 67 95 101 70 58 70 68 Initial wet grip 113 108 112 109 110 112 113 119 106 109 107 performance Example Comparative Example 12 13 14 15 1 2 3 4 5 6 7 Amount Modified SBR 1 for (parts silica (alkoxysilyl- by mass) modified) Modified SBR 2 for 80 80 80 80 80 80 80 80 80 80 80 silica (amine-modified) High-cis BR 1 (Nd 20 20 20 20 20 20 20 20 20 20 20 catalyst) Modified BR for silica (low cis) Carbon black (N220) 5 5 5 5 5 5 5 5 5 5 5 Silica (VN3) 75 75 75 75 75 75 75 75 60 60 75 Silane coupling 6 6 6 6 6 6 6 6 4.8 4.8 6 agent (Si75) Wax 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 Process oil 7 17 17 17 17 17 17 17 0 17 30 Antioxidant 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 TO-125 (softening point: 125 C., Tg: 64 C.) T160 (softening point: 10 160 C., Tg 100 C.) Sylvares 4401 10 10 10 10 10 10 10 10 10 10 (softening point: 85 C., Tg: 43 C.) C10 (softening point: 10 C., Tg 30 C.) Rosin P (rosin ester 20 resin, acid value: 9) Rosin TF (rosin ester resin, acid value: 10) Sulfur-containing 3.0 2.4 oligomer 1 (sulfur content: 55%, Mw: 21,000) Sulfur-containing oligomer 2 (liquid, sulfur content: 55%, Mw: 2,670) Sulfur-containing 3.0 oligomer 3 (liquid, sulfur content: 55%, Mw: 1,250) Sulfur-containing 3.0 oligomer 4 (sulfur content: 58%, Mw: 16,000) Hybrid crosslinking 2.5 agent 1 Hybrid crosslinking 2.5 agent 2 Sulfur 1.50 0.50 1.00 1.50 1.50 1.50 1.50 Vulcanization 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 accelerator 1 Vulcanization 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 accelerator 2 Total amount 237.9 227.3 227.9 227.9 226.4 227.9 228.4 226.4 193.2 210.2 239.4 Evaluation Tensile M100 2.3 1.8 2.1 2.2 2.4 2.3 2.4 2.5 2.2 1.6 1.4 properties M300 7.8 7.6 8.0 7.9 11.7 11.5 11.4 12.5 10.2 8.3 9.8 EB 635 655 595 620 484 500 495 475 450 570 550 EB/M300 81 86 74 79 41 43 43 38 44 69 56 Initial wet grip 120 123 109 113 100 100 101 94 87 82 90 performance

[0234] As shown in Table 1, the tread rubber compositions containing a diene rubber, silica, and sulfur and/or a sulfur-containing compound, and having predetermined EB/M300, M100, and EB defined by relationships (1) to (3) were excellent in wet grip performance during the initial phase of running. They also had good tensile properties, cut and chip resistance, and handling stability.

[0235] A higher silica content tends to result in a higher EB/M300 but is accompanied by a lower M100, so that initial wet grip performance is not much improved (Examples 6 and 7). This is because the amount of the polymer component is reduced, resulting in a lower M100. The sulfur-containing oligomers 1 and 2 and TO-125 have an effect of reducing M300, i.e., promoting uniform crosslinking. Owing to the effect, an EB/M300 of about 70 can be achieved (Examples 1, 2, 5, and 6).