RUBBER COMPOSITION, TIRE AND PREPARATION METHOD OF RUBBER COMPOSITION

Abstract

According to the rubber composition of the present invention comprising a starting chemical comprising a rubber component comprising styrene-butadiene rubber, a filler comprising silica, a silane coupling agent and an organoaluminum compound, a rubber composition for a tire having enhanced wet grip performance and abrasion resistance as well as enhanced fuel efficiency and a tire tread and tire produced using the rubber composition can be provided.

Claims

1. A rubber composition comprising a starting chemical comprising a rubber component comprising a styrene-butadiene rubber, a filler comprising silica, a silane coupling agent and an organoaluminum compound.

2. The rubber composition of claim 1, wherein the silane coupling agent is a silane coupling agent having a mercapto group and is at least one selected from the group consisting of a silane coupling agent comprising a linking unit A represented by the following formula (I) and a linking unit B represented by the following formula (II) and a silane coupling agent represented by the following formula (III): ##STR00007## wherein in the formulae, x is an integer of 0 or more, and y is an integer of 1 or more. R.sup.1 represents hydrogen, halogen, a branched or un-branched alkyl group having 1 to 30 carbon atoms, a branched or un-branched alkenyl group having 2 to 30 carbon atoms, a branched or un-branched alkynyl group having 2 to 30 carbon atoms, or the alkyl group at the end of which hydrogen has been replaced by a hydroxyl group or a carboxyl group; R.sup.2 represents a branched or un-branched alkylene group having 1 to 30 carbon atoms, a branched or un-branched alkenylene group having 2 to 30 carbon atoms, or a branched or un-branched alkynylene group having 2 to 30 carbon atoms; a ring structure may be formed with R.sup.1 and R.sup.2: ##STR00008## wherein in the formula, R.sup.1001 is a monovalent group selected from —Cl, —Br, —OR.sup.1006, —O(O═)CR.sup.1006, —ON═CR.sup.1006R.sup.1007, —NR.sup.1006R.sup.1007 and (OSiR.sup.1006R.sup.1007).sub.h(OSiR.sup.1006R.sup.1007R.sup.1008) (R.sup.1006, R.sup.1007 and R.sup.1008 may be the same or different, each of them is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and an average value of h is 1 to 4); R.sup.1002 is R.sup.1001, a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms; R.sup.1003 is R.sup.1001, R.sup.1002, a hydrogen atom, or a [O(R.sup.1009O).sub.j].sub.0.5— group (R.sup.1009 is an alkylene group having 1 to 18 carbon atoms, j is an integer of 1 to 4); R.sup.1004 is a divalent hydrocarbon group having 1 to 18 carbon atoms; R.sup.1005 is a monovalent hydrocarbon group having 1 to 18 carbon atoms; and x, y and z are numerals satisfying relations of x+y+2z=3, 0≤x≤3, 0≤y≤2 and 0≤z≤1.

3. The rubber composition of claim 1, wherein a CTAB specific surface area of silica is 100 m.sup.2/g or more and a BET specific surface area by nitrogen adsorption of silica is 110 m.sup.2/g or more.

4. The rubber composition of claim 3, wherein the CTAB specific surface area of silica is 180 m.sup.2/g or more and the BET specific surface area by nitrogen adsorption of silica is 185 m.sup.2/g or more.

5. The rubber composition of claim 1, wherein the filler further comprises carbon black.

6. The rubber composition of claim 5, wherein a compounding amount of the silica is 50 to 150 parts by mass, a compounding amount of the carbon black is 5 to 50 parts by mass, and a compounding amount of the organoaluminum compound is 5 to 45 parts by mass based on 100 parts by mass of the rubber component and a compounding amount of the silane coupling agent is 1 to 20 parts by mass based on 100 parts by mass of the silica.

7. The rubber composition of claim 1, wherein the organoaluminum compound is an aluminum alcolate represented by the formula (1):
Al(OR.sup.a)(OR.sup.b)(OR.sup.c).sub.3  (1) wherein R.sup.a, R.sup.b and R.sup.C independently represent aliphatic hydrocarbon groups, respectively.

8. A tire tread produced using the rubber composition of claim 1.

9. A tire having the tire tread of claim 8.

10. A method of preparing a rubber composition comprising a starting chemical comprising a rubber component comprising a styrene-butadiene rubber, a filler comprising silica, a silane coupling agent and an organoaluminum compound, the method comprising: a kneading step comprising at least two stages comprising a former stage for kneading the starting chemical containing no vulcanization chemical and a latter stage for adding a vulcanization chemical to a kneaded product obtained in the former stage and kneading a mixture, wherein in the former stage, a discharge temperature of the kneaded product is within a predetermined temperature range and the kneaded product is held at the discharge temperature for a predetermined period of time in order to remove alcohol generated during the kneading.

11. A method of preparing a rubber composition comprising a starting chemical comprising a rubber component comprising a styrene-butadiene rubber, a filler comprising silica, a silane coupling agent and an organoaluminum compound, the method comprising: a kneading step comprising at least two stages comprising a former stage for kneading the starting chemical containing no vulcanizing agent and a latter stage for adding the vulcanizing agent to a kneaded product obtained in the former stage and kneading a mixture, wherein the former stage is a stage, where a basic vulcanization accelerator is added to the starting chemical comprising the rubber component, the filler, the silane coupling agent and the organoaluminum compound, and a mixture is kneaded.

Description

EXAMPLE

[0251] The present invention is then explained by means of Examples, but is not limited to the Examples.

[0252] A variety of chemicals used herein will be explained below. The various chemicals were subjected to refining by a usual method according to necessity.

<Various Chemicals Used for Preparation of Rubber Composition>

[0253] S-SBR: BUNA VSL 2525-0 available from LANXESS Japan (solution-polymerized SBR, bonded styrene amount: 25% by mass, vinyl content: 25 mole %, Tg=−49° C.)
Silica A: ULTRASIL VN3 (CTAB specific surface are: 165 m.sup.2/g) (N.sub.2SA: 175 m.sup.2/g) manufactured by Evonik Degussa GmbH
Silica B: Zeosil HRS1200MP (CTAB specific surface are: 195 m.sup.2/g) (N.sub.2SA: 200 m.sup.2/g) available from Solvay Japan, Ltd.
Silica C: Zeosil Premium200MP (CTAB specific surface are: 200 m.sup.2/g) (N.sub.2SA: 220 m.sup.2/g) available from Solvay Japan, Ltd.
Silica D: Zeosil 1115MP (CTAB specific surface are: 105 m.sup.2/g) (N.sub.2SA: 115 m.sup.2/g) available from Solvay Japan, Ltd.
Carbon black: N220 (N.sub.2SA: 114 m.sup.2/g) manufactured by Mitsubishi Chemical Corporation
Aluminum hydroxide: Higilite H-43 (brand name) (average primary particle size: 0.75 μm) manufactured by SHOWA DENKO K.K.
Organoaluminum compound: Aluminum isopropylate (chemical compound name) PADM (brand name) manufactured by Kawaken Fine Chemicals Co., Ltd.
Oil: TDAE manufactured by JX Nippon Oil & Energy Corporation Silane coupling agent A: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa GmbH
Silane coupling agent B: NXT Silane (3-octanoylthiopropyltriethoxysilane) available from Momentive Performance Materials Inc.
Silane coupling agent C: NXT-Z45 (a copolymer of a linking unit A and a linking unit B (linking unit A: 55 mole %, linking unit B1-45 mole %)) available from Momentive Performance Materials Inc.
Antioxidant: NOCRAC 6C (N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine) (6PPD) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Stearic acid: Bead stearic acid TSUBAKI manufactured by NOF Corporation
Zinc oxide: Class 2 zinc oxide manufactured by MITSUI MINING & SMELTING CO., LTD
Vulcanization accelerator A: Nocceler NS manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
Vulcanization accelerator B: Nocceler CZ (N-cyclo-hexyl-2-benzothiazolylsulfeneamide: CBS) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
Basic vulcanization accelerator: Nocceler D (1,3-diphenylguanidine: DPG) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

First Embodiment

[0254] Examples 1 to 3 and Comparative Examples 1 to 5 relating to the first embodiment are shown below.

<Preparation of Rubber Composition for Tire>

[0255] Materials other than sulfur and vulcanization accelerators were subjected to kneading at 150° C. for five minutes in accordance with the formulations shown in Table 1 using a 1.7 liter Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Subsequently sulfur and a vulcanization accelerator A were added to the obtained kneaded product, and a mixture was subjected to kneading at 80° C. for five minutes using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was subjected to press-vulcanization at 170° C. for 20 minutes with a 2 mm thick metal mold to obtain a vulcanized rubber composition. The obtained unvulcanized rubber composition was molded into a form of a tread, and an extrudate was laminated with other tire members on a tire molding machine to form an unvulcanized tire, followed by vulcanization at 170° C. for 12 minutes to produce a test tire (tire size: 195/65R.sup.15).

<Evaluation>

(Wet Grip Index)

[0256] A test piece was cut out from the vulcanized rubber composition obtained above, and while spraying water against the test piece, making sure that a water film could be formed on a top of the test piece, and increasing a linear speed of the test piece up to 7 km/h, a dynamic friction coefficient (μ) was measured in accordance with a known measuring method using a Dynamic Friction Tester (D.F. Tester) manufactured by NIPPO SANGYO LTD. Assuming that a wet grip index of a reference comparative example was 100, each of the dynamic friction coefficients (μ) of the respective formulations was obtained by the following equation and was indicated by an index. The larger the dynamic friction coefficient (μ) is and the larger the wet grip index is, the higher the wet grip performance and safety during running are.

(Wet grip index)=(μ of each formulation÷(μ of Reference Comparative Example)×100

(Fuel Efficiency Index)

[0257] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (tan δ) of each vulcanized rubber sheet at 70° C. was measured at an initial strain of 10%, a dynamic strain of 1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a fuel efficiency index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The lower the tan δ value is and the larger the fuel efficiency index is, the more excellent the fuel efficiency is.

(Index of fuel efficiency)=(tan δ of Reference Comparative Example)÷(tan δ of each formulation)×100

(Breaking Strength Index of Rubber)

[0258] The obtained vulcanized rubber composition was subjected to tensile test according to JIS K6251 using a No. 3 dumbbell type test piece, to measure a tensile strength at break (TB) and an elongation at break (EB) (%). And, a TB×EB1−2 value was determined as a breaking strength. A breaking strength of each formulation was obtained by the following equation and was indicated by an index, assuming that a breaking strength index of a reference comparative example was 100. The larger the index is, the more excellent the breaking strength is.

(Breaking strength index)=(TB×EB1−2 of each formulation)/(TB×EB1−2 of Reference Comparative Example)×100

(Abrasion Resistance Index)

[0259] An abrasion loss of a vulcanized rubber composition was measured with a Lambourn abrasion testing machine under the conditions of a room temperature, a load of 1.0 kgf, and a slip rate of 30%. Assuming that an abrasion resistance index of a reference comparative example was 100, an abrasion loss of each formulation was obtained by the following equation and was indicated by an index. The smaller the abrasion loss is and the larger the abrasion resistance index is, abrasion resistance is excellent.

(Abrasion resistance index)=(Abrasion loss of Reference Comparative Example)/(Abrasion loss of each formulation)×100

(Results)

[0260] The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 1 2 3 4 5 Compounded amount (part by mass) S-SBR 100 100 100 100 100 100 100 100 Silica A 83 82 81 85 83 82 81 80 Carbon black 10 10 10 10 10 10 10 10 Aluminum hydroxide 0 0 0 0 5 10 15 20 Organoaluminum compound 12.5 25 37.5 0 0 0 0 0 Oil 50 50 50 50 50 50 50 50 Silane coupling agent A 8.3 8.2 8.1 8.5 8.3 8.2 8.1 8 Antioxidant 2 2 2 2 2 2 2 2 Wax 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 Vulcanization accelerator A 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Evaluation Wet grip index 105 107 110 100 102 104 107 110 Fuel efficiency index 105 107 107 100 105 105 105 105 Rubber breaking strength index 108 115 127 100 100 104 97 97 Abrasion resistance index 104 102 100 100 98 96 94 92

Second Embodiment

[0261] Examples 4 to 10 and Comparative Examples 6 to 8 relating to the second embodiment are shown below.

<Preparation of Rubber Composition for Tire>

[0262] Materials other than sulfur and vulcanization accelerators were subjected to kneading at 150° C. for five minutes in accordance with the formulations shown in Table 2 using a 1.7 liter Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Subsequently sulfur and a vulcanization accelerator A were added to the obtained kneaded product, and a mixture was subjected to kneading at 80° C. for five minutes using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was subjected to press-vulcanization at 170° C. for 20 minutes with a 2 mm thick metal mold to obtain a vulcanized rubber composition. The obtained unvulcanized rubber composition was molded into a form of a tread, and an extrudate was laminated with other tire members on a tire molding machine to form an unvulcanized tire, followed by vulcanization at 170° C. for 12 minutes to produce a test tire (tire size: 195/65R15).

<Evaluation>

(Wet Grip Index)

[0263] A test piece was cut out from the vulcanized rubber composition obtained above, and while spraying water against the test piece, making sure that a water film could be formed on a top of the test piece, and increasing a linear speed of the test piece up to 7 km/h, a dynamic friction coefficient (μ) was measured in accordance with a known measuring method using a Dynamic Friction Tester (D.F. Tester) manufactured by NIPPO SANGYO LTD. Assuming that a wet grip index of a reference comparative example was 100, each of the dynamic friction coefficients (μ) of the respective formulations was obtained by the following equation and was indicated by an index. The larger the dynamic friction coefficient (μ) is and the larger the wet grip index is, the higher the wet grip performance and safety during running are.

(Wet grip index)=(μ of each formulation÷(μ of Reference Comparative Example)×100

(Fuel Efficiency Index)

[0264] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (tan δ) of each vulcanized rubber sheet at 70° C. was measured at an initial strain of 10%, a dynamic strain of 1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a fuel efficiency index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The lower the tan δ value is and the larger the fuel efficiency index is, the more excellent the fuel efficiency is.

(Index of fuel efficiency)=(tan δ of Reference Comparative Example)÷(tan δ of each formulation)×100

(Breaking Strength Index of Rubber)

[0265] The obtained vulcanized rubber composition was subjected to tensile test according to JIS K6251 using a No. 3 dumbbell type test piece, to measure a tensile strength at break (TB) and an elongation at break (EB) (%). And, a TB×EB1−2 value was determined as a breaking strength. A breaking strength of each formulation was obtained by the following equation and was indicated by an index, assuming that a breaking strength index of a reference comparative example was 100. The larger the index is, the more excellent the breaking strength is.

(Breaking strength index)=(TB×EB1−2 of each formulation)/(TB×EB1−2 of Reference Comparative Example)×100

(Abrasion Resistance Index)

[0266] An abrasion loss of a vulcanized rubber composition was measured with a Lambourn abrasion testing machine under the conditions of a room temperature, a load of 1.0 kgf, and a slip rate of 30%. Assuming that an abrasion resistance index of a reference comparative example was 100, an abrasion loss of each formulation was obtained by the following equation and was indicated by an index. The smaller the abrasion loss is and the larger the abrasion resistance index is, abrasion resistance is excellent.

(Abrasion resistance index)=(Abrasion loss of Reference Comparative Example)/(Abrasion loss of each formulation)×100

(Results)

[0267] The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Comparative Example Example 6 7 8 4 5 6 7 8 9 10 Compounded amount (part by mass) S-SBR 100 100 100 100 100 100 100 100 100 100 Silica A 82 82 82 82 82 82 82 82 82 82 Carbon black 10 10 10 10 10 10 10 10 10 10 Aluminum hydroxide 25 25 25 0 0 0 0 0 0 0 Organoaluminum compound 0 0 0 5 10 15 20 20 20 20 Oil 50 50 50 50 50 50 50 50 50 50 Silane coupling agent A (Si69) 1.64 8.2 9.84 — — — — — — — Silane coupling agent B (NXT) — — — 1.64 3.28 4.92 6.56 8.2 9.84 — Silane coupling agent C (NXT-Z45) — — — — — — — — — 8.2 Antioxidant 2 2 2 2 2 2 2 2 2 2 Wax 2 2 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 2 2 Vulcanization accelerator A 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Evaluation Wet grip index 100 109 104 104 106 109 112 112 107 110 Fuel efficiency index 100 102 100 105 97 101 105 110 105 108 Rubber breaking strength index 100 125 119 106 113 119 125 138 123 135 Abrasion resistance index 100 128 122 109 116 122 128 147 128 145

Third Embodiment

[0268] Examples 11 to 13 and Comparative Examples 9 to 17 relating to the third embodiment are shown below.

<Preparation of Rubber Composition for Tire>

[0269] Materials other than sulfur and vulcanization accelerators were subjected to kneading at 150° C. for five minutes in accordance with the formulations shown in Table 3 using a 1.7 liter Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Subsequently sulfur and a vulcanization accelerator A were added to the obtained kneaded product, and a mixture was subjected to kneading at 80° C. for five minutes using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was subjected to press-vulcanization at 170° C. for 20 minutes with a 2 mm thick metal mold to obtain a vulcanized rubber composition. The obtained unvulcanized rubber composition was molded into a form of a tread, and an extrudate was laminated with other tire members on a tire molding machine to form an unvulcanized tire, followed by vulcanization at 170° C. for 12 minutes to produce a test tire (tire size: 195/65R15).

<Evaluation>

(Un-Reactivity Index of Coupling Agent)

[0270] An un-vulcanized rubber composition was cut into pieces which were subjected to extraction in ethanol for 24 hours. An amount of an un-reacted coupling agent extracted in an extract was measured with a gas chromatography, and a ratio (% by mass) of the un-reacted coupling agent was calculated from the compounded amount of the coupling agent. Assuming that an un-reactivity index of the coupling agent of the reference comparative example was 100, an un-reactivity index of the coupling agent of each formulation was obtained by the following equation and was indicated by an index. As the ratio of the un-reacted coupling agent is smaller and the un-reactivity index of the coupling agent is smaller, it means that an amount of the un-reacted coupling agent being present in the un-vulcanized rubber composition after termination of the kneading step is small. Namely, it means that a larger amount of the coupling agent was reacted in the kneading step, which is satisfactory.

(Un-reactivity index of coupling agent)=(Ratio of an amount of un-reacted coupling agent of each formulation)÷(Ratio of an amount of un-reacted coupling agent of Reference Comparative Example)×100

(Wet Grip Index)

[0271] A test piece was cut out from the vulcanized rubber composition obtained above, and while spraying water against the test piece, making sure that a water film could be formed on a top of the test piece, and increasing a linear speed of the test piece up to 7 km/h, a dynamic friction coefficient (μ) was measured in accordance with a known measuring method using a Dynamic Friction Tester (D.F. Tester) manufactured by NIPPO SANGYO LTD. Assuming that a wet grip index of a reference comparative example was 100, each of the dynamic friction coefficients (μ) of the respective formulations was obtained by the following equation and was indicated by an index. The larger the dynamic friction coefficient (μ) is and the larger the wet grip index is, the higher the wet grip performance and safety during running are.

(Wet grip index)=(μ of each formulation÷(μ of Reference Comparative Example)×100

(Fuel Efficiency Index)

[0272] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (tan δ) of each vulcanized rubber sheet at 70° C. was measured at an initial strain of 10%, a dynamic strain of 1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a fuel efficiency index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The lower the tan δ value is and the larger the fuel efficiency index is, the more excellent the fuel efficiency is.

(Index of fuel efficiency)=(tan δ of Reference Comparative Example)÷(tan δ of each formulation)×100

(Breaking Strength Index of Rubber)

[0273] The obtained vulcanized rubber composition was subjected to tensile test according to JIS K6251 using a No. 3 dumbbell type test piece, to measure a tensile strength at break (TB) and an elongation at break (EB) (%). And, a TB×EB1−2 value was determined as a breaking strength. A breaking strength of each formulation was obtained by the following equation and was indicated by an index, assuming that a breaking strength index of a reference comparative example was 100. The larger the index is, the more excellent the breaking strength is.

(Breaking strength index)=(TB×EB1−2 of each formulation)/(TB×EB1−2 of Reference Comparative Example)×100

(Abrasion Resistance Index)

[0274] An abrasion loss of a vulcanized rubber composition was measured with a Lambourn abrasion testing machine under the conditions of a room temperature, a load of 1.0 kgf, and a slip rate of 30%. Assuming that an abrasion resistance index of a reference comparative example was 100, an abrasion loss of each formulation was obtained by the following equation and was indicated by an index. The smaller the abrasion loss is and the larger the abrasion resistance index is, abrasion resistance is excellent.

(Abrasion resistance index)=(Abrasion loss of Reference Comparative Example)/(Abrasion loss of each formulation)×100

(Results)

[0275] The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Com. Comparative Example Example Ex. 9 10 11 12 13 14 15 16 11 12 13 17 Compounded amount (part by mass) S-SBR 100 100 100 100 100 100 100 100 100 100 100 100 Silica A (CTAB: 165 m.sup.2/g, N.sub.2SA: 85 — — — 82 — — — 82 — — — 175 m.sup.2/g) Silica B (CTAB: 195 m.sup.2/g, N.sub.2SA: — 85 — — — 82 — — — 82 — — 200 m.sup.2/g) Silica C (CTAB: 200 m.sup.2/g, N.sub.2SA: — — 85 — — — 82 — — — 82 — 220 m.sup.2/g) Silica D (CTAB: 105 m.sup.2/g, N.sub.2SA: — — — 85 — — — 82 — — — 82 115 m.sup.2/g) Carbon black 10 10 10 10 10 10 10 10 10 10 10 10 Aluminum hydroxide — — — — 25 25 25 25 — — — — Organoaluminum compound — — — — — — — — 20 20 20 20 Oil 50 50 50 50 50 50 50 50 50 50 50 50 Silane coupling agent A 8.5 8.5 8.5 8.5 8.2 8.2 8.2 8.2 8.2 8.2 8.2 8.2 Antioxidant 2 2 2 2 2 2 2 2 2 2 2 2 Wax 2 2 2 2 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 2 2 2 2 Vulcanization accelerator A 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Evaluation Un-reactivity index of 100 100 100 100 100 100 100 100 3 3 3 3 coupling agent 100 97 95 107 107 104 102 114 112 109 107 119 Wet grip index Fuel efficiency index 100 102 104 106 100 102 104 106 102 105 107 109 Rubber breaking strength index 100 105 109 70 98 103 107 68 102 109 113 70 Abrasion resistance index 100 105 109 80 96 101 105 76 102 110 114 86

Fourth Embodiment

[0276] Examples 14 to 17 and Comparative Examples 18 to 21 relating to the fourth embodiment are shown below.

<Preparation of Rubber Composition for Tire>

(Step I (Former Stage of Kneading Step))

[0277] Kneading was performed for five minutes in accordance with the formulations shown in Table 4 using a 1.7 liter Banbury mixer manufactured by Kobe Steel, Ltd., followed by holding of a kneaded product at a predetermined discharge temperature and a predetermined holding time shown in Table 4, and then discharging to obtain a kneaded product.

(Step II (Latter Stage of Kneading Step))

[0278] Subsequently, each chemical was added to the obtained kneaded product in accordance with the formulation shown in Table 4, followed by kneading at 80° C. for five minutes using an open roll to obtain an unvulcanized rubber composition.

(Vulcanizing Step)

[0279] The obtained unvulcanized rubber composition was subjected to vulcanization at 170° C. for 20 minutes to obtain a vulcanized rubber composition.

<Evaluation>

(Processability)

[0280] One kg of an unvulcanized rubber composition was wound in a width of 20 cm and a thickness of 4 mm on an 8-inch open roll and was subjected to kneading until a temperature of the unvulcanized rubber composition reached 50±10° C. Then the unvulcanized rubber composition was cut into a rubber sheet and a surface roughness of a rubber compound was observed visually to evaluate the surface roughness under the following criteria.

◯: Surface is smooth and edges are also smooth.
Δ: Surface is rough and edges are waved (forming into a sheet is possible).
X: Surface roughness is significant and forming into a sheet is difficult.

(Wet Grip Index)

[0281] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (low temperature tan δ) of each vulcanized rubber sheet at 0° C. was measured at an initial strain of 10%, a dynamic strain of 0.1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a wet grip index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The higher the low temperature tan δ value is and the larger the wet grip index is, the more excellent the wet grip performance is and the higher the safety in running is.

(Wet grip index)=(tan δ of each formulation)/(tan δ of Reference Comparative Example)×100

(Fuel Efficiency Index)

[0282] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (high temperature tan δ) of each vulcanized rubber sheet at 70° C. was measured at an initial strain of 10%, a dynamic strain of 1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a fuel efficiency index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The lower the high temperature tan δ value is and the larger the fuel efficiency index is, the more excellent the fuel efficiency is.

(Index of fuel efficiency)=(tan δ of Reference Comparative Example)/(tan δ of each formulation)×100

(Abrasion Resistance Index)

[0283] An abrasion loss of each vulcanized rubber composition was measured with a Lambourn abrasion testing machine under the conditions of a room temperature, a load of 1.0 kgf, and a slip rate of 30%. Assuming that an abrasion resistance index of a reference comparative example was 100, an abrasion loss of each formulation was obtained by the following equation and was indicated by an index. The smaller the abrasion loss is and the larger the abrasion resistance index is, abrasion resistance is excellent.

(Abrasion resistance index)=(Abrasion loss of Reference Comparative Example)/(Abrasion loss of each formulation)×100

(Results)

[0284] The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Comparative Example Example 18 19 20 21 14 15 16 17 Compounded amount (part by mass) Step I S-SBR 100 100 100 100 100 100 100 100 Silica A 80 80 80 80 80 80 80 80 Carbon black 10 10 10 10 10 10 10 10 Organoaluminum compound 20 20 20 20 20 20 20 20 Oil 30 30 30 30 30 30 30 30 Silane coupling agent A 8 8 8 8 8 8 8 8 Stearic acid 2 2 2 2 2 2 2 2 Step II Antioxidant 2 2 2 2 2 2 2 2 Wax 2 2 2 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 Vulcanization accelerator B 2 2 2 2 2 2 2 2 Basic vulcanization accelerator 2 2 2 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Step I Discharge temperature (° C.) 150 130 190 170 150 170 150 170 Holding time (sec) 0 30 15 200 15 15 100 100 Evaluation Processability ∘ ∘ x x ∘ ∘ ∘ ∘ Wet grip index (low temp. tanδ) 100 90 105 103 105 107 107 110 Fuel efficiency index (high temp. tanδ) 100 90 107 105 102 103 105 107 Abrasion resistance index 100 85 107 105 102 105 107 110

Fifth Embodiment

[0285] Examples 18 to 20 and Comparative Example 22 relating to the fifth embodiment are shown below.

<Preparation of Rubber Composition for Tire>

(First Stage at Former Stage of Kneading Step)

[0286] Kneading was performed at a discharge temperature of 160° C. for five minutes in accordance with the formulations shown in Table 5 using a 1.7 liter Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. In Table 5, with respect to the basic vulcanization accelerator to be introduced at the first stage of the former stage of the kneading step, “introduction in the former half” means introduction of the basic vulcanization accelerator together with the filler and the organoaluminum compound. On the other hand, “introduction in the latter half” means introduction of the basic vulcanization accelerator after an electric power has reached a first peak after introduction of the filler and the organoaluminum compound. In the kneading step, usually an electric power—time curve has two peaks after introduction of the rubber component and the filler, and the first peak is a first peak of the two peaks.

(Second Stage at Former Stage of Kneading Step)

[0287] Subsequently, each chemical was added to the obtained kneaded product in accordance with the formulation shown in Table 5, followed by kneading at a discharge temperature of 150° C. for four minutes using a 1.7 liter Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product.

(Latter Stage of Kneading Step)

[0288] Subsequently, each chemical was added to the obtained kneaded product in accordance with the formulation shown in Table 5, followed by kneading at 80° C. for five minutes using an open roll to obtain an unvulcanized rubber composition.

(Vulcanizing Step)

[0289] The obtained unvulcanized rubber composition was subjected to vulcanization at 170° C. for 20 minutes to obtain a vulcanized rubber composition.

<Evaluation>

(Wet Grip Index)

[0290] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (low temperature tan δ) of each vulcanized rubber sheet at 0° C. was measured at an initial strain of 10%, a dynamic strain of 0.1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a wet grip index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The higher the low temperature tan δ value is and the larger the wet grip index is, the higher the wet grip performance and safety in running are.

(Wet grip index)=(tan δ of each formulation)/(tan δ of Reference Comparative Example)×100

(Fuel Efficiency Index)

[0291] A test piece was cut out from each of the vulcanized rubber compositions and a loss tangent (high temperature tan δ) of each vulcanized rubber sheet at 70° C. was measured at an initial strain of 10%, a dynamic strain of 1% and a frequency of 10 Hz using a viscoelasticity spectrometer manufactured by Ueshima Seisakusho Co., Ltd. Assuming that a fuel efficiency index of a reference comparative example was 100, tan δ of each formulation was obtained by the following equation and was indicated by an index. The lower the high temperature tan δ value is and the larger the fuel efficiency index is, the more excellent the fuel efficiency is.

(Index of fuel efficiency)=(tan δ of Reference Comparative Example)/(tan δ of each formulation)×100

(Abrasion Resistance Index)

[0292] An abrasion loss of each vulcanized rubber composition was measured with a Lambourn abrasion testing machine under the conditions of a room temperature, a load of 1.0 kgf, and a slip rate of 30%. Assuming that an abrasion resistance index of a reference comparative example was 100, an abrasion loss of each formulation was obtained by the following equation and was indicated by an index. The smaller the abrasion loss is and the larger the abrasion resistance index is, the more excellent the abrasion resistance is.

(Abrasion resistance index)=(Abrasion loss of Reference Comparative Example)/(Abrasion loss of each formulation)×100

(Results)

[0293] The results are shown in Table 5.

TABLE-US-00005 TABLE 5 Com. Ex. Example 22 18 19 20 Compounded amount (part by mass) Kneading step Former stage First stage S-SBR 100 100 100 100 Silica A 60 60 60 60 Carbon black 10 10 10 10 Organoaluminum compound 20 20 20 20 Oil 40 40 40 40 Silane coupling agent A 6 6 6 6 Basic vulcanization accelerator — 2 — — (introduction in the former half) Basic vulcanization accelerator 2 (introduction in the latter half) Second stage Silica A 20 20 20 20 Silane coupling agent A 2 2 2 2 Oil 10 10 10 10 Basic vulcanization accelerator — — — 2 Stearic acid 2 2 2 2 Latter stage Antioxidant 2 2 2 2 Wax 2 2 2 2 Zinc oxide 2 2 2 2 Basic vulcanization accelerator 2 — — — Vulcanization accelerator B 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 Evaluation Wet grip index (low temp. tanδ) 100 100 100 102 Fuel efficiency index (high temp. tanδ) 100 101 103 107 Abrasion resistance index 100 102 105 110