Organic silicon compound, and additive for rubber and rubber composition using same

Abstract

Provided is an organic silicon compound represented by formula (1), which when added to a rubber composition, can improve the wet traction performance of a cured product of the rubber composition, and significantly reduce a hysteresis loss of the cured product, and provides a rubber composition that can be used to implement a desired tire having high fuel efficiency. ##STR00001##
(In the formula, each R.sup.1 independently represents an alkyl group having 1-10 carbon atoms or an aryl group having 6-10 carbon atoms, each R.sup.2 independently represents an alkyl group having 1-10 carbon atoms or an aryl group having 6-10 carbon atoms, f represents a number equal to or larger than 0, e, g, and h each independently represent a number equal to or larger than 0, and m represents an integer of 1-3. Note that the repeating units can be present in any order.)

Claims

1. A rubber compounding ingredient comprising an organosilicon compound having formula (1) having a number-average molecular weight of 10,500 to 40,000, ##STR00007## wherein each R.sup.1 is independently an alkyl group of 1 to 10 carbon atoms or an aryl group of 6 to 10 carbon atoms, each R.sup.2 is independently an alkyl group of 1 to 10 carbon atoms or an aryl group of 6 to 10 carbon atoms, f is a number of 0 or more, e, g and h are each independently a number larger than 0, and m is an integer from 1 to 3, with the proviso that individual recurring units are arranged in any order, and a sulfide group-containing organosilicon compound.

2. A method for producing an organosilicon compound having formula (1) having a number-average molecular weight of 10,500 to 40,000, ##STR00008## wherein each R.sup.1 is independently an alkyl group of 1 to 10 carbon atoms or an aryl group of 6 to 10 carbon atoms, each R.sup.2 is independently an alkyl group of 1 to 10 carbon atoms or an aryl group of 6 to 10 carbon atoms, f is a number of 0 or more, e, g and h are each independently a number larger than 0, and m is an integer from 1 to 3, with the proviso that individual recurring units are arranged in any order, comprising the step of carrying out hydrosilylation between a butadiene-styrene copolymer of formula (2) ##STR00009## wherein e, f, g and h are as defined above, and an organosilicon compound of formula (3) ##STR00010## wherein R.sup.1, R.sup.2 and m are as defined above, in the presence of a platinum compound-containing catalyst and an optional co-catalyst.

3. The organosilicon compound production method of claim 2, wherein the co-catalyst is an ammonium salt of an inorganic acid, an acid amide compound or a carboxylic acid.

4. The organosilicon compound production method of claim 3, wherein the ammonium salt of an inorganic acid is one or more selected from the group consisting of ammonium carbonate and ammonium bicarbonate.

5. The organosilicon compound production method of claim 3, wherein the acid amide compound is one or more selected from the group consisting of formamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, acrylamide, malonamide, succinamide, maleamide, fumaramide, benzamide, phthalamide, palmitamide and stearamide.

6. The organosilicon compound production method of claim 3, wherein the carboxylic acid is acetic acid.

7. The rubber compounding ingredient of claim 1 which further comprises at least one type of powder, wherein the weight ratio of the combined amount (A) of the organosilicon compound and the sulfide group-containing organosilicon compound with respect to the powder content (B) satisfies the condition (A)/(B)=70/30 to 5/95.

8. A rubber composition comprising the rubber compounding ingredient of claim 1.

9. A tire obtained by molding the rubber composition of claim 8.

Description

EXAMPLES

(1) The invention is illustrated more fully below by way of Working Examples and Comparative Examples, although the invention is not limited by these Examples.

(2) All references to “parts” below stand for parts by weight. The molecular weight is the polystyrene-equivalent number-average molecular weight obtained by measurement using gel permeation chromatography (GPC). The viscosity is the value measured at 25° C. using a rotational viscometer.

(3) [1] Production of Organosilane Compounds

Working Example 1-1

(4) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of Ricon 181 (from Cray Valley; number-average molecular weight, 7,100; in above formula (2), e=52, (f+g)=22 and h=29), 200 g of toluene, a toluene solution of platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (amount in terms of platinum atoms, 3.1×10.sup.−3 mole), and 0.2 g (3.1×10.sup.−3 mole) of ammonium bicarbonate. Next, 51 g (0.31 mole) of triethoxysilane was added dropwise over 2 hours at an internal temperature of 75 to 85° C., following which the system was stirred at 80° C. for 1 hour. Results for percent conversion of triethoxysilane, as determined by gas chromatographic analysis, are shown in Table 1.

(5) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 8,000 mPa.Math.s and a number-average molecular weight of 10,500. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=0, g=22 and h=29.

Working Example 1-2

(6) Aside from changing the ammonium bicarbonate to 0.2 g (1.5×10.sup.−3 mole) of acetic acid, reaction and work-up were carried out in the same way as in Working Example 1-1, giving a clear brown liquid having a viscosity of 8,000 mPa.Math.s and a number-average molecular weight of 10,500. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=0, g=22 and h=29.

(7) Results for percent conversion of triethoxysilane, as determined by gas chromatographic analysis, are shown in Table 1.

Working Example 1-3

(8) Aside from changing the ammonium bicarbonate to 0.2 g (1.5×10.sup.−3 mole) of acetamide, reaction and work-up were carried out in the same way as in Working Example 1-1, giving a clear brown liquid having a viscosity of 8,000 mPa.Math.s and a number-average molecular weight of 10,500. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=0, g=22 and h=29.

(9) Results for percent conversion of triethoxysilane, as determined by gas chromatographic analysis, are shown in Table 1.

Working Example 1-4

(10) Aside from excluding ammonium bicarbonate, reaction and work-up were carried out in the same way as in Working Example 1-1, giving a clear brown liquid having a viscosity of 14,000 mPa.Math.s and a number-average molecular weight of 7,100. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=21.8, g=0.2 and h=29.

(11) Results for percent conversion of triethoxysilane, as determined by gas chromatographic analysis, are shown in Table 1.

(12) TABLE-US-00001 TABLE 1 Working Example 1-1 1-2 1-3 1-4 Co-catalyst ammonium bicarbonate acetic acid acetamide none Conversion (%) 98 98 98 1

(13) As shown in Table 1, by using an ammonium salt of an inorganic acid, a carboxylic acid or an acid amide compound as the co-catalyst, the reaction proceeds more efficiently.

Working Example 1-5

(14) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of Ricon 181 (from Cray Valley; number-average molecular weight, 7,100; in above formula (2), e=52, (f+g)=22, h=29), 200 g of toluene, a toluene solution of platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (amount in terms of platinum atoms, 1.5×10.sup.−3 mole), and 0.1 g (1.5×10.sup.−3 mole) of acetic acid. Next, 25 g (0.15 mole) of triethoxysilane was added dropwise over 2 hours at an internal temperature of 75 to 85° C., following which the system was stirred at 80° C. for 1 hour.

(15) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 10,500 mPa.Math.s and a number-average molecular weight of 8,800. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=11, g=11 and h=29.

Working Example 1-6

(16) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of Ricon 181 (from Cray Valley; number-average molecular weight, 7,100; in above formula (2), e=52, (f+g)=22, h=29), 200 g of toluene, a toluene solution of platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (amount in terms of platinum atoms, 1.0×10.sup.−3 mole), and 0.07 g of acetic acid (1.0×10.sup.−3 mole). Next, 17 g (0.10 mole) of triethoxysilane was added dropwise over 2 hours at an internal temperature of 75 to 85° C., following which the system was stirred at 80° C. for 1 hour.

(17) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 11,500 mPa.Math.s and a number-average molecular weight of 8,200. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=15, g=7 and h=29.

Working Example 1-7

(18) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of Ricon 181 (from Cray Valley; number-average molecular weight, 7,100; in above formula (2), e=52, (f+g)=22, h=29), 200 g of toluene, a toluene solution of platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (amount in terms of platinum atoms, 0.5×10.sup.−3 mole), and 0.04 g (0.5×10.sup.−3 mole) of acetic acid. Next, 8 g (0.05 mole) of triethoxysilane was added dropwise over 2 hours at an internal temperature of 75 to 85° C., following which the system was stirred at 80° C. for 1 hour.

(19) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 12,500 mPa.Math.s and a number-average molecular weight of 7,500. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=52, f=19, g=3 and h=29.

Working Example 1-8

(20) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of Ricon 184 (from Cray Valley; number-average molecular weight, 17,000; in above formula (2), e=126, (f+g)=54, h=70), 200 g of toluene, a toluene solution of platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (amount in terms of platinum atoms, 3.1×10.sup.−3 mole), and 0.2 g (3.1×10.sup.−3 mole) of acetic acid. Next, 51 g (0.31 mole) of triethoxysilane was added dropwise over 2 hours at an internal temperature of 75 to 85° C., following which the system was stirred at 80° C. for 1 hour.

(21) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 38,000 mPa.Math.s and a number-average molecular weight of 25,000. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=126, f=0, g=54 and h=70.

Working Example 1-9

(22) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of Ricon 184 (from Cray Valley; number-average molecular weight, 17,000; in above formula (2), e=126, (f+g)=54, h=70), 200 g of toluene, a toluene solution of platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (amount in terms of platinum atoms, 1.5×10.sup.−3 mole), and 0.1 g (1.5×10.sup.−3 mole) of acetic acid. Next, 25 g (0.15 mole) of triethoxysilane was added dropwise over 2 hours at an internal temperature of 75 to 85° C., following which the system was stirred at 80° C. for 1 hour.

(23) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 45,000 mPa.Math.s and a number-average molecular weight of 21,000. The product, based on its molecular weight and the average structure as determined from the .sup.1H-NMR spectrum, was an organosilicon compound of above formula (1) in which e=126, f=27, g=27 and h=70.

Comparative Example 1-1

(24) Referring to JP-A 2005-250603, an organosilicon compound was synthesized by the following method.

(25) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of R-45H (from Idemitsu Kosan Co., Ltd.; number-average molecular weight, 2,800), 18 g of KBE-9007 (Shin-Etsu Chemical Co., Ltd.; 3-isocyanatopropyltriethoxysilane) and 0.5 g of dioctyltin oxide catalyst (Tokyo Chemical Industry Co., Ltd.), and the flask contents were stirred at an internal temperature of 60° C. for 2 hours.

(26) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 8,000 mPa.Math.s and a number-average molecular weight of 3,300.

Comparative Example 1-2

(27) Referring to JP-A S62-265301, an organosilicon compound was synthesized by the following method.

(28) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of B-1000 (Nippon Soda Co., Ltd.), 200 g of toluene and 129 g (0.8 mole) of 3-mercaptopropyltriethoxysilane, and the flask contents were stirred at an internal temperature of 100° C. for 4 hours.

(29) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 5,000 mPa.Math.s and a number-average molecular weight of 2,000.

Comparative Example 1-3

(30) Referring to JP-A S62-265301, an organosilicon compound was synthesized by the following method.

(31) A one-liter separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer was charged with 100 g of B-1000 (Nippon Soda Co., Ltd.), 200 g of toluene and 23 g (0.1 mole) of 3-mercaptopropyltriethoxysilane, and the flask contents were stirred at an internal temperature of 100° C. for 4 hours.

(32) Following the completion of stirring, vacuum condensation and filtration were carried out, giving a clear brown liquid having a viscosity of 900 mPa.Math.s and a number-average molecular weight of 1,600.

(33) [2] Preparation of Rubber Compositions

Working Examples 2-1 to 2-3

(34) A masterbatch was prepared by blending together, as shown in Table 2: 110 parts of the oil-extended emulsion polymer SBR (#1712, from JSR Corporation), 20 parts of NR (RSS #3 grade), 20 parts of carbon black (N234 grade), 50 parts of silica (Nipsil AQ, from Nippon Silica Industries), 6.5 parts of the organosilicon compound obtained in Working Example 1-2 or a combined amount of 6.5 parts of this organosilicon compound and KBE-846 (Shin-Etsu Chemical Co., Ltd.; bis(triethoxysilylpropyl)tetrasulfide), 1 part of stearic acid and 1 part of the antidegradant 6C (Nocrac 6C, from Ouchi Shinko Chemical Industry Co., Ltd.).

(35) To this were added 3 parts of zinc white, 0.5 part of the vulcanization accelerator DM (dibenzothiazyl disulfide), 1 part of the vulcanization accelerator NS (N-t-butyl-2-benzothiazolyl sulfenamide) and 1.5 parts of sulfur, and kneading was carried out, giving a rubber composition.

Working Examples 2-4 to 2-8

(36) Aside from changing, as shown in Table 2, the organosilicon compound obtained in Working Example 1-2 to the respective organosilicon compounds obtained in Working Examples 1-5 to 1-9, rubber compositions were obtained in the same way as in Working Example 2-3.

Comparative Examples 2-1 to 2-3

(37) Aside from changing, as shown in Table 3, the organosilicon compound obtained in Working Example 1-2 to the respective organosilicon compounds obtained in Comparative Examples 1-1 to 1-3, rubber compositions were obtained in the same way as in Working Example 2-3.

Comparative Example 2-4

(38) Aside from changing, as shown in Table 3, the organosilicon compound obtained in Working Example 1-2 to KBE-846, a rubber composition was obtained in the same way as in Working Example 2-1.

(39) The properties of the rubber compositions obtained in Working Examples 2-1 to 2-8 and Comparative Examples 2-1 to 2-4, both in the unvulcanized form and the vulcanized form, were measured by the following methods. The results are shown in Tables 2 and 3.

(40) [Properties of Unvulcanized Compositions]

(41) (1) Mooney Viscosity

(42) Measured in accordance with JIS K 6300 after allowing 1 minute for sample to reach thermal equilibrium with viscometer; measurement was carried out for 4 minutes at 130° C. The results are expressed as numbers relative to an arbitrary value of 100 for the result obtained in Comparative Example 2-4. A smaller number indicates a lower Mooney viscosity and thus a better processability.

(43) [Properties of Vulcanized Compositions]

(44) (2) Dynamic Viscoelasticity

(45) Using a viscoelastic tester (Rheometrics), measurement was carried out at 5% dynamic strain under tension, a frequency of 15 Hz, and at 0° C. and 60° C. Using sheets having a thickness of 0.2 cm and a width of 0.5 cm as the test specimens, the clamping interval in the tester was set to 2 cm and the initial load was set to 160 g. The tan δ values are expressed as numbers relative to an arbitrary value of 100 for the result in Comparative Example 2-4. A larger value at 0° C. indicates a better wet grip performance. A smaller value at 60° C. indicates a smaller hysteresis loss and lower heat buildup.

(46) (3) Wear Resistance

(47) Testing was carried out in general accordance with JIS K 6264-2: 2005 using a Lambourn abrasion tester under the following conditions: room temperature, 25% slip ratio. The results are expressed as numbers relative to an arbitrary value of 100 for the result in Comparative Example 2-4. A larger number indicates a lower abrasion loss and a better wear resistance.

(48) TABLE-US-00002 TABLE 2 Working Example Formulation (pbw) 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 SBR 110 110 110 110 110 110 110 110 NR 20 20 20 20 20 20 20 20 Carbon black 20 20 20 20 20 20 20 20 Silica 50 50 50 50 50 50 50 50 Organosilicon Working Example 1-2 6.5 3.3 1.6 — — — — — compound Working Example 1-5 — — — 1.6 — — — — Working Example 1-6 — — — — 1.6 — — — Working Example 1-7 — — — — — 1.6 — — Working Example 1-8 — — — — — — 1.6 — Working Example 1-9 — — — — — — — 1.6 KBE-846 — 3.2 4.9 4.9 4.9 4.9 4.9 4.9 Stearic acid 1 1 1 1 1 1 1 1 Antidegradant 6C 1 1 1 1 1 1 1 1 Zinc white 3 3 3 3 3 3 3 3 Vulcanization accelerator DM 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Vulcanization accelerator NS 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 [Properties of unvulcanized composition] Mooney viscosity 99 98 96 99 98 99 98 98 [Properties of vulcanized composition] Dynamic viscoelasticity tan δ (0° C.) 100 106 106 112 108 103 105 108 Dynamic viscoelasticity tan δ (60° C.) 98 85 83 88 93 97 93 93 Wear resistance 100 104 105 105 105 104 103 103

(49) TABLE-US-00003 TABLE 3 Comparative Example Formulation (pbw) 2-1 2-2 2-3 2-4 SBR 110 110 110 110 NR 20 20 20 20 Carbon black 20 20 20 20 Silica 50 50 50 50 Organosilicon Comparative Example 1-1 1.6 — — — compound Comparative Example 1-2 — 1.6 — — Comparative Example 1-3 — — 1.6 — KBE-846 4.9 4.9 4.9 6.5 Stearic acid 1 1 1 1 Antidegradant 6C 1 1 1 1 Zinc white 3 3 3 3 Vulcanization accelerator DM 0.5 0.5 0.5 0.5 Vulcanization accelerator NS 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 [Properties of unvulcanized composition] Mooney viscosity 99 103 102 100 [Properties of vulcanized composition] Dynamic viscoelasticity tan δ (0° C.) 100 101 99 100 Dynamic viscoelasticity tan δ (60° C.) 103 105 109 100 Wear resistance 85 89 87 100

(50) It is apparent from Tables 2 and 3 that, compared with the rubber compositions of Comparative Examples 2-2 to 2-4, each of the rubber compositions of Working Examples 2-1 to 2-8 has a low Mooney viscosities and an excellent processability.

(51) It is also apparent that, compared to the vulcanized rubber compositions of Comparative Examples 2-1 to 2-4, each of the vulcanized rubber compositions of Working Examples 2-1 to 2-8 has an excellent wet grip performance, a low heat buildup, and moreover an excellent wear resistance.

Working Examples 2-9 to 2-11

(52) A masterbatch was prepared by blending together, as shown in Table 4: 100 parts of NR (RSS #3 grade), 38 parts of process oil, 5 parts of carbon black (N234 grade), 105 parts of silica (Nipsil AQ, from Nippon Silica Industries), 8.4 parts of the organosilicon compound obtained in Working Example 1-2 or a combined amount of 8.4 parts of this organosilicon compound and KBE-846 (Shin-Etsu Chemical Co., Ltd.; bis(triethoxysilylpropyl)tetrasulfide), 2 parts of stearic acid and 2 parts of the antidegradant 6C (Nocrac 6C, from Ouchi Shinko Chemical Industry Co., Ltd.).

(53) To this were added 2 parts of zinc white, 3 parts of the vulcanization accelerator CZ (Nocceler CZ, from Ouchi Shinko Chemical Industry Co., Ltd.; N-cyclohexyl-2-benzothiazolyl sulfenamide) and 2 parts of sulfur, and kneading was carried out, giving a rubber composition.

Working Examples 2-12 to 2-16

(54) Aside from changing, as shown in Table 4, the organosilicon compound obtained in Working Example 1-2 to the respective organosilicon compounds obtained in Working Examples 1-5 to 1-9, rubber compositions were obtained in the same way as in Working Example 2-11.

Comparative Examples 2-5 to 2-7

(55) Aside from changing, as shown in Table 5, the organosilicon compound obtained in Working Example 1-2 to the respective organosilicon compounds obtained in Comparative Examples 1-1 to 1-3, rubber compositions were obtained in the same way as in Working Example 2-11.

Comparative Example 2-8

(56) Aside from changing, as shown in Table 5, the organosilicon compound obtained in Working Example 1-2 to KBE-846, a rubber composition was obtained in the same way as in Working Example 2-9.

(57) Next, the properties of the rubber composition when unvulcanized (Mooney viscosity) and when vulcanized (dynamic viscoelasticity, wear resistance) were measured in the same way as described above. The results, expressed as numbers relative to an arbitrary value of 100 for the result obtained in Comparative Example 2-8, are shown in Tables 4 and 5.

(58) TABLE-US-00004 TABLE 4 Working Example Formulation (pbw) 2-9 2-10 2-11 2-12 2-13 2-14 2-15 2-16 NR 100 100 100 100 100 100 100 100 Process oil 38 38 38 38 38 38 38 38 Carbon black 5 5 5 5 5 5 5 5 Silica 105 105 105 105 105 105 105 105 Organosilicon Working Example 1-2 8.4 4.2 2.1 — — — — — compound Working Example 1-5 — — — 2.1 — — — — Working Example 1-6 — — — — 2.1 — — — Working Example 1-7 — — — — — 2.1 — — Working Example 1-8 — — — — — — 2.1 — Working Example 1-9 — — — — — — — 2.1 KBE-846 — 4.2 6.3 6.3 6.3 6.3 6.3 6.3 Stearic acid 2 2 2 2 2 2 2 2 Antidegradant 6C 2 2 2 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 Vulcanization accelerator CZ 3 3 3 3 3 3 3 3 Sulfur 2 2 2 2 2 2 2 2 [Properties of unvulcanized composition] Mooney viscosity 100 100 101 101 98 100 100 100 [Properties of vulcanized composition] Dynamic viscoelasticity tan δ (60° C.) 98 96 96 97 96 99 96 96 Wear resistance 110 111 109 108 108 102 107 106

(59) TABLE-US-00005 TABLE 5 Comparative Example Formulation (pbw) 2-5 2-6 2-7 2-8 NR 100 100 100 100 Process oil 38 38 38 38 Carbon black 5 5 5 5 Silica 105 105 105 105 Organosilicon Comparative Example 1-1 2.1 — — — compound Comparative Example 1-2 — 2.1 — — Comparative Example 1-3 — — 2.1 — KBE-846 6.3 6.3 6.3 8.4 Stearic acid 2 2 2 2 Antidegradant 6C 2 2 2 2 Zinc white 2 2 2 2 Vulcanization accelerator CZ 3 3 3 3 Sulfur 2 2 2 2 [Properties of unvulcanized composition] Mooney viscosity 101 102 105 100 [Properties of vulcanized composition] Dynamic viscoelasticity tan δ (60° C.) 108 108 110 100 Wear resistance 90 87 90 100

(60) It is apparent from Tables 4 and 5 that, compared with the vulcanized rubber compositions of Comparative Examples 2-5 to 2-8, each of the vulcanized rubber compositions of Working Examples 2-9 to 2-16 has a low dynamic viscoelasticity, i.e., the hysteresis loss is small and heat buildup is low, and moreover has an excellent wear resistance.