Rubber composition having improved wet skid resistance and rolling resistance

A rubber composition comprising (i) 100 parts by weight of a rubber and (ii) 10 to 180 parts by weight of a composite composed of an oxidative condensate obtained by oxidative condensation of a &pgr;-electron aromatic compound and carbon black and a pneumatic tire using the same as a tire tread.

EXAMPLES The present invention will now be further illustrated by, but is by no means limited to, the following Examples. 
 Examples 1 to 22 and Comparative Examples 1 to 2 Rubber compositions containing mixtures of the composites of the present invention (Composites 1 to 11) produced by the production process shown below and, as a comparison, carbon black (N339, N 2 SA&equals;92 m 2 /g) in the ratios (parts by weight) shown in Table 1 and Table 2 were produced, then vulcanized at 160° C. for 20 minutes. The unvulcanized rubber compositions and vulcanized rubber compositions were tested as follows. The results are shown in Table 1 and Table 2. Production of Composite 1 (Aniline Oxidative Condensate/Carbon Black Composite) 5 g of aniline (53.7 mmol), 5.6 g of hydrochloric acid (53.7 mmol), and 40 mg of ferrous sulfate were dissolved in 80 g of water. 100 g of carbon black (N339) was treated on the surface with this aniline aqueous solution, then the surface of the carbon black was treated with 20 g of water in which 5.2 g of hydrogen peroxide (53.7 mmol) was dissolved. The surface treated carbon black was dried at 110° C. for 24 hours to thereby obtain a composite of an aniline oxidative condensate and carbon black. Production of Composite 2 (Aniline Oxidative Condensate/Carbon Black Composite) 5 g of aniline (53.7 mmol), 5.6 g of hydrochloric acid (53.7 mmol), 5.1 g of p-toluene sulfonic acid (26.8 mmol), and 40 mg of ferrous sulfate were dissolved in 80 g of water. 100 g of carbon black (N339) was treated on the surface with this aniline aqueous solution, then the surface of the carbon black was treated with 20 g of water in which 5.2 g of hydrogen peroxide (53.7 mmol) was dissolved. The surface treated carbon black was dried at 110° C. for 24 hours to thereby obtain a composite of an aniline oxidative condensate and carbon black. Production of Composite 3 (Aniline oxidative Condensate/Carbon Black Composite) 5 g of aniline (53.7 mmol), 5.6 g of hydrochloric acid (53.7 mmol), 7.8 g of sodium dodecylsulfonate (26.8 mmol), and 40 mg of ferrous sulfate were dissolved in 80 g of water. 100 g of carbon black (N339) was treated on the surface with this aniline aqueous solution, then the surface of the carbon black was treated with 20 g of water in which 5.2 g of hydrogen peroxide (53.7 mmol) was dissolved. The surface treated carbon black was dried at 110° C. for 24 hours to thereby obtain a composite of an aniline oxidative condensate and carbon black. Production of Composite 4 (Aniline Oxidative Condensate/Carbon Black Composite) 5 g of aniline (53.7 mmol), 5.6 g of hydrochloric acid (53.7 mmol), 5.1 g of p-toluenesulfonic acid (26.8 mmol), and 40 mg of ferrous sulfate were dissolved in 100 g of water at 70° C. 5.2 g of hydrogen peroxide (53.7 mmol) was added to the aniline aqueous solution, then this was stirred at 70° C. for 4 hours to thereby obtain an aqueous solution in which the aniline oxidative condensate was uniformly dispersed. 100 g of carbon black (N339) was treated on the surface with this aqueous solution containing the aniline oxidative condensate, then was dried at 110° C. for 24 hours. The above procedure resulted in a composite of an aniline oxidative condensate and carbon black. Production of Composite 5 (Aniline Oxidative Condensate/Carbon Black Composite) 5 g of aniline (53.7 mmol), 5.6 g of hydrochloric acid (53.7 mmol), 7.8 g of sodium dodecylsulfonate (26.8 mmol), and 40 mg of ferrous sulfate were dissolved in 100 g of water at 70° C. 5.2 g of hydrogen peroxide (53.7 mmol) was added to the aniline aqueous solution, then this was stirred at 70° C. for 4 hours to thereby obtain an aqueous solution in which the aniline oxidative condensate was uniformly dispersed. 100 g of carbon black (N339) was treated on the surface with this aqueous solution containing the aniline oxidative condensate, then was dried at 110° C. for 24 hours. The above procedure resulted in a composite of an aniline oxidative condensate and carbon black. Production of Composite 6 (Aniline Oxidative Condensate/Carbon Black Composite) 100 g of carbon black (N339) was treated on the surface with 100 g of an aqueous solution containing aniline black homogeneously dispersed, comprised of 5 g of aniline (made by Tokyo Shikizai Kogyo, No. 25 Aniline Black) and 100 g of water, then was dried at 110° C. for 24 hours. The above procedure resulted in a composite of aniline black (aniline oxidative condensate) and carbon black. Production of Composite 7 (Aniline Oxidative Condensate (Polyaniline)/Carbon Black Composite) 100 g of carbon black (N339) was treated on the surface with 100 g of a polyaniline aqueous solution (5% by weight polyaniline sulfonate aqueous solution made by Aldrichs), then was dried at 110° C. for 24 hours. The above procedure resulted in a composite of an aniline oxidative condensate (polyaniline) and carbon black. Production of Composite 8 (Pyrrole Oxidative Condensate/Carbon Black Composite) 5 g of pyrrole (74.5 mmol), 6.5 g of sodium dodecylsulfonate (22.5 mmol), and 40 mg of ferrous sulfate were dissolved in 80 g of water. 100 g of carbon black (N339) was treated on the surface with this aqueous pyrrole solution, then the surface of the carbon black was treated with 20 g of water in which 7.2 g of hydrogen peroxide (74.5 mmol) was dissolved. The surface treated carbon black was dried at 110° C. for 24 hours to thereby obtain a composite of a pyrrole oxidative condensate and carbon black. Production of Composite 9 (Pyrrole Oxidative Condensate/Carbon Black Composite) 5 g of pyrrole (74.5 mmol), 6.5 g of sodium dodecylsulfonate (22.5 mmol), and 40 mg of ferrous sulfate were dissolved in 100 g of water at 70° C. 7.2 g of hydrogen peroxide (74.5 mmol) was added to the pyrrole aqueous solution, then this was stirred at 70° C. for 4 hours to thereby obtain an aqueous solution in which the pyrrole oxidative condensate was uniformly dispersed. 100 g of carbon black (N339) was treated on the surface with this aqueous solution containing the pyrrole oxidative condensate, then was dried at 110° C. for 24 hours. The above procedure resulted in a composite of a pyrrole oxidative condensate and carbon black. Production of Composite 10 (Thiophene Oxidative Condensate/Carbon Black Composite) 5 g of thiophene (59.4 mmol), 5.1 g of sodium dodecylsulfonate (17.7 mmol), and 40 mg of ferrous sulfate were dissolved in 80 g of water. 100 g of carbon black (N339) was treated on the surface with this thiophene aqueous solution, then the surface of the carbon black was treated with 20 g of water in which 5.8 g of hydrogen peroxide (59.4 mmol) was dissolved. The surface treated carbon black was dried at 110° C. for 24 hours to thereby obtain a composite of a thiophene oxidative condensate and carbon black. Production of Composite 11 (Thiophene Oxidative Condensate/Carbon Black Composite) 5 g of thiophene (53.7 mmol), 5.1 g of sodium dodecylsulfonate (17.7 mmol), and 40 mg of ferrous sulfate were dissolved in 100 g of water at 70° C. 5.8 g of hydrogen peroxide (59.4 mmol) was added to the thiophene aqueous solution, then this was stirred at 70° C. for 4 hours to thereby obtain an aqueous solution in which the thiophene oxidative condensate was uniformly dispersed. 100 g of carbon black (N339) was treated on the surface with this aqueous solution containing the thiophene oxidative condensate, then was dried at 110° C. for 24 hours. The above procedure resulted in a composite of a thiophene oxidative condensate and carbon black. Mooney Viscosity This was measured at 100° C. according to JIS K6300. The smaller the value, the more improved the processability and the better. Scorch Time This was measured at 125° C. according to JIS K6300. Vulcanization time The time (minutes) until reaching a vulcanization degree of 95% at 125° C. was measured according to JIS K6300 and made the vulcanization time. The smaller the vulcanization time, the faster the vulcanization speed. Tensile Properties The 100% modulus (MPa), 300% modulus (MPa), breakage strength (MPa), and elongation at break (%) were measured according to JIS K6251. tan&dgr; The viscoelastic properties at 0° C. and 60° C. were measured using a viscoelasticity spectrometer made by Toyo Seiki Seisakusho under conditions of an initial strain of 10%, an amplitude of 2%, and a frequency of 20 Hz. Abrasion Resistance The amount of abrasion loss as measured using a Lambourn abrasion tester (made by Iwamoto Seisakusho) under conditions of a load of 5 kg, a slip of 25%, a time of 4 minutes, and room temperature was shown indexed to Comparative Example 1 in Table 1 and Comparative Example 2 in Table 2 as 100. Note that the larger the value, the better the abrasion resistance indicated. 1 TABLE 1 Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 1 SBR 1 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 Composite 1 80 — — — — — — — — — — — Composite 2 — 80 — — — — — — — — — — Composite 3 — — 80 — — — — — — — — — Composite 4 — — — 80 — — — — — — — — Composite 5 — — — — 80 — — — — — — — Composite 6 — — — — — 80 — — — — — — Composite 7 — — — — — — 80 — — — — — Composite 8 — — — — — — — 80 — — — — Composite 9 — — — — — — — — 80 — — — Composite 10 — — — — — — — — — 80 — — Composite 11 — — — — — — — — — — 80 — Carbon black — — — — — — — — — — — 80 Zinc oxide 3 3 3 3 3 3 3 3 3 3 3 3 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Antioxidant 1 1 1 1 1 1 1 1 1 1 1 1 Aromatic oil 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator Sulfur 2 2 2 2 2 2 2 2 2 2 2 2 Mooney viscosity 52 53 51 54 49 48 52 50 54 53 52 53 Scorch time (min) 47 48 46 49 47 48 49 45 47 46 48 45 Vulcanization 11 12 13 10 11 13 11 12 13 11 10 12 time (min) Tensile properties 100% modulus (MPa) 2.3 2.4 2.3 2.3 2.4 2.5 2.4 2.3 2.2 2.1 2.3 2.1 300% modulus (MPa) 10.3 10.4 10.6 10.4 10.5 10.3 10.7 10.5 10.4 10.3 10.4 10.3 Tensile strength at 20.4 20.5 20.7 20.9 20.4 20.6 20.8 20.7 20.3 20.4 20.2 20.2 break (MPa) Elongation at 558 555 550 557 552 553 551 554 554 550 549 551 break (%) tan&dgr; (0° C.) 0.479 0.480 0.478 0.481 0.483 0.478 0.482 0.478 0.479 0.480 0.481 0.478 tan&dgr; (60° C.) 0.242 0.240 0.245 0.246 0.239 0.244 0.241 0.242 0.239 0.240 0.242 0.294 Abrasion resistance 103 104 102 103 104 105 103 100 101 103 104 100 (index) 2 TABLE 2 Comp. Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20 Ex. 21 Ex. 22 Ex. 2 SBR 2 50 50 50 50 50 50 50 50 50 50 50 50 Natural rubber 50 50 50 50 50 50 50 50 50 50 50 50 Composite 1 50 — — — — — — — — — — — Composite 2 — 50 — — — — — — — — — — Composite 3 — — 50 — — — — — — — — — Composite 4 — — — 50 — — — — — — — — Composite 5 — — — — 50 — — — — — — — Composite 6 — — — — — 50 — — — — — — Composite 7 — — — — — — 50 — — — — — Composite 8 — — — — — — — 50 — — — — Composite 9 — — — — — — — — 50 — — — Composite 10 — — — — — — — — — 50 — — Composite 11 — — — — — — — — — — 50 — Carbon black — — — — — — — — — — — 50 Zinc oxide 3 3 3 3 3 3 3 3 3 3 3 3 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Antioxidant 1 1 1 1 1 1 1 1 1 1 1 1 Aromatic oil 50 50 50 50 50 50 50 50 50 50 50 50 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator Sulfur 2 2 2 2 2 2 2 2 2 2 2 2 Mooney viscosity 56 57 55 56 58 57 55 58 57 56 57 58 Scorch time (min) 23 25 23 22 23 24 25 22 23 24 25 22 Vulcanization 10 9 10 10 11 9 10 10 8 9 10 10 time (min) Tensile properties 100% modulus (MPa) 3.4 3.3 3.4 3.4 3.5 3.3 3.4 3.3 3.2 3.3 3.5 3.3 300% modulus (MPa) 14.8 14.9 14.8 15 14.8 14.9 15.1 15.2 15 15 14.9 14.9 Tensile strength at 22.3 22.6 22.4 22.5 22.7 22.4 22.8 22.9 22.8 23 22.7 22.5 break (MPa) Elongation at 430 432 425 429 430 432 428 430 429 432 435 427 break (%) tan&dgr; (0° C.) 0.587 0.586 0.588 0.589 0.586 0.587 0.587 0.587 0.588 0.586 0.586 0.586 tan&dgr; (60° C.) 0.148 0.145 0.152 0.149 0.147 0.146 0.145 0.153 0.142 0.143 0.149 0.182 Abrasion resistance 100 100 103 101 102 103 104 102 100 100 100 100 (index) The following were used for the components in Table 1 and Table 2: SBR 1: Solution polymerized SBR, Nipol 1712, made by Nippon Zeon, oil extended product containing 37.5 parts by weight of aromatic oil, based upon 100 parts by weight of rubber SBR 2: Solution polymerized SBR, Nipol 1712, made by Nippon Zeon Carbon black: Carbon Black N339, made by Tokai Carbon, nitrogen specific area (N 2 SA)&equals;92 m 2 /g Antioxidant: (N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine), made by Bayer. Vulcanization accelerator: N-cyclohexyl-2-benzothiazolylsulfenamide, made by Toyo Kagaku. From Table 1 and Table 2, it is clear that, compared with the rubber compositions, in which carbon black was compounded shown in Comparative Examples 1 and 2, the rubber compositions of Examples 1 to 22 including Composites 1 to 11 were reduced in the tan&dgr; (60° C.), while maintained or increased in the tan&dgr; (0° C.), and were improved in the low rolling resistance, without reducing the wet skid resistance. On the other hand, regarding the processability (Mooney viscosity and scorch time), tensile properties, and abrasion resistance, the rubber compositions of Examples 1 to 22 including Composites 1 to 11 maintained the properties of rubber compositions in which carbon black was blended shown in Comparative Examples 1 and 2 and were held down in terms of reduction of the mechanical properties. Further, Composites 1 to 11 could be easily produced without a complicated production process with a large number of production steps as with the above-mentioned conventional compounding agents. As explained above, according to the present invention, by compounding a composite composed of an oxidative condensate obtained by oxidative condensation of a &pgr;-electron aromatic compound and carbon black to a rubber composition, it is possible to obtain an excellent wet skid resistance and low rolling resistance by an easy-to-produce compounding agent. 
 Examples 23 to 30 and Comparative Example 3 Rubber compositions containing of mixtures of composites of &pgr;-conjugated polymer and carbon black (Composites 12 to 19) produced by the process of production shown below and carbon black and, as a comparison, carbon black in the ratios (parts by weight) shown in Table 3 were produced, then vulcanized at 160° C. for 20 minutes. These were tested as follows. The results are shown in Table 3. Production of Composite 12 (Polvaniline/Carbon Black Composite) 2 g of aniline (21.5 mmol), 2.24 g of hydrochloric acid (21.5 mmol), and 7.01 g of dodecylbenzenesulfonic acid (21.5 mmol) were added to 500 ml of water. 100 g of carbon black (N220) was added to the obtained aqueous solution while stirring vigorously. The solution was cooled to 5° C., then 5.89 g of ammonium persulfate (25.8 mmol) was added and the mixture stirred for 5 hours while keeping the reaction temperature below 10° C. After the end of the reaction, the black powder in the reaction solution was obtained by filtration and washed with water and methanol. The filtrate and the washings when filtering the composite comprised of the polyaniline and carbon black from the reaction solution did not exhibit the green coloring derived from polyaniline, so it was learned that the reaction was complete and the polyaniline in the doped state formed a composite with the carbon black quantitatively. Further, the composite obtained was dried at 80° C. for 8 hours to obtain a composite of polyaniline in the doped state and carbon black. The amount of the polyaniline in the composite was 2% by weight. Production of Composite 13 (Polvaniline/Carbon Black Composite) 2 g of aniline (21.5 mmol), 2.24 g of hydrochloric acid (21.5 mmol), and 7.01 g of dodecylbenzenesulfonic acid (21.5 mmol) were added to 500 ml of water. 100 g of carbon black (N220) was added to the obtained aqueous solution while stirring vigorously. The solution was cooled to 5° C., then 5.89 g of ammonium persulfate (25.8 mmol) was added. The mixture was stirred for 5 hours while keeping the reaction temperature below 10° C. After the end of the reaction, sodium carbonate powder was added until the reaction solution exhibited basicity by pH test paper, then the mixture was stirred for 4 hours. The black powder in the reaction solution was obtained by filtration and washed with water and methanol. The filtrate and the washings when filtering the composite comprised of the polyaniline and carbon black from the reaction solution did not exhibit the blue coloring derived from polyaniline in the undoped state, so it was learned that the reaction was complete and the polyaniline in the undoped state formed a composite with the carbon black quantitatively. Further, the composite obtained was dried at 80° C. for 8 hours to obtain a composite of polyaniline in the undoped state and carbon black. The amount of the polyaniline in the composite was 2% by weight. Production of Composite 14 (Polyaniline/Carbon Black Composite) The same procedure as with Composite 12 was followed to obtain a composite comprised of polyaniline and carbon black except for changing the amounts of the aniline, hydrochloric acid, dodecylbenzenesulfonic acid, and ammonium persulfate used for the production of Composite 12 to 5 g (53.7 mmol), 5.6 g (53.7 mmol), 17.5 g (53.7 mmol), and 14.7 g (64.4 mmol), respectively. The filtrate and the washings when filtering the composite comprised of the polyaniline and carbon black from the reaction solution did not exhibit the green coloring derived from polyaniline in the undoped state, so it was learned that the polyaniline in the doped state formed a composite with the carbon black quantitatively. Further, the composite obtained was dried at 80° C. for 8 hours to obtain a composite of polyaniline in the undoped state and carbon black. The amount of the polyaniline in the composite was 5% by weight. Production of Composite 15 (Polyaniline/Carbon Black Composite) The same procedure as with Composite 13 was followed to obtain a composite comprised of polyaniline and carbon black except for changing the amounts of the aniline, hydrochloric acid, dodecylbenzenesulfonic acid, and ammonium persulfate used for the production of Composite 13 to 5 g (53.7 mmol), 5.6 g (53.7 mmol), 17.5 g (53.7 mmol), and 14.7 g (64.4 mmol), respectively. The filtrate and the washings when filtering the composite comprised of the polyaniline and carbon black from the reaction solution did not exhibit the green coloring derived from polyaniline in the undoped state, so it was learned that the reaction was complete and the polyaniline in the undoped state formed a composite with the carbon black quantitatively. Further, the composite obtained was dried at 80° C. for 8 hours to obtain a composite of polyaniline in the undoped state and carbon black. The amount of the polyaniline in the composite was 5% by weight. Production of Composite 16 (Polyaniline/Carbon Black Composite) 2 g of aniline (21.5 mmol), 2.24 g of hydrochloric acid (21.5 mmol), and 6.19 g of sodium dodecylsulfonate (21.5 mmol) were added to 200 ml of water and stirred well, then the aqueous solution was cooled to under 5° C. While holding the reaction solution at under 5° C., 4.90 g of ammonium persulfate (21.5 mmol) was added while stirring and a reaction caused for 5 hours. Along with the progress of the reaction, a uniform green solution was obtained. This uniform polyaniline aqueous solution was added to 100 g of carbon black (N220) while stirring vigorously. Part of the obtained composite of polyaniline and carbon black was taken and washed with water and methanol, whereupon the green coloring derived from polyaniline was not observed, so it was learned that the reaction was complete and the polyaniline in the doped state formed a composite with the carbon black quantitatively. The remaining composite comprised of the polyaniline and carbon black was dried at 80° C. for 8 hours to obtain a composite of polyaniline in the doped state and carbon black. The amount of the polyaniline in the composite was 2% by weight. Production of Composite 17 (Polyaniline/Carbon Black Composite) The same procedure as for Composite 16 was followed to obtain a composite containing polyaniline and carbon black except for changing the amounts of the water, aniline, hydrochloric acid, sodium dodecylsulfonate, and ammonium persulfate used for the production of the Composite 16 to 500 ml, 5 g (53.7 mmol), 5.6 g (53.7 mmol), 15.5 g (53.7 mmol), and 12.3 g (53.7 mmol), respectively. Part of the obtained composite of polyaniline and carbon black was taken and washed with water and methanol, whereupon the green coloring derived from polyaniline was not observed, so it was learned that the reaction was complete and the polyaniline in the doped state formed a composite with the carbon black quantitatively. The remaining composite comprised of the polyaniline and carbon black was dried at 80° C. for 8 hours to obtain a composite of polyaniline in the doped state and carbon black. The amount of the polyaniline in the composite was 5% by weight. Production of Composite 18 (Polypyrrole/Carbon Black Composite) 2 g of pyrrole (29.8 mmol) and 9.73 g of dodecylbenzenesulfonic acid (29.8 mmol) were added to 500 ml of water. 100 g of carbon black (N220) was added to the obtained aqueous solution while stirring vigorously. The solution was cooled to 5° C., then 8.16 g of ammonium persulfate (35.8 mmol) was added and the mixture stirred for 5 hours while keeping the reaction temperature below 10° C. After the end of the reaction, the black powder in the reaction solution was obtained by filtration and washed with water and methanol. The filtrate and the washings when filtering the composite comprised of the polyaniline and carbon black from the reaction solution did not exhibit the green-brown coloring derived from polypyrrole, so it was learned that the reaction was complete and the polypyrrole in the doped state formed a composite with the carbon black quantitatively. Further, the obtained composite was dried at 80° C. for 8 hours to obtain a composite of polypyrrole in the doped state and carbon black. The amount of the polypyrrole in the composite was 2% by weight. Production of Composite 19 (Polypyrrole/Carbon Black Composite) 2 g of pyrrole (29.8 mmol) and 9.73 g of dodecylbenzenesulfonic acid (29.8 mmol) were added to 500 ml of water. 100 g of carbon black (N220) was added to the obtained aqueous solution while stirring vigorously. The solution was cooled to 5° C., then 8.16 g of ammonium persulfate (35.8 mmol) was added. The mixture was stirred for 5 hours while keeping the reaction temperature below 10° C. After the end of the reaction, sodium carbonate powder was added until the reaction solution exhibited basicity by pH test paper, then the mixture was stirred for 4 hours. The black powder in the reaction solution was obtained by filtration and washed with water and methanol. The filtrate and the washings when filtering the composite comprised of the polypyrrole and carbon black from the reaction solution did not exhibit the brown coloring derived from polypyrrole in the undoped state, so it was learned that the reaction was complete and the polypyrrole in the undoped state formed a composite with the carbon black quantitatively. Further, the composite obtained was dried at 80° C. for 8 hours to obtain a composite of polypyrrole in the undoped state and carbon black. The amount of the polypyrrole in the composite was 2% by weight. Note that the Mooney viscosity, scorch time, vulcanization time, tensile properties, and tan&dgr; were measured by the same methods as explained above. Note that the abrasion resistance is the abrasion loss measured using a Lambourn abrasion tester (made by Iwamoto Seisakusho) under conditions of a load of 5 kg, a slip of 25%, a time of 4 minutes, and room temperature indexed to the value of Comparative Example 3 as 100. Note that the larger the value, the better the abrasion resistance shown. 3 TABLE 3 Comp. Ex. 23 Ex. 24 Ex. 25 Ex. 26 Ex. 27 Ex. 28 Ex. 29 Ex. 30 Ex. 3 SBR 3 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 137.5 Composite 12 80 — — — — — — — — Composite 13 — 80 — — — — — — — Composite 14 — — 80 — — — — — — Composite 15 — — — 80 — — — — — Composite 16 — — — — 80 — — — — Composite 17 — — — — — 80 — — — Composite 18 — — — — — — 80 — — Composite 19 — — — — — — — 80 — Carbon black — — — — — — — — 80 Zinc oxide 3 3 3 3 3 3 3 3 3 Stearic acid 2 2 2 2 2 2 2 2 2 Antioxidant 1 1 1 1 1 1 1 1 1 Aromatic oil 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator Sulfur 2 2 2 2 2 2 2 2 2 Mooney viscosity 48 46 49 47 46 48 47 47 48 Scorch time (min) 16.5 17.2 16.8 16.5 17.2 16.8 16.7 16.6 16.5 Vulcanization time (min) 8.96 9.04 9.12 9.93 8.87 9.08 9.42 9.56 10.1 Tensile properties 100% modulus (MPa) 2.32 2.35 2.28 2.34 2.27 2.34 2.37 2.34 2.22 300% modulus (MPa) 10.3 10.4 10.6 10.4 10.5 10.3 10.7 10.5 10.6 Tensile strength at 20.9 20.5 20.7 20.9 20.4 20.6 20.8 20.7 20.7 break (MPa) Elongation at break (%) 545 549 550 543 549 549 551 547 548 tan&dgr; (0° C.) 0.532 0.531 0.535 0.536 0.538 0.537 0.537 0.533 0.531 tan&dgr; (60° C.) 0.295 0.298 0.259 0.262 0.293 0.257 0.258 0.259 0.325 Abrasion resistance 102 102 104 103 104 104 105 102 100 (index) The following were used for the components in Table 3: SBR 3: Solution polymerized SBR, Nipol 1712, made by Nippon Zeon Carbon black: Carbon Black N220, made by Tokai Carbon, nitrogen specific area (N 2 SA)&equals;115 m 2 /g Antioxidant: (N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine), made by Bayer. Vulcanization accelerator: N-cyclohexyl-2-benzothiazolylsulfenamide, made by Toyo Kagaku. From Table 3, it is clear that, compared with the rubber composition in which carbon black was blended shown in Comparative Example 3, the rubber compositions of Examples 23 to 30 including composites of &pgr;-conjugated polymers and carbon black (Composites 12 to 19) were reduced in the tan&dgr; (60° C.) while maintained or increased in the tan&dgr; (0° C.) and were improved in the low rolling resistance without the wet skid resistance being reduced. On the other hand, regarding the processability (Mooney viscosity and scorch time), tensile properties, and abrasion resistance, the rubber compositions of Examples 23 to 30 including Composites 12 to 19 maintained the properties of a rubber composition in which carbon black was blended shown in Comparative Example 3 and were held down in terms of reduction of the mechanical properties. Further, Composites 12 to 19 could be easily produced without a complicated production process with a large number of production steps as with the above-mentioned conventional compounding agents. As explained above, according to the present invention, by compounding a composite composed of a &pgr;-conjugated polymer compound and carbon black to a rubber composition, it is possible to obtain an excellent wet skid resistance and low rolling resistance by an easy-to-produce compounding agent.