Method for producing rubber composition

1. A method for producing a rubber composition containing 5 to 95 parts by weight of natural rubber (NR), 95 to 5 parts by weight of chloroprene rubber (CR) and 20 to 90 parts by weight of carbon black (CB), using a kneading machine,

comprising a first step of producing a master batch (M1) containing NR and CB; a second step of producing a master batch (M2) containing CR and CB, and a third step of mixing the M1 and M2 with each other to produce a master batch (M3) containing NR, CR and CB;

wherein when the total amount of CB in the rubber composition is regarded as 100% by weight, the amount of CB contained in the M2 is from 40 to 70% by weight, and

when the M2 is discharged from the kneading machine after the second step, the actually measured temperature of the rubber composition is from 100 to 130° C.

2. The method for producing a rubber composition according to claim 1 , wherein the third step is a step of performing: a first stage of charging, into the kneading machine, either one of the two that are approximately a half of the amount of the M1, and approximately a half of that of the M2, and next charging the other into the kneading machine; and a second stage of charging, into the kneading machine, either one of the two that are the remaining substantial half of that of the M1, and the remaining substantial half of that of the M2, and next charging the other into the kneading machine, thereby kneading these charged components with one another to produce the master match (M3) containing NR, CR and CB.

3. The method for producing a rubber composition according to claim 1 , wherein the third step is a step of charging, into the kneading machine, approximately a half of the amount of the M1, approximately a half of that of the M2, the remaining substantial half of that of the M1, and the remaining substantial half of that of the M2 in this order, and then kneading the charged components to produce the master match (M3) containing NR, CR and CB.

4. The method for producing a rubber composition according to claim 1 , wherein the third step is a step of charging, into the kneading machine, approximately a half of the amount of the M2, approximately a half of that of the M1, the remaining substantial half of that of the M2, and the remaining substantial half of that of the M1 in this order, and then kneading the charged components to produce the master match (M3) containing NR, CR and CB.

5. The method for producing a rubber composition according to claim 1 , wherein the third step is a step of charging, into the kneading machine, approximately a half of the amount of the M1, approximately a half of that of the M2, the remaining substantial half of that of the M2, and the remaining substantial half of that of the M1 in this order, and then kneading the charged components to produce the master match (M3) containing NR, CR and CB.

6. The method for producing a rubber composition according to claim 1 , wherein the third step is a step of charging, into the kneading machine, approximately a half of the amount of the M2, approximately a half of that of the M1, the remaining substantial half of that of the M1, and the remaining substantial half of that of the M2 in this order, and then kneading the charged components to produce the master match (M3) containing NR, CR and CB.

7. The method for producing a rubber composition according to claim 1 , further comprising, after the third step, a fourth step of kneading a blending agent other than zinc oxide and any vulcanizing agent with the M3 to produce an M4 containing the blending agent other than zinc oxide and any vulcanizing agent, and the M3.

8. The method for producing a rubber composition according to claim 7 , further comprising, after the fourth step, a fifth step of kneading zinc oxide and a vulcanizing agent with the M4 to produce the rubber composition.

9. The method for producing a rubber composition according to claim 2 , further comprising, after the third step, a fourth step of kneading a blending agent other than zinc oxide and any vulcanizing agent with the M3 to produce an M4 containing the blending agent other than zinc oxide and any vulcanizing agent, and the M3.

10. The method for producing a rubber composition according to claim 3 , further comprising, after the third step, a fourth step of kneading a blending agent other than zinc oxide and any vulcanizing agent with the M3 to produce an M4 containing the blending agent other than zinc oxide and any vulcanizing agent, and the M3.

11. The method for producing a rubber composition according to claim 4 , further comprising, after the third step, a fourth step of kneading a blending agent other than zinc oxide and any vulcanizing agent with the M3 to produce an M4 containing the blending agent other than zinc oxide and any vulcanizing agent, and the M3.

12. The method for producing a rubber composition according to claim 5 , further comprising, after the third step, a fourth step of kneading a blending agent other than zinc oxide and any vulcanizing agent with the M3 to produce an M4 containing the blending agent other than zinc oxide and any vulcanizing agent, and the M3.

13. The method for producing a rubber composition according to claim 6 , further comprising, after the third step, a fourth step of kneading a blending agent other than zinc oxide and any vulcanizing agent with the M3 to produce an M4 containing the blending agent other than zinc oxide and any vulcanizing agent, and the M3.