Withstand-voltage tire

A tire having excellent withstand-voltage property, wear resistance and resistance against heat build-up is disclosed. The tire has a tread, at least the contact area of the tread with road surface being made of a rubber composition containing a specifically limited softening agent and a specifically limited carbon black.

What is claimed is:

1. A withstand-voltage tire having a cap-base structure tread comprising a thread cap and a tread base, said tread cap having a thickness of at least 1/2 of the thickness of the tread or extending to a position below a line connecting the groove bottoms of the tread patterns, and said tread cap being made of a rubber composition consisting of 100 parts by weight of a rubber selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber and blends thereof, 1-10 parts by weight of at least one softening agent selected from the group consisting of natural rosin, glycerine ester of rosin, polymerized rosin and a phenolic resin, and 30-90 parts by weight of carbon black having an iodine adsorbability of from more than 83 mg/g to 150 mg/g and a dibutyl phthalate absorbability of 80-120 ml/100 g, and said tread base being made of a rubber composition consisting of 100 parts by weight of a rubber selected from the group consisting of natural rubber, polyisoprene rubber, polybutadiene rubber and blends thereof, 0-3 parts by weight of at least one softening agent selected from the group consisting of natural rosin, glycerine ester of rosin, polymerized rosin and a phenolic resin, and 20-50 parts by weight of carbon black having an iodine adsorbability of 40-83 mg/g and a dibutyl phthalate absorbability of 80-120 ml/100 g.

2. A withstand-voltage tire according to claim 1, wherein the amount of the at least one softening agent used in the tread cap is 1-5 parts by weight.

3. A withstand-voltage tire according to claim 1, wherein said carbon black used in the tread cap has an iodine adsorbability of 110-150 mg/g and a dibutyl phthalate absorbability of 100-120 ml/100 g.

4. A withstand-voltage tire according to claim 1, wherein the amount of said carbon black used in the tread cap is 40-50 parts by weight.

5. A withstand-voltage tire according to claim 1, wherein said carbon black used in the tread base has an iodine adsorbability of 30-50 mg/g and a dibutyl phthalate absorbability of 100-120 ml/100 g.

6. A withstand-voltage tire according to claim 1, wherein the amount of said carbon black used in the tread base is 30-40 parts by weight.