Pneumatic tire with high speed durability
View Patent ↗A pneumatic tire with superior durability having a tread part comprising a cap tread layer (layer A) and an under tread layer (layer B), wherein, in the pneumatic tire, when storage elastic moduli of the rubber compositions constituting the layer A and the layer B are designated as E A and E B , the storage elastic moduli E A (60° C.) and E B (60° C.) determined at a temperature of 60° C. satisfy the following formulae (1) and (2): E A (60° C.)/ E B (60° C.)≦0.66 (1) 10(MPa)≦ E B (60° C.) (2)
1. A pneumatic tire having a tread part comprising a cap tread layer (i.e., layer A) and an under tread layer (i.e., layer B), wherein, in the pneumatic tire, when storage elastic moduli of the rubber compositions constituting the layer A and the layer B, respectively, are designated as E A and E B , the storage elastic moduli E A at 60° C. and E B at 60° C. determined at a temperature of 60° C. satisfy the following formulae (1) and (2):
E A (60° C.)/ E B (60° C.)≦0.66 (1)
10(MPa)≦ E B (60° C.) (2), and
a difference between a storage elastic modulus E B (20° C.) of the rubber of the layer B determined at 20° C. and a storage elastic modulus E B (60° C.) determined at 60° C. satisfies the following formula (3):
E B (20° C.)− E B (60° C.)≦4.5(MPa) (3),
and wherein, when a cross-sectional area of the layer A is A A and a cross-sectional area of the layer B is A B , a ratio of A A /(A A +A B ) satisfies the following formula (4):
0.30≦ A A /( A A +A B )≦0.60 (4),
and wherein said rubber composition for layer B consists essentially of:
(a) 100 parts by weight of a polymer component consisting of (i) 25-50 parts by weight (phr) of a polybutadiene rubber including syndiotactic crystal ingredient, and
(ii) 75-50 parts by weight (phr) of natural rubber (NR),
(b) 65-100 parts by weight of carbon black having a nitrogen adsorption specific surface area (N 2 SA) of 60-140 m 2 /g and a dibutyl phthalate adsorption (DBP) of 70-180 cm 3 /100 g and (c) aromatic oil, sulfur and stearic acid, and
(d) as the only vulcanization or cross-linking accelerator at least one member selected from the group consisting of N-tert-butylbenzothiazole-2-sulfenamide, N-cyclohexyl-benzothiazole-2-sulfenamide, and diphenyl guanidine and optionally,
(e) silica, as a filler, other than said carbon black (b).
2. A pneumatic tire as claimed in claim 1 , wherein 70 to 100 parts by weight of carbon black, based upon 100 parts by weight of rubber, is used in the layer B.
3. A pneumatic tire as claimed in claim 1 , wherein formula (4) is
0.45≦ A A /( A A +A B )≦0.50 (4).