Rubber composition

A vulcanized rubber composition comprising 100 parts by weight of a vulcanizable rubber, a reinforcing filler, and a sulfur compound (1) having the formula (I):

• —(SxR1)— (I)
• wherein, R1 represents an organic group,
• x is an average number of 3 to 5, and
• n is an integer of 1 to 100 in an amount of not more than 20 parts by weight, or the sulfur compound (1) and sulfur (2) in a ratio by weight (1)/(2) of at least 0.5 and in a total weight of (1)+(2) of not more than 20 parts by weight, vulcanized by compounding at least one vulcanization accelerator (3) selected from the group consisting of a thiazole base, sulfenamide base, thiuram base, and diothio acid base accelerators in an amount so as to give a ratio by weight [(1)+(2)]/(3) of not more than 2.2, wherein
• a value VM is obtained from the degree of change before and after toluene swelling of the vulcanized rubber composition treated in a lithium aluminum hydride saturated tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution using the formula (A):
• 10 VM = - 1 Vs · [ ln ⁡ ( 1 - vr M ) + vr M + μ ⁣ · vr M 2 vr M 1 / 3 - vr M / 2 ] ⁢ ⁢ wherein ⁢ ⁢ vr M = 1 - φ X M - φ ( A )
• wherein XM is the degree of change before and after toluene swelling (volume after toluene swelling/volume before toluene swelling)after treatment in a lithium aluminum hydride saturated tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution,
• φ is the volume percentage of the reinforcing filler in the rubber composition,
• Vs is the molecular volume of toluene, μ is the rubber•toluene interaction coefficient, and vrM is the volume percentage of rubber in the swelled rubber after treatment in a lithium aluminum hydride saturated tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution,
• a value V[D+M] is obtained from the degree of change before and after toluene swelling of the vulcanized rubber composition treated in a propane-2-thiol (0.4 mol/l)/piperidine (0.4 mol/l) added tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution using the formula (D):
• 11 V ⁡ [ D + M ] = - 1 Vs · [ ln ⁡ ( 1 - vr D + M ) + vr D + M + μ · vr D + M 2 vr D + M 1 / 3 - vr D + M / 2 ] wherein ⁢ ⁢ vr D + M = 1 - φ x D + M - φ ( D )
• wherein XD+M is the degree of change before and after toluene swelling (volume after toluene swelling/volume before toluene swelling)after treatment in a propane-2-thiol (0.4 mol/l)/piperidine (0.4 mol/l) added tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution,
• φ, Vs, μ, and vrM are as defined above, and
• vrD+M is the volume percentage of rubber in the swelled rubber after treatment in a propane-2-thiol (0.4 mol/l)/piperidine (0.4 mol/l) added tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution, and
• a value VT is obtained from the degree of change before and after toluene swelling of the untreated vulcanized rubber composition using formula (C):
• 12 VT = - 1 Vs · [ ln ⁡ ( 1 - vr T ) + vr T + μ · vr T 2 vr T 1 / 3 - vr T / 2 ] wherein ⁢ ⁢ vr T = 1 - φ X T - φ ( C )
• wherein XT is the degree of change before and after toluene swelling when untreated (volume after toluene swelling/volume before toluene swelling) and
• vrT is the volume percentage of rubber in the swelled rubber when untreated
• are such that VM/VT is not more than 0.3 and (VT−V[D+M])/VT is at least 0.4 and further are such that the ratio VM/VD of VD(=V[D+M]−VM) and VM is at least 0.4 and wherein
• the rate of retention of the tensile strength at break and the elongation at break of the vulcanized rubber composition before and after heat aging at 100° C. for 96 hours is at least 0.7.

A rubber composition comprising 100 parts by weight of a vulcanizable rubber, a reinforcing filler, and a sulfur compound (1) having the formula (I):

• —(SxR1)n— (I)
• wherein R1 represents an organic group,
• x is an average number of 3 to 5, and
• n is an integer of 1 to 100
• and sulfur (2) in a ratio (1)/(2) of the sulfur compound (1) and the sulfur (2) of less than 0.5 and in a total weight of (1)+(2) of not more than 20 parts by weight.

A rubber composition for a heavy duty tire tread comprising 100 parts by weight of a diene rubber, 40 to 85 parts by weight of a reinforcing filler, 1 to 10 parts by weight of at least one resin selected from the group consisting of a rosin base resin, a cyclopentane diene base resin, and mixtures thereof, a sulfur compound having formula (I) or (II):

• —(SxR1)n— (I)
• wherein R1 indicates an organic group,
• x is an integer of 3 to 5, and
• n is an integer of 1 to 100
• 2
• wherein n′ is an integer of 3 or 4 and, optionally, sulfur or a sulfur donor.