Tire with tread having base layer comprised of diverse zoned rubber compositions
The invention relates to a tire having a rubber tread comprised of cap/base construction where the tread outer cap rubber layer contains the running surface of the tread and the tread base rubber layer underlies the tread cap layer wherein the base layer provides a transition zone between the tread cap layer and the remainder of the tire carcass and is not intended to be ground-contacting. For this invention, the tread base rubber layer is comprised of three distinct zones, namely a circumferential annular central rubber zone positioned between two lateral annular rubber zones. In one aspect, the rubber tread cap layer and zoned rubber tread base layer are co-extruded together to form an integral tread rubber composite.
1. A tire having a circumferential rubber tread composite configured with a cap/base layered construction comprised of an outer tread cap rubber layer containing the running surface of the tread and an internal underlying zoned tread base rubber layer, wherein the underlying zoned tread base rubber layer is comprised of a circumferential central tread base rubber zone and two circumferential lateral tread base rubber zones individually adjoining and positioned on each side of said central tread base rubber zone;
wherein said central tread base rubber zone comprises from about 55 to about 80 percent of the width of the tread base rubber layer and the lateral tread base rubber zones are of substantially equal widths and occupy the remainder of the width of the tread base rubber layer;
wherein the rubber composition of said lateral tread base zones are significantly stiffer than the rubber composition of said central tread base zone in a sense of:
(A) the rubber composition of said lateral tread base rubber zones have a modulus G′ value, at 15 percent shear strain, 25° C. and 10 Hertz, in a range of from about 2.5 to about 10 MPa, and the rubber composition of said central tread base rubber zone has modulus G′ value, at 15 percent shear strain, 25° C. and 10 Hertz, in a range of from about 0.5 to about 1.5 MPa, and
(B) the G′ modulus value of the rubber composition of said central tread base zone is at least 1 MPa lower than the G′ modulus of said rubber composition of said lateral tread base zones, and
wherein the rubber compositions of the central and lateral tread base zones are comprised of cis 1,4-polyisoprene and at least one of cis 1,4-polybutadiene and styrene/butadiene conjugated diene rubbers together with reinforcing filler comprised of rubber reinforcing carbon black and wherein reinforcing filler for at least one of the central and lateral tread base rubber zones further contains precipitated silica and coupling agent for the precipitated silica having a moiety reactive with hydroxyl groups contained on the surface of said precipitated silica and another moiety interactive with said conjugated diene-based rubber(s);
wherein the rubber composition of at least one of said lateral tread base zones contains, to the exclusion of said central tread base zone, from about 1 to about 10 phr of rubber stiffness promoting ingredient comprised of:
(C) short fibers consisting of at least one of carbon, aramid, nylon and polyester fibers, or
(D) a combination of syndiotactic polybutadiene and short fibers wherein said short fibers consist of at least one of carbon, aramid, nylon and polyester fibers.
2. The tire of claim 1 wherein at least one of said lateral tread base zones contains, to the exclusion of said central tread base zone, from about 1 to about 10 phr of rubber stiffness promoting ingredient comprised of short fibers wherein said short fibers consist of at least one of carbon, aramid, nylon and polyester fibers.
3. The tire of claim 1 wherein at least one of said lateral tread base zones contains, to the exclusion of said central tread base zone, from about 1 to about 10 phr of rubber stiffness promoting ingredients comprised of a combination of syndiotactic polybutadiene and short fibers, wherein said short fibers consist of at least one of carbon, aramid, nylon and polyester fibers.