Method for forming a green tread rubber and a pneumatic tire formed by using the green tread rubber

Abstract

In a method for forming a green tread rubber comprised of a cap rubber layer which outer surface forms a tread surface and a base rubber layer that adjoins the same inside thereof in the radial direction, a cap rubber having a rubber component of styrene/butadiene rubber or being a mixed rubber of natural rubber and butadiene rubber is used as the cap rubber layer. The base rubber layer is formed as an annular body in which a strap-like rubber extruded body of wide width, which is extruded from a rubber extruder and is cut into constant size, is wound around a molding drum by a single round with their end portions in a circumferential direction being joined with each other. The cap rubber layer is formed as a strip layered body in which a long strap-like rubber strip of narrow width, which is extruded from an rubber extruder, is successively wound by overlapping the same on the annular body in the circumferential direction and in a spiral manner. A thickness T 2 of the base rubber layer on a tire equator is defined to be 0.05 to 0.7 times a thickness T 0 of the green tread rubber on the tire equator.

1 . A method for forming a green tread rubber composed of a cap rubber layer of which outer surface forms a tread surface and a base rubber layer adjoining to the radially inside of the cap rubber layer, wherein the base rubber layer is made of a base rubber, and the cap rubber layer is made of a cap rubber, the method comprising the steps of:
 forming an annular base rubber layer by winding a strap-like base rubber one turn around a molding drum and jointing the circumferential end portions thereof with each other, wherein the strap-like base rubber is extruded from a rubber extruder and is cut into a certain length; and   forming the cap rubber layer by successively winding and overlapping a long strip of the cap rubber in the circumferential direction and in a spiral manner on the annular base rubber layer, wherein the long strip is extruded from a rubber extruder and has a smaller width than that of the strap-like base layer, wherein   a thickness T 2  of the base rubber layer is 0.05 to 0.7 times a thickness T 0  of the green tread rubber measured at the tire equator,   the rubber component of the cap rubber comprises a styrene-butadiene rubber,   the rubber component of the base rubber comprises a styrene-butadiene rubber, and   the cap rubber after vulcanization has a complex elastic modulus E 1 * of 5.0 to 9.0 MPa.   
   
   
       2 . The method according to  claim 1 , wherein
 the base rubber after vulcanization has a complex elastic modulus E 2 * larger than the complex elastic modulus E 1 * of the cap rubber.   
   
   
       3 . The method according to  claim 1 , wherein
 a hardness Hs 1  of the cap rubber after vulcanization is 60 to 90 degrees, and   a hardness Hs 2  of the base rubber after vulcanization is such that the difference |HS 1 −Hs 2 | between the hardness HS 1  and hardness Hs 2  is not more than 10 degrees.   
   
   
       4 . The method according to  claim 1 , wherein
 the strip of the cap rubber has a width of 5 to 30 mm and a thickness of 0.5 to 3.0 mm.   
   
   
       5 . The method according to  claim 1 , wherein
 the rubber component of the cap rubber comprises not less than 80 parts by mass of the styrene/butadiene rubber per 100 parts by mass of the rubber base material.   
   
   
       6 . A method for forming a green tread rubber composed of a cap rubber layer of which outer surface forms a tread surface and a base rubber layer adjoining to the radially inside of the cap rubber layer, wherein the base rubber layer is made of a base rubber, and the cap rubber layer is made of a cap rubber, the method comprising the steps of:
 forming an annular base rubber layer by winding a strap-like base rubber one turn around a molding drum and jointing the circumferential end portions thereof with each other, wherein the strap-like base rubber is extruded from a rubber extruder and is cut into a certain length; and   forming the cap rubber layer by successively winding and overlapping a long strip of the cap rubber in the circumferential direction and in a spiral manner on the annular base rubber layer, wherein the long strip is extruded from a rubber extruder and has a smaller width than that of the strap-like base layer, wherein   a thickness T 2  of the base rubber layer is 0.05 to 0.7 times a thickness T 0  of the green tread rubber measured at the tire equator,   the rubber component of the cap rubber consists of 30 to 70 parts by mass of a natural rubber and 70 to 30 parts by mass of a butadiene rubber,   the rubber component of the base rubber consists of 30 to 70 parts by mass of a natural rubber and 70 to 30 parts by mass of a butadiene rubber, and   the cap rubber after vulcanization has a complex elastic modulus E 1 * of 2.0 to 5.0 MPa.   
   
   
       7 . The method according to  claim 6 , wherein
 the base rubber after vulcanization has a complex elastic modulus E 2 * larger than the complex elastic modulus E 1 * of the cap rubber.   
   
   
       8 . The method according to  claim 6 , wherein
 a hardness HS 1  of the cap rubber after vulcanization is 40 to 60 degrees, and   a hardness Hs 2  of the base rubber after vulcanization is larger than the hardness Hs 1 .   
   
   
       9 . The method according to  claim 6 , wherein
 the strip of the cap rubber has a width of 5 to 30 mm and a thickness of 0.5 to 3.0 mm.   
   
   
       10 . A pneumatic tire formed by using the green tread rubber obtained through the method as claimed in any one of  claims 1 - 9 .