Pneumatic tire

Abstract

A pneumatic tire comprising a tread portion which comprises a surface rubber layer which is disposed in an outer portion of the tread portion in the radial direction of said tire and has a specific resistance of 10 8 Ω·cm or more after curing by vulcanization and conductive rubber members which comprise a rubber composition having a specific resistance of 10 6 Ω·cm or less and replace a portion of the surface rubber layer, wherein the conductive rubber members are disposed in portions of the surface rubber layer extending from the outer surface to the inner surface in the radial direction of said tire discontinuously in the circumferential direction of said tire at the outer surface of the surface rubber layer in the radial direction of said tire, is provided. The pneumatic tire shows not only an excellent effect of static discharge but also excellent durability.

What is claimed is:  
     
         1 . A pneumatic tire comprising a tread portion which comprises a surface rubber layer which is disposed in an outer portion of the tread portion in the radial direction of said tire and has a specific resistance of 10 8  Ω·cm or more after curing by vulcanization, and conductive rubber members which comprise a rubber composition having a specific resistance of 10 6  Ω·cm or less and with which portions of the surface rubber layer are replaced, 
 wherein the conductive rubber members are disposed in portions of the surface rubber layer extending from the outer surface to the inner surface in the radial direction of said tire discontinuously in the circumferential direction of said tire at the outer surface of the surface rubber layer in the radial direction of said tire.  
 
     
     
         2 . A pneumatic tire according to  claim 1 , wherein the conductive rubber members have a width of 0.1 to 3.0 mm and are disposed in such a manner that at least some of the conductive rubber members are placed inside an area of the surface of said tire which is in contact with a road surface.  
     
     
         3 . A pneumatic tire according to  claim 1 , wherein the conductive rubber members are disposed at at least three positions which are placed in an area of the surface of said tire which is in contact with a road surface and which are placed in the same cross section in the transverse direction of said tire.  
     
     
         4 . A pneumatic tire according to  claim 1 , wherein the length of the conductive rubber members in the circumferential direction of said tire is the same as or less than the length of an area of the surface of said tire which is in contact with a road surface.  
     
     
         5 . A pneumatic tire according to  claim 4 , wherein the length of the conductive rubber members in the circumferential direction of said tire is {fraction (1/12)} or less of the length of the circumference of said tire.  
     
     
         6 . A pneumatic tire according to  claim 2 , wherein the conductive rubber members have a width of 0.5 to 2.0 mm.  
     
     
         7 . A pneumatic tire according to  claim 1 , wherein the tread portion has a structure consisting of at least two layers comprising the surface rubber layer which is disposed in an outer portion of the tread portion in the radial direction of said tire and an inner rubber layer which is disposed in an inner portion of the tread portion in the radial direction of said tire and has a specific resistance of 10 6  Ω·cm or less after curing by vulcanization.  
     
     
         8 . A pneumatic tire according to  claim 7 , wherein the conductive rubber members have a width of 0.1 to 3.0 mm and are disposed in such a manner that at least a portion of the conductive rubber members are placed inside an area of the surface of said tire which is in contact with a road surface.  
     
     
         9 . A pneumatic tire according to  claim 7 , wherein the conductive rubber members are disposed at at least three positions which are placed in an area of the surface of said tire which is in contact with a road surface and which are placed in the same cross section in the transverse direction of said tire.  
     
     
         10 . A pneumatic tire according to  claim 7 , wherein the length of the conductive rubber members in the circumferential direction of said tire is the same as or less than the length of an area of the surface of said tire which is in contact with a road surface.  
     
     
         11 . A pneumatic tire according to  claim 1 , wherein the conductive rubber members are made from a rubber cement having a specific resistance of 10 6  Ω·cm or less after curing by vulcanization.  
     
     
         12 . A pneumatic tire according to  claim 1 , wherein the conductive rubber members have the shape of a column having a small diameter and is disposed in portions of the surface rubber layer extending from the outer surface to the inner surface in the radial direction of said tire and in separate locations at the outer surface of the surface rubber layer in the radial direction of said tire.  
     
     
         13 . A pneumatic tire according to  claim 12 , wherein 30 or more of the conductive rubber members having the shape of a column having a small diameter are disposed in an area of the surface of said tire which is in contact with a road surface.  
     
     
         14 . A pneumatic tire according to  claim 13 , wherein the shape of a column having a small diameter is the shape of an approximately round column and has a diameter of 0.1 to 3 mm.  
     
     
         15 . A pneumatic tire according to  claim 14 , wherein the shape of an approximately round column has a diameter of 0.5 to 2.0 mm.  
     
     
         16 . A pneumatic tire according to  claim 12 , wherein the tread portion has a structure consisting of at least two layers comprising the surface rubber layer which is disposed in an outer portion of the tread portion in the radial direction of said tire and an inner rubber layer which is disposed in an inner portion of the tread portion in the radial direction of said tire and has a specific resistance of 10 6  Ω·cm or less after curing by vulcanization.  
     
     
         17 . A pneumatic tire according to  claim 12 , wherein the conductive rubber members are made from a rubber cement having a specific resistance of 10 6  Ω·cm or less after curing by vulcanization.  
     
     
         18 . A pneumatic tire according to  claim 1 , wherein the conductive rubber members are disposed in portions of the tread portion extending from the outer surface to the inner surface in the radial direction of said tire and are discontinuous in the circumferential direction of said tire at the outer surface of the tread portion in the radial direction of said tire and continuous at least in the circumferential direction of said tire at an inner portion of the tread portion in the radial direction of said tire.  
     
     
         19 . A pneumatic tire according to  claim 18 , wherein the surface area of the conductive rubber members exposed at the outer surface of the tread portion is 1 to 50% of the surface area of the conductive rubber members if the conductive rubber members were extended continuously in the circumferential direction of said tire at the outer surface of the tread portion in the radial direction of said tire.  
     
     
         20 . A pneumatic tire according to  claim 18 , wherein the conductive rubber members are disposed at at least three positions which are placed in an area of the surface of said tire which is in contact with a road surface and which are placed in the same cross section in the transverse direction of said tire.