Pneumatic tire and production method therefor

Abstract

Static electricity in a vehicle is discharged to a road surface without deteriorating uniformity. Tread rubber 2 G includes base portion 9 made of a non-conductive rubber which is disposed radially inward and extends continuously from one tread edge e 1 side to the other tread edge e 2 side, cap portion 10 made of a non-conductive rubber and disposed radially outward of the base portion 9 to form ground-contacting surface 2 a , and conductive portion 11 made of a conductive rubber and having one end exposed on the ground-contacting surface 2 a and the other end connected to sidewall rubber 3 G electrically conductive with a rim when the tire is mounted on the rim. The cap portion 10 are divided into right and left and includes first cap portion 10 A and second cap portion 10 B. The conductive portion 11 extends radially inwardly from the ground-contacting surface 2 a between the first cap portion 10 A and the second cap portion 10 B and further extends axially between the base portion 9 and one of the first and second cap portions 10 A and 10 B to connect to the sidewall rubber 3 G.

1 . A pneumatic tire comprising a toroidal carcass extending from a tread portion to bead cores in bead portions through sidewall portions, a tread reinforcing cord layer disposed radially outward of the carcass in the tread portion, and a tread rubber disposed radially outward of the tread reinforcing cord layer,
 the tread rubber including:   a base portion made of a non-conductive rubber containing silica which is disposed on a radially inner side and continuously extends from one tread edge side to the other tread edge side,   a cap portion made of a non-conductive rubber containing silica which is disposed radially outward of the base portion to form a ground-contacting surface, and   a conductive portion made of a conductive rubber having one end exposed on the ground-contacting surface and the other end connected to a sidewall rubber or a topping rubber of the carcass each forming an electrical conductive path to a rim when the tire is mounted on the rim,   the cap portion comprising a first cap portion and a second cap portion which have been divided into left and right, and   the conductive portion extending radially inwardly between the first cap portion and the second cap portion from the ground-contacting surface and further extending between the base portion and one of the first cap portion and the second cap portion in the tire axial direction to connect with the sidewall rubber or the topping rubber.   
     
     
         2 . The pneumatic tire of  claim 1 , wherein the conductive portion is made of a strip laminated body formed by spirally winding a ribbon-like rubber strip. 
     
     
         3 . The pneumatic tire of  claim 1 , wherein the conductive portion is made of a sheet-wound body formed by winding a rubber sheet having a width which is continuous from said one end to said the other end. 
     
     
         4 . The pneumatic tire of any one of  claims 1  to  3 , wherein the base portion or the cap portion is made of a strip laminated body formed by spirally winding a ribbon-like rubber strip. 
     
     
         5 . The pneumatic tire of any one of  claims 1  to  3 , wherein at least one of the base portion and the cap portion is formed by splicing a rubber extruded by a rubber extrusion machine. 
     
     
         6 . The pneumatic tire of any one of  claims 1  to  5 , wherein a direction of attaching the tire to a vehicle is specified, and said one end of the conductive portion which is exposed on the ground-contacting surface is disposed on a side closer to an inner side of the vehicle than the tire equator. 
     
     
         7 . The pneumatic tire of any one of  claims 1  to  6 , wherein the tread rubber has a protrusion on the ground-contacting surface, the protrusion including any of a spew sucked up into a vent hole of a mold during vulcanization and formation, a spew resection mark that a part of the spew has been resected, and a burr sucked up into between divided surfaces of the mold, and the conductive portion constitutes at least a part of the protrusion. 
     
     
         8 . The pneumatic tire of  claim 7 , wherein the protrusion included in the conductive portion is the spew or the spew resection mark, and at least two protrusions are always present in a ground contacting region when the tire is mounted on a normal rim and inflated to a normal pressure and the tire in such a normal condition is loaded with a normal load and is rotated on a flat surface at a camber angle of 0°. 
     
     
         9 . A method for manufacturing a pneumatic tire having a tread rubber, comprising:
 a tread rubber forming step for forming a tread rubber, and   a vulcanizing step for vulcanizing a raw tire including the tread rubber, wherein   the tread rubber forming step includes:   a stage for forming a base portion made of a non-conductive rubber containing silica which is disposed on a radially inner side and continuously extends from one tread edge side to the other tread edge side,   a stage for forming a first cap portion made of a non-conductive rubber containing silica on a radially outer side of the base portion, the first cap portion extending from its axially outer end located on a side of one end of the base portion to its axially inner end having an outer surface tapered on the base portion to cover only the one end side of the base portion,   a stage for forming a conductive portion made of a conductive rubber, the conductive portion having one end exposed on a ground-contacting surface and extending in the opposite direction of the first cap port along the tapered outer surface and an outer surface of the base portion to have the other end at a location axially outward of the other end of the base portion, and   a stage for forming a second cap portion made of a non-conductive rubber containing silica, the second cap portion covering an entire outer surface of the conductive portion except the exposed one end thereof and terminating at a location axially outward of the other end of the conductive portion.   
     
     
         10 . The method of  claim 9 , wherein the stage for forming the conductive portion is carried out by spirally winding a ribbon-like rubber strip made of a conductive rubber. 
     
     
         11 . The method of  claim 9 , wherein the stage for forming the conductive portion is carried out by winding a rubber sheet having a width which is continuous from said one end of the conductive portion to said the other end of the conductive portion. 
     
     
         12 . The method of any one of  claims 9  to  11 , wherein at least one of the stage for forming the base portion, the stage for forming the first cap portion and the stage for forming the second cap portion is carried out by spirally winding a ribbon-like rubber strip. 
     
     
         13 . The method of any one of  claims 9  to  12 , wherein the vulcanizing step is carried out using a mold having a vent hole, and the vulcanizing step includes a step for sucking up a part of the conductive portion into the vent hole by conducting the vulcanizing in a state that at least a part of the conductive portion appearing on the ground-contact surface faces the vent hole of the mold. 
     
     
         14 . The method of any one of  claims 9  to  13 , wherein the vulcanizing step is carried out using a mold having divided surfaces, and the vulcanizing step includes a step for sucking up a part of the conductive portion into a gap between the divided surfaces by conducting the vulcanizing in a state that at least a part of the conductive portion appearing on the ground-contacting surface faces the divided surfaces. 
     
     
         15 . A pneumatic tire comprising a toroidal carcass extending from a tread portion to bead cores in bead portions through sidewall portions, a tread reinforcing cord layer disposed radially outward of the carcass in the tread portion and electrically conducted with a rim when the tire is mounted on the rim, and a tread rubber disposed radially outward of the tread reinforcing cord layer,
 the tread rubber including:   a base portion made of a non-conductive rubber containing silica and disposed radially outward of the tread reinforcing cord layer,   a cap portion made of a non-conductive rubber containing silica and disposed radially outward of the base portion to form a ground-contacting surface, and   a conductive portion made of a conductive rubber and having one end exposed on the ground-contacting surface and the other end connected to the tread reinforcing cord layer,   wherein the base portion is formed by spirally winding a ribbon-like rubber strip from one tread edge side to the other tread edge side and it has a gap portion formed by separating side edges of adjacent rubber strips during the winding to expose the tread reinforcing cord layer at the gap portion,   the cap portion is divided into right and left parts and comprises a first cap portion on one tread edge side and a second cap portion on the other tread edge side, and   the conductive portion extends radially inwardly between the first cap portion and the second cap portion from the ground-contacting surface and is connected to the tread reinforcing cord layer at the gap portion of the base portion.   
     
     
         16 . The pneumatic tire of  claim 15 , wherein the gap portion includes a portion in which the rubber strip is wound at a winding pitch which is larger than the width of the rubber strip but not larger than two times the width of the rubber strip. 
     
     
         17 . The pneumatic tire of  claim 15  or  16 , wherein the conductive portion is made of a strip laminated body formed by spirally winding a ribbon-like rubber strip. 
     
     
         18 . The pneumatic tire of any one of  claims 15  to  17 , wherein the first cap portion and the second cap portion are made of a strip laminated body formed by spirally winding a ribbon-like rubber strip. 
     
     
         19 . The pneumatic tire of any one of  claims 15  to  18 , wherein the tread rubber has a protrusion on the ground-contacting surface, the protrusion including any of a spew sucked up into a vent hole of a mold during vulcanization and formation, a spew resection mark that a part of the spew has been resected, and a burr sucked up into between divided surfaces of the mold, and the conductive portion constitutes at least a part of the protrusion. 
     
     
         20 . The pneumatic tire of  claim 19 , wherein the protrusion included in the conductive portion is the spew or the spew resection mark, and at least two protrusions are always present in a ground contacting region when the tire is mounted on a normal rim and inflated to a normal pressure and the tire in such a normal condition is loaded with a normal load and is rotated on a flat surface at a camber angle of 0°. 
     
     
         21 . A method for manufacturing a pneumatic tire having a tread reinforcing cord layer electrically conducted with a rim when the tire is mounted on the rim, and a tread rubber disposed radially outward of the tread reinforcing cord layer, the method comprising:
 a tread rubber forming step for forming a tread rubber, and   a vulcanizing step for vulcanizing a raw tire including the tread rubber,   the tread rubber forming step comprising:   a stage for forming a base portion having a gap portion by spirally winding a ribbon-like non-conductive rubber strip containing silica around a radially outer side of the tread reinforcing cord layer from one tread edge side to the other tread edge side and separating side edges of adjacent rubber strips during the winding to form the gap portion at which the tread reinforcing cord layer is exposed,   a stage for forming a first cap portion made of a non-conductive rubber containing silica radially outward of the base portion to extend from its axially outer end located on one end side of the base portion to near the gap portion so as to cover a region of the one end side of the base portion,   a stage for forming a conductive portion made of a conductive rubber along an inner end portion of the first cap portion so as to have one end exposed on a ground-contacting surface and the other end connected to the tread reinforcing cord layer through the gap portion of the base portion, and   a stage for forming a second cap portion made of a non-conductive rubber containing silica on an outer side of the base portion in a tire width direction and in a region of the other end side extending from the conductive portion to the other tread edge side.   
     
     
         22 . The method of  claim 21 , wherein the stage for forming the conductive portion is carried out by spirally winding a ribbon-like rubber strip. 
     
     
         23 . The method of  claim 21 , wherein the stage for forming the conductive portion is carried out by winding a rubber sheet having a width which is continuous from said one end to said the other end of the conductive portion. 
     
     
         24 . The method of any one of  claims 21  to  23 , wherein the stages for forming the first cap portion and the second cap portion are carried out by spirally winding a ribbon-like rubber strip. 
     
     
         25 . The method of any one of  claims 21  to  24 , wherein the vulcanizing step is carried out using a mold having a vent hole, and the vulcanizing step includes a step for sucking up a part of the conductive portion into the vent hole by conducting the vulcanizing in a state that at least a part of the conductive portion appearing on the ground-contact surface faces the vent hole of the mold. 
     
     
         26 . The method of any one of  claims 20  to  24 , wherein the vulcanizing step is carried out using a mold having divided surfaces, and the vulcanizing step includes a step for sucking up a part of the conductive portion into a gap between the divided surfaces by conducting the vulcanizing in a state that at least a part of the conductive portion appearing on the ground-contacting surface faces the divided surfaces.