Resilient tires and wheels – Tires – resilient – With electrical conducting means
Reexamination Certificate
1998-08-04
2002-04-09
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
With electrical conducting means
C152S209500, C152SDIG002, C156S123000, C156S128600
Reexamination Certificate
active
06367525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antistatic pneumatic tire showing improved durability.
2. Description of the Related Art
Heretofore, carbon black has generally been used as the reinforcing agent for tires. However, in recent years, improvement in the fuel economy of automobiles has been demanded to deal with environmental problems and much study has centered on how to decrease the rolling resistance of a tire. Therefore, tread rubbers having formulations containing a decreased amount of carbon black which causes hysteresis loss and using silica as a reinforcing material have been developed. Tread rubbers comprising silica as a reinforcing material provide increased braking ability on wet roads (referred to as wet traction, hereinafter) and decreased rolling resistance. However, tread rubbers comprising silica have a problem in that the electric resistance thereof is higher than that of tread rubbers comprising carbon black without silica, and electricity conducted from the body of an automobile and electricity generated by internal friction during deformation of the rubber are accumulated.
To solve the problem of static electricity accumulation, for example, antistatic tires having a surface covered with a layer of a conductive rubber have been proposed in the specifications of European Patent No. 705722 and European Patent No. 718126. However, these tires have a problem in that the electric conductivity decreases when abrasion of the tread rubber takes place in the intermediate to final period of the life span of the tire.
In the specification of European Patent No. 681931, an antistatic pneumatic tire comprising a conductive rubber member disposed in the circumferential direction of the tire has been proposed. In the specifications of the U.S. Pat. No. 5,518,055 and European Patent No. 658,452, antistatic tires comprising two conductive rubber member disposed between the tread portion and the sides of the tires have been proposed. However, these tires have a problem in that the tires are weak against a force applied from a transverse direction because these tires have a structure shown in
FIG. 6
in which conductive rubber members
20
having the same thickness as that of tread rubbers
10
are disposed between the tread portions
10
. Separation tends to takes place at the boundaries of the conductive rubber members
20
and the tread portions
10
as shown in FIG.
7
. When separation takes place at a portion of the tire, the separation extends in the circumferential direction over the whole tire, and the durability of the tire markedly decreases.
SUMMARY OF THE INVENTION
The present invention has been made in accordance with the above facts and has an object of providing a pneumatic tire showing not only excellent static discharge effects but also excellent durability.
The present inventors paid attention to the arrangement of conductive rubber members, and it was found as the result of extensive studies that the above object can be achieved by the means explained below. The present invention has been made on the basis of this knowledge.
The pneumatic tire of the present invention is described.
The pneumatic tire of the present invention comprises 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
&OHgr;·cm or more after curing by vulcanization, and conductive rubber members which comprise a rubber composition having a specific resistance of 10
6
&OHgr;·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.
The pneumatic tire of the first embodiment of the present invention comprises 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
&OHgr;·cm or more after curing by vulcanization, and conductive rubber members which comprise a rubber composition having a specific resistance of 10
6
&OHgr;·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, are discontinuous in the circumferential direction of said tire at the outer surface of the surface rubber layer in the radial direction of said tire, 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 contacts with a road surface.
In this pneumatic tire, it is preferable that the conductive rubber members are disposed at at least three positions which are placed in an area of the surface of said tire in contact with a road surface and are placed in the same cross section in the transverse direction of said tire.
It is preferable that the length of the conductive rubber member 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 in contact with a road surface. It is further preferable that the length of the conductive rubber member in the circumferential direction of said tire is {fraction (1/12)} or less of the length of the circumference of said tire. It is also preferable that the conductive rubber members have a width of 0.5 to 2.0 mm.
The tread portion may have a structure consisting of at least two layers comprising a 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 at an inner portion of the tread portion in the radial direction of said tire and has a specific resistance of 10
6
&OHgr;·cm or less after curing by vulcanization.
It is preferable that the conductive rubber members are made from a rubber cement having a specific resistance of 10
6
&OHgr;·cm or less after curing by vulcanization.
The pneumatic tire of the first embodiment of the present invention is characterized in that, when the conductive paths are formed by disposing conductive rubber members in the tread portion, the conductive rubber members are separated from each other in the circumferential direction with portions of the tread disposed between the conductive rubber members in the circumferential direction, and not in such a manner that a continuous single conductive rubber member is formed around the complete circumference.
Because of the above structure, force in the transverse direction of the tire is effectively dispersed, and movement of the conductive rubber members and deformation of the rubber at the boundaries thereof is suppressed preventing separation of the conductive rubber members. As a result, durability of the tire is improved.
The pneumatic tire of the second embodiment of the present invention comprises 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
&OHgr;·cm or more after curing by vulcanization and conductive rubber members which comprise a rubber composition having a specific resistance of 10
6
&OHgr;·cm or less, have the shape of a column having a small diameter, and replace portions of the surface rubber layer, wherein the conductive rubber member having a shape of a column having a small diameter 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 and are scattered discontinuously on the outer surface of the surface
Hiruma Masato
Kusano Akio
Mouri Hiroshi
Suzuki Gen
Bridgestone Corporation
Maki Steven D.
Sughrue & Mion, PLLC
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