Resilient tires and wheels – Tires – resilient – With electrical conducting means
Reexamination Certificate
1998-08-07
2001-03-20
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
With electrical conducting means
C152S209500, C152S209800, C152SDIG002, C156S123000, C156S128100, C156S128600, C156S129000
Reexamination Certificate
active
06202724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire comprising a silica-rich compound tread rubber provided with an antistatic conductive rubber layer. It particularly relates to a pneumatic tire having improved safety based on durability and extrusion productivity.
2. Description of the Related Art
In a prior pneumatic tire, a proper amount of carbon black is contained in tread rubber, and there is no problem relating to electrical resistance of a tire or a problem relating to accumulation of charge amount. However, environmental concerns have recently been serious, and a movement of lowering fuel consumption of vehicles has been accelerated. In order to attain low fuel consumption, i.e., mitigation of rolling resistance by improving tread rubber, it is necessary to decrease carbon black as a cause for producing hysteresis loss, and there is today given attention to silica —containing tread rubber by decreasing an amount of carbon black, as tread rubber having excellent low fuel consumption performance. In order to coexist running performance and low fuel consumption performance of a tire at a high level, particularly in a pneumatic radial tire having cap/base structure of a tread, there is a tendency to increase cases of using silica-rich compound rubber as rubber for a cap layer. As a result, there is newly caused a problem relating to electrical resistance and a problem relating to accumulation of a charge amount.
As a solution of such problems, for example, as disclosed in European Patent Specification No. 658 452, there has been known a technique of inserting a conductive rubber layer 20 from a tread surface to tread underlayer rubber at the width directional center portion of a tread 10 (FIG. 7). In this pneumatic tire, as illustrated, a connected face between the conductive rubber layer 20 and the silica-rich rubber layer 10 provided in the tread is perpendicular to the ground-contact surface of the tire.
As described above, a pneumatic tire in which the conductive rubber layer is provided to be perpendicular to the ground-contact surface of the tire sufficiently exhibits antistatic effect because the layer is constantly grounded, but the conductive rubber layer and the silica-rich rubber layer tend to peel off at the connected face due to strain produced in the tire when running, and thus there is a problem from the aspect of tire safety. That is, as disclosed in the above European Patent Specification No. 658 452, if the conductive rubber layer is inserted from the surface to the underlayer rubber in the silica-rich compound tread, in such a case that the tire receives the transverse directional force particularly when the vehicle receives a side wind during high speed running, as shown in FIG. 8, the conductive rubber layer 20, which is heterogeneous from the other tread portion 10, peels off from the boundary face, and this peeling-off has a problem to be continuously extended on the circumference of the tire. Such problem also occurs at the time of revolving and running in like manner. Once the peeling-off occurs, tire durability is considerably lowered.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a pneumatic tire capable of positively securing antistatic effect without damaging driving safety based on durability of the tire.
Moreover, another object of the invention is to provide a pneumatic tire sufficiently exhibiting antistatic effect and simultaneously showing driving safety viewed from durability, and further having improved extrusion productivity.
As a result of study for solving the above problems, in case of forming a current path by applying a conductive rubber layer to a tread, the inventors have found that the conductive rubber layer can be prevented from peeling off by extending a divisional layer consisting one conductive rubber layer to the oblique direction against the thickness direction in a width directional section of the tread rubber layer, to effectively disperse force received from the tire transverse direction, and to restrain movement of the conductive rubber layer and rubber deformation at the boundary face.
Moreover, the inventors have found that further higher extrusion productivity can be obtained by arranging a conductive rubber layer of specific thickness in V-shape or reverse V-shape in a width directional section at the tread of a silica-rich rubber layer of the tire to form a conductive path.
According to the invention, there is the provision of a pneumatic tire having a silica-rich compound rubber layer on at least the surface portion of a tread, in which the silica-rich compound rubber layer is divided at at least one portion in a width directional section of the tire by a conductive rubber layer extended in a circumferential direction substantially over the whole thickness of the rubber layer, wherein a thickness direction distance a in a width directional section of the rubber layer and an edge face length b of a divisional rubber layer consisting of the conductive rubber layer in a width directional section satisfy a relation formulated by the following expression, a<b.
In a preferred embodinent of the invention, a specific resistance value of the silica-rich compound rubber layer after curing is not less than 10
8
&OHgr;·cm, a specific resistance value of the conductive rubber layer is not more than 10
6
&OHgr;·cm, the conductive rubber layer is 0.1-3.0 mm, preferably 0.5-2.0 mm in width, and the edge face length b is 50-100% of a ground-contact width W of the tire.
In another preferred embodiment of the invention, a divisional form in a width directional section of the divisional rubber layer shows a substantially linear shape or a corrugated shape.
In the other preferred embodiment of the invention, the tread has at least two-layer structure comprising a cap rubber layer of the silica-rich compound rubber layer in its surface portion and a base rubber layer which is in downward from the cap rubber layer in the radial direction.
According to the invention, it is preferable that the conductive rubber layer consists of a rubber cement layer or conductive sheet having a specific resistance value of not more than 10
6
&OHgr;·cm after curing.
In the still other preferred embodiment of the invention, the conductive rubber layer is formed into a V- or a reverse V-shape with 0.1-3.0 mm thick in a width directional section of the tire. In this case, it is favorable that the ratio (A/B) of a sectional area A of the conductive rubber layer to a sectional area B of the silica-rich compound rubber layer in a width directional section of the tire is within a range of 0.02-0.1, and when the tread has at least two-layer structure comprising a cap rubber layer of the silica-rich compound rubber layer in its surface portion and a base rubber layer which is downward from the cap rubber layer in the radial direction, the ratio (A/B) of the sectional area A to the sectional area B of the cap rubber layer is within a range of 0.02-0.1.
According to the invention, both wings of the tread may be provided with miniside rubber layers.
Further, the invention provides a method of manufacturing a pneumatic tire, which comprises simultaneously extruding a tread portion of silica-rich compound and an antistatic conductive rubber layer, so as to form the conductive rubber layer of 0.1-3.0 mm thick into a V- or a reverse V-shape in a width directional section of the tire at the tread.
Furthermore, the invention provides a method of manufacturing a pneumatic tire, which comprises dividing a tread portion of silica rich compound into three portions in a V- or a reverse V-shape in a width directional section of the tire, adhering a conductive rubber layer consisting of a conductive rubber sheet or conductive cement layer to at least one of the surfaces resulted from the division, thereafter connecting both the divided tread pieces into one through the conductive rubber layer.
In the latter method invention, it is preferable that the temperature is not less than room te
Fujita Yasuyo
Hiruma Masato
Kusano Akio
Bridgestone Corporation
Maki Steven D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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