Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-04-30
2003-10-07
Weisberger, Richard (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S373000, C428S374000, C428S379000, C428S397000, C428S295100, C057S213000
Reexamination Certificate
active
06630241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber-steel cord composite and a pneumatic tire for passenger cars. More particularly, it relates to a rubber-steel cord composite showing excellent adhesion at high temperatures and excellent durability, and a pneumatic tire for passenger cars showing excellent durability without any adverse effect on performance in an inflated condition in which pressure inside the tire (hereinafter referred to as internal pressure) is maintained and which can be safely used under decreased internal pressure.
2. Description of the Related Art
Composites having steel cords embedded in a rubber composition are used in tires, belts and hoses. Stable adhesion between the steel cord and the rubber composition is required to increase durability. To achieve stable adhesion between the steel cord and the rubber composition, heretofore, direct adhesion in which the cord is plated with brass, i.e., an alloy of copper and zinc, and the brass-plated cord is reacted with sulfur in the rubber composition is generally conducted.
On the other hand, various attempts have been made to achieve stable adhesion by adopting a suitable structure of a steel cord.
For example, the decrease in the life of products due to corrosion of steel filaments by water that penetrates into the products has been a problem in products reinforced with steel cords. When a steel cord has a cavity, water penetrating into the steel cord through cracks formed in a product is transferred through the cavity to other portions of the steel cord in the longitudinal direction of the cord. As the result, the formation of rust due to water spreads to a wider area and adhesion of the rubber and the steel cord decreases at portions having rust. Finally, separation takes place.
To prevent such expansion of corrosion into a wider area, cord structures that allow penetration of rubber sufficiently into spaces inside the cord (spaces between metal filaments) through gaps between adjacent filaments when vulcanization is conducted under a high pressure, have been proposed.
As an examples of the above cord structure, a so-called 1+5 structure comprising one core filament and 5 sheath filaments, which contains gaps between the sheath filaments to facilitate penetration of rubber and can be produced with high productivity because the structure can be formed in a single twisting step, is disclosed in Japanese Patent Application Laid-Open No. (hereinafter abbreviated as JP-A No.) 60-38208 and JP-A No. 59-1790.
However, although the average space of the gaps is sufficient, the above structure has a drawback in that the sheath filaments are not uniformly arranged and may contain portions where filaments are tightly attached together. Therefore, portions not penetrated by rubber may be formed due to random variations of the structure of the cord in the production of the cord.
It is suggested in JP-A 56-131404 that a cord having a 1+5 structure may be formed using a core filament made to have a slightly wavy shape. However, because the diameter of the core filament is smaller than the diameter of the sheath filaments, the above structure has drawbacks in that gaps between sheath filaments are small to make the penetration of rubber difficult, that the effect obtained by the wavy shape decreases due to decreased rigidity of the core filament and that the strength decreases when the core filament is shaped to a larger degree to improve penetration of rubber.
A structure can also be considered wherein the diameter of the core filament is made larger than the diameter of the sheath filament and the gaps between adjacent sheath filaments are kept to a specific size or larger to achieve penetration of rubber into the inside of the cord. However, when this structure is used, the weight of the entire cord increases and productivity decreases. Penetration of rubber is insufficient because deviations occur in the disposal of portions of the sheath filaments, which may become attached together. Therefore, expansion of corrosion into a wider area cannot be prevented sufficiently.
As pneumatic tires that can be used under reduced internal pressure, i.e., under a so-called run-flat condition, (hereinafter referred to as pneumatic safety tires), two types of tires are known with respect to the tire wheel. One such tire is a tire of the internal wheel type, in which an internal ring wheel made of a metal or a synthetic resin is attached to a rim at a portion inside the air chamber of the tire. The other such tire is a tire of the side reinforcement type, in which a layer of a relatively rigid rubber composition is disposed in the vicinity of a carcass in an area ranging from the bead portion to the shoulder portion of the tire side wall. Of these two types, the tire of the internal wheel type has a higher ability to support a load in the run-flat condition and is used for vehicles for transportation of goods and vehicles for military use which do not require a high degree of riding comfort. The tire of the side reinforcement type is used for vehicles carrying a relatively small load and requiring a higher degree of riding comfort. Both types of tires have been accepted as tires showing useful performance.
The tire of the side reinforcement type which is suitable for a pneumatic tire for passenger cars is reinforced with a relatively rigid reinforcing rubber layer having a cross-section of a crescent shape which is disposed on an inner face of the carcass layer in the side wall portion such that one end portion thereof is placed at a position under a belt layer, with the carcass disposed between them, and the other end portion is disposed at a position over a rubber filler. When the tire has a puncture and the air inside is lost, the load is carried by the rigidity of the side wall itself which is reinforced with the reinforcing rubber layer and the tire can be used for a predetermined distance in the run-flat condition although the speed must be decreased to some degree.
However, it is the actual situation at present that, even when the tire of the side reinforcement type is used, performance of the tire is not satisfactory in the run-flat condition.
Although the load carried by a general use tire for passenger cars is relatively small, the load per one tire is as large as about 500 kgf in the case of large size passenger cars. In this case, bending of side walls increases in a punctured condition and the side walls completely buckle under a dynamic load, which increases several times during driving The punctured tire is used while this phenomenon repeatedly takes place in the tire. As the result, the bead portion in the side wall is pushed up by a flange of the rim The cover rubber and the turned-up portion of the carcass which are placed between the curved flange and the rubber filler melt by heat or are fractured. The tire in this condition cannot be used any more even after the portion of the puncture has been repaired.
When a safety tire of a size for general purposes is driven in the run-flat condition, the temperature inside the tire increases to a temperature as high as 200° C. or higher. Therefore, adhesion between rubber and fiber at a high temperature is not sufficient even when fibers having excellent heat resistance such as polyethylene terephthalate (PET) is used. Specifically in the case of a tire using PET for the carcass, the main cause of trouble during use in the run-flat condition is separation at the interface of PET and an adhesive layer. Moreover, even when a fiber showing excellent adhesion with rubber at high temperatures such as 66-Nylon is used, the surface of the cord is softened and the reinforcing effect decreases in a tire at a high temperature. Specifically in the case of a tire using 66-Nylon for the carcass, the main cause of trouble during use in the run-flat condition is separation due to melting of the surface layer of the 66-Nylon cords. Therefore, further improvement in durability in the run-flat condition is desired in both the case in w
Kobayashi Kazuomi
Matsuo Kenji
Nishikawa Tomohisa
Bridgestone Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Weisberger Richard
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