Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1998-12-21
2001-04-03
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S517000, C152S555000, C152S556000
Reexamination Certificate
active
06209604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire for passenger cars, and more particularly to a pneumatic tire for passenger cars which has excellent durability and can be safely used even when the internal pressure of the tire is reduced.
2. Description of the Related Art
Cords of aliphatic polyamide fibers such as nylon 66 fiber are frequently used as reinforcing cords for tires because of their high strength and excellent resistance to wear. However, these cords do not always give satisfactory results when they are used for pneumatic tires as passenger cars.
Pneumatic tires for passenger cars have been improved remarkably in recent years by the use of cords of polyester fibers which show excellent dimensional stability and have high strength in place of the above fibers for reinforcement of the tires.
Among the polyester fibers, polyethylene terephthalate fibers (PET) are generally used as the reinforcing material for rubber such as tire cords because PET has a Young's modulus higher than that of nylon 66 fiber and about the same as that of rayon and shows a better balance of physical properties than other fiber materials.
However, PET exhibits inferior dimensional stability under heating because of a decrease in the Young's modulus although PET has a relatively high Young's modulus at room temperature. Therefore, in spite of the high Young's modulus, PET manufactured to suit industrial applications such as the reinforcement of rubber has a drawback in that the Young's modulus decreases under heating to about the same value as that of general use PET used for clothing.
Polyethylene naphthalate fibers (PEN) stretched sufficiently by a heat treatment show a Young's modulus almost twice that of PET at room temperature. Moreover, PEN has a Young's modulus as high as 100 g/d or more at 100° C. or higher and exhibits excellent dimensional stability under heating such as a dry heat shrinkage of 2% or less at 150° C. Therefore, the application of PEN as the reinforcing material of rubber such as tire cords has been attempted.
However, heat buildup inside a tire is extremely large when the tire is used with a lower internal pressure, i.e., under so-called run-flat conditions. Therefore, adhesion at high temperatures is not sufficient even when PET or PEN is used. The main cause of failure of a tire during use in a run-flat condition is separation at the interface of the PET or PEN and the adhesive layers.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a pneumatic tire for passenger cars which shows excellent durability because separation at the interfaces of adhesive layers and reinforcing fibers does not take place during use, particularly during use in a run-flat condition, and a layer of a rubber-filament fiber composite is disposed at side wall portions of the tire.
As the result of studies in detail by the inventors on the behavior of carcass plies when used in a run-flat condition, it was found that a pneumatic tire for passenger cars showing an excellent durability can be provided when a specific aliphatic polyamide is used for the reinforcing cords and a rubber-filament fiber composite is disposed at the side wall portions. The present invention has been completed based on the above knowledge.
The present invention provides a pneumatic tire for passenger cars comprising:
a pair of left and right bead cores;
a carcass formed in which a plurality of reinforcing cords disposed parallel to each other are embedded in a coating rubber;
a tread layer disposed at an outer side of the carcass portion in the radial direction of the tire; and
a pair of side wall portions disposed at the left and right of the tread portion;
wherein a rubber reinforcing layer having a crescent-shaped cross-section and at least one sheet of a rubber-filament fiber composite having a thickness of 0.05 to 2.0 mm which is formed from a rubber component and filament fibers having a diameter or a maximum cross-sectional dimension of 0.0001 to 0.1 mm and a length of 8 mm or more are disposed in each of the side wall portions; and
the reinforcing cord of carcass ply is made of an aliphatic polyamide fiber having a melting point of 250° C. or higher as measured by differential scanning calorimetry (DSC).
It is preferable that the filament fiber in the rubber-filament fiber composite is a fiber selected from the group consisting of aromatic polyamide fiber, rayon fiber, polyethylene naphthalate fiber, polyimide fiber, carbon fiber, glass fiber and steel wire, that the filament fiber in the rubber-filament fiber composite has a diameter or a maximum cross-sectional dimension of 0.0001 to 0.005 mm and a length of 10 mm or more, that the content of the filament fiber in said rubber-filament fiber composite is 4 to 50% by weight, that said rubber-filament fiber composite is formed from a rubber and a nonwoven fabric having a weight per area of 10 to 300 g/m
2
, that said nonwoven fabric has a thickness of 0.1 to 0.5 mm and that said reinforcing cord of carcass ply is made of nylon 66 fiber or nylon 46 fiber.
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Patent Abstracts of Japan, vol. 097, No. 007, Jul. 31, 1997 & JP 09-058229 A (Yokohama Rubber Co Ltd), Mar. 4, 1997.
Kobayashi Kazuomi
Matsuo Kenji
Nishikawa Tomohisa
Bridgestone Corporation
Johnstone Adrienne C.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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