Pneumatic tire with hybrid material bead apex

Details Pneumatic tire with hybrid material bead apex Pneumatic tire with hybrid material bead apex

1999-06-17

2001-11-20

Johnstone, Adrienne C. (Department: 1733)

Resilient tires and wheels

Tires, resilient

Pneumatic tire or inner tube

C152S540000, C152S541000, C152S547000

Reexamination Certificate

active

06318430

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire in which a occurrence of voids in bead portions can be controlled and bead durability can be improved.
2. Description of the Related Art
In a pneumatic tire, as shown in FIG.
6
(A), a carcass (a) is turned up around bead cores (b) to be secured thereto, and bead apex rubber (c) is filled between a ply main portion (a
1
) and each ply turnup portion (a
2
) of the carcass (a), thereby ensuring necessary bead rigidity.
In conventional heavy duty tires for trucks, buses and the like, the volume of the bead apex rubber (c) is increased to increase the bead rigidity and thereby to improve bead durability.
On the other hand, in recent years, a bead structure is revamped for weight reduction of the tire. FIG.
6
(B) shows such a technique for reducing weight while improving the bead durability. In this technique, contrary to the above, the volume and height of bead apex rubber (c) are greatly decreased, and the height of a ply turnup portion (a
2
) is increased so that the ply turnup portion (a
2
) adjoins the ply main portion (a
1
). (hereinafter, referred to as a new bead structure).
In this new bead structure, the bead apex rubber (c) requires higher strength and higher rigidity than in the conventional structure. Therefore, the carbon black and/or crosslinking agent are increased. However, when the amount of carbon black is increased, rubber flowing during vulcanizing the tire becomes insufficient because of high viscosity, and, in the vulcanized tire, voids are liable to occur near the radially outer end (e) of the bead apex rubber (c). When the large amount of crosslinking agent is added, quality of a product tends to be impaired because rubber scorching may occur during extruding the rubber.
In the new bead structure, further, the height (h) is set as small as possible for the bead durability. However, as a degree of bending of the carcass ply turnup portion (a
2
) occurring below the adjacent region (g) is greatly increased due to the decreased bead apex rubber volume, its spring-back force during vulcanization is strong, and thus a tendency of occurrence of voids is further increased as the height (h) is decreased.
BRIEF SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide a pneumatic tire in which occurrence of voids can be effectively controlled, without hindering the weight reduction and the improvement in bead durability.
According to the present invention, a pneumatic tire comprises a tread portion, a pair of sidewall portions, a pair of bead portions, a bead apex disposed in each bead portion, and a carcass ply extending between the bead portions and turned up in each bead portion so as to wrap the bead apex therein, the bead apex made of a hybrid material which is compounded from rubber, synthetic resin and short fiber at least.
Preferably, the short fiber has an average diameter of 0.01 to 0.20 mm and an average length of 1.0 to 10.0 mm, and the proportion of the short fiber is 3 to 15 parts by weight with respect to 100 parts by weight of the rubber. The hybrid material has a 100% modulus of at least 10.0 MPa, a tensile strength of at least 10.0 MPa, a breaking elongation EB of at least 200%, a Mooney viscosity of from 30 to 50 ML
1
+4, and a scorch time (t
10
) of at least 20 minutes.


REFERENCES:
patent: 1349898 (1920-08-01), Marquette
patent: 1606885 (1926-11-01), Maynard
patent: 1611144 (1926-12-01), Hopkins
patent: 4236563 (1980-12-01), Moers et al.
patent: 4711285 (1987-12-01), Ogawa et al.
patent: 5593522 (1997-01-01), Neddenriep et al.
patent: 0645424A1 (1995-03-01), None
patent: 3-28243 (1991-02-01), None

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