Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-07-27
2001-07-03
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S450000, C152SDIG001
Reexamination Certificate
active
06253814
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to a tire having an airtight layer with a ductile layer.
Tubeless tires have an interior surface of low air permeability in order to avoid deflation of the tire and to protect the sensitive internal areas of the latter against intake of oxygen and water, such as the plies containing wire cords sensitive to oxidation. Today such protection of the interior surface of tires is provided by coatings made of butyl rubber.
Since fuel economy and the need to protect the environment have become a priority, it is desirable to produce airtight coatings with a weight and a hysteresis as low as possible. Performances in terms of airtightness of butyl rubber are linked to a not negligible minimum thickness of rubber (in the order of one millimeter) and therefore to a certain weight, which makes it impossible to respond to these new requirements efficiently.
In order to accomplish such objective of weight reduction of the coating, while maintaining good airtightness properties, numerous solutions have been proposed. The very great majority of those solutions have concentrated essentially on the use of materials of very low air permeability other than butyl rubber. In particular, the use of lamellar composite structures has been proposed, consisting of one or more layers of barrier material, to which is added or not an adhesive layer ensuring maintenance on the compound to be coated.
By way of illustrative examples of this prior art, U.S. Pat Nos. 4,874,670 and 5,036,113, describe the development of an elastomer inner liner consisting of a photoreticulated polymer film maintained in the internal compound of the casing by means of an adhesive (formophenol resin or alcohol acrylate with polymerized long chain). In spite of a reduced thickness and air permeability relative to the butyl rubber-base inner liner, this film has a mediocre adherence temperature resistance as well as overly high vitreous transition temperature values (Tg) for use as a tire casing inner liner.
Furthermore, the oxygen permeability of polyurethanes increases in the presence of water, which is unfavorable for the role of protection by the inner liner of the internal plies against corrosion of the cords, as well as for the maintenance of inflation pressure. The same problem appears in U.S. Pat. No. 5,264,524, where the barrier coating consists of an acrylonitrile/butadiene/polyurea copolymer.
Other solutions have also been proposed, such as presented in U.S. Pat. No. 5,236,030, which describes the lining of a tire casing consisting of a thin polyethylene film of ultrahigh molecular weight (UHMWPE), the airtightness and lightness of which are augmented in relation to a butyl rubber inner liner, without requiring the use of an adhesive layer, although no proof of adhesive sufficiency of the UHMWPE layer is presented. This layer is placed directly inside the tire casing, which probably results, upon forming in the tire casing and upon vulcanization, in an alteration of crystallinity of the film, which is a parameter essential for low air permeability.
In the variant applications presented in patents JP 4062009 and JP 4212602, the UHMWPE film in emulsified powder form is sprayed or brushed on the internal compound of the crude tire formed, then dried and vulcanized. Such a method necessitates perfect mastery of the drying phase and entails an operating time incompatible with an industrial application.
Another solution, such as patent WO 92/20538 describing the use of a reticular chlorinated polyethylene elastomer (CPE), whose oxygen permeability, weight and cost are reduced in relation to a butyl rubber inner liner, does not seem any more satisfactory, the airtightness function not being accomplished efficiently enough.
It is to be feared, moreover, that the thermoplastic character of most of the materials used is incompatible with the mechanical stresses to which the interior surfaces are subjected on different phases of assembly and vulcanization and on the rolling of said tires.
SUMMARY OF THE INVENTION
The invention is aimed at providing a new coating intended for airtight tires and overcoming such difficulties.
It has been discovered surprisingly that the metallized plastic films whose barrier properties are well known for the manufacture of packaging, notably, to preserve foods and protect them from oxidation, could be transposed to tires with certain adaptations. This application seems all the more amazing considering that the expert is aware of the incompatibilities of such films with elastomers at the same time, from the standpoint of producing a good bond between those materials, indispensable for an application to tires, and the insufficient elasticity of such films to accompany the deformations undergone by their support in applications to tires.
Thus, the invention concerns a toroidal-shaped tire containing an airtight layer, characterized in that the airtight layer contains at least one ductile metal layer.
In fact, the presence of a metal layer makes it possible to ensure wholly satisfactory airtightness, compatible with tire requirements. Furthermore, the ductility of the metal layer enables the airtight layer to accompany the deformations sustained by the tire carcass in the course of assembly, curing and rolling.
The airtight layer can be placed on either side of the tire carcass ply, but it can also be a standard airtight coating placed on the interior surface of the tire.
According to another characteristic, the thickness of the metal layer is less than or equal to 5 &mgr;m (micrometers) and preferably ranges between 30 and 200 nm (nanometers). This fineness thus makes it possible, on the one hand, thanks to the ductility of the metal, to accompany strong deformations of the tire and, on the other, to reduce the weight of the airtight layer considerably, while preserving the same airtightness capacity, if not improving it.
The metal layer consists preferably of aluminum. In fact, aluminum can be easily used to make metallized films by vacuum deposition.
According to a variant embodiment of the invention, the airtight layer comprises at least one protective layer covering the metal layer and facilitating handling of the metal layer for use of the coating in manufacture of the tire.
Said protective layer can be removed or retained once the tire is finished, in which case it consists advantageously of an extendible polymer in order to follow the deformations sustained by the tire and to help the metal layer follow them.
REFERENCES:
patent: 3106210 (1963-10-01), Reynolds et al.
patent: 3586005 (1971-06-01), Lippman, Jr. et al.
patent: 0557091 (1993-08-01), None
patent: 0760297 (1997-03-01), None
patent: 769286 (1957-03-01), None
Patent Abstracts of Japan, Publication No. 56138005, Application No. 55041848, Bridgestone Corp., Decorated Tire, Oct. 28, 1981, Abstract.
Baker & Botts L.L.P.
Compagnie Generale des Etablissements Michelin - Michelin & Cie
Johnstone Adrienne C.
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