Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-09-22
2002-05-21
Cain, Edward J. (Department: 1714)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152SDIG001, C524S047000, C524S495000
Reexamination Certificate
active
06390164
ABSTRACT:
FIELD
The present invention relates to a pneumatic tire having a layer, preferably an innerliner, for prevention, or retardation, of air permeation from its inner chamber into the remainder of the tire. The innerliner is of a butyl rubber composition which contains a dispersion of a starch/plasticizer composite.
BACKGROUND
A pneumatic rubber tire is conventionally of a toroidal shape and comprised of a carcass with a cavity in which its closure is typically completed with a rigid rim onto which the tire is to be mounted. Such pneumatic tire and pneumatic tire/rim assembly is well known.
The inner surface of a pneumatic tire, namely a surface of said cavity which is sometimes referred to as an “innerliner” is typically composed of an elastomeric composition designed to prevent, or retard, the permeation of air and moisture into the tire carcass from the aforesaid cavity which becomes the tire's inner air chamber. Such tire innerliners are well to those having skill in such art.
Butyl rubber is typically relatively impermeable to air and moisture and is often used as a major portion of the tire innerliner composition and can be in a form of butyl rubber or halobutyl rubber such as, for example, bromobutyl rubber. For example, see U.S. Pat. No. 3,808,177. Butyl rubber, while containing a minor amount of units derived from a diene such as, for example isoprene, is not considered herein as being a diene-based rubber since it contains less than 15 percent of its content derived form a diene monomer and, therefore, sulfur vulcanizes at a much slower rate than diene-based elastomers which contain at least, for example, 30 percent of their elastomer content derived from diene monomers. Such innerliner concept is well known to those skilled in such art.
Accordingly, it is sometimes desired to enhance, or reduce, an already low air permeability of a carbon black reinforced butyl rubber and particularly a halobutyl rubber based tire innerliner.
In the description of this invention, the term “phr” where used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
In the description of this invention, the terms “rubber” and “elastomer” where used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, where used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term “carbon black” as used herein means “carbon blacks having properties typically used in the reinforcement of elastomers, particularly sulfur-curable elastomers”.
A reference to an elastomer's Tg refers to its glass transition temperature which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10° C. per minute.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with one aspect of this invention, a pneumatic tire is provided which contains an air permeation prevention layer (innerliner) comprised of, based upon 100 parts by weight of rubber (phr), 100 parts by weight of at least one rubber selected from butyl rubber and halobutyl rubber having a dispersion therein comprised of (A) from about 30 to about 70, alternately about 40 to about 60 phr of carbon black and (B) about 5 to about 30, alternately about 10 to about 20, phr of a starch/plasticizer composite; wherein said starch composite is comprised of starch and a plasticizer for said starch; wherein said starch is composed of amylose units to amylopectin units in a ratio of about 15/85 to about 100/0, alternately about 20/80 to about 80/20; where said starch has a softening point according to ASTM No. D1228 in a range of about 180° C. to about 220° C.; wherein said starch/plasticizer composite has a softening point in a range of about 110° C. to about 170° C. according to ASTM No. D1228 and, wherein the starch/plasticizer weight ratio is in a range of about 0.4/1 to about 5/1, alternately about 1/1 to about 3/1, so long as the softening point thereof is in a range of about 110° C. to about 170° C.
Preferably, said innerliner has a thickness in a range of about 2.5 to about 6 mm.
A significant aspect of the invention is the use of a dispersion within the carbon black reinforced butyl rubber, or halobutyl rubber, of a particulate starch/plasticizer composite.
It is considered herein that the addition of the dispersion of the starch/plasticizer composite can act to enhance, or reduce, the already low air permeability of the butyl rubber-based composition.
Therefore, it is also considered herein that a new, novel, integral tire innerliner is provided which also has a relatively low air permeability property.
This is considered to be a significant departure from past practice of simply providing carbon black reinforced butyl and halobutyl rubber-based tire innerliners.
In practice, it is considered herein that starch has too high of a softening point (e.g.: at least 180° C. and usually at least 200° C. and higher) to be useful for very many elastomer formulations for tires.
Starch/plasticizer composites with a lower softening point have a greater potential for use in such circumstances for creating a dispersion within the carbon black reinforced butyl or halobutyl rubber-based tire innerliner.
U.S. Pat. Nos. 5, 672,639, 5,403,923, 5,258,430, and 4,900,361 disclose the preparation and use of various starch compositions including use thereof for various tire components.
Starch is understood herein to be a composition which might be represented as a carbohydrate polymer having repeating units of amylose (anhydroglucopyranose units joined by glucosidic bonds) and usually amylopectin, a branched chain structure, as is well known to those having skill in such art. Typically, starch is composed of about 25 percent amylose and about 75 percent amylopectin. (
The Condensed Chemical Dictionary
, Ninth Edition (1977), revised by G. G. Hawley, published by Van Nostrand Reinhold Company, page 813). Starch can be, reportedly, a reserve polysaccharide in plants such as, for example, corn (e.g.: corn starch), potatoes, rice and wheat as typical commercial sources.
It is considered herein that a development of a starch/plasticizer composition, or compositions, with a softening point significantly lower than that of the starch alone, allows the starch to be more easily mixed and processed in conventional elastomer processing equipment.
In practice, it is desired that the synthetic plasticizer itself is compatible with the starch, and has a softening point lower than the softening point of the starch so that it causes the softening of the blend of the plasticizer and the starch to be lower than that of the starch alone. This phenomenon of blends of compatible polymers of differing softening points having a softening point lower than the highest softening point of the individual polymer(s) in the blend is well known to those having skill in such art.
In one aspect, a lowering of a softening point for the starch may be the use of, for example, a polymeric plasticizer such as, for example, poly(ethylenevinyl alcohol) with a softening point of less than 160° C. Other plasticizers, and their mixtures, are contemplated for use in this invention, provided that they have softening points of less than the softening point of the starch, and preferably less than 160° C., which might be, for example, one or more copolymers and hydrolyzed copolymers thereof selected from ethylene-vinyl acetate copolymers having a vinyl acetate molar content of from about 5 to about 90, alternatively about 20 to about 70, percent, ethylene-glycidal acrylate copolymers and ethylene-maleic anhydride copolymers. As hereinbefore stated hydrolyzed forms of copolymers are also contemplated. For example, the corresponding ethylene-vinyl alcohol copolymers, and ethylene-acetate vinyl alcohol terpolymers may be contemplated so long as they have a
Cain Edward J.
Lee Katarzyna W.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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