Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-02-25
2001-10-02
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S259000, C525S329900, C525S333100, C525S419000, C152S209100
Reexamination Certificate
active
06297325
ABSTRACT:
FIELD
This invention relates to rubber compositions comprised of cis-1,4-polyisoprene and a polymeric di-maleamic acid and to articles of manufacture having at least one component comprised thereof, including tires. The polymeric di-maleamic acid has been observed to enhance green strength of such rubber composition.
BACKGROUND OF THE INVENTION
Unvulcanized cis-1,4-polyisoprene elastomers, both natural and synthetic, particularly the synthetic elastomer, typically do not have sufficiently desirable green strength in order to permit assembling, or building, various rubber composition-based components which contain such elastomers to form articles of manufacture such, as for example, tires.
A typical major deficiency of unvulcanized synthetic cis-1,4-polyisoprene, and therefore various rubber compositions which contain unvulcanized synthetic cis-1,4-polyisoprene is a usual lack of sufficient green strength and tack needed for satisfactory processing or building properties required in the building of articles of manufacture including the building of tires. The abatement of such usual deficiency has often been sought and may assist in facilitating a replacement, or at least a partial replacement, of natural rubber for appropriate rubber compositions.
The term “green strength”, while being commonly employed and generally understood by persons skilled in the rubber industry, is nevertheless a difficult property to precisely define. Basically, green strength may be thought of as the tensile strength developed when an unvulcanized polymer composition of proper configuration is stressed under controlled conditions. Beyond an initial yield point, unvulcanized natural cis-1,4-polyisoprene rubber compositions will show increasing strength against rupture, or significant deformation, while unvulcanized synthetic cis-1,4-polyisoprene will typically fall below the yield point or will increase only slightly above it. In certain practical applications such as uncured tires, belting, shoes and a number of other products in the course of manufacture, green strength is important in promoting the integrity and cohesiveness, including dimensional stability, of the assembly of various rubber components between building or assembly thereof and the ultimate molding and accompanying vulcanization of the assembled article.
Green strength often manifests itself secondarily in the tack or adhesiveness imparted to various unvulcanized rubber compositions employed in the manufacture of a number of rubber articles such as tires, belting, etc. Other things being equal, an unvulcanized rubber or rubber composition having higher green strength will often exhibit better building tack or adhesion to other unvulcanized rubber-based components and will accordingly ease various fabrication, processing and handling problems associated with the building and the ultimate molding and vulcanization of fabricated articles.
Various additive compounds or agents which have heretofore been utilized to improve green strength of synthetic rubber elastomers, for example, numerous nitroso compounds as mentioned in U.S. Pat. Nos. 2,457,331, 2,477,015, 2,518,576, 2,526,504, 2,540,596, 2,690,780 and 3,093,614. Additionally, various compounds have been mentioned such as those described in U.S. Pat. Nos. 2,969,341, 3,037,954, 3,160,595 and British Patent No. 896,309. Yet another class of additives or compounds are the diesters of 5-norbonene as mentioned in U.S. Pat. Nos. 3,817,883 and 3,843,613. In U.S. Pat. No. 4,124,750 a dihydrazide compound is suggested for cross-linking a synthetic rubber to enhance its green strength.
In the description of this invention, the term “phr” is used to designate parts by weight of a material per 100 parts by weight of elastomer. In the further description, the terms “rubber” and “elastomer” may be used interchangeably unless otherwise mentioned. The terms “vulcanized” and “cured” may be used interchangeably, as well as “unvulcanized” or “uncured”, unless otherwise indicated.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, a rubber composition comprised of cis-1,4-polyisoprene is provided which contains from about 0.1 to about 20, alternately about one to about 10, phr of a polymeric di-maleamic acid.
Preferably said cis-1,4-polyisoprene elastomer is synthetic cis-1,4-polyisoprene because it typically possesses less green strength than natural cis-1,4-polyisoprene elastomer.
Alternately, the cis-1,4-polyisoprene may constitute both the natural and synthetic cis-1,4-polyisoprene elastomers or may simply be a natural rubber.
It is to be appreciated that such rubber composition may contain other conjugated diene-based elastomers such as, for example homopolymers and copolymers of isoprene (other than cis-1,4-polyisoprene) and 1,3-butadiene and copolymers of isoprene and 1,3-butadiene with a vinyl aromatic compound such as styrene and/or alphamethyl styrene, preferably styrene.
In further accordance with this invention, a rubber composition comprises, based upon 100 parts by weight elastomers (phr),
(A) 100 phr of unvulcanized conjugated diene based elastomers comprised of
(1) about 10 to about 90, alternately about 20 to about 80, phr of cis-1,4-polyisoprene elastomer and, correspondingly
(2) about 90 to about 10, alternately about 80 to about 20, phr of at least one additional conjugated diene-based elastomer, and
(B) about 0.1 to about 20, alternately about one to about 10, phr of polymeric di-maleamic acid.
While the mechanism may not be entirely understood, in practice it is believed that the polymeric di-maleamic acid may, to a degree, create some crosslinks between the olefinic portion of the maleamic acid and the olefinic portion of the unvulcanized cis-1,4-polyisoprene diene-based elastomer to thereby increase the green strength of the overall rubber composition.
The resulting rubber compositions may be used as various components of articles of manufacture, particularly various components of tires such as, for example sidewall, carcass ply, tread and apex.
The polymeric di-maleamic acid may be characterized as a polyoxypropylene polymer of about 200 to about 10,000 molecular weight with unsaturated half amide-acid functional groups on each end.
Such polymeric di-maleamic acid might be prepared, for example, by reacting a 2000 molecular weight polyoxypropylene polymer (e.g. Jeffamine D2000® from the Texaco Company) which contains terminal primary amino groups (one on each end of the polymer) with two molar equivalents of maleic anhydride in acetone solution with reflux for 14 hours before the solvent is removed under reduced pressure. The resulting polymeric di-maleamic acid is a polyoxypropylene backbone polymer with a maleamic acid termination on each end of the polymer. The terminal di-maleamic acid functional groups arise from the reaction of the two molar equivalents of maleic anhydride with the two terminal primary amino groups of the polyoxypropylene.
In the practice of this invention, as hereinbefore pointed out, the rubber composition of this invention may contain at least one additional diene-based elastomer. Thus, it is considered that the elastomer is a sulfur curable elastomer.
The additional diene based elastomer may be selected, for example, from homopolymers and copolymers of at least one diene selected from isoprene and 1,3-butadiene (other than the aforesaid natural and synthetic cis-1,4-polyisoprene) and copolymers of at least one diene selected from isoprene and 1,3-butadiene with a vinyl aromatic compound selected from at least one of styrene and alphamethyl styrene, preferably styrene.
Representative of such additional elastomers are, for example, at least one of styrene/butadiene copolymer elastomers (aqueous emulsion polymerization derived and organic solvent solution polymerization derived elastomers), isoprene/butadiene copolymer rubbers, styrene/isoprene copolymer rubbers, styrene/isoprene/butadiene terpolymer rubbers, cis-1,4-polybutadiene rubber, high vinyl polybutadiene rubber with a vinyl 1,2- content in a range of about 30 to about 90 perc
Sandstrom Paul Harry
Wideman Lawson Gibson
Asinowsky Olga
Seidleck James J.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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