Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-11-09
2004-03-23
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of metal
C428S461000, C428S463000, C524S556000, C524S560000, C524S565000, C525S102000, C525S123000
Reexamination Certificate
active
06709758
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to protective coatings on elastomers.
BACKGROUND OF THE INVENTION
Elastomeric materials are utilized in numerous industrial applications. For example, elastomeric materials are utilized in the manufacture of various hoses, seals, mounting, damping and insulating devices found in the engine compartments of automobiles and other vehicles. In addition, devices for mounting the engines within these vehicles typically comprise one or more metal parts adhesively bonded to one or more vulcanized elastomeric parts. In these and many other industrial applications utilizing vulcanized elastomeric materials, the elastomeric materials are typically exposed to corrosive and degrading materials such as various solvents, oils and fuels. Elastomeric materials have a tendency to degrade when exposed to these types of materials, and there is a continuing search within the elastomer industry to create an elastomer which is resistant to corrosive materials.
One method of rendering elastomeric materials resistant to corrosive materials is to apply a protective coating to the elastomeric material. Various corrosion-resistant coatings previously utilized for both flexible substrates (e.g., elastomeric substrates) and rigid substrates (e.g., steel, stainless steel, aluminum or plastic) include polyurethanes, polysulfides and fluorocarbon elastomers. When applied to rigid substrates, traditional corrosion-resistant coatings such as fluorocarbon elastomers have been found to provide excellent resistance to oil and fuel. However, when applied to flexible elastomeric substrates such as natural rubber or polybutadiene, the fluorocarbon elastomers suffer from poor fatigue resistance, poor low temperature characteristics, and poor adhesion to the natural rubber or polybutadiene substrate.
U.S. Pat. No. 4,774,288 discloses a hydrogenated copolymer of a conjugated diene and an &agr;,&bgr;-unsaturated nitrile containing an active phenol-formaldehyde resin vulcanization system. The disclosure is directed to the bulk vulcanizate, which is characterized as having good compression set properties and a good resistance to oils and good resistance to oxidative attack in air at elevated temperature aging under oxidizing conditions, however no mention is made suggesting that solvent borne coatings could be formed on flexible elastomeric substrates such as natural rubber and polybutadiene which might provide useful properties.
U.S. Pat. No. 5,314,955 discloses a coating composition consisting of (a) a hydrogenated acrylonitrile-butadiene copolymer, (b) a phenolic resin, (c) a curing component, and (d) a solvent. This coating solves many of the problems of adhesion to rubber substrates combined with fatigue resistance and fuel resistance. One of the drawbacks of this coating composition is that it requires a high temperature bake to cure the coating and to promote adhesion to adjacent metal surfaces. Some parts such as helicopter rotor bearings are damaged by the high temperature bake. The high temperature bake is also costly in production since it adds a time delay and additional handling of the parts. There still exists a need for improved protective coatings for flexible elastomeric substrates such as natural rubber and polybutadiene that are resistant to fatigue and temperature variability, and that exhibit effective adhesion to the substrate, and that cure at room temperature.
SUMMARY OF THE INVENTION
The coating composition of the invention is resistant to fatigue and temperature variability and provides for excellent adhesion to flexible elastomeric substrates and it cures at room temperature. More specifically, the coating composition of the invention comprises (A) a carboxylated hydrogenated acrylonitrile-butadiene copolymer, (X-HNBR) (B) a curing component which contains at least one isocyanate group and a group which forms crosslinks, and (C) a solvent. In another aspect, there is a method for coating a substrate comprising applying the aforementioned solvent-based coating to the surface of a vulcanized rubber substrate which is bonded to metal, drying the coating and allowing the dried coating to cure at ambient conditions, optionally with application of heat. It is preferred to provide the coating also onto the portion of exposed metal around the periphery of the elastomer. The present invention provides coatings for elastomer-metal composites with excellent adhesion to the elastomer substrate, resistance to corrosive materials and resistance to flex- fatigue over a wide temperature range.
DETAILED DESCRIPTION OF THE INVENTION
(A) X-HNBR
To provide the ethylenically unsaturated nitrile-conjugated diene rubber with high saturation, the hydrogenation of carboxylated nitrile butadiene rubber is conducted. The hydrogenation serves to saturate at least 80 of the unsaturated bonds of the rubber. When the degree of saturation is less than 80%, the rubber's heat resistance is low, and when it exceeds a preferred value of 99%, the rubber's elasticity shown by compression set, etc. is decreased too much. The more preferred degree of saturation of the rubber is 90-98%.
The conjugated dienes useful for preparing the carboxylated acrylonitrile-butadiene copolymers which are further hydrogenated can be any of the well-known conjugated dienes including 1,3-butadiene; 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene; 1,3-pentadiene; 1,3-hexadiene; 2,4-hexadiene; 1,3-heptadiene; piperylene; and isoprene, with 1,3-butadiene presently being preferred.
Carboxyl groups are present in the X-HNBR from &agr;,&bgr;-unsaturated monocarboxylic acids with 3 to 5 C-atoms such as acrylic acid, methacrylic acid and crotonic acid and/or other known carboxyl group-containing monomers such as, but not limited to &agr;,&bgr;-unsaturated dicarboxylic acids with 4 to 5 C-atoms, e.g., maleic acid, fumaric acid, citraconic acid and itaconic acid. The bound unsaturated carboxylic acid may be present in an amount of from about 1 to about 10 weight percent of the copolymer, with this amount displacing a corresponding amount of the conjugated diolefin.
Further, a third optional monomer may be used in production of the polymer. Preferably, the third monomer is an unsaturated mono- or di-carboxylic acid derivative (e.g., esters, amides and the like).
The unsaturated nitrile comonomer copolymerized to form a carboxylated acrylonitrile-diene copolymer typically correspond to the following formula:
wherein each A is hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms. Examples of A groups include alkyl and cycloalkyl, such as methyl, ethyl, isopropyl, t-butyl, octyl, decyl, cyclopentyl, cyclohexyl, etc., and aryls such as phenyl, tolyl, xylyl, ethylphenyl, t-butylphenyl, etc. Acrylonitrile and methacrylonitrile are the presently preferred unsaturated nitriles.
The X-HNBR copolymers are polymerized by reaction of the any of the aforementioned exemplary conjugated dienes, unsaturated nitrile and unsaturated carboxyl-group containing comonomers in the presence of a free radical initiator by methods well known to those skilled in the art. Suitable free radical initiators are beyond the scope of this disclosure, and are typically organic oxides, peroxides, hydroperoxides, and azo compounds, etc., such as hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, di-tert-butyl peroxide, ascaridole, acetyl peroxide, tert-butyl hydroperoxide, trimethylamine oxide, dimethylaniline oxide, isopropylperoxydicarbonate, diisobutylene ozonide, peracetic acid, nitrates, chlorates, perchlorates, azobisisobutyronitrile, etc.
The preferred commercially available X-HNBR is made from a carboxylated nitrile-diene copolymer that is hydrogenated in two steps. It is known that the C—C double bonds of the 1,2-vinyl-configured butadiene units in NBR are hydrogenated very rapidly, followed by the 1,4-cis configured units. The 1,4-trans configured butadiene units are hydrogenated comparatively slowly. The NBR products used for hydrogenation are distinguished by a predominant proportion of the 1,4-tr
Halladay James R.
Krakowski Frank J.
Dearth Miles B.
Lord Corporation
Short Patricia A.
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