Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1997-01-07
1998-11-17
Chen, Vivian
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
428203, 428413, 4284231, 523400, 525107, 525111, 525117, 525119, 525207, 525221, 525453, B32B 2706, B32B 2708, B32B 2738
Patent
active
058373535
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a curable coating composition particularly useful as a top coat in multi-layered coating systems.
Base coat-clear coat systems have found wide acceptance in the past decade as automotive finishes. Continuing effort has been directed to such coatings systems to improve the overall appearance, the clarity of the top coat, and the resistance to deterioration. Further effort has been directed to the development of coating compositions having low volatile organic content (VOC) and which cure at ambient temperature.
Previous efforts at improving the etch resistance and durability of coatings had suggested the use of anhydride resins having pendant non-cyclic anhydride moieties in combination with resins that react with the polyanhydride resins to cure under curing conditions. However, a continuing need exists for coating formulations which can be sprayed at low VOC and which exhibit outstanding performance characteristics after application, and particularly resistance to environmental etching, and which cure at room temperature or ambient conditions.
EPA 598,131 discloses curable compositions that may contain two noncyclic acid anhydride groups, not 3 groups as employed herein to insure branching.
SUMMARY OF THE INVENTION
The present invention provides a sprayable coating composition which can be easily applied at high solids and exhibits outstanding appearance and durability after application and ease of maintenance.
Specifically, the instant invention provides a curable coating composition for curing at ambient conditions comprising organic solvent and binder comprising
(a) an anhydride resin having a molecular weight of less than about 3000 that contains (1) a central moiety, and (2) on average, at least 3 pendant, non-cyclic anhydride moieties bonded to each central moiety;
(b) An oligomer or polymer having a molecular weight of 150 to 20,000 and having epoxy functionality of at least 2, at least a portion of which oligomer or polymer has at least one hydroxy functionality to enable curing at ambient conditions;
(c) an optional amount of an isocyanate crosslinking agent; and
(d) A functional effective amount of at least one active catalyst, and
wherein the ratio of equivalents of hydroxy to anhydride is at least 0.05 to 1.0.
DETAILED DESCRIPTION OF THE INVENTION
The compositions according to the present invention comprise anhydride resins having a (weight average) molecular weight of less than about 3000 and having a central moiety with more than one pendant, non-cyclic anhydride moiety bonded to each central moiety. This anhydride can suitably be used in the amount of 10 to 80 percent by weight of binder, preferably 35 to 60 percent. The anhydride is asymmetrical, and preferably contains a moiety represented by the following formula: ##STR1## wherein (CM) is a central moiety, (R.sup.1) is an organic moiety, and n is a number of pendant anhydride groups that averages greater than one.
The central moiety can be a simple organic moiety, such as an aliphatic, cycloaliphatic or aromatic moiety, with a plurality of anhydride groups bonded to it. Alternatively, it can contain a plurality of repeating units which are bonded to one or more pendant anhydride groups. Examples of suitable non-polymeric central moieties are those derived from multifunctional alcohols such as pentaerythritol, trimethylolpropane and neopentyl glycol. The multifunctional alcohols are reacted with cyclic, monomeric anhydride such as methyl hexahydrophthalic anhydride to give a multifunctional acid containing moiety. The resulting product is then reacted with ketene to form the linear pendant anhydride.
The central moiety is linked to more than one non-cyclic anhydride moiety, on average. It is preferably linked to at least about 2 non-cyclic anhydride groups on average and more preferably to at least about 3 non-cyclic anhydride groups on average. The anhydride equivalent weight (formula weight per anhydride group) is preferably at least about 200 and preferably no more tha
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Barsotti Robert J.
Harper Lee R.
Chen Vivian
Costello James A.
E. I. Du Pont de Nemours and Company
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