Coatings derived from polyester crosslinked with melamine formaldehyde
View Patent ↗A coating composition is based on a polyester mixed with an alkyl-etherified melamine formaldehyde. The coating composition is partially cured in a first stage to provide a thermoformable partially cured, tack-free, non-blocking, coating layer, followed by application to generally a contoured substrate and thermoforming to conform thereto. The contoured partially cured coating layer is then heat cured to form a cured coating. A hydroxyl-terminated polyoxetane containing repeat units derived from oxetane monomers having one or two pendent —CH 2 —O—(CH 2 ) n —Rf groups, wherein Rf is partially or fully fluorinated, can be esterified with polyester-forming reactants to form a fluorinated polyoxetane-modified polyester.
1. A method of providing a sheet capable of being thermoformed into an exterior surface layer of an article, said method comprising:
a) applying a composition to a substrate so as to form a composite that comprises a layer of said composition coating a surface of said substrate, said composition comprising
1) a polyester,
2) an alkyl-etherified melamine formaldehyde compound and, based on the combined weight of the polyester and alkyl-etherified melamine formaldehyde compound,
3) from about 1 to about 15% of a thermally activatable catalyst;
b) heating said composite to a temperature of from about 49° to about 77° C. for about 2 to about 60 seconds so as to partially cure said composition, thereby making said composition layer non-tacky,
thereby providing a thermoformable sheet suitable for forming an exterior, outward facing surface of said article upon application thereto.
2. The method of claim 1 wherein said thermo-formable sheet is suitable for forming an exterior, outward facing surface of a non-planar article.
3. The method of claim 1 wherein said substrate comprises poly(vinyl chloride).
4. The method of claim 1 wherein said polyester comprises fluorinated polyoxetane units.
5. The method of claim 4 wherein said polyester further comprises a C 2 -C 4 cyclic ether repeating unit.
6. The method of claim 4 wherein each of said fluorinated oxetane units comprises a pendent —CH 2 O(CH 2 ) n Rf group where n is an integer of from 1 to 3 inclusive.
7. The method of claim 1 wherein said composite is heated to a temperature of from about 66° to about 71° C.
8. The method of claim 1 wherein said composite is heated for about 10 to about 20 seconds.
9. The method of claim 1 wherein the partially cured composition exhibits at least about 150% elongation when measured at 82° C.
10. The method of claim 1 wherein said alkyl-etherified melamine formaldehyde compound of said composition comprises the reaction product of a melamine formaldehyde and at least two C 1 -C 6 alkyl alcohols.
11. The method of claim 10 wherein said at least two C 1 -C 6 alkyl alcohols comprise two alcohols having at least a two carbon atom differential in their chain lengths.
12. The method of claim 11 wherein said at least two C 1 -C 6 alkyl alcohols comprise methanol and propyl alcohol.
13. The method of claim 10 wherein said at least two C 1 -C 6 alkyl alcohols comprise two alcohols having at least a three carbon atom differential in their chain lengths.
14. The method of claim 13 wherein said at least two C 1 -C 6 alkyl alcohols comprise methanol and butyl alcohol.
15. The method of claim 1 wherein said melamine formaldehyde of said alkyl-etherified melamine formaldehyde compound of said composition comprises at least three methylol groups.
16. The method of claim 15 wherein said melamine formaldehyde of said alkyl-etherified melamine formaldehyde compound of said composition comprises at least four methylol groups.
17. The method of claim 16 wherein said melamine formaldehyde of said alkyl-etherified melamine formaldehyde compound of said composition comprises at least five methylol groups.
18. The method of claim 17 wherein said melamine formaldehyde of said alkyl-etherified melamine formaldehyde compound of said composition comprises six methylol groups.
19. The method of claim 15 wherein at least one of said at least three methylol groups is alkyl etherified.
20. The method of claim 15 wherein each of said at least three methylol groups is alkyl etherified.