Cross-linked polyester protective coatings
View Patent ↗The invention relates to protective coating systems derived from a functional polyester resin, a cross-linker and a phenol-formaldehyde resin. Also provided is a method of coating a metal substrate using the protective coating systems to produce a cross-linked protective coating. Further provided is a composite material prepared with the coating system and, in certain embodiments, useful in fabricating metal foodstuffs storage containers. The composite material may be particularly useful in fabricating foodstuffs storage containers and “easy-open” end closures wherein the cross-linked protective coating contacts the foodstuffs.
1. A composition comprising:
a hydroxyl-functional polyester resin,
a carboxyl-functional polyester resin having an acid number from about 100 to about 300 milligrams KOH per gram,
a cross-linker, and
one or more phenol-formaldehyde resin;
wherein the composition is in the form of a hardenable coating composition and is substantially free of BPA, BPF, BADGE and BFDGE.
2. The composition of claim 1 , wherein the hydroxyl-functional polyester resin exhibits a hydroxyl number from about 5 to about 200 milligrams KOH per gram.
3. The composition of claim 1 , wherein the hydroxyl-functional polyester resin exhibits a number average molecular weight from about 1,000 to about 7,500 Daltons.
4. The composition of claim 1 , wherein the hydroxyl-functional polyester resin is present in an amount from about 75 to about 90 percent by weight of the hardenable coating composition on a non-volatile solids basis.
5. The composition of claim 1 , wherein the carboxyl-functional polyester resin exhibits a number average molecular weight from about 2,000 to about 5,000 Daltons.
6. The composition of claim 1 , wherein the carboxyl-functional polyester resin is present in an amount from about 0.1 to about 5 percent by weight of the hardenable coating composition on a non-volatile solids basis.
7. The composition of claim 1 , wherein the cross-linker is selected from one or more of the group consisting of a phenoplast cross-linker, an aminoplast cross-linker and a blocked isocyanate cross-linker.
8. The composition of claim 1 , wherein the cross-linker is a blocked isocyanate cross-linker present in an amount from about 1 to about 5 percent by weight of the hardenable coating composition on a non-volatile solids basis.
9. The composition of claim 1 , wherein the phenol-formaldehyde resin is present in an amount from about 1 to about 5 percent by weight of the hardenable coating composition on a non-volatile solids basis.
10. The composition of claim 1 , further comprising a resole-formaldehyde resin.
11. The composition of claim 10 , wherein the resole-formaldehyde resin is present in an amount from about 2 to about 5 percent by weight of the hardenable coating composition on a non-volatile solids basis.
12. The composition of claim 1 , further comprising a substantially nonaqueous carrier liquid.
13. The composition of claim 1 , further comprising from about 0.1 to about 5 weight percent of a catalyst on a non-volatile solids basis.
14. The composition of claim 1 , further comprising a pigment.
15. A composition, comprising:
one or more functional polyester resin having at least one hydroxyl group, at least one carboxylic group, a hydroxyl number from about 5 to about 150 milligrams KOH per gram, and an acid number of from about 50 to about 250 milligrams KOH per gram,
a cross-linker, and
one or more phenol-formaldehyde resin;
wherein the composition is in the form of a hardenable coating composition and is substantially free of BPA, BPF, BADGE and BFDGE.
16. A method of applying a hardenable coating composition to a metal substrate, comprising:
applying a first hardenable coating composition to at least one surface of a substrate,
applying a second hardenable coating composition over the first hardenable coating composition, said second hardenable coating composition including:
a hydroxyl-functional polyester resin,
a carboxyl-functional polyester resin having an acid number from about 100 to about 300 milligrams KOH per gram,
a cross-linker, and
a phenol-formaldehyde resin,
wherein the second hardenable coating composition is substantially free of BPA, BPF, BADGE and BFDGE; and
curing the first and second hardenable coating compositions to provide a hardened composite coating on the metal substrate.
17. The method of claim 16 , wherein the first hardenable coating composition is substantially identical in chemical composition to the second hardenable coating composition.
18. The method of claim 16 , wherein each of the first and second hardenable coating compositions is applied at a coating weight of from about 6 to about 12 grams per square meter on a non-volatile solids basis.
19. A metal foodstuffs container having at least an interior surface coated with a hardened coating composition produced according to the method of claim 16 .
20. A metal foodstuffs container according to claim 19 , wherein the metal foodstuffs container is a multi-part can having at least one easy-open end closure with at least an interior surface of the easy-open end closure coated with a hardened coating composition according to the method of claim 16 .
21. The composition of claim 15 , wherein the cross-linker comprises a blocked isocyanate cross-linker.