Polyester coil coating
View Patent ↗A coil coating composition producing a coil coating with excellent properties at a lower peak metal temperature includes (a) a first, branched polyester prepared by condensation of a polyol component consisting essentially of a flexibilizing diol, 2-methyl-1,3-propanediol, and a polyol having at least three hydroxyl groups and an acid component consisting essentially of isophthalic acid; (b) a second, essentially linear polyester prepared by condensation of a polyol component consisting essentially of a flexibilizing diol and 2-methyl-1,3-propanediol and an acid component consisting essentially of isophthalic acid; and (c) a crosslinking agent.
1. A coil coating composition comprising:
(a) a first polyester prepared by condensation of a polyol component consisting essentially of a flexibilizing diol, 2-methyl-1,3-propanediol, and a polyol having at least three hydroxyl groups and an acid component consisting essentially of isophthalic acid;
(b) a second polyester prepared by condensation of a polyol component consisting essentially of a flexibilizing diol and 2-methyl-1,3-propanediol and an acid component consisting essentially of isophthalic acid; and
(c) a crosslinking agent.
2. A coil coating composition according to claim 1 , wherein the flexibilizing diol of the first polyester and the flexibilizing diol of the second polyester are each independently selected from the group consisting of α,ω-alkylene diols having four or more carbon atoms, diols containing cyclic moieties, dimer fatty alcohol, and combinations thereof.
3. A coil coating composition according to claim 1 , wherein the flexibilizing diol of the first polyester and the flexibilizing diol of the second polyester are each independently selected from the group consisting of 1,4-butanediol, 1,6-hexanediol, cyclohexanedimethanol, dimer fatty alcohol, and combinations thereof.
4. A coil coating composition according to claim 1 , wherein the polyol having at least three hydroxyl groups is selected from the group consisting of trimethylolethane, trimethylolpropane, pentaerthritol, and combinations thereof.
5. A coil coating composition according to claim 1 , wherein the polyol component of the first polyester consists essentially of
from about 6.5% by weight to about 23% by weight of the flexibilizing diol,
from about 41% by weight to about 75% by weight of 2-methyl-1,3-propanediol, and
from about 15% by weight to about 46% by weight of the polyol having at least three hydroxyl groups,
based on the total combined weights of the flexibilizing diol, 2-methyl-1,3-propanediol, and the polyol having at least three hydroxyl groups.
6. A coil coating composition according to claim 1 , wherein the polyol component of the first polyester consists essentially of
from about 8% by weight to about 20% by weight of the flexibilizing diol,
from about 45% by weight to about 65% by weight of 2-methyl-1,3-propanediol, and
from about 20% by weight to about 40% by weight of the polyol having at least three hydroxyl groups,
based on the total combined weights of the flexibilizing diol, 2-methyl-1,3-propanediol, and the polyol having at least three hydroxyl groups.
7. A coil coating composition according to claim 1 , wherein the polyol component of the first polyester consists essentially of
from about 10% by weight to about 15% by weight of the flexibilizing diol,
from about 50% by weight to about 60% by weight of 2-methyl-1,3-propanediol, and
from about 20% by weight to about 30% by weight of the polyol having at least three hydroxyl groups,
based on the total combined weights of the flexibilizing diol, 2-methyl-1,3-propanediol, and the polyol having at least three hydroxyl groups.
8. A coil coating composition according to claim 1 , wherein the first polyester has an hydroxyl number of from about 100 to about 160 mg KOH/gram nonvolatile.
9. A coil coating composition according to claim 1 , wherein the first polyester has a number average molecular weight from about 2800 to about 3600 and a weight average molecular weight from about 5400 to about 8000.
10. A coil coating composition according to claim 1 , wherein the polyol component of the second polyester consists essentially of
from about 22% by weight to about 50% by weight of the flexibilizing diol and
from about 50% by weight to about 78% by weight of 2-methyl-1,3-propanediol,
based on the total combined weights of the flexibilizing diol and 2-methyl-1,3-propanediol.
11. A coil coating composition according to claim 1 , wherein the polyol component of the second polyester consists essentially of
from about 25% by weight to about 45% by weight of the flexibilizing diol and
from about 55% by weight to about 75% by weight of 2-methyl-1,3-propanediol,
based on the total combined weights of the flexibilizing diol and 2-methyl-1,3-propanediol.
12. A coil coating composition according to claim 1 , wherein the polyol component of the second polyester consists essentially of
from about 30% by weight to about 40% by weight of the flexibilizing diol and
from about 60% by weight to about 70% by weight of 2-methyl-1,3-propanediol,
based on the total combined weights of the flexibilizing diol and 2-methyl-1,3-propanediol.
13. A coil coating composition according to claim 1 , wherein the second polyester has an hydroxyl number of from about 35 to about 75 mg KOH/gram nonvolatile.
14. A coil coating composition according to claim 1 , wherein the second polyester has a number average molecular weight from about 3800 to about 5200 and a weight average molecular weight from about 5400 to about 8000.
15. A coil coating composition according to claim 1 , wherein the crosslinking agent comprises a melamine formaldehyde resin and wherein the composition further comprises a strong acid catalyst.
16. A coil coating composition according to claim 1 , comprising
about 5% by weight to about 25% by weight of the first polyester;
about 60% by weight to about 80% by weight of the second polyester; and
about 5% by weight to about 25% by weight of the crosslinking agent,
based on the total combined nonvolatile weights of the first polyester, the second polyester, and the crosslinking agent.