Carbodiimide Curing For Packaging Coating Compositions
Coated packages and methods for coating such packages is disclosed The coating compositions comprise a carboxyl-containing polymer and a polycarbodiimide.
1 . A coated package composing a coating applied to the surface of the package, the coating being derived from a composition comprising:
(a) a carboxyl-containing polymer, and
(b) a polycarbodiimide having the following structural unite (a) or (b) including mixtures thereof:
where e is an integer of from 2 to 20; f and g are each at least 1, and f+g is an integer up to 20; E is a radical selected from
where R 2 comprises a cyclic radical and R 3 is a linear hydrocarbon radical containing at least 4 carbon atoms and R 4 is hydrogen or an alkyl radical.
2 . The coated package of claim 1 in which the package is a food or beverage container.
3 . The coated package of claim 2 in which the coating is applied to a food-contacting surface of the container.
4 . The coated package of claim 2 in which the coating composition is applied to a can end.
5 . The coated package of claim 1 in which the composition is an aqueous-based composition in which (a) and (b) are dispersed in aqueous medium.
6 . The coated package of claim 1 in which the carboxyl-containing polymer comprises a carboxyl group-containing (meth)acrylic polymer or a carboxyl group-containing polyester polymer, including mixtures thereof.
7 . The coated package of claim 1 in which the calculated molar ratio of carboxyl groups to carbodiimide groups is from 0.5 to 5:1.
8 . The coated package of claim 1 in which the polycarbodiimide has a structure comprising (a) or (b), including mixtures thereof:
where e is an integer of from 2 to 20; f and g are each at least 1, and f+g is an integer up to 20; E is a radical selected from
where R 2 comprises a cyclic radical and R 3 is a linear hydrocarbon radical containing at least 4 carbon atoms; R 4 is hydrogen or an alkyl radical; Y is a radical of the structure:
including mixed radicals, where R is C 1 to C 4 alkyl; a is 5 to 50 and b is 0 to 35, and when b is present the mole ratio of a to b is at least 1:1; R 1 is hydrogen or a hydrocarbon radical and D is a divalent linking group or a chemical bond.
9 . The coated package of claim 8 where R 2 comprises a cycloaliphatic radical or an alkaryl radical.
10 . The coated package of claim 8 in which the cyclic radical is of the structure:
11 . The coated package of claim 8 in which E is a polyethylene moiety having a number average molecular weight of 96 to 10,000.
12 . The coated package of claim 8 in which Y comprises:
where a=15 to 25 and b=1 to 5 and the mole ratio of a:b is at least 5.
13 . The coated package of claim 1 in which the polycarbodiimide has a weight average molecular weight of 2600 to 12,000.
14 . The coated package of claim 1 in which the polycarbodiimide has a diimide equivalent weight of at least 600.
15 . A method of applying a crosslinked coating to a package comprising:
(a) providing a coating composition comprising:
(i) a carboxyl-containing polymer, and
(ii) a polycarbodiimide having the following structural units (a) or (b) including mixtures thereof:
where e is an integer of from 2 to 20; f and g are each at least 1, and f+g is an integer up to 20; E is a radical selected from
where R 2 comprises a cyclic radical and R 3 is a linear hydrocarbon radical optionally including hetero atoms containing at least 4 carbon atoms and R 4 is hydrogen or an alkyl radical;
(b) applying the coating composition to a substrate prior to or after forming the substrate into a package or a portion thereof; and
(c) heating the coated substrate to a temperature and for a time sufficient to crosslink the coating composition.
16 . The method of claim 15 in which the package is a food or beverage container.
17 . The method of claim 16 in which the coating composition is applied to the food-contacting surface of the container.
18 . The method of claim 16 in which the coating composition is applied to a can end.
19 . The method of claim 15 in which the coating composition is an aqueous-based composition in which (i) and (ii) are dispersed in aqueous medium.
20 . The method of claim 15 in which the carboxyl-containing polymer comprises a carboxyl group-containing (meth)acrylic polymer or a carboxyl group-containing polyester polymer, including mixtures thereof.
21 . The method of claim 15 in which the calculated molar ratio of carboxyl groups to carbodiimide groups is from 0.5 to 5:1.
22 . The method of claim 15 in which the substrate is formed into a food or beverage container and the coating composition applied to the food or beverage container.
23 . The method of claim 15 in which the coating composition is applied to a planar substrate; the coating composition heated for a time and temperature sufficient to crosslink the coating composition; forming the substrate into a food or beverage container or a portion thereof.
24 . The method of claim 23 in which the coating composition is applied continuously to a length of coil metal sheet stock.
25 . The method of claim 15 in which the polycarbodiimide has a structure (a) or (b), including mixtures thereof:
where e is an integer of from 2 to 20; f and g are each at least 1, and f+g is an integer up to 20; E is a radical selected from
where R 2 comprises a cyclic radical and R 3 is a linear hydrocarbon radical optionally including hetero atoms containing at least 4 carbon atoms; R 4 is hydrogen or an alkyl radical; Y is a radical of the structure:
including mixed radicals, where R is C 1 to C 4 alkyl; a is 5 to 50 and b is 0 to 35, and when b is present the mole ratio of a to b is at least 1:1; R 1 is hydrogen or a hydrocarbon radical and D is a divalent linking group or a chemical bond.
26 . The method of claim 25 where R 2 comprises a cycloaliphatic radical or an alkaryl radical.
27 . The method of claim 25 in which the cyclic radical is of the structure:
28 . The method of claim 25 in which E is a polyethylene moiety having a number average molecular weight of 96 to 10,000.
29 . The method of claim 25 in which Y comprises:
where a=15 to 25 and b=1 to 5 and the mote ratio of a:b is at least 5.
30 . The method of claim 15 in which the polycarbodiimide has a weight average molecular weight of 2600 to 12,000.
31 . The method of claim 15 in which the polycarbodiimide has a diimide equivalent weight of at least 600.