Powder Corrosion and Chip-Resistant Coating
A powder composition including a resin and from 5% to 70%, by weight based on powder composition weight, of a corrosion-inhibiting pigment, optionally including from 0% to 65%, by weight based on powder composition weight, zinc, the composition being substantially free from pigment providing a metallic effect is provided. The corrosion-inhibiting pigment may be present in amounts of up to 50%, by weight based on powder composition weight, for example, up to 35%. A method for coating a substrate with the powder composition and the coated substrate so formed are also provided.
1 . A method of coating a high tensile steel substrate with a chip and corrosion resistant coating, the method comprising
(a) applying to the substrate a powder composition comprising
(i) an epoxy resin based on bisphenol A,
(ii) a polyhydroxyl functional phenolic curing agent having a HEW of about 200 to about 500, and
(iii) from 5% to 70% by weight based on powder composition weight of a corrosion-inhibiting pigment selected from the group consisting of molybdates, chromates, metal phosphides, silicates and phosphates,
wherein the composition comprises zinc in an amount of 0% to 65% by weight based on the powder composition; and
(b) heating the applied powder composition to fuse and cure the composition.
2 . The method according to claim 1 wherein the powder composition further comprises at least one additive that toughens the powder composition, aids in foaming the powder composition, or reinforces the powder composition.
3 . The method according to claim 1 wherein the epoxy resin is a thermoplastic resin or a thermoset resin.
4 . The method according to claim 1 wherein the epoxy resin has an epoxy equivalent weight of less than 2300.
5 . The method according to claim 1 wherein the epoxy resin is adducted to an elastomer.
6 . The method according to claim 1 wherein the corrosion-inhibiting pigment is selected from the group consisting of simple molybdates, complex molybdates, simple chromates, complex chromates, metal phosphides, silicates, simple phosphates and complex phosphates.
7 . The method according to claim 1 wherein said powder composition is substantially free from pigment providing a metallic effect.
8 . The method according to claim 2 wherein the at least one additive is an additive that toughens the powder composition, wherein the additive is selected from the group consisting of elastomeric modifications, a random or block copolymer addition, addition of plasticizers, crosslinked or non-crosslinked core/shell resins, hollow spherical particles and discrete micro-domains thereof.
9 . The method according to claim 8 wherein the additive is a random or block copolymer addition.
10 . The method according to claim 1 wherein the at least one corrosion-inhibiting pigment is selected from the group consisting of zinc phosphate, strontium zinc phosphosilicate, calcium borosilicate, iron phosphide, strontium chromate, zinc molybdate and mixtures thereof.