Waterborne shop primer
A coating system for application to metal components prior to assembly or fabrication into large metal objects is described. The system includes a composition comprising a water-dispersible polymer component, a crosslinking agent, and a conductive material. When applied to a metal substrate, the coating system is weldable and provides optimal corrosion resistance during fabrication or assembly.
1. A method of making a corrosion-resistant metal article, comprising
providing an article having a metal substrate;
applying thereon a coating composition comprising, based on the total weight of the coating composition:
a two-component composition including
about 10 to 20 wt % of an epoxy polymer component having number average molecular weight (M n ) of 800 to 1500 and EEW of about 200 to about 500; and
about 1 to 5 wt % of a polyamide crosslinker having amine equivalent weight is about 250; and
about 15 to 25 wt % of an aqueous carrier in which the binder is dispersed;
about 1 to 5 wt % of a conductive material;
about 1 to 5 wt % of a pigment;
about 1 to 5 wt % of a first solvent;
about 5 to 10 wt % of a second solvent; and
about 30 to 40% wt % of non-reactive zinc; and
drying the coating to form a corrosion-resistant film at dry film thickness of about 2 to 20 μm on the metal substrate, wherein the film emits no harmful byproducts on welding.
2. The method of claim 1 , wherein the conductive material is a conductive pigment selected from calcium, cobalt, nickel, iron, copper, carbonaceous material, or mixtures thereof.
3. The method of claim 2 , wherein the carbonaceous material is selected from carbon black, graphite, or carbon fiber.
4. The method of claim 1 , wherein the coating composition further includes a corrosion inhibitor.
5. The method of claim 4 , wherein the corrosion inhibitor is selected from aluminum triphosphate, barium triphosphate, calcium phosphosilicate, calcium silicate and mixtures thereof.
6. The coating method of claim 1 , wherein the corrosion-resistant film formed by drying is weldable.
7. The coating method of claim 1 , wherein the metal substrate comprises steel, iron, aluminum, zinc, or alloys of iron, aluminum, or zinc.
8. The method of claim 1 , wherein the composition is substantially free of elemental or metallic zinc.
9. The method of claim 1 , wherein the composition includes less than about 1 weight percent of an anti-settling component.
10. The coating method of claim 1 , wherein the metal substrate is a component of a prefabricated article requiring temporary corrosion protection during manufacture.
11. The coating method of claim 1 , wherein the metal substrate is a component or part of a shipping container.
12. The coating method of claim 1 , wherein the corrosion-resistant film formed by drying the composition is heat-resistant in a humid environment.
13. The method of claim 1 , wherein the polyamide component is water-dispersible.