Process for forming multilayer coating with radiation curable polyene/polythiol coating compositions
A process for forming a color-clear multilayer coating on a substrate is disclosed. The clear topcoat comprises a polyene and a polythiol that is radiation curable.
1. A process for refinishing a motor vehicle part comprising forming a multilayer coating on a substrate comprising:
(a) forming a basecoat layer containing organic and/or inorganic color- and/or effect-imparting pigments on the substrate that is a metal or plastic part of a motor vehicle precoated with a primer, primer surfacer or other it coating;
(b) forming a clear topcoat layer on the basecoat layer by depositing a radiation curable topcoat composition onto the basecoat layer in which the topcoat composition comprises:
(i) a polyene comprising polyurethane (meth)acrylate or polyester (meth)acrylate,
(ii) a polythiol; and
(c) exposing the topcoat composition to radiation to cure the topcoat.
2. The process of claim 1 wherein the basecoat layer is deposited from a waterborne composition.
3. The process of claim 1 wherein the basecoat layer is deposited from an organic solventborne composition.
4. The process of claim 1 in which the polythiol has the structural formula R 1 —(SH) n where R 1 is an organic moiety and n is at least 2.
5. The process of claim 4 in which R 1 contains ester groups.
6. The process of claim 4 in which R 1 is derived from a polyol.
7. The process of claim 4 in which the polythiol is the reaction product of a thiol-functional organic acid and a polyol.
8. The process of claim 4 in which n is from 2 to 4.
9. The process of claim 1 in which the polyene is present in the topcoat composition in amounts of 50 to 98 percent by weight and the polythiol is present in amounts of 2 to 20 percent by weight; the percentages by weight being based on weight of polyene and polythiol.
10. The process of claim 1 in which the polyene is present in the topcoat composition in amounts of 90 to 95 percent by weight and the polythiol is present in amounts of 5 to 10 percent by weight; the percentages by weight being based on weight of polyene and polythiol.
11. The process of claim 1 in which the topcoat is exposed to ultraviolet radiation falling within the 200-400 nanometer wavelength interval.
12. The process of claim 11 in which the ratio of UV-B content to UV-A content of the radiation is 1:1 or less.
13. A substrate coated with a multilayer coating in accordance with claim 1 .
14. A process for refinishing a motor vehicle part comprising forming a multilayer coating on a substrate comprising:
(a) forming a basecoat layer containing organic and/or inorganic color- and/or effect-imparting pigments on the substrate that is a metal or plastic part of a motor vehicle precoated with a primer, primer surfacer or other intermediate coating;
(b) forming a clear topcoat layer on the basecoat layer by depositing a radiation curable topcoat composition onto the basecoat layer in which the topcoat composition comprises:
(i) a polyene comprising polyurethane (meth)acrylate,
(ii) a polythiol; and
(c) exposing the topcoat composition to radiation to cure the topcoat.