Low bake melamine cured coating compositions

Abstract

The present invention provides reactive aqueous or solvent borne compositions comprising one or more low-temperature curing alkylether functional aminoplast resins having an average degree of polymerization of from 1.0 to 2.0, preferably alkylether group containing melamines, one or more hydroxyl group containing resins or polymers, such as acrylics and polyesters, one or more unblocked acid catalysts each having a pKa of 0.25 to 1.0, such as organic sulfonic acids, and one or more volatile amines, e.g. N-dipropylamine, that have a relative evaporation rate (RER) of 50-500, wherein, RER equals (p)(M) / 11.6, with p being the vapor pressure of the amine in mm Hg and M being the molecular weight of the amine. The compositions cure at from 60 DEG C. to 135 DEG C., e.g. below 105 DEG C., to form durable coatings suitable for plastic substrates, such as automotive plastics. The present invention also provides methods of forming the compositions comprising mixing the said aminoplast resins, hydroxyl group containing resins or polymers, unblocked acids and volatile amines to form a mixture, wherein the acids and the amines are added separately into the mixture.

Description

technical field [0001] This invention relates to low-baking, reactive one-pack and two-pack coating compositions for coating plastic substrates. More particularly, the present invention relates to a one-part shelf stable alkyl ether functional aminoplast resin cured coating composition which can be cured at 60-105°C to form an automotive base coat, a decorative paint or Monocoats, topcoats and clear finishing coats, the invention also relates to a process for the preparation of such compositions. Background technique [0002] To date, coatings for low melting point substrates such as ABS and other plastics have included non-reactive one-component coatings, one-component reactive blocked isocyanate systems, or two-component coatings containing isocyanates. Non-reactive one-component coatings such as lacquers often perform poorly in physical tests. One-component reactive blocked isocyanates have proven to be costly to put into use, often as natural lacquers, and present prob...

AI Technical Summary

Problems solved by technology

The Heaps et al. patent touts the durability of the resulting coating; however, the patent does not provide a storage-stable one-component coating

The Heaps et al. patent provides poor gloss retention and therefore poor resistance to acids, which may include acid rain, when cured at low temperatures of 77-104°C