The technology of coating substrates with a coating material has advanced in the fields of automotive parts, domestic electric appliances, building materials and the like for the purpose of rust prevention, coloration, brightening and so forth. In such coating, the substrate surface is generally subjected to the steps of under coating, intermediate coating, top coating, and the like to give a finished product. Among coating materials used for these coating steps,
powder coating in which no organic solvent is used are free of the risk of environmental pollution and give a good coat film appearance within a short curing time and, accordingly, they have been widely used in recent years.
Such
powder coating is produced, for instance, by admixing a thermosetting resin serving as a binder resin with a curing agent, a pigment and other additives, melting and kneading the mixture under conditions such that the crosslinking of resin molecules will not substantially proceed, extruding the same in the form of pellets and pulverizing the latter.
For improving or modifying the coatability and coat film performance characteristics of the
powder coating of the present invention, said coating powder may be blended with one or more of various natural resins, synthetic resins, elastomers and the like.
For the production of the
powder coating of the present invention, all processes, apparatus and so on that are conventional in the art can be used. The most general process comprises admixing raw materials preliminarily, then melt-mixing the same and pulverizing and classifying the mixture. It is also possible, in certain instances, to mix up the compound in the state of suspension, emulsion or solution and then subjecting the mixture to spray drying to give a powder.
