Coating powders having enhanced electrostatic chargeability

Abstract

Inert nitrogen-containing compounds, such as melamine, urea, dicyandiamide, and benzoguanamine and derivatives of such compounds are added to thermosetting resin powder coatings to enhance the electrostatic charge of the powders. Such enhancement improves coating processes for non-conductive and conductive substrates.

Description

[0001] The present invention relates to thermosetting resin coating powder compositions having enhanced electrostatic chargeability. The coatings are applied using conventional electrostatic equipment and then fused and cured. The coating powder compositions of the invention include inert nitrogen-containing compounds that function as electrostatic charge enhancing agents. By inert, it is meant that these compounds are not chemically reactive with other compounds of the coating powder under the conditions the compounds are normally exposed, i.e., during powder manufacturing and coating. Melamine, urea, dicyandiamide, and benzoguanamine and derivatives thereof are inert nitrogen-containing compounds that enhance chargeability. The use of these coating powders eliminates or minimizes the need for the surface preparation of non-conductive substrates prior to electrostatic application and serves to improve coating thickness, uniformity, and quality.BACKGROUND OF THE INVENTION[0002] Coat...

AI Technical Summary

Benefits of technology

0014] The coating powders of the invention include as a component an inert nitrogen-containing compound such as melamine, urea, benzoguanamine, dicyandiamine, and derivatives of such compounds. The term "inert" means that the compounds do not react with other components of the coating powder during manufacturing steps of the powder, such as extrusion, or during coating temperatures when the powder is applied to a substrate. Thus, the essentially unreacted compound is free to perform its function as an electrostatic charge enhancement agent during the coating process. The balance of the powder is a thermosetting resin polymer that may contain other ingredients that are typically included in coating powders.

0015] In one advantageous aspect, the process of the invention involves coating non-conductive substrates by providing the above described coating powder, electrostatical

Problems solved by technology

Although powder coatings have many benefits, it is difficult to coat electrically non-conducting substrates such as plastic, wood, and wood composites.

The two main challenges are the need for low curing temperatures and the need for enhancement of the electrostatic attraction of coating powder to non-conductive substrates.

A further challenge remains in the enhancement of the attraction of coating powders to non-conductive substrates prior to curing.

However, this technique has the disadvantage that modification of the character of the substrate is required.

Due to the varying nature of the wood substrates, controlling the moisture content is very difficult.

Should the moisture content be too low, even preheating the part will not sufficiently improve electrostatic application.

Excessive preheating to improve conductivity can also be detrimental to the substrate.

Moreover, preheating parts that have sharp edges permits moisture to escape more rapidly from such edges than from thicker areas, thereby rendering powder application very difficult.

Electrically conductive coatings can interfere with some intended uses of the finished part, which otherwise would not exhibit electrical conductivity.

A limitation of this approach is that multiple steps are involved in finishing operations.

These agents cannot be incorporated into coating powder formulations because such agents are commonly used at very low levels (less than 0.5 part per 100 parts of resin) as catalysts in many coating powder formulations.

This approach is limited with respect to the amount of material that can be incorporated in the formulation because ammonium compounds also function as cure catalysts for most coating powder formulations.

The implementation of this approach has been hindered by the lack of commercial availability of the charge control agents as well as the cost of these materials.

The chemical structure of these hindered amine compounds can impart performance characteristics to the coating powders that may not be desirable, at least in some formulations.

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