Powder Coatings Formulation

Formulation of thermosetting decorative powder coatings

The selection of the individual components and their composition (formulation) will be influenced by:

1) The ultimate film properties required including gloss, hardness, flexibility, adhesion, chemical and corrosion resistance

2) Application technique

3) Curing conditions including type of oven, curing time and temperature

4) Production procedures and conditions.

The component properties will influence the quality of the ultimate powder coating material.

Polymer: the selection of the correct grade of polymer or blend of polymers is very important, as these form the basic properties of the powder coating material and also control the film properties such as melting point, flow and levelling.

Usual polymers include epoxies, polyurethane, polyester and acrylics.

Curing Agent (also known as hardener): the hardener is used to cross-link the resin at a given temperature. The degree of cross-linking can also be used to determine the gloss level, degree of surface `orange peel’ and other aspects including structure and texture effects. The curing agent should be unreactive at ambient temperatures, and should react fully at stoving temperatures. This reaction should not be so rapid as to prevent complete flow out of the fused resin and not so slow that it creates commercial implications.

Usual crosslinkers are amines, anhydrides and blocked isocyanates. Catalysts are used to accelerate the curing speed.

Pigments and extenders: pigments must be inert, lightfast and heat resistant. As with most coatings they are used to create a decorative effect.

ü Titanium dioxide creates white, pastel and light tints

ü Carbon black creates blacks and greys

ü Phthalocyanine creates blues and greens

ü Aluminium and bronze creates metallic effects.

Organic pigments have to be handled with care as some of them can react during processing and curing. This can result in loss of brightness and cleanliness and in these cases alternative pigmentation has to be used.

Certain inorganic extenders can be incorporated into the formulations without reducing the film quality.

Additives: even after the optimum resin, hardener and pigments have been selected, adjustments to the formulation may still be required to modify flow and film properties to suit the application and curing conditions (i.e. Thixotropic agents to slow down the flow, UV stabilisers). Other functions of additives are:

Increase/decrease electrostatic attraction

Increase/decrease surface levelling

Creation of decorative effects

Decrease stoving temperature requirement

Changing conductivity

Increase re-coatability

Increase surface hardness