Spraying Metallic Paints

Question:

I have experienced some difficulty in color matching between methods of spray application, primarily with metallic colors. The problem is seen while trying to spray a silver metallic through our electrostatic rotary atomizer bell. The color comes out with a much duller, grayer tone than when sprayed through a conventional spray gun. What causes this, and what can be done to overcome it? D.W.

Answer:

Congratulations, you have just found our about “The innate perversity of inanimate objects.” In this case, the perversity is caused by physics, not chemistry (I’m glad, because as an organic chemist I’m tired of taking the blame for the world’s problems).

The problem is caused by the way the flake-like metallic pigment particles are aligned as the film is applied. If the metallic flakes align themselves parallel to the surface they “sparkle.” On the other hand, if they align themselves perpendicular to the surface they look like gray pigment. A few years ago the converse was true. Metallics looked good when sprayed with a conventional air-atomized gun and looked bad when using electrostatics. Other contributing factors are the wetness of the applied film and the “set” time. In some cases the metallic flakes will align themselves if given enough time.

A lot of work was done by the paint chemists to correct this physical problem. Without going into the details, they reformulated their products to allow them to be sprayed using electrostatic equipment. To overcome this problem you may have to ask your supplier for a product that can be sprayed using conventional equipment.