Spraying Metallic Paints

Question:

I have experienced some difficulty in color matching between methods of spray application, primarily on metallic colors. The problem is seen while trying to spray 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 to occur? What can be done to overcome it? Thank you. D.W.

Answer:

Congratulations, you have just found out 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 has been done by 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 electrostatic equipment.