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Flourescent powder-coating techniques

By Marcus Thielen

Three parameters determine a neon tube's color: the fill-gas type, the glass tube color (in some cases) and the fluorescent coating. The fluorescent material converts invisible, UV light into visible light. Its color depends upon the material's chemical and crystallographic composition (see ST, May 2004, page 22).

Because glass isn't transparent (luckily) to UV light, the fluorescent material must be placed between the gas discharge that emits the UV light and the glass blocking it (on the glass tube's inner surface). Most U.S. neon shops buy glass tubes already precoated with the fluorescent material. However, every shop owner should know about in-house coating.

In most cases, fluorescent materials comprise solids crushed into powder. By mixing different base materials, you can obtain a composite color mix of the ingredients' base colors. Some neon-tube colors represent more than five fluorescent materials. In all coating procedures, the goal is a uniform, powder layer that adheres to the tube's inner surface.

Precoating

Coating glass tubes with fluorescent material is only effective when straight and uniformly long tubes are produced in large quantities. The largest coating facilities, which operate on conveyor belts that require several thousand square feet of shop space, produce roughly eight miles of coated tubing daily. All precoating processes are wet