Single-bake two-layer enamelling with electrostatic powder coating

US4265929A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Gebhard Wagner · Odenthal, DE
• Werner Joseph · Cologne, DE

Key dates

• Filing date: Nov 21, 1979
• Grant date: May 5, 1981
• Expiry date: Nov 21, 1999

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C03C2207/04
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

In a two-layer enamelling process in which the ground coat and surface coat powders are electrostatically applied to metallic substrates and subsequently baked together, the improvement which comprises employing a ground coat powder having an electrical resistivity of about 10.sup.10 to 10.sup.14 ohm. cm and a surface coat powder having an electrical resistivity of about 10.sup.14 to 10.sup.16 ohm. cm. Advantageously the surface tension of the ground coat amounts to at least about 0.280 N/m and the surface tension of the surface coat to at most about 0.260 N/m, the difference between the surface tensions of the ground coat and surface amounts to at least about 0.050 N/m, the ground coat powder has an electrical resistivity 10.sup.12 to 10.sup.14 ohm. cm and at least about 10.sup.2 ohm. cm lower than that of the surface coat powder, the ground coat powder contains at least one of an alkaline earth metal, zinc, manganese or iron oxide in a total concentration of about 20 to 30% by weight, the zinc oxide content not exceeding about 12% by weight and the manganese oxide plus iron oxide content not exceeding about 9% by weight, about 3 to 5% by weight of finely divided iron oxide is add…