| 摘要 |
<p>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 1010 to 1014 ohm. cm and a surface coat powder having an electrical resistivity of about 1014 to 1016 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 1012 to 1014 ohm. cm and at least about 102 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 added to the ground coat powder before adjustment of its electrical resistivity, and the ground coat powder is applied in such a quantity that, after baking, the ground coat has a layer thickness of about 0.02 to 0.03 mm.</p> |
