METHOD FOR JUDGING CHEMICAL CONVERSION FILM

摘要

PURPOSE:To prejudge the finished appearance of a coating film after electrodeposition coating with high precision at the time of applying chemical conversion treatment on the surface of a material to be treated and then electrodeposition-coating the material by rapidly judging the property of the film greatly involving the finish coating. CONSTITUTION:When the surface of a material is coated by cationic electrodeposition coating, etc., a chemical conversion film of zinc phosphate, etc., is formed on the surface in the pretreating stage, and then the material is coated. In this case, a cathode 2 as the material coated with the chemical conversion film and an anode 3 consisting of a carbon electrode are dipped in the cationic electrodeposition coating material in an electrodeposition bath 4, and a current at a constant low current density is applied for a specified time by a constant-current regulated power 1 to which a dummy resistance 5 and a switch SW are connected in parallel and an ammeter 6 in series. The relation between the voltage and time is recorded by a recorder 7, the change in the voltage-time curve (deposition curve) is observed, whether the chemical conversion film is adequate to the subsequent electrodeposition coating or not is judged, hence the quality of the coating film after electrodeposition is estimated, and the yield of the coated material is improved.