Formation and detachment of gas bubbles during cathodic electrocoating: Quantitative determination by means of buoyancy measurements

Cathodic electrodeposition paints have been used for decades to protect automobile bodies and other metallic objects from corrosion. Nevertheless, it is still a major challenge to establish deposition models with a high degree of precision exclusively from both bath and application data. In recent years, the impact of the gas bubbles emerged during the painting procedure on the deposition behavior has become the focus of relevant studies. For the first time, in this work, the formation of gas bubbles and their detachment during the coating process are accurately recorded via buoyancy measurements. The evaluation of the results clearly shows the formation of more gas volume than should be formed according to Faraday's law. The excess gas volume is assumed to be due to the formation of carbon dioxide, being generated by alkaline hydrolysis of urethane groups during the deposition process. Furthermore, the influence of the layer of insulating gas bubbles on film formation could be clearly demonstrated. These results provide crucial insights for the development of more advanced and precise deposition models.