Robert R. Zwack

Predicting electrocoat efficiency: a simple data-based model for predicting electrocoat usage

Abstract Cationic electrodeposition coatings have had large economic impact, especially in the area of corrosion protection. These primers, along with the use of clad steels, have led auto manufacturers to the extended corrosion warranties now offered. A large part of this and other benefits, such as smoothness, come from the uniform coverage of the cationic electrodeposition process. This highly complex, dynamic process covers the visible and hidden areas of the workpiece with paint of high uniformity. The ability to reach recessed areas has historically been measured by throwpower. This property has great impact not only on the corrosion properties of the coating but also on the economics of coating. We propose a simplified model of the electrodeposition which allows prediction of process parameters and relative usage. The model is founded on observations of currents and voltages measured during the electrodeposition process in the field. This simple model is supplied with data from controlled laboratory experiments: film build versus time over a range of voltages. The model correlates well with observations from the field. Examples of the model include comparisons of PPG 5th and 4th generation electrocoats for both laboratory and field baths. These show the models utility for predicting usage and for optimizing application properties. A final example involves predicting the feasibility both for process parameters and for the ability to meet coating thickness specifications during the development of a prototype material. Our model provides a systematic way of measuring the implications of improved throwpower. We can assess both the economic (relative usage) and deposition parameters to optimize the overall process.