Electro-deposition Paint

Electro-deposition coating (EDC) is widely used in the automotive industry. The importance of cathodic EDC is its ability to create an especially corrosion-resistant base coat in a single-layer process. The coating in a direct-current electrical field leads to preferential deposition of coating at corners, edges, and protrusions [W. Collong, M. Osterhold, Y.Voskuhl: Applied Rheology 1996(2) 27].

In the following, the cross-linking kinetics of a EDC is investigated. Using the results of kinetic analysis and of a simulation routine for the temperature field in a drying tunnel - a special module of CADFEM/ANSYS - the distribution of degree of reaction over the whole bodywork is predicted.

Heating of Paint shows two effects of different directions: endothermal melting and exothermal curing. This data could not be analyzed by model free method required all effects having the same direction. The only way to analyze these data is model based analysis, where some steps have different direction.

DSC Measurements
InstrumentNETZSCH DSC 204 Phoenix®
Heating rates/(K/min) 1, 2, 5, 10, 20 
AtmosphereN2; 20 ml/min 
CrucibleAluminum, pierced 
Sample mass/mg 9.9 ... 10.1

 

The DSC measurements on freeze-dried paint material show a endothermal melting peak directly transferring into the exothermal cross-linking process.  

The comparison of the distribution of temperature and degree of reaction shows the correlation: at the hottest places the largest degree of reaction is predicted. 

But the relation between both is not linear: the cross-linking reaction starts first at temperatures higher than 116 ¡C. 

Fig.1. Comparison of experiments (symbols) and calculations (black solid lines)
Fig.2. Temperature distribution at bodywork during the drying process. time: 20 min
Fig.3. Distribution of degree of reaction of electro-deposited paint on a bodywork during the drying process. time: 20 min