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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.
DSC Measurements
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Instrument
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NETZSCH DSC 204 Phoenix®
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Heating rates/(K/min)
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1, 2, 5, 10, 20
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Atmosphere
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N2; 20 ml/min
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Crucible
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Aluminum, pierced
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Sample mass/mg
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9.9 ... 10.1
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The DSC measurements on freeze-dried paint material show a endothermal melting peak directly transferring into the exothermal cross-linking process.
Comparison of experiments (symbols) and calculations (black solid lines)
Temperature distribution at bodywork during the drying process.
time: 20 min
Distribution of degree of reaction of electro-deposited paint on a bodywork during the drying process.
time: 20 min
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.
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