UV stable electrocoats for corrosion protection and structural bonding

The coating process in the industry segment of mobile machinery, e.g. agricultural machines, is usually done after welding the framework with a variety of parts. The current painting process consists of an anti-corrosive primer and a weather resistant colored top coat. The presented study is part of a research project investigating a new concept combining a new sequence in construction with the big advantage of a sole one coat system. This innovative technology enables inversion of the classical process: At first, the smaller pieces of the framework of the machine is coated with a single layer electrocoat (via cathodic electrodeposition CED). In the following step the parts are connected by structural bonding on the coating layer – instead of welding. This smart production enables the construction of the machines in modules, keeps the volume of an electrocoating dipping bath at a minimum level, and replaces the custom painting procedure with much overspray by an economical and ecological coating technology. To realize this new technology, the coating systems has to perform as effective anti-corrosive system, provide a sufficient outdoor weather resistance in different color shades and must have sufficient adhesion strength for bonding. Therefore, the following coating properties are explored - Modification of the paint formulation and development of different color shades - Testing the anti-corrosive properties via salt spray test, humidity tests, cyclic corrosion tests - Evaluation of barrier properties with electrochemical impedance spectroscopy - Adhesion and other mechanical tests - Testing UV- and weather resistance - Determination of the process window of the electrocoat systems - Investigation of structural bonding on the coating system The cathodic electrodeposition coat is based on a low VOC hybrid acrylic-epoxy self-crosslinking binder system. Different formulations are modified and tested in order to improve anti-corrosive properties, the adhesion on steel substrates, to improve the UV- and weather resistance and the pre-requisites for structural bonding of the coating surface. First results show that the electrocoat in different color shades (dry film thickness: 40 µm) shows anti-corrosive properties up to 1000 h salt spray test with low undercreepage values. UV- and weather resistance were acceptable up to 2000 h CAM 180, but depends on the color shade