Film Properties of an Anionic Electro-Coatings Relationships between baking schedule and film properties

Abstract

The appropriate baking schedules were determined for an anionic electro-coating material of maleic acid and synthetic oil modified polybutadien type by testing pencil hardness, impact resistance, corrosion resistance, adhesion, and humidity resistance (blistering, adhesion after humidity test) in variant combinations of baking temperatures (140-190°C) and minutes (15-60 min.).
The test results showed that the electro-coating (EC) required at least 25min. at 150°C, equivalent to 94% of gelation, to achieve the acceptable film properties mentioned above.
It was found, however, that the additional baking for a filler (150°C×20 min.) and a top coat (150°C×20 min.) subsequently applied on to the said EC film could put its minimum baking schedule down to 140°C×20 min., equivalent to 87% of gelation, where the film properties of the total coatings system (EC+filler+top coat) turned out to be sufficient despite that the EC was insufficiently baked.
When the EC was overbaked at such baking schedules as 190°C×25 min. and 180°C×60 min., the impact resistance of the total coatings system could not reach the acceptable value. This indicates that overbaking should be avoided for the EC of this type.
Since clear correlations were observed between the pencil hardness and the corrosion resistance, and between the pencil hardness and the impact resistance, it was concluded that the pencil hardness test could be employed as a means of quality control on the EC film in actual automotive production lines.