The leveling of the electrocoat film can be quantitatively measured using a roughness tester, expressed as the Ra value. A lower Ra value indicates better leveling.
Electrophoretic paint consists of water, carbon black, titanium dioxide pigments or fillers, alcohol solvents, and resin. The size of pigment particles and the reactivity of solvents directly impact coating performance. If pigment particles exceed the optimal range, issues like particle protrusion, buildup, or flow may occur, leading to a rough surface and poor leveling.
Precise control of current is essential to avoid factors like bubbles or deposits that affect coating quality. Additionally, after electrocoating, the curing stage requires proper temperature control. Inadequate curing temperature can result in a rough surface, impacting leveling.
The roughness of the substrate surface affects electrocoat leveling. A high Ra value (poor surface quality) can lead to a rough coating film with poor leveling (cold-rolled steel typically requires a bare substrate roughness of Ra ≤ 1.2 microns).
The quality of the phosphating film impacts leveling. An uneven or rough phosphating film can directly cause poor leveling in the electrocoat film. Incomplete water rinsing, leaving acid or oil residues, will transfer to the electrocoat layer, affecting leveling.
Improper control of bath liquid parameters—such as low solid content, elevated pH, temperature imbalances, pigment-to-binder ratio issues, excessive impurity ions, or abnormal solvent content—can lead to uneven film deposition, negatively affecting leveling.
The coating film thickness must be controlled within a specific range. Extensive testing shows that a film thickness of 18–20 microns achieves optimal leveling. If the film is too thin, coating unevenness occurs, leading to poor leveling. If too thick, surface roughness (Ra value) increases, also resulting in poor leveling.
2. Precise Control of Coating Conditions: Control electrophoretic voltage, duration, and temperature to maintain stable bath pH, avoid excessive current causing bubbles, and strictly regulate curing temperature.
4. Control Bath Liquid Parameters: Regularly monitor and control pH, temperature, impurity content, and conductivity to keep them within optimal ranges. Ensure solid content concentration is appropriate to further improve film leveling.
6. Control Film Thickness: Manage electrophoretic voltage and duration to keep film thickness within the optimal range.
By systematically addressing these factors, the surface quality of the coating film can be significantly improved, achieving a mirror-like finish.