In automotive body electrocoating, throwing power is a critical technical parameter. It directly affects coating efficiency and film corrosion resistance. Given the complex structure of vehicle bodies with numerous cavities, achieving full paint coverage on both exterior and interior surfaces requires high-throwing-power electrocoat. Therefore, several key factors influencing throwing power deserve special attention.
1. Inherent Properties of the Electrocoat
-
Bath conductivity and wet film resistance: The former ensures sufficient film thickness in recessed (box-section) areas, while the latter controls film thickness on outer panels.
-
During full-body electrophoresis, the bath requires high solids content (typically ~20%), resulting in higher conductivity to ensure adequate film deposition in internal cavities. The lower the paint resistivity and the higher the deposited wet film resistance, the better the throwing power.
2. Electrocoating Conditions
-
Coating time, temperature, and voltage
-
These parameters are crucial during electrophoresis and represent the primary means for on-site personnel to directly adjust throwing power.
3. Structure of the Coated Object (Vehicle Body)
-
Unreasonable body design prevents the electric field from reaching internal cavities, leading to no film formation in those areas—a primary cause of early severe corrosion or perforation.
-
Therefore, drainage and access holes must be strategically designed in body and complex cavity areas to meet throwing power targets and ensure complete internal coating.
4. Compatibility Between Pretreatment Process and Electrocoat
-
Impact of conversion coating on coating voltage and wet film resistance
With growing demands for environmental protection and energy savings, non-polluting pretreatment processes (phosphorus-free, heavy metal-free) have become the trend. Traditional phosphating is being replaced by eco-friendly non-phosphorus conversion coatings (e.g., zirconium or silane-based treatments).
-
Traditional phosphating is mature and stable, offering high wet film resistance and consistent film formation.
-
Eco-friendly non-phosphorus treatments have lower resistance, faster film formation, but unstable throwing power.
Thus, electrocoat must be optimized to match these new systems.
Jingtu’s demonstrates excellent compatibility with various eco-friendly non-phosphorus pretreatments, particularly excelling in throwing power, low-temperature curing, and silane compatibility. It is currently in successful trial on multiple domestic OEM vehicle electrocoating lines.