In electrocoating production, coating experts understand the critical importance of bath liquid temperature. The temperature directly affects the stability of the electrocoat bath, paint film quality, rework rates, and production efficiency, ultimately influencing economic benefits. However, temperature impacts are not limited to bath liquid temperature; ambient temperature is also a significant but often overlooked factor.
01 Effects of Rising Bath Liquid Temperature
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When the bath liquid temperature rises, the following phenomena occur:
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Accelerated movement of paint particles
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Decreased bath liquid viscosity
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Increased electrodeposition
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Reduced bath liquid resistance
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Decreased throwing power
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Increased electrophoretic current
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Accelerated solvent evaporation
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Reduced bath liquid stability
Severely elevated bath liquid temperatures can render the entire bath of electrocoat unusable!
02 Effects of High Bath Liquid Temperature
As the bath liquid temperature rises or remains excessively high, the electrocoatt film exhibits:
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Increased film thickness
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Pronounced or severe orange peel effect
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Significant particle formation
03 Bacterial Growth in Electrophoretic Bath Liquid
Many report that electrophoretic bath liquid is prone to bacterial growth. What causes this issue?
Electrocoat consists of organic resins, organic solvents, pigments and fillers, neutralizers, and water, with pH and temperature maintained within specific ranges. During spring and autumn, suitable pH and temperature conditions, combined with water and organic matter, create an ideal environment for microbial growth (bacteria and mold), gradually degrading the bath liquid and affecting product quality.
In the past, electrocoat were less susceptible to bacterial growth due to high levels of organic solvents and heavy metals, which were unfavorable to bacterial survival. However, according to the European Chemicals Agency’s REACH Regulation (No. 1907/2006) high-concern substance list and the RoHS Amendment Directive (EU) 2015/863, which restrict organic additives and heavy metals, environmentally friendly electrocoat with reduced organic solvents and no heavy metals are more prone to bacterial contamination. Most microorganisms are mesophilic and acidophilic, thriving in the pH range of 5–7 and temperature range of 25–35°C typical of cathodic electrocoat working liquids. Some microorganisms have an optimal growth temperature of 30–40°C, making these conditions ideal for their proliferation.
04 Impact of Bath Liquid Turnover Rate on Bacteria and Film Formation
When the bath liquid turnover rate is high, the addition of fresh paint replenishes effective film-forming substances and suppresses bacterial growth. However, when the turnover rate slows or the replacement cycle extends, the bath liquid remains in a relatively static state, increasing biodegradation and component damage while reducing effective film-forming substances. This amplifies the destructive impact of bacteria on the bath liquid.
Regular testing of the bath liquid, with adjusted testing frequency based on usage, enables timely control and prevention of bacterial growth. Low bath liquid temperatures favor bath stability but increase viscosity and reduce electrodeposition, leading to issues such as thin paint films, low gloss, poor hiding power, insufficient coating in workpiece cavities, and rough or matte paint films. Therefore, strictly controlling the bath liquid temperature within the specified range using a heat exchanger is crucial.
Conclusion
By controlling bath liquid temperature and implementing robust bacterial prevention measures, electrocoating production can achieve greater stability and efficiency, ensuring product quality and economic benefits.