Stability is a critical parameter for all chemical products, but what does stability mean for electrocoat bath liquid? It refers to the ability of the bath liquid to produce a paint film that meets performance requirements under specified electrocoating conditions. At Holsen, we rigorously test the stability of both the original electrocoat and the bath liquid during R&D and production. Only after meeting the required parameters is the product approved for formal production, serving as a prerequisite for quality assurance by electrocoat manufacturers.
Accelerated Test Method for Bath Liquid Stability
1. Scope and Description
This method is used to measure the dilution stability of electrocoating bath liquid, specifically evaluating its stability at ambient temperature.
2. Materials and Equipment
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Tinplate (or phosphated plate)
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8L plastic measuring cup
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Thermometer
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Constant-temperature water bath
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Electrophoretic power supply
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Connecting wires
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Cathode rod
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Iron wire
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Constant-temperature drying oven
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Magnetic stirrer
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Precision stirrer (or constant-speed stirrer)
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Electrophoretic bath liquid to be tested
3. Test Procedure
3.1 Prepare 8L of bath liquid according to the product’s formulation scheme.
3.2 After 24 hours of bath liquid circulation, test the bath liquid parameters (pH, conductivity, solids content, solvent content, etc.).
3.3 As circulation time increases, voltage may need to be raised to maintain a film thickness close to that of the first day:
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Days 1–5: 120–130 V
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Days 6–10: Approximately 150 V
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Days 10–15: Approximately 180 V
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Over 15 days: 200 V (Voltage adjustment ranges are for reference only; operators should adjust based on product characteristics.)
3.4 Add deionized water daily to maintain the initial liquid level from the first day of preparation. Return any remaining bath liquid used for testing to the bath.
3.5 After the initial 24-hour circulation test, prepare test panels and measure parameters every other day.
3.6 Test pH, conductivity, solids content, and solvent content every 4 days (once a week) and record the solvent content when film application becomes difficult, using it as a basis for solvent replenishment.
3.7 Complete a detailed circulation record report, documenting bath liquid parameters, panel appearance, film thickness, gloss, and bath adjustments.
3.8 Upon completion of circulation, promptly finalize the bath liquid tracking, performance test report, and summary.
4. Results Interpretation
4.1 If no precipitation or sedimentation occurs at the bath bottom by the end of circulation, and the panel surface shows no defects such as pinholes or particles, the bath liquid stability is rated as good. If precipitation or sedimentation occurs, or if parameter changes exceed the specified ranges, the stability is rated as poor.
4.2 If the voltage increase is ≤50%, and the final day’s panel film thickness is close to the first day’s (within 2–3 μm difference), the film application is rated as good. A difference of 4–6 μm is rated as fair, and a difference greater than 6 μm is rated as poor. If the voltage increase is between 50%–70%, and the final day’s film thickness differs by ≤3 μm from the first day, it is rated as fair; a difference >3 μm is rated as poor.
Precautions:
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Magnetic stirring accelerates bath liquid aging and precipitation, making it suitable for quickly testing circulation stability, typically within 4 weeks.
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Mechanical stirring (using a precision or constant-speed stirrer) closely mimics on-site circulation conditions at client facilities, suitable for open circulation tests lasting over 4 weeks, providing a more accurate reflection of stability changes during actual use.