Guide to Bacterial Control and MEQ Value Testing for Electrocoat

During prolonged use, electrocoat can be adversely affected by bacterial growth, leading to reduced coating performance and quality, and in severe cases, rendering the bath liquid unusable. Timely detection of bacterial content in the bath liquid and implementing appropriate control measures are essential to maintain the long-term stability of electrocoatings. Adding bactericides promptly can effectively inhibit the growth and reproduction of microorganisms, ensuring the quality and performance of the coating. One testing method is outlined below:

1. Equipment

• Stirring rod (capable of entraining air during stirring)

• Thermostat (maintaining a constant temperature of 30°C)

2. Reagents

• Electrocoat to be tested (2–3 kg)

• Antibacterial agent (calculated at 300 ppm based on the paint volume)

3. Testing Procedure

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1. Measure the MEQ (Milliequivalent) value of the paint.

2. Divide the paint into two portions (1–1.5 kg each).

3. Continuously stir the paint samples at a constant temperature of 30°C. Ensure the stirring speed allows air to be entrained in the paint, and keep the paint in an open state during stirring.

4. Add the antibacterial agent to one of the paint samples at a concentration of 0.03% (dilute the antibacterial agent to a 10% concentration before adding).

5. Measure the MEQ value of both paint samples every two days, record the results, and plot them on a graph (see figure below).

6. Result Evaluation: For the paint sample without the antibacterial agent:

• 6.1 If the MEQ-time curve resembles the △ pattern in the figure, the likelihood of bacterial growth in the paint is high.

• 6.2 If the MEQ-time curve resembles the pattern in the figure, the likelihood of bacterial growth in the paint is low.

Notes

1. Characteristics of Bacterial Growth in Electrophoretic Bath Liquid:

1. Sharp decline in MEQ value (decreased conductivity, increased pH).

2. Increased filter residue and more frequent filter bag replacements.

3. Deterioration in surface appearance of horizontal workpiece areas (poor leveling effect).

4. Reduced ultrafiltration (UF) permeate volume.

5. Sand-like deposits on the inner walls of the paint and UF rinse tanks.

6. Odor at the discharge points of paint and rinse water.

2. Antibacterial Agent Precautions:

Avoid contact with eyes and skin. In case of contact, rinse thoroughly with plenty of water and seek medical attention.

Bacterial control in electrocoat is not only critical for product quality and production line stability but also a key factor in cost savings and enhancing enterprise competitiveness. Therefore, we must prioritize bacterial control measures to ensure the performance and quality of electrocoatings, safeguarding the development of the enterprise.