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Coating Basics: Q&A Of Defoamer Use Experience

Jun 02, 2020

1. Why does waterborne paint foam?

Answer: Because surfactants, dispersants, latent solvents and resins all have the ability to form and stabilize air bubbles; pure water (or any pure liquid) will not produce foam.

2. What should be done to control the foaming test?

A: Although the effectiveness of a chemical mixture to control bubbles can be determined by theoretical calculations, they cannot be used to predict its sustainability, side effects, and ease of mixing. Therefore, it is recommended to use the "post-addition method", that is, to select a paint containing no defoamer as a control sample, subject it to shear, vibration and heat aging, and evaluate it after coating. Using this method may get more specific data.

3. What are the adverse side effects of defoamers?

A: Although the amount of defoaming agent used in the coating is very small, it is generally added at 0.1% to 1% of the total weight of the formula. Floating colors, silk patterns, moon shadow stripes and other undesirable effects. The so-called improper use refers to the wrong choice of defoamer type, too little or too much dosage.

4. How to deal with coating film defects?

Answer: Correct by correcting its formula. Generally, no other additives are used to control side effects. For example, if there are fish eyes (sometimes considered to be cratering), then the variable factors in the formula should be carefully checked, and the type, concentration and addition method of each component in the formula should be adjusted instead of Anti-crater should be used without consideration. According to the correct manufacturing steps, the use of suitable defoamers in appropriate concentrations should not cause these coating defects.

5. Why is it recommended to use more than one defoamer in the formula?

Answer: A single variety of defoamer can either control foam more effectively during the manufacturing process or control foam more effectively during coating construction. Both are not compatible. This is a general rule. Occasionally, there are cases where the same defoamer is used in the two stages of grinding and paint mixing, but for best results, always use silicone-type defoamers for grinding and non-silicon types for paint mixing Defoamer such a method. Synergies play a role here.

6. Why should we recommend defoamer products containing silicone?

Answer: The defoamer product containing silicone is the most durable (refers to modified silicone, not a simple dimethyl polysiloxane liquid). Proper selection and addition has almost no adverse effect on the acceptability of the pigment, at least less than most non-silicone products. Throughout the manufacturing process, during storage, during high-shear flow or during roller coating applications, durability may be required.

7. How adaptable is the recoating of silicone-containing defoamers?

Answer: If the product containing silicone is selected properly, and the dosage and addition method are correct, the adaptability of recoating is not a problem.

8. For factory applications, why are laboratory screening results not always correct?

A: The most important reason is that the actual manufacturing conditions cannot be completely simulated in laboratory tests. The laboratory screening process should be as close as possible to the manufacturing process, and the process requirements and quality control should be strictly observed during the manufacturing process.