Product innovation of water-based bismuth catalyst for two-component cathode epoxy electrophoretic paint system

Previously, our company developed a water-based bismuth catalyst (BI CAT WS-075), which was promoted in China and has been in mass production for 3 years. However, the sales volume has not been large, just 80 tons in 2023. Therefore, starting from October last year, we visited 24 domestic mainstream electrophoretic paint customers and had in-depth technical exchanges with them. We found that the product is not perfect or has low universal applicability. Generally, there is no problem in polyamide combined with lactic acid system. However, in the mid-to-high-end market, the mainstream is the system of ketimine combined with strong acid (such as formic acid, acetic acid, sulfamic acid and methylsulfonic acid, etc.). In this type of system, adding our 075 product, whether added to color paste or emulsion, will precipitate more or less at the bottom of the color paste or emulsion over time, that is, it has poor stability.

When you find a problem, you have to solve it. After reviewing the literature and the experience accumulated over the years, we analyzed that it should be that strong acid replaced the weak acid carrier and formed bismuth-based substances that are insoluble in water. So we returned to the laboratory and continued to work hard. After a month of research, we continued to look for and try new ideas, and repeatedly verified them in several commonly used neutralizing acid systems. Finally, a new water-based bismuth product (BI CAT-1050) was developed, which mainly has the following improvements:

1. Bismuth content: increased from 7.5% to 10.5%, requiring lower addition amount;

2. Hydrophilicity: The water evaporates under high temperature and can be dissolved again by adding water;

3. Low temperature resistance: After solidification in a low temperature environment below 0 degrees Celsius, the liquid can be restored to its original state after heating;

4. pH value: increased from the original 3.05 to 5.25, which has little impact on the overall pH of the emulsion or color paste;

5. Acid resistance and hydrolysis resistance: It exists stably under strong acid to weak alkali (pH 7.5) conditions. Bismuth ions are more stable in aqueous solutions and are not easy to become inorganic powder. It is more versatile in various systems.

In December last year, it passed the verification of 15 domestic mainstream electrophoretic paint customers. There are no problems with the stability of the emulsion (or color paste) added with 1050 products and the leveling of the paint film. And the added amount only needs 4-5 thousandths of the emulsion to reduce the baking temperature by 10 degrees Celsius. Compared with DBTO, DOTO, bismuth hydroxide, etc., it is more environmentally friendly and cost-effective.

This is an innovative product for the old water-based bismuth catalyst. I believe that in the water-based electrophoretic paint industry where environmental protection is a major trend, there will be greater room for development in the future. Looking forward to your consultation.

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