Preparation of high-quality zinc borate flame retardant: The existence mechanism and synergistic coupling separation of chloride ions in zinc borate

High-quality, low-chloride zinc borate is a low-smoke, non-toxic and environmentally friendly flame retardant with improved electrical properties for printed circuit board (PCB), so it can be used as a new type of flame retardant to replace brominated flame retardants. However, the chlorine content of zinc borate itself is high, and long-term use of zinc borate circuit boards will cause leakage and may cause a fire. To solve this problem, commercially available zinc borate (analytically pure) with a high chlorine content was used for the study. The presence of chloride ions in zinc borate was determined by X-ray photoelectron spectroscopy (XPS) and point of zero charge (PZC) and found to be mainly in the form of soluble salts and electrostatic adsorption. Based on the existing form of chloride ions, the synergistic technology of electrodialysis and washing with Na2CO3 solutions was used to remove most of the chloride ions from zinc borate, and the removal effect was up to 94.03%. The optimal process was optimized by the reaction surface curve method, the separation kinetics and electrical properties were investigated, and the membrane lifetime was evaluated. Zinc borate can be used as a flame retardant in printed circuit boards after contrast treatment. This study provides an important reference and guide for the removal of impurity ions from other inorganic flame retardants. In addition, it provides technical support for the production of high-quality zinc borate flame retardants.