Applications of Zinc Borate

Zinc borate has a wide range of applications, especially in flame retardant systems where it is widely used in various plastic polymers. CAS: 1332-07-6, Chemical Formula: 2ZnO.3B2O3.3.5H2O, 1% water loss occurs at 250℃, making it suitable for various engineering plastics. It can replace antimony oxide in flexible, semi-rigid, and filled PVC, as well as in plastisols. In PVC sheathing formulations for wires and cables, a mixture of zinc borate and antimony trioxide significantly improves the oxygen index and smoke suppression effect, reducing the maximum smoke density of the material from 696 to 324.

1. In halogen-free flame-retardant EVA cable materials, PE, epoxy resins, acrylates, and synthetic rubber, 2ZnO.3B2O3.3.5H2O also exhibits a synergistic effect with aluminum hydroxide. In silicon-containing polymers used as cable materials, it can itself act as a flame retardant/smoke suppressant.

2. It can promote char formation. The char formed from PVC containing zinc borate at 560°C contains 80% boron and 62% zinc from the original zinc borate. Zinc can also catalyze the dehydrochlorination of PVC, causing cross-linking and resulting in char formation.

3. It can act simultaneously in both the gas and condensed phases. It reacts with halogenated polymers to produce zinc chloride and zinc oxychloride, both of which are free radical terminators, similar to the effect of Sb₂O₃.

4. Zinc borate is inexpensive, non-toxic, and non-irritating. Even below 260°C, it retains hydrated water, covalently bonded to hydroxyl groups. Another characteristic of zinc borate is that it has little effect on the strength, elongation, and thermal aging properties of many polymers.

5. Zinc borate can also form a viscous liquid layer on the polymer surface. This layer can weaken the flame and prevent the underlying char layer from oxidizing.

6. Besides its use in PVC,2ZnO.3B2O3.3.5H2O is also an effective synergistic flame retardant for some other halogen-containing materials (such as brominated polyesters, nylon, and epoxy resins).

7. It is often used in combination with other flame retardants to exert a synergistic flame retardant effect and smoke suppression function. It can be widely used as a flame retardant for unsaturated polyesters, epoxy resins, PBT, PET, PA, polyphenylene ether, EVA, EEA, PE, EPDM, acrylates, etc. In silicone rubber, zinc borate alone also has excellent flame retardant efficiency.

Zinc borate used in fibers can improve the processability and component dispersibility of the material. Mixtures with aluminum hydroxide are used as high-temperature charring flame retardants. Compounds of ultrafine zinc borate with magnesium compounds can be used for low-smoke wire and cable sheathing.