Zinc Borate (Molecular formula of zinc borate 2ZnO·3B2O3·3.5H2O ) a unique form of zinc borate with multifunctional fire retardant applications in plastic and rubber compounds. Since ZB2335 releases its water of hydration at temperatures exceeding 290°C (554°F), it can be used in systems requiring high processing temperatures. Zinc Borate (Molecular formula of zinc borate 2ZnO·3B2O3·3.5H2O ) has a refractive index similar to that of most polymer systems, which results in the retention of considerable translucency and allows the use of low pigment loading. It can be fed to extruders, calenders, or injection molding equipment in much the same way as other solid polymer additives.can be used to replace partially (or even completely) other fire retardant additives such as antimony oxide
Molecular Structure and Characteristics
Chemical composition: Taking 3.5 water zinc borate as an example, its molecular formula 2ZnO·3B₂O₃·3.5H₂O indicates that the molecule is composed of zinc oxide, boron trioxide, and crystalline water. Zinc provides a stable metal framework, while boron acts as a flame retardant by forming a film to isolate oxygen and suppress flammable gases. Crystalline water releases heat at high temperatures, reducing combustion temperature.
Physical form: White crystalline powder or amorphous powder, small particle size (average particle size 3-5 μ m), light specific gravity (2.67g/cm ³), easy to uniformly disperse in polymers, without affecting material color and mechanical properties.
Thermal stability: Crystalline water is stable below 300 ℃, gradually released above 320 ℃, and forms molten borate to cover the combustion surface, forming an "oxygen barrier layer" and a "carbon layer" to block the combustion chain reaction.
Physical and Chemical Properties
| Items | Unit | ZB-2335 |
| Appearance | — | White Powder |
| B2O3 | % | 47.0 ～ 49.0 |
| ZnO | % | 37.5 ～ 39.5 |
| Moisture | % | ≤0.3 |
| Loss on Ignition | % | 13.0~15.5（450℃) |
| Whiteness | % | ≥96.0 |
| Particle Size,D50 | µm | ≤7.0 |
| TGA(1%) | ℃ | ≥345 |
| Chloride(Cl- ) | % | ≤0.05 |
| Sulphate(SO42-) | % | ≤0.005 |
application area
1. Plastic industry
Flame retardant modification: In plastics such as PVC, PE, PP, PA, etc., it replaces traditional halogen containing flame retardants (such as antimony trioxide) to reduce smoke toxicity.
Synergistic effect enhancement: When compounded with halogen-free flame retardants such as aluminum hydroxide and magnesium hydroxide, a synergistic system of "metal oxide+boron system" is formed, which improves the oxygen index (OI) of the material and reduces the total amount of flame retardants added.
2. Rubber and elastomers
Rubber products: flame retardant formulas used for natural rubber, styrene butadiene rubber, and chloroprene rubber, such as rubber sealing strips for automobiles and insulation layers for wires and cables. Adding 5-10% zinc borate can form a carbonized layer during rubber combustion, preventing flame spread.
Mechanical performance maintenance: Due to its small particle size and good dispersibility, it has little impact on the tensile strength and elongation at break of rubber, making it suitable for high demand industrial scenarios.
3. Coatings and Coatings
Fireproof coating: used as an additive in steel structure, wood, and building wall coatings, it generates a glassy protective layer at high temperatures and delays the heating of the substrate. For example, adding 15-20% zinc borate to acrylic resin coatings can achieve a fire rating of GB 12441-2018 standard.
Anti corrosion synergy: The chemical stability of boron element can enhance the anti-corrosion protection of coatings on metal substrates, achieving a dual effect of "flame retardant+anti-corrosion".
4. Other fields
Textiles and papermaking: used in the post-treatment process of flame-retardant carpets, curtains, and other fabrics, or directly added to pulp to give the material self extinguishing properties.
New Energy and Electronics: Used as flame retardant fillers in lithium battery separators and electronic packaging materials to reduce the risk of fire caused by circuit short circuits.
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