Zinc borate has a remarkable flame-retardant effect in coatings, and its mechanism of action is mainly reflected in the following aspects:
First, heat absorption, cooling and dilution effects
When the temperature exceeds a certain threshold (such as 300℃), zinc borate will undergo thermal decomposition and release crystalline water. This process not only absorbs a large amount of heat, achieving the effect of heat absorption and cooling, but also dilutes the concentration of oxygen and flammable gases in the air, keeping them below the lower limit of combustion, thereby preventing the combustion from continuing.
Second, the function of covering and isolating
Under high-temperature conditions, zinc borate decomposes to form B₂O₃ solid, which can closely adhere to the surface of the coating, forming an inorganic expansive coating or glassy covering layer. This covering layer acts as a barrier, effectively suppressing the generation of flammable gases and preventing further oxidation and thermal decomposition, thereby playing a role in isolating air and heat.
Third, promote carbon formation and hinder volatilization
Zinc borate can also promote the formation of carbon layers during the combustion process of the coating. These carbon layers have excellent heat insulation and oxygen isolation properties, which can effectively protect the unburned parts inside the coating. Meanwhile, zinc borate can also prevent the escape of volatile combustibles, further reducing the spread speed of fires.
Fourth, synergistic flame retardant effect
Zinc borate can also produce a synergistic flame-retardant effect with other flame retardants. For instance, when used in combination with flame retardants such as hydroxides, zinc borate can accelerate the decomposition of hydroxides, thereby enhancing the flame retardant performance of the entire system. This synergistic effect makes the flame-retardant effect of zinc borate in coatings more significant.
