What is the fire-retardant principle of fire-retardant coatings?

The fire-retardant principle of fire-retardant coatings essentially lies in the physical and chemical changes that occur within the coating itself under high-temperature fire conditions, forming a protective system that provides thermal insulation, flame retardancy, and smoke suppression. This system slows down the temperature rise of the substrate, prevents the spread of fire, and extends the fire-resistance duration of the substrate.

Depending on the type of fire-retardant coating—whether intumescent or non-intumescent—their fire-protection mechanisms differ. Specifically, they can be categorized into two main types:

1. Intumescent Fire-Resistant Coating (Thin-Coat Type, with Excellent Decorative Properties)

This is currently a widely used type in architectural and industrial components. Its core principle lies in the “expanding carbonization” effect at high temperatures, which occurs in three distinct stages:

During the thermal decomposition stage of a fire, when the temperature reaches 150–300℃, the foaming agents in the coating—such as azo compounds and phosphates—decompose upon heating, releasing large amounts of inert gases like nitrogen and carbon dioxide. At the same time, the char-forming agents in the coating—such as polyols and starch—and the acid sources—such as ammonium polyphosphate—react with each other to generate acidic catalysts, including phosphoric acid.

During the expansion and carbonization stage, inert gases form numerous bubbles within the coating, causing the coating to expand dramatically—its volume can increase by tens to hundreds of times its original size. An acidic catalyst promotes the dehydration and carbonization of the carbonizing agent, ultimately forming a porous, dense, sponge-like carbonized insulation layer.

In the insulation and flame-retardant stage, the char layer exhibits high porosity and an extremely low thermal conductivity, effectively preventing flames and heat from transferring to the substrate and thus averting rapid temperature rise in the substrate (such as steel or wood). At the same time, the char layer itself is non-combustible and can also block oxygen from coming into contact with the substrate, thereby inhibiting the combustion reaction. Moreover, the inert gases produced during decomposition can dilute the concentration of flammable gases in the fire zone, providing an auxiliary effect of suffocating and extinguishing the fire.

Applicable scenarios: Indoor steel structures, wooden furniture, decorative components, and other substrates that have aesthetic requirements.