Heat insulation principle of thin steel fireproof coating

The fire insulation principle of ultra-thin or thin steel fireproof coating coated on steel structure is that the fireproof coating layer expands and foams when it is subjected to fire, and the foam layer not only isolates oxygen. The foam layer not only isolates oxygen, but also has good thermal insulation property because of its loose texture, which can retard the speed of heat transfer to the protected substrate.

According to the analysis of physicochemical principle, the process of the foam layer produced by the expansion of the coating foam layer shows heat absorption reaction because of the expansion of volume, which also consumes the heat of combustion and helps to reduce the temperature of the system.

In the glassy state, when the polymer is heated, as the temperature of Ta increases, the molecule has already expanded in volume, but the temperature/K free volume does not expand, and the temperature reaches Tg
Later, the volumes of the two parts expand at the same time. The high molecular polymer segment obtains sufficient kinetic energy and necessary free space for diffusion and conformation adjustment. Therefore, the glass transition temperature can also be defined as the point at which the temperature expansion (or shrinkage) coefficient of the polymer changes.
Only when the temperature is higher than Tg, the free volume exceeds 2.5%, which depends on the temperature difference (T-T) and the volume expansion coefficient.

Co-film formation mechanism
The film formation of latex paint is a continuous film fused into a continuous film by the evaporation of water, the deformation of latex particles and the diffusion and winding of latex molecular chains. Both latex particle deformation and molecular segment diffusion require a free volume greater than 2.5% in the latex polymer system. The so-called latex polymer system here refers to a mixture of all components in latex paint except pigments and fillers. Otherwise, the latex particles are in a glassy state and cannot be deformed, and the molecular segments and free volume of the latex are in a frozen state and cannot be diffused.

In other words, the film forming temperature of the latex paint must be higher than the Tg of the latex polymer system. Two issues should be noted here: First, the T of the latex polymer system changes during the film forming process. With the volatilization of the film-forming aid and water, the T of the latex polymer system will increase. Second, in fact, due to the influence of pigments and fillers, the minimum film-forming temperature of latex paint will be higher than the T of the latex polymer system. In other words, with the addition of pigments and fillers, the difficulty of film formation will increase. The minimum film forming temperature of latex paint refers to the lowest temperature at which the latex paint forms a continuous coating film without cracking. It is different from the lowest film-forming temperature of emulsions for latex paints. In latex paints with pigments and fillers, it is higher than the lowest film-forming temperature of emulsions for latex paints.

It can be seen that the film-forming mechanism of the film-forming aid is to provide enough free volume during the film-forming process to deform the latex particles and the latex molecular segments to diffuse and twist and fuse into a continuous film.