The expansion type fireproofing coating develops rapidly and protects the base material together with other coatings at room temperature. When heated, it has a synergistic effect with the fireproofing agent in the coating. The entire coating expands and carbonizes, forming a dense, stable and low thermal conductivity carbonized layer, which plays the role of heat insulation, heat absorption and protecting the substrate.
Epoxy emulsion is a kind of normal temperature can crosslinking curing two-component thermosetting coating, bonding will system of various components together, forming a uniform coating in the surface of base material, and its network structure is conducive to the stability of the coating and corrosion resistance, but also makes the coating internal free volume reduction, when heated fireproof agent ammonium polyphosphate, melamine and pentaerythritol expansion effect is difficult to give full play to in the coating, expansion ratio, a hole inside the bubble carbonization layer uniformity is a bit poor. On the other hand, the epoxy system contains amino groups, benzene rings and other groups. When the coating is decomposed by heat, the flue gas will escape. In order to improve the deficiency of emulsion, adding filler is an effective method. On the one hand, this kind of packing should play a synergistic role with the expansion system and promote foaming. On the other hand, it can enhance the toughness of coating and carbonized layer and improve the anti-gas scour ability. Expandable graphite is a kind of natural crystalline graphite which can expand rapidly into vermicular graphite at high temperature after special treatment.
Expandable graphite has the following characteristics:
Stable crystal type exists at room temperature and has good corrosion and weather resistance.
When heated inserted layer (2) in decomposition of volatile substances in the scaly graphite into a worm-like, a large amount of heat at the same time, the volume of expandable graphite rapid expansion, generate carbon layer density is small, the fibrous carbon body in the system exists in the form of crosslinked network, to enhance the stability of the carbonized layers and can prevent the charring layer falls off, the inert, stability is good.
Torque expandable graphite is a good conductor of heat, allowing heat to spread evenly and rapidly. It is found that expandable graphite can enhance the strength of the carbonized layer and increase the fire resistance limit of the fireproof coatings. Experts say there is a good value in the amount of expandable graphite. The relationship of expandable graphite with different physical and chemical properties to fire resistance has not been systematically studied.
Functions of expandable graphite:
As a physical expansion filler, expansible graphite can significantly improve the fireproofing performance of expansive fireproofing coatings based on epoxy emulsion, increase the foaming rate, improve the morphology of the foaming layer and the time temperature back curve of the substrate, enhance the strength of the carbonized layer, and eliminate the odor and smoke generated during the expansion.
The effects of particle size on the dispersion of EG and the interaction between other additives are analyzed, and the small particle size has good fire resistance. The initial expansion temperature is closely related to the melting process of matrix resin and the chemical decomposition of fire retardant. The expansion volume affects the fireproofing property of the coating and the height of the final carbonization layer, but the relationship between the expansion volume and the fireproofing property is not as significant as the previous two factors.