Because steel structure has the advantages of light quality, high strength and convenient construction, it is widely used in large buildings. But poor fireproof property of the steel structure, easy to heat conduction, when its temperature over 540 ℃, the loss of almost all the mechanical strength, which can lead to collapse of buildings cannot support their own quality and, thus bring huge losses to people's life and property. Therefore, it is necessary to protect steel structures against fire. The surface of the steel structure is coated with fireproof paint, which is simple and convenient to operate and has obvious fireproof effect. Meanwhile, it also has certain decorative function. There are many kinds of classification methods for fireproofing coatings, which can be divided into expansion type and non-expansion type according to fire prevention mechanism. According to its coating thickness, it can be divided into thick slurry type (thickness: 8-50mm), thin layer type (thickness: 3-7mm) and ultra-thin type (thickness: less than 3mm). According to the use object can be divided into steel structure fire - proofing paint, prestressed floor fire - proofing paint, cable fire - proofing paint and decorative surface - type fire - proofing paint. Ultra-thin and expansive fire resistant coatings consume less materials, convenient construction, strong decorative properties, and excellent fire protection effect. But the ultrathin intumescent fire coatings that sells on the market still exist some shortcomings, such as poor resistance to water, the water is easy to fall off, swell, durability is also poor, more important is fire prevention performance is difficult to guarantee, although inflation layer foaming expansion, but spongy carbon layer frame strength is not enough, easy to wash away by the strong flame flow, even will melt with carbonaceous layer, severely reduces their fireproof heat insulation effect. Therefore, it is necessary to study a kind of fireproofing coating with enough strength of expansion layer to ensure its fireproofing effect.
Composition and fire prevention mechanism of ultra-thin and expansive fire resistant coatings
Usually, the main components of ultra-thin and expansive fireproofing coatings are: film forming materials, charring agents, foaming agents, dewatering agents, pigments, fillers, various additives and solvents.
Film forming material on the performance of the expansion type fire retardant coatings have a significant impact, its compatibility with other components, guarantee the coating used in normal temperature condition with various properties, function bonding on the one hand, on the other hand it to the fire after the carbonized layer expansion height and strength all have great influence, in the role of fire or high temperature, with the expansion of the flame retardant properties and excellent effect. Film-forming materials are usually composed of resins, including water-based resins (such as ammonium polyphosphate vinyl emulsion, polyvinyl alcohol, etc.), nitrogen-containing resins (such as melamine formaldehyde resin, polyamide resin, etc.), and other resins (such as chlorinated rubber, chlorinated resin, epoxy resin, etc.).
The proportion of inorganic fillers is small for expansive fireproofing coatings, because the high content of inorganic fillers will affect the foaming height of the coating and reduce the foaming effect, so as to reduce the fireproofing property of the coating and achieve the purpose of heat insulation. However, a small amount of fillers is essential, which can increase the refractory limit of the coating, make the fire-resistant coating play a role in the middle and late period of fire, and help to form a high strength carbonization layer with low expansion rate, so that the foam layer is more compact and stronger, so as to improve its fireproofing performance. As a kind of white pigment, titanium dioxide not only has strong hiding power and good chemical stability, but also can make the formed carbonized layer compact and improve the thermal insulation performance of the carbonized layer, making it the first choice. Generally, aluminum hydroxide and zinc oxide can be used as fillers. Expansion type fire-retardant coating in when heated, NH3, H2O and other non-combustible inert gas, on the one hand, dilute combustible gas won't burn or burn at a slower pace, on the other hand the foaming effect, into carbon agent under the effect of catalyst dehydration into charcoal, together forming spongiform carbon foaming agent layer, closed a protected object, heat isolation, delay to the base material of heat transfer, prevent burning or strength decline caused by the temperature, effectively protect the base material.