The fire insulation principle of thick steel structure fireproof coating coated on steel members is that the coating basically does not change volume when the fireproof coating is subjected to fire, but the thermal conductivity of the coating is very low, which delays the speed of heat transfer to the insured substrate, the coating of fireproof coating itself is non-combustible, which acts as a barrier and prevents thermal radiation to the steel members, avoiding the flame and high temperature from attacking the steel members directly.
Some components of the coating react with each other when they meet fire and generate non-flammable gas is a heat absorption reaction, which also consumes a lot of heat and helps to reduce the system temperature.
For latex polymer systems, T can be calculated by the modified Fox equation [Equation (18-1)].
1/Tg=V, /Tg+aV./T, (18-1) where Tg——the glass transition temperature of the emulsion polymer and film-forming aid system, K; what is teflon wax
Te, Tg, one is the glass transition temperature of the emulsion polymer and the film-forming aid, K;
Vp, V. Respectively are the volume fractions of emulsion polymer and film-forming aids;
α Compared with the internal plasticizing comonomer, the plasticizing efficiency coefficient of the film-forming aid,
For styrene-acrylic emulsion, Texan ol’s a=1.014
The glass transition temperature of some film forming aids.
—Water and surfactants will also affect the Tg of the latex polymer system, and will affect the minimum film-forming temperature of the latex paint. Of course, Tao can be calculated from equation (18-1) by water, but some people believe that the MFT of emulsion polymer is lower than Tg due to the plasticizing effect of water. The T including the plasticization of water is regarded as MFT.
K=MFT/T, (18-2) where K=0.92~0,98.
Combining formula (18-1) and formula (18-2), considering Vp=1-V, we get ,
1/MFT=V.[(wT, -Ta) /(KT g, Te)] +1/(KT g) (18-3) where V is the volume fraction of the film-forming aid in the formula.
Taking 1/MFT to V is a straight line. Hoy’s research concluded that when the amount of film-forming aid is less than 5g/100g of dry resin, this is also a straight line.
The surface drying of latex paint is relatively fast, generally no more than 2h under standard conditions. However, the complete film formation time of latex paint is relatively long, which takes several weeks to one month. Free volume is the main factor affecting the film formation rate, and the free volume is largely determined by the temperature difference (T-Tg) .
Based on the well-known WLF equation, Win nik et al. derived an equation for evaluating the plasticizing efficiency of film-forming additives.
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