The film-forming process of latex paint
The dry film formation of such coatings is related to ambient temperature, humidity, film-forming aids and resin glass transition temperature. Environmental humidity greatly restricts the evaporation rate of water in the wet stage of film formation, and increasing the air flow rate can greatly accelerate the evaporation of water in the coating film; when the latex particles are kept in contact with each other, the evaporation rate of water drops to 5%~10% of that in the wet stage . At this time, if the deformability of the emulsion is very poor, a loose, opaque and dull discontinuous coating film will be obtained. In order to endow the latex paint film with application performance, the glass transition temperature of the resin is above normal temperature, so a film-forming aid is added to increase the deformation ability of the emulsion particles at normal temperature, so that the minimum film-forming temperature of the latex paint can reach above 10°C, The emulsion particles will be further deformed and fused into a continuous coating film. After the emulsion particles are fused, the water molecules in the coating film escape by diffusion and are released very slowly.
Generally, the latex paint is surface-dried within 2 hours, hard-dried for about 24 hours, and fully dried for about two weeks. The volatilization rate of film-forming aids from the coating film decreases in order of ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol butyl ether acetate, ethylene glycol, and diethylene glycol monobutyl ether. Ethylene glycol monomethyl ether evaporates too quickly and is completely lost before reaching the dry film; glycol ether acetate is essentially completely distributed in the resin phase. These two additives have little effect on the evaporation of water in the stage. Ethylene glycol butyl ether tends to partition between the water phase and the resin phase, and water evaporation is affected by its partition ratio. The presence of ethylene glycol makes it form a continuous swelling hydrophilic network structure, which makes it easy for the polar coalescence agent to diffuse and escape. However, ethylene glycol is more hygroscopic than propylene glycol, and the coating film dries slowly. The latex paint film added with propylene glycol retains very little water or coalescent after a few weeks, so that the coating film (especially outdoor paint) will not produce Negative Effects.
