Low gloss wood is very popular, the varnish used in addition to the desired gloss, but also no fog shadow, must be used matting agent.
When light is projected onto the lacquer film, part of it is reflected directly, part of it is absorbed by the lacquer film and the substrate or refracted and reflected and re-emitted from the lacquer film, its intensity is already very weak and scattered, so it has little effect on the luster. When the surface of the film is uniform and microscopic roughness, those reflected from the surface of the film is highly scattered, and the observer sees the light is very weak, then the extinction of light.
Extinction agent is the refractive index and the coating resin refractive index is very close to the micro-fine, narrow particle size distribution and small apparent density of the powder, in the coating process, with the volatile medium volatilization in the wet film formed in the up and down convection and be entrained to the surface layer of the wet film. As the surface layer is where the volatile medium escapes, so the solids are higher, i.e., the viscosity is larger, and thus the matting agent is retained, thus locally increasing the pigment volume concentration (PVC) on the surface of the paint film, and by the shrinkage of the paint film in the process of film formation and projection on the surface, forming a uniform and micro-fine rough paint film.
There are two types of matting agents, inorganic-based and polymer-based. The inorganic base is mainly silica, in order to reduce the apparent density to strengthen the upper and lower convection in the easy to be entrained, ebs amide wax, so made of high porosity to improve the efficiency of matting. When used in solvent-based coatings, the resin dissolved in the solvent can enter these pores, however, when used in water-dispersible coatings, those dispersed in granular resin is not easy to enter, so the residual air in these pores refractive index = 1.0 because of the difference in refractive index = 1.45-1.55 refractive index with the resin and produced a haze, acceptable in semi-glossy fashion, in flat light due to the increase in the amount of matting agent and less acceptable.
Polymer-based matting agent is mostly vinyl polymer beads, no pores, so there is no above disadvantages. However, the matting efficiency of 60o gloss is poor, but the difference between 60o and 850 gloss is very small, which is important for flat lacquers, so that there is no difference in gloss from one side to another in the view of the observer. In addition, the apparent density of silica-based matting agents is very small, making it difficult to add high enough pvc to obtain the desired low gloss. Table 1 shows the gloss of polymeric matting agents made from methacrylic acid methacrylate with ethylene glycol dimethacrylate as cross-linking agent compared to silica matting agents at different pvc.
Leave a message
We’ll get back to you soon