What is the role of silica for matting powder in solvent coatings?
What is the role of silica matting powder in solvent coatings? More commonly used matting powder can be divided into organic and inorganic types: inorganic matting agent is mainly silicon dioxide matting agent, its chemical composition is ultra-fine sio2, which can be divided into two types of surfaces: organic matter treated and untreated. Now we mainly discuss the application of silica matting agent in coatings. Pigments or fillers are added to the coating and uniformly distributed in the coating film to produce a slightly rough surface. Light calcium carbonate or talc powder is used to produce matt coatings with large dosage, which often exceeds the critical pigment volume concentration of the coating, resulting in poor physical properties of the coating, such as delamination and hard precipitation. The use of matt powder can avoid the larger the surface particles, the greater the micro roughness, and the lower the gloss.
Matting powder
The matting mechanism of silica matting powder: the varnish film without matting agent is flat. When the light reaches the surface of the mirror film, part of the incident light is absorbed, part is reflected, and part of the reflection makes the film shiny. The paint film containing silica matting agent is evenly distributed in the paint film, producing a slightly rough surface.
It can be clearly seen from the scanning electron microscope photos of the film section that the extinction particles are evenly distributed in the film. When the incident light reaches the uneven paint film surface, it will produce diffuse reflection, that is, scattering will produce low gloss matt and extinction appearance. High porosity is adopted. Good particle size distribution and appropriate surface treatment of silica matting agent can obtain good matting effect.
Silica matting powder: the powder made of natural sio2 by grinding has a high impurity content. The main component is sio2, which cannot be called silicon dioxide and has no extinction characteristics. It can only be used as filler in paint, without matting effect. Silica matting agent, as a coating, mainly generates sio2, which is divided into gaseous silica and precipitated silica. Its microstructure is amorphous or glassy.
Silica system generated by precipitation method is mainly made of quartz sand, and it is melted with sodium hydroxide or sodium carbonate at high temperature in the kiln. Compared with natural silicon dioxide, silicon dioxide has high purity of silicon dioxide. Great inertia. UV resistant. The refractive index of amorphous silica is 1.46, which is close to the refractive index of many epoxy resins in the coating industry. Therefore, amorphous silica can be used as the matting powder of coatings and has excellent optical properties.