The principle of coating matting and coating matting agent should have the characteristics
Gloss is one of the important physical properties of the coating film, expressed in terms of gloss. Can make the coating surface gloss significantly reduced substances called coating matting agent, the largest amount of ultra-fine synthetic silica, followed by micronized wax, aluminum, calcium, magnesium, zinc stearate amount is smaller. In addition, adding body pigments, increasing pigment content, adding incompletely compatible resin components and using mechanical methods to make the coating surface rough or surface embossing can also reduce the gloss of the coating film.
There are some occasions when a glossy film is needed and some occasions when a glossy film is not needed. Whether to use high gloss coatings or low gloss low gloss is not only related to fashion and appearance, but also related to gloss effect, touch feeling, risk reduction and other factors. General transportation for safety reasons are used non-glossy matte paint, the interior decorative surface is also basically matte; skyscraper surface is also generally not brushed with glossy paint, but covered with pre-painted plates on steel or aluminum substrate, and all use matte paint to avoid producing dangerous reflections that irritate the eyes of pedestrians or car drivers. And economy and practicality is another important factor in choosing low gloss coatings. When certain substrates are scuffed, slightly pitted or soiled, it is difficult to cover such defects with glossy paint, and the use of matting coatings can disguise these defects.
The loss of gloss on the surface of the coating film is caused by the formation of tiny dimples on the dried coating film surface, which creates a diffuse reflection of the incident light. There are two conditions for the formation of tiny unevenness on the coating surface, one is the presence of sufficient amount of particle size suitable for matting agent particles in the wet film; the other is the volume shrinkage during the drying or curing process of the coating film. There is a condition can not be fully met, the matting effect is also not ideal. During the coating process, the surface of the coating film just applied is not very flat, due to the surface tension, in order to maintain the minimum surface area, it will become a smooth wet film, the use of leveling agent to accelerate this process. Before the surface of the coating film dries, the gloss level tends to be high due to the solvent. When the coating film dries, the surface shrinks continuously due to the evaporation of the solvent, causing the matting agent particles, which are evenly distributed among them, to form very small bumps on the surface. The tiny bump formed on the surface of the coating by using matting agent is optically uneven and invisible to the naked eye. Therefore, when the light is irradiated to the coating surface at a certain angle, if its surface is close to the optical plane, it will cause total reflection, and its reflection angle will be equal to the incident angle, and the gloss will be high; when the incident light reaches the surface of the tiny bump, as the average roughness of the coating surface increases, the scattered light will gradually replace the reflected light, so that its gloss will keep decreasing, and eventually a lightless coating will be formed.
Traditional solvent-based coatings with volatile matter content between 30%-80%, in the drying or curing process, with the volatile matter evaporation, the coating film shrinkage is obvious, matting is easier; water-based coatings with water as dispersant, in the drying or curing process, due to the evaporation of water, coating film shrinkage is also obvious, matting is also not difficult. For high solids coatings, the solid content is generally 70%-90%, the difficulty of matting is relatively increased; UV light-cured coatings, solid content 100%, curing shrinkage is less than 10%, it is difficult to matting; and powder coatings without organic volatilization, solid content 100%, the most difficult to matting. For these coatings, in the drying or curing process, the coating film shrinkage is very small or even not shrinkage, so the need to form a tiny bump on the surface of the coating, generally using matting agent matting.
Coating with matting agent to have the following characteristics: 1, high chemical inertia, does not react with any component of the coating film; 2, the transparency of the coating film interference is small, the impact of the coating rheology is small; 3, good matting performance, low addition can produce strong matting performance; 4, in the liquid coating, good suspension, long storage, will not produce hard precipitation; 5, the mechanical properties of the coating film and chemical properties of small impact, and It is easy to disperse, does not pollute the environment, and will not cause harm to human body.