Extinction is to use certain methods to reduce the gloss of the coating surface.
1. extinction principle
Combined with the mechanism of the film surface gloss and the factors affecting the gloss, people believe that extinction is to use various means to destroy the smoothness of the film, increase the surface micro roughness of the film, and reduce the reflection of the film surface to light. It can be divided into physical extinction and chemical extinction. The principle of physical matting is: add matting agent to make the surface of the coating uneven in the film-forming process, increase the scattering of light and reduce reflection. Chemical extinction is to obtain low gloss by introducing some light absorbing structures or groups such as polypropylene grafted substances into UV coatings.
2. extinction method
Matting agent, in today’s UV coating industry, people generally use the method of adding matting agent. There are mainly the following categories:
(1) Metal soap
Metal soap is a kind of matting agent commonly used by early people. It is mainly some metal stearates, such as aluminum stearate, zinc stearate, calcium stearate, magnesium stearate and so on. Aluminum stearate is the most widely used. The extinction principle of metal soap is based on its incompatibility with coating components. It is suspended in the coating with very fine particles, which are distributed on the surface of the coating when the film is formed, resulting in micro roughness on the surface of the coating and reducing the reflection of light on the surface of the coating to achieve the purpose of extinction.
(2) Wax
Wax is an earlier and more widely used matting agent, which belongs to organic suspension matting agent. After the coating construction, with the volatilization of the solvent, the wax in the coating film is separated out and suspended on the surface of the coating film with fine crystals, forming a layer of rough surface scattering light and playing the role of extinction. As a matting agent, wax is easy to use, and can give the film good hand feeling, water resistance, moisture and heat resistance, and stain resistance. However, after the wax layer is formed on the film surface, it will also prevent the volatilization of solvent and the infiltration of oxygen, affecting the drying and recoating of the film. The development trend in the future is to synthesize polymer wax and silica to obtain the best extinction effect.
(3) Functional fines
Physical pigments, such as diatomite, kaolin and fumed silica, are functional fines specially used as matting agents. They belong to inorganic filled matting agents. When the film is dry, their tiny particles will form a micro rough surface on the film surface to reduce the reflection of light and obtain an Matt appearance. The matting effect of this kind of matting agent is restricted by many factors. Taking silica as an example, when it is used as a matting agent, its matting effect will be affected by such factors as pore volume, average particle size and particle size distribution, dry film thickness and whether the particle surface has been treated. Experiments show that the extinction performance of silica dioxide with large pore volume, uniform particle size distribution and matching particle size with dry film thickness is better.
In addition to the above three types of commonly used matting agents, some dry oils, such as tung oil, can also be used as matting agents in UV coatings. It mainly uses the high reactivity of the conjugated double bond of tung oil to make the bottom of the film have different oxidation and cross-linking speeds, so that the surface of the film is uneven to achieve the matting effect.
Post time: Jun-07-2022