Why is plastic coated before vacuum coating?
Most plastics in the vacuum coating before the general first coating, the main reasons are as follows:
One: plastic in molding, the surface must have a certain degree of roughness, such as 0.5um roughness.
Vacuum coating layer is very thin, it is difficult to cover up the uneven surface of the substrate, if the bottom coating technology, uv curing coating thickness of about 10~20um, coating roughness in 0.1um below, so can greatly improve the brightness of the coating.
Two: plastic contains water, residual solvent, monomer, low polymer, plasticizer, etc., volatile small molecules will escape the surface in the vacuum or temperature environment, seriously affect the adhesion of the vacuum coating on the substrate, and the use of substrate coating technology can hinder the escape of these small molecules, improve the adhesion of the vacuum coating on the substrate.
Three: plastic substrate and vacuum coating is usually metal) the thermal expansion coefficient of the two is very different, in the vacuum coating heating and cooling process, the film is easy to break, the thicker the film, the greater the possibility of rupture, so choose the appropriate coating as a transition layer, can reduce the accumulation of internal stress and rupture.