Although plastic can replace metal in many occasions, it is obvious that it lacks the texture of metal. To this end, a certain method is needed to coat the surface of plastic with a layer of metal (aluminum, zinc, copper, silver, gold, chromium, etc.). The method is similar to electroless plating and electroplating, and the other is to vacuum-spray metal directly on the surface of the plastic—that is, after the metal is melted under vacuum, it is deposited in the form of molecules or atoms on the surface of the plastic to form 5-10 μm. Metal film.
The vacuum metallization needs a good fit with the plastic surface primer. The thickness of the primer is usually 10-20 μm. The main function is to prevent the water, organic solvent and plasticizer in the plastic from affecting the metal adhesion. The coating is required to have a high hardness and the primer can modify the plastic defects to provide a smooth, flat surface to facilitate vacuum plating and to adhere to the plastic substrate and the metal to be plated. Two-component room temperature curing polyurethane and epoxy coatings, low temperature baking amino coatings and thermoplastic acrylate coatings are commonly used.
Metal coatings are easily oxidized and darkened in the air, and there are also defects such as fine vacuum, so a 5-10 μm protective topcoat is applied. The requirements for the topcoat are: transparent, excellent water resistance, abrasion resistance, weather resistance, no metallization film, and strong adhesion to the metal coating. Acrylate varnish, polyester varnish, polyurethane varnish, etc. can be used. When the primer is made of thermoplastic acrylate coating, weak solvent and quick-drying topcoat can be used to prevent the topcoat solvent from eroding the primer through the coating defect. Such as acrylic modified alkyd varnish, polyvinyl butyral varnish, urethane oil and the like.
The process of vacuum metallization is: plastic surface treatment (purification, activation) → prime coating → drying → vacuum metallization → topcoat → drying.
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