Although plastic can replace metal on many occasions, it is obvious that the lacks metal texture, for this reason, it is necessary to use a certain method to plate a layer of metal (aluminum, zinc, copper, silver, gold, chromium, etc.) on the surface of plastic, one method is to use a similar chemical plating and electroplating method, the other is directly on the surface of plastic vacuum spray metal – that is, in a vacuum state, the metal After melting, the metal is deposited in a molecular or atomic form on the plastic surface to form a 5-10μm metal film.
Vacuum metal spraying requires good coordination with the plastic surface primer, which is usually 10-20μm thick, mainly to prevent the discharge of water, organic solvents, plasticizers, etc. from the plastic to affect the adhesion of the metal. Require high hardness of the coating, primer with plastic defects can be modified, can provide a smooth, flat plane to facilitate the performance of vacuum plating, and with the plastic substrate and the metal plated firmly attached. Usually, two-component room-temperature curing polyurethane and epoxy coatings, low-temperature baking amino coatings, and thermoplastic acrylate coatings are used.
Metal coatings are prone to oxidation and darkening in air, and there are also defects such as fine vacuum, so a 5-10μm protective topcoat is applied again. The requirements for the top coat are transparent, excellent water resistance, abrasion resistance, weather resistance, no operation of the metal coating film, and firm adhesion to the metal coating. Usually can be used as acrylate varnish, polyester varnish, polyurethane varnish, etc. When the primer is used thermoplastic acrylate coating, in order to prevent the top coat solvent through the coating defects dissolved primer, you can use weak solvent, fast drying top coat, such as acrylic modified alkyd varnish, polyvinyl butyral varnish, urethane oil, etc.
The vacuum metal plating process is plastic surface treatment (purification, activation) → coating primer → drying → vacuum metal plating → coating top coat → drying.
