Process description of plastic vacuum coating(Plastic vacuum coating equipment)
Although plastic can replace metal in many occasions, it obviously lacks the texture of metal. Therefore, it is necessary to adopt certain methods to coat a layer of metal (aluminum, zinc, copper, silver, gold, chromium, etc.) On the surface of plastic products. One method is similar to electroless plating and electroplating, and the other is to directly vacuum plating metal on the surface of plastic - that is, in a vacuum state, the metal melts and deposits on plastic in the form of molecules or atoms.
The vacuum coating process requires that the surface of plastic products should be well matched with the primer, and the thickness of the primer is usually 15-25 μ m. The main function is to prevent the discharge of water, organic solvents, plasticizers, etc. Affect metal adhesion. It is required that the coating has high hardness, the primer has modifiable plastic defects, and can provide a smooth and flat plane to facilitate the fullness, gloss, adhesion and other properties of the vacuum coating, so as to ensure that the plastic substrate is firmly attached to the plated metal. Generally, two-component polyurethane and epoxy coatings are selected to cure at room temperature, with low baking amino paint and thermoplastic acrylate paint.
The metal coating is easy to oxidize and blacken in the air, and also has slight defects such as vacuum. Therefore, it is necessary to apply a layer of 10-15 μ M protective finish. The requirements of surface paint are: transparent, excellent water resistance, wear resistance and weather resistance, do not operate the metal coating, and have firm adhesion to the metal coating. Generally, there are acrylic varnish, polyester varnish, polyurethane varnish, etc. Can be used. When the primer is thermoplastic acrylate paint, in order to prevent the solvent of the topcoat from corroding the primer through coating defects, weak solvent and quick drying topcoat can be selected, such as acrylic modified alkyd varnish, polyvinyl butyral varnish, polyurethane oil, etc.
The process flow of vacuum metallization is: plastic surface treatment (purification and activation) → primer coating → drying → vacuum metallization → finish coating → drying. The process flow is briefly introduced: product surface cleaning - > electrostatic removal - > primer spraying - > baking primer - > vacuum coating - > topcoat spraying - > baking topcoat - > packaging.
In the whole process, the following points determine the success or failure of the process:
1. The surface state of the parts to be processed, including whether the products have defects, surface state, surface pollutants, etc.
2. The existence of surface defects will lead to the final aesthetic appearance of external parts. Of course, the existence of minor defects can be covered up by the spraying process. However, this batch of defective products caused in the process of injection molding or stamping must be removed before incoming inspection.
3. Surface state, which involves whether it is transparent and the design of special surface roughness. If the design state requires, the overall process route must be considered before formulating the process, otherwise it is difficult to get the expected appearance effect after completion.
4. Surface pollutants. For batch products, how to remove the residual pollutants in the previous process is the key to quality and efficiency. For example, remove the release agent produced in the injection molding process.
5. Fixture design, including whether the fixture is applicable to all process flows, and whether it can ensure surface uniformity and clamping efficiency.
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