Vacuum coating equipment can coat a variety of workpieces and substrates, including both hardware and flexible substrates. Generally, hardware coating uses single-unit machines or continuous lines, while flexible substrate coating uses roll-to-roll coating equipment. Currently, popular electronic copper foil is produced using roll-to-roll vacuum coating equipment to coat copper foil on both sides of PET, achieving the specifications required by manufacturers. Today, Puyuan Vacuum will explain the advantages of vacuum coating equipment for coating plastic films, hoping to be helpful to everyone:
One,Adhesion: The substrate to be coated should have good adhesion strength to the vacuum coating material. It is generally believed that polyester materials have the strongest adhesion to the aluminum coating layer (such as PET). The standard for measuring good adhesion performance is the surface free energy (surface activity index) of the plastic part. Generally, plastics with a surface free energy <33-35×10⁻⁵ N/cm are considered weakly polar (such as PP). Among commonly used plastic materials, the order of adhesion strength from highest to lowest is ABS → ABS+PC → PC → PVC. The adhesion between the vacuum coating and the substrate can be improved by applying a primer, as well as by chemical cleaning, immersion, and plasma pretreatment.
Two,Vacuum outgassing: Some materials may contain volatile small molecules (including moisture, plasticizers, residual solvents, unreacted monomers, additives, etc.) which will escape in gaseous form under vacuum, damaging the adhesion, smoothness, and appearance of the coating layer. Outgassing is not significant at room temperature, but under vacuum, the outgassing increases with temperature. Different materials exhibit significant differences in outgassing. For example, the moisture content of ABS and ABS+PC is generally between 0.5% and 0.2%. Under vacuum, ABS outgassing mainly contains moisture, CO, and hydrogen. Nylon, nylon+fiber, and polyvinyl alcohol materials are more prone to moisture absorption, resulting in higher moisture content that severely interferes with the coating. Currently, there are two methods to address this problem: one is preheating and baking to control the moisture content below 0.1%; the other is UV sealing with a primer. However, excessively high moisture content is undesirable; for example, plasticizers with a content of over 10% will overflow.
Three,Heat resistance: Regardless of the process used in vacuum coating, the material must be subjected to the test of temperature rise. The radiant heat from the evaporation source, the high-energy particles, vaporized atoms, molecular plasma, etc. of the coating material, as well as the condensation heat and kinetic energy on the material, will cause the material (shallow surface layer) to heat up rapidly. If the material has poor heat resistance, wrinkles will appear during vacuum coating, or even the whole material will shrink. Excessive heating can also lead to the decomposition of plastics, blistering and peeling of the coating.
Vacuum coating equipment comes in a wide variety of types, with different applications, models, processes, and technologies. Most vacuum coating equipment is non-standard and customized.
