(1) Environmental Requirements for Vacuum Coating
The cleaning of the substrate surface is crucial for vacuum coating processes. Before entering the coating chamber, the substrate should undergo thorough pre-coating cleaning to remove oil, dirt, and water.
Surface contamination originates from various dust, lubricating oil, machine oil, polishing paste, grease, sweat, etc., adhering to the parts during processing, transport, and packaging; oxide films formed on the parts surface in humid air; and gases absorbed and adsorbed by the parts surface. These contaminants can generally be removed using degreasing or chemical cleaning methods.
Cleaned surfaces should not be stored in the atmosphere but in sealed containers or clean cabinets to minimize dust contamination. Storing glass substrates in freshly oxidized aluminum containers minimizes the adsorption of hydrocarbon vapors, as these containers preferentially adsorb hydrocarbons. For highly unstable surfaces sensitive to water vapor, they should generally be stored in a vacuum drying oven. Maintaining a high level of cleanliness and removing dust from the coating chamber are fundamental environmental requirements for the coating process.
In areas with high humidity, in addition to thoroughly cleaning the substrate and all components within the vacuum chamber before coating, baking and degassing are also necessary. To prevent oil from entering the vacuum chamber, attention must be paid to oil backflow from the oil diffusion pump; for diffusion pumps with high heating power, oil-blocking measures must be implemented.
(2) Basic Principles of Coating and Film Coating
A. Raw Materials and Basic Principles: Raw materials include resins, polymers, Teflon, silicone, acrylic acid, and silicates, but the auxiliary materials, formulations, and quantities vary. For example, the amount of emulsifier added will affect the emulsion's state, resulting in watery, milky, or paste-like forms. After emulsification and demulsification, these substances partially penetrate or form a thin film.
B. Characteristics and Differences:
Coating: Good penetration (depending on the particle size of the raw materials), superior surface smoothness, suitable for European and American car paint surfaces with many "capillaries," roughness, repainting, or a hard surface requiring increased gloss.
Film Coating: Film-forming aids and curing agents are added to film-forming products, allowing for instant film formation, thus altering the properties of the coating.
The coating environment and coating layer required by the vacuum coating machine are very important factors. If the vacuum level is not high enough, the coating conditions are not met, and the yield rate will be far from the ideal value.
