White haze on the inside of the workpiece in a vacuum coating machine is more complex to cause than on the outside. Possible causes include:
1. Film structure issues: Loose columnar structure of the outer film, or an overly rough outer film;
2. Excessive evaporation angle, resulting in a rough film structure;
3. Temperature difference: Excessive temperature difference between the inside and outside of the lens when it is removed from the coating;
4. Moisture: Moisture in the environment where the lens is placed after removal from the coating;
5. Excessive moisture during the thawing of the POLYCOLD in the vacuum chamber;
6. Incomplete oxygenation during vapor deposition, resulting in an uneven film structure;
7. Stress between films.
Improvement strategies: Since there are many causes of white haze on the outside of the film, each with its own characteristics, targeted solutions are recommended. The main strategies are: first, to make the film denser and smoother to prevent adsorption; and second, to improve the environment to reduce the objects that can be adsorbed.
Improvement Strategies:
1. Improve the film system by adding silica to the outer layer to make the film surface smooth and less prone to adsorption. Improve the environment during lens removal (dry and clean).
2. Reduce the lens temperature during removal (extend the cooling time in the vacuum chamber) to reduce temperature difference and stress.
3. Improve oxygenation (increase the amount) and improve the film structure.
4. Appropriately reduce the evaporation rate to improve the columnar structure.
5. Use ion-assisted coating to improve the film structure.
6. Add a small gas valve during polycold thawing (its function is to remove moisture promptly).
7. Improve the evaporation angle by modifying the evaporation source and fixture.
8. Improve the surface roughness of the substrate.
9. Pay attention to the vacuum level during polycold thawing.
White haze forms within the coating layer on vacuum-coated workpieces and cannot be removed by wiping.
Possible causes:
1. Dirty substrate, residue from previous processes.
2. Corrosion contamination on the lens surface.
3. Incompatibility between coating materials and between coating material and substrate.
4. Insufficient oxygenation of oxides.
5. The first layer of zirconium oxide coating may cause white haze on some substrates.
6. Moisture contamination of the substrate before (after cleaning) before encapsulation.
7. Poor cleaning or wiping, leaving cleaning or wiping marks.
8. Dirty vacuum chamber, excessive moisture.
9. High ambient humidity.
Improvement Strategy: The substrate itself is likely the primary issue, while coating aims to compensate for it. The most significant problem with the coating itself is likely the compatibility of the coating materials.
Improvement Measures:
1. Improve the coating system; avoid using zirconium oxide as the first layer.
2. Minimize vacuum chamber opening time; ensure thorough cleaning and coating preparation between vacuum chambers within the shortest possible time.
3. After replacing the protective plate and cleaning the vacuum chamber, it is best to perform a vacuum baking process with an empty chamber. Replaced protective plates and other vacuum chamber components must be dry and clean.
4. Improve the environment.
5. Properly protect the lenses on the umbrella-shaped plates before they enter the vacuum chamber from contamination.
6. Improve cleaning and wiping effects.
7. Improve coating compatibility (consider using Al2O3 for the first layer).
8. Improve the oxygenation and evaporation rates of the coating (reduce them).
9. Speed up the pre-processing workflow. Strengthen the protection of already processed polished surfaces in the pre-processing stage.
10. Polished surfaces must be cleaned immediately after polishing; no polishing powder or other impurities should adhere and dry.
