— A Systematic Analysis from Film Structure to Process Control
1. What Does “Color Fading After Coating” Really Mean?
In the vacuum coating industry, color fading is not merely a visual color change. It typically manifests as:
Gradual color degradation or shift over time
Color deviation after humidity, thermal aging, or UV exposure tests
Local discoloration, graying, or loss of metallic luster
Fundamentally, color fading is not caused by unstable color itself, but by structural, material, or process-related failures within the coating system.
2. Key Causes of Color Fading After Vacuum Coating
2.1 Insufficient Film Density Leading to Oxidation or Moisture Ingress
During PVD evaporation or magnetron sputtering, insufficient deposition energy or low plasma density can result in a columnar growth structure with high porosity.
Such films are prone to:
Oxygen and moisture diffusion along grain boundaries
Oxidation or corrosion of the metallic layer
Alteration of optical interference conditions
This ultimately leads to color degradation or distortion.
2.2 Improper Selection of Coating Material Systems
Different coating materials exhibit significantly different environmental stability:
Pure metal films (e.g., Al, Cr) are highly susceptible to oxidation without protective layers
Certain colored metals or alloys are sensitive to humid and thermal environments
Refractive index drift in dielectric layers directly causes color variation
Without a properly designed metal layer + dielectric protection layer structure, the risk of color fading increases substantially.
2.3 Inadequate Film Thickness Control and Interference Instability
Decorative and functional coating colors are often generated by optical interference effects, which are extremely sensitive to film thickness.
Issues such as:
Quartz crystal monitor drift or improper sensor positioning
Deposition rate fluctuations
Non-uniform substrate rotation or shielding
can result in thickness deviation, leading to color variation and batch inconsistency.
2.4 Insufficient Adhesion Causing Micro-Delamination
If substrate cleaning is inadequate, or plasma pretreatment and ion-assisted activation are insufficient, adhesion between the film and substrate may be weak.
Under thermal cycling, mechanical stress, or environmental aging, micro-cracks or localized delamination may occur, appearing macroscopically as color fading or unevenness.
2.5 Lack of Effective Protective Layer Design
In automotive interior, lighting, or high-humidity applications, the absence of:
Dense dielectric protection layers such as SiO₂ or SiNx
Anti-fingerprint (AF) or wear-resistant top coatings
exposes the film directly to environmental attack, accelerating aging and color fading.
3. Engineering Solutions to Prevent Color Fading
3.1 Enhancing Deposition Energy and Film Density
By optimizing:
Magnetron sputtering power density
Ion-assisted deposition (IAD) parameters
Substrate bias and temperature
film densification can be significantly improved, effectively suppressing oxidation and moisture ingress.
3.2 Optimizing Coating Stack Design
Adopting metal reflective layers combined with multilayer dielectric protection structures ensures both visual performance and long-term environmental stability.
3.3 Implementing Closed-Loop Thickness Monitoring and Control
Quartz crystal monitoring systems combined with closed-loop control algorithms ensure high thickness repeatability and batch-to-batch consistency.
3.4 Strengthening Surface Pretreatment and Interface Engineering
Plasma cleaning and ion bombardment activation enhance interfacial bonding strength between the coating and substrate.
4. Conclusion
Color fading after vacuum coating is rarely caused by a single parameter error. It is the result of system-level failures involving material selection, coating stack design, and process control.
Only through a holistic engineering approach can long-term color stability and mass-production consistency be achieved.
–This article was published by vacuum coating equipment manufacturer Zhenhua Vacuum
Post time: Dec-18-2025