Dual-Layer Vacuum Coating: Color Plating + Transparent Anti-Fingerprint & Anti-Oxidation Layers on Silver, Copper, and S
2025-12-29
Dual-Layer Vacuum Coating: Color Plating + Transparent Anti-Fingerprint & Anti-Oxidation Layers on Silver, Copper, and Stainless Steel Jewelry
1. Introduction
In the global jewelry market, consumers increasingly pursue products that balance aesthetic elegance with long-term functionality. Fingerprint smudges, surface oxidation, and color fading have become persistent pain points for silver, copper, and stainless steel jewelry—even after traditional plating. Vacuum coating machine technology addresses these challenges through a dual-layer deposition system: a color-specific base layer (gold, rose gold, silver) that delivers visual appeal, and a transparent anti-fingerprint & anti-oxidation top layer that safeguards performance without compromising appearance. This article systematically details target material selection, pre-treatment protocols, step-by-step coating processes, and dual-layer film characteristics for three core applications: gold-plated + anti-fingerprint/anti-oxidation layers, rose gold-plated + anti-fingerprint/anti-oxidation layers, and silver-plated + anti-fingerprint/anti-oxidation layers. By clarifying the material composition and functional synergy of each layer, it provides actionable technical guidance for jewelry manufacturers aiming to enhance product durability and market competitiveness.
2. Target Material Selection: Dual-Layer Synergy for Color and Protection
The performance of the dual-layer coating depends entirely on the compatibility and functional complementarity of target materials for the color layer and the transparent top layer. Each target must meet strict requirements: color layer targets ensure vivid, consistent hues and adhesion to the substrate, while transparent anti-fingerprint/anti-oxidation targets guarantee optical clarity, low surface energy (anti-fingerprint), and dense barrier properties (anti-oxidation). All targets comply with the "Jewelry Surface Coating Safety Standard" (EN 1811:2019) and have a purity of ≥99.95% to avoid defects like pinholes or haze.
2.1 Targets for Gold-Plated + Transparent Anti-Fingerprint & Anti-Oxidation Layers
• Color Layer Targets:
◦ Titanium Nitride (TiN) Targets: The most widely used for gold plating, as TiN forms a warm, 18K gold-like film with a hardness of 2000–2500 HV. Doped with 5–8% aluminum (Al), TiN-Al targets improve adhesion to silver substrates by reducing thermal expansion mismatch and inhibiting silver sulfide formation.
◦ Zirconium Nitride (ZrN) Targets: Preferred for copper jewelry, ZrN exhibits superior corrosion resistance against copper’s inherent oxidation, maintaining a bright gold tone for years.
◦ TiN-Au Alloy Targets (Au content: 10–15%): Used for stainless steel jewelry, the gold addition enhances color saturation to match natural gold, while the TiN ceramic phase provides foundational wear resistance.
◦ Fluorine-Doped Silicon Oxide (F-SiO₂) Targets: The core choice for the top layer, F-SiO₂ deposits a nanoscale (15–25 nm) transparent film with a surface energy . Fluorine doping creates hydrophobic/oleophobic properties (anti-fingerprint), while the silica matrix forms a dense barrier against oxygen and moisture (anti-oxidation).
◦ Fluorinated Diamond-Like Carbon (F-DLC) Targets: For high-end applications, F-DLC offers enhanced wear resistance (hardness: 1800–2200 HV) alongside transparency (light transmittance ≥95%) and anti-fingerprint performance. The amorphous carbon structure blocks ion diffusion, preventing substrate oxidation and color layer degradation.
2.2 Targets for Rose Gold-Plated + Transparent Anti-Fingerprint & Anti-Oxidation Layers
• Color Layer Targets:
◦ Titanium-Chromium (Ti-Cr) Alloy Targets (Cr content: 30–40%): Sputtered in a nitrogen atmosphere, Ti-Cr-N forms a soft pinkish-gold film ideal for silver jewelry. Chromium enhances adhesion to silver, while nitrogen doping fine-tunes the rose hue (higher nitrogen content deepens the pink tone).
◦ Nitrogen-Doped Ti-Cr (Ti-Cr-N) Targets: Used for copper jewelry, the pre-nitrided target eliminates in-chamber nitrogen fluctuation, ensuring uniform color and forming a nitride barrier that inhibits copper ion diffusion to the surface.
◦ Silicon-Chromium (Si-Cr) Alloy Targets + TiN Composite: For stainless steel jewelry, Si-Cr (Si: 20%, Cr: 80%) sputtered with TiN creates a rose gold film with improved toughness. Silicon pre-conditions the surface for better top-layer adhesion.
◦ Silicon Nitride (Si₃N₄) Targets: A highly transparent (transmittance ≥96%) ceramic target that forms a dense, corrosion-resistant film. Si₃N₄’s low porosity blocks moisture and oxygen, while its surface can be modified with fluorine post-deposition to achieve anti-fingerprint properties (water contact angle >115°).
◦ F-SiO₂-TiO₂ Composite Targets: The TiO₂ component boosts scratch resistance (hardness: 2000 HV) without sacrificing transparency, making it suitable for jewelry prone to daily wear (e.g., bracelets, rings).
2.3 Targets for Silver-Plated + Transparent Anti-Fingerprint & Anti-Oxidation Layers
• Color Layer Targets:
◦ Pure Titanium (Ti) Targets: Ideal for silver jewelry base plating, Ti forms a thin (0.1–0.2 μm) dense barrier layer that prevents silver oxidation while maintaining a bright, reflective silver tone.
◦ Aluminum (Al) Targets: Used for copper jewelry, Al’s high light reflectivity (≥92%) mimics pure silver, and its compatibility with copper avoids galvanic corrosion.
◦ Ti-Si Alloy Targets (Si content: 15–20%): For stainless steel jewelry, Ti-Si deposits a silver film with enhanced anti-tarnish properties. Silicon reduces surface roughness, creating a smooth base for the transparent top layer.
◦ Aluminum Oxide (Al₂O₃) Targets: A cost-effective option with excellent transparency (transmittance ≥94%) and anti-oxidation performance. Al₂O₃’s hexagonal crystal structure forms a impermeable barrier, while surface treatment with perfluorinated compounds (PFCs) imparts anti-fingerprint functionality.
◦ F-SiO₂-ZrO₂ Composite Targets: Zirconium oxide (ZrO₂) enhances thermal stability, making the top layer resistant to temperature fluctuations (e.g., during jewelry cleaning). The film retains transparency and anti-fingerprint properties even after exposure to 150°C.
3. Pre-Treatment Process: Foundation for Dual-Layer Adhesion
Pre-treatment is critical to eliminate surface contaminants (oil, oxides, polishing residues) and activate the substrate, ensuring strong adhesion between the base metal, color layer, and transparent top layer. All processes follow ISO 12944-4:2018 corrosion protection standards and are tailored to the unique properties of silver, copper, and stainless steel.
3.1 Pre-Treatment for Silver Jewelry
Silver’s high susceptibility to sulfidation (black silver sulfide) requires targeted cleaning:
1. Precision Polishing: Use 0.5–1 μm diamond paste for mechanical polishing to remove scratches, followed by 0.1 μm alumina paste for a mirror finish.
2. Ultrasonic Dewaxing: Immerse in an alkaline solution (sodium hydroxide: 50 g/L, sodium carbonate: 30 g/L, non-ionic surfactant: 5 g/L) at 55±5°C for 12–15 minutes. Ultrasonic frequency (40 kHz) ensures removal of polishing wax residues from crevices.
3. Oxide Stripping: Dip in 6–8% citric acid solution at 25°C for 3–4 minutes to dissolve Ag₂S, then rinse with deionized water (DI water) at 40°C to neutralize acid.
4. Plasma Activation: Treat in an argon (Ar) plasma chamber (RF power: 350–450 W, pressure: 5×10⁻² Pa) for 2.5–3 minutes. High-energy Ar ions remove adsorbed water and organic matter, increasing surface energy from 35 mN/m to ≥50 mN/m for improved layer adhesion.
5. Vacuum Drying: Dry at 70±5°C for 15 minutes in a vacuum oven (pressure: 1×10⁻¹ Pa) to prevent re-oxidation.
3.2 Pre-Treatment for Copper Jewelry
Copper’s tendency to form green patina (CuO/CuCO₃) demands rigorous oxide removal:
1. Graded Grinding: Start with 400-mesh sandpaper to strip thick oxide layers, then 1000-mesh and 2000-mesh sandpaper for surface smoothing.
2. Alkaline Degreasing: Immerse in a heated bath (sodium hydroxide: 100 g/L, sodium phosphate: 50 g/L, sodium silicate: 20 g/L) at 75±5°C for 18–20 minutes. Agitation (50 rpm) ensures uniform degreasing.
3. Acid Activation: Treat in 10% sulfuric acid solution at 25°C for 1.5–2 minutes to remove residual oxides, then rinse with DI water three times (each 2 minutes) to eliminate acid traces.
4. Dual-Gas Plasma Cleaning: Use an Ar-H₂ plasma (Ar:H₂ = 3:1, RF power: 450–550 W) for 3–3.5 minutes. Hydrogen reduces remaining CuO to pure copper, while Ar ions etch the surface for better mechanical bonding.
5. Vacuum Drying: Dry at 75°C for 20 minutes in a nitrogen-purged vacuum chamber to avoid re-tarnishing.
3.3 Pre-Treatment for Stainless Steel Jewelry
Stainless steel’s passive chromium oxide (Cr₂O₃) film must be modified for layer compatibility:
1. Ultrasonic Cleaning: Clean in a neutral detergent solution (pH 7–8) at 45±5°C for 10 minutes (ultrasonic frequency: 60 kHz) to remove dust and oil.
2. Passive Film Etching: Immerse in 5% hydrochloric acid solution at 25°C for 2–2.5 minutes to etch the Cr₂O₃ film, exposing a fresh Fe-Cr-Ni substrate.
3. Oxygen Plasma Etching: Treat in an oxygen (O₂) plasma chamber (RF power: 550–650 W, pressure: 4×10⁻² Pa) for 3–4 minutes. Oxygen oxidizes surface contaminants and forms hydroxyl groups (-OH), improving wettability of coating materials.
4. Quick Drying: Dry at 80°C for 10 minutes in a clean air oven to ensure a moisture-free surface.
The process adopts magnetron sputtering—recognized for uniform film thickness, precise composition control, and strong adhesion—with separate stages for color layer and transparent anti-fingerprint/anti-oxidation layer deposition. Key parameters are optimized for each substrate-color combination to ensure consistency.
4.1 Pre-Coating Preparation
1. Load and Chamber Sealing: Place pre-treated jewelry on a rotating fixture (rotation speed: 10–15 rpm) to ensure uniform coating. Seal the vacuum chamber and perform a leak test (leak rate ≤1×10⁻⁶ Pa·m³/s).
2. Vacuum Pumping:
◦ Primary pumping: Use a mechanical pump to reduce pressure to 7.0 Pa (removes 90% of air/water vapor).
◦ High vacuum pumping: Activate a turbomolecular pump to reach a final pressure of 3×10⁻³ Pa. This high-purity environment prevents gas molecule interference with sputtered target atoms, avoiding porosity in both layers.
4.2 Plasma Bombardment (Post-Pumping Activation)
Introduce argon gas at a flow rate of 220–280 sccm and apply a negative bias voltage (-350 to -450 V) to the jewelry fixture. High-energy Ar ions bombard the surface for 6–9 minutes:
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