Chromated 3105 aluminum closure sheet is produced by applying a chromate conversion coating on standard 3105 aluminum sheets to improve corrosion resistance, adhesion, and surface chemical stability. This process forms a dense, uniform, and self-healing chromate conversion film on the aluminum surface.

The film not only provides excellent corrosion protection but also significantly enhances the adhesion of inks and coatings. It is the ideal material for multi-color lithography printing and deep drawing processes, widely adopted in the international bottle cap industry.

Chromated 3105 aluminum sheets are commonly used for ROPP tamper-evident caps, wine caps, beverage caps, and small vial seals. Whether for stamping, drawing, spinning, or coating, chromated 3105 aluminum ensures stable and reliable performance.

Common Temper Options for 3105 Aluminum Closure Sheet

• H14 / H24: High strength with good formability, suitable for most bottle cap applications

• H16 / H26: Higher strength, suitable for caps requiring higher compressive resistance

• H18 / H28: Full hard, highest strength, but relatively lower formability

Technical Parameters of 3105 Aluminum Closure Sheets

Chromate Conversion Coating Process

Chromate conversion coating is a chemical surface treatment that forms a protective, non-metallic film on aluminum by immersion in a chromate-containing solution. The film mainly consists of trivalent and hexavalent chromium compounds, with a thickness typically between 0.5–1.5 μm.

Process Steps:

• Degreasing & Cleaning: Removes oils and surface contaminants

• Water Rinse: Eliminates residual degreasing agents

• Chromate Treatment: Chemical conversion under controlled temperature and time

• Secondary Rinse: Removes excess chromate

• Drying: Cures the conversion film

Precise control of solution concentration, temperature, and treatment time is critical to ensure uniformity and density of the conversion layer.

Performance Improvements after Treatment:

• Enhanced Corrosion Resistance: The film blocks corrosive agents from contacting the aluminum substrate, improving salt-spray resistance by 3–5 times

• Improved Coating Adhesion: The porous structure provides excellent anchoring for inks and coatings, increasing adhesion by over 50%

• Increased Surface Hardness: The film resists scratches and mechanical wear

• Electrical Conductivity Maintained: Unlike anodizing, chromated sheets retain good electrical conductivity

Why Choose 3105 Chromated Aluminum Sheet?

1. High Strength: Stronger than 1060 or 8011 alloys, capable of withstanding internal pressure (e.g., carbonated beverages) and torque during capping without deformation. Ideal for long-neck wine caps and pressurized beverage caps.

2. Low Earing Rate: Ensures smoother edges during deep drawing, reducing trimming waste and increasing material utilization-critical for large-scale production.

3. Corrosion Resistance: As an Al-Mn alloy, 3105 combined with chromate film effectively resists oxidation from alcoholic beverages, acidic drinks, and external environments, ensuring product safety during storage.

4. Excellent Formability: Provides consistent strength while allowing complex forming processes.

5. Enhanced Adhesion: Chromate treatment optimizes surface properties, ensuring durable, vibrant printing without color fading, uneven coverage, or defects during transportation and use.

6. Environmental & Safety Benefits: Aluminum is 100% recyclable. Chromate-treated sheets prevent aluminum migration into packaged contents, ensuring hygiene and safety.

Applications of 3105 Aluminum Closure Sheets

• ROPP Tamper-Evident Caps: For whiskey, vodka, and other spirits

• Long Skirt Wine Caps (STELVIN® type): Maintains perfect skirt shape due to high strength

• Carbonated Beverage Caps: Withstand internal pressure

• Pharmaceutical & Nutraceutical Caps: Sealing oral liquids, syrups, and supplement bottles