Pre-Press Treatment of Aluminum Alloy Metal Plates

Pretreatment Processes for Screen Printing on Metal Surfaces

Screen printing on metal surfaces requires a thorough pretreatment process to ensure optimal adhesion and aesthetic quality of the printed designs. This pretreatment, often referred to as prepress processing, encompasses various techniques tailored to the specific needs of the metal being printed on. Common methods include degreasing, polishing, drawing, oxidation, sandblasting, and spray painting. Each technique can be applied independently or in combination, depending on the characteristics of the metal and the desired outcome.

Aluminum Alloy Plates: A Focus on Surface Treatment

Aluminum alloy plates are among the most commonly used materials in the screen printing sector. The pretreatment of these plates serves two main purposes: enhancing the decorative appeal by eliminating surface defects and improving the surface finish to ensure better adhesion of printing inks. Several pretreatment methods are employed for aluminum alloys, which are outlined below.

1. Degreasing Treatment

Degreasing is a critical initial step in the pretreatment process. It involves removing oils and contaminants from the surface of the aluminum plate to improve its compatibility with printing inks. Common methods include using fine sawdust to wipe off encapsulant oils or employing organic solvents and alkaline solutions for oils from machining processes. Typical formulations for alkaline degreasing solutions include:

• Basic Formula:

  • Sodium carbonate: 50-60g
  • Water: 1000ml
  • Temperature: 60-80°C
  • Cleaning time: 2-5 minutes

• Commonly Used Formula:

  • Sodium carbonate: 30g
  • Phosphorus: 50g
  • Sodium silicate: 10g
  • Water: 1000ml
  • Temperature: 60-80°C
  • Cleaning time: 2-5 minutes

2. Polishing

Polishing enhances the surface finish of metal materials and is categorized into mechanical, chemical, and electrochemical polishing. Mechanical polishing uses cloth wheel polishers and pastes to achieve a smooth surface, often applied to anodized aluminum products. Chemical polishing typically occurs in acidic solutions, while electrochemical polishing provides a higher-quality finish and reduces oxidation.

• Chemical Polishing Example:
  • Phosphoric acid: <1.7, 90% (w) 75%
  • Nickel sulfate: 2g/1000ml
  • Sulfuric acid: <1.84, 98% (w) 15%
  • Nitric acid: <1.42, 65% (w) 10%
  • Temperature: 100-115°C
  • Polishing time: 1-15 minutes

3. Drawing and Spiral Processing

Drawing techniques create various surface textures, including straight, random, ripple, and spiral patterns. Straight-line drawing involves machining the aluminum surface with mechanical friction, while random pattern drawing uses high-speed copper wire brushes for irregular designs. Ripple patterns are produced with axial movements of grinding rollers, and spiral patterns are created through rotational polishing methods.

4. Sandblasting

Sandblasting is employed to achieve a decorative finish or a subtle reflective surface, enhancing the bond between printed materials and substrates. This process is performed in specialized sandblasting equipment, where quartz sand is applied to create a uniform surface texture that mitigates common defects.

5. Oxidation Dyeing

Oxidation dyeing is a prevalent method for creating silk screen signage on aluminum substrates. Suitable materials include high-purity aluminum and specific aluminum alloys. Prior to oxidation, the metal undergoes chemical or electrochemical treatments. Oxidation processes are classified into chemical and electrochemical methods, each with distinct characteristics and quality outcomes.

• Anodizing Solutions Examples:

  • Decorative Sulfuric Acid Anodizing:
  • Sulfuric acid: 150-200g/L
  • Anode current density: 0.8-1A/DM²
  • Operating temperature: 15-25°C
  • Time: 40-60 minutes

  • Voltage: 18-24V

  • Hard Film Sulfuric Acid Anodizing:

  • Sulfuric acid: 700-1000g/L
  • Anode current density: 0.5A/DM²
  • Operating temperature: 0±5°C
  • Time: 15 minutes
  • Voltage: 20V

In conclusion, the pretreatment of metal surfaces, particularly aluminum alloys, is essential for achieving high-quality screen printing results. By employing various methods such as degreasing, polishing, drawing, sandblasting, and oxidation dyeing, manufacturers can significantly enhance the aesthetic appeal and durability of printed products. Each technique plays a vital role in preparing the metal surface for optimal ink adhesion and visual impact.