- Bottle Surface Pre-Treatment: Establishing the Foundation for Adhesion
1.1 Surface Cleaning and Contaminant Removal
Physical cleaning: Use high-pressure air blowers or ultrasonic cleaning to remove dust, grease, release agents, and other residues from the bottle surface. For example, glass bottles may retain silicate release agents from manufacturing, and metal bottles (e.g., aluminum) may have stamping oil residues. These contaminants form a barrier layer that reduces label adhesion.
Chemical cleaning: Choose appropriate cleaners based on bottle material. Glass bottles can be wiped with neutral detergent solutions; metal bottles (e.g., aluminum or iron) should be degreased with ethanol or isopropanol. For plastic bottles (e.g., PET), avoid strong solvents—use mild surfactant solutions to prevent surface corrosion.
Drying control: After cleaning, use hot air circulation (temperature 40–60°C) or lint-free cloths to dry the surface. Ensure moisture content is below 0.5% to avoid bubbling around label edges.
1.2 Surface Roughness Optimization
Glass bottles: Sandblasting (using aluminum oxide particles of 50–100μm) can create a microscopically rough surface in the labeling area. Maintain a roughness (Ra) of 1.5–3.0μm to enhance mechanical adhesion. This technique is often used on premium wine bottles for better adhesion and a frosted aesthetic.
Metal bottles: Aluminum bottles can undergo anodization to form a porous oxide layer (15–25% porosity), while iron bottles can be treated with phosphating to form a crystalline phosphate layer. Recommended roughness is Ra 2.0–4.0μm to strengthen label anchoring.
Plastic bottles: Use corona treatment (10–15kV, 0.5–1s) to raise surface tension to 38–42mN/m or flame treatment (5–10mm flame distance, speed 5–10cm/s) to improve the distribution of polar groups and prevent label detachment due to plastic’s inert surface.
- Metal Label Material and Structural Design: Tailored to Bottle Characteristics
2.1 Selection of Metal Substrates and Performance Matching
Aluminum foil (Al):
Advantages: Low density (2.7g/cm³), excellent ductility (elongation ≥15%), suitable for curved surfaces (e.g., round or oval bottles). Typical thickness: 30–50μm. Annealing at 200–300°C for 1 hour can further enhance flexibility.
Applications: Cylindrical wine or whiskey bottles, where aluminum foil conforms naturally to curvature and avoids edge lifting.
Copper foil (Cu):
Characteristics: Excellent conductivity (≥58% IACS), but prone to oxidation. Requires nickel (2–3μm) or chrome (0.5–1μm) plating. Thickness: 40–60μm, elongation ≥10%. Suitable for flatter surfaces (e.g., square bottles) requiring a metallic finish.
Stainless steel foil (SS):
Advantages: High strength (≥500MPa tensile strength), corrosion-resistant. Commonly uses 304 stainless steel (thickness 50–80μm), but with lower ductility (elongation ≤8%), making it suitable only for flat or slightly curved surfaces (e.g., vodka bottles). Requires pre-bending (radius ≥20mm) to minimize stress during adhesion.
2.2 Label Structure Optimization
Base layer: In addition to metal foil, a PET film (10–20μm) may be laminated to enhance tear resistance—especially around corners or edges (e.g., square bottle angles), where PET helps relieve stress on the foil.
Adhesive layer:
Solvent-based adhesives: Acrylic-based adhesives (50–60% solids), with initial tack ≥ steel ball No.10 (ball rolling test), and holding power ≥24h under 1kg load. Suitable for glass and metal bottles. Temperature range: -20°C to 70°C.
Hot melt adhesives: EVA-based, melting point 70–90°C, applied at 20–30g/m². Ideal for plastic bottles. Fast curing (<5s), but bonding temperature (80–100°C) must be carefully controlled to avoid bottle deformation.
Silicone adhesives: Silicone rubber adhesives (Shore A 30–40), resistant to extreme temperatures (-50°C to 200°C). Suitable for bottles undergoing high-temperature sterilization (e.g., whiskey), though more expensive.
Protective layer: Apply UV varnish (2–3μm) or a PET protective film (10μm) to increase abrasion resistance (≥2H pencil hardness) and chemical resistance (≥50 alcohol wipes with 5% ethanol). This prevents oxidation or scratches on the label after application.
- Application Process and Equipment Parameter Control: Achieving Seamless Bonding
3.1 Adhesion Methods and Key Techniques
Roll-on application (for cylindrical bottles):
Equipment: Three-roll labeler (drive roll, follower roll, pressure roll), with silicone rubber rollers (Shore A 60–70), 150–200mm in diameter.
Parameters: Application speed 5–10m/min, pressure 0.2–0.4MPa. Temperature: aluminum foil can be applied at room temperature; stainless steel foil should be preheated to 30–40°C to improve flexibility and prevent cracking.
Key point: Axis alignment error between bottle and rollers should be ≤0.5mm to ensure even pressure and wrinkle-free edges.
Heat-press application (for irregular or complex surfaces):
Equipment: Heat-press mold machine, with aluminum alloy molds (chrome-plated surface, roughness Ra ≤0.8μm). Electric heating with ±2°C precision.
Parameters: Adhesive temperature—acrylic 60–80°C, hot melt 80–100°C; pressure 0.5–0.8MPa; dwell time 10–15s.
Application: Square or conical bottles, such as champagne bottles with large shoulder curvature, where heat-press molds the metal label to the bottle’s shape to avoid air gaps at corners.
Vacuum application (for high-precision bonding):
Principle: Uses vacuum suction (≤-90kPa) to bond the label tightly to the bottle, eliminating bubbles. Equipment includes a vacuum chamber (at least 100mm larger than bottle size) and a flexible silicone membrane.
Steps: Bottle positioning → label placement → vacuuming (5–10s) → compressed air pressurization (0.1–0.2MPa) to assist bonding.
Application: Premium wine labels (e.g., laser-etched metal labels) where precise alignment and bubble-free adhesion are essential.
