Aluminum Foil Lamination: Challenges and Practical Solutions

Aluminum foil lamination is a challenging process in solventless lamination. Many users find it difficult to master due to specific issues, primarily stemming from the nature of aluminum foil as a rigid substrate with minimal thickness and low initial adhesive tack, making it challenging to achieve proper initial bonding.

Aluminum foil lamination is typically done in three or four-layer structures. We recommend two methods for users: the stepwise method and the one-step method.

1. Stepwise Method: In this approach, lamination is performed in two steps for three-layer structures and in three steps for four-layer structures. Between each lamination, either full curing or partial curing can be applied. We strongly recommend the partial curing method, wherein lamination for the next layer occurs within 2-4 hours after the previous lamination. This technique is unique to Tongze and helps reduce backside transfer issues, shorten production cycles, and enhance efficiency.
2. One-Step Method: The one-step method involves laminating all layers (three or four) in a single process, provided that the necessary equipment is available.

Challenges may vary depending on the chosen technique. Based on our extensive experience collaborating with users, here are solutions to common issues:

1) Composite White Spots: This issue is common in PET (printing film) and aluminum foil lamination. Aluminum foil adhesives, generally having higher viscosity than other flexible packaging adhesives, are prone to uneven ink thickness distribution during the curing process, leading to the formation of white spots.

Solutions:

• Choose suitable inks with finer particles to reduce adhesive application.
• Adjust machine speed to 100-150 m/min.
• Optimize temperature settings for metering rolls (40-45°C), coating rolls (50-55°C), and lamination rolls (45-55°C), based on adhesive properties.

2) Adhesive Penetration (Backside Transfer): Backside transfer is common in regular aluminum foil lamination due to the slow curing process, which allows adhesives to penetrate aluminum foil pinholes, resulting in backside transfer.

Solutions:

• Select aluminum foils with fewer pinholes; thicker aluminum foils tend to have fewer pinholes, making lamination easier. Choose Grade A or above, 6.5μm-7μm thickness AL foils.
• Use high-viscosity adhesives such as polyurethane cooking-grade adhesives or specialized high-viscosity AL adhesives suitable for the slower lamination speeds.
• Control the time gap between PET/AL/PE lamination layers to 2-4 hours.

3) Roll Slippage: This issue is more likely to occur in aluminum foil/PE lamination.

Solutions:

• Control adhesive application rates and reduce application rates when slowing down the equipment.
• Adjust roll pressure and roll surface in accordance with adhesive characteristics.
• Maintain appropriate tension during winding to prevent slippage.

4) Roll Soft Wrinkles: Soft wrinkles tend to occur near the core and joint areas.

Solutions:

• Use high-quality cores or printing plate rollers for cores.
• Ensure that winding rolls are free from any significant vibrations.
• Control winding tension and taper correctly. Recommended parameters for a 1000mm width material include a tension of 40-50Kg/full width and a taper of 60%-80%.

In summary, these challenges in aluminum foil lamination can be effectively addressed with careful consideration of materials, equipment, and process parameters. Adhering to these recommendations will help ensure smoother and more efficient production while reducing the risk of defects. #Sinomech Converting Machinery Manufacturer | Home | SINOMECH (laminationsolution.com)