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.
- Stepwise method: in this approach, adhesive lamination for three-layer structures is performed in two steps 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 and helps reduce backside transfer issues, shorten production cycles, and enhance efficiency.
- One-step method: this approach involves laminating all layers 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 laminating adhesive, generally having higher viscosity than other flexible packaging adhesive, are prone to uneven ink thickness distribution during the curing process, leading to the formation of white spots. The solutions are to choose suitable inks with finer particles to reduce adhesive application, adjust machine speed to 100-150m/min, and optimize temperature settings for metering rolls(40-45℃), coating rolls(50-55℃), and lamination rolls(45-55℃), based on adhesive properties.
2. Adhesive penetration(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. The solutions are to select aluminum foil with fewer pinholes; thicker aluminum foils tend to have few pinholes, making lamination easier. Choose grade A or above, 6.5-7um thickness aluminum foil; use high viscosity adhesives or specialized Al adhesive for the slower lamination speeds.
3. Roll slippage: this issue is more likely to occur in aluminum foil/PE lamination; the solutions are control adhesive application rates and reduce application rates when slowing down the equ
4. Ipment, adjust roll pressure and roll surface in accordance with adhesive characteristics, maintain appropriate tension during winding to prevent slippage.
5. Roll soft wrinkles: it tends to occur near the core and joint areas; the solutions are to use high-quality cores or printing plate roller for cores; to ensure that winding rolls are free from any significant vibrations, to control winding tension and taper correctly. (recommended parameters for a 1000mm width material with a tension of 40-50kg/full width and a taper of 60-80%.
