Tunneling is where a small areas across the web delaminates between the PET film and Aluminum foil, the tunneling defect occurs after the dry bond lamination.
Tunnels or post lamination wrinkles that manifest from the heat seal or zipper areas are created when the adhesive layer is plasticized by heat seals and the extensible film shrinks back to the pre stretched profile before laminating. Tunnels in the primary layer may not appear immediately after sealing, it may take 12-24 hours to appear.
Causes of Tunnels:
● Incorrect adhesive mix ratio.
● Heat Sealing before the adhesive has fully cured.
● Excess mismatched elongation of films.
● Interference from retain solvents contaminating the adhesive layer.
● Interference from a blown film additive contaminating the adhesive layer ie: antistatic or slip.
● Expired adhesive or co-reactant.
