a metal can end has a metal pull tab attached to a score - defined detachable portion of the can end by direct welding of protective polymer coatings whose surfaces at least are derived from the same monomer and which are provided on the upper side of the can and the under side of a shank portion of the pull tab . the coatings may be composite films each comprising an inner layer of a bonding resin and an outer layer of a polyolefin , polyamide or polyester . the welding may be effected by heat or preferably by ultrasonic energy .