SEAL QUALITY INSPECTION METHOD FOR PACKAGING MATERIAL OF LAMINATED STRUCTURE INCLUDING INTERMEDIATE METAL LAYER

PROBLEM TO BE SOLVED: To provide an inspection method which does not require any special inspection device when inspecting appropriateness for the seal of a packaging material in a laminated structure including an intermediate metal layer.SOLUTION: Regarding a packaging material accommodating snack food therein, a sheet is folded into two and its three sides are welded thermally to obtain a sealed bag. In the sheet, an inner-most sealant layer is comprised of co-extruded polypropylene (CPP), a second inner layer is comprised of PE, an intermediate layer is comprised of an aluminum layer, a second outer layer is comprised of PE and an outer-most layer is comprised of oriented polypropylene (OPP). The packaging bag is immersed in a 6N-aqueous sodium hydroxide, thereby dissipating at least an aluminum layer of a seal portion. Preferably, the seal portion that becomes transparent is immersed in a colored liquid and in accordance with whether the colored liquid is infiltrated to the seal portion or a contour shape of that colored liquid when the colored liquid is infiltrated, the state of a seal defect can be confirmed visually.