Flexible packaging structure and process for making it

Claim 1

A process for making a multiple layer laminate packaging material and for making a package from said material, the process comprising the steps of: coextruding a multiple layer film having as one outside layer thereof polypropylene modified with a fused ring acid anhydride, the layer adjoining said modified polypropylene layer being a polypropylene layer; drawing said coextruded film and an unprimed aluminum foil into and through a nip of rolls, with said modified polypropylene layer being positioned in face to face relation with said foil; applying effective amounts of heat and pressure, over effective periods of time respectively to adhere said foil to said film at the interface of said foil with said modified polypropylene layer, forming therefrom a multiple layer laminate packaging material, said pressure being applied at said nip, said heat being applied during contact of said sheet-like materials with said rolls; adhesively laminating a biaxially oriented, abuse resistant, polymer film to the surface of said foil opposite the surface adhered to said anhydride modified polypropylene; forming a portion of said multiple layer packaging material into a pouch; filling a product into the pouch; closing and sealing the pouch; and heating the filled and sealed pouch under retort conditions of at least about 100° C. for at least about 5 minutes, to affect increased levels of adhesion between said foil and said modified polypropylene layer.