Polymers which can be used as the binder constituting the oxygen-impermeable layer of this invention include homo- and copolymers of acrylonitrile, alkyl acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate, alkyl methacrylates such as methyl methacrylate and ethyl methacrylate, methacrylonitrile, alkyl vinyl esters such as vinyl acetate, vinyl propionate, vinyl ethyl butyrate and