PURPOSE: A multilayer film is provided to contain more than one polyolefin having at least one functional part of unsaturated carboxylic acid and its anhydride. CONSTITUTION: A multilayer film manufacturing method has the steps of: containing more than one polyolefin that has more than one functional part of unsaturated carboxylic acid and an anhydride, as a step of coextruding a melting polyolefin layer that is attached to both sides of a melting polyamide layer through a coextrusion die; and forming a polyamide layer and a polyolefin layer that are expanded with vapor by blowing vapor through a jet that is a concentric circle and a first and a second circular die.
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