Blow molding die for producing blown film

A blow molding die used in forming a blown film from a thermoplastic resin which manifests anisotropy in molten state, wherein the die comprises:

• a die body having a hollow portion;
• a mandrel placed in the hollow portion of said die body;
• a plurality of supporting means which are placed in an annular resin flow path formed in a gap between said die body and said mandrel;
• and
• an aeration path for passing a gas to expand cylindrical resin extruded through a resin outlet of said resin flow path,
• at least one of said plurality of supporting means being located in one of opposing intersecting regions of 45° formed by two lines passing through the central line of said mandrel and other supporting means being located in other opposing intersecting regions at 45°,
• the total maximum horizontal cross section of said plurality of supporting means is one-fifth or less of the horizontal cross section of said resin flow route at any location of said plurality of supporting means,
• and said resin flow path having a horizontal cross section decreasing toward said resin outlet from said plurality of supporting means.