| 摘要 |
PURPOSE:To provide an annular thermoplastic resin film, the inner surface of which is roughened, by a method wherein molten thermoplastic resin is discharged annularly from a resin discharge port so as to hold the air in the interior of the resin in order to mold an annular thermoplastic resin film in such a manner as to form a coarse surface with uniform and fine ruggedness onto the inner surface of the film. CONSTITUTION:Blown-film extrusion is done by using a die 5 equipped with a cooling medium passage 7 formed in annulus along a resin discharge port 6 in the vicinity of the outer surface of a mandrel 1 located inside the resin discharge port 6 which communicates with a resin passage 3, of the die 5. In order to blown-extruded thermoplastic resin, molten thermoplastic resin is flowed in the resin passage 3 and, on the other hand, cooling medium is introduced from a cooling medium leading-in port 8 so as to circulate in the cooling medium passage 7 in order to annularly discharge the molten thermoplastic resin from the resin discharge port 6 under the state that only the outer surface located inside the resin discharge port, of the mandrel is cooled. In this case, when the cooling temperature of the inner surface at the portion which ranges from the lower end of the resin discharge port to the location 30mm or less in the axial direction from the lower end of the resin discharge port, is held lower by 5-60 deg.C than the outside temperature, especially excellent effect is obtained. |
