The independent seam which is superior in crookedness restoration Characteristic it is not the cylindrical tube or its production manner

摘要

PURPOSE:To obtain a self-standing seamless cylindrical tube with smooth surface and excellent bending recovering characteristics by molding a cylindrical tube having a specified thickness, a specified bore and a crosssectional shape in the peripheral direction with a specified roundness with a partially crosslinked thermoplastic polyurethane resin having a JIS A hardness and a melt index each with a specified value. CONSTITUTION:A partially crosslinked thermoplastic polyurethane resin with a JIS A hardness of at least 80 Hs and a melt index at 190 deg.C of 0.01-5g/10min is extrusion- molded to prepare a cylindrical tube 1 with a thickness of 2-5mm, a bore of 30-120phi and a crosssectional shape in the peripheral direction of at least 80% roundness. In this case, the partially crosslinked thermoplastic polyurethane resin is extruded into a tube-like shape by means of a downward water-cooling type tubular extruder and it is cooled with water under a condition wherein the round shape is kept until the hardness recovering rate of the tube reaches 90% while the inner pressure of the melted tube is kept const. to prepare a seamless tube 1 with a roundness, which is then cut into a specified length.