| 摘要 |
PURPOSE: To obtain a crystalline polyolefin tube small in the age contraction in the diametral direction. CONSTITUTION: Crystalline polyolefin resin of molten condition is extruded out of an annular head to form a tubular shape by a former, then, the resin is cooled by passing through a cooling water tank, then, the polyolefin tube after cooling is maintained for a predetermined period of time at a temperature higher than 60 deg.C and lower than the melting point of the crystalline polyolefin resin and, thereafter, both ends of the polyolefin tube are opened to cool gradually from the outer peripheral side and inner peripheral side of the tube. According to this method, a crystalline polyolefin tube, excellent in dimensional stability and never causing contraction in the diametral direction thereof due to aging especially can be obtained. |
