| 摘要 |
PURPOSE:To reduce a shrinkage factor of a PVC tube only in the axial direction at high temp. without decreasing a shrinkage factor in the diameter direction and to attempt to improve heat resistance of the tube, by drawing an extrusion- molded undrawn PVC tube substantially only in the diameter direction and crosslinking properly it by irradiating it with electron beam. CONSTITUTION:A compsn. wherein 100pts.wt. PVC is added with 1-30pts.wt. polyfunctional monomer or oligomer having two or more functional groups in its molecule is extruded into a tube-shape product. In this case, a shrinkage factor in the axial direction at 180 deg.C is made to be 30% or less by adjusting extrusion temp. and drawdown ratio of PVC. The extruded tube is drawn in the diameter direction after either cooling to a temp. suitable to drawing or once cooling and reheating up to a temp. suitable to drawing. A shrinkage factor in the diameter direction at 100 deg.C is thereby made to be 30-55%. Then, after the drawn tube is cooled, it is irradiated with electron beam of 1-20Mrad to crosslink it so that the gel fraction can become to 5-80wt.%. It is thereby possible easily obtain a drawn tube having a shrinkage factor at 180 deg.C in the axial direction of 20% or less, pref. 15% or less and it is possible to attempt to prevent shoulder edges from uncovering. |
