| 摘要 |
PROBLEM TO BE SOLVED: To enhance deformation followability and to improve an earthquake resistance by crosslinking at least a part of a polyolefin resin. SOLUTION: A polyethylene resin having a density of not more than 0.940 g/cm3 is introduced into an extruder, and a billet 2 is manufactured. Then, the billet 2 is pushed into a space between a mandrel 12 and a die 13, biaxially oriented simultaneously in radial and axial directions, and a biaxially oriented polyethylene tube is formed. Thereafter, a part of the polyethylene resin of the obtained tube is crosslinked by an electron beam crosslinking method so that its gel fraction becomes 10 to 50%. Thus, molecular chains of a noncrystal part having a weak tensile drag are crosslinked with each other so that even when the polyolefin resin is tensioned, the molecular chains are not extended caused by slipping to each other. Accordingly, deformation followability of the obtained tube can be enhanced. |
