| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a crosslinked polyolefin tube having excellent pressure resistant creep strength by controlling a molecular structure in a molding by a simpler method than a prior art. SOLUTION: In the case of water crosslinking a polyolefin tube extrusion molded by melt kneading a mixture made of polyolefin resin, silane compound and radical generating agent, a pressure difference is applied between an inner surface and an outer surface of the tube to advance water crosslinking while applying a circumferential force of 0.5 to 8 MPa to the tube. As the polyolefin resin, single polymer of ethylene, ethylene and -olefin copolymer, single polymer of propylene or ethylene and propylene copolymer is used. The used silane compound is silane compound having an olefin unsaturated bond and hydrolyzable organic group. A stress is generated in a circumferential direction of the tube by the pressure difference between the outer surface and inner surface of the tube. Orientation of the tube in the circumferential direction is generated by the pressure difference. Orientation of graft molecule is induced by the stress. That is, crosslinking chain is oriented in a thickness direction of the tube, and water crosslinking is advanced in this state. Accordingly, the obtained crosslinked polyethylene tube is improved in the stress of its thickness direction. |
