| 摘要 |
PROBLEM TO BE SOLVED: To obtain a molded item which has a low-expansion structure, a high tensile strength, a very good resistance to creep strain, and an excellent uniformity of external appearance by causing an ultrahigh-mol.wt. polyethylene resin to sorb a nonreactive gas at the m.p. of the resin or higher, then molding the resin under pressure into a desired shape, and depressurizing the molded resin at a specified temperature. SOLUTION: 100 pts.wt. polyolefin resin having a viscosity average mol.wt. of 1,000,000 or higher is caused, at the m.p. of the resin or higher under a high pressure, to sorb 6-50 pts.wt. nonreactive gas which is gaseous at normal temperature and pressure. The resin with the gas sorbed is molded into a desired shape under a pressure of 25-120 MPa and then is depressurized while the temp. of the molded resin is kept in the range of from 30 deg.C lower than to 15 deg.C higher than the crystal peak temperature in decreasing the temperature of the resin, thus giving the objective molded item, which has an expansion ratio of 1.01-3, a tensile strength of 70 MPa or higher, and a creep strain (measured after 200 hr has elapsed under a load of half the tensile strength) of 1.0 or lower.
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