| 摘要 |
PROBLEM TO BE SOLVED: To improve resistance to impact by retaining a molded body formed by melt molding polypropylene resin of specified isotacticity rate and then water cooling the resin in a specified temperature range for a given time. SOLUTION: A molded body formed by melt molding polyprepylene resin of isotacticity rate of 95% or more and then water cooling the resin is retained in a temperature range of 120 deg.C or higher to the melting point or lower for a given time. When the isotacticity rate is less than 95%, the increase of impact absorbing energy is not larger compared with the processes heretofore available. When the retaining temperature is lower than 120 deg.C, the increase of impact absorbing energy is not larger either compared with the processes heretofore available. In that case, it is not necessary to retain the molded body at the given temperature, but the temperature gradient can be generated in the temperature range. As the time of retaining heat treatment is vaired by the thickness and shape of the molded body, the optimum time is determined each time. |
