| 摘要 |
<p> A polypropylene strap for use in packaging articles is manufactured by stretching a belt-like sheet (3) of polypropylene which has been extruded from a die, in the lengthwise direction thereof at a relatively high draw ratio for example, 4-9, heating the surfaces of the resulting sheet to put the molecular chains in the superficial layers (21) only thereof in a non-oriented state, and then stretching the sheet (3) at a relatively low draw ratio of, for example, 1.2-3. Such a polypropylene strap has a high tensile strength, a low elongation, a high rigidity, a high abrasion resistance, and flexible surfaces, and it is not easily split in the longitudinal direction.</p> |
