| 摘要 |
This invention describes a process for orienting and drawing multiple-layer thermoplastic materials, in particular of a tubular type, wherein a) the tubular exiting from the heating tunnel is brought up to the orienting temperature of a first material having the highest orienting temperature, while the material of the remaining layers is still in a plastic state; b) said first material is subjected to a first partial drawing process, while the remaining layers plastically deform to follow its expansion; c) the temperature of the tubular is dropped to the orienting temperature of a second layer; d) this second layer is drawn, while at the same time continuing to draw the previous layer; e) the phases c) and d) are repeated for the subsequent layers, until the maximum allowable degree of drawing is achieved for each layer.
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