Process for processing a semicrystalline thermoplastic
US6391432B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | May 23, 2000 |
| Grant date | May 21, 2002 |
| Priority date | — |
| Expiry date | May 23, 2020 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10T428/31855
- WIPO fieldOther special machines
- WIPO sectorMechanical engineering
Abstract
A process for processing a thermoplastic, which includes, in succession, the following steps:(1) a molten semicrystalline thermoplastic extrudate is cooled to a temperature T1 which is greater than the crystallization temperature (Tc) of the thermoplastic and is less than Tf+5° C., Tf denoting the melting point of the thermoplastic;(2) next, the extrudate is drawn in the molten state;(3) next, the extrudate is relaxed, at a temperature T3 which is between Tc and Tf, for a duration at least equal to the average relaxation time (&tgr;3) of the thermoplastic at the relaxation temperature, and after the drawing;(4) next, the extrudate is quenched to a temperature T4 which is less than Tc.In particular, this process makes it possible to manufacture a film essentially consisting of at least one propylene homopolymer, with a thickness of from 100 to 250 &mgr;m and having a hot shrinkage of at most 20%, a haze of less than or equal to 3% and a total transparency with respect to air of greater than 70%.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.