| 摘要 |
The method comprises a) an extrusion stage wherein a extruded tube made of a thermoplastic material is formed by extrusion with the aid of an extrusion die having a diameter D0, a slit width E0 and a section S0; b) a stage wherein the extruded tube is radially expanded in order to form a radially expanded tube having a diameter D2, a thickness E2 and corresponding section of area S1; c) a truncating stage wherein the expanded tube is broken down into tube portions; d) a stage in which the tube portions are formed in such a way that a heat-shrinkable cap is obtained and in which an axial drawing stage is incorporated, between extrusion stage a) and expansion stage b), at the output of the extrusion die, in order to obtain an axially drawn tube having a diameter D1 which is typically smaller than D0 and D2, and a thickness E1 which is typically lower than E0, such that S0/S1 typically ranges between 2 and 10. The advantages of the invention are as follows: it is possible to obtain caps which are economic, easily heat-shrinkable and which have a stable axial dimension, thereby avoiding any axial distortion, i.e. any axial distortion of the impression. |
