| abstract |
Method and apparatus for the production of porous tubing. One extrudes a homogeneous mixture of at least two components, one component a meltable polymer and the other component a liquid inert in relation to the polymer, both components forming a binary system which in liquid aggregate state displays a range of complete miscibility and a range with a miscibility gap, at a temperature above the separation temperature, substantially vertically upwardly using a circular slot nozzle and blowing of gas or dosing-in of liquid into the interior of the nozzle, into a bath, which displays a temperature below the separation temperature, allows the tubing to solidify, and extracts or lixiviates the tubing. Preferred embodiments include the use of water at a temperature from 15° to 90° C. as bath liquid; use of polypropylene as the polymer and N,N-bis-(2-hydroxyethyl)-hexadecylamine as liquid; blowing nitrogen gas into the interior of the nozzle; lixiviating with alcohol; thermally insulating the circular slot nozzle from the bath; having a non-insulated zone between the circular slot and the thermal insulation; the non-insulated zone of the nozzle having a breadth of about 0.5 to 1 mm; using thermal insulation based upon asbestos cement. The apparatus for the production of the porous tubing by extrusion of such homogeneous mixture contains a circular slot nozzle, having a circular slot and provided with means thermally insulating in relation to the bath liquid, displaying a zone without thermal insulation between said circular slot and said thermally means. |