FILM MANUFACTURING METHOD

摘要

This invention relates to a method of, and apparatus for, controlling the diameter of a blown film, typically a cellulose blown film (84), during manufacture. A cellulose/NMMO dope solution (82) is injected into an extrusion die (38) for precipitation of a cellulose tubular film (84) in a precipitation bath (44). A dip pipe (76), liquid supply conduit (70), liquid return conduit (72) and air vent conduit (98) are provided, which are movable in a direction substantially parallel to their longitudinal axes through an internal bore (65) of an extrusion die plug (63). A volume (89) of air is isolated by dip pipe (76) between an inner surface of the film (84) and an outer surface of the dip pipe (76), and a second volume (91) of air is isolated within dip pipe (76) itself. In use, a liquid level (94) in volume (91) is determined by the pressure of air in the volume (89). Variations in the pressure of air in volume (89) thus allow the diameter of the blown cellulose tubular film (84) to be varied and controlled.