Film manufacturing method for improved surface smoothness

摘要

A method for manufacturing film without melt fracturing in which a flow of a polymer solution having a high viscosity extruded from a die slit onto a running and spreading plane is extruded through the die slit together with a low viscosity solution with the polymer solution is covered by the low viscosity solution. In a first preferred embodiment, the low viscosity solution is passed through a confluence tube so as to surround the high viscosity solution in the form of a coaxial cylinder after which the two solutions are passed through a slit die which maintains the covering relationship between the high and low viscosity solutions. In another preferred embodiment, a slit die is provided which has a central passage into which the high viscosity fluid is supplied and side passages of a slit-like shape similar to that of the main passage into which the low viscosity solution is supplied.