Method for preparing microporous polyolefin film with improved productivity and easy control of physical properties

摘要

Provided is a method of manufacturing a microporous polyolefin film useable as a battery separator, which is easy to control strength, permeability and shrinking properties of the microporous film and embodies excellent quality uniformity and production stability in fabricating the microporous film.

主权项

1. A method of manufacturing a microporous polyolefin film using a roll-type stretching machine, comprising:
(a) melting, mixing, and extruding a composition containing a polyolefin composition having a weight-average molecular weight of not less than 1×105 to less than 1×106 (component I) and a diluent (component II) in a weight ratio of 15-50:85-50, and shaping the composition into a sheet form through a T-die; (b) using the roll-type stretching machine, which comprises at least three rolls, to stretch the sheet uniaxially in the machine direction, and then, after stretching uniaxially in the machine direction, stretching the sheet in transverse direction using a tenter-type stretching machine, in order to form a film by sequential biaxial stretching; and (c) extracting the diluent from the stretched film and then drying the film, wherein the roll-type stretching machine includes at least one preheating roll, at least one stretching roll and at least one cooling roll or air-cooled device, and a total roll contact time of the sheet on the preheating roll ranges from 1 to 500 seconds, the stretching is executed in at least one section between rolls, a stretching ratio in one section between two rolls ranges from 1.05 to 6 times, a roll contact coefficient of the sheet on the stretching roll ranges from 1.5 to 54 degree (of angle)×m, where m is the radius of the roll, and a coefficient of non-contact section between rolls ranges from 0.1×10−3 to 200×10−3 min.