BIAXIALLY ORIENTED POLYESTER FILM AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film for capacitors, having excellent electrical properties and slip properties. SOLUTION: A polyester melt containing 0.05-3wt.% porous silica particles comprising an aggregate of primary particles having a mean particle diameter of 0.01-0.1μm and having a pore volume of 0.5-2.0ml/g and a mean particle diameter of 0.1-5μm is filtered through a nonwoven-cloth type filter made of small-gauge wires and having an average opening of 10-30μm so as to give a filtrate which can give a biaxially oriented film containing 10/m<2> or below coarse aggregated particles having a size of 50μm or above.