| abstract |
PURPOSE:To obtain a thermoplastic polymer film decreased in break during film formation, improved in slip and processability, and improved in dielectric breakdown voltage and mechanical strengths, by adding porous inert fine inorganic particles and spherical silica particles to a thermoplastic polymer constituting the film. CONSTITUTION:0.01-3wt.% porous inert fine inorganic particles of a void volume of 50-95% and a mean particle diameter of 0.05-5mum (e.g., alumina, silica, titania or zirconia) and 0.005-1wt.% spherical silica particles having a mean particle diameter which is smaller than the thickness of the film and is 0.2-4mum, an aspect ratio of 1.0-1.2 and preferably having a relative standard deviation of particle diameters of 0.5 or below as defined by the formula [wherein Di is the equivalent diameter of equal surface circle (mum) of an individual particle, D bar is the mean of the equivalent diameters of equal surface circles of formula II, and n is the number of particles] are added to a thermoplastic polymer such as PE, PP, PS or an ethylene/vinyl acetate copolymer. This mixture is formed into the title film of a thickness <=4mum. |