| 摘要 |
PROBLEM TO BE SOLVED: To produce a film in high breakdown strength without imperiling the break down strength of polypropylene proper by specifying the gross content of ionic material contained in the film as well as the surface roughness on both sides of the film. SOLUTION: Polypropylene in isotactic degree of about 98% is fed to an extruder to be melted down by extruding in a sheetlike shape from a slitted T die for cooling down setting. Later, said resin is drawn both in the length and width directions further to be heat-treated for the production of the title film in the surface roughness exceeding 0.01 but not exceeding 0.15μm. At this time, the content of ionic material of the polypropylene is specified not to exceed 25ppm. Especially, it is recommended that the aluminum content and the titanium content do not exceed respectively 5ppm and 3ppm in terms of the breakdown strength of said film.
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