| 摘要 |
PURPOSE:To provide the title film which is a new and excellent film suitable for use as an air filter for filtering off fine suspended particles from the air or gas to be used in clean rooms in, e.g. the semiconductor industry, and which causes little pressure loss of the air or gas. CONSTITUTION:A semi-sinter of polytetrafluoroethylene is stretched and then heat-set at a temp. higher than the melting point of a polytetrafluoroethylene sinter to thereby produce a porous polytetrafluoroethylene film in which the areal ratio of fibrils to knots is 99:1 to 75:25, the average fibril diameter is 0.05-0.2mum, the area of the largest knot is 2mum<2> or smaller, and the average pore diameter is 0.2-0.5mum, these properties being determined from the image processing of a scanning electron photomicrograph of the film. |
