JPS5757206A - Method of measuring thickness of hollow film such as inflation film and black body furnace for measurement - Google Patents

Abstract

PURPOSE:To permit the measurement of a film thickness in the circumferential direction, by a method wherein a black body furnace capable of emitting a reference light in the radial direction from is axial center is disposed at the center of a hollow film and an intensity of the light irradiated onto the inner surface of the film and after passing through the same is measured. CONSTITUTION:A black body furnace made capable of emitting a reference light in the radial direction from its axial center is disposed at the center of a hollow film. The light from the black body firnace is irradiated onto the inner surface of the film and an intensity of the light after passing through the film is measured on the outer side, thereby to obtain a thickness of the hollow film such as an inflation film. For example, a black body furnace 10 capable of emitting a reference light in the radia direction is made in such a manner that heaters are buried in its body in the radial forms with respect to the axial center thereof and a permeable glass and a protective layer are provided on the outer periphery of the body. Such black body furnace 10 is disposed at the center of a hollow film 20 and the reference light is irradiated onto the film from its inner side. An intensity of the light after passing through the film is measured by a detector 31 along the overall circumference of the film, thereby to measure a film thickness. A surface thermometer 32 is used to obtain a signal for temperature compensation.