Abstract: A persistent photoconductive element comprising an electroconductive support, a pigment layer formed on said support and composed mainly of a phthalocyanine pigment or Indanthrene Blue GCD and a polymer layer formed on said pigment layer and composed mainly of a polyvinyl carbazole, said polymer layer containing at least one member selected from the group consisting of aliphatic halogenated hydrocarbons, halogenated acyl compounds, halogenated keto compounds and hydrogen donor compounds. This element exhibits an improved photoconductive sensitivity and prolonged photoconductivity over the prior art, whereby it is highly useful in electrophotographic processes requiring persistent photoconductivity. Additives, such as plasticizer and binding agent, may be incorporated in the polymer and pigment layers to improve the flexibility and mechanical durability of the persistent photoconductive element.

Abstract: An infrared light is applied to a polymer film having a thickness of less than 30.mu., and the infrared light is spectroscopically separated before or after being applied to the polymer film to obtain an infrared interference fringe spectrum based on the polymer film, and then the extreme points of the infrared interference fringe spectrum are detected by processing, whereby to measure the thickness of the polymer film.

Abstract: A method and an apparatus for measuring the thicknesses of film layers of different synthetic resins forming a composite multilayer film or sheet by utilizing infrared rays. Infrared rays of sample wavelengths, each equal to the infrared absorption wavelength of each film layer, and at least one reference wavelength different from the infrared absorption wavelength of each film layer are projected onto the multilayer film to be measured. Ratios are obtained between the amounts of infrared lights of the sample and reference wavelengths transmitted through the multilayer film. An operation is achieved for solving a simultaneous equation including the ratios and the infrared absorption coefficients of the film layers at the sample and reference wavelengths as coefficients and the thicknesses of the film layers as unknowns, thereby obtaining the thicknesses of the film layers.