PURPOSE: To perforate an exceedingly accurate electron beam through hole in a shadow mask material by applying case-exposure treatment that decreases a photosensitive coat which is left behind or oozes out on the exposure surface of a shadow mask material in which the electron beam through hole is formed.
CONSTITUTION: A shadow mask material made of an amber plate of 0.10mm thick is provided and both principal surfaces are cleaned and then are coated with a photosensitive liquid to which the ammonium dichromate with the principal component of casein is applied as the sensitizer. Subsequently, a photosensitive coat that is left behind and is eluted on the surface of the shadow mask material for which the burning process is completed is treated by spraying a case- exposure liquid. This case-exposure liquid is treated by a mixed liquid of oxalic acid, hydrogen peroxide water, and concentrated sulfric acid or a mixed liquid of oxalic acid and caustic soda, for example, and is further treated by a potassium permanganate. If the small hole side negative original version dimension D1 and the large hole side negative original version dimension D2 are set to 50μm and 110μm separately by applying this case-exposure process, exudation is nullified.
HARIKAE MAKOTO
OOTAKE YASUHISA
