PURPOSE: To produce a shadow mask having no purity drift in the stage of producing the shadow mask from a thin sheet-like metallic plate consisting of iron and Ni by performing annealing in a vacuum and cooling in a reducing atmosphere.
CONSTITUTION: Many apertures are punched to a thin sheet-like metallic plate consisting essentially of iron and Ni and the metallic plate is annealed at ≥1,000°C in a vacuum kept under ≤10-1Torr. The metallic plate is then cooled in a reducing atmosphere by continuing charging of gaseous hydrogen until the furnace temp. decreases to 500°C and thereafter the plate is cooled to form a black oxide film thereon. The yield point strength of the shadow mask is thus decreased and the deformation rate in the stage of press forming is suppressed; at the same time, the conversion of the shadow mask surface to a stainless steel is suppressed and the growth of the good oxide film is obtd. The shadow mask is kept stored in a deoxidizing atmosphere during the time after the end of annealing until formation of the black oxide film.
FUJINUMA MAKOTO
OOTAKE YASUHISA
INABA MICHIHIKO
