Method for etching shadow mask and regenerating etchant

Claim 1

In the manufacture of a color cathode ray tube shadow mask characterized by having a steel substrate layer and a thin aperture-defining layer, a method for etching a pattern of apertures in the substrate layer through a pattern of apertures preformed in the aperture-defining layer without substabtially further etching the aperture-defining layer, and for reclaiming the etchant employed, said method comprising, etching said substrate layer of said shadow mask through said pattern of apertures in said aperture-defining layer with a ferric sulphate etchant drawn from a main reservoir, said etching process being characterized by a reaction of said ferric sulphate forming a used etchant containing ferrous sulphate; continuously removing a portion of said used etchant material; efficiently regenerating said portion of said used etchant by adding to it sulfuric acid and hydrogen peroxide wherein said hydrogen peroxide is caused to be sucked from a source of hydrogen peroxide into a narrow stream of said portion of said used etchant to effect a mixing of said hydrogen peroxide with said used etchant without exposure of the etchant to the atmosphere, without the introduction of substantial gravitational effects, and without any risk of inducing a backflow of said used etchant material into the source of hydrogen peroxide; and returning the thus regenerated ferric sulphate formed from a chemical reaction of said ferrous sulphate, said sulfuric acid, and said hydrogen peroxide to the main reservoir.