Method of producing a color display tube with an improved color selection electrode

Abstract

One of the process steps in the manufacturing process of shadow masks (13) for color display tubes (1) is blackening. In this process step, the shadow mask (13) is heated for example to a temperature of at least 600° C. in a furnace in a gentle oxidative atmosphere of a mixture of carbon monoxide and carbon dioxide. Under these conditions the shadow mask (13) is covered with a layer of Fe3O4, also referred to as ‘black rust’. After this the shadow mask (13) is cooled down. The invention describes a new blackening process which has a much higher cooling rate than usual. In the present-day process, a cooling rate of 50° C./min (21) is used; this invention discloses a cooling rate of at least 500° C./min (22) or even more. This results in an improvement by at least 20% of the thermal expansion coefficient, leading to a color display tube (1) with a shadow mask (13) having a higher mechanical stability and hence to an increased picture performance.

Dependencies are inferred from the claim text.