GB1516687A - Imaging method - Google Patents

Abstract

1516687 Etching ENERGY CONVERSION DEVISES Inc 8 Oct 1975 [17 Oct 1974] 41268/75 Heading B6J [Also in Division G2] The tonal value of a dot image is corrected by ' lateral etching. The dots are prepared by exposing a film comprising a substrate 22, an opaque layer 24 and overlying photosensitive layer 26 to a dot image and then removing, using a solvent or mechanical means, areas of layer 26 and the underlying opaque layer 24 to leave the dots as shown in Fig. 6. The tonal value of the image is altered by further etching the dots to reduce the area they cover, however as their inner and outer faces are protected by the substrate and overlying layer their thick- ness, and hence opacity, is not reduced, as shown in Fig. 8. If during etching so much of the dot is removed that the overlying layer touches the substrate, thus preventing further etching, the material can be exposed through the substrate. The dot prevents exposure of the portion of the layer immediately over it, whereas the excess portions are exposed and removed, thus permitting etching to continue. The opaque layer comprises tellurium, molybdenum, polonium, cobalt, zinc, aluminium, copper, nickel, iron, tin, vanadium, germanium or silver or an alloy of any of the above. The etch solutions comprise aqueous solutions of sodium, potassium or lithium hypochlorite which can include sodium or potassium bicarbonate and alkali metal hydroxides. Alternatively hydrogen peroxide, sodium or potassium chlorate together with a weak organic acid, e.g. citric acid, or ferric chloride may be used.