Patent GB-506667-A (GB)
Title: Improvements in or relating to the production of diffration gratings and of multi-colour screens for use in colour photography
IPC: G03C7/10
Filed: 1937-12-01
Abstract: 506,667. Colour photography; diffraction gratings. SEASE, V. B. Dec. 1, 1937, No. 33274. Convention date, Dec. 7, 1936. [Classes 97 (i) and 98 (ii)] A screen formed of fine lines, such as a multicolour screen, or a diffraction grating leaving coloured lines, is produced by exposing closelyadjacent separated areas of a moving lightsensitive band to a strip of light or other radiation extending transversely or obliquely to the direction of movement of the band, the light being modulated to give intermittent flashes at high frequency in order to produce alternating exposed and unexposed lines on the layer, and converting the exposed lines into lines of colour. To produce a two-colour screen the unexposed lines may be exposed and converted to a second colour. To produce a three-colour screen an intermediate esposure is given to the moving band by means of the modulated light-strip to produce alternating exposed and unexposed lines crossing the first set of lines, the exposed lines being converted to lines of a second colour, and the remaining uncoloured spaces being converted into areas of a third colour. A four-colour screen may similarly be produced by three exposures with the slit at, different angles, Reference is made to apparatus for light modulation sumilar to that used for recording a variable-density sound track in order to produce a screen of mesh 1000 lines per inch. For producing the colours, a silver halide emulsion may be used which may be chemically or dye toned, or may be developed with colour developers after the various exposures, e.g. for red, a developer compounded from thioindoxyl-carboxylic acid in acetone, and mono - ethyl-para - phenylenediamine hydrochloride, potassium carbonate and sodium sulphite in water ; for blue a developer compounded from alpha-naphthol in acetone and dimethyl-para-phenylenediamine hydrochloride, potassium carbonate and sodium sulphite ; and for green a developer compounded from 2 : 3 : 4 trichlor-alpha-naphthol and alphachlor-ethylacetate in acetone, and diethyl-paraphenylenediamine hydrochloride, potassium carbonate and sodium sulphite in water. The silver images are removed by forricyanide and hypo, either in the same or in separate solutions. The ratio of the aggregates of the coloured areas may be varied by exposure conditions to obtain the desired balance of colours. The method may be used to produce two-, three., and four-colour screens of various patterns. For the successive exposures the layer may be treated with a resensitizing bath, e.g. sodium sulphite. The finished screen may be covered with varnish overcoated with sensitive emulsion. British Specifications 15055/12 and 2562/13, [both in Class 98 (ii)], and U.S.A. Specification 1,102,028 are referred to. The Specification as open to inspection under Sect. 91 refers also to the use, instead of a silver halide layer, of a layer sensitized with bichromate, iron salts, diazo compounds, &c. This subject-matter does not appear in the Specification as accepted.