Patent GB-682853-A (GB)
Title: Lenticulated films and methods for their production
IPC: G03C7/14
Filed: 1950-02-13
Abstract: 682,853. Producing lenticular films for colour and stereoscopic projection.. GRETENER, E. Feb. 13, 1950 [Feb. 23, 1949], No. 3648/50. Classes 97 (i) and 98 (ii). A process for manufacturing films with two lenticulated surfaces comprises applying to the smooth side of a film already having one side lenticulated, preferably by a mechanical process, a layer of light-sensitive material, prefcrably bichromated gelatine, capable of producing a relief image on wash-off development after differential hardening by exposure to light, and exposing with light coming from a surface of a chosen shape and brightness distribution and being focused by the elements on the already lenticulated side of the film, so that on development the lenticular gelatine relief elements are of the desired form and in register with the mechanically formed lenticular elements. As shown, a nitrocellulose film having lenticulations formed on it by mechanical means is coated on its smooth face, which is subbed with a gelatine solution containing glacial acetic acid and ethyl and methyl alcohols, with a gelatine solution including thymol to form a layer which is then sensitized by immersing the film in a potassium bichromate solution including ammonium carbonate and a wetting agent, and the gelatine layer is then exposed to light from a surface of an appropriate shape illuminated with a H.P.M.V. lamp or an arc lamp and an ultraviolet filter. The exposed layer is then developed by washing to yield a lenticular gelatine relief which may be subsequently hardened with formaldehyde or chrome alum solution. The gelatine layer of the doubly lenticulated film so formed is then sensitized with a solution containing a diazonium salt, a metal salt and an organic acid, e.g. either 4-diethylaminobenzene 1-diazonium fluoro-boride, silver nitrate and tartaric acid, or including an o-hydroxybenzene diazonium compound and a mercurous salt, as described in Philips Technical Review, Volume 9. The sensitized film after printing is treated with steam and the weak image produced is intensified with a solution containing hydroquinone, citric acid, and silver nitrate. The film may be used for recording colour, stereoscopic, or colour stereoscopic pictures. In producing a doubly lenticulated film 45 for use in a projection system wherein the illuminating beam is not parallel, as in Fig. 3, the exposing light beam used in making the second lenticular grid is similarly non-parallel, as in Fig. 4. Such a film used in converging light is disposed so that the two grids are homothetically-related to the point of convergence of the illuminating beam. The grids may be either spherical, when the beam converges to the point 50 at the centre of the projection lens 46, or cylindrical, when it converges to a line perpendicular to the axis of the projection system through said point. A film to be used in parallel light is made by interposition of a collimating plano-convex lens in the exposing beam and is used for projection with a plano-convex field lens forming an image of the film at the centre of the projection lens. Instead of using a film with mechanically formed lenticulations to produce the second set of registering gelatine relief lenticulations, a film having the first set of lenticulations may also be formed by a photographic wash-off gelatine relief process.