GB1269749A - Photographic printing of cathode ray tube screen structure - Google Patents

Abstract

1,269,749. Luminescent screens. RCA CORPORATION. 21 July, 1970 [25 July, 1969], No. 35248/70. Heading H1D. [Also in Division G2] In a photo-resist process of manufacture of a luminescent screen, in particular a multi-dot screen for colour television, the intensity of the light used to expose the photo-resist may vary over the area of the screen, and this is corrected by means of a filter comprising finely divided, preformed, non - metallic, light - absorbing particles such as carbon having a mean diameter between 5 and 50 millimicrons, and preferably between 9 and 29 millimicrons. The filter may be formed by a photo-resist process using the same light field as is used in the manufacture of the screen, and may comprise a layer on the correction lens or on the wedge lens used in the "lighthouse " or on a separate optical element which may be disposed between the two lenses (Fig. 3, not shown) or between the lens system and the shadow mask. Filter, manufacture.-The lens on which the filter layer is to be formed is cleaned and rinsed and coated with a thin film of 0À05% gelatine solution; after drying this is rinsed in deionized water at 50‹ C. to wash away most of the gelatine and leave a thin monolayer precoating. This is coated with a light-sensitive composition comprising 120 g. carbon particles, 12 g. sulphated lignin powder dispersing agent, 42 g. non-ionic oxyethylene alcohol wetting agent, 1380 g. of gelatine, 10 kg of deionized water, 37 g. of a hardener such as 4,4<SP>1</SP>-diazidostilbene- 2,2<SP>1</SP>-disulphonic acid sodium salt which is a sensitizer for the gelatin, and 300 g. ammonium hydroxide solution. A quantity of this composition at 40‹ C. is poured on the lens which is spun to form a uniform layer 1 mil. thick. After cooling and drying, the lens is exposed in the lighthouse for about 2-5 minutes at about 45 foot candles. The exposed lens is placed in dilute potassium alum at 25‹ C. for 5 minutes to insolubilize the anionic dispersing agents and partially harden the gelatine. Unexposed material is then washed away in the three-compartment laminar flow trough shown in Fig. 4 filled with water at 50‹ C. which flows through a metal wool baffle 93, down across the filter plate 61 which has its coated side 71a downwards, and under a solid baffle 95. The water flow continues for 30 minutes and the inlet temperature of the water is then lowered to 15‹ C. to harden the gelatine. The solid baffle 95 is removed and when the outlet temperature of the water is below 20‹ C. the lens is removed and dried and is then ready for use.