Patent GB-755811-A (GB)
Title: Improvements in or relating to the treatment of lithographic printing foils
IPC: B41N3/08
Filed: 1954-12-14
Abstract: 755,811. Printing-machines. RITZERFELD, W., and RITZERFELD, G. Dec. 14, 1954 [Dec. 23, 1953], No. 36108/54. Class 100(2). Damping liquids.-A damping. liquid for application to a lithographic printing plate comprises water and sorbitol (C 6 H 14 O 6 ), or other hexavalent alcohol, in combination with a monohexose and an inorganic salt so that the damping liquid, after printing dries to form a solid homogeneous protective film for protecting the printing plate during storage. This film is removed at the beginning of the printing operation, the same damping liquid being used for dissolving the protective film away. Owing to the addition of the monohexose and inorganic salt the damping liquid is rendered highly hygroscopic and retains moisture for a considerable time. Phosphoric acid, or lactic acid may also be added to the damping liquid, these substances helping to preserve the scrip on the printing plate. The liquid used for the step of replacing the protective film may be more concentrated or more in amount than that used for the plate moistening during printing. Damping apparatus.-A machine adapted to use the damping liquid described comprises two moistening devices, one serving for the normal plate moistening necessary for printing and the other for removing the protective film at the beginning of the printing operation and for replacing it afterwards. The second moistening device may apply a more concentrated liquid than the first. As shown in Fig. 1, the second moistening device comprises a series of rollers 30, 33, 34, the applying roller 33 being mounted on arms 32 swinging about the axis 29 of the reservoir roller 30. An eccentric 36 bearing on extensions of the arms 32 is arranged to swing the roller 33 towards and away from the plate cylinder 1. Bearing on the roller 30 is a cleaning roller 34. The roller 33 may be of sponge rubber, the roller 30 of rubber and the cleaning roller 34 of a harder substance, e.g. vulcanite or metal. The moistening device for moistening the printing plate during printing comprises rollers 17, 18, 19 and 20, the applying roller 17 being mounted on spring-loaded arms 25 and urged against the printing plate and the pick-up roller 20 dipping in a reservoir 28. The plate is inked by rollers 9, 10. In use after the dry printing plate has been attached to the cylinder 1 the eccentric is turned to bring roller 33 with engagement with it for a few revolutions. After the printing has been effected the eccentric is turned again to apply a film over the surface of the plate. Instead of using two separate moistening devices a single device may be used with means for altering the degree of moistening as shown in Fig. 4. The moisture applying roller 38, e.g. of rubber, is mounted in brackets 39 swingable about a shaft 40. Each bracket co-operates with a cam 42 so that the roller 38 is periodically appled to the printing plate. Bearing on roller 38 is a friction roller 43, e.g. of metal, rotatable and axially movable on shaft 40. The pick-up roller, e.g. of brass, 69 dips in a reservoir 66 and is mounted in bearing blocks 60 on a lever 61, the other end of which is connected to an eccentric 62 which is rotatable by lever 64 to vary the pressure between roller 69 and roller 67 in order to vary the amount of moistening liquid transferred to the printing plate. The intermediate roller 67 may be omitted.