GB883443A - Improvements in or relating to methods of duplicating and duplicating machines for performing the same - Google Patents

Abstract

883,443. Coated and impregnated papers used in copying. RITZERFELD, W., and RITZERFELD, G. May 19, 1959 [May 20, 1958], No. 16947/59. Drawings to Specification. Class 96. [Also in Group XVI] A method of duplicating copy sheets or cards from a printing master sheet having initially non-staining or initially only slightly staining image areas comprises the steps of attaching the printing master sheet to the printing drum of a rotary duplicating machine and applying, otherwise than by transfer from the copy sheets, an activating liquid to the image areas by rotation of the drum, a moistening device applying activating liquid directly to the printing master sheet or moistening an activating sheet which is attached to the drum in contact with the master sheet for at least one revolution of the drum before printing. The activating liquid may be alkaline or acid, or have as its active constituent a salt or an oxydizing agent such as potassium permanganate and a neutral " copying " liquid may be used for damping the copy sheets. According to Example I a printing master sheet having a silver halide emulsion of the auto reversal type in a layer which also comprises a slightly coloured, finely-dispersed, water-insoluble dye former, e.g. the leuco base of malachite green, is prepared by being exposed by reflection to a positive original. The master sheet is developed and the leuco base is oxidized to a dye base in a separate device outside the duplicator. When attached to the printing drum of the duplicator the master sheet is activated by being moistened with a 4% formic acid aqueous solution. The insoluble dye base is thereby converted into a water- and alcohol-soluble dye salt. The copy sheets are damped with alcohol. The master sheet may be reactivated when the quality of the copies deteriorates. According to Example II the activating acid is dilute amido-sulphuric acid.