Patent DE-19746174-C1 (DE)
Title: Printing cylinder
Inventor: LEHMANN UDO DR
IPC: B41M1/10
Filed: 1997-10-18
Granted: 1999-07-08
Abstract: For a gravure printing process, a transparent printing cylinder (10) carries a number of small cups and has an inner energy supply.  The cups are fed with a continuous supply of a fluid printing ink (11) forming a surface tension.  The energy supply (17) gives an induced movement to the ink (11) within the cups to alter the ink vol. and position, so that the ink surface projects over the cylinder (10) surface to apply an ink dot to the printed material (16). The printing form is a rotating printing cylinder (10), with surface cups in a layout representing the printed image.  A static unit within the cylinder delivers an energy beam (17) which activates the ink (11) in the cups to deposit ink dots on the printed material (16). The printing cylinder (10) is of a transparent material, to allow the energy beam (17) through, such as of glass or a polymer. The energy beam (17) transfers its energy to an absorption layer at the cups to effect a heat transfer to the ink (11).  This triggers a thermal/physical reaction in the ink (11) from an absorption layer which can be at the inner and/or outer side of the ink cups. The printed image is transferred to the material by digital modulation of the energy beam (17). The printed image required is shown on a non-transparent material placed at the inner surface of the cylinder (10), and perforated at points where the energy beam (17) is to pass through to give the ink dots for the printed image.  The layer is given a direct digital control, and is of a replaceable polymer film prepared by a photo-chemical process.  The transparent and non-transparent points are prepared by a magneto-optical process. The ink (11) in the cups can be activated by an external energy beam (17), with energy absorption within the ink cups.  The energy can be directed at the ink cups from behind, through the transparent printing cylinder, into an absorption layer to give an indirect heating to evaporate or expand the ink. The ink cups have a second and smaller opening, as a link to the ink supply container. A printing cylinder (10), with ink cups, is charged with ink, and the ink cups are cleared of surplus ink by one or more rollers. An ink-repellent protective layer is used on the web surfaces (13) of the printing cylinder (10). The position changes of the ink (11) surface tension in the ink cups is through different electrostatic attraction forces, where wither the printing cylinder (10) or the image drum, or both, have point charges.  Or the surface tension changes are through different magnetic attraction forces, using magnetic inks, with point magnetism at either the printing cylinder (10) or image drum, or both.  The image drum can be cleared of an electrostatic charge at local points. The same or different printing speeds are set for the printing cylinder (10) and the printed material (16). The printing cylinder (10) has a smooth inner and outer surface.  A seamless and transparent sleeve, fitted with ink cups, is fitted round the outer surface, or the sleeve is formed from a replaceable sheet which is wrapped round the cylinder.