Process of offset printing on sheet material with high viscosity greasy ink

A process of offset printing on sheet material with high viscosity greasy ink with a rotary offset printing press having a horizontal rotatable plate cylinder, a horizontal rotatable inking cylinder for applying ink to the plate cylinder, said inking cylinder having a covering layer of flexible plastic material, means for rotating said plate cylinder and inking cylinder in contact with one another in opposite directions at equal peripheral speeds about parallel horizontal axes, and an inking device for applying a uniform thin film of said high viscosity greasy ink to the inking cylinder for transfer to the plate cylinder,

• said inking device comprising a rotary small diameter horizontal wiping rod disposed laterally of said inking cylinder and engaging the peripheral surface of the inking cylinder in a contact zone extending horizontally along the inking cylinder on the side thereof where the peripheral surface of the inking cylinder is moving downwardly, means for pressing the wiping rod against and into the elastic covering layer of the inking cylinder in said contact zone, variable speed electric motor means for rotating the wiping rod independently of said inking cylinder at a continuously variable speed in the same direction of rotation as the inking cylinder so as to move the peripheral surface of the wiping rod upwardly in said contact zone, and trough means for holding a body of said greasy ink against said inking cylinder in a space extending upwardly from said contact zone, said pressing means comprising a horizontal rigid elongate body having at one side thereof a longitudinal V-shaped groove facing said inking cylinder and rotatably receiving said wiping rod, said elongate body having in said groove bearing surfaces of very hard material which bear on said wiping rod in line contact and thereby wipe ink from the peripheral surface of said wiping rod in a zone between exposure of said wiping rod to said body of ink and engagement of said wiping rod with said inking cylinder,
• said process comprising supplying to said trough means, high viscosity greasy ink having a viscosity at least of the order of 50 poise, rotating said inking cylinder and plate cylinder in directions to move the peripheral surface of said inking cylinder downwardly through said contact zone so as to carry a film of said ink on said inking cylinder from said body of ink down past said wiping rod, pressing said wiping rod against and into the elastic covering of said inking cylinder so that variation in penetration of said wiping rod into said elastic covering has little effect on the thickness of said ink film, rotating said wiping rod in the same direction of rotation as said inking cylinder at a selected speed of rotation so that the peripheral surface of said wiping rod moves upwardly in said contact zone, wiping ink from the peripheral surface of said wiping rod subsequently to exposure of said peripheral surface of the wiping rod to said body of ink and prior to engagement of said peripheral surface of the wiping rod with inking cylinder in said contact zone, sensing the optical density of an area printed on said sheet material and controlling the speed of said variable speed electric motor to adjust the speed of rotation of said wiping rod to maintain the optical density of said printing constant and uniform at a selected value.