Novel Printing Press for Waterless Lithography, 1996 International Printing & Graphic Arts Conference Proceedings

Shem M. Chou

Rockwell Graphic Systems

Lawrence J. Bain

Rockwell Graphic Systems

Richard Durand, Jr.

Sun Chemical Corporation

Eric Sanderson

Weyerhaeuser Paper Company

Temperature is the most critical factor to the success of waterless lithography. Background toning occurs due to viscosity breakdown of waterless inks at elevated temperature, especially at higher printing speeds on web presses. The objectives of this paper are to study thermal characteristics of waterless presses and to design new presses with a more uniform distribution of temperature. It was found that roller-to-roller variation in temperature of more than 15 degrees Celsius was not unusual. Temperature differences as high as 4 degrees Celsius were also observed across the plate cylinder surface. External cooling could reduce the rate of temperature rise but might not effectively stabilize the plate temperature to below the critical toning point. It did not equalize the cross-press temperature either. The cross-press temperature variation is related to the zonal image coverage of the plate. The lower the image coverage of a printing zone, the higher the plate temperature. This phenomenon was attributed to the lubrication of roller nips by the ink and the throughput rate of ink to the web. When the ink feed rate was significantly increased across the entire press and the excess ink was removed from the inker by a doctor blade, this novel press design dramatically reduced the cross-press temperature variation. Computer simulation results also indicate that the overall press performance is better for the presses with a return-film removal arrangement than the conventional keyed presses.