Offset lithographic printing plates, until several years ago, used incoherent light sources for image creation in light sensitive coatings. These light sources are primarily in the ultraviolet light region. Image creation, using an incoherent light source, requires either a film negative or positive and long exposure times. Exposure time is dependent on the sensitivity of the light sensitive coating and the light intensity. In recent years both equipment and plate suppliers have been working to develop offset lithographic printing plates which use coherent laser light for image creation. To date all recorded developments have worked on light hardening image creation techniques. At present there has been no recorded effort in developing a thermal curing technique, using a coherent infrared laser beam, for image creation. The infrared laser light would be used to thermal-harden image areas only and leave non-image areas soft or unexposed. After exposure, non-image areas would be removed with a developing solvent. This thesis was conducted to determine if image creation would be possible based on thermal curing of a modified phenolic resin. Ten experiments were conducted to determine the image creation requirements of different coating formulations and various exposure conditions. Several coating formulations were used to determine the optimum coating for thermal curing using a carbon dioxide infrared laser. Exposure time, exposure speed and light intensity (laser output power) were varied to determine the effect each has on thermal -hardening of the modified phenolic resin coating. Experimental results supported the theory that images could be created in a modified phenolic resin coating. Both halftone dots and solids could be created in the coating. Solids required much less energy than halftone dots. It is believed that this is due to the poor infrared absorption of the coating. Solids received much longer exposure time than halftone dots. This longer exposure time enables the coating to absorb more infrared light. Further studies of the thermal response of the modified phenolic resin coating could make the plate a useable product in the future. It is believed that the phenolic resin coating could become a useable method of image creation with further modifications. Infrared absorption of the coating must be increased to enable images to be created at higher exposure speeds and shorter exposure times. Other exposure techniques could also be investigated to reduce the amount of energy required to thermal-harden the coating.
Library of Congress Subject Headings
Photolithography; Lithography--Metal plate processes; Offset printing
Department, Program, or Center
School of Media Sciences (CIAS)
Leonard, Eric, "Thermalhardening Offset Lithographic Printing Plate" (1977). Thesis. Rochester Institute of Technology. Accessed from
RIT – Main Campus