In conventional lithography, a halftone screen is used to photographically convert the continuous- tone image of the original into a grid of very small, closely spaced dots of constant density but varying areas. Screenless or continuous-tone lithography is a printing process capable of reproducing images with gradated tones without the use of a halftone screen. Screenless lithography has a high quality potential because it has few of the inherent problems that limit the quality of the halftone process. This thesis investigates the image mechanisms in screenless lithography and in particular the role of variable water receptivity. It was hypothesized that in screenless lithography which uses a particular image carrier known as the Association Products plate, the continuous-tone image is due to selective emulsification of the ink resulting in a varying ink layer thickness and therefore varying densities. It was theorized that the plate has a water receptivity which varies with exposure to light and that this results in varying degrees of water-in-ink emulsification when the plate is dampened and inked. When transferred to paper and dried this results in an ink layer of varying thickness, which in turn causes a variation in optical density. A mathematical relationship was developed relating optical density, percentage of emulsified water, and ink layer thickness. This relationship allowed prediction of the amount of water-in-ink emulsification necessary to produce a given density range and a prediction of the amount of emulsification expected on a given plate area associated with a particular printed density. Testing proved that these predicted values were not present in actual printing from the plates. It was concluded that the hypothesis is invalid.
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Department, Program, or Center
School of Media Sciences (CIAS)
Martin, Charles, "Image Mechanisms in Screenless Lithography" (1975). Thesis. Rochester Institute of Technology. Accessed from
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