Dark reaction is a condition in which the plate acts as if it is exposed to a low level of active light, even though it is being stored in the dark. The Stouffer scale or the sensitivity guide is used to measure this dark reaction which takes place also as a result of high temperature and relative humidity. If there is much dark reaction taking place, more solid steps will show up on a negative working plate. For the purpose of this experiment diazo and photopolymer presensitised, negative working, lithographic plates were chosen. These plates were cut into small sections to eliminate plate variables. They were then subjected to different levels of temperature and relative humidity in a temperature controllable oven. The relative humidity being controlled by using various super- saturated salt solutions. A light integrator was used to expose the plates to the same amount of light energy, with a sensitivity guide. The plates were then developed by hand and the critical or solid step determined visually to measure the dark reaction undergone by the plates due to variations in temperature, relative humidity, and time. With the results obtained curves were drawn to study the relationship between dark reaction and temperature, dark reaction and relative humidity, and dark reaction and time. The curves show an increase in dark reaction with an increase in temperature, relative humidity, and time in the case of diazo plates. The photopolymer plates, on the other hand, seemed to be more stable at higher temperatures, but a high relative humidity destroys the plate coating. A statistical analyses was done on the results and the percentage dependence of dark reaction on temperature, relative humidity, and time were determined. It is concluded that dark reaction does occur in diazo and photopolymer presensitized plates. And that these plates would last longer if stored under the optimum temperature and relative humidity as suggested by analyzing the data. The results obtained disprove the assumption that photopolymer presensitized plates are not influenced by temperature and relative humidity.
Library of Congress Subject Headings
Lithography, Direct--Testing--Evaluation; Plate-printing--Testing--Evaluation
Department, Program, or Center
School of Media Sciences (CIAS)
Adityan, Kannan, "A study on the relationship of dark reaction of diazo and photopolymer presensitized, negative working, lithographic plates with temperature relative humidity, and time" (1986). Thesis. Rochester Institute of Technology. Accessed from
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