Spectral Sensitivity of Photosensitive Acid Resists.

Several resins, both synthetic and natural, used as acid resists in photoengraving, are rendered photosensitive by the addition of alkali dichromates. The mechanism of this photosensitization is not entirely clear, and the spectral sensitivity of the reaction for widely different resins may be of aid in a study of the reactions involved. In addition such sensitometric data are useful in the practical application of the resists. Aluminum plates, coated with the resins, were exposed in a medium quartz spectograph using a controlled white flame arc and rotating logarithmic spiral sector to produce wedge spectra. Calibration of the spectral energy incident on the plate was made from 2500 A. to the long wave length sensitivity limit of the material at 5000 A. Spectral sensitivities for the several resins are qualitatively similar when expressed in terms of incident energy. Coating thicknesses are of the order of 1 micron. At this thickness only a fraction of the incident energy is absorbed, as shown by transmission spectra through similar coatings on crystalline quartz plates.