Quality Loss of Offset Printing Ink Film Due to Photo Irradiation

In Relation with Changes in Reflected Light Intensity and Colour Difference

Abstract

Quality loss of offset print subjected to photo irradiation was investigated. Specimens tested in this experiment were solid and half tone printed ink films, including also un-coated and coated papers as their substrates generally used in offset printing, and all cut in 5cm squared. The specimens were irradiated by means of high-pressure Hg lamp with the maximum irradiation energy at the line spectrum of 3650-3663 Å the total of which reaches 3.8×10^-3J/cm²sec. The quality loss was estimated by; the change in optical properties obtained by both intensity distribution curves of reflected light from the specimen surfaces and their colour differences calculated due to the change in spectral reflectance. Experimental results were compared with the published radiation energy of sunshine measured relating to the visible light, to predict the limiting conditions for the quality loss of offset print exposed outdoors. The lowering in gloss of printed surfaces with solid yellow ink was observed to take place by the exposure of more than 37MJ/m² that may be comparable to the sunshine energy of about 460 hours obtained at Shinjuku, Tokyo in August, 1984-1986. Also the gloss lowering appeared more pronouncedly for the coated paper rather than for the un-coated paper.