Gas fading of inkjet prints with ozone

Abstract

Ground-level ozone is a common part of the air atmosphere and has a strong oxidative effect, mainly on inkjet dyes. The resistance of inkjet prints to ozone is mainly given by gas absorption capacity of the ink receiving layer and by the sensitivity of dyes to oxidation. The ground-level ozone concentration is usually low, from 20 to 80 mg m–3 of air. In spite of such a low concentration, it can cause a total print deterioration in the course of several weeks when displayed. A test target was designed in PhotoShop and printed using Epson printer R220, MIS Dyebase inks (ESC-R200-4-C, M, Y) and Quad Tone RIP. The target contains patches of pure inks with dot area 5, 10, 20, 30, 40 a 100 % and their overprints C+Y, C+M a Y+M and composite black. Ilford Gallery Smooth Gloss (290 g m–2) and Hahnemühle-Photo Rag Baryta (315 g m–2) photo paper were used as the inkreceiving layer. Gas fading of prints was performed in glass chambers flowed with ozone, generated by discharge way from a mixture of nitrogen and oxygen. Reflective VIS spectra of each patch on the target were recorded and colorimetric quantities were calculated. An accelerated ozone test with approx. 1000 times higher ozone concentration compared to the natural conditions was performed. Effect of ozone is very complex and ambiguous, moreover no ISO standard describes process of ozone ageing and its evaluation. Therefore, several methods for ozone ageing evaluation were proposed. Dye fading was evaluated by three methods: 1) optical density decrease, 2) dye concentration calculation from spectral data and 3) quantity accepted by many users — total colour difference value. The dye concentration calculation of pure ink patches and overprinted inks patches enables to judge the catalytic fading. That means one dye fading is accelerated by the products of other dye degradation. The principles of all evaluation procedures used in this research are fully described.