engleski

Accelerated and natural ageing of offset prints covered with different varnishes

The aim of this work was to determine the dependence of the colour fading of offset prints on the ageing process, relative to prints overprinted with water-based dispersion varnish and UV-cured varnish. Natural ageing (outdoor conditions and the exposure to sunlight filtered by glass windows) and accelerated ageing (moisl heat and light xenon arc lamp) treatments were carried out. In order lo determine colour fading, colour difference, 2D gamut values and characteristic cross sections L20, L50 and L80, as well as 3D gamut values were used. The yellow colour showed the largest colour difference when offset prints were exposed to accelerated ageing by means of exposure to xenon light. Magenta followed yellow. No significant stability was achieved by varnishing the yellow print with water-based dispersion varnish and UV-cured varnish. This was also the case with magenta. An increase of the gamut occurred after one week's exposure of prints coated with water-based dispersion varnish to moist heat ageing. In contrast, on exposure of prints coated with UV-cured varnish, a decrease of gamut appeared. On further exposure of prints covered with either kind of varnish a decrease of gamut was evident. Indoor exposure of varnished prints to sunlight through a glass window had a minor influence on the gamut volume change in comparison with the exposure of prints to outdoor conditions.

ageing; offset; water-based dispersion varnish; UV varnish; colour difference; Gamut

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