COLOR FADING ANALYSIS
of ink-media combinations (case 23)
What causes color fading?
For improvement of the weathering performance of UV-curable inkjet prints, a failure analysis of the degradation mechanism was needed, including both identification of leading weathering factors and relevance of the printing substrate. That way, color fading and other issues could be prevented.
Laboratory environmental testing
Various ink-media combinations were tested in a laboratory Xe-arc weatherometer using different combinations of weathering parameters. Leading environmental testing parameters were cumulative UV irradiance and level of fatigue-stress related to the number of periodic light/dark-cycles, with significant changes of the black panel temperature and/or water-spray.
For higher throughput, the ink-media combinations were periodically sampled for inspection and measurement, and then placed back. Inspection covered color fading measurements and micro-image capture in order to document the onset of coating degradation over the environmental test.
The appropriate set-up and automation of the micro-image capture was realized in co-operation with our HT lab, allowing semi-automatic image capture of the same patch areas of the samples.
Micro-image capture of coating failures during environmental testing. Same position imaged at the start of the test (top row) and after the 4th sampling equivalent to 8 weeks test duration (bottom row).
Improved ink development
Thanks to the systematic micro-image capture, several degradation mechanisms were identified in the course of the environmental testing, including light fading and hydrolysis of pigments as well as fatigue-stress-induced failure modes (cracking, flaking-off and adhesive failure).
These ‘mechanical failure modes’ are strongly dependent on the nature of the substrate. During the failure analysis, a number of hypotheses were formed that translated the observed performance into material properties. Based on these recommendations, an improved generation of inks could be developed.
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