Accelerated laboratory xenon-arc exposures were performed on an identical set of lithographic ink samples. As stated earlier, the goal is twofold: (1) How well does the laboratory exposure mimic real-world exposure in terms of its actual degradation pattern and relative rank order? (2) How much faster is laboratory exposure than natural exposure?
1. Why do xenon arc test?
Historically, the ink industry has used accelerated laboratory testing to get results quickly. Xenon arc Testers are widely used because they can provide fast results by accelerating critical environmental stresses such as light spectrum, light intensity, RH, and temperature. For most indoor products, direct sunlight through windows is the most severe condition for indoor lighting. A recent Kodak study concluded that indirect, window-filtered daylight dominates the lighting environment in domestic interiors (Bugner, LaBarca et al., 2003). Therefore, this GATF/QPanel study used a Q-Sun xenon Tester equipped with a "window glass filter" to obtain the proper spectrum (Figure 18.9).
2. Test procedure
GATF and Q-Panel's Q-Lab Weathering Research Services testing ink samples in the Q-Sun xenon Test Chamber (Fig. 18.10). One xenon Tester is a small "tabletop" unit without RH control (Xe-1), while the other is a full-size, full-featured xenon Tester with RH precision control (Xe-3H). Exposures were performed in these different xenon-arc models to see if reproducible results could be obtained (Table 18.3).
3. Xenon arc test
Results After 10 days, the desktop xenon arc and the full-function xenon arc detected the ink with good performance and the ink with poor performance, respectively. Figure 18.11 shows the fade resistance of 8 ink colors in a benchtop xenon arc Tester.
4. Relative humidity
To determine the effect of RH, the ink was exposed to a xenon arc with a controlled RH of 50% (Q-Sun Xe-3-H) and another xenon arc with an effective RH of approximately 15% (Q-Sun Xe-1) .
Figure 18.10 Inks tested by GATF and Q-Lab in the Q-Sun Xenon Test Chamber.
Figure 18.11 Q-Sun Fade Resistance Range
Figure 18.12 Effect of Relative Humidity delta E
18.2.5 Xenon Arc Exposure Compared to Florida Outdoor Glass Exposure
The outdoor glass exposure established a benchmark for the ink's fade resistance in the extreme environments of Florida and Arizona. Next, compare the xenon arc exposure to outdoor benchmark data. Figure 18.13 compares the results of 10 days of xenon gas exposure and 35 days of Florida glass exposure. Although the numerical results are not identical, the results show an excellent order correlation between the two irradiations. In this comparison, 10 days of xenon arc exposure is roughly equivalent to 35 days in Florida. For this particular set of test samples, xenon arc exposure provided an acceleration factor of almost 4 to 1.
