Test on Coating Film
Occasionally, this color change returns to the original color showing that this is a reversible phenomenon. We have been receiving requests for technical consultations regarding these failed products in which color change occurred.
In view of the above, with respect to such color change in the dark red lacquerware, we carried out a washing test where sample lacquerware dishes for school lunch supplied by Echizen lacquerware cooperation are washed in an industrial dishwasher and a test on layered boxes whose color has changed observing how the level of color change varies while altering the surrounding environment in which the layered boxes are placed. We show the results below.
- Washing test on sample lacquerware dishes for school lunch
The sample dishes were washed in the automatic dishwasher TJW-300TD under the following condition:
Washing: temperature 60 degrees, time 70s, intermission 4s
Rinsing: temperature 80 degrees, time 7s
Time till finish: 9s
This cycle of 90s was counted as 1 cycle, and 1000 cycles were carried out.
[Detergent: Liquid detergent for industrial dishwasher]
・DU SHINE LB ( DiverseyLever 14 )
・[potassium hydroxide, carboxylate salt, anion surface activating agent, non-ionic surface activating agent]
[Rinsing agent: Dry finishing agent for industrial dishwasher]
・DRI-IT ( DiverseyLever 14 )
・(sorbitan fatty acid ester, polyol)
- Measuring change over time in the light intensity characteristic of a bowl
- At 0 cycle, 200 cycle, 400 cycle, 600 cycle, 800 cycle and 1000 cycle, change in the light intensity characteristic of a bow was measured with polychlomator photometry system PSS-100 (manufactured by Shimazu Corporation14).
Similarly, at 0 cycle, 200 cycle, 400 cycle, 600 cycle, 800 cycle and 1000 cycle, pictures of the sample was taken with the digital camera CAMEDIA C-200ZOOM (manufactured by Olympus Optical Co.,Ltd.).
- Results of washing test of a bowl
- In order to evaluate the detergent resistance characteristic of a bowl in the washing test, 1000 cycles of washing were carried out (200 cycles per year=5 years). After the test, there were no decrease in adhesiveness and intensity of the coating film such as peeling off and cracking.
- Test on color change due to altering of surrounding environment
- The set of layered boxes manufactured at the end of 1997 was purchased and the boxes were taken out from the box about one year later. Their color changed rapidly. If the boxes are placed in a highly humidified environment, their color was restored. However, in a normal environment, their color remained brownish yellow.
The boxes whose color has changed and the boxes of normal color manufactured at around the same time were dried in a vacuum dryer for 24 hours at the temperature of 40 degrees. Thereafter, they were placed in an environment where temperature is maintained at 23 degrees and humidity is maintained at 95% using the thermo-hydrostat testing device FX720P (manufactured by Kusumoto Chemicals, LTD.14). The boxes were taken out every hour and their colors were measured by using the colorimeter Eagle Eye (manufactured by Sakata Inx14). Then, the boxes were placed in an environment where temperature is maintained at 23 degrees and humidity is maintained at 37% and they were measured in the same manner as described above.
- Results of color measuring
- The color difference ΔE over time is shown in FIGS. 1 and 2. In both conditions where the boxes are switched to the high humidity environment (temperature being 23 degrees and humidity being 95%) to the low humidity environment (temperature being 23 degrees and humidity being 37%) and vice versa, the ΔE changes of 15 or more were observed in few hours. On the other hand, ΔE did not change much in the boxes of normal color after one hour.
Further, setting the state of boxes of normal color after being placed in the low humidity environment for 48 hours or more as a standard state, luminosity and hue were compared. If the boxes whose color has changed are placed in the high humidity environment, their luminosity decreases and the color becomes close to the normal color. However, if the boxes are returned to the low humidity environment, their luminosity increases and the color becomes brownish yellow.
With respect to the hue, in both cases of switching to the high humidity environment and switching to the low humidity environment, the shift Δb was greater than the shift Δa. If the boxes are switched to the high humidity environment from the low humidity environment, first, the hue changes to –b (blue) from b (yellow) and then shifts to –a (green) from a (red).
First shifted to the state shown in FIG. 3 and then shifted in the a direction (see FIG. 4). Next, infrared spectroscopic analysis was carried out to the surfaces of both boxes whose color has changed and boxes of normal color with the microscope FT-IR・raman analyzer (Nexus 870 manufacture by Nicolet Japan). Although the boxes whose color has changed has slightly high value at the peak near 990cm-1, a significant difference was not observed.
- FIG. 1 Change in color difference over time (low humidity environment to high humidity environment)
- FIG. 2 Change in color difference over time (high humidity environment to low humidity environment)
- Test results
- With respect to such color change in the transparent processing using black and red lacquer, we carried out a washing test where sample lacquerware dishes for school lunch supplied by Echizen lacquerware cooperation are washed in an industrial dish washer and a test on layered boxes whose color has changed observing how the level of color change varies while altering the surrounding environment where the layered boxed are placed.
As a result, it is understood that the color change is reversible according to the surrounding environment such as changes in temperature and humidity, that is, there are cases where the original color is restored. As for the cause of color change, effects of hardening condition, additive added to lacquer, detergent used in the washing test, etc. can be considered.