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Color difference after nozzle cleaning in UV printing?
2016-11-16 17:56:28
In the process of UV inkjet printing, once stop to clean printing head, it will appear a very wide shallow color. And this situation is especially obvious when spraying solid colors(bicolour). Any use of digital printer with nozzles arranged up and down will occur this problem more and less. 
How this happens? First of all, we analyze the structure of the device. It is clear that this situation appears mostly on the devices of 4 color arranged up and down with relatively small mount of jetting ink. Because UV ink belongs to volatile liquid, if the ink drying too fast, while the washing time is relatively long, and some substrates have a strong penetration for themselves, the ink sprayed firstly has been dried, and the later ink is difficult to re-integration, in which cause the color change.
Now, we have found out the reason, and how we can solve it? General operation is to check nozzle status, and clean the printhead if it is necessary before digital UV printing of each pattern, trying to avoid nozzle cleaning during the printing. If it is necessary to clean the printhead during UV inkjet printing, finish it as soon as possible, or clean them separately, so as to avoid colour difference. However, a little color difference is inevitable in actual operation. Another method can be adopted is to keep the higher environment humility.
The fast drying speed of UV inks we said above can be solved by UV ink manufacturers, i.e., try to slow down the rate of ink evaporation and prolong the drying time. But the experience tells us that if the drying rate is low, there will be sticky picture, and this can be solved by adding ink adhesion additives into the ink, but the costs will be increased.

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