In the printing process of self-adhesive labels, the quality problems that often occur are: the reverse side of the self-adhesive label material is smeared, the ink is penetrated, the ink is flying, and the static electricity. These problems affect printing quality, and it is necessary to take corresponding measures to eliminate them. Below, we will analyze the causes of the above problems one by one and find out how to deal with them.
1. Flying ink
The phenomenon of fine droplets of ink flying in the air is called “flying ink”, also known as ink mist, which is the most common problem of self-adhesive labels in high-speed rotary letterpress printing machines. To slow down the “flying ink” phenomenon, you can add humidity in the printing room and use conductive inks such as water-based inks.
2. Through printing
Ink penetrating refers to the phenomenon that the positive imprint can be seen on the reverse side of the self-adhesive label. To avoid ink penetrating, it is possible to choose a tight paper for printing, increase the viscosity of the ink, and appropriately lower the printing pressure.
3. Smudge the back side
The ink printed on the self-adhesive label sticks to the reverse side of another printed sheet, causing smearing on the reverse side. To avoid smudging on the back side, a powder spraying device is generally installed in the paper delivery part of the printing press to disperse the fine particles of calcium carbonate between the printed sheets. In addition, speeding up the drying of the ink, reducing the height of the printed sheet stack, and putting paper with good ink absorption between the printed sheets have an inhibitory effect on smearing.
4. Static electricity
During the printing process, the self-adhesive labels are not easy to separate, the paper on the delivery table is not neatly received, or the paper on the delivery table is tilted and overprinting is prohibited, etc., all may be caused by static electricity. To eliminate printing static electricity, a static eliminator is generally installed on the printing press to ionize the air around the printing press, thereby neutralizing the positive and negative static electricity on the paper. It is also possible to spray an appropriate amount of water mist around the printing press or above and behind the impression cylinder to eliminate static electricity on the paper. In addition, increasing the humidity in the printing workshop is conducive to the elimination of static electricity.
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