Spot color printing keeps producing small tailing streaks, at both high and low viscosity; after scratching with a chopstick, they reappear after a while. What is the cause?
- When printing a large-area spot color on pearlized OPP by surface printing, small tailing streaks appear at both high and low viscosity and recur some time after being scratched with a chopstick.
- Peers mostly recommend filtering the ink first, suspecting impurities, oversized particles or insufficient fineness, and checking whether the doctor blade is clogged.
- One unverified claim is that at most 1.5 kg of water can be added to 20 kg of ink to eliminate static in the ink and increase slippage between the plate and doctor blade, but over-addition should be avoided and a small-scale trial is advisable.
- Check the pattern: streaks along the blade's oscillation path with consistent spacing may point to the doctor blade, while irregular trailing is more likely static and can be addressed with antistatic liquid in the ink; static tends to cause burrs rather than blade lines.
- The combined advice points to plate and ink: control the proportion of old ink, filter the ink, control environmental dust, have the platemaker grind the plate once during copper plating, and polish it if problems occur during use.
A flexible packaging plant: We are printing a large-area spot color on a surface-printed product and keep getting small tailing streaks, at both high and low viscosity. After scratching with a chopstick, they reappear after a while. Is it due to slow machine speed, coarse ink particles, or other reasons? Pearlized OPP, surface printing ink.
Shenzhen – Packaging Bags: Try filtering the ink.
Yinteng Packaging Yu Dingzhao: The ink probably has impurities. Try filtering it.
Shangyang Packaging - Qi: Try adding a little water to the ink.
Yinteng Packaging Yu Dingzhao: This water-adding method is rarely used, but those who use it are experts. I heard that at most 1.5KG of water can be added to 20KG of ink. I have not verified it — have you tried it?
Shangyang Packaging - Qi: When ordinary ink is used to print PET and OPP, ink lines appear; adding a little water during production can often solve it. But you must not add too much — too much won't work. I saw this at Zhongshan Tiancai, and the effect was really good. You can try it on a small scale.
A flexible packaging plant: Can water be added to surface printing ink?
Yinteng Packaging Yu Dingzhao: I just asked a technician. The function of adding water to ink is to eliminate static electricity in the ink and increase the slipperiness between the plate and the doctor blade.
Guangzhou Yiying Color Printing: See whether there is regularity. If regular, it may be the blade; if irregular, it is static electricity. Does it appear along the blade's oscillation path? First check for regularity, then consider the ink and other causes. The blade oscillates; if the back-and-forth distance is the same, that is regularity. If it is the plate, it would be fixed and unchanging. If it drags irregularly, you can add antistatic liquid to the ink to prevent trailing.
Yantai Flexible Packaging - Wu: It should be caused by ink particles being too large. Also check whether the doctor blade is clogged. Static electricity causes burrs, not blade lines. What is the workshop humidity?
Zhuhai Ruilong Water-based Ink: It should be caused by insufficient ink fineness.
Wu Xianchao: This kind of problem is generally a plate and ink issue. Ink: control the proportion of old ink used, filter the ink; control dust in the environment. Plate: during copper plating, ask the plate-making factory to grind it once; during use, if problems occur, polish the plate.
Sichuan Tianyi - Li: Polish the plate cylinder and try a smaller doctor blade angle.
Yantai Flexible Packaging - Wu: First polish the plate cylinder.
Wu Xianchao: Polishing the plate cylinder before chrome plating gives the best effect.
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