[Discussion] Pearlescent OPP, surface printing ink: small trailing streaks keep appearing when printing large spot-color areas, at both high and low viscosity—what should we do?
- On pearlescent OPP surface-printed large spot-color areas, small trailing streaks recur at both high and low viscosity and reappear after being wiped with a chopstick.
- Forum suggestions include filtering the ink and checking for impurities or insufficient ink fineness, plus doctor-blade clogging, plate issues, workshop dust, and humidity.
- Streak regularity helps diagnose the cause: regular marks along the blade oscillation path point to the doctor blade, while irregular trailing suggests static electricity and can be addressed with antistatic liquid in the ink.
- Practitioners report that a small water addition can reduce ink lines with ordinary PET/OPP inks, citing an unverified upper limit of 1.5 kg water per 20 kg ink, and a technician says water eliminates ink static and improves slip between plate and doctor blade.
- Other recommendations are to control the proportion of old ink, filter the ink, and ask the plate-making factory to grind the plate once during copper plating to rule out plate problems.
A flexible packaging company: When printing large spot-color areas on a surface-printed product, small trailing streaks keep appearing, at both high and low viscosity. After wiping with a chopstick, they reappear after a while. Is it because the machine speed is too slow, the ink particles are too coarse, or some other reason? Pearlescent 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 small amount of water to the ink.
Yinteng Packaging - Yu Dingzhao: Adding water 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 haven't verified it—have you tried it?
Shangyang Packaging - Qi: When ordinary PET and OPP inks produce ink lines, adding a little water during production often solves the problem. But don't 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 company: Can water be added to surface printing ink?
Yinteng Packaging - Yu Dingzhao: I just asked a technician. The role 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: Check whether there is any 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 stays fixed. If the drag marks are irregular, you can add antistatic liquid to the ink to prevent trailing.
Yantai Flexible Packaging - Wu: It should be caused by overly large ink particles. Also check whether the doctor blade is clogged. Static electricity causes burrs, not blade streaks. What is the workshop humidity?
Zhuhai Ruilong Water Ink: It should be caused by insufficient ink fineness.
Wu Xianchao: This kind of problem is generally a plate or ink issue. Ink: control the proportion of old ink used, filter the ink; control dust in the environment. Plate: when 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. (From the Packaging Frontier flexible packaging technology QQ group. You are welcome to join: Main group: 121451012; Group I: 64311965; Group II: 37848282; Group III: 119411638; Group IV: 116162302; Group V: 256925591. For more technical content, see the bimonthly magazine Packaging Frontier. Welcome to subscribe: Mr. Xie: 020~85626447/605, 13310896471. For more content, visit the Packaging Frontier website www.pack168.com.)
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