Blockage, poor ink transfer, and missing dots are three types of faults that must often occur, right? Moreover, due to similar performance results, it is particularly difficult to distinguish. Do you want to learn the technique of "grasping"? Then look down!
1. Blocking plate
In gravure printing, the phenomenon of plate blocking is generally manifested as: shallow dot printing cannot be transferred (such as human skin color); The transfer amount of ink in deep dot printing is reduced, usually from 50% to 70% to 20% to 30%.
Cause of occurrence:
① In printing, the increase in ink viscosity caused by solvent evaporation prevents it from entering small mesh holes or wires, causing the ink to gradually dry and solidify, leading to plate blockage.
② In printing, the distance between the Doctor blade and the plate cylinder is too large or the angle is unreasonable; Due to the large diameter of the plate drum or insufficient depth into the ink tank, the hot air blown out from the drying equipment can affect the plate drum and also cause plate blockage. This situation is very common in domestic printing machines.
③ The engraving depth and angle of the printing plate mesh hole are not suitable.
④ The high temperature of the printing environment causes the solvent to evaporate too quickly, resulting in plate blockage.
⑤ With the addition of a curing agent series of inks, as the machine time increases, the ink solidifies in the printing plate mesh, gradually reducing the depth of the printing plate and causing plate blockage.
⑥ The ink formula design is unreasonable, using solvents that dry too quickly.
Solution:
① Adjust the ink drying speed and choose a slow drying solvent according to the actual situation.
② Add inking oil to improve and enhance the fluidity of the ink.
③ After printing, clean the printing plate immediately.
④ According to the actual printing situation, add appropriate solvents in a timely manner to ensure the consistency of ink printing viscosity as much as possible.
⑤ Redesign the ink formula to reduce the initial dryness and dryness of the ink, and increase its fluidity and transferability.
⑥ For blockages caused by curing agents, it is advisable to add as little or no curing agents as possible; If it is indeed necessary to add curing agent, it is necessary to regularly check whether there are any blockages and promptly handle them.
2. Poor ink transfer
In printing, due to poor transferability, the amount of ink transferred to the plastic film cannot meet the color concentration or saturation requirements of the original design and standard printing samples, resulting in printing failures.
Cause of occurrence:
① Due to plate blockage, the drying speed of the ink on the printing plate is too fast.
② The selected ink does not match and cannot bond and adhere to the plastic film.
③ The ink formula design is incorrect, resulting in light ink color or insufficient color saturation of the ink itself.
Solution:
① If there is a malfunction caused by printing blockage, the cause of the blockage should be analyzed and corresponding countermeasures should be taken.
② Switch to a matching ink variety.
③ Improve the ink formula by selectively selecting suitable raw materials, such as pigments with strong color saturation and high coloring power, and resins with good transferability.
3. Missing branch
During the printing process, the uniform flat screen on the printing plate becomes a filter mesh due to the inability of the ink to flow flat and the appearance of individual dots, even resulting in missing dots. Generally, starting from the second color group, this phenomenon is more obvious.
Cause of occurrence:
① Ink viscosity or yield value is too high, resulting in poor ink transferability.
② The ink dries too quickly and is not evenly distributed on the printing plate, resulting in premature drying and curing.
③ The wettability between the ink and the printing plate is poor (surface tension does not match), and the transferred ink is not easy to spread.
④ The scraper pressure is high, while the printing roller pressure is insufficient.
⑤ The screen cable of the printing plate is too thick, the spacing between the screen holes is large, and the ink is not easy to spread.
Solution:
① To reduce the viscosity of ink and improve its transferability, it is recommended to use special additives for gravure printing ink.
② Adjust the position of the doctor blade holder to shorten the distance between the Doctor blade and the plate cylinder.
③ Use slow drying solvents to reduce ink drying speed and increase dot gain rate.
④ Adjust the scraper pressure and printing roller pressure.
⑤ Remake the plate to change the shape and angle of the mesh holes.