Adhesion
The ink layer after winding appears in flakes or streaks attached to other contact surfaces (usually the reverse side of the original film).
Abnormal reasons:
Excessive ink amount, and the drying efficiency of the equipment cannot keep up.
Incorrect solvent or incorrect solvent ratio, resulting in slow ink drying.
Insufficient drying capacity.
Excessive winding tension.
Excessive winding diameter.
Significant differences in the depth of the printing plate dots, some areas are completely blank with no graphics; in some areas, the graphics dots are too deep, causing longitudinal veins after winding.
Excessive temperature at the winding point.
External abnormal pressure.
Insufficient ink cohesion.
Countermeasures:
Reduce the ink amount appropriately.
Use the appropriate solvent or correct the solvent ratio.
Increase the drying temperature of the oven appropriately (but not too high, otherwise, the ink surface may be skinned while the middle is not dried, making it more prone to adhesion).
Reduce winding tension appropriately, pay attention to the curling tightness during printing, especially for nylon film.
For orders prone to adhesion due to large winding diameters, do not cut large rolls, try to cut small rolls for production.
Add a swinging device at the winding point, swing left and right regularly to cross-wind the areas with deep dots that are prone to veins.
Reduce the temperature at the winding point appropriately and increase ventilation.
Eliminate external abnormal pressure: Printed semi-finished products should be stored vertically rather than horizontally; when placing them, they should be dispersed, not overly concentrated. For some special orders, when unwinding, use your hands to support rather than using an unwinding vehicle.
For metallic ink (such as gold or silver ink), which has weak cohesion, sometimes adhesion may occur due to slight external pressure. Without affecting the coloring effect, appropriately add ink thinner (also called a diluent).
[Special Reminder]:
It needs to be distinguished from the 10th abnormality "Ink Deficiency," the 11th abnormality "Missing Dots," and the 18th abnormality "Ink Adhesion."
Ink Deficiency, Missing Dots: Abnormalities that occur when the printed film leaves the impression roller in the printing process.
Ink Adhesion: The film leaves the impression roller normally but exhibits abnormalities after passing through the drying oven, cooling rollers, or other units at the back. It should not be confused with Ink Deficiency and Missing Dots.
Oil Stain (Oil Contamination)
Non-graphic parts of the plate show ink adhesion, forming a foggy contamination phenomenon, usually appearing as dark contamination in blank or light-colored graphics.
Abnormal reasons:
Wear or poorly ground doctor blade, low pressure, improper angle leading to low efficiency of ink removal from the plate.
High ink viscosity.
Ink abnormalities (containing coarse particles, impurities, or ink formulation defects).
Poor plating.
Countermeasures:
Resharpen or replace the doctor blade; the harder the material, the greater the pressure, the larger the angle, the more effective.
Print with the lowest possible ink viscosity, and consider adding new ink. Additionally, adding a fast-drying solvent and using a backside blowing device during printing can be effective.
If the doctor blade, pressure, angle, and ink viscosity are all normal but there is significant contamination, the ink may be defective. Replace the ink with another supplier and discuss improvement with the ink manufacturer.
Sand the plate surface. If the plate has severe damage, it should be re-plated.
Plate Damage
As the name suggests, the plate is bumped or bruised. The phenomenon is exactly the opposite of ink deficiency. Ink deficiency is the absence of graphics where they should be, while plate damage is the mysterious appearance of graphics where there shouldn't be any. Assuming there are nine identical plates around the plate, plate damage generally only appears on one of the plates. Even if plate damage appears on two or three plates at times, they are non-identical and their shapes and positions cannot be exactly the same.
Abnormal reasons:
Plate damaged during storage.
Plate damaged during transportation.
Plate damaged during plate mounting or dismounting.
Hard foreign objects (such as falling screws) cause damage during printing.
Damage during cleaning by hard foreign objects in the cleaning machine.
Preventive measures:
During storage, pay attention to the surrounding environment (such as pallets) for hard objects such as nails that may cause plate damage.
During transportation (including shipment from the plate factory, workshop turnover), handle with care to prevent dumping and damage.
Be careful when mounting and dismounting before starting the machine, use your hands to guard against damage, and avoid the machine's edges causing plate damage.
Replace backup plates before stopping the machine.
Some powerful printing factories have plate cleaning machines. During the plate cleaning process, when hard foreign objects dropped in the cleaning machine are washed away at high pressure, it may cause damage to the plate.
These three items are preventive measures. For plates that have already suffered plate damage, if the plate damage is outside the effective graphics area or even outside the original film width range, it can be ignored, and normal production can continue. If the plate damage is within the effective graphics area and affects the appearance of the product packaging, the following solutions are available:
Slight plate damage: For printing machines with a blowing device, open the blowing device at the corresponding position of the plate damage; for machines without a blowing device, a rubber tube can be used to blow air to the plate damage area, generally making the plate damage less noticeable. If there are shallow mesh dots around the plate damage, blowing should be avoided to prevent dot loss. Consider replacing backup plates for production. If there are no backup plates, consult whether to continue production.
Mild plate damage: In the stopped state or before the plate is mounted, use 400-grit sandpaper wrapped around a bamboo stick or the fine end of an oil-based pen or marker to grind the plate damage area. Then, polish with 1000-grit sandpaper. Generally, the scope of plate damage can be reduced, making it less noticeable. If there are shallow mesh dots around the plate damage, grinding should be avoided to prevent dot loss. Consider replacing backup plates for production. If there are no backup plates, consult whether to continue production.
Moderate to severe plate damage: In most cases, blowing air and grinding the plate may not significantly improve the situation. It is recommended to directly replace the backup plate. If there are no backup plates, consider changing the job for production.