How to avoid air bubble problem for flexo printing

Bubbles (uneven ink)
Bubbles, also known as uneven inking or poor inking, appear as irregular white spots on the printed pattern, the direction is vertical, the width is about 2mm–5mm, the length is different, the slight is about 5mm, and even serious 100mm, the probability of bubbles appearing on the surface of the field is much larger than that of the screen printing.

Gearless CI flexo printing machine
Gearless CI flexo printing machine

More information about DH flexo printing machine, please visit here.

There are several reasons for bubbles:

1. Ink cause
During the printing process, the ink circulates back and forth under the action of the ink pump, and air is inevitably present in the ink. When the ink with air circulates into the ink chamber to transfer ink to the anilox roller, the bubbles formed will attached to the anilox roller, the bubble will block the ink from entering the anilox roll cell. As the anilox roll rotates, the bubble is scraped by the doctor blade, and the small area on the anilox roll naturally has no new ink transfer.


1 If the ink bubbles are very serious, add an appropriate amount of defoamer, depending on the foam in the ink tank, the ratio is 0.1%-0.5%.

2 Add a fine filter to the ink inlet of the ink pump to allow the bubbles to break up as ink passes.

3 Use air agitator to break the bubbles.


  2. Blade reason

1 When the printing factory replaces the doctor blade and the ink-block, it will apply vaseline on the knife holder and the ink-block. If the vaseline is improperly applied, it will be incorporated into the ink and then  transferred to the anilox roll and causing poor inking problem.

Solution: Apply according to the standard requirements, avoid excessive or improper application.

2 On chamber system, the exhaust pipe will be connected at both ends of the chamber. The exhaust pipe will be blocked after a long time use, resulting in poor exhaust or insufficient ink level in the chamber.

Solution: Unblock the exhaust pipe of the chamber, and regularly check whether the venting holes on both sides are unobstructed, so that the air in the chamber can be smoothly discharged.

      3. Ink pump reasons

When the ink pump is used for a long time, the diaphragm will be aging and damaged. The slightly damaged diaphragm can still work, but the amount of ink drawn will be lower than the normal value, and the air will be sucked into the ink to cause poor ink.

Solution: Replace the diaphragm and periodically check the ink circulation of the ink pump. If the circulation is much lower than the normal value (refer to the equipment manual), the diaphragm of the ink pump may be damaged and need to be replaced.

For the air exhaust pipe, ink pump and other components on the equipment, it should be included in the usual weekly maintenance and monthly maintenance plan, and the maintenance work should be done as required to avoid various defects in printing.