How to deal with these problems in flexo printing process? Here are the main ideas!

Flexography is an eco - friendly and efficient printing method that's developing fast in China, with rapid tech and process updates. Yet, due to different technical levels, companies using flexo printing often encounter issues like misregistration, fringing, and hollow dots, causing much trouble. This article lists common flexo faults and solutions to help readers.

01 Fringing
Fringing refers to the sawtooth or irregular overflow at the edges of printed text and images. It's mainly caused by ink issues like high viscosity or fast drying. Sometimes, partial ink drying on the plate, followed by transfer with small scabs, causes fringing. This can even happen with low - viscosity ink. Usually, at 25°C, keeping the ink pH between 8.5 - 9.5 is ideal.
Excessive ink volume can also lead to fringing by increasing ink buildup around dots. In this case, use a high - line or low - ink - volume anilox roll.
Static electricity during printing can affect ink transfer, causing fringing. Anti - static devices can reduce or eliminate this.
The cleanliness of the substrate's surface affects ink flow. Excessive paper fuzz or dust can cause fringing, so cleaning the substrate helps.
Fast drying speeds reduce ink flow, leading to fringing. Adding slow - drying agents can slow ink drying on the substrate for more uniform ink distribution.

Unsuitable surface tension of the substrate can hinder ink penetration, causing ink to accumulate on the surface. Generally, the substrate's surface tension should be slightly higher than the ink's surface tension.

02 Hollow Dots
Hollow dots are common in flexo printing, often caused by excessive printing pressure. The emergence of flat - top dot plates has alleviated this. As long as the pressure isn't too off, complete dots can be printed.

Low ink adhesion can also cause hollow dots. Ink adjusters can help. Low ink viscosity can cause similar issues, so monitor viscosity closely, especially in high - temperature workshops where new ink viscosity differs greatly from used ink. Regular testing is needed.

03 Incomplete Printing
Incomplete printing, or very light/missing ink in some areas, is a typical ink transfer issue. It's mostly due to insufficient printing pressure, such as inconsistent contact pressure between the anilox roll and plate, or between the plate and substrate. Inconsistent pressure can result from inadequate pressure application or poor transverse balance of unit components. Regular checks can prevent this.
The plate's surface condition (like oil contamination, depressions, or insufficient thickness) can also cause ink leakage. Oil stains can be removed with alcohol; other issues require a new plate.

Insufficient ink supply can lead to incomplete printing. Advanced equipment with closed ink chambers may have this issue if the ink pumped by the air pump is too low to fully wet the anilox roll. Also, a severely clogged anilox roll can't transfer ink properly, so maintaining the entire ink pathway is essential.

04 Misregistration
Misregistration, caused by inaccurate color station alignment, results in blurry or distorted images.
Many factors cause misregistration. For plates, though film output is good and the spiral angle impact is minimal, different manufacturers' calibration standards can make plates from various sources incompatible, including laser plates. For plate mounting, the initial registration line is usually based on the plate center. Mounting outward from there reduces errors, provided the mounting machine is pre - calibrated.
If plates and mounting are fine, consider the press's original registration accuracy. For example, stack - type presses have a 0.2mm accuracy, and satellite presses have a 0.15mm accuracy. While 100% accuracy is ideal, it's challenging to achieve.
If misregistration still occurs, check equipment and materials. Equipment issues involve plate cylinder drive settings, auto - registration, and tension control. Material issues relate to roll diameter, stretching, and heat - induced deformation. Adjustments can be made accordingly during operation.

The above content addresses common issues in flexo printing and offers solutions. In production, many other problems may arise. Always diagnose accurately and address the root cause.

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