Industry News

As a user of flexo press, do you habitually increase the ink roller pressure when adjusting it? Industry data shows that when the ink gloss width increases by 50%, the pressure between the ink rollers increases by over 350%; when the ink gloss width increases by 100%, the pressure increases by over 825%. A small adjustment places a huge burden on flexo presses, directly leading to decreased printing quality and increased energy consumption on products such as coffee paper cups, PVC/PET bottle labels, cement sugar packaging valve bags, and children's superdry disposable diapers. This article will analyze the working principle of flexo printing machinery, the dangers of excessive pressure, and the correct strategies for controlling pressure.

Flexo Printing Machine for Rice Paper Bowl

How a Flexographic Printing Machine Works

A flexographic printing machine uses a flexible printing plate made of rubber or photosensitive polymer to directly contact the substrate to complete the printing process. Its operation mainly consists of the following three steps:

First, a high-quality ceramic anilox roller precisely measures and transfers ink from the ink fountain to the raised image portion of the printing cylinder. The anilox roller is arguably the heart of a flexographic printer. Its finely textured surface controls the amount of ink transport, ensuring high-quality printing on products such as salad paper bowls, fast food takeaway paper bags, and food packaging nuts pouches.

Next, the printing plate, in conjunction with the impression cylinder, presses the inked image onto a substrate such as paper, plastic film, or corrugated cardboard.

Finally, the image on the substrate is dried and cured by hot air or UV, completing the printing process.

Flexographic Printing Machine for Chocolate Bar Paper Box

Flexography machines are characterized by short ink paths, fast color changes, and wide applicability to a wide range of materials. They use environmentally friendly inks such as water-based and UV inks, offering high printing speeds and low costs. Widely used in food flexible packaging, labels, and cartons, flexography is one of the fastest-growing mainstream printing methods in the modern packaging industry.

Flexographic Press for Paper Gift Box

What are the Dangers of Excessive Stress

Excessive pressure on the ink rollers of a flexographic machine can lead to severe dot gain and deformation, a sharp decrease in printing plate durability, damage to the flexographic printing press, and malfunctions of the doctor blade or doctor roller.

Severe Dot Gain and Deformation

Flexographic printing plates can be squeezed and deformed due to excessive pressure. The dots spread and expand outwards, causing double images to appear on printed products such as thank you sticker labels, gold foil shampoo stickers, and medical paper pouches.

Rapid Decline in Plate Durability

Excessive pressure accelerates plate wear, leading to ink buildup and plate clogging. This can cause dirty spots on printed products such as non-woven shopping bags, sealing sterilization pouches, and non-woven cotton face tissues.

Flexo Printing Machinery for Cigarette Paper Box

Risk of Damage to the Flexographic Printing Press

Overpressure may result in bending and deformation at both ends of the anilox roller and ink roller, gear runout, and even broken gear teeth—leading to serious mechanical failures in the flexographic printing press.

Abnormal Doctor Blade or Metering Roller Performance

Excessive pressure can cause the rubber metering roller to arch upward in the center, resulting in uneven ink metering and inconsistent color density. It also shortens the service life of the doctor blade.

Flexographic Printer for Feed Corn Grain Non-Woven Bags

How to Properly Control Printing Pressure

Compared with excessive pressure, insufficient pressure is easier to detect and correct. When a flexo printing machine shows symptoms such as the plate failing to pick up ink, poor ink transfer, or printed products like ice cream paper cups, kraft paper bags, and rice packaging bags appearing light in color or unclear, the pressure can be gradually fine-tuned and increased. This adjustment method will not cause irreversible damage to the flexographic printing machine.

Doctor blade pressure should be controlled so that the anilox roller surface displays a uniform and consistent ink film; it may be slightly higher than other pressure settings.

Ink transfer pressure should be controlled so that the anilox roller and plate cylinder maintain level contact, with compression controlled within 0.02–0.03 mm.

Impression pressure should be controlled so that dots do not enlarge, or enlargement is minimized, and the indentation depth into the substrate does not exceed 0.3 mm.

Flexo Printerr for Vitamin Medical Bottle Labels

The fundamental reason behind the principle of “lighter rather than heavier” in flexographic printing is that excessive pressure often causes irreversible damage, while insufficient pressure usually results only in temporary ink transfer issues that can be easily corrected through fine adjustment. Therefore, setting the ink roller pressure slightly below the recommended value in the operating manual can not only ensure excellent print quality for products such as wedding cake paper packaging boxes, soya bean milk packaging bags, and adult baby diapers, but also maximize protection of the flexo printing press and extend its service life.