This article is part of the FLEXO FLAW FIXING series

What Is The Dirty Print Effect In Flexography?

Set up an antistatic device. Flexographic printers frequently encounter dirty and mottled print. Maintaining a clean and uniform print can result in significant savings in downtime and waste reduction. This flaw, which has several probable sources, has a significant influence on image quality in high-resolution areas.

Causes Of Dirty Print Effect in flexographic printing

Among the many typical flexo printing flaws, unclean print is particularly perplexing. Contamination, ink consistency, plate/sleeve difficulties, pressroom climate, and everything in between can all contribute to it. 

Dirty print is frequently characterised by speckles in the ink that give the print a dirty look, as well as instances of excessive dot gain in high-resolution areas.

Dirt is the defect’s name. Airborne pollutants are always around us, especially in an active industrial flexo printing press room. The static charge generated by working machinery attracts floating dust, paper particles, and other impurities to your ink, anilox, image carrier, and/or substrate. Other possible reasons include:

  • Ink drying
  • Ink viscosity is incorrect.
  • Incorrect anilox
  • substrate with irregularities

The Appearance Of The Dirty Print Effect:

You will see ink speckles that give the ink a filthy look or indications of excessive dot gain.

What Are The Flaws Of Dirty Print Effects In Flexographic Printing?

  1. Dirt and Contamination

Everywhere we walk, microscopic airborne particles and toxins surround us. It’s true in our homes, but it’s especially true in an industrialized press room. Machinery in operation generates static electricity, which attracts floating dust, microscopic paper particles, and other pollutants to positively or negatively charged items in the area in any industrial environment.

The result? A small coating of dust builds on your flexographic printing press and its sleeves/cylinders/plates, anilox roll, doctor blade, ink chambers, and other components. The composition of the ink will thus be affected wherever it comes into touch with these pollutants.

  1. Ink Drying

Similarly, dried ink in anilox cells or on printing sleeves, cylinders, and plates can result in unclean prints. So how frequently do you check your dryers? They are certainly one of the most frequently overlooked press components.

If the ink dries too rapidly, improperly, or unevenly, it may stay on the anilox, doctor blade, and/or image carrier, causing major ink transfer concerns. On one end of the range, these ink transfer issues might include skip out (when too little ink is transmitted) or a flexo printing flaw such as filthy print (when too much is transferred).

Temperature and humidity in the pressroom always have an impact on how fast and fully inks dry. The more heated and dry the environment, the faster the ink’s water, alcohol, and solvent bases evaporate. To avoid the environment as a potential source of filthy printing, industry experts recommend keeping the press room at 72°F or 20°C and 50 percent humidity.

  1. Ink Viscosity Incorrect

Ink may be flowing or sticky, like maple syrup. It is more viscous if it is thick and “syrupy.” This has a significant influence on how ink transfers from the anilox roll to the image carrier and then to the substrate.

The viscosity of the ink determines how quickly it collects beside the press ink-transfer components. This can result in flexo printing problems such as bridging and filling in, in addition to unclean printing.

  1. Improper Anilox

The anilox is a cylinder that transfers ink from the image carrier to the anilox. A network of microscopic, precisely sized dimples called cells on the anilox surface controls the amount of ink delivered.

  • Too much ink on the anilox might eventually lead to too much ink on the substrate.
  • You must select an anilox that has the appropriate cell volume and cell count:
    • Cell volume: the entire amount of space accessible on the surface of a cell to store ink. Greater quantities are typically utilized for brighter, bolder work, whereas smaller volumes are employed for works requiring precise detail.
    • Cell count: The number of cells per inch measured along the engraving angle, which is the cell arrangement about the axis roll of the anilox.

A Solution To Prevent Dirty Print In Flexographic printing:

Flexo printing is a pressure-sensitive technique with several variables. As a result, you should always strive to optimise the pressure at the ink contact places along the press. However, several factors can contribute to dirty printing, ranging from ink viscosity and drying time to anilox selection and ink contamination. Your inks may also contain too much pigment, or the mounting adhesive may be too thick or stiff.

  1. Improvements in anilox screen count and cell volume selection
  2. Monitor ink viscosity and maintain inks constant throughout the print run
  3. Set the printing pressure to make a kiss (minimum) imprint
  4. Experiment with softer cushion mounting tape
  5. Use a balanced extender to adjust the ink strength
  6. Lower ink viscosity
  7. Modify the printing speed
  8. Verify that the doctor’s blade pressure is accurate
  9. Clean your printing forms and anilox rollers