This article is part of the FLEXO FLAW FIXING series

Unclean print is one of the most baffling of the numerous common flexo printing faults. Contamination, ink consistency, plate/sleeve issues, pressroom environment, and anything else can all play a role. Dirty print is frequently characterised by speckles in the ink that give the print a dirty appearance, as well as instances of excessive dot gain in high-resolution areas.

What Causes Dirty Prints? Locate Solutions to Your Flexo Printing Issues

We’ll start with the most obvious reason, which also happens to be the name of this printing flaw: dirt.

Dirt & Contaminants

Machinery in operation generates static electricity, which attracts floating dust, microscopic paper particles, and other pollutants to positively or negatively charged objects in the area in any industrial setting. The composition of the ink will thus be compromised wherever it comes into contact with these pollutants.

Drying Ink

Dried ink in anilox cells, as well as on printing sleeves, cylinders, and plates, can also result in filthy prints. On one end of the range, these ink transfer issues could include skip out (when too little ink is transferred) or a flexo printing flaw such as filthy print (when too much is transferred). To avoid the environment as a potential source of filthy printing, industry experts recommend keeping the press room at 22ยฐC / 72ยฐF and 50% humidity.

Incorrect Ink Viscosity

The viscosity of the ink determines how quickly it accumulates beside the press ink-transfer components. This can cause flexo printing issues such as bridging and filling in, as well as dirty printing.

Improper Anilox

The anilox is a cylinder that receives ink from the image carrier and transfers it to the anilox. You must choose an anilox with the correct cell volume and cell count:

  • Cell volume: The total surface area available to hold ink in 1 square inch. Greater quantities are typically utilized for brighter, bolder work, whereas smaller volumes are employed for works requiring fine detail.
  • Cell count: The number of cells per inch measured along the engraving angle, which is the arrangement of cells around the roll’s axis.

How to Clean Up Your Dirty Prints?

Flexo printing is a pressure-sensitive process with numerous variables. As a result, you should always endeavour to optimise the pressure at the points of ink contact along the press. Your inks could be overly pigmented, or the mounting adhesive could be too thick or stiff.