You may notice areas of your substrate don’t print fully, sometimes leaving tiny unprinted areas about the size of a pinhole. Quite appropriately, this common flexographic printing defect is called pinholing.
In many cases, you’re likely dealing with an ink transfer issue, which in turn could have multiple causes on its own. Among the other potential culprits, you may also have a dirty anilox or an irregular substrate surface.
Don’t fret. We’ve compiled some explanations and troubleshooting solutions for you.
Are Your Flexo Prints Pinholing? Here’s Why
The origin of your pinholing could be either mechanical or chemical.
Poor Ink Transfer
Your inks aren’t fully wetting out on the substrate. Optimal ink transfer is critical to achieving a smooth coating from your anilox roll to your image carrier to your substrate.
Depending on the type of ink (here’s a guide to 4 types and their best applications) it could be drying too quickly, ultimately failing to transfer onto the printing form. This could be a result of atmospheric conditions in your press room. Pay close attention to the following variables:
- Humidity
- Temperature
- Air circulation
Each can cause inks, particularly the water-based and alcohol-based varieties, to dry either too quickly or too slowly. Use a solvent with a slower evaporation and adjust the power of the dryers.
High Ink Viscosity
Highly viscous inks can cause problems with tackiness. Higher ink tack causes difficult image transfer to the substrate. Adjust the ink viscosity, if necessary, with additives to promote fluidity without being so thin as to become runny.
Anilox Has Lost Cell Volume or Become Dirty
Your anilox could lose cell volume due to dirty cells or wear over time. Less volume equals less space on the anilox for ink to be picked up and transferred to the image carrier. The ink then will not build up a uniform film on the substrate.
As part of routine maintenance, you should check the condition of the anilox roller and replace it, if necessary. More often, however, the anilox has become dirty with dried ink, in which case it needs a thorough cleaning with non-caustic chemicals and a non-abrasive brush.
You should also regularly clean the impression cylinder, which applies pressure to the plate/sleeve cylinder.
Substrate Has an Irregular or Damaged Surface
It’s difficult, if not impossible, to achieve full wet out on an irregular or damaged substrate surface. If your substrate is pitted or polluted, it will reject ink transfer.
As a solution, you can adjust the surface treatment of the substrate. In some cases, a material change may be a general solution.
Flexographic Printing: The Causes of Pinholing
Pinholing can be an aggravating flexographic printing defect. It could easily look like your anilox and image carrier are transferring enough ink to the substrate, but meanwhile, mechanical or chemical issues are creating an incomplete print.
Some solutions include adjusting ink viscosity, monitoring air conditions in the press room, and cleaning your anilox. Of course, there could be other variables leading to the pinholing defect. Perhaps increasing printing speed or using a softer printing form or softer mounting tape will help your cause for printing perfection.
Let’s not waste press downtime and substrate. Let’s find solutions. If you experience pinholing or any of these 11 other common flexographic printing defects, don’t hesitate to get a second opinion for troubleshooting solutions. Call (888) 545-2270.
The free guide below explains print defects in further detail.
Editor's Note: This blog post was originally published Feb 6, 2018 and was re-published November 11, 2019 to reflect updated insight.
