If you work in the flexographic printing industry, you know better than anyone that there are hundreds of moving parts to align, test, and measure to get the perfect print. These considerations are only increasing as new technologies and tighter printing requirements emerge. This makes the pursuit of the ideal print appear nearly impossible at times.

However, one aspect of flexo has been present since the beginning of the process: ink surface tension. Surface tension testing is a difficult task, but it can eliminate potentially costly defects while also improving your prints.

Mastering Print Quality: Enhancing Ink Surface Tension and Bonding in flexo printing

When print after print fails due to poor ink adhesion (or ink bonding), it’s all too easy to blame the image carrier. What is frequently overlooked is that the image carrier cannot function independently; its surface energy must fit between the surface tensions of your ink and your substrate. If you’re having issues with your flexo prints and are seeing defects like:

It could be due to low ink surface tension and adhesion. To avoid ink adhesion defects, you must test the surface tension of your:

  • Ink
  • Image Carrier
  • Substrate

So, while testing is important, what is the key to improved ink surface tension and adhesion? The devil has taken up residence in the dynes.

The Art and Science of Ink: Tips and Techniques for Optimal Printing

When printing, you want your ink to have the lowest dyne levels possible. Due to the differences in ink types, it is impossible to provide an exact range of dynes for ink. Water-based inks, solvent-based inks, UV inks, oil-based inks, and others all have different dyne levels.

Many press operators add additives to their ink, such as more solvent to counteract humidity or a surfactant to break up beading in water-based inks. This alters the surface tension of the original ink, which can result in defects if not re-tested before printing.

Note: When sending ink to your image carrier manufacturer for testing, always send press-readyink that accounts for any additives.

Unveiling the Image Carrier: A Comprehensive Guide for Printing Professionals

It is critical to ensure that your image carrier surface energy is greater than that of your ink but less than that of your substrate. What does a press run look like if that rule of thumb is broken? If the surface energy of your image carrier is too high, it will do the opposite of what you want and pull the ink away from the substrate. 

If it is too low, it will not pick up the necessary amount of ink from the anilox, resulting in a faulty final print. Consider the following general image carrier surface energy considerations:

  • Your surface energy will typically range between 20 and 38 dynes.
  • Photopolymers have one of the lowest surface energies of image carrier materials, typically falling below 30.
  • When printing flood rolls or large areas of solid color, a dyne level on the higher end of the spectrum is desired.
  • Fine detail work should be printed at the mid-range to lower end of the spectrum.

Unlocking the Potential of Substrate: Maximizing Print Quality through Material Selection

As mentioned earlier, your substrate needs to have a higher surface energy than your ink and image carrier. The surface energy of a substrate is determined by its material composition and can vary significantly. For instance, film substrates are usually treated between 38 and 45 dynes, although some exceptions exist.

It is advisable to conduct a surface energy test on your substrate before printing, just like you would for your ink. This test will ensure that your substrate has a suitable surface energy level to ensure proper bonding with the ink and image carrier. If your substrate has a surface energy treatment, it is essential to store and maintain it properly to avoid degradation. 

Failure to do so could cause the surface energy treatment to break down over time. This Leads to potential print quality issues. Understanding the surface energy of your substrate and ensuring it has the proper surface energy level is crucial to achieving high-quality prints. It is important to conduct regular testing and maintenance to ensure that the substrate maintains the desired surface energy level for optimal printing performance.

Beyond the Surface: Discovering the Most Effective Methods to Test Ink Surface Tension and Energy in flexo printing

Sending your press-ready samples to a testing facility, which can include image carrier vendors that offer the services to their customers, is the best way to test your surface tension and energy. Based on the results of the test, they can also recommend an image carrier that would be ideal for ink adhesion.

You can run a test on your press for a faster method that provides a good estimate. It entails comparing various test liquids with pre-determined surface tensions to your pre-print surface tensions. Here is a guide to measuring surface tension with an ink test that explains the different types of inks, how the test works in detail, and other important surface tension considerations in case you missed it.

Read next about Flexo printing on film substrates