Formulating Flexo Ink for Non-Dryer Applications

Jim asks:

I work in product development for white top liners and have run into cases where Flexo Folder-Gluers or Rotary Diecutters are smudging the ink because it isn’t setting well enough before diecutting or folding.   This is not an issue on equipment with dryers for the ink, but the ones without dryers seem to be more challenging for some of our liners. My background is in flexo printed labels, where drying is a necessity on coated paper labels, so the flexo units without drying are new to me.

 Could you provide any guidance on compatibility of ink with white top liner on post print flexo stations that don’t utilize a drying station?  Is there a way to test the liner to determine if it will absorb the ink enough that it won’t smudge in the diecutter or gluer, or do you have any ideas on how to make the ink set faster so it won’t cause these issues?

We do Cobb testing but that hasn’t been a good predictor of poor or improved performance.  We have an ink smear designed for offset (Croda) that seems to be a good indicator, but it is an oil based offset ink.   It shows when ink will penetrate more versus holding out. For offset, less penetration is normally better for print fidelity, but in this case, we see that less penetration indicates that the ink will be more prone to smearing. But it is oil based so it is not comparable to a water based flexo ink.

We print test on a Mark Andy Flexo press but I suspect that the label ink we use is not the right ink for liner board.

I am working with our full white uncoated liner. The product we’re making is performing very well in preprint, and in post print digital or Flexo with drying.  This liner is denser than typical linerboard, some customers love that, but the post print Flexo converters who are not drying their ink are having more difficulty with ink smearing where other liners absorb the ink more readily.

We’re trying to understand the post print Flexo ink chemistry to see if we can make our liner more receptive. I think we have too much ink holdout – not letting it soak in fast enough – but it’s not showing up in Cobb testing.

Sounds like the denser fiber structure is emulation a coating. The easiest answer is to only run orders with this paper on machines with dryers. However, everybody doesn’t have dryers and I understand that. And if you’re using the Mark Andy with label ink to proof your print, you’re correct, you’re trying to proof an apple with an orange.

I’ve reached out to Adam Bland, President of AICC Associate Member company Quantum Ink. Here’s what he has to say.

Adam Bland:

Great questions Jim, and we have certainly formulated hundreds if not thousands of individual formulations for this type of problem specifically on Flexo Folder-Glues (FFGs) without dryers.  When it comes to ink formulation I wrote an article years ago about this particular problem in part, in the Brunton Publication Corrugated Today publication March/April 2019, page 50.

The equation that I use as a simple method to formulate or explain ink formulation for any particular application is: Job Details + Volume (anilox) + Substrate – Limiting factors = Ink Formulation.  To put it simply, FFGs without drying capabilities present one of those “Limiting Factors” in terms of ink drying time vs. run ability, printing clean, penetration, etc.  And as you indicated from the label days, every printing application comes with its own set of limiting factors that dictate the balancing of variables.

As an ink formulator, this would definitely fit the bill for the potential of a “special match” and trial run to work towards eliminating the smear problem while maintaining a user-friendly ink.  Also, potentially making anilox decisions depending on how far ink formulation alone can move the needle.  I can definitely share with you some tactics and ways that I as a formulator would use and or the type of testing I would recommend pre-press as well to have a reliable measuring stick for projected performance.

Honestly, if you can make time for a quick phone call with me that would probably be the best foot forward as there is on one hand a simple way to think about this, and on the other a more complex way depending on how far down the rabbit hole of optimization you want to go across the board including an ink that prints well, lays well in mind along with solving the smearing problem.

— Ralph