Flexographic printing works effectively on varied materials like paper, plastic, metallic film, and cellophane to produce a quality job; and presses can be run cost-effectively at extremely high speeds for long runs and large orders.
A great looking design can be ruined if the ink does not adhere properly, causing delays and cost overruns.
The trick is to know how each decision impacts the final outcome. Here are some tips and tricks to help you achieve better ink bonding during the flexographic printing process.
Use The Right Ink For Better Flexo Ink Bonding
Flexographic printing can use a wide range of inks, but the different types will adhere differently to the substrate:
Water-Based Inks
Because these inks generally have the highest surface tension and they work great for printing on corrugated packaging and other absorbent substrates. With the proper surface treatments, they also work well on film.
Solvent-Based Inks
Composed mainly of alcohol, acetate, and pigment, solvent-based inks have a lower surface tension and quicker drying time than water-based. They are usually used for printing flexible packaging or industrial films.
Curable Inks
These inks are composed of monomers, prepolymers, photo initiators, and pigments that dry and adhere only when exposed to an ultraviolet light or electron beam. They have a higher viscosity and are appropriate for the outer wraps of food packaging.
Additionally, they provide excellent resistance to chemical and physical degradation without additional protective varnish and are commonly used for label printing.
Oil-Based Inks
These can be composed of hydrocarbons and pigments, but some of the solvents can be very harsh. These inks are used most often for printing publications and medical charts/ graphs.
Best Practices for Flexographic Ink BondingIn theory, any ink in the right formulation could work on nearly any substrate, but some combinations just work better than others. Other considerations to keep in mind include:
Surface Tension
Since inks naturally want to flow to the higher dyne level, the ink should be at a lower dyne level, the printing surface should be at a higher level, and the substrate should be at the highest dyne level. This allows more ink to transfer and bond to the substrate.
We have a complete guide to measuring surface tension here!
Substrate Absorbency
If the substrate is absorbent, both water-based and solvent-based inks dry satisfactorily. If the substrate is non-absorbent, then it becomes harder to ensure that the ink dries properly. Make sure that your non-absorbent film is treated higher than your inks.
Additionally, working with solvent-based inks and curable inks may also help with absorbency issues.
- For solvent-based inks since they dry by evaporation, a treatment method that increases surface tension is best for optimizing adhesion.
- For water-based inks, the substrate surface should be about 10 dynes/cm higher than the surface energy of the ink so that the ink resin and binder can adhere effectively.
- Curable inks generally have a high surface tension, which means the surface energy must also be quite high.
Best Materials for Flexographic Image Carriers
The final piece of the better ink bonding puzzle is the material of the flexographic image carrier itself. The choice of elastomer sleeves, cylinders, and plates versus photopolymer sleeves, cylinders, and plates affects how well the selected ink is transferred onto the specific substrate.
If you’re looking to optimize your ink bonding, talk to a printing expert about your options. Luminite has 30+ materials to choose from, and one of our experienced printing technicians can walk you through the best options for your ink bonding.
Editor's Note: This article was originally published on July 2, 2018 and was updated on July 29, 2019 to reflect updated information and additional resources.
