Environmental awareness is driving the printing industry to consider other ink systems in order to print more ecological packaging. Water-based inks are often praised as a green solution for a more sustainable product. They are comparatively ecofriendly.
But when it comes to printing inks onto films and plastics, water creates problems. Unless we print on high absorbency substrates, water inks require significant heat to dry and to leave a cured film on the material. In other words, they require energy that negates any positive ecological benefits from their use.
Water has a high surface tension, which can print beautiful perfect dots, but also can create mottled/pinholed solids. This means that, in order to “wet out” on most plastics, the surface tension has to be reduced considerably in order to achieve good print quality and smooth laydown of ink. That is done by adding a surfactant or solvent, which contaminates the water immediately. Depending on the substrate, type of press and printing speed, the amount of solvent can range between 2 percent to 20 percent of the press-ready ink.
Water-based ink is also susceptible to foaming, creating micro bubbles that thicken the ink and create a reduced ink transfer. In order to solve this, the ink can be adjusted with anti foam agents, which in turn create drying issues and trapping problems. Water has to be combined with solvents in order to dissolve the kinds of resins that provide good adhesion on packaging films. In order words—more chemicals.
Switching from a solvent-based to water-based ink cannot be done overnight, because of the different transferring capabilities. It often means modification to the anilox rolls because a shallower, more open cell structure is required to print water-based inks.
And contamination between solvent inks and water-based inks creates an adverse chemical reaction that can result in the ink setting solid. This can lead to having to undergo a major cleaning of the anilox, pumps and pipes. Therefore, a press is required to be dedicated to water-based inks to ensure efficiency is maintained and print is viable.
Water-Based Ink Print Problems
Critics have doubts on the printability of water-based inks as well. They appear to result in:
- Poor scratch and rub resistance (especially just after printing)
- Difficulty re wetting
- Difficulty cleaning
- Comparatively lower gloss and poorer color strength
- Ink sets onto the plates, creating buildup and inconsistent print
- Slow drying and therefore requiring more heat/energy
- A higher risk of clogging inside the anilox cells (especially with low volume anilox rolls)
- Difficulty controlling and guaranteeing a consistent and repeatable ink transfer (because of the pH and viscosity)
Water-Based Ink Print Solutions
Some ink suppliers and machine manufacturers believe that water-based inks are the future of printing. And a major part of the success of printing water-based inks lies in the actual transfer. Many of the issues discussed here can easily be solved when the properly configured anilox roll is used.
Apex International has performed several successful trials with different ink and machine manufacturers.
There were several noteworthy results from the study:
- The shallow surface structure of open slalom laser engraving technology results in no clogging. It is among the most effective ink transfer methods, allowing for the maximum replenishment within the anilox surface compared to the restricted limits of conventional engraving. A very thin layer of ink can be transferred and less drying time is needed
- In a closed cell structure, air gets trapped inside. When it comes to water-based inks, that is an especially disastrous combination. With the open slalom structure, the ink flows freely and the air will not get stuck inside the cell. Less air means a better laydown of ink, and better results on gloss and color strength
- A side effect of having no air inside the print process is the fact that a defoamer is no longer needed, which makes water-based printing an even greener way to print packages
- With an open structure, dot dipping does not occur. The explanation for why this is the case is simple: pressure causes counter pressure, ink escapes through the opening and the result is overinking. The water-based ink does not set onto the plates and will not cause buildup
Many of the print issues stemming from water-based ink that are outlined here can be fixed, and that is a continued step in the direction of a greener flexo future.
About the Author: Jeanine Graat is marketing manager for Apex International. The firm is the creator of GTT Anilox technology.