Think About Ink
How to Fix Poor Print Results
Often, when we’re approached with questions regarding print defects, it is difficult not to sound like a politician, blaming everyone but ourselves. Potential plate material defects must be considered, and due diligence demands inspection of plate-making files and, for corrugated printing, hand brayed proofs to verify that the plates were correct when delivered. Many times the issue turns out to be the ink.
Water-based ink, most often used in flexographic printing, has a number of difficult tasks to perform. Adding to the challenge, the fact that it is ‘water-based’ means it is affected by many factors including ambient conditions in the pressroom.
Consider the changes you may have noticed over the course of a long press run. Once the plates are in register, the press settings have been established and color has been approved… there’s nothing left to monitor over the next several hours until the run is complete, right?
Surprise! Somehow the color of the last sheet doesn’t match the approved sheet.
But how? The plates are the same. The press settings weren’t changed. The paper was all from the same lot. Even the same kits of ink are still in the press. So, what has changed?
Being able to appropriately identify and remedy ink issues on press can save you a lot of time and finger pointing at other variables. Ink can become a hazardous variable simply because of its inherent volatility.
This is due to a number of reasons, some of which we will discuss in this article.
When printing, the consistency of the ink may be affecting your prints, perhaps leaving defects like dot bridging and filling in.
If working in a hot environment, some components within the ink evaporate. When this happens, the shades of color alter, reds, blues, or greens for instance, won’t quite look the same or may also appear less visible.
PH, which stands for potential for hydrogen, must be controlled throughout the printing process so the ink re-wets first down to the last down. As a general rule: the first down ink has the highest pH, usually around 9.8 and should be kept above a pH of 9.2 for best printing results.
The consistency of the ink, whether it’s runny or thick (i.e. viscosity), has an enormous impact on how the ink is released from the anilox roll to the image carrier and then to the substrate. Be sure to measure the viscosity with a Zahn cup or similar instrument to maintain consistency. If you’re unsure of what adjustments to make when viscosity changes (helpful hint: most often the correct answer is NOT “add more water”), consider hiring an ink specialist for your more impactful print runs.
Particles in the air may affect the ink used in your print run, and thus affecting your printing results. When dust contaminates the ink, it runs the risk of altering the ink consistency.
To reduce contamination, keep your printing area clean, cool, and running for as little time as possible to prevent the build-up of dust and other contaminants. Your specific environment, location and print set up all affect your level and rate of ink contamination. If you find you are having issues, consider going through an environmental ink study with an ink professional.
Ink build up on Plate
Screened flexographic plates are made up of many tiny dots. The separation between the dots creates a valley that fills up with ink as it continually re-wets throughout a print run. Depending on the type of plate you have, you may find that you are taking down plates and cleaning some more often than others. If you are someone who is constantly pushing for faster print-runs, consider choosing a patented PRP ExSpect® plate that has deeper valleys providing for less press down time and higher quality print to help meet your deadlines.
When it comes to ink, you get what you pay for
If producing irregular prints, it’s worth hiring an in-house ink specialist. This ensures your ink is consistent, producing high-quality results, and avoiding defects on each print run. Likewise, if possible, try not to re-use old ink on a new job as this may result in poor overall print quality.
Remember: Next time you face poor printing results, check the ink first as that is the variable you can control on press