By Maarten Hummelen, GSE Dispensing
In the fast-paced world of package printing, precision and flexibility are paramount, particularly when it comes to ink formulations. With increasing demands for consistent print quality, shorter runs and the use of various substrates, printers may have to adjust ink recipes more often right before dispensing.
In flexo and gravure, achieving consistent quality depends on several variables. Anilox roll specification and condition, ink viscosity, atmospheric conditions, and printing speed all affect the end-result.
Variables can change reasons both beyond and within the printer’s control – anilox roll wear, changes in humidity or temperature, or the need to go faster in order to ramp up output, for example.
In any of these cases, the printer compensates for such changes by making temporary adjustments – like using ink with a different viscosity or adding more hardener.
Fine-tuning these factors ensures that the ink behaves optimally, delivering the desired colour, adhesion and drying time, while avoiding common issues like over-inking, poor curing, or smudging. But such changes often require adapting the ink recipe to get the right results.
Permanently storing adaptations for each job would be overwhelming for the ink room. With GSE’s Ink manager software, you can define and select standard adjustments on a case-by-case basis, without changing the formula. This level of customization can make the difference between a successful print run and costly downtime.
Let’s look in detail at how users can adapt ink recipes to compensate anilox specifications or conditions, changing atmospheric conditions, and shortened drying times:
Anilox corrections
Anilox corrections in ink recipes involve fine-tuning the amount of ink ingredients to match the specific properties of the anilox roller. The anilox roller, crucial in flexographic printing, determines the amount of ink transferred by holding it in microscopic cells.
Anilox rolls with a low volume (or low BCM – “Billion Cubic Microns”) and a high cell-count (measured in LPI – “Lines Per Inch”) may require lower viscosity inks for better flow. Rolls with a high BCM and low LPI, on the other hand, typically need thicker inks.
A dirty anilox roll can affect ink transfer and reduce color strength on the substrate. Reducing the dilution can help preserve stronger color.
Anilox roll wear can significantly reduce the BCM, meaning that printers may need to shift to higher-viscosity or diluted inks over time, to achieve the desired print quality.
The viscosity of water-based inks can be reduced by adding water or co-solvents, or increased by lowering water-content and adding acrylic thickeners. Solvent-based inks can be thinned with organic solvents. They may be thickened by reducing solvent content or adding resins/thixotropic agents. UV-curable inks can be made less viscous with low-viscosity monomers or diluents, and made more viscous by reducing diluent amounts or adding modifiers.
Accounting for press conditions
Press conditions, including temperature, humidity and press speed, can fluctuate over time or vary with each print job.
Higher temperatures can speed up ink drying, especially in solvent-based systems, causing issues like clogged plates and inconsistent colors. To slow drying, retarders can be added, while faster-evaporating solvents are useful in colder conditions.
High humidity slows drying for water-based inks, which can be managed by reducing water content or increasing co-solvents. For solvent-based inks, adjusting the balance of fast- and slow-drying solvents can help.
For longer press runs, higher speeds require faster drying, achieved by increasing fast-drying solvents and adding catalysts, possibly lowering viscosity. Slower speeds allow more drying time but may need reduced fast-drying solvents to prevent ink from drying on the press.
Adjusting hardeners and promoters
Our experience with flexible packaging printers shows that it is common to adjust ink recipes by modifying the amounts of hardener and promoter.
Hardener (or crosslinker) enhances chemical and abrasion resistance by crosslinking the resin. Promoters (or catalysts) accelerate the crosslinking process, allowing control over drying time, which is vital for high production speeds.
To achieve the right balance between adhesion, durability, and drying time per job, printers adjust the formula before they go to press.
The ‘Additive / Anilox’ function in GSE Ink manager
If you create a new formula for every adjustment to account for the key variables as discussed above, you’ll quickly end up with a vast database of different formulas – causing confusion and increasing the risk of mistakes.
That’s why GSE has included functionality in its GSE Ink manager software to define standard adjustments on existing formulas without the need to create a new one.
With a standard adjustment, the user can change the dispense quantity of any ingredient in a formula – by increasing or reducing the ingredient’s share of the ‘base’ formula that’s stored in the system. Multiple ingredients can be increased or reduced as desired, within the same adjustment. The user then stores this standard adjustment on the system, for future use. You can create as many standard adjustments as you want and modify them on-the-fly, for example, based on the wear of your anilox.
Before going to press, the operator can select the base formula and pick a standard ‘Additive / Anilox’ adjustment from a drop-down list. The software then recalculates the percentage parts of all ingredients and dispenses the adjusted formula accordingly.
After dispensing, a label can be printed with information about the base formula and the adjustment. And for any repeat order, the ink will be dispensed according to the adjusted formula
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