Printing Flaws

[Flexo Flaw Fixing] Ink Build-up around Screen Dots

This article is part of the FLEXO FLAW FIXING series

Achieving pristine print quality is paramount in flexo printing. A common challenge that can significantly hinder this goal in flexo printing is ink build-up around screen dots. This phenomenon not only affects the clarity and sharpness of the printed image, but also leads to a variety of print inconsistencies. Addressing this problem requires a deep understanding of its causes, consequences and, most importantly, the implementation of effective remedies.

Causes and Remedies of Ink Build-up

Anilox Roller with High Transfer Volume
  • Cause: The core of the problem often lies with the anilox roller, specifically when it transfers an excessive amount of ink. This excess leads to an excess of ink on the plates which, if not properly managed, will build up around the screen dots.
  • Remedy: The remedy is simple, yet effective. Using an anilox roller designed to transfer a smaller volume of ink can significantly mitigate this problem, ensuring that just the right amount of ink makes it onto the plate and ultimately onto the substrate.
Low Printing Speed
  • Cause: Another factor that contributes to ink build-up is press speed. If the speed is too slow, the ink has more time to dry and build up on the screen dots, disrupting the uniformity of the print.
  • Remedy: The solution is twofold: first, make sure the plate is clean and free of previous build-up. Second, increasing the printing speed can help maintain the fluidity of the ink so that it transfers more smoothly from the plate to the substrate.
High Ink Viscosity
  • Cause: Ink viscosity plays a critical role in the quality of flexographic printing. High viscosity can hinder seamless ink transfer, resulting in build-up around screen dots.
  • Remedy: Adjusting the ink viscosity to a lower, more appropriate level can significantly reduce the risk of build-up and promote cleaner, more consistent printing.
Usage of Incorrect Solvents
  • Cause: The choice of solvent is also critical. The wrong solvents can lead to poor ink performance and, consequently, increased build-up.
  • Remedy: If solvent compatibility problems occur, the solution is to replace the ink with one formulated with solvents appropriate for the specific printing process and materials being used.
Excessive Pressure Between Plate Cylinder and Substrate
  • Cause: Excessive pressure between the plate cylinder and the substrate can squeeze the ink, increasing the likelihood of build-up.
  • Remedy: Adjusting the pressure settings to an optimal level can prevent excessive squeezing of the ink, thereby reducing build-up and ensuring high-quality prints.
Unsuitable Ink Recipe
  • Cause: The ink formulation itself can sometimes be a source of problems. If the ink formulation is inappropriate for the materials or the printing process, it can lead to compatibility problems and, as a result, ink build-up.
  • Remedy: Selecting or formulating an ink formulation that is tailored to the substrates and process can significantly mitigate this problem.
Worn Printing Plate
  • Cause: The condition of the printing plate is another influencing factor. A worn plate, especially one with reduced relief depth, can impede effective ink transfer and increase the risk of build-up.
  • Remedy: Replacing the plate with one that has the optimal relief depth can ensure effective ink transfer and reduce the likelihood of build-up.
High Relative Humidity
  • Cause: Finally, environmental factors such as high relative humidity can exacerbate ink build-up problems. The condensation of water in solvent-based inks can alter the behaviour of the ink, making it more susceptible to build up.
  • Remedy: A proactive approach that includes adjusting solvent formulations to include retarders and anhydrous solvents can help counteract the effects of high humidity on ink performance.

Advanced Technologies and Solutions

Technological advances and material innovations also offer promising solutions to the ink build-up challenge. For example, new anilox rollers and plates designed to optimise ink transfer and reduce waste can have a significant impact. In addition, advanced ink formulations specifically designed to minimise build-up can further improve print quality and consistency.

In Summary

Managing ink build-up around screen dots in flexo requires a strategic, multi-faceted approach. By understanding the various causes and implementing targeted remedies – from adjusting equipment and ink formulations to optimising environmental conditions – printers can significantly improve print quality and consistency.

Continual adaptation and adoption of advanced technologies are also critical to staying ahead of challenges such as ink build-up and ensuring that flexography remains a vibrant and quality-driven field.