This article is part of the FLEXO FLAW FIXING series

In the intricate world of flexo printing, smudging and bleeding stand out as critical challenges. They are characterised by the premature spreading and mixing of ink on the substrate, severely compromising print quality. These problems not only affect the visual appeal of the output, but can also result in significant material and financial losses. Overcoming these challenges isn’t just a matter of troubleshooting. It’s about maintaining the integrity of the flexo printing process and ensuring the highest quality printed materials.

Causes and Remedies for Smudging and Bleeding

High Relative Humidity
  • Cause: This cause is a notorious catalyst for smudging and bleeding. Moisture in the air can cause condensation to mix with the solvent-based inks. It largely upsets the delicate balance necessary for clean, crisp prints.
  • Remedy: The remedy is to use fresh ink, adjust the solvent mix, improve the performance of the dryers, and carefully monitor the water content in the solvents. Taken together, these measures will help maintain the proper conditions for ink application and drying.
Excessive Use of Retarder
  • Cause: It slows down the drying process, which is essential for fast and efficient printing.
  • Remedy: Switch to a fresh ink that requires less retarder. Or use a faster drying solvent to speed up the process. This adjustment will ensure that the ink settles quickly, reducing the likelihood of smudging.
High ink viscosity
  • Cause: This is where the thick and sticky nature of the ink can lead to over-application on the substrate.
  • Remedy: The strategic addition of solvent lightens the consistency of the ink. It can greatly improve its manageability and prevent excessive deposition.
Excessive Ink Volume Transfer
  • Cause: This occurs when the transfer mechanism deposits more ink than the substrate can absorb, resulting in smudging.
  • Remedy: Choosing an anilox roller that transfers a lower volume of ink can solve this problem and ensure that the substrate is not overloaded.
Excessive Print Speed
  • Cause: This can outpace the drying capabilities of the ink, making it susceptible to bleeding as it moves across the substrate.
  • Remedy: By slowing down the printing process or increasing the drying speed of the ink, a better balance between productivity and print quality can be achieved.
Improper Colourants
  • Cause: This misuse can directly affect the adhesion and appearance of the ink.
  • Remedy: Carefully selected, compatible colourants help in formulating new ink. With improved formulation, printers can overcome this challenge and ensure that every print meets the desired standards.
Excessive Layers of Ink
  • Cause: This can also cause significant problems as multiple layers may not dry or adhere properly.
  • Remedy: Reducing the number of layers or redesigning the printed image to require fewer layers can significantly improve print clarity and adhesion.
Poor Material & Press Settings
  • Cause: This can lead to substrate failure under the pressure of repeated printing, as well as ink misapplication.
  • Remedy: To avoid these problems, it is important to select high-quality, flexo-compatible materials and ensure that press settings are perfectly matched to the ink and substrate type.

To further reduce the risk of smudging and bleeding, printers should follow several preventive strategies. Preheating the printer before starting a job can improve ink stability, while regularly cleaning the print heads can help prevent buildup that can lead to smudging. Verifying print settings and media quality prior to printing, along with careful text and image placement, can also play an important role in preventing these problems.

In Conclusion

Managing smudging and bleeding in flexo printing is essential to maintaining the high standards of print quality that customers expect. By understanding the causes of these problems and implementing the remedies and preventive measures discussed, printers can significantly improve the accuracy and aesthetics of their output.