Dirty print in flexo printing

This article is part of the FLEXO FLAW FIXING series

In flexo printing, gear marks, often referred to as chatter or banding, pose a significant challenge to print quality. These defects appear as alternating light and dark lines that run perpendicular to the web direction. They can significantly detract from the visual appeal of printed materials.

Diagnosing Gear Marks

Identifying gear marks requires a keen eye for detail and a tuned ear. The unnatural streaks in your prints, especially in screens and vignettes, are telltale signs. In severe cases, the mechanical irregularities responsible for gear marks may be audible, providing a preliminary diagnostic tool.

Causes and Remedies for Gear Marks

Mechanical Wear and Damage
  • Cause: Continuous operation results in the inevitable wear and erosion of press gears. Without regular attention, this deterioration becomes a significant cause of gear marks.
  • Remedy: Periodic inspections for signs of gear deterioration are critical. Implementing a meticulous maintenance program ensures that all components are kept in pristine condition, and timely replacement of worn parts prevents further damage. Beyond maintenance, investing in high quality gears and components will reduce the rate of wear, providing a longer-term solution to gear marking problems.
Mismatched Gears
  • Cause: Using gears that are not perfectly matched in size or specification will disrupt the smooth operation of the press and cause gear marks.
  • Remedy: Thoroughly checking the compatibility of gears and components – including sleeve/plate cylinders, anilox rolls, and impression cylinders – ensures synchronised operation. Regular wear and compatibility assessments are essential for preventive adjustments to avoid misalignment and the problems it causes. Routine inspection of gear systems for signs of incompatibility or wear helps prevent problems before they manifest as print defects.
Printing Pressure Issues
  • Cause: Pressure imbalance between printing elements, especially between elastomer and photopolymer sleeves or anilox roll and plate, is a direct contributor to gear marks.
  • Remedy: Fine-tuning printing pressures within the recommended range and performing frequent checks will ensure balanced interactions between printing components. This balance is essential for maintaining print quality and avoiding gear marks. Establishing a protocol for periodic recalibration of pressure settings will prevent the gradual shifts that can lead to imbalance and subsequent print defects.
Lubrication and Ink Pressure Concerns
  • Cause: Neglecting to lubricate moving parts can cause premature wear. While unbalanced ink pressure between the doctor blade and anilox roll can exacerbate gear marks.
  • Remedy: Adherence to a strict lubrication schedule and precise control of ink flow are essential to maintaining the smooth operation of press components. These practices not only extend press life, but also ensure consistent print quality. Scheduled evaluations of lubrication systems and ink flow parameters allow for early detection of potential problems, facilitating timely adjustments to prevent gear marks.
Vibrations
  • Cause: Vibrations within the press are usually caused by mechanical or electrical irregularities. They play a significant role in the formation of gear marks. These vibrations can disrupt the even transfer of ink to the substrate, resulting in uneven print quality.
  • Remedy: Modifying press settings to optimise speed and equipment configuration can significantly reduce vibration. In addition, the use of dampening systems or vibration isolators can provide a mechanical solution to this challenge. Regularly checking and adjusting the mechanical and electrical settings of the press to ensure smooth operation minimises the risk of vibration. Conducting regular audits of the press infrastructure to identify and correct potential sources of vibration before they affect print quality is critical.

Conclusion

Addressing gear marks is critical to maintaining the high quality of flexographic printing. By diligently diagnosing, understanding the root causes, and taking proactive measures, printers can significantly reduce the incidence of these defects. Regular maintenance, careful calibration of press mechanics, and adherence to press operation best practices are essential strategies for maintaining print excellence. By taking these steps, the battle against gear marks can be decisively won. It ensures that flexo printing continues to deliver outstanding results.