Pinholing in Flexo Printing

This article is part of the #FlexoFlawFixing series

Pinholing, characterised by the appearance of tiny, unprinted, pinhole-sized dots, is emerging as a major challenge in flexo printing. Not only does it detract from the visual appeal of the printed product, but it also affects production efficiency.

This article will go straight to the heart of pinholing – its causes and the comprehensive strategies to mitigate it. Addressing this issue head-on is essential to maintaining the integrity of print quality. Thus, we can ensure the seamless execution of print projects.

Comprehensive Approach to Pinholing: Causes and Remedies

Dirty Anilox and Poor Ink Transfer

• Cause: One of the primary causes of pinholing is poor anilox roller cleanliness, which hinders effective ink transfer.
• Remedy: Regular maintenance routines for anilox rollers, including careful cleaning and inspection, are paramount. In addition, adjusting ink formulations to slow the drying process and adjusting dryer settings can significantly improve ink transfer efficiency.

High Ink Viscosity and Fast Drying

• Cause: High viscosity and fast-drying inks create an environment conducive to pinholing.
• Remedy: To counteract this, adjusting the viscosity of the ink to a more optimal level can facilitate a smoother transfer to the substrate. The use of solvents with a slower evaporation rate also helps to ensure that the ink remains transferable for a longer period.

Environmental Factors in the Pressroom

• Cause: Pressroom conditions, specifically humidity, temperature, and air circulation, play a key role in ink behaviour and, consequently, the manifestation of pinholing.
• Remedy: Achieving and maintaining equilibrium in the pressroom environment is critical. Adjusting humidity levels, temperature settings and ensuring effective air circulation can mitigate rapid ink drying and reduce the incidence of pinholing.

Substrate Irregularities

• Cause: An uneven or imperfect substrate surface is fertile ground for pinholing.
• Remedy: The selection of appropriate substrates, together with modifications to the substrate surface treatment, can significantly reduce ink rejection. This ensures a more uniform ink film and minimises the occurrence of pinholes.

Reducing Anilox Cell Spacing

• Cause: For more stubborn cases of pinholing, one might turn to re-evaluating the design of the anilox roller itself.
• Remedy: Reducing the space between the anilox cells improves ink flow. It can be a critical factor in overcoming persistent pinhole problems. This strategy requires a delicate balance to avoid unnecessarily increasing production costs.

Plate Surface Adjustments

• Cause: An uneven plate surface is a possible cause of pinholes.
• Remedy: The creation of microscopic cells on the plate surface is designed to carry more ink, thereby improving ink transfer to the substrate. This approach allows more ink to be applied without disproportionately increasing production costs or compromising the efficiency of the printing process.

Conclusion

Tackling pinholing in flexo printing is a multifaceted endeavour that requires a deep understanding of both the causes and the most effective remedies. From maintaining anilox rolls in pristine condition to optimising the pressroom environment to redesigning anilox roll and plate designs, each strategy plays a critical role in mitigating this pervasive problem.

By taking a proactive approach to these strategies, flexo printers can significantly improve print quality and maintain production efficiency. Pinholing, while challenging, is not insurmountable, and with the right approach, remarkable improvements in print quality are within reach.

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