How to Fix Ghosting in Flexo Printing | 5-Step Troubleshooting Guide

Defining the Problem: What is Flexo Ghosting?

In the world of high-quality packaging, few defects are as frustrating as ghosting. It appears as a faint, unintended replica of a design element—typically a shadow or a lighter area—repeating itself in the solid background of the print. For converters, this means wasted substrate and costly downtime.

Ghosting is rarely caused by a single factor. It is usually a symptom of a mismatch between the ink consumption rate and the ink replenishment capability of the press. To resolve it, operators must move beyond guesswork and follow a structured diagnostic path involving ink chemistry, mechanical settings, and anilox condition.

1. The "Ink Starvation" Phenomenon

The most common culprit is mechanical ghosting, often referred to as anilox starvation. This occurs when the anilox roll cannot refill its cells with ink quickly enough to supply the printing plate for the next revolution. If a design has a heavy solid area followed immediately by another image, the anilox may be depleted, resulting in a density difference that looks like a ghost image.

To combat this, ensure your chambered doctor blade system is functioning correctly. Increasing the flow rate of the ink pump can sometimes help refill the cells faster. Additionally, verify that the anilox volume is sufficient for the coverage required by the artwork.

2. Optimizing Ink Viscosity and Drying Speed

Ink chemistry plays a pivotal role. If the ink dries too slowly on the plate, it can re-transfer back onto the anilox or substrate in unwanted areas. Conversely, if the viscosity is too high, the ink will not flow evenly out of the cells, exacerbating the starvation issue described above.

Regular monitoring is essential. Use a Zahn cup or an automated viscosity control system to keep the ink within the manufacturer's recommended range. For challenging applications, such as printing on Paper Cup Printing Machines where heavy ink coverage is common, switching to a faster-drying solvent blend or increasing the dryer airflow can significantly reduce ghosting artifacts.

3. Mechanical Checks: Plate and Impression Settings

Physical vibrations, known as "press bounce," can also mimic ghosting. This happens when the printing plate is not mounted securely, or when there is a significant gap in the plate cylinder design, causing the cylinder to lose contact with the substrate momentarily.

Operators should check that the plate mounting tape (sticky back) is of the correct hardness. Using a softer cushion tape can help absorb the shock and reduce bounce. Furthermore, over-impression (too much pressure) allows ink to accumulate on the edges of the dot, leading to a slurring effect that looks like a double image. Always back off the pressure to "kiss" contact settings.

4. Pre-Press and Design Adjustments

Sometimes, the solution lies in the artwork itself. If a layout features a large solid bar running parallel to a fine text block, ghosting is almost inevitable due to the uneven ink draw.

Pre-press engineers can mitigate this by distributing the artwork differently across the web or by adding "bearer bars" (solid strips on the sides of the waste matrix) to help stabilize the cylinder and ensure consistent ink draw from the anilox. Changing the screen angle or dot shape can also help mask the visual appearance of ghosting without changing the press mechanics.

Summary: A Quick Checklist for Operators

Before calling for service, run through this quick isolation list:

• Clean the anilox roll thoroughly to remove dried ink residue.
• Check and adjust ink viscosity to a lower, more fluid level.
• Reduce impression pressure between the plate and the substrate.
• Increase the ink pump speed to improve anilox refilling.
• Inspect the plate mounting tape for air bubbles or lifting edges.

By systematically eliminating these variables, you can restore print consistency and minimize material waste.