In the flexographic printing process, the "ghosting" issue manifests like an elusive, invisible flaw. It subtly appears at the edges of printed images or within large solid-color areas, compromising the overall visual effect. This not only affects aesthetics but also degrades product quality. This phenomenon is not accidental; rather, it stems from the combined influence of equipment, process, materials, and operational factors. To eradicate this problem, a deep understanding of its root causes and systematic optimization measures are essential.
Ghosting often originates with the printing plate used on the flexographic printers. When plate engraving precision is insufficient or dot distribution is uneven, ink transfer becomes unbalanced. Furthermore, if plate hardness is too high or too low, it impacts ink release performance. Additionally, improper plate mounting causing uneven local pressure can lead to ink piling or starvation, laying the groundwork for ghosting. The adjustment of printing pressure is equally critical. Excessive pressure can cause ink to squeeze and spread, creating doubling (heavy shadow); insufficient pressure results in inadequate ink transfer, causing faint shadows. In multi-color printing, matching the pressure across color units is particularly crucial, as even minor discrepancies can affect registration stability.
Ink properties are also vital. Viscosity that is too high or too low affects leveling and transfer efficiency; inappropriate drying speed may cause uncured ink to transfer secondarily; poor pigment dispersion can lead to local sedimentation, forming uneven ink films. The substrate's influence is significant too. Materials with poor ink absorption (like certain plastic films) prevent uniform ink adhesion; uneven substrate elasticity causes inconsistent deformation under printing pressure; unstable surface tension severely compromises ink wettabilityon the flexographic printers.
To eliminate ghosting entirely, action must start at the source. Firstly, during plate making for the flexographic printers, high precision should be pursued. Laser engraving technology should ensure uniform dot distribution, and plate hardness should be selected based on the characteristics of the printed design. Pressure adjustment requires meticulous attention, adhering to the "principle of light-pressure printing" – minimizing pressure while ensuring sufficient ink transfer. Ink formulations should be tailored to the substrate, optimizing viscosity and drying speed. For non-absorbent materials, corona treatment can enhance surface tension. Simultaneously, strict control of the workshop's temperature and humidity environment is essential to create ideal printing conditions.
Flexo printing machine stability is paramount. Regularly calibrating roller concentricity, checking gear and bearing wear, and promptly replacing aged components can effectively reduce the impact of mechanical vibration. In production, appropriately reducing printing speed allows more time for ink transfer and drying, especially crucial for fine-detail printing. Furthermore, establishing standardized operating procedures and quality monitoring systems is indispensable. Implementing first-article inspection and real-time color management can nip ghosting problems in the bud.
With the advancement of smart manufacturing, new AI vision inspection systems integrated into the machine impression flexo can now capture ghosting in real-time and automatically adjust printing parameters using machine learning algorithms. This technology is particularly suitable for high-speed CI (Central Impression) presses, reducing the time to detect and address ghosting by over 90%.
Video Introduction
Below is the workflow of the plastic films stack flexo printing machine.
Long-term ghosting solutions demand strategic planning beginning at the equipment selection stage.For businesses primarily printing on films, CI flexo presses may be the better choice; packaging printers with diverse products might prioritize the flexibility of stack-type presses. Regardless of the chosen machine impression flexo, deeply understanding its operating principles and establishing a preventive maintenance system are fundamental to eradicating ghosting.
