Identification of gear marks in flexographic printing is an uncomplicated task, as they manifest as alternating linear areas of light and dark that traverse perpendicular to the web directly on the press, frequently appearing at periodic intervals across the substrate. Commonly known as chatter or banding, the origin of gear marks is a pressing issue. How do you rectify it?
Of the dozen common flexo printing defects that are encountered frequently, gear marks have the fewest primary causes: press mechanics and pressure. Nevertheless, numerous potential concerns within these two causes can ruin the print’s quality.
A glimmer of hope lies in the fact that in severe instances, off-kilter press mechanics can be heard during the printing process. Now it’s time to get down to brass tacks and resolve this pesky issue!
Flawless Printing: How to Identify and Overcome Gear Marks in Flexographic Printing
Likely, you’ve already identified the issue at hand. Those abnormal linear patterns that disrupt the flow of your images, especially in screens and vignettes, are quite distinctive.
While other defects in flexo printing can be remedied by making adjustments to the ink transfer characteristics or performing regular upkeep on cylinders, sleeves, and plates, gear marks are typically caused by wear and tear on the mechanics of the press. In certain cases, it may be necessary to perform maintenance or replace parts to ensure that your press continues to operate smoothly.
| Gear Marks | |
| Symptoms: A set of printed lines running parallel across the surface. The lines will match and appear at regular intervals. | |
| Why? | Fixes |
| Incorrect/damaged gear | Check gear condition and size |
| Base is undersized | Check base diameter |
| Too much pressure between the anilox roll and the printing form | Adjust printing pressures to normal levels, and monitor ink transfer on printing form and anilox |
| Too much ink pressure in the doctor blade chamber | Control the ink flow to/from the ink chamber and ensure the anilox cell volume is correct |
| Image positioning on the printing form is lacking balance | Alter the layout of the design and/or plates |
| Concentricity (total indicated runout or T.I.R.) of rotating parts (printing form, anilox) are out of tolerance | Adjust the concentricity of the printing form and the anilox roll |
| Vibrations of the printing press due to mechanical or electrical issues | Adjust the printing form package to best accommodate the press and its speed setting |
| The printing form or plate/tape package is too thin | Modify printing speed to reduce vibration or harmonic effects at certain speeds |
| Examine the printing press to identify and address any additional issues or malfunctions. | |
The Secret Culprit behind Poor Printing: Worn Gears and Their Impact on Flexographic Printing
Paying attention to the sounds your press makes is crucial when dealing with severe gear issues. Monitoring the wear and tear of gears over time is also important. When gears become worn, they tend to produce gear marks in a uniform pattern within your printed image.
It’s important to note, however, that these marks may not always correspond to the location of the damaged gear tooth, but instead, may result from the uneven bouncing that arises from the imbalance of the gears. It is imperative to regularly clean and lubricate the drive gears to facilitate the perfect meshing of gear teeth.
Poor lubrication could lead to gear grinding, which may cause the aforementioned bouncing on the press. Over time, gear teeth may wear down or sharpen, leading to increased space between them. This can result in gear backlash vibration, which further contributes to bouncing on the press.
Perfecting the Pressure: Achieving Optimal Tolerances between Elastomer and Photopolymer in Flexographic Printing
In general, those who are accustomed to using traditional photopolymer may be accustomed to applying more impression force than is necessary for in-the-round (ITR) elastomer sleeves or cylinders. With the precision grinding and robustness of elastomer, a mere kiss impression is sufficient to achieve a high-quality print.
The Missing Piece of the Puzzle: Solving Printing Problems Caused by Mismatched Gears in Flexographic Printing
Ensure that your gear has the appropriate number of teeth for the desired print repeat, as well as the right pitch and tooth angle. The sleeve/plate cylinder, anilox, and impression cylinder must rotate in perfect harmony to produce a quality print. When the gears are mismatched, the speeds will be affected, leading to vibrations on the press and producing uneven impressions or gear marks caused by excessive or insufficient impressions at regular intervals.
Unlocking the Mystery: Understanding the Many Causes of Gear Marks in Flexo Printing and Their Connection to Pressure and Press Mechanics
Performing regular cleaning and maintenance can help prevent various flexo printing defects. However, if you encounter gear marks in your prints, there is a possibility that you might be able to audibly determine the cause of the problem.
Read next about: Demystifying Mottled Print for Optimal Flexo Printing Quality