The primary goal of flexographic printing is to keep the finished product of high quality. This must be accomplished in the face of increasing productivity, reducing waste, and lowering costs.
Although great strides have been made toward these objectives, printers may still encounter issues when printing on various substrates. Consider the following troubleshooting tips if your print shop is having problems with flexo printing on film substrates.
Dissecting the Root Causes of Flexo Printing Defects
Each flexographic printing flaw has its distinct flavor, with its distinct style and cause. Unfortunately, they can take time and diligent research to solve.
That’s how troubleshooting works. Here’s a quick look at the 2 most common defects we see, their symptoms, and what might be causing them.
1. Excessive Dot Gain
Every print has dot gain. Indeed, this is the essence of flexographic printing. But there is a problem when it becomes excessive.
Appearance: Images appear darker and, in some cases, lower resolution than intended.
Most likely causes: There may be too much pressure between the printing sleeve/cylinder/plate and the substrate. Choose in-the-round (ITR) elastomer sleeves to avoid swelling because they are extremely durable and resistant to swelling.
Here are a few more possibilities:
- Incorrect ink viscosity
- Too much anilox cell volume
- Dots dipped into anilox (cell count too low)
- Press damage or wear
- Dirty image carrier
- If using plates, the mounting tape is too thick or there is trapped air
More information on how to troubleshoot and repair dot gain can be found here.
2. Gear Marks
This is frequently also called gear chatter or banding. Avoiding this flexo printing flaw necessitates regular press monitoring and maintenance. In a nutshell, machinery wears out and breaks down, and it is critical to keep it running.
Appearance: On the press, alternating lines of light and dark typically run perpendicular to the web’s direction.
Most likely causes: Gear marks are caused by press mechanics and excessive pressure. Gears deteriorate over time, with teeth eroding and even breaking. Improperly sized gears will not mesh properly, resulting in imbalance and bouncing.
Other potential causes:
- Poor drive gear lubrication
- Pressure tolerances of elastomer sleeves/plates and photopolymer sleeves/plates
- Inadequate cleaning
Printing Issues Associated With Flexo Printing on Film
Printing on film, according to the FTA, presents unique challenges. Common flicks presently in use include polyolefins (polyethylene and polypropylene), polyamide, and polyester.
Films are generally non-porous, extremely smooth, and relatively flexible, with veritably low shell energy. Some of the issues associated with flexo printing on film substrates are as follows:
Because films are typically non-absorbent and have low surface energy, wetting can be a unique challenge. The ink can pull on itself, prompting pinholes and fish eyes. To avoid this printing flaw, the surface energies of the ink, image carrier, and film must be closely aligned.
Elastomer image carriers provide much more flexibility and control than standard photopolymer plates due to their wider range of surface energies. An inline surface treatment, for example, corona treatment, flame, or plasma can be utilized to raise the film’s surface energy.
2. Substrate Wrinkling:
Some film substrates can be extremely flimsy, which can prompt wrinkling on the off chance that the strain isn’t changed as expected during the printing system. The material must be taut enough to avoid web breakage while remaining flexible enough to flow through the print rollers.
3. Ink Flaking:
Because the film does not absorb ink solvents, all ink drying must take place on the surface. The ink that does not dry properly may not adhere to the film surface and may flake off or come off when the material is flexed. This could be due to insufficient ink, viscosity, surface tension, solvent, or drying procedure.
4. Film Variants:
As the printing and packaging industries evolve, new substrates are introduced that may put previous processes to the test. Traditional plastic films are being replaced in some cases by biodegradable and compostable films, which may not respond in the same way during printing. Research on this variable has tracked down a relationship between optical thickness and wettability, as well as surface free energy.
How to Solve Common Film Flexo Print Issues
Poor print quality, inefficient drying, clean-up issues, and other mishaps can all be problems when flexo printing on film. Tips on the best way to further develop the interaction include:
- Drying: Select an ink that will dry and adhere properly.
- Wetting: To achieve maximum adhesion, use inks that can completely wet the film surface.
- Tension: Change the pressure to keep the film adequately close.
- Contamination: Maintain the image carrier and anilox in good working order, and keep an eye out for dried ink and other particulates.
- Anilox: Pick an anilox with cells that help the fitting ink move volume.
Flexo Problem Still Not Solved?
Contact a flexographic printing expert for more information on troubleshooting flexo film printing problems to minimize dot gain, reduce wrinkling, maximize ink coverage, and produce vibrant colors.