Doughnut Effect in Flexo Printing

What Is The Doughnuts Effect?

The screen dots on the print have a smudged or distorted appearance. This doughnut effect flaw in flexo printing is not a delectable confectionery delicacy. It’s an inconvenient and perhaps costly condition to have.

Causes of Doughnut Effect in flexo printing

While pressure is another possible source of doughnuts, cylinder or plate swelling is the most likely culprit. Aggressive inks and solvents can cause printed materials to expand and distort, rendering pictures virtually unintelligible.

A potential approach is to use more solvent-resistant, direct-laser engraved (DLE) ITR elastomer sleeves. Other possible reasons include Conformity of print-to-web speed, pressure, Ink transfer, etc.

The Appearance Of The Doughnut Effect

You will see slurred and warped screen dots with blank or semi-blank areas in the center. They resemble lopsided doughnuts.

What Are The Flaws Of The Doughnut Effect In Flexo Printing?

The good news is that the likely causes of doughnuts are minimal and reasonably simple to correct. You’re most likely dealing with key, potentially interconnected causes:

• Plate/cylinder enlargement
• Printing pressure
• ink transfer speed (viscosity and draw)
• Conformity of print-to-web speed 

1. Plate/Cylinder Enlargement

Swollen flexo printing plates or sleeves are more significant than they were initially. As is the picture it bears – and if you’re lucky, the image won’t be distorted beyond recognition.

Flexographic printing plates typically expand due to strong inks and solvents. However, the inks may be just incompatible with your image carrier. If there is still excess solvent on the plate, you may need to extend the drying time during processing.

You may consider in-the-round (ITR) elastomer sleeves to be the panacea. ITR elastomer sleeves withstand abrasive chemicals, heat, and frequent usage wear. In addition, they can print continuously for 2 to 4 times as long as typical photopolymer plates.

2. Printing Pressure

Flexographic printing is a pressure-sensitive method of printing. If there is too much pressure between your printing cylinder and your substrate, you may have significant picture quality concerns; if there is too little pressure, not enough ink will transfer to your substrate.

If you see doughnuts in the printed dots, you may be using too much printing pressure. To troubleshoot, adjust the pressure as needed. If you’re successful, the dots will self-regulate, and you’ll have spent minimal time and substrate in the process.

3. Ink Transfer Speed

The right amount of ink to wet out on the substrate is essential for high-quality printing. Again, too much or too little will result in a poor-looking reproduction. 

Ink transfer starts with the anilox roll transferring the appropriate amount of ink to the image carrier, which then transfers it to your printed substrate.

When not enough ink reaches the substrate, the anilox roll may have decreased cell volume or a build-up of dried ink, hindering smooth transfer. However, if doughnuts form, it is most likely because your ink viscosity is too low or your ink has too much draw. 

To remedy these problems, Adjust the thickness and tackiness using solvents to avoid becoming too thin and runny.

4. Conformity of Print-to-Web Speed

It’s not so much an issue of whether your web is traveling too quickly or too slowly through the press as it is of whether it is moving at the same rate as the print cylinder. 

If they’re out of sync, image skewing is unavoidable. However, it shouldn’t take too much testing to get them back in sync, and you shouldn’t spend too much press downtime.

How to Overcome Doughnuts effect?

Elastomer Sleeves Solve ‘Doughnuts’ in Flexo Printing. Instead of eating the doughnuts, solve them.

The machines are frequently stopped to correct flexo printing faults. However, doughnuts in your prints may be easily solved if you investigate them:

• Condition of the plate/sleeve
• Synchronization of Pressure and Speed
• Transfer of ink

Let us not squander press downtime or substrate.

A Solution To Prevent The Doughnuts Effect In Flexo Printing

1. Set the printing pressure to the regular setting.
2. Make use of softer printing forms and mounting tape.
3. Using the appropriate solvent, check and adjust the ink drawing.
4. Return the viscosity to its original level.

Featured image source: https://blog.luminite.com/hs-fs/hubfs/Doughnuts.jpg?width=510&name=Doughnuts.jpg

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