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Flexo printing machines are environmentally friendly and highly efficient. Flexographic printing machine technologies and processes are rapidly evolving. However, due to varying technical capabilities, flexo printing machinery often encounters problems during the printing process, such as misregistration, burrs, and hollow dots. This presents significant challenges for companies producing paper cups, such as fruit paper cup, coffee paper cups, milk tea paper cups, and juice paper cups. This article lists four common flexographic printing issues—burrs, hollow dots, missed prints, and misregistration—and their solutions.

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Burrs

Burrs are irregular, jagged edges or irregular overflows of text and images printed on a flexo press. Ink, static electricity during printing, substrate surface cleanliness and tension, and the drying speed of the equipment can all affect the appearance of burrs on cold beverage paper cups, bubble tea paper cups, cake paper cup and Coke paper cups.

Ink

Ink viscosity is too high or dries too quickly.

This problem doesn't necessarily arise from excessive ink viscosity; it can also occur with lower viscosity. Sometimes the ink dries partially on the plate, and then transfers with the surrounding scabs, causing burrs. Generally, at room temperature of 25°C, the ideal pH for ink is between 8.5 and 9.5.

Excessive ink loading: Excessive ink loading can increase ink concentration around dots, causing burrs. In this case, choose an anilox roller with a high line count or low ink loading.

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Printing Static Electricity

Printing static electricity can also affect ink transfer, causing rough edges on beer paper cups, wine paper cups, beverage paper cups, pudding paper cups and cola sprite cups. Corona treater can reduce or eliminate static electricity.

Substrate Surface Cleanliness and Tension

Excessive lint or fine dust on the substrate surface can also cause rough edges. Therefore, it's important to clean the substrate surface promptly.

Inappropriate substrate surface tension can sometimes affect ink penetration, causing ink to accumulate on the surface and become difficult to spread. Generally speaking, the substrate surface tension should be slightly greater than the ink surface tension.

Drying Speed of the Equipment

If the drying speed is too fast, the ink will not level properly. In this case, you can add some retarder to slow down the drying speed of the ink on the substrate surface, making the ink more even.

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Hollow Dots

Hollow dots are common in flexographic presses, primarily due to excessive printing pressure. Low ink adhesion can also cause the dots to lose their ability to hold ink, resulting in a hollow appearance. This can be corrected by using an appropriate amount of ink conditioning oil. Low ink viscosity can also cause similar problems, so be aware of changes in ink viscosity.

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Missed Prints

Missed prints occur when the ink is very light or completely missing in certain areas on printed products such as hot chocolate paper cup, popcorn paper cup, jelly paper cup, soda cups, latte cups, and milkshake cups. Missed prints are primarily caused by insufficient printing pressure or the surface condition of the printing plate.

Printing Pressure

Inconsistent contact pressure between the anilox roller and the printing plate, and between the printing plate and the substrate, prevents effective ink transfer.

Printing Plate Surface Condition

Oil stains, depressions, or insufficient plate thickness can also cause missed prints. These can be removed with alcohol or by replacing the printing plate.

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Misregistration

Misregistration is a common flexographic printing failure caused by inaccurate color group positioning, which results in blurred or even distorted printed images.

Printing Plates

Currently, film output is quite good, and the vertical and horizontal spiral inclination of the film output should have little impact. However, calibration standards vary between manufacturers.

Plate Mounting

Generally speaking, the starting registration lines are located at the center of the printing plate. This allows the plate to be mounted to the sides, minimizing significant errors. This assumes the plate mounter is calibrated in advance.

Flexographic Printer Models

Different flexographic printers have different factory-set overprint accuracy settings. For example, inline flexographic machines typically have an accuracy of 0.2mm, while central drum flexographic printing machines have an accuracy of 0.15mm.

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Despite continuous technological advancements, flexo presses still face various challenges in actual production. However, by gaining a deeper understanding of issues such as burrs, hollow dots, missed prints, and misregistration, and implementing appropriate solutions, we can effectively reduce these issues, improve print quality and production efficiency, and provide a more environmentally friendly and efficient production experience for companies producing paper cups such as ice water paper cups, yogurt paper cups, ice cream paper cups, lemonade paper cups, and cappuccino paper cups. This will help companies stand out in the fierce market competition and achieve sustainable development.