Industry News

Flexographic printing machine as a widely used printing equipment, its printing quality is affected by many factors. In the actual production process, problems such as speckling, missing print lines and color variation occur from time to time. These problems not only affect the appearance quality of coffee paper cup, ice cream paper bowl, pet food paper bag, chocolate bar paper box, mineral water bottle labels, etc., but also may lead to reduced productivity and increased costs. In this paper, we will analyze the causes of these problems and improvement measures to improve the printing quality and production efficiency of flexographic press.

Inline Type Flexo Label Printing Machine for Wine Beer Bottle Label

Speckling

Speckling is one of the common problems in the flexo printing process. It is mainly manifested as irregular color dots or color blotches on the surface of printed products such as cupcake paper cup, paper jewelry boxes, rice packaging bags, aluminum foil soya bean milk packaging bag, fries chicken kraft paper box, etc.

What Causes Speckling

First of all, uneven coating or thickness of substrate can lead to uneven distribution of ink in the flexo printing process, resulting in speckling. Secondly, incorrect printing pressure can cause poor contact between the printing plate and substrate, which affects the transfer effect of ink. In addition, coated or exposed fibrous tissue on the surface of the substrate may also cause the ink to fail to adhere uniformly, resulting in speckling. Ink viscosity that is too low or too much water added to the ink resulting in a loss of balance will cause the ink to flow too much during the printing process, making it prone to speckling. Uncleaned or stuffed anilox rollers can affect the transport and distribution of the ink, which can lead to the formation of speckling. Contamination of the ink on the flexo printing machinery and a low pH value of the ink can also lead to a change in the ink's properties, affecting the quality of flexo printing. Poor ink formulation can also lead to speckling.

Central Impression Flexo Press for Beverage Paper Cup

How to Avoid Speckling

For speckling, the following improvement measures can be taken:

Increase the Printing Pressure, Ink Viscosity & Ink Transfer Volume to make the ink layer thicker.

Use A Low-Durometer Printing Plate or Change the Ink Formulation to improve the ink transfer effect and adhesion properties.

Adjust the Printing Pressure to ensure good contact between the printing plate and substrates.

Replace the Substrates or Check the Ink Supplier for Related Products or Additives to ensure the quality of the material being printed and the ink.

Add Fresh Ink to increase the ink viscosity and improve the printing performance of the ink.

Clean or Replace Anilox Roller to ensure smooth and even ink delivery.

Clean the Printing Unit to replace the ink to prevent ink contamination on the printing quality.

Check and Adjust the PH Value of the Ink to keep it within the proper range.

Ask the Ink Supplier's Advice to optimize the ink formulation.

Stacking Type Flexographic Machine for Hamburger Wrapping Paper

Missing Print Lines

Missing print lines are white lines that appear on the surface of printed materials such as ice cream paper cups, sandwich wrappers, baking paper bags, soup paper bowls, potato chip bags, wedding cake paper packaging boxes, and so on.

What Causes Missing Print Lines

Two-roller inking system may cause uneven ink supply, resulting in missing print lines. A clogged or damaged Anilox roller, an overly wide cell wall, or an overly large LPI will cause uneven ink distribution during the delivery process, resulting in missing print lines. A Gigh-durometer printing plate will reduce the printing plate's ability to adsorb ink, affecting the ink transfer effect. Too low ink viscosity will make the ink too fluid during printing, making missing print lines more likely to occur. The overly smooth surface of the flexo printer's printing plate will result in insufficient ink adhesion. Improper ink formulation may also lead to missing print lines.

Stacked Type Flexographic Printer for Candy Paper Bag

How to Avoid Missing Print Lines

For missing print lines, the following improvement measures can be taken:

Reduce the Ink on the Surface of the Anilox Roller, improve the supply and distribution of ink by increasing the pressure of the ink roller, using a harder ink roller, using a chambered doctor blade inking system or changing the ink.

Replace or Clean the Anilox Roller, use a different or higher LPI anilox roller, change the ink viscosity or formula to improve the ink delivery effect and printing quality.

Add Fresh Ink to increase viscosity and improve the printing performance of the ink.

Missing Print Lines in Flexo Press Printing

Color Variation

Uneven printing color is one of the common quality problems in the flexographic printing process. It is mainly manifested in the uneven color depth of the printed surface, which affects the overall appearance of printed products such as take-away paper bags, salad paper bowls, hamburger paper boxes, flour powder grain bags, etc.

What Causes Color Variation

The causes of color variation mainly include the following aspects: the ink supply system of flexography machine lacks adjustment or is damaged, resulting in uneven ink supply, which leads to uneven printing color.The uneven printing plate leads to uneven ink distribution, which affects the uniformity of printing color.In addition, the main reasons for uneven printing color between printed pieces are insufficient ink flow, loose printing plate, and roller vibration caused by gear or bearing damage.

Anilox Roller of Flexo Printing Machine for Flour Powder Grain Bag

How to Avoid Color Variation

For color variation, the following improvement measures can be taken:

Check, Adjust or Replace the Parts of the flexographic printing press to ensure the normal operation of the flexo printing press and the uniform supply of ink.

Check the Parallelism of All Anilox Rollers, Ink Rollers and Doctor Blades to ensure good coordination between the parts and improve the ink delivery and distribution effect.

Replace the Cleaning Roller and Doctor Blade, reduce the doctor blade pressure or replace the doctor blade to improve the cleaning effect of the printing plate and the ink transfer effect.

Remount the Printing Plate to ensure the accurate installation position of the printing plate and improve the printing effect.

Doctor Blade of Flexo Label Printing Machine for Vitamin Medical Bottle Label

Flexo printing machinery plays an important role in the field of modern printing. However, problems such as speckling, missing print lines, and color variation have seriously affected the quality and production efficiency of printed products such as coffee bean paper packaging bags, nuts packaging pouches, cans sticker labels, and wine labels. In actual production, printing companies should strengthen the daily maintenance and management of flexographic printing equipment, regularly check the operating status of the equipment, and promptly discover and solve potential problems.