Industry News

UV flexographic printing has become a mainstream method in the label industry due to its efficiency, environmental benefits, and vibrant colors. However, common issues like poor ink curing, poor ink adhesion, and ink build-up can arise during production. This article examines these problems, analyzes their causes, and offers targeted solutions.

UV Flexo Printing in Inline Flexo Press for Label Sticker

Poor Ink Curing

Incomplete curing of UV ink leads to poor adhesion, causing the ink layer to stick to adjacent prints. The uncured ink layer is also prone to friction and scratching, severely affecting print quality.

Why Does the Ink Cure Poorly?

Poor curing of UV ink is mainly caused by problems with the ink and printing material itself, too thick ink layer, insufficient or aging UV lamp power, and too fast printing speed.

Problems With Ink and Printing Materials: Improper ink formulation or slow curing can result in incomplete curing. Some materials, such as certain plastic films, may hinder UV ink penetration and curing.

Plastic Films for Food Packaging Printed by Label Flexo Press

Too Thick Ink Layer: A thick ink layer can block UV ray penetration, preventing full curing of the bottom ink. To achieve the desired color, operators may increase ink thickness, leading to poor curing.

Insufficient Power or Aging of UV Lamp: Insufficient UV lamp power or aging can reduce ultraviolet intensity, preventing ink curing. Dust on the reflector cover can also affect UV irradiation effectiveness.

UV Lamp of Horizontal In-Line Flexo Printing Machine for Bottle Label

Too Fast Printing Speed: Excessive printing speed reduces the time UV rays act on the ink, impairing the curing effect.

How to Avoid Ink Poor Curing？

Change Ink: Choose UV ink with faster curing speed or higher color concentration.

Pre-Treat the Printing Material: The adhesion and curing effect of UV ink can be improved through surface treatment technologies such as corona treatment and primer coating.

Corona Treater of Stack Type Flexographic Printing Machine for QR Code Label

Adjust the Ink Layer Thickness: Use ink with higher color concentration and adjust printing pressure, anilox roller lpi, and other parameters to control ink layer thickness, reducing heat buildup and preventing ink degradation.

Increase the Power of UV Lamp or Replace UV Lamp: Replace aged UV lamps or increase their power, and clean the reflector cover regularly to maintain UV radiation effectiveness.

Control Panel for Speed Control on Label Flexographic Printer

Adjust Printing Speed: Reduce printing speed to extend ink residence time, allowing UV rays to fully cure the ink and improve the curing effect.

Poor Ink Adhesion

Poor ink adhesion causes the ink layer to peel off during processes like die-cutting, laminating, and varnishing, as well as during use due to friction or collision, affecting the appearance and durability of printed products.

Why Does the Ink Adheres Poorly?

The poor adhesion of UV ink is mainly caused by problems with printing materials, ink formulation, improper curing conditions, and printing process.

Problems With Printing Materials: Some materials with low surface energy, such as plastic films, gold and silver cardboard, and laser cardboard, have poor adhesion to UV ink. In addition, impurities such as oil and dust on the surface of the printing material will also cause the ink adhesion to decrease.

Facial Cream Packaging Printed on Gold and Silver Cardboard

Ink Formulation Issues: For example, the resin in the ink does not match the surface chemical properties of the substrate, or the additives in the ink affect the adhesion of the ink, which may lead to poor compatibility between the ink and the substrate.

Printing Process Issues: The temperature, humidity, printing pressure during the printing process is too high or too low, and the ink layer is too thick or too thin, etc., which will affect the adhesion of the ink.

How to Avoid Poor Ink Adhesion？

Using Primer Process

To improve UV ink adhesion, apply a transparent primer with excellent adhesion before printing the color ink. This can be done in the first unit of the press with UV curing. Alternatively, use water-based varnish as a primer on materials like laser cardboard, applying it by roll coating and infrared drying to prevent issues like ink splattering or bleeding.

Laser Cardboard for Printing Perfume and Jewelry Packaging Box

Ink Build-Up

Ink build-up on the rubber blanket, printing plate, and anilox roller leads to poor ink transfer and blurred images, affecting print quality. It also increases cleaning and maintenance costs and, in severe cases, can cause press stoppages, reducing production efficiency.

Ink Build-Up Around Screen Dots in Printing

Why Does the Ink Build-Up?

UV ink accumulation is caused by poor ink fluidity, insufficient fineness and paper quality problems:

Poor Fluidity: The ink viscosity, stickiness and thixotropy are poor, the transfer is uneven, and it is easy to accumulate.

Insufficient Fineness: Large particles are easy to clog the anilox roller, aggravating ink accumulation.

Paper Problems: Paper powder and paper fibers peel off and mix into the ink, reducing the transfer performance and causing ink accumulation.

How to Avoid Ink Build-Up

To solve the problem of ink build-up, you can use ink reducer or ink remover to adjust the viscosity of the ink. If it is offset printing, you can use ink with good water resistance, and the amount of water in the printing production process should not be too large.

In short, although the poor ink curing, poor ink adhesion and ink build-up problems of UV ink in label flexographic printing will bring many troubles, they can be effectively solved by rationally selecting inks, optimizing printing processes, adjusting curing conditions and pre-treating printing materials.