Do these issues frequently occur during UV ink use? Here's the solution—check it out!

Do these issues frequently occur during UV ink use? Here's the solution-check it out!

UV ink is widely used in label printing due to its vivid colors, high gloss, water resistance, solvent resistance, abrasion resistance, and fast curing speed. It is widely used in label printing, including letterpress, flexograph, offset printing, and digital printing. In this article, I will briefly share how to use UV ink effectively, as well as some common issues that arise during its use, hoping to draw your attention.

Prerequisites for making good use of UV ink

To ensure the curing effect of UV ink, the wavelength of the UV lamp is generally required to be between 180~420nm, and the power must not be less than 80W/cm². The typical service life of UV lamps is 1000 hours; if they exceed the service period, curing efficiency cannot be guaranteed. If conditions permit, the UV lamp can be rotated 90°, which helps ensure that all UV rays effectively radiate onto the printing ink layer, improving curing performance. Additionally, during use, ensure that cooling and ventilation equipment is in good condition to guarantee that the working temperature of the UV curing device always stays within the allowable range.

As is well known, the viscosity of UV ink is closely related to ambient temperature. Low temperature means low viscosity, high temperature means high viscosity. Therefore, before use, ink should be taken to the workshop and left for a period of time to maintain normal printing temperature. Additionally, during printing, the UV ink curing effect must be monitored. After the print cools to room temperature, 3M-600 tape can be used to test the adhesion strength of the ink layer. Generally, after 24 hours of storage, the ink adhesion is optimal.

These are prerequisites for using UV ink well, but in actual printing, some issues may inevitably arise, such as incomplete ink curing and poor adhesion. Below is an analysis of the causes and solutions of several common issues encountered in the printing process.

Common Issues Using UV Ink Analysis

01

Incomplete ink curing

Problem description

Ink is present on the paper guide roller between printing units and transfers to the substrate; After rolling, the back of the printed product gets dirty.

Solution

To solve the problem of incomplete UV ink curing, you need to look for the causes from three aspects: the curing device, printing operation, and the ink itself, and then address the problem accordingly.

First, check whether dirt is blocking the UV light on the surface of the UV lamp and reflector. If so, clean it and develop the habit of regularly cleaning the UV lamp, lampshade, and reflector with anhydrous alcohol. At the same time, check the usage time of the UV lamp. If it has exceeded its lifespan, it should be replaced to ensure the lamp has sufficient power, or use several sets of UV lamps to increase UV radiation energy.

Printing speed that is too fast causes the UV ink to receive insufficient UV radiation energy, resulting in a curing time that is too short, resulting in incomplete curing of the UV ink. In this case, reducing the printing speed can be resolved. If the ink layer is too thick, only the surface of the UV ink cures while the inside is incomplete. In this case, the anilox roller should be replaced, and the ink amount should be appropriately reduced to lower the thickness.

The above are external reasons for incomplete curing of UV ink, while the internal cause is that the UV ink's absorption spectrum matches the emission spectrum of the UV lamp within a relatively narrow range. In this case, an appropriate amount of photosensitizer can be added to the ink at a ratio of 1%~3%. By expanding the absorption spectrum of the ink, curing efficiency can be improved, thereby enhancing the curing effect.

02

Poor ink layer adhesion

Problem description

When testing ink layer adhesion with 3M-600 tape, ink may detach from the substrate surface, or subsequent ink may detach from the pre-printed ink layer.

Solution

Improper selection of substrate or low surface tension are the most common causes of poor ink adhesion. If the substrate does not match the ink, it needs to be replaced; For plastic film materials, corona treatment can increase surface tension or add coatings to improve adhesion. In short, ensure the surface tension reaches above 38 dynes.

In some cases, poor ink adhesion is also related to the ink formulation. If this issue exists in different batches of ink compared during testing, a pre-printed coating can be applied before printing the ink.

When using stamping before printing, if the ink adheres poorly to the surface of the stamping foil and easily peels off, varnish can be applied for protection. Poor adhesion between ink layers is often caused by over-curing of the pre-color ink, so the curing power of the pre-color UV lamp can be appropriately reduced. Incomplete ink curing is also one of the reasons for poor ink adhesion. Find the cause and take appropriate measures.

03

Random line-like color spots appear

Problem description

On the same page and in the same color, irregular linear dots appear, like shooting stars.

Solution

Various issues with the squeegee are the most common causes of this phenomenon. If the squeegee is damaged, it needs to be replaced; If the squeegee is thin or the material is soft, you can add a back blade or switch to a scraper blade with a thickness of 0.15mm~0.3mm. Additionally, incorrect contact angles can also cause this issue. It is recommended to set the squeegee angle to 20°~35°. High squeegee pressure is also one of the reasons, so it is best to use the lightest squeegee pressure.

To solve this problem, you can also start with anilox rollers. While ensuring ink transfer volume, replacing them with rollers with higher line counts can also provide good improvement. Additionally, excessive ink viscosity can lead to poor ink transfer and problems. Adding thinner can be used to reduce ink viscosity. To preserve color concentration, heating can also be used, especially in northern regions during winter.

04

Printed products are not sun-resistant

Problem description

Labels fade after being exposed to sunlight for a period of time.

Solution

Different inks have different levels of sun resistance. To achieve ideal sun resistance, you must choose inks with higher resistance levels. When mixing spot color inks, attention should also be paid to the sun-resistant level of spot color inks depending on the sun-resistant level of each primary color ink used. If the selected sun-resistant ink is already sufficiently durable but still cannot meet the required sun-resistant time, the ink layer thickness can be appropriately increased.

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