How to Ensure the Curing Quality of UV Ink During Printing?

Posted on 05-07-2024 by

UV ink can be applied in various printing methods such as offset printing, gravure printing, flexographic printing, etc. Regardless of the printing method employed, the fundamental concern for industry professionals is the curing quality of UV ink. UV ink undergoes a photochemical reaction under the radiation of ultraviolet light, thereby achieving curing. From this curing principle, it is known that UV ink exhibits different properties before and after exposure to ultraviolet light. Before exposure, UV ink maintains stable rheological properties, while after exposure, it rapidly cures. It is evident that factors affecting ultraviolet radiation will also impact the curing quality of UV ink. Therefore, to ensure effective ultraviolet radiation, the following three aspects must be addressed.

1. Maintain Ink-Water Balance Control

In the offset printing process, UV ink exhibits weak polarity. Poor ink-water balance control can easily lead to emulsification, resulting in opaque ink film, directly affecting the transmittance of ultraviolet light, thus slowing down the curing speed of UV ink and leaving uncured areas within the ink film. Folding or rubbing such prints or using adhesive tape to peel off surface graphics will cause scratching or streaking on the print surface.

Therefore, controlling the ink-water balance during the printing process is one of the important factors in ensuring the curing quality of UV ink. Since UV ink exhibits greater viscosity, stronger adhesion between molecules leads to increased water resistance. Hence, to reduce the emulsification value of UV ink, it is essential to maintain a low water content during the printing process, ensuring vibrant colors, thick ink layers, and clear, full dots on the print.

2. Maintain Suitable Workshop Temperature and Humidity

During printing, variations in workshop temperature and humidity can affect the performance of UV ink and substrates. For instance, when the workshop temperature is low and humidity is high, the photopolymerization reaction of UV ink slows down, and its adhesion to substrates decreases. Therefore, when using UV ink for printing, workshop temperature and humidity must be controlled within appropriate ranges. Generally, the workshop temperature should be maintained at 20-25°C, with relative humidity controlled at 50%-65%.

3. Ensure UV Lamp Intensity

Firstly, selecting UV lamps with appropriate power according to printing speed and product type is crucial. The ultraviolet light intensity of UV lamps directly affects the curing time of UV ink and is a key factor in the internal hardening of the ink film. When the ultraviolet light intensity decreases, even increasing the irradiation time to accumulate more light cannot improve the internal hardening of the ink film. Therefore, UV lamps exceeding their actual service life cannot effectively cure UV ink. Typically, UV equipment is equipped with a timer for UV lamp usage, with imported UV lamps having a service life of about 1000 hours and domestically produced UV lamps about 600 hours. To ensure the curing quality of UV ink, UV lamps should be replaced promptly when they reach their actual service life.

Secondly, if impurities are present in the ink or dust adheres to the surface of UV lamps during the production process, it will weaken the ultraviolet light intensity, significantly reducing the curing quality of UV ink. Therefore, after using UV lamps for a period, the lamp housing should be removed, and the surface of the UV lamps gently wiped with a clean, soft cloth dipped in anhydrous ethanol to ensure they are clean and bright.

Lastly, the reflector inside the UV lamp housing concentrates 80% of the ultraviolet light onto the print. If paper dust or dirt adheres to the reflector, it will affect its reflection efficiency. Therefore, regular cleaning and maintenance of the reflector are necessary during daily production to maintain its reflection angle and capacity. This task can be performed simultaneously with cleaning the UV lamps, using a clean, soft cloth dipped in anhydrous ethanol for cleaning. During cleaning and maintenance, the reflector should be manually closed, and its closure status and integrity of the closing device should be checked. Generally, pneumatic components are used for the closing device, which can be monitored for its working status using photocells or electromagnets. Additionally, the condition of the emission plate should be checked, and if the surface of the reflector becomes dull or uneven, it should be replaced promptly.

In addition to these factors, the purity and quantity of pigments in the UV ink system, the arrangement of printing colors, printing speed, etc., will also have certain effects on the curing of UV ink.