How to choose and use UV inks effectively? A quick guide
UV inks are popular in label printing due to their bright colours, high gloss, water, solvent and abrasion resistance, and fast curing speed. They are widely used in flexographic, gravure, offset, and other printing methods. Choosing and using UV inks properly, especially understanding the factors affecting curing, evaluation methods, and solutions, is crucial for reducing printing faults and improving label quality.
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Current status of UV ink applications
1. Variable UV ink quality
Currently, the quality of UV inks in the domestic label printing market varies greatly, leading to common printing issues like dry rollers, ink piling, ink splashes, and dirty plates. UV-printed labels often suffer from poor adhesion, low gloss, and insufficient opacity, especially with white ink. These problems are usually caused by low-end UV inks, affecting both printing efficiency and product quality.
To avoid potential UV ink issues and meet the quality requirements for various materials, applications, and printing processes, UV ink suppliers continue to improve and launch new products.
2. No unified UV light standards
The curing effect of UV inks is directly influenced by the UV light. There is currently no unified standard for UV light spectrum ranges, so commercial UV light sources vary in spectrum and power. Poor matching between UV light and ink can result in incomplete curing or over-curing of the surface, leading to adhesion and other quality issues.
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How to choose UV ink
The curing performance of ink is key to the quality of UV-printed products. Therefore, when choosing UV ink, consider whether the emission wavelength of your UV lamps matches the activation wavelength of the ink's photoinitiators. Different brands and types of UV inks also vary in curing speed and adhesion. Generally, as long as white and black inks meet the requirements, other colours are usually fine, so focus on black and white inks.
1. UV light characteristics
UV light ranges from 200 to 600nm. At 254nm, it produces ozone, and above 400nm, heat. Ozone pollutes the environment and harms health; heat can cause print distortion and waste energy. Low-energy UV lamps (HUV/LEC) emit 280–600nm, avoiding the ozone range but still generating heat. LED lamps solve this, with wavelengths of 365nm, 385nm, and 395nm, avoiding ozone and heat, concentrating energy for efficient, safe curing.
2. Choosing UV ink according to light matching
UV ink requires UV light that the photoinitiators can absorb to generate free radicals, enabling resin and monomers to crosslink and cure. Traditional UV inks have activation wavelengths of 220–580nm, low-energy UV inks 280–400nm, and LED-UV inks 365–405nm. When choosing ink, ensure the sensitive wavelength range matches your UV lamp and consider the system's actual curing energy to select the correct type.
3. Selecting UV ink based on black and white ink performance
Colour affects curing speed; different pigments absorb UV light differently. Magenta cures fastest, black is hardest due to pigment particle blocking, requiring higher energy. White also needs higher energy as it reflects visible light fully, slowing curing. The overall series curing depends on black and white; if these work well, other colours are generally fine.
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Essential UV printing knowledge
Choosing the right UV ink brand and type is just the first step. Understanding ink characteristics, influencing factors, and performance changes is necessary to use UV inks properly and improve label printing quality. Key points include composite colour reproduction and evaluating complete curing.
1. Colour differences in composite printing
To maintain print quality, strict colour management is needed. Digital management is based on Lab values. Monochrome inks may have the same Lab value, but composite colours may differ due to varying transparency of inks. When overprinting, less transparent ink covers underlying colours more, causing noticeable differences even with similar Lab values from different suppliers. Spot colour mixing works similarly, producing darker, richer colours for even, solid printing, common in packaging and labels.
2. How to determine if UV ink is fully cured
Whether UV ink can fully cure determines the adhesion of the printed ink layer, the reproduction of print colours, and the glossiness of the printed ink layer. Making a quick and accurate judgment on-site is very important, so people have summarised several methods in practice, which can be classified into appearance observation, physical testing, and chemical testing.
Appearance observation does not require any tools and determines curing by checking if the UV ink layer has a shiny surface. Fully cured UV ink layers are very glossy.
There are two common physical testing methods. Method one: place a sheet of paper on the UV ink layer of the print and rub it with your hand. If the curing is incomplete, the ink surface will be damaged. Method two: scratch the UV ink layer with a pin and then observe the scratch under a 200x magnifying glass. If the scratch appears serrated, it indicates that the UV ink layer is fully cured.
Chemical testing requires acetone. Drop it on the UV ink layer, and if the layer dissolves, it indicates it is not fully cured.
Above, I have shared some key points regarding the selection and use of UV ink from the perspectives of current application, how to choose, and essential knowledge, hoping it helps. The next article will share common problems in UV ink printing and their solutions, so stay tuned!