UV inks work by using ultraviolet radiation to dry printing ink. UV light is a natural by-product of our sun and, in very small amounts, is harmless. But in offset printing, this spectrum is amplified onto drying inks, across light wavelengths between 100 and 380 nanometres.
[Image: light spectrum for UV inks]
This spectrum is almost invisible, since the human eye can only pick up light starting at around 380 nanometres.
Note that the diagram above shows four UV light bands:
EUV — stands for Extreme Ultraviolet light (10–180 nm). While this light band can be used in the printing industry, fewer than 50 printing companies in the world use it. This extreme light has very limited applications in printing.
UVC — stands for Ultraviolet light, C band (180–280 nm). This part of the spectrum allows for instant curing of the ink. It doesn’t have the penetrating power to reach deeper layers, but it provides a fast, cured surface on the printing ink layer.
UVB — stands for Ultraviolet light, B band (280–315 nm). This wavelength penetrates deeper into the ink. It’s therefore more effective than UVC.
UVA — stands for Ultraviolet light, A band (315–400 nm). This is the spectrum most commonly used by offset presses. Because the human eye can pick up this light, there’s a visible glow to the lights. It penetrates deeper and dries, making it very well suited to offset presses that apply thicker ink films to paper.
Advantages of UV offset printing
It’s better for the environment. Energy savings matter. Many drying systems require direct heat, which consumes a great deal of energy. The UV curing method requires far less — just the electricity to run the lamps.
The entire UV curing system is also VOC-free. No harmful emissions are released. This means no exhaust system is required during the curing process, and it poses no health or safety risk to press operators.
A smaller press footprint. Lamps are easily fitted between print units. There’s no need to add a dryer to the end of the press. Some heat-set presses require a very long hot-air dryer; with UV, the length of an offset press can be reduced by nearly a third.
It works on almost any type of substrate. UV inks can be used on almost any type of surface, including:
glossy paper
matte paper
card stock
metal substrates
plastic films
glass
This includes substrates of different sizes, such as large sheets or narrow webs.
The ink stays fresh. Offset printers report that as long as the ink isn’t exposed to UV light, it doesn’t skin over in the fountain. Ink buildup on the blanket is also reported to be significantly lower. Because the ink cures immediately after leaving the print unit, it doesn’t get picked back up by the next unit. This removes ink trapping as an issue in process-colour printing.
Gloss levels are higher. Traditional offset can achieve a glossy surface, particularly on coated paper. But with UV inks, an even higher gloss level is achieved. That’s a selling point for advertisers looking to add impact to their ads.
Less anti-set-off powder is needed. Because the ink is cured, there’s almost no set-off. Press operators report they can work with little or no set-off powder.
Faster production speeds. The curing process is extremely fast, allowing the press to run much faster without having to worry about set-off.
Disadvantages of UV offset printing
Skin irritation. Press operators report experiencing skin irritation when working with the ink. Manufacturers generally report low toxicity, but care must be taken to avoid skin contact with the ink. Safety data sheets recommend wearing skin and eye protection.
Initial start-up costs. UV curing lamps are expensive. They last a long time, but eventually burn out. This ongoing cost needs to be factored in.
The ink won’t dry without UV light. If a lamp goes out while running, it can make a mess on the press. The ink only cures with UV light.
