There are two basic curing units used for curing UV inkjet prints: Mercury vapor UV lamps and UV LED curing systems. Mercury vapor lighting is an old technology, which has been around for at least a century. UV inks were originally developed for this type of lighting, which emits a broad spectrum of UV light.
Mercury vapor UV lamps also generate significant heat-producing infrared light. As much as 40% of the energy consumed is converted to heat, which serves no function in the curing process. Since much of the media used in wide format digital printing is plastic, that heat can cause problems including shrinking, warping and discoloration.
UV LED curing systems provide a cooler cure for these heat related problems. Lower temperatures allow for printing on heat sensitive materials, such as pressure sensitive vinyls and unsupported polycarbonate films. Because UV LEDs minimize the incidence of warping media, the chance of a head strike is less likely.
One of the criticisms of UV LED systems is that the spectrum of light emitted is much narrower than that of Mercury vapor UV curing systems. In recent years, this issue has been diminished with the development of new UV LED systems and new ink formulations.
The latest generation of LED curing systems, which feature a more dense arrangement of the LEDs, produces a more energy to more fully cure the ink. The higher output of these newer systems also allows for higher production speeds.
As UV LED systems have improved and gain greater acceptance in the marketplace, ink manufacturers have shifted the emphasis in R&D to formulating inks for the newer, emerging technology. The challenge for the ink companies is in formulating inks which will cure fully when exposed to a narrower spectrum of UV light.
How well the ink cures is critical for a variety of reasons. While ink adhesion is vitally important, so are the physical properties of the ink, such as abrasion resistance, outdoor durability, chemical resistance and compatibility with a range of media as well as other components in a pressure sensitive sandwich, such as transfer adhesives.
Advantages of UV LED Inkjet Systems
Compared to Mercury Vapor lamps, UV LEDs provide the print provider with a number of cost advantages:
- Longer service life for a reduced lifetime investment in equipment;
- LEDs consume 60% to 80% less power, so operating costs are significantly lower; and
- Fewer service issues, which reduces maintenance costs. Mercury vapor lamps deteriorate at a fast rate. By comparison, UV LEDs are said to perform continuously for 15,000 to 20,000 hours. Component replacement costs are also lower.
UV LED systems are also more environmentally friendly than Mercury vapor curing systems in the following ways:
- UV LED systems contain no mercury;
- UV LED systems emit no ozone; and
- UV LED systems consume less power.
The transition from UV inkjet systems utilizing Mercury Vapor curing to those using LED curing will not likely happen immediately. Nevertheless this technology shift is happening. Because UV LED curing systems are more cost efficient to operate and more environmentally friendly, it is the smart choice for printers investing in UV inkjet printing equipment.