This story was originally published in June/July 2019 in Screen Printing.

WHILE UV LED CURING in the digital printing space has grown significantly, many screen-printing operations have continued to use traditional curing technology. The primary obstacle wasn’t the readiness of the technology, but the cost. Until recently, LEDs were expensive, and the need in a screen-printing line to cure the full width of the print at once meant that many more LEDs were required compared to a wide-format inkjet printer. This tended to limit early development in the screen-printing industry to containers and other smaller formats where equipment cost was less of a factor.

Now that the costs have come down, the economic, environmental, and safety benefits of the technology have captured the interest of screen-printing companies, equipment manufacturers, and ink developers. Today, a growing number of companies would like to replace their old mercury vapor curing systems with UV LED units.

During the past 10 years, the power of the lamps used in UV LED curing systems has more than doubled, the physical size of the lamps has been reduced, and costs have come down. Some manufacturers estimate that retrofitting a 20-inch-wide conveyor two decades ago would have cost four or five times as much as it does today. Today, you’re getting a proven curing system at a fraction of the cost.

Here are four facts you should know about UV LED screen printing:

UV LED Curing is More Efficient than Mercury Vapor UV Curing

1 Traditional UV lamps produce light by generating an electric arc inside an ionized gas chamber (typically mercury). After the atoms in the gas chamber are excited, they decay and emit photons. Mercury arc lamps produce light across the full spectrum of ultraviolet light (from 100 nanometers [nm] to 1800 nm). In addition to UV-A rays, this includes harmful UV-B and UV-C radiation that is hazardous to workers’ eyes and skin.
Mercury lamps run very hot, which can cause heat-sensitive printed materials to warp and wrinkle. Plus, mercury UV-curing systems generate ozone that must be vented away from the work area. Using LEDs to cure UV inks doesn’t generate ozone — nor does it transfer much heat to the printed surface.

UV LED lamps are solid-state semiconductor devices. They produce light by generating a voltage to join positive holes with negative electrons, emitting energy in the form of photons. The light is focused within a narrow spectrum of ultraviolet wavelengths. Phoseon LED curing units produce light only within the UV-A range, with wavelengths of 365 nm, 385 nm, 395 nm, or 405 nm.

Because the power going into a mercury lamp is distributed across a broad spectrum, less than 10% of the power going into the lamp is converted into UV curing energy. In contrast, Phoseon LED curing lamps convert greater than 30% of the input power to UV curing energy.

Unlike mercury lamps that need time to warm up and typically run all day, LEDs provide energy instantly and can be switched on and off as needed. Print shop employees can turn off the LEDs every time they take a 15-minute break; and some units are configured so the LEDs turn off between prints, providing further efficiency. LED curing units are expected to operate for more than 20,000 hours compared to less than 2,000 hours for a mercury arc lamp.

UV-LED curing systems are offered either in air-cooled or water-cooled packages to ensure that the LEDs operate at a consistent junction temperature (the highest operating temperature of the semiconductor) during production and withstand harsh production environments.

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A Growing Number of UV LED Inks are Available

2 To take advantage of UV LED curing, you need inks that are formulated to cure within the high UV-A wavelengths produced by the LED lamp. UV LED screen inks include photoinitiators that absorb the specified UV-A wavelengths needed to ensure a full cure at the desired speed.

As the benefits of UV LED curing are now proven in real-world applications, screen ink manufacturers have followed this trend by introducing formulations that enable more screen printers to use the technology.

Today, companies such as Nazdar, Norcote, Sun Chemical, and Ruco offer UV LED inks for specific applications, including bottle decorating, container printing, durable decals, membrane switches, and indoor and outdoor point-of-purchase graphics. Some UV LED screen inks are “dual-cure” formulations that also work with traditional mercury vapor curing systems.

Each new ink formulation must provide the desired curing performance at the speed of production and must meet the adhesion and durability requirements of specific application. For instance, the performance of UV LED inks has been proven in the glass-bottle decorating business for many years. Because retrofitting industrial equipment can be expensive, buyers of glass-decorating or container-decorating equipment often specify UV-LED curing units when purchasing screen-printing equipment for high-speed, high-volume container decorating.

UV LED Lamps Can Be Built into Industrial Screen Presses

3 In 2011, Empire Screen Printing collaborated with Nazdar, Phoseon, and KBA-Kammann to develop the first roll-to-roll screen-printing press with built-in UV LED curing technology. Empire continues to use this Kammann K61 Eco-Press to produce rolls or sheets of outdoor-durable labels.

According to John Freismuth, of Empire Screen Printing, UV LED curing improved the company’s manufacturing process and allowed it to go from raw materials to finished goods in a one-piece flow. The shop’s production team also likes the lower energy costs, reduced downtime, ability to print on a wider range of substrates, and ozone-free, environmentally friendly nature of the UV LED curing process.

Since installing the first unit in 2011 and converting a 6-color screen-printing press that used mercury lamps into a 12-color UV LED screen line, Empire has gone on to convert 75% of their presses to LED.

Screen-Printing Shops of All Sizes Can Benefit

4 In addition to Empire, other well-known large screen-printing companies are using UV LED inks successfully. But UV LED curing can benefit smaller shops too. Many smaller screen-printing operations face limitations in the amount of electrical power their shops can consume. If they reduce the amount of power they utilize in their curing lines, more energy will be available for other steps in the process. Plus, if small shops can replace a thermal oven that’s 50 feet long and 6 feet wide with a unit one-tenth that size, they can make room for other equipment.

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