Screen Printing - June/July 2019 - 21

hile UV LED curing in the digital printing space
has grown significantly over the past decade, most screenprinting 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. Although
relatively few new screen-printing presses are being
built, a growing number of companies would like to
replace their old mercury vapor curing systems with
UV LED units.
Over the past five 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. Mike Higgins, director of sales, Americas, for
Phoseon Technology, estimates that retrofitting a 20-inch-wide
conveyor five years ago would have cost four or five times as
much as it does today: "You're getting a proven curing system
at a fraction of the cost."
Here are five facts you should know about UV LED
screen printing.

#1: UV LED CURING IS MORE EFFICIENT THAN
MERCURY VAPOR UV CURING
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.
According to Higgins, 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 a
lot of 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.

UV LED inks and curing systems have been engineered for applications
such as bottle decorating, container printing, durable decals,
membrane switches, and more. Courtesy of Phoseon Technology.

Because the power going into a mercury lamp is distributed
across a broad spectrum, less than 10 percent of the power
going into the lamp is converted into UV curing energy. In
contrast, Phoseon LED curing lamps convert greater than 30
percent 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;
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 2000 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. Phoseon has
been making patented LED solutions for life sciences and
industrial curing applications since 2002. For the printing
industry, they make UV-LED curing systems for inkjet,
screen, and narrow-web flexographic printing systems.
JUNE / JULY 2019

Screen Printing - June/July 2019

Table of Contents for the Digital Edition of Screen Printing - June/July 2019