UV LED curing technology is a great fit for screen printing, in applications such as printing of glass, plastic bottles and closures. UV LED offers significant advantages over traditional UV curing for screen printing, including smaller and lighter lamps, less maintenance and downtime, which translates into higher productivity rates, better adhesion on pigmented products, less scrap and higher quality end products at lower costs. The use of traditional UV lamps to cure inks on heat-sensitive substrates, such as plastic cosmetic objects, can result in deformation. UV LEDs allow high adhesion on covering inks, enabling strong colors on the more difficult substrates. Due to narrow, high UV-A wavelength, UV LEDs produce significantly less heat. The UV-A wavelength also allows for a more penetrative cure, which is an advantage when faced with thicker sections.

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.

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.

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.

Growing Number of UV LED Inks Are Available

 In order 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.

Today, companies 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 also meet the adhesion and durability requirements of specific applications.

The performance of UV LED inks has been proven in the glass-bottle decorating business for several 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.

Here are a few of the inks currently available:

·       The Nazdar 2300 series of UV/UV LED screen inks are formulated to print on the glass and plastic bottles used to package cosmetics, household chemicals, and other products. The 2400 series is formulated for screen printing membrane switches. The 2600 series can be used to print graphics on the rigid substrates commonly used for P-O-P graphics and indoor/outdoor advertising. The 2800 series of UV/UV LED screen ink adheres to the vinyl used to make fleet markings and other durable decals.

·       The Nazdar NSC340 series of durable UV LED Air Texture Clear screen inks provides a higher level of outdoor durability than Nazdar NCS40 and NCS50 Indoor Air Texture Clears. The NSC340 inks can be used to apply decorative first-surface texture effects on durable polycarbonate and some treated polyester films.

·       Ruco 937LED inks are dual-cure inks that offer excellent adhesion to glass, ceramics, and metal, plus resistance to chemicals, water, and abrasion. They can be used for high-speed decoration of bottles and glassware that will be chilled or run through a dishwasher. Ruco 947LED inks are formulated for plastic containers, including PET, polyethylene, polypropylene, acrylic, and more. These inks are suitable for high-speed bottle decoration lines as well as semi-automatic machines. Ruco 955LED-LM is a low-migration, silicone-free formulation for the external printing of plastic tubes and hollow bodies used to package food or cosmetics.

·       Marabu Ultra Pack LEDC is an LED-curable screen-printing ink for container printing, packaging, and flatbed label applications. The inks, designed to provide good adhesion, opacity, and gloss, are suitable for a variety of substrates including pretreated HDPE/LDPE, polypropylene, PET/PETG, rigid PVC, polycarbonate, and polystyrene.

·       Norcote LED First-Surface series inks are suitable for almost all graphic/P-O-P and plastic-container printing applications. They cure rapidly, provide a scratch-resistant surface when properly cured, and have good adhesion to a number of substrates.

·       Norcote LED MSK series inks were created for second-surface printing in industrial graphic applications. The inks are compatible with polycarbonate and treated polyester and most pressure-sensitive adhesives.

·       Sun Chemical offers five UV LED screen inks, including PD-LED for industrial applications, MPC-LED for plastic containers, COMETAL-LED for coated metals, VYB-LED for vinyl substrates, and SunVetro VTGL for glass.