Comparison of technologies
The operating technology of conventional UV lamps is based on plasma physics and optics, whereas UV LEDs are based on semiconductor technology and optics.
LEDs are based on semiconductor technology. Specific wavelengths are directly emitted by the current input. The spectrum is a quasi-monochromatic radiation in defined wavelengths, e.g. 365nm, 385nm or 405nm.
• Printers can expand substrate offerings.
• Handle heat-sensitive substrates safely.
• LED UV lamps last significantly longer.
• Heat, ozone and mercury are eliminated improving environmental impact.
• UV inks are free of solvents, so LED UV curing eliminates the release of VOCs (Volatile organic compounds (VOCs) are organic chemicals that have a high vapor pressure at ordinary room temperature.)
• The energy costs and heat-related hazards.
• Value-added coatings can be used efficiently.
• Unsupported films, shrink sleeves and many delicate heat-sensitive materials are safer to process with LED UV.
Application areas on LED Curing
• Printing industry (digital, flex, screen-printing)
• Adhesive and paint curing
• Glass printing
• Coating of surfaces
• Automotive industry
• Printed electronics
What happens after the lifespan (20,000 hours) of the LED lamps?
Over the first 20,000 hours of life, a typical LED system will lose about 15-20% of its UV output. After 20,000 hours the LEDs will continue to work but output will degrade more quickly and the probability of LED failure increases.
When a single LED fails, the user will not notice, as surrounding LEDs automatically increase in power to accommodate the loss. However, eventually, enough LEDs in a single area will fail and curing results will suffer. At this point, the user can either replace the failed LED module or choose to replace the whole array to maintain uniformity of output across the curing width.
Mercury Arc UV Lamp
A high-voltage arc between two electrodes leads to the vaporization of mercury and any optional doping within the lamp. A continuous UV spectrum between 200 nm and 450 nm is emitted.
Mercury Arc lamps are ideal light sources for applications that require high intensity spectral lines emitted in the deep UV to visible light regions. Their unique UV emission spectra make them popular for unique applications that need enhanced UV output such as UV spectroscopy, UV curing and other industrial processes, and environmental and medical applications.
• Has been the standard of Curing UV inks for the past several years.
• Mercury lamps have a broader spectral distribution.
• UV lamps have a lower replacement cost.
• Produce no VOC’s or ozone when vented properly.
• Coating cost are lower.
• Maintenance and cleaning is fast and easy to access.
• Many spectrums and wave lengths available.
• Higher line speeds easily achieved.
• Varnishes, spot colors and special low migration ink formulations achieve a better cure with Mercury Arc lamps.
LED and Mercury Arc Lamp on the field
Production expectations as much as the technology dictate the uptake of LED and the speed with which it replaces Mercury Arc curing.
But its just a matter of time before LED technology can match Mercury Arc curing’s performance. When it reaches that point it will cease to be viable, but that point is still on a far horizon.
During the 2017 tradeshows, we at FLAAR Reports were able to see the SkyAir-Ship SkyJet SDM330 handling both LED and Mercury Arc curing mechanism in different printers, providing the wide-format market a range to decide from either both curing mechanism depending on the needs of its clients.
Source: Alpha-Cure, FESPA Digital, APPPEXPO 2017