UV LEDs for Curing Applications

Powerful UV LED special light sources can be used for different curing and drying applications. Heraeus Noblelight manufactures tailored UV LED systems for individual industrial processes.

In conventional lighting, visible LEDs (Light Emitting Diodes) are seeing explosive growth in a variety of applications driven by low power consumption, long life and environmentally friendly materials used in their construction. According to the US Department of Energy from 2010-2030 the cumulative energy savings are estimated to total approximately 1,488 terawatt-hours, representing $120 billion at today's energy prices, and would reduce greenhouse gas emissions by 246 million metric tons of carbon.

UV LEDs are also seeing ever increasing adoption in curing applications for many of the same reasons - high efficiency, greater than 10,000 hours lifetime, green technology with no mercury disposal issues, no ozone production and no volatile solvents. Additionally, with optimized formulations of inks and adhesives, cure quality and durability have been found to be superior. Early adopters of UV LEDs have shown a long term commitment to environmental and energy concerns.

What is unique about UV LEDs?

LEDs are semiconductors devices and often referred to as solid state lighting or SSL. The manufacturing process is much like that used for making computer chips – many thin layers of semiconductor materials are deposited that when energized - emit light. For high power UV LEDs, Aluminum Gallium Nitride (AlGaN) is the material of choice. The UV LED chip is quite small ~1mm, in comparison to the packaging, which includes the electrical connections, heat sink and lens.

The light output of UV LEDs is much closer to that of semiconductor lasers regarding wavelength in that they are monochromatic, emitting at a single wavelength. This wavelength is determined during the production of LEDs. Adding more aluminum to the semiconductor mix creates shorter wavelength UV LEDs. Figure 1 shows the wavelength of three different UV LEDs. As such, the UV LED wavelength must be specified to match the material being cured.

Advantages and issues with using UV LEDs in curing applications

In a wide range of applications, UV LEDs have demonstrated numerous advantages such as:

Power consumption - As in conventional lighting using LEDs, UV LEDs show an advantage for low power usage when the process is optimized for their use. Furthermore, UV LED efficiency is constantly improving as new manufacturing techniques are employed.

Long life - UV LEDs are typically characterized by greater than 10,000 hours of operation thereby greatly reducing maintenance requirements and down time for lamp replacement.

Green technology - Increasingly, customers are adopting a social responsibility for the environment and energy consumption. Ink, adhesive and equipment manufacturers are exploring ways to meet these requirements. UV LEDs offer low power use, no volatile chemical use, no ozone production and no mercury disposal issues.

Safety - UV LEDs offer many safety advantages e.g. no high temperature operation, no glass tubes, no damaging UVC wavelengths to the skin and no toxic ozone or mercury exposure.

Cure quality - In cooperation with formulators, the chemistry has shown to be able to produce materials using UV LED curing to produce durable, resilient and visual dramatic results.

Easy integration - UV LED heads are quite compact and have low weight. Water cooled units are plumbed externally and air-cooled units are also available. LEDs are instant on/off and require no shutters or venting and no external reflectors or optics. Due to the small size of LEDs, they can be easily adapted to any form factor, such as 360 degree exposure for in-situ pipe curing or fiber coating curing. The mini-modules can be packaged to any linear length as well.

No infrared heating - Because there is no IR radiation from UV LEDs, it is considered a cold light source making it ideal for any heat sensitive material such as thin polymers, medical devices, etc.

As with any new disruptive technology, a few considerations also need to be taken into account. Although the initial capital costs are higher, the return on investment can be substantial.

The single wavelength of UV LEDs requires photo-initiators with an absorption matching to the light source. Nevertheless, the formulators have acknowledged that UV LEDs are the source of choice going forward and have released products optimized for UV LED activation. Lastly, commercially reliable UV LEDs are currently limited to a minimum wavelength of 365 nm and as such not viable for ultra-short wavelength applications. However, forecasts show that by the middle of the decade suitable LEDs will be available for applications such as medical and disinfection.

Heraeus Noblelight has been involved in UV applications for over 100 years having invented the first UV lamp. Customers profit from this competence and know-how in developing and manufacturing UV lamps, components and UV-LED systems. The newly formed “Optoelectronics” business division of Heraeus Noblelight is building on this knowledge to provide high performance UV LED solutions for curing applications.