Beneeits of UV LED for wood coating application

UV curing is a polymerisation process that uses UV energy to change a liquid to a solid. Upon absorption of the UV energy, the photoinitiator(PI) produces free radicals, which initiate cross-linking with binders(monomers and oligomers) in a polymerisation reaction to cure or solidify the ink, coating or adhesives such as stabilisers, wetting agents, adhesion promoters, defoamers and pigments to provide desirable characteristics or colour of the cured material.

UV LED curing technology has advanced significantly in the past few years and is now readily available for a variety of applications, especially in the area of wood coatings. There are many benefits driving companies to move toward acceptance of UV LED technology, such as higher productivity and a more environmentally friendly solution, which more and more end customers are demanding. As manufacturers are developing uv led curing systems, konwing how the key sub-components work together, will help in creating the optimum system and thereby reducing the overall environmental impact of the process and, at the same time, maintaining or improving productivity and product performance.

The benefits of UV LED are numerous and significant for wood caoting oprations. UV LEDS are more environmentally friendly because they do not generate ozone and contain no mercury. The electrical to optical conversion efficiency of UV LEDs is higher, plus the instant on/off and no warm-up time results in a combined saving of 60% on electricity. They are a coll source, largely due to no output in the infrared range. This reduced heat eliminates complicated cooling mechanisms such as cooling air(quieter opration) and external shutters, and enables applications on heat sensitive wood substrates such as glued veneers and resinous woods.

Wavelength output comparison
A UV LED generates UV energy in and entirely different way. As an electric current or electrons, move through a semiconductor device called a diode, it emits energy in the form of photons. The specific materials in the diode detemine the wavelengths of these photons and, in the case of UV LEDs, the ouput is typically in a very narrow band+-10nm. The wavelength is dependent on the band gap between excited state and the ground state of the semiconductor material

Chat 1 compares the output of a 395nm UV LED lamp with a typical mercury arc lamp. It is important to note te difference in intensity and wavelength of the ouput, both are key to understanding a UV curing process.
Given latest advancements made in availability of UV LED optimised materials that give users the same benefits of increased throughput, yield, scratch resistance and durable curing; UV LED sources have become a very attractive option for many applications.

Not only is UV LED curing for wood coatings possible today, UV LED lamp technology has progressed to the point where air-cooled lamps have the performance needed for these demanding applications. The combination of continuous high irradiance with uniform output and flexible scaling, now allows users to implement air-cooled LED curing into environments for wood coatings applications that were previously only attainable with water-cooled solutions.
Industrial processes require products that can work in tough, sometimes harsh environments. UV LEDS are solid state devices and there high reliability and low energy consumption are ideal for wood coatings applications. In addition, automated precesses can take advantage of the LED’s ability to be instantly turned on or off or controlled remotely for varying intensity.

UV LED curing technology is ideally suited for the wood coatings industy for applications such as edge coating, roller coating and digital printing. UV LED technology drastically reduces energy consumption and significantly reduces workpiece surface temperature. Edge coating lines utilise UV LED to ensure consistent, high-quality reults. Machines can be made more compact due to small form factor; speed can be increased due to consistent UV ouput; and the diffuse nature of UV LED light can be used to more effectively cure shaped surfaces, which previously required multiple mercury lamps at various angles.
UV LED is a perfect match for roller coating lines, both for gelling and full-cure staions. The benefits include:better factory floor utilistaion due to shorter, more efficient lines; increased uptime with no degradation in UV ouput, cheaper input stock due to lack of infrared heat; and reduced operating cots by more efficient electricity use and no need for costly air ducting systems.
While technically not a wood application, creating a wood-grain look on diverse materials is made possible with UV LED and flatbed inkjet printing. By using a combination of printing and full-cure lamps, realisic look and more importantly feel is enabled by creating texture to mimic the grains of natural wood. This is especially valuable in decorative and accent applications.

Light-emitting diodes for ultraviolet curing applications, UV LEDs, have been commercially avaliable for a decade now. However, their unique output characteristics work best with newly formulated UV material chemistries that take advantage of UV LEDs’ many benefits. Initially UV LEDs were used in applications such as inkjet printing but with increasing energy outputs and lower initial costs, wood coating and other high performance applications became commercially viable.