A rapid cure with LED

The term ‘UV curing’ has been around for a very long time, but UV ‘LED’ curing is a newer concept that has emerged into the marketplace. Dr Richa Anand of Phoseon Technology presents her company’s view.

UV LED technology is unique because it utilises an ultraviolet electronic light source with LEDs (light emitting diodes) for drying inks, coatings, adhesives and other UV sensitive materials through polymerisation instead of evaporation. These solid state devices provide instant on-off ability with no warm up time or mechanical shutters. The rapid growth of this technology continues as more and more OEMs and end users become aware of the substantial benefits of the technology. UV LEDs are finally taking their place as a mainstream curing technology. Rapid technological advancements being made in all areas of printing, from digital inkjet to flexo and even into offset, demonstrate the far reaching potential and growing acceptance of the technology. End users are increasingly asking equipment manufacturers for LED options, and the market leading vendors are responding. Confronted with such exciting and rapidly evolving technology, system builders and end users are closely monitoring the ever changing UV LED curing landscape.

Benefits

The emerging growth of solid state UV LED light sources has dramatically transformed the printing industry offering substantial benefits beyond traditional UV curing methods. UV LED inkjet systems combined with optimised ink allow printing on unsupported and heat sensitive materials, including shrink sleeve, opening up new opportunities for label converters in the labels and packaging market. The benefits of low heat and narrow wavelength allows for advanced capability beyond traditional UV curing products. UV LED curing offers advanced capabilities, economic and environmental advantages beyond anything available on the market today. This is an ideal solution for a variety of narrow web printing applications. Printers can offer media versatility at its peak and can now run thinner materials through the machine without curling or warping. As a side benefit, these thinner substrates also reduce shipping costs, both of the raw materials and the finished product, providing further economic benefit to end users and their customers. UV LED light sources are small form-factor units that will enable smaller, more efficient narrow web machines and provide improved floor space utilisation.

Market uses

Here are some examples of narrow web applications that use this technology.
• Flexographic Printing: Flexography is the primary narrow web application around the world due to its high throughput speeds. Labels and packaging are the primary applications driving the increased demand for narrow web flexographic printing. New high power UV LED lamps are now available that meet the high speed demand (> 100 metres per minute) for flexo machines. The technology offers space savings, lower heat, and controllable power intensity across the narrow web.
• Labels: The small size of the curing lamps make them ideal for narrow web machines with limited space. It also allows for printing on heat-sensitive substrates and ever thinner labels. These solutions enable users to process a variety of materials at maximum production speeds, with low input power requirements.

‘UV LED curing offers advanced capabilities, economic and environmental advantages beyond anything available on the market today.’

• Pharmaceuticals: The pharmaceutical industry demands exacting product development and production in a sterile and clean environment. The industry has continued to push the envelope of what is possible; enabling new advances in medicine. UV LED technology brings inherent advantages to the world of printing, including the lack of IR radiation in heat-sensitive applications in clean room conditions.
• Coding and Marking: The compact curing lamps offer advanced capability and energy savings for coding and marking applications. The LEDs are instant on/off, so only switch on when ink curing has to occur. This saves energy and increases the life of the unit even further. UV LED curing is the ideal choice for high resolution variable data printing on a wide variety of substrates.

Ink formulation and materials

Ink formulation for LED technology has evolved significantly in past years and today there are a growing number of suppliers developing inks that work well with this technology. As it becomes more powerful and more compatible inks become available, the advanced capability in UV printing will be substantial. Material suppliers have responded to the demand and challenge in the printing world to formulate raw materials that absorb energy corresponding to output wavelength of UV LED curing units. 

One of the key ingredients in the chemical formulation is a photoinitiator that serves as a catalyst to initiate the polymerisation process when exposed to narrow spectrum UV LED energy. The driving factors in advancement of chemistry of raw materials is increased capability and cost effectiveness of commercially available UV LED curing lamps. With the rapid development of these curing systems, over 20 ink and material vendors offer support and ability to formulate for LED. In response to the increasing need for improved sustainable print solutions, Flint Group Narrow Web is introducing a series of ink technologies suitable for use with this technology under the EkoCure brand. These inks will be the first commercially available inks designed for combination print formulated specifically for UV LED curing. EkoCure is developed using specially selected photoinitiators that match the narrow and targeted wavelength area that is typical for the output from these lamps. The main advantages with UV LED can be summarised as ecological and economical:

• Ecological benefits – energy will be saved; UV LED lamps are ozone and mercury free (improved worker and environmental safety); EkoCure is formulated on bio-renewable resources.

• Economical benefits – energy consumption will be significantly reduced; manufacturing space is reduced; UV LED lamps are nearly maintenance free.