Specialty Light Sources for the Printing Industry

Depending on the printing ink or adhesive, infrared or UV technology is used for drying and curing. Heraeus Noblelight shows its competence in the field of specialty light sources and systems for printing plants at the drupa in Düsseldorf from 3 to 16 May 2012. Heraeus presents individually developed infrared emitters, UV lamps and UV LEDs for more efficient printing processes at stand C35 in hall 3.

These days the efficient use of energy is an important issue. It is therefore worthwhile to examine industrial processes, such as printing in detail to find methods and technologies that yield the best results while at the same time saving as much energy as possible.

Infrared emitters dry digital prints cost effectively

A change from toner to digital printing promised major cost savings at the British company Bemrose Booth in Hull. Thanks to the use of Heraeus carbon infrared emitters to print car park tickets, drying can now keep pace with the new high-speed print heads.

Bemrose Booth offers a wide range of products such as gift cards, vouchers, calendars and lottery and other tickets. An important feature of car park ticket reels is the use of black ink blocks which signal that the reel is nearly finished and needs to be replaced. These "signal blocks" require application of large amounts of ink. In the past, toner was used for this which did not need to be dried but because of the high costs, a decision was made to change to digital printing. Print heads are used which apply up to 205 million drops of water-based ink per second. However, the very great economic advantages promised by the use of the high-tech printing system could be realised only if drying of the ink kept pace with the printing speed. Following successful tests at the Heraeus Applications Competence Center, a customer-specific infrared drying system was developed and installed at the Hull branch.

The system comprises medium-wave carbon infrared emitters and dries the ink with high efficiency because medium-wave infrared radiation is especially well absorbed by water. The system measures the temperature of the substrate when it leaves the heating module. Depending on the printing speed or ambient conditions, the infrared emitters are regulated to keep the defined temperature. Due to their very short response times, the infrared emitters are switched off virtually immediately when the paper stops and a fan cools the heat-sensitive paper.

Graham Winship, Operations Manager at Bemrose Booth, explains: "It was important to dry the ink quickly and thoroughly at paper speeds of up to 60 metres per minute without damaging the sensitive paper. The Heraeus system does exactly this!"

UV lamp cassette for efficient "lamp" exchange

The emission spectrum of UV radiation is very important for the curing process. The radiation must cause as many photons as possible to react with the coating to completely cure the material and to merge the coating to the substrate. Therefore, any curing process is complex and each coating system has its own parameters. In close cooperation with OEM partners, Heraeus has developed a large number of especially adapted UV lamps and replacement lamps for these demanding processes.

An efficient and advanced method to replace the UV lamps in digital printing machines at the end of their service life is to replace a complete UV lamp cassette.

Field tests have shown that the efficiency of the reflectors decreases over time under the influence of temperature. Moreover, it is difficult to maintain the original shape of the reflector when a lamp is exchanged. Even if a reflector is well adjusted, up to 15 percent of the ultraviolet radiation may be lost which actually was to be used to dry the ink. Accordingly, more UV power needs to be used to achieve an optimal curing result. In contrast, replacing the entire UV lamp cassette makes the change more efficient and saves operating costs in the long run.

Compact UV LEDs for optimal curing processes

In the field of conventional lighting, the number of LEDs (light emitting diodes) used in a multitude of applications is growing very rapidly. The use of special LEDs such as UV LEDs for industrial processes also shows a strong growth. Their low power consumption, high efficiency and long life of more than 10,000 hours enables UV LEDs to deliver optimal drying and curing results. Recipes for printing inks and adhesives make very specific requirements on the curing process. Ideally, they are adjusted to monochromatic wavelengths which are emitted by the UV LEDs.

For its customers, Heraeus Noblelight develops UV LED systems that meet the special requirements of the respective machine environment. The individual system components are put together from modules. Different sizes of UV LED modules and different wavelengths can be realised. The compact design of UV LED systems makes integration into the curing process simple. The Heraeus UV LED system contains all peripheral components such as control unit, power supply and cooling. The systems are available with water or air cooling. If you use UV LEDs, you will above all save energy during the curing process. LEDs can be switched on and off without any delay. Accordingly, energy is consumed only when it is needed — without any impairment of the output and service life of the LEDs.