- By Peter Müller, R&D Equipment Technology Manager, DELO Industrial Adhesives ( http://www.delo.de ) -
DELOLUX 80: Customized development for fast polymerization of light- and UV-curing products
LED is the magic word concerning light nowadays. By selecting different materials and dopings, the electronic semiconductor elements can generate different types of light in an exactly defined, narrow spectral area. Having been predominantly used in niche applications for a long time due to the low yield of light and the missing availability of all light colors, the LED now conquers wide application areas, for example, in lighting technology.
One decisive reason for this success was the development of so-called III-V semiconductors which emit their light in the blue and green spectral area and enable the generation of white light. Furthermore, the developers have worked on a multiplication of the LED intensity in the past 10 years.
In the meantime, very efficient LED dies are available which open up further application areas: the polymerization of photoinitiated-curing adhesives and UV lacquers previously only cured with classic discharge lamps.
In the field of adhesive curing, the use of LED technology offers, in principle, the following advantages over conventional lamps. The service life of LEDs is higher by the factor of 20 compared to discharge lamps. In addition to
this, discharge lamps have to be permanently switched on in the process.
An LED can be switched on and off as often as required and only has to shine during the actual adhesive curing process step. As switching on and off does not have any influence on the service life and only the total operating time counts, the effective service life of the LED increases many times over.
Light emitting diodes can be controlled unlimitedly. The intensity is continuously variable between 0 % and 100 % through the specification of the electric current. Switch-on processes in the millisecond range ensure an exact synchronization in the process. Due to these properties, any shapes of irradiation ramps and impulses can be generated.
All LEDs are cold light sources and do not release any radiation in the near and middle infrared regions which could cause adhesive or component heating. The first LED hand-held lamps for industrial adhesive curing have already been introduced on the market.
In practice, this has turned out to be problematic as the time in which the lamps can be operated at full power is heavily limited due to the lack of efficient cooling. The semiconductor light sources convert only approx. 15 % to 20 % of the electrical energy into light, the rest is converted into heat; therefore, proper thermal management is a precondition for the optimal use of LEDs.