LED technology has become a real alternative solution in the sphere of light curing. To date, the efficiency of both the individual LEDs and the system as a whole have been increased, resulting in further improved drying quality. Simple integration, dispensing with ozone and mercury and the lack of thermal radiation favour a broad range of applications for this technology in industrial curing.
Whether in the curing of printing inks, adhesives or varnishes on various substrates – LED UV curing is seeing high growth rates in coating industries. However, distribution of the two technologies differs widely in the various segments. Overall, LED systems are most frequently used in inkjet and adhesives applications.
In principle, the polymerization process with an LED system is identical to the familiar UV technology. The only difference is that the chemistry of reactivity and surface properties has to be optimized. If the aforementioned conditions are satisfied in terms of inks, varnishes, adhesives, coatings etc., LED systems are successfully used in a printing press, for example. This new curing technology is more and more used in inkjet applications. For curing purposes, LED systems use the property of light-emitting diodes to convert electrical current straight into light. They are based on semiconductor compounds which give off energy in the form of ultraviolet radiation or even visible light as soon as electrical current flows through an LED in the forward direction.
Industrial LED technology used for cross-linking work at wavelengths between 365 nm and 405 nm, with the range between 385 and 395 nm is being used the most frequently. The modules can take 100 or more LEDs. An intelligent circuit controls these modules, also allowing them to be switched in zones. Zone circuits allow adaptation to working width, resulting in energy-saving potential. The compact output packages obviously generate waste heat. As a rule of thumb, the following applies: the greater the efficiency of the individual LED, the less waste heat is produced. For a long service life, the waste heat which arises needs to be routed away. If this is effected with a high level of efficiency, then a long service life is associated with high emissions. The task of development is to get the radiation emitted by the LED to the substrate without loss if at all possible. Optical decoupling is of key significance for this. The subjects of thermal and optical decoupling have been successfully implemented by XT8 technology, and a saving of 30 % is associated with this.
Under what conditions does an LED system save electricity? This is probably the most common question in connection with LED technology and does not have just one simple answer; it always depends on operating and machine conditions. It is now essentially possible to save energy when curing using LED systems, as the reactivity of the chemistry has been improved. In addition, an LED UV system is ready to use as soon as it is switched on, so there are no stand-by times. Format switching allows LEDs to be switched off outside the active working width. Triggered pause switching between individual products allows further savings. There is also energy-saving potential from having the right metrology options to determine intensity per unit surface area during the drying process.
The unit W/cm² has become established in metrology for LED systems. This unit is the value of maximum intensity per unit surface area. However, as intensity decreases as distance increases, the value immediately below the exit window is frequently quoted. It should furthermore be noted that a suitable UV measuring system needs to be used. This is characterized by sensitivity which is high and as constant as possible in the wavelength range emitted by the LED. We would be delighted to provide you with information about this.
LEDs have already become a popular choice for lighting. LED UV technology has already made inroads in terms of curing printing inks in the printing industry, too. Applications in other industrial spheres are on the threshold, but awaiting the development of LEDs with shorter wavelengths.