In times of surging energy costs, it comes as no surprise that the glass decoration industry too is taking more and more interest in energy-efficient manufacturing techniques. The use of LED technology with screen printing inks is a promising option in this context.
 
Based on its 935UV ‘flagship’ series of screen printing inks for glass decoration, German ink specialist RUCO Druckfarben is now also offering an LED UV-curing version. In addition to being a potential cost-saving factor, these 935UV-LED inks also enable shorter production cycles and improved process security to be achieved. In contrast to conventional inks, which require subsequent post-curing of at least 24 hours, cross hatch testing can be carried out immediately after printing. Moreover 935UV-LED inks offer advantages with regard to environmental and safety aspects.
 
Benefits of UV-LED technology Compared to Conventional UV-Curing Systems
Conventional UV bulbs like those in mercury vapor lamps cure UV inks within the UV C and UV B spectrums comprising wavelengths of 100–280 nanometers and 280–320 nanometers, respectively.
 
By contrast, LED UV lamps have a narrow spectral output, most commonly at 365 or 395 nm with +/- 20 nm at peak wavelength. LED-modified UV inks contain additional photoinitiators that have been tailored to react at these specific wavelengths. Due to this primarily chemical reaction in the long wavelength spectrum, LED UV systems can achieve excellent depth of cure, which results in better adhesion on the glass surface directly after the printing and curing process.
 
But for UV inks to cure properly, it is vital not only that they are exposed to the correct wavelengths, but also that the UV light intensity is sufficient. If this is very low, the adhesion of the ink on the surface will in all probability not be acceptable. So the intensity of the lamps should be checked first. This can be done using a UV light intensity integrator.
 
LED Hybrid UV-Curing Systems
There are two different LED UV-curing system possibilities: either the use of UV LED lamps exclusively, or in combination with UV-C bulbs at the end of the curing process to achieve excellent surface durability. To provide maximum flexibility for users, UV LED inks are normally formulated as a “hybrid version.” This means they are suitable for LED curing, and they can also be cured using a combination of LED UV and UV–C bulbs. Currently there are LED bulb systems with 4, 8, 12 and 16 W/cm² available on the market.
 
Improved Process Security
When using conventional UV-based systems, the glass will require a post-curing process, which means that users have to wait between 24 and 36 hours before they can check the adhesion of the ink film on the glass surface. With UV LED inks, this can be done immediately after curing.
 
Color Matching
Due to their good depth of cure, UV LED inks allow for greater layer thicknesses, which results in higher opacity. This is beneficial both for difficult substrates and for the application of difficult colors.
 
When compared to ceramic inks, which must be exposed to high temperatures during the curing process before the final color can be seen, with UV LED based inks users can check the color accuracy directly after curing.
 
Conclusion
Ink curing by means of UV LED is a new forward-looking technology. The use of light-emitting diodes offers a number of advantages compared with conventional systems, with lower energy consumption being one major factor. Moreover, LEDs do not create ozone so that the need for expensive exhaust systems is eliminated, plus they have an extremely long service life.
 
The use and application of the UV LED printing process and of conventional UV printing cannot and is not designed to completely replace the use of ceramic inks. However, in many cases, UV LED curable inks can provide a suitable alternative, bringing with them environmental benefits as well as new and unique decorating opportunities.