By Sabine A. Slaughter
More and more large format printers are employing UV technology. Increasingly UV LED is being implemented. At the show we have registered five different companies and printers that are employing this technology. What is the difference and why should printers use one or the other technology?
Inkjet printing is a complex tech- nology encompassing machines, printheads, inks and substrates – all of which need to complement each other in order to achieve good results. But the applications play an important role in determining which large and super wide format printer is most applicable. Let's take a look at the technologies and their implications. Inkjet is a non-contact printing method for highly precise direct printing on concave, convex and flat material surfaces. Traditional screen printing and pad printing methods have difficulties printing on uneven surfaces, however, brilliant colours, full-colour photo image data and even smooth gradations are achieved by inkjet printing methods. Inkjet printers using UV ink have to cure the ink because UV ink incorporates monomers – a kind of liquid with very small molecules that need to be fused together in a process called polymerization in order to be firmly fixed onto the material. When the particles are exposed to UV light they are cured, so as fuse the molecules together as well as to make them adhere to the substrate. This polymerizing reaction is called monomer binding. UV curable ink, which cures soon after printing usually does not contain VOCs (Volatile organic compounds) and is therefore environmentally friendly. Direct printing on non- absorbent materials is made possible since the coated layers of the resinous polymers produce printed images on the surface of the materials. The ink is instantly dried after irradiation with UV light. This explains why UV ink does not seep into the surfaces and ink penetration is kept at minimum. UV ink enables print service providers to print on many types of plastics as well as different substrates offering a broad spectrum of applications. However, the UV lamps used in this process generate a lot of heat which restricts the kind of substrate that can be used for UV printing. In addition the whole UV light spectrum is output.
Newer developments of printers, like MImaki's UJV-160, UJF-3042, JFX- family,or Roland DG's VersaUV to name just a few use another radiation source for the curing process: UV LEDs. These consist of UV light diodes thawt emit rays within a narrow UV light range. Inks whose monomers have been sensitized to this specific range can be cured via the same process as with UV lamps. As UV diodes do not generate heat, many more substrates such as membrane switches, heat- sensitive PVC and other plastics, films and papers can be used. This broadens the choice of applications that can be produced on a printer. Additionally, the warm-up and cool-down time of UV lamps is eliminated. UV LEDs can be switched on and off immediately. Power consumption of the respective machines is decisively reduced as not only the LEDs need less power but also can be switched off when not needed. The lifetime of UV LEDs is far higher than of conventional UV lamps.