Digital UV inkjet printing on three-dimensional plastic products is “ready for prime time.” Advancements in UV LED curing technology overcome many curing problems related to traditional mercury vapor lamps. UV LED lamps are superior for curing low-viscosity UV inks on non-wettable, heat-sensitive polymeric and urethane/rubber substrates. However, not all LEDs are constructed exactly the same or exhibit equal performance characteristics. This article is the very first in the series to offer process advancements for industrial uv printer on plastics.
Until recently, UV LEDs have been confronted with technical and economic barriers that have prevented broad commercial acceptance. High cost and limited accessibility of LEDs, low output and efficiency, and thermal management problems – coupled with ink compatibility – were limiting factors preventing market acceptance. With advancements in UV LED technology, utilization of UV LEDs for curing could well be among the most significant breakthroughs in inkjet printing on plastics.
Easy to operate and control, UV LED curing has lots of advantages over mercury (Hg) vapor lamps. Small profile semiconductor devices are created to last beyond 20,000 hours operating time (about ten times longer) than UV lamps. Output is extremely consistent for long periods. UV LED emits pure UV without infrared (IR), so that it is process friendly to heat-sensitive plastic substrates. Reference Table 1 UV LEDs vs. Mercury Vapor Lamps.
LED and Hg vapor bulbs have different emission spectra. Photoinitiators are matched for the lamp, monomers, speed and applications. To attain robust cure, LED requires different photoinitiators, and as a result, different monomer and oligomers in the formulations.
Probably the most scrutinized parts of UV LED technology will be the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy being delivered to the curable ink. Mercury Hg bulbs routinely have reflectors that focus the rays so the light is most concentrated at the ink surface. This greatly raises peak power and negates any competing reactions. Early LED lamps were not focused.
High power and efficiency are achievable with garment printer by concentrating the radiant energy through optics and/or packaging. High-power systems utilize grouping arrays of LED die. Irradiance is inversely proportional to the junction temperature in the LED die. Maintaining a cooler die extends life, improves reliability and increases efficiency and output. Historical challenges of packaging UV LEDs into arrays have already been solved, and alternative solutions can be purchased, in relation to application. Much of the development and adoption of LED technologies have been driven by electronic products and displays.
First, formulating changes and materials happen to be developed, and also the vast knowledge has been shared. Many chemists now discover how to reformulate inks to match the lamps.
Second, lamp power has grown. Diodes designs are improved, and cooling is more efficient so diodes get packed more closely. That, consequently, raises lamp power, measured in watts per unit area with the lamp face, or better, at the fluid.
Third, lenses on lamp assemblies focus the strength, so peak irradiance is higher. A combination of such developments is making LED directly competitive, if not superior, to Hg bulbs in several applications.
Depending upon the applying and variety of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are accessible for select chemistries. As wavelength raises the output power, efficiency and costs also scale, e.g., 365nm LEDs provide less output than 395nm LEDs.
The performance from the die is much better at longer wavelengths, and the cost per watt output is lower while delivering more energy. Application history demonstrates that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, occasionally, 365nm or shorter wavelengths are needed to achieve robust cure.
LED cure best complements digital inkjet printing. On reciprocating printheads, hot and high Hg bulbs require massive scanning system frames, which can be not essential with LED. Fixed head machines possess the print heads assembled in modules and set up in overlapping rows. The compact, cool UV lamp fits nicely linked to a head module. Further, digital printing often is short run with frequent stops, so immediate “On/Off” yields greater productivity and revenue.
There are 2 implementations of thermal management: water and air-cooling. Water cooling is definitely an efficient way of extracting heat, specifically in applications by which high power densities are needed over large curing areas. With water cooling, lower temperatures can be found with higher efficiency and reliability.
A second good thing about water cooling will be the compact UV LED head size, which permits integration where there is limited space round the curing area. The drawbacks water cooling solutions dexjpky05 the heavier weight in the curing unit and added complexity and expenses for chillers and water piping.
Another thermal management option would be air-cooling. Air-cooling inherently is less effective at extracting heat from water. However, using enhanced airflow methods and optics yields highly effective air-cooling curing systems, typically up to 12W per square centimeter. The key benefits of air-cooled systems include easy integration, light weight, lower costs with out external chillers.
Maximization of A4 UV Printer output power is crucial. Via selective optics, the energy from LEDs could be delivered safer to the substrate or ink. Different techniques are included in integrated systems which range from reflection to focused light using lenses. Optics can be customized in order to meet specific performance criteria. Whilst the OEM (consumer) must not necessarily be worried about just how the optics are offered from the UV LED lamp, they should notice that suppliers’ expertise varies, and all UV LED systems are certainly not made the same.