Digital UV inkjet printing on three-dimensional plastic products is “ready for prime time.” Advancements in UV LED curing technology overcome many curing problems connected with traditional mercury vapor lamps. UV LED lamps are superior to treat low-viscosity UV inks on non-wettable, heat-sensitive polymeric and urethane/rubber substrates. However, not all LEDs are constructed a similar or exhibit equal performance characteristics. This article is the first within a series to show process advancements for industrial led uv printer on plastics.
Until recently, UV LEDs happen to be confronted with technical and economic barriers who have prevented broad commercial acceptance. High cost and limited availability of LEDs, low output and efficiency, and thermal management problems – along 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.
Very easy to operate and control, UV LED curing has numerous advantages over mercury (Hg) vapor lamps. Small profile semiconductor devices are designed to last beyond 20,000 hours operating time (about 10 times longer) than UV lamps. Output is quite 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 in turn, different monomer and oligomers inside the formulations.
One of the most scrutinized aspects of UV LED technology will be the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy being transported to the curable ink. Mercury Hg bulbs most often have reflectors that focus the rays and so the light is most concentrated with 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 dtg printer by concentrating the radiant energy through optics and/or packaging. High-power systems utilize grouping arrays of LED die. Irradiance is inversely proportional towards 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 happen to be solved, and alternative solutions can be purchased, based upon application. A great deal of the development and adoption of LED technology has been driven by consumer electronics and displays.
First, formulating changes and materials have been developed, and the vast knowledge has become shared. Many chemists now realize how to reformulate inks to match the lamps.
Second, lamp power has grown. Diodes designs are improved, and cooling is much more efficient so diodes get packed more closely. That, in turn, raises lamp power, measured in watts per unit area at the lamp face, or better, at the fluid.
Third, lenses on lamp assemblies focus the strength, so peak irradiance is higher. A combination of these developments is making LED directly competitive, otherwise superior, to Hg bulbs in several applications.
Depending upon the application and variety of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are around for select chemistries. As wavelength improves the output power, efficiency and expenses also scale, e.g., 365nm LEDs provide less output than 395nm LEDs.
The performance in the die is better at longer wavelengths, along with the cost per watt output is lower while delivering more energy. Application history implies that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, in some circumstances, 365nm or shorter wavelengths must achieve robust cure.
LED cure best complements digital inkjet printing. On reciprocating printheads, hot and heavy Hg bulbs require massive scanning system frames, which can be not necessary with LED. Fixed head machines hold the print heads assembled in modules and placed in overlapping rows. The compact, cool UV lamp fits nicely mounted on a head module. Further, digital printing often is short term with frequent stops, so immediate “On/Off” yields greater productivity and revenue.
The two main implementations of thermal management: water and air-cooling. Water cooling is certainly a efficient means of extracting heat, particularly in applications where high power densities will be required over large curing areas. With water cooling, lower temperatures can be had with higher efficiency and reliability.
A second advantage of water cooling is definitely 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 of the curing unit and added complexity and costs for chillers and water piping.
The 2nd thermal management option would be air-cooling. Air-cooling inherently is less efficient at extracting heat from water. However, using enhanced airflow methods and optics yields very effective air-cooling curing systems, typically up to 12W per square centimeter. The benefits of air-cooled systems include comfort of integration, lightweight, lower costs without any external chillers.
Maximization of A4 UV Printer output power is essential. Via selective optics, the vitality from LEDs can be delivered preferable to the substrate or ink. Different techniques are integrated into integrated systems including reflection to focused light using lenses. Optics could be customized in order to meet specific performance criteria. Whilst the OEM (end user) must not necessarily be worried about how the optics are offered inside the UV LED lamp, they need to notice that suppliers’ expertise varies, and UV LED systems will not be made the same.