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 for curing low-viscosity UV inks on non-wettable, heat-sensitive polymeric and urethane/rubber substrates. However, its not all LEDs are constructed the same or exhibit equal performance characteristics. This information is the initial within a series to show process advancements for industrial led uv printer on plastics.
Until recently, UV LEDs are already confronted with technical and economic barriers who have prevented broad commercial acceptance. High cost and limited accessibility of LEDs, low output and efficiency, and thermal management problems – put together with ink compatibility – were limiting factors preventing market acceptance. With advancements in UV LED technology, using UV LEDs to treat is arguably amongst the most significant breakthroughs in inkjet printing on plastics.
Very easy to operate and control, UV LED curing has several advantages over mercury (Hg) vapor lamps. Small profile semiconductor devices are created to last beyond 20,000 hours operating time (about 10 times longer) than UV lamps. Output is quite consistent for very long periods. UV LED emits pure UV without infrared (IR), which makes it 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 within the formulations.
One of the most scrutinized regions of UV LED technology is the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to get shipped to the curable ink. Mercury Hg bulbs most often have reflectors that focus the rays hence the light is most concentrated in 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 or packaging. High-power systems utilize grouping arrays of LED die. Irradiance is inversely proportional for the junction temperature of 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 are offered, in relation to application. A great deal 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 the vast knowledge has become shared. Many chemists now learn how to reformulate inks to suit the lamps.
Second, lamp power has increased. Diodes designs are improved, and cooling is much more efficient so diodes get packed more closely. That, therefore, raises lamp power, measured in watts per unit area on the lamp face, or better, with the fluid.
Third, lenses on lamp assemblies focus the energy, so peak irradiance is higher. The mixture of the developments is making LED directly competitive, or else superior, to Hg bulbs in lots of applications.
Based upon the application and selection 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 costs also scale, e.g., 365nm LEDs provide less output than 395nm LEDs.
The performance from the die is better at longer wavelengths, and also the cost per watt output is less while delivering more energy. Application history shows that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, occasionally, 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, that are not required with LED. Fixed head machines have the print heads assembled in modules and set up in overlapping rows. The compact, cool UV lamp fits nicely attached 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 certainly a efficient means of extracting heat, particularly in applications through which high power densities are essential over large curing areas. With water cooling, lower temperatures can be had with higher efficiency and reliability.
A second benefit from water cooling may be the compact UV LED head size, which permits integration in which there has limitations space throughout the curing area. The drawbacks water cooling solutions dexjpky05 the heavier weight of your curing unit and added complexity and expenses for chillers and water piping.
Another thermal management solution is air-cooling. Air-cooling inherently is less efficient at extracting heat from water. However, using enhanced airflow methods and optics yields successful air-cooling curing systems, typically approximately 12W per square centimeter. The advantages of air-cooled systems include ease of integration, light weight, lower costs without any external chillers.
Maximization of uv printer output power is crucial. Via selective optics, the vitality from LEDs may be delivered easier to the substrate or ink. Different techniques are integrated into integrated systems ranging from reflection to focused light using lenses. Optics can be customized in order to meet specific performance criteria. Even though the OEM (end user) ought not necessarily be worried about the way the optics are provided in the UV LED lamp, they should notice that suppliers’ expertise varies, and all UV LED systems will not be made the same.