Digital UV inkjet printing on three-dimensional plastic products is “ready for prime time.” Advancements in UV LED curing technology overcome many curing problems associated 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, not all LEDs are constructed the identical or exhibit equal performance characteristics. This post is the first in a series to offer process advancements for industrial UV inkjet printing on plastics.
Until recently, UV LEDs have been confronted with technical and economic barriers who have prevented broad commercial acceptance. High cost and limited accessibility to LEDs, low output and efficiency, and thermal management problems – combined with ink compatibility – were limiting factors preventing market acceptance. With advancements in UV LED technology, utilization of UV LEDs for curing could well be some of the most significant breakthroughs in Cafe Printer on plastics.
Very easy to operate and control, UV LED curing has lots of advantages over mercury (Hg) vapor lamps. Small profile semiconductor devices are designed to last beyond 20,000 hours operating time (about ten times longer) than UV lamps. Output is incredibly consistent for too long periods. UV LED emits pure UV without infrared (IR), rendering it process friendly to heat-sensitive plastic substrates. Reference Table 1 UV LEDs vs. Mercury Vapor Lamps.
UV LED early development factors
LED and Hg vapor bulbs have different emission spectra. Photoinitiators are matched towards the lamp, monomers, speed and applications. To attain robust cure, LED requires different photoinitiators, and as a result, different monomer and oligomers within the formulations.
One of the most scrutinized regions of UV LED technology is definitely the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to become shipped to the curable ink. Mercury Hg bulbs routinely have reflectors that focus the rays and so the light is most concentrated on 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 Phone Case Printer by concentrating the radiant energy through optics and/or packaging. High-power systems utilize grouping arrays of LED die. Irradiance is inversely proportional for 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 found, based on application. Most of the development and adoption of LED technologies have been driven by electronic products and displays.
Recent significant developments
First, formulating changes and materials have been developed, and the vast knowledge continues to be shared. Many chemists now understand how to reformulate inks to fit 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 in the lamp face, or better, in the fluid.
Third, lenses on lamp assemblies focus the energy, so peak irradiance is higher. The mixture of these developments is making LED directly competitive, if not superior, to Hg bulbs in numerous applications.
Based upon the application form and selection 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 of the die is way better at longer wavelengths, and also the cost per watt output is less while delivering more energy. Application history suggests that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, in some circumstances, 365nm or shorter wavelengths have to achieve robust cure.
Integrated systems solutions
LED cure best complements digital inkjet printing. On reciprocating printheads, hot and high Hg bulbs require massive scanning system frames, which 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 mounted on a head module. Further, digital printing often is short run with frequent stops, so immediate “On/Off” yields greater productivity and revenue.
Thermal management and optics
There are two implementations of thermal management: water and air-cooling. Water cooling is definitely a efficient approach to extracting heat, especially in applications in which high power densities are required over large curing areas. With water cooling, lower temperatures can be obtained with higher efficiency and reliability.
An additional advantage of water cooling is definitely the compact T-Shirt Printing Machine head size, which permits integration in which there has limitations space around the curing area. The drawbacks water cooling solutions are the heavier weight in the curing unit and added complexity and expenses for chillers and water piping.
The next thermal management option is air-cooling. Air-cooling inherently is less efficient at extracting heat from water. However, using enhanced airflow methods and optics yields untyft effective air-cooling curing systems, typically as much as 12W per square centimeter. The advantages of air-cooled systems include ease of integration, light weight, lower costs with no external chillers.
Maximization of UV LED output power is critical. Via selective optics, the power from LEDs could be delivered preferable to the substrate or ink. Different techniques are integrated into integrated systems which range from reflection to focused light using lenses. Optics may be customized to meet specific performance criteria. While the OEM (end user) must not necessarily be concerned with the way the optics are provided within the UV LED lamp, they ought to notice that suppliers’ expertise varies, and all of UV LED systems are not created equal.