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 information is the initial in a series to offer process advancements for industrial UV inkjet printing on plastics.
Until recently, UV LEDs happen to be faced 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 – coupled with ink compatibility – were limiting factors preventing market acceptance. With advancements in UV LED technology, utilization of UV LEDs for curing is arguably among the most significant breakthroughs in Coffee Ripples on plastics.
Simple 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 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 for the lamp, monomers, speed and applications. To attain robust cure, LED requires different photoinitiators, and as a consequence, different monomer and oligomers in the formulations.
Just about the most scrutinized regions of UV LED technology will be the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to be sent to the curable ink. Mercury Hg bulbs normally have reflectors that focus the rays therefore 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 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 been solved, and alternative solutions are available, dependant on application. Much 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 already been developed, and the vast knowledge has become 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 a lot more efficient so diodes get packed more closely. That, subsequently, raises lamp power, measured in watts per unit area on the lamp face, or better, in the fluid.
Third, lenses on lamp assemblies focus the ability, so peak irradiance is higher. The mixture of these developments is making LED directly competitive, or even superior, to Hg bulbs in many applications.
Based upon the applying and choice of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are for sale to select chemistries. As wavelength increases the output power, efficiency and expenses also scale, e.g., 365nm LEDs provide less output than 395nm LEDs.
The performance in the die is much better at longer wavelengths, and also the cost per watt output is less while delivering more energy. Application history implies that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, in some instances, 365nm or shorter wavelengths have to achieve robust cure.
Integrated systems solutions
LED cure best complements digital inkjet printing. On reciprocating printheads, hot and heavy Hg bulbs require massive scanning system frames, that are not necessary with LED. Fixed head machines possess 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 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 method of extracting heat, specifically in applications where high power densities are needed over large curing areas. With water cooling, lower temperatures can be acquired with higher efficiency and reliability.
A second benefit of water cooling is definitely the compact T-Shirt Printing Machine head size, which permits integration in which there is limited space across the curing area. The drawbacks of water cooling solutions are definitely the heavier weight of the curing unit and added complexity and expenses for chillers and water piping.
The 2nd 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 up to 12W per square centimeter. The advantages of air-cooled systems include easy integration, lightweight, lower costs with no external chillers.
Maximization of UV LED output power is crucial. Via selective optics, the vitality from LEDs can be delivered better 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 to satisfy specific performance criteria. As the OEM (end user) should not necessarily be concerned with just how the optics are supplied inside the UV LED lamp, they should notice that suppliers’ expertise varies, and all sorts of UV LED systems are not made the same.