Digital UV inkjet printing on three-dimensional plastic products is “ready for prime time.” Innovations in UV LED curing technology get over 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, 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 cafe printer on plastics.
Until recently, UV LEDs happen to be up against technical and economic barriers which 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, consumption of UV LEDs for curing is arguably 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 incredibly consistent for very 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 accomplish robust cure, LED requires different photoinitiators, and as a result, different monomer and oligomers within the formulations.
Probably the most scrutinized regions of phone case printer is definitely the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to be delivered to the curable ink. Mercury Hg bulbs normally have reflectors that focus the rays therefore 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 LED systems by concentrating the radiant energy through optics and 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 iaddzf of packaging UV LEDs into arrays happen to be solved, and alternative solutions can be found, based upon application. A lot of the development and adoption of LED technologies have been driven by consumer electronics and displays.
Recent significant developments
First, formulating changes and materials happen to be developed, as well as the vast knowledge continues to be shared. Many chemists now understand how to reformulate inks to match the lamps.
Second, lamp power has increased. Diodes designs are improved, and cooling is a lot more efficient so diodes get packed more closely. That, consequently, raises lamp power, measured in watts per unit area in the lamp face, or better, on the fluid.
Third, lenses on lamp assemblies focus the ability, so peak irradiance is higher. The combination of these developments is making LED directly competitive, or even superior, to Hg bulbs in numerous applications.
Based on the application and collection of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are available for select chemistries. As wavelength boosts 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 shows that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, in some instances, 365nm or shorter wavelengths are required to achieve robust cure.
Integrated systems solutions
LED cure best complements dtg printer. On reciprocating printheads, hot and heavy Hg bulbs require massive scanning system frames, which can be not necessary 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 2 implementations of thermal management: water and air-cooling. Water cooling is definitely a efficient method of extracting heat, particularly in applications where high power densities are essential over large curing areas. With water cooling, lower temperatures can be acquired with higher efficiency and reliability.
An additional benefit from water cooling is definitely the compact UV LED head size, which permits integration in which there has limitations space across the curing area. The drawbacks of water cooling solutions are definitely the heavier weight from the curing unit and added complexity and expenses for chillers and water piping.
The 2nd 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. Some great benefits of air-cooled systems include easy integration, light weight, lower costs without any external chillers.
Maximization of UV LED output power is critical. Via selective optics, the energy from LEDs could be delivered safer to the substrate or ink. Different techniques are incorporated into integrated systems starting from reflection to focused light using lenses. Optics may be customized to meet specific performance criteria. Whilst the OEM (end user) should not necessarily be concerned with how the optics are offered inside the UV LED lamp, they ought to notice that suppliers’ expertise varies, and all of UV LED systems are not created equal.