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 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 information is the first inside a series to show process advancements for industrial led uv printer 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 – put together with ink compatibility – were limiting factors preventing market acceptance. With advancements in UV LED technology, usage of UV LEDs for curing is arguably amongst the most significant breakthroughs in inkjet printing on plastics.
Simple to operate and control, UV LED curing has several 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 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.
LED and Hg vapor bulbs have different emission spectra. Photoinitiators are matched towards the lamp, monomers, speed and applications. To obtain robust cure, LED requires different photoinitiators, and as a consequence, different monomer and oligomers from the formulations.
Just about the most scrutinized regions of UV LED technology is definitely the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to be sent to the curable ink. Mercury Hg bulbs routinely have reflectors that focus the rays so 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 garment printer 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 of your LED die. Maintaining a cooler die extends life, improves reliability and increases efficiency and output. Historical challenges of packaging UV LEDs into arrays are already solved, and alternative solutions are offered, based on application. Much of the development and adoption of LED technologies have been driven by electronic products and displays.
First, formulating changes and materials have been developed, and the vast knowledge has become shared. Many chemists now learn how to reformulate inks to suit the lamps.
Second, lamp power has grown. Diodes designs are improved, and cooling is far more efficient so diodes get packed more closely. That, consequently, raises lamp power, measured in watts per unit area with the lamp face, or better, in the fluid.
Third, lenses on lamp assemblies focus the energy, so peak irradiance is higher. A combination of these developments is making LED directly competitive, or even superior, to Hg bulbs in lots of applications.
Based on the application and choice of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are around 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 your die is much better at longer wavelengths, along with 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, sometimes, 365nm or shorter wavelengths are required to 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 positioned in overlapping rows. The compact, cool UV lamp fits nicely linked to a head module. Further, digital printing often is short run 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 definitely a efficient means of extracting heat, particularly in applications where high power densities are needed over large curing areas. With water cooling, lower temperatures can be found with higher efficiency and reliability.
A 2nd benefit from water cooling is definitely the compact UV LED head size, which permits integration where there is limited space round the curing area. The drawbacks of water cooling solutions dexjpky05 the heavier weight of the curing unit and added complexity and costs for chillers and water piping.
Another thermal management option would be air-cooling. Air-cooling inherently is less effective 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 simplicity of integration, very light, lower costs and no external chillers.
Maximization of uv printer output power is critical. Via selective optics, the electricity from LEDs may be delivered easier to the substrate or ink. Different techniques are integrated into integrated systems starting from reflection to focused light using lenses. Optics might be customized to meet specific performance criteria. Whilst the OEM (consumer) should never necessarily be concerned with just how the optics are supplied inside the UV LED lamp, they must notice that suppliers’ expertise varies, and UV LED systems usually are not created equal.