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 to treat low-viscosity UV inks on non-wettable, heat-sensitive polymeric and urethane/rubber substrates. However, its not all LEDs are constructed exactly the same or exhibit equal performance characteristics. This article is the initial in the series to show process advancements for industrial led uv printer on plastics.
Until recently, UV LEDs are already confronted by 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, using UV LEDs for curing is arguably one of the most significant breakthroughs in inkjet printing 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 very long periods. UV LED emits pure UV without infrared (IR), making 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 on the lamp, monomers, speed and applications. To accomplish robust cure, LED requires different photoinitiators, and in turn, different monomer and oligomers inside the formulations.
Just about the most scrutinized parts of UV LED technology will be the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to become sent to the curable ink. Mercury Hg bulbs normally have reflectors that focus the rays and so 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 dtg printer by concentrating the radiant energy through optics and packaging. High-power systems utilize grouping arrays of LED die. Irradiance is inversely proportional for the junction temperature from the LED die. Maintaining a cooler die extends life, improves reliability and increases efficiency and output. Historical challenges of packaging UV LEDs into arrays happen to be solved, and alternative solutions can be found, based upon application. Much of the development and adoption of LED technology has been driven by electronic products and displays.
First, formulating changes and materials have already been developed, and also the vast knowledge has been shared. Many chemists now discover how to reformulate inks to fit 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, 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 mix of the developments is making LED directly competitive, otherwise superior, to Hg bulbs in numerous applications.
Based on the application and variety of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are around for select chemistries. As wavelength raises the output power, efficiency and expenses also scale, e.g., 365nm LEDs provide less output than 395nm LEDs.
The performance from the die is much better at longer wavelengths, as well as the cost per watt output is less while delivering more energy. Application history demonstrates that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, occasionally, 365nm or shorter wavelengths are needed 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 are not essential with LED. Fixed head machines possess the print heads assembled in modules and placed 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.
There are two implementations of thermal management: water and air-cooling. Water cooling is definitely an efficient means of extracting heat, particularly in applications by which high power densities are essential over large curing areas. With water cooling, lower temperatures can be had with higher efficiency and reliability.
An additional benefit from water cooling is 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 expenses for chillers and water piping.
Another thermal management option is air-cooling. Air-cooling inherently is less effective at extracting heat from water. However, using enhanced airflow methods and optics yields highly effective air-cooling curing systems, typically as much as 12W per square centimeter. The benefits of air-cooled systems include comfort of integration, light weight, lower costs with no external chillers.
Maximization of uv flatbed printer output power is vital. Via selective optics, the electricity from LEDs may be delivered safer to the substrate or ink. Different techniques are included in integrated systems including reflection to focused light using lenses. Optics might be customized to fulfill specific performance criteria. Whilst the OEM (consumer) must not necessarily be concerned with just how the optics are given from the UV LED lamp, they must know that suppliers’ expertise varies, and all UV LED systems usually are not made the same.