The choice of UV LED should avoid the "pit" and the status quo of development.

The list of applications that can use UV LED continues to grow as the number of system vendors, formulaters, and OEM equipment manufacturers supporting these applications continues to grow. This continued growth bodes well for the overall market direction of UV LED technology. So if you haven't yet learned if UV LEDs are right for your curing needs, it's probably time to start

. This article is intended to provide insight into the growing UV LED market space for new visitors, and those who have been tracking or even using the technology for years, and to provide general guidance on how to match UV LED curing systems to the needs of specific applications.
UV output
. The UV output is indicated by wavelength (nm), irradiance (W/cm2), and energy density (J/cm2). Understanding how these three factors interact with UV LED inks, coatings and adhesives under specific production conditions is critical to developing controlled curing applications and ensuring success. A key advantage of UV LED curing is that once the best combination of these three factors is established for a particular application, a matching and designed UV curing light source system will provide a stable, reliable and repeatable UV output at all times.
Figure 1. Relative wavelength distribution of UV LEDs
UV LED light source system emits a relatively single wavelength, representing a narrow bell-shaped distribution, with a symmetrical peak irradiance of 365, 385, 395 and 405nm, as shown in Figure 1. The exact wavelength and distribution shape of the peak depend entirely on the original material structure of the diode and cannot be adjusted after the diode is regulated. Although two or more wavelength distributions can be mixed in a single UV LED device, most curing systems typically contain only one wavelength distribution. Due to different material structures, the current maximum irradiance of 365nm is about 20% weaker than the three longer wavelengths, as can be seen from its shorter peak in the figure.
wavelengths, irradiance and energy density are highly variable indicators of UV LED output. The index data of the light source emission window and substrate curing surface are determined by many factors in the overall design of the lamp head. Irradiance and energy density vary by product model and are generally adjustable for the specified system and are largely affected by the configuration at installation time. This adjustable advantage is that it allows the user to optimize the manufacturing process precisely and efficiently.
for UV LED curing systems, peak irradiance should not be considered an indicator of energy density during dynamic manufacturing processes. Instead, these values should be given by the supplier and can be measured. You can then infer additional data points that match the required manufacturing conditions. When reporting irradiance and energy density, information on measuring instruments, parameter settings, and data collection methods should always be given, as these three indicators have an impact on observations.
2. Dynamic irradiance profile. The chart is provided by Eminem UV
we first need to identify two concepts: irradiance is peak power, and energy density is the total amount of energy delivered. In mathematical terms, energy density is the integration of irradiance over a period of time, expressed by the area contained in the irradiance/time graph.
2 (a) is a graphical illustration of a point on the cured surface (along the x-axis) moving horizontally at a fixed vertical working distance under the UV LED lamp. Each point on the curve is the irradiance experienced by the cured surface at each moment. The area below the curve is the total energy density emitted. As shown in Figure 2 (b), UV LED systems with the same peak irradiance do not always provide the same energy density.
note that the four different scenarios in (b) do not contain the same area. The outer outerst scene has the largest area, which provides the maximum energy density, while the inner inner layer contains the smallest area and provides the least energy density.
two systems with different irradiances can also provide the same total energy density, as shown in Figure 2 (c). The peak irradiance of one curve is half that of the other curve; One of the head design differences that produces this result is that the width of the higher peak UV LED emission window is half the width of the lower peak emission window.
These three examples illustrate the importance of understanding emission and obtained irradiance, and the impact of energy density, and why not all UV LED systems behave the same in laboratory installations or commercial configurations when matching UV LED systems to applications.
inks, coatings and adhesives are made to react chemically to a given UV LED output under specific process conditions. For each application and formulation, there is a UV process window for acceptable curing. This window is not narrow, but there is a set of optimal wavelengths, as well as a combination of minimum and maximum irradiance, and energy density, for proper curing.
always operates within this process window to ensure optimum transfer speeds, non-stick surfaces, adequate adhesion, adequate curing effects, minimal migration after curing, and required product life, as well as other required performance metrics. The establishment and maintenance of UV curing process windows for a given application is essential for continuous optimal yield efficiency and access to high quality products.
UV LED technology performs well when the UV energy output is properly matched to the application needs and is matched with the right preparation of inks, coatings or adhesives. Unfortunately, there is no universal UV LED system or process window for all applications. Appropriate UV LED solutions and energy outputs should be selected for formulation products, plant or shop environments, as well as for the configuration and transfer speed of material handling systems.
benefits of UV LED technology is that the discrete nature of the LEDs themselves allows for a wider range of curing systems to better meet the needs of each unique application. This allows form factors and UV outputs to be tailored to their respective markets and applications, enabling them to achieve more efficient and cost-effective UV LED curing solutions than conventional curing technologies.figure
. The UV LED
application evolution
UV digital inkjet needle curing on wide-area coating machines, and the full curing of printers using scanning and single-channel mode, as well as the point curing of adhesives, were the first applications to use UV LED curing in the printing and bonding process. Many of the early installations were hybrids that took advantage of some of the features of traditional curing and combined with UV LEDs.
the application market for these early adopters, with slower line speeds and longer workware processing times, UV LED technology was successfully enabled in the mid-2000s. Its manufacturing process method allows sufficient energy density to be accumulated in static devices through longer exposure times and multiple curings in dynamic devices.
equipment also allows UV LED headers to be installed within 10mm of the curing surface and typically requires less total number and length of lamps per machine. It takes only one or two smaller lights and less commercial investment than a larger, wider high-speed commercial press. All of these factors are critical because early UV LED systems were not energy-efficient enough and tended to be much more expensive than conventional equipment.
the past 15 years, UV LED technology has improved significantly in terms of performance, reliability, service life and output. In addition, more formulation optimizations have been made for the output of UV LEDs. The market has also learned to understand and design process windows. The price of equipment and formulations has also been reduced as a result of the development of economies of scale and increased competition throughout the supply chain. This enables UV LED curing technology to exceed the needs of UV digital inkjet needle curing and point curing applications to more demanding, high-speed, and broader commercial applications, including analog and digital technologies.
Table 1. Applications of UV LED technology
table 1 lists the increasing use of UV LED technology today. Although market penetration varys from sector to sector, UV LEDs may not be suitable for all applications in each segment - but this technology will continue to evolve and evolve over time. Different UV LED lamp designs, as well as application-specific formulations, make these different printing, coating and bonding processes possible.
based on these fit requirements, there must be a strong working relationship connection between the parties involved in each application , including UV LED curing system suppliers, formulators, OEM machine manufacturers, integrators, and end users. In all scenarios, viable UV LED solutions can often be achieved through trial and error, as well as process optimization. It all boils down to optimizing process variables and matching UV LED systems to applications, formulations, and material handling equipment.
to match UV LED systems to applications, formulations, and material handling equipment
there are now a growing number of UV LED curing systems and suppliers to choose from. The product features and operating advantages they advertise are very similar, with the most obvious differences being peak irradiance, cooling, and the shape of the lamp. Unfortunately, understanding this knowledge alone is not enough to match UV LED curing systems to specific applications, and there is little explanation in the specification table as to which product is best suited for which application and why. These general guidelines should be taken into account when selecting and applying UV LED curing systems that match.
final curing performance
should be clear about the physical and physical characteristics required after final curing, as well as the intended use of the product. This will help drive chemical considerations in formulations and even the current suitability of UV LED curing solutions. For example, inks, light oils, and adhesives are typically cured well with LEDs and meet most graphics printing requirements. However, silicone stripping and industrial hard coating applications are still under development, with at least three to five years to go before large-scale commercial availability.
wavelengths
commercial applications currently include 365, 385, 395 and 405nm. For most ink applications, 395nm is the preferred wavelength, with less use of 365 and 385nm wavelengths. Adhesives are usually best suited for 365 or 405nm, depending on the formulation, but they can also cure at 385 or 395nm. The hood oil usually matches the 395nm wavelength of ink applications, but when it comes to industrial coatings, whether functional or hardened, there is no consensus, as the development of these applications is still in its infancy.
irradiance window
the formula must be cured between minimum and maximum peak irradiance (W/cm2). Lower than minimum irradiance leads to insufficient curing, and increasing curing when irradiance exceeds the maximum peak does not necessarily result in better curing results. As long as the lamp can emit enough energy density, it can always get a good curing effect in the established irradiance window. Unfortunately, there is no universal irradiance to meet the needs of all formulations.
application is different, the optimal emission irradiance window is possible from a few hundred mW/cm2 to any value between 20 and even 30 watts/cm2. At the same time, more important than the irradiance emitted by the LED lamp is the actual irradiance transmitted to the surface of the cured substrate, as the irradiance decreases rapidly as the distance of light passes.
energy density window
the required energy density (J/cm2) is determined by the formulation and production line speed. Higher energy densities often result in better overall curing, faster lines, and sometimes lower peak irradiance. Not all systems that emit the same peak irradiance provide the same energy density.
energy density can be achieved by using a designed luminaire system, including using multiple lamps at the same time, reducing line speed, or increasing exposure time.
working distance
this is defined as the distance between the UV LED emission window and the cured surface. The operating distance must be specified for the application and machine settings, as irradiance decreases rapidly as the distance increases. To accommodate larger working distances, consider more powerful lamps (higher irradiance or/and higher energy density) or LED solutions with optical or reflective covers.
cooling system
plant environment, the preferences of OEM manufacturers or end users, and the design of the UV LED system itself determine the composition of the cooling system (air-cooled or water-cooled). Not all UV LED devices offer air-cooled options. High-power systems are usually water-cooled.
installation space
installation location and machine settings determine the required space for the UV LED head. Water-cooled systems are generally more compact than air-cooled systems. The air cooling system has minimal space around the air inlet, as it ensures adequate circulation of the air.
and shields
the distance and orientation of the luminaires relative to areas that should not be cured can affect the use of optics and shields. Special care should be taken to ensure that UV rays are blocked from digital inkjet printheads, ink and coating trays, and thermal materials on the machine. In addition, all light should be blocked from any direct exposure by the operator.
extreme heterogeneity workmangeture scenarios
in scenes with extreme alien workmangees, the curing surface or production line requires LED lights to be installed at a greater distance (a few inches or more). This remains a challenge for UV LED coatings that require particularly hard, scratch-resistant, and chemical resistance, and should still be considered a requirement still under development for the foreseeable future.
UV LED technology will continue to develop in the next few years, and undoubtedly in more and more applications have been well matched. While it is not possible to replace the same fully interchangeable curing system in the list of applications listed earlier, there are unique UV LED solutions that meet many application needs. While OEMs can match LED curing devices and formulations to buyers before purchase, we always recommend that users test or refer to previous installations.