08.03.2016
Some transparent plastics such as PC and PMMA are UV blocking and in these cases an adhesive that cures with the visible light range must be used.
While UV curing materials should be protected from fluorescent and sunlight, these do not have sufficient intensity to effect a full cure. Dymax have a very wide range of adhesives and coatings for many other specialised applications. Relative to visible LEDs, UV LEDs are a quiet market at only $30 million, yet recent breakthroughs in radiant power and intensity have enabled the displacement of mercury-vapor lamps in applications including UV curing and counterfeit detection, reports LAURA PETERS.
Curing involves the cross-polymerization of a photosensitive material, which can be an ink (printing), adhesive or coating, and is primarily performed at 395 nm, 385 nm or 365 nm, wavelengths which are part of the UV-A spectrum (315-400 nm). In the UV-B spectrum (280-315 nm), applications for UV LEDs include curing, medical light therapy, forensic analysis and drug discovery. Beyond these applications, UV-B radiation is known to have beneficial health properties including the natural synthesis of vitamin D in humans who are exposed to sunlight.
In the lower UV-C spectral range (100-280 nm), the primary LED applications are air and water sterilization and a range of analytical tools including those that perform spectroscopic and fluorescence measurements. UV in the 250-275 nm range sterilizes water, air and surfaces by breaking-up the DNA and RNA of microorganisms and preventing their reproduction.
In production curing operations, mercury-vapor lamps are hindered by short lifetime (2000-10,000 hr), slow warm-up and cool-down times, and wide spectral power distribution. The mercury lamp has a main peak at 365 nm but several smaller peaks in the visible and infrared regions (Fig.
Metcalf added that many people who would not have considered UV curing because of the complexity of standard curing processes a€“ the high voltage, heat of mercury bulbs and environmental issues a€“ will now consider UV-LED curing because it subverts the traditional hassles of the old process. UV LEDs bring such benefits as knowing precisely what power level is being delivered to the curing medium, as well as other advantages LEDs are known for, such as the ability to pulse-width-modulate the output, stated Eskow. The transition to UV LEDs also opened the door to more environmentally friendly curing formulations.
For the longer-wavelength UV devices, in a similar manner to blue LED fabrication, InGaN-based epilayers are grown on sapphire substrates to produce 385, 395 and 405 nm UV LEDs for curing. In addition to producing more power, the higher-wavelength UV LEDs feature higher wall-plug efficiencies. Stacy Volk, marketing communications specialist at Phoseon Technology in Hillboro, OR, a maker of UV-LED curing systems, pointed out some of the additional advantages associated with UV-LED curing include a controlled curing intensity, scalable equipment, and the fact that the machines are smaller and compact.
One of the issues the curing industry has faced has been inconsistencies in measurement practice and parameter definitions, for example, defining radiometric intensity.
Companies that manufacture UV-LED chips include Crystal IS, based in Green Island, NY (Fig.
UV-LED manufacturers focus on continually improving the efficiency and lifetime of their devices while reducing cost. Tim Bettles, director of marketing and sales at SETi stated that its manufacturing agreement with Seoul Optodevice is designed to help SETi drive its volumes of UV LEDs and lamps higher while driving down costs.
Devin Tang, marketing manager of SemiLEDs stated that the company has a full line of bare dice and surface-mount high power packaged LEDs in the 360-400-nm range. Epigap Optronic, based in Berlin, Germany, the main distributor for Dowaa€™s UV LEDs, stated that Dowa manufactures 265, 280, 310, 325 and 340 nm bare dice or packaged LEDs. Recently, Theodore Moustakas of Boston University has pioneered the use MBE (molecular beam epitaxy) to grow more efficient (high internal quantum efficiency) UV LED devices using AIGaN-based layers on sapphire substrates.
Even though UV LED manufacturers have been working hard to improve internal quantum efficiency and optical efficiency, overall efficiency remains below 20%, meaning a great deal of heat must be dissipated from the diodea€™s junction.
While some UV LED arrays are packaged on ceramic substrates, many manufacturers, particularly of single-chip devices, use TO-can type through-hole packages with a glass top that offers high transmission of UV.


The choice of whether to use hermetic sealing in the package is sometimes determined by the materials in the chip. It is important to recognize that some of the same qualities that make UV LEDs very powerful and useful a€“ their low wavelength and high energy a€“ are also the qualities that make them dangerous.
When asked to identify the key issue that might keep UV users from changing over from mercury-vapor sources to UV LEDs, many industry participants say it comes down to breaking existing industry momentum and, of course, cost. Sponsored Content is made possible by our sponsor; it does not necessarily reflect the views of our editorial staff. Subscribe to the magazine or email newsletter today at no cost and receive the latest news and information. Instead of haphazardly squeezing some adhesive out of a tube, Offerman’s Bondic system allows you to join two materials together with liquid plastic that hardens under UV light. To use Bondic, you simply apply your desired amount of liquid plastic to whatever you’re hoping to repair.
After about four seconds of direct UV exposure, the plastic becomes hard as a rock but not so hard that it resists sanding and finishing.
And the best part? A Bondic starter kit (which includes the dispenser, UV hardening light, and a 4-gram tube of adhesive) is just 22 bucks.
Ranging from 100 to 400 nm, the radiation can effectively be used to sterilize cosmetics, perform forensic analysis, cure materials (Fig.
UV-B also accelerates the production of polyphenols in certain leafy vegetables such as red lettuce. Specifically, 275 nm is believed to be the most effective wavelength for eradicating pathogens such as E-coli in water. With the next generation of products that ink, coating and adhesive companies were developing, they used the opportunity to phase-out volatile organic compounds (VOCs) associated with the solvent-based formulations of past chemistries. Metcalf describes large flat-bed banner printers as being able to use lower-power LEDs, but higher speed digital, offset and flexographic technologies require closely-spaced banks of high-flux-density LEDs. Seoul Optodevice has a manufacturing partnership agreement with SETi, which manufactures a broad range of UV LEDs and lamps, and performs everything from wafer processing to custom lamp design. The replacement of epoxy lenses with flat or dome-shaped glass capable of UV transmission is a relatively new development, and one that has allowed an extension of lifetimes from around 5000 hours up to as high as 30,000 hours.
The warning labels on UV LEDs and their products are clear but bear noting: UV-LEDs emit invisible ultraviolet radiation when in operation, which may be harmful to eyes or skin, even for brief periods. Lim thinks that a rounding out of the wavelength portfolio would go a long way toward adoption. You know those little UV glue guns that dentists use to fill minor cavities before they get too serious?
The goop can bond practically anything (plastic, metal, fiberglass, wood, fabric, etc.), and the high-precision extruder tip allows you to apply exactly as much adhesive as you need.
UV-LED flashlights in this range are used to detect fraudulent identification and currency, and offer the benefit of use in well-lit environments, which is difficult using a mercury-vapor lamp. He added that the UV output of a mercury vapor lamp drops off rapidly over its operational life because some of its electrode material vaporizes, depositing a film on the inside of the quartz tube which the UV cannot penetrate. A downside to these extraneous peaks is the generation of heat during printing and other curing operations. At 385 nm, this efficiency improves, but only to ~15%, making the higher-wavelength chip the better choice. Depending on the equipment and curing application, the media can be 1 to 100 mm from the emitter window, for which AMS has produced special optics.
Even though the radiation is not visible, collimating optics are utilized to deliver the radiation with a uniform power level across the target media.


The association also seeks to help speed development of applications especially suited to UV LEDs, educate researchers, integrators and end users regarding the benefits of UV LEDs, and provide a forum for industry communication and collaboration. The company provides UV emitters in hermetically-sealed metal-glass packages (TO-18, TO-39 and TO-3), with standard products and custom solutions spanning the wavelength range from 240 to 355 nm.
We are now gearing SETia€™s capacity for high-volume manufacturing to cater to new demands coming from mainstream consumer markets,a€? said Bettles. Crystal IS manufactures 260 nm UV LEDs and is the only company to produce LEDs on AlN substrates. Nonetheless, AlN substrates are only available in small sizes and remain much more expensive than sapphire wafers, thereby limiting this market.
This is only possible with an LED package capable of handling extreme power densities for the life of the product. UV accelerates degradation of the epoxy material in a non-linear manner, directly impacting lifetime.
The new copper- and glass-based package from Schott offers the advantages of high thermal conductivity and hermeticity. It’s basically the exact same adhesive technology, just tweaked a little and redesigned for a different purpose. This adhesive will remain in liquid form until you hit it with a blast of UV light, so you’re free to fiddle with it and make adjustments before you commit to hardening. Today, as is the case with LEDs in the visible spectrum, UV LEDs are only beginning to replace the established UV sources in a likewise diverse array of markets.
As a result, the user cannot easily predict the amount of UV generated at a later time; often this is a critical process parameter. All the major providers of curing formulations (photoinitiators and resins), have recently brought higher-wavelength inks and coatings to market to fill this need. Digital inkjet curing was the first segment to adopt UV LEDs due to the required close distance to the media for the print heads to optimally perform. Figure 6 shows examples of UV-LED arrays in lamps designed to deliver radiation in the 300-320 nm range for phototherapy applications such as the treatment of skin conditions such as psoriasis or eczema. SETi recently announced the purchase of a new facility, where it plans to manufacture over 100 million UV LEDs per year. A thermally matched stress-free package and glass lens help eliminate common packaging failure modes associated with UV LEDs,a€? said Thomas.
Interestingly, we have evidence that when those plants are exposed to UV-B LEDs a short time before harvest, their polyphenol content is boosted without compromising plant mass,a€? explained Cary Eskow, global director of advanced LEDs and illumination for Avnet Electronics Marketing in Phoenix, AZ, which distributes UV LEDs. SETi has demonstrated disinfection of drinking water in an in-line flow-through system using less than 40 mW of UV power.
He gave examples that include plastic gift cards or credit cards, which use sheet-fed lithographic printing.
This was a natural fit for UV-LED lamps as the curing intensity is highest at the emitter window.
He described LED Engina€™s patented multi-layer ceramic substrate with extremely low thermal resistance that quickly conducts heat from the die junction (Fig. Another alternative is to combine a glass lens with silicone encapsulant to accommodate even higher flux density and higher efficiency yet shorter lifetime (15,000-20,000 hr). He continued a€?This is a novel method for increasing the appeal of some foods without using chemicals.



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Comments Uv adhesive curing light manual

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