7 Myths About LED Curing of Light-Curable Materials
LED curing light sources continue to evolve with the goal of replacing mercury arc curing lamps, the industry standard for more than thirty years. However, there seems to be some spawned misinformation and about the technology.
We’re busting 7 Myths about LED light-curing to help you make a sound purchasing decision.
Myth No. 1—LED light sources can seamlessly replace arc lamps in most curing processes.
LED curing lights can work well while offering savings and efficiencies, but changing from arc lamp to LED curing lights may not be a simple, direct conversion. Many details must be considered, the most important of which are differences in the wavelength distribution of LED and arc-lamp light sources. Furthermore, although a light- curable product that may be considered compatible with both arc lamps and LED light sources, switching to an LED light source can result in significant differences in post-cure bond performance.
The wavelength distribution emitted by an arc lamp and an LED are quite different. The wavelength distribution from a LED light source is narrow and bell shaped and can peak in the UV or visible light range depending upon the selection of the LED. The wavelength distribution from an arc lamp has multiple energy peaks spread over a wide range of wavelengths. Arc-lamp-energy spectral distribution varies depending upon the design of the arc lamp and other components of the curing system. The disparity in the wavelength distribution curves illustrate that a light-curable chemistry optimized for an arc lamp may perform inadequately when cured with a LED light source. Replacing an arc lamp with an LED light source might be as simple as modifying curing parameters of an existing process, or more complex such as changing of the adhesive to one properly formulated for the spectral-distribution characteristics of the LED light source.
Myth No. 2— LED spot-lamp systems and light-curable chemistries can be selected based on datasheet specifications and website information.
Datasheet and website specifications, although useful, may lack application-specific information. Some adhesive manufacturers may not state the irradiance and spectral distribution requirements for optimum curing and performance.
Myth No. 3—Bond performance is similar whether you are using an LED or a conventional lamp light source.
The direct replacement of an arc lamp spot-curing system with a LED spot-curing system—without evaluation and process adjustment—can result in substandard bond performance. Therefore, verification that your adhesive can provide the flexibility to use both types of light sources is strongly recommended to ensure successful results.
Myth No. 4—UV LED light sources best cure formulations when the wavelength peak is at 365 nm.
Traditional mercury arc lamps indeed emit a high level of energy at the wavelength peak of 365 nm. However, this does not mean that an LED light source with a 365 nm peak will provide the best performance. The reality is that many light-curable chemistries, including acrylated adhesives, use photo initiators that respond best to the narrow, bell-shaped spectral curve.
Myth No. 5—Manufacturers’ LED power ratings are comparable and correspond to performance.
A thorough review is required to properly interpret the claimed power ratings and associated advantages of LED curing systems. LED curing-equipment manufacturers may use LED power ratings as a sales tool, claiming that a higher power rating equates to better performance.
Myth No. 6—The energy supplied by LEDs enables you to cure heat-sensitive substrates without fear of product damage or substandard bonding.
LED sources do not generate or emit the multiple frequency irradiances across the spectrum as found in a conventional lamp. LED sources operate in a narrow spectral range that is specific for adhesive curing, resulting in “cooler” curing charicteristics. However, when energy from an LED source reaches a substrate or chemistry being exposed, it has two options. Depending on absorbtion characteristics of the irradiated materials (substrates and chemistry), the energy may be absorbed or reflected. Energy that is absorbed will genreally cause some level of thermal rise of the materials being exposed. Even under the “cool” energy supplied by an LED light source, the substrate and the chemistry can experience a thermal rise that may alter their structure and influence bond performance.
Myth No. 7—Wand-mounted LED light sources are better than using lightguides to transmit light energy from cabinet-mounted LED light sources.
Mounting the light source in the control cabinet offers provisions for efficient energy generation and heat dissipation. LED power output decreases with increases in temperature. LED operating temperature variation can also lead to frequency shifts in the emitted energy. The precision cooling offered by cabinet-mounted LED designs results in more consistent power output with less regulation. Furthermore, transitioning from arc lamp to cabinet-mounted LED light sources may obviate the need to replace existing lightguides or application fixturing.
There is no shortcut to success as you consider adopting LED curing technology in a manufacturing process. Consider a total-solutions provider that can complete application studies using your substrates and process requirements.