Guide to UV Measurement
UV Irradiator
Reflector
The reflector is an extremely important component of the UV curing system irradiator. Sixty-eighty (60%-80%) percent of the UV energy that reaches the cure surface is reflected energy. It is important to keep the reflector clean and in good condition.
The reflector shape is usually elliptical or parabolic. An elliptical reflector will focus the reflected radiant power from the lamp to a point on the substrate that is approximately equal to the diameter of the lamp. This is referred to as the peak irradiance, and is important to achieving penetration through the chemistry to the substrate. A parabolic reflector will flood the surface area with UV energy rather than focused to a point. When maintaining the system, reassemble it as it was designed. Changing the distance between the irradiator-substrate and/or the irradiator-bulb can change the amount and way the UV is delivered.
The only practical material that will reflect the full spectrum on UV is pure aluminum. Reflectors are made from highly polished aluminum, stainless steel, or quartz and coated with vapor-deposited aluminum, followed by an inorganic protective coating. Dichroic coatings can be applied that will reflect the UV energy but absorb the IR wavelengths. IR “heat” is then removed from the system via the cooling air and/or water.
The reflector may be a fixed part in the irradiator, or it may be incorporated with a shutter mechanism.
Lamps
Bulb lengths can reach approximately 90 inches for arc lamps. Microwave-powered lamps are individual 6 inch and 10 inch modules that are then placed one next to the other (end-to-end) to form the desired width.
Shutter
Some arc systems incorporate shutters to prevent UV energy from reaching the substrate when the production process is idle. Shutters are utilized most with temperature sensitive substrates or on web systems. Microwave-powered systems turn on and off as required, thus eliminating the need for shutters.