Paint & Coatings Industry - February 2009 - (Page 18) Ultraviolet (UV) for Formulators: Part I F or those involved in UV processes, UV measurement and process control is an important topic. Measurement answers critical questions like “How do we know whether a process is running properly?” “How do we troubleshoot problems with cure?” “How do we set up our production process in the first place?” or “How do we maintain a process we have set up?” These are the kind of problems that an understanding of UV measurement helps solve. And these are the kind of issues that much of the existing information about UV measurement has addressed. But these concerns are different for formulators and raw material providers, as they also need to consider how to establish a UV specification for their customers to follow, how to optimize and communicate their curing specification and how their specifications can be reproduced and applied in the field. While end users are often concerned with relative UV measurement (Are my UV levels today different than yesterday? Can I run production?), suppliers often need to express UV measurement in absolute terms. For a specific product and application, these are the conditions and ranges that we have identified as starting points to get an “adequate cure”. And while it may be sufficient for manufacturers to develop a language that is unique to their own production environment, suppliers need to speak in a more universal language so that any customer can clearly understand and implement the information and also communicate with their entire supply chain Clear, meaningful and useful communication is the goal. Often the release of clear, meaningful and useful information is at odds with the proprietary nature of formulations. We hope that the formulator, perhaps on an individual basis, can work with their customers to get them the information needed to succeed. The formulator must provide his customer with enough starting information to enable the customer to reproduce the laboratory cure conditions in his plant. But in order to do so, both should understand what information is necessary to fully describe and repeat the process. It’s also helpful when making these measurements to be aware of subtle factors that can distort or confuse these measurements so that appropriate care is taken. This paper is aimed at suppliers of UV equipment and chemicals, though it will certainly be useful to manufacturers as well. In fact, as the ads for a well-known men’s clothing manufacturer used to say, “an educated consumer is our best customer.” For suppliers, the more everybody in the chain understands and speaks the same language, the smoother things will probably go. The formulator, as a benefit to clear communication, may also notice a reduction in the dreaded “your product is not curing” phone call. FIGURE 1 | Medium-pressure mercury discharge lamp spectral distribution. 100 90 80 Relative Intensity (%) 70 60 50 40 30 20 10 0 200 250 300 350 400 450 500 550 Wavelength(nm) 600 650 700 750 800 UV Measurement Basics W We begin with a review of the three fundamental p parameters at the top of the UV measurement list: wavelength, irradiance and energy density. Wavelength R Radiation is nothing more than the movement of (elect tromagnetic) energy from one point to another. Visible r radiation is present when a light bulb is on. Infrared r radiation is present when an oven broiler is turned on. U Ultraviolet radiation is present when a UV source is on. U UV is characterized by the emission of energy in a port tion of the electromagnetic spectrum, which is as the n name implies, “ultra” (Latin for beyond) violet. Violet light, at the extreme end of visible light, has the shortest wavelength, near 400 nanometers (nm). Ultraviolet p picks up where violet ends, with wavelengths running f from 10 nm to 400 nm. UV below approximately 200 nm exists primarily exist p maril i ily l vacuum and not particularly acuu uum articularly rticularl nm exists primarily in a vacuum and is not particularly By Paul Mills | UV Robotics, LLC, Cleveland, OH; and Jim Raymont | EIT Incorporated, Sterling, VA 18 FE BRUARY 200 9 | W W W . P C I M A G . C O M EB RUA RY 2009 BRUA R B UARY
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