Paint & Coatings Industry - April 2008 - (Page 34)

Designing UV-Curable Materials For High-Temperature Optical Fiber Applications FIGURE 3 | A typical TGA plot of a UV-cured film. color and tensile properties after aging at progressively higher temperatures. Secondly, a number of monomeric and oligomeric components were cured and heat aged to assess resistance to weight loss as baseline information for further coating development. Coatings Evaluated Table 1 gives a breakdown of the different components present in the six optical fiber coatings tested. Nine different types of urethane acrylate (UA) oligomers, one bisphenol-A epoxy diacrylate oligomer and various acrylate monomers are present in these chemistries. An α-hydroxy ketone photoinitiator and a standard bis-phenolic antioxidant are present in each of these as well. These coatings were cured using a Fusion 600 Watt/inch irradiator with an “H” bulb. The radiant energy density, or UV dose used to cure these coatings, was 1000 mJ/cm2. A 3-mil bird applicator was used to cure films on glass. The coating, glass and applicator were all allowed to equilibrate to 85 °C before curing in order to minimize vitrification effects, as these coatings have glass transition temperatures well above room temperature, typically >75 °C. After curing, the films were removed from glass and allowed to equilibrate in a 23 ± 2 °C/ 50 ± 5% RH environment before subjecting them to aging at 125, 175, and 225 °C heating in forced air ovens. Weight Loss Change Figure 1 shows the weight loss of these coatings after 24 hours at 125, 175, and 225 °C. Figure 2 shows weight loss after 1, 2 and 24 hours at 225 °C. From this data, it is clear they lose a significant fraction of their weight at 225 °C after only a short period of time. Exposure to this condition can serve as a quick screening process for relative heat resistance, but the data at 125 and 175 °C may provide a better metric as to continuous service temperature. The SC-3 formula has a slightly higher weight loss than the other formulas at 125 °C, but also contains the highest level of photoinitiator in the set, much of which is not actually bound into the crosslinked structure. At higher temperatures, the weight loss of SC-3 is significantly lower than that of the other formulas. The best weight loss resistance appears to be with the SC-3, 4, and 5 formulas. Weight loss at elevated temperature is theorized to be due to both (a) the loss of volatile components in the film such as unreacted photoinitiators, monomers, oligomers antioxidants, and other additives, and (b) the thermally initiated scission of covalent bonds, producing lower-molecular-weight materials that eventually migrate to the surface of the film and volatilize. Figure 3 shows a typical TGA plot of a UVcured film similar in composition to that of formulas FIGURE 4 | Delta E values after aging at 225 °C. 70.00 60.00 50.00 Delta E 40.00 30.00 20.00 10.00 0.00 SC-1 SC-2 SC-3 SC-4 SC-5 24 hour 2 hour 1 hour SC-6 34 APRIL 2008 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM

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Paint & Coatings Industry - April 2008 Contents Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News Snapshots of Success – Automotive Applications Designing UV-Curable Materials for High-Temperature Optical Fiber Applications The Future of UV Coatings is Now! Milling Media Review Part 1 – Bead Density Effect Preparation and Properties of UV-Curable Polyurethane Acrylate Resins for Metal Surfaces Conquering Color Harmony High-Performance PU Crosslinkers for Two-Component Waterborne Applications Decorative Film Laminates How Long Will the Gilding Glitter? Gaining a Competitive Advantage Using Benchmarking Supplier Showcase Materials Watch Products and Literature Classifieds Advertiser Index Automotive Color Trends New England Museum Solves Century-Old Vanderbilt Mansion Mystery

Paint & Coatings Industry - April 2008

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