Paint & Coatings Industry - November 2008 - (Page 58)

Highly Weather-Resistant Radiation-Curable Monomers and Oligomers for Exterior Applications can be attained quickly, in less than 1000 hours of exposure. But using this method as the lone test criteria will result in coatings that are over engineered due to the severity of the test. Xenon testing is less severe than QUV testing and very closely replicates the results that are produced in a Florida test. The least severe is Q-TRAC testing, as the conditions tend to be very arid and may mask the effect of surface erosion induced by rain and high humidity. Parameters Measured The main criteria for monomers and oligomers that are intended for outdoor use is the ability to resist yellowing and chalking when exposed to heat and light radiation. Also, they must be impervious to surface erosion through moisture exposure. This is typically evidenced by loss of surface gloss. The gloss retention and the Yellowness Index were recorded as a function of accelerated weathering exposures as well as “real time” Florida exposure. Gloss was measured at 60º by following the ASTM D 523-89 FIGURE 8 | Yellowness index, QUV exposure vs. backbone structure of oligomers, 35-40 microns. 45 40 35 Yellowness Index 30 25 20 15 10 5 0 0 100 200 300 400 Hours TABLE 3 | Oligomer results, Florida Inland, facing South at 5°, gloss at 60° and yellowness index. Product # CN9001 CN981 CN982 CN985B88 CN929 CN9006 CN2920 CN991 CN2921 CN2922 56 CN 9001 CN 2003 CN 120 CN 2003/Stabilizer procedure and by using a micro-gloss meter from BYKGardner. A BYK Color Guide (geometry 45/0, illuminant/observer: D65/10) was used to measure the Yellowness Index (YI) according to ASTM E 131-98. Physical properties of the cured films are important to the formulator for selection of the correct materials to meet the end-use application requirements. Tensile experiments were performed on an Instron 1122 apparatus according to the ASTM D 882 procedure. Sample sizes were 25 mm x 8 mm with a thickness of 100 microns. The stress-strain curves were recorded to determine the Young’s Modulus (YM), the stress and strain at break (percent elongation @ failure). Since oligomers tend to be more flexible they were tested “neat”, while monomers can at times be too brittle to test. The monomers were added to very flexible oligomers known to have excellent weathering properties. Since these blends can be very high in viscosity they were cut with 50% acetone and applied to cold-rolled steel having an electrocoat primer and white basecoat. Unless otherwise specified, all formulations contained 3.0% of TPO photoinitiator (2,4,6-trimethylbenzoyl diphenylphosphine oxide) known for its photo-bleaching properties. These mixtures were applied to the substrate to yield a film thickness of 35-40 microns, after the acetone was evaporated. This is the film thickness used throughout this study unless otherwise stated. A 600 w/in. “V” lamp in air followed by a 600 w/in. “H” lamp in nitrogen was used for curing. The conveyor speed was set at 10 FPM. QUV Testing As mentioned, this device is an excellent screening tool that allows for rapid screening of monomer and oligomer variables. Early in this study this equipment was used to optimize the weathering performance of materials prior to embarking on longer-term testing. One of the parameters studied was the effect of molecular weight of the oligomer and its influence on gloss retention and YI (Figure 7). It is interesting to note that these oligomers are identical in backbone structure but the gloss retention is poorer and the YI higher as molecular weight of the oligomer increases. This is an indication that in order to have extended outdoor weathering properties lower molecular weight oligomers are preferred in most cases. QUV Testing was also used to screen oligomers having very different backbone structures. These materials consisted of a Bis A epoxy acrylate (CN120), a di-functional polyester acrylate (CN2003) with and without HALS, and the “control” oligomer, (CN9001), a di-functional aliphatic polyester acrylate. 500 600 700 800 YI, Initially 1.6 1.0 1.7 1.2 2.6 1.0 1.0 1.0 1.0 0.8 YI aft. 900MJ, TUVR 1.3 1.2 0.6 0.5 1.0 4.5 0.7 1.0 0.5 1.6 Initial Gloss 86.5 85.6 89.0 92.0 88.0 96.0 88.0 82.0 90.0 89.0 Gloss aft. 900 MJ, TUVR 85.0 86.0 83.0 89.0 72.0 55.0 90.0 78.0 90.0 90.0 NOV EMBER 2008 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM

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Paint and Coatings Industry - November 2008 Contents Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News HiTone Resins for Enhanced Pigment Affinity of Powder Coatings New Water-Based Interior Coatings Combine Innovation and Quality With Respect for the Environment Novel, UV-Curable Nanotechnology-Enabled Coatings Highly Weather-Resistant Radiation-Curable Monomers and Oligomers for Exterior Applications Konica Minolta — Sensing Success for Viracon Self-Crosslinkable Thermosetting Acrylics for Use in Water-Dilutable Coatings Paint and Criminal Forensic Science Supplier and Application/Curing Showcases Materials Watch Classifieds Advertiser Index

Paint & Coatings Industry - November 2008

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