Paint & Coatings Industry - November 2008 - (Page 60)

Highly Weather-Resistant Radiation-Curable Monomers and Oligomers for Exterior Applications Bis A epoxies have been the workhorse oligomer for UV curing applications for many years as they are low in cost along with being very hard and abrasion resistant. A high degree of chemical resistance is also observed. Results again support that for ultimate outdoor performance aliphatic urethane acrylates are needed. However a good cost/performance compromise can be attained using polyester acrylates. Epoxy acrylates are most often offered as a blend with monomers to reduce the viscosity to a workFIGURE 9 | UV vs. 2K vs. PI selection, Q Sun testing. 14 12 2KPUR CN9001/TPO CN9001/KIP150 CN9001/Benzophenone 6 4 2 0 +2 able level. In addition, epoxy acrylates yellow quite badly, thus are not suitable for any application where yellowing resistance is critical. In contrast polyester acrylates are fast curing and tend to have a much lower viscosity than Bis A type oligomers. They also inherently have better yellowing resistance than epoxies. When HALS is added to the formulation they can offer a reasonable degree of yellowing resistance as depicted in Figure 8. Q-SUN, Testing (Xenon Test Chamber) The Q-SUN, Model 3100, was used to examine the effects of differing PIs on yellowing resistance when blended with the control oligomer, CN9001. All PIs were added at a 3.0% level. These results were compared to a 2K polyurethane commonly used for automotive topcoats. The PIs tested were benzophenone, TPO and a polymeric alpha hydroxyl ketone type initiator, Esacure® KIP-150. The results are presented in Figure 9. Each of the test panels was exposed for a total of 4,000 hours. This is the equivalent of more than three years of Florida exposure. It is not surprising benzophenone does not resist yellowing well. TPO on the other hand has an initially high YI. But since TPO is photo-bleaching the YI drops significantly after 500 hours exposure. In contrast Esacure KIP-150 is low in YI from the start and remains so for the duration of the test. The 2K urethane has the lowest YI initially and increases slowly throughout the study. It is important to note that the UV cured chemistry outperforms the polyurethane without the aid of HALS. It also shows that PI selection is critical to attain weathering resistance. Yellowness Index 10 8 0 500 1000 1500 2000 3000 4000 Hours of Exposure TABLE 4 | Physical property data – aliphatic urethane acrylate oligomers. Product # CN9001 CN981 CN982 CN985B88 CN929 CN9006 CN2920 CN991 CN2921 CN2922 Viscosity @ 60 ºC, cps 46,500 6,190 6,300 205 400 1,400 25,000 660 3,036 6,166 Modulus, psi 11,225 43,100 65,000 345,000 7,000 Too 110,000 19,400 34,336 11,200 Tensile, psi 3,300 6,041 6,481 7,600 1,974 Brittle 9,000 5,400 3,371 2,825 % Elongation 143 79 44 5 62 To Test 7 79 63 175 Tg ºC by DSC 24 22 50 103 43 83 59 27 60 16 Florida Weathering Results Accelerated laboratory tests are useful for performance optimization of the chemistry relatively quickly. However there is no substitute, especially when it comes to automotive applications for, real time Florida exposure. After much lab testing and reformulation a series of oligomers and monomers were selected for testing. The oligomers were tested “neat” while the monomers were added to CN9001 at a 50% level. Three replicate panels were prepared for each chemistry variable. No HALS or light absorbers were added. Table 3 lists the oligomers tested along with YI and gloss retention data initially and after an exposure of 900 Mega-joules/sq. meter Total Ultraviolet Radiation (TUVR). Assuming there is 280 MJ/sq. m TUVR in an average year in Florida this represents 3.2 years of Florida testing. All of the oligomers perform well with the exception of CN929 and CN9006, where a rather dramatic TABLE 5 | Monomer results, Florida Inland, facing South at 5°, gloss at 60° and yellowness index. Product # Description Functionality SR531 SR506 SR238 CD564 SR351 SR454 CTFA IBOA HDDA Alkoxylated HDDA TMPTA EO TMPTA 1 1 2 2 3 3 Gloss YI aft. Initial YI, aft. 900, 900MJ, Gloss Initially TUVR TUVR 0.5 1.3 1.7 1.3 1.3 0.5 0.5 0.7 0.5 3.5 0.7 1.0 89.0 87.0 90.0 75.0 88.0 88.0 86.0 84.0 88.0 45.0 85.0 48.0 58 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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