Paint & Coatings Industry - April 2008 - (Page 56)

Preparation and Properties of UV-Curable Polyurethane Acrylate Resins for Metal Surfaces standard and THF as an eluent. The hydroxyl value of the resin was determined by titration (Table 1). Sample Characterization Coating sample viscosities were determined by a Brookfield Viscometer, and refractive index was determined by a Mettler Refractometer (Toledo RE 40D). Data is shown in Table 3. Coating Sample Preparation Coating samples were prepared by using resin, hydroxylcyclohexyl phenyl ketone (HPCK, 25% by wt.) and reactive diluents in different ratios. The sample designations are given in Table 2. TABLE 1 | Characteristics of polyurethane–acrylate resin. Sample Name PU-Acrylate Curing The UV-cured PU-acrylate films were prepared by applying the various coating formulations on mild steel panels using a bar applicator. The dry film thickness was maintained at ~12 microns with the help of a film applicator for the evaluation of various mechanical and chemical resistance properties. The panels were then exposed to a UV lamp chamber (GT Ultra Cure, 120 w/cm) maintained as follows. • UV dryer type : GT Ultra Cure 250 • Curing width: 250 mm • Bulb type: UV (medium pressure)-GT 250 pure • Transparent: 120 watt/cm • Silica Quartz • Air cooling: 100 mm • Operating voltage: 440 volts 3 phase A.C. • Speed: 50 cycles • Power consumption: 120 w/cm for UV Hydroxyl Value 77.8 Number Average Molecular Weight (Mn) 355 Weight Average Molecular Weight (Mw) 1853 Poly Dispersity Index (PDI) Mw/Mn 5.226 TABLE 2 | Formulation of coating samples. S No. 1. 2. 3. 4. Sample Code A B C D Molar Ratio Resin:Monomer 50:50 60:40 70:30 80:20 TABLE 3 | Viscosity and refractive index of the coating samples. Monomer Ethoxylated Phenol Mono Acrylate (EOPA) 1,6 Hexane Diol Diacrylate (HDDA) Trimethylol Propane Triacrylate (TMPTA) Coating Samples A B C D A B C D A B C D Viscosity in cps @30 0C 1800 6350 10400 19160 700 3500 5900 8860 7100 22800 36750 50840 R I @ 25 ºC 1.4892 1.4910 1.4908 1.4911 1.4735 1.4760 1.4797 1.4838 1.4823 1.4838 1.4856 1.4887 Results and Discussion Infrared Analysis Figure 4 shows the IR spectrum of the PU-acrylate resin. A weak band 1180 cm-1 is attributed to C-N stretching. A band at 1651 cm-1 confirms the formation of the urethane group. A band at 1534 cm-1 is attributed to N-H deformation. A strong band at 1735 is from the acrylate ester carbonyl group present in PU-acrylate resin. A strong band at 2963 cm-1 is believed to be due to C-H stretching and a strong band at 3345 cm-1 is thought to be arising from –OH stretching, due to residual hydroxyl group present in the resin. Moreover, the absence of any band at 2270 cm-1 in the spectrum confirms that unreacted NCO groups are not present. TABLE 4 | Scratch hardness of coating films. Sample Code A B C D FIGURE 4 | Infrared spectrum of PU-acrylate resin. EOPA 1800 1650 1600 1500 HDDA 2100 2100 2000 1900 TMPTA 2300 2250 2200 2100 TABLE 5 | Cross-hatch hardness of coating films. Sample Code A B C D 56 APRIL 2008 | W W W . P C I M A G . C O M EOPA Good Good Fair Fair HDDA Good Good Fair Fair TMPTA Excellent Excellent Excellent Excellent 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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