Paint & Coatings Industry - April 2008 - (Page 55)

Acid Value mg KOH/g solid The acrylated urethanes ideally combine the abrasion resistance, toughness, tear strength and good low-temperature properties of PU with the superior optical properties and weatherability of polyacrylates.7-9 The reactive diluent phase is more compatible with the hard segments of polyurethane rather than the soft segments, due to similar polarity and hydrogen bonding formation between the urethane NH and acrylate carbonyls.10 This paper considers the preparation and properties of UV-curable polyurethane acrylates. The NCO-terminated polyurethane prepolymers were synthesized from toluene diisocynate (TDI) and polyester polyol followed by tipping with 2-hydoxyethylmethacrylate (HEMA). In addition, three types of reactive diluents having mono-, di- and tri- functionality were used in different concentrations. A series of coating compositions having PU acrylate and reactive diluents were prepared, and their mechanical, chemical, optical and stain-resistant properties studied. urethane methacrylate precursor was maintained at 50 °C, and a mixture of hydroxyl functional polyester polyol and hydroquinone (50 ppm) was added over a half-hour period. An inert gas atmosphere was maintained in the reaction flask by blanketing dry nitrogen gas throughout the reaction period. The reaction completion was determined by monitoring the hydroxyl value of the resin at definite intervals (Figure 3). Evaluation and Characterization An FTIR spectrum of polyurethane acrylate resin was recorded using a NaCl cell on a Perkin-Elmer 1750 FT-IR spectrophotometer. Molecular weight of the resin was obtained by GPC (model HPLC 600, RI detector on a styragel column) using polystyrene as a FIGURE 1 | Acid value of polyester polyol. 90 80 70 60 50 40 30 20 10 0 0 50 100 150 200 250 Reaction Time (minutes) Experimental Reagents TDI (an 80/20 mixture of 2,6 and 2,4 isomers) was obtained from BASF and Narmada Chematur. The purity was 98% and was used as such. Laboratory reagent (LR)-grade adipic acid, 1,6-hexanediol, ethylene glycol, 2-hydoxyethylmethacrylate (HEMA) and hydroquinone of M/s Thomas Baker, Mumbai, were used. Reactive diluents were procured from M/s Cognis, Thailand, and photoinitiators were procured from M/s Ciba chemicals. FIGURE 2 | Hydroxyl value of polyester polyol. OH Value mg KOH/g solid 200 180 160 140 120 100 80 70 60 40 20 0 50 100 150 200 250 Reaction Time (minutes) Polyester Polyol Synthesis Initially ethylene glycol, adipic acid and 1,6-hexanediol were placed in a three-neck, round-bottom flask in the molar ratio of 1.6 : 3.4 : 4.0 respectively. The esterification reaction was catalyzed by adding dibutyl tin oxide (0.1%) as a catalyst. The temperature was maintained at 140 – 150 °C. An inert atmosphere was maintained by blanketing the reaction mixture with nitrogen. Acid and hydroxyl values (Figures 1 and 2) of the resin were checked at fixed time intervals. Urethane Acrylate Synthesis The reaction flask was charged with 2.2 moles of TDI under dry nitrogen gas at 50 °C; a blend of 2.4 moles of HEMA with hydroquinone (50 ppm) was added continuously over a period of one half hour while maintaining a maximum temperature of 60 °C. After the addition was complete, the reaction mass was kept at 60 °C for half an hour to assure the complete conversion of the hydroxyl group of HEMA. FIGURE 3 | Hydroxyl value of PU-acrylate resin. OH Value mg KOH/g solid 140 120 100 80 60 40 20 0 0 50 100 150 200 250 Polyurethane Acrylate Synthesis The temperature of the reaction flask containing Reaction Time (minutes) PA I N T & C O A T I N G S I N D U S T R Y 55

Table of Contents Feed for the Digital Edition of Paint & Coatings Industry - April 2008

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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