| Résumé : |
Polyurethane coatings are known for their durability and overall good balance of mechanical properties. Both acrylics and polyesters are used as polyols in two-component, solventborne polyurethane coatings. Polyester polyols containing isophthalic acid (PIA) weather extremely well, but they have poor flexibility. Usually, a combination of a flexible diacid, such as adipic acid (AD), and PIA are used to achieve a hardness/flexibility balance in the coating. While improving flexibility, AD has an adverse effect on the beneficial properties of PIA, especially outdoor durability. CHDA (1,4-cyclohexanedicarboxylic acid) exhibits a unique balance of properties that are characteristic of linear aliphatic and aromatic diacids. These properties include rapid reactivity, a hardness/flexibility balance, and resistance to chemicals and humidity.
The objective of these experiments was to evaluate the performance, particularly outdoor durability, of high-solids, two-component, pigmented polyurethane coatings containing CHDA. Experimental variables included the CHDA/PIA molar ratio in a model polyester polyol, coating crosslink density, and effect of a commonly used ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS) package. Comparisons were made to control polyester polyols containing AD/PIA and commercially available acrylic polyols marketed for exterior applications. Responses included coating viscosity, cured film glass transition temperature, gloss, hardness, flexibility, acid resistance, and Florida weathering over a three and a half year period. |
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Performance of CHDA in polyester polyols for weatherable 2K polyurethane coatings in COATINGS TECH, Vol. 2, N° 21 (10/2005)
