Preparation of Polyester Polyurethane Coatings Modified by Citric Acid

The high- solid polyurethane coating is formulated with citric acid polyester polyol as hydroxyl resin. The process for preparing hydroxyl resin is optimized by the orthogonal experiment. The results show that the comprehensive performances of the obtained product can reach the best when the oleic acid, citric acid and 1,4- butanediol react between 150°C and 160°C for 3 hours at first and then continue to react at 190～ 200°C for 2 to 3 hours with the molar ratio of 1.0:1.0:3.5. The effects of the hydroxyl value of polyester polyol and the ratios of — NCO to — OH on the properties of polyurethane coatings are discussed. It is proved that the properties of the coating film would meet the requirements of the S01- 3 Standard (the Standard of Polyurethane Varnish) when the hydroxyl value of polyester polyol is 148 mgKOH/g and the molar ratio of — NCO to — OH is 1.2 to 1. In addition, it is found that the dry- to- touch time can reach 25～ 30 min if the mass ratio of BTSL to citric acid polyester polyol is 0.08% ～ 0.1% .