Preparation And Properties Of Hydroxyl Acrylate Emulsion For Two-Component Waterborne Polyurethane Coatings

Water-based coating has become a trend in the coating investigation at the present. Two-component waterborne polyurethane(2K-WPU) possesses excellent film properties, and consists of aqueous polymer polyols and aqueous curing agents. The hydroxyl acrylic emulsion is the first polyol to prepare 2K-WPU because it has excellent weather-resistance and its molecular weight, Tg and the hydroxyl contents are easy to control. However, the hydroxyl acrylic emulsion also has some disadvanteges including the polymerization stable is not so good, the appearance, hardness and chemical resistance of 2K-WPU film are not good enough. In this research, the influence of various factors on the polymerization stability and film properties of the hydroxyl acrylic emulsion are investigated.The polymerization stability of the hydroxyl acrylic emulsions were studied, and found that the polymerization stability of hydroxyethyl acrylate emulsion is good by using pre-emulsification process and aldehyde and ketone resins were added with the pre-emulsified seed as well as small molecule polyols were dissolved in water and added before neutralizing. The emulsion polymerization stability decreases with incereasing of the hydroxyl monomer hydrophilia. In addition, the hydroxyl acrylate emulsion polymerization stability was also good with using large HLB value emulsifiers, adding COPS-1/2 as a primer emulsifier as well as ER-10/30 as a pre-emulsion emulsifier; monomers were added by starved feeding motheds to keep slow reaction rates and added chain transfer agents to adjust the average molecular weights.The effects of hydroxyethyl acrylate emulsion on the 2K-WPU film properties were investigated, it was found that the optimized recipes were obtainted by using HEMA as a hydroxyl monomer, SLS(0.5%)/ER-30(0.75%)/COPS-2(0.75%) as emulsifiers, the total hydroxyl contents was about 2.0%, Tg = 40℃, 0.5% of chain transfer agents, 3.0% of the aldehyde-ketone resin KR-120 B, and 1.0% of the small molecule polyol Di-TMP.2K-WPU coating was prepared by using Di-TMP-PA hydroxyl acrylate emulsion and the influence of constructing and drying conditions on the film properties were investigated. It was found that the viscosities of 2K-WPU coating prepared by using DI-TMP-PA hydroxyl acrylate emulsion firstly decreases and later increases, and therefore the coating must stand for about 20 mins until the viscosities no longer decreases, and then the coating viscosities would be controlled with adding water. By this method, the pot life is about 4h, the molar ratios of NCO: OH is usually between 1.0-1.8, the infrared-microwave coupled drying technology is better suitable than that of hot air drying technology, and the suitable drying humidity of 2K-WPU film is about 40-60%.