Synthesis And Application Research Of Polyester Resin For Exterior Low Temperature Curing Powder Coatings

Powder coatings, which is a hot research topic, has the advantage of zero VOC, excellent performance and relative unexpensive. Nowdays, Powder coatings are widely used in the field of household appliances, machinery and equipment, anti-corrosion pipe and construction materials, but the high curing temperature between180℃to200℃limits the development of the powder coatings.The paper aims to develop outdoor polyester resins for low temperature curing between120℃to150℃, and determine the formulations and synthesis process of the outdoor polyester resin for a low temperature curing. The result as the follows:(1)Use the melt polycondensation and the two-step synthesis the indoor polyester resin for the low-temperature curable powder coatings, Hydroxy pivalic acid neopentyl glycol monoester, neopentyl glycol, trimethylol propane,2-Butyl-2-ethyl-1,3-propanediol, trimethylol propane, isophthalic acid, terephthalic acid as the main synthesis, and select trimellitic anhydride as the last acid anhydride. The result show that Isophthalic acid, terephthalic acid: neopentyl glycol:2-butyl-2-ethyl-1,3-propanediol:trimethylolpropane: adipic acid:trimellitic anhydride (mol ratio)=0.85:0.1:1.02:0.1:0.007:0.11:0.045, the amount of antioxidants0.25%of the total is the optimal formula polyester resin, vacuum time for60the polyester resin has an acid value of50mgKOH/g, the viscosity26P, the reactivity of the polyester resin is best, it can chieve low temperature curing within the range of from120℃to150℃, the coating performance of the polyester resin is very superior, and effective solution to the problem at the conditions of low temperature curing coating is easy to blooming and yellowed.(2) The structure of polyester resin was characterized by a different methods.IR spectra shows that the synthesized product is a polyester resin.Gel chromatography results showed that the polyester resin number average molecular weight and molecular weight distribution was3561and1.5, The result of the differential scanning calorimetry shows that the glass transition temperature of the polyester resin is57.3℃, which ensure the storage stability of the powder coating. The result of the thermogravimetric analysis shows that the polyester resin has good heat resistance, and the initial degradation temperature is309℃. The result of X-ray diffraction (XRD) shows that the crystallinity of the polyester resin is very small, so, the polyester resin owning a suitable molecular weight and molecular weight distribution width, suitable glass transition temperature, good stability and heat resistance.(3) Conducted a study on the film properties of the polyester resin, test the performance of the coating film within a range of from120℃to150℃under different curing conditions. The result show that the synthesized polyester resin of using the optimal formula can completely cured under the conditions of120℃/40min,13O℃/3Omin,140℃/20min and150℃/15min low temperature, and the film properties is very good.(4) By the test of gloss retention and using the total reflection infrared spectroscopy to track and analyze the aging of the polyester coating, the results show that the low-temperature curable polyester resin has excellent weather resistance.