| Polyester powder coating, due to its good good performance, weather resistant ability and relative unexpensive, is used widely in many fields, such as construction, automobile, external facility and etc. Now, more than half of thermosetting powder coatings are based on polyester resin as matrix resin. With the rapid expansion of the application fields, UV-resistance polyester based powder coating exposed insufficient seriously. The key of weathering resistance for polyester powder coating is still matrix resin. In this article, super weatherable polyester which used in powder coating was synthesized by molten polymerization, with choosing excellent weatherability glycol and acid monomers and optimizing the synthesis process. The conclusions as follows:(1) Different polyester were synthesized with different monomers, and performance was tested. With neopentyl glycol, isophthalic acid and cyclohexane acid as the main raw material, polyester which was synthesized by molten polymerization had the best weatherability and effects of the feed methods, the ratio of alcohol to acid, optimal quantity of polylol, vacuum time and heat preservation temperature on polyester resin performance were studied. The experimental results showed that feed methods for two step, the ratio of alcohol to acid was1.1, polyols adding amount of5wt.%, vacuum time for60-75minutes and the heat preservation temperature for230-245℃, the performance that polyester had abtained was best;(2) Polyester resin structure was characterized by FTIR, GPC, DSC, TG and XRD etc. FTIR spectrum showed product which was the polyester resin. Number average molecular weight and molecular weight distribution were10909and1.5respectively. DSC showed that glass transition temperature of the synthetic polyester resin was53℃, which meet the powder coating storage temperature requirements. TG curve indicated that the synthetized polyester resin had good thermal stability performance with initial degradation temperature293℃and the maximum temperature442℃. XRD results showed that synthetic polyester resin only existed trace amounts of crystallization;(3) With ΔE, gloss retention and ATR-FTIR tracking analysis, The effects of antioxidants3114,1076and168on durable properties of polyester resin which used neopentyl glycol, isophthalic acid as raw material were studied. Antioxidants, appropriate proportion for main and auxiliary antioxidants compound and relative content of appropriate proportion were studied respectively. It turned out that antioxidants3114and168showed better delay the ability of light degradation.3114/168was better than1076/168, in addition3114/168=1/0.5was superior to the else proportion, the appropriate amount of proportion was0.5wt.%;(4) Be compared by synthetic super resist polyester (neopentyl glycol, isophthalic acid and cyclohexane acid as raw material), P-6600and NH-3307. Results showed that gloss retention of the coating which made with synthetic super resistance polyester stayed in78%after QUV-B artificial accelerated aging nearly1000hours, had the best gloss retention and had the least ΔE which was1.79. The surface of the super resist polyester became black, yellow and green more and more, and ΔE was increasing with the increase of aging time. TG thermal-oxidative stability analysis results showed that synthetic super resist polyester had the best thermal-oxidative stability performance among these with initial degradation temperature329℃and the maximum degradation temperature429.1℃.ATR-FTIR monitored the ageing process, with the increase of aging time,2960cm-11450cm-1placing C-H absorption peaks1725cm-1carbonyl absorption peaks and3250-3600cm-1hydroxyl absorption peaks etc existed different degree of change. Synthetic super resist polyester reached the performance of P-6600polyester resin in inhibiting aging degradation;(5) By using SEM to track the aging process, Results showed the surface of the super weather-resistance polyester took minimum changes after the same aging time, Element analysis showed that the relative surface (O/C) content of the super weather-resistance polyester coating increased continuously and aging degradation accorded with zero order reaction dynamics. |
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