| Powder coatings have the advantages of non-volatile organic solvents,high recovery,low energy consumption and excellent cured film properties,which is an environmental friendly coating in line with the development of the new era.Among them,polyester powder coatings have been developed rapidly because of its excellent chemical resistance and weather resistance,which are widely used in road sign,electrical enclosure,automobile wheels and other fields.In addition,their production has always ranked first.However,TGIC curing agent has the problem of strong irritation and genotoxicity,which is a serious risk to human health.With the enhancing awareness of environmental protection,the development of curing agent for polyester powder coating is facing the huge challenges.It is particularly important to develop and study the curing agent with environmental protection,non-toxic and good cured film performance.In this study,1,3,5-Benzenetricarboxylic acid tris(oxiranylmethyl)ester(TOTC)curing agent was synthesized by trimesic acid and allyl chloride,and the curing kinetics of TOTC powder coating was studied.The main researches are shown as following.(1)The curing agent TOTC was synthesized by the epoxidation of 3-chloroperoxybenzoic acid instead of epichlorohydrin.Firstly,triallyl 1,3,5-benzenetricarboxylate(TATC)was synthesized.The effects of raw material ratio,reaction time,reaction temperature,type and dosage of alkali on the yield of the reaction product were discussed.The optimum process conditions were as follows.The molar ratio of raw materials was 1:9;the reaction temperature was at 65?;the reaction time was 7 h;triethylamine was chosen as organic base and its dosage is 3.5 mol than trimesic acid.At this time,the highest yield of TATC can reach 75.2%.Then,1,3,5-Benzenetricarboxylic acid tris(oxiranylmethyl)ester(TOTC)was synthesized by TATC epoxidation.Its process conditions were as follows.3-chloroperoxybenzoic acid was chosen as epoxidator;the molar ratio of raw materials is 1:6;the reflux condensation was at room temperature for 12 h.The epoxy value of TOTC can reach 0.85 mol/100g.The chemical structure of TOTC was characterized by Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance spectroscopy(NMR).(2)The powder coating was prepared by TOTC and polyester resin NH-3307.The curing kinetics and behavior were studied by non-isothermal differential scanning calorimetry(DSC),and its optimum theoretical curing temperature was obtained.According to Kissinger equation and Flynn-Wall-Ozawa equation,the activation energy Ea required for curing reaction was75.95 and 71.75 k J·mol-1,respectively.The curing system was evaluated by Friedman method and Malek method.The results showed that the curing process of TOTC/NH-3307 powder coating was a two-parameter autocatalytic reaction process dominated by n-order reaction.On this basis,the curing kinetic parameters were calculated by(?)est(?)k-Berggren model.The curing reaction rate equation of the system was established,and the theoretical and practical data were fitted.Because curing reaction of powder coatings was a very complex process.the reaction mechanism of TOTC powder coating during curing was discussed based on the study of kinetic.(3)TOTC/NH-3383 powder coating,HAA/NH-3307 powder coating and TGIC/NH-3307powder coating were prepared by TOTC and the commercial curing agent of TGIC and HAA,and their performance were compared.The properties of three powder coatings were studied by TGA and SEM.The results showed that the thermal stability of TOTC powder coating was the same as that of TGIC powder coating,and there was no strong irritation and toxicity.In terms of decorative performance,the gloss of TOTC powder coating was 98%,and the coating surface was neat and artistic without pinholes.In addition,the weather resistance and heat resistance,TOTC powder coating was better than that of HAA powder coating.Therefore,TOTC curing agent has great development potential in high gloss weather resistant powder coatings. |
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