| In recent years,solvent-based coating has occupied the majority of the coating market.However,with the sustained development of the economy,people's living standards improved continuously,solvent-based coating leads to environmental contamination,waste of energy,security issue and other drawbacks,which were gradually exposed.Whereas,the traditional waterborne coating uses water as a dilutent or solvent,which has many advantages over the solvent-based coating,such as no organic solvent,harmless to human bodies,pollution-free to the environment.However,some problems need to be solved.The coating rate during curing process is low,or it even requires drying at elevated temperature so that the energy consumption is high.Moreover,due to the low solid content of waterborne coating,the cost of transportation is high.In order to avoid the drawbacks of solvent-based coatings and tackle the issues of water-based coatings,it is necessary to develop solvent-free coatings.Solvent-free coatings are composed of the pure film-forming materials with almost non-VOC emission.Its volatility,inflammability,toxicity and the solvent content of harmful organic matters are very low,which belongs to the environmentally friendly coating.Besides,the curing rate is fast and the energy consumption is low.Therefore,the research on solvent-free coatings is of great practical significance.According to the performance requirements of the application field,the molecular structure of the resin was designed first and the active resin with terminal isocyanate was prepared.The specific scheme was as follows: Isocyanate containing monomers and alcohol monomers were used as the raw material of reaction,and commercial PC-15 was used as the catalyst.The reaction was conducted in a water bath pot at 75 ? for 2 h.The viscosity of the resin was small.But the curing rate was slow.As a result,the hardness of the film-forming material reaches 4 H.Whereas,its flexibility is not enough and brittleness is relatively large.The test time of resistance to neutral salt spray is 67 h.The comprehensive performance cannot meet the requirement of application.Acrylic resin has good light retention,light resistance and aging resistance,and would be non-oxidized and discoloration under high temperature,and it is easy to process.Solvent-free reactive acrylic resin was selected as the film forming system of solvent-free coatings.The effects of reaction temperature,initiator and chain transfer agent on the reaction process were investigated.The effects of curing agents on the curing time,flexibility,hardness and corrosion resistance of the coating were discussed.The infrared spectra and thermal stability of the film were analyzed.The effect of hydroxyl group density on curing rate and corrosion resistance of the coatings were investigated.The optimal process was as follows: The acrylic monomer containing hydroxyl and methyl methacrylate monomers were used as the reaction raw materials,the amount of initiator was 0.3% and the amount of chain transfer agent was3%.The reaction was conducted at an oil bath pot at a constant temperature of 100 ? for 20 min.Then,the reaction was conducted at a lower temperature of 75 ? for 2 h.The resin film has good fluidity,proper viscosity,good heat resistance after curing process.Further,the weight loss of the film at 350 ? is about 7% and the hardness of the film is 6 H.The curing rate is very fast(25 s curing at 190 ?).The surface of the film is flat and smooth with good microscopic morphology.Besides,the cured coating has good adhesion,flexibility,impact resistance and other good performance.However,the corrosion resistance of the coating is poor,and the neutral salt spray test can only reach 150 h,which limit its practical application.The acrylate resin containing epoxy group was prepared by radical polymerization of acrylate monomers containing hydroxyl groups and acrylate monomers containing epoxy groups.The infrared spectra and thermal stability of the film were analyzed.The influence of the monomer dosage on corrosion resistance of the coating was discussed.The effects of different curing agents on the corrosion resistance and overall performance of the coating were discussed.The optimal synthesis process was obtained: The dosage of initiator is 0.3%and the dosage of chain transfer agent is 10%.The first step of reaction is at 85 ? for 30 min.Then cool rapidly to 70 ? and maintain the temperature for 2 h.The viscosity of the resin at room temperature is about 60 mPa.The fluidity is good,which is suitable for spraying,roller,brush and other coating process.The film,prepared by the resin and cured by the N-3900 curing agent,is prepared at 190 ? for 15 s.The weight loss of the film at 350 ? is about 9%.The adhesion of the film reaches level 0 and the hardness of the film is 6 H.Impact resistance of 120 cm is obtained.The boiling water resistance test is 10 h.The neutral salt spray test of the film reaches 600 h,and the overall performance is also good.In sum,the acrylate resin coating has good environmental performance,fast curing rate,good film performance,good application prospect. |
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