Study On Preparation And Performance Of Waterborne Epoxy Curing Agent By Emulsion Polymerization

In the water-based epoxy coating system,water-based curing agent is very important,which can be divided into water-soluble type and emulsion type.The watersoluble curing agent is widely used in the market,but the water-soluble curing agent have a high content of hydrophilic groups,which is easy to have a negative effect on the performance of the later paint film;Emulsion typed curing agent have a good compatibility with epoxy emulsion,and it can be cured with good endurance under the control of the appropriate amount of emulsifier,but the storage of the emulsion curing agent Poor stability limits its application.This paper aims to develop a new method to prepare epoxy curing agent emulsion with strong structure design and good stability.The epoxy curing agent emulsion and epoxy resins are formulated into two-component waterborne epoxy varnishes to study the curing kinetics and curing properties.(1)Preparation of thiol epoxy curing agent emulsionUsing diene monomers and polythiol compounds as raw materials,a series of thiol epoxy curing agent emulsions were prepared by thiol-ene emulsion polymerization.The factors affecting the performance of thiol epoxy curing agent emulsions were systematically explored.The results showed that the solid content of the designed thiol epoxy curing agent emulsion is 42%,when the amount of initiator was 0.5%,the amount of emulsifier was 4%,and the polymerization temperature was 85 ?.After 4 hours of reaction,thiol curing agent emulsion has high monomer conversion rate,small particle size,excellent storage and calcium ion stability.Among them,the monomer in the TH curing agent is trimethylolpropane tri(3-mercaptopropionate)and 1,6-hexanediol diacrylate,and the monomer in the PH curing agent is pentaerythritol tetrakis(3-mercapto(Propionic acid)ester and 1,6-hexanediol diacrylate,the monomers in the TD curing agent are trimethylolpropane tri(3-mercaptopropionate)and dipropylene phthalate,PD curing agent The monomers are pentaerythritol tetrakis(3-mercaptopropionate)and dipropylene phthalate,and the feed ratios are 1.5: 1,1.1: 1,1.5: 1,1.4: 1.(2)Study on the curing kinetics of thiol epoxy curing agent emulsionNon-isothermal Differential Scanning Calorimetry(DSC)was used to explore the effect of the ratio of thiol epoxy curing agent emulsion PD and commercially available epoxy emulsion Hexion 6520 on curing performance;The apparent activation energy and reaction series of the curing system were calculated by the Kissinger,Ozawa and Crane equations,and the appropriate curing process parameters were determined.The results show that:when the mass ratio of the curing agent to the epoxy resin reaches 0.8: 1,the heat release of curing reaction is the largest,the activation energy of the curing system is E = 142.79 k J / mol,the reaction series n=0.95.After the curing kinetics analysis,The solidification process can be determined by the T-? extrapolation method: after the coating surface is dry.it is dried in a gradient oven at 75 ? / 1h + 105 ? / 2h + 220 ? / 1h.(3)Application performance of thiol epoxy curing agent emulsionTH,TD,PH,and PD thiol epoxy curing agent emulsions were compounded and cured with Hexion 6520,and the crosslinking degree and application performance of the coatings were studied respectively.The results show that when the ratio of the active hydrogen to epoxy mass of TD,PD curing agent and epoxy resin emulsion is 1: 1,and the curing process is 105 ?/2h or 115 ?/1.5h,the appearance of the coating film is transparent,smooth and flat,the glossiness is 105.6° and 113.2°,crosslinking degree up to 93%,water resistance of 53 h,coating film flexibility of 1mm,adhesion of grade 1,positive and negative impact resistance of 50/50,pencil hardness up to H and 2H respectively.