Preparation Of Polythiourethane Acrylate And Its Properties Of UV-cured Coatings On Metal

The development of UV-cured,waterborne,powdery and other environment friendly coatings is encouraged in the Fourteenth Five-Year Plan of the Chinese Coatings Industry.Due to the advantages of fast curing rate and environment friendly curing process,UV-cured coatings are widely used in various industries(wood,plastic and paper).However,the shrinkage stress of the coating cannot be released in time and may accumulate inside the coating because of high UV-curing speed,which leads to poor adhesion,even warpage or peeling from substrate interface.The poor adhesion of the UV-cured coating limits its application on metal.In the work,the improved adhesion can be achieved via the exchange reaction of dynamic thiourethane bonds.Specifically,a series of polythiourethane acrylate(PTUA)containing dynamic thiocarbamate bonds were synthesized,which were used to prepared UV-curable coating.In this chapter,the mechanism of improved adhesion by incorporating the dynamic thiocarbamate bonds was studied.Meanwhile,the effect of the molecular weight on the curing process and the properties of coatings was investigated.PTUA was synthesized via click reaction of 3,6-dioxa-1,8-octanedithiol(EDDT)and isophorone diisocyanate(IPDI),following the reaction between 2-hydroxyethyl acrylate(HEA)and IPDI.By adjusting the feeding ratio,a series of PTUA with different molecular weights were synthesized.The successful synthesis of PTUA was confirmed by ~1H-NMR,FTIR and GPC.The incorporation of dynamic thiourethane bonds in UV-cured PTUA coating could release shrinkage stress via dissociative exchange of thiourethane bonds upon heating.After heating,the adhesion strength of PTUA coating could be significantly improved and the coating composed of the highest molecular weight PTUA had maximum pull-off strength(4.90 MPa),which was 1.5-fold increase compared with the coating without heating.In the second chapter,the effect of different functionalities and structure of photosensitive groups on the curing process and the properties of coatings was studied.The main raw materials include IPDI,EDDT,HEA,hydroxyethyl methacrylate(HEMA)and pentaerythritol triacrylate(PET3A).By varying the photosensitive capping agents,PTUA with different functionalities and reactive group were synthesized.The successful synthesis of PTUA was confirmed by FTIR and GPC.Compared to acrylate oligomers,methacrylate oligomers had lower UV-curing speed,leading to lower shrinkage stress and higher adhesion.With the increasing functionalities,the adhesion strength of the UV-cured coating was decreased due to the high shrinkage stress of coatings.Meanwhile,the hardness,glass transition temperature and thermal stability of PTUA coatings were increased.In this chapter,the effect of different chain extenders on the curing process and the properties of coatings was examined.At the same time,polypropylene glycol(PPG1000)was introduced into the oligomer backbone to improve the performance of coatings.The glycol mercaptopropionate(GDMP),hexanedithiol(HDT)was respectively used as chain extenders to prepare PTUA.The structure of products was characterized by FTIR.The results showed that the structure of chain extender had no significant effect on the curing speed and adhesion.However,the performance of PTUA coatings were related to the structure of chain extender.PTUA with GDMP as the chain extender had excellent tensile strength and adhesion after heat treatment,while PTUA with HDT as the chain extender had excellent water resistance and impact resistance.