| Adhesives for bonding organic or inorganic lenses to lens barrel are mainly divided into hot melt adhesives and UV adhesives.Although UV adhesive has the advantages of the rapid curing at room temperature compared with hot melt adhesives,it still has the disadvantages such as poor temperature and moisture resistance,high curing shrinkage,and low bonding strength.This paper synthesized a polycarbonate(PC)modified polyurethane acrylate prepolymer and studied the effects of the functionality and molecular weight of prepolymer,on the properties of the adhesive.The polyurethanes were synthesized by the polyaddition reaction of excess hexamethylene diisocyanate(HDI)with different molecular weight polycarbonate diol(PCDL)at 40 °C,,and the degree of reaction was determined by dibutylamine titration.(With 0.1wt % dibutyl dilaurate as the tin catalyst,the prepolymers were prepared by end-capping reaction of the polyurethane and hydroxy acrylates with different functionalities in the presence of 0.1 wt% dibutyl dilaurate tin as a catalyst.The adhesives were prepared by compounding prepolymer,acrylate,photoinitiator,silica filler,and silane coupling agents,and their adhesive properties were studied by using PC-PC and glass-PC as the substrates.The monofunctional prepolymer exhibited better adhesion performance,curing shrinkage,and temperature and moisture resistance than multifunctional prepolymer.The high molecular weight PDCL was beneficial to improve the heat resistance and cure shrinkage of the adhesive,and showed the best comprehensive performance with the prepolymer content of 35 wt%.The addition of silica can effectively enhance the mechanical properties,heat resistance,and adhesion properties of the adhesive as well as effective decrease of curing shrinkage rate.The silane coupling agents can significantly increase the bond strength with glass and improve the dispersion of silica fillers in adhesives.Therefore,the prepolymer(PUA-H2)with monofunctional degree and the PCDL molecular weight of 2000 was selected for comparative experiments.It was found that the best raw material ratio was 35.5 wt% prepolymer2,32.8 wt%acrylate,4.1 wt% photoinitiator,27.6 wt% silica filler,and 1 wt% silane coupling agent.The main properties of the resulting adhesive are as follows:The bonding strengths of the adhesive to PC-PC substrate and glass chip-PC substrate at room temperature were 9.33 MPa and 8.99 MPa,while the bonding strengths after storage for 1000 h at high temperature(85 °C)and high humidity(85% relative humidity)were 7.63 MPa and 13.78 MPa,respectively.The main reason for the improvement of the bonding strength of the latter is that the silane coupling agent is easily hydrolyzed into silanol under high temperature and high humidity to migrate to the glass surface and reacts with the hydroxyl group on the glass,producing strong covalent bonding forces.The 5% of curing shrinkage,the 53 HD of hardness of the cured film,the 10.18% of elongation at break,and the 3.116 cm curing depth were observed.Therefore,the comprehensive performance of the present adhesive was better than that the adhesive made by using commercial prepolymer(Sartomer CN9001S). |
PDF Full Text Request