| One component moisture-curing polyurethane sealant with high flexibility,and excellent adhesive properties were widely used in the direct assembly of automobile windshields.In this paper,a silylated polyurethane primer was prepared by solution polymerization to improve the viscosity,adhesive strength,and poor weatherability of the polyurethane sealant.The effects of different polyols,catalysts,silane coupling agents on the surface drying-time and adhesion properties of primer were discussed via the single factor method.The results showed that:(1)the synthesized primer with polycarbonate polyol(PCDL1000)and polyether polyol(N210)as prepolymer and acetone and ethyl acetate mixture as the solvent had better coating operation and storage stability.(2)A good synergy was achieved when organometallics(DY-12)and tertiary amine compounds(DMDEE)were used as co-catalysts and the surface drying-time of the primer was 8 min when 1‰ catalyst was used with a ratio of DY-12:DMDEE=3:7.(3)Compared to other common used silane coupling agents,the primer synthesized with highly functionalized silane coupling agent T generated a better adhesive performance.(4)The main components of primers contains polyurethane prepolymers,cross-linking agents(PAPI)and silane coupling agents,which were functionalized as film-forming,cross-link curing and adhesion promotion,respectively.The bonding strength bettwen primer and glass was significantly improved,when the adding amounts of prepolymer and crosslinking agent were 15% and 3%,respectively,and the silane coupling agent terminated ratio was 10%.After soaking in water for 7 d,80? for 1 d,70?,100% RH for 7 d,the shear strength decreased from 1.48 MPa to 1.40 MPa.The bonding strength of primer was increased by 32% compared to the non-primer(1.06 MPa).The destructional form shifted to complete cohesive failure from interface failure,and the adhesion grade reached level 1.Infrared analysis and thermal analysis(TG)were used to characterize the synthetic primers.It was confirmed that the polyurethane primer modified silane synthesized in this thesis include two curing mechanisms: moisture curable and siloxane hydrolytic crosslinking.The two curing systems could be effectively balanced by adjusting the silane terminated rate.When the silane terminated rate was 10%,the prepared primer had a surface drying-time of 10 min and a shear strength of 1.40 MPa.The contact angles of distilled water and diiodomethane on the surface of the solid polymer were determined by the sessile drop method,and the solid surface energy was estimated by Owens and Wendt methods.The results showed that: the surface energy between the glass and aluminum and polyurethane sealant was varied greatly.The gap of surface energy between the substrate and polyurethane sealant could be narrowed from 4 m N/m to 1 to 2 m N/m with the use of primer due to the benefited diffusion,which played an important role in enhancing the adhesion strength.The differences in the surface tension between the substrate and primer may lead to shrinkage phenomena in the coating process.The use of suitable polyols and reaction solvent can reduce the probability of shrinkage.At the same time,the addition of 1.5‰ wetting agent of silicone modified polyether could effctively reduce the shrinkage. |
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