| The moisture-curable polyurethane hot melt adhesive(PUR) is a kind of environmentalgreen adhesive which is solvent-free and100%solid content. Its properties of mechanical, heatresistance and aging resistance could be improved through moisture curing with no pollution tothe environment and harmless to the human body. This paper explored the preparation of PURand its applications on the car lights.This paper used the bulk polymerization and discussed some factors which affected theproperties of PUR, such as reaction temperature, reaction time, stirring speed, index ofisocyanate (the molar ratio of NCO/OH), the ratio of polyester and polyether, the structure ofhard segment, the structure and relative molecular mass of soft segment, and the bondingsubstrate.The results showed that: in the preparation of PUR, adding the measurement of isocyanateat70℃which could avoid system implosion and gel phenomenon effectively. The PUR withexcellent performance could be prepared by increasing the stirring speed of the reaction to400r/min while the temperature rised to85℃, then improving the temperature of the system to95~100℃, stirring uniformly for2h, and defoaming for30min.Through the discussion of bonding properties of the PUR with different structures, thispaper showed that: in the structures of hard segments the MDI-type PUR had the bestcomprehensive properties, the anti-yellowing properties of HDI and HMDI were better; in thestructures of soft segments, the crystallization behavior of the PUR prepared by PBA or PTMGwas good while the bonding property of the PUR made by PBA was better than by PTMG orPCD; the larger the relative molecular mass of PBA was, the better the initial viscosity andcuring rate of PUR were; when the value of R=1.8to2.4, m(polyester):m(polyether)=65:35, theT-peel strength of PUR reached to100N/25mm; the bonding property to polycarbonatematerials of the PUR prepared by polycarbonate was better than other PUR because of "likedissolves like"; the catalyst could accelerate the curing rate of PUR significantly, and thecatalytic effect of two-component hybrid catalyst was better than the single one, for example,when the amount of T12and DMDEE was0.05to0.20percent (relative to the quality of thepolyol), the ultimate bonding strength of the PUR could be achieved after12h; when theamount of catalyst was more than0.40percent, although the PUR could completely cure in ashort time, the bonding property would have an obvious decrease in the next12to48h.The paper also researched the factors that affected the performance of PUR for the carlights, such as the amount of different polyols, the rate of silicone capped, the content of NCO,selection and amount of filler, the relative molecular mass of high-crystalline polyester polyol Aand selection and amount of thermoplastic resin. The results show that: when the amount ofPCD, polyol A, polyol B,7250, polyether polyol, TPU, the capped rate of KH-550and thecontent of–NCO was30,30,10,20,10,2to6,20to30, and1.80to2.05percent, respectively,the PUR for the car lights was prepared. Its open time was50s, melt viscosity was15000 mPa·s at120℃, fully cured after5d, the initial peel strength was60N/25mm, the final peelstrength was900N/25mm, no soften flowing at180℃, the optimum sizing temperature(120℃)and optimum thermal properties (analysis of DSC and TG). Compared with other similaradhesives, this PUR has reached the targets and been on a par with imported products. At thesame time, it has been authorized by cooperative enterprises and passed pilot plant test. |
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