| Stealth coating (more than400micron) painted on aircraft general need5~6days,the damaged coating of aircraft must be repaired after each flight in order to satisfythe requirement of high frequency fighting, the research of stealth coating rapidsolidification technology has great significance and urgency. And a new type of quick,environment friendly and energy-saving curing method which named UV-ignitedfrontal polymerization was used. Combined with the optical/thermal initiatorcompounding technology, quick-solidified radar absorbing coatings with excellentperformance was prepared by composite iron powder absorbent and epoxy resinmodified by epoxy terminated polyurethane. Eventually got quick-solidified thickabsorbing coatings and the coating has potential application value in rapid repair ofabsorbing coatings. Different types of epoxy terminated polyurethane weresynthesized. Then UV-ignited frontal polymerization of varnish prepared by the resinand curing process of the coating was studied. And the effect of silane coupling agentand surface treatment process on coating performance were discussed in detail. Themain research contents and conclusions are as follows:1. Synthesis and characterization of epoxy terminated polyurethane. The effect ofreaction temperature, reaction time and the content of dibutyltin dilaurate on thedegree of reaction of epoxy terminated polyurethane. The products were characterizedby FTIR and1HNMR. Synthetic conditions: The first reaction temperature was70℃,The second reaction temperature was60℃, and the content of dibutyltin dilaurate was1‰of the total mass of reactants. The cured flexibility of flexible epoxy terminatedpolyurethane and E-44terminated polyurethane resin system were compared. Theresults showed that the breaking elongation rate of flexible epoxy terminatedpolyurethane was40.8%, obviously superior to the latter.2. The study on photofrontal polymerization of varnish system. Curing behaviorand frontal polymerization behavior of varnish were studied via paperless recorderand differential scanning calorimeter. The results indicated that, the epoxy terminatedpolyurethane prepared by different molecular weight of polyethylene glycol,-OH:-NCO:-OH molar ratio and diisocyanate have important influence on curingbehavior and frontal polymerization behavior of varnish. With the increase of the molecular weight of polyethylene glycol, ignition time reduced, the maximumtemperature of the propagating front gradually increased. The smaller isocyanateindex R of polyurethane prepolymer, the greater the front velocity and the longer thephotoinitiator time, but the value of R has no effect on the maximum temperature ofphotoactivated frontal polymerization. The epoxy terminated polyurethane preparedby HDI has larger front velocity, shorter time to reach the maximum temperature ofpropagating front and longer ignition time.3. The study on curing process and the interface behavior of Quick-solidifiedradar absorbing coatings. The effect of silane coupling agent surface treatment onabsorbent, surface treatment with silane coupling agent hydrolysis solution andabrading on the substrate on the adhesion of coatings were studied. The resultsindicated that, the adhesion of coatings was increased by surface treatment withabrading. Absorbers was ball milled by silane coupling agent (2wt%KH-560),adhesion of coatings was improved as55.6%(25.174MPa). Substrate was treated by3wt%KH-560hydrolysis solution, adhesion of coatings was improved as90.67%(27.885MPa). The resin system has great influence on flexibility of coating. Thesmaller the molecular weight of polyethylene glycol and the isocyanate index R ofpolyurethane prepolyme, the better the flexibility of epoxy terminated polyurethanesystem coating. The flexibility of HDI, aliphatic isocyanate, was good. The coatingwhich prepared by resin with it has good flexibility, and the more the content of epoxyterminated polyurethane in the adhesive the better the flexibility of coating. Theproportion of absorbent and adhesive was6:1. The flexibility of quick-solidified radarabsorbing coatings could be up to12mm.The effect of different power and distance of UV lamp on curing time needed forquick-solidified radar absorbing coatings were studied. The results showed that, thegreater the power of UV lamp and the smaller the distance, the shorter the curing timeof coating, but the greater power of UV lamp made the light distance smaller，andsome defects will exist in the surface of coating. On the contrary, the coating couldnot be cured completely. The power of UV lamp was2000W, the distance was15cm.Eventually quick-solidified radar absorbing coatings can be cured in2min withexcellent performance, the properties of Quick-solidified radar absorbing coatingswere shown as follows: the adhesion of0level, the flexibility of12mm, the impactstrength of50kg cm. |
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