Study On Curing Reaction And Properties Of Isocyanate/Epoxy

Epoxy adhesive are widely utilized in a number of application, due togood designability and excellent combined performance. The performance ofthe epoxy adhesive depends on the structure of epoxy resin and curing agents,the structure of curing agents plays an important role in the processperformance, curing properties, heat resistance and service performance of theepoxy adhesive, therefore, an important research method in the epoxyadhesive is changing the structure of the curing agent. The reaction of thecommonly curing agent with epoxy is cycloaddition to formthree-dimensional network structure. With the development of moderntechnology, especially in the electronics industry and the aviation industry, theepoxy adhesive in the dielectric properties (dielectric constant and dielectricloss), temperature resistance and moisture resistance is difficult to meet therequirements, which become the bottleneck of the epoxy resin applications.Though designing and development of new epoxy resin to improve theperformance is also common method, but industrialization is different.Therefore, to strengthen research and develop new curing agent, to expand itsscope of application by the new type of curing mechanism and performancenot only of theoretical significance, but also has important practicalsignificance.Epoxy groups and the isocyanate-NCO groups can react to generatefive-membered heterocyclic ring structure composed of carbon, oxygen,nitrogen oxazolidone. Compared with epoxy structure after cured with thenormal amine and anhydride, the rigidity of the molecular chain is enhancedand the number of weak bonds and the hydroxyl number in the main chainis reduced, thereby the toughness, thermal stability, dielectric properties, waterresistance and solvent resistance of the epoxy adhesive is improved, but thereare many problems of science and practical application is not clear when the isocyanate is used in epoxy curing agents, which impact the application ofsuch curing system.In this paper, isocyanate is as to curing agents of epoxy resin in order toget the epoxy adhesive with good heat resistance, low moisture absorption,low dielectric. The curing reaction mechanism, the reaction kinetics and theproperties of the isocyanate/epoxy system are introduced. The main contentsare listed as follows:1. The influence of stoichiometry and curing conditions on the finalstructure of the isocyanate/epoxy system is researched. The differentmechanism of the catalysts is described. The results show that the reactionbetween epoxides and isocyanates can lead to thermosets containingisocyanate and oxazolidone rings in their structure. With increasing of epoxy,the amount of the oxazolidone increased, and with increasing of isocyanate,the amount of the isocyanunate increased. The results indicated that when thereaction temperature was below140trimerization of isocyanate groups intoisocyanurate was observed; when the temperature was up to200theformation of oxazolidone ring by the reaction between epoxy andisocyanunate occurred; when the temperature was heated above230thetransformation reaction of isocyanurate with the structure ofcarbon-carbon-oxygen by epoxy self-poly to oxazolidone happened. The mainmechanism of formation of isocyanurate and oxazolidone is that intermediateswere formed by attracking of the catalyst to the isocyanate.2. The influence of the different structure of catalysts on the MDI/E-51curing system and the reaction kinetics of isocyanate/epoxy with differentcatalysts are researched. The ionic liquid catalysts are developed according tothe catalytic mechanism. The results show that the DMP-30can significantlyreduce the activation energy of second and the third reaction, the catalyticefficiency of [AMIM]Cl to the first reaction is higher.3. The properties of the isocyanate/epoxy of different stoichiometry isresearched. The results show that the glass transition temperature, elasticmodulus and crosslink density increase by increasing the initial proportionof isocyanate. The results of the thermogravimetric show that oxazolidionerings confer higher thermal stability than isocyanate rings. The mechanicalproperties of the cured resin increase at first then decreases with increasing ofisocyanate proportion. The cured materials have excellent dielectric properties, the dielectric constant is between3.0and3.2. The dielectric loss tangent valueis less than0.005. The thermal conductivity of the MDI/E-51system hasincreasing trend with increasing of isocyanate proportion.