Research Of Colorless Solvent-free Fast-curing Epoxy Adhesives

Epoxy adhesive are a class of adhesive that has excellent adhesion and excellentphysical and chemical properties of epoxy resin. Example for heat resistance, impact resistance,corrosion resistance, durability, resistance to the space environment, wetting curable, lowtemperature curing so that make it applied in various fields covering daily adhered to thecutting-edge areas of high-tech applications. Colorless transparent epoxy adhesives commonlyused in the bonding of optical instruments and a variety of transparent materials due to itsexcellent light transmittance and refractive index. So the prospect of colorless transparent epoxyadhesive is great. Multi-thiol curing agent is a compound contain multiple thiol functionals. It canquickly react to epoxy at room temperature with tertiary amine accelerators, and the product iscolorless and transparent.In this project, multi-thiol-propionate is synthesized from pentaerythritol and β-thiolpropionate, and then, prolong the chain by E-51epoxy resin and a variety of diisocyanates to getmulti-thiol curing agent. Finally, multi-thiol curing agent used in combination with E-51epoxyresin, formed colorless transparent fast-curing epoxy adhesive. This project is divided into thefollowing three steps to start research work: Synthesis of multi-thiol compound and processoptimization; chain extender of multi-thiol esterified and optimization of the reaction condition;performance comparison and research of different products;First, use pentaerythritol and β-thiol propionate as raw materials, G-10as water, C-10,C-20, C-30as a catalyst, reaction was carried under nitrogen, Joining the absorbing agent A-10when the water yield close to the theoretical value to promote reaction. After the reaction, eliminate the dryer and a small amount of water by filtration and vacuum distillation. After theoptimize of the additional amount of C-10and G-10, accelerated the reaction rate, lower thedegree of oxidation of the thiol group, improved purity and quality of product. Assess the productby thiol value test, optimal the synthesis. The product is colorless and transparent and his yield ofsynthesized product is above90%. Thiol value is0.79mol/100g.Select E-51, HDI, HMDI, IPDI prolong the chain of multi-thiol esterified to raise theviscosity and the compatibility with the epoxy resin. Determine the chain extender reactionconditions were: E-5170℃/2h; HDI70℃/1.5h; HMDI70℃/2.5h; IPDI70℃/2h. Get fourkinds of curing agent: E-5, H-5, M-6, I-5. Respectively, the viscosity is:311mPa.s (70℃),306mPa.s (70℃),300mPa.s (70℃),671mPa.s (70℃), as a curing agent colorless and transparent,suitable viscosity and good stability.Prepared adhesives with E-51epoxy and agent self-made curing agent, adding complexaccelerators of DBU and Benzyldimethylamine in an amount of10%of curing agent. Theadhesive can be gelled at room temperature for10min, initial curing with a certain strength for30h, tensile shear strength can be achieved more than15MPa after1d. Test and contrast ultravioletvisible light, tensile shear strength, electrical properties, surface energy and water absorption ofdifferent adhesives. Except I-5A, the tensile strength of other adhesives is above18MPa,especially, the date of M-6A is up to20MPa or more, so mechanical properties of the adhesivesare better than the majority of the product in the market. Except I-5A, the maximum visible lighttransmission rate of adhesives is above85%. The date of H-5A is more than90%.