Preparation Of Waterborne Silicon-based Polyisocyanate And Their Application In Coating

The aqueous two-component polyurethane coating is an environmentally friendly paint.It’s mainly composed of aqueous polyisocyanate and aqueous hydroxy acrylic resin. Thecoating has a low film formation temperature, strong adhesion, wear resistance, hardness,chemical resistance, weather resistance and superior performance. It is widely used in surfacefinishing such as the protection of wood, metal, plastic and automotive. In this thesis wedesigned and synthesized a series of waterborne silicon-based polyisocyanate by use ofalkoxysilanes as starting material and by means of nonionic and ionic modification. By usethis polyisocyanate, the film properties of waterborne two-component polyurethane such ashardness, gloss and water resistance were improved.Firstly, we studied on the preparation of aqueous silicon-based polyisocyanate. It wasmainly using industrialized alkoxysilanes and polyethylene-glycol as raw material. Thesiloxanes reacted with polyethylene glycol by transesterification reaction in order to make asiloxane structure in polyethylene glycol. Then this modified polyethylene glycol reactedwith polyisocyanate so that the molecular chain of the final product has the structure of theorganosiloxane. In the preparation of the two-component coating process, the remainingalkoxy hydrolyzed into silanol and then dehydrated and condensed to form Si-O-Si bond infilm. This bond together with urethane bond formed a double crosslinked structure. Givenfilm high hardness, gloss, heat-resistance and water resistance.Secondly, we studied the methods of nonionic, ionic and block modifications by usepolyethylene glycol, polyethylene glycol monomethyl ether, aliphatic polycarbonate diols(APC), trimethylol propane(TMP), alkoxysilanes (TOS) and methyl ethyl ketone oxime asmodifiers or blocking agents. Then the modifiers or blocking agents reacted with toluenediisocyanate (TDI) or hexamethylene diisocyanate to prepare a series of waterbornepolyisocyanates. These modified polyisocyanates prepared with aqueous polyacrylatedispersion to compose the two component aqueous polyurethane coating. The filmperformance of gloss, hardness, adhesion, impact resistance, flexibility, water resistance andother properties were tested.Finally, a queous hydroxyl acrylic dispersion (WDA) was synthesized by solution polymerization. The resin viscosity affected by reaction temperature, dosage of initiator andchain transfer agent was researched. The performance of waterborne two-componentpolyurethane coating film affected by acid value, hydroxyl value and the NCO/OH ratio wasdiscussed. The aqueous two-component polyurethane coating was prepared by usewaterborne silicon polyether polyisocyanate (WSiP), and the film performance was tested inorder to the development of final product.