Study On Synthesis Of Epoxy Resin-modified Polyurethane Dispersions And Its Anti-corrosive Performances

The metallic corrosion results in enormous loss of national economy every year. Painting anti-corrosive coatings is one of the most effective and common methods to protect iron substrates from being eroded. Nowadays, the research of waterborne anti-corrosive coatings obtains more and more recognition, while the use of solvent-based coatings is limited due to its high VOC. The key to high performance waterborne anti-corrosive coatings is the preparation of aqueous dispersions with excellent combined properties. In this thesis, An epoxy resin-modified polyurethane dispersions was prepared using hexamethylene diisocyanate (HDI), polyether diols (Diol-1000), dimethylolpropionic acid (DMPA), ethylenediamine (EDA) and epoxy resin (E-20) as main raw materials, whose film possessed good anti-corrosion.The technics and formulation of the synthesis of epoxy resin-modified polyurethane dispersions have been studied. The properties of dispersions and coating are obviously impacted by several factors, such as material dehydration, DMPA adding mode, stirring intensity, reaction temperature, NCO/OH value, polyether Diol-1000 dosage, -COOH group content, epoxy resin E-20 content, the neutralization degree and ethylenediamine content etc. It is indicated that DMPA should be added after being dissolved, the reaction temperature between Diol-1000 and HDI should be controlled at 84℃, DMPA reaction temperature should be controlled at 78℃, epoxy resin reaction temperature should be controlled at 70℃, NCO/OH ratio should be 1.3~1.4:1, Diol-1000 and epoxy resin content should be 20% and 45% respectively, -COOH content should be 1.4%, neutralization degree should be 95%, and ethylenediamine content should be 3.5%.The anti-corrosion of the films were studied by electrochemical polarization curves, electrochemical impedance spectroscopy (EIS) and salt spray test. We also studied the electrochemical corrosion of coatings with different thickness and different corrosive time. It is indicated that the anti-corrosion of the films were improved with the increasing of epoxy resin content. As the basic material of epoxy resin, the epoxy resin content should be as high as we can. However, the epoxy resin content should be controlled at around 45%.The epoxy resin-modified polyurethane dispersion is one-pack, micro-transparent, bluish and stable. It can be applied in the preparation of waterborne anti-corrosion coatings, whose excellent properties are following: pencil hardness 3H, 48h water absorption≤20%, 60°gloss≥90, excellent water resistance, flexibility≤1mm, the adhesion level l, good anti-corrosion performance.