Study On Phenolic Curing Agents For Epoxy Powder Coating

Epoxy powder coating is free of organic solvent and environmental friendly.It is widely used in oil and gas transportation pipes,automobiles,electronic products.It can have protective and decorative and other specific functions.Curing agents have a great influence on the properties of powder coating.The thesis studies the synthesis of a series of different types of phenols curing agents,and their curing properties.The main research and conclusions are as follows,(1)Nine curing agents were synthesized based on three different epoxy resins(CYD-128?4080E?NPEF170)via the reaction with bisphenol A(BPA),The curing agents are named CYD-128-BPA-1:1.5;CYD-128-BPA-1:1.2;CYD-128-BPA-1:3;4080E-BPA-1:1.5;4080E-BPA-1:2;4080E-BPA-1:3;NPEF170-BPA-1:1.5;NPEF170-BPA-1:2;NPEF170-BPA-1:3.The cathodic disbonding test of the cured coating shows that:when curing agent is CYD-128-BPA,the cathodic disbonding radius is between 2-5 mm;when curing agent is 4080E-BPA-1:2,the cathodic disbonding radius is less than 5.2 mm;when curing agent is 4080E-BPA-1:3,the cathodic disbonding radius is less than 2 mm;when curing agent is NPEF170-BPA-1:2,the cathodic disbonding radius is less than 1.1 mm.The anti-cathodic disbonding performance of the above cured coating meet the requirements of the standard SY/T 0315-2005(<6.5 mm).However,the coating have poor adhesion strength and fails to meet the standard requirement therein.(2)Two kinds of epoxy resin(CYD-128?387SD)were modified by five modifiers(R1?R2?R3?R4?R5)and then reacted with bisphenol A to obtain a series of modified phenolic curing agents.The cathodic disbonding test of the cured coating shows that:when the epoxy resin CYD-128 and modifier R3 are used with the mole ratio:epoxy group/modifier/phenolic hydroxyl/=1/0.25/2.75,the anti-cathodic disbonding performance of the coating is poor,and the rest of four kinds coating can meet the requirements of standard SY/T 0315-2005(<6.5mm).When the epoxy 387SD is used,and with the ratio epoxy group/modifier/phenolic hydroxyl=1/0.1/2.9,the anti-cathodic disbonding performance of the coating can meet the requirement of the standard SY/T 0315-2005(<6.5 mm)except modified by R2.Adhesion test shows that:when the epoxy resin used is CYD-128 and with the ratio epoxy group/modifier/phenolic hydroxyl=1/0.1/2.9 or when 387SD epoxy resin is used with the ratio epoxy group/modifier/phenolic hydroxyl=1/0.25/2.75,adhesion performance can meet the requirement of SY/T0315-2005.(3)The phenolic curing agents containing polyurethane structure have been synthesized by the reaction of uretdiones(Desmodur N3400,Desmodur XP2730),isocyanurate(Desmodur N3600,Desmodur N3900)and bisphenol A.The curing agents are named Desmodur N3400-BPA,Desmodur XP2730-BPA,Desmodur N3600-BPA,Desmodur N3900-BPA.FT-IR shows that:the-NCO disappeared and the uretdione structure completely decomposed.The cathodic disbonding test of the cured coating shows that:when the curings agents are Desmodur XP2730-BPA,Desmodur N3400-BPA,the maximum disbonding radius are 5.7 and 5.4 mm,respectively,The coating can meet the requirement of the standard SY/T 0315-2005(<6.5 mm),and the rest cannot meet the requirement.Adhesion tests show that:the adhesion of the coating can meet the requirement of the standard SY/T0315-2005(within 1-3 grades)except Desmodur N3900-BPA.