Synthesis And Characterization Of Insulating Waterborne Polyurethane Dispersion

Water-based insulating coating has the advantages of solvent-free volatilization,safety,non-toxicity,and convenient transportation and storage.It has become one of the choices of protective coatings in the electronics industry.As a new type of polyurethane material,water-based polyurethane has excellent abrasion resistance,easy curing at low temperature,chemical corrosion resistance,electrical insulation and other advantages.It was suitable for using as water-based insulating coatings.However,most of the currently available polyurethane insulating coatings are solvent-based,the research and application of water-based polyurethane insulation coatings are relatively rare.This paper aims to synthesize an insulating waterborne polyurethane dispersion,which can be used as an insulating coating on electronic substrates such as printed circuit boards(PCB).Firstly,carboxylate hydrophilic monomer(AAA)was synthesized by diamine(IPDA),methyl acrylate(MA),and triethylamine(TEA)through Michael addition reaction;Then,using hydroxy-terminated polybutadiene(HTPB)and dimer acid polyester polyol(PDFA)as soft segments;tetramethyl m-xylylene diisocyanate(TMXDI),self-made amino carboxylate(AAA),and isophorone diamine(IPDA)as the hard segments,through the combination of acetone-prepolymer method.to synthesis insulating water-based polyurethane dispersion(PUD).Focus on the effects of HTPB addition,R value(NCO/OH)and hydrophilic monomer(HGC)content on the properties of polyurethane emulsion and film,and determine the best synthesis process and formula.A variety of characterization methods were used to characterize the structure and performance of PUD.The infrared spectrum showed that the prepared carboxylate hydrophilic monomer(AAA)and PUD was the target product.Most of the PUD can be stored stably at room temperature for6 months.The average particle size of the PUD dispersion increases with the increase of HTPB content and R value(NCO/OH),and decrease with the increase of hydrophilic monomer content(HGC).;The change of viscosity is opposite to the change of particle size.TEM analysis shows that most of PUD dispersion colloidal particles have obvious regular spherical structure.The PUD film was tested for heat resistance,DSC test show that the glass transition temperature Tg of PUD film decreases with the increase of HTPB,and increases with the increase of R value(NCO/OH);Thermogravimetric analysis shows that the prepared PUD film has good heat resistance stability.The water resistance test results show that,except for the H₀sample,the water absorption of the rest of the PUD film is below 5%,indicating that the prepared PUD film has good water resistance.The PUD film was tested for electrical insulation.Except for the H₀ sample,the volume resistivity of other PUD was above 10¹⁴?.cm,which has strong electrical insulation.After heat-resistant treatment of PUD,the volume resistivity of each PUD film does not change much.When the PUD film is subjected to moisture-resistant heat treatment,the volume resistivity of each PUD is reduced by 1-2 orders of magnitude,but it still remains above 10¹²?.cm,Which can well meet the requirements of insulation resistance(10¹¹?.cm).The hardness of PUD film increased gradually with the increase of HTPB content,R value(NCO/OH)and hydrophilic monomer(HGC)content,showing a strong hardness.The results of adhesion test of PUD coating showed that Except for a few samples(H5,A1),the other PUD have excellent adhesion on the PCB board.