Component Design And Rheological Properties Study Of Conductive Ink

The effect of the components and their content of the curing conductive ink on theoperational performance and process performance was studied systematically. In viewof the study of the theory of solubility parameter solvent evaporation, the ink bindersystem was designed to meet the adhesion and solvent evaporation requirements. Theeffect of annealing on the microstructure and performance of the silver powder wasstudied systematically. It was found that annealing on the silver powder cansignificantly reduce the square resistance of the conductive film. The rheologicalproperties of the conductive ink were also studied. Moreover, the relation between therheological properties and operational performance of link was established.The solubility parameters of the acrylic resin were calculated using the groupcontribution method. According to the theory of solubility parameters, a mixed solvent,which have a good ability to dissolve the acrylic resin was selected. The conductive inkprepared with acrylic resin, mixed solvent and silver powder have a suitable rate ofevaporation. When curing at120℃for30minutes, the square resistance of theconductive film layer can achieve stability. Furthermore, the volatile gradient of solventwas obtained in the curing process of the conductive ink.Considering that the hard agglomerates of the silver powder will not occur afterannealing, the heat treatment process of the silver powder was determined. The effect ofannealing on the surface morphology, lattice constant, internal residual distortionenergy and microstructure of the silver flake was studied systematically. It was foundthat the thickness of the silver flake increases, whereas the bulk density, tap density andthe specific surface decreases and the morphology become more irregular after heattreatment. Meanwhile, the lattice constant of the silver powder increases and themicro-strain decreases. Transmission electron microscopy analysis showed that theoriginal silver flake has more grain boundary. Moreover, the twin crystal was found andthe twin plane and twin zone axis was determined by the calibration and calculation ofthe diffraction spots. The new nuclei were found at the grain boundary of silver flakeafter annealing treatment. These new nuclei do not have clear orientation relationshipwith original grain. The lattice distortion of the silver powder is also significantlyreduced after the annealing treatment. The effect of the type of silver powder on theconductive ink viscosity properties, electrical properties and solvent release was studied.The results show that the larger the surface area ratio of the silver powder, the lowerfluidity and square resistance of the conductive ink. The square resistance of theconductive ink prepared with the silver powder decreased significantly after annealingtreatment. Large diameter amalgam is not conducive to the release of the solvent andthe heat treatment of silver powder does not have a big impact on the release of the solvent.Viscosity characteristics, dynamic viscoelastic properties, yield stress, stabilitycharacteristics, thixotropy and the recovery characteristics after shearing of theconductive ink were studied using a rheometer. The effect of the size of silvermorphology, polymer molecular weight, as well as thixotropic agents on the rheologicalproperties of the ink was investigated. The results show that the amalgam morphologysize mainly affect the viscosity and thixotropy of the ink, and the larger the specificsurface area of the silver powder, the greater the thixotropy of conductive ink. Polymermolecular weight has the greatest impact on the rheological properties of the conductiveink. Conductive ink prepared with smaller molecular weight of the polymer has agreater thixotropy and viscosity, as well as an enhanced recovery ability after shearing.Thixotropic agents mainly affect the thixotropic properties of the ink. The addition ofthixotropic agents in the ink increases the viscosity at low shear and decreases theviscosity at high shear. Moreover, the thixotropy increases and the recovery ability ofthe ink is enhanced after shearing. However, the addition is considered to have littleimpact on the viscoelastic properties and yield stress of the ink.