Preparation And Property Research Of Conductive Silver Carbon Pastes

In recent years, Printed Electronics, as an emerging technology, developing very fast,it’s an important innovation of microelectronics. It is widely used in sensors, paper battery,membrane switches, solar cells, RFID smart labels and other fields. The key point of Printed Electronics is transferring a variety of electrical properties of the ink onto the substrate by printing, making it has a corresponding electrical properties and achieving the production of electronic components.Currently, conductive carbon pastes with graphite and carbon black as conductive fillers and metal conductive pastes with silver, copper and other metals as conductive fillers are the most commonly seen on the market, while few researches on conductive pastes with combination of metals and carbon as conductive fillers have been conducted. This study selected multiwalled carbon nanotubes and homemade nano silver as conductive fillers and successfully made a kind of conductive silver-carbon paste by adding appropriate binders and addition agents. Since discovery, carbon nanotube has received much concern with its excellent electrical conductivity and mechanical property, they are difficult to disperse due to the absence of polar groups on the surface of the carbon nanotubes. Furthermore, since the carbon nanotubes are too close to each other, Molecular van der Waals force is too large,the solvent molecules is difficult to overcome the intramolecular and intermolecular Van der Waals force, into the layer and layer, so it is difficult to infiltrate, so that it is difficult to disperse in water and some organic solvents . In order to make carbon nanotubes favorably dispersed in deionized water, this study comprehensively adopted multiple dispersion methods. Firstly, mixed acids (volume ratio of concentrated sulfuric acid to concentrated nitric acid being 3:1) were adopted to oxidize the multiwalled carbon nanotubes, so as to make its surface bring carboxyl groups and other hydrophilic groups, secondly, the dispersion effects of three kinds of surface active agents including polyvinylpyrrolidone(PVP), sodium dodecyl benzene sulfonate(SDBS) and sodium dodecyl sulfate (SDS) on carbon nanotubes were comprehensively compared. Nano silver colloid was prepared by using sodium borate as reducing agent, and properties of conductive silver carbon pastes prepared by different experimental methods were compared.The following conclusions were drawn by experiments: among the three kinds of surface active agents, polyvinylpyrrolidone achieved the best dispersion effect on multiwalled carbon nanotubes, so it was selected as the dispersant to prepare conductive silver carbon pastes; the optimal experimental method for preparation of conductive silver carbon pastes was gotten: firstly, nanosilver colloid was prepared by using sodium borohydride as the reducing agent via liquid phase reduction method, secondly, Silver nanoparticles were washed with deionized water, ethanol and acetone in turn and purified by centrifugal method, so as to remove some incompletely reacted reducing agents and impurities, then carbon nanotube suspension with carboxylic acid groups was added into the wet mud nano silver undergone washing, finally, sodium carboxymethyl cellulose and other addition agents were added and ultrasonic dispersion was conducted to prepare the conductive silver carbon pastes; the conductive silver carbon paste prepared by this method has favorable property, with viscosity under 25℃ of 8.0cP and adhesion grade of 5B; the paste was coated on a conductive film using glass slide as the substrate material and went through high sintering at 180℃, the measured electrical resistivity of the conductive film was 1.23mΩ·cm; the prepared conductive silver carbon pastes with the best performance were filled into a glue pen to make a conductive pen, with which the conducting circuit was drawn on resin coated photographic paper, and after the diode was connected to the battery,it was powered on and became shiny.