Preparation And Application Of Ag@Cu Core-shell Structured Conductive Paste

With the rise of printed electronics technology,nano-silver based conductive ink with strong conductivity and high stability has become core materials.It is suitable for the lightweight,flexible and large-scale production process.However,the high price of silver material has restricted its practical applications.Therefore,it is necessary to develop an alternative material with low price and similar conductive properties to reduce the cost of conductive inks.In this study,low-cost copper nanoparticles are synthesized,and a nano-silver layer is coated on the surface of the copper nanoparticles to prepare Ag@Cu core-shell structure.On the basis of ensuring conductivity and stability,the content of silver nanomaterials is reduced,so that the cost can be reduced.As to the application,conductive film and near field communication(NFC)antennas are printed through screening printing technology.In this study,a glycerol/water binary solvent method is used to prepare copper nanoparticles.The reaction is carried out in short time(4h)at 90?with CuCl2·2H2O as a copper source,ascorbic acid(Vc)as a reducing agent,and polyvinylpyrrolidone(PVP)as a dispersant.It is found that the particle size and dispersibility of nano-copper can be changed by controlling the volume ratio of glycerol/water solvent.Under the conditions of glycerol/water volume ratio of 3:2,ascorbic acid concentration of 0.004 mol/L,and PVP concentration of 0.006 mol/L,the nano-copper has the best morphology with a particle size range of 80±10 nm.If ultrasonic coating is further performed by using citric acid or oleic acid,its thermal stability can be effectively improved.The Ag@Cu core-shell structure is prepared by liquid phase chemical reduction method with nano-copper particles prepared under optimized conditions as the core.Specifically,the water bath reaction is carried out at 60? for 40 minutes with AgNO3 as a silver source,glucose as a reducing agent,and ammonia as a complexing agent,and the ethylenediamine is used to adjust the pH of the reaction system.The apparent color,bulk density,XRD,SEM,EDX,particle size,and TGA analysis were conducted.It is revealed that when the molar ratio of Cu:AgNO3 is 4:3,the molar ratio of C6H12O6:AgNO3 is 8:3,and the molar ratio of PVP:AgNO3 is 2:1,and the pH range of liquid B adjusted by ethylenediamine is 9.5-10,the obtained core-shell structure has uniform particle size,good coating effect,and can maintain good thermal stability at no higher than 400?.Based on the above findings,a conductive paste is prepared with Ag@Cu core-shell structure synthesized at optimized condition,then the conductive film and NFC antenna are screen-printed.The conductive paste(35%Ag@Cu,35%resin,and 30%deionized water)is printed into a 30 mm×40 mm conductive film by screen printing with a coated paper as the substrate.After being sintered at 180? for 1 minute,the square resistance is 0.78 ?/sq,and it remains stable in the 90 times of 3M tape tear resistance test.Under the condition of 5 cm line length,the two ends of the conductive film can be connected when the line width of the conductive film is no less than 0.6 mm.At the line width of more than 0.4 mm,the square resistance of the conductive film decreases linearly while the line length decreases from 5 cm to 1.5 cm.When the polyimide modified with 2 mol/L NaOH solution is used as the substrate,a 30 mm×40 mm conductive film is screen-printed.The film shows stable square resistance of 0.8 ?/sq in 1000 bending tests and 60 times of 3M tape tear resistance tests.The prepared“SUST" shaped conductive electrode is connected to the circuit for 30 minutes,which shows stable electrical stability under the conditions of no strain,lateral bending of 180° and longitudinal bending of 180°.Furthermore,the NFC antenna assembled chip printed with the conductive paste(45%Ag@Cu,45%resin,10%deionized water)can complete the response within 1 second,of which the success rate is greater than 90%.