Preparation Of Pristine Graphene Conductive Paste For Screen Printing And Its Applications

Graphene conductive pastes are poised to apply in making flexible electronics via a screen-printing way because of its excellent electrical and mechanical properties.However,it is still a big issue to prepare the pristine graphene-based conductive pastes with good dispersion and stability due to the graphene aggregation,limiting its applications.In order to solve this problem,in this thesis,a new formulation of a conductive paste with high pristine graphene loading concentration was designed by studying the influence of the composition of the organic vehicle on its performance.Then by screen printing,the printed pattern with good conductivity was obtained.In order to study the effect of the content of graphene and the addition of additives on the properties of paste and the conductivity of the film,the paste composed of terpineol,ethyl cellulose(EC)and graphene was first investigated.When the organic vehicle was composed of terpineol and 5wt%EC,the optimum graphene content was 16.7 wt%.The electric conductivity of printed film on polyethylene terephthalate substrate was5758 S/m at 38?m thickness.The paste showed apparent precipitation after 11 days.The effect of the addition of the auxiliary agents on the performance of the paste was investigated to improve the dispersibility of paste.After adding 4 wt%span-85 and 5 wt%ethyl acetate into the above organic vehicle,the optimum graphene content was increased to 20 wt%,and the paste was stably stored more than 40 days.However,the high concentration of auxiliary agents would seriously affect the conductivity of the film that decreased to 1373 S/m at 50?m thickness.The single solvent terpineol would volatilize at a concentrate temperature during the drying process of the printed film,causing pores on the surface of the film which will decrease the conductivity.Therefore,a graphene conductive paste with a ternary solvent which has excellent dispersibility and stability was designed.By studying the investigation of volatility and rheological properties,the organic vehicle composed a ternary solvent of 50 wt%terpineol-40 wt%DPM-10 wt%cyclohexanone,and the auxiliaries of 5 wt%EC,2 wt%span-85 and 2 wt%1,4-butyrolactone,showed hierarchical volatilization and good rheological properties was prepared.The optimum graphene content was 20 wt%,which was stable more than two months without apparent precipitation.The printed pattern obtained by screen printing on a polyimide substrate,after printing four times,annealing at 350?for 30 min and mechanical pressing at 20 MPa for 1 min,had a high conductivity of 9×10~4 S/m at 10?m thickness that is among the highest for pristine graphene pastes for screen printing.The printed graphene pattern showed good flexibility.The resistivity of the printed pattern increased slightly despite 1000 bending cycles.Also,the pattern also has excellent electrical heating performance and heat dissipation.Therefore,the graphene conductive paste prepared in this paper can be applied in the preparation of high conductive patterns which can be applied in the fields of flexible electronic devices,wearable devices,and so on.