Preparation Of Graphene-Based Composite Conductive Paste And Its Electrothermal Property

Graphene is favored in the field of conductive pastes because of its excellent electrical and mechanical properties.However,its practical application is limited due to its weak adhesion to the substrate,and the pollution caused by the discharge of toxic,harmful organic solvents used in the preparation process.In this paper,the graphene,prepared by supercritical carbon dioxide-assisted shearing,was used as the conductive filler.The effects of binder,solvent,additive,and surface functionalization of graphene on the properties of the conductive paste were explored,and the waterborne graphene conductive paste with high electrical conductivity and strong adhesion was prepared.A graphene-based electrothermal film with excellent electrothermal performance was developed by screen printing.The main research contents and conclusions are as follows.First of all,the paste mixture consisting of terephthalol,polyurethane,polyether polyols,and graphene was developed based on paste fluidity and conductivity,and the effects of ball milling and three roller post-processing on the conductivity of the graphene-based film made by screen-printed method on polyethylene terephthalate were investigated.When the contents of the graphene and polyether polyols were 25%and 0.8%respectively,the ratio of the graphene and polyurethane was 2:3,and the mixing was 2 h using three-rolling machine,the sheet resistance of the film made by the as-prepared paste reduced from 4000 to 850Ω/?,the adhesion of the pattern on the PET substrate reached 4B grade.The prepared electrothermal film could be up to 54℃under the applying voltage of 20 V in an atmospheric environment.In order to improve the conductivity of graphene pastes,graphene/silver pastes were prepared by adding metallic silver nanowires.Firstly,the synthesis of silver nanowires was studied,and the effects of temperature,inducer and molecular weight of PVP on morphology and structure of silver nanowires were investigated.When the reaction temperature was 170℃,ammonium chloride was inducer,the molar ratio of Cl~-/Ag~+was 0.2267,the mixed PVP(made by mixing the molecular weight of 58k and1300k at 1:1,w/w)was as the protective agent,and the ratio(w/w)of the mixed PVP and silver nitrate was 3:2,the silver nanowires with the aspect ratio of 875 were obtained.Secondly,the influence of the content of silver nanowires on the properties of graphene-based pastes was investigated.When Ag NW:Graphene=1:10(w/w),Graphene:P(VP/VA)=1:3(w/w),and the 2-propanediol methyl ether(DPM)as solvent,the paste concentration of 71.4 mg/ml,the sheet resistance of the electrothermal film with 30μm thickness made by screen-print the paste on PI substrate reached 0.88Ω/?,and the adhesion reached4B grade.The influence of voltage on the electrothermal performance of the graphene-based film was investigated.The temperature of the film increased with the voltage.At the voltage of 5 V,the temperature reached65℃.In order to solve the problem of organic solvents used in the preparation of graphene pastes,the preparation and properties of environmentally friendly water-based graphene pastes were studied.Firstly,we used plasma technology to modify graphene at the rf power of 55w and40 k Hz.It was proved that the plasma-treated graphene had hydrophilic oxygen-containing groups by characterization using IR,Raman,contact angle,and scanning electron microscope(SEM).The weak-oxidized hydrophilic graphene oxide was obtained.The effects of plasma treatment time,the content of binder-polyvinylpyrrolidone and vinyl acetate(P(VP/VA))and the co-solvent system composed of dipropylene glycol methyl ether,ethylene glycol and propylene triol on the conductivity and adhesion of graphene-based aqueous paste were studied.When the plasma processing time was 15 min,the co-solvent system composed of1:1:1(v/v/v)dipropylene glycol methyl ether,ethylene glycol and propylene triol and the ratio of the binder to graphene of 1:10,the electrical conductivity of the patterns made via screen-printing the paste reached1.34×10~4 S/m.The adhesion of the pattern on the PI substrate reached 4B grade.The influences of voltage and power on the electrothermal performance of the as-prepared graphene-based film were studied.The relationship between the highest temperature of the electrothermal film and voltage was studied.The dynamic heating curve of electrothermal film was studied under the fixed voltage.The cycle stability and flexibility of the electrothermal flim was examined.The heating temperature was still stable after fast switching on-off for 10 cycles and repeatedly bending in 180°for600 times.The film pattern with the conductivity of 2.36×10~4 S/m was obtained,which reached 60℃within 1 min under the 9 V voltage,indicating that it had good thermal performance.The waterbased graphene paste developed in this paper has a broad application prospect in the field of electrothermal.