CN111662594B

CN111662594B - Preparation method of PTC graphene-based conductive ink and PTC graphene-based conductive ink

Info

Publication number: CN111662594B
Application number: CN202010501750.2A
Authority: CN
Inventors: 曾垂彬; 吴立刚; 李正博; 李明
Original assignee: Guangdong Kangxi Technology Co Ltd
Current assignee: Guangdong Kangxi Technology Co Ltd
Priority date: 2020-06-04
Filing date: 2020-06-04
Publication date: 2022-08-09
Anticipated expiration: 2040-06-04
Also published as: CN111662594A

Abstract

The invention provides a preparation method of PTC graphene-based conductive ink, which comprises the following steps in parts by weight: preparing a palladium quantum dot doped graphene dispersion liquid, preparing a palladium quantum dot doped graphene-carbon black color paste, preparing a PTC mixed liquid, preparing a palladium quantum dot doped graphene-based mixed liquid and preparing PTC graphene-based conductive ink. The methoxy polyethylene glycol acrylate modified polylactic acid-polyethylene glycol block copolymer has a proper glass transition temperature range and adhesion capacity, on one hand, the polylactic acid-polyethylene glycol block copolymer is subjected to glass transition in the proper temperature range, and on the other hand, the integral anti-stripping effect of the ink is also improved. The invention also provides the PTC graphene-based conductive ink prepared by the preparation method of the PTC graphene-based conductive ink.

Description

Preparation method of PTC graphene-based conductive ink and PTC graphene-based conductive ink

Technical Field

The invention relates to the technical field of ink printing, in particular to a preparation method of PTC graphene-based conductive ink, and the invention also relates to the PTC graphene-based conductive ink prepared by the preparation method of the PTC graphene-based conductive ink.

Background

Graphene is a polymer formed from carbon atoms through sp ² The hybridized orbitals form a hexagonal two-dimensional nano material which is in a honeycomb lattice structure and only has one layer of carbon atom thickness. The unique structure of graphene gives it a number of excellent properties, such as a high theoretical specific surface area (2630 m) ² G) and ultrahigh electron mobility (200000 cm) ² /v.s), high thermal conductivity (5300W/m.K), high Young's modulus (1.0TPa), and high light transmittance (97.7%), among others. Based on the advantages of the structure and the performance of the graphene, the graphene can be applied to energy storage and conversion devices, nano electronic devices, multifunctional sensors, flexible wearable electronics and electromagnetismHas great application prospect in the fields of shielding, corrosion prevention and the like. In view of the flexibility and the conductive characteristic of graphene, the graphene slurry is added into the printing ink to prepare the conductive printing ink, and the graphene heating layer is further prepared by spraying and drying the printing ink to prepare the graphene heating body.

Along with the trend of people to good and healthy life, the traditional heating system is improved, more economic and clean alternative energy is searched, and the development of a novel green low-carbon heating system is reluctant. An electric heating technology based on graphene infrared emission performance (far infrared rays with the wavelength of 5-14 microns), namely a graphene-based infrared heating ink and an infrared heating body technology thereof, provides an effective solution for solving the problems. Compared with the traditional heating methods such as coal combustion, steam, hot air and resistance, the graphene heating method has the advantages of high heating speed, high electricity-heat conversion rate, automatic temperature control, zone control, stable heating, no abnormal sound in the heating process, high heat conduction efficiency, low operation cost (the power consumption of each square meter of the graphene electrothermal film can be reduced to 0.5 degree every day), relatively uniform heating, small floor area, low investment and production cost, long service life, high working efficiency and the like, and is more favorable for popularization and application. The energy-saving heating device replaces the traditional heating device, has particularly remarkable electricity-saving effect, can generally save electricity by about 30 percent, and even can reach 60 to 70 percent in individual occasions.

The most central part of devices such as graphene infrared heating murals, wallpaper, floors and the like is a graphene heating plate/functional layer. In the prior art, graphene is generally prepared into graphene slurry, ink or paint, and then prepared into a graphene heating coating and the like through a printing method. However, the graphene heating coating prepared by the methods has a general defect: when the local temperature of the graphene heating coating is too high, the graphene heating coating is damaged, even a fire is caused, for example, due to a short circuit or the like, or due to an excessive local temperature caused by uneven heat dissipation. Chinese patent publication No. CN 107446408A discloses PTC graphene heating ink, which is prepared by uniformly mixing and grinding a PTC functional material and a conductive filler, wherein the conductive filler can be graphene or the mixture of the graphene and one or more of graphite powder, carbon black, carbon fiber powder and carbon nano tubes. However, the PTC graphene heating ink has the defects that the sheet resistance of the graphene heating ink is large, the resistance value is difficult to recover after resin glass transition, the conductive filler is easy to precipitate after long-term use, the adhesion capability of the conductive ink and a substrate is reduced, and the like because the conductive filler and the PTC functional material are randomly mixed and adhered.

Disclosure of Invention

In view of the above, the invention provides a preparation method of the PTC graphene-based conductive ink, and the invention also provides the PTC graphene-based conductive ink prepared by the preparation method of the PTC graphene-based conductive ink, when the PTC graphene-based conductive ink is printed to form a film and used, when the local temperature of the graphene heating coating is too high, such as short circuit and other current overload conditions, and the local temperature caused by uneven heat dissipation is too high, the modified PTC mixture is subjected to glass transition due to local temperature rise, and is converted from a crystalline state or semi-crystalline state resin into an amorphous state, and then conductive substances in the conductive film, such as palladium quantum dots doped with graphene, carbon black and the like, are mutually pulled apart, so that the resistance of the PTC graphene-based conductive ink printed film is increased, the function of protecting the conductive film is realized by reducing power and generating heat, and the fire can be effectively prevented. When the temperature of the conductive film is reduced to a certain degree, the modified PTC mixture is converted from an amorphous state to a crystalline state or a semi-crystalline state, the distance between the conductive substances is shortened, the original resistance and power are recovered, and reversible PTC protection is realized.

In a first aspect, the invention provides a preparation method of PTC graphene-based conductive ink, which comprises the following steps in parts by weight:

preparing a palladium quantum dot doped graphene dispersion liquid: providing a graphite oxide allyl ketone dispersion liquid, adding heteropoly acid into the graphite oxide allyl ketone dispersion liquid, stirring and mixing uniformly, centrifuging, collecting a first precipitate, drying, re-suspending the first precipitate with acetone, adding palladium acetylacetonate, stirring and mixing uniformly again, centrifuging, collecting a second precipitate, drying, reducing the second precipitate in a hydrogen environment to obtain palladium quantum dot doped graphene, and re-suspending with ethanol to obtain the palladium quantum dot doped graphene dispersion liquid;

preparing palladium quantum dot doped graphene-carbon black color paste: taking and stirring 50-250 parts of first dispersing agent, and slowly adding 15-40 parts of palladium quantum dot doped graphene dispersion liquid and 5-25 parts of conductive carbon black into the first dispersing agent to obtain palladium quantum dot doped graphene-carbon black color paste;

preparing PTC mixed liquid: providing 1-8 parts of powdery methoxy polyethylene glycol acrylate and 15-35 parts of powdery polylactic acid-polyethylene glycol block copolymer, uniformly mixing the powdery polylactic acid-polyethylene glycol block copolymer and the powdery methoxy polyethylene glycol acrylate, then carrying out melt blending, granulation, grinding into a micron-sized granular modified PTC mixture, adding the granular modified PTC mixture into 50-250 parts of a second dispersing agent, and stirring to obtain a PTC mixed solution;

preparing a mixed solution of palladium quantum dots and graphene doped: respectively and slowly dripping the PTC mixed solution and 500-2500 parts of the third dispersing agent into the stirred palladium quantum dot doped graphene-carbon black color paste, transferring the mixed solution into a reaction kettle at 55-65 ℃ after finishing dripping, naturally cooling after reacting for 1-4 h, and continuously stirring in the reaction process to prepare a palladium quantum dot doped graphene-based mixed solution;

preparing PTC graphene-based conductive ink: adding 0.5-2.5 parts of structure stabilizer, 0.5-2.5 parts of polyacrylonitrile-maleic anhydride copolymer and 2-8 parts of flatting agent into the palladium quantum dot doped graphene base mixed solution while stirring the palladium quantum dot doped graphene base mixed solution, and stirring at 500-5000 rpm for 0.5-6 hours to prepare PTC graphene base conductive ink;

the heteropolyacid comprises one or more of phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid and silicotungstic acid.

The preparation method of the PTC graphene-based conductive ink comprises the steps of preparing a palladium quantum dot doped graphene dispersion liquid, preparing a palladium quantum dot doped graphene-carbon black color paste, preparing a PTC mixed liquid, preparing a palladium quantum dot doped graphene-based mixed liquid and preparing the PTC graphene-based conductive ink, and the PTC graphene-based conductive ink and the corresponding PTC graphene-based conductive film which are stable in structure and complete in function can be prepared through the steps.

Firstly, a space separation scheme is adopted to prepare a palladium quantum dot doped graphene dispersion liquid, namely, a wet chemical method is utilized to modify the surface of graphene oxide with heteropoly acid molecules, then a metal precursor with strong interaction with the heteropoly acid molecules, namely palladium acetylacetonate, is introduced, and then hydrogen reduction is carried out to prepare palladium quantum dots loaded on the heteropoly acid modified graphene, and meanwhile, the palladium quantum dots have a certain reduction effect on the graphene oxide. The palladium quantum dot doped graphene prepared by the method has the advantages of uniform doping of the palladium quantum dots, uniform nano-size of the quantum dots, small average particle size, stable structure of the graphene after hydrogen reduction and the like. The step of preparing the palladium quantum dot doped graphene-carbon black color paste can fully combine the conductive capacities of the graphene and the carbon black, reduce the sheet resistance and promote the dispersion of the graphene and the carbon black conductor. The step of preparing PTC mixed liquid is used for preparing the methoxy polyethylene glycol acrylate modified polylactic acid-polyethylene glycol block copolymer, and the modification process can reduce the glass transition temperature of the polylactic acid-polyethylene glycol block copolymer, namely the PTC protection temperature of the whole ink; on the other hand, the adhesion performance of the polylactic acid-polyethylene glycol block copolymer can be enhanced, namely, the anti-stripping effect of the whole ink is improved, and particularly when the PTC graphene-based conductive ink is printed on a PET film or a PI film (substrate). The preparation method comprises the steps of preparing a mixed solution of palladium quantum dots and graphene, combining electric conductors such as palladium quantum dots doped graphene and carbon black on the surface of a PTC material (a methoxy polyethylene glycol acrylate modified polylactic acid-polyethylene glycol block copolymer) through a reaction kettle reaction to form a structure that the PTC material is wrapped by the electric conductors, and regulating and controlling the distance between the electric conductors through the transition of the glass transition temperature of the PTC material so as to regulate and control the resistance value of the conductive ink. And finally, the structural stabilizer, the polyacrylonitrile-maleic anhydride copolymer and the leveling agent are added to mainly blend the uniformity of the ink, reduce the viscosity and the surface tension of the ink, and simultaneously play a role in maintaining the long-term stability of the ink structure and prolonging the effective storage period.

In a specific embodiment of the invention, in the step of preparing the palladium quantum dot doped graphene dispersion liquid, the graphene oxide is transferred to a high-temperature carbonization furnace to be carbonized for 30-90 seconds at high temperature, inert gas is filled in the high-temperature carbonization furnace, the temperature of the high-temperature carbonization furnace is 500-1200 ℃, and the graphene oxide expanded at high temperature is prepared into the graphene oxide allyl ketone dispersion liquid with the concentration of 5-150 mg/mL. Therefore, the distance between graphene oxide layers can be effectively pulled back through the high-temperature expansion process of graphene oxide, the surface area of graphene is increased, a 'crenellated structure' of few graphene layers is formed, the overall stability of the printing ink is enhanced, meanwhile, the doping of the palladium quantum dots to the graphene oxide layers can be promoted, and the formed palladium quantum dot doped graphene has the advantages of uniform doping of the palladium quantum dots, uniform nano size of the quantum dots, small average particle size, stable structure of the graphene oxide and the like. The fully doped palladium quantum dot doped graphene has excellent electronic conductivity, and can remarkably improve the conductivity of the ink.

Preferably, in the step of preparing the palladium quantum dot doped graphene dispersion liquid, adding heteropoly acid into the graphite oxide allyl ketone dispersion liquid, wherein the mass ratio of the heteropoly acid to the graphite oxide allyl ketone dispersion liquid is 1-5: 1000;

and (3) adding heteropoly acid, carrying out water bath ultrasonic treatment on the graphite oxide allyl ketone dispersion liquid for 20-90 min, wherein the water bath temperature is 20-25 ℃, stirring the ultrasonic graphite oxide allyl ketone dispersion liquid for 2-12 h at 600-1400 rpm, centrifuging at 8000-15000 rpm, collecting a first precipitate, and drying the first precipitate for 30-120 min at 60-80 ℃.

Preferably, in the step of preparing the palladium quantum dot doped graphene dispersion liquid, the first precipitate is resuspended by acetone and palladium acetylacetonate is added, wherein the mass ratio of the first precipitate to the palladium acetylacetonate is 1000: 0.5-5;

and stirring the mixed solution at 600-1400 rpm for 2-12 h, centrifuging at 8000-15000 rpm to collect a second precipitate, and drying the second precipitate at 60-80 ℃ for 30-120 min. The method adopts a space separation scheme based on the principle of anion-cation action, firstly modifies the surface of a graphene carrier by heteropoly acid molecules by a wet chemical method, then introduces a metal precursor with strong interaction with heteropoly acid molecules, namely palladium acetylacetonate, so that the palladium quantum dot precursor is effectively and uniformly loaded, and the palladium quantum dot doped graphene can be obtained by reducing the palladium quantum dot precursor. On one hand, the conductive capability of the graphene is improved through mutual doping between the palladium quantum dots and the graphene, on the other hand, the palladium quantum dots or the graphene can be effectively prevented from being agglomerated, and the effect of stabilizing the structure is achieved.

Preferably, in the step of preparing the palladium quantum dot doped graphene dispersion solution, transferring the second precipitate to a quartz tube of a tube furnace, and introducing a reducing gas for reduction, wherein the reducing gas is a hydrogen/nitrogen gas mixture or a hydrogen/argon gas mixture;

wherein the volume percentage of the hydrogen is 5-20%, the flow rate of the mixed gas is 30-150 mL/min, the reduction reaction temperature is 160-200 ℃, and the reaction time is 1-4 h. The palladium quantum dots loaded on the graphene modified by the heteropoly acid are prepared by introducing hydrogen at the temperature of 160 plus materials and 200 ℃ for reduction, the average particle size of palladium nano particles in the palladium quantum dot doped graphene is about 1nm, and the loading capacity of the palladium quantum dots is large and can reach 0.5-1 wt%.

Preferably, in the step of preparing the palladium quantum dot doped graphene-carbon black color paste, the first dispersing agent comprises 1-10 mol/L of strong acid solution, ethanol and cellulose derivatives, wherein the weight ratio of the strong acid solution to the ethanol to the cellulose derivatives is 10: 50-300: 5-20;

the strong acid solution is hydrochloric acid solution or sulfuric acid solution, and the cellulose derivative is one or more of methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate and cellulose nitrate. The first dispersing agent has the function of promoting the dispersion of the palladium quantum dot doped graphene and the conductive carbon black, and the acid liquid in the first dispersing agent also has the function of catalyzing the subsequent reaction of the reaction kettle. The palladium quantum dot doping can enhance the conductivity and flexibility of the printing ink and the corresponding conductive film, and the conductive printing ink is conveniently printed on a flexible base material to prepare a flexible heating plate.

Preferably, in the step of preparing the PTC mixed solution, the relative molecular weight of the powdery methoxy polyethylene glycol acrylate is 8000-15000, the relative molecular weight of the powdery polylactic acid-polyethylene glycol block copolymer is 8000-12000, and the size of the micron-sized granular modified PTC mixture is 0.5-50 μm;

the second dispersing agent comprises dichloromethane and isopropanol, and the volume ratio of the dichloromethane to the isopropanol is 1-5: 1. Therefore, the polylactic acid-polyethylene glycol block copolymer with the proper molecular weight is selected, so that the glass transition temperature of the polylactic acid-polyethylene glycol block copolymer and the modification difficulty of the methoxypolyethylene glycol acrylate can be effectively controlled, the granular modified PTC mixture is ground into micron size, and the modified PTC mixture is dissolved and dispersed into the second dispersing agent.

Preferably, in the step of preparing the palladium quantum dot doped graphene-based mixed solution, the third dispersant includes one or more of cyclohexanol, terpineol and ethyl acetate. Therefore, the PTC mixed liquid and the palladium quantum dot doped graphene-carbon black color paste are fully dispersed and uniformly mixed through the third dispersing agent, the reaction and combination between the palladium quantum dot doped graphene-carbon black color paste and the PTC mixture are assisted, the palladium quantum dot doped graphene and the carbon black are promoted to be combined on the PTC mixture, the structural stability of the palladium quantum dot doped graphene-carbon black color paste is improved, and the PTC effect of the ink is improved.

Preferably, in the step of preparing the PTC graphene-based conductive ink, the leveling agent comprises polypyrrole and also comprises polyvinyl alcohol or polyethylene glycol, wherein the mass ratio of the polypyrrole to the polyvinyl alcohol or the polyethylene glycol is 8: 1-5;

the structural stabilizer comprises ethylenediamine and p-methylphenol, the mass ratio of the ethylenediamine to the p-methylphenol is 10: 1-15, and the polymerization degree of the polyacrylonitrile-maleic anhydride copolymer is 100-200. The polyacrylonitrile-maleic anhydride copolymer and the flatting agent play a role in blending the ink, can enhance the uniformity and the fluidity of the ink, reduce the viscosity of the ink and facilitate the printing or spraying of the ink. The structural stabilizer can maintain the structural stability of the printing ink for a long time, particularly, through constructing a reducing environment, partial active graphene oxide surface functional groups are stable, and the structural stability of the printing ink and the corresponding conductive thin film is enhanced.

In a second aspect, the invention further provides a PTC graphene-based conductive ink, which is prepared by the preparation method of the PTC graphene-based conductive ink of the first aspect.

When the PTC graphene-based conductive ink is used after being printed into a film, when the local temperature of the graphene heating coating is too high, such as short circuit and other current overload conditions, and high local temperature caused by uneven heat dissipation, the PTC mixture is subjected to glass transition due to local temperature rise and is converted from a crystalline state or a semi-crystalline state into an amorphous state, and further conductive substances in the conductive film, such as palladium quantum dots doped with graphene, carbon black and the like, are mutually pulled apart to increase the resistance of the printed film of the PTC graphene-based conductive ink, so that the function of protecting the conductive film is realized through the action of reducing power and generating heat, and fire can be effectively prevented. When the temperature of the conductive film is reduced to a certain degree, the PTC mixture is converted from an amorphous state to a crystalline state or a semi-crystalline state, the distance between the conductive substances is shortened, the resistance value and the power of the original conductive film are recovered, and reversible PTC protection is realized.

The PTC graphene-based conductive ink contains a PTC mixture (methoxy polyethylene glycol acrylate modified polylactic acid-polyethylene glycol block copolymer), and the glass transition temperature of the polylactic acid-polyethylene glycol block copolymer can be reduced through the methoxy polyethylene glycol acrylate modified polylactic acid-polyethylene glycol block copolymer, so that the PTC response temperature of the whole PTC graphene-based conductive ink is reduced, and the PTC protection requirement of low-temperature heating equipment is met. The methoxy polyethylene glycol acrylate modification process can also improve the anti-stripping performance of the PTC graphene-based conductive ink, and plays a role in protecting a conductive film printed by the PTC graphene-based conductive ink.

The PTC graphene-based conductive ink contains a palladium quantum dot doped graphene dispersion liquid, conductive carbon black, a PTC mixture, a polyacrylonitrile-maleic anhydride copolymer, a structure stabilizer, a first dispersing agent, a second dispersing agent, a third dispersing agent and a leveling agent. Palladium quantum dots are loaded through the graphene lamellar structure, on one hand, the palladium quantum dots can be fully doped between the graphene lamellar structures, the function of assisting multi-layer graphene lamellar layers to disperse to form few graphene lamellar layers is achieved, and the palladium quantum dots are prevented from being agglomerated; on the other hand, the dispersed few-layer graphene sheet layer has a larger specific surface area, can realize more thorough doping with palladium quantum dots, and improves the overall conductivity of the ink. The enlarged graphene oxide surface area can enhance reaction and combination with other components in the ink, promote the adsorption of the palladium quantum dot doped graphene oxide to the surface of the PTC mixture (for example, wrapping the surface of the PTC mixture to form a composite electric conductor), enhance the stability of the whole ink, and adjust the distance between the electric conductors through glass transition based on the PTC mixture. When the PTC mixture reaches the glass transition temperature, the PTC mixture enlarges the distance between the conductor (the palladium quantum dot doped graphene oxide) and the conductor due to deformation, the resistance of the conductive film is enlarged, the power is reduced, the heat generation is reduced, and the PTC protection effect is realized. When the temperature of the PTC mixture is reduced to the lower limit of the glass transition temperature, the PTC mixture restores to the original shape, the distance between the conductor and the conductor is restored to the original distance again along with the distance, the resistance value of the conductive film is reduced, the power is restored, and the heat generation is also restored along with the reduction of the resistance value and the power.

The conductive carbon black and the graphene material are both electric conductors, and the conductive carbon black and the graphene material are complemented and filled based on the size, so that the number of the electric conductors in the conductive ink is further increased, and the sheet resistance of the conductive ink is reduced. The first dispersing agent, the second dispersing agent and the third dispersing agent play roles in stabilizing graphene surface active functional groups and promoting dispersion of all components of the printing ink, and have functions of protecting graphene and enhancing conductivity. The polyacrylonitrile-maleic anhydride copolymer and the flatting agent play a role in blending the ink, can enhance the uniformity and the fluidity of the ink, reduce the viscosity of the ink and facilitate the printing or spraying of the ink. The structural stabilizer can maintain the structural stability of the printing ink for a long time, particularly, through constructing a reducing environment, the partial active graphene oxide surface base groups are stable in structure, and the structural stability of the printing ink and the corresponding conductive thin film is enhanced.

Advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the invention.

Drawings

In order to more clearly illustrate the contents of the present invention, a detailed description thereof will be given below with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic structural diagram of a temperature sensor disposed on a PET substrate according to the present invention;

fig. 2 shows the results of the temperature-resistance change test provided by the present invention.

Detailed Description

The following is a description of the preferred embodiments of the present invention, and it should be noted that those skilled in the art can make various modifications and improvements without departing from the principle of the present invention, and such modifications and improvements are also considered to be within the scope of the present invention.

The following describes in detail the preparation method of the PTC graphene-based conductive ink according to the present invention and the PTC graphene-based conductive inks prepared in the respective examples.

Example 1

Preparing a graphite oxide allyl ketone dispersion liquid: 500mg of graphite powder is provided, and Graphene Oxide (GO) is prepared by adopting a modified Hummers method. In order to further obtain few-layer graphene oxide, the graphene oxide is placed in an ice water bath, ultrasonic treatment is carried out for 10 minutes under the power of 250W by using an ultrasonic dispersion instrument, the ultrasonic treatment is repeated once, and the supernatant is taken for centrifugation and acetone resuspension to prepare graphene oxide allyl ketone dispersion liquid with the thickness ranging from 12 to 20 layers and the transverse dimension ranging from 700 nm to 1000 nm. The concentration was centrifuged as required to adjust the concentration of the graphite oxide allyl ketone dispersion to 150 mg/ml.

Preparing a palladium quantum dot doped graphene dispersion liquid: 500ml of the graphite oxide allyl ketone dispersion prepared above was taken, 0.05g of phosphomolybdic acid was added thereto, and after stirring at 600rpm for 10 hours, the mixture was centrifuged at 15000rpm for 30 minutes, and the first precipitate at the bottom of the centrifuge tube was collected and transferred to a 60 ℃ drying oven to be dried for 120 minutes, to obtain a dried first precipitate. And (3) resuspending the first precipitate by using 100ml of acetone, adding 0.05g of palladium acetylacetonate, stirring at 600rpm for 10h again, uniformly mixing, centrifuging at 15000rpm for 30min, collecting a second precipitate at the bottom of a centrifuge tube, transferring to a 60 ℃ drying oven, and drying for 120min to obtain a dried second precipitate. And (4) putting the second precipitate into a quartz tube of a tube furnace, and introducing diluted hydrogen for reduction. The reduction conditions are as follows: the reducing gas is hydrogen/nitrogen mixed gas, wherein the volume percentage of the hydrogen is 5 percent, the flow rate of the mixed gas is 30 ml/min, the reduction reaction temperature is 160 ℃, and the reaction time is 4 hours. And (3) resuspending the palladium quantum dot doped graphene by 400ml of ethanol to prepare the palladium quantum dot doped graphene dispersion liquid.

Preparing palladium quantum dot doped graphene-carbon black color paste: 200mL of 2mol/L sulfuric acid solution and 400g of methylcellulose are taken, the sulfuric acid solution and the methylcellulose are respectively added into ethanol, and the ethanol is complemented to 2500mL while stirring, so as to prepare the first dispersing agent. And slowly adding 400mL of the prepared palladium quantum dot doped graphene dispersion liquid and 250g of conductive carbon black into the first dispersing agent, and continuously stirring at 1500rpm for 30min to obtain the palladium quantum dot doped graphene-carbon black color paste.

Preparing PTC mixed liquid: 10g of powdery methoxypolyethylene glycol acrylate and 150g of powdery polylactic acid-polyethylene glycol block copolymer are provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer is 8000, and the relative molecular weight of the methoxypolyethylene glycol acrylate is 8000. Uniformly mixing the powdery polylactic acid-polyethylene glycol block copolymer and the powdery methoxy polyethylene glycol acrylate, adopting a micro extruder to melt and blend at 160 ℃, granulating, and grinding into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 1:1, mixing coarse powder obtained by mixing methoxy polyethylene glycol acrylate and polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a modified PTC mixture with the average particle size of 0.5 mu m grade, and preparing the PTC mixed solution.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution and 5000ml of terpineol into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. And after the dropwise addition is finished, transferring the mixed solution into a reaction kettle at the temperature of 55 ℃, reacting for 1h, naturally cooling after the reaction is finished, continuously stirring at a high speed of 500rpm in the reaction process, and concentrating the reaction solution into the mixed solution of the palladium quantum dots and the graphene base.

Preparing PTC graphene-based conductive ink: while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500rpm, 5g of a structural stabilizer, 5g of a polyacrylonitrile-maleic anhydride copolymer with a polymerization degree of 100 and 20g of a leveling agent were added to the palladium quantum dot doped graphene-based mixed solution. Wherein, 5g of the structure stabilizer comprises 2g of ethylenediamine and 3g of p-methylphenol, and 20g of the flatting agent comprises 17.5g of polypyrrole and 2.5g of polyvinyl alcohol. And after the addition is finished, stirring at 500rpm for 4 hours to obtain the PTC graphene-based conductive ink.

Example 2

Preparing a graphite oxide allyl ketone dispersion liquid: 500mg of graphite powder is provided, and Graphene Oxide (GO) is prepared by adopting a modified Hummers method. And further transferring the prepared graphene oxide to a high-temperature carbonization furnace for high-temperature carbonization for 30s, and filling nitrogen into the high-temperature carbonization furnace, wherein the temperature of the high-temperature carbonization furnace is 1200 ℃. In order to further obtain few-layer graphene oxide, the graphene oxide after high-temperature expansion is placed in an ice water bath, ultrasonic treatment is carried out for 20 minutes under the power of 250W by using an ultrasonic dispersion instrument, the ultrasonic treatment is repeated once, and the supernatant is taken for centrifugation and acetone resuspension to prepare the graphene oxide allyl ketone dispersion liquid with the thickness ranging from 8 to 15 layers and the transverse dimension ranging from 700 nm to 1000 nm. The concentration was centrifuged as required to adjust the concentration of the graphite oxide allyl ketone dispersion to 150 mg/mL.

Preparing a palladium quantum dot doped graphene dispersion liquid: 500ml of the graphite allyl ketone oxide dispersion prepared above was taken, 0.15g of silicomolybdic acid was added thereto, and after stirring at 600rpm for 10 hours, the mixture was centrifuged at 15000rpm for 30 minutes, and the first precipitate at the bottom of the centrifuge tube was collected and transferred to a 60 ℃ drying oven to be dried for 120 minutes, to obtain a dried first precipitate. And (3) resuspending the first precipitate by using 100ml of acetone, adding 0.15g of palladium acetylacetonate, stirring at 600rpm for 10h again, uniformly mixing, centrifuging at 15000rpm for 30min, collecting a second precipitate at the bottom of a centrifuge tube, transferring to a 60 ℃ drying oven, and drying for 120min to obtain a dried second precipitate. And (4) putting the second precipitate into a quartz tube of a tube furnace, and introducing diluted hydrogen for reduction. The reduction conditions are as follows: the reducing gas is hydrogen/nitrogen mixed gas, wherein the volume percentage of the hydrogen is 8 percent, the flow rate of the mixed gas is 60 ml/min, the reduction reaction temperature is 170 ℃, and the reaction time is 3 h. And (3) resuspending the palladium quantum dot doped graphene by 400ml of ethanol to prepare the palladium quantum dot doped graphene dispersion liquid.

Preparing palladium quantum dot doped graphene-carbon black color paste: 100mL of 6mol/L hydrochloric acid solution and 150g of hydroxymethyl cellulose are taken, the hydrochloric acid solution and the hydroxymethyl cellulose are respectively added into ethanol, and the ethanol is complemented to 2000mL while stirring, so as to prepare the first dispersing agent. And slowly adding 350mL of the prepared palladium quantum dot doped graphene dispersion liquid and 200g of conductive carbon black into the first dispersing agent, and continuously stirring at 3000rpm for 20min to obtain the palladium quantum dot doped graphene-carbon black color paste.

Preparing PTC mixed liquid: 25g of powdery methoxy polyethylene glycol acrylate and 200g of powdery polylactic acid-polyethylene glycol block copolymer are provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer is 9000, and the relative molecular weight of the methoxy polyethylene glycol acrylate is 10000. Uniformly mixing the powdery polylactic acid-polyethylene glycol block copolymer and the powdery methoxy polyethylene glycol acrylate, adopting a micro extruder to melt and blend at 160 ℃, granulating, and grinding into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 2:1, mixing coarse powder obtained by mixing methoxy polyethylene glycol acrylate and polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a modified PTC mixture with the average particle size of 1 micron level, continuously adding 500ml of the second dispersing agent into the PTC mixture, and stirring and uniformly mixing to obtain the PTC mixed solution.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution and 7500ml of cyclohexanol into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. After the dropwise addition, the mixed solution is transferred to a reaction kettle at the temperature of 58 ℃ for reaction for 1.5h, the reaction solution is naturally cooled after the reaction is finished, the stirring is carried out at a high speed of 500rpm continuously during the reaction process, and the reaction solution is concentrated into the mixed solution of the palladium quantum dots and the graphene.

Preparing PTC graphene-based conductive ink: while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500rpm, 10g of a structural stabilizer, 10g of a polyacrylonitrile-maleic anhydride copolymer with a polymerization degree of 100 and 30g of a leveling agent are added to the palladium quantum dot doped graphene-based mixed solution. Wherein, 10g of the structure stabilizer comprises 8g of ethylenediamine and 2g of p-methylphenol, and 30g of the flatting agent comprises 25g of polypyrrole and 5g of polyethylene glycol. And after the addition is finished, stirring is continuously carried out at 1000rpm for 6 hours, so that the PTC graphene-based conductive ink is prepared.

Example 3

Preparing a palladium quantum dot doped graphene dispersion liquid: 500ml of the graphene oxide acetone dispersion liquid prepared in the above example 2 was taken and added with 0.2g of silicotungstic acid, and the graphene oxide acetone dispersion liquid was subjected to ultrasonic treatment in a water bath at 25 ℃ for 30 min. After the ultrasonic treatment is finished, stirring the graphite oxide allyl ketone dispersion liquid at 600rpm for 10h, centrifuging at 15000rpm for 30min, collecting the first precipitate at the bottom of a centrifuge tube, transferring to a drying oven at 60 ℃ and drying for 120min to obtain a dried first precipitate. And (3) resuspending the first precipitate by using 100ml of acetone, adding 0.2g of palladium acetylacetonate, stirring at 600rpm for 10h again, uniformly mixing, centrifuging at 15000rpm for 30min, collecting a second precipitate at the bottom of a centrifuge tube, transferring to a 60 ℃ drying oven, and drying for 120min to obtain a dried second precipitate. And (4) putting the second precipitate into a quartz tube of a tube furnace, and introducing diluted hydrogen for reduction. The reduction conditions are as follows: the reducing gas is hydrogen/argon gas mixture, wherein the volume percentage of the hydrogen is 12 percent, the flow rate of the gas mixture is 80 ml/min, the temperature of the reduction reaction is 180 ℃, and the reaction time is 2.5 h. And (3) resuspending the palladium quantum dot doped graphene by 400ml of ethanol to prepare a palladium quantum dot doped graphene dispersion solution.

Preparing palladium quantum dot doped graphene-carbon black color paste: 100mL of 8mol/L hydrochloric acid solution, 50g of methylcellulose and 50g of cellulose acetate are taken, the sulfuric acid solution, the methylcellulose and the cellulose acetate are respectively added into ethanol, and the ethanol is complemented to 2000mL while stirring, so as to prepare the first dispersing agent. And slowly adding 300mL of the prepared palladium quantum dot doped graphene dispersion liquid and 175g of conductive carbon black into the first dispersing agent, and continuously stirring at 2000rpm for 30min to obtain the palladium quantum dot doped graphene-carbon black color paste.

Preparing PTC mixed liquid: 35g of powdery methoxypolyethylene glycol acrylate and 250g of powdery polylactic acid-polyethylene glycol block copolymer are provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer is 9000, and the relative molecular weight of the methoxypolyethylene glycol acrylate is 11000. Uniformly mixing the powdery polylactic acid-polyethylene glycol block copolymer and the powdery methoxy polyethylene glycol acrylate, adopting a micro extruder to melt and blend at 160 ℃, granulating, and grinding into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 3:1, mixing coarse powder obtained by mixing methoxy polyethylene glycol acrylate and polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a modified PTC mixture with the average particle size of 5 mu m grade, continuously adding 1000ml of the second dispersing agent into the PTC mixture, and stirring and uniformly mixing to obtain the PTC mixed solution.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution and 10000ml of ethyl acetate into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. And after the dropwise addition is finished, transferring the stirred mixed solution into a reaction kettle at the temperature of 60 ℃, reacting for 2 hours, naturally cooling after the reaction is finished, continuously stirring at a high speed of 500rpm in the reaction process, and concentrating the reaction solution into a palladium quantum dot doped graphene mixed solution.

Preparing PTC graphene-based conductive ink: while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500rpm, 15g of a structural stabilizer, 15g of a polyacrylonitrile-maleic anhydride copolymer with a polymerization degree of 150 and 40g of a leveling agent are added to the palladium quantum dot doped graphene-based mixed solution. Wherein, 15g of the structure stabilizer comprises 8g of ethylenediamine and 7g of p-methylphenol, and 40g of the leveling agent comprises 32g of polypyrrole and 8g of polyethylene glycol. And after the addition is finished, stirring at 1500rpm for 3 hours to obtain the PTC graphene-based conductive ink.

Example 4

Preparing a palladium quantum dot doped graphene dispersion liquid: 500ml of the graphene oxide acetone dispersion prepared in example 2 was taken, 0.25g of phosphotungstic acid was added thereto, and the graphene oxide acetone dispersion was subjected to water bath ultrasonic treatment at 22 ℃ for 50 minutes. After the ultrasonic treatment is finished, stirring the graphite oxide allyl ketone dispersion liquid at 600rpm for 10h, centrifuging at 15000rpm for 30min, collecting the first precipitate at the bottom of a centrifuge tube, transferring to a drying oven at 60 ℃ and drying for 120min to obtain a dried first precipitate. And (3) resuspending the first precipitate by using 100ml of acetone, adding 0.25g of palladium acetylacetonate, stirring at 600rpm for 10h again, uniformly mixing, centrifuging at 15000rpm for 30min, collecting a second precipitate at the bottom of a centrifuge tube, transferring to a 60 ℃ drying oven, and drying for 120min to obtain a dried second precipitate. And (4) putting the second precipitate into a quartz tube of a tube furnace, and introducing diluted hydrogen for reduction. The reduction conditions are as follows: the reducing gas is a hydrogen/nitrogen mixed gas, wherein the volume percentage of the hydrogen is 15%, the flow rate of the mixed gas is 100 ml/min, the reduction reaction temperature is 188 ℃, and the reaction time is 2 h. And (3) resuspending the palladium quantum dot doped graphene by 400ml of ethanol to prepare a palladium quantum dot doped graphene dispersion solution.

Preparing palladium quantum dot doped graphene-carbon black color paste: taking 100mL of 5mol/L sulfuric acid solution, 100g of hydroxymethyl cellulose and 100g of cellulose acetate, respectively adding the sulfuric acid solution, the hydroxymethyl cellulose and the cellulose acetate into ethanol, and complementing the ethanol to 1500mL while stirring to obtain a first dispersing agent. And slowly adding 250mL of the prepared palladium quantum dot doped graphene dispersion liquid and 150g of conductive carbon black into the first dispersing agent, and continuously stirring at 2000rpm for 40min to obtain the palladium quantum dot doped graphene-carbon black color paste.

Preparing PTC mixed liquid: 50g of powdery methoxy polyethylene glycol acrylate and 300g of powdery polylactic acid-polyethylene glycol block copolymer are provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer is 10000, and the relative molecular weight of the methoxy polyethylene glycol acrylate is 12000. Uniformly mixing the powdery polylactic acid-polyethylene glycol segmented copolymer and the powdery methoxy polyethylene glycol acrylate, adopting a micro extruder to melt and blend at 160 ℃, granulating, and grinding into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 3:1, mixing coarse powder obtained by mixing methoxy polyethylene glycol acrylate and polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a modified PTC mixture with the average particle size of 10 mu m, continuously adding 1500ml of the second dispersing agent into the PTC mixture, and stirring and uniformly mixing to obtain the PTC mixed solution.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution, 5000ml of terpineol and 10000ml of cyclohexanol into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. And after the dropwise addition is finished, transferring the stirred mixed solution into a 62 ℃ reaction kettle, reacting for 2.5 hours, naturally cooling after the reaction is finished, continuously stirring at a high speed of 500rpm in the reaction process, and concentrating the reaction solution into a palladium quantum dot doped graphene mixed solution.

Preparing PTC graphene-based conductive ink: while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500rpm, 15g of a structural stabilizer, 15g of a polyacrylonitrile-maleic anhydride copolymer with a polymerization degree of 150 and 50g of a leveling agent are added to the palladium quantum dot doped graphene-based mixed solution. Wherein, 15g of the structure stabilizer comprises 10g of ethylenediamine and 5g of p-methylphenol, and 50g of the flatting agent comprises 35g of polypyrrole and 15g of polyvinyl alcohol. And after the addition is finished, stirring at 2000rpm for 2 hours to obtain the PTC graphene-based conductive ink.

Example 5

Preparing a palladium quantum dot doped graphene dispersion liquid: 500ml of the graphene oxide acetone dispersion prepared in example 2 was taken, 0.3g of phosphomolybdic acid was added thereto, and the graphene oxide acetone dispersion was subjected to water bath ultrasound for 80min at a water bath temperature of 20 ℃. After the ultrasonic treatment is finished, stirring the graphite oxide allyl ketone dispersion liquid at 600rpm for 10h, centrifuging at 15000rpm for 30min, collecting the first precipitate at the bottom of a centrifuge tube, transferring to a drying oven at 60 ℃ and drying for 120min to obtain a dried first precipitate. And (3) resuspending the first precipitate by using 100ml of acetone, adding 0.3g of palladium acetylacetonate, stirring at 600rpm for 10h again, uniformly mixing, centrifuging at 15000rpm for 30min, collecting a second precipitate at the bottom of a centrifuge tube, transferring to a 60 ℃ drying oven, and drying for 120min to obtain a dried second precipitate. And (4) putting the second precipitate into a quartz tube of a tube furnace, and introducing diluted hydrogen for reduction. The reduction conditions are as follows: the reducing gas is a hydrogen/nitrogen mixed gas, wherein the volume percentage of the hydrogen is 15 percent, the flow rate of the mixed gas is 120 ml/min, the temperature of the reduction reaction is 195 ℃, and the reaction time is 1.5 h. And re-suspending the palladium quantum dot doped graphene by 400ml of ethanol to prepare a palladium quantum dot doped graphene dispersion solution.

Preparing palladium quantum dot doped graphene-carbon black color paste: taking 100mL of 4mol/L sulfuric acid solution and 100g of ethyl cellulose, respectively adding the sulfuric acid solution and the ethyl cellulose into ethanol, and complementing the ethanol to 1000mL while stirring to obtain a first dispersing agent. And slowly adding 200mL of the prepared palladium quantum dot doped graphene dispersion liquid and 100g of conductive carbon black into the first dispersing agent, and continuously stirring at 1500rpm for 60min to obtain the palladium quantum dot doped graphene-carbon black color paste.

Preparing PTC mixed liquid: 65g of powdery methoxy polyethylene glycol acrylate and 300g of powdery polylactic acid-polyethylene glycol block copolymer are provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer is 11000, and the relative molecular weight of the methoxy polyethylene glycol acrylate is 14000. Uniformly mixing the powdery polylactic acid-polyethylene glycol segmented copolymer and the powdery methoxy polyethylene glycol acrylate, adopting a micro extruder to melt and blend at 160 ℃, granulating, and grinding into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 4:1, mixing coarse powder obtained by mixing methoxy polyethylene glycol acrylate and polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a modified PTC mixture with the average particle size of 25 mu m, continuously adding 1500ml of the second dispersing agent into the PTC mixture, and stirring and uniformly mixing to obtain the PTC mixed solution.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution, 15000ml of cyclohexanol and 5000ml of ethyl acetate into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. And after the dropwise addition is finished, transferring the stirred mixed solution into a reaction kettle at 64 ℃, reacting for 3 hours, naturally cooling after the reaction is finished, continuously stirring at a high speed of 500rpm in the reaction process, and concentrating the reaction solution into a palladium quantum dot doped graphene mixed solution.

Preparing PTC graphene-based conductive ink: while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500rpm, 20g of a structural stabilizer, 20g of a polyacrylonitrile-maleic anhydride copolymer with a polymerization degree of 200 and 65g of a leveling agent were added to the palladium quantum dot doped graphene-based mixed solution. Wherein, 20g of the structure stabilizer comprises 10g of ethylenediamine and 10g of p-methylphenol, and 65g of the flatting agent comprises 40g of polypyrrole and 25g of polyvinyl alcohol. And after the addition is finished, stirring is carried out at 3500rpm for 1.5h to prepare the PTC graphene-based conductive ink.

Example 6

Preparing a palladium quantum dot doped graphene dispersion liquid: 500ml of the graphene oxide acetone dispersion prepared in example 2 was taken, 0.35g of silicotungstic acid was added thereto, and after stirring at 1400rpm for 2 hours, the mixture was centrifuged at 8000rpm for 120min, and the first precipitate at the bottom of the centrifuge tube was collected and transferred to a 60 ℃ drying oven to be dried for 120min, to obtain a dried first precipitate. And (3) resuspending the first precipitate by using 100ml of acetone, adding 0.35g of palladium acetylacetonate, stirring at 600rpm for 10h again, uniformly mixing, centrifuging at 15000rpm for 30min, collecting a second precipitate at the bottom of a centrifuge tube, transferring to a 60 ℃ drying oven, and drying for 120min to obtain a dried second precipitate. And (4) putting the second precipitate into a quartz tube of a tube furnace, and introducing diluted hydrogen for reduction. The reduction conditions are as follows: the reducing gas is hydrogen/argon gas mixture, wherein the volume percentage of the hydrogen is 20 percent, the flow rate of the gas mixture is 150 ml/min, the reduction reaction temperature is 200 ℃, and the reaction time is 1 h. And (3) resuspending the palladium quantum dot doped graphene by 400ml of ethanol to prepare a palladium quantum dot doped graphene dispersion solution.

Preparing palladium quantum dot doped graphene-carbon black color paste: taking 12.5mL of 10mol/L sulfuric acid solution and 10g of methyl cellulose 15g of ethyl cellulose, respectively adding the sulfuric acid solution, the methyl cellulose and the ethyl cellulose into ethanol, and complementing the ethanol to 500mL while stirring to obtain the first dispersing agent. And slowly adding 150mL of the prepared palladium quantum dot doped graphene dispersion liquid and 50g of conductive carbon black into the first dispersing agent, and continuously stirring at 2500rpm for 40min to obtain the palladium quantum dot doped graphene-carbon black color paste.

Preparing PTC mixed liquid: 80g of powdery methoxypolyethylene glycol acrylate and 350g of powdery polylactic acid-polyethylene glycol block copolymer were provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer was 12000 and the relative molecular weight of the methoxypolyethylene glycol acrylate was 15000. Uniformly mixing the powdery polylactic acid-polyethylene glycol segmented copolymer and the powdery methoxy polyethylene glycol acrylate, adopting a micro extruder to melt and blend at 160 ℃, granulating, and grinding into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 5:1, mixing coarse powder obtained by mixing methoxy polyethylene glycol acrylate and polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a modified PTC mixture with the average particle size of 50 microns, continuously adding 2000ml of the second dispersing agent into the PTC mixture, and stirring and uniformly mixing to obtain the PTC mixed solution.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution, 10000ml of cyclohexanol, 10000ml of terpineol and 5000ml of ethyl acetate into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. And after the dropwise addition is finished, transferring the stirred mixed solution into a reaction kettle at 65 ℃, reacting for 4 hours, naturally cooling after the reaction is finished, continuously stirring at a high speed of 500rpm in the reaction process, and concentrating the reaction solution into a palladium quantum dot doped graphene-based mixed solution.

Preparing PTC graphene-based conductive ink: while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500rpm, 25g of a structural stabilizer, 25g of a polyacrylonitrile-maleic anhydride copolymer with a polymerization degree of 200 and 80g of a leveling agent are added to the palladium quantum dot doped graphene-based mixed solution. Wherein, 25g of the structure stabilizer comprises 10g of ethylenediamine and 15g of p-methylphenol, and 80g of the flatting agent comprises 60g of polypyrrole and 20g of polyethylene glycol. And after the addition is finished, stirring at 5000rpm for 1h to prepare the PTC graphene-based conductive ink.

Comparative example 1

Preparing a palladium quantum dot doped graphene dispersion liquid: a palladium quantum dot-doped graphene dispersion was prepared with reference to example 4.

Preparing palladium quantum dot doped graphene-carbon black color paste: and preparing palladium quantum dot doped graphene-carbon black color paste according to example 4.

Preparing PTC mixed liquid: a PTC mixed solution was prepared with reference to example 4.

Preparing a mixed solution of palladium quantum dots and graphene doped: and (3) slowly dropwise adding the prepared PTC mixed solution, 5000ml of terpineol and 10000ml of cyclohexanol into the palladium quantum dot doped graphene-carbon black color paste while stirring, wherein the stirring speed is 500 rpm. After the dropwise addition, the stirred mixed solution is transferred to a vacuum-pumping condition of 40 ℃ for concentration, and the mixed solution is continuously stirred at a high speed of 500rpm while being concentrated, and then the mixed solution is concentrated into a mixed solution of the palladium quantum dot doped graphene.

Preparing PTC graphene-based conductive ink: a PTC graphene-based conductive ink was prepared with reference to example 4.

Comparative example 2

Preparing PTC mixed liquid: 300g of a powdery polylactic acid-polyethylene glycol block copolymer was provided, wherein the relative molecular weight of the polylactic acid-polyethylene glycol block copolymer was 10000. The powdery polylactic acid-polyethylene glycol block copolymer is melted, blended and granulated at 160 ℃ by a micro extruder and ground into coarse powder. Providing a second dispersing agent with the mass ratio of dichloromethane to isopropanol being 3:1, mixing coarse powder of the polylactic acid-polyethylene glycol block copolymer with 500ml of the second dispersing agent, conveying the mixture to a three-roll grinder for grinding until the mixture is ground into a granular modified PTC mixture with the average grain diameter of 10 mu m grade. And continuously adding 1500ml of second dispersing agent into the granular modified PTC mixture, and uniformly stirring to obtain PTC mixed liquid.

Preparing a mixed solution of palladium quantum dots and graphene doped: a palladium quantum dot-doped graphene-based mixed solution was prepared with reference to example 4.

Preparing PTC graphene-based conductive ink: preparation of PTC graphene-based conductive ink with reference to example 4

Comparative example 3

Preparing PTC graphene-based conductive ink: and (3) adding 15g of polyacrylonitrile-maleic anhydride copolymer with the polymerization degree of 150 and 50g of leveling agent into the palladium quantum dot doped graphene-based mixed solution while stirring the palladium quantum dot doped graphene-based mixed solution at a high speed of 500 rpm. Wherein, 50g of the flatting agent comprises 35g of polypyrrole and 15g of polyvinyl alcohol. And after the addition is finished, stirring at 2000rpm for 2 hours to obtain the PTC graphene-based conductive ink.

Effect embodiment:

(1) adhesion Performance test

The PTC graphene-based conductive inks prepared in examples 1 to 6 and comparative examples 1 to 3 were respectively knife-coated on PET films, and the PET films were transferred to a 45 ℃ forced air drying oven to be dried for 10 hours, thereby obtaining PTC graphene-based conductive films. Hardness was tested according to the national standard GB/T6739-1996 using a Chinese pencil, and the results are shown in Table 1. According to the national standard GB/T13217.4-2008, the adhesive force is tested by using the 3M special adhesive tape, and the test result is shown in Table 1.

TABLE 1

As can be seen from the results in table 1, the PTC graphene-based conductive inks prepared in examples 1 to 6 respectively have good adhesion to a PET film or a PET plate, which indicates that the PTC graphene-based conductive inks prepared in the present invention can be applied to the preparation of a PET graphene conductive film, for example, the PTC graphene-based conductive inks are applied to a PET substrate by blade coating, spin coating, direct writing, screen printing, inkjet printing or electrostatic spinning, and a flexible PTC graphene conductive film (graphene conductive film) can be obtained after curing. The PTC graphene-based conductive inks prepared in comparative examples 1-3 had poor adhesion to the PET substrate, compared to the PTC graphene-based conductive inks prepared in examples 1-6. In the PTC graphene-based conductive ink according to comparative example 1, active groups, in which a portion of oxidized graphene is exposed on the surface, are not sufficiently mixed, reacted, and combined with the PTC mixture, resulting in poor adhesion effect of the prepared ink film to a PET substrate. In the comparative example 2, powdery methoxy polyethylene glycol acrylate which can improve the adhesion of the PTC graphene-based conductive ink to the PET material is not added, so that the adhesion of the prepared ink film to the PET substrate is greatly reduced. In comparative example 3, no structural stabilizer was added, and a part of graphene oxide in the prepared PTC graphene-based conductive ink was not subjected to a reduction process, and the graphene oxide was in an unstable state, which also affected the adhesion effect between the ink film and the PET substrate.

(2) Service life test

The PTC graphene-based conductive inks prepared in examples 1 to 6 and comparative examples 1 to 3 were printed on a PET plate by a relief printing technique, and the printed PET plate was transferred to a forced air drying oven at a temperature of 45 ℃ to be dried and cured for 10 hours, thereby obtaining a PTC graphene conductive film having a thickness of 10 μm.

The PTC graphene conductive film with the length and the width of 10cm is cut by a blade to carry out an initial sheet resistance test, and the test results are shown in table 2. Inserting metal electrodes into opposite corners of two ends of the cut PTC graphene conductive film respectively and connecting commercial power to perform service life test, wherein the test method comprises the following steps: the PTC graphene conductive film was continuously electrified to generate heat, and the sheet resistance value structure of the PTC graphene conductive film was measured every other week (W) as shown in table 2.

TABLE 2

As can be seen from the results in table 2, the PTC graphene conductive films according to examples 1 to 6 did not change the overall sheet resistance value significantly after being continuously energized for 5W heat generation, and thus were used for the heat generation layer of the electric heating device heated for a long time. The large variation in sheet resistance of the PTC graphene conductive films corresponding to comparative examples 1-3 may be related to the instability of the graphene oxide structure and the overall ink mixing system therein.

(3) Test of anti-aging Performance

The PTC graphene conductive film with the length and the width of 1m is cut by a blade to carry out the anti-aging performance test, and the test results are shown in table 3. And inserting metal electrodes into opposite corners of two ends of the cut PTC graphene conductive film respectively and connecting the metal electrodes to mains supply to perform continuous heat production. Firstly, the initial heat generation power of the PTC graphene conductive film is tested by instruments such as an ammeter, the heat generation power of the PTC graphene conductive film is tested by the instruments such as the ammeter after continuous operation for 300 hours, the heat generation power attenuation rate of the PTC graphene conductive film is calculated, and the result is shown in table 3.

After the continuous operation for 300h, as shown in fig. 1, 9 temperature sensors are sequentially arranged on the PET plate to test the temperature of each position of the PTC graphene conductive film (the ambient temperature is 4 ℃), and the difference between the maximum value and the minimum value in the 9 temperature sensors is selected to be recorded as the temperature nonuniformity of the PTC graphene conductive film, as shown in table 3.

TABLE 3

As can be seen from the results in table 3, the power attenuation rate and the temperature non-uniformity of the PTC graphene conductive films according to examples 1 to 6 are not large, which indicates that the PTC graphene conductive films prepared according to the present invention can be used for long-term heat generation, and the power and the non-uniformity of heat generation do not change much. In contrast, the PTC graphene conductive films corresponding to comparative examples 1 to 3 have large power attenuation rates and temperature non-uniformity, and are not suitable for long-term heat generation of a heat-generating conductive film, which may be related to the unstable structure of graphene oxide.

(4) Temperature-resistance change test

The method comprises the steps of cutting a PTC graphene conductive film with the length and the width of 10cm by a blade, attaching the PTC graphene conductive film to a temperature control device, respectively inserting metal electrodes into opposite corners of two ends of the cut PTC graphene conductive film, and connecting the metal electrodes to an ohm meter for testing the change of the resistance value of the PTC graphene conductive film along with the temperature, as shown in fig. 2.

As can be seen from fig. 2, when the PTC graphene conductive film prepared in example 4 is subjected to a temperature-resistance change test, the resistance value of the PTC graphene conductive film changes negligibly (less than 0.6K Ω) when the temperature is lower than 50 ℃, and the PTC graphene conductive film can be used for continuous energization and heat generation. When the temperature is increased from 55 ℃ to 60 ℃, the resistance value of the PTC graphene conductive film is rapidly increased to more than 60 times, the power of the PTC graphene conductive film is rapidly reduced, and a good self-temperature limiting effect is achieved.

The resistance value of the PTC graphene conductive film prepared in comparative example 1 does not change much until the temperature reaches 45 ℃. When the temperature of the PTC graphene conductive film prepared in comparative example 1 is increased from 45 ℃ to 55 ℃, the resistance value of the PTC graphene conductive film is slowly increased to about 6.7K Ω. When the temperature of the PTC graphene conductive film is further increased, the resistance value of the PTC graphene conductive film is rapidly increased to more than 70 times, and the power is rapidly reduced. The PTC graphene conductive film has a resistance value which slowly rises from 40-55 ℃, and has a remarkable PTC protection effect only at about 60-65 ℃, so that the PTC graphene conductive film is not suitable for being used as a low-temperature PTC flexible heating film.

Before the temperature of the PTC graphene conductive film prepared in comparative example 2 reaches 55 ℃, the resistance value of the PTC graphene conductive film slowly rises, but the PTC graphene conductive film is generally difficult to play a role in PTC protection. When the temperature further rises, especially when the temperature reaches more than 65 ℃, the resistance value of the PTC graphene conductive film is exponentially improved, and the power is rapidly reduced. The self-limiting temperature protection temperature is too high, and the heating requirement and the PTC protection requirement of the existing low-temperature heating equipment cannot be met. When the temperature of the PTC graphene conductive film prepared in comparative example 3 reaches 45 ℃, the resistance value of the PTC graphene conductive film has risen to more than 6 times of the initial (20 ℃) resistance value, and when the temperature further rises to 55 ℃, the resistance value of the PTC graphene conductive film is rapidly increased to more than 50 times, and the power is rapidly reduced. The resistance value of the PTC graphene conductive film is unstable along with the rise of temperature, so that the long-term heating use requirement is difficult to meet.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The preparation method of the PTC graphene-based conductive ink is characterized by comprising the following steps of:

preparing a mixed solution of palladium quantum dots and graphene doped: respectively and slowly dropwise adding the PTC mixed solution and 500-2500 parts of the third dispersing agent into the stirred palladium quantum dot doped graphene-carbon black color paste, transferring the mixed solution into a reaction kettle at 55-65 ℃ after dropwise adding is finished, naturally cooling after reacting for 1-4 h, and continuously stirring in the reaction process to prepare the palladium quantum dot doped graphene-based mixed solution;

preparing PTC graphene-based conductive ink: while stirring the mixed solution of the palladium quantum dots and the graphene base, adding 0.5-2.5 parts of a structure stabilizer, 0.5-2.5 parts of a polyacrylonitrile-maleic anhydride copolymer and 2-8 parts of a flatting agent into the mixed solution of the palladium quantum dots and the graphene base, and stirring at 500-5000 rpm for 0.5-6 hours to prepare the PTC graphene base conductive ink;

2. The method of preparing the PTC graphene-based conductive ink according to claim 1, wherein in the step of preparing the palladium quantum dot doped graphene dispersion liquid, the graphene oxide is transferred to a high temperature carbonization furnace to be carbonized at a high temperature for 30-90 s, the high temperature carbonization furnace is filled with an inert gas, the temperature of the high temperature carbonization furnace is 500-1200 ℃, and the graphene oxide expanded at a high temperature is prepared into the graphene oxide allyl ketone dispersion liquid with a concentration of 5-150 mg/mL.

3. The preparation method of the PTC graphene-based conductive ink according to claim 1, wherein in the step of preparing the palladium quantum dot doped graphene dispersion liquid, heteropoly acid is added into the graphite oxide allyl ketone dispersion liquid, and the mass ratio of the heteropoly acid to the graphite oxide allyl ketone dispersion liquid is 1-5: 1000;

4. The method for preparing the PTC graphene-based conductive ink according to claim 3, wherein in the step of preparing the palladium quantum dot doped graphene dispersion liquid, the first precipitate is resuspended by acetone and palladium acetylacetonate is added, and the mass ratio of the first precipitate to the palladium acetylacetonate is 1000: 0.5-5;

and stirring the mixed solution at 600-1400 rpm for 2-12 h, centrifuging at 8000-15000 rpm to collect a second precipitate, and drying the second precipitate at 60-80 ℃ for 30-120 min.

5. The method for preparing the PTC graphene-based conductive ink according to claim 4, wherein in the step of preparing the palladium quantum dot-doped graphene dispersion solution, the second precipitate is transferred to a quartz tube of a tube furnace, and a reducing gas is introduced for reduction, wherein the reducing gas is a hydrogen/nitrogen mixed gas or a hydrogen/argon mixed gas;

wherein the volume percentage of the hydrogen is 5-20%, the flow rate of the mixed gas is 30-150 mL/min, the reduction reaction temperature is 160-200 ℃, and the reaction time is 1-4 h.

6. The preparation method of the PTC graphene-based conductive ink according to claim 1, wherein in the step of preparing the palladium quantum dot doped graphene-carbon black color paste, the first dispersing agent comprises 1-10 mol/L of a strong acid solution, ethanol and a cellulose derivative, wherein the ratio of the strong acid solution, the ethanol and the cellulose derivative is 10: 50-300: 5-20;

the strong acid solution is hydrochloric acid solution or sulfuric acid solution, and the cellulose derivative is one or more of methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate and cellulose nitrate.

7. The method for preparing the PTC graphene-based conductive ink according to claim 1, wherein in the step of preparing the PTC mixture solution, the powdery methoxy polyethylene glycol acrylate has a relative molecular weight of 8000 to 15000, the powdery polylactic acid-polyethylene glycol block copolymer has a relative molecular weight of 8000 to 12000, and the micron-sized modified PTC mixture has a size of 0.5 to 50 μm;

the second dispersing agent comprises dichloromethane and isopropanol, and the volume ratio of the dichloromethane to the isopropanol is 1-5: 1.

8. The method of preparing a PTC graphene-based conductive ink according to claim 1, wherein in the step of preparing the palladium quantum dot-doped graphene-based mixed solution, the third dispersant comprises one or a combination of more of cyclohexanol, terpineol, and ethyl acetate.

9. The preparation method of the PTC graphene-based conductive ink according to claim 1, wherein in the step of preparing the PTC graphene-based conductive ink, the leveling agent comprises polypyrrole, and the leveling agent further comprises polyvinyl alcohol or polyethylene glycol, wherein the mass ratio of the polypyrrole to the polyvinyl alcohol or polyethylene glycol is 8: 1-5;

the structural stabilizer comprises ethylenediamine and p-methylphenol, the mass ratio of the ethylenediamine to the p-methylphenol is 10: 1-15, and the polymerization degree of the polyacrylonitrile-maleic anhydride copolymer is 100-200.

10. A PTC graphene-based conductive ink, characterized in that it is prepared by the method for preparing a PTC graphene-based conductive ink according to any one of claims 1 to 9.