Method for preparing conductive thin film through plasma-assisted electrospray, conductive thin film and application of conductive thin film

Abstract

The invention belongs to the related technical field of flexible electronic micro-nano manufacturing, and discloses a method for preparing a conductive thin film through plasma-assisted electrospray, the conductive thin film and application of the conductive thin film, and the method comprises the following steps: (1) carrying out surface modification treatment on an insulating substrate by adopting plasma to improve the charge dissipation speed and hydrophilicity of the surface of the insulating substrate; and (2) preparing a thin film on the surface of the insulating substrate in an electrostatic spraying manner to obtain the conductive thin film. The surface of the insulating substrate is subjected to plasma modification treatment to improve the charge dissipation speed and hydrophilicity of the surface of the insulating substrate, electrostatic spraying is adopted to perform electrostatic paint spraying on the surface of the insulating substrate to prepare the conductive film, and the modification treatment improves the electrofluid spraying performance of the surface of the insulating substrate; and the continuous, compact and defect-free conductive film on the surface of the insulating substrate is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field related to flexible electronic micro-nano manufacturing, and more specifically, relates to a method for preparing a conductive film by plasma-assisted electrospray, the conductive film, and its applications. Background Art

[0002] In recent years, with the rise of the concept of intelligent skin design and manufacturing, the manufacturing process of curved conformal circuits has become a current research hotspot. Conformal electronics also has broad application prospects in fields such as health monitoring, 5G / 6G communication, and intelligent transportation. At present, with the rapid development of conformal electronics manufacturing technology, there is a greater demand for the portability, multi-scenario applicability, and wearability of devices. The flexibility, curvature, and stretchability of electronic devices have become an inevitable trend. Conformal electronic components usually consist of multiple curved substrates, curved conductive patterns, vertical interconnection structures, heat dissipation structures, etc. In the field of curved conformal circuit manufacturing, most substrates of electronic devices are insulating materials. As a key part of the conformal circuit, the materials of the circuit substrate mainly include polyethylene naphthalate (PEN), polyimide (PEI), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyimide (PI), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), insulating glass, insulating ceramics, and insulating composite materials, etc. These materials have good deformation ability, insulation, flexibility, and strength requirements.

[0003] The current main surface film - forming methods include preparing electrode films by the doctor - blade casting method, electrospun fiber networks, electrospraying, hydrothermal / solvothermal methods, electrochemical deposition methods, atomic layer deposition technology, and physical vapor deposition methods, etc. Among them, for the doctor - blade casting method to prepare electrode films, electrode materials are mixed in a certain proportion to form a slurry, and then the uniformly mixed slurry is evenly coated on the substrate surface with a doctor - blade. The prepared thin films are uneven, with low productivity, and are not suitable for curved surface manufacturing. The electrospun fiber network is more complex than the electrospray film - forming process, with many influencing factors. It can be divided into solution properties such as viscosity, elasticity, conductivity, and surface tension, control variables such as the static voltage in the capillary, the potential at the capillary orifice, and the distance between the capillary orifice and the collector, and environmental parameters such as solution temperature, air humidity and temperature in the electrospinning environment, and air flow velocity, etc. The hydrothermal / solvothermal method is one of the common methods for synthesizing materials. It is a synthesis method in a closed system (high - pressure autoclave), using water or a non - aqueous solvent as the solvent, and under a certain temperature and the autogenous pressure of the solution, the original mixture undergoes a chemical reaction. If the original reaction mixture and a specific substrate are placed in the closed system at the same time, after the reaction, the required nanomaterials can be deposited on the surface of the specific substrate. The hydrothermal method is often only applicable to the preparation and treatment of oxide functional materials or a few chalcogenide compounds that are not sensitive to water. It is not applicable to the preparation and treatment of some compounds that are sensitive to water (react with water, hydrolyze, decompose, or are unstable), such as III - V group semiconductors, carbides, fluorides, and the preparation and treatment of new phosphate (arsenate) molecular sieve three - dimensional framework structure materials. The electrochemical deposition method generally uses an electrochemical workstation to establish a two - electrode or three - electrode system. The selected specific substrate is used as the working electrode, and different electrochemical test procedures (such as constant - current method, cyclic voltammetry, chronoamperometry, etc.) are selected according to requirements. After a certain period of time, relatively uniform nanomaterials can be obtained on this substrate. This method requires that the substrate for receiving nanomaterials is itself conductive, otherwise it is difficult to form an electrical circuit. Atomic layer deposition technology, as the name implies, is deposition at the atomic level. Specifically, it is a method of depositing substances layer by layer in the form of a single - atom film on the substrate surface. As long as the appropriate reaction precursor substances are selected, nanomaterials can be successfully deposited on the substrate surface. The biggest drawback of this method is its extremely high cost. Whether it is the preparation of precursor reaction substances or the operation and maintenance of atomic layer deposition equipment, it is a huge expense, which also greatly limits the large - scale application of this technology. Physical vapor deposition technology means that under vacuum conditions, physical methods are used to vaporize the material source - solid or liquid surface into gaseous atoms, molecules, or partially ionize them into ions, and through a low - pressure gas (or plasma) process, deposit a thin film with a certain special function on the substrate surface. The bonding force between the thin film and the substrate prepared by this method is weak, the coating is not wear - resistant, and it has directionality, and it is difficult to remove chemical impurities.

[0004] Electrostatic spraying technology is a method of atomizing droplets by applying an external voltage. During the electrostatic spraying process, the liquid ejected from the high-potential metal nozzle is dispersed into nano-scale or micro-scale tiny droplets under the action of the electric field force. The tiny droplets continue to be affected by the electric field force, come into contact with each other, and deposit on the substrate to form film micro-elements. These film micro-elements are stacked on top of each other from bottom to top to form a continuous, dense, and defect-free thin film. When using electrostatic spraying technology to prepare thin films, a relatively rich variety of materials can be selected, and thin films with various properties can be prepared. Electrostatic spraying has many advantages such as the ability to achieve the preparation of sub-micron thickness thin films, good ink compatibility, and a wider range of material applications. However, there are still many defects in current electrostatic technology. For example, the substrate needs to be a conductive material to form an electric field between the nozzle and the substrate after connecting the voltage to drive the ink, and the substrate needs to be a hydrophilic surface to keep the thickness of the aqueous thin film deposited on the substrate surface uniform. For many fields such as curved electronics and aircraft skins, the substrates are mostly non-planar insulating materials. In the case of non-conductive insulating substrates, although a Taylor cone can be formed at the tip of the nozzle, due to the radial electric field force and charge accumulation in the electric field, it cannot develop further, and it is very difficult to deposit a continuous, dense, and defect-free thin film on the insulating substrate.

[0005] Although the above technologies each have their own characteristics, they all show some limitations in the process of film formation on large curved insulating surfaces. The blade casting method for preparing electrode films is uneven, has low productivity, and is not suitable for curved surface manufacturing; the electrospinning fiber network is more complex than the electrostatic spraying film formation process and has many influencing factors; the hydrothermal / solvothermal method designs a closed system and is not applicable to large curved surface processing; the electrochemical deposition method requires the preparation of a conductive layer in advance before film formation on an insulating surface, the process is complex, and for the surface electrochemical deposition of large curved surfaces, a specific large electrochemical workstation and a large amount of reaction solution are required, resulting in a large cost; physical vapor deposition involves vacuum processing and is not applicable to the surface film formation of large curved surface components; traditional electrostatic spraying film formation cannot deposit a uniform and continuous thin film on an insulating hydrophobic surface.

[0006] The above methods have achieved film formation on large insulating substrates to a certain extent, but their control is complex and the printing materials are limited, which restricts the further popularization of the curved conformal circuit technology. In summary, the existing technologies face great challenges in realizing the preparation of a uniform and dense thin film on an insulating hydrophobic surface. Therefore, in order to deposit a uniform and dense thin film on an insulating substrate by the method of electrostatic spraying, a new film formation process method for the surface of an insulating hydrophobic substrate is needed, which can prepare a continuous, dense, and defect-free thin film on the curved insulating hydrophobic surface. Summary of the Invention

[0007] In view of the above deficiencies or improvement requirements of the prior art, the present invention provides a method for preparing a conductive thin film by plasma-assisted electrospray, a conductive thin film and its application, aiming to solve the problem of being unable to prepare a continuous and dense conductive thin film on an insulating substrate.

[0008] To achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a conductive thin film by plasma-assisted electrospray, the method comprising the following steps:

[0009] (1) The insulating substrate is subjected to surface modification treatment by plasma to improve the charge dissipation rate and hydrophilicity of the surface of the insulating substrate;

[0010] (2) A thin film is prepared on the surface of the insulating substrate by electrostatic spraying to obtain a conductive thin film.

[0011] Further, an electrostatic microdisk nozzle is used for electrostatic spraying to prepare a thin film on the surface of the insulating substrate.

[0012] Further, the electrostatic microdisk nozzle is obtained by laser cutting a 20-micron-thick stainless steel foil and has a diameter of 5 mm.

[0013] Further, the electrostatic microdisk nozzle is connected to the ink outlet through a stainless steel needle.

[0014] Further, the surface of the insulating substrate is subjected to plasma modification treatment by low-pressure plasma or atmospheric pressure plasma.

[0015] Further, the insulating substrate is a curved substrate.

[0016] Further, the insulating substrate is a flexible insulating substrate, and its material is any one of polyethylene naphthalate, polyimide, polytetrafluoroethylene, polymethyl methacrylate, polyimide, polyethylene terephthalate, and polyphenylene sulfide.

[0017] The present invention also provides a conductive thin film prepared by the method for preparing a conductive thin film by plasma-assisted electrospray as described above.

[0018] The present invention also provides an application of the conductive thin film as described above in health monitoring, 5G / 6G communication, and intelligent transportation.

[0019] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the method for preparing a conductive thin film by plasma-assisted electrospray, the conductive thin film and its application provided by the present invention mainly have the following beneficial effects:

[0020] 1. The present invention improves the charge dissipation rate and hydrophilicity of the surface of an insulating substrate through plasma modification treatment, and prepares a conductive film by electrostatic spraying paint on the surface of the insulating substrate. The modification treatment improves the performance of electrohydrodynamic spraying on the surface of the insulating substrate, and a continuous, dense, and defect-free conductive film is obtained on the surface of the insulating substrate. At the same time, complex pretreatment processes before electroplating are not required, and only plasma treatment is needed to achieve the preparation of metal films, improving the preparation speed of metal films.

[0021] 2. The present invention uses an electrostatic microdisk nozzle for spraying, which can generate a large number of Taylor cones, improving the efficiency and quality of metal film preparation.

[0022] 3. The method provided by the present invention is applicable to the preparation of metal films on the surface of large curved insulating substrates. Compared with the electroplating film preparation method that requires the substrate to be immersed in an electroplating bath for treatment and is not friendly to porous composite materials, this method is processed in the atmospheric environment throughout the process and does not involve an electrochemical immersion step.

[0023] 4. The present invention is applicable to the preparation of metal patterns on the surface of large curved insulating substrates, which makes up for the deficiency that photolithography is not compatible with large curved substrates. At the same time, compared with the method of laser engraving to prepare curved metal patterns, it is more friendly to curved substrates and will not damage the surface of the substrate.

[0024] 5. The pretreatment method of using plasma modification treatment for insulating substrates proposed by the present invention improves the uniformity of metal films and patterns and the interfacial strength between metal films and insulating substrates; by increasing the dissipation rate of charges on the surface of the insulating substrate, the induced charges carried by the droplets deposited on the surface of the insulating substrate by electrostatic spraying are neutralized more quickly through volume dissipation and surface dissipation, reducing the influence of the electric field formed by the induced charges on the surface of the insulating substrate on the subsequent deposited droplets. By increasing the hydrophilicity of the surface of the insulating substrate, the tiny droplets deposited on the surface of the insulating material by electrostatic spraying can be evenly spread on the surface of the insulating material substrate, improving the continuity and uniformity of electrohydrodynamic printing to prepare films on the surface of the insulating substrate. Description of the Drawings

[0025] Figure 1 Among them, (a) and (b) are schematic diagrams of the electrospray effects before and after plasma treatment provided in Embodiment 1 of the present invention;

[0026] Figure 2 is a schematic diagram of plasma-assisted electrospray film formation on a curved insulating surface provided in Embodiment 2 of the present invention;

[0027] Figure 3 is a schematic diagram of plasma-assisted electrospray film formation on a curved insulating surface provided in Embodiment 3 of the present invention.

[0028] In all the drawings, the same reference numerals are used to denote the same elements or structures, where: 1 - ink outlet, 2 - electrostatic micro-disk nozzle, 3 - droplet movement direction, 4 - large droplet, 5 - insulating substrate, 6 - high-voltage power supply, 7 - spray ink, 8 - spray droplet particles, 9 - accumulated charge, 10 - first liquid film, 11 - surface charge dissipation, 12 - volume charge dissipation, 15 - first electrostatic micro-disk spray nozzle, 19 - first curved insulating substrate, 20 - conformal mask, 21 - first atmospheric pressure plasma nozzle, 22 - second electrostatic micro-disk spray nozzle, 23 - second liquid film, 24 - first near-infrared sintering lamp, 25 - first conductive metal layer. Detailed implementation manners

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The present invention provides a method for preparing a conductive film by plasma-assisted electrospray. The method improves the charge dissipation rate and hydrophilicity of the surface of the insulating substrate through plasma modification treatment, and enhances the performance of electrohydrodynamic spraying on the surface of the insulating substrate; at the same time, a spraying method based on an electrostatic micro-disk nozzle is adopted to improve the spraying performance and efficiency of electrostatic spraying on the insulating substrate, and a continuous, dense and defect-free film on the surface of the insulating substrate is obtained.

[0031] The method mainly includes the following steps:

[0032] Step 1, cleaning the insulating substrate.

[0033] The insulating substrate can be a flexible insulating substrate, and the material can be polyethylene naphthalate (PEN), polyimide (PEI), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyimide (PI), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), etc., or can also be a non-flexible insulating substrate laminated composite material, insulating ceramic, glass, etc.

[0034] The cleaning treatment of the insulating substrate includes ultrasonic water cleaning and cleaning with anhydrous ethanol.

[0035] Step 2, performing surface modification treatment on the insulating substrate by using plasma to improve the charge dissipation rate and hydrophilicity of the surface of the insulating substrate.

[0036] Plasma modification of the insulating substrate can improve the consistency and continuity of the subsequent electrostatic spray deposition film by changing the electrical properties and microscopic morphology of the insulating substrate surface.

[0037] The surface of the insulating substrate is subjected to plasma modification using low-pressure plasma or atmospheric pressure plasma.

[0038] Step 3: A film is prepared on the surface of the insulating substrate by electrostatic spraying, and the film is subjected to conductive sintering to obtain a conductive film.

[0039] Continuous, dense, defect-free film deposition is carried out on the surface of the plasma-treated insulating substrate by electrostatic spraying. The spray ink includes, but is not limited to, nano silver paste, nano copper paste, conductive ink, liquid metal, etc.

[0040] The nozzle used in this embodiment is an electrostatic microdisk nozzle, which is obtained by laser cutting a 20-micron-thick stainless steel foil. The diameter of the disk is 5 mm, and it is connected to the ink outlet through a stainless steel needle. The ink flows to the disk through the outside of the needle. During the electrohydrodynamic spraying process, the plasma-treated multi-layer curved circuit substrate is placed on a grounded platform, and the electrohydrodynamic spraying nozzle is connected to a high-voltage DC power supply. A high-intensity electric field on the edge of the disk induces the generation of a large number of Taylor cone sprays. After plasma modification treatment, induced charges are generated on the surface of the insulating substrate, and an electric field pointing from the latter to the former is formed between the insulating substrate and the electrostatic spraying nozzle. The tiny droplets formed by electrostatic spraying move towards the surface of the insulating substrate under the action of the electric field and finally deposit on the surface of the insulating substrate. After a period of electrostatic spraying, the tiny droplets deposit on the surface of the insulating substrate to form a film with a certain thickness, continuous, dense, and defect-free.

[0041] The modification treatment only acts on the surface of the insulating material without excessively changing the properties of the material matrix. Plasma treatment is an effective method widely used to modify the surface properties of insulating materials, with low energy consumption and no chemical pollution. The treatment area is only dozens of nanometers deep on the material surface, so it will not affect the performance of the bulk.

[0042] The modification treatment changes the micro-nano structure of the insulating material surface, increases the bulk conductivity and surface conductivity, and reduces the energy level depth.

[0043] Plasma treatment of the surface of an insulating material can not only improve the surface composition of the material, but also improve its surface roughness and hydrophilicity / hydrophobicity. Plasma treatment of the surface of an insulating substrate to improve its surface roughness enhances the electron capture ability of the insulating substrate surface and increases the vacuum surface flashover voltage. Plasma treatment of the surface of an insulating substrate can increase the surface conductivity of the insulating substrate and make the surface trap energy level of the insulating substrate shallower. The increase in surface conductivity and the shallowing of the surface trap energy level change the electrical characteristics of the insulating material surface due to the charge dissipation on the insulating substrate surface, resulting in an increased charge dissipation rate on the insulating substrate surface.

[0044] By increasing the charge dissipation rate on the insulating substrate surface, the induced charges carried by the droplets electrostatically sprayed onto the insulating substrate surface are neutralized more quickly through the ways of bulk dissipation and surface dissipation, reducing the influence of the electric field formed by the induced charges on the insulating substrate surface on the subsequently deposited droplets. By increasing the hydrophilicity of the insulating substrate surface, the tiny droplets electrostatically sprayed onto the surface of the insulating material can spread evenly on the surface of the insulating material substrate, improving the continuity and uniformity of the thin film prepared by electrohydrodynamic printing on the insulating substrate surface.

[0045] In one embodiment, the spraying area is defined by methods such as attaching a patterned mask, so as to achieve the purpose of restricting the spraying area and realize the preparation of conductive patterns on an insulating planar substrate and the preparation of conductive patterns on an insulating curved substrate.

[0046] The following specific examples are used to further elaborate on the present invention in detail.

[0047] Example 1

[0048] In this Example 1, the surface of the substrate is modified by low-pressure plasma treatment, so as to achieve the purpose of increasing the charge dissipation speed and hydrophilicity of the substrate surface.

[0049] Specifically, in this example, the surface of the insulating hydrophobic substrate is modified by using a reactive ion etching device. Before the plasma modification treatment, the insulating substrate is in an atmosphere surrounded by oxygen. The surface charges of the insulating substrate will undergo weak surface charge dissipation and bulk charge dissipation. There are deep-level traps and shallow-level traps on the insulating substrate. After the plasma treatment, the surface roughness of the insulating substrate increases. The coral-shaped particles formed on the surface of the insulating substrate provide a large number of physical interfaces for the shallow traps, reducing the cumulative value of the surface charges of the deep traps and enhancing the ability of the insulating substrate surface to capture free charges. Secondly, after the plasma treatment, both the surface charge dissipation and bulk charge dissipation of the insulating substrate are significantly improved. Both are conducive to dissipating more surface charges along the surface and through the bulk. After the plasma treatment, both the trap density distribution and the energy level depth decrease, with the deep-level traps decreasing and the shallow-level traps increasing. These all help to inhibit the accumulation of surface charges and accelerate the dissipation of surface charges. In addition, the hydrophilicity of the insulating substrate after the plasma modification treatment is significantly improved. The contact angle between the insulating substrate and water changes from 90° before the modification treatment to 10°. Therefore, after the plasma treatment, the charge dissipation rate and hydrophilicity of the insulating substrate are significantly improved. This provides a basis for subsequent electrostatic spray deposition of continuous, dense, and defect-free thin films.

[0050] Please refer to the attached Figure 1 , which is a schematic diagram of the electrostatic spray effect before and after the plasma modification of the surface of the insulating material of the present invention. Due to the slow surface charge dissipation rate of the insulating substrate without plasma modification, the droplets deposited on the surface of the insulating substrate by electrostatic spray will always carry the same accumulated charge 9 as the subsequent deposited droplets. As the droplets are continuously deposited, the surface charge amount on the insulating substrate 5 increases continuously and forms an electric field, affecting the deposition of the subsequent electrohydrodynamic spray droplet particles 8, resulting in the inability of the tiny droplets generated by the subsequent electrostatic spray to be deposited on the substrate surface. The tiny droplets formed by the electrostatic spray are gradually repelled by the same charges deposited on the substrate and move to the metal surface around the substrate. At the same time, since the insulating substrate without plasma modification is a hydrophobic surface, the tiny droplets deposited on the substrate surface aggregate into multiple large droplets 4 and cannot spread evenly on the substrate surface to form a continuous and uniform thin film. The surface charge dissipation 11 rate of the insulating substrate after the plasma modification treatment increases. The charges on the tiny droplets deposited on the surface of the insulating substrate by electrostatic spray are quickly neutralized through bulk charge dissipation 12 and surface charge dissipation 11, reducing the accumulation of surface charges and no longer affecting the deposition of the tiny droplets generated by the subsequent electrostatic spray on the surface of the insulating substrate. The surface of the insulating substrate after the plasma modification treatment becomes a hydrophilic surface, and the tiny droplets deposited on the substrate surface spread evenly on the substrate surface to form a continuous and uniform first liquid film 10.

[0051] Based on the above principle explanation of improving the effect of thin film preparation by electrostatic spraying through insulating surface plasma modification, the method of plasma-assisted electrostatic spraying on insulating surface for thin film preparation is described by taking the plasma modification treatment of insulating glass surface for electrostatic spraying to prepare conductive silver nanoparticle thin film as a specific embodiment. The steps are as follows:

[0052] Step S1: Provide an insulating glass substrate.

[0053] Step S2: Clean the insulating glass substrate. Clean the surface of the glass substrate with anhydrous ethanol and lint-free paper to ensure the surface of the glass substrate is clean. After waiting for the anhydrous ethanol on the surface of the glass substrate to completely volatilize, place the glass substrate in an ultrasonic cleaning tank and ultrasonically clean it for 2 minutes. After the ultrasonic cleaning is completed, take out the glass substrate with tweezers and use high-pressure nitrogen to blow off the remaining water on the surface of the glass substrate.

[0054] Step S3: Use a reactive ion etching machine to perform plasma modification treatment on the insulating glass substrate.

[0055] Specifically, turn on the power supply of the equipment and the power supply of the cooling device, and then fill the vacuum chamber with air so that the air pressure in the vacuum chamber returns to atmospheric pressure. Open the vacuum chamber, place the insulating glass substrate on the lower substrate tray, and close the vacuum chamber. Perform a vacuum pumping treatment on the vacuum chamber to reduce the pressure in the vacuum chamber to 10 -3 Pa. Turn on the plasma treatment program to perform plasma modification treatment on the insulating glass substrate, and use oxygen plasma to treat the insulating glass substrate for 60 s. Fill the vacuum chamber with air so that the air pressure in the vacuum chamber returns to atmospheric pressure. Open the vacuum chamber and take out the insulating glass substrate after plasma modification treatment. Close the vacuum chamber and perform vacuum protection, and turn off the power supply of the device and the power supply of the cooling device.

[0056] Step S4: Perform electrostatic spraying on the surface of the insulating glass substrate after plasma modification treatment to deposit and form a thin film.

[0057] Specifically, use an electrohydrodynamic printing platform to perform electrostatic spraying thin film deposition on the surface of the insulating glass substrate after plasma modification treatment. Please refer to the attached Figure 1, first place the plasma-modified insulating substrate on an insulating moving platform. Use nano-silver paste with a viscosity of 100 cp and a solid content of 75% as the printing ink 7. Select an electrostatic disk with a diameter of 5 mm connected to a stainless-steel needle as the nozzle, that is, an electrostatic micro-disk nozzle 2. Connect it to the ink outlet 1 through a conductive tape. The spraying height is 20 mm, the ink back pressure is 50 Kpa, or the flow pump controls the flow rate at 15 μL / min. The nozzle is connected to a 6600 V DC high-voltage power supply 6. The substrate moving speed is 4 mm / s, the moving path is a parallel line, the distance between parallel lines is 5 mm, the nozzle scanning speed is 5 mm / s, and the droplets move along the droplet movement direction 3. Import the printing circuit path to complete the printing of the electrohydrodynamic printing circuit.

[0058] Step S5, sinter the printing ink to make it conductive.

[0059] Specifically, place the insulating glass substrate printed with the circuit on a hot plate for conductive thermal sintering. The sintering temperature is 150 °C and the sintering time is 20 minutes.

[0060] To control the thickness and conductivity of the silver thin film deposited on the surface of the insulating glass, the number of droplets deposited by single electrostatic spraying can be increased by increasing the ink back pressure and voltage, reducing the substrate transfer speed, and decreasing the distance between the parallel lines of the trajectory. It is also possible to repeat Step S4 and Step S5 multiple times to deposit and sinter the metal thin film on the surface of the insulating glass substrate, so as to achieve the effect of increasing the film thickness and reducing the sheet resistance of the conductive thin film.

[0061] Furthermore, the sheet resistance deviation of the conductive silver thin film prepared by the above method is <10%, the conductivity > 1×10 7 S / m, and the adhesion > 10 N.

[0062] The electrohydrodynamic printing circuit method for plasma modification treatment on the surface of insulating glass provided by this specific embodiment uses a reactive ion etching device to generate oxygen plasma to modify the insulating glass substrate, increasing the surface charge dissipation rate of the modified insulating glass substrate, thereby improving the electrohydrodynamic printing circuit effect of the insulating glass substrate and obtaining a printed circuit on the surface of the insulating substrate with high precision and high resolution, that is, a conductive thin film.

[0063] Example 2

[0064] A plasma-assisted electrostatic spraying film-forming method on an insulating surface proposed in Embodiment 2 of the present invention is not only applicable to electrostatic spraying film-forming on the surface of small planar insulating substrates, but also applicable to electrostatic spraying film-forming on the surface of large curved substrates. Due to the large size and three-dimensional structure of large curved substrates, it is impossible to perform plasma modification treatment by the method of reactive ion etching low-pressure plasma. In this embodiment, a robot equipped with an atmospheric plasma nozzle at the end is used to perform plasma modification treatment on the surface of large curved insulators.

[0065] Please refer to Figure 2 , based on the above principle description of improving the effect of electrostatic spray preparation of thin films by insulating surface plasma modification, the method of plasma-assisted electrostatic spray preparation of curved thin films on an insulating surface will be described by taking the plasma modification treatment of a curved insulating laminated composite substrate for electrostatic spray preparation of conductive silver nanoparticle thin films as a specific embodiment. The specific steps are as follows:

[0066] Step S1: Provide a curved insulating composite substrate.

[0067] Step S2: Clean the curved insulating composite substrate, and use anhydrous ethanol and dust-free paper to clean the surface of the glass substrate to ensure the cleanliness of the glass substrate surface.

[0068] Step S3: Use an atmospheric pressure plasma spray head to perform plasma modification treatment on the curved insulating composite substrate.

[0069] Specifically, fix the curved insulating composite substrate on a rotating base, and use a robot equipped with an atmospheric pressure plasma spray head at the end to perform plasma modification treatment on the surface of the curved insulating composite substrate. The gas type of the atmospheric plasma spray head is oxygen, the gas flow rate is 3000 sccm, the high-voltage pulse is 5 kV, the pulse width is 1 μs, and the frequency is 2 kHz.

[0070] Step S4: Use the first electrostatic micro-disk spray head 15 to perform electrostatic spray deposition of a thin film on the surface of the curved insulating composite substrate after plasma modification treatment.

[0071] Specifically, use a robotic electrohydrodynamic printing platform to perform electrostatic spray thin film deposition on the surface of the curved insulating composite substrate after plasma modification treatment. First, place the insulating substrate after plasma modification treatment on an insulating motion platform, use a nano-silver paste with a viscosity of 100 cp and a solid content of 75% as the printing ink, select an electrostatic disk with a diameter of 5 mm connected to a stainless steel needle as the spray head, connect it to the ink outlet through a conductive tape, the spray height is 20 mm, the ink back pressure is 50 Kpa or the flow rate pump controls the flow rate to be 15 μL / min, the spray head is connected to a 6600 V DC voltage, the substrate moving speed is 4 mm / s, the moving path is a parallel conformal curve projected on the curved substrate, and the parallel line spacing is 5 mm. Import the printing circuit path to complete the deposition of the liquid silver paste thin film 15.

[0072] Step S5, sinter the conductive printing ink.

[0073] Specifically, a robotic platform equipped with a near-infrared sintering lamp at its end is used to dry and sinter the liquid silver paste film deposited on the surface of the curved insulating composite material. Further, first, low-power near-infrared light is used to dry the liquid silver paste film deposited on the curved surface, and the moving trajectory of the near-infrared sintering end is consistent with the moving trajectory of the electrostatic spray nozzle described in step S4. After the silver paste film is dried, the power of the near-infrared light is increased to sinter and aggregate the silver nanoparticles in the silver paste film into a conductive silver film, thereby obtaining a continuous, dense, and defect-free conductive silver film on the surface of the curved insulating composite material.

[0074] Further, the square resistance deviation of the conductive silver film prepared by the above method is <10%, the conductivity > 1×10 7 S / m, and the adhesion > 10N.

[0075] In order to control the thickness and conductivity of the silver film deposited on the surface of the curved insulating composite material, the number of droplets deposited by single electrostatic spray can be increased by increasing the ink back pressure and voltage, reducing the substrate transfer speed, and decreasing the distance between parallel tracks; or the steps S4 and S5 can be repeated multiple times to deposit and sinter the metal film on the surface of the curved insulating composite material substrate, so as to achieve the effect of increasing the film thickness and reducing the square resistance of the conductive film.

[0076] Example 3

[0077] A plasma-assisted electrostatic spray film forming method on an insulating surface proposed in Embodiment 3 of the present invention is applicable not only to electrostatic spray film forming on the surface of a small planar insulating substrate, but also to preparing conductive or insulating patterns on the insulating substrate surface by attaching a mask to the insulating substrate surface.

[0078] Please refer to Figure 3 , based on the above principle description of improving the effect of electrostatic spray film preparation by plasma modification of the insulating surface, taking the plasma modification treatment of the curved insulating laminated composite material substrate attached with a patterned mask and then electrostatic spray to prepare conductive silver nanoparticle metallized clusters as a specific embodiment to describe the plasma-assisted electrostatic spray method for preparing a patterned film on an insulating surface. The specific steps are as follows:

[0079] Step S1: Provide a first curved insulating substrate 19.

[0080] Step S2: Clean the first curved insulating substrate 19. Use anhydrous ethanol and dust-free paper to clean the surface of the glass substrate to ensure the surface of the substrate is clean.

[0081] Step S3: Provide a batch of conformal hollow conformal masks 20 that conform to the curved insulating composite material substrate. In this example, the material of the conformal mask 20 is a thermally releasable adhesive film, and the excess material is removed by laser cutting to obtain a hollow mask that conforms to the composite material substrate.

[0082] Step S4: Attach a conformal mask conforming to the curved surface insulating composite substrate to the curved surface insulating composite substrate.

[0083] Step S5: Perform plasma modification treatment on the curved surface insulating composite substrate using the first atmospheric pressure plasma spray head 21.

[0084] Specifically, fix the curved surface insulating composite substrate on a rotating base, and use a robot with the first atmospheric pressure plasma spray head 21 at its end to perform plasma modification treatment on the surface of the curved surface insulating composite substrate. The gas type of the atmospheric plasma spray head is oxygen, the gas flow rate is 3000 sccm, the high-voltage pulse is 5 kv, the pulse width is 1 μs, the frequency is 2 kHz, and the spray head scanning speed is 5 mm / s.

[0085] To ensure the uniformity of spraying, the plasma treatment area should be the substrate and its surrounding area masked by the hollow mask that cannot be covered.

[0086] Step S6: Perform electrostatic spray deposition on the surface of the curved surface insulating composite substrate after plasma modification treatment using the second electrostatic micro-disk spray head 22 to form the second thin film 23.

[0087] Specifically, use a robotic electrohydrodynamic printing platform to perform electrostatic spray thin film deposition on the surface of the curved surface insulating composite substrate with a hollow mask after plasma modification treatment. Place the plasma-modified insulating substrate with a hollow mask on an insulating motion platform, use a nano-silver paste with a viscosity of 100 cp and a solid content of 75% as the printing ink, select an electrostatic disk with a diameter of 5 mm connected to a stainless steel needle as the spray head, connect it to the ink outlet through a conductive tape, the spray height is 20 mm, the ink back pressure is 50 Kpa or the flow pump controls the flow rate to be 15 μL / min, the spray head is connected to a 6600 V DC voltage, the substrate moving speed is 4 mm / s, the moving path is a parallel conformal curve projected on the curved surface substrate, and the parallel line spacing is 5 mm. Import the path of the electrostatic spray head to complete the deposition of the liquid silver paste thin film 3 - 5 within the hollow mask area.

[0088] Step S7, near-infrared drying of the silver paste thin film.

[0089] Specifically, use a robot platform with the first near-infrared sintering lamp 24 at its end to dry the second liquid thin film 23 deposited on the curved surface insulating composite surface. Further, use low-power near-infrared light to dry the second liquid thin film 23 deposited on the curved surface. The moving trajectory of the near-infrared sintering end is the same as the moving trajectory of the electrostatic spray head described in S4.

[0090] Step S8, conductive near-infrared sintering of the silver paste thin film.

[0091] After the silver paste film is dried, the near-infrared light power is increased, causing the nano-silver particles in the silver paste film to sinter and aggregate into conductive silver, thereby obtaining a continuous, dense, and defect-free film on the surface of the curved insulating composite material. Further, during the process of sintering the liquid silver paste film with high-power near-infrared light, a large amount of heat is generated, causing the temperature of the substrate surface to rise, and then the hollow mask made of the thermal release tape to fall off. After removing the hollow mask, the first conductive metal layer 25 on the surface of the curved insulating composite material can be obtained.

[0092] In order to control the thickness and conductivity of the first conductive metal layer 25 deposited on the surface of the curved insulating composite material, the number of droplets deposited by single electrostatic spray can be increased by increasing the ink back pressure, ink flow rate and voltage, decreasing the substrate transfer speed, and reducing the distance between the parallel tracks. Steps S6 and S7 can also be repeated multiple times to deposit and dry the metal film on the surface of the curved insulating composite material substrate, so as to achieve the effects of increasing the film thickness and reducing the sheet resistance of the conductive film.

[0093] In the present invention, the surface of the insulating substrate is modified by plasma treatment, which improves the charge dissipation speed and hydrophilicity of the insulating substrate surface. The treatment process is environmentally friendly and pollution-free, and the plasma treatment modification of the surface of a large curved insulating substrate can be realized by a robotic atmospheric plasma nozzle. The spraying efficiency can be improved by using the electrostatic microdisk spraying method to deposit a film on the surface of the insulating substrate; the film deposition on the surface of a large curved insulating substrate can be realized by a robotic electrostatic spraying platform. This method has good material compatibility and is suitable for spraying a variety of conductive or insulating materials; the liquid film deposited on the surface of the insulating substrate is dried and sintered by thermal sintering or near-infrared sintering to obtain a continuous, dense, and defect-free film on the insulating surface.

[0094] The present invention also provides a conductive film, which is prepared by the method for preparing a conductive film by plasma-assisted electrospray as described above.

[0095] The present invention also provides an application of the conductive film as described above in health monitoring, 5G / 6G communication, and intelligent transportation.

[0096] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a conductive film by plasma-assisted electrospraying, characterized in that: The method comprises the following steps: (1) using plasma to perform surface modification treatment on an insulating substrate to improve the charge dissipation rate and hydrophilicity of the surface of the insulating substrate; (2) A thin film is prepared on the surface of the insulating substrate by electrostatic spraying to obtain a conductive film.

2. The method for preparing a conductive film by plasma-assisted electrospraying according to claim 1, characterized in that: An electrostatic micro-disc nozzle is used for electrostatic spraying to prepare a thin film on the surface of the insulating substrate.

3. The method for preparing a conductive film by plasma-assisted electrospraying according to claim 2, characterized in that: The electrostatic micro-disc nozzle is obtained by laser cutting from a stainless steel foil with a thickness of 20 microns and a diameter of 5 mm.

4. The method for preparing a conductive film by plasma-assisted electrospraying according to claim 2, characterized in that: The electrostatic micro-disc nozzle is connected to the ink outlet through a stainless steel needle.

5. The method for preparing a conductive film by plasma-assisted electrospraying according to any one of claims 1 to 4, characterized in that: The surface of the insulating substrate is subjected to plasma modification treatment using low-pressure plasma or atmospheric pressure plasma.

6. The method for preparing a conductive film by plasma-assisted electrospraying according to any one of claims 1 to 4, characterized in that: The insulating substrate is a curved substrate.

7. The method for preparing a conductive film by plasma-assisted electrospraying according to any one of claims 1 to 4, characterized in that: The insulating substrate is a flexible insulating substrate, and its material is any one of polyethylene naphthalate, polyimide, polytetrafluoroethylene, polymethyl methacrylate, polyimide, polyethylene terephthalate, and polyphenylene sulfide.

8. A conductive film, characterized in that: The conductive film is prepared by the method for preparing a conductive film by plasma-assisted electrospraying as described in any one of claims 1 to 7.

9. Application of the conductive film according to claim 8 in health monitoring, 5G / 6G communication, and intelligent transportation.

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