A flexible transparent conductive film and its preparation method and application

Abstract

The invention discloses a flexible transparent conductive film, a preparation method and an application. The flexible transparent conductive film is composed of a flexible substrate, a functional transition layer containing an ionic liquid and a single-walled carbon nanotube layer self-assembled on the surface. First, a functional transition layer containing an imidazole ionic liquid is coated on the surface of a transparent plastic substrate, and after solidification into a film, an aqueous dispersion of single-walled carbon nanotubes is coated, and after drying, the flexible transparent conductive film is subjected to plasma etching treatment and cleaning to remove the surfactant, thereby obtaining the flexible transparent conductive film. Since the imidazole groups of the ionic liquid in the functionalized transition layer interact with the carbon nanotubes, and the ionic liquid itself has good conductivity, a molecular-scale and nano-scale synergistic conductive network can be constructed, the self-assembly behavior of the single-walled carbon nanotubes and the substrate is realized, good adhesion and conductive stability are obtained, and the surface resistance is significantly reduced, so that a low-resistance flexible transparent conductive film can be obtained. The film is widely used in flexible display, electric heating, defogging, anti-icing, induction switch, etc.

Description

Technical Field

[0001] The invention belongs to the field of new nano materials, and particularly relates to a flexible transparent conductive film and a preparation method and application thereof. Background Art

[0002] Single-walled carbon nanotubes are a type of carbon nanomaterial with a single-layer graphite coil structure. The perfect sp2 hybrid bond gives it superior comprehensive performance. The combination of excellent conductivity and huge aspect ratio makes the volume filling amount (conductivity threshold) required to form a conductive network very low, making it the best conductive filling material. Moreover, at this extremely low conductivity threshold, it still maintains a very high transmittance. Coupled with its own high strength and flexibility, it is one of the best materials for preparing flexible transparent conductive films. Flexible transparent conductive films prepared from single-walled carbon nanotubes have the advantages of flexibility, no attenuation, and adjustable transmittance, and have received great attention in the fields of flexible display and touch control.

[0003] The preparation methods of carbon nanotube transparent conductive film include vacuum filtration, coating, electrodeposition, self-assembly and chemical vapor deposition. Although the direct film formation method of chemical vapor deposition does not involve the dispersion of carbon nanotubes, and there is no increase in resistance caused by residual surfactants, the preparation of single-walled carbon nanotube chemical vapor deposition itself is quite difficult, and how to control the uniformity of direct film formation in chemical vapor deposition is quite challenging. Therefore, wet film formation is still the easiest method to achieve at present, especially large-area coating technology is relatively mature, suitable for low-cost large-area preparation. Wet film formation first disperses single-walled carbon nanotubes into a uniform dispersion, and then deposits single-walled carbon nanotube films on the substrate by coating or spraying. Since the dispersants used are all non-conductive organic matter, they must be carefully removed after post-processing. At the same time, there is no interaction between carbon nanotubes and the substrate, and the adhesion is weak, which seriously restricts subsequent use. Researchers have explored a large number of preparation and post-processing techniques to solve these difficult problems.

[0004] Chinese invention patent CN201510695800.4 discloses a high-quality carbon nanotube transparent conductive film and its preparation method and application, using a gridded metal silver wire as a substrate, and then depositing carbon nanotubes on its surface, using highly conductive metal to improve the conductivity of the transparent conductive film. Chinese invention patent CN201310430346.0 discloses a method for quickly preparing a large-area carbon nanotube flexible transparent conductive film and improving its conductivity, coating a single-walled carbon nanotube dispersion dispersed by a surfactant on a plastic substrate, and then removing the residual surfactant through HNO3 and SOCl2 treatment, and at the same time achieving the effect of oxidative doping, thereby improving the conductivity of the film. Chinese invention patent CN201310430911.3 discloses a method for preparing a carbon nanotube flexible transparent conductive film, first washing a PET substrate with nitric acid, and then spraying a single-walled carbon nanotube dispersion on its surface, to improve and enhance conductivity and adhesion. Chinese invention patent CN202010492836.3 discloses a carbon nanotube transparent conductive film and its preparation method, wherein a carbon nanotube solution is obtained by mixing a carbon nanotube dispersion with a bonding resin, and then a conductive film is formed on the surface of a plastic substrate by spraying. However, no matter which method is used, how to balance the adhesion with the substrate and effectively remove the negative effects of surface activity and bonding resin has not been well solved. The development of a carbon nanotube transparent conductive film with high transmittance and low resistance is still a challenging task. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a flexible transparent conductive film and its application, so as to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A flexible transparent conductive film comprises a flexible transparent plastic substrate, a functionalized transition layer containing an ionic liquid and a single-walled carbon nanotube layer, wherein:

[0008] The flexible transparent plastic substrate can be a flexible transparent film material such as polyester (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), etc., with a thickness of 1-200 microns;

[0009] The ionic liquid in the functionalized transition layer is an imidazole ionic liquid, wherein the cation can be any one of 1-alkyl imidazole, 1-alkyl-3-methyl imidazole, 1-alkyl-2,3-dimethyl imidazole, etc., and the anion can be any one of chlorine, bromine, iodine, tetrafluoroboric acid, hexafluorophosphoric acid, acetic acid, bistrifluoromethanesulfonyl imide, nitric acid, perchloric acid, hydrogen sulfate, dihydrogen phosphate, trifluoromethanesulfonic acid, trifluoroacetic acid, p-toluenesulfonic acid, etc. The thickness of the transition layer is 0.05 micrometers to 1 micrometer;

[0010] The single-walled carbon nanotubes can be prepared by arc method, chemical vapor deposition method, laser ablation method, high-pressure carbon monoxide method, etc., with a diameter of 0.4-3 nanometers and a coating thickness of 10 nanometers to 500 nanometers.

[0011] A method for preparing a flexible transparent conductive film, applied to a flexible transparent conductive film, comprises the following steps:

[0012] 1) Mix a certain proportion of ionic liquid and water-based saturated polyester, apply it to the surface of the flexible plastic substrate after corona treatment by wire rod coating, and bake at 80-100°C for 1-10 minutes to obtain an imidazole-functionalized plastic substrate;

[0013] 2) Mix the single-walled carbon nanotubes with a dispersant, a wetting agent, etc., disperse them by nano-grinding or high-pressure homogenization, and filter them through a 300-600 mesh filter to obtain a uniformly dispersed single-walled carbon nanotube aqueous dispersion;

[0014] 3) Apply the single-walled carbon nanotube aqueous dispersion on the surface of the imidazole-functionalized plastic substrate, bake at 80-140° C. for 1-10 minutes to obtain a flexible transparent conductive film;

[0015] 4) The flexible transparent conductive film original film is treated with plasma to partially etch the single-walled carbon nanotube dispersant, and then the residual surfactant is washed with an ethanol solution to obtain the final flexible transparent conductive film.

[0016] Furthermore, the aqueous saturated polyester in step 1 can be any one of emulsion type, water-dispersible type and water-soluble type saturated polyester, with a molecular weight>7000, and the ratio of ionic liquid to aqueous saturated polyester is 1:100 to 1:1.

[0017] Furthermore, the carbon nanotube aqueous dispersion in step 2 comprises:

[0018] Single-walled carbon nanotubes 0.05-4%

[0019] Dispersant 0.05-10%

[0020] Wetting agent 0.01-1%

[0021] Water balance;

[0022] The dispersant is a surfactant, which is a combination of anionic surfactant and nonionic surfactant in a ratio of 1:1 to 10:1;

[0023] The wetting agent is a polysiloxane aqueous wetting agent, which may be any one of BYK190, BYK191, BYK192, BYK194, BYK151, BYK154, BYK180, BYK184, BYK187, BYK345, BYK346, BYK2010, BYK2015, etc.;

[0024] The nano-grinding and dispersing method has a grinding and dispersing disk linear speed of 2-15 m / s, a grinding medium of zirconia beads with a diameter of 0.5-2.5 mm, and a grinding number of 5-20 times;

[0025] The high pressure homogenization and dispersion has a working pressure of 50-350 MPa and a homogenization frequency of 5-20 times.

[0026] Furthermore, the single-walled carbon nanotube coating process in step three can be any one of spray coating, roll coating and scraper coating.

[0027] Furthermore, the plasma treatment in step 4 may be corona discharge, glow discharge, arc discharge, etc., with a treatment temperature of <80° C. and a power of 1KW-60KW.

[0028] A flexible transparent conductive film is applied to a flexible transparent conductive film, which can be used as a flexible transparent electrode for flexible display, flexible transparent electric heating film, electric heating deicing, electric heating defogging, smart window film and other thin film materials. It can also be used in anti-static, shielding, transparent sensing film and other fields. It has the advantages of low resistance, high transmittance and stable conductivity.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The imidazole group of the imidazole ionic liquid has a strong pie-pie interaction with carbon nanotubes. Through the pre-coating functional transition layer of water-based saturated polyester, the ionic liquid migrates to the surface during baking, forming an imidazole functional layer on the surface of the transparent plastic substrate that has a strong force on the carbon nanotubes, which will greatly facilitate the subsequent adhesion of single-walled carbon nanotubes on the surface and strengthen their self-assembly behavior to obtain a conductive network with a uniform structure.

[0031] 2) Imidazole ionic liquids are also conductive materials. They interact with single-walled carbon nanotubes through molecular conjugation to form a synergistic conductive network at the molecular scale of ionic liquids and the nanoscale of carbon nanotubes, thereby obtaining a transparent conductive film with lower surface resistance. At the same time, this type of composite method avoids the adverse effects of excessive ionic liquids such as re-adhesion caused by conventional simple mixing methods;

[0032] 3) Physical cleaning methods such as plasma can partially etch the residual surfactant, which is more conducive to subsequent ethanol cleaning to obtain a cleaner surface, thereby further reducing the surface resistance;

[0033] 4) The preparation process is a water-based process, which does not require the pickling process used in large quantities in conventional wet film formation. It is safe and environmentally friendly and suitable for large-scale preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a preparation flow chart of the present invention;

[0035] Figure 2 This is a scanning electron microscope photograph of the film surface of Example 1. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is further described below in conjunction with the examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention. Example

[0037] The specific implementation steps are as follows:

[0038] 1) Mix and dissolve 10 parts of ionic liquid 1-ethyl-3-methylimidazolium bromide and 90 parts of aqueous saturated polyester (molecular weight 7000) to form a uniform and stable mixed solution;

[0039] 2) Use a No. 3 wire rod to scrape on the surface of the corona-treated PET substrate (thickness 50 microns), bake at 100°C for 5 minutes to form a functional transition layer with a thickness of 0.5 microns;

[0040] 3) The single-walled carbon nanotubes (tube diameter 1-2 nm) prepared by chemical vapor deposition were dispersed in water by nano-grinding process. The grinding medium was zirconia beads with a diameter of 0.8 mm. The linear speed of the dispersion plate was 10 m / s. The single-walled carbon nanotube dispersion was prepared by filtration with a 300-mesh filter. The dispersion formula was:

[0041] Single-walled carbon nanotubes 0.2%

[0042] Dispersant (sodium dodecyl sulfate: methyl cellulose = 1:1) 0.4%

[0043] Wetting agent (BYK180) 0.2%

[0044] Water balance;

[0045] 4) Use No. 3 wire rod to apply the carbon nanotube dispersion on the surface of the plastic substrate pre-coated with ionic liquid, bake at 120°C for 5 minutes to form a single-walled carbon nanotube layer with a thickness of 20 nanometers, and obtain a flexible transparent conductive film original film;

[0046] 5) The flexible transparent conductive film original film is treated with 2KW corona etching, the substrate temperature is less than 80°C, and then the residual surfactant is washed with an ethanol solution to obtain the final flexible transparent conductive film;

[0047] 6) Use a four-probe instrument to test its surface resistance, use a visible light transmittance tester to test the film transmittance, use 3M tape to test the adhesion of the surface carbon nanotubes, and observe whether there is any carbon nanotube shedding. Example

[0048] The specific implementation steps are as follows:

[0049] 1) Mix and dissolve 1 part of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate and 99 parts of aqueous saturated polyester (molecular weight 13000) to form a uniform and stable mixed solution;

[0050] 2) Use a No. 3 wire rod to scrape on the surface of the corona-treated PS substrate (thickness 10 microns), bake at 80°C for 10 minutes to form a functional transition layer with a thickness of 0.05 microns;

[0051] 3) The single-walled carbon nanotubes (tube diameter 0.8-1.5 nm) prepared by the arc method were dispersed in water by high-pressure homogenization process, the working pressure was 150 MPa, the homogenization was repeated 10 times, and the single-walled carbon nanotube dispersion was prepared by filtering with a 400-mesh filter. The dispersion formula was:

[0052] Single-walled carbon nanotubes 0.1%

[0053] Dispersant (sodium dodecylbenzenesulfonate: Triton TX100 = 2:1) 0.2%

[0054] Wetting agent (BYK345) 0.1%

[0055] Water balance;

[0056] 4) Spraying process: Coat the carbon nanotube dispersion on the surface of the plastic substrate pre-coated with ionic liquid, bake at 80°C for 1 minute to form a single-walled carbon nanotube layer with a thickness of 10 nanometers, and obtain a flexible transparent conductive film;

[0057] 5) The flexible transparent conductive film original film is treated with 2KW corona etching, the substrate temperature is less than 80°C, and then the residual surfactant is washed with an ethanol solution to obtain the final flexible transparent conductive film;

[0058] 6) Use a four-probe instrument to test its surface resistance, use a visible light transmittance tester to test the film transmittance, use 3M tape to test the adhesion of the surface carbon nanotubes, and observe whether there is any carbon nanotube shedding. Example

[0059] The specific implementation steps are as follows:

[0060] 1) Mix and dissolve 50 parts of ionic liquid 1-ethyl-3-methylimidazolium chloride and 50 parts of aqueous saturated polyester (molecular weight 50,000) to form a uniform and stable mixed solution;

[0061] 2) Use a No. 3 wire rod to scrape on the surface of the corona-treated PC substrate (thickness 200 microns), bake at 100°C for 10 minutes to form a functional transition layer with a thickness of 1 micron;

[0062] 3) The single-walled carbon nanotubes (tube diameter 0.5-1.5 nm) prepared by the high-pressure carbon monoxide method were dispersed in water using a nano-grinding process. The grinding medium was zirconia beads with a diameter of 2.5 mm. The linear speed of the dispersion plate was 15 m / s. The single-walled carbon nanotube dispersion was prepared by 20 grindings and filtered through a 600-mesh filter. The dispersion was formulated as follows:

[0063] Single-walled carbon nanotubes 0.4%

[0064] Dispersant (polyacrylamide: polyvinyl pyrrolidone = 10:1) 0.8%

[0065] Wetting agent (BYK2015) 0.4%

[0066] Water balance;

[0067] 4) The carbon nanotube dispersion is applied to the surface of the plastic substrate pre-coated with the ionic liquid by a roll coating process, and baked at 140°C for 10 minutes to form a single-walled carbon nanotube layer with a thickness of 500 nanometers, thereby obtaining a flexible transparent conductive film;

[0068] 5) The flexible transparent conductive film original film is treated with 60KW corona etching, the substrate temperature is less than 80°C, and then the residual surfactant is washed with ethanol solution to obtain the final flexible transparent conductive film;

[0069] 6) Use a four-probe instrument to test its surface resistance, use a visible light transmittance tester to test the film transmittance, use 3M tape to test the adhesion of the surface carbon nanotubes, and observe whether there is any carbon nanotube shedding. Example

[0070] The specific implementation steps are as follows:

[0071] 1) Mix and dissolve 5 parts of ionic liquid 1,3-dimethylimidazolium chloride and 95 parts of aqueous saturated polyester (molecular weight 25000) to form a uniform and stable mixed solution;

[0072] 2) Use a No. 3 wire rod to scrape on the surface of the PMMA substrate (thickness 50 microns) treated with corona, bake at 100°C for 5 minutes to form a functional transition layer with a thickness of 0.5 microns;

[0073] 3) The single-walled carbon nanotubes (tube diameter 1-2 nm) prepared by chemical vapor deposition were dispersed in water by high-pressure homogenization process, the working pressure was 150 MPa, the homogenization was repeated 10 times, and the single-walled carbon nanotube dispersion was prepared by filtering with a 500-mesh filter. The dispersion formula was:

[0074] Single-walled carbon nanotubes 0.2%

[0075] Dispersant (sodium dodecyl sulfate: methyl cellulose = 1:1) 0.4%

[0076] Wetting agent (BYK191) 0.2%

[0077] Water balance;

[0078] 4) Use No. 3 wire rod to apply the carbon nanotube dispersion on the surface of the plastic substrate pre-coated with ionic liquid, bake at 80°C for 10 minutes to form a single-walled carbon nanotube layer with a thickness of 30 nanometers, and obtain a flexible transparent conductive film original film;

[0079] 5) The flexible transparent conductive film original film is treated with 10KW corona etching, the substrate temperature is less than 80°C, and then the residual surfactant is washed with ethanol solution to obtain the final flexible transparent conductive film;

[0080] 6) Use a four-probe instrument to test its surface resistance, use a visible light transmittance tester to test the film transmittance, use 3M tape to test the adhesion of the surface carbon nanotubes, and observe whether there is any carbon nanotube shedding. Example

[0081] The specific implementation steps are as follows:

[0082] 1) Mix and dissolve 20 parts of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 80 parts of aqueous saturated polyester (molecular weight 7000) to form a uniform and stable mixed solution;

[0083] 2) Use a No. 3 wire rod to scrape on the surface of the corona-treated PET substrate (thickness 50 microns), bake at 100°C for 5 minutes to form a functional transition layer with a thickness of 0.05 microns;

[0084] 3) The single-walled carbon nanotubes (tube diameter 1-2 nm) prepared by chemical vapor deposition were dispersed in water by high-pressure homogenization process, with a working pressure of 350 MPa, homogenized for 5 times, and filtered through a 600-mesh filter to obtain a single-walled carbon nanotube dispersion, wherein the dispersion formula is:

[0085] Single-walled carbon nanotubes 0.05%

[0086] Dispersant (sodium dioctyl sulfosuccinate: hydroxyethyl cellulose = 1:1) 0.1%

[0087] Wetting agent (BYK190) 0.05%

[0088] Water balance;

[0089] 4) Use No. 3 wire rod to apply the carbon nanotube dispersion on the surface of the plastic substrate pre-coated with ionic liquid, bake at 120°C for 5 minutes to form a single-walled carbon nanotube layer with a thickness of 15 nanometers, and obtain a flexible transparent conductive film original film;

[0090] 5) The flexible transparent conductive film original film is treated with 5KW corona etching, the substrate temperature is less than 80°C, and then the residual surfactant is washed with an ethanol solution to obtain the final flexible transparent conductive film;

[0091] 6) Use a four-probe instrument to test its surface resistance, use a visible light transmittance tester to test the film transmittance, use 3M tape to test the adhesion of the surface carbon nanotubes, and observe whether there is any carbon nanotube shedding.

[0092] This comparative example adopts the same process as that of Example 1, except that the ionic liquid is not added to the transition layer. The surface resistance, light transmittance and adhesion of the prepared flexible transparent conductive film are tested.

[0093] This comparative example uses the same formula as Example 1, except that the ionic liquid is directly added to the carbon nanotube dispersion and coated on the surface of the plastic substrate to form a transparent conductive film of ionic liquid and carbon nanotubes, and its surface resistance, transmittance and adhesion are tested.

[0094] Table 1 Summary of data of examples and comparative examples

[0095] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A flexible transparent conductive film comprising a flexible transparent plastic substrate, a functionalized transition layer containing an ionic liquid and a single-walled carbon nanotube layer, characterized in that: The flexible transparent plastic substrate is any one of a flexible transparent film material of polyester, polycarbonate, polymethyl methacrylate, and polystyrene, with a thickness of 1-200 μm; The ionic liquid in the functionalized transition layer is an imidazole ionic liquid, wherein the cation is any one of 1-alkyl imidazole, 1-alkyl-3-methyl imidazole, and 1-alkyl-2,3-dimethyl imidazole, and the anion is any one of chlorine, bromine, iodine, tetrafluoroboric acid, hexafluorophosphoric acid, acetic acid, bistrifluoromethanesulfonyl imide, nitric acid, perchloric acid, hydrogen sulfate, dihydrogen phosphate, trifluoromethanesulfonic acid, trifluoroacetic acid, and p-toluenesulfonic acid, and the thickness of the transition layer is 0.05 micrometers to 1 micrometer; The single-walled carbon nanotubes are prepared by arc method, chemical vapor deposition method, laser ablation method, and high-pressure carbon monoxide method, with a diameter of 0.4-3 nanometers and a coating thickness of 10 nanometers to 500 nanometers; A method for preparing a flexible transparent conductive film, applied to the above-mentioned flexible transparent conductive film, comprises the following steps: Step 1: Mix a certain proportion of ionic liquid and water-based saturated polyester, apply the mixture to the surface of a flexible transparent plastic substrate after corona treatment by wire rod coating, and bake at 80-100° C. for 1-10 minutes to obtain an imidazole-functionalized plastic substrate; Step 2: Mix the single-walled carbon nanotubes with a dispersant and a wetting agent, disperse by nano-grinding or high-pressure homogenization, and filter through a 300-600 mesh filter to obtain a uniformly dispersed single-walled carbon nanotube aqueous dispersion; Step 3: coating the single-walled carbon nanotube aqueous dispersion on the surface of the imidazole-functionalized plastic substrate, and baking at 80-140° C. for 1-10 minutes to obtain a flexible transparent conductive film; Step 4: subjecting the original flexible transparent conductive film to plasma treatment to partially etch the single-walled carbon nanotube dispersant, and then washing the residual surfactant with an ethanol solution to obtain the final flexible transparent conductive film; The aqueous saturated polyester in step 1 is any one of an emulsion type, a water-dispersible type and a water-soluble type saturated polyester, the molecular weight is >7000, and the ratio of the ionic liquid to the aqueous saturated polyester is 1:100 to 1:1; The carbon nanotube aqueous dispersion in step 2 comprises: Single-walled carbon nanotubes 0.05-4% Dispersant 0.05-10% Wetting agent 0.01-1% Water balance; The dispersant is a surfactant, which is a combination of anionic surfactant and nonionic surfactant in a ratio of 1:1 to 10:1; The wetting agent is a polysiloxane aqueous wetting agent, which is any one of BYK190, BYK191, BYK192, BYK194, BYK151, BYK154, BYK180, BYK184, BYK187, BYK345, BYK346, BYK2010, and BYK2015; The nano-grinding and dispersing method has a grinding and dispersing disk linear speed of 2-15 m / s, a grinding medium of zirconia beads with a diameter of 0.5-2.5 mm, and a grinding number of 5-20 times; The high pressure homogenization and dispersion has a working pressure of 50-350 MPa and a homogenization frequency of 5-20 times.

2. The flexible transparent conductive film according to claim 1, characterized in that: The single-walled carbon nanotube coating process in step three is any one of spray coating, roll coating and scraper coating.

3. The flexible transparent conductive film according to claim 1, characterized in that: The plasma treatment in step 4 is corona discharge, glow discharge, arc discharge, the treatment temperature is <80°C, and the power is 1KW-60KW.

4. The use of a flexible transparent conductive film as claimed in claim 1, characterized in that: As a flexible transparent electrode used in thin film materials for flexible displays, flexible transparent electric heating films, electric deicing, electric defogging, smart window films, or in the fields of antistatic, shielding, and transparent sensing films, it has the advantages of low resistance, high transmittance, and stable conductivity.

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