Silver nanowire conductive film and preparation method thereof
阅读说明：本技术 银纳米线导电薄膜及其制备方法 (Silver nanowire conductive film and preparation method thereof ) 是由 李奇琳 甘堃 陈超云 于 2019-09-24 设计创作，主要内容包括：本发明属于纳米材料技术领域,具体涉及一种银纳米线导电薄膜及其制备方法。该制备方法包括如下步骤：提供基板；在所述基板上涂布银纳米线墨水,然后进行第一干燥处理,得到初始银纳米线薄膜；在所述初始银纳米线薄膜表面涂布聚酰亚胺溶液,然后进行第二干燥处理,形成覆盖所述初始银纳米线薄膜的聚酰亚胺层,得到银纳米线导电薄膜。本发明通过涂布可溶的线性高分子聚酰亚胺层代替现有不可溶的体型高分子材料保护层,既可以很好地保护银纳米线,又可以使银纳米线与银浆搭接,保证银纳米线导电薄膜的导电性和可靠性。(The invention belongs to the technical field of nano materials, and particularly relates to a silver nanowire conductive film and a preparation method thereof. The preparation method comprises the following steps: providing a substrate; coating silver nanowire ink on the substrate, and then carrying out first drying treatment to obtain an initial silver nanowire film; and coating a polyimide solution on the surface of the initial silver nanowire film, and then carrying out second drying treatment to form a polyimide layer covering the initial silver nanowire film so as to obtain the silver nanowire conductive film. According to the invention, the existing insoluble body type high molecular material protective layer is replaced by coating the soluble linear high molecular polyimide layer, so that the silver nanowire can be well protected, and the silver nanowire can be lapped with silver paste, thereby ensuring the conductivity and reliability of the silver nanowire conductive film.)
1. The preparation method of the silver nanowire conductive film is characterized by comprising the following steps:
providing a substrate;
coating silver nanowire ink on the substrate, and then carrying out first drying treatment to obtain an initial silver nanowire film;
and coating a polyimide solution on the surface of the initial silver nanowire film, and then carrying out second drying treatment to form a polyimide layer covering the initial silver nanowire film so as to obtain the silver nanowire conductive film.
2. The method for preparing a silver nanowire conductive film according to claim 1, wherein the polyimide solution comprises, based on 100% by mass of the polyimide solution: 0.5-10% of polyimide, 0.01-1% of surface flatting agent, 0.01-1% of surface wetting agent and the balance of organic solvent.
3. The method for preparing the silver nanowire conductive film according to claim 2, wherein the polyimide has a structural formula as follows:
wherein n is the degree of polymerization, R1Is a dianhydride residue, R2Is a diamine residue; and/or the presence of a gas in the gas,
the surface leveling agent is selected from at least one of Glide-100, Glide-432, Glide-435, Glide-440, Flow-300, Flow-425, BYK-333, BYK-361, BYK-371 and BYK-373; and/or the presence of a gas in the gas,
the surface wetting agent is selected from at least one of DISPERBYK-111, DISPERBYK-168, DISPERBYK-180, Dispers-652 and Dispers-710; and/or the presence of a gas in the gas,
the organic solvent is at least one selected from N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, diacetone alcohol, tetrahydrofuran, methyl acetate, ethyl acetate, N-butyl acetate, butyl valerate, dimethyl succinate, dimethyl glutarate and dimethyl adipate.
4. The method of preparing a silver nanowire conductive film of claim 3, wherein R in the polyimide is R1Is selected from
r in the polyimide2Is selected from
the weight average molecular weight of the polyimide is 50000-500000.
5. The method for preparing a silver nanowire conductive film according to any one of claims 1 to 4, wherein the temperature of the first drying treatment is 50 to 150 ℃; and/or the presence of a gas in the gas,
the time of the first drying treatment is 2min-2 h; and/or the presence of a gas in the gas,
the temperature of the second drying treatment is 80-150 ℃; and/or the presence of a gas in the gas,
the time of the second drying treatment is 2min-2 h.
6. A silver nanowire conductive film comprising a silver nanowire layer and a polyimide layer disposed on a substrate, the polyimide layer comprising soluble polyimide, the polyimide layer covering the silver nanowire layer, and silver nanowires in the silver nanowire layer being located within the polyimide layer.
7. The silver nanowire conductive film of claim 6, wherein the polyimide has a general structural formula as follows:
wherein n is the degree of polymerization, R1Is a dianhydride residue, R2Is a diamine residue.
8. The silver nanowire conductive film of claim 7, wherein R in the polyimide is R1Is selected from
r in the polyimide2Is selected from
the weight average molecular weight of the polyimide is 50000-500000.
9. The silver nanowire conductive film of claim 6, wherein the polyimide layer comprises polyimide, a surface leveling agent, and a surface wetting agent; wherein the mass ratio of the polyimide to the surface leveling agent to the surface wetting agent is (0.5-10): (0.01-1): (0.01-1).
10. The silver nanowire conductive film of any one of claims 6-9. The polyimide film is characterized in that the thickness of the polyimide layer is 200-600 nm: and/or the presence of a gas in the gas,
the substrate is selected from any one of a PET film, a TAC film, a PEN film, a CPI film, a COP film, a PDMS film and a glass film.
Technical Field
The invention belongs to the technical field of nano materials, and particularly relates to a silver nanowire conductive film and a preparation method thereof.
Background
Silver Nanowires (AgNWs) generally refer to one-dimensional Silver metal materials with a length on the micrometer scale and a diameter on the nanometer scale. Silver (Ag)The transparent conductive film made of the nanowires has the advantages of good transparency, low sheet resistance, flexibility and the like, and can be applied to the fields of large-size touch control, flexible touch control and the like. The silver nano-wire has large specific surface area and is easy to react with water vapor, oxygen and sulfide in the air to generate Ag2O and Ag2S, etc., which causes the silver nanowire transparent conductive film to lose conductivity. At present, the common practice in the industry is to coat a layer of organic polymer paint as a protective layer (OC) on a dried silver nanowire layer.
When the silver nanowire transparent conductive film is used for preparing a device downstream, in order to better transmit an electric signal to the film and conduct the electric signal out of the film, conductive silver paste is generally required to be printed on the conductive surface of the silver nanowire transparent conductive film. However, the organic polymer protective layer affects the lap joint of the silver nanowires and the conductive silver paste, so that the contact resistance is very high, and even the conduction is not realized. If the thickness of the protective layer is reduced (<100nm), most areas of the silver nanowires are exposed, the conduction problem can be solved, but the exposed silver nanowires quickly lose conductivity under the comprehensive action of oxygen, water vapor, an electric field and the like. The contradiction between the conductivity and the reliability of the silver nanowire transparent conductive film has been a difficult problem which besets the industry.
Therefore, the prior art is in need of improvement.
Disclosure of Invention
The invention aims to provide a silver nanowire conductive film and a preparation method thereof, and aims to solve the technical problem that an organic polymer protective layer of the existing silver nanowire conductive film cannot give consideration to both conductivity and water and oxygen insulation in lap joint with silver paste.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a preparation method of a silver nanowire conductive film, which comprises the following steps:
providing a substrate;
coating silver nanowire ink on the substrate, and then carrying out first drying treatment to obtain an initial silver nanowire film;
and coating a polyimide solution on the surface of the initial silver nanowire film, and then carrying out second drying treatment to form a polyimide layer covering the initial silver nanowire film so as to obtain the silver nanowire conductive film.
The preparation method of the silver nanowire conductive film provided by the invention comprises the steps of preparing initial silver nanowire film on a substrate by silver nanowire ink, and coating polyimide solution on the surface of the initial silver nanowire film to form a polyimide layer covering the initial silver nanowire film; the polyimide has excellent thermal property, mechanical property and electrical property, the soluble polyimide solution has the characteristics of controllable viscosity, good film forming property and flexible process, and is coated on the surface of the silver nanowire to be used as a protective layer for covering a silver nanowire film, so that the silver nanowire can be more tightly and more firmly lapped in the polyimide layer, the silver nanowire can be well protected, and when conductive silver paste is printed subsequently, the polyimide can be dissolved by a solvent of the conductive silver paste, so that the lapping of the silver nanowire and the conductive silver paste can not be influenced by the polyimide layer; and the linear thermal expansion coefficient of the polyimide is about 40ppm/K, the conductive silver paste is about 30ppm/K, the linear thermal expansion coefficient and the conductive silver paste are closer, the stress at the lap joint is smaller, and the reliability is higher than that of the existing protective layer. Therefore, the silver nanowire protective film can well protect the silver nanowires and enable the silver nanowires to be lapped with silver paste by coating the soluble linear polymer polyimide layer to replace the existing insoluble body type polymer material protective layer, and the conductivity and the reliability of the silver nanowire conductive film are guaranteed.
Another aspect of the present invention provides a silver nanowire conductive film including a silver nanowire layer and a polyimide layer disposed on a substrate, the polyimide layer containing soluble polyimide, the polyimide layer covering the silver nanowire layer, and silver nanowires in the silver nanowire layer being located within the polyimide layer.
According to the silver nanowire conductive film, the protective layer is the polyimide layer, the polyimide layer covers the silver nanowire layer, and the silver nanowires in the silver nanowire layer are located in the polyimide layer. Like this, replace current insoluble size macromolecular material protective layer through soluble linear polymer polyimide layer, both can protect silver nano wire well, can make silver nano wire and silver thick liquid overlap joint again, guarantee silver nano wire conductive film's electric conductivity and reliability.
Drawings
Fig. 1 is a schematic flow chart of a method for preparing a silver nanowire conductive film according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a silver nanowire conductive film according to an embodiment of the present invention;
fig. 3 is a schematic structural view of a silver nanowire conductive film of a comparative example of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It is to be understood that the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.
In one aspect, an embodiment of the present invention provides a method for preparing a silver nanowire conductive film, as shown in fig. 1, the method includes the following steps:
s01: providing a substrate;
s02: coating silver nanowire ink on the substrate, and then carrying out first drying treatment to obtain an initial silver nanowire film;
s03: and coating a polyimide solution on the surface of the initial silver nanowire film, and then carrying out second drying treatment to form a polyimide layer covering the initial silver nanowire film so as to obtain the silver nanowire conductive film.
According to the preparation method of the silver nanowire conductive film, silver nanowire ink is prepared into an initial silver nanowire film on a substrate, and a polyimide solution is coated on the surface of the initial silver nanowire film to form a polyimide layer covering the initial silver nanowire film; the polyimide has excellent thermal property, mechanical property and electrical property, the soluble polyimide solution has the characteristics of controllable viscosity, good film forming property and flexible process, and is coated on the surface of the silver nanowire to be used as a protective layer for covering a silver nanowire film, so that the silver nanowire can be more tightly and more firmly lapped in the polyimide layer, the silver nanowire can be well protected, and when conductive silver paste is printed subsequently, the polyimide can be dissolved by a solvent of the conductive silver paste, so that the lapping of the silver nanowire and the conductive silver paste can not be influenced by the polyimide layer; the linear thermal expansion coefficient of the polyimide is about 40ppm/K, the conductive silver paste is about 30ppm/K, the linear thermal expansion coefficient and the conductive silver paste are closer (the UV curing type coating of the existing protective layer is about 85ppm/K), the stress of the lap joint is smaller, and the reliability is higher than that of the existing protective layer. Therefore, the embodiment of the invention can well protect the silver nanowire and ensure the lap joint of the silver nanowire and the silver paste by coating the soluble linear polymer polyimide layer to replace the existing insoluble body type polymer material protective layer, thereby ensuring the conductivity and the reliability of the silver nanowire conductive film.
The polyimide used in the examples of the present invention is colorless and transparent, and is soluble in an organic solvent, so that a polyimide solution can be prepared in the present application. If the polyimide is insoluble in organic solvents (generally brown or amber), the polyimide film has darker color due to easy formation of Charge Transfer Complex (CTC) in the molecular structure, which limits the application in the optical field, therefore, the insoluble polyimide is not suitable for preparing the polyimide solution in the application, and is not in the protection scope of the present invention.
The solvent of the commercially available laser conductive silver paste is generally a mixture of isophorone, dimethyl succinate, dimethyl glutarate, dimethyl adipate, etc., and can dissolve the soluble polyimide in the embodiment of the present invention. Therefore, the polyimide solution is coated on the surface of the silver nanowire to form the polyimide layer covering and coating the silver nanowire, so that the silver nanowire can be well protected, and even if the polyimide layer is thick, the lapping of the silver nanowire and the conductive silver paste cannot be influenced, and the lapping becomes tighter and firmer.
The silver nanowire conductive film prepared by the embodiment of the invention is a transparent conductive film. In the step S01, the substrate for coating is a flexible substrate, and specifically, the substrate is any one of a PET (Polyethylene terephthalate) film, a TAC (Triacetyl Cellulose) film, a PEN (Polyethylene Naphthalate) film, a PDMS (Polydimethylsiloxane) film, a CPI (Colorless transparent Polyimide) film, a COP (cyclic olefin copolymer) film, and a glass film.
In the step S02, the silver nanowires in the silver nanowire ink for coating can be synthesized by an alcohol thermal method, a hydrothermal method, a polyol reduction method, or the like. In the silver nanowire ink, the diameter of the silver nanowire is 15-95nm, the length-diameter ratio is 500-2500, and the concentration of the silver nanowire is 0.01-0.2%. The silver nanowire ink can contain assistants such as a thickening agent and a wetting dispersant besides the silver nanowires, wherein the thickening agent can be hydroxypropyl methyl cellulose, and the mass fraction of the thickening agent is 0.01-0.8%. The wetting dispersant can be a high molecular type hyperdispersant, and is at least one of DISPERBYK-180, DISPERBYK-184, DISPERBYK-190, DISPERBYK-191, DISPERBYK-192, DISPERBYK-194, DISPERBYK-2010 and DISPERBYK-2015, and the mass fraction is 0.01-0.8%. And finally, the balance of the silver nanowire ink is a mixture of water and an alcohol solvent, wherein the mass of alcohol/the mass of water is (0.001-1): 1. the alcohol solvent may be at least one of ethanol and isopropanol. The coating method for coating the silver nanowire ink on the substrate is any one selected from slot coating, dimple coating, blade coating and roller coating.
In one embodiment, the silver nanowire ink is coated on the substrate, and the temperature for performing the first drying treatment is 50-150 ℃; the time of the first drying treatment is 2min-2 h; the specific steps may include: coating silver nanowire ink on a clean flexible transparent substrate, and then putting the flexible transparent substrate into an oven with the temperature of 50-150 ℃ for drying for 2min-2 h.
In the above step S03, the polyimide solution for coating includes, based on 100% by mass of the polyimide solution: 0.5-10% of polyimide, 0.01-1% of surface flatting agent, 0.01-1% of surface wetting agent and the balance of organic solvent. The polyimide solution can form a good coating for coating the surface of the silver nanowire film. Specifically, the viscosity of the polyimide solution is 1 to 50 cps.
In one embodiment, the structural formula of the polyimide is as follows:
wherein n is the degree of polymerization, R1Is a dianhydride residue, R2Is a diamine residue;
specifically, R in the polyimide1Is selected from
R in the polyimide2Is selected from
Above-mentioned group containing R1And R2The structural general formula of (1) introduces a fluorine-containing group, an ester ring main chain structure or an asymmetric structure, inhibits the formation of CTC, enables the polyimide to be colorless and transparent, simultaneously weakens intermolecular acting force, and can be dissolved in an organic solvent. In one embodiment, R of the polyimide resin1Is 3-carboxymethyl-1, 2, 4-cyclopentane tricarboxylic acid 1,4:2, 3-dianhydride R2When the compound is 4, 4' -bis (4-aminophenyl) thioether, the effect is better: r is as defined above1Of cyclopentane structure and R2The thioether bond(s) of (a) causes the Charge Transfer Complex (CTC) of the polyimide itself to be broken, thereby rendering the polyimide colorless and transparent and soluble in an organic solvent. In addition, thioether bonds can be complexed with the surface of the silver nanowire and can also capture Ag+So that the silver nanowire transparent conductive film has better weather resistance and ion migration resistance.
In the polyimide solution, the surface leveling agent is at least one selected from the group consisting of Glide-100, Glide-432, Glide-435, Glide-440, Flow-300, Flow-425, BYK-333, BYK-361, BYK-371 and BYK-373; the surface wetting agent is selected from at least one of DISPERBYK-111, DISPERBYK-168, DISPERBYK-180, Dispers-652 and Dispers-710; the organic solvent is at least one selected from N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, diacetone alcohol, tetrahydrofuran, methyl acetate, ethyl acetate, N-butyl acetate, butyl valerate, dimethyl succinate, dimethyl glutarate and dimethyl adipate.
In one embodiment, the weight average molecular weight of the polyimide is 50000-500000; when the weight average molecular weight of the polyimide is less than 50000, the brittleness and the film forming property are poor, a continuous and complete protective layer cannot be formed, and the reliability of the conductive film is poor. When the weight average molecular weight of the polyimide is more than 500000, the viscosity is too high, and the polyimide is relatively difficult to synthesize. Preferably, the weight average molecular weight of the polyimide is 10000-300000.
And after the polyimide solution is coated, performing secondary drying to form the complete silver nanowire conductive film. Wherein the temperature of the second drying treatment is 80-150 ℃; the time of the second drying treatment is 2min-2 h.
In another aspect, an embodiment of the present invention further provides a silver nanowire conductive film, as shown in fig. 2, including a silver nanowire layer and a polyimide layer disposed on a substrate, where the polyimide layer contains soluble polyimide, the polyimide layer covers the silver nanowire layer, and silver nanowires in the silver nanowire layer are located in the polyimide layer.
According to the silver nanowire conductive film provided by the embodiment of the invention, the protective layer is the polyimide layer, the polyimide layer covers the silver nanowire layer, and the silver nanowires in the silver nanowire layer are positioned in the polyimide layer. Therefore, the soluble linear polymer polyimide layer in the silver nanowire conductive film provided by the embodiment of the invention replaces an insoluble body-type polymer material protection layer (as shown in fig. 3) in the existing silver nanowire conductive film, so that the silver nanowire can be well protected, the silver nanowire can be lapped with silver paste, and the conductivity and reliability of the silver nanowire conductive film are ensured.
In one embodiment, the thickness of the polyimide layer is 200-600 nm; within the thickness range, the silver nanowire can well obstruct water and oxygen, protect the silver nanowire and can be well lapped with conductive silver paste printed subsequently.
In one embodiment, the substrate is selected from any one of a PET film, a TAC film, a PEN film, a CPI film, a COP film, a PDMS film, and a glass film.
In one embodiment, the formulation of the polyimide solution used to form the polyimide layer is described in detail above, and the polyimide solution comprises: 0.5-10% of polyimide, 0.01-1% of surface flatting agent, 0.01-1% of surface wetting agent and the balance of organic solvent. The finally formed polyimide layer comprises polyimide, a surface leveling agent and a surface wetting agent; wherein the mass ratio of the polyimide to the surface leveling agent to the surface wetting agent is (0.5-10): (0.01-1): (0.01-1).
The surface leveling agent can improve the film forming property of the protective layer, reduce the surface roughness of the protective layer and further reduce the haze of the conductive film. The surface wetting agent can improve the contact interface of the protective layer and the substrate, and is beneficial to improving the reliability of the conductive film and reducing the haze; therefore, the effect of the protective layer formed in the above-described mass ratio range is better.
The invention is described in further detail with reference to a part of the test results, which are described in detail below with reference to specific examples.
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