CN110791136A

CN110791136A - Silver nanowire coating solution and transparent conductive film

Info

Publication number: CN110791136A
Application number: CN201910912495.8A
Authority: CN
Inventors: 强骥鹏; 曾西平; 靳世东; 王海波; 巫春荣; 陆华俊; 肖谢; 詹世治; 李晓明
Original assignee: Shenzhen Huake Tek Co Ltd
Current assignee: Shenzhen Huake Tek Co Ltd
Priority date: 2019-09-25
Filing date: 2019-09-25
Publication date: 2020-02-14

Abstract

The invention relates to the field of nano photoelectronic material preparation, in particular to a silver nanowire coating solution and a transparent conductive film. Aiming at the problems of high surface resistance, large roughness, poor transmittance and haze and the like of the conventional transparent conductive film, the invention provides a coating solution containing complexing dispersion resin and a flux and a transparent conductive film prepared by the coating solution. The complexing dispersion resin can be complexed with metal ions on the surface of the nanowire to improve the distribution uniformity of the nanowire in the film, improve the spreadability and smoothness of the nanowire and reduce the surface roughness of the film; the flux can braze the nodes of the nanowires to form an interconnected network structure in the drying process of the film layer, so that the surface resistance of the film is reduced. Thereby the transparent conductive film has high optical transmittance, low surface resistance, high conductive uniformity, low surface roughness and low haze.

Description

Silver nanowire coating solution and transparent conductive film

Technical Field

The invention relates to the field of nano photoelectronic material preparation, in particular to a silver nanowire coating solution and a transparent conductive film.

Background

The transparent conductive film is a functional film with high visible light transmittance and certain conductive capability, and is widely applied to liquid crystal displays, touch screens, organic light emitting diodes and thin film solar cells as a transparent electrode, and is used as an anti-static coating and an electromagnetic shielding layer. The transparent conductive film can simultaneously realize high visible light transmittance and high conductivity, and thus can maintainDemonstrating the simultaneous transmission of visible photons and carriers. So far, the transparent conductive material with the longest use history and the best comprehensive performance is tin-doped indium oxide (ITO), and the transparent conductive material can reach the square resistance value of less than 10 omega and the resistivity of less than 1.5 multiplied by 10 under the condition that the visible light transmittance is 80 percent^-4Ω·cm^-1. However, ITO suffers from several problems: first, global indium resources are exhausted, the price is saved and increased, and the situation is further aggravated along with the rapid expansion of an LCD flat panel display market and a thin film solar cell market; secondly, expensive vacuum coating equipment is needed and the high-quality ITO film can be prepared at a high substrate temperature, so that the equipment investment is huge; third, when deposited on flexible substrates, the substrate temperature is typically below 200 ℃, quality is difficult to optimize, and ITO is prone to cracking and failure as the substrate flexes during use.

To overcome these difficulties, the industry has developed a variety of novel transparent conductive thin film materials, the most typical examples of which are conductive polymers, aluminum-doped zinc oxide (AZO), and Carbon Nanotube (CNT) transparent conductive thin films. However, the conductive polymer has low conductivity, strong absorption in the visible light region, and poor chemical stability; aluminum-doped zinc oxide and ITO also have the problem of easy cracking, and because zinc oxide is an amphoteric oxide, the chemical and environmental stability is not good enough; however, the carbon nanotube transparent conductive film has a large contact resistance between carbon nanotubes, and it is difficult to simultaneously achieve a low sheet resistance and a high visible light transmittance. In a conventional conductive composite material composed of a conductive nanowire (nanotube) and a visible light transparent polymer, the conductive nanowire (nanotube) and the polymer are uniformly mixed and dispersed at a certain ratio to form a block, a fiber or a film having a specific shape. Since the organic polymer can hinder electron transport between nanowires (nanotubes), a high mixing ratio of the conductive nanowires (nanotubes) is required to achieve a certain conductive ability, but the visible light transmittance is inevitably reduced.

Compared with novel transparent conductive materials such as graphene, carbon nanotubes, organic polymers and etched metal grids, the silver nanowire conductive film has the advantages of preparation process, substrate selectivity, conductivity, wide spectrum and high transmittance, and is the preferred material for the next generation of transparent conductive films.

The conductive mechanism of the silver nanowire transparent conductive film is that the silver nanowires are arranged in disorder to form a conductive network, the random distribution of the nanowires causes poor conductive uniformity of the film, and meanwhile, the node resistance among the silver nanowires is the main reason of higher surface resistance of the transparent conductive film; poor conduction uniformity directly affects the performance of the device, and high surface resistance results in higher power consumption of the device. The silver nanowires are randomly arranged on the substrate, and have poor spreadability and smoothness, so that the surface of the film has high microroughness, which is part of the reason of high haze of the film; the rough surface is easy to cause short circuit of materials deposited subsequently in the process of preparing the device, and the performance and the working stability of the device are influenced. The virtual lapping among the silver nanowires causes poor bending performance of the film; the silver nano-wire and the flexible substrate have poor binding force, and the silver nano-film is easy to damage. These deficiencies limit their application to flexible electronic devices and there is a need to improve the uniformity of the distribution of nanowires and to solder thin films of silver nanowires. The traditional brazing method for realizing the silver nanowire film, such as heating, mechanical pressure application, medium introduction, irradiation nano brazing and the like, can reduce the node resistance among the silver nanowires, optimize the resistance of the transparent conductive film and meet the use requirement of the transparent conductive electrode. However, most of the conventional brazing methods for silver nanowires are only suitable for laboratories, and cannot be directly applied to the industrial production of large-batch silver nanowire films. The reasons for this are mainly: flexible film substrates such as PET cannot reach the heat brazing temperature (at least 200 ℃) that is resistant to silver nanowires; the mechanical pressure application stress of the silver nanowires is up to 81GPa, the silver nanowires are easy to fall off in the pressure application process, higher pressure application requirements are provided for industrial coating equipment, and the equipment cost is higher; the introduction of media (such as PEDOT: PSS, HAuCl4, etc.) causes the transmittance of the silver nanowire film to be reduced or the haze to be increased, which restricts the application of the silver nanowire film as a transparent conductive film, and the coating step of the silver nanowire film is complicated.

Two important parameters of a transparent conductive film are optical transmittance (T,%) and sheet surface resistance (RS, Ω). Higher optical transmission allows for clear image quality for display applications, higher efficiency for lighting and solar energy conversion applications. Lower resistivity can reduce device power consumption while resistance uniformity is critical to device performance such as emission uniformity of OLEDs.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for improving the conductive uniformity of a silver nanowire film and brazing nodes of the silver nanowire film, and solves the problems of overhigh surface resistance, relatively poor bending resistance, relatively poor transmittance and haze and the like of the silver nanowire film.

Firstly, the invention relates to a silver nanowire coating solution, wherein dispersion resin of the solution can be complexed with metal ions on the surface of a nanowire, so that the distribution uniformity of the nanowire is improved, the spreadability and smoothness of the nanowire are improved, and the surface roughness of a film is reduced;

secondly, the coating solution contains a metal flux, the flux can reduce metal ions on the surface of the nanowire into metal in the film drying process, and the nanowire is brazed into a whole through the nodes of the nanowire to form an intercommunicated network structure;

the invention further relates to a transparent conductive film comprising the metal nano network and the dispersion resin, wherein the nano wires in the transparent conductive film are uniformly dispersed, the spreadability and the smoothness are good, and the surface roughness is lower; and an interworking network structure is formed by the nodes of the nanowires. Therefore, the film has low surface resistance and high conduction uniformity while having high optical transmittance.

In addition, the transparent conductive film of the invention solders the metal nanowires into a whole in the preparation process, and the method comprises drying the metal nanowire film for 20S-10 min at a temperature of 100 ℃ to 200 ℃.

According to the transparent conductive film, the complexing dispersion resin can be complexed with metal ions on the surfaces of the nanowires to improve the distribution uniformity of the nanowires in the film, improve the spreadability and smoothness of the nanowires and reduce the surface roughness of the film; the flux can braze the nodes of the nanowires to form an interconnected network structure in the drying process of the film layer, so that the surface resistance of the film is reduced. Thereby the transparent conductive film has high optical transmittance, low surface resistance, high conductive uniformity, low surface roughness and low haze.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is an SEM image of a transparent conductive film in example 1 of the present invention;

FIG. 2 is an SEM photograph of a transparent conductive film according to comparative example 1 of the present invention;

FIG. 3 is a laser microscope photograph (x 50 times) of a transparent conductive film according to comparative example 2 of the present invention;

FIG. 4 is a laser microscope photograph (magnification ×. 50) of the transparent conductive film in comparative example 3 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Method of producing a composite material

In one aspect, the present invention discloses a method for manufacturing a transparent conductive film, the transparent conductive film comprising a plurality of metal nanowires in an interconnected network, the network comprising metal nanowire nodes soldered together, the method comprising the steps of:

providing a substrate; and

forming a film comprising a metal nanowire interconnecting network on a substrate; and forming a plurality of metal nanowire nodes which are brazed into a whole between the adjacent metal nanowires.

In one embodiment, a method of forming a transparent conductive film includes the steps of:

dispersing the nanowires in a dispersion resin solution to prepare a nanowire coating solution;

coating the coating solution onto a substrate to form a coating film;

and drying the coating film at a temperature of 100-200 ℃.

Substrate

As long as it is a transparent material, it can be used without particular limitation. The substrate of the present invention can be preferably used as long as it has a transmittance of 80% or more at a wavelength (380 to 780nm) in the visible light range, and the substrate can be rigid or flexible.

Suitable rigid substrates include, for example, glass, polycarbonate, acrylic, and the like.

When the nanowire coating solution for the transparent conductive film is coated on a flexible substrate, the substrate may be a flexible, transparent polymer film having any desired thickness and composed of one or more polymer materials. The substrate needs to maintain dimensional stability and adhesion to the conductive film during the coating and drying of the conductive layer. Polymeric materials that can be used to make such substrates include, but are not limited to, polyesters (e.g., polyethylene terephthalate (PET) and polyethylene naphthalate (PEN)), Polyimides (PI), polyamides, Polyetheretherketones (PEEK), Polyethersulfones (PES), Polyetherimides (PEI), polyolefins (e.g., linear, branched, and cyclic polyolefins), polyvinyls (e.g., polyvinyl chloride, polyvinylidene chloride, polystyrene, etc.), polyvinyl acetals, polycarbonates, cellulose ester substrates (e.g., cellulose triacetate, cellulose acetate). Preferred substrates are composed of polymers with good thermal stability, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and Polyimide (PI). The substrate may also be heat treated or annealed to reduce shrinkage and promote dimensional stability. Transparent multilayer substrates may also be used.

Silver nanowires

Silver nanowires are the primary component that imparts conductivity to conductive films and articles made using conductive films. The conductivity of a silver nanowire-based transparent conductive film is mainly controlled by a) the conductivity of a single nanowire, b) the number of nanowires between terminals, and c) the number of connections and contact resistance between nanowires. Below a certain concentration of nanowires (also called percolation threshold) the conductivity between the terminals is zero, because the nanowires are spaced too far apart to provide a continuous current path. Above this concentration, there is at least one current path available. As more current paths are provided, the overall resistance of the film layer will decrease. However, when more current paths are provided, the transparency (i.e., optical transmittance) of the conductive film is decreased due to light absorption and scattering by the nanowires. Also, when the amount of silver nanowires in the conductive film is increased, haze of the transparent film is increased due to light scattering caused by the silver nanowires. A similar effect will occur in transparent articles prepared using conductive films.

In order for the film to have good transparency and low haze, nanowires with a small range of diameters are required. Specifically, it is desirable that the metal nanowires have an average diameter of not more than 250nm, preferably not more than 100nm, more preferably 10nm to 50 nm. With respect to average length, nanowires having longer lengths are expected to provide better conductivity within the network. In general, the metal nanowires can have an average length of at least 1 micron, preferably at least 2.5 microns, more preferably from about 5 microns to about 100 microns.

In general, the aspect ratio (length/diameter) of silver nanowires is 20 to 5000. The preferred aspect ratio (length/diameter) of the silver nanowires is 500 to 3000. Silver nanowires having a length of 5 to 100 μm and a diameter of 10 to 200nm are usable. Silver nanowires with a diameter of 10nm to 50nm and a length of 10 μm to 50 μm are also particularly suitable for constructing transparent conductive network films.

Silver nanowires can be prepared by methods known in the art. Specifically, silver nanowires can be synthesized by liquid phase reduction of a silver salt (e.g., silver nitrate) in the presence of a polyol (e.g., ethylene glycol or propylene glycol) and poly (vinylpyrrolidone). According to, for example, Ducamp-Sanguisa, C.et al [ J.of Solid State Chemistry, (1992),100, 272-; sun, Y, et al [ chem.Mater. (2002),14, 4736-; sun, Y, et al [ Nano Letters, (2003),3(7), 955-; U.S. patent application publication 2012/0063948 published on 3/15/2012; U.S. patent application publication 2012/0126181 published on 24/5/2012; U.S. patent application publication 2012/0148436 published on 6/14/2012; the methods described in U.S. patent application publication 2012/0207644, published on 8/16/2012, which is incorporated by reference in its entirety, allow for the large-scale production of silver nanowires of consistent dimensions.

The formation of the transparent conductive film includes dispersing the metal nanowires in a suitable dispersion resin solution and applying the dispersion as a coating solution onto the selected substrate surface. The concentration of the dispersion can be selected to obtain good dispersion of the nanowires to provide the desired conductive properties of the resulting coating.

Dispersing resins

For the practical manufacturing process of the transparent conductive film, it is important to have a conductive component (e.g., silver nanowires) and a dispersion resin in a coating solution. The dispersion resin solution plays a dual role as a dispersant to facilitate the dispersion of the silver nanowires and as a tackifier to stabilize the silver nanowire coating solution so that the settling of the silver nanowires does not occur at any point in the coating process. It is also desirable to have silver nanowires and dispersion resins in a single coating dispersion. This simplifies the coating process and allows one-time coating, and avoids the method of first coating bare silver nanowires to form a weak and brittle film, and then coating a polymer on the outside to form a transparent conductive film.

In order for the transparent conductive film to be useful for various device applications, it is also important that the dispersion resin of the transparent conductive film be optically transparent and flexible, but still have high mechanical strength, good hardness, high thermal stability, and light stability. This requires T of the dispersion resin to be used for the transparent conductive film_g(glass transition temperature) is higher than the use temperature of the transparent conductive film.

Known in the artTransparent, optically clear polymeric binders are all useful as dispersing resins. Examples of suitable dispersing resins include, but are not limited to, polyacrylic, such as polymethacrylates (e.g., poly (methyl methacrylate)), polyacrylates, and polyacrylonitrile; polyvinyl alcohol; polyesters (e.g., polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate); polymers with high aromaticity, such as phenolic resins or cresol-formaldehyde resins.

) (ii) a Polystyrene, polyvinyltoluene, polyvinylxylene, polyimide, polyamide, polyamideimide, polyetheramide, polysulfide, polysulfone, polyphenylene, and polyphenylene ether; polyurethane (PU); a polycarbonate; an epoxy resin; polyolefins (e.g., polypropylene, polymethylpentene, and cyclic olefins); acrylonitrile-butadiene-styrene copolymer (ABS); celluloses; silicones and other silicon-containing polymers (e.g., polysilsesquioxanes and polysilanes); polyvinyl chloride (PVC); polyvinyl acetate; polynorbornene; synthetic rubbers (e.g., EPR, SBR, EPDM) and fluoropolymers (e.g., polyvinylidene fluoride, polytetrafluoroethylene (TFE), or polyhexafluoropropylene); copolymers of fluoroolefins and hydrocarbon olefins (e.g.,

) And amorphous fluorocompound polymers or copolymers (e.g., developed by Asahi Glass Inc.)

Or developed by DuPont

AF); polyvinyl acetals; gelatin; polysaccharides and starches.

Resins containing N, O, S or the like coordinating atoms are particularly suitable for use as the dispersing resin, and in order to disperse and stabilize silver nanowires in the polymer coating solution, it is advantageous to use a dispersing resin having a high oxygen content. Oxygen-containing groups such as hydroxyl groups, carboxyl groups and sulfonic acid groups (such as rosin resin, alkyd resin, modified rosin resin, polystyrene sulfonic acid, sulfonated polyester, hydroxycellulose, carboxycellulose and the like) have strong affinity for binding with the surfaces of the silver nanowires and promote dispersion and stability, and particularly, the carboxyl groups and the sulfonic acid groups can be complexed with metal ions on the surfaces of the nanowires to ensure that the nanowires have good dispersion uniformity, so that the nanowires are flatly laid in the film to avoid being exposed on the surface, and the surface roughness of the film is reduced. Many oxygen-rich polymers also have good solubility in polar organic solvents commonly used to prepare organic solvent coating materials, while other oxygen-rich polymers have good solubility in water or aqueous solvent mixtures commonly used to prepare aqueous solvent coating materials.

The dispersion resin enables the silver nanowires to be uniformly dispersed and coated on the surfaces of the nanowires, a layer of protective film is formed in the film drying process to prevent the nanowires from being oxidized, and carboxyl or sulfonic groups in the protective film are complexed with silver ions on the surfaces of the nanowires to be dissolved to provide a metal ion source and are reduced into metal silver by the brazing flux.

In certain embodiments, cellulose ester polymers, such as Cellulose Acetate Butyrate (CAB), Cellulose Acetate (CA), or Cellulose Acetate Propionate (CAP), are superior to other oxygen-rich dispersion resins when used to prepare silver nanowire-based transparent conductive films coated from organic solvents, such as 2-butanone (methyl ethyl ketone, MEK), methyl isobutyl ketone, acetone, methanol, ethanol, 2-propanol, ethyl acetate, propyl acetate propionate, or mixtures thereof. Their use results in transparent conductive films in which the optical light transmittance and conductivity of the coated film are greatly improved. In addition, these cellulose ester polymers have glass transition temperatures of at least 100 ℃ and provide transparent flexible films with high mechanical strength, good hardness, high thermal stability and light stability.

The dispersion resin may be present in an amount of 40 to 90 wt.% of the dried transparent conductive film. Preferably, they are present in 50 to 80 wt.% of the dried film. In some configurations, a mixture of a polymer containing carboxyl or sulfonic acid groups with one or more additional polymers may be used. These polymers should be compatible with the cellulosic polymers. By compatible is meant that when dried, the mixture comprising at least one cellulose acetate polymer and one or more additional polymers forms a clear, single phase composition. The additional polymer or polymers may provide additional benefits such as promoting adhesion to the substrate and improving hardness and scratch resistance. As noted above, the total weight percent of all polymers is 40 to 90 wt.% of the dry transparent conductive film. Preferably, the total weight of all polymers is 50 to 80 wt.% of the dry film. Polyester polymers, polyurethanes, and polyacrylics are examples of additional polymers that may be used in blends with the dispersing resin.

In other embodiments, water-soluble dispersion resins such as polyvinyl alcohol, gelatin, polyacrylic acid, polyimide may also be used. Other water dispersible latex polymers may also be used, such as polyacrylates and polymethacrylates containing methacrylic acid units. Coating from aqueous solutions is environmentally friendly and reduces the emission of volatile organic compounds during manufacturing.

The use of a water-soluble polymer, such as polyvinyl alcohol or gelatin, as a binder for a silver nanowire-based transparent conductor yields an excellent transparent conductive film with greatly improved film transmittance and conductivity. Transparent conductive films prepared using polyvinyl alcohol or gelatin dispersion resins also exhibit excellent transparency, scratch resistance, and hardness when a polymer crosslinking agent is added to the polymer solution. The transparent conductive film prepared according to the present invention provides a transmittance of at least 80% in a spectral range of 380nm to 800nm and a surface resistivity of 500 Ω/□ or less.

The transparent conductive article comprising silver nanowires and a water-soluble dispersion resin also exhibits excellent transparency, high scratch resistance, and hardness. In addition, transparent conductive films prepared using these dispersion resins have good adhesion to substrates comprising polyethylene terephthalate (PET), poly (methyl methacrylate), polycarbonate, and the like, when a suitable subbing layer is applied between the substrate and the conductive layer.

The water-soluble dispersion resin is present in 40 to 90 wt.% of the total weight of the dried transparent conductive film. Preferably, they are present in 50 to 80 wt.% of the dried film.

Sometimes up to 50 wt.% of the gelatin or polyvinyl alcohol dispersion resin may be replaced by one or more additional polymers. These polymers should be compatible with gelatin or polyvinyl alcohol dispersion resins. By compatible is meant that all polymers form a clear, single phase mixture when dried. The additional polymer or polymers may provide additional benefits such as promoting adhesion to the substrate and improving hardness and scratch resistance. Water-soluble acrylic polymers are particularly preferred as the additional polymer. Examples of such polymers are polyacrylic acids and polyacrylates, and copolymers thereof. As noted above, the total weight percent of all polymers is 40 to 90 wt.% of the dry transparent conductive film. Preferably, the total weight of all polymers is 50 to 80 wt.% of the dry film.

The scratch resistance and hardness of the transparent conductive film having these dispersion resins to the substrate can be improved by crosslinking the dispersion resins using a crosslinking agent, if necessary. Isocyanates, alkoxysilanes, and melamines are examples of typical crosslinkers for cellulose ester polymers containing free hydroxyl groups. Vinyl sulfone and aldehyde are examples of typical cross-linking agents for gelatin adhesives.

Flux for brazing

The flux is a composition of a reducing organic amine and an organic acid or an inorganic acid or a salt thereof. The organic amine and the acid can be respectively added into the solvent to form a neutral solution, or the salt of the organic amine can be directly added. The reducing organic amine is preferably, but not limited to, primary, secondary and tertiary amines or N-containing heterocyclic compounds such as ethylenediamine, diethylamine, aniline, diethanolamine, triethanolamine, hydrazines, guanidines, pyridine, quinoline, and the like. Organic acids are preferably, but not limited to, formic acid, acetic acid, maleic acid, oxalic acid, succinic acid, adipic acid, succinic anhydride (succinic anhydride), NA anhydride, dibrominated succinic acid, sebacic acid, glutaric acid, itaconic acid, salicylic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid (palmitic acid), octadecanoic acid, stearic acid, palmitic acid, tartaric acid, DL-malic acid, sorbic acid, phthalic acid, benzoic acid, p-tert-butylbenzoic acid, chloroglycolic acid, glycolic acid, maleic anhydride (maleic anhydride), maleic acid, lactic acid, malonic acid, azelaic acid, suberic acid, dodecanedioic acid, dimethylolpropionic acid, polymeric acids, oleic acid, citric acid, and the like; the inorganic acid is preferably, but not limited to, hydrochloric acid, nitric acid, hydrofluoric acid, hydrobromic acid, sulfurous acid, thiosulfuric acid, fluoroboric acid, phosphorous acid, and the like.

The flux can be decomposed into amine and corresponding acid in the film drying process, and the reducing amine can reduce metal ions on the surfaces of the nanowires into metal in the film drying process. And the acid can dissolve or partially remove the residual PVP on the surface of the nanowire, and meanwhile, the oxide on the metal surface is dissolved to provide metal ions required by the reduction process for the metal ions. And halogen ions in hydrochloric acid, hydrofluoric acid, hydrobromic acid and the like can drive the low-temperature brazing of the metal nanowires to form an interconnected network structure. The halogen ions form metal halides on the surface of the metal nanowires, which enhance the mobility/diffusivity of the metal ions, which causes brazing of the contacts or near-contact points between the nanowires to form a brazed network. There is evidence that when a halide flux is used, a metal halide shell forms on the resulting brazing nanowire network. While not wishing to be bound by theory, it is believed that the metal halide coating on the metal nanowires causes metal atoms/ions from the nanowires to move such that the moving ions condense to form junctions between adjacent nanowires, forming a nanostructured network, and possibly lowering the free energy when forming a braze network with net movement of metal atoms within the nanostructures.

The flux is preferably, but not limited to, ethylenediamine hydrochloride, aniline hydrochloride, hydrazine dihydrochloride, cyclohexylamine hydrobromide, diethylamine hydrobromide, cyclohexylamine hydrochloride, diethylamine hydrochloride, diethylaminoethanol hydrochloride, dimethylamine hydrochloride, triethanolamine hydrochloride, diphenylguanidine hydrobromide, diphenylguanidine hydrochloride, 2-bromoethylamine hydrobromide, succinic acid amide, salicylic acid amide, ethylenediamine tetraacetic acid, ethylenediamine dinitrate, and the like.

Solvent(s)

The metal nanowires and the flux are dispersed in a dispersion resin solution to form a nanowire coating solution, and the coating solution may be water-soluble or organic solvent-based depending on the difference in solubility of the dispersion resin.

The silver nanowire coating solution may be prepared by mixing the various components with one or more polymeric binders in a suitable organic solvent system, which typically comprises one or more solvents such as ketones, esters, ethers (e.g., glycol ethers), aromatic compounds, alkanes, and the like or mixtures thereof, preferably but not limited to toluene, 2-butanone (methyl ethyl ketone, MEK), methyl isobutyl ketone, acetone, methanol, ethanol, 2-propanol, ethyl acetate, propyl acetate, butyl acetate, ethyl lactate, tetrahydrofuran, or mixtures thereof.

The aqueous coating solution for the transparent silver nanowire film may be prepared by mixing various components with one or more polymer binders in water or in water and a water-miscible solvent such as acetone, acetonitrile, tetrahydrofuran or a mixture thereof, short-chain alcohols (methanol, ethanol, isopropanol, isobutanol, t-butanol), other alcohols having a straight chain or branched chain with up to 7 carbon atoms, ethylene glycol, propylene glycol, diacetone alcohol, ethyl lactate, methoxyethanol, methoxypropanol, other glycol ethers (e.g., alkyl cellosolve and alkyl carbitol), or the like or a mixture thereof. Preferably, an alcohol solvent may be used, and among these, isopropyl alcohol having a boiling point relatively close to that of water is preferable.

Wetting agent

The nanowire coating fluid may optionally incorporate a rheology modifier or a combination thereof. In some embodiments, the coating liquid may include a wetting agent or surfactant to reduce surface tension, and the wetting agent may be useful for improving coating properties. The humectant is generally soluble in the solvent.

The wetting agent may be used to improve the coating process performance of the metal nanowire coating solution and the quality of the metal nanowire dispersion. Specifically, the humectant can reduce the surface energy of the ink, allowing the ink to spread sufficiently over the surface after application. The wetting agent may be a surfactant and/or a dispersant. Surfactants are a class of materials that act to reduce surface energy, and surfactants can improve material solubility. Surfactants generally have a hydrophilic molecular portion and a hydrophobic molecular portion that contribute to their properties. A wide range of surfactants, such as nonionic, cationic, anionic, zwitterionic surfactants, are commercially available. In some embodiments, non-surfactant humectants (e.g., dispersants) are also known in the art and can be effective in improving the wetting ability of the ink if the characteristics associated with the surfactant are not an issue.

Suitable surfactants include, but are not limited toFluorosurfactants of surfactants comprising

FSN、

FSO、

FSA、FSH (DuPont chemical Co.) and NOVEC^TM(3M). Other exemplary surfactants include nonionic surfactants based on alkylphenol ethoxylates. Preferred surfactants include, for example, such as TRITON^TM(X100, X114, X45) and polyoxyethylene octylphenol ethers such as TERGIT^TM15-S series (Dow chemical Co.) secondary alcohol polyoxyethylene ethers. Additional exemplary nonionic surfactants include, for example, DYNOL^TM(604, 607) (aerochemical) acetylenic surfactant and n-dodecyl β -D-maltoside.

Coating solution

A silver nanowire coating solution comprising

0.01-5.0 wt.% of silver nanowires, preferably 0.02-4.0 wt.% of silver nanowires, more preferably 0.05-2.0 wt.% of silver nanowires;

0.02 to 10 wt.% of a dispersion resin, preferably 0.04 to 8.0 wt.% of a dispersion resin, more preferably 0.1 to 4.0 wt.% of a dispersion resin;

0.002 to 1.0 wt.%, preferably 0.004 to 0.8 wt.%, more preferably 0.01 to 0.4 wt.%;

0.001 to 0.2 wt.% of a wetting agent, preferably 0.002 to 0.15 wt.%, more preferably 0.005 to 0.1 wt.%;

83.82-99.966 wt.%, preferably 87.1-99.934 wt.%, more preferably 93.5-99.835 wt.% of solvent.

The above concentration ranges are intended to be illustrative and not limiting, and those skilled in the art will recognize that other ranges outside the above explicit ranges are encompassed and within the present disclosure.

Coating of conductive film

The transparent conductive article can be prepared by applying the above-described coating liquid onto a transparent substrate using various wet coating processes including, but not limited to, electrostatic spraying, screen printing, wire bar coating, dip coating, blade coating, curtain coating, slide coating, slot die coating, roll coating, gravure coating, or extrusion coating.

Drying of films

After the coating solution forms a coating, the film may be dried to remove the solvent. The node brazing takes place during the drying of the film. The film may be dried, for example, with an air heating gun, oven, heat lamp, or the like, but in some embodiments via air drying. In general, brazing is considered a low temperature process, and any application of heat to promote drying is incidental to brazing.

The drying temperature is 50-300 ℃, preferably 80-250 ℃, and more preferably 100-200 ℃.

The drying time is 1S to 30min, preferably 10S to 20min, and more preferably 20S to 10 min.

The above temperatures and ranges are intended to be illustrative and not limiting, and those skilled in the art will recognize that other ranges outside the explicit ranges above are contemplated and are within the present disclosure.

Examples

The silver nanowires are synthesized according to a polyol liquid phase reduction method of a literature, are dispersed in isopropanol after being washed by water/acetone for many times, have the diameter of about 20-30 nm and the length of about 20-30 mu m, and are coated by a 20 mu m wire rod. The optical transmittance and haze were directly measured with a BYK4775 light transmittance haze meter, the sheet surface resistance was measured with a SZT-2C four-probe measuring instrument (sample size: 100X 50mm, 10 points), the silver nanowire distribution and surface roughness were measured with a laser confocal microscope (KEYENCE VK-X1000), and the nanowire node brazing was measured with a field emission scanning electron microscope (SEM, HITACHI Regulus 8100).

Example 1 Water-soluble nanowire coating solution 1

Using a mixture of hydroxypropyl methylcellulose and sulfonated polystyrene as a dispersion resin, ethylenediamine hydrochloride as a flux, FSO-100 as a wetting agent, and a mixture of water and isopropanol as a solvent to prepare a nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in table one:

watch 1

The coating liquid was coated on a 12 μm PET substrate, and dried in an oven at 130 ℃ for 3 min.

Example 2 Water-soluble nanowire coating solution 2

Using a mixture of hydroxypropyl methylcellulose and a water-soluble maleic rosin resin as a dispersion resin, ethylenediamine hydrochloride as a flux, Triton X100 as a wetting agent, and a mixture of water and isopropanol as a solvent, preparing a nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in table two:

watch two

The coating liquid was coated on a 12 μm PEN substrate and dried in an oven at 160 ℃ for 3 min.

Example 3 organic solvent nanowire coating solution 1

Taking a mixture of cellulose acetate butyrate and water white rosin as dispersion resin, ethylene diamine tetraacetic acid as a flux, Sago-9760 as a wetting agent, and a mixture of isopropanol and n-propyl acetate as a solvent, preparing a nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in Table III:

watch III

The coating liquid is coated on a 10 mu m PI substrate, dried for 30 seconds at 80 ℃ in an oven and then dried for 1min at 180 ℃.

Example 4 organic solvent nanowire coating solution 2

Using a mixture of cellulose acetate butyrate and polymerized rosin as a dispersion resin, ethylenediamine dinitrate as a flux, DYNOL 604 as a wetting agent, and a mixture of isopropanol and ethyl lactate as a solvent, preparing a nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in table four:

watch four

The coating liquid was coated on a 12 μm PET substrate, and dried in an oven at 120 ℃ for 5 min.

Comparative example 1 No complexing resin, No flux

Using hydroxypropyl methylcellulose as dispersion resin, no flux, FSO-100 as wetting agent, and water and isopropanol mixture as solvent to prepare nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in table five:

watch five

Comparative example 2 No Complex resin, with flux

Using hydroxypropyl methylcellulose as dispersion resin, ethylenediamine hydrochloride as flux, Triton X100 as wetting agent, and water and isopropanol mixture as solvent to prepare nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in table six:

watch six

Comparative example 3 with Complex resin, no fluxing agent

Using a mixture of cellulose acetate butyrate and water white rosin as a dispersion resin, Sago-9760 as a wetting agent, and a mixture of isopropanol and n-propyl acetate as a solvent, preparing a nanowire coating solution, wherein the percentage (wt.%) of the total weight of the solution is as shown in table seven:

watch seven

The coating liquid was coated on a 10um PI substrate, dried in an oven at 80 ℃ for 30S and then dried at 180 ℃ for 1 min.

Comparison of film Properties

Optical transmittance (T,%), haze (H,%), surface roughness R of the films of the different examples_a(nm) sheet resistance R_sThe value of (omega/□) is shown in table eight,

table eight

Analysis of film Properties

As shown in fig. 1-2 and table eight, it can be seen from example 1 and comparative example 1 that, in the case of the same silver nanowire content, the sheet surface resistance is greatly reduced and the surface roughness is significantly reduced due to the node brazing; however, because the metal oxide on the surface and the nodes of the film is reduced into metal, the reflection and scattering are increased, the haze is slightly increased, and the optical transmittance is reduced to a certain degree; meanwhile, the surface resistance uniformity is greatly improved by the complexation of the dispersion resin.

It can be seen from example 2 and comparative example 2 that, under the condition of the same content of silver nanowires, the halogen compound can anchor the nodes together, so the haze is lower. But no complex ion provides a metal ion source, the reducing action of reducing amine is not obvious, and the nodes are mainly anchored by metal halide, so that the conductivity is poor, and meanwhile, the distribution uniformity of the nanowires is poor, and the surface resistance uniformity is poor; meanwhile, part of the nanowires are exposed on the surface of the film, resulting in higher surface roughness.

It can be found from comparative example 2 (fig. 3) and comparative example 3 (fig. 4) that the distribution uniformity of the nanowires can be greatly improved by the complexation of the dispersion resin, and that the nano-wires have good spreadability and smoothness, high surface resistance uniformity, and low surface roughness.

The present invention has been further described with reference to specific embodiments, but it should be understood that the detailed description should not be construed as limiting the spirit and scope of the present invention, and various modifications made to the above-described embodiments by those of ordinary skill in the art after reading this specification are within the scope of the present invention.

Claims

1. A silver nanowire coating solution is characterized by comprising silver nanowires, a dispersion resin, a flux, a wetting agent and a solvent.

2. The silver nanowire coating solution of claim 1, comprising 0.01 to 5.0 wt.% of silver nanowires, 0.02 to 10 wt.% of a dispersing resin, 0.002 to 1.0 wt.% of a flux, 0.001 to 0.2 wt.% of a wetting agent, and 83.82 to 99.966 wt.% of a solvent.

3. The silver nanowire coating solution of claim 1, comprising 0.02 to 4.0 wt.% of silver nanowires, 0.04 to 8 wt.% of a dispersing resin, 0.004 to 0.8 wt.% of a flux, 0.002 to 0.15 wt.% of a wetting agent, and 87.1 to 99.934 wt.% of a solvent.

4. The silver nanowire coating solution of claim 1, comprising 0.05 to 2.0 wt.% of silver nanowires, 0.1 to 4 wt.% of a dispersion resin, 0.01 to 0.4 wt.% of a flux, 0.005 to 0.1 wt.% of a wetting agent, and 93.5 to 99.835 wt.% of a solvent.

5. The silver nanowire coating solution of claim 1, wherein the silver nanowires have an aspect ratio of 20-5000, a length of 5 μ ι η to 100 μ ι η, and a diameter of 10nm to 200 nm.

6. The silver nanowire coating solution as claimed in claim 1, wherein the silver nanowire has an aspect ratio of 500-3000, a length of 10-50 μm and a diameter of 10-50 nm.

7. The silver nanowire coating solution of claim 1, wherein the dispersing resin is a resin containing N, O, S coordinating atoms.

8. The silver nanowire coating solution of claim 1, wherein the dispersion resin has a group having a strong affinity with the surface of the silver nanowire.

9. The silver nanowire coating solution of claim 1, wherein the dispersing resin can promote dispersion and stabilization of the silver nanowires, improve spreadability and smoothness of the nanowires during coating, reduce surface roughness of the thin film, make the nanowires more uniformly distributed in the film, and improve uniformity of conductivity.

10. The silver nanowire coating solution of claim 1, wherein the dispersion resin can provide metal ions required for a soldering process and coat the surface of the nanowires to prevent the metal from being oxidized during a film drying process.

11. The silver nanowire coating solution of claim 1, wherein the flux agent is a composition of a reducing organic amine and an organic or inorganic acid or a salt thereof.

12. The silver nanowire coating solution of claim 11, wherein the reducing organic amine is capable of reducing metal ions to metal during film drying and brazing the nanowires into a whole through nodes to form an interconnected network.

13. The silver nanowire coating solution of claim 11, wherein the reducing organic amine comprises a primary amine, a secondary amine, and a tertiary amine or a N-containing heterocyclic compound.

14. The silver nanowire coating solution of claim 11, wherein the reducing organic amine comprises ethylenediamine, diethylamine, aniline, diethanolamine, triethanolamine, hydrazines, guanidines, pyridine, quinoline.

15. The silver nanowire coating solution of claim 11, wherein the organic or inorganic acid can dissolve or partially remove residual PVP from the surface of the nanowires while dissolving the oxide from the metal surface to provide the metal ions needed for the reduction process.

16. The silver nanowire coating solution of claim 11, wherein the inorganic acid comprises hydrochloric acid, nitric acid, hydrofluoric acid, hydrobromic acid, sulfurous acid, thiosulfuric acid, fluoroboric acid, phosphorous acid.

17. The silver nanowire coating solution of claim 11, wherein the organic acid comprises formic acid, acetic acid, maleic acid, oxalic acid, succinic acid, adipic acid, succinic anhydride, NA anhydride, dibromic succinic acid, sebacic acid, glutaric acid, itaconic acid, salicylic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, stearic acid, palmitic acid, tartaric acid, DL-malic acid, sorbic acid, phthalic acid, benzoic acid, p-tert-butylbenzoic acid, chloroglycolic acid, glycolic acid, maleic anhydride, maleic acid, lactic acid, malonic acid, azelaic acid, suberic acid, dodecanedioic acid, dimethylolpropionic acid, polymeric acids, oleic acid, citric acid.

18. A transparent conductive film comprising a substrate, and a silver nanowire film on the substrate, wherein the silver nanowire film is prepared by coating the silver nanowire coating solution of any one of claims 1 to 17 on the substrate and drying the coating solution.

19. The transparent conductive film according to claim 18, wherein the drying temperature is 50 to 300 ℃ and the drying time is 1S to 30 min.

20. The transparent conductive film according to claim 18, wherein the drying temperature is 80 to 250 ℃ and the drying time is 10S to 20 min.

21. The transparent conductive film according to claim 18, wherein the drying temperature is 100 to 200 ℃ and the drying time is 20S to 10 min.