HK1235545A1 - Metal nanowire inks for the formation of transparent conductive films with fused networks - Google Patents

Description

Metal nanowire inks for forming transparent conductive films with fused networks

Technical Field

The present invention relates to inks comprising metal nanowires suitable for forming transparent conductive films, especially films forming fused nanostructured metal networks. The invention further relates to structures formed with the inks and methods of making and using the inks.

Background

Functional films can provide important functions in a range of situations. For example, conductive films can be important for static dissipation when static can be undesirable or dangerous. Optical films can be used to provide various functions such as polarizing, anti-reflective, phase shifting, brightness enhancement, or other functions. High quality displays may include one or more optical coatings.

Transparent conductors can be used in a number of optoelectronic applications, including, for example, touch screens, Liquid Crystal Displays (LCDs), flat panel displays, Organic Light Emitting Diodes (OLEDs), solar cells, and smart windows. Historically, Indium Tin Oxide (ITO) has been the material of choice due to its relatively high transparency at high conductivity. However, ITO has several disadvantages. For example, ITO is a brittle ceramic that requires deposition using sputtering, a manufacturing process that involves high temperatures and vacuum, and is therefore relatively slow and not cost effective. In addition, ITO is known to crack easily on flexible substrates.

Disclosure of Invention

In a first aspect, the present invention relates to a metal nanowire ink comprising from about 0.001 wt% to about 4 wt% metal nanowires, from about 0.05 wt% to about 5 wt% hydrophilic polymer binder, and from about 0.0001 wt% to about 0.5 wt% metal ions.

In another aspect, the present invention relates to a metal nanowire ink comprising from about 0.001 wt% to about 4 wt% metal nanowires, from about 0.0001 wt% to about 0.5 wt% metal ions, and from about 20 wt% to about 60 wt% aqueous liquid alcohol solution (pH of from about 5.5 to about 7.5 pH units).

In another aspect, the present invention relates to a transparent conductive film comprising a fused metal nanostructured network and a polymeric polyol, wherein the film comprises about 40% to about 600% polymeric polyol by weight relative to the weight of the metal.

In an additional aspect, the present disclosure relates to a method of forming a transparent conductive network comprising depositing a fused metal nanowire ink onto a substrate surface and drying the metal nanowire ink to form a transparent conductive film. The metal nanowire ink may comprise from about 0.001 wt% to about 4 wt% metal nanowires, from about 0.05 wt% to about 5 wt% hydrophilic polymer binder, and from about 0.0001 wt% to about 0.5 wt% metal ions. The transparent conductive film formed after the drying step may include fused metal nanowires in the form of a fused metal nanostructured network having a sheet resistance of no more than about 250 ohms/square.

In other aspects, the invention relates to a transparent conductive film comprising a sparse metal conductive element having a sheet resistance of about 45 to about 250 ohms/square and a haze of no more than about 0.8%, or a sheet resistance of about 30 to about 45 ohms/square and a haze of about 0.7 to about 1.2%.

Further, the present invention may relate to a method of sintering a metal nanowire ink having metal ions as deposited, the method comprising drying a metal nanowire film at a temperature of about 60 ℃ to about 99 ℃ for at least about 1 minute at a relative humidity of at least about 40%. In some embodiments, the metal nanowire film is formed via deposition of a metal nanowire ink comprising about 0.001 wt% to about 4 wt% metal nanowires, about 0.05 wt% to about 5 wt% hydrophilic polymer binder, and about 0.0002 wt% to about 0.5 wt% metal ions.

Drawings

Fig. 1 is a schematic diagram showing a fused metal network forming a conductive pattern in a single path along a substrate surface.

Fig. 2 is a schematic diagram showing a fused metal nanostructured film forming a conductive pattern with a plurality of conductive paths along the substrate surface.

FIG. 3 is a side view of the substrate and the fused film of FIG. 2, taken along arrows 3, with a polymer overcoat placed on the conductive film.

Fig. 4 is a side view of an alternative embodiment of a substrate and a fused film with conductive metal wires patterned under an overcoat.

FIG. 5 is a top view of a patterned film having a metal trace and a polymer overcoat layer configured for incorporation into a touch screen or other sensor device.

Fig. 6 is a schematic diagram showing a process flow of disposing a conductive metal trace in contact with a patterned film and depositing an outer polymer coating on the metal trace and the patterned film.

Fig. 7 is a schematic diagram showing a capacitance-based touch sensor.

Fig. 8 is a schematic diagram showing a resistance-based touch sensor.

Fig. 9 is a photograph of nine different ink systems after two weeks of storage without mixing.

Fig. 10 is a graph of sheet resistance for four samples dried under different conditions before application of an overcoat.

Detailed Description

Stable metal nanowire inks provide for the formation of transparent conductive films with excellent optical properties and low sheet resistance, wherein the sparse metal conductive layer generally comprises a fused nanostructured metal network with a polymeric binder formed under controlled conditions. Inks typically comprise metal nanowires, a dispersion of metal ions as a thickener and an aqueous system comprising a polymeric binder. In some embodiments, the ink includes an alcohol, which can impart desirable properties to the ink and/or treat the ink as a film. In some embodiments, the stable ink has a pH towards neutral, as further described below, which facilitates handling and can form an effective stable fused metal nanowire ink without the addition of an acid. The ink may be stable with respect to avoiding settling for a significant period of time to provide convenient handling under commercially reasonable circumstances. The resulting transparent conductive films can have low sheet resistance as well as good optical properties, such as high optical transparency and low haze, and very low haze values have been achieved with reasonably low sheet resistance values. The transparent conductive film may be patterned via printing into a desired pattern and/or by etching the film to form the desired pattern. Transparent conductive films can be incorporated into a range of products such as touch sensors or photovoltaic devices.

Silver nanowire-based films have been commercially used for forming transparent conductive electrodes or the like. The metal in the nanowires is inherently conductive, but in structures formed with metal nanowires, insufficient contact between wires can create resistance to provide longer range conductance. Efforts to improve the conductivity of metal nanowire films may be based on improving nanowire characteristics as well as improving the contact at junctions between adjacent metal nanowires. It has been found that the fusion of adjacent metal nanowires to form a fused nanostructured metal network can be a flexible and efficient method of forming transparent conductive films having desirable characteristics.

As noted above, the sparse metal conductive layer can be effectively formed from metal nanowires. In particularly interesting embodiments, the metal nanostructure network can be formed of fused metal nanowires with desirable results with respect to forming a transparent conductive film. In particular, fused metal nanostructured networks can be formed with excellent electrical and optical quality, can be suitably patterned, and can be combined with a polymeric binder to form an initially stable conductive film. Metal nanostructure networks formed from fused metal nanowires provide a desirable alternative to other nanowire-based transparent conductive film structures.

The metal nanowires can be formed from a range of metals, and the metal nanowires are commercially available. While metal nanowires are inherently conductive, the vast majority of the resistance in metal nanowire-based films is believed to be due to incomplete bonding between nanowires. Depending on processing conditions and nanowire characteristics, the sheet resistance of a relatively transparent nanowire film when deposited without fusing can be very large, for example in the gigaohm/square range or even higher, although similar unfused films may not necessarily be large. Various methods have been proposed to reduce the resistance of nanowire films without destroying optical transparency. It has been found that low temperature chemical fusion to form a metallic nanostructured network is extremely effective in reducing electrical resistance while maintaining optical transparency. The use of a fused metal nanowire film provides significant stability of the conductive film and provides highly desirable properties, particularly less critical dependence on metal nanowire characteristics.

In particular, a significant advance in achieving metal nanowire-based conductive films has been the discovery of a sufficiently controllable process of forming a fused metal network in which adjacent portions of the metal nanowires are fused. In particular, it was found in previous work that halide ions can drive the fusing of metal nanowires to form fused metal nanostructures. The incorporation of a fusing agent comprising a halide anion in various ways to successfully achieve fusing with a corresponding sharp drop in resistance. In particular, the fusing of metal nanowires with halide anions has been accomplished with vapors and/or solutions of acidic halides and halogen salt solutions. The fusion of Metal nanowires with a halide source is further described in Virkar et al, published U.S. patent application 2013/0341074 entitled "Metal Nanowire Networks and Transmission connective Material" and in Virkar et al, 2013/0342221 entitled "Metal Nanostructured Networks and Transmission connective Material" (the' 221 application), both of which are incorporated herein by reference. The' 221 application describes efficient patterning based on selective delivery of hydrochloric acid vapor for forming high conductivity contrast patterns that are effectively invisible to a normal observer under room illumination.

The metal halide formed along the surface of the metal nanowires is believed to increase the mobility/diffusivity of the metal ions, causing the points of contact or near-contact between the nanowires to fuse, forming a fused network. Evidence suggests that when a halide thickener is used, a metal halide shell forms on the resulting fused nanowire network. While not wishing to be bound by theory, it is believed that when a fused network is formed by the net motion of metal atoms within the nanostructure, the metal halide coated on the metal nanowires causes the metal atoms/ions to move from the nanowires, such that the moving ions condense to form bonds between adjacent nanowires, forming a nanostructured network and possibly lowering the free energy.

The extension of the process for forming the fused metal nanowire network is based on reduction/oxidation (redox) reactions that can be provided to produce the fused nanowires without destroying the optical properties of the resulting film. Without wishing to be bound by theory, the driving force appears to also decrease the free energy via metal migration to the junction to form a fused nanostructured network. The metal deposited at the junction may be effectively added as a dissolved metal salt or may be dissolved from the metal nanowire itself. Effective use of redox chemistry for Fusing Metal nanowires into Nanostructured Networks is further described in Virkar et al, published U.S. patent application 2014-0238833 (application 833) entitled "Fused Metal Nanostructured Networks, Fused Solutions With Reducing Agents and Methods for Forming Metal Networks," which is incorporated herein by reference. The' 833 application also describes a single solution process for forming a fused metal nanostructure network, and describes herein a stable ink for single solution deposition for forming a fused metal nanostructure network with excellent performance.

Another method of nanowire fusion has been described based on providing a high pH, i.e., basic, fusion solution to a metal nanowire film. See, e.g., published U.S. patent application 2015-0144380('380 application) to Yang et al, entitled "TRANSPARENT connective Based on Metal Nanowings and Polymer Binders, Solution Processing theory, and Pattern applications," which is incorporated herein by reference. Generally, to achieve effective fusion, the pH can be greater than about 9.5 pH units. It is believed that the alkaline conditions are effective to move the metal ions along the surface of the metal nanowires. Subsequently, the metal selectively migrates to a contact point or a nearly contact point between adjacent metal nanowires to fuse the wires. Thus, basic fusion provides another alternative to halide-based fusion or redox-based fusion.

For some applications, it is desirable to pattern the conductive portions of the film to introduce a desired function, such as a unique area of the touch sensor. Of course, the patterning can be done by just changing the metal loading on the substrate surface: by printing metal nanowires at selected locations while other locations are effectively devoid of metal, or etching or otherwise ablating metal from selected locations to remove at least some of the metal at the etched/ablated locations. Various masking, focused radiation, lithographic techniques, combinations thereof, or the like may be used to support the patterning method.

In a single solution or one ink system, dissolved metal ions can be provided as a metal source, such that corresponding inks that are free of metal ions are not typically observed to result in metal nanowire condensation. For one ink system, it has been found that maintaining the pH between about 1.5 pH units and 8 pH units or a narrower range can desirably limit metal mobility and improve stability in the ink. At these pH values, since moderate pH values do not cause significant metal migration from the wire, fusion is still observed by proper formulation of the ink based on the metal ions added to the ink. In some embodiments, suitable fused metal nanowire inks can be formed without the addition of an acid, although some amount of acid can still be effectively used to form a transparent conductive film. In some processing situations, less acidic inks may also be desirable from a processing standpoint, as acids may corrode some processing equipment, and it may also be desirable to avoid low pH inks. While binder selection has been diversified for the two ink systems with unique fusing solutions outlined above added to the nanowire film as deposited, while providing good fusing and corresponding desirable film properties for a stable one, it has been found that hydrophilic polymers facilitate fusing to achieve the desired low sheet resistance in the resulting film. The fusing is believed to occur during the drying process when the concentration of the various components increases upon removal of the solvent. As described further below, in some embodiments, improved fusing may be achieved using a more gradual drying process under humid conditions.

A desirable ink that cures into an effective single deposition ink of fused nanostructured metal networks includes the desired amount of metal nanowires to achieve proper metal loading in the resulting film. In an appropriate solution, the ink is stable prior to deposition and drying. The ink may include a reasonable amount of polymer binder that facilitates stable conductive film formation for further processing. To obtain good fusion results, hydrophilic polymers, such as cellulose or chitosan based polymers, have been found to be effective. As a metal source for the fusion process, the metal ions are supplied as soluble metal salts.

As demonstrated in the examples, low thin resistive films can be formed with suitable other ink components in the absence of alcohol solvents. In particular, some suitable polymeric binders may have functional groups that can reduce the metal ions used to drive the fusing process. However, it may be desirable for the solvent used in the ink to be an aqueous alcohol solution. In some embodiments, the solution may include about 5 wt% to about 80 wt% alcohol relative to the total liquid. Typically, the majority of the liquid remainder is water, although some amount of other organic solvent may be used. In additional or alternative embodiments, blends of alcohols have been used with efficacy. In particular, blends of isopropanol and ethanol have been found to produce inks with good stability and fusing characteristics. Stability is discussed further below, but stable inks generally have no solids settling after 1 hour of settling without agitation, and have limited visible separation after two weeks of settling without agitation.

By one ink treatment, metal nanowire ink fusing with improved stability has generally been achieved without significant acidification of the ink while still providing good fusing of the metal nanowires. Furthermore, to reduce corrosion of processing equipment, it may be desirable for the pH of the ink to not be highly acidic. In some embodiments, some mild acidification may be performed to improve the dissolution of the polymeric binder and/or to facilitate the fusion process to another degree. Acidification to a pH of less than about 1.5 pH units, and in some embodiments less than about 3 pH units, generally results in an ink with undesirable acidity. It has been found that good fusion of metal nanowires can be achieved without strong acidification. Thus, the use of metal ions as a metal source without any acidification or strengthening of the ink is surprisingly effective in forming an ink for direct treatment against the fused nanostructured metal network. However, there may be specific applications where greater acidification may be tolerated and may provide desirable conductive films.

The use of a two-solution process with separate fused solutions has provided greater flexibility in forming patterns with fused and unfused regions with similar metal loadings. Upon formation, an un-fused film with a polymer binder can be formed with a high sheet resistance value. The formation of a fused metal nanostructured metal network using a single solution suggests a metal-loading based patterning process. In particular, patterning methods include, for example, printing ink to directly form a pattern (where the formed areas are free of ink) and/or removing portions of the deposited ink to reduce its conductivity. As explained further below, removal of the metal loading from regions of the substrate may generally be performed before or after drying to complete the fusion and/or may involve some or substantially all of the metal in selected regions.

The metal nanowires are fused to form a fused nanostructured metal network by an ink treatment. The optical properties correspond to those of the sparse metal layer, and good optical transparency and low haze can be exhibited. The resulting film may exhibit unique characteristics that are clearly consistent with the concept of adjacent metal nanowire fusion. As a starting material, previous work involving a single ink fusion process was examined by electron microscopy, where the image shows the fused connection between adjacent wires. See, for example, the above-referenced' 221 application. Similar micrographs of the inventive membrane showing the fusion of metal nanowires into a fused network have been obtained. Furthermore, the control solution without metal ions did not exhibit the very low sheet resistance achieved observed with the fused system. Additional evidence is found in the data for curing/drying processes carried out in a humid atmosphere. For some silver nanowires, the fusion process appears to progress slower, and the fusion can be performed for an extended period of time. Drying may be performed in a humid atmosphere to more slowly dry the film and provide additional fusing of the metal structure with a corresponding reduction in sheet resistance observed. In addition, it is important that the fused nanostructured metal network provide stability to the resulting transparent conductive film, allowing the formation of structures incorporating the film, which applicants believe have not been achieved with conventional unfused metal nanowire films. Thus, films with fused nanostructured metal networks may be more suitable than unfused nanowire films for applications in devices with stretchable and bendable transparent conductive films. The formed Transparent Conductive film is described in co-pending U.S. patent application 61/978,607 entitled "Formable Transparent Conductive Films With metallic nanotubes" to Kambe et al, which is incorporated herein by reference.

In some embodiments of particular interest, the metal nanowire inks are stable in that no solid settling is observed after one hour or possibly more without agitation. Of course, for use, the ink may be stirred immediately prior to use to ensure the desired level of uniformity and performance. However, the stability of the ink can provide desirable commercial advantages with respect to shelf life and handling methods. Consistent with the formation of stable inks, the rheology of the inks can be adjusted within reasonable ranges to provide commercial deposition processes.

Various printing methods can be used to print the ink in a pattern on the substrate. For example, photolithography may be used for patterning. For example, a photoresist, such as a commercially available composition, can be used to block portions of the substrate from which resist is subsequently removed, correspondingly removing metal loading not associated with the exposed substrate. Alternatively, screen printing, spray coating, gravure printing, or the like can be used to selectively deposit the metal nanowire ink onto portions of the substrate. Alternatively or additionally, the metal load may be partially removed after deposition onto the substrate, e.g., via etching or the like. The partial removal of the metal loading may include partial or complete removal of the metal at selected locations. Suitable etching methods include, for example, radiation-based etching and/or chemical etching. Radiation-based etching may be performed by focused radiation or masking to control exposure to radiation. For example, a laser or focused electron beam may be used for focused radiation etching. The focused radiation can also be effectively masked. With respect to chemical etching, masking may be used to control the chemical etching. For example, photolithography may be used to form patterns for direct chemical etching.

To be incorporated into a product, a protective layer is typically placed on a transparent conductive film and formed into a stacked structure having structures that can be subsequently incorporated into the product. While a range of structures may be formed to suit a particular product specification, a typical structure may include one or more layers as a substrate, a conductive film with or without patterning on the substrate, and one or more top coats. Thicker laminate top coats can be effectively used to protect conductive films.

Conductive films formed by a single ink fusing process can achieve a desirably low level of sheet resistance, e.g., no more than about 75 ohms/square. Of course, the sheet resistance may be adjusted with various parameters (e.g., metal loading), and very low levels of sheet resistance may not be specified for lower cost components. At the same time, the films can have very good optical transparency and low haze with low sheet resistance. Thus, the resulting structure is well suited for a range of applications of transparent conductive electrodes.

Ink composition and characteristics

A single ink formulation deposits the desired metal loading as a film on the substrate surface while providing a component in the ink that induces the fusion process when the ink is dried under appropriate conditions. These inks may be suitably referred to as fused metal nanowire inks, with the understanding that fusing generally does not occur until drying. The ink generally includes an aqueous solvent, which in some embodiments may further include an alcohol and/or other organic solvent. The ink may further include a dissolved metal salt as a metal source for the fusing process. Without wishing to be bound by theory, it is believed that the components of the ink (e.g., the alcohol) reduce the metal ions from the solution that are used to drive the fusing process. Previous experience with the fusion process in these systems has shown that metal is preferentially deposited at the junctions between adjacent metal nanowires. A polymeric binder may be provided to stabilize the film and affect the ink characteristics. The particular formulation of the ink can be adjusted to select ink characteristics suitable for a particular deposition method and having particular coating characteristics desired. It has been found that in the case of an ink system to form a fused metal nanostructured network, desirable sheet resistance values can be achieved with hydrophilic polymers, such as cellulose-based polymers or chitosan-based polymers. As described further below, the drying conditions can be selected to effectively carry out the fusion process.

Thus, for the improved embodiments described herein, the fused metal nanowire inks may generally include metal nanowires, an aqueous solvent, a dissolved metal salt, an optional hydrophilic polymer binder, and optionally other additives. The concentration of the metal nanowires affects the fluid properties of the ink and the metal loading deposited onto the substrate. The metal nanowire ink may generally include from about 0.001 wt% to about 4 wt% metal nanowires, in other embodiments from about 0.005 wt% to about 2 wt% metal nanowires, and in additional embodiments from about 0.01 wt% to about 1 wt% metal nanowires. One of ordinary skill will recognize that additional ranges of metal nanowire concentrations within the explicit ranges above are contemplated and are within the present invention.

In general, nanowires can be formed from a range of metals, such as silver, gold, indium, tin, iron, cobalt, platinum, palladium, nickel, cobalt, titanium, copper, and alloys thereof, which can be desirable due to high electrical conductivity. Commercial metal nanowires are commercially available from Sigma-Aldrich (Missouri, u.s.a.), cagzhou Nano-Channel Material co., Ltd. (China), Blue Nano (North Carolina, u.s.a.), emfutur (spain), Seashell Technologies (California, u.s.a.), aiden (korea), nanocomix (u.s.a.), K & b (korea), ACS Materials (China), chuang Advanced Materials (China), and Nanotrons (u.s.a.). Alternatively, silver nanowires can also be synthesized using various known synthesis routes or variations thereof. Silver in particular provides excellent electrical conductivity and commercial silver nanowires are available. To have good transparency and low haze, the nanowires are required to have a small diameter range. In particular, it is desirable that the average diameter of the metal nanowires be no more than about 250nm, in other embodiments no more than about 150nm, and in other embodiments from about 10nm to about 120 nm. With respect to average length, nanowires of longer length are expected to provide better conductivity within the network. In general, the average length of the metal nanowires may be at least one micron, in other embodiments at least 2.5 microns and in other embodiments from about 5 microns to about 100 microns, although future developed improved synthesis techniques may enable longer nanowires. Aspect ratios can be specified as the ratio of the average length divided by the average diameter, and in some embodiments the aspect ratio of the nanowires can be at least about 25, in other embodiments from about 50 to about 10,000, and in additional embodiments from about 100 to about 2000. One of ordinary skill will recognize that additional ranges of nanowire sizes within the explicit ranges above are contemplated and are within the present invention.

Solvents for the inks generally include aqueous solvents that optionally also include alcohols. Alcohols can provide the ability to reduce driven nanowire condensation and can provide desirable ink characteristics, such as improved coating quality. For embodiments including an alcohol, the solvent may include water and from about 5 wt% to about 80 wt% alcohol, in other embodiments from about 10 wt% to about 70 wt%, in additional embodiments from about 15 wt% to about 65 wt%, and in other embodiments from about 20 wt% to about 60 wt% alcohol. Suitable alcohols are generally soluble or miscible in water within a suitable concentration range and include, for example, short chain alcohols such as methanol, ethanol, isopropanol, isobutanol, tertiary butanol, other alcohols having a straight or branched chain containing up to 7 carbon atoms, ethylene glycol, propylene glycol, diacetone alcohol, ethyl lactate, methoxyethanol, methoxypropanol, other glycol ethers (such as alkyl cellosolve and alkyl carbitol) or the like or blends thereof. Solvents comprising a blend of isopropanol and ethanol in an aqueous solvent are described in the examples below. In some embodiments, the solvent may optionally include small amounts of other soluble organic liquids including, for example, ketones, esters, ethers (e.g., glycol ethers), aromatics, alkanes, and the like, and mixtures thereof, such as methyl ethyl ketone, glycol ethers, methyl isobutyl ketone, toluene, hexane, ethyl acetate, butyl acetate, PGMEA (2-methoxy-1-methyl ethyl acetate), or mixtures thereof. If the optional organic solvent is present, the nanowire ink typically includes no more than about 10 wt% non-alcoholic organic solvent, in other embodiments from about 0.5 wt% to about 8 wt%, and in additional embodiments from about 1 wt% to about 6 wt% non-alcoholic organic solvent. One of ordinary skill will recognize that additional ranges of solvent concentrations within the explicit ranges above are contemplated and are within the present invention.

The metal ions provide a metal source for the fused metal nanowires, and the ink includes a suitable concentration of metal ions. Metal ions are supplied as dissolved salts in the solvent. Generally, the metal nanowire inks include from about 0.0001 wt% to about 0.5 wt% metal ions, in other embodiments from about 0.00025 wt% to about 0.075 wt%, in other embodiments from about 0.0003 wt% to about 0.06 wt%, in additional embodiments from about 0.0005 wt% to about 0.05 wt%, and in some embodiments, from about 0.00075 wt% to about 0.025 wt% metal ions. One of ordinary skill will recognize that additional ranges within the explicit ranges of metal ion concentrations described above are contemplated and are within the present invention. The metal salt also includes a counter ion, which is generally considered to be inert during film formation, although the selection of a particular salt should provide complete and rapid solubility in the solvent of the ink. In general, suitable anions include, for example, nitrate, sulfate, perchlorate, acetate, fluoride, chloride, bromide, iodide, and the like. The particular anion selection may be slightly photolytically responsive to metal ion activity due to some mismatching with ions in solution, and may be empirically adjusted based on the teachings herein. The metal ions generally correspond to the metal element of the nanowires, and thus in the case of silver nanowires, silver salts are generally used to supply the metal ions used to fuse the nanowires. However, if the metal element corresponding to the metal ion corresponds to a metal element having an oxidation potential approximately similar to or greater than (i.e., more difficult to oxidize) the metal of the nanowire, it is possible to use other metal ions or combinations thereof. Thus, for silver nanowires, gold ions, platinum ions, palladium ions, zinc ions, nickel ions, or the like may be used in addition to or as an alternative to silver ions, and the appropriate ions for other nanowires may be similarly selected based on the teachings herein.

The pH of the fused metal nanowire ink may or may not be adjusted by the addition of an acid. In some embodiments, it has been found that stable metal nanowire inks can be formed without the addition of an acid, resulting in inks having a relatively neutral pH, e.g., from about 5.5 pH units to about 8 pH units. If no acid is added, the pH is determined by the purity of the component solvent, dissolved CO₂The nature of the additives (e.g., polymeric binders), and the like. The addition of acid may be required to facilitate dissolution of the polymer binder, affect the properties of the transparent conductive film, affect other properties of the ink, or for other reasons. From a handling standpoint, inks that are not excessively acidic may be desirable for reducing corrosion of process equipment. Thus, in some embodiments, the ink pH is desirably from about 3 pH units to about 8 pH units, in other embodiments from about 3.4 pH units to about 7.6 pH units, and in additional embodiments from about 3.8 pH units to about 7.3 pH units. In alternative embodiments, more acidic inks may be used, but at sufficiently high acidity, the stability of the ink may generally become difficult to maintain. For more acidic stable inks, the pH is generally maintained at a value of no less than about 1.5 pH units, in other embodiments no less than about 1.75, and in additional embodiments from about 2 pH units to about 3 pH units. The skilled artisan will recognize that additional ranges of pH are contemplated and within the present invention. In general, any reasonable acid may be used to adjust the pH, such as strong acids, e.g., nitric acid, sulfuric acid, perchloric acid, hydrochloric acid, sulfonic acids, and the like, or weak acids, e.g., acetic acid, citric acid, other carboxylic acids, or the like, for higher pH values. The particular acid and pH are generally selected to avoid damage to the polymeric binder and other ink components.

The ink may optionally include a hydrophilic polymer component dissolved in a solvent. The ink generally includes from about 0.01 wt% to about 5 wt% hydrophilic polymer, in additional embodiments from about 0.02 wt% to about 4 wt% and in other embodiments from about 0.05 wt% to about 2 wt% hydrophilic polymer. The skilled artisan will recognize that additional ranges of hydrophilic polymer concentrations within the explicit ranges above are contemplated and are within the present invention. As used herein, the term polymer is used to refer to molecules having an average molecular weight of at least about 1000 grams/mole, and polymers in pure form of particular interest are solids, although in some embodiments crosslinking may be introduced after deposition to alter polymer properties. Some polymers may be difficult to evaluate with respect to molecular weight, and cellulose-based polymers may be such polymers. However, polymers that are difficult to evaluate with respect to molecular weight are generally understood to have at least moderate molecular weights and will be recognized as having molecular weights greater than 500 grams/mole, even though more specific values are difficult to assign to a composition due to the macromolecular nature of the composition. Hydrophilic polymers generally include polar functional groups such as hydroxyl groups, amide groups, amine groups, acid groups, and the like, and suitable polymers having multiple hydroxyl groups, which may be referred to as polymeric polyols. Polysaccharides are one type of polymeric polyol that can have desirable properties for ink formation. The polysaccharide is a sugar polymer having a plurality of hydroxyl groups or a derivative thereof. Polysaccharides include, for example, cellulose-based polymers and chitosan-based polymers, and desirable inks based on these binders are described in the examples below. Cellulose-based polymers include cellulose esters and cellulose ethers, which are formed by partially digesting natural cellulose and reacting a portion of the hydroxyl groups in the cellulose. Specific cellulose-based polymers include, for example, cellulose acetate, cellulose propionate, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, and the like. In general, commercial cellulose-based polymers are not characterized by molecular weight, but it can be assumed that the average molecular weight of these polymers is within the range of the polymers as specified herein. Similarly, chitosan is a polysaccharide made by reacting the natural product chitin found in the shell of crustaceans and in fungi. Chitosan may be characterized by the degree of deacetylation of native chitin and a molecular weight generally in the range of about 3500 g/mol to about 220,000 g/mol. Chitosan is soluble in dilute aqueous acid and can be incorporated into nanowire inks using, for example, weak carboxylic acids.

Although it has been found that the presence of the hydrophilic polymer in the ink is significant when a binder is used in the ink, additional polymeric binders may be effectively included with the hydrophilic polymer. Suitable adhesives include polymers that have been developed for coating applications. Crosslinkable scratch-resistant protective coatings (which may be referred to as hardcoat polymers or resins, such as radiation curable coatings) are commercially available, for example, as curable (e.g., crosslinkable) materials for a range of applications, which may be selected for dissolution in aqueous or non-aqueous solvents. Suitable classes of radiation curable polymers include, for example, polyurethanes, acrylics, acrylic copolymers, polyethers, polyesters, epoxy-containing polymers, and mixtures thereof. As used herein, polymeric polyols are not considered hardcoat polymers. Examples of commercial polymeric binders include, for exampleAcrylic resin (DMS NeoResins (DMS) and acrylic resin (DMS NeoResins)),acrylic copolymers (BASFResins),Acrylic resin (Lucite International),Carbamate (Lubrizol advanced materials), BAYHYDROL^TM(ii) polyurethane dispersions of brands (Bayer MaterialScience),Polyurethane dispersions (Cytec Industries, Inc.) are known,Card holderVinyl butyral (Kuraray America, Inc.), polyvinyl acetate, mixtures thereof, and the like. The polymeric binder may self-crosslink upon exposure to radiation, and/or it may crosslink with a photoinitiator or other crosslinking agent. In some embodiments, the photocrosslinker may form radicals upon exposure to radiation, and the radicals subsequently induce a crosslinking reaction based on the radical polymerization mechanism. Suitable photoinitiators include, for example, commercially available products, e.g.Playing card (BASF), GENOCURE^TMBrands (Rahn USACorp.) andbrand name (Double Bond Chemical ind., Co, Ltd.), combinations thereof, or the like.

If a UV curable resin binder is used with a hydrophilic binder (e.g., a polymeric polyol), the ink generally includes from about 0.01 wt% to about 2.5 wt% curable binder, in other embodiments from about 0.025 wt% to about 2 wt%, and in additional embodiments, from about 0.05 wt% to about 1.5 wt% curable binder. To facilitate crosslinking of the binder, the metal nanowire ink may include about 0.0005 wt% to about 1 wt% of a crosslinking agent (e.g., a photoinitiator), in other embodiments about 0.002 wt% to about 0.5 wt%, and in additional embodiments about 0.005 to about 0.25 wt%. The skilled artisan will recognize that additional ranges of curable adhesives and crosslinkers within the explicit ranges above are contemplated and within the present invention. Applicants have found that, in some embodiments, the combination of at least a hydrophilic adhesive with a curable resin (e.g., a hardcoat adhesive) can provide advantageous properties to the transparent conductive film. In particular, the hydrophilic polymer facilitates the fusing process of one ink format such that desirably low sheet resistance values can be achieved, while the curable resin is believed to provide protection to the film from environmental degradation after incorporation into the product.

The nanowire inks can optionally include a rheology modifier or a combination thereof. In some embodiments, the ink may include a humectant or surfactant to reduce surface tension, and the humectant may be useful to improve coating properties. The humectant is generally soluble in the solvent. In some embodiments, the nanowire ink may include from about 0.01 wt% to about 1 wt% humectant, in other embodiments from about 0.02 wt% to about 0.75 wt%, and in other embodiments, from about 0.03 wt% to about 0.6 wt% humectant. Thickeners may optionally be used as rheology modifiers to stabilize the dispersion and reduce or eliminate settling. In some embodiments, the nanowire ink may optionally include from about 0.05 wt% to about 5 wt% thickener, in other embodiments from about 0.075 wt% to about 4 wt%, and in other embodiments, from about 0.1 wt% to about 3 wt% thickener. The skilled artisan will recognize that additional ranges of humectant and thickener concentrations within the above-identified ranges are contemplated and within the present invention.

The wetting agent can be used to improve coatability of the metal nanowire ink and 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 commercial humectants include, for example, COATOSIL^TMBranded epoxy functionalized silane oligomers (momentumPerformance Materials), SILWET^TMBrand organopolysiloxane surfactants (Momentum PerformanceMaterials), THETAWET^TM(iii) short chain nonionic fluorosurfactants (ICT Industries, Inc.),Brand polymeric dispersants (Air Products Inc.),Branded polymeric dispersant (Lubrizol), XOANON WE-D545 surfactant (Anhui Xoarons Chemical Co., Ltd.), EFKA^TMPU4009 polymeric dispersant (BASF), MASURF FP-815CP, MASURF FS-910(Mason Chemicals), NOVEC^TMFC-4430 fluorinated surfactant (3M), mixtures thereof, and the like.

Thickeners can be used to improve the stability of the dispersion by reducing or eliminating settling of solids from the metal nanowire ink. Thickeners may or may not significantly alter the viscosity or other fluid properties of the ink. Suitable thickeners are commercially available and include, for example, CRAYVALLAC^TMModified ureas of brand name (e.g., LA-100) (Cray Valley acrylic, USA), polyacrylamide, THIXOL^TM53L brand acrylic thickener, COAPUR^TM2025、COAPUR^TM830W、COAPUR^TM6050、COAPUR^TMXS71(Coatex,Inc.)、Modified ureas of brand name (BYK Additives), Acrysol DR 73, Acrysol RM-995, Acrysol RM-8W (Dow Coating materials), Aquaflow NHS-300, Aquaflow XLS-530 hydrophobically modified polyether thickeners (Ashland Inc.), Borchi Gel L75N, Borchi Gel PW25(OMGBorchers), and the like.

Additional additives may be added to the metal nanowire inks, typically each in an amount of no more than about 5 wt%, in other embodiments no more than about 2 wt%, and in other embodiments no more than about 1 wt%. Other additives may include, for example, antioxidants, UV stabilizers, defoamers or anti-foaming agents, anti-settling agents, viscosity modifiers, or the like.

In general, the ink may be formed in any reasonable order of the combined components, but in some embodiments it may be desirable to begin with a preferred dispersion of the metal nanowires. The metal nanowires are typically dispersed in water, alcohol, or blends thereof. Suitable mixing methods can be used to blend the ink with the added components.

The fully blended ink may be stable with respect to settling without continuous stirring. For example, a stable ink may have no visible settling after one hour without any agitation. Visible settling can be assessed as visible inhomogeneity of the solids on the bottom of the container and/or the ink-containing container from top to bottom. In some embodiments, the fused metal nanowire inks do not settle out of solids for at least one day, in other embodiments for at least three days, and in additional embodiments for at least one week, although the inks may not exhibit solid self-dispersion settling for a significantly longer period of time. In some embodiments, the fused metal nanowire ink may be free of visible inhomogeneities after at least 4 hours, in additional embodiments at least one day, and in other embodiments at least 4 days without agitation, although the ink may stabilize visible inhomogeneities for a significantly longer period of time. The skilled artisan will recognize that additional ranges of sedimentation stability periods within the explicit ranges above are contemplated and are within the present invention. Of course in a commercial environment, the ink will be stirred immediately prior to use to ensure very thorough mixing of the solution for deposition, and some settling should not interfere with good thorough mixing and well characterized ink for deposition. However, stable inks provide improved shelf life for storing finished inks before an undesirable degree of settling occurs, and reduced attention to mixing during ink use to maintain properly reproducible ink deposition. Therefore, the fused metal nanowire inks are well suited for commercial applications for forming transparent conductive films.

Ink and treatment of structures incorporating transparent conductive films

In a particularly interesting embodiment, a process is used wherein a sparse nanowire coating is initially formed with a fused metal nanowire ink and subsequent processing fuses the metal nanowires into a metal nanostructure network, which is electrically conductive. It is believed that the fusing process generally occurs during drying of the membrane. After drying, a fused nanostructured metal film is typically formed on the selected substrate surface. In general, the dried films have good optical properties, including, for example, transparency and low haze. As described further below, the processing may be suitable for patterning of films. One or more polymer overcoats, patterned or unpatterned, may be coated on the conductive film to provide protective coverage and the polymer may be selected to maintain optical transparency.

In general, suitable substrates can be selected as desired based on the particular application. The substrate surface may comprise, for example, a sheet of polymer, glass, inorganic semiconductor material, inorganic dielectric material, polymer glass laminate, composites thereof, or the like. Suitable polymers include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylates, poly (methyl methacrylate), polyolefins, polyvinyl chloride, fluoropolymers, polyamides, polyimides, polysulfones, polysiloxanes, polyetheretherketones, polynorbornenes, polyesters, polystyrenes, polyurethanes, polyvinyl alcohol, polyvinyl acetate, acrylonitrile-butadiene-styrene copolymers, polycarbonates, copolymers or blends thereof or the like. Further, the material may have a polymeric overcoat layer placed over the fused metal nanowire network, and the overcoat polymer may comprise the polymers listed for the above substrates and/or the curable resins described above contained in the ink, such as UV curable hardcoat polymers. Furthermore, other layers may be added on top of the conductive film and the substrate or between the two to reduce reflection losses and improve the overall transmission of the stack.

For deposition of the fused metal nanowire ink, any reasonable deposition method may be used, such as dip coating, spray coating, knife-edge coating, bar coating, Meyer-rod coating, slot-die coating, gravure printing, spin coating, or the like. The inks may have properties, such as viscosity, for the desired deposition method, suitably adjusted by additives. Similarly, the deposition method directs the amount of liquid deposition, and the concentration of the ink can be adjusted to provide the desired loading of the metal nanowires on the surface.

After forming the coating with the dispersion, the nanowire network can be dried to remove the liquid. It is believed that the fusing occurs during the drying of the liquid. The film may be dried, for example, with an air heating gun, oven, heat lamp, or the like, although films that may be air dried may be desirable in some embodiments. In general, the fusion is considered a low temperature process, and any application of heat to facilitate drying is incidental to the fusion. In some embodiments, the film may be heated during drying to a temperature of from about 50 ℃ to about 150 ℃, in other embodiments from about 60 ℃ to about 145 ℃, and in additional embodiments, from about 65 ℃ to about 135 ℃. The heating to drive drying may be performed for at least about 30 seconds, in other embodiments from about 45 seconds to about 2 hours, and in other embodiments from about 1 minute to about 45 minutes. In some embodiments, improved conductivity that may be associated with increased condensation within the network has been obtained by drying with increased humidity during the drying process. For example, the relative humidity may be set at about 15% to about 75%, in other embodiments about 20% to about 70%, and in additional embodiments about 25% to about 65%. The corresponding temperature when drying with increased humidity may be, for example, from about 50 ℃ to about 99 ℃, in other embodiments from about 60 ℃ to about 95 ℃, and in other embodiments from about 65 ℃ to about 90 ℃. Humidity naturally slows down drying time relative to an equivalent system without humidity, although humidity appears to improve and may speed up the fusing process. One of ordinary skill will recognize that additional ranges of temperature, drying time, and humidity within the explicit ranges above are contemplated and are within the present invention. The fusion is improved by drying at lower temperatures under more humid conditions in line with the chemically driven fusion process. After drying to induce the fusion process, the film may be washed, for example, with an alcohol or other solvent or solvent blend, such as ethanol or isopropanol, one or more times to remove excess solids to reduce turbidity.

After the metal nanowires are fused into a network, individual nanowires generally no longer exist, but the physical properties of the nanowires used to form the network can be reflected in the properties of the fused metal nanostructure network. Metal fusion is believed to contribute to the observed increased conductivity and to the good optical properties achievable at low levels of resistance. It is believed that the fusion occurs at the point of near contact of adjacent nanowires during processing. Thus, fusing may involve end-to-end fusing, sidewall-to-sidewall fusing, and end-to-sidewall fusing. The degree of fusion may be related to the processing conditions as indicated above in the case of humidity. Adjustment of processing conditions can be used to achieve good fusing without degradation of the fused nanowire network so that desirable film properties can be achieved.

The amount of nanowires transferred onto the substrate can involve a balance of factors to achieve the desired amount of transparency and conductivity. While the thickness of a nanowire network can in principle be estimated using scanning electron microscopy, the network can be relatively sparse to provide optical transparency, which can complicate the measurement. In general, the average thickness of the fused metal nanowire network will be no more than about 5 microns, in other embodiments no more than about 2 microns, and in other embodiments from about 10nm to about 500 nm. However, fused nanowire networks are generally relatively open structures with significant surface texture on the sub-micron scale, and thickness can generally be estimated using only indirect methods. The loading level of the nanowires can provide a suitable network parameter that can be easily evaluated, and the loading value provides an alternative parameter related to thickness. Thus, as used herein, the loading level of nanowires on a substrate is typically presented as milligrams of nanowires of a one-square meter substrate. In general, the loading of the nanowire network can be from about 0.1 milligrams (mg)/square meter to about 300mg/m²And in other embodiments about 0.5mg/m²To about 200mg/m²And in other embodiments about 1mg/m²To about 150mg/m². Those of ordinary skill will recognize that additional ranges of thicknesses and loads within the explicit ranges above are contemplated and are within the present invention.

It may be desirable for a polymer overcoat or layer to be placed on the metal layer, which may or may not be patterned. In general, the polymeric hardcoat adhesives described in the previous section may be suitable for use as a polymeric topcoat, although additional polymers may be used. Further, with respect to processing, the polymeric outer coating can be applied using solution coating techniques or other processing methods, such as extrusion, lamination, calendering, melt coating techniques, or the like. If multiple outer polymer coatings are present, they may or may not be applied using a similar process. For solution-treated topcoats, the various coating methods described above may be equally applicable to these layers. However, the solution treatment of the polymer overcoat can be directed to solvents that are not necessarily compatible with forming a good metal nanowire dispersion.

In general, the average thickness of the polymeric overcoat layer can be about 50 nanometers (nm) to about 25 microns, in other embodiments about 75nm to about 15 microns, and in additional embodiments about 100nm to about 10 microns. One of ordinary skill will recognize that additional ranges of overcoat thickness within the explicit ranges above are contemplated and are within the present invention. In some embodiments, it is possible to select the overcoat layer by choice of refractive index and thickness such that the pattern of conductive and insulating regions is less visible after application of the overcoat layer. The overcoat layer may contain conductive particles, which may have an average particle diameter in the range of about 3nm to 20 microns. The particles (i.e., conductive elements) can range from 0.0001 wt% to 1.0 wt% of the coating solution, which typically has between about 0.1 wt% and 80 wt% solids. These particles may be composed of metal or metal coatings, metal oxides, conductive organic materials and conductive allotropes of carbon (carbon nanotubes, fullerenes, graphene, carbon fibers, carbon black or the like), and mixtures of the foregoing materials. While the overcoat layer should not achieve a high level of conductivity, these conductive particles can allow for the deposition of thicker overcoat layers and still allow for the conductivity of trace electrodes. Additionally, an overcoat layer may be deposited on the conductive or patterned film after depositing the trace electrodes. This allows the use of thicker overcoats with corresponding stability advantages, while still allowing the conductivity between the transparent conductive layer and the silver (or other) bus to be maintained.

The overcoat may or may not cover the entire substrate surface. In general, the polymer used for the overcoat can be selected to have good optical clarity. In some embodiments, the optical properties of the film with the polymeric overcoat are not significantly different from the optical properties described above for the conductive film.

Electrical and optical properties of the film

Fused metal nanostructured networks can provide low electrical resistance while providing good optical properties. Therefore, the film can be suitably used as a transparent conductive electrode or the like. Transparent conductive electrodes may be suitable for a range of applications, such as electrodes along the light receiving surface of a solar cell. For displays and touch screens in particular, the films may be patterned to provide conductive patterns formed from the films. Substrates having patterned films generally have good optical properties in corresponding portions of the pattern.

Sheet resistance can be expressed as sheet resistance, which is reported in units of ohms/square (Ω/□ or ohms/square) to distinguish between sheet resistance and bulk resistance values according to parameters related to the method of measurement. The sheet resistance of the film is typically measured using a four-point probe measurement or equivalent method. In the examples below, the sheet resistance of the films was measured using a four point probe, or by making squares using a flash dried silver paste to define squares. The fused metal nanowire network may have a sheet resistance of no more than about 300 ohms/square, in other embodiments no more than about 200 ohms/square, in additional embodiments no more than about 100 ohms/square, and in other embodiments no more than about 60 ohms/square. One of ordinary skill will recognize that additional ranges of sheet resistance within the explicit ranges above are contemplated and are within the present invention. Depending on the particular application, commercial specifications for sheet resistance for use with a device may not necessarily be for lower sheet resistance values, such as when additional costs may be involved, and current commercially relevant values may be 270 ohms/square for example, as target values for touch screens of different quality and/or size, contrast 150 ohms/square, contrast 100 ohms/square, contrast 50 ohms/square, contrast 40 ohms/square, contrast 30 ohms/square, or 30 ohms/square or less, and each of these values defines a range between particular values as an endpoint of the range, such as 270 to 150 ohms/square, 270 to 100 ohms/square, 150 to 100 ohms/square, and the like, with 15 particular ranges defined. Thus, lower cost membranes may be suitable for certain applications in exchange for suitably higher sheet resistance values. In general, sheet resistance can be reduced by increasing nanowire loading, but from other perspectives, increasing loading may be undesirable, and metal loading is only one of many factors in achieving low sheet resistance values.

For application as transparent conductive films, it is desirable that the fused metal nanowire network maintain good optical transparency. In principle, optical transparency is inversely related to load, with higher loads leading to reduced transparency, although network processing can also significantly affect transparency. In addition, the polymeric binder and other additives may be selected to maintain good optical clarity. Optical clarity can be evaluated with respect to transmitted light through the substrate. For example, the transparency of the conductive films described herein can be measured by using a UV visible spectrophotometer and measuring the total transmission through the conductive film and the support substrate. The transmittance is the intensity of transmitted light (I) and the intensity of incident light (I)_o) The ratio of (a) to (b). Transmittance through film (T)_Film) Can be estimated by dividing the total transmittance (T) by the transmittance (T) through the support substrate_sub) To measure. (T ═ I/I)_oAnd T/T_sub＝(I/I_o)/(I_sub/I_o)＝I/I_sub＝T_Film) Thus, the reported total transmission can be corrected to remove the transmission through the substrate, obtaining only the transmission of the film. While it is generally desirable to have good optical transparency through the visible spectrum, for convenience, optical transmission can be reported as light at a wavelength of 550 nm. Alternatively or additionally, the total transmission of light that can be transmitted at wavelengths of 400nm to 700nm is reported, and such results are reported in the examples below. In general, for fused metal nanowire films, the measurements of 550nm transmittance and total transmittance (or simply "total transmittance" for convenience) of 400nm to 700nm are qualitatively different. In some embodiments, the total transmission (TT%) of the film formed from the fused network is at least 80%, in other embodiments at least about 85%, in additional embodiments at least about 90%, in other embodiments at least about 94%, and in some embodiments from about 95% to about 99%. The transparency of the film on the transparent polymeric substrate can be determined using the standard ASTM D1003 ("blend of transparent plasticsStandard test methods for Haze and Luminous Transmittance (Standard Transmission of molecular Plastics) ") were evaluated, and the standards are incorporated herein by reference. One of ordinary skill will recognize that additional ranges of transmissivity within the explicit ranges are contemplated and are within the present invention. When the optical properties of the measured films were adjusted in the examples of the following substrates, the films had excellent transmission and haze values, which were achieved together with the low sheet resistance observed.

The fused metal network may also have low haze and high transmission of visible light, while having desirably low sheet resistance. Haze can be measured using a haze meter based on ASTM D1003 mentioned above, and the haze contribution of the substrate can be removed to provide a haze value for the transparent conductive film. In some embodiments, the haze value of the sintered network film may be no more than about 1.2%, in other embodiments no more than about 1.1%, in additional embodiments no more than about 1.0%, and in other embodiments from about 0.9% to about 0.2%. As described in the examples, very low values of haze and sheet resistance have been achieved simultaneously by appropriate selection of silver nanowires. The load may be adjusted to balance sheet resistance values with haze values, where a very low haze value may be accompanied by a good sheet resistance value. Specifically, haze values of no more than 0.8%, and in other embodiments from about 0.4% to about 0.7%, may be achieved with sheet resistance values of at least about 45 ohms/square. Further, haze values of 0.7% to about 1.2%, and in some embodiments, about 0.75% to about 1.05% may be achieved with sheet resistance values of about 30 ohms/square to about 45 ohms/square. All of these films maintained good optical clarity. Those of ordinary skill will recognize that additional ranges of turbidity within the explicit ranges above are contemplated and are within the present invention.

Patterning

Some devices involve patterning transparent conductive electrodes, and the transparent conductive films described herein may be patterned accordingly. The specific pattern of the fused conductive metal nanostructure network along the substrate surface is generally guided by the desired product. In other words, the conductive pattern generally introduces a function in the field such as a touch screen or the like. Of course, for some products, the entire surface may be conductive, and for these applications, patterning is not generally performed. For embodiments involving patterning, the proportion of the surface comprising the conductive fused metal nanostructured network can generally be selected based on the chosen design. In some embodiments, the fused network comprises from about 0.25% to about 99%, in other embodiments from about 5% to about 85%, and in additional embodiments from about 10% to about 70% of the surface of the substrate. Those of ordinary skill will recognize that additional ranges of surface coverage within the explicit ranges above are contemplated and are within the present invention.

As illustrative examples, the fused metal nanostructure network may form a conductive pattern along the substrate surface 100 having a single conductive path 102 surrounded by resistive regions 104, 106 (as shown in fig. 1), or a pattern along the substrate surface 120 having a plurality of conductive paths 122, 124, and 126 surrounded by resistive regions 128, 130, 132, 134 (as shown in fig. 2). As shown in fig. 2, the fused regions correspond to three unique conductive regions corresponding to conductive paths 122, 124, and 126. A side view of a structure having the patterned film of fig. 2 on a polymer substrate 140 having a polymer overcoat 142 is shown in fig. 3. Although a single connecting conductive region and three independent connecting conductive regions have been illustrated in fig. 1-3, it will be understood that patterns of independent conductive paths or regions having more than two, four or 4 conductivities may be formed as desired. For many commercial applications, quite intricate patterns can be formed with a variety of elements. In particular, by available patterning techniques suitable for patterning of the films described herein, very fine patterns with high resolution features can be formed. Similarly, the shape of a particular conductive region may be selected as desired.

An alternative embodiment is shown in fig. 4, where a metal electrode is placed under the overcoat, in contact with the conductive fused metal network. Referring to fig. 4, the fused metal nanostructure networks 150, 152 are separated by resistive regions 154, 156, 158. The films represented by the networks 150, 152 are supported on a substrate 160. The metal electrodes 162, 164 provide electrical connection of the conductive networks 150, 152 to appropriate circuitry. A polymer overcoat 166 covers and protects the conductive networks 150, 152 and the metal electrodes 162, 164. Since the metal electrodes 162, 164 are under the overcoat, a thicker overcoat can be used if desired without adversely altering the properties due to the electrically insulating effect of the overcoat. A schematic of the top of a thin conductive film integrated into the sensor design is shown in fig. 5. The sensor 170 includes conductive metal nanostructured film portions 172 that show rolled square shapes separated by insulating regions 174, and which may or may not include unfused metal nanowires. The metal traces 176, 178, 180, and 182 are connected to the plurality of row conductive films 172, respectively. The traces 176, 178, 180, 182 include connecting segments 184 between adjacent conductive film portions 172 and conductive portions leading to a connecting region 186 at the edge of the sensor, in which connecting region 186 the traces can be connected to a circuit. A polymer overcoat 190 is placed over the conductive film.

Metal-loading based patterning can involve selective deposition of metal nanowire inks on selected portions of a substrate surface and/or selective removal of deposited metal nanowire or nanostructure films. Patterning during deposition is described above in the context of depositing metal nanowire ink. If the metal nanowire ink is deposited on the substrate surface, the selected regions can be developed to remove metal from the regions before or after fusing and before or after curing the polymeric binder. The metal may be removed via an appropriate etch or wash or other suitable method. For example, laser ablation of metal nanowires is described in japanese patent 5289859B entitled "Method of Manufacturing Conductive Pattern-coated Body, and Conductive Pattern coated Body" to nissha printing co.ltd., which is incorporated herein by reference. An acid etchant or other suitable wet etchant may be used. Dry etching may also be performed. The patterning of the etching/developing may be performed using a resist composition or the like. A wide range of resists, such as photoresists, are useful for patterning and are commercially available. Photolithography using light (e.g., UV light) or an electron beam may be used to form high resolution patterns, and patterning of metal nanowires or nanostructured films may be accomplished by forming a resist via window etching. Both positive tone and negative tone photoresists may be used. Common positive tone photoresists, such as FujiFilm OCG825, TOK THMR-i-P5680 and the like, and negative tone photoresists Micro Resist Technology MR-N415 and the like can be used. Patterning using a resist may be performed using photolithography, in which radiation exposure and development are performed to pattern the resist. Alternatively or additionally, a resist may be printed to pattern the resist, such as by screen printing or gravure printing, completing the patterning of the treatments described herein. In general, for embodiments in which the electrically insulating region has a lower metal loading than the electrically conductive region, the electrically insulating region may have a metal loading at least 1.5 times lower, in some embodiments at least 5 times lower, in other embodiments at least 10 times lower, and in other embodiments at least 20 times lower, relative to the electrically conductive region. In some embodiments, the electrically insulating region may be approximately free of metal. Those of ordinary skill will recognize that additional ranges of reduced metal loading within the explicit ranges above are contemplated and are within the present invention.

In some embodiments, the metal nanostructured films can be used as an alternative to other materials, such as thin films of conductive metal oxides (e.g., indium tin oxide). For example, a polymer roll with a fused metal nanostructured film can be incorporated into the process flow. A polymer overcoat can be disposed prior to patterning. Patterning with, for example, laser etching or masking with wet or dry etching may be used to form a desired pattern of conductive films separated by at least some regions of metal removed. The polymeric overcoat layer may, for example, be replaced with or possess an additional overcoat layer. The trace or current collector may be disposed on or penetrate the outer coating or a portion thereof. The addition of some conductive diluent to the polymeric overcoat layer can reduce the resistance of the overcoat layer without shorting the conductive pattern.

In additional or alternative embodiments, patterning can be performed prior to the placement of the polymeric overcoat layer. Referring to fig. 6, method flow is depicted by flow arrows indicating the flow of the method, which generally corresponds to temporal flow but may or may not correspond to physical motion. In a first view, a substrate 250 having a patterned film with conductive regions 252 and non-conductive regions 254 is shown. Although the figures indicate a particular substrate material, i.e., a thermally stable PET polymer with an additional polymer hard coating, the process can generally be performed with any reasonable substrate. In some embodiments, conductive region 252 comprises a fused metal nanostructured network and non-conductive region 254 comprises a lower metal loading due to, for example, etching or selective printing of a fused metal nanowire ink. Referring to the intermediate view of fig. 6, a metal current collector or trace 256 is deposited in contact with the conductive region 252. Although the metal traces 256 may be deposited and/or patterned using any reasonable process, in some embodiments, conductive silver or copper pastes may be screen printed and heated to form the metal traces. In some embodiments, silver, copper, or other metal traces may be deposited by electroplating, thermal decomposition, evaporation, sputtering, or other reasonable thin film deposition techniques. In the final view of fig. 6, a polymer overcoat 260 is placed on coated substrate 250 to cover metal trace 256.

Touch sensor

The transparent conductive films described herein can be effectively incorporated into touch sensors for touch screens that can be suitable for use with many electronic devices. Some representative embodiments are generally described herein, but transparent conductive films may be suitable for other desired designs. A common feature of touch sensors is generally the presence of two transparent conductive electrode structures in a spaced configuration in the natural state (i.e., when not touched or otherwise externally contacted). For sensors based on capacitive operation, a dielectric layer is typically between the two electrode structures. Referring to FIG. 7, a representative capacitance-based touch sensor 302 includes a display component 304, an optional bottom substrate 306, a first transparent conductive electrode structure 307, a dielectric layer 308 (e.g., a polymer or glass sheet), a second transparent conductive electrode structure 310, an optional top cover 312, and measurement circuitry 314 that measures changes in capacitance associated with a touch of the sensor. Referring to FIG. 8, a representative resistance-based touch sensor 340 includes a display assembly 342, an optional lower substrate 344, a first transparent conductive electrode structure 346, a second transparent conductive electrode structure 348, spaced apart support structures 350, 352 supporting the electrode structures in their natural configuration, an upper cover layer 354, and a resistance measurement circuit 356.

The display components 304, 342 may be, for example, LED-based displays, LCD displays, or other desired display components. The substrates 306, 344 and the cover layers 312, 354 may independently be transparent polymer sheets or other transparent sheets. The support structure may be formed of a dielectric material, and the sensor structure may include additional supports to provide a desired stabilization device. The measurement circuits 314, 356 are known in the art.

Transparent conductive electrodes 307, 310, 346, and 348 can be effectively formed using a fused metal network, which can be appropriately patterned to form unique sensors, but in some embodiments the fused metal network forms some transparent electrode structures while other transparent electrode structures in the device can include materials such as indium tin oxide, aluminum doped zinc oxide, or the like. As described herein, the fused metal network can be effectively patterned, and it can be desirable to form a patterned film in one or more electrode structures of the sensor, such that multiple electrodes in the transparent conductive structure can be used to provide position information related to the touch process. The use of patterned transparent Conductive electrodes for forming patterned Touch sensors is described, for example, in U.S. patent 8,031,180 entitled "Touch Sensor, Display With Touch Sensor, and Method for generating position Data" to Miyamoto et al and published U.S. patent application 2012/0073947 entitled "Narrow Frame Touch Input Sheet, Manufacturing Method of Same, and Conductive Sheet Used in Narrow Frame Touch Input Sheet" to Sakata et al, both of which are incorporated herein by reference.

Examples of the invention

Commercial silver nanowires with average diameters between 25nm and 50nm and average lengths from 10 to 30 microns were used in the examples below. Silver nanowire (AgNW) films were formed using the following procedure. Commercially available silver nanowires (agnws) are obtained from commercial suppliers as aqueous dispersions or dispersed in solvents to form aqueous AgNW dispersions. AgNW dispersions typically range from 0.05 wt% to 1.0 wt%. The dispersion is then combined with one or more solutions comprising the other components of the metal nanowire ink, optionally in an alcohol solvent. The resulting dispersion or ink is then deposited on the surface of a polyethylene terephthalate (PET) sheet using the hand-draw rod method (hand-draw rodaproach) or by knife coating. The AgNW films were then heat treated in an oven to cure the films as described in the specific examples below.

The hydrophilic adhesive is first dissolved in water to obtain a clear solution at the time of use. It was then mixed with the AgNW and other components of the ink under stirring to form a homogeneous suspension, referred to as the base ink. The base ink as prepared typically contains 0.1 wt% to 1 wt% binder. After combining with the remaining ingredients (metal ions) in the appropriate fused solution to obtain the final coating solution, the agnws are typically present at a level between 0.1 and 1.0 wt% and the binder is present at about 0.01 to 1 wt%.

The fused solution is composed of a suitable metal salt dissolved in a suitable solvent. Fused solutions typically contain between 0.05mg/mL (0.005 wt%) and 5.0mg/mL (0.5 wt%) of metal ions.

Total Transmission (TT) and haze of AgNW film samples were measured through the film on the polymer substrate using a haze meter. To adjust the haze measurements for the following samples, the substrate haze value can be subtracted from the measurements to obtain only approximate haze measurements for the transparent conductive film. The instrument is designed to evaluate optical properties based on the ASTM D1003 standard ("standard test method for haze and luminous transmittance of clear plastics"), which is incorporated herein by reference. The total transmission and haze of these films included a PET substrate with a base total transmission and haze of about 92.9% and 0.15% to 0.40%, respectively. Unless otherwise indicated, sheet resistance was measured using a 4-point probe method. In the examples below, several different formulations of fused metal nanowire inks and optical and sheet resistance measurements are presented.

Sheet resistance was measured by a 4-point probe method, a non-contact resistance meter, or using the following silver paste squares. For measurements prior to formation, squares of silver paste are sometimes used by applying the paste to the sample surface to define a square or rectangular shape, followed by annealing at about 120 ℃ for 20 minutes to cure and dry the silver paste. The alligator clip was connected to the silver paste and the wire was connected to a commercial resistance measuring device. Electrical connections are made to expose end portions of the membrane.

Example 1 fused nanowire ink with hydrophilic binder and nitric acid

This example tested the ability of cellulose-based polymers (CBPs) to act as binders and thickeners for AgNW inks without interfering with the fusing process.

The initial AgNW dispersion included deionized water and isopropanol. The ink also contains a binder of CBP as described above. In this example, 15 samples were prepared using the base ink. The fused solutions or ethanol were each combined with some samples at a 3:1 ratio of AgNW ink to fused solution or ethanol by volume. The fused solution contained between 15 and 80 μ L/mL HNO in silver nitrate and ethanol as specified above₃. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

To dry the film, the film was heated in an oven at 100 ℃ for 10min in ambient atmosphere. The properties of the films after heating are compared in table 1. The film formed from the ink containing the condensed solution had a reduced resistance compared to the film without the condensed solution, confirming that the metal nanowires in the relevant sample were condensed. All samples exhibited good optical properties based on transparency and haze.

TABLE 1

Sample (I)	Resistance (omega/□)	％TT	% haze
				AgNW ink	461	91.0	1.76
AgNW ink	>20K	91.6	1.19
				AgNW ink	2300	91.6	1.32
Ag NW ink + fused solution	65	91.1	1.43
				Ag NW ink + fused solution	138	91.5	1.09
Ag NW ink + fused solution	116	91.6	1.04
				Ag NW ink + fused solution	131	91.5	1.08
Ag NW ink + fused solution	122	91.6	1.05
				Ag NW ink + fused solution	84	91.8	0.93
Ag NW ink + fused solution	76	91.6	1.11
				Ag NW ink + fused solution	80	91.9	0.99
Ag NW ink + fused solution	80	91.7	0.99
				Ag NW ink + ethanol	693	91.4	1.33

EXAMPLE 2 fused solution composition

This example tests the ability of various formulations of the compositions to act as a fused solution of AgNW inks to form desirable transparent conductive films.

The initial AgNW dispersion included a solvent of deionized water with a small amount of isopropanol. The base ink also contains a binder of CBP as described above. The fused solutions or ethanol were each combined with 12 formally unique samples in a 3:1 or 4:1 ratio of AgNW ink to fused solution or ethanol by volume, and two additional samples were processed as base inks. The fused solution contains between 0.05mg/mL and 5mg/mL of metal ions in ethanol and between 15 μ L/mL and 80 μ L/mL of HNO₃(samples 7 to 10) or half the above concentration of the components (samples 11 to 14). The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10min in ambient atmosphere to dry the film. The properties of the films after heating are compared in table 2. Films formed from inks containing the fused solutions had reduced resistance compared to films without the fused solutions, indicating that the nanowires in the respective films were fused. All samples exhibited good optical properties, but the samples with the more dilute fused solutions exhibited slightly higher sheet resistance and greater haze.

TABLE 2

Example 3 effect of different AgNW samples

This example tests the suitability of various AgNW samples to serve as AgNW sources for an ink system.

AgNW inks were produced in deionized water using agnws from two different commercial sources (a and B). As described above, the ink contains CBP acts as a binder. Subsequently, the fused solution or ethanol was combined with some samples at a ratio of 3:1 AgNW ink to fused solution or ethanol, respectively, by volume. The fused solution consists of metal ions between 0.05mg/mL and 5.0mg/mL in ethanol and HNO between 8 μ L/mL and 80 μ L/mL₃And (4) forming. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10min to dry the film. The properties of the films after heating are compared in table 3. Films formed with agnws from the a source had higher sheet resistance when no fused solution was used and lower sheet resistance when fused solution was used compared to films made with agnws from the B source. However, films formed from inks with agnws from a B source had greater transparency and lower haze.

TABLE 3

EXAMPLE 4 Effect of various heavy Metal ions in an ink System

This example tests the effect of different heavy metal ions on the resistance, transmittance and haze of the resulting film in an ink AgNW system.

The initial AgNW dispersion included an isopropanol solvent. The stock ink contains CBP as a binder and also contains a humectant in water. The fused solution was combined with the ink at a ratio of 1:1 AgNW ink to fused solution by volume. As described above, the fused solutions contain different metal ions in ethanol. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10min to dry the film. The properties of the films after heating are compared in table 4. Generally, films produced with specific metal ions in the fused solution (e.g., Ni (II) and Ag (I)) have lower sheet resistance relative to control sample E, while other metal ions (Co (II) and Cu (II)) do not exhibit the fusing behavior.

TABLE 4

Sample (I)	Fused solutions (Metal ions)	Resistance (omega/□)	％TT	% haze
					A	Cu(II)	161	92.1	1.13
B	Ni(II)	63	92.1	1.11
					C	Co(II)	91	92.2	1.11
D	Ag(I)	50	92.1	1.08
					E	EtOH	90	92.0	1.08

Example 5 stability of ink formulation and acid-free ink

This example tests the effect of various formulations on ink stability and other properties in an ink AgNW system.

Stock AgNW inks were produced in deionized water from three different commercial sources (A, B and C), forming the base ink as described above. The following outlines the results based on agnws from the fourth vendor D. Three different solution compositions were formed from each of the three stock inks, resulting in 18 unique samples. The first solution (No. 1) was produced by mixing the stock ink with the fused solution immediately prior to coating. The fused solution contained between 0.05mg/mL and 5.0mg/mL of silver ions in ethanol and it was added to solution No. 1 at a ratio of 1:1 stock ink to fused solution by volume. A second solution (No. 2) was produced by mixing the stock ink with the metal ion stock solution and stored until use. The metal ion stock solution contains between 50mg/mL and 200mg/mL of metal ions in deionized water. The amount of metal ions in the blend of the reservoir ink and the reservoir metal ion solution was the same as in the first solution (No. 1). Ethanol was added to solution No. 2 at a 1:1 solution to ethanol ratio by volume immediately prior to coating. A third solution (No. 3) was formed by mixing the stock ink with the fused solution and stored until use. The fused solution contained between 0.05mg/mL and 5.0mg/mL of metal ions in ethanol and it was added to solution No. 3 at a ratio of 1:1 stock ink to fused solution by volume. Solution No. 3 was stored and then coated directly without any further mixing. The ink was then coated onto a PET substrate using a mel bar or a doctor blade. The stability of the ink is shown in fig. 9. Fig. 9 depicts each of the solutions after storage for two weeks without mixing.

The film was then heated in an oven at 100 ℃ for 10min to dry the film. The properties of the films after fusing are compared in table 5A. These results demonstrate that low sheet resistance, indicating silver nanowire condensation, can occur effectively without the addition of any acid in the ink. Excellent optical properties based on high% TT and low haze were also observed. The nanowires supplied by supplier C resulted in a slightly greater haze for the film. No significant change in the treatment sequence suggests a stable ink result.

TABLE 5A

AgNW is from a fourth vendor D. The solution was created by mixing the stock ink with the fused solution immediately prior to coating. The fused solution contained between 0.05mg/mL and 5.0mg/mL of metal ions in ethanol and was added to the solution at a ratio of 1:1 stock ink to fused solution by volume. Three different solutions were prepared by mixing increasing metal ion concentrations C1< C2< C3. Films were then formed from these solutions as described above immediately after mixing the fused solution with the nanowire stock solution. The results are presented in table 5B below. Transparent conductive films formed with these nanowires have extremely low haze values for certain sheet resistance values. Accordingly, haze values were generally lower by 0.2% or more than 0.2% at similar sheet resistance values as the samples formed in table 5A with nanowires a or B.

TABLE 5B

EXAMPLE 6 Effect of Chitosan Binder in an ink formulation

This example tests the effect of chitosan binder on resistance, transmission and turbidity in an ink AgNW system.

The initial AgNW dispersion included a solvent of deionized water with a small amount of isopropanol. Stock AgNW inks containing between 0.1 and 0.3 wt% silver nanowires, between 0.01 and 0.1 wt%(available from BASF) as a co-dispersant, between 0.3 and 0.5 wt% of a different grade of chitosan as a binder, and between 0.05 and 0.1 wt% of a wetting agent. The ink was mixed with a fused solution (containing between 0.5mg/mL and 5mg/mL of metal ions in ethanol) or an ethanol solvent at a 1:1 ratio of ink to fused solution or ethanol by volume. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10min to dry the film. The properties of the films after fusing are compared in table 6. All films made with inks containing the fused solutions exhibited excellent properties.

TABLE 6

Example 7 Effect of a blend of polyvinylpyrrolidone and CBP as a Binder

This example tests the effect of polyvinylpyrrolidone as binder on resistance, transmission and turbidity in an ink AgNW system.

AgNW inks were produced in deionized water from two different commercial sources (a and B). The reserve AgNW ink contains between 0.1 wt% and 0.3 wt% silver nanowires, between 0.3 wt% and 0.75 wt% CBP as binder, between 0.01 wt% and 0.1 wt% polyvinylpyrrolidone (PVP) as dispersant/binder, and between 0.05 wt% and 0.1 wt% humectant. The ink was mixed with a fused solution containing between 0.5mg/mL and 5mg/mL of metal ions in ethanol at a ratio of 1:1 by volume. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10min to dry the film. The properties of the films after fusing are compared in table 7.

TABLE 7

EXAMPLE 8 Effect of moisture on Performance

This example tests the effect of moisture on film performance during the drying process.

The stock AgNW ink contained between 0.1 wt% and 0.30 wt% silver nanowires in isopropanol from an a source. The ink was mixed with a fused solution containing between 0.5mg/mL and 5mg/mL of metal ions in ethanol at a ratio of 1:1 by volume. One additional ink was mixed with ethanol at a 1:1 ratio of ink to ethanol immediately prior to coating. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film is then heated in an oven at 85 ℃ for 20 minutes, 15 minutes or 5 minutes at 60% relative humidity, or at 130 ℃ for 5 minutes in a drying oven to dry the film. The sheet resistance of the films after drying under different conditions is compared in fig. 10. The introduction of humidity allows for a reduction in time and temperature to achieve the same level of fusion (reduction in sheet resistance) for at least some samples. Drying in a humid atmosphere provides improved fusing of these inks, as indicated by the decrease in sheet resistance.

Example 9 films were stabilized by adding a UV curable polymer to the ink

This example tests the effect of UV curable polymers on the robustness of AgNW films.

A base AgNW ink was produced by mixing AgNW ink having an AgNW concentration between 0.1 and 0.3 wt% in isopropanol and UV curable polymer between 2 and 7.5 wt% in Propylene Glycol Methyl Ether (PGME) at a 4:1 ink to UV curable polymer ratio by volume. The ink was mixed with a fused solution containing silver ions at a concentration C1 of between 0.05mg/mL and 0.5mg/mL in ethanol or C2 ═ 10 xc 1 at a ratio of 1:1 by volume. The ink was then coated on a PET substrate using a mel bar coating at a setting of 10 or 20.

The film was then cured using a UV conveyor. The properties of the films are compared in table 8. The introduction of the UV curable resin results in high haze of the coating, but the abrasion resistance is significantly improved after UV curing. The film formed without the condensed solution has an extremely high sheet resistance value. Thus, these films of UV curable compositions mixed into fused inks provide a greater contrast in electrical resistance between films formed with and without fused solutions. The data further show that films of UV curable compositions mixed into fused inks can exhibit significant thermal stability. After UV curing, the base coat did not exhibit an increase in sheet resistance (R) beyond the original value (R) after 30min treatment in an oven at 150 ℃₀) (samples 4 and 6).

TABLE 8

Sample (I)	Fused solutions	Rod	Resistance (omega/□)	％TT	Turbidity of the mixture	R/Ro(150℃，30min)
							1	Is free of	10	>200M	92.4	3.60	-
2	Is free of	20	>200M	91.2	3.34	-
							3	C1	10	About 3,400	92.1	2.53	-
4	C1	20	60	88.7	4.65	0.87
							5	C2	10	143	91.2	2.16	-
6	C2	20	42	86.5	4.91	0.9

EXAMPLE 10 Effect of alcohol-free condensed solution

This example tested the effect of using an alcohol-free fused solution on membrane performance.

The stock AgNW ink contained silver nanowires in isopropanol from the a source or silver nanowires in water from the B source. The ink contains between 0.05 wt% and 0.3 wt% AgNW. The ink is mixed with a fused aqueous solution containing between 0.05mg/mL and 5.0mg/mL of metal ions at a ratio of 1:1 ink to fused solution by volume. Comparative samples were similarly prepared with water instead of the fused solution. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10 minutes to dry the film. The properties of the films after the heating step are shown in table 9. The use of the alcohol-free, metal ion-containing, fused solution resulted in an effective conductivity improvement, indicated as "improvement" in table 9, expressed as a percentage of resistance reduction, with respect to the corresponding comparative example.

TABLE 9

Example 11 Effect of Polyox as a Binder on AgNW inks

This example tested the effect of Polyox binder in an ink AgNW system.

The initial AgNW dispersion included a solvent of deionized water with a small amount of isopropanol. The AgNW ink has between 0.05 wt% and 0.25 wt% silver nanowires. The ink also contains a Polyox (polyethylene oxide) binder in a concentration of between 0.075 and 0.10% by weight, a humectant in a concentration of between 0.10 and 0.15% by weight. The fused solution was added at a ratio of 3:1 AgNW ink to fused solution by volume. The fused solution contains between 0.05mg/mL and 5.0mg/mL silver ions in ethanol and between 15 μ L/mL and 80 μ L/mL HNO₃. The ink was then coated onto a PET substrate using a mel bar or a doctor blade.

The film was then heated in an oven at 80 ℃ for 10min to dry the film. In table 10, the properties of the films after heating were compared with those formed with CBP and with the fused solution or EtOH alone (as a control). In general, inks with Polyox binders resulted in low resistance films when fused solutions were used, indicating that the silver nanowires were fused. In the case of inks with Polyox binders, films formed without the fused solution have high sheet resistance.

Watch 10

Sample (I)	Adhesive agent	Fused solutions	Resistance (omega/□)	％TT	% haze
						1	CBP-60SH-10k	-	203	92.0	1.05
2	CBP-60SH-10k	Is that	115	91.9	1.06
						3	Polyox N16	-	>20K	92	1.30
4	Polyox N16	Is that	185	91.9	1.36
						5	Polyox N60	-	>20K	92	1.19
6	Polyox N60	Is that	164	91.9	1.42
						7	Polyox 310	-	>20K	92.2	0.89
8	Polyox 310	Is that	1720	92.2	0.88

EXAMPLE 12 Effect of sodium Metal ions in an ink System

This example tests the effect of sodium metal ions on transmission and turbidity in an ink AgNW system.

The initial AgNW dispersion included a solvent of deionized water with a small amount of isopropanol. As has been described above in the context of the present invention,the ink contains CBP as a binder. The fused solution or ethanol containing between 0.05mg/mL and 5.0mg/mL of metal ions was then combined with some samples, each at a 3:1 ratio of AgNW ink to fused solution or ethanol by volume. The condensed solution is prepared by mixing metal ions (Na or Ag) in ethanol and HNO₃And (4) forming. In the form of two concentrations of the compound,<the fused solution was added at 1 wt% of the initial concentration or ten times the initial concentration (10 ×) the ink was then coated onto a PET substrate using a Meyer rod or a doctor blade.

The film was then heated in an oven at 100 ℃ for 10min to dry the film. The properties of the films after fusing are compared in table 11. The results show that the film formed with sodium ions in the fusing solution does not exhibit fusing, while the film formed with silver ions does undergo fusing.

TABLE 11

	Fused solutions	Resistance (omega/□)	％TT	% haze
					1	Na(1×)	107	92.0	0.98
2	Na(10×)	1078	92.3	1.81
					3	Ag(1×)	55	91.9	1.01
4	Ag(10×)	46	91.6	1.28

The above embodiments are intended to be illustrative and not restrictive. Additional embodiments are within the claims. Additionally, although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Any incorporation by reference of documents above is limited such that subject matter that is contrary to the explicit disclosure herein is not incorporated.

Claims (25)

1. A metal nanowire ink comprising from about 0.001 wt% to about 4 wt% metal nanowires, from about 0.05 wt% to about 5 wt% hydrophilic polymeric binder, and from about 0.0001 wt% to about 0.5 wt% metal ions.

2. The metal nanowire ink of claim 1 wherein the hydrophilic polymer binder comprises a polymeric polyol.

3. The metal nanowire ink of claim 1 wherein the hydrophilic polymer binder comprises a polysaccharide.

4. The metal nanowire ink of claim 1 wherein the hydrophilic polymer binder comprises a cellulose-based polymer or a chitosan-based polymer.

5. The metal nanowire ink of any one of claims 1-4 comprising from about 0.01% to about 2% by weight silver nanowires, from about 0.1% to about 2% by weight polysaccharide polymer binder, and from about 0.001% to about 0.2% by weight silver ions.

6. The metal nanowire ink of any one of claims 1-4 comprising from about 0.01% to about 2% by weight silver nanowires, from about 0.1% to about 2% by weight polysaccharide polymer binder, and from about 0.001% to about 0.2% by weight metal ions selected from the group consisting of: silver, gold, platinum, palladium, zinc, nickel, and combinations thereof.

7. The metal nanowire ink of any one of claims 1-6 comprising from about 5% to about 60% by weight of a liquid alcohol aqueous solution.

8. The metal nanowire ink of any one of claims 1-7 having a pH of at least about 3 pH units.

9. The metal nanowire ink of any one of claims 1-8 wherein no visible sedimentation is observed after one hour of standing without agitation.

10. The metal nanowire ink of any one of claims 1-9 further comprising from about 0.01 wt% to about 2.5 wt% curable binder.

11. A metal nanowire ink comprising from about 0.001 wt% to about 4 wt% metal nanowires, from about 0.0001 wt% to about 0.5 wt% metal ions, and from about 20 wt% to about 60 wt% of a liquid aqueous alcohol solution having a pH of from about 5.5 to about 7.5 pH units.

12. A transparent conductive film comprising a fused metal nanostructured network and a polymeric polyol, wherein the film comprises about 40% to about 600% polymeric polyol by weight relative to the weight of the metal.

13. The transparent conductive film of claim 12 wherein the metal loading of the fused metal nanostructured network is about 0.1mg/m²To about 300mg/m²。

14. The transparent conductive film of claim 12 or claim 13 wherein the film comprises about 100 wt.% to about 450 wt.% polymeric polyol relative to metal loading.

15. The transparent conductive film according to any one of claims 12-14, wherein the polymeric polyol comprises a cellulose-based polymer or a chitosan-based polymer.

16. The transparent conductive film of any of claims 12-15 having a sheet resistance of no more than about 140 ohms/square, a% TT of at least about 95%, and a haze of no more than about 1.2%, wherein the metal nanostructure network comprises silver.

17. A structure comprising the transparent conductive film of any one of claims 12-16 and a polymer substrate supporting the transparent conductive film.

18. A transparent conductive film comprising a sparse metal conductive element having a sheet resistance of about 45 ohms/square to about 250 ohms/square and a haze of no more than about 0.8%, or a sheet resistance of about 30 ohms/square to about 45 ohms/square and a haze of about 0.7% to about 1.2%.

19. A method of forming a transparent conductive network, the method comprising:

depositing a fused metal nanowire ink onto a substrate surface, wherein the metal nanowire ink comprises from about 0.001 wt% to about 4 wt% metal nanowires, from about 0.05 wt% to about 5 wt% hydrophilic polymer binder, and from about 0.0001 wt% to about 0.5 wt% metal ions; and

drying the metal nanowire ink to form a transparent conductive film comprising fused metal nanowires in a fused metal nanostructured network, the transparent conductive film having a sheet resistance of no more than about 250 ohms/square.

20. The method of claim 19, wherein the metal nanowires comprise silver nanowires and the metal ions comprise silver ions, and wherein the depositing is performed to cover all or a portion of the substrate surface with a metal loading at the covered locations of about 0.1mg/m²To about 300mg/m²。

21. The method of claim 19, wherein the metal nanowires comprise silver nanowires, and wherein the metal nanowire ink comprises from about 0.1 wt% to about 2 wt% polysaccharide polymer binder and from about 0.001 wt% to about 0.2 wt% of a metal ion selected from the group consisting of: silver, gold, platinum, palladium, zinc, nickel, and combinations thereof.

22. The method of any one of claims 19 to 21, wherein the drying is performed by heating to a temperature of about 50 ℃ to about 150 ℃ for no more than about 2 hours.

23. The method of any one of claims 19 to 22, wherein the metal nanowire ink further comprises from about 5 wt% to about 60 wt% liquid alcohol.

24. The method of any one of claims 19 to 23, wherein the metal nanowire ink further comprises a curable polymeric binder and the method further comprises curing the binder.

25. A method of sintering a metal nanowire ink having metal ions as deposited, the method comprising:

drying a metal nanowire film at a temperature of about 60 ℃ to about 99 ℃ for at least about 1 minute at a relative humidity of at least about 40%, wherein the metal nanowire film is formed via deposition of a metal nanowire ink comprising about 0.001 wt% to about 4 wt% metal nanowires, about 0.05 wt% to about 5 wt% hydrophilic polymer binder, and about 0.0001 wt% to about 0.5 wt% metal ions.