Forming conductive layers and inks at near ambient temperatures using silver nanoparticle processing

Abstract

Near ambient temperature processing has successfully produced a highly conductive coating formed from silver nanowires. The conductive material may have a high silver loading and a low resistivity. The highly conductive material may be formed using an aqueous ink having a high loading of silver nanowires, the aqueous ink having greater than 3% by weight of a metal predominantly of silver nanowires. A method of making a high load ink may include forming a good dispersion of silver nanowires and removing the solvent to concentrate the dispersion. A series of adhesives comprising, for example, UV-crosslinkable adhesives may be used. Generally, the organic matter concentration of the high-conductivity material is not more than 25 wt%, which can correspond to higher organic matter volume fractions but still achieve good conductivity.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to co-pending U.S. provisional application 63 / 441,671, filed by Yang et al. on January 27, 2023, entitled "Forming a conductive layer at near-ambient temperature using silver nanoparticle processing and ink for forming the layer," which is incorporated herein by reference. Technical Field

[0003] The present invention relates to near-ambient temperature processing for forming thin conductive coatings that may be transparent. The present invention also relates to certain silver nanowire inks for forming conductive coatings and conductive coatings on temperature-sensitive substrates. Background Art

[0004] Functional films can provide important functions in a range of situations. For example, conductive layers can be important for dissipating static electricity, where it may be undesirable or potentially dangerous. Transparent conductive films can be used as electrodes. High-quality displays may include one or more transparent conductive layers.

[0005] 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 combined with high conductivity. However, ITO has several disadvantages. For example, ITO is a fragile ceramic that needs to be deposited using sputtering, a process that involves high temperatures and a vacuum and is therefore relatively slow and not cost-effective. In addition, ITO is known to crack easily on flexible substrates. Newer portable electronic devices are moving towards thinner and more flexible versions.

[0006] Other applications use non-transparent conductors with much higher conductivity than ITO for a variety of functions, including, for example, circuits, interconnects, conductive traces, borders, shielding, heat dissipation or sinks, etc. It is desirable to create such metallic conductive films, circuits, or components from inks that can be deposited by a variety of methods and processed at lower temperatures, which can increase the range of potentially compatible surfaces and structures that can be electrified and reduce the overall cost of manufacturing. Summary of the Invention

[0007] In a first aspect, the present invention relates to a conductive composite material comprising at least about 75 weight percent (wt%) silver particles and a polymer binder, wherein the silver particles comprise at least about 67 wt% silver nanowires having an aspect ratio of at least about 75. The polymer binder may be included in an amount of at least about 2 wt% of the conductive composite material. The conductive composite material may have a thickness of no more than about 5×10 -3 Resistivity in Ohm-cm.

[0008] In a second aspect, the present invention relates to a conductive structure comprising a conductive composite material, wherein the structure has a visible light transmittance of no more than about 70%. The conductive structure may comprise a layer having an average thickness of from about 0.2 micrometers to about 2 millimeters, or a layer having an average thickness of no more than about 5 micrometers and a sheet resistance of no more than about 5 ohms / sq. The conductive structure may comprise the conductive composite material disposed on a heat-sensitive substrate that is unstable above about 100°C. The conductive structure may comprise the conductive composite material that has been processed at a temperature below about 100°C.

[0009] In another aspect, the present invention relates to an ink for forming a conductive deposit. The ink may comprise an aqueous solvent and at least about 3% by weight of metal particles, the metal particles comprising at least about 67% by weight of silver nanowires. The ink may remain stable for at least 24 hours without visible settling, without agitation. The ink may comprise from about 3% to about 20% by weight of metal particles, the metal particles comprising at least about 67% by weight of silver nanowires. Upon removal of the aqueous solvent, the ink may form a conductive material.

[0010] In another aspect, the present invention relates to a method for forming an ink for forming a conductive deposit, the method comprising: forming a good solvent blend dispersion of silver nanowires having a concentration of no more than about 2.5 wt. %, wherein the solvent comprises at least about 20 vol. % of an alcohol having a boiling point of no more than about 99° C.; and removing the solvent to concentrate the good solvent blend dispersion to form an aqueous dispersion having at least about 3 wt. % silver nanowires. The good solvent blend dispersion can remain stable for at least three months without any significant settling in a sealed environment to prevent solvent evaporation or contamination.

[0011] In another aspect, the present invention relates to a method for forming a conductive composite material, comprising: casting an ink comprising a solid solution to form a cast structure, the solid solution having from about 75 wt % to about 98 wt % silver particles and at least about 2 wt % of a polymer binder precursor, wherein the silver particles comprise at least about 67 wt % silver nanowires having an aspect ratio of at least about 75; and curing the cast structure to form the conductive composite material. Curing can be performed at a temperature not exceeding about 100° C.

[0012] In another aspect, with respect to highly conductive opaque structures, the present invention relates to a substrate having a deposit comprising metal nanowires having an average thickness of no more than about 5 microns, a sheet resistance of no more than about 5 ohms / square, and a resistivity of no more than about 5×10 -3 Ohm-cm. In addition to the metal nanowires, the deposit may also contain other metal nanoparticles. In some embodiments, the metal nanowires comprise at least about 10% by weight of the metal nanoparticles. The deposit may include a polymer binder such that the metal content of the deposit is about 75% to about 99% by weight. The polymer binder may include a polysaccharide to aid in forming a good coatable dispersion and / or an ultraviolet (UV) cross-linkable resin or polymer to improve mechanical stability.

[0013] In some aspects, the present invention relates to an ink comprising a polar solvent, in some embodiments comprising at least 80% by weight water, and at least about 3% by weight of metal nanoparticles, comprising metal nanowires, wherein the ink remains stable for at least 24 hours without visible sedimentation in the absence of agitation. Furthermore, when stored at room temperature, the ink remains suitably stable and maintains its overall properties and performance for days, weeks, or longer, and overcomes common problems of poor stability, which can be associated with extensive sedimentation, irreversible aggregate formation, unintentional metal plating associated with highly reactive metal deposition precursors, or other instability issues that arise when attempting to induce good conductivity at ambient temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a partial side view of a film having a conductive layer and various additional transparent layers on either side of the conductive layer.

[0015] Figure 2 Schematic diagram showing the relative differences in processing temperature versus time, energy, and cost for contemporary electrode technologies.

[0016] Figure 3Graph showing the percent total transmittance as a function of sheet resistance for an ink coating containing AgF and dried under ambient conditions.

[0017] Figure 4 Graph showing the haze percentage as a function of sheet resistance for ink coatings containing AgF and dried under ambient conditions.

[0018] Figure 5A The photographs show the resistance measurement of the ink coating of the present invention dried on a medical grade polyurethane substrate under ambient conditions.

[0019] Figure 5B The photographs show the resistance of the ink coating of the present invention dried on a medical bandage measured under ambient conditions.

[0020] Figure 5C The photographs show the measurement of the electrical resistance of the ink coating of the present invention dried on a leaf under ambient conditions.

[0021] Figure 5D Photographs showing the resistance of an ink coating of the present invention dried on a Ziploc® bag measured under ambient conditions.

[0022] Figure 5E The photographs show the resistance measurement of the ink coating of the present invention dried on a shrinkwrap substrate under ambient conditions.

[0023] Figure 5F To illustrate the measurement of the ink coating of the present invention dried under ambient conditions on a Scotch TM Photograph of the resistor on the adhesive layer of a tape substrate.

[0024] Figure 5G Shown are photographs measuring the resistance of an ink coating of the present invention dried under ambient conditions, the ink coating being formed into a circuit on a polyethylene terephthalate substrate.

[0025] Figure 5H Photographs showing the resistance of dried ink coatings of the present invention formed into circuits on a packaged paperboard substrate measured under ambient conditions. DETAILED DESCRIPTION

[0026] Easily processable inks containing silver nanowires can form highly conductive materials at room temperature. As described herein, the conductive materials can be formed into opaque structures with very low electrical resistance. For highly loaded opaque materials, good conductivity can be achieved with or without fusing the nanowires, but fusing is generally required to form transparent coatings with good mechanical properties, improved stability, and enhanced optical characteristics. Highly loaded nanoparticle structures can achieve metallic properties even without fusing the structure, while also having a significant volume fraction of organic matter. Depending on the structure formed, fusing with a reducing metal salt may or may not improve conductivity, but the effect is generally modest. Processing to form transparent conductors typically involves inks containing appropriate amounts of polysaccharide binders (e.g., cellulose ethers) and / or other binders (e.g., UV-crosslinkable polymers, monomers, oligomers, or resins). For low transmittance or fully opaque embodiments, low amounts of polymer binder have been found to effectively form conductive structures with high silver density and low electrical resistance. The polymer binder is a solid composition, but it can be delivered from the ink as a dissolved polymer or resin (which solidifies and optionally crosslinks upon drying), or as a liquid monomer, oligomer, or liquid polymer (which is polymerized and / or crosslinked to form a solid polymer binder) with an optional compatible solvent. Metallic connectivity can be increased with or without a reduced metal / silver deposit to improve conductivity. The nanowire aspect ratio appears to be important for achieving high conductivity. Additional silver particles can be added to supplement the metallic species, but a majority of silver nanowires should be used to impart high conductivity to structures formed at low (near-ambient) temperatures.

[0027] To achieve higher levels of conductivity and correspondingly lower resistivity, the amount of polymer binder was reduced. The current work revealed that sparse layers present specific challenges for establishing conductive pathways. These challenges can be overcome by using compatible organics (e.g., polymers). In particular, polyol polymers facilitate nanowire placement and facilitate nanowire junctions, creating an overall structure with correspondingly good conductivity along the interconnected network. Surprisingly, the high-metal-loading materials self-assemble to establish good connections and fusion, which may or may not be effective in further enhancing conductivity. Such high conductivity results were not observed with high-loading spherical silver particles, which require fusion to create highly conductive materials. High-loading silver nanowire materials can be processed at room temperature or significantly lower temperatures to achieve the required drying time. Fusion, as described herein, involves reducing metal ions and complexes to form metal deposits that chemically, physically, and electrically connect the metal particles. Because this fusion is not typically involved in the basic processing of the high-loading composites described herein, processing times can be short, on the order of minutes. Deposition of reduced metal can be performed, and slight improvements or decreases in conductivity have been observed, so minor improvements from metal deposition should be achievable. If silver or other metal ions are reduced to deposit the metal in the composite, it is unclear whether a fused, interconnected structure is formed. If no metal is reduced and deposited, the silver particles remain as discrete particles despite being bound in the polymer binder. Rapid, low-temperature or room-temperature processing can provide significant advantages for applications where these parameters enable previously unattainable processing speeds or the use of desired materials that are limited under different processing conditions.

[0028] It has been discovered that inks with relatively high silver concentrations can be formed that are stable at concentrations exceeding 2% by weight. In some embodiments, the inks are amenable to various coating processes, such as slot coating, dipping, spraying, or jet deposition, and can be applied to a range of substrate surfaces. Furthermore, higher viscosity inks can be formed from precursor inks based on higher concentrations of nanowires, which are amenable to processes such as printing, spraying, and screen printing. Processing for forming high-concentration silver nanowire inks can include forming a dilute dispersion and evaporating the solvent to achieve the desired concentration. Alternative solvents can be incorporated if their boiling point is higher than that of the original solvent for the more dilute dispersion. To form opaque, low-resistance structures, it has been discovered that high particle loadings can be achieved with minimal polymer binder and without fusion, with evidence suggesting a shift to a different conduction mechanism. Such materials have a high metal density, greater than 25% of the bulk density. Viewed another way, the deposit can be at least 25% silver metal by volume, with the remainder of the volume occupied by polymer binder, resin, other organic matter (e.g., process aids, surfactants, etc.), and potential porosity. While metal nanowires contribute to conductive properties through their ability to form conductive points at multiple locations, other metal particle shapes may also be incorporated into the conductive structure for less transparent materials. Room temperature processing and / or high particle loadings may advantageously make processing applicable to a range of previously unsuitable substrate materials and may also provide energy savings, particularly simplified processing procedures and associated cost savings. Some substrate materials may be unstable above certain temperatures (e.g., above 100°C, above 125°C, or above 150°C), and most organic polymers decompose at temperatures below 800°C. Instability may be manifested by loss of mechanical stability (e.g., curling), chemical stability (e.g., polymer decomposition), or a combination thereof. One of ordinary skill in the art will recognize that additional unstable temperature ranges within the explicit ranges above are contemplated and fall within the scope of the present disclosure.

[0029] Silver nanowires have been successfully produced as transparent conductive coatings of high optical quality, while maintaining electrical conductivity while possessing desirable mechanical properties, such as stretchability and stability against repeated folding and unfolding. The processing extension described herein maintains excellent optical quality and extends the processing required for forming conductive coatings that are less transparent or opaque conductive films. A dispersion or ink of silver nanowires can be deposited on a surface and processed into a conductive coating. Under appropriate processing conditions, the resulting conductive coating (optionally transparent) can be desirable for its mechanical properties (e.g., flexibility, formability, a combination of these characteristics, or other aspects of the conductive coating). In the art, the term "nanoparticle" is also used to specifically refer to generally spherical nanostructures, as well as to nanostructures of any shape. To simplify this terminology, "nanoparticulate" is used herein to refer to nanostructures of any shape, while "nanoparticle" refers only to generally spherical nanostructures (i.e., having a diameter ratio along the three major axes that is less than approximately 2 on average). Regarding transparent coatings, the use of nanowires to form transparent conductive coatings can have important applications in devices with displays and touch sensors. As the metal loading becomes higher, the resistance is found to decrease, while the transmittance of visible light decreases. Even fully purified silver nanowires contain small amounts of other silver nanoparticle contaminants, and in the context of less transparent or non-transparent applications, the nanowires can be mixed with slightly larger weight fractions of other nanoparticles. It has also been found that these concepts can be further extended to the opaque range, where even higher metal loadings can achieve lower resistivity. In order to achieve dense metal nanoparticle deposits, it has been discovered how to form stable dispersions in polar solvents that have a high concentration of metal nanoparticles containing metal nanowires. Other polar solvents (such as alcohols) are also suitable solvents for achieving high concentrations of metal nanowires.

[0030] As the transparent conductive film forms, a sparse metallic conductive layer is formed, through which light can propagate, as the nanowires typically have diameters smaller than the wavelength of light and the gaps between them provide pathways for light to pass. Due to good contact between the silver nanowires and sufficient loading, a percolation mechanism can be used to explain the conductive path. Applicants have discovered that fusing the nanowires into a unified structure enables direct electrical conduction through the structure without significant junction resistance, meaning that percolation is avoided. While not wishing to be bound by theory, the results here suggest that for high loadings of silver nanowires, the material exhibits metallic properties, meaning that even in the presence of a large volume fraction of organic matter surrounding the metal nanowires, overlapping conductive paths extend through the material. Furthermore, as the number of connection points / junctions increases, the overall series resistance of the film decreases in a manner similar to the well-known macroscopic behavior of parallel resistors. The aspect ratio of the nanowires appears to contribute to these conductive properties, although the silver nanowires can be supplemented or partially replaced by other silver nanoparticles. The material can be processed from silver nanowire ink at room temperature, although heating can also be used. Use reducible metal salts and complexes (i.e. Nanoglue TM ) may or may not improve conductivity and can be used as needed. For some metal salts, some heating may be necessary. Low resistivity values ​​have been achieved using room temperature processing.

[0031] Due to the ability to process at room temperature, the formation of non-transparent conductive layers can be desirable on temperature-sensitive substrates. For optically insensitive coatings, the inclusion of additional nanoparticles may be desirable to improve conductivity or reduce cost (less purification). Therefore, the processing described herein has practical application in a wider range of conductive coating applications. Room-temperature processing of transparent and semi-transparent conductive films is described in co-pending U.S. patent application Ser. No. 18 / 212,297 to Yang et al., entitled "Formation of Electrically Conductive Layers at Room Temperature Using Nanoparticulate Processing and Inks for Forming the Layers," which is incorporated herein by reference. Of course, to increase the conductivity or reduce the resistance of the structure, the thickness of the silver nanowire / nanoparticle coating can be increased and / or multiple layers can be added. It is discovered here that through appropriate processing and nanoparticle selection, materials can be formed with unique and surprising conductive properties. Materials with a large volume fraction of polymer binder can exhibit resistivities comparable to tin or lead metals. Clearly, this material could be a solder alternative with extremely low toxicity and can be processed at room temperature.

[0032] The one-dimensional morphology of the nanowires facilitates the formation of sparse metallic conductive layers and fused metallic nanostructured networks, which have been found to exhibit desirable electrical, optical, and mechanical properties. To form transparent conductive films, the applicant's application of the fusion process can be controlled to selectively deposit metal at the junctions between the metal nanowires, or to form a fusion of lower conductive structures regardless of the nanoparticles. In the fused structure, unlike the non-fused structure, electrons can be conducted through the network rather than jumping between separate nanowires. The one-dimensional morphology of the silver nanowires appears to contribute significantly to the conductive properties of the discovered high-conductivity materials described herein, even though the materials are not sparse and transparent. Unless otherwise specified, conductivity referred to herein refers to electrical conductivity. However, it should also be noted that highly conductive structures and composites are generally also expected to have high thermal conductivity because both thermal and electrical conductivity are related to the kinetic energy of the electrons, which can typically dominate over phonon transport in metallic systems.

[0033] In the applicant's previous work based on thermodynamically driven fusing, this processing was carried out at relatively low temperatures. However, heat is used to control the drying rate and the fusing process and to accelerate other kinetic processes, reaction rates, and diffusion. In the context of commercial processing of conductive films, roll-to-roll processing has been developed using existing processing equipment to provide the required heating with consistent product quality, and moderate heating is easy to implement. However, heating does consume energy and does impose constraints on the substrate. Specifically, many plastic substrates, polymer substrates, and bio-related substrates exhibit low glass transition temperatures and / or low melting temperatures, which require low processing temperatures.

[0034] When faced with processing particularly heat-sensitive substrates, efforts have been made to reduce processing temperatures. Surprisingly, a system has been developed that achieves low sheet resistance with rapid results using room-temperature processing with a single ink deposition. These results are consistent with a well-prepared thermodynamic system that can be guided to achieve the desired results through appropriately tuned chemical combinations, as described herein. With these results, it is recognized that the desired processing improvements can also be applied to applications with less stringent optical property requirements, or even to non-transparent applications with beneficial effects.

[0035] As demonstrated by the results presented herein, the composition of the silver nanowire ink determines its effectiveness in forming a good conductive layer, with or without fusing the nanowires into a fused metal nanostructure network or other fused conductor, at temperatures not exceeding about 60°C, in additional embodiments not exceeding about 55°C, in other embodiments not exceeding about 50°C, in some embodiments not exceeding about 40°C, and in yet other embodiments not exceeding about 30°C, particularly at room temperature. For purposes herein, room temperature may be considered to be from about 16°C to about 28°C, although in some embodiments, it may be appropriate to consider the range of room temperature to be from about 18°C ​​to about 26°C, from about 20°C to about 25°C, or other suitable sub-ranges within the broad ranges provided. One of ordinary skill in the art will recognize that additional temperature ranges within the explicit ranges above are contemplated and are within the present disclosure. Drying may be facilitated by a gentle breeze, with or without low-temperature heating of the air.

[0036] Since the initial efforts to use silver nanowires to form conductive coatings, efforts have been made to reduce the sheet resistance resulting from the junction resistance between the nanowires. As demonstrated by applicant's initial fusing work, simply depositing a dispersion of nanowires to form a sparse metal layer can produce very high sheet resistance values, for example, in the megaohm / sq. range. For example, see the '207 patent cited below. Various efforts have been used in this effort, such as applying pressure and using various energy sources. A corresponding concern has been the processability of nanowire inks in forming consistent, high-quality coatings. Applicants have made an important leap in this effort by the invention of chemical fusing, i.e., enabling unfused structures to have very high sheet resistance, which can also be effective.

[0037] As an aid to the fusion process, the applicants have introduced processing aids (particularly binders) and coating agents to provide commercially processable and reproducible coating properties. In order to utilize these processing aids consistent with achieving fusion itself, the applicants have found that the choice of binder is important. The use of hydrophilic binders has been particularly successful with polysaccharide binders. Cellulose-based binders are convenient polysaccharides due to their widespread commercial use in many applications, including similar applications. Although not explicitly stated, the applicants' early work in the '968 patent cited below found that the use of polysaccharide binders provided considerable improvements in sheet resistance without the application of pressure or any further processing steps. Although not fully understood, appropriate polymers can reduce the junction resistance to approximately the level of extremely high pressure, although chemical fusion still provides a significant further reduction due to the bonding of the silver nanowires when forming a unitary structure. While not wishing to be bound by theory, this observation strongly suggests that some interaction between the polysaccharide binder and the metal nanowires allows the nanowires to be brought into close proximity, allowing them to electrically associate with each other and, if the correct chemistry and processing are employed, good conductivity can be achieved within the network of nanowires and polysaccharide binder. Without wishing to be bound by theory, this evidence also suggests some driving force and beneficial assembly between the polymer and the nanowires at the nanoscale, which tends to increase silver-silver contact while also providing significant surface association of the silver nanowires with the cellulose.

[0038] Furthermore, the synthesis of silver nanowires often involves the use of polyvinylpyrrolidone (PVP) as a capping agent to promote nanowire growth. Purification of the nanowires synthesized in this manner generally removes excess PVP, but some PVP often remains bound to the nanowires. Aggressive processing to remove PVP can lead to undesirable agglomeration of the silver nanowires. The silver nanowire inks described herein carry some PVP. Additional polymer binders may be added to impart desired material properties to the final product material, such as hydrophilic polymers (e.g., cellulosic polymers) or UV-crosslinkable polymers and resins. Due to the high density of metallic silver, relatively low amounts of organic matter can still yield a moderately high volume fraction of organic matter. Generally, purified silver nanowires retain approximately 5% to 20% PVP by weight relative to the weight of the silver nanowires. Because small amounts of added binder can be used, PVP can be the primary organic component. Preliminary results suggest that the amount of PVP can be reduced through further purification, but because PVP also acts as a dispersant, excessive removal of PVP can lead to agglomeration, and moderate removal of PVP is consistent with well-dispersed inks and high conductivity. Thus, dispersions can be formed with 1% to 20% PVP by weight, or in some embodiments, from about 2% to about 7% PVP by weight relative to the weight of the silver nanowires. While the aspect ratio of the silver nanowires is important for establishing high conductivity, a portion of the silver can be replaced with other silver particle shapes, such as silver flakes or silver nanoparticles. In particular, an equilibrium will be reached in the dispersion between PVP bound to the surface ("bound PVP") and PVP found dissolved in the solvent ("free PVP").

[0039] Applicants' efforts in room-temperature fusing have identified the unusual result that different silver salts used as fusing agents exhibit significantly different chemical properties during the fusing process. Specifically, in comparable ink systems using the same nanowires, binder, and solvent, fusing with silver fluoride significantly favors fusing over silver acetate and possibly other silver salts. Silver fluoride was used as one of several fluxes tested in the '746 patent and provided comparable results to silver nitrate in the process described there. Results herein are compared with a silver acetate flux. As shown in the results of the following examples, attempts to fuse with silver acetate without any heating did not provide the desired results. This result suggests that, even though the anion is believed to be a spectator in the relevant reactions, the anionic identity may alter the free energy of the reaction and / or may affect various activity and energy barriers associated with diffusion and reduction, although applicants do not wish to be bound by theory. In any case, the results strongly suggest that these systems exhibit controlled fusing near equilibrium, so that relatively small changes in free energy have observable effects. It is possible that other anions or complexes may lead to similar effects as fluoride, but this is not known. Other silver halides are insoluble in the relevant solvents, and soluble silver salts generally have anions that appear more similar to the acetate anion.

[0040] For the highly conductive materials of the present invention, the addition of silver salts as fluxing agents appears to slightly reduce conductivity in some embodiments and slightly increase conductivity in other embodiments, and it is not clear why this is the case. However, preliminary results suggest that fluxing agents are not as beneficial for the highly conductive materials described herein as compared to sparse metal layers. Fusing with metal salts is a tool that can be used to potentially increase conductivity to some extent, and the mechanical properties of the material may also be affected. Although not wishing to be limited by theory, as the number of contact points (junctions) between metallic particles increases, the total resistance decreases in the limiting case of infinite connections, which mathematically would approach the bulk metal resistance (for a system with junction resistances mixed across an infinite number of parallel resistors, Since each metallic segment (i.e., non-junction) also has an intrinsic resistance, once a sufficient number of low-resistance junctions are present, the inter-segment resistance and inter-particle resistance can become roughly of the same order of magnitude, and it is not necessary to fuse and / or fully sinter into an electrically and chemically bonded structure to achieve very low resistance. Although not wishing to be bound by theory, for sparse networks, which can have higher optical transparency, there are far fewer junctions and long inter-particle segments than for the opaque dense structures described herein, and therefore the dominance of the junctions on the total resistance in sparse networks can be much more severe than in dense networks.

[0041] For commercial silver nanowire inks used to form transparent conductive films, uniform coating on many substrates involves reducing the surface tension of the ink. Using higher silver nanowire concentrations to form highly conductive materials may be desirable, but conventional knowledge of silver nanowire ink compositions can be used to formulate these higher concentration inks to form highly conductive materials. In principle, various surfactants can be used, and fluorosurfactants have gained popularity for various practical reasons. Alcohols can act as both solvents and wetting agents, forming good coatings at higher concentrations. For room temperature processing, high-alcohol inks have been shown to be effective in forming highly conductive coatings with or without fusion. Alcohols can be selected to have a sufficiently low boiling point to evaporate relatively efficiently at room temperature. The choice of alcohol may be related to the amount of alcohol used. Although dependent on the specific branching structure and placement of the hydroxyl groups, boiling points tend to increase with increasing molecular weight, so higher alcohols with more carbon atoms tend to have higher boiling points and, accordingly, lower vapor pressures at room temperature. Generally speaking, the alcohols of interest can be C1 to C10 (based on the total number of carbon atoms in the molecule) alcohols at a concentration of 20% to 100% by volume based on the solvent liquid.

[0042] As described herein, it is possible to produce thin, opaque, highly conductive coatings using room temperature processing as described herein. With respect to transparent conductive films, applicants' development efforts have provided high-quality transparent conductive layers with outstanding optical qualities comparable to the highest quality indium tin oxide in a bendable and formable material (such that the material can be stretched and repeatedly folded within the durability of electrical conductivity). On the other hand, higher levels of electrical conductivity can be achieved by sacrificing some transparency. These coatings can be formed on flexible materials that can be temperature-sensitive substrates. For embodiments where good optical properties are not a goal, lower quality silver nanowires can be used, which can tolerate the presence of a larger proportion of non-nanowire nanoparticles, such as shape blends blended with the nanowires.

[0043] Transparent materials are generally considered in the art to have an average visible light transmittance of at least 60%, and this concept is adopted herein. After processing at room temperature, thin transparent conductive coatings can achieve sheet resistances of approximately less than about 3 ohms / square. To achieve even lower sheet resistance values, the material becomes translucent and ultimately opaque. The conversion of sheet resistance to resistivity is related to thickness, as further described below.

[0044] Chemical sintering has been discussed in the context of non-transparent structures. Room temperature sintering has been achieved using roughly spherical silver nanoparticles in the context of forming a pre-coat or subsequent deposition of a cationic chloride polymer (polydiallyldimethylammonium chloride, poly-DADMAC). See published U.S. patent application 2012 / 0168684 to Magdassi et al., entitled "Process for Sintering Nanoparticles at Low Temperatures" (hereinafter referred to as the '684 application), which is incorporated herein by reference. Poly-DADMAC is a polyelectrolyte that is not a suitable component in many situations. In some embodiments, the '684 application describes the inclusion of a sintering salt, NaCl, in the nanoparticle dispersion, but for these systems, it is necessary to heat the deposited material to achieve sintering.

[0045] The resulting structure taught by Magdassi differs significantly from the present material. For the present material, fusing with NanoGlue is not required to produce good conductivity, although it may have some effect. The present results strongly suggest a transition to a conductive material, which appears to be related to direct conduction along the nanowire structure and sufficient conductive band overlap due to the high loading of nanoparticle silver. While not wishing to be bound by theory or the applicant's knowledge, these conductive properties had not been observed prior to this work. Similar low-temperature processing of silver paste using silver flakes is described in U.S. Patent 11,084,950 to Graddy Jr. et al., entitled "Fast Conductivity Polymer Silver," which is incorporated herein by reference. The '950 patent does not report resistivity, but the material in the '950 patent appears to exhibit resistivity several orders of magnitude higher than that of the present work.

[0046] Although the '684 application mentions carboxymethyl cellulose, it does not teach the appropriate use of polysaccharide binders and, in particular, does not exemplify good conductivity without chemical sintering based on halide ions and chlorides. Although applicants have found that polysaccharide binders (e.g., cellulose) make particularly desirable contributions to transparent conductive films, in the highly conductive materials described herein, since the effects of polymer binders on the conductivity of the organic components are similar, the polymer binders appear to be interchangeable, as long as they do not destabilize the ink or cause nanowire agglomeration. Thus, the polymer binder can be selected to influence the mechanical properties of the dried conductive material. The use of silver nanowires appears to impart qualitatively different conductive properties, apparently due to the morphology associated with the high aspect ratio and possibly due to the number density of connection points / junctions formed between the conductive particles.

[0047] Silver provides excellent electrical conductivity and has the highest conductivity among elemental metals. To form non-transparent conductive coatings, the properties of the metal nanoparticles may become less important, although processing schemes here are generally based on nanowire processing. Even at high concentrations and high conductivities, nanowire morphology appears to contribute significantly to conductivity. For forming thin, opaque conductive coatings, high-quality nanowires may not be critical in terms of performance, so the resulting cost can be significantly lower. At higher silver loadings, any nanoparticles and other non-linear shapes can contribute more to electrical conduction by forming conductive pathways at higher densities.

[0048] Although the fusion technique has not been found to have a significant impact on the highly conductive materials that are the focus of this work, a brief summary of this work is provided. Regarding the applicant's proprietary fusion technique, it was initially discovered that halide ions can drive the fusion of metal nanowires to form fused metal nanostructures. Fluxes containing halide anions were introduced in various ways to successfully achieve fusion with a correspondingly significant decrease in electrical resistance. It should be noted that halide ions in this processing context should not be confused with the halide ions used in the nanowire synthesis reaction. Fusing metal nanowires with a halide source is further described in U.S. Patent No. 10,029,916 to Virkar et al., entitled “Metal Nanowire Networks and Transparent Conductive Material,” and U.S. Patent No. 9,920,207 to Virkar et al., entitled “Metal Nanostructured Networks and Transparent Conductive Material” (the '207 patent), both of which are incorporated herein by reference.

[0049] An extension of the process for forming fused metal nanowire networks is based on a reduction / oxidation (redox) reaction, which can be provided to produce fused nanowires without destroying the optical properties of the resulting coating. The metal used for deposition at the junction can be effectively added in the form of a dissolved metal salt or dissolved from the metal nanowires themselves. The effective use of redox chemistry to fuse metal nanowires into nanostructured networks is further described in U.S. Patent No. 10,020,807 to Virkar et al., entitled "Fused Metal Nanostructured Networks, Fusing Solutions with Reducing Agents and Methods for Forming Metal Networks" (the '807 patent), which is incorporated herein by reference. A single-solution approach for forming a fused metal nanostructured layer is further described in U.S. Patent No. 9,183,968 B1 to Li et al., entitled "Metal Nanowire Inks for the Formation of Transparent Conductive Films with Fused Networks" (hereinafter referred to as the '968 patent), which is incorporated herein by reference. The ink may further contain a dissolved metal salt as a metal source for the fusing process. Without wishing to be bound by theory, components of the polystyrene ink (e.g., hydroxyl groups or other organic components) reduce metal ions from solution to drive the fusing process—particularly with respect to the reduction of silver from ions introduced into the ink. Previous experience with fusing processes in these systems indicates that metal preferentially deposits at the junctions between adjacent metal nanowires, although the deposition mechanism in current dense opaque or translucent systems may differ. While not wishing to be bound by theory, similar materials are known to help catalyze reduction compared to the "homogenous nucleation" scenario in the absence of a solid support (i.e., a solid silver surface lowers the activation energy for the reduction of silver ions or complexes). Cluster stability and barriers to diffusion and decomposition are also prioritized in the presence of a solid substrate (i.e., a metal surface). Finally, similar to applicants' earliest work, it seems highly plausible that the regions of the recesses / junctions between particles will be the most thermodynamically and kinetically favorable locations for additional metal deposition and reduction. These junctions and intersections also have a significant impact on the final resistivity of the structure.

[0050] A polymer binder can be provided to stabilize the coating and influence ink properties. For highly conductive materials, polymer binder selection can influence the properties of the final material, as long as the polymer binder precursor is compatible with the silver nanowire dispersion. The specific formulation of the ink can be adjusted to select ink properties suitable for a specific deposition protocol and resulting in specific coating properties on the substrate surface. Inks with higher loadings have been found to exhibit non-Newtonian behavior, which can influence the choice of deposition protocol.

[0051] For room temperature fusion processes, the process conditions can be adjusted as appropriate relative to blowing air over the deposited coating at room temperature. If necessary, slight heating can be used in some embodiments. The air flow with or without heating can accelerate the solvent removal and the corresponding silver ion concentration to provide a reasonable fusion rate. As long as the ion mobility is maintained and a sufficiently reactive silver salt is applied, solvent evaporation and drying (even at low temperatures) can produce fusion and excellent conductivity. In the context of lower temperature processing, the conductive inks described herein even provide process advantages over commercial alternatives. Referring to Table 1 below, "typical" products refer to silver nanoparticle pastes or inks that have been on the market for some time, an example of which is Toyobo 520H-19 or 520H-41 that cures at 130°C to 150°C for 30 minutes. Low temperature 1 products refer to the next generation of nanoparticle-based products that can be processed at slightly lower temperatures. Examples of commercially available low temperature silver pastes include those from DuPont TM PE828 (ULTRA-LOW TEMPERATURE CURE SILVERCONDUCTOR), which can be processed at 60°C to 100°C.

[0052] Table 1

[0053]

[0054] The ability to form room-temperature conductive coatings is both a desirable processing improvement and a step toward enabling processing of heat-sensitive substrates. The ability to select a polymer binder allows for tuning the properties of the conductive material to provide varying degrees of flexibility or rigidity and enables UV curing. These materials could significantly expand the performance parameters of previously developed conductive silver pastes.

[0055] Concepts arising from room temperature fusion processing based on nanowires have made further progress in forming dense metal nanowire-based structures with high metal loading and very low resistance without the use of flux or high amounts of binders. Evidence suggests the existence of a new electrical conduction mechanism that is not yet fully understood. In some embodiments, the metal density of the resulting conductive structure can be at least about 25% of the bulk metal density. The sheet resistance of the structure can be less than 5 Ohms / sq, and in some embodiments less than 1 Ohm / sq, and the resistivity can be less than 20 times the resistivity of bulk silver. To impart more structural stability, a low amount of a cross-linkable polymer binder can be included to impart wear resistance and better adhesion.

[0056] Useful compositions for forming these highly conductive, dense particle structures involve forming concentrated aqueous or alcoholic dispersions of metal nanowires at concentrations greater than about 3% by weight, and in some embodiments, greater than about 5% by weight. Furthermore, the metal nanoparticles typically comprise at least about 75% by weight of the solids in the dispersion. Without agitation, the dispersions remain stable for at least 24 hours without observed settling. These concentrated solutions can have moderately high viscosities and exhibit shear thinning behavior, making them more suitable for a wide range of deposition techniques. Low-shear viscosities can be greater than 2500 centipoise (cPs). By using fewer additives, rather than more, to influence properties, the viscosity of the dispersion is surprisingly achieved, resulting in a significant portion of the solid content being metal. While a significant portion of the metal content can be metal nanowires, several additional metal nanoparticle shapes can be used to form the dispersion and the resulting conductive structure. Specific processing is used to achieve highly concentrated dispersions in water or other polar solvents. The ability to achieve extremely low electrical resistance opens the possibility for a wider range of suitable applications. Those of ordinary skill in the art will recognize that additional ranges of metal density, resistance values, viscosities, dispersion concentrations, and other values ​​associated with non-transparent, highly conductive embodiments are contemplated and are within the scope of the present disclosure.

[0057] The processing for forming opaque, highly conductive nanoparticle metal deposits can be performed at room temperature, which is desirable from an energy and process flow perspective. The removal of the solvent appears to form a conductive structure. From this perspective, the application of moderate heat is not expected to have an adverse effect on accelerating the solvent removal rate. Since it is believed that these structures and corresponding processing are reported for the first time, even if lower temperature processing has desirable aspects, the disclosure herein is not intended to imply that low temperature processing (e.g., not exceeding 60°C) is necessary, because slightly higher temperatures should also be appropriate for a limited period of time. For example, temperatures up to about 150°C should be acceptable for a short period of time.

[0058] Silver nanowire ink and deposition

[0059] Silver nanowire inks used to form highly conductive materials can exhibit specific properties. To reduce solvent usage and correspondingly reduce solvent removal, more concentrated inks have been developed, and if consistent with processing, these more concentrated inks are desirable. As nanowire concentration increases, the rheology of the ink changes accordingly. In contrast, to form transparent conductive films using silver nanowire inks, the required processing has tended to favor balance (near equilibrium) and fineness over the strong formation of fused metal nanostructured networks. Fineness is also effective for forming non-transparent conductive structures, but under these constraints, fusion is not believed to be involved, and the approach for forming dense metal deposits has been found to successfully form a new material with high conductivity based on high metal density and the resulting collective effect. Applicants' experience in forming state-of-the-art transparent conductive films has provided insights into the importance of forming well-dispersed silver nanowires at the beginning of processing. This experience has led to the high-concentration inks and highly conductive materials described herein. Formation of higher concentration inks involves forming a well-diluted dispersion, which is then concentrated by removing solvent to provide well-dispersed silver nanowires in a more concentrated dispersion. Aqueous dispersions can be formed with up to about 20% by weight silver nanowires. Traditional methods of forming higher concentration silver nanowire dispersions rely on ultrasonic treatment, which can damage the nanowires and is not efficient, or use the dispersion without forming a good dispersion.

[0060] In some embodiments, processing of the desired highly conductive structures from the ink using silver nanowire inks can be performed at room temperature, but some heating can be used to accelerate solvent evaporation, thereby making the processing gentler while achieving good conductivity. Therefore, ink processing involves the appropriate selection of components in the appropriate amounts. First, there are silver nanowires, which are discussed in detail below and can be mixed with small amounts of other silver nanoparticles and / or silver flakes. The solvent is typically aqueous and can contain a relatively small or large amount of alcohol. A surfactant (e.g., a fluorosurfactant) may or may not be used, and the suitability of the surfactant may depend on the alcohol content of the solvent. A polymer binder may be used. In new approaches to low-temperature processing of dense metal nanowire-based structures for non-transparent, low-resistance structures, the ink has a high percentage of the metal component as part of the solids in the dispersion and a relatively high metal concentration. A crosslinkable monomer, oligomer, or polymer with good mechanical strength can be added to the highly conductive structures to provide good mechanical stability.

[0061] Silver nanowires and, if desired, other silver particles can be selected to suit the intended application, and these can range from high-quality, very thin, uniform nanowires to thicker nanowires mixed with nanoparticles and other particles. Applicants produce and sell a range of silver nanowires, ranging in quality from very high-quality silver nanowires (which can be used to achieve excellent optical quality) to thicker, shorter silver nanowires (which can be used at higher concentrations at specific viscosities). Other silver particles can be included to provide a more conductive bulk metal at lower cost and with improved blending capabilities. For the highly conductive materials described herein, the majority of the silver is in the form of silver nanowires, as the silver nanowires appear to contribute significantly to the observed high conductivity, likely due to a conduction band extending along the length of the nanowires.

[0062] Applicants have made significant progress in understanding the properties of concentrated silver nanowire dispersions, their formation, and their uses. The shape of the metal nanowires tends to lead to irreversible agglomeration, so appropriate care must be taken in processing the nanowire dispersion to avoid agglomerate formation. The shape of the metal nanowires also contributes to the strong concentration dependence of viscosity on concentration. A higher aspect ratio tends to exacerbate the increase in viscosity, so shorter and thicker nanowires may be desirable for forming opaque materials using nanowires. On the other hand, a high aspect ratio can contribute to good electrical conductivity, and the results demonstrated herein appear to rely on a high aspect ratio of the nanowires. Similarly, other silver metal shapes (e.g., silver flakes and / or silver nanoparticles or other nanoparticles) can increase the metal density without a corresponding impact on the rheological properties of an equivalent mass of nanowires of the same order of magnitude.

[0063] Since the highly conductive materials described herein do not appear to benefit from chemical fusion using additional silver salts, a polymer binder may be used in addition to the hydrophilic polymers typically used to form transparent conductive films of fused metal nanostructured networks. The organic contribution to the ink provides a significantly lower density component relative to silver. The majority of the organic matter may be polyvinylpyrrolidone loaded from the nanoparticle synthesis. The composition and amount of the added polymer binder may be selected based on the desired composition of the final composite material. The inks described herein comprise an aqueous solvent, up to about 20% by weight silver particles, at least about 67% by weight silver nanowires, and from about 1% to about 25% by weight non-volatile organic matter. Further details regarding the ink formulation are set forth below.

[0064] Opaque conductive layers can be formed from dispersions of lower purity metal nanowires. The examples presented below are conductive films that form transparent or translucent coatings, but of lower optical quality, formed from scrap of synthetic high purity silver nanowires, where the scrap contains a range of nanowire morphologies, nanoparticles, and various other nanoparticle shapes. This work points to the possibility of supplementing nanowires with nanoparticles of other shapes for non-transparent applications. Commercial conductive products are typically based on silver flakes and / or silver nanoparticles and microparticles. These other silver shapes do not contribute to longer range conductivity, but they can be dispersed with little effect on the viscosity of the dispersion. Conductive pastes with silver flakes have been described as having the ability to achieve low resistivity. See, for example, published U.S. Patent Application No. 2015 / 0262728 to Ogiwara et al., entitled "Electrically Conductive Paste Composition and Method of Forming an Electrical Circuit on a Polymer Substrate," which is incorporated herein by reference. Comparable results were obtained for some embodiments using the silver flakes obtained herein, as greater than 90% by weight of the solids were silver flakes and the processing was performed at 120° C. for 0.5 hours.

[0065] In addition to silver nanowires, other metal particles (e.g., silver particles) can have any reasonable shape, but certain particles are commercially available for use in loaded polymers, adhesives, or resins. In particular, metal flakes and generally spherical particles are readily available for commercial scale production at reasonable cost. Silver nanoparticles with generally spherical shapes are commercially available in nanometer-sized sizes, with average particle sizes not exceeding approximately 200 nanometers, and can range from approximately 10 nanometers or less to as large as 200 to 300 nanometers. Micrometer-sized, generally spherical particles are also available, with average particle sizes ranging from approximately 1 micron to approximately 100 microns. A reasonable balance between performance and cost can be achieved with average particle sizes ranging from approximately 100 nanometers to approximately 5 microns. Suitable suppliers of silver particles (micrometer-sized particles or nanoparticles) include, for example, Heraeus, Inframat Advanced Materials, Ames Goldsmith, Sigma Aldrich, SS Nano, Cerrion Nano, SkySpring Nanomaterials, and Nanocomposix. The silver flakes can have a micrometer-scale length (or equivalent diameter) and a small thickness, for example, an average diameter of about 1 micrometer to about 20 micrometers and an average thickness of about 100 nanometers to about 2 micrometers. Representative descriptions of the synthesis of silver nanoflakes can be found, for example, in Hori et al., published U.S. Patent Application No. 2016 / 0114390, entitled "Flake-Like Silver Powder, Conductive Paste, and Method for Producing Flake-Like Silver Powder," which is incorporated herein by reference. Silver flakes are commercially available from companies such as Tanaka, Ferro, Reade, and Inverman Advanced Materials. In principle, any suitable conductive particle and its blends can be used, such as silver-plated particles, copper particles, nickel particles, and the like.

[0066] Silver provides excellent electrical conductivity. ®) inks sell silver nanowire inks for forming fused metal nanostructured networks. Applicant has recently developed a thicker line of silver nanowires suitable for opaque applications. A description of the synthesis of these thicker silver nanowires can be found in co-pending U.S. Provisional Application No. 63 / 459,495 to Virkar et al., entitled "High Loadings of Silver Nanowires; Dispersions and Conductive Pastes; and Corresponding Methods," which is incorporated herein by reference. Other sources of silver nanowires are commercially available, and the basic fusing technology is described in detail in the '207 patent and the '807 patent cited above. GEN5 Active Grid ® The vast majority (>98%) of the silver nanowires in the 7th generation (GEN7) ActiveGrid have diameters less than 25 nanometers. ® The vast majority (>98%) of the silver nanowires in the product have a diameter less than 22 nanometers. The synthesis of thin silver nanowires is described in U.S. Patent No. 10,714,230 B2, "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed from the Nanowires," by Hu et al., which is incorporated herein by reference. For purposes of this disclosure, nanowires are considered to have an average diameter less than 200 nanometers, and in some embodiments, less than 100 nanometers, an average length of at least about 1 micrometer, and in further embodiments, at least about 2 micrometers, and an average aspect ratio of at least about 10, in further embodiments, at least about 50, in other embodiments, at least about 75, and in some embodiments, at least about 100. Various silver nanowires are commercially available from the applicant or other sources. Nanoparticles can be identified by at least one average particle dimension being no greater than 200 nanometers, and in further embodiments no greater than about 150 nanometers, in further embodiments no greater than about 100 nanometers, and in other embodiments no greater than about 80 nanometers. Thus, nanoparticles may include, for example, nanoplates, nanoparticles, nanoshells, nanorods, and branched nanorods. As described above, silver microparticles may also be used. One of ordinary skill in the art will recognize that additional ranges of silver nanowire and metal nanoparticle sizes within the explicit ranges above are contemplated and are within the scope of the present disclosure.

[0067] The solvent used in the ink may be aqueous (at least about 51% by weight and 51% by volume water), in some embodiments at least about 60% by volume water, in yet other embodiments at least about 75% by volume water, and in other embodiments at least about 95% by volume water. In some embodiments, the solvent is essentially water. Other volatile components of the ink may include other liquids that are miscible in water, or at least soluble within a relevant concentration range. Organic solvents may include alcohols (which can improve the rheological properties of the ink) or other polar solvents. If an alcohol is used, its choice is generally not critical, but the alcohol should generally have a low boiling point to allow for good drying at room temperature or with mild heating. From this perspective, the alcohol is typically a monohydroxylated aliphatic alcohol having no more than 10 carbon atoms, with methanol, ethanol, propanol, isopropanol, and mixtures thereof being convenient. Smaller amounts of higher-boiling-point polar components (e.g., ethylene glycol) may be added to influence the ink's properties. In some embodiments, the solvent comprises from 0.1 volume percent (vol%) to about 49 volume percent alcohol, in further embodiments from about 0.5 volume percent to about 40 volume percent alcohol, and in other embodiments from about 1 volume percent to about 25 volume percent alcohol. A high-loading dispersion method may include initially dispersing the silver nanowires in an alcohol to form a good dispersion of the silver nanowires, as further described below. One of ordinary skill in the art will recognize that additional solvent concentration ranges within the explicit ranges above are contemplated and within the scope of the present disclosure. The solvent may also contain up to about 5 volume percent of other components, such as polar solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methyl ethyl ketone, glycol ethers (e.g., ethylene glycol methyl ether and propylene glycol methyl ether), methyl isobutyl ketone, ethyl acetate, butyl acetate, ethyl lactate, ethyl 2-methoxy-1-methylacetate (PGMEA), dimethyl carbonate, or mixtures thereof. While the solvent should be selected based on its ability to form a good dispersion of the metal nanowires, it should also be compatible with other selected additives such that the additives are soluble in the solvent.

[0068] In a suitable solution, the ink is stable before it is deposited and dried. The ink may contain a reasonable amount of polymer binder, which helps to form a stable conductive coating for further processing. In the ink, the polymer binder precursor may contain dissolved solid polymers and / or liquid monomers, oligomers or polymers for deposition. After deposition, the polymer binder precursor may form a polymer binder by drying and / or by polymerization, crosslinking or both polymerization and crosslinking, which may or may not be based on the same chemical mechanism. To promote the formation of the polymer binder, the ink may contain a crosslinker, a free radical initiator, a catalyst, etc., which are usually present in small amounts as additives. In order to form a transparent conductive film and to obtain good fusion results using an ink system, it has been found that hydrophilic polymers can be effectively used as binders, in particular, for example, cellulose, chitosan, xanthan gum or other polysaccharide polymers. In some embodiments, the polysaccharide binder may have an average molecular weight of less than 10,000 g / mol. Suitable cellulose binders include, for example, cellulose ethers such as methylcellulose, ethylcellulose, ethylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and mixtures thereof. Other (polar) resins and oligomers are also suitable. To form highly conductive, dense metal structures, some polysaccharides may be suitable processing aids, and small amounts of cross-linkable, mechanically strong polymer binders may be used to reinforce the structure without sacrificing conductivity. While polysaccharides exhibit significant properties as binders for silver nanowires in transparent conductive films, they do not exhibit similar advantages over other binders for forming opaque materials with high silver loadings. Other binders (e.g., cross-linkable binders) may be used to provide the desired mechanical properties for the conductive material. Other suitable binders include, for example, suitable water-based resins such as acrylates, epoxies, urethanes, and blends thereof. See, for example, Jiao et al., "Advances in Waterborne Acrylic Resins: Synthesis, Principles, Modification Strategies, and Their Applications," ACS Omega, 2021, 6, 2443-2449, incorporated herein by reference. Crosslinkable water-soluble resins are commercially available, and three acrylate resins from Arkema Sartomer Americas are exemplified below. Polymer binders are further discussed below in the context of processed materials.

[0069] A single ink formulation provides the desired metal loading for deposition as a coating on a substrate surface while also providing constituent components in the ink that provide the desired properties for a cured conductive material. In order to form a highly conductive material, in addition to having a high proportion of metal conductor to ink solids, the ink should also have a high concentration of metal particles, which in some embodiments is at least about 3.0% by weight, in yet other embodiments is at least about 3.5% by weight, and in other embodiments is at least about 4% by weight. High concentrations of metal nanowires and, optionally, other nanoparticles in the ink can be achieved by forming a good dispersion using a mostly polar organic solvent (e.g., an alcohol such as ethanol or isopropanol) with a boiling point not exceeding about 95° C., and evaporating the solvent to produce a suitably concentrated dispersion or ink, which may or may not be aqueous. One of ordinary skill in the art will recognize that additional ranges of nanoparticle concentrations and solvent boiling points within the explicit ranges above are contemplated and within the scope of the present disclosure.

[0070] The formation of inks for depositing highly conductive, high metal density materials results from improvements in forming metal nanowire dispersions that contain lower amounts of polymeric dispersants while still providing stable dispersions with good particle packing. As discussed above, forming more concentrated solutions is desirable to facilitate and mitigate solvent evaporation issues. To concentrate the solution, one method of forming the ink includes evaporating an organic solvent to achieve a desired concentration. In some embodiments, the organic solvent may have a boiling point of no more than about 95°C to concentrate the aqueous dispersion of metal nanowires, thereby forming an ink having a metal nanowire concentration of at least 3% by weight, wherein the ink remains stable for at least 24 hours without visible settling, without agitation.

[0071] For embodiments of particular interest, the nanowires are silver nanowires, and for fused embodiments, the metal ion source is a dissolved silver salt, although other metal salts may also be used to deposit the reduced metal. The ink may contain silver ions at a concentration of about 0.005 mg / ml to about 50.0 mg / ml silver ions, in further embodiments at a concentration of about 0.01 mg / ml to about 25.0 mg / ml, and in other embodiments at a concentration of about 0.05 mg / ml to about 10.0 mg / ml. One of ordinary skill in the art will recognize that additional ranges of metal nanowire concentrations and metal ion concentrations within the explicit ranges above are contemplated and are within the scope of the present disclosure. The concentration of the metal nanowires affects the metal loading on the substrate surface and the physical properties of the ink.

[0072] Metal nanowires typically comprise silver. Applicants have used silver nanowires coated with precious metals to form transparent conductive films with good optical properties. See U.S. Patent 9,530,534 to Hu et al., entitled "Transparent Conductive Film," which is incorporated herein by reference. In general, other metal nanowires would be expected to exhibit similar properties. Gold nanowires, platinum nanowires, palladium nanowires, copper nanowires, and other metal nanowires would be expected to exhibit similar performance. Silver nanowires are preferred for highly conductive materials due to their high electrical conductivity, but precious metal coatings can improve the durability of the nanowires without significantly adversely affecting electrical conductivity.

[0073] About ink formula, polymer binder and / or organic resin and solvent are usually selected in unison so that polymer binder is soluble in or can be dispersed in solvent.Based on example, binder can be considered to be divided into polysaccharide binder and other binders.If not distinguished, then can be interpreted as total binder when mentioning binder.As mentioned above, non-volatile organic matter can account for about 0.1 weight % to about 25 weight % of ink solids, in some embodiments, account for about 1 weight % to about 20 weight %, in other embodiments, account for about 2 weight % to about 15 weight %, and in some embodiments, account for about 2.5 weight % to about 12.5 weight %, this comprises non-volatile ink component.Can be based on respective density, weight percentage value is converted into volume percentage value, and because silver is relative to the relatively high density of organic matter, therefore the volume percentage of binder will be correspondingly significantly higher and can be main volume component.Usually, organic matter volume percentage can be about 10 volume % to about 95 volume %, in some embodiments, be about 15 volume % to about 90 volume %, and in other embodiments, be about 20 volume % to about 87.5 volume %. Correspondingly, the metal volume percentage may range from about 5% to about 90% by volume in some embodiments, from about 10% to about 85% by volume in yet another embodiment, and from about 12.5% ​​to about 80% by volume in other embodiments. Non-volatile organics typically include polymer binders, resins, crosslinkable monomers, and oligomers, but a portion of the non-volatile organics may be processing aids, such as surfactants, crosslinkers, or other suitable additives. As described above, silver nanowire synthesis typically results in polyvinylpyrrolidone (PVP) loaded onto the silver nanowires. While the amount of PVP can be reduced with further purification, conventional purification can yield PVP in an amount of 5% to about 20% by weight, with a rough estimate of about 10% by weight. Thus, in addition to PVP, the ink may contain no added polymer binder or, in some embodiments, from about 1% to about 95% by weight of non-volatile organics, in yet other embodiments, from about 10% to about 90% by weight, and in other embodiments, from about 20% to about 85% by weight. One of ordinary skill in the art will recognize that additional organic concentration ranges within the explicit ranges above are contemplated and are within the scope of the present disclosure.

[0074] In some embodiments, the nanowire ink may optionally include a rheology modifier or a combination thereof. In particular, the ink may include a wetting agent or surfactant to reduce surface tension, and wetting agents can be used to improve coating properties. A variety of surfactants, such as nonionic surfactants, cationic surfactants, anionic surfactants, zwitterionic surfactants, and Gemini surfactants, are commercially available. Fluorosurfactants can provide desirable ink properties but may not be required for certain applications and final formulations. The purpose of fluorosurfactants is to act as wetting agents, providing low surface tension, good wetting, and film formation on the substrate. Wetting agents are typically soluble in the solvent used. In some embodiments, the nanowire ink may include from about 0.001% to about 1% wetting agent by weight, in further embodiments from about 0.002% to about 0.75% wetting agent by weight, and in other embodiments from about 0.003% to about 0.6% wetting agent by weight. One of ordinary skill in the art will recognize that additional ranges of binder concentration and wetting agent concentration within the explicit ranges above are contemplated and within the scope of the present disclosure. As mentioned above, higher alcohol concentrations in the solvent can provide effective wetting and processing. In some embodiments, in situations where the alcohol concentration is high, it was found that the presence of a separate surfactant inhibited room temperature processing, but in other low alcohol solvents, it was found that a separate surfactant worked well. In general, other processing aids, such as thickeners, antioxidants, etc., may or may not be used in various inks, and some of these processing aids may inhibit room temperature processing, while other processing aids may be good. Based on the teachings of this article, one of ordinary skill in the art can easily test this. However, in general, other additives will not exceed about 5% by weight of the solids considered as non-volatile components.

[0075] Silver nanowires used commercially to form transparent conductive films are typically deposited by slot coating, and this can be done in a roll-to-roll format. Coating and fusing can be conveniently performed in this format. Applicants have outlined this processing for extremely thin polymer sheets with double-sided conductive coatings, as described in published U.S. patent application 2020 / 0245457 to Chen et al., entitled "Thin Flexible Structures With Surfaces With Transparent Conductive Films and Processes for Forming the Structures," which is incorporated herein by reference. For non-flat surfaces, dip coating, spray coating, etc. can be used. For non-transparent, highly conductive structures, the structure can be deposited to form a thicker deposit after drying, providing lower circuit resistance when the structure is connected to an appropriate bus, etc. Highly conductive structures formed from denser metals can also be used as bus bars, etc.

[0076] In general, the same nanowire ink formulations used for slot coating, inkjetting, dispensing, printing, other jetting, and screen printing can be used for these alternative coating processes, but specific embodiments may require modifications. The higher viscosity and non-Newtonian shear-thinning behavior of denser inks are more suitable for a wider range of deposition processes. The conductive layer can be patterned using laser patterning, etchants, or photolithography, but some applications may not involve patterning, and if the ink can be printed, the required patterning can be formed during deposition. Nanowire morphology complicates the printing of nanowire inks with fine feature sizes, although several developments in new printing techniques are underway in academic and industrial labs to print NW-based inks at higher resolutions. A description of metal nanowire printing can be found in U.S. Patent 8,454,859 to Lowenthal et al., entitled "Metallic Nanofiber Ink, Substantially Transparent Conductor, and Fabrication Method," which is incorporated herein by reference.

[0077] The nanowire loading on a substrate can typically be expressed as milligrams of nanowires or metal particles per square meter of substrate and can be calculated based on the known deposited amount and area. For transparent applications, the nanowire network can have a loading of about 1 mg / m² to about 500 mg / m² for a transparent film, about 0.5 mg / m² to about 200 mg / m² in further embodiments, and about 1 mg / m² to about 150 mg / m² in other embodiments, while for opaque films, the loading can be greater than 1000 mg / m², greater than 10,000 mg / m², or even greater. Those skilled in the art will recognize that additional ranges of thickness and loading within the explicit ranges above are contemplated and are within the scope of this disclosure. For non-transparent applications, metal loading is not particularly limited, but depending on the properties of the nanoparticles, there will be a range of semi-transparent metal loadings, with opaque films having even higher metal loadings. Using more concentrated inks to form denser metal deposits can provide lower resistivity and lower circuit resistance for appropriate applications. Multiple coatings can be performed to increase the loading and reduce sheet resistance. The metal loading effectively depends on the concentration of nanowires or other silver particles in the ink and the wet coating thickness.

[0078] For processing at room temperature, the processing performed after the ink is applied can be minimal. For consistency and slightly faster drying, unheated air can be gently delivered to remove solvent vapors and accelerate drying. Whether or not blowing is used, sufficient drying can be achieved for the film within a few minutes to achieve fusion or to achieve the required conductivity in the absence of flux. For practical reasons, thicker coatings can take correspondingly longer to dry. These times are short compared to traditional coating processing times, so no effort has been made to push the times to a shorter amount, but if necessary, this time can be optimized. An air knife or the like can also be used to dry the solvent to provide the final conductive film.

[0079] Although not required for appropriate systems, some heat may be applied to accelerate the process. For example, the blown air may be heated, or the coated substrate may be placed in an oven or the like at a selected temperature. However, in general, to save costs, reduce the environmental footprint, and make the process applicable to a wider range of applications, it is advantageous to process without added heat (if possible). In particular, heat may be applied to promote and accelerate the drying and / or crosslinking of the polymer binder. Drying temperatures are typically below 250°C, although higher temperatures may be tolerated for short periods of time. In further embodiments, the drying temperature may be from about 40°C to about 225°C, and in yet other embodiments, from about 45°C to about 200°C. In some embodiments, heating may be performed for from about 5 seconds to about 90 minutes, in still other embodiments for from about 10 seconds to about 75 minutes, and in other embodiments for from about 20 seconds to about 65 minutes. Similarly, radiation (e.g., ultraviolet radiation) may be used to crosslink suitable polymer binders, resins, monomers, and oligomers, and the choice of resin and photoinitiator can guide the appropriate irradiation process. One of ordinary skill in the art will recognize that additional temperature and heating time ranges within the explicit ranges above are contemplated and are within the scope of the present disclosure.

[0080] Conductive structure

[0081] Conductive structures can be designed to suit specific applications. Since the range of conductive materials that can be formed using the processing described herein is large, the range of properties can accordingly cover a wide range for different applications. Therefore, a full range of properties can be considered, and the coatings can be grouped to help focus on the range of potential target applications. Although many of the applicant's previous efforts have focused on transparent conductive films, the current focus is on opaque materials, although thin applications of the materials can be translucent. Reasonable groupings of optical properties can have translucent materials (conductive layer transmittance from slightly above 0 to about 70%) and opaque materials (zero transmittance).

[0082] As optical quality and high transmittance become less important, blends of nanoparticles become more applicable. Therefore, if optimal transparency is not the goal, nanowires do not necessarily need to be highly purified to avoid other particle shapes. Removal and purification of nanoparticles formed during synthesis can be a significant cost factor. Nanoparticles and other unusual silver particle shapes may contribute disproportionately to scattering and reflection relative to their contribution to conductivity, but as optical properties become less relevant, the taboo regarding the presence of non-nanowire shapes also becomes less relevant. Consequently, opaque and translucent conductive films and other structures can be formed at a lower cost than high-quality nanowire coatings. Once the conductive coating becomes opaque, the coating may no longer be sparse, and nanoparticle shape becomes less relevant, although based on results obtained to date, the nanowires still contribute disproportionately to conductivity relative to their weight. Specifically, the aspect ratio of the silver nanowires also contributes to conductivity, so for the highly conductive materials described herein, the majority of the metal agglomerates should be metal nanowires as described above.

[0083] For opaque structures, the processed coating can more closely resemble a uniform, dense material. In principle, thickness is not a limitation for opaque structures. This is particularly true for structures formed using concentrated nanowire inks. For highly conductive, opaque or slightly translucent structures formed from highly concentrated inks, the structure can have an average thickness of at least about 50 nanometers, and in some embodiments, at least about 100 nanometers, and in yet other embodiments, at least about 500 nanometers, as well as subranges within these ranges. Assuming the structure is not porous and summing the densities of the components in proportion to their contribution to mass, the thickness can be estimated by total mass loading per unit area and calculating the density. Thickness can be influenced by the desired electrical resistance of the structure, which decreases proportionally with thickness. Thickness can be estimated using a weighted average of the densities or can be measured directly, for example, using a micrometer.

[0084] refer to Figure 1, a representative conductive film 100 includes a substrate 102, an optional undercoat layer 104, a metal conductive layer 106, an overcoat layer 108, an adhesive layer 110, and a protective surface layer 112, although not all embodiments include all layers. Although polymer sheets are the desired substrate for many applications, for other substrates, the film 100 can be equivalently considered to be a conductive structure, so the "film" described herein can be equivalently considered to be any reasonable structure. For transparent embodiments, the metal conductive layer 106 will be sparse, the substrate 102 will be transparent, and the adhesive layer will be optically transparent, and the other layers can be made appropriately transparent in a similar manner. Typically, the adhesive layer 110 and the protective surface layer 112 are added after the important processing described herein is completed to improve the stability of one or more conductive layers. Transparent conductive films typically include a sparse metal conductive layer and at least one layer located on each side of the sparse metal conductive layer.

[0085] For some opaque embodiments, the total thickness of the conductive structure based on metal nanowires may typically have an average thickness of 0.25 microns to about 2 mm, in some other embodiments about 1 micron to about 1 mm, and in other embodiments about 5 microns to about 0.5 mm, but generally any reasonable thickness can be used for opaque structures. It should also be noted that for opaque embodiments, the thickness is generally not limited, and the conductive structure can be placed directly on the structure to incorporate conductive features, wherein in some embodiments, the conductive structure can form a bus or similar conductive connection. Those of ordinary skill in the art will recognize that additional thickness ranges within the above-specified ranges are contemplated and are within the scope of the present disclosure. In some embodiments based on conductive films, the length and width of the produced film can be selected to be suitable for a specific application so that the film can be directly introduced for further processing into a product. In additional or alternative embodiments, the film width can be selected for a specific application, while the length of the film can be long in the case where it is desired that the film can be cut to the desired length for use. For example, the structure can be in the form of a long sheet or placed on a roll. Similarly, in some embodiments, the film may be provided on a roll or in another large standard form, and the assembly of film may be cut to the desired length and width for use.

[0086] Given the range of potential applications, substrate compositions can be selected from a wide range of possibilities, particularly for opaque embodiments. Examples are provided on cardboard and fresh leaves, so even some porosity can be tolerated, although significantly more extreme substrates may not be suitable. As mentioned above, for these broader applications, the structure can be considered a membrane, rather than the term thin film. Therefore, glass, ceramics, polymers, various organics, and composites may be suitable substrates for opaque embodiments. Generally speaking, many polymeric and biological substrates require low processing temperatures due to melting, decomposition, unwanted reactions, or other adverse transformations and effects (glass transition, softening, diffusion, color loss, modulus change). Therefore, the ability to generate conductive layers at ambient temperature or with minimal heating could enable a wide range of new applications and commercial products. Conductive inks or composite precursors can also be deposited directly onto active components (such as displays, sensors, or the like), or used as interconnects to electrically or thermally connect other components, electronic devices, or devices.

[0087] The substrate can generally have any reasonable size. For many commercial applications, roll-to-roll processing can be a convenient form of processing. Typically, for roll-to-roll embodiments, the substrate can have an average thickness of about 1 micron to about 1.5 millimeters, in further embodiments about 5 microns to about 1 millimeter, and in additional embodiments about 10 microns to about 500 microns. Specifically, for foldable structures, especially double-sided foldable structures, the substrate thickness can be no more than about 27 microns, and in further embodiments can be about 5 microns to about 25 microns. With appropriate choice of adhesive and processing, the highly conductive nanowire-based material should be reasonably flexible. One of ordinary skill in the art will recognize that additional ranges of substrate thickness within the above-specified ranges are contemplated and are within the scope of the present disclosure.

[0088] Suitable polymers for the substrate include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylates, poly(methyl methacrylate), polyolefins, polyvinyl chloride, fluoropolymers, polyamides, polyimides, polysulfones, polysiloxanes, polyetheretherketones, polyethersulfones, polynorbornene, polyesters, polystyrene, polyurethanes, polyvinyl alcohol, polyvinyl acetate, acrylonitrile-butadiene-styrene copolymers, cycloolefin polymers, cycloolefin copolymers, polycarbonates, copolymers of the foregoing polymers, or blends of the foregoing polymers. Suitable commercial polycarbonate substrates include, for example, MAKROFOL SR243-1-1CG, commercially available from Bayer Material Science; TAP® plastics, commercially available from TAP Plastics; and LEXAN TM 8010CDE, commercially available from SABIC Innovative Plastics. Polyimide substrates are available from Kolon, and polysulfone substrates are available from Solvay. Cyclic polyolefin (COP) is available from Zeon Corporation. The reduction in processing temperature described herein allows the use of a wider range of polymers and other substrates. For non-transparent substrates, most reasonably coatable materials other than polymers can be used. The deposition substrate or surface can also be metal, glass, ceramic and / or specific components or devices. Optionally, encapsulants, adhesives, barrier layers or other protective coatings can be added, depending on the final reliability requirements and device design and architecture.

[0089] The substrate polymer may also be suitable as a binder polymer. Binder polymers are typically hydrophilic. Thus, suitable binder polymers may include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylates, poly(methyl methacrylate), polyamides, polyimides, polysulfones, polysiloxanes, polyesters, epoxy resins, polyurethanes, polyvinyl alcohol, polyvinyl acetate, copolymers thereof, or blends of these polymers. The corresponding ink may contain a dissolved polymer or polymer precursor or a mixture thereof, where the mixture means a mixture of possible polymers, a mixture of polymer precursors, or a mixture of a polymer and a precursor. As described above, the polymer binder is provided in the ink in the form of a monomer, an oligomer, a dissolved polymer, or a mixture thereof, and is subsequently further polymerized or cross-linked.

[0090] If surface coating issues predominate, a primer layer may be applied to improve adhesion to specific materials. Additionally, potential adhesion promoters and selected resins may be added to improve adhesion. Thus, a thin polymer layer can provide a suitable surface for applying a conductive layer, although direct application of the conductive layer has been achieved on a range of materials. The primer polymer may independently comprise the polymer classes described above for the substrate and may be applied by solution coating and, if desired, subsequent crosslinking (e.g., by UV exposure or thermal curing). The primer polymer may be applied using the same techniques as the nanowire ink. Particularly for less transparent or opaque embodiments, the thickness of these layers may not be critical, but for transparent embodiments and some other embodiments, the topcoat layer may have an average thickness of about 5 nanometers to about 2 microns, in some embodiments about 7 nanometers to about 1 micron, and in other embodiments about 8 nanometers to about 250 nanometers. Those skilled in the art will recognize that additional thickness ranges within the explicit ranges above are contemplated and within the scope of this disclosure.

[0091] Coating / Material Properties

[0092] Conductive coatings or deposits from opaque materials can be formed into non-transparent structures. Non-transparent layers (e.g., translucent or opaque layers) are typically formed with high metal loadings to impart lower sheet resistance. Haze and other optical properties are generally not a particular concern for these coatings. These highly conductive structures can be used to form metal traces, bus bars, electromagnetic shielding, and more.

[0093] The electrical resistance of thin coatings can be expressed as sheet resistance (Rs), which is reported in ohms per square (Ω / □ or ohms / sq) to distinguish between sheet resistance and bulk resistance values ​​based on parameters related to the measurement process. The sheet resistance along the surface is typically measured using a four-point probe measurement or another suitable method. If the thickness of the structure is known or measurable, the resistivity (ρ) can be estimated as ρ = R s·t, where t is the average thickness. Resistivity is an intrinsic parameter that is independent of size and has units of ohms times length. For non-transparent coatings, sheet resistance values ​​below 1 ohm / square can be achieved, and translucent coatings can be formed from approximately this value or on the order of magnitude greater. Although not being limited by theory, it is believed that low resistance can be achieved by simply increasing the silver loading and / or by thicker coatings, and low resistivity close to the resistivity of bulk silver can be achieved by increasing the density. One of ordinary skill in the art will understand that this system can be well simulated using a parallel resistor model, where the resistance can be estimated by the thickness. For example, if the thickness of the conductive coating is increased by a factor of 2 from the thickness at which 1 ohm / square is achieved, the thicker (2x) film should have a resistance of 0.5 ohms / square. Although the measured sheet resistance depends on the intrinsic properties and dimensions of the corresponding structure, assuming the material is homogeneous, the resistivity is an intrinsic property of the material and is independent of the structure. Bulk silver resistivity is reported to be 1.59×10 -6 Ohm-cm, which is the lower limit of the resistivity of silver-based conductors. High-loaded silver materials can achieve no more than about 5×10 -3 Ohm-cm, in some embodiments no more than about 5×10 -4 Ohm-cm, in still other embodiments no more than about 1×10 -4 Ohm-cm and in other embodiments about 5×10 -5 to about 5×10 -6 Ohm-cm resistivity. In general, for these low binder embodiments, fusion with reduced silver salts does not appear to reduce resistivity. Thus, by low temperature processing, the silver nanowires and any other nanoparticles remain as separate particles within the composite, as compared to the fused metal nanostructured network. One of ordinary skill in the art will recognize that additional sheet resistance ranges within the explicit ranges above are contemplated and are within the scope of the present disclosure.

[0094] In principle, optical transparency is inversely proportional to loading, with higher loadings resulting in reduced transparency, although processing of the network can also significantly affect transparency. In addition, polymer binders and other additives can be selected to influence optical transparency. Optical transparency can be assessed relative to the transmitted light through the substrate. Using the high-load inks described herein, the formation of thin coatings can be used to form semi-transparent conductive films. 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 supporting substrate. Transmittance is the ratio of the transmitted light intensity (I) to the incident light intensity (I o ) ratio. The transmittance through the coating (T coating ) can be calculated by dividing the measured total transmittance (T) by the transmittance through the supporting substrate (T sub) to estimate. (T = I / I o And T / T sub = (I / I o ) / (I sub / I o ) = I / I sub = T coating ). Therefore, the reported total transmission can be corrected to remove the transmission through the substrate and obtain the transmission of the coating itself. The transmission can be reported as the total transmittance of light with a wavelength of 400 nm to 700 nm. Generally, for metal nanowire-based films, the measurement of 550 nm transmittance is not qualitatively different from the total transmittance (or just "total transmittance" for convenience) from 400 nm to 700 nm. The transparency of films on transparent polymer substrates can be evaluated using standard ASTM D1003 ("Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics"), which is incorporated herein by reference. In general, the properties of the materials and films can be adjusted to produce a selected transmittance of 0% to 70% for a translucent film.

[0095] Examples

[0096] General Materials and Methods

[0097] As shown in Table 2, inks S1 to S7 were prepared based on ActiveGrid® inks from applicant C3 Nano GmbH. The ActiveGrid® inks include a fifth generation ActiveGrid® ink having silver nanowires with an average diameter of less than 25 nm, a seventh generation ActiveGrid® ink having silver nanowires with an average diameter of about 18 nm, and an eighth generation ActiveGrid® ink having silver nanowires with an average diameter of 13 nm to 15 nm. The inks contain a hydroxyalkyl alkyl cellulose binder. Some ink formulations include silver salts AgOAc or AgF, and each silver salt is applied in different amounts in each example as detailed below. In the seventh generation (1x G7 ) ink and eighth generation (1x G8 The standard amount of AgF (1x) in the 5th Generation ink is approximately 50% higher than that in the 5th Generation ink. Silver salts are used in the inks of each example and are referred to as NanoGlue® AgOAc and NanoGlue® AgF.

[0098] Table 2

[0099]

[0100] As shown in Table 3, the inks were applied to various polymer substrates. The substrates included 50-micron polyethylene terephthalate (PET) with and without a hardcoat, and cyclic olefin polymer (COP). The inks were applied using a slot coater set to different gap thicknesses of 1.5 mils (38.1 microns) or 4.0 mils (101.6 microns). For some samples, the inks were applied using a #14 wire wound rod to provide a gap thickness of 1.4 mils (35.6 microns).

[0101] Table 3

[0102]

[0103] The samples were subjected to various processing conditions, as detailed below for each example. Some wet coatings were initially dried using an air gun (with room temperature ~ 25°C air) approximately 1.5 inches to 3 inches above the film for about 30 seconds to 60 seconds, and some were further heated in an oven at various temperatures ranging from 35°C to 120°C and for various times ranging from 0.5 minutes to 210 minutes. Some wet coatings were dried at room temperature without any heating. Some wet coatings were dried at room temperature using a fan to blow cool air at approximately 21°C over the samples.

[0104] The average sheet resistance was measured using a sheet resistance measurement device from SURAGUS GmbH. The average total transmittance (%TT) and average haze (%H) were measured using a haze meter. The average b* was measured using a colorimeter.

[0105] In general, the processing used to form the transparent conductive film is essentially as described in Example 5 of the '968 patent cited above, wherein the silver nanowires are synthesized as described in U.S. Patent 10,714,230 B2, entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed From the Nanowires" by Hu et al., which is incorporated by reference herein.

[0106] Example 1 - Processing with different fluxes with or without heating - Transparent sample

[0107] This example demonstrates the effectiveness of silver nanowire films with different silver salts dried and / or processed under different conditions as shown below in Tables 4 and 5. Coatings with a gap thickness of 1.5 mils were prepared on primed PET.

[0108] Table 4

[0109]

[0110] Table 5

[0111]

[0112] As shown in Table 4, Sample 2, dried in an oven at 120°C for 2 minutes, exhibited the lowest sheet resistance of 37 ohms / square. Samples 3 through 5, dried in an oven at 50°C for 90 to 210 minutes, exhibited similar sheet resistances of 42 to 43 ohms / square, with no significant decrease in sheet resistance after 90 minutes, at least until 210 minutes. Sample 6, dried in an oven at 50°C for 60 minutes, exhibited a sheet resistance of 45 ohms / square. Thus, for Samples 3 through 9, dried at 50°C, the sheet resistance decreased with increasing drying time, with the sheet resistance approaching the lowest value achieved by Sample 2, dried at 120°C. Even after 210 minutes, the samples dried at 50°C may not have fused to the same degree as Sample 2, dried at 120°C. Compared to the samples dried using heat, Samples 1 and 10, dried without oven heating, exhibited the highest sheet resistance. Sample 1, which was dried with a heat gun and not placed in an oven, had a sheet resistance of 57 ohms / square, and the sample that was not dried with a heat gun or placed in an oven had a sheet resistance of 64 ohms / square.

[0113] As shown in Table 5, Samples 9 to 11 were not oven-dried and exhibited the lowest sheet resistances of 31 to 32 ohms / square. Sample 9 was dried using only a heat gun, while Samples 10 and 11 were dried without heating. Samples 2 to 5, dried at 50°C for 0.5 to 2 minutes, exhibited similar sheet resistances of 33 to 35 ohms / square, with Samples 2 and 3 being duplicates. Regardless of temperature or time, Samples 6 to 8, dried at 35 to 40°C for 1 to 2 minutes, exhibited approximately the same sheet resistance, similar to that obtained at 50°C. Sample 1, dried at 120°C in an oven using a heat gun, exhibited a sheet resistance of 35 ohms / square, which is comparable to or higher than the sheet resistance exhibited by Samples 2 and 3, dried at 50°C.

[0114] The data shown in Tables 4 and 5 illustrate the difference in sheet resistance achieved using AgF as a flux versus AgOAc as a flux. The sheet resistance of S2, fused using AgF, is approximately independent of processing conditions, but this is not the case for S1, fused using AgOAc. The sheet resistance of S2 is roughly the same for temperatures ranging from room temperature to 120°C, at least for times between 1 and 2 minutes. However, the data indicates that processing without heating provides more optimal results in terms of sheet resistance than drying at temperatures as low as 35°C. The processing conditions for the sample containing AgF provide more optimal results in terms of sheet resistance than drying under any of the conditions studied when using AgOAc.

[0115] Example 2 - Processing of ink with smaller diameter silver nanowires using AgF

[0116] This example demonstrates the effectiveness of a silver nanowire ink comprising silver nanowires having diameters smaller than those in the S1 and S2 inks of Example 1. G7 The seventh generation of ActiveGrid TM The inks were applied at different thicknesses and subjected to different processing conditions, although the base amount (1x) was a slightly higher concentration for thinner nanowires.

[0117] Ink S4 with a 1x amount (1x amount) of AgF was applied to the COP at a gap thickness of either 1.5 mils or 4.0 mils, and samples of each thickness were processed as described in Table 10. An S4 ink with a higher amount of Ag (labeled Ag-1x) and the same 1x amount of AgF was also prepared. This S4 ink was applied at a thickness of 4.0 mils and processed in cold air. The results are shown in Table 10. Table 6 reports the transmittance of the overall structure and the transmittance of only the transparent conductive film (TCF) in parentheses.

[0118] Table 6

[0119]

[0120] For samples prepared from ink S4 with 1x the amount of AgF, the data in Table 6 show that for any thickness, the surface resistance or %TT exhibits little or no change with processing conditions. Compared to samples coated at 1.5 mils, samples coated at a thickness of 4.0 mils exhibit approximately 23 ohms / sq lower sheet resistance and approximately 3% to 4% lower %TT. The data for sheet resistance and %TT are comparable to those obtained for the S2 ink prepared using the fifth-generation ink, but the sheet resistance is slightly lower. These results again indicate that nearly complete fusion appears to occur without any applied heat (cold fan). These results indicate that it is possible to form a clear coating (greater than 70% TT) with a sheet resistance of 3 ohms / sq.

[0121] Depending on the processing conditions, the %H value increased by approximately 0.1% at 1.5 mil thickness and by approximately 0.37% at 4.0 mil thickness. At 1.5 mil thickness, both samples exhibited %H values ​​between 0.6% and 0.8%. At 4.0 mil thickness, the effect of processing conditions was more pronounced, with the sample processed in cold air exhibiting a %H of 1.76% and the sample processed at 120°C for 2 minutes exhibiting a %H of 2.13%.

[0122] Example 3 - Optical and Conductive Performance of Inks Processed under Ambient Conditions

[0123] This example further demonstrates the optical performance and electrical conductivity of ink coatings processed under ambient conditions.

[0124] Inks with varying AgNW loadings were coated onto COPs at varying gap thicknesses (4.0 mils, 3.0 mils, and 1.5 mils) to achieve a wide range of sheet resistances, and the samples were processed under ambient conditions for approximately 1 minute. Selected performance data are shown in Table 14. The transmittance of the overall structure and only the transparent conductive film (TCF) is reported in parentheses in Table 14. Figure 3 and Figure 4 The relationship curves between sheet resistance and %TT and %H are shown respectively.

[0125] Table 7

[0126]

[0127] 1. Dry for 1 minute, ambient conditions; on COP

[0128] 2. Estimate

[0129] The results indicate that for ink coatings dried under ambient conditions, excellent optical properties as well as desirable conductive properties can be achieved.

[0130] The ink containing fifth-generation nanowires and AgF was formed as a coating or circuit on a variety of substrates, including heat-sensitive substrates, and dried under ambient conditions. Substrates include medical-grade polyurethane, medical bandages, leaves, Ziploc® bags, shrink wrap, Scotch™ tape (coating on the adhesive layer of the tape), PET, and packaging cardboard. Figures 5A to 5H As shown, the resistance was measured by direct contact measurement. Although rough resistance measurements were attempted, no attempt was made to obtain accurate measurements for many of these substrates, and the nature of the substrates led to uncertainty.

[0131] Example 4 - Byproduct Silver Nanoparticle Ink - Efficacy of Transparent or Semi-transparent Conductive Film

[0132] This example demonstrates the effectiveness of inks prepared from silver byproducts generated from the synthesis of silver nanowires.

[0133] A by-product silver nanoparticle mixture was recovered from the centrifugation residue of a purification process used to produce fifth-generation silver nanowires.

[0134] The three samples were characterized using titration and thermogravimetric analysis (745°C), and the results are summarized in Table 8.

[0135] Table 8

[0136]

[0137] 1. Titration

[0138] 2. Thermogravimetric analysis

[0139] Ink S17 was formulated using byproduct W1 at 4x Ag loading and 1x cellulose binder, using AgF as a flux. Ink S18 was formulated using all components in the same ratios, except that the concentration of all solids was approximately 60% higher than in ink S17. The inks were applied and dried to produce coatings as shown in Table 9, and the results are included in Table 9.

[0140] Table 9

[0141]

[0142] Using AgF as a flux, ink S19 was formulated using byproduct W2 (W1 filtered through a 400-mesh filter) with a 4x Ag loading and 1x cellulose binder. Ink S20 was formulated identically to ink S19, except that no flux was added. The inks were applied and dried to produce coatings as shown in Table 10, and the results are included in Table 10.

[0143] Table 10

[0144]

[0145] Ink S21 was formulated using byproduct W3 (W1 further concentrated by the aggregation step) with 4x Ag loading and 1x cellulose binder using AgF as flux. The ink was coated and dried to prepare coatings as shown in Table 11, and the results are included in Table 11.

[0146] Table 11

[0147]

[0148] Examples 5 to 10 - Opaque Conductive Materials

[0149] The following materials were used in Examples 5 to 10.

[0150] HPMC10K, (hydroxypropyl) methylcellulose, average M n ~10K

[0151] Hydroxypropyl methylcellulose, (hydroxypropyl) methylcellulose

[0152] MC311, Methocell™ 311

[0153] SR415, ethoxylated (20) trimethylolpropane triacrylate

[0154] SR740A, polyethylene glycol 1000 dimethacrylate

[0155] SR9038, ethoxylated (30) bisphenol A diacrylate

[0156] Example 5 - (HPMC) High AgNW Loading with Reduced Binder Amount

[0157] This example was conducted to compare the performance of films formed from inks with different silver nanowire and binder concentrations.

[0158] Inks 1-a to 1-d were prepared using the formulations shown in Table 12. As in the previous examples, NanoGlue® (NG) was AgF and the concentrations were as described above.

[0159] Table 12

[0160]

[0161] Coatings with Inks 1-a to 1-d were prepared by knife coating the inks onto 125-micron-thick PET (PET-HC) with a hardcoat on one side. Each ink was applied at two different slot-die gap thicknesses: 1.5 mils and 6.0 mils. Two coatings were prepared for each thickness and dried for 2 minutes at either room temperature or 120°C. The sheet resistance of each coating was measured, and the resistivity was calculated. The resistivity was calculated based on the thickness, which was measured by estimating the dry thickness from a given solids loading and wet coating thickness. The results are shown in Tables 13 and 14.

[0162] Table 13

[0163]

[0164] Table 14

[0165]

[0166] The data shows that:

[0167] · Relative to Ag, the resistivity is lower when the binder content is low

[0168] When the AgNW loading was high, the specific nanogel (10x AgF) did not show a positive impact on the higher alcohol formulation.

[0169] NanoGlue® in the more diluted “standard” ink formulation showed improved conductivity when dried at room temperature (1-b vs. 1-d)

[0170] Example 6 - High AgNW loading with reduced amounts of various binders

[0171] This example was conducted to compare the effectiveness of films formed from inks having different binders.

[0172] Inks 2-I to 2-V were prepared using the formulations shown in Table 15.

[0173] Table 15

[0174]

[0175] Coatings with Ink 2-I to Ink 2-V were prepared by knife coating PET-HC using a gap thickness of 1.5 mils. Each coating was prepared twice and dried at room temperature or 120°C for 2 minutes. For each sample, sheet resistance was measured and resistivity was calculated. Each sample was also measured to determine total transmittance, haze, and b*. For samples dried at 120°C, 1.8 J / cm² was applied. 2Adhesion testing was conducted on samples before and after UV exposure (see Figure 1). The adhesion test involved applying 3M's Scotch® LightDuty Packaging Tape 610 to the coated side of the sample and removing it after 60 seconds by grasping the free end and quickly pulling it back toward itself at an angle as close to 180° as possible (without yanking). The amount of coating removed from the substrate was evaluated on a scale of 0B to 5B, with 5B indicating good adhesion and 0B indicating poor adhesion. The data is shown in Tables 16 and 17.

[0176] Table 16

[0177]

[0178] Table 17

[0179]

[0180] 0B: The coating is moved outside the area in contact with the tape

[0181] 5B: The coating has not been removed or peeled off

[0182] The data show the following:

[0183] HPMC of different molecular weights showed similar potency (2-I to 2-III)

[0184] When AgNW loading is high, a specific nanogel (AgF is 3x lower than in previous experiments) does not show a positive effect on the higher alcohol formulation, but seems to "get worse" when heated.

[0185] UV-curable diacrylates exhibit similar performance to HPMC in formulations, but achieve significantly better adhesion after UV curing.

[0186] Example 7 - Fully Aqueous, High Ag NW, with HPMC and Epoxy Resin Blend

[0187] This example was conducted to evaluate the effectiveness of films formed from inks to which epoxy compounds were added.

[0188] Ink 3-i to Ink 3-v were prepared using the formulations shown in Table 18.

[0189] Table 18

[0190]

[0191] Coatings containing Inks 3-i through 3-v were prepared by knife coating the inks onto PET-HC using a gap thickness of 1.5 mils. Each coating was first dried at room temperature and then further treated at 120°C for 2 minutes. Sheet resistance was measured and resistivity calculated for each sample after each step. Each sample was also measured to determine total transmittance, haze, and b*. Adhesion testing was performed on the samples dried at 120°C as described in Example 6. The data is shown in Table 19.

[0192] Table 19

[0193]

[0194] 0B: The coating is moved outside the area in contact with the tape

[0195] The data show the following:

[0196] Epoxy compounds combined with HPMC did not improve adhesion even after heating

[0197] Example 8 - High solid ink obtained by evaporation with UV curable resin

[0198] This example was carried out to obtain a coating with very low sheet resistance by concentrating the ink.

[0199] Inks 4-I to 4-V were prepared using the formulations shown in Table 20.

[0200] Table 20

[0201]

[0202] Coatings containing Inks 4-I through 4-V were prepared by knife coating onto PET-HC using a gap thickness of 1.5 mils. Each coating was first dried at room temperature and then further treated at 120°C for 2 minutes. Sheet resistance was measured after each step, and resistivity was calculated. Each sample was also measured to determine total transmittance, haze, and b*. The data are shown in Table 21.

[0203] Table 21

[0204]

[0205] The ink was concentrated by removing EtOH and coated onto PET-HC by knife coating using a gap thickness of 1 mil and dried at room temperature. The sheet resistance was measured and the resistivity was calculated. The data are shown in Table 22.

[0206] Table 22

[0207]

[0208] The data show the following:

[0209] The performance of triacrylate SR415 in ink performance is similar to that of diacrylate SR9038

[0210] Concentrated inks are available to achieve extremely low sheet resistance

[0211] The rheological results of concentrated inks 4-I' to 4-V' are given in Table 23. It can be seen that the concentrated inks exhibit shear thinning behavior.

[0212] Table 23

[0213]

[0214] Example 9 - Obtaining high solid ink by evaporation with UV curable resin and using photoinitiator

[0215] Inks 6-a to 6-f were prepared using the formulations shown in Table 24. The results are summarized in Table 25.

[0216] Table 24

[0217]

[0218] Table 25

[0219]

[0220] The ink was concentrated by removing EtOH and coated onto PET-HC using a knife coating with a gap thickness of 3 mils. The ink was dried at room temperature for 2 minutes using a heat gun. The sheet resistance was measured, and the resistivity and sheet resistance per mil thickness were calculated. The data are shown in Table 26.

[0221] Table 26

[0222]

[0223] The data show the following:

[0224] Triacrylate SR415 shows better performance in improving UV curing and adhesion

[0225] Use of photoinitiators can further aid curing and adhesion after UV curing

[0226] Concentrated inks (6-a' to 6-f') produce very low sheet resistance even when dried at low temperatures

[0227] Table 27 gives the rheological results for concentrated inks 6-a' to 6-f'.

[0228] Table 27

[0229]

[0230] Example 10 - Inks with different resin and PI concentrations

[0231] Ink 8-1 to Ink 8-4 were prepared using the formulations shown in Table 28.

[0232] Table 28

[0233]

[0234] The ink was concentrated by removing EtOH and coated onto PET-HC by knife coating. Sheet resistance and resistivity were measured after drying at room temperature and after UV curing, and the data are shown in Table 29.

[0235] Table 29

[0236]

[0237] Table 30 gives the rheological results for concentrated inks 8-1' to 8-4'.

[0238] Table 30

[0239]

[0240] The data show the following:

[0241] • Different amounts of triacrylate SR415 or in combination with diacrylate SR740A do not show large changes, but lower adhesive usage results in lower calculated resistivity

[0242] Ink 8-1' to Ink 8-4' were applied in various thicknesses through multiple passes up to 10. The coating quality was visually assessed and evaluated as follows, and the results are summarized in Table 31:

[0243] a = Almost everything is removed

[0244] b = Mixing failure - large pores

[0245] c = Mixing failure - small holes

[0246] d = Most adhesion failures

[0247] Table 31

[0248]

[0249] The data shows that:

[0250] There is no significant change in adhesion under different coating thicknesses. Generally speaking, using a lower adhesive is not conducive to improving adhesion.

[0251] The above examples are intended to be illustrative and not restrictive. Additional embodiments are within the scope of the present invention. In addition, although the present invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present invention. Any incorporation of the above documents by reference is limited so that no subject matter that violates the explicit disclosure herein is incorporated. For the use of components, elements, ingredients or other divisions to describe specific structures, compositions and / or process methods in this article, it should be understood that the disclosure herein covers the specific embodiments, embodiments comprising the specific components, elements, ingredients, other divisions or combinations thereof, and embodiments consisting essentially of specific components, ingredients or other divisions or combinations thereof that may include other features that do not change the basic properties of the target object, as suggested in the discussion, unless otherwise specifically stated. The term "about" as used herein refers to the expected uncertainty of the relevant value as would be understood by one of ordinary skill in the art in a particular context.

Claims

1. A conductive composite material comprising from about 75% to about 98% by weight of silver particles and at least about 2% by weight of a polymer binder, wherein the silver particles comprise at least about 67% by weight of silver nanowires having an aspect ratio of at least about 75.

2. The conductive composite material according to claim 1, wherein the conductive composite material has a -3 Resistivity in ohm-cm.

3. The conductive composite material according to claim 1, wherein the conductive composite material has a -4 Resistivity in ohm-cm.

4. The electrically conductive composite material of any one of claims 1 to 3, wherein the composite material has at least about 25 volume percent silver.

5. The electrically conductive composite material according to any one of claims 1 to 4, wherein the polymer binder comprises a polysaccharide.

6. The conductive composite material of any one of claims 1 to 4, wherein the polymer binder comprises polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyamide, polyimide, polysulfone, polysiloxane, polyester, epoxy resin, polyurethane, polyvinyl alcohol, polyvinyl acetate, copolymers thereof, or polymer blends thereof.

7. The conductive composite material of any one of claims 1 to 6, wherein the composite material consists essentially of discrete silver particles, the polymer binder, and no more than about 2 weight percent of a crosslinker and / or viscosity modifier.

8. The conductive composite material according to any one of claims 1 to 7, wherein the silver nanowires have an average diameter of about 15 nm to about 80 nm and an aspect ratio of about 100 to about 1500.

9. The conductive composite material of any one of claims 1 to 8, wherein the silver particles comprise at least about 90% by weight nanowires.

10. The electrically conductive composite material of any one of claims 1 to 9, comprising at least about 90% by weight silver particles.

11. A conductive structure comprising the conductive composite material according to any one of claims 1 to 10 and having a visible light transmittance of not more than about 70%.

12. The conductive structure of claim 11, wherein the conductive structure comprises a layer having an average thickness of about 0.2 microns to about 2 millimeters.

13. The conductive structure of claim 11, wherein the conductive structure comprises a layer having an average thickness of no more than about 5 microns and a sheet resistance of no more than about 5 ohms / square.

14. The conductive structure of any one of claims 11 to 13, wherein the conductive structure comprises an opaque layer having an average thickness of no more than about 5 microns and a sheet resistance of no more than about 1 ohm / square.

15. The conductive structure of any one of claims 11 to 14, wherein the conductive structure comprises a layer comprising at least about 90% by weight silver particles, and wherein the silver particles comprise at least about 90% by weight silver nanowires.

16. The conductive structure of any one of claims 11 to 15, wherein the conductive composite material has a thickness of no more than about 5×10 -4 Resistivity in ohm-cm.

17. An electrically conductive structure according to any one of claims 11 to 16, wherein the composite material is free of deposits of in situ reduced metal.

18. The electrically conductive structure of any one of claims 11 to 17, wherein the electrically conductive structure comprises the electrically conductive composite material disposed on a heat sensitive substrate that is unstable above about 100°C.

19. An electrically conductive structure according to any one of claims 11 to 18, wherein the electrically conductive composite material is in the form of an electrical interconnect.

20. The electrically conductive structure of any one of claims 11 to 19, wherein the electrically conductive structure (composite material) is processed at a temperature below about 100°C.

21. The conductive structure of any one of claims 11 to 20, wherein the conductive composite material is provided on a substrate in the form of a roll.

22. An ink for forming a conductive deposit, the ink comprising an aqueous solvent and at least about 3 weight percent metal particles, the metal particles comprising at least about 67 weight percent silver nanowires, wherein the ink is stable without visible settling for at least 24 hours without agitation.

23. The ink of claim 22 comprising at least about 5% by weight silver particles.

24. The ink of claim 22 comprising from about 3% to about 20% by weight of metallic particles.

25. The ink of any one of claims 22 to 24, wherein the silver particles comprise at least about 90% by weight silver nanowires.

26. The ink of any one of claims 22 to 25, further comprising from about 3% to about 25% by weight of non-volatile organic material.

27. The ink of any one of claims 22 to 25, wherein the ink comprises up to about 20% by weight metallic particles and from about 2% to about 25% by weight non-volatile organic matter.

28. The ink of any one of claims 22 to 27, wherein the ink comprises about 2 to 20 wt% polyvinylpyrrolidone relative to the total weight of the silver nanowires.

29. The ink of claim 28, wherein the non-volatile organic material comprises at least about 50% by weight polyvinyl pyrrolidone.

30. The ink of any one of claims 22 to 29, wherein the ink further comprises a silver ion or complex at a concentration of about 0.005 mg / mL to about 50.0 mg / mL.

31. The ink of claim 30, wherein the aqueous solvent comprises at least about 80% by weight water.

32. An ink according to claim 30 or claim 31 , wherein the ink forms a conductive material upon removal of the aqueous solvent.

33. The ink of any one of claims 27 to 32, wherein the non-volatile organic material comprises a polysaccharide, a polyacrylate precursor, or a mixture thereof.

34. The ink of any one of claims 27 to 33, wherein the non-volatile organic compound comprises a curable resin.

35. The ink of any one of claims 30 to 34, wherein the solvent further comprises a volatile alcohol.

36. The ink of any one of claims 27 to 35, wherein the non-volatile organic material comprises a polymer precursor comprising a monomer, an oligomer, a liquid or solid dissolved polymer, or a mixture thereof, which upon drying and curing forms polyethylene terephthalate (PET), polyethylene naphthalate (PEN), a polyacrylate, poly(methyl methacrylate), a polyamide, a polyimide, a polysiloxane, a polyester, an epoxy resin, a polyurethane, polyvinyl alcohol, polyvinyl acetate, a copolymer or a blend thereof.

37. The ink of any one of claims 27 to 36 having non-Newtonian rheology.

38. A method for forming an ink for forming a conductive deposit, the method comprising: forming a good solvent blend dispersion of silver nanowires having a concentration of no more than about 2.5 wt %, wherein the solvent comprises at least about 20 vol % of an alcohol having a boiling point no more than about 99° C.; and The solvent is removed to concentrate the good solvent blend dispersion to form an aqueous dispersion having at least about 3 wt % silver nanowires.

39. The method of claim 38, wherein the solvent in the good solvent blend dispersion comprises ethanol, isopropanol, or a mixture thereof.

40. The method of claim 38 or claim 39, wherein the good solvent blend dispersion of silver nanowires has a silver nanowire concentration of about 1.5 wt% to about 2.1 wt%.

41. The method of any one of claims 38 to 40, wherein the good solvent blend dispersion is stable for at least 3 months without any significant settling in a sealed environment to prevent solvent evaporation or contamination.

42. The method of any one of claims 38 to 41, wherein removing the solvent comprises applying negative pressure to facilitate evaporation of the solvent.

43. The method of any one of claims 38 to 42, wherein removing the solvent comprises applying heat to promote evaporation of the solvent.

44. The method of any one of claims 38 to 43, further comprising adding a selected amount of water prior to the step of removing the solvent.

45. The method of any one of claims 38 to 44, wherein removing the solvent provides an aqueous dispersion of silver nanowires having a selected concentration of silver nanowires.

46. ​​The method according to any one of claims 38 to 45, further comprising: A polymeric binder precursor is added to the aqueous dispersion to form a coatable ink.

47. The method of claim 46, wherein the polymeric binder precursor comprises a monomer, oligomer, or resin that is a liquid in neat form.

48. The method of claim 46, wherein the polymeric binder precursor comprises a dissolved polymer that is a solid in neat form.

49. The method of any one of claims 46 to 48, further comprising adding additional silver particles to the aqueous dispersion.

50. A method according to any one of claims 46 to 49, wherein the coatable ink is any one of the inks according to claims 22 to 37.

51. A method for forming a conductive composite material, the method comprising: casting an ink comprising a solid component having from about 75 wt % to about 98 wt % silver particles and at least about 2 wt % of a polymeric binder precursor to form a cast structure, wherein the silver particles comprise at least about 67 wt % silver nanowires having an aspect ratio of at least about 75, and The cast structure is cured to form the conductive composite material.

52. The method of claim 51, wherein the curing is performed at room temperature.

53. The method of claim 51, wherein the curing is performed at a temperature not exceeding about 100°C.

54. The method of any one of claims 51 to 53, wherein the curing consists of solvent removal.

55. The method of claim 51, wherein curing comprises UV irradiation to crosslink the polymer binder.

56. The method of claim 51, wherein curing comprises cross-linking the polymer binder.

57. The method of any one of claims 51 to 56, wherein casting comprises slot coating the ink onto a substrate.

58. A method according to any one of claims 51 to 56, wherein casting comprises dipping, spraying or jet deposition or screen printing.

59. The method according to any one of claims 51 to 58, wherein the ink is any one of the inks according to 22 to 37.

60. The method of any one of claims 51 to 59, wherein the conductive material is the conductive material of any one of claims 1 to 10.

61. The method of any one of claims 51 to 60, wherein the cast structure after curing is any one of the conductive structures of claims 11 to 21.

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