Coatings and processing of transparent conductive films for stabilization of sparse metal conductive layers

Abstract

This invention relates to a transparent conductive film comprising a rarefied metal conductive layer, wherein the film is treated after coating with an outer coating layer to reduce the sheet resistance. The rarefied metal conductive layer may comprise a molten metal nanostructured network. The coating (such as a polymer outer coating or a polymer undercoat) may be a noble metal ion, which can be further reduced by applying heat and, if necessary, humidity. Specifically, it has been demonstrated that, regardless of whether it is molten, silver ions in the coating provide significant stabilization of the rarefied metal conductive layer upon application of heat and humidity. The coating may further comprise a metal salt stabilizing composition.

Description

[Previous Technology]

[0001] Functional films can provide important functions in a range of situations. For example, conductive films can be important for the dissipation of static electricity when it is undesirable or dangerous. Transparent conductive films can be used as electrodes. High-quality displays may contain one or more transparent conductive layers.

[0002] Transparent conductors can be used in several 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 preferred material due to its relatively high transparency while maintaining high conductivity. However, ITO has several drawbacks. For example, ITO is a brittle ceramic, requiring sputtering (a manufacturing method involving high temperatures and vacuum), which is relatively slow and not cost-effective. Additionally, ITO is known to be prone to cracking on flexible substrates. New portable electronic devices are evolving towards thinner forms. [Summary of the Invention]

[0003] In a first embodiment, the present invention relates to a transparent conductive film comprising a transparent polymer substrate, a rare-metal conductive layer supported by the substrate, and a polymer outer coating adjacent to the rare-metal conductive layer, wherein the transparent conductive film has a visible light transmittance of at least about 88% and a sheet resistance of not more than about 120 ohm / sq, and wherein the polymer outer coating comprises a polymer and about 0.01 wt% to about 20 wt% noble metal ions.

[0004] In another embodiment, the present invention relates to a method for reducing the sheet resistance of a transparent conductive film comprising a substrate, a transparent conductive layer, and a polymeric outer coating, the transparent conductive layer comprising a molten metal nanowire network and a polymeric polyol adhesive, wherein the polymeric outer coating has an average thickness of about 5 nm to about 250 nm, the method comprising the step of heating the transparent conductive film to a temperature of at least about 55°C for at least about 10 minutes to reduce the sheet resistance by at least about 5%. This heating step can be performed in a structure without an optically transparent adhesive. In some embodiments, the molten metal nanostructured network comprises silver, and the film has a sheet resistance of no more than 120 ohms / sq and a visible light transmittance of at least about 88%.

[0005] In another embodiment, the present invention relates to a transparent conductive film comprising a substrate, a transparent conductive layer comprising a molten metal nanostructured network, and a polymer outer coating, wherein the transparent conductive film has a transmittance of at least about 88% and a sheet resistance of no more than about 120 ohms / sq, wherein the transparent conductive film has been modified by heat and, if necessary, humidity treatment for at least about 10 minutes to reduce the sheet resistance by at least about 5%. In some embodiments, the polymer outer coating and / or the undercoat comprises metal ions.

Implementation Method

[0006] Cross-reference to related applications

[0007] This application claims priority to provisional patent application 62 / 936,681 filed on November 18, 2019, by Yang et al., entitled “Post Coating Processing of Transparent Conductive Films Formed With Fused Silver Nanowires”, which is incorporated herein by reference.

[0008] As demonstrated herein, controlled application of heat (with increased humidity as needed) can be used to reduce the sheet resistance of molten metal nanostructured networks with a protective polymer overcoat. This treatment can be applied to transparent conductive films with a protective polymer overcoat to further enhance electrical properties. This treatment is effective for molten metal nanostructured networks in which deposited metal has been directed to the junctions between metal nanowires. It has been further found that placing noble metal ions (specifically silver) within a polymer coating (such as an overcoat) adjacent to a rarefied metal conductive layer (such as a molten metal nanostructured network) is suitable for further stabilizing the conductive structure. An advantage of noble metals in coatings is that they do not necessarily require additional treatment to be usable, as they can provide benefits in use. If the rarefied metal conductive layer does not contain a molten metal nanostructured network, the results in the examples of this invention demonstrate that the significant stabilization resulting from noble metal ions in the overcoat has a profound impact on stability under light and humidity, possibly due to melting with metal ions from the overcoat. The results are confirmed with silver-based conductors. These transparent conductive films can exhibit high transmittance and low haze. Processing time and conditions can be controlled to avoid significant degradation while achieving performance enhancement. Similarly, after processing, the film shows significantly enhanced stability under accelerated abrasion conditions, high temperature, and high humidity. This processing is suitable for use in large-scale commercial applications together with films formed using roll-to-roll processing.

[0009] A dispersion of silver nanowires or ink can be deposited on a surface and processed into a conductive film. Under appropriate processing conditions, the resulting transparent conductive film can be desirable due to its mechanical properties, transparency to visible light, flexibility, a combination of these characteristics, or other forms of the conductive film. Specifically, using these nanowires to form a transparent conductive film can have important applications in devices with displays and touch sensors.

[0010] Transparent conductive elements (e.g., films) based on metals comprise sparse metallic conductive layers. These conductive layers are generally sparse to provide the desired amount of optical transparency through the conductive structure rather than around it, thus the metal coverage typically has significant (though small) gaps in the layers of the conductive element. For example, a transparent conductive film may comprise metal nanowires deposited along the layer, providing sufficient contact for electron percolation to provide a suitable conduction path. In embodiments of particular interest, the transparent conductive film may comprise a molten metal nanostructured network, which has been found to exhibit the desired electrical and optical properties. Unless otherwise explicitly indicated, conductivity as referred to herein means electrical conductivity.

[0011] As described in more detail below, a controlled melting process can be used to carefully deposit metal at the junctions between metal nanowires. This melting process can be controlled to deposit the required amount of silver associated with these junctions. The system is prepared for thermodynamically driven melting primarily at the junctions between adjacent metal nanowires, which are components forming a molten metal nanostructured network. After melting, a monolithic structure is formed, which has been named the molten metal nanostructured network, and the original metal nanowires within this conductive structure lose their individual identities. Evidence suggests that the molten metal merges the original individual nanowires to reduce or eliminate junction resistance. For commercial products, it is desirable to improve the durability of these transparent conductive films under a range of realistic conditions, and the treatment described herein has been shown to improve this durability under specific accelerated wear tests.

[0012] Within the text concerning transparent conductors based on silver nanowires, the advantages of forming molten metal nanostructured networks are still well understood. The melting process for forming molten metal nanostructured networks has been found to result in highly transparent and highly conductive structures with very low haze. These molten metal nanostructured networks exhibit very good stability under accelerated wear conditions using appropriate stabilizers. The addition of noble metal ions (such as silver) to the outer coating provides an additional degree of stabilization, and results indicate that for the adhesive system of the present invention, which has a hydrophilic adhesive in the transparent conductive layer used herein, molten and / or noble metal ions are required in the outer coating to obtain reasonable stability in established thermal and humidity tests.

[0013] For commercial processing, a thin protective polymer overcoat is typically placed on a transparent conductive layer. The protective coating typically has a thickness not exceeding approximately 250 nm. As demonstrated in the results below, when the transparent conductive film with the molten metal nanostructured network and protective polymer overcoat is subjected to heat and, depending on the desired humidity, a decrease in sheet resistance is observed, followed by an eventual increase due to degradation. No similar decrease in resistance was observed for the corresponding unmelted film. Therefore, the structure with the molten metal nanostructured network is found to be more stable than structures previously tested under the same conditions. Heat treatment may further support improvements in the melting process. Introducing humidity during heat treatment can achieve a significant reduction in sheet resistance.

[0014] It has been previously observed that using humidity during the melting process allows for lower temperatures and shorter processing times to obtain comparable values ​​for the film's resistance. See Li et al., U.S. Patent 9,183,968B, entitled "Metal Nanowire Inks for the Formation of Transparent Conductive Films with Fused Networks," which is incorporated herein by reference. This observation may or may not be relevant to current observations. The current processing time is much longer than that used in standard melting processes.

[0015] If the polymer is hydrophilic, heat and / or humidity can cause the polymer adhesive to expand around the conductive elements. If these conductive elements are not molten, the expansion of the adhesive can reduce conductivity and increase sheet resistance due to reduced contact between them. For molten metal nanostructured networks, these molten elements are bonded. While not wishing to be theoretically limited, this expansion can promote the migration of metal nanoparticles or any residual metal ions to facilitate junction melting, which can further reduce sheet resistance. A decrease in sheet resistance has been observed in the examples below. Similarly, if the outer coating contains metal ions, these can migrate over time to further contribute to junction melting, which can mitigate damage and lead to a further decrease in sheet resistance.

[0016] The structure with a protective polymer outer coating after heat treatment may be qualitatively or indefinitely different from the previously formed structure. However, the observations are consistent with the further migration of silver into the molten metal nanostructured network, making the overall structure appear to have fewer nanoparticles scattering and absorbing light from a distance within the molten metal nanostructured network. Regarding the degree of formation of the new structure, the study concludes that the new structure achieves improved stability during thermal testing, while the optical properties are generally maintained or improved.

[0017] The information presented herein provides data related to methods for improving conductivity and, simultaneously, data on wear tests of transparent conductive films. Improvement in wear test results can be achieved through post-treatment after applying a polymer overcoat and / or by adding metal ions into the overcoat over time. It is hypothesized that if the process is stopped once the sheet resistance reaches a low value, the material can be used to form products with lower sheet resistance and the desired stability. Generally, the post-treated transparent conductive film can have a sheet resistance that is at least about 5% lower than the initial sheet resistance value after melting, at least about 7.5% lower in some embodiments, and at least about 10% lower in other embodiments.

[0018] Regarding changes in environmental stability, we consider two methods to assess this parameter. In a simple sense, the initial sample can be considered. Again, these samples involve a thin protective polymer overcoat. These initial samples can show that the treatment at 65°C and 90% relative humidity maintains a sheet resistance divided by the initial sheet resistance (R / R0) of less than 1.2 (referred to as 65 / 90 stability) for at least about 200 hours, in some embodiments at least about 300 hours, and in other embodiments at least about 400 hours. If the heat-treated material showing a lower sheet resistance is a new material with previously unobtained structural modifications, we can refer to the thermal stability time observed for the modified material relative to the thermal stability time of the initial material.

[0019] The results presented herein are in which heating is performed at 85°C and ambient humidity, at 85°C and 85% relative humidity, and at 65°C and 90% relative humidity. Generally, depending on the processing conditions for temperature and relative humidity, the processing to form the modified material can be carried out over a period of approximately 10 minutes to approximately 100 hours. If a new material is formed, the processing to form this new material is presumably optimized.

[0020] Silver provides excellent electrical conductivity. The applicant sells silver nanowire inks for forming molten metal nanostructured networks under the trademark ActiveGrid® Ink. Other sources of silver nanowires are commercially available, and the basic melting techniques are fully described in the '207 and '807 patents cited below. The vast majority (>98%) of the silver nanowires in the Gen 5 ActiveGrid® products have a diameter of less than <25 nm, while the vast majority (>98%) of the silver nanowires in the Gen 7 ActiveGrid® silver nanowires have a diameter of <22 nm. The synthesis of fine silver nanowires is described in U.S. Patent 10,714,230 B2 to Hu et al., entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed from the Nanowires," which is incorporated herein by reference.

[0021] Improved properties have been found for molten metal nanostructured networks, addressing the desired high electrical conductivity and optical properties of transparency and low haze. The melting of adjacent metal nanowires can be carried out using chemical methods under commercially suitable processing conditions.

[0022] Specifically, significant progress has been made in achieving conductive films based on metal nanowires. A sufficiently controllable method has been discovered to form molten metal networks, in which adjacent portions of the metal nanowires melt into a monomeric structure without distinct nanowires within the conductive network. Specifically, it was initially discovered that halide ions can drive the melting of metal nanowires to form molten metal nanostructures. Various methods have been used to introduce fluxes containing halide anions to successfully achieve melting and a corresponding significant decrease in resistance. It should be noted that halide ions in this context should not be confused with the halide ions used in the nanowire synthesis reaction. Specifically, the melting of metal nanowires and halide anions has been accomplished using acid halide vapors and / or solutions, as well as solutions using halide salts. The melting system of metal nanowires and halide sources is further described in U.S. Patent 10,029,916 to Virkar et al., entitled "Metal Nanowire Networks and Transparent Conductive Material" and U.S. Patent 9,920,207 ('207 patent) to Virkar et al., entitled "Metal Nanostructured Networks and Transparent Conductive Material", both of which are incorporated herein by reference.

[0023] An extension of the method for forming molten metal nanowire networks is based on reduction / oxidation (redox) reactions, which can provide these redox reactions to obtain molten nanowires without damaging the optical properties of the resulting film. The metal used for deposition at the interface can be effectively added as a dissolved metal salt or can be dissolved from the metal nanowires themselves. The effective use of redox chemistry processes to melt metal nanowires into nanostructured networks is further described in U.S. Patent 10,020,807 ('807 Patent) to Virkar et al., entitled "Fused Metal Nanostructured Networks, Fusing Solutions with Reducing Agents and Methods for Forming Metal Networks," which is incorporated herein by reference. The '807 Patent also describes a single-solution method for forming molten metal nanostructured networks. The single-solution method for forming molten metal nanostructured layers is further described in U.S. Patent 9,183,968 B1 (hereinafter referred to as the '968 Patent) entitled "Metal Nanowire Inks for the Formation of Transparent Conductive Films with Fused Networks" by Li et al., which is incorporated herein by reference, and the single-solution or ink treatment for forming molten metal nanostructured networks is used in the examples below.

[0024] The ink required to achieve an effective single deposition ink for solidifying into a molten nanostructured metal network contains a required amount of metal nanowires to achieve appropriate metal loading in the resulting film. The ink is stable in a suitable solution prior to deposition and drying. These inks may contain a reasonable amount of polymeric binder, which helps to form a stable conductive film for further processing. Hydrophilic polymers, such as cellulose or chitosan-based polymers, have been found to be effective as binders for obtaining good melting results in an ink system. Metal ions as the metal source for the melting process can be supplied as soluble metal salts.

[0025] A single ink formulation provides the metal load required for deposition as a film on the substrate surface and simultaneously provides components in the ink that induce a melting process when the ink dries under suitable conditions. These inks may conveniently be referred to as molten metal nanowire inks, but it should be understood that melting generally does not occur until drying. These inks generally contain an aqueous solvent, and in some embodiments, may further contain alcohols and / or other organic solvents. These inks may further contain dissolved metal salts as a metal source for the melting process. Not wanting to be limited by theory, it is believed that the ink components (e.g., alcohols or other organic compositions) reduce metal ions from solution to drive the melting process. Previous experience with the melting process in these systems indicates that metal preferentially deposits at the interface between adjacent metal nanowires. Polymer binders may be provided to stabilize the film and influence ink properties. Specific formulations of the ink can be adjusted to select ink properties suitable for a particular deposition method and having specific coating properties on the substrate surface. As further described below, drying conditions can be selected to effectively carry out the melting process.

[0026] Generally, one or more solutions or inks used to form a metal nanostructured network may collectively comprise well-dispersed metal nanowires, a melt, and optional additional components, such as polymeric adhesives, crosslinking agents, wetting agents (e.g., surfactants), thickeners, dispersants, other optional additives, or combinations thereof. If different from the nanowire ink, the solvent used for the metal nanowire ink and / or the molten solution may comprise an aqueous solvent, an organic solvent, or a mixture thereof. Specifically, suitable solvents include, for example, water, alcohols, ketones, esters, ethers (such as glycol ethers), aromatic compounds, alkanes and their analogues and mixtures thereof. Specific solvents include, for example, water, ethanol, isopropanol, isobutanol, tert-butanol, methyl ethyl ketone, glycol ethers, methyl isobutyl ketone, toluene, hexane, ethyl acetate, butyl acetate, ethyl lactate, PGMEA (2-methoxy-1-methylethyl acetate), dimethyl carbonate, or mixtures thereof. While the solvent should be selected based on its ability to form well-dispersed metal nanowires, it should also be compatible with other selected additives so that the additives are soluble in the solvent. In embodiments where a melt flux is included in a single solution containing metal nanowires, the solvent or its components may or may not be a significant component of the molten solution (such as an alcohol) and can therefore be selected as needed.

[0027] The metal nanowire ink formulated with one or two inks may include about 0.01 to about 1% by weight of metal nanowires, in other embodiments about 0.02 to about 0.75% by weight of metal nanowires, and in additional embodiments about 0.04 to about 0.5% by weight of metal nanowires. For embodiments of particular interest, the nanowires are silver nanowires and the metal ion source is a dissolved silver salt. The ink may contain silver ions at the following concentrations: about 0.01 mg / mL and about 2.0 mg / mL silver ions, in other embodiments about 0.02 mg / mL and about 1.75 mg / mL, and in other embodiments about 0.025 mg / mL and about 1.5 mg / mL. Those skilled in the art will understand that the additional ranges of metal nanowire concentration and metal ion concentration within the clearly defined range above are carefully considered and are within the scope of this invention. The concentration of metal nanowires affects the metal loading on the substrate surface and the physical properties of the ink.

[0028] Regarding the ink formulation, the polymeric binder and solvent are generally chosen such that the polymeric binder is soluble or dispersible in the solvent. In suitable embodiments, the metal nanowire ink generally contains about 0.02 to about 5% by weight of binder, in other embodiments about 0.05 to about 4% by weight of binder, and in additional embodiments about 0.1 to about 2.5% by weight of polymeric binder. In some embodiments, the polymeric binder contains a crosslinkable organic polymer, such as a radiation-crosslinkable organic polymer and / or a thermosetting organic binder. The desired binder includes, for example, polymeric polyols, such as polysaccharide-cellulose-based polymers, chitosan-based polymers, and the like. To promote crosslinking of the binder, in some embodiments the metal nanowire ink may contain about 0.0005% to about 1% by weight of crosslinking agent, in other embodiments about 0.002% to about 0.5% by weight, and in additional embodiments about 0.005% to about 0.25% by weight. The nanowire ink may, as needed, contain rheology modifiers or combinations thereof. In some embodiments, the ink may contain wetting agents or surfactants to reduce surface tension, and the wetting agents may be used to improve coating properties. A wide range of surfactants, such as nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants, are commercially available. The wetting agent is generally soluble in the solvent. In some embodiments, the nanowire ink may contain about 0.001% to about 1% by weight of wetting agent, in other embodiments about 0.002% to about 0.75% by weight, and in other embodiments about 0.003% to about 0.6% by weight of wetting agent. Thickeners may, as needed, be used as rheology modifiers to stabilize dispersions and reduce or eliminate sedimentation. In some embodiments, the nanowire ink may, as needed, contain about 0.05% to about 5% by weight of thickener, in other embodiments about 0.075% to about 4% by weight, and in other embodiments about 0.1% to about 3% by weight of thickener. Those skilled in the art will understand that the additional ranges of adhesive, wetting agent, and thickener concentrations within the clearly defined range above are carefully considered and are within the scope of this invention.

[0029] The stability of the transparent conductive layer is an important consideration for the applicability of these structures in commercial devices (such as smartphones, tablets, computer touchscreens, large-format touchscreens, foldable electronics, wearable electronics, and the like). The reliability of touch sensors formed with transparent conductive layers is important for widespread commercial applications and allows for greater material reliability in a wider range of devices. The processes and structures described herein offer even greater commercial viability for structures already found for use in commercial devices.

[0030] Referring to FIG. 1, a representative transparent conductive film 100 includes a substrate 102, an optional undercoat 104, a rare-metal conductive layer 106, an outer coating 108, an optically transparent adhesive layer 110, and a protective surface layer 112; however, not all embodiments include all layers. Generally, the optically transparent adhesive layer 110 and the protective surface layer 112 are added after the important processing described herein to improve the stability of the transparent conductive layer. The transparent conductive film generally includes a rare-metal conductive layer and at least one layer on each side of the rare-metal conductive layer. The total thickness of the transparent conductive film can generally have an average thickness of about 5 micrometers to about 2 millimeters (mm), about 10 micrometers to about 1 mm in other embodiments, and about 12 micrometers to about 0.5 mm in other embodiments. Those skilled in the art will understand that additional ranges of thickness within the explicitly defined range above are carefully considered and are within the scope of this invention. In some embodiments, the length and width of the film thus produced can be selected to suit a particular application so that the film can be directly introduced for further processing into a product. In additional or alternative embodiments, the width of the film can be selected for a specific application, while the length of the film can be long, ideally allowing it to be cut to the required length for use. For example, the film can be in the form of a sheet or a roll. Similarly, in some embodiments, the film can be on a roll or in another standard form, and the elements of the film can be cut to the required length and width for use.

[0031] The substrate 102 generally comprises a durable support layer formed of one or more suitable polymers. In some embodiments, the substrate may have an average thickness of about 1 micrometer to about 1.5 mm, in other embodiments about 5 micrometers to about 1 mm, and in additional embodiments about 10 micrometers to about 100 micrometers. Specifically for foldable structures, particularly the double-sided foldable structures described below, the substrate thickness generally does not exceed about 27 micrometers and in other embodiments about 5 micrometers to about 25 micrometers. Those skilled in the art will understand that the additional range of substrate thickness within the express range above is carefully considered and is within the scope of this invention. Suitable optically transparent polymers with very good transparency, low haze, and good protective capabilities can be used for the substrate.

[0032] The amount of nanowires delivered to the substrate for the rarefied metallic conductive layer 106 involves balancing factors to achieve the desired amount of transparency and conductivity. While the thickness of the nanowire network can in principle be assessed using scanning electron microscopy, the network can be relatively sparse to provide optical transparency, which can complicate measurement. Generally, the rarefied metallic conductive structure (e.g., a molten metal nanowire network) should have an average thickness of no more than about 5 micrometers, in other embodiments no more than about 2 micrometers, and in other embodiments about 10 nm to about 500 nm. However, such rarefied metallic conductive structures are generally relatively open structures with significant submicron-level surface texture. The loading of these nanowires provides a useful parameter of the network that can be easily assessed, and the loading value provides an alternative parameter related to thickness. Therefore, as used herein, the loading of nanowires on the substrate is generally expressed as milligrams of nanowires per square meter of substrate. Generally, such nanowire networks can have a load of about 0.1 mg / m² to about 300 mg / m², about 0.5 mg / m² to about 200 mg / m² in other embodiments, and about 1 mg / m² to about 150 mg / m² in other embodiments. Those skilled in the art will understand that additional ranges of thickness and load within the explicitly defined ranges above are carefully considered and are within the scope of this invention. If the sparse metallic conductive layer is patterned, the discussion of thickness and load applies only to areas where the metal is not excluded or significantly reduced by the patterning method.

[0033] Polymers used for the substrate include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyolefin, polyvinyl chloride, fluoropolymer, polyamide, polyimide, polyurethane, polysiloxane, polyetheretherketone, polynorbornene, polyester, polystyrene, polyurethane, polyvinyl alcohol, polyvinyl acetate, acrylonitrile-butadiene-styrene copolymer, cyclic olefin polymer, cyclic olefin copolymer, polycarbonate, copolymers thereof, or blends thereof or the like. Suitable commercial polycarbonate substrates include, for example, MAKROFOL SR243 1-1 CG purchased from Bayer Material Science; TAP® Plastic purchased from TAP Plastics; and LEXANT M8010CDE purchased from SABIC Innovative Plastics. The protective surface layer 112 may independently have a thickness and composition that covers the same range of thickness and composition as the substrate described above.

[0034] For structures having a transparent conductive layer that can be patterned independently on both sides, a UV-absorbing transparent substrate can be used, as shown in Figure 2, which is described below. Specifically, for these embodiments, suitable polymers include, for example, polyimides, polysulfides (such as Pylux™, Ares Materials), polyurethane (such as Udel® from Solvay), or polyether urethane (such as Veradel® from Solvay or Ultrason® from BASF), and polyethylene naphthalate (such as Teonex® from DuPont). Examples are provided below based on transparent polyimides. Conventional aromatic polyimides are colored. However, recently developed polyimides are transparent to visible light. These transparent polyimides absorb ultraviolet light. Transparent polyimide is available from Kolon (Korea), Taimide Tech. (Taiwan), Sumitomo (Japan), SKC Inc. (GA, USA) and NeXolve (AL, USA).

[0035] Optional base coat 104 and / or outer coat 108 may be placed below or above the sparse metallic conductive layer 106, respectively. Coatings 104 and 108 may contain curable polymers, such as thermosetting or radiation-curing polymers. Coatings 104 and 108 may have an average thickness as described in the following sections specifically covering the outer and base coats. The thickness and composition of the outer coat may be selected such that sheet resistance measurements through the outer coat are not significantly different from measurements without the outer coat. Coatings 104 and 108 may contain important additives for stabilizing the conductive layer, as described in more detail below. Suitable coating polymers are described below.

[0036] Optional optically clear adhesive layer 110 may have an average thickness of about 10 micrometers to about 300 micrometers, about 15 micrometers to about 250 micrometers in other embodiments, and about 20 micrometers to about 200 micrometers in other embodiments. Those skilled in the art will understand that additional ranges in the thickness of the optically clear adhesive layer within the clearly defined range above are carefully considered and are within the scope of this invention. Suitable optically clear adhesives may be contact adhesives. Optically clear adhesives include, for example, coatable compositions and adhesive tapes. Optically clear adhesive tapes may be double-sided adhesive tapes with a carrier film between two adhesive layers, see, for example, 3M 8173KCL. UV-curable liquid optically clear adhesives may be obtained based on acrylic or polysiloxane chemicals. Suitable adhesive tapes may be purchased, for example, from Lintec (MO series); Saint Gobain Performance Plastics (DF713 series); Nitto Americas (Nitto Denko) (LUCIACS CS9621T and LUCIAS CS9622T); LG Hausys OCA (OC9102D, OC9052D); DIC (DAITAC LT series OCA, DAITAC WS series OCA and DAITAC ZB series); PANAC Plastic Films (PANACLEAN series); Minnesota Mining and Manufacturing (3M, Minnesota USA, product numbers 8146, 8171, 8172, 8173, 9894 and similar products) and Adhesive Research (e.g., product 8932).

[0037] Some optically clear adhesive tapes contain a carrier film, such as polyethylene terephthalate (PET), which can be embedded in the adhesive tape between two adhesive surfaces. Based on earlier work using organic stabilizers, it has been found that the presence of a carrier film in the optically clear adhesive layer, combined with such stabilizers, effectively improves the stabilization properties of the optically clear adhesive tape compared to a corresponding film in an optically clear adhesive tape without a carrier film. While not wanting to be limited by theory, it is speculated that the improvement in stability may be due to the reduced permeability of water and oxygen through the carrier film. Using the metal-based stabilizers described herein, it has been found that the stabilization properties are not significantly dependent on the specific optically clear adhesive used, which is an advantage of the metal-based stabilizers (such as V(+5) salts).

[0038] An embodiment of a double-sided structure having two transparent conductive structures is shown in FIG2. FIG2 shows a general structure of a double-sided conductive element in the form of a single unit on a core substrate. Referring to FIG2, the double-sided conductive sheet 150 may include a substrate polymer sheet 152, an optional first hard coating 154, a first rare-sparse metal conductive layer 156, a first outer coating 158, an optional second hard coating 160, a second rare-sparse metal conductive layer 162, a second outer coating 164, an optional first releasable protective film 166, and an optional second releasable protective film 168.

[0039] One or both sides of the sheet having the transparent conductive layer can be produced in a roll-to-roll configuration. This roll 190 is schematically shown in Figure 3. The formation of the roll-to-roll configuration of the two-sided flexible structure is described in U.S. Patent Application No. 2020 / 0245457, entitled "Thin Flexible Structures With Transparent Conductive Films and Processes for Forming the Structures," published by Chen et al., which is incorporated herein by reference.

[0040] Generally, silver nanoline inks can be applied using any reasonable method, such as dip coating, spraying, knife-edge coating, bar coating, Mayer bar coating, slot coating, gravure printing, spin coating, or the like. For commercial roll-to-roll processing, slot coating is generally used. These films can be dried, for example, using a hot air gun, oven, heat lamp, warm air stream, or the like. In some embodiments, the films can be heated to a temperature of about 50°C to about 150°C during drying. To facilitate the melting process, heat transfer generally lasts from about 30 seconds to about fifteen minutes. Those skilled in the art will understand that additional ranges of temperature and time within the explicitly stated range above are carefully considered and are within the scope of this invention.

[0041] Transparent conductive films can be used in a range of products incorporating transparent conductive electrodes (such as solar cells). Their excellent optical properties make these transparent conductive films particularly valuable for use in touch sensors integrated within displays. These transparent conductive layers can be patterned using lithography, laser ablation, or other suitable techniques. Patterned transparent conductive layers are a suitable form of touch sensor. These touch sensors can be used in portable electronic products and large-format displays.

[0042] Polymer Coating (Outer Coating and / or Primer) The polymer coating provides the desired functions and is generally described within the overall structure above. Specifically, the polymer outer coating provides several functions. First, it provides mechanical protection for the transparent conductive layer during further processing. Second, it may have a stabilizing composition to improve the abrasion resistance of the transparent conductive layer. The primer provides the desired surface for placing the transparent conductive layer with the molten metal nanostructured network and provides a stabilizing composition. As described herein, the inclusion of noble metal ions (such as silver ions) in the coating (outer coating and / or primer) can lead to an increase in the melting of the molten metal nanostructured network to reduce sheet resistance and improve thermal stability.

[0043] The sparse metallic conductive layer is generally covered with a polymer overcoat to provide mechanical protection to the conductive layer. In some embodiments, the overcoat may be selected such that haze is significantly reduced without significantly degrading other properties after the overcoat is applied. Similarly, the thickness and composition of the overcoat may be selected such that the sheet resistance measurement through the overcoat is not significantly changed relative to the measurement without the overcoat. The incorporation of additional stabilizers into the coating is further described below and disclosed in U.S. Patent Application 2018 / 0105704 (hereinafter referred to as '704 Application') entitled "Stabilized Sparse Metal Conductive Films and Solutions for Delivery of Stabilizing Compounds" by Yang et al., which is incorporated herein by reference.

[0044] In some embodiments, the outer coating is generally thin enough that conductivity can occur through it, although the outer coating polymer is generally dielectric. In other words, the surface having the outer coating should generally have a sheet resistance substantially the same as the surface without the outer coating. To provide conductivity through the polymer outer coating, it is desirable that the polymer outer coating has an average thickness of no more than about 250 nm, in some embodiments about 5 nm to about 200 nm, in other embodiments about 8 nm to about 125 nm, and in other embodiments about 10 nm to about 100 nm. Those skilled in the art will understand that additional ranges of thickness within the explicitly defined range above are carefully considered and are within the scope of this invention.

[0045] As noted above, the conductive structure may include an underlayer between a polymer substrate and a sparse metal conductive layer generally having a molten metal nanostructured network. The underlayer adjacent to the transparent conductive layer may be referred to as the undercoat. The undercoat may include a polymer hard coating. As the undercoat, the polymer hard coating does not provide mechanical protection, but it does provide protection against chemical attack. In some embodiments, the polymer hard coating undercoat provides significant stability to some of the molten metal nanostructured layers of the polymer substrate.

[0046] Suitable hard-coating polymers are generally highly cross-linked polymers of cross-linked polyacrylates, which can be combined with other cross-linked components (such as polyurethanes, epoxy polymers, polysiloxanes, and / or other cross-linked polymers). Branched acrylate monomers can provide for the formation of highly cross-linked polymers, and cross-linked acrylates can be copolymerized with other components (such as polyurethane acrylates or the like) to form cross-linked polymers. Hard coating polymers are commercially available, such as coating solutions for POSS® coatings from Hybrid Plastics, Inc. (Mississippi, USA), silica-filled siloxane coatings from California Hardcoating, Inc. (California, USA), Acier® hybrid hard coating materials from Nidek (Japan), SK1100 series hard coatings from Dexerials, Inc. (Japan), Lioduras™ from TOYOCHEM (Japan), HC-5619 hard coatings from Addison Clear Wave (IL, USA), CrystalCoat UV-curable coatings from SDC Technologies, Inc. (California, USA), and Optoclear® from JSR Corporation (Japan). Hard coating polymers are further described in published U.S. Patent Application 2016 / 0369104, entitled "Transparent Polymer Hardcoats and Corresponding Transparent Films," which is incorporated herein by reference. Suitable hard coating polymers can be obtained, which are highly transparent to the relevant thickness so that the hard coating does not significantly reduce light transmittance through the structure. Suitable crosslinking agents and additives are those described above for adhesives, and these are equally applicable to coatings (e.g., optional base coat 104 and outer coat 108), which will not be explicitly discussed again here.

[0047] The structure after initial treatment generally has a cross-linked outer coating that provides a relatively non-sticky surface. To protect the structure for transport, storage, or the like, one or both surfaces may be protected with a releasable polymer layer. This releasable polymer layer may be formed with a thickness of about 15 micrometers to about 200 micrometers, in other embodiments about 20 micrometers to about 180 micrometers, in other embodiments about 25 micrometers to about 170 micrometers, and in additional embodiments about 40 micrometers to about 150 micrometers. Those skilled in the art will understand that additional ranges of thickness within the explicitly defined range above are carefully considered and are within the scope of this invention. A suitable range of non-sticky polymers may be used for the polymer release layer, and optical properties are irrelevant because the release layer is removed for further processing. Suitable polymers include, for example, polyethylene, polypropylene, polyester, polyamide, polysiloxane, copolymers thereof, and the like. Specific polymers should be selected to have low viscosity such that the peel strength of the release layer is low enough that the material is not damaged when the release layer is peeled off from the substrate.

[0048] Regarding the further post-coating treatments described herein for the roll-to-roll configuration, a release layer is generally present. This release layer may be selectively designed to remain too viscous during the application of heat and humidity selected for the further processing. As described above, after any post-coating treatment is completed, the prepared transparent conductive film may be used for assembly into devices (such as touch sensors), which may involve patterning using optically clear adhesives and the application of additional layers.

[0049] The stabilizing composition, outer coating, and / or undercoat may contain a stabilizing composition that provides improved stability to the molten metal nanostructured network. These compositions can be evaluated using accelerated wear testing, for example, by applying heat and, if necessary, increased humidity. Previous work has shown that vanadium (+5) compounds are effective in providing the desired stability. Other iron (+2) and other metal salts have been found to be effective stabilizers; see Allemand, U.S. Patent Application No. 2015 / 0270024A1, entitled "Light Stability of Nanowire-Based Transparent Conductors," which is incorporated herein by reference. Similarly, cobalt (+2) ions misaligned with ligands have been found to provide stabilization within the molten metal nanostructured network layer. The properties of these stabilizing compositions, individually or in combination, can be further enhanced by incorporating noble metal ions (especially silver ions) into the coating (outer coating and / or undercoat) to further enhance stability, possibly due to the further melting of the structure by the migration of these metal ions. Although the presence of noble metal ions in the coating may be advantageous during post-deposition heat / humidity treatment prior to assembly into the final product, the benefits of such noble metal ions in the coating may be similar to those of pentavalent vanadium during actual use of the structure in the product.

[0050] For inclusion in coatings, vanadium compounds with a +5 valence have been found to produce the desired stabilization under prolonged wear testing. Suitable compounds include those with vanadium as a cation and those with vanadium as a part of a polyatomic anion (such as metavanadate (VO3-) or orthovanadate (VO4-3)). Corresponding salt compounds of oxometalates having a pentavalent vanadium anion include, for example, ammonium metavanadate (NH4VO3), potassium metavanadate (KVO3), tetrabutylammonium vanadate (NBu4VO3), sodium metavanadate (NaVO3), sodium orthovanadate (Na3VO4), other metal salts and the like or mixtures thereof. Suitable pentavalent vanadium cationic compounds include, for example, vanadium trialkoxy (VO(OR)3, where R is an alkyl group, such as n-propyl, isopropyl, ethyl, n-butyl, or similar combinations thereof), vanadium trihalomethanes (VOX3, where X is Cl, F, Br, or combinations thereof), vanadium complexes (such as VO2Z1Z2, where Z1 and Z2 are independently ligands, such as those further described below with respect to Co+2 complexes, or combinations thereof). In the coating, pentavalent vanadium may be present, for example, from about 0.01 wt% to about 9 wt%, in other embodiments from about 0.02 wt% to about 8 wt%, and in additional embodiments from about 0.05 wt% to about 7.5 wt%. In the coating solution, the solution generally contains some solvent along with a solid that primarily comprises a curable polymer. Generally, the corresponding coating solution may have a concentration of pentavalent vanadium compound from about 0.0001 wt% to about 1 wt%. Those skilled in the art will understand that additional ranges of concentrations within the clearly defined range above are carefully considered and are within the scope of this invention. In additional or alternative embodiments, in addition to or in place of pentavalent vanadium ions, iron (+2) or other metal ions may be included.

[0051] In addition, noble metal ions, and specifically silver ions, may also be included in the solution for coating formation. As used herein, noble metal ions refer to ions of silver, gold, platinum, indium, osmium, ruthenium, and rhodium. These noble metal ions may be added as suitable salts, such as nitrates, sulfates, perchlorates, hexafluorophosphates, hexafluoroantimonates, and halides. Suitable metal salts for providing these metal ions include, for example, chloroauric acid and palladium chloride. For silver salts, if the coating polymer is deposited in an alcohol or other non-aqueous organic solvent, suitable silver salts for obtaining sufficient solubility include, for example, silver tetrafluoroborate (AgBF4), silver hexafluorophosphate (AgPF6), silver perchlorate (AgClO4), silver hexafluoroantimonate (AgSbF6), silver trifluoroacetate (CF3COO), silver heptafluorobutyrate (AgC4HF6O2), silver methanesulfonate (AgCH3SO3), silver toluenesulfonate (AgCH3C6H4SO3), or mixtures thereof. In the coating, these noble metal ions may be present, for example, from about 0.01 wt% to about 20 wt%, in other embodiments from about 0.05 wt% to about 15 wt%, in other embodiments from about 0.1 wt% to about 12 wt%, in some embodiments from about 0.2 wt% to about 9 wt%, and in additional embodiments from about 0.25 wt% to about 7.5 wt%. The coating solution generally contains some solvent along with a solid that primarily comprises a curable polymer. Those skilled in the art will understand that additional ranges of concentrations within the clearly defined range above are carefully considered and are within the scope of this invention.

[0052] For direct use in transparent conductive layers, especially in transparent conductive layers with molten metal nanostructured networks, cobalt with a +2 valence has been found to be effective for stabilization without interfering with the melting process. Suitable cobalt compounds include, for example, Co(NO3)2 having various wedge ligands such as nitrite (NO2-), diethylamine, ethylenediamine (en), azirmonotriacetic acid, iminobis(methylenephosphonic acid), aminotris(methylenephosphonic acid), ethylenediaminetetraacetic acid (EDTA), 1,3-propanediaminetetraacetic acid (1,3-PDTA), triethylenetetramine, tris(2-aminoethyl)amine, 1,10-phenanthroline, 1,1 O-Phenyline-5,6-dione, 2,2'-bipyridine, 2,2'-bipyridine-4,4'-dicarboxylic acid, dimethylglyoxime, salicylaldehyde oxime, diethyltriaminepentaacetic acid, 1,2-cyclohexanediaminetetraacetic acid, iminodiacetic acid, methyliminodiacetic acid, N-(2-acetylamine)iminoacetic acid, N-(2-carboxyethyl)iminodiacetic acid, N-(2-carboxymethyl)iminodiapropionic acid, pyridinecarboxylic acid, dipyridinecarboxylic acid, histidine, and combinations thereof. In the aforementioned '833 application, cobalt ions were previously suggested as an ion source suitable for molten metal at nanowire junctions. As shown in the '704 application, unless Co+2 misaligns with the ligand, it effectively destabilizes transparent conductive films. Regarding the use of cobalt+2 stabilizing compounds in layers having the molten metal nanostructured network, these stabilizing compounds will add silver salts or other salts of more easily reduced cations so that the cobalt+2 cations remain in the material after the melting process. On the other hand, it has been found that the stoichiometry of Co+2 ligands interferes with the melting process to form the molten nanostructured network. In layers having the molten metal nanostructured network, the concentration of the cobalt+2 stabilizing compound can be from about 0.1 wt% to about 10 wt%, in other embodiments from about 0.02 wt% to about 8 wt%, and in additional embodiments from about 0.025 wt% to about 7.5 wt%. For cobalt compositions that are effective without interfering with the melting process, the misaligned ligands can be present in amounts from about 0.1 to about 2.6 ligand binding equivalents per mole of cobalt, in other embodiments from about 0.5 to about 2.5, and in other embodiments from about 0.75 to about 2.4 ligand binding equivalents per mole of cobalt. Regarding equivalents, this term is intended to indicate that the multidentate ligands correspondingly have a molar ratio of the range described above divided by their equivalent coordination number. Regarding the inks used to deposit these metallic nanowires, the solution may contain approximately 0.0001 wt% to approximately 1 wt% of the cobalt+2 compound; however, further details of these nanowire inks are presented below. Those skilled in the art will understand that additional ranges of concentrations within the clearly defined ranges above are carefully considered and are within the scope of this invention.

[0053] Although a range of solutions for forming the coating may be used, in some embodiments, such solutions are based on an organic solvent together with a crosslinkable hard coating precursor. Generally, the coating solution contains at least about 7% by weight of solvent, and in other embodiments, about 10% to about 70% by weight of solvent, with the remainder being non-volatile solids. Generally, such solvents may contain water, organic solvents, or suitable mixtures thereof. Suitable solvents generally include, for example, water, alcohols, ketones, esters, ethers (such as glycol ethers), aromatic compounds, alkanes, and the like and mixtures thereof. Specific solvents include, for example, water, ethanol, isopropanol, isobutanol, tributanol, methyl ethyl ketone, methyl isobutyl ketone, cyclic ketones (such as cyclopentanone and cyclohexanone), diacetone alcohol, glycol ethers, toluene, hexane, ethyl acetate, butyl acetate, ethyl lactate, propylene carbonate, dimethyl carbonate, PGMEA (2-methoxy-1-methylethyl acetate), N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, formic acid, or mixtures thereof. In some embodiments, non-aqueous solvents may be desired. Solvent selection is generally based to some extent on the composition of the hard coating polymer. Suitable coating polymers are presented above. Generally, polymers used for coating (generally crosslinkable polymers) are available as commercial coating compositions or formulated with selected polymer compositions.

[0054] The polymer concentration and corresponding concentrations of other non-volatile agents can be selected to achieve the desired rheology of the coating solution, such as the viscosity suitable for the selected coating method. Solvents can be added or removed to adjust the total solids concentration. The relative amount of solids can be selected to adjust the composition of the final coating composition, and the total amount of solids can be adjusted to achieve the desired thickness of the dried coating. Generally, the coating solution may have a polymer concentration of about 0.025 wt% to about 70 wt%, in other embodiments about 0.05 wt% to about 50 wt%, and in additional embodiments about 0.075 wt% to about 40 wt%. Those skilled in the art will appreciate that the additional ranges of polymer concentrations within the specific ranges described above are carefully considered and are within the scope of this invention. Stabilizing salts can be incorporated into the polymer coating composition using suitable mixing equipment.

[0055] Post-coating processing of the transparent conductive layer into an apparatus generally involves several steps. After coating a nanowire solution onto a transparent substrate, the coating is dried under conditions that promote a melting process. Although this melting is a thermodynamically driven process, some heating has been observed to provide activation of the melting process. Although an increase in color (on the order of b*) can be observed with respect to melting, the amount of molten ions can be adjusted to result in complete melting, as indicated by a suitable flat area in the sheet resistance, without significantly degrading optical transmittance or haze. After melting, an outer coating polymer layer is added to the transparent conductive layer. In a roll-to-roll manner, which is desirable from a commercial production standpoint, all of this processing is carried out on a moving sheet forming the substrate, where the coated structure is rolled up for further processing. Although the processing can be carried out on different forms (such as sheets), further processing can then be carried out based on the roll of coated product.

[0056] Evidence suggests that further heat treatment involves the formation of additional melt. Overall observations indicate that these processes have a longer timeframe than the initial melt. While not wanting to be limited by theories based on operating mechanisms, overall observations suggest that some residual metal ion sources can be gradually consumed during further treatment to form additional metal at the melt interface. The expansion of a hydrophilic adhesive around the molten metal nanostructured network facilitates the treatment of this network, which is not separate from the expansion of the polymer. Heat and humidity during the process can be used to control the treatment, both of which promote further melting and provide a degradation pathway. As demonstrated in the examples, proper control of treatment conditions can lead to reduced sheet resistance and mitigated degradation pathways for transparent conductors based on molten metal nanostructured networks.

[0057] For subsequent coating treatments, the temperature is at least about 55°C, in other embodiments about 60°C to about 100°C, and in additional embodiments about 70°C to about 95°C. Humidity can be maintained at ambient humidity, but improved results have been observed for increased relative humidity. Due to the increased temperature, the relative humidity in the hot air generated by ambient humidity alone is generally low. In some embodiments, the relative humidity may be at least about 60%, in other embodiments at least about 65%, and in other embodiments at least about 70%. The processing time for stabilizing the molten metal nanostructured network may be at least about 10 minutes, in other embodiments about 20 minutes to about 50 hours, and in other embodiments about 25 minutes to about 40 hours. Those skilled in the art will understand that the additional ranges of temperature, relative humidity, and processing time within the clearly defined ranges above are carefully considered and are within the scope of this invention.

[0058] Processing with heat and, if necessary, enhanced humidity can be performed under suitable controlled environmental conditions. If humidity is uncontrolled, the environment can be exposed to ambient air, and suitable structures may include ovens or other suitable heaters. Smaller samples can be processed in test chambers designed for applications requiring controlled temperature and pressure. Commercially available test equipment providing heat and humidity control includes, for example, the ESPEC Model BTL-433 environmental chamber (ESPEC Corp. North America, Inc. Hudsonville, MI, USA) or the Thermotron SM-3.5-3800 benchtop environmental chamber (Thermotron Inc., Holland, MI, USA). Larger controlled environmental chambers are available for purchase.

[0059] Generally, treatment can be performed on coated films that are not assembled into a structure with additional layers (such as those used to form the final device). Similarly, accelerated wear testing in a stacked structure involves the placement of additional layers. Thermal and optional humidity treatments are generally not performed on the stacked structure, which includes adhesive layers (such as optically clear adhesives). This heat and humidity can destabilize the stack for commercial processing. Although some instability is acceptable for sample testing, instability is generally not acceptable for product manufacturing. Therefore, treatments for reducing sheet resistance and stabilization are generally performed on samples with an outer coating and a possible release layer.

[0060] The film loaded on the roller in roll form can be heated at a selectable high relative humidity. As noted above, the outer coating can be provided with a non-stick surface by covering it with a release layer in a roll-to-roll manner to facilitate rolling and spreading, and a suitable release layer is described above. Because these rollers are generally formed immediately after production and because of a period of heat treatment, the roller specifications are particularly suitable for commercial production. After this heat treatment, these samples can be assembled into the final product.

[0061] Transparent Film Electrical and Optical Properties: Transparent conductive layers (such as those with fused metal nanostructured networks) can provide low resistance while simultaneously providing good optical properties. Therefore, the film is suitable as a transparent conductive electrode or the like. Such transparent conductive electrodes are suitable for a range of applications such as electrodes along the light-receiving surface of a solar cell. For displays and, specifically, for touch screens, such films can be patterned to provide conductive patterns formed by the film. The substrate with the patterned film generally has good optical properties at individual portions of the pattern.

[0062] The resistance of a thin film can be expressed as sheet resistance, which is reported in ohms per square (Ω / □ or ohms / sq) to distinguish this value from the bulk resistance value according to parameters associated with the measurement method. The sheet resistance of the film can generally be measured using a four-point probe or other suitable methods. In some embodiments, the molten metal nanowire network may have a sheet resistance of no more than about 300 ohms / sq, in other embodiments no more than about 200 ohms / sq, in additional embodiments no more than about 100 ohms / sq, and in other embodiments no more than about 60 ohms / sq. Those skilled in the art will understand that the additional ranges of sheet resistance within the clearly defined range above are carefully considered and are within the scope of this invention. Depending on the specific application, the commercial specifications for chip resistors used in a device may not be for lower chip resistor values, such as when additional cost is involved. Currently commercially relevant values ​​may be, for example, 270 ohms / sq compared to 150 ohms / sq, compared to 100 ohms / sq, compared to 50 ohms / sq, compared to 40 ohms / sq, compared to 30 ohms / sq, compared to 20 ohms / sq, or smaller as target values ​​for different qualities and / or sizes of touch screens. Each of these values ​​defines a range between these specific values, which serve as the endpoints of the range, such as 270 ohms / sq to 150 ohms / sq, 270 ohms / sq to 100 ohms / sq, 150 ohms / sq to 20 ohms / sq, etc., defining 15 specific ranges. Therefore, lower-cost films can be used in certain applications in exchange for moderately higher sheet resistance values. Generally, sheet resistance is reduced by increasing the loading of these nanowires, but increasing the loading from other perspectives may not be desirable, and metallic loading is only one of many factors contributing to achieving low sheet resistance values.

[0063] For applications as transparent conductive films, it is desirable to maintain good optical transparency in the molten metal nanowire network or other sparse metal conductive layer. In principle, optical transparency is negatively correlated with load; higher loads lead to reduced transparency. However, the processing of the network can also significantly affect transparency. Similarly, polymer adhesives and other additives can be selected to maintain good optical transparency. This optical transparency can be evaluated relative to the transmitted light through the substrate. For example, the transparency of the conductive film described herein can be measured using a UV-Vis spectrophotometer and by measuring the total transmittance through the conductive film and the supporting substrate. Transmittance is the ratio of transmitted light intensity (I) to incident light intensity (Io). The transmittance through the film (Tfilm) can be estimated by dividing the measured total transmittance (T) by the transmittance through the supporting substrate (Tsubstrate). (T = I / Io and T / T<substrate = (I / Io) / (I<substrate / Io) = I / I<substrate = Tfilm). Therefore, the reported total transmittance can be corrected to remove the transmittance through the substrate to obtain the transmittance of the film alone. While good optical transparency across the entire visible spectrum is generally expected, for convenience, optical transmittance may be reported at a wavelength of 550 nm. Alternatively, transmittance may be reported as the total transmittance at wavelengths from 400 nm to 700 nm, and these results are reported in the examples below. Generally, for molten metal nanowire films, measurements of 550 nm transmittance and total transmittance from 400 nm to 700 nm (or simply "total transmittance" for convenience) are non-qualitatively different. In some embodiments, films formed from molten meshes have a total transmittance (TT%) of at least 80%, in other embodiments at least about 85%, in additional embodiments at least about 90%, in other embodiments at least about 94%, and in some embodiments about 95% to about 99%. The transparency of films on transparent polymer substrates may be assessed using the standard ASTM D1003 ("Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics"), which is incorporated herein by reference. The TT% of the entire film includes the reduction in transmittance due to the substrate and outer coating, and can be filtered from 1% to 10% of the lower half of the transmittance range above, and in some embodiments from 2.5% to 5%. Those skilled in the art or of the general art will understand that the additional range of transmittance within the clearly defined range above is carefully considered and is within the scope of this invention. When the optical properties of the film were measured for the substrate in the examples below, these films exhibited very good transmittance and haze values, which were achieved together with the observed low film resistance.

[0064] The molten metal mesh can also have low haze and high transmittance of visible light while simultaneously having the desired low sheet resistance. Haze can be measured using a haze meter based on ASTM D1003 as referenced above, and the haze contribution of the substrate can be removed to provide a haze value for the transparent conductive film. In some embodiments, the sintered mesh film can have a haze value of no more than about 1.2%, in other embodiments no more than about 1.1%, in additional embodiments no more than about 1.0%, and in other embodiments about 0.9% to about 0.2%. As described in the examples, very low haze and sheet resistance values ​​have been achieved simultaneously using appropriately selected silver nanowires. The load can be adjusted to balance the sheet resistance and haze values, wherein a very low haze value can still result in a good sheet resistance value. Specifically, a haze value of no more than 0.8%, and in other embodiments about 0.4% to about 0.7%, and a sheet resistance value of at least about 45 ohms / sq can be achieved. Similarly, haze values ​​of 0.7% to approximately 1.2%, and in some embodiments, from approximately 0.75% to approximately 1.05%, and sheet resistance values ​​of from approximately 30 ohms / sq to approximately 45 ohms / sq can be achieved. All of these films maintain good optical transparency. Those skilled in the art will understand that additional ranges of haze within the clearly defined ranges above are carefully considered and are within the scope of this invention.

[0065] Regarding the corresponding properties of multilayer films, additional components are generally chosen to have a minimal impact on optical properties, and various coatings and substrates are commercially available for use in transparent elements. The above summarizes suitable optical coatings, substrates, and associated materials. Some of the structural materials can be electrically insulating, and if thicker insulating layers are used, the film can be patterned to provide gaps or voids through these insulating layers, providing access to and electrical contact points for additional embedded conductive elements. Some components of the final device can be covered from the line of sight with opaque or translucent coverings to hide from the visible parts of the structure, such as connections through conductive transparent elements. This covering protects the conductive layers from light, but heat generation due to light absorption and stability issues at the edges of the covering strip and the transition between the transparent and covered areas can occur; these stability issues are addressed in the examples.

[0066] The stability and stability testing of transparent conductive films are intended to ensure that the transparent conductive film continues for a commercially acceptable period of time, such as the lifespan of the corresponding device. Given that the stabilizing compositions and structures described herein serve this purpose, and that the properties of the sparse metal conductive layer (e.g., molten metal nanostructured networks) are adequately maintained, some simulated accelerated aging tests are used in the processing and corresponding evaluation. However, these accelerated aging tests generally use more layered structures to more closely correspond to the structures in actual devices (such as displays). Qualitative trends are believed to remain very meaningful; however, direct quantitative comparisons with the applicant's earlier accelerated aging tests are not robust.

[0067] Example 1: Using heat and humidity treatment to reduce sheet resistance. This example demonstrates the performance of silver nanowire structures containing NanoGlue® flux under various environmental conditions by measuring relative sheet resistance. Generally, the treatments and compositions described in Examples 1 and 2 do not significantly alter the optical properties of these structures compared to earlier reports on such materials.

[0068] Laboratory Coating: Figures 4 to 6 show graphs of the relative sheet resistance (R / R0) as a function of time for the samples in which the transparent polymer substrate was coated using a manual trough coating method in a laboratory environment with one of four silver nanowire ink compositions. The first sample group (S1 and S2) was prepared with GEN5 ActiveGrid™ ink from Applicant C3Nano, Inc., and the diameter of the silver nanowires was <25 nm; one sample (S1) included NanoGlue® melt and the other sample (S2) was meltless. The second sample group (S3 and S4) was prepared with GEN7 ActiveGrid™ ink and the diameter of the silver nanowires was <20 nm; one sample (S3) included NanoGlue® melt and the other sample (S4) was meltless. The silver nanowire ink composition with NanoGlue® and the process for forming a transparent conductive film are substantially as described in Example 5 of the '968 patent, which is cited above as describing the synthesized silver nanowires in U.S. Patent 10,714,230B2, entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed From the Nanowires," which is incorporated herein by reference.

[0069] Following coating, the transparent conductive film structure was air-dried at room temperature and then further baked in an oven at 120°C for approximately 2 minutes to induce melting and form a molten metal nanostructured network. The amount of silver deposited was selected to provide a film with a sheet resistance of approximately 70 ohms / sq as measured after drying. A commercial overcoat was manually applied to each dried transparent conductive film structure. This overcoat was dried and crosslinked with a UV lamp to form an overcoat with a thickness of approximately 85 nm. This overcoat also included a stabilizing compound as described in the '704 application cited above.

[0070] The effects of heat treatment or treatment with heat and humidity were studied using commercial testing equipment that provides control over such heat and humidity. Samples were placed indoors and tested under various conditions of temperature (65°C or 85°C) and relative humidity (85%, 90%, or unadjusted) without illumination. In contrast to conventional testing of films based on metal nanowires, these samples were tested using only the polymer outer coating, which, in contrast to conventional testing, involves testing transparent conductive films within a stack of additional, thicker protective polymer layers.

[0071] The relative sheet resistance (R / R0) of the samples was measured as a function of time. Figure 4 shows the data for 85°C without humidity adjustment; Figure 5 shows the data for 85°C and 85% relative humidity; Figure 6 shows the data for 65°C and 90% relative humidity. The transparent conductive film formed from finer silver nanowires and NanoGlue® flux (sample S3) shows the lowest relative sheet resistance for the longest test time under the teaching conditions, indicating the highest long-term stability performance. Comparing Figures 4 with Figures 5 and 6, it can be seen that drying and heating at 85°C does not significantly increase the sheet resistance, but high humidity causes a significant increase in sheet resistance. Comparing Figures 4 and 5 with Figures 6, the excellent performance of the samples with NanoGlue® flux (S1 and S3) under high relative humidity (90%) conditions is evident, especially for times greater than 50 hours. As can be seen from the significantly different results for S3 and S4 in Figures 5 and 6, the stabilizing effect of the NanoGlue® flux is particularly pronounced for smaller diameter nanowire structures under high relative humidity. The finer silver nanowires have a larger surface area to volume ratio, and the observed effect of NanoGlue® in samples S3 and S4 is due to the increased number of contacts and reduced contact area for the finer nanowires.

[0072] Treatment at 85°C and 85% relative humidity (Figure 5) provides the maximum initial reduction in relative sheet resistance. Under various environmental conditions, the sheet resistance decreases (approximately 10% or greater) during the initial hours of testing for samples (S1 and S3) with NanoGlue® in the coating. After approximately 75 hours, except for S1 in an unregulated humidity environment at 85°C (Figure 4), samples with NanoGlue® flux show a lower relative sheet resistance at a given test time compared to samples without the flux. Samples (S2 and S4) formed without the NanoGlue® flux do not show any reduction in relative sheet resistance during treatment. In these samples, the relative sheet resistance increases only over time.

[0073] Roll-to-Roll Coating: Figure 7 shows the results of samples in which the substrate was coated using a die coating process in a roll-to-roll manner with one of three silver nanowire ink compositions. These three silver nanowire ink compositions were prepared using GEN7 ActiveGrid™ ink and different amounts of NanoGlue® flux: 1.5x NanoGlue®, 3x NanoGlue®, or no NanoGlue® (as a control), where the amount of NanoGlue® is relative to the standard amount in commercial inks. After coating, the structure was air-dried at room temperature and then further dried in an oven at 120°C for up to 10 minutes to dry the ink. The resistance of the nanowire ink coating samples as a function of time was tested in an air atmosphere at 65°C and 90% relative humidity. Two samples with ink coatings containing NanoGlue® showed an initial decrease in relative sheet resistance of approximately 10% after approximately 80 hours. After the initial decrease, the relative sheet resistance of the NanoGlue® coated samples increased but remained below the initial resistance value until approximately t = 300 hours. The final relative sheet resistance (R / R0) of the two samples with NanoGlue® flux was 1.4. The 1.5x NanoGlue® samples generally showed lower sheet resistance than the 3x samples. Throughout the testing period, the samples without flux showed an initial increase in sheet resistance of approximately 19% and subsequent increases. This final relative sheet resistance was approximately 2.1. The target threshold value of 1.2 R / R0 for the increase in sheet resistance is shown as a horizontal line.

[0074] This experiment shows that nanowire inks with 1.5x or 3x NanoGlue® melt reduce the resistivity of the nanowire coating structure by approximately 33%. Samples without NanoGlue® cross the 1.2 target after approximately 125 hours, while samples with NanoGlue® cross the 1.2 target threshold after approximately 650 hours.

[0075] Laboratory and roll-to-roll results show that the environmental durability of the conductive silver nanowire film is improved by using NanoGlue® flux. These results indicate that the initial resistance decrease observed in the NanoGlue® samples indicates that NanoGlue® provides an additional metal source to the transparent conductive film. The improved stability observed with NanoGlue® under high temperature / high humidity conditions is consistent with the reduction / elimination of junction resistance by melting; without melting, the junction resistance increases more rapidly under high temperature / high humidity conditions. These results indicate that initial heat and humidity treatment of coated products can be used to reduce sheet resistance and potentially improve the stability of the transparent conductive film before assembly into a device.

[0076] Example 2: Stabilization of molten metal nanostructured networks with silver ions in an outer coating This example demonstrates the stabilizing effect of NanoGlue® flux in an outer coating layer adjacent to the molten metal nanostructured network.

[0077] Figure 8 shows a graph of the relative sheet resistance (R / R0) as a function of time for stacked optical structure samples with various outer coatings. These structures include a transparent polymer substrate with a rarefied metal conductive layer, which may be melted to form a rarefied metal nanostructured network or not melted, and the formation of this structure is described in Example 1. The layer system of these stacked optical structure samples is illustrated in Figure 8. Each sample has a PET substrate. As described in Example 1, the substrate is coated with GEN5 silver nanowire ink with NanoGlue® flux and then dried. Next, an outer coating consisting of a UV-curable polymer resin containing a selective amount of silver salt (such as NanoGlue®) is applied to each structure. Finally, each structure is stacked on A-type glass. Five outer coating compositions were prepared with different amounts of NanoGlue® flux: NanoGlue® grades 1x, 1.5x, 2x, 3x, or no NanoGlue® (as a control), where the reference amount of NanoGlue® (1x) is approximately 3.0% to approximately 3.5% by weight of silver ions. These samples were tested under high temperature / high humidity conditions: 85°C and 85% relative humidity. The samples with the NanoGlue® outer coating showed an initial decrease in relative sheet resistance, which became more significant with increasing NanoGlue® grade. Further high temperature / high humidity treatment of the optical stack structure revealed a significant effect of NanoGlue® in the outer coating on the sheet resistance of the silver nanowire structure.

[0078] This example demonstrates that in structures containing both a NanoGlue® outer coating and a silver nanowire layer, the reduction in sheet resistance after high-temperature / high-humidity treatment can be even more significant. For example, after approximately 95 hours, comparing S1 in Figure 5 with NanoGlue® level 3x in Figure 8, the samples exhibit relative sheet resistances of 1.07 and 0.85, respectively. This reduction in sheet resistance is consistent with the chemical reduction of silver ions in the outer coating to metallic silver conductors at the junction sites.

[0079] Figure 9 shows the effect of NanoGlue® level 3x in the outer coating on GEN5 silver nanowire films without NanoGlue®, where the stack is tested with only the polymer outer coating and no additional OCA or other layers. The results show the sample with NanoGlue® in the outer coating and another sample without NanoGlue® under high temperature / high humidity conditions of 85°C and 85% relative humidity. The sample with NanoGlue® in the outer coating shows an initial decrease in relative sheet resistance, followed by a sustained decrease. Conversely, the sample without NanoGlue® in the outer coating shows a significant increase. At approximately 45 hours, the values ​​for these two samples are 0.87 and 1.36, respectively.

[0080] This example shows that the presence of NanoGlue® in the outer coating and the presence or absence of NanoGlue® in the silver nanowire layer can significantly reduce sheet resistance and provide significant stabilization under accelerated wear testing.

[0081] The foregoing embodiments are intended to illustrate and not limit. Additional embodiments are within the scope of the claims. Furthermore, although the invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the invention. Limitations are made by incorporating any of the foregoing documents so as not to introduce an object contrary to the explicit disclosure herein. To the extent that a particular structure, composition, and / or method is described herein as a component, element, ingredient, or other dispensing, unless otherwise expressly indicated, it should be understood that the disclosure herein covers specific embodiments, embodiments comprising such specific components, elements, ingredients, other dispensings, or combinations thereof, and embodiments substantially constituted by such specific components, ingredients, other dispensings, or combinations thereof, which may include additional features that do not alter the essential nature of the object, as indicated in the discussion. As will be understood by those skilled in the art in the specific text, the term "about" used herein refers to the anticipated uncertainty of a relevant value. [Simplified Explanation of the Diagram]

[0083] Figure 1 is a partial side view of a film having a sparse metal conductive layer and various additional transparent layers on either side of the sparse metal conductive layer.

[0084] Figure 2 is a schematic side view of a double-sided structure having a sparse metal conductive layer on each side of a thin polymer substrate.

[0085] Figure 3 is a schematic side view of the roller of the transparent conductive film.

[0086] Figure 4 is a graph showing the relative sheet resistance as a function of processing time for a group of silver nanowire structure samples prepared by hand coating with silver nanowire inks of different grades of NanoGlue®. The samples were processed at 85°C.

[0087] Figure 5 is a graph showing the relative sheet resistance as a function of processing time for a group of silver nanowire structure samples prepared by hand coating with silver nanowire inks of different grades of NanoGlue®. The samples were processed at 85°C and 85% relative humidity.

[0088] Figure 6 is a graph showing the relative sheet resistance as a function of processing time for a group of silver nanowire structure samples prepared by hand coating with silver nanowire inks of different grades of NanoGlue®. The samples were processed at 65°C and 90% relative humidity.

[0089] Figure 7 is a graph showing the relative sheet resistance as a function of processing time for a group of silver nanowire structure samples prepared by roller-to-roll coating with silver nanowire inks of different grades of NanoGlue®. The samples were processed at 65°C and 90% relative humidity.

[0090] Figure 8 is a graph showing the relative sheet resistance as a function of processing time for a group of stacked optical structure samples prepared with silver nanowire inks containing NanoGlue® and having different grades of NanoGlue® outer coatings. The samples were processed at 85°C and 85% relative humidity.

[0091] Figure 9 is a graph showing the relative sheet resistance as a function of processing time for two stacked optical structure samples prepared with silver nanoline ink (without NanoGlue®) and with or without a coating of NanoGlue®. The samples were processed at 85°C and 85% relative humidity.

Claims

1. A transparent conductive film comprising a transparent polymer substrate, a rare-metal conductive layer supported by the substrate, and a polymer outer coating adjacent to the rare-metal conductive layer, wherein the transparent conductive film has a visible light transmittance of at least about 88% and a sheet resistance of not more than about 120 ohms / sq, and wherein the polymer outer coating comprises a polymer and about 0.01 wt% to about 20 wt% of noble metal ions, wherein the noble metal ions comprise silver, gold, platinum, indium, osmium, ruthenium, or rhodium.

2. The transparent conductive film of claim 1, wherein the outer coating has an average thickness of about 5 nm to about 250 nm.

3. The transparent conductive film of claim 1, wherein the polymer of the outer coating comprises polysiloxane, polysilsesquioxane, polyurethane, acrylic resin, acrylic copolymer, cellulose ether and / or ester, nitrocellulose, other water-insoluble structural polysaccharides, polyether, polyester, polystyrene, polyimide, fluoropolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, polysulfide, epoxy-containing polymer, copolymer thereof, or mixture thereof.

4. The transparent conductive film of claim 1, wherein the polymer outer coating comprises about 0.1% to about 9% by weight of a vanadium (+5) stabilizing composition.

5. The transparent conductive film of claim 1, wherein the polymer outer coating has an average thickness of about 10 nm to about 125 nm, wherein the polymer of the outer coating comprises polyacrylate, and wherein the polymer outer coating comprises about 0.5 wt% to about 5 wt% of a vanadium(+5) stabilizing composition comprising ammonium metavanadate (NH4VO3), tetrabutylammonium vanadate (NBu4VO3), potassium metavanadate (KVO3), sodium metavanadate (NaVO3), sodium orthovanadate (Na3VO4), tripropanol vanadium oxy, triethanolamine vanadium oxy, triisopropanol vanadium oxy, tributanol vanadium oxy, or mixtures thereof.

6. The transparent conductive film of claim 1, wherein the rare-metal conductive layer comprises a molten metal nanostructured network including silver and wherein the noble metal ions comprise silver ions.

7. The transparent conductive film of claim 1, wherein the transparent conductive film has a transmittance of at least about 90% and a sheet resistance of not more than about 90 ohms / sq.

8. The transparent conductive film of claim 1, wherein the polymer outer coating comprises about 0.25% by weight to about 12% by weight of silver ions, provided as silver tetrafluoroborate (AgBF4), silver hexafluorophosphate (AgPF6), silver perchlorate (AgClO4), silver hexafluoroantimonate (AgSbF6), silver trifluoroacetate (AgCF3COO), silver heptafluorobutyrate (AgC4HF6O2), and silver methanesulfonate (AgCH3SO3), silver toluenesulfonate (AgCH3C6H4SO3), or mixtures thereof.

9. The transparent conductive film of claim 1, wherein the sparse metal conductive layer is patterned.

10. A method for reducing the sheet resistance of a transparent conductive film comprising a substrate, a transparent conductive layer, and a polymeric outer coating, the transparent conductive layer comprising a molten metal nanowire network and a polymeric polyol adhesive, wherein the polymeric outer coating has an average thickness of about 5 nm to about 250 nm, the method comprising: The transparent conductive film is heated to a temperature from about 55°C to about 100°C for about 10 minutes to about 50 hours to reduce the resistance of the film by at least about 5%.

11. The method of claim 10, wherein during the heating step, the transparent conductive film is contained in a releasable polymer layer on the polymer outer coating, and the transparent conductive film is wound on a roller.

12. The method of claim 10, wherein the heating step is performed at a relative humidity of at least about 60%.

13. The method of claim 10, wherein the heating is performed at a temperature of about 60°C to about 100°C and at a relative humidity of at least about 60% for about 20 minutes to about 50 hours, and wherein the transparent conductive film is free of optically transparent adhesive.

14. The method of claim 10, wherein the molten metal nanostructured network comprises silver, and the film has a sheet resistance of not more than 120 ohms / sq and a visible light transmittance of at least about 88%.

15. The method of claim 10, further comprising, prior to applying the polymer outer coating, heating the substrate having the coating of solvent, metal nanowires and metal ions to a temperature of about 45°C to about 130°C for at least about 2 minutes to dry the coating and form the molten metal nanostructured network.

16. The method of claim 15, wherein the polymer outer coating comprises a vanadium (+5) stabilizing composition and silver ions.

17. The method of claim 15, wherein the polymer outer coating has an average thickness of about 20 nm to about 125 nm, wherein the polymer of the polymer outer coating comprises polyacrylate, and wherein the polymer outer coating comprises about 0.5 wt% to about 5 wt% of a vanadium(+5) stabilizing composition.

18. The method of claim 17, wherein the polymer outer coating comprises about 0.1% to about 20% by weight of noble metal ions, wherein the noble metal ions comprise silver, gold, platinum, indium, osmium, ruthenium, or rhodium.

19. The method of claim 10, wherein the molten metal nanostructured network comprises silver and wherein the polymer outer coating comprises about 0.25% by weight to about 15% by weight of silver ions.

20. The method of claim 10, wherein the method further includes terminating the heating before the resistance of the plate begins to increase.

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