Coating and treatment of transparent conductive films for stabilizing rare metal conductive layers

Abstract

A transparent conductive film comprising a rarefied metallic conductive layer is treated after being coated with an outer coating to reduce the film's sheet resistance. The rarefied metallic conductive layer may comprise a fused metallic nanostructured network. The coating (e.g., a polymer outer coating or a polymer undercoat) may contain noble metal ions that can further reduce sheet resistance upon application of heat and optional humidity. In particular, it has been demonstrated that silver ions in the coating provide significant stabilization of the rarefied metallic conductive layer upon application of heat and humidity, regardless of fusion. The coating may also contain a metal salt stabilizing composition.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to co-pending provisional patent application 62 / 936,681 filed by Yang et al. on November 18, 2019, entitled “Post-coating treatment of transparent conductive film formed by fused silver nanowires”, which is incorporated herein by reference. Background Technology

[0003] Functional films can provide important functions in a variety of situations. For example, conductive films are important for dissipating static electricity when it may be unsuitable or dangerous. Transparent conductive films can be used as electrodes. High-quality displays may include one or more transparent conductive layers.

[0004] Transparent conductors can be used in a variety of optoelectronic applications, including touchscreens, 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 high transparency at high conductivity. However, ITO has several drawbacks. For example, ITO is a brittle ceramic that requires sputtering for deposition, a fabrication process involving high temperatures and vacuum, which is therefore slow and not cost-effective. Additionally, ITO is known to be prone to cracking on flexible substrates. Newer portable electronic devices are pushing towards thinner forms. Summary of the Invention

[0005] In a first aspect, the present invention relates to a transparent conductive film comprising a transparent polymer substrate, a rare-sparse metal conductive layer supported by the substrate, and a polymer overcoat adjacent to the rare-sparse metal conductive layer, wherein the transparent conductive film has a visible light transmittance of at least about 88% and a sheet resistance of no more than about 120 ohms / sq, and wherein the polymer overcoat comprises a polymer and about 0.01 wt% to about 20 wt% noble metal ions.

[0006] In another aspect, 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 polymer outer coating, the transparent conductive layer comprising a fused metal nanowire network and a polymeric polyol binder, wherein the polymer outer coating has an average thickness of about 5 nm to about 250 nm, the method comprising heating the transparent conductive film at a temperature of at least about 55°C for at least about 10 minutes to reduce the sheet resistance by at least about 5%. The heating step can be performed in a structure without an optically transparent binder. In some embodiments, the fused 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%.

[0007] In another aspect, the present invention relates to a transparent conductive film comprising a substrate, a transparent conductive layer comprising a fused metal nanostructured network, and a polymer overcoat, 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 heating and optionally processing (hereinafter sometimes referred to as "processing") for at least about 10 minutes to reduce the sheet resistance by at least about 5%. In some embodiments, the polymer overcoat and / or undercoat comprises metal ions. Attached Figure Description

[0008] Figure 1 This is a partial side view of a film having a sparse metal conductive layer and a plurality of additional transparent layers on either side of the sparse metal conductive layer.

[0009] Figure 2 This is a schematic side view of a double-sided structure with a sparse metallic conductive layer on each side of a thin polymer substrate.

[0010] Figure 3 This is a schematic side view of a roller for a transparent conductive film.

[0011] Figure 4 By manually applying different levels The graph shows the relative sheet resistance (as a function of processing time) of a group of silver nanowire structure samples prepared by silver nanowire ink. The samples were treated at 85℃.

[0012] Figure 5 By manually applying different levels The graph shows the relative sheet resistance (as a function of processing time) of a group of silver nanowire structure samples prepared by silver nanowire ink. The samples were treated at 85°C and 85% relative humidity.

[0013] Figure 6 By manually applying different levels The graph shows the relative sheet resistance (as a function of processing time) of a group of silver nanowire structure samples prepared by silver nanowire ink. The samples were processed at 65 °C and 90% relative humidity.

[0014] Figure 7 Different levels are achieved through roll-to-roll coating. The graph shows the relative sheet resistance (as a function of processing time) of a group of silver nanowire structure samples prepared by silver nanowire ink. The samples were treated at 65 °C and 90% relative humidity.

[0015] Figure 8 It utilizes the content Silver nanowires were prepared and configured with different levels of ink. The relative sheet resistance (as a function of processing time) of a set of stacked optical structure samples with an outer coating. The samples were processed at 85°C and 85% relative humidity.

[0016] Figure 9 It utilizes silver nanowire ink (without) ) and have or not A graph showing the relative thin-film resistance (as a function of processing time) of two stacked optical structure samples prepared with an outer coating. The samples were processed at 85°C and 85% relative humidity. Detailed Implementation

[0017] As demonstrated herein, heating, optionally coupled with controlled application of humidity, can be used to reduce the sheet resistance of fused metal nanostructured networks with a protective polymer overcoat. This treatment can be applied to transparent conductive films with a protective polymer overcoat to further improve electrical properties. This treatment can be effective for fused 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, particularly silver, in a polymer coating (e.g., an overcoat) adjacent to a rare metal conductive layer (e.g., the fused metal nanostructured network) is suitable for further stabilizing the conductive structure. In the case of a noble metal in the coating, the advantages do not necessarily require additional treatment to develop, as benefits can be generated during use. If the rare metal conductive layer does not include the fused metal nanostructured network, the results in this embodiment show that the significant stabilization produced by noble metal ions in the overcoat has a significant effect on stability under light and humidity, likely due to fusion with metal ions in the overcoat. The results are demonstrated in silver-based conductors. Transparent conductive films can have high transmittance and low haze. Process time and conditions can be controlled to avoid significant degradation while achieving performance enhancement. Similarly, after treatment, the membrane exhibits significantly enhanced stability under accelerated abrasion conditions as well as at high temperatures and high humidity. This treatment is suitable for use with membranes formed through roll-to-roll processing for large-scale commercial applications.

[0018] 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 ideal due to its mechanical properties, visible light transparency, flexibility, a combination of these characteristics, or other aspects of the conductive film. In particular, the use of nanowires to form transparent conductive films can have important applications in devices with displays and touch sensors.

[0019] Metal-based transparent conductive elements (e.g., films) comprise sparse metallic conductive layers. The conductive layers are typically sparse to provide the desired amount of optical transparency through the conductive structure rather than around it; thus, the metallic overlays on the conductive element typically have, though small, noticeable gaps. For example, transparent conductive films may comprise metal nanowires deposited along a layer, within which sufficient contact can be provided for electron permeation to offer a suitable conductive path. In embodiments of particular interest, transparent conductive films may comprise fused metal nanostructured networks, which have been found to exhibit desirable electrical and optical properties. Unless otherwise explicitly stated, conductivity as used herein refers to electrical conductivity.

[0020] As explained in more detail below, the fusion process can be controlled to carefully deposit metal at the junctions between metal nanowires. The fusion process can be controlled to deposit the required amount of junction-related silver. The system can be balanced to provide a thermodynamic drive for fusion, causing it to occur primarily at the junctions between adjacent metal nanowires that are components forming the fused metal nanostructured network. After fusion, an integral structure, termed the fused metal nanostructured network, is formed, and the original metal nanowires within the conductive structure lose their individual identity. Evidence suggests that the fused metal causes the original individual nanowires to merge, thereby reducing or eliminating junction resistance. For commercial products, it is desirable to improve the durability of transparent conductive films under various real-world conditions, and the treatment described herein has been shown to improve durability under specific accelerated wear tests.

[0021] The advantages of forming fused metal nanostructured networks in the case of transparent conductors based on silver nanowires remain well understood. The fusion process for forming fused metal nanostructured networks has been found to yield highly transparent and highly conductive structures with very low haze. Fused metal nanostructured networks exhibit excellent stability under accelerated wear conduction with appropriate stabilizers. The addition of noble metal ions (such as silver) to the outer coating provides an additional level of stabilization, and results indicate that, for the current binder system used in this paper with a hydrophilic binder in the transparent conductive layer, the noble metal ions in the fusion and / or outer coating need to achieve reasonable stability under defined heating and humidity tests.

[0022] For commercial processing, a thin protective polymer overcoat is typically applied over the transparent conductive layer. This protective overcoat is usually no more than about 250 nm thick. The following results demonstrate that when a transparent conductive film with a fused metal nanostructured network and a protective polymer overcoat is subjected to heating and, optionally, humidity, the film resistance decreases before eventually increasing due to degradation. No similar decrease in resistance was observed for the corresponding unfused film. As a result, it can be found that the structure with the fused metal nanostructured network is more stable than the previously tested structures under the corresponding test conditions. Heat treatment may further support improvements in the fusion process. Introducing humidity during heat treatment can lead to a greater reduction in film resistance.

[0023] It has been previously observed that using humidity during the fusion process allows for achieving comparable sheet resistance values ​​with lower temperatures and shorter processing times. See U.S. Patent 9,183,968B to Li et al., entitled “Metallic Nanowire Ink for Forming Transparent Conductive Films with Fusion Networks,” which is incorporated herein by reference. This observation may or may not be relevant to current observations. The current processing time is significantly longer than that used in standard fusion processes.

[0024] If the polymer is hydrophilic, heating and / or humidity can cause the polymer binder around the conductive elements to swell. If the conductive elements are not fused, the swelling of the binder may reduce conductivity and increase sheet resistance due to reduced contact between the conductive elements. In the case of a fused metal nanostructured network, the fused elements are bonded together. While not wishing to be limited by theory, swelling can facilitate the migration of metal nanoparticles or any residual metal ions, thereby facilitating fusion at the joint, which can further reduce sheet resistance. A decrease in sheet resistance was observed in the following examples. Similarly, if the outer coating contains metal ions, they can migrate over time to further contribute to fusion at the joint, which can mitigate damage and lead to a further decrease in sheet resistance.

[0025] The structure with a protective polymer outer coating after heat treatment may differ in quality from the previously formed structure, or it may not differ in quality. Nevertheless, the observed results are consistent with further migration of silver into the fused metal nanostructured network, resulting in a structure that appears to have fewer nanoparticles descattering and absorbing light leaving the fused metal nanostructured network. Regarding the formation of new structures, the study shows that the new structures achieve improved stability during thermal testing while generally maintaining or improving optical properties.

[0026] The data presented herein provide both information related to the process of improving conductivity and data on wear testing of the transparent conductive film. Improved wear testing can be achieved through post-treatment, specifically by incorporating metal ions into the outer coating after the polymer coating is applied and / or over time. Generally, if the process is stopped once the film resistance reaches a lower value, the material can be used to form products with lower film resistance and desirable stability. Typically, the post-treated transparent conductive film can have a film resistance that is at least about 5% lower, in some embodiments at least about 7.5% lower, and in other embodiments at least about 10% lower than the initial film resistance value after fusion.

[0027] Regarding changes in environmental stability, the inventors considered two ways to evaluate this parameter. Simply put, initial samples can be considered. Again, these samples comprise a thin, protective polymer overcoat. These initial samples can exhibit that, after treatment at 65°C and 90% relative humidity, the ratio of the film resistivity divided by the initial film resistivity (R / R0) remains 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 exhibiting a lower film resistivity value is a novel material due to previously unobtained structural improvements, the thermal stability time observed for the improved material can be used as a reference to the thermal stability time relative to the initial material.

[0028] Results are provided for heating at 85°C and ambient humidity, at 85°C and 85% relative humidity, and at 65°C and 90% relative humidity. Typically, the process for forming an improved material can be carried out over a period of approximately 10 minutes to approximately 100 hours, depending on the process conditions regarding temperature and relative humidity. If a new material is formed, the process for forming this new material can likely be optimized.

[0029] Silver provides excellent electrical conductivity. The applicant uses the trade name... This product is a commercially available silver nanowire ink for forming fused metal nanostructured networks. Other sources of silver nanowires are commercially available, and the basic fusion technology is fully described in the following cited '207 and '807 patents. Gen 5 Most (>98%) of the silver nanowires in the product have a diameter of less than <25 nm, and are of generation 7 (GEN7). Most (>98%) of the 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 “Fine and Uniform Silver Nanowires, Synthesis Method, and Transparent Conductive Film Formed from the Nanowires,” which is incorporated herein by reference.

[0030] Improved properties have been discovered in fused metal nanostructured networks, including high electrical conductivity and desirable optical properties such as transparency and low haze. The fusion of adjacent metal nanowires can be achieved through chemical processes under commercially suitable processing conditions.

[0031] In particular, a significant advancement in realizing conductive films based on metal nanowires is the discovery of a fully controllable process for forming fused metal networks, in which adjacent portions of the metal nanowires fuse into a monolithic structure, without distinct nanowires within the conductive network. Specifically, it was initially discovered that halide ions can drive the fusion of metal nanowires to form fused metal nanostructures. Fusing agents containing halide anions have been introduced in various ways to successfully achieve fusion with a correspondingly significant decrease in resistance. It should be noted that the halide ions in this treatment should not be confused with the halide ions used in the nanowire synthesis reaction. Specifically, the fusion of metal nanowires utilizing halide anions has been accomplished using vapors and / or solutions of acyl halides, as well as solutions of halide salts. The fusion of halide-derived metal nanowires is further described in U.S. Patent 10,029,916 entitled “Metal Nanowire Networks and Transparent Conductive Materials” by Virkar et al. and U.S. Patent 9,920,207 (′207 Patent) entitled “Metal Nanostructured Networks and Transparent Conductive Materials” by Virkar et al., both of which are incorporated herein by reference.

[0032] An extension of the process for forming fused metal nanowire networks is based on a reduction / oxidation (redox) reaction that can provide the optical properties of the resulting film without damaging the fused nanowires. The metal used for deposition at the junction can be efficiently added as a dissolved metal salt or dissolved from the metal nanowires themselves. The efficient use of redox chemistry for fusing metal nanowires into a nanostructured network is further described in U.S. Patent 10,020,807 (′807 Patent) to Virkar et al., entitled “Fused Metal Nanostructured Networks, Fusion Solution with Reducing Agent, and Method for Forming Metal Networks,” which is incorporated herein by reference. The ′807 Patent also describes a single-solution approach for forming fused metal nanostructured networks. The single-solution approach for forming fused metal nanostructured layers is further described in U.S. Patent 9,183,968 B1 (hereinafter referred to as the '968 Patent) entitled "Metal Nanowire Ink for Forming 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 fused metal nanostructured networks is used in the following embodiments.

[0033] An ideal ink for achieving efficient monodeposition of a solidified, fused nanostructured metal network comprises the required amount of metal nanowires to achieve proper metal filling in the resulting film. The ink is stable in a suitable solution prior to deposition and drying. The ink may contain a reasonable amount of polymeric binder, which facilitates the formation of a stable conductive film for further processing. Hydrophilic polymers, such as cellulose or chitosan-based polymers, have been found effective as binders for obtaining good fusion results using monodeposition systems. Metal ions, as the source of the metal for the fusion process, can be supplied as soluble metal salts.

[0034] Single-ink formulations provide the metal as the desired filler for a film on a substrate surface, and simultaneously provide the components of the ink that induce a fusion process when the ink is dried under appropriate conditions. These inks can be conveniently referred to as fused metal nanowire inks, given that fusion typically does not occur until drying. The inks typically contain an aqueous solvent, which in some embodiments may further contain alcohols and / or other organic solvents. The inks may also contain dissolved metal salts as a source of the metal for the fusion process. It is not desirable to be theoretically limited to the assumption that the components of the ink (e.g., alcohols or other organic compositions) reduce metal ions from the solution to drive the fusion process. Previous experience with fusion processes in these systems suggests that the metal preferentially deposits at the junction between adjacent metal nanowires. Polymer binders can be provided to stabilize the film and influence the ink properties. The specific formulation of the ink can be tailored to select ink properties suitable for a particular deposition pathway and exhibiting specific coating properties on the substrate surface. Drying conditions can be selected to effectively carry out the fusion process, as further described below.

[0035] Typically, one or more solutions or inks used to form a metallic nanostructured network may collectively comprise well-dispersed metallic nanowires, a fluxing agent, and optional other components, such as polymeric binders, crosslinking agents, wetting agents (e.g., surfactants), thickeners, dispersants, other optional additives, or combinations thereof. Solvents used for the metallic nanowire ink and / or fluxing solution, if different from the nanowire ink, may include aqueous solvents, organic solvents, or mixtures thereof. In particular, suitable solvents include, for example, water, alcohols, ketones, esters, ethers such as glycol ethers, aromatic compounds, alkanes, etc., 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 a good dispersion of the metallic nanowires, it should also be compatible with other selected additives so that the additives are soluble in the solvent. In embodiments in which a fusing agent is included in a single solution containing metal nanowires, the solvent or its components may or may not be important components of the fusing solution, such as alcohols, and may be selected accordingly as needed.

[0036] Metal nanowire inks configured as single or dual inks may contain about 0.01 to about 1% by weight of metal nanowires, in another embodiment about 0.02 to about 0.75% by weight of metal nanowires, and in other 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 dissolved silver salt. The ink may contain silver ions at concentrations of about 0.01 mg / mL to about 2.0 mg / mL, in another embodiment about 0.02 mg / mL to about 1.75 mg / mL, and in other embodiments about 0.025 mg / mL to about 1.5 mg / mL. Those skilled in the art will recognize that further ranges of metal nanowire concentration and metal ion concentration within the aforementioned defined ranges are considered and are within the scope of this disclosure. The concentration of metal nanowires affects the filling of the metal on the substrate surface and the physical properties of the ink.

[0037] Regarding ink formulations, polymer binders and solvents are generally and consistently chosen such that the polymer binder is soluble or dispersible in the solvent. In suitable embodiments, metallic nanowire inks typically contain 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 other embodiments about 0.1 to about 2.5% by weight of polymer binder. In some embodiments, the polymer binder comprises crosslinkable organic polymers, such as radiation-crosslinkable organic polymers and / or thermosetting organic binders. Desired binders include, for example, polymeric polyols, such as polysaccharide-cellulose polymers, chitosan polymers, etc. To promote crosslinking of the binder, metallic nanowire inks may contain about 0.0005% to about 1% by weight of crosslinking agent in some embodiments, about 0.002% to about 0.5% by weight of crosslinking agent in other embodiments, and about 0.005% to about 0.25% by weight of crosslinking agent in other embodiments. Nanowire inks may optionally contain rheology modifiers or combinations thereof. In some embodiments, the ink may contain a wetting agent or surfactant to reduce surface tension, and the wetting agent may be useful for improving coating performance. A variety of surfactants are commercially available, such as nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants. The wetting agent is generally soluble in a solvent. In some embodiments, the nanowire ink may contain about 0.001 to about 1% by weight of a wetting agent, in other embodiments about 0.002 to about 0.75% by weight of a wetting agent, and in still other embodiments about 0.003 to about 0.6% by weight of a wetting agent. A thickener may optionally be used as a rheology modifier to stabilize the dispersion and reduce or eliminate sedimentation. In some embodiments, the nanowire ink may optionally contain about 0.05 to about 5% by weight of a thickener, in other embodiments about 0.075 to about 4% by weight of a thickener, and in still other embodiments about 0.1 to about 3% by weight of a thickener. Those skilled in the art will recognize that additional ranges of binder concentration, wetting agent concentration, and thickener concentration within the above-defined ranges are considered and are within the scope of this disclosure.

[0038] The stability of the transparent conductive layer is a crucial consideration for applying these structures to commercial devices, such as mobile phones, tablets, computer touchscreens, large touchscreens, foldable electronic devices, and wearable electronic devices. The reliability of touch sensors formed using transparent conductive layers is important for widespread commercial applications, and higher material reliability allows for a wider range of devices. The processes and structures described in this paper offer even greater commercial viability for structures already used in commercial devices.

[0039] Transparent conductive film structure

[0040] Reference Figure 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, although not all embodiments include all layers. Typically, 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 one or more transparent conductive layers. The transparent conductive film typically 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 typically 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 recognize that other ranges of thickness within the aforementioned explicit ranges are considered and are within the scope of this disclosure. In some embodiments, the length and width of the produced film can be selected to suit a particular application so that the film can be directly introduced for further processing into a product. In other or alternative embodiments, the width of the membrane can be selected for a specific application, while the length of the membrane can be relatively long, with the expectation that it can be cut to the required length for use. For example, the membrane can be in the form of a long sheet or roll. Similarly, in some embodiments, the membrane can be on a roller or in another large standard form, and the membrane elements can be cut according to the length and width required for use.

[0041] Substrate 102 typically includes 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 still other embodiments about 10 micrometers to about 100 micrometers. Particularly for foldable structures, especially the double-sided foldable structures described below, the substrate thickness typically does not exceed about 27 micrometers, and in other embodiments is about 5 micrometers to about 25 micrometers. Those skilled in the art will recognize that other ranges of substrate thickness within the aforementioned explicit ranges are considered and are within the scope of this disclosure. Suitable optically transparent polymers with very good transparency, low haze, and good protective capabilities can be used for the substrate.

[0042] The amount of nanowires delivered to the substrate for the rarefied metallic conductive layer 106 can involve a balance between factors that achieve the desired amount of transparency and conductivity. While the thickness of the nanowire network can theoretically be evaluated using scanning electron microscopy, the network may be relatively sparse to provide optical transparency, which can complicate measurements. Typically, rarefied metallic conductive structures (e.g., fused metallic nanowire networks) have an average thickness of no more than about 5 micrometers, in another embodiment no more than about 2 micrometers, and in other embodiments about 10 nm to about 500 nm. However, rarefied metallic conductive structures are typically structures with relatively open structures having significant surface texture at the submicrometer scale. The nanowire loading level can provide a useful parameter of the network that can be easily evaluated, and the loading value provides an alternative parameter related to thickness. Therefore, as used herein, the nanowire loading level onto the substrate is typically given in milligrams of nanowires per square meter of substrate. Typically, a nanowire network can have about 0.1 milligrams (mg) / m². 2 Approximately 300 mg / m 2 In another implementation scheme, approximately 0.5 mg / m³ 2 Approximately 200 mg / m 2 And in other embodiments, approximately 1 mg / m³ 2 Approximately 150 mg / m 2 The amount of filler. Those skilled in the art will recognize that other ranges of thickness and filler within the above-defined ranges are considered and are within the scope of this disclosure. If the sparse metallic conductive layer is patterned, the discussion of thickness and filler applies only to areas that do not exclude metal or areas not significantly reduced by the patterning process.

[0043] Suitable polymers for substrates include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyolefins, polyvinyl chloride, fluoropolymers, polyamides, polyimides, polysulfones, polysiloxanes, polyetheretherketones, polynorbornene, polyesters, polystyrene, polyurethanes, polyvinyl alcohol, polyvinyl acetate, acrylonitrile-butadiene-styrene copolymers, cyclic olefin polymers, cyclic olefin copolymers, polycarbonates, copolymers thereof, or blends thereof. Suitable commercial polycarbonate substrates include, for example, MAKROFOL SR243 1-1 CG, commercially available from Bayer Material Science. Plastic, available commercially from TAP Plastics; and LEXAN TM8010CDE is commercially available from SABIC Innovative Plastics. The protective surface layer 112 may independently have a thickness and composition that covers the same range of thicknesses and compositions as the substrate described above in this paragraph.

[0044] For structures with double-sided, individually patternable transparent conductive layers, UV-absorbing transparent substrates can be used. Such structures... Figure 2 As shown in the diagram, and described below. While applicable to all embodiments, suitable polymers, particularly for these embodiments, include, for example, polyimides, polysulfides (such as Pylux). TM AresMaterials), polysulfone (such as Solvay's), ) or polyethersulfone (such as Solvay's) Or BASF ) and polyethylene naphthalate (such as DuPont's) Examples are given below based on transparent polyimides. Traditional aromatic polyimides are colored. However, recently developed polyimides are transparent to visible light. Transparent polyimides absorb ultraviolet light. Transparent polyimides are available from Kolon (Korea), TaimideTech (Taiwan), Sumitomo (Japan), SKC Inc. (GA, USA), and NeXolve (AL, USA).

[0045] Optional undercoat 104 and / or outer coating 108 may be disposed below or above the sparse metallic conductive layer 106. Coatings 104 and 108 may contain curable polymers, such as thermosetting or radiation-curable polymers. Coatings 104 and 108 may have an average thickness as described in the sections specifically covering the outer coating and undercoat below. The thickness and composition of the outer coating can be selected such that the sheet resistance measurement through the outer coating does not change significantly compared to measurements without an outer coating. 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.

[0046] Optional optically clear adhesive layer 110 may have an average thickness of about 10 micrometers to about 300 micrometers, in another embodiment about 15 micrometers to about 250 micrometers, and in other embodiments about 20 micrometers to about 200 micrometers. Those skilled in the art will recognize that other ranges of thickness for the optically clear adhesive layer within the aforementioned defined range are considered and are within the scope of this disclosure. Suitable optically clear adhesives may be contact adhesives. Optically clear adhesives include, for example, coatable compositions and tapes. Optically clear 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 are chemically available based on acrylic or polysiloxane. Suitable tapes are commercially available, for example, from the following companies: Lintec Corporation (MO series); Saint Gobain Performance Plastics (DF713 series); Nitto Americas (NittoDenko) (LUCIAC S CS9621T and LUCIAS CS9622T); LG Hausys OCA (OC9102D, OC9052D); DICCorporation (DAITAC LT series OCA, DAITAC WS series OCA and DAITAC ZB series); PANAC PlasticFilm Company (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).

[0047] Some optically transparent tapes include a carrier film, such as polyethylene terephthalate (PET), which can be embedded in the tape between two adhesive surfaces. Based on previous work on organic stabilizers, it has been found that the presence of a carrier film in the optically transparent adhesive layer effectively combines with those stabilizers that improve the stabilizing properties of the optically transparent tape, relative to corresponding films in optically transparent tapes without a carrier film. While not wishing to be limited by theory, it is inferred that the improvement in stability may be due to reduced water and oxygen permeability through the carrier film. Using the metal-based stabilizers described herein, it was found that the stabilizing properties are not significantly dependent on the specific optically transparent adhesive used, which is an advantage of metal-based stabilizers such as V(+5) salts.

[0048] An embodiment of a double-sided structure with two transparent conductive structures is in Figure 2 As shown in the image. Figure 2 This illustrates a general structure of a monolithic double-sided conductive element on a core substrate. (Refer to...) Figure 2 The double-sided conductive sheet 150 may include a substrate polymer sheet 152, an optional first hard coat 154, a first rare-sparse metal conductive layer 156, a first outer coating 158, an optional second hard coat 160, a second rare-sparse metal conductive layer 162, a second outer coating 164, an optional first release film 166, and an optional second release film 168.

[0049] Single-sided or double-sided sheets with a transparent conductive layer can be fabricated in a roll-to-roll configuration. Such a roll 190... Figure 3 The diagram is schematically shown. The formation of a double-sided flexible structure in a roll-to-roll manner is described in U.S. Patent Application 2020 / 0245457, entitled “Thin Flexible Structure with Transparent Conductive Film and Method for Forming the Structure”, by Chen et al., which is incorporated herein by reference.

[0050] Generally, silver nanowire ink can be coated using any reasonable method, such as dip coating, spray coating, blade coating, doctor blade coating, Meyer bar coating, slot extrusion coating, gravure printing, spin coating, etc. For commercial roll-to-roll processing, slot extrusion coating is commonly used. The film can be dried, for example, using a hot air gun, oven, hot lamp, warm airflow, etc. In some embodiments, the film can be heated to a temperature of about 50°C to about 150°C during drying. To facilitate the fusion process, heat transfer typically lasts from about 30 seconds to about 15 minutes. Those skilled in the art will recognize that other ranges of temperature and time within the above-defined ranges are considered and are within the scope of this disclosure.

[0051] Transparent conductive films can be used in a variety of products that include transparent conductive electrodes, such as solar cells. Their excellent optical properties make them particularly valuable for use in touch sensors integrated into displays. Transparent conductive layers can be patterned using photolithography, laser ablation, or other suitable techniques. Patterned transparent conductive layers are suitable for forming touch sensors. Such touch sensors are used in portable electronic devices and large displays.

[0052] Polymer coating (top coat and / or base coat)

[0053] Polymer coatings can provide desirable functionalities, as outlined in the overall structure above. In particular, the polymer outer coating offers several functionalities. First, it provides mechanical protection to the transparent conductive layer during further processing. Second, it can have a stabilizing composition to improve the wear durability of the transparent conductive layer. The primer coating provides an ideal surface for arranging the transparent conductive layer with a fused metal nanostructured network and can also provide a stabilizing composition. As described herein, the inclusion of noble metal ions (such as silver ions) in the coatings (outer coating and / or outer coating) can lead to increased fusion of the fused metal nanostructured network, thereby simultaneously reducing film resistance and improving thermal stability.

[0054] Typically, a polymer overcoat is used to cover the rarefied metallic conductive layer to provide mechanical protection for the conductive layer. In some embodiments, the overcoat can be selected such that, after the overcoat is applied, haze is significantly reduced without significantly reducing other properties. Additionally, the thickness and composition of the overcoat can be selected such that the resistance measurement of the thin film through the overcoat does not change significantly compared to the measurement without the overcoat. The inclusion of additional stabilizers in the coating is further described below and in U.S. Patent Application 2018 / 0105704 (hereinafter referred to as '704 application), entitled "Stabilized Rare Metal Conductive Film and Solution for Delivering Stabilizing Compounds" by Yang et al., which is incorporated herein by reference.

[0055] In some embodiments, the outer coating is typically thin enough that conductivity can occur through it, even if the outer coating polymer is typically dielectric. In other words, the surface with 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 for the polymer outer coating to have an average thickness of no more than about 250 nm, about 5 nm to about 200 nm in some embodiments, about 8 nm to about 125 nm in other embodiments, and about 10 nm to about 100 nm in yet another embodiment. Those skilled in the art will recognize that other ranges of thickness within the aforementioned explicit ranges are considered and are within the scope of this disclosure.

[0056] As described above, the conductive structure may include a lower layer between a polymer substrate and a rarefied metallic conductive layer, typically having a fused metal nanostructured network. The lower layer adjacent to the transparent conductive layer may be referred to as the undercoat. The undercoat may include a polymer hard coating. As an undercoat, the polymer hard coating does not provide mechanical protection, but it can provide protection against chemical damage. In some embodiments, the polymer hard coating undercoat provides significant stability to the fused metal nanostructured layer used on certain polymer substrates.

[0057] Suitable hard-coating polymers are typically highly crosslinked polymers of crosslinked polyacrylates, which can be bonded to other crosslinked components such as polyurethanes, epoxy polymers, polysiloxanes, and / or other crosslinked polymers. Branched acrylate monomers can provide for the formation of highly crosslinked polymers, and the crosslinked acrylates can be copolymerized with other components (such as polyurethane acrylates) to form interwoven crosslinked polymers. Commercially available hard-coating polymers, such as those from Hybrid Plastics, Inc. Coating solutions from Coatings (Mississippi, USA), silica-filled siloxane coatings from California Hardcoating Company (California, USA), and coatings from Nidek. Hybrid hard coatings (Japan), SK1100 series hard coatings from Dexerials Corporation (Japan), Lioduras from TOYOCHEM TM (Japan), HC-5619 hard coating from AddisonClear Wave (IL, USA), CrystalCoat UV-curable coating from SDC Technologies, Inc. (California, USA), and JSR Corporation (Japan). Hard coating polymers are further described in U.S. Patent Application 2016 / 0369104, entitled “Transparent Polymer Hard Coating and Corresponding Transparent Film,” by Gu et al., which is incorporated herein by reference. Suitable hard coating polymers are available that are highly transparent at the relevant thickness, such that the hard coating does not significantly reduce light transmittance through the structure. Suitable crosslinking agents and additives have been described above with respect to binders, and they are equally applicable to coatings (e.g., optional base coat 104 and outer coat 108), and need not be explicitly repeated here.

[0058] The structure after initial treatment typically has a cross-linked outer coating that provides a relatively non-sticky surface. To protect the structure for transport, storage, etc., one or both surfaces can be protected with a release polymer layer. The release polymer layer can be formed to have a thickness of about 15 micrometers to about 200 micrometers, in another embodiment about 20 micrometers to about 180 micrometers, in other embodiments about 25 micrometers to about 170 micrometers, and in yet another embodiment about 40 micrometers to about 150 micrometers. Those skilled in the art will recognize that other ranges of thickness within the aforementioned defined ranges are considered and are within the scope of this disclosure. Various suitable non-sticky polymers can be used for the polymer release layer, and optical properties are irrelevant since further processing is performed after the release layer is removed. Suitable polymers include, for example, polyethylene, polypropylene, polyester, polyamide, polysiloxane, copolymers thereof, etc. A specific polymer should be selected to have low viscosity so that the peel strength of the release layer is sufficiently low to avoid damaging the material when the release layer is peeled from the substrate.

[0059] For further post-coating treatments in the roll-to-roll configuration described herein, a release layer is typically present. The release layer can be selected to remain non-sticky during the application of heat and humidity chosen for further processing. After any post-coating treatment is completed, the resulting transparent conductive film can be used for assembly into devices such as touch sensors, which may involve the patterning and application of additional layers, typically using optically transparent adhesives, as described above.

[0060] Stabilized Composition

[0061] The outer coating and / or undercoat may contain stabilizing compositions that provide improved stability to the fused metal nanostructured network, the stability of which can be evaluated using accelerated wear testing, for example, using heating and optionally increased humidity. Previous work has found that vanadium (+5) compounds can effectively provide the desired stability. Other work has found that iron (+2) and other metal salts can be effective stabilizers; see Allemand’s published U.S. Patent Application 2015 / 0270024A1 entitled “Photostabilization of a Transparent Conductor Based on Nanowires,” which is incorporated herein by reference. Additionally, cobalt (+2) ions that coordinate with ligands have been found to provide stabilization within the fused metal nanostructured network layer. The properties of these stabilizing compositions, individually or in combination, can be further enhanced by incorporating noble metal ions, particularly silver ions, into the coating (outer coating and / or undercoat) to further enhance stability, possibly by utilizing metal ion migration to further fuse the structure. The benefits of noble metal ions in the coating can be similar to those of pentavalent vanadium being utilized during actual use of the structure in the product, although alternatively or additionally, the presence of noble metal ions in the coating during post-deposition heating / humidity treatment prior to assembly into the final product can be beneficial.

[0062] For incorporation into coatings, vanadium compounds with a +5 valence have been found to exhibit ideal stabilization under long-term wear testing. Suitable compounds include those with vanadium as a cation and those with vanadium as a polyatomic anion (such as metavanadate (VO3)). - ) or orthovanadate (VO4) -3Compounds that are part of a group of metal oxometalates. Corresponding salt compounds having a pentavalent vanadium anion in metal oxometalates include, for example, ammonium metavanadate (NH4VO3), potassium metavanadate (KVO3), tetrabutylammonium metavanadate (NBu4VO3), sodium metavanadate (NaVO3), sodium orthovanadate (Na3VO4), other metal salts, or mixtures thereof. Suitable pentavalent vanadium cations include, for example, vanadium trialkoxy (VO(OR)3, where R is an alkyl group, such as n-propyl, isopropyl, ethyl, n-butyl, etc., or combinations thereof), vanadium trihalide (VOX3, where X is Cl, F, Br, or combinations thereof), vanadium complexes (such as VO221Z2, where Z1 and Z2 are independently ligands, such as those further described below with respect to Co+2 complexes), or combinations thereof. Pentavalent vanadium may be present in the coating, for example, from about 0.01 wt% to about 9 wt%, in another embodiment from about 0.02 wt% to about 8 wt%, and in other embodiments from about 0.05 wt% to about 7.5 wt%. In the coating solution, the solution typically contains some solvent and a solid comprising primarily a curable polymer. Typically, the corresponding coating solution may have a concentration of about 0.0001 wt% to about 1 wt% of the pentavalent vanadium compound. Those skilled in the art will recognize that other ranges of concentration within the aforementioned specific ranges are considered and are within the scope of this disclosure. In other or alternative embodiments, iron (+2) or other metal ions may be included in addition to or as a substitute for pentavalent vanadium ions.

[0063] In addition, the solution used to form the coating may contain noble metal ions, particularly silver ions. As used herein, noble metal ions refer to ions of silver, gold, platinum, indium, osmium, ruthenium, and rhodium. Noble metal ions can be added as suitable salts, such as nitrates, sulfates, perchlorates, hexafluorophosphates, hexafluoroantimonates, and halides. Suitable metal salts for providing metal ions include, for example, chloroauric acid and palladium chloride. For silver salts, if the coating polymer is deposited using 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. Noble metal ions may be present in the coating, for example, […]. The coating solution contains approximately 0.01 wt% to approximately 20 wt%, in other embodiments approximately 0.05 wt% to approximately 15 wt%, in other embodiments approximately 0.1 wt% to approximately 12 wt%, in some embodiments approximately 0.2 wt% to approximately 9 wt%, and in other embodiments approximately 0.25 wt% to approximately 7.5 wt% of noble metal ions. The coating solution typically contains some solvent and a solid comprising primarily a curable polymer. Those skilled in the art will recognize that further ranges of concentration within the aforementioned specific ranges are considered and are within the scope of this disclosure.

[0064] For direct use in transparent conductive layers, especially those with fused metal nanostructured networks, cobalt with a +2 valence has been found to be effective for stabilization without interfering with the fusion process. Suitable cobalt compounds include, for example, Co(NO3)2 with various coordinating ligands, such as nitrite (NO2). -), diethylamine, ethylenediamine (en), aminotriacetic acid, iminobis(methylenephosphonic acid), aminotri(methylenephosphonic acid), ethylenediaminetetraacetic acid (EDTA), 1,3-propanediaminetetraacetic acid (1,3-PDTA), triethylenetetramine, tri(2-aminoethyl)amine, 1,10-phenanthroline, 1,10-phenanthroline-5,6-dione, 2,2'-bipyridine, 2,2'-bipyridine-4,4'-dicarboxylic acid, dimethylglyoxime, salicylaldehyde oxime, diethylenetriaminepentaacetic acid, 1,2-cyclohexanediaminetetraacetic acid, iminodiacetic acid, methyliminodiacetic acid, N-(2-acetamide)iminoacetic acid, N-(2-carboxyethyl)iminodiacetic acid, N-(2-carboxymethyl)iminodipropionic acid, pyridinecarboxylic acid, pyridinedicarboxylic acid, histidine, and combinations thereof. Cobalt ions have previously been suggested as a suitable ion source for fusing metals at nanowire junctions in the aforementioned '833 application. As shown in '704 application, Co+2 effectively destabilizes transparent conductive films unless it ligands. Regarding the use of a cobalt+2 stabilizing compound in layers having a fused metal nanostructured network, this stabilizing compound is added together with a silver salt or a salt of another more easily reduced cation, so that the cobalt+2 cation remains in the material after the fusing process. On the other hand, it has been found that stoichiometric amounts of ligands for Co+2 interfere with the fusing process for forming the fused nanostructured network. In layers having a fused metal nanostructured network, the concentration of the cobalt+2 stabilizing compound can be from about 0.1 wt% to about 10 wt%, in another embodiment from about 0.02 wt% to about 8 wt%, and in other embodiments from about 0.025 wt% to about 7.5 wt%. For cobalt compositions that are effective without interfering with the fusion process, the coordinating ligand may be present in amounts of about 0.1 to about 2.6 ligand-binding equivalents / molar cobalt, in another embodiment about 0.5 to about 2.5 ligand-binding equivalents / molar cobalt, and in other embodiments about 0.75 to about 2.4 ligand-binding equivalents / molar cobalt. Regarding equivalents, this term is intended to indicate that the multidentate ligands accordingly have a molar ratio of the above range divided by their coordination number. Regarding the ink for depositing metal nanowires, the solution may contain a cobalt+2 compound at a concentration of about 0.0001 wt% to about 1 wt%, although further details of the nanowire ink are given below. Those skilled in the art will recognize that additional ranges of concentration within the aforementioned defined ranges are considered and are within the scope of this disclosure.

[0065] While a variety of solutions can be used to form the coating, in some embodiments the solution is based on an organic solvent and a crosslinkable hard coating precursor. Typically, 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. Typically, the solvent can include water, organic solvents, or suitable mixtures thereof. Suitable solvents typically include, for example, water, alcohols, ketones, esters, ethers such as glycol ethers, aromatic compounds, alkanes, etc., and mixtures thereof. Specific solvents include, for example, water, ethanol, isopropanol, isobutanol, tert-butanol, 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 desirable. Solvent selection is typically based in part on the hard coating polymer composition. Suitable coating polymers have been given above. Generally, polymers used for coatings, typically crosslinkable polymers, are available as commercial coating compositions or can be formulated using selected polymer compositions.

[0066] The polymer concentration and the concentration of other corresponding non-volatile reagents can be selected to achieve the desired rheological properties of the coating solution, such as viscosity suitable for the selected coating process. 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 dry coating thickness. Typically, the coating solution can have a polymer concentration of about 0.025 wt% to about 70 wt%, in another embodiment about 0.05 wt% to about 50 wt%, and in other embodiments about 0.075 wt% to about 40 wt%. Those skilled in the art will recognize that other ranges of polymer concentrations within the specific ranges described above are considered and are within the scope of this disclosure. Stabilizing salts can be blended into the polymer coating composition using suitable mixing equipment.

[0067] Post-coating treatment

[0068] Fabricating a transparent conductive layer into a device typically involves several steps. After coating a nanowire solution onto a transparent substrate, the coating is dried under certain conditions to promote the fusion process. Although fusion is a thermodynamically driven process, some heating has been observed to provide activation for the fusion process. The amount of fusion ions can be adjusted to achieve complete fusion, indicated by an approximate plateau in the sheet resistance, without significant degradation in optical transmittance or haze, although an increase in color (increase in b* size) can be observed with fusion. Following fusion, an outer coating polymer layer is added onto the transparent conductive layer. In a roll-to-roll configuration (which can be ideal from a commercial production standpoint), this processing is entirely performed on a moving sheet forming the substrate, where the coated structure is rolled up for further processing. Further processing can then be performed based on the roll of coated product, although processing can be carried out on different forms, such as sheets.

[0069] Evidence suggests that further thermal processing involves the formation of additional fusion. Overall observations indicate that these processes have a longer timeframe than the initial fusion. While it is undesirable to limit ourselves to principles based on the operating mechanism, overall observations suggest that some residual sources of metal ions may be gradually consumed during further processing, resulting in the formation of additional metal at the fusion joint. Swelling of the hydrophilic binder around the fused metal nanostructured network can facilitate the processing of the fused metal nanostructured network, which does not separate as the polymer swells. Heating and humidity during the process can be used to control the processing, both of which favor further fusion and facilitate the degradation process. As demonstrated in the examples, appropriate control of process conditions can lead to a reduction in the sheet resistance of the transparent conductor based on the fused metal nanostructured network and a slowing of the degradation process.

[0070] For this post-coating processing, the temperature is at least about 55°C, in another embodiment about 60°C to about 100°C, and in other embodiments about 70°C to about 95°C. Humidity can be maintained at ambient humidity, but improved results are observed as the relative humidity level increases. Due to the increased temperature, the relative humidity in the heated air derived solely from ambient humidity is typically a lower value. In some embodiments, the relative humidity can be at least about 60%, in another embodiment at least about 65%, and in other embodiments at least about 70%. The processing time for stabilizing the fused metal nanostructured network can be at least about 10 minutes, in another embodiment about 20 minutes to about 50 hours, and in other embodiments about 25 minutes to about 40 hours. Those skilled in the art will recognize that other ranges of temperature, relative humidity, and processing time within the clearly defined ranges described above are considered and are within the scope of this disclosure.

[0071] Processing using heating and optionally increased humidity can be performed under suitable controlled environmental conditions. If humidity is not controlled, 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 to apply controlled temperatures and pressures. Commercially available test equipment offering control over heating and temperature 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 environment chambers are commercially available.

[0072] Typically, processing can be performed on coated films not assembled into structures with additional layers (such as those used to form the final device). Additionally, accelerated wear testing in layered laminates involves the placement of additional layers. Heating and optional humidity treatments may be performed outside of laminate structures including adhesive layers (such as optically transparent adhesives). Heating and humidity can destabilize laminates intended for commercial processing. While some instability may be acceptable for sample testing, it is generally unacceptable for product manufacturing. Therefore, treatments for reducing and stabilizing sheet resistance are typically performed on samples with an outer coating and possibly a release layer.

[0073] Heating and optionally high relative humidity can be applied to the roll film loaded onto the rollers. As mentioned above, a release layer can be applied to cover the outer coating in a roll-to-roll manner to provide a non-sticky surface, thereby facilitating winding and unwinding, and suitable release layers are described above. Because rolls are typically formed immediately after production, and because heat treatment takes some time, roll form can be particularly convenient for commercial production. After heat treatment, samples can be assembled into the final product.

[0074] Electrical and optical properties of transparent films

[0075] Transparent conductive layers, such as those with fused metal nanostructured networks, can provide low resistance while offering good optical properties. Therefore, these films can be used as transparent conductive electrodes. Transparent conductive electrodes are suitable for a variety of applications, such as electrodes along the light-receiving surface of a solar cell. For displays, especially touchscreens, the films can be patterned to provide conductive patterns formed by the films. Substrates with patterned films typically exhibit good optical properties at various points along the pattern.

[0076] The resistance of a thin film can be expressed as sheet resistance (reported in ohms / □ (Ω / □ or ohms / sq)) to distinguish the value from the bulk resistance value based on parameters associated with the measurement process. The sheet resistance of a film can typically be measured using a four-point probe method or other suitable methods. In some embodiments, the fused 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 still other 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 recognize that other ranges of sheet resistance within the aforementioned defined ranges are considered and are within the scope of this disclosure. Depending on the specific application, the commercial specifications for the sheet resistance used in a device may not necessarily specify a lower limit for the sheet resistance value, for example, when additional costs may be involved. Currently, commercially relevant values ​​that can serve as target values ​​for touchscreens of different qualities and / or sizes are, for example, 270 ohms / sq relative to 150 ohms / sq, relative to 100 ohms / sq, relative to 50 ohms / sq, relative to 40 ohms / sq, relative to 30 ohms / sq, relative to 20 ohms / sq, or lower. Each of these values ​​defines a range between specific values ​​as 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, in exchange for a suitably higher sheet resistance value, a lower-cost film can be suitable for certain applications. Typically, sheet resistance can be reduced by increasing the amount of nanowires, but the increased amount of nanowires may be undesirable in other respects, and the amount of metal filling is only one of many factors used to achieve low sheet resistance values.

[0077] Regarding applications as transparent conductive films, good optical transparency is ideal for fused metal nanowire networks or other sparse metal conductive layers. In principle, optical transparency is negatively correlated with filler content, as higher filler content leads to reduced transparency, although network fabrication can also significantly affect transparency. Additionally, polymer binders and other additives can be selected to maintain good optical transparency. 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 (I0). o The ratio of the transmittance (T) through the membrane. 膜 This can be achieved 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 膜 Therefore, the reported total transmittance can be corrected to remove transmission through the substrate, thus obtaining the transmittance of the film alone. Although good optical transparency in the visible spectrum is generally ideal, for convenience, optical transmittance at a wavelength of 550 nm can be reported. Alternatively or additionally, transmittance can be reported as total transmittance at wavelengths from 400 nm to 700 nm, and such results are reported in the following embodiments. Generally, for fused metal nanowire films, there is no qualitative difference between measurements of 550 nm transmittance and total transmittance from 400 nm to 700 nm (or, for convenience, simply referred to as "total transmittance"). In some embodiments, the film formed by the fused network has a total transmittance (TT%) of at least 80%, in other embodiments at least about 85%, in other embodiments at least about 90%, in still other embodiments at least about 94%, and in some embodiments about 95% to about 99%. The transparency of a film on a transparent polymer substrate can be evaluated using standard ASTM D1003 (“Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics”), which is incorporated herein by reference. The TT% across the entire film includes the decrease in transmittance due to the substrate and outer coating, and can deviate from the lower limit of the aforementioned transmittance range by 1% to 10%, and in some embodiments by 2.5% to 5%. Those skilled in the art will recognize that other ranges of transmittance within the aforementioned defined ranges are considered and are within the scope of this disclosure. When the optical properties of the film measured in the following examples are adjusted for the substrate, the film exhibits very good transmittance and haze values, which are achieved in conjunction with observed low sheet resistance.

[0078] The fused metal network can also exhibit low haze and high visible light transmittance, while possessing ideally low sheet resistance. Haze can be measured using a haze meter based on ASTM D1003 as referenced above, and the haze contribution from the substrate can be removed to provide the haze value of the transparent conductive film. In some embodiments, the sintered network film can have a haze value of no more than about 1.2%, in other embodiments no more than about 1.1%, in still other 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 ​​are achieved simultaneously using appropriately selected silver nanowires. The filler content can be adjusted to balance the sheet resistance and haze values, making it possible to achieve very low haze values ​​while still maintaining good sheet resistance. Specifically, haze values ​​of no more than 0.8%, and in other embodiments about 0.4% to about 0.7%, can be achieved with a sheet resistance of at least about 45 ohms / sq. Furthermore, with a film resistivity of approximately 30 ohms / sq to approximately 45 ohms / sq, haze values ​​of 0.7% to approximately 1.2%, and in some embodiments, approximately 0.75% to approximately 1.05%, can be achieved. All these films maintain good optical transparency. Those skilled in the art will recognize that additional ranges of haze within the aforementioned specific ranges are considered and are within the scope of this disclosure.

[0079] Regarding the corresponding properties of multilayer films, additional components with minimal impact on optical performance are typically selected, and various coatings and substrates are commercially available for transparent elements. Suitable optical coatings, substrates, and related materials have been outlined above. Some of the structural materials can be electrically insulating, and if a thicker insulating layer is used, the film can be patterned to provide locations where gaps or voids through the insulating layer can provide access and electrical contact for other embedded conductive elements. Some components of the final device can be covered by opaque or translucent coverings to conceal parts of the structure, such as connections through conductive transparent elements. Coverings can shield the conductive layers from light, but can cause heating due to light absorption, and the cover tape and edges at the transition between the transparent and covered areas may present stability issues as addressed in the embodiments.

[0080] Stability of transparent conductive film and stability test

[0081] Ideally, transparent conductive films should be maintained for a commercially acceptable time, such as the lifespan of the corresponding device. The stabilization compositions and structures described herein take this objective into account and adequately preserve the performance of the sparse metallic conductive layers (e.g., fused metallic nanostructured networks). Some aspects of the processing and corresponding evaluations simulated accelerated aging tests. However, accelerated aging tests typically use more layered structures to more closely correspond to the structures in actual devices (e.g., displays). Qualitative trends are still considered very meaningful, although direct quantitative comparisons with the applicant's previous accelerated aging tests may be unreliable.

[0082] Example

[0083] Example 1 - Processing to reduce the resistivity of thin films using heating and humidity

[0084] This embodiment demonstrates the presence of [a substance] by measuring the relative thin-film resistance. The properties of the silver nanowire structure with a binder under various environmental conditions. Generally, the treatments and compositions described in Examples 1 and 2 do not significantly alter the optical properties of the structure compared to those previously reported with respect to these materials.

[0085] Laboratory coating: Figure 4-6 A graph showing the relative sheet resistance (R / R0) (as a function of time) of the sample is presented, in which a transparent polymer substrate was coated with one of four silver nanowire ink compositions using a manual slit coating process under laboratory conditions. The sample was created using GEN5 ActiveGrid from the applicant, C3Nano, Inc. TM The first sample group (S1 and S2) was prepared using ink, wherein the diameter of the silver nanowires was <25 nm, and one sample (S1) contained... The sample had a flux, while the other sample (S2) did not. (Using GEN7 ActiveGrid) TM The second sample group (S3 and S4) was prepared using ink, wherein the diameter of the silver nanowires was <20 nm, and one sample (S3) contained... One sample (S4) contained a flux, while the other sample (S4) did not. The silver nanowire ink composition and the process for forming a transparent conductive film are essentially as described in Example 5 of the above-cited '968 patent, wherein the silver nanowires are synthesized as described in U.S. Patent 10,714,230B2 to Hu et al. entitled "Fine and Uniform Silver Nanowires, Method of Synthesis and Transparent Conductive Film Formed from the Nanowires", which are incorporated herein by reference.

[0086] After 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 fusion, thereby forming a fused metal nanostructured network. The amount of silver deposited was selected to provide a film with a sheet resistance of approximately 70 ohms / sq (measured after drying). A commercial outer coating was manually slit-coated onto each dried transparent conductive film structure. The outer coating was dried and crosslinked with a UV lamp to form an outer coating with a thickness of approximately 85 nm. The outer coating also contained a stabilizing compound as described in the following cited '704 application.

[0087] Commercial testing equipment providing control over heating and humidity was used to study the effects of heat treatment or treatments utilizing heat and humidity. Samples were placed in a chamber and tested in the absence of light under various temperature (65°C or 85°C) and relative humidity (85%, 90%, or unregulated) conditions. This testing differed from conventional testing of films based on metal nanowires, which involves testing samples with only a polymer outer coating, where transparent conductive films are tested as laminates with an additional, thicker protective polymer layer.

[0088] The relative sheet resistance (R / R0) of the sample as a function of time is measured. Figure 4 Data is shown for a condition of 85°C without humidity adjustment; Figure 5 Data for conditions of 85°C and 85% relative humidity are shown; Figure 6 Data for conditions of 65°C and 90% relative humidity are shown. This is achieved using fine silver nanowires and... The transparent conductive film formed by the flux, i.e., sample S3, exhibited the lowest relative sheet resistance for the longest test time under each condition, indicating the highest long-term stability performance. Figure 4 and Figure 5 and 6 Comparative analysis showed that drying and heating at 85℃ did not significantly increase the film resistivity, but increased humidity resulted in a large increase in film resistivity. Figure 4 and 5 and Figure 6 Comparison, having The superior performance of the flux samples (S1 and S3) under high relative humidity (90%) conditions is evident, especially for times greater than 50 hours. (As shown by...) Figure 5 and 6 The clearly different results seen in S3 and S4 are as follows. The stabilizing effect of the flux is particularly pronounced at elevated relative humidity for lower diameter nanowire structures. The finer silver nanowires exhibit a larger surface area to volume ratio, and the observed... The effect in samples S3 and S4 may be due to the increased number of contacts and reduced contact area for finer metal wires.

[0089] Treatment at 85℃ and 85% relative humidity Figure 5 This provides the largest initial reduction in relative thin-film resistance. Under each environmental condition, for coatings with... For samples (S1 and S3), the sheet resistance decreased (by more than 10%) in the first few hours of testing. This was except for S1, which showed a decrease after approximately 75 hours in an environment at 85°C without humidity control. Figure 4 ),have The sample with flux showed a lower relative sheet resistance at a given test time compared to the sample without flux. The samples (S2 and S4) formed with the flux did not show any decrease in relative sheet resistance under the treatment. In these samples, the relative sheet resistance increased only with time.

[0090] Roll-to-roll coating: Figure 7 The results show the results of coating a substrate with one of three silver nanowire ink compositions using a slit extrusion coating process in a roll-to-roll manner. The three silver nanowire ink compositions were applied using GEN7 ActiveGrid. TM Ink and different amounts Fusing agent preparation: 1.5x 3x or none (As a comparison), among which The amount of ink used was based on the standard amount found in commercial inks. After coating, the structure was air-dried at room temperature and then further baked in an oven at 120°C for up to 10 minutes to dry the ink. The resistivity of the nanowire ink-coated sample was tested in air at 65°C and 90% relative humidity as a function of time. Two samples of the ink showed an initial decrease in relative film resistivity of approximately 10% after about 80 hours. Following this initial decrease, the coating... The relative thin-film resistivity of the sample increased, but remained below the initial resistance value until approximately t = 300 hours. The final relative sheet resistance (R / R0) of the two samples of the flux was 1.4. 1.5x The sample generally showed a lower sheet resistance compared to the 3x sample. The sample without the flux showed an initial increase in sheet resistance of approximately 19%, followed by a gradual increase in sheet resistance throughout the test time. The final relative sheet resistance was approximately 2.1. The target limit of 1.2R / R0 for the increase in sheet resistance is shown by a horizontal line.

[0091] This experiment shows that it has 1.5x or 3x The flux in the nanowire ink reduces the electrical resistance of the nanowire-coated structure by approximately 33%. (No further information provided.) The sample exceeded the 1.2 target at approximately 125 hours, while having The sample exceeded the 1.2 target limit after approximately 650 hours.

[0092] Laboratory and roll-to-roll results show that by making the sheet The flux improved the environmental durability of the conductive silver nanowire film. Results showed that... The initial resistance decrease observed in the sample is Provides indication of the additional metal source for the transparent conductive film. In use The improved stability observed under high temperature / high humidity conditions is consistent with the reduction / elimination of junction resistance through fusion, which, without fusion, might increase more rapidly under these conditions. These results suggest that initial heat and humidity treatment of coated products can be used to reduce film resistance and may decrease the stability of transparent conductive films before assembly into devices.

[0093] Example 2- Stabilizing the fused metal nanostructured network using silver ions in the outer coating

[0094] This embodiment illustrates an outer coating adjacent to a fused metal nanostructured network. The stabilizing effect of the flux.

[0095] Figure 8 A graph showing the relative sheet resistance (R / R0) (as a function of time) of stacked optical structure samples with various outer coatings is presented. The structures comprise a transparent polymer substrate with a sparse metallic conductive layer, which is either fused to form a sparse metallic nanostructured network or not fused, and the formation of this structure is described in Example 1. The individual layers of the stacked optical structure samples... Figure 8 As shown in the figure. Each sample has a PET substrate. As described in Example 1, the substrate is coated with a PET substrate. The GEN5 silver nanowires were coated with a flux and then dried. Next, a mixture containing a selected amount of silver salt (for...) was applied. An outer coating composed of a UV-curable polymer resin is applied to each structure. Finally, each structure is provided as a laminate on type A glass. Different amounts of... Five types of outer coating compositions for the flux: Level 1x, 1.5x, 2x, 3x, or none (As a comparison), among which The reference amount (1x) is about 3.0 wt% to about 3.5 wt% silver ions. Samples were tested under high temperature / high humidity conditions: 85 °C and 85% relative humidity. Each of the samples with an outer coating containing showed an initial decrease in the relative sheet resistance, which became more pronounced as the level increased. During further high temperature / high humidity treatment of the optical laminate structure, the in the outer coating showed a significant effect on the sheet resistance of the silver nanowire structure.

[0096] This example shows that in a structure having both an outer coating containing and a silver nanowire layer, the decrease in sheet resistance after high temperature / high humidity treatment can be even more significant. For example, comparing S1 with a Figure 5 level of 3x for about 95 hours, these samples had relative sheet resistances of 1.07 and 0.85 respectively. This decrease in sheet resistance is consistent with the chemical reduction of silver ions in the outer coating to metallic silver conductors at the junction positions. Figure 8 of

[0097] Figure 9 shows the effect of a level of 3x in the outer coating on a GEN5 silver nanowire film without . The test was only for laminates with a polymer outer coating and no additional OCA or other layers. For high temperature / high humidity conditions of 85 °C and 85% relative humidity, a sample with in the outer coating and another sample without in the outer coating are shown. The sample with in the outer coating showed an initial decrease in the relative sheet resistance and then a continuous decrease. In contrast, the sample without in the outer coating showed a significant increase. At about 45 hours, the two samples were 0.87 vs. 1.36.

[0098] This example shows that with or without in the silver nanowire layer, in the outer coating can significantly reduce the sheet resistance and provide significant stabilization during accelerated wear testing.

[0099] The above embodiments are intended to be illustrative and not restrictive. Other embodiments are also included 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. Any inclusion of the foregoing references is limited to excluding subject matter contrary to the explicit disclosure herein. The extent to which specific structures, compositions, and / or processes are described herein using terms such as components, elements, ingredients, or other divisions should be understood, unless otherwise expressly stated, to cover specific embodiments, embodiments comprising specific components, elements, ingredients, other divisions, or combinations thereof, and embodiments consisting primarily of such specific components, ingredients, or other divisions, or combinations thereof, which may include additional features that do not alter the essential nature of the subject matter, as indicated in the discussion. The term “about” used herein refers to anticipated uncertainty in relevant values, as would be understood by those skilled in the art in certain circumstances.

Claims

1. A transparent conductive film comprising a transparent polymer substrate, a rare-metal conductive layer comprising silver and 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 88% and a sheet resistance of not more than 120 ohms / sq, and wherein the polymer outer coating comprises a polymer and 0.01% to 20% by weight of noble metal ions.

2. The transparent conductive film of claim 1, wherein the polymer outer coating has an average thickness of 5 nm to 250 nm, and the noble metal ions include ions of silver, gold, platinum, osmium, ruthenium, or rhodium.

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

4. The transparent conductive film of claim 2, wherein the polymer of the outer polymer coating comprises polysiloxane, polysilsesquioxane, polyurethane, acrylic resin, acrylic copolymer, cellulose ether and / or ester, nitrocellulose, other non-water-soluble structural polysaccharides, polyether, polyester, polystyrene, polyimide, fluoropolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, polysulfide, epoxy-containing polymer, copolymers thereof, or mixtures thereof.

5. The transparent conductive film according to any one of claims 1-4, wherein the polymer outer coating further comprises 0.1% to 9% by weight of a pentavalent vanadium stabilizing composition.

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

7. The transparent conductive film according to any one of claims 1-4, wherein the rare-sparse metal conductive layer comprises a fused metal nanostructured network containing silver, and wherein the noble metal ions comprise silver ions.

8. The transparent conductive film according to any one of claims 1-4, wherein the transparent conductive film has a transmittance of at least 90% and a sheet resistance of not more than 90 ohms / sq.

9. The transparent conductive film according to any one of claims 1-4, wherein the polymer outer coating comprises 0.25% to 12% by weight of silver ions, said silver ions being provided as silver tetrafluoroborate (AgBF4), silver hexafluorophosphate (AgPF6), silver perchlorate (AgClO4), silver hexafluoroantimonate (AgSbF6), silver trifluoroacetate (AgCF3COO), silver heptafluorobutyrate (AgC4HF6O2), silver methanesulfonate (AgCH3SO3), silver toluenesulfonate (AgCH3C6H4SO3), or mixtures thereof.

10. The transparent conductive film according to any one of claims 1-4, wherein the sparse metal conductive layer is patterned.

11. A method for reducing the sheet resistance of a transparent conductive film, the transparent conductive film comprising a substrate, a transparent conductive layer, and a polymer outer coating, the transparent conductive layer comprising a fused metal nanostructured network and a polymeric polyol binder, wherein the polymer outer coating has an average thickness of 5 nm to 250 nm and contains 0.01 wt% to 20 wt% noble metal ions, the method comprising: The transparent conductive film is heated to a temperature of at least 55°C for at least 10 minutes to reduce the resistance of the thin film by at least 5%.

12. The method of claim 11, wherein during the heating, the transparent conductive film is on a roller, and wherein the polymer outer coating is covered by a release layer.

13. The method of claim 11 or claim 12, wherein the heating is performed at a relative humidity adjusted to at least 60%.

14. The method of claim 11 or claim 12, wherein the heating is performed at a temperature of 60°C to 100°C for a period of 20 minutes to 50 hours at a relative humidity of at least 60%, and wherein the transparent conductive film is free of optically transparent adhesives.

15. The method of any one of claims 11-12, wherein the fused 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 88%.

16. The method of any one of claims 11-12, further comprising: Before applying the polymer outer coating, the substrate having the coating of solvent, metal nanowires and metal ions is heated to a temperature of 45°C to 130°C for at least 2 minutes to dry the coating and form the fused metal nanostructured network.

17. The method of claim 16, wherein the coating comprises a pentavalent vanadium stabilizing composition and silver ions.

18. The method of any one of claims 11-12, wherein the polymer outer coating has an average thickness of 20 nm to 125 nm, wherein the polymer of the polymer outer coating comprises polyacrylate, and wherein the polymer outer coating comprises 0.5 wt% to 5 wt% of a pentavalent vanadium stabilizing composition.

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

20. The method of any one of claims 11-12, wherein the fused metal nanostructured network comprises silver, and wherein the polymer outer coating comprises a polymer and 0.25% to 15% by weight of silver ions.

21. The method of claim 11, wherein, The heating is stopped before the resistance of the thin film begins to increase.

22. The method of claim 11, wherein, Before the heating, the sheet resistance of the transparent conductive film is no greater than 120 ohms / sq.

23. A transparent conductive film comprising a substrate, a transparent conductive layer comprising a fused metal nanostructured network, and a polymer outer coating, wherein the transparent conductive film has a transmittance of at least 88% and a sheet resistance of not more than 120 ohms / sq, wherein the transparent conductive film has been modified by heating and optionally under humidity for at least 10 minutes, thereby reducing the sheet resistance by at least 5%.

24. The transparent conductive film of claim 23, wherein the polymer outer coating and / or undercoat comprises metal ions.

25. The transparent conductive film of claim 24, wherein the metal ions comprise silver ions at a concentration of 0.01% to 20% by weight.

26. The transparent conductive film of claim 24 or claim 25, wherein the metal ions comprise pentavalent vanadium at a concentration of 0.5% to 5% by weight.

27. The transparent conductive film of claim 23, wherein the fused metal nanostructured network comprises silver, and wherein the processing comprises heating at a temperature of 60°C to 100°C and at a relative humidity of at least 60%, while the transparent conductive film is free of optically transparent adhesives.

28. The transparent conductive film of claim 27, wherein the polymer outer coating has an average thickness of 5 nm to 250 nm and comprises cross-linked polyacrylate and pentavalent vanadium ions at a concentration of 0.5 wt% to 5 wt%.

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