Formation of an Electrically Conductive Layer at Room Temperature Using a Silver Nanoparticle Substance Treatment, and an Ink for Forming Those Layers

Abstract

By room temperature treatment, a highly conductive coating formed from silver nanowires and a cellulose binder was successfully obtained. This conductive coating can be formed with a silver salt to melt the silver nanowires into an integrated molten metal nanostructured network. Even without adding a silver salt, a low sheet resistance value can be obtained. The room temperature treatment can be effective over a range of transmittance values from highly transparent to slightly transparent, translucent, and opaque. The ability to form a transparent coating extends the treatment to a wide range of substrates that cannot be processed at higher process temperatures.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 354,465, filed Jun. 22, 2022, by Yang et al. entitled “Formation of Fused Silver Nanostructured Networks With Room Temperature Processing and / or on Temperature Sensitive Materials,” and U.S. Provisional Patent Application No. 63 / 407,310, filed Sep. 16, 2022, by Yang et al. entitled “Formation of Electrically Conductive Layers at Room Temperature Using Silver Nanoparticulate Processing and Inks for Forming the Layers,” which are hereby incorporated by reference herein in their entirety.

[0002] The present invention relates to room - temperature processing for forming thin, possibly transparent, electrically conductive coatings. The present invention further relates to certain silver nanowire inks for forming electrically conductive coatings and electrically conductive coatings on temperature - sensitive substrates.

Background Art

[0003] Functional films can provide important functions in a range of situations. For example, an electrically conductive layer can be important for dissipating static electricity when static electricity is undesirable or dangerous. Transparent conductive films can be used as electrodes. High - quality displays can include one or more transparent conductive layers.

[0004] Transparent conductors can be used in several optoelectronic applications such as 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 optimal material due to its relatively high transparency at high conductivity. However, there are several drawbacks associated with ITO. For example, ITO is a brittle ceramic and needs to be deposited using sputtering, which involves high temperatures and vacuum and thus is a relatively slow and cost-ineffective manufacturing process. Furthermore, ITO is known to crack easily on flexible substrates. Latest portable electronic devices are being pushed towards thinner and flexible formats.

Summary of the Invention

Means for Solving the Problems

[0005] In a first aspect, the present invention relates to a method of forming a conductive layer, the method comprising depositing a metal nanowire ink on an inert surface to form a coating, and drying the coating at room temperature to form a conductive film. The ink can include from about 0.001 wt% to about 4 wt% of metal nanowires and from about 0.05 wt% to about 5 wt% of a polysaccharide. The conductive film can have a sheet resistance of about 1000 ohms / sq or less.

[0006] In a further aspect, the present invention relates to an ink for forming a conductive layer, the ink comprising from about 0.001 wt% to about 4 wt% of metal nanowires, from about 0.05 wt% to about 5 wt% of a hydroxyalkyl-functionalized polymer binder, from about 20 vol% to about 100 vol% of a C1-C 10 aqueous solvent containing alcohol, and from about 0.001 wt% or less of a surfactant.

[0007] In another aspect, the present invention relates to a method for forming an electrically conductive coating, the method comprising: applying a silver nanoparticle-based material ink onto a substrate surface to form an undried coating; and drying the undried coating at a temperature of 60 °C or lower to form a dried coating having a sheet resistance of 25 ohms / sq or lower. The silver nanoparticle-based material ink can include an aqueous solvent, a silver nanoparticle-based material having silver nanowires with an average diameter of 50 nm or less and an aspect ratio of 10 or more, and a cellulose binder, with the silver nanowires accounting for 85 wt% or less.

[0008] In another aspect, the present invention relates to a silver nanoparticle-based material ink comprising an aqueous solvent, a silver nanoparticle-based material having silver nanowires with an average diameter of 50 nm or less and an aspect ratio of 10 or more, and a cellulose binder, with the weight ratio of cellulose to the silver nanoparticle-based material being about 0.05 to about 3. BRIEF DESCRIPTION OF THE DRAWINGS

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 7D

Figure 7E

Figure 7F

Figure 7G

Figure 7H

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0010] A thin layer of an electrically conductive material can be formed at room temperature from an ink containing silver nanowires that can be easily processed. In some embodiments, the conductive coating may be transparent, and even highly transparent with very little scattering. Good electrical conductivity can be achieved with or without melting the nanowires, but melting is generally desirable to form a transparent coating with good mechanical properties, improved stability, and better optical properties. The nanowires can melt to form a molten metal nanostructured network, which is a single structure with desirable properties. The process generally involves an ink containing a polysaccharide binder such as a suitable amount of cellulose ether. Generally, these inks can be applied to various coating processes such as slot coating, dip coating, spraying, or jet deposition and can be applied to a range of substrate surfaces. Room temperature processing can advantageously extend processing to a range of substrate materials that were previously unsuitable and can also reduce energy and cost.

[0011] High-quality optically transparent conductive coatings that maintain electrical conductivity while having desirable mechanical properties such as stretchability and stability against repeated folding and unfolding have been successfully fabricated from silver nanowires. The extension of the processes described herein can maintain excellent optical properties and extend to desirable processes for conductive coatings that form films that are less transparent or opaque and have low conductivity. A dispersion or ink of silver nanowires can be deposited on a surface and processed to obtain a conductive coating. Under appropriate process conditions, the resulting conductive coating, which may be transparent, can be desirable for its mechanical properties, such as flexibility, formability, combinations of these features, or other aspects of the conductive coating. In the art, the term "nanoparticle" also serves the further role of meaning, in particular, substantially spherical nanostructures and nanostructures of any shape. To place less of a burden on this term, herein the term "nanoparticulate" is used to mean nanostructures of any shape, and "nanoparticle" means only substantially spherical nanostructures, i.e., having an average ratio of diameters along three principal axes of less than about 2. With respect to transparent coatings, the use of nanowires to form transparent conductive coatings can have great utility in devices having displays and touch sensors. With a greater amount of metal used, a decrease in electrical resistance is seen, while at the same time the transmittance of visible light decreases. Even highly purified silver nanowires have some small amount of contaminants of other silver nanoparticulate materials, and in situations of less transparent or non-transparent applications, the nanowires can be mixed with a somewhat higher weight fraction of other nanoparticulate materials. The ability to process at room temperature desirably allows for the formation of non-transparent conductive layers on temperature-sensitive substrates. The incorporation of additional nanoparticles can be desirable for improving the conductivity or reducing the cost (less purification) of coatings with little optical impact. Thus, the processes described herein can be practically applied to a wider range of uses of electrically conductive coatings.The room temperature treatment was first described in the specification of U.S. Provisional Patent Application No. 63 / 354,465 to Yang et al., filed on June 22, 2022, entitled "Formation of Fused Silver Nanostructured Networks With Room Temperature Processing and / or on Temperature Sensitive Materials", which is incorporated herein by reference.

[0012] In some embodiments, a metal-based transparent electrically conductive element, e.g., a coating, includes a sparse metal conductive layer. The conductive layer is overall sparse such that a desired amount of optical transparency is obtained through the conductive structure rather than around it, and thus has microscopic gaps across the layer of the conductive element, although the metal coverage is generally large. For example, a transparent electrically conductive coating can include metal nanowires deposited along a layer that can obtain sufficient contact for electronic percolation to obtain a suitable conductive path. The one-dimensional form of the nanowires is conductive for the formation of a sparse metal conductive layer. In particular embodiments of interest, the transparent electrically conductive coating can include a fused metal nanostructured network, which has been found to exhibit desired electrical, optical, and mechanical properties. In the fused structure, unlike the non-fused structure, electrons can conduct through the network rather than hopping between separate nanowires. Unless otherwise indicated, conductivity referred to herein means electrical conductivity. However, the described electrically conductive coating can also function as a transparent heater by Joule heating under an applied voltage. The structures described herein can also be effective for the formation of non-transparent conductive coatings that are processed at room temperature using a solution coating process.

[0013] The melting process of the applicant's application can be controlled to selectively deposit metal at the junctions between metal nanowires or to form a fused mass of a low-conductivity structure regardless of the nanoparticle material. When forming a molten metal nanostructure network, the melting process can be controlled to deposit a desired amount of silver associated with the junctions. The balance of the system can be adjusted so as to obtain the thermodynamic driving force of melting that mainly occurs at the junctions between adjacent metal nanowires, which are the components where the molten metal nanostructure network is formed. After melting, a single structure named the molten metal nanostructure network is formed, and the original metal nanowires in the conductive structure lose their individual identities. It is suggested that the melting of the metal combines the original individual nanowires, reducing or eliminating the resistance of the junction, which means the junction of individual nanowires. For commercial products, it is desirable to improve the durability of the transparent conductive coating under a series of real-world conditions. These principles are obtained in the case of the room-temperature treatment described herein.

[0014] In the case of a transparent coating, when good-quality silver nanowires are used, it has been found that a structure with very low haze, high transparency, and high conductivity can be obtained by the melting process for forming a molten metal nanostructure network. The molten metal nanostructure network has been shown to have very good stability under abrading conditions using a suitable stabilizer. Further stabilization can be obtained by adding noble metal ions such as silver into the overcoat, as described in US Patent Application Publication No. 2021 / 0151216 to Yang et al. titled "Coatings and Processing of Transparent Conductive Films for Stabilization of Sparse Metal Conductive Layers" (incorporated herein by reference).

[0015] In the applicant's previous research based on thermodynamically driven melting, this process was carried out at relatively low temperatures. However, heat was used to control the drying rate, control the melting process, and promote another kinetic process, reaction rate, and diffusion. In the context of the industrial processing of conductive films, roll-to-roll processing was developed using existing process equipment to obtain the desired heating with stable product quality, and moderate heating was easy to implement. Nevertheless, heating consumes energy and causes limitations to the substrate. In particular, various plastic substrates, polymer substrates, and biologically related substrates exhibit low glass transition temperatures and / or low melting temperatures, thus requiring low processing temperatures.

[0016] In particular, when facing the processing of heat-sensitive substrates, efforts have been made to reduce the process temperature. Surprisingly, a system has been developed that can achieve a low sheet resistance with rapid results with room temperature processing and a single ink deposition. These results are again consistent with a balanced thermodynamic system that can be induced to obtain the desired results using a little trust and a properly adjusted chemical combination, and these have been discovered as described herein. By realizing these results, it can be recognized that it is applicable to applications with less stringent requirements for optical properties or even non-transparent applications with advantageous effects due to the improvement of the desired processing.

[0017] As demonstrated from the results shown herein, depending on the composition of the silver nanowire ink, a molten metal nanostructure network or another molten conductor can be formed from a good conductive layer with or without using melting of the nanowires at a temperature of about 60 °C or less, in a further embodiment about 55 °C or less, in another embodiment about 50 °C or less, in some embodiments about 40 °C or less, and in a further embodiment about 30 °C or less, particularly at room temperature. Chemical melting is effective for further reducing the sheet resistance, and a method for achieving good melting at room temperature is described. For the purposes herein, room temperature can be considered to be from about 16 °C to about 28 °C, although in some embodiments the range of room temperature can appropriately be considered to be from about 18 °C to about 26 °C, from about 20 °C to about 25 °C, or another suitable sub-range within the broad ranges shown. Those skilled in the art will understand that further temperature ranges within the above-specified ranges are contemplated and are within the scope of the present disclosure. Drying can be facilitated by gentle blowing with or without the use of slight heating of the air.

[0018] Since the first attempts to use silver nanowires to form conductive coatings, efforts have been made to reduce the sheet resistance due to the resistance of the junctions between the nanowires. As shown in the applicant's first melting study, simple deposition of the nanowire dispersion generally results in very high sheet resistance values, such as in the megaohm / sq. range. See, for example, the '207 patent cited below. A variety of attempts have been used in this effort, such as applying pressure and using various energy sources. The corresponding problem is the processability of the silver nanowire ink to consistently form coatings of good quality. The present application has achieved a significant leap in this effort through the chemical melting of the present invention, which can be effective even when the non-molten structure has a very high sheet resistance.

[0019] As an aid to the melting process, Applicant has introduced processing aids, in particular binders, to obtain industrially processable and reproducible coating properties. In order to utilize these processing aids themselves in a manner compatible with the achievement of melting, Applicant has discovered that the choice of binder is important. It has been found that the use of hydrophilic binders, and in particular polysaccharide binders, is particularly fruitful. Due to the wide range of commercial specifications in many applications such as similar uses, cellulose-based binders were polysaccharides that were convenient for adoption. Although not explicitly pointed out, in the Applicant's earlier research in the '968 patent cited below, it was discovered that the sheet resistance was greatly improved using a polysaccharide binder without applying pressure or performing further processing steps. Although not yet fully understood, a suitable polymer can reduce the resistance of the joint to approximately the same extent as when applying a very high pressure, but due to chemical melting, in the formation of the integrated structure, silver nanowires join together, resulting in a further significant reduction. Without wishing to be limited by theory, this observation strongly suggests that due to a certain interaction between the polysaccharide binder and the metal nanowires, the nanowires can be brought close enough to be recognized, and thereby, if appropriate chemistry and processing are used, the nanowires can be electrically coupled to each other and good conductivity can be achieved in the network of nanowires and polysaccharide binder. Without wishing to be limited by theory, this also suggests a certain degree of driving force and beneficial assembly at the nanoscale between the polymer and the nanowires, thereby tending to obtain a large surface bond between the silver nanowires and the cellulose while increasing the contact between silver and silver.

[0020] However, this earlier research still involved the use of moderate heat. Therefore, the results herein show excellent results with no heat applied or very little heat applied, whether or not melting occurs, and the results are further improved by melting. For even less understood reasons, some metal salts seem to interfere with the sufficient establishment of conductivity at room temperature when melting is not induced.

[0021] The results presented herein indicate that in equivalent ink systems using the same nanowires, binders, and solvents, melting with silver fluoride significantly promotes melting with silver acetate and possibly other silver salts. Using silver fluoride as one of the several fluxes tested in the '746 patent resulted in equivalent results to silver nitrate in the process described in that patent. The results herein are compared to silver acetate fluxes. Attempting to melt with silver acetate without heating did not yield desirable results, as shown in the results of the following examples. Changing to the use of silver fluoride salts results in desirable optical properties while observing low sheet resistance values here. This indicates that melting occurred at room temperature using silver fluoride salts.

[0022] For room temperature melting, the choice of metal source is important. In particular, silver fluoride (AgF) appears to be a suitable silver salt. The metal ion source should be soluble. AgF was used in earlier melting studies described in the '968 patent, and various metal ion sources were thought to be approximately equivalent under the original process conditions. Further tests using silver acetate as a flux suggested that heating was required to induce the melting process. In the attempts of the present invention, testing with AgF showed the surprising result that melting occurred using AgF at room temperature, but subsequent additional tests failed to achieve melting using AgOAc. Preliminary results using AgNO3 and AgBF4 suggest that low temperature melting does not occur with these salts. This is shown in the results provided in the following examples.

[0023] The anion is thought to be a spectator in the related reactions, but the results suggest that the free energy of the reaction may vary depending on the type of anion and / or may affect various energy barriers associated with diffusion and / or reduction, although the Applicant does not wish to be limited by theory. In any case, the results strongly suggest that these systems are balanced near equilibrium to control melting, so that relatively modest free energy changes have observable effects. Another silver halide is insoluble in the related solvent, and soluble silver salts generally have anions that appear to be similar to acetate anions.

[0024] The Applicant has achieved good sheet resistance using room temperature processing with or without melting, but melting can be effective to reduce the sheet resistance without significantly affecting the optical properties. Melting also appears to significantly stabilize the conductive coating in embodiments where the electrical conductive layer is bent or stretched. Thus, melting is highly desirable for many applications.

[0025] In the case of commercial inks, uniform coating on many substrates involves reducing the surface tension of the ink. In principle, various surfactants can be used, and it has been found that fluorosurfactants are widespread for various practical reasons. Alcohol can function as both a solvent and a wetting agent to form a good coating at a higher concentration. When using room temperature treatment, high-alcohol inks have been shown to be effective in forming highly conductive coatings with or without melting. Alcohol can be selected to have a sufficiently low boiling point to evaporate relatively effectively at room temperature. The choice of alcohol may be related to the amount of alcohol used. Although influenced by the individual branched structure and the position of the hydroxyl group, the boiling point tends to increase with the molecular weight, so higher alcohols with more carbon atoms tend to have a higher boiling point and correspondingly a lower vapor pressure at room temperature. Generally, the alcohol of interest may be a C1 - C10 alcohol (based on the total number of carbon atoms in the molecule) at a concentration of 20 volume percent to 100 volume percent based on the liquid of the solvent.

[0026] Generally, through the applicant's development efforts, a high-quality transparent conductive layer with remarkable optical quality equivalent to indium tin oxide has been obtained in a bendable and moldable material so that electrical conduction is improved and stretching and repeated bending are possible. On the other hand, to some extent sacrificing transparency, a higher level of electrical conduction can be achieved. There may even be cases where it is desirable to form a thin electrically conductive coating that is not transparent using the room temperature treatment described herein. These coatings can be formed on a material that may be a temperature-sensitive substrate and may be flexible. In embodiments where good optical properties are not the goal, lower quality silver nanowires can be used, which allows a higher proportion of non-nanowire nanoparticle materials, such as blends of multiple shapes blended with nanowires.

[0027] Transparent materials are generally regarded in the art as having an average transmittance of at least 70% of visible light, and this perspective is adopted herein. A thin transparent conductive coating can achieve a sheet resistance of approximately less than about 3 ohms / sq after room temperature treatment. At the other end of the transmittance scale, highly transparent conductive coatings with low haze, low L * , reflection scattering, and low sheet resistance can also be achieved by room temperature treatment. Therefore, heating is not required to achieve the excellent transparent conductive coatings previously realized by the applicant.

[0028] Chemical sintering has been discussed in relation to non-transparent structures. Room temperature sintering was achieved using nearly spherical silver nanoparticles in either the formation of a precoating of a cationic chlorinated polymer (polydiallyldimethylammonium chloride, poly-DADMAC) or the subsequent deposition of a cationic chlorinated polymer. See U.S. Patent Application Publication No. 2012 / 0168684 to Magdassi et al. entitled “Process for Sintering Nanoparticles at Low Temperatures” (hereinafter the ’684 application), which is incorporated herein by reference. Poly-DADMAC is a polyelectrolyte that is not a desirable component in many situations. In some embodiments, the ’684 application describes the inclusion of NaCl in the nanoparticle dispersion, but in these systems, it was necessary to heat the deposited material to achieve sintering.

[0029] In the ’684 application, a wide range of fluxes are claimed, many of which clearly do not induce chemical melting or effective agglomeration. Carboxymethyl cellulose is mentioned in the ’684 application, but the proper use of polysaccharide binders is not taught, and thus, good conductivity without chemical sintering based on halide ions and especially chlorides is not exemplified. This study, in which the melting of silver nanowires is used for the formation of a molten metal nanostructured network at room temperature, is believed to be the first formation of a thin electrically conductive coating with a sheet resistance of less than 1000 ohm / sq. using any form of metal nanoparticle material at room temperature on an inert surface with or without melting in a single ink deposition.

[0030] Excellent electrical conductivity can be obtained with silver. In the case of forming a non-transparent electrically conductive coating, the properties of the metal nanoparticle material may become less important, but the processing methods herein are generally based on nanowire processing. When good transmittance and low scattering are important objectives, the silver nanowires can be made purer in order to remove silver nanoparticles and other non-wire shapes that contribute minimally to conductivity and cause light scattering. Similarly, in a method for producing high-quality silver nanowires for high-quality transparent conductive coatings, a large amount of silver waste is generated having a completely suitable silver material except that the silver nanoparticles are of low quality with respect to nanowire properties, having many spherical nanoparticles, thicker nanowires, short nanorods, nanoplatelets, and / or nanoparticles of special shapes. When forming a non-transparent thin conductive coating, high-quality nanowires are not required, and as a result, the cost can be much lower. At higher silver usage levels, any nanoparticles and other non-wire shapes can contribute more significantly to electrical conduction by forming conduction paths at higher density.

[0031] Regarding high electrical conductivity and desirable optical properties regarding transparency and low haze, the molten metal nanostructured network can exhibit improved properties. The melting of adjacent metal nanowires can be carried out based on a chemical process under industrially suitable processing conditions.

[0032] In particular, a significant improvement regarding the realization of an electrically conductive coating based on metal nanowires has been the discovery of a sufficiently controllable process for forming a molten metal nanostructured network in which adjacent segments of the metal nanowires melt to form a single structure that does not contain distinct nanowires in the conductive network. In particular, it was first discovered that the melting of metal nanowires to form a molten metal nanostructure can be promoted by halide ions. The introduction of a flux containing halide anions in various ways enabled successful melting and correspondingly a significant reduction in electrical resistance. It should be noted that the halide ions in the context of this process should not be confused with the halide ions used during the nanowire synthesis reaction. In particular, the melting of metal nanowires using halide anions has been achieved using the vapors and / or solutions of acid halides, as well as solutions of halide salts. The melting of metal nanowires using halide salts is further described in U.S. Patent No. 10,029,916 to Virkar et al. entitled “Metal Nanowire Networks and Transparent Conductive Material” and U.S. Patent No. 9,920,207 to Virkar et al. entitled “Metal Nanostructured Networks and Transparent Conductive Material” (the ’207 patent), both of which are incorporated herein by reference.

[0033] One extension of the method for forming a molten metal nanowire network was based on a reduction / oxidation (redox) reaction that could be provided to obtain molten nanowires without degrading the optical properties of the resulting coating. Metals for deposition at the junctions could be effectively added as dissolved metal salts or could be dissolved from the metal nanowires themselves. The effective use of redox chemistry to melt metal nanowires into a nanostructured network is further described in U.S. Patent No. 10,020,807 to Virkar et al., entitled “Fused Metal Nanostructured Networks, Fusing Solutions with Reducing Agents and Methods for Forming Metal Networks” (the ’807 patent), which is incorporated herein by reference. The ’807 patent also describes a single solution method for forming a molten metal nanostructured network. The single solution method for forming a molten metal nanostructured layer is further described in U.S. Patent No. 9,183,968B1 to Li et al., entitled “Metal Nanowire Inks for the Formation of Transparent Conductive Films with Fused Networks” (hereinafter the ’968 patent), which is incorporated herein by reference, and a single solution or ink treatment for forming a molten metal nanostructured network is used in the following examples.

[0034] With a single ink formulation, a desired amount of metal is deposited as a coating on a substrate, and components in the ink that induce a melting process are obtained when the ink is dried under appropriate conditions. These inks can conveniently be referred to as fusible metal nanowire inks, generally under the understanding that melting does not occur until drying. These inks generally contain an aqueous solvent and, in some embodiments, can further contain an alcohol and / or another organic solvent. These inks can further contain a dissolved metal salt as a metal source for the melting process. Without wishing to be limited by theory, it is believed that components of the ink, such as hydroxyl groups, or another organic composition, reduce metal ions from the solution to drive the melting process. Previous experience with the melting process in these systems suggests that metal preferentially deposits at the junctions between adjacent metal nanowires. A polymer binder can be added to stabilize the coating and affect the properties of the ink. Hydroxyl functional groups that function to reduce silver ions are obtained by polysaccharides. The individual formulations of the ink can be adjusted to select ink properties appropriate for a particular deposition method and particular coating characteristics on the substrate surface. As further described below, the drying conditions can be selected to effectively perform the melting process.

[0035] In the case of a room temperature melting process, the process conditions can optionally be adjusted with respect to blowing air at room temperature across the entire deposited coating. In some embodiments, slight heating can be used if desired. The solvent removal can be promoted by an air flow with or without heating, and correspondingly, the enrichment of silver ions can be promoted to obtain an appropriate melting rate. If the ion mobility is maintained and a sufficiently reactive silver salt is utilized, melting can be caused (even at low temperatures) by evaporation and drying of the solvent, and excellent conductivity can be obtained. Due to the commonly used hydrophilic binder, the water associated with the binder can be dried relatively slowly. Results are shown in the examples, showing sheet resistance values over a selected range of values, 35 ohms / sq. in some embodiments, about 3 ohms / sq. in another embodiment, and good transmittance values are obtained for the realized sheet resistance values.

[0036] In the context of lower temperature processing, the transparent conductive inks described herein provide process advantages even over non-transparent alternatives. Referring to Table 1 below, “typical” products refer to silver nanoparticle pastes or inks that have been commercially available for some time, examples of which are Toyobo 520H-19 or 520H-41 which cure at 130 - 150 °C for 30 minutes. Low Temp 1 products refer to next-generation nanoparticle-based products that can be processed at somewhat lower temperatures. An example of a commercially available low-temperature silver paste is DuPont™'s PE828 (“ULTRA-LOW TEMPERATURE CURE SILVER CONDUCTOR”) which can be processed at 60 - 100 °C.

[0037] [Table 1]

[0038] The ability to form room temperature conductive coatings is both an improvement in desirable processing and an opportunity to enable the processing of heat-sensitive substrates.

[0039] Silver Nanowire Ink and Deposition When using silver nanowire ink, the desirable processes for transparent conductive coatings tend to favor a balance (near the balance of equilibrium) and expediency rather than brute force, and this continues to hold true for the desired processing methods described herein. These results are extended here to silver nanowire ink, but the processes become even gentler while achieving good electrical conductivity. For example, the ink involves an appropriate selection of components in appropriate amounts. First, silver nanowires are present, and these are discussed in detail below. When the optical properties are low or not important, the silver nanowires can be mixed with another nanoparticle material. For transparent conductive coatings with good optical properties, high-quality silver nanowires are discussed below. The solvent is generally aqueous and can have lesser or greater amounts of alcohol. Surfactants, such as fluorosurfactants, may or may not be used, and the compatibility of the surfactant can be determined by the alcohol content of the solvent. Embodiments that avoid fluorosurfactants may be desirable from that perspective since fluorosurfactants can have environmental issues.

[0040] As the binder, polysaccharides are desirable, and in some embodiments, other polymer binders should be avoided or highly limited in the context of room-temperature processing. As the flux, silver fluoride is desirable. In some embodiments, other components that interact unfavorably with silver ions and impede melting are limited or completely avoided. Based on the teachings herein, one of ordinary skill in the art can experimentally test small amounts of processing additives to determine whether they are compatible with the formation of conductive structures.

[0041] For use in the intended applications, silver nanowires with another nanoparticle material can be selected, which can range from very thin, high-quality, uniform nanowires to mixtures with thicker nanowires, nanoparticles, and other nanoparticle materials. In transparent film applications, relatively pure silver nanowires are generally used. The applicant sells very high-quality silver nanowires such as those used in the following examples, which can be used to obtain very good optical quality.

[0042] A slightly transparent, translucent, or opaque conductive layer can be formed from a less purified dispersion of metal nanowires. Examples of the formation of transparent or translucent coatings with lower optical quality but higher electrical conductivity films are shown below, which are formed from the waste obtained in the synthesis of very purified silver nanowires, and this waste includes a range of nanowire forms, nanoparticles, and various other nanoparticulate shapes. This research has focused on the possibility of supplementing nanowires with other shaped nanoparticle materials for non-transparent applications.

[0043] Silver provides excellent electrical conductivity. The Applicant sells silver nanowire ink under the trade name ActiveGrid® ink for forming a molten metal nanostructured network. Another source of silver nanowires is commercially available, and its basic melting technology is fully described in the '207 patent and the '807 patent cited below. Most (>98%) of the silver nanowires in the Generation 5 (GEN5) ActiveGrid® product have a diameter of less than 25 nm, and most (>98%) of the silver nanowires in the Generation 7 (GEN7) ActiveGrid® silver nanowires have a diameter of less than 22 nm. The synthesis of thin silver nanowires is described in U.S. Patent No. 10,714,230 B2 to Hu et al. entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed from the Nanowires" (incorporated herein by reference). High-quality silver nanowire products with small and uniform diameters and high purity are desirable for some applications in displays, but for applications with fewer optical requirements, lower grade silver nanowires may be sufficient. Here, the nanowires are considered to have an average diameter of less than 100 nm, and in some embodiments less than 50 nm, and an average aspect ratio of at least about 10 nm, and in further embodiments at least about 25 nm. Another commercial silver nanowire is commercially available. Those skilled in the art will recognize that further ranges of silver nanowire dimensions within the ranges specified above are contemplated and are within the scope of the present disclosure.

[0044] The solvent is aqueous. The solvent can contain alcohol, by which the rheology of the ink can be improved. When alcohol is used, the selection of the alcohol is generally not important, but the alcohol should generally have a low boiling point to enable good drying at room temperature. From this perspective, the alcohol is generally a monohydroxyl aliphatic alcohol having 10 or fewer carbon atoms, and methanol, ethanol, propanol, isopropanol, mixtures thereof, etc. are convenient. Many alcohols form low-boiling azeotropes with water, and in appropriate amounts, this promotes their evaporation. Next, the selection of the alcohol can be affected by the amount of alcohol. In some embodiments, the solvent contains alcohol from 0.1 volume percent (vol%), in further embodiments from about 0.5 volume % to about 100 volume %, and in another embodiment from about 1 volume % to about 80 volume %. If desired, the solvent can conceptually be divided into a high-alcohol solvent having more than 51 volume % alcohol and a low-alcohol solvent having less than 50 volume % alcohol. Those skilled in the art will recognize that further ranges of alcohol concentrations within the ranges specified above are contemplated and are within the present disclosure. The solvent can also contain another component of about 5 volume % or less, such as a polar solvent, such as methyl ethyl ketone, glycol ethers (such as ethylene glycol methyl ether and propylene glycol methyl ether), methyl isobutyl ketone, toluene, hexane, ethyl acetate, butyl acetate, ethyl lactate, PGMEA (2-methoxy-1-methylethyl acetate), dimethyl carbonate, or mixtures thereof. The solvent should be selected based on its ability to form a good dispersion of the metal nanowires, but the solvent should also be compatible with another selected additive such that the additive is soluble in the solvent.

[0045] For transparent applications, the desirable ink to achieve an effective single ink that cures to a molten nanostructured metal network contains a desirable amount of metal nanowires to achieve an appropriate metal usage in the resulting coating. In a suitable solution, the ink is stable before deposition and drying of the ink. The ink can contain a moderate amount of polymer binder that contributes to the formation of a stable conductive coating for further processing. To obtain good melting results using one ink system, it has been found that hydrophilic polymers, especially, for example, cellulose, chitosan, xanthan gum, or another polysaccharide-based polymer, are effective as binders. As mentioned above, polysaccharides exhibit properties worthy of note in the context of binders for silver nanowires. Metal ions as the metal source for the melting process can be supplied as soluble metal salts, and AgF is suitable for room temperature processing.

[0046] With a single ink formulation, a desired amount of metal is deposited as a coating on the substrate surface, and at the same time, components in the ink that induce the melting process are obtained when the ink is dried under appropriate conditions. These inks can be conveniently called fusible metal nanowire inks, understanding that melting generally does not occur until some drying has taken place. The ink generally contains an aqueous solvent as described above, and the ink can further contain dissolved metal salts as the metal source for the melting process. Without wishing to be limited by theory, it is believed that components of the ink, for example, hydroxy moieties or other organic functional groups, reduce metal ions from the solution to drive the melting process. Previous experience using the melting process in these systems suggests that metal preferentially deposits at the junctions between adjacent metal nanowires. A polymer binder can be added to stabilize the film and affect the properties of the ink. The individual formulations of the ink can be adjusted so that ink properties appropriate for the individual deposition method are selected and specific coating properties are obtained on the substrate surface. As further described below, drying conditions can be selected to effectively carry out the melting process.

[0047] The metal nanowire ink can include from about 0.01 wt% to about 3 wt% of metal nanowires (nanoparticle substances), in a further embodiment from about 0.02 wt% to about 1.5 wt% of metal nanowires (nanoparticle substances), and in a further embodiment from about 0.04 wt% to about 1.0 wt% of metal nanowires (nanoparticle substances). In embodiments of high transparency, the nanoparticle substances are maintained at low levels, while in embodiments with fewer optical requirements, the ink can include significant amounts of other nanoparticle substance shapes. In some embodiments, the nanoparticle substances include at least about 20 wt% of nanowires, in a further embodiment from about 25 wt% to about 95 wt%, and in another embodiment from about 30 wt% to about 80 wt% of metal nanowires. The other nanoparticlate shapes can vary and can optionally be mixed and can be, for example, nanoparticles, nanocubes, nanoplates, etc. In embodiments of particular interest, the nanowires are silver nanowires and the metal ion source is a dissolved silver salt. The ink can include silver ions at a concentration from about 0.01 mg / mL and about 2.0 mg / mL, in a further embodiment from about 0.02 mg / mL and about 1.75 mg / mL, and in another embodiment from about 0.025 mg / mL and about 1.5 mg / mL. Further ranges of metal nanowire concentrations and metal ion concentrations within the explicitly stated ranges above are contemplated and will be recognized by those skilled in the art as being within the scope of the present disclosure. The concentration of the metal nanowires affects the amount of metal used on the substrate surface and the physical properties of the ink.

[0048] Metal nanowires generally contain silver. The applicant has formed a transparent conductive film having good optical properties using silver nanowires coated with a noble metal. See U.S. Patent No. 9,530,534 to Hu et al. entitled "Transparent Conductive Film" (incorporated herein by reference). Generally, other metal nanowires are expected to have similar properties. Gold nanowires, platinum nanowires, palladium nanowires, copper nanowires, and other metal nanowires are expected to exhibit similar performance.

[0049] Regarding an ink formulation, the polymer binder and the solvent are generally consistently selected such that the polymer binder is soluble or dispersible in the solvent. In suitable embodiments, the metal nanowire ink generally contains from about 0.02 wt% to about 10 wt% of a binder, in further embodiments from about 0.05 wt% to about 8 wt% of a binder, and in further embodiments from about 0.1 wt% to about 5 wt% of a polymer binder. Suitable binder concentrations can be determined by the molecular weight of the binder. In some embodiments, the polysaccharide can have an average molecular weight of less than 10,000 g / mol. The weight ratio of the polymer binder to the metal nanowire / nanoparticle material can also be important. The weight ratio of the polymer binder to the silver nanowire or nanoparticle material can be at least about 0.05, in some embodiments at least about 0.1, in further embodiments from about 0.2 to about 3, in further embodiments from about 0.3 to about 2, and can be in a range having different combinations of these lower and upper ends. Those skilled in the art will recognize that further ranges within these expressly stated ranges are contemplated and are within the scope of the present disclosure. Desirable binders include, for example, polysaccharides such as cellulose-based polymers, chitosan-based polymers, and the like. Suitable cellulose binders include, for example, ether celluloses such as methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, mixtures thereof, and the like.

[0050] In some embodiments, the nanowire ink can optionally include rheology modifiers or combinations thereof. In particular, the ink can include a wetting agent or surfactant to reduce surface tension, and the wetting agent can be useful for improving coating properties. A wide range of surfactants are commercially available, such as nonionic surfactants, cationic surfactants, anionic surfactants, zwitterionic surfactants, gemini surfactants, etc. Fluoro surfactants may provide desirable ink properties, but can be undesirable for some applications and end formulations. The purpose of fluoro surfactants is to function as wetting agents to obtain lower surface tension, good wettability, and film formation on the substrate. Wetting agents are generally soluble in the solvents used. In some embodiments, the nanowire ink can include from about 0.001 wt% to about 1 wt% wetting agent, in further embodiments from about 0.002 wt% to about 0.75 wt%, and in another embodiment from about 0.003 wt% to about 0.6 wt% wetting agent. Additional ranges of binder and wetting agent concentrations within the above - specified ranges are contemplated, and those skilled in the art will recognize that they are within the scope of the present disclosure. Effective wetting and processing can be obtained by higher alcohol concentrations in the solvent as described above. In some embodiments, at high alcohol concentrations, it has been found that the presence of a separate surfactant interferes with room - temperature processing, but in another low - alcohol solvent, the separate surfactant functions well. Generally, other processing aids such as thickeners, antioxidants, etc. may or may not be used in various inks. Some of these may interfere with room - temperature processing, while others may be advantageous. Those skilled in the art can easily test this based on the teachings herein. However, generally, other additives are considered solids that are non - volatile components of about 5 wt% or less.

[0051] Silver nanowires for commercial use are generally deposited by slot coating, which can be done in a roll-to-roll process. All of the coating and melting can be conveniently done in this way. The Applicant has generalized this process for very thin polymer sheets having conductive coatings on both sides, as described in the specification of US Patent Application Publication No. 2020 / 0245457 to Chen et al., entitled "Thin Flexible Structures With Surfaces With Transparent Conductive Films and Processes for Forming the Structures" (incorporated herein by reference). For non-flat surfaces, dip coating, spray coating, etc. can be used. Generally, the same nanowire ink formulation for slot coating can be used for these alternative coating processes, although modifications may be suggested in certain embodiments. The conductive layer can be patterned by laser patterning or photolithography. Another similar coating process can be used. Due to the morphology of the nanowires, the printing of nanowire ink is complicated. Coarse printing of metal nanowire ink can be considered, but printing of metal nanowire ink with good resolution for commercial production has not been realized to the knowledge of the Applicant. A description of the printing of metal nanowires can be found in the specification of US Patent No. 8,454,859 to Lowenthal et al., entitled "Metallic Nanofiber Ink, Substantially Transparent Conductor, and Fabrication Method" (incorporated herein by reference).

[0052] The amount of silver deposited affects the optical properties and sheet resistance. For high transparency applications, the amount of silver used is generally selected to obtain the desired conductivity, and the quality of the nanowires is important for improving the optical properties. The amount of nanowires used on the substrate is generally expressed as the number of milligrams of nanowires per square meter of the substrate and can be calculated based on the deposition. For transparent applications, the nanowire network can have an amount of about 1 mg / m 2 ~ about 500 mg / m 2 and, in further embodiments, about 0.5 mg / m 2 ~ about 200 mg / m 2 and, in another embodiment, about 1 mg / m 2 ~ about 150 mg / m 2 . Further ranges of thicknesses and amounts within the explicitly stated ranges above are contemplated and will be recognized by those skilled in the art as being within the scope of the present disclosure. When patterned into a sparse metal conductive layer, this discussion of thickness and amount applies only to areas where the metal is not removed or only slightly reduced by the patterning process. For non-transparent applications, the amount of metal used is not particularly limited but depends on the properties of the nanoparticle material, there is a range of semi-transparent metal usage, and there are opaque films with even higher metal usage. Multiple coatings can be performed to increase the amount used and decrease the sheet resistance. The amount of metal used is effectively determined by the concentration of nanowires or other silver particles in the ink and the thickness of the undried coating.

[0053] In the case of room temperature processing, the post-treatment after ink coating may be minimal. For consistency and to slightly promote drying, non-heated air can be gently blown to remove moisture. Whether or not air blowing is used, sufficient drying to achieve melting without using a flux or to achieve a desired conductivity can be achieved in minutes. Compared with conventional coating processing times, these times are short, and no effort has been made to further shorten them, but if desired, this time can probably be optimized. An air knife or the like can also be used for drying the solvent to obtain the final conductive film. Air blowing does not seem to be necessary to obtain desirable results, but in commercial production, even if it is not strictly necessary, it can be one of the desirable options to help ensure consistent product quality.

[0054] In a suitable system, although not necessary, some heat can be applied. In some embodiments, some gentle heating may be considered advantageous when some alternative solvents are used or some additives can affect the process. For example, the air blowing can be slightly heated to the aforementioned temperature or the substrate to be coated can be placed in an oven at a sufficiently low temperature. However, generally, it is advantageous to process without heating for cost reduction and reducing the environmental footprint, and to open up the process to a wider range of applications. In industrial coating, it can be useful to use a low temperature setting with IR, convection, or another heating system for drying.

[0055] Electrically Conductive Structure The electrically conductive structure can be designed to suit individual applications. Since the range of conductive coatings that can be formed using the room-temperature processes described herein is broad, the range of coating properties can, correspondingly, extend over a broad range of various applications. Thus, the full range of properties can be considered and the coatings can be grouped to serve the focus on the range of potential target applications. Appropriate groupings for separate consideration are selected as highly transparent (at least about 90% conductive layer transmittance), transparent (about 70% to about 90% conductive layer transmittance), translucent (0 to about 70% conductive layer transmittance), and opaque (0 transmittance). These groupings are essentially arbitrary and the boundaries are ill-defined, but they seem to be more appropriately divided and focused by potential applications. The above transparencies are related to the visible portion of the electromagnetic spectrum, but it should also be noted that this can be extended to other portions of the spectrum such as infrared.

[0056] As described above, the transmittance is a function of the amount of metal used and the nanowire quality, i.e., additional particulate matter. The metal coating should be sparse in order to have transmittance through rather than around the conductor. Nanowires have a shape suitable for forming a conductive path with large gaps for light to pass through, which the applicant has named a sparse metal layer. Since the diameter of the nanowires is well below the wavelength of visible light, the nanowires are not resolved by visible light and thus their coating appears as a uniform material under visible light, but has some scattering and absorption due to plasmon response or metal nanostructures. Metal nanowires are used to form transparent conductive layers due to their structure, but other shaped nanoparticulate materials generally cannot form transparent conductive coatings because they cannot form conductive paths and cannot form holes of appropriate dimensions for light to pass through the conductive structure.

[0057] When optical quality and high transmittance become less important, blends of nanoparticle materials become appropriate. Thus, nanowires do not necessarily need to be highly purified from other particle shapes. Nanoparticles and other special silver particle material shapes contribute disproportionately to scattering and reflection compared to their contribution to electrical conductivity, but as the relevance of optical properties decreases, the taboo against the presence of non-nanowire shapes also decreases. For example, low transmittance and translucent conductive films can be formed at a lower cost than high-quality nanowire coatings. When the conductive coating becomes opaque, perhaps the coating is no longer sparse, and the relevance of the shape of the nanoparticle material decreases, but the nanowires still contribute disproportionately to conductivity for their weight.

[0058] Next, the amount and ratio of silver nanowires used as the metal fraction affect the properties of the coated material after treatment. In the case of a sparse metal coating with nanowires as the main metal component, the average thickness becomes somewhat inaccurate due to gaps in the structure and can represent an approximate thickness if desired, but depending on the metal usage and nanowire diameter, an essentially sparse coating is represented. In contrast, in the case of an opaque structure, the treated coating can approach a material that is uniformly densified. In principle, for an opaque structure, the thickness is not limited.

[0059] Referring to FIG. 1, a representative electrically conductive film 100 includes a substrate 102, an optional undercoat layer 104, a metal conductive layer 106, an overcoat layer 108, an adhesive layer 110, and a protective surface layer 112, although not all embodiments include all layers. A polymer sheet is a desirable substrate for many applications, but in the case of another substrate, the film 100 may be considered equivalent to an electrically conductive structure, and thus, as used herein, the term "film" can be considered equivalent to any suitable structure. In the case of transparent embodiments, the metal conductive layer 106 is sparse, the substrate 102 is transparent, the adhesive layer is optically transparent, and the other layers can be similarly made transparent as appropriate. Generally, the adhesive layer 110 and the protective surface layer 112 are added after completion of the important processes described herein to improve the stability of the conductive layer. A transparent conductive film generally includes a sparse metal conductive layer and at least one layer on each side of the sparse metal conductive layer.

[0060] In the case of transparent embodiments, the overall thickness of the transparent conductive film can generally have an average thickness of 5 microns to about 2 millimeters (mm), in a further embodiment about 10 microns to about 1 mm, and in another embodiment about 12 microns to about 0.5 mm. Further ranges of thickness within the explicitly stated ranges above are contemplated, and those skilled in the art will recognize that they are within the scope of the present disclosure. In some embodiments, the film length and width when manufactured can be selected to be appropriate for the individual application, and thus the film can be sent directly to further processing on the product. In a further or alternative embodiment, the width of the film can be selected for the individual application, while the length of the film can be made long in anticipation that the film can be cut to the desired length when used. For example, the film can be a long sheet or roll. Similarly, in some embodiments, the film can be present on a roll, or another large standard type and element of film can be cut to the desired length and width when used.

[0061] In the case of the range of potential uses, the composition of the substrate can be selected from a wide range of possibilities, especially in the case of opaque embodiments. As examples, it can be provided on cardboard and fresh leaves, and thus a certain degree of porosity can be tolerated, although clearly extreme substrates may not be suitable. As mentioned above, in the case of these broader uses, the film may be considered a structure that does not have the meaning attributed to the term "film". Thus, in the case of transparent embodiments, glass and transparent ceramics may be suitable, along with polymers, and in the case of opaque embodiments, ceramic materials, various organic materials, and composite materials may be suitable substrates, along with polymers. Generally, multiple polymer substrates and biological substrates require low processing temperatures due to melting, decomposition, unwanted reactions, or other adverse transitions and effects (glass transition, softening, diffusion, color reduction, change in modulus). Thus, the ability to form the conductive layer at ambient temperature can enable many new uses and products.

[0062] Substrate 102 can generally have any reasonable dimensions. Roll-to-roll processing can be a convenient processing method for many commercial applications. Generally, in the case of roll-to-roll embodiments, the substrate can have an average thickness of from about 1 micron to about 1.5 mm, in a further embodiment from about 5 microns to about 1 mm, and in a further embodiment from about 10 microns to about 500 microns. In the case of a particularly foldable structure, especially a structure foldable on both sides, the thickness of the substrate can be about 27 microns or less, and in a further embodiment from about 5 microns to about 25 microns. Those skilled in the art will recognize that further ranges of substrate thickness within the ranges specified above are contemplated and are within the scope of the present disclosure. Suitable optically transparent polymers having very good transparency, low haze, and good protective ability can be used as the substrate.

[0063] Suitable polymers for the transparent substrate include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyolefin, polyvinyl chloride, fluoropolymer, polyamide, polyimide, polysulfone, polysiloxane, polyether ether ketone, polyether sulfone, polynorbornene, polyester, polystyrene, polyurethane, polyvinyl alcohol, polyvinyl acetate, acrylonitrile-butadiene-styrene copolymer, cyclic olefin polymer, cyclic olefin copolymer, polycarbonate, their copolymers, or blends thereof, and the like. Suitable commercially available polycarbonate substrates include, for example, MAKROFOL SR243 1-1 CG commercially available from Bayer Material Science; TAP (registered trademark) Plastic commercially available from TAP Plastics; and LEXAN (trademark) 8010CDE commercially available from SABIC Innovative Plastics. Optically quality PET substrates are available, for example, from DuPont-Teijin and Toray Films (Lumirror (trademark)). Polyimide substrates are available from Kolon, and polysulfone substrates are available from Solvay. Cyclic polyolefin (COP) is available from Zeon Corporation. By reducing the process temperature as described herein, the use of a wider range of polymers and other substrates becomes possible. In the case of non-transparent substrates, most substrates that can be moderately coated can be used. The protective surface layer 112 can independently have a thickness and composition that range within the same thickness and composition ranges as the substrates described above in this paragraph.

[0064] When the problems of the surface coating become prominent, an undercoat can be applied. For example, a thin polymer layer can provide a suitable surface for the application of the conductive layer, but in some cases, the conductive layer can be directly applied onto a range of materials. Also, in many embodiments, an overcoat polymer may be desirable as a protective coating. The polymers of the undercoat and / or overcoat can independently include the types of polymers described above with respect to the substrate, can be applied by solution coating, and can optionally be cross-linked later, such as by exposure to UV light. The polymers of the overcoat and undercoat can be applied using the same techniques as the nanowire ink. In particular, in embodiments with lower transparency or opacity, the thickness of these layers may not be critical, but in transparent embodiments and some other embodiments, the overcoat can have an average thickness of about 5 nm to about 2 microns, in further embodiments about 7 nm to about 1 micron, and in other embodiments about 8 nm to about 250 nm. In some embodiments, the overcoat can include cross-linked polyacrylates, their copolymers, or blends thereof.

[0065] The overcoat and / or undercoat can include stabilizing compounds that can help extend good electrical conduction while being exposed to environmental attack. Prior research has found that vanadium(+5) compounds can be effective for obtaining the desired stability. See U.S. Patent Application Publication No. 2018 / 0105704 to Yang et al. entitled “Stabilized Sparse Metal Conductive Films and Solutions for Delivery of Stabilizing Compounds” (hereinafter the ’704 application), which is incorporated herein by reference. Other research has found that iron(+2) and other metal salts can be effective stabilizers; see U.S. Patent Application Publication No. 2015 / 0270024A1 to Allemand entitled “Light Stability of Nanowire-Based Transparent Conductors”, which is incorporated herein by reference. Also, cobalt(+2) ions complexed with ligands have been found to achieve stabilization in a molten metal nanostructured network layer. The performance of these stabilizing compositions, alone or in combination, can be improved by incorporating noble metal ions, particularly silver ions, into the coating (overcoat and / or undercoat), which can further improve stability, probably because the metal ions move and the structure further melts. The advantage of noble metal ions in the coating is that pentavalent vanadium can be similarly utilized during the actual use of the structure in the product, but separately or in addition to this, it can be beneficial to have noble metal ions in the coating during the post-deposition heat / humidity treatment before assembling the final product.

[0066] Suitable vanadium +5 compounds include compounds having vanadium as a cation, and metavanadate (VO3 - ) or orthovanadate (VO4 -3)Compounds having vanadium as part of a polyatomic anion such as are included. Corresponding salt compounds having a pentavalent vanadium anion in the oxometalate include, for example, ammonium metavanadate (NH4VO3), potassium metavanadate (KVO3), tetrabutylammonium vanadate (NBu4VO3), sodium metavanadate (NaVO3), sodium orthovanadate (Na3VO4), other metal salts, etc., or mixtures thereof. Suitable pentavalent vanadium cation compounds include, for example, vanadium oxytrisalkoxide (VO(OR)3, where R is an alkyl group such as n-propyl, isopropyl, ethyl, n-butyl, etc., or combinations thereof), oxytrifluorovanadium (VOX3, where X is Cl, F, Br, or combinations thereof), vanadium complexes such as VO2Z1Z2 (where Z1 and Z2 are independently ligands such as those further described below with respect to Co+2 complexes), or combinations thereof. During the coating, pentavalent vanadium can be present, for example, in an amount of about 0.01 wt% to about 9 wt%, in a further embodiment about 0.02 wt% to about 8 wt%, and in a further embodiment about 0.05 wt% to about 7.5 wt%. In the coating solution, the solution generally contains a certain amount of solvent together with a solid mainly comprising a curable polymer. Generally, the corresponding coating solution can have a pentavalent vanadium compound at a concentration of about 0.0001 wt% to about 1 wt%. Further ranges of concentrations within the explicitly stated ranges above are contemplated and will be recognized by those skilled in the art to be within the scope of the present disclosure. In a further or alternative embodiment, in addition to or alternatively to pentavalent vanadium ions, iron(+2) or other metal ions can be included.

[0067] Furthermore, the solution for forming the coating can also contain noble metal ions, particularly silver ions. As used herein, noble metal ions mean ions of silver, gold, platinum, indium, osmium, ruthenium, and rhodium. The noble metal ions can be added as appropriate salts such as nitrates, sulfates, perchlorates, tetrafluoroborates, hexafluorophosphates, hexafluoroantimonates, and halides. Suitable metal salts for obtaining metal ions include, for example, chloroauric acid and palladium chloride. In the case of silver salts, if the coating polymer is deposited using an alcohol or another non-aqueous organic solvent, suitable silver salts and complexes for obtaining sufficient solubility include, for example, silver tetrafluoroborate (AgBF4), silver hexafluorophosphate (AgPF6), silver perchlorate (AgClO4), silver hexafluoroantimonate (AgSbF6), silver trifluoroacetate (AgCF3COO), silver heptafluorobutyrate (AgC4F7O2), silver methylsulfonate (AgCH3SO3), silver tolylsulfonate (AgCH3C6H4SO3), or mixtures thereof. In the coating, the noble metal ions can be present, for example, in an amount of about 0.01 wt% to about 20 wt%, in a further embodiment about 0.05 wt% to about 15 wt%, in another embodiment about 0.1 wt% to about 12 wt%, in some embodiments about 0.2 wt% to about 9 wt%, and in a further embodiment about 0.25 wt% to about 7.5 wt%. In the coating solution, the solution generally contains a certain amount of solvent together with a solid mainly containing a curable polymer. Those skilled in the art will recognize that further ranges of concentrations within the above-specified ranges are contemplated and are within the scope of the present disclosure.

[0068] Particularly when directly used in a transparent conductive layer having a molten metal nanostructured network, cobalt having a valence of +2 has been found to be effective for stabilization without interfering with the melting process. Suitable cobalt compounds include, for example, nitrites (NO2 -) Diethylamine, ethylenediamine (en), nitrilotriacetic acid, iminobis(methylenephosphonic acid), aminotris(methylenephosphonic acid), ethylenediaminetetraacetic acid (EDTA), 1,3-propylenediaminetetraacetic 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, salicylaldoxime, diethylenetriaminepentaacetic acid, 1,2-cyclohexanediaminetetraacetic acid, iminodiacetic acid, methyliminodiacetic acid, N-(2-acetamido)iminodiacetic acid, N-(2-carboxyethyl)iminodiacetic acid, N-(2-carboxymethyl)iminodipropionic acid, picolinic acid, dipicolinic acid, histidine, and Co(NO3)2 having various complex-forming ligands such as combinations thereof. Cobalt ions have been previously suggested as a suitable ion source for melting metals at the nanowire junctions in the above-cited '807 patent. As shown in the '704 application, Co+2 actually destabilizes the transparent conductive film unless it forms a complex with a ligand. Regarding the use of cobalt +2 stabilizing compounds in a layer having a molten metal nanostructured network, the stabilizing compounds include silver salts or salts of cations that are much more easily reduced, so that cobalt +2 cations remain in the material after the melting process. On the other hand, a stoichiometric amount of ligand for Co+2 has been found to interfere with the melting process for forming the molten nanostructured network. In a layer having a molten metal nanostructured network, the concentration of the cobalt +2 stabilizing compound may be from about 0.1 wt% to about 10 wt%, in a further embodiment from about 0.02 wt% to about 8 wt%, and in a further embodiment from about 0.025 wt% to about 7.5 wt%. For cobalt compositions that are effective without interfering with the melting process, the complex-forming ligand can be present in an amount of about 0.1 to about 2.6 ligand-binding equivalents per mole of cobalt, in a further embodiment about 0.5 to about 2.5 ligand-binding equivalents per mole of cobalt, and in another embodiment about 0.75 to about 2.4 ligand-binding equivalents per mole of cobalt.With regard to equivalents, this term is intended to indicate that polydentate ligands have corresponding molar ratios within the above ranges divided by their coordination numbers. With regard to the ink used for depositing metal nanowires, the solution can contain cobalt +2 compound at a concentration of about 0.0001 wt% to about 1 wt%, but further details of the nanowire ink are shown below. Those skilled in the art will recognize that further ranges of concentrations within the above-specified ranges are contemplated and are within the scope of the present disclosure.

[0069] Coating properties The electrically conductive coating can be formed in the case of a transparent or non-transparent layer. In suitable embodiments, a transparent conductive layer, such as one having a molten metal nanostructured network, can obtain good optical properties while obtaining low electrical resistance. Thus, the above structure can be useful as a transparent conductive electrode or the like. The transparent conductive electrode can be suitable for a series of applications, such as an electrode along the light-receiving surface of a solar cell. In the case of a display, and particularly a touch screen, the film can be patterned to obtain an electrically conductive pattern formed by the above structure. A substrate having a patterned structure generally has good optical properties in each part of the pattern. Non-transparent layers, such as semi-transparent or opaque, are generally formed with a greater amount of metal used to obtain a lower sheet resistance. In the case of these coatings, generally haze and other optical properties are not particularly important.

[0070] The electrical resistance of a thin coating can be expressed as sheet resistance, which is reported in units of ohms per square (Ω / □ or ohm / sq) to distinguish it from the bulk electrical resistance value by parameters related to the measurement method. The sheet resistance along the surface can generally be measured using a four-point probe measurement or another suitable method. In some embodiments, the molten metal nanowire network can have a sheet resistance of about 1000 ohm / sq or less, in some embodiments about 500 ohm / sq or less, in further embodiments about 200 ohm / sq or less, in further embodiments about 100 ohm / sq or less, in another embodiment about 80 ohm / sq or less, and in some embodiments about 50 ohm / sq or less. For a transparent film with a visible light transmittance reduced to about 70%, a reduction in the sheet resistance value of up to about 3 ohm / sq has been achieved, and it seems that this can be slightly lowered by certain optimizations. For a non-transparent coating, a sheet resistance value of less than 1 ohm / sq can be achieved, and a semi-transparent coating can be formed within a range approximately between these values. Without intending to be limited by theory, it is believed that arbitrarily low resistance can be achieved by simply increasing the amount of silver used and / or by making the coating thicker. Those skilled in the art will understand that this system can be adequately modeled using a parallel resistor model where the resistance can be estimated by the thickness. For example, if the thickness of the conductive coating increases to twice the thickness at which 1 ohm / sq is achieved, the thicker (twice as thick) film should have a resistance of 0.5 ohm / sq. Further ranges of sheet resistance within the explicitly stated ranges above are contemplated, and those skilled in the art will recognize that they are within the scope of the present disclosure.

[0071] Depending on the specific application, the commercial specifications for sheet resistance for use in a device as a transparent conductive film may not necessarily need to aim for a lower sheet resistance value, such as when additional costs may be required. Current commercially reasonable values can be, for example, 250 ohms / sq, 150 ohms / sq, 100 ohms / sq, 50 ohms / sq, 40 ohms / sq, 30 ohms / sq, 20 ohms / sq or less as target values for touchscreens of different qualities and / or sizes. Each of these values defines a range between specific values as endpoints of the range, such as 150 ohms / sq to 20 ohms / sq. For example, a lower-cost coating may be appropriate for certain applications in exchange for a slightly higher sheet resistance value. Generally, the sheet resistance can be reduced by increasing the amount of nanowires used, but an increase in the amount used may not be desirable from another perspective, and the amount of metal used is only one of many factors for achieving a low sheet resistance value.

[0072] The transparent conductive layer is generally formed with attention to other optical properties. On the other hand, semi-transparent and opaque conductive layers are generally formed without particularly emphasizing optical properties, but some attention to optical properties can be carried out based on the teachings herein. The following discussion is directed to the optical properties of the transparent coating.

[0073] For applications as a transparent conductive film, it is desirable to maintain good optical transparency for a molten metal nanowire network or another sparse metal conductive layer. In principle, optical transparency is inversely proportional to the amount used, and transparency decreases with an increase in the amount used, but the processing of the network can also significantly affect transparency. Also, the polymer binder and other additives can be selected so that good optical transparency is maintained. Optical transparency can be evaluated with respect to the transmitted light passing through the substrate. For example, the transparency of the conductive film described herein can be measured by measuring the total transmittance passing through the conductive film and the support substrate using a UV-visible spectrophotometer. The transmittance is the incident light intensity (I) of the transmitted light intensity (I o) is the ratio with respect to. The transmittance (T coating ) through the coating can be evaluated by dividing the measured total transmittance (T) by the transmittance (T sub ) through the support substrate (T = I / I o and T / T sub =(I / I o ) / (I sub / I o )=I / I sub =T coating)。Therefore, the reported total transmittance can be corrected to obtain the transmittance of only the coating by removing the transmittance through the substrate. Generally, it is desirable to have good optical transparency over the visible spectrum. For convenience, the light transmittance can be reported at a wavelength of 550 nm. Alternatively, or in addition to this, the transmittance can be reported as the total transmittance of light wavelengths from 400 nm to 700 nm, and such results are reported in the following examples. Generally, for molten metal nanowire films, the measurement of the transmittance at 550 nm and the total transmittance from 400 nm to 700 nm (or for convenience, simply "total transmittance") are not qualitatively different. In some embodiments, the total transmittance (TT%) of the coating formed by the molten network is at least 70%, in some embodiments at least about 80%, in further embodiments at least about 85%, in further embodiments at least about 90%, in another embodiment at least about 94%, in further embodiments at least about 95, in some embodiments from about 96% to about 99.5%. The transparency of the film on the transparent polymer substrate can be evaluated using the standard ASTM D1003 ("Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics"), which is incorporated herein by reference. The TT% passing through the entire structure includes a reduction in transmittance due to the substrate and the overcoat, and the lower end of the transmittance in the above range may shift by 1% to 10%, and in some embodiments by 2.5% to 5%. Further ranges of transmittance within the explicitly stated ranges above are contemplated and will be recognized by those skilled in the art or those of ordinary skill as being within the scope of the present disclosure. When adjusting the optical properties measured in the coatings in the following examples to match the substrate, the coatings have very good transmittance and haze values, which are achieved along with the observed low sheet resistance.

[0074] The molten metal network can have a desirable low sheet resistance while having a high transmittance of visible light and a low haze. The haze can be measured using a haze meter based on ASTM D1003 of the above reference, and the contribution of the haze of the substrate can be removed to obtain the haze value of the transparent conductive film. In some embodiments, the transparent coating can have a haze value of about 1.2% or less, in further embodiments about 1.1% or less, in further embodiments about 1.0% or less, and in another embodiment as low as 0.1%. As described in the examples, when appropriately selected silver nanowires are used, very low values of haze and sheet resistance can be achieved simultaneously. The amount used can be adjusted to balance the sheet resistance and the haze value, and a very low haze value can still be achieved together with a good sheet resistance value. In particular, a haze value of 0.8% or less, in further embodiments about 0.4% to about 0.7%, can be achieved together with a sheet resistance value of at least about 45 ohms / sq. Also, a haze value of 0.7% to about 1.2%, in some embodiments about 0.75% to about 1.05%, can be achieved together with a sheet resistance value of about 30 ohms / sq to about 45 ohms / sq. Good optical transparency was exhibited by all of these coatings. Those skilled in the art will recognize that further ranges of haze within the ranges specified above are contemplated and are within the scope of the present disclosure.

Examples

[0075] General materials and methods As shown in Table 2, inks S1 to S7 were prepared based on the ActiveGrid (registered trademark) ink of the applicant's C3Nano, Inc. The ActiveGrid (registered trademark) ink includes GEN5 ActiveGrid (registered trademark) ink having silver nanowires with an average diameter of <25 nm, GEN7 ActiveGrid (registered trademark) ink having silver nanowires with an average diameter of about 18 nm, and GEN8 ActiveGrid (registered trademark) ink having silver nanowires with an average diameter of 13 to 15 nm. The ink contained a hydroxyalkyl alkyl cellulose binder. Some ink formulations contained the silver salts AgOAc or AgF, and each silver salt was used at different levels as detailed below in each example. The AgF in the standard level (1x) of GEN7 (1x G7 ) and GEN8 (1x G8 ) inks is about 50% more than that in the GEN5 ink. The silver salts were used in the inks of the examples and are called NanoGlue (registered trademark) AgOAc and NanoGlue (registered trademark) HF.

[0076]

Table 2

[0077] As shown in Table 3, the inks were coated on various polymer substrates. The substrates included 50-μm PET (polyethylene terephthalate) with or without a hard coat layer, and COP (cyclic olefin polymer). The inks were coated using a slot coater set to different gap thicknesses of 1.5 mils (38.1 μm) or 4.0 mils (101.6 μm). For some samples, the inks were coated using a wound rod #14 to obtain a gap thickness of 1.4 mils (35.6 μm).

[0078]

Table 3

[0079] Various processing conditions were used on the samples as detailed below in each example. A portion of the undried coating was first dried for about 30 - 60 seconds using an air gun (with air at room temperature - 25°C) about 1.5 - 3 inches above the film, and a portion was further heated in an oven at different temperatures in the range of 35°C - 120°C for different times in the range of 0.5 minutes - 210 minutes. A portion of the undried coating was dried at room temperature without any heating. A portion of the undried coating was dried under room temperature conditions using a fan that blows cold air at about 21°C over the sample.

[0080] The average sheet resistance was measured using a sheet resistance measuring device from SURAGUS GmbH. The average percent total transmittance (%TT) and average percent haze (%H) were measured using a haze meter. The average b * was measured using a colorimeter.

[0081] Generally, the process for forming the transparent conductive film is essentially as described in Example 5 of the above - cited '968 patent and uses silver nanowires synthesized as described in U.S. Patent No. 10,714,230B2, entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed From the Nanowires" by Hu et al. (incorporated herein by reference).

[0082] Example 1 - Treatments Using Different Fluxes With or Without Heat This example shows the performance of silver nanowire films having different silver salts dried and / or processed under different conditions as described in Tables 4 and 5 below. The coating was formed on primed PET with a gap thickness of 1.5 mils.

[0083]

Table 4

[0084]

Table 5

[0085] As shown in Table 4, Sample 2 dried in an oven at 120 °C for 2 minutes showed the lowest sheet resistance of 37 ohms / sq. Samples 3 to 5 dried in an oven at 50 °C for 90 to 210 minutes showed similar sheet resistances of 42 to 43 ohms / sq, and the sheet resistance did not decrease much after 90 minutes and at least up to 210 minutes. Sample 6 dried in an oven at 50 °C for 60 minutes showed a sheet resistance of 45 ohms / sq. Therefore, in the case of Samples 3 to 9 dried at 50 °C, the sheet resistance decreased as the drying time increased and approached the lowest value obtained with Sample 2 dried at 120 °C. Even after 210 minutes, the samples dried at 50 °C did not seem to melt as much as Sample 2 dried at 120 °C. Samples 1 and 10 dried without heating in the oven showed the highest sheet resistances compared to the samples dried using heat. Sample 1 dried using a heat gun and not placed in the oven had a sheet resistance of 57 ohms / sq, and the sample not dried with a heat gun and not placed in the oven had a sheet resistance of 64 ohms / sq.

[0086] As shown in Table 5, Samples 9 to 11 were not dried in the oven and showed the lowest sheet resistances of 31 to 32 ohms / sq. Sample 9 was dried using only a heat gun, and Samples 10 and 11 were dried without applying heat. Samples 2 to 5 dried at 50 °C for 0.5 to 2 minutes showed similar sheet resistances of 33 to 35 ohms / sq, and Samples 2 and 3 were repeated samples. Samples 6 to 8 dried at 35 to 40 °C for 1 to 2 minutes showed almost the same sheet resistance regardless of temperature or time, and these were similar to the sheet resistances obtained at 50 °C. Sample 1 dried using a heat gun and in an oven at 120 °C showed a sheet resistance of 35 ohms / sq, which could be equal to or higher than that shown by Samples 2 and 3 dried at 50 °C.

[0087] The data shown in Tables 4 and 5 illustrate the difference in sheet resistance obtained using AgF and AgOAc as fluxes. The sheet resistance of S2 melted with AgF was almost independent of the processing conditions, but this was not the case for S1 melted with AgOAc. The sheet resistance of S2 was almost the same regardless of the temperature in the range from room temperature to 120 °C over a time period of at least 1 - 2 minutes. However, the data suggest that for the non-heated treatment, more desirable results are obtained for the sheet resistance compared to drying at a lower temperature of 35 °C. For the processing conditions of the samples containing AgF, more desirable results for the sheet resistance are obtained compared to drying under any of the conditions examined when using AgOAc.

[0088] Example 2 - Treatment Using AgOAc with or without Heat This example shows the performance of silver nanowire films with different levels of AgOAc used in the ink. A coating with S1 ink was formed by coating on both sides of HC-PET with a gap thickness of 1.5 mils. The data shown in Table 6 are for samples dried using cold air from a fan and are plotted in Figure 3. The data shown in Table 7 are for samples dried at room temperature and then heated at 120 °C for 2 minutes and are plotted in Figure 4. The difference between the data shown in Tables 6 and 7 is shown in Table 8.

[0089] [Table 6]

[0090] [Table 7]

[0091] [Table 8]

[0092] The data in Table 6 (cold air) shows that in the case of AgOAc, the sheet resistance increases up to the 1x level, but then decreases to the same level as the 0x at 1.5x. The data in Table 7 (heated at 120 °C) shows that the sheet resistance decreases as a function of increasing AgOAc. When AgOAc is present at the 1.5x level in the ink, the resulting sheet resistance varies depending on whether the sample is treated with cold air or heated at 120 °C. The difference in properties between the room temperature treated values in Table 6 and the heat treated samples in Table 7 is shown in Table 8. As shown in Table 8, the sheet resistance of the sample with 1.5x AgOAc treated with cold air is 158 ohms / sq less than that of the sample treated by heating at 120 °C. Table 8 also shows that the sheet resistance of the sample treated with cold air without AgOAc is 40 ohms / sq greater than that of the sample treated by heating at 120 °C. The behavior in Table 6 is somewhat surprising because simply adding silver acetate salt significantly increases the sheet resistance. One plausible explanation is that silver acetate as a polar salt interferes with the interaction between the cellulose binder and the silver nanowires or changes the microscopic structure of the film when it is formed. The applicant has previously confirmed that this system containing cellulose is very effective in inducing good interaction between the non-molten silver nanowires compared to another organic binder, so that when this favorable microscopic structure is disrupted, high sheet resistance values can be observed. Some celluloses may have the potential to improve the contact of silver nanowires when forming a conductive film. This has been shown using at least aqueous and alcoholic systems. On the other hand, changing the solvent system can still result in very different results.

[0093] Regarding %H, the data in Table 6 shows that the values are approximately the same when the value is from 0.25x to 1x, but probably %H increases at the 1.5x level. The level of 1.5x of Nanoglue® is useful as it further reduces the sheet resistance, but a certain degree of deterioration in optical properties is confirmed. The data in Table 7 shows the same trend, and %H increases more significantly at the 1.5x level. Regarding %TT, the data in Tables 6 and 7 shows that the values are maintained constant regardless of the processing conditions. b * Regarding, the data in Table 6 shows that the values are approximately the same when the value is from 0.25x to 1.5x, and shows an increase of about 0.1% compared to the 0x sample. The data in Table 7 shows that in the case of heating vs. cold air, it does not increase much from 0.25x to 1x, but at the level from 1x to 1.5x b * doubles.

[0094] Example 3 - Treatment Using HF with or without Using Heat This example shows the performance of silver nanowire ink having GEN5 ink and 1x level of HF when coated with different thicknesses and under different processing conditions.

[0095] Ink S2 having 1x level of HF was coated on the COP at a gap thickness of 1.5 mil or 4.0 mil, and samples of each thickness were processed as described in Table 9. Since the ink concentration does not change, at a larger gap thickness, the amount of metal used proportionally increases. S2 ink having the same 1x level of AgF but a higher level of Ag (designated as Ag-1X) was also prepared, coated at a thickness of 4.0 mil, and processed with cold air. The results are shown in Table 9. The transmittance in Table 9 is reported for both the entire structure and only the transparent conductive film (TCF) in parentheses.

[0096]

Table 9

[0097] For samples made from Ink S2 with 1x level of HF, the data in Table 9 indicate that for any thickness, the change in surface resistance or %TT due to different processing conditions is slight or non-existent. Samples coated at a thickness of 4.0 mils showed a sheet resistance approximately 26 ohms / sq lower and a %TT decrease of approximately 3 - 4% compared to samples coated at 1.5 mils. This then suggests that it melts almost completely at room temperature (cooling fan).

[0098] The value of %H increased by approximately 0.1% at a thickness of 1.5 mils and by approximately 0.35% at a thickness of 4.0 mils depending on the processing conditions. At a thickness of 1.5 mils, both samples showed a %H of 0.8 - 0.9. At a thickness of 4.0 mils, the influence of the processing conditions became more significant, with the sample processed with cold air showing a %H of 2.35% and the sample processed at 120 °C for 2 minutes showing a %H of 2.70%.

[0099] Example 4 - Treatment of Ink with Silver Nanowires of Smaller Diameter and with HF This example shows the performance of a silver nanowire ink containing silver nanowires with a smaller diameter than those contained in Ink S3 of Example 3. 1x G7 GEN7 ActiveGrid (trademark) ink with 1x level of HF was coated at different thicknesses and different processing conditions were used, but the base amount (1x) is somewhat higher concentration in the case of thinner nanowires.

[0100] Ink S4 with 1x level of HF was coated on COP at a gap thickness of 1.5 mils or 4.0 mils, and samples of each thickness were processed as described in Table 10. S4 ink with a higher level of Ag (designated as Ag - 1X) and the same 1x level of AgF was also prepared, coated at a thickness of 4.0 mils, and processed with cold air. The results are shown in Table 10. The transmittance in Table 10 is reported for both the entire structure and for the transparent conductive film (TCF) only within parentheses.

[0101]

Table 10

[0102] For the samples made from Ink S4 with 1x level of HF, the data in Table 10 indicate that for any thickness, the change in surface resistance or %TT due to the difference in processing conditions is slight or non-existent. The sample coated with a thickness of 4.0 mils shows a sheet resistance approximately 23 ohms / sq lower and a %TT decrease of approximately 3 - 4% compared to the sample coated with 1.5 mils. The data on sheet resistance and %TT are equivalent to those obtained for Ink S2 prepared using GEN5 ink, but the sheet resistance is somewhat lower. Also in this case, these results indicate that melting almost completely occurs when no heat is applied at all (cooling fan). These results show that a transparent coating (>70%TT) can be formed with a sheet resistance of 3 ohms / sq.

[0103] The value of %H increased by approximately 0.1% at a thickness of 1.5 mils and by approximately 0.37% at a thickness of 4.0 mils depending on the processing conditions. At a thickness of 1.5 mils, both samples showed a %H of 0.6 - 0.8%. At a thickness of 4.0 mils, the influence of the processing conditions became more significant. The sample processed with cold air showed a %H of 1.76%, and the sample processed at 120 °C for 2 minutes showed a %H of 2.13%.

[0104] Example 5 - Comparison of Inks with Silver Nanowires of Different Diameters and with HF The differences in the data shown in Tables 9 and 10 are shown in Table 11.

[0105]

Table 11

[0106] The data shown in Table 11 indicates that S4 ink generally has a lower average sheet resistance than S3 ink. Except for the S4 ink prepared using Ag-1x showing a %TT of about 79%, %TT ranges from about 92% to about 85% for all coatings. %H is lower for S4 ink than for S2 ink, except for the S4 ink formulated using Ag-1x showing an increase of about 1.3%.

[0107] Example 6 - Treatment with Cold Air of Ink with AgF In this example, the performance of ink coatings on different polymer substrates is examined when the ink is treated by drying with cold air for about 1 to 5 minutes. The ink is formulated using silver nanowires of different diameters and the coatings have different thicknesses. Data for various coatings and performances are summarized in Table 12. The transmittance in Table 12 is reported for both the entire structure and for the transparent conductive film (TCF) only within parentheses.

[0108]

Table 12

[0109] The data shown in Table 12 suggests that coatings formed from S4 ink generally showed a lower average sheet resistance than those from S2 ink. For all coatings, %TT ranges from about 89% to about 92%. %H generally was lower for S4 ink than for S2 ink. Coatings formed with a 4.0 mil gap thickness showed a lower sheet resistance than the corresponding 1.5 mil coatings, %TT was slightly lower for the thicker coatings, and %H was slightly higher for the thicker coatings. Overall, the differences among primed PET, PET with a hard coat, and COP ranged from slight to non-existent.

[0110] Example 7 - Treatment with Cold Air of Ink with or without AgF In this example, the performance of ink coatings with or without AgF as a flux is further investigated. Inks were formulated using silver nanowires of different average diameters and coated onto COP and PU respectively. All samples were processed by drying using cold air. Various coating and performance data are summarized in Table 13. The transmittance in Table 13 is reported for both the entire structure and the transparent conductive film (TCF) only in parentheses.

[0111]

Table 13

[0112] The data shown in Table 13 suggest that coatings formed using a flux in the ink generally exhibited lower average sheet resistance than the corresponding coatings without a flux. The difference in sheet resistance was greater for coatings formed on PU than on COP. For example, the inks S7 and S4 coated on COP showed differences of -45 ohm / sq respectively, while the difference on PU was -94 ohm / sq. All coatings showed a %TT of approximately 92%. The change in %H between inks with and without a flux ranged from slight to none at all, and overall, the coatings formed on PU were greater than those formed on COP.

[0113] Example 8 - Optical and Conductive Performance of Inks Processed under Ambient Conditions In this example, the optical performance and conductivity of ink coatings processed under ambient conditions are further shown.

[0114] Inks with various AgNW usage fees were coated on the COP at different (4.0, 3.0, and 1.5 mil) gap thicknesses to achieve a wide range of sheet resistances, and the samples were processed under ambient conditions for about 1 minute. For the selected performance structure and only the transparent conductive film (TCF) within the parentheses. A plot of the sheet resist data is shown in Table 14. The transmittance in Table 14 is reported for both cases, and the totalance vs. %TT and %H are shown in Figures 5 and 6 respectively.

[0115]

Table 14

[0116] These results indicate that desirable conductive properties can be obtained along with excellent optical properties for ink coatings dried under ambient conditions.

[0117] Coatings or circuits were formed from inks containing GEN5 nanowires and AgF on various substrates including heat-sensitive substrates and dried under ambient conditions. The substrates included medical-grade polyurethane, medical bandages, leaves, Ziploc® bags, shrink wrap, Scotch® Tape (coatings on the adhesive layer of the tape), PET, and packaging cardboard. Resistance was measured by direct contact measurement as shown in Figures 7A - 7H. Attempts were made to measure the resistance as it was, but accurate measurements have not been attempted on many of these substrates, and the nature of the substrates was consequently uncertain.

[0118] Example 9 - Difference between high-alcohol ink and AgF ink formulation This example shows the performance of inks prepared using alcohol as the main solvent compared to water, and the performance differences related to the presence of fluorosurfactants in the inks. Generally, the cellulose used as a binder is soluble in the EtOH - H2O mixture.

[0119] GEN5 ActiveGrid™ ink in 80% ethanol in water was used to prepare inks with a high alcohol content. These inks were prepared with and without a nonionic fluorosurfactant as a wetting agent and with and without AgF as a fluxing agent. The formulations are summarized in Table 15. Inks S8 - S11 were coated onto PET with a hard coat (described in Table 2) with a gap thickness of 1.5 mils. The coating was dried at room temperature using a fan that blew cold air at approximately 21 °C over the sample. The results are shown in Table 16. The transmittance in Table 16 is reported for both the entire structure and for the transparent conductive film (TCF) only in parentheses.

[0120]

Table 15

[0121]

Table 16

[0122] In the case of S8 and S9 without a wetting agent, the presence of a fluxing agent resulted in a 38 ohm / sq decrease in sheet resistance, and it was confirmed that the differences in %TT, %H, and b * ranged from slight to non - existent. In the case of S10 and S11 with a wetting agent, the presence of a fluxing agent resulted in a 700 ohm / sq decrease in sheet resistance, and it was confirmed that the differences in %TT, %H, and b * ranged from slight to non - existent. However, the sheet resistance was much higher for S10 and S11 than for S8 and S9. For example, it was 900 ohm / sq for S10 compared to 84 ohm / sq for S8. %TT, %H, and b * were the same for all coatings.

[0123] Example 10 - High - Alcohol Ink, Addition of NaF This example shows the performance of inks prepared using alcohol as the main solvent compared to water, and the differences in performance related to the presence of alkali fluoride salts in the inks.

[0124] Inks with a high alcohol content were prepared using GEN5 ActiveGrid (trademark) ink in ethanol containing 64 - 70% water. These inks were prepared using AgOAc, AgF, NaF, and an equimolar combination of AgOAc and NaF. The formulations are summarized in Table 17. Inks S12 - S16 were coated on HC - PET with a gap thickness of 1.5 mils. Different treatments were performed on these coatings as shown in Table 17. Some coatings were dried at room temperature using a fan that blew cold air at approximately 21 °C onto the samples. After measuring the sheet resistance of the resulting films, the samples were further heated at 120 °C for 2 minutes. The results are shown in Tables 17 - 19. The transmittance in Table 19 is reported for both the entire structure and for the transparent conductive film (TCF) only within parentheses.

[0125] [Table 17]

[0126] [Table 18]

[0127] [Table 19]

[0128] Data from Tables 17 - 19 are plotted in FIGS. 8 and 9. FIG. 8 shows the reciprocal of the sheet resistance of S12 - S16 versus haze processed under the respective conditions described above. FIG. 9 shows a comparison of the sheet resistance values obtained with coatings using the same flux or no flux. In the case of S12 - S16, when the coating was heated after drying at room temperature, the sheet resistance decreased by more than 10 ohms / sq, except for S13 where the sheet resistance was maintained at approximately the same level. S13 also obtained the lowest sheet resistance. Regarding %TT and %H, the differences were found to range from negligible to non - existent, but b * increased by approximately 0.3 to approximately 0.6 when heating was used. This example shows that at the levels used, room - temperature melting is not promoted by fluoride anions alone. Therefore, the data suggests that only the combination of silver cations and fluoride anions is important.

[0129] Example 11 - Performance of Silver Nanoparticle - like Sub - product Ink This example shows the performance of an ink prepared from silver by - products obtained in the synthesis of silver nanowires.

[0130] A silver nanoparticle - like sub - product mixture was recovered from the centrifugation residue of the purification process for the production of GEN 5 silver nanowires.

[0131] Characterization of three samples was performed using titration and thermogravimetric analysis (745 °C), and the results are summarized in Table 21.

[0132]

Table 20

[0133] Ink S17 was formulated using a by - product W1 with 4x the Ag usage and 1x cellulose binder, and AgF as the flux. Ink S18 was formulated using all components in the same ratio, except that the concentration of all solids was approximately 60% higher than that of Ink S17.

[0134]

Table 21

[0135] Using the by-product W2 (W1 filtered through a 400-mesh filter) with an Ag usage of 4x and 1x of the cellulose binder, Ink S19 was formulated using AgF as a fluxing agent. Except for not adding the fluxing agent, Ink 20 was formulated in the same manner as Ink S19.

[0136]

Table 22

[0137] Using the by-product W3 (W1 further concentrated by an agglomeration step) with an Ag usage of 4x and 1x of the cellulose binder, Ink S21 was formulated using AgF as a fluxing agent.

[0138]

Table 23

[0139] The above embodiments are intended to be illustrative and not restrictive. Further embodiments are within the scope of the claims. Additionally, while the invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes in form and detail are possible without departing from the spirit and scope of the invention. The incorporation by reference of any of the above documents is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. To the extent that a particular structure, composition, and / or process is described herein with components, elements, constituents, or other parts, the disclosure herein can include additional embodiments, particular components, elements, constituents, other parts, or combinations thereof that do not change the fundamental nature of the subject matter as suggested in the discussion, without being specifically shown, and embodiments that consist essentially of such particular components, constituents, or other parts, or combinations thereof. The use of the term "about" herein means the uncertainty expected among the relevant values as would be understood by those skilled in the art in an individual situation.

Claims

Claim 1 A method for forming a conductive layer, comprising: depositing a metal nanowire ink on an inert surface to form a coating, wherein the ink contains from about 0.001 wt% to about 4 wt% of metal nanowires and from about 0.05 wt% to about 5 wt% of a polysaccharide; drying the coating at room temperature to form a conductive film having a sheet resistance of about 1000 ohms / sq or less; The method includes the above steps. Claim 2 The method according to claim 1, wherein the metal nanowires include silver nanowires and the metal nanowire ink contains a silver salt. Claim 3 The method according to claim 1, wherein the metal nanowire ink contains silver ions from 0.001 mg / mL to about 2.0 mg / mL, and a molten metal nanostructure network is formed after drying. Claim 4 The method according to claim 2, wherein the silver salt includes AgF. Claim 5 The method according to claim 1, wherein the sheet resistance is less than about 100 ohms / sq and the coating has at least about 98.6% %TT. Claim 6 The method according to claim 1, wherein the sheet resistance is less than about 100 ohms / sq. Claim 7 wherein the inert surface is the surface of a polymeric substrate, and the substrate having the coating has a total transmittance of at least about 90%, a haze of less than about 1.0%, and a b of less than about 2.0 ＊ The method of claim 1, forming a conductive film exhibiting Claim 8 The method according to claim 1, wherein the metal nanowire ink does not contain an added metal salt. Claim 9 wherein the inert surface is the surface of the polymeric substrate, and the substrate having the coating has at least about 90% total percent transmittance, less than about 1.0% haze, and less than about 1.0 b ＊ The method of claim 8, forming a conductive film exhibiting ＊ . Claim 10 An ink for forming a conductive layer, comprising from about 0.001 wt% to about 4 wt% of metal nanowires, from about 0.05 wt% to about 5 wt% of a hydroxyalkyl-functionalized polymer binder, from about 20 vol% to about 100 vol% of a C １ to C １０ alcohol-containing aqueous solvent, and from about 0.001 wt% or less of a surfactant. Claim 11 The ink according to claim 10, wherein the hydroxyalkyl-functionalized polymer binder includes cellulose. Claim 12 The ink according to claim 10, wherein the hydroxyalkyl-functionalized polymer binder includes alkyl cellulose, hydroxyalkyl cellulose, or a mixture thereof. Claim 13 The ink according to claim 10, wherein the ink further contains metal ions from 0.001 mg / mL to about 2.0 mg / mL. Claim 14 The ink according to claim 10, wherein the metal nanowires include silver nanowires. Claim 15 The ink according to claim 14, wherein the ink further contains a silver salt. Claim 16 The ink according to claim 15, wherein the silver salt includes AgOAc or AgF. Claim 17 The ink according to claim 16, wherein silver ions from the silver salt are present in an amount from 0.001 mg / mL to about 2.0 mg / mL. Claim 18 The ink according to claim 10, wherein the metal nanowires have an average diameter of 25 nm or less. Claim 19 The ink according to claim 10, wherein the metal nanowires have an average diameter of 20 nm or less. Claim 20 The ink according to claim 10, wherein the metal nanowire has an average diameter of 15 nm or less.

21. The ink according to claim 10, wherein the metal nanowire has a noble metal coating.

22. Said C １ to C １０ The alcohol is C １ to C ５ The ink according to claim 10, containing C to C alcohol.

23. The ink according to claim 10, wherein the surfactant includes a nonionic surfactant.

24. The ink according to claim 10, wherein the surfactant includes a fluorinated surfactant.

25. A method for forming an electrically conductive coating having a very low sheet resistance, comprising: applying a silver nanoparticle material ink onto a substrate surface to form an undried coating, wherein the ink includes an aqueous solvent, a silver nanoparticle material having 85 wt% or less of silver nanowires having an average diameter of 50 nm or less and an aspect ratio of 10 or more, and a cellulose binder; drying the undried coating at a temperature of 60 °C or lower to form a dried coating having a sheet resistance of 25 ohms / sq or less. A method comprising the above steps.

26. The method according to claim 25, wherein the ink includes a silver salt.

27. The method according to claim 25, wherein the ink contains silver ions from 0.001 mg / mL and about 2.0 mg / mL, and a molten silver nanostructure network is formed after drying.

28. The method according to claim 26, wherein the silver salt includes AgF.

29. The method according to claim 25, wherein the sheet resistance is less than about 20 ohms / sq, and the coating has at least about 50% %TT.

30. The method according to claim 25, wherein the ink is formed from a solution used for synthesizing the silver nanowires.

31. The method according to claim 25, wherein the inert surface is the surface of a polymer substrate.

32. The method according to claim 25, wherein the ink does not contain an added metal salt.

33. The method according to claim 25, wherein the ink includes silver nanowires in an amount of about 30 wt% to about 80 wt% based on all the silver nanoparticles.

34. The method according to claim 25, wherein the ink includes a solvent having more than 51 volume percent of alcohol and does not contain a fluoro surfactant.

35. An ink comprising an aqueous solvent, a silver nanoparticle material comprising 85 wt% or less of silver nanowires having an average diameter of 50 nm or less and an aspect ratio of 10 or more, and a cellulose binder, wherein the weight ratio of cellulose to the silver nanoparticle material is from about 0.05 to about 3.

36. From about 0.001 wt% to about 4 wt% of silver nanowires, from about 0.05 wt% to about 5 wt% of a hydroxyalkyl-functionalized polymer binder, from about 20 vol% to about 100 vol% of C １ ~C １０ An aqueous solvent containing alcohol, and a surfactant of about 0.001 wt% or less, the ink according to claim 35.

37. The ink according to claim 35, wherein the cellulose binder comprises a hydroxyalkyl-functionalized polymer binder.

38. The ink according to claim 35, wherein the cellulose binder comprises a hydroxyalkyl-functionalized polymer binder, an alkyl cellulose, a hydroxyalkyl cellulose, or a mixture thereof.

39. The ink according to claim 35, further comprising silver ions from 0.001 mg / mL and about 2.0 mg / mL.

40. The ink according to claim 35, further comprising a silver salt.

41. The ink according to claim 40, wherein the silver salt comprises AgOAc or AgF.

42. The ink according to claim 40, wherein the silver ions from the silver salt are present in an amount from about 0.001 mg / mL and about 2.0 mg / mL.

43. The ink according to claim 35, wherein the silver nanoparticles are provided in the form of a solution used for the synthesis of the silver nanowires.

44. The ink according to claim 35, wherein the silver nanowires have a noble metal coating.

45. The foregoing C １ to C １０ The alcohol is C １ to C ５ The ink according to claim 36, which contains alcohol

46. The ink according to claim 36, wherein the ink does not contain a fluorosurfactant.

47. The ink according to claim 35, wherein the silver nanoparticle material further comprises spherical nanoparticles, nanorods, nanoplates, nanocubes, nanoparticles of special shapes, or a mixture thereof.

48. The ink according to claim 35, wherein the silver nanoparticle material further comprises silver nanowires having an average diameter exceeding 50 nm.

49. The ink according to claim 34, wherein the silver nanoparticle material comprises from about 30 wt% to about 80 wt% silver nanowires, and the ink has from about 0.2 wt% to about 3 wt% silver nanoparticles.

Images