HK1216050B - Conductive films having low-visibility patterns and methods of producing the same - Google Patents

Description

Conductive film having low-visibility pattern and method for producing same

Background

The transparent conductor refers to a conductive thin film coated on a surface or substrate having high light transmittance. Transparent conductors can be fabricated to have surface conductivity while maintaining suitable optical transparency. Such surface-conductive transparent conductors are widely used as transparent electrodes in flat liquid crystal displays, touch panels, electroluminescent devices, and thin film photovoltaic cells; as an antistatic layer; and as an electromagnetic wave shielding layer.

Currently, vacuum deposited metal oxides, such as Indium Tin Oxide (ITO), are industry standard materials for providing optical transparency and electrical conductivity to dielectric surfaces such as glass and polymer films. However, metal oxide films are susceptible to cracking and damage when bent or otherwise subjected to physical stress. It also requires expensive manufacturing processes and specialized manufacturing equipment. Metal oxide films are typically deposited in a vacuum chamber at elevated deposition temperatures and high annealing temperatures to achieve the desired conductivity. Furthermore, vacuum deposition is not conducive to direct patterning and circuitry, which requires specialized patterning methods, such as photolithography.

The special method for manufacturing the metal oxide film has severe restrictions on the substrate. Typically, a rigid substrate such as glass is the only viable option. On the other hand, flexible substrates (e.g., plastics) tend not to adhere to metal oxides due to the absorption properties of the substrate.

Electrically conductive polymers are also used as optically transparent electrical conductors. However, it generally has lower conductivity and higher light absorption (especially in visible light wavelengths) compared to metal oxide films, and lacks chemical stability and long-term stability.

Accordingly, there remains a need in the art to provide transparent conductors having desirable electrical, optical, and mechanical properties; in particular, transparent conductors that can fit any substrate and can be fabricated and patterned in a low cost, high throughput process.

Disclosure of Invention

Patterned transparent conductors including a conductive layer coated on a substrate are described. More specifically, the patterned transparent conductor includes: a non-conductive substrate; a first conductive line on a non-conductive substrate, the first conductive line comprising a first conductive nanostructured network and having a first longitudinal direction; a second conductive line over the non-conductive substrate, the second conductive line comprising a second conductive nanostructured network and having a second longitudinal direction; and an insulating region electrically isolating the first conductive line and the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along a first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along a second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on a non-conductive substrate and electrically isolated from each other by non-conductive gaps, each island of conductive material comprising a respective plurality of conductive nanostructures.

More specifically, the non-conductive gap, the first and second non-conductive boundaries do not have a conductive network of metal nanostructures.

In another embodiment, the first longitudinal direction and the second longitudinal direction in the patterned transparent conductor are substantially parallel to each other.

In various embodiments, the first non-conductive boundary may be straight or irregular. The second non-conductive boundary may be straight or irregular.

In other embodiments, the conductive material islands may be parallelogram shaped or may be irregularly shaped.

In another embodiment, the islands of conductive material have a surface area in the range of 0.1 to 10 square millimeters or 0.5 to 2 square millimeters.

In various embodiments, the metal nanostructures are absent from the non-conductive gap, the first and second non-conductive boundaries.

In other embodiments, the non-conductive gap, the first and second non-conductive boundaries have metal nanostructures with band-structure defects such that the metal nanostructures cannot form a conductive network.

Another embodiment provides a method of preparing a transparent conductor having a low-visibility pattern, the method comprising: printing directly on a non-conductive substrate according to a pattern a coating composition having a volatile liquid carrier and a plurality of metallic nanostructures; and removing the volatile liquid carrier, wherein the pattern defines a first conductive line having a first longitudinal direction on the non-conductive substrate; a second conductive line having a second longitudinal direction on the non-conductive substrate, and an insulating region electrically isolating the first conductive line from the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along the first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along the second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on the non-conductive substrate and electrically isolated from each other by non-conductive gaps, each island of conductive material comprising a plurality of corresponding conductive nanostructures, and wherein the non-conductive gaps, the first and second non-conductive boundaries are free of any metal nanostructures.

Yet another embodiment provides a method of manufacturing a transparent conductor having a low visibility pattern, the method comprising: applying a coating composition on a non-conductive substrate, the coating composition having a volatile liquid carrier and a plurality of metallic nanostructures; removing the volatile liquid carrier to provide a conductive network of metallic nanostructures; and etching the conductive mesh according to a pattern, wherein the pattern defines a first conductive line having a first longitudinal direction on the non-conductive substrate; a second conductive line having a second longitudinal direction on the non-conductive substrate, and an insulating region electrically isolating the first conductive line and the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along the first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along the second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on the non-conductive substrate and electrically isolated from each other by non-conductive gaps, each island of conductive material comprising a respective plurality of conductive nanostructures. More specifically, the non-conductive gap, the first and second non-conductive boundaries do not have a conductive network of metal nanostructures.

In one embodiment, the etching completely removes all of the metal nanostructures in the non-conductive gaps, the first and second non-conductive boundaries. In another embodiment, the etching partially etches the metal nanostructures within the non-conductive gaps, the first and second non-conductive boundaries, causing structural defects.

Drawings

In the drawings, like reference numbers indicate similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.

Fig. 1 shows a prior art transparent conductor in which the pattern of conductive lines is visible.

Fig. 2-4 illustrate transparent conductors having invisible or low visibility patterns according to various embodiments of the present disclosure.

Detailed Description

Transparent conductive films are basic elements in flat panel displays such as touch screens or Liquid Crystal Displays (LCDs). They not only determine the electrical properties of these devices, but also have a direct impact on the optical performance and durability of these components.

For touch screen sensors, whether capacitive or resistive, one or two transparent conductive films are used to carry current under the touch panel. The transparent conductive film is patterned into conductive lines to detect coordinates of a touch input position. When the touch panel is touched, a small voltage change is detected at the touch input position (in a resistive touch sensor).

Typically, the transparent conductor can be patterned by etching or direct printing. Patterning is performed to create electrically insulating regions that are free of conductive material and that have been removed by etching or printing. The conductive and insulating regions in the patterned transparent conductor typically interact differently with ambient light or backlight of the device. Thus, the pattern becomes visible.

Therefore, when creating a pattern of conductive lines on a film for a flat panel display, it is desirable to minimize the visibility of the pattern. For ITO-based transparent conductors, the pattern is visible due to the difference in refractive index of the ITO and the etched and insulated regions. Therefore, as a countermeasure, the etched pattern of ITO typically requires a refractive index matched coating.

For conductive films comprising a network of metal nanowires, light scattering from the reflective metal surface also contributes to the visibility of the pattern. Fig. 1 shows a portion of a patterned transparent conductor (10) comprising a conductive line (20) having a line width of 1 mm. Every two adjacent conductive lines are electrically insulated by a 3mm wide insulating region (30) without metal nanostructures. In these respects, the pattern is generally visible when compared to the insulating regions (30) due to the difference in the amount of light scattered in the conductive regions (20).

One way to minimize the visibility of the pattern is to minimize the optical difference between the conductive and insulating regions. Us patent No. 8018569 and us published application No. 2008/0143906 describe transparent conductors with low visibility patterns created by partially etching nanowires to provide insulating regions. The partial etching does not completely remove the nanowires. Rather, it breaks or creates nicks in the nanostructure such that it is non-conductive without substantially changing its light scattering properties.

Disclosed herein are alternative methods of minimizing optical differences between conductive and insulating regions. In particular, a low-visibility or invisible pattern is created by "low visibility or invisibility of the islands". In various embodiments, the conductive lines (comprised of metal nanostructures) are electrically insulated from each other by insulating regions. The insulating regions are not free of conductive material. In contrast, the insulating regions are mainly filled with conductive material islands (i.e. also consisting of metal nanowires), which are electrically insulated from each other by non-conductive gaps. This approach effectively minimizes the total non-conductive area without light scattering nanostructures, thus making it more difficult to visualize. At the same time, the electrical insulation between the conductive wires is maintained by a non-conductive gap.

Accordingly, the present disclosure provides a patterned transparent conductor comprising:

a substrate, a first electrode and a second electrode,

a first conductive line on the substrate, wherein the first conductive line comprises a first conductive nanostructured network and has a first longitudinal direction;

a second conductive line on the substrate, wherein the second conductive line comprises a second conductive nanostructured network and has a second longitudinal direction; and

an insulating region electrically insulating the first conductive line from the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along a first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along a second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on a non-conductive substrate and electrically insulated from each other by non-conductive gaps, each island of conductive material comprising a respective plurality of conductive nanostructures.

Fig. 2-4 show specific embodiments for the "invisible through islands" approach. Fig. 2 shows a patterned transparent conductor (100) comprising conductive lines (110a, 110b, and 110c) composed of a metal nanostructured network (116). Two adjacent conductive lines are electrically isolated by an insulating region (120a, 120b, or 120 c). The insulating region (120a) adjoins two adjacent conductive lines (120a and 120b) by a first non-conductive boundary (130a) and a second non-conductive boundary (130b), respectively. The insulating region (e.g., 120a) also includes a plurality of islands of conductive material (e.g., 140a, 144a), each island being composed of a metal nanostructure (118). In this embodiment, the conductive material islands are regular-shaped parallelograms (including rectangles, squares, diamonds, rhombuses, etc.), and the first and second non-conductive boundaries are substantially straight and parallel to the longitudinal direction (160a, 160b, 160c) of the conductive lines (110a, 110b, 110c), respectively. The islands of conductive material are electrically isolated from each other by a non-conductive gap (150).

As shown in fig. 2, the conductive material islands make the patterned conductive lines less visible when compared to the conductive lines in fig. 1. However, due to the significance of the human brain in distinguishing patterns, the observer is still able to distinguish regular patterns such as the rectangular island rows in fig. 2, depending on the observation conditions (e.g., illumination, viewing angle).

Thus, in another embodiment, the islands of conductive material are irregularly shaped. In other words, the non-conductive gaps are irregular and random. As shown in fig. 3, the patterned transparent conductor (200) has conductive lines (210a, 210b, 210c) composed of a metallic nanostructured network (216). Two adjacent conductive lines are electrically isolated by an insulating region (220a, 220 b). The insulating region (220a) adjoins two adjacent conductive lines (210a and 210b) by a first non-conductive boundary (230a) and a second non-conductive boundary (230b), respectively. The insulating region (e.g., 220a) also includes a plurality of islands of conductive material (e.g., 240a, 244a), each island of conductive material being composed of a metal nanostructure (218). In this embodiment, although the first and second non-conductive boundaries defining the conductive line are substantially flat and parallel to the longitudinal direction (260a, 260b, 260c) of the conductive line (210a, 210b, 210c), respectively, the islands of conductive material do not have a discernible pattern as to their respective shape and size, meaning that the non-conductive gaps (250) that electrically isolate any adjacent islands are also irregular.

In yet another embodiment, because the non-conductive boundary defining the conductive line is irregularly shaped, the conductive material is also irregularly shaped. In this embodiment, the transparent conductor is considered to be "patterned" in that it provides conductive lines that extend substantially along the same longitudinal direction, despite the islands and the boundaries defining the conductive lines being irregular and random. As shown in fig. 4, the patterned transparent conductor (200) has conductive lines (310a, 310b, 310c) composed of a metallic nanostructured network (316). Two adjacent conductive lines are electrically isolated by an insulating region (320a, 320 b). The insulating region (320a) adjoins two adjacent conductive lines (310a and 310b) by a first non-conductive boundary (330a) and a second non-conductive boundary (330b), respectively. The insulating region (e.g., 320a) also includes a plurality of conductive material islands (e.g., 340a, 344a), each of the conductive material islands being composed of metal nanostructures (318). In the present embodiment, the first and second non-conductive boundaries defining the conductive line are irregular, but generally extend along the longitudinal direction (360a, 360b, 360c) of the conductive line (310a, 310b, 310c), respectively. The conductive material islands (e.g., 340a, 340b) have no discernable pattern with respect to their respective shapes and sizes, meaning that the non-conductive gaps (350) that electrically isolate any adjacent islands are also irregular. The combined effect of the irregular boundaries of the conductive lines and the random shape of the islands of conductive material disturbs the human brain's ability to recognize patterns while minimizing the optical differences between the conductive lines and the insulating regions. As a result, the pattern of the conductive lines is not visible or has low visibility.

In each of the embodiments described herein, there is no conductive nanostructured network within the non-conductive boundaries and non-conductive gaps (collectively, "non-conductive regions"), thereby forming electrical insulation between any adjacent islands of conductive material (e.g., 140a and 144a) or between a conductive line (110a) and an adjacent island of conductive material (140 a).

In certain embodiments, the conductive network is not present in the non-conductive areas because the metal nanostructures are not present in the non-conductive areas, i.e., they are completely removed by etching or are not printed on the non-conductive areas.

In other embodiments, the metal nanostructures, although present in the non-conductive region, do not form a conductive network due to certain structural defects in the metal nanostructures. In particular, the metal nanostructures in the non-conductive region may be partially etched, causing the nanostructures to break down or to be notched out of the conductive network. Thus, the non-conductive region retains a certain amount of the non-conductive nanostructures. The combined effect of the partial etching and the islands provides an improved level of low visibility.

Generally, the conductive lines (110a, 110b, 110c) may be 0.5-5mm wide. In various embodiments, the line width may be about 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, or 5mm, or any range between any two of the foregoing values.

As discussed in further detail herein, the line widths of the non-conductive gaps and non-conductive boundaries are determined by a particular etching or printing method. Typically, to minimize visibility while maintaining effective electrical isolation, the line width is about 10-500 microns, or more commonly 100-500 microns. In some embodiments, the line width is about 200 microns.

The islands of conductive material, regardless of their (regular or random) shape, may be of the same or different sizesCun. The surface area of the islands of conductive material is generally in the range of 0.1 to 10mm²Or, more commonly, 0.5-2mm²Within the range of (a).

As used herein, "about" means within ± 20% of a particular value. For example, the phrase "about 1 mm" may include a range of 1 millimeter ± 20%, i.e., 0.8 to 1.2 microns.

Certain features of the present disclosure are discussed further below in greater detail.

Metal nanostructures

As used herein, "metal nanostructures" generally refers to electrically conductive, nano-sized structures having at least one dimension (i.e., width or diameter) less than 500 nm; more typically, less than 100nm or 50 nm. In various embodiments, the width or diameter of the nanostructures is in the range of 10 to 40nm, 20 to 40nm, 5 to 20nm, 10 to 30nm, 40 to 60nm, 50 to 70 nm.

The nanostructures may be of any shape or geometry. One method for defining the geometry of a given nanostructure is by its "aspect ratio," which refers to the ratio of the length and width (or diameter) of the nanostructure. In certain embodiments, the nanostructures are isotropic in shape (i.e., aspect ratio of 1). Typical isotropic or substantially isotropic nanostructures comprise nanoparticles. In a preferred embodiment, the shape of the nanostructures is anisotropic (i.e., aspect ratio ≠ 1). Anisotropic nanostructures typically have a longitudinal axis along their length. Exemplary anisotropic nanostructures include nanowires (solid nanostructures having an aspect ratio of at least 10, more typically at least 50), nanorods (solid nanostructures having an aspect ratio of less than 10), and nanotubes (hollow nanostructures).

The length of the anisotropic nanostructures (e.g., nanowires) in the longitudinal direction each exceeds 500nm, or exceeds 1 μm, or exceeds 10 μm. In various embodiments, the nanostructures have a length in the range of 5 to 30 μm, or in the range of 15 to 50 μm, 25 to 75 μm, 30 to 60 μm, 40 to 80 μm, or 50 to 100 μm.

The metal nanostructures are typically metallic materials, including metallic elements (e.g., transition metals) or metallic compounds (e.g., metal oxides). The metallic material may also be a bimetallic material or a metal alloy, which includes two or more metals. Suitable metals include, but are not limited to, silver, gold, copper, nickel, gold and silver plated, platinum, and palladium. It should be noted that while the present disclosure primarily describes nanowires (e.g., silver nanowires), any nanostructure within the above definition may be employed as well.

Typically, the metal nanostructures are metal nanowires having an aspect ratio in the range of 10 to 100000. Larger aspect ratios may be advantageous for obtaining transparent conductor layers because they may enable the formation of more efficient conductive meshes while allowing lower overall densities for high transparency wires. In other words, when using conductive nanowires with a high aspect ratio, the density of nanowires that realize the conductive network can be low enough to make the conductive network substantially transparent.

The metal nanowires can be prepared by methods well known in the art. Specifically, silver nanowires can be synthesized by liquid phase reduction of a silver salt (e.g., silver nitrate) containing a polyol (e.g., ethylene glycol) and polyvinylpyrrolidone. Mass production of uniform size silver nanowires can be prepared and purified according to the methods described in U.S. published applications No. 2008/0210052, 2011/0024159, 2011/0045272, and 2011/0048170, under the name of Cambrios Technologies, inc.

Conductive mesh

Conductive mesh refers to a layer of interconnected metallic nanostructures (e.g., nanowires) that provide a conductive medium for a transparent conductor. Since electrical conductivity is achieved by the penetration of charge from one metal nanostructure to another, sufficient metal nanowires must be present in the conductive network to reach the electrical percolation threshold and conduct electricity. The surface conductivity of the conductive network is inversely proportional to its surface resistivity, sometimes referred to as sheet resistance, which can be measured by methods well known in the art. As used herein, "conductive" or simply "conducting" corresponds to a surface resistivity of no more than 104 Ω/□, or more typically no more than 1000 Ω/□, or more typically no more than 500 Ω/□, or more typically no more than 200 Ω/□. The surface resistivity depends on a number of factors such as aspect ratio, alignment, cohesion and resistivity of the interconnected metal nanostructures.

In certain embodiments, the metal nanostructures can form a conductive network on the substrate without the use of an adhesive. In other embodiments, an adhesive may be present to facilitate adhesion of the nanostructures to the substrate. Suitable adhesives include light transmissive polymers including, but not limited to: polyacrylates such as polymethacrylates (e.g., poly (methyl methacrylate)), polyacrylates and polyacrylonitriles, polyvinyl alcohols, polyesters (e.g., polyethylene terephthalate (PET), polyester naphthalenes, and polycarbonates), polymers such as phenolics or cresol formaldehyde (r: (r))) High aromatic polymers of (a), polystyrene, polyvinyltoluene, polyvinylxylene, polyimide, polyamide, polyamideimide, polyetherimide, polysulfide, polysulfone, polyphenylene and polyphenylene ether, Polyurethane (PU), epoxy resin, polyolefin (e.g., polypropylene, polymethylpentene and cycloolefin), acrylonitrile-butadiene-styrene copolymer (ABS), cellulose, silicone and other silicon-containing polymers (e.g., polysilsesquioxane and polysilane), polyvinyl chloride (PVC), polyacetate, polynorbornene, synthetic rubber (e.g., EPR, SBR, EPDM), and fluoropolymers (e.g., polyvinylidene fluoride, polytetrafluoroethylene (TFE) or polyhexafluoropropylene), fluoro-olefin copolymers and olefins (e.g.,) And amorphous fluorocompound polymer or copolymerPolymer (e.g., of Asahi Glass Inc.)Or Du Pont corporationAF)。

By "substrate" is meant a non-conductive material on which the metal nanostructures are coated or laminated. The substrate may be rigid or flexible. The substrate may be transparent or opaque. Suitable rigid substrates include, for example, glass, polycarbonate, acrylic, and the like. Suitable flexible substrates include, but are not limited to: polyesters (e.g., polyethylene terephthalate (PET), polyester naphthalene, and polycarbonate), polyolefins (e.g., linear, branched, and cyclic polyolefins), polyethylenes (e.g., polyvinyl chloride, polyvinylidene chloride, polyvinyl acetal, polystyrene, polyacrylates, etc.), cellulose ester groups (e.g., cellulose triacetate, cellulose acetate), polysulfones such as polyethersulfones, polyimides, silicones, and other common polymer films. Other examples of suitable substrates can be found, for example, in U.S. patent No. 6975067.

In general, the optical transparency or clarity of a transparent conductor (that is, a conductive mesh on a non-conductive substrate) can be quantitatively defined by parameters including light transmittance and haze. "light transmittance" (or "light transmittance") refers to the percentage of incident light that is transmitted through a medium. In various embodiments, the light transmittance of the conductive layer is at least 80%, and can be as high as 98%. Performance enhancing layers, such as adhesive layers, anti-reflective layers, or anti-glare layers, may also help reduce the overall optical transmission of the transparent conductor. In various embodiments, the light transmittance (T%) of the transparent conductor may be at least 50%, at least 60%, at least 70%, or at least 80%, and may be as high as at least 91% to 92%, or at least 95%.

Haze (H%) is a measure of light scattering. It refers to the percentage of the amount of light that separates and scatters from the incident light during transmission. Unlike light transmission, which depends largely on the media properties, haze is generally a product of interest and is typically caused by surface roughness and particle or compositional heterogeneity embedded in the media. In general, the haze of a conductive film can be significantly affected by the diameter of the nanostructures. Larger diameter nanostructures (e.g., thicker nanowires) are generally associated with higher haze. In various embodiments, the haze of the transparent conductor is no more than 10%, no more than 8%, or no more than 5%, and can be as low as no more than 2%, no more than 1%, or no more than 0.5%, or no more than 0.25%.

Coating composition

The patterned transparent conductor according to the present disclosure is prepared by coating a coating composition comprising nanostructures on a non-conductive substrate. To form a coating composition, the metal nanowires are typically dispersed in a volatile liquid to facilitate the coating process. It is to be understood that any non-corrosive, volatile liquid in which the metal nanowires can be stably dispersed, as used herein, can be employed. Preferably, the metal nanowires are dispersed in water, alcohol, ketone, ether, hydrocarbon or aromatic solvent (benzene, toluene, xylene, etc.). More preferably, the liquid is volatile, having a boiling point of no more than 200 ℃, no more than 150 ℃, or no more than 100 ℃.

In addition, the metal nanowire dispersion may include additives and binders to control viscosity, corrosivity, adhesion, and nanowire dispersion. Examples of suitable additives and binders include, but are not limited to, carboxymethylcellulose (CMC), 2-hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), Methylcellulose (MC), polyvinyl alcohol (PVA), tripropylene glycol (TPG), and Xanthan Gum (XG), as well as surfactants and copolymers thereof such as ethoxylates, alkoxylates, ethylene oxide, and propylene oxide, sulfonates, sulfates, sulfonates, sulfosuccinates, phosphate esters, and fluorosurfactants (e.g., DuPont corporation's, Inc.))。

In one example, the nanowire dispersion or "ink" includes (by weight) from 0.0025% to 0.1% of a surfactant (e.g., for use inPreferred ranges for FSO-100 are from 0.0025% to 0.05%), from 0.02% to 4% viscosity modifiers (e.g., preferred ranges for HPMC are from 0.02% to 0.5%), from 94.5% to 99.0% solvent, and from 0.05% to 1.4% metal nanowires. Representative examples of suitable surfactants includeTriton (x100, x114, x45), Dynol (604, 607), n-dodecyl-b-D-maltoside and Novek. Examples of suitable viscosity modifiers include Hydroxypropylmethylcellulose (HPMC), methylcellulose, xanthan gum, polyvinyl alcohol, carboxymethylcellulose, and hydroxyethylcellulose. Examples of suitable solvents include water and isopropanol.

The concentration of the dispersed nanowires can be influenced or determined by parameters such as thickness, conductivity (including surface conductivity), optical transparency, and mechanical properties of the nanowire mesh layer. The percentage of solvent can be adjusted to provide the desired concentration of nanowires in the dispersion. However, in preferred embodiments, the relative ratios of the other ingredients may remain the same. In particular, the ratio of surfactant to viscosity modifier is preferably in the range of about 80 to about 0.01; the ratio of viscosity modifier to metal nanowires is preferably in the range of about 5 to about 0.000625; and the ratio of metal nanowires to surfactant is preferably in the range of about 560 to about 5. The ratio of the dispersed components can be modified depending on the substrate and the application method used. The preferred viscosity range for the dispersion of nanowires is between about 1 and 100 cP.

After coating, the volatile liquid is removed by evaporation. Evaporation can be accelerated by heating (e.g., baking). The resulting nanowire mesh layer may require post-processing to make it conductive. As described below, such post-treatment may be a treatment step comprising thermal exposure, plasma, corona discharge, ultraviolet ozone or pressure.

Examples of suitable coating compositions are described in U.S. published applications nos. 2007/0074316, 2009/0283304, 2009/0223703, and 2012/0104374, all in the name of cambrios technologies, inc.

The coating composition is applied to the substrate by, for example, plate coating, web coating, printing, and laminating methods to provide a transparent conductor. Additional information for fabricating transparent conductors from conductive nanostructures is disclosed, for example, in U.S. published patent applications nos. 2008/0143906 and 2007/0074316, both in the name of cambrios technologies, inc.

Patterned transparent conductor

As used herein, "patterning" refers broadly to methods for creating conductive lines and insulating regions. The "patterning" does not have to create any repeating features, other than any two conductive lines that are electrically insulated from each other by insulating regions. Typically, the conductive lines extend substantially in the same longitudinal direction even though they have irregular non-conductive boundaries (see, e.g., fig. 4).

The patterning also provides islands of conductive material within the insulating regions. As discussed herein, the conductive material islands may or may not have a regular or repeating shape, and may or may not have the same or different surface area. However, the insulating regions are considered to be "patterned" as long as the islands of conductive material are electrically isolated from each other by the non-conductive gaps.

Thus, a "patterned" transparent conductor defines an arrangement of conductive lines and insulating regions with islands. As used herein, the pattern of transparent conductors described herein is invisible or has low visibility because the conductive lines and the insulating regions have substantially the same light scattering or haze. In particular, any difference in haze corresponding to light scattering should be less than 1%, or more typically, less than 0.5%, or less than 0.1%, or less than 0.01%.

Patterning can be performed by direct printing, laser ablation, or etching, all of which involve applying a nanostructure-containing coating composition. In certain embodiments, the coating composition may be printed directly on the substrate according to a desired pattern, i.e., arrangement of conductive lines and insulating regions with islands. Suitable printing methods may include, for example, screen printing. Accordingly, one embodiment provides a method of manufacturing a transparent conductor having a low visibility pattern. The method comprises the following steps: printing directly on a non-conductive substrate a coating composition having a plurality of metallic nanostructures and a volatile liquid carrier according to a pattern, and removing the volatile liquid carrier, wherein the pattern defines a first conductive line having a first longitudinal direction on the non-conductive substrate; a second conductive line having a second longitudinal direction on the non-conductive substrate, and an insulating region electrically isolating the first conductive line from the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along the first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along the second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on the non-conductive substrate and electrically isolated from each other by non-conductive gaps, each island of conductive material comprising a corresponding plurality of conductive nanostructures, and wherein the non-conductive gaps and the first and second non-conductive boundaries do not have any metal nanostructures.

In some embodiments, the non-conductive boundary and the non-conductive gap are etched in successive steps (e.g., using two different masks). In other embodiments, they are etched in a single step (e.g., using one mask).

In another embodiment, the pattern is created by first coating the metal nanostructures and then etching the metal nanostructures to form non-conductive regions comprising non-conductive boundaries and non-conductive gaps between the islands. More specifically, the method comprises: applying a coating composition on a non-conductive substrate, the coating composition having a plurality of metallic nanostructures and a volatile liquid carrier; removing the volatile liquid carrier to provide a conductive network of metal nanostructures; and etching the conductive mesh according to a pattern, wherein the pattern defines a first conductive line having a first longitudinal direction on the non-conductive substrate; a second conductive line having a second longitudinal direction on the non-conductive substrate, and an insulating region electrically isolating the first conductive line from the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along the first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along the second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on the non-conductive substrate and electrically insulated from each other by non-conductive gaps, each island of conductive material comprising a corresponding plurality of conductive nanostructures, and a conductive mesh wherein the non-conductive gaps and the first and second non-conductive boundaries do not have metal nanostructures.

In some embodiments, the non-conductive gap and the first and second non-conductive boundaries are completely etched such that no metal nanostructures are present.

Typically, the etching solution is screen printed onto the nanostructure-coated substrate through a mask that defines the conductive lines and islands. Thus, the etching provides a non-conductive region comprising the non-conductive gap and the first and second non-conductive boundaries. Suitable etching solutions typically include strong acids (e.g., HNO)₃) And optionally one or more oxidizing agents (e.g., KMnO)₄). Examples of suitable etching solutions include those described in U.S. published patent application No. 20080143906 in the name of Cambrios Technologies, inc.

In other embodiments, the non-conductive gap and the first and second non-conductive boundaries are partially etched such that the metal nanostructures are broken or notched and no conductive mesh is formed. Etching solutions capable of partially etching metal nanostructures are described in U.S. published patent applications No. 20100243295 and No. 2011/0253668, in the name of Cambrios Technologies, inc.

The structure of the transparent conductor, its electrical and optical properties, and the patterning method are explained in more detail by the following non-limiting examples.

Examples of the invention

Example 1

Synthesis of silver nanowires

Silver nanowires are synthesized by reducing silver nitrate dissolved in ethylene glycol containing poly (vinyl pyrrolidone) (PVP) according to the "polyol" method described, for example, in "Crystalline silver nanowires by soft solution treatment" (y. sun, b. gates, b. mayers, & y. xia), Nanoletters, (2002), 2(2) 165-. The modified polyol process described in U.S. application No. 11/766552, entitled Cambrios Technologies, inc, produces more uniform silver nanowires at higher yields than the traditional "polyol" process. This application is incorporated by reference herein in its entirety.

Example 2

Low visibility patterning

A suspension of HPMC, silver nanowires and water was prepared. The suspension was spin coated on a glass substrate to form a conductive film of silver nanowires in an HPMC matrix. The conductive layer is optically transparent, having a light transmission (% T) of about 88.1% and a haze (% H) of about 2.85%. The conductive layer is also highly surface conductive, having a surface resistivity of about 25 Ω/□.

Thereafter, a region of the conductive film is treated with an oxidizing agent (e.g., a bleaching solution with 0.5% hypochlorite) for 2 minutes. The treated membrane was then rinsed with water and dried in a nitrogen environment. The treated regions of the film exhibited approximately the same transmission (89.1% T) and haze (5.85% H) as compared to the optical properties of the untreated regions. The treated and untreated areas were visually consistent.

However, the surface resistivity of the treated region increases by several orders of magnitude and becomes effectively insulating.

In addition, the silver nanowires are destroyed or may have been converted to an insoluble and insulating silver salt, such as silver chloride.

Conductive films based on silver nanowires are treated with a stronger and more concentrated oxidant-30% hydrogen peroxide. In the treatment zone, almost all of the nanowires and the organic HPMC matrix were dissolved. The optical properties in the treated and untreated areas are significantly different.

Example 3

Photoresist patterning method

A silver nanowire dispersion comprising 0.2% HPMC, 250ppm triton x100, and silver nanowires was prepared. The dispersion was spin coated onto the substrate and baked at 180 ℃ for 90 seconds. This nanowire film was then spin-coated using AZ-3330F photoresist to prepare a 2.5 μm transparent conductive film. Then, the transparent conductor was baked at 110 ℃ for 60 seconds. The photomask was placed in contact with portions of the photoresist layer and the transparent conductor was exposed to 12MW/cm2 for 20 seconds. Then, the conductor was baked at 110 ℃ for 60 seconds.

The photoresist was then developed, rinsed and spin dried using AZ300MIF developer. Thereafter, the conductor was exposed to a silver etchant from Transene corporation for 10 seconds, rinsed and spin dried. Then, the photoresist was stripped using acetone. The transparent conductor was overcoated with 2.5% diluted polyester resin PCX35-39B in PGME and then cured at 180 ℃ for 45 minutes. The resulting patterned transparent conductor has a line width of from 5 to 10 μm. Larger pattern linewidths can also be obtained using photoresists and other patterning methods disclosed herein.

For example, line widths of 10 μm to 300 μm and 10 μm to 50 μm have been obtained.

Example 4

Low visibility patterning by copper chloride etchant

By mixing 240 grams of CuCI₂-2H₂O and 180 g of concentrated saltAn acid (37% w/w) and 580 grams of water were used to prepare the etchant solution. CuCI₂Is about 19%, and hydrochloric acid is 6.8%.

Silver nanowire conductive films were prepared according to the methods described herein. The conductive film was etched, and it was observed that the two regions showed almost no difference in optical properties, but the etched region had lower conductivity and had a resistivity of about 20.000 Ω/sq.

Example 5

Low visibility patterning by thermal etching

Example 5 illustrates the creation of a low visibility pattern in a conductive film by a combination of a partial etch step and a subsequent heating step. As discussed herein, heating completes the etch by further causing the etched region to be non-conductive or low conductive.

Table 1 shows a separate heating step that actually increases the conductivity of the unetched conductive film. In tests a and B, the conductive film (or sample) was heated for five and thirty minutes, respectively, and its sheet resistivity (R) was_s) Respectively reduced by 5% and 10%.

TABLE 1

Table 2 shows the effect of heating on the partially etched samples. In the three tests listed, samples were tested using CuCI₂The etchant (as described in example 18) chemically etches until its sheet resistivity is approximately 1000 Ω/sq. It is then heated at 130 ℃ for up to five minutes, but may be as little as one minute. In each test, the heating step was sufficient to render the sample non-conductive. In other words, the damage of the nanowire network, initially caused by the etching process, is accomplished by the heating process.

TABLE 2

Table 3 shows that if the initial chemical etching step is insufficient, i.e. the damage of the nanowires is insufficient; it is difficult to render the sample non-conductive even with a subsequent heating step. In test F, the sample was etched until its resistance value changed from 108 Ω/sq to 120 Ω/sq. Followed by heating at 130 c for one minute without changing the resistance of the sample. In test G, another sample was etched until its resistance value changed from 121 Ω/sq to 198 Ω/sq. Subsequently, heating at 130 ℃ for up to 25 minutes, continuously increasing the resistivity of the sample; however, the sheet resistance failed to exceed 685 Ω/sq. This indicates that the initial partial etch is important to bring the etched region to a threshold resistivity (which represents the degree of damage to the nanostructure) in order to complete the etch using the heating step.

TABLE 3

Table 4 compares the optical properties of two patterned samples: the samples in test I were chemically etched (by CuCI2 etchant) to render them non-conductive, while the coupon portion in test H was etched followed by heating.

In test H, the initial partial etch changed the resistivity from 105 Ω/sq to 602 Ω/sq, which was sufficient to render the sample non-conductive for the subsequent heating step. As shown, the final optical properties of the samples were nearly identical to the initial properties (before etching), i.e., the difference in haze (H%) was about 0.01% and the difference in transmission (T%) was about 0.1%. The samples had a low visibility pattern.

In test I, the sample was etched to be completely non-conductive. Herein, although the transmittance before and after etching remained the same, the haze was reduced by about 0.07% compared to the haze value of the pre-etching. The larger difference between the haze of the etched and unetched regions of the film in trial I (compared to trial H) makes those etched regions in trial H more visible.

TABLE 4

All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the application data sheet, are incorporated herein by reference, in their entirety.

From the foregoing, it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention.

Claims (13)

1. A patterned transparent conductor comprising:

a non-conductive substrate;

a first conductive line on the non-conductive substrate, the first conductive line comprising a first conductive nanostructured network and having a first longitudinal direction;

a second conductive line on the non-conductive substrate, the second conductive line comprising a second conductive nanostructured network and having a second longitudinal direction; and

an insulating region electrically isolating the first conductive line from the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along the first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along the second longitudinal direction,

wherein the insulating region comprises a plurality of islands of conductive material disposed on the non-conductive substrate and electrically isolated from each other by non-conductive gaps, each island of conductive material comprising a corresponding plurality of conductive nanostructures, the non-conductive gaps being partially etched from the first and second non-conductive boundaries without forming a conductive mesh.

2. The patterned transparent conductor of claim 1 wherein the first longitudinal direction and the second longitudinal direction are parallel to each other.

3. The patterned transparent conductor of claim 1 wherein the first non-conductive boundary is straight.

4. The patterned transparent conductor of claim 1 wherein the second non-conductive boundary is straight.

5. The patterned transparent conductor of claim 1 wherein the first non-conductive boundary is irregular.

6. The patterned transparent conductor of claim 5 wherein the second non-conductive boundary is straight.

7. The patterned transparent conductor of claim 1 wherein the islands of conductive material are parallelogram shaped.

8. The patterned transparent conductor of claim 1 wherein the conductive material islands are irregularly shaped.

9. The patterned transparent conductor of claim 1 wherein the islands of conductive material have a surface area in the range of 0.1-10 square millimeters.

10. The patterned transparent conductor of claim 1 wherein the islands of conductive material have a surface area in the range of 0.5-2 square millimeters.

11. The patterned transparent conductor of claim 1 wherein the non-conductive gaps, the first non-conductive boundary, and the second non-conductive boundary have metallic nanostructures with band-structure defects that render the metallic nanostructures incapable of forming a conductive mesh.

12. A method of manufacturing a transparent conductor having a low-visibility pattern, the method comprising:

applying a coating composition on a non-conductive substrate, the coating composition having a volatile liquid carrier and a plurality of metallic nanostructures;

removing the volatile liquid carrier to provide a conductive network of metal nanostructures; and

etching the conductive mesh according to a pattern, wherein the pattern defines a first conductive line having a first longitudinal direction on the non-conductive substrate; a second conductive line having a second longitudinal direction on the non-conductive substrate, and an insulating region electrically insulating the first conductive line from the second conductive line, the insulating region having a first non-conductive boundary laterally abutting the first conductive line along the first longitudinal direction and a second non-conductive boundary laterally abutting the second conductive line along the second longitudinal direction, wherein the insulating region comprises a plurality of islands of conductive material disposed on the non-conductive substrate, each island of conductive material comprising a respective plurality of conductive nanostructures, the non-conductive gaps and the first and second non-conductive boundaries being partially etched without forming a conductive mesh.

13. The method of claim 12, wherein the etching partially etches the metal nanostructures within the non-conductive gaps, the first non-conductive boundary, and the second non-conductive boundary, resulting in structural defects.