Conductive ink for rollerball pen and conductive trace formed on substrate

Abstract

To provide a conductive ink for a rollerball pen and a conductive trace formed on a substrate.SOLUTION: A conductive ink for a rollerball pen comprises an aqueous solvent and conductive particles comprising one or more metals dispersed therein at a concentration of at least about 30 wt.%. The conductive particles include conductive flakes and conductive nanoparticles. A dispersant covers the conductive particles at a loading level of at least about 0.1 mg / m2 to about 0.8 mg / m2. A conductive trace deposited on a substrate from a rollerball pen comprises a percolative network of conductive particles comprising one or more metals. The conductive particles include conductive flakes and conductive nanoparticles. The conductive trace has a conductivity of at least about 1% of a bulk metal conductivity, and a reflectance of more than 40%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] (Related Applications) This patent document claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62 / 005,305, filed May 30, 2014, which is hereby incorporated by reference in its entirety.

[0002] (Technical field) FIELD OF THE DISCLOSURE This disclosure relates generally to ink formulations and more particularly to conductive inks that can be written onto paper and other substrates to form conductive traces. [Background technology]

[0003] (background) Printed electronics constitute an emerging class of materials with potential applications in photovoltaics, transistors, displays, batteries, antennas, and sensors. Recent attention has focused on paper substrates as a low-cost platform material that enables flexible, lightweight, and disposable devices. Such devices require conductive electrodes, which to date have been deposited by sputter coating, inkjet printing, and airbrush spraying. However, these deposition methods can be expensive or use dilute inks that tend to penetrate the paper substrate.

[0004] Paper substrates offer many advantages for printed electronic devices. Not only is paper widely available and inexpensive, it is lightweight, biodegradable, and can be rolled or folded into three-dimensional (3D) shapes. Functional electronic components have recently been fabricated on paper substrates, including thermochromic displays, disposable radio frequency identification (RFID) tags, and cellulosic batteries. The variety of available paper textures, compositions, and coatings can be exploited to enable specific device architectures. A facile means for creating devices "on the fly" under ambient conditions would enable the full potential of paper-based printed electronics to be exploited. Summary of the Invention [Means for solving the problem]

[0005] (Brief summary) A conductive ink for a rollerball pen includes an aqueous solvent and conductive particles, including one or more metals, dispersed in the aqueous solvent at a concentration of at least about 30 wt %. The conductive particles include conductive flakes and conductive nanoparticles. The dispersant has a concentration of at least about 0.1 mg / m 2 to approximately 0.8 mg / m 2 The conductive particles are coated at a loading level of 0.1g.

[0006] The conductive trace deposited on the substrate from the rollerball pen comprises a percolated network of conductive particles comprising one or more metals. The conductive particles include conductive flakes and conductive nanoparticles. The conductive trace has a conductivity of at least about 1% of the bulk metal conductivity and a reflectivity of greater than 40%.

[0007] The conductive traces are formed by supplying conductive ink to a rollerball pen; moving the rollerball pen over a surface to deposit the conductive ink on the surface; and and drying the conductive ink, thus forming the conductive traces. The conductive ink comprises an aqueous solvent and conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %. The conductive particles include conductive flakes and conductive nanoparticles. The dispersant is preferably at a concentration of about 0.1 mg / m 2 to approximately 0.8 mg / m 2 The conductive particles are coated at a loading level of 0.1g.

[0008] A method for forming a conductive trace includes supplying a conductive ink to a rollerball pen, moving the rollerball pen over a surface to deposit the conductive ink on the surface, and drying the conductive ink at room temperature, thereby forming a conductive trace. The conductive ink includes an aqueous solvent and conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %. The conductive particles include conductive flakes and conductive nanoparticles, and the dispersing agent is at a concentration of about 0.1 mg / m 2 to approximately 0.8 mg / m 2 The conductive particles are coated at a loading level of 0.1g.

[0009] The terms "comprise," "comprise," "include," and "have" are used interchangeably throughout this disclosure as open-ended terms referring to listed elements (or steps) without excluding unlisted elements (or steps). [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows several conductive traces formed on a piece of paper to provide connections between electronic devices.

[0011] [Figure 2] 2A and 2B show scanning electron microscope (SEM) images of exemplary conductive traces formed on copy paper at two different magnifications.

[0012] [Figure 3] 3A and 3B show SEM images of exemplary conductive traces formed on photo paper at two different magnifications.

[0013] [Figure 4] FIG. 4 shows the deposition of conductive ink onto a paper substrate from a rollerball pen held in place and moved by a plotter.

[0014] [Figure 5] FIG. 5 shows computed tomography (CT) images of conductive traces formed on copy paper and photo paper at different plotter scanning speeds (1 mm / s, 10 mm / s, and 100 mm / s). DETAILED DESCRIPTION OF THE INVENTION

[0015] (Detailed explanation) Highly stable, fast-drying conductive ink formulations have been developed for use in rollerball pens to form conductive traces on a wide range of substrates. The conductive traces can contain metals such as silver and exhibit conductivities approaching 20% ​​of the bulk conductivity of the metal. The conductive inks can be deposited on paper, plastic, and other flexible or rigid substrates to form traces that can be used as wiring for electronic devices, as shown, for example, in Figure 1.

[0016] 2A and 2B show scanning electron microscope (SEM) images at two different magnifications of an exemplary conductive trace formed on copy paper, and FIGS. 3A and 3B show SEM images at two different magnifications of an exemplary conductive trace formed on photographic paper. The conductive trace comprises a percolated network of conductive particles comprising silver. As shown in FIGS. 2B and 3B, the conductive particles can include conductive particles of different sizes and morphologies, including flakes and nanoparticles.

[0017] The conductive ink used to form the traces comprises an aqueous solvent and conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %. 2 to approximately 0.8 mg / m 2 The conductive particles include conductive flakes and conductive nanoparticles, as shown, for example, in FIG. 2B after deposition.

[0018] Due to the high loading levels of conductive particles in conductive ink formulations, low resistance conductive traces can be formed when the ink is deposited on paper (or another substrate). Also, the use of conductive particles with bimodal size distributions and / or different morphologies can improve particle packing in the conductive traces, thereby promoting percolation (the formation of electrically continuous pathways through the conductive particles).

[0019] Preferably, the conductive ink has a long shelf life or dispersion stability, which, as will be appreciated by those skilled in the art, may not be compatible with achieving high solids (particle) loadings. The addition of dispersants to enhance ink stability can also adversely affect the conductivity of traces written on the substrate. However, the inventors have found that, in combination with an appropriate ratio of conductive flakes to conductive nanoparticles, as discussed below, a conductive ink with a loading of 0.1 mg / m 2 to approximately 0.8 mg / m 2 It has been found that by using an amount of dispersant in the range of 0.1 to 1.5 wt %, it is possible to produce a conductive ink that is stable and fast drying, even at high solids loading levels. When applied to a substrate such as paper using a rollerball pen, the conductive ink dries to form a highly conductive trace that is also characterized by high reflectivity and good adhesion to the substrate.

[0020] Ideally, to form traces with the desired conductivity, the concentration of conductive particles in the ink is at least about 40 wt%, at least about 50 wt%, at least about 60 wt%, at least about 70 wt%, or at least about 80 wt%, and the concentration can also be as high as about 85 wt%, or as high as about 90 wt%.

[0021] The amount of dispersant is at least about 0.2 mg / m 2 , at least about 0.3 mg / m 2 , at least about 0.4 mg / m 2 , or at least about 0.5 mg / m 2 where the unit is defined as 1 m of conductive particles. 2 This represents the mass (mg) of dispersant per surface area of ​​the surface. Typically, the amount of dispersant is about 0.7 mg / m 2 , or about 0.8 mg / m 2 When adsorbed on the surface of the conductive particles (flakes and / or nanoparticles), the dispersant prevents or minimizes agglomeration, thus improving the stability of the ink composition. However, the dispersant concentration should not exceed 0.8 mg / m 2 If more than this amount is used, it may interfere with the electrical contact between the conductive flakes and particles, reducing the conductivity of the conductive traces.

[0022] The dispersant may include a polymer, such as a polyelectrolyte having a molecular weight greater than about 1000 g / mol (e.g., polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and / or hydroxypropyl cellulose (HPC)). Generally speaking, the polymer may be selected from the group consisting of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), hydroxypropyl cellulose (HPC), polyvinyl methyl ether (PVME), polyvinyl alcohol (PVA), polyoxyethylene glycol sorbitan alkyl ester, polyoxypropylene glycol alkyl ether, polyoxyethylene glycol alkyl ether, and polyoxyethylene glycol octylphenol ether. Alternatively, the dispersant may be polymer-free. For example, the dispersant may be perfluorooctane sulfonate (PFOS) or perfluorononanoic acid (PFNA).

[0023] The conductive flakes are plate-like in shape with an average thickness that is much smaller than the average lateral dimension of the flakes. In this context, "lateral dimension" refers to the linear dimension (e.g., width, length, and / or diameter) measured perpendicular to the thickness of the flake. Typically, the average thickness of the conductive flakes is one to two orders of magnitude smaller than the average width (or other lateral dimension). For example, the conductive flakes may have an average width of several microns (e.g., about 1 to 5 microns), while the average thickness of the conductive flakes may be tens to hundreds of nanometers. Typically, the average lateral dimension of the conductive flakes may be at least about 500 nm, at least about 750 nm, at least about 1 micron, or at least about 2 microns, and is typically about 5 microns or less, about 4 microns or less, or about 3 microns or less. The average thickness of the conductive flakes may be at least about 10 nm, at least about 50 nm, or at least about 100 nm, and is typically about 300 nm or less, about 200 nm or less, or about 100 nm or less. Values ​​expressed herein as "average" values, such as average thickness or average width, represent nominal values ​​for a plurality of particles or flakes. As will be appreciated by those skilled in the art, individual particles or flakes within a plurality may exhibit variation from the average value.

[0024] The conductive nanoparticles have a substantially spherical shape and may therefore be referred to as conductive nanospheres. Alternatively, the conductive nanoparticles may have irregular or other morphologies, such as faceted or needle-like shapes. The conductive nanoparticles typically have average linear dimensions (length, width, and / or diameter) of about 500 nm or less, about 200 nm or less, or about 100 nm or less. The average linear dimensions may also be at least about 10 nm, at least about 50 nm, or at least about 100 nm. For example, the average linear dimensions of the conductive nanoparticles may range from about 10 nm to about 200 nm, or from about 100 nm to about 500 nm.

[0025] By including an appropriate weight ratio of conductive flakes to conductive nanoparticles, good particle packing can be achieved in the conductive ink so that a percolated network of conductive particles can form in the deposited conductive traces. For example, the weight ratio can be at least about 0.1:1, at least about 1:1, at least about 3:1, at least about 6:1, or at least about 9:1. Typically, the weight ratio is no more than about 20:1, or no more than about 15:1.

[0026] Conductive particles, including conductive flakes and conductive nanoparticles, may contain one or more metals selected from transition metals, semimetals, and / or rare earth metals. For example, the one or more metals may be selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Preferred metals may include Ag, Au, Cu, Ni, Pt, and / or Pd. The conductive particles may comprise substantially pure metals, metal alloys, and / or metal oxides (e.g., tin oxide or indium-tin oxide) containing only unavoidable impurities. It is also contemplated that the conductive particles may include a coating (e.g., a conductive coating or a passivation layer) on individual flakes and / or particles. The coating may include one or more of the metals listed above.

[0027] The conductive ink may further include a thickener to adjust the flow behavior of the ink. For example, the thickener may be selected from hydroxyethyl cellulose (HEC), xanthan gum, and guar gum. In one example, the thickener is HEC at a concentration of about 2 wt% to about 3 wt% relative to the conductive particles. The viscosity of the conductive ink may range from about 4000 centipoise to about 6000 centipoise under zero shear stress conditions.

[0028] Surfactants may be added to the conductive ink to lower the surface tension and also promote good wetting of the paper or other substrate. When used, surfactants include BYK (registered trademark) Polymeric fluorosurfactants such as BYK-Chemie GmbH, Wesel, Germany may be included.

[0029] Conductive inks can be prepared by forming a mixture containing conductive flakes and nanoparticles in an aqueous solvent (e.g., water) along with a dispersant (e.g., PAA). The mixture can be sonicated to ensure the flakes and nanoparticles are well dispersed. A thickener can be added to increase the viscosity of the mixture, and a small amount of a surface tension modifier (surfactant) can also or alternatively be added to improve the smoothness of the ink dispensed on paper or other substrate. After adding and mixing all the desired components of the conductive ink, the ink can be loaded into a rollerball pen for writing. Rollerball pens known in the art typically have ball diameters ranging from 250 microns to nearly 1 millimeter. A preferred range of diameters for rollerball pens used with conductive inks is from about 800 microns to about 1000 microns.

[0030] Conductive inks designed as described above may exhibit dispersion stability or shelf life of at least about 8 months, or at least about 12 months. The shelf life may also be about 24 months or more. Typically, the dispersion stability / shelf life is about 8 to about 12 months.

[0031] The conductive traces may be formed from a conductive ink by first dispensing the conductive ink into a rollerball pen, wherein the conductive ink, as described above, comprises an aqueous solvent and conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %, the conductive particles including conductive flakes and conductive nanoparticles, and the dispersant is at least about 0.1 mg / m 2 to approximately 0.8 mg / m 2 The rollerball pen is then moved over the surface to deposit the conductive ink onto the surface. The conductive ink is allowed to dry at room temperature to form the conductive traces.

[0032] Conductive inks are designed to dry quickly. Drying times can be 40 seconds or less, 30 seconds or less, about 20 seconds or less, about 10 seconds or less, or about 5 seconds or less. Drying times can be determined by measuring the time it takes for the resistivity of a conductive trace to stabilize after depositing the conductive ink on a surface, where resistivity (ρ) is defined as ρ = (A / L)R, where A is the cross-sectional area, L is the length, and R is the electrical resistance. A two-point probe can be used to perform resistivity measurements, which involve passing a current (I) through a specimen and measuring the voltage drop (V), where R can be determined from Ohm's Law, V = IR. A profilometer can be used to measure the cross-sectional area, A.

[0033] The conductive traces formed upon drying may comprise a percolated network of conductive particles comprising one or more metals, for example, as shown in Figure 2B. The conductive particles include conductive flakes and conductive nanoparticles, and the conductive traces may have a conductivity of at least about 1% of the bulk metal conductivity and a reflectivity of greater than about 40%, as described below.

[0034] As described above in the description of the conductive ink, the one or more metals of the conductive traces may be selected from transition metals, semimetals, and / or rare earth metals. For example, the one or more metals may be selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Preferred metals may include Ag, Au, Cu, Ni, Pt, and / or Pd. The conductive particles may comprise substantially pure metals, metal alloys, and / or metal oxides (e.g., tin oxide or indium-tin oxide) containing only unavoidable impurities. The conductive particles may be formed by distributing the conductive particles among the individual frames. It is also contemplated that the arcs and / or particles may include a coating (e.g., a conductive coating or a passivation layer). The coating may include one or more metals as described above.

[0035] The conductive flakes and conductive nanoparticles of the conductive traces can have any of the morphologies and sizes described above in the description of the conductive ink. Because the ink is deposited and dried at room temperature, over-firing is avoided, and the flakes and nanoparticles of the conductive traces can be similar or the same in morphology / size as those of the conductive ink as deposited.

[0036] Also, as explained above, an appropriate weight ratio of conductive flakes to conductive nanoparticles can be selected to achieve good particle packing and the formation of a percolation network of conductive particles in the deposited conductive traces. For example, the weight ratio can be at least about 0.1:1, at least about 1:1, at least about 3:1, at least about 6:1, or at least about 9:1. Typically, the weight ratio is no more than about 20:1, or no more than about 15:1.

[0037] The aqueous solvent that serves as a carrier for the conductive particles in the ink formulation is removed when the ink is dried; however, the dispersant remains after drying. Thus, the percolation network of conductive particles may include the dispersant coating them, and the dispersant may be present in an amount of about 0.1 mg / m 2 to approximately 0.8 mg / m 2 , or about 0.5 mg / m 2 to approximately 0.8 mg / m 2 It may be present in an amount ranging from 0.1 to 1.0.

[0038] The conductive trace exhibits a conductivity of at least 0.1% of the bulk metal conductivity, where bulk metal conductivity refers to the bulk conductivity of the metal that makes up the majority or entirety of the conductive trace. The conductivity may also be at least about 1% of the bulk metal conductivity, at least about 5% of the bulk metal conductivity, at least about 10% of the bulk metal conductivity, or at least about 15% of the bulk metal conductivity. Since conductivity is the reciprocal of resistivity, the conductivity of the conductive trace (or bulk metal) can be determined by measuring the resistivity (ρ) presented above. Two-point probe or four-point probe methods can be used with a surface profilometer. Advantageously, the electrical resistivity of the conductive trace is at least about 10 -5 ohm-cm or less. The conductivity can be as high as about 20% of the bulk metal conductivity.

[0039] In addition to good electrical conductivity, the conductive trace may also have a highly reflective surface. A UV-Vis reflectance spectrophotometer can be used to measure the intensity (I) of light reflected from the conductive trace. When compared to the intensity (I) of light reflected from a standard material, e.g., WS-1, a Teflon diffuse reflectance standard, the I / I ratio (reflectance) can be determined. Reflectance is typically multiplied by 100 and expressed as a percentage (% reflectance). Thus, when determined by UV-Vis reflectance measurements, the conductive trace may exhibit a reflectance value of at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%. The reflectance of the conductive trace may be as great as about 90%, or even as great as about 99%.

[0040] It is advantageous for the conductive trace to adhere strongly to the substrate. Adhesion of the trace to the substrate can be measured according to ASTM standard D3359. This test method involves making a cross-hatch cut in the conductive trace and applying tape to the cross-hatched area. After the tape is removed, the cut area is inspected and scored. Conductive traces produced as described herein are found to have sufficient adhesion to the substrate to pass the test, as shown in the table below.

[0041] A method of forming a conductive trace includes supplying conductive ink to a rollerball pen, moving the rollerball pen over a surface to deposit the conductive ink on the surface, and drying the conductive ink at room temperature to form a conductive trace. The conductive ink, as described above, includes an aqueous solvent and conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %, where the conductive particles include conductive flakes and conductive nanoparticles, and the dispersant is at a concentration of about 0.1 mg / m 2 to approximately 0.8 mg / m 2 The conductive particles are coated at a loading level of .

[0042] Drying times are extremely rapid, as noted above, on the order of 30 seconds or less.Conductive traces formed by the above method can have any of the characteristics previously described.

[0043] The rollerball pen can be moved over the substrate manually or automatically (e.g., by a plotter, as shown in FIG. 4). Thus, the conductive ink can be deposited onto the substrate at any desired speed. Deposition speeds of at least about 1 mm / s, at least about 10 mm / s, or at least about 100 mm / s are readily achievable, and exemplary traces formed at these speeds are shown in FIG. 5 by computed tomography (CT) images. Typical traces range in width and thickness from about 500 microns to about 1200 microns.

[0044] Considering room temperature processing conditions, the substrate can include any of several materials, including heat-sensitive materials such as polymers and paper (e.g., photo paper, copy paper, card stock, etc.), as well as ceramics, metals, and / or semiconductors. [Table 1] [Example]

[0045] Example 1 The conductive ink formulation contains 90% by weight of silver flakes (average size 1-3 microns) and 10% by weight of silver nanoparticles (average size 50-500 nm) at 0.2 mg / m 2 Loading level The conductive silver ink is prepared by dispersing the silver particles in a poly(acrylic acid) dispersant at 2000 kJ / min using a 1000 kJ / min solution. The nanoparticles are substantially spherical in shape. The weight percent (solids loading) of silver in the solution is adjusted to 20 wt %, and the viscosity is increased by adding hydroxyethyl cellulose as a thickener at a concentration of 3 wt % of the silver. The conductive silver ink is thoroughly mixed, and the final viscosity is measured to be 4000 cP. The ink is deposited on a substrate (paper) and dries quickly at room temperature to form silver traces. After drying, the resistivity of the silver traces is ≦10 -4 ohm-cm, which is approximately the same as the bulk silver conductivity (the resistivity of Ag is 1.59× -6 This corresponds to a conductivity of about 1% of the electrical conductivity (in ohm-cm), and the silver traces are observed to have a metallic appearance.

[0046] Example 2 The conductive ink formulation contains 90% by weight of silver flakes (average size 1-3 microns) and 10% by weight of silver nanoparticles (average size 50-500 nm) at 0.2 mg / m 2The conductive silver ink is prepared by dispersing the silver particles in a poly(acrylic acid) dispersant at a loading level of 1000 kJ / cm². The nanoparticles are substantially spherical in shape. The weight percent of silver (solid loading) in the solution is adjusted to 50 wt%, and the viscosity is increased by adding hydroxyethyl cellulose as a thickener at a concentration of 3 wt% of the silver. The conductive silver ink is thoroughly mixed, and the final viscosity is measured to be 4000 cP. The ink is deposited on a substrate and rapidly dries at room temperature to form silver traces. After drying, the resistivity of the silver traces is ≦5×10 -5 It is measured to be 300 ohm-cm, which corresponds to a conductivity of about 2% of the bulk silver conductivity at room temperature, and the silver traces are observed to have a metallic appearance.

[0047] Example 3 The conductive ink formulation contains 90% by weight of silver flakes (average size 1-3 microns) and 10% by weight of silver nanoparticles (average size 50-500 nm) at 0.2 mg / m 2 The conductive silver ink is prepared by dispersing the silver particles in a poly(acrylic acid) dispersant at a loading level of 1000 ppm. The nanoparticles are substantially spherical in shape. The weight percent of silver (solid loading) in the solution is adjusted to 80 wt %, and the viscosity is increased by adding hydroxyethyl cellulose as a thickener at a concentration of 3 wt % of the silver. The conductive silver ink is thoroughly mixed, and the final viscosity is measured to be 4000 cP. The ink is deposited on a substrate and rapidly dries at room temperature to form silver traces. After drying, the resistivity of the silver traces is ≦10 -5 It is measured to be 300 ohm-cm, which corresponds to a conductivity of about 10% of the bulk silver conductivity at room temperature, and the silver traces are observed to have a metallic appearance.

[0048] Example 4 The conductive ink formulation contains 90% by weight of silver flakes (average size 1-3 microns) and 10% by weight of silver nanoparticles (average size 50-500 nm) at 0.2 mg / m 2The conductive silver ink is prepared by dispersing the silver particles in a poly(acrylic acid) dispersant at a loading level of 1000 ppm. The nanoparticles are substantially spherical in shape. The weight percent of silver (solid loading) in the solution is adjusted to 50 wt %, and the viscosity is increased by adding hydroxyethyl cellulose as a thickener at a concentration of 3 wt % of the silver. The conductive silver ink is thoroughly mixed, and the final viscosity is measured to be 4000 cP. The ink is deposited on a substrate and rapidly dries at room temperature to form silver traces. After drying, the resistivity of the silver traces is ≦10 -5 It is measured to be 300 ohm-cm, which corresponds to a conductivity of about 4% of the bulk silver conductivity at room temperature, and the silver traces are observed to have a metallic appearance.

[0049] Example 5 The conductive ink formulation contains 50% by weight of silver flakes (average size 1-3 microns) and 50% by weight of silver nanoparticles (average size 50-500 nm) at 0.2 mg / m 2 The nanoparticles are prepared by dispersing them in poly(acrylic acid) dispersants at loading levels of 10 ... The morphology of the silver is substantially spherical. The weight percent of silver (solids loading) in the solution is adjusted to be 50 wt %, and the viscosity is increased by adding hydroxyethyl cellulose as a thickener at a concentration of 3 wt % of the silver. The conductive silver ink is mixed thoroughly, and the final viscosity is measured to be 4000 cP. The ink is deposited on a substrate and dries quickly at room temperature to form silver traces. After drying, the resistivity of the silver traces is ≦10 -5 It is measured to be 300 ohm-cm, which corresponds to a conductivity of about 5% of the bulk silver conductivity at room temperature, and the silver traces are observed to have a metallic appearance.

[0050] Example 6 The conductive ink formulation contains 10 wt% silver flakes (average size 1-3 microns) and 90 wt% silver nanoparticles (average size 50-500 nm) at 0.2 mg / m 2The conductive silver ink is prepared by dispersing the silver particles in a poly(acrylic acid) dispersant at a loading level of 1000 ppm. The nanoparticles are substantially spherical in shape. The weight percent of silver (solid loading) in the solution is adjusted to 50 wt %, and the viscosity is increased by adding hydroxyethyl cellulose as a thickener at a concentration of 3 wt % of the silver. The conductive silver ink is thoroughly mixed, and the final viscosity is measured to be 4000 cP. The ink is deposited on a substrate and rapidly dries at room temperature to form silver traces. After drying, the resistivity of the silver traces is ≦10 -4 It is measured to be 300 ohm-cm, which corresponds to a conductivity of about 5% of the bulk silver conductivity at room temperature, and the silver traces are observed to have a metallic appearance.

[0051] Although the present invention has been described in considerable detail with reference to specific embodiments thereof, other embodiments are possible without departing from the invention. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein. All embodiments that come within the meaning of the claims, either literally or by equivalents, are intended to be embraced within their scope.

[0052] Moreover, the above advantages are not necessarily the only advantages of the present invention, and it is not necessarily expected that all described advantages will be achieved by all embodiments of the present invention.

[0053] According to a preferred embodiment of the present invention, for example, the following is provided: (Section 1) 1. A conductive ink for a rollerball pen, comprising: aqueous solvent; conductive particles comprising one or more metals dispersed in said aqueous medium at a concentration of at least about 30 wt %, the conductive particles including conductive flakes and conductive nanoparticles; and Approximately 0.1mg / m 2 to approximately 0.8 mg / m 2 a dispersant coating said conductive particles at a loading level of 1. A conductive ink comprising: (Section 2) Item 1. The conductive ink according to item 1, wherein the weight ratio of the conductive flakes to the conductive nanoparticles is at least about 3:1. (Section 3) 3. The conductive ink according to item 2, wherein the weight ratio is at least about 9:1. (Section 4) 4. The conductive ink according to any one of items 1 to 3, wherein the concentration of the conductive particles is at least about 50 wt %. (Section 5) The dispersant loading level is about 0.5 mg / m 2 to approximately 0.8 mg / m 2 The above Item 5. The conductive ink according to any one of items 1 to 4. (Section 6) 6. The conductive ink according to any one of items 1 to 5, wherein the one or more metals are selected from the group consisting of Ag, Au, Cu, Ni, Pt, and Pd. (Section 7) 7. The conductive ink of any one of paragraphs 1 to 6, wherein the conductive flakes have average lateral dimensions of about 1 micron to about 4 microns and an average thickness of about 10 nm to about 100 nm. (Section 8) 8. The conductive ink according to any one of items 1 to 7, wherein the conductive nanoparticles comprise conductive nanospheres having a substantially spherical shape. (Section 9) Item 9. The conductive ink of any one of items 1 to 8, wherein the conductive nanoparticles have an average linear dimension of about 500 nm or less. (Section 10) 10. The conductive ink of any one of items 1 to 9, having a shelf life of at least about 8 months. (Section 11) 11. The conductive ink according to item 10, having a shelf life of at least about 12 months. (Section 12) 12. The conductive ink according to any one of items 1 to 11, having a viscosity of about 4000 centipoise to about 6000 centipoise. (Section 13) 13. The conductive ink according to any one of items 1 to 12, further comprising a thickener in the aqueous solvent. (Section 14) Item 14. The conductive ink according to item 13, wherein the thickener is selected from the group consisting of hydroxyethyl cellulose (HEC), xanthan gum, and guar gum. (Section 15) 15. The conductive ink according to any one of items 1 to 14, further comprising a surfactant in the aqueous solvent to reduce surface tension. (Section 16) Item 16. The conductive ink according to item 15, wherein the surfactant comprises a polymeric fluorosurfactant. (Section 17) A conductive trace formed on a substrate from a rollerball pen, a percolation network of conductive particles comprising one or more metals, said conductive particles comprising conductive flakes and conductive nanoparticles; Including, having a conductivity of at least about 1% of the bulk metal conductivity and a reflectivity of greater than 40%; Conductive traces. (Section 18) 18. The conductive trace of claim 17, wherein the one or more metals are selected from the group consisting of Ag, Au, Cu, Ni, Pt, and Pd. (Section 19) 19. The conductive trace of claim 17 or 18, wherein the weight ratio of the conductive flakes to the conductive particles is at least about 3:1. (Section 20) 20. The conductive trace of claim 19, wherein the weight ratio is at least about 9:1. (Section 21) 21. The conductive trace of any one of paragraphs 17 to 20, wherein the conductive flakes have average lateral dimensions of about 1 micron to about 4 microns and an average thickness of about 10 nm to about 100 nm. (Section 22) 22. The conductive trace of any one of paragraphs 17 to 21, wherein the conductive nanoparticles comprise conductive nanospheres having a substantially spherical shape. (Section 23) 23. The conductive trace of any one of paragraphs 17 to 22, wherein the conductive nanoparticles have an average linear dimension of about 500 nm or less. (Section 24) The conductive particles include a dispersant coating them, and the dispersant has a concentration of about 0.5 mg / m 2 to approximately 0.8 mg / m 2 24. The conductive trace of any one of paragraphs 17 to 23, wherein the conductive trace is present in an amount of (Section 25) about 10 -5 25. The conductive trace of any one of paragraphs 17 to 24 above, having an electrical resistivity of ohm-cm or less. (Section 26) an aqueous solvent; conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %, the conductive particles including conductive flakes and conductive nanoparticles; and 2 to approximately 0.8 mg / m 2 a dispersant that coats the conductive particles at a loading level of 0.01 to 0.01; moving the rollerball pen over a surface to deposit the conductive ink on the surface; drying the conductive ink at room temperature, thereby forming conductive traces comprising the one or more metals; Conductive traces formed by (Section 27) 27. The conductive trace of claim 26, having a conductivity of at least 1% of the bulk metal conductivity. (Section 28) 28. The conductive trace of claim 26 or 27, wherein the conductivity is at least about 5% of the bulk metal conductivity. (Section 29) 29. The conductive trace of any one of paragraphs 26 to 28, wherein the one or more metals are selected from the group consisting of Ag, Au, Cu, Ni, Pt and Pd. (Section 30) 30. The conductive trace of any one of paragraphs 26 to 29, having a reflectivity of at least about 40%. (Section 31) 1. A method of forming a conductive trace, comprising: an aqueous solvent; conductive particles comprising one or more metals dispersed in the aqueous solvent at a concentration of at least about 30 wt %, the conductive particles including conductive flakes and conductive nanoparticles; and 2 to approximately 0.8 mg / m 2 a dispersant that coats the conductive particles at a loading level of 0.01 to 0.01; moving the rollerball pen over a surface to deposit the conductive ink on the surface; drying the conductive ink at room temperature, thereby forming the conductive trace; A method comprising: (Section 32) 32. The method according to claim 31, wherein the drying time is about 30 seconds or less. (Section 33) 33. The method according to claim 32, wherein the drying time is about 10 seconds or less.

Claims

[Claim 1] A conductivity of at least about 1% of the bulk metal conductivity.

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