Conductive inks and films

Abstract

To provide a highly practical conductive ink and a conductive film containing a conductive filler that essentially comprises a metal superior to silver in oxidation resistance, namely, a noble metal other than silver.SOLUTION: The conductive ink contains foil-like fine particles essentially comprising gold as a conductive filler, in which (1) the content percentage of the fine particles is 0.15 to 15 mass% with respect to the whole amount, (2) the fine particles have an average thickness of 0.01 to 0.5 μm and a main surface having an average area of 3 to 70 μm, or (3) the ink further contains a solid content such as a resin other than the fine particles and the content percentage of the fine particles is 15 mass% or more and less than 80 mass% in terms of a solid content ratio. A conductive film 1 contains the above foil-like fine particles as a conductive filler 11 and has a conductive path 15 formed by a plurality of the fine particles in contact with each other, in which 70% or more of the fine particles are oriented in such a manner that a vertical line to the main surface of the particle and a thickness direction T of the film form an angle of less than 45 degrees, and the content percentage of the fine particles is less than 80 mass%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to conductive inks and conductive films containing conductive fillers. [Background technology]

[0002] From the viewpoint of process simplification, etc., attention has been focused on the production of conductive films by the printing method using conductive ink instead of the vacuum deposition method. Silver particles are often used as the conductive filler in conductive ink.

[0003] Patent Document 1 discloses a conductive ink containing polyaniline and silver microparticles. This conductive ink has a reduced content of silver microparticles while maintaining a low resistance value in order to reduce raw material costs. An example of Patent Document 1 discloses a conductive ink in which the content of silver microparticles is 60 to 70 mass % of the total amount.

[0004] Patent Document 2 also discloses a conductive ink in which non-compressible conductive fine particles such as nickel fine particles are added together with silver fine particles in order to reduce raw material costs. In the examples of Patent Document 2, a conductive ink containing 70 mass % of silver fine particles and 5 mass % of nickel fine particles is disclosed.

[0005] As disclosed in Patent Documents 1 and 2, conductive inks typically contain conductive fillers that account for more than half of the total amount by mass. Because conductive inks contain volatile components, the conductive filler content is even higher when expressed in terms of solid content. For example, the conductive ink in the examples of Patent Document 1 contains silver microparticles at a solid content ratio of approximately 80% by mass or more. The conductive ink in the examples of Patent Document 2 contains silver microparticles at a solid content ratio of 89% by mass or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-195695 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-157941 Summary of the Invention [Problem to be solved by the invention]

[0007] Considering the use of conductive films under conditions where they are prone to oxidation, it is desirable to use metals with better oxidation resistance than silver as the conductive filler material, such as precious metals such as gold and platinum. However, at present, the need to reduce the raw material costs even for silver fine particles is emphasized, and there has been little progress in concrete studies on using raw materials that are even more expensive than silver.

[0008] An object of the present invention is to provide a highly practical conductive ink containing a conductive filler having better oxidation resistance than silver fine particles. Another object of the present invention is to provide a highly practical conductive film containing a conductive filler having better oxidation resistance than silver fine particles. [Means for solving the problem]

[0009] The present invention provides a conductive ink containing foil-like fine particles containing gold as a conductive filler, the content of the fine particles being 0.15 to 15 mass % of the total amount.

[0010] The present invention also provides a conductive filler containing foil-like fine particles mainly composed of gold, the fine particles having an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 70 μm. 2 and a major surface which is

[0011] The present invention also provides a conductive ink comprising foil-shaped microparticles containing gold as a conductive filler and solids other than the microparticles, wherein the content of the microparticles, expressed as a solids ratio, is 15% by mass or more and less than 80% by mass.

[0012] Furthermore, the present invention includes foil-like fine particles containing gold as a main component as a conductive filler, a conductive path formed by a plurality of the particles in contact with each other; 70% or more of the foil-like fine particles constituting the conductive path are oriented so that a perpendicular to a main surface forms an angle of 45 degrees or less with the thickness direction of the film, The present invention provides a conductive film having a content of the fine particles of less than 80 mass %.

[0013] Furthermore, the present invention includes foil-like fine particles containing gold as a main component as a conductive filler, a conductive path formed by a plurality of the particles in contact with each other; The fine particles have an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 70 μm 2 and a major surface which is [Effects of the Invention]

[0014] The conductive ink according to the present invention is suitable for efficiently reducing the resistance of a conductive film with a small amount of conductive filler. The conductive film according to the present invention is suitable for achieving a low resistance with a small amount of conductive filler. Therefore, according to the present invention, it is possible to mitigate the resulting cost increase while using a raw material that is more expensive than silver. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective view illustrating the shape of a conductive filler. [Figure 2] 1 is a cross-sectional view of an example of a conductive film according to the present invention. [Figure 3] FIG. 2 is a cross-sectional view of another example of a conductive film according to the present invention. [Figure 4] FIG. 2 is a cross-sectional view illustrating the dispersion state of conductive fillers in a film. [Figure 5A] 1 is a cross-sectional view illustrating an angle θ between a normal to a main surface of a conductive filler and a thickness direction T of the film. [Figure 5B] 5B is a cross-sectional view for explaining the angle θ, similar to FIG. 5A. [Figure 6]1 is a graph showing the relationship between the content of conductive filler in the conductive ink according to the present invention and the resistance value of the conductive film. [Figure 7] 7 is a graph showing an enlarged view of a part of FIG. 6. [Figure 8] FIG. 1 shows the results of observing the cross section of a film (gold fine particle 1, gold fine particle content in conductive ink: 0.225% by mass) with a scanning electron microscope (SEM). [Figure 9] FIG. 1 is a diagram showing the results of SEM observation of a cross section of a film (gold fine particle 3, gold fine particle content: 0.225% by mass). [Figure 10] FIG. 1 shows the results of observing a film (gold fine particle 1, gold fine particle content 0.225% by mass) from the back side of a glass substrate using an optical microscope. [Figure 11] FIG. 1 shows the results of observing a film (gold fine particles 3, gold fine particle content 0.225% by mass) from the back side of a glass substrate using an optical microscope. [Figure 12] FIG. 1 shows the results of SEM observation of a cross section of a film (gold fine particle 1, gold fine particle content: 0.475% by mass). [Figure 13] FIG. 1 shows the results of SEM observation of a cross section of a film (gold fine particle 2, gold fine particle content: 0.475% by mass). [Figure 14] FIG. 1 shows the results of SEM observation of a cross section of a film (gold fine particle 3, gold fine particle content: 0.475% by mass). [Figure 15] FIG. 1 shows the results of SEM observation of a cross section of a film (gold fine particle 4, gold fine particle content: 0.475% by mass). [Figure 16] 1 is a graph showing the relationship between the content of the conductive filler in the conductive ink according to the present invention and the sheet resistance of the conductive film. [Figure 17] 1 is a graph showing the relationship between the heat treatment conditions and content of the conductive filler in the conductive ink according to the present invention and the sheet resistance of the conductive film, as well as the change in sheet resistance over time due to storage. [Figure 18] FIG. 1 shows the results of SEM observation of conductive fillers derived from gold foil. [Figure 19] 1 is a graph showing the results of X-ray diffraction analysis of various gold films or foils. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0017] [Conductive ink] (Conductive filler) In the present invention, the conductive filler contains gold as its main component. In this specification, "main component" refers to the component with the highest content by mass. However, the conductive filler may contain elements other than gold, such as silver, platinum, palladium, rhodium, iridium, ruthenium, osmium, copper, zinc, tin, iron, nickel, cobalt, chromium, titanium, magnesium, aluminum, indium, sodium, calcium, carbon, oxygen, and silicon. The gold content of the conductive filler may be 70% by mass or more, or even 80% by mass or more, and in some cases 90% by mass or more.

[0018] Gold is the most malleable precious metal. Therefore, conductive fillers primarily composed of gold are highly flexible and have a high ability to absorb stress due to deformation. These properties of gold are suitable for ensuring contact between conductive fillers in conductive films, i.e., for forming and maintaining conductive paths. Furthermore, gold has high oxidation resistance, so no oxide layer forms on its surface. Therefore, conductive paths can be easily formed even when conductive ink is dried at low temperatures (e.g., around 40 to 60°C, or in some cases, room temperature). In contrast, an oxide layer forms on the surface of silver microparticles, requiring heat treatment at around 120°C or higher to develop conductivity. The ability to form conductive paths at such low temperatures is an advantageous feature that enables the formation of conductive films on substrates or their substitutes with low heat resistance, specifically, paper, clothing, etc., and in some cases, direct deposition on human skin.

[0019] The conductive filler may be composed solely of gold. However, a foil-shaped conductive filler composed solely of gold is very soft and easily deformed. Therefore, to facilitate the conductive filler maintaining its foil shape in the conductive film, it is preferable to include an element other than gold in the conductive filler. The element other than gold is not particularly limited and may be, for example, any of the elements from silver to silicon listed above, but is preferably silver and / or copper. The content of the element other than gold is, for example, 0.1% by mass or more, preferably 0.3% by mass or more, and in some cases 0.5% by mass or more. The upper limit of the content of the element other than gold is not particularly limited as long as gold is the main component, but is, for example, 45% by mass or less, particularly 10% by mass or less.

[0020] Examples of alloy compositions that are particularly suitable for the conductive filler are shown below, but the alloy compositions that make up the conductive filler are not limited to the following. Gold: 50~99.9% by mass Silver: 0.1~45% by mass Copper: 0~5% by mass

[0021] The conductive filler has a foil-like outer shape. Figure 1 shows an example of a foil-like conductive filler. The conductive filler 11 has a pair of parallel main surfaces 51, 52. The distance between the main surfaces 51, 52 corresponds to the thickness t of the conductive filler 11. Foil-like conductive fillers tend to contact each other at surfaces rather than at points in the conductive film, making them advantageous for forming conductive paths compared to needle-like or other shapes.

[0022] The conductive filler has an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 70 μm. 2 The average thickness of the conductive filler may be 0.05 μm or more, or even 0.07 μm or more, and may be 0.3 μm or less, or even 0.2 μm or less. The average area of ​​the main surface of the conductive filler is 5 μm 2 Above, another 7 μm 2 It may be more than 50 μm 2 Below 40 μm 2 Below, especially 30 μm 2Below, especially 20 μm 2 Preferably less than 15 μm, in some cases 2 It may be the following:

[0023] The conductive filler containing gold as the main component may be obtained from a thin film formed by a thin film formation method such as vapor deposition or sputtering, or may be formed from gold foil. Gold foil is produced by stretching gold or an alloy containing gold as the main component and then beating it. Conductive fillers formed from gold foil have relatively high uniformity in size and shape, making them suitable for incorporation into conductive films. Furthermore, according to the analysis of the present inventors, foil-shaped fine particles derived from gold foil have a preferred orientation in the (100) plane, unlike foil-shaped fine particles obtained from a thin film formed by a vapor deposition method, sputtering, or the like. The foil-shaped fine particles formed from gold foil have a preferred orientation in the (100) plane, with the average area of ​​the main surface being 70 μm. 2 Although there are known ones that exceed this, it is preferable that the average area of ​​the main surfaces is as small as the above.

[0024] The average thickness and average area of ​​the main surfaces of the conductive filler can be determined by measuring the thickness and area of ​​at least 30, preferably 100, conductive fillers using a scanning electron microscope (SEM) and calculating the simple average.

[0025] When conductivity must be ensured using a very small amount of conductive filler, it is advantageous for the average area of ​​the main surfaces of the conductive filler to be relatively small. According to the inventor's investigations, a conductive filler with a relatively small main surface requires a relatively small amount of conductive filler to form a conductive path in the conductive film, compared to a conductive filler with a relatively large main surface. Therefore, particularly in a conductive ink in which the content of the conductive filler is low, for example, 0.75 mass % or less of the total amount, or even 0.5 mass % or less, it is advantageous for the average area of ​​the main surfaces of the conductive filler to be 50 μm 2 Below, especially 40 μm 2 It is preferable that:

[0026] The average ratio of the long side to the short side of the principal surface of the conductive filler is preferably 20 or less, and particularly preferably 10 or less. Here, the long side and short side of the principal surface are the longest and shortest sides of the principal surface that are set on the surface so as to pass through the center of gravity of the principal surface. The average values ​​of these sides can also be determined using SEM, as with the average thickness and average area.

[0027] (Solid content other than foil-like fine particles, which are conductive fillers) The conductive ink may further contain solid components other than the above-mentioned fine particles that are the conductive filler. The solid components preferably include a resin. The resin may be added to the conductive ink in a dissolved or dispersed state. The resin may be a general-purpose resin such as a polyolefin such as polyethylene, a polyester such as polyethylene terephthalate, or polystyrene, or may be polyurethane, polyamide, or the like. The resin is not limited to the above-mentioned thermoplastic resin, but may also be a thermosetting resin.

[0028] Examples of preferred resins include water-soluble resins such as polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polyacrylamide, carboxymethyl cellulose, polyvinylpyrrolidone, and sodium polyacrylate.

[0029] Another example of a preferable resin is a conductive resin, such as a resin containing a conductive polymer such as polypyrrole, polythiophene, polyacetylene, polyaniline, polyfluorene, poly(p-phenylene), poly(p-phenylene vinylene), or polyethylenedioxythiophene (PEDOT).

[0030] Instead of or in addition to the resin, the conductive ink may contain a resin precursor. The resin precursor is, for example, a monomer of the polymer that constitutes the resin. In this specification, components (e.g., monomers) that are contained in the conductive ink in a form different from the solid content (e.g., polymer) contained in the conductive film and that can provide the solid content of the conductive film are also treated as solid content contained in the conductive ink. Note that, as will be described in detail later, the solid content is not limited to resin or its precursor.

[0031] (dispersion medium) The dispersion medium for dispersing the conductive filler is preferably water, but an organic solvent can also be used as the dispersion medium. The dispersion medium can also function as a solvent for dissolving at least a portion of the resin and other components.

[0032] (Other ingredients) As with conventional conductive inks, lubricants, viscosity modifiers, surfactants, particle protectants, stabilizers, and other ingredients can be added to the conductive ink as needed. When a monomer is added as a resin precursor, it is desirable to add a polymerization initiator. A preferred polymerization initiator is a photopolymerization initiator. When a photopolymerization initiator is added, a photopolymerization accelerator, a sensitizer, etc. may also be added.

[0033] (Conductive filler content) In conductive inks, the content of the conductive filler, foil-shaped gold-based particles, is preferably 0.15% by mass or more, more preferably 0.25% by mass or more, and particularly preferably 0.375% by mass or more, relative to the total amount of the conductive ink. If a low resistance value is required for the conductive film, a value greater than 0.5% by mass, such as 0.75% by mass or more, is appropriate. However, the increase in raw material costs due to the excessive addition of conductive filler may negate the benefit of reduced resistance of the conductive film. Therefore, the content of the conductive filler may be 15% by mass or less, more preferably 5% by mass or less, particularly 2% by mass or less, relative to the total amount of the conductive ink, and in some cases may be 1.5% by mass or less, or even 1% by mass or less. If the required resistance value of the conductive film is not particularly low, the content may be 0.5% by mass or less.

[0034] The content of the conductive filler, expressed as the solids ratio of the conductive ink (ratio to the total solids), is preferably 15% by mass or more, 20% by mass or more, or even 30% by mass or more. If a low resistance value is to be imparted to the conductive film, 45% by mass or more is appropriate. However, the increase in raw material costs due to the excessive addition of conductive filler may negate the advantage of reduced resistance value of the conductive film. Therefore, the content of the conductive filler, expressed as the solids ratio of the conductive ink, may be less than 80% by mass, or even 75% by mass or less, and may be less than 50% by mass for applications that do not require sufficiently low resistance. Here, "solids" refers to components that can constitute the conductive film, specifically including conductive fillers and resins, but excluding the dispersion medium, which is a volatile component.

[0035] [Conductive film] FIG. 2 shows a cross section of an example of a conductive film according to the present invention. The conductive film 1 contains a conductive filler 11 and a solid content 12 other than the fine particles of the conductive filler. The conductive film 1 has conductive paths 15 formed by a plurality of conductive fillers 11 in contact with each other. The conductive paths 15 extend in the film surface direction of the conductive film 1. The conductive film 1 also has one or more protective layers 14, together with the conductive paths 15, which support the conductive paths 15 on the substrate 2 side of the film 1 or which cover the conductive paths 15 on the surface side of the film 1. The protective layers 14 contain the solid content 12. The conductive film 1 can be formed by applying the above-mentioned conductive ink onto the substrate 2.

[0036] The solid content 12 preferably contains a resin. However, the solid content 12 is not limited to a resin and may contain other compounds. The solid content other than the resin is, for example, the various components described above as (other components) of the conductive ink. The solid content other than the resin is not limited to these, and may be various organic or inorganic compounds, for example, various oxides. Examples of oxides include insulating oxides such as silicon oxide and aluminum oxide, and conductive oxides such as titanium oxide, indium oxide, zinc oxide, and tin oxide. The oxide as the solid content may be formed from, for example, its precursor, specifically, a compound capable of hydrolysis and polycondensation, such as silicon tetraalkoxide.

[0037] The conductive film 1 may contain conductive fillers 13 that do not form conductive paths 15. Furthermore, as shown in FIG. 3, the conductive film 1 may contain multiple conductive paths 15. The thickness of the conductive paths 15 may be less than 50%, or even 30% or less, of the thickness of the conductive film 1. When multiple conductive paths 15 are present, the thickness of the conductive path 15 is defined as the sum of the thicknesses of the paths 15. The thickness of the protective layer 14 may be greater than the thickness of the conductive path 15. When multiple protective layers 14 are present, the thickness of the protective layer 14 is defined as the sum of the thicknesses of the layers 14.

[0038] Unlike FIG. 4, in FIGS. 2 and 3, the majority of the conductive fillers are oriented so that their principal surfaces are substantially parallel to the film surface. Here, "substantially parallel to the film surface" refers to an angle θ between a perpendicular line 21 to the principal surface 51 and the thickness direction T of the film being less than 45 degrees, preferably 40 degrees or less, and more preferably 35 degrees or less, as shown in FIGS. 5A and 5B. If the principal surface 51 is not flat (see FIG. 5B), the angle θ varies depending on the location at which the perpendicular line 21 is drawn. Taking this into consideration, when measuring the angle θ, the perpendicular line 21 is set so that it passes through the center 53 of the principal surface 51 facing the surface of the film when the cross section of the conductive filler 11 is observed. The thickness direction T of the film is, more precisely, a direction perpendicular to the bottom surface 19 of the film 1 that contacts the substrate 2. The orientation of the conductive fillers can be determined by observing the cross section of the conductive fillers using an SEM. It is desirable to measure at least 30, preferably 100, conductive fillers to determine the orientation.

[0039] The substantially parallel orientation of the conductive filler is suitable for forming conductive paths 15 with a small amount of conductive filler. Therefore, it is preferable that 70% or more, preferably 80% or more, and more preferably 90% or more of the conductive filler be oriented substantially parallel to the film surface in the conductive film 1. When 70% or more of the conductive filler are oriented substantially parallel to the film surface, it becomes possible to form conductive paths 15 even if the content of the conductive filler in the conductive film 1 is as low as less than 80% by mass, further less than 75% by mass, or even less than 50% by mass in some cases.

[0040] In the film 1 of Figures 2 and 3, all of the conductive fillers 11 are oriented approximately parallel to the film surface. In contrast, in the film 3 of Figure 4, conductive fillers 13 that are oriented approximately parallel to the film surface and conductive fillers 17 that are not oriented approximately parallel to the film surface are present, and the proportion of conductive fillers 13 to all conductive fillers 13, 17 remains in a low range. In the state of Figure 4, it is not easy for a small amount of conductive fillers 13, 17 to form a conductive path.

[0041] The preferred shape of the conductive filler is as described above, specifically, an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 70 μm 2 The foil has an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 40 μm. 2 The foil shape having a main surface of is particularly suitable for efficiently forming conductive paths 15 in a conductive film 1 having a conductive filler content of less than 50 mass %.

[0042] The sheet resistance of the conductive film 1 can be determined appropriately depending on the application, for example, 1000 Ω / sq (Ω / □) or less, preferably 100 Ω / sq or less, particularly 30 Ω / sq or less, and especially 10 Ω / sq or less. The conductive film 1 can have a sheet resistance of 7 Ω / sq or less, 5 Ω / sq or less, even 3 Ω / sq or less, particularly 1 Ω / sq or less, and in some cases 0.8 Ω / sq or less. While it is possible to have such a low sheet resistance, the conductive film 1 can be formed without the need for heating to high temperatures or a reduced pressure atmosphere. The lower limit of the sheet resistance is not particularly limited, but is, for example, 0.1 Ω / sq or more, even 0.3 Ω / sq or more.

[0043] The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the present invention.

[0044] Example 1 Four types of gold microparticles (gold microparticles 1 to 4) made from gold leaf were used as conductive fillers. These gold microparticles are commercially available as gold powder. Gold powder is gold microparticles derived from gold leaf that are manufactured and sold primarily for craft applications, specifically for the production of lacquerware and decorations for Buddhist altars. All of the gold powders used have a composition containing gold as the main component with trace amounts of silver and copper as secondary components. This composition is shown in mass % in Table 1. Judging from their composition, gold microparticles 1 to 4 should be referred to as alloy microparticles 1 to 4, etc. However, considering that foils and powders whose main component is gold are called gold leaf and gold powder, respectively, they will be referred to as "gold microparticles" here.

[0045] [Table 1]

[0046] Furthermore, when gold particles 1 to 4 were observed using an SEM, they were all found to be flake-like particles with a thickness of 0.1 to 0.15 μm. Furthermore, 100 particles of each gold particle were randomly selected, and the average area (unit: μm) of their main surfaces was measured. 2 ) was measured. The results are shown in Table 1. Furthermore, when the average ratio of the long side to the short side of the main surface of each of the 100 gold microparticles was calculated, all were below 10.

[0047] The conductive ink was prepared by mixing a predetermined amount of gold nanoparticles 1 to 4 with an equal mixture of PEDOT:PSS solution (Clevios® PH1000; Heraeus) and pure water. The solid content of the PEDOT:PSS solution used was 1.0 to 1.3% by mass, and the solvent was water. The prepared conductive ink was dropped onto a glass substrate and cast to form a conductive film. The formed conductive film was dried on a hot plate at 40°C and 60°C for 1 hour each, and then heat-treated at 130°C for 30 minutes. Note that the heat treatment at 130°C was performed to completely remove moisture in a short time; the formation of a conductive film itself is possible without this treatment. The resistivity of the formed conductive film in the film surface direction was measured by the two-probe method using a 2614B SourceMeter® (Keithley). The results are shown in Figures 6 and 7. The resistance of the film formed using only the PEDOT:PSS solution without adding gold particles was 6.6 × 10 3 It was Omega.

[0048] The sheet resistance of the conductive film formed as described above was measured by the four-probe method using a 2614B SourceMeter (registered trademark, manufactured by KEITHLEY). The results are shown in Figure 16. As shown in Figure 16, the sheet resistance of the conductive films doped with gold nanoparticles 1 to 4 tended to decrease with increasing gold nanoparticle content, similar to the resistance measured by the two-probe method. In particular, the sheet resistance of the conductive films doped with 1.8 to 2.0 mass% of each gold nanoparticle was less than 1 Ω / sq. Specifically, the sheet resistance of the conductive film doped with 1.88 mass% gold nanoparticles 1 was 0.88 Ω / sq, the sheet resistance of the conductive film doped with 1.93 mass% gold nanoparticles 2 was 0.70 Ω / sq, the sheet resistance of the conductive film doped with 1.87 mass% gold nanoparticles 3 was 0.45 Ω / sq, and the sheet resistance of the conductive film doped with 1.94 mass% gold nanoparticles 4 was 0.67 Ω / sq. The sheet resistance of the film formed using only PEDOT:PSS solution without adding gold nanoparticles was approximately 1.0×10 4 Since the sheet resistance was Ω / sq, the addition of gold particles 1 to 4 reduced the sheet resistance to about 1 / 10,000.

[0049] 6, 7, and 16, the horizontal axis represents the content (mass%) of gold particles 1 to 4 in the conductive ink. The horizontal axis values ​​of 0.15%, 0.25%, 0.5%, 1%, 1.5%, and 2% correspond to approximately 19-23%, 28-33%, 43-50%, 61-67%, 70-75%, and 75-80% solids content in the conductive ink. These solids content rates correspond to the content of gold particles 1 to 4 in the conductive film.

[0050] Figures 8 and 9 show SEM observations of cross sections of films formed from conductive inks containing approximately 0.225% by mass of gold particles 1 and 3, respectively. Figures 10 and 11 show the results of optical microscope observations of these films from the glass substrate side. Figures 12 to 15 show SEM observations of cross sections of films formed from conductive inks containing approximately 0.475% by mass of gold particles 1 to 4, respectively.

[0051] Gold microparticles 1 have a superior ability to form conductive paths compared to gold microparticles with larger principal surfaces, but this ability is inferior compared to gold microparticles 2 to 4. As can be seen from Figure 7, when using gold microparticles 1, it is desirable to add a conductive filler in an amount of 0.5 mass% or more in the conductive ink, or 45 mass% or more, or 50 mass% or more in solid content. At this level of content, unlike Figures 8 and 12, approximately 70% or more of gold microparticles 1 are oriented substantially parallel to the film surface. As shown in Figure 9, gold microparticles 2 to 4 are oriented substantially parallel to the film surface with a smaller amount of addition. As a result, unlike Figure 10, as shown in Figure 11, the in-plane coverage of the gold microparticles is improved and conductive paths are easily formed. Note that in the conductive films shown in Figures 13 to 15, more than 90% of gold microparticles 2 to 4 are oriented substantially parallel to the film surface. Furthermore, in Figures 9, 13 to 15, the thickness of the layer excluding the conductive paths (protective layer) is greater than the thickness of the conductive paths.

[0052] Example 2 Next, conductive films were formed and their resistance values ​​were measured in the same manner as in Example 1, except that polymer solutions of PVA (polyvinyl alcohol), PEO (polyethylene oxide), PS (polystyrene), and PMMA (polymethyl methacrylate) were used instead of the PEDOT:PSS solution. The solvent for the PVA and PEO solutions was water, the solvent for the PS solution was chlorobenzene, and the solvent for the PMMA solution was toluene. The polymer concentration in each polymer solution was 0.9 to 1.1% by mass. The gold particle content in the prepared conductive ink was approximately 0.45 to 0.5% by mass. Table 2 shows the resistance measurement results when each polymer solution was used, along with the results when a PEDOT:PSS solution with the same gold particle content range was used.

[0053] [Table 2]

[0054] Although the resistance values ​​obtained from PVA and PS were not as high as those obtained from the conductive resin (PEDOT:PSS), they were one order of magnitude lower than those obtained from PEO and PMMA.

[0055] Example 3 Furthermore, the influence of the heat treatment temperature on the resistance of the conductive film was confirmed, and the storage stability of the conductive film was investigated. Specifically, a conductive film was formed in the same manner as in Example 1, except that the drying and heat treatment were performed in one of the ways A to E shown in Figure 17, and the sheet resistance was measured. Gold particles 3 were used as the gold particles, and the gold particle content in the conductive ink was either 0.5 mass%, 1.0 mass%, or 2.0 mass%. The sheet resistance was measured immediately after preparation, and 7, 14, and 22 days after preparation. The prepared conductive film was stored at room temperature in the atmosphere.

[0056] The results are shown in Figure 17. Figure 17 confirms that conductive films containing foil-like gold microparticles can exhibit sufficiently low resistance and excellent storage stability even when subjected to only a drying treatment in which the film is heated to room temperature or below 100°C (treatments A and B). This result indicates that a practical conductive film with low resistance can be formed even on a substrate that is sensitive to heat. Furthermore, as shown in Figure 17, the difference in sheet resistance due to treatment was particularly small for conductive films with sufficiently low sheet resistance.

[0057] Example 4 Figure 18 shows the results of SEM observation of conductive filler (gold microparticle 3) derived from gold foil. As is clearly visible in this SEM image, the conductive filler derived from gold foil has a nearly uniform square main surface and is highly uniform in size. In contrast, conductive filler produced by vapor deposition has relatively large variations in the shape and size of the main surface. In fact, when conductive films were fabricated with the same amount of conductive filler added, the sheet resistance of the conductive film with gold foil-derived conductive filler added (approximately 1 Ω / sq) was significantly lower than the sheet resistance of the conductive film with vapor deposition-based conductive filler added (approximately 12 Ω / sq).

[0058] Figure 19 shows the results of X-ray diffraction (XRD) analysis of a gold thin film (approximately 83 nm thick) formed by vapor deposition, a gold thin film (approximately 100 nm thick) formed by sputtering, a gold foil (approximately 108 nm thick) obtained by drawing and rolling, and a gold thick film. The gold foil used had the same composition as that of gold microparticle 3 (see Table 1). The gold thin film and gold thick film consisted solely of gold. Figure 19 confirms that the gold foil has a preferred orientation in the (100) plane, whereas the gold thin films formed by vapor deposition or sputtering have a preferred orientation in the (111) and (100) planes. The characteristic shape of the conductive filler derived from gold foil, which is desirable for reducing the resistance of the conductive film (see Figure 18), is thought to be related to the preferred orientation in the (100) plane of the foil-like microparticles derived from gold foil. [Industrial Applicability]

[0059] The present invention has great industrial value in that it promotes the industrial use of gold-based foil-like fine particles, such as gold powder, which have previously been used primarily in the field of crafts, for example, as a material for electrodes in various devices. [Explanation of symbols]

[0060] 1. Conductive film 2 boards 11,13,17 Conductive filler 12 Solid content of resin etc. 14 Protective layer 15 Conductive Path 21 Normal to the principal surface 51,52 Main surface

Claims

1. The conductive filler contains foil-like fine particles that satisfy the following i) and / or ii): The conductive ink has a content of the fine particles of 0.15 to 5 mass % based on the total amount. i) An alloy having a composition of 50 to 99.9 mass % gold, 0.1 to 45 mass % silver, and 0 to 5 mass % copper. ii) The composition has a content of elements other than gold of 45 mass % or less.

2. The particles have an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 70 μm 2 10. The conductive ink of claim 1, having a major surface which is

3. The conductive filler contains foil-like fine particles that satisfy the following i) and / or ii): The particles have an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 40 μm 2 and a main surface which is a conductive ink, and a content of the fine particles is less than 50 mass % expressed as a solid content ratio. i) An alloy having a composition of 50 to 99.9 mass % gold, 0.1 to 45 mass % silver, and 0 to 5 mass % copper. ii) The composition has a content of elements other than gold of 45 mass % or less.

4. The conductive filler includes foil-like fine particles that satisfy the following i) and / or ii) and solid components other than the fine particles, the solid content other than the fine particles is a resin, the resin being polyvinyl alcohol or polystyrene; The conductive ink has a content of the fine particles of 15% by mass or more and less than 50% by mass, expressed as a solid content ratio. i) An alloy having a composition of 50 to 99.9 mass % gold, 0.1 to 45 mass % silver, and 0 to 5 mass % copper. ii) The composition has a content of elements other than gold of 45 mass % or less.

5. 4. The conductive ink according to claim 1, further comprising a solid content other than the fine particles.

6. The conductive ink according to claim 5 , wherein the solid content is a resin.

7. The conductive ink of claim 6 , wherein the resin is a conductive resin.

8. The conductive ink according to any one of claims 1 to 7, wherein the foil-shaped fine particles further contain silver and / or copper.

9. 9. The conductive ink according to claim 1, wherein the foil-like fine particles are preferentially oriented in the (100) plane.

10. The conductive filler contains foil-like fine particles that satisfy the following i) and / or ii): a conductive path formed by a plurality of the particles in contact with each other; 70% or more of the foil-like fine particles are oriented such that a normal to a principal surface forms an angle of less than 45 degrees with the thickness direction of the film, The conductive film has a content of the fine particles of less than 50% by mass. i) An alloy having a composition of 50 to 99.9 mass % gold, 0.1 to 45 mass % silver, and 0 to 5 mass % copper. ii) The composition has a content of elements other than gold of 45 mass % or less.

11. The conductive filler contains foil-like fine particles that satisfy the following i) and / or ii): a conductive path formed by a plurality of the particles in contact with each other; The particles have an average thickness of 0.01 to 0.5 μm and an average area of ​​3 to 40 μm 2 and a main surface which is The conductive film has a content of the fine particles of less than 50% by mass. i) An alloy having a composition of 50 to 99.9 mass % gold, 0.1 to 45 mass % silver, and 0 to 5 mass % copper. ii) The composition has a content of elements other than gold of 45 mass % or less.

12. Further, the protective layer contains solid content other than the fine particles. The conductive film according to claim 10 or 11, wherein the thickness of the protective layer is greater than the thickness of the conductive paths.

13. The conductive film according to claim 12 , wherein the solid content is a resin.

14. The conductive film according to claim 13 , wherein the resin is a conductive resin.

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