JP2013155440A - Method for manufacturing metal nanowire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal nanowire that has superior conductivity and improved stability and durability, and a method for manufacturing the same, and to provide a transparent electric conductor which has high light transmittance, low surface resistance and improved stability and durability, and reduces the manufacturing costs and environmental load by forming a liquid-phase film.SOLUTION: A metal nanowire contains silver and at least one metal other than silver, and is characterized in that a metal composition on the surface is a uniform composition containing the at least one metal other than silver.

Description

  The present invention relates to a metal nanowire excellent in stability and durability, a method for producing the same, and a transparent conductor having high conductivity and good transparency and having both excellent stability and durability.

  In recent years, various types of display technologies such as liquid crystal, plasma, organic electroluminescence, and field emission have been developed in response to the increasing demand for thin TVs. In any of these displays having different display methods, a transparent electrode using a transparent conductive film is an essential constituent technology. In addition to televisions, transparent conductive films are an indispensable technical element in touch panels, mobile phones, electronic paper, various solar cells, and various electroluminescent light control elements.

Conventionally, as a transparent conductive film, various metal thin films such as Au, Ag, Pt, and Cu, indium oxide doped with tin and zinc (ITO, IZO), zinc oxide doped with aluminum and gallium (AZO, GZO), fluorine And metal oxide thin films such as tin oxide (FTO, ATO) doped with antimony, conductive nitride thin films such as TiN, ZrN, and HfN, and conductive boride thin films such as LaB ₆ are also known. Various electrodes such as Bi ₂ O ₃ / Au / Bi ₂ O ₃ , TiO ₂ / Ag / TiO _2, etc., are also known. In addition to inorganic substances, a transparent conductive film using a conductive polymer has also been proposed (see, for example, Non-Patent Document 1).

  However, since the metal thin film, nitride thin film, boron thin film and conductive polymer thin film described above cannot have both light transmission properties and conductive properties, special technical fields such as electromagnetic shielding and the like are relatively high. It was used only in the touch panel field where resistance values are allowed.

  On the other hand, metal oxide thin films are becoming the mainstream of transparent conductive films because they can achieve both light transmittance and conductivity and are excellent in durability. In particular, among the exemplified metal oxide materials, ITO has a good balance between light transmittance and conductivity, and it is easy to form an electrode fine pattern by wet etching using an acid solution. Widely used as an electrode. In general, for the production of a metal oxide thin film including ITO, a vapor deposition method such as a vacuum deposition method, a sputtering method, or an ion plating method is used. However, since these film forming methods require a vacuum environment, the apparatus is large and complicated, and since a large amount of energy is consumed for film forming, it is necessary to develop a technology that can reduce the manufacturing cost and environmental load. It was done. On the other hand, as represented by a liquid crystal display and a touch display, an increase in the area of the transparent conductive film is directed, and accordingly, demands for light weight and flexibility of the transparent conductive material have increased.

  In response to such a demand, a method of forming a transparent conductive film by a liquid phase film forming method such as coating or printing using a liquid material containing conductive fine particles has been proposed. For example, Patent Document 1 discloses a method of forming a transparent conductive film by applying a heat treatment by applying a dispersion containing conductive metal oxide particles made of indium oxide or tin oxide on a support. . Patent Document 2 discloses a film forming method in which the surface of inorganic oxide fine particles applied on a substrate is dissolved and then stabilized by heat treatment. Further, Patent Documents 3 to 5 disclose a method of forming a transparent conductive film by applying a dispersion containing CNT (carbon nanotube) or metal nanowire on a support.

  In a transparent conductive film using conductive fibers such as CNTs and metal nanowires as a conductor, conductivity is manifested by forming an electrical network between the conductive fibers, but several μm to several tens μm depending on one conductive fiber. Therefore, the percolation threshold for the material containing the conductive fiber to exhibit conductivity is very small, and therefore both conductivity and transparency can be achieved. In addition, unlike the case of using a conductive metal oxide as described above, it is possible to form a transparent conductive film on a resin support such as a plastic film because no heat treatment is required. It has excellent properties as a transparent conductive material that can be formed into a film.

  CNT has a structure in which a six-membered ring network (graphene sheet) made of carbon has a single-layer or multi-layer coaxial tubular shape, and is excellent in stability and durability. In addition, the conductivity varies depending on the number of layers and the structure, and single-walled CNT exhibits the most excellent conductivity. Single-walled CNTs have three types of structures depending on the orientation of the six-membered ring network. Two types are semiconducting and the other type is metallic. This metallic CNT (armchair type single-walled CNT) is said to have the same degree of conductivity as copper, and is preferred as a conductive material, but no industrially selectable method has been developed. In addition, it is practically difficult to select and use metallic CNT, such as the yield of metallic CNT isolation technology (see Non-Patent Document 2) is only 1%. At present, the transparent conductive film has not achieved a sufficiently low resistance.

On the other hand, although metal varies depending on the element, the metal generally has a high conductivity, and the nanowire of the metal element having a bulk conductivity of 1 × 10 ⁷ S / m or more can be applied to various methods such as a liquid phase method and a gas phase method. It has been reported that it can be produced by For example, Non-Patent Documents 3 and 4 etc. as the production method of Ag nanowire, Patent Literature 6 etc. as the production method of Au nanowire, Patent Literature 7 etc. as the production method of Cu nanowire, Are described in Patent Document 8 and the like, and can be referred to. In particular, silver has the highest conductivity among metals, and according to Non-Patent Document 3 and Non-Patent Document 4, since silver nanowires can be easily produced in an aqueous system, transparent conductivity using conductive fibers is used. In the film, silver nanowires can be positioned as the best conductive material. However, an element using silver as an electrode is prone to failure due to a phenomenon in which silver precipitates and grows from the electrode (hereinafter also referred to as migration), and the surface is sulfided due to a reaction with a sulfide compound in the environment. There are known problems with stability and durability, such as the formation of a silver film and the resulting deterioration of resistance over time, which is a major obstacle to the use of transparent conductive materials using silver nanowires. ing.

Japanese Patent No. 3251066 JP 2006-245516 A JP 2005-255985 A JP 2006-519712 A US2007 / 0074316A1 Specification JP 2006-233252 A JP 2002-266007 A Japanese Patent Application Laid-Open No. 2004-149871

"Technology of transparent conductive film", page 80 (Ohm Publishing Co.) URL: http: // www. aist. go. jp / aist_j / press release / pr2006 / pr2006060215 / pr20066021. html Chem. Mater. 2002, 14, 4736-4745 Adv. Mater. 2002, 14, 833-837

  As described above, in the prior art, none of the methods can solve the problem of obtaining a transparent electrode satisfying various characteristics. Accordingly, an object of the present invention is to provide a transparent conductive material having high light transmittance and low surface resistance, and improved stability and durability. Specifically, the object is to provide a metal nanowire having excellent conductivity and improved stability and durability, and a method for producing the same, and further has high light transmittance and low surface resistance, and is stable and durable. It is an object of the present invention to provide a transparent conductor having improved properties and capable of reducing manufacturing cost and environmental load by liquid phase film formation.

  A metal nanowire containing silver and at least one metal other than silver, the surface of the metal nanowire having a substantially uniform metal composition containing at least one metal other than silver and silver. The inventors have found that the problems can be solved and have reached the present invention. In addition, by using a transparent resin film for the transparent support, a transparent conductor satisfying both lightness and flexibility can be obtained.

  That is, the above object according to the present invention is achieved by the following configuration.

  1. A metal nanowire containing silver and at least one metal other than silver, wherein the metal composition on the surface is a uniform composition containing at least one metal other than silver.

  2. 2. The metal nanowire according to 1, wherein the surface has a thin layer containing at least one metal other than silver.

  3. 3. The metal nanowire according to 1 or 2, wherein the at least one metal other than silver is at least one metal selected from precious metals, iron, cobalt, copper, and tin.

  4). In a solution containing a reducing compound and a protective colloid agent, silver ions and at least one metal ion other than silver are coexisted and reduced, thereby containing at least one metal other than silver and silver The manufacturing method of the metal nanowire characterized by manufacturing the metal nanowire to perform.

  5. Silver nanowires produced by reducing silver ions in a solution containing a reducing compound and a protective colloid agent, and at least one metal other than silver in the solution containing the reducing compound and the protective colloid agent It is produced by forming a thin layer containing at least one metal other than silver on the surface of the silver nanowire by mixing at least one metal nanoparticle produced by reducing ions. A method for producing metal nanowires.

  6). 6. The method for producing metal nanowires according to 4 or 5, wherein the at least one metal other than silver is at least one metal selected from precious metals, iron, cobalt, copper, and tin.

  7). The transparent conductor which has a conductive layer on a transparent support body, The metal nanowire of any one of said 1-3 is included in this conductive layer, The transparent conductor characterized by the above-mentioned.

  According to the above-described means of the present invention, it is possible to obtain a metal nanowire having excellent conductivity and improved stability and durability as an effect thereof, and a method for producing the same, and further has high light transmittance and low surface resistance. In addition, it is possible to obtain a transparent conductor having improved stability and durability, and reduced manufacturing cost and environmental load by liquid phase film formation. The transparent conductor of the present invention is used for various optoelectronic devices such as transparent electrodes such as flat panel displays and solar cells that require high transparency and high conductivity, and electronic paper and touch panels that require lightweight and flexibility. It can be preferably used for transparent electrodes, transparent circuits, and transparent wiring.

  The metal nanowire of the present invention is a metal nanowire containing at least one metal other than silver and silver, and at least the surface thereof has a substantially uniform metal composition containing at least one metal other than silver and silver. It is the metal nanowire which has. This feature is a technical feature common to claims 1 to 8 according to the present invention.

  Hereinafter, the present invention, its components, and the best mode for carrying out the present invention will be described in detail.

[Metal nanowires]
In general, a metal nanowire refers to a linear structure having a metal element as a main constituent element and having a diameter from the atomic scale to the nm size.

  When the metal nanowire is used as a transparent conductive material, the average diameter is preferably smaller than 200 nm in order to reduce the influence of light scattering and increase the transparency. On the other hand, in order to increase the conductivity, the larger average diameter is required. Is preferred. In this invention, 10-200 nm is preferable as an average diameter of metal nanowire, and it is more preferable that it is 30-180 nm.

  In the transparent conductor of the present invention, the conductive layer exhibits conductivity by forming a three-dimensional conductive network structure by bringing the metal nanowires into contact with each other. Therefore, a longer metal nanowire is preferable because it is advantageous for forming a conductive network. On the other hand, when the metal nanowire is too long, the metal nanowires are entangled with each other to form an aggregate, and as a result, light scattering may occur. Since the rigidity and diameter of the metal nanowire influence the formation of the conductive network and the formation of aggregates, it is preferable to use a metal wire having an optimum wire length according to the material of the metal nanowire to be used. When the metal nanowire of the present invention is used for the transparent conductor of the present invention, the average length of the metal nanowire is preferably about 3 to 500 μm, more preferably 5 to 300 μm.

  In the present invention, the average diameter and average length and average aspect ratio (average length / average diameter) of the metal nanowires of the present invention are obtained by taking an electron micrograph of a sufficient number of metal nanowires, From the measured length, it can be obtained by arithmetic average. Strictly speaking, the length of the metal nanowire should be measured in a linearly stretched state, but in reality it may be curved, so the projected diameter of the nanowire can be measured using an image analyzer from an electron micrograph. Further, the projected area may be calculated and calculated assuming a cylindrical body (length = projected area / projected diameter). The number of measured metal nanowires is preferably at least 100 or more, and more preferably 300 or more.

  The metal nanowire of the present invention is characterized by containing silver and at least one metal other than silver.

  A metal other than silver contained in the metal nanowire of the present invention is not particularly limited, and may contain at least one kind of noble metal or base metal, but noble metals other than silver (for example, gold, platinum, palladium, rhodium, iridium) , Ruthenium, osmium), iron, cobalt, copper, and at least one metal belonging to the group consisting of copper and tin, and more preferably noble metals other than silver.

  Since silver has the highest conductivity among metals, it is preferable that the average silver content in the average metal composition of the metal nanowire of the present invention is higher. On the other hand, silver is considered to be the metal that is most likely to cause migration among metals, and in order to enhance the effect of preventing sulfidation, oxidation, and magnetization of the metal nanowire, the average metal composition on the surface of the metal nanowire of the present invention It is preferable to increase the total content of metals excluding silver. Specifically, the average content of silver in the average metal composition of the metal nanowire of the present invention is 50.0 atomic% (hereinafter abbreviated as at%) or more, and is 50.0 to 99.5 at%. It is preferably 90.0 to 99.5 at%. The total content of metals excluding silver in the average metal composition on the surface of the metal nanowire of the present invention is 1.0 at% or more, preferably 1.0 to 99.0 at%, and preferably 3.0 to 90 More preferably, it is 0.0 at%.

  In the metal nanowire containing silver and at least one metal other than silver in the present invention, the metal composition on at least the surface of the metal nanowire has a uniform metal composition including at least one metal other than silver. It is characterized by. In the present invention, the surface of the metal nanowire means a portion having a thickness of several atomic layers to several tens of atomic layers from the outermost surface to the inside of the metal nanowires. Specifically, electron microanalysis (EPMA) is performed. It means an analysis thickness region that can be used for quantitative analysis. In the present invention, the uniform metal composition may be an ordered alloy in which the microscopic atomic arrangement of each constituent metal element is regular, or the microscopic atomic arrangement of each constituent metal element may be It may be an irregular (random) irregular alloy. The metal nanowire of the present invention may have a metal composition on the surface that may be the same as or different from the metal composition of the entire nanowire or the metal composition inside the nanowire.

  In the present invention, having a thin layer containing at least one kind of metal other than silver on the surface of the silver nanowire means that an epitaxial junction having a metal composition containing at least one kind of metal other than silver is formed on almost the entire area of the surface of the silver nanowire. The case where it has a layer on the surface of the silver nanowire or the case where it has a solid solution layer or alloy layer of at least one metal other than silver on the surface of the silver nanowire.

  In the present invention, the average metal composition of metal nanowires can be quantitatively analyzed using, for example, X-ray photoelectron spectroscopy (XPS). The metal composition on the surface of the metal nanowire can be quantitatively analyzed using, for example, electron beam microanalysis (EPMA). Similarly, the uniformity of the metal composition on the surface of the metal nanowire can be evaluated by measuring at least 5 discrete metal compositions on each surface for 10 or more metal nanowires using EPMA. In the present invention, that the metal composition on the surface of the metal nanowire is uniform means that the silver content distribution (= standard deviation of silver content / average silver content × 100%) in the surface metal composition is 20% or less. Means the case.

  The metal composition of the inside and the surface of the metal nanowire is prepared by preparing a cross-section sample of the metal nanowire using a microtome etc. It can investigate by analyzing using etc. In the present invention, the metal nanowire having a thin layer containing at least one metal other than silver on the surface of the silver nanowire is formed by uniformly forming a metal layer containing at least one metal other than silver on the surface of the silver nanowire. The metal composition of the inner region and the surface region of the manufactured metal nanowire or the metal nanowire analyzed by the above method is such that the metal composition of the inner region is silver and the metal composition of the surface region is at least one other than silver A metal nanowire containing a metal. In the present invention, the thickness of the thin layer is preferably 10 nm or less, and preferably 0.5 to 5 nm.

[Metal nanowire manufacturing method]
In general, metal nanowires can be produced by reducing metal ions to form metal nanoparticles and forming metal nanowires by Ostwald ripening between metal nanoparticles, or by first reducing metal ions in the nucleation step. After forming nanoparticles as nuclei, there is a method of forming metal nanowires by growing metal particles by reducing and depositing metal ions on the nuclei particles in the particle growth step. From the viewpoint of improving controllability of the form (diameter and length) of the nanowire and the metal composition, a method of forming the metal nanowire by separating the nucleation step and the particle growth step is used.

  In the present invention, the nanoparticles used as the nucleus when forming the metal nanowire by separating the nucleation step and the particle growth step may be silver nanoparticles, or at least one metal other than silver and silver. The metal nanoparticle containing this may be sufficient, and the metal nanoparticle containing at least 1 sort (s) of metals other than silver may be sufficient.

  The metal nanowire production method of the present invention includes 1) a step of reducing silver ions and at least one metal ion other than silver in a solution containing a reducing compound and a protective colloid agent. , A method of producing a metal nanowire containing silver and at least one metal other than silver, or 2) a silver nanowire produced by reducing silver ions in a solution containing a reducing compound and a protective colloid agent, The surface of the silver nanowire is mixed with at least one metal nanoparticle prepared by reducing at least one metal ion other than silver in a solution containing a reducing compound and a protective colloid agent. Metal nanowires are produced by a method of producing a thin layer containing at least one metal other than silver.

  In the method 1), metal nanowires containing silver and at least one metal other than silver and having a uniform metal composition on the surface and inside of the metal nanowires can also be formed. As a method for adding metal ions, for example, a silver salt solution and at least one metal salt solution other than silver may be prepared and added, respectively, or at least one metal salt other than silver salt and silver may be added. You may prepare and add the solution containing together.

  In the method 2), metal nanoparticles containing at least one metal other than silver mixed with silver nanowires are dissolved by Ostwald ripening action and re-deposited on the surface of the silver nanowires. It is possible to uniformly form an epitaxial junction layer composed of a metal composition of the above and a thin layer composed of a solid solution layer of silver and the metal nanoparticles on the surface of the silver nanowire, so that stability and durability (migration resistance, sulfidation resistance, Oxidation resistance) and electrical conductivity are preferable. In the case of forming a thin layer containing at least two kinds of metals other than silver on the surface of the silver nanowire by the method 2), one kind of metal nanoparticles composed of at least two kinds of metals other than silver is used. Alternatively, a plurality of types of metal nanoparticles having different metal compositions may be used.

  In the present invention, there are no particular limitations on the source of silver ions and at least one metal ion other than silver, and metal halides, acetate metal salts, metal perhalogenates, metal sulfates, metal nitrates, metal carbonates Various metal salts such as salts and oxalic acid metal salts can be used. Usually, these metal salts can be dissolved in a solvent such as water and used as a metal salt solution. The concentration of silver ions or at least one metal ion other than silver in the solution can be appropriately set to a preferable concentration. However, when the concentration is reduced, the reduction reaction of ions in the reaction solution, metal nanowires or metal On the other hand, it is preferable to make the formation reaction of the nanoparticles uniform. On the other hand, it is preferable to increase the concentration because the yield of metal nanoparticles and metal nanowires can be increased. Therefore, the volume molar concentration of the solution added in the present invention is preferably 0.001 to 1M.

  In the metal nanowire according to the present invention, the improvement in migration resistance, sulfidation resistance, and oxidation resistance is obtained by the feature that the metal composition on the surface of the metal nanowire is uniform including at least one metal other than silver.

  As a simple method of forming a layer containing a metal other than silver on the surface of the silver nanowire, the silver nanowire is immersed in a metal salt aqueous solution having a smaller ionization tendency than silver, and the silver nanowire surface is more ionized than silver ions and silver. There is a method of replacing small metal ions (conversion method). However, in the conversion method, a metal having a lower ionization tendency than silver is localized on a part of the surface of the silver nanowire, so that a uniform thin layer cannot be formed. Therefore, the effect of improving stability and durability cannot be obtained.

[Compound having reducibility]
In the method for producing metal nanowires of the present invention, the reducing compound used for the production of metal nanowires, silver nanowires, or metal nanoparticles is not particularly limited as long as it is a compound that can reduce the target metal. And at least one selected from general chemical reducing agents can be used. Examples of compounds having reducibility that can be preferably used in the present invention include primary or secondary alcohols, glycols, ethers in which a hydrogen atom is bonded to a carbon atom adjacent to an oxygen atom, ethanolamines, Examples thereof include at least one selected from the group consisting of borohydrides and hydrazines.

[Protective colloid agent]
In the present invention, the protective colloid agent used in the production of metal nanowires, silver nanowires, or metal nanoparticles has a protective colloid action on microstructures such as target metal nanowires and nanoparticles. If it is a compound, there will be no restriction | limiting in particular, For example, a hydrophilic polymer, a metal coordination molecule, an amphiphilic molecule, an anionic compound etc. can be mentioned.

  Examples of the hydrophilic polymer applicable to the present invention include amide groups, hydroxyl groups such as polyvinylpyrrolidone [eg, poly (N-vinyl-2-pyrrolidone)], polyvinyl alcohol, and poly (meth) acrylate. In addition to polymers containing carboxyl groups and / or amino groups or copolymers of these monomers for forming a hydrophilic homopolymer, natural products such as cyclodextrin, aminopectin, methylcellulose, gelatin and the like can be mentioned.

  Examples of metal coordinating molecules applicable to the present invention include functional groups capable of coordinating to metals such as amino groups, thiol groups, disulfide groups, amide groups, carboxylic acid groups, phosphine groups, and sulfonic acid groups. Mention may be made of organic molecules having one or more, carbon monoxide, and nitric oxide.

  Examples of amphiphilic molecules applicable to the present invention include various monofunctional or polyfunctional surfactants (any of anionic, cationic, nonionic, and amphoteric), such as sodium dodecyl sulfate, polyethylene glycol monolaur. Rate.

  Examples of anionic compounds applicable to the present invention include halides such as chlorides, perchlorates, various alkoxides, and salts of carboxylic acids such as oxalic acid, tartaric acid, and citric acid. Examples thereof include alkali metal salts, ammonium salts, and amine salts.

  In this invention, the usage-amount of a protective colloid agent should just exist 0.1 mol or more with respect to 1 mol of metals, Preferably it is 1-50 mol. In addition, when the colloid protective agent is a polymer, the one converted to the number of moles per monomer unit is applied.

[Form control agent]
In the present invention, it is preferable to use a shape control agent in order to form metal nanowires. The shape control agent is a compound having a function of defining the growth direction of metal particles in a one-dimensional manner. In many cases, the shape control agent preferentially or selectively adsorbs on a specific crystal plane of a target particle to control the growth orientation by suppressing the growth of the adsorption plane. In the present invention, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol and the like listed as exemplary compounds of the protective colloid agent can be preferably used as a form control agent for nanowire particle formation.

[Transparent conductor]
In the transparent conductor of the present invention, the conductive layer may contain a transparent binder material or additive in addition to the metal nanowire of the present invention. The transparent binder material can be selected from a wide range of natural polymer resins or synthetic polymer resins. For example, transparent thermoplastic resin (eg, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, nitrocellulose, chlorinated polyethylene, chlorinated polypropylene, vinylidene fluoride), heat / light / electron beam A transparent curable resin that is cured by radiation (for example, melamine acrylate, urethane acrylate, epoxy resin, polyimide resin, silicone resin such as acrylic-modified silicate) can be used. Examples of additives include stabilizers such as plasticizers and antioxidants, surfactants, dissolution accelerators, polymerization inhibitors, and colorants such as dyes and pigments. Furthermore, from the viewpoint of improving workability such as coating properties, solvents (for example, water, organic solvents such as alcohols, glycols, cellosolves, ketones, esters, ethers, amides, hydrocarbons, etc.) are used. May be included.

  The thickness of the conductive layer containing the metal nanowires varies depending on the average diameter and content of the metal nanowires to be used, but as a rough guide, it is preferably not less than the average diameter of the metal nanowires and not more than 500 nm. It is preferable to reduce the thickness of the conductive layer including the metal nanowire of the present invention because the network formation of conductive fibers in the thickness direction can be made dense.

  The transparent conductor of the present invention may contain a conductive polymer in the conductive layer according to the present invention or other conductive layers. Examples of the conductive polymer that can be used in the transparent conductor of the present invention include polypyrrole, polyaniline, polythiophene, polythienylene vinylene, polyazulene, polyisothianaphthene, polycarbazole, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, poly Examples thereof include compounds selected from the group consisting of phenylacetylene, polydiacetylene and polynaphthalene derivatives.

  The transparent conductor of the present invention may contain one kind of conductive polymer alone or may contain two or more kinds of conductive polymers in combination, but from the viewpoint of conductivity and transparency. To polyaniline having a repeating unit represented by the following general formula (I) or general formula (II) or a derivative thereof, a polypyrrole derivative having a repeating unit represented by the following general formula (III), or the following general formula (IV) More preferably, it contains at least one compound selected from the group consisting of polythiophene derivatives having a repeating unit represented by the formula:

  In the above general formula (III) and general formula (IV), R is mainly a linear organic substituent, preferably an alkyl group, an alkoxy group, an allyl group, or a combination of these groups. As long as it does not lose its properties, a sulfonate group, an ester group, an amide group, or the like may be bonded to or combined with these. Note that n is an integer.

The conductive polymer used in the transparent conductor of the present invention can be subjected to a doping treatment in order to further increase the conductivity. As a dopant for the conductive polymer, for example, a sulfonic acid having a hydrocarbon group having 6 to 30 carbon atoms (hereinafter also referred to as a long-chain sulfonic acid) or a polymer thereof (for example, polystyrene sulfonic acid), a halogen atom Lewis acid, proton acid, transition metal halide, transition metal compound, alkali metal, alkaline earth metal, MClO ₄ (M = Li ⁺ , Na ⁺ ), R ₄ N ⁺ (R = CH ₃ , C ₄ H ₉ , C ₆ H ₅ ), or R ₄ P ⁺ (R═CH ₃ , C ₄ H ₉ , C ₆ H ₅ ). Of these, the long-chain sulfonic acid is preferable.

Examples of the long chain sulfonic acid include dinonyl naphthalene disulfonic acid, dinonyl naphthalene sulfonic acid, and dodecylbenzene sulfonic acid. Examples of the halogen include Cl ₂ , Br ₂ , I ₂ , ICl ₃ , IBr, IF _{5 and the} like. Examples of the Lewis acid include PF ₅ , AsF ₅ , SbF ₅ , BF ₃ , BCl ₃ , BBr ₃ , SO ₃ , and GaCl ₃ . Examples of the protonic acid include HF, HCl, HNO ₃ , H ₂ SO ₄ , HBF ₄ , HClO ₄ , FSO ₃ H, ClSO ₃ H, CF ₃ SO ₃ H, and the like. The transition metal _{halide, NbF 5, TaF 5, MoF} 5, WF 5, RuF 5, BiF 5, TiCl 4, ZrCl 4, MoCl 5, MoCl 3, WCl 5, FeCl 3, TeCl 4, SnCl 4, SeCl ₄ , FeBr ₃ , SnI _{5 and the} like. The transition metal _{compound, AgClO 4, AgBF 4, La} (NO 3) 3, Sm (NO 3) 3 and the like. Examples of the alkali metal include Li, Na, K, Rb, and Cs. Examples of the alkaline earth metal include Be, Mg, Ca, Sc, and Ba.

The dopant for the conductive polymer may be introduced into fullerenes such as hydrogenated fullerene, hydroxylated fullerene, and sulfonated fullerene. In the transparent electrode, the dopant is preferably contained in an amount of 0.001 part by mass or more with respect to 100 parts by mass of the conductive polymer. Furthermore, it is more preferable that 0.5 mass part or more is contained. The transparent conductor of the present invention includes a long-chain sulfonic acid, a polymer of long-chain sulfonic acid (for example, polystyrene sulfonic acid), halogen, Lewis acid, proton acid, transition metal halide, transition metal compound, alkali metal, Both at least one dopant selected from the group consisting of alkaline earth metals, MClO ₄ , R ₄ N ⁺ , and R ₄ P ⁺ and fullerenes may be included.

  As the conductive polymer used in the transparent conductor of the present invention, a conductive polymer modified by a metal disclosed in JP-T-2001-511581, JP-A-2004-99640, JP-A-2007-165199, or the like. Can also be used.

  The conductive layer containing the conductive polymer according to the transparent conductor of the present invention may contain a water-soluble organic compound. Among water-soluble organic compounds, compounds having an effect of improving conductivity by adding to a conductive polymer material are known, and 2nd. Sometimes called a dopant (or sensitizer). 2nd. Which can be used in the transparent conductor of the present invention. There is no restriction | limiting in particular in a dopant, It can select suitably from well-known things, For example, an oxygen containing compound is mentioned suitably.

  The oxygen-containing compound is not particularly limited as long as it contains oxygen, and examples thereof include a hydroxyl group-containing compound, a carbonyl group-containing compound, an ether group-containing compound, and a sulfoxide group-containing compound. Examples of the hydroxyl group-containing compound include ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, and glycerin. Among these, ethylene glycol and diethylene glycol are preferable. Examples of the carbonyl group-containing compound include isophorone, propylene carbonate, cyclohexanone, and γ-butyrolactone. Examples of the ether group-containing compound include diethylene glycol monoethyl ether. Examples of the sulfoxide group-containing compound include dimethyl sulfoxide. These may be used alone or in combination of two or more, but it is particularly preferable to use at least one selected from dimethyl sulfoxide, ethylene glycol, and diethylene glycol.

  In the conductive layer containing the conductive polymer according to the transparent conductor of the present invention, the 2nd. 0.001 mass part or more is preferable, as for content of a dopant, 0.01-50 mass parts is more preferable, and 0.01-10 mass parts is especially preferable.

  The conductive layer containing the conductive polymer according to the transparent conductor of the present invention may contain a transparent resin component or additive in addition to the conductive polymer in order to ensure film formability and film strength. . The transparent resin component is not particularly limited as long as it is compatible or mixed and dispersed with the conductive polymer, and may be a thermosetting resin or a thermoplastic resin. For example, polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, polyimide resins such as polyimide and polyamideimide, polyamide resins such as polyamide 6, polyamide 6,6, polyamide 12 and polyamide 11, polyvinylidene fluoride, Fluorine resin such as polyvinyl fluoride, polytetrafluoroethylene, ethylene tetrafluoroethylene copolymer, polychlorotrifluoroethylene, etc., vinyl resin such as polyvinyl alcohol, polyvinyl ether, polyvinyl butyral, polyvinyl acetate, polyvinyl chloride, epoxy resin, xylene Resin, aramid resin, polyurethane resin, polyurea resin, melamine resin, phenol resin, polyether, acrylic resin and their co-polymer Body, and the like.

  Various functional layers such as a hard coat layer, a non-glare coat layer, a barrier coat layer, an anchor coat layer, a carrier transport layer, and a carrier accumulation layer can be added to the transparent conductor of the present invention as necessary. When providing a hard coat layer or a non-glare coat layer, it is preferable to place the transparent support on the opposite side of the conductive layer according to the present invention, and when providing a barrier coat layer, a transparent support. Is preferably disposed between the conductive layer according to the present invention, and in the case of providing an anchor coat layer, a carrier transport layer, or a carrier accumulation layer, the transparent support is the same as the conductive layer according to the present invention. It is preferable to arrange on the side.

  There is no restriction | limiting in particular in the thickness of the transparent conductor of this invention, Although it can select suitably according to the objective, Generally it is preferable that it is 10 micrometers or less, and since transparency improves as thickness becomes thin, it is more preferable. .

The total light transmittance in the transparent conductor of the present invention is preferably 60% or more, more preferably 70% or more, and particularly preferably 80% or more. The total light transmittance can be measured according to a known method using a spectrophotometer or the like. The electrical resistance value of the transparent electrode of the present invention is preferably 10 ⁴ Ω / □ or less, more preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less as the surface resistivity. It is particularly preferred. If it exceeds 10 ⁴ Ω / □, when used as a transparent electrode or an electromagnetic shielding material such as a liquid crystal display or a transparent touch panel, it may not function sufficiently as an electrode, or sufficient electromagnetic shielding characteristics may not be obtained. The surface resistivity can be measured based on, for example, JIS K7194, ASTM D257, etc., and can also be easily measured using a commercially available surface resistivity meter.

(Transparent support)
The transparent support constituting the transparent conductor of the present invention is not particularly limited as long as it has high light transmittance, and its material, shape, structure, thickness, etc. are appropriately selected from known ones. Can do. For example, a glass substrate, a resin substrate, a resin film, and the like are preferable in terms of excellent hardness as a base material and ease of formation of a conductive layer on the surface. It is preferable to use a resin film from the viewpoint. The resin is not particularly limited and can be appropriately selected from known ones. For example, polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, polyvinyl chloride resin, polyethersulfone resin, polycarbonate resin, Polystyrene resin, polyimide resin, polyetherimide resin, polyvinyl acetate resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyvinyl butyral resin, polymethyl methacrylate resin, polyacrylonitrile resin, polyolefin polystyrene Examples thereof include resins, polyamide resins, polybutadiene resins, cellulose acetate, cellulose nitrate, and acrylonitrile-butadiene-styrene copolymer resins. These may be used individually by 1 type and may be used in combination of 2 or more type. Among these, polyethylene terephthalate resin is preferable in terms of excellent transparency and flexibility.

[Method for producing transparent conductor]
The method for producing the transparent conductor of the present invention is not particularly limited, but from the viewpoints of productivity and production cost, electrode quality such as smoothness and uniformity, and reduction of environmental burden, a coating method is used for forming the conductive layer. It is preferable to use a liquid phase film forming method such as a printing method. As coating methods, roll coating method, bar coating method, dip coating method, spin coating method, casting method, die coating method, blade coating method, bar coating method, gravure coating method, curtain coating method, spray coating method, doctor coating method Etc. can be used. As the printing method, a letterpress (letter) printing method, a stencil (screen) printing method, a lithographic (offset) printing method, an intaglio (gravure) printing method, a spray printing method, an ink jet printing method, and the like can be used. Moreover, a transparent conductive material containing the metal nanowire of the present invention can be patterned on a transparent support to form a transparent wiring or a transparent circuit. In addition, as necessary, physical surface treatment such as corona discharge treatment or plasma discharge treatment may be applied to the transparent support surface as a preliminary treatment for improving adhesion and coating properties.

  In the present invention, metal nanowires produced in an aqueous system can be subjected to a hydrophobization treatment as necessary. As a method for hydrophobizing metal nanowires, for example, JP 2007-500606 A can be referred to.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

Example 1
<Production of metal nanowires>
[Production of Metal Nanowire SW-10: Comparative Example]
Using ethylene glycol (EG) as a reducing agent and polyvinylpyrrolidone (PVP) as a protective colloid agent and form control agent with reference to the method described in Non-Patent Document 4 (Adv. Mater. 2002, 14, 833-383) In addition, the nucleation step and the particle growth step 1 were separated, and silver nanowires were produced by the following method.

(Nucleation process)
While stirring 100 ml of EG solution maintained at 170 ° C. in the reaction vessel, 10 ml of EG solution of silver nitrate (silver nitrate concentration: 1.5 × 10 ⁻⁴ mol / L) was added at a constant flow rate for 10 seconds. Thereafter, aging was carried out at 170 ° C. for 10 minutes to form silver core particles. The reaction solution after completion of ripening exhibited a yellow color derived from surface plasmon absorption of silver nanoparticles, and it was confirmed that silver ions were reduced and silver nanoparticles were formed.

(Particle growth process 1)
The reaction solution containing the core particles after completion of the ripening is kept at 170 ° C. with stirring, and 100 ml of an EG solution of silver nitrate (silver nitrate concentration: 1.0 × 10 ⁻¹ mol / L) and an EG solution of PVP (PVP) 100 ml of a concentration of 5.0 × 10 ⁻¹ mol / L) was added at a constant flow rate for 100 minutes using the double jet method. When the reaction solution was sampled every 20 minutes in the particle growth process and confirmed with an electron microscope, the silver nanoparticles formed in the nucleation process grew mainly in the long axis direction of the nanowires over time. No new core particles were observed in the grain growth process.

(Washing process)
After completion of the particle growth step, the reaction solution was cooled to room temperature, filtered using a filter, and the silver nanowires separated by filtration were redispersed in ethanol. Filtration of silver nanowires with a filter and redispersion in ethanol were repeated 5 times. Finally, an ethanol dispersion of silver nanowires was prepared to produce metal nanowire SW-10.

  When a small amount of the obtained dispersion was collected and confirmed with an electron microscope, it was confirmed that silver nanowires having an average diameter of 85 nm and an average length of 7.4 μm were formed.

[Production of Metal Nanowire SW-11: Present Invention]
Metal nanowire SW-11, which is a silver-platinum nanowire, was produced in the same manner as in the production of metal nanowire SW-10 except that particle growth step 1 was changed to particle growth step 2 shown below.

(Particle growth process 2)
The reaction solution containing the ripened core particles is kept at 170 ° C. with stirring, and a mixed EG solution of silver nitrate and platinum (II) chloride (silver nitrate concentration: 9.5 × 10 ⁻² mol / L, platinum chloride concentration: 0.5 × 10 ⁻² mol / L) and 100 ml of PVP EG solution (PVP concentration: 5.0 × 10 ⁻¹ mol / L) were added at a constant flow rate for 100 minutes using the double jet method. did. When the reaction solution was collected every 20 minutes in the particle growth step and confirmed with an electron microscope, the silver nanoparticles formed in the nucleation step grew mainly in the major axis direction of the nanowire with time, Generation of new core particles in the grain growth process was not observed.

[Production of Metal Nanowire SW-12: Present Invention]
In the production of the metal nanowire SW-10, a metal nanowire SW-12 that is a silver-gold nanowire was produced in the same manner except that the particle growth step 1 was changed to the particle growth step 3 shown below.

(Particle growth process 3)
The reaction solution containing the core particles after ripening was kept at 170 ° C. with stirring, and a mixed EG solution of silver nitrate and chloroauric acid (silver nitrate concentration: 9.5 × 10 ⁻² mol / L, chloroauric acid concentration: 0) .5 × 10 ⁻² mol / L) and 100 ml of PVP EG solution (PVP concentration: 5.0 × 10 ⁻¹ mol / L) were added at a constant flow rate for 100 minutes using the double jet method. . In the particle growth process, the reaction solution was sampled every 20 minutes and confirmed with an electron microscope. The silver nanoparticles formed in the nucleation process grew mainly in the major axis direction of the nanowires over time. No new core particles were observed in the grain growth process.

[Production of Metal Nanowire SW-13: Present Invention]
J. et al. Phys. Chem. With reference to the method described in B205, 109, 16326-16331, a dispersion of PVP-protected platinum nanoparticles prepared by reducing platinum ions in the presence of a PVP-protected colloid was prepared in advance. In the same manner as in the production of the metal nanowire SW-10, the process up to the particle formation process was completed to produce a silver nanowire. Subsequently, metal nanowire SW-13 which is a silver-platinum nanowire was produced by the particle ripening process and the water washing process shown below.

(Particle ripening process)
After carrying out the processing up to the particle growth step in the same manner as in the preparation of the metal nanowire SW-10, the PVP-protected platinum nanoparticle dispersion 3 prepared in advance while maintaining the reaction solution at 170 ° C. and stirring. An amount equivalent to × 10 ⁻⁴ mol was added over 5 minutes, and further aging was performed at 170 ° C. for 10 minutes.

(Washing process)
The treatment was performed in the same water washing step as used in the production of the metal nanowire SW-10.

[Production of Metal Nanowire SW-14: Present Invention]
J. et al. Phys. Chem. With reference to the method described in B205, 109, 16326-16331, a dispersion of PVP-protected gold nanoparticles prepared by reducing gold ions in the presence of a PVP-protected colloid was prepared in advance. In the same manner as in the production of the metal nanowire SW-10, the process up to the particle formation process was completed to produce a silver nanowire. Subsequently, metal nanowire SW-14 which is silver-gold nanowire was produced by the particle ripening process and the water washing process shown below.

(Particle ripening process)
After carrying out the processing up to the particle growth step in the same manner as in the preparation of the metal nanowire SW-10, the PVP-protected gold nanoparticle dispersion 3 prepared in advance was kept while stirring at 170 ° C. An amount equivalent to × 10 ⁻⁴ mol was added over 5 minutes, and further aging was performed at 170 ° C. for 10 minutes.

(Washing process)
The treatment was performed in the same water washing step as used in the production of the metal nanowire SW-10.

[Production of Metal Nanowire SW-15: Comparative Example]
A silver nanowire was formed in the same manner as in the production of the metal nanowire SW-10, and then washed with water. Next, an ethanol solution of chloroauric acid was added in an amount equivalent to 3 × 10 ⁻⁴ mol at 23 ° C. with stirring, and the mixture was allowed to stand with stirring for 10 minutes to produce a metal nanowire SW-15 that was a silver-gold nanowire. did.

<Composition analysis of metal nanowires>
About each metal nanowire produced as mentioned above, an average metal composition, the metal composition of each metal nanowire surface, and uniformity were measured using the above-mentioned method and analytical instrument, and the obtained result is shown in Table 1. In addition, as for the display method of the metal composition described in Table 1, for example, in the description of Ag _m Pt _n , the average content of Ag is m (at%), and the average content of Pt is n (at%). It means that there is.

  As apparent from the results shown in Table 1, the metal nanowire SW-11 formed by simultaneously adding and simultaneously reducing silver ions and at least one metal ion other than silver according to the production method of the present invention; It can be seen that SW-12 has a highly uniform metal composition including a metal other than silver on its surface.

  Moreover, in metal nanowire SW-15 by which gold | metal | money was provided to silver nanowire by the conventionally known conversion method, the silver content distribution of the surface has a very large value. This is presumably because the substitution reaction between silver ions and gold ions on the surface of the silver nanowire does not occur uniformly over the entire surface, and a local substitution reaction occurs. On the other hand, silver nanowires prepared by reducing silver ions in a solution containing a protective colloid agent according to the production method of the present invention, and at least one metal ion other than silver in a solution containing the protective colloid agent The metal nanowires SW-13 and SW-14 formed by mixing at least one kind of metal nanoparticles produced by reduction have a highly uniform metal composition including a metal other than silver on the surface thereof. You can see that Further, in contrast to the metal nanowires SW-11 and SW-12, the metal nanowires SW-13 and SW-14 are made of metal other than silver on the surface in spite of a small relative molar addition amount of metal other than silver to silver. It can be seen that the content is high, and metals other than silver are uniformly localized on the surface.

Example 2
<< Production of transparent conductor >>
[Production of Transparent Conductor TC-20: Comparative Example]
Using the dispersion liquid of metal nanowire SW-10 produced in Example 1, a transparent conductor TC-20 was produced according to the method shown below.

On a polyethylene terephthalate (PET) support having a total light transmittance of 90%, a dispersion of metal nanowire SW-10 was applied using a spin coater so that the amount of metal nanowires was 0.3 g / m ² and dried. did. Subsequently, after applying a calender treatment to the coating layer of the metal nanowire SW-10, a methyl isobutyl ketone solution of urethane acrylate was applied using a spin coater and dried to prepare a transparent conductor TC-20. In addition, the film thickness of the urethane acrylate layer was set to a thickness at which a part of the metal nanowire layer was exposed from the urethane acrylate layer without completely burying the metal nanowire layer and the metal nanowire layer could be fixed to the support.

  The total light transmittance and surface resistivity (based on JIS K7194) of the produced transparent conductor sample TC-20 were measured. As a result, the transparent conductor TC-20 had a total light transmittance of 86% and a surface resistivity of 32Ω / □.

[Production of Transparent Conductors TC-21 to TC-25]
In the production of the transparent conductor TC-20, the transparent conductors TC-21 to TC- were similarly used except that the metal nanowires SW-11 to SW-15 were used instead of the metal nanowires SW-10 used. 25 was produced.

  Subsequently, the total light transmittance and surface resistivity of each transparent conductor were measured by the same method as the transparent conductor TC-20. As a result, it was confirmed that all of the transparent conductors TC-21 to TC-25 had the same total light transmittance and surface resistivity as the transparent conductor TC-20 within the measurement error range. In particular, the transparent conductors TC-23 and TC-24 produced using the metal nanowires SW-13 and SW-14 contain a metal having a lower conductivity than silver on the surface based on the results of Example 1. However, it is considered that the surface resistivity equivalent to that of the transparent conductor TC-20 was obtained because the surface layer containing a metal other than silver was very thin.

Example 3
<< Evaluation of transparent conductor >>
Using the transparent conductors TC-20 to TC-25 produced in Example 2, the migration resistance was evaluated by a forced deterioration test as follows.

  Each transparent conductor was cut into a 4 cm × 1 cm strip, and gold electrodes with a width of 0.5 cm were formed on both short sides by vapor deposition. In accordance with the environmental conditions of the steady test method of JIS-O60068-2-3, a constant current is passed between both gold electrodes using a constant temperature and humidity chamber at 40 ° C. and 93% RH, and urethane on the surface of the transparent conductor The time-dependent change of the metal nanowires exposed from the acrylate layer was observed and evaluated with an electron microscope.

The results obtained by observation with an electron microscope were subjected to sensory evaluation, and sheet glare resistance was evaluated according to the following criteria.
◎: No change in metal nanowires is observed. ○: Almost no change in metal nanowires is observed. △: Metal nanowires are slightly dissolved, precipitated, or deformed by migration. : Dissolution, precipitation, and deformation of metal nanowires due to migration are clearly recognized. Evaluations located in the middle of the respective ranks are indicated by, for example, Δ to ○ and × to Δ.

  The results obtained as described above are shown in Table 2.

  As is clear from the results shown in Table 2, the transparent conductor TC-21 of the present invention using the metal nanowire of the present invention is compared to the transparent conductor TC-20 of the comparative example using the silver nanowire SW-10. It can be seen that migration resistance is greatly improved in TC-24. Among them, the migration resistance of the transparent conductors TC-23 and TC-24 using metal nanowires containing a metal having a lower conductivity than silver on the surface is better. In addition, the transparent conductor TC-25 using the metal nanowire SW-15 containing a metal other than silver shows an improvement tendency as compared with the transparent conductor TC-20, but the effect is not sufficient. As can be seen from the measurement result of the silver content distribution on the surface of Example 1, in the metal nanowire SW-15, the substitution reaction of silver ions and gold ions on the surface of the silver nanowire occurs locally, and contains gold. Surface part containing only silver because the surface part and the surface containing gold only are not mixed or silver nanowires substituted with gold ions and silver nanowires not replacing gold ions are mixed This is expected to be caused by migration progressing.

Example 4
Using the transparent conductors TC-20 to TC-25 prepared in Example 2, the resistance to sulfidation is determined from the change in surface resistivity under a dilute hydrogen sulfide gas atmosphere, and the resistance to oxidation is determined from the change in surface resistivity under an oxygen atmosphere. As in Example 3, good results were obtained in the transparent conductors TC-21 to TC-24 of the present invention.

Claims (7)

  A metal nanowire containing silver and at least one metal other than silver, wherein the metal composition on the surface is a uniform composition containing at least one metal other than silver.   The metal nanowire according to claim 1, wherein the surface has a thin layer containing at least one metal other than silver.   The metal nanowire according to claim 1 or 2, wherein the at least one metal other than silver is at least one metal selected from precious metals, iron, cobalt, copper, and tin.   In a solution containing a reducing compound and a protective colloid agent, silver ions and at least one metal ion other than silver are coexisted and reduced, thereby containing at least one metal other than silver and silver The manufacturing method of the metal nanowire characterized by manufacturing the metal nanowire to perform.   Silver nanowires produced by reducing silver ions in a solution containing a reducing compound and a protective colloid agent, and at least one metal other than silver in the solution containing the reducing compound and the protective colloid agent It is produced by forming a thin layer containing at least one metal other than silver on the surface of the silver nanowire by mixing at least one metal nanoparticle produced by reducing ions. A method for producing metal nanowires.   6. The method for producing metal nanowires according to claim 4, wherein the at least one metal other than silver is at least one metal selected from precious metals, iron, cobalt, copper and tin.   The transparent conductor which has a conductive layer on a transparent support body, The metal nanowire of any one of Claims 1-3 is included in this conductive layer, The transparent conductor characterized by the above-mentioned.