JP2009140788A - Conductive material, inkjet ink and transparent conductive film using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive material excellent in conductivity and adhesiveness; an inkjet ink containing the same; and a transparent conductive film having a conductive metal pattern formed by using the ink. <P>SOLUTION: The conductive material contains a metal fiber having a major axis size of 2 to 30 μm, and a minor axis size of 60 to 300 nm. An inkjet ink containing the same and a transparent conductive film having a conductive metal pattern formed by using the ink are also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conductive material having excellent conductivity and adhesion, an inkjet ink using the conductive material, and a transparent conductive film.

  A method of using a conductive metal pattern and a transparent conductive film in combination as one of methods for producing a flexible transparent conductive film used in liquid crystal displays, electroluminescent displays, plasma displays, electrochromic displays, solar cells, electronic paper, touch panels, etc. In view of simplification of the process and the like, there is a method in a preferable mode in which the conductive metal pattern is formed by an ink jet method (see Patent Document 1).

However, it has been difficult to achieve both dispersibility and conductivity in the conductive ink using metal fine particles. As a method for solving this problem, a conductive material containing a wire-like metal fiber having a major axis of 400 nm or more and a minor axis of 50 nm or less has been proposed (see Patent Document 2). However, by using this conductive material, good conductivity can be obtained, but since the content of the wire-like metal fiber with respect to the binder is large, the adhesion is not sufficiently satisfactory. In addition, since nozzle clogging is likely to occur, sufficient conductivity cannot be obtained by an ink jet method with a small amount of binder.
JP-A-2005-338230 JP 2005-317395 A

  The present invention has been made in view of the above problems and situations, and the problem to be solved is a conductive material excellent in conductivity and adhesiveness, an inkjet ink containing the conductive material, and a conductive material formed using the ink. It is providing the transparent conductive film which has a conductive metal pattern.

  The above-mentioned problem according to the present invention is solved by the following means.

  1. A conductive material comprising a metal fiber having a major axis diameter of 2 to 30 μm and a minor axis diameter of 60 to 300 nm.

  2. 2. The conductive material according to 1 above, wherein the conductive material contains a binder, and a mass ratio of the metal fiber to the binder is 7: 1 to 2: 1.

  3. 3. The conductive material according to 1 or 2, wherein the metal fiber contains an element selected from gold, platinum, silver, palladium, rhodium, iridium, ruthenium, osmium, iron, cobalt, copper, and tin. material.

  4). An ink-jet ink comprising the conductive material according to any one of 1 to 3 above.

  5). A transparent conductive film having a conductive metal pattern on a transparent film substrate, wherein the conductive metal pattern is formed using the inkjet ink described in 4 above.

  By the above means of the present invention, it is possible to provide a conductive material excellent in conductivity and adhesion, an inkjet ink containing the same, and a transparent conductive film having a conductive metal pattern formed using the ink. .

  That is, by means of the present invention, it is possible to provide a flexible transparent conductive film having high conductivity such as a liquid crystal display, an electroluminescence display, a plasma display, an electrochromic display, a solar cell, electronic paper, and a touch panel.

  The conductive material of the present invention is characterized by containing metal fibers having a major axis diameter of 2 to 30 μm and a minor axis diameter of 60 to 300 nm. This feature is a technical feature common to the inventions according to claims 1 to 5.

  As an embodiment of the present invention, an embodiment in which the conductive material contains a binder and the mass ratio of the metal fiber to the binder is 7: 1 to 2: 1 is preferable. The metal fiber preferably contains an element selected from gold, platinum, silver, palladium, rhodium, iridium, ruthenium, osmium, iron, cobalt, copper, and tin.

  The conductive material of the present invention can be suitably used for inkjet inks, and is further suitable for the production of a transparent conductive film having a conductive metal pattern formed using the ink on a transparent film substrate.

  In the present application, “transparent” means that the total light transmittance in the visible light wavelength region measured by a method in accordance with JIS K 7361-1: 1997 (plastic-transparent material total light transmittance test method) is 70. % Or more.

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

[Metal fiber]
The conductive material of the present invention is characterized by containing metal fibers having a major axis diameter of 2 to 30 μm and a minor axis diameter of 60 to 300 nm. Here, the “metal fiber” refers to a fibrous structure having a metal element as a main component.

  The metal fiber according to the present invention has a long axis diameter of 2 to 30 μm and a short axis diameter of 60 to 300 nm, and is very thin and long. When the major axis diameter is less than 2 μm or the minor axis diameter is less than 60 nm, sufficient conductivity cannot be obtained unless the content is increased, and conversely, the adhesion to the substrate is increased by increasing the content. Inferior to sex. On the other hand, when the major axis diameter is longer than 30 μm, the metal fibers are entangled with each other to easily form an aggregate, and when used as an inkjet ink, problems such as clogging of the head easily occur.

  The major axis diameter is more preferably 5 to 15 μm and the minor axis diameter is more preferably 90 to 200 nm. In addition, the distribution of the major axis diameter is preferably 40% or less, and the particle size distribution in the minor axis direction is preferably 20% or less.

In the present invention, the average value of the length, diameter, and aspect ratio (= length / diameter) of the metal fibers is obtained by taking an electron micrograph of a sufficient number of metal fibers and calculating the arithmetic average of the measured values of the individual metal fiber images. Can be obtained from The length of the metal fiber should be measured in a linearly stretched state, but in reality it may be bent, so the projected diameter of the metal fiber and The projected area may be calculated and calculated assuming a cylindrical body (length = projected area / projected diameter). The particle size distribution in the major axis direction or minor axis direction is represented by a value obtained by multiplying the value obtained by dividing the standard deviation of the measured particle size by the average particle size by 100.
Particle size distribution [%] = standard deviation of particle size / average particle size × 100
The number of metal fibers to be measured is preferably at least 100, more preferably 300 or more.

  The metal composition of the metal fiber according to the present invention is not particularly limited and may be composed of one or more metals of a noble metal element and a base metal element, but gold, platinum, silver, palladium, rhodium, iridium, It preferably contains a metal selected from ruthenium, osmium, iron, cobalt, copper, and tin, and more preferably contains at least silver from the viewpoint of conductivity. Furthermore, in order to achieve both electrical conductivity and stability (sulfurization and oxidation resistance of metal fibers, and resistance to magnesium), it is more preferable to include at least one metal belonging to noble metal excluding silver and silver. When the metal fiber according to the present invention contains two or more kinds of metal elements, for example, the metal composition may be different between the inside and the inside of the metal fiber, or the entire metal fiber has the same metal composition. May be.

  The metal fibers can be produced by reducing metal ions to form metal nanoparticles and forming metal fibers by Ostwald ripening between metal nanoparticles, or by first reducing metal ions in the nucleation step to form nuclei. There is a method of forming metal fibers by forming metal particles by reducing and depositing metal ions on the core particles in the particle growth step after forming the nanoparticles to be formed.

  The particle formation step according to the present invention is preferably carried out separately from the nucleation step and the particle growth step from the viewpoint of improving the controllability of the form (diameter and length) of the metal fibers and the metal composition.

  In the present application, the “nucleation step” refers to the growth nucleus in the particle growth step by adding at least one metal salt solution to the solution containing the reducing agent in the reaction vessel to reduce metal ions. The process for forming the metal fine particle (nuclear particle) to become.

  On the other hand, the “particle growth step” refers to the formation of nuclei by adding at least one metal salt solution to a solution containing a reducing agent, nuclear particles, and a shape control agent in a reaction vessel to reduce metal ions. It means a process for growing the metal core particles formed in the process into metal particles having a fibrous form.

  In order to improve the uniformity of the form (diameter and length) of the metal fibers to be formed, it is important to control the reduction reaction of metal ions so that new metal fine particles are not generated in the particle growth process. For this purpose, it is necessary to adjust the addition rate of the metal salt solution and the reduction rate of the metal ions in the particle growth step.

  In the present invention, in order to control the addition rate of the metal salt solution, it is effective to use a single jet method or a multi jet method. In order to control the reduction reaction rate, it is effective to set the kind and concentration of the reducing agent, the reaction temperature, pH, and the like to preferable conditions.

  In the single jet method and the multi jet method according to the present invention, the amount of liquid fed is controlled as necessary using an appropriate liquid feeding device or the like, and one or a plurality of additive liquids are respectively added to the liquid in the reaction vessel. It is a method of reacting in the liquid in the container by dropping or spraying or injecting on the liquid surface or in the liquid, and in the present invention, a solution containing one or more metal salt solutions and a form control agent, It can be carried out by using a solution containing an anti-aggregation agent, a solution containing a reducing agent, or the like as the additive solution.

  In the present invention, the molar ratio of the metal salt (metal ion) used in the nucleation step and the particle growth step can be arbitrarily changed. In addition, the particle size and aspect ratio can be controlled by adjusting the molar ratio. For example, when forming a metal fiber having a high average aspect ratio, it is advantageous to reduce the molar ratio of the metal salt used in the nucleation process to the metal salt used in the entire particle production process. This is because the particle growth process greatly contributes to the formation of metal fibers. Accordingly, in the present invention, the molar ratio of the metal salt used in the nucleation step is preferably set to 10 mol% or less, more preferably 5 mol% or less, and further preferably 0.001 to 1 mol%. .

  In the present invention, the type of metal salt used in the nucleation step and the grain growth step is not particularly limited, and is a metal halide, metal acetate, metal perhalogenate, metal sulfate, metal nitrate, metal carbonate. 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 metal ions in the solution can be appropriately set to a preferable concentration, but reducing the concentration is preferable in order to make the reduction reaction of metal ions in the reaction solution and the formation reaction of metal fibers uniform, On the other hand, it is preferable to increase the concentration because the metal fiber yield can be increased. Therefore, the volume molar concentration of the metal salt solution added in the present invention is preferably 0.001 to 1M.

  In the present invention, when forming a metal fiber by separating the nucleation step and the particle growth step, the type of metal salt used in the nucleation step and the type of metal salt used in the particle growth step are the same. May be different.

  The “form control agent” used in the particle formation step according to the present invention is a compound having a function of defining the growth direction of metal particles in a one-dimensional manner, and is formed in the particle formation step by using the form control agent. The ratio of metal fibers that are made can be increased. 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.

  Examples of the shape control agent used in the particle forming step according to the present invention include hydrophilic polymers and amphiphilic molecules.

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

  Examples of amphiphilic molecules include various monofunctional or polyfunctional surfactants (any of anionic, cationic, nonionic, and amphoteric), such as sodium dodecyl sulfate, polyethylene glycol monolaurate, and the like. it can.

  The amount of the form control agent used is preferably 0.1 mol or more, more preferably 1 to 50 mol, relative to 1 mol of the metal. When the form control agent is a polymer, the molar amount means a value converted to the number of moles of the monomer unit.

  In the present invention, the aggregation preventing agent used in the particle forming step according to the present invention in the particle forming step is not particularly limited as long as it is a compound having a protective colloid function with respect to the target metal nanowire. And a conductive polymer, a metal coordinating molecule, an amphiphilic molecule, and an anionic compound.

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

  Examples of metal coordinating molecules include organic molecules having one or more 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. And carbon monoxide and nitric oxide.

  Examples of amphiphilic molecules include various monofunctional or polyfunctional surfactants (any of anionic, cationic, nonionic, and amphoteric), such as sodium dodecyl sulfate, polyethylene glycol monolaurate, and the like. it can.

  Examples of the anionic compound include halides such as chlorides, perchlorates, various alkoxides, and salts of carboxylic acids such as oxalic acid, tartaric acid, citric acid, and the like. Examples thereof include salts, ammonium salts, and amine salts.

  In the particle forming step according to the present invention, among the above compounds, it is preferable to use a water-soluble polymer containing an amide group, a hydroxyl group, a carboxyl group and / or an amino group.

  Polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and the like listed as exemplary compounds of the form control agent also function as an anti-aggregation agent for forming metal nanowires, and therefore can be preferably used in the present invention as an anti-coagulation agent. .

  In the present invention, the reducing agent for reducing the metal ion is not particularly limited as long as it is a compound capable of reducing the target metal, and at least one selected from general chemical reducing agents can be used. Examples of the reducing agent 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, borohydride. And at least one selected from the group consisting of hydrazines.

  Furthermore, in this invention, it is preferable to have the process (form control agent removal process) which removes the form control agent used at the particle formation process using an ultrafiltration membrane etc. after the particle formation process.

  Moreover, in this invention, it is preferable to have a dispersion | distribution process for the purpose of preventing aggregation of a metal fiber.

  In the production method according to the present invention, as a method for suppressing the aggregation of the metal fibers in the metal fiber dispersion and highly dispersing the polymer fibers, an active agent having a polar part and a nonpolar part is used as the metal fiber. A method of adsorbing on the surface and suppressing the formation of aggregates by the steric hindrance effect is effective. In the present invention, the structure of the dispersant is not particularly limited, and can be appropriately selected from phosphoric acid-based, sulfonic acid-based, carboxylic acid-based, nonionic-based, cationic-based, etc., but amino group, thiol group, disulfide group It is preferable to use at least one dispersant having one or more functional groups capable of coordinating to a metal such as an amide group, a carboxylic acid group, a phosphine group, or a sulfonic acid group. The molecular weight of the dispersant is preferably 50,000 or less, more preferably 100 to 20,000, and most preferably 500 to 10,000. If the molecular weight is too large, the dispersant is not preferable because it forms bridging aggregates between metal fibers or inhibits conductivity between metal fibers. If the molecular weight is too small, the molecular chain is short and sufficient steric hindrance effect cannot be obtained.

  When the metal fiber according to the present invention is dispersed in a non-aqueous solvent, it can be coordinated to a metal such as an amino group, a thiol group, a disulfide group, an amide group, a carboxylic acid group, a phosphine group, or a sulfonic acid group. It is preferable to use a dispersant having a compound having one or more functional groups and having an affinity for a non-aqueous solvent.

  The dispersion operation in the production method of the present invention can be carried out using any one of an ultrasonic disperser and a high-speed stirring disperser, or a combination thereof.

[Conductive material]
The conductive material of the present invention preferably further contains a binder, and the mass ratio of the metal fiber to the binder is preferably 7: 1 to 2: 1, and more preferably 5: 1 to 3: 1. When the ratio of the metal fibers is high, the conductivity is sufficient but the adhesion is poor, and when the ratio of the metal fibers is low, it is difficult to obtain sufficient conductivity.

  In the present invention, the kind of the binder is not particularly limited, and for example, an acrylic resin, an alkyd resin, a polyester resin, a polyurethane resin, an epoxy resin, a phenol resin, a melamine resin, a vinyl chloride resin, a silicone, which are usually used for oil-based inks. Used as UV curable ink for water-soluble acrylic resin, water-soluble alkyd resin, water-soluble melamine resin, water-soluble urethane emulsion resin, water-soluble epoxy resin, water-soluble polyester resin, etc. An acrylic urethane-based resin, a polyester acrylate-based resin, an epoxy acrylate-based resin, a polyol acrylate-based resin, and the like containing a monomer having an ethylenically unsaturated double bond. In particular, the binder is preferably an acrylic resin, a polyurethane resin, or a phenol resin.

  As the solvent, toluene, xylene, butyl acetate, glycol ether solvent, ester solvent, alcohol solvent, water, glycol solvent, ketone solvent and the like can be used.

  The dispersant is not particularly limited, but examples thereof include anionic surfactants such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene. Nonionic surfactants such as glycols and polyoxyethylene / polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In addition, a polymeric surfactant can also be used, for example, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer, styrene. -Maleic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene- A maleic acid copolymer etc. can be mentioned.

[Inkjet ink]
The ink-jet ink according to the present invention is characterized by containing the conductive material of the present invention containing the metal fiber. In addition to the metal fiber, the conductive material preferably contains a binder, a solvent, a dispersant, and the like as described above.

  In the inkjet ink according to the present invention, an organic solvent or a surfactant can be used in addition to the conductive material.

  As the surfactant, the same as the dispersant for the conductive material may be used, or a different one may be used. Preferred surfactants include, for example, Disperbyk manufactured by BYK-Chemie, Emulgen manufactured by Kao, Avisia Solspers, Ajinomoto Fine Techno Ajisper, Disparon manufactured by Enomoto Kasei, and a mixture of two or more surfactants. May be.

  Examples of the organic solvent include alcohols such as ethanol, propanol, and butanol, glycols, ethers such as ethylene glycol monomethyl ether, etc., or a mixture of these, or a combination of these compounds and water. .

  The content of the metal fiber in the ink dispersion medium is preferably 2 to 50% by mass, the content of the surfactant and the resin component is 0.3 to 30% by mass, and the viscosity is preferably 3 to 30 mPa · s.

[Transparent conductive film]
As a method for producing a conductive film of the present invention, it is preferable to form a conductive metal pattern on a transparent film substrate using an inkjet ink using the conductive material.

  The “conductive metal pattern” according to the present invention is one in which the conductive material is arranged in a mesh shape, a comb shape or the like. The pattern shape is not particularly limited, but examples include geometric figures combining triangles, squares, rectangles, rhombuses, parallelograms, trapezoidal squares, (positive) hexagons, (positive) octagons, etc. Can do.

  The line width and line interval of the conductive metal pattern may be arbitrary values, but the line width needs to be increased in order to increase the conductivity. On the other hand, from the viewpoint of transparency, it is preferable to increase the aperture ratio (the ratio of the portion having no fine line forming the pattern to the whole), that is, the line width is narrow and the line interval is wide. The aperture ratio is preferably 80% or more, and most preferably 90% or more.

  Thus, from the viewpoint of transparency and conductivity, the line width is preferably 1 μm or more and 100 μm or less, and the line interval is preferably 50 μm to 1000 μm.

  As an ink jet apparatus for forming the conductive metal pattern, a known thermal ink jet, piezo ink jet, or electrostatic ink jet method can be used.

  The conductive film of the present invention more preferably forms a transparent conductive film containing a conductive polymer, a conductive metal oxide, metal particles and the like on the conductive metal pattern.

  The conductive polymer used in the present invention is preferably an organic polymer having a π-conjugated main chain, such as polypyrroles, polythiophenes, polyacetylenes, polyphenylenes, polyphenylene vinylenes, polyanilines, polyacene. , Polythiophene vinylenes, and copolymers thereof. Among these, a polymer selected from polypyrrole, polythiophene, poly (N-methylpyrrole), poly (3-methylthiophene), poly (3-methoxythiophene), poly (3,4-ethylenedioxythiophene), or A copolymer is preferably used. Polypyrrole, polythiophene, and poly (3,4-ethylenedioxythiophene) are particularly preferable.

  Examples of the conductive metal oxide used in the present invention include so-called ITO, ZnO, and IZO.

  Examples of the transparent conductive film containing metal particles used in the present invention include those in which metal nanoparticles are dispersed in the conductive polymer, and base metals such as nickel and aluminum are deposited, sputtered, plated, electrodeposition The base metal is oxidized by the conductive polymer by being deposited on the conductive polymer by the method and allowed to stand for several hours to several days, and the base metal is incorporated as an oxide in the conductive polymer. Can be mentioned.

  Although there is no restriction | limiting in particular in the thickness of the transparent conductive film of this invention, 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 conductive film 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. As the electric resistance of the transparent electrode according to the present invention, the functionality of an electrode, from the viewpoint of electromagnetic wave shielding properties, is preferably 10 ⁴ Ω / □ or less as the surface resistivity, 10 ³ Ω / □ More preferably, it is more preferably 10 ² Ω / □ or less.

  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.

  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 conductive film 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 side opposite to the conductive layer according to the present invention, and when providing a barrier coat layer, It is preferable to dispose between the conductive layers according to the present invention. When an anchor coat layer, a carrier transport layer, or a carrier accumulation layer is provided, the transparent support is disposed on the same side as the conductive layer according to the present invention. It is preferable to make it.

[Transparent film substrate]
A plastic film can be used as the transparent film substrate used in the present invention.

  Examples of the raw material for the plastic film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene, and cyclic olefin resins, polyvinyl chloride, and polychlorinated chloride. Use vinyl resins such as vinylidene, polyether ether ketone (PEEK), polysulfone (PSF), polyether sulfone (PES), polycarbonate (PC), polyamide, polyimide, acrylic resin, triacetyl cellulose (TAC), etc. Can do.

  Of these, a biaxially stretched polyethylene terephthalate film, an acrylic resin film, and a triacetylcellulose film are preferable, and a biaxially stretched polyethylene terephthalate film is most preferable in terms of transparency, heat resistance, ease of handling, and cost.

  The transparent film substrate is preferably provided with a surface treatment or an easy-adhesion layer in order to ensure wettability and adhesion of the coating solution. Conventionally known techniques can be used for the surface treatment and the easy-adhesion layer, but when the transparent film substrate is a biaxially stretched polyethylene terephthalate film, the refractive index of the easy-adhesion layer adjacent to the film is 1.57-1. By setting it to 63, the interface reflection between the film substrate and the easy adhesion layer can be reduced and the transmittance can be improved, which is more preferable. As a method for adjusting the refractive index, the refractive index can be prepared by appropriately adjusting the ratio of the oxide sol having a relatively high refractive index such as tin oxide sol or cerium oxide sol and the binder resin. The easy-adhesion layer may be a single layer, but in order to improve the adhesiveness, it may be composed of two or more layers.

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

[Preparation of silver fiber A]
(Particle formation process)
Reference Adv. Mater. With reference to the method described in 2002, 14, 833 to 837, ethylene glycol (EG, Kanto Chemical: purity> 99.5%) as a reducing agent, polyvinylpyrrolidone (PVP, (Tokyo Kasei: having an average molecular weight of 40,000) was used, and the nucleation step and the particle growth step were separated to form particles to prepare a silver fiber dispersion.

《Nucleation process》
While stirring 100 ml of EG solution maintained at 160 ° C. in a reaction vessel, 10 ml of EG solution (silver nitrate concentration: 1.5 × 10 ⁻⁴ mol / l) of silver nitrate (Kanto Chemical: purity> 99.8%) It was added over 10 seconds at a constant flow rate. Thereafter, the silver ions were reduced while being held at 160 ° C. for 10 minutes to form silver core particles. The reaction solution exhibited a yellow color derived from surface plasmon absorption of nano-sized silver fine particles, and it was confirmed that silver ions were reduced to form silver fine particles (nuclear particles).

<Grain growth process>
The reaction liquid containing the core particles after the completion of the nucleation step 1 is maintained at 160 ° C. with stirring, 100 ml of an EG solution of silver nitrate (silver nitrate concentration: 1.0 × 10 ⁻¹ mol / l), and PVP 100 ml of EG solution (vinyl pyrrolidone concentration conversion: 6.0 × 10 ⁻¹ mol / l) was added over 120 minutes at a constant flow rate using the double jet method. In the particle growth process, the reaction solution was collected every 20 minutes and confirmed with an electron microscope. As a result, the core particles formed in the nucleation process grew into a fibrous form over time, and the particle growth process. The formation of new fine particles was not observed. About the silver fiber finally obtained, the electron micrograph was image | photographed, the major axis diameter and the minor axis diameter of 300 silver fiber images were measured, and the arithmetic average was calculated | required. The minor axis average diameter was 94 nm, and the major axis average diameter was 8.1 μm.

(Form control agent removal step)
After cooling the reaction liquid after the particle formation step to room temperature, the reaction liquid is externally circulated from the reaction vessel to an ultrafiltration membrane (VIVAFLOW 50 Zartorius) having a molecular weight cut off of 0.2 μm and a liquid feed pump to obtain PVP. The form control agent removal step was carried out by discharging flux containing residual materials and by-products from the ultrafiltration membrane. The form control agent removal cycle of “concentrate the liquid volume to 15% of the initial volume and then add EtOH to return to the initial volume” was repeated three times. Finally, the liquid volume was concentrated to 100 ml to add EtOH of silver fiber. A dispersion was prepared.

[Production of silver fibers B to I]
In the production method described above, the metal fiber was similarly prepared except that the amount of the reducing agent ethylene glycol and the form-controllable polyvinyl pyrrolidone, the concentration of silver nitrate, the addition amount, etc. were adjusted to the major axis diameter and minor axis diameter shown in Table 1. B to I EtOH dispersions were prepared.

[Transparent conductive film 101]
Using the silver fiber EtOH dispersion A, a conductive material was prepared according to the following formulation.

Silver fiber 10 parts Azisper PB821 (manufactured by Ajinomoto Fine Techno Co., Ltd.) 3 parts Acrylic resin 2.5 parts Ethylene glycol monobutyl ether acetate 200 parts Using this conductive material as an ink jet ink, 100 μm thick biaxially stretched transparent PET film A conductive metal pattern was formed on one side of the substrate in a lattice shape having a width of 10 μm, a spacing of 160 μm, and a height of 3 μm using an inkjet printer.

  Furthermore, dimethyl sulfoxide (DMSO: manufactured by Wako Pure Chemical Industries, Ltd.) was added to PEDOT / PSS in a dispersion of 1.3% by mass of conductive polymer PEDOT / PSS (BaytronPH500: manufactured by HC Starck) on the conductive metal pattern. A transparent conductive film 101 was produced by applying a solution added so as to be 5% by mass with respect to PSS so that the film thickness at the time of drying was 100 nm.

[Transparent conductive films 102 to 109]
In the production of the transparent conductive film 101, the silver fiber EtOH dispersion A was changed to the silver fiber EtOH dispersions B to I, respectively, and the silver fiber addition ratio (silver fiber mass ratio to 1 part of binder) was changed to the ratio described in Table 2. Transparent conductive films 102 to 109 were produced in the same manner except for the above.

  The transparent conductive films 101 to 109 obtained as described above were evaluated for surface resistance and adhesion by the following methods.

[Measurement of surface resistivity]
In accordance with JIS K 7194: 1994 (resistivity test method using a four-probe method for conductive plastics), measurement was performed using a Lorester GP (MCP-T610 type) manufactured by Mitsubishi Chemical Corporation.

[Evaluation of adhesion]
Mending tape no. One minute after completely attaching 810 (manufactured by Sumitomo 3M Co., Ltd.) to the transparent conductive film, peeling was performed by pulling it off from the end of the tape at once. Evaluation was based on changes in surface resistance before and after the adhesion test.

○: Almost no peeling, surface resistance value change 0.1 or less Δ: Slightly peeled, surface resistance value change 0.25 or less ×: considerably peeled, surface resistance value change 0.25 or more Is shown in Table 2.

  As is clear from Table 2, it can be seen that the surface resistance and adhesion of the transparent conductive film using the conductive material of the present invention are superior to the comparative example.

  That is, by means of the present invention, it is possible to provide a conductive material excellent in conductivity and adhesiveness, an inkjet ink containing the same, and a transparent conductive film having a conductive metal pattern formed using the ink. it can.

Claims (5)

A conductive material comprising a metal fiber having a major axis diameter of 2 to 30 μm and a minor axis diameter of 60 to 300 nm. The conductive material according to claim 1, wherein the conductive material contains a binder, and a mass ratio of the metal fibers to the binder is 7: 1 to 2: 1. The metal fiber contains an element selected from gold, platinum, silver, palladium, rhodium, iridium, ruthenium, osmium, iron, cobalt, copper, and tin, according to claim 1 or 2. Conductive material. An ink-jet ink comprising the conductive material according to claim 1. A transparent conductive film having a conductive metal pattern on a transparent film substrate, wherein the conductive metal pattern is formed using the inkjet ink according to claim 4. .