JP2014224199A - Production method for silver nanowire ink, and silver nanowire ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for a silver nanowire ink and a silver nanowire ink which shows high conductivity and no decrease in transmittance even when a dispersant or a viscosity modifier is added to improve coating property.SOLUTION: A production method for a silver nanowire ink includes a step of adding a dispersant and a viscosity modifier to a dispersion liquid of silver nanowires prepared by dispersing silver nanowires in a solvent, wherein the dispersant is added by 0.01 to 0.5 wt.% of the ink total amount. Further, the viscosity modifier is added by 0.01 to 0.5 wt.% of the ink total amount. Fluorine-based, nonionic or cationic surfactants can be used for the dispersant.

Description

  The present invention relates to a method for producing a silver nanowire ink used as a conductor of a transparent conductive film and a silver nanowire ink.

  In various displays such as liquid crystal, plasma, organic electroluminescence, and various solar cells, a transparent electrode using a transparent conductive film is an essential constituent technology. As a material for the transparent conductive film, a metal oxide thin film such as ITO is mainly used. The metal oxide thin film can achieve both light transmittance and conductivity, and has excellent durability. In particular, ITO has a good balance between light transmittance and conductivity, and electrode fine pattern formation by wet etching. Therefore, it is widely used as a transparent electrode for various optoelectronics.

  Metal oxide thin films used for transparent conductive films are generally manufactured by vacuum deposition or sputtering, but the thin films are metal oxides, so they are vulnerable to bending and hinder the flexibility of the final product. There is a case. In addition, since the vacuum deposition method and the sputtering method require a vacuum environment, there are problems such as a large and complicated processing apparatus and a large amount of energy consumed for film formation. Development of improved technology is required.

  In response to such demands, it has been proposed to use metal nanowires as the conductor of the transparent conductive film. When the metal nanowire is used as a conductor, the metal nanowire comes into contact with each other to form a conductive network and develop conductivity. When a metal nanowire having a thickness of 300 nm or less and a length of 3 μm or more is used, both the conductivity and transparency of the transparent conductive film can be achieved. Ag, Cu, Au, and the like have been studied for the metal constituting the metal nanowire, but Ag is considered preferable because it is excellent in electrical conductivity and oxidation resistance, and the metal price is not significantly high. Technology is actively developed. Such silver nanowires as transparent conductors are disclosed in Patent Documents 1 to 4, for example.

US2007 / 0074316 Publication US2009 / 0129004 gazette US2010 / 0272993 US2010 / 0243295

  The characteristics of silver nanowires as a transparent conductive material are the coating film when the silver nanowire dispersion liquid itself is applied, or when applied onto a substrate in a state after being converted into an ink in which a viscosity modifier or a dispersant is added to this dispersion liquid. It is evaluated by the sheet resistance and optical characteristics.

  An object of the present invention is to provide a method for producing a silver nanowire ink and a silver nanowire ink having high conductivity without impairing optical properties even when a coating agent is improved by adding a dispersant or a viscosity modifier. There is.

  In order to solve the above problem, the present invention adds a dispersant of 0.01 to 0.5 wt% of the total amount of ink and a viscosity modifier to a dispersion of silver nanowires in which silver nanowires are dispersed in a solvent. A method for producing a silver nanowire ink is provided.

  The viscosity modifier is preferably added in an amount of 0.01 to 0.5 wt% of the total amount of ink.

  Further, the present invention comprises a silver nanowire, a solvent, a dispersant, and a viscosity modifier. The concentration of the dispersant is 0.01 to 0.5 wt%, and the concentration of the viscosity modifier is 0.01 to Provided is a silver nanowire ink characterized by being 0.5 wt%.

  In the silver nanowire ink, the dispersant may be a fluorine-based, nonionic-based, or cationic surfactant. The solvent may be water or isopropyl alcohol.

  According to the present invention, by adjusting the concentration of the dispersant to be added, the coating property of the silver nanowire ink is improved, and in the transparent conductive film using the silver nanowire as a conductor, high conductivity and good optical properties are obtained. Can be realized.

  Embodiments of the present invention will be described below. In the embodiment of the present invention, the heated first solution (solution A) and the second solution (solution B) are mixed to obtain a silver nanowire from the reaction solution obtained by mixing the solution A and the solution B. A silver nanowire ink is produced by adding a dispersant and a viscosity modifier.

  First, preparation of the solution A as the first solution will be described. Solution A contains a solvent, an organic protective agent, and a halogen compound.

  As the solvent of the solution A, a polyol can be used. Preferable examples of the polyol include ethylene glycol, propylene glycol, 1,3-propanediol, glycerol and a mixed solvent thereof. Polyol has an appropriate reducing power with respect to silver, is suitable for production of silver nanowires, has a relatively high boiling point, and has an advantage that silver nanowires can be produced under normal pressure.

  As the organic protective agent contained in the solution A, a high molecular organic substance can be used. For example, PVP (polyvinylpyrrolidone) is preferably used. In general, it is considered that when an organic protective agent adheres to a specific crystal plane when silver is reduced, the silver produced by the reduction becomes a wire. PVP used as an organic protective agent is considered to have a great effect of suppressing the growth of a specific crystal face by attaching to a specific crystal face with respect to silver produced by reduction, and produces wire-like silver. It becomes easy to let you.

  The kind of the halogen compound contained in the solution A is not particularly limited, and for example, NaCl, KCl, CTAB (cetyltrimethylammonium bromide), TBAC (tetrabutylammonium chloride) or the like can be used.

  As described above, the solution A is obtained by mixing a polyol, an organic protective agent, and a halogen compound.

  Next, preparation of the solution B (second solution) as the second solution will be described. Solution B consists of a solvent and a silver compound.

  As the solvent of the solution B, a polyol can be used. Preferable examples of the polyol include ethylene glycol, propylene glycol, 1,3-propanediol, glycerol and a mixed solvent thereof. Polyol has an appropriate reducing power with respect to silver, is suitable for producing silver nanowires, has a relatively high boiling point, and has an advantage that silver nanowires can be produced under normal pressure.

  Moreover, the kind of silver compound contained in the solution B is not particularly limited as long as it dissolves in the solvent of the solution B. For example, silver nitrate, silver acetate, and silver oxide can be used. In addition, it is preferable to use silver nitrate from the viewpoint of solubility in a solvent and cost.

  As described above, the solution B is obtained by mixing a polyol and a silver compound. In addition, it is preferable that the temperature of the solution B shall be 5-50 degreeC. This is because if the solution temperature is too low, the silver compound dissolution process may take time, and if the solution temperature is too high, the silver reduction reaction may proceed due to the solvent alcohol. . The temperature of the solution B is more preferably 10 to 40 ° C.

  Next, the production | generation reaction process of silver nanowire is demonstrated.

  First, the solution A is heated. At this time, it is preferable that the temperature of the solution A is 70 ° C. or more and not more than the boiling point of the solvent to be used. This is because when the temperature is out of the range, silver nanowires may not be generated sufficiently. In order to shorten the time required for the production of silver nanowires, it is more preferable that the temperature of the solution A is 90 ° C. or higher and the boiling point of the solvent used.

  Thereafter, the solution B is added to the heated solution A and stirred. Thereby, the reaction liquid containing a silver nanowire can be obtained.

  Next, the silver nanowire cleaning process will be described.

  After the reaction time has elapsed, the reaction solution containing silver nanowires is cooled, and the reaction solution is subjected to solid-liquid separation by centrifugation or decantation. Then, by adding a solvent to the solid-liquid separated silver nanowires and stirring, the reaction product of the reaction solution is removed, and a dispersion of silver nanowires dispersed in a clean solvent can be obtained. This centrifugation or decantation, addition of solvent, and stirring are repeated.

  As described above, for example, silver nanowires having a diameter of 1 to 500 nm and a length of 5 to 100 μm or more are obtained. Then, by adding a dispersant and a viscosity modifier to a dispersion of silver nanowires dispersed in a clean solvent, a silver nanowire ink with improved coatability can be obtained.

  The silver nanowire ink includes a silver nanowire, a solvent, a dispersant, and a viscosity modifier. As the solvent, water, isopropyl alcohol (IPA), or the like can be used. As the dispersant, a fluorine-based, non-ionic, cationic, or other surfactant can be used. Commercially available dispersants include nonionic “Zonyl FSO (DuPont product)” and nonionic “Triton X-100 (Roche Diagnostics product)”. In order to improve applicability and obtain appropriate resistance and transmittance, the dispersant concentration is preferably 0.01 to 0.5 wt%, and more preferably 0.02 to 0.3 wt%. Moreover, as the viscosity modifier, for example, a cellulose-based one such as hydroxypropylmethylcellulose (HPMC) is used, and the viscosity modifier concentration is preferably 0.01 to 0.5 wt%.

  The silver nanowire coating film is formed by applying the silver nanowire ink added by adjusting the concentration of the dispersant and the viscosity modifier in this manner to a substrate or the like.

  As described above, according to the present invention, by adjusting the concentration of the dispersant and the viscosity modifier added to the dispersion containing silver nanowires, the coating property of the silver nanowire ink to be produced is improved, and at the same time, The transmittance performance can also be made appropriate. As a result, in a transparent conductive film using silver nanowires as a conductor, both high conductivity and good optical characteristics can be achieved.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  Silver nanowire inks were produced by the production method according to the present invention (Examples 1 to 5).

  First, 1.04 g of PVP (manufactured by Wako Pure Chemical Industries) and 0.0029 g of NaCl (manufactured by Wako Pure Chemical Industries) were added to 90 ml of ethylene glycol and dissolved to obtain a solution A. Next, 0.85 g of silver nitrate was added to 10 ml of ethylene glycol and dissolved to obtain a solution B.

  Thereafter, the entire amount of the solution A was heated from room temperature to 105 ° C. with stirring. Thereto, 10 ml of solution B having a liquid temperature of 25 ° C. was added over 60 min while maintaining the temperature of solution A at 105 ° C. to obtain a reaction solution. While the reaction solution was stirred at a stirring speed of 100 rpm for 6 hours, a temperature of 105 ° C. was maintained. Thereafter, the reaction solution was cooled to 25 ° C. to obtain a solution containing silver nanowires.

  After centrifuging this solution at 2500 rpm for 45 min, the supernatant was removed, and then 100 ml of pure water was added and stirred to disperse the silver nanowires to obtain a dispersion. By repeating this decanting and dispersing operation by centrifugation three times, the silver nanowires were washed to obtain a dispersion containing silver nanowires.

  Then, in a dispersion containing about 0.3 wt% of silver nanowires, 0.025 wt% (Example 1), 0.15 wt% (Example 2) of “Zonyl FSO (DuPont product)” as a dispersant, "Triton X-100 (Roche Diagnostics)" 0.05 wt% (Example 3), 0.15 wt% (Example 4), 0.30 wt% (Example 5), viscosity modifier As a result, 0.2 wt% of HPMC (Examples 1 to 5) and about 99.45 wt% of water (Examples 1 to 5) were mixed to obtain a silver nanowire ink.

  The silver nanowire inks of Examples 1 to 5 were each applied to one surface of a glass substrate (manufactured by Matsunami Glass Industrial Co., Ltd., S7213, thickness 0.9 mm) using a bar coater to form a coating film. . After coating, the coating film was dried by heating at 120 ° C. for 10 minutes.

  Further, as a comparative example, a dispersion containing silver nanowires was produced in the same manner as in the examples, and silver nanowire ink added with 0.2 wt% of HPMC as a viscosity modifier without adding a dispersant was used as the surface of a glass substrate. To form a coating film. After coating, the coating film was dried by heating at 120 ° C. for 10 minutes.

  About Examples 1-5 produced as mentioned above and the comparative example, the surface resistance value of the transparent conductive thin film apply | coated to the glass base material was measured. For the measurement, “Loresta HP MCP-T410” manufactured by Mitsubishi Chemical Analytech Co., Ltd. was used, and measurement was performed by the four-terminal method. Furthermore, the total light transmittance of the transparent conductive thin film applied to the glass substrate was measured. The total light transmittance was measured by using a haze meter “NDH 2000” manufactured by Nippon Denshoku Industries Co., Ltd. as a measuring instrument. Further, an uncoated glass substrate was used as a reference sample for measuring optical characteristics, and the optical characteristics of only the coated film were measured.

  Table 1 shows the conditions of the dispersant and the viscosity modifier, and the measurement results of the coating film characteristics for Examples 1 to 5 and Comparative Example.

  As shown in Table 1, each of Examples 1 to 5 according to the present invention achieved high transmittance as compared with the comparative example. Further, the resistance value was almost the same value as when no dispersant was used.

  The present invention can be applied to a metal nanowire ink that is applied to a substrate and used as a conductor of a transparent conductive film.

Claims (5)

  A method for producing a silver nanowire ink, comprising adding a dispersant of 0.01 to 0.5 wt% of a total amount of ink and a viscosity modifier to a dispersion of silver nanowires in which silver nanowires are dispersed in a solvent.   The method for producing a silver nanowire ink according to claim 1, wherein the viscosity modifier is added in an amount of 0.01 to 0.5 wt% of the total amount of the ink.   It consists of a silver nanowire, a solvent, a dispersant, and a viscosity modifier, and the concentration of the dispersant is 0.01 to 0.5 wt%, and the concentration of the viscosity modifier is 0.01 to 0.5 wt%. Silver nanowire ink characterized by the above.   The silver nanowire ink according to claim 3, wherein the dispersant is a fluorine-based, nonionic-based, or cationic-based surfactant.   The silver nanowire ink according to claim 3 or 4, wherein the solvent is water or isopropyl alcohol.