JP5293202B2 - Method for synthesizing metal nanoparticles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To synthesize metal nanoparticles which do not contain a corrosive material, from an insoluble metal salt, and to produce the metal nanoparticles which are preferably used for an electrically conductive material. <P>SOLUTION: The method for synthesizing the metal nanoparticles includes the steps of: preparing an aqueous solution A of the metal salt by dissolving the metal salt in water; preparing an aqueous solution B of a carboxylic acid by dissolving a compound such as glycolic acid in water; preparing an aqueous solution C of a reducing agent; preparing a basic aqueous solution D; producing a mixture solution by adding the basic aqueous solution D dropwise into the aqueous solution A of the metal salt while stirring the mixed product; producing a suspension of the carboxylate by adding the aqueous solution B of the carboxylic acid dropwise into the mixture solution while stirring the mixed product; and producing the metal nanoparticle by adding the aqueous solution C of the reducing agent dropwise into the suspension of the carboxylate while stirring the mixed product. Metal elements contained in the metal salt contain 75 wt.% or more silver. In the step of producing the metal nanoparticle by adding the aqueous solution C of the reducing agent dropwise, the mixed product is stirred at a temperature of 25 to 95&deg;C. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for synthesizing metal nanoparticles.

  Conventionally, metal nanoparticles having a particle size of several nanometers are dramatically different in melting point from those of bulk, and therefore are expected to be applied as conductive pastes that can be used by low-temperature firing. And in order to manufacture such a metal nanoparticle, the method of reducing a metal in a solvent conventionally is known. And, in order to prepare the target metal nanoparticles as a uniform dispersion, it is said that it is necessary to use a raw material metal salt (metal compound) that is soluble in the liquid (solvent). The raw materials have been limited. For example, when silver nanoparticles are obtained, silver nitrate and silver perchlorate have been used exclusively in aqueous solvents, and soluble compounds such as silver complexes have been exclusively used in organic solvents.

  However, as a silver raw material, silver halide can be easily obtained from the viewpoint that silver halide has already been produced in large quantities as a photographic raw material, and can be easily managed as a solid. From such an insoluble silver salt, silver nanoparticles can be obtained. If it can manufacture, it is preferable. From this point of view, it is a method for producing silver nanoparticles by reducing a silver salt in a solvent, using silver halide as the silver salt, and as a protective agent for the silver salt as a raw material, There has been proposed a method in which a metal coordination compound that dissolves and coordinates to silver is used as a protective material, and reduction is performed in the presence of a protective agent comprising the compound (see, for example, Patent Document 1). This is because it has been found that by using a specific protective agent, an insoluble silver salt such as silver halide can be effectively reduced in a solvent to produce nanoparticles, According to this method, silver nanoparticles can be produced from an insoluble silver salt.

Japanese Patent Laying-Open No. 2003-253311 (specifications [0002] to [0005])

  However, in the conventional method for producing metal nanoparticles using silver halide as the silver salt, the silver halide used as a raw material contains halogen causing corrosion, and sulfur is used as a part of the raw material. For this reason, when the dispersion liquid in which silver obtained by this production method is dispersed is used as an electronic device wiring as a paste or the like, there still remains a problem of lacking long-term stability to be solved. In particular, since a thiol-based compound is used as a protective agent for silver nanoparticles, it is expected that sulfur will remain in the wiring even after firing.

  An object of the present invention is to provide a method for synthesizing metal nanoparticles capable of producing metal nanoparticles suitable for use as a conductive material by synthesizing metal nanoparticles from an insoluble metal salt without containing a corrosive material. It is in.

  As shown in FIG. 1, the first aspect of the present invention is a step of preparing a metal salt aqueous solution A by dissolving a metal salt, glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, A step of preparing a carboxylic acid aqueous solution B by dissolving one or more compounds selected from the group consisting of succinic acid, tartaric acid and salts thereof, a step of preparing a reducing agent aqueous solution C, and a basic aqueous solution A step of preparing D, a step of adding a basic aqueous solution D to the aqueous metal salt solution A while stirring and forming a mixed solution, and a step of adding a carboxylic acid aqueous solution B to the mixed solution and stirring the carboxylate suspension. A step of forming a liquid, and a step of dropping a reducing agent aqueous solution C into a carboxylate suspension while stirring to form metal nanoparticles, wherein the metal element contained in the metal salt contains 75% by weight of silver. Including above, drops of reducing agent aqueous solution C A step of stirring to produce metal nanoparticles while is a synthetic method of the metal nanoparticles, characterized in that it is carried out by stirring at a temperature below 95 ° C. 25 ° C. or higher.

In this first method for synthesizing metal nanoparticles, the basic aqueous solution D is added dropwise to the aqueous metal salt solution A while stirring to adjust the pH so that the yield of carboxylate precipitated in the next step is improved. By preparing an adjusted mixed solution and stirring while dropping the aqueous carboxylic acid solution B into the mixed solution, a carboxylate suspension in which the carboxylate is precipitated in a high yield is formed. By stirring at a temperature of 25 ° C. or higher and 95 ° C. or lower while adding the reducing agent aqueous solution C dropwise, a technical effect that the precipitated carboxylate is reduced and metal nanoparticles are generated can be obtained. Moreover, as a raw material, all except a raw material metal is comprised by CHNO, and does not contain a corrosive substance. For this reason, despite producing metal nanoparticles from an insoluble metal salt, metal nanoparticles free from corrosive materials suitable for use as a conductive material can be obtained. The metal nanoparticles synthesized by this method can be sintered at a low temperature. For example, in the case of silver nanoparticles, an electrode having a volume resistivity of the order of 10 ⁻⁶ [Ω · cm] It becomes possible to form a conductive reflective film having a certain high reflectance at a low temperature.

  The second aspect of the present invention is an invention based on the first aspect, and further comprises a group consisting of gold, platinum, palladium and ruthenium in the balance other than silver of the metal element contained in the metal salt of the metal salt aqueous solution A. 1 type or 2 or more types of metals chosen more are contained, It is characterized by the above-mentioned.

  In the method for synthesizing metal nanoparticles according to the second aspect, the reflectance is obtained by taking a so-called core-shell structure in which the other forms a shell at the center of one element, a mixture, an alloy, or one element of different metal nanoparticles. There is an effect of controlling the volume resistivity.

  A third aspect of the present invention is the invention based on the first or second aspect, wherein the reducing agent is one selected from the group consisting of hydrazine, ascorbic acid, oxalic acid, formic acid and salts thereof. Or it is 2 or more types of compounds, It is characterized by the above-mentioned.

  A fourth aspect of the present invention is the invention based on the first or second aspect, wherein the reducing agent is one or two selected from the group consisting of sodium borohydride, potassium borohydride and glucose. It is a compound of more than species.

  In the synthesis methods of the third and fourth aspects, if the compound is of the above kind, it does not contain a corrosive substance and can be easily decomposed by firing even if it remains in the product dispersion. An effect is obtained.

  A fifth aspect of the present invention is a method for producing a dispersion liquid in which metal nanoparticles obtained by the synthesis methods of the first to fourth aspects are dispersed in a dispersion medium to obtain a metal nanoparticle dispersion liquid.

  A sixth aspect of the present invention includes a step of dispersing metal nanoparticles obtained by the synthesis method of the first to fourth aspects in a dispersion medium to obtain a metal nanoparticle dispersion, and the metal nanoparticle dispersion. A metal film production method comprising a step of applying a metal film on a substrate by a wet coating method to form a metal film.

  In the synthesis method of the first aspect of the present invention, the pH was adjusted so as to improve the yield of the carboxylate salt precipitated in the next step by stirring while dropping the basic aqueous solution D into the aqueous metal salt solution A. Prepare a mixed solution and stir while dropping the aqueous carboxylic acid solution B into the mixed solution to form a carboxylate suspension in which the carboxylate is precipitated in a high yield. By stirring at a temperature of 25 ° C. or more and 95 ° C. or less while dropping the aqueous agent solution C, a technical effect that the precipitated carboxylate is reduced to produce metal nanoparticles can be obtained. Moreover, as a raw material, all except a raw material metal is comprised by CHNO, and does not contain a corrosive substance. For this reason, despite producing metal nanoparticles from an insoluble metal salt, metal nanoparticles free from corrosive materials suitable for use as a conductive material can be obtained.

It is a figure which shows the flow of the manufacturing method of embodiment of this invention.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  As shown in FIG. 1, in the synthesis method of the present invention, first, a step of preparing a metal salt aqueous solution A, a step of preparing a carboxylic acid aqueous solution B, a step of preparing a reducing agent aqueous solution C, and a basic aqueous solution D are prepared. Process.

<Preparation process of metal salt aqueous solution A>
The metal salt aqueous solution A is prepared by dissolving the metal salt in water as a solvent. It is preferred to prepare a saturated aqueous solution at room temperature by dissolving the metal salt in deionized water. The metal salt to be dissolved here contains at least a silver salt. And when the mass of the whole metal element part contained in a metal salt is set to 100, the silver is adjusted so that it may occupy 75 mass% or more. Therefore, although silver may occupy 100% by mass in the metal element, when a metal salt other than silver is included, the balance other than silver of the metal element contained in the metal salt is gold, platinum, palladium. And one or more metals selected from ruthenium are preferably included. Thereby, the effect of controlling reflectivity and volume resistivity can be obtained by adopting a so-called core-shell structure in which the other part forms an outer shell at the center of one element or a mixture of different metal nanoparticles or an alloy.

<Preparation process of carboxylic acid aqueous solution B>
The carboxylic acid aqueous solution B is prepared by dissolving the carboxylic acid in water as a solvent. It is preferable to prepare a saturated aqueous solution at room temperature by dissolving carboxylic acids in deionized water. The carboxylic acids to be dissolved here are one or more selected from the group consisting of glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid, tartaric acid, and salts using these. A compound. The reason for limiting the carboxylic acids to this is that they function well as a protective material for modifying the surface of the metal nanoparticles. Moreover, it is because a corrosive substance like thiol etc. is not included. Furthermore, it is because the pH at the time of synthesis | combination can be set to the base side by making these into salts, such as sodium, copper, and ammonia.

<Preparation process of reducing agent aqueous solution C>
The reducing agent aqueous solution C is prepared by dissolving the reducing agent in water as a solvent. It is preferable to prepare a saturated aqueous solution at room temperature by dissolving the reducing agent in deionized water. The reducing agent to be dissolved here is one or more compounds selected from the group consisting of hydrazine, ascorbic acid, oxalic acid, formic acid and salts thereof. Thereby, even if it does not contain a corrosive substance and remains in the product dispersion, it can be easily decomposed by firing.

  On the other hand, the reducing agent dissolved in water as a solvent may be one or more compounds selected from the group consisting of sodium borohydride, potassium borohydride and glucose. Also in this case, even if it does not contain a corrosive substance and remains in the product dispersion, it can be easily decomposed by firing.

<Preparation process of basic aqueous solution D>
The basic aqueous solution D is prepared by dissolving a basic compound in water as a solvent. The concentration is adjusted to a range of 1 to 5M, but mainly because of ease of handling and preparation, and is not particularly limited to this range. Examples of the basic compound to be dissolved include sodium hydroxide, potassium hydroxide, and ammonia.

<First mixing step>
First, the basic aqueous solution D is added dropwise to the metal salt aqueous solution A while stirring to form a mixed solution. By stirring while adding the basic aqueous solution D to the aqueous metal salt solution A, a mixed solution having a pH adjusted so as to improve the yield of the carboxylate salt precipitated in the next step is prepared. The dropping ratio is preferably such that the basic compound contained in the basic aqueous solution D is 0.3 to 3 mol per 1 mol of the metal element contained in the metal salt aqueous solution A. If it is less than the lower limit, the particle size of the produced nanoparticles increases and the specific resistance increases, and if it exceeds the upper limit, an unnecessary dropping operation of the aqueous carboxylic acid solution B occurs and the cost increases. . Moreover, it is preferable to perform dripping and stirring of the basic aqueous solution D with respect to the metal salt aqueous solution A in the temperature range of 25-95 degreeC under atmospheric pressure.

<Second mixing step>
Carboxylic acid suspension is formed by stirring while dropping the carboxylic acid aqueous solution B into the mixed solution. By stirring while dropping the aqueous carboxylic acid solution B into the mixed solution, a carboxylate suspension in which the carboxylate is precipitated in a high yield is formed. The dropping ratio is such that the total amount of carboxylic acid, carboxylic acid salt or carboxylic acid and carboxylic acid salt contained in the carboxylic acid aqueous solution B is 0.3 to 3.0 mol with respect to 1 mol of the metal element as the raw material of the mixed solution. It is preferable that If it is less than the lower limit value, the particle size of the produced nanoparticles increases and the specific resistance increases, and if the upper limit value is exceeded, unnecessary dripping of the basic aqueous solution D occurs and the cost increases. . Moreover, it is preferable to perform dripping and stirring of the carboxylic acid aqueous solution B with respect to a liquid mixture in the temperature range of 25-95 degreeC under atmospheric pressure. When the carboxylic acid aqueous solution B is added dropwise to the mixed solution and stirred, a hardly soluble carboxylate precipitates and a carboxylate suspension is obtained. Therefore, it is preferable that the stirring after the carboxylic acid aqueous solution B is dropped into the mixed solution is performed for a time sufficient to obtain the suspension.

<Third mixing step>
After the suspension in which the carboxylate is precipitated is obtained, the reducing agent aqueous solution C is added dropwise to the suspension and stirred to produce metal nanoparticles. That is, the technical effect that the precipitated carboxylate is reduced to produce metal nanoparticles by stirring the reducing agent aqueous solution C while dropping the reducing agent aqueous solution C into the carboxylate suspension can be obtained. The dropping ratio is preferably 0.1 to 3.0 mol of the reducing agent contained in the reducing agent aqueous solution C with respect to 1 mol of the metal element that is the raw material of the suspension. If the amount is less than the lower limit, a problem that the yield decreases is caused. If the value exceeds the upper limit, an unnecessary dropping operation of the reducing agent aqueous solution C is caused and the cost is increased. Moreover, dropping and stirring of the reducing agent aqueous solution C to the carboxylate suspension are performed in a temperature range of 25 to 95 ° C. under atmospheric pressure. When stirred in this temperature range, the average particle diameter of the generated particles can be made 100 nm or less, and when the dispersion using the obtained metal nanoparticles is used as a composition for electrode formation, A low volume resistivity can be achieved. Moreover, it is preferable to perform dripping of the reducing agent aqueous solution C with respect to carboxylate suspension within 10 minutes. When dripping exceeds an upper limit, the particle size of the produced | generated nanoparticle will increase and the malfunction which a specific resistance will increase will arise. In this way, by stirring the reducing agent aqueous solution C to the suspension while stirring in a predetermined temperature range, the metal salt is reduced and metal nanoparticles can be generated.

  Dispersion stability can be increased by removing excess salts from the reaction solution containing the metal nanoparticles after reduction using various separation techniques. Examples of the method for separating excess salts include centrifugation, ultrafiltration, ion exchange membranes, ion exchange resins, and the like. And the volume resistivity of the electrode obtained by applying and firing the metal nanoparticles generally tends to approach the value of the bulk metal as the excess salts are removed.

In the method for synthesizing metal nanoparticles of the present invention comprising such steps, metal nanoparticles can be produced from an insoluble metal salt. In the present invention, it is used as a raw material to form a salt with a raw material metal and carvone, or when sodium borohydride or the like is used as a reducing agent, such as sodium or calcium as a basic compound of a basic aqueous solution. Except for boron, it is composed entirely of CHNO and does not contain corrosive substances. For this reason, it becomes possible to obtain metal nanoparticles suitable for use as a conductive material without containing corrosive materials. Moreover, the metal nanoparticles synthesized by the method of the present invention can be sintered at a low temperature. For example, in the case of silver nanoparticles, it is possible to form an electrode having a volume resistivity of the order of 10 ⁻⁶ [Ω · cm] and a conductive reflective film having a high reflectance that is characteristic of silver at a low temperature. .

  In the above-described embodiment, the case where the carboxylic acid aqueous solution B and the metal salt aqueous solution A are first prepared and then mixed is described, but the carboxylic acid aqueous solution B and the metal salt aqueous solution A are mixed. The step of forming the mixed solution includes a case where the solute of the carboxylic acid aqueous solution B and the solute of the metal salt aqueous solution A are mixed in advance, and water is added thereto for dissolution.

  Next, a method for producing a metal film using the metal nanoparticles obtained by the method for synthesizing metal nanoparticles will be described. Specifically, the metal film production method includes a dispersion step of dispersing metal nanoparticles obtained by the synthesis method in a dispersion medium to obtain a metal nanoparticle dispersion liquid, and producing the metal nanoparticle dispersion liquid from a metal film. And a metal film forming step of forming a metal film by applying a wet coating method on a substrate as a composition for use. Details of these steps will be described below.

<Dispersing process>
In this step, a metal nanoparticle dispersion is prepared by adding and mixing the metal nanoparticles obtained by the above synthesis method into a dispersion medium and dispersing the particles in the dispersion medium. The content of the metal nanoparticles including silver nanoparticles in the dispersion is 2.5 to 95.0% by mass, preferably 3.5 to 90% with respect to 100% by mass of the composition comprising the metal nanoparticles and the dispersion medium. It is prepared so that it may contain 0.0 mass%. The dispersion medium may contain 1% by mass or more, preferably 2% by mass or more of water and 2% by mass or more, preferably 3% by mass or more of alcohols with respect to 100% by mass of all the dispersion media. Is preferred. For example, when the dispersion medium is composed of only water and alcohols, it contains 98% by mass of alcohol when it contains 2% by mass of water, and 98% by mass of water when it contains 2% by mass of alcohol. Here, the content of the metal nanoparticles including the silver nanoparticles was limited to the range of 2.5 to 95.0% by mass with respect to 100% by mass of the composition composed of the metal nanoparticles and the dispersion medium. If it is less than 5% by mass, the properties of the metal film after firing are not particularly affected, but it is difficult to obtain a metal film having a required thickness. If it exceeds 95.0% by mass, ink or This is because the necessary fluidity as a paste is lost. In addition, the content of water is limited to a range of 1% by mass or more with respect to 100% by mass of all the dispersion media. When the content is less than 1% by mass, a film obtained by applying the composition by a wet coating method is used. It is difficult to sinter at low temperatures, and the conductivity and reflectance of the fired metal film are reduced, so that the content of alcohols is limited to a range of 2% by mass or more with respect to 100% by mass of all dispersion media. If it is less than 2% by mass, it is difficult to sinter the film obtained by applying the composition by the wet coating method at a low temperature in the same manner as described above, and the conductivity and reflectance of the fired metal film are reduced. Because it will do.

  The alcohols are preferably one or more selected from the group consisting of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, glycerol, isobornyl hexanol and erythritol.

  By passing through the said process, the dispersion liquid in which the metal nanoparticle which controlled the shape and the particle size in the wide range was disperse | distributed is obtained.

<Metal film formation process>
This step is a step of forming a metal film using the metal nanoparticle dispersion described above. First, the metal nanoparticle dispersion is used as a metal film-forming composition, and this metal film-forming composition is applied onto a substrate by a wet coating method. Coating by this wet coating method is performed so that the thickness after firing is in the range of 0.1 to 2.0 μm, preferably 0.3 to 1.5 μm. The substrate is selected from the group consisting of silicon, glass, ceramics containing a transparent conductive material, a polymer material or a metal substrate, or silicon, glass, ceramics containing a transparent conductive material, a polymer material and a metal. It can be a laminate of two or more types. Moreover, it is preferable that a base material is either a solar cell element or a solar cell element with a transparent metal film. As the transparent metal film, indium tin oxide (ITO), antimony-doped tin oxide (ATO), Nesa (tin oxide SnO ₂ ), IZO (Indium Zic Oxide), AZO (aluminum-doped ZnO) ) And the like. It is preferable that the said metal film formation composition is apply | coated to the surface of the photoelectric conversion semiconductor layer of a solar cell element, or the surface of the transparent metal film of a solar cell element with a transparent metal film. Further, the wet coating method is particularly a spray coating method, a dispenser coating method, a spin coating method, a knife coating method, a slit coating method, an ink jet coating method, a screen printing method, an offset printing method or a die coating method. Although it is preferable, the present invention is not limited to this, and any method can be used. The spray coating method is a method in which the metal film forming composition is made into a mist form with compressed air and applied to the substrate, or the metal film forming composition itself is pressurized into a mist form and applied to the substrate. The coating method is, for example, a method in which a metal film forming composition is placed in a syringe and a piston of the syringe is pushed to discharge the metal film forming composition from a fine nozzle at the tip of the syringe and apply it to a substrate. The spin coating method is a method in which a metal film forming composition is dropped on a rotating substrate, and the dropped metal film forming composition is spread on the periphery of the substrate by its centrifugal force. The knife coating method is a knife coating method. A base material with a predetermined gap is provided so as to be movable in the horizontal direction, and the metal film forming composition is supplied onto the base material upstream of this knife, and the base material is moved horizontally toward the downstream side. It is a method to make it. The slit coating method is a method in which a metal film forming composition is allowed to flow out of a narrow slit and applied onto a substrate. The ink jet coating method is performed by filling a metal film forming composition into an ink cartridge of a commercially available ink jet printer, This is a method of ink-jet printing on a material. The screen printing method is a method in which a metal film forming composition is transferred to a substrate through a plate image formed thereon using wrinkles as a pattern indicating material. The offset printing method utilizes the water repellency of the ink so that the metal film forming composition attached to the plate is not directly attached to the substrate, but is transferred from the plate to the rubber sheet and then transferred again from the rubber sheet to the substrate. It is a printing method. The die coating method is a method in which a metal film forming composition supplied into a die is distributed by a manifold and extruded from a slit onto a substrate, and the surface of the traveling substrate is applied. The die coating method includes a slot coat method, a slide coat method, and a curtain coat method.

  Next, the base material formed on the upper surface is fired in the air at a temperature of 130 to 400 ° C., preferably 140 to 200 ° C., for 10 minutes to 1 hour, preferably 15 to 40 minutes. Here, the film thickness of the coating film formed on the substrate is limited so that the thickness after firing is in the range of 0.1 to 2.0 μm. If it is a battery, the surface resistance value of the metal film required for it will be insufficient, and if it exceeds 2.0 μm, there will be no problem in characteristics, but the amount of material used will be more than necessary and the material will be wasted. is there. Moreover, the reason for limiting the firing temperature of the coating film formed on the substrate to the range of 130 to 400 ° C. is that the sintering between metal nanoparticles becomes insufficient when the temperature is lower than 130 ° C., and the low temperature process when the temperature exceeds 400 ° C. This is because the production merit cannot be utilized, that is, the manufacturing cost increases and the productivity decreases. Furthermore, the firing time of the coating film formed on the base material was limited to the range of 10 minutes to 1 hour because the sintering between the metal nanoparticles became insufficient when the time was less than 10 minutes, and the property was exceeded when the time exceeded 1 hour. This is because the manufacturing cost increases more than necessary and the productivity decreases.

The metal nanoparticle dispersion liquid that is the metal film forming composition contains a large amount of metal nanoparticles having a primary particle size of 10 to 50 nm and a relatively large size, so that the specific surface area of the metal nanoparticles is reduced. As a result, when a metal film of a solar cell is formed using the metal film forming composition, a metal film containing silver as a main component and containing substantially no organic substance can be obtained. Therefore, even if the solar cell on which the metal film is formed is used for many years, the organic matter is not deteriorated or deteriorated, and the conductivity and reflectance of the metal film are maintained in a high state. An excellent metal film can be obtained. Specifically, an electromagnetic wave having a wavelength of 750 to 1500 nm, that is, a visible light region even after the metal film is accommodated in a constant temperature and humidity chamber having a temperature of 100 ° C. and a humidity of 50%. 80% or more of the electromagnetic wave from the infrared region to the infrared region can be reflected by the metal film, and the conductivity of the metal film, that is, the volume resistivity of the metal film is less than 2 × 10 ⁻⁵ Ω · cm (20 × 10 ⁻⁶ Ω · cm) And can be maintained at a very low value. The solar cell using the metal film formed in this way can maintain high conductivity and high reflectance even when used for many years, and is excellent in aging stability.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Examples 1 to 13, Comparative Examples 1 to 4>
First, a metal salt containing a metal element shown in the following Table 1, a carboxylic acid or a carboxylate salt, and a reducing agent were dissolved in deionized water to prepare saturated aqueous solutions at room temperature. In addition, as a metal salt, nitrate was used, and a chlorine compound was used only for Au and Pt. Moreover, the basic compound shown in the following Table 1 was dissolved in deionized water so as to have a concentration of 3M to prepare a basic aqueous solution, and the molar ratio shown in the following Table 1 was added.

  Next, it mixed according to the synthetic | combination flow shown in FIG.

  Here, in the dropping of the reducing agent aqueous solution C, the carboxylate suspension is heated to the reaction temperature described in the column of “Reaction Temperature” in Table 1 using a water bath, and after reaching the reaction temperature, the mixture is refluxed. Stirring was continued for 4 hours at a rotational speed of 400 rpm with a magnetic stirrer. The obtained reaction liquids were designated as Examples 1 to 13 and Comparative Examples 1 to 4, and the relationship among these carboxylic acid aqueous solution B, metal salt aqueous solution A, reducing agent aqueous solution C and basic aqueous solution D is shown in Table 1.

  In addition, after reaction for 4 hours, about Examples 1-13, although the dried material of the reaction liquid was evaluated by the X-ray diffraction method, the added metal carboxylate was not detected.

＜比較試験及び評価＞
反応終了後における実施例１〜１３，比較例１〜４の反応液を１０００Ｇで３分間遠心分離した。得られた沈殿物に、沈殿物重量の５０倍の０．１Ｍアンモニア水を加えて１０分間撹拌した後、再度１０００Ｇで３分間遠心分離した。この沈殿物に水と溶媒を加えて撹拌し、金属ナノ粒子分散液を得た。得られた実施例１〜１３，比較例１〜４における分散液の組成を表２に示す。

<Comparison test and evaluation>
After completion of the reaction, the reaction solutions of Examples 1 to 13 and Comparative Examples 1 to 4 were centrifuged at 1000 G for 3 minutes. To the obtained precipitate, 0.1 M ammonia water 50 times the weight of the precipitate was added and stirred for 10 minutes, and then centrifuged again at 1000 G for 3 minutes. Water and a solvent were added to the precipitate and stirred to obtain a metal nanoparticle dispersion. Table 2 shows the compositions of the dispersions obtained in Examples 1 to 13 and Comparative Examples 1 to 4.

  The dispersions in Examples 1 to 13 and Comparative Examples 1 to 4 were applied on the base material shown in Table 2 using the coating method shown in Table 2, and the firing temperature shown in Table 2 in the atmosphere was applied for 30 minutes. And fired respectively. Table 2 shows the coating thickness after firing, the volume resistivity of the resulting coating, and the average particle size of the metal nanoparticles. As a method for measuring the average particle diameter of metal nanoparticles, first, the obtained metal nanoparticles are photographed with a TEM (Transmission Electron Microscope) at a magnification of about 500,000 times. Next, a primary particle size is measured for 200 metal nanoparticles from the obtained image, and a particle size distribution is created based on the measurement result. Next, the average value obtained from the created particle size distribution was defined as the average particle size. The volume resistivity was measured and calculated by the four probe method, and the film thickness was measured with a micrometer.

  In the column of alcohols in Table 2, “ME” represents methanol, “ET” represents ethanol, “EG” represents ethylene glycol, “BU” represents butanol, and “PG” represents propylene glycol. “DEG” indicates diethylene glycol, “GL” indicates glycerose, “ER” indicates erythritol, “IH” indicates isobornylhexanol, and “PR” indicates propanol.

  In the other solvent column of Table 2, “A” indicates a mixed solution of acetone and isopropyl glycol mixed at a weight ratio of 1: 1, and “B” indicates cyclohexane and methyl ethyl ketone at a weight ratio of 1: 1 indicates a mixed liquid, and “C” indicates a mixed liquid in which toluene and hexane are mixed at a weight ratio of 1: 1.

表２から明らかなように、実施例１〜１３では、塗膜の体積抵抗率は、いずれも１０^-6Ω・ｃｍオーダーであり、導電材料として好適な値を示した。また、平均粒径は２０〜７０ｎｍの範囲にあり、いわゆる金属ナノ粒子を形成した。

As is clear from Table 2, in Examples 1 to 13, the volume resistivity of the coating film was on the order of 10 ⁻⁶ Ω · cm, and showed a suitable value as a conductive material. Moreover, the average particle diameter was in the range of 20 to 70 nm, and so-called metal nanoparticles were formed.

  On the other hand, in Comparative Examples 1 to 4, the volume resistivity of the coating film shows a value one digit higher, which is not suitable as a conductive material. In Comparative Example 1, the effect as a protective agent for chemically modifying the particle surface of acetic acid added as a carboxylic acid is small, and as a result of the increase in particle size, it is considered that the sintering effect at low temperature peculiar to nanoparticles was decreased. In Comparative Example 2, since the reaction temperature was low and unreacted carboxylate remained, it was thought that the volume resistivity was high as a result of this hindering the sintering of the nanoparticles. In Comparative Example 3, on the contrary, since the reaction temperature was high, the grain growth during the reaction progressed, and it is considered that the sintering effect at low temperature peculiar to nanoparticles was reduced as in Comparative Example 1. In Comparative Example 4, Pd was added up to 40% by mass exceeding 25% by mass of Ag, so that it is considered that an increase in volume resistivity and an increase in particle size occurred.

A Metal salt aqueous solution B Carboxylic acid aqueous solution C Reducing agent aqueous solution D Basic aqueous solution

Claims (6)

Preparing a metal salt aqueous solution (A) by dissolving the metal salt;
One or more compounds selected from the group consisting of glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid, tartaric acid and their salts are dissolved to prepare an aqueous solution of carboxylic acids (B )
Preparing a reducing agent aqueous solution (C);
Preparing a basic aqueous solution (D);
Forming a mixed solution by stirring while dropping the basic aqueous solution (D) into the metal salt aqueous solution (A);
A step of forming a carboxylate suspension by stirring while dropping the aqueous carboxylic acid solution (B) into the mixed solution;
A step of dropping the aqueous reducing agent solution (C) into the carboxylate suspension while stirring to produce metal nanoparticles, and
The metal element contained in the metal salt contains 75% by weight or more of silver,
A method for synthesizing metal nanoparticles, wherein the step of producing metal nanoparticles by stirring while dropping the reducing agent aqueous solution (C) is performed at a temperature of 25 ° C. or higher and 95 ° C. or lower.   2. The metal salt contained in the metal salt of the metal salt aqueous solution (A) other than silver is one or more metals selected from the group consisting of gold, platinum, palladium and ruthenium. Method for synthesizing metal nanoparticles.   The method for synthesizing metal nanoparticles according to claim 1 or 2, wherein the reducing agent is one or more compounds selected from the group consisting of hydrazine, ascorbic acid, oxalic acid, formic acid and salts thereof.   The method for synthesizing metal nanoparticles according to claim 1 or 2, wherein the reducing agent is one or more compounds selected from the group consisting of sodium borohydride, potassium borohydride and glucose.   The manufacturing method of the dispersion liquid which disperse | distributes the metal nanoparticle obtained by the synthesis method of any one of Claim 1 thru | or 4 to a dispersion medium, and obtains a metal nanoparticle dispersion liquid. A step of dispersing metal nanoparticles obtained by the synthesis method according to any one of claims 1 to 4 in a dispersion medium to obtain a metal nanoparticle dispersion;
Applying the metal nanoparticle dispersion as a metal film production composition onto a substrate by a wet coating method to form a metal film.

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