JP2012251222A - Method for producing silver nanoparticle, and ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing silver nanoparticles while considering environmental impact, and excellent in workability, and to provide ink.SOLUTION: The method for producing the silver nanoparticles includes a process of preparing an aqueous solution in which an aliphatic carboxylic acid having at least one hydroxy group or a salt thereof is dissolved, and a process of mixing the aqueous solution, silver nitrate, citrate and an amine compound to reduce the silver nitrate.

Description

  The present invention relates to a method for producing silver nanoparticles and an ink.

In recent years, silver fine particles have been used to form wiring of electronic circuits and electrodes.
Generally, as a method for producing metal fine particles, a vapor phase method such as a CVD method or a spray pyrolysis method and a wet method using a chemical reduction reaction are known, but fine particles produced by a conventional wet method are aggregated. Because of its high properties and difficulty in obtaining monodisperse particles, many high-purity silver fine particles with little aggregation have been produced by a gas phase method. On the other hand, metal fine particles obtained by a vapor phase method are excellent in monodispersibility, but have a problem that production costs are high and particle size control is difficult. Then, the wet manufacturing method of the metal fine particle excellent in the dispersibility is tried.

Patent Document 1 discloses a method for producing silver fine particles by stirring and heating powdered silver oxide, a long-chain fatty acid and an amine compound in a nonpolar solvent such as toluene. Here, silver ions are reduced while being eluted as a fatty acid salt from the surface of silver oxide to produce silver fine particles, and the produced silver fine particles are dispersed and stabilized by coordination of an amine compound on the surface.
Patent Document 2 discloses a method for reducing silver chloride in ethanol in the presence of a specific protective agent.

JP 2008-25005 A JP-A-10-265812

  However, in Patent Documents 1 and 2, since a large amount of an organic solvent is used, handleability is not good, and there is a concern about influence on the environment.

  According to the present invention, a step of preparing an aqueous solution in which an aliphatic carboxylic acid having at least one hydroxyl group or a salt thereof is dissolved in water, the aqueous solution, silver nitrate, citrate, and an amine compound are mixed. And a method for producing silver nanoparticles comprising reducing the silver nitrate to obtain silver nanoparticles.

  According to this invention, silver nitrate is reduced in an aqueous solution, and silver nanoparticles can be obtained without using a large amount of organic solvent. Therefore, it becomes a manufacturing method which can consider the influence on the environment and has excellent workability.

  Moreover, according to this invention, the ink for inkjets which has the silver nanoparticle manufactured by the manufacturing method mentioned above and the solution in which the said silver nanoparticle was disperse | distributed can also be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and ink of a silver nanoparticle which can consider the influence on an environment and were excellent in workability | operativity are provided.

6 is a graph showing the particle size distribution of silver nanoparticles obtained in Example 2. FIG.

Embodiments of the present invention will be described below.
The method for producing silver nanoparticles of the present embodiment includes a step of preparing an aqueous solution in which an aliphatic carboxylic acid having at least one hydroxyl group or a salt thereof is dissolved in water, the aqueous solution, silver nitrate, citrate, Mixing with an amine compound to reduce the silver nitrate to obtain silver nanoparticles.
Here, the silver nanoparticle means a particle having an average particle diameter (D50) of nano-order, and the average particle diameter (D50) is preferably 50 nm or less. The lower limit of the average particle diameter is not particularly limited, but is preferably 1 nm or more.

(Process for preparing aqueous solution)
Here, an aliphatic carboxylic acid having at least one hydroxyl group or a salt thereof is dissolved in water to prepare an aqueous solution (hereinafter referred to as an aqueous solution in which an aliphatic carboxylic acid having a hydroxyl group or the like is dissolved).
An aliphatic carboxylic acid having one or more hydroxyl groups or a salt thereof acts as a dispersant for silver nanoparticles.
Any aliphatic carboxylic acid having a hydroxyl group may be used as long as it can dissolve in water and form a chelate with silver. Examples thereof include citric acid, gluconic acid, malic acid, tartaric acid, heptonic acid, and lactic acid.
Examples of the aliphatic carboxylate having a hydroxyl group include alkali metal salts of any of the above-described aliphatic carboxylic acids, specifically potassium salts and sodium salts.
From the viewpoint of dispersibility, it is preferable to use any one of gluconic acid, gluconate, malic acid, and malate.
Two or more kinds of aliphatic carboxylic acids and aliphatic carboxylates may be used in combination.
The aliphatic carboxylic acid or salt thereof as described above is dissolved in water. At this time, it is preferable to carry out at room temperature without heating or cooling. By doing in this way, it becomes the thing excellent in workability | operativity.
In addition, it is preferable that the usage-amount of aliphatic carboxylic acid and aliphatic carboxylate is 1.5 mol-3 mol with respect to 1 mol of silver nitrate from a dispersible viewpoint.

(Step of reducing silver nitrate)
Next, the aqueous solution, silver nitrate, citrate, and amine compound are mixed.
In the present invention, silver nitrate is used as a raw material for silver nanoparticles. By using silver nitrate, silver nanoparticles having a small particle diameter can be obtained.
Citrate is used as a reducing agent for silver nitrate. Moreover, an amine compound is used as a catalyst.
The citrate is not particularly limited as long as it is a water-soluble salt, and examples thereof include lithium citrate, sodium citrate, potassium citrate, and ammonium dihydrogen citrate. Of these, sodium citrate or diammonium hydrogen citrate is preferable from the viewpoint of solubility.
It is preferable that citrate is dissolved in water and then added to the aqueous solution.
It is preferable that the usage-amount of a citrate is 0.5-3 mol with respect to 1 mol of silver nitrate from a viewpoint of reaction rate and manufacturing cost.
In addition, you may use 2 or more types of different citrates together as a citrate.

The amine compound is not particularly limited as long as it is water-soluble and soluble in water. Primary amines such as lysine, ethylamine and ethanolamine, secondary amines such as diethylamine and diethanolamine, triethylamine, dimethylaminoethanol and the like And tertiary amine, imidazole, triazole and the like. Among these, it is preferable to use dimethylaminoethanol, imidazole or triethylamine from the viewpoint of producing silver nanoparticles having a small particle diameter. The amine compound is used in an amount of 1/20 or more and 1/5 or less in terms of molar ratio with respect to silver nitrate in order to moderate the reaction rate and reduce the particle size of the resulting silver nanoparticles. Preferably there is.
Two or more different amine compounds may be used in combination as the amine compound.

After the amine compound is dissolved in water, it is preferably added to the aqueous solution in which the aliphatic carboxylic acid having a hydroxyl group and the like are dissolved.
In this step, the aqueous solution in which an aliphatic carboxylic acid having a hydroxyl group or the like is dissolved, silver nitrate, citrate, and an amine compound may be mixed.
However, after adding silver nitrate to the aqueous solution in which the aliphatic carboxylic acid having a hydroxyl group and the like is dissolved, it is preferable to add a solution in which the amine compound is dissolved in water and a solution in which the citrate is dissolved in water. By doing in this way, aggregation of a silver nanoparticle can be suppressed and a particle size can be controlled.
A solution in which the amine compound is dissolved in water and a solution in which the citrate is dissolved in water may be added at the same time, or after adding a solution in which the citrate is dissolved in water, the amine compound is dissolved in water. Solution may be added. Further, a solution in which an amine compound is dissolved in water may be added, and then a solution in which citrate is dissolved in water may be added.
In addition, as a method for adding a solution in which citrate is dissolved in water and a solution in which an amine compound is dissolved in water, it is preferable to add dropwise to the aqueous solution in which an aliphatic carboxylic acid having a hydroxyl group or the like is dissolved. By doing in this way, the average particle diameter of the silver nanoparticle obtained can be made small. Moreover, the average particle diameter of the silver nanoparticle obtained can be made small by making comparatively long dripping time of the solution which melt | dissolved the citrate in water, and the solution which melt | dissolved the amine compound in water.

After mixing all the raw materials as mentioned above, it stirs for about 1 to 2 hours, and obtains a reaction liquid. Agitation can be carried out at room temperature.
The silver nitrate concentration in the reaction solution is preferably 0.01 mol / l or more and 0.1 mol / l or less. Thus, it becomes possible to control the average particle diameter of the obtained silver nanoparticle small by setting it as a comparatively thin density | concentration.
In the present invention, all the steps described above can be carried out at 10 ° C. or higher and 50 ° C. or lower, and more preferably carried out at room temperature without heating or cooling. By doing in this way, it becomes a manufacturing method excellent in workability | operativity. In addition, by setting it as 50 degrees C or less, reaction rate can be suppressed and a silver nanoparticle with a small average particle diameter can be obtained. Moreover, the fall of reaction rate can be suppressed by setting it as 10 degreeC or more.
Moreover, in this invention, since there is no especially intense heat_generation | fever in all the processes mentioned above, it becomes a manufacturing method excellent in workability | operativity.
Furthermore, since the production method of the present invention does not use a large amount of an organic solvent, it is possible to consider the influence on the environment and is a production method excellent in workability.

The reaction solution obtained as described above is centrifuged, and the supernatant is discarded. Then, water is added to the obtained precipitate and centrifuged again, and the supernatant is discarded. By repeating this operation, an aqueous dispersion in which silver nanoparticles are dispersed can be obtained. In the present invention, since water-soluble raw materials such as citrate and amine compound are used, it is considered that impurities are hardly mixed in the precipitate after centrifugation.
Further, in the aqueous dispersion, the silver nanoparticles are hardly aggregated and the dispersibility of the silver nanoparticles is good. The reason why the dispersibility of the silver nanoparticles is good is considered as follows. It is considered that the hydroxyl group or carboxyl group (or carboxyl residue) of the aliphatic carboxylic acid or aliphatic carboxylate is coordinated with the silver nanoparticles to form a chelate. Thereby, it is estimated that the dispersibility of silver nanoparticles is good.
Moreover, the average particle diameter (D50) of the silver nanoparticles is 50 nm or less and 1 nm or more. Especially, it is preferable that the average particle diameter (D50) of a silver nanoparticle is 10 nm or less and 1 nm or more. Further, the silver nanoparticles have a spherical shape.
The average particle size (D50) is determined by measuring 200 primary particles of silver nanoparticles with a TEM image, and the average particle size (D50) is 50% from the small particle size side. The diameter (median diameter D50).

The silver nanoparticle aqueous dispersion obtained as described above is processed into an inkjet ink. For example, an ink jet ink can be obtained by mixing an alcohol such as ethanol with an aqueous dispersion of silver nanoparticles.
In addition, after applying the aqueous dispersion of the ink and silver nanoparticles obtained as described above, it is baked at 110 ° C. or higher and 300 ° C. or lower for 30 minutes or more, and further washed with a solution such as water to conduct electricity. A film having properties can be obtained.
Note that the baking temperature is preferably 110 ° C. or higher and 180 ° C. or lower. Thus, even when baking is performed at a relatively low temperature, a conductive film can be obtained. Therefore, for example, a conductive film can be formed on a base material having relatively low heat resistance such as polyethylene terephthalate.

  It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

Next, examples of the present invention will be described.
In addition, in each Example, although the average particle diameter of silver nanoparticle is measured, the measuring method is as follows.
(Measuring method of average particle size)
The silver nanoparticle aqueous dispersion obtained in each example was dried, and a TEM (transmission electron microscope) image was observed. As an apparatus, JEOL JEM2010 was used. The particle diameter of 200 primary particles of silver nanoparticles was measured, and the particle diameter (D50) at which the cumulative number from the small particle diameter side was 50% was defined as the average particle diameter (median diameter D50).

Example 1
1 g of sodium gluconate was dissolved in 20 ml of distilled water to obtain an aqueous solution. Next, 0.5 g of silver nitrate was added to the aqueous solution. Thereafter, a solution prepared by dissolving 0.88 g of sodium citrate in 20 ml of distilled water was added dropwise to the aqueous solution containing silver nitrate and sodium gluconate at room temperature for 20 minutes. After the dropwise addition, a solution prepared by dissolving 0.027 g of dimethylaminoethanol in 0.5 ml of distilled water was added dropwise and stirred for 1 hour. For stirring, a water bath stirrer manufactured by AS ONE was used.
The obtained reaction solution was centrifuged at 5000 rpm for 1 minute, the supernatant was discarded, distilled water was added to the precipitate, and centrifuged at 5000 rpm for 2 minutes to obtain a precipitate. The precipitate was further centrifuged once more, and the precipitate was redispersed in water to obtain an aqueous dispersion of silver nanoparticles. All the above steps were performed at room temperature.
In the aqueous dispersion of silver nanoparticles, it was confirmed that the silver nanoparticles were not aggregated and had excellent dispersibility. Moreover, when the obtained silver nanoparticle was observed by TEM, it turned out that it is spherical. The average particle size is 5 nm. It was found that the particle size distribution was very narrow and monodispersed, and the particle size was almost uniform.
The obtained aqueous dispersion was applied to a film, baked at 150 ° C. for 1 hour in the atmosphere under atmospheric pressure, and immersed in water for a predetermined time. Thereafter, the water was dried and the resistivity was measured. The results are shown in Table 1. It can be seen that conductivity is exhibited when the immersion time is 30 minutes or more.

  Further, the obtained aqueous dispersion was applied to a film, fired in the atmosphere at atmospheric pressure as shown in Table 2, and immersed in a 0.1 mol / l potassium hydroxide aqueous solution for a predetermined time. . Thereafter, it was washed with water and dried to measure the resistivity. The results are shown in Table 2. It turns out that electroconductivity is shown.

(Example 2)
An aqueous solution was obtained by dissolving 2 g of sodium gluconate in 20 ml of distilled water. Next, 0.5 g of silver nitrate was added to the aqueous solution. Thereafter, a solution prepared by dissolving 0.88 g of sodium citrate in 20 ml of distilled water was added dropwise to the aqueous solution containing silver nitrate and sodium gluconate at room temperature for 20 minutes. After the dropwise addition, a solution prepared by dissolving 0.027 g of dimethylaminoethanol in 0.5 ml of distilled water was added dropwise and stirred for 1 hour. For stirring, a water bath stirrer manufactured by AS ONE was used.
The obtained reaction solution was centrifuged at 5000 rpm for 1 minute, the supernatant was discarded, distilled water was added to the precipitate, and centrifuged at 5000 rpm for 2 minutes to obtain a precipitate. The precipitate was further centrifuged once more, and the precipitate was redispersed in water to obtain an aqueous dispersion of silver nanoparticles. All the above steps were performed at room temperature.
Moreover, it was found that the average particle diameter of the obtained silver nanoparticles was 6 nm, the particle diameter distribution was very narrow and monodispersed, and the particle diameter was almost uniform. FIG. 1 shows the particle size distribution of the silver nanoparticles obtained. A peak is observed in the range of 5.61 to 7.53 nm, and it can be seen that the distribution is very narrow. A Zetasizer NanoSeries manufactured by Malvern Instruments was used as the apparatus.
Furthermore, in the aqueous dispersion of silver nanoparticles, the silver nanoparticles were not agglomerated and it was confirmed that the dispersion was excellent. Moreover, when the obtained silver nanoparticle was observed by TEM, it turned out that it is spherical.
The obtained aqueous dispersion was applied to a film, baked at atmospheric pressure under atmospheric pressure as shown in Table 3, and immersed in a 0.1 mol / l aqueous potassium hydroxide solution for a predetermined time. Then, it dried and measured the resistivity. The results are shown in Table 3. It can be seen that both have low resistivity and conductivity.

(Example 3)
1 g of disodium DL-malate was dissolved in 20 ml of distilled water. Next, 0.5 g of silver nitrate was added to the aqueous solution. A solution obtained by dissolving 0.88 g of sodium citrate in 20 ml of distilled water was added dropwise to the solution thus obtained at room temperature for 20 minutes. After the dropwise addition, a solution prepared by dissolving 0.027 g of dimethylaminoethanol in 0.5 ml of distilled water was added dropwise and stirred for 1 hour. For stirring, a water bath stirrer manufactured by AS ONE was used.
The obtained reaction solution was centrifuged at 5000 rpm for 1 minute, the supernatant was discarded, distilled water was added to the precipitate, and centrifuged at 5000 rpm for 2 minutes to obtain a precipitate. The precipitate was further centrifuged once more, and the precipitate was redispersed in water to obtain an aqueous dispersion of silver nanoparticles. All the above steps were performed at room temperature.
The average particle size of the obtained silver nanoparticles was 5 nm, the particle size distribution was very narrow and monodispersed, and the particle size was almost uniform. Furthermore, in the aqueous dispersion of silver nanoparticles, the silver nanoparticles were not agglomerated and it was confirmed that the dispersion was excellent. Moreover, when the obtained silver nanoparticle was observed by TEM, it turned out that it is spherical.
The obtained aqueous dispersion was applied to a film, baked at atmospheric pressure under atmospheric pressure as shown in Table 4, and immersed in water for a predetermined time. Thereafter, the water was dried and the resistivity was measured. The results are shown in Table 4. It can be seen that conductivity is exhibited when the immersion time is 30 minutes or more.

Example 4
1 g of sodium gluconate was dissolved in 20 ml of distilled water to obtain an aqueous solution. Next, 0.5 g of silver nitrate was added to the aqueous solution. Thereafter, a solution prepared by dissolving 0.88 g of sodium citrate in 20 ml of distilled water was added dropwise to the aqueous solution containing silver nitrate and sodium gluconate at room temperature for 20 minutes. After the dropwise addition, a solution prepared by dissolving 0.02 g of imidazole in 0.5 ml of distilled water was added dropwise and stirred for 1 hour. For stirring, a water bath stirrer manufactured by AS ONE was used.
The obtained reaction solution was centrifuged at 5000 rpm for 1 minute, the supernatant was discarded, distilled water was added to the precipitate, and centrifuged at 5000 rpm for 2 minutes to obtain a precipitate. The precipitate was further centrifuged once more, and the precipitate was redispersed in water to obtain an aqueous dispersion of silver nanoparticles. All the above steps were performed at room temperature.
Moreover, it was found that the average particle size of the obtained silver nanoparticles was 10 nm, the particle size distribution was very narrow and monodispersed, and the particle size was almost uniform. Furthermore, in the aqueous dispersion of silver nanoparticles, the silver nanoparticles were not agglomerated and it was confirmed that the dispersion was excellent. Moreover, when the obtained silver nanoparticle was observed by TEM, it turned out that it is spherical.

(Example 5)
1 g of sodium gluconate was dissolved in 20 ml of distilled water to obtain an aqueous solution. Next, 0.5 g of silver nitrate was added to the aqueous solution. Thereafter, a solution prepared by dissolving 0.88 g of sodium citrate in 20 ml of distilled water was added dropwise to the aqueous solution containing silver nitrate and sodium gluconate at room temperature for 20 minutes. After dropping, a solution of 0.03 g of triethylamine dissolved in 0.5 ml of distilled water was added dropwise and stirred for 1 hour. For stirring, a water bath stirrer manufactured by AS ONE was used.
The obtained reaction solution was centrifuged at 5000 rpm for 1 minute, the supernatant was discarded, distilled water was added to the precipitate, and centrifuged at 5000 rpm for 2 minutes to obtain a precipitate. The precipitate was further centrifuged once more, and the precipitate was redispersed in water to obtain an aqueous dispersion of silver nanoparticles. All the above steps were performed at room temperature.
Moreover, it was found that the average particle diameter of the obtained silver nanoparticles was 5 nm, the particle diameter distribution was very narrow and monodispersed, and the particle diameter was almost uniform. Furthermore, in the aqueous dispersion of silver nanoparticles, the silver nanoparticles were not agglomerated and it was confirmed that the dispersion was excellent. Moreover, when the obtained silver nanoparticle was observed by TEM, it turned out that it is spherical.

(Example 6)
1 g of sodium gluconate was dissolved in 20 ml of distilled water to obtain an aqueous solution. Next, 0.5 g of silver nitrate was added to the aqueous solution. Thereafter, a solution prepared by dissolving 0.68 g of diammonium hydrogen citrate in 20 ml of distilled water was added dropwise to the aqueous solution containing silver nitrate and sodium gluconate at room temperature for 20 minutes. After the dropwise addition, a solution prepared by dissolving 0.02 g of imidazole in 0.5 ml of distilled water was added dropwise and stirred for 1 hour. For stirring, a water bath stirrer manufactured by AS ONE was used.
The obtained reaction solution was centrifuged at 5000 rpm for 1 minute, the supernatant was discarded, distilled water was added to the precipitate, and centrifuged at 5000 rpm for 2 minutes to obtain a precipitate. The precipitate was further centrifuged once more, and the precipitate was redispersed in water to obtain an aqueous dispersion of silver nanoparticles. All the above steps were performed at room temperature.
Further, it was found that the average particle diameter of the obtained silver nanoparticles was 4 nm, the particle diameter distribution was very narrow and monodispersed, and the particle diameter was almost uniform. Furthermore, in the aqueous dispersion of silver nanoparticles, the silver nanoparticles were not agglomerated and it was confirmed that the dispersion was excellent. Moreover, when the obtained silver nanoparticle was observed by TEM, it turned out that it is spherical.

In addition, when it measured by UV visible absorption spectroscopy about the silver nanoparticle (before baking) obtained in Examples 1-6, absorption was seen by 400 nm vicinity. This is the plasmon resonance absorption of silver nanoparticles.
In addition, when the silver nanoparticles (before firing) obtained in Examples 1 to 6 were identified using EDS (energy dispersive X-ray spectroscopy), a peak of silver nanoparticles was shown in the vicinity of 3 keV. No metal components other than were observed.
Moreover, after air-drying the aqueous dispersion of silver nanoparticles obtained in Examples 1 to 6 at room temperature, re-dispersed silver nanoparticles could be obtained by adding water and stirring. The redispersibility of the silver nanoparticles was found to be very good.
In addition, when the aqueous dispersion of silver nanoparticles obtained in Examples 1 to 6 (no precipitation immediately after stirring) was allowed to stand and observed after 30 minutes, the silver nanoparticles were precipitated. Not confirmed.
The dispersibility of the silver nanoparticles obtained in Examples 1 to 6 is better than those disclosed in Patent Documents 1 and 2.

Furthermore, referring to Examples 1 to 3, it can be seen that a conductive film can be obtained by baking and washing with water or an aqueous potassium hydroxide solution.
In addition to this, referring to Examples 1 and 3, it can be seen that a conductive film is obtained by performing baking at 150 ° C. to 160 ° C. Since a conductive film can be obtained by firing at a relatively low temperature in this way, it is possible to form a conductive film on a relatively low heat resistant substrate such as polyethylene terephthalate. It becomes.

Claims (7)

Preparing an aqueous solution in which an aliphatic carboxylic acid having at least one hydroxyl group or a salt thereof is dissolved in water;
A method for producing silver nanoparticles, comprising: mixing the aqueous solution, silver nitrate, citrate, and an amine compound, and reducing the silver nitrate to obtain silver nanoparticles. In the manufacturing method of the silver nanoparticle of Claim 1,
The aliphatic carboxylic acid or a salt thereof is a dispersant for silver nanoparticles,
The method for producing silver nanoparticles, wherein the citrate is a reducing agent that reduces the silver nitrate. In the manufacturing method of the silver nanoparticle of Claim 1 or 2,
In the step of preparing the aqueous solution, a method for producing silver nanoparticles using gluconic acid or gluconate, or malic acid or malate as the aliphatic carboxylic acid or a salt thereof. In the manufacturing method of the silver nanoparticle in any one of Claims 1 thru | or 3,
The method for producing silver nanoparticles, wherein the amine compound is dimethylaminoethanol, imidazole or triethylamine. In the manufacturing method of the silver nanoparticle in any one of Claims 1 thru | or 4,
A method for producing silver nanoparticles, wherein the citrate is sodium citrate or diammonium hydrogen citrate. In the manufacturing method of the silver nanoparticle in any one of Claims 1 thru | or 5,
A method for producing silver nanoparticles, wherein the silver nanoparticles have an average particle diameter (D50) of 50 nm or less and 1 nm or more.   An ink-jet ink comprising silver nanoparticles produced by the production method according to claim 1 and a solution in which the silver nanoparticles are dispersed.

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