JP7032976B2 - Metal particle dispersion and its manufacturing method - Google Patents

Description

The present invention relates to a metal particle dispersion and a method for producing the same.

Metal particles are used for various purposes as catalyst materials, semiconductor materials, conductive materials and the like. For example, the conductive material is used for electrodes, circuits, antistatic transparent coatings, electromagnetic wave shielding transparent coatings, capacitor electrodes and the like of various electronic devices (see Non-Patent Document 1).

As a method for producing such metal particles, a method for producing metal particles by reducing a metal salt in an organic solvent has been proposed (see, for example, Patent Documents 1 and 2). However, the metal particles obtained by the method using this organic solvent have a problem of low conductivity.

Therefore, in order to obtain metal particles with higher conductivity, it has been attempted to produce a metal particle dispersion in water, but oxidation and ionization of the metal particles are likely to occur, and a stable metal particle dispersion can be obtained. difficult.

Japanese Unexamined Patent Publication No. 2005-281781 Japanese Unexamined Patent Publication No. 2008-75181

"Science of Metals and Semiconductor Nanoparticles" Author / Chemical Society of Japan, Publisher / Ryosuke Sone, Publisher / Kagaku-Dojin (2012)

An object of the present invention is to provide a metal particle dispersion having high storage stability.

By cleaning the metal particles obtained by reducing the metal salt with a cleaning liquid containing fine bubbles, oxidation and ionization of the metal particles are suppressed, and the storage stability of the metal particle dispersion liquid and the coating liquid using the same are suppressed. Was found to be enhanced.
The liquid containing microbubbles has a higher dissolved oxygen concentration and a higher redox potential than the conventionally used degassed (deoxidized) treated water with an inert gas such as _N2 bubbling water, and is therefore used in the reduction reaction system. This is generally considered unfavorable. However, surprisingly, by cleaning the metal particles with the liquid containing the fine bubbles, the storage stability of the produced metal particle dispersion is improved, and the coating liquid using this metal particle dispersion is used. I found that the pot life also improved.

It was also found that the metal particles obtained by reducing the metal salt can be washed with a washing liquid containing fine bubbles to obtain the metal particles in high yield.

Furthermore, it was found that the coating film formed by using the metal particles produced by washing with a washing liquid containing fine bubbles has high conductivity.

That is, the present invention includes a particle preparation step of reducing metal salts in a liquid to prepare metal particles, and a cleaning step of cleaning the metal particles prepared in this particle preparation step with a cleaning liquid containing fine particles. The present invention relates to a method for producing a characteristic metal particle dispersion liquid. The present invention also relates to a method for producing a coated base material, which comprises applying a coating liquid for forming a film containing metal particles prepared by this production method onto the base material.

It is possible to obtain a metal particle dispersion having high storage stability in which oxidation and ionization of metal particles are suppressed.

In the method for producing a metal particle dispersion liquid of the present invention, a particle preparation step of reducing a metal salt in a liquid (hereinafter, may be referred to as a reaction liquid) to prepare metal particles and a metal particle prepared in the particle preparation step are used. It includes a cleaning step of cleaning with a cleaning liquid containing fine particles. This manufacturing method may include other steps before and after each of the above steps. For example, the cleaning step may be followed by a coarse particle removing step of removing the coarse particles.

By using a liquid containing fine bubbles in the cleaning step, it is possible to suppress the oxidation and ionization of the metal particles and improve the storage stability of the metal particle dispersion liquid. In addition, the pot life of the coating liquid using this metal particle dispersion liquid can be extended.
With this production method, metal particles can be obtained in high yield. Further, the coating film using the metal particles has high conductivity. Although the reason for these is not clear, it is presumed that the microbubbles contained in the reaction solution have a protective action for the metal particles to exist as a metal without being oxidized.

[Manufacturing method of metal particle dispersion]
<Particle preparation process>
In the particle preparation step, as described above, the metal salt is reduced in the reaction solution to prepare metal particles. The reaction solution may be an organic solvent or water. However, it is more effective in the case of water. If an oxidizing gas such as oxygen is present in the reaction solution, the metal may be oxidized. Therefore, it is desirable to reduce the oxidizing gas as much as possible in the space in contact with the reaction solution and the reaction solution. This step is preferably performed in a state of being purged with an inert gas such as _N2 gas or a rare gas in order to suppress the mixing of oxidizing gas. Further, it is preferable to bubbling the reaction solution with an inert gas in order to suppress the mixing of oxidizing gas. Further, it is particularly preferable to use a liquid containing fine bubbles (including a bubbling liquid containing fine bubbles), which will be described later.
Here, as the oxidizing gas, oxygen, ozone, carbon dioxide gas, nitric oxide, nitric oxide dinitrogen, nitrogen dioxide, fluorine, chlorine, chlorine dioxide, nitrogen trifluoride, chlorine trifluoride, silicon tetrachloride, difluoride. Examples thereof include oxygen fluoride and perchlorylfluoride.

The reaction solution in this step preferably has an oxidation-reduction potential of −50 mV or less, more preferably −100 mV or less. The pH is preferably 4.0 to 11.0, more preferably 4.5 to 7.0. By reducing the metal salt within the range of this redox potential and pH, the formation of metal particles is smoothly performed. The reaction temperature is preferably 10 to 80 ° C.

《Micro bubbles》
The microbubbles are preferably microbubbles (micro-nano bubbles) having an average bubble diameter of 40 nm to 10 μm. Such microbubbles include at least one of so-called nanobubbles having a bubble diameter of 40 to 100 nm (0.1 μm) and so-called microbubbles having a bubble diameter of 0.1 to 10 μm, and those containing both are preferable. .. The upper limit of the average bubble diameter of the fine bubbles is preferably 500 nm, more preferably 350 nm, and even more preferably 200 nm. The lower limit of the average bubble diameter of the fine bubbles is preferably 50 nm, more preferably 60 nm, and even more preferably 65 nm.

The content of microbubbles is preferably 1.0 × 10 ³ cells / mL or more, more preferably 1.0 × 10 ⁵ cells / mL or more, and even more preferably 1.0 × 10 ⁸ cells / mL or more. The upper limit is not particularly limited, but 1.0 × 10 ¹¹ pieces / mL is preferable, 5.0 × 10 ¹⁰ pieces / mL is more preferable, and 1.0 × 10 ¹⁰ pieces / mL is further preferable.

The average bubble diameter and the number of bubbles of the fine bubbles are obtained by analyzing the Brownian motion moving speed of the bubbles in the liquid by the nanoparticle tracking analysis method (NTA). For example, it can be measured using "Nanosite NS300" manufactured by Malvern.

The gas forming the fine bubbles is preferably a non-oxidizing gas. Specifically, at least one of nitrogen, hydrogen, and a rare gas is preferable.

《Metal salt》
The metal salt used as the raw material for the metal particles is one of the metals selected from the 4th, 5th, 6th, 8th, 9th, 10th, 11th, 13th, 14th and 15th groups of the periodic table. Salt is used. Examples of the type of salt include chloride salt, nitrate, sulfate, organic acid salt and the like.

Preferred metal elements are Ti in Group 4, Ta in Group 5, W in Group 6, Ru in Group 8, Co, Rh in Group 9, Ni, Pd, Pt in Group 10, and Cu, Ag, Au in Group 11. Examples are Al and In in the 13th group, Sn in the 14th group, and Sb in the 15th group. This production method is also applicable to easily oxidizable metals other than Au and Ag.

《Reducing agent》
A reducing agent is usually used for the reduction reaction in the particle preparation step.
Examples of the reducing agent include ferrous sulfate, NaBH ₄ , hydrazine, hydrogen, alcohol, trisodium citrate, tartrate acid, sodium hypophosphite, formic acid, LiBH ₄ , LiAlH ₄ , and diboran. Of these, trisodium citrate, tartaric acid, and formic acid are preferable. They have both reducing and stabilizing functions. Therefore, the process for removing the impure component is reduced and the stability is improved.

The amount of the reducing agent used varies depending on the reducing property of the metal salt, but is preferably 0.5 to 10 mol, more preferably 1 to 5 mol, with respect to 1 mol of the metal salt. Here, if the reducing agent is less than 0.5 mol with respect to 1 mol of the metal salt, the reduction may be insufficient and the desired metal particles may not be obtained. If the reducing agent exceeds 10 mol with respect to 1 mol of the metal salt, metal particles having a larger particle diameter than necessary may be generated.

《Organic stabilizer》
In the particle preparation step, it is preferable to use an organic stabilizer. By adding the organic stabilizer, the organic stabilizer is adsorbed on the metal salt, the dispersibility of the metal salt is improved, and the reduction of the metal salt can be performed more smoothly. In addition, the generated metal particles are stably dispersed in the dispersion medium.

The organic stabilizer may be any as long as it can be adsorbed on a metal salt or metal particles to enhance dispersion stability. For example, gelatin, polyvinyl alcohol, polyvinylpyrrolidone, vinyl acetate, polyacrylic acid, carboxylic acid compounds and the like are suitable. Among them, a carboxylic acid compound having a carboxyl group having a large interaction with the surface of a metal salt or metal particles is preferable, and a polyvalent carboxylic acid compound is particularly preferable.

The carboxylic acid compounds include, for example, anthic acid, hydroxyanthracene carboxylic acid, hydroxynaphthoic acid, galvanic acid, cresotic acid, parahydroxybenzoic acid, ortho-acetylsalicylic acid, malic acid, mandelic acid, gluconic acid, citric acid, tartaric acid, lactic acid. , Benzenecarboxylic acid, formic acid, acetic acid, butanoic acid, propionic acid, pentanoic acid, hexanoic acid, heptanic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, 9-hexadecenoic acid, Examples thereof include heptadecanoic acid, octadecanoic acid, glycolic acid, L-ascorbic acid, fumaric acid, maleic acid, adipic acid and salts thereof. These may be used alone or in admixture of two or more. Of these, citric acid or a salt thereof is preferable, and trisodium citrate is particularly preferable because it has a large interaction with the surface of a metal salt or metal particles.

The amount of the organic stabilizer used is preferably 0.5 to 10 mol, more preferably 1 to 5 mol, relative to 1 mol of the metal salt. Here, when the amount of the organic stabilizer is less than 0.5 mol with respect to 1 mol of the metal salt, the amount of the organic stabilizer adsorbed on the metal salt is too small, and the dispersibility of the metal salt becomes insufficient, resulting in insufficient metal dispersibility. There is a risk that the reduction of salts and the dispersibility of metal particles will be insufficient. On the contrary, when the amount of the organic stabilizer exceeds 10 mol per 1 mol of the metal salt, the dispersibility and reducibility of the metal salt and the dispersibility of the metal particles are not particularly improved, and the organic stability in the subsequent cleaning step is not improved. Extra labor may be required for the removal treatment of the agent and the wastewater treatment.

<< pH adjuster >>
A pH adjuster can be used so that the pH of the reaction solution in the particle preparation step is 4.0 to 11.0. A mineral acid or an organic acid is suitable as the pH adjuster. Of these, organic acids having C ₁ to C ₃ carbon atoms are preferable. The organic stabilizer may also function as a pH adjuster.

<Washing process>
In the cleaning step, the metal particles prepared in the particle preparation step are washed with a cleaning liquid. Here, desalting is performed and the organic stabilizer is removed. Here, the salt is a substance other than the metal particles generated by the reduction treatment of the metal salt, and exists as an ion in the reaction solution. Specific examples thereof include metal ions such as sodium and iron, boron ions, chloride ions, nitrate ions, sulfate ions, and organic acid ions.
This cleaning liquid preferably contains fine bubbles. It is preferable that the metal particle dispersion produced after washing also contains fine bubbles.

Water or alcohol is suitable as the cleaning liquid containing fine bubbles, and other components may be contained. The cleaning liquid containing microbubbles may be a microbubble-containing bubbling cleaning liquid using a bubbling liquid from which oxygen has been removed by bubbling an inert gas in advance. The details of the cleaning liquid containing fine bubbles are the same as the liquid containing fine bubbles (reaction liquid) used in the particle preparation step.

By cleaning the metal particles with a cleaning liquid containing fine bubbles, ionization and oxidation of the metal particles are prevented, and the storage stability of the metal particle dispersion liquid and the pot life of the coating liquid using this metal particle dispersion liquid are dramatically improved. Can be improved. In addition, the dispersibility of the produced metal particles is improved, and the amount of the organic stabilizer in the final dispersion can be reduced. Therefore, when the film is formed, the metal particles come into direct contact with each other, the resistance at the particle boundary is reduced, and as a result, a film having high conductivity can be formed.

Examples of the cleaning method include a decantation method and a cleaning method using an adventitia film or a ceramic film. In the decantation method, for example, metal particles are recovered from the metal particle dispersion liquid prepared in the particle preparation step, and the recovered metal particles are immersed in the cleaning liquid for cleaning (desalting). This cleaning liquid preferably contains a high concentration of an organic stabilizer. This makes it possible to appropriately agglomerate the metal particles and elute the impure components such as nitrate ions and sulfate ions into the supernatant liquid to remove the impure components. Further, it is preferable to purify using an ion exchange resin. The organic stabilizer used in the cleaning step may be the same as that used in the particle preparation step, or may be different.

In the present invention, the impure component can be sufficiently removed even when a cleaning liquid having a relatively low concentration of the organic stabilizer can be used, and the subsequent treatment with an ion exchange resin can be simplified (reduction of the amount of resin), which is efficient. Can produce metal particles. In addition, it is possible to reduce the number of washings, which also enables efficient production of metal particles. By simplifying the cleaning process, the loss of metal particles can be reduced and the yield can be improved. Further, since the induction of oxidation of the metal particles is suppressed by the simplification of the cleaning step, the coating film formed by using the metal particles has high conductivity.

<Coarse particle removal process>
After the washing step, it is preferable to remove the coarse particles by centrifugation or the like.

[Metal particle dispersion]
The metal particle dispersion liquid of the present invention is characterized in that metal particles are dispersed in a liquid containing fine bubbles. The details of the liquid containing fine bubbles are the same as the liquid containing fine bubbles (reaction liquid) used in the particle preparation step. Examples of the metal particles include metal particles of the 4th, 5th, 6th, 8th, 9th, 10th, 11th, 13th, 14th, and 15th groups of the periodic table. A plurality of types of metal particles may be mixed and used. This metal particle dispersion can be produced by the above-mentioned production method.
Water or an organic solvent is suitable as the dispersion medium. Here, the organic solvent is not particularly limited in type, but alcohols are preferable because of the ease of processing as a coating liquid and the ease of producing a coated base material. Of these, methanol and ethanol are preferable.

The storage stability of the metal particle dispersion is usually about several hours to one month, although it depends on the metal species when it is produced using only a solvent bubbled with an inert gas. On the other hand, the storage stability of the metal particle dispersion of the present invention exceeds 3 months. It is considered that this is different from the action when bubbles are simply present, and some action is acting between the fine bubbles and the metal particles.

With the current technology, it is difficult to measure the average bubble diameter and the number of bubbles of the fine bubbles in the dispersion liquid in which the metal particles and the fine bubbles coexist. Therefore, the metal particles are removed with an ultrafiltration membrane, and the fine bubbles contained in this filtrate are measured to obtain the average bubble diameter and the number of fine bubbles. That is, the average bubble diameter and the number of bubbles of the present invention refer to those obtained by measuring a filtrate that has passed through an ultrafiltration membrane having a molecular weight cut-off of 4000.

The redox potential (ORP) of the metal particle dispersion is preferably 0 to 300 mV, more preferably 100 to 250 mV. Here, when the ORP is less than 0 mV, the dispersibility of the metal particles may become unstable because it is in the reducing field. On the contrary, when the ORP exceeds 300 mV, the metal particles may be oxidized.
The pH is usually 4.0 to 7.0, preferably 4.5 to 6.5. Here, when the pH is less than 4.0, it exists in an ionic state, and metal particles may not be obtained. On the contrary, when the pH exceeds 7.0, the metal particles may aggregate due to the high salt concentration.

The electrical conductivity of the metal particle dispersion is preferably 10 to 500 μS / cm, more preferably 50 to 300 μS / cm. Here, when the electric conductivity is less than 10 μS / cm, the amount of the dispersant may be small and the storage stability may be lowered (the life may be short). On the contrary, when the electric conductivity exceeds 500 μS / cm, the salt concentration becomes high, so that the storage stability may decrease. Further, even if a conductive film is formed, the conductivity may deteriorate.

The content of each of the impure components of the metal particle dispersion is preferably 100 ppm or less, more preferably 80 ppm or less, still more preferably 50 ppm or less, based on the metal particles. Here, if it exceeds 100 ppm, the salt concentration becomes high, so that the storage stability may decrease. Further, even if a conductive film is formed, the conductivity may deteriorate. The impure content of the metal particle dispersion is a substance other than metal particles, a dispersion medium, an organic stabilizer, and various additives. This is a substance other than the metal particles generated by the reduction treatment of the metal salt, and exists as ions in the reaction solution. Specifically, metal ions such as sodium and iron, boron ions, chloride ions, nitrate ions, sulfate ions and the like are exemplified.

The amount of the organic stabilizer in the metal particle dispersion is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass with respect to the metal particles. Here, when the amount of the organic stabilizer is less than 0.1% by mass with respect to the metal particles, the amount of the organic stabilizer adsorbed on the metal particles is too small, and the dispersibility of the metal particles may be insufficient. There is. On the contrary, if the amount of the organic stabilizer exceeds 5% by mass with respect to the metal particles, the cleaning is insufficient, the dispersibility of the metal particles is not improved, and the particles may rather aggregate with each other. The content of the organic stabilizer contained in this metal particle dispersion can be determined by analyzing the amount of C (carbon) derived from the organic stabilizer.

The average particle size of the metal particles contained in this metal particle dispersion is preferably 3 to 200 nm, more preferably 5 to 70 nm. When the average particle size is 3 to 200 nm, a highly transparent conductive film can be obtained.
The average particle size of the metal particles is obtained by taking an electron micrograph, measuring the particle size of any 500 particles, and obtaining the average value thereof.

The metal particle dispersion liquid of the present invention can suppress oxidation and ionization of metal particles. Therefore, even in an aqueous system, long-term storage stability that could not be realized in the past can be realized. In addition, a long-term pot life that could not be realized in the past can be realized even with a coating liquid using this metal particle dispersion liquid. Further, the metal particle dispersion liquid of the present invention has a very low content of oxide particles and can produce a highly conductive film. Here, it is preferable that the metal oxide is not detected by X-ray diffraction. The content thereof is preferably 500 ppm or less, more preferably 200 ppm or less, still more preferably 100 ppm or less with respect to the particles. If the content of the metal oxide exceeds 500 ppm, the storage stability of the dispersion is lowered, and the particles may aggregate and precipitate. Further, when the metal particles are ionized, they do not exist as particles in the liquid, and even if they are used as a coating liquid, a desired film cannot be obtained.

[Coating liquid for film formation]
A coating liquid for forming a film can be produced using the metal particles contained in the metal particle dispersion liquid of the present invention. Various conventionally known additives can be added to the coating liquid for film formation.

In the production of a coated base material, the coating liquid for forming a coating is applied onto the base material, dried, and fired if necessary.

Examples of the base material include film-like and sheet-like base materials made of glass, plastic, ceramic, metal and the like. Examples of the coating method of the coating liquid include a dipping method, a spinner method, a spray method, a roll coater method, a flexographic printing method and the like. The film thickness of the film is preferably about 30 to 300 nm, more preferably about 50 to 200 nm.

The drying temperature is, for example, a temperature of about room temperature to 90 ° C. The firing temperature is, for example, about 120 to 900 ° C., and may be about 150 to 350 ° C. Since the metal particles contained in the dispersion liquid of the present invention have little adhesion of organic substances such as an organic stabilizer, it is not necessary to bake them at a high temperature such as 400 ° C. or higher to remove the organic substances. As a result, it is possible to prevent aggregation and fusion of metal particles due to high-temperature firing, and it is possible to suppress deterioration of the haze of the obtained film.

[Example 1]
<Particle preparation process>
Bubbling ultrapure water (pH (25 ° C., same hereafter) 6.32, electrical conductivity 0.05 μS / S, dissolved oxygen amount (DO) 6.17 ppm, redox potential (ORP) 350 mV) with _N2 . After 1 hour, N ₂ bubbling water (pH 6.6, electrical conductivity 0.6 μS / cm, DO 0.6 ppm, ORP 260 mV) from which dissolved oxygen had been removed was prepared.
400 g of trisodium citrate dihydrate (organic stabilizer) was dissolved in 930 g of _N2 bubbling water to prepare a solution (S1-1).
180 g of ferrous sulfate heptahydrate (reducing agent) was dissolved in 600 g of _N2 bubbling water to prepare a solution (S1-2).
The solution (S1-1) and the solution (S1-2) were mixed and stirred for 30 minutes to prepare a solution A1.

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of _N2 bubbling water to prepare a solution B1. Then, the solution A1 was added to the solution B1 and stirred for 10 hours, and the metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Washing process>
N ₂ micro-nano bubble water (average bubble diameter 70 nm, number of bubbles 240 million cells / mL) by contacting ultrapure water with N ₂ using a swirling flow type bubble generator (HYK-20-SD manufactured by Ligaric Co., Ltd.) , PH 5.79, electrical conductivity 1.17 μS / cm, DO 1.70 ppm, ORP330 mV). The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using _N2 micro-nanobubble water, washed (demineralized), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal equivalent concentration of 2.5% by mass was prepared using _N2 micro-nano bubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-1) having a concentration of 2.5% by mass in terms of metal.

[Average bubble diameter and number of microbubbles]
For the fine particles in the metal particle dispersion (P-1), the metal particle dispersion is filtered through an ultrafiltration membrane (SEP-1013 fractional molecular weight 4000 manufactured by Asahi Kasei) to remove the metal particles, and the fine particles in the filtrate are removed. The average bubble diameter and the number of bubbles were measured. The average bubble diameter and the number of bubbles of the fine bubbles were measured by measuring the Brownian motion moving speed of the bubbles in the liquid by using the nanoparticle tracking analysis method. Specifically, about 20 mL of the measurement sample (solution A1, solution B1 or the filtrate of the metal particle dispersion (P-1)) is injected into the measuring instrument (“Nanosite NS300” manufactured by Malvern) while sucking the nanoparticles. It was measured by the tracking analysis method. The micro-nano bubble water was measured by the above method as it was without filtration treatment.

Physical properties of the solution after reduction in the particle preparation step (pH, ORP), physical properties of the finally obtained metal particle dispersion (average bubble diameter and number of microbubbles, pH, ORP, content and collection of metal particles) Rate, average particle size of primary particles, average particle size of secondary particles, presence / absence of metal oxide, impure content (Fe, Na, B, SO ₄ , NO ₃ ), C (carbon) amount, storage stability ) Is shown in Table 1 (the same applies to the following examples and comparative examples).

[Electrical conductivity]
The electrical conductivity was measured by the AC two-electrode method. Specifically, a pH meter (F-74 manufactured by HORIBA, Ltd., electrode model number 3551-10D) was obtained by immersing the electrode in the liquid to be measured in the conductivity measurement mode. The temperatures of the bubbling water, the micro-nano bubble water, and the metal particle dispersion were adjusted to 25 ° C.

[Redox potential (ORP)]
The redox potential (Oxidation Reduction Potential) was determined by immersing the electrode in a liquid for measuring the electrode in the ORP measurement mode for setting the pH meter (F-74 manufactured by Horiba Seisakusho, electrode model number 9300-10D). The temperatures of the bubbling water, the micro-nano bubble water, and the metal particle dispersion were adjusted to 25 ° C.

[Dissolved oxygen concentration (DO)]
Dissolved Oxygen concentration was measured by the septal galvanic cell method. Specifically, a pH meter (OM-51 manufactured by HORIBA, Ltd., electrode model number 9520-10D) was obtained by immersing the electrode in the liquid to be measured in the conductivity measurement mode under atmospheric pressure. The temperatures of the bubbling water, the micro-nano bubble water, and the metal particle dispersion were adjusted to 25 ° C.
[Particle yield]
The yield of metal particles is calculated by calculating the amount of metal in the metal particle dispersion from the metal concentration in the metal dispersion measured by ICP, and dividing this by the theoretical amount of metal calculated from the charged metal salt. Was multiplied by 100.

[Average particle size of primary particles]
The average particle size of the metal particles was measured by an image analysis method. Specifically, the metal particle dispersion is dried on a collodion film of a copper cell for an electron microscope by a transmission electron microscope (H-800 manufactured by Hitachi, Ltd.), and a photograph is taken at a magnification of 250,000 times. The particle size of any 500 particles in the obtained photographic projection was measured, and the average value was taken as the average particle size of the metal particles.

[Average particle size of secondary particles]
The metal particle dispersion was placed in the cell as it was, measured by the microtrac method, and the average value (D50) was taken as the average particle diameter of the metal particles.

[Confirmation of the presence or absence of metal oxides by X-ray diffraction]
The metal particle dispersion was analyzed by X-ray diffraction with the solution as it was, and the presence or absence of the metal oxide was confirmed. The qualitative analysis of the sample by X-ray diffraction was performed by X-RAY DIFFRACT METER (SmartLab) manufactured by RIGAKU Co., Ltd. Specifically, the sample is placed in a cell, set in a device, tube voltage 45.0 kV, tube current 200.0 mA, anti-cathode Cu, measurement range: start angle to end angle (2θ) 5.000 ° to 70.000. The measurement was performed at ° and a scan speed of 5.000 ° / min.
If no metal oxide peak is observed: ○
When a peak of metal oxide is observed: ×

[ICP analysis]
The mass spectrometry of each element was carried out by chemical analysis using an inductively coupled plasma spectrophotometer. Specifically, a solution prepared by dissolving a metal particle dispersion in concentrated nitric acid and adjusting the concentration to 10 to 100 mass ppm with water was analyzed by SEQUENTIAL PLASMA SPECTROMETER (ICPS-8100) manufactured by Shimadzu Corporation.

[Ion chromatographic analysis]
The metal particle dispersion was diluted 100-fold with ultrapure water, and the concentrations of SO ₄ , Cl, and NO ₃ were measured using an ion exchange chromatograph (TSKgel SuperQ-5PW manufactured by Tosoh).

[Measurement of C (carbon) amount]
The carbon content in the metal particles was measured by drying the metal particle dispersion at 100 ° C. and using a carbon sulfur analyzer (EMIA-320V manufactured by HORIBA).

[Storage stability]
The presence or absence of oxidation of the metal particles and the change in conductivity by X-ray diffraction (XRD) of the metal particle dispersion stored at 25 ° C. were confirmed.

<Preparation of coating liquid for film formation and substrate with film>
The obtained metal particle dispersion liquid (P-1) was diluted with ethanol to 0.5% by mass to prepare a coating liquid for film formation. This was applied to glass by a spin coating method, and then fired at 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a coated substrate. The conductivity of this coated substrate was measured with a low resta (NSP probe manufactured by Mitsubishi Chemical Corporation). In addition, a part of the coating film was peeled off with a cutter knife to create a step, and this step was measured with a laser microscope, and this was used as the film thickness. These results are shown in Table 1 (the same applies to the following examples and comparative examples).

[Example 2]
<Particle preparation process>
Ultrapure water was bubbling with Ar for 1 hour to prepare Ar bubbling water (pH 6.64, electrical conductivity 0.8 μ / cm, DO 0.51 ppm, ORP 260 mV) from which dissolved oxygen was removed. 400 g of trisodium citrate dihydrate was dissolved in 930 g of this Ar bubbling water to prepare a solution (S2-1).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of Ar bubbling water to prepare a solution (S2-2).
The solution (S2-1) and the solution (S2-2) were mixed and stirred for 30 minutes to prepare a solution A2.

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of Ar bubbling water to prepare a solution B2. Then, the solution A2 was added to the solution B2, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
Ar micro-nano bubble water (average bubble diameter 70 nm, number of bubbles 240 million cells / mL, pH 6) by contacting ultrapure water with Ar using a swirling flow type bubble generator (HYK-20-SD manufactured by Ligaric Co., Ltd.). 0.25, electrical conductivity 0.95 μS / cm, DO1.52 ppm, ORP300 mV) was prepared. The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using Ar micro-nano bubble water, washed (demineralized), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and an aqueous dispersion of metal particles having a metal-equivalent concentration of 2.5% by mass was prepared using Ar micro-nanobubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-2) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-2) was used.

[Example 3]
<Particle preparation process>
_N2 bubbling water was prepared in the same manner as in Example 1.
400 g of trisodium citrate dihydrate was dissolved in 930 g of _N2 bubbling water to prepare a solution (S3-1).
A solution (S3-2) was prepared by dissolving 100 g of ferrous sulfate heptahydrate in 500 g of _N2 bubbling water.
The solution (S3-1) and the solution (S3-2) were mixed and stirred for 30 minutes to prepare a solution A3.

57 g of silver nitrate (I) was dissolved in 300 g of _N2 bubbling water to prepare a solution B3. Then, the solution A3 was added to the solution B3, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
_N2 micro-nano bubble water was prepared in the same manner as in Example 1. The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 30% by mass prepared using _N2 micro-nanobubble water, washed (demineralized), and then separated and recovered by centrifugation. Similarly, the metal particles separated and recovered are immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using N ₂ micro-nano bubble water, washed (demineralized), and then separated and recovered by centrifugation again. did.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal equivalent concentration of 2.5% by mass was prepared using _N2 micro-nano bubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-3) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-3) was used.

[Example 4]
<Particle preparation process>
_N2 bubbling water was prepared in the same manner as in Example 1.
Nickel nitrate hexahydrate (Ni (NO ₃ ) _{26H 2 O} ) (manufactured by Kanto Chemical Co., Ltd.) 50 g and citric acid hydrate (organic stabilizer) (Kishida Chemical Co., Ltd.) in 450 g of N ₂ bubbling water. )) 0.5 g was dissolved to prepare a solution A4.

50 g of sodium borohydride (reducing agent) was dissolved in 1000 g of _N2 bubbling water to prepare a solution B4. While stirring the solution A4, the solution B4 was added and stirred for 1 hour. At this time, the liquid changed from green to black. Metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Washing process>
_N2 micro-nano bubble water was prepared in the same manner as in Example 1. The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using _N2 micro-nanobubble water, washed (demineralized), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal-equivalent concentration of 2.5% by mass was prepared using _N2 micro-nanobubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black metal particle dispersion (P-4) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-4) was used.

[Example 5]
<Particle preparation process>
_N2 bubbling water was prepared in the same manner as in Example 1.
400 g of trisodium citrate dihydrate was dissolved in 930 g of _N2 bubbling water to prepare a solution (S5-1).
A solution (S5-2) was prepared by dissolving 100 g of ferrous sulfate heptahydrate in 500 g of _N2 bubbling water.
The solution (S5-1) and the solution (S5-2) were mixed and stirred for 30 minutes to prepare a solution A5.

57 g of silver nitrate (I) was dissolved in 300 g of _N2 bubbling water to prepare a solution B5. Then, the solution A5 was added to the solution B5, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
_N2 micro-nano bubble water was prepared in the same manner as in Example 1. The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using _N2 micro-nanobubble water, washed (demineralized), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal equivalent concentration of 2.5% by mass was prepared using _N2 micro-nano bubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-5) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-5) was used.

[Example 6]
<Particle preparation process>
_N2 micro-nano bubble water was prepared in the same manner as in Example 1.
400 g of trisodium citrate dihydrate was dissolved in 930 g of N ₂ micro-nano bubble water to prepare a solution (S6-1).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of _N2 micro-nano bubble water to prepare a solution (S6-2).
The solution (S6-1) and the solution (S6-2) were mixed and stirred for 30 minutes to prepare a solution A6.

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of N ₂ micro-nano bubble water to prepare a solution B6. Then, the solution A6 was added to the solution B6, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using the N ₂ micro-nano bubble water, washed (demineralized), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal-equivalent concentration of 2.5% by mass was prepared using N ₂ micro-nano bubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-6) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-6) was used.

[Example 7]
<Particle preparation process>
_N2 bubbling water was prepared in the same manner as in Example 1.
400 g of trisodium citrate dihydrate was dissolved in 930 g of _N2 bubbling water to prepare a solution (S7-1).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of _N2 bubbling water to prepare a solution (S7-2).
The solution (S7-1) and the solution (S7-2) were mixed and stirred for 30 minutes to prepare solution A7).

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of _N2 bubbling water to prepare a solution B7. Then, the solution A7 was added to the solution B7, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
_N2 micro-nano bubble water was prepared in the same manner as in Example 1.
The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using this N ₂ micro-nano bubble water, washed (demineralized), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal-equivalent concentration of 2.5% by mass was prepared using the above _N2 bubbling water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-7).

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-7) was used.

[Example 8]
<Particle preparation process>
_N2 bubbling water was prepared in the same manner as in Example 1.
400 g of trisodium citrate dihydrate was dissolved in 930 g of _N2 bubbling water to prepare a solution (S8-1).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of _N2 bubbling water to prepare a solution (S8-2).
The solution (S8-1) and the solution (S8-2) were mixed and stirred for 30 minutes to prepare solution A8).

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of _N2 bubbling water to prepare a solution B8. Then, the solution A8 was added to the solution B8, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
The metal particles separated and recovered were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using the _N2 bubbling water, washed (demineralized), and then separated and recovered by centrifugation again.

_N2 micro-nano bubble water was prepared in the same manner as in Example 1.
The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a metal equivalent concentration of 2.5% by mass was prepared using _N2 micro-nano bubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-8).

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (P-8) was used.

[Comparative Example 1]
<Particle preparation and cleaning process>
_N2 bubbling water was prepared in the same manner as in Example 1. A metal particle dispersion (RP-1) was obtained in the same manner as in Example 1 except that the _N2 bubbling water was used as a dispersion medium for the preparation and washing of the solution A1 and the solution B1 and the metal particle dispersion. ..

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (RP-1) was used.

[Comparative Example 2]
<Particle preparation and cleaning process>
The metal particle dispersion liquid ₍ RP- 2) was obtained.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (RP-2) was used.

[Comparative Example 3]
<Particle preparation and cleaning process>
The metal particle dispersion liquid ₍ RP- 3) was obtained.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (RP-3) was used.

[Comparative Example 4]
<Particle preparation and cleaning process>
The metal particle dispersion liquid ₍ RP- 4) was obtained.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (RP-4) was used.

[Comparative Example 5]
<Particle preparation and cleaning process>
CuCl ₂ powder, water as a solvent, CTAB as a dispersant, and citric acid as a protective agent for suppressing the oxidation of copper nanoparticles were used. Put water in a beaker with a volume of 100 ml, pour nitrogen into the water, and in a state of stirring, add 1.0 × 10 ⁻² M copper chloride, 0.0364 g of CTAB, and 1.5 × 10 ^-3 M of citric acid. After mixing with water, 0.4 M hydrazine was added as a reducing agent to prepare copper nanoparticles. The amount of water was adjusted so that the total amount of the reagent and water added at this time was 20 ml. After stirring at room temperature for 3 hours, the obtained particles were centrifuged three times, and then a metal particle dispersion (RP-5) aqueous dispersion having a metal equivalent concentration of 2.5% by mass using pure water was used. Was prepared.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (RP-5) was used.

[Comparative Example 6]
<Particle preparation and cleaning process>
0.1 mol of copper sulfate, 0.4 mol of sodium hypophosphite, 1 mol of PVP and 500 ml of ethylene glycol were mixed in a beaker, heated to 40 ° C., and then dissolved using a stirrer to prepare a mixed solution. .. The prepared mixed solution was put into a microwave oven and irradiated with microwaves for 3 minutes. When a dark brown reaction product was obtained by the reduction reaction, microwave irradiation was stopped, and 500 ml of pre-cooled distilled water was added to the mixed solution for rapid cooling. Black-brown copper nanoparticles are recovered by centrifugation, washed three times with acetone and distilled water, and then metal particles ethylene glycol dispersion (RP) having a metal-equivalent concentration of 2.5% by mass using ethylene glycol. -6) was prepared.

<Preparation of coating liquid for film formation and substrate with film>
A coating liquid for film formation and a substrate with a coating were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid (RP-6) was used.

Since the metal particle dispersion liquid of the present invention can be used for forming a conductive film or the like, it is industrially useful.

Claims (9)

A particle preparation process that reduces metal salts in a liquid to prepare metal particles,
A cleaning step of cleaning the metal particles with a cleaning solution containing fine bubbles made of non-oxidizing gas , and
A method for producing a metal particle dispersion liquid, which comprises. The method for producing a metal particle dispersion liquid according to claim 1, wherein the solvent of the cleaning liquid and the dispersion medium of the metal particle dispersion liquid to be produced are water containing fine bubbles. The method for producing a metal particle dispersion liquid according to claim 1 or 2, wherein the liquid in the particle preparation step contains an organic stabilizer. The method for producing a metal particle dispersion liquid according to any one of claims 1 to 3, wherein the liquid in the particle preparation step contains fine bubbles. A method for producing a coated base material, which comprises applying a coating liquid for forming a film containing metal particles prepared by the method according to any one of claims 1 to 4 onto a base material. A metal particle dispersion liquid in which metal particles are dispersed in a liquid containing fine bubbles made of a non-oxidizing gas and the redox potential is 0 to 300 mV . The metal particle dispersion liquid according to claim 6, wherein the liquid containing fine bubbles is water containing fine bubbles. Claims characterized in that the metal particles contain at least one metal selected from Group 4, Group 5, Group 6, Group 8, Group 9, Group 10, Group 11, Group 13, Group 14, and Group 15. Item 6. The metal particle dispersion liquid according to Item 6. The metal particle dispersion liquid according to any one of claims 6 to 8 , wherein the pH is 4.0 to 7.0.