JP2015199992A - Alloy particulate dispersion liquid and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide dispersion liquid in which AuAg alloy particulates are dispersed at a high concentration.SOLUTION: There is provided a dispersion liquid of alloy particulates which contains gold (Au) and silver (Ag) as constituent elements, wherein the maximum absorption wavelength measured using an absorptiometer is 520 nm or less, the molar concentration in terms of constituent metal elements of the alloy particulates is 10 to 80 mM and the sediments containing the alloy particulates are not visually observed in a stationary state. In addition, there is provided an alloy particulate dispersion liquid in which the polydispersity index (PDI) of the alloy particulates is 0.6 or less based on a dynamic light scattering method. There is provided an alloy particulate dispersion liquid in which the maximum frequency grain size on a number basis of the alloy particulates is 10 to 20 nm.

Description

  The present invention relates to an alloy fine particle dispersion containing a high concentration of alloy fine particles containing gold (Au) and silver (Ag) as constituent elements. Moreover, it is related with the manufacturing method of this dispersion liquid.

Conventionally, cadmium (Cd) -based materials (for example, cadmium red) have been used as vivid red materials in the coloring of ceramics such as tableware and ornaments. However, since Cd is harmful to the human body, an alternative material has been demanded.
As an example of such an alternative material, gold (Au) nanoparticles having a particle diameter of about several to several tens of nanometers can be given. Au nanoparticles can exhibit a bright red color due to the interaction with visible light. In addition, by forming an AuAg alloy fine particle by alloying with silver (Ag), it is possible to produce a slightly different red color (for example, dark red to orange), which is promising as a coloring material. However, for use in industry, it is necessary to stably produce such fine particles at a relatively low cost. In consideration of the use as a coloring material, it is preferably a high-concentration dispersion.

As a method for synthesizing the Au nanoparticle dispersion, for example, a synthesis method using citric acid as a reducing agent is known (for example, Non-Patent Document 1). However, according to the study by the present inventors, it was difficult to obtain an Au fine particle dispersion with a high concentration by such a synthesis method. Further, when an AuAg alloy fine particle dispersion is synthesized by such a synthesis method, a time difference occurs in the reduction between the Au component and the Ag component, and it is not easy to obtain these alloy fine particles.
Non-Patent Document 2 discloses that an aqueous solution containing an Au salt and sodium citrate and an aqueous solution containing an Ag salt and sodium citrate are separately heated, and then these two solutions are mixed in a boiled state to obtain AuAg. A method for producing an alloy fine particle dispersion is disclosed.

G.Frens, "Controlled nucleation for the Regulation of the particle Size in Monodisperse Gold Suspensions", Nature Phys. Sci. 1973, 241, p.20-22 Edit Csapo et al., Colloids and Surfaces A: Physicochem. Eng. Aspects, 2012, 415, p.281-287

  In the synthesis method of Non-Patent Document 2, the reduction of Au ions and Ag ions proceeds at a stroke in a boiling state, and AuAg alloy fine particles can be obtained. However, such a method is difficult to synthesize under conditions where the raw material concentration is high, and a high-concentration dispersion cannot be obtained directly (without concentration).

  The present invention has been made in view of these circumstances, and an object of the present invention is to provide a high-concentration AuAg alloy fine particle dispersion by synthesizing (without concentrating) raw material concentrations. Another related object is to provide a method for producing such an alloy fine particle dispersion easily and stably.

  According to the present invention, a dispersion of alloy fine particles containing gold (Au) and silver (Ag) as constituent elements is provided. The alloy fine particle dispersion has (1) a maximum absorption wavelength measured with an absorptiometer of 520 nm or less, (2) a molar concentration of the alloy fine particles in terms of a constituent metal element is 10 mM or more, and (3 ) The precipitate containing the alloy fine particles is not visually recognized in a stationary state.

  Since the alloy fine particle dispersion disclosed here contains AuAg alloy fine particles, the maximum absorption wavelength is 520 nm or less and a deep red color is exhibited. Moreover, although the molar concentration in terms of constituent metal elements is as high as 10 mM or more, there is no aggregation and a stable dispersion state is maintained. Therefore, according to the present invention, a highly concentrated AuAg alloy fine particle dispersion excellent in color developability can be stably provided.

In this specification, "the molar concentration of constituent metal elements in terms of" the sum of the molar concentration M _Ag molarity M _Au and silver (Ag) elemental gold (Au) element constituting the alloy particles (M _Au + M _Ag ). Further, in this specification, “maximum absorption wavelength” means that after the alloy fine particle dispersion is diluted with purified water and the molar concentration of the alloy fine particles is adjusted to about 0.2 mM, the spectrophotometer is used. When the UV-vis absorption spectrum is measured, it means the absorption wavelength having the largest absorption intensity. Further, in this specification, “the precipitate is not visually recognized in the stationary state” means that the alloy fine particle dispersion is macroscopically viewed (typically a state after being left for 12 hours or more, For example, when it is in a state after standing for half a day to 2 days), it means that the presence or precipitation of coarse particles is not visually recognized.

  In a preferred embodiment of the alloy fine particle dispersion disclosed herein, the molar concentration in terms of the constituent metal elements is 80 mM or less. Thereby, agglomeration and precipitation of alloy fine particles can be suppressed to a higher degree, and a dispersion having higher stability (for example, excellent long-term stability) can be realized.

In a preferred embodiment of the alloy fine particle dispersion disclosed herein, a polydispersity index (PDI) based on a dynamic light scattering method of the alloy fine particles is 0.6 or less. When the PDI is in the above range, a sharp and clear colored alloy fine particle dispersion can be stably realized.
In this specification, “PDI” means that the alloy fine particle dispersion is diluted with purified water to adjust the molar concentration of the alloy fine particles as a constituent metal element to about 0.2 mM, and then the dynamic light scattering method ( The particle size distribution is measured using DLS (Dynamic light scattering), and the obtained result is analyzed by a cumulant method. Such a value can be an index representing the breadth of the particle size distribution, and the smaller the numerical value, the narrower (and sharper) the particle size distribution.

In a preferred embodiment of the alloy fine particle dispersion disclosed herein, the number-based maximum frequency particle size based on the dynamic light scattering method of the alloy fine particles is 10 nm or more and 20 nm or less. When the maximum frequency particle size is in the above range, a more vividly colored alloy fine particle dispersion can be realized.
In the present specification, “maximum frequency particle size” means that after the alloy fine particle dispersion is diluted with purified water and the molar concentration of the alloy fine particles is adjusted to about 0.2 mM, the dynamic light The particle size distribution is measured by using the scattering method (DLS), and the particle size distribution having the largest peak in the number-based particle size distribution obtained by analyzing the obtained result by the non-negative least square method (NNLS method).

Moreover, this invention provides the method of manufacturing the dispersion liquid of the alloy fine particle which contains gold | metal | money (Au) and silver (Ag) as a structural element as another side surface. The present inventors have studied from various angles in order to synthesize the AuAg alloy fine particle dispersion under conditions where the raw material concentration is high. As a result, it came to the conclusion that the mixing conditions of raw materials and the timing of addition are important. In addition, since nanoparticles have extremely high adhesion and aggregation properties, it is important to control the aggregation / dispersion state of the particles. Therefore, the present inventors have made further intensive studies on these synthesis conditions, and have come to create a method for synthesizing a stable dispersion of AuAg alloy fine particles.
The manufacturing method includes the following steps: (a) preparing a solution A containing gold ions and not containing a reducing agent; (b) a solution B containing silver ions, a reducing agent and a dispersing agent. Preparing; (c) heating the solution A and the solution B to a temperature range of 60 ° C. or more and 100 ° C. or less, respectively; (d) mixing the solution A and the solution B in the temperature range; -Stirring. In the above (a) and (b), the preparation of the solution A and the solution B includes the number of moles m1 of the Au ions contained in the solution A and the number of moles m2 of the Ag ions contained in the solution B. However, 0 <(m2 / (m1 + m2)) ≦ 0.3 is satisfied. In (d) above, the total molar concentration (M1 + M2) of the molar concentration M1 of Au ions and the molar concentration M2 of Ag ions when the solution A and the solution B are mixed is 20 mM or more. Prepare. According to this manufacturing method, the AuAg alloy fine particle dispersion having the above-described properties can be easily and stably manufactured.

  The AuAg alloy fine particle dispersion disclosed herein has a high concentration and exhibits an intermediate color (for example, bright red) between red, which is an intrinsic color of gold fine particles, and yellow, which is an intrinsic color of silver fine particles. For this reason, it can use suitably for the use which colors a test body as a coloring material (coloring material, typically red material). Therefore, as another aspect of the present invention, there is provided an instrument (for example, pottery such as tableware or decoration) colored using such a coloring material. In the coloring portion of the device, for example, AuAg alloy fine particles having a particle diameter of about several nanometers are densely arranged, and thereby a clear color can be realized.

It is a flowchart for demonstrating the manufacturing method which concerns on one Embodiment. It is a flowchart for demonstrating the manufacturing method which concerns on a comparative example.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of a person skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

≪Alloy fine particle dispersion≫
The alloy fine particle dispersion disclosed herein is a dispersion (colloidal solution) in which AuAg alloy fine particles containing gold (Au) and silver (Ag) as constituent elements are dispersed in a liquid medium. The AuAg alloy fine particle dispersion has the following characteristics (1) to (3):
(1) The maximum absorption wavelength measured using an absorptiometer is 520 nm or less;
(2) The molar concentration of the alloy fine particles in terms of constituent metal elements is 10 mM or more;
(3) The precipitate containing the alloy fine particles is not visually recognized in a stationary state;
Characterized by. Accordingly, the other properties are not particularly limited, and can be arbitrarily determined in light of various standards. For example, various components can be blended or the composition thereof can be changed.

  In general, a dispersion containing fine metal particles such as gold and silver has unique optical characteristics (for example, a strong light absorption band) in the ultraviolet to visible region due to surface plasmon resonance (SPR). The condition (1) above, that is, that the maximum absorption wavelength measured using an absorptiometer is 520 nm or less, indicates the presence of alloy fine particles containing Au and Ag as constituent elements. The maximum wavelength of the dispersion disclosed herein is 520 nm or less, and typically can be 510 to 520 nm, such as 515 to 520 nm. A dispersion having such a maximum absorption wavelength is visually recognized as bright red. When the dispersion liquid has a high concentration, it may look black at first glance, but it can be visually recognized as a bright red color by dilution. If the maximum wavelength of the dispersion greatly exceeds 520 nm, the alloy fine particles may be aggregated or precipitated. In such a case, the dispersion typically can exhibit a bluish red (red purple).

  The dispersion disclosed here contains AuAg alloy fine particles in a high concentration. Specifically, the above condition (2), that is, the molar concentration of the alloy fine particles in terms of constituent metal elements is 10 mM or more is satisfied. The molar concentration in terms of constituent metal elements is typically 18 to 90 mM, preferably 20 to 80 mM, for example 20 to 40 mM. The dispersion disclosed herein satisfies the above condition (3) at the same time, despite having such a high concentration. That is, in the dispersion liquid, although it is a high concentration dispersion liquid, the occurrence of aggregation and precipitation is highly suppressed.

  The chemical composition of the AuAg alloy fine particles is not particularly limited, but when the ratio of Ag in 1 mol of the alloy fine particles is x, the value of X is 0 <x ≦ 0.3 (typically 0.1 ≦ x ≦ 0.3) may be satisfied. In other words, the molar ratio of Au to Ag in the alloy fine particles may be in the range of Au: Ag = 9: 1 to 7: 3. By setting it as the range of this composition, the stable state of a dispersion liquid can be maintained at a still higher level, and the outstanding long-term storage property is realizable. Moreover, alloy fine particles can be produced in a high yield.

In the technique disclosed herein, the average particle diameter of the AuAg alloy fine particles is not particularly limited, but is usually nanometer size (about 1 to 1000 nm), typically 10 to 600 nm, preferably 10 to 100 nm. And more preferably 10 to 50 nm. Thereby, the specific surface area of the whole AuAg alloy fine particles increases, and vivid color development can be realized with a smaller amount. Alternatively, it is possible to realize a dense coloring portion with little color unevenness.
In the present specification, “average particle size” means that after the alloy fine particle dispersion is diluted with purified water and the molar concentration of the alloy fine particles is adjusted to about 0.2 mM, the dynamic light scattering is performed. The particle size distribution is measured using the method (DLS), and the obtained result is analyzed by the cumulant method (Z-Average).

  Further, the maximum frequency particle diameter of the AuAg alloy fine particles is typically 1 nm or more, for example, 3 nm or more, and preferably 10 nm or more. By setting the maximum frequency particle size, the color developability by the alloy fine particles can be improved, and vivid color can be stably obtained. Further, the maximum frequency particle diameter of the AuAg alloy fine particles is typically 50 nm or less, for example, 30 nm or less, and preferably 20 nm or less. By setting it as the said maximum frequency particle size, the effect of light scattering can be suppressed and it can prevent that it becomes a dull color tone or purple-bluish color development.

  The polydispersity index (PDI) of the AuAg alloy fine particles is typically 0.6 or less, preferably 0.5 or less, more preferably 0.3 or less, and particularly 0.2. It may be the following. The smaller the PDI value, that is, the narrower and sharper the particle size distribution of the alloy fine particles, the more vividly colored dispersion liquid can be realized. The lower limit is not particularly limited, but is preferably 0.1 or more from the viewpoint of ease of production.

The liquid medium is not particularly limited as long as the AuAg alloy fine particles can be uniformly dispersed. For example, one or more of the solvents conventionally used in this type of fine metal particle dispersion can be used as appropriate. Specifically, an aqueous solvent and an organic solvent can be considered roughly. Examples of the aqueous solvent include water or a mixed solvent mainly containing water. Examples of the solvent other than water constituting the mixed solvent include organic solvents such as lower alcohol and lower ketone that can be uniformly mixed with water. On the other hand, examples of organic solvents include amide solvents, alcohol solvents, ketone solvents, ester solvents, amine solvents, ether solvents, nitrile solvents, cyclic ether solvents, and aromatic hydrocarbon solvents. The
As a preferable example, an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, and further preferably 95% by mass or more) of the entire liquid medium is water can be given. Among these, from the viewpoint of environmental protection and waste reduction, an aqueous solvent substantially composed of water (for example, water) is preferable.

In the technology disclosed herein, the AuAg alloy fine particles may be in a form in which a dispersant (protective agent, stabilizer) is attached or coordinated to at least a part of the surface of the alloy fine particles. Thereby, grain growth (coarseness) of alloy fine particles and aggregation of alloy fine particles can be highly suppressed, and further stabilization as a dispersion system can be realized. As such a dispersant, one of conventionally known dispersants may be used alone, or two or more thereof may be used in combination. In a preferred embodiment, a polymer compound having a weight average molecular weight Mw of 1000 or more (typically 10,000 or more, for example, 10,000 to 100,000, preferably 10,000 to 60,000) is used. By using a polymer compound having such properties, an appropriate distance can be maintained between the alloy fine particles, and the interface of the alloy fine particles can be more stably maintained. Therefore, the effect of the present invention can be realized at a higher level. Specific examples of such a polymer compound include polyvinylpyrrolidone (PVP), polyethyleneimine, polyacrylamide, polyacrylic acid, carboxymethylcellulose, polyvinyl alcohol, polyethylene oxide and the like.
The weight average molecular weight Mw can be measured by a general gel chromatography (GPC: Gel Permeation Chromatography) method.

  Among the above polymer compounds, compounds having an element having an unshared electron pair such as nitrogen (N) or sulfur (S), that is, amide compounds, amine compounds, thiol compounds, and the like can be preferably used. . Such an element can form a specific bond (for example, Au—N bond or Au—S bond) with the surface of the AuAg alloy fine particle, and thereby a stable protective film can be formed on the surface of the alloy fine particle. Therefore, the alloy fine particles can be stabilized at a higher level. A particularly preferred example is polyvinylpyrrolidone.

  The alloy fine particle dispersion disclosed herein may contain other components in addition to the alloy fine particles and the liquid medium as long as the effects of the present invention are not significantly impaired. As such components, for example, unreacted reducing agents and dispersants, decomposition products thereof, by-products (for example, Au or Ag salts) accompanying the synthesis of the alloy fine particles, various additives, and the like can be considered. . Examples of the reducing agent include citric acid, sodium citrate, acetic acid, malic acid, succinic acid, tartaric acid and other aliphatic carboxylic acids; ascorbic acid and sodium ascorbate; alcohols such as methanol, ethanol and isopropyl alcohol; The Examples of additives include viscosity modifiers, antioxidants, pH adjusters, preservatives, plasticizers, and the like for the purpose of improving dispersion stability and storage stability of the dispersion. .

<< Production Method of Alloy Fine Particle Dispersion >>
In order to obtain such a high-concentration AuAg alloy fine particle dispersion, for example, both ions are reduced with a reducing agent while Au ions and Ag ions, which are raw materials of the alloy, are mixed in a high concentration in the reaction system. Thus, it is preferable to obtain AuAg alloy fine particles.
FIG. 1 is a flowchart for explaining a manufacturing method according to an embodiment. The manufacturing method shown in FIG. 1 generally includes the following steps:
(A) preparing a solution A containing gold ions and no reducing agent;
(B) preparing a solution B containing silver ions, a reducing agent and a dispersing agent;
(C) heating the solution A and the solution B to a temperature range of 60 ° C. or more and 100 ° C. or less, respectively; and
(D) mixing and stirring the solution A and the solution B in the heated state;
Is included. According to the production method of this aspect, the reduction of gold ions and silver ions and the progress of the alloying reaction proceed efficiently, the generation of unnecessary by-products is suppressed to a minimum, and AuAg alloy fine particles are produced in a high yield. (Typically 50 mol% or more, such as 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and particularly substantially 100%). That is, according to such a manufacturing method, rather than concentrating the finished dispersion to increase the concentration of fine particles, it is possible to obtain a high concentration AuAg alloy fine particle dispersion from the beginning by synthesizing under a high raw material concentration condition. it can. Hereinafter, each step will be described.

a. Preparation of Solution A In the manufacturing method disclosed herein, first, a solution A containing gold ions is prepared. For the solution A, for example, an Au source as a raw material is prepared, and this is typically dispersed or dissolved in a predetermined liquid medium (typically in water) in a room temperature environment (for example, 25 ± 5 ° C.). Can be prepared. As the liquid medium, for example, the above-mentioned aqueous solvents and organic solvents can be used as appropriate. Among these, the use of an aqueous solvent is preferable from the viewpoints of dispersibility of Au ions, environmental protection, and the like.

For example, when an aqueous solvent (typically water) is used as the liquid medium, an ionic compound having high solubility in the aqueous solvent can be preferably used as the Au source. As a preferred example, tetrachloroaurate (HAuCl ₄₎ and tetrabromo aurate (HAuBr _4), and compounds such as tetrachloro sodium gold (NaAuCl _4), their hydrates, and salts. Of these, the use of tetrachloroauric acid (typically hydrates such as HAuCl ₄ .4H ₂ O) is preferred. The concentration of Au ions in the solution A can be arbitrarily determined as long as the solubility of the Au source is not exceeded.

  Solution A is characterized by containing substantially no reducing agent. When the present inventors started studying the production method disclosed herein, it was a problem that only the Au component settled early before obtaining the desired AuAg alloy fine particles. Thus, the Au component and the reducing agent are not brought into contact until the subsequent alloying start (specifically, (d. Reduction, alloying step)). As a result, it is possible to prevent the Au component alone from being reduced and deposited / precipitated.

In addition, as long as it does not have a bad influence on the reduction | restoration and alloying reaction mentioned later, other arbitrary components except a reducing agent can be added to the solution A. As an example of such an optional component, a dispersant (protective agent), a viscosity modifier, a pH adjuster, and the like for the purpose of improving dispersion stability can be considered. In other words, for example, the above-described dispersant may or may not be included in the solution A. It should be noted that a compound that can function as both a dispersant and a reducing agent, such as citric acid, is not preferable because it may cause the above-described problems (that is, only the Au component is reduced alone). It is not included in the dispersant. For example, when adding a dispersant as an optional component to the solution A, the ratio of the dispersant to 1 mol of Au ions is usually about 0 to 200 mol as a monomer, for example, 0 to 40 mol. It is preferable to do.
In a preferred embodiment, solution A is substantially free of dispersant in addition to the reducing agent. Thereby, it is possible to suitably obtain monodispersed AuAg alloy fine particles having a small PDI.

  In preparing the solution A, stirring may be performed as necessary. According to the stirring operation, a homogeneous solution A can be stably prepared in a relatively short time. Such agitation can be performed using an appropriate agitation means such as a magnetic stirrer or an ultrasonic wave. The stirring time is not particularly limited, but may be, for example, several minutes to several hours (typically 1 minute to 5 hours, for example, 5 minutes to 1 hour).

b. Preparation of Solution B Next, in the manufacturing method disclosed herein, a solution B containing silver ions, a reducing agent, and a dispersing agent is prepared. The solution B is prepared, for example, at least an Ag source, a reducing agent, and a dispersing agent as raw materials, and these raw materials are typically contained in a predetermined liquid medium (typically in a room temperature environment (for example, 25 ± 5 ° C.)). Can be prepared by dispersing or dissolving in water. The order of adding the raw materials is not particularly limited, and all the raw materials may be mixed at the same time, and divided into several times (for example, after dispersing or dissolving one raw material in a liquid medium, (Added, dispersed or dissolved). Moreover, it is the same as that of the said solution A that a stirring operation can be employ | adopted suitably.
As the liquid medium, for example, the above-mentioned aqueous solvents and organic solvents can be used as appropriate. Among these, the use of an aqueous solvent is preferable from the viewpoints of dispersibility of Ag ions, environmental protection, and the like.

As an Ag source, for example, when an aqueous solvent (typically water) is used as a liquid medium, an ionic compound (Ag salt) having high solubility in the aqueous solvent can be preferably used. As a suitable example, silver nitrate (AgNO ₃ ), silver sulfide (Ag ₂ SO ₄ ), silver fluoride (AgF), silver methanesulfonate (CH ₃ SO ₃ Ag) and the like can be mentioned. Of these, the use of silver nitrate is preferred. The concentration of Ag ions in the solution B can be arbitrarily determined as long as the solubility of the Ag source is not exceeded.

  In the technique disclosed here, the number of moles m1 of the Au ions contained in the solution A and the number of moles m2 of the Ag ions contained in the solution B are 0 <(m2 / (m1 + m2)) ≦ 0.3 ( Typically, the Ag ion concentration is adjusted to satisfy 0.1 ≦ (m2 / (m1 + m2)) ≦ 0.3). As a result, Au ions and Ag ions react without excess and deficiency, and AuAg alloy fine particles having the composition and properties described above can be obtained in high yield. In addition, generation of unnecessary by-products can be suppressed.

Although it does not specifically limit as a reducing agent, In order to prevent that Ag of the solution B precipitates independently before solution mixing, what has a comparatively weak reducing power can be used preferably. Thereby, the reduction reaction can be caused relatively slowly, and AuAg alloy fine particles having the above-described properties can be stably obtained. Specific examples of such a reducing agent include the above-mentioned aliphatic carboxylic acid and ascorbic acid. Of these, citric acid (C ₆ H ₈ O ₇ ) and salts thereof (typically alkali metal salts such as sodium salts) are preferably used from the viewpoint of controlling the particle diameter of AuAg alloy fine particles within the above-mentioned range. Can do.
The addition amount of the reducing agent in the solution B is preferably an amount sufficient to reduce the Au ions together with the Ag ions to form an alloy. As such addition amount, the following formula: number of charges given by the reducing agent / {(number of Au ions × valence) + (number of Ag ions × valence)} is usually 1 to 100, for example, 2 It may be determined to satisfy ~ 20.

Although it does not specifically limit as a dispersing agent, The above-mentioned high molecular compound can be used preferably. Among these, a compound including an element having an unshared electron pair (typically nitrogen (N) or sulfur (S)), such as polyvinyl pyrrolidone (PVP), can be preferably used. Such a dispersant can be useful for controlling the nucleation rate and the grain growth rate of AuAg alloy fine particles in a series of reduction and alloying reaction. Further, it can be useful for preventing aggregation and precipitation of fine particles in the AuAg alloy fine particle dispersion. That is, by adding such a dispersant, for example, the maximum frequency particle size is suppressed to about several tens of nanometers, and / or the alloy fine particles whose PDI, which is an index indicating the dispersibility of particles, is suppressed to 0.6 or less. Can be obtained stably.
The amount of the dispersant added in the solution B is about 100 while controlling the maximum frequency particle size of the alloy fine particles to a size of several nanometers to several tens of nanometers (for example, 1 to 100 nm, particularly 10 to 20 nm). In order to obtain a yield close to%, it is appropriate that the monomer is usually about 5 to 200 mol, for example 10 to 100 mol, relative to the number of moles of metal ions constituting the alloy fine particles. preferable.

  As a means for suppressing the particle growth and aggregation of metal nanoparticles, it is a known means to use a polymer dispersant. However, in the synthesis of high-concentration alloys as disclosed herein, the concentration is low. Since the reactivity of the contained components is increased as compared with the case where it is diluted or not containing the polymer dispersant, the reaction between Au ions and Ag ions is controlled, and these metal ions are reduced almost simultaneously to form AuAg alloy fine particles. Difficult to do. In general synthesis of alloy fine particles, Au salt, Ag salt, and a dispersing agent are first dissolved or dispersed in a liquid medium, and then a reducing agent is added (for example, while heating). Therefore, it is difficult to obtain AuAg alloy fine particles by such a method.

c. Temperature adjustment of solution A and solution B In the manufacturing method disclosed herein, next, the temperature of the solution A and the solution B is set to a temperature range of 60 ° C. or more and 100 ° C. or less using an appropriate heating device. Until heated. By heating the two kinds of solutions to a temperature range of 60 ° C. or higher in advance, the reaction rate in reduction and alloying can be adjusted and controlled. That is, in the subsequent (d. Reduction, alloying step), nucleation and grain growth of alloy fine particles can be advanced at once, and nanometer-sized alloy fine particles can be suitably generated. Further, from the viewpoint of productivity and low cost, the heating temperature may be 100 ° C. or lower (typically 80 ° C. or lower). Moreover, in this process, it is good to perform this heating, stirring. Such heating and stirring can be performed using, for example, a magnetic hot stirrer.

d. Reduction, Alloying In the production method disclosed herein, the solution A and the solution B are then maintained while maintaining the heating state so that the liquid temperatures of the solution A and the solution B are kept in the temperature range, respectively. Are mixed together and stirred. Thereby, Au ions contained in the solution A and Ag ions contained in the solution B are reduced at once by the reducing agent, and alloy fine particles (AuAg alloy fine particles) containing Au and Ag as constituent elements are generated in the liquid medium. Can do. The stirring speed is not particularly limited, but is usually about 100 to 1000 rpm. Further, the stirring time is not particularly limited, but may be, for example, several minutes to several hours (typically 1 minute to 5 hours, for example, 5 to 30 minutes).

  In the technology disclosed herein, the total molar concentration (M1 + M2) of the molar concentration M1 of Au ions and the molar concentration M2 of Ag ions in the mixed solution in this step (immediately after mixing) is adjusted to 10 mM or more. In order to efficiently obtain a dispersion having a higher concentration, the total molar concentration (M1 + M2) is typically 18 mM or more, for example, 20 mM or more. Further, in order to prevent aggregation and precipitation of the alloy fine particles and maintain high stability (storability) of the dispersion, the total molar concentration (M1 + M2) is 80 mM or less, typically 60 mM or less, for example, 40 mM or less. It is good to prepare so that it may become. As a result, a homogeneous AuAg alloy fine particle dispersion (a colloid solution of AuAg alloy fine particles) having a high concentration and no precipitation can be obtained with high reproducibility.

  The mixing ratio (volume ratio) of the solution A and the solution B is such that immediately after mixing (before particle formation), the number of moles m1 of the solution A and the number of moles m2 of the solution B are 0 <(m2 / (m1 + m2)) ≦ There is no particular limitation as long as it satisfies the range of 0.3 and the molar concentration M1 of the solution A and the molar concentration M2 of the solution B satisfy the range of (M1 + M2) ≧ 10 mM. As a practical process, when the volume of the solution A is Va and the volume of the solution B is Vb, Va / (Va + Vb) is usually 0.05 to 0.95, typically 0.10 to It is good to mix so that it may become 0.90, Preferably it is 0.20-0.70, More preferably, it is 0.35-0.45.

When the chemical composition (molar ratio) of the AuAg alloy fine particles thus obtained is Au _(1-x) Ag _x , the value of X is, for example, 0 <x ≦ 0.3 (typically 0.1 ≦ x ≦ 0.3) may be satisfied. Further, the AuAg alloy fine particles can satisfy at least one property among the following conditions.
The number-based maximum frequency particle size based on the dynamic light scattering method is 10 nm or more and 20 nm or less.
The polydispersity index (PDI) based on the dynamic light scattering method is 0.6 or less.
-The average particle diameter based on a dynamic light scattering method is nanometer size (about 1-1000 nm).

Such an alloy fine particle dispersion is less susceptible to fading or discoloration due to aggregation of alloy fine particles, and can stably realize excellent color development. For this reason, it can use suitably as a coloring material (paint) for coloring the surface of the test piece consisting of earthenware, porcelain, stoneware, glass, resin, a metal, wood, etc. using this property. As specific examples of the specimen, tableware, ornaments, tiles, bricks, roof tiles and the like can be considered.
For example, in the case of coloring a ceramic as a specimen, a colored glass frit is prepared by adding a colorant containing the alloy fine particle dispersion to the glass frit, and this is applied to the surface of the specimen. Thereafter, a method of firing at a predetermined temperature is exemplified. In other words, by the technique disclosed herein, an instrument (for example, pottery such as tableware or a decorative device) colored using the coloring material is disclosed.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

In the synthesis methods of Example 1 and Example 2, an AuAg alloy fine particle dispersion was prepared under the conditions shown in Table 1 based on the flowchart shown in FIG. This is a method (comparative example) based on Non-Patent Document 2. Note that “1 to 10” in FIG. 2 correspond to the column of the number (process) in Table 1, respectively. As an example, the synthesis method of Example 1 is specifically shown below.
First, tetrachloroauric acid tetrahydrate (HAuCl ₄ .4H ₂ O) was prepared and dissolved in pure water to prepare 9 ml of 0.4 mM aqueous solution (step 1). Next, trisodium citrate (Na ₃ C ₆ H ₅ O ₇ ) as a reducing agent was prepared, and this was dissolved in pure water to prepare 9 ml of a 2M aqueous solution (step 2). The two aqueous solutions were mixed to obtain a solution A (18 ml).
Next, silver nitrate (AgNO ₃ ) was prepared and dissolved in pure water to prepare 1 ml of an aqueous solution having a concentration of 0.4 mM (step 4). Next, trisodium citrate (Na ₃ C ₆ H ₅ O ₇ ) as a reducing agent was prepared, and this was dissolved in pure water to prepare 1 ml of an aqueous solution having a concentration of 2M (Step 5). The two aqueous solutions were mixed to obtain a solution B (2 ml).
Next, the solution A and the solution B were heated using a magnetic hot stirrer at a rotational speed of about 600 rpm until reaching 100 ° C. (steps 7 and 8).
And the said solution A and the solution B were mixed at a stretch and stirred for 5 minutes (process 9). During this time, the mixed solution was heated to be kept at 100 ° C., and stirring was continued at the same rotational speed as described above. This obtained the AuAg alloy fine particle dispersion which concerns on Example 1 (process 10). After filtering the AuAg alloy fine particles in a dispersed state, Au ions and Ag ions in the filtrate were measured by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry), and the alloy fine particles were measured. When the yield was calculated backwards, it was about 100%.

In the synthesis method after Example 3, AuAg alloy fine particle dispersions were prepared under the conditions shown in Tables 1 to 3 based on the flowchart shown in FIG. Note that “1 to 10” in FIG. 1 correspond to the column of the number (process) in Tables 1 to 3, respectively, and “−” indicates that the process was not performed. As an example, the synthesis method of Example 15 is specifically shown below.
First, tetrachloroauric acid tetrahydrate (HAuCl ₄ .4H ₂ O) is prepared and dissolved in pure water to prepare 2.25 ml of an aqueous solution having a concentration of 40 mM (step 1), and solution A (2 .25 ml).
Next, silver nitrate (AgNO ₃ ) was prepared and dissolved in pure water to prepare 0.25 ml of an aqueous solution having a concentration of 40 mM (step 4). Next, trisodium citrate (Na ₃ C ₆ H ₅ O ₇ ) as a reducing agent was prepared and dissolved in pure water to prepare 2.5 ml of an aqueous solution having a concentration of 200M (Step 5). After mixing these two aqueous solutions, 0.111 g of PVP as a dispersant (polymer protective agent) was added and mixed to obtain a solution B (2.75 ml).
Next, the solution A and the solution B were heated using a magnetic hot stirrer at a rotational speed of about 600 rpm until reaching 100 ° C. (steps 7 and 8).
And the said solution A and the solution B were mixed at a stretch and stirred for 5 minutes (process 9). During this time, the mixed solution was heated to be kept at 100 ° C., and stirring was continued at the same rotational speed as described above. This obtained the AuAg alloy fine particle dispersion which concerns on Example 15 (process 10).
Similarly, AuAg alloy fine particle dispersions were prepared for Examples 3 to 14 and 16 to 23. In addition, when the yield of alloy fine particles was calculated in the same manner as in Example 1 and Example 2, it was about 100% in all examples.

The synthesis conditions are summarized in Table 4.
In addition, the following items were confirmed and measured for the obtained dispersions (Examples 1 to 23). The results are shown in the corresponding columns of Table 5, respectively. Table 5 also shows the AuAg concentration (mM) immediately after mixing of solution A and solution B in step 9 (before particle formation) and the chemical composition of AuAg.
1. The state of the solution in each step was visually observed to check for the presence of coarse particles and sedimentation. The results are shown in the column of “Process that produced precipitate” in Table 5. In this column, “-” indicates that no precipitation was observed until the AuAg dispersion (step 10). Moreover, the process is shown, when precipitation produces | generates.
2. Using a particle size distribution measuring device (product name: Zetasizer Nano ZS) manufactured by Malvern Instruments, the particle size distribution of the AuAg fine particle dispersion is measured by the method described above, and the maximum frequency particle size and average particle size (Z-Ave. ) And the spread of the particle size distribution (PDI). The results are shown in Table 5.
3. The UV-Vis absorption spectrum was measured using a spectrophotometer (product name: U-3900H) manufactured by Hitachi High-Technologies Corporation. The results are shown in the column of “maximum absorption wavelength (nm)” in Table 5.

The comprehensive evaluation shown in Table 5 is given based on the following criteria.
"X": When precipitation was recognized or the maximum absorption wavelength exceeded 520 nm.
“Δ”: no precipitation was observed and the maximum absorption wavelength was 520 nm or less, but the molar concentration of the alloy fine particles in terms of constituent metal elements was less than 20 mM.
“◯”: When no precipitation was observed, the maximum absorption wavelength was 520 nm or less, and the molar concentration of the alloy fine particles in terms of constituent metal elements was 20 mM or more.
“◎”: When all of the following particle size distributions are satisfied among the above “◯”.
-Maximum frequency particle size is 15 nm or less (10-15 nm).
-Average particle diameter is 25 nm or less (15-25 nm).
-PDI is 0.2 or less (0.1-0.2).

From Table 5, it was found that according to the production method described above, a highly concentrated AuAg alloy fine particle dispersion excellent in color developability can be produced directly and stably at a high yield (approximately 100%). In particular, as shown in Examples 15 to 17 and Example 19, a solution A containing only an Au salt (not containing PVP as a dispersing agent) and a solution B containing an Ag salt, a reducing agent, and a dispersing agent are separated. After heating to a temperature range of 60 to 100 ° C. respectively, the two types of solutions are mixed at once, so that the maximum frequency particle size is several tens of nanometers (for example, 10 to 30 nm, preferably 10 to 15 nm). And the average particle diameter is several tens of nanometers (for example, 10 to 50 nm, preferably 15 to 25 nm), and PDI is small (for example, 0.5 or less, preferably 0.4 or less, more preferably It was found that a homogeneous dispersion containing AuAg alloy fine particles at a high concentration can be obtained.
When PVP is added to the solution A, the cause of the increase in particle size (maximum frequency particle size or average particle size) and / or PDI may be the reduction of Au ions by PVP. That is, it is considered that PVP acts as a very weak reducing agent, and the produced nuclei slowly bulked or aggregated into large particles. On the other hand, when PVP is not added to the solution A, such a phenomenon does not occur, and the alloy fine particles are generated only by a relatively fast reduction reaction with citric acid, and thus it is considered that the dispersion is monodispersed.
Since the AuAg alloy fine particle dispersion produced in this way is excellent in color developability, it can be suitably used industrially as a practical coloring material (paint).

Claims (7)

A dispersion of alloy fine particles containing gold (Au) and silver (Ag) as constituent elements,
The maximum absorption wavelength measured using an absorptiometer is 520 nm or less,
The molar concentration of the alloy fine particles in terms of constituent metal elements is 10 mM or more,
An alloy fine particle dispersion in which a precipitate containing the alloy fine particles is not visually recognized in a stationary state.   The alloy fine particle dispersion liquid according to claim 1, wherein the molar concentration of the alloy fine particles in terms of the constituent metal elements is 80 mM or less.   The alloy fine particle dispersion according to claim 1 or 2, wherein a polydispersity index (PDI) based on a dynamic light scattering method of the alloy fine particles is 0.6 or less.   The alloy fine particle dispersion containing the alloy fine particle dispersion according to any one of claims 1 to 3, wherein the number-based maximum frequency particle size based on a dynamic light scattering method of the alloy fine particles is 10 nm or more and 20 nm or less.   A coloring material for coloring the surface of a specimen, comprising the alloy fine particle dispersion according to claim 1.   An instrument colored with the colorant according to claim 5. A method for producing a dispersion of alloy fine particles containing gold (Au) and silver (Ag) as constituent elements,
Preparing a solution A containing Au ions and no reducing agent;
Preparing a solution B containing Ag ions, a reducing agent, and a dispersing agent;
Heating the solution A and the solution B to a temperature range of 60 ° C. or higher and 100 ° C. or lower, respectively; and
Mixing and stirring the solution A and the solution B in the temperature range to obtain AuAg alloy fine particles;
Including
Here, in the solution A and the solution B, the number of moles m1 of the Au ions contained in the solution A and the number of moles m2 of the Ag ions contained in the solution B are 0 <(m2 / (m1 + m2). )) Prepare to satisfy ≦ 0.3,
A method for producing an alloy fine particle dispersion in which the total molar concentration (M1 + M2) of the molar concentration M1 of Au ions and the molar concentration M2 of Ag ions when mixing the solution A and the solution B is 10 mM or more.

Images