Composite metal nanoparticle carrier, method for manufacturing the same, antibacterial composition including composite metal nanoparticle carrier, and coating composition

Abstract

To provide: a composite metal nanoparticle carrier capable of preventing composite metal nanoparticles including a plurality of metals from aggregating, improving environment resistance, subjecting expensive noble metal to resource saving and improving various kinds of characteristics and functions expressed as metal nanoparticles; a method for manufacturing the same; an antibacterial composition including the composite metal nanoparticle carrier; and a coating composition.SOLUTION: A composite metal nanoparticle carrier obtained by carrying composite metal nanoparticles on an electrical insulation carrier includes: first metal nanoparticles including first metal consisting of single metal or alloy and carried on the electrical insulation carrier; and a second metal electroless plating layer including a part of the first metal nanoparticles substituted with second metal by electroless plating. At least a part of the first metal nanoparticle surface has a structure covered with the second metal electroless plating layer by forming the second metal electroless plating layer on a part or the entire circumference of a composite metal nanoparticle surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a composite metal nanoparticle carrier that suppresses aggregation of composite metal nanoparticles by supporting composite metal nanoparticles containing a plurality of metals on a carrier, improves environmental resistance, saves resources of precious metals, and improves various properties exhibited as metal nanoparticles or imparts new functions, a method for producing the same, an antibacterial composition containing the composite metal nanoparticle carrier, and a coating composition.

Background Art

[0002] Since metal nanoparticles tend to aggregate in a dispersion medium and easily form aggregates, various metal nanoparticle carriers in which various metal nanoparticles are supported on a metal oxide carrier such as silica, alumina, or titania have been studied as solutions to this technical problem. These metal nanoparticle carriers have already been proposed for various uses as antibacterial agents, building material coating agents, or coloring pigments, and are well-known materials (see, for example, Patent Document 1 and Non-Patent Document 1).

[0003] In addition, as a metal nanoparticle carrier, it has also been proposed to apply an alloy nanoparticle carrier in which an alloy composed of a plurality of metals is supported on a carrier as an exhaust gas purification catalyst (see, for example, Patent Document 2).

[0004] Furthermore, instead of the above alloy form, a composite metal nanoparticle support in which each of a plurality of metal nanoparticles is independently supported on a support has been proposed (see, for example, Patent Documents 4 to 6). Patent Document 4 discloses a composite metal nanoparticle support in which a second metal nanoparticle is further supported on the surface of a first metal nanoparticle supported on a support. Patent Document 5 proposes a support-metal nanoparticle composite in which a first metal and a second metal and metal nanoparticles including one or more cavities continuous from the outer surface are supported on a support. Patent Document 6 discloses a composite metal nanoparticle support produced by putting a support for supporting composite metal nanoparticles into a composite metal nanoparticle colloid produced by a physical method using a vacuum chamber. These inventions were made in the expectation that composite metal nanoparticles composed of two or more types of metals not only have the properties of each element but also exhibit novel properties, and attempts have been made to use them as catalysts for fuel cells and exhaust gas purification devices, for magnetic media, and for semiconductors.

[0005] On the other hand, the composite metal nanoparticles themselves without the form of a support have also been conventionally studied for various applications. For example, Patent Documents 6 and 7 propose composite metal nanoparticles in which a composite metal is coated in two or more layers on the surface of metal nanoparticles or nanoparticles such as silica, and the production is carried out by an electroless plating method.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

[0007] [Non-Patent Document 1] Atsunori Shiraishi, "Development of New Materials by Nanoparticle Composite", Saga Prefectural Ceramic Technology Center Research Report for Fiscal Year 2006 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] A carrier supporting metal nanoparticles composed of a plurality of metals can not only solve the problem of aggregation of metal nanoparticles, but also improve various properties, save resources of expensive noble metals such as Au, Pt, Pd, etc., compared with a metal nanoparticle carrier made of a single metal, and can be expected to have effects such as imparting new functions in the use for exhaust gas purification catalysts, reaction catalysts, etc. Therefore, it has attracted particular attention in recent years.

[0009] As a conventional technology of a metal nanoparticle carrier, for example, in the case of a nanoparticle carrier of a single metal such as Ag, Cu, Fe, etc. disclosed in Patent Document 1 and Non-Patent Document 1, oxides or hydroxides may be formed due to oxidation or moisture absorption during storage or use, and there is a problem that characteristic variations such as antibacterial properties or characteristic degradation such as discoloration become significant.

[0010] In addition, an alloy nanoparticle carrier is disclosed in Patent Document 2 as a metal nanoparticle carrier composed of a plurality of metals. However, these alloy nanoparticles are supported on a carrier in a form in which a plurality of different types of metals are partially alloyed by heat treatment or reduction treatment, and only a single characteristic and function as an alloy prepared according to the composition ratio of the plurality of metals are expressed. Therefore, the expression of characteristics in which each metal functions synergistically has not been considered.

[0011] As another example of a metal nanoparticle carrier composed of a plurality of metals, composite metal nanoparticles have been proposed in Patent Documents 3 to 5. However, since these are those in which a mixture of a plurality of metals is supported on a carrier, it has not been possible to avoid damage due to environmental influences such as oxidation and moisture absorption to which each metal is individually susceptible. In addition, the Ag-Au composite metal nanoparticle carrier disclosed in Patent Document 3 has a form in which second nanoparticles made of Au are deposited on the surface of first nanoparticles made of Ag, and it is considered that the second nanoparticles are likely to easily detach or disperse from the first nanoparticles. In that case, it becomes difficult to maintain the characteristics as Ag-Au composite metal nanoparticles over time. The composite metal nanoparticle carrier disclosed in Patent Document 4 is one in which metal nanoparticles containing a first metal and a second metal are supported on a carrier in a form in which one or more cavities are formed through micelle formation by surfactants having different chain lengths. Therefore, not only is it likely to be susceptible to environmental influences such as oxidation and moisture absorption even inside the composite metal nanoparticles, but it is also considered that it is likely to detach from the carrier in the short term due to the influence of the encapsulated cavities. In addition, although the composite metal nanoparticles disclosed in Patent Document 5 can be alloyed by heat treatment, in that case, similar to the alloy nanoparticles disclosed in Patent Document 2, it is not possible to expect the synergistic functions and characteristics of each metal to be exhibited. Furthermore, manufacturing composite metal nanoparticles by a physical method in a vacuum chamber has been difficult to stably mass-produce because it requires skill not only in setting raw materials but also in controlling vacuum, heating temperature, chamber rotation speed, etc.

[0012] On the other hand, as for the metal-coated powder disclosed in Patent Document 6 as composite metal nanoparticles having no carrier form, aggregation of the composite metal nanoparticles remains a major technical issue. In addition, the metal-coated powder disclosed in Patent Document 7 is one in which a base plating treatment is performed on the entire surface of a powder having a particle size on the order of μm, and then a uniform metal coating is formed, and it has been difficult to directly apply this technique to a composite metal nanoparticle carrier that meets the object of the present invention.

[0013] The present invention has been made to solve such problems, and by supporting composite metal nanoparticles containing a plurality of metals on an insulating carrier, aggregation of the composite metal nanoparticles is suppressed, and oxidation resistance, moisture resistance, sulfur resistance, or hydrocarbon poisoning resistance, etc. can not only improve the environmental resistance, but also reduce the consumption of expensive noble metals such as Au, Pt, Pd, etc., and expect improvement of various properties or imparting of new functions compared to conventional composite metal nanoparticle formation. It is an object of the present invention to provide a composite metal nanoparticle carrier, a method for producing the same, an antibacterial composition containing the composite metal nanoparticle carrier, and a coating composition.

Means for Solving the Problems

[0014] The inventor of the present invention has found that a composite metal nanoparticle carrier capable of solving the above problems can be obtained by forming an electroless plating layer in which a part of the metal nanoparticles made of the first metal supported on the electrically insulating carrier is replaced with the second metal on a part or the entire circumference of the surface of the nanoparticles of the first metal, and thus arrived at the present invention.

[0015] That is, the configuration of the present invention is as follows. [1] The present invention provides a composite metal nanoparticle carrier in which composite metal nanoparticles are supported on an electrically insulating carrier, comprising: nanoparticles of a first metal made of a single metal or an alloy, which are supported on the electrically insulating carrier; and an electroless plating layer of a second metal in which a part of the nanoparticles of the first metal is replaced by the second metal by electroless plating, wherein the electroless plating layer of the second metal is formed on a part or the entire circumference of the surface of the composite metal nanoparticles, so that at least a part of the surface of the nanoparticles of the first metal is covered with the electroless plating layer of the second metal. [2] The present invention provides a composite metal nanoparticle carrier as described in [1], wherein on the electrically insulating carrier, the composite metal nanoparticles and nanoparticles containing at least one of the first metal, an oxide of the first metal, and a hydroxide of the first metal are supported, the nanoparticles containing at least one of the first metal, an oxide of the first metal, and a hydroxide of the first metal are supported at a location different from the location where the composite metal nanoparticles are supported on the surface of the insulating carrier, and the particle size (D) of the composite metal nanoparticles and the particle size (d) of the nanoparticles containing at least one of the first metal, an oxide of the first metal, and a hydroxide of the first metal satisfy the relationship D > d. [3] The present invention provides a composite metal nanoparticle carrier as described in [1] or [2], wherein the nanoparticles of the first metal are metal nanoparticles supported on the electrically insulating carrier by electroless plating. [4] The present invention provides a composite metal nanoparticle carrier as described in [3], wherein the first metal is any metal or alloy selected from the group consisting of Ag, Co, Cu, Fe, Zn, Ni, an alloy of Ag and Ni, and an alloy of Ag and Pd, and the second metal is any metal selected from the group consisting of Au, Pt, and Pd. [5] The present invention provides a composite metal nanoparticle carrier as described in [4], wherein the electrically insulating carrier is a metal oxide, a ceramic, or a plastic having any shape selected from the group consisting of particulate, plate-like, and fibrous shapes. [6] The present invention provides a composite metal nanoparticle carrier as described in [5], wherein the electrically insulating carrier is a metal oxide having nanoparticles or a nanoporous structure. [7] The present invention provides a composite metal nanoparticle composite as described in [6], wherein the first and second metals are Ag and Au, Co and Pt, or Ni and Pt, respectively, and the electrically insulating carrier is a metal oxide having nanoparticles. [8]The present invention relates to a method for producing a composite metal nanoparticle carrier in which composite metal nanoparticles are supported on an electrically insulating carrier, the method including a step of supporting first metal nanoparticles made of a single metal or an alloy on the electrically insulating carrier, and a step of using ions of a second metal different from the metal of the first metal nanoparticles to replace a part of the first metal contained in the first metal nanoparticles supported on the electrically insulating carrier with the second metal by electroless plating to form an electroless plating layer of the second metal. By forming the electroless plating layer of the second metal on a part or the entire circumference of the surface of the composite metal nanoparticles, at least a part of the surface of the nanoparticles of the first metal is covered with the electroless plating layer of the second metal, thereby providing a method for producing a composite metal nanoparticle carrier. [9]The present invention provides a method for producing a composite metal nanoparticle carrier according to claim 8, characterized in that by changing the concentration of the second metal ions contained in the electroless plating solution used in the step of forming the electroless plating layer of the second metal, the coverage range of the electroless plating layer of the second metal formed on at least a part of the surface of the first metal nanoparticles and the elemental concentration of the second metal contained in the composite metal nanoparticles are respectively adjusted.

[10] The present invention provides a method for producing a composite metal nanoparticle carrier according to claim 9, characterized in that in the number average particle diameter (Dn) and volume average particle diameter (Dv) obtained by performing dynamic light scattering (DLS) measurement of a plating solution containing the composite metal nanoparticle carrier obtained as a colloidal dispersion after electroless plating, the number average particle diameter (Dn) satisfies the following formula (1) with respect to the average particle diameter (D0) of the electrically insulating carrier, and the electroless plating layer of the second metal is formed using an electroless plating solution prepared so that Dv / Dn satisfies the following formula (2). 0.5 < Dn / D0 < 1.0 (1) 1.0 < Dv / Dn < 1.6 (2)

[11] The present invention provides a method for producing a composite metal nanoparticle carrier according to any one of [8] to

[10] , characterized in that the step of supporting the first metal nanoparticles composed of the single metal or alloy on the electrically insulating carrier is carried out by electroless plating method of reducing one or more metal ions in an electroless plating solution having one or more metal ions constituting the first metal nanoparticles to support the first metal nanoparticles on the electrically insulating carrier.

[12] The present invention provides a method for producing a composite metal nanoparticle carrier according to

[11] , characterized in that the first metal is any metal or alloy selected from the group consisting of Ag, Co, Cu, Fe, Zn, Ni, an alloy of Ag and Ni, and an alloy of Ag and Pd, and the second metal is any metal selected from the group consisting of Au, Pt, and Pd.

[13] The present invention provides a method for producing a composite metal nanoparticle carrier according to

[12] , characterized in that the electrically insulating carrier is a metal oxide, ceramics, or plastic having any shape selected from the group consisting of particulate, plate-like, and fibrous shapes.

[14] The present invention provides a method for producing a composite metal nanoparticle carrier according to

[13] , characterized in that the electrically insulating carrier is a metal oxide of nanoparticles or a metal oxide having a nanoporous structure.

[15] The present invention provides a method for producing a composite metal nanoparticle composite according to

[14] , characterized in that the first and second metals are Ag and Au, Co and Pt, or Ni and Pt, respectively, and the electrically insulating carrier is a metal oxide of nanoparticles.

[16] The present invention provides an antibacterial composition containing a composite metal nanoparticle carrier, comprising at least one of the composite metal nanoparticle carrier according to [1] or [2], water or an organic solvent for dispersing the composite metal nanoparticle carrier, and a binder resin for encapsulating the composite metal nanoparticle carrier.

[17] The present invention provides a coating composition for paints containing a composite metal nanoparticle carrier as a colorant or a coloring pigment, the coating composition including the composite metal nanoparticle carrier described in [1] or [2] above, at least one of water or an organic solvent for dispersing the composite metal nanoparticle carrier, and a binder resin for encapsulating the composite metal nanoparticle carrier.

[18] The present invention provides a coating composition containing a composite metal nanoparticle carrier as a colorant or a coloring pigment for coloring the surface of a glass body or a ceramic, the coating composition including the composite metal nanoparticle carrier described in [1] or [2] above, and a glass flux or polysilazane composed of a plurality of metal oxides.

Advantages of the Invention

[0016] The composite metal nanoparticle carrier according to an embodiment of the present invention suppresses aggregation of composite metal nanoparticles by supporting composite metal nanoparticles composed of a first and a second metal on an electrically insulating carrier, and forms a second metal film, which is more inert to damages such as oxidation, sulfidation, or moisture absorption that the first metal supported on the electrically insulating carrier is susceptible to, or the influence of hydrocarbon poisoning, on a part or the entire circumference of the surface of the first metal nanoparticles, thereby reducing or eliminating such influences. Further, the composite metal nanoparticles can achieve resource conservation of expensive noble metals while having characteristics and functions equivalent to or superior to those of single metal nanoparticles composed of such expensive noble metals, for example, by forming a metal film made of an expensive second metal such as Au, Pt, Pd, etc. on the surface of nanoparticles composed of a relatively inexpensive first metal such as Ag, Ni, Cu, Co, Zn, Fe, etc.

[0017] Furthermore, the composite metal nanoparticle carrier according to an embodiment of the present invention has a core-shell structure of a first metal, a second metal, and the first and second metals, and in the core-shell structure, each composition ratio can be adjusted to a desired range according to the degree of formation of the shell layer. Therefore, not only the functions due to the characteristics of each metal element alone but also the synergistic functions of the plurality of metal nanoparticles due to the core-shell structure are possessed. Thereby, improvements in various characteristics and functional enhancements can be achieved compared to conventional metal nanoparticle carriers. Specifically, it is used as a coloring agent or a coloring pigment contained in an antibacterial composition for improving antibacterial properties and its stability over time, or an inorganic or organic coating composition for improving various properties such as preventing discoloration. Also, in the development of exhaust gas purification catalysts, organic synthesis catalysts, electrodes of various batteries, etc., not only can the respective characteristics and performances be improved, but new functions can also be imparted.

[0018] The method for manufacturing a composite metal nanoparticle carrier according to an embodiment of the present invention can easily manufacture a composite metal nanoparticle carrier by performing, in a step of coating a part or the entire circumference of the surface of nanoparticles of a first metal composed of a single metal or an alloy with an electroless plating layer of a second metal, using a conventionally known electroless plating method. Here, the composition ratios of the first metal, the second metal, and the bonding layer between the first and second metals in the composite metal nanoparticles can be easily adjusted by optimizing the ion concentration of each metal contained in the electroless plating solution or the manufacturing conditions of the electroless plating, respectively. Also, by adopting the electroless plating method in the step of supporting the first metal nanoparticles on an electrically insulating carrier, it is possible to manufacture a composite metal nanoparticle carrier in which the state where the composite metal nanoparticles are supported on the electrically insulating carrier can be maintained not only initially but also over time.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0020] The nanoparticles defined in the present invention mean particles having a diameter in the nano order of less than 1 μm and substantially having a diameter of 1 to 600 nm. Further, the shape of the nanoparticles includes not only spherical but also elliptical or irregular shapes. In the case where the shape of the nanoparticles of the present invention is elliptical or irregular, the distance between the peripheral end portions on the major axis or the distance between the end portions having the maximum length of the cross section is defined as the particle diameter.

[0021] <Configuration and Structure of the Composite Metal Nanoparticle Carrier> Hereinafter, the configuration and structure of the composite metal nanoparticle carrier according to an embodiment of the present invention will be described in detail.

[0022] Figure 1 shows a TEM image of the composite metal nanoparticle carrier 1 according to an embodiment of the present invention observed by a transmission electron microscope (TEM). The composite metal nanoparticle carrier 1 shown in Figure 1 has AgAu nanoparticles 2 with a particle size of about 15 nm as composite metal nanoparticles supported on silica (SiO2) nanoparticles 3 with a particle size of 90 to 100 nm as an insulating carrier. The AgAu nanoparticles 2 are in a dispersed state without aggregating with each other by being supported on the surface of the silica nanoparticles 3. Further, in the composite metal nanoparticle carrier 1, together with the AgAu nanoparticles 2, residual Ag nanoparticles 4 with a particle size smaller than that of the AgAu nanoparticles 2 (about 1 nm) are supported on the silica nanoparticles 3.

[0023] The particle formation mechanism of the composite metal nanoparticle carrier 1 shown in Figure 1 will be described with reference to the schematic diagram in Figure 2. First, as shown in Figures 2(a) and 2(b), Ag nanoparticles 5 are supported on the silica nanoparticles 3. Then, as shown in Figure 2(c), all or part of the Ag of the Ag nanoparticles 5 supported on the silica nanoparticles 3 is replaced by Au by electroless plating. As the electroless Au plating progresses, an electroless Au plating layer 6 is formed on a part of the surface of the AgAu nanoparticles 2. At that time, the AgAu nanoparticles 2 have a structure in which at least a part of the surface of the Ag nanoparticles 5 is covered with the electroless Au plating layer 6, as shown in Figure 2(d). Further, when the electroless Au plating layer 6 is formed over the entire circumference of the surface of the AgAu nanoparticles 2 by proceeding with the electroless plating, AgAu nanoparticles 7 having a structure in which the entire surface of the Ag nanoparticles 5 is covered with the electroless Au plating layer 6 are formed, as shown in Figure 2(e).

[0024] Thus, in the composite metal nanoparticle carrier 1, when an electroless Au plating layer 6 is formed on a part or the entire circumference of its surface, at least a part of the surface of the Ag nanoparticles 5 is covered with the electroless Au plating layer 6. When the entire circumferential surface of the Ag nanoparticles, which are the first metal, is covered with Au, which is the second metal, it is possible to achieve resource saving of the expensive noble metal Au while having almost the same characteristics and functions as expensive single Au nanoparticles.

[0025] In the electroless Au plating layer 6 formed in this way, Au atomic diffusion occurs over time from part or all of the surface of the AgAu nanoparticles 2 or 7 toward the inside. Therefore, as the form of the electroless Au plating layer 6, not only the surface of the AgAu nanoparticles 2 or 7 but also those formed from the surface toward the inside are included.

[0026] As shown in FIGS. 1 and 2, on the composite metal nanoparticle carrier 1, together with the AgAu nanoparticles 2 or 7, residual Ag nanoparticles 4 having a particle size smaller than that of the AgAu nanoparticles 2 or 7 (about 1 nm) are supported on the silica particles 3. The AgAu nanoparticles 2 are formed by performing substitution electroless plating 6 of Au on the Ag nanoparticles 5 supported on the silica nanoparticles 3. Here, depending on the manufacturing conditions during the substitution electroless plating of Au, Ag nanoparticles in a state not substituted by Au may remain on the surface of the composite metal nanoparticle carrier 1 as a residue after the Ag of the Ag nanoparticles 5 has melted and Au has precipitated. These remaining nano-Ag particles are shown as residual Ag nanoparticles 4 in FIGS. 1 and 2.

[0027] As described above, the composite metal nanoparticle carrier 1 according to one embodiment of the present invention essentially includes AgAu nanoparticles 2 as the composite metal nanoparticles. However, it may be not only a carrier on which the AgAu nanoparticles 2 or 7 are supported alone but also a carrier on which the residual Ag nanoparticles 4 are supported together with the AgAu nanoparticles 2 or 7.

[0028] As shown in FIGS. 1 and 2, the particle size of the remaining Ag nanoparticles 4 is smaller than that of the AgAu nanoparticles 2 or 7 by the amount that Ag has only dissolved out by electroless plating and no substitution with Au has occurred. Further, although the remaining Ag nanoparticles 4 may change to an oxide or hydroxide of Ag due to the influence of oxidation or moisture absorption over time, the coating layer of the oxide or hydroxide of Ag is thinner than the electroless plating layer of Au. Therefore, the respective nanoparticles are supported on silica (SiO2) nanoparticles 3 which are electrically insulating carriers such that the particle size (D) of the AgAu nanoparticles 2 or 7 and the particle size (d) of the remaining nanoparticles 4 containing at least any one of Ag, an oxide of Ag, and a hydroxide of Ag satisfy the relationship D>d.

[0029] Although a part of the remaining Ag nanoparticles 4 may change to Ag oxide during storage, even in that case, the Ag oxide is known to exhibit bactericidal antibacterial properties. Therefore, the composite metal nanoparticle carrier 1 shown in FIGS. 1 and 2 can obtain an additional effect in terms of antibacterial properties even when both the AgAu nanoparticles 2 or 7 and the remaining Ag nanoparticles 4 are supported, as compared with the case where only the composite metal nanoparticles are supported. On the other hand, when suppressing or preventing the change of Ag nanoparticles in an environment such as vacuum sealing or a reducing atmosphere, since the bactericidal antibacterial properties by the remaining Ag nanoparticles 4 are expressed as they are, a significant improvement in antibacterial properties can be achieved by the combined use of the AgAu nanoparticles 2 and the remaining Ag nanoparticles 4. By ensuring a similar environment even when remaining metal nanoparticles made of a metal other than Ag are supported, in addition to the composite metal nanoparticles having a core-shell structure, a composite metal nanoparticle carrier having characteristics and functions expressed by the remaining metal nanoparticles alone can be obtained.

[0030] The loading of the Ag nanoparticles 5 shown in FIGS. 2(a) and 2(b) is carried out, for example, by the following methods including known methods. (a) A method of physically adsorbing or electrically loading onto a carrier by mixing and contacting a colloidal solution of metal nanoparticles or a dispersion of alloy nanoparticles with a carrier colloidal solution, (b) Diammine silver ion [Ag(NH3)2] of an ammoniacal silver nitrate aqueous solution+ A method for performing a silver mirror reaction using (c) A method of carrying out a reduction treatment using a reducing agent or the like while stirring and contacting a metal salt of the metal constituting the metal nanoparticles with a carrier in an aqueous solution or passing through a carrier slurry packed bed, and supporting the reduced metal nanoparticles on the carrier, and (d) A method of generating metal oxide particles with an alkali or the like after contacting a metal salt of the metal constituting the metal nanoparticles with a carrier in an aqueous solution, and reducing the metal oxide by a reducing agent or ultraviolet irradiation.

[0031] In the case where the first metal is an alloy in the method of (a) above, a dispersion of alloy nanoparticles prepared by mixing a plurality of single metal nanoparticle colloids and subjecting them to heat treatment and reduction treatment may be used. Further, as disclosed in Patent Document 2, a hydrophilic polymer or an amphiphilic molecule is used as a metal fine particle dispersion, and reduction treatment is performed in a state where a metal salt containing each metal ion constituting the alloy is dispersed in the metal fine particle dispersion in a solution. The carrier may be supported using a cluster dispersion or suspension containing alloy nanoparticles prepared by the above method. In the embodiment of the present invention, among the above methods, from the viewpoint of achieving both the particle size control and the loading retention of the metal nanoparticles and the ease of production (productivity), either the electroless plating method of (b) or (c) may be adopted. However, considering that not only can various metal nanoparticles be supported, but also the loading retention of the metal nanoparticles can be further improved, it is practical to adopt the electroless plating method in which reduction treatment is performed with a reducing agent from the aqueous solution of the metal salt of (c).

[0032] The composite metal nanoparticle carriers shown in FIGS. 1 and 2 list Ag and Au as examples of the first and second metals, respectively. However, in the embodiments of the present invention, they are not limited to these metal combinations. As the first metal, in addition to Ag, any metal or alloy selected from the group consisting of single metals such as Co, Cu, Fe, Zn, and Ni, and alloys of Ag and Ni, and alloys of Ag and Pd may be used as long as the expression of functions as antibacterial, purification catalyst, or reaction catalyst can be expected. Further, as the second metal, a noble metal having a lower ionization tendency than the first metal and being inert to damages such as oxidation, sulfidation, or moisture absorption and the influence of hydrocarbon poisoning is used. In addition to Au, for example, Pt or Pd may be mentioned depending on the required characteristics. These Au, Pt, and Pd are expected to exhibit functions as antibacterial, purification catalyst, or reaction catalyst, similar to the first metal.

[0033] In the embodiments of the present invention, in particular, from the viewpoint that a metal nanoparticle carrier having a uniform particle size and excellent loadability on the carrier can be stably and efficiently obtained, combinations of Ag and Au, Co and Pt, or Ni and Pt are suitable as the first and second metals, respectively.

[0034] The electrical insulating carrier is not limited to the silica nanoparticles shown in FIGS. 1 and 2. Further, examples of the electrical insulating carrier include metal oxides, ceramics, or plastics having any shape selected from the group consisting of particulate, plate-like, and fibrous shapes. The pretreatment method of electroless plating, which involves activating the surface by applying a catalyst to the electrical insulating carrier, can easily produce the first metal nanoparticle carrier not only when using metal oxides but also when using electrical insulating carriers of ceramics or plastics. Moreover, since the bonding strength between the electrical insulating carrier and the first metal nanoparticles is improved, the detachment of the first metal nanoparticles from the electrical insulating carrier is suppressed over time. Furthermore, electroless plating for substituting a part of the first metal nanoparticles supported on metal oxides, ceramics, or plastics with a second metal is also selectively performed on the surface of the first metal nanoparticles from the functional point of view of substitution electroless plating. As described above, since the supportability of the first metal nanoparticles supported on metal oxides, ceramics, or plastics to these electrical insulating carriers is improved, the composite metal nanoparticles selectively formed at the location where the first metal nanoparticles are supported are also naturally suppressed from detaching from these electrical insulating carriers over time.

[0035] Also, as the electrical insulating carrier, considering points such as improving various properties and functions expressed as a composite metal nanoparticle carrier and expecting to endow new functions, metal oxides having metal oxide nanoparticles or a nanoporous structure among the above-mentioned metal oxides, ceramics, or plastics may be used. Examples of the metal oxide of nanoparticles include at least one type of nanoparticles selected from silica, alumina, ceria, titania (titanium dioxide), zirconia, yttria, magnesia, zeolite, and vanadium oxides. These may be commercially available metal oxide nanoparticles used as they are, or may be compounds having a metal-oxygen bond synthesized by the sol-gel method in a precursor solution using metal alkoxide as a raw material.

[0036] In addition, as the metal oxide having a nanoporous structure, those having pore bodies with a diameter of 2 nm or more, relatively uniform pore sizes, high specific surface areas, and various three-dimensional pore structures are used. For example, mesoporous silica, mesoporous titania, and metal oxide nanopores containing at least one component selected from tin oxide, vanadium oxide, tungsten oxide, and manganese oxide can be mentioned.

[0037] <Method for producing a composite metal nanoparticle carrier> Next, the method for producing the composite metal nanoparticle carrier of the present invention will be described.

[0038] The method for producing a composite metal nanoparticle carrier according to an embodiment of the present invention is a method for producing a composite metal nanoparticle carrier in which composite metal nanoparticles are supported on an electrically insulating carrier, and a first metal nanoparticle made of a single metal or an alloy is supported on the electrically insulating carrier. And a step of substituting a part of the first metal contained in the first metal nanoparticles supported on the electrically insulating carrier with a second metal by electroless plating using ions of a second metal different from the metal of the first metal nanoparticles to form an electroless plating layer of the second metal. Through these steps, the electroless plating layer of the second metal is formed on a part or the entire circumference of the surface of the composite metal nanoparticles. Thereby, at least a part of the surface of the nanoparticles of the first metal is covered with the electroless plating layer of the second metal.

[0039] As described above, the above-mentioned step of "supporting the first metal nanoparticles made of a single metal or an alloy on the insulating carrier" practically adopts an electroless plating method in which metal nanoparticles are prepared by performing a reduction treatment on a salt of the first metal with a reducing agent. As the first metal, since the expression of various functions can be expected as an antibacterial agent, a purification catalyst, or a reaction catalyst, for example, any metal or alloy selected from the group consisting of single metals of Ag, Co, Cu, Fe, Zn, and Ni, and alloys of Ag and Ni, and alloys of Ag and Pd can be mentioned.

[0040] The plating solution used when performing electroless plating contains an essential component, i.e., a plating metal salt and a reducing agent, and optional components such as a complexing agent, a pH adjuster, a surfactant, etc. As the plating metal salt, a water-soluble salt is preferable. As described above, for example, nitrates, sulfates, perchlorates, acetates, etc. containing metals such as Ag, Co, Cu, Fe, Zn, and Ni mentioned as the first metals can be mentioned. These metal salts are selected as desired from the viewpoints of the properties and characteristics of the electroless plating solution used according to the type of metal. Further, in order to form alloy nanoparticles of Ag-Ni and Ag-Pd as the first metal, these plural metal salts may be added as desired. Among them, as the first metal salt, metal salts of Ag, Co, and Ni are particularly preferable. Examples of the reducing agent include hypophosphite, formalin, hydrazine, boron hydride compounds, etc. As the pH adjuster, known ones that are inexpensive and easily available may be used, for example, sodium acetate, sodium hydroxide, etc. As the complexing agent, known ones such as hydroxycarboxylic acids and their salts, phosphates, ammonium salts, carboxylic acids and their salts, amines having an amino group and a carboxyl group and their salts, etc. may be used, for example, malic acid, succinic acid, acetic acid, glycine, sodium potassium tartrate, sodium citrate, etc. can be mentioned. Also, as the surfactant, a desired one can be used from among anionic surfactants, cationic surfactants, amphoteric ion surfactants, and nonionic surfactants according to the type of metal salt contained in the electroless plating solution.

[0041] As the electroless plating treatment method, as also described in paragraph

[0060] of Patent Document 7, it is roughly classified into four types according to the contact method of an electrically insulating carrier, a plating metal salt solution, and a reducing agent solution. Among them, in the embodiments of the present invention, from the viewpoints of the particle size uniformity of metal nanoparticles, reduction of the adverse effects caused by residual unreacted reducing agents that easily occur with the addition of the reducing agent, and improvement of the loading and holding properties, etc., it is preferable to adopt the method of "previously dispersing the carrier in the reducing agent solution and adding the plating metal salt thereto". This method is also a known method performed as a pretreatment method for electroless plating.

[0042] The above-described pretreatment method for electroless plating is a method in which (1) a sensitization treatment is performed by adding an aqueous solution containing a reducing agent such as stannous chloride to a carrier colloidal aqueous solution, followed by (2) an activation treatment by adding a metal salt. By the action of the metal reduced and deposited by the activation treatment, such as Ag, acting as a self-catalyst, Ag nanoparticles are almost uniformly dispersed and supported on the surface of the carrier. Further, since the reducing agent has already been uniformly supported on the carrier in the sensitization treatment before the addition of the metal salt in the activation treatment, there is no need to consider the problem that unreacted reducing agent remains after the activation treatment. If unnecessary components such as unreacted reducing agent remain after the activation treatment, not only the activation treatment but also subsequent steps, that is, a step of replacing a part of the first metal with a second metal by electroless plating and forming an electroless plating layer of the second metal, may cause the unnecessary components to act as impurities and adversely affect the formation of the electroless plating. Furthermore, the metal nanoparticles supported on the carrier through (1) the sensitization treatment and (2) the activation treatment also have the effect of improving the adhesion to the electrically insulating carrier. In the (1) sensitization step, an acid component such as hydrochloric acid, trifluoroacetic acid, or acetic acid is simultaneously added as an ionization promoter for the reducing agent together with the reducing agent such as stannous chloride. From the viewpoints of the effect of the ionization promoter and the danger of the material, acetic acid is preferred in the embodiment of the present invention.

[0043] The electroless plating method can be applied to metal oxides, ceramics, or plastics having any shape selected from the group consisting of particulate, plate-like, and fibrous as an electrically insulating carrier. In addition to metal oxides and ceramics having a relatively rough surface shape, when applying to plastics having a flat surface, by performing roughening treatment on the plastic surface in advance before performing the electroless plating method, the adhesion between the metal nanoparticles and the plastic carrier can be improved. The roughening treatment of the plastic surface may be performed, for example, by combining alkali washing and etching treatment with a liquid such as sulfuric acid and chromic anhydride. Thus, the formation of the first metal nanoparticles by the pretreatment method of electroless plating does not depend on the material of the metal oxide, ceramics, or plastics which is an electrically insulating carrier. Also, as described above, since it hardly depends on the shape of the metal oxide, ceramics, or plastics, the metal oxide, ceramics, or plastics may be any of particulate, plate-like, and fibrous.

[0044] Also, as the electrically insulating carrier, as described above, considering points such as improving various characteristics and functions expressed as a composite metal nanoparticle carrier, and expecting to impart new functions, a metal oxide of nanoparticles or a metal oxide having a nanoporous structure may be used from among the above metal oxides, ceramics, or plastics.

[0045] The step of "replacing a part of the first metal contained in the first metal nanoparticles supported on the electrically insulating carrier with a second metal by electroless plating to form an electroless plating layer of the second metal" is to reduce or eliminate damage such as oxidation, sulfidation, or moisture absorption to which the first metal supported on the electrically insulating carrier is susceptible, or the influence of hydrocarbon poisoning, etc., by forming a second metal film that is inert to these influences on a part or the entire circumference of the surface of the first metal nanoparticles, and is also performed to improve the characteristics and functions exhibited by the composite metal nanoparticles. In this step, as described above, a noble metal with a lower ionization tendency than the first metal and that is inert to damage such as oxidation, sulfidation, or moisture absorption, or the influence of hydrocarbon poisoning, etc., is used as the second metal. Examples of the second metal include Au, Pt, Pd, etc. These metals, like the first metal, are expected to exhibit functions as antibacterial agents, purification catalysts, or reaction catalysts.

[0046] In the electroless plating for the replacement of the first metal with the second metal, when the second metal is Au, for example, an electroless plating solution containing chloroauric acid (HAuCl4·2H2O), formalin reducing agent (HCHO), sodium bicarbonate (NaHCO3), and sodium sulfite (Na2SO3), an electroless plating solution containing potassium gold cyanide (KAu(CN)2) and potassium tetrahydroborate or dimethylamine borane as a reducing agent, etc., can be mentioned. When the second metal is Pt, an electroless plating solution containing a platinum salt such as dinitrodiammine platinum or potassium tetranitroplatinate, a reducing agent such as hydrazine, and a stabilizer such as hydroxylamine salt may be used. Also, when the second metal is Pd, an electroless plating solution containing a palladium complex using ethylenediamine as a complexing agent and phosphinate or phosphonate as a reducing agent may be used.

[0047] In the step of forming the electroless plating layer of the second metal, the coverage range of the electroless plating layer of the second metal formed on at least a part of the surface of the first metal nanoparticles and the elemental concentration of the second metal contained in the composite metal nanoparticles are adjusted by changing the concentration of the second metal ions (metal salts) contained in the plating solution used in the step of forming the electroless plating layer of the second metal. For example, when the composite metal nanoparticles are AgAu nanoparticles, the production of AgAu nanoparticles is carried out by changing the addition amount of Au ions (Au metal salts) in the electroless Au plating solution according to the ratio to the elemental concentration of Ag at the time of producing Ag nanoparticles as the first metal. The AgAu nanoparticles thus produced change in such a form that the elemental concentration ratio of Au to Ag changes corresponding to the addition amount of the Au metal salt. Here, the elemental concentration ratio of Au shows a value close to that calculated from the addition amount of the Au metal salt. And as the elemental concentration ratio of Au to Ag increases, while no significant change is observed in the particle size of the AgAu nanoparticles, it was confirmed that the coverage range of the Au electroless plating layer formed on the surface of the Ag nanoparticles increases (see Examples 1 to 3 described later). This means that the Au electroless plating layer is a thin layer formed by partial substitution of Ag. Thus, the elemental concentration ratio of the second metal to the first metal can be changed to a value close to the designed value by the molar concentration of the second metal ions (metal salts) in the electroless plating solution. Therefore, it is also possible to form the Au plating layer on the entire surface of the AgAu nanoparticles by optimizing the addition amount of the metal ions of the second metal in the electroless plating solution.

[0048] In addition, the particle shape and aggregation state of the composite metal nanoparticle carrier supported on the electrically insulating carrier are affected by the components of the electroless plating solution containing the second metal ion (metal salt) and plating conditions such as the plating temperature. For example, when the ionic strength of the plating solution increases, aggregation is observed between the composite metal nanoparticles supported on the carrier. In the embodiments of the present invention, as physical quantities that can grasp the particle shape and aggregation state of the composite metal nanoparticle carrier, the number average particle diameter (Dn) and volume average particle diameter (Dv) of the metal nanoparticle carrier obtained by dynamic light scattering (DLS) measurement are used, using the plating solution containing the composite metal nanoparticle carrier obtained as a colloidal dispersion after electroless plating. Here, Dn and Dv are calculated in a form including the three types: the nanoparticles of the first metal, the composite nanoparticles of the first metal and the second metal, and the composite metal nanoparticle carrier. As a result of examining Dn and Dv of various colloidal dispersions after electroless plating, by optimizing the components of the plating solution and the plating conditions so that Dn does not deviate significantly from the average particle diameter D0 of the electrically insulating carrier and the range of Dv / Dn defined as the scale of the particle size distribution falls within a predetermined range, it has been found that a composite metal nanoparticle carrier with relatively uniform average particle diameters can be stably and efficiently produced. Here, the average particle diameter D0 of the carrier uses a value measured in advance. Specifically, the ranges of Dn / D0 and Dv / Dn need to satisfy the relationships shown in the following equations (1) and (2), respectively. 0.5 < Dn / D0 < 1.0 (1) 1.0 < Dv / Dn < 1.6 (2)

[0049] Even if Dn / D0 is 0.5 or less and Dv / Dn is 1.6 or more, it is possible to manufacture the composite metal nanoparticle carrier, but aggregation of the composite metal nanoparticle carrier, or significant liberation and detachment of many single composite metal nanoparticles from the carrier will occur. In that case, a sieving process for making the particle sizes of the composite metal nanoparticle carriers uniform is required, which not only increases the man-hours and lowers the yield, but also easily causes deterioration of the product quality. Therefore, in order to efficiently manufacture a composite metal nanoparticle carrier with relatively uniform average particle sizes, it is required that Dn / D0 exceeds 0.5 and approaches 1.0, which is the ideal value as much as possible, and Dv / Dn is less than 1.6 and approaches 1, which is the ideal value as much as possible.

[0050] Note that since the ionic strength of the electroless plating solution is also affected by the metal salt, reducing agent, and complexing agent and pH adjuster, etc., which are optional components contained in the plating solution, it is difficult to uniformly stipulate. Also, depending on the electroless plating conditions such as the plating solution temperature, the particle shape and aggregation state of the composite metal nanoparticle carrier supported on the electrically insulating carrier are affected. Therefore, in the embodiments of the present invention, it is practical to optimize the types and blending amounts of the respective components contained in the electroless plating solution and the plating conditions so that the colloidal dispersion containing the composite metal nanoparticle carrier after substitution electroless plating satisfies the above formulas (1) and (2).

[0051] The composite metal nanoparticle carrier manufactured as described above is separated and taken out from the plating solution by a method such as filtration or centrifugation after substitution electroless plating with the second metal ion. The composite metal nanoparticle carrier is washed with water and dried if necessary, but may be baked at a temperature of 100°C or higher depending on the application.

[0052] <Antibacterial composition> The composite metal nanoparticle carrier obtained according to an embodiment of the present invention may be applied as an antibacterial composition as one of its uses. It is widely known that each ion of Ag, Au, Cu, and Zn has an antibacterial effect on microorganisms such as bacteria. Since the composite metal nanoparticle carrier obtained according to an embodiment of the present invention contains at least two or more of these metals, not only the antibacterial effect of each metal ion alone but also the expression of a synergistic antibacterial effect by a plurality of metal ions can be expected. The antibacterial composition is used, for example, in the form of a resin composition having an antibacterial function, a composition for a molded article, or a composition for a paint, and includes the composite metal nanoparticle carrier obtained according to an embodiment of the present invention, water or an organic solvent for dispersing the composite metal nanoparticle carrier, and at least one of a binder resin for encapsulating the composite metal nanoparticle carrier.

[0053] The antibacterial composition obtained by dissolving or uniformly dispersing the composite metal nanoparticle carrier in water or an organic solvent to obtain a liquid containing the composite metal nanoparticle carrier may be applied or sprayed on wood, paper, resin, glass, fiber, cloth, non-woven fabric, plastic, etc., and then applied or adhered to their surfaces by natural drying or heat drying in the atmosphere. As the organic solvent, water, ethanol, and a mixed solvent thereof are preferable because they are suitable for the production of the antibacterial composition, have low invasiveness to the base material such as the paper, and are safe.

[0054] The antibacterial composition obtained as a liquid containing the composite metal nanoparticle carrier may contain a binder to the extent that the antibacterial effect is not impaired. Examples of the binder include monomers, oligomers, or polymers having at least one of the functions of thermosetting, photocuring, and electromagnetic wave curing. The polymer may be one that can be dissolved or dispersed in water or an organic solvent and forms a polymer film or polymer particles after drying of water or the organic solvent.

[0055] In addition, the antibacterial composition according to the embodiment of the present invention may be in the form of a resin composition in which the composite metal nanoparticle carrier is encapsulated in a resin. The resin is not particularly limited, and examples thereof include general-purpose polyolefin resins such as polyethylene and polypropylene, general-purpose polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and thermosetting polyester, polyurethane resins, and silicone resins such as dimethyl silicone and modified silicone. In the case of a resin composition, the composite metal nanoparticle carrier is uniformly dispersed and mixed into a liquid or solid resin by a mixer, blender, etc. at room temperature or while heating. In that case, not only the resin but also a solvent for mixing may be contained as a part of the resin composition. Further, it may be used in a form in which an inorganic filler such as calcium carbonate, silica, or talc is contained and mixed with the resin.

[0056] The above resin composition may be used as a molded product such as a block, sheet, film, or fiber by molding it by any known method. As the molding method, an injection molding method, a transfer molding method, an injection compression molding method, an extrusion molding method, a blow molding method, an inflation molding method, a press molding method, a calendar molding method, a vacuum molding method, etc. can be adopted. Further, it may be a foamed molded body by performing foaming molding such as injection foaming, extrusion foaming, or foaming blow.

[0057] The composite metal nanoparticle carrier according to the embodiment of the present invention has good dispersibility not only in a solvent such as water or an organic solvent but also in a resin, and no aggregation or segregation is observed. Therefore, as the composite metal nanoparticles, for example, a combination of two types such as Ag / Au, Cu / Au, Zn / Au, Fe / Au, or a combination of three or more types of at least two or more of Ag, Cu, Zn, Fe and Au is adopted. Since the oxidation inhibitory effect of Ag, Cu, Zn, or Fe used as the first metal is obtained by the Au plating coating layer of the second metal, not only the maintenance of antibacterial performance over a long period of time but also a synergistic effect can be expected for the improvement of antibacterial properties. Thus, the resin composition according to the embodiment of the present invention can improve antibacterial performance in the form of a resin composition, a composition for a molded product, or a composition for a paint.

[0058] <Coating composition for paints> Colored metal pigments containing metals such as Au, Pt, Pd, Ag, Cu, and Ni are used as coating compositions for paints having an excellent metallic feeling in design. Among them, metal nanoparticles or composite metal nanoparticles containing Au, Ag, Cu, Ni, etc. have been studied as coloring materials based on surface plasmon resonance. However, paints containing metal nanoparticles as coloring materials have a problem that color unevenness is likely to occur due to aggregation of the metal nanoparticles. In addition, metal nanoparticles such as Ag, Cu, and Ni are likely to fade due to oxidation, moisture absorption, etc., and there is also a problem that the design property deteriorates over time.

[0059] The composite metal nanoparticle carrier according to an embodiment of the present invention may be used as a colorant or a colored pigment contained in a coating composition by being blended into paints, inks, etc. to solve the above problems. The coating composition includes, for example, paints and their coatings, or inks and their printed matters. As the paint and the ink, either an organic solvent type or an aqueous type can be adopted. However, in the case of an aqueous paint or an aqueous ink, since improving light resistance and weather resistance is an important technical issue, the composite metal nanoparticle carrier is particularly effective when blended into an aqueous paint or an aqueous ink.

[0060] The composite metal nanoparticle carrier in the coating composition is blended within the range of 0.1 to 30% by mass of the coating composition. When the blending amount is 0.1% by mass or more, the decorative effect such as a metallic effect is good, and when it is 30% by mass or less, the weather resistance, corrosion resistance, mechanical strength, etc. of the coating composition are good. Furthermore, it is more preferable that the blending amount of the composite metal nanoparticle carrier in the coating composition is within the range of 1 to 20% by mass of the coating composition. The coating composition is obtained by appropriately blending a paint resin with the composite metal nanoparticle carrier. Examples of the paint resin include an acrylic resin, an alkyd resin, a polyester resin, a polyurethane resin, a polyvinyl acetate resin, a nitrocellulose resin, a fluororesin, etc.

[0061] In addition to the composite metal nanoparticle carrier and the coating resin, another coloring pigment, extender pigment, or dye may be used in combination in the coating composition. Examples of the coloring pigment used in combination include phthalocyanine, quinacridone, isoindolinone, perylene, azo lake, iron oxide, lead yellow, carbon black, titanium oxide, pearl mica, and the like. Further, in addition to the above components, water and an organic solvent may be blended as additives in the coating composition, and if necessary, a surfactant, a curing agent, an ultraviolet absorber, an antistatic agent, a thickener, etc. may also be appropriately blended. When forming a coating film using the coating composition, the coating film may be formed on an undercoat layer or an intermediate coat layer by electrodeposition coating or the like, and in the coating composition according to the embodiment of the present invention, a top coat layer may be further formed on the formed coating film.

[0062] The composite metal nanoparticle carrier according to the embodiment of the present invention has good dispersibility not only in solvents such as water or organic solvents but also in resins, and no aggregation or segregation is observed. Therefore, as the composite metal nanoparticles, for example, combinations of two types such as Ag / Au, Cu / Au, Ni / Au, Ag / Pt, Cu / Pt, Ni / Pt, Ag / Pd, Cu / Pd, Ni / Pd, or combinations of at least two or more of Ag, Cu, and Ni with any one of Au, Pt, or Pd are adopted. Since the effect of suppressing oxidation and moisture resistance of Ag, Cu, or Ni used as the first metal is obtained by the plating coating layer of Au, Pt, or Pd used as the second metal, not only the colorability is maintained over a long period of time, but also another effect of being able to produce various colors can be obtained.

[0063] <Coating Composition for Glass or Ceramics> As disclosed in Non-Patent Document 1, it has been proposed to add silica in which Ag nanoparticles are dispersed as a yellow coloring material to a lead-free frit (glass flux) and bake it on a ceramic plate for use as overglaze (glass). Further, Non-Patent Document 1 describes that when mixing with a glass flux in the form of metal nanoparticles, it is necessary to suppress the aggregation of the metal nanoparticles in order to maintain the coloring function. Since the composite metal nanoparticle carrier according to the embodiment of the present invention is previously supported on an electrically insulating carrier such as silica in order to suppress the aggregation of the composite metal nanoparticles, it is possible to solve the technical problem that the composite metal nanoparticles aggregate in the coating composition.

[0064] Further, as the composite metal nanoparticle carrier, for example, a carrier in which a part of the surface of Ag nanoparticles, which are the first metal, is coated with a plating layer of Au, which is a second metal that is inert to oxidation, suppresses the oxidation of Ag nanoparticles in a high-temperature atmosphere when baking a coating composition containing the same. Thereby, not only is the discoloration due to the oxidation of the Ag nanoparticles suppressed, but also since the Au plating layer is thin, the yellow coloring property by the Ag nanoparticles is sufficiently ensured. On the other hand, when the entire circumference of the surface of the Ag nanoparticles is coated with the Au plating layer, the color can also be changed to red due to Au or orange, which is a mixed color of Ag and Au, depending on the surface coverage ratio of the Au plating layer.

[0065] The combination of the first metal and the second metal is not limited to Ag / Au. For example, metals used when coloring glass with metal elements, such as Cu, Co, Ni, Fe, etc., can also be used as nanoparticles composed of the first metal. Nanoparticles such as Cu, Co, Ni, Fe, etc. may be used in the form of metal oxides by adjusting the surface coverage range by a plating layer composed of a second metal such as Au. In that case, it can be used as a coating composition for forming an overglaze layer that exhibits the unique coloring of the oxide of each metal.

[0066] As the glass frit, for example, those mainly composed of SiO2, B2O3, and Al2O, and optionally containing metal oxides selected from the group of R2O (alkali metal oxides including at least Li2O among Li2O, Na2O, and K2O), CaO, MgO, Zr2O, and ZnO, are each selected and used according to components suitable for a desired fired overpainting. These metal oxides are melted at a high temperature of 1000 °C or higher for a predetermined time and then ground to a predetermined particle size using a dry or wet grinder. The ground glass flux is mixed with the composite metal nanoparticle carrier, which is a coloring pigment, and further mixed with an organic material and, if necessary, a thermal expansion coefficient adjusting material to prepare a coating composition. The coating composition thus prepared is applied to glass or porcelain in directions such as direct painting with a brush, direct screen printing, or transfer (indirect screen printing), and then fired at a temperature of 700 °C or higher for painting. Thereby, an overpaint layer fused to the glaze layer applied to the surface of the glass or porcelain is formed.

[0067] Instead of the glass flux composed of a plurality of the above metal oxides, polysilazane used as a glass coating agent may be used for the coating composition. Polysilazane has silicon, nitrogen, an active hydrogen group, and a chemical reaction group, and is a kind of silane compound represented by the chemical structure of [-Si-N-H]n. A liquid composition prepared by mixing the composite metal nanoparticle carrier and an organic solvent is used as the coating composition. The coating composition is applied to the surface of glass or porcelain by methods such as dipping, bar coating with an applicator, brush painting, spray coating, or flow coating, and then dried at a temperature of 100 °C or higher to form a glassy film of SiO2 that exhibits coloring as an overpaint layer on their surfaces.

[0068] The coating composition may contain metal oxides composed of other metals such as Cr, Co, Cu, Mn, and Fe in addition to the composite metal nanoparticle carrier as a colorant or coloring pigment.

Examples

[0069] The present invention will be described by way of examples, but the scope of the present invention is not limited to these examples.

[0070] [Example 1] The configuration, morphology, properties, and manufacturing method of AgAu nanoparticles supported on SiO2 particles (hereinafter also abbreviated as SiO2 / AgAu) as a composite nanoparticle carrier will be described. <Fabrication of SiO2 Particles> First, SiO2 particles, which are electrically insulating carriers, were fabricated as follows. Water (H2O) was added to ethyl alcohol maintained at a liquid temperature of 35°C and stirred for 5 minutes, and then a tetraethoxysilane (TEOS) solution, which is an organic silane compound as a SiO2 source, was added. After stirring for 5 minutes, an aqueous NH4OH solution as a base catalyst was added and stirred for 5 hours. Thereafter, a SiO2 particle colloidal solution was prepared by performing centrifugal washing at a centrifugal force of 1000 rpm. In the SiO2 particle colloidal solution, the concentrations of TEOS and NH4OH in the solution were 0.2 mol and 0.5 mol, respectively. The average particle diameter and particle size dispersion of the SiO2 particles in the SiO2 particle solution thus fabricated were determined from a TEM image observed at an acceleration voltage of 200 kV using a transmission electron microscope (TEM) [manufactured by JEOL Ltd.: JEM-2100]. The sample for TEM observation was prepared by directly dropping the fabricated SiO2 particle colloidal solution onto a collodion film-attached mesh, allowing it to dry naturally, and then performing vacuum drying. In the measured TEM observation image, the diameter of one SiO2 particle was determined as the equivalent circle diameter, and image analysis was performed for 50 to 100 SiO2 particles. As a result of the image analysis, the average particle diameter and particle size dispersion of the SiO2 particles were 92.5 nm and 7.91%, respectively.

[0071] Using the SiO2 particle colloidal solution obtained by the above method, SiO2 / Ag nanoparticles were fabricated by an electroless plating pretreatment method according to the method shown in FIG. 3, and then a composite nanoparticle carrier of SiO2 / AgAu in which at least a part of the surface of the SiO2 / Ag nanoparticles was replaced by Au was fabricated by an electroless plating method.

[0072] <Fabrication of SiO2 / Ag nanoparticles by electroless plating method> As shown in the upper part of Fig. 3, a SiO2 particle colloidal solution was added to pure water (H2O) set at a temperature of 35 °C and stirred for 5 minutes. To this solution, H2O, acetic acid (CH3COOH), and stannous chloride (SnCl2) were added and mixed to prepare an SiO2 / Sn 2+ aqueous solution, which was further stirred for 45 minutes to produce a solution containing SiO2 particles whose surface was modified with Sn 2+ (hereinafter abbreviated as SiO2 Sn2+ colloidal solution). Subsequently, the SiO2 Sn2+ colloidal solution was centrifugally washed (centrifugation speed: 1000 rpm, centrifugation time: 30 minutes × 2 times), and then, while maintaining the SiO2 Sn2+ colloidal solution at a temperature of 35 °C, [Ag(NH3)2] + aq. was added and stirred for 5 minutes. Here, [Ag(NH3)2] + aq. prepared by previously mixing H2O, silver nitrate (AgNO3), and aqueous ammonium hydroxide (NH4OH aq.) was used. Here, the concentration of Ag Sn2+ in the SiO2 + colloidal solution was adjusted so that it would be 1.0×10 Sn2+ mol with respect to 25 mL of the SiO2 -3 colloidal solution by adjusting the addition amount of [Ag(NH3)2] + aq. Thereafter, the SiO2 Sn2+ colloidal solution was centrifugally washed (centrifugation speed: 1000 rpm, centrifugation time: 30 minutes × 3 times) to produce an SiO2 / Ag nanoparticle colloidal solution in which Ag nanoparticles were supported on SiO2 particles. Thus, in Example 1, an SiO2 / Ag nanoparticle colloidal solution was prepared by the pretreatment method of electroless plating.

[0073] <Fabrication of SiO2 / AgAu nanoparticles by electroless plating method> The preparation procedure of the SiO2 / AgAu nanoparticle colloidal solution is shown in the lower part of Fig. 3. While maintaining the SiO2 / Ag colloidal solution obtained by the above method at a temperature of 2°C, H2O and an Au plating solution were added to the solution and stirred for 24 hours. Here, the Au plating solution was prepared by mixing H2O, sodium bicarbonate (NaHCO3), sodium sulfite (Na2SO3), an aqueous solution of chloroauric acid (HAuCl4), and a formaldehyde solution (HCHO). The addition amount in the Au plating solution was adjusted so that the concentration of Au ions in the Au plating solution was in a ratio of 10% by elemental ratio to the concentration of Ag + (1.0×10 -3 mol) in the SiO2 / Ag nanoparticle colloidal solution. As will be described in Examples 2 and 3 below, when increasing the concentration of Au ions in the SiO2 / AgAu nanoparticle colloidal solution, while keeping the total addition amount of H2O and the Au plating solution constant, the addition amount of the Au plating solution was increased, and instead, the addition amount of H2O was decreased.

[0074] Thereafter, by performing centrifugal washing (centrifugal speed: 1000 rpm, centrifugal time: 30 minutes × 2 times), a SiO2 / AgAu nanoparticle colloidal solution in which AgAu nanoparticles were supported on SiO2 particles was prepared.

[0075] [Example 2] In the method shown in Fig. 3, except that the addition amount of the Au plating solution was adjusted so that the concentration of Au ions in the Au plating solution was in a ratio of 20% by elemental ratio to the concentration of Ag + (1.0×10 -3 mol) in the SiO2 / Ag nanoparticle colloidal solution, SiO2 / AgAu nanoparticles were prepared in the same manner as in Example 1 above. In this Example 2, while keeping the total addition amount of Si2O and the Au plating solution constant when adding to the SiO2 / Ag colloidal solution, the addition amount of H2O was decreased, and the addition amount of the Au plating solution was increased to twice that of Example 1, so that the concentration of Au ions was adjusted to be 20% by elemental ratio to the concentration of Ag + in the SiO2 / Ag nanoparticle colloidal solution.

[0076] [Example 3] In the method shown in Fig. 3, except that the concentration of Au ions in the Au plating solution was adjusted to be 30% of the designed value with respect to the concentration of Ag (1.0×10 + mol) contained in the SiO2 / Ag nanoparticle colloidal solution, SiO2 / AgAu nanoparticles were prepared in the same manner as in Example 1 above. In Example 3, while keeping the total addition amount of Si2O and the Au plating solution constant when adding to the SiO2 / Ag nanoparticle colloidal solution, the addition amount of H2O was reduced, and the addition amount of the Au plating solution was increased by 3 times compared to Example 1, so that the concentration of Au ions was Ag contained in the SiO2 / Ag nanoparticle colloidal solution -3 The element ratio was adjusted to be 30% with respect to the concentration of. +

[0077] In addition, in order to compare the form of the metal nanoparticles and the properties exhibited as metal nanoparticles with SiO2 / AgAu nanoparticles, Ag nanoparticles were prepared by the following method.

[0078] [Comparative Example 1] To H2O at 35°C, tetrakis(hydroxymethyl)phosphonium chloride (THPC: 80 mass% reagent manufactured by Tokyo Kako Co., Ltd.), a commercially available reagent as a reducing agent, was added and stirred for 5 minutes, and then an aqueous silver nitrate solution (AgNO3aq.) was added as an Ag source. Thereafter, the mixture was stirred for 30 minutes to react to prepare an Ag nanoparticle colloidal solution.

[0079] [Measurement of the form of metal nanoparticles and the properties exhibited as metal nanoparticles] Regarding the SiO2 / Ag nanoparticle colloidal solution and SiO2 / AgAu nanoparticle colloidal solution prepared in Examples 1 to 3 above, and the Ag nanoparticle colloidal solution prepared in Comparative Example 1, the structure, form, properties of each metal nanoparticle contained in each colloidal solution, and the properties they exhibit were measured by the following method.

[0080] (1) Transmission electron microscope (TEM) observation image ​Transmission electron microscopy (TEM) observations were performed on the SiO2 / AgAu nanoparticles, SiO2 / Ag nanoparticles, and Ag nanoparticles contained in each colloidal solution. For the TEM observations, a transmission electron microscope (TEM) (manufactured by JEOL Ltd., JEM-2100) was used. Samples for TEM observations were prepared by directly dropping each of the above colloidal solutions onto a collodion film-attached mesh (manufactured by Nisshin Co., Ltd., Cat. No. 6511, 200 mesh), allowing them to dry naturally, and then performing vacuum drying.

[0081] (2) Average particle size and particle size dispersion of metal nanoparticles From the TEM observation images of the SiO2 / AgAu nanoparticles and SiO2 / Ag nanoparticles contained in each colloidal solution, the average particle size and particle size dispersion of the SiO2 particles, AgAu nanoparticles supported on SiO2, and Ag nanoparticles supported on SiO2 were determined, respectively. The average particle size and particle size dispersion were calculated by extracting 50 to 100 metal nanoparticles from the TEM image and performing image analysis, assuming that the diameter of each individual particle observed as a TEM image was the equivalent circle diameter [√(projected area / π)]. Here, the particle size dispersion is a physical quantity defined as (standard deviation of particle size) / (average particle size) × 100.

[0082] (3) Measurement of Ag and Au concentrations in the SiO2 / AgAu nanoparticle colloidal solution The concentrations of Ag and Au contained in the SiO2 / AgAu nanoparticle colloidal solutions prepared in Examples 1 to 3 were determined by high-frequency inductively coupled (ICP) emission analysis. To 1 mL of each prepared colloidal solution, 3 mL of aqua regia was added, and after standing for 2 hours, 6 mL of H2O was added to prepare a sample for ICP measurement. The concentrations of Ag and Au in each of the thus-prepared colloids were measured using an ICP-AES apparatus (manufactured by Shimadzu Corporation, ICPS-7510), and each concentration was calculated by the calibration curve method. The wavelengths of the emission to be measured were λ = 328.2 nm for Ag and λ = 242.8 nm for Au.

[0083] (4) Analysis of the crystal structure of metal nanoparticles Regarding the SiO2 / AgAu nanoparticles and SiO2 / Ag nanoparticles contained in each colloidal solution, the crystal structures of the Ag nanoparticles and AgAu nanoparticles supported on the SiO2 particles were measured by an X-ray diffractometer (XRD: Rigaku Corporation, Ultima IV) to analyze the crystal structures of the respective metal nanoparticles.

[0084] For the XRD measurement samples, each particle colloidal solution was centrifugally washed (centrifugal speed: 1000 rpm, centrifugal time: 30 minutes), and the powder after vacuum drying was used. The measurement voltage and current for ADR were 10 kV and 20 mA, respectively. Also, depth detection was performed using a high-speed etching ion gun (acceleration voltage: 500X). The measurement peaks were analyzed by curve fitting using APSPEAK41 software.

[0085] (5) Identification of Chemical Species and Their Bonds on the Surface of Metal Nanoparticles Regarding the SiO2 / AgAu nanoparticles, SiO2 / Ag nanoparticles, and Ag nanoparticles contained in each colloidal solution, the chemical species and their bonds on the surface of the respective metal nanoparticles were identified by measuring the Ag nanoparticles and AgAu nanoparticles supported on the SiO2 particles, as well as the Ag nanoparticles, using an X-ray photoelectron spectrometer (XPS: JEOL Ltd., JPS-9010).

[0086] For the XPS measurement samples, the particle colloidal solution after ultrasonic irradiation was centrifugally washed (centrifugal speed: 1000 rpm, centrifugal time: 30 minutes), and the powder after vacuum drying was used. The output of XPS was set to 1.2 kW, CuKα1 line was used, and the measurement angle (2θ) was set to 10 - 80 or 60 - 70 deg for measurement. A slit of 1 / 2 deg was used, and the scan speed was 1 or 2 deg / min. The calculation of the crystallite size was performed assuming that the metal particles were completely crystallized.

[0087] (6) Oxidation Resistance of Metal Nanoparticles The oxidation resistance of the SiO2 / AgAu nanoparticles obtained in Example 3 and the Ag nanoparticles obtained in Comparative Example 1 was evaluated by measuring the extinction spectra of the respective metal nanoparticles. For the measurement of the extinction spectra of each colloidal solution, a UV-visible near-infrared spectrophotometer (UV-vis; UV-310PC manufactured by Shimadzu Corporation) was used. The measurement was performed using a measurement sample in which about 3 mL of each colloid was injected into a 1 cm square cell made of quartz.

[0088] TEM images observed for the SiO2 / AgAu nanoparticles (Au nanoparticles supported on carrier SiO2 particles) prepared during the production process in Example 1 and the SiO2 / AgAu nanoparticles (AgAu nanoparticles supported on carrier SiO2 particles) obtained in Examples 1 to 3 are shown in Fig. 4. In Fig. 4, (a) is a TEM image of the SiO2 / Ag nanoparticles, and (b) to (d) are TEM images of the SiO2 / AgAu nanoparticles obtained in Examples 1 to 3, respectively. Also, on the right side of each of the figures in Fig. 4(a) to (d), the average particle size of the Ag nanoparticles or AgAu nanoparticles is shown together.

[0089] As shown in Fig. 4, it can be seen that the average particle size of the AgAu nanoparticles in which at least a part of the surface of the Ag nanoparticles supported on the SiO2 particles is replaced by Au increases due to the replacement of Ag by Au. On the other hand, as shown in Fig. 4(b) to (d), until the [Au] / [Ag] (element ratio) of Au to Ag calculated as a design value from the Au ion concentration contained in the solution obtained by combining the above H2O and the Au plating solution reaches 10% to 20%, the number of AgAu nanoparticles supported per SiO2 particle tends to increase, but no significant difference was observed between 20% and 30%. Also, the average particle size of the AgAu nanoparticles hardly changed even when the Au ion concentration was increased from 10% to 30%. Thus, it can be seen that the AgAu nanoparticles do not increase in particle size by increasing the Au ion concentration (design value), and the coverage range (coverage rate) of the surface of the nanoparticles by Au increases.

[0090] To verify the considerations derived from the morphology and average particle size of the AgAu nanoparticles shown in Fig. 4, the chemical species and their bonds on the surfaces of the Ag nanoparticles and AgAu nanoparticles supported on SiO2 particles were identified by XPS measurement. At the same time, the concentrations of Ag and Au contained in the SiO2 / AgAu nanoparticle colloidal solution were determined by high-frequency inductively coupled (ICP) emission analysis.

[0091] Fig. 5 shows the measurement results by XPS of the Ag nanoparticles and AgAu nanoparticles supported on SiO2 particles. For the Ag nanoparticles, only peaks at 374.5 eV and 368.5 eV derived from Ag were observed. On the other hand, for the AgAu nanoparticles, in addition to the above-mentioned peaks derived from Ag, peaks at 374.5 eV and 368.5 eV derived from Au were observed. As a result, the complexation of Ag and Au was confirmed in the AgAu nanoparticles.

[0092] From the results shown in Fig. 5, it was confirmed that the AgAu nanoparticles were complexed with Ag and Au. Furthermore, in the XDR measurement, the analysis was advanced by narrowing the measurement angle of 2θ to a narrow range of 62 to 68°. For the SiO2 / AgAu nanoparticles, as the [Au] / [Ag] (element ratio) increased, peaks were observed at 2θ = 64.54° and 64.62°, which shifted to the higher angle side from 2θ = 64, 48° of the Ag powder and 2θ = 64.41° of the (220) plane of Ag. This is considered that the crystal structure changed due to the intrusion of Au atoms between Ag atoms by the complexation of Au, and the peak shifted to the (64, 68°) side derived from the (220) plane of Au. Since this phenomenon was promoted with the increase in the Au concentration, it is considered that the alloying of Ag and Au was suggested. Thus, it was confirmed that the SiO2 / AgAu nanoparticles had a form in which the surface of the Ag nanoparticles was coated with Au.

[0093] From the XPS measurement results shown in Fig. 5, the elemental ratio of Au to Ag ([Au] / [Ag]) can also be determined simultaneously. Therefore, a comparison was made with [Au] / [Ag] calculated from the Ag concentration and Au concentration determined by high-frequency inductively coupled (ICP) emission analysis of the SiO2 / AgAu nanoparticle colloidal solution. These results are shown in Table 1 below together with [Au] / [Ag] calculated as a design value from the Au ion concentration in the solution obtained by combining the above-mentioned H2O and the Au plating solution.

[0094]

Table 1

[0095] As shown in Table 1 above, the [Au] / [Ag] (elemental ratio) of the AgAu nanoparticles calculated from the XPS measurement results is larger than the [Au] / [Ag] (elemental ratio) calculated as a design value from the Au ion concentration in the solution obtained by combining the above-mentioned H2O and the Au plating solution. From this, it can be seen that Au is distributed more on the Ag surface. Also, it can be seen that the [Au] / [Ag] (elemental ratio) calculated from the charged concentration and the [Au] / [Ag] (elemental ratio) calculated from the ICP measurement results or the [Au] / [Ag] (elemental ratio) measured by XPS are almost in a proportional relationship. Thus, it was confirmed that in Examples 1 to 3, the coverage range and elemental concentration of Au on the surface of the Ag nanoparticles of the SiO2-supported AgAu nanoparticles were determined almost as designed by the Au ion concentration contained in the Au plating solution used.

[0096] Next, nitric acid was added to the Ag nanoparticle colloidal solution of Comparative Example 1, a 5-fold diluted solution of the SiO2 / Ag nanoparticle colloidal solution obtained during the production process in Example 3 (the same as the SiO2 / Ag nanoparticle colloidal solution obtained during the production process in Example 1), and a 5-fold diluted solution of the SiO2 / AgAu nanoparticle colloidal solution prepared in Example 3, and then the time-dependent changes in the aggregation state and oxidation degree of each metal nanoparticle were examined by performing elapsed-time observation to accelerate oxidation. Here, for the above-mentioned SiO2 / Ag nanoparticle colloidal solution and SiO2 / AgAu nanoparticle colloidal solution, 5-fold dilution was performed to improve the measurement accuracy.

[0097] Fig. 6 shows TEM observation images of each metal nanoparticle, and on the right side thereof, the aggregation state of each metal nanoparticle is schematically shown. Fig. 7 shows the extinction spectra measured using the colloidal solution containing the SiO2 carrier supporting each metal nanoparticle. In Fig. 6 and Fig. 7, "before addition" represents the state before nitric acid addition, and "0 day", "1 day", "3 days", and "23 days" represent the states after the respective elapsed days after nitric acid addition.

[0098] As can be seen from Fig. 6(a), aggregation of the Ag nanoparticles had already occurred before nitric acid addition. On the other hand, aggregation of each metal particle was not observed in the SiO2 / Ag nanoparticles and SiO2 / AgAu nanoparticles not only before nitric acid addition but also during long-term storage after sulfuric acid addition (see (b) and (c) of Fig. 6). It can be understood that the SiO2 carrier supporting the Ag nanoparticles and AuAu nanoparticles functions as an aggregation inhibitor for the metal nanoparticles.

[0099] In the extinction spectrum shown in Fig. 7, in Fig. 7(a), an absorption peak around 400 nm due to Ag was observed before the addition of nitric acid. It can be seen that this absorption peak around 400 nm decreased significantly in a short time of less than one day after the addition of nitric acid. As can be seen from Fig. 6(a), the significant decrease in the absorption peak around 400 nm is due to the aggregation of Ag nanoparticles. That is, due to the aggregation of Ag nanoparticles, surface plasmon resonance is less likely to occur, resulting in a significant decrease in the absorption intensity. Therefore, it can be seen that the significant decrease in the absorption peak around 400 nm is not affected by the oxidation caused by the addition of nitric acid.

[0100] Also, in the extinction spectrum shown in Fig. 7(b), an absorption peak around 400 nm due to Ag was observed before the addition of nitric acid and immediately after the addition of nitric acid (0 day). However, one day after the addition of nitric acid (1 day), the absorption peak around 400 nm decreased significantly, and no absorption peak was observed three days after (3 days). Thus, in the SiO2 / Ag nanoparticle colloidal solution, although the aggregation of Ag nanoparticles was suppressed by loading on SiO2 particles, it can be seen that the oxidation caused by the addition of nitric acid had a great influence.

[0101] On the other hand, in the SiO2 / AgAu nanoparticle colloidal solution, as shown in Fig. 7(c), the absorption peak around 400 nm shifted to the long wavelength side around 460 nm, and a blue shift of the wavelength showing the maximum of the absorption peak was observed. This is due to the formation of a Au plating layer on the surface of the supported Ag nanoparticles and the growth of nanoparticles due to Au composite. Also, for SiO2 / AgAu nanoparticles, the absorption peak around 460 nm decreases with the passage of time after the addition of nitric acid, but this absorption peak was still observed even after a long period of 23 days (23 days). Thus, it can be seen that SiO2 / AgAu nanoparticles not only suppressed the aggregation of AgAu nanoparticles by loading on SiO2 particles, but also obtained a great effect on oxidation suppression by complexation with Au.

[0102] When applying the SiO2 / AgAu nanoparticles obtained in Examples 1 to 3 as components contained in, for example, an antibacterial composition, they have good dispersibility not only in solvents such as water or organic solvents but also in resins, and no aggregation or segregation is observed. Furthermore, since the Au plating coating layer of the second metal has good oxidation resistance, almost no deterioration in the properties and performance as an antibacterial agent is observed. In normal use, which is not an extreme oxidation atmosphere such as the addition of nitric acid, not only can the antibacterial performance be maintained over a long period, but also a synergistic effect between Ag and Au can be obtained for improving antibacterial properties.

[0103] Also, as another use, when applied as a colorant or coloring pigment contained in a coating composition for paints, it can solve the problems of color unevenness that is likely to occur due to aggregation of Ag nanoparticles and discoloration caused by oxidation, moisture absorption, etc. Therefore, it is used as a coating composition for paints having an excellent metallic feeling and design property.

[0104] Furthermore, as another use, when applied as a colorant or coloring pigment contained in a coating composition for glass or ceramics, since the aggregation of AgAu nanoparticles in the glass frit is suppressed, the coloring function is sufficiently maintained. Also, the AgAu nanoparticle carrier coated with an Au plating layer that is inert to oxidation suppresses the oxidation of Ag nanoparticles in a high-temperature atmosphere when firing the coating composition containing it. Therefore, it is effective against the problem of discoloration due to oxidation.

[0105] In addition, the SiO2 / AgAu nanoparticles prepared in Examples 1 to 3 have an [Au] / [Ag] (element ratio) of AgAu nanoparticles up to 30%. However, in the embodiments of the present invention, this value can be further increased and brought closer to 100%. Thereby, SiO2 / AgAu nanoparticles in which the entire circumference of the surface of the AgAu nanoparticles is coated with Au may be prepared. In that case, not only can a significant improvement in oxidation resistance be achieved, but also the color can be changed from yellow caused by Ag to red caused by Au due to a blue shift in the wavelength showing the maximum of the absorption peak. Also, the color can be changed to orange, which is a mixed color of Ag and Au, according to the surface coating range (surface coating rate) of the Au plating layer.

[0106] [Example 4] SiO2 / AgAu nanoparticles were prepared in the same manner as in Example 1, except that the preparation of the SiO2 / Ag nanoparticles in Example 1 was carried out by a silver mirror reaction instead of the electroless plating method. The SiO2 / Ag nanoparticles by the silver mirror reaction were prepared by the following method.

[0107] [Preparation of SiO2 / Ag Nanoparticles by Silver Mirror Reaction] The SiO2 particle colloidal solution was added to pure water (H2O) set at a temperature of 35 °C and stirred for 5 minutes. An aqueous ammonium silver ion solution [Ag(NH3)2] aq. prepared by adding H2O, aqueous ammonium hydroxide solution (NH4OH aq.) and silver nitrate (AgNO3) to the solution was added, and the mixture was stirred for 15 minutes to modify the surface of the SiO2 particles with Ag. + to obtain a SiO2 / Ag colloidal solution modified with Ag. + colloidal solution. + This SiO2 / Ag + colloidal solution was centrifugally washed (centrifugation speed: 1000 rpm, centrifugation time: 30 minutes × 2 times), and then 1% diluted formaldehyde solution (HCHO) was added to the SiO2 / Ag + colloidal solution and stirred for 30 minutes. Thereafter, centrifugal washing (centrifugation speed: 1000 rpm, centrifugation time: 30 minutes × 3 times) was carried out to prepare a SiO2 / Ag nanoparticle colloidal solution in which Ag nanoparticles were supported on SiO2 particles.

[0108] [Preparation of SiO2 / AgAu Nanoparticles by Electroless Plating Method] Using the thus obtained SiO2 / Ag nanoparticle colloidal solution, SiO2 / AgAu nanoparticles were prepared by the same substitution electroless plating method as in Example 1. For the SiO2 / AgAu nanoparticles contained in the SiO2 / AgAu nanoparticle colloidal solution, transmission electron microscope (TEM) observation was carried out in the same manner as in Example 1.

[0109] From the observed TEM images, the presence of particles of about 4 nm supported on SiO2 was confirmed. The average particle size and degree of dispersion of the SiO2 / AgAu nanoparticles determined from the observed TEM images were 4.2 nm and 19.2, respectively. These were presumed to be Ag nanoparticles or AgAu nanoparticles, but on the other hand, aggregates of the particles were also observed simultaneously. It was presumed that these aggregates were formed by the particles grown by adding an Au source during electroless plating of Au being peeled off and aggregated by the stress of water during stirring. That is, it was found that the Ag nanoparticles supported on the SiO2 particles by the silver mirror reaction were not strongly bonded to the surface of the SiO2 particles. When the Au ion concentration in the Au plating solution was increased to the same level as in Examples 2 and 3, these aggregates were observed in the form of larger grown particle aggregates. Thus, in the preparation of SiO2 / AgAu nanoparticles using the silver mirror reaction, it was found that the adhesion of the Ag nanoparticles supported on the SiO2 particles (the supportability of the Ag nanoparticles to the SiO2 particles) was inferior compared to those prepared in Examples 1 to 3. When preparing Ag nanoparticles supported on SiO2 particles using the silver mirror reaction, a method for improving the adhesion of the Ag nanoparticles may be adopted, such as surface modification of the SiO2 particles or heat treatment after supporting the Ag nanoparticles.

[0110] [Example 5] As described above, the particle shape and aggregation state of the AgAu nanoparticle support supported on the surface of the SiO2 support are affected by the composition of the electroless plating solution containing Au ions (Au salt) and plating conditions such as the plating temperature. Therefore, as physical quantities that can grasp the particle shape and aggregation state of the SiO2 / AgAu nanoparticle support, attention was paid to the number average particle size (Dn) and volume average particle size (Dv) of the metal nanoparticle support determined by dynamic light scattering (DLS) measurement of the plating solution containing the SiO2 / AgAu nanoparticle support obtained as a colloidal dispersion after electroless plating. In this example, regarding the following three factors (A), (B), and (C) among the constituent components and production conditions of the Au plating solution, the Dn and Dv of the colloidal dispersion after electroless plating of Au were determined, respectively, and the relationship between Dn and Dv for optimizing the electroless plating solution and plating conditions was clarified.

[0111] (A) Influence of Au concentration in the Au plating solution: Comparison when using the colloidal dispersion after electroless plating prepared in Examples 1 to 3 above. (B) Influence of Na2SO3 concentration in the Au plating solution: In Example 2 above, when the Na2SO3 concentration contained in the Au plating solution was set as X (mol), and the Na2SO3 concentration was increased to 7×X (mol) and 13×X (mol), which are 7 times and 13 times of X mol respectively, for comparison. (C) Influence of reaction temperature of Au electroless plating: In Example 2 above, when the reaction temperature of Au electroless plating was set as 2°C, and further increased to 35°C for comparison.

[0112] The Dn and Dv of the plating solution containing the SiO2 / AgAu nanoparticle carrier obtained as a colloidal dispersion after electroless plating were determined as follows by dynamic light scattering (DLS) measurement. The particle size distribution of the metal nanoparticles was measured using a Zeta potential meter (manufactured by Malvern, Zetasizer nano ZS90), and Dn and Dv were obtained by analyzing from the particle size distribution curve. Also, assuming that the average particle diameter (D0) of the SiO2 particles described later is a constant value, it was obtained by performing image analysis of the TEM image in the same method as in Example 1 above. In this example, a value of 92.5 nm was used as the average particle diameter (D0) of the SiO2 particles.

[0113] (A) Influence of Au concentration in the Au plating solution The measured values of Dn and Dv when changing the Au concentration in the Au plating solution are shown in Table 2 below. Table 2 below shows the relationship between Dn / D0 and Dv / Dn, together with the presence or absence of aggregation of the AgAu nanoparticle carrier or AgAu nanoparticles alone. Dn / D0 is a parameter defined to grasp that the number average particle diameter Dn of various particles contained in the colloidal dispersion after electroless plating does not deviate significantly from the average particle diameter D0 of the carrier having the largest particle diameter. Also, Dv / Dn is a parameter uniquely defined in the present invention as a scale for grasping the particle size distribution of the AgAu nanoparticle carrier, and Dv / Dn = 1 is the ideal value when all particle diameters can be represented by one value.

[0114] [Table 2]

[0115] As can be seen from Table 2 above, the change in the Au concentration in the Au plating solution has little effect on the presence or absence of aggregation of the AgAu nanoparticle carriers or AgAu nanoparticles alone. No aggregation of these nanoparticles was observed within the range of Au concentrations examined. Furthermore, even when the Au concentration in the Au plating solution was increased to the extent that the entire circumference of the surface of the AgAu nanoparticles was covered by the Au plating layer, considering the trends of Dn / D0 and Dv / Dn shown in Table 2 above, it was predicted that no aggregates of metal nanoparticles would be observed.

[0116] (B) Influence of Na2SO3 Concentration in Au Plating Solution The measured values of Dn and Dv when the Na2SO3 concentration in the Au plating solution was changed are shown in Table 3 below. Table 3 below shows the relationship between Dn / D0 and Dv / Dn, together with the presence or absence of aggregation of the metal nanoparticles.

[0117] [Table 3]

[0118] The Na2SO3 concentration in the Au plating solution has a great influence on the change in the ionic strength in the Au plating solution. As can be seen from Table 3 above, when the Na2SO3 concentration increases beyond the optimum value in Example 2, the ionic strength increases, so that AgAu nanoparticles alone come to exist in the plating solution. Furthermore, when the Na2SO3 concentration is the highest (Na2SO3 concentration = 13 × x mol), aggregation occurs between the SiO2 / AgAu nanoparticle carriers.

[0119] (C) Influence of Reaction Temperature of Electroless Au Plating The measured values of Dn and Dv when changing the reaction temperature of electroless Au plating are shown in Table 4 below. Table 4 below shows the relationship between Dn / D0 and Dv / Dn, along with the presence or absence of aggregation of metal nanoparticles.

[0120] [Table 4]

[0121] As can be seen from Table 4 above, when the reaction temperature was set to 35 °C, which is higher than that in Example 2, partial aggregation of AgAu nanoparticles supported on SiO2 was confirmed. This is considered to be due to the progress of the local plating reaction at a high reaction temperature, resulting in the detachment and aggregation of overgrown AgAu nanoparticles.

[0122] Based on the results in Tables 2 to 4 above, in order to optimize the components of the plating solution and the plating conditions so that a composite metal nanoparticle support with relatively uniform particle sizes can be stably and efficiently produced without particle aggregation, it is practical to set the condition that Dn does not deviate significantly from the average particle size D0 of the support so that Dn / D0 satisfies the following formula (1), and the range of Dv / Dn defined as a measure of the particle size distribution of the AgAu nanoparticle support satisfies the following formula (2). Also, the following formulas (1) and (2) may be used as parameters for managing the Au plating solution by performing an extraction inspection of the Au plating solution during the production of the SiO2 / Ag nanoparticle support. 0.5 < Dn / D0 < 1.0 (1) 1.0 < Dv / Dn < 1.6 (2)

[0123] As described above, the composite metal nanoparticle carrier according to the embodiment of the present invention suppresses aggregation of composite metal nanoparticles by supporting composite metal nanoparticles composed of the first and second metals on an electrically insulating carrier, and also reduces or eliminates damage such as oxidation, sulfidation, or moisture absorption, and the influence of hydrocarbon poisoning, by means of a second metal film that is inert to these influences. Further, as the composite metal nanoparticles, for example, a metal film made of an expensive second metal such as Au, Pt, Pd, etc. is formed on the surface of nanoparticles made of a relatively inexpensive first metal such as Ag, Ni, Cu, Co, Zn, Fe, etc., so that, compared with single metal nanoparticles made of these expensive noble metals, while having characteristics and functions equivalent to or higher than those of these single metal nanoparticles, resource saving of expensive noble metals may be achieved.

[0124] Furthermore, since the composite metal nanoparticle carrier according to the embodiment of the present invention has a core-shell structure of the first metal, the second metal, and the first metal and the second metal, not only the functions due to the characteristics of each metal element alone, but also the synergistic functions of multiple metals are possessed because the complexation (alloying) of multiple metals occurs at the interface of the core-shell structure. Thereby, improvement of various characteristics and function enhancement can be achieved compared with conventional metal nanoparticle carriers. For example, it is used as a colorant or a coloring pigment contained in an antibacterial composition or an inorganic or organic coating composition for improving various characteristics such as anti-fading. In the future, it is expected not only to improve respective characteristics and performances but also to impart new functions in the development of exhaust gas purification catalysts, organic synthesis catalysts, and electrodes of various batteries.

[0125] In addition, the method for manufacturing the composite metal nanoparticle carrier according to the embodiment of the present invention can easily manufacture the composite metal nanoparticle carrier by using a conventionally known electroless plating method.

Explanation of Reference Numerals

[0126] 1 ··· Composite metal nanoparticle carrier 2, 7 ··· AgAu nanoparticles 3 ··· Silica nanoparticles 4···Undissolved residual Ag nanoparticles 5···Ag nanoparticles 6···Electroless plating layer of Au

Claims

1. A composite metal nanoparticle carrier in which composite metal nanoparticles are supported on an electrically insulating carrier, wherein the first metal composed of a single metal or an alloy is the nanoparticles of the first metal supported on the electrically insulating carrier, and the electroless plating layer of the second metal in which a part of the nanoparticles of the first metal is replaced by the second metal by electroless plating, and the electroless plating layer of the second metal is formed on a part or the entire circumference of the surface of the composite metal nanoparticles, so that at least a part of the surface of the nanoparticles of the first metal is covered with the electroless plating layer of the second metal. A composite metal nanoparticle carrier characterized by having a structure.

2. The composite metal nanoparticles and nanoparticles containing at least one of the first metal, an oxide of the first metal, and a hydroxide of the first metal are supported on the electrically insulating carrier, nanoparticles containing at least one of the first metal, an oxide of the first metal, and a hydroxide of the first metal are supported at a location different from the location where the composite metal nanoparticles are supported on the surface of the electrically insulating carrier, and the particle size (D) of the composite metal nanoparticles and the particle size (d) of the nanoparticles containing at least one of the first metal, an oxide of the first metal, and a hydroxide of the first metal satisfy the relationship D > d. The composite metal nanoparticle carrier according to claim 1.

3. The composite metal nanoparticle carrier according to claim 1 or 2, wherein the nanoparticles of the first metal are metal nanoparticles supported on the electrically insulating carrier by electroless plating.

4. The first metal is any metal or alloy selected from the group consisting of Ag, Co, Cu, Fe, Zn, Ni, an alloy of Ag and Ni, and an alloy of Ag and Pd, and the second metal is any metal selected from the group consisting of Au, Pt, and Pd. The composite metal nanoparticle carrier according to claim 3, characterized in that

5. The composite metal nanoparticle carrier according to claim 4, wherein the electrically insulating carrier is a metal oxide, ceramics, or plastic having any shape selected from the group consisting of particulate, plate-like, and fibrous shapes.

6. The composite metal nanoparticle carrier according to claim 5, wherein the electrically insulating carrier is a metal oxide having a nanoparticle metal oxide or a nanoporous structure.

7. The composite metal nanoparticle complex according to claim 6, wherein the first and second metals are Ag and Au, Co and Pt, or Ni and Pt, respectively, and the electrically insulating carrier is a metal oxide of nanoparticles.

8. A method for manufacturing a composite metal nanoparticle carrier in which composite metal nanoparticles are supported on an electrically insulating carrier, a step of supporting first metal nanoparticles made of a single metal or an alloy on the electrically insulating carrier; using ions of a second metal different from the metal of the first metal nanoparticles, a part of the first metal contained in the first metal nanoparticles supported on the insulating carrier is replaced with the second metal by electroless plating to form an electroless plating layer of the second metal, and a method for manufacturing a composite metal nanoparticle carrier, wherein at least a part of the surface of the nanoparticles of the first metal is covered with the electroless plating layer of the second metal by forming the electroless plating layer of the second metal on a part or the entire circumference of the surface of the composite metal nanoparticles.

9. By changing the concentration of the second metal ions contained in the electroless plating solution used in the step of forming the electroless plating layer of the second metal, the coverage range of the electroless plating layer of the second metal formed on at least a part of the surface of the first metal nanoparticles and the elemental concentration of the second metal contained in the composite metal nanoparticles are each adjusted. The method for manufacturing a composite metal nanoparticle carrier according to claim 8.

10. The number average particle size (Dn) and volume average particle size (Dv) obtained by performing dynamic light scattering (DLS) measurement of the plating solution containing the composite metal nanoparticle carrier obtained as the colloidal dispersion after electroless plating, wherein the number average particle size (Dn) satisfies the following formula (1) with respect to the average particle size (D ０ ) and the electroless plating solution is prepared so that Dv / Dn satisfies the following formula (2), and the step of forming the electroless plating layer of the second metal is performed. The method for producing a composite metal nanoparticle carrier according to claim 9, characterized in that 0.5 < Dn / D ０ < 1.0 (1) 1.0 < Dv / Dn < 1.6 (2)

11. The method for manufacturing a composite metal nanoparticle carrier according to any one of claims 8 to 10, wherein the step of supporting the first metal nanoparticles made of a single metal or an alloy on the electrically insulating carrier is performed by an electroless plating method in which reduction of one or more metal ions constituting the first metal nanoparticles is performed in an electroless plating solution having the one or more metal ions.

12. The method for manufacturing a composite metal nanoparticle carrier according to claim 11, wherein the first metal is any metal or alloy selected from the group consisting of Ag, Co, Cu, Fe, Zn, Ni, an alloy of Ag and Ni, and an alloy of Ag and Pd, and the second metal is any metal selected from the group consisting of Au, Pt, and Pd.

13. The method for producing a composite metal nanoparticle carrier according to claim 12, wherein the electrically insulating carrier is a metal oxide, a ceramic, or a plastic having any shape selected from the group consisting of particulate, plate-like, and fibrous shapes.

14. The method for producing a composite metal nanoparticle carrier according to claim 13, wherein the electrically insulating carrier is a metal oxide of nanoparticles or a metal oxide having a nanoporous structure.

15. The method for producing a composite metal nanoparticle complex according to claim 14, wherein the first and second metals are Ag and Au, Co and Pt, or Ni and Pt, respectively, and the electrically insulating carrier is a metal oxide of nanoparticles.

16. An antibacterial composition containing a composite metal nanoparticle carrier, the composite metal nanoparticle carrier according to claim 1 or 2, and at least one of water or an organic solvent for dispersing the composite metal nanoparticle carrier and a binder resin for encapsulating the composite metal nanoparticle carrier. An antibacterial composition comprising the same.

17. A coating composition for paints containing a composite metal nanoparticle carrier as a colorant or a coloring pigment, the composite metal nanoparticle carrier according to claim 1 or 2, and at least one of water or an organic solvent for dispersing the composite metal nanoparticle carrier and a binder resin for encapsulating the composite metal nanoparticle carrier. A coating composition comprising the same.

18. A coating composition containing a composite metal nanoparticle carrier as a colorant or a coloring pigment for coloring the surface of a glass body or a ceramic, the composite metal nanoparticle carrier according to claim 1 or 2, and a glass flux or polysilazane composed of a plurality of metal oxides. A coating composition comprising the same.

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