JP2023069015A - Non-conductive metal composite material, and method for producing the same - Google Patents

Abstract

To provide a non-conductive metal composite material having a metal arranged with high density.SOLUTION: A method for producing a non-conductive metal composite disclosed herein includes: preparing a composition containing metal particles whose surface is at least partially coated with a non-conductive inorganic oxide; forming or applying the composition to a predetermined base material; and sintering the composition to obtain a non-conductive metal composite material.SELECTED DRAWING: Figure 3

Description

The present invention relates to a non-conductive metal composite material, a composition for use in making the same, and a method for making the non-conductive metal composite material.

The surface of ceramic products represented by ceramics, glass, tiles, etc. is sometimes decorated with gold or silver to give an elegant or luxurious impression. Among such ceramic products, there are products that are expected to be heated by a microwave oven (for example, tableware, etc.). Therefore, it is desirable that the decorative portion does not spark due to high-frequency electromagnetic waves (for example, a frequency of about 2.45 GHz) emitted by the microwave oven.

For example, Patent Literature 1 discloses liquid gold for overglaze painting containing Au, Bi, In, Si and Ba. According to Patent Document 1, by firing this mercury, a conductive metal exhibiting a color tone such as Au and a non-conductive oxide such as silica are precipitated, and exposed to high-frequency electromagnetic waves emitted by a microwave oven. It is said that it is possible to realize a decorative body that does not damage the metal and has a bright gold or silver color tone.

Further, Patent Document 2 discloses a surface-decorated article having a plurality of plate-like elements decorated with precious metals on the surface of the ceramic article. In this technique, the length of the plate-like elements is set to a predetermined value or more, the arrangement interval of the plate-like elements is set to a predetermined value or more, and the plate-like elements are covered with a frit layer so that the plate-like elements are not damaged even when used in a microwave oven. It is said that a surface decorative article having excellent chemical durability and color developability can be achieved.

JP-A-6-48779 JP-A-9-235169

By the way, in the decorative portion, it is preferable that the presence density of the metal portion is high in order to achieve good color development in addition to having non-conductivity to withstand high-frequency electromagnetic waves of a microwave oven. A low density of metal parts is more susceptible to design limitations. Therefore, it is desired to realize a decorative portion having a high presence density of metal portions and having non-conductivity. In addition, since the size of the metal portion (for example, area and grain size) is important for color tone, a technique for controlling the size of the metal portion is desired.

Accordingly, the present invention has been made in view of the circumstances described above, and a main object thereof is to provide a non-conductive metal composite material in which metals are densely arranged. Another object is to provide a composition for use in producing the non-conductive metal composite material. Furthermore, another object of the present invention is to provide a method for producing the non-conductive metal composite material.

In order to achieve the above object, a method for producing a non-conductive metal composite material disclosed herein comprises preparing a composition containing metal particles having at least a portion of the surface coated with a non-conductive inorganic oxide. , molding or applying the composition to a given substrate, and firing the composition to obtain a non-conductive metal composite.
According to this configuration, the inorganic oxide coated on the surface of the metal particles can suppress the sintering of the metal particles, so that a non-conductive metal composite material can be realized. In addition, by including metal particles preliminarily coated with an inorganic oxide in the composition, a non-conductive metal composite material in which metals are arranged at high density can be produced.

In a preferred embodiment of the method for producing a non-conductive metal composite material disclosed herein, in the average particle size based on the electron microscope image of the metal particles, the average particle size after the firing is _Da (nm), D _a ≤ D _b , where D _b (nm) is the average particle size before firing.
By using metal particles having such properties, it is possible to suppress destruction (cracking) of the coating layer due to thermal expansion of the metal particles. This makes it possible to manufacture a metal composite material that is more reliably non-conductive.

Further, in a preferred aspect of the method for producing a non-conductive metal composite material disclosed herein, the firing temperature is equal to or lower than the sintering temperature of the metal particles coated with the inorganic oxide. As a result, it is possible to further suppress the sintering of the metal particles, so that a non-conductive metal composite material having a higher volume resistivity can be produced.

Further, in a preferred aspect of the method for producing a non-conductive metal composite material disclosed herein, the metal particles are at least selected from the group consisting of Pt, Au, Ag, Pd, Rh, Ir, Ru and Os. Contains a kind of metal. According to such a configuration, it is possible to realize a non-conductive metal composite material with good gloss.

Also, in a preferred aspect of the method for producing a non-conductive metal composite material disclosed herein, the inorganic oxide contains at least one compound selected from the group consisting of silica, alumina, zirconia and yttria. According to such a configuration, since the inorganic oxide has high transparency, it is possible to realize a non-conductive metal composite material with better color development.

A preferred embodiment of the method for producing a non-conductive metal composite material disclosed herein includes applying the above composition to a predetermined base material, and the base material is an insulating article. According to such a configuration, it is possible to manufacture tableware that does not spark with, for example, high-frequency electromagnetic waves of a microwave oven.

The present disclosure also provides compositions (paints) for use in the manufacture of tableware decorations. The compositions disclosed herein comprise metal particles having at least a portion of their surface coated with a non-conductive inorganic oxide, wherein the volume ratio of said metal particles to said inorganic oxide to said inorganic oxide is (Inorganic oxide/metal particles) is 0.1 or more and 0.8 or less. According to such a composition, a non-conductive metal composite material in which metals are densely arranged can be produced.

In a preferred aspect of the composition disclosed herein, the metal particles have internal voids. According to such a configuration, internal sintering occurs in the metal particles when the composition is fired, so cracking of the coating layer due to expansion of the metal particles is suppressed. Thereby, sintering between metal particles can be suppressed.

Moreover, in one preferred aspect of the composition disclosed herein, the metal particles contain at least one metal selected from the group consisting of Pt, Au, Ag, Pd, Rh, Ir, Ru and Os. According to such a configuration, it is possible to realize a non-conductive metal composite material with good gloss.

Moreover, in one preferred aspect of the composition disclosed herein, the inorganic oxide contains at least one compound selected from the group consisting of silica, alumina, zirconia and yttria. According to such a configuration, a non-conductive metal composite material with higher resistivity can be realized.

Also provided by the present disclosure are non-conductive metal composites. The non-conductive metal composite material disclosed herein includes metal particles having a coating layer containing a non-conductive inorganic oxide on at least a part of the surface, and the entire non-conductive metal composite material is 100 vol% , the volume ratio of the metal particles is 30 vol% or more, and 90% by number or more of the metal particles with the coating layers are in contact with the other three or more metal particles with the coating layers. In the average thickness (nm) of the coating layer and the average particle diameter (nm) based on the electron microscope image of the metal particles, the value of (average thickness / average particle diameter) is 0.01 or more 0.15 or less, and a volume resistivity of 1×10 ⁻¹ Ω·cm or more. According to the production method disclosed herein, a non-conductive metal composite material having such a configuration in which metals are densely arranged can be realized.

Further, in a preferred aspect of the non-conductive metal composite material disclosed herein, the coefficient of variation of particle size based on an electron microscope image of the metal particles is 0.6 or less. According to such a configuration, since the variation in particle size of the metal particles is small, the metal particles can be arranged at a higher density.

In a preferred aspect of the non-conductive metal composite material disclosed herein, the metal particles have an average particle diameter of 10 nm or more and 1000 nm or less based on an electron microscope image. According to such a configuration, the color development of the non-conductive metal composite material becomes better.

In addition, the non-conductive metal composite material disclosed herein has metals arranged at a high density, so that it can be suitably used as a decorative part of tableware with good color development that is compatible with heating in a microwave oven. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view schematically showing the configuration of metal particles contained in a non-conductive metal composite material disclosed herein, and (A) to (C) are respectively one aspect that can be observed in a non-conductive metal composite material. is shown. FE-SEM images observed from the surface of the dried body and the fired body of Example 1, (A) showing the dried body and (B) the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 2, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and the fired body of Example 3, (A) showing the dried body and (B) the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 4, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and the fired body of Example 5, (A) showing the dried body and (B) the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 6, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 7, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 8, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 9, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and the fired body of Example 11, (A) showing the dried body and (B) the fired body. FE-SEM images observed from the surface of the dried body and the fired body of Example 12, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 13, (A) showing the dried body and (B) showing the fired body. FE-SEM images observed from the surface of the dried body and the fired body of Example 14, (A) showing the dried body and (B) the fired body. FE-SEM images observed from the surface of the dried body and the fired body of Example 15, (A) showing the dried body and (B) the fired body. FE-SEM images observed from the surface of the dried body and fired body of Example 16, (A) showing the dried body and (B) showing the fired body. 1 shows a TEM-EDX elemental mapping image of the sintered body of Example 2. FIG. 1 shows a TEM-EDX elemental mapping image of the sintered body of Example 6. FIG. 1 shows a TEM-EDX elemental mapping image of the sintered body of Example 9. FIG.

Preferred embodiments of the technology disclosed herein are described below. Matters other than the matters specifically referred to in this specification that are necessary for implementation (for example, the production of a substrate to which the composition is applied, etc.) are the technical content taught by this specification. and common technical knowledge of those skilled in the art. The content of the technology disclosed here can be implemented based on the content disclosed in this specification and common general knowledge in the field. In this specification, the notation "A to B" indicating the range means from A to B and includes the case of exceeding A and falling below B.

The non-conductive metal composite material disclosed here has non-conductivity in spite of the fact that the metals are densely arranged. This makes it possible to suitably add metallic properties (eg, metallic luster, ferromagnetism, etc.) to materials that are required to be non-conductive. In this specification, the term “non-conductive” refers to the property of having a volume resistivity of 1×10 ⁻¹ Ω·cm or more as measured by a four-probe method.

FIG. 1 is a cross-sectional view schematically showing the configuration of metal particles contained in the non-conductive metal composite material disclosed herein. The non-conductive metal composite material includes metal particles 12 , and at least a portion of the surface of the metal particles 12 is covered with a non-conductive coating layer 14 . As shown in FIG. 1(A), the entire surface of the metal particle 12 may be covered with the coating layer 14, and as shown in FIG. 1(B), the surface of the metal particle 12 A part may not be covered with the covering layer 14 . 1A and 1B, the coating layer 14 exists between the metal particles 12, so that the metal particles 12 are not bonded (necked) to each other, and the metal particles 12 are separated from each other. Due to the arrangement, non-conductivity is achieved. Moreover, as shown in FIG. 1(C), the metal composite material may have a neck portion 16 in which the metal particles 12 are necked to the extent that the metal composite material as a whole is non-conductive. Also, the non-conductive metal composite may have voids between the metal particles 12 .

The metal particles 12 may be appropriately changed according to the application of the non-conductive metal composite material, and may contain, for example, noble metal elements, transition metal elements, and the like. Noble metal elements include platinum (Pt), gold (Au), silver (Ag), palladium (Pd), iridium (Ir), ruthenium (Ru), rhodium (Rh), and osmium (Os). A noble metal element imparts an excellent metallic luster to the non-conductive metal composite material, and is therefore suitable, for example, when the non-conductive metal composite material is used as a decorative part of tableware. Examples of transition metal elements include iron (Fe), nickel (Ni), cobalt (Co), and the like. Fe, Ni, and Co are metals exhibiting ferromagnetism, and are suitable, for example, when non-conductive metal composite materials are used for powder magnetic cores.

The average particle size of the metal particles 12 is preferably 10 nm or more, and can be, for example, 20 nm or more, 30 nm or more, or 40 nm or more. If the average particle size is less than 10 nm, the metallic luster may be insufficient, or color development may occur due to plasmon absorption, making it difficult to control the color tone. Also, the average particle diameter of the metal particles 12 is typically preferably 1000 nm or less, and can be, for example, 200 nm or less, 150 nm or less, or 100 nm or less. If the average particle size exceeds 1000 nm, the conductivity may increase, or the surface of the non-conductive metal composite material may become uneven, resulting in poor color development. As used herein, the term “average particle diameter” refers to the directional diameter (Ferret diameter) of 200 or more particles randomly selected from an image of particles obtained by an electron microscope (for example, a scanning electron microscope (SEM)). - diameter). In addition, when the particles are necked, the particles are divided by connecting the constrictions at both ends of the neck portion with a straight line, and the particles are measured as separate particles.

The variation coefficient of the particle size of the metal particles 12 is preferably 0.6 or less, more preferably 0.3 or less, still more preferably 0.25 or less, and particularly preferably 0.2 or less (for example, 0.15 or less). is. The smaller the coefficient of variation, the smaller the dispersion of the particles, which improves the stability of color development and makes it easier to control color development. The coefficient of variation can be obtained by dividing the standard deviation by the arithmetic mean (standard deviation/arithmetic mean).

The coating layer 14 contains a non-conductive material, typically composed of a non-conductive inorganic oxide. Examples of such inorganic oxides include highly transparent inorganic oxides such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), and yttria (Y ₂ O ₃ ). Thereby, the luster and color development of the metal particles 12 can be satisfactorily exhibited. In addition, the transparency of the inorganic oxide allows the particle size of the metal particles 12 to be measured by electron microscope observation.

The average thickness of the covering layer 14 may be, for example, 10 nm or less, and may be 6 nm or less, 4 nm or less, or 2 nm or less. The smaller the average thickness of the coating layer 14, the more densely the metal particles 12 can be arranged. The lower limit of the average thickness of the coating layer 14 is not particularly limited as long as the non-conductive metal composite material has non-conductivity, and can be, for example, 0.5 nm or more. In addition, the average thickness of the coating layer 14 in this specification has an average particle diameter based on the volume ratio of the metal particles 12 and the coating layer 14 calculated from EDX analysis (see the test examples described later for specific examples). It means the thickness when it is assumed that the coating layer 14 having a uniform thickness is formed on the surface of the metal particles 12 . Such a thickness is given below, where T is the average thickness of the coating layer 14, r is the radius that is half the average particle size of the metal particles 12, and volume of the coating layer 14:volume of the metal particles 12=A:B. The formula for:
(4/3) π(T+r) ³ : (4/3) πr ³ = (A+B): B
can be obtained from

From the viewpoint of ensuring non-conductivity, the ratio of the average thickness of the coating layer 14 to the average particle size of the metal particles 12 (average thickness/average particle size) is preferably 0.01 or more, for example, 0.01. 015 or more, 0.02 or more. Moreover, from the viewpoint of arranging the metal particles 12 at high density, the ratio is preferably 0.15 or less, such as 0.1 or less, 0.05 or less, or 0.025 or less.

The volume ratio of the metal particles 12 in the non-conductive metal composite material is, for example, 30 vol% or more, preferably 50 vol% or more, more preferably 60 vol% when the total volume of the non-conductive metal composite material is 100 vol%. % or more, more preferably 70 vol% or more, particularly preferably 80 vol% or more, for example, 85 vol% or more, 90 vol% or more. The higher the volume ratio of the metal particles 12, the more effectively the metal properties of the metal particles 12 (eg, metallic luster, ferromagnetism, etc.) are exhibited. For example, when the metal particles 12 are composed of a noble metal element, a non-conductive metal composite material with excellent luster and color tone can be obtained. Moreover, the upper limit of the volume ratio of the metal particles 12 is not particularly limited as long as the non-conductive metal composite material has non-conductivity, but it can be, for example, 99 vol % or less, or 95 vol % or less. Note that the volume ratio of the entire non-conductive metal composite material does not include the volume of voids that may exist between the metal particles 12 . The volume ratio of the metal particles 12 can be calculated, for example, from the results of EDX elemental analysis.

The volume ratio (inorganic oxide/metal particle) between the metal particles 12 in the non-conductive metal composite material and the inorganic oxide contained in the coating layer 14 is, for example, 1 or less, preferably 0.8 or less. , more preferably 0.6 or less, still more preferably 0.4 or less, particularly preferably 0.2 or less, and may be, for example, 0.15 or less, or 0.11 or less. The smaller the volume ratio, the smaller the ratio of the volume of the inorganic oxide to the volume of the metal particles 12, so the distance between the metal particles 12 can be made smaller. As a result, the volume ratio of metal particles 12 in the non-conductive metal composite material can be increased. Moreover, the lower limit of the volume ratio is not particularly limited as long as the non-conductive metal composite material is non-conductive, and may be, for example, 0.05 or more, or 0.1 or more. Such a volume ratio is calculated using, for example, the weight ratio of the elements constituting the metal particles obtained by EDX elemental analysis and the constituent elements other than oxygen contained in the inorganic oxide (for example, Si in the case of silica). can be found at An example of calculation is shown in the test example described later.

The molar ratio (inorganic oxide/metal particle) between the metal particles 12 in the non-conductive metal composite material and the inorganic oxide contained in the coating layer 14 is, for example, 0.5 or less, preferably 0.5. It is 3 or less, more preferably 0.1 or less, and still more preferably 0.05 or less. The lower the molar ratio, the smaller the amount of inorganic oxide present relative to the metal particles 12, so that the thickness of the coating layer 14 can be further reduced and the metal particles 12 can be arranged at a higher density. Moreover, the lower limit of the molar ratio is not particularly limited as long as the non-conductive metal composite material has non-conductivity, but it can be, for example, 0.01 or more. This molar ratio can be measured by EDX elemental analysis. Specifically, it can be obtained by measuring the ratio between the metal element that constitutes the metal particles 12 and the element contained in the inorganic oxide.

Since the metal particles 12 are densely arranged in the non-conductive metal composite material, when the non-conductive metal composite material is observed from the surface, the area ratio occupied by the metal particles 12 is high. For example, the area ratio of the area of the metal particles 12 to the area of the coating layer 14 (coating layer/metal particle) is preferably 0.5 or less, preferably 0.35 or less, and more preferably 0.25 or less. , and more preferably 0.15 or less. The smaller the value of the area ratio, the higher the percentage of the surface of the non-conductive metal composite material occupied by the metal particles 12 . This can further improve the metallic luster of the non-conductive metal composite material. Moreover, the lower limit of the above area ratio is not particularly limited as long as the non-conductive metal composite material has non-conductivity, and may be, for example, 0.1 or more.
The above area ratio can be obtained, for example, by image analysis of an EDX elemental mapping image from the surface of the non-conductive metal composite material.

The method for producing the non-conductive metal composite material disclosed herein will be described below. The method for producing a non-conductive metal composite material disclosed herein comprises preparing a composition containing metal particles at least a portion of the surface of which is coated with a non-conductive inorganic oxide (hereinafter also referred to as a “preparation step”). ), molding the composition or applying it to a predetermined substrate (hereinafter also referred to as a “molding/coating step”), and firing the composition to obtain a non-conductive metal composite material (hereinafter , also referred to as “firing step”).

The preparation step prepares the compositions disclosed herein. The compositions disclosed herein comprise metal particles having at least a portion of their surfaces coated with an inorganic oxide. An example of manufacturing metal particles having such a configuration will be described below. In addition, the method for producing such metal particles is not limited to the following production examples.

In order to generate metal particles, first, a solution for generating metal particles is prepared by dissolving a metal compound containing the target metal element. As the metal compound used here, a salt or complex of the target metal (for example, Pt) can be preferably used. Salts include, for example, halides such as chlorides, bromides and iodides, hydroxides, sulfides, sulfates, nitrates and the like. Complexes include ammine complexes, cyano complexes, halogeno complexes, hydroxy complexes, and the like.

As a solvent for dissolving the metal compound described above, for example, an aqueous solvent can be used. As the aqueous solvent, water (eg, pure water, deionized water, etc.) or a mixed solution containing water as a main component (eg, mixed solution of water and lower alcohol) can be used. In this specification, the term "mixed liquid mainly composed of water" refers to a mixed liquid in which 50 vol% or more of the mixed liquid is water.

Although the amount of the metal compound mixed in the metal particle generating solution is not particularly limited, for example, the concentration of the metal compound is 0.01M to 0.2M (eg, 0.01M to 0.08M). A solution can be prepared as follows. In preparing such solutions, various additives can be added in addition to the metal compound and solvent. Examples of such additives include protective agents and complexing agents.

Polyvinylpyrrolidone (PVP) is preferably used as protective agent. PVP can adhere to the surface of metal particles produced by the subsequent reduction treatment. The PVP attached to the surface of the metal particles can promote the sol-gel reaction under alkaline conditions (for example, in the presence of ammonia), which will be described later, so that the surfaces of the metal particles can be more uniformly coated with the inorganic oxide. In addition, since the particles have a structure in which the protective agent (PVP) is incorporated into the inside of the particles, volumetric shrinkage may occur due to the burn-through of the protective agent. The amount of PVP to be mixed can be, for example, 10 to 1000 wt % when the mass of the metal element contained in the metal compound is 100 wt %.

Further, when PVP is used, it is preferable that the metal particle generating solution contains a lower alcohol. When PVP is used, the particle size of the metal particles produced tends to be a single nano size of less than 10 nm. Therefore, it is difficult to obtain metal particles having a particle size of about 10 nm to 1000 nm and a sharp particle size distribution (that is, a small coefficient of variation). In addition, if the concentration of the metal compound is increased or the amount of PVP mixed is reduced in order to increase the particle size of the metal particles, aggregation and necking of the metal particles are likely to occur. Therefore, as a result of investigations by the present inventors, by mixing a lower alcohol into a solution, even in the presence of PVP, it has an average particle size of about 10 nm to 1000 nm, and the variation in particle size is small ( For example, it was found that metal particles with a coefficient of variation of 0.6 or less can be efficiently obtained.

In addition, metal particles produced by mixing PVP and a lower alcohol as described above tend to be polycrystalline and may have voids inside the metal particles. Typically, the inorganic oxide contained in the coating layer has a lower coefficient of thermal expansion than the metal particles, and therefore cracks are likely to occur due to the expansion of the metal particles during heat treatment. Therefore, in the case of metal particles having polycrystals, high crystallization and densification occur due to disappearance of grain boundaries by heat treatment, and volumetric shrinkage of the metal particles can occur. In addition, if the metal particles have internal voids, the heat treatment causes internal sintering, which can cause volumetric shrinkage of the metal particles. As a result, cracking of the coating layer due to thermal expansion of the metal particles is suppressed, and sintering of the metal particles can be suppressed.
By analyzing the metal particles by an X-ray diffraction (XRD) method, the crystallite size can be determined, so whether or not the metal particles are polycrystalline can be evaluated. In addition, the ratio of voids (porosity) inside the metal particles is, for example, 0.1% to 20% or less, and can be about 0.5% to 15% or 1% to 10%. The internal porosity of the metal particles is, for example, the following formula:
Porosity (%) = 100 × (1 - (apparent density of metal powder obtained by dry density measurement by constant volume expansion method) / (true density of metal material in literature))
can be obtained by

The ratio of the lower alcohol is, for example, preferably 20 vol % to 40 vol %, preferably 30 vol % to 35 vol %, of the entire metal particle generating solution. The lower alcohol may be mixed with the metal particle generating solution before dissolving the metal compound, or may be mixed after dissolving the metal compound. Lower alcohols include methanol, ethanol, butanol, isopropanol and the like.

As a complexing agent, for example, aqueous ammonia, potassium cyanide, or the like can be used. By adding an appropriate amount of a complexing agent, a complex in which the desired metal element serves as the central metal ion can be easily formed in the liquid. As a result, the desired metal particles can be easily produced by the subsequent reduction treatment.

When preparing the metal particle generating solution, it is preferable to stir while maintaining the temperature condition within a certain range. The temperature condition at this time is preferably about 20° C. to 60° C. (more preferably 30° C. to 50° C.). The rotation speed for stirring is preferably about 100 rpm to 1000 rpm (more preferably 300 rpm to 800 rpm, for example 500 rpm).

Next, a suitable reducing agent is added to the metal particle-generating solution prepared in this manner, and a reduction treatment is performed to generate metal particles. As the reducing agent, for example, hydrazine compounds such as hydrazine carbonate, hydrazine, hydrazine hydrate, phenylhydrazine, hydrazine sulfate, hydrazine dihydrochloride, and alkylhydrazine can be used. Other examples of reducing agents include organic acids such as tartaric acid, citric acid, and ascorbic acid, salts thereof (tartrates, citrates, ascorbates), and sodium borohydride. Among these, hydrazine carbonate, tartrate (e.g., sodium tartrate), citrate (e.g., sodium citrate), etc., which are not poisonous substances and can form uniform metal particles with smooth surfaces, are preferably used. be able to.

The amount of the reducing agent to be added is not particularly limited, as it may be appropriately set according to the state of the reaction system. Moreover, the particle size of the metal particles can be controlled by appropriately adjusting the concentration of the reducing agent. Generally, the particle size of the metal particles can be reduced by increasing the concentration of the reducing agent. Further, it is preferable to adjust the pH to 8 or more, for example, about 9 to 11 by adding a pH adjuster to the metal particle generating solution during the reduction treatment. Examples of pH adjusters that can be used include sodium hydroxide (NaOH), aqueous ammonia, other basic compounds, and the like. The reduction treatment time can be set as appropriate. Although there is no particular limitation, for example, about 0.5 hours to 3 hours is preferable. In this way, metal particles are generated in the liquid, and a metal particle dispersion liquid can be obtained.
In order to favorably precipitate the metal particles, it is preferable to allow the reduction reaction to proceed while stirring the mixture after adding the reducing agent. The means for stirring at this time is not particularly limited, but for example, stirring using a magnetic stirrer, an ultrasonic stirrer, or the like can be preferably employed.

The average particle size of the metal particles contained in the composition is preferably 10 nm or more, and may be, for example, 20 nm or more, 30 nm or more, 40 nm or more, or 50 nm or more. If the average particle diameter is less than 10 nm, the produced non-conductive metal composite material may have insufficient metallic luster, and coloring due to plasmon absorption may occur, making it difficult to control the color tone. Also, the average particle size of the metal particles is typically preferably 1000 nm or less, and may be, for example, 200 nm or less, 150 nm or less, 110 nm or less, or 100 nm or less. If the average particle size exceeds 1000 nm, the electrical conductivity of the non-conductive metal composite material may increase, or the surface of the non-conductive metal composite material may become uneven, resulting in poor color development, for example.

In addition, the coefficient of variation of the particle size of the metal particles contained in the composition is preferably 0.3 or less, more preferably 0.2 or less, still more preferably 0.17 or less, and particularly preferably 0.15 or less ( for example, 0.1 or less). The smaller the variation in particle size, the more the variation in particle size of the metal particles is suppressed even in the fired body (non-conductive metal composite material), and the stability of color development can be improved.

It is preferable that the metal particles do not increase in particle size by firing. In other words, the average particle size of the metal particles after firing is D _a (nm), and the average particle size of the metal particles before firing is D _b (nm) , it is preferable to have D _a ≦D _b . In addition, the shrinkage rate (particle shrinkage rate) of the metal particles due to firing is preferably 0% or more (no shrinkage (i.e., 0%) or greater than 0% if shrinkage), 2% or more, 5% or more. , 10% or more. If the shrinkage ratio of the metal particles is 0% or more, the inorganic oxide on the surface of the metal particles is suppressed from being destroyed by the thermal expansion of the metal particles, and it is easy to suppress the metal particles from being bonded to each other by sintering. Become. On the other hand, if the particle shrinkage rate is too high, it may become difficult for the metal particles to be arranged at a high density in the non-conductive metal composite material. % or less. In addition, the particle shrinkage rate is the following formula:
((D _b −D _a )/D _b )×100
can be obtained by

Next, using the metal particle dispersion obtained above, an inorganic oxide coating is formed on the metal particle surfaces by a sol-gel method. In such a method, the alkoxide is brought into contact with water by mixing the alkoxide with the metal particle dispersion. As a result, the alkoxide is hydrolyzed, so that an inorganic oxide is generated on the surface of the metal particles, and metal particles coated with the inorganic oxide can be obtained. In this reaction, it is preferable to mix the alkoxide while stirring the metal particle dispersion in order to coat the metal particle surfaces more uniformly with the inorganic oxide. The treatment time for such reaction is not particularly limited, but can be, for example, about 12 hours to 24 hours.

Any alkoxide that is generally used in the sol-gel method can be used without particular limitation. For example, when silica is coated as an inorganic oxide, alkoxides such as methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, tetraethoxysilane (TEOS), 1,2-bistri Methoxysilylethane, silicon alkoxide in which 1 to 4 alkoxy groups are bonded to the Si atom, silicon alkoxide in which a functional group such as a glycidyl group is introduced, and the like can be preferably used.

The amount of alkoxide to be mixed is not particularly limited, but if the amount of alkoxide to be mixed is too small, for example, the amount of inorganic oxide coated on the surface of the metal particles may be insufficient. Therefore, the molar ratio between the alkoxide and the metal compound (alkoxide/metal compound) is, for example, preferably 0.01 or more, and may be 0.035 or more, 0.065 or more, or 0.1 or more. Also, if the amount of the alkoxide mixed is too large, the amount of the inorganic oxide coated on the surface of the metal particles will be too large, and it may not be possible to arrange the metal particles at a high density in the non-conductive metal composite material. be. Therefore, the molar ratio may be, for example, 1 or less, and may be 0.5 or less, 0.45 or less, 0.4 or less, 0.3 or less, or 0.2 or less.

In the sol-gel method, it is preferable to adjust the metal particle dispersion under alkaline conditions in order to adjust the reaction rate of the hydrolysis reaction of the alkoxide and to more uniformly coat the surfaces of the metal particles with the inorganic oxide. As alkaline conditions, for example, the metal particle dispersion may be adjusted to a pH of 8 or higher, for example, a pH of about 9 to 13. For such adjustment, for example, sodium hydroxide, ammonia, other basic compounds, etc. can be used as a pH adjuster, and among them, it is preferable to use ammonia.

In this way, metal particles having at least a portion of the surface coated with a non-conductive inorganic oxide can be produced. Since the produced particles are dispersed in the liquid, they can be recovered by, for example, sedimentation by standing or centrifugal separation followed by removal of the supernatant. Further, it is preferable to perform a cleaning treatment with pure water, lower alcohol, or the like.

In the metal particles coated with the inorganic oxide produced above, the molar ratio of the inorganic oxide to the metal particles (inorganic oxide/metal particles) is, for example, 0.5 or less, preferably 0.5. It is 3 or less, more preferably 0.1 or less, and still more preferably 0.05 or less. The lower the molar ratio, the smaller the amount of the inorganic oxide relative to the metal particles, so that the thickness of the inorganic oxide can be further reduced and the metal particles can be arranged at a higher density. Moreover, the lower limit of the molar ratio is not particularly limited as long as the non-conductive metal composite material is non-conductive, and can be, for example, 0.01 or more. This molar ratio can be measured by EDX elemental analysis.

In the metal particles coated with the inorganic oxide produced above, the volume ratio of the metal particles to the coated inorganic oxide (inorganic oxide/metal particle) is, for example, 1 or less, preferably 0.8 or less, more preferably 0.6 or less, still more preferably 0.4 or less, particularly preferably 0.2 or less, and may be, for example, 0.15 or less, or 0.11 or less. The smaller the volume ratio, the smaller the ratio of the volume of the inorganic oxide to the volume of the metal particles, so that a non-conductive metal composite material in which the metal particles are arranged at a higher density can be produced. Moreover, the lower limit of the volume ratio is not particularly limited, but may be, for example, 0.05 or more and 0.1 or more. The specific calculation method for this volume ratio is the same as the method for obtaining the volume ratio between the metal particles 12 and the coating layer 14 in the non-conductive metal composite material, and the metal particles obtained by EDX elemental analysis. It can be calculated using the weight ratio of the element that does so and the constituent element other than oxygen contained in the inorganic oxide (for example, Si in the case of silica).

In the metal particles coated with the inorganic oxide produced above, the average thickness of the inorganic oxide (coating layer) may be, for example, 10 nm or less, and may be 6 nm or less, 4 nm or less, or 2 nm or less. A non-conductive metal composite material in which metal particles are arranged at a higher density can be produced as the average thickness of the coating layer is smaller. The lower limit of the average thickness of the coating layer is not particularly limited, but can be, for example, 0.5 nm or more. The average thickness of the coating layer is based on the volume ratio of the metal particles and the coating layer calculated from the EDX analysis, and it is assumed that a coating layer having a uniform thickness is formed on the surface of the metal particles having an average particle size. It means the thickness of the case. A specific calculation method is the same as the average thickness of the coating layer 14 in the non-conductive metal composite material described above.

In addition, the metal particles coated with the inorganic oxide produced in this way have a ratio of the average thickness of the coating layer to the average particle size of the metal particles (average thickness / average particle size). From the viewpoint of ensuring the non-conductivity of the conductive metal composite material, it is preferably 0.01 or more, for example, 0.015 or more, or 0.02 or more. Moreover, from the viewpoint of arranging the metal particles at a high density, the ratio is preferably 0.15 or less, such as 0.1 or less, 0.05 or less, or 0.025 or less.

The composition disclosed herein contains, in addition to the metal particles coated with the inorganic oxide produced above, for example, an organic solvent, a matrix-forming material, Other additives may be included. Examples of organic solvents include 1,4-dioxane, 1,8-cineol, 2-pyrrolidone, 2-phenylethanol, N-methyl-2-pyrrolidone, p-tolualdehyde, benzyl benzoate, butyl benzoate, eugenol. , caprolactone, geraniol, methyl salicylate, cyclohexanone, cyclohexanol, cyclopentyl methyl ether, citronellal, di(2-chloroethyl) ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, dihydrocarbon, dibromomethane, dimethyl sulfoxide, dimethylformamide, nitrobenzene, pyrrolidone , propylene glycol monophenyl ether (PhFG), pulegone, benzyl acetate, isobutanol, benzyl alcohol, benzaldehyde, pinene, pine oil, turpentine oil, lavender oil and the like. These can be used singly or in combination of two or more.

The matrix-forming material is a material capable of forming an amorphous matrix in an oxide state by firing. The amorphous matrix can adjust the color development, conductivity, adhesion, stability, strength, chemical resistance, etc. of the non-conductive metal composite. Examples of matrix-forming materials include metal resinates and metal complexes. Examples of metal elements contained in the matrix-forming material include bismuth (Bi), silicon (Si), aluminum (Al), alkali metal elements, alkaline earth metal elements, and rare earth elements. Among these, it is preferable to adopt a matrix-forming material containing Bi. By including Bi, the adhesive strength of the non-conductive metal composite material to the substrate can be improved.

Other additives include, for example, organic binders, protective agents, surfactants, thickeners, pH adjusters, preservatives, antifoaming agents, plasticizers, stabilizers and antioxidants.

The compositions disclosed herein can be obtained by mixing the inorganic oxide-coated metal particles produced above with the optional ingredients described above. Such a composition can be obtained as a pasty kneaded product (including forms such as slurry and dispersion; the same shall apply hereinafter) by kneading by a conventionally known method.

Next, the molding/coating process will be described. In the molding/application step, the composition prepared above is molded or applied to a given substrate. When molding the composition, the molding method is not particularly limited, and for example, pressure molding, press molding, or the like can be performed. When the composition is applied to a given base material, the type of base material is not particularly limited, and for example, insulating ware such as pottery, porcelain, earthenware, stoneware, and glass can be preferably used. can. Moreover, the coating method is not particularly limited, and for example, brush coating, screen printing, inkjet printing, or the like can be employed.

The molded or applied composition may be dried prior to firing. The drying method is not particularly limited, and for example, natural drying, hot air drying, vacuum drying, etc. can be carried out.

Next, the firing process will be described. In the firing step, by firing the molded or applied composition, a non-conductive metal composite material, which is a fired body of the composition, can be obtained. The sintering temperature can typically be equal to or lower than the sintering temperature of the metal particles coated with the inorganic oxide contained in the composition. Since it varies depending on the diameter, shape, type of inorganic oxide, film thickness, etc., it can be changed as appropriate. In one example, when the metal particles are Pt particles and the inorganic oxide is silica, the firing temperature can be set, for example, in the range of 400° C. to 800° C., and the firing time at this firing temperature is 10 minutes to 30 minutes. can be set to an extent.

In the non-conductive metal composite material produced in this way, although the metal particles are arranged at a high density, the rate of necking between the metal particles is low, so the volume resistivity is high. , is non-conductive. In the non-conductive metal composite material produced by the above method, the percentage of necking metal particles is, for example, 50 number% or less, 40 number% or less, 30 number% or less, 20 number% or less, It may be 10% by number or less, or even 5% by number or less (eg, 1% by number or less). In this specification, the ratio of necking particles is obtained by randomly selecting 200 or more metal particles from an image of particles obtained by an electron microscope (e.g., SEM), and calculating the number of necking particles. It can be obtained by counting. At this time, the necking metal particles are counted as one.

Also, the non-conductive metal composite material thus produced may have coated metal particles placed in contact with each other, e.g., 90 number percent or more of the coated metal particles are It is in contact with 3 or more of the metal particles. Even in such a case, since the metal particles have a coating layer on their surfaces, most of the contact portions are in contact with each other through the coating layer, so non-conductivity is achieved. As long as it has non-conductivity, the contact portion may be any of the coating layers, the coating layer and the metal particles, or the metal particles. It is preferably 90% or more, more preferably 90% or more. Evaluation of such a contact portion can be performed based on TEM-EDX, and for example, the ratio can be obtained by observing 100 or more randomly selected metal particles.

Also, the non-conductive metal composites thus produced may have voids between the coated metal particles. The resistivity of air (approximately 10 ¹⁶ Ω·m) is higher than that of various inorganic oxides (e.g., silica: approximately 10 ¹⁴ Ω·m, alumina: approximately 10 ¹³ Ω·m), making it non-conductive. It can effectively increase the resistivity of the flexible metal composite material. The volume resistivity of the non-conductive metal composite material is at least 1×10 ⁻¹ Ω·cm or more, preferably 4×10 ⁻¹ Ω·cm or more, more preferably 1 Ω·cm or more, further preferably 1 ×10 ³ Ω·cm or more, particularly preferably 1 × 10 ⁵ Ω·cm or more (for example, 1 × 10 ⁶ Ω·cm or more).

The non-conductive metal composite material disclosed here can be suitably used, for example, as a decorative part of tableware. In particular, by providing a non-conductive metal composite material on the surface of an insulating utensil, it can be used as a microwaveable tableware that does not spark when heated in a microwave oven. Also, the non-conductive metal composite material can be suitably used as, for example, a dust core. In addition, the use of the non-conductive metal composite material disclosed here is not limited to the above.

Test examples relating to the technology disclosed here will be described below, but the technology disclosed here is not intended to be limited to such test examples.

[Test 1]
A film-like fired body (Examples 1 to 16) containing metal particles (Pt particles) or Pt particles at least part of which is coated with an inorganic oxide (silica) is produced, and its microwave resistance and gloss are examined. rice field. In Examples 2, 3 and 9, the molar ratio, area ratio and volume ratio of Pt particles and silica were measured.

(Example 1)
0.104 g of potassium tetrachloroplatinate (II) was added to 16.66 mL of pure water, stirred with a magnetic stirrer to dissolve, and then 8.33 mL of ethanol was added. 0.278 g of polyvinylpyrrolidone (PVP K90, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto and dissolved with stirring. With further stirring, 0.125 mL of 70% hydrazine carbonate was added, and the mixture was stirred for 30 minutes to precipitate Pt particles. After adding 0.5 mL of 28% aqueous ammonia while stirring, 27 μL of tetraethoxysilane (TEOS) was added and stirred overnight. As a result, Pt particles having at least part of the surface coated with silica (hereinafter also referred to as “silica-Pt particles”) were obtained. The molar ratio of potassium tetrachloroplatinate(II) and TEOS used in the production is shown in Table 1 as "prepared Si/Pt molar ratio".
The resulting silica-Pt particle dispersion was sedimented using a centrifuge, and the supernatant was removed. After adding pure water and re-dispersing, the washing process of sedimenting with a centrifuge and removing the supernatant was repeated twice. A similar washing step was performed twice using ethanol instead of pure water, and then a similar washing step was performed using WA oil (reference number: J2012, manufactured by Noritake Co., Ltd.) as an organic solvent. The resulting precipitate was kneaded using a rotation-revolution mixer (product name: Awatori Mixer, manufactured by Thinky Co., Ltd.) to obtain a paste-like silica-Pt particle-WA oil kneaded product.
The resulting silica-Pt particle-WA oil kneaded product was applied to quartz glass and dried at 60° C. for 30 minutes to form a dry film. The dried body was heated at a heating rate of 10° C./min in an air atmosphere, held at 800° C. for 10 minutes, and then allowed to cool. Thus, a film-like sintered body of Example 1 was obtained.

(Example 2)
A sintered body of Example 2 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 24 μL.
(Example 3)
A sintered body of Example 3 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 18 μL.
(Example 4)
A sintered body of Example 4 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 12 μL and the sintering temperature was changed to 600°C.
(Example 5)
A sintered body of Example 5 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 6 μL and the sintering temperature was changed to 400°C.

(Example 6)
A sintered body of Example 6 was obtained in the same manner as in Example 1 except that the pure water was changed to 2.08 mL, the amount of ethanol added was changed to 1.04 mL, and the amount of TEOS added was changed to 24 μL.
(Example 7)
A sintered body of Example 7 was obtained in the same manner as in Example 6, except that the amount of TEOS added was changed to 3.9 μL.
(Example 8)
A sintered body of Example 8 was obtained in the same manner as in Example 6 except that the amount of TEOS added was changed to 2.1 μL and the sintering temperature was changed to 600°C.
(Example 9)
A sintered body of Example 9 was obtained in the same manner as in Example 8, except that the sintering temperature was changed to 400°C.

(Example 10)
A sintered body of Example 10 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 270 μL.
(Example 11)
A sintered body of Example 11 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 12 μL.
(Example 12)
A sintered body of Example 12 was obtained in the same manner as in Example 1, except that the amount of TEOS added was changed to 6 µL and the sintering temperature was changed to 600°C.
(Example 13)
A sintered body of Example 13 was obtained in the same manner as in Example 8, except that the sintering temperature was changed to 800°C.
(Example 14)
A sintered body of Example 14 was obtained in the same manner as in Example 1, except that 28% aqueous ammonia was not added.

(Example 15)
4.16 g of potassium tetrachloroplatinate (II) was added to 200 mL of pure water, stirred with a magnetic stirrer to dissolve, and then 100 mL of ethanol was added. 33.3 g of polyvinylpyrrolidone (PVP K90, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto and dissolved with stirring. With further stirring, 5 mL of 70% hydrazine carbonate was added and stirred for 30 minutes. Pt particles were precipitated.
The Pt particles obtained were washed in the same manner as in Example 1. Further, heat treatment was performed in the same manner as in Example 1 except that the heating temperature was changed to 600°C. Thus, a sintered body of Example 15 was obtained.
(Example 16)
A sintered body of Example 16 was obtained in the same manner as in Example 15, except that the sintering temperature was changed to 400°C.

<Measurement of average particle size>
The surface of the dried body and fired body of each example was observed by FE-SEM (manufactured by Hitachi High-Tech Co., Ltd., SU-8230). In each example, 200 or more Pt particles were randomly selected, the unidirectional diameters (Ferret diameters) of the Pt particles were measured, and the arithmetic mean of these was determined as the average particle diameter of the Pt particles. Also, the coefficient of variation of the average particle size was obtained. Table 1 shows the results.
FE-SEM images observed from the surface of the dried body and the fired body are shown in FIGS. 2 to 16 are images of the dried bodies ((A) in the figure) and fired bodies ((B) in the figure) of Examples 1 to 9 and 11 to 16, respectively, observed from the surface.

<Evaluation of Particle Shrinkage Rate>
The particle shrinkage rate of the Pt particles due to firing was obtained. The particle shrinkage ratio is expressed by the formula: ((D _b −D _a )/D, where D _b (nm) is the average particle diameter of the metal particles in the dried body and D _a (nm) is the average particle diameter of the Pt particles in the fired body. _b ) Determined by ×100. Table 1 shows the results.

<Measurement of molar ratio of Pt and Si>
The molar ratio of Pt and Si (Si/Pt) was determined by TEM-EDX analysis from the surface of the fired body. Table 1 shows the results.

<Measurement of Area Ratio of Pt and Si>
Using TEM-EDX elemental mapping, the area ratio (Si/Pt) of Pt and Si in the image from the surface of the fired body was measured using image analysis software. Table 1 shows the results.

In addition, the positions of Pt and Si were confirmed using TEM-EDX elemental mapping. The results of Examples 2, 6 and 9 are shown in Figures 17-19. DF in the figure means a TEM dark field image.

<Measurement of volume ratio of Pt and silica>
The volume ratio of Pt and silica was obtained by calculation from the ratio of Pt and Si obtained by TEM-EDX. Specifically, the mass of Pt was assumed to be 1, and the mass ratio of Si to Pt was assumed to be x. Further, the molecular weight of silica (SiO ₂ ) was 60.08 g/mol, the atomic weight of Si was 28.09 g/mol, the density of amorphous silica was 2.2 g/cm ³ , and the density of Pt was 21.45 g/cm ³ . . And the formula below:
(Silica/Pt volume ratio) = ((x x 60.08/28.09)/2.2)/(1/21.24)
The silica/Pt volume ratio was determined by Also, based on this volume ratio, the Pt volume ratio (vol%) was obtained when the volume of silica and Pt was 100 vol%. Further, using the volume ratio and the average particle size of the Pt particles, it is assumed that a silica coating layer having a uniform thickness is formed on the surface of the Pt particles having an average particle size. The thickness (nm) was determined. Furthermore, the ratio of the average thickness of the coating layer to the average particle size of the Pt particles (average thickness/average particle size) was determined. Table 1 shows the results.

<Evaluation of microwave resistance>
The sintered body was heated in a microwave oven at 1000 W for 1 minute, and the presence or absence of sparks was confirmed. Table 1 shows the results. It should be noted that "○" indicates that no spark occurred, and "X" indicates that there was spark.

<Evaluation of Gloss>
After polishing the surface of the sintered body by ion milling, the metallic luster was visually evaluated. When the surface of the sintered body was observed at an angle of about 45 degrees, the surface of the sintered body was rated as "O" when it had a platinum-colored gloss, and was rated as "X" when it did not have a platinum-colored gloss. Table 1 shows the results.

As shown in Table 1, the fired bodies of Examples 1 to 9 had resistance to microwave ovens and good gloss. These sintered bodies showed good color development with little variation in the particle size of the Pt particles (variation coefficient of 0.6 or less). In addition, since the particle shrinkage ratio was 0% to 21%, it is considered that the Pt particles contracted due to firing (however, the particle size was maintained in Example 3), and the sintering of the Pt particles was suppressed. . As is clear from the FE-SEM images shown in FIGS. 2 to 10, while the Pt particles are densely arranged in any of the fired bodies of Examples 1 to 9, sintering between the Pt particles is suppressed. I know there is. Moreover, when some metal particles are severely sintered like the sintered body of Example 3 shown in FIG. Even if the metal particles are necked with each other, as in the fired body shown in , it was confirmed that non-conductivity is realized by not sintering the metal particles so that the entire metal particles are joined. .

Moreover, as shown in FIGS. 17 and 18, in the fired bodies of Examples 2 and 6, it was confirmed that Si was present so as to cover the periphery of the Pt particles. Furthermore, as shown in FIG. 19, in the sintered body of Example 9, it was confirmed that Si partially covered the surface of the Pt particles. In addition, in the TEM-EDX elemental mapping of Examples 2, 6, and 9, in any example, 90 number% or more of the metal particles are through or not through the other three or more metal particles and the coating layer was confirmed to be in contact with In any of these cases, since non-conductivity was achieved, at least part of the surface of the Pt particles was coated with Si (presumed to be coated with silica), and FIG. 10, it can be seen that non-conductivity is achieved by suppressing sintering between Pt particles.

Moreover, the Pt volume ratios of Examples 2, 6 and 9 all showed 50 vol % or more, and in particular, Examples 6 and 9 showed a very high value of 87 vol % or more. Considering that the organic solvent is removed by sintering, these sintered bodies are substantially composed of Pt particles and silica, so this value can be interpreted as the Pt volume ratio in the whole sintered body. That is, it can be said that a non-conductive metal composite material in which metal particles are densely arranged is realized.

On the other hand, the fired body of Example 10 had resistance to microwave ovens, but had poor gloss. In addition, in Example 10, in the FE-SEM observation of the dry body, the Pt particles were obscured because they were buried in the silica matrix, making it impossible to measure the particle size of the Pt particles. From this, it is considered that in Example 10, TEOS, which is a raw material for silica coating, was excessively mixed with Pt, so that the presence density of Pt particles decreased and the gloss was poor.

The fired bodies of Examples 11-15 did not have microwave resistance. As is clear from the FE-SEM images shown in (B) of each of FIGS. 11 to 15, in the fired bodies of Examples 11 to 15, the Pt particles are sintered more violently than the fired bodies of Examples 1 to 9. Was. It is believed that this increased the conductivity and did not have resistance to microwave ovens.

Moreover, when comparing Example 11 and Example 4, Example 11 has the same manufacturing method except that the firing temperature is higher by 200°C. Also, in Examples 12 and 5, the manufacturing method is the same, except that the firing temperature is 200° C. higher in Example 12. Moreover, in Examples 13, 8, and 9, the manufacturing method is the same except that the firing temperature is different. From these results, it can be seen that a non-conductive metal composite material can be produced by firing at a temperature equal to or lower than the sintering temperature of the metal particles coated with the inorganic oxide.

In Example 14, 28% aqueous ammonia was not mixed in the reaction to coat the Pt particles with silica. Therefore, it is considered that the pH in the liquid did not rise, the silica coating of the Pt particles became insufficient, and the Pt particles were sintered.

Example 15 is an example in which TEOS, which is a raw material of silica, was not mixed. Therefore, in Example 15, the Pt particles are likely to be sintered together, and it is considered that the Pt particles were sintered by firing at 600°C. In Example 16, the firing temperature of Example 15 was changed to 400°C. As shown in FIG. 16, when the firing temperature was 400° C., even Pt particles without silica coating did not sinter between Pt particles. However, since it does not have a silica coating, it is considered that the electrical conductivity is high and it does not have microwave resistance.

[Test 2]
In test 2, the organic solvent was changed from WA oil to propylene glycol monophenyl ether (PhFG) or isobutanol (IBA). Also, the base material used was changed from quartz glass to slide glass (soda lime glass). The sintered bodies (Examples 17 to 19) produced in Test 2 were evaluated for microwave oven resistance and gloss in the same manner as in Test 1, and further measured for volume resistivity. These results are shown in Table 2.

(Example 17)
1.04 g of potassium tetrachloroplatinate (II) was added to 166.6 mL of pure water, stirred with a magnetic stirrer to dissolve, and then 83.3 mL of ethanol was added. 2.78 g of PVP K90 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto and dissolved with stirring. With further stirring, 1.25 mL of 70% hydrazine carbonate was added, and the mixture was stirred for 30 minutes to precipitate Pt particles. After adding 5 mL of 28% aqueous ammonia while stirring, 270 μL of TEOS was added and stirred overnight. Silica-Pt particles were thus obtained.
The resulting silica-Pt particle dispersion was sedimented using a centrifuge, and the supernatant was removed. After adding pure water and re-dispersing, the washing process of sedimenting with a centrifuge and removing the supernatant was repeated twice. A similar cleaning step was performed twice using ethanol instead of pure water, and then a similar cleaning step was performed using PhFG as an organic solvent. The resulting precipitate was kneaded using a rotation-revolution mixer (product name: Awatori Mixer, manufactured by Thinky Co., Ltd.) to obtain a paste-like Pt-silica particle-PhFG kneaded product.
The resulting silica-Pt particle-PhFG kneaded product was applied to a slide glass and dried at 60° C. for 30 minutes to form a dry film. The dried body was heated at a heating rate of 10° C./min in an air atmosphere, held at 800° C. for 10 minutes, and then allowed to cool. Thus, a film-like sintered body of Example 17 was obtained.

(Example 18)
A sintered body of Example 18 was obtained in the same manner as in Example 17 except that IBA was used instead of PhFG.
(Example 19)
A sintered body of Example 19 was obtained in the same manner as in Example 17, except that the amount of TEOS added was changed to 480 μL.

<Measurement of volume resistivity>
The volume resistivity of the sintered body was measured by the four-probe method. A low resistivity meter Loresta-GP (manufactured by Mitsubishi Chemical Corporation) was used for such measurements.

As shown in Table 2, regardless of the type of organic solvent, a fired body having microwave oven resistance and good gloss was obtained. In addition, regardless of the type of organic solvent, the sintered body could be immobilized on the slide glass. This is probably because the interface of the slide glass was melted by firing at a temperature higher than the softening point of the slide glass, and the silica-Pt particles were immobilized in the melted glass.
In addition, the sintered body of Example 19 had a significantly higher volume resistivity than those of Examples 17 and 18. It is considered that this is because the amount of silica coated on the Pt particles was increased by increasing the charged Si/Pt molar ratio.

Specific examples of the technology disclosed herein have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

12 metal particles 14 coating layer 16 neck portion

Claims (14)

A method for producing a non-conductive metal composite material, comprising:
providing a composition comprising metal particles having at least a portion of their surface coated with a non-conductive inorganic oxide;
molding or applying the composition to a given substrate; and
calcining the composition to obtain a non-conductive metal composite;
A non-conductive metal composite manufacturing method. In the average particle diameter based on the electron microscope image of the metal particles, Da ( _nm ) is the average particle diameter after firing, and D _b (nm) is the average particle diameter before firing, where _Da ≤ _Db The non-conductive metal composite manufacturing method according to claim 1, comprising: 3. The method for producing a non-conductive metal composite material according to claim 1, wherein the firing temperature is equal to or lower than the sintering temperature of the metal particles coated with the inorganic oxide. The non-conductive metal according to any one of claims 1 to 3, wherein the metal particles contain at least one metal selected from the group consisting of Pt, Au, Ag, Pd, Rh, Ir, Ru and Os. Composite material manufacturing method. The method for producing a non-conductive metal composite material according to any one of claims 1 to 4, wherein the inorganic oxide contains at least one compound selected from the group consisting of silica, alumina, zirconia and yttria. The method for producing a non-conductive metal composite material according to any one of claims 1 to 5, comprising applying the composition to a predetermined base material, the base material being an insulating article. A composition for use in the manufacture of decorative parts of tableware,
At least a portion of the surface contains metal particles coated with a non-conductive inorganic oxide,
A volume ratio (inorganic oxide/metal particle) between the metal particles and the inorganic oxide is 0.1 or more and 0.8 or less,
Composition. 8. The composition of claim 7, wherein said metal particles have internal voids. 9. The composition according to claim 7 or 8, wherein said metal particles comprise at least one metal selected from the group consisting of Pt, Au, Ag, Pd, Rh, Ir and Ru. The composition according to any one of claims 7 to 9, wherein said inorganic oxide comprises at least one compound selected from the group consisting of silica, alumina, zirconia and yttria. A non-conductive metal composite material comprising metal particles having a coating layer containing a non-conductive inorganic oxide formed on at least a portion of the surface,
When the entire non-conductive metal composite material is 100 vol%, the volume ratio of the metal particles is 30 vol% or more,
90 number percent or more of the metal particles having the coating layer formed thereon are in contact with other three or more metal particles having the coating layer formed thereon,
In the average thickness (nm) of the coating layer and the average particle size (nm) based on the electron microscope image of the metal particles, the value of (the average thickness/the average particle size) is 0.01 or more and 0.15 or less. can be,
Volume resistivity is 1 × 10 ^-1 Ω cm or more,
Non-conductive metal composites. 12. The non-conductive metal composite material according to claim 11, wherein the metal particles have a particle size variation coefficient of 0.6 or less based on an electron microscope image. The non-conductive metal composite material according to claim 11 or 12, wherein the metal particles have an average particle diameter of 10 nm or more and 1000 nm or less based on an electron microscope image. The non-conductive metal composite material according to any one of claims 11 to 13, which is used as a decorative part of tableware.

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