JP7350604B2 - Composite particles, method for producing composite particles, and ink containing composite particles - Google Patents

Description

The present invention relates to composite particles, a method for producing composite particles, and an ink containing composite particles.

As a conductive material that can be sintered at a low temperature, a conductive material using silver nanoparticles is known. However, since the particle size of conventional silver nanoparticles is small, when a conductive layer (wiring) is formed by printing using silver nanoparticles as a conductive material, the thickness of the conductive layer is only a few μm at most. , the film thickness was thin. Therefore, there was a problem in that it was difficult to produce a conductive layer (wiring) having sufficient conductivity.

To solve this problem, Patent Document 1 (Japanese Unexamined Patent Publication No. 2012-182111) proposes first metal particles whose surfaces are coated with a capping material such as a fatty acid and whose particle size is less than 100 nm, and which has a particle size of 100 nm or more. conductive metal paste compositions are disclosed that include second metal particles having a particle size.

Furthermore, in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2016-98398), metal silver is interposed on the surface of metallic copper or its alloy to form a composite by surface treatment, which results in fusion bonding between metallic copper (alloy). A method of surface treating metals to cause bonding to occur at relatively low temperatures is disclosed.

Japanese Patent Application Publication No. 2012-182111 JP2016-98398A

However, in Patent Document 1, there is a problem that particles of 100 nm or less have a low melting point and can be sintered at low temperatures, but particles of 100 nm or more are difficult to sinter at low temperatures and contribute little to conductivity.

Further, in Patent Document 2, diffusion of silver and copper easily occurs, and a silver-copper alloy is likely to be formed. Therefore, there is a problem that deterioration over time such as a decrease in conductivity and oxidation is likely to occur.

In view of the above circumstances, an object of the present invention is to provide a conductive material that can form thick wiring, can be sintered at low temperature, and has excellent conductivity.

[1] A composite particle containing at least a first particle whose surface is made of silver or a silver alloy, and a second particle whose surface is made of silver or a silver alloy,
The first particles have an average particle diameter of 100 nm or more and 100 μm or less,
The second particles have an average particle diameter of 1 nm or more and 50 nm or less,
A composite particle in which at least one second particle is attached to a surface of the first particle.

[2] The composite particle according to [1], wherein the first particle includes a core particle and a coating layer made of silver or a silver alloy provided on the surface of the core particle.

[3] The composite particle according to [2], wherein the core particle is made of at least one selected from the group consisting of aluminum, alumina, silica, copper, nickel, resin, and carbon.

[4] A forming step of forming second particles made of silver or a silver alloy by heating the silver amine complex;
an adhering step of adhering the second particles to the surface of the first particles, at least the surface of which is made of silver or a silver alloy;
A method for producing composite particles, comprising:
The first particles have an average particle diameter of 100 nm or more and 100 μm or less,
The second particles have an average particle diameter of 1 nm or more and 50 nm or less.

[5] The forming step and the adhering step are carried out by mixing and heating the first particles and the silver amine complex to form the second particles attached to the surface of the first particles. The manufacturing method according to [4].

[6] An ink containing the composite particles according to any one of [1] to [3].

In the composite particles of the present invention, by using the first particles with an average particle diameter of 100 nm or more and 100 μm or less, it is possible to increase the thickness of the conductive layer (wiring) when forming the conductive layer (wiring) by printing. .

Further, by using second particles having an average particle diameter of 50 nm or less, low-temperature sintering becomes possible by partially melting.

In addition, since the second particles are attached to the surface of the first particles, the first particles and the second particles are not separated, and when sintered, the first particles having a large average particle size are separated from each other. It becomes possible to bond two particles through each other. This provides a conductive material (composite particle) with excellent conductivity.

Therefore, according to the present invention, it is possible to form a thick wiring, to perform low-temperature sintering, and to provide a conductive material with excellent conductivity.

This is a reference photograph in Example 1. This is a reference photograph in Example 1. This is a reference photograph in Example 2. This is a reference photograph in Example 2. This is a reference photograph in Example 3. This is a reference photograph in Example 3. This is a reference photograph in Example 4. This is a reference photograph in Example 4.

<Composite particles>
The composite particles of the present invention contain first particles whose surfaces at least are made of silver or a silver alloy, and second particles whose surfaces are made of silver or a silver alloy. At least one second particle is attached to the surface of the first particle. Note that the first particle and the second particle are attached to each other by, for example, van der Waals force. The proportion of silver contained in the silver alloy is preferably 99% by mass or more.

The average particle diameter (D50) of the composite particles is not particularly limited, but is preferably 100 nm or more and 100 μm.

In addition, in this specification, "D50" means the cumulative 50% particle size from the fine particle side (also referred to as the "median diameter") in a volume-based particle size distribution measured by a laser diffraction scattering method. .

The composite particles of the present invention can be prepared, for example, in the form of a dispersion in an organic solvent (a polar solvent such as an alcohol solvent or an ester solvent, a non-polar solvent such as octane, or a mixed solvent thereof) at a predetermined concentration. , can be used for certain purposes. In addition, the dispersion liquid may contain components such as a resin and a dispersant as necessary. It can also be used as a paste composition.

(first particle)
At least the surface of the first particles is made of silver or a silver alloy. Note that the entire surface of the first particle does not necessarily need to be made of silver or a silver alloy, and it is sufficient that at least a part of the surface of the first particle is made of silver or a silver alloy. Further, the inner material is not particularly limited as long as the surface is made of silver or a silver alloy. That is, the first particle may be a particle (particle having a core-shell structure) in which only the surface is made of silver or a silver alloy and the inside is made of a material other than silver or silver alloy, or the first particle may be a particle (particle having a core-shell structure) in which only the surface is made of silver or a silver alloy. and the interior thereof) may be composed of silver or a silver alloy.

The first particles have an average particle diameter (D50) of 100 nm or more and 100 μm or less. The average particle diameter of the first particles is preferably 1 μm or more and 10 μm or less. When the thickness is less than 100 nm, it becomes difficult to increase the thickness of the conductive layer when forming the conductive layer (wiring) by printing using the composite particles. On the other hand, if the thickness is 100 μm or more, it becomes difficult to reduce the width of the wiring.

The form of the first particles is not particularly limited, and examples include plate-like (flake), linear (wire), spherical, irregularly shaped, and the like.

The first particles preferably include a core particle and a coating layer made of silver or a silver alloy provided on the surface of the core particle.

The material for the core particles can be used without any particular limitation, and examples thereof include metals, ceramics, resins, and the like. The metal is not particularly limited, but is preferably a metal other than silver and silver alloys. Examples of metals other than silver and silver alloys include aluminum, copper, and nickel. Examples of ceramics include alumina and silica.

As a method for coating the core particles with silver or a silver alloy, known methods such as electroless plating, chemical vapor deposition, and physical vapor deposition can be used without particular limitation.

The core particles are preferably made of at least one member selected from the group consisting of aluminum, alumina, silica, copper, nickel, resin, and carbon. By using such a material as the material of the core particle and using a particle having a core-shell structure in which the surface of the core particle is coated with silver (or silver alloy), it is possible to create a particle entirely made of silver (or silver alloy). Composite particles with excellent electrical conductivity can be obtained while reducing the amount of expensive silver used, compared to the case where such particles are used as the first particles.

Further, by using a light material such as aluminum, silica, alumina, resin, carbon, etc. as the material of the core particle, the weight of the composite particle (conductive material) can be reduced.

In addition, when a conductive material such as aluminum or carbon is used as the material for the core particle, the core particle also has conductivity, so it is possible to use a conductive layer formed from composite particles with excellent conductivity. It can be done.

In addition, since at least the surface of the first particles is made of silver or a silver alloy, even if the second particles made of silver or silver alloy with a size of 1 nm or more and 50 nm or less are attached, the alloy will not be formed due to the diffusion of silver into the first particles. It is possible to prevent Thereby, deterioration of the composite particles over time can be suppressed.

(Second particle)
The second particles are particles entirely made of silver or a silver alloy. Although impurities may be included as long as the effects of the present invention can be obtained, particles that do not contain any elements other than silver and unavoidable impurities are preferable.

The second particles have an average particle diameter of 1 nm or more and 50 nm or less. The average particle diameter of the second particles is preferably 5 nm or more and 20 nm or less. If the diameter is less than 1 nm, the second particles tend to adhere to each other, making it difficult to produce them as independent particles. On the other hand, if it exceeds 50 nm, the effect of lowering the melting point of the nanoparticles will not be sufficiently obtained and the sintering temperature will increase.

The average particle diameter of the second particles in the composite particles is determined by measuring the particle diameter of the second particles one by one in an electron microscope image obtained by FE-SEM observation, etc. It can be calculated by finding the average value of the particle diameter of the second particles.

The amount of the second particles is preferably from 5 parts by volume to 200 parts by volume, more preferably from 10 parts by volume to 50 parts by volume, per 100 parts by volume of the first particles. If the amount is less than 5 parts by volume, the first particles cannot be sufficiently bonded to each other via the second particles when sintered, and the conductivity of the conductive layer formed using the composite particles may be reduced. If the amount of the second particles exceeds 200 parts by volume, the second particles may not be able to fully adhere to the first particles and may become loose, increasing the viscosity and making it difficult to form a conductive layer by printing.

<Manufacture of composite particles>
The method for producing composite particles of the present invention includes:
a formation step of forming second particles by heating the silver amine complex (second particle formation step);
The method includes an adhesion step of adhering second particles to the surface of the first particles (second particle adhesion step).

Note that the first particles and second particles are the same as above.
In the formation step, the silver amine complex is thermally decomposed by heating to form second particles made of silver or a silver alloy.

The heating temperature in the formation step varies depending on the silver amine complex used, but is preferably 70°C or more and 150°C or less, more preferably 80°C or more and 120°C or less.

In the attachment step, the second particles can be attached to the surfaces of the first particles, for example, by mixing the obtained second particles with the first particles and heating the mixture.

The heating temperature when heating is performed in the adhesion step is preferably 70°C or more and 150°C or less. If the temperature is lower than 70°C, there is a possibility that the second particles and the first particles cannot be sufficiently attached. On the other hand, if the temperature exceeds 150°C, there is a risk that the second particles will melt.

The above formation step and adhesion step may be performed separately, but by mixing and heating the silver amine complex, which is the raw material for the second particles, and the first particles, the surface of the first particles can be formed. By forming the second particles, both the forming step and the adhering step may be performed.

[Silver amine complex]
The silver amine complex used for producing the second particles is a complex formed from a silver-containing compound and an alkylamine. In such a silver amine complex, the structure of the silver-containing compound becomes unstable and the thermal decomposition temperature decreases.

In addition, even after the silver-containing compound is thermally decomposed, the alkylamine that has formed the complex coordinates to the surface of the second particles (silver nanoparticles) made of silver or silver alloy, so that the second particles are It is thought that it functions to prevent coarse agglomeration.

(silver compound)
As the silver compound (compound containing silver) that forms a silver amine complex, a silver compound that can form a complex with various alkyl amines and easily thermally decomposes by heating to produce simple silver is preferably used. Ru.

Examples of such silver compounds include silver salts of carboxylic acids such as formic acid, acetic acid, oxalic acid, malonic acid, benzoic acid, and phthalic acid, as well as silver chloride, silver nitrate, silver carbonate, etc.; Alternatively, a mixture of two or more types can be used as appropriate.

Among them, silver oxalate is preferably used because it leaves virtually no by-products in the reaction system after thermal decomposition. Silver oxalate is easy to thermally decompose at a low temperature of around 200°C even if it does not form an amine complex, and since oxalate ions are removed as carbon dioxide during thermal decomposition, it is advantageous in that impurities are unlikely to remain. It is.

As the silver oxalate used in the method of the present invention, for example, commercially available silver oxalate can be used. Furthermore, a silver compound in which part of the oxalate ions of silver oxalate is replaced with one or more of carbonate ions, nitrate ions, and oxide ions may be used. In addition, two or more types of silver compounds may be mixed and used if necessary.

(alkylamine)
The alkylamine used for preparing the silver amine complex is not particularly limited, but for example, monoamines in which an amino group is bonded to an alkyl group, diamines having two amino groups, etc. are preferably used. In addition, in this specification, the alkylamine includes a monoamine having one amino group and a diamine having two amino groups. In addition, when distinguishing between the two, they are described as monoamine and diamine, respectively.

Incidentally, even when a monoamine is mainly used as the alkylamine, a diamine can be appropriately mixed and used.

The alkylamine is a primary alkylamine (R-NH ₂ ) or a secondary alkylamine (R ₁ R ₂ -NH) in order to form a coordination bond via an amino group on the surface of a silver atom. It is preferable that there be. The above R, R ₁ and R ₂ represent independent hydrocarbon groups, but these hydrocarbon groups may contain a hetero atom such as an oxygen atom, a nitrogen atom, a sulfur atom or a silicon atom. These alkylamines not only form a complex with a silver compound, but also can coordinate to form an alkylamine coating on the surface of second particles made of silver or silver alloy produced by thermal decomposition.

As the alkylamine, one or more of these alkylamines can be used. In particular, it is preferable to use a diamine or a short-chain monoamine having 5 or less carbon atoms in combination with a long-chain monoamine having 6 or more carbon atoms. Long-chain monoamines are generally difficult to evaporate and have a high affinity with organic solvents. Therefore, a film containing a predetermined proportion of long-chain alkyl monoamine is formed on the surface of the second particles generated by thermal decomposition of the silver amine complex, improving storage stability. Further, the dispersibility in nonpolar organic solvents can be improved.

Examples of such long-chain monoamines include dipropylamine, dibutylamine, hexylamine, cyclohexylamine, heptylamine, 3-butoxypropylamine, octylamine, nonylamine, decylamine, 3-aminopropyltriethoxysilane, and dodecylamine. Examples include amine, hexadecylamine, oleylamine, octadecylamine, and the like. However, the present invention is not limited to these, and other long-chain monoamines having 6 or more carbon atoms can also be used as appropriate.

On the other hand, generally, as the alkyl chain of a monoamine becomes longer, it becomes difficult to form a complex with a silver compound.

On the other hand, when a diamine or a short-chain monoamine having 5 or less carbon atoms is used, it is possible to form a complex with a silver compound relatively easily. Therefore, when silver nanoparticles (second particles) are formed by thermal decomposition of an amine complex, it is effective to use such a diamine or a short-chain monoamine having 5 or less carbon atoms as the alkylamine. However, in particular, short-chain monoamines having 5 or less carbon atoms have a high vapor pressure, so evaporation becomes a problem when heating the amine complex to thermally decompose the silver compound. Furthermore, when a large amount of diamine is used, the protective film formed on the silver surface becomes difficult to detach during sintering or the like.

Based on the characteristics of the various alkylamines mentioned above, we have found that long-chain monoamines, which are expected to provide stability after the formation of silver nanoparticles and form a good protective film, are the main components, while diamines and short-chain monoamines with a carbon number of 5 or less are used as main components. By using a chain monoamine mainly as an auxiliary agent for complex formation in a predetermined proportion, it is possible to take advantage of the advantages of both.

Examples of the above-mentioned short-chain monoamines include amylamine, 2-ethoxyethylamine, 4-methoxybutylamine, diisopropylamine, butylamine, diethylamine, propylamine, isopropylamine, ethylamine, dimethylamine, and the like.

The diamine preferably has a boiling point of 100° C. or higher, taking into account the thermal decomposition temperature of the complex. Further, from the viewpoint of low-temperature fusing and sinterability of the produced composite particles, it is preferable that the composite particles have a boiling point of 250° C. or lower.

Examples of such diamines include ethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, N,N'-diethylethylenediamine, 1,3-propanediamine, 2, 2-dimethyl-1,3-propanediamine, N,N-dimethyl-1,3-diaminopropane, N,N'-dimethyl-1,3-diaminopropane, N,N-diethyl-1,3-diaminopropane , 1,4-diaminobutane, 1,5-diamino-2-methylpentane, 1,6-diaminohexane, N,N'-dimethyl-1,6-diaminohexane, 1,7-diaminoheptane, 1,8 -Diaminooctane, etc.

(Complex formation aid)
In addition to the above-mentioned alkylamines, when forming a complex between a silver compound and an alkylamine, a complex formation aid (such as another polar organic compound) can be used to form a complex between a silver compound and an alkylamine. more likely to form.

Examples of such polar organic compounds include alcohol compounds and compounds containing heteroatoms that form multiple bonds. Such polar organic compounds may be used alone or in combination of two or more. It is preferable that such a polar organic compound is a solvent having excellent compatibility with an alkylamine.

Examples of such alcohol compounds include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, allyl alcohol, phenol, benzyl alcohol, pinacol, propylene glycol, menthol, catechol, hydroquinone, salicyl alcohol, and pentanol. Examples include erythritol, sucrose, glucose, xylitol, methoxyethanol, triethylene glycol monomethyl ether, ethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene glycol.

The amount of alcohol compound used when forming the silver amine complex is preferably 5 mol% or more and 500 mol% or less, more preferably 10 mol% or more and 300 mol% or less, based on the alkylamine. It is particularly preferable that the amount is mol % or more and 100 mol % or less. If it is less than 5 mol %, there is a tendency that the effect of promoting complex formation becomes insufficient. On the other hand, if the amount is more than 500 mol %, the activity of the alkylamine tends to decrease and the formation of a complex tends to be inhibited.

Additionally, as the proportion of the alcohol compound increases within this range, the time for complex formation generally shortens, and the particle size of the second particles produced by thermal decomposition of the complex increases, resulting in dispersion of the produced second particles in the polar solvent. There is a tendency for performance to improve.

In addition to alcohol compounds, for example, compounds containing heteroatoms that form multiple bonds can be used as complex formation aids, although their specific effects are not clear.Such compounds ( Compounds containing heteroatoms forming multiple bonds include, for example, carbonyl compounds and isocyanate compounds containing carbon-oxygen double bonds, oxime compounds containing carbon-nitrogen multiple bonds, Schiff base compounds, and nitrile compounds; Examples thereof include nitro compounds or nitroso compounds containing multiple bonds between oxygen and nitrogen, and azo compounds, diazo compounds, and azides containing multiple bonds between nitrogen atoms.

Further, the formation of a complex between a silver compound and an alkylamine can also be promoted by a compound containing sulfur, phosphorus, or the like as a heteroatom.

The compound used as a complex formation aid changes depending on the basic structure of the compound, but when the number of carbon atoms contained in the compound exceeds 14, the effect of promoting complex formation tends to decrease. On the other hand, when the number of carbon atoms contained in the compound is 7 or less, a remarkable effect of promoting complex formation is generally observed.

Examples of other compounds that can be used as complex formation aids include ketone compounds. Non-limiting examples of ketone compounds include, for example, aliphatic ketones, cycloaliphatic ketones, aromatic ketones, and the like.

Aliphatic ketones include acetone, methyl ethyl ketone, acetylacetone, 2-butanone, 3-pentanone, 4-heptanone, 4-methyl-3-penten-2-one (mesityl oxide), 4-methyl-2-pentanone, diacetyl , pinacolin, 2,4-dimethylpentanone, 2,6-dimethyl-3-heptanone, isoamylmethylketone, 3-methyl-2-butanone, 5-methyl-heptanone, 4-methyl-2-pentanone, ethynyl isopropyl ketone , 2-octanone, and the like.

Examples of the alicyclic ketone include cyclopentanone, cyclohexanone, 2-cyclohexenone, isophorone, and dicyclohexyl ketone.

Examples of aromatic ketones include acetophenone, benzophenone, 4-phenyl-2-butanone, isobutyrophenone, benzalacetone, and propiophenone.

Furthermore, the ketone compounds include methyl acetoacetate, ethyl acetoacetate, dimethyl acetyl succinate, α-acetyl-γ-butyrolactone, acetoacetic acid, methyl pyruvate, pyruvic acid, N,N-dimethylacetoacetamide, acetoacetanilide, Mention may also be made of keto acid compounds such as N-acetoacetylmorpholine.

Another example is an aldehyde compound in which one hydrogen atom is bonded to a carbonyl carbon. Non-limiting examples of such aldehyde compounds include propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-pentylaldehyde, 2-methylbutyraldehyde, n-hexylaldehyde, 2-methylpentanal, n-heptyl Aldehydes, 2-hexenal, n-octylaldehyde, benzaldehyde, cuminaldehyde, anisaldehyde, chlorobenzaldehyde, cinnamaldehyde, crotonaldehyde, isobutyraldehyde, butyraldehyde, pyruvaldehyde, terephthalaldehyde, tolualdehyde, ethynyl phenyl ketone, furfural, etc. Can be mentioned.

Other examples include ester compounds, amide compounds, isocyanate compounds (RN=C=O), oxime compounds (>C=N-OH), nitrile compounds, azo compounds, diazo compounds, and azides.

(Preparation of silver amine complex)
The silver amine complex can be prepared, for example, by mixing a predetermined amount of alkyl amine with a powdered silver compound.

During this preparation, the formation of the amine complex can be promoted, for example, by adding the above-mentioned complex formation aid, a small amount of water, and the like. Note that the complex formation aid may be added to the alkylamine in advance before mixing with the silver compound. Alternatively, the alkylamine may be added after mixing the complex formation aid with the silver compound and crushing the silver compound.

In the process of forming a silver amine complex, the end point of the complex formation reaction can be detected, for example, by detecting the end of the color change of the mixture due to the reaction using spectroscopy or the like. Note that when silver oxalate is used as the silver compound, the silver amine complex formed is generally colorless (white), but even in this case, the end point of the complex formation reaction can be detected based on changes in the viscosity of the mixture. be able to.

In addition, in the step of forming the silver amine complex, heating may be performed within a temperature range that can suppress thermal decomposition of the formed silver amine complex and evaporation of alkylamines. Furthermore, since the formation reaction of the silver amine complex is accompanied by heat generation, in order to suppress the thermal decomposition reaction of the silver compound, the reaction may be cooled to room temperature or lower, if necessary.

In forming the silver amine complex, the total amount of alkyl amine used is preferably at least the stoichiometric amount relative to the silver atoms contained in the silver compound. If the total amount of alkylamine is less than the stoichiometric amount of the silver compound, the silver compound that does not form a complex remains. Therefore, during the production of silver nanoparticles (second particles), there is a risk that the silver nanoparticles (second particles) may become enlarged or a portion of the silver compound may remain without being thermally decomposed. Typically, second particles having a uniform particle size can be stably obtained by mixing an alkylamine in an amount twice as much molar amount as silver atoms or more when forming a complex. In addition, since the excess alkylamine that does not form a complex with the silver compound remains in the reaction system, it can be used as is as a reaction medium when attaching the second particles to the surface of the first particles in the next step. .

(Second particle formation step)
By heating and thermally decomposing the above-mentioned silver amine complex, single silver is liberated, and second particles (silver nanoparticles) made of silver or a silver alloy are formed.

The step of forming the second particles is preferably performed by heating the silver amine complex in a reaction medium containing an alkylamine. Further, if necessary, an appropriate alkylamine or the like may be further mixed therein to serve as a reaction medium for producing the second particles. Alternatively, the silver amine complex may be separated from the mixture containing the formed silver amine complex by a method such as centrifugation.

The temperature at which the silver amine complex is thermally decomposed to produce the second particles varies depending on the type of amine complex used, but is generally within the temperature range above the temperature at which the production of the second particles begins, but is not excessively high. It is preferable to carry out the test in the area. If excessive heating is performed, the coordination bond of the alkylamine to the silver is likely to come off, making the silver precipitation process unstable and coarse particles etc. likely to be produced. Furthermore, from the viewpoint of active evaporation of alkylamines and the like forming the reaction medium, the temperature at which the silver amine complex is thermally decomposed is preferably as low as possible within the range at which thermal decomposition occurs.

From this viewpoint, the heating temperature in the step of forming the second particles is preferably 70°C or more and 150°C or less, more preferably 80°C or more and 120°C or less.

(Second particle adhesion process)
For example, by mixing and heating the second particles obtained in the above formation step and the first particles, the second particles are attached to the surfaces of the first particles.

The heating temperature in the adhesion step is preferably 70°C or higher and 150°C. If the temperature is less than 70°C, sufficient adhesion may not be possible, and if it exceeds 150°C, the second particles may melt.

Note that the adhesion step is preferably performed in a dispersion medium such as an alkylamine.
For example, if no reaction occurs between the first particles and each component constituting the silver amine complex, the surface of the first particles may be mixed and heated. Both the forming step and the adhering step may be performed simultaneously by forming the second particles attached to the second particles.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

(Example 1)
In this example, the second particle formation step and attachment step were performed in one step.

First, in a centrifuge tube, 0.1 g of silver oxalate, 1 g of silver coated aluminum powder as the first particles (manufactured by Toyo Aluminum Co., Ltd., TecFiler TFM-A05P, spherical, average particle diameter D50: 6 μm), 7. Add 3×10 ⁻² g of n-hexylamine, 5.8×10 ⁻² g of n-dodecylamine, and 5.1×10 ⁻² g of N,N dimethyl-1,3-diaminopropane. and mixed.

0.85 g of n-hexylamine was added to the resulting mixture and stirred at 110° C. for 30 minutes. After adding methanol to the obtained mixture and dispersing it, the obtained dispersion liquid was centrifuged to remove the supernatant, thereby washing the reaction product. A purple precipitate was obtained by performing the same methanol washing three times in total. By adding α-terpineol to the obtained precipitate and dispersing the precipitate, a dispersion of composite particles in which silver nanoparticles (second particles) were attached to silver-coated aluminum particles (first particles) was obtained.

Photographs (SEM images taken with a field emission scanning electron microscope (manufactured by Hitachi High-Technologies, Inc., FE-SEM); the same applies hereinafter) of the obtained composite particles are shown in FIGS. 1(a) to (c). Note that FIGS. 2(a) and 2(b) are photographs of only the silver-coated aluminum powder used as the first particles used in Example 1. From the photographs shown in FIG. 1 or 2, it can be seen that the second particles are attached to the first particles. More specifically, when comparing the surface SEM photograph of the second particle attached to the first particle (FIG. 1(a)) and the surface SEM photograph of only the first particle (FIG. 2(a)), FIG. In a), spherical particles with a size of about 20 nm are seen scattered. This is the second particle, and the SEM photograph (FIG. 1(a)) shows that the second particle is attached to the first particle.

The average particle diameter of the second particles in the composite particles can be determined by measuring the particle diameters of the second particles one by one in an electron microscope image and calculating the average value of the particle diameters of any 20 second particles. Calculated.

(Example 2)
In this example, the second particles were formed first, and the second particles were attached to the first particles in the next step.

(Second particle formation step)
In a centrifuge, 1.152 g of n-hexylamine, 0.885 g of n-dodecylamine, 0.778 g of N,N-dimethyl-1,3-diaminopropane, 0.0502 g of oleic acid, and 1 .52 g of silver oxalate was added and stirred for 30 minutes. The resulting mixture was heated to 110°C to allow the reaction to proceed. After adding methanol to the obtained reaction product and dispersing it, the reaction product was washed by centrifuging the obtained dispersion and removing the supernatant. Second particles were obtained by performing similar methanol washing three times in total.

The obtained second particles were dispersed in a solvent (a 1:4 mixture of butanol and octanol) to obtain a dispersion. When the second particles in the obtained dispersion were observed with a field emission scanning electron microscope (manufactured by Hitachi High-Technologies, FE-SEM), the average particle diameter was 20 nm. Note that the average particle diameter of the second particles was calculated in the same manner as in Example 1.

(Second particle adhesion process)
10 g of silver-coated aluminum powder (manufactured by Toyo Aluminum Co., Ltd., TecFiler TFM-A05P, average particle diameter D50: 6 μm) as the first particles was added to 2 g of the obtained second particle dispersion (solid content 1 g). 1 particle was dispersed.

Next, the dispersion was heated at 100° C. for 30 minutes to obtain a dispersion of composite particles in which the second particles were attached to the surfaces of the first particles.

Photographs of the obtained composite particles are shown in FIGS. 3(a) to (d) and FIGS. 4(a) to (b). From the photographs shown in FIGS. 3 and 4, it can be seen that the second particles are attached to the first particles. More specifically, when comparing the surface SEM photograph of the second particle attached to the first particle (FIG. 3(c)) and the surface SEM photograph of only the first particle (FIG. 2(a)), FIG. In c), spherical particles with a size of about 20 nm are aggregated but scattered. This is the second particle, and the SEM photograph (FIG. 3(c)) shows that the second particle is attached to the first particle.

(Example 3)
The first particles were changed from silver-coated aluminum powder to silver-coated silica powder (manufactured by Toyo Aluminum Co., Ltd., TecFiler TFM-C02P, average particle diameter D50: 2 μm). A composite particle dispersion was obtained in the same manner as in Example 1 except for the above.

Photographs of the obtained composite particles are shown in FIGS. 5(a) to (c) and 6(a) to (b). From the photographs shown in FIGS. 5 and 6, it can be seen that the second particles are attached to the first particles. More specifically, in the SEM photograph (FIG. 5(c)) of the surface of the first particle with the second particle attached thereto, spherical particles with a size of about 20 nm are seen scattered. This is the second particle, and the SEM photograph (FIG. 5(c)) shows that the second particle is attached to the first particle.

(Example 4)
The ratio of second particles to first particles was increased as shown in Table 1. A composite particle dispersion was obtained in the same manner as in Example 1 except for the above.

Photographs of the obtained composite particles are shown in FIGS. 7(a) to (c) and FIGS. 8(a) to (b). From the photographs shown in FIGS. 7 and 8, it can be seen that the second particles are attached to the first particles. More specifically, when comparing the surface SEM photograph of the second particle attached to the first particle (FIG. 7(b)) and the surface SEM photograph of only the first particle (FIG. 2(a)), FIG. In b), spherical particles with a size of about 20 nm aggregate and can be seen over the entire surface. This is the second particle, and the SEM photograph (FIG. 7(b)) shows that the second particle is attached to the first particle.

(Example 5)
The first particles were changed from silver-coated aluminum powder to flaky silver-coated copper powder (manufactured by Toyo Aluminum Co., Ltd., TecFiler TFM-C05F, average particle diameter D50: 5 μm). A composite particle dispersion was obtained in the same manner as in Example 1 except for the above.

(Comparative example 1)
The first particles were changed from silver-coated aluminum powder to atomized aluminum powder (D50: 5 μm, manufactured by Toyo Aluminum Co., Ltd.). A composite particle dispersion was obtained in the same manner as in Example 1 except for the above.

(Comparative example 2)
The second particles obtained in the "second particle formation step" of Example 2 were changed to commercially available 30 nm silver nanoparticles NAG-71 (manufactured by Daiken Chemical Industry Co., Ltd.).

After the first particles were added to a commercially available dispersion of second particles and dispersed, the second particles were not attached by heating. A mixed dispersion of first particles and second particles was obtained in the same manner as in the "second particle adhesion step" of Example 2 except for the above.

(Comparative example 3)
A composite particle dispersion was obtained in the same manner as in Example 1, except that the first particles (silver coated aluminum powder) were not added.

[Measurement of sheet resistance]
Samples were prepared by applying each of the dispersions of Examples and Comparative Examples dropwise onto a glass substrate, followed by sintering at 150° C. for 1 hour. The sheet resistance of each sample (a simulated sample of a wiring layer made using composite particles) was measured using "Loresta" manufactured by Mitsubishi Chemical Analytech. The results are shown in Table 1.

In Table 1, the column "Printing characteristics (sample thickness)" indicates the measurement results of the sample thickness. In addition, the section "Possibility of low-temperature firing (adhesion after heating at 150°C for 30 minutes)" indicates the adhesion between the first and second particles after heating the composite particles at 150°C for 30 minutes. There is. The adhesion was evaluated as "A" when the resistance of the film after firing could be measured, and as "B" when the resistance could not be measured and peeling or cracking occurred.

From the results shown in Table 1, when the surface of the first particle is coated with silver (Examples 1 to 5), the sheet resistance is higher than when the first particle is made of only aluminum (Comparative Example 1). The result was low. From this, since not only the second particle but also the surface of the first particle is made of highly conductive silver, sintering progresses sufficiently even at low temperatures, and the conduction between the first particle and the second particle is sufficient. Therefore, it is thought that the conductivity of a conductor layer (wiring) etc. made of sintered composite particles is improved.

In addition, since the sheet resistance of Comparative Example 2 is also higher than that of the Example, it is thought that the high conductivity as in the Example cannot be obtained due to insufficient adhesion between the first and second particles. It will be done.

Furthermore, from the results of the printing characteristics (sample thickness) of Comparative Example 3, it was found that it was not possible to form a sufficiently thick conductor layer (wiring) using only the second particles, the sheet resistance was high, and sufficient conductivity was not achieved. It turns out that you can't get it.

The embodiments and examples disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

Claims (6)

A composite particle containing at least a first particle whose surface is made of silver or a silver alloy, and a second particle whose surface is made of silver or a silver alloy,
The first particles have an average particle diameter of 100 nm or more and 100 μm or less,
The second particles have an average particle diameter of 1 nm or more and 50 nm or less,
At least one second particle is attached to the surface of the first particle ,
The amount of the second particles is 1.9 parts by volume or more and 9.6 parts by volume or less per 100 parts by volume of the first particles . The composite particle according to claim 1, wherein the first particle includes a core particle and a coating layer made of silver or a silver alloy provided on the surface of the core particle. The composite particle according to claim 2, wherein the core particle is made of at least one selected from the group consisting of aluminum, alumina, silica, copper, nickel, resin, and carbon. A forming step of forming second particles made of silver or a silver alloy by heating the silver amine complex;
an adhering step of adhering the second particles to the surface of the first particles, at least the surface of which is made of silver or a silver alloy;
A method for producing composite particles, comprising:
The first particles have an average particle diameter of 100 nm or more and 100 μm or less,
The second particles have an average particle diameter of 1 nm or more and 50 nm or less,
The manufacturing method, wherein the amount of the second particles in the composite particles is from 1.9 parts by volume to 9.6 parts by volume per 100 parts by volume of the first particles. The forming step and the adhering step are performed by mixing and heating the first particles and the silver amine complex to form the second particles attached to the surface of the first particles. The manufacturing method according to claim 4. An ink comprising the composite particles according to any one of claims 1 to 3.