Method for manufacturing metal nanoparticle dispersions

Abstract

The present invention relates to a method for producing a metal fine particle dispersion liquid in which the generation of coarse particles is suppressed. 【Solution means】A raw material mixture containing a metal oxide A, a divalent alcohol B, a polyalkylene glycol dialkyl ether C, and a polymer D having an anionic hydrophilic group is obtained, and a mixing reaction step of performing a reduction reaction on the raw material mixture is provided. The divalent alcohol B is a divalent alcohol represented by the following general formula (1). A method for producing a metal fine particle dispersion. JPEG2026089850000007.jpg2685 (In the general formula (1), R 1 and R 2 are a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and R 3 is at least one alkylene group selected from an ethylene group and a propylene group, and n is an integer of 0 or more and 30 or less. However, in the general formula (1), when both R 1 and R 2 are hydrogen atoms, R 3 contains at least a propylene group, and n is 1 or more.)

Description

[Technical Field]

[0001] This invention relates to a method for producing a dispersion of metal microparticles. [Background technology]

[0002] Metal nanoparticles are expected to have a wide range of industrial applications due to the diversity of functions and physical properties that emerge when metals are miniaturized to the nanoscale. To promote the industrial use of metal nanoparticles, various methods for producing them are being investigated. For example, known chemical methods for generating metal nanoparticles include wet methods such as reducing metal ions eluted from metal compounds in a liquid, and extracting metal atoms by thermal decomposition of metal complexes. Methods using metal complexes require heat treatment at high temperatures, and there are problems with removing residual organic matter from the reducing solution used to reduce the metal complexes. Therefore, efforts have been made to investigate production methods that are highly practical for industrial use.

[0003] For example, Patent Document 1 describes a method for producing a metal nanoparticle dispersion containing metal nanoparticles a dispersed in polymer B, with the aim of providing a method for producing a metal nanoparticle dispersion containing fine metal nanoparticles with a particle size of 100 nm or less at a high concentration, and an ink containing the metal nanoparticle dispersion, comprising step 1 of mixing metal oxide A, polymer B, and compound C, wherein polymer B has hydrophilic groups, compound C is a dihydric alcohol represented by a specific general formula, and the average cumulant particle size of the metal nanoparticles a is 50 nm or less. Furthermore, Patent Document 2 describes a metal microparticle dispersion that can form a metal film with excellent storage stability and low resistivity, an ink containing the metal microparticle dispersion, and a method for printing printed materials using the ink. The dispersion contains metal microparticles A, polyalkylene glycol dialkyl ether B, and polyol C, and the mass ratio of polyalkylene glycol dialkyl ether B to metal microparticles A (polyalkylene glycol dialkyl ether B / metal microparticles A) is 0.5 or more and 1.5 or less, and the metal microparticles A are dispersed in a dispersant D. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-63507 [Patent Document 2] Japanese Patent Publication No. 2022-32959 [Overview of the project] [Problems that the invention aims to solve]

[0005] For example, when using metal microparticle dispersions in coatings such as conductive inks, the presence of coarse particles in the dispersion can lead to reduced ejection performance during printing and decreased conductivity of the resulting coating, thus diminishing the desired functionality. Furthermore, since the raw materials for metal microparticle dispersions are expensive, it is crucial from a manufacturing cost perspective to be able to produce them in high yield. The technologies described in Patent Documents 1 and 2 sometimes failed to adequately suppress the generation of coarse particles during the manufacturing process of metal microparticle dispersions. Therefore, there is a need for a method of producing metal microparticle dispersions that generates fewer coarse particles. This invention relates to a method for producing a dispersion of metal microparticles in which the generation of coarse particles is suppressed. [Means for solving the problem]

[0006] The inventors of the present invention have found that a method for producing a metal fine particle dispersion having a mixing reaction step of mixing a metal oxide A, a divalent alcohol B having a specific structure, a polyalkylene glycol dialkyl ether C, and a polymer D having an anionic hydrophilic group and performing a reduction reaction can solve the above problems. The present invention relates to the following [1]. [1] A method for producing a metal fine particle dispersion, comprising obtaining a raw material mixture liquid containing a metal oxide A, a divalent alcohol B, a polyalkylene glycol dialkyl ether C, and a polymer D having an anionic hydrophilic group, and having a mixing reaction step of performing a reduction reaction on the raw material mixture liquid, wherein the divalent alcohol B is a divalent alcohol represented by the following general formula (1). [Chemical formula] (In general formula (1), R 1 and R 2 are a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R 3 is at least one alkylene group selected from an ethylene group and a propylene group, and n is an integer of 0 or more and 30 or less. However, in general formula (1), when both R 1 and R 2 are hydrogen atoms, R 3 contains at least a propylene group, and n is 1 or more.) [Advantages of the Invention]

[0007] According to the present invention, a method for producing a metal fine particle dispersion in which the generation of coarse particles is suppressed can be provided. [Brief Description of the Drawings]

[0008] [Figure 1] It is a schematic diagram of a continuous reactor used in Examples and Comparative Examples. [Embodiments for Carrying Out the Invention]

[0009] [Method for Producing Metal Fine Particle Dispersion] The method for producing a metal fine particle dispersion of the present invention includes obtaining a raw material mixture containing a metal oxide A, a divalent alcohol B, a polyalkylene glycol dialkyl ether C, and a polymer D having an anionic hydrophilic group (hereinafter also simply referred to as "polymer D"), and has a mixing reaction step of performing a reduction reaction on the raw material mixture. The divalent alcohol B is a divalent alcohol represented by the following general formula (1).

[0010] [Chemical formula] (In the general formula (1), R 1 and R 2 are a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R 3 is at least one alkylene group selected from an ethylene group and a propylene group, and n is an integer of 0 or more and 30 or less. However, in the general formula (1), when both R 1 and R 2 are hydrogen atoms, R 3 contains at least a propylene group, and n is 1 or more.)

[0011] According to the present invention, a metal fine particle dispersion in which the generation of coarse particles is suppressed can be obtained. The reason is not clear, but it is considered as follows. In the present invention, metal fine particles can be generated by reducing metal ions eluted from the metal oxide A with the divalent alcohol B, and a metal fine particle dispersion can be obtained. However, when the metal oxide A is used, it has been found that a reduction reaction also occurs on the surface of the metal oxide A, and coarse particles aggregated with the metal oxide A as a nucleus are generated. In the present invention, by further mixing the polyalkylene glycol dialkyl ether C, the reduction reaction occurring on the surface of the metal oxide A can be suppressed, so it is considered that the generation of coarse particles can be suppressed. Furthermore, since the present invention mixes the polymer D having an anionic hydrophilic group, the metal fine particles generated by the reduction reaction can be efficiently dispersed in the solvent, so it is considered that the aggregation of the metal fine particles can be suppressed and the generation of coarse particles can be suppressed.

[0012] The present invention comprises a mixing reaction step (hereinafter also simply referred to as the "mixing reaction step") in which a raw material mixture containing a metal oxide A, a dihydric alcohol B, a polyalkylene glycol dialkyl ether C, and a polymer D having an anionic hydrophilic group is obtained, and the raw material mixture is subjected to a reduction reaction. In the mixing reaction step, metal oxide A is reduced by dihydric alcohol B, and the formation of coarse particles is suppressed by polyalkylene glycol dialkyl ether C, resulting in the formation of metal nanoparticles dispersed in polymer D having anionic hydrophilic groups, thereby obtaining a metal nanoparticle dispersion. The method of the mixed reaction process is not particularly limited, and batch or continuous processes can be selected as appropriate, but a continuous process is preferable from the viewpoint of productivity.

[0013] (Batch method) When the mixing reaction step is in a batch format, the method of the mixing reaction step is not particularly limited, but metal oxide A, dihydric alcohol B, polyalkylene glycol dialkyl ether C, and polymer D may be mixed at once and subjected to a reduction reaction, or metal oxide A, dihydric alcohol B, polyalkylene glycol dialkyl ether C, and polymer D may be mixed sequentially and subjected to a reduction reaction. If the mixing reaction step is a batch process, the method of the mixing reaction step may be, for example, to mix dihydric alcohol B, polyalkylene glycol dialkyl ether C, and polymer D, then mix in metal oxide A, and carry out a reduction reaction. Furthermore, if the mixing reaction process is batch-type, the temperature conditions for the reduction reaction may be set to a constant temperature or changed in stages. When a constant temperature is set, from the viewpoint of promoting the reduction reaction and suppressing the generation of coarse particles, it is preferably 30°C or higher, more preferably 32°C or higher, even more preferably 35°C or higher, and preferably 70°C or lower, more preferably 60°C or lower, and even more preferably 50°C or lower. From the viewpoint of production stability, it is preferable to gradually increase the reaction temperature in the reduction reaction. Therefore, when the mixing reaction process is batch type, the temperature conditions in the initial stage of the reduction reaction are preferably 30°C or higher, more preferably 32°C or higher, even more preferably 35°C or higher, and preferably 70°C or lower, more preferably 60°C or lower, and even more preferably 50°C or lower, from the viewpoint of suppressing the amount of heat generated by the reaction. Furthermore, when the mixing reaction process is batch type, the temperature conditions in the later stages of the reduction reaction, when the amount of heat generated by the reaction decreases, are preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 80°C or lower, from the viewpoint of promoting the reduction reaction and suppressing the generation of coarse particles.

[0014] (Continuous type) When the mixing reaction process is continuous, a known continuous reactor can be used, and it is preferable to use, for example, a continuous tank reactor as the reaction section of the continuous reactor. If the mixing reaction process is continuous, the method of the mixing reaction process may be to pass a single raw material mixture solution, in which metal oxide A, dihydric alcohol B, polyalkylene glycol dialkyl ether C, and polymer D are mixed and passed through the reactor, or to pass metal oxide A, dihydric alcohol B, polyalkylene glycol dialkyl ether C, and polymer D through the reactor as two or more different raw material mixture solutions. When the mixing reaction process is continuous, the preferred method of the mixing reaction process is to pass metal oxide A and dihydric alcohol B to the reactor as mixed solutions of different raw materials, from the viewpoint of preventing the reduction reaction from proceeding before the mixture is passed to the reactor and suppressing the generation of coarse particles. That is, when the mixing reaction process is continuous, the preferred method of the mixing reaction process is to pass raw material 1 containing metal oxide A and raw material 2 containing dihydric alcohol B through the reactor, more preferably a method in which raw material 1 containing metal oxide A and polyalkylene glycol dialkyl ether C and raw material 2 containing dihydric alcohol B are passed through the reactor, and even more preferably a method in which raw material 1 containing metal oxide A, polyalkylene glycol dialkyl ether C and polymer D and raw material 2 containing dihydric alcohol B and polymer D are passed through the reactor. Raw materials 1 and 2 may be mixed beforehand before being charged into the reaction apparatus. Furthermore, raw materials 1 and 2 may contain water as needed. Raw materials 1 and 2 are mixed in the reaction apparatus to form a raw material mixture, which is then subjected to a reduction reaction. Furthermore, in the case of a continuous mixed reaction process, the external heating temperature of the reaction section is preferably 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher, from the viewpoint of promoting the reduction reaction and suppressing the generation of coarse particles, and preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 80°C or lower, from the viewpoint of suppressing the amount of heat generated by the reaction.

[0015] <Metal Oxide A> The metals (metallic elements) contained in metal oxide A include Group 4 transition metals such as titanium and zirconium, Group 5 transition metals such as vanadium and niobium, Group 6 transition metals such as chromium, molybdenum and tungsten, Group 7 transition metals such as manganese, technetium and rhenium, Group 8 transition metals such as iron and ruthenium, Group 9 transition metals such as cobalt, rhodium and iridium, Group 10 transition metals such as nickel, palladium and platinum, Group 11 transition metals such as copper, silver and gold, Group 12 transition metals such as zinc and cadmium, Group 13 metals such as aluminum, gallium and indium, and Group 14 metals such as germanium, tin and lead. The aforementioned metal may be used as a single metal or as an alloy by combining two or more metals. Furthermore, metal oxide A can be used alone or as a mixture of two or more metal oxides. In particular, metal oxide A is preferably an oxide of a transition metal from Group 4 to Group 11, Period 4 to Period 6; more preferably an oxide of a precious metal such as copper, gold, silver, platinum, or palladium; even more preferably at least one oxide selected from gold, silver, copper, and palladium; even more preferably at least one selected from gold oxide, silver oxide, and copper oxide; even more preferably at least one selected from silver oxide and copper oxide; and even more preferably silver oxide.

[0016] The average particle size of metal oxide A is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, even more preferably 20 μm or more, and preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less, and even more preferably 35 μm or less, from the viewpoint of suppressing the generation of coarse particles and from the viewpoint of conductivity and gloss of the coated surface of the metal fine particle ink.

[0017] In the reduction reaction of the mixing reaction step, the content of metal oxide A in the raw material mixture (in the raw material mixture at the start of the reduction reaction) is preferably 30% by mass or more, more preferably 32% by mass or more, even more preferably 35% by mass or more, and preferably 50% by mass or less, more preferably 48% by mass or less, and even more preferably 45% by mass or less, from the viewpoint of promoting the reduction reaction and suppressing the generation of coarse particles.

[0018] <Dihydric alcohol B> Dihydric alcohol B is a dihydric alcohol represented by the following general formula (1). In the present invention, dihydric alcohol B functions as a reducing agent for metal oxide A and also functions as a dispersion medium for metal nanoparticle dispersions.

[0019] [ka] (In general formula (1), R 1 and R 2 R is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. 3 R is at least one alkylene group selected from ethylene and propylene groups, and n is an integer between 0 and 30. However, in general formula (1), R 1 and R 2 If all of them are hydrogen atoms, then R 3 (It contains at least a propylene group, and n is 1 or greater.)

[0020] In the above general formula (1), R 1 and R 2 These may be the same or different, but from the viewpoint of availability and economy, preferably one is a hydrogen atom and the other is a hydrocarbon group having 1 to 3 carbon atoms, more preferably one is a hydrogen atom and the other is a methyl group, and even more preferably R 1 R is a methyl group 2 That is a hydrogen atom. In the above general formula (1), R 3R is at least one alkylene group selected from ethylene and propylene groups, and is preferably a propylene group from the viewpoint of promoting the reduction reaction. 1 and R 2 If all of them are hydrogen atoms, then R 3 It contains at least a propylene group. 3 When R is a propylene group, it is preferably a 1,2-propanediyl group represented by -CH(CH3)CH2- or -CH2CH(CH3)-. Also, when n is 2 or more, there are multiple R groups in the molecule. 3 They may be the same or different from one another. In the above general formula (1), n ​​is R 3 R represents the average number of moles of oxyalkylene groups added, and is preferably 0 or 1 or more from the viewpoint of availability and economy. 1 and R 2 When all of them are hydrogen atoms, n is 1 or greater, and from the viewpoint of availability and economics, it is preferably 20 or less, more preferably 10 or less, even more preferably 5 or less, and even more preferably 3 or less.

[0021] The boiling point of dihydric alcohol B is preferably 175°C or higher, more preferably 185°C or higher, and preferably 240°C or lower, more preferably 200°C or lower, and even more preferably 190°C or lower, from the viewpoint of promoting the reduction reaction, as well as from the viewpoint of availability and economy. When two or more types of dihydric alcohol B are used in combination, the boiling point of dihydric alcohol B is a weighted average value weighted by the content (mass%) of each dihydric alcohol.

[0022] Examples of dihydric alcohol B include alkanediols such as 1,2-propanediol (propylene glycol), 1,2-butanediol, 2,3-butanediol, and 1,2-pentanediol; and polyalkylene glycols such as polypropylene glycol. Dihydric alcohol B can be used alone or in combination of two or more types. Among these, preferably is a dihydric alcohol having a 1,2-propanediyl skeleton, more preferably at least one selected from 1,2-propanediol and polypropylene glycol with a degree of polymerization of 2 to 20, even more preferably at least one selected from 1,2-propanediol and dipropylene glycol, and even more preferably 1,2-propanediol.

[0023] In the mixing reaction step, other reducing agents that act as reducing agents may be mixed in addition to dihydric alcohol B. Other reducing agents that can be used include both organic and inorganic reducing agents. Examples of organic reducing agents include alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 2-propanol, 1-butanol, 2-methyl-1-propanol, and 1-methoxy-2-propanol; aldehydes such as formaldehyde, acetaldehyde, and propionaldehyde; acids such as ascorbic acid and citric acid and their salts; and amines such as triethylamine, N,N-dimethylaminoethanol, and N-methyldiethanolamine. Examples of inorganic reducing agents include borohydride salts such as sodium borohydride and ammonium borohydride; aluminum hydride salts such as lithium aluminum hydride and potassium aluminum hydride; hydrazines such as hydrazine and hydrazine carbonate; and hydrogen gas. Furthermore, other reducing agents may be used individually or in combination of two or more.

[0024] In the present invention, the mass ratio of dihydric alcohol B to metal oxide A (dihydric alcohol B / metal oxide A) is preferably 0.3 or higher, more preferably 0.4 or higher, even more preferably 0.45 or higher, and even more preferably 0.5 or higher, from the viewpoint of promoting the reduction reaction, and from the viewpoint of suppressing the generation of coarse particles and productivity, it is preferably 2.0 or lower, more preferably 1.5 or lower, even more preferably 1.0 or lower, and even more preferably 0.8 or lower.

[0025] In the reduction reaction of the reaction step, the content of dihydric alcohol B in the raw material mixture (raw material mixture at the start of the reduction reaction) is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of promoting the reduction reaction, and preferably 55% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of suppressing the generation of coarse particles.

[0026] <Polyalkylene glycol dialkyl ether C> The present invention, by including polyalkylene glycol dialkyl ether C, suppresses the direct reduction of the surface of metal oxide A by dihydric alcohol B during the reduction reaction, thereby suppressing the formation of coarse particles with metal oxide A as the nucleus.

[0027] The polyoxyalkylene group constituting the polyalkylene glycol dialkyl ether C is preferably at least one selected from polyoxyethylene groups and polyoxypropylene groups, more preferably a polyoxyethylene group, from the viewpoint of suppressing the direct reduction of the surface of metal oxide A by dihydric alcohol B and suppressing the generation of coarse particles with metal oxide A as a nucleus. Examples of alkyl groups constituting polyalkylene glycol dialkyl ether C include methyl, ethyl, propyl, butyl, and pentyl groups. From the viewpoint of improving the dispersion stability of metal fine particles, improving the storage stability of the dispersion, reducing the resistivity of the metal film, and from the viewpoint of availability and cost-effectiveness, the number of carbon atoms in the alkyl group is preferably 1 to 5, more preferably 1 to 4, even more preferably 1 to 3, even more preferably 1 to 2, and even more preferably 1. Polyalkylene glycol dialkyl ether C may be used alone or in combination of two or more types.

[0028] Examples of polyalkylene glycol dialkyl ether C include polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether. Examples of polyethylene glycol dialkyl ethers include polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol dipropyl ether, polyethylene glycol dibutyl ether, polyethylene glycol dipentyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, and diethylene glycol dibutyl ether. Examples of polypropylene glycol dialkyl ethers include polypropylene glycol dimethyl ether, polypropylene glycol diethyl ether, polypropylene glycol dipropyl ether, polypropylene glycol dibutyl ether, polypropylene glycol dipentyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, and tripropylene glycol dimethyl ether. Among these, polyalkylene glycol dialkyl ether C is preferably at least one selected from polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether, more preferably polyethylene glycol dialkyl ether, even more preferably polyethylene glycol dimethyl ether, even more preferably at least one selected from triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and pentaethylene glycol dimethyl ether, and even more preferably at least one selected from triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0029] The number-average molecular weight of the polyalkylene glycol dialkyl ether C is preferably 134 or higher, more preferably 150 or higher, even more preferably 160 or higher, and even more preferably 175 or higher, and preferably 300 or lower, more preferably 280 or lower, even more preferably 260 or lower, and even more preferably 250 or lower, from the viewpoint of suppressing the direct reduction of the surface of the metal oxide A by the dihydric alcohol B and suppressing the generation of coarse particles with the metal oxide A as a nucleus. The number-average molecular weight of polyalkylene glycol dialkyl ether C can be measured by gel permeation chromatography (GPC).

[0030] In the present invention, the mass ratio of polyalkylene glycol dialkyl ether C to metal oxide A (polyalkylene glycol dialkyl ether C / metal oxide A) is preferably 0.1 or higher, more preferably 0.12 or higher, even more preferably 0.5 or higher, and even more preferably 0.65 or higher, from the viewpoint of suppressing the generation of coarse particles and productivity, and from the viewpoint of promoting the reduction reaction, it is preferably 1.5 or lower, more preferably 1.3 or lower, even more preferably 1.0 or lower, and even more preferably 0.8 or lower.

[0031] In the reduction reaction of the reaction step, the content of polyalkylene glycol dialkyl ether C in the raw material mixture (raw material mixture at the start of the reduction reaction) is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of suppressing the generation of coarse particles, and from the viewpoint of promoting the reduction reaction, it is preferably 40% by mass or less, more preferably 38% by mass or less, even more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0032] <Polymer D having anionic hydrophilic groups> In the present invention, polymer D has an anionic hydrophilic group. Furthermore, in the present invention, polymer D functions as a dispersant for metal nanoparticles contained in a metal nanoparticle dispersion. The anionic hydrophilic groups of polymer D include carboxyl groups (-COOM), sulfonic acid groups (-SO3M), phosphate groups (-OPO3M2), etc., which exhibit acidity when they dissociate and release hydrogen ions, or their dissociated ionic forms (-COO-, -SO3-, -OPO3 2- ,-OPO3 - Examples include M). In the above chemical formula, M represents a hydrogen atom, an alkali metal, an ammonium, or an organic ammonium. Among these, the anionic hydrophilic group of polymer D is preferably a carboxyl group, from the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion.

[0033] When the anionic hydrophilic group of polymer D is a carboxyl group, it is preferable that the carboxyl group contained in polymer D is introduced into the polymer backbone by a monomer (d-1) having a carboxyl group. That is, from the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal fine particles in a metal fine particle dispersion, it is preferable that polymer D contains a constituent unit derived from a monomer (d-1) having a carboxyl group. In particular, as polymer D, a vinyl polymer d (hereinafter simply referred to as "polymer d") containing constituent units derived from monomer (d-1) having a carboxyl group (hereinafter also referred to as "monomer (d-1)"), constituent units derived from hydrophobic monomer (d-2) (hereinafter also referred to as "monomer (d-2)"), and constituent units derived from monomer (d-3) having a polyalkylene glycol segment (hereinafter also referred to as "monomer (d-3)") is preferred. Polymer d can be obtained by copolymerizing raw material monomers (hereinafter simply referred to as "raw material monomers") containing monomer (d-1), monomer (d-2), and monomer (d-3). Polymer d may be a block copolymer, a random copolymer, or an alternating copolymer.

[0034] [Monomers containing a carboxyl group (d-1)] The carboxyl group contained in monomer (d-1) is as described above. Examples of monomer (d-1) include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, and 2-methacryloyloxymethylsuccinic acid; and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and citraconic acid. The unsaturated dicarboxylic acid may also be an anhydride. Monomer (d-1) may be used alone or in combination of two or more types. From the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion, monomer (d-1) is preferably at least one selected from (meth)acrylic acid and maleic acid. In this invention, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acrylic acid" hereafter.

[0035] [Hydrophobic monomer (d-2)] From the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion, monomer (d-2) is preferably used as a monomer component of polymer d. In the present invention, "hydrophobic" means that when the monomer is dissolved in 100 g of ion-exchanged water at 25°C until saturated, the amount dissolved is less than 10 g. From the viewpoint of improving the content of fine metal particles, the amount of monomer (d-2) dissolved is preferably 5 g or less, more preferably 1 g or less. The monomer (d-2) is preferably at least one selected from aromatic group-containing monomers and (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols. In this invention, "(meth)acrylate" refers to at least one selected from acrylate and methacrylate. The same applies to "(meth)acrylate" below.

[0036] The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have substituents including heteroatoms, and more preferably one or more selected from styrene monomers and aromatic group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500 from the viewpoint of polymer productivity, i.e., reactivity. Examples of styrene monomers include styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), and divinylbenzene. However, from the viewpoint of polymer productivity, availability, and economics, styrene and α-methylstyrene are preferred. From the viewpoint of polymer productivity, availability, and economics, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. are preferred as aromatic group-containing (meth)acrylates, with benzyl (meth)acrylate being more preferred.

[0037] (Meth)acrylates having hydrocarbon groups derived from aliphatic alcohols are preferably those having hydrocarbon groups derived from aliphatic alcohols with 1 to 22 carbon atoms, from the viewpoint of suppressing the formation of coarse particles and improving the dispersibility of metal nanoparticles in metal nanoparticle dispersions. Examples include (meth)acrylates having linear alkyl groups such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; (meth)acrylates having branched alkyl groups such as isopropyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and (meth)acrylates having alicyclic alkyl groups such as cyclohexyl (meth)acrylate. Among these, from the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion, it is more preferable to have an alkyl group having 6 to 10 carbon atoms. The monomer (d-2) may be used alone or in combination of two or more types.

[0038] From the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal fine particles in the metal fine particle dispersion, monomer (d-2) is preferably an aromatic group-containing monomer, more preferably a styrene monomer, even more preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, and 4-vinyltoluene (4-methylstyrene), and even more preferably at least one selected from styrene and α-methylstyrene.

[0039] [Monomers having polyalkylene glycol segments (d-3)] From the viewpoint of improving the content of fine metal particles, monomer (d-3) is preferably used as a monomer component of polymer d. From the viewpoint of improving the content of fine metal particles, monomer (d-3) is preferably a monomer that can introduce a polyalkylene glycol segment as a side chain of polymer d. Examples of such monomers include polyalkylene glycol (meth)acrylate, alkoxy polyalkylene glycol (meth)acrylate, and phenoxyalkylene glycol (meth)acrylate. Monomer (d-3) may be used alone or in combination of two or more types.

[0040] From the viewpoint of improving the content of fine metal particles and from the viewpoint of availability and cost-effectiveness, monomer (d-3) is preferably at least one selected from polyalkylene glycol (meth)acrylate and alkoxy polyalkylene glycol (meth)acrylate, and more preferably alkoxy polyalkylene glycol (meth)acrylate. From the viewpoint of availability and cost-effectiveness, the number of carbon atoms in the alkoxy group of the alkoxy polyalkylene glycol (meth)acrylate is preferably 1 to 8, more preferably 1 to 4. Examples of the alkoxy polyalkylene glycol (meth)acrylate include methoxypolyalkylene glycol (meth)acrylate, ethoxypolyalkylene glycol (meth)acrylate, propoxypolyalkylene glycol (meth)acrylate, butoxypolyalkylene glycol (meth)acrylate, octoxypolyalkylene glycol (meth)acrylate, and the like.

[0041] The monomer (d-3) polyalkylene glycol segment preferably contains units derived from an alkylene oxide having 2 to 4 carbon atoms, from the viewpoint of availability and economic efficiency. Examples of the alkylene oxide include ethylene oxide, propylene oxide, and butylene oxide. The number of alkylene oxide-derived units in the polyalkylene glycol segment is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, and preferably 100 or less, more preferably 70 or less, and even more preferably 50 or less, from the viewpoint of availability and economic efficiency. The polyalkylene glycol segment is preferably a copolymer containing ethylene oxide-derived units and propylene oxide-derived units, from the viewpoint of improving the content of fine metal particles. The molar ratio [EO / PO] of ethylene oxide units (EO) to propylene oxide units (PO) is preferably 60 / 40 or more, more preferably 65 / 35 or more, even more preferably 70 / 30 or more, and preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less. The copolymer containing units derived from ethylene oxide and units derived from propylene oxide may be a block copolymer, a random copolymer, or an alternating copolymer.

[0042] Specific examples of commercially available monomers (d-3) include NK ester AM-90G, AM-130G, AMP-20GY, AMP-230G, M-20G, 40G, 90G, 230G, etc. from Shin Nakamura Chemical Industry Co., Ltd.; and Bremmer PE-90, 200, 350, etc., PME-100, 200, 400, 1000, 4000, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50PEP-300, 50POEP-800B, 43PAPE-600B, etc. from NOF Corporation.

[0043] (Content of each monomer component or constituent unit in the raw material monomer or polymer d) When polymer d is manufactured, the content of monomers (d-1) to (d-3) in the raw material monomers (content as unneutralized amount, the same applies hereinafter) or the content of constituent units derived from monomers (d-1) to (d-3) in polymer d is as follows, from the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion. The monomer (d-1) content is preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, and preferably 40 mol% or less, more preferably 35 mol% or less, and even more preferably 30 mol% or less. The monomer (d-2) content is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 65 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, and even more preferably 80 mol% or less. The monomer (d-3) content is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 7 mol% or more, and preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 15 mol% or less.

[0044] From the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion, polymer d preferably contains constituent units derived from (meth)acrylic acid and maleic acid as monomer (d-1), constituent units derived from styrene monomers as monomer (d-2), and constituent units derived from alkoxy polyalkylene glycol (meth)acrylate as monomer (d-3). Polymer d may be synthesized by known methods or may be a commercially available product. Examples of commercially available polymer d include DISPERBYK-190 and 2015 from BYK.

[0045] The number-average molecular weight of polymer D is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 3,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, even more preferably 10,000 or less, and even more preferably 7,000 or less. If the number-average molecular weight of polymer D is within the above range, it can exhibit sufficient adsorption to metal nanoparticles and dispersion stability.

[0046] The acid value of polymer D is preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, even more preferably 20 mg KOH / g or more, and preferably 200 mg KOH / g or less, more preferably 100 mg KOH / g or less, even more preferably 50 mg KOH / g or less, and even more preferably 30 mg KOH / g or less, from the viewpoint of suppressing the generation of coarse particles and improving the dispersibility of metal nanoparticles in the metal nanoparticle dispersion.

[0047] In the present invention, the mass ratio of polymer D having anionic hydrophilic groups to metal oxide A (polymer D having anionic hydrophilic groups / metal oxide A) is preferably 0.01 or higher, more preferably 0.03 or higher, even more preferably 0.04 or higher, and even more preferably 0.05 or higher, from the viewpoint of suppressing the generation of coarse particles, and from the viewpoint of promoting the reduction reaction, it is preferably 0.20 or lower, more preferably 0.15 or lower, even more preferably 0.12 or lower, and even more preferably 0.10 or lower.

[0048] In the reduction reaction of the reaction step, the content of polymer D in the raw material mixture (in the raw material mixture at the start of the reduction reaction) is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of suppressing the generation of coarse particles.

[0049] <Water> In the mixing reaction step of the present invention, water may be further added. In the present invention, the water content in the raw material mixture (the raw material mixture at the start of the reduction reaction) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 0.3% by mass or less, from the viewpoint of promoting the reduction reaction. Furthermore, in the present invention, it is preferable that the raw material mixture does not contain water from the viewpoint of suppressing the generation of coarse particles.

[0050] [Metal fine particle dispersion] The metal nanoparticle dispersion of the present invention is obtained by the method for producing the metal nanoparticle dispersion described above. Therefore, the metal nanoparticle dispersion of the present invention comprises metal nanoparticles obtained by reduction of metal oxide A, a dihydric alcohol B and a polyalkylene glycol dialkyl ether C as dispersion media, and a polymer D as a dispersant for the metal nanoparticles. Furthermore, the metal nanoparticle dispersion of the present invention may contain water as needed. The metal nanoparticle dispersion of the present invention comprises metal nanoparticles dispersed in polymer D in a dispersion medium. Since the metal microparticle dispersion of the present invention is obtained by the above-described method for producing metal microparticle dispersions, the generation of coarse particles during manufacturing is suppressed, and therefore it has the characteristic of having a low content of coarse particles.

[0051] In the metal nanoparticle dispersion of the present invention, the metal (metal atom) constituting the metal nanoparticles is a metal obtained by reducing the above-mentioned metal oxide A, preferably a transition metal of the 4th to 6th period in groups 4 to 11, more preferably at least one selected from gold, silver, copper, and palladium, even more preferably at least one selected from gold, silver, and copper, even more preferably at least one selected from silver and copper, and even more preferably silver.

[0052] Polymer D can exist in a dispersion of metal nanoparticles in three forms: adsorbed onto metal nanoparticles, encapsulated within metal nanoparticles containing polymer D, and unadsorbed. From the viewpoint of dispersion stability of metal nanoparticles, the form in which polymer D is contained within metal nanoparticles is preferred, and the encapsulated state in which polymer D is contained within metal nanoparticles is more preferred.

[0053] In the metal nanoparticle dispersion of the present invention, the content of metal nanoparticles in the metal nanoparticle dispersion is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of facilitating the preparation of the ink described later, and from the viewpoint of the dispersion stability of the metal nanoparticles, it is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0054] In the metal nanoparticle dispersion of the present invention, the content of polymer D in the metal nanoparticle dispersion is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, from the viewpoint of the dispersion stability of the metal nanoparticles, and preferably 10% by mass or less, more preferably 7.0% by mass or less, and even more preferably 5.0% by mass or less, from the viewpoint of performance expression such as conductivity in conductive ink.

[0055] In the metal nanoparticle dispersion of the present invention, the cumulant average particle size of the metal nanoparticles is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, and preferably 50 nm or less, and more preferably 45 nm or less, from the viewpoint of conductivity and gloss of the metal nanoparticle ink coated surface. The cumulant average particle size is measured by the method described in the examples.

[0056] The viscosity of the metal fine particle dispersion of the present invention at 25°C is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, even more preferably 15 mPa·s or more, and preferably 40 mPa·s or less, more preferably 30 mPa·s or less, and even more preferably 25 mPa·s or less, from the viewpoint of use as a raw material for inkjet printing inks.

[0057] The metal nanoparticle dispersion of the present invention has a low content of coarse particles and can therefore be used in a wide range of applications. Examples of such applications include various inks; conductive materials such as wiring materials, electrode materials, and multilayer ceramic capacitors (hereinafter also referred to as "MLCCs"); bonding materials such as solder; various sensors; antennas such as tags for radio frequency identifier (RFID) technology using short-range wireless communication; catalysts; optical materials; and medical materials. Furthermore, because the metal fine particle dispersion of the present invention contains a low amount of coarse particles, it can be particularly suitable for use in various inks, and is even more suitable for use as an inkjet printing ink. [Examples]

[0058] The raw materials used in the examples and comparative examples are as follows: [Metal Oxide A] • Silver oxide: AMES GOLDSMITH, Type-2 Silver oxide, medium volume particle size (D 50 ) 30 μm [Dihydric alcohol B] • PG: 1,2-propanediol [Polyalkylene glycol dialkyl ether C] PAGDA-1: Polyethylene glycol dimethyl ether, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade, number average molecular weight 240 PAGDA-2: Triethylene glycol dimethyl ether, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade, number average molecular weight 178 PAGDA-3: Tetraethylene glycol dimethyl ether, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade, number average molecular weight 222 [Polymer D] • DISPER BYK-2015: Aqueous solution of styrene / α-methylstyrene / acrylic acid / maleic acid / alkoxy (polyethylene glycol / polypropylene glycol) acrylate (alkylene oxide units: 32 mol, molar ratio [EO / PO] = 75 / 25) copolymer (solids content 40% by mass), manufactured by BYK, number average molecular weight: 4,500, acid value: 10 mg KOH / g (Note that in Examples 1-6 and Comparative Example 2, DISPER BYK-2015 was allowed to dry completely, and only the solid content was used. In this case, the acid value was 24 mgKOH / g.)

[0059] [Medium volume particle size of metal oxide A] Using the LA-920 laser diffraction / scattering particle size distribution analyzer manufactured by Horiba, Ltd., ion-exchanged water is added to the measurement cell as the measurement solvent, and the volume median particle size (D) is measured at a concentration that results in an appropriate absorbance range. 50 ) was measured.

[0060] [Acid value of polymer D] The acid value of polymer D was measured according to the method of JIS K 0070. However, the measurement solvent was changed from the ethanol and ether mixture specified in JIS K 0070 to an acetone and toluene mixture (acetone:toluene = 4:6 (volume ratio)).

[0061] <Preparation of metal nanoparticle dispersions> (Batch method) Example 1 In a 5L stainless steel separable flask, 40g of completely dry DISPER BYK-2015 (polymer D), 60g of deionized water, 300g of PAGDA-1 (polyalkylene glycol dialkyl ether C), and 300g of PG (dihydric alcohol B) were added. The mixture was stirred at a speed of 150 rpm using a Maxblend stirring blade (blade diameter 100mm) until uniformly dissolved. Subsequently, 500g of silver oxide (metal oxide A) was added and stirred for 15 minutes under the same stirring conditions. Then, the internal temperature was raised to 40°C using a water bath and stirred for 105 minutes, including the heating period, under the same stirring conditions. Since a rise in internal temperature was confirmed due to the reduction reaction, the temperature of the water bath was adjusted as needed using ice water to maintain the internal temperature at 40°C. Subsequently, the internal temperature was raised to 65°C and stirred for 120 minutes, including the heating period, at the same stirring speed. A dispersion of metal nanoparticles was obtained by the above procedure.

[0062] Examples 2-5 A metal nanoparticle dispersion was obtained in the same manner as in Example 1, except that the formulations of each raw material were changed to those shown in Table 1.

[0063] Comparative Example 1 In a 5L stainless steel separable flask, 100g of DISPER BYK-2015 (40% solids by mass) as polymer D and 600g of PG as dihydric alcohol B were added. The mixture was stirred at a speed of 150 rpm using a Maxblend stirring blade (blade diameter 100mm) until uniformly dissolved. Subsequently, 500g of silver oxide A was added and stirred for 15 minutes under the same stirring conditions. After that, the internal temperature was raised to 40°C using a water bath and stirred under the same stirring conditions. Since an increase in internal temperature was confirmed due to the reduction reaction, the temperature of the water bath was adjusted as needed using ice water to maintain the internal temperature at 40°C. In Comparative Example 1, 60 minutes after the heating was completed, the liquid inside became gel-like and could no longer be stirred. Therefore, it was determined that the reaction could not be continued, and the metal nanoparticle dispersion could not be obtained.

[0064] Comparative Example 2 In a 5L stainless steel separable flask, 40g of oven-dried DISPER BYK-2015 (polymer D) and 660g of PAGDA-1 (polyalkylene glycol dialkyl ether C) were added. The mixture was stirred at 150 rpm using a Maxblend stirring blade (blade diameter 100mm) until uniformly dissolved. Subsequently, 500g of silver oxide (metal oxide A) was added, and the mixture was stirred for 15 minutes under the same stirring conditions. After that, the internal temperature was raised to 40°C using a water bath, and the mixture was stirred for 150 minutes, including the heating period, under the same stirring conditions. Then, the internal temperature was raised to 65°C, and the mixture was stirred for 120 minutes, including the heating period, at the same stirring speed. No increase in internal temperature was observed during stirring. In Comparative Example 2, since dihydric alcohol B was not added, the reduction reaction did not occur, and a dispersion of metal nanoparticles was not obtained.

[0065] (Continuous type) Figure 1 shows a schematic diagram of the continuous reactor used in Example 6 and Comparative Example 3.

[0066] Example 6 (Preparation and preparation of raw material 1) In a 3L beaker, 809.2g of PAGDA-1 as polyalkylene glycol dialkyl ether C, 1136.5g of silver oxide as metal oxide A, 49.3g of completely dry DISPER BYK-2015 as polymer D, and 4.9g of deionized water were added. The mixture was stirred for 45 minutes at a stirring speed of 7000 rpm using a disperser blade (blade diameter 40mm) to obtain a silver oxide slurry as raw material 1. The obtained raw material 1 was placed in raw material tank 1 for raw material 1. To prevent the particles in raw material 1 from settling, stirring was continuously performed at a stirring speed of 300 rpm using stirring device 2 (anchor blade, blade diameter 40 mm). (Preparation and preparation of raw material 2) In the raw material tank 4 for raw material 2, 937.1g of PG as dihydric alcohol B, 57.1g of completely dry DISPER BYK-2015 as polymer D, and 5.7g of deionized water were added, and the mixture was manually mixed and uniformly dissolved to obtain raw material 2. (Reduction reaction) Silicone oil (KF-96-10cs, manufactured by Shin-Etsu Chemical Co., Ltd.), temperature-controlled to 70°C, was circulated from the hot oil circulation device 8 into the temperature-controlled jacket 7 for the continuous tank reactor. Subsequently, using pumps 3 for raw material 1 and 5 for raw material 2, raw material 1 and raw material 2 were delivered to the first tank of the continuous tank reactor 6 (multi-stage type (total of 6 tanks), capacity of each tank: 2 mL), and the reaction was carried out continuously. The flow rates were 7.33 g / min for raw material 1 and 2.67 g / min for raw material 2. During the reaction, the inside of the continuous tank reactor 6 was stirred using a magnetic stirrer. The liquid was drained from the sixth tank (final tank) of the continuous tank reactor into the receiver 10 using a draining pump 9. 280 g of the extracted liquid was placed in a 300 mL glass separable flask, the internal temperature was raised to 65°C using a water bath, and the mixture was stirred for 2 hours at a stirring speed of 450 rpm using an inclined paddle blade (4 blades, 40 mm diameter). A dispersion of metal microparticles was obtained by the above procedure.

[0067] Comparative Example 3 (Preparation and preparation of raw material 1) 720g of PG as dihydric alcohol B and 600g of silver oxide as metal oxide A were added to a 2L glass beaker. The mixture was stirred for 20 minutes at a stirring speed of 7000 rpm using a disperser blade (blade diameter 40 mm) to obtain a silver oxide slurry as raw material 1. The obtained raw material 1 was placed in raw material tank 1 for raw material 1. To prevent the particles in raw material 1 placed in raw material tank 1 for raw material 1 from settling, stirring was continuously performed at a stirring speed of 300 rpm using stirring device 2 (anchor blade, blade diameter 40 mm). (Preparation and preparation of raw material 2) As raw material 2, DISPER BYK-2015 (40% solids by mass) was used as is. 100g of DISPER BYK-2015 (40% solids by mass) was added as polymer D to raw material tank 4 for raw material 2. (Reduction reaction) Silicone oil (KF-96-10cs, manufactured by Shin-Etsu Chemical Co., Ltd.), temperature-controlled to 70°C, was circulated from the hot oil circulation device 8 into the temperature-controlled jacket 7 for the continuous tank reactor. Subsequently, using pumps 3 for raw material 1 and 5 for raw material 2, raw material 1 and raw material 2 were delivered to the first tank of the continuous tank reactor 6, and the reaction was carried out continuously. The flow rates were 4.07 g / min for raw material 1 and 0.37 g / min for raw material 2. During the reaction, the inside of the continuous tank reactor 6 was stirred using a magnetic stirrer. The liquid was drained from the sixth tank (final tank) of the continuous tank reactor into the receiver 10 using draining pump 9. 280 g of the obtained drained liquid was placed in a 300 mL glass separable flask, the internal temperature was raised to 65°C using a water bath, and the mixture was stirred for 2 hours at a stirring speed of 450 rpm using an inclined paddle blade (4 blades, blade diameter 40 mm). A dispersion of metal fine particles was obtained by the above operation.

[0068] <Rating> (Centrifugal yield) 500 g of the metal microparticle dispersion obtained in the examples and comparative examples was placed in a 1 L centrifuge tube, and centrifuged for 30 minutes at 3000 rpm using a CR7 centrifuge (rotor R7A, manufactured by Hitachi Koki Co., Ltd.). After centrifugation, the supernatant was collected, and the centrifugation yield was calculated using the following formula. [Centrifugal yield (mass%)] = [Total amount of supernatant after centrifugation (g)] / [Total amount of metal particle dispersion charged into the centrifuge tube (g)] × 100 A higher centrifugal separation yield indicates a lower amount of coarse particles in the metal nanoparticle dispersion. In other words, a higher centrifugal separation yield indicates that the generation of coarse particles is suppressed. The evaluation results are shown in Tables 1 and 2.

[0069] (Particle size of metal nanoparticles in a dispersion of metal nanoparticles) The particle size of the metal nanoparticles in the metal nanoparticle dispersion obtained in Example 6 was measured as follows. 2 μL of the supernatant liquid obtained after centrifugation of the metal microparticle dispersion obtained in Example 6 was added dropwise to 10 g of deionized water and mixed with a vortex mixer to obtain a diluted solution of the metal microparticle dispersion. The cumulant average particle size of the metal microparticles (silver microparticles) in the obtained diluted solution of the metal microparticle dispersion was measured using a particle size measurement system (ELSZ-1000S, manufactured by Otsuka Electronics Co., Ltd.). The average particle size of the silver nanoparticle cumulant in the metal nanoparticle dispersion of Example 6 was 33 nm, confirming that nano-sized particles could be synthesized.

[0070] (Content of metal nanoparticles and polymer D in the metal nanoparticle dispersion) The content of metal nanoparticles (silver nanoparticles) and polymer D in the metal nanoparticle dispersion obtained in Example 6 was measured as follows. Using a differential thermogravimetric analyzer (TG-DTA) (manufactured by Hitachi High-Tech Science Corporation, product name: STA7200RV), 20 mg of the sample was weighed into an aluminum pancell and heated from 35°C to 550°C at a heating rate of 10°C / min. The mass loss was measured under an air flow of 50 mL / min. The mass loss from 300°C to 550°C was taken as the mass of polymer D, and the remaining mass at 550°C was taken as the mass of metal nanoparticles. The concentrations were then calculated based on the following formula. Polymer D content (mass%) = Mass loss from 300°C to 550°C (mass of polymer D (mg)) / Sample mass (20 mg) × 100 Metal particle content = Residual mass at 550°C (Mass of metal particles (mg)) / Sample load mass (20 mg) × 100 In Example 6, the supernatant liquid obtained after centrifugation of the metal nanoparticle dispersion contained 39.2% by mass of metal nanoparticles (silver nanoparticles) and 2.9% by mass of polymer D.

[0071] (Viscosity of metal particle dispersions) The viscosity of the metal nanoparticle dispersion obtained in Example 6 was measured as follows. A 1 mL metal particle dispersion was measured into the measuring section of a viscometer (manufactured by Toki Sangyo Co., Ltd., product name: TV-25 viscometer), which was maintained at 25°C, and the viscosity was measured at a rotation speed of 10 rpm. The viscosity of the supernatant liquid after centrifugation of the metal nanoparticle dispersion obtained in Example 6 was 19.4 mPa·s.

[0072] (Gloss rating of the ink) The coating properties of the ink using the metal nanoparticle dispersion obtained in Example 6 were evaluated. [Preparation of evaluation ink] In a 300 mL polyethylene beaker, 35.5 g of the supernatant liquid obtained after centrifugation of the metal nanoparticle dispersion obtained in Example 6, 34.5 g of deionized water, 9.6 g of PG, 15.8 g of 1,3-dihydroxypropane, 3.0 g of 1,2-hexanediol, 0.5 g of Tego Wet 280 (polyethersiloxane copolymer, manufactured by Evonik Operations GmbH), and 1.2 g of isopropanolamine were added. The mixture was stirred with a magnetic stirrer for 30 minutes to obtain the evaluation ink. [Gloss evaluation of ink-coated surfaces] The obtained evaluation ink was coated onto KOKUYO glossy photo paper using a bar coater (wet film thickness 8 μm). It was then dried at room temperature for 10 minutes. The 8° gloss of each obtained coating film was measured using an integrating sphere spectrophotometer (model: CM-700d, manufactured by Konica Minolta, Inc.). The 8° gloss is calculated by subtracting SCE (diffuse reflection only) from SCI (specular reflection including) and converted to a gloss equivalent value, corresponding to the gloss at a specular reflection angle of 8°. A higher 8° gloss value indicates better metallicity of the metal film. The resulting coated surface had an 8° gloss of 1247, indicating good metallic properties.

[0073] [Table 1]

[0074] [Table 2]

[0075] Tables 1 and 2 show that the metal nanoparticle dispersions obtained by Examples 1 to 6 have a high centrifugal separation yield and a low content of coarse particles. Therefore, it is confirmed that the method for producing metal nanoparticles of the present invention can suppress the generation of coarse particles. [Explanation of symbols]

[0076] 1 Raw material tank for raw material 1 2. Stirring device 3. Pump for raw material 1 4. Raw material tank for raw material 2 5. Pump for raw material 2 6. Continuous tank reactor 7 Temperature-regulating jacket 8 Hot oil circulation device 9. Pump for draining fluid 10 Receiver

Claims

1. The process includes a mixing reaction step in which a raw material mixture containing a metal oxide A, a dihydric alcohol B, a polyalkylene glycol dialkyl ether C, and a polymer D having an anionic hydrophilic group is obtained, and a reduction reaction of the raw material mixture is carried out. A method for producing a metal nanoparticle dispersion, wherein the dihydric alcohol B is a dihydric alcohol represented by the following general formula (1). 【Chemistry 1】 (In general formula (1), R １ and R ２ R is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ３ R is at least one alkylene group selected from ethylene and propylene groups, and n is an integer between 0 and 30. However, in general formula (1), R １ and R ２ If all of them are hydrogen atoms, then R ３ (It contains at least a propylene group, and n is 1 or greater.)

2. A method for producing a metal nanoparticle dispersion according to claim 1, wherein metal oxide A is silver oxide.

3. A method for producing a metal fine particle dispersion according to claim 1, wherein the content of metal oxide A in the raw material mixture is 30% by mass or more and 50% by mass or less.

4. A method for producing a metal fine particle dispersion according to claim 1, wherein the dihydric alcohol B is propylene glycol.

5. A method for producing a metal fine particle dispersion according to claim 1, wherein the mass ratio of dihydric alcohol B to metal oxide A (dihydric alcohol B / metal oxide A) is 0.3 or more and 2.0 or less.

6. A method for producing a metal fine particle dispersion according to claim 1, wherein the number average molecular weight of polyalkylene glycol dialkyl ether C is 134 or more and 300 or less.

7. A method for producing a metal fine particle dispersion according to claim 1, wherein polyalkylene glycol dialkyl ether C is polyethylene glycol dimethyl ether.

8. A method for producing a metal fine particle dispersion according to claim 1, wherein the mass ratio of polyalkylene glycol dialkyl ether C to metal oxide A (polyalkylene glycol dialkyl ether C / metal oxide A) is 0.1 or more and 1.0 or less.

9. A method for producing a metal nanoparticle dispersion according to claim 1, wherein the anionic hydrophilic group of polymer D having an anionic hydrophilic group is a carboxyl group.

10. A method for producing a metal fine particle dispersion according to claim 1, wherein the mass ratio of polymer D having anionic hydrophilic groups to metal oxide A (polymer D having anionic hydrophilic groups / metal oxide A) is 0.01 or more and 0.20 or less.

11. A method for producing a metal fine particle dispersion according to claim 1, wherein the water content in the raw material mixture is 10% by mass or less.

Images