Method for producing ink containing metal particles

Abstract

The present invention relates to a method for producing a metal-fine-particle-containing ink, said method comprising a step 1 for mixing a metal oxide A, a polymer B, formic acid, and a solvent C to obtain a liquid mixture 1; a step 2 for heating the liquid mixture 1 to obtain a metal fine particle dispersion; and a step 3 for mixing the metal fine particle dispersion and formic acid to obtain a metal-fine-particle-containing ink, wherein: the polymer B includes a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group; the solvent C includes at least one type of solvent selected from the group consisting of water, C1-C4 aliphatic monoalcohols, and C3-C4 ketones; in the liquid mixture 1, the content of metal constituting the metal oxide A is 28-57 mass%; and in the liquid mixture 1, the mass ratio [polymer B / (polymer B+metal)] of the content of the polymer B to the combined amount of the content of the polymer B and the content of the metal constituting the metal oxide A is 0.05-0.17.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an ink containing fine metal particles, an ink containing fine metal particles, an ink for inkjet printing, and a method for producing a printed matter. [Background technology]

[0002] It is known that when metals are miniaturized to nano-size, various functions and physical properties are manifested, such as lowering of the melting point, optical properties, catalytic properties, etc. Therefore, due to the diversity of functions, metal fine particles are expected to be developed into a wide range of industrial applications. One of the industrial applications being considered is wiring formation technology using metal fine particles as conductive materials for printed electronics.

[0003] JP 2016-525266 A (Patent Document 1) describes a metal nanoparticle dispersion containing one or more additives selected from a thickener, a high-boiling-point solvent, and a wetting agent, with the aim of providing a method for producing a highly conductive coating or pattern from a metal nanoparticle dispersion under moderate curing conditions. JP 2015-522713 A (Patent Document 2) describes a metallic nanoparticle dispersion in which the dispersion medium contains a solvent having a specific amide structure, with the aim of obtaining a stable metallic nanoparticle dispersion without the need for a polymeric dispersant. JP 2011-517728 A (Patent Document 3) describes metal nanoparticles stabilized with derivatized polyethyleneimine or polyvinylamine, with the aim of providing a method for producing metal nanoparticles that is suitable for producing highly concentrated aqueous solutions of metal nanoparticles, particularly silver nanoparticles, platinum nanoparticles, and palladium nanoparticles, and that does not cause aggregation of the metal nanoparticles. Summary of the Invention

[0004] The present invention includes a step 1 of mixing a metal oxide A, a polymer B, formic acid, and a solvent C to obtain a mixed solution 1; a step 2 of heating the mixed solution 1 to obtain a metal fine particle dispersion; and step 3 of mixing the metal fine particle dispersion liquid with formic acid to obtain a metal fine particle-containing ink, the polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, the content of the metal constituting the metal oxide A in the mixed solution 1 is 28% by mass or more and 57% by mass or less, The present invention relates to a method for producing a metal microparticle-containing ink, wherein the mass ratio of the content of the polymer B to the total content of the polymer B and the metal constituting the metal oxide A in the mixed liquid 1 [polymer B / (polymer B+metal)] is 0.05 or more and 0.17 or less. DETAILED DESCRIPTION OF THE INVENTION

[0005] Due to the growing demand for small-lot, high-mix manufacturing, device manufacturing using inkjet printing, which does not require complicated processes, has been attracting attention in recent years. Conventional photolithography methods have issues such as the need for special equipment to form conductive layers and the production of large amounts of metal waste, so there is growing demand for inkjet printing methods that can print and form wiring only in desired areas. In inkjet printing, ejection performance is an important characteristic that determines the reliability and productivity of printed matter. To ensure this characteristic consistently, high dispersion stability of the ejected particles is essential. Furthermore, improved electrical conductivity is required for wiring materials in order to improve the performance of electronic devices and reduce power consumption. Furthermore, when metal fine particles are used as wiring materials, high productivity of the metal fine particles is required. However, the technology of Patent Document 1 requires a purification step to replace the solvent after producing the metal microparticles, and therefore does not meet the productivity requirements. The technology of Patent Document 2 does not use a polymer dispersant, so it cannot provide high dispersion stability and does not meet the performance requirements for inkjet printing. Furthermore, the technology of Patent Document 3 produces metal microparticles under excessively high concentration conditions, which generates coarse particles and reduces conductivity. Therefore, further improvements in productivity, conductivity, and ejection properties are required for inks containing metal fine particles used in printing. The present invention relates to a method for producing a metal microparticle-containing ink that can be easily replaced with any solvent or does not require solvent replacement and has improved conductivity and ejection properties, a metal microparticle-containing ink that has improved conductivity and ejection properties, and a method for producing an ink for inkjet printing and a printed matter using the metal microparticle-containing ink.

[0006] The present inventors have found that a method for producing a metal particle-containing ink includes a step of obtaining a metal particle dispersion using a mixed solution containing a metal oxide, a polymer having specific functional groups, formic acid, and a solvent having a specific chemical structure, where the content of the metal constituting the metal oxide and the mass ratio of the polymer content to the total content of the polymer and the metal content constituting the metal oxide are each within a predetermined range, and further includes a step of mixing formic acid with the obtained metal particle dispersion, thereby suppressing the generation of coarse particles and particle aggregates and improving the conductivity of the obtained metal particle-containing ink.As a result, they have found that it is possible to provide a method for producing a metal particle-containing ink that is easy to replace with any solvent or does not require solvent replacement and has improved conductivity and ejection properties, a metal particle-containing ink that has improved conductivity and ejection properties, and a method for producing an ink for inkjet printing and a printed material using the metal particle-containing ink. That is, the present invention relates to the following [1] to [4]. [1] Step 1: Mixing metal oxide A, polymer B, formic acid, and solvent C to obtain mixed solution 1; a step 2 of heating the mixed solution 1 to obtain a metal fine particle dispersion; and step 3 of mixing the metal fine particle dispersion liquid with formic acid to obtain a metal fine particle-containing ink, the polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, the content of the metal constituting the metal oxide A in the mixed solution 1 is 28% by mass or more and 57% by mass or less, A method for producing an ink containing metal microparticles, wherein the mass ratio of the content of the polymer B to the total content of the polymer B and the metal constituting the metal oxide A in the mixed solution 1 [polymer B / (polymer B+metal)] is 0.05 or more and 0.17 or less. [2] A solution containing metal fine particles a dispersed in polymer B, formic acid, and solvent C, the polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, The content of the metal fine particles a is 8% by mass or more and 17% by mass or less, The metal microparticle-containing ink has a mass ratio [polymer B / (polymer B+metal microparticle a)] of the content of the polymer B to the total content of the polymer B and the content of the metal microparticle a) of 0.05 or more and 0.17 or less. [3] An inkjet printing ink containing the metal fine particle-containing ink according to [2] above and a surfactant. [4] A method for producing a printed matter, comprising step 5 of applying at least one ink selected from the group consisting of the metal fine particle-containing ink described in [2] above and the ink for inkjet printing described in [3] above onto a substrate, to obtain a printed matter on which a metal film is formed.

[0007] According to the present invention, it is possible to provide a method for producing a metal microparticle-containing ink that can be easily replaced with any solvent or does not require solvent replacement and has improved conductivity and ejection properties, a metal microparticle-containing ink that has improved conductivity and ejection properties, and a method for producing an ink for inkjet printing and a printed matter using the metal microparticle-containing ink.

[0008] [Method of manufacturing ink containing metal particles] The method for producing a metal microparticle-containing ink of the present invention comprises step 1 (hereinafter also referred to simply as "step 1") of mixing metal oxide A, polymer B, formic acid and solvent C to obtain mixed liquid 1, step 2 (hereinafter also referred to simply as "step 2") of heating mixed liquid 1 to obtain a metal microparticle dispersion, and step 3 (hereinafter also referred to simply as "step 3") of mixing the metal microparticle dispersion and formic acid to obtain a metal microparticle-containing ink, wherein polymer B contains a structural unit derived from monomer (b-1) having a carboxy group and a structural unit derived from monomer (b-2) having a polyoxyalkylene group, solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the content of metals constituting metal oxide A in mixed liquid 1 is 28% by mass or more and 57% by mass or less, and the mass ratio of the content of polymer B to the total content of polymer B and the content of metals constituting metal oxide A in mixed liquid 1 [polymer B / (polymer B + metal)] is 0.05 to 0.17.

[0009] The metal microparticle-containing ink obtained by the manufacturing method according to the present invention comprises metal microparticles a dispersed in a medium. Here, the form of the metal microparticles a is not particularly limited, as long as the particles are formed from at least metal microparticles and polymer B. For example, the form includes a particle form in which metal microparticles are encapsulated in polymer B, a particle form in which metal microparticles are uniformly dispersed in polymer B, a particle form in which metal microparticles are exposed on the surface of polymer B particles, and mixtures thereof.

[0010] The manufacturing method according to the present invention has the effect of making it possible to easily replace the solvent with any solvent or to eliminate the need for solvent replacement, and to obtain a metal fine particle-containing ink with improved conductivity and ejection properties. The reason for this is unclear, but is thought to be as follows. First, by setting the content of the metal constituting metal oxide A in mixed solution 1 to 57 mass% or less, it is believed that the generation of aggregates during the synthesis of metal fine particles a can be suppressed, resulting in improved conductivity and ejection performance. Furthermore, by setting the content of the metal constituting metal oxide A in mixed solution 1 to 28 mass% or more, it is believed that the generation of coarse metal particles during the synthesis of metal fine particles a can be suppressed, resulting in improved conductivity and ejection performance. Furthermore, by setting the mass ratio of the polymer B content to the total content of the polymer B content and the metal content constituting the metal oxide A in the mixed solution 1 [polymer B / (polymer B + metal)] to 0.05 or more, it is possible to ensure a sufficient amount of polymer B, which in turn improves the dispersion stability of the metal fine particles a and improves dischargeability. Furthermore, it is believed that sufficient dispersion stability leads to a uniform printed coating film and improved conductivity. Furthermore, by setting the [polymer B / (polymer B + metal)] to 0.17 or less, it is possible to reduce the amount of polymer B not adsorbed to the metal fine particles a, which in turn improves conductivity and dischargeability. In addition, solvent C, which contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, has a low boiling point and therefore has excellent quick-drying properties, and is easily replaced with any solvent or does not require solvent replacement. Furthermore, the formic acid added in step 3 promotes the detachment of polymer B from the surface of the metal microparticles, and the reducing action of formic acid further suppresses oxidation of the surface of the metal microparticles, promoting sintering of the metal microparticles. This is thought to enable the formation of a dense metal film and maintain good electrical conductivity of the metal film. For the above reasons, it is believed that the manufacturing method according to the present invention makes it possible to obtain an ink containing metal microparticles that can be easily replaced with any solvent or does not require solvent replacement, and that has improved conductivity and ejection properties.

[0011] (Process 1) Step 1 is a step in which metal oxide A, polymer B, formic acid, and solvent C are mixed to obtain mixed solution 1. In the subsequent step 2, it is believed that metal oxide A is reduced by formic acid to form metal fine particles a dispersed in polymer B.

[0012] <Metal oxide A> Examples of metals (metal atoms) constituting the 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 metals constituting the metal oxide A may be used alone or in combination as an alloy of two or more. Furthermore, the metal oxide A may be used alone or in combination of two or more. Among these, from the viewpoint of improving electrical conductivity and ejection properties, metal oxide A preferably contains an oxide of a transition metal of Groups 4 to 11 and Periods 4 to 6, more preferably contains an oxide of a noble metal such as copper, nickel, gold, silver, platinum, or palladium, even more preferably contains an oxide of at least one type selected from gold, silver, copper, nickel, and palladium, even more preferably contains at least one type selected from gold oxide, silver oxide, and copper oxide, even more preferably contains at least one type selected from silver oxide and copper oxide, even more preferably contains silver oxide, and even more preferably is silver oxide. The type of metal can be confirmed by high-frequency inductively coupled plasma atomic emission spectrometry. From the viewpoint of improving conductivity and ejection properties, the content of silver oxide in metal oxide A is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that the material may contain unintentionally contained components, such as unavoidable impurities.

[0013] <Polymer B> Polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, from the viewpoint of improving the dispersion stability of the metal microparticle-containing ink and improving the conductivity and ejection properties.

[0014] Examples of the basic structure of polymer B include vinyl polymers such as acrylic resins, styrene resins, styrene-acrylic resins, and acrylic silicone resins; and condensation polymers such as polyesters and polyurethanes. Among these, vinyl polymers are preferred from the viewpoint of improving conductivity and ejection properties. From the viewpoint of improving the dispersion stability of the metal particle-containing ink and improving the conductivity and ejection properties, the polymer B is preferably a vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group. The polymer B can be obtained by copolymerizing raw material monomers including the monomer (b-1) and the monomer (b-2). When the vinyl polymer is a copolymer, the vinyl polymer may be any of a block copolymer, a random copolymer, and an alternating copolymer.

[0015] [Monomer (b-1) having a carboxy group] Examples of the monomer (b-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 acids may be anhydrides. The monomer (b-1) may be used alone or in combination of two or more kinds. The monomer (b-1) is preferably at least one selected from (meth)acrylic acid and maleic acid, from the viewpoint of improving the dispersion stability of the metal fine particle-containing ink and improving the conductivity and ejection properties. In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acrylic acid" below.

[0016] [Monomer (b-2) having a polyoxyalkylene group] From the viewpoint of improving the dispersion stability of the metal particle-containing ink and improving the conductivity and ejection properties, the monomer (b-2) is preferably a monomer that can introduce a polyalkylene glycol segment into the side chain of the polymer B. Examples of such a monomer include polyalkylene glycol (meth)acrylate, alkoxy polyalkylene glycol (meth)acrylate, and phenoxy polyalkylene glycol (meth)acrylate. The monomer (b-2) may be used alone or in combination of two or more. In this specification, "(meth)acrylate" refers to at least one selected from acrylate and methacrylate. The "(meth)acrylate" used below has the same meaning.

[0017] From the viewpoints of improving the dispersion stability of the metal particle-containing ink and improving the conductivity and ejection properties, the monomer (b-2) is preferably at least one selected from polyalkylene glycol (meth)acrylates and alkoxy polyalkylene glycol (meth)acrylates, more preferably alkoxy polyalkylene glycol (meth)acrylates. From the same viewpoints as above, 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 methoxy polyalkylene glycol (meth)acrylate, ethoxy polyalkylene glycol (meth)acrylate, propoxy polyalkylene glycol (meth)acrylate, butoxy polyalkylene glycol (meth)acrylate, and octoxy polyalkylene glycol (meth)acrylate.

[0018] From the viewpoint of improving the dispersion stability of the metal fine particle-containing ink and improving the conductivity and ejection properties, the polyoxyalkylene group of the monomer (b-2) preferably contains a unit derived from an alkylene oxide having from 2 to 4 carbon atoms. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and the like. Preferably, it is one or more selected from ethylene oxide and propylene oxide, and more preferably ethylene oxide. From the viewpoint of improving the dispersion stability of the metal microparticle-containing ink and improving its conductivity and ejection properties, the number of units derived from alkylene oxide in the polyoxyalkylene group is preferably 2 or more, more preferably 3 or more, even more preferably 5 or more, even more preferably 10 or more, even more preferably 15 or more, even more preferably 20 or more, and is preferably 100 or less, more preferably 70 or less, even more preferably 50 or less, even more preferably 40 or less, even more preferably 35 or less. From the viewpoint of improving the dispersion stability of the metal particle-containing ink and improving its conductivity and jetting ability, the polyoxyalkylene group is preferably a copolymer containing units derived from ethylene oxide and units derived from propylene oxide. The molar ratio of ethylene oxide units (EO) to propylene oxide units (PO) [EO / PO] is preferably 60 / 40 or more, more preferably 65 / 35 or more, even more preferably 70 / 30 or more, and is preferably 90 / 10 or less, more preferably 85 / 15 or less, even more preferably 80 / 20 or less. The copolymer containing units derived from ethylene oxide and units derived from propylene oxide may be any of a block copolymer, a random copolymer, and an alternating copolymer.

[0019] Specific examples of commercially available monomer (b-2) include NK Ester AM-90G, AM-130G, AM-230G, AMP-20GY, M-20G, M-40G, M-90G, and M-230G, manufactured by Shin-Nakamura Chemical Co., Ltd.; and Blenmar PE-90, PE-200, PE-350, PME-100, PME-200, PME-400, PME-1000, PME-4000, PP-500, PP-800, PP-1000, AP-150, AP-400, AP-550, 50PEP-300, 50POEP-800B, and 43PAPE-600B, manufactured by NOF Corporation.

[0020] [Hydrophobic Monomer (b-3)] From the viewpoint of improving the electrical conductivity and ejection properties, it is preferable that the polymer B further contains a structural unit derived from a hydrophobic monomer (b-3). In this specification, the term "hydrophobic monomer" refers to a monomer whose dissolution amount is less than 10 g when the monomer is dissolved to saturation in 100 g of ion-exchanged water at 25° C. From the viewpoint of improving the electrical conductivity and the ejection property, the dissolution amount of the monomer (b-3) is preferably 5 g or less, and more preferably 1 g or less. When polymer B is the vinyl polymer, monomer (b-3) is preferably at least one selected from aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol. In this specification, "(meth)acrylate" refers to at least one selected from acrylate and methacrylate. The "(meth)acrylate" used below has the same meaning.

[0021] From the viewpoint of improving conductivity and ejection properties, the aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500. Examples of styrene-based monomers include styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), and divinylbenzene, and from the viewpoint of improving the conductivity and ejection properties, styrene and α-methylstyrene are preferred. As the aromatic group-containing (meth)acrylate, from the viewpoint of improving the conductivity and ejection property, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. are preferred, and benzyl (meth)acrylate is more preferred.

[0022] The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, from the viewpoint of improving the conductivity and ejection properties. Examples include (meth)acrylates having a straight-chain alkyl group 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 a branched-chain alkyl group 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 an alicyclic alkyl group such as cyclohexyl (meth)acrylate. Among these, those having an alkyl group having 6 to 10 carbon atoms are more preferred. The monomer (b-3) may be used alone or in combination of two or more.

[0023] From the viewpoint of improving the conductivity and ejection property, the monomer (b-3) is preferably an aromatic group-containing monomer, more preferably a styrene-based 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.

[0024] (Content of each monomer in the raw material monomers of polymer B or content of each structural unit in polymer B) When polymer B contains a structural unit derived from monomer (b-1) and a structural unit derived from monomer (b-2), but does not contain a structural unit derived from monomer (b-3), the contents of monomers (b-1) and (b-2) in the raw material monomers during production of polymer B (content as unneutralized amount; the same applies hereinafter) or the contents of structural units derived from monomer (b-1) and structural units derived from monomer (b-2) in polymer B are as follows, from the viewpoint of improving conductivity and dischargeability. The content of monomer (b-1) is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, even more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less, even more preferably 75 mol% or less. The content of monomer (b-2) is preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, even more preferably 25 mol% or more, and preferably 90 mol% or less, more preferably 80 mol% or less, even more preferably 70 mol% or less, even more preferably 60 mol% or less, even more preferably 50 mol% or less, even more preferably 40 mol% or less. The molar ratio of the monomer (b-1) to the monomer (b-2) [monomer (b-1) / monomer (b-2)] is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 1.5 or more, and is preferably 5.0 or less, more preferably 4.0 or less, even more preferably 3.5 or less, even more preferably 3.0 or less, even more preferably 2.5 or less.

[0025] When polymer B further contains a structural unit derived from monomer (b-3), the contents of monomers (b-1) to (b-3) in the raw material monomers during production of polymer B (content as unneutralized amount; the same applies hereinafter) or the contents of structural units derived from monomers (b-1) to (b-3) in polymer B are as follows, from the viewpoint of improving electrical conductivity and dischargeability. The content of monomer (b-1) is preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, and preferably 60 mol% or less, more preferably 50 mol% or less, even more preferably 45 mol% or less. The content of monomer (b-2) 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 25 mol% or less, even more preferably 20 mol% or less. The content of monomer (b-3) is preferably 30 mol% or more, more preferably 35 mol% or more, even more preferably 40 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less. The molar ratio of the monomer (b-1) to the monomer (b-2) [monomer (b-1) / monomer (b-2)] is preferably 0.5 or more, more preferably 1 or more, even more preferably 1.5 or more, and is preferably 5 or less, more preferably 4 or less, even more preferably 3.5 or less.

[0026] From the viewpoint of improving the conductivity and ejection property, polymer B is preferably a vinyl polymer containing, as monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, and, as monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate, and more preferably a vinyl polymer containing, as monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, as monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate, and, as monomer (b-3), a structural unit derived from at least one selected from a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol. Polymer B may be synthesized by a known method or may be a commercially available product, such as DISPERBYK-190 and DISPERBYK-2015 manufactured by BYK.

[0027] The content of the vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group in polymer B is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving the dispersion stability of the metal fine particle-containing ink and improving the conductivity and ejection properties. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include polymer B components other than the vinyl polymer contained in the vinyl polymer.

[0028] The content of the vinyl polymer containing the structural unit derived from the monomer (b-1) having a carboxy group, the structural unit derived from the monomer (b-2) having a polyoxyalkylene group, and the structural unit derived from the hydrophobic monomer (b-3) in the polymer B is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving the dispersion stability of the metal fine particle-containing ink and improving the conductivity and ejection properties. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include polymer B components other than the vinyl polymer contained in the vinyl polymer.

[0029] The content of the vinyl polymer in polymer B, which contains as monomer (b-1) a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid and as monomer (b-2) a structural unit derived from an alkoxypolyalkylene glycol (meth)acrylate, is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving the dispersion stability of the metal particle-containing ink and improving the conductivity and ejection properties. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include polymer B components other than the vinyl polymer contained in the vinyl polymer.

[0030] The content of the vinyl polymer in polymer B, which includes as monomer (b-1) a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, as monomer (b-2) a structural unit derived from an alkoxypolyalkylene glycol (meth)acrylate, and as monomer (b-3) a structural unit derived from at least one selected from a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol, is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving the dispersion stability of the metal particle-containing ink and improving the conductivity and dischargeability. Here, "substantially 100% by mass" means that unintentional components may be included. Examples of unintentional components include polymer B components other than the vinyl polymer contained in the vinyl polymer.

[0031] From the viewpoint of improving the dispersion stability of the metal fine particle-containing ink and improving the conductivity and ejection properties, the number average molecular weight Mn of polymer B is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 3,000 or more, and is 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. The number average molecular weight Mn is measured by the method described in the examples.

[0032] From the viewpoint of improving the dispersion stability of the metal microparticle-containing ink and improving its conductivity and ejection properties, the acid value of polymer B is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, and even more preferably 15 mgKOH / g or more, and is preferably 200 mgKOH / g or less, and more preferably 120 mgKOH / g or less. The acid value of Polymer B can be measured by the method described in the Examples, but can also be calculated from the mass ratio of the constituent monomers.

[0033] <Solvent C> The mixed liquid 1 contains a solvent C containing at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, in order to improve the dispersion stability of the metal microparticle-containing ink and improve its conductivity and ejection properties.

[0034] From the viewpoint of improving the dispersion stability of the metal microparticle-containing ink and improving its conductivity and ejection properties, solvent C preferably contains at least one selected from methanol, ethanol, n-propanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and water, more preferably contains at least one selected from ethanol, n-propanol, isopropanol, isobutanol, methyl ethyl ketone, and water, even more preferably contains at least one selected from ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water, even more preferably contains at least one selected from ethanol and water, and even more preferably contains ethanol.

[0035] The boiling point of solvent C at 1 atmosphere is preferably 50° C. or higher, more preferably 60° C. or higher, even more preferably 70° C. or higher, and even more preferably 75° C. or higher, from the viewpoint of improving the dispersion stability and jetting properties of the metal fine particle-containing ink, and is preferably 120° C. or lower, more preferably 110° C. or lower, even more preferably 105° C. or lower, and even more preferably 100° C. or lower, from the viewpoint of improving quick-drying properties, solvent substitution properties, and conductivity. When two or more solvents C are used in combination, the boiling point of solvent C is a weighted average value weighted by the content (% by mass) of each solvent.

[0036] Solvent C may contain at least one solvent (hereinafter also referred to as "solvent C2") selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms (hereinafter also referred to as "solvent C1"). However, from the viewpoint of improving the dispersion stability of the metal microparticle-containing ink and improving its quick-drying properties, solvent substitution properties, conductivity, and ejection properties, it is preferable that the content of solvent C2 is an amount such that the weighted average value of the boiling points of solvent C satisfies the above-mentioned boiling point range. The content of solvent C2 in mixed solution 1 is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and even more preferably substantially 0% by mass, from the viewpoint of improving the dispersion stability of the metal particle-containing ink and improving its quick-drying properties, solvent substitution properties, conductivity, and ejection properties. Here, "substantially 0% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include solvent C2 contained in solvent C1.

[0037] The total content of water, aliphatic monoalcohol having 1 to 4 carbon atoms, and ketone having 3 to 4 carbon atoms (solvent C1) in solvent C is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, even more preferably 99.9% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving quick-drying properties, solvent displacement properties, conductivity, and ejection properties. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include solvents C other than solvent C1 contained in solvent C1.

[0038] From the viewpoint of improving quick-drying properties, solvent substitution properties, conductivity, and ejection properties, the total content of methanol, ethanol, n-propanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and water in solvent C is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, even more preferably 99.9% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include solvent C other than the above solvent contained in the above solvent.

[0039] From the viewpoint of improving quick-drying properties, solvent substitution properties, conductivity, and ejection properties, the total content of ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water in solvent C is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, even more preferably 99.9% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include solvent C other than the above solvent contained in the above solvent.

[0040] (Composition of Mixture 1) From the viewpoint of improving the conductivity and ejection property, the content of metal oxide A in mixed liquid 1 is preferably 30% by mass or more, more preferably 33% by mass or more, even more preferably 35% by mass or more, and is preferably 62% by mass or less, more preferably 60% by mass or less, even more preferably 59% by mass or less. From the viewpoint of improving the conductivity and ejection property, the content of polymer B in mixed liquid 1 is preferably 2.0% by mass or more, more preferably 2.5% by mass or more, even more preferably 2.8% by mass or more, and is preferably 10% by mass or less, more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, even more preferably 6.0% by mass or less, even more preferably 5.4% by mass or less. From the viewpoint of improving the conductivity and ejection property, the content of formic acid in the mixed liquid 1 is preferably 5.0% by mass or more, more preferably 5.5% by mass or more, even more preferably 6.0% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 9.5% by mass or less. From the viewpoint of improving the conductivity and ejection property, the content of solvent C in mixed liquid 1 is preferably 12% by mass or more, more preferably 15% by mass or more, even more preferably 17% by mass or more, and is preferably 50% by mass or less, more preferably 47% by mass or less, even more preferably 44% by mass or less.

[0041] From the viewpoint of improving the conductivity and ejection property, the content of the metal constituting the metal oxide A in the mixed liquid 1 is 28% by mass or more, preferably 32% by mass or more, more preferably 37% by mass or more, even more preferably 40% by mass or more, and 57% by mass or less, preferably 55% by mass or less, more preferably 51% by mass or less, even more preferably 45% by mass or less.

[0042] The ratio of the content of polymer B to the total content of polymer B and the content of the metal constituting metal oxide A in mixed solution 1 [polymer B / (polymer B+metal)] is 0.05 or more, preferably 0.055 or more, more preferably 0.06 or more, from the viewpoint of improving conductivity and ejection property, and is 0.17 or less, preferably 0.15 or less, more preferably 0.13 or less, and even more preferably 0.12 or less, from the viewpoint of improving ejection property.

[0043] From the viewpoint of improving the conductivity and ejection properties, the molar ratio of the content of formic acid to the content of the metal constituting the metal oxide A in the mixed liquid 1 [formic acid / metal] is preferably 0.05 or more, more preferably 0.13 or more, even more preferably 0.20 or more, even more preferably 0.30 or more, even more preferably 0.35 or more, and is preferably 1.00 or less, more preferably 0.80 or less, even more preferably 0.70 or less, even more preferably 0.60 or less, and still more preferably 0.50 or less.

[0044] In the mixed liquid 1, from the viewpoint of improving the conductivity and ejection property, the content of metal oxide A is preferably 30% by mass or more and 62% by mass or less, the content of polymer B is preferably 2.0% by mass or more and 10% by mass or less, the content of formic acid is preferably 5.0% by mass or more and 15% by mass or less, and the content of solvent C is preferably 12% by mass or more and 50% by mass or less.

[0045] In step 1, the metal oxide A, the polymer B, the formic acid, and the solvent C can be mixed by a known method. From the viewpoint of improving productivity, a method is preferred in which a mixed solution containing the metal oxide A, the polymer B, and the solvent C is obtained in advance, and then formic acid is added and mixed.

[0046] The mixing temperature in step 1 is preferably -10°C or higher, more preferably 0°C or higher, even more preferably 10°C or higher, even more preferably 15°C or higher, and even more preferably 20°C or higher, from the viewpoint of improving productivity, and is preferably 45°C or lower, more preferably 40°C or lower, even more preferably 35°C or lower, and even more preferably 30°C or lower, from the viewpoint of improving the uniformity, conductivity, and ejection property of the metal microparticles.

[0047] The stirring speed in step 1 is preferably 1 m / s or more, more preferably 2 m / s or more, and even more preferably 4 m / s or more, from the viewpoint of improving the uniformity, conductivity, and ejection property of the metal microparticles, and is preferably 21 m / s or less, more preferably 13 m / s or less, and even more preferably 8 m / s or less, from the viewpoint of improving productivity.

[0048] The mixing time in step 1 is preferably 2 minutes or more, more preferably 5 minutes or more, from the viewpoint of improving the uniformity, conductivity, and ejection properties of the metal microparticles, and is preferably 60 minutes or less, more preferably 45 minutes or less, and even more preferably 35 minutes or less, from the viewpoint of improving productivity.

[0049] (Process 2) Step 2 is a step of heating the mixed liquid 1 obtained in step 1 to obtain a metal fine particle dispersion liquid. The heating temperature in step 2 is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 55°C or higher, from the viewpoint of improving productivity, uniformity of the metal microparticles, conductivity, and ejection properties, and is preferably 120°C or lower, more preferably 100°C or lower, even more preferably 80°C or lower, and even more preferably 70°C or lower, from the viewpoint of improving productivity.

[0050] The stirring speed in step 2 is preferably 1 m / s or more, more preferably 2 m / s or more, and even more preferably 4 m / s or more, from the viewpoint of improving the uniformity, conductivity, and ejection properties of the metal microparticles, and is preferably 21 m / s or less, more preferably 13 m / s or less, and even more preferably 8 m / s or less, from the viewpoint of improving productivity.

[0051] The heating time in step 2 is preferably 45 minutes or more, more preferably 60 minutes or more, and even more preferably 90 minutes or more, from the viewpoint of improving the uniformity, conductivity, and ejection property of the metal microparticles, and is preferably 420 minutes or less, more preferably 300 minutes or less, and even more preferably 150 minutes or less, from the viewpoint of improving productivity.

[0052] (Step 3) This is a step in which the metal particle dispersion liquid obtained in step 2 is mixed with formic acid to obtain an ink containing metal particles. The mixing temperature in step 3 is preferably -10°C or higher, more preferably 0°C or higher, even more preferably 10°C or higher, even more preferably 15°C or higher, and even more preferably 20°C or higher, from the viewpoint of improving productivity, and is preferably 45°C or lower, more preferably 40°C or lower, even more preferably 35°C or lower, and even more preferably 30°C or lower, from the viewpoint of improving the uniformity, conductivity, and ejection property of the metal microparticles.

[0053] The stirring speed in step 3 is preferably 0.05 m / s or more, more preferably 0.1 m / s or more, and even more preferably 0.2 m / s or more, from the viewpoint of improving the uniformity, conductivity, and ejection properties of the metal microparticle-containing ink, and is preferably 2 m / s or less, more preferably 1 m / s or less, and even more preferably 0.5 m / s or less, from the viewpoint of improving productivity.

[0054] The mixing time in step 3 is preferably 5 minutes or more, more preferably 15 minutes or more, from the viewpoint of improving the uniformity, conductivity, and ejection properties of the metal microparticle-containing ink, and is preferably 90 minutes or less, more preferably 75 minutes or less, even more preferably 60 minutes or less, and even more preferably 45 minutes or less, from the viewpoint of improving productivity.

[0055] The amount of formic acid mixed in step 3, when the total amount of the metal microparticle-containing ink obtained in step 3 is taken as 100% by mass, is preferably 0.8% by mass or more, and more preferably 0.9% by mass or more, from the viewpoint of improving conductivity, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, even more preferably 9% by mass or less, even more preferably 8% by mass or less, and even more preferably 7.5% by mass or less, from the viewpoint of improving ejection properties.

[0056] [Ink containing metal particles] The metal microparticle-containing ink of the present invention contains metal microparticles a dispersed in polymer B, formic acid, and solvent C, wherein polymer B contains a structural unit derived from monomer (b-1) having a carboxy group and a structural unit derived from monomer (b-2) having a polyoxyalkylene group, solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, the content of metal microparticles a is 8 to 17% by mass, and the mass ratio of the content of polymer B to the total content of polymer B and metal microparticles a [polymer B / (polymer B + metal microparticles a)] is 0.05 to 0.17. The metal fine particle-containing ink of the present invention can be obtained, for example, by the method for producing the metal fine particle-containing ink of the present invention described above.

[0057] The metal microparticle-containing ink according to the present invention comprises metal microparticles a dispersed in a medium. The form of the metal microparticles a is not particularly limited, as long as the particles are formed from at least metal microparticles and polymer B. For example, the form includes a particle form in which metal microparticles are encapsulated in polymer B, a particle form in which metal microparticles are uniformly dispersed in polymer B, a particle form in which metal microparticles are exposed on the surface of polymer B particles, and mixtures thereof.

[0058] The metal fine particle-containing ink according to the present invention has the effect of easily replacing the solvent with any solvent or not requiring solvent replacement, and can improve conductivity and ejection properties. The reason for this is not clear, but is thought to be as follows. First, by setting the content of metal fine particles a to 17% by mass or less, it is believed that the generation of aggregates of metal fine particles a can be suppressed, thereby improving conductivity and ejectability.Furthermore, by setting the content of metal fine particles a to 8% by mass or more, it is believed that the generation of coarse particles of metal fine particles a can be suppressed, thereby improving conductivity and ejectability. Furthermore, by setting the mass ratio of the content of polymer B to the total content of polymer B and metal fine particle a [polymer B / (polymer B + metal)] to 0.05 or more, it is possible to ensure a sufficient amount of polymer B, which in turn improves the dispersion stability of metal fine particle a and improves dischargeability. Furthermore, it is believed that the sufficient dispersion stability leads to a uniform printed coating film and improved conductivity. Furthermore, by setting the [polymer B / (polymer B + metal)] to 0.17 or less, it is possible to reduce the amount of polymer B that is not adsorbed to metal fine particle a, which in turn improves conductivity and dischargeability. In addition, solvent C, which contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, has a low boiling point and therefore has excellent quick-drying properties, and is easily replaced with any solvent or does not require solvent replacement. Furthermore, the inclusion of formic acid in the metal particle-containing ink promotes the detachment of polymer B from the surface of the metal particles, and the reducing action of formic acid inhibits oxidation of the surface of the metal particles, promoting sintering of the metal particles. As a result, the printed coating becomes more uniform and the conductivity is thought to be further improved. For the above reasons, it is believed that the metal fine particle-containing ink according to the present invention can be easily replaced with any solvent or does not require solvent replacement, and can improve conductivity and ejection properties.

[0059] <Metal fine particles a> Examples of metals (metal atoms) constituting the metal fine particles 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 metals constituting the metal fine particles a may be used alone or in combination as an alloy of two or more. Furthermore, the metal fine particles a may be used alone or in combination of two or more. Among these, from the viewpoint of improving conductivity and ejection properties, the metal constituting the metal fine particles a preferably includes a transition metal of Groups 4 to 11 and Periods 4 to 6, more preferably includes a precious metal such as copper, nickel, gold, silver, platinum, or palladium, even more preferably includes at least one selected from gold, silver, copper, nickel, and palladium, even more preferably includes at least one selected from gold, silver, and copper, even more preferably includes at least one selected from silver and copper, even more preferably includes silver, and even more preferably is silver. The type of metal can be confirmed by high-frequency inductively coupled plasma atomic emission spectrometry. From the viewpoint of improving conductivity and ejection properties, the content of metal in the metal microparticles a is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass. From the viewpoint of improving conductivity and ejection properties, the silver content in the metal microparticles a is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that the material may contain unintentionally contained components, such as unavoidable impurities.

[0060] <Polymer B> A preferred embodiment of the polymer B used in the metal fine particle-containing ink of the present invention is the same as the polymer B used in the method for producing the metal fine particle-containing ink of the present invention described above.

[0061] <Solvent C> A preferred embodiment of the solvent C used in the metal fine particle-containing ink of the present invention is the same as the solvent C used in the method for producing the metal fine particle-containing ink of the present invention described above.

[0062] (Composition of ink containing metal particles) The content of metal fine particles a in the metal fine particle-containing ink according to the present invention is 8% by mass or more, preferably 10% by mass or more, more preferably 11.5% by mass or more, from the viewpoint of improving conductivity, and 17% by mass or less, preferably 16.5% by mass or less, from the viewpoint of improving ejection performance. Taking these points into consideration, the content of metal fine particles a in the metal fine particle-containing ink according to the present invention is 8% by mass or more and 17% by mass or less, preferably 10% by mass or more and 17% by mass or less, more preferably 11.5% by mass or more and 17% by mass or less, and even more preferably 11.5% by mass or more and 16.5% by mass or less.

[0063] The content of polymer B in the metal fine particle-containing ink according to the present invention is preferably 0.7% by mass or more, more preferably 0.8% by mass or more, and even more preferably 0.9% by mass or more from the viewpoint of improving ejection performance, and is preferably 2.5% by mass or less, more preferably 2.3% by mass or less, even more preferably 2.1% by mass or less, even more preferably 1.9% by mass or less, and even more preferably 1.7% by mass or less from the viewpoint of improving conductivity. Taking these viewpoints into consideration, the content of polymer B in the metal fine particle-containing ink according to the present invention is preferably 0.7% by mass or more and 2.5% by mass or less, more preferably 0.7% by mass or more and 2.3% by mass or less, even more preferably 0.7% by mass or more and 2.1% by mass or less, even more preferably 0.7% by mass or more and 1.9% by mass or less, even more preferably 0.7% by mass or more and 1.7% by mass or less.

[0064] The content of formic acid in the metal fine particle-containing ink according to the present invention is preferably 0.8% by mass or more, more preferably 0.9% by mass or more, from the viewpoint of improving conductivity, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, even more preferably 9% by mass or less, even more preferably 8% by mass or less, and even more preferably 7.5% by mass or less, from the viewpoint of improving ejection properties. Taking these viewpoints into consideration, the content of formic acid in the metal fine particle-containing ink according to the present invention is preferably 0.8% by mass or more and 15% by mass or less, more preferably 0.8% by mass or more and 12% by mass or less, even more preferably 0.8% by mass or more and 10% by mass or less, even more preferably 0.8% by mass or more and 9% by mass or less, even more preferably 0.8% by mass or more and 8% by mass or less, and even more preferably 0.9% by mass or more and 7.5% by mass or less.

[0065] The content of solvent C in the metal microparticle-containing ink of the present invention is preferably 70% by mass or more, more preferably 72% by mass or more, even more preferably 73% by mass or more, and even more preferably 75% by mass or more, from the viewpoint of improving ejection properties, and is preferably 90% by mass or less, more preferably 88% by mass or less, and even more preferably 86% by mass or less, from the viewpoint of improving conductivity.

[0066] The mass ratio of the content of polymer B to the total content of polymer B and metal fine particles a in the metal fine particle-containing ink according to the present invention [polymer B / (polymer B+metal)] is preferably 0.05 or more, more preferably 0.055 or more, and even more preferably 0.06 or more from the viewpoint of improving ejection performance, and is preferably 0.17 or less, more preferably 0.155 or less, even more preferably 0.14 or less, and even more preferably 0.125 or less from the viewpoint of improving conductivity. Taking these viewpoints into consideration, the mass ratio of the content of polymer B to the total content of polymer B and metal fine particles a in the metal fine particle-containing ink according to the present invention [polymer B / (polymer B+metal)] is 0.05 or more and 0.17 or less, preferably 0.05 or more and 0.155 or less, even more preferably 0.05 or more and 0.14 or less, even more preferably 0.05 or more and 0.125 or less, even more preferably 0.055 or more and 0.125 or less, and even more preferably 0.06 or more and 0.125 or less.

[0067] The molar ratio of the content of formic acid to the content of the metal constituting the metal fine particles a in the metal fine particle-containing ink according to the present invention [formic acid / metal] is preferably 0.1 or more, more preferably 0.12 or more, even more preferably 0.14 or more, and even more preferably 0.16 or more from the viewpoint of improving conductivity, and is preferably 2 or less, more preferably 1.9 or less, even more preferably 1.6 or less, even more preferably 1.4 or less, and even more preferably 1.3 or less from the viewpoint of improving ejection performance. Taking these viewpoints into consideration, the molar ratio of the content of formic acid to the content of the metal constituting the metal fine particles a in the metal fine particle-containing ink according to the present invention [formic acid / metal] is preferably 0.1 or more and 2 or less, more preferably 0.1 or more and 1.9 or less, even more preferably 0.12 or more and 1.6 or less, even more preferably 0.12 or more and 1.4 or less, even more preferably 0.12 or more and 1.3 or less, even more preferably 0.14 or more and 1.3 or less, and even more preferably 0.16 or more and 1.3 or less.

[0068] (Physical properties of ink containing metal particles) The average particle size of the metal fine particles a in the metal fine particle-containing ink according to the present invention is preferably 3 nm or more, more preferably 10 nm or more, even more preferably 20 nm or more, even more preferably 30 nm or more, from the viewpoint of improving conductivity and ejection properties, and is preferably 100 nm or less, more preferably 90 nm or less, even more preferably 80 nm or less, even more preferably 70 nm or less. The average particle size of the metal fine particles a can be calculated by cumulant analysis after measuring the particle size by dynamic light scattering using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions are a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 accumulations. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent. The measurement sample is weighed into a screw tube (No. 5, manufactured by Maruemu Co., Ltd.) and a solids concentration of 5 × 10 ‐3 Water can be added to the solution so that the concentration becomes 5% by mass, and the solution can be stirred at 25°C for 1 hour using a magnetic stirrer.

[0069] From the viewpoint of improving conductivity and jetting performance, the viscosity of the metal fine particle-containing ink according to the present invention at 30°C is preferably 1 mPa·s or more, more preferably 1.5 mPa·s or more, even more preferably 1.8 mPa·s or more, and is preferably 60 mPa·s or less, more preferably 50 mPa·s or less, even more preferably 30 mPa·s or less, even more preferably 10 mPa·s or less, even more preferably 5 mPa·s or less, even more preferably 3 mPa·s or less. The viscosity of the ink can be measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TV-25, using a standard cone rotor 1°34' x R24, rotation speed 100 rpm).

[0070] From the viewpoint of improving conductivity and ejection properties, the pH of the metal fine particle-containing ink according to the present invention at 20°C is preferably 7.0 or more, more preferably 7.2 or more, even more preferably 7.5 or more, and is preferably 11 or less, more preferably 10 or less, even more preferably 9.5 or less. The pH of the ink can be measured by a conventional method.

[0071] The metal fine particle-containing ink according to the present invention can improve the ejection properties and form a metal film with improved conductivity, and therefore can be suitably used for various printing methods, particularly inkjet printing, flexographic printing, gravure printing, screen printing, offset printing, dispenser printing, etc. Among these, the metal fine particle-containing ink according to the present invention is preferably used for inkjet printing because it can improve the ejection properties as described above.

[0072] The metal particle-containing ink according to the present invention can improve ejection properties and form metal films with improved conductivity, making it suitable for a wide range of applications. Examples of such applications include decorative materials that impart specular gloss; conductive materials such as wiring materials, electrode materials, and multilayer ceramic capacitors (hereinafter also referred to as "MLCCs") used to form conductive circuits; joining materials such as solder; various sensors; antennas such as tags for automatic identification technology using short-range wireless communication (radio frequency identifiers (RFIDs), hereinafter also referred to as "RFIDs"); catalysts; optical materials; and medical materials. Among these, the metal particle-containing ink according to the present invention is preferably used for producing printed materials on which conductive circuits are formed.

[0073] [Inkjet printing ink] When the metal microparticle-containing ink according to the present invention is used for inkjet printing, the method for producing the inkjet printing ink preferably includes step 4 of mixing the metal microparticle-containing ink according to the present invention, a surfactant, and, if necessary, a solvent to obtain the inkjet printing ink. That is, the ink for ink-jet printing according to the present invention contains the metal fine particle-containing ink according to the present invention and a surfactant.

[0074] The surfactant is preferably a nonionic surfactant, and from the viewpoint of maintaining the ink at an appropriate surface tension and improving its wettability to the printing medium, one or more surfactants selected from an acetylene glycol surfactant and a silicone surfactant are more preferred, and it is even more preferred to use an acetylene glycol surfactant and a silicone surfactant in combination. Examples of acetylene glycol surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, and ethylene oxide adducts thereof. Examples of silicone surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, and carboxy-modified silicone, with polyether-modified silicone being preferred from the same viewpoint as above.

[0075] From the viewpoint of improving the conductivity and ejection properties, the solvent is preferably at least one selected from the group consisting of water, aliphatic monoalcohols having from 1 to 4 carbon atoms, and ketones having from 3 to 4 carbon atoms. From the viewpoint of improving the conductivity and ejection properties, the solvent preferably contains at least one selected from methanol, ethanol, n-propanol, isopropanol, isobutanol, butanol, acetone, methyl ethyl ketone, and water, more preferably contains at least one selected from ethanol, n-propanol, isopropanol, isobutanol, acetone, methyl ethyl ketone, and water, and even more preferably contains at least one selected from ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water.

[0076] In step 4, from the viewpoint of improving the uniformity, conductivity, and ejection properties of the metal fine particles, it is preferable to add and mix the surfactant and solvent in this order to the metal fine particle-containing ink. The mixing temperature in step 4 is, for example, 20°C or higher and 35°C or lower. The inkjet printing ink is preferably filtered from the viewpoint of improving the conductivity and ejection properties.

[0077] (Inkjet printing ink composition) The content of surfactant in the ink for inkjet printing according to the present invention is preferably 0% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.05% by mass or more, from the viewpoint of improving droplet formation and wettability, and is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, from the viewpoint of improving the uniformity, conductivity, and ejection properties of the metal microparticles. The content of metal fine particles a in the ink for inkjet printing according to the present invention is preferably 8% by mass or more, more preferably 10% by mass or more, and even more preferably 11.5% by mass or more, from the viewpoint of improving conductivity, and is preferably 17% by mass or less, more preferably 16.5% by mass or less, from the viewpoint of improving ejection properties. The content of polymer B in the ink for inkjet printing according to the present invention is preferably 0.7% by mass or more, more preferably 0.8% by mass or more, and even more preferably 0.9% by mass or more, from the viewpoint of improving the ejection properties, and is preferably 2.5% by mass or less, more preferably 2.3% by mass or less, even more preferably 2.1% by mass or less, even more preferably 1.9% by mass or less, and even more preferably 1.7% by mass or less, from the viewpoint of improving the conductivity. The content of formic acid in the ink for inkjet printing according to the present invention is preferably 0.8% by mass or more, and more preferably 0.9% by mass or more, from the viewpoint of improving conductivity, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, even more preferably 9% by mass or less, even more preferably 8% by mass or less, and even more preferably 7.5% by mass or less, from the viewpoint of improving jetting properties. The content of solvent C in the ink for inkjet printing according to the present invention is preferably 70% by mass or more, more preferably 72% by mass or more, even more preferably 73% by mass or more, and even more preferably 75% by mass or more, from the viewpoint of improving the ejection properties, and is preferably 90% by mass or less, more preferably 88% by mass or less, and more preferably 86% by mass or less, from the viewpoint of improving the conductivity.

[0078] The mass ratio of the content of polymer B to the total content of polymer B and metal microparticles a in the ink for inkjet printing according to the present invention [polymer B / (polymer B+metal)] is preferably 0.05 or more, more preferably 0.055 or more, and even more preferably 0.06 or more, from the viewpoint of improving ejection properties, and is preferably 0.17 or less, more preferably 0.155 or less, even more preferably 0.14 or less, and even more preferably 0.125 or less, from the viewpoint of improving conductivity.

[0079] The ink of the present invention may contain various additives other than the above-described components, such as a fixing aid such as a dispersion of polymer particles, a moisturizer, a wetting agent, a penetrating agent, a viscosity adjuster, an antifoaming agent, an antiseptic, an antifungal agent, and an antirust agent, as long as the effects of the present invention are not impaired.

[0080] [Manufacturing method for printed matter] The method for producing a printed matter according to the present invention preferably includes step 5 of applying at least one ink selected from the group consisting of a metal fine particle-containing ink obtained by the method for producing a metal fine particle-containing ink according to the present invention and an inkjet printing ink obtained by the method for producing an inkjet printing ink according to the present invention onto a substrate, thereby obtaining a printed matter on which a metal film is formed. This makes it possible to obtain a printed item on which a metal film having excellent conductivity, specular gloss, etc. is formed. In printing using the ink, a patterned metal film can be formed by forming a patterned printing image on a substrate, and this patterned metal film can be used as a conductive circuit. In other words, the method for producing a printed item according to the present invention is preferably used as a method for producing a printed item on which a conductive circuit is formed on a substrate. In the production of printed matter on which conductive circuits are formed, the base material is sometimes called a "substrate."

[0081] (base material) Examples of the substrate include paper, fabric, resin, metal, glass, ceramic, and composite materials thereof. Examples of paper substrates include coated paper (coated paper, art paper, etc.), uncoated paper, plain paper, kraft paper, synthetic paper, processed paper, and paperboard. Examples of fabrics used for the substrate include fabrics made of natural fibers such as cotton, silk, and linen, and synthetic fibers such as rayon, acetate, nylon, and polyester, as well as blended fabrics made of two or more of these fibers. Examples of resin substrates include synthetic resin films such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polypropylene (PP), polyamide (PA), polyimide (PI), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), and polycarbonate (PC). Examples of metal substrates include substrates made of metals such as gold, silver, copper, palladium, platinum, aluminum, nickel, and tin. Among these, from the viewpoint of bending resistance, the substrate is preferably at least one selected from a paper substrate and a resin substrate, and more preferably a paper substrate. The substrate may be either a rigid substrate or a flexible substrate, but is preferably a flexible substrate from the viewpoint that the metal fine particle-containing ink can form a metal film that is excellent in bending resistance.

[0082] As a method for printing the ink onto a substrate, various pattern printing methods such as inkjet printing, flexographic printing, gravure printing, screen printing, offset printing, dispenser printing, etc. are preferred, and inkjet printing is more preferred. By using the pattern printing method, it is possible to form a fine conductive circuit on the substrate and also to apply a design with an excellent mirror surface design to the substrate. The amount of ink applied to the substrate can be adjusted appropriately depending on the size and type of the circuit or electrode to be formed, the desired level of specular gloss, and the design.

[0083] (inkjet printing) When the metal microparticle-containing ink according to the present invention is used for inkjet printing, and when the ink for inkjet printing is used, the ink can be loaded into a known inkjet printing device and ejected as ink droplets onto a substrate to form a printed image. Inkjet printing devices are classified into thermal and piezo types, and the ink is more preferably used for thermal inkjet printing.

[0084] The head temperature of the inkjet head is preferably 15°C or higher, more preferably 20°C or higher, even more preferably 23°C or higher, and is preferably 45°C or lower, more preferably 40°C or lower, even more preferably 35°C or lower, even more preferably 30°C or lower. From the viewpoint of printing efficiency, etc., the drive frequency of the head is preferably 1 kHz or more, more preferably 5 kHz or more, even more preferably 8 kHz or more, and preferably 50 kHz or less, more preferably 40 kHz or less, even more preferably 20 kHz or less, even more preferably 15 kHz or less.

[0085] The ejected volume of the ink according to the present invention is preferably 3 pL or more, more preferably 5 pL or more, and preferably 30 pL or less, more preferably 20 pL or less, and even more preferably 10 pL or less per droplet. In the present invention, the printing resolution is preferably 200 dpi or higher, more preferably 300 dpi or higher, and preferably 1,000 dpi or lower, more preferably 800 dpi or lower, and even more preferably 700 dpi or lower. Here, "resolution" in this specification refers to the number of dots per inch (2.54 cm) formed on the substrate. For example, "a resolution of 600 dpi" means that when ink droplets are ejected onto the substrate using a line head with nozzle holes arranged at 600 dpi (dots per inch) per length of the nozzle row, a corresponding row of dots at 600 dpi per inch is formed in the direction perpendicular to the substrate transport direction, and when ink droplets are ejected while the substrate is moving in the transport direction, a row of dots at 600 dpi per inch is also formed on the substrate in the transport direction. In this specification, the resolution in the direction perpendicular to the substrate transport direction and the resolution in the transport direction are expressed as the same value.

[0086] (sintering process) In the method for producing a printed matter according to the present invention, from the viewpoint of reducing the volume resistivity and improving the conductivity, and from the viewpoint of improving the specular gloss, it is preferable that after printing on a substrate using the ink, a sintering treatment is carried out to sinter the metal fine particles a in the ink coating on the substrate. By the sintering process, the ink solvent in the ink film is evaporated and dried, and further the metal fine particles a are sintered to form a conductive circuit made of a metal film with low volume resistivity.

[0087] The temperature of the sintering treatment is preferably lower than the temperature at which the substrate deforms, i.e., the heat resistance temperature. Specifically, from the viewpoint of reducing the resistivity of the metal film, the temperature is preferably 25°C or higher, more preferably 50°C or higher, even more preferably 100°C or higher, even more preferably 120°C or higher, even more preferably 140°C or higher, and preferably 200°C or lower, more preferably 180°C or lower, even more preferably 160°C or lower, under normal pressure. The relative humidity of the surrounding environment during the sintering treatment is preferably 20% or more, more preferably 30% or more, and is preferably 65% ​​or less, more preferably 60% or less, and even more preferably 50% or less. In particular, the sintering treatment is preferably performed at a high temperature of 100° C. or higher, followed by storage at a low temperature. Here, the low-temperature treatment is preferably performed by storing at room temperature (10° C. or higher and 35° C. or lower). The time of the high-temperature treatment in the sintering treatment can be adjusted appropriately depending on the treatment temperature, but from the viewpoint of reducing the resistivity of the metal film, it is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 7 minutes or more, and from the viewpoint of productivity, it is preferably 6 hours or less, more preferably 3 hours or less, even more preferably 1 hour or less, and even more preferably 30 minutes or less. The time for the low-temperature treatment in the sintering treatment can be adjusted appropriately depending on the treatment temperature, but from the viewpoint of reducing the resistivity of the metal film, it is preferably 1 hour or more, more preferably 3 hours or more, even more preferably 6 hours or more, and even more preferably 12 hours or more, and from the viewpoint of productivity, it is preferably 36 hours or less, more preferably 24 hours or less. The sintering treatment may be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen gas, but if the substrate is a metal that is easily oxidized, it is preferably carried out in a nitrogen gas atmosphere. The sintering method is not particularly limited, and examples include a method of heating by contacting a heater with the surface of the substrate opposite to the surface on which the ink coating is formed; a method of heating by applying hot air to the ink coating surface on the substrate; a method of heating by bringing a heater close to the ink coating surface on the substrate; a method of storing the substrate on which the ink coating has been formed in a thermostatic device that can maintain a constant temperature; a method of heating by steam curing using high-temperature steam at normal or high pressure; and a method of heating by irradiation with light such as near-infrared light or ultraviolet light.

[0088] The printed matter obtained by the production method according to the present invention has good electrical conductivity and can be used as a conductive composite material containing a substrate and a conductive circuit in various electronic and electrical devices. The conductive composite material can be used in various devices such as RFID tags, capacitors such as MLCCs, LTCC substrates, electronic paper, image display devices such as liquid crystal displays, organic electroluminescence displays, and touch panels, organic electroluminescence elements, organic transistors, wiring boards such as printed wiring boards and flexible wiring boards, organic solar cells, flexible batteries, and sensors such as flexible sensors.

[0089] In addition to the above-described embodiments, the present invention also discloses the following embodiments. <1> Step 1: Mixing a metal oxide A, a polymer B, formic acid, and a solvent C to obtain a mixed solution 1; a step 2 of heating the mixed solution 1 to obtain a metal fine particle dispersion; and step 3 of mixing the metal fine particle dispersion liquid with formic acid to obtain a metal fine particle-containing ink, the polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, the content of the metal constituting the metal oxide A in the mixed solution 1 is 28% by mass or more and 57% by mass or less, A method for producing an ink containing metal microparticles, wherein the mass ratio of the content of the polymer B to the total content of the polymer B and the metal constituting the metal oxide A in the mixed solution 1 [polymer B / (polymer B+metal)] is 0.05 or more and 0.17 or less. <2> Step 1: Mixing a metal oxide A, a polymer B, formic acid, and a solvent C to obtain a mixed solution 1; a step 2 of heating the mixed solution 1 to obtain a metal fine particle dispersion; and step 3 of mixing the metal fine particle dispersion liquid with formic acid to obtain a metal fine particle-containing ink, Metal oxide A contains silver oxide, the polymer B comprises a vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, the content of the metal constituting the metal oxide A in the mixed solution 1 is 28% by mass or more and 57% by mass or less, A method for producing an ink containing metal microparticles, wherein the mass ratio of the content of the polymer B to the total content of the polymer B and the metal constituting the metal oxide A in the mixed solution 1 [polymer B / (polymer B+metal)] is 0.05 or more and 0.17 or less. <3> Step 1: Mixing a metal oxide A, a polymer B, formic acid, and a solvent C to obtain a mixed solution 1; a step 2 of heating the mixed solution 1 to obtain a metal fine particle dispersion; and step 3 of mixing the metal fine particle dispersion liquid with formic acid to obtain a metal fine particle-containing ink, Metal oxide A contains silver oxide, the polymer B comprises a vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group, a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, and a structural unit derived from a hydrophobic monomer (b-3); the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, The boiling point of the solvent C is 70°C or higher and 105°C or lower, the content of the metal constituting the metal oxide A in the mixed solution 1 is 28% by mass or more and 57% by mass or less, A method for producing an ink containing metal microparticles, wherein the mass ratio of the content of the polymer B to the total content of the polymer B and the metal constituting the metal oxide A in the mixed solution 1 [polymer B / (polymer B+metal)] is 0.05 or more and 0.15 or less. <4> The polymer B comprises a vinyl polymer containing, as the monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, and, as the monomer (b-2), a structural unit derived from an alkoxypolyalkylene glycol (meth)acrylate. <1> ~ <3> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <5> The polymer B comprises, as the monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, as the monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate, and as the monomer (b-3), a structural unit derived from at least one selected from a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol. <1> ~ <4> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <6> The solvent C contains at least one selected from methanol, ethanol, n-propanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and water. <1> ~ <5> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <7> The solvent C contains at least one selected from ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water. <1> ~ <6> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <8> In the mixed liquid 1, the content of metal oxide A is 30% by mass or more and 62% by mass or less, the content of polymer B is 2.0% by mass or more and 10% by mass or less, the content of formic acid is 5.0% by mass or more and 15% by mass or less, and the content of solvent C is 12% by mass or more and 50% by mass or less. <1> ~ <7> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <9> the molar ratio of the content of formic acid to the content of metal constituting metal oxide A in mixed solution 1 [formic acid / metal] is 0.05 or more and 1.00 or less; <1> ~ <8> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <10> The content of silver oxide in metal oxide A is 80 mass% or more. <2> ~ <9> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <11> the content of the vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group in the polymer B is 80% by mass or more; <2> ~ <10> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <12> the content of the vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group, a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, and a structural unit derived from a hydrophobic monomer (b-3) in the polymer B is 80% by mass or more; <3> ~ <11> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <13> the content of a vinyl polymer containing, as the monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid and, as the monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate in the polymer B is 80% by mass or more; <4> ~ <12> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <14> the content of a vinyl polymer in polymer B including, as monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, as monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate, and, as monomer (b-3), a structural unit derived from at least one selected from a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol, is 80% by mass or more; <5> ~ <13> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <15> the total content of water, the aliphatic monoalcohol having 1 to 4 carbon atoms, and the ketone having 3 to 4 carbon atoms in solvent C is 80 mass% or more; <1> ~ <14> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <16> the total content of methanol, ethanol, n-propanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and water in solvent C is 80 mass% or more; <6> ~ <15> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <17> the total content of ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water in solvent C is 80% by mass or more; <7> ~ <16> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <18> the content of the formic acid in the metal fine particle-containing ink is 0.8% by mass or more and 15% by mass or less; <1> ~ <17> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <19> the molar ratio of the content of the formic acid to the content of the metal constituting the metal fine particles a in the metal fine particle-containing ink [formic acid / metal] is 0.1 or more and 2 or less; <1> ~ <18> 1. A method for producing an ink containing metal fine particles according to any one of claims 1 to 9. <20> The polymer B contains metal particles a dispersed therein, formic acid, and a solvent C. the polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, The content of the metal fine particles a is 8% by mass or more and 17% by mass or less, The metal microparticle-containing ink has a mass ratio [polymer B / (polymer B+metal microparticle a)] of the content of the polymer B to the total content of the polymer B and the content of the metal microparticle a) of 0.05 or more and 0.17 or less. <21> The polymer B contains metal particles a dispersed therein, formic acid, and a solvent C. The metal fine particles a contain silver, the polymer B comprises a vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, The content of the metal fine particles a is 8% by mass or more and 17% by mass or less, The metal microparticle-containing ink has a mass ratio [polymer B / (polymer B+metal microparticle a)] of the content of the polymer B to the total content of the polymer B and the content of the metal microparticle a) of 0.05 or more and 0.17 or less. <22> The polymer B contains metal particles a dispersed therein, formic acid, and a solvent C. The metal fine particles a contain silver, the polymer B comprises a vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group, a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, and a structural unit derived from a hydrophobic monomer (b-3); the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having 1 to 4 carbon atoms, and ketones having 3 to 4 carbon atoms, The boiling point of the solvent C is 70°C or higher and 105°C or lower, The content of the metal fine particles a is 8% by mass or more and 17% by mass or less, A metal microparticle-containing ink, wherein the mass ratio of the content of the polymer B to the total content of the polymer B and the content of the metal microparticles a [polymer B / (polymer B+metal microparticles a)] is 0.05 or more and 0.155 or less. <23> The polymer B comprises a vinyl polymer containing, as the monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, and, as the monomer (b-2), a structural unit derived from an alkoxypolyalkylene glycol (meth)acrylate. <20> ~ <22> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <24> The polymer B comprises, as the monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, as the monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate, and as the monomer (b-3), a structural unit derived from at least one selected from a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol. <20> ~ <23> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <25> The solvent C contains at least one selected from methanol, ethanol, n-propanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and water. <20> ~ <24> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <26> The solvent C contains at least one selected from ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water. <20> ~ <25> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <27> In the metal fine particle-containing ink, the content of metal fine particles a is 8% by mass or more and 17% by mass or less, the content of polymer B is 0.7% by mass or more and 2.5% by mass or less, the content of formic acid is 0.8% by mass or more and 15% by mass or less, and the content of solvent C is 70% by mass or more and 90% by mass or less, <20> ~ <26> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <28> a molar ratio [formic acid / metal] of the content of the formic acid to the content of the metal constituting the metal fine particles a in the metal fine particle-containing ink is 0.1 or more and 2 or less; <20> ~ <27> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <29> The silver content in the metal fine particles a is 80 mass% or more. <21> ~ <28> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <30> the content of the vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group in the polymer B is 80% by mass or more; <21> ~ <29> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <31> the content of the vinyl polymer containing a structural unit derived from a monomer (b-1) having a carboxy group, a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, and a structural unit derived from a hydrophobic monomer (b-3) in the polymer B is 80% by mass or more; <22> ~ <30> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <32> the content of a vinyl polymer containing, as the monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid and, as the monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate in the polymer B is 80% by mass or more; <23> ~ <31> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <33> the content of a vinyl polymer in polymer B including, as monomer (b-1), a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid, as monomer (b-2), a structural unit derived from an alkoxy polyalkylene glycol (meth)acrylate, and, as monomer (b-3), a structural unit derived from at least one selected from a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol, is 80% by mass or more; <24> ~ <32> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <34> the total content of water, the aliphatic monoalcohol having 1 to 4 carbon atoms, and the ketone having 3 to 4 carbon atoms in solvent C is 80 mass% or more; <20> ~ <33> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <35> the total content of methanol, ethanol, n-propanol, isopropanol, isobutanol, n-butanol, acetone, methyl ethyl ketone, and water in solvent C is 80 mass% or more; <25> ~ <34> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <36> the total content of ethanol, n-propanol, isopropanol, methyl ethyl ketone, and water in solvent C is 80% by mass or more; <26> ~ <35> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <37> <20> ~ <36> 10. An ink for inkjet printing, comprising the metal fine particle-containing ink according to any one of claims 1 to 9 and a surfactant. <38> <20> ~ <36> The metal fine particle-containing ink according to any one of <37> 5. A method for producing a printed matter, comprising: applying at least one ink selected from the group consisting of the inks for ink-jet printing described in 1. above onto a substrate to obtain a printed matter on which a metal film is formed. <39> a method for applying the ink onto the substrate is an inkjet printing method; <38> A method for producing a printed matter according to claim 1. [Example]

[0090] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples. In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. Various physical properties were measured or calculated by the following methods.

[0091] [Measurement of number average molecular weight Mn of polymer B] The measurement was performed by gel permeation chromatography. The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of eluent in a glass vial, stirring with a magnetic stirrer at 25°C for 10 hours, and filtering with a syringe filter (DISMIC-13HP PTFE 0.2 μm, manufactured by Advantec Toyo Co., Ltd.). The measurement conditions are shown below. GPC equipment: Tosoh Corporation "HLC-8320GPC" Column: Tosoh Corporation "TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H" Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kit manufactured by Tosoh Corporation: "PStQuick B (F-550, F-80, F-10, F-1, A-1000)", PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0092] [Measurement of Acid Value of Polymer B] The acid value of Polymer B was measured in accordance with JIS K 0070-1992 (potentiometric titration method), except that the measurement solvent was changed from the ethanol and ether mixed solvent specified in JIS K 0070-1992 to an acetone and toluene mixed solvent (acetone:toluene = 4:6 (volume ratio)).

[0093] [Cumulant average particle diameter of metal particles a in metal particle-containing ink] The cumulant average particle size of metal particles a in the metal particle-containing ink was measured by cumulant analysis using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 accumulations. The refractive index of water (1.333) was used as the refractive index of the dispersion solvent, and the concentration of the measurement sample was 5 x 10 -3 The values ​​are expressed in mass % (solid concentration equivalent).

[0094] [Mass ratio in ink containing metal particles [Polymer B / (Polymer B + Metal particles a)]] Using a simultaneous thermogravimetry and differential thermal analyzer (TG / DTA) "STA7200RV" (Hitachi High-Tech Science Corporation), 10 mg of sample was weighed into an aluminum pan and heated from 35°C to 550°C at a heating rate of 10°C / min. The mass loss was measured under a nitrogen flow of 50 mL / min. The mass loss from 200°C to 550°C was defined as the mass of polymer B, and the remaining mass at 550°C was defined as the mass of metal particle a, and the mass ratio [polymer B / (polymer B + metal particle a)] was calculated.

[0095] Polymer B used in the evaluation Polymer B-1: Acrylic acid / maleic acid / alkoxy (polyethylene glycol / polypropylene glycol) acrylate (number of alkylene oxide-derived units: 32 moles, molar ratio [EO / PO] = 75 / 25) / styrene / α-methylstyrene copolymer (BYK, DISPERBYK-2015 (aqueous solution with a polymer concentration of 40%), Mn: 4500, acid value: 10 mg KOH / g) Polymer B-2: Produced by the following method. 20.0 g of ethanol (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was placed in a 1000 mL four-neck round-bottom flask equipped with a thermometer, two 100 mL dropping funnels with nitrogen bypasses, and a reflux device, and the internal temperature of the flask was heated to 80°C in an oil bath, after which nitrogen bubbling was carried out for 10 minutes. Next, 15.3 g of methacrylic acid (Fujifilm Wako Pure Chemical Industries, Ltd., special reagent grade), 10.0 g of styrene (Fujifilm Wako Pure Chemical Industries, Ltd., special reagent grade), 7.2 g of methyl methacrylate (Fujifilm Wako Pure Chemical Industries, Ltd., special reagent grade), 67.5 g of methoxypolyethylene glycol (EO23 mol) methacrylate (NOF Corporation, "PME-1000"), 1.0 g of 3-mercaptopropionic acid (Fujifilm Wako Pure Chemical Industries, Ltd., special reagent grade), and 28.7 g of ethanol were dissolved in a polybeaker and placed in the dropping funnel (1). Separately, 51.3 g of ethanol and 1.3 g of 2,2'-azobis(2,4-dimethylvaleronitrile) (Fujifilm Wako Pure Chemical Industries, Ltd., "V-65", polymerization initiator) were dissolved in a polybeaker and placed in the dropping funnel (2). Next, the mixtures in the dropping funnels (1) and (2) were simultaneously added dropwise to the flask over 90 minutes. The internal temperature of the flask was then raised to 90°C, and stirring was continued for another hour to terminate the reaction. The resin solution was freeze-dried using a freeze dryer (Tokyo Rikakikai Co., Ltd., Model: FDU-2110) equipped with a dry chamber (Tokyo Rikakikai Co., Ltd., Model: DRC-1000) under drying conditions (freezing at -25°C for 1 hour, vacuum at -10°C for 9 hours, vacuum at 25°C for 5 hours, vacuum level 5 Pa) to obtain bone-dried polymer B-2 (methacrylic acid / methyl methacrylate / styrene / methoxypolyethylene glycol (EO23 mol) methacrylate polymer, acid value: 100 mgKOH / g, Mn: 8,300).

[0096] Example 1 (1) Manufacturing of ink containing metal particles (Process 1) A 1,000 mL stainless steel separable flask equipped with a thermometer, one 100 mL dropping funnel with a nitrogen bypass, and a reflux apparatus was charged with 240 g of ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, concentration 95%, containing 5% water) as solvent C, 60 g of polymer B-1, and 300 g of silver oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) as metal oxide A, and stirred for 15 minutes at 25°C and a stirring speed of 3,000 rpm using a Disper-type stirring impeller (manufactured by Shinto Scientific Co., Ltd., impeller diameter 40 mm) at 25°C. Next, 54.17 g of formic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, concentration 88%, containing 12% water) was added to the dropping funnel and added dropwise to the flask over 10 minutes, followed by stirring for 5 minutes at a stirring speed of 3,000 rpm to obtain Mixture 1.

[0097] (Process 2) The mixed solution 1 was stirred for 2 hours in a water bath at a stirring speed of 3,000 rpm while controlling the temperature at 60° C., and after cooling in air, a dark brown metal fine particle dispersion solution of Synthesis Example 1 was obtained.

[0098] (Step 3) 30.00 g of the metal microparticle dispersion of Synthesis Example 1 obtained in step 2, 68.86 g of ethanol (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, concentration 95%, containing 5% water), and 1.14 g of formic acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, concentration 88%, containing 12% water) were mixed for 30 minutes using a magnetic stirrer (diameter 20 mm) at 25°C and a stirring speed of 200 rpm to obtain metal microparticle-containing ink 1.

[0099] Examples 2 to 16 and Comparative Examples 1 to 4 Mixture 1 was obtained in the same manner as in step 1 of Example 1, except that the formulation was changed to that shown in Table 1, and then metal microparticle dispersions of Synthesis Examples 2 to 14 were produced in the same manner as in step 2 of Example 1. Furthermore, metal microparticle-containing inks 2 to 20 were obtained in the same manner as in step 3 of Example 1, except that the formulation was changed to that shown in Table 3.

[0100] [Table 1] * EtOH: Ethanol

[0101] [Table 2] * EtOH: Ethanol

[0102] [Table 3]

[0103] The obtained metal fine particle-containing inks 1 to 20 were each subjected to evaluation by the following methods. The results are shown in Table 4.

[0104] <Evaluation> [Evaluation of conductivity] Using a bar coater (No. 12, wet film thickness 27.48 μm), the metal fine particle-containing inks obtained in the examples and comparative examples were coated onto a polyester film (manufactured by Toray Industries, Inc., product name: Lumirror T60, thickness 75 μm, water absorption capacity 2.3 g / m 2 Subsequently, the coating was dried for 24 hours in an air atmosphere at a temperature of 25±1°C and a relative humidity of 30±5%RH. Next, the volume resistivity (Ω·cm) of an area of ​​25 mm × 25 mm was measured using a resistivity meter (main body: Loresta-GP, four-point probe: PSP probe, both manufactured by Mitsubishi Chemical Analytech Co., Ltd.) Measurements were also made in the same way at other locations on the test piece, and the arithmetic average of the volume resistivity (Ω·cm) at a total of three locations is shown in Table 4.

[0105] [Evaluation of ejection properties] (1) Manufacturing ink for inkjet printing (Step 4) 100 g of the metal microparticle-containing ink obtained in each of the Examples and Comparative Examples and 0.2 g of an acetylene glycol surfactant ("Surfynol 104PG-50" manufactured by Nissin Chemical Industry Co., Ltd., a propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active ingredient 50%) were added to a 300 mL polyethylene beaker and stirred with a magnetic stirrer at 25°C for 30 minutes. After stirring, the resulting inkjet printing ink was filtered using a 5 μm disposable membrane filter (Minisart manufactured by Sartorius, pore size 5 μm) to obtain each inkjet printing ink. The resulting inkjet printing ink was evaluated using the following methods.

[0106] (2) Evaluation of inkjet ejection In an air atmosphere with a temperature of 25±1°C and a relative humidity of 30±5%RH, the ink containing metal microparticles was filled into an inkjet printing evaluation device (manufactured by K-SOLUTION Co., Ltd.) equipped with an inkjet head (manufactured by Seiko Epson Corporation, product name: S800-A1, piezo type, 800 nozzles). The printing conditions were a head frequency of 10 kHz, a head temperature of 25° C., and a printing resolution of 600 dpi, and the ejection evaluation was performed using a waveform that could eject 7 pL, which is the standard droplet volume of the inkjet head. The discharge properties were evaluated using a liquid observation device (manufactured by Meteor Inkjet) attached to the inkjet printing evaluation device. The discharge state was observed 0, 5, 10, 15, 20, 25, and 30 minutes after the start of discharge, and the time at which the discharge became distorted or the nozzle clogged was recorded as the continuous discharge time. The results are shown in Table 4. The longer the continuous discharge time, the better the discharge properties. In addition, a state in which no discharge occurred or there was nozzle chipping during the initial discharge was recorded as initial discharge x.

[0107] [Table 4]

[0108] As can be seen from Table 4, the metal particle-containing inks of Examples 1 to 16 had better volume resistivity and ejection properties in inkjet printing than the metal particle-containing inks of Comparative Examples 1 to 4. Furthermore, the metal particle-containing inks of Examples 1 to 16 used a low-boiling point solvent, so they had good quick-drying properties and did not require solvent replacement.

Claims

1. Step 1: Mixing a metal oxide A, a polymer B, formic acid, and a solvent C to obtain a mixed solution 1; a step 2 of heating the mixed solution 1 to obtain a metal fine particle dispersion; and step 3 of mixing the metal fine particle dispersion liquid with formic acid to obtain a metal fine particle-containing ink, the polymer B contains a structural unit derived from a monomer (b-1) having a carboxy group and a structural unit derived from a monomer (b-2) having a polyoxyalkylene group, the solvent C contains at least one selected from the group consisting of water, aliphatic monoalcohols having from 1 to 4 carbon atoms, and ketones having from 3 to 4 carbon atoms, the content of the metal constituting the metal oxide A in the mixed solution 1 is 28% by mass or more and 57% by mass or less, a mass ratio of the content of the polymer B to the total content of the polymer B and the content of the metal constituting the metal oxide A in the mixed solution 1 [polymer B / (polymer B+metal)] of 0.05 or more and 0.17 or less.

2. The method for producing an ink containing fine metal particles according to claim 1 , wherein the metal oxide A includes silver oxide.

3. The method for producing a metal fine particle-containing ink according to claim 1 or 2, wherein the content of the formic acid in the mixed liquid 1 is 5.0% by mass or more and 15% by mass or less.

4. The method for producing a metal fine particle-containing ink according to any one of claims 1 to 3, wherein the content of the formic acid in the metal fine particle-containing ink is 0.8% by mass or more and 15% by mass or less.

5. 5. The method for producing a metal fine particle-containing ink according to claim 1, wherein the content of said solvent C in said mixed liquid 1 is 12% by mass or more and 50% by mass or less.

6. 6. The method for producing a metal microparticle-containing ink according to claim 1, wherein the molar ratio [formic acid / metal] of the content of the formic acid to the content of the metal constituting the metal oxide A in the mixed solution 1 is 0.05 or more and 1.00 or less.

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