Metallic particle-containing ink

Abstract

The present invention relates to a metallic-fine-particle-containing ink containing metallic fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, wherein: the polymer B is a vinyl polymer containing structural units derived from a monomer (b-1) having a carboxy group and structural units derived from a monomer (b-2) having a polyoxyalkylene group; the carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; the amine D is a C2-C6 amine; the solvent E is at least one selected from C1-C4 primary alcohols and C3-C4 ketones; the molar ratio [amine D / carboxylic acid C] of the amine D to the carboxylic acid C is 0.2-40 (inclusive); and the amine D content is 0.5-40% (inclusive) by mass. The present invention also relates to a method for producing a printed work using said ink.

Description

[Technical Field]

[0001] The present invention relates to an ink containing fine metal particles. [Background technology]

[0002] Metallic fine particles can be sintered to form conductive metal films, and are therefore used to form circuits and electrodes in various electronic components, or to bond components together. For example, Japanese Patent Laid-Open No. 2009-74171 (Patent Document 1) describes a dispersion liquid containing metal colloid particles composed of metal nanoparticles and a protective colloid that coats the metal nanoparticles, the protective colloid being composed of an organic compound having a carboxyl group and a polymer dispersant, and a solvent, with the aim of providing metal colloid particles that have few coarse particles, contain metal nanoparticles at a high concentration, and have excellent long-term storage stability. Summary of the Invention

[0003] The present invention provides a metal fine particle-containing ink containing metal fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, Polymer B is 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 carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 or more and 40 or less, The present invention relates to a metal fine particle-containing ink, in which the content of amine D is 0.5% by mass or more and 40% by mass or less. DETAILED DESCRIPTION OF THE INVENTION

[0004] Inks containing metal particles are being printed on flexible substrates such as paper and resin films for conductive applications in printed electronics. To prevent damage to the substrate due to heating, printing on such flexible substrates requires the formation of conductive metal films at temperatures ranging from room temperature to approximately 100°C. Furthermore, solvents with relatively low boiling points, such as low-carbon alcohols, are sometimes used to achieve conductivity and fast drying on non-absorbent substrates such as PET film. However, in this case, due to the ink drying characteristics within the inkjet head, improved inkjet printing reliability is required, with minimal nozzle chipping even when the inkjet nozzle surface is left unprotected for a specified period of time. However, it has been found that the technique of Patent Document 1 does not sufficiently achieve both the conductivity of the metal film and the ejection reliability of inkjet printing. The present invention relates to an ink containing fine metal particles that maintains good electrical conductivity in the metal film formed and has excellent ejection reliability in inkjet printing, and a method for producing a printed item using the ink.

[0005] The present inventors have discovered that a metal particle-containing ink containing metal particles dispersed in a polymer, a carboxylic acid, an amine, and a solvent, wherein the polymer is a vinyl polymer containing a constituent unit derived from a monomer having a carboxy group and a constituent unit derived from a monomer having a polyoxyalkylene group, the carboxylic acid, the amine, and the solvent are specific compounds, and by setting the molar ratio of the amine to the carboxylic acid and the content of the amine within specific ranges, the dispersion stability of the metal particles is improved, and a metal particle-containing ink can be provided which has excellent ejection reliability in inkjet printing while maintaining good conductivity of the formed metal film. That is, the present invention relates to the following [1] and [2]. [1] A metal particle-containing ink containing metal particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, Polymer B is 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 carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 or more and 40 or less, An ink containing fine metal particles, the content of amine D being 0.5% by mass or more and 40% by mass or less. [2] A method for producing a printed matter, comprising printing the metal fine particle-containing ink according to [1] above onto a resin substrate by inkjet printing to obtain a printed matter having a metal film formed on the substrate.

[0006] According to the present invention, it is possible to provide an ink containing fine metal particles that maintains good electrical conductivity in the formed metal film and has excellent ejection reliability in inkjet printing, and a method for producing a printed item using the ink.

[0007] [Ink containing metal particles] The metal microparticle-containing ink (hereinafter also simply referred to as "ink") of the present invention is a metal microparticle-containing ink containing metal microparticles A dispersed in polymer B, carboxylic acid C, amine D, and solvent E, in which polymer B is a vinyl polymer containing 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, carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid, amine D is an amine having 2 to 6 carbon atoms, solvent E is at least one selected from primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 to 40, and the content of amine D is 0.5 to 40 mass%.

[0008] According to the present invention, the effect of maintaining good electrical conductivity of the formed metal film while achieving excellent ejection reliability in inkjet printing is achieved. The reason for this is not clear, but is thought to be as follows. The ink of the present invention contains a solvent selected from a primary alcohol having 1 to 4 carbon atoms and a ketone having 3 to 4 carbon atoms. This solvent tends to volatilize, resulting in the metal particles being easily concentrated. However, the vinyl polymer contained in the ink of the present invention contains structural units derived from specific monomers, and the carboxylic acid contains a formyl group, a hydroxyl group, or a carbonyl group in addition to a carboxyl group in the molecule. This allows the vinyl polymer and the carboxylic acid to adsorb to the surface of the metal particles, preventing the metal particles from aggregating even when the metal particles are concentrated to a high concentration. This is believed to maintain good dispersion stability of the metal particles. Therefore, even when the inkjet nozzle surface is left unprotected for a predetermined period of time, it is believed that the occurrence of aggregates of metal particles in the nozzle can be reduced, improving ejection reliability. Furthermore, although the ink of the present invention contains a solvent that is easily volatilized, it also contains a specific amount of an amine having a specific number of carbon atoms, with the molar ratio of the amine to the carboxylic acid being within a specific range. This is believed to result in superior dispersion stability of the metal particles, and to inhibit corrosion of the inkjet head due to acidification of the ink, thereby further improving ejection reliability. Furthermore, after printing using the ink of the present invention, the carboxylic acid promotes the detachment of the polymer from the surface of the metal fine particles, and the reducing action of the carboxylic acid further suppresses oxidation of the surface of the metal fine particles, thereby promoting sintering of the metal fine particles, making it possible to form a dense metal film and maintain good conductivity of the metal film.

[0009] <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 types. In particular, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the formed metal film, 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 copper, nickel, or a noble metal such as gold, silver, platinum, or palladium, even more preferably includes at least one selected from gold, silver, and copper, even more preferably includes silver, and still more preferably is silver. The type of metal can be confirmed by high-frequency inductively coupled plasma atomic emission spectrometry.

[0010] The total content of gold, silver, and copper 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, still 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 microparticles and improving the ink ejection reliability and the conductivity of the metal film. 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, still 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 microparticles and improving the ink ejection reliability and the conductivity of the metal film. Here, "substantially 100% by mass" means that the material may contain unintentionally contained components, such as unavoidable impurities.

[0011] The content of metal fine particles A in the ink of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, from the viewpoint of improving the conductivity of the metal film to be formed, and is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 40% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ejection reliability of the ink.

[0012] <Polymer B> The metal fine particles A according to the present invention are dispersed in a polymer B from the viewpoint of improving the dispersion stability of the metal fine particles, thereby improving the ink ejection reliability and the conductivity of the formed metal film. From the same viewpoint as above, the polymer B is a vinyl polymer containing a constituent unit derived from a monomer (b-1) having a carboxy group and a constituent unit derived from a monomer (b-2) having a polyoxyalkylene group. The vinyl polymer may be any of a block copolymer, a random copolymer, and an alternating copolymer.

[0013] [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. From the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, the monomer (b-1) is preferably at least one selected from (meth)acrylic acid and maleic acid, and more preferably (meth)acrylic acid. 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.

[0014] [Monomer (b-2) having a polyoxyalkylene group] Examples of the monomer (b-2) include polyalkylene glycol (meth)acrylate, alkoxy polyalkylene glycol (meth)acrylate, phenoxy polyalkylene glycol (meth)acrylate, etc. 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.

[0015] From the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, the monomer (b-2) is preferably at least one selected from polyalkylene glycol (meth)acrylate and alkoxy polyalkylene glycol (meth)acrylate, more preferably alkoxy polyalkylene glycol (meth)acrylate. From the same viewpoint 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.

[0016] 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, and butylene oxide. Among these, the polyoxyalkylene group more preferably contains a unit derived from ethylene oxide, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ejection reliability of the ink and the conductivity of the metal film. The number of units derived from alkylene oxide in the polyoxyalkylene group (hereinafter also referred to as "n") is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, still more preferably 20 or more, from the viewpoint of improving the dispersion stability of metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, and is preferably 100 or less, more preferably 70 or less, even more preferably 50 or less, and still more preferably 40 or less. The polyoxyalkylene group may be a copolymer containing ethylene oxide-derived units and propylene oxide-derived units, from the viewpoint of improving the dispersion stability of the metal fine particles, thereby improving the ink ejection reliability and the conductivity of the metal film. The molar ratio of the ethylene oxide-derived units (EO) to the propylene oxide-derived units (PO) [EO / PO] (hereinafter also referred to as "molar ratio [EO / PO]") is preferably 60 / 40 or more, more preferably 65 / 35 or more, even more preferably 70 / 30 or more, and preferably 90 / 10 or less, more preferably 85 / 15 or less, 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.

[0017] 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.

[0018] [Hydrophobic Monomer (b-3)] Polymer B is a vinyl polymer that preferably further contains a structural unit derived from a hydrophobic monomer (b-3) in addition to 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 metal microparticles and thereby improving the ink ejection reliability and the conductivity of the metal film. As used herein, 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 same viewpoint as above, the dissolution amount of the monomer (b-3) is preferably 5 g or less, more preferably 1 g or less. Examples of the monomer (b-3) include styrene-based monomers, (meth)acrylic acid esters, etc. The monomer (b-3) may be used alone or in combination of two or more.

[0019] As the styrene-based monomer, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, styrene and styrene derivatives such as styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), and divinylbenzene (vinylstyrene) are preferred, and styrene and α-methylstyrene are more preferred.

[0020] Examples of the (meth)acrylic acid ester include aromatic group-containing (meth)acrylic acid esters and (meth)acrylic acid esters having a hydrocarbon group derived from an aliphatic alcohol. As the aromatic group-containing (meth)acrylic acid ester, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. are preferred, and benzyl (meth)acrylate is more preferred. The (meth)acrylic acid ester having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, from the viewpoint of improving the dispersion stability of metal fine particles and improving the ink ejection reliability and the conductivity of the metal film. Examples of the (meth)acrylic acid ester having a hydrocarbon group derived from an aliphatic alcohol include (meth)acrylates having a linear alkyl group, (meth)acrylates having a branched alkyl group, and (meth)acrylates having an alicyclic alkyl group. Examples of (meth)acrylates having a linear alkyl group include 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. Examples of (meth)acrylates having a branched alkyl group include 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. Examples of the (meth)acrylate having an alicyclic alkyl group include cyclohexyl (meth)acrylate. Among these, the (meth)acrylic acid ester is preferably a (meth)acrylic acid ester having a hydrocarbon group derived from an aliphatic alcohol, more preferably a (meth)acrylic acid ester having an alkyl group having 6 to 10 carbon atoms.

[0021] From the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, the monomer (b-3) is preferably at least one selected from a styrene-based monomer and a (meth)acrylic acid ester, more preferably at least one selected from styrene, a styrene derivative, and a (meth)acrylic acid ester, even more preferably at least one selected from styrene and a styrene derivative, still 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.

[0022] (Content of each monomer in the raw material monomers of polymer B or content of each structural unit in polymer B) When the vinyl polymer used as polymer B contains structural units derived from monomers (b-1) and (b-2) but does not contain structural units derived from monomer (b-3), the contents of monomers (b-1) and (b-2) in the raw material monomers during the production of polymer B (content as unneutralized amounts; the same applies hereinafter) or the contents of structural units derived from monomers (b-1) and (b-2) in polymer B are as follows, from the viewpoint of improving the dispersion stability of metal microparticles and improving the ink ejection reliability and the conductivity of the metal film. 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, still more preferably 20 mol% or more, even more preferably 25 mol% or more, and preferably 50 mol% or less, more preferably 45 mol% or less, even more preferably 40 mol% or less, and still more preferably 35 mol% or less. The content of monomer (b-2) is preferably 50 mol% or more, more preferably 55 mol% or more, even more preferably 60 mol% or more, still more preferably 65 mol% or more, and preferably 95 mol% or less, more preferably 90 mol% or less, even more preferably 85 mol% or less, still more preferably 80 mol% or less, still more preferably 75 mol% or less. The molar ratio of the monomer (b-1) to the monomer (b-2) [monomer (b-1) / monomer (b-2)] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and is preferably 2 or less, more preferably 1.5 or less, even more preferably 1 or less, still more preferably 0.7 or less, and even more preferably 0.5 or less.

[0023] When the vinyl polymer as polymer B contains structural units derived from monomers (b-1) to (b-3), the content of monomers (b-1) to (b-3) in the raw material monomers during the production of polymer B (content as unneutralized amount; the same applies hereinafter) or the content of structural units derived from monomers (b-1) to (b-3) in polymer B is as follows, from the viewpoint of improving the dispersion stability of metal microparticles and improving the ejection reliability of the ink and the conductivity of the metal film. 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 40 mol% or less, more preferably 35 mol% or less, even more preferably 30 mol% or less. The content of monomer (b-2) is preferably 3 mol% or more, more preferably 5 mol% or more, even more preferably 7 mol% or more, and preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 15 mol% or less. The content of monomer (b-3) is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 65 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, 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 3 or less, more preferably 2.5 or less, even more preferably 2 or less. The total content of the structural units derived from monomer (b-1) and the structural units derived from monomer (b-2) in polymer B is preferably 8 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, and still more preferably 20 mol% or more, and is preferably 70 mol% or less, more preferably 50 mol% or less, and even more preferably 40 mol% or less.

[0024] 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.

[0025] From the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, the polymer B preferably 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), and more preferably comprises a structural unit derived from at least one selected from (meth)acrylic acid and maleic acid as the monomer (b-1), a structural unit derived from an alkoxypolyalkylene glycol (meth)acrylate as the monomer (b-2), and a structural unit derived from a sucrose as the monomer (b-3). The present invention relates to a vinyl polymer comprising, 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(polyethylene glycol / polypropylene glycol)(meth)acrylate (wherein n is 2 or more and 100 or less, and the molar ratio [EO / PO] is 60 / 40 or more and 90 / 10 or less), and as monomer (b-3), a structural unit derived from at least one selected from styrene and a styrene derivative. Furthermore, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, polymer B is preferably a vinyl polymer containing 5 mol% to 40 mol% of structural units derived from monomer (b-1), 3 mol% to 30 mol% of structural units derived from monomer (b-2), and 50 mol% to 80 mol% of structural units derived from monomer (b-3), and more preferably a vinyl polymer containing 10 mol% to 30 mol% of structural units derived from monomer (b-1), 5 mol% to 15 mol% of structural units derived from monomer (b-2), and 60 mol% to 80 mol% of structural units derived from monomer (b-3).

[0026] 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, still 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 particles and improving the ink ejection reliability and the conductivity of the metal film. 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.

[0027] 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 styrene and a styrene derivative, 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 metal fine particles and improving the ink ejection reliability and the conductivity of the metal film. 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.

[0028] 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 alkoxy(polyethylene glycol / polypropylene glycol)(meth)acrylate (where n is 2 or more and 100 or less, and the molar ratio [EO / PO] is 60 / 40 or more and 90 / 10 or less), and as monomer (b-3) a structural unit derived from at least one selected from styrene and a styrene derivative, is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving the dispersion stability of metal fine particles and improving the ink ejection reliability and the conductivity of the metal film. 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.

[0029] From the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, 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, still more preferably 4,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, still more preferably 10,000 or less, and still more preferably 7,000 or less. The number average molecular weight Mn is measured by the method described in the examples.

[0030] From the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, the acid value of polymer B is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 15 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 100 mgKOH / g or less, even more preferably 70 mgKOH / g or less, and even more preferably 50 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.

[0031] The content of polymer B in the ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, and is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 2% by mass or less, and even more preferably 1% by mass or less, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film.

[0032] The mass ratio of the content of polymer B to the total content of metal fine particles A and polymer B in the ink of the present invention [polymer B / (metal fine particles A+polymer B)] is preferably 0.01 or more, more preferably 0.03 or more, and even more preferably 0.04 or more, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, and is preferably 0.3 or less, more preferably 0.2 or less, even more preferably 0.1 or less, and even more preferably 0.07 or less, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film. The mass ratio [polymer B / (metal fine particles A+polymer B)] is calculated from the masses of metal fine particles A and polymer B measured by the method described in the Examples using a thermogravimetric / differential thermal analyzer (TG / DTA).

[0033] <Carboxylic acid C> The ink of the present invention contains carboxylic acid C from the viewpoint of improving the dispersion stability of the metal fine particles, thereby improving the ink ejection reliability and the conductivity of the metal film formed. From the same viewpoint as above, carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid, preferably includes at least one selected from formic acid, lactic acid, and glyoxylic acid, and more preferably includes at least one selected from formic acid and lactic acid. The carboxylic acid C can be used alone or in combination of two or more.

[0034] The total content of formic acid, lactic acid, and glyoxylic acid in carboxylic acid C is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still 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 particles and improving the ink ejection reliability and the conductivity of the metal film. Here, "substantially 100% by mass" means that unintentionally contained components may be included. For example, when the total content of formic acid, lactic acid, and glyoxylic acid in carboxylic acid C is substantially 100% by mass, unintentionally contained components include carboxylic acid C components other than the formic acid, lactic acid, and glyoxylic acid contained in the formic acid, lactic acid, and glyoxylic acid used as raw materials. From the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, the total content of formic acid and lactic acid in carboxylic acid 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, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that unintentionally contained components may be included. For example, when the total content of formic acid and lactic acid in carboxylic acid C is substantially 100% by mass, unintentionally contained components include carboxylic acid C components other than the formic acid and lactic acid contained in the formic acid and lactic acid used as raw materials.

[0035] The content of carboxylic acid C in the ink of the present invention is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, and is preferably 19% by mass or less, more preferably 12% by mass or less, even more preferably 8% by mass or less, still more preferably 5% by mass or less, and even more preferably 3.5% by mass or less, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film.

[0036] The mass ratio of the content of carboxylic acid C to the content of metal fine particles A in the ink of the present invention [carboxylic acid C / metal fine particles A] is, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, preferably 0.005 or more, more preferably 0.01 or more, even more preferably 0.03 or more, still more preferably 0.07 or more, still more preferably 0.1 or more, and still more preferably 0.15 or more, and from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film, is preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less.

[0037] <Amine D> The ink of the present invention contains amine D from the viewpoints of improving the dispersion stability of metal fine particles, thereby improving the ink jetting reliability and the conductivity of the formed metal film, and of suppressing corrosion of the inkjet head due to the acidification of the ink, thereby improving the ink jetting reliability. For the same reasons as above, amine D is an amine having from 2 to 6 carbon atoms. The number of carbon atoms in amine D is 2 or more from the viewpoint of ink ejection reliability and safety, and is 6 or less, preferably 4 or less, from the viewpoint of ink ejection reliability and solubility. Amine D can be used alone or in combination of two or more. From the viewpoint of ink ejection reliability, the number of amino groups in amine D is preferably 1 or more, and from the viewpoint of ink ejection reliability, preferably 3 or less, more preferably 2 or less, and even more preferably 1. That is, amine D is more preferably a monoamine.

[0038] Amine D may have a functional group other than an amino group in the same molecule, such as a functional group containing a hetero atom, such as a hydroxy group or an alkoxy group. Examples of the amine D include alkylamines, alkanolamines, aminoalkanediols, alkoxyamines, and heterocyclic amines. Examples of alkylamines include ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, isopropylamine, diisopropylamine, n-butylamine, tert-butylamine, sec-butylamine, n-pentylamine, n-hexylamine, N,N-dimethylethylamine, N,N-diethylmethylamine, and N,N-dimethylbutylamine. Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, n-propanolamine, isopropanolamine, 2-amino-2-methyl-1-propanol, N-methylethanolamine, N-ethylethanolamine, Nn-butylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dimethylpropanolamine, N,N-dimethylisopropanolamine, 2-(dimethylamino)-2-methyl-1-propanol, N-(2-aminoethyl)ethanolamine, and 2-(2-aminoethoxy)ethanol. Examples of aminoalkanediols include 2-amino-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, 3-(methylamino)-1,2-propanediol, and 3-(dimethylamino)-1,2-propanediol. Examples of the alkoxyamine include 3-methoxypropylamine and 3-ethoxypropylamine. Examples of heterocyclic amines include pyrrolidine, piperidine, piperazine, 1-(2-hydroxyethyl)piperazine, and morpholine. Furthermore, examples of amines other than the above alkylamines, alkanolamines, aminoalkanediols, alkoxyamines and heterocyclic amines include allylamine, aniline, ethylenediamine and the like.

[0039] The boiling point of amine D at 1 atmosphere is preferably 40°C or higher, more preferably 100°C or higher, even more preferably 120°C or higher, and even more preferably 150°C or higher, from the viewpoints of suppressing corrosion of the inkjet head due to acidification of the ink and improving the ejection reliability of the ink, and is preferably 250°C or lower, more preferably 220°C or lower, even more preferably 200°C or lower, and even more preferably 180°C or lower, from the viewpoints of promoting evaporation and removal of the amine in the ink coating when forming a metal film, thereby maintaining good conductivity of the metal film and improving the ejection reliability of the ink. When two or more types of amine D are used, the boiling points of the amines D are calculated as a weighted average value.

[0040] The boiling point of the amine D is preferably higher than the boiling point of the carboxylic acid C, from the viewpoint of suppressing corrosion of the inkjet head due to acidification of the ink and improving the ejection reliability of the ink. From the viewpoints of suppressing corrosion of the inkjet head due to acidification of the ink and improving the ejection reliability of the ink, the difference in boiling point between the amine D and the carboxylic acid C is preferably 5°C or more, more preferably 10°C or more, even more preferably 15°C or more, still more preferably 25°C or more, still more preferably 30°C or more, still more preferably 35°C or more, and is preferably 140°C or less, more preferably 120°C or less, still more preferably 100°C or less, still more preferably 80°C or less, and still more preferably 75°C or less.

[0041] Among these, from the viewpoint of improving the ejection reliability of the ink, amine D preferably has at least one group selected from a hydroxy group and an alkoxy group, more preferably a hydroxy group, in the same molecule. That is, from the viewpoint of improving the ejection reliability of the ink, amine D preferably contains an amine having 2 to 6 carbon atoms and having at least one group selected from a hydroxy group and an alkoxy group, more preferably a monoamine having 2 to 6 carbon atoms and having at least one group selected from a hydroxy group and an alkoxy group, even more preferably a monoamine having 2 to 6 carbon atoms and having a hydroxy group, still more preferably a monoamine having 2 to 4 carbon atoms and having a hydroxy group, and still more preferably an alkanolamine having 2 to 4 carbon atoms.

[0042] From the viewpoint of improving the ejection reliability of the ink, the content of the monoamine having 2 to 6 carbon atoms in the amine D is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that the amine D may contain unintentionally contained components. Examples of unintentionally contained components include amine D components other than the monoamine contained in the monoamine raw material. From the viewpoint of improving the ejection reliability of the ink, the content of the monoamine having 2 to 4 carbon atoms in the amine D is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that the amine D may contain unintentionally contained components. Examples of unintentionally contained components include amine D components other than the monoamine contained in the monoamine raw material. From the viewpoint of improving the ink ejection reliability, the content of the amine having 2 to 6 carbon atoms and at least one selected from a hydroxy group and an alkoxy group in amine D 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 unintentionally contained components may be included. Examples of unintentionally contained components include amine D components other than the monoamine contained in the monoamine raw material. From the viewpoint of improving the ink ejection reliability, the content of the monoamine having 2 to 6 carbon atoms and at least one selected from a hydroxy group and an alkoxy group in amine D is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% 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 amine D components other than the above monoamine contained in the above monoamine raw material. From the viewpoint of improving the ejection reliability of the ink, the content of the monoamine having a hydroxy group and having 2 to 6 carbon atoms in amine D is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% by mass or more, and even more preferably substantially 100% by mass. Here, "substantially 100% by mass" means that the amine D may contain unintentionally contained components. Examples of unintentionally contained components include amine D components other than the monoamine contained in the monoamine raw material. From the viewpoint of improving the ejection reliability of the ink, the content of the monoamine having a hydroxy group and having 2 to 4 carbon atoms in the amine D 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 amine D may contain unintentionally contained components. Examples of unintentionally contained components include amine D components other than the monoamine contained in the monoamine raw material. From the viewpoint of improving ink ejection reliability, the content of alkanolamines having 2 to 4 carbon atoms in amine D is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% 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 amine D components other than the above alkanolamines contained in the above alkanolamines that are raw materials.

[0043] The content of amine D in the ink of the present invention is 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and even more preferably 3.5% by mass or more, from the viewpoint of improving the dispersion stability of the metal microparticles, thereby improving the ink ejection reliability and the conductivity of the metal film formed, and from the viewpoint of suppressing corrosion of the inkjet head due to acidification of the ink and improving the ink ejection reliability, and is 40% by mass or less, preferably 35% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 6% by mass or less, from the viewpoint of improving the ink ejection reliability while maintaining good conductivity of the metal film formed.

[0044] The molar ratio of amine D to carboxylic acid C in the ink of the present invention [amine D / carboxylic acid C] is 0.2 or more, preferably 0.5 or more, more preferably 0.8 or more, from the viewpoint of improving the dispersion stability of the metal microparticles, thereby improving the ink ejection reliability and the conductivity of the metal film formed, and from the viewpoint of suppressing corrosion of the inkjet head due to acidification of the ink and improving the ink ejection reliability; and from the viewpoint of improving the ink ejection reliability while maintaining good conductivity of the metal film formed, it is 40 or less, preferably 26 or less, more preferably 6 or less, even more preferably 4 or less, and even more preferably 3.5 or less.

[0045] <Solvent E> The ink of the present invention contains a solvent E from the viewpoint of improving the dispersion stability of the metal fine particles, thereby improving the ink ejection reliability and the conductivity of the metal film formed. From the same viewpoint as above, solvent E is at least one selected from primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, preferably includes a primary alcohol having 1 to 4 carbon atoms, more preferably includes at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol, even more preferably includes at least one selected from ethanol, n-propanol, and isopropanol, and still more preferably includes ethanol. The solvent E can be used alone or in combination of two or more.

[0046] The content of the primary alcohol having 1 to 4 carbon atoms in solvent E is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still 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 particles and improving the ink ejection reliability and the conductivity of the metal film. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include solvent E components other than the primary alcohol contained in the primary alcohol used as a raw material. The total content of ethanol, n-propanol, and isopropanol in Solvent E is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still 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 particles and improving the ink ejection reliability and the conductivity of the metal film. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include Solvent E components other than the ethanol, n-propanol, and isopropanol contained in the raw materials ethanol, n-propanol, and isopropanol. The content of ethanol in solvent E is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still 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 particles and improving the ink ejection reliability and the conductivity of the metal film. Here, "substantially 100% by mass" means that unintentionally contained components may be included. Examples of unintentionally contained components include solvent E components other than ethanol that are contained in the ethanol raw material.

[0047] The content of solvent E in the ink of the present invention is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 45% by mass or more, still more preferably 60% by mass or more, still more preferably 70% by mass or more, and still more preferably 75% by mass or more, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film, and is preferably 90% by mass or less, more preferably 88% by mass or less, and still more preferably 86% by mass or less, from the viewpoint of improving the dispersion stability of the metal microparticles and improving the ink ejection reliability and the conductivity of the metal film.

[0048] The ink of the present invention may contain various additives other than the above-mentioned components A to E, such as fixing aids such as dispersions of polymer particles, humectants, wetting agents, penetrating agents, surfactants, viscosity modifiers, antifoaming agents, preservatives, antifungal agents, and antirust agents, as long as the effects of the present invention are not impaired.

[0049] The ink of the present invention may contain a solvent other than solvent E, provided that the effects of the present invention are not impaired. In this case, the boiling point at 1 atmosphere of the mixed solvent contained in the ink of the present invention (i.e., the mixed solvent of solvent E and a solvent other than solvent E) is preferably 110°C or lower, more preferably 100°C or lower, even more preferably 90°C or lower, and even more preferably 80°C or lower. The boiling point of the mixed solvent is calculated as a weighted average value. The content of solvents other than solvent E in the ink of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 1% by mass or less, and even more preferably substantially 0% by mass, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ink ejection reliability and the conductivity of the metal film. Here, "substantially 0% by mass" means that the ink may contain unintentionally contained components. Examples of unintentionally contained components include solvent components other than solvent E contained in the above components A to E.

[0050] (Production of ink containing metal particles) The ink of the present invention can be obtained by, for example, a method in which polymer B, carboxylic acid C, amine D, solvent E, and, if necessary, the additives are added and mixed with metal fine particles A prepared in advance by a known method; a method in which a metal source compound, a reducing agent, and polymer B as a dispersant are mixed, the metal source compound is reduced to obtain a dispersion of metal fine particles dispersed in polymer B, and then carboxylic acid C, amine D, solvent E, and, if necessary, the additives are added and mixed. Among these, from the viewpoint of improving the dispersion stability of the metal fine particles and improving the ejection reliability of the ink and the conductivity of the metal film, a method in which carboxylic acid C, amine D, solvent E, and, if necessary, the additives are added and mixed with dry powder of metal fine particles containing polymer B is preferred. The dry powder of metal microparticles can be obtained by mixing a metal source compound, a reducing agent, and polymer B, reducing the metal source compound with the reducing agent to obtain a dispersion of metal microparticles dispersed in polymer B, and then drying the dispersion of metal microparticles by freeze-drying or the like.

[0051] There are no particular limitations on the metal raw material compound, as long as it is a compound containing the metal that constitutes the metal fine particles A described above. Examples of the metal source compound include metal salts of inorganic or organic acids, metal oxides, metal hydroxides, metal sulfides, and metal halides, each containing one of the metals exemplified for the metal fine particles A. Examples of the metal salt include metal salts of inorganic acids such as nitrates, nitrites, sulfates, carbonates, ammonium salts, and perchlorates; and metal salts of organic acids such as acetates. The metal source compounds can be used alone or in combination of two or more.

[0052] The reducing agent is not particularly limited, and either an inorganic reducing agent or an organic reducing agent can be used, but an organic reducing agent is preferred. The reducing agent may be used alone or in combination of two or more. Examples of organic reducing agents include alcohols, aldehydes, acids and their salts, and amines. Examples of alcohols include ethylene glycol and propylene glycol. Examples of aldehydes include formaldehyde, acetaldehyde, and propionaldehyde. Examples of acids and salts thereof include ascorbic acid, citric acid, and salts thereof. Examples of the amines include alkanolamines, alkylamines, (poly)alkylenepolyamines, heterocyclic amines, aromatic amines, and aralkylamines.

[0053] Examples of inorganic reducing agents include borohydrides such as sodium borohydride and ammonium borohydride; aluminum hydrides such as lithium aluminum hydride and potassium aluminum hydride; hydrazines such as hydrazine and hydrazine carbonate; and hydrogen gas.

[0054] The temperature of the reduction reaction is preferably 5° C. or higher, more preferably 10° C. or higher, even more preferably 20° C. or higher, and even more preferably 30° C. or higher, from the viewpoint of producing metal fine particles stably, and is preferably 100° C. or lower, more preferably 80° C. or lower, and even more preferably 50° C. or lower, from the viewpoint of stably producing metal fine particles. The reduction reaction may be carried out in an air atmosphere or an inert gas atmosphere such as nitrogen gas.

[0055] In producing the ink of the present invention, the dispersion of metal particles may be purified before freeze-drying in order to remove impurities such as unreacted reducing agent and excess polymer B that does not contribute to the dispersion of metal particles A. The method for purifying the dispersion of metal fine particles is not particularly limited, and examples thereof include membrane treatments such as dialysis and ultrafiltration; and centrifugation. Among these, membrane treatments are preferred, and dialysis is more preferred, from the viewpoint of efficiently removing impurities. Regenerated cellulose is preferred as the material for the dialysis membrane used for dialysis. From the viewpoint of efficiently removing impurities, the molecular weight cutoff of the dialysis membrane is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 70,000 or less. The ink of the present invention can be obtained by further adding the various additives described above as necessary and then filtering the ink using a filter or the like.

[0056] (Physical properties of ink containing metal particles) The average particle size of the metal fine particles A contained in the ink of the present invention is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, from the viewpoint of improving the dispersion stability of the metal fine particles and thereby improving the ink ejection reliability and the conductivity of the metal film, and is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less, from the viewpoint of improving the dispersion stability of the metal fine particles and thereby improving the ink ejection reliability and the conductivity of the metal film. The average particle size of the metal fine particles A can be measured by the method described in the Examples. The viscosity of the ink of the present invention at 30°C is preferably 0.5 mPa·s or more, more preferably 1.0 mPa·s or more, even more preferably 1.3 mPa·s or more, and still more preferably 1.6 mPa·s or more, from the viewpoint of improving the ink ejection reliability, and is preferably 15 mPa·s or less, more preferably 10 mPa·s or less, and even more preferably 8 mPa·s or less, from the viewpoint of improving the ink ejection reliability. The viscosity of the ink is measured using an E-type viscometer by the method described in the Examples. The pH of the ink of the present invention at 20°C is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher, from the viewpoint of improving ink ejection reliability. Furthermore, from the viewpoint of component resistance and skin irritation, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. The pH of the ink can be measured by a conventional method.

[0057] The ink of the present invention can form a metal film having excellent conductivity, and therefore can be suitably used for various printing methods, such as inkjet printing, flexographic printing, gravure printing, screen printing, offset printing, dispenser printing, etc. Among these, the ink of the present invention is preferably used for inkjet printing because it has excellent discharge reliability as described above.

[0058] The ink of the present invention can form a good metal film with excellent conductivity, and therefore can be used in a wide range of applications. Examples of such applications include conductive materials such as wiring materials, electrode materials, and multilayer ceramic capacitors (hereinafter also referred to as "MLCC") 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 (RFID (radio frequency identifier), hereinafter also referred to as "RFID"); catalysts; optical materials; medical materials; and decorative materials that impart specular gloss. Among these, the ink of the present invention is preferably used in the production of printed matter on which a conductive circuit is formed.

[0059] [Manufacturing method for printed matter] The ink of the present invention is preferably used in a method for producing a printed matter by printing on a substrate to obtain a printed matter having a metal film formed on the substrate. This allows for the production of a printed matter having a metal film with excellent conductivity, etc. In printing using the metal fine particle-containing ink, a patterned printing image is formed on the substrate to form a patterned metal film, and this patterned metal film can be used as a conductive circuit. In the production of printed matter on which conductive circuits are formed, the base material is sometimes called a "substrate."

[0060] [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. The substrate may be a rigid substrate or a flexible substrate. Among these, from the viewpoint of conductivity, the substrate is preferably at least one selected from a resin substrate and a paper substrate, and more preferably a resin substrate. As described above, the ink of the present invention contains a specific volatile solvent as solvent E, carboxylic acid C, and amine D, and therefore can form a metal film with excellent conductivity even on a resin substrate, which is a non-liquid-absorbent substrate that does not absorb solvents. Therefore, the ink of the present invention is preferably used for printing on resin substrates as well.

[0061] Preferred examples of the method for printing the metal fine particle-containing ink onto a substrate include various patterning printing methods such as inkjet printing, flexographic printing, gravure printing, screen printing, offset printing, dispenser printing, etc. By using the patterning printing method, a fine conductive circuit can be formed on the substrate. The amount of the metal fine particle-containing ink applied to the substrate can be adjusted appropriately depending on the size and type of the circuit or electrode to be formed.

[0062] [Inkjet printing] In the printing method of the present invention, from the viewpoint of ejection reliability and from the viewpoint of forming a fine conductive circuit on the substrate, it is preferable to print the metal fine particle-containing ink onto the substrate by inkjet printing. When the metal fine particle-containing ink is used for inkjet printing, the ink can be loaded into a known inkjet printing device and ejected as ink droplets onto the substrate to form a metal film with a printed image. Inkjet printing devices include thermal and piezo types, but from the viewpoint of ejection reliability, the ink is more preferably used for thermal inkjet printing. The head temperature of the inkjet head is preferably 15°C or higher, more preferably 20°C or higher, even more preferably 25°C or higher, and is preferably 45°C or lower, more preferably 40°C or lower, even more preferably 35°C or lower. From the viewpoint of printing efficiency, etc., the head voltage of the inkjet head is preferably 5 V or more, more preferably 10 V or more, even more preferably 15 V or more, and is preferably 40 V or less, more preferably 35 V or less, even more preferably 30 V or less. From the viewpoint of printing efficiency, etc., the driving frequency of the inkjet head is preferably 1 kHz or more, more preferably 5 kHz or more, even more preferably 10 kHz or more, and is preferably 50 kHz or less, more preferably 40 kHz or less, even more preferably 35 kHz or less. The ejected volume of the ink according to the present invention is preferably 5 pL or more, more preferably 10 pL or more, and is preferably 30 pL or less, more preferably 20 pL or less per droplet. The amount of the ink of the present invention applied to the substrate is preferably 0.5 g / m2 in terms of solid content. 2 More preferably, 1 g / m 2 More preferably, 2 g / m 2 and preferably 20 g / m 2 Less than 15 g / m, more preferably 2 More preferably, 10 g / m or less 2 The following is the result.

[0063] [Sintering process] In the method for producing a printed matter of the present invention, from the viewpoint of improving the conductivity of the metal film, it is preferable to carry out a sintering treatment after printing on a substrate using the ink to sinter the metal fine particles A in the ink coating on the substrate. By the sintering process, the solvent E remaining in the ink film is evaporated and removed, and further the metal particles A are sintered to form a metal film with excellent conductivity.

[0064] The temperature of the sintering treatment is preferably lower than the temperature at which the substrate is deformed. Specifically, from the viewpoint of improving the conductivity of the metal film, the temperature is preferably 25°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and even more preferably 70°C or higher under normal pressure, and is preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 100°C or lower. The relative humidity of the surrounding environment during the sintering treatment is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, and is preferably 65% ​​or less, more preferably 60% or less. In particular, the sintering treatment is preferably performed by heating at 60° C. or higher, followed by storing 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 for the heat treatment in the sintering process can be adjusted appropriately depending on the treatment temperature, but from the viewpoint of improving the conductivity of the metal film, it is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more, and from the viewpoint of productivity, it is preferably 6 hours or less, more preferably 4 hours or less, and even more preferably 2 hours 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 improving the conductivity 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.

[0065] 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.

[0066] The sheet resistance of the formed metal film is preferably 8 Ω / □ or less, more preferably 6 Ω / □μ or less, even more preferably 5 Ω / □ or less, even more preferably 4 Ω / □ or less, and even more preferably 3.5 Ω / □ or less, and from the viewpoint of ease of production of printed matter, is preferably 0.3 Ω / □ or more, more preferably 0.5 Ω / □ or more. The sheet resistance can be measured by the method described in the Examples.

[0067] The printed matter obtained by the production method of the present invention has excellent conductivity of the metal film formed on the substrate, and therefore can be used as a conductive composite material including the 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 EL displays, and touch panels, organic EL 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.

[0068] In addition to the above-described embodiments, the present invention also discloses the following embodiments. <1> A metal fine particle-containing ink containing metal fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, Polymer B is 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 carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 or more and 40 or less, An ink containing fine metal particles, the content of amine D being 0.5% by mass or more and 40% by mass or less. <2> A metal fine particle-containing ink containing metal fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, Polymer B is 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 carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 or more and 40 or less, The content of amine D is 0.5% by mass or more and 40% by mass or less, The metal constituting the metal fine particles A contains 80 mass % or more of silver, Polymer B contains 80% by mass or more of a vinyl polymer including 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), Amine D contains 80% by mass or more of monoamines having 2 to 6 carbon atoms, Solvent E contains 80% by mass or more of a primary alcohol having 1 to 4 carbon atoms. <1> 2. The metal fine particle-containing ink according to claim 1. <3> A metal fine particle-containing ink containing metal fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, Polymer B is 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 carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 or more and 40 or less, The content of amine D is 0.5% by mass or more and 40% by mass or less, The metal constituting the metal fine particles A contains 80 mass % or more of silver, Polymer B contains 80% by mass or more of a vinyl polymer 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 styrene and a styrene derivative; Amine D contains 80% by mass or more of monoamines having 2 to 6 carbon atoms and having at least one group selected from a hydroxy group and an alkoxy group, Solvent E contains 80 mass% or more of at least one selected from ethanol, n-propanol, and isopropanol. <1> or <2> 2. The metal fine particle-containing ink according to claim 1. <4> A metal fine particle-containing ink containing metal fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, Polymer B is 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 carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of primary alcohols having 1 to 4 carbon atoms and ketones having 3 to 4 carbon atoms, the molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] is 0.2 or more and 40 or less, The content of amine D is 0.5% by mass or more and 40% by mass or less, Metal A constituting the metal microparticles contains 80 mass % or more of silver, Polymer B contains 80% by mass or more of a vinyl polymer 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 styrene and a styrene derivative; the carboxylic acid C contains 80% by mass or more of at least one selected from formic acid and lactic acid; Amine D contains 80 mass% or more of alkanolamines having 2 to 4 carbon atoms, Solvent E contains 80% by mass or more of ethanol, <1> ~ <3> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <5> The content of metal fine particles A in the metal fine particle-containing ink is 5% by mass or more and 70% by mass or less, the content of polymer B in the metal fine particle-containing ink is 0.1% by mass or more and 10% by mass or less, the content of carboxylic acid C in the metal fine particle-containing ink is 0.05% by mass or more and 19% by mass or less, The content of solvent E in the metal fine particle-containing ink is 20% by mass or more and 90% by mass or less, 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 [polymer B / (polymer B+metal fine particles A)] is 0.01 or more and 0.3 or less; <1> ~ <4> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <6> The content of metal fine particles A in the metal fine particle-containing ink is 5% by mass or more and 30% by mass or less, the content of polymer B in the metal fine particle-containing ink is 0.1% by mass or more and 2% by mass or less, the content of carboxylic acid C in the metal fine particle-containing ink is 1% by mass or more and 5% by mass or less, the content of amine D in the metal fine particle-containing ink is 1% by mass or more and 10% by mass or less, The content of solvent E in the metal fine particle-containing ink is 60% by mass or more and 90% by mass or less, 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 [polymer B / (polymer B+metal fine particles A)] is 0.03 or more and 0.1 or less; <1> ~ <5> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <7> The boiling point of amine D is higher than that of carboxylic acid C. <1> ~ <6> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <8> The difference in boiling point between amine D and carboxylic acid C is 5°C or more and 140°C or less. <7> 2. The metal fine particle-containing ink according to claim 1. <9> the mass ratio of the content of carboxylic acid C to the content of metal fine particles A in the metal fine particle-containing ink [carboxylic acid C / metal fine particles A] is 0.005 or more and 0.5 or less; <1> ~ <8> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <10> The average particle size of the metal fine particles A is 15 nm or more and 100 nm or less. <1> ~ <9> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <11> The viscosity at 30°C is 1.6 mPa·s or more and 10 mPa·s or less. <1> ~ <10> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <12> For inkjet printing, <1> ~ <11> 10. The metal fine particle-containing ink according to any one of claims 1 to 9. <13> <1> ~ <12> 1. A method for producing a printed matter, comprising printing the metal fine particle-containing ink according to any one of claims 1 to 9 onto a resin substrate by inkjet printing to obtain a printed matter having a metal film formed on the substrate. [Example]

[0069] In the following Preparation 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.

[0070] (1) 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 B with 10 mL of the eluent described below in a glass vial, stirring the mixture with a magnetic stirrer at 25°C for 10 hours, and filtering it 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" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation 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)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0071] (2) Acid value of polymer B The acid value of Polymer B was measured based on the method of JIS K 0070: 1992. However, the measurement solvent was changed from the mixed solvent of ethanol and ether specified in JIS K 0070: 1992 to a mixed solvent of acetone and toluene (acetone:toluene = 4:6 (volume ratio)).

[0072] (3) Mass ratio [polymer B / (metal particle A + polymer B)] 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 / (metal particle A + polymer B)] was calculated.

[0073] (4) Average particle size of metal particles A Using a laser particle analysis system "ELS-8000" (Otsuka Electronics Co., Ltd.), particle size was measured by dynamic light scattering and calculated by cumulant analysis. 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 input as the refractive index of the dispersion solvent. The measurement sample was weighed into a screw tube (Maruem Co., Ltd. No. 5) and the solids concentration was 5 × 10 -3 Water was added to the mixture so that the concentration reached 5% by mass, and the mixture was stirred at 25°C for 1 hour using a magnetic stirrer.

[0074] (5) Viscosity of ink containing metal particles The viscosity of the ink at 30° C. was measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TV-25, using a standard cone rotor 1°34′×R24, rotation speed 100 rpm).

[0075] Preparation Example 1 (Preparation of Polymer B-1) An acrylic acid / maleic acid / alkoxy(polyethylene glycol / polypropylene glycol) acrylate (number of alkylene oxide units n: 32 moles, molar ratio [EO / PO] = 75 / 25) / styrene / α-methylstyrene copolymer [aqueous solution of the copolymer (manufactured by BYK, product name: DISPERBYK-2015) with a solids content of 40%] was dried at a temperature of 110°C and a pressure of 50 Torr for 48 hours using a vacuum dryer "VO420" (manufactured by Advantec Co., Ltd.) to obtain polymer B-1 (number average molecular weight: 4,500, acid value: 24 mgKOH / g).

[0076] Production Example 1 (Production of Metal Fine Particle Dry Powder 1) 10 g of silver oxide (FUJIFILM Wako Pure Chemical Industries, Ltd., special grade), 0.8 g of polymer B-1, and 30 g of propylene glycol (FUJIFILM Wako Pure Chemical Industries, Ltd., special grade) as a reducing agent were placed in a 100 mL eggplant-shaped flask and stirred with a magnetic stirrer for 0.5 hours at 25°C. The resulting mixture was then heated in a 40°C water bath, and after the mixture reached 40°C, stirred for 1 hour and then air-cooled to obtain a dark brown dispersion containing dispersed silver microparticles. The entire amount of the resulting dispersion was placed in a dialysis tube ("Spectra / Por 6" manufactured by REPLIGEN, dialysis membrane: regenerated cellulose, molecular weight cutoff (MWCO) = 50K), and the top and bottom of the tube were sealed with closures. This tube was immersed in 5 L of ion-exchanged water in a 5 L glass beaker, and the water temperature was maintained at 20-25°C and stirred for 1 hour. The ion-exchanged water was then replaced every hour, a process repeated three times. Sampling was then performed every hour. Dialysis was terminated when the mass ratio [polymer B / metal particle A] calculated from the masses of polymer B and metal particle A measured by the method described above (3) using a thermogravimetric / differential thermal analyzer (TG / DTA) reached 0.5 / 10 (mass ratio [polymer B / (metal particle A + polymer B)] = 0.5 / 10.5 = 0.048), and a purified dispersion was obtained. The purified dispersion 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 metal microparticle dry powder 1.

[0077] Example 1 A 500 mL polyethylene beaker was charged with 1.05 g of metal microparticle dry powder 1, 0.25 g of formic acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) as carboxylic acid C, 0.46 g of 3-methoxypropylamine (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) as amine D, and 8.24 g of ethanol (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) as solvent E. The mixture was dispersed for 3 hours using an ultrasonic disperser (Nippon Seiki Seisakusho, Model US-3001) while stirring with a magnetic stirrer. The mixture was then filtered using a 5 μm disposable membrane filter (Sartorius, Minisart) to obtain a metal microparticle-containing ink. The average particle size and viscosity of the resulting ink are shown in Table 1. The resulting ink was evaluated as follows. The results are shown in Table 1.

[0078] Examples 2 to 11 and Comparative Examples 1 to 3 Each ink containing metal fine particles was obtained in the same manner as in Example 1, except that the type of carboxylic acid C, amine D, or solvent E, or the composition of the ink, was changed according to Table 1. The average particle size and viscosity of each ink obtained are shown in Table 1. The following evaluations were carried out using each ink obtained. The results are shown in Table 1.

[0079] <Evaluation> [Evaluation of discharge reliability (open time measurement)] The ink in the black cartridge of an inkjet printer (Hewlett-Packard, model number: Deskjet 6122, thermal type) was refilled with the metal particle ink in an environment of 25±1°C temperature and 30±5% relative humidity. Once all nozzles in the head were able to eject ink without any problems, the inkjet printer was used to inkjet print a solid image, 80mm wide x 25mm long, created in Photoshop (registered trademark) with RGB set to 0, onto a commercially available PET film "Lumirror T60" (Toray, Inc., thickness 250μm) as a substrate. In inkjet printing, after performing a cleaning operation once, the nozzle surface was left as is for 5 minutes without being protected. Then, inkjet printing was started under the same printing conditions as above, and the presence or absence of nozzle chipping was confirmed. If no nozzle chipping was found, the cleaning operation was performed once more, and the nozzle surface was left as is for 5 minutes without being protected. Then, inkjet printing was started under the same printing conditions as above, and the presence or absence of nozzle chipping was confirmed. In the same manner, the leaving time was increased in 5-minute increments, up to a maximum of 30 minutes. The longest time during which no nozzle chipping was found was taken as the open time (minutes). The longer the open time, the better the ejection reliability.

[0080] [Evaluation of conductivity (measurement of sheet resistance (Ω / □)] The ink in the black cartridge of the inkjet printer was refilled with the metal particle ink in an environment of 25±1°C temperature and 30±5% relative humidity. Once all nozzles of the head were able to eject ink without any problems, the inkjet printer was used to inkjet print a solid image, 80mm wide x 25mm long, created in Photoshop (registered trademark) with RGB set to 0, onto a commercially available PET film "Lumirror T60" (manufactured by Toray Industries, Inc., thickness 250μm) as a substrate. Next, the PET film with the ink coating was heated on a hot stage at 80°C for 60 minutes, and then stored in an environment at 25°C and 55% relative humidity for 24 hours to undergo a sintering process, resulting in a printed matter with a metal film formed on the PET film. Next, the sheet resistance (Ω / □) of an area of ​​10 mm × 15 mm was measured using a resistivity meter (main body: Loresta-GP, four-point probe: PSP probe, both manufactured by Mitsubishi Chemical Analytech Co., Ltd.) Similar measurements were taken at other locations on the test piece, and the arithmetic average of the sheet resistance (Ω / □) at a total of three locations is shown in Table 1.

[0081] [Table 1]

[0082] It is clear that the metal fine particle-containing inks of Examples 1 to 11 have a long open time and are excellent in ejection reliability, whereas the inks of Comparative Examples 1 to 3 have an open time of 0 minutes and have no ejection reliability at all. Furthermore, regarding the conductivity of the formed metal film, the ink containing metal microparticles of Comparative Example 3 was not conductive, but the inks containing metal microparticles of Examples 1 to 11 all had a conductivity of 5 Ω / □ or less, indicating that they were able to maintain good conductivity. [Industrial Applicability]

[0083] According to the present invention, it is possible to obtain a metal fine particle-containing ink that has excellent discharge reliability in inkjet printing while maintaining good conductivity of the formed metal film, and therefore the metal fine particle-containing ink of the present invention is suitable for conductive applications in printed electronics.

Claims

1. A metal fine particle-containing ink containing metal fine particles A dispersed in a polymer B, a carboxylic acid C, an amine D, and a solvent E, polymer B is 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, and having an acid value of 5 mgKOH / g or more and 200 mgKOH / g or less; the carboxyl group-containing monomer (b-1) is at least one selected from the group consisting of an unsaturated monocarboxylic acid, an unsaturated dicarboxylic acid, and an anhydride of the unsaturated dicarboxylic acid; the carboxylic acid C is at least one selected from formic acid, lactic acid, pyruvic acid, and glyoxylic acid; Amine D is an amine having from 2 to 6 carbon atoms, Solvent E is at least one selected from the group consisting of a primary alcohol having from 1 to 4 carbon atoms and a ketone having from 3 to 4 carbon atoms, a molar ratio of amine D to carboxylic acid C [amine D / carboxylic acid C] of 0.2 or more and 40 or less; An ink containing fine metal particles, wherein the content of amine D is 0.5% by mass or more and 40% by mass or less.

2. The metal fine particle-containing ink according to claim 1 , wherein the content of the carboxylic acid C in the metal fine particle-containing ink is 0.05% by mass or more and 19% by mass or less.

3. The metal fine particle-containing ink according to claim 1 or 2, wherein the amine D comprises a monoamine having from 2 to 4 carbon atoms.

4. 4. The metal microparticle-containing ink according to claim 1, wherein the mass ratio of the content of polymer B to the total content of polymer B and metal microparticles A in the metal microparticle-containing ink [polymer B / (polymer B + metal microparticles A)] is 0.01 or more and 0.3 or less.

5. 5. The metal fine particle-containing ink according to claim 1, wherein the metal constituting the metal fine particles A includes silver.

6. 6. The metal fine particle-containing ink according to claim 1, wherein the content of the metal fine particles A in the metal fine particle-containing ink is 5% by mass or more and 70% by mass or less.

7. 7. The metal fine particle-containing ink according to claim 1, wherein the content of polymer B in the metal fine particle-containing ink is 0.1% by mass or more and 10% by mass or less.

8. 8. The metal fine particle-containing ink according to claim 1, wherein the solvent E comprises at least one selected from the group consisting of ethanol, n-propanol, and isopropanol.

9. 9. The metal fine particle-containing ink according to claim 1, wherein the content of the solvent E in the metal fine particle-containing ink is 20% by mass or more and 90% by mass or less.

10. 10. The metal fine particle-containing ink according to claim 1, wherein the boiling point of the amine D is higher than the boiling point of the carboxylic acid C.

11. 11. The metal fine particle-containing ink according to claim 1, wherein the amine D comprises an alkanolamine having from 2 to 4 carbon atoms.

12. 12. The metal fine particle-containing ink according to claim 1, wherein the carboxylic acid C includes at least one selected from the group consisting of formic acid, lactic acid, and glyoxylic acid.

13. The metal fine particle-containing ink according to any one of claims 1 to 12, wherein the vinyl polymer further contains a structural unit derived from a hydrophobic monomer (b-3).

14. The metal fine particle-containing ink according to any one of claims 1 to 13, wherein the mass ratio of the content of carboxylic acid C to the content of metal fine particles A in the metal fine particle-containing ink [carboxylic acid C / metal fine particle A] is 0.005 or more and 0.5 or less.

15. The metal fine particle-containing ink according to any one of claims 1 to 14, wherein the metal fine particles A have an average particle size of 15 nm or more and 100 nm or less.

16. The metal fine particle-containing ink according to any one of claims 1 to 15, wherein the ink has a viscosity at 30°C of 1.6 mPa·s or more and 10 mPa·s or less.

17. The metal fine particle-containing ink according to any one of claims 1 to 16, which is for inkjet printing.

18. A method for producing a printed matter, comprising printing the metal fine particle-containing ink according to any one of claims 1 to 17 onto a resin substrate by inkjet printing to obtain a printed matter having a metal film formed on the substrate.

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