Metallic ink, method for producing metallic ink, and method for producing sintered body

Abstract

To obtain a sintered compact which improves sinterability while suppressing the coagulation of metallic particles and suitably transmits visible light when being used as metallic ink and improves cleanability to suppress or dissolve clogging when being used as a cleaning fluid.SOLUTION: Metallic ink 10 comprises: metallic particles 12; a solvent 16; polyhydric alcohol 14 which includes two or more OH groups and is soluble in water and lower alcohol; and an additive 17 which includes a phosphate compound soluble in water.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a metallic ink, a method for producing a metallic ink, a method for producing a sintered body, a sintered body, and a cleaning liquid. [Background technology]

[0002] As an example of forming a metal layer on a member, Patent Document 1 describes forming a solder layer on a member. For example, Patent Document 2 describes forming a metal layer using silver paste. Silver paste can be sintered under relatively low temperature conditions, and the melting point of the bonding layer formed after sintering is equivalent to that of silver. Therefore, the metal layer made of the sintered body of this silver paste has excellent heat resistance and can be used stably even in high-temperature environments and large current applications. On the other hand, from the viewpoint of material costs, copper paste may be used, for example, as shown in Patent Document 3.

[0003] Furthermore, when forming a metal layer in this manner, a metal ink in which metal particles are dispersed in a liquid may be used instead of a metal paste such as a copper paste, which may be advantageous in terms of manufacturing because it can be sprayed from a nozzle, for example.

[0004] Furthermore, in inkjet devices used for forming metal layers, problems such as drying, settling, coagulation, and solidification of ink occur in piping, flow paths, and ejection ports inside the device due to long-term storage or exposure to high temperature and low humidity environments. In response to this problem, cleaning methods have been proposed that use cleaning solutions containing organic solvents and surfactants as shown in Patent Document 4, or cleaning solutions that are high-alkaline solutions or surfactant solutions as shown in Patent Document 5. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-172378 A [Patent Document 2] Patent No. 6531547 [Patent Document 3] JP 2019-67515 A [Patent Document 4] Japanese Patent Application Publication No. 4-115954 [Patent Document 5] Japanese Patent Application Publication No. 6-8471 Summary of the Invention [Problem to be solved by the invention]

[0006] Such metal inks may cause deterioration of the properties of the product, such as a decrease in the density of the sintered body, due to the aggregation of metal particles. In addition, when the cleaning solution contains a high-viscosity material, as in the above-mentioned cleaning solution and cleaning method, there is a problem that the residue after cleaning aggregates and becomes highly viscous, which is likely to cause malfunctions. In addition, when the cleaning solution is a highly alkaline solution, there is a problem that the alkali corrodes the equipment components. Therefore, there is a demand for metal inks that suppress the aggregation of metal particles. There is also a demand for improving the sinterability of metal inks. There is also a demand for the resulting sintered bodies to adequately transmit visible light. There is also a demand for cleaning fluids that improve cleaning properties and can suppress or eliminate clogging.

[0007] The present invention has been made in consideration of the above, and aims to provide, when used as a metal ink, that suppresses aggregation of metal particles while improving sinterability and can obtain a sintered body that appropriately transmits visible light, and, when used as a cleaning liquid, that improves cleaning properties and suppresses or eliminates clogging. [Means for solving the problem]

[0008] The metal ink of the present disclosure comprises metal particles, a solvent, a polyhydric alcohol that contains two or more OH groups and is soluble in water and lower alcohols, and an additive that includes a water-soluble phosphate compound.

[0009] The metal ink of the present disclosure preferably further contains an organic solvent that has a boiling point of 150° C. or higher at atmospheric pressure and is miscible with water.

[0010] The additive is preferably contained in an amount of 0.01% to 10% by mass relative to the total amount of the metal ink.

[0011] The molecular weight of the phosphate compound is preferably 90 or more and 200 or less.

[0012] The additive preferably includes at least one of phosphoric acid, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, trimethyl phosphate, triethyl phosphate, diisopropyl phosphate, monoisopropyl phosphate, 2-aminoethyl dihydrogen phosphate, diisopropyl phosphite, and dimethyl phosphite.

[0013] The polyhydric alcohol is preferably contained in an amount of 0.01% to 20% by mass relative to the total amount of the metal ink.

[0014] The polyhydric alcohol preferably has a melting point of 30° C. or higher.

[0015] The organic solvent is preferably contained in an amount of 0.01% to 30% by mass relative to the total amount of the metal ink.

[0016] The organic solvent preferably includes at least one of a glycol ether and an aprotic polar solvent.

[0017] The metal particles are preferably contained in an amount of 1% to 50% by mass with respect to the total amount of the metal ink.

[0018] The metal particles are preferably copper particles.

[0019] The solvent preferably contains water.

[0020] It is preferable that the additive further contains, as a dispersant, a phosphate ester compound having a higher molecular weight than the phosphate compound contained in the additive.

[0021] The solvent preferably contains a lower alcohol.

[0022] The solvent preferably includes a high-boiling point solvent which is a liquid that contains one or more OH groups, has a boiling point of 150° C. or higher, and is poorly soluble or insoluble in water.

[0023] It is preferable that the metal particles are copper, the solvent contains water, the polyhydric alcohol contains at least one polyhydric alcohol that contains two or more OH groups, is soluble in water and lower alcohols, and has a melting point of 30°C or higher, and the additive is a phosphate compound having a molecular weight of 90 or more and 200 or less.

[0024] The method for producing a metal ink of the present disclosure involves mixing metal particles, a solvent, a polyhydric alcohol that contains two or more OH groups and is soluble in water and lower alcohols, and an additive that contains a phosphate compound that is soluble in water, to produce a metal ink containing the metal particles, the solvent, the polyhydric alcohol, and the additive.

[0025] In the method for producing a metal ink of the present disclosure, it is preferable to mix the metal particles, water as the solvent, the polyhydric alcohol, and the additive to produce a first metal ink, which is a metal ink containing the metal particles, water, the polyhydric alcohol, and the additive.

[0026] In the method for producing a metal ink of the present disclosure, it is preferable to also mix an organic solvent that has a boiling point of 150° C. or higher at atmospheric pressure and is miscible with water, to produce the first metal ink that also contains the organic solvent.

[0027] In the method for producing a metal ink of the present disclosure, it is preferable to mix the first metal ink with a lower alcohol as the solvent to produce a second metal ink, which is a metal ink containing the metal particles, water, the lower alcohol, the polyhydric alcohol, and the additive.

[0028] The method for producing a metal ink of the present disclosure preferably comprises mixing the second metal ink with a high-boiling point solvent as the solvent, which contains one or more OH groups, has a boiling point of 150°C or higher, and is a liquid that is poorly soluble or insoluble in water, to produce a third metal ink, which is a metal ink containing the metal particles, water, the lower alcohol, the high-boiling point solvent, the polyhydric alcohol, and the additive.

[0029] In the method for producing a sintered body according to the present disclosure, the sintered body is preferably formed by heating the metal ink.

[0030] The sintered body of the present disclosure is preferably made using the metal ink.

[0031] The cleaning solution of the present disclosure contains metal particles, a solvent, a polyhydric alcohol that contains two or more OH groups and is soluble in water and lower alcohols, and an additive that contains a water-soluble phosphoric acid compound. Effect of the Invention

[0032] According to the present invention, when used as a metal ink, it is possible to suppress aggregation of metal particles, improve sinterability, and obtain a sintered body that appropriately transmits visible light, and when used as a cleaning liquid, it is possible to improve cleaning properties and suppress or eliminate clogging. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a schematic diagram of a metal ink according to this embodiment. [Diagram 2] FIG. 2 is a flowchart illustrating the method for producing a metal ink according to this embodiment. [Diagram 3] FIG. 3 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 4] FIG. 4 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Diagram 5]FIG. 5 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 6] FIG. 6 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 7] FIG. 7 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 8] FIG. 8 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 9] FIG. 9 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 10] FIG. 10 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 11] FIG. 11 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 12] FIG. 12 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 13] FIG. 13 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 14] FIG. 14 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 15] FIG. 15 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 16] FIG. 16 is a table showing the contents of components in the metallic ink and the evaluation results for each example. [Figure 17] FIG. 17 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 18] FIG. 18 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 19] FIG. 19 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 20] FIG. 20 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 21] FIG. 21 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 22] FIG. 22 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 23] FIG. 23 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 24] FIG. 24 is a table showing the contents of components of the metal ink in each example and the evaluation results. [Diagram 25] FIG. 25 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 26] FIG. 26 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 27] FIG. 27 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 28] FIG. 28 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 29] FIG. 29 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 30] FIG. 30 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 31] FIG. 31 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 32] FIG. 32 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 33] FIG. 33 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 34] FIG. 34 is a table showing the contents of components of the metal ink in each example and the evaluation results. [Diagram 35] FIG. 35 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 36]FIG. 36 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 37] FIG. 37 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 38] FIG. 38 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Figure 39] FIG. 39 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 40] FIG. 40 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 41] FIG. 41 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 42] FIG. 42 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 43] FIG. 43 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 44] FIG. 44 is a table showing the contents of components of the metal ink in each example and the evaluation results. [Diagram 45] FIG. 45 is a table showing the contents of components in the metal ink and the evaluation results for each example. [Diagram 46] FIG. 46 is a table showing the contents of the components in the cleaning liquid and the evaluation results for each example. [Figure 47] FIG. 47 is a table showing the contents of the components in the cleaning liquid and the evaluation results for each example. [Figure 48] FIG. 48 is a table showing the contents of the components in the cleaning liquid and the evaluation results for each example. [Figure 49] FIG. 49 is a table showing the contents of the components in the cleaning liquid and the evaluation results for each example. [Figure 50] FIG. 50 is a table showing the contents of the components in the cleaning liquid and the evaluation results for each example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter, referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be appropriately combined. Also, the numerical values ​​include the range of rounding.

[0035] Fig. 1 is a schematic diagram of a metal ink according to this embodiment. As shown in Fig. 1, a metal ink 10 according to this embodiment contains metal particles 12, a polyhydric alcohol 14, a solvent 16, an additive 17, and an organic solvent 18. The metal ink 10 refers to an ink-like substance in which the metal particles 12 are not dissolved in the liquid solvent 16, but are present in solid form in the solvent 16. In the metal ink 10, the metal particles 12 may be precipitated in the solvent 16, or the metal particles 12 may be dispersed. The metal ink 10 does not need to contain the organic solvent 18.

[0036] The metal ink 10 is used to form a sintered body (metal layer) (e.g., wiring). For example, the metal ink 10 is sprayed from a nozzle onto a substrate (a film of resin, metal, etc., or a substrate of resin, metal, ceramic, etc., or a composite of these), dried, and then heated under an inert gas atmosphere or reducing gas atmosphere to sinter or melt the metal particles 12 while removing other components, and then cooled, forming a sintered body (metal layer) made of the metal components of the metal particles 12 on the substrate. The metal ink 10 is sprayed from a nozzle onto a substrate (a film of resin, metal, etc., or a substrate of resin, metal, ceramic, etc., or a composite of these), dried, and then heated under an oxidizing gas atmosphere to oxidize and sinter the metal particles 12 while removing other components, and then cooled, forming a sintered body (metal oxide layer) made of the metal oxide components of the oxidized metal particles 12 on the substrate. The sintered body formed by the metal ink 10 may be used for any purpose, and examples thereof include wiring made of the metal components of the metal particles 12 and a layer of, for example, cuprous oxide, made of the metal oxide components of the metal particles 12. However, the uses of the metal ink 10 are not limited to these and may be any use.

[0037] (metal particles) The metal particles 12 are particles of a metal. In this embodiment, it is preferable that the metal particles 12 are copper particles.

[0038] The particle size of the metal particles 12 (peak value of particle size distribution (number)) is preferably 10 nm or more and 1000 nm or less. The particle size of the metal particles 12 in the metal ink 10 can be determined as the peak value of the particle size distribution (number) of the metal particles 12 by setting physical property values ​​such as the refractive index of the metal particles 12 and the refractive index and viscosity value of the solvent in the ink using a particle size measuring device (Zetasizer Nano Series ZSP, manufactured by Malvern Instruments), and measuring at 20°C or 25°C according to the temperature conditions of the physical property values. In the measurement of the particle size distribution, if the concentration of the metal particles 12 in the metal ink 10 is high and sufficient measurement quality cannot be obtained, the metal particles 12 may be diluted and dispersed about 10 to 1000 times with the main solvent in the metal ink 10 (water, lower alcohol, or high boiling point solvent) before measurement.

[0039] If the particle size is 10 nm or less, the specific surface area increases inversely proportional to the particle size, which increases the effect of surface oxidation and may reduce the sinterability of a coating film obtained using the metal particles 12. On the other hand, if the particle size of the metal particles 12 is 1000 nm or more, the particle size becomes too large and may cause the metal particles 12 to easily settle and separate in an ink dispersed in a solvent. The particle size of the metal particles 12 is preferably in the range of 30 nm to 500 nm, and particularly preferably in the range of 30 nm to 300 nm.

[0040] The BET specific surface area of ​​the metal particles 12 can be determined by measuring the amount of gas adsorption of the metal particles 12 using nitrogen or krypton gas as a measurement gas with a specific surface area measuring device (QUANTACHROME AUTOSORB-iQ2 manufactured by Quantachrome Instruments). 2 / g or more 8.0m 2 / g or less, and 3.5m 2 / g or more 8.0m 2 / g or less, and more preferably 4.0m 2 / g or more 8.0m 2 / g or less. The shape of the metal particles 12 is not limited to a spherical shape, and may be a needle shape or a flat plate shape.

[0041] It is preferable that the surfaces of the metal particles 12 are partially or entirely coated with an organic substance. By being coated with an organic substance, oxidation of the metal particles 12 is suppressed, and a decrease in sinterability due to oxidation of the metal particles 12 is further prevented. The organic substance coating the metal particles 12 is not formed by the polyhydric alcohol 14 or the solvent 16, and can be said to be not derived from the polyhydric alcohol 14 or the solvent 16. It can also be said that the organic substance coating the metal particles 12 is not a metal oxide (copper oxide) formed by oxidation of a metal.

[0042] The fact that the metal particles 12 are coated with an organic substance can be confirmed by analyzing the surface of the metal particles 12 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). For example, if the metal particles 12 are copper, the metal particles 12 are coated with an organic substance. + C3H3O3 vs. ion detection amount - Ratio of detected ions (C3H3O3 - / Cu + It is preferable that the ratio is 0.001 or more. C3H3O3 - / Cu + It is more preferable that the ratio is within the range of 0.05 to 0.2. Note that the surface of the metal particles 12 in this analysis does not refer to the surface of the metal particles 12 when the organic matter is removed from the metal particles 12, but refers to the surface of the metal particles 12 including the covering organic matter (i.e., the surface of the organic matter).

[0043] When the metal particles 12 are copper, the surface is analyzed using time-of-flight secondary ion mass spectrometry to determine that the metal particles 12 are C3H4O2 - Cu ions and ions of C5 or higher may be detected. + C3H4O2 vs. ion detection amount - Ratio of detected ions (C3H4O2 - / Cu + The ratio is preferably 0.001 or more. + The ratio of the amount of ions detected that are C5 or more to the amount of ions detected (C5 or more ions / Cu + It is preferable that the ratio is less than 0.005.

[0044] C3H3O3 detected by time-of-flight secondary ion mass spectrometry - Ions and C3H4O2 - The ions and C5 or higher ions originate from the organic matter that coats the surface of the metal particles 12. - / Cu + Ratio and C3H4O2 - / Cu +When each of these ratios is 0.001 or more, the surface of the metal particles 12 is less likely to be oxidized, and the metal particles 12 are less likely to aggregate. - / Cu + Ratio and C3H4O2 - / Cu + When the ratio is 0.2 or less, the oxidation and aggregation of the metal particles 12 can be suppressed without excessively decreasing the sinterability of the metal particles 12, and further, the generation of decomposition gas of organic matter during heating can be suppressed, so that a bonding layer with fewer voids can be formed. - / Cu + Ratio and C3H4O2 - / Cu + The ratio is preferably in the range of 0.08 to 0.16. + If the ratio is 0.005 or more, the particle surface contains a large amount of organic matter with a relatively high desorption temperature, resulting in insufficient sintering and making it difficult to obtain a strong bonding layer. + Preferably, the ratio is less than 0.003.

[0045] The organic matter that coats the metal particles 12 is preferably a carboxylic acid derived from a carboxylate metal used in producing the metal particles 12. A method for producing the metal particles 12 coated with an organic matter derived from a carboxylic acid will be described later. The amount of the organic matter coated on the metal particles 12 is preferably in the range of 0.5% by mass to 2.0% by mass, more preferably in the range of 0.8% by mass to 1.8% by mass, and even more preferably in the range of 0.8% by mass to 1.5% by mass, based on 100% by mass of the metal particles. When the amount of the organic matter coated is 0.5% by mass or more, the metal particles 12 can be uniformly coated with the organic matter, and oxidation of the metal particles 12 can be more reliably suppressed. In addition, when the amount of the organic matter coated is 2.0% by mass or less, it is possible to suppress the generation of voids in the sintered body (bonding layer) of the metal particles due to gas generated by decomposition of the organic matter by heating. The amount of the organic matter coated can be measured using a commercially available device. For example, the amount of the organic matter coated can be measured using a differential thermobalance TG8120-SL (manufactured by RIGAKU Corporation). In this case, for example, metal particles from which moisture has been removed by freeze-drying are used as samples. Measurements are performed in nitrogen (G2 grade) gas to suppress oxidation of the metal particles, and the temperature rise rate is set to 10°C / min. The weight loss rate when heated from 250°C to 300°C can be defined as the amount of organic coating. In other words, the amount of coating = (sample weight after measurement) / (sample weight before measurement) x 100 (wt%). Measurements are performed three times for each metal particle from the same lot, and the arithmetic mean value can be used as the amount of coating.

[0046] It is preferable that 50% by mass or more of the organic matter in the metal particles 12 is decomposed when heated for 30 minutes at a temperature of 300° C. in an atmosphere of an inert gas such as argon gas. The organic matter derived from carboxylic acid generates carbon dioxide gas, nitrogen gas, evaporated acetone gas, and water vapor during decomposition.

[0047] (Polyhydric alcohol) The polyhydric alcohol 14 is an alcohol that contains two or more OH groups and is soluble in water and lower alcohols. The polyhydric alcohol 14 preferably has a melting point of 30° C. or higher. The lower alcohol refers to an alcohol having 5 or less carbon atoms (C).

[0048] The polyhydric alcohol 14 may be, for example, at least one of 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2-hydroxymethyl-2-methyl-1,3-propanediol, 1-phenyl-1,2-ethanediol, 1,1,1-tris(hydroxymethyl)propane, erythritol, pentaerythritol, ribitol, resorcinol, (pyro)catechol, 5-methylresorcinol, pyrogallol, 1,2,3-cyclohexanetriol, and 1,3,5-cyclohexanetriol.

[0049] Polyhydric alcohol 14 is a non-electrolyte, and is present in metal ink 10 in a state dissolved in solvent 16 (in a state in which molecules of polyhydric alcohol 14 are dispersed in solvent 16). However, polyhydric alcohol 14 may be present in metal ink 10 in any form, and may be in a state in which it is not dissolved in solvent 16.

[0050] By including the polyhydric alcohol 14 in the metal ink 10, the polyhydric alcohol 14 is coordinated around the metal particles 12, thereby making it possible to appropriately suppress aggregation of the metal particles 12. That is, in this embodiment, it is preferable that the polyhydric alcohol 14 is coordinated around the metal particles 12.

[0051] (solvent) The solvent 16 is a liquid (medium) for dispersing the metal particles 12. The details of the solvent 16 will be described later.

[0052] (Additives) Additive 17 includes a phosphate compound. The phosphate compound used as additive 17 is water-soluble, and is present in metal ink 10 in a dissolved state in solvent 16 (a state in which the molecules of the phosphate compound are dispersed in solvent 16). By including additive 17 including a phosphate compound in metal ink 10, it is possible to obtain a sintered body that has appropriate transmittance for visible light while appropriately sintering metal particles 12.

[0053] The molecular weight of the phosphate compound used as the additive 17 is preferably 90 to 200, more preferably 100 to 200, and even more preferably 140 to 190. When the molecular weight of the phosphate compound is in this range, it can be appropriately dissolved in the solvent 16 without causing aggregation of the metal particles 12, and the organic components remaining in the firing can be reduced or eliminated, so that the sinterability between the metal particles can be improved more suitably without being hindered. The molecular weight here can be measured by, for example, the vapor pressure depression method, the boiling point elevation method, the freezing point (melting point) depression method (Rust method), the isothermal distillation method (Buerger method), mass spectrometry, etc. In addition, the molecular weight here refers to the molecular weight excluding the molecular weight of water even in the case of a hydrate, and the same applies hereinafter.

[0054] The solubility of the phosphate compound used as additive 17 in water at 1 atmosphere and 20° C. is preferably 10 g or more, more preferably 20 g or more, and even more preferably 50 g or more per 100 g of water. When the solubility is in this range, the phosphate compound dissolves appropriately when water is used as solvent 16, and the sinterability can be more suitably improved.

[0055] Any phosphate compound may be used for additive 17, and examples of the phosphate compound used for additive 17 include phosphoric acid, monosodium phosphate (sodium dihydrogen phosphate), disodium phosphate (disodium hydrogen phosphate), trisodium phosphate, monopotassium phosphate (potassium dihydrogen phosphate), dipotassium phosphate (dipotassium hydrogen phosphate), trimethyl phosphate, triethyl phosphate, diisopropyl phosphate, monoisopropyl phosphate, 2-aminoethyl dihydrogen phosphate (O-phosphorylethanolamine), diisopropyl phosphite, dimethyl phosphite, etc. As additive 17, one of these may be used, or two or more may be used.

[0056] (Organic solvent) The organic solvent 18 is an organic solvent having components different from those of the polyhydric alcohol 14 and the solvent 16. The organic solvent 18 is an organic solvent having a boiling point of 150° C. or higher at atmospheric pressure and miscible with water. The organic solvent 18 more preferably has a boiling point of 200° C. or higher. Miscible here means that the organic solvent 18 can be mixed with water in any ratio (i.e., they can be completely dissolved in each other at any concentration). In this embodiment, the organic solvent 18 is preferably miscible with the solvent 16.

[0057] The organic solvent 18 is preferably a glycol ether or an aprotic polar solvent. More specifically, the organic solvent 18 may include both a glycol ether and an aprotic polar solvent, in other words, it is preferable that the organic solvent 18 includes at least one of a glycol ether and an aprotic polar solvent. Examples of glycol ethers contained in the organic solvent 18 include diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol isobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monoallyl ether, diethylene glycol monobenzyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, and diethylene glycol diethyl ether. When the organic solvent 18 contains a glycol ether, it may contain at least one selected from the above. Examples of the aprotic polar solvent contained in the organic solvent 18 include N-methylpyrrolidone, dimethylformamide, 2-pyrrolidone, and propylene carbonate. When the organic solvent 18 contains an aprotic polar solvent, it may contain at least one selected from these listed solvents.

[0058] (impurities) In addition to the components listed above, the metal ink 10 may contain unavoidable impurities, such as substances generated when the components listed above react with themselves, other components, or oxygen due to light or heat, resulting in decomposition, polymerization, addition, oxidation, reduction, or other reactions.

[0059] (Metallic Ink) The content of metal particles 12 in the metal ink 10 is preferably 1% to 50% by mass, more preferably 5% to 50%, and even more preferably 5% to 30% by mass, relative to the entire metal ink 10. Having the content of metal particles 12 within this range makes it possible to suppress a decrease in the fluidity of the metal ink 10 while maintaining a sufficient concentration of the metal particles 12, which is advantageous in terms of production, for example by improving the jetting ability from a nozzle.

[0060] The content of polyhydric alcohol 14 in metal ink 10 is preferably 0.01% or more and 20% or less by mass with respect to the entire metal ink 10. When the content of polyhydric alcohol 14 is within this range, it is possible to appropriately disperse metal particles 12 while preventing the concentration of metal particles 12 from becoming too low.

[0061] The content of the solvent 16 in the metal ink 10 is preferably 50% to 99%, more preferably 50% to 95%, and even more preferably 60% to 95%, by mass ratio relative to the entire metal ink 10. Having the content of the solvent 16 within this range makes it possible to suppress a decrease in the fluidity of the metal ink 10 while maintaining a sufficient concentration of the metal particles 12, which is advantageous in terms of production, for example by improving the jetting ability from a nozzle.

[0062] The content of additive 17 in metal ink 10 is preferably 0.01% to 10% by mass, more preferably 0.1% to 10%, and even more preferably 0.1% to 5% by mass, relative to the total mass of metal ink 10. When the content of additive 17 is within this range, the concentration of metal particles 12 can be sufficiently maintained, and metal particles 12 can be sintered more suitably.

[0063] The content of organic solvent 18 in metal ink 10 is preferably 0.01% to 30% by mass, and more preferably 0.1% to 30% by mass, relative to the entire metal ink 10. When the content of organic solvent 18 is within this range, even if metal ink 10 is left for a long period of time, it has sufficient mold resistance and can be appropriately stored for a long period of time.

[0064] Metal ink 10 may contain ionized metal particles 12 (ions of the metal that constitutes metal particles 12). In other words, ionized metal particles 12 may be contained in the liquid component of metal ink 10. The ionized metal particles 12 may be copper ions.

[0065] The metal ink 10 described above can have a variety of components in the solvent 16. Below, metal inks 10 each having a different solvent 16 component will be described.

[0066] (First metal ink) One of the metal inks 10 having different components of the solvent 16 is referred to as a first metal ink 10A. In the first metal ink 10A, the solvent 16 is water. In the first metal ink 10A, the polyhydric alcohol 14, the additive 17, and the organic solvent 18 are dissolved in water as the solvent 16, and metal particles 12 are mixed in the water. In other words, the first metal ink 10A contains the metal particles 12 in an aqueous solution of the polyhydric alcohol 14, the additive 17, and the organic solvent 18. Note that the first metal ink 10A does not necessarily need to contain the organic solvent 18, and in this case, the organic solvent 18 does not need to be added in the manufacturing process of the first metal ink 10A.

[0067] The content of metal particles 12 in first metal ink 10A is preferably 1% to 50% by mass, more preferably 5% to 50%, and even more preferably 5% to 30% by mass, relative to the entire first metal ink 10A. Having the content of metal particles 12 within this range makes it possible to suppress a decrease in the fluidity of first metal ink 10A while maintaining a sufficient concentration of metal particles 12, which is advantageous in terms of production, for example by improving the jetting ability from a nozzle.

[0068] In the first metal ink 10A, the content of polyhydric alcohol 14 is preferably 0.1% to 20% by mass, more preferably 0.5% to 20%, and even more preferably 1% to 20% by mass, relative to the entire first metal ink 10A. When the content of polyhydric alcohol 14 is within this range, the metal particles 12 can be appropriately dispersed while preventing the concentration of the metal particles 12 from becoming too low.

[0069] In first metal ink 10A, the content of additive 17 is preferably 0.1% to 10% by mass, more preferably 0.5% to 10%, and even more preferably 1% to 5% by mass, relative to the total mass of first metal ink 10A. When the content of additive 17 is within this range, metal particles 12 can be sintered more suitably while the concentration of metal particles 12 is sufficiently maintained.

[0070] The content of organic solvent 18 in first metal ink 10A is preferably 0.5% to 30%, more preferably 1% to 30%, and even more preferably 2% to 30% by mass relative to the entire first metal ink 10A. When the content of organic solvent 18 falls within this range, the ink can be appropriately stored for a long period of time.

[0071] In this embodiment, the first metal ink 10A preferably does not contain any substances other than the metal particles 12, the polyhydric alcohol 14, the solvent 16 which is water, the additives 17, and the organic solvent 18, except for unavoidable impurities. However, without being limited thereto, the first metal ink 10A may contain additives (such as a dispersant, an adhesion imparting agent, a rheology modifier, an anti-rust agent, and an anti-settling agent) other than the metal particles 12, the polyhydric alcohol 14, the solvent 16 which is water, the additives 17, and the organic solvent 18.

[0072] For example, the first metal ink 10A may contain a dispersant that is a component other than the metal particles 12, the polyhydric alcohol 14, the solvent 16 which is water, the additive 17, and the organic solvent 18. Examples of the dispersant include cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants. Among these, examples of the anionic dispersants include carboxylic acid dispersants, sulfonic acid dispersants, and phosphoric acid dispersants. In particular, phosphoric acid ester compounds are preferably used as phosphoric acid dispersants. The phosphoric acid ester compound used as the dispersant preferably has a higher molecular weight than the phosphoric acid compound used as the additive 17. The molecular weight of the phosphoric acid ester compound used as the dispersant is preferably 200 or more and 3500 or less, more preferably 300 or more and 3000 or less, and even more preferably 400 or more and 2500 or less. A molecular weight of 200 or more provides sufficient hydrophobic groups, resulting in good dispersibility of the metal particles in water, and a molecular weight of 3,500 or less enables decomposition and reaction at the target heating temperature (approximately 200 to 350°C), without the risk of interfering with sintering of the metal particles. Furthermore, the phosphate ester compound used in the dispersant may be any of mono-, di-, or tri-esters, neutralized salts, etc., so long as it has good solubility in water. In the case of mono-, di-, or tri-esters, the HLB (Hydrophilic-Lipophilic Balance) value is preferably 6 or more and 20 or less, more preferably 8 or more and 20 or less, and even more preferably 10 or more and 20 or less. The phosphate ester compound used in the dispersant may be any, and examples thereof include polyoxyethylene alkyl (aliphatic) ether phosphate ester, polyoxyethylene phenyl (aromatic) ether phosphate ester, alkyl (aliphatic) phosphate ester, phenyl (aromatic) phosphate ester, and neutralized salts thereof. As the dispersant, one of these may be used, or two or more of them may be used.

[0073] When the first metal ink 10A contains a phosphate ester compound as a dispersant, the content of the phosphate ester compound in the first metal ink 10A is preferably 0.001% to 2% by mass, more preferably 0.001% to 1% by mass, and even more preferably 0.01% to 1% by mass. By having the content of the phosphate ester compound in this range, aggregation of the metal particles 12 can be more effectively suppressed.

[0074] (Second metallic ink) One of the metal inks 10 having different components of the solvent 16 is referred to as the second metal ink 10B. The second metal ink 10B contains a lower alcohol as the solvent 16, and more specifically, the solvent 16 may contain a substance other than a lower alcohol, and in this embodiment, may contain water. The second metal ink 10B is obtained by mixing the polyhydric alcohol 14, the additive 17, and the organic solvent 18 dissolved in the solvent 16 with the metal particles 12 mixed therein. That is, for example, the second metal ink 10B is obtained by mixing the metal particles 12 in an aqueous solution of the polyhydric alcohol 14, the additive 17, the organic solvent 18, and the lower alcohol. The second metal ink 10B may not contain the organic solvent 18, and in this case, the organic solvent 18 may not be added in the manufacturing process of the second metal ink 10B.

[0075] The lower alcohol here refers to an alcohol having 5 or less C (carbons). More specifically, the lower alcohol used in the solvent 16 preferably refers to an alcohol having one OH group, and is preferably an alcohol having 1 to 4 C (carbons). Examples of the lower alcohol include methanol, ethanol, propyl alcohol, isopropyl alcohol, butyl alcohol, and sec-butyl alcohol. One or more of these may be used as the lower alcohol.

[0076] The content of metal particles 12 in second metal ink 10B is preferably 1% to 50% by mass, more preferably 5% to 50%, and even more preferably 5% to 30% by mass, relative to the entire second metal ink 10B. Having the content of metal particles 12 within this range makes it possible to suppress a decrease in the fluidity of second metal ink 10B while maintaining a sufficient concentration of metal particles 12, which is advantageous in terms of production, for example by improving the jetting ability from a nozzle.

[0077] In the second metal ink 10B, the content of the polyhydric alcohol 14 is preferably 0.01% to 10% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.1% to 5% by mass, relative to the entire second metal ink 10B. When the content of the polyhydric alcohol 14 is within this range, the metal particles 12 can be appropriately dispersed while preventing the concentration of the metal particles 12 from becoming too low.

[0078] The second metal ink 10B preferably has a lower alcohol content of 5% to 99% by mass, more preferably 5% to 95% by mass, and even more preferably 10% to 95% by mass. By having the lower alcohol content within this range, it is possible to suppress a decrease in the fluidity of the second metal ink 10B while maintaining a sufficient concentration of the metal particles 12, which is advantageous in terms of production, for example, in terms of improving the ejection properties from a nozzle. When multiple types of alcohol are contained as lower alcohols, the lower alcohol content here refers to the total content of each of the lower alcohols. The same applies to other components.

[0079] In second metal ink 10B, the content of additive 17 is preferably 0.05% to 5% by mass, more preferably 0.1% to 5% by mass, and even more preferably 0.1% to 2% by mass, relative to the entire second metal ink 10B. When the content of additive 17 is within this range, the concentration of metal particles 12 can be sufficiently maintained, and metal particles 12 can be sintered more suitably.

[0080] In the second metal ink 10B, the content of organic solvent 18 is preferably 0.01% to 30% by mass, more preferably 0.1% to 20%, and even more preferably 0.5% to 20% by mass, relative to the entire second metal ink 10B. When the content of organic solvent 18 is within this range, the ink can be appropriately stored for a long period of time.

[0081] In this embodiment, the second metal ink 10B may contain no substances other than the metal particles 12, the polyhydric alcohol 14, the solvent 16 (here, water and lower alcohol), the additives 17, and the organic solvent 18, except for unavoidable impurities. However, without being limited thereto, the second metal ink 10B may contain additives (such as dispersants, adhesion imparting agents, rheology modifiers, rust inhibitors, and anti-settling agents) other than the metal particles 12, the polyhydric alcohol 14, the solvent 16, the additives 17, and the organic solvent 18.

[0082] For example, the second metal ink 10B may contain a dispersant that is a component other than the metal particles 12, the polyhydric alcohol 14, the solvent 16, the additive 17, and the organic solvent 18. Examples of the dispersant include cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants. Among these, examples of the anionic dispersants include carboxylic acid dispersants, sulfonic acid dispersants, and phosphoric acid dispersants. In particular, phosphoric acid ester compounds are preferably used as phosphoric acid dispersants. The phosphoric acid ester compound used as the dispersant preferably has a higher molecular weight than the phosphoric acid compound used as the additive 17. The molecular weight of the phosphoric acid ester compound used as the dispersant is preferably 200 or more and 3500 or less, more preferably 300 or more and 3000 or less, and even more preferably 400 or more and 2500 or less. A molecular weight of 200 or more provides sufficient hydrophobic groups, allowing the metal particles to be well dispersed in lower alcohols, and a molecular weight of 3,500 or less allows decomposition and reaction at the target heating temperature (approximately 200 to 350°C), eliminating the risk of interfering with sintering of metal particles. Furthermore, the phosphate ester compound used in the dispersant may be any of mono-, di-, and triesters, neutralized salts, and the like, so long as it has good solubility in lower alcohols. In the case of mono-, di-, and triesters, the HLB value is preferably 4 or more and 15 or less, more preferably 5 or more and 15 or less, and even more preferably 5 or more and 13 or less. The phosphate ester compound used in the dispersant may be any, and examples thereof include polyoxyethylene alkyl (aliphatic) ether phosphate ester, polyoxyethylene phenyl (aromatic) ether phosphate ester, alkyl (aliphatic) phosphate ester, phenyl (aromatic) phosphate ester, and neutralized salts thereof. As the dispersant, one of these may be used, or two or more of them may be used.

[0083] When the second metal ink 10B contains a phosphate ester compound as a dispersant, the content of the phosphate ester compound in the second metal ink 10B is preferably 0.001% to 2% by mass, more preferably 0.001% to 1% by mass, and even more preferably 0.01% to 1% by mass. By having the content of the phosphate ester compound in this range, aggregation of the metal particles 12 can be more effectively suppressed.

[0084] In metal inks that use lower alcohols as the main solvent, there is a risk that the lower alcohols may cause the metal particles to aggregate. In contrast, in second metal ink 10B, polyhydric alcohol 14 is mixed in, so that, for example, polyhydric alcohol 14 is coordinated around metal particles 12, thereby preventing aggregation of metal particles 12.

[0085] (Third Metal Ink) One of the metal inks 10 having different components of the solvent 16 is referred to as a third metal ink 10C. The third metal ink 10C contains a high-boiling point solvent as the solvent 16, and more specifically, the main solvent, which is the main component of the solvent 16, is a high-boiling point solvent. For example, the third metal ink 10C contains metal particles 12 in the solvent 16 while polyhydric alcohol 14, additives 17, and organic solvent 18 are dissolved therein. The third metal ink 10C may contain a solvent 16 other than the high-boiling point solvent, which is the main solvent. The third metal ink 10C may contain at least one of water and a lower alcohol, and in this embodiment, contains both water and a lower alcohol. The third metal ink 10C may not contain the organic solvent 18, and in this case, the organic solvent 18 may not be added in the manufacturing process of the third metal ink 10C.

[0086] The high boiling point solvent is a liquid that contains one or more OH groups, has a boiling point of 150°C or higher, and is poorly soluble or insoluble in water. The high boiling point solvent that is poorly soluble or insoluble in water is preferably a solvent that is classified as a water-insoluble liquid in Appendix 3 of the Cabinet Order on the Regulation of Hazardous Materials in the Fire Service Act. The high boiling point solvent is preferably a so-called organic solvent, and may be, for example, at least one of α-terpineol and 2-ethyl-1,3-hexanediol. Any of the solvents may contain isomers.

[0087] The content of metal particles 12 in third metal ink 10C is preferably 1% to 50% by mass, more preferably 5% to 50%, and even more preferably 5% to 30% by mass, relative to the entire third metal ink 10C. Having the content of metal particles 12 within this range makes it possible to suppress a decrease in the fluidity of second metal ink 10B while maintaining a sufficient concentration of metal particles 12, which is advantageous in terms of production, for example by improving the jetting ability from a nozzle.

[0088] In third metal ink 10C, the content of polyhydric alcohol 14 is preferably 0.01% to 5% by mass, more preferably 0.01% to 5% by mass, and even more preferably 0.01% to 3% by mass, relative to the total mass of third metal ink 10C. When the content of polyhydric alcohol 14 is within this range, metal particles 12 can be appropriately dispersed while preventing the concentration of metal particles 12 from becoming too low.

[0089] The content of the high boiling point solvent in third metal ink 10C is preferably 50% to 99% by mass, more preferably 50% to 95%, and even more preferably 60% to 95% by mass, relative to the entire third metal ink 10C. Having the content of the high boiling point solvent within this range makes it possible to suppress a decrease in the fluidity of third metal ink 10C while maintaining a sufficient concentration of metal particles 12, which is advantageous in terms of production, for example by improving the jetting ability from a nozzle.

[0090] In third metal ink 10C, the content of additive 17 is preferably 0.01% to 2% by mass, more preferably 0.1% to 2%, and even more preferably 0.1% to 1% by mass, relative to the total mass of third metal ink 10C. When the content of additive 17 is within this range, metal particles 12 can be sintered more suitably while the concentration of metal particles 12 is sufficiently maintained.

[0091] In third metal ink 10C, the content of organic solvent 18 is preferably 0.01% to 30% by mass, more preferably 0.01% to 10%, and even more preferably 0.1% to 10% by mass, relative to the entire third metal ink 10C. When the content of organic solvent 18 is within this range, the ink can be appropriately stored for a long period of time.

[0092] The third metal ink 10C preferably contains a dispersant that is a component other than the metal particles 12, the polyhydric alcohol 14, the solvent 16, the additive 17, and the organic solvent 18. Examples of the dispersant include cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants. Among these, examples of the anionic dispersants include carboxylic acid dispersants, sulfonic acid dispersants, and phosphoric acid dispersants. In particular, phosphoric acid ester compounds are preferably used as phosphoric acid dispersants. The phosphoric acid ester compound used as the dispersant preferably has a higher molecular weight than the phosphoric acid compound used as the additive 17. The molecular weight of the phosphoric acid ester compound used as the dispersant is preferably 200 or more and 3500 or less, more preferably 300 or more and 3000 or less, and even more preferably 400 or more and 2500 or less. A molecular weight of 200 or more provides sufficient hydrophobic groups, allowing the metal particles to be well dispersed in high-boiling point solvents, and a molecular weight of 3,500 or less allows decomposition and reaction at the target heating temperature (approximately 200 to 350°C), eliminating the risk of interfering with sintering of metal particles. Furthermore, the phosphate ester compound used in the dispersant may be any of mono-, di-, and triester, neutralized salts, etc., so long as it has good solubility in lower alcohols. In the case of mono-, di-, and triester, the HLB value is preferably 2 or more and 15 or less, more preferably 3 or more and 15 or less, and even more preferably 4 or more and 13 or less. The phosphate ester compound used in the dispersant may be any, and examples thereof include polyoxyethylene alkyl (aliphatic) ether phosphate ester, polyoxyethylene phenyl (aromatic) ether phosphate ester, alkyl (aliphatic) phosphate ester, phenyl (aromatic) phosphate ester, and polyoxyethylene alkyl ether phosphate ester, such as laureth-n phosphate, oleth-n phosphate, steareth-n phosphate (n=2-10), and alkyl phosphate ester. As the dispersant, one of these may be used, or two or more may be used.

[0093] The third metal ink 10C preferably contains a dispersant in a mass ratio of 0.01% to 5%, more preferably 0.1% to 5%, and even more preferably 0.1% to 3%. When the dispersant content is in this range, aggregation of the metal particles 12 can be appropriately suppressed.

[0094] In this embodiment, third metal ink 10C preferably does not contain any substances other than metal particles 12, polyhydric alcohol 14, solvent 16 (here, water, a lower alcohol, and a high boiling point solvent), additive 17, organic solvent 18, and dispersant, except for unavoidable impurities. However, without being limited thereto, third metal ink 10C may not contain a dispersant, or may contain additives other than metal particles 12, polyhydric alcohol 14, solvent 16, additive 17, organic solvent 18, and dispersant (adhesion imparting agent, rheology modifier, rust inhibitor, anti-settling agent, etc.).

[0095] Metal inks that use a high-boiling point solvent as the main solvent may have the risk of agglomeration of metal particles 12 due to the high-boiling point solvent. In contrast, third metal ink 10C contains polyhydric alcohol 14, which, for example, coordinates around metal particles 12, making it possible to suppress aggregation of metal particles 12.

[0096] (Metal Ink Manufacturing Method) Next, a description will be given of a method for producing the above-described metal ink 10. Fig. 2 is a flowchart illustrating a method for producing the metal ink according to this embodiment.

[0097] (Production of metal particles) As shown in FIG. 2, in this manufacturing method, a metal carboxylate aqueous dispersion and a reducing agent are mixed to generate metal particles 12 (step S10). Specifically, first, a metal carboxylate aqueous dispersion (e.g., copper carboxylate) is prepared, and a pH adjuster is added to the metal carboxylate aqueous dispersion to adjust the pH to 2.0 to 7.5. Next, in an inert gas atmosphere, a hydrazine compound capable of reducing metal ions is added as a reducing agent to the pH-adjusted metal carboxylate aqueous dispersion and mixed. The resulting mixture is heated to a temperature of 60° C. to 80° C. in an inert gas atmosphere and held for 1.5 to 2.5 hours. As a result, the metal ions eluted from the metal carboxylate are reduced to generate metal particles 12, and an organic substance derived from the metal acid is formed on the surface of the metal particles 12. The carboxylic acid used here may be glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid, tartaric acid, oxalic acid, phthalic acid, benzoic acid, or a salt thereof, etc. The reducing agent used is a hydrazine compound, but is not limited thereto, and may be hydrazine, ascorbic acid, oxalic acid, formic acid, or a salt thereof, etc.

[0098] (Metal particles: Manufacturing of copper particles) The following describes a method for producing the metal particles 12 when the metal particles 12 are copper particles. The aqueous dispersion of copper carboxylate can be prepared by adding powdered metal carboxylate to pure water such as distilled water or ion-exchanged water to a concentration of 25% by mass or more and 40% by mass or less, and stirring with a stirring blade to uniformly disperse the metal carboxylate. Examples of pH adjusters include triammonium citrate, ammonium hydrogen citrate, and citric acid. Among these, triammonium citrate is preferred because it is easy to adjust the pH to a mild level. The reason why the pH of the aqueous dispersion of copper carboxylate is set to 2.0 or more is to increase the elution rate of copper ions eluted from the copper carboxylate, to rapidly advance the generation of copper particles, and to obtain the target fine copper particles. The reason why the pH is set to 7.5 or less is to suppress the eluted metal ions from becoming copper hydroxide (II) and to increase the yield of copper particles. The reason why the pH is set to 7.5 or less is to suppress the reducing power of the hydrazine compound from becoming excessively high, and the target copper particles can be easily obtained. The pH of the aqueous dispersion of copper carboxylate is preferably adjusted to within the range of 4 or more and 6 or less.

[0099] The reduction of copper carboxylate with a hydrazine compound is carried out under an inert gas atmosphere. This is to prevent oxidation of copper ions dissolved in the liquid. Examples of inert gases include nitrogen gas and argon gas. When reducing copper carboxylate under acidic conditions, hydrazine compounds have the advantages of not producing residues after the reduction reaction, being relatively safe, and being easy to handle. Examples of this hydrazine compound include hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride, and hydrazine sulfate. Among these hydrazine compounds, hydrazine monohydrate and anhydrous hydrazine are preferred, as they do not contain components that can become impurities such as sulfur and chlorine.

[0100] Generally, copper generated in an acidic solution with a pH of less than 7 dissolves. However, in this embodiment, a hydrazine compound, which is a reducing agent, is added and mixed with an acidic solution with a pH of less than 7, and copper particles are generated in the resulting mixed solution. Therefore, the components derived from the carboxylic acid generated from the carboxylate copper quickly cover the surfaces of the copper particles, suppressing the dissolution of the copper particles. It is preferable to keep the temperature of the aqueous dispersion of the carboxylate copper after adjusting the pH at 50°C or higher and 70°C or lower to facilitate the progress of the reduction reaction.

[0101] The mixed solution containing the hydrazine compound is heated to a temperature of 60°C or more and 80°C or less under an inert gas atmosphere and held for 1.5 hours or more and 2.5 hours or less in order to generate copper particles and to form and coat the surfaces of the generated copper particles with organic matter. The reason for holding the mixture under an inert gas atmosphere is to prevent oxidation of the generated copper particles. The starting material, carboxylate copper, usually contains about 35% by mass of copper components. By adding a hydrazine compound, which is a reducing agent, to a carboxylic acid aqueous dispersion containing this amount of copper components, heating it to the above temperature, and holding it for the above time, the generation of copper particles and the generation of organic matter on the surfaces of the copper particles proceed in a well-balanced manner, so that copper particles having an organic matter coating amount in the range of 0.5% by mass to 2.0% by mass can be obtained with respect to 100% by mass of copper particles. If the heating temperature is less than 60°C and the holding time is less than 1.5 hours, the carboxylate metal is not completely reduced, the generation rate of the copper particles becomes too slow, and the amount of organic matter coating the copper particles may become excessive. If the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, the copper particles may be generated too quickly, resulting in a risk of the amount of organic matter coating the copper particles being too small. The preferred heating temperature is 65°C or higher and 75°C or lower, and the preferred holding time is 2 hours or higher and 2.5 hours or lower.

[0102] The copper particles produced in the mixed liquid may be washed, desalted, or the like from the mixed liquid under an inert gas atmosphere using pure water or the like. Furthermore, by dehydrating the mixture using, for example, a centrifuge, a water slurry containing metal particles 12 with a certain solid-liquid ratio (for example, solid-liquid ratio: 50 / 50 [mass %]) can be obtained. In some cases, copper particles whose surfaces are coated with an organic substance can be obtained by performing solid-liquid separation and drying using a freeze-drying method or a vacuum drying method. Since the surfaces of these copper particles are coated with an organic substance, they are less likely to oxidize even when stored in the air.

[0103] (Manufacture of the first metal ink) Next, the metal particles 12, water as the solvent 16, the polyhydric alcohol 14, the additive 17, and the organic solvent 18 are mixed to produce the first metal ink 10A (step S12). Here, it is preferable to produce the first metal ink 10A by mixing the metal particles 12, the polyhydric alcohol 14, the additive 17, the organic solvent 18, and water so that the contents of the metal particles 12, the polyhydric alcohol 14, the additive 17, and the organic solvent 18 are within the numerical ranges described above. Note that the method of mixing the metal particles 12, the polyhydric alcohol 14, the additive 17, the organic solvent 18, and the water is arbitrary. For example, an aqueous solution of the polyhydric alcohol 14 and the organic solvent 18 containing the polyhydric alcohol 14, the additive 17, the organic solvent 18, and water may be mixed with a water slurry containing the metal particles 12, or an aqueous solution of the polyhydric alcohol 14, the additive 17, and the organic solvent 18 may be mixed with the metal particles 12 not containing water. If necessary, the mixture may be filtered through a filter having a predetermined mesh size in order to remove foreign matter or aggregates of the metal particles 12. Such filtering may be performed at any stage in the subsequent manufacturing process of the metal ink.

[0104] (Manufacture of second metal ink) Next, the first metal ink 10A is mixed with a lower alcohol as the solvent 16 to produce the second metal ink 10B (step S14). Here, it is preferable to produce the second metal ink 10B by mixing the first metal ink 10A with a lower alcohol so that the contents of the metal particles 12, the polyhydric alcohol 14, the additive 17, the lower alcohol, and the organic solvent 18 are within the numerical ranges described above. The first metal ink 10A and the lower alcohol may be mixed by any method. For example, the first metal ink 10A obtained in step S12 may be left to stand for a predetermined time (for example, about one day) or centrifuged under predetermined conditions, and then a part of the supernatant may be removed, and a lower alcohol may be added to the first metal ink 10A from which the supernatant has been removed. Alternatively, the second metal ink 10B may be produced by mixing the metal particles 12, water and a lower alcohol as the solvent 16, the polyhydric alcohol 14, the additive 17, and the organic solvent 18 without going through step S12.

[0105] (Manufacture of third metal ink) Next, the second metal ink 10B is mixed with a high-boiling point solvent as the solvent 16 and a dispersant to produce a third metal ink 10C (step S16). Here, it is preferable to produce the third metal ink 10C by mixing the second metal ink 10B with the high-boiling point solvent and the dispersant so that the contents of the metal particles 12, the polyhydric alcohol 14, the additive 17, the high-boiling point solvent, the dispersant and the organic solvent 18 are within the numerical ranges described above. The second metal ink 10B, the high-boiling point solvent and the dispersant may be mixed in any manner. For example, the second metal ink 10B obtained in step S14 may be left to stand for a predetermined time (for example, about one day) or centrifuged under predetermined conditions, after which a part of the supernatant liquid is removed, and the high-boiling point solvent may be added to the second metal ink 10B from which the supernatant liquid has been removed. The addition of a dispersant is not essential. Furthermore, a solvent (water, a lower alcohol, a high boiling point solvent, etc.) may be removed from or added to the third metal ink 10C so as to achieve the numerical range described above.

[0106] The third metal ink 10C produced in this manner is used as the metal ink 10. In the above description, the second metal ink 10B is produced using the first metal ink 10A, and the third metal ink 10C is produced using the second metal ink 10B. In other words, the first metal ink 10A and the second metal ink 10B are intermediate substances for producing the third metal ink 10C. However, the first metal ink 10A and the second metal ink 10B are not limited to being intermediate substances, and the first metal ink 10A and the second metal ink 10B themselves may be used as the metal ink 10.

[0107] The above-described method for producing the metal particles 12 and the metal ink 10 is merely an example, and the metal particles 12 and the metal ink 10 may be produced by any method.

[0108] (Cleaning solution) The metal ink 10 described above is used as a raw material for a sintered body. For example, the metal ink 10 is discharged or sprayed from a nozzle through a flow path inside various coating and patterning devices to obtain a coating film, coating pattern, or molded body of the metal ink 10. By heating these, the metal ink 10 is sintered to obtain a sintered film, sintered pattern, or sintered body. In this way, when the flow path or nozzle inside the device that discharges or sprays the metal ink 10 is stopped for a long time, for example, the flow may become poor due to the sedimentation of the metal particles 12 contained in the metal ink 10 or the drying due to the volatilization of the solvent components contained in the metal ink 10, or in the worst case, the flow may become clogged. In order to suppress or eliminate such clogging of the flow path or nozzle, it is effective to redisperse or dissolve the components that have settled or dried in the flow path or nozzle using a cleaning liquid. In this case, it is desirable to redisperse the solid components that have settled or dried using a cleaning liquid.

[0109] As a result of extensive research, the present inventors have found that clogging of flow paths and nozzles can be effectively suppressed and eliminated by using the above-described metal ink 10 itself as a cleaning liquid. That is, the cleaning solution in this embodiment contains metal particles 12, a solvent 14, a polyhydric alcohol 16 that contains two or more OH groups and is soluble in water and lower alcohols, and an additive 17 that contains a phosphoric acid compound that is soluble in water. Suitable components of the cleaning solution are similar to those of the metal ink 10 described above, and therefore a description thereof will be omitted. For example, the first metal ink 10A, the second metal ink 10B, or the third metal ink 10C described above may be used as the cleaning solution.

[0110] However, the content of metal particles 12 in the cleaning solution is preferably less than the content of metal particles 12 in the above-described metal ink 10. The content of metal particles 12 in the cleaning solution is preferably 0.5% by mass or more and 5% by mass or less, more preferably 1% by mass or more and 5% by mass or less, and even more preferably 1% by mass or more and 3% by mass or less, based on the total amount of the cleaning solution.

[0111] In this case, the above-mentioned cleaning liquid is supplied to the inside of the flow path or nozzle in which the above-mentioned metal ink 10 is stored, and the cleaning liquid is sprayed from the nozzle. By cleaning the flow path or nozzle with such a cleaning liquid, clogging of the flow path or nozzle caused by the metal particles 12 remaining in the nozzle can be suitably suppressed or eliminated. Therefore, by using the metal ink 10 according to this embodiment as a cleaning liquid, clogging can be suppressed or eliminated, making it possible to appropriately obtain a sintered body.

[0112] (Other examples of cleaning fluids) As described above, the cleaning liquid is preferably one having the same components as the metal ink 10, but is not limited thereto. For example, the cleaning liquid may be one containing only water for the metal ink 10A, one containing water and a lower alcohol for the metal ink 10B, or one containing a lower alcohol and a high-boiling point solvent that is a liquid that is poorly soluble or insoluble in water for the metal ink 10C. In this case, the cleaning liquid is supplied to the inside of the flow path or nozzle in which the metal inks 10A to C are stored, and is sprayed from the nozzle. As a result, the metal particles 12 remaining in the flow path or nozzle are redispersed together with the cleaning liquid and sprayed from the nozzle, thereby suitably suppressing or eliminating clogging of the flow path or nozzle. Furthermore, it can be said that the cleaning liquid containing only water for the metal ink 10A, one containing water and a lower alcohol for the metal ink 10B, or one containing a lower alcohol and a high-boiling point solvent that is a liquid that is poorly soluble or insoluble in water for the metal ink 10C does not leave the metal particles 12 in the flow path or nozzle, and is therefore preferable.

[0113] (effect) As described above, the metal ink 10 according to the present embodiment includes metal particles 12, a solvent 16, a polyhydric alcohol 14 that contains two or more OH groups and is soluble in water and lower alcohols, and an additive 17 that contains a phosphoric acid compound that is soluble in water. Here, in a metal ink in which metal particles are dispersed in a solvent, the metal particles may aggregate. If the metal particles aggregate, this may lead to a deterioration in the properties of the product, such as a decrease in the density of the sintered body. In contrast, since the metal ink 10 according to the present embodiment contains the polyhydric alcohol 14, the polyhydric alcohol 14 can suppress the aggregation of the metal particles 12. According to the metal ink 10 according to the present embodiment, the aggregation of the metal particles 12 can be suppressed, and therefore the deterioration of the properties of the product can be suppressed, and an appropriate sintered body can be obtained. In addition, for example, when the metal ink 10 is sprayed from a nozzle, the aggregation of the metal particles 12 can be suppressed to suppress manufacturing defects such as nozzle clogging. Furthermore, since the metal ink 10 according to this embodiment contains the additive 17 containing a phosphate compound, when the metal ink 10 is heated to produce a sintered body of the metal particles 12 in the metal ink 10, the sinterability of the sintered body can be improved. Furthermore, since the metal ink 10 according to this embodiment contains the additive 17 containing a phosphate compound, a sintered body having appropriate transmittance for visible light can be obtained. Therefore, the sintered body sintered using the metal ink 10 according to this embodiment can be appropriately applied to a tandem solar cell combined with a crystalline Si solar cell. However, the use of the sintered body sintered using the metal ink 10 may be arbitrary.

[0114] It is preferable that the metal ink 10 further contains an organic solvent 18 that has a boiling point of 150° C. or higher at atmospheric pressure and is miscible with water. By containing the organic solvent 18, the metal ink 10 has sufficient mold resistance even when left for a long period of time, and can be appropriately stored for a long period of time.

[0115] Moreover, the additive 17 is preferably contained in an amount of 0.01% to 10% by mass with respect to the total amount of the metal ink 10. By setting the content of the additive 17 within this range, it is possible to improve the sintering property while suppressing the aggregation of the metal particles 12, and to obtain a sintered body that appropriately transmits visible light.

[0116] Moreover, the molecular weight of the phosphate compound used as the additive 17 is preferably from 90 to 200. By setting the molecular weight of the phosphate compound within this range, it is possible to appropriately dissolve the phosphate compound in the solvent 16 and to more suitably improve the sinterability.

[0117] Moreover, it is preferable that the additive 17 contains at least one of phosphoric acid, monosodium phosphate (sodium dihydrogen phosphate), disodium phosphate (disodium hydrogen phosphate), trisodium phosphate, monopotassium phosphate (potassium dihydrogen phosphate), dipotassium phosphate (dipotassium hydrogen phosphate), trimethyl phosphate, triethyl phosphate, diisopropyl phosphate, monoisopropyl phosphate, 2-aminoethyl dihydrogen phosphate (O-phosphorylethanolamine), diisopropyl phosphite, and dimethyl phosphite. By using such an additive 17, the sinterability can be more suitably improved, and a sintered body that appropriately transmits visible light can be obtained.

[0118] The polyhydric alcohol 14 is preferably contained in an amount of 0.01% to 20% by mass with respect to the total amount of the metal ink 10. This makes it possible to appropriately disperse the metal particles 12 while preventing the concentration of the metal particles 12 from becoming too low.

[0119] Moreover, the polyhydric alcohol 14 preferably has a melting point of at least 30° C. This makes it possible to appropriately disperse the metal particles 12 while preventing the concentration of the metal particles 12 from becoming too low.

[0120] The organic solvent 18 is preferably contained in an amount of 0.01% to 30% by mass relative to the total amount of the metal ink 10. This ensures that the metal ink 10 has sufficient mold resistance even when left to stand for a long period of time, allowing it to be appropriately stored for a long period of time.

[0121] Moreover, it is preferable that the organic solvent 18 contains at least one of glycol ether and aprotic polar solvent, which ensures that the metal ink 10 has sufficient mold resistance even when left for a long period of time, and can be appropriately stored for a long period of time.

[0122] The metal particles 12 are preferably contained in an amount of 1% to 50% by mass with respect to the total amount of the metal ink 10. This makes it possible to suppress a decrease in the fluidity of the metal ink 10 while maintaining a sufficient concentration of the metal particles 12.

[0123] Moreover, it is preferable that the metal particles 12 are made of copper. According to this embodiment, a copper sintered body can be appropriately manufactured.

[0124] Moreover, it is preferable that the solvent 16 contains water. According to the present embodiment, it is possible to improve the sinterability while suppressing the aggregation of the metal particles 12, and to obtain a sintered body that appropriately transmits visible light.

[0125] In addition, it is preferable that the solvent 16 contains a lower alcohol. According to the present embodiment, it is possible to improve the sinterability while suppressing the aggregation of the metal particles 12, and to obtain a sintered body that appropriately transmits visible light.

[0126] Moreover, it is preferable that the metal ink 10 further contains, as a dispersant, a phosphate ester compound having a higher molecular weight than the phosphate compound contained in the additive 17. According to this embodiment, aggregation of the metal particles 12 can be suitably suppressed. More specifically, if water-soluble polyhydric alcohol 14 is present in metal ink 10A or 10B during drying, the solvent 16 such as water or a lower alcohol will volatilize, increasing the content ratio of polyhydric alcohol 14, which may reduce the dispersion of the metal particles 12 in the film. In response to this, by adding a dispersant made of a phosphate compound with a high molecular weight, it is possible to maintain dispersibility even immediately before drying.

[0127] Moreover, it is preferable that the solvent 16 contains a high-boiling point solvent that is a liquid that contains one or more OH groups, has a boiling point of 150° C. or higher, and is poorly soluble or insoluble in water. According to this embodiment, the sinterability can be more appropriately improved.

[0128] Moreover, the metal particles 12 are copper, the solvent 16 contains water, the polyhydric alcohol 14 contains at least one polyhydric alcohol that contains two or more OH groups, is soluble in water and lower alcohols, and has a melting point of 30° C. or higher, and the additive 17 preferably has a molecular weight of 90 or more and 200 or less. According to this embodiment, it is possible to improve the sinterability while suppressing the aggregation of the metal particles 12, and to obtain a sintered body that appropriately transmits visible light.

[0129] Furthermore, the method for producing metal ink 10 according to the present disclosure involves mixing metal particles 12, a solvent 16, a polyhydric alcohol 14 that contains two or more OH groups and is soluble in water and lower alcohols, and an additive 17 that contains a phosphate compound that is soluble in water, to produce metal ink 10 that contains metal particles 12, solvent 16, polyhydric alcohol 14, and additive 17. According to the present disclosure, it is possible to produce metal ink 10 that can suitably improve sinterability while suppressing aggregation of metal particles 12, and it is also possible to obtain a sintered body that has appropriate transmittance to visible light.

[0130] Furthermore, the method of producing metal ink 10 according to the present disclosure preferably involves mixing metal particles 12, water as a solvent 16, polyhydric alcohol 14, and additive 17 to produce first metal ink 10A, which is a metal ink containing metal particles 12, water, polyhydric alcohol 14, and additive 17. According to the present disclosure, it is possible to produce first metal ink 10A that can suitably improve sinterability while suppressing aggregation of metal particles 12.

[0131] Furthermore, in the method for producing metal ink 10 according to the present disclosure, it is preferable to produce a first metal ink 10A that also contains organic solvent 18, which has a boiling point of 150°C or higher at atmospheric pressure and is miscible with water. According to the present disclosure, it is possible to produce a first metal ink 10A that can suitably improve sinterability while suppressing aggregation of metal particles 12. Furthermore, even if left for a long period of time, the metal ink 10 maintains sufficient anti-mildew properties, allowing it to be appropriately stored for a long period of time.

[0132] Furthermore, the method of producing metal ink 10 according to the present disclosure preferably involves mixing first metal ink 10A with a lower alcohol as solvent 16 to produce second metal ink 10B, which is a metal ink containing metal particles 12, water, a lower alcohol, a polyhydric alcohol 14, and an additive 17. According to the present disclosure, it is possible to produce second metal ink 10B that can suitably improve sinterability while suppressing aggregation of metal particles 12.

[0133] Furthermore, the method of producing metal ink 10 according to the present disclosure preferably involves mixing second metal ink 10B with a high-boiling point solvent, which is solvent 16 and is a liquid that contains one or more OH groups, has a boiling point of 150° C. or higher, and is poorly soluble or insoluble in water, to produce third metal ink 10C, which is a metal ink containing metal particles 12, water, a lower alcohol, a high-boiling point solvent, polyhydric alcohol 14, and additive 17. According to the present disclosure, it is possible to produce third metal ink 10C that can suitably improve sinterability while suppressing aggregation of metal particles 12.

[0134] Furthermore, the method for producing a sintered body according to the present disclosure forms a sintered body by heating the metal ink 10. According to the present disclosure, it is possible to suitably improve the sinterability while suppressing aggregation of the metal particles 12. The conditions for producing a sintered body using the metal ink 10 may be arbitrary, but it is preferable to heat the metal ink 10 in an oxidizing gas atmosphere, an inert gas atmosphere, or a reducing gas atmosphere.

[0135] The cleaning solution according to the present disclosure contains metal particles 12, a solvent 16, a polyhydric alcohol 14 that contains two or more OH groups and is soluble in water and lower alcohols, and an additive 17 that contains a water-soluble phosphoric acid compound. By using such a cleaning solution, it is possible to properly clean, for example, flow paths and nozzles that contain the metal ink 10 according to the present embodiment.

[0136] (Example) Next, examples will be described. Figures 3 to 45 are tables showing the content of components in the metal ink and the evaluation results for each example. Figures 46 to 50 are tables showing the content of components in the cleaning liquid and the evaluation results for each example. In the "Dispersant (phosphate ester compound)" column of each table, steareth-2-phosphate has an HLB value of 4-13 and a molecular weight range of 400-2500. Oleth-4-phosphate has an HLB value of 6-20 and a molecular weight range of 500-3000. (C12-C15) pareth-6-phosphate has an HLB value of 8-20 and a molecular weight range of 500-3000. (C12-C15) pareth-10-phosphate has an HLB value of 10-20 and a molecular weight range of 700-3000. Polyoxyethylene (18EO) alkyl (C13) ether phosphate has an HLB value of 13-20 and a molecular weight range of 1000-3500. Furthermore, polyoxyethylene alkyl (C8) ether phosphate monoethanolamine salt has an HLB value of 10 to 20 and a molecular weight range of 500 to 1500. Furthermore, polyoxyethylene (C18 unsaturated) ether phosphate sodium salt has an HLB value of 10 to 20 and a molecular weight range of 700 to 1500. Furthermore, CRODAFOS O3A has an HLB value of 6 to 20 and a molecular weight range of 400 to 2500.

[0137] (First Experimental Example) As a first experimental example, a metallic ink was produced and evaluated.

[0138] Example 1 In Example 1, copper phthalate was prepared as the starting material, copper carboxylate. Copper phthalate was placed in ion-exchanged water at room temperature and stirred with a stirring blade to prepare an aqueous dispersion of copper phthalate with a concentration of 30% by mass. Next, an aqueous solution of ammonium phthalate was added as a pH adjuster to the aqueous dispersion of copper phthalate to adjust the pH of the aqueous dispersion to 3. Next, the pH-adjusted liquid was heated to 50°C, and an aqueous solution of hydrazine monohydrate (diluted 2-fold) with an oxidation-reduction potential of -0.5V, which is 1.2 times the equivalent amount capable of reducing copper ions, was added to the pH-adjusted liquid as a reducing agent in a nitrogen gas atmosphere, and mixed uniformly using a stirring blade. Furthermore, in order to synthesize the target copper particles (metal particles), the mixture of the aqueous dispersion and the reducing agent was heated to a holding temperature of 70°C under a nitrogen gas atmosphere and held at 70°C for 2 hours. Furthermore, the mixture was dehydrated and desalted using a centrifuge to obtain an aqueous slurry of copper particles (copper powder concentration: 50% by mass).

[0139] 18 g of the obtained aqueous slurry of copper particles (metal particles) (copper powder concentration: 50% by mass), 36 g of an aqueous solution of 2,5-dimethyl-2,5-hexanediol (concentration: 5% by mass) as a polyhydric alcohol, 1.8 g of trimethyl phosphate (molecular weight: 140.08) as an additive, and 34.2 g of water were mixed to obtain 90 g of copper ink (metal ink) whose solvent was water. The masses and content ratios of each component of the copper ink in Example 1 are as shown in FIG. 3. The copper ink in Example 1 is an example of the first metal ink 10A of this embodiment.

[0140] (Examples 2 to 337, Comparative Examples 1 to 48) In Examples 2 to 337 and Comparative Examples 1 to 48, copper inks were produced in the same manner as in Example 1, except that the raw materials for the metal ink and the amounts of the raw materials added were as shown in FIG. 3 and thereafter. Comparative Examples 1 to 24 did not contain an additive containing a phosphoric acid compound. Comparative Examples 25 to 48 did not contain a polyhydric alcohol (a polyhydric alcohol containing two or more OH groups and soluble in water and lower alcohols).

[0141] (Evaluation method: dispersibility) Regarding the dispersibility of the copper ink (metallic ink) obtained in the examples and comparative examples, the above obtained metallic ink was thoroughly dispersed using an ultrasonic cleaner or the like, and then 10 g of the metallic ink was collected in a 20 ml glass sample container and left in a refrigerator overnight. After being left overnight, when the height from the bottom of the sample container to the liquid surface of the metallic ink was taken as 100, the height of the interface of the settling and separation of the metal particles in the metallic ink from the bottom of the container was 50 or more, which was evaluated as "○", and when it was less than 50, which was evaluated as "×". (Evaluation method: sinterability) In addition, the copper ink (metal ink) with dispersibility of "○" in the examples was applied to the center of a polyimide film with a thickness of 100 μm and a size of 50 mm×50 mm by an inkjet device to a size of 10 mm×10 mm and dried. After that, it was heated in a nitrogen atmosphere at 200° C. for 30 seconds to obtain a fired film of the metal ink with a thickness of about 1 to 3 μm. The sinterability was evaluated by observing the cross section of the fired film with an SEM (scanning electron microscope; Hitachi High-Tech Corporation, observation magnification 10,000 times). In the cross-sectional SEM image, when the ratio of voids in the film was 15% or less, the sinterability was evaluated as "◎", when it was more than 15% and less than 20%, the sinterability was evaluated as "○", when it was more than 20% and less than 30%, the sinterability was evaluated as "△", and when it was more than 30%, the sinterability was evaluated as "×". (Evaluation method: light transmittance) Furthermore, the copper ink (metal ink) with dispersibility of "○" in the examples was applied to the center of a soda glass with a thickness of 0.7 mm and a size of 50 mm x 50 mm by an inkjet device to a size of 20 mm x 20 mm, and then dried. Thereafter, in a high-temperature observation microscope SMT Scope SK-8000 (manufactured by Sanyo Seiko), the ink was heated at 300°C for 30 seconds (heating rate to peak temperature was 1°C / second) in air atmosphere (oxygen concentration of about 20%) using a halogen lamp heater (mainly emitting light with a spectral distribution having a peak wavelength in the visible to infrared region, more specifically light with a spectral distribution having a peak wavelength of 1 μm) manufactured by Ushio Electric Co., Ltd., which is used in the above device, to obtain a sintered body with a thickness of about 0.5 to 1 μm in which the copper particles were oxidized and sintered. The degree of transmittance of the obtained sintered body to light in the visible to infrared region was evaluated. In the evaluation of the degree of transmittance, the transmittance of the sintered body was measured using a Hitachi High-Tech Science ultraviolet-visible near-infrared spectrophotometer (UH4150) as a visible infrared spectrophotometer, with the data mode set to transmittance measurement (%T), the start wavelength set to 1200 nm, the end wavelength set to 300 nm, the scan speed set to 600 nm / min, and the sampling interval set to 1.00 nm. At this time, the average transmittance of 50% or more in the wavelength range of 600 nm to 1200 nm was evaluated as "good" for light transmittance, and the transmittance of less than 50% was evaluated as "x".

[0142] (Evaluation Results) The evaluation included dispersibility, sinterability, and light transmittance. In Examples 1 to 337, which contain additives including polyhydric alcohol and phosphoric acid compounds, the evaluations of dispersibility, sinterability, and light transmittance were all "○" or "◎", so that excellent sinterability was guaranteed while suppressing the aggregation of metal particles, and light transmittance was obtained in the sintered body obtained by heating in an air atmosphere. Therefore, it can be seen that the copper oxide sintered body (film) having excellent light transmittance can be applied to a tandem solar cell combined with a crystalline Si solar cell as an application. On the other hand, in Comparative Examples 1 to 24, which contain polyhydric alcohol but do not contain an additive made of a phosphoric acid compound, the dispersibility and sinterability were "○", but the light transmittance was "×". In addition, it can be seen that in Comparative Examples 25 to 48, which do not contain polyhydric alcohol, the aggregation of metal particles could not be suppressed and the metal particles settled. In addition, since the metal particles in the ink were aggregated and settled / separated, the ink could not be applied by an inkjet device, and the subsequent evaluation of sinterability and light transmittance could not be performed, so the evaluations of sinterability and light transmittance were "-". Furthermore, for Examples 52 to 337, which contain at least one of a lower alcohol, an organic solvent miscible with water or a high-boiling point solvent having a boiling point of 150°C or higher at atmospheric pressure, although the results are not shown in the table, the long-term storage stability of the metallic ink was also evaluated for mildew resistance according to the method described in "6. Paint testing" in the Japanese Industrial Standards (JIS Z 2911) (mildew resistance test: instead of a test piece, the metallic ink was used as a sample and placed in a hole with a diameter of 30 mm in the center of the culture medium). No hyphae were observed in the metallic ink, indicating good long-term storage stability.

[0143] (Second Experimental Example) As a second experimental example, metal inks and cleaning solutions corresponding to each metal ink were manufactured and evaluated.

[0144] (Examples 1 to 18, Comparative Examples 1 to 18) In Examples 1 to 18 and Comparative Examples 1 to 18, the metal inks and cleaning solutions used in the evaluations were prepared in the same manner as in Experimental Example 1. The masses and content ratios of each component in Examples 1 to 18 and Comparative Examples 1 to 18 are shown in Figures 46 to 50.

[0145] (Evaluation method: cleaning ability) The cleaning ability of the first metal ink A1 was evaluated using the cleaning solutions of Examples 1 to 3 and Comparative Examples 1 and 2; the cleaning ability of the first metal ink A2 was evaluated using the cleaning solutions of Examples 4 to 6 and Comparative Examples 3 and 4; the cleaning ability of the first metal ink A3 was evaluated using the cleaning solutions of Examples 7 to 9 and Comparative Examples 5 and 6; the cleaning ability of the second metal ink B1 was evaluated using the cleaning solutions of Examples 10 to 12 and Comparative Examples 7 to 10; the cleaning ability of the second metal ink B2 was evaluated using the cleaning solutions of Examples 13 to 15 and Comparative Examples 11 to 14; and the cleaning ability of the third metal ink was evaluated using the cleaning solutions of Examples 16 to 18 and Comparative Examples 15 to 18. The cleaning properties of the cleaning liquid obtained in the examples and comparative examples were evaluated according to the procedure shown below. 20 μl of metal ink was dropped using a micropipette into a glass bottle (9 ml) containing 1 ml of cleaning liquid previously measured using a micropipette. The dispersion state of the metal ink and the powder components in the metal ink immediately after the addition was visually confirmed. Immediately after the addition, the metal ink and the powder components in the metal ink that did not show any precipitation were rated as "◯: good", and those that showed precipitation were rated as "×: poor".

[0146] (Evaluation Results) For Examples 1 to 18, which contained metal particles, a solvent, a polyhydric alcohol, and a phosphate compound (additive), the cleaning ability was evaluated as "◯: good," whereas for Comparative Examples 1 to 18, which did not contain at least one of metal particles, a solvent, a polyhydric alcohol, and a phosphate compound (additive), the cleaning ability was evaluated as "×: poor," and the results showed that they were not suitable as cleaning fluids.

[0147] Although the embodiment of the present invention has been described above, the embodiment is not limited to the contents of this embodiment. The above-mentioned components include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-mentioned components can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the gist of the above-mentioned embodiment. [Explanation of symbols]

[0148] 10 Metallic Ink 12 Metal particles 14 Polyhydric alcohols 16 Solvents 17 Additives 18 Organic Solvents

Claims

1. Metal particles, which are copper particles; A solvent; a polyhydric alcohol containing two or more OH groups and soluble in water and a lower alcohol; an additive including a water-soluble phosphoric acid compound; Including, The molecular weight of the phosphoric acid compound is 100 or more and 200 or less. Metallic ink.

2. 2. The metallic ink according to claim 1, further comprising an organic solvent miscible with water and having a boiling point of 150° C. or higher at atmospheric pressure.

3. The metallic ink according to claim 1 or 2, wherein the additive is contained in an amount of 0.01% to 10% by mass with respect to the total amount of the metallic ink.

4. 3. The metallic ink of claim 1 or claim 2, wherein the additive comprises at least one of phosphoric acid, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, trimethyl phosphate, triethyl phosphate, diisopropyl phosphate, monoisopropyl phosphate, 2-aminoethyl dihydrogen phosphate, diisopropyl phosphite, and dimethyl phosphite.

5. The metal ink according to claim 1 or 2, wherein the polyhydric alcohol is contained in an amount of 0.01% to 20% by mass with respect to the total amount of the metal ink.

6. The metal ink according to claim 1 or 2, wherein the polyhydric alcohol has a melting point of 30° C. or higher.

7. The metal ink according to claim 2 , wherein the organic solvent is contained in an amount of 0.01% to 30% by mass with respect to the total amount of the metal ink.

8. The metallic ink of claim 2 or claim 7, wherein the organic solvent comprises at least one of a glycol ether and an aprotic polar solvent.

9. The metal ink according to claim 1 or 2, wherein the metal particles are contained in an amount of 1% to 50% by mass with respect to a total amount of the metal ink.

10. The metal ink according to claim 1 or 2, wherein the solvent comprises water.

11. The metallic ink according to claim 10 , further comprising a phosphate ester compound having a molecular weight higher than that of the phosphate compound contained in the additive as a dispersant.

12. The metallic ink of claim 10 , wherein the solvent comprises a lower alcohol.

13. The metal ink according to claim 12 , wherein the solvent comprises a high-boiling point solvent that contains one or more OH groups, has a boiling point of 150° C. or higher, and is a liquid that is poorly soluble or insoluble in water.

14. 3. The metal ink according to claim 1, wherein the solvent includes water, and the polyhydric alcohol includes at least one polyhydric alcohol that includes two or more OH groups, is soluble in water and a lower alcohol, and has a melting point of 30° C. or higher.

15. mixing metal particles, which are copper particles, a solvent, a polyhydric alcohol containing two or more OH groups and soluble in water and lower alcohols, and an additive containing a phosphoric acid compound that is soluble in water and has a molecular weight of 100 or more and 200 or less, to produce a metal ink containing the metal particles, the solvent, the polyhydric alcohol, and the additive; A method for producing metallic ink.

16. The method for producing a metal ink according to claim 15, further comprising mixing the metal particles, water as the solvent, the polyhydric alcohol, and the additive to produce a first metal ink, which is a metal ink containing the metal particles, water, the polyhydric alcohol, and the additive.

17. The method for producing a metal ink according to claim 16 , further comprising mixing an organic solvent that has a boiling point of 150° C. or higher at atmospheric pressure and is miscible with water to produce the first metal ink that also contains the organic solvent.

18. 18. The method for producing a metal ink according to claim 16 or 17, further comprising mixing the first metal ink with a lower alcohol as the solvent to produce a second metal ink, which is a metal ink containing the metal particles, water, the lower alcohol, the polyhydric alcohol, and the additive.

19. 19. The method for producing a metal ink according to claim 18, further comprising mixing the second metal ink with a high-boiling point solvent as the solvent, the high-boiling point solvent being a liquid that contains one or more OH groups, has a boiling point of 150°C or higher, and is poorly soluble or insoluble in water, to produce a third metal ink, which is a metal ink containing the metal particles, water, the lower alcohol, the high-boiling point solvent, the polyhydric alcohol, and the additive.

20. 3. A sintered body is formed by heating the metal ink according to claim 1 or 2. A method for manufacturing a sintered body.

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