Conductive ink or conductive paste and method for manufacturing the same

Abstract

The present invention provides a conductive ink or a conductive paste having high conductivity and excellent low-temperature sinterability. One aspect of the present invention relates to a conductive ink or a conductive paste comprising metal nanoparticles, water or a hydrophilic solvent having a vapor pressure of 10 hPa or more, and an additive solvent, the distance Ra between the Hansen solubility parameter of the metal nanoparticles and the Hansen solubility parameter of the additive solvent being in the range of 2.5 to 13, and the distance Rb between the Hansen solubility parameter of the water or the hydrophilic solvent and the Hansen solubility parameter of the additive solvent being 35 or less. Other aspects of the present invention relate to a method for producing a conductive ink or a conductive paste, and a method for selecting an additive solvent to be contained in a conductive ink or a conductive paste.

Description

Technical Field

[0001] This invention relates to conductive inks or conductive pastes and methods for manufacturing the same. Background Technology

[0002] As a method for manufacturing wiring or bonding materials for electronic circuits, inkjet printing and other printing methods are replacing the traditional etching methods. In the printing method, conductive ink or conductive paste is printed onto a substrate to form a pattern of the conductive ink or conductive paste. The substrate with the pattern is then heated to sinter the conductive ink or conductive paste, thereby forming the wiring or bonding material on the substrate. Conductive ink is typically in the form of a dispersion of conductive metal particles in a solvent. Conductive paste is typically in the form of a high-viscosity dispersion of a high content of conductive metal particles in a solvent. Water, hydrophilic solvents, and hydrophobic solvents can be used in conductive inks and conductive pastes. However, in recent years, considering the need to reduce environmental impact, there is a demand for conductive inks or conductive pastes using water or hydrophilic solvents.

[0003] For example, Patent Document 1 describes a metallic ink for coating a substrate to form a metallic pattern. This metallic ink contains a metal colloid and a dispersion medium. At least the region of the substrate where the metallic pattern is formed contains a thermoplastic resin. The distance Dc between the dispersion medium and the metal colloid, based on the Hansen solubility parameter, is 10 MPa. 0.5 Hereinafter, the distance Ds between the dispersion medium and the Hansen solubility parameter of the thermoplastic resin is 10 MPa. 0.5 above.

[0004] Patent document 2 describes a conductive ink characterized by containing silver colloidal particles, water, and diethylene glycol monoisobutyl ether, wherein the silver colloidal particles contain silver nanoparticles and a dispersant.

[0005] Patent document 3 describes a silver nanoparticle ink, characterized in that it contains silver nanoparticles, water, and a compound of formula (1): RO-(C3H6O2). n -H (where R represents a straight-chain or branched alkyl or alkenyl group with 8 to 22 carbon atoms having hydroxyl groups, and n is 1 to 20) represents a compound and a polyol, wherein the content of the compound represented by formula (1) is 0.1 to 2.9 by mass.

[0006] Patent document 4 discloses a conductive ink, which is a conductive ink composed of a solid component and a solvent. The solid component is mainly composed of metal colloidal particles composed of metal components and organic components. The conductive ink is characterized in that the solvent contains water and a polyol compound in the range of 1% to 40% by weight. The polyol compound is polyethylene glycol in the range of 600 to 1,000 by weight, and / or a polyol in the range of 4 to 6 carbon atoms and 2 to 3 hydroxyl groups.

[0007] Prior art literature

[0008] Patent Document 1: International Publication No. 2019 / 116978

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-204013

[0010] Patent Document 3: Japanese Patent Application Publication No. 2020-90561

[0011] Patent Document 4: Japanese Patent Application Publication No. 2008-214591 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Conductive inks and conductive pastes used in the fabrication of wiring or bonding materials for electronic circuits by printing methods require not only high conductivity but also excellent low-temperature sintering properties. However, conventional conductive inks and conductive pastes have several problems.

[0014] In recent years, water or hydrophilic solvents have been commonly used in conductive inks and pastes to reduce environmental impact. However, in such aqueous conductive inks and pastes, the dispersibility of metal particles is typically low. Therefore, in aqueous conductive inks and pastes, dispersion media and / or dispersants that improve the dispersibility of metal particles are sometimes added (e.g., Patent Documents 1-4). However, when using high-boiling-point dispersion media, even when sintering the conductive ink or paste at low temperatures, the dispersion media may not evaporate sufficiently. Similarly, when using non-volatile or low-volatility dispersants, the dispersant may remain in the sintered body of the conductive ink or paste. This can result in an increase in the volume resistivity and a decrease in conductivity of the sintered body. Furthermore, the slow evaporation of the dispersion media remaining in the sintered body may cause delamination of the sintered body, leading to reduced durability.

[0015] Therefore, the object of the present invention is to provide a conductive ink or conductive paste with high conductivity and excellent low-temperature sintering properties.

[0016] Methods for solving problems

[0017] The inventors have conducted various studies on methods for solving the aforementioned problems. They have discovered that by selecting water or a hydrophilic solvent with a predetermined vapor pressure and choosing the added solvent based on the Hansen solubility parameter in a conductive ink or conductive paste containing metal nanoparticles, water or a hydrophilic solvent, and an added solvent, it is possible to obtain a conductive ink or conductive paste with high conductivity and excellent low-temperature sintering properties. Based on the above insights, the inventors have completed this invention.

[0018] That is, the present invention includes the following technical solutions and implementation methods.

[0019] (Embodiment 1) A conductive ink or conductive paste comprising metal nanoparticles, water or a hydrophilic solvent having a vapor pressure of 10 hPa or higher, and additive solvents.

[0020] The distance Ra between the Hansen solubility parameter of the metal nanoparticles and the Hansen solubility parameter with added solvent is in the range of 2.5–13.

[0021] The distance Rb between the Hansen solubility parameter of water or hydrophilic solvent and the Hansen solubility parameter of the added solvent is less than 35.

[0022] (Embodiment 2) According to the conductive ink or conductive paste described in Embodiment 1 above, the content of the added solvent is in the range of 0.5% to 15% by mass relative to the total mass of the conductive ink or conductive paste.

[0023] (Embodiment 3) According to the conductive ink or conductive paste described in Embodiment 1 or 2 above, the metal nanoparticles have a protective agent, which is a compound containing nitrogen atoms or sulfur atoms and having strong adsorption to metals and hydrophilicity.

[0024] (Embodiment 4) In the conductive ink or conductive paste described in Embodiment 3 above, the protective agent is polyvinylpyrrolidone.

[0025] (Embodiment 5) In the conductive ink or conductive paste described in any one of Embodiments 1 to 4 above, the water or hydrophilic solvent is water, methanol, ethanol, propanol, tert-butanol or glycidol.

[0026] (Embodiment 6) In the conductive ink or conductive paste described in Embodiment 5 above, the water or hydrophilic solvent is water or ethanol.

[0027] (Embodiment 7) According to any one of the conductive inks or conductive pastes described in Embodiments 1 to 6 above, the added solvent is 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol, N,N-dimethylacetamide, tetrahydrofurfuryl alcohol, tetramethylurea, N,N-dimethylformamide, methylcyclohexanol, heptanol, hexanol or ethylene glycol, or a mixture thereof.

[0028] (Embodiment 8) The conductive ink or conductive paste described in Embodiment 7 above is provided with a solvent of 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol or N,N-dimethylacetamide.

[0029] (Embodiment 9) A method for manufacturing a conductive ink or conductive paste, which is a method for manufacturing the conductive ink or conductive paste described in any one of Embodiments 1 to 8 above, includes a material preparation step and a solvent selection step.

[0030] In the material preparation step, metal nanoparticles and water or a hydrophilic solvent with a vapor pressure of 10 hPa or higher are prepared.

[0031] In the solvent selection step, a solvent with a Hansen solubility parameter that is in the range of 2.5 to 13 between the distance Ra between the solvent and the metal nanoparticles and the distance Rb between the solvent and the Hansen solubility parameter of water or a hydrophilic solvent is less than 35 is selected.

[0032] (Embodiment 10) A method for selecting an additive solvent contained in a conductive ink or conductive paste, wherein the conductive ink or conductive paste comprises metal nanoparticles, water or a hydrophilic solvent having a vapor pressure of 10 hPa or higher, and an additive solvent, the method comprising an additive solvent selection step.

[0033] In the solvent selection step, a solvent with a Hansen solubility parameter that is in the range of 2.5 to 13 between the distance Ra between the solvent and the metal nanoparticles and the distance Rb between the solvent and the Hansen solubility parameter of water or hydrophilic solvent is less than 35 is selected.

[0034] The effects of the invention

[0035] According to the present invention, it is possible to provide a conductive ink or conductive paste having high conductivity and excellent low-temperature sintering properties. Detailed Implementation

[0036] The preferred embodiments of the present invention will now be described in detail.

[0037] <1: Conductive inks or conductive pastes>

[0038] One technical solution of the present invention relates to conductive inks or conductive pastes. The conductive inks or conductive pastes of this technical solution comprise metal nanoparticles, water or a hydrophilic solvent, and additive solvents.

[0039] [1-1: Metal Nanoparticles]

[0040] In the conductive ink or conductive paste of this technical solution, metal nanoparticles refer to any metal particles with a nanometer-scale particle size. The metal constituting the metal nanoparticles is not limited; examples include gold, silver, platinum, copper, nickel, iron, and cobalt. The metal constituting the metal nanoparticles can be an element of the metal elements exemplified above or an alloy thereof.

[0041] The particle size of the metal nanoparticles is preferably in the range of 2 to 2,000 nm, more preferably in the range of 2 to 1,000 nm, even more preferably in the range of 3 to 100 nm, and even more preferably in the range of 5 to 80 nm. In the prior art, conductive inks or conductive pastes containing metal particles with a particle size of several nm are known to improve low-temperature sintering properties. However, the manufacturing cost of such small-particle-size metal particles may be high. In contrast, as explained below, the conductive ink or conductive paste of this technical solution, by selecting water or a hydrophilic solvent with a predetermined vapor pressure and selecting the added solvent based on the Hansen solubility parameter, can exhibit excellent low-temperature sintering properties. Therefore, the conductive ink or conductive paste of this technical solution can exhibit excellent low-temperature sintering properties even when containing metal nanoparticles with particle sizes within the ranges exemplified above.

[0042] In embodiments of the conductive ink of this technical solution, the content of metal nanoparticles relative to the total mass of the conductive ink is typically 95% by mass or less, preferably in the range of 5% to 95% by mass, more preferably in the range of 5% to 50% by mass, and even more preferably in the range of 10% to 25% by mass. In embodiments where the content of metal nanoparticles relative to the total mass of the conductive ink is less than 1% by mass, the conductive ink of this technical solution is sometimes specifically described as a "conductive paste".

[0043] In the embodiments of the conductive paste of this technical solution, the content of metal nanoparticles relative to the total mass of the conductive paste is preferably in the range of 60-95% by mass, more preferably in the range of 70-95% by mass, and even more preferably in the range of 80-95% by mass.

[0044] In one embodiment, the metal nanoparticles may contain a protective agent. The protective agent is a compound possessing strong adsorption to metals and hydrophilicity, thereby substantially inhibiting the aggregation of metal nanoparticles. The protective agent is typically a compound containing nitrogen or sulfur atoms, possessing strong adsorption to metals and hydrophilicity. Preferred protective agents are polyvinylpyrrolidone (PVP), adenosine, dodecylamine, dodecyl mercaptan, or polyacrylic acid, more preferably PVP. In the conductive ink or conductive paste of this technical solution, the presence of a protective agent on the metal nanoparticles substantially inhibits the aggregation of the metal nanoparticles.

[0045] [1-2: Water or hydrophilic solvent]

[0046] In the conductive ink or conductive paste of this technical solution, the water or hydrophilic solvent typically has a vapor pressure of 10 hPa or higher. The vapor pressure of the water or hydrophilic solvent is preferably in the range of 10–150 hPa, more preferably in the range of 10–100 hPa, and even more preferably in the range of 10–70 hPa. If the vapor pressure of the water or hydrophilic solvent is lower than the aforementioned lower limit, it may not azeotropically react with the added solvent, and instead, the water or hydrophilic solvent may evaporate independently. In such cases, even if the conductive ink or conductive paste of this technical solution is sintered in a low-temperature region, the added solvent may remain, potentially leading to an increase in the volume resistivity of the sintered body and a decrease in conductivity. Furthermore, the slow evaporation of the added solvent remaining in the sintered body may cause peeling of the sintered body, resulting in reduced durability. If the vapor pressure of the water or hydrophilic solvent exceeds the aforementioned upper limit, the water or hydrophilic solvent may not evaporate sufficiently during sintering in a low-temperature region. In such cases, the volume resistivity of the sintered conductive ink or conductive paste may increase, resulting in decreased conductivity. Therefore, by using water or a hydrophilic solvent with a vapor pressure within the aforementioned range, the conductive ink or conductive paste of this technical solution can exhibit high conductivity and excellent low-temperature sintering properties.

[0047] Water or a hydrophilic solvent is preferably water, methanol, ethanol, propanol, tert-butanol, or glycidol, more preferably water or ethanol. By using the water or hydrophilic solvents exemplified above, the conductive ink or conductive paste of this technical solution can have high conductivity and excellent low-temperature sintering properties.

[0048] [1-3: Adding solvent]

[0049] In the conductive ink or conductive paste of this technical solution, the added solvent refers to a dispersion medium that improves the dispersibility of metal nanoparticles. The inventors have discovered that by using an added solvent with the distance Ra between the Hansen solubility parameter of the metal nanoparticles and the Hansen solubility parameter of the added solvent, and the distance Rb between the Hansen solubility parameter of water or a hydrophilic solvent and the Hansen solubility parameter of the added solvent, within a predetermined range, conductive inks or conductive pastes with high conductivity and excellent low-temperature sintering properties can be obtained.

[0050] The Hansen solubility parameter (HSP) is an indicator of the degree to which one substance can dissolve in another. HSP is a vector parameter that divides the Hildebrand solubility parameter into three cohesive components: dispersion force, interpolar force, and hydrogen bond force. In the HSP vector, the component corresponding to the dispersion force is represented as the dispersion term (δD), the component corresponding to the interpolar force is represented as the polar term (δP), and the component corresponding to the hydrogen bond force is represented as the hydrogen bond term (δH).

[0051] Since HSP is a vector, it is known that almost no pure substances have exactly the same value. Furthermore, a database has been constructed that includes the HSP values ​​of commonly used, well-known substances. Therefore, those skilled in the art can obtain the HSP value of a desired substance by referring to this database. Even for substances whose HSP values ​​are not included in the database, those skilled in the art can calculate the HSP value based on its chemical structure using computer software such as HSPiP (Hansen Solubility Parameters in Practice). These computer software programs also include a database containing the HSP values ​​of the well-known substances described above.

[0052] The distance between the HSP of one substance and the HSP of another substance represents the solubility of these substances. Generally, the smaller the distance between the HSPs of one substance and the HSPs of another substance, the higher the solubility of these substances. As mentioned above, the HSP is a vector composed of δD, δP, and δH. Therefore, the distance between the HSPs of one substance and the HSPs of another substance can be calculated as the distance between HSPs existing in a three-dimensional space composed of δD, δP, and δH (hereinafter also referred to as "HSP space"). When there are multiple other substances with the same degree of solubility relative to a reference substance, if the HSP values ​​of each substance are plotted in HSP space, the HSP values ​​of the other substances are plotted on the surface of a sphere centered on the HSP value of the reference substance (hereinafter also referred to as "Hansen's solubility sphere").

[0053] The distance Ra between the HSP of the metal nanoparticles and the HSP of the added solvent is typically in the range of 2.5 to 13. Ra is preferably in the range of 2.9 to 12.6. When Ra is within the range illustrated above, the wettability of the added solvent to the metal nanoparticles increases. Therefore, the dispersibility of the metal nanoparticles in the conductive ink or conductive paste of this invention increases. In this case, the liquid-phase sintering properties of the conductive ink or conductive paste of this invention can be improved in the low-temperature region. Therefore, by using an added solvent with Ra within the range illustrated above, the conductive ink or conductive paste of this invention can exhibit excellent low-temperature sintering properties.

[0054] The distance Rb between the HSP of water or hydrophilic solvent and the HSP of the added solvent is typically 35 or less. Rb is preferably in the range of 2.5 to 35, more preferably in the range of 2.6 to 32.5. When Rb exceeds the above upper limit, the water or hydrophilic solvent may not azeotropically react with the added solvent, and the water or hydrophilic solvent may evaporate separately. In such cases, even when the conductive ink or conductive paste of this technical solution is sintered in a low-temperature region, the added solvent will remain, potentially leading to an increase in the volume resistivity of the sintered body of the conductive ink or conductive paste and a decrease in conductivity. Furthermore, the slow evaporation of the added solvent remaining in the sintered body may cause peeling of the sintered body, resulting in a decrease in the durability of the sintered body. Therefore, by using an added solvent with Rb within the range illustrated above, the conductive ink or conductive paste of this technical solution can exhibit high conductivity and excellent low-temperature sintering properties.

[0055] The addition of solvents within the ranges exemplified above for the distances Ra and Rb of HSP can be selected by implementing the manufacturing method of the conductive ink or conductive paste described below, or by selecting the solvent.

[0056] The solvent content is preferably in the range of 0.5% to 15% by mass relative to the total mass of the conductive ink or conductive paste. If the solvent content is below the lower limit, the desired effect as a dispersion medium may not be fully realized. Furthermore, if the solvent content exceeds the upper limit, even if the conductive ink or conductive paste of this invention is sintered in a low-temperature region, the solvent will remain, potentially leading to an increase in the volume resistivity and a decrease in conductivity of the sintered conductive ink or conductive paste. Therefore, by using the solvent in the ranges illustrated above, the conductive ink or conductive paste of this invention can exhibit high conductivity and excellent low-temperature sintering properties.

[0057] The preferred solvents are 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol, N,N-dimethylacetamide, tetrahydrofurfuryl alcohol, tetramethylurea, N,N-dimethylformamide, methylcyclohexanol, heptanol, hexanol, or ethylene glycol, or mixtures thereof, more preferably 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol, or N,N-dimethylacetamide. By using the solvents exemplified above, the conductive ink or conductive paste of this technical solution can exhibit high conductivity and excellent low-temperature sintering properties.

[0058] Preferably, the conductive ink or conductive paste of this technical solution,

[0059] Contains metal nanoparticles with or without a protective agent, water, and 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol, or N,N-dimethylacetamide, or

[0060] It contains metal nanoparticles with or without protective agents, ethanol, and propylene glycol.

[0061] By including the components exemplified above, the conductive ink or conductive paste of this technical solution can possess high conductivity and excellent low-temperature sintering properties.

[0062] In various technical solutions of the present invention, the conductive ink typically comprises a dispersion containing metal nanoparticles having the characteristics described above, water or a hydrophilic solvent having the characteristics described above, and an added solvent having the characteristics described above. Additionally, in various technical solutions of the present invention, the conductive paste typically comprises a high-viscosity dispersion containing metal nanoparticles having the characteristics described above, water or a hydrophilic solvent having the characteristics described above, and an added solvent having the characteristics described above.

[0063] As described above, compared to the conductive ink of this technical solution, the conductive paste of this technical solution typically contains a high content of metal nanoparticles. Therefore, the conductive paste of this technical solution can have a higher viscosity than the conductive ink of this technical solution.

[0064] In addition to the components described above, the conductive ink or conductive paste of this technical solution may also contain a binder. By including a binder, the conductive ink or conductive paste of this technical solution can have the appropriate viscosity described below.

[0065] The viscosity of the conductive ink in this technical solution is typically in the range of 1 to 10,000 mPa·s, for example, 1 to 1,000 mPa·s, more specifically, 1 to 100 mPa·s, and particularly 1 to 20 mPa·s. It is known that conductive inks suitable for printing have a viscosity range of 1 to 20 mPa·s. Therefore, the conductive ink of this technical solution, having a viscosity within the aforementioned exemplary range, is suitable for printing.

[0066] The viscosity of the conductive paste in this technical solution is typically 10 Pa·s or higher, for example, in the range of 10 to 100 Pa·s. It is known that conductive pastes suitable for printing methods have a viscosity of 10 Pa·s or higher. Therefore, the conductive paste of this technical solution, having a viscosity within the aforementioned exemplary range, is suitable for printing methods.

[0067] The surface tension of the conductive ink in this technical solution is typically in the range of 20–40 mN / m, for example, 25–38 mN / m. It is known that the surface tension of conductive inks suitable for printing methods is in the range of 20–40 mN / m. When the surface tension of the conductive ink is less than the aforementioned lower limit, the wettability of the conductive ink becomes high, and it may be difficult to form fine patterns on the substrate during the manufacture of articles using this conductive ink. Conversely, when the surface tension of the conductive ink exceeds the aforementioned upper limit, the wettability of the conductive ink becomes low, and the pattern of the conductive ink may be interrupted on the substrate during the manufacture of articles using this conductive ink. Therefore, the conductive ink of this technical solution, with a surface tension within the aforementioned exemplary range, is suitable for printing methods.

[0068] The surface tension of the conductive paste in this technical solution, when measurable, generally only needs to be within the same range as the preferred range for the surface tension of the conductive ink described above. When the viscosity of the conductive paste in this technical solution is high, sometimes the surface tension cannot be measured. Even in such cases, as long as the viscosity of the conductive paste in this technical solution is within the preferred range described above, the conductive paste in this technical solution can be used in printing methods.

[0069] <2: Application of conductive inks or conductive pastes in finished products>

[0070] One embodiment of the present invention provides a conductive ink or conductive paste that exhibits high conductivity and excellent low-temperature sintering properties. Therefore, another embodiment of the present invention relates to articles obtained or available from the conductive ink or conductive paste of one embodiment of the present invention.

[0071] The article of this technical solution has a substrate and a sintered body on which a metal pattern is formed by a conductive ink or conductive paste according to one aspect of the present invention is disposed. In the article of this technical solution, the sintered body with the metal pattern formed by the conductive ink or conductive paste according to one aspect of the present invention is disposed as a wiring material or bonding material on the substrate. The conductive ink or conductive paste according to one aspect of the present invention has high conductivity and excellent low-temperature sintering properties. Therefore, the article of this technical solution can exhibit high conductivity.

[0072] The products described in this technical solution are not limited to specific examples; for instance, they may include antennas, touch panels, circuits, heaters, and solar cell electrodes. The exemplified products described above are obtained using the conductive ink or conductive paste of one of the technical solutions of this invention, and these products exhibit high conductivity.

[0073] The product of this technical solution can be manufactured using a method that includes a substrate preparation process, a pattern forming process, and a sintering process.

[0074] In the substrate preparation process, the substrate is prepared.

[0075] In the pattern forming process, a conductive ink or conductive paste according to one of the technical solutions of the present invention is coated onto the substrate to form a pattern of the conductive ink or conductive paste.

[0076] In the sintering process, a substrate with a pattern of conductive ink or conductive paste is heated to form a sintered body with a metallic pattern.

[0077] In the manufacturing method of the product according to this technical solution, the material and shape of the substrate can be appropriately selected according to the product. As described below, the sintering process in the manufacturing method of the product according to this technical solution is carried out in a low-temperature region. Therefore, the material of the substrate can be a material with a low heat resistance temperature.

[0078] In the manufacturing method of the article of this technical solution, the pattern forming process can be implemented by any method commonly used in this technical field, such as inkjet printing, screen printing, letterpress printing, gravure printing, reverse printing, micro-contact printing, immersion printing, spraying, bar coating, spin coating, dispenser method, casting method, flexographic method, gravure printing, injection molding, and brush coating.

[0079] In the manufacturing method of the product according to this technical solution, the heating temperature of the sintering process is preferably 50°C or higher, more preferably in the range of 50–100°C, and even more preferably in the range of 60–100°C. Furthermore, the heating time of the sintering process is preferably in the range of 5–120 minutes, more preferably in the range of 5–60 minutes. By performing the sintering process with the heating temperature and heating time within the above-described exemplary range, there is substantially no undesirable impact on the quality of the product, and the water or hydrophilic solvent contained in the conductive ink or conductive paste, as well as any added solvents, can substantially evaporate, forming a sintered body with a metallic pattern.

[0080] <3: Manufacturing method of conductive ink or conductive paste>

[0081] Another technical solution of the present invention relates to a method for manufacturing a conductive ink or conductive paste according to one of the technical solutions of the present invention. The manufacturing method of this technical solution includes a material preparation step and a solvent selection step. The manufacturing method of this technical solution may also include a dispersion step if necessary. The steps are described below.

[0082] [3-1: Material Preparation Process]

[0083] The manufacturing method of this technical solution includes a material preparation step of preparing metal nanoparticles and water or a hydrophilic solvent with a vapor pressure of 10 hPa or higher.

[0084] The metal nanoparticles, protective agent, and water or hydrophilic solvent prepared in this process have the characteristics described above. These metal nanoparticles, protective agent, and water or hydrophilic solvent can be prepared by purchasing commercially available products or by making their own.

[0085] In this process, when modulating metal nanoparticles, the metal nanoparticles can be modulated by heating and reducing an aqueous solution of the corresponding metal ions in the presence of a reducing agent.

[0086] In embodiments where the metal nanoparticles have a protective agent, the metal nanoparticles can be modulated by heating and reducing an aqueous solution of the corresponding metal ions in the presence of a protective agent and a reducing agent.

[0087] In the modulation of metal nanoparticles, aqueous solutions of metal ions, such as aqueous solutions of nitrates, cyanide salts, and acetates of the metal, can be used. Reducing agents, such as N,N-dimethylformamide (DMF), citric acid, formalin, ascorbic acid, oxalic acid, hydrogen peroxide, and hydrazine, can be used.

[0088] In the modulation of metal nanoparticles, the heating temperature is preferably 50°C or higher, more preferably in the range of 50–100°C, and even more preferably in the range of 60–90°C. Furthermore, the heating time is preferably in the range of 5–120 minutes, more preferably in the range of 10–40 minutes. By performing heating and reduction at the heating temperature and heating time within the ranges exemplified above, metal nanoparticles can be formed.

[0089] [3-2: Solvent Selection Process]

[0090] The manufacturing method of this technical solution includes a solvent selection step of selecting an added solvent in which the distance Ra between the Hansen solubility parameter of the metal nanoparticles and the Hansen solubility parameter of the added solvent is in the range of 2.5 to 13, and the distance Rb between the Hansen solubility parameter of water or hydrophilic solvent and the Hansen solubility parameter of the added solvent is less than 35.

[0091] The solvent selected for this process has the characteristics described above.

[0092] In this process, the HSP value of the metal nanoparticles can be determined, for example, by the following steps: A dispersion containing metal nanoparticles, such as a conductive ink or conductive paste according to one embodiment of the present invention, is centrifuged to obtain a precipitate of metal nanoparticles. The obtained precipitate of metal nanoparticles is added to various known solvents with known HSP values ​​to achieve predetermined concentrations. The dispersions of each known solvent are stirred and then allowed to stand. After standing, the dispersion is determined to be "1" when the metal nanoparticles are dispersed and "0" when they are precipitated. The HSP values ​​(δD, δP, and δH) of each known solvent contained in the dispersion determined to be "1" are plotted in HSP space to create Hansen's dissolution spheres. The creation of Hansen's dissolution spheres can be performed using computer software such as HSPiP. The HSP value of the silver nanoparticles is determined based on the center coordinates of the dissolution spheres.

[0093] In this process, the HSP values ​​of water or hydrophilic solvents and the added solvents can be obtained by referring to a database containing the HSP values ​​of known substances. If the HSP values ​​of the hydrophilic solvent and / or the added solvent are unknown, the HSP values ​​can be calculated from their chemical structures using computer software such as HSPiP. Alternatively, the HSP values ​​of such hydrophilic solvents and / or the added solvents can be determined using the same method as that used to determine the HSP values ​​of the metal nanoparticles described above.

[0094] In this process, the distance Ra can be calculated as the distance between the HSP of the metal nanoparticles existing in the HSP space and the HSP of the added solvent. Similarly, the distance Rb can be calculated as the distance between the HSP of water or a hydrophilic solvent existing in the HSP space and the HSP of the added solvent. The calculations of Ra and Rb can be performed using computer software such as HSPiP.

[0095] In this process, by calculating Ra and Rb using the steps described above, it is possible to select an added solvent that meets the predetermined conditions.

[0096] [3-3: Dispersion Process]

[0097] The manufacturing method of this technical solution may include, as needed, a dispersion step of dispersing metal nanoparticles in water or a hydrophilic solvent, and adding solvents.

[0098] In this process, the dispersion of metal nanoparticles can be carried out using conventional methods such as ultrasonic treatment.

[0099] By implementing the manufacturing method of this technical solution, which includes the steps described above, it is possible to manufacture a conductive ink or conductive paste according to one of the technical solutions of this invention.

[0100] <4: Methods for Selecting Added Solvents>

[0101] Another technical solution of the present invention relates to a method for selecting an additive solvent in a conductive ink or conductive paste according to one of the technical solutions of the present invention. The method of this technical solution includes a solvent selection step.

[0102] In the solvent selection process, a solvent with a Hansen solubility parameter that is in the range of 2.5 to 13 between the distance Ra between the solvent and the metal nanoparticles and the distance Rb between the solvent and the Hansen solubility parameter of water or hydrophilic solvent is less than 35 is selected.

[0103] This process can be carried out in the same way as the solvent selection process in the manufacturing method of one of the technical solutions of the present invention described above.

[0104] Example

[0105] The present invention will now be described in more detail using examples. However, the scope of the present invention is not limited to these examples.

[0106] <I: Manufacturing of Conductive Inks>

[0107] [I-1: Modulation of Metal Nanoparticles]

[0108] A silver nitrate aqueous solution (concentration: 400 mM) as a metal ion was added to a PVP aqueous solution (weight average molecular weight: 40,000 g / mol, concentration: 150 mM). Then, N,N-dimethylformamide (DMF) (concentration: 4,000 mM) was added, followed by a predetermined amount of purified water to achieve the aforementioned concentrations, thus preparing the reaction solution. The resulting reaction solution was placed in a 500 mL detachable flask and stirred with a magnetic stirrer at 90°C (reaction temperature) for 40 minutes (reaction time), thereby preparing a dispersion of silver nanoparticles with an average particle size of 25 nm, protected by PVP. A dispersion of silver nanoparticles without a protective agent was prepared following the same procedure as above, except that the PVP aqueous solution was removed. A dispersion of silver nanoparticles with tannic acid as a protective agent was prepared following the same procedure as above, except that a tannic acid aqueous solution (concentration: 150 mM) was used instead of the PVP aqueous solution.

[0109] [I-2: Choice of Solvent]

[0110] Solvent selection was performed using the commercially available computer software HSPiP (Hansen Solubility Parameters in Practice). From HSPiP's database of over 1200 solvents, only solvents with boiling points below 250°C were extracted. Solvents designated as highly toxic or containing halogens were removed from the extracted solvents to create a primary solvent group.

[0111] The HSP values ​​of the silver nanoparticles prepared in I-1 were determined according to the following steps. The dispersion of silver nanoparticles was centrifuged to obtain a precipitate of silver nanoparticles. The precipitate of silver nanoparticles was added to the solvents shown in Table 1 at a concentration of 0.1% by mass. The dispersions of each solvent were stirred at room temperature (25°C) for 10 minutes. After stirring, the dispersions were allowed to stand at room temperature (25°C) for 1 hour. After standing, the dispersions were classified as "1" for dispersed silver nanoparticles and "0" for precipitated silver nanoparticles. Using HSPiP, the HSP values ​​(δD, δP, and δH) of each solvent contained in the dispersions classified as "1" were plotted in HSP space to create Hansen's dissolution spheres. The HSP values ​​of the silver nanoparticles were determined based on the center coordinates of the dissolution spheres.

[0112] Table 1

[0113] No. solvent 1 acetone 2 benzyl alcohol 3 1-Butanol 4 Butyl acetate 5 Butyl butyrate 6 Dimethylacetamide 7 Dimethyl sulfoxide 8 ethanol 9 γ-Butyrolactone 10 hexane 11 Methyl benzoate 12 Methyl isobutyl ketone (MIBK) 13 N-Methylpyrrolidone (NMP) 14 Tetrahydrofuran (THF) 15 N-methylformamide

[0114] Based on the measured HSP values ​​of the silver nanoparticles and the HSP values ​​of the solvents contained in the primary group, the solvents were arranged in ascending order of the distance Ra between their HSP values. The first 85 solvents were extracted from the arranged solvents to form a secondary group of solvents. The solvents contained in the secondary group were then sorted into groups from 1 to 85 according to their arrangement.

[0115] Based on the HSP values ​​of 85 solvents sorted according to Ra and the HSP values ​​of water or hydrophilic solvents (such as ethanol or hexanediol), the solvents are arranged in order of increasing distance Rb between their HSP values. The arranged solvents are then ranked according to their order of arrangement, with scores ranging from 1 to 85.

[0116] Eighty-five solvents, sorted based on Ra and Rb, were arranged in ascending order of boiling point. The sorted solvents were then ranked according to their order of arrangement, from 1 to 85.

[0117] For the 85 solvents contained in the secondary group, the average values ​​of Ra, Rb, and boiling point were calculated in ascending order. The solvents were then arranged in ascending order of the calculated average values ​​to form a candidate group for adding solvents.

[0118] [I-3: Modulation of dispersions of metal nanoparticles]

[0119] The dispersion of metal nanoparticles was ultrafiltered at room temperature for 3 hours. Pure water was used as the washing solution during ultrafiltration. The conductivity of the filtration residue of the metal nanoparticles was below 20 μS / cm. The solvent (water) of the filtration residue of the metal nanoparticles was evaporated using an evaporator (BUCHI, rotary evaporator B-490) to obtain a dispersion of metal nanoparticles with a solid content of 20% by mass.

[0120] The dispersion of metal nanoparticles obtained according to the above steps was ultrasonically treated using an ultrasonic homogenizer (Hypershall Co., Ltd., UP400St) (time: 10 minutes, output power: 200W). An amount of solvent, calculated to achieve a predetermined final concentration, was added to the ultrasonically treated dispersion. For example, with a predetermined final concentration of 5% by mass, one-quarter the mass of the metal nanoparticles was weighed and added as solvent relative to the dispersion of metal nanoparticles having 20% ​​by mass solids. The solvent in the dispersion of metal nanoparticles with added solvent was evaporated using an evaporator (BUCHI Co., Ltd., rotary evaporator B-490) in a 40°C hot water bath to obtain a dispersion of metal nanoparticles having 15% by mass solids. In the above steps, it was confirmed beforehand that the added solvent would not evaporate. The obtained dispersion of metal nanoparticles was ultrasonically treated using an ultrasonic homogenizer (Hypershall Co., Ltd., UP400St) (time: 15 minutes, output power: 200W) to obtain a conductive ink as a dispersion of metal nanoparticles.

[0121] Table 2 shows the HSP values ​​of each component contained in the conductive inks of the examples and comparative examples. In the table, in the column for metal nanoparticles, "A" represents silver nanoparticles with PVP as a protective agent, "B" represents silver nanoparticles with tannic acid as a protective agent, and "C" represents silver nanoparticles without a protective agent.

[0122] Table 2

[0123]

[0124]

[0125]

[0126] <II: Evaluation of Conductive Inks>

[0127] [II-1: Viscosity Measurement of Conductive Inks]

[0128] Using a viscometer (TA Instalment Co., Ltd., DHR-2), at 23°C for 10 seconds... -1 The viscosity of conductive ink was determined under the specified conditions.

[0129] [II-2: Modulation of Sintered Films of Conductive Inks]

[0130] The obtained conductive ink was dropped into a sliding chamber. The sliding chamber was then placed in a constant temperature bath at 80°C for 60 minutes. This process allowed the conductive ink from the metal nanoparticles to sinter and form a film.

[0131] [II-3: Crack Observation of Sintered Films of Conductive Ink]

[0132] The cross-section of the sintered film of the conductive ink was observed using a scanning electron microscope to confirm the presence or absence of cracks.

[0133] [II-4: Resistivity Measurement of Sintered Films of Conductive Inks]

[0134] The volume resistivity of the sintered film of conductive ink was measured using a resistivity meter (Nitto Seiko Analite Co., Ltd., Rodster GX MCP-T700).

[0135] The composition and physical properties of the conductive inks of the examples and comparative examples, along with their evaluation results, are shown in Table 3. In the table, in the column for metal nanoparticles, "A" represents silver nanoparticles with PVP as a protective agent, "B" represents silver nanoparticles with tannic acid as a protective agent, and "C" represents silver nanoparticles without a protective agent. Additionally, in the column for cracks, "○" indicates that no cracks were observed, and "×" indicates that cracks were observed.

[0136]

[0137] As shown in Table 3, the conductive inks of the embodiments all have a viscosity in the range of 1 to 4 mPa·s. In contrast, the conductive inks of Comparative Examples 1, 3, and 4 all have a viscosity in the range of less than 1 mPa·s. Furthermore, the conductive ink of Comparative Example 5 has a viscosity of 270 mPa·s. The viscosity of conductive inks suitable for printing is in the range of 1 to 20 mPa·s; therefore, it can be seen that the conductive inks of the embodiments are suitable for printing.

[0138] No cracks were found in the sintered films of the conductive inks in the embodiments. In contrast, cracks were found in the sintered films of the conductive inks in Comparative Examples 1 and 2. This result indicates that the conductive inks of the embodiments exhibit excellent low-temperature sintering properties. Furthermore, the sintered films of the conductive inks of the embodiments all showed low volume resistivity below 20 μΩ·cm. In contrast, the sintered films of the conductive inks of the comparative examples all showed high volume resistivity.

[0139] Furthermore, the present invention is not limited to the above embodiments, but includes various modifications. For example, the above embodiments are described in detail for ease of understanding of the present invention and are not limited to having all the described structures. In addition, for a part of the structure of each embodiment, other structures may be added, deleted, and / or replaced.

Claims

1. A conductive ink or a conductive paste comprising metal nanoparticles, water or a hydrophilic solvent having a vapor pressure of 10 hPa or more, and an additive solvent, a distance Ra between a Hansen solubility parameter of the metal nanoparticles and a Hansen solubility parameter of the additive solvent is in a range of 2.5 to 13, a distance Rb between a Hansen solubility parameter of the water or the hydrophilic solvent and a Hansen solubility parameter of the additive solvent is 35 or less, a content of the additive solvent is in a range of 5 to 15 mass% with respect to a total mass of the conductive ink or the conductive paste, The viscosity of the conductive ink is in the range of 1 to 4 mPa-s at 23°C under the conditions of 10 s -1 -1. The viscosity of the conductive paste is in the range of 10 to 100 Pa-s at 23°C under the condition of 10 s -1 -1.

2. The conductive ink or the conductive paste according to claim 1, the metal nanoparticles having a protective agent, the protective agent being a compound containing a nitrogen atom or a sulfur atom, having a strong adsorption force to a metal and a hydrophilicity.

3. The conductive ink or the conductive paste according to claim 2, the protective agent being polyvinylpyrrolidone.

4. The conductive ink or the conductive paste according to claim 1, the water or the hydrophilic solvent being water, methanol, ethanol, propanol, t-butanol, or glycidol.

5. The conductive ink or the conductive paste according to claim 4, the water or the hydrophilic solvent being water or ethanol.

6. The conductive ink or the conductive paste according to claim 1, the additive solvent being 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol, N,N-dimethylacetamide, tetrahydrofurfuryl alcohol, tetramethylurea, N,N-dimethylformamide, methylcyclohexanol, heptanol, hexanol, or ethylene glycol, or a mixture thereof.

7. The conductive ink or the conductive paste according to claim 6, the additive solvent being 3-methoxy-3-methylbutanol, diacetone alcohol, ethyl lactate, propylene glycol, or N,N-dimethylacetamide.

8. A manufacturing method of a conductive ink or a conductive paste, which is a method of manufacturing the conductive ink or the conductive paste according to claim 1, comprising a material preparation step and an additive solvent selection step, in the material preparation step, metal nanoparticles and water or a hydrophilic solvent having a vapor pressure of 10 hPa or more are prepared, in the additive solvent selection step, an additive solvent having a Hansen solubility parameter with a distance Ra from a Hansen solubility parameter of the metal nanoparticles in a range of 2.5 to 13 and a distance Rb from a Hansen solubility parameter of the water or the hydrophilic solvent of 35 or less is selected.

9. A selection method of an additive solvent contained in a conductive ink or a conductive paste, which is a method of selecting the additive solvent contained in the conductive ink or the conductive paste according to claim 1, the conductive ink or the conductive paste comprising metal nanoparticles, water or a hydrophilic solvent having a vapor pressure of 10 hPa or more, and an additive solvent, the method comprising an additive solvent selection step, in the additive solvent selection step, an additive solvent having a Hansen solubility parameter with a distance Ra from a Hansen solubility parameter of the metal nanoparticles in a range of 2.5 to 13 and a distance Rb from a Hansen solubility parameter of the water or the hydrophilic solvent of 35 or less is selected.

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