Conductive inkjet ink

Abstract

To provide a technique to improve the dischargeability of conductive inkjet ink comprising metal powder composed of a metal with a specific gravity of 9 or more.SOLUTION: A conductive ink disclosed herein is used to produce electronic components. The conductive ink contains metal powder composed of a metal with a specific gravity of 9 or more, a binder resin, a cationic dispersant, and an organic solvent. Here, the conductive ink has a surface tension of 27 mN / m or more and 29 mN / m or less. An example of the binder resin is polyvinyl acetal resin. The polyvinyl acetal resin has a hydroxy group content of 22 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to conductive inkjet inks. [Background technology]

[0002] Inkjet printing has long been used as a printing method for drawing images such as patterns and characters onto a printing surface. Because inkjet printing allows for high-precision image printing at low cost and on demand, and causes minimal damage to the printing surface, its application in various fields is being explored. For example, in recent years, inkjet printing has been considered for use in forming conductive films that constitute conductive circuit patterns (electrodes, etc.) of electronic components. Using inkjet printing can reduce variations in the thickness of conductive films compared to screen printing. Therefore, it is expected that inkjet printing will reduce variations in the conductivity of conductive films and enable the printing of finer conductive circuit patterns.

[0003] In the manufacture of such electronic components, conductive inkjet inks (hereinafter also referred to as "conductive inks") are used, for example, in which inorganic powders containing metal particles are added as conductive materials. As an example of such conductive inks, Patent Document 1 discloses an ink containing nanometal powders such as silver and silver-copper alloys. Patent Document 2 discloses an ink containing metal oxide fine particles that are reduced by heat treatment, such as silver oxide, copper oxide, palladium oxide, nickel oxide, lead oxide, and cobalt oxide. In order to form a suitable conductive circuit pattern by inkjet printing, for example, the conductive ink must have low viscosity and a high concentration of inorganic powder. Patent Documents 1 and 2, mentioned above, propose techniques for obtaining these inkjet suitability requirements.

[0004] Furthermore, in conductive inks, stable dispersion of inorganic powders within the ink is required to ensure ejection during printing and conductivity after printing. For example, Patent Document 3 discloses a technique for improving the dispersibility of solid fine particles on which acidic and basic sites are mixed on the surface, by adding a first dispersant having only either an acidic adsorbent group or a basic adsorbent group, and a second dispersant having both an acidic adsorbent group and a basic adsorbent group.

[0005] Furthermore, in conductive inks, it is desirable to reduce variations in the thickness of the conductive film from the viewpoint of reducing variations in the conductivity of the conductive film and realizing fine conductive circuit patterns. For example, Patent Document 4 discloses the addition of an organic solvent that increases surface tension in order to reduce the wetting spread of a spacer particle dispersion printed by an inkjet device. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2008-513565 [Patent Document 2] Japanese Patent Publication No. 2012-216425 [Patent Document 3] Japanese Patent Publication No. 2015-62871 [Patent Document 4] Japanese Patent Publication No. 2008-111985 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, conductive materials used in the manufacture of electronic components sometimes include metals with a specific gravity of 9 or higher, such as silver, gold, platinum, palladium, tungsten, and molybdenum. The inventors are considering forming these components by inkjet printing using a conductive ink containing metal powder composed of metals with a specific gravity of 9 or higher. Furthermore, the inventors want to achieve sufficient productivity (printing speed) for inkjet printing using conductive ink as wiring miniaturization progresses in semiconductor manufacturing.

[0008] In order to achieve sufficient productivity in inkjet printing using conductive ink, it is desirable to increase the number of ejections per unit time, for example. For instance, the volume of each drop ejected from the nozzle of an inkjet head is set for each head. Therefore, by increasing the ejection frequency from the inkjet head, a large number of drops can be ejected stably, thereby achieving high productivity. Commercially available inkjet heads in recent years allow the ejection frequency to be set to, for example, a maximum of 20kHz to 50kHz. For this reason, it is considered desirable for various heads to be able to eject at a frequency of around 20kHz.

[0009] However, in conductive inks containing metal powder composed of metals with a specific gravity of 9 or higher, the metal powder is prone to aggregation and sedimentation. If the particle size of the metal powder changes due to aggregation and sedimentation, there is a risk of clogging of the inkjet nozzle. In this regard, for example, if the surface tension of the conductive ink is reduced, the ink will quickly fill the nozzle surface (refill) after the ink is ejected from the nozzle of the print head, making it suitable for higher ejection frequencies. On the other hand, when the surface tension is reduced, it is difficult to maintain the dispersibility of the metal powder in the conductive ink. Therefore, conventionally, there were no conductive inks with reduced surface tension that could handle ejection at frequencies of 20 kHz or higher.

[0010] Therefore, the present invention has been made in view of the above circumstances, and its main objective is to provide a technology for improving the ejection performance of conductive inkjet ink containing metal powder composed of a metal with a specific gravity of 9 or higher. [Means for solving the problem]

[0011] The conductive inkjet ink disclosed herein is used in the manufacture of electronic components. This conductive inkjet ink comprises a metal powder composed of a metal with a specific gravity of 9 or more, a binder resin, a cationic dispersant, and an organic solvent. The surface tension of the conductive inkjet ink is 27 mN / m or more and 29 mN / m or less. The binder resin contains polyvinyl acetal resin. The hydroxyl group content of the polyvinyl acetal resin is 22 mol% or less.

[0012] Conductive inks with this configuration have improved discharge performance because their surface tension is set within the range of 27 mN / m to 29 mN / m. Furthermore, by including polyvinyl acetal resin as a binder resin, and setting the amount of this polyvinyl acetal resin to 22 mol% or less, the aggregation and sedimentation of metal powders composed of metals with a specific gravity of 9 or higher can be suppressed in conductive inks having the above-mentioned surface tension range. Therefore, in addition to the improved discharge performance, the long-term stability of the conductive ink is also improved.

[0013] In one preferred embodiment of the conductive inkjet ink disclosed herein, the average particle size of the metal powder is 150 nm to 500 nm. With this configuration, both the ejection performance and the long-term stability of the conductive ink can be improved.

[0014] In another preferred embodiment of the conductive inkjet ink disclosed herein, the conductive ink has a viscosity of 4 mPa·s to 13 mPa·s. This configuration allows for better realization of the above effects. In addition to the above effects, it is also possible to suppress variations in the thickness of the conductive film.

[0015] In another preferred embodiment of the conductive inkjet ink disclosed herein, when the total amount of the conductive inkjet ink is 100 wt%, the content of the metal powder is 30 wt% or more and 70 wt% or less. According to such a configuration, in addition to the effect of improving the ejection property of the conductive ink and the effect of improving the stability over time, the productivity by inkjet printing can be improved.

[0016] [[ID=Q]]In another preferred embodiment of the conductive inkjet ink disclosed herein, the metal powder is composed of a high melting point metal having a melting point of 1200 °C or higher. Further, the high melting point metal is preferably tungsten powder or molybdenum powder. According to such a configuration, in addition to the above effects, the heat resistance of the conductive ink can be enhanced.

Brief Description of the Drawings

[0017] [Figure 1] It is a cross-sectional view schematically showing a stirring and pulverizing machine used for manufacturing the conductive ink. [Figure 2] It is an overall view schematically showing an example of an inkjet device. [Figure 3] It is a cross-sectional view schematically showing an inkjet head of the inkjet device in FIG. 2.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the technology disclosed herein will be described. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The content of the technology disclosed here can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. When a numerical range is described in this specification as "A to B (A and B are arbitrary numerical values)", it has the same general interpretation and means "A or more and B or less (including the range that exceeds A but is less than B)".

[0019] 1. Conductive Inkjet Ink The conductive inkjet inks disclosed herein may include, for example, (A) inorganic powder, (B) binder resin, (C) dispersant, and (D) organic solvent. The components contained in the conductive inkjet inks disclosed herein will be described below.

[0020] (A) Inorganic powder The inorganic powder is a material that constitutes the main component (base material) of the printed layer (conductive circuit pattern) after firing. In the conductive ink disclosed herein, the inorganic powder may contain, as a main component, a metal powder composed of a first metal M1 (hereinafter also referred to as "first metal powder"). The first metal powder consists, for example, of first metal particles composed of the first metal M1. The first metal particles are, for example, metal particles containing at least 95%, preferably 97%, and more preferably 99% or more of the first metal M1 element. Other elements that may be contained in the first metal particles are unavoidable impurities that may be introduced during the production of the first metal particles, etc., and are not particularly limited. Furthermore, depending on the type of first metal M1, oxides of the first metal M1 produced by oxidation by oxygen in the atmosphere may be present on the particle surface of the first metal particles.

[0021] The first metal M1 may be a metal with a specific gravity of 9 or higher (preferably 10 or higher, or 15 or higher). Examples of the first metal M1 include platinum group elements such as silver (Ag) (approximately 10.5), gold (Au) (approximately 19.3), platinum (Pt) (approximately 21.5), palladium (Pd) (approximately 12.0), rhodium (Rh) (approximately 12.4), iridium (Ir) (approximately 22.4), ruthenium (Ru) (approximately 12.4), and osmium (Os) (approximately 22.6); and chromium group elements such as tungsten (W) (approximately 19.3) and molybdenum (Mo) (approximately 10.2). The specific gravity of each metal is listed along with the metal name and element symbol. The first metal powder may consist of one type of first metal M1, or it may consist of two or more types of first metal M1.

[0022] Incidentally, some electronic components require plasma resistance (for example, electrostatic chucks). In such plasma-resistant electronic components, ceramic materials such as alumina and aluminum nitride are used as the base material. Furthermore, in the manufacturing process of plasma-resistant electronic components, for example, high-temperature firing at 1200°C or higher is performed to sinter the inorganic base material containing the ceramic material. In order to maintain the shape of the conductive circuit pattern during the high-temperature firing described above, high-melting-point metals with a melting point of 1200°C or higher, such as tungsten, palladium, platinum, molybdenum, cobalt, nickel, iron, and chromium (hereinafter also simply referred to as "high-melting-point metals"), are sometimes used as the conductive material for these plasma-resistant electronic components.

[0023] The first metal powder is preferably composed of a high-melting-point metal with a specific gravity of 9 or higher. By using such a high-melting-point metal as the first metal powder (conductive material), a conductive circuit pattern that can suitably maintain its shape even when exposed to a high-temperature environment can be formed. Suitable examples of such high-melting-point metals include tungsten, palladium, platinum, and molybdenum. Among these, tungsten is particularly advantageous because it has excellent chemical stability, a low volume resistivity ρV (Ω·cm), and is among the less expensive high-melting-point metals. Therefore, by using tungsten particles as the main component of the first metal powder, high-quality plasma-resistant electronic components (such as electrostatic chucks) can be manufactured inexpensively.

[0024] Furthermore, the inorganic powder may contain inorganic particles other than the first metal powder, as long as they do not hinder the effects of the technology disclosed herein. For example, the inorganic powder may contain a second metal powder. The second metal powder consists of second metal particles composed of a second metal M2 different from the first metal M1, for example. The second metal M2 is, for example, a metal with a specific gravity of less than 9. Examples of the second metal M2 include high-melting-point metals such as cobalt (Co), nickel (Ni), iron (Fe), and chromium (Cr). Other examples of the inorganic particles include ceramic particles such as ZrO2, Al2O3, Ag2O, Cu2O, PdO, NiO, and CoO. Since these ceramic particles have higher melting points than general metal particles, mixing them with the first metal powder can improve the heat resistance of the conductive circuit pattern.

[0025] When the inorganic powder contains inorganic particles other than the first metal powder, the content of the first metal powder, when the total inorganic powder is considered to be 100 wt%, is, for example, 70 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, even more preferably 95 wt% or more, and particularly preferably 99 wt% or more. As the content of the first metal powder in the inorganic powder increases, the effects such as stabilization of the conductive circuit pattern, reduction of volume resistivity ρV, and reduction of manufacturing costs become greater. On the other hand, there is a tendency for a decrease in stability over time due to aggregation and precipitation of the first metal powder to occur. However, the conductive ink disclosed herein contains a binder resin containing polyvinyl acetal resin as described later. Therefore, even when using inorganic powder containing 70 wt% or more of the first metal powder, a decrease in stability over time due to aggregation and precipitation of the first metal powder can be effectively prevented.

[0026] Furthermore, as will be described in more detail later, the conductive ink disclosed herein contains a cationic dispersant that improves dispersibility by adhering to the surface of the first metal powder. From the viewpoint of appropriately exhibiting the dispersibility-improving effect of such cationic dispersant, it is preferable that the first metal powder has a specific surface area of ​​a certain magnitude or more. For example, the specific surface area of ​​the first metal powder is 1.5 m². 2 Preferably 2.0 m2 More preferably 2.5m / g or more, 2 A value of 4.0 m² or more is particularly preferred. On the other hand, if the specific surface area of ​​the first metal powder becomes too large, aggregation of particles becomes more likely. From this viewpoint, the specific surface area of ​​the first metal powder is 4.0 m². 2 Preferably less than / g, and 3.5m 2 / g or less is more preferable, and 3.0m 2 A value of less than or equal to / g is particularly preferred. In this specification, "specific surface area" refers to the BET specific surface area measured according to the BET method specified in JIS Z 8830:2013.

[0027] Furthermore, the particle size of the first metal powder in the conductive ink is one of the factors that can affect ejection performance and long-term stability. For example, if the particle size of the first metal powder in the conductive ink is too large, the ejection port of the inkjet device may become clogged with the first metal powder, potentially leading to a significant decrease in ejection performance. For this reason, the average particle size of the first metal powder added to the inkjet ink is preferably 500 nm or less, more preferably 450 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 320 nm or less. On the other hand, if the particle size of the first metal powder becomes too small, a decrease in long-term stability due to aggregation of particles is more likely to occur. From this viewpoint, the average particle size of the first metal powder is preferably 150 nm or more, more preferably 200 nm or more, and even more preferably 220 nm or more. In this specification, "average particle size" refers to the average particle size based on the dynamic light scattering (DLS) method. The average particle size based on this DLS method can be measured in accordance with JIS Z 8828:2013.

[0028] The content of the first metal powder in the conductive ink is not particularly limited and can be adjusted as appropriate depending on the printing purpose (e.g., the conductive circuit pattern to be formed). For example, as the content of the first metal powder in the conductive ink increases, it becomes easier to form a conductive circuit pattern of a suitable thickness with fewer printing cycles. From this viewpoint, when the total conductive ink is considered to be 100 wt%, the content of the first metal powder is preferably 30 wt% or more, and more preferably 35 wt% or more. On the other hand, as the content of the first metal powder decreases, the stability over time and ejection performance tend to improve. From this viewpoint, when the total conductive ink is considered to be 100 wt%, the content of the first metal powder is preferably 70 wt% or less, more preferably 60 wt% or less, and particularly preferably 55 wt% or less.

[0029] (B) Binder resin The binder resin is an organic compound used to fix inorganic powder onto a substrate after inkjet printing of conductive ink onto the substrate. The conductive ink printed on the substrate is, for example, heated and dried on the substrate, and then subjected to a firing treatment. Therefore, it is preferable that the binder resin completely disappears (burns out) during the firing treatment. Furthermore, as will be described in more detail later, the conductive ink disclosed herein contains a cationic dispersant. Therefore, it is preferable that the binder resin does not react with the cationic dispersant to inhibit the dispersibility of the first metal powder by the dispersant.

[0030] The conductive ink disclosed herein contains a polyacetal resin as a binder resin. In addition to the function of fixing inorganic powder to a substrate as described above, polyvinyl acetal resin has the function of dispersing in an organic solvent and assisting the dispersant in suppressing the precipitation of the first metal powder. For this reason, polyacetal resin is suitable as a binder resin for the conductive ink disclosed herein.

[0031] Polyvinyl acetal resin is a resin produced, for example, by acetalizing a polyvinyl alcohol resin with an aldehyde. Examples of polyvinyl acetal resins include resins produced by acetalizing a polyvinyl alcohol resin with aldehydes having 1 to 5 carbon atoms, such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and amylaldehyde; or aromatic aldehydes, such as benzaldehyde and methylbenzaldehyde. Among these, polyvinyl butyral resin and polyvinyl formal resin can be preferably used.

[0032] Furthermore, in the conductive ink disclosed herein, the hydroxyl group content of the polyvinyl acetal resin is 22 mol% or less. This hydroxyl group content is, for example, the hydroxyl group content of the polyvinyl acetal resin when the hydroxyl group content of the polyvinyl alcohol resin before acetalization with an aldehyde is set to 100 mol%. The binder resin is required to have, for example, excellent solubility in organic solvents. When the hydroxyl group content of the polyvinyl acetal resin is 22 mol% or less, suitable hydrophobicity that is easily soluble in organic solvents can be achieved, for example. Therefore, the above-mentioned functions can be suitably exhibited, for example, in organic solvents. Furthermore, as shown in detail in the examples described later, as a result of the inventors' diligent research, it has been found that by using a polyvinyl acetal resin with a hydroxyl group content of 22 mol% or less, aggregation and sedimentation of the first metal powder in a conductive ink with a predetermined surface tension can be suppressed, thereby achieving stable and high dispersibility, and consequently, the long-term stability of the conductive ink can be improved.

[0033] The hydroxyl group content of the polyvinyl acetal resin may be, for example, less than 22 mol%, may be 21 mol% or less, or may be 20 mol% or less. Although not particularly limited, it is preferably one that can be moderately adsorbed on the first metal powder. The hydroxyl group of the polyvinyl acetal resin is, for example, preferably 10 mol% or more, preferably 15 mol% or more, more preferably 18 mol% or more, and even more preferably 19 mol% or more. Note that as the hydroxyl group content of the polyvinyl acetal resin, for example, the nominal value of the manufacturer or the like can be adopted. Alternatively, the measured value obtained by using the measurement method described in JIS K0070:1992 "Test Methods for Acid Value, Saponification Value, Ester Value, Iodine Value, Hydroxyl Value and Unsaponifiable Matter of Chemical Products" may be adopted.

[0034] The molecular weight of the polyvinyl acetal resin can be appropriately adjusted as long as it does not inhibit the effects of the technology disclosed herein. For example, if the average molecular weight of the polyvinyl acetal resin becomes too small, the function of assisting the precipitation suppression effect tends to decrease. Therefore, the average molecular weight of the polyvinyl acetal resin is 0.5×10 4 or more is appropriate. From the viewpoint of more preferably exerting the precipitation suppression effect, the average molecular weight is preferably 1.0×10 4 or more, more preferably 2.0×10 4 or more, even more preferably 2.5×10 4 or more, and particularly preferably 3.0×10 4 or more. On the other hand, if the average molecular weight of the polyvinyl acetal resin becomes too large, the viscosity of the conductive ink increases, so the ink ejection property may conversely decrease. From such a viewpoint, the upper limit of the average molecular weight of the polyvinyl acetal resin is appropriately 30×l0 4 or less. From the viewpoint of ensuring suitable ejection property, the upper limit of the above average molecular weight is preferably 20×10 4 or less, more preferably 10×10 4 or less, even more preferably 5.0×10 4 or less, and particularly preferably 4.0×10 4The following are particularly preferred. The average molecular weight of the polyvinyl acetal resin and the dispersant described later may be the average molecular weight on a weight basis, measured by, for example, gel permeation chromatography (GPC) and converted using a standard polystyrene calibration curve. For such measurement, for example, a GPC instrument (HLC-8320) manufactured by Tosoh Corporation may be used. Alternatively, the manufacturer's nominal value or a value calculated based on the chemical formula may be used.

[0035] The glass transition temperature of the polyvinyl acetal resin can be adjusted as appropriate, as long as it does not hinder the effects of the techniques disclosed herein. For example, from the viewpoint of forming a dry film with excellent adhesion, the glass transition temperature of the polyvinyl acetal resin is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. Such a glass transition temperature is, for example, 100°C or lower, preferably 90°C or lower, and more preferably 80°C or lower. In this specification, "glass transition temperature" refers to the glass transition temperature (Tg) based on differential scanning calorimetry (DSC). Alternatively, a nominal value from a manufacturer or the like may be used.

[0036] Furthermore, the binder resin content can be adjusted as appropriate, as long as it does not hinder the effects of the technology disclosed herein. For example, when the total organic vehicle of the conductive ink is 100 wt%, the binder resin content may be, for example, 0.3 wt% or more, preferably 0.5 wt% or more, and more preferably 0.7 wt% or more. On the other hand, the binder resin content may be, for example, 5 wt% or less, preferably 3 wt% or less, more preferably 2 wt% or less, and even more preferably 1.5 wt% or less. In this specification, "organic vehicle" refers to, for example, a mixture of binder resin, dispersant, and organic solvent in a conductive ink.

[0037] (C) Dispersant A dispersant is an organic compound that uniformly disperses inorganic particles in the ink and suppresses the aggregation and sedimentation of said inorganic particles. In the conductive ink disclosed herein, the dispersant includes a cationic dispersant.

[0038] Cationic dispersants are dispersants having cationic functional groups. Cationic dispersants adhere to the surface of first metal particles, for example, via cationic functional groups, causing steric hindrance. This suppresses aggregation of first metal particles and, consequently, improves the long-term stability of conductive ink. For example, if the first metal powder is composed of tungsten particles or molybdenum particles, the surface of such first metal particles becomes weakly acidic due to oxidation by oxygen in the atmosphere. Therefore, cationic dispersants easily adhere to the surface of such first metal particles. Furthermore, even if the first metal particles are composed of metal particles different from the above-mentioned metal particles, in other words, metal particles with fewer acid sites on their surface (for example, noble metal particles), cationic dispersants can still improve the long-term stability of conductive ink by adhering to the surface of the metal particles, as described above.

[0039] As the cationic dispersant, conventionally known cationic dispersants used for this type of application can be used without particular limitation. Examples of cationic dispersants include amine dispersants, imidazoline dispersants, and quaternary ammonium dispersants. Examples of amine dispersants include alkyl polyamine dispersants, polyalkylene polyamine dispersants, fatty acid amine dispersants, and polyester amine dispersants. Examples of imidazoline dispersants include alkylimidazolines. Note that cationic dispersants may be used alone or in combination of two or more types.

[0040] As the cationic dispersant for the conductive ink disclosed herein, an amine-based dispersant may be preferably used. The amine-based dispersant is, for example, an organic compound having an amine group in its molecule. Among these, a chain-like amine-based dispersant having an amine group at at least one end may be preferably used. Preferred examples of such amine-based dispersants include fatty acid amine-based dispersants and polyester amine-based dispersants. Although not particularly limited, the average molecular weight of such amine-based dispersants is, for example, 1 × 10⁻⁶. 3 ~5×10 4 It is preferable to set it to this. Specific examples of cationic dispersants include HypermerKD-1, HypermerKD-2, and HypermerKD-3 from Croda Japan Co., Ltd., and the Esream AD series (registered trademark) AD-508E from NOF Corporation.

[0041] Furthermore, the content of the cationic dispersant can be adjusted as appropriate, as long as it does not hinder the effects of the technology disclosed herein. For example, when the total organic vehicle of the conductive ink is 100 wt%, the content of the cationic dispersant is preferably 0.3 wt% or more, more preferably 0.5 wt% or more, and more preferably 0.7 wt% or more, from the viewpoint of suppressing the aggregation of first metal particles in the conductive ink. On the other hand, the content of the cationic dispersant is preferably 5 wt% or less, more preferably 3 wt% or less, more preferably 2 wt% or less, and even more preferably 1.5 wt% or less, from the viewpoint of forming a conductive film with appropriate conductivity in inkjet printing using the conductive ink.

[0042] Furthermore, when the total amount of dispersant contained in conductive ink is considered to be 100 wt%, the content of cationic dispersant should be set to 80 wt% or more, for example, 90 wt% or more is good, 95 wt% or more is preferable, and the closer to 100 wt% the better.

[0043] Furthermore, the dispersant may include a nonionic dispersant, provided that it does not hinder the effects of the technology disclosed herein. A nonionic dispersant is a dispersant that does not have a group that ionizes when dissolved in water. Nonionic dispersants are less likely to adhere to the surface of first metal particles compared to cationic dispersants. However, for example, if a cationic dispersant having a cationic functional group (e.g., an amine group) at one end adheres to the surface of first metal particles, a nonionic dispersant may adhere to the other end of the cationic dispersant. In this case, the steric hindrance can be strengthened by the cationic dispersant formed on the surface of the first metal particles. Therefore, aggregation of the first metal powder due to the dispersant can be suppressed.

[0044] Regarding nonionic dispersants, conventionally known nonionic dispersants used in this type of application can be used without particular restriction. Examples of such nonionic dispersants include ether-based dispersants, ester-based dispersants, ether-ester-based dispersants, and nitrogen-containing dispersants. Specific examples of nonionic dispersants include Hypermer KD-13 and Hypermer KD-14 from Croda Japan Co., Ltd., and Synperonic PE / L101 from Croda Corporation.

[0045] The content of the nonionic dispersant can be adjusted as appropriate, as long as it does not hinder the effects of the technology disclosed herein. When the total amount of dispersant contained in the conductive ink is considered to be 100 wt%, the content of the nonionic dispersant is appropriately set to, for example, 20 wt% or less, preferably 10 wt% or less, and more preferably 5 wt% or less.

[0046] (D) Organic solvents The organic solvent can be any conventionally known organic solvent used in this type of application, as long as it does not hinder the effects of the technology disclosed herein. From the viewpoint of preventing rapid drying during the drying process and forming a stable dried film, the boiling point of the organic solvent is preferably, for example, 140°C to 260°C. Furthermore, from the viewpoint of improving the discharge performance of the conductive ink, the viscosity of the organic solvent is preferably, for example, 0.5 mPa·s to 20 mPa·s. In addition, in order to set the surface tension of the conductive ink, which will be described later, within a predetermined range, the surface tension of the organic solvent is not particularly limited, but is preferably, for example, 26 mN / m to 30 mN / m (preferably 27 mN / m to 29 mN / m). When mixing and using multiple types of organic solvents, the viscosity and surface tension of the mixed solvent can be set within the above range. The viscosity and surface tension of the organic solvent can be, for example, the nominal values ​​from the manufacturer, or measured values ​​obtained using commercially available measuring devices (see the test examples described later).

[0047] Suitable examples of such organic solvents include glycol acetates, glycol ethers, and aliphatic monoalcohols. Examples of glycol acetates include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether acetate, butyl monoglycol acetate (BMGAC), butyl diglycol acetate (BDGAC), and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate. Examples of glycol ethers include diethylene glycol dibutyl ether and diethylene glycol butyl methyl ether. Examples of aliphatic monoalcohols include linear or branched aliphatic alcohols such as methanol, ethanol, propanol, isopropanol, butanol, n-amyl alcohol, hexanol, heptanol, n-octanol, 2-ethylhexanol, isooctanool, nonanol, decanol, isoundecanol, lauryl alcohol, cetyl alcohol, and stearyl alcohol. The organic solvent may be a single type or a mixed solvent of two or more types.

[0048] While not particularly limited, from the viewpoint of improving the discharge performance of conductive ink, when the total organic vehicle is considered to be 100 wt%, the content of the organic solvent is, for example, 80 wt% or more, preferably 90 wt% or more, and more preferably 95 wt% or more.

[0049] (E) Other ingredients The conductive ink disclosed herein may further contain known additives that can be used in inkjet inks (e.g., conductive inkjet inks), to the extent that they do not impair the effects of the technology disclosed herein. Examples of such additives include the polyvinyl acetal resin described above, and resin components excluding the dispersant described above. Furthermore, the conductive ink disclosed herein may contain additives other than such resin components. The types and amounts of such additives can be appropriately changed based on conventionally known common technical knowledge and do not characterize the technology disclosed herein. Therefore, a detailed explanation is omitted here.

[0050] <Physical properties of conductive ink> The surface tension of the conductive ink disclosed herein is 27 mN / m or more and 29 mN / m or less. By setting the surface tension of the conductive ink within this range, for example, the ejection performance of the conductive ink can be improved. By using such a conductive ink, for example, inkjet printing with an ejection frequency of 20 kHz or higher can be suitably performed. The higher the surface tension of the conductive ink, the less likely the conductive ink is to spread on the substrate after ejection. Also, the higher the surface tension of the conductive ink, the less likely the first metal powder is to settle. For this reason, by setting the surface tension of the conductive ink to 27 mN / m or more (for example, exceeding 27.0 mN / m, preferably 27.1 mN / m or more), it is possible to suppress variations in the thickness of the conductive film and suppress the settling of the first metal powder. On the other hand, the lower the surface tension of the conductive ink, the more the inkjet ejection performance can be improved. From this viewpoint, the surface tension of the conductive ink is preferably less than 29.0 mN / m, and more preferably 28.5 mN / m or less. The surface tension of the conductive ink was measured using a commercially available static surface tension measuring device, as described in the test examples below.

[0051] The viscosity of the conductive ink is not particularly limited, as long as it can realize the effects of the technology disclosed herein. The lower the viscosity of the conductive ink, the less likely it is to adhere to the ejection port of the inkjet device, and the ejection performance of the conductive ink can be improved. From this viewpoint, the viscosity of the conductive ink is preferably 30 mPa·s or less, more preferably 25 mPa·s or less, and more preferably 20 mPa·s or less. On the other hand, the higher the viscosity of the conductive ink, the less likely the ejected ink is to spread, and the occurrence of variations in the thickness of the conductive film can be suppressed. From this viewpoint, the viscosity of the conductive ink is preferably more than 1 mPa·s, more preferably 2 mPa·s or more, and more preferably 3 mPa·s or more. In one preferred embodiment, the viscosity of the conductive ink is 4 mPa·s or more and 13 mPa·s or less. The viscosity of the ink is a measured value obtained using a commercially available B-type viscometer, as described in the test examples below.

[0052] 2. Preparation of conductive ink Next, the procedure for preparing (manufacturing) the conductive ink disclosed herein will be described. The conductive ink disclosed herein is prepared by mixing the above-mentioned components and then crushing and dispersing the inorganic powder. Figure 1 is a schematic cross-sectional view showing a stirring and grinding machine used in the manufacture of the conductive ink. The following description is merely an example of a means for preparing the conductive ink disclosed herein and is not intended to limit the technology disclosed herein.

[0053] In manufacturing the conductive ink disclosed herein, first, a slurry (including paste and suspension), which is a precursor to the ink, is prepared by weighing and mixing the above-mentioned components. Then, the conductive ink is prepared by stirring the slurry and crushing the inorganic powder using a stirring and grinding machine 100 as shown in Figure 1. Specifically, after adding fine crushing beads (for example, zirconia beads with an average particle size of 10 μm to 50 μm) to the slurry, the slurry is supplied from the supply port 110 into the stirring container 120. Inside the stirring container 120 is a shaft 134 having a plurality of stirring blades 132. One end of the shaft 134 is attached to a motor (not shown), and by operating the motor and rotating the shaft 134, the plurality of stirring blades 132 stir the slurry while sending it downstream in the liquid supply direction D. During this stirring, the inorganic particles, including the first metal particles, are crushed by the crushing beads, and the finely pulverized inorganic powder is dispersed in the slurry.

[0054] The slurry, which has been sent downstream in the liquid delivery direction D, then passes through the filter 140. As a result, inorganic particles that have not been atomized and crushing beads are collected in the filter 140, and conductive ink with sufficiently dispersed inorganic powder is discharged from the outlet 150. In this process, by adjusting the pore size of the filter 140, the average particle size of the crushing beads, etc., the "average particle size of the inorganic powder (e.g., first metal powder)" and the "specific surface area of ​​the inorganic powder (e.g., first metal powder)" in the conductive ink can be adjusted to a desired range.

[0055] 3. Applications of conductive inks Next, the applications of the conductive ink disclosed herein will be described. The conductive ink disclosed herein is used in the manufacture of electronic components. In this specification, "used in electronic components" includes not only the method of directly printing the conductive ink disclosed herein onto the surface of an inorganic substrate, but also the method of indirectly adhering the conductive ink to the surface of an inorganic substrate via an intermediate material such as transfer paper.

[0056] (1) Print Figure 2 is a schematic overall view showing an example of an inkjet device. Figure 3 is a schematic cross-sectional view showing the inkjet head of the inkjet device in Figure 2.

[0057] The conductive ink disclosed herein is printed onto the surface of a printing target by an inkjet device 1 as shown in Figure 2. The material and shape of the inorganic substrate W to be printed are not particularly limited, and any substrate that can be used as a substrate for general electronic components can be used without particular restriction. When using platinum powder, palladium powder, tungsten powder, or molybdenum powder, which are composed of high-melting-point metals, as the first metal powder of the conductive ink disclosed herein, an inorganic substrate W that has been subjected to high-temperature firing at 1200°C or higher (for example, an alumina substrate or an aluminum nitride substrate) can be used particularly preferably.

[0058] Next, the structure of the inkjet device 1 shown in Figure 2 will be described. This inkjet device 1 includes an inkjet head 10 that stores conductive ink. This inkjet head 10 is housed inside a printing cartridge 40. The printing cartridge 40 is inserted through a guide shaft 20 and is configured to reciprocate along the axial direction X of the guide shaft 20. Although not shown in the figure, this inkjet device 1 also includes a moving mechanism for moving the guide shaft 20 in the vertical direction Y. This allows the inkjet device 1 to eject conductive ink to a desired position on the inorganic substrate W.

[0059] The inkjet head 10 shown in Figure 2 uses, for example, a piezo-type inkjet head as shown in Figure 3. This piezo-type inkjet head 10 is provided with a storage section 13 for storing ink within a case 12, and the storage section 13 communicates with an ejection section 16 via a liquid delivery path 15. The ejection section 16 is provided with an ejection port 17 that is open to the outside of the case 12, and a piezo element 18 is positioned opposite the ejection port 17. In this inkjet head 10, the ink in the ejection section 16 is ejected from the ejection port 17 toward the inorganic substrate W (see Figure 2) by vibrating the piezo element 18. At this time, the conductive ink disclosed herein achieves excellent long-term stability and excellent ejection performance, so it can be ejected with high precision over a long period of time. For this reason, with the conductive ink disclosed herein, it is possible to print very precise patterns (images) on the surface of the inorganic substrate W. Furthermore, the conductive ink disclosed herein supports ejection at frequencies of 20 kHz or higher. Therefore, the conductive ink disclosed herein enables high productivity in pattern printing on the surface of an inorganic substrate W.

[0060] (2) Drying treatment Next, the inorganic substrate W to which the ink is attached is subjected to a drying treatment by heating it at a predetermined temperature. This removes the organic solvent from the ink and forms a dry film on the inorganic substrate W. The conductive ink disclosed herein contains the binder resin described above. Therefore, such a conductive ink is better suited to fixing the dry film to the surface of the inorganic substrate W. It is preferable to set the heating temperature in the drying treatment to a temperature at which the organic solvent is removed and sintering of the inorganic powder does not occur (for example, 50°C to 150°C, preferably 60°C to 80°C).

[0061] (3) Firing The manufacturing method disclosed herein includes firing the inorganic substrate W after the formation of a dried film. This burns away the organic components, including the binder resin, and sintersects the inorganic powder, including the first metal powder, to adhere to the surface of the inorganic substrate W. As a result, an electronic component having a conductive circuit pattern mainly composed of the first metal is manufactured. The firing temperature can be appropriately set depending on the type of inorganic powder (e.g., the first metal powder) contained in the conductive ink. For example, the firing temperature can be set to 500°C to 2000°C. Furthermore, if the first metal powder is composed of a high-melting-point metal, firing can be performed under conditions such that the maximum firing temperature is 1200°C or higher (preferably 1200°C to 2000°C, more preferably 1300°C to 1600°C). In this case, since the first metal powder does not melt during firing, it is possible to prevent the shape of the conductive circuit pattern from collapsing during firing. Therefore, an electronic component having a very precise conductive circuit pattern can be reliably formed.

[0062] [Example Test] The following describes examples of tests relating to the technology disclosed herein. These test examples are not intended to limit the scope of the technology disclosed herein. Unless otherwise specified, percentages in the following test examples are based on weight.

[0063] Evaluation of the solubility of binder resins First, the solubility of binder resins B1 to B10 in organic solvents was evaluated. The types of binder resins are as follows: <Polyvinyl acetal resin> • Binder resin B1: Sekisui Chemical Co., Ltd., "BL-5Z" • Binder resin B2: Sekisui Chemical Co., Ltd., "SV-22" • Binder resin B3: Sekisui Chemical Co., Ltd., "SV-17" • Binder resin B4: Manufactured by Kuraray Co., Ltd., "Mowital B 30HH" • Binder resin B5: Manufactured by Sekisui Chemical Co., Ltd., "BL-S" • Binder resin B6: Manufactured by Sekisui Chemical Co., Ltd., "KS-1" • Binder resin B7: Manufactured by Sekisui Chemical Co., Ltd., "BL-1H" • Binder resin B8: Manufactured by Sekisui Chemical Co., Ltd., "BH-S" <Acrylic resin> • Binder resin B9: Manufactured by Mitsubishi Chemical Corporation, "BR-105" • Binder resin B10: Manufactured by Mitsubishi Chemical Corporation, "MB7991"

[0064] Diethylene glycol butyl methyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., "7382-32-3") was used as the organic solvent. Each binder resin was mixed into the organic solvent to a concentration of 1% of the total volume, obtaining a mixture of the organic solvent and each binder resin. The mixture was stirred using a commercially available stirrer (rotation speed: 500 rpm, mixing time: 2 hours). After stirring, the solubility of each binder resin in the organic solvent was evaluated visually. The results are shown in Table 1. In the "Solubility" column of Table 1, "Y" is indicated if the binder resin dissolved in the organic solvent, and "N" is indicated if the binder resin did not dissolve in the organic solvent. Table 1 also includes the hydroxyl group content and average molecular weight of each binder resin. These hydroxyl group content and average molecular weight are the nominal values ​​from each manufacturer.

[0065] [Table 1]

[0066] As shown in Table 1, binder resins B1-B5, B9, and B10 were confirmed to be soluble in organic solvents. On the other hand, binder resins B6 and B7 did not dissolve in organic solvents. Binder resin B8 dissolved in organic solvents, but stringing was observed (*1). For this reason, in the following conductive ink preparation and other tests, binder resins B1-B5, B9, and B10 were used, and binder resins B6-B8 were not used.

[0067] Preparation of conductive ink -Examples 1-22- Twenty-two types of conductive inks (Examples 1-22) containing metal powder, binder resin, cationic dispersant, and organic solvent were prepared. First, the metal powder and organic vehicle (organic solvent, binder resin, and cationic dispersant) were mixed in weight ratios of 53:47 (Examples 1-16), 30:70 (Examples 17, 18), 45:55 (Example 19), and 36:64 (Examples 20-22) to prepare a slurry. The slurry was subjected to a crushing and dispersion treatment using crushing beads (zirconia beads with an average particle size of 30 μm) (rotation speed: 1500 rpm, mixing time: 4 hours), and conductive ink was obtained by filter filtration under pressure. The proportions of each component in the organic vehicle (the proportions of the organic solvent, binder resin, and cationic dispersant, respectively, when the total organic vehicle is considered 100%) are shown in Table 3. The following details the materials used in the preparation of the conductive ink.

[0068] (metal powder) In Examples 1-19, the metal powder has a specific surface area of ​​2.9 m². 2 Tungsten (W) powder with a specific gravity of 19 / g was used. In Examples 20-22, molybdenum powder with a specific gravity of 10 was used as the metal powder.

[0069] (Organic solvents) As organic solvents, the following organic solvents S1 to S7 were used individually or in combination of two or more. Table 3 shows the composition ratio (%) of the types of organic solvents used in each example, with the total organic solvents being 100%. • Organic solvent S1: Diethylene glycol butyl methyl ether, manufactured by Tokyo Chemical Industry Co., Ltd., "7382-32-3" • Organic solvent S2: Diethylene glycol dibutyl ether, manufactured by Tokyo Chemical Industry Co., Ltd., "112-73-2" • Organic solvent S3: Butyl monoglycol acetate (BMGAC), manufactured by Daicel Corporation, "112-07-2" • Organic solvent S4: Propylene glycol monomethyl ether acetate (PGMEA), Hayashi Pure Chemical Industries, Ltd., "108-65-6" • Organic solvent S5: Butyl diglycol acetate (BDGAC), manufactured by Daicel Corporation, "124-17-4" • Organic solvent S6: 2,2,4-trimethyl-1,3-pentanediol 1-monoisobutyrate (NG-120), "25265-77-4" • Organic solvent S7: Methyl benzoate, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "93-58-3"

[0070] Table 2 shows the boiling point (°C), surface tension (mN / m), water solubility (g / L), and viscosity (mPa·s) of each organic solvent. Of the physical properties shown in Table 2, the boiling point and water solubility of each organic solvent are the nominal values ​​from each manufacturer. The surface tension of each organic solvent shown in Table 2 was measured using a static surface tensile meter (DYNEMASTER DY-300, manufactured by Kyowa Interface Science Co., Ltd.). The viscosity of each organic solvent shown in Table 2 was measured using a B-type viscometer (DV-III ULTRA spindle SC4-14, manufactured by Brookfield Corporation) (rotation speed of the B-type viscometer: 5 rpm).

[0071] Table 3 also shows the average surface tension (mN / m) of the organic solvents. The "average surface tension (mN / m)" shown in Table 3 is the surface tension of the organic solvent used in each example. When the organic solvent contains two or more types of organic solvents, the average surface tension (mN / m) is the measured value obtained by measuring the mixture of organic solvents using the static surface tensimeter described above.

[0072] [Table 2]

[0073] (Binder resin) Binder resins B1-B5, B9, and B10 were used as binder resins.

[0074] (Dispersant) The following dispersants were used as dispersants. <Cationic dispersants> • Dispersant C1: "Hypermer KD-1" manufactured by Croda Japan Co., Ltd. • Dispersant C2: "Hypermer KD-2" manufactured by Croda Japan Co., Ltd. • Dispersant C3: NOF Corporation, "S-Ream AD Series (registered trademark) AD-508E" <Nonionic dispersants> • Dispersant N1: "Hypermer KD-13" manufactured by Croda Japan Co., Ltd.

[0075] [Table 3]

[0076] In Examples 12 and 13, particles aggregated and settled in the prepared conductive ink. Furthermore, in Examples 21 and 22, the metal powder aggregated, preventing the above-mentioned filter filtration, and thus the conductive ink could not be prepared. Therefore, the evaluation tests described below were not performed for Examples 12, 13, 21, and 22. A "-" in the corresponding column of Table 3 indicates that the test was not performed.

[0077] <Evaluation Test> A. Ink properties (A-1) Viscosity The viscosity (mPa·s) of the conductive ink was measured using the aforementioned B-type viscometer while maintaining the prepared conductive ink at 25°C. The rotor speed of the B-type viscometer was set to 5 rpm. The results are shown in Table 3.

[0078] (A-2) Surface tension The surface tension (mN / m) of the conductive ink was measured using the static surface tensile meter described above. The results are shown in Table 3.

[0079] (A-3) Average particle diameter The average particle size of particles contained in conductive ink was measured using dynamic light scattering (DLS). The results are shown in Table 3.

[0080] (A-4) Daily measurement (measurement of daily stability) After preparation, a portion of the conductive ink was collected in two storage bottles. One bottle was stored at 25°C and the other at 60°C. The average particle size of each ink, stored at 1 week, 2 weeks, 3 weeks, and 4 weeks after preparation, was measured using dynamic light scattering (DLS). For both the 25°C and 60°C environments, an average particle size of 320 nm or less after 4 weeks was evaluated as "○ (excellent long-term stability)," and a size greater than 320 nm was evaluated as "× (poor long-term stability)." The results are shown in Table 3.

[0081] B. Printing Test The following pattern printing and ejection tests were conducted using conductive inks from Examples 1-11 and 20. Note that printing tests were not performed for Examples 14-19, which were evaluated as "×" based on the results of daily measurements. A "-" in the "Printing Test" column of Table 3 indicates that the test was not performed.

[0082] (B-1) Pattern printing test The pattern-forming ability of conductive inks in each example was evaluated using an inkjet printer (Fujifilm Corporation: Material Printer DMP-2831). In this test, the inkjet printer's ejection frequency was set to 1.5 kHz, 3.0 kHz, 5.0 kHz, 10 kHz, or 20 kHz, and four 10 cm x 10 cm patterns were solid-printed together on the surface of an alumina substrate. Precipitation outside the printed pattern was visually confirmed. The results are shown in Table 3. The frequency listed in the corresponding column of Table 3 is the maximum ejection frequency at which pattern printing was successful. After the solid printing, if there was no leakage of conductive ink from a predetermined area, it was determined that "pattern printing was successful."

[0083] (B-2) Discharge test The continuous and intermittent ejection performance (open-time ejection performance) of the conductive inks in each example were evaluated using the inkjet printer described above. In the evaluation tests for both performances, the conductive inks in each example were printed in a film-like manner on the surface of an alumina substrate under ejection conditions of 10 pl / dot and 1200 dpi. At this time, the ejection state of the conductive ink was visually observed using a camera attached to the inkjet printer.

[0084] (Continuous discharge performance) In the continuous ejection performance evaluation test, we assessed whether conductive ink could be ejected continuously for 10 minutes. Continuous ejection for 10 minutes was rated as "◎", and continuous ejection for 5 minutes was rated as "〇". The results are shown in Table 3.

[0085] (Intermittent discharge performance) For the conductive inks that received a "◎" rating for continuous ejection performance as described above, the intermittent ejection performance (open-time ejection performance) was evaluated. In the intermittent ejection performance evaluation test, after the 10-minute continuous ejection test described above, a 10-minute ejection stop time was provided, and then it was evaluated whether ejection was possible again. If ejection was possible, it was evaluated as "〇". The results are shown in Table 3. Note that for the conductive ink in Example 4, which received a "〇" rating for continuous ejection performance as described above, the intermittent ejection performance evaluation test was not performed. The "-" in the corresponding column in Table 3 indicates that the evaluation test was not performed.

[0086] The results shown in Table 3 indicate that the conductive inks of Examples 1-9 and 20 exhibit excellent long-term stability and superior pattern-forming ability at an ejection frequency of 20 kHz. Furthermore, the conductive inks of Examples 1-9 and 20 demonstrated excellent ejection performance. Therefore, it was found that a conductive inkjet ink containing metal powder composed of a metal with a specific gravity of 9 or higher, a binder resin, a cationic dispersant, and at least one organic solvent, having a surface tension of 27 mN / m to 29 mN / m, and containing polyvinyl acetal resin as the binder resin with a hydroxyl group content of 22 mol% or less, is preferable. Additionally, the results from Examples 1-3 and 5-7 suggest that a viscosity of 4 mPa·s to 13 mPa·s for the conductive ink is even more preferable.

[0087] The specific examples of the technology disclosed herein have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above. [Explanation of Symbols]

[0088] 1. Inkjet device 10 inkjet heads 12 cases 13 Storage section 15. Fluid delivery routes 16 Discharge part 17 Discharge port 18 Piezo elements 20 Guide axis 40 Print Cartridges 100 Mixing and Grinding Machine 110 Supply port 120 stirring vessel 132 Agitator blades 134 shaft 140 filters 150 Outlet

Claims

1. A conductive inkjet ink used in the manufacture of electronic components, Metal powder composed of metals with a specific gravity of 9 or higher, Binder resin and Cationic dispersants, Organic solvents and Includes, Here, the surface tension of the conductive inkjet ink is 27 mN / m or more and 29 mN / m or less. The aforementioned binder resin contains polyvinyl acetal resin, The hydroxyl group content of the polyvinyl acetal resin is 22 mol% or less. Conductive inkjet ink.

2. The conductive inkjet ink according to claim 1, wherein the average particle size of the metal powder is 150 nm or more and 500 nm or less.

3. A conductive inkjet ink according to claim 1 or 2, having a viscosity of 4 mPa·s or more and 13 mPa·s or less.

4. The conductive inkjet ink according to any one of claims 1 to 3, wherein when the entire conductive inkjet ink is considered to be 100 wt%, the content of the metal powder is 30 wt% or more and 70 wt% or less.

5. The conductive inkjet ink according to any one of claims 1 to 4, wherein the metal powder is composed of a high-melting-point metal having a melting point of 1200°C or higher.

6. The conductive inkjet ink according to claim 5, wherein the high melting point metal is tungsten powder or molybdenum powder.

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