JP3796476B2 - Conductive ink - Google Patents

Description

【００５２】
この銀コロイド水溶液に、表２に示した各種アルコール類化合物を添加した後、更にイオン交換水を添加して、最終固形分が１５重量％になるように調整し導電性インクとした。得られた導電性インクをスライドガラス上に刷毛塗りし自然乾燥した後、ギヤオーブン中で１２０℃×１時間の条件で加熱処理し被膜を形成した。
【００５３】
【表２】

【００５４】
（評価）
（１）乾燥による導電性インクの変質
各実施例及び比較例において得られた導電性インクを自然乾燥し、一旦被膜化したものを再び溶媒に浸漬し、超音波をかけながら１分間放置し、状態変化を観察し再溶解性を評価した。
【００５５】
（２）描画テスト
各実施例及び比較例において得られた導電性インクを用いて、市販のインクジェットプリンタによる描画テストを行い、インク充填後、ノズルが詰まって使用不可能になるまでに要する時間を評価した。
【００５６】
（３）被膜の導電性
各実施例及び比較例において得られた被膜について、横川電機社製ＰＯＲＴＡＢＬＥ ＤＯＵＢＬＥ ＢＲＩＤＧＥ２７６９を用いてダブルブリッジ法により体積抵抗率を求めた。
評価結果を表３に示した。
【００５７】
【表３】

【００５８】
【発明の効果】
本発明は、上述の構成よりなるので、低温での加熱処理が可能であることから基材の種類に制約を受けることなく導電性に優れた導電パターンを形成することが可能であることに加えて、乾燥によるインクの変質が起こりにくいためパターニング適性に優れ、幅広い描画装置、印刷機械等に適用可能な導電性インクを提供することができる。特にインクジェット方式、ディスペンサーといった精細な描画を行う装置に広く応用することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive ink capable of obtaining a coating film having high conductivity even at a low heating temperature and at the same time satisfying the conflicting requirements of not being deteriorated by drying before drawing.
[0002]
[Prior art]
Conventionally, for example, metal vacuum deposition, chemical vapor deposition, ion sputtering and the like have been performed as a method for producing a conductive coating. However, since these methods require work in a vacuum system or a closed system, there are problems such as complicated operations and a large apparatus, requiring space, increasing costs, and lacking in mass productivity. .
[0003]
There is also a method of forming a conductive film by plating, but in this case, it is necessary to treat a large amount of waste liquid, and there is a problem that a material loss is large and an extra cost is required, and the burden on the environment is large.
[0004]
When forming a wiring pattern with a conductive film, a photolithography method is widely used. In this case, an extra step of masking a necessary portion of the conductive film formed on the substrate is necessary. Further, since a large amount of the photosensitive resin used, the removed metal coating, and the waste liquid in which they are dissolved are discharged, the processing cost is high and the environmental load is large.
[0005]
In contrast to these methods, the method of drawing on a substrate using a material that forms a conductive film as a coating agent can be produced with simple equipment without the need for special equipment, and therefore requires a large space. Less cost. In addition, since material loss and waste liquid hardly occur, it is advantageous in terms of cost, and the environmental load can be reduced.
[0006]
As the coating agent, conventionally, a metal paste in which silver or other metal particles are kneaded with a resin component or an organic solvent, or a so-called conductive ink is used, and these are applied by a dispenser or screen printing. A conductive film is often formed. Recently, a method of forming a wiring pattern by drawing an ink jet method using a colloidal metal dispersion having a low viscosity as a conductive ink has been attempted.
[0007]
As the solvent for the conductive ink, either an organic solvent or a non-organic solvent can be used. However, by using a non-organic solvent, particularly water, the influence on the human body and the burden on the environment can be reduced.
[0008]
When drawing a wiring pattern using such conductive ink, it is necessary to dry the conductive ink immediately after drawing, and at the same time, the conductive ink before printing must not be altered by drying. It is necessary to satisfy the characteristics.
[0009]
In particular, in the case of the ink jet system, the nozzle from which the ink is ejected has a very fine structure, and when solid matter agglomerates due to drying, there is a problem that the nozzle is clogged and drawing is impossible.
In addition, the wiring pattern after drawing sinters the metal particles by heat treatment and expresses high conductivity. However, if this heat treatment temperature is high, the substrate on which the drawing is performed is damaged such as deformation, melting, and deterioration. Therefore, the material selection of the base material is restricted.
[0010]
For this reason, the conductive ink is required to have a design that allows heat treatment at the lowest possible temperature. However, at the same time, this has led to the fact that metal particles tend to form aggregates in terms of alteration during drying as described above, and it has been extremely difficult to achieve both.
[0011]
Patent Document 1 and Patent Document 2 describe a silver colloid solution for forming a wiring pattern on a substrate, but it is compatible with drying immediately after drawing and preventing deterioration due to drying before printing. Solvents for obtaining are not disclosed.
[0012]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-35255
[Patent Document 2]
Japanese Patent Laid-Open No. 2001-35814
[Problems to be solved by the invention]
An object of the present invention is to provide a conductive ink that can provide a coating film having high conductivity even at a low heating temperature and can satisfy both conflicting demands that it does not change in quality even after drying before drawing.
[0015]
[Means for Solving the Problems]
The present invention relates to a conductive ink composed of a solid content mainly composed of metal colloidal particles composed of a metal component and an organic component, and a solvent, and is heated at a heating rate of 10 ° C./min with respect to the solid content. The weight loss at 100 to 500 ° C. when performing gravimetric analysis is 0.01 to 7% by weight, and the solvent includes water and 1,3-propanediol, 1,2-propanediol, ethylene glycol or glycerin. It is the conductive ink characterized by comprising.
The present invention is described in detail below.
[0016]
The conductive ink of the present invention comprises a solid content mainly composed of metal colloid particles composed of a metal component and an organic component, and a solvent.
The metal component is preferably made of a metal whose ionization sequence is more noble than hydrogen. Examples of such a metal include gold, silver, copper, platinum, palladium, rhodium, ruthenium, iridium, and osmium. it can. These metals may be used independently and 2 or more types may be used together. Among the above metals, silver, copper, platinum, and palladium are preferable.
[0017]
The conductive ink of the present invention is preferably a mixed colloidal solution of silver and other metals. When silver is used, the conductivity of the film formed using the conductive ink is improved. However, when silver is used as the electronic material, it is necessary to consider the problem of migration. By using a mixed colloidal solution composed of silver and other metals, migration becomes difficult to occur. Said other metals are said gold | metal | money, copper, platinum, palladium, rhodium, ruthenium, iridium, and osmium. Of these, copper, platinum, and palladium are preferable.
[0018]
When using the above mixed colloidal liquid, the ratio of silver to other metals in the conductive ink is 30 to 99% by weight with respect to the total amount of silver and other metals. It is preferable. When the ratio of silver exceeds 99% by weight, it becomes difficult to solve the migration. If the silver ratio is less than 30% by weight, the conductivity of the resulting conductive ink may be reduced. A more preferred lower limit is 40% by weight, and a more preferred upper limit is 95% by weight. A more preferred lower limit is 60% by weight, and a more preferred upper limit is 90% by weight.
[0019]
As said organic component, the organic substance used as a dispersing agent or a reducing agent can be mentioned, for example. The reducing agent is not particularly limited as long as it dissolves in a suitable solvent and exhibits a reducing action, and tannic acid and hydroxy acid are preferably used. Tannic acid and hydroxy acid function as a reducing agent and at the same time exert an effect as a dispersing agent. These dispersants and reducing agents may be used alone or in combination of two or more.
[0020]
When the tannic acid is used, the dispersion stability of the metal colloidal particles is improved, and a film having excellent conductivity can be obtained by drying and heating the conductive ink. As said tannic acid, all what is generally called a tannic acid can be used, and what is expressed as gallotannic acid, a pentaploid tannin, etc. is contained.
[0021]
As content of the said tannic acid, it is preferable that it is 0.01-6g with respect to metal ion monovalent / g. For example, in the case of monovalent silver ions, the tannic acid content per gram of silver ions is 0.01 to 6 g. In the case of trivalent gold ions, the tannic acid content per gram of gold ions is Content is 0.03-18g. If the tannic acid content is too small, the reduction reaction does not proceed sufficiently, and if it is too large, it may be excessively adsorbed and remain in the coating. A more preferable lower limit is 0.1 g, and a more preferable upper limit is 1.5 g.
[0022]
When a hydroxy acid or a salt thereof having three or more COOH groups and OH groups in total and the number of COOH groups is equal to or more than the number of OH groups, the dispersion stability of the metal colloid particles is improved, A film having excellent conductivity can be obtained by drying and heating the conductive ink. Examples of the hydroxy acid include trisodium citrate, tripotassium citrate, trilithium citrate, disodium malate, disodium tartrate, and the like.
If the content of the hydroxy acid is too small, the effect does not appear. If the content is too large, impurities are formed and the conductivity of the film is inhibited. Therefore, the content is preferably 0.1 to 15 g with respect to monovalent metal ions / g. .
[0023]
In the conductive ink of the present invention, the form of the metal colloid particles composed of the metal component and the organic component is not particularly limited, and examples thereof include those in which an organic component is attached to the surface of the particles composed of the metal component, Examples thereof include particles having a metal component as a core and the surface of which is coated with an organic component, and particles in which a metal component and an organic component are uniformly mixed. Of these, particles having the metal component as a core and the surface of which is coated with an organic component, and particles in which a metal component and an organic component are uniformly mixed are preferable.
[0024]
The amount of the organic component in the metal colloid particles is preferably 0.5 to 30% by weight. If it is less than 0.5% by weight, the storage stability of the resulting conductive ink tends to be poor, and if it exceeds 30% by weight, the conductivity of the conductive film using the resulting conductive ink is poor. Tend to be. A more preferred lower limit is 1% by weight, and a more preferred upper limit is 20% by weight. In the conductive ink of the present invention, the “organic component” of the metal colloidal particle is an organic substance that substantially constitutes the particle together with the metal component, and a trace amount of organic substance contained as an impurity from the beginning in the metal, Does not include trace amounts of organic substances adhering to the metal components that are mixed in the manufacturing process described below, or trace amounts of organic substances such as residual reducing agents and residual dispersants that cannot be removed during the cleaning process, and those that adhere to the metal components. . In the conductive ink of the present invention, the “trace amount” specifically refers to less than 1% by weight in the metal colloid particles.
In the conductive ink of the present invention, since the metal colloid particles contain an organic component, the dispersion stability of the particles in the solution is high. Therefore, even if the metal content of the conductive ink is increased, the metal colloid particles are less likely to agglomerate and good dispersibility is maintained.
[0025]
The average particle size of the metal colloid particles is preferably 1 to 400 nm. Even if the average particle size of the metal colloidal particles is less than 1 nm, a coating film having good conductivity can be obtained, but generally, the production of such fine metal colloidal particles is expensive and impractical. If it exceeds 400 nm, the dispersion stability of the metal colloid particles tends to change over time. A more preferred upper limit is 70 nm.
[0026]
In the conductive ink of the present invention, the concentration of the solid content is preferably 1 to 70% by weight. Here, the solid content refers to the solid content remaining when most of the solvent is removed from the conductive ink with silica gel and then dried at a temperature of 70 ° C. or less. Consists of colloidal particles, residual dispersant, residual reducing agent, and the like.
[0027]
When the solid content is less than 1% by weight, the metal content of the obtained conductive ink is too small. Therefore, when the conductive film is formed, it is repeatedly applied to obtain the necessary thickness. This is an industrial disadvantage. If the concentration of the solid content exceeds 70% by weight, the viscosity increases and it becomes difficult to handle, which is also industrially disadvantageous. A more preferred lower limit is 3% by weight, and a more preferred upper limit is 50% by weight.
[0028]
In the conductive ink of the present invention, the weight loss at 100 to 500 ° C. when the thermogravimetric analysis is performed at a temperature rising rate of 10 ° C./min with respect to the solid content is preferably 7% by weight or less.
When the solid is heated to 500 ° C., organic matter and the like are oxidatively decomposed, and most of them are gasified and disappear. For this reason, it may be considered that the weight loss due to heating up to 500 ° C. corresponds approximately to the amount of organic matter in the solid content.
[0029]
If the weight loss is large, the dispersion stability of the metal colloid liquid is excellent. However, if the weight loss is too large, the organic matter remaining in the metal film as an impurity inhibits the conductivity of the film. In particular, in order to obtain high conductivity by heating at a low temperature of about 100 ° C., the weight loss is preferably 7% by weight or less. On the other hand, since the dispersion stability in a colloidal state is impaired when the weight loss is too small, it is preferably 0.01% by weight or more. A more preferred lower limit is 0.05% by weight, and a more preferred upper limit is 4.5% by weight.
[0030]
The solvent is composed of water and an alcohol compound having a vapor pressure of 17 mmHg or less at 20 ° C. By using an alcohol compound having a vapor pressure at 20 ° C. of 17 mmHg or less as the solvent, the solvent evaporates quickly after drawing and the coating is dried. No alteration occurs. A preferred lower limit is 0.001 mmHg, and a preferred upper limit is 8.5 mmHg.
[0031]
Examples of the alcohol compounds include butanol, propanediol, butanediol, pentanediol, ethylene glycol, glycerin and the like. Especially, the polyhydric alcohol which has 2 or more of hydroxyl groups in a molecule | numerator is preferable, for example, 1, 3- propanediol is used suitably in terms of volatilization suppression at normal temperature and volatilization at the time of heat processing.
[0032]
The content of the alcohol compound can be arbitrarily selected according to the characteristics of the machine used for drawing and the demand for the drying speed after drawing. However, if the amount is too small, the effect does not appear, and if too much, the dispersion stability of the metal colloidal particles This is contrary to the purpose of reducing the impact on the human body and the environmental load by using water as the main solvent. For this reason, when there is much solid content, it is preferable that it is 1.0-30.0 weight part with respect to 100 weight part of solid content, and when solid content is little, it is 1.0 with respect to 100 weight part of water. It is preferably ˜30.0 parts by weight.
[0033]
The conductive ink of the present invention may contain a surfactant. By containing the above-mentioned surfactant, it is possible to form a uniform film by suppressing the roughening of the surface of the film and the unevenness of the solid content due to the difference in volatilization rate at the time of drying, which tends to occur in multi-component solvent inks. It becomes. The surfactant is not particularly limited, and any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. Examples thereof include alkylbenzene sulfonates and quaternary ammonium salts. However, it is preferable since the effect can be obtained by adding a small amount of a fluorosurfactant.
[0034]
If the content of the surfactant is too small, the effect cannot be obtained. If the content is too large, the remaining amount of impurities in the film becomes an impurity and inhibits conductivity. Part by weight is preferred.
[0035]
The conductive ink of the present invention may further contain other additives for modifying the properties of the liquid.
The other additives are not particularly limited, and examples thereof include an antifoaming agent, a leveling agent, and a thickener.
[0036]
Since the conductive ink of the present invention comprises a solid content mainly composed of metal colloidal particles and a solvent, the conductivity can be 10 mS / cm or less. Conventional conductive inks may be sensitive to the concentration of the electrolyte component present and agglomerate and settle, which may impair storage stability. However, if the electrical conductivity is 10 mS / cm or less, this effect is sufficient. It is possible to prevent the storage stability from deteriorating due to increase in electrolyte concentration over time due to alkali outflow due to storage in a glass container and dissolution of carbon dioxide in the air. Further, when the conductivity of the conductive ink is 10 mS / cm or less, the dispersion stability of the conductive ink is high, so that the production of the conductive ink having a high solid content concentration is facilitated, and the volume can be reduced. And handling during transportation becomes easy. The high-concentration conductive ink may be adjusted to an optimum concentration for use later using an appropriate solvent.
[0037]
A method for producing the conductive ink of the present invention is not particularly limited, and examples thereof include a method of first producing a solution containing metal colloid particles and then washing the solution.
The method for producing the solution containing the metal colloidal particles is not particularly limited as long as it is a chemical reduction method. For example, a metal salt or metal ion dispersed in a solution using a dispersant is reduced by any method. You can do it.
[0038]
The metal salt is not particularly limited as long as it can be dissolved in a dispersion medium and reduced by some means. For example, silver nitrate, silver sulfate, silver chloride, silver oxide, silver acetate, silver nitrite, silver chlorate, Silver salts such as silver sulfide; Gold salts such as chloroauric acid, gold chloride and sodium chloride; Platinum salts such as chloroplatinic acid, platinum chloride, platinum oxide, potassium chloroplatinate; palladium nitrate, palladium acetate, chloride Palladium salts such as palladium, palladium oxide and palladium sulfate can be exemplified. These metal salts may be used independently and 2 or more types may be used together.
[0039]
The method for reducing the metal salt is not particularly limited, and may be reduced using a reducing agent, or may be reduced using light such as ultraviolet rays, electron beam, thermal energy, or the like. The reducing agent is not particularly limited as long as it can be dissolved in a dispersion medium and reduce the metal salt. For example, amine compounds such as dimethylaminoethanol, methyldiethanolamine, triethanolamine, phenidone, and hydrazine; Hydrogen compounds such as sodium borohydride, hydrogen iodide, hydrogen gas; oxides such as carbon monoxide and sulfurous acid; hydroxy acid salts such as trisodium citrate and sodium glycolate; ferrous sulfate, iron oxide and fumaric acid Low-valent metal salts such as iron, iron lactate, iron oxalate, iron sulfide, iron acetate, tin chloride, tin diphosphate, tin oxalate, tin oxide, tin sulfate; formaldehyde, hydroquinone, pyrogallol, tannin, tannic acid And organic compounds such as sugars such as salicylic acid and D-glucose. These reducing agents may be used independently and 2 or more types may be used together.
When using the above reducing agent, the reduction reaction may be further promoted by applying light or heat.
[0040]
As a method for producing a solution containing metal colloidal particles using the metal salt, the dispersant and the reducing agent, for example, the metal salt is dissolved in pure water to prepare a metal salt solution, and the metal salt solution is gradually added. And the like, and the like, in which the dispersant and the reducing agent are dissolved in an aqueous solution.
[0041]
In the solution containing the metal colloidal particles obtained as described above, the residue of the reducing agent and the dispersing agent are present in addition to the metal colloidal particles, and the electrolyte concentration of the entire liquid is high. Since the liquid in such a state has high electrical conductivity, the metal colloidal particles are likely to coagulate and precipitate easily. By washing the solution containing the metal colloid particles to remove excess electrolyte, a metal colloid solution having an electric conductivity of 10 mS / cm or less can be obtained.
[0042]
As the washing method, for example, the solution containing the obtained metal colloid particles is allowed to stand for a certain period of time, and after removing the resulting supernatant, pure water is added and stirred again, and the mixture is further allowed to stand for a certain period. A method of repeating the process of removing the produced supernatant several times, a method of performing centrifugation instead of the above-mentioned standing, a method of desalting with an ultrafiltration device, an ion exchange device or the like can be mentioned. Of these, the desalting method is preferred. Moreover, you may concentrate the liquid which desalted etc. suitably.
[0043]
The method for producing a conductive ink composed of a plurality of metals is not particularly limited. For example, in the case of producing a conductive ink composed of silver and other metals, the silver colloid liquid and others are produced by the above method. The metal colloid solution may be prepared separately and then mixed, or the silver ion solution and other metal ion solution may be mixed and then reduced.
[0044]
A conductive film can be formed by applying the conductive ink of the present invention on a substrate and drying it.
The base material is not particularly limited. For example, a heat resistant base material made of heat-resistant metal, glass, ceramic, etc .; high temperature such as polyester resin, acrylic resin, polyamide resin, polycarbonate resin, vinyl resin is applied. And polymeric base materials that may be deformed or decomposed.
According to the conductive ink of the present invention, a film exhibiting high conductivity can be formed even by a low-temperature heat treatment at about 100 ° C. Therefore, a conductive film can be formed even on a relatively heat-sensitive substrate. Can do.
Examples of the shape of the substrate include a plate shape and a film shape.
[0045]
In order to increase the adhesion between the substrate and the conductive coating, the substrate may be subjected to a surface treatment.
Examples of the surface treatment method include dry treatment such as corona treatment, plasma treatment, UV treatment, and electron beam treatment; a method of previously providing a primer layer and a conductive ink receiving layer on a substrate, and the like.
[0046]
The method for applying the conductive ink of the present invention on the substrate is not particularly limited. For example, dipping, screen printing, spray method, bar coating method, spin coating method, ink jet method, dispenser method, application by brush, etc. Can be mentioned.
[0047]
The conductive film formed from the conductive ink of the present invention is used for electromagnetic shielding of cathode ray tubes, infrared shielding of building materials or automobiles, antistatic materials for electronic devices and mobile phones, heat rays of frosted glass, circuit substrates and IC cards. It is suitably used for wiring, electrodes for flat panel displays, coating for imparting conductivity to resin, through-holes, or the circuit itself.
[0048]
The conductive ink of the present invention can form a film exhibiting high conductivity even at a low-temperature heat treatment of about 100 ° C., while at the same time satisfying the conflicting requirements of preventing deterioration of the conductive ink due to drying before drawing. It becomes possible to do.
For this reason, according to the present invention, in addition to being able to form a conductive pattern excellent in conductivity without being restricted by the type of base material, the ink is hardly deteriorated by drying, so a wide range of drawing devices, It can be used for printing machines.
[0049]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[0050]
Examples 1-4 and Comparative Examples 1-5
The conductive ink in each example and comparative example was manufactured as follows.
17 mL of trisodium citrate dihydrate and 0.36 g of tannic acid were dissolved in 50 mL of water made alkaline by adding 3 mL of 10N-NaOH aqueous solution. To the obtained solution, 3 mL of 3.87 mol / L silver nitrate aqueous solution was added and stirred for 2 hours to obtain a silver colloid aqueous solution. The obtained silver colloid aqueous solution was desalted by dialysis until the electric conductivity became 30 μS / cm or less. After dialysis, the coarse metal colloid particles were removed by centrifugation at 3000 rpm for 10 minutes. The solid content in the aqueous silver colloid solution was determined by the dry weight method, and the obtained solid content was measured in the atmosphere from room temperature to 500 ° C. at a temperature rising rate of 10 ° C./min using TG / DTA300 manufactured by Seiko Denshi Kogyo. The thermogravimetric change in was calculated and the weight loss from 100 ° C to 500 ° C was calculated. Table 1 shows the solid content in the silver colloid aqueous solution and the weight loss by thermogravimetric analysis.
[0051]
[Table 1]

[0052]
After adding various alcohol compounds shown in Table 2 to this silver colloid aqueous solution, ion exchange water was further added to adjust the final solid content to 15% by weight to obtain a conductive ink. The obtained conductive ink was brush-coated on a slide glass and naturally dried, and then heat-treated in a gear oven at 120 ° C. for 1 hour to form a film.
[0053]
[Table 2]

[0054]
(Evaluation)
(1) Deterioration of conductive ink by drying The conductive ink obtained in each Example and Comparative Example was naturally dried, and once coated, it was immersed again in a solvent and left for 1 minute while applying ultrasonic waves. The state change was observed and re-solubility was evaluated.
[0055]
(2) Drawing test Using the conductive ink obtained in each of the examples and comparative examples, a drawing test using a commercially available ink jet printer is performed. After the ink is filled, the time required until the nozzle becomes clogged and becomes unusable. evaluated.
[0056]
(3) Conductivity of coating The volume resistivity of the coating obtained in each Example and Comparative Example was determined by the double bridge method using PORTABLE DOUBLE BRIDGE 2769 manufactured by Yokogawa Electric Corporation.
The evaluation results are shown in Table 3.
[0057]
[Table 3]

[0058]
【The invention's effect】
Since the present invention has the above-described configuration, it is possible to form a conductive pattern having excellent conductivity without being restricted by the type of the substrate because heat treatment at low temperature is possible. Thus, it is possible to provide a conductive ink that is excellent in patterning suitability and is applicable to a wide range of drawing apparatuses, printing machines, and the like because the ink hardly changes due to drying. In particular, the present invention can be widely applied to apparatuses that perform fine drawing such as an ink jet method and a dispenser.

Claims (5)

A conductive ink comprising a solid content mainly composed of metal colloidal particles composed of a metal component and an organic component, and a solvent,
The weight loss of 100 to 500 ° C. when the thermogravimetric analysis is performed at a heating rate of 10 ° C./min with respect to the solid content is 0.01 to 7% by weight,
The solvent is a mixed solution of water and 1,3-propanediol, 1,2-propanediol, ethylene glycol or glycerin.
A conductive ink characterized by the above. 2. The conductive ink according to claim 1, wherein the metal component is made of a metal whose ionization column is nobler than hydrogen and contains 0.01 to 6 g of tannic acid with respect to 1 valence / g of metal ion. The metal component is made of at least one metal selected from the group consisting of gold, silver, copper, platinum, palladium, rhodium, ruthenium, iridium and osmium, and has a conductivity of 10 mS / cm or less. Item 3. The conductive ink according to Item 2. 4. The hydroxy acid or salt thereof having three or more COOH groups and OH groups in total and having the number of COOH groups equal to or more than the number of OH groups. Conductive ink. The conductive ink according to claim 1, wherein the conductive ink contains a surfactant.