JP5239700B2 - Coating film forming method using metal fine particle dispersion and coating film using the same - Google Patents

Description

  The present invention relates to a coating film forming method using a metal fine particle dispersion and a coating film using the same, and more specifically, when forming a coating film using a metal fine particle dispersion composed of metal fine particles and a solvent. When used as a pigment, there is no crack on the surface after drying and there is a metallic luster, and a coating film with excellent durability is obtained, and when used as a conductive film forming material, by baking at low temperature after drying, A coating film forming method in which the volume resistivity of a coating film after firing (hereinafter sometimes referred to as a fired film) is reduced and a low resistance coating film is obtained, and a design or electronic component using the coating film forming method The present invention relates to a coating film suitable for forming a circuit.

  Conventionally, a metal fine particle dispersion containing metal fine particles having a particle size of 100 nm or less has high smoothness of the coating film surface when applied, and also has high sinterability and clogging of nozzles when ejected by inkjet. Due to the difficulty and the like, application to materials for forming conductive films by printing, design pigments, and the like is being promoted. However, depending on the type of dispersion and the thickness of the coating film, problems such as deterioration in thickness uniformity due to uneven drying and cracks due to volume shrinkage are likely to occur during drying. In particular, the coating film has a thickness of, for example, 1 μm or more. These problems tend to occur when the film is thickened.

  By the way, as the material for forming the conductive film, the resistance value can be reduced as the thickness increases, and as the design pigment, the durability can be improved by applying the coating pigment thickly, and the hiding power to the base can be improved. Thickening is actively performed. However, when the obtained coating film has poor uniformity and has defects, the expected performance improvement as described above cannot be achieved.

For this reason, various methods have been proposed to form a uniform and defect-free coating film.
For example, a method for producing a functional film, which includes a step of applying a solution in which a functional material is dissolved or dispersed in a solvent to a substrate, a step of removing the solvent under reduced pressure, and a step of baking in an inert gas atmosphere. (See, for example, Patent Document 1). However, in this method, since drying is performed under reduced pressure, special equipment is required, so that the equipment cost is high and the process is complicated. Here, the boiling point of the solvent used in the particle dispersion is 200 to 300 ° C., and when a conductive film is obtained by low-temperature firing, the resistance value is expected to deteriorate due to the residual solvent.

  In addition, a method for forming a metal film (for example, a method of applying a metal fine particle dispersion containing metal fine particles, water, a volatile organic solvent, and a non-volatile organic compound to the surface of the substrate, drying, and firing) (See Patent Document 2). However, since this method contains a large amount of volatile organic solvent in the dispersion, the drying speed is very fast, handling properties deteriorate, and when applied to inkjet, the nozzle may be clogged with dry matter and may not be ejected. There is. Furthermore, when a low-resistance conductive film is formed, it is necessary to heat to a temperature higher than the thermal decomposition temperature of the nonvolatile organic compound, and it is difficult to say that the low-temperature firing property is excellent.

  Further, as a method for forming a low-resistance conductive film, a highly conductive ink composition containing an organic solvent, nanoscale metal particles or a decomposable metal organic compound, and a thermally decomposable polymer, and the highly conductive ink composition A method for producing a metal conductive pattern to be heated (for example, see Patent Document 3) has been proposed. However, this method relates to the formation of a low-resistance conductive film, and is unclear as to application to a design pigment, and is also limited in application because it is essential to form heat after coating. It was a thing.

  By the way, in the metal fine particle dispersion, the coating film obtained by using the copper particle micron dispersion is useful as a conductive film because low resistance is obtained by the high conductivity of copper. Since a unique color tone is obtained, it has been attracting attention because it has high designability and is very useful as a pigment. However, conventionally, when copper fine particles are used, there is a disadvantage that the oxidation resistance is inferior compared with the case of noble metal fine particles such as silver. Therefore, the design changes due to oxidation of the copper fine particles in the dispersion or after coating and drying. It is inferior in long-term storability, low-temperature sinterability, etc., and has not been put into practical use.

As a solution to this, as a copper fine particle dispersion for circuit formation that requires electrical conductivity, copper fine particles having a particle diameter of 100 nm or less coated with a water-soluble polymer and hydroxycarboxylic acid, hydroxycarboxylic acid, polyhydric alcohol and / or The thing which consists of polar solvents (for example, refer patent document 4) is proposed. However, since this proposal is an application for forming a circuit on the premise of low-temperature firing, the application is limited when used for printing that requires design. In addition, since the disclosed firing temperature is 250 to 300 ° C., further reduction of the firing temperature is demanded for the copper fine particle dispersion for circuit formation.
From the above situation, there is a demand for a method capable of forming a coating film suitable for design or circuit formation of electronic parts using a metal fine particle dispersion.

JP 2006-068598 A (first page, second page) JP 2006-321948 A (first page, second page) JP 2007-182547 A (first page, second page) WO2007 / 013393 (first page)

  In view of the above-mentioned problems of the prior art, the object of the present invention is to form a coating film using a metal fine particle dispersion composed of metal fine particles and a solvent. There is no metallic luster and a coating film with excellent durability is obtained. When used as a conductive film forming material, the volume resistivity of the fired film is reduced by low-temperature firing after drying, resulting in low resistance. It is in providing the coating film suitable for the coating-film formation method from which the coating film of this is obtained, and the design using the same, or the circuit formation of an electronic component.

  In order to achieve the above object, the present inventors have conducted intensive research on a method for forming a coating film using a metal fine particle dispersion composed of metal fine particles and a solvent, and as a result, have a specific average particle diameter. Using a metal fine particle dispersion containing metal fine particles and a specific solvent, a coating solution containing a specific amount of hydroxycarboxylic acid was prepared, and after applying this, it was subjected to a drying treatment under specific conditions. Improves uniformity, improves oxidation resistance of metal fine particles, gives a coating film without defects, and has a metallic luster with no cracks on the surface after drying when used as a pigment. When a coating film having excellent properties is obtained, and further subjected to a baking treatment under specific conditions following the drying treatment, when used as a material for forming a conductive film, it is fired at a low temperature. Volume fraction of Rate is lowered, it found that coating of a suitable low resistance is obtained as the circuit-forming electronic components, thus completing the present invention.

That is, according to the first aspect of the present invention, there is provided a method for forming a coating film using a metal fine particle dispersion composed of metal fine particles and a solvent,
Hydroxycarboxylic acid is further added to the metal fine particle dispersion satisfying the following requirements (a) and (b) to prepare a coating solution satisfying the requirement (c). By applying a drying treatment at a temperature of ˜120 ° C., the uniformity of the coating film is improved, cracking of the coating film is suppressed, and a coating film having a metallic luster and having excellent design properties is obtained. A method for forming a coating film is provided.
(A) The metal fine particles have an average particle size of 10 to 100 nm.
(B) The solvent is a polar solvent.
(C) The coating solution has a hydroxycarboxylic acid content in the solvent of 5 to 40% by mass.

  According to a second aspect of the present invention, there is provided the coating film forming method according to the first aspect, wherein the drying treatment is performed in a non-reducing atmosphere.

  According to a third invention of the present invention, in the first or second invention, the coating film is further subjected to a baking treatment at a temperature of 200 ° C. or more and less than 250 ° C. following the drying treatment. A forming method is provided.

  According to a fourth aspect of the present invention, there is provided the coating film forming method according to any one of the first to third aspects, wherein the hydroxycarboxylic acid is citric acid.

  According to a fifth invention of the present invention, in any one of the first to fourth inventions, the metal fine particles are at least one fine particle selected from gold, palladium, platinum, silver or copper. A method for forming a coating film is provided.

  According to a sixth invention of the present invention, in any one of the first to fifth inventions, the metal fine particles have a halogen element content of 20 ppm by mass or less. Is provided.

  According to a seventh invention of the present invention, in any one of the first to sixth inventions, the metal fine particle dispersion is in at least one solution selected from ethylene glycol, diethylene glycol, or triethylene glycol. Addition of metal oxides, hydroxides or salts of metal fine particles, a water-soluble polymer as a dispersant, and a noble metal compound or noble metal colloid for nucleation, and heating to reduce precipitation. Further, a method for forming a coating film characterized by comprising a metal fine particle and a solvent is provided.

  According to an eighth aspect of the present invention, in the seventh aspect, the halogen element content of the metal fine particle dispersion is 20 ppm by mass or less based on the metal fine particles in the dispersion. A method for forming a coating film is provided.

According to the ninth invention of the present invention, in the seventh or eighth invention, instead of the requirement (c), the following requirement (d) is satisfied: Is provided.
(D) The coating liquid has a hydroxycarboxylic acid content in the solvent of 15 to 35% by mass.

  According to a tenth aspect of the present invention, there is provided the coating film forming method according to the ninth aspect, wherein the metal is copper.

According to the eleventh aspect of the present invention, there is provided a coating film made of copper obtained by the coating film forming method of the tenth invention, which is baked at 220 ° C. for 1 hour in a nitrogen atmosphere after being applied to the substrate. There is provided a coating film characterized in that the film thickness obtained in this case is 1 μm or more and the volume resistivity of the fired film is 50 μΩ · cm or less.

  The method for forming a coating film using the metal fine particle dispersion according to the present invention improves the uniformity of the coating film when the coating film is formed using the metal fine particle dispersion composed of the metal fine particles and the solvent. Since the oxidation resistance of the fine particles is improved and a coating film having no defect is obtained, when used as a pigment, the coating film has a metallic luster without cracking on the surface after drying and has excellent durability. When used as a forming material, the volume resistivity of the fired film is reduced by firing at a low temperature, and a low-resistance coating film is a coating film forming method that can be easily obtained. Since the coating film is a coating film suitable for design or circuit formation of electronic parts, its industrial value is extremely large.

Hereinafter, a coating film forming method using the metal fine particle dispersion of the present invention and a coating film using the same will be described in detail.
1. Coating film forming method using metal fine particle dispersion The coating film forming method using the metal fine particle dispersion of the present invention is a coating film forming method using a metal fine particle dispersion composed of metal fine particles and a solvent. ,
Hydroxycarboxylic acid is further added to the metal fine particle dispersion satisfying the following requirements (a) and (b) to prepare a coating solution satisfying the requirement (c). By applying a drying treatment at a temperature of ˜120 ° C., the uniformity of the coating film is improved, cracking of the coating film is suppressed, and a coating film having a metallic luster and having excellent design properties is obtained. And
(A) The metal fine particles have an average particle size of 10 to 100 nm.
(B) The solvent is a polar solvent.
(C) The coating solution has a hydroxycarboxylic acid content in the solvent of 5 to 40% by mass.
As a result, when used as a pigment, a coating film excellent in durability suitable for design can be obtained because the surface has no crack after drying and has a metallic luster.

  Further, in the coating film forming method, if it is further subjected to a baking treatment at a temperature of 200 ° C. or more and less than 250 ° C. following the drying treatment, it is fired at a low temperature when used as a conductive film forming material. As a result, the volume resistivity of the fired film is lowered, and a low-resistance coating film suitable for circuit formation of electronic parts is obtained.

In the present invention, hydroxycarboxylic acid is added to a metal fine particle dispersion composed of metal fine particles having an average particle diameter of 10 to 100 nm and a polar solvent, and the content of hydroxycarboxylic acid in the solvent is 5 to 5. It is important to prepare a coating solution of 40% by mass and apply it, followed by a drying treatment at a temperature of room temperature to 120 ° C. or a low-temperature baking treatment at a temperature of 200 ° C. or more and less than 250 ° C. .
Thereby, the coating film excellent in the designability which has a metal luster without a defect by a simple method is obtained. That is, by adding the hydroxycarboxylic acid, the hydroxycarboxylic acid acts as a binder during the drying treatment, the uniformity of the coating film is improved, and drying unevenness and cracking due to shrinkage can be suppressed. Moreover, the volume resistivity of the coating film can be reduced during the firing treatment. In addition, the decrease in volume resistivity is that the hydroxycarboxylic acid reacts with the metal on the surface of the metal fine particles to form a hydroxycarboxylic acid metal such as copper hydroxycarboxylate, in addition to preventing cracking during drying, This is probably because the highly active metals produced by decomposition during firing sinter together.

The hydroxycarboxylic acid content of the coating solution satisfies the following requirement (c), and preferably satisfies the following requirement (d).
(C) The coating solution has a hydroxycarboxylic acid content in the solvent of 5 to 40% by mass.
(D) The coating liquid has a hydroxycarboxylic acid content in the solvent of 15 to 35% by mass.
That is, the amount of hydroxycarboxylic acid added is adjusted so that the content of hydroxycarboxylic acid in the solvent of the coating solution is 5 to 40% by mass, preferably 10 to 40% by mass, more preferably 15 to 35% by mass. . Here, if content of the said hydroxycarboxylic acid is less than 5 mass%, a big effect is not seen in the improvement of the uniformity of a coating film. On the other hand, when the content of the hydroxycarboxylic acid exceeds 40% by mass, no significant effect is seen in the improvement of uniformity, and the particles tend to agglomerate due to a rapid drop in pH. When copper fine particles are used as the fine particles, the dissolution of copper by hydroxycarboxylic acid becomes remarkable.

  The hydroxycarboxylic acid is not particularly limited, and examples thereof include lactic acid, malic acid, citric acid, gluconic acid, and the like, and one of these is considered in consideration of solubility in a solvent, viscosity adjustment, and the like. Alternatively, two or more kinds can be appropriately selected and used, and among these, citric acid is particularly preferable because it has high solubility in polar solvents such as water and alcohol and has a large antioxidant effect on metal fine particles.

The content of the metal fine particles in the coating solution is not particularly limited, and is preferably 2 to 70% by mass, and more preferably 30 to 60% by mass with respect to the total amount of the coating solution.
That is, if the content of the metal fine particles is less than 2 mass, there is a possibility that a printed surface exhibiting a good metallic luster cannot be achieved. On the other hand, when the content of the metal fine particles exceeds 70% by mass, clogging due to drying or increase in viscosity causes a decrease in ink ejection stability and good printing when used for printing in an ink jet system. May not be achieved.

  The drying treatment is to bind the metal fine particles after coating to a certain degree, have a metallic luster, and obtain a sufficient strength as a coating film. In this invention, after apply | coating a coating liquid, by applying to a drying process at the temperature of room temperature-120 degreeC, the coating film which was excellent in the designability which has a metal luster without a defect by the binder effect of hydroxycarboxylic acid mentioned above. Is obtained. On the other hand, in the conventional method, in order to have a metallic luster and to obtain a sufficient strength as a coating film, firing at a higher temperature is indispensable.

The temperature of the drying treatment is more preferably a room temperature of, for example, about 5 to 40 ° C. from the viewpoint of simplicity and cost, where heating or cooling operation is unnecessary.
The atmosphere for the drying treatment is not particularly limited, but can be performed in a non-reducing atmosphere, for example, an air atmosphere. That is, it is not necessary to employ a reducing atmosphere for preventing oxidation by using a hydroxycarboxylic acid having a low drying treatment temperature and an effect of preventing the metal fine particles from being oxidized.

  The firing treatment is performed in order to obtain a low-resistance coating film suitable for forming a circuit of an electronic component when used as a conductive film forming material. The temperature is preferably 200 ° C. As mentioned above, it is less than 250 degreeC, More preferably, it is 200-230 degreeC. Thereby, the coating film excellent in the electrical conductivity of a low resistance without a defect can be obtained. That is, when the temperature of the baking treatment is less than 200 ° C., the metal fine particles are not sufficiently sintered, and the resistance value of the coating film may not be sufficiently reduced. On the other hand, when the temperature of the baking treatment is 250 ° C. or higher, the resistance value can be reduced, but as a base material or substrate to be applied, it is limited to a particularly highly heat-resistant material, and is generally the most commonly used polyimide resin, Since polyetherimide resin, polyethylene naphthalate resin, polyphenylene sulfide resin, and the like are limited in terms of heat resistance temperature, the application of the coating solution is limited.

  The atmosphere for the firing treatment is not particularly limited, but is preferably a non-oxidizing atmosphere, particularly a nitrogen gas atmosphere from the viewpoint of simplicity and cost, in order to prevent oxidation of the metal fine particles. That is, it is not necessary to employ a reducing atmosphere because the temperature of the baking treatment is low.

(1) Metal fine particle dispersion used in coating film forming method The metal fine particles and solvent in the metal fine particle dispersion used in the coating film forming method satisfy the following requirements (a) and (b): It is.
(A) The metal fine particles have an average particle size of 10 to 100 nm.
(B) The solvent is a polar solvent.

The average particle size of the metal fine particles is important to be 10 to 100 nm. That is, when the average particle size is less than 10 nm, the shrinkage of the coating film becomes too large during the drying treatment. On the other hand, when the average particle diameter exceeds 100 nm, the smoothness of the surface of the coating film decreases, and when the coating film is baked, the sinterability decreases and the nozzle is ejected by the inkjet method. Prone to blockage.
The average particle diameter of the metal fine particles is measured by SEM observation as described in detail in the examples.

  The metal fine particles are not particularly limited, and for example, various metal fine particles such as gold, silver, platinum, copper, aluminum, palladium, nickel, cobalt, tin, and iron can be used. In consideration of conductivity and design properties, at least one kind of fine particles selected from gold, palladium, platinum, silver or copper is preferable, and copper fine particles capable of obtaining a coating film having a specific design property and low resistance are used. Is more preferable.

  The halogen element content of the metal fine particles is not particularly limited, and is particularly preferably 20 ppm by mass or less for use as an electronic component material such as a conductive film. That is, if the content of the halogen element exceeds 20 ppm by mass, there is a risk of corroding the base material and other members, and the low-temperature sinterability is lowered and the resistance value of the coating film after firing is increased. Cheap.

It is important to use a polar solvent as the solvent in the metal fine particle dispersion.
The polar solvent is not particularly limited, and in addition to water, monovalent alcohols such as methanol, ethanol, isopropanol, butanol, methyl carbitol, ethyl carbitol, butyl carbitol, ethylene glycol, diethylene glycol, Polyhydric alcohols (polyols) such as triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerin and the like can be mentioned, and the drying condition and viscosity of the coating solution can be adjusted by appropriately combining these. Among these, water and ethylene glycol, diethylene glycol or triethylene glycol are particularly preferably combined as appropriate because adjustment is easy.

  The content ratio of the metal fine particles and the solvent in the metal fine particle dispersion is not particularly limited and varies depending on the production method of the metal fine particle dispersion, and finally, when the coating liquid is prepared. By adding hydroxycarboxylic acid to the solvent, the content ratio of the metal fine particles and the solvent is adjusted.

  The halogen element content in the metal fine particle dispersion is not particularly limited, but particularly in applications for electronic component materials, the halogen content is reduced to 20 mass ppm or less with respect to the metal fine particles in the dispersion. Is preferable. That is, if the content of the halogen element exceeds 20 ppm by mass, there is a risk of corroding the base material and other members, and the low-temperature sinterability is lowered and the resistance value of the coating film after firing is increased. Cheap.

(2) Method for producing metal fine particle dispersion by polyol method The metal fine particle dispersion is not particularly limited, and for example, by using the polyol method, ethylene glycol (EG), diethylene glycol (DEG) or triethylene is used. In a solution comprising at least one selected from glycol (TEG), a metal oxide, hydroxide or salt constituting the metal fine particles, a water-soluble polymer as a dispersant, and a noble metal for nucleation A compound or a precious metal colloid is preferably added and heated, and is preferably composed of metal fine particles that have been reduced and precipitated and a solvent. That is, the metal fine particle dispersion obtained by this method has a small variation in the particle size of the metal fine particles, and its dispersion stability is high.

Below, the manufacturing method of the said metal fine particle dispersion is demonstrated concretely about the case of the copper fine particle dispersion using a polyol method.
As a method for producing a copper fine particle dispersion using a polyol method, an oxide, hydroxide or salt of copper, which is a raw material of copper fine particles, is mixed with a water-soluble polymer as a dispersant and a nucleus in the polyol solution. By heating in a solution to which a noble metal compound or noble metal colloid for production is added, reduction is performed to synthesize copper fine particles in the liquid phase. The polyol method has good dispersion stability, conductivity, and oxidation resistance of particles, and is suitable for mass production.

  When the above-described reduction in halogen is intended, the halogen element content in the copper fine particle dispersion is preferably controlled to 20 ppm by mass or less with respect to the copper fine particles in the dispersion. For that purpose, copper oxide used as the raw material of the copper fine particles, hydroxide or salt used in the above production method, ethylene glycol, diethylene glycol or triethylene glycol as a dispersion medium, water-soluble polymer as a dispersant, In addition, for each of the noble metal compound or the noble metal colloid for nucleation, it is preferable to reduce the halogen elements contained so that the total content thereof is 20 mass ppm or less with respect to the copper fine particles. That is, the halogen element, especially chlorine, is not only adsorbed on the surface of the copper fine particles, but also contained inside, so it is removed to an acceptable range for electronic component materials, for example, 20 ppm by mass or less with respect to the copper fine particles. It is usually very difficult to do.

There are no particular limitations on the copper oxide, hydroxide or salt that is the raw material of the copper fine particles, but examples include copper oxides such as copper oxide (CuO) and cuprous oxide (Cu ₂ O). Copper salt powders such as copper hydroxide and copper acetate are used. Here, when low halogenation is intended, it is preferable to satisfy the requirement that the halogen element content of these raw materials is less than 5 ppm by mass. For example, among raw materials used in a normal polyol method, a material that satisfies this requirement is selected. Even when the halogen element content is higher than this requirement, those which can be removed by washing can be used.

The noble metal compound or noble metal colloid for nucleation has an action of generating more uniform and fine copper fine particles.
The noble metal compound is not particularly limited, and those that are more easily reduced than copper in a polyol solution are used. Here, the noble metal compound can be added in a powder state, but it is particularly preferable to add the noble metal compound in a state dissolved in a polar solvent such as water. That is, in this method, fine noble metal particles can be uniformly formed, and the copper fine particles obtained in the dispersion are also uniform and fine. Accordingly, it is preferable to use a noble metal compound that is soluble in a polar solvent, that is, a water-soluble noble metal compound. For example, palladium salts such as palladium ammonium chloride, palladium chloride, palladium nitrate, and palladium ammonium nitrate, and silver such as silver nitrate and silver chloride. Salt is used. In particular, in the case of low halogenation, palladium nitrate or palladium ammonium nitrate containing no halogen element is preferable.

On the other hand, a noble metal hydroxide or noble metal oxide having low solubility can be used as the noble metal compound. That is, noble metal compounds suitable as nucleation substances, such as palladium nitrate and palladium ammonium nitrate, contain strongly oxidizing nitrate ions. In contrast, hydroxides and oxides do not contain strong oxidizing ions such as nitrate ions, and no harmful elements are used as component elements. For this reason, since there is no reduction inhibitory action by oxidizing ions, reduction at a lower temperature is possible, which is advantageous from an industrial point of view.
Here, when the halogen reduction is intended, a compound having a halogen element as a component element cannot be used. In addition, even when a compound that does not contain a halogen element as a component element is used, care must be taken because it may be mixed as an impurity.

  The noble metal colloid is not particularly limited, and a colloid of silver, palladium, platinum, or gold is used, for example, since it does not cause a substitution reaction in the polyol solution, and has a lower ionization tendency than copper. preferable. Here, since the particle size of the obtained copper fine particles is inversely proportional to the number of added noble metal nuclei and the amount of expensive noble metal used is preferably as small as possible, the average of noble metal fine particles in the colloid added as nuclei The particle size is preferably 20 nm or less, and more preferably 10 nm or less. That is, when the average particle size exceeds 20 nm, the particle size of the obtained copper fine particles becomes too large, and the amount of noble metal used increases and the cost increases.

  The noble metal colloid may be a commercially available one, but can be easily synthesized by using a known polyol method. For example, it is produced by adding a water-soluble noble metal compound and a water-soluble polymer to a polyol solution. Here, the water-soluble noble metal compound is preferably a compound that does not contain a halogen element as a component element, such as palladium nitrate or palladium ammonium nitrate. Moreover, as a water-soluble polymer, polyvinylpyrrolidone etc. are preferable. The addition amount of the water-soluble noble metal compound and the water-soluble polymer is determined in consideration of synthesis conditions such as temperature so that a necessary particle size can be obtained. For example, when the addition amount of the water-soluble noble metal compound is 5 g / L in terms of palladium concentration and the addition amount of the water-soluble polymer is 10 g / L, a palladium colloid containing fine particles having a particle diameter of 10 to 15 nm can be obtained.

When noble metal colloids are used, the synthesis of noble metal colloids can be separated from the production of copper fine particles compared to the case where noble metal compounds are added directly, so that noble metal colloids can be synthesized under optimum conditions. There is an advantage that the fine noble metal fine particles in the colloid can be easily controlled. That is, since the noble metal fine particles serve as a nucleus of copper fine particle generation, fine particle control of the noble metal fine particles can further improve the particle size control and particle size uniformity of the copper fine particles. Further, if the noble metal colloid is subjected to substitution washing with an ultrafiltration membrane or the like, it is possible to eliminate from the reaction system as much as possible harmful components and contamination of components unnecessary for the production of copper fine particles.
Here, when low halogenation is intended, the content of the halogen element is controlled to be less than about 20 ppm by mass with respect to copper, like the noble metal compound.

  The addition amount of the noble metal compound or noble metal colloid for nucleation is not particularly limited, and the mass ratio of noble metal to copper (noble metal / Cu) is 0.0004 to 0.01 regardless of the form. It is preferable to set it as the range. That is, when the mass ratio is less than 0.0004, the amount of noble metal fine particles is insufficient, so that the copper reduction reaction and the formation of copper fine particles do not proceed sufficiently. Even when copper fine particles are formed, the number of noble metal fine particles serving as nuclei is insufficient, and the particle size may become coarse. On the other hand, when the mass ratio exceeds 0.01, copper fine particles can be obtained, but the effect of refining the particle diameter cannot be obtained for an increase in the amount of expensive noble metal added. Among the above conditions, it is particularly preferable to use palladium (Pd) as the noble metal compound for nucleation or the noble metal colloid, and to make the Pd / Cu mass ratio in the range of 0.0006 to 0.005. . Thereby, copper fine particles having an average particle size of 100 nm or less and excellent in particle size uniformity can be obtained.

  The water-soluble polymer that is the dispersant is not particularly limited, and a polymer that can be dissolved in a polyol solution that is a polar solvent is used. In particular, ethylene glycol, diethylene glycol, or triethylene glycol can be used. Any material that dissolves and adsorbs to the generated noble metal particles and copper particles to form steric hindrance, for example, polyethyleneimine, polyvinylpyrrolidone, or polyallylamine is preferable, and among them, polyethylene having high affinity with copper Imine is particularly preferred. Here, the water-soluble polymer is a copper having excellent dispersibility with almost no agglomeration by covering the surfaces of the noble metal fine particles and copper fine particles that have been reduced or added, and preventing contact between the fine particles due to steric hindrance. Has the effect of promoting the formation of fine particles.

  As addition amount of the said polyethyleneimine (PEI), the mass ratio (PEI / Cu) with respect to copper has the preferable range of 0.005-0.1, and the range of 0.01-0.03 is more preferable. That is, when the mass ratio is less than 0.005, the coverage of the fine particles is reduced, the noble metal fine particles serving as nuclei or the produced copper fine particles are aggregated during the reaction, and the resulting copper fine particles are coarsened. On the other hand, if the mass ratio exceeds 0.1, the viscosity of the solution becomes too high, and it takes time for solvent substitution and concentration with a polar solvent later, and the residual amount of water-soluble polymer increases after concentration. It is not preferable.

  In general, polymer dispersants have different adsorption capacities for target fine particles depending on the adsorbing group, so that the fine particles for the precious metal particles that are generated or added at the initial stage of the reaction and the copper fine particles that are formed by reducing and precipitating the precious metal particles For use, it is effective to use a mixture of a plurality of different polymer dispersants. Specifically, it is particularly preferable to use at least one of polyvinylpyrrolidone and polyallylamine in addition to the polyethyleneimine. In this case, the addition amount of polyvinyl pyrrolidone (PVP) and / or polyallylamine (PAA) is preferably such that the total mass ratio to copper ((PVP + PAA) / Cu) is less than 0.8, 0.01 to 0 A range of .5 is more preferred. In other words, the addition of polyvinylpyrrolidone or polyallylamine can make the noble metal fine particles that are the core finer, but if the total addition amount exceeds 0.8, the viscosity of the solution becomes too high as in polyethyleneimine. Further, it takes time for solvent substitution and concentration with a polar solvent later, and the residual amount of water-soluble polymer increases after concentration.

Here, when halogen reduction is intended, when halogen elements are mixed from the water-soluble polymer, the halogen elements remain in the finally produced copper fine particles and dispersion liquid. Need to use.
In particular, polyethyleneimine is likely to be mixed with halogen elements in the production process, but when mixed, most of the halogen elements can be removed using an anion exchange resin. Here, as the anion exchange resin, resins other than halogen ion type such as OH ^{− type} and NO ₃ ^{− type} can be used, but it is preferable to use OH ^{− type} resin which does not adversely affect the reduction reaction. . As a removal method, a water-soluble polymer solution is brought into contact with an anion exchange resin, and halogen ions are exchanged and removed. Moreover, as a contact method with resin, well-known methods, such as a batch type and a column type, can be used. By reducing the halogen element content in the water-soluble polymer to less than 1000 ppm by mass, preferably to less than 400 ppm by mass, the halogen content in the finally produced copper fine particles can be made to be less than 20 ppm by mass. it can.

Below, the procedure of the manufacturing method of the copper fine particle dispersion by the polyol method using these raw materials is demonstrated concretely.
As an apparatus used in the above polyol method, an apparatus used in an ordinary polyol method can be used. However, an apparatus in which copper fine particles are difficult to adhere is preferable, and a metal coated with a glass container, a fluororesin or the like is preferable. A container or the like is used. Moreover, in order to perform a reductive reaction uniformly, what is equipped with the stirring apparatus is preferable.

First, the copper raw material, a noble metal compound or a noble metal colloid, and a water-soluble polymer are added to a polyol solution. Next, while stirring and heating the obtained polyol solution to a predetermined maximum temperature, copper fine particles having a water-soluble polymer adsorbed on the surface are generated.
Here, during temperature rising and holding, it is preferable to stir to make the reaction uniform. Although the polyol solution also has an antioxidant effect, nitrogen gas is preferably blown during temperature rise and holding in order to promote the reduction reaction and prevent reoxidation of the copper fine particles.
Further, in order to finely and uniformly generate nuclei for forming copper fine particles, the noble metal compound or the noble metal colloid may be added later to the polyol solution which is being heated by adding other raw materials. Similarly, part or all of the water-soluble polymer can be added later to the polyol solution being heated.

  The highest temperature is preferably 120 to 200 ° C. in order to synthesize uniform copper fine particles. That is, when the highest temperature is less than 120 ° C., the reduction reaction rate of copper is slow, and not only a long time is required until the reaction is completed, but also the resulting copper fine particles are coarsened. On the other hand, when the maximum temperature reaches 200 ° C., the protective effect of the polymer dispersant is reduced, and the particles grow into coarse cohesive particles.

(3) Manufacturing method of coating liquid Below, the manufacturing method of the coating liquid using the polyol solution containing the copper fine particle which adsorb | sucks water-soluble polymer to the fine particle surface obtained by the manufacturing method of the said copper fine particle dispersion is shown. explain.
The copper fine particles in the copper fine particle dispersion obtained by the above production method adsorb water-soluble polymer on the surface of the fine particles, so when used as a material for forming a conductive film, the resistance value after firing is reduced. Therefore, the amount of the water-soluble polymer adsorbed on the surface is preferably less than 1.5% by mass. Therefore, subsequently, a step of substituting the water-soluble polymer with hydroxycarboxylic acid is added to reduce the amount of the water-soluble polymer adsorbed on the surface of the obtained copper fine particles.

  For example, by adding a hydroxycarboxylic acid or a hydroxycarboxylic acid solution to the obtained polyol solution and stirring, one of the water-soluble polymers that coat the surface of the copper fine particles while maintaining the dispersibility of the copper fine particles. Parts can be replaced with hydroxycarboxylic acids. Here, the released water-soluble polymer is discharged by ultrafiltration. If the amount of the water-soluble polymer covering the surface of the copper fine particles is reduced, the copper fine particles are likely to be oxidized, but the oxidation can be suppressed by coating with a hydroxycarboxylic acid.

  Here, the amount of hydroxycarboxylic acid added is as described above. As content of a coating liquid, content of the hydroxycarboxylic acid in the solvent is 5-40 mass%, Preferably it is 10-40 mass%, More preferably, it is 15-35 mass%.

  However, the polyol solution to which the hydroxycarboxylic acid is added contains an excess of water-soluble polymer in addition to the copper fine particles. Moreover, when this water-soluble polymer is used as an electronic material, if it is excessively present in the conductive paste product for wiring material, it causes problems such as an increase in electrical resistance and structural defects. Therefore, following this, it is preferable to remove the water-soluble polymer as much as possible by adding a solvent substitution and concentration step using at least one polar solvent selected from water, alcohol, or ester.

  As this general method, after the obtained copper fine particle dispersion is diluted with the polar solvent, solvent replacement and concentration are performed by ultrafiltration or the like. Thereafter, if necessary, further dilution with a polar solvent, solvent substitution, and concentration are repeated to obtain a copper fine particle dispersion adjusted to have a desired copper fine particle content and impurity content. Here, in order to improve the coating property, the hydroxycarboxylic acid is added and the content of the hydroxycarboxylic acid in the solvent is adjusted to 5 to 40% by mass. A suitable coating solution can be obtained.

2. Coating Film The coating film of the present invention is a coating film obtained by the above-described coating film forming method, and has a volume resistivity of a fired film obtained when fired at 220 ° C. for 1 hour in a nitrogen atmosphere after being applied to a substrate. 50 μΩ · cm or less.
The volume resistivity of the fired film is achieved when the coating liquid is obtained by adjusting the content of hydroxycarboxylic acid in the solvent to 15 to 35% by mass. At this time, the thickness of the coating film is not particularly limited, but is preferably 1 to 3 μm. That is, a low volume resistivity can be obtained by setting the film thickness to 1 μm or more. However, if the film thickness exceeds 3 μm, the uniformity of the coating film decreases, and the volume resistivity increases.

Further, when the content of hydroxycarboxylic acid in the solvent of the coating solution is 5% by mass or more and less than 15% by mass, an increase in volume resistivity due to cracking during drying can be suppressed, but the volume resistivity is 60 μΩ. -About cm.
On the other hand, when no hydroxycarboxylic acid is added, the volume resistivity increases to 100 μΩ · cm or more due to cracks during drying.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the analysis method of the metal used by the Example and the comparative example, the particle size by SEM observation, and the evaluation method of the film thickness and volume resistivity of a baked film are as follows.
(1) Metal analysis: ICP emission analysis was performed.
(2) Particle size measurement by SEM observation: Observation using a field emission electron microscope (FE-SEM, model S-4700) manufactured by Hitachi, Ltd., and randomly selecting 200 copper fine particles from the field of view Then, the particle diameter was measured, and the average particle diameter (d) and the relative standard deviation (standard deviation σ / average particle diameter d) were calculated.
(3) Measurement of film thickness and volume resistivity of fired film: film thickness measured by substrate cross-section observation with field emission electron microscope (FE-SEM, model S-4700) manufactured by Hitachi, Ltd. It was determined from the surface resistivity measured by a resistivity meter (model MCP-T600) manufactured by Dia Instruments Co., Ltd.

Example 1
Using the copper fine particle dispersion obtained by the following [Method for producing copper fine particle dispersion], a coating liquid was produced, and the coating film obtained by the following formation method was evaluated.
[Method for producing copper fine particle dispersion]
The following raw materials were used. Cuprous oxide and polyethyleneimine (PEI) were used after low halogenation.
(A) Copper raw material: cuprous oxide (Cu ₂ O) (manufactured by Chemet)
(B) Noble metal compound: palladium ammonium nitrate (manufactured by N.E. Chemcat)
(C) Polyol solvent: ethylene glycol (EG) (manufactured by Nippon Shokubai Co., Ltd.)
(D) Dispersant: Polyvinylpyrrolidone (PVP) with a molecular weight of 10,000 (manufactured by IPS Japan Ltd.), polyethyleneimine (PEI) with a molecular weight of 1,800 (manufactured by Nippon Shokubai Co., Ltd.)
(E) Hydroxycarboxylic acid: citric acid (special grade, manufactured by Wako Pure Chemical Industries, Ltd.)

(1) Low halogenation treatment 600 g of cuprous oxide (Cu ₂ O) powder having a chlorine content of 40 mass ppm is added to 3 liters of a sodium hydroxide aqueous solution having a concentration of 0.1 mol / L to form a suspension at 80 ° C. The mixture was stirred at the temperature of 1 hour and filtered. The obtained cuprous oxide was added to 3 liters of pure water and stirred for 30 minutes, followed by filtration and vacuum drying at a temperature of 80 ° C. to obtain washed Cu ₂ O powder. The chlorine content of the washed Cu ₂ O powder was 2 ppm by mass with respect to Cu.
On the other hand, 10 g of polyethyleneimine (PEI) having a chlorine content of 3000 ppm by weight was diluted with water so as to have a concentration of 10% by mass, and an anion exchange resin converted into an OH ⁻ form using an aqueous sodium hydroxide solution ( 10 g of Mitsubishi Chemical Corp. (SA-10A) was added and stirred for 8 hours. Thereafter, the resin was separated by filtration and vacuum-dried at a temperature of 80 ° C. to obtain washed PEI. The chlorine content of the washed PEI was 200 ppm by mass.

(2) Synthesis of copper fine particle dispersion First, 1 liter of ethylene glycol (EG) as a solvent, 110 g of washed Cu ₂ O powder, 1.5 g of washed polyethyleneimine (PEI), and a chlorine content of 3 mass ppm After adding 40 g of polyvinylpyrrolidone (PVP), the mixture was stirred and heated while blowing nitrogen gas. Next, 0.2 g of a palladium solution in which palladium ammonium nitrate is dissolved in aqueous ammonia is added and held at a temperature of 150 ° C. for 30 minutes to reduce and precipitate copper fine particles. A dispersion liquid containing copper fine particles (A) Got. In addition, the total content of chlorine in all raw materials with respect to copper fine particles is 6 ppm by mass, the mass ratio of PEI to Cu (PEI / Cu) is 0.015, and the mass ratio of palladium to Cu (Pd / Cu) is also the same. 0.002.
Here, the obtained copper fine particles were filtered, and the average particle diameter (d) and the relative standard deviation (standard deviation σ / average particle diameter d) of the obtained copper fine particles were measured, and further observed by SEM. As a result, the average particle diameter (d) of the obtained copper fine particles was 32 nm, and the relative standard deviation (standard deviation σ / average particle diameter d) was 48%. An SEM photograph is shown in FIG. As can be seen from FIG. 1, the particles are not aggregated.

(3) Solvent substitution / concentration of copper fine particle dispersion Next, a copper fine particle dispersion (B) obtained by substituting most of the solvent ethylene glycol (EG) with water from the obtained dispersion (A) containing copper fine particles. Was prepared.
Specifically, a mixed solvent of pure water and ethylene glycol (weight ratio is pure water: ethylene glycol = 8: 1) is added to 1 liter of the dispersion liquid (A) (Cu: 10% by mass) containing the obtained copper fine particles. A washing solution in which 10 g of citric acid was added to 1 liter was added, and concentrated to about 1/10 by ultrafiltration. Thereafter, the same washing liquid as described above was added until the volume became 2 liters, and the mixed filtrate of pure water and ethanol was discharged out of the system by ultrafiltration, and the solution containing copper fine particles was concentrated to 100 mL. Furthermore, the same washing liquid as above was added to the concentrated liquid again until 1 liter, and the filtrate was discharged out of the system by ultrafiltration to dilute the original liquid to 1/10. By repeating this process twice more, the reaction solvent was brought to the original concentration of 1/200000. Thereafter, the solution after solvent substitution / concentration was recovered to obtain 50 mL of a copper fine particle dispersion (B).

The obtained copper fine particle dispersion (B) is Cu: 57% by mass, Cl: 6% by mass, Pd: 0.1% by mass, and citric acid 0.5% by mass with the balance being pure water and ethylene glycol. The chlorine content with respect to the copper fine particles was 11 mass ppm.
Further, after the copper fine particle dispersion (B) was dried in a vacuum at a temperature of 80 ° C. for 3 hours, a thermogravimetric analysis was performed up to a temperature of 600 ° C. in a nitrogen gas atmosphere. A weight loss of 4.6% by mass was detected over the period from 1.2 to 1.2% by mass from 300 ° C. to 600 ° C. In addition, from the results of thermogravimetric analysis of citric acid, PEI, and PVP separately performed, citric acid started to decompose at around 180 ° C. and almost completely decomposed and evaporated at 300 ° C., and for PEI and PVP, 300 ° C. It has been confirmed that carbon begins to decompose near and completely decomposes and evaporates at 600 ° C., and carbon does not remain as a solid. From this, it is thought that the weight reduction of 300 degreeC-600 degreeC is a weight reduction resulting from decomposition | disassembly of PEI and PVP adsorbed to copper. Therefore, it was found that the water-soluble high molecular weight adsorbed on the copper fine particles was 1.2% by mass.

[Manufacture of coating liquid and evaluation of coating film]
To the copper fine particle dispersion (B), citric acid is added and dissolved by stirring to prepare a coating solution having a citric acid content in the solvent of 11% by mass. The coating was performed on a glass substrate using a 4-bar coater. Then, when the obtained coating film was dried at room temperature (25 degreeC) in air | atmosphere atmosphere, the coating-film surface had specular gloss. As a result of observing the surface of the coating film with a JEOL electron microscope (SEM, model JSM-6360A), no cracks or the like were observed. In addition, the SEM image of the coating-film surface is shown in FIG.
Then, when baked at a temperature of 220 ° C. for 1 hour in a nitrogen atmosphere, the baked film had a specular gloss as before baking. Subsequently, the film thickness and volume resistivity of the fired film were measured. The results are shown in Table 1.

(Example 2)
A coating film was obtained in the same manner as in Example 1 except that a coating solution having a citric acid content of 20% by mass in the solvent was prepared. Note that the surface of the coating film after drying had a specular gloss, and the fired film also had a specular gloss as before the firing. Then, the film thickness and volume resistivity of this fired film were measured. The results are shown in Table 1.

(Example 3)
A coating film was obtained in the same manner as in Example 1 except that a coating solution having a citric acid content of 33% by mass in the solvent was prepared. Note that the surface of the coating film after drying had a specular gloss, and the fired film also had a specular gloss as before the firing. Then, the film thickness and volume resistivity of this fired film were measured. The results are shown in Table 1.

Example 4
In the synthesis of the copper fine particle dispersion, the amount of washed polyethyleneimine (PEI) used was reduced to 0.75 g, and instead of polyvinylpyrrolidone (PVP) having a chlorine content of 3 mass ppm, the chlorine content was Copper fine particles were reduced and precipitated in the same manner as in Example 1 except that polyvinylpyrrolidone (PVP) having a mass of 54 ppm was used. Here, the total content of chlorine in all raw materials relative to the copper fine particles was 25 mass ppm. The obtained copper fine particles were filtered and observed with an SEM. As a result, they were fine particles without aggregation. The copper fine particles had an average particle diameter (d) of 37 nm and a relative standard deviation (standard deviation σ / average particle diameter d) of 55%.

From the obtained dispersion liquid (A ′) containing copper fine particles, a copper fine particle dispersion liquid (B ′) in which most of the solvent ethylene glycol (EG) was replaced with water was prepared in the same manner as in Example 1. The obtained copper fine particle dispersion (B ′) was Cu: 45 mass%, Pd: 0.05 mass%, Na: less than 10 mass ppm, Mg: less than 10 mass ppm, Cl: 13 mass ppm, and citric acid. It was 0.6 mass%, the balance was pure water and ethylene glycol, and the chlorine content with respect to the copper fine particles was 29 mass ppm. Moreover, when the water-soluble high molecular weight adsorb | sucking to this copper fine particle was calculated | required by thermogravimetric analysis similarly to Example 1, it turned out that it is 1.2 mass%.
Furthermore, [Production of coating solution and evaluation of coating film] was carried out in the same manner as in Example 1 except that a coating solution having a citric acid content in the solvent of 9% by mass was prepared. The surface of the coating film had a specular gloss. The fired film also had a specular gloss as before firing. Subsequently, the film thickness and volume resistivity of the fired film were measured. The results are shown in Table 1.

(Comparative Example 1)
A coating film was obtained in the same manner as in Example 1 except that the coating liquid was prepared without adding citric acid to the copper fine particle dispersion. In addition, the coating film surface after drying was cloudy. When an SEM image of the cloudy portion was observed, it was confirmed that fine cracks were generated. In addition, the SEM image of the coating-film surface is shown in FIG. Further, the obtained fired film also had a cloudy coating surface as before firing. Then, the film thickness and volume resistivity of this fired film were measured. The results are shown in Table 1.

(Comparative Example 2)
A coating film was obtained in the same manner as in Example 1 except that a coating solution having a citric acid content of 42% by mass in the solvent was prepared. In addition, the mirror surface gloss was not seen on the coating-film surface after drying, and it was exhibiting black. Further, the obtained fired film was also black as before firing. Then, the film thickness and volume resistivity of this fired film were measured. The results are shown in Table 1.

From Table 1, in Examples 1 to 4, hydroxycarboxylic acid is added to a metal fine particle dispersion composed of metal fine particles having an average particle diameter of 10 to 100 nm and a polar solvent, and the hydroxycarboxylic acid contained in the solvent After preparing and applying a coating solution having an amount of 5 to 40% by mass, it is subjected to a drying treatment at a temperature of room temperature to 120 ° C., and further to a low-temperature baking treatment at a temperature of 200 ° C. or more and less than 250 ° C. In addition, since it was carried out according to the method of the present invention, it was possible to form a highly uniform metallic gloss coating without cracking by drying in the air, and to reduce the volume resistivity of the fired film to 100 μΩ · cm or less. Furthermore, by setting the halogen quality contained in the copper fine particles to 20 mass ppm or less and the content of hydroxycarboxylic acid in the solvent to 15 to 35 mass%, the film thickness is 1 μm or more and the volume That can reduce the anti-rate to below 50μΩ · cm can be seen.
In contrast, in Comparative Example 1 or 2, since the addition of hydroxycarboxylic acid is different from these conditions, it can be seen that satisfactory results cannot be obtained in the surface state and volume resistivity of the coating film.

  As is clear from the above, the coating film forming method using the metal fine particle dispersion of the present invention does not use a special apparatus, and has a metallic luster that does not crack even when the film thickness is 1 μm or more when dried in the air. Since a coating film can be obtained, it is suitably used as a designable pigment having high durability. In addition, since a low-resistance film can be obtained by low-temperature firing, it is also preferably used for a conductive film for electronic materials.

In Example 1, it is the SEM photograph of the copper fine particle which filtered the copper fine particle of the dispersion liquid (A) containing a copper fine particle, and was observed with SEM. In Example 1, it is a SEM image of the film | membrane surface after drying. In Comparative example 1, it is a SEM image of the film | membrane surface after drying.

Claims (11)

A method of forming a coating film using a metal fine particle dispersion composed of metal fine particles and a solvent,
Hydroxycarboxylic acid is further added to the metal fine particle dispersion satisfying the following requirements (a) and (b) to prepare a coating solution satisfying the requirement (c). By applying a drying treatment at a temperature of ˜120 ° C., the uniformity of the coating film is improved, cracking of the coating film is suppressed, and a coating film having a metallic luster and having excellent design properties is obtained. A method for forming a coating film.
(A) The metal fine particles have an average particle size of 10 to 100 nm.
(B) The solvent is a polar solvent.
(C) The coating solution has a hydroxycarboxylic acid content in the solvent of 5 to 40% by mass.   The coating film forming method according to claim 1, wherein the drying treatment is performed in a non-reducing atmosphere.   Furthermore, following the said drying process, it attaches to a baking process at the temperature of 200 to 250 degreeC, The coating-film formation method of Claim 1 or 2 characterized by the above-mentioned.   The method for forming a coating film according to claim 1, wherein the hydroxycarboxylic acid is citric acid.   The coating film forming method according to claim 1, wherein the metal fine particles are at least one kind of fine particles selected from gold, palladium, platinum, silver, or copper.   The coating film forming method according to claim 1, wherein the metal fine particles have a halogen element content of 20 mass ppm or less.   The metal fine particle dispersion is a water-soluble substance which is a metal oxide, hydroxide or salt constituting the metal fine particles and a dispersant in at least one solution selected from ethylene glycol, diethylene glycol or triethylene glycol. 7. The method according to claim 1, wherein the polymer is composed of a metal fine particle and a solvent which are reduced and precipitated by adding and heating a polymer and a noble metal compound or a noble metal colloid for nucleation. The coating film formation method in any one.   The coating film forming method according to claim 7, wherein the content of the halogen element in the metal fine particle dispersion is 20 mass ppm or less with respect to the metal fine particles in the dispersion. 9. The method for forming a coating film according to claim 7, wherein the following requirement (d) is satisfied instead of the requirement (c).
(D) The coating liquid has a hydroxycarboxylic acid content in the solvent of 15 to 35% by mass.   The coating film forming method according to claim 9, wherein the metal is copper. A coating film made of copper obtained by the coating film forming method according to claim 10,
A coating film characterized by having a film thickness of 1 μm or more obtained after baking on a substrate at 220 ° C. for 1 hour in a nitrogen atmosphere , and a volume resistivity of the fired film of 50 μΩ · cm or less.

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