WO2014084275A1

WO2014084275A1 - Conductive paste and method for producing same

Info

Publication number: WO2014084275A1
Application number: PCT/JP2013/081958
Authority: WO
Inventors: 丸山　浩樹
Original assignee: ナミックス株式会社
Priority date: 2012-11-30
Filing date: 2013-11-27
Publication date: 2014-06-05
Also published as: JP6140189B2; JPWO2014084275A1

Abstract

Provided are: a conductive paste which is capable of forming a conductive film having excellent conductivity at a heat treatment temperature of 300°C or less; and a method for producing the conductive paste. A conductive paste which contains: 100 parts by mass of (A) fine silver particles which have (i) an average particle diameter of the primary particles of 40-350 nm, (ii) a crystallite diameter of 20-70 nm and (iii) a ratio of the average particle diameter to the crystallite diameter of 1-5; 1-40 parts by mass of (B) an aliphatic primary amine; and 1-20 parts by mass of (C) a carboxylic acid having a molecular weight of 75-200. A method for producing a conductive paste, which comprises: (1) a step wherein (a) a silver salt of a carboxylic acid and (B) an aliphatic primary amine are mixed with each other; (2) a step wherein (c) a reducing agent is added thereto and a reaction is caused at a reaction temperature of 20-80°C; (3) a step wherein the reaction product is separated into layers and a layer containing (A) fine silver particles is recovered; and (4) a step wherein 1-20 parts by mass of (C) a carboxylic acid having a molecular weight of 75-200 is mixed thereinto per 100 parts by mass of (A) fine silver particles contained in the recovered layer.

Description

Conductive paste and manufacturing method thereof

The present invention relates to a conductive paste containing silver fine particles and a method for producing the same.

In recent years, silver fine particles have been widely used as a raw material for conductive paste for forming electrodes and circuit patterns of electronic components. For example, for a circuit pattern, a conductive paste containing silver fine particles is printed on a substrate, a pattern with a wiring width of about 100 μm is printed by screen printing or the like, and then fired at a high temperature of 500 ° C. or higher to form a conductive film. Is done.

Recently, in addition to the use of polyimide flexible circuit boards in the field of mobile phones, there is a movement to use cheaper PET (polyethylene terephthalate) films, PEN (polyethylene naphthalate) films, and the like. The conductive paste used for these substrates is required to be baked at a low temperature of 200 ° C. or lower.

The conductive paste that can be fired at a low temperature contains fine metal particles. The metal fine particles are produced, for example, by a chemical reduction method in which a reducing agent is added to an aqueous solution containing a metal compound, the metal is reduced in the aqueous solution, and the metal fine particles are precipitated (Patent Document 1). The metal fine particles produced by the chemical reduction method are almost monodisperse and are independent spherical particles. However, in the chemical reduction method described in Patent Document 1, the particle diameter of the silver fine particles specifically produced in the examples is as large as about 1 μm, and it is difficult to fire at a low temperature. Even if silver particles having a particle size of about 1 μm are used for the conductive paste, it is difficult to form a circuit pattern that is further refined because the particle size is large.

As metal fine particles that can be heat-treated at low temperature, the present applicant has (i) an average primary particle size of 40 to 350 nm, (ii) a crystallite size of 20 to 70 nm, and (iii) a crystallite. Silver fine particles having a ratio of the average particle diameter of primary particles to the diameter of 1.5 to 5 have been proposed (Patent Document 2). As the conductive paste containing silver fine particles, a conductive paste has been proposed that can form a conductive film having sufficient conductivity even at a low temperature of 200 ° C. or less, specifically 180 ° C. or less (Patent Document 2).

Japanese Patent Laid-Open No. 10-317022 Japanese Patent No. 4487143

The object of the present invention is to satisfy the above-mentioned situation and satisfy the requirement for forming a fine circuit pattern, while having sufficient conductivity at a heat treatment temperature of 300 ° C. or lower, more preferably 200 ° C. or lower. An object is to provide a conductive paste capable of forming a film and a method of manufacturing the same.

Invention 1 includes (i) an average primary particle size of 40 to 350 nm, (ii) a crystallite size of 20 to 70 nm, and (iii) an average primary particle size with respect to the crystallite size. 100 parts by weight of silver fine particles (A) having a ratio of 1 to 5, 1 to 40 parts by weight of aliphatic primary amine (B), and 1 carboxylic acid (C) having a molecular weight of 75 to 200 The present invention relates to a conductive paste containing about 20 parts by mass.

The present invention 2 is a reaction comprising silver fine particles (A) obtained by mixing a silver salt of a carboxylic acid (a) and an aliphatic primary amine (B) and then adding a reducing agent (c) and reacting them. The present invention relates to a conductive paste obtained by mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200 with 100 parts by mass of silver fine particles (A) in the reaction mixture.

The present invention 3 relates to the conductive paste according to the present invention 1 or 2, wherein the carboxylic acid (C) is a carboxylic acid having a molecular weight of 75 to 160.
Invention 4 is a carboxylic acid (C) comprising an aliphatic monocarboxylic acid containing a linear or branched hydrocarbon group having 6 to 9 carbon atoms and an aliphatic hydroxy acid having 2 to 6 carbon atoms. The present invention relates to the conductive paste according to any one of the first to third aspects, which is at least one carboxylic acid selected.
The invention 5 is characterized in that the carboxylic acid (C) is at least one carboxylic acid selected from the group consisting of hexanoic acid, 2-ethylhexanoic acid, octanoic acid, 4-methyl-n-octanoic acid, lactic acid and glycolic acid. The present invention relates to the conductive paste according to any one of the present inventions 1 to 4.
Invention 6 relates to Inventions 1 to 3, wherein the aliphatic primary amine (B) is at least one aliphatic primary amine selected from the group consisting of 3-methoxypropylamine and 1,2-diaminocyclohexane. 5. The conductive paste according to any one of 5 above.
The present invention 7 relates to the conductive paste according to any one of the present inventions 2 to 6, wherein the reducing agent (c) is at least one reducing agent selected from the group consisting of formic acid, formaldehyde, ascorbic acid and hydrazine.
The present invention 8 is the conductive paste according to any one of the present inventions 2 to 7, wherein the silver salt (a) of the carboxylic acid is a silver salt of at least one carboxylic acid selected from the group consisting of acetic acid and propionic acid. About.
The present invention 9 relates to the conductive paste according to any one of the present inventions 1 to 8, further comprising 1 to 20 parts by mass of a binder resin (D).
The present invention 10 is the present invention, wherein the binder resin (D) is at least one binder resin selected from the group consisting of a phthalic acid-based glycidyl type epoxy resin, an oxetane resin, a thermosetting phenol resin, a urethane resin, and an acrylic resin. The present invention relates to the conductive paste according to the ninth aspect.

The present invention 11 includes (1) a step of mixing a silver salt of a carboxylic acid (a) and an aliphatic primary amine (B), (2) adding a reducing agent (c), and a reaction temperature of 20 to 80 ° C. (3) The step of separating the reaction product into layers and recovering the layer containing silver fine particles (A), (4) 100 parts by mass of silver fine particles (A) contained in the recovered layer On the other hand, the present invention relates to a method for producing a conductive paste including a step of mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200.

The present invention 12 includes (1) a step of mixing a silver salt of a carboxylic acid (a) and an aliphatic primary amine (B) in the presence of an organic solvent, and (2) adding a reducing agent (c). A step of reacting at a reaction temperature of 20 to 80 ° C., (3) a step of separating the reaction product into layers and collecting a layer containing silver fine particles (A), and (4) a silver fine particle contained in the collected layer (A) The present invention relates to a method for producing a conductive paste, comprising a step of mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200 with respect to 100 parts by mass.

In the present invention, the denseness and surface smoothness of the conductive film are ensured at a heat treatment temperature of 300 ° C. or less, preferably 200 ° C. or less, for example, 120 to 180 ° C., and sufficient conductivity (for example, volume resistivity 5.5 μΩ · cm or less, more preferably a level of less than 5 μΩ · cm) can be formed. Moreover, since the conductive paste containing silver fine particles of the present invention has a small average particle size of silver fine particles, it can meet the demand for forming a circuit pattern that is further refined.

The state of the surface of the conductive film of Example 2 and Comparative Example 1 after heat-treating each conductive paste of Example 2 and Comparative Example 1 at 100 ° C. for 30 minutes, 150 ° C. for 30 minutes, and 200 ° C. for 30 minutes is defined as FE. -Shows the relationship between SEM (Field Emission-Scanning Electron Microscope, magnification 80,000 to 200,000 times) and the volume resistivity (Ω · cm) of the conductive film after heat treatment Figure. Heat treatment temperature and heat treatment for each conductive paste of Example 2 and Comparative Example 1 at 90 ° C. for 30 minutes, 120 ° C. for 30 minutes, 150 ° C. for 30 minutes, 200 ° C. for 30 minutes, and 300 ° C. for 30 minutes The graph which shows the relationship with the volume resistivity (ohm * cm) of a subsequent electrically conductive film.

In the present invention, (i) the average particle diameter of primary particles is 40 to 350 nm, (ii) the crystallite diameter is 20 to 70 nm, and (iii) the average particle diameter of the primary particles relative to the crystallite diameter 100 parts by mass of silver fine particles (A) having a ratio of 1 to 5, 1 to 40 parts by mass of aliphatic primary amine (B), and 1 to 1 of carboxylic acid (C) having a molecular weight of 75 to 200 A conductive paste containing 20 parts by mass.

In the present specification, the average particle diameter of the silver fine particles (A) is measured by FE-SEM (JSM7500F) manufactured by JEOL Ltd., and an arithmetic average value of the diameters of 300 arbitrarily selected particles is obtained. The particle diameter was taken. Further, in this specification, the crystallite diameter is obtained by measuring the half width of the plane index (1,1,1) plane peak from the measurement by the powder X-ray diffraction method using Cu Kα ray as the source, and the Scherrer equation. This is the value of the result calculated.

The silver fine particles (A) have (i) an average primary particle diameter of 40 to 350 nm, preferably 50 to 200 nm, more preferably 60 to 180 nm. The silver fine particles (A) used in the present invention are usually almost spherical. Silver fine particles (A) whose primary particles have an average particle size of 40 to 350 nm have good storage stability when they are pasted, because aggregation of silver fine particles is suppressed. (I) Silver fine particles (A) having an average primary particle size of 40 to 350 nm are suitable as a raw material for a conductive paste for printing a fine circuit pattern.

The silver fine particles (A) have a (ii) crystallite diameter of 20 to 70 nm, preferably 20 to 50 nm. (Ii) The conductive paste using the silver fine particles (A) having a crystallite diameter of 20 to 70 nm suppresses volume shrinkage during the heat treatment, and has high density and surface smoothness of the conductive film formed after the heat treatment. Secured. The conductive film is a silver film. (Ii) The silver fine particles (A) having a crystallite diameter of 20 to 70 nm are also suitable as a raw material for a conductive paste for printing a fine circuit pattern of a precise electronic circuit.

The silver fine particles (A) have (iii) the ratio of the average primary particle diameter to the crystallite diameter (average particle diameter / crystallite diameter) of 1 to 5, preferably 1.5 to 4.5. More preferably, it is 2-4. (Iii) The conductive paste using silver fine particles (A) having a ratio of the average particle diameter of primary particles to the crystallite diameter (average particle diameter of primary particles / crystallite diameter) of 1 to 5 is 300 ° C. or lower. It is possible to form a conductive film that ensures denseness and smoothness at the heat treatment temperature. The heat treatment temperature is preferably 200 ° C. or lower, more preferably 180 ° C. or lower, still more preferably 120 to 180 ° C., and particularly preferably 120 to 150 ° C. (Iii) Silver fine particles (A) having a ratio of the average particle diameter of primary particles to the crystallite diameter (average particle diameter of primary particles / crystallite diameter) of 1 to 5 are conductive films having sufficient conductivity. It is suitable as a raw material for the conductive paste capable of forming the film.

The silver fine particles (A) are prepared by mixing a silver salt of a carboxylic acid (a) and an aliphatic primary amine (B), and then adding a reducing agent (c) at a reaction temperature of 20 to 80 ° C. Can be produced by precipitating silver fine particles.

First, a silver salt of carboxylic acid (a) and an aliphatic primary amine (B) are mixed to obtain a solution in which the silver salt of carboxylic acid is dissolved. In solution, it is considered that an aliphatic primary amine is coordinated to a silver salt of carboxylic acid to form a kind of amine complex.

The silver salt (a) of carboxylic acid is preferably silver acetate or silver propionate, particularly preferably silver acetate. These may be used alone or in combination of two.

The aliphatic primary amine (B) may be a chain aliphatic primary amine or a cyclic aliphatic primary amine. The aliphatic primary amine (B) may be a monoamine compound or a polyamine compound such as a diamine compound. The aliphatic primary amine (B) includes those in which an aliphatic hydrocarbon group is substituted with an alkoxy group such as a hydroxyl group, a methoxy group, an ethoxy group, or a propoxy group. The aliphatic primary amine (B) is preferably at least one aliphatic primary amine selected from the group consisting of 3-methoxypropylamine, 3-aminopropanol and 1,2-diaminocyclohexane. The aliphatic primary amine (B) is more preferably at least one selected from the group consisting of 3-methoxypropylamine and 1,2-diaminocyclohexane. An aliphatic primary amine (B) may be used individually by 1 type, or may use 2 or more types together.

The amount of the aliphatic primary amine (B) used is determined depending on the process requirements such as the post-treatment of the silver fine particles to be generated and the conditions of the equipment to be used. The amount of the aliphatic primary amine (B) used is preferably 1 equivalent or more with respect to 1 equivalent of the carboxylic acid silver salt (a) in order to obtain silver fine particles having a controlled particle size. Moreover, even if an excessive amount of the aliphatic primary amine (B) is present, stable production of silver fine particles is possible. The amount of the aliphatic primary amine (B) used is preferably not more than 3.0 equivalents relative to 1 equivalent of the carboxylic acid silver salt (a) so as not to increase the amount of amine released to the environment. Preferably it is 2.0 equivalent or less, Most preferably, it is 1.6 equivalent or less. In particular, when a liquid in which silver fine particles are precipitated by a reducing agent is used as a conductive paste as it is in a subsequent step, an excessive amount of an aliphatic primary amine may be vaporized by heating. The amount of the aliphatic primary amine (B) used is 1 to 3 equivalents relative to 1 equivalent of the silver salt of the carboxylic acid (a) so that the aliphatic primary amine (B) is not excessive. Preferably there is.

The mixing of the carboxylic acid silver salt (a) and the aliphatic primary amine (B) can be carried out in the absence or presence of an organic solvent. When an organic solvent is used, the silver salt of carboxylic acid (a) and the aliphatic primary amine (B) can be easily mixed. Examples of the organic solvent include alcohols such as ethanol, propanol and butanol, ethers such as propylene glycol dibutyl ether, and aromatic hydrocarbons such as toluene. An organic solvent may be used individually by 1 type, or may use 2 or more types together. The amount of the organic solvent used can be set to an arbitrary amount from the viewpoint of convenience of mixing and productivity of silver fine particles in the subsequent steps.

The mixture of the silver salt of carboxylic acid (a) and the aliphatic primary amine (B) is, for example, a primary aliphatic amine (B) or a mixture of a primary aliphatic amine (B) and an organic solvent. While stirring, the silver salt (a) of carboxylic acid is added. Stirring can be continued as necessary even after the addition of the silver salt (a) of carboxylic acid is completed. The temperature during the mixing of the carboxylic acid silver salt (a) and the aliphatic primary amine (B) is preferably maintained at 20 to 80 ° C., more preferably 20 to 60 ° C.

Thereafter, a reducing agent (c) is added to the mixture of the silver salt of carboxylic acid (a) and the aliphatic primary amine (B) to precipitate silver fine particles. The reducing agent is preferably at least one selected from the group consisting of formic acid, formaldehyde, ascorbic acid and hydrazine from the viewpoint of controlling the reaction. The reducing agent is more preferably formic acid. A reducing agent may be used individually by 1 type, or may use 2 or more types together.

The amount of the reducing agent (c) used is usually not less than the redox equivalent relative to the silver salt of the carboxylic acid (a), and the redox equivalent is preferably 0.5 to 5 times, more preferably 1 to 3 times. When the silver salt of carboxylic acid (a) is a silver salt of monocarboxylic acid and formic acid is used as the reducing agent (c), the amount of formic acid used in terms of mole is 1 mol of silver salt of carboxylic acid (a). The amount is preferably from 0.25 to 2.5 mol, more preferably from 0.5 to 1.5 mol, still more preferably from 0.5 to 1.0 mol.

During the addition of the reducing agent (c) and in the subsequent reaction, the reaction temperature is maintained at 20 to 80 ° C. The reaction temperature is preferably 20 to 70 ° C, more preferably 20 to 60 ° C. When the reaction temperature is 20 to 80 ° C., the silver fine particles have sufficient particle growth, high productivity, and secondary aggregation is suppressed. The time required for the addition of the reducing agent and the subsequent reaction depends on the size of the reaction apparatus, but is usually 10 minutes to 10 hours. In addition, during the addition of the reducing agent and in the subsequent reaction, an organic solvent such as an alcohol such as ethanol, propanol or butanol, an ether such as propylene glycol dibutyl ether, or an aromatic hydrocarbon such as toluene is added as necessary. can do.

The layer containing silver fine particles (A) precipitated by the reaction can be used as it is as a conductive paste. The layer containing silver fine particles (A) precipitated by the reaction can be used as a conductive paste after the silver fine particles (A) are precipitated and the supernatant is removed by decantation or the like. When the silver fine particles (A) are precipitated, alcohols such as methanol and ethanol can be added to the layer containing the silver fine particles (A) to accelerate the precipitation of the silver fine particles (A). Moreover, the layer containing silver fine particles (A) can also raise the silver content contained in a layer by distilling off methanol which remains with an evaporator as needed. When a layer containing silver fine particles (A) precipitated by the reaction is used as a conductive paste, the silver fine particles (A) immediately before the solvent contained in the layer is distilled off by an evaporator in order to adjust the viscosity of the paste. A solvent such as dihydroterpineol or benzyl alcohol can be added to the layer containing. The silver content of the conductive paste thus obtained is preferably 30 to 95% by mass, more preferably 50 to 92% by mass.

It is considered that the aliphatic primary amine (B) is coordinated around the silver fine particles (A) to form a kind of amine complex. The amines present around the silver fine particles prevent aggregation of silver fine particles having a particle size of submicron or less. On the other hand, it is considered that amines coordinated with silver fine particles hinder the fusion of silver fine particles when the conductive paste is heat-treated, and become a factor of lowering conductivity.

In the present invention, a layer containing silver fine particles containing 100 parts by mass of silver fine particles (A) and 1 to 40 parts by mass of aliphatic primary amine (B) is further added to a carboxylic acid (C ) Was added to 1 to 20 parts by mass to obtain a conductive paste. In the conductive paste of the present invention, the amines coordinated to the silver fine particles that hindered the fusion of the silver fine particles during the heat treatment are removed from the periphery of the silver fine particles, and the silver fine particles are fused by the low-temperature heat treatment. Can be promoted. The conductive paste of the present invention has a low heat treatment temperature of 300 ° C. or less, and the fusion of the silver fine particles (A) contained in the conductive paste proceeds to ensure the denseness and smoothness, while maintaining the conductivity. It is possible to form a conductive film with improved resistance. The heat treatment temperature is preferably 200 ° C. or lower, more preferably 180 ° C. or lower, still more preferably 120 to 180 ° C., and particularly preferably 120 to 150 ° C.

In the layer containing silver fine particles (A) that can be used as a conductive paste, unreacted aliphatic primary amine (B), silver salt of carboxylic acid (a), and reducing agent (c) were reacted. Carboxylic acid, a salt produced by the reaction of this carboxylic acid and an aliphatic primary amine, etc. remain. Even if a carboxylic acid having a low molecular weight such as acetic acid or propionic acid is present in the layer containing the silver fine particles (A), such a low carboxylic acid is coordinated with the silver fine particles (A). Cannot be removed from the periphery of the silver fine particles (A).

The molecular weight of the carboxylic acid (C) is 75 to 200, more preferably 75 to 160. Since carboxylic acids having a molecular weight of less than 75, such as acetic acid and propionic acid, have a low boiling point, the amines coordinated to the silver fine particles (A) at the time of the heat treatment are removed before the silver fine particles (A) are removed from the surroundings. The amines that have prevented the fusion of the silver fine particles due to the volatilization of the acid cannot be removed from the periphery of the silver fine particles. Since the carboxylic acid having a molecular weight exceeding 200 has a high boiling point or a high thermal decomposition temperature, the carboxylic acid remains between the silver fine particles during the heat treatment at a low temperature of 200 ° C. or lower. May prevent fusion.

The carboxylic acid (C) having a molecular weight of 75 to 200 is 1 to 20 with respect to a mixture containing 100 parts by mass of the silver fine particles (A) and 1 to 40 parts by mass of the aliphatic primary amine (B). Part by mass, preferably 2 to 18 parts by mass, more preferably 3 to 15 parts by mass, and particularly preferably 4 to 12 parts by mass are added. When the amount of the carboxylic acid (C) having a molecular weight of 75 to 200 is less than 1 part by mass, the amount added is too small and the silver fine particles are subjected to heat treatment at a low temperature of 300 ° C. or lower, preferably 200 ° C. or lower (A) The amines that hindered the fusion between each other cannot be removed. When the amount of the carboxylic acid (C) having a molecular weight of 75 to 200 exceeds 20 parts by mass, the silver fine particles (A) tend to aggregate with each other and the stability as a conductive paste is impaired.

Examples of the carboxylic acid (C) having a molecular weight of 75 to 200 include an aliphatic monocarboxylic acid containing a linear or branched hydrocarbon group having 6 to 9 carbon atoms, and an aliphatic hydroxy acid having 2 to 6 carbon atoms. It is preferably at least one carboxylic acid selected from the group consisting of The melting point of the aliphatic hydroxy acid having 2 to 6 carbon atoms is preferably 120 ° C. or lower, and more preferably 80 ° C. or lower. These may be used individually by 1 type, or may use 2 or more types together.

Examples of the aliphatic monocarboxylic acid containing a linear or branched hydrocarbon group having 6 to 9 carbon atoms include hexanoic acid, 3-methylpentanoic acid, heptanoic acid, 2-methylhexanoic acid, 3-methylhexanoic acid, 2-ethylpentanoic acid, octanoic acid, 2-methylheptanoic acid, 6-methylheptanoic acid, 2-ethylhexanoic acid, nonanoic acid, 2-methyl-n-octanoic acid, 4-methyl-n-octanoic acid, 7- And methyl-n-octanoic acid.

Aliphatic hydroxy acids having 2 to 6 carbon atoms include glycolic acid, lactic acid, tartronic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, γ-hydroxybutyric acid, malic acid, tartaric acid, citramalic acid, and citric acid , Isocitric acid, leucine acid, mevalonic acid and the like.

The carboxylic acid (C) having a molecular weight of 75 to 200 is at least one carboxylic acid selected from the group consisting of hexanoic acid, 2-ethylhexanoic acid, octanoic acid, 4-methyl-n-octanoic acid, lactic acid and glycolic acid. It is preferable that Of these, 2-ethylhexanoic acid is preferable. These may be used alone or in combination of two.

The conductive paste of the present invention comprises a layer containing silver fine particles containing 100 parts by mass of silver fine particles (A) and 1 to 40 parts by mass of an aliphatic primary amine (B), and further adding 1 to 1 binder resin (D). It is preferable to include 20 parts by mass. The content of the binder resin (D) in the conductive paste is more preferably 1 to 15 parts by mass, still more preferably 2 to 12 parts by mass, and particularly preferably 3 to 10 parts by mass. By containing the binder resin (D) in the conductive paste, the printability and adhesion to the substrate can be improved.

The binder resin (D) preferably contains an epoxy resin containing an ester bond. The epoxy resin containing an ester bond is not particularly limited as long as it is an epoxy resin containing one or more ester bonds in the molecule. The number of ester bonds in the molecule is preferably 2 so as not to inhibit the sintering of the silver fine particles. The binder resin is preferably, for example, a phthalic acid glycidyl ester type epoxy resin in order to obtain good conductivity. Phthalic acid-based glycidyl ester type epoxy resins are phthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester and alkyl substitution products thereof; for example, dimethyl glycidyl phthalate, methyl glycidyl glycidyl phthalate, diethyl Examples thereof include glycidyl phthalate, dipropyl glycidyl phthalate, and dibutyl glycidyl phthalate. Among these, hexahydrophthalic acid diglycidyl ester is particularly preferable. These may be used individually by 1 type, or may use 2 or more types together.

The binder resin (D) is not limited to an epoxy resin containing an ester bond such as a phthalic acid-based glycidyl ester type epoxy resin, and other oxetane resins, thermosetting phenol resins, urethane resins, acrylic resins. Thermosetting resins such as these can also be used, and these may be used alone or in combination of two or more.

In the case where the conductive paste contains the binder resin (D), it may further contain a curing agent. When the binder resin (D) is an epoxy resin having an ester bond, the curing agent is not particularly limited as long as it cures the epoxy resin. For example, a cationic polymerization initiator, an amine curing agent, an acid An anhydride curing agent, a phenolic curing agent, and the like can be used. As the curing agent, a cationic polymerization initiator is particularly preferable in order that fusion between silver particles proceeds and good conductivity is obtained. These may be used individually by 1 type, or may use 2 or more types together.

Examples of cationic polymerization initiators include Lewis acid salts, onium salts, and fatty acid metals. Among them, the cation salt is preferably an onium salt. The onium salt is particularly preferably a diaryliodonium tetrakis (pentafluorophenyl) boron salt such as 4-methylphenyl [4- (1-methylethyl) phenyl] iodonium tetrakis (pentafluorophenyl) borate.

The content of the curing agent in the conductive paste is not particularly limited because it varies greatly depending on the type of the curing agent and the combination with the binder resin. For example, when the binder resin in the conductive paste is an epoxy resin containing an ester bond and the curing agent is a cationic polymerization initiator, the curing agent is preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the binder resin. More preferably, 2.5 to 8 parts by mass are added.

In addition, the conductive paste of the present invention includes titanium coupling agents (for example, titanate esters such as isopropyl triisostearoyl titanate), silane coupling agents, flame retardants, leveling agents, thixotropic agents, antifoaming agents, ion A scavenger and the like can be contained.

The method for producing a conductive paste of the present invention comprises (1) a step of mixing a silver salt of carboxylic acid (a) and an aliphatic primary amine (B), and (2) adding a reducing agent (c) to react. A step of reacting at a temperature of 20 to 80 ° C., (3) a step of separating the reaction product into layers and recovering a layer containing silver fine particles (A), and (4) a silver fine particle contained in the recovered layer (A ) 1 to 20 parts by weight of a carboxylic acid (C) having a molecular weight of 75 to 200 is mixed with 100 parts by weight.

The method for producing a conductive paste of the present invention comprises (1) a step of mixing a silver salt of a carboxylic acid (a) and an aliphatic primary amine (B) in the presence of an organic solvent, (2) a reducing agent ( c) adding and reacting at a reaction temperature of 20 to 80 ° C., (3) separating the reaction product into layers and recovering the layer containing silver fine particles (A), and (4) the recovered layer. A step of mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200 with 100 parts by mass of silver fine particles (A) contained therein. In the steps (1) to (4), an organic solvent may be added as necessary during the addition of the reducing agent and the subsequent reaction. Examples of the organic solvent include alcohols such as ethanol, propanol, and butanol, ethers such as propylene glycol dibutyl ether, and aromatic hydrocarbons such as toluene.

When the conductive paste of the present invention contains (D) a binder resin and other additives such as a curing agent, simultaneously with the step of mixing the carboxylic acid (C) having a molecular weight of 75 to 200, the (D) binder Resins, curing agents, and the like can be added. Alternatively, (D) a binder resin, a curing agent, or the like can be added before or after the step of mixing the carboxylic acid (C) having a molecular weight of 75 to 200.

Using a conductive paste produced by the above method, a conductive film can be formed by printing or coating on a substrate or the like by a conventionally known method such as screen printing, followed by heat treatment. The heat treatment temperature is preferably 60 to 300 ° C, more preferably 100 to 250 ° C, still more preferably 120 to 200 ° C, particularly preferably 120 to 180 ° C, and most preferably 120 to 150 ° C. Further, the silver fine particles contained in the conductive paste have a small average particle diameter, and can meet the demand for forming a circuit pattern that is further refined.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to these examples.

[Paste containing silver fine particles (AI)]
When 4 kg (45 mol) of 3-methoxypropylamine is put into a reaction vessel and 5 kg (30 mol) of silver acetate is added while maintaining the reaction temperature at 40 ° C. or lower while stirring, the silver acetate becomes a slightly yellow clear solution. Dissolved. To this, 0.7 kg (15 mol) of 95% by weight of formic acid was slowly added dropwise, and while maintaining the reaction temperature at 30 to 40 ° C., silver fine particles were formed with the addition of formic acid, and a slightly yellow and clear solution was gradually formed. It changed to black. After formic acid was added dropwise to complete the reaction, methanol was added to the resulting reaction mixture while stirring, and then allowed to stand at 25 ° C. to separate into two layers. The upper layer was a clear yellow liquid, and black silver fine particles (AI) were precipitated in the lower layer. The upper layer liquid is removed by decantation, and methanol is added and allowed to stand, and the decantation is repeated until 0.3 kg of dihydroterpineol is added and mixed, and the remaining methanol is distilled off by an evaporator. A conductive paste having a silver content of 90% by mass containing silver fine particles (AI) was obtained.

[Paste containing silver fine particles (AII)]
After putting 1.5 kg of toluene in a reaction vessel and adding 0.9 kg (8.0 mol) of 1,2-diaminocyclohexane, 2.5 kg of silver acetate (while maintaining the reaction temperature at 45 ° C. or lower with stirring) 15.0 mol) was added. After confirming that the reaction system was almost uniform, 0.5 kg (10.5 mol) of formic acid was added little by little while stirring. Meanwhile, the reaction temperature was kept at 40-45 ° C. After formic acid was added dropwise to complete the reaction, methanol was added to the resulting reaction mixture while stirring, and then allowed to stand at 20 ° C. to separate into two layers. 40 g of dihydroterpineol was added to and mixed with the paste from which the upper layer liquid was removed by decantation, and the remaining methanol was distilled off with an evaporator to obtain a conductive paste containing silver fine particles (AII) with a silver content of 52 mass%. It was.

The particle characteristics of the silver fine particles (AI) and (AII) in the paste containing silver fine particles were measured and evaluated. The results are shown in Table 1.

The silver fine particles were measured and evaluated as follows.

Average particle diameter: Measured by FE-SEM (JSM7500F) manufactured by JEOL Ltd., an arithmetic average value of 300 arbitrarily selected diameters was obtained, and the value was used as the average particle diameter.

Crystallite diameter: The half-value width of the plane index (1,1,1) plane peak using Cu Kα ray as the radiation source was determined by measurement with an X-ray diffraction measurement device (M18XHF22) manufactured by Mac Science, and the Scherrer equation was used. The crystallite size was calculated.

(Examples 1 to 6, Comparative Examples 1 to 3)
In Comparative Example 1, a paste containing silver fine particles (AI) (silver content 90 mass%) was used as it was as a conductive paste.
In Examples 1 to 6, paste containing silver fine particles (AI) (silver content: 90% by mass) was added to hexanoic acid, 2-ethylhexanoic acid, octanoic acid, 4-methyl-n-octanoic acid, lactic acid, Glycolic acid was added in an amount of 5.6 parts by mass with respect to 100 parts by mass of silver fine particles to obtain a conductive paste. In the conductive paste containing 90% by mass of silver containing silver fine particles (AI), 3-methoxypropylamine is 2.2 parts with respect to 100 parts by mass of silver fine particles, and dihydroterpineol is used as the solvent. 9 parts are included with respect to parts by mass.
In Comparative Example 2, 5.6 parts by mass of formic acid (molecular weight: 46) was added to a paste containing silver fine particles (AI) (silver content 90 mass%) to obtain a conductive paste.
In Comparative Example 3, 5.6 parts by mass of acetic acid (molecular weight: 60) was added to a paste (silver content 90 mass%) containing silver fine particles (AI) to obtain a conductive paste.
Table 2 shows the blends of the conductive pastes of Examples 1 to 6 and Comparative Examples 1 to 3. In Tables 2 to 4, numerical values without unit description indicate parts by mass.

Volume resistivity: Using the conductive paste of each example and comparative example, each conductive paste was 10 mm wide, 50 mm long, and thick on a slide glass having a width of 26 mm, a length of 76 mm, and a thickness of 1.2 to 1.5 mm. It apply | coated to the pattern of about 0.05 mm. After heat-treating the test piece coated with the conductive paste at 200 ° C. for 30 minutes, the thickness and resistance value of the conductive film obtained from the conductive paste were measured as follows.
The thickness of the thin film was measured using a surface roughness shape measuring machine (manufactured by Tokyo Seimitsu Co., Ltd., SURFCOM 1500SD2-12). Moreover, resistance value was measured using the digital multimeter (Toyo Technica company make, 2001 type). From the measurement results, the volume low efficiency was determined by the following formula (1).
Volume resistivity (Ω · cm) = R × W × t / (L × 10000) (1)
R: resistance [Ω], t: thickness [μm]
W: Pattern width 10 mm, L: Pattern length 50 mm

Table 2 shows the measurement results of volume resistivity of the conductive pastes of Examples 1 to 6 and Comparative Examples 1 to 3. In Table 2, the volume resistivity is expressed by using a power of 10 (for example, 2.7 × 10 ^{−6 in} Example 1) and E (for example, 2.7E-06 in Example 1). Shall.

As shown in Table 2, the conductive paste of the present invention contains a carboxylic acid (C) having a molecular weight of 75 to 200, so that it has an excellent volume resistivity of less than 3 μΩ · cm at a heat treatment temperature of 200 ° C. A conductive film with improved conductivity could be formed. The conductive film is a silver film. On the other hand, the conductive paste of Comparative Example 1 not containing carboxylic acid (C) and the conductive pastes of Comparative Examples 2 and 3 containing carboxylic acid having a molecular weight of less than 75 all had a volume resistivity exceeding 3 μΩ · cm. .

Further, for the conductive pastes of Example 2 and Comparative Example 1, a plurality of test pieces were prepared by applying a pattern on a slide glass in the same manner as in Example 1, and each test piece was 30 to 90 ° C. at 30 to 300 ° C., respectively. After heat-treating for minutes, the resistance value and film thickness were measured in the same manner as in Example 1 to determine the volume resistivity. The results are shown in Table 3.

FIG. 1 shows a test piece coated with a conductive paste (Comparative Example 1) using a layer containing silver fine particles (AI) as it is and a conductive paste (Example 2) to which 2-ethylhexanoic acid is added. FE-SEM photographs after heat treatment at 100 ° C. for 30 minutes, 150 ° C. for 30 minutes, and 200 ° C. for 30 minutes, and numerical values of volume resistivity (Ω · cm) are shown. FIG. 2 is a graph showing the relationship between the heat treatment temperature of the conductive paste of Example 2 or Comparative Example 1 and the volume resistivity (Ω · cm) of the conductive film obtained by heat-treating each conductive paste.

As shown in Table 3, FIG. 1 and FIG. 2, the conductive paste of Example 2 can form a conductive film having excellent conductivity with a volume resistivity of 4 μΩ · cm or less at a heat treatment temperature of 150 ° C. It was. Further, the conductive paste of Example 2 was able to form a conductive film having excellent conductivity with a volume resistivity of 5 μΩ · cm or less at a heat treatment temperature of 120 ° C. The conductive paste of Example 2 could form a conductive film having a volume resistivity of about 30 μΩ · cm at a heat treatment temperature of 100 ° C. The conductive paste of Example 2 forms a conductive film with improved conductivity by progressing fusion of silver fine particles contained in the conductive paste even at a low heat treatment temperature of 180 ° C. or lower, preferably 150 ° C. or lower. We were able to. As shown in the FE-SEM photograph of FIG. 1, the conductive paste of Example 2 is preferably a conductive film excellent in denseness and smoothness at a heat treatment temperature of 120 to 180 ° C., more preferably 120 to 150 ° C. It was confirmed that it could be formed. The conductive film of Example 2 is a silver film.

(Example 7)
In addition to the conductive paste of Example 2, 3.3 parts by mass of hexahydrophthalic acid diglycidyl ester as a binder resin and 4-methylphenyl [4- (1-methylethyl) phenyl] iodonium tetrakis (pentafluoro) as a curing agent 0.17 parts by mass of phenyl) borate was added to obtain a conductive paste of Example 7. Table 4 shows the composition of the conductive pastes of Example 7 and Comparative Example 1.

<Measurement of volume resistivity>
Using the conductive pastes of Example 7 and Comparative Example 1, each conductive paste was 10 mm wide, 50 mm long, and about 0.0 mm thick on a slide glass having a width of 26 mm, a length of 76 mm, and a thickness of 1.2 to 1.5 mm. It apply | coated to the pattern of 05 mm. The test piece thus coated was heat-treated at 80 to 200 ° C. for 30 minutes, then the thickness and resistance value of the thin film obtained from the conductive paste were measured, and the volume resistivity was obtained in the same manner as in Example 2. It was. The results are shown in Table 4.

As shown in Table 4, the conductive paste of Example 7 has excellent conductivity with a volume resistivity of 4 μΩ · cm or less at a heat treatment temperature of 150 ° C. even when it contains a binder resin and a curing agent. A film could be formed. Even when the conductive paste of Example 7 includes a binder resin and a curing agent, a conductive film having excellent conductivity with a volume resistivity of 5.5 μΩ · cm or less is formed at a heat treatment temperature of 120 ° C. I was able to. Even when the conductive paste of Example 7 contained a binder resin and a curing agent, a conductive film having a conductivity of 20 μΩ · cm or less could be formed even at a low heat treatment temperature of 100 ° C. The conductive film of Example 7 is a silver film.

According to the conductive paste of the present invention, the denseness and surface smoothness of the conductive film are ensured at a low heat treatment temperature of 300 ° C. or less, preferably 200 ° C. or less, for example, 120 to 180 ° C., and sufficient conductivity (for example, , A volume resistivity of 5.5 μΩ · cm or less, more preferably a level of less than 5 μΩ · cm) can be formed. The conductive paste of the present invention can meet the demand for forming a circuit pattern that is further miniaturized. Furthermore, in the field of mobile phones and other fields, as a substrate, market demands to change from a polyimide flexible circuit board to a more inexpensive PET (polyethylene terephthalate) film, PEN (polyethylene naphthalate) film, etc. The electrically conductive paste of this invention can respond and is very useful industrially.

Claims

(I) The average particle diameter of primary particles is 40 to 350 nm, (ii) the crystallite diameter is 20 to 70 nm, and (iii) the ratio of the average particle diameter of the primary particles to the crystallite diameter is 1 to 100 parts by mass of silver fine particles (A) 5, 1 to 40 parts by mass of aliphatic primary amine (B), and 1 to 20 parts by mass of carboxylic acid (C) having a molecular weight of 75 to 200 A conductive paste.
A reaction mixture containing silver fine particles (A) obtained by mixing a silver salt of a carboxylic acid (a) and an aliphatic primary amine (B) and then adding a reducing agent (c) and reacting the mixture is added to the reaction mixture. A conductive paste obtained by mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200 with 100 parts by mass of silver fine particles (A) in the mixture.
The conductive paste according to claim 1 or 2, wherein the carboxylic acid (C) is a carboxylic acid having a molecular weight of 75 to 160.
The carboxylic acid (C) is at least one selected from the group consisting of an aliphatic monocarboxylic acid containing a linear or branched hydrocarbon group having 6 to 9 carbon atoms and an aliphatic hydroxy acid having 2 to 6 carbon atoms. The conductive paste according to any one of claims 1 to 3, which is a carboxylic acid of
The carboxylic acid (C) is at least one carboxylic acid selected from the group consisting of hexanoic acid, 2-ethylhexanoic acid, octanoic acid, 4-methyl-n-octanoic acid, lactic acid and glycolic acid. 5. The conductive paste according to any one of 1 to 4.
The aliphatic primary amine (B) is at least one aliphatic primary amine selected from the group consisting of 3-methoxypropylamine and 1,2-diaminocyclohexane. The conductive paste according to item.
The conductive paste according to any one of claims 2 to 6, wherein the reducing agent (c) is at least one reducing agent selected from the group consisting of formic acid, formaldehyde, ascorbic acid and hydrazine.
The conductive paste according to any one of claims 2 to 7, wherein the silver salt (a) of the carboxylic acid is a silver salt of at least one carboxylic acid selected from the group consisting of acetic acid and propionic acid.
The conductive paste according to any one of claims 1 to 8, further comprising 1 to 20 parts by mass of a binder resin (D).
The conductive resin according to claim 9, wherein the binder resin (D) is at least one binder resin selected from the group consisting of a phthalic acid-based glycidyl type epoxy resin, an oxetane resin, a thermosetting phenol resin, a urethane resin, and an acrylic resin. paste.
(1) A step of mixing a silver salt of carboxylic acid (a) and an aliphatic primary amine (B),
(2) adding a reducing agent (c) and reacting at a reaction temperature of 20 to 80 ° C .;
(3) Step of recovering a layer containing silver fine particles (A) by separating the reaction product into layers;
(4) A method for producing a conductive paste, comprising a step of mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200 with respect to 100 parts by mass of silver fine particles contained in the collected layer.
(1) mixing a carboxylic acid silver salt (a) and an aliphatic primary amine (B) in the presence of an organic solvent;
(2) adding a reducing agent (c) and reacting at a reaction temperature of 20 to 80 ° C .;
(3) Step of recovering a layer containing silver fine particles (A) by separating the reaction product into layers;
(4) Production of a conductive paste comprising a step of mixing 1 to 20 parts by mass of a carboxylic acid (C) having a molecular weight of 75 to 200 with 100 parts by mass of silver fine particles (A) contained in the recovered layer. Method.