WO2012161201A1 - Conductive paste, base having conductive film obtained using same, and method for producing base having conductive film - Google Patents

Abstract

Provided is a conductive paste which is capable of forming a conductive film that is able to maintain low volume resistivity for a long period of time, while being suppressed in the formation of an oxide coating film. A conductive paste which contains (A) copper particles, (B) a chelating agent which is composed of a compound that has a stability constant logK_cu with copper ions of 5-15 at 25°C at an ionic strength of 0.1 mol/L, (C) a thermosetting resin and (D) an ester or amide of an organic acid having a pKa of 1-4. A conductive film is formed by applying the conductive paste onto a base and then heating and curing the conductive paste at a temperature of less than 150°C.

Description

Conductive paste, base material with conductive film using the same, and method for producing base material with conductive film

The present invention relates to a conductive paste, a base material with a conductive film using the same, and a method for manufacturing a base material with a conductive film.

Conventionally, a method of using a conductive paste for forming a wiring conductor such as an electronic component or a printed wiring board (printed circuit board) is known. Of these, for example, in the production of printed circuit boards, a conductive paste is applied in a desired pattern shape on an insulating substrate made of glass, ceramics, etc., and then heated to 150 ° C. or higher to be baked to form a wiring pattern. It is done by.

As the conductive paste, a silver paste mainly composed of silver (Ag) was mainly applied from the viewpoint of ensuring high conductivity. However, when the silver paste is energized in a high-temperature and high-humidity environment, ion migration (silver electrodeposition) in which silver atoms are ionized and moved by being attracted by an electric field is likely to occur. If ion migration occurs in the wiring pattern, problems such as a short circuit between the wirings occur, which may hinder the reliability of the wiring board.

From the viewpoint of improving the reliability of electronic devices and wiring boards, a technique has been proposed in which a copper paste is used instead of a silver paste as a conductive paste. Since the copper paste hardly causes a migration phenomenon, it is possible to improve the connection reliability of the electric circuit.

However, since copper is generally easy to oxidize, when left in the atmosphere in a high humidity environment, copper oxide is likely to be produced due to reaction with moisture, oxygen, etc. in the atmosphere. For this reason, the conductive film formed by baking the copper paste has a problem that the volume resistivity tends to be high due to the influence of the oxide film.

In order to solve such a problem, a technique for producing a copper powder blended in a copper paste by a wet reduction method has been proposed (for example, refer to Patent Document 1 and Patent Document 2). However, even with the above-described conventional technique, the increase in volume resistivity due to the formation of an oxide film in the conductive paste for wiring conductors has not been sufficiently improved.

On the other hand, in recent years, resin base materials such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polycarbonate have been used as insulating base materials for printed circuit boards. There is a need for a conductive paste capable of forming a conductive film to be a wiring pattern by heating at a sufficiently low temperature of less than 150 ° C., specifically, 120 to 140 ° C.

However, when the conventional copper paste is heated at a temperature as low as 120 to 140 ° C., the resin in the copper paste is insufficiently cured, and the residual ratio of methylol group OH groups in the thermosetting resin. And the hydrophilicity of the film formed of the copper paste increases. As a result, since water vapor easily diffuses in the film formed of copper paste in a high humidity environment, copper oxide is likely to be generated by reaction with diffused moisture, oxygen, etc., and the volume resistivity is greatly increased. There was a problem.

Japanese Unexamined Patent Publication No. 2007-184143 Japanese Unexamined Patent Publication No. 1-158081

The present invention has been made to solve the above-described problems, and is a conductive film that can be cured at a lower temperature than before to suppress the formation of an oxide film and can maintain a low volume resistivity for a long period of time. It is an object to provide a conductive paste capable of forming a film. Moreover, this invention aims at provision of the base material with the electrically conductive film which has the electrically conductive film using the said electrically conductive paste.

The present invention provides the following conductive paste, a substrate with a conductive film, and a method for producing a substrate with a conductive film.
(1) a chelating agent (B) comprising a compound having a stability constant logK _Cu of 5 to 15 between copper particles (A) and copper ions at 25 ° C. and an ionic strength of 0.1 mol / L, and a thermosetting resin A conductive paste comprising (C) and an ester or amide (D) of an organic acid having a pKa of 1 to 4.

(2) The conductive paste according to (1), wherein the copper particles (A) have a surface oxygen concentration ratio O / Cu calculated by X-ray photoelectron spectroscopy of 0.5 or less.

(3) The conductive paste according to (1) or (2), wherein the copper particles (A) are surface-modified copper particles reduced in a dispersion medium having a pH value of 3 or less.
(4) The copper particles (A) are composite metal copper particles in which metal copper fine particles having an average primary particle diameter of 1 to 20 nm are aggregated and adhered to the surface of the metal copper particles having an average primary particle diameter of 0.3 to 20 μm. The conductive paste according to any one of (1) to (3).

(5) In the chelating agent (B), the functional group (a) containing a nitrogen atom and the functional group (b) containing an atom having a lone pair other than the nitrogen atom are arranged at the ortho position of the aromatic ring. The conductive paste according to any one of (1) to (4), which is an aromatic compound.
(6) The conductive paste according to (5), wherein the functional group (b) containing an atom having a lone electron pair other than the nitrogen atom is a hydroxyl group or a carboxyl group.
(7) The conductive paste according to (5) or (6), wherein the nitrogen atom and an atom having a lone electron pair other than the nitrogen atom are bonded via two or three atoms.
(8) The chelating agent (B) is at least one selected from the group consisting of salicylhydroxamic acid, salicylaldoxime and o-aminophenol, according to any one of (1) to (7) Conductive paste.

(9) The conductive paste according to any one of (1) to (8), wherein the thermosetting resin (C) is at least one selected from the group consisting of a phenol resin, a melamine resin, and a urea resin. .
(10) The organic acid ester or amide (D) is at least one selected from the group consisting of formamide, methyl salicylate, dimethyl oxalate, dimethyl malonate and dimethyl maleate (1) to (9) The electrically conductive paste as described in any one of these.

(11) The content of the chelating agent (B) is 0.01 to 1 part by mass with respect to 100 parts by mass of the copper particles (A), according to any one of (1) to (10). Conductive paste.
(12) The content of the thermosetting resin (C) is 5 to 50 parts by mass with respect to 100 parts by mass of the copper particles (A), according to any one of (1) to (11). Conductive paste.
(13) The content of the organic acid ester or amide (D) is 0.5 to 15 parts by mass with respect to 100 parts by mass of the thermosetting resin (C). The electrically conductive paste as described in any one.

(14) A base material with a conductive film having a base material and a conductive film formed by curing the conductive paste according to any one of (1) to (13) on the base material.
(15) The base material with a conductive film according to (14), wherein the base material is at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polycarbonate.
(16) The substrate with a conductive film according to (14) or (15), wherein the conductive film has a volume resistivity of 1.0 × 10 ⁻⁴ Ωcm or less.

(17) A step of applying the conductive paste according to any one of (1) to (13) on a substrate, and heating and curing the conductive paste at a temperature of less than 150 ° C. to form a conductive film. And a process for producing a substrate with a conductive film.

According to the conductive paste of the present invention, it can be cured at a temperature lower than the conventional temperature of less than 150 ° C., the formation of copper oxide is suppressed in a high humidity environment, and a low volume resistivity can be maintained for a long time. A conductive film can be formed. In addition, by using such a conductive paste, a resin or the like is used as an insulating base material, which is highly reliable as a wiring board or the like, and with a conductive film in which an increase in volume resistivity due to formation of an oxide film is suppressed. A substrate can be obtained.

It is a cross-sectional schematic diagram which shows an example of the base material with an electrically conductive film of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
The conductive paste according to an embodiment of the present invention comprises a chelating agent (A) comprising a compound having a stability constant logK _Cu of 5 to 15 between copper particles (A) and copper ions at 25 ° C. and an ionic strength of 0.1 mol / L. B), a thermosetting resin (C), and an ester or amide (D) of an organic acid having a pKa of 1 to 4, respectively.

According to the conductive paste of the embodiment of the present invention, the stability constant logK _Cu with copper ions at 25 ° C. and ionic strength 0.1 mol / L is within a predetermined range as the chelating agent (B) together with the copper particles (A). Since a certain compound is blended, the amount of copper ions that react with oxygen or the like contained in the atmosphere can be reduced, and a conductive paste in which the formation of copper oxide is suppressed can be obtained.

Further, since an ester or amide (D) of an organic acid having a pKa of 1 to 4 is blended as a curing agent (curing accelerator) of the thermosetting resin (C), the temperature is less than 150 ° C., more specifically 120 By heating at a low temperature of ˜140 ° C., the conductive paste can be sufficiently cured, the amount of copper ions reacting with oxygen contained in the atmosphere can be reduced, and the formation of copper oxide is suppressed. It can be.

Furthermore, in a conductive film formed of such a conductive paste, an oxide film containing copper oxide as a main component is difficult to form, and therefore, with a conductive film that suppresses an increase in volume resistivity even in a high humidity environment. It can be a substrate.

[Conductive paste]
The conductive paste of the embodiment contains copper particles (A), a chelating agent (B), a thermosetting resin (C), and an ester or amide (D) of an organic acid having a pKa of 1 to 4. Hereinafter, each component which comprises an electrically conductive paste is demonstrated.

<Copper particles (A)>
The copper particles (A) serve as a conductive component of the conductive paste, and the surface oxygen concentration ratio O / Cu obtained by X-ray photoelectron spectroscopy is 0.5 or less. Hereinafter, the surface oxygen concentration ratio O / Cu obtained by X-ray photoelectron spectroscopy is simply referred to as “surface oxygen concentration ratio O / Cu”.

The surface oxygen concentration ratio O / Cu is represented by the ratio of the surface oxygen concentration (atomic%) to the surface copper concentration (atomic%) of the copper particles measured by X-ray photoelectron spectroscopy. In the present specification, “surface copper concentration (atomic%)” and “surface oxygen concentration (atomic%)” are respectively defined for the particle surface layer in the range from the copper particle surface to the depth of about 3 nm from the center to the center. These are measured values obtained by performing X-ray photoelectron spectroscopic analysis. The range from the surface of the copper particle to the depth of about 3 nm toward the center is a range in which the surface state of the copper particle can be sufficiently grasped by measuring the concentration of each component in the particle region in this range.

When the surface oxygen concentration ratio O / Cu of the copper particles (A) exceeds 0.5, the amount of copper oxide present on the surface of the copper particles (A) is excessive, and when a conductive film is formed, the contact resistance between the particles Is large and the volume resistivity may be high. By using the copper particles (A) having a surface oxygen concentration ratio O / Cu of 0.5 or less, the contact resistance between the copper particles can be reduced, and the conductivity of the conductive film can be improved. The surface oxygen concentration ratio O / Cu of the copper particles (A) is preferably 0.3 or less.

Further, it is preferable that the copper particles (A) have an oxygen concentration contained in the whole particles of 700 ppm or less. The oxygen concentration contained in the copper particles can be measured using, for example, an oxygen concentration meter.

As the copper particles (A), various copper particles can be used as long as the surface oxygen concentration ratio O / Cu is 0.5 or less. The copper particles (A) may be metal copper particles, copper hydride fine particles, or metal copper fine particles obtained by heating copper hydride fine particles (hereinafter also referred to as copper fine particles). Moreover, as a copper particle (A), the composite particle of the form which these metal copper particles and copper fine particle compounded may be sufficient. Examples of the composite particles include those in which copper fine particles are attached or bonded to the surface of metal copper particles. Details of the composite particles will be described later.

The average particle diameter of the copper particles (A) is preferably 0.01 to 20 μm. The average particle diameter of the copper particles (A) can be appropriately adjusted within the range of 0.01 to 20 μm according to the shape of the copper particles (A). If the average particle diameter of a copper particle (A) is 0.01 micrometer or more, the flow characteristic of the electrically conductive paste containing this copper particle will become favorable. Moreover, if the average particle diameter of a copper particle (A) is 20 micrometers or less, it will become easy to produce fine wiring with the electrically conductive paste containing this copper particle.

When the copper particles (A) contain metallic copper particles, the average particle size (average primary particle size) is preferably 0.3 to 20 μm. Further, when the copper particles (A) are composed only of copper fine particles, the average particle diameter of the aggregated particles is preferably 0.01 to 1 μm, and more preferably 0.02 to 0.4 μm.
When the copper particles (A) contain metallic copper particles and the average particle size (average primary particle size) is 0.3 μm or more, the flow characteristics of the conductive paste containing the copper particles are good. Further, when the copper particles (A) are composed only of copper fine particles and the average particle diameter of the aggregated particles is 0.01 μm or more, the flow characteristics of the conductive paste containing the copper particles are good.

Also, when the copper particles (A) contain metallic copper particles and the average particle size (average primary particle size) is 20 μm or less, the conductive paste containing these copper particles makes it easy to produce fine wiring. Further, when the copper particles (A) are composed only of copper fine particles and the average particle diameter of the aggregated particles is 1 μm or less, it becomes easy to produce fine wiring by the conductive paste containing the copper particles.

As the copper particles (A) having a surface oxygen concentration ratio O / Cu of 0.5 or less, for example, the following copper particles (A1) to (A5) can be preferably used.
(A1) Metallic copper particles having an average primary particle diameter of 0.3 to 20 μm.
(A2) Metallic copper particles having an average primary particle size of 0.3 to 20 μm and copper hydride fine particles adhering to the surface of the metallic copper particles, the average particle of the aggregated particles Copper composite particles having copper hydride fine particles having a diameter of 20 to 400 nm.
(A3) Copper hydride fine particles, wherein the agglomerated particles have an average particle size of 10 nm to 1 μm.
(A4) metal copper particles, the metal copper particles having an average primary particle size of 0.3 to 20 μm, and metal copper particles obtained by heating the copper hydride particles adhering to the surface of the metal copper particles, Composite metal copper particles having metal copper fine particles having an average particle diameter of 20 to 400 nm of the aggregated particles.
(A5) Metallic copper fine particles, wherein the aggregated particles have an average particle size of 10 nm to 1 μm.

The composite metal copper particles (A4) are obtained by converting the copper hydride fine particles of the copper composite particles (A2) into metal copper fine particles by heat treatment. The metal copper fine particles (A5) are obtained by converting the copper hydride fine particles (A3) by heat treatment.

In the present specification, the average particle size is determined as follows.
That is, the average primary particle diameter of the metallic copper particles was measured by measuring the Feret diameter of 100 particles randomly selected from a scanning electron microscope (hereinafter referred to as “SEM”) image. It is calculated by averaging the diameters.
The average particle diameter of the aggregated particles made of copper fine particles was measured by measuring the Feret diameter of 100 particles randomly selected from a transmission electron microscope (hereinafter referred to as “TEM”) image. The average particle size is calculated.
Further, for example, in the case of a composite particle including copper particles that are metal copper particles and copper hydride fine particles attached to the surface of the copper particles, such as copper composite particles (A2), the entire composite particles are obtained by SEM. Observing, measuring the Feret diameter of the whole particle including the copper fine particles, and averaging the obtained particle diameter.

As described above, the composite metal copper particles (A4) in the present invention are obtained by attaching metal copper fine particles to at least a part of the surface of the metal copper particles. “Composite metal copper particles” are obtained by heating “copper composite particles” in which copper hydride fine particles adhere to the surface of metal copper particles, and converting the copper hydride fine particles into metal copper fine particles. In addition, the presence or absence of adhesion of fine particles on the surface of the metal copper particles can be confirmed by observing the SEM image. The copper hydride fine particles attached to the surface of the metal copper particles can be identified using an X-ray diffractometer (manufactured by Rigaku Corporation, TTR-III).

As the metal copper particles of the copper composite particles, known copper particles generally used for conductive paste can be used. The metal copper particles may have a spherical shape or a plate shape.

The average particle diameter of the metal copper particles of the copper composite particles is preferably 0.3 to 20 μm, and more preferably 1 to 10 μm.
When the average particle size of the metallic copper particles is less than 0.3 μm, sufficient flow characteristics cannot be obtained when a conductive paste is obtained. On the other hand, when the average particle diameter of the metal copper particles exceeds 20 μm, it may be difficult to produce fine wiring using the obtained conductive paste. The average particle size of the metallic copper particles is more preferably 1 to 10 μm. The average particle diameter of the metal copper particles is calculated by measuring the Feret diameters of 100 metal copper particles randomly selected from the SEM image and averaging the measured values.

The copper hydride fine particles of the copper composite particles exist mainly in a state where the copper hydride fine particles of about 1 to 20 nm are aggregated. The particle shape of the copper hydride fine particles may be spherical or plate-shaped. The average particle diameter of the aggregated particles of copper hydride fine particles is preferably 20 to 400 nm, more preferably 30 to 300 nm, and even more preferably 50 to 200 nm. Particularly preferred is 80 to 150 nm. When the average particle size of the aggregated particles of copper hydride fine particles is less than 20 nm, the copper hydride fine particles are likely to be fused and grown, and when a conductive film is formed, defects such as cracks due to volume shrinkage occur. There is a fear. On the other hand, when the average particle diameter of the aggregated particles of copper hydride fine particles exceeds 400 nm, the particle surface area is not sufficient, the surface melting phenomenon hardly occurs, and it may be difficult to form a dense conductive film. The average particle diameter of the copper hydride fine particles is calculated by measuring the Feret diameter of 100 copper hydride fine particles randomly selected from the TEM image and averaging the measured values.

The amount of the copper hydride fine particles adhering to the surface of the metal copper particles is preferably 5 to 50% by mass, more preferably 10 to 35% by mass of the amount of the metal copper particles.
When the amount of the copper hydride fine particles is less than 5% by mass with respect to the amount of the metal copper particles, the conductive path is not sufficiently formed between the metal copper particles, and the effect of reducing the volume resistivity of the conductive film is sufficient. May not be obtained. On the other hand, if the amount of copper hydride fine particles exceeds 50% by mass with respect to the amount of metal copper particles, it becomes difficult to ensure sufficient fluidity as a conductive paste.
The amount of copper hydride fine particles adhering to the surface of the metal copper particles is, for example, the copper ion concentration in the water-soluble copper compound solution before adding the reducing agent and the reaction liquid after the completion of copper hydride fine particle production. It can be calculated from the difference from the remaining copper ion concentration.

The composite metal copper particles can reliably form a conductive path by the metal copper fine particles present between the metal copper particles, and the volume resistivity when the conductive metal copper particles are formed can be reduced. Further, as described above, by converting the copper hydride fine particles to the metal copper fine particles, the metal copper fine particles can be hardly separated from the metal copper particles. Therefore, it can be set as the electrically conductive paste by which the raise of the viscosity of the electrically conductive paste by the metal copper fine particle being liberated in the electrically conductive paste was suppressed.

The heat treatment of the copper composite particles is preferably performed at a temperature of 60 to 120 ° C, more preferably 60 to 100 ° C, and further preferably 60 to 90 ° C. When the heating temperature exceeds 120 ° C., fusion between the metal copper fine particles is likely to occur, and the volume resistivity when the conductive film is formed may be increased. On the other hand, when the heating temperature is less than 60 ° C., the time required for the heat treatment becomes longer, which is not preferable from the viewpoint of production cost. In addition, 3 mass% or less is preferable and, as for the residual moisture content of the composite metal copper particle obtained after heat processing, 1.5 mass% or less is more preferable.

The heat treatment of the copper composite particles is preferably performed under a reduced pressure of −101 to −50 kPa as a relative pressure. When the heat treatment is performed under a pressure higher than −50 kPa, the time required for drying becomes long, which is not preferable from the viewpoint of production cost. On the other hand, if the pressure during the heat treatment is less than −101 kPa, it is necessary to use a large apparatus for removing excess solvent such as water and drying, which increases the manufacturing cost.

When the average particle size of the metal copper particles of the “composite metal copper particles” is less than 0.3 μm, there is a possibility that sufficient flow characteristics cannot be obtained when a conductive paste is obtained. On the other hand, when the average particle diameter of the metal copper particles exceeds 20 μm, it may be difficult to produce fine wiring by the obtained conductive paste. The average particle diameter of the metal copper particles in the “composite metal copper particles” is more preferably 1 to 10 μm.

The copper fine particles of the “composite metal copper particles” exist mainly in a state where copper fine particles of about 1 to 20 nm are aggregated, like the copper hydride fine particles in the copper composite particles. The copper fine particles may have a spherical shape or a plate shape. If the average particle diameter of the aggregated particles of the copper fine particles is less than 20 nm, the copper fine particles are likely to be fused and grown, and there is a possibility that defects such as cracks accompanying volume shrinkage may occur when the conductive film is formed. On the other hand, if the average particle diameter of the aggregated particles of the copper fine particles exceeds 400 nm, the particle surface area is not sufficient, the surface melting phenomenon hardly occurs, and it becomes difficult to form a dense conductive film. The average particle diameter of the aggregated particles of copper fine particles is more preferably 30 to 300 nm, and more preferably 50 to 200 nm. Particularly preferred is 80 to 150 nm.

In addition, the average particle diameter of the metallic copper particles is calculated by measuring the Feret diameters of 100 metallic copper particles randomly selected from the SEM image and averaging the measured values. The average particle diameter of the copper fine particles is calculated by measuring the Feret diameter of 100 copper hydride fine particles randomly selected from the TEM image and averaging the measured values.

Moreover, as the copper particles (A), for example, “surface modified copper particles” obtained by reducing the surface of the copper particles can be suitably used.
The “surface-modified copper particles” in the present invention are obtained by reducing the surface of copper particles in a dispersion medium having a pH value of 3 or less. “Surface modified copper particles” include, for example, (1) a step of dispersing copper particles in a dispersion medium to form a “copper dispersion”, and (2) a step of adjusting the pH value of the copper dispersion to a predetermined value or less. (3) It can be produced by a wet reduction method having the following steps (1) to (3) of adding a reducing agent to the copper dispersion.

The surface-modified copper particles obtained by the steps (1) to (3) are mainly composed of metallic copper particles. The average primary particle diameter of the surface-modified copper particles is preferably 0.3 to 20 μm (metal copper particles (A1)). In the surface-modified copper particles, if the average primary particle diameter is 0.3 μm or more, the flow characteristics of the conductive paste containing the copper particles are good. Moreover, if the average primary particle diameter of the surface-modified copper particles is 20 μm or less, it becomes easy to produce a fine wiring by the conductive paste containing the copper particles.

The steps (1) to (3) for producing the surface-modified copper particles will be described below.

(1) Preparation of copper dispersion The copper particle generally used as a conductive paste can be used for the copper particle disperse | distributed to a copper dispersion. The particle shape of the copper particles dispersed in the copper dispersion may be spherical or plate-shaped.

The average particle diameter of the copper particles dispersed in the copper dispersion is preferably 0.3 to 20 μm, and more preferably 1 to 10 μm. There exists a possibility that the fluidity | liquidity of an electrically conductive paste may fall that the average particle diameter of a copper particle is less than 0.3 micrometer. On the other hand, when the average particle diameter of the copper particles exceeds 20 μm, it becomes difficult to produce fine wiring with the obtained conductive paste. By setting the average particle diameter of the copper particles to 0.3 to 20 μm, it is possible to obtain a conductive paste having good fluidity and suitable for the production of fine wiring.
The average particle diameter of the copper particles is obtained by measuring the Feret diameter of 100 metal copper particles randomly selected from the SEM image and calculating the average value.

The copper dispersion can be obtained by putting the above copper particles in powder form into a dispersion medium. The concentration of copper particles in the copper dispersion is preferably 0.1 to 50% by mass. When the concentration of the copper particles is less than 0.1% by mass, the amount of the dispersion medium contained in the copper dispersion becomes excessive, and the production efficiency may not be maintained at a sufficient level. On the other hand, when the concentration of the copper particles exceeds 50% by mass, the influence of the aggregation between the particles becomes excessive, and the yield of the surface-modified copper particles may be reduced. When the concentration of the copper particles in the copper dispersion is in the range of 0.1 to 50% by mass, the surface-modified copper particles can be obtained in a high yield.

The dispersion medium for the copper dispersion is not particularly limited as long as it can disperse the copper particles, but those having high polarity can be suitably used. Examples of the highly polar dispersion medium include water, alcohols such as methanol, ethanol and 2-propanol, glycols such as ethylene glycol, and a mixed medium obtained by mixing these. As the highly polar dispersion medium, water can be particularly preferably used.

(2) Adjustment of pH value of copper dispersion liquid The pH value of the copper dispersion liquid obtained by said (1) is adjusted. The pH value can be adjusted by adding a pH adjuster to the copper dispersion.
An acid can be used as a pH adjuster for the copper dispersion. As the pH adjuster for the copper dispersion, for example, carboxylic acids such as formic acid, citric acid, maleic acid, malonic acid, acetic acid, propionic acid, and inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid and the like can be suitably used.

The pH value of the copper dispersion is preferably 3 or less. By adjusting the pH value of the copper dispersion to 3 or less, the oxide film on the particle surface can be removed smoothly in the subsequent reduction treatment step, and the surface oxygen concentration of the resulting surface-modified copper particles can be reduced. . When the pH value of the dispersion exceeds 3, the effect of removing the oxide film formed on the copper particle surface cannot be sufficiently obtained, and the oxygen concentration on the copper particle surface may not be sufficiently reduced. On the other hand, the pH value of the dispersion is preferably 0.5 or more. When the pH value of the dispersion is less than 0.5, copper ions are excessively eluted, and the surface modification of the copper particles may not proceed smoothly. The pH value of the dispersion is more preferably from 0.5 to 2. If the pH value of the dispersion is 3 or less, the dispersion may be reduced as it is.

(3) Reduction treatment of copper dispersion The reduction treatment is performed by adding a reducing agent to the copper dispersion whose pH value is adjusted.
The reducing agent added to the copper dispersion is at least selected from metal hydrides, hydride reducing agents, hypophosphorous acid, hypophosphites such as sodium hypophosphite, amine boranes such as dimethylamine borane, and formic acid. One type can be used. Metal hydrides include lithium hydride, potassium hydride, and calcium hydride. Examples of the hydride reducing agent include lithium aluminum hydride, lithium borohydride, and sodium borohydride. Of these, hypophosphorous acid and sodium hypophosphite can be suitably used.

By performing the surface treatment in the above steps (1) to (3), the copper oxide (Cu ₂ O, CuO) present on the surface of the copper particles as the starting material can be reduced to copper atoms, thereby inhibiting conductivity. This can reduce the amount of copper oxide that becomes a factor.

<Chelating agent (B)>
The chelating agent (B) contained in the conductive paste of the embodiment of the present invention is composed of a compound that can coordinate with copper ions and form a complex with copper ions by the reaction represented by the following formula (1).

However, the symbols in the formulas have the following meanings.
M: Copper ion Z: Chelating agent (B)
MZ: Complex salt x: Number of chelating agent (B) binding to one copper

The chelating agent (B) is composed of a compound having a stability constant logK _Cu of 5 to 15 with copper ions in the case of x = 1 in the above formula (1) at 25 ° C. and an ionic strength of 0.1 mol / L. Is. The stability constant logK _Cu is an index indicating the strength of the binding force between the chelating agent and the metal, and can be obtained as a logarithmic value of the equilibrium constant K _{Cu in} the reaction equation represented by the above formula (1). Specifically, K _Cu can be obtained by the following formula (2).

(In the above formula (2), [] represents the concentration of each component in parentheses.)

With respect to the “stability constant logK _Cu ” in the present invention, specific numerical values for various compounds include, for example, chemical column (Maruzen), Stability Constants of Metal-Ion Complexes (PERGAMON PRESS), Journal of Chemical Engineering. (ACS Publications).

As a chelating agent (B), by compounding a compound having a stability constant logK _Cu of 5 or more with copper ions, at least a part of the copper ions generated in the paste forms a complex with the chelating agent (B). I think that. Therefore, it is possible to reduce the amount of copper ions that react with moisture, oxygen, etc. (for example, O ₂ , H ₂ O, etc.) in the atmosphere, and to suppress the formation of copper oxide in the paste. In addition, since the chelating agent (B) is difficult to dissociate from copper ions, the state of the complex can be maintained for a long time even when left in a high humidity environment. Therefore, the conductive paste can form a conductive film in which an oxide film is hardly formed and an increase in volume resistivity is suppressed.

When the stability constant logK _Cu of the chelating agent (B) is less than 5, since the binding force to copper ions is not sufficient, the amount of copper ions that react with moisture, oxygen, etc. in the atmosphere cannot be sufficiently reduced, It becomes difficult to suppress the production of copper oxide. Moreover, when the stability number logK _Cu of the chelating agent (B) exceeds 15, the binding force of the chelating agent (B) to the copper ions is too strong, which may inhibit the contact between the copper particles and reduce the conductivity. There is. This is presumably because the chelating agent (B) acts not only on the copper ions present on the surface of the copper particles but also on copper (metal copper). The stability constant logK _Cu is more preferably 7 to 14.

As the chelating agent (B), the functional group (a) containing a nitrogen atom and the functional group (b) containing an atom having a lone pair other than the nitrogen atom are arranged at the ortho position of the aromatic ring, An aromatic compound in which the “nitrogen atom” of the functional group (a) and the “atom having a lone pair” of the functional group (b) are bonded via two or three atoms can be preferably used.
By compounding the compound having the molecular structure as a chelating agent (B), a stable complex with copper ions can be formed.

Examples of the atoms interposed between the “nitrogen atom” of the functional group (a) and the “atom having a lone pair” of the functional group (b) include a carbon atom. That is, as the chelating agent (B), among the aromatic compounds, the nitrogen atom of the functional group (a) and the atom having a lone pair of the functional group (b) have 2 or 3 carbon atoms. Those intervened and bonded are preferably used.

Suitable examples of the functional group (b) containing an atom other than a nitrogen atom having a lone electron pair include a hydroxyl group and a carboxyl group.

As the chelating agent (B), specifically, at least one selected from salicylhydroxamic acid, salicylaldoxime, and o-aminophenol can be used.

When salicylaldoxime is used as the chelating agent (B), a complex with copper ions is formed by the reaction represented by the following formula (I).

The content of the chelating agent (B) in the conductive paste is preferably 0.01 to 1 part by mass, more preferably 0.05 to 0.5 part by mass with respect to 100 parts by mass of the copper particles (A). preferable.
When the content of the chelating agent (B) is less than 0.01 parts by mass, the effect of suppressing the increase in volume resistivity may not be sufficiently obtained when the conductive film is formed. On the other hand, when content of a chelating agent (B) exceeds 1 mass part, there exists a possibility that the contact of copper particles may be inhibited and electroconductivity may be reduced.

<Thermosetting resin (C)>
As thermosetting resin (C) contained in the electrically conductive paste of embodiment of this invention, the well-known thermosetting resin used as a resin binder of a normal electrically conductive paste can be used.

As a thermosetting resin (C), a phenol resin, a melamine resin, a urea resin etc. can be used conveniently, for example. Among these, a phenol resin can be particularly preferably used. As the phenol resin, a novolac type phenol resin and a resol type phenol resin can be used, and among these, a resol type phenol resin can be particularly preferably used.
In order to adjust the glass transition point (Tg) of the resin, the above-mentioned thermosetting resin includes diallyl phthalate resin, unsaturated alkyd resin, epoxy resin, isocyanate resin, bismaleidotriazine resin, silicone resin and acrylic resin. You may contain suitably at least 1 type selected from resin.

The thermosetting resin (C) can be added as long as the cured resin component does not impair the conductivity.
The content of the thermosetting resin (C) in the conductive paste can be appropriately selected according to the ratio between the volume of the copper particles and the volume of the voids existing between the copper particles. The amount is preferably 5 to 50 parts by mass, more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the copper particles (A). When the content of the thermosetting resin (C) is less than 5 parts by mass, it becomes difficult to obtain sufficient flow characteristics as a conductive paste. On the other hand, when the content of the thermosetting resin (C) exceeds 50 parts by mass, contact between the copper particles is hindered by the cured resin component, and the volume resistivity of the conductor may be increased.

<Organic acid ester or amide (D)>
In order to cure the ester or amide (D) of the organic acid contained in the conductive paste of the embodiment of the present invention at a temperature of less than 150 ° C. by promoting the curing of the thermosetting resin (C). Blended. The organic acid constituting the ester or amide has a pKa of 1 to 4. If the pKa of the organic acid is less than 1, the storage stability of the conductive paste may be adversely affected. Moreover, when pKa of organic acid exceeds 4, the production | generation of the intermediate body which accelerates | stimulates hardening of the said thermosetting resin (C) becomes slow, and there exists a possibility that the hardening acceleration effect of resin may not be acquired as a result. The pKa of the organic acid is more preferably 1 to 3.

Organic acids having a pKa of 1 to 4 include oxalic acid (1.27), maleic acid (1.92), malonic acid (2.86), salicylic acid (2.97), and fumaric acid (3.02). , Tartaric acid (3.06), citric acid (3.16), formic acid (3.76) and the like.
Among these organic acids having a pKa of 1 to 4, the reasons why esters or amides can be suitably used include the following.

(1) When an ester or amide of an organic acid having a pKa of 1 to 4 is used, the effect of allowing an intermediate of a thermosetting resin (for example, a phenol resin, a melamine resin, or a urea resin) to exist stably is large. This is because the above-mentioned ester or amide is coordinated to a dimethylene ether type intermediate which is an intermediate of the thermosetting resin. This coordination increases the electron density on oxygen of one methylol group at the reaction site, and decreases the electron density on carbon of the opposite methylol group. Therefore, since the dimethylene ether type intermediate is present stably, the reaction probability of the intermediate is increased and curing is promoted. As a result, the durability of the cured conductive film at high temperature and high humidity can be improved.

(2) The reactivity of the above-mentioned intermediate methylenecarbonium ion can be greatly improved by coordination of an ester or amide of an organic acid having a pKa of 1 to 4. Therefore, the contribution to the acceleration of curing is large, and the durability of the conductive film after curing at high temperature and high humidity can be improved.

(3) Organic acid esters and amides are less reactive with metals compared to organic acids and therefore have little effect of corroding metals, and can suppress an increase in volume resistivity of the conductive film after curing. . When a single organic acid having a pKa of 1 to 4 is used, the metal in the conductive paste may be corroded to increase the volume resistivity of the conductive film after curing.

(4) Organic acid esters and amides have little effect on promoting the curing of the thermosetting resin in the paste when the paste is stored, and therefore have little adverse effect on the storage stability (pot life) of the conductive paste.

(5) Since organic acid esters and amides do not inhibit the action of chelating agents that contribute to improving the durability of the conductive film after curing, the durability can be sufficiently maintained.

Examples of the ester or amide of the organic acid having a pKa of 1 to 4 include formamide, methyl salicylate, methyl formate, ethyl formate, dimethyl oxalate, dimethyl maleate, and dimethyl malonate. Although it is not limited to these, It is preferable that it is at least 1 sort (s) selected from these.
Among these esters or amides of organic acids having a pKa of 1 to 4, esters or amides of organic acids not containing sulfur (S) can be preferably used. This is because S may react with copper to produce a sulfide, and even an organic acid ester or amide may adversely affect paste storage stability. Specifically, formamide, methyl salicylate, dimethyl oxalate, dimethyl malonate, and dimethyl maleate can be preferably used.

The content of the organic acid ester or amide (D) in the conductive paste is preferably 0.5 to 15 parts by mass with respect to 100 parts by mass of the thermosetting resin (C). Is more preferable. If the content of the organic acid ester or amide (D) is less than 0.5 parts by mass, the effect of promoting the curing of the resin may not be sufficiently obtained. On the other hand, when content of the said organic acid ester or amide (D) exceeds 15 mass parts, there exists a possibility that the contact of copper particles may be inhibited and electroconductivity may be reduced.

<Other ingredients>
If necessary, the conductive paste of the present invention may contain a solvent and various additives (leveling agent, coupling agent, viscosity modifier, antioxidant, adhesive agent, etc.) in addition to the components (A) to (D). Other components such as.) May be included as long as the effects of the present invention are not impaired. In particular, in order to obtain a paste body having appropriate fluidity, it is preferable to contain a solvent capable of dissolving the thermosetting resin.

Examples of the solvent contained in the conductive paste include cyclohexanone, cyclohexanol, terpineol, ethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol, diethylene glycol monoethyl. Ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate and the like can be suitably used.
From the viewpoint of setting an appropriate viscosity range for the printing paste body, the amount of the solvent contained in the conductive paste is preferably 1 to 10% by mass with respect to the copper particles (A).

The conductive paste according to the embodiment of the present invention can be obtained by mixing the components (A) to (D) with other components such as a solvent.

The mixing of the components (A) to (D) can be carried out while heating at a temperature that does not cause curing of the thermosetting resin or volatilization of the solvent. The temperature during mixing and stirring is preferably 10 to 40 ° C. More preferably, the temperature is 20 to 30 ° C. When forming the conductive paste, by setting the temperature to 10 ° C. or higher, the viscosity of the paste can be sufficiently reduced, and stirring can be performed smoothly and sufficiently. Moreover, the copper hydride produced | generated on the copper particle surface can be made into a copper atom. On the other hand, when the temperature at which the conductive paste is formed exceeds 40 ° C., the thermosetting resin (C) may be cured in the paste or the particles may be fused.
In order to prevent the copper particles from being oxidized during mixing, it is preferable to mix in a container substituted with an inert gas.

According to the conductive paste of the present invention described above, it is difficult to oxidize in the air, and it is possible to form a conductive film in which an increase in volume resistivity due to the formation of copper oxide is suppressed as compared with a conventional conductive paste.

[Substrate with conductive film]
For example, as shown in FIG. 1, the base material 10 with a conductive film of the present invention has a conductive film 12 formed by curing the above-described conductive paste on a base material 11. This base material 10 with a conductive film is formed by applying the conductive paste to the surface of the base material 11 to form a conductive paste film, removing volatile components such as a solvent, and then the thermosetting resin (C ) Is cured to form the conductive film 12.

As the base material 11, a glass substrate, a plastic base material (for example, a film-like base material made of a polyimide film, a polyester film or the like), a fiber reinforced composite material (a glass fiber reinforced resin substrate or the like), a ceramic substrate, or the like is used. be able to. When the conductive paste of the present invention is used, the conductive film 12 is formed by curing the thermosetting resin (C) by heating at a temperature of less than 150 ° C. (for example, 120 to 140 ° C.), as will be described later. Therefore, a plastic substrate such as polyester such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polycarbonate, or the like can be particularly preferably used.

Examples of the method for applying the conductive paste include known methods such as screen printing, roll coating, air knife coating, blade coating, bar coating, gravure coating, die coating, and slide coating.
Among these, since a smooth wiring shape in which the occurrence of unevenness on the surface and side surfaces is suppressed can be efficiently formed on the substrate 11, the screen printing method is preferably used.

The curing of the thermosetting resin (C) can be performed by holding the substrate on which the conductive paste film is formed at a temperature of less than 150 ° C. (for example, 120 to 140 ° C.). By setting the curing temperature to 120 ° C. or higher, the thermosetting resin can be sufficiently cured. On the other hand, by setting the curing temperature to 140 ° C. or lower, curing can be performed without deforming the substrate even when a substrate such as a plastic film is used. Examples of the heating method include warm air heating, thermal radiation, and IR heating. Note that the conductive film may be formed in the air or in a nitrogen atmosphere with a small amount of oxygen.

The thickness of the conductive film 12 on the substrate 11 is preferably 1 to 200 μm, and more preferably 5 to 100 μm, from the viewpoint of ensuring stable conductivity and maintaining the wiring shape. . The volume resistivity of the conductive film 12 is preferably 1.0 × 10 ⁻⁴ Ωcm or less. If the volume resistivity of the conductive film 12 exceeds 1.0 × 10 ⁻⁴ Ωcm, there is a possibility that sufficient conductivity cannot be obtained as a conductor for electronic equipment.

In the base material 10 with a conductive film according to the present invention, since the conductive film 12 is formed using the conductive paste of the present invention described above, an oxide film made of copper oxide is hardly generated, and a conventional base material with a conductive film is formed. In comparison with, a substrate with a conductive film having a low volume resistivity and suppressed increase in volume resistivity even when used for a long time in a high humidity environment can be obtained.

As mentioned above, although an example was given and demonstrated about the base material with an electrically conductive film of this invention, a structure can be suitably changed as needed in the limit which is not contrary to the meaning of this invention. Moreover, in the manufacturing method of the base material with a conductive film of this invention, it can change suitably about the formation order of each part etc. in the limit in which manufacture of a base material with a conductive film is possible.

Hereinafter, the present invention will be described in more detail with reference to examples. Examples 1 to 4 are examples of the present invention, and examples 5 to 10 are comparative examples.

The copper particles were subjected to a reduction treatment to obtain copper particles (A) (surface modified copper particles).
That is, first, 3.0 g of formic acid and 9.0 g of a 50 mass% hypophosphorous acid aqueous solution were put into a glass beaker, and the beaker was put in a water bath and kept at 40 ° C.

Next, 5.0 g of copper particles (trade name: “1400 YP”, average primary particle diameter: 7 μm, manufactured by Mitsui Mining & Smelting Co., Ltd.) are gradually added to this beaker and stirred for 30 minutes to obtain a “copper dispersion”. It was. The obtained “copper dispersion liquid” was centrifuged at 3000 rpm for 10 minutes using a centrifuge to collect a precipitate. This precipitate was dispersed in 30 g of distilled water, and the aggregate was precipitated again by centrifugation, thereby separating the precipitate. The obtained precipitate was heated at 80 ° C. for 60 minutes under a reduced pressure of −35 kPa, and the residual water was volatilized and removed gradually to obtain copper particles (A-1) whose particle surfaces were modified. .

About the obtained copper particles (A-1), the surface oxygen concentration [atomic%] and the surface copper concentration [under the following conditions were measured by an X-ray photoelectron spectrometer (trade name: “ESCA5500” manufactured by ULVAC-PHI). Atomic%] was measured.
・ Analysis area: 800mm ² Φ
・ Pass Energy: 93.9eV
・ Energy Step: 0.8eV / step

When the surface oxygen concentration ratio O / Cu was calculated by dividing the obtained surface oxygen concentration by the surface copper concentration, the surface oxygen concentration ratio O / Cu of the copper particles (A-1) was 0.16.
The amount of oxygen in the copper particles (A-1) was 460 ppm as measured using an oximeter (manufactured by LECO, trade name: “ROH-600”).

(Example 1)
To a resin solution obtained by mixing 0.74 g of phenol resin (manufactured by Gunei Chemical Co., Ltd., trade name: “Resitop PL 6220”, resin solid content: 58 mass%) and 0.43 g of ethylene glycol monobutyl ether acetate, 0. After adding 005 g and dissolving, 0.0215 g of formamide was added and dissolved. Next, 5.0 g of the copper particles (A-1) was blended in the obtained resin solution and mixed in a mortar to obtain a conductive paste 1.

This conductive paste 1 was applied to a wiring shape (band shape) having a width of 1 mm and a thickness of 20 μm on a PET substrate by a screen printing method, and heated at 130 ° C. for 15 minutes to cure the phenol resin. Thus, the base material 1 with a conductive film having the conductive film 1 was formed.

(Example 2)
A conductive paste 2 was obtained in the same manner as in Example 1 except that 0.0215 g of formamide was changed to 0.0215 g of methyl salicylate. Subsequently, it replaced with the electrically conductive paste 1, and apply | coated the electrically conductive paste 2 on the PET board | substrate, and obtained the base material 2 with an electrically conductive film similarly to Example 1 except having formed the electrically conductive film 2. FIG.

(Example 3)
0.005 g of salicylhydroxamic acid was changed to 0.005 g of salicylaldoxime, and 0.0215 g of formamide was changed to 0.0215 g of dimethyl oxalate. Otherwise in the same manner as in Example 1, a conductive paste 3 was obtained. Subsequently, it replaced with the electrically conductive paste 1, and apply | coated the electrically conductive paste 3 on the PET board | substrate, and obtained the base material 3 with an electrically conductive film similarly to Example 1 except having formed the electrically conductive film 3. FIG.

(Example 4)
A conductive paste 4 was obtained in the same manner as in Example 3 except that 0.0215 g of dimethyl oxalate was changed to 0.0215 g of dimethyl maleate. Subsequently, it replaced with the electrically conductive paste 3, and applied the electrically conductive paste 4 on the PET board | substrate, and except having formed the electrically conductive film 4, it carried out similarly to Example 3, and obtained the base material 4 with the electrically conductive film.

(Example 5)
0.0215 g of formamide was not added to the resin solution. Otherwise in the same manner as in Example 1, a conductive paste 5 was obtained.

(Example 6)
A conductive paste 6 was obtained in the same manner as in Example 1 except that 0.0215 g of propylene carbonate was added to the resin solution instead of 0.0215 g of formamide.

(Example 7)
A conductive paste 7 was obtained in the same manner as in Example 1 except that 0.0215 g of phenyl acetate was added to the resin solution instead of 0.0215 g of formamide.

(Example 8)
A conductive paste 8 was obtained in the same manner as in Example 1 except that 0.0215 g of salicylic acid was added to the resin solution instead of 0.0215 g of formamide.

(Example 9)
A conductive paste 9 was obtained in the same manner as in Example 1 except that 0.0215 g of oxalic acid was added to the resin solution instead of 0.0215 g of formamide.

(Example 10)
A conductive paste 10 was obtained in the same manner as in Example 1 except that 0.0215 g of maleic acid was added to the resin solution instead of 0.0215 g of formamide.

Next, instead of the conductive paste 1, conductive pastes 5 to 10 were respectively applied on a PET substrate and heated at 130 ° C. for 15 minutes to form conductive films 5 to 10. Otherwise in the same manner as in Example 1, substrates 5 to 10 with conductive film (Examples 5 to 10) were obtained.

(Conductor wiring resistance)
The resistance values of the obtained conductive films 1 to 10 were measured using a resistance meter (trade name: “Milliohm Hitester” manufactured by Keithley) to determine the initial volume resistivity.

(Durability test)
Durability tests were conducted on the substrates 1 to 10 with the conductive film in a high-temperature and high-humidity environment. That is, the resistance values of the conductive films 1 to 10 were measured after holding the conductive film-coated substrates 1 to 10 in a bath at 60 ° C. and 90% RH at a high temperature and high humidity for 240 hours. And the volume resistivity after a durability test was calculated | required.

Table 1 shows the initial volume resistivity thus obtained and the rate of change (increase rate) of the volume resistivity after the durability test.
In addition, in Table 1, the addition amount of a hardening | curing agent is shown with the addition amount (mass part) with respect to 100 mass parts of solid content of a phenol resin.

As is apparent from Table 1, the conductive film substrates 1 to 4 in which the conductive films 1 to 4 are formed from the conductive pastes 1 to 4 containing an ester or amide of an organic acid having a pKa of 1 to 4 (Example 1) In (4) to (4), the volume resistivity was low, and the fluctuation rate (increase rate) of the volume resistivity after the durability test in a high temperature and high humidity environment was also kept low.

On the other hand, in the base material 5 with the conductive film in which the conductive film 5 is formed with the conductive paste 5 formed without blending the ester or amide of the organic acid (Example 5), after the durability test in a high temperature and high humidity environment. The variation rate of the volume resistivity was as high as 20%, and the durability was poor.

In addition, in the base materials 6 to 7 with conductive films 6 to 7 (Examples 6 and 7) in which the conductive films 6 to 7 are formed by the conductive pastes 6 and 7 containing an ester or amide of an organic acid having a pKa of more than 4, high temperature and high humidity The variation rate of the volume resistivity after the durability test under the environment was further increased to 20 to 27%, and the durability was inferior.
Furthermore, the conductive film bases 8 to 10 (Examples 8 to 10) in which the conductive films 8 to 10 are formed by using the conductive pastes 8 to 10 in which an organic acid itself having a pKa of 1 to 4 is blended instead of an ester or an amide, The fluctuation rate of the volume resistivity after the durability test in a high temperature and high humidity environment was as high as 23 to 26%, and the durability was inferior.

Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2011-114604 filed on May 23, 2011, the contents of which are incorporated herein by reference.

According to the conductive paste of the present invention, it can be cured at a temperature lower than the conventional temperature of less than 150 ° C., the formation of copper oxide is suppressed in a high humidity environment, and a low volume resistivity can be maintained for a long time. A conductive film can be formed. In addition, by using such a conductive paste, a resin or the like is used as an insulating base material, which is highly reliable as a wiring board or the like, and with a conductive film in which an increase in volume resistivity due to formation of an oxide film is suppressed. A substrate can be obtained.

DESCRIPTION OF SYMBOLS 10 ... Base material with a conductive film, 11 ... Base material, 12 ... Conductive film.

Claims (17)

1. A chelating agent (B) composed of a compound having a stability constant logK _Cu of 5 to 15 between the copper particles (A) and copper ions at 25 ° C. and an ionic strength of 0.1 mol / L, and a thermosetting resin (C) And a conductive paste comprising an ester or amide (D) of an organic acid having a pKa of 1 to 4.
2. 2. The conductive paste according to claim 1, wherein the copper particles (A) have a surface oxygen concentration ratio O / Cu calculated by X-ray photoelectron spectroscopy of 0.5 or less.
3. The conductive paste according to claim 1 or 2, wherein the copper particles (A) are surface-modified copper particles that have been reduced in a dispersion medium having a pH value of 3 or less.
4. The copper particles (A) are composite metal copper particles in which metal copper fine particles having an average primary particle diameter of 1 to 20 nm are aggregated and adhered to the surface of the metal copper particles having an average primary particle diameter of 0.3 to 20 μm. Item 4. The conductive paste according to any one of Items 1 to 3.
5. The chelating agent (B) is an aromatic in which a functional group (a) containing a nitrogen atom and a functional group (b) containing an atom having a lone pair other than the nitrogen atom are arranged at the ortho position of the aromatic ring. The conductive paste according to any one of claims 1 to 4, which is a compound.
6. The conductive paste according to claim 5, wherein the functional group (b) containing an atom having a lone electron pair other than the nitrogen atom is a hydroxyl group or a carboxyl group.
7. The conductive paste according to claim 5 or 6, wherein the nitrogen atom and an atom having a lone electron pair other than the nitrogen atom are bonded via two or three atoms.
8. The conductive paste according to any one of claims 1 to 7, wherein the chelating agent (B) is at least one selected from the group consisting of salicylhydroxamic acid, salicylaldoxime and o-aminophenol.
9. The conductive paste according to any one of claims 1 to 8, wherein the thermosetting resin (C) is at least one selected from the group consisting of a phenol resin, a melamine resin, and a urea resin.
10. 10. The organic acid ester or amide (D) is at least one selected from the group consisting of formamide, methyl salicylate, dimethyl oxalate, dimethyl malonate, and dimethyl maleate. The electrically conductive paste as described.
11. The conductive paste according to any one of claims 1 to 10, wherein a content of the chelating agent (B) is 0.01 to 1 part by mass with respect to 100 parts by mass of the copper particles (A).
12. The conductive paste according to any one of claims 1 to 11, wherein a content of the thermosetting resin (C) is 5 to 50 parts by mass with respect to 100 parts by mass of the copper particles (A).
13. The content of the organic acid ester or amide (D) is 0.5 to 15 parts by mass with respect to 100 parts by mass of the thermosetting resin (C). Conductive paste.
14. A base material with a conductive film having a base material and a conductive film formed by curing the conductive paste according to any one of claims 1 to 13 on the base material.
15. The base material with a conductive film according to claim 14, wherein the base material is at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polycarbonate.
16. The substrate with a conductive film according to claim 14 or 15, wherein the conductive film has a volume resistivity of 1.0 × 10 ^-4 Ωcm or less.
17. A process comprising: applying a conductive paste according to any one of claims 1 to 13 on a substrate; and heating and curing the conductive paste at a temperature of less than 150 ° C. to form a conductive film. The manufacturing method of a base material with a film.

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