TW201301303A - 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 logKcu with copper ions of 5-15 at 25 DEG 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 DEG C.

Description

Conductive paste, substrate using conductive film therewith, and method of manufacturing substrate with conductive film

The present invention relates to a conductive paste, a substrate to which the conductive film is attached, and a method of manufacturing a substrate 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 circuit board (printed substrate) has been known. For example, the printing substrate is produced by applying a conductive paste to a desired pattern shape on an insulating substrate including glass or ceramics, heating it to 150° C. or higher, and firing it to form a wiring pattern. .

As the conductive paste, a silver paste containing silver (Ag) as a main component is mainly used from the viewpoint of ensuring high conductivity. However, in the case of silver paste, if it is energized in an environment of high temperature and high humidity, ion migration (electrodeposition of silver) in which silver atoms are ionized and moved by an electric field is likely to occur. When ion migration occurs in the wiring pattern, defects such as short-circuiting between wirings may occur, and the reliability of the wiring substrate may be hindered.

From the viewpoint of improving the reliability of an electronic device or a wiring board, a technique of using a copper paste instead of a silver paste as a conductive paste has been proposed. The copper paste is less prone to migration, so the connection reliability of the electronic circuit can be improved.

However, since copper is usually oxidized, if it is placed in the atmosphere in a high humidity environment, copper oxide is easily generated by reaction with moisture or oxygen in the atmosphere. Therefore, the conductive film formed by calcining the copper paste has a problem that the volume resistivity is easily increased by the influence of the oxide film.

In order to solve the above problems, it is proposed to manufacture and mix copper in the form of wet reduction. The technique of the copper powder in the paste (for example, refer to Patent Document 1 and Patent Document 2). However, the actual situation is that the increase in volume resistivity caused by the formation of the oxide film in the conductive paste for wiring conductors is not sufficiently improved according to the above-described prior art.

On the other hand, in recent years, a resin substrate such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polycarbonate has been used as a printed substrate. Since the insulating base material is required to be formed, a conductive film which becomes a wiring pattern by heating at a temperature of not more than 150 ° C, specifically 120 to 140 ° C, which is sufficiently lower than the heat resistant temperature of the substrate, is required. Conductive paste.

However, when the above copper paste is heated at a lower temperature of 120 to 140 ° C, the hardening of the resin in the copper paste becomes insufficient, and the OH group of the methylol group in the thermosetting resin The residual rate is increased, and the hydrophilicity of the film formed by the copper paste is increased. As a result, there is a problem in that in a high-humidity environment, water vapor is easily diffused in a film formed of a copper paste, so that it is easy to generate copper oxide by reaction with water or oxygen which is diffused, and thus volume The resistivity has increased significantly.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2007-184143

Patent Document 2: Japanese Patent Laid-Open No. 1-158081

The present invention has been made to solve the above problems, and an object thereof is to provide a conductive paste which can be cured at a temperature lower than a previous temperature to suppress formation of an oxide film and can form a low volume resistance for a long period of time. The rate of the conductive film. Moreover, an object of the present invention is to provide a substrate having a conductive film using a conductive film of the above conductive paste.

The present invention provides a conductive paste, a substrate with a conductive film, and a method of producing a substrate with a conductive film.

(1) A conductive paste characterized by comprising a copper particle (A), a chelating agent comprising a compound having a stability constant logK _Cu of 5 to 15 with respect to copper ions at 25 ° C and an ionic strength of 0.1 mol/L ( B), a thermosetting resin (C), and an ester of an organic acid having a pKa of 1 to 4 or a decylamine (D).

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

(3) The conductive paste according to (1) or (2) above, wherein the copper particles (A) are surface-modified copper particles which are subjected to reduction treatment in a dispersion medium having a pH of 3 or less.

(4) The conductive paste according to any one of (1) to (3) above, wherein the copper particles (A) are metal copper fine particles having an average primary particle diameter of 1 to 20 nm, and are adhered to the average primary particle diameter. Composite metal copper particles formed on the surface of metallic copper particles of 0.3 to 20 μm.

(5) The conductive paste according to any one of (1) to (4) above, wherein the chelating agent (B) is a functional group (a) containing a nitrogen atom, and a lone pair having a nitrogen-containing atom The functional group (b) of the atom is disposed in the ortho position of the aromatic ring An aromatic compound.

(6) The conductive paste according to (5) above, 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) above, wherein the nitrogen atom and the atomic system having an isolated electron pair other than the nitrogen-removing atom are bonded via two or three atoms.

(8) The conductive paste according to any one of (1) to (7) above, wherein the chelating agent (B) is at least one selected from the group consisting of salicylic acid, salicylaldoxime and ortho-aminophenol.

(9) The conductive paste according to any one of (1) to (8) above, 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 conductive paste according to any one of (1) to (9) above, wherein the ester of the above organic acid or the decylamine (D) is selected from the group consisting of formamide, methyl salicylate, and dimethyl ethanedicarboxylate. At least one of a group consisting of an ester, dimethyl malonate, and dimethyl maleate.

The conductive paste according to any one of the above (1) to (10), wherein the content of the chelating agent (B) is 0.01 to 1 part by mass based on 100 parts by mass of the copper particles (A).

(12) The conductive paste according to any one of the above (1) to (11), wherein the content of the thermosetting resin (C) is 5 to 50 parts by mass based on 100 parts by mass of the copper particles (A).

(13) The conductive paste according to any one of (1) to (12) above, wherein the content of the organic acid ester or the decylamine (D) is relative to the thermosetting resin (C) 100 The mass fraction is 0.5 to 15 parts by mass.

(14) A substrate with a conductive film, comprising: a substrate; and a conductive film formed by hardening the conductive paste according to any one of (1) to (13) above.

(15) The substrate with a conductive film according to the above (14), wherein the substrate is selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polycarbonate. At least one of the group consisting of.

(16) The substrate with a conductive film according to the above (14) or (15), wherein the conductive film has a volume resistivity of 1.0 × 10 ^-4 Ωcm or less.

(17) A method of producing a substrate with a conductive film, comprising the steps of: applying a conductive paste according to any one of (1) to (13) above to a substrate; and less than 150 ° C The conductive paste is heated and hardened at a temperature to form a conductive film.

The conductive paste according to the present invention can be hardened at a temperature lower than 150 ° C lower than the previous temperature, and inhibits the formation of copper oxide in a high humidity environment, and can form a conductive material capable of maintaining a low volume resistivity for a long period of time. membrane. In addition, by using such a conductive paste, it is possible to obtain a conductive film which uses a resin or the like as an insulating base material, has high reliability as a wiring board, and suppresses an increase in volume resistivity due to formation of an oxide film. The substrate.

Hereinafter, embodiments of the present invention will be described in detail.

The conductive paste according to the embodiment of the present invention contains copper particles (A) and a chelating agent (B) containing a compound having a stability constant logK _Cu of 5 to 15 at 25 ° C and an ionic strength of 0.1 mol/L. ), a thermosetting resin (C), and an ester of an organic acid having a pKa of 1 to 4 or a decylamine (D).

The conductive paste according to the embodiment of the present invention has a stability constant logK _Cu of copper ions in the condition of copper particles (A) and chelating agent (B) at 25 ° C and an ionic strength of 0.1 mol/L. Since the compound is in a specific range, it is possible to form a conductive paste which reduces the amount of copper ions which react with oxygen or the like contained in the atmosphere and suppresses the formation of copper oxide.

Further, since an ester of an organic acid having a pKa of 1 to 4 or a guanamine (D) is blended as a curing agent (hardening accelerator) of the thermosetting resin (C), it is not more than 150 ° C, more specifically Heating at a lower temperature of 120 to 140 ° C can sufficiently harden the conductive paste, thereby reducing the amount of copper ions which react with oxygen contained in the atmosphere, and can be made into a conductive paste which suppresses the formation of copper oxide. .

Further, in the conductive film formed using such a conductive paste, it is difficult to form an oxide film containing copper oxide as a main component. Therefore, even in a high-humidity environment, an increase in volume resistivity can be suppressed. A substrate of a conductive film.

[Electrically conductive paste]

The conductive paste of the embodiment contains copper particles (A), a chelating agent (B), a thermosetting resin (C), and an organic acid ester or decylamine (D) having a pKa of 1 to 4. Hereinafter, each component constituting the conductive paste will be described.

<Copper particles (A)>

The copper particles (A) are conductive components of the conductive paste, and the surface oxygen concentration ratio O/Cu determined 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 only It is shown as "surface oxygen concentration ratio O/Cu".

The surface oxygen concentration ratio O/Cu is expressed by the ratio of the surface oxygen concentration (atomic %) measured by X-ray photoelectron spectroscopy to the surface copper concentration (atomic %) of the copper particles. In the present specification, "surface copper concentration (atomic %)" and "surface oxygen concentration (atomic %)" are X-ray photoelectrons in the surface region of the particle in the range from the surface of the copper particle toward the center of about 3 nm. The measured value obtained by spectroscopic analysis. The range from the surface of the copper particle toward the center at a depth of about 3 nm is sufficient to grasp the range of the surface state of the copper particles by measuring the concentration of each component in the particle region of the 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 the conductive film is formed, the contact resistance between the particles is large, and the volume resistance is large. The rate becomes higher. By using the copper particles (A) having a surface oxygen concentration ratio of O/Cu of 0.5 or less, the contact resistance between the copper particles can be lowered, and the conductivity at the time of forming 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, the oxygen concentration contained in all the particles of the copper particles (A) is preferably 700 ppm or less. The oxygen concentration contained in the copper particles can be measured, for example, using 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, or may be copper hydride fine particles or metal copper fine particles (hereinafter also referred to as copper fine particles) obtained by heating hydrogenated copper fine particles. Further, the copper particles (A) may be composite particles in a form in which the metal copper particles are combined with the copper fine particles. Examples of the composite particles include copper microparticle attachment or bonding. Formed on the surface of metallic copper particles. Regarding the composite particles, the details are as follows.

The average particle diameter of the copper particles (A) is preferably from 0.01 to 20 μm. The average particle diameter of the copper particles (A) can be appropriately adjusted in the range of 0.01 to 20 μm in accordance with the shape of the copper particles (A). When the average particle diameter of the copper particles (A) is 0.01 μm or more, the flow characteristics of the conductive paste containing the copper particles are good. In addition, when the average particle diameter of the copper particles (A) is 20 μm or less, it is easy to produce fine wiring by using the conductive paste containing the copper particles.

When the copper particles (A) contain metallic copper particles, the average particle diameter (average primary particle diameter) is preferably from 0.3 to 20 μm. Further, when the copper particles (A) contain only copper fine particles, the average particle diameter of the aggregated particles is preferably 0.01 to 1 μm, more preferably 0.02 to 0.4 μm.

When the copper particles (A) contain metallic copper particles, when the average particle diameter (average primary particle diameter) is 0.3 μm or more, the flow characteristics of the conductive paste containing the copper particles are good. In the case where the copper particles (A) contain only copper fine particles, when 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.

In the case where the copper particles (A) contain metallic copper particles, when the average particle diameter (average primary particle diameter) is 20 μm or less, it is easy to produce fine wiring by using the conductive paste containing the copper particles. In the case where the copper particles (A) contain only copper fine particles, when the average particle diameter of the aggregated particles is 1 μm or less, it is easy to form fine wiring by using the conductive paste containing the copper particles.

As the copper particles (A) having a surface oxygen concentration ratio of O/Cu of 0.5 or less, for example, the following copper particles (A1) to (A5) can be preferably used.

(A1) A metallic copper particle having an average primary particle diameter of 0.3 to 20 μm.

(A2) A copper composite particle comprising: metallic copper particles having an average primary particle diameter of 0.3 to 20 μm; and copper hydride fine particles attached to the surface of the metallic copper particles, wherein an average particle diameter of the aggregated particles is 20~400 nm.

(A3) A copper hydride fine particle having an aggregated particle having an average particle diameter of 10 nm to 1 μm.

(A4) A composite metal copper particle comprising: metallic copper particles having an average primary particle diameter of 0.3 to 20 μm; and metallic copper microparticles for heating copper hydride fine particles attached to the surface of the metallic copper particles The average particle size of the agglomerated particles is 20 to 400 nm.

(A5) A metal copper microparticle having an average particle diameter of aggregated particles of 10 nm to 1 μm.

Further, 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. Further, 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 diameter is determined as follows.

In other words, the average primary particle diameter of the metallic copper particles is measured by a Feret diameter of 100 particles randomly selected from a scanning electron microscope (hereinafter referred to as "SEM (Scanning Electron Microscope)" image, and is calculated. The average of these particle diameters is calculated.

In addition, the average particle diameter of the aggregated particles containing the copper microparticles is measured by the Feret diameter of 100 randomly selected particles in a transmission electron microscope (hereinafter referred to as "TEM (Transmission Electron Microscope)" image, and these are calculated. Calculated by the average of the particle diameters.

Further, for example, when copper particles as metallic copper particles and composite particles of copper hydride fine particles adhering to the surface of the copper particles are contained as in the case of the copper composite particles (A2), the composite particles are observed by SEM. The Feret diameter of the entire particle including the copper fine particles was measured, and the average value of the obtained particle diameter was calculated and calculated.

As described above, the composite metal copper particles (A4) in the present invention are those in which metallic copper fine particles are adhered to at least a part of the surface of the metallic copper particles. The "composite metal copper particles" are obtained by heating "copper composite particles" obtained by adhering hydrogenated copper fine particles to the surface of metallic copper particles, and converting the copper hydride fine particles into metal copper fine particles. Further, the SEM image was observed to confirm whether or not fine particles were adhered to the surface of the metallic copper particles. Further, the identification of the copper hydride fine particles adhering to the surface of the metal copper particles can be carried out using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, TTR-III).

As the metal copper particles of the copper composite particles, known copper particles which are generally used in a 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 from 0.3 to 20 μm, more preferably from 1 to 10 μm.

If the average particle diameter of the metallic copper particles is less than 0.3 μm, sufficient flow characteristics cannot be obtained when the conductive paste is formed. On the other hand, if the metal copper particles When the average particle diameter exceeds 20 μm, it is difficult to produce fine wiring by using the obtained conductive paste. The average particle diameter of the metallic copper particles is preferably from 1 to 10 μm. Further, the average particle diameter of the metallic copper particles was calculated by measuring the Feret diameter of 100 metal copper particles randomly selected from the SEM image, and calculating the average value of the measured values.

The copper hydride fine particles of the copper composite particles are mainly present in a state in which hydrogenated copper fine particles of about 1 to 20 nm are aggregated. The shape of the particles of the copper hydride microparticles may be spherical or plate-shaped. The average particle diameter of the agglomerated particles of the copper hydride fine particles is preferably from 20 to 400 nm, more preferably from 30 to 300 nm, still more preferably from 50 to 200 nm. Especially good is 80~150 nm. When the average particle diameter of the agglomerated particles of the copper hydride fine particles is less than 20 nm, fusion or growth of the copper hydride fine particles is likely to occur, and when the conductive film is formed, defects such as cracks due to volume shrinkage may occur. On the other hand, when the average particle diameter of the agglomerated particles of the copper hydride fine particles exceeds 400 nm, the surface area of the particles is insufficient, and surface melting is less likely to occur, and it is difficult to form a dense conductive film. The average particle diameter of the copper hydride fine particles was calculated by measuring the Feret diameter of 100 hydrogenated copper fine particles randomly selected from the TEM image, and calculating the average value of the measured values.

The amount of the copper hydride fine particles adhering to the surface of the metal copper particles is preferably from 5 to 50% by mass, more preferably from 10 to 35% by mass, based on the amount of the metal copper particles.

When the amount of the copper hydride fine particles is less than 5% by mass based on the amount of the metal copper particles, the conductive passages are not sufficiently formed between the metal copper particles, and the effect of lowering the volume resistivity of the conductive film cannot be sufficiently obtained. On the other hand, when the amount of the copper hydride fine particles exceeds 50% by mass based on the amount of the metal copper particles, it is difficult to ensure sufficient fluidity as the conductive paste.

Further, the amount of the copper hydride fine particles attached to the surface of the metal copper particles may be, for example, the copper ion concentration in the water-soluble copper compound solution before the addition of the reducing agent and the copper remaining in the reaction liquid after completion of the formation of the copper hydride fine particles. Calculated by the difference in ion concentration.

Regarding the composite metal copper particles, the metal copper fine particles existing between the metal copper particles can be used to form the conductive path reliably, and the volume resistivity at the time of forming the conductive film can be reduced. Further, as described above, by converting the copper hydride fine particles into metal copper fine particles, it is possible to produce a peeling of the metallic copper fine particles from the metallic copper particles. Therefore, a conductive paste which suppresses an increase in the viscosity of the conductive paste due to the release of the metallic copper fine particles in the conductive paste can be obtained.

The heat treatment of the copper composite particles is preferably carried out at a temperature of from 60 to 120 ° C, more preferably from 60 to 100 ° C, and still more preferably from 60 to 90 ° C. When the heating temperature exceeds 120 ° C, the metal copper particles are easily fused to each other, and the volume resistivity at the time of forming the conductive film is increased. On the other hand, if the heating temperature is less than 60 ° C, the time required for the heat treatment becomes long, which is not preferable in terms of manufacturing cost. In addition, the residual moisture content of the composite metal copper particles obtained after the heat treatment is preferably 3% by mass or less, and more preferably 1.5% by mass or less.

The heat treatment of the copper composite particles is preferably carried out under a reduced pressure of -101 to -50 kPa under a relative pressure. If the heat treatment is carried out at a pressure of more than -50 kPa, the time required for drying becomes long, which is not preferable in terms of production cost. On the other hand, if the pressure during the heat treatment is set to less than -101 kPa, it is necessary to remove and dry excess solvent such as water. Large installations will increase manufacturing costs.

When the average particle diameter of the metallic copper particles of the "composite metal copper particles" is less than 0.3 μm, sufficient flow characteristics cannot be obtained when the conductive paste is formed. On the other hand, when the average particle diameter of the metallic copper particles exceeds 20 μm, it is difficult to produce fine wiring by using the obtained conductive paste. The average particle diameter of the metallic copper particles in the "composite metal copper particles" is preferably from 1 to 10 μm.

The copper microparticles of the "composite metal copper particles" are the same as the copper hydride microparticles in the copper composite particles, and are mainly present in a state in which copper microparticles of about 1 to 20 nm are aggregated. The particle shape of the copper microparticles may be spherical or plate-shaped. When the average particle diameter of the agglomerated particles of the copper microparticles is less than 20 nm, the copper microparticles are likely to be fused and grown, and when the conductive film is formed, defects such as cracks accompanying volume shrinkage may occur. On the other hand, when the average particle diameter of the aggregated particles of the copper fine particles exceeds 400 nm, the surface area of the particles is insufficient, and surface melting is less likely to occur, and it is difficult to form a dense conductive film. The average particle diameter of the agglomerated particles of the copper microparticles is preferably from 30 to 300 nm, more preferably from 50 to 200 nm. Especially good is 80~150 nm.

Further, the average particle diameter of the metal copper particles was calculated by measuring the Feret diameter of 100 metal copper particles randomly selected from the SEM image, and averaging the measured values. Further, the average particle diameter of the copper microparticles was calculated by measuring the Feret diameter of 100 hydrogenated copper microparticles randomly selected from the TEM image, and calculating the average value of the measured values.

Further, as the copper particles (A), for example, "surface-modified copper particles" obtained by subjecting the surface of copper particles to reduction treatment can be preferably used.

The "surface-modified copper particles" in the present invention are obtained by subjecting the surface of copper particles to a reduction treatment in a dispersion medium having a pH of 3 or less. The "surface-modified copper particles" can be produced, for example, by a wet reduction method including the following steps (1) to (3): (1) dispersing copper particles in a dispersion medium to form a "copper dispersion" The step of (2) adjusting the pH of the copper dispersion to a specific value or less, and (3) the step of adding a reducing agent to the copper dispersion.

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

Hereinafter, steps (1) to (3) for producing surface-modified copper particles will be described.

(1) Production of copper dispersion

As the copper particles dispersed in the copper dispersion, copper particles which are generally used as a conductive paste can be used. The shape of the particles 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 from 0.3 to 20 μm, more preferably from 1 to 10 μm. When the average particle diameter of the copper particles is less than 0.3 μm, the fluidity of the conductive paste is lowered. On the other hand, when the average particle diameter of the copper particles exceeds 20 μm, it is difficult to produce fine wiring by using the obtained conductive paste. By making the average particle diameter of the copper particles 0.3 to 20 μm, it is possible to obtain a conductive paste which is excellent in fluidity and suitable for the production of fine wiring.

Further, the average particle diameter of the copper particles was 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 copper particles into a powder form in a dispersion medium. The concentration of the copper particles in the copper dispersion is preferably from 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 liquid is too large, and the production efficiency cannot be maintained at a sufficient level. On the other hand, when the temperature of the copper particles exceeds 50% by mass, the influence of aggregation of the particles becomes excessive, and the yield of the surface-modified copper particles decreases. By setting the concentration of the copper particles in the copper dispersion to be 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 of the copper dispersion liquid is not particularly limited as long as it can disperse the copper particles, and those having high polarity can be preferably used. As the highly polar dispersion medium, for example, water, an alcohol such as methanol, ethanol or 2-propanol, a glycol such as ethylene glycol, or a mixed medium in which these are mixed may be used. As the highly polar dispersion medium, water is particularly preferably used.

(2) Adjustment of pH of copper dispersion

The pH of the copper dispersion obtained in the above (1) was adjusted. The adjustment of the pH can be carried out by adding a pH adjuster to the copper dispersion.

As the pH adjuster of the copper dispersion, an acid can be used. As the pH adjuster for the copper dispersion, for example, a carboxylic acid such as formic acid, citric acid, maleic acid, malonic acid, acetic acid or propionic acid, or a mineral acid such as sulfuric acid, nitric acid or hydrochloric acid can be preferably used.

The pH of the copper dispersion is preferably set to 3 or less. By using copper dispersion When the pH is set to 3 or less, the oxide film on the surface of the particles can be smoothly removed in the subsequent reduction treatment step, and the surface oxygen concentration of the surface-modified copper particles obtained can be lowered. When the pH of the dispersion exceeds 3, the effect of removing the oxide film formed on the surface of the copper particles cannot be sufficiently obtained, and the oxygen concentration on the surface of the copper particles cannot be sufficiently reduced. On the other hand, the pH of the dispersion is preferably set to 0.5 or more. When the pH of the dispersion is less than 0.5, copper ions are excessively eluted, and it is difficult to smoothly reform the surface of the copper particles. The pH of the dispersion is more preferably 0.5 or more and 2 or less. Further, when the pH of the dispersion is 3 or less, the dispersion may be directly subjected to reduction treatment.

(3) Reduction treatment of copper dispersion

A reducing agent is added to the copper dispersion having a pH adjusted to carry out a reduction treatment.

As the reducing agent to be added to the copper dispersion, a hypophosphite such as a metal hydride, a hydride reducing agent, a hypophosphite or a sodium hypophosphite, an amine borane such as dimethylamine borane, and formic acid can be used. At least one of them. Examples of the metal hydride include lithium hydride, potassium hydride, and calcium hydride. Examples of the hydride reducing agent include lithium aluminum hydride, lithium borohydride, and sodium borohydride. Among these, hypophosphorous acid and sodium hypophosphite can be preferably used.

By performing the surface treatment of the above steps (1) to (3), copper oxide (Cu ₂ O, CuO) present on the surface of the copper particles as a starting material can be reduced to copper atoms, and can be reduced to inhibit conduction. The main factor of sex is the amount of copper oxide present.

<chelating agent (B)>

The chelating agent (B) contained in the conductive paste of the embodiment of the present invention is The copper ion is coordinated and contains a compound which can form a complex with copper ions by a reaction represented by the following formula (1).

Wherein, the symbols in the formula represent the following meanings.

M: copper ion

Z: chelating agent (B)

MZ: wrong salt

x: the number of chelating agents (B) bonded to one copper.

The chelating agent (B) is a compound containing a copper ion having a stability constant log K _Cu of 5 to 15 when x=1 of the above formula (1) at 25 ° C and an ionic strength of 0.1 mol/L. The stability constant logK _Cu is an index indicating the strength of the bonding force between the chelating agent and the metal, and can be obtained as a logarithmic value of the equilibrium constant K _Cu of the reaction formula 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 the parentheses).

The "stability constant log K _Cu " in the present invention is described, for example, in the chemical handbook (Maruzen), Stability Constants of Metal-Ion Complexes (PERGAMON PRESS), and Journal of Chemical Engineering Data (ACS Publications). Etc. in the literature.

It is considered that a compound having a stability constant constant log K _Cu of copper ions of 5 or more is used as the chelating agent (B), whereby at least a part of the copper ions generated in the paste form a complex with the chelating agent (B). Therefore, the amount of copper ions which react with moisture or oxygen in the atmosphere (for example, O ₂ , H ₂ O, etc.) can be reduced, and formation of copper oxide in the paste can be suppressed. Further, since the chelating agent (B) is not easily dissociated from the copper ions, the state of the complex compound can be maintained for a long period of time even when placed in an environment of high humidity. Therefore, it is possible to form a conductive paste which is less likely to form an oxide film and which can form a conductive film which suppresses an increase in volume resistivity.

When the stability constant logK _Cu of the chelating agent (B) is less than 5, the bonding force with respect to copper ions is insufficient, so that the amount of copper ions which react with moisture or oxygen in the atmosphere cannot be sufficiently reduced, and it is difficult to suppress. The formation of copper oxide. Further, when the stability degree logK _Cu of the chelating agent (B) exceeds 15, the bonding force of the chelating agent (B) to the copper ions is too strong, and the contact of the copper particles is inhibited, and the conductivity is lowered. It is presumed that the reason is that the chelating agent (B) acts not only on the copper ions present on the surface of the copper particles but also on the copper (metal copper). The stability constant logK _{Cu is} preferably from 7 to 14.

As the chelating agent (B), a functional group (a) containing a nitrogen atom and a functional group (b) having an atom having a lone electron pair other than the nitrogen atom may be preferably disposed at the ortho position of the aromatic ring. Further, an aromatic compound in which a "nitrogen atom" of the functional group (a) and a "group of atoms having a lone pair of electrons" of the functional group (b) are bonded via two or three atoms.

By formulating a compound having the above molecular structure as the chelating agent (B), a stable complex with copper ions can be formed.

Examples of the atom between the "nitrogen atom" of the functional group (a) and the "atom having a lone electron pair" of the functional group (b) include a carbon atom. That is, as the chelating agent (B), among the above aromatic compounds, it is preferred to use a nitrogen atom of the functional group (a) and an atom having a lone pair of electrons of the functional group (b) via two or three carbon atoms. And the key is the person.

Examples of the functional group (b) which is suitable as an atom having a group other than a nitrogen atom having a lone pair of electrons include a hydroxyl group and a carboxyl group.

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

In the case where salicylaldoxime is used as the chelating agent (B), a complex with copper ions is formed by a reaction represented by the following formula (1).

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, per 100 parts by mass of the copper particles (A).

When the content of the chelating agent (B) is less than 0.01 parts by mass, when the conductive film is formed, the effect of suppressing an increase in volume resistivity cannot be sufficiently obtained. On the other hand, when the content of the chelating agent (B) exceeds 1 part by mass, the copper particles are prevented from coming into contact with each other, and the conductivity is lowered.

<thermosetting resin (C)>

a thermosetting tree contained in the conductive paste as an embodiment of the present invention As the fat (C), a known thermosetting resin which is used as a resin binder of a usual conductive paste can be used.

As the thermosetting resin (C), for example, a phenol resin, a melamine resin, a urea resin or the like can be preferably used. Among these, a phenol resin can be particularly preferably used. As the phenol resin, a novolac type phenol resin or a resol type phenol resin can be used, and among these, a resol type phenol resin can be preferably used.

Further, in order to adjust the glass transition point (Tg) of the resin, a diene phthalate resin, an unsaturated alkyd resin, an epoxy resin, an isocyanate resin, or the like may be appropriately contained in the thermosetting resin. Bismaleimide III At least one of a resin, an anthrone resin, and an acrylic resin.

In the thermosetting resin (C), the cured resin component can be added in a range that does not inhibit conductivity.

The content of the thermosetting resin (C) in the conductive paste can be appropriately selected depending on the ratio of the volume of the copper particles to the volume of the voids existing between the copper particles. It is preferably 5 to 50 parts by mass, more preferably 5 to 20 parts by mass, per 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 is difficult to obtain sufficient flow characteristics as the conductive paste. On the other hand, when the content of the thermosetting resin (C) exceeds 50 parts by mass, the resin component after curing hinders the contact between the copper particles and increases the volume resistivity of the conductor.

<Organic acid ester or decylamine (D)>

The ester of the organic acid or the decylamine (D) contained in the conductive paste according to the embodiment of the present invention promotes the hardening of the thermosetting resin (C), thereby making the above-mentioned hot hard The resin (C) is formulated for the purpose of hardening at a temperature of less than 150 °C. The organic acid constituting the ester or guanamine is set to have a pKa of 1 to 4. If the pKa of the organic acid is less than 1, there is a problem that the storage stability of the conductive paste is adversely affected. In addition, when the pKa of the organic acid exceeds 4, the formation of the intermediate which promotes the hardening of the thermosetting resin (C) is slowed, and as a result, the curing effect of the resin cannot be obtained. The pKa of the organic acid is preferably from 1 to 3.

Examples of the organic acid 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.

The reason why the ester or the decylamine is preferably used in the organic acid having a pKa of 1 to 4 is as follows.

(1) When an ester of an organic acid having a pKa of 1 to 4 or a guanamine is used, the effect of stably forming an intermediate of a thermosetting resin (for example, a phenol resin or a melamine resin or a urea resin) is large. The reason for this is that the above ester or guanamine is bonded to a dimethylene ether type intermediate which is an intermediate of the above thermosetting resin. By this coordination, the electron density on the oxygen of one methylol group at the reaction site increases, and the electron density on the carbon of the methylol group decreases. Therefore, since the dimethylene ether type intermediate is stably present, the reaction probability of the intermediate increases and the hardening 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 methylene carbocation of the above intermediate can be greatly enhanced by the coordination of the ester of the organic acid having a pKa of 1 to 4 or the decylamine. Therefore, it is more helpful for the promotion of hardening, and the durability of the conductive film after hardening at high temperature and high humidity can be improved.

(3) Since the organic acid ester or the decylamine has a smaller reactivity with the metal than the organic acid, the effect of corroding the metal is small, and the increase in the volume resistivity of the conductive film after hardening can be suppressed. In the case of using an organic acid monomer having a pKa of 1 to 4, the metal in the conductive paste is corroded to increase the volume resistivity of the cured conductive film.

(4) The ester of an organic acid or decylamine has a small effect of promoting hardening of the thermosetting resin in the paste during storage of the paste, and thus has less adverse effect on the preservability (applicability period) of the conductive paste.

(5) The ester of the organic acid or the guanamine does not inhibit the function of the chelating agent which contributes to the improvement of the durability of the conductive film after hardening, and therefore the durability can be sufficiently maintained.

Examples of the ester or guanamine of the organic acid having a pKa of 1 to 4 include formazan, methyl salicylate, methyl formate, ethyl formate, dimethyl oxalate, and maleic acid. Dimethyl ester, dimethyl malonate, and the like. Although not limited to these, it is preferably selected from at least one of these.

Among the esters of the organic acid or the guanamine having a pKa of 1 to 4, an ester of an organic acid containing no sulfur (S) or a guanamine can be preferably used. The reason for this is that there is a reaction between S and copper to form a sulfide, and therefore, even an ester of an organic acid or a guanamine has an adverse effect on the preservability of the paste. Specifically, formamide, methyl salicylate, dimethyl oxalate, dimethyl malonate, and dimethyl maleate can be preferably used.

The content of the above-mentioned organic acid ester or decylamine (D) in the conductive paste is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, per 100 parts by mass of the thermosetting resin (C). If the content of the above organic acid ester or decylamine (D) is less than 0.5 In the case of the mass portion, the effect of promoting the hardening of the resin may not be sufficiently obtained. On the other hand, when the content of the organic acid ester or the decylamine (D) exceeds 15 parts by mass, the copper particles are prevented from coming into contact with each other, and the conductivity is lowered.

<Other ingredients>

In addition to the components of the above (A) to (D), the conductive paste of the present invention may contain a solvent or various additives (a leveling agent, a coupling agent, a viscosity modifier, and an anti-resistant agent) as needed within a range not impairing the effects of the present invention. Other ingredients such as oxidants, adhesives, etc.). In particular, in order to obtain a paste having moderate fluidity, it is preferred to contain a solvent which can dissolve the thermosetting resin.

As the solvent contained in the conductive paste, for example, cyclohexanone, cyclohexanol, rosinol, ethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate can be preferably used. Ester, ethylene glycol monobutyl ether acetate, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether Acid esters, etc.

The amount of the solvent contained in the conductive paste is preferably from 1 to 10% by mass based on the copper particles (A) from the viewpoint of a suitable viscosity range as the paste for printing.

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

When the components (A) to (D) are mixed, the heating can be carried out while the thermosetting resin is hardened or the solvent is volatilized. The temperature during mixing and stirring is preferably set to 10 to 40 ° C, more preferably 20 to 30 ° C. When the conductive paste is formed, by setting the temperature to 10 ° C or higher, the viscosity of the paste can be sufficiently lowered, and the stirring can be smoothly and sufficiently performed. Further, the copper hydride formed on the surface of the copper particles 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) is hardened in the paste or the particles are fused to each other.

Further, in order to prevent oxidation of the copper particles during mixing, it is preferred to mix in a vessel substituted with an inert gas.

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

[Substrate with conductive film]

For example, as shown in FIG. 1, the substrate 10 with a conductive film of the present invention has a conductive film 12 formed by hardening the conductive paste on the substrate 11. The substrate 10 with a conductive film can be produced by applying the conductive paste to the surface of the substrate 11 to form a conductive paste, and after removing volatile components such as a solvent, the thermosetting property in the conductive paste is obtained. The resin (C) is hardened to form the conductive film 12.

As the substrate 11, a glass substrate, a plastic substrate (for example, a film-form substrate including a polyimide film or a polyester film), a fiber-reinforced composite material (such as a glass fiber-reinforced resin substrate), a ceramic substrate, or the like can be used. In the case of using the conductive paste of the present invention, the thermosetting resin (C) can be hardened to form a conductive by heating at a temperature of less than 150 ° C (for example, 120 to 140 ° C) as follows. For the film 12, a plastic substrate such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polycarbonate or the like can be particularly preferably used.

As a coating method of a conductive paste, a screen printing method and a roll coating are mentioned. A known method such as a cloth method, an air knife coating method, a knife coating method, a bar coating method, a gravure coating method, a die coating method, or a swash plate coating method.

Among these, a smooth wiring shape in which the occurrence of irregularities on the surface and the side surface can be effectively formed on the substrate 11, and therefore, a screen printing method can be preferably used.

The hardening of the thermosetting resin (C) can be carried out by maintaining the substrate on which the conductive paste film is formed at a temperature of less than 150 ° C (for example, 120 to 140 ° C). The thermosetting resin can be sufficiently cured by setting the curing temperature to 120 ° C or higher. On the other hand, when the curing temperature is 140 ° C or lower, even when a substrate such as a plastic film is used, the substrate can be cured without being deformed. Examples of the heating method include hot air heating, heat radiation, and IR (Infrared Radiation) heating. Further, the formation of the conductive film can be carried out in the air, or in a nitrogen atmosphere in which the amount of oxygen is small.

The thickness of the conductive film 12 on the substrate 11 is preferably from 1 to 200 μm, more preferably from 5 to 100 μm, from the viewpoint of ensuring stable conductivity and easily maintaining the wiring shape. Further, the volume resistivity of the conductive film 12 is preferably 1.0 × 10 ^-4 Ωcm or less. When the volume resistivity of the conductive film 12 exceeds 1.0 × 10 ^-4 Ωcm, sufficient conductivity as a conductor for an electronic device cannot be obtained.

In the substrate 10 with a conductive film of the present invention, the conductive film 12 is formed by using the above-described conductive paste of the present invention, so that an oxide film due to copper oxide is not easily formed, and the substrate of the prior conductive film is formed. Ratio can be made to have a low volume resistivity and can be used for a long period of time even in a high humidity environment. A substrate to which a conductive film is suppressed from which an increase in the resistivity is suppressed.

In the above, an example of the substrate to which the conductive film of the present invention is applied is described, but the configuration may be appropriately changed as needed within the scope of the gist of the invention. Further, in the method for producing a substrate with a conductive film of the present invention, the order of formation of the respective portions may be appropriately changed within a range in which the substrate with the conductive film can be produced.

Example

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

The copper particles are subjected to a reduction treatment to obtain copper particles (A) (surface-modified copper particles).

Specifically, first, 3.0 g of formic acid and 9.0 g of a 50% by mass aqueous solution of phosphorous acid were placed in a glass beaker, and the beaker was placed in a water bath and kept at 40 °C.

Then, 5.0 g of copper particles (trade name: "1400YP", average primary particle diameter: 7 μm) was added to the beaker slowly, and the mixture was stirred for 30 minutes to obtain a "copper dispersion". The obtained "copper dispersion" was centrifuged at a rotation speed of 3000 rpm for 10 minutes using a centrifugal separator to recover a precipitate. The precipitate was dispersed in 30 g of distilled water, and the aggregate was again precipitated by centrifugation, and the precipitate was separated. The obtained precipitate was heated at 80 ° C for 60 minutes under reduced pressure of -35 kPa to volatilize residual moisture and slowly removed, thereby obtaining copper particles (A-1) which modify the surface of the particles.

X-ray photoelectron spectroscopy analysis of the obtained copper particles (A-1) The surface oxygen concentration [atomic %] and the surface copper concentration [atomic %] were measured under the following conditions (manufactured by ULVAC-PHI Co., Ltd., trade name: "ESCA 5500").

. Analysis area: 800 mm ² Φ

. Pass Energy: 93.9 eV

. Energy Step: 0.8 eV/stage

The surface oxygen concentration ratio O/Cu was calculated by dividing the obtained surface oxygen concentration by the surface copper concentration. As a result, the surface oxygen concentration ratio O/Cu of the copper particles (A-1) was 0.16.

In addition, the amount of oxygen in the copper particles (A-1) was measured using an oxygen meter (manufactured by LECO Corporation, trade name: "ROH-600"), and it was 460 ppm.

(example 1)

Water was added to a resin solution in which a phenol resin (manufactured by Kyoei Chemical Co., Ltd., trade name: "Resitop PL6220", resin solid content: 58% by mass) of 0.74 g and ethylene glycol monobutyl ether acetate 0.43 g was mixed. The hydroxyhydroxamic acid was 0.005 g and dissolved, and then 0.015 g of formamide was added and dissolved. Then, 5.0 g of the above copper particles (A-1) was blended in the obtained resin solution, and mixed in a mortar to obtain a conductive paste 1.

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

(Example 2)

Change 0.015 g of methotrexate to 0.0215 g of methyl salicylate, except Further, the conductive paste 2 was obtained in the same manner as in Example 1. Then, a substrate 2 with a conductive film was obtained in the same manner as in Example 1 except that the conductive paste 2 was applied onto the PET substrate to form the conductive film 2 instead of the conductive paste 1.

(Example 3)

0.005 g of salicyl hydroxamic acid was changed to 0.005 g of salicylaldehyde oxime, and 0.0215 g of methotrexate was changed to 0.0215 g of dimethyl oxalate. A conductive paste 3 was obtained in the same manner as in Example 1 except the above. Then, a substrate 3 with a conductive film was obtained in the same manner as in Example 1 except that the conductive paste 3 was applied to the PET substrate to form the conductive film 3 instead of the conductive paste 1.

(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. Then, a substrate 4 with a conductive film was obtained in the same manner as in Example 3 except that the conductive paste 4 was applied to the PET substrate to form the conductive film 4 instead of the conductive paste 3.

(Example 5)

No 0.0015 g of formamide was added to the resin solution. Otherwise, the conductive paste 5 was obtained in the same manner as in Example 1.

(Example 6)

A conductive paste 6 was obtained in the same manner as in Example 1 except that 0.015 g of the formamide was added and 0.0215 g of propyl carbonate was added to the resin solution.

(Example 7)

A conductive paste 7 was obtained in the same manner as in Example 1 except that 0.015 g of the carbamide was added to the resin solution.

(Example 8)

A conductive paste 8 was obtained in the same manner as in Example 1 except that 0.015 g of methamine was added and 0.0215 g of salicylic acid was added to the resin solution.

(Example 9)

A conductive paste 9 was obtained in the same manner as in Example 1 except that 0.015 g of the carbamide was added to the resin solution.

(Example 10)

A conductive paste 10 was obtained in the same manner as in Example 1 except that 0.015 g of methamine was added and 0.0215 g of maleic acid was added to the resin solution.

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

(resistance of conductor wiring)

The resistance values of the obtained conductive films 1 to 10 were measured using a resistance meter (manufactured by Keithley, trade name: "M-ohm HiTESTER"), and the initial volume resistivity was obtained.

(durability test)

The substrate 1 to 10 with a conductive film was subjected to a durability test in an environment of high temperature and high humidity. In other words, the substrates 1 to 10 with the conductive film were held in a bath of high temperature and high humidity of 60 ° C and 90% RH for 240 hours, and then the resistance values of the conductive films 1 to 10 were measured. Further, the volume resistivity after the durability test was determined.

The initial volume resistivity thus obtained and the rate of change (increased rate) of the volume resistivity after the durability test are shown in Table 1.

In addition, in Table 1, the addition amount of the hardening agent is shown by the addition amount (mass part) with respect to 100 mass parts of solid content components of a phenol-type resin.

Table 1 shows that the conductive substrates 1 to 4 of the conductive films 1 to 4 are formed by using the conductive pastes 1 to 4 in which an ester of an organic acid having a pKa of 1 to 4 or a guanamine is blended (Examples 1 to 4). Among them, the volume resistivity is low, and the rate of change (increased rate) of the volume resistivity after the durability test in a high-temperature and high-humidity environment is also suppressed to be low.

On the other hand, the substrate 5 (Example 5) with the conductive film of the conductive film 5 is formed by the conductive paste 5 formed without dissolving the ester of the organic acid or the guanamine, and is subjected to a durability test in a high-temperature and high-humidity environment. The subsequent rate of change in volume resistivity is high and is 20% and the durability is poor.

Further, the conductive pastes 6 and 7 of the conductive films 6 to 7 are formed by blending the conductive pastes 6 and 7 of the organic acid ester or the guanamine having a pKa of more than 4, and the substrates 6 to 7 (Examples 6 and 7) are attached to the high temperature and high humidity. The rate of change of the volume resistivity after the durability test in the environment is higher and is 20 to 27% and the durability is poor.

Further, a conductive paste 8 to 10 having an organic acid having a pKa of 1 to 4 is prepared by dissolving an ester or a guanamine, and a conductive film of the conductive film 8 to 10 is formed. 8 to 10 (Examples 8 to 10), the rate of change in volume resistivity after the durability test in a high-temperature and high-humidity environment is also high, and is 23 to 26%, and the durability is poor.

Although the present invention has been described in detail with reference to the specific embodiments thereof, it is understood that various changes and modifications may be made without departing from the spirit and scope of the invention.

The present application is based on Japanese Patent Application No. 2011-114604, filed on May 23, 2011, the content of

Industrial availability

The conductive paste according to the present invention can be cured at a temperature lower than the previous temperature of less than 150 ° C to suppress the formation of copper oxide in a high humidity environment, and can form a conductive film capable of maintaining a low volume resistivity for a long period of time. In addition, by using such a conductive paste, it is possible to obtain a resin or the like as an insulating base material, and it is highly reliable as a wiring board or the like, and the increase in volume resistivity due to formation of an oxide film is suppressed. A substrate of a conductive film.

10‧‧‧Substrate with conductive film

11‧‧‧Substrate

12‧‧‧Electrical film

Fig. 1 is a schematic cross-sectional view showing an example of a substrate with a conductive film of the present invention.

10‧‧‧Substrate with conductive film

11‧‧‧Substrate

12‧‧‧Electrical film

Claims (17)

A conductive paste characterized by comprising a copper particle (A), a chelating agent (B) comprising a compound having a stability constant logK _Cu of 5 to 15 with respect to copper ions at 25 ° C and an ionic strength of 0.1 mol/L, The thermosetting resin (C) and the ester of the organic acid having a pKa of 1 to 4 or the decylamine (D). The conductive paste of claim 1, wherein the copper particle (A) has a surface oxygen concentration ratio O/Cu of 0.5 or less as determined by X-ray photoelectron spectroscopy. The conductive paste of claim 1 or 2, wherein the copper particles (A) are surface-modified copper particles which have been subjected to reduction treatment in a dispersion medium having a pH of 3 or less. The conductive paste according to any one of claims 1 to 3, wherein the copper particles (A) are metal copper fine particles having an average primary particle diameter of 1 to 20 nm and adhered to a metal having an average primary particle diameter of 0.3 to 20 μm. Composite metal copper particles formed on the surface of copper particles. The conductive paste according to any one of claims 1 to 4, wherein the chelating agent (B) is a functional group (a) which will contain a nitrogen atom, and a functional group containing an atom having a lone pair of electrons other than the nitrogen atom ( b) an aromatic compound which is disposed in the ortho position of the aromatic ring. The conductive paste of claim 5, wherein the functional group (b) having an atom having a lone pair of electrons other than a nitrogen atom is a hydroxyl group or a carboxyl group. The conductive paste of claim 5 or 6, wherein the nitrogen atom is bonded to the atomic system having an isolated electron pair other than the above nitrogen atom via two or three atoms. The conductive paste according to any one of claims 1 to 7, wherein the chelating agent (B) is selected from the group consisting of salicyl hydroxamic acid, salicylaldoxime and ortho-aminophenol. At least one of them. 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. The conductive paste according to any one of claims 1 to 9, wherein the organic acid ester or the decylamine (D) is selected from the group consisting of formamide, methyl salicylate, dimethyl oxalate, and malonic acid At least one of a group consisting of a methyl ester and dimethyl maleate. The conductive paste according to any one of claims 1 to 10, wherein the content of the chelating agent (B) is 0.01 to 1 part by mass based on 100 parts by mass of the copper particles (A). The conductive paste according to any one of claims 1 to 11, wherein the content of the thermosetting resin (C) is 5 to 50 parts by mass based on 100 parts by mass of the copper particles (A). The conductive paste according to any one of claims 1 to 12, wherein the content of the organic acid ester or the decylamine (D) is 0.5 to 15 parts by mass based on 100 parts by mass of the thermosetting resin (C). A substrate with a conductive film having a substrate and a conductive film formed by hardening the conductive paste according to any one of claims 1 to 13 on the substrate. The substrate of the conductive film of claim 14, wherein the substrate is selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polycarbonate. At least one of them. The substrate of the conductive film according to claim 14 or 15, wherein the conductive film has a volume resistivity of 1.0 × 10 ^-4 Ωcm or less. A method for producing a substrate with a conductive film, comprising the steps of: applying a conductive paste according to any one of claims 1 to 13 to a substrate, and conducting the conductive layer at a temperature of less than 150 ° C The paste is heated and hardened to form a conductive film.