WO2010032841A1

WO2010032841A1 - Conductive filler, conductive paste and article having conductive film

Info

Publication number: WO2010032841A1
Application number: PCT/JP2009/066420
Authority: WO
Inventors: 啓中西; 英之平社; 一志小林; 啓介阿部
Original assignee: 旭硝子株式会社
Priority date: 2008-09-19
Filing date: 2009-09-18
Publication date: 2010-03-25
Also published as: TW201022152A; JPWO2010032841A1

Abstract

Disclosed are a conductive filler which has excellent oxidation resistance and can be sintered easily, a conductive paste which has excellent storage stability in the air and is capable of forming a conductive film with high conductivity, and an article having conductive film with high conductivity. The conductive filler is characterized by containing a copper filler having an average aggregate particle diameter of 0.5-20 μm, copper nanoparticles having an average aggregate particle diameter of 50-200 nm and an aliphatic carboxylic acid. The conductive filler is also characterized in that the copper nanoparticles are contained in an amount of 5-50 parts by mass per 100 parts by mass of the copper filler, and the aliphatic carboxylic acid is contained in an amount of 1-15 parts by mass per 100 parts by mass of the total of the copper filler and the copper nanoparticles.

Description

Article having conductive filler, conductive paste and conductive film

The present invention relates to an article having a conductive filler, a conductive paste, and a conductive film.

There is known a method of manufacturing a printed circuit board or the like having a conductive film having a desired wiring pattern by applying and baking a conductive paste on a substrate in a desired wiring pattern.
As the conductive paste used in the method, for example, the following has been proposed.
(1) A metal paste containing metallic silver nanoparticles having an average particle diameter of 1 to 100 nm, a metal filler having an average particle diameter of 5 to 20 μm, and a resin binder (Patent Document 1).

The metal paste of the above (1) realizes a reduction in resistance that could not be realized only with a metal filler by fusing metal fillers together using the surface melting phenomenon of metal silver nanoparticles. However, since silver is a metal that easily undergoes ion migration, when considering the reliability of electronic parts such as a printed circuit board manufactured using the metal paste of (1), copper is used as the material of the metal nanoparticles. preferable. However, metallic copper nanoparticles are very easy to oxidize.

Moreover, the following are proposed as a nanoparticle containing copper excellent in oxidation resistance.
(2) Copper hydride nanoparticles whose surface is coated with a long-chain organic compound (Patent Document 2). However, since the surface of the copper hydride nanoparticles of (2) above is coated with a long-chain organic compound, it is difficult to sinter with the metal filler, and the conductive film after firing is insufficient in conductivity.

International Publication No. 2002/35554 Pamphlet International Publication No. 2004/110925 Pamphlet

The present invention relates to a conductive filler excellent in oxidation resistance and easy to sinter, a conductive paste excellent in storage stability in air and capable of forming a conductive film having high conductivity, and a conductive film having high conductivity. An article is provided.

The present invention has the following gist.
[1] A copper filler having an average aggregate particle diameter of 0.5 to 20 μm, copper nanoparticles having an average aggregate particle diameter of 50 to 200 nm, and an aliphatic carboxylic acid, and the amount of the copper nanoparticles is 5 to 50 parts by mass with respect to 100 parts by mass of the copper filler, and the amount of the aliphatic carboxylic acid is 1 to 15 parts by mass with respect to a total of 100 parts by mass of the copper filler and the copper nanoparticles. A conductive filler characterized by being a part.
[2] The conductivity according to [1], wherein the copper nanoparticles are copper hydride nanoparticles whose surfaces are coated with formic acid, or metal copper nanoparticles obtained by thermally decomposing the copper hydride nanoparticles. Filler.

[3] The conductive filler according to [1] or [2], wherein the aliphatic carboxylic acid is an unsaturated carboxylic acid.
[4] The conductive filler according to [3], wherein the unsaturated carboxylic acid has a boiling point or decomposition temperature of 250 ° C. or lower.
[5] The conductive filler according to [1] or [2], wherein the aliphatic carboxylic acid is a compound represented by the following formula (1).
R-COOH (1)
However, R in the formula (1) represents a hydrocarbon group having 4 to 20 carbon atoms.
[6] A copper filler having an average aggregate particle diameter of 0.5 to 20 μm, copper nanoparticles having an average aggregate particle diameter of 50 to 200 nm, an aliphatic carboxylic acid, and a resin binder, Is 5 to 50 parts by mass with respect to 100 parts by mass of the copper filler, and the amount of the aliphatic carboxylic acid is 1 to 100 parts by mass with respect to a total of 100 parts by mass of the copper filler and the copper nanoparticles. A conductive paste comprising 15 parts by mass, and the amount of the resin binder is 5 to 50 parts by mass with respect to 100 parts by mass in total of the copper filler and the copper nanoparticles.
[7] The above-mentioned [6], wherein the copper nanoparticles are copper hydride nanoparticles whose surfaces are coated with formic acid, or metal copper nanoparticles obtained by thermally decomposing the copper hydride nanoparticles. Conductive paste.
[8] The conductive paste according to [6] or [7], wherein the aliphatic carboxylic acid is an unsaturated carboxylic acid.
[9] The conductive paste according to [8], wherein the unsaturated carboxylic acid has a boiling point or decomposition temperature of 250 ° C. or lower.
[10] The conductive paste according to [6] or [7], wherein the aliphatic carboxylic acid is a compound represented by the following formula (1).
R-COOH (1)
However, R in the formula (1) represents a hydrocarbon group having 4 to 20 carbon atoms.
[11] The conductive paste according to any one of [6] to [10], wherein the resin binder is a binder made of a polyester resin.
[12] The conductive paste according to [11], wherein the polyester resin has a hydroxyl value of 5 to 20 KOH mg / g.
[13] An article having a base material and a conductive film formed by applying and baking the conductive paste according to any one of [6] to [12] on the base material.

The conductive filler of the present invention is excellent in oxidation resistance and easy to sinter.
According to the conductive paste of the present invention, a conductive film having high conductivity can be formed even after storage in air.
The article of the present invention has a conductive film having high conductivity.

It is a figure which shows an example of IR spectrum of the copper hydride nanoparticle by which the surface was coat | covered with formic acid.

In this specification, the compound represented by the formula (1) is also referred to as the compound (1). Moreover, the average aggregate particle diameter in this specification is a number average average aggregate particle diameter.

<Conductive filler>
The conductive filler of the present invention includes a copper filler having an average aggregate particle diameter of 0.5 to 20 μm, copper nanoparticles having an average aggregate particle diameter of 50 to 200 nm, and an aliphatic carboxylic acid.

(Copper filler)
As a copper filler, the well-known metal copper particle used for an electrically conductive paste is mentioned.
The average aggregate particle diameter of the copper filler is 0.5 to 20 μm, preferably 1 to 10 μm. By including a copper filler having an average aggregate particle size of 0.5 μm or more, the flow characteristics of the conductive paste are improved. By including a copper filler having an average aggregate particle diameter of 20 μm or less, it becomes easy to produce fine wiring.
The average agglomerated particle diameter of the copper filler in the present invention was determined by measuring the agglomerated particle diameter of 100 copper fillers randomly selected from a scanning electron microscope (hereinafter referred to as SEM) image, and calculating the average. Ask by taking.

The amount of the copper filler is preferably 60 to 85% by mass, more preferably 80 to 85% by mass, out of 100% by mass of the conductive filler. If the amount of the copper filler is 60% by mass or more, good conductivity can be secured. When the amount of the copper filler is 85% by mass or less, the conductive paste can be easily applied to the substrate.

(Copper nanoparticles)
The copper nanoparticles are preferably copper hydride nanoparticles or metal copper nanoparticles from the viewpoint that a conductive film having high conductivity can be formed.
Copper hydride is a compound containing hydrogen in addition to copper as an element. The copper atom exists in a state of being bonded to a hydrogen atom and has a property of decomposing into metallic copper and hydrogen at 60 to 100 ° C.

The average aggregate particle diameter of the copper nanoparticles is 50 to 200 nm, preferably 70 to 150 nm. By including copper nanoparticles having an average aggregate particle diameter of 50 nm or more, cracks generated in the conductive film due to volume shrinkage accompanying the fusion and growth of copper nanoparticles are unlikely to occur. By including copper nanoparticles having an average aggregate particle size of 200 nm or less, the surface melting temperature is sufficiently lowered, so that surface melting is likely to occur, and a dense conductive film can be formed, so that improvement in conductivity can be expected. .
The average agglomerated particle diameter of the copper nanoparticles in the present invention is determined by measuring the agglomerated particle diameter of 100 copper nanoparticles randomly selected from the SEM image and taking the average.
In the present invention, copper hydride nanoparticles and copper nanoparticles are used as aggregated particles. These agglomerated particles are formed by agglomerating primary particles having an average primary particle diameter of about 10 to 100 nm, preferably 20 to 50 nm. The average primary particle size of the nanoparticles is determined by measuring the primary particle size of 100 nanoparticles randomly selected from the TEM image and taking the average.

The amount of the copper nanoparticles is 5 to 50 parts by mass, preferably 10 to 35 parts by mass with respect to 100 parts by mass of the copper filler. If the amount of copper nanoparticles is 5 parts by mass or more, the number of conductive paths between copper fillers can be increased, and the volume resistivity of the conductive film can be kept low. If the amount of copper nanoparticles is 50 parts by mass or less, a decrease in fluidity of the conductive paste accompanying the addition of copper nanoparticles can be suppressed.
As will be described later, the copper hydride nanoparticles can be produced through the following steps (a) to (d), and the metal copper nanoparticles obtained by thermally decomposing the copper hydride nanoparticles are further processed in the following steps (e ) Can be manufactured through.
(A) A step of preparing an aqueous solution containing copper ions by dissolving a water-soluble copper compound in water.
(B) A step of adjusting the pH to 3 or less by adding an acid to the aqueous solution.
(C) A step of adding a reducing agent to the aqueous solution while stirring the aqueous solution having a pH of 3 or less to reduce copper ions to produce copper hydride nanoparticles having an average aggregate particle size of 10 to 200 nm.
(D) The process of refine | purifying the said copper hydride nanoparticle with the mixed dispersion medium of water and methanol as needed.
(E) A step of thermally decomposing the copper hydride nanoparticles to produce metallic copper nanoparticles.

Examples of the acid used in the step (b) include formic acid, citric acid, maleic acid, malonic acid, acetic acid, propionic acid, sulfuric acid, nitric acid, hydrochloric acid and the like, and formic acid is preferable. These acids are used to adjust the pH of an aqueous solution containing copper ions, but the acid may cover the surface of the copper nanoparticles and may affect the conductivity of the copper nanoparticles. .
Since formic acid is an acid having a reducing action, it is considered that using formic acid in the step (b) has an effect of suppressing oxidation of the surface of the obtained copper nanoparticles.

The copper nanoparticles are particularly preferably copper hydride nanoparticles whose surface is coated with formic acid, or metal copper nanoparticles obtained by firing the copper hydride nanoparticles.
The surface of the copper hydride nanoparticles covered with formic acid is measured by measuring the IR spectrum of the copper hydride nanoparticles and, as shown in FIG. 1, formic acid that does not interact with the surface of the copper hydride nanoparticles. Absorption near 1700 cm ⁻¹ due to the stretching of C═O derived from C is not present or small, and 1500-1600 cm ⁻¹ due to COO ⁻ derived from formic acid interacting with the surface of the copper hydride nanoparticles. It can be confirmed by the presence of absorption.

When formic acid interacts with the surface of the copper hydride nanoparticles, the carboxylic acid of formic acid is —COO 2 ^— . Since the negative charge in —COO 2 ^— is delocalized on two oxygen atoms, there is no carbonyl group (C═O) in —COO 2 ^— . On the other hand, when the copper hydride nanoparticles and formic acid are simply blended, the above-mentioned interaction does not occur. Therefore, in the blend, there is absorption around 1700 cm ⁻¹ due to stretching of C═O, and COO ⁻ There is no absorption of 1500-1600 cm ⁻¹ .
The coating amount of formic acid is preferably 1 to 40% by mass, more preferably 5 to 20% by mass, out of 100% by mass of the entire copper hydride nanoparticles (including formic acid).
The coating amount of formic acid is obtained by thermally decomposing copper hydride nanoparticles using a thermal analyzer and measuring the mass loss between 150 and 500 ° C.

Hereinafter, the case where formic acid is used as the acid in the step (b) will be described as an example, but the same operation can be performed when the above acid is used.
Copper hydride nanoparticles whose surface is coated with formic acid can be produced through the following steps (a), (b1), (c), and (d), and the copper hydride nanoparticles are pyrolyzed. The resulting copper metal nanoparticles can be further manufactured through the following step (e).
(A) A step of preparing an aqueous solution containing copper ions by dissolving a water-soluble copper compound in water.
(B1) A step of adding formic acid to the aqueous solution to adjust the pH to 3 or less.
(C) A step of adding a reducing agent to the aqueous solution while stirring the aqueous solution having a pH of 3 or less to reduce copper ions to produce copper hydride nanoparticles having an average aggregate particle size of 10 to 200 nm.
(D) The process of refine | purifying the said copper hydride nanoparticle with the mixed dispersion medium of water and methanol as needed.
(E) A step of thermally decomposing the copper hydride nanoparticles to produce metallic copper nanoparticles.

Step (a):
Examples of the water-soluble copper compound include copper sulfate, copper nitrate, copper formate, copper acetate, copper chloride, copper bromide, copper iodide and the like.
The concentration of the water-soluble copper compound is preferably 0.1 to 30% by mass and more preferably 1 to 20% by mass in 100% by mass of the aqueous solution. If the density | concentration of the water-soluble copper compound in aqueous solution is 0.1 mass% or more, the quantity of water will be restrained and the production efficiency of a copper hydride nanoparticle will become favorable. If the density | concentration of the water-soluble copper compound in aqueous solution is 30 mass% or less, the fall of the yield of a copper hydride nanoparticle will be suppressed.

Step (b):
By adjusting the pH of the aqueous solution to 3 or less, copper ions in the aqueous solution are easily reduced by the reducing agent, and copper hydride nanoparticles are easily generated. When pH of aqueous solution exceeds 3, there exists a possibility that a metal copper nanoparticle may produce | generate, without producing | generating a copper hydride nanoparticle. The pH of the aqueous solution is preferably 0.5 to 2.0, more preferably 0.7 to 1.5, from the viewpoint that copper hydride nanoparticles can be formed in a short time.
In addition, you may perform a process (a) and a process (b) simultaneously.

Step (c):
Copper ions are reduced by a reducing agent under acidic conditions, and copper hydride nanoparticles are gradually grown to produce copper hydride nanoparticles having a particle diameter of 10 to 200 nm. The surface of the copper hydride nanoparticles is immediately covered with the formic acid present together and stabilized.

As the reducing agent, metal hydride or hypophosphorous acid is preferable because of its large reducing action. Examples of metal hydrides include lithium aluminum hydride, lithium borohydride, sodium borohydride, lithium hydride, potassium hydride, calcium hydride, and the like. Lithium aluminum hydride, lithium borohydride, borohydride Sodium is preferred.

The addition amount of the reducing agent is preferably 1.5 to 10 times the number of equivalents to copper ions, more preferably 2 to 5 times the number of equivalents. If the amount of the reducing agent added is 1.5 times the number of equivalents or more of copper ions, the reducing action is sufficient. When the addition amount of the reducing agent is 10 times the number of equivalents or less with respect to copper ions, the amount of impurities (sodium, boron, phosphorus, etc.) contained in the copper hydride nanoparticles can be suppressed.
The temperature of the aqueous solution when adding the reducing agent is preferably 5 to 60 ° C, more preferably 20 to 50 ° C. If the temperature of aqueous solution is 60 degrees C or less, decomposition | disassembly of a copper hydride nanoparticle will be suppressed.

Step (d):
When the suspension containing copper hydride nanoparticles is allowed to stand, the copper hydride nanoparticles aggregate and precipitate. The precipitate is separated and then re-dispersed in a dispersion medium, and then purified by a method in which the copper hydride nanoparticles are agglomerated again and precipitated to obtain highly purified copper hydride nanoparticles.

As the dispersion medium used for purification, a mixed dispersion medium of water and methanol or ethanol is preferable. With water alone, the surface tension of water is large, so water cannot enter the pores of the aggregates of copper hydride nanoparticles, and the effect of purification is small. On the other hand, with methanol alone, the dielectric constant of methanol is small, so that the impurity sodium cannot be released into the dispersion medium as ions, and the purification effect is small.
The proportion of water in the mixed dispersion medium is preferably 40 to 90% by mass, more preferably 50 to 85% by mass with respect to the entire mixed dispersion medium.
The amount of sodium contained in the copper hydride nanoparticles is preferably 800 ppm or less, and more preferably 100 ppm or less.

Step (e):
Thermal decomposition is performed under an inert atmosphere. The oxygen concentration in the atmosphere is preferably 1000 ppm or less. When it exceeds 1000 ppm, cuprous oxide will be produced by oxidation.
The thermal decomposition temperature is preferably 60 to 100 ° C, more preferably 70 to 90 ° C. If the temperature is 60 ° C. or higher, thermal decomposition proceeds smoothly. If this temperature is 100 degrees C or less, the fusion | melting of copper nanoparticles will be suppressed.

The copper hydride nanoparticles are excellent in oxidation resistance and easy to sinter with a copper filler for the following reasons (i) and (ii).
(I) Since the copper hydride nanoparticles exist in a state in which copper atoms and hydrogen atoms are bonded, they are less susceptible to oxidation in metal atmosphere than metal copper nanoparticles, and have excellent storage stability. Yes.
(Ii) Since the copper hydride nanoparticles have the property of decomposing into metallic copper and hydrogen at a temperature of 60 to 100 ° C., when the copper hydride nanoparticles are applied to a substrate and fired, In contrast, an oxide film is hardly formed on the particle surface. Accordingly, the copper nanoparticles are melted by the surface melting phenomenon, and the copper nanoparticles or the copper nanoparticles and the metal filler are sintered, so that the conductive film can be formed promptly.

In addition, copper hydride nanoparticles whose surface is coated with formic acid, and metal copper nanoparticles obtained by thermally decomposing the copper hydride nanoparticles are further resistant to acid resistance for the following reasons (iii) to (iv). It is easy to sinter with copper filler.
(Iii) Since the surface of the copper hydride nanoparticles coated with formic acid is coated with formic acid having a reducing property (ie, —CHO group), it is coated with other organic acids in the air atmosphere. Compared to copper hydride nanoparticles, it is less oxidized. Therefore, the conductive film formed by firing is excellent in conductivity.
(Iv) When copper hydride nanoparticles whose surface is coated with formic acid are thermally decomposed to form metal copper nanoparticles, an oxide film is hardly formed on the particle surface. Therefore, there are few oxide films formed on the surface of the obtained metal copper nanoparticles.

<Conductive paste>
The conductive paste of the present invention includes a copper filler having an average aggregate particle diameter of 0.5 to 20 μm, copper nanoparticles having an average aggregate particle diameter of 50 to 200 nm, an aliphatic carboxylic acid, and a resin binder. .
The conductive paste of the present invention may be prepared by mixing (i) the conductive filler of the present invention and a resin binder, and (ii) a conductive material containing a copper filler and copper nanoparticles. It may be prepared by mixing a filler and a resin binder to which an aliphatic carboxylic acid is added.

(Aliphatic carboxylic acid)
The amount of the aliphatic carboxylic acid is 1 to 15 parts by weight, preferably 3 to 15 parts by weight, and particularly preferably 3 to 10 parts by weight with respect to a total of 100 parts by weight of the copper filler and the copper nanoparticles. When the amount of the aliphatic carboxylic acid is 1 part by mass or more, the oxide film on the surfaces of the copper nanoparticles and the copper filler can be sufficiently removed. If the amount of the unsaturated carboxylic acid is 15 parts by mass or less, the excessive unsaturated carboxylic acid does not hinder the conductivity and deteriorate the volume resistivity.

As the aliphatic carboxylic acid, either monocarboxylic acid or polycarboxylic acid can be used. As the polycarboxylic acid, dicarboxylic acid is preferable.

As the aliphatic carboxylic acid, an unsaturated carboxylic acid can be preferably used. The boiling point or decomposition temperature of the unsaturated carboxylic acid is preferably 250 ° C. or lower, and more preferably 160 ° C. or lower.
As unsaturated carboxylic acid, acrylic acid (molecular weight 72.06 g / mol, melting point 12 ° C., boiling point 141 ° C.), propiolic acid (molecular weight 70.05 g / mol, melting point 16 ° C. boiling point 102 ° C.), methacrylic acid (molecular weight 86. 09 g / mol, melting point 16 ° C., boiling point 163 ° C., palmitoleic acid (molecular weight 254.4 / mol, melting point 0.5 ° C., boiling point 162 ° C.), crotonic acid (molecular weight 86.09 g / mol, melting point 72 ° C., boiling point 185) ° C), maleic acid (molecular weight 116.07 g / mol, melting point 134-138 ° C, decomposition temperature 160 ° C), linoleic acid (molecular weight 280.45 g / mol, melting point -5 ° C, boiling point 230 ° C), linolenic acid (molecular weight 298 .45 g / mol, melting point −11 ° C., boiling point 231 ° C.), arachidonic acid (molecular weight 304.5 g / mol, melting point −49 ° C., boiling point 17 0 ° C.) and the like, and acrylic acid or maleic acid is particularly preferable. Unsaturated carboxylic acid may be used individually by 1 type, and may be used in combination of 2 or more type.
Since the lower limit of the boiling point or decomposition temperature of the unsaturated carboxylic acid is appropriately selected depending on the performance and properties required for the conductive filler and conductive paste of the present invention, it is not necessarily limited, but is usually about 100 ° C. .

In the present invention, a compound represented by the following formula (1) can also be preferably used as the aliphatic carboxylic acid.
R-COOH (1)
However, R in the formula represents a hydrocarbon group having 4 to 20 carbon atoms.

R in the compound (1) is a hydrocarbon group having 4 to 20 carbon atoms. The hydrocarbon group may be an alkyl group, an alkenyl group, or an alkynyl group, and is preferably an alkyl group or an alkenyl group. R may be a linear structure or a branched structure.
Further, the carbon number of R is preferably 4 to 18, and more preferably 6 to 18.
Examples of the compound (1) include oleic acid, stearic acid, hexanoic acid, octanoic acid, 2-ethylhexanoic acid, decanoic acid, dodecanoic acid, myristic acid and the like, and oleic acid is particularly preferable.
As the compound represented by the formula (1), one type may be used alone, or two or more types may be used in combination.

Since the conductive filler of the present invention described above contains an aliphatic carboxylic acid, it is excellent in oxidation resistance and easily sintered. The aliphatic carboxylic acid is considered to decompose and remove the oxide film on the surfaces of the copper nanoparticles and the copper filler by the action of the carboxylic acid. And it is estimated that the copper salt of aliphatic carboxylic acid is producing | generating in this process.
When the copper salt of the aliphatic carboxylic acid is present in the vicinity of the copper nanoparticles or the copper filler (such as the interface between the copper nanoparticles or the copper filler and the binder resin), there is a concern that conductivity may be hindered. However, the copper salt of the aliphatic carboxylic acid is considered to be easily dispersed in the binder resin by having a hydrocarbon group, and it is assumed that this improves the conductivity. This effect is considered to be particularly expected when the number of carbon atoms contained in the hydrocarbon group in the aliphatic carboxylic acid is 4 or more, preferably 6 or more.

In addition, when the aliphatic carboxylic acid has an unsaturated bond, the copper salt of the aliphatic carboxylic acid is decomposed by heating at the time of producing the conductive film described later, and a reducing substance is generated, whereby a copper filler or There seems to be a possibility of suppressing oxidation of copper nanoparticles. This effect is considered to be an effect particularly expected when the unsaturated carboxylic acid has an alkenyl group having 4 or less carbon atoms or when the unsaturated carboxylic acid is a dicarboxylic acid.
In the conductive paste of the present invention, a conductive film having a lower volume resistivity than the conventional conductive paste can be formed due to the above effects.

In the present invention, carboxylic acid may be used also in the step of preparing copper hydride nanoparticles (the step (b)). In this case, the carboxylic acid used in the step (b) is a conductive material. May also serve as a carboxylic acid used in the preparation of the adhesive paste.
The carboxylic acid is required to be water-soluble in the step (b), and it is considered that the paste preparation step contributes to the oxidation inhibition of the copper nanoparticles and the copper filler and the improvement of the dispersibility in the resin binder. If the carboxylic acid satisfies both of these characteristics, the conductive filler of the present invention containing the carboxylic acid used in step (b) is mixed with a resin binder without mixing another carboxylic acid, The conductive paste of the invention may be prepared.
However, in general, it is preferable to make the carboxylic acid used in the step (b) different from the carboxylic acid used in the step of preparing the conductive paste. Specifically, formic acid having a reducing action is preferably used, and an aliphatic carboxylic acid having a hydrocarbon group having 4 to 20 carbon atoms is preferably used in the paste preparation step.

(Resin binder)
Examples of the resin binder include known resin binders (thermosetting resins, thermoplastic resins, etc.) used for conductive pastes, and a resin component that is sufficiently cured at the firing temperature is selected and used. It is preferable.
Thermosetting resins include phenol resin, epoxy resin, unsaturated polyester, vinyl ester resin, diallyl phthalate resin, oligoester acrylate resin, xylene resin, bismaleidotriazine resin, furan resin, urea resin, polyurethane resin, melamine resin, silicon Examples thereof include resins, acrylic resins, oxetane resins, and oxazine resins, and pheno resins, epoxy resins, and oxazine resins are preferable.
Examples of the thermoplastic resin include polyamide resin, polyimide resin, acrylic resin, ketone resin, polystyrene resin, and polyester resin.

When a polyester resin is used as the resin binder, a known polyester resin used for conductive paste or the like can be used. In addition, an amorphous polyester resin is preferred because of its excellent solubility in a solvent and good workability when applying the resulting conductive paste.
The polyester resin preferably has a hydroxyl value of 5 to 20 KOHmg / g, and particularly preferably 5 to 10 KOHmg / g. This is because the compatibility with the copper compound (1) salt is excellent.
These polyester resins may be selected from commercially available products. Specifically, Byron (manufactured by Toyobo Co., Ltd.), Polyester (manufactured by Nippon Synthetic Chemical Co., Ltd.), Espel (manufactured by Hitachi Chemical Co., Ltd.), Elitel (manufactured by Unitika) Etc.

The amount of the resin binder in the conductive paste may be appropriately selected according to the ratio between the volume of the copper nanoparticles and the metal copper filler and the space between them, and usually the copper nanoparticles and the metal copper filler. Is 5 to 50 parts by mass, preferably 5 to 20 parts by mass. When the amount of the resin binder is 5 parts by mass or more, the flow characteristics of the paste are good. When the resin binder is 50 parts by mass or less, the volume resistivity of the conductive film can be kept low.
The conductive paste of the present invention does not impair the effects of the present invention, if necessary, with a solvent, known additives (metal chelating agent, leveling agent, coupling agent, viscosity modifier, antioxidant, etc.) and the like. It may be included in the range.

Since the conductive paste of the present invention described above contains the conductive filler of the present invention, it is possible to form a conductive film having a lower volume resistivity and higher oxidation stability than the conventional conductive paste.

<Article>
The article of the present invention has a base material and a conductive film formed by applying and baking the conductive paste of the present invention on the base material.
Examples of the base material include glass substrates, plastic substrates (polyimide substrates, polyester substrates, etc.), fiber reinforced composite materials (glass fiber reinforced resin substrates, etc.), and the like.

Examples of coating methods include known methods such as screen printing, roll coating, air knife coating, blade coating, bar coating, gravure coating, die coating, and slide coating.

Examples of the firing method include warm air heating and thermal radiation.
The firing temperature and firing time may be appropriately determined according to the characteristics required for the conductive film. The firing temperature is preferably 80 to 150 ° C, more preferably 120 to 150 ° C. If a calcination temperature is 80 degreeC or more, sintering with a metal copper filler and a copper nanoparticle will advance easily. If the firing temperature is 150 ° C. or lower, a plastic base material can be used as the base material for forming the conductive film, so that the degree of freedom in selecting the base material is increased.

The volume resistivity of the conductive film is preferably 1.0 × 10 ⁻⁴ Ωcm or less. If the volume resistivity exceeds 1.0 × 10 ⁻⁴ Ωcm, it may be difficult to use as a conductor for electronic equipment.
In the article of the present invention described above, since the conductive film is formed from the conductive paste of the present invention, the volume resistivity of the conductive film is lower than that of a conventional copper conductive film.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Examples 1 to 5, 7, and 9 to 17 are examples, and examples 6 and 8 are comparative examples.

(Particle size)
The average agglomerated particle size of copper filler and copper nanoparticles was measured by measuring the agglomerated particle size of 100 particles randomly selected from SEM images obtained by SEM (manufactured by JEOL Ltd., S-4300). And obtained by taking the average. In the case of non-spherical particles, the average value of the major axis and the minor axis was taken as the particle diameter.
In the present invention, since the particles are aggregated and used, the value of the average aggregated particle diameter measured by SEM is used. The reason why the SEM is used is that the particles that have been agglomerated are difficult to transmit with an electron beam and are difficult to measure with a TEM. For reference, the primary particle diameter measured by TEM is also described. This is because the primary particle diameter needs to be observed at a high magnification ratio, and it is difficult to cope with the SEM.

(Thickness of conductive film)
The thickness of the conductive film was measured by using DEKTAK3 (manufactured by Veeco metrology group).
(Volume resistivity of conductive film)
The volume resistivity of the conductive film was measured using a four-probe type volume resistivity meter (manufactured by Mitsubishi Yuka Co., Ltd., model: lorestaIP MCP-T250).
(Hydroxyl value)
The hydroxyl value of the polyester resin was measured using a titration method.

[Example 1]
In a glass container, 5.2 g of copper (II) acetate hydrate was dissolved in 30 g of distilled water and 3.3 g of formic acid to prepare an aqueous solution containing copper ions. The pH of the aqueous solution was 2.7.
While the aqueous solution was vigorously stirred, 23 g of a 4 mass% sodium borohydride aqueous solution was slowly added dropwise to the aqueous solution at 20 ° C. After completion of the dropwise addition, stirring was continued for 10 minutes to obtain a suspension.

The aggregate in the suspension was precipitated by centrifugation, and the precipitate was separated. The precipitate was redispersed in 30 g of 2-propanol, and then the aggregate was precipitated again by centrifugation to separate the precipitate. When the precipitate after purification was identified by X-ray diffraction, it was confirmed to be copper hydride nanoparticles. Moreover, IR spectrum was measured and it confirmed that the surface of the copper hydride nanoparticle was coat | covered with formic acid. The average primary particle diameter of the copper hydride nanoparticles measured by TEM was 30 nm, and the primary particle diameter range was 20 to 45 nm. Moreover, the average aggregate particle diameter of the copper hydride nanoparticles measured by SEM was 100 nm.

1 g of copper hydride nanoparticles, 3 g of copper filler (Mitsui Metal Mining Co., Ltd., 1400 YP, average aggregated particle size: 7 μm, aggregated particle size range: 3 to 10 μm) and 0.4 g of maleic acid were mixed with 2-propanol. In addition to 20 g, the mixture was stirred to obtain a dispersion. The dispersion was heated to 80 ° C. under a reduced pressure of −35 kPa, and 2-propanol was volatilized from the dispersion and gradually removed. At this time, the copper hydride nanoparticles were decomposed into metallic copper nanoparticles, and a conductive filler in which the surface of the copper filler was coated with metallic copper nanoparticles and maleic acid was obtained. The average primary particle diameter of the metallic copper nanoparticles measured by TEM was 50 nm, and the primary particle diameter range was 35 to 65 nm. Moreover, the average aggregate particle diameter measured by SEM was 100 nm.

A resin binder solution of 0.33 g of a conductive filler and 0.135 g of an amorphous polyester resin (Toyobo Co., Ltd., Byron 103) dissolved in 0.315 g of cyclohexanone (Pure Chemical Co., Ltd., special grade) were added. To 45 g. The amount of the amorphous polyester resin was 10.1 parts by mass with respect to a total of 100 parts by mass of the copper filler and the metal copper nanoparticles. The mixture was mixed in a mortar and then placed under reduced pressure at room temperature to remove cyclohexanone to obtain a conductive paste.

The conductive paste was applied to a glass substrate and baked at 150 ° C. for 1 hour in a nitrogen gas atmosphere to form a conductive film having a thickness of 100 μm. The volume resistivity of the conductive film was measured. The results are shown in Table 1.
After storing the conductive paste in the air for 5 days, it was applied to a glass substrate and baked in a nitrogen gas atmosphere at 150 ° C. for 1 hour to form a conductive film having a thickness of 100 μm. The volume resistivity of the conductive film was measured. The results are shown in Table 1.

[Example 2]
A conductive filler was obtained in the same manner as in Example 1 except that the amount of maleic acid added was changed to 0.6 g. The average primary particle diameter of the metal nanoparticles is 50 nm, the primary particle diameter is 35 to 65 nm (average aggregate particle diameter measured by SEM is 100 nm), the average aggregate particle diameter of the copper filler is 7 μm, and the aggregate particle diameter is The range was 3-10 μm. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 3]
A conductive filler was obtained in the same manner as in Example 1 except that the amount of maleic acid added was changed to 0.12 g. The average primary particle diameter of the metal nanoparticles is 50 nm, the primary particle diameter is 35 to 65 nm (average aggregate particle diameter measured by SEM is 100 nm), the average aggregate particle diameter of the copper filler is 7 μm, and the aggregate particle diameter is The range was 3-10 μm. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 4]
1 g of copper hydride nanoparticles prepared in the same manner as in Example 1 and 3 g of copper filler (Mitsui Metal Mining Co., Ltd., 1400 YP, average aggregated particle size: 7 μm, aggregated particle size range: 3 to 10 μm) Was stirred and a dispersion was obtained. The dispersion was heated to 80 ° C. under a reduced pressure of −35 kPa, and 2-propanol was volatilized from the dispersion and gradually removed. At this time, the copper hydride nanoparticles were decomposed into metallic copper nanoparticles, and a conductive filler in which the surface of the copper filler was coated with metallic copper nanoparticles was obtained. The average primary particle diameter of the metal copper nanoparticles was 50 nm, and the primary particle diameter range was 35 to 65 nm. Moreover, the average aggregate particle diameter measured by SEM was 100 nm.

1.2 g of conductive filler, 0.12 g of acrylic acid and 0.135 g of amorphous polyester resin (byron 103, manufactured by Byron 103) are dissolved in 0.315 g of cyclohexanone (made by Junsei Chemical, special grade). Was added to 0.45 g of the prepared resin binder solution. The amount of the amorphous polyester resin was 10.1 parts by mass with respect to a total of 100 parts by mass of the copper filler and the metal copper nanoparticles. The mixture was mixed in a mortar and then placed under reduced pressure at room temperature to remove cyclohexanone to obtain a conductive paste. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 5]
A conductive paste was obtained in the same manner as in Example 2 except that acrylic acid was changed to linolenic acid. The average primary particle diameter of the metal copper nanoparticles is 50 nm, the primary particle diameter is 35 to 65 nm (average aggregate particle diameter measured by SEM is 100 nm), the average aggregate particle diameter of the copper filler is 7 μm, and the aggregate particle diameter The range was 3 to 10 μm. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 6]
A conductive filler was obtained in the same manner as in Example 1 except that maleic acid was not added. The average primary particle diameter of the metal copper nanoparticles is 50 nm, the primary particle diameter is 35 to 65 nm (average aggregate particle diameter measured by SEM is 100 nm), the average aggregate particle diameter of the copper filler is 7 μm, and the aggregate particle diameter The range was 3 to 10 μm.
A conductive paste was obtained in the same manner as in Example 1 except that the conductive filler was used. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 7]
A conductive filler was obtained in the same manner as in Example 1 except that maleic acid was changed to malonic acid. The average primary particle diameter of the metal copper nanoparticles is 50 nm, the primary particle diameter is 35 to 65 nm (average aggregate particle diameter measured by SEM is 100 nm), the average aggregate particle diameter of the copper filler is 7 μm, and the aggregate particle diameter The range was 3 to 10 μm.
A conductive paste was obtained in the same manner as in Example 1 except that the conductive filler was used. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 8]
In the same manner as in Example 2, a conductive filler was obtained. The average primary particle diameter of the metal copper nanoparticles was 50 nm, and the primary particle diameter range was 35 to 65 nm. Moreover, the average aggregate particle diameter measured by SEM was 100 nm.
A conductive paste was obtained in the same manner as in Example 2 except that acrylic acid was changed to octene. A conductive film was formed on a glass substrate in the same manner as in Example 1, and the volume resistivity was measured. The results are shown in Table 1.

[Example 9]
In a glass container, 117 g of copper (II) acetate hydrate was dissolved in 1700 g of distilled water and 30 g of formic acid to prepare an aqueous solution containing copper ions. The pH of the aqueous solution was 2.7.
While vigorously stirring the aqueous solution, 180 g of a 50 mass% hypophosphorous acid aqueous solution was added to the aqueous solution at 40 ° C. After completion of the addition, stirring was continued for 30 minutes to obtain a suspension.

The aggregate in the suspension was precipitated by centrifugation, and the precipitate was separated. The precipitate was redispersed in 30 g of 2-propanol, and then the aggregate was precipitated again by centrifugation to separate the precipitate. When the precipitate after purification was identified by X-ray diffraction, it was confirmed to be copper hydride nanoparticles. In addition, the average aggregate particle diameter of the copper hydride nanoparticles was 100 nm.

Add 10 g of copper hydride nanoparticles, 30 g of copper filler (Mitsui Metal Mining Co., Ltd., 1400 YP, average agglomerated particle size: 7 μm) and 1.2 g of oleic acid to 200 g of 2-propanol, stir, and disperse the dispersion. Obtained. The dispersion was heated to 80 ° C. under a reduced pressure of −35 kPa, and 2-propanol was volatilized from the dispersion and gradually removed. At this time, the copper hydride nanoparticles were decomposed into metallic copper nanoparticles, and a filler in which the surface of the metallic copper filler was coated with metallic copper nanoparticles and oleic acid was obtained.

13.3 g of the filler in which the surface of the metallic copper filler is coated with metallic copper nanoparticles and oleic acid, and 1.35 g of amorphous polyester resin (manufactured by Toyobo Co., Ltd., Byron 103) are cyclohexanone (manufactured by Junsei Chemical Co., Ltd.). , Special grade) was added to 4.50 g of the resin binder solution dissolved in 3.15 g. The amount of the amorphous polyester resin was 10.1 parts by mass with respect to a total of 100 parts by mass of the copper filler and the metal copper nanoparticles. The mixture was mixed in a mortar and then placed under reduced pressure at room temperature to remove cyclohexanone to obtain a conductive paste.

The conductive paste was applied to a glass substrate and baked at 150 ° C. for 1 hour in a nitrogen gas atmosphere to form a conductive film having a thickness of 30 μm. The volume resistivity of the conductive film was measured. The results are shown in Table 1.
After storing the conductive paste in the air for 5 days, it was applied to a glass substrate and baked at 150 ° C. for 1 hour in a nitrogen gas atmosphere to form a conductive film having a thickness of 30 μm. The volume resistivity of the conductive film was measured. The results are shown in Table 2.
In addition, "addition amount (mass part)" in Table 2 is the addition amount (mass part) of the compound (1) with respect to a total of 100 mass parts of a copper nanoparticle and a copper filler. The hydroxyl value is the hydroxyl value of the amorphous polyester resin.

[Example 10]
A conductive paste was obtained in the same manner as in Example 9 except that oleic acid was changed to 0.8 g. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 11]
A conductive paste was obtained in the same manner as in Example 9 except that oleic acid was changed to 2.0 g. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 12]
A conductive paste was obtained in the same manner as in Example 9 except that the polyester resin was changed from Byron 103 to Byron 200. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 13]
A conductive paste was obtained in the same manner as in Example 9 except that the polyester resin was changed from Byron 103 to Byron GK880. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 14]
A conductive paste was obtained in the same manner as in Example 9 except that oleic acid was changed to stearic acid. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 15]
A conductive paste was obtained in the same manner as in Example 9 except that oleic acid was changed to decanoic acid. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 16]
A conductive paste was obtained in the same manner as in Example 9 except that oleic acid was changed to hexanoic acid. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

[Example 17]
A conductive paste was obtained in the same manner as in Example 9 except that the polyester resin was changed from Byron 103 to Byron 226. A conductive film was formed on a glass substrate in the same manner as in Example 9, and the volume resistivity was measured. The results are shown in Table 2.

The conductive filler and conductive paste of the present invention can be used for various applications. For example, it can be used for applications such as formation and repair of wiring patterns on printed wiring boards, interlayer wiring in semiconductor packages, and bonding between printed wiring boards and electronic components.
The specification, claims, drawings and abstract of Japanese Patent Application No. 2008-2441073 filed on September 19, 2008 and Japanese Patent Application No. 2009-91429 filed on April 3, 2009. Is hereby incorporated by reference as a disclosure of the specification of the present invention.

Claims

A copper filler having an average agglomerated particle size of 0.5 to 20 μm;
Copper nanoparticles having an average aggregate particle diameter of 50 to 200 nm,
An aliphatic carboxylic acid,
The amount of the copper nanoparticles is 5 to 50 parts by mass with respect to 100 parts by mass of the copper filler,
In addition, the conductive filler is characterized in that the amount of the aliphatic carboxylic acid is 1 to 15 parts by mass with respect to 100 parts by mass in total of the copper filler and the copper nanoparticles.
The conductive filler according to claim 1, wherein the copper nanoparticles are copper hydride nanoparticles whose surface is coated with formic acid, or metal copper nanoparticles obtained by thermally decomposing the copper hydride nanoparticles.
The conductive filler according to claim 1 or 2, wherein the aliphatic carboxylic acid is an unsaturated carboxylic acid.
The conductive filler according to claim 3, wherein the boiling point or decomposition temperature of the unsaturated carboxylic acid is 250 ° C or lower.
The conductive filler according to claim 1 or 2, wherein the aliphatic carboxylic acid is a compound represented by the following formula (1).
R-COOH (1)
However, R in the formula (1) represents a hydrocarbon group having 4 to 20 carbon atoms.
A copper filler having an average agglomerated particle size of 0.5 to 20 μm;
Copper nanoparticles having an average aggregate particle diameter of 50 to 200 nm,
An aliphatic carboxylic acid;
Including a resin binder,
The amount of the copper nanoparticles is 5 to 50 parts by mass with respect to 100 parts by mass of the copper filler,
The amount of the aliphatic carboxylic acid is 1 to 15 parts by mass with respect to a total of 100 parts by mass of the copper filler and the copper nanoparticles, and
The conductive paste is characterized in that the amount of the resin binder is 5 to 50 parts by mass with respect to 100 parts by mass in total of the copper filler and the copper nanoparticles.
The conductive paste according to claim 6, wherein the copper nanoparticles are copper hydride nanoparticles whose surface is coated with formic acid or metal copper nanoparticles obtained by thermally decomposing the copper hydride nanoparticles.
The conductive paste according to claim 6 or 7, wherein the aliphatic carboxylic acid is an unsaturated carboxylic acid.
The conductive paste according to claim 8, wherein the unsaturated carboxylic acid has a boiling point or decomposition temperature of 250 ° C or lower.
The conductive paste according to claim 6 or 7, wherein the aliphatic carboxylic acid is a compound represented by the following formula (1).
R-COOH (1)
However, R in the formula (1) represents a hydrocarbon group having 4 to 20 carbon atoms.
The conductive paste according to any one of claims 6 to 10, wherein the resin binder is a binder made of a polyester resin.
The conductive paste according to claim 11, wherein the polyester resin has a hydroxyl value of 5 to 20 KOHmg / g.
An article comprising: a base material; and a conductive film formed by applying and baking the conductive paste according to any one of claims 6 to 12 on the base material.