JPWO2012102304A1 - Conductive paste and manufacturing method thereof - Google Patents

Abstract

Provided is a conductive paste that can be heat-treated at a low temperature of 200 ° C. or lower and can obtain a conductive film having a sufficiently low electric resistivity. The conductive paste of the present invention contains (A) a silver powder surface-treated with a liquid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent. Alternatively, the conductive paste of the present invention comprises (A) a silver powder surface-treated with a liquid fatty acid and a solid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent. including. The conductive paste of the present invention may further include (A ′) silver powder surface-treated only with solid fatty acids.

Description

  The present invention relates to a conductive paste containing silver powder surface-treated with a liquid fatty acid and a method for producing the same.

  In recent years, silver fine particles have been used as a raw material for conductive paste for forming electrodes and circuit patterns of electronic components. Since the conductive paste is easy to handle, it is used in various applications such as experimental applications and electronic industry applications.

  In order to form a circuit pattern, first, a conductive paste containing silver fine particles is applied to a substrate by, for example, screen printing. Next, the conductive paste applied to the substrate is heated and baked. Thereby, for example, a circuit pattern having a wiring width of about 50 μm can be formed.

  The conductive paste can be roughly classified into two types, “high temperature firing type” and “heat curing type”. The high-temperature firing type conductive paste can be processed at a high temperature of about 550 to 900 ° C. On the other hand, the heat-curable conductive paste can be processed at a relatively low temperature of about room temperature (about 20 ° C.) to 200 ° C. In recent years, heat-curable conductive pastes have attracted attention from the viewpoint of energy saving because they can form conductors at low temperatures.

Since the heat-curing type conductive paste can be cured at a low temperature, it can be applied to a material having poor heat resistance.
For example, in the field of mobile phones, polyimide flexible circuit boards are used. Alternatively, cheaper PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) films may be used. Since these substrates are inferior in heat resistance, it is preferable to apply a heat curing type conductive paste that can be cured at a low temperature of 200 ° C. or lower.
In the field of touch panels and thin film solar cells, a metal oxide film is formed on a substrate. Since the substrate on which the metal oxide film is formed is inferior in heat resistance, it is preferable to apply a heat-curable conductive paste that can be cured at a low temperature of 200 ° C. or lower.

However, in general, a conductive film obtained using a heat-curing type conductive paste has a higher electrical resistivity (that is, lower conductivity) than a conductive film obtained using a high-temperature firing type conductive paste. There is a problem.
That is, a conductive film obtained by heating a high-temperature firing type conductive paste has a low electrical resistivity equivalent to that of a bulk metal because metal powders are bonded to each other by heating. In contrast, a conductive film obtained by heating a thermosetting type conductive paste has a relatively high electrical resistivity because a conductive path is formed by contact between metal powders.

As described above, the conductive films obtained by heating two types of conductive pastes differ in the mechanism for conducting electricity.
In addition, the conductive film obtained by heating the high-temperature firing type conductive paste has a specific resistance value of 1 × 10 ⁻⁴ Ω · m or less, whereas the heat-curing type conductive paste is heated. The obtained conductive film has a specific resistance value of about 10 × 10 ⁻⁴ Ω · m, and it cannot be said that the specific resistance value is sufficiently low.
Under such circumstances, there is a demand for a conductive paste that can be heat-treated at a low temperature of 200 ° C. or lower and can obtain a conductive film having a low electrical resistivity.

As a method for obtaining a conductive film having a low electrical resistivity, it is conceivable to increase the contact area between metal powders contained in the conductive paste.
The following factors can be considered as factors that inhibit efficient contact between metal powders contained in the conductive paste, for example.
(1) The resin ratio in the conductive paste is high.
(2) An oxide film is formed on the surface of the metal powder contained in the conductive paste, and this oxide film inhibits electrical conduction.
(3) Dispersibility of the metal powder contained in the conductive paste is not good.

  Patent Document 1 describes a technique for improving the oxidation resistance of the surface of the metal powder by forming an organic coat and an inorganic coat on the surface of the metal powder. The organic coating contains an organic fatty acid such as oleic acid. However, in the technique described in Patent Document 1, it is necessary to heat the metal powder at a high temperature of 350 ° C. or higher in order to promote the recrystallization of the central metal. For this reason, the technique described in Patent Document 1 cannot be applied to a material such as a PET film having poor heat resistance.

  Patent Document 2 describes a silver paste that has a low sheet resistance and can obtain a silver thin film having a thickness of 2.5 microns or less. This silver paste contains organic acid silver such as silver oleate. However, the silver paste described in Patent Document 2 needs to be baked at a high temperature of about 500 ° C. in order to decompose organic substances contained in the paste. For this reason, the silver paste disclosed in Patent Document 2 cannot be applied to a material such as a PET film having poor heat resistance.

JP 2005-133119 A WO2006-035908

  An object of this invention is to provide the electrically conductive paste which can obtain the electrically conductive film which can heat-process at the low temperature of 200 degrees C or less, and has a sufficiently low electrical resistivity.

  The present inventor has found that it is effective to use a silver paste containing silver powder surface-treated with a liquid fatty acid such as oleic acid in order to obtain a conductive film having a sufficiently low electrical resistivity. The present invention has been completed based on such a novel discovery.

The present invention is as follows.
[1] A conductive paste comprising (A) a silver powder surface-treated with a liquid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent.
[2] A conductive paste comprising (A) a silver powder surface-treated with a liquid fatty acid and a solid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent.
[3] The conductive paste according to [1] or [2], further including (A ′) a silver powder surface-treated only with solid fatty acids.
[4] The conductive paste according to any one of [1] to [3], wherein the liquid fatty acid is a fatty acid having a melting point of −20 ° C. to + 20 ° C.
[5] The conductive paste according to any one of [2] to [4], wherein the solid fatty acid is a fatty acid having a melting point higher than + 20 ° C.
[6] The conductive paste according to any one of [1] to [5], wherein the amount of the fatty acid is 0.1 to 5% by mass with respect to the total amount of the silver powder and the fatty acid.
[7] The liquid fatty acid is selected from the group consisting of butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, myristoleic acid, palmitoleic acid, ricinoleic acid, oleic acid, linoleic acid, and linolenic acid. The conductive paste according to any one of [1] to [6], which is at least one kind.
[8] The conductive paste according to [7], wherein the liquid fatty acid is oleic acid and / or linolenic acid.
[9] The conductive paste according to any one of [1] to [8], wherein the thermosetting resin is an epoxy resin and a phenol resin.
[10] The thermoplastic resin according to any one of [1] to [9], wherein the thermoplastic resin is at least one selected from the group consisting of a phenoxy resin, a butyral resin, a cellulose resin, an acrylic resin, and a polyester resin. Conductive paste.
[11] The conductive paste according to any one of [1] to [10], wherein the diluent is a reactive diluent.
[12] The conductive material according to [11], wherein the reactive diluent is 1,2-epoxy-4- (2-methyloxiranyl) -1-methylcyclohexane or 4-tert-butylphenylglycidyl ether. Sex paste.
[13] A conductive film obtained by heating the conductive paste according to any one of [1] to [12].
[14] An electronic component comprising the conductive film according to [13].
[15] A step of surface-treating silver powder with liquid fatty acid;
And a step of mixing the silver powder, the thermosetting resin and / or the thermoplastic resin, and a diluent.

According to the present invention, it is possible to obtain a conductive film that can be heat-treated at a low temperature of 200 ° C. or lower and has a sufficiently low electrical resistivity (for example, 0.50 × 10 ⁻⁴ Ω · m or lower). An electrically conductive paste can be provided.

It is an electron micrograph of the electrically conductive film obtained by heating the electrically conductive paste which concerns on Example 1. FIG. It is an electron micrograph of the electrically conductive film obtained by heating the electrically conductive paste which concerns on the comparative example 1.

The conductive paste of the present invention contains (A) a silver powder surface-treated with a liquid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent.
Alternatively, the conductive paste of the present invention comprises (A) a silver powder surface-treated with a liquid fatty acid and a solid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent. including.

  The shape of the silver powder contained in the conductive paste of the present invention is not particularly limited. The silver powder may have any shape such as a spherical shape, a flake shape, a flake shape, and a needle shape. A plurality of silver powders having different shapes can be mixed and used.

It is preferable that the average particle diameter of silver powder is 0.015-30 micrometers. When the silver powder is spherical, the average particle diameter of the silver powder is more preferably 0.2 to 5 μm. When silver powder is flaky, it is more preferable that the average particle diameter of silver powder is 5-30 micrometers.
When the average particle diameter of the silver powder is in the above range, the surface state of the film after printing or applying the conductive paste becomes good. In addition, the conductivity of the conductive film obtained by heating the conductive paste is improved.

In the present specification, the definition of “average particle diameter” of silver powder is as follows.
When the silver powder is spherical, the average particle diameter means an average value of the diameters of the particles.
When the silver powder is in the form of flakes or flakes, the average particle diameter means the average value of the length of the longest part of the particles.
When the silver powder is needle-shaped, the average particle diameter means an average value of the length of the longest part of the particle.
An average particle diameter can be calculated | required as a calculation average value of the result of measuring the particle size of a predetermined number (for example, 100 particles).

  The average particle diameter of the silver powder can be measured, for example, by observing the silver powder particles with a scanning electron microscope (SEM). Or the average particle diameter of silver powder can also be measured by image analysis.

The electrically conductive paste of this invention contains the silver powder surface-treated with the liquid fatty acid.
Or the electrically conductive paste of this invention contains the silver powder surface-treated with the liquid fatty acid and the solid fatty acid.

A liquid fatty acid is a liquid fatty acid at room temperature (20 ° C.).
The liquid fatty acid is preferably a fatty acid having a melting point of −20 ° C. or higher and + 20 ° C. or lower.
The solid fatty acid is a solid fatty acid at room temperature (20 ° C.).
The solid fatty acid is preferably a fatty acid having a melting point higher than + 20 ° C.

  The fatty acid used for the surface treatment of the silver powder is preferably soluble in the diluent.

The conductive film obtained by heating the conductive paste of the present invention has a lower electrical resistivity than the conductive film obtained by heating the conventional conductive paste. The reason is considered as follows.
The electrically conductive paste of this invention contains the silver powder surface-treated with the liquid fatty acid, and a diluent. Liquid fatty acids are readily soluble in the diluent. For this reason, when the conductive paste is heated, the fatty acid present on the surface of the silver powder easily evaporates together with the diluent. As a result, in the conductive film obtained by heating the conductive paste of the present invention, the exposed area of the surface of the silver powder is large, and the contact area between the silver powders is large. Furthermore, the conductive film obtained by heating the conductive paste of the present invention has a good contact state between silver powders, and at least a part of the silver powder may be fused and integrated.

  In addition, it is also considered to use the silver powder which is not surface-treated with a fatty acid as the silver powder contained in the conductive paste. However, such silver powder is unsuitable as a raw material for the conductive paste because of its poor wettability with the resin.

  Examples of liquid fatty acids include saturated fatty acids such as butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, non-resisting acids such as myristoleic acid, palmitoleic acid, ricinoleic acid, oleic acid, linoleic acid, linolenic acid Mention may be made of saturated fatty acids. These fatty acids may be used alone or in combination of two or more. Among these, it is preferable to use oleic acid, linoleic acid or a mixture thereof.

The conductive paste of the present invention may include silver powder surface-treated with liquid fatty acid and solid fatty acid.
Examples of solid fatty acids include saturated fatty acids having 10 or more carbon atoms such as capric acid, palmitic acid and stearic acid, and unsaturated fatty acids such as crotonic acid and sorbic acid.

  The solid fatty acid preferably has a boiling point of 200 ° C. or lower. This is because when a fatty acid having a boiling point of 200 ° C. or less is used, when the conductive paste is heated, the fatty acid on the surface of the silver powder evaporates, so that the area of the exposed portion of the surface of the silver powder becomes larger. An example of such a fatty acid is crotonic acid.

  In the case where a liquid fatty acid and a solid fatty acid are used in combination, the ratio of the liquid fatty acid to the total amount of the fatty acid is preferably 20% by mass or more.

  In addition to the components (A), (B), and (C), the conductive paste of the present invention may include (A ′) silver powder that is surface-treated only with solid fatty acids.

Silver powder contained in the conductive paste of the present invention can be prepared, for example, by the following methods (1) to (3).
(1) The silver powder is treated with a liquid fatty acid.
(2) After mixing a liquid fatty acid and a solid fatty acid, silver powder is processed with this mixture.
(3) The silver powder is separately treated with a liquid fatty acid and a solid fatty acid. Next, the silver powder processed with the liquid fatty acid and the silver powder processed with the solid fatty acid are mixed.
In the case of said (3), it is preferable that the ratio of the silver powder processed with the liquid fatty acid with respect to the whole quantity of silver powder is 20 mass% or more.

In order to treat silver powder with a fatty acid, for example, the following methods (1) to (3) can be used.
(1) The silver powder is immersed in a liquid fatty acid.
(2) After mixing a liquid fatty acid, a solid fatty acid, and silver powder, this mixture is stirred in a solvent.
(3) After mixing the solid fatty acid and the solvent, the silver powder is stirred in this mixture.
As the solvent, for example, an organic solvent such as water or alcohol can be used. For example, ethanol can be used as the alcohol.

The silver powder may be flaked by a pot mill.
When flaking silver powder by a pot mill, a fatty acid may be added to the pot mill. Thereby, the surface of silver powder can be processed with a fatty acid simultaneously with flaking silver powder. It is considered that at least a part of the fatty acid is physically adsorbed on the surface of the silver particles.

  The amount of the fatty acid used in the surface treatment step of the silver powder is preferably 1 to 100 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the silver powder.

  The electrically conductive paste of this invention contains the silver powder surface-treated with the fatty acid. The amount of fatty acid contained in the conductive paste is preferably 0.1 to 5% by mass and more preferably 0.2 to 2% by mass with respect to the total amount of silver powder and fatty acid. By adjusting the amount of the fatty acid within this range, a conductive film having a smaller electrical resistivity can be obtained.

  The amount of silver powder contained in the conductive paste is preferably 75 to 98% by mass, more preferably 80 to 97% by mass.

  The conductive paste of the present invention contains (B) a thermosetting resin and / or a thermoplastic resin as a binder.

It is preferable that the thermosetting resin used for this invention is a thermosetting resin hardened | cured at the temperature of 200 degrees C or less.
As the thermosetting resin, for example, an epoxy resin, a phenol resin, or a mixture thereof can be used.

  Examples of thermosetting resins include amino resins such as urea resins, melamine resins, and guanamine resins; high molecular weight bisphenol A type epoxy resins, biphenyl type epoxy resins such as diglycidyl biphenyl, novolac type epoxy resins, and tetrabromobisphenol. Epoxy resins such as A-type epoxy resins and tris (hydroxylphenyl) methane-type epoxy resins; oxetane resins; resol-type phenol resins, alkylresole-type phenol resins, novolac-type phenol resins, alkyl novolak-type phenol resins, aralkyl novolak-type phenol resins Phenolic resins such as: silicone-modified resins such as silicone epoxy and silicone polyester; bismaleimide, polyimide resins and the like. A bismaleimide triazine resin (BT resin) can also be used. These resins may be used alone or in combination of two or more.

The thermosetting resin used in the present invention is preferably liquid at normal temperature. Here, “normal temperature” means a temperature of + 5 ° C. to + 35 ° C. By using a liquid thermosetting resin, the amount of diluent used can be reduced.
The thermosetting resin used in the present invention is preferably a liquid epoxy resin and / or a liquid phenol resin.

  A resin that is solid at room temperature or a resin that is ultra-highly viscous at room temperature may be added to the thermosetting resin. The resin to be added is preferably compatible with the thermosetting resin. Moreover, it is preferable to add resin to a thermosetting resin within the range in which resin after mixing has fluidity | liquidity. Examples of such resins include high molecular weight bisphenol A type epoxy resins, biphenyl type epoxy resins such as diglycidyl biphenyl, novolac type epoxy resins, tetrabromobisphenol A type epoxy resins, resol type phenol resins, aralkyl novolac type phenols. Resin.

  Examples of thermoplastic resins include novolac phenolic resin, phenoxy resin, butyral resin, cellulose resin, acrylic resin, methacrylic resin, polyester resin, polyurethane resin, polyamide resin, thermoplastic xylene resin, hydroxystyrene polymer, cellulose derivative Or the mixture of 2 or more types of these is mentioned. In these, a phenoxy resin or a butyral resin is preferable.

  The amount of the thermosetting resin and the thermoplastic resin contained in the conductive paste is preferably 1 to 12% by mass, and more preferably 1.5 to 8% by mass.

  When both the thermosetting resin and the thermoplastic resin are included in the conductive paste, the mass ratio of the thermosetting resin and the thermoplastic resin is preferably 1: 0.02 to 1: 0.42. It is more preferable that it is 1: 0.05-1: 0.25.

The conductive paste of the present invention contains (C) a diluent.
The diluent is used to adjust the viscosity of the conductive paste and dissolve fatty acids present on the surface of the silver powder.
The diluent is preferably one that evaporates when the conductive paste is heated. That is, the diluent is preferably removed from the conductive paste by heating.
Moreover, a solvent can also be used as a diluent.

  The diluent evaporates without reacting with other components when the conductive paste is heated. This can be confirmed by measuring the decrease in mass before and after heating the conductive paste.

  Examples of solvents include aromatic hydrocarbons such as toluene, xylene, mesitylene, and tetralin; ethers such as tetrahydrofuran; ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; 2-pyrrolidone, 1-methyl-2-pyrrolidone Lactams such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether (butyl carbitol), and propylene glycol derivatives corresponding thereto Ether alcohols; corresponding esters such as acetic acid esters; dicarboxylic acids such as malonic acid and succinic acid It can be mentioned diesters such as Chiruesuteru or ethyl ester. Of these, butyl carbitol is preferred.

A reactive diluent can also be used as the (C) diluent contained in the conductive paste. The reactive diluent is a diluent having a functional group such as a glycidyl group in the molecule.
Examples of reactive diluents include 1,2-epoxy-4- (2-methyloxiranyl) -1-methylcyclohexane, 4-tert-butylphenylglycidyl ether, 1,3-bis (3-glycidoxy Propyl) -1,1,3,3-tetramethyldisiloxane, neodecanoic acid glycidyl ester, and the like. Among these, 1,2-epoxy-4- (2-methyloxiranyl) -1-methylcyclohexane or 4-tert-butylphenylglycidyl ether is preferable.

  The amount of the diluent contained in the conductive paste is preferably 1 to 25% by mass, more preferably 1 to 15% by mass. When the amount of the diluent contained in the conductive paste is less than 1% by mass, a conductive film having a sufficiently low electrical resistivity may not be obtained. When the amount of the diluent contained in the conductive paste is larger than 25% by mass, the stability of the conductive paste may be deteriorated.

  The reactive diluent has a higher viscosity than other diluents (for example, butyl carbitol and butyl carbitol acetate). For this reason, the conductive paste can be easily adjusted to a viscosity suitable for printing by adding a reactive diluent to the conductive paste. Moreover, the specific resistance of the electrically conductive film obtained by heating an electrically conductive paste can be made small by adding a reactive diluent to an electrically conductive paste.

  When apply | coating a conductive paste to a board | substrate by screen printing, it is preferable to adjust the apparent viscosity at normal temperature of a conductive paste to 10-500 Pa.s with a diluent. A more preferable apparent viscosity of the conductive paste is 15 to 300 Pa · s.

The conductive paste of the present invention may contain a known additive.
For example, the conductive paste may contain a dispersion aid.
Examples of dispersing aids include aluminum chelate compounds such as diisopropoxy (ethylacetoacetate) aluminum; titanates such as isopropyltriisostearoyl titanate; aliphatic polycarboxylic esters; unsaturated fatty acid amine salts; sorbitan mono Surfactants such as oleate; polymer compounds such as polyesteramine salts and polyamides can be used.

  The conductive paste of the present invention may contain at least one selected from the group consisting of inorganic pigments, organic pigments, silane coupling agents, leveling agents, thixotropic agents, and antifoaming agents.

The method for producing the conductive paste of the present invention includes:
(1) a step of surface-treating silver powder with liquid fatty acid;
(2) The process which mixes the said silver powder, a thermosetting resin, and / or a thermoplastic resin, and a diluent is included.

The method for producing the conductive paste of the present invention includes:
(1) a step of surface-treating silver powder with liquid fatty acid and solid fatty acid;
(2) The process which mixes the said silver powder, a thermosetting resin, and / or a thermoplastic resin, and a diluent is included.

  In the step (2), (A ′) silver powder surface-treated only with solid fatty acid may be further mixed.

  The conductive paste of the present invention contains silver powder, a thermosetting resin and / or a thermoplastic resin, and a diluent. These components can be uniformly mixed by an apparatus such as a reika machine, a propeller stirrer, a kneader, a roll, or a pot mill. The temperature at which these components are mixed is preferably 10 to 40 ° C.

  The conductive paste of the present invention can be applied to a substrate by a known method such as screen printing. After the conductive paste is applied to the substrate, the conductive paste can be heated to form a conductive film.

  When the conductive paste contains a thermosetting resin as a binder, the heating temperature of the conductive paste is preferably 60 to 200 ° C, more preferably 60 to 150 ° C. In this case, the heating time of the conductive paste is preferably 1 to 60 minutes from the viewpoint of workability.

  When the conductive paste includes a thermosetting resin as a binder, the conductive paste may be dried before heating.

  The thickness of the conductive paste applied to the substrate is preferably 10 to 200 μm, more preferably 20 to 100 μm.

  When the conductive paste contains a thermoplastic resin as a binder, the conductive paste can be heated at, for example, 80 to 160 ° C. to form a conductive film. Alternatively, the conductive film can be formed by drying the conductive paste at room temperature.

  A conductive film can be formed by heating or drying the conductive paste of the present invention. With this conductive film, an electrode or a circuit pattern of an electronic component can be formed.

The conductive paste of the present invention can be applied not only to a ceramic substrate but also to a substrate made of a material having low heat resistance such as PET (polyethylene terephthalate).
The conductive paste of the present invention can also be applied to a substrate of a solar cell on which a metal oxide film having low heat resistance is formed.

  Examples of the present invention and comparative examples will be described below.

In Examples 1 to 13 and Comparative Examples 1 to 4, conductive pastes were prepared according to the blending ratios shown in Tables 1 to 3 below.
Therefore, six kinds of silver powders of silver powder a, silver powder b, silver powder c, silver powder d, silver powder e, and silver powder f were prepared as raw materials for the conductive paste.

(Silver powder a)
Surface treatment method: Surface treatment with oleic acid Particle shape: Flake shape Average particle size: 7 μm
BET specific surface area: 0.662 m ² / g
Tap density: 5.33 g / cm ³
Iglos value (loss on ignition): 0.56%

(Silver powder b)
Surface treatment method: 1000 g of silver powder and 20 g of oleic acid are mixed in a pot mill Particle shape: Flakes Average particle size: 10 μm
BET specific surface area: 0.776 m ² / g
Tap density: 5.13 g / cm ³
Iglos value (loss on ignition): 0.53%

(Silver powder c)
Surface treatment method: Surface treatment with a 1: 1 (mass ratio) mixture of oleic acid and palmitic acid Particle shape: Flakes Average particle size: 3 μm
BET specific surface area: 0.708 m ² / g
Tap density: 4.88 g / cm ³
Iglos value (loss on ignition): 0.59%

(Silver powder d)
Surface treatment method: A mixture of 1000 g of silver powder, 20 g of stearic acid, and 100 g of ethanol was stirred in a pot mill to perform surface treatment of the silver powder.
Particle shape: Flakes Average particle size: 3 μm
BET specific surface area: 1.007 m ² / g
Tap density: 4.76 g / cm ³
Iglos value (loss on ignition): 0.48%

(Silver powder e)
Surface treatment method: Silver powder was surface treated by immersing 1000 g of silver powder in a solution of 20 g of oleic acid dissolved in 100 g of ethanol.
Particle shape: spherical Average particle size: 0.3 μm
BET specific surface area: 0.635 m ² / g
Tap density: 1.32 g / cm ³
Iglos value (loss on ignition): 1.98%

(Silver powder f)
Surface treatment method: 1000 g of silver powder was immersed in a mixture of 20 g of stearic acid and 100 g of ethanol, and stirred with a dissolver to perform silver powder surface treatment.
Particle shape: spherical Average particle size: 0.3 μm
BET specific surface area: 1.095 m ² / g
Tap density: 1.13 g / cm ³
Iglos value (loss on ignition): 1.98%

The physical property values of the above-described silver powders a to f were measured by the following procedure.
The BET specific surface area was measured using a commercially available measuring instrument (Furosorb II manufactured by Shimadzu Corporation).
The tap density was measured using a tapping machine (manufactured by Kuramochi Scientific Instruments).
The Iglos value (loss on ignition) was calculated from the mass of the residue after baking silver powder at 800 ° C. for 30 minutes.
The gross value indicates the amount (% by mass) of fatty acid present on the surface of the silver powder. For example, in silver powder a, the mass of oleic acid present on the surface of the silver powder is 0.56% with respect to the total amount of silver powder and oleic acid. In silver powder c, the mass of oleic acid and palmitic acid present on the surface of the silver powder is 0.59% with respect to the total amount of silver powder, oleic acid, and palmitic acid.

  Next, conductive pastes according to Examples 1 to 13 and Comparative Examples 1 to 4 were prepared.

Example 1
In a reaction vessel, 95 parts by mass of silver powder a, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0.40 of carboxy-terminated acrylonitrile / butadiene copolymer. Part by mass, 0.10 parts by mass of a curing accelerator, and 4.97 parts by mass of butyl carbitol as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. This prepared the electrically conductive paste which concerns on Example 1. FIG.

(Example 2)
A conductive paste according to Example 2 was prepared by the same procedure as Example 1 except that silver powder b was used instead of silver powder a.

(Example 3)
In a reaction vessel, 98 parts by mass of silver powder a, 0.63 parts by mass of phenol resin, 1.07 parts by mass of epoxy resin, 0.10 parts by mass of butyral resin, 0.16 parts of carboxy-terminated acrylonitrile-butadiene copolymer Part by mass, 0.04 part by mass of a curing accelerator, and 1.99 parts by mass of butyl carbitol as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. As a result, a conductive paste according to Example 3 was prepared.

(Example 4)
A conductive paste according to Example 4 was prepared by the same procedure as Example 3 except that silver powder b was used instead of silver powder a.

(Example 5)
In a reaction vessel, 24.25 parts by mass of silver powder a, 72.75 parts by mass of silver powder f, 0.95 parts by mass of phenol resin, 1.61 parts by mass of epoxy resin, 0.15 parts by mass of butyral resin, carboxy 0.23 parts by mass of terminal acrylonitrile-butadiene copolymer, 0.06 parts by mass of a curing accelerator, and 2.99 parts by mass of butyl carbitol as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. As a result, a conductive paste according to Example 5 was prepared.

(Example 6)
A conductive paste according to Example 6 was prepared by the same procedure as Example 5 except that silver powder e was used instead of silver powder f.

(Example 7)
In the reaction vessel, 94.00 parts by mass of silver powder a, 6.00 parts by mass of phenoxy resin (number average molecular weight 1,180), and 14.00 parts by mass of butyl carbitol as a diluent were charged. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. As a result, a conductive paste according to Example 7 was prepared.

(Example 8)
In a reaction vessel, 95.00 parts by mass of silver powder c, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0 of carboxy-terminated acrylonitrile-butadiene copolymer .40 parts by mass, 0.10 parts by mass of a curing accelerator, and 4.97 parts by mass of butyl carbitol as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. Thus, a conductive paste according to Example 8 was prepared.

Example 9
In a reaction vessel, 95 parts by mass of silver powder a, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0.40 of carboxy-terminated acrylonitrile / butadiene copolymer. 0.10 parts by mass of a mass accelerator, a curing accelerator, and 5.33 parts by mass of 1,2-epoxy-4- (2-methyloxiranyl) -1-methylcyclohexane as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. Thereby, a conductive paste according to Example 9 was prepared.

(Example 10)
In a reaction vessel, 95 parts by mass of silver powder a, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0.40 of carboxy-terminated acrylonitrile / butadiene copolymer. 0.10 parts by mass of a mass accelerator, a curing accelerator, and 5.33 parts by mass of 4-tert-butylphenylglycidyl ether as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. Thus, a conductive paste according to Example 10 was prepared.

(Example 11)
In a reaction vessel, 95 parts by mass of silver powder a, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0.40 of carboxy-terminated acrylonitrile / butadiene copolymer. 0.10 parts by mass of a curing accelerator, and 5.33 parts by mass of 1,3-bis (3-glycidoxypropyl) -1,1,3,3-tetramethyldisiloxane as a diluent I put it in. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. As a result, a conductive paste according to Example 11 was prepared.

(Example 12)
In a reaction vessel, 95 parts by mass of silver powder a, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0.40 of carboxy-terminated acrylonitrile / butadiene copolymer. 0.10 parts by mass of a mass accelerator, a curing accelerator, and 5.33 parts by mass of neodecanoic acid glycidyl ester as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. As a result, a conductive paste according to Example 12 was prepared.

(Example 13)
In a reaction vessel, 95 parts by mass of silver powder a, 1.58 parts by mass of phenol resin, 2.68 parts by mass of epoxy resin, 0.24 parts by mass of butyral resin, 0.40 of carboxy-terminated acrylonitrile / butadiene copolymer. Part by mass, 0.10 parts by mass of a curing accelerator, and 4.97 parts by mass of butyl carbitol acetate as a diluent were added. Next, these mixtures were stirred at 25 ° C. with a hybrid mixer for 15 seconds. As a result, a conductive paste according to Example 13 was prepared.

(Comparative Example 1)
A conductive paste according to Comparative Example 1 was prepared by the same procedure as in Example 1 except that silver powder d was used instead of silver powder a.

(Comparative Example 2)
A conductive paste according to Comparative Example 2 was prepared by the same procedure as Example 3 except that silver powder d was used instead of silver powder a.

(Comparative Example 3)
A conductive paste according to Comparative Example 3 was prepared by the same procedure as Example 7 except that silver powder d was used instead of silver powder a.

(Comparative Example 4)
The conductive paste according to Comparative Example 4 was prepared by adding 0.50 parts by mass of oleic acid to the conductive paste according to Comparative Example 1 later.

Specific names and physical property values of the raw materials used in Examples 1 to 13 and Comparative Examples 1 to 4 are as follows.
・ Phenolic resin:
Softening point 98-102 ° C., hydroxyl (OH) equivalent 104-106 g / eq
·Epoxy resin:
Tris (hydroxylphenyl) methane type solid epoxy resin, epoxy equivalent of 169 to 179 g / eq
・ Butyral resin:
Polyvinyl alcohol: polyvinyl butyral: polyvinyl acetate = 83: 16: 1 (mass ratio), average polymerization degree 2,400
・ Carboxy-terminated acrylonitrile / butadiene copolymer:
Number average molecular weight 10,000
・ Curing accelerator:
2-ethyl-4-methylimidazole

(Measurement of specific resistance)
Next, the specific resistance (electrical resistivity) of the conductive films produced using the conductive pastes obtained in Examples 1 to 13 and Comparative Examples 1 to 4 was measured.

The specific resistance was measured by the following procedure.
A zigzag pattern having a length of 71 mm, a width of 1 mm, and a thickness of 20 μm was printed on an alumina substrate having a width of 20 mm, a length of 20 mm, and a thickness of 1 mm using a 250 mesh stainless steel screen.

The conductive pastes according to Examples 1 to 4 and 7 to 13 and Comparative Examples 1 to 4 were heated at 150 ° C. for 30 minutes.
The conductive paste according to Examples 5 and 6 was heated at 200 ° C. for 30 minutes.

The thickness of the pattern was determined by averaging the measured values at six points intersecting the pattern using a surface roughness profile measuring instrument (product name: Surfcom 1400) manufactured by Tokyo Seimitsu Co., Ltd.
About the electrically conductive film obtained by heating or drying an electrically conductive paste, specific resistance was measured by the 4 terminal method using the LCR meter. The measurement results of specific resistance are shown in Tables 1 to 3.
The numbers shown in Tables 1 to 3 are expressed in parts by mass unless otherwise specified.

In Tables 1 to 3,
“Resin amount (%)” is the ratio of the total amount of resin to the total amount of silver powder, resin (curing agent, thermosetting resin, thermoplastic resin and acrylonitrile-butadiene copolymer), and curing accelerator. .
“Resin amount (%) in the entire system” is the resin content relative to the total amount of silver powder, resin (curing agent, thermosetting resin, thermoplastic resin and acrylonitrile-butadiene copolymer), curing accelerator and diluent. It is a percentage of the total amount.
“Amount of silver powder in the entire system (%)” is the amount of silver powder relative to the total amount of silver powder, resin (curing agent, thermosetting resin, thermoplastic resin and acrylonitrile-butadiene copolymer), curing accelerator and diluent. It is a percentage of the total amount.
“Ratio of thermosetting resin (%)” is the total amount of curing agent and thermosetting resin relative to the total amount of resin (curing agent, thermosetting resin, thermoplastic resin and acrylonitrile-butadiene copolymer). It is a ratio.

From the result shown in Table 1, it turned out that the electrically conductive paste which concerns on Examples 1-13 has the outstanding characteristic.
The electrically conductive paste which concerns on Examples 1-13 contains the silver powder surface-treated with the oleic acid which is a liquid fatty acid at room temperature (about 20 degreeC).

On the other hand, it turned out that the electrically conductive paste which concerns on Comparative Examples 1-4 does not have the outstanding characteristic.
The conductive pastes according to Comparative Examples 1 to 4 include silver powder surface-treated with stearic acid, which is a solid fatty acid at room temperature (about 20 ° C.).

  The conductive film obtained by heating the conductive paste according to Examples 1 to 13 has a significantly lower specific resistance than the conductive film obtained by heating the conductive paste according to Comparative Examples 1 to 4. I understood.

  It was found that the specific resistance of the conductive film was further reduced by mixing spherical silver powder with the flaky silver powder (Examples 5 and 6).

It was found that a conductive film obtained by heating a conductive paste containing silver powder surface-treated with oleic acid and silver powder surface-treated with stearic acid had a sufficiently small specific resistance (Example 5).
Oleic acid is a liquid fatty acid and stearic acid is a solid fatty acid.

It was found that a conductive film obtained by heating a conductive paste containing silver powder surface-treated with a mixture of oleic acid and palmitic acid had a sufficiently small specific resistance (Example 8).
Oleic acid is a liquid fatty acid, and palmitic acid is a solid fatty acid.

The specific resistance of the conductive film obtained by heating the conductive paste obtained by adding oleic acid to the conductive paste containing silver powder surface-treated with stearic acid was not reduced (Comparative Example) 4).
This indicates that silver powder surface-treated with liquid fatty acid (oleic acid) must be used in order to obtain a conductive film having a low specific resistance. That is, even if liquid fatty acid (oleic acid) is added to the conductive paste later, the specific resistance of the conductive film does not decrease.

1 is an electron micrograph of a conductive film obtained by heating a conductive paste according to Example 1. FIG. As shown in FIG. 1, the conductive film obtained by heating the conductive paste according to Example 1 has a good contact state between silver powders, and some parts appear to be fused with each other. . This is considered that the specific resistance of the conductive film is extremely low.
FIG. 2 is an electron micrograph of a conductive film obtained by heating the conductive paste according to Comparative Example 1. As shown in FIG. 2, the conductive film obtained by heating the conductive paste according to Comparative Example 1 is not very good in contact state between silver powders. This is considered to increase the specific resistance of the conductive film.

According to the present invention, it is possible to obtain a conductive film that can be heat-treated at a low temperature of 200 ° C. or lower and has a sufficiently low electrical resistivity (for example, 0.50 × 10 ⁻⁴ Ω · m or lower). An electrically conductive paste can be provided.
According to the present invention, since an electrode and a circuit pattern can be formed even on a material having low heat resistance, it has industrial applicability.

Claims (15)

  (A) A conductive paste containing silver powder surface-treated with liquid fatty acid, (B) a thermosetting resin and / or a thermoplastic resin, and (C) a diluent.   (A) A conductive paste containing silver powder surface-treated with liquid fatty acid and solid fatty acid, (B) a thermosetting resin and / or thermoplastic resin, and (C) a diluent.   Furthermore, (A ') The electrically conductive paste of Claim 1 or Claim 2 containing the silver powder surface-treated only with the solid fatty acid.   The electrically conductive paste according to any one of claims 1 to 3, wherein the liquid fatty acid is a fatty acid having a melting point of -20 ° C to + 20 ° C.   The conductive paste according to any one of claims 2 to 4, wherein the solid fatty acid is a fatty acid having a melting point higher than + 20 ° C.   The electrically conductive paste of any one of Claims 1-5 whose quantity of the said fatty acid is 0.1-5 mass% with respect to the total amount of the said silver powder and the said fatty acid.   The liquid fatty acid is at least one selected from the group consisting of butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, myristoleic acid, palmitoleic acid, ricinoleic acid, oleic acid, linoleic acid and linolenic acid. The conductive paste according to claim 1, which is a seed.   The conductive paste according to claim 7, wherein the liquid fatty acid is oleic acid and / or linolenic acid.   The conductive paste according to any one of claims 1 to 8, wherein the thermosetting resin is an epoxy resin or a phenol resin.   The conductive material according to any one of claims 1 to 9, wherein the thermoplastic resin is at least one selected from the group consisting of a phenoxy resin, a butyral resin, a cellulose resin, an acrylic resin, and a polyester resin. Sex paste.   The conductive paste according to any one of claims 1 to 10, wherein the diluent is a reactive diluent.   The conductive paste according to claim 11, wherein the reactive diluent is 1,2-epoxy-4- (2-methyloxiranyl) -1-methylcyclohexane or 4-tert-butylphenylglycidyl ether.   The electrically conductive film obtained by heating the electrically conductive paste of any one of Claims 1-12.   An electronic component comprising the conductive film according to claim 13. Surface treatment of silver powder with liquid fatty acid;
And a step of mixing the silver powder, the thermosetting resin and / or the thermoplastic resin, and a diluent.