TWI683322B - Method for producing conductive paste - Google Patents

Abstract

Provided is a conductive paste favorable for obtaining a metal microparticle sintered body layer excellent in adhesion with an ITO substrate. In a nonpolar solvent, a powdery silver oxide powders is dispersed and an excess of formic acid is added. By the action of formic acid, the powdery silver oxide is converted into powdery silver formate (HCOOAg).  The powdery silver formate is acted by the primary amine to form a primary amine addition salt of silver formate, then a decomposing reduction reaction of the primary amine addition salt of silver formate is conducted at a liquid temperature about 70℃, forming silver nanoparticles having a surface coating layer consisting of the primary amine. To the silver nanoparticle dispersion obtained, based on 100 parts by mass of silver, an amount from more than 0 to not more than 2.0 parts by mass of a titanium compound or a manganese compound is added.

Description

Manufacturing method of conductive paste

The present invention relates to a method for producing a conductive paste suitable for the purpose of forming a conductive thin film on a conductive ITO (Indium Tin Oxide) substrate.

The conductive ITO film is used as a light-transmissive electrode layer in liquid crystal display devices for flat panel displays and the like.

Patent Document 1 discloses a method capable of producing a fine metal thin film pattern with excellent adhesion to the surface of a conductive ITO film with high drawing accuracy, workability, and reproducibility. In this method, a solution obtained by dissolving a transition metal compound including organic anions and cations of a transition metal in an organic solvent is applied to the surface of the glass substrate of the ITO film and the underlying substrate, and is subjected to a heat treatment to form a thin film layer of the transition metal. On the surface of the transition metal thin film layer, a dispersion liquid of selected metal particles having an average particle size in the range of 1 to 100 nm is applied to a specified film thickness, and a sintered body layer of metal particles is formed by heating and calcination, thereby forming good adhesion The fine metal film pattern. That is, before forming the metal thin film pattern with the conductive paste, by conducting a primer treatment on the conductive ITO film, it is possible to increase the distance between the metal thin film pattern formed by the conductive paste and the conductive ITO film The tightness.

Patent Document 2 discloses a conductive metal paste suitable for forming a metal fine particle sintered body layer having good adhesion to a glass substrate.

Patent Document 3 discloses a manufacturing method that uses silver oxide as a raw material to prepare a silver nanoparticle dispersion liquid having a surface coating layer composed of an amine compound by a reduction reaction in a liquid phase. [Prior Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Application Publication No. 2005-293937 Patent Document 2: WO2006/011180 A1 Patent Document 3: Japanese Patent Application Publication No. 2005-293937

[Problems to be solved by the invention]

According to Patent Document 1, a conductive thin film can be used to form a metal thin film pattern having good adhesion to an ITO film. However, this method must be primed. From the viewpoint of reducing steps, it may be expected that no primer treatment is performed.

The conductive metal pastes described in Patent Documents 2 and 3 are not quite suitable for obtaining a metal fine particle sintered body layer having good adhesion to a substrate made of ITO.

The object of the present invention is to provide a conductive paste suitable for obtaining a metal fine particle sintered body layer having good adhesion to a substrate composed of ITO. [Means to solve the problem]

According to one aspect of the present invention, a method for manufacturing a conductive paste is provided, which includes the following steps: A) preparing silver nanoparticles having an average particle diameter of 5 nm to 20 nm with a coating layer composed of coating agent molecules on the surface Here, the preparation step of the silver nanoparticles is to use powdered silver oxide (I) as a raw material in the liquid phase, and formic acid acts on the powdered silver oxide (I) and is converted into silver formate (I) , Reducing the silver cations contained in the silver (I) formate to silver atoms, and preparing silver nanoparticles from the silver atoms, step i: using a hydrocarbon solvent to prepare the powdered silver (I) dispersion; step ii: Formic acid is added to the dispersion of the powdered silver oxide (I), so that the formic acid acts on the powdered silver oxide (I) and is converted into silver (I), so that the powder of silver (I) formed is dispersed in the hydrocarbon A solvent to prepare a powdery silver (I) formate dispersion; step iii: adding a primary amine to the silver (I) formate dispersion, and allowing the primary amine to act on the powdered silver (I) formate to produce The primary amine complex of silver (I) formate is formed by dissolving the primary amine complex of silver (I) formed in the hydrocarbon solvent to form the primary amine complex of silver (I) formate Silver nanoparticles with an average particle size of 5 nm to 20 nm composed of silver atoms generated by the decomposable reduction reaction of the substance, here, the silver nanoparticles with an average particle size of 5 nm to 20 nm generated in step iii, the primary amine uses its amine The lone electron pair existing on the base nitrogen atom and the silver atom on the surface of which is coated by coordination bonding; and B) the dispersion of the silver nanoparticles obtained in step A is selected from One or more metal compounds in the group consisting of a titanium compound and a manganese compound, the metal contained in the metal compound is more than 0 parts by mass relative to 100 parts by mass of silver contained in the silver nanoparticle dispersion obtained in step A Parts, less than 2.0 parts by mass.

The titanium compound is preferably selected from more than one group selected from the group consisting of titanium alkoxide, titanium carboxy, and titanium acetonate; the manganese compound is preferably selected from the group consisting of manganese carboxy, and manganese acetonate More than one of them.

The metal contained in the metal compound added in step B is preferably 0.5 to 2.0 parts by mass relative to 100 parts by mass of silver contained in the dispersion liquid of silver nanoparticles obtained in step A.

The hydrocarbon solvent used in step i is selected from the range of 350 parts by mass to 550 parts by mass per 100 parts by mass of the powdered silver oxide (I) of the raw material. In addition, the boiling point of the hydrocarbon solvent is preferably in the range of 65°C to 155°C. The hydrocarbon solvent may be a chain hydrocarbon solvent or a cyclic hydrocarbon solvent.

The hydrocarbon solvent used in step i is preferably a hydrocarbon having 6 to 9 carbon atoms.

The formic acid used in step ii is preferably selected from the range of 1.1 moles to 1.4 moles per 1 mole of silver cations contained in the powdered silver oxide (I) of the raw material.

In step iii, a monocarboxylic acid having 8 to 11 carbon atoms can be added.

In step iii, a primary amine having 9 to 11 carbon atoms is used as the primary amine, and a secondary amine can be added.

The primary amine used in step iii is selected from the range of 1.2 mol to 1.8 mol per 1 mol of silver cations contained in the powdered silver oxide (I) of the raw material. In addition, the primary amine is preferably a primary amine (R-NH ₂ ) composed of an atomic group R having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent and an amine group.

On the other hand, among the primary amines (R-NH ₂ ) composed of the atomic group R and the amine group of the aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent, of the aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent The atomic group R is preferably selected from (alkoxy) alkyl, (alkylamino) alkyl, (dialkylamino) alkyl, and alkyl having a total carbon number of 7-12.

In addition, a primary amine (R-NH ₂ ) composed of an atomic group R having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent and an amine group is preferably an amine compound having a boiling point exceeding 170°C. In addition, a primary amine (R-NH ₂ ) composed of an atomic group R having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent and an amine group is preferably an amine compound having a boiling point in the range of 200°C to 270°C.

For example, a primary amine (R-NH ₂ ) is a 3-alkoxypropylamine (R′-O-CH ₂ CH) composed of a radical R and an amine group having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent ₂ CH ₂ -NH ₂ ), the alkyl group (R') constituting the alkoxy radical (R'-O-) can be appropriately selected from the alkyl groups having 4 to 9 carbon atoms.

In addition, a primary amine (R-NH ₂ ) series 3-(dialkylamino) propylamine (R ¹ N(R ² ) consisting of an atomic group R and an amine group having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent -CH ₂ CH ₂ CH ₂ -NH ₂ ), the sum of the carbon numbers of the alkyl groups (R ¹ and R ² ) constituting the dialkylamine group (R ¹ N(R ² )-) can be selected from 4 to 9 Appearance.

In addition, in this step iii: a primary amine (R-NH ₂ ) composed of an atomic group R and an amine group having an affinity for the hydrocarbon solvent is diluted with the hydrocarbon solvent to a diluted solution, and then added to the In the dispersion of powdered silver (I) formate, the dilution solution is preferably diluted by adding the hydrocarbon solvent in the range of 20 parts by mass to 45 parts by mass per 100 parts by mass of the primary amine.

Usually in this step iii: In addition to the reaction of the primary amine on the powdered silver (I) formate to form the primary amine complex of silver (I) formate, the following reaction is also carried out: the added primary The amine acts on the remaining formic acid because it is not consumed in the reaction of step ii with powdered silver oxide (I), and the primary amine addition salt of formic acid is formed; the reaction results in the primary amine addition salt of the formic acid The heat of reaction will cause the liquid temperature to rise ideally.

In addition, in step A, after step iii, it is preferable to adopt a configuration further including the following steps iv to step vi.

Step iv: After the end of step iii, the hydrocarbon solvent contained in the reaction solution containing silver nanoparticles whose surface is coated with the primary amine having an average particle diameter of 5 nm to 20 nm is distilled off under reduced pressure, and the surface coating is recovered The silver nanoparticles with an average particle size of the primary amine of 5 nm to 20 nm, the residue containing the primary amine addition salt of the formic acid, and the residual primary amine; Step v: For the residue recovered in step iv, add The powdered silver oxide (I) of the raw material is selected from the range of 200 parts by mass to 300 parts by mass per 100 parts by mass of methanol, and the distilled water selected from the range of 50 parts by mass to 300 parts by mass to be contained in the residue The formic acid primary amine addition salt and the residual primary amine are dissolved in the mixed solvent of methanol and distilled water, and layered into a sediment containing silver nanoparticles with an average particle size of 5-20 nm coated on the surface of the primary amine Layer, and a liquid phase layer formed by dissolving the formic acid primary amine addition salt and primary amine in the mixed solvent, and removing the liquid phase formed by dissolving the formic acid primary amine addition salt and primary amine in the mixed solvent Layer, and recover the sediment layer containing silver nanoparticles whose surface is covered with the primary amine with an average particle size of 5-20 nm; Step vi: For the sediment layer recovered in step v, add the powdered silver oxide in the raw material (I) For every 100 parts by mass, a hydrocarbon solvent with a boiling point within the range of 65°C to 155°C selected from the range of 100 parts by mass to 200 parts by mass, the surface contained in the sediment layer is covered with the primary amine Silver nanoparticles with an average particle size of 5-20 nm are uniformly dispersed in the hydrocarbon solvent with a boiling point in the range of 65°C to 155°C to form a dispersion, and the layering is a small amount impregnated in the sediment layer The layer of the mixed solvent of methanol and distilled water, and the layer of the dispersion liquid using the hydrocarbon solvent with a boiling point in the range of 65°C to 155°C as the dispersion solvent, and removing the small amount of the layer of the mixed solvent of methanol and distilled water, and The layer in which the hydrocarbon solvent having a boiling point in the range of 65°C to 155°C is used as the dispersion solvent is recovered.

The silver nanoparticles prepared by the above-described method for preparing silver nanoparticles of the present invention have a coating layer composed of a primary amine of an atomic group R having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent. Silver nanoparticles with a diameter of 5 nm to 20 nm can be stored in the form of a dispersion liquid dispersed in the hydrocarbon solvent. [Effect of invention]

According to the present invention, it is possible to provide a conductive paste suitable for obtaining a metal fine particle sintered body layer having good adhesion to a substrate composed of ITO.

The form of the present invention will be described in more detail below, but the present invention is not limited to the description. In addition, the metal particle sintering system produced using the conductive paste provided by the present invention has not only adhesion to ITO, but also good adhesion to glass.

(Terms) In this specification, the average particle diameter refers to the particle diameter of 50% of the cumulative value of the particle distribution (volume basis) measured by the laser diffraction method. The term "boiling point" refers to the boiling point at 1 atmosphere pressure. The term "printing ink" means that the paste is particularly suitable for printers. In addition, when referring to the amount (mass or content) of silver nanoparticles, unless otherwise specified, it refers to the amount of only silver nanoparticles (so no coating agent is included). On the other hand, when referring to the particle size of the silver nanoparticles, unless otherwise specified, it refers to the particle size of the coating agent attached to the surface containing the silver nanoparticles.

(Step A) Step A, that is, the preparation step of the silver nanoparticles includes the following steps i to iii.

(Step i) Preparation of powdered silver oxide (I) dispersion: In the present invention, powdered silver oxide (I) (Ag ₂ O; formula weight: 231.74, density: 7.22 g/cm ³ ) is used as a starting point raw material. Powdered silver oxide (I) cannot be dissolved in a non-polar solvent, such as a chain hydrocarbon solvent, but if it becomes a fine powder, it may be uniformly dispersed in a non-polar solvent, such as a chain hydrocarbon solvent. Specifically, when preparing a uniform dispersion liquid, it is suitable to use powder silver oxide (I) whose particle size distribution converges within a range of 200 mesh or less (75 μm or less).

In the present invention, the dispersion solvent of powdered silver (I) oxide is also used as a solvent for dissolving the primary amine. Therefore, a hydrocarbon solvent is used as the dispersion solvent for the powdery silver (I) oxide. In addition, in the following steps of recovering and separating the prepared silver nanoparticles from the reaction liquid, the dispersion solvent contained in the reaction liquid is distilled off under reduced pressure to remove it. It selects a hydrocarbon solvent that shows distillable evapotranspiration under reduced pressure. Therefore, in the present invention, as the dispersing solvent for the powdery silver (I), a hydrocarbon solvent having a boiling point in the range of 65°C to 155°C, preferably a boiling point in the range of 80°C to 130°C is selected. For example, as a dispersing solvent for powdered silver (I) oxide, hydrocarbons having 6 to 9 carbon atoms (for example, alkanes) are preferably used. In addition, for linear alkanes having 6 to 9 carbon atoms, for example, hexane (boiling point: 68.74°C, 0.6603g/cm ³ ), heptane (boiling point: 98.42°C, 0.684g/cm ³ ), Octane (boiling point: 125.67°C, 0.7026g/cm ³ ) and nonane (boiling point: 150.8°C, 0.7g/cm ³ ), among which, it is desirable to use linear alkanes having 6 to 9 carbon atoms. In particular, it is more desirable to use alkane having a boiling point in the range of 80°C to 100°C, for example, heptane (boiling point: 98.42°C, 0.684 g/cm ³ ) which is a linear alkane having a boiling point in the range of 80°C to 100°C. In addition, as a dispersing solvent for powdery silver (I) oxide, naphthenes such as methylcyclohexane (boiling point: 100.9°C) can also be used. Cyclic olefins such as toluene can also be used.

For example, if a hydrocarbon solvent with a boiling point lower than the boiling point of formic acid (100.75°C) is selected, especially alkane with a boiling point in the range of 80°C to 100°C, accompanied by the formation reaction of powdered silver (I) formate described later When the temperature of the reaction liquid rises due to the exothermic heat, the liquid temperature will not exceed the boiling point of the hydrocarbon solvent, so the evaporation of formic acid can be suppressed. In addition, when distilling off the hydrocarbon solvent under reduced pressure in the separation step described later, considering the workability, it is more preferable to use an alkane having a boiling point in the range of 80°C to 100°C.

It can be used in the range of 350 parts by mass to 550 parts by mass per 100 parts by mass of raw powdered silver oxide (I), preferably 350 parts by mass to 500 parts by mass, more preferably 400 parts by mass to 550 parts by mass A hydrocarbon solvent selected within a range of parts is used to prepare the powdered silver (I) dispersion. The powdered silver (I) oxide dispersion can be prepared using a hydrocarbon solvent having a boiling point in the range of 65°C to 155°C, preferably in the range of 80°C to 130°C.

(Step ii) Preparation of powdered silver (I) formate dispersion: In the present invention, formic acid (HCOOH; formula 46.025, boiling point 100.75°C) is applied to the powdered silver (I) oxide in the dispersion ( Ag ₂ O) and converted to silver (I) formate (HCOOAg).

Formic acid (HCOOH) is formed into a dimer (HCOOH: HOOCH) by hydrogen bonding. It is mostly dissolved in the hydrocarbon solvent in the state of forming the dimer. Therefore, when the dimer of formic acid (HCOOH: HOOCH) acts on the powdered silver oxide (I) (Ag ₂ O) in the dispersion, silver formate is generated by the reaction represented by the following formula (i) ( I) (HCOOAg).

Ag ^I ₂ O+(HCOOH:HOOCH) → 2[(HCOO ^- )(Ag ^I ) ⁺ ] + H ₂ O Silver (I) (HCOOAg) produced by formula (i) is because of its extremely low solubility in hydrocarbon solvents, Aggregates of [(HCOO ^- )(Ag ^I ) ⁺ ] are formed and become dispersed in the hydrocarbon solvent.

The reaction shown in the above formula (i) corresponds to the "neutralization reaction" of silver (I) oxide (Ag ₂ O) and formic acid dimer (HCOOH: HOOCH) which are basic metal oxides, and is exothermic reaction. By selecting the ratio of the dispersion solvent to the powdered silver (I) oxide (Ag ₂ O) to be within the above range, the increase in the liquid temperature of the entire dispersion can be suppressed to about 40°C. In other words, it is possible to suppress an excessive increase in the liquid temperature, and it is possible to prevent formic acid having a reducing agent function from acting on the produced silver (I) formate (HCOOAg) to perform a possible reduction reaction as shown in the following formula (A1). In addition, it is possible to prevent the decomposing reduction reaction of silver (I) (HCOOAg) itself which may occur as shown in the following formula (A2).

2[(HCOO ^- )(Ag ^I ) ⁺ ]+HCOOH → 2Ag+2HCOOH+CO ₂ ↑ Formula (A1) 2[(HCOO ^- )(Ag ^I ) ⁺ ] → 2Ag+HCOOH+CO ₂ ↑ Formula (A2) For the reaction of the above formula (i), formic acid is added in an amount ranging from 1.1 moles to 1.4 moles per mole of silver cations contained in the powdered silver oxide (I) of the raw material. It is more preferable to select within the range of 1.2 moles to 1.3 moles. By adding excess formic acid, all powdered silver oxide (I) of the raw material is converted into silver (I) formate (HCOOAg), and a dispersion of agglomerates of [(HCOO ^- )(Ag ^I ) ⁺ ] can be made .

It is speculated that most of the by-produced water molecules (H ₂ O) in the reaction of the above formula (i) will be included in the aggregate of [(HCOO ^- )(Ag ^I ) ⁺ ] produced in the form of "crystal water" in. Specifically, the reaction of formula (i) is presumably carried out through the following two basic processes (i-1) and (i-2). As a result, the by-produced water molecules (H ₂ O) will be in a state of solvation of the generated [(HCOO ^- )(Ag ^I ) ⁺ ], and it is speculated that most of it will be included in the formation in the form of "crystal water" Of [(HCOO ^- )(Ag ^I ) ⁺ ] in the condensate. (i-1)Ag ₂ O+(HCOOH:HOOCH) →[HCOOAg:AgOH:HOOCH] (i-2)[HCOOAg:(HO)Ag:HOOCH] →[(HCOO ^- )(Ag ^I ) ⁺ ](H ₂ O)[ ⁺ (Ag ^I )( ^- OOCH)] If excessive formic acid is added, unreacted formic acid will remain and be dissolved in a hydrocarbon solvent in the form of dimer of formic acid (HCOOH: HOOCH).

(Step iii) Formation of first-grade amine complex of silver (I) formate and decomposable reduction reaction: After the end of step ii, when the liquid temperature drops to 30℃, it will condense in [(HCOO ^- )(Ag ^I ) ⁺ ] the liquid dispersion added with an aliphatic amine has an affinity for the hydrocarbon chains (R-NH ₂₎ to the hydrocarbon solvent, (R-NH ₂₎ may be applied to the formation of aggregates of [(HCOO primary amine ^- )(Ag ^I ) ⁺ ]. That is, the first-order amine complex (HCOOAg: NH ₂ -R) of silver (I) (HCOOAg) is produced by the reaction represented by the following formula (ii). 2[(HCOO ^- )(Ag ^I ) ⁺ ]+2R-NH ₂ → 2[(HCOO ^- )(Ag ^I ) ⁺ : NH ₂ -R] Formula (ii) of silver formate (I) (HCOOAg) In the primary amine complex (HCOOAg: NH ₂ -R), the atomic group R of the primary amine (R-NH ₂ ) part has an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent, so it will be dissolved in the hydrocarbon solvent. Specifically, the reaction of formula (ii) is presumably carried out through the following two basic processes (i-1) and (i-2). (ii-1) [HCOOAg](H ₂ O) [AgOOCH]+R-NH ₂ → [R-NH ₂ : Ag ^+- OCHO](H ₂ O)[AgOOCH] (ii-2) [R-NH ₂ : Ag ^+- O-CHO] (H ₂ O)[AgOOCH]+ R-NH ₂ → [R-NH ₂ : Ag ^+- O-CHO] (H ₂ O)[HCOO ^-+ Ag: NH _2- R] The silver (I) formate (HCOOAg) in the aggregate contains water molecules (H ₂ O) in the form of “crystal water” to form the shape of [HCOOAg](H ₂ O)[AgOOCH]. If the primary amine (R-NH ₂ ) acts and is placed in the silver cation ((Ag ^I ) ⁺ ) in silver (I) (HCOOAg), it will convert the silver (I) (HCOOAg) into a primary amine complex (HCOOAg: NH ₂ -R). At this time, in the form of "crystal water" of the water molecules contained therein (H ₂ O) with an amine complexes will (HCOOAg: NH ₂ -R) of the acid anion ^- Part (O-CHO) forming "solvent "Solvation". Specifically, the two carboxylic acid anion ^(- O-CHO) can form hydrogen bonds, the water molecules (H ₂ O) a state "solvate"of; presumably will ^{be: - O-CHO ‥ H- (} HO) ‥ H -COO ^-. Therefore, it is speculated that the final-formed silver (I) formate (HCOOAg) primary amine complex will form a "solvated" state with the above water molecule (H ₂ O) and dissolve in the hydrocarbon solvent.

On the other hand, unreacted formic acid remains in the dispersion, and is dissolved in a hydrocarbon solvent in the form of dimer of formic acid (HCOOH: HOOCH). If the primary amine (R-NH ₂ ) is added to the hydrocarbon solvent, the primary amine (R-NH ₂ ) will also act on the dimer of formic acid (HCOOH: HOOCH). That is to say, through the reaction represented by the following formula (iii), a formic acid primary amine addition salt (HCOOH: NH ₂ -R) is produced. (HCOOH:HOOCH)+2R-NH ₂ → 2(R-NH ₂ :HOOCH) Formula (iii) The first-grade amine addition salt of formic acid of formula (iii) above is equivalent to the neutralization of acid groups and bases "Reaction" is an exothermic reaction. The resulting formic acid primary amine addition salt (HCOOH: NH ₂ -R) whose atomic group R of the primary amine (R-NH ₂ ) part has an aliphatic hydrocarbon chain that has affinity for the hydrocarbon solvent, so it will dissolve in the Hydrocarbon solvent. As the formic acid primary amine addition salt formation reaction of the above formula (iii) proceeds, the temperature of the reaction liquid will rise. In addition, if the temperature of the reaction liquid is close to the boiling point of the hydrocarbon solvent used, because the hydrocarbon solvent will start to evaporate, the temperature of the reaction liquid will not exceed the boiling point of the hydrocarbon solvent.

When the liquid temperature rises, the first-grade amine complex of silver formate (I) (HCOOAg) (HCOOAg: NH ₂ -R) starts to undergo a decomposable reduction reaction represented by the following formula (iv). Because the decomposable reduction reaction shown in this formula (iv) is an endothermic reaction, it hardly proceeds until the temperature of the reaction liquid reaches a certain temperature. 2(R-NH ₂ : Ag-OOCH) → 2[R-NH ₂ : Ag]+HCOOH+CO ₂ ↑ Formula (iv) The decomposable reduction reaction shown in formula (iv) may be The two basic processes (iv-1) and (iv-2) are described. (iv-1) [R-NH ₂ : Ag ^+- O-CHO](H2O)[HCOO ^-+ Ag: NH ₂ -R] → (R-NH ₂ : Ag)+O=CHOH+[HO‥H‥ COO ^-+ Ag: NH ₂ -R] (iv-2) [HO‥H‥COO ^-+ Ag: NH ₂ -R] → [HOH‥COO]+(Ag: NH ₂ -R) → (Ag: NH ₂ -R)+H ₂ O+CO ₂ ↑ Because carbon dioxide (CO ₂ ) generated by the decomposable reduction reaction shown in the above formula (iv) will form bubbles, bubbling can be observed in the reaction solution. In addition, the by-product formic acid (HCOOH) initially forms a dimer of formic acid (HCOOH: HOOCH), but it will be converted to formic acid by the reaction represented by the above formula (iii) by the reaction with the primary amine dissolved in the reaction solution First-grade amine addition salt (HCOOH: NH ₂ -R).

On the other hand, the metal silver atoms [Ag:NH ₂ -R] generated in the decomposable reduction reaction shown in formula (iv) are aggregated to form an aggregate of metal silver atoms. At this time, with the formation of aggregates of metallic silver atoms, a part of the primary amine (R-NH ₂ ) coordinated to metallic silver atoms will thermally dissociate. Therefore, the formed aggregate of metallic silver atoms becomes silver nanoparticles composed of a spherical core composed of metal atoms and a coating agent molecular layer composed of a primary amine (R-NH ₂ ) coated on the surface.

The thermally dissociated primary amine (R-NH ₂ ) is used in the formation reaction of the primary amine complex (HCOOAg: NH ₂ -R) of silver (I) (HCOOAg) of formula (ii) above with formula (iii) The formation reaction of a formic acid amine addition salt.

When step ii is completed, by adjusting the amount of remaining unreacted formic acid, the amount of primary amine added, and the amount of the entire reaction solution, the temperature of the reaction solution can be prevented from rising above 70°C.

If there is excess primary amine (R-NH ₂ ) in the reaction solution, the formation reaction of the primary amine addition salt of formic acid of formula (iii) above will proceed, so the concentration of dissolved dimer of formic acid (HCOOH:HOOCH) is maintained At a low level. Therefore, it is possible to prevent the formic acid having a reducing agent function from proceeding the possible reduction reaction shown in the above formula (A1).

In addition, if the liquid temperature of the reaction solution is prevented from rising above 70°C, the formation reaction of the first-order amine complex (HCOOAg: NH ₂ -R) of silver (I) (HCOOAg) of the above formula (ii) is preferentially performed Therefore, it is possible to avoid possible decomposition reaction of silver formate (I) itself as shown in the above formula (A2).

Used in the above-mentioned formula (iii) formic acid primary amine addition salt formation reaction and formula (ii) silver formate (I) primary amine complex formation reaction as an aliphatic having affinity for the hydrocarbon solvent The primary amine of the hydrocarbon chain (R-NH ₂ ), whose atomic group R is, for example, a C 7-12 alkyl group and the like, a C 7-12 chain hydrocarbon group, and the total carbon number is 7-12 (alkoxy (Alkyl)alkyl, (alkylamino)alkyl or (dialkylamino)alkyl having a total carbon number of 7-12. For example, as the primary amine (R-NH ₂ ), 3-alkoxypropylamine (R′-O-CH ₂ CH ₂ CH ₂ -NH ₂ ), which constitutes the alkoxy radical ( The alkyl group (R') of R'-O-) is a C 4-9 alkyl group, more preferably a C 6-8 alkyl compound.

In addition, as the primary amine (R-NH ² ), a 3-(dialkylamino)propylamine (R ¹ N(R ² )-CH ₂ CH ₂ CH ₂ -NH ₂ ) can be used and constitute the dialkylamino group Compounds having a total carbon number of the alkyl groups (R ¹ and R ² ) of the radical (R ¹ N(R ² )-) of 4 to 9.

On the other hand, since the primary amine (R-NH ₂ ) is used as a coating agent molecule covering the surface of the silver nanoparticles, it is preferably an amine compound having a boiling point exceeding 170°C, and further preferably having a boiling point of 200°C to 270 Amine compounds in the range of ℃. For example, 2-ethylhexyloxypropylamine having 2-ethylhexyl group having a C8 alkyl group (boiling point: 235°C) and dibutylaminepropylamine having a dibutylamine propyl group (boiling point) are preferably used : 238℃), etc. are 3-(alkoxy)propylamine (R'-O-CH ₂ CH ₂ CH ₂ -NH ₂ ) or 3-(dialkylamino)propylamine (R'-O-CH ₂ CH ₂ CH ₂ -NH ₂ ) within the range of 200℃～270℃ R"R'N-CH ₂ CH ₂ CH ₂ -NH ₂ ), as a primary amine (R-NH ₂ ) of an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent.

In addition, the addition amount of the primary amine (R-NH ₂ ) of the aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent is per mole of silver cations contained in the powdered silver oxide (I) of the raw material, It is preferably in the range of 1.2 moles to 1.8 moles, more preferably in the range of 1.3 moles to 1.6 moles.

Moreover, the molar amount of primary amine (R-NH ₂ ) added is selected to exceed the molar amount of formic acid (HCOOH) added in step ii. The ratio of the molar amount of formic acid (HCOOH) added in step ii to the molar amount of the primary amine (R-NH ₂ ) added in step iii, [primary amine/formic acid] should be selected as 1.2 The range of /1.1 to 1.8/1.4 is more preferably the range of 1.3/1.1 to 1.6/1.3, and further preferably the range of 1.4/1.2 to 1.6/1.3.

In this primary amine (R-NH ₂ ), the atomic group R has (alkoxy)alkyl, (alkylamino)alkyl, (dialkylamino)alkyl, or alkyl having a total carbon number of 7-12. As the total carbon number of the atomic group R increases, the melting point and boiling point also increase. Therefore, those who are solid at room temperature are also included. Or it may be included as a liquid but not very fluid. In consideration of this, the primary amine (R-NH ₂ ) is preferably added in the form of a solution that has been dissolved in a hydrocarbon solvent. That is to say, the above boiling point is preferably in the range of 65°C to 155°C, more preferably a hydrocarbon solvent with a boiling point in the range of 80°C to 130°C to be diluted into a diluted solution, and then added to the powdered silver formate ( I) in the dispersion. At this time, the diluted solution is preferably in the range of 20 parts by mass to 45 parts by mass per 100 parts by mass of the primary amine, more preferably in the range of 35 parts by mass to 45 parts by mass, and further preferably 35 parts by mass to It is added within the range of 40 parts by mass. The boiling point is within the range of 65°C to 155°C, and it is more preferred to be diluted with a hydrocarbon solvent having a boiling point within the range of 80°C to 130°C. In addition, when the form of the solution is diluted, because the primary amine is added, the mixing will proceed quickly after the addition.

In terms of results, the reaction liquid in step iii should preferably be contained in the range of 65°C to 155°C, preferably 100% by mass of powdered silver oxide (I) as the raw material. The total hydrocarbon solvent in the range of 80°C to 130°C is in the range of 385 parts by mass to 545 parts by mass, preferably in the range of 435 parts by mass to 540 parts by mass, and further preferably in the form of 450 parts by mass to 540 parts by mass.

In step iii, after adding the diluted solution of the primary amine (R-NH ₂ ), the reaction solution is stirred while the reaction is proceeding to avoid uneven distribution of the temperature of the reaction solution and the concentration of the primary amine (R-NH ₂ ).

In step iii, the silver nanoparticles are formed by the decomposing reduction reaction of the first-grade amine complex of silver (I) formate (HCOOAg: NH ₂ -R) uniformly dissolved in the hydrocarbon solvent, which can reduce the production of silver nanoparticles The error of the particle size of rice particles. In addition, the average particle diameter of the silver nanoparticles produced within the range of the above conditions can be easily adjusted to the range of 5 nm to 20 nm.

In the above step iii, when the reaction is completed, accompanied by the decomposing reduction reaction of the first-order amine complex of silver (I) formate (HCOOAg: NH ₂ -R) of formula (iv) above, the raw material is in powder form The silver cation contained in silver oxide (I) consumes 1/2 molar amount of formic acid (HCOOH) per 1 molar amount, but it is advisable to add the primary amine of formic acid generated by the reaction of formula (iii) in the reaction solution. Salt formation and unreacted primary amine remain.

A coating agent molecular layer composed of the primary amine is formed on the surface of the produced silver nanoparticles, and is balanced with the unreacted primary amine dissolved in the reaction solution. The total amount of the primary amine forming the molecular layer of the coating agent and the unreacted primary amine dissolved in the reaction solution should be more than one mole of silver cations contained in the powdered silver oxide (I) of the raw material. 1/2 molar amount.

In the present invention, after step iii of step A, in order to recover the prepared silver nanoparticles from the reaction solution, it is preferable to adopt a composition further including the following steps iv to step vi. Specifically, most of the formic acid primary amine addition salt and unreacted primary amine generated in the reaction of formula (iii) are removed to prepare a dispersion of silver nanoparticles, which contains a primary amine formed on the surface. The silver nanoparticles constituting the coating agent molecular layer and the appropriate amount of primary amine necessary to maintain the coating agent molecular layer composed of the primary amine.

(Step iv) Removal of the hydrocarbon solvent: The reaction in the above step iii was stirring the reaction liquid, but no foaming phenomenon due to the decomposing reduction reaction of formula (iv) was observed, when the liquid temperature dropped to 40°C , Then stop stirring.

The reaction liquid containing silver nanoparticles whose surface is coated with the above-mentioned primary amine and having an average particle diameter of 5 nm to 20 nm should preferably have a boiling point in the range of 65°C to 155°C, and more preferably have a boiling point of 80°C to 130°C The hydrocarbon solvent within the range is distilled off under reduced pressure.

In the reaction solution, the formic acid primary amine addition salt and unreacted primary amine are dissolved, and the boiling point of the formic acid primary amine addition salt is higher than the boiling point of the primary amine. In addition, the boiling point of the primary amine is 170°C or higher, and the above-mentioned distillation process under reduced pressure is preferably a process with a boiling point in the range of 65°C to 155°C, and more preferably a boiling point in the range of 80°C to 130°C. Does not evaporate. Therefore, it is possible to recover residues including silver nanoparticles having an average particle diameter of 5 nm to 20 nm covered with the primary amine, the primary amine addition salt of the formic acid, and the residual primary amine.

(Step v) Remove the formic acid primary amine addition salt and unnecessary primary amine: For the residue recovered in step iv above, add 200 parts by mass to 300 parts by mass per 100 parts by mass of the powdered silver oxide (I) of the raw material The range of parts is preferably methanol selected within the range of 200 parts by mass to 270 parts by mass, and within the range of 50 parts by mass to 300 parts by mass, preferably within the range of 200 parts by mass to 300 parts by mass, more preferably 200 parts by mass ~ 270 parts by mass of distilled water selected.

The formic acid primary amine addition salt and primary amine are dissolved in the mixed solvent of methanol and distilled water. Specifically, the methanol contained in the mixed solvent is fused to these compounds. On the other hand, the solvated methanol is rich in water affinity, so the formic acid primary amine addition salt and primary amine can be dissolved in this aqueous Mixed solvent. On the other hand, silver nanoparticles are formed on the surface of the coating agent molecular layer composed of a primary amine. In the primary amine constituting the coating agent molecular layer, although methanol is solvated, the overall size of the silver nanoparticles is the average particle diameter 5nm ~ 20nm, so it does not reach the necessary affinity for dispersion in an aqueous mixed solvent.

Therefore, the silver nanoparticles forming the coating agent molecular layer composed of the primary amine on the surface cannot be dispersed in the above-mentioned aqueous mixed solvent and become a sediment layer. On the other hand, the formic acid primary amine addition salt and the primary amine are dissolved in the aqueous mixed solvent and form a liquid phase layer, so the layer is divided into a liquid phase layer/sediment layer.

After delamination, the liquid layer is removed and the sediment layer is recovered. Specifically, the supernatant is removed by decantation, and the sediment layer impregnated with the aqueous mixed solvent is recovered. Due to the difference in solubility of the formic acid primary amine addition salt and primary amine in the mixed solvent of methanol and distilled water, the surface of the silver nanoparticles contained in the sediment layer, except for the coating agent molecular layer composed of primary amine In addition, there are still some amounts of primary amine attached to the coating agent molecular layer.

(Step vi) Redispersion of silver nanoparticles: The silver nanoparticles contained in the sediment layer recovered in the above step v and forming a coating agent molecular layer composed of a primary amine on the surface are redispersed in a hydrocarbon solvent.

In the sediment layer recovered in the above step v, because the mixture liquid impregnated with methanol and distilled water is added in an appropriate amount, the boiling point should be within the range of 65°C to 155°C, and the boiling point should be within the range of 80°C to 130°C. The hydrocarbon solvent disperses the silver nanoparticles forming the coating agent molecular layer composed of primary amine on the surface in the chain hydrocarbon solvent.

Specifically, the amount of the hydrocarbon solvent used in the redispersion is in the range of 100 parts by mass to 200 parts by mass per 100 parts by mass of the powdered silver oxide (I) of the raw material, more preferably 120 parts by mass to 180 parts by mass Choose within the scope of the share. The silver nanoparticles forming a coating agent molecular layer composed of a primary amine on the surface, the atomic group R of the primary amine (R-NH ₂ ) has an aliphatic hydrocarbon chain having affinity for a hydrocarbon solvent, and is dispersed in the hydrocarbon solvent. In addition, most of the primary amine remaining in the sediment layer is dissolved in the hydrocarbon solvent.

Because the above-mentioned aqueous mixed solvent has poor compatibility with the hydrocarbon solvent, it will be separated into two layers of the aqueous mixed solvent/hydrocarbon solvent. The layer of the mixed solvent (aqueous mixed solvent) of methanol and distilled water is removed, and the layer of the hydrocarbon solvent is recovered.

In the recovered hydrocarbon solvent layer, silver nanoparticles are formed by forming a coating agent molecular layer composed of a primary amine on the surface. At this time, a considerable portion of the primary amine (R-NH ₂ ) remaining in the sediment layer will be dissolved in the hydrocarbon solvent that is the dispersion solvent. Thus, recovery of the silver dispersion of nanoparticles and dissolved in a hydrocarbon solvent of the primary amine with an amine of the surface of the silver coating agent nanoparticles (R-NH ₂₎ composed of the (R-NH ₂₎ to reach equilibrium dissociation 'S state.

Although water does not dissolve in the hydrocarbon solvent, because methanol has some dissolved in the hydrocarbon solvent, a certain amount of methanol will be dissolved in the dispersion of silver nanoparticles. Using the vapor pressure difference between methanol and the hydrocarbon solvent, methanol is selectively distilled off under reduced pressure.

By performing the above-mentioned series of recovery operations from step iv to step vi, the silver nanoparticles forming the coating agent molecular layer composed of the primary amine on the surface can be recovered in a state of being re-dispersed in an appropriate amount of hydrocarbon solvent. The silver nanoparticles prepared by the method for preparing silver nanoparticles of the present invention have a coating layer composed of a primary amine of an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent on the surface, and the average particle diameter Silver nanoparticles of 5 nm to 20 nm are usually stored in the form of a dispersion liquid dispersed in the hydrocarbon solvent.

The prepared redispersion solution of silver nanoparticles contains silver nanoparticles forming a coating agent molecule composed of a primary amine on the surface, a primary amine, and a hydrocarbon solvent. In this case, the total amount of silver nanoparticles per 100 parts by mass of the primary amine is desirably 20 to 30 parts by mass, and more preferably 22 to 30 parts by mass. In addition, for every 100 parts by mass of silver nanoparticles, the hydrocarbon solvent containing the dispersion solvent is desirably in the range of 100 parts by mass to 200 parts by mass, more preferably in the range of 120 parts by mass to 180 parts by mass.

The dispersion liquid of silver nanoparticles obtained in step A, preferably a redispersion liquid of silver nanoparticles obtained in step vi, is used to prepare a conductive paste according to the following steps.

(Step B, conductive paste) In step B, one or more metal compounds selected from the group consisting of titanium compounds or manganese compounds are added to the silver nanoparticle dispersion prepared in step A. The conductive paste can be obtained from step B. It is also possible to add another suitable solvent (a solvent other than the solvent contained in the silver nanoparticle dispersion liquid) to the silver nanoparticle dispersant. Alternatively, a part or all of the solvent contained in the silver nanoparticle dispersion liquid can be replaced with another solvent.

As the titanium compound, one or more titanium compounds selected from the group consisting of titanium alkoxide, titanium carboxylate, and titanium acetone titanium can be used.

Examples of the titanium compound include titanium tetraisopropoxide and titanium (2-ethylhexanoate).

As the manganese compound, one or more manganese compounds selected from the group consisting of manganese carboxyl and manganese acetone manganese can be used.

Examples of manganese compounds include manganese 2-ethylhexanoate and manganese (III) acetone acetone.

From the viewpoint of adhesion to ITO, the metal contained in the metal compound added in step B is more than 0 parts by mass relative to 100 parts by mass of silver contained in the dispersion liquid of silver nanoparticles obtained in step A , Less than 2.0 parts by mass, preferably 0.5 to 2.0 parts by mass.

Although the dispersing solvent of the silver nanoparticle redispersion liquid is preferably a hydrocarbon solvent having a boiling point in the range of 65°C to 155°C, this hydrocarbon solvent can be replaced with a high boiling point hydrocarbon solvent having a boiling point in the range of 180°C to 310°C. The conductive paste is preferably prepared with a high boiling point hydrocarbon solvent having a boiling point in the range of 200°C to 310°C, and more preferably in the range of 210°C to 310°C.

Examples of usable high-boiling-point hydrocarbon solvents include tetradecane (boiling point: 253.6°C) and the like with a carbon number ranging from 12 to 16, or naphthene/paraffin (paraffin) ) Of the mixed solvent, AF NO. 7 solvent (trade name, boiling point: 275-309°C) manufactured by Nippon Petroleum, IP solvent 2028 (trade name, boiling point: 213-262°C) manufactured by Idemitsu Corporation, etc. In addition, mixtures of multiple high-boiling hydrocarbon solvents can also be used.

For every 100 parts by mass of silver nanoparticles contained in the redispersion liquid of the silver nanoparticles, the high boiling point hydrocarbon solvent is in the range of 43 parts by mass to 58 parts by mass, more preferably 45 parts by mass to 55 parts by mass Range added. Next, the difference in vapor pressure between the hydrocarbon solvent and the high boiling point hydrocarbon solvent is used to selectively distill off the hydrocarbon solvent under reduced pressure.

As a result, a conductive paste in which silver nanoparticles forming a coating agent molecular layer composed of a primary amine on the surface are uniformly dispersed in the high-boiling hydrocarbon solvent is prepared.

The prepared conductive paste contains silver nanoparticles, a primary amine, and a high-boiling hydrocarbon solvent that form a coating agent molecular layer composed of primary amine on the surface. At this time, it is desirable that the conductive paste contains a total of 20 parts by mass to 30 parts by mass for each 100 parts by mass of silver nanoparticles, preferably 22 parts by mass to 30 parts by mass. In addition, for every 100 parts by mass of the silver nanoparticles, it is desirable to contain the high boiling point hydrocarbon solvent in the range of 43 parts by mass to 58 parts by mass, preferably in the range of 45 parts by mass to 55 parts by mass.

When using the prepared conductive paste for inkjet printing, the volume ratio of silver nanoparticles contained in the conductive paste is preferably adjusted to the range of 8% by volume to 12% by volume. In other words, the silver nanoparticles contained in the droplets applied by the inkjet printing method should be maintained in a uniformly dispersed state by selecting the volume ratio described above.

In addition, by adjusting the viscosity of the prepared conductive paste to be in the range of 8 mPa·s to 20 mPa·s (20°C), preferably in the range of 8 mPa·s to 15 mPa·s (20°C), the prepared conductive paste The agent can be suitable for inkjet printing.

In the coated conductive paste, the distribution of the film thickness of the coating liquid film depends on the average density of the dispersion liquid, the wettability of the dispersion solvent used, and its surface tension. To adjust the wettability and surface tension of the dispersion solvent, for example, an effective method may be to mix two or more solvents in which the wettability and surface tension of each solvent are different from each other.

In addition, the dispersibility of the silver nanoparticles forming a coating molecular layer composed of a primary amine on the surface depends on the affinity of the aliphatic hydrocarbon chain existing in the atomic group R of the primary amine (R-NH ₂ ) to the dispersion solvent . When adjusting the dispersibility of the silver nanoparticles, two or more solvents may be mixed in consideration of the wettability and surface tension of the dispersing solvent and the affinity with the primary amine (R-NH ₂ ).

After the conductive paste is applied, if it is heated in the range of 120°C to 150°C, the primary amine (R-NH ₂ ) constituting the coating agent molecular layer on the surface of the silver nanoparticles will be eluted into the dispersion solvent. The rice particles settle, and the silver nanoparticles directly contact each other with their metal surfaces, and are sintered at a low temperature. Finally, a conductive film composed of a low-temperature sintered body of silver nanoparticles is formed.

(About the materials added in step iii) In step iii, a primary amine is added to the dispersion of powdered silver (I) formate. At this time, the secondary amine can also be added together with the primary amine. In this case, the molecular weight of the secondary amine is preferably 100 or more and 150 or less. The secondary amine preferably has an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent.

In addition, in step iii, when a primary amine is added to the powdery silver (I) formate dispersion, it may be carried out in the presence of a monocarboxylic acid. In this case, a monocarboxylic acid having 8 to 11 carbon atoms is preferable.

For example, in step iii, for each mole of silver cations contained in silver (I) formate, 0.05 mole of monocarboxylic acid to 0.3 mole of monocarboxylic acid and 0.05 mole of primary amine to 0.3 For the molar amount, the above secondary amine is used so that the total molar amount of the primary amine and the secondary amine is in the range of 1.1 molar amount to 1.5 molar amount. 【Example】

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following description.

(Example 1)-Step A First, in step A, a silver nanoparticle dispersion liquid is prepared.

・Step i Disperse 100 parts by mass (0.43 moles) of powdered silver (I) (Ag ₂ O, formula 231.735) in 550 parts by mass of methylcyclohexane (boiling point 100.9°C, density 0.7737) .

・Step ii For the obtained dispersion liquid, 50 parts by mass (1.09 mole parts) of formic acid (HCOOH, formula 46.03, boiling point 100.75°C) was added dropwise over 3 to 5 minutes while stirring at room temperature (25°C). Due to the addition of formic acid, the exothermic reaction proceeds and the liquid temperature rises to about 45°C. After the powdered silver oxide is converted to silver formate, the temperature of the reaction solution drops.

・Step iii When the temperature of the obtained reaction liquid drops below 27°C, 230 parts by mass of 2-ethylhexyloxypropylamine (C ₁₁ H ₂₅ NO, formula 187.32, boiling point 235°C) are dissolved in 50 A solution obtained by mass parts of ethylcyclohexane was added to the reaction liquid.

The addition of amine causes the acid-base neutralization reaction to raise the liquid temperature to about 65°C. As the liquid temperature rises, the decomposing reduction reaction of silver formate occurs via the silver formate amine complex. The primary amine (2-ethylhexyloxypropylamine) in the system protects the silver nanoparticles precipitated through the reduction reaction. After the liquid temperature rose to about 65°C, the reaction liquid was continuously stirred, and the stirring was stopped when the liquid temperature dropped to 45°C.

・Step iv Transfer the obtained dark blue dispersion to an eggplant-shaped flask, and distill off the reaction solvent methylcyclohexane or diisopropylamine under reduced pressure. The contents of the eggplant-shaped flask containing the silver nanoparticles changed into a slurry form due to the removal of the solvent and the like.

・Step v Add 280 parts by mass of methanol (boiling point 64.7°C) and 50 parts by mass of distilled water to the residue after desolvation treatment.

In a mixed solvent composed of methanol and distilled water, diisopropylamine addition salt of formic acid or neodecanoic acid, 2-ethylhexyloxypropylamine addition salt of formic acid or neodecanoic acid, and methylcyclopropane are dissolved. On the other hand, silver nanoparticles do not disperse in aqueous methanol but settle.

The supernatant phase of the mixed solvent (aqueous methanol) was removed by decantation.

In order to improve the removal efficiency of residual components, 280 parts by mass of methanol was added to the sedimentation phase obtained by decantation again and stirred, and the supernatant liquid phase was removed by decantation.

・Step vi Add 120 parts by mass of heptane to the sedimentation phase obtained by decantation. The deposited silver nanoparticles are dispersed in methylcyclohexane. The methanol-based heptane remaining in the settled silver particles has poor compatibility, and thus phase separation occurs. The part of the phase-separated methanol phase (aqueous methanol) is removed.

・Purification procedure In the heptane layer in which silver nanoparticles have been dispersed, a certain amount of methanol is dissolved and mixed. The mixed methanol was distilled off under reduced pressure. The difference between the boiling points of methanol and heptane is used to selectively distill off methanol. Specifically, after the methanol removal was performed at 150°Pa for 5 minutes at 45°C (bath temperature), the degree of reduced pressure was increased to 120hPa, and the methanol removal was performed again for 3 minutes.

The obtained heptane solution with silver nanoparticle dispersion was filtered through a 0.2 μm filter membrane to remove agglomerates. As the filtrate obtained by filtration, a silver nanoparticle dispersion liquid was obtained.

・Evaluation of silver nanoparticle dispersion liquid The total amount of metallic silver contained in the silver nanoparticle dispersion liquid obtained by the measurement was measured, and the production based on the silver content in the silver oxide (I) of the starting material was calculated. rate. The calculated yield is 98%.

The method of measuring the total amount of metallic silver is as follows. Weigh the obtained silver nanoparticle dispersion into the crucible, use a hot air dryer to remove the methyl cyclohexane contained in it, after obtaining the solid, put the crucible into a muffle furnace and calcinate at 700℃ 30 minutes. Because only metal remains after calcination, the amount of metal is weighed, and the total amount of metallic silver is calculated from the concentration of the dispersion.

In addition, after the obtained silver nanoparticle dispersion liquid was allowed to stand at room temperature for one week, it was visually observed whether the particles settled. No particle settling was observed.

The particle size of the silver nanoparticles dispersed in the obtained silver nanoparticle dispersion liquid was measured using a light scattering type particle size distribution measuring device (manufactured by MicrotracBEL Corp., trade name: Nanotrac UPA150). From the measurement results, it can be known that the average particle diameter of the silver nanoparticles uniformly dispersed in the filtrate is 9 nm.

In the obtained silver nanoparticle dispersion liquid, there are 25.0 parts by mass per 100 parts by mass of silver nanoparticles coated with 2-ethylhexyloxypropylamine (excluding the coating agent and only 100 parts by mass of silver). The 2-ethylhexyloxypropylamine coats the surface of the silver nanoparticles.

The method of measuring the amount of the coating agent that covers the silver nanoparticles is as follows. That is, a dispersion liquid in which 0.1 g of silver nanoparticles are dispersed in heptane is weighed into a glass bottle, and the solvent is dried into a powder form using a dryer (cold air). Approximately 10 mg of dry powder was heated to 500° C. in a thermal analysis device (trade name: TG/DTA6200, manufactured by SII NanoTechnology Inc.) and measured, and the coating dose was calculated from the weight reduction rate.

・Step B The silver nanoparticle dispersion obtained in step A, the amount of silver contained in the dispersion is 60 parts by mass, and 38.2 parts by mass of tetradecane (boiling point 253.6°C, density 0.7624g/ cm ³ ), 1.8 parts by mass of titanium tetraisopropoxide (made by Wako Pure Chemical Industries).

The heptane contained in the obtained mixed liquid was distilled off under reduced pressure to prepare a printing ink (conductive paste for printing) using tetradecane as a dispersion solvent. The amount of metallic titanium contained in the ink is 0.5 parts by mass relative to 100 parts by mass of silver.

The viscosity of the prepared ink is 11mPa·s (20℃), and the metal content is 55.2% by mass. Using the prepared conductive ink, spin coating was applied to glass with an ITO film 25 mm wide and 75 mm long. The average film thickness of this coating film was 6 μm. The obtained coating film was heat-treated at 200°C for 60 minutes in an air environment using an air-drying furnace to sinter the silver nanoparticles contained in the coating film. The low-temperature calcined film of the prepared silver nanoparticles was measured for resistivity. The film thickness after calcination was 0.9 μm, and the resistivity of the low-temperature calcined film was 13 μΩ·cm. Regarding the adhesion of the calcined film to the glass with the ITO film, a cross peel test was carried out. After confirming whether there was peeling, no peeling was found in all 81 squares of 1 mm×1 mm.

(Examples 2 to 9 and Comparative Examples 1 to 3) In Step B, the conductive paste formulations shown in Table 1 were used, except that the conductive paste was prepared in the same manner as in Example 1. And evaluation. The results are shown in Table 1. However, for example, in Example 4, titanium (IV) 2-ethylhexanoate was used as the metal compound. In addition, in Examples 5 to 7, for example, in order to add a metal compound, a 2-ethylhexanoic acid manganese mineral spirit solution (manufactured by Wako Pure Chemical Industries, Mn 8% by mass) was used.

In Comparative Example 1, no metal compound was added to the conductive paste. In Comparative Example 1, in the cross-cut peel test, 40 squares were peeled out of all 81 squares of 1 mm×1 mm.

In Comparative Example 2 and Comparative Example 3, cracking occurred after the conductive paste was calcined, and the conductivity and the film thickness after calcination could not be measured.

[產業上利用性][Table 1]

[Industry availability]

The silver nanoparticles produced by the present invention can be suitably used, for example, for mounting electronic parts on an ITO film or glass, or for forming wiring on the ITO film or glass.

Claims (15)

A method for manufacturing a conductive paste, which includes the following steps: A) preparing silver nanoparticles having an average particle diameter of 5 nm to 20 nm with a coating layer composed of coating agent molecules on the surface, where the silver nanoparticles In the preparation step, powdered silver oxide (I) is used as a raw material in the liquid phase, formic acid acts on the powdered silver oxide (I), and is converted into silver formate (I). The silver cation having is reduced to silver atoms, and silver nanoparticles are prepared from the silver atoms. Step i: Use a hydrocarbon solvent to prepare the dispersion of the powdered silver oxide (I); Step ii: For the powdered silver oxide (I) The dispersion liquid is added with formic acid to make the formic acid act on the powdered silver (I) oxide and converted into silver (I) formate, and the powder of the produced silver (I) formate is dispersed in the hydrocarbon solvent to prepare powdered silver formate (I) Dispersion; Step iii: Add primary amine to the silver (I) formate dispersion, and make the primary amine act on the powdered silver (I) to produce the primary amine of silver (I) Complex, the primary amine is a primary amine (R-NH ₂ ) composed of the radical R and the amine group of the aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent, and the resulting silver (I) formate is a primary When the amine complex is dissolved in the hydrocarbon solvent, silver nanoparticles with an average particle diameter of 5 nm to 20 nm composed of silver atoms generated by the decomposing reduction reaction of the primary amine complex of silver (I) formate are formed. Here, the silver nanoparticles with an average particle size of 5 nm to 20 nm generated in step iii are the primary amine using the lone electron pair existing on its amine nitrogen atom, and the silver atoms on the surface thereof are covered by coordination bonds. In the form of; and B) Adding one or more metal compounds selected from the group consisting of titanium compounds and manganese compounds to the dispersion of silver nanoparticles obtained in step A, the metal contained in the metal compound is relatively 100 parts by mass of silver contained in the dispersion liquid of silver nanoparticles obtained in step A is more than 0 parts by mass and 2.0 parts by mass or less. A method for manufacturing a conductive paste as claimed in item 1 of the patent application, wherein the titanium compound is selected from at least one group selected from the group consisting of titanium alkoxide, titanium carboxylate, and titanium acetone, and the manganese compound is selected from More than one of the group consisting of manganese carboxyl and manganese acetone manganese. For example, the method for manufacturing a conductive paste according to item 1 or 2 of the patent application, wherein the metal contained in the metal compound added in step B is 100% of the silver contained in the dispersion of silver nanoparticles obtained in step A The part is 0.5 to 2.0 parts by mass. The method for manufacturing a conductive paste according to any one of claims 1 or 2, wherein the hydrocarbon solvent used in step i is 350 mass per 100 parts by mass of powdered silver oxide (I) in the raw material A hydrocarbon solvent with a boiling point in the range of 65°C to 155°C is selected in the range of 1 part to 550 parts by mass. For example, the method for manufacturing a conductive paste according to any one of claims 1 or 2, wherein the hydrocarbon solvent used in step i is a hydrocarbon having 6 to 9 carbon atoms. The method for manufacturing a conductive paste according to any one of claims 1 or 2, wherein the formic acid used in step ii is a silver cation contained in powdered silver oxide (I) relative to the raw material Each mole is selected from the range of 1.1 moles to 1.4 moles. The method for manufacturing a conductive paste according to any one of claims 1 or 2, wherein in step iii, a primary amine having a carbon number of 9 to 11 is used as the primary amine, and a secondary amine is added. The method for manufacturing a conductive paste according to any one of the patent application items 1 or 2, wherein the first-stage amine is used in step iii, and the silver cation contained in the powdered silver oxide (I) of the raw material is 1 mole per 1 A primary amine (R-NH ₂ ) composed of an atomic group R and an amine group of an aliphatic hydrocarbon chain having an affinity for the hydrocarbon solvent is selected within the range of 1.2 moles to 1.8 moles. For example, in the method of manufacturing a conductive paste of claim 8, the primary amine (R-NH ₂ ) consisting of the atomic group R and the amine group of the aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent, The atomic group R having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent is selected from (alkoxy) alkyl, (alkylamino) alkyl, (dialkylamino) having a total carbon number of 7-12 Alkyl, alkyl. For example, the method for manufacturing a conductive paste according to item 8 of the patent application, in which the primary amine (R-NH ₂ ) is composed of an atomic group R and an amine group having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent, is An amine compound whose boiling point exceeds 170°C. For example, the manufacturing method of the conductive paste in the tenth patent application, wherein the primary amine (R-NH ₂ ) is composed of the atomic group R and the amine group of the aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent. An amine compound with a boiling point in the range of 200°C to 270°C. A method for manufacturing a conductive paste as described in any of the 8th items of the patent application, wherein the primary amine (R-NH) is composed of an atomic group R and an amine group having an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent ₂ ), is 3-alkoxypropylamine (R'-O-CH ₂ CH ₂ CH ₂ -NH ₂ ), the alkyl (R') constituting the alkoxy radical (R'-O-) is the carbon number 4-9 alkyl. The method for manufacturing a conductive paste according to any one of claims 1 or 2, wherein in step iii, it will consist of an atomic group R and an amine group of an aliphatic hydrocarbon chain having affinity for the hydrocarbon solvent The primary amine (R-NH ₂ ) is diluted with the hydrocarbon solvent into a diluted solution, and then added to the powdered silver (I) formate dispersion. The diluted solution is added to 20 mass parts per 100 mass parts of the primary amine. Dilute the hydrocarbon solvent in the range of ~45 parts by mass. The method for manufacturing a conductive paste according to any one of the patent application items 1 or 2, wherein in this step iii, in addition to the action of a primary amine on the powdered silver (I) formate to produce silver (I) The reaction of the primary amine complex is carried out as follows: the added primary amine acts on formic acid that is not consumed in the step ii due to the reaction with the powdered silver oxide (I) but is formed The primary amine addition salt of formic acid; the liquid temperature rises due to the reaction heat of the reaction of the primary amine addition salt forming the formic acid. For example, the method for manufacturing a conductive paste according to any one of claims 1 or 2 includes the following steps: in step A, after step iii, it further includes the following steps iv to step vi, Step iv: After the end of step iii, the hydrocarbon solvent contained in the reaction solution containing the silver nanoparticles whose surface is coated with the primary amine having an average particle diameter of 5 nm to 20 nm is distilled off under reduced pressure, and the surface containing is recovered The silver nanoparticles coated with the average particle size of the primary amine 5nm~20nm, the formic acid primary amine addition salt, the residual primary amine residue; Step v: For the residue recovered in step iv, add The powdered silver oxide (I) of the raw material is selected from the range of 200 parts by mass to 300 parts by mass per 100 parts by mass of methanol, and the distilled water selected from the range of 50 parts by mass to 300 parts by mass to contain the residue The formic acid primary amine addition salt and the residual primary amine are dissolved in the mixed solvent of methanol and distilled water, and are layered into sediments containing silver nanoparticles with an average particle size of 5-20 nm coated with the primary amine Layer, and a liquid phase layer formed by dissolving the formic acid primary amine addition salt and primary amine in the mixed solvent, and removing the liquid phase formed by dissolving the formic acid primary amine addition salt and primary amine in the mixed solvent Layer, and recover the sediment layer containing silver nanoparticles whose surface is coated with the primary amine with an average particle size of 5-20 nm; Step vi: For the sediment layer recovered in step v, add the powdered silver oxide in the raw material (I) For every 100 parts by mass, a hydrocarbon solvent with a boiling point in the range of 65°C to 155°C selected from the range of 100 parts by mass to 200 parts by mass, the surface contained in the sediment layer is covered with the primary amine Silver nanoparticles with an average particle size of 5-20 nm are evenly dispersed in the hydrocarbon solvent with a boiling point in the range of 65°C to 155°C to make a dispersion, Layering is a layer of a small amount of a mixed solvent of methanol and distilled water impregnated in the sediment layer, and a layer of a dispersion liquid using the hydrocarbon solvent having a boiling point in the range of 65°C to 155°C as a dispersion solvent, and removing the A small amount of the layer of the mixed solvent of methanol and distilled water, and recover the layer of the dispersion liquid with the hydrocarbon solvent having a boiling point in the range of 65°C to 155°C as the dispersion solvent.