JP7740913B2 - Copper powder with coating layer and method for producing same - Google Patents

Description

The present invention relates to copper powder having a coating layer and a method for producing the same.

Since oxidation of copper powder begins immediately after its production and progresses while it is stored in powder form, technologies have been developed to prevent this oxidation. For example, Patent Document 1 proposes copper powder with a surface lightness L* of 46.3 or higher that is resistant to discoloration due to oxidation, and describes that the copper powder contains a rust inhibitor containing a triazole compound.

Japanese Patent Application Laid-Open No. 2019-183242

The object of the present invention is to provide copper powder with excellent oxidation resistance and a method for producing the same.

As a result of extensive research into solving the above problems, the inventors discovered that forming a specific coating layer on copper powder resulted in excellent oxidation resistance, leading to the completion of the present invention.

That is, the present invention provides:
[1]
Copper powder having a coating layer containing a nitrogen-containing heteroaromatic compound and a polyol having a molecular weight of 150,000 or less;
[2]
A method for producing copper powder having a coating layer, comprising a mixing step of mixing copper powder with a coating composition containing a nitrogen-containing heteroaromatic compound and a polyol having a molecular weight of 150,000 or less;
etc.

The present invention provides copper powder with excellent oxidation resistance and a method for producing the same.

The copper powder and the method for producing the same according to this embodiment will be described below.
One embodiment of the present invention is a copper powder having a coating layer containing a nitrogen-containing heteroaromatic compound and a specific polyol.

<Copper powder with coating layer>
The copper powder of the present invention has a coating layer. The coating layer is not particularly limited, but may be formed on the copper powder in an amount of, for example, 10 to 100 mg/ ^m² . The copper powder may or may not have one or more other layers between the copper surface and the coating layer. The copper powder may or may not have one or more other layers on the surface of the coating layer. Examples of other layers include, but are not limited to, a copper oxide coating layer, a metal layer other than copper, such as silver or nickel, and a surface treatment layer formed in the surface treatment step described below. When other layers are present, the other layers may cover part or all of the underlying copper surface or coating layer.

<Copper powder>
The copper powder is not particularly limited as long as it is a metal powder containing copper as a primary component, and examples thereof include pure copper powder and copper alloy powder (particularly copper alloy powder having a Cu content of 80% by mass or more). Commercially available copper powders or those prepared by known means can be used. Examples of copper powders that can be used include wet copper powder, electrolytic copper powder, atomized copper powder, vapor-phase reduced copper powder, and copper powder obtained by mechanical pulverization. The shape of the copper powder may be spherical, approximately spherical, flake-like, leaf-like, dendritic, plate-like, needle-like, or grape-like. The copper powder may also be a mixture of two or more types of copper powders with different shapes. Such copper powders are readily available from manufacturers of metal powders. Furthermore, the copper powders of the above shapes may be further deformed by applying physical force. The D50 of the copper powder, i.e., the volume-cumulative particle size D50 measured by a laser diffraction/scattering particle size distribution analyzer, is not particularly limited, but may be, for example, 0.01 μm to 100.0 μm.

<Coating layer>
The coating layer contains a nitrogen-containing heteroaromatic compound and a predetermined polyol. The mass ratio of the nitrogen-containing heteroaromatic compound to the polyol contained in the coating layer is not particularly limited as long as the effects of the present invention are achieved, but is, for example, in the range of 5:40 to 40:5.

<Nitrogen-containing heteroaromatic compound>
Examples of nitrogen-containing heteroaromatic compounds include benzotriazole and its derivatives, triazole and its derivatives, tetrazole and its derivatives, thiazole and its derivatives, benzothiazole and its derivatives, imidazole and its derivatives, and benzimidazole and its derivatives.
In the present invention, derivatives of benzotriazole, triazole, tetrazole, thiazole, benzothiazole, imidazole, and benzimidazole refer to compounds in which one or more hydrogen atoms of these compounds have been substituted with a substituent having a hydroxy group, a carboxy group, a sulfo group, or the like.
In the present invention, the nitrogen-containing heteroaromatic compound may have a functional group capable of reacting with a hydroxy group of the polyol described below, such as a hydroxy group, a carboxy group, or a sulfo group.

Benzotriazole and its derivatives include 1,2,3-benzotriazole and its sodium salt, tolyltriazole, carboxybenzotriazole, 4-carboxybenzotriazole, 5-carboxybenzotriazole, 6-carboxybenzotriazole, 7-carboxybenzotriazole, 5,6-dicarboxybenzotriazole, hydroxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2-2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole. Triazole and its derivatives include 1,2,3-triazole and 1,2,4-triazole. Examples of tetrazole and its derivatives include 5-amino-1H-tetrazole and 1-phenyl-5-mercapto-1H-tetrazole. Examples of thiazole and its derivatives include 2-(methylthio)-2-thiazoline. Examples of benzothiazole and its derivatives include benzothiazole, 2-methylbenzothiazole, and 2-mercaptobenzothiazole. Examples of imidazole and its derivatives include 2-mercapto-1-methylimidazole. Benzimidazole and its derivatives include 2-mercaptobenzimidazole, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-carboxybenzimidazole, 1,3-dihydro-1-phenyl-2H-benzimidazole-2-thione, 2-hydroxybenzimidazole, 2-bromobenzimidazole, 2-mercaptobenzimidazole-5-sodium sulfonate dihydrate, 1-isopropenylbenzimidazole-2-one, 1-(2-propenyl)benzimidazole-2-one, 2-methylbenzimidazole, 2-mercapto-5-nitrobenzimidazole, and 2-mercapto-5-aminobenzimidazole.

<Polyol>
A polyol is an organic compound having two or more alcoholic hydroxy groups in the molecule. Examples of polyols include diols (e.g., methylene glycol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, hexylene glycol, 1,3-butanediol, 1,4-butanediol, polyalkylene glycols, etc.), triols (e.g., glycerin, etc.), diglycerin, polyglycerin, sugars and derivatives thereof (e.g., monosaccharides such as glucose, fructose, mannose, galactose, ribose, etc.; disaccharides such as xylobiose, trehalose, maltose, saccharose, etc.; polysaccharides such as dextrin, starch, glycogen, cellulose, etc.), aldonic acids and salts thereof (e.g., gluconic acid, glucoheptonic acid, mannonic acid, mannoheptonic acid, galactonic acid, galactoheptonic acid, and sodium salts, potassium salts, amine salts, ammonium salts thereof), and sugar alcohols (e.g., erythritol, xylitol, sorbitol, mannitol, etc.). Examples of polyalkylene glycols include diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, polytetramethylene glycol, etc. The polyol may have a structure (aldehyde group, etc.) that exhibits reducing properties, such as glucose.

In one embodiment of the present invention, the molecular weight of the polyol is 150,000 or less. The molecular weight of the polyol may be, for example, 100,000 or less, or 50,000 or less. Here, molecular weight refers to the sum of the atomic weights of the elements constituting the molecule when the polyol is composed of a single molecule such as glucose and has no molecular weight distribution. However, when the polyol is an aggregate of molecules with various molecular weights, such as synthetic polymers such as polyethylene glycol or natural polymers such as gum arabic, i.e., when the polyol has a molecular weight distribution, it refers to the number average molecular weight. Here, the number average molecular weight refers to a value measured by gel permeation chromatography (GPC). The GPC conditions are as follows:
(GPC conditions)
Column: Semi-micro column (manufactured by Tosoh Corporation); two columns were used in series. Standard sample: PStQuick B (manufactured by Tosoh Corporation). Mobile phase: N,N-dimethylformamide (DMF).
・Detection equipment: RI

<Other ingredients>
In addition to the nitrogen-containing heteroaromatic compound and a predetermined polyol, the coating layer may or may not contain other components such as glue, gelatin, a coupling agent and/or its condensate, a fatty acid, an aliphatic amine, etc. Furthermore, the coating layer may or may not contain a metal compound and/or metal such as a silver compound and/or silver, a nickel compound and/or nickel, etc.
Examples of the coupling agent include silane coupling agents, titanate coupling agents, aluminate coupling agents, and zirconate coupling agents. Examples of the silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryl ... Methoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 1-aminopropyltrimethoxysilane, 2-aminopropyltrimethoxysilane, 1,2-diaminopropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, Amino-1-propenyltrimethoxysilane, 3-amino-1-propynyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyl Examples of the titanate coupling agent include isopropyl triisostearoyl titanate, isopropyl tristearoyl titanate, isopropyl tricaproyl titanate, isopropyl trilauroyl titanate, isopropyl tripalmitoyl titanate, diisopropyl diisostearoyl titanate, diisopropyl dilauroyl titanate, diisopropyl dipalmitoyl titanate, triisopropoxy titanium octanoate, tetraoctyl bis(isopropylmethylsilane), tetraisopropoxy titanium octanoate, ... (ditridecyl phosphite) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraisopropyl bis(distearyl phosphite) titanate, tetraisopropyl bis(dilauryl phosphite) titanate, isopropyl tris(dioctyl pyrophosphate) titanate, isopropyl tris(dilauryl pyrophosphate) titanate, isopropyl tris(dimyristyl pyrophosphate) titanate, Diisopropyl tris(distearyl pyrophosphate) titanate, bis(dioctyl pyrophosphate) oxyacetate titanate, bis(dioctyl pyrophosphate) ethylene titanate, diisopropyl bis(dioctyl pyrophosphate) titanate, diisopropyl bis(distearyl pyrophosphate) titanate, octyl tris(dioctyl pyrophosphate) titanate, dioctyl bis(dioctyl pyrophosphate) ) titanate, bis(dioctyl phosphate)ethylene titanate, isopropyl tris(dioctyl phosphate)titanate, isopropyl tris(distearyl phosphate)titanate, butyl tris(dioctyl phosphate)titanate, tris(dioctyl phosphate)octyloxytitanium, isopropyl tris(dodecylbenzenesulfonyl)titanate, diisopropyl bis(dodecylbenzenesulfonyl)titanate.
Examples of fatty acids include benzoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, and stearic acid. Examples of aliphatic amines include pentylamine, hexylamine, octylamine, decylamine, laurylamine, oleylamine, and stearylamine.

(Method for producing copper powder having a coating layer)
The copper powder of this embodiment has a coating layer containing a nitrogen-containing heteroaromatic compound and a predetermined polyol. The method for producing the copper powder of this embodiment is not particularly limited as long as it can form a coating layer on the copper powder, and includes a mixing step of mixing copper powder with a coating composition containing a nitrogen-containing heteroaromatic compound and a predetermined polyol. In the production method of this embodiment, pretreatment such as degreasing or pickling of the copper powder may or may not be performed before the mixing step. If pretreatment is performed, subsequent treatments such as water washing, solid-liquid separation, and drying may or may not be performed, either alone or in combination as appropriate. Furthermore, water washing, solid-liquid separation, and drying may or may not be performed after the mixing step. If necessary, a surface treatment step using a component such as a coupling agent, fatty acid, or aliphatic amine may or may not be performed before, during, or after the mixing step. If necessary, a silver coating step in which the copper powder is coated with silver may or may not be performed before, during, or after the mixing step.

<Pretreatment of copper powder>
The degreasing method may be any method capable of removing grease and dirt adhering to the surface of the metal material, and examples thereof include known methods using solvent degreasing and alkaline or acidic degreasing agents. Examples of pickling methods include pickling of copper powder using organic acids such as formic acid, acetic acid, and fatty acids, or inorganic acids such as sulfuric acid and hydrochloric acid. Water washing and solid-liquid separation may or may not be performed before or after degreasing or before or after pickling. If necessary, copper powder that has been degreased, pickled, and washed may or may not be solid-liquid separated and dried before mixing with the coating composition. Furthermore, if copper powder is produced by a wet method or the like and obtained in the form of a solvent-containing slurry during the production process, it may be used without completely evaporating the solvent.

<Method for producing a coating composition containing a nitrogen-containing heteroaromatic compound and a predetermined polyol>
The coating composition containing a nitrogen-containing heteroaromatic compound and a predetermined polyol can be produced, for example, by mixing the nitrogen-containing heteroaromatic compound, the polyol, and, if necessary, the other components in a solvent. The mixing order is not particularly limited, and can be appropriately adjusted depending on the components used.
As the solvent, any solvent can be used as long as it can dissolve or disperse the nitrogen-containing heteroaromatic compound and the polyol, and aqueous media and organic solvents can be used without any restrictions.
The aqueous medium is not particularly limited as long as it contains 50% by mass or more of water, and may be composed of water alone or a mixture containing water and a water-miscible organic solvent. The water-miscible organic solvent is not particularly limited as long as it is miscible with water, and examples thereof include ketone solvents such as acetone and methyl ethyl ketone; amide solvents such as N,N'-dimethylformamide and dimethylacetamide; alcohol solvents such as methanol, ethanol, and isopropanol; ether solvents such as ethylene glycol monobutyl ether and ethylene glycol monohexyl ether; and pyrrolidone solvents such as 1-methyl-2-pyrrolidone and 1-ethyl-2-pyrrolidone. One of these water-miscible organic solvents may be mixed with water, or two or more may be mixed with water.

<Mixing process>
The mixing method may be any method that can mix copper powder with a coating composition containing a nitrogen-containing heteroaromatic compound and a predetermined polyol, bring the composition into contact with the copper powder, and form a coating layer on the copper powder. For example, a method of adding copper powder to the composition and appropriately stirring the mixture can be used, but is not limited to this. The mixing temperature and mixing time are appropriately set depending on the composition and concentration of the composition. The mixing temperature and mixing time are typically within the range of 40°C to 90°C, and the mixing time is within the range of 1 minute to 30 minutes, but are not limited thereto. Furthermore, the ratio of copper powder to coating composition in the mixing process, and the ratio of copper powder to the components in the coating composition, can be appropriately set depending on the shape and specific surface area of the copper powder. The mixture of the coating composition and copper powder obtained by mixing in this manner can be used as a powder paste and is useful for resistors, inductors, capacitors, wiring and electrodes for ceramic substrates, printed circuit boards, solar cells, touch panels, etc.

<Surface treatment process>
A surface treatment step using a surface treatment component such as a coupling agent, a fatty acid, or an aliphatic amine may be carried out before, during, or after the mixing step. The surface treatment step can be carried out by contacting the surface treatment component with the copper powder, and typically by mixing the surface treatment component with the copper powder in an aqueous medium. When the surface treatment is carried out during the mixing step, the coating composition and the surface treatment component can be simultaneously present in the mixture. The surface treatment step forms a surface treatment layer on the copper powder.

<Surface treatment ingredients>
Examples of surface treatment components include glue, gelatin, coupling agents, fatty acids, and aliphatic amines, which are listed above under <Other Components>.

<Silver coating process>
A silver coating step in which the copper powder is coated with silver may be performed before, during, or after the mixing step. The method for coating the copper powder with silver may be any method capable of producing silver-coated copper powder. Examples of methods that can be used include, but are not limited to, a reduction method utilizing a substitution reaction between copper and silver, a reduction method using a reducing agent to precipitate silver or a silver compound on the surface of the copper powder, or a method in which fine silver particles are attached to the surface of the copper powder. Precipitation methods include, for example, a method in which a solution containing copper powder and silver or a silver compound in a solvent is stirred to precipitate silver or a silver compound on the surface of the copper powder, or a method in which a solution containing copper powder and an organic substance in a solvent is mixed with a solution containing silver or a silver compound and an organic substance in a solvent and stirred to precipitate silver or a silver compound on the surface of the copper powder. Silver coating during the mixing step can be performed by simultaneously adding the coating composition and silver or a silver compound to the mixture. A silver-containing layer is formed on the copper powder by the silver coating step.

A surface treatment layer can be formed on the copper powder in a surface treatment process, and then the copper powder is mixed with a coating composition containing a nitrogen-containing heteroaromatic compound and a specified polyol, and the copper powder is brought into contact with the composition to form a coating layer on the copper powder. A silver-containing layer can be formed on the copper powder in a silver coating process, and then the copper powder is mixed with a coating composition containing a nitrogen-containing heteroaromatic compound and a specified polyol, and the copper powder is brought into contact with the composition to form a coating layer on the copper powder. A silver-containing layer can be formed on the copper powder in a silver coating process, and then a surface treatment layer can be formed on the copper powder in a surface treatment process, and then the copper powder is mixed with a coating composition containing a nitrogen-containing heteroaromatic compound and a specified polyol, and the copper powder is brought into contact with the composition to form a coating layer on the copper powder.

The copper powder on which the coating layer is formed after the mixing process may or may not be washed with water, subjected to solid-liquid separation, and dried. For example, when the copper powder of this embodiment is used as a raw material (filler) for a conductive paste, after the mixing process, washing with water and solid-liquid separation may be performed as appropriate, and the powder may be used in the form of a slurry containing copper powder and a solvent, or the copper powder may be isolated and dried before use.

The presence of a coating layer on copper powder can be confirmed, for example, by subjecting the copper powder to XPS (X-ray photoelectron spectroscopy) survey measurement and detecting elements contained in the nitrogen-containing heteroaromatic compound or polyol. The XPS survey measurement will now be described in detail. First, 0.5 g of copper powder is filled into cylindrical containers with a diameter of 0.5 mm, and the powder is spread so that the bottom surface is completely covered. The upper surface of the copper powder spread in the cylindrical container is subjected to XPS survey measurement (semi-quantitative analysis of elements attached to the surface of the upper half of the copper powder) using the following equipment and conditions to identify the elements present on the copper powder surface.
Apparatus: ULVAC-PHI 5600MC
Ultimate vacuum: 5.7×10 ^-9 Torr
Excitation source: monochromated AlKα
Output: 210W
Detection area: 800 μmφ
Incidence angle, extraction angle: 45°
Use Neutralization Gun

<Applications of copper powder>
The copper powder according to the present invention has high oxidation resistance and can maintain its conductivity, and therefore can be suitably used as a conductive filler contained in conductive pastes, etc. Conductive pastes are flowable compositions in which a conductive filler is dispersed in a vehicle consisting of a resin binder and a solvent, and are widely used for forming electrical circuits, external electrodes of ceramic capacitors, various conductive films, etc.

The present invention will be explained in more detail using examples and comparative examples. However, the present invention is not limited to the following examples.

(Preparation of Coating Composition)
A nitrogen-containing heteroaromatic compound (compound B) shown in Table 1 was mixed with ethanol, and then the mixture and a polyol (compound A) shown in Table 1 were mixed with deionized water to prepare coating compositions No. 1 to 12 having the concentrations shown in Table 1.

In Table 1, the details of each number in the Compound A and Compound B columns are as follows:

(Preparation of copper powder samples with coating layers)
250 g of copper powder (manufactured by DOWA Electronics Co., Ltd., D50 = 1.0 μm) and 1 L of each coating composition (Nos. 1 to 12) were mixed and stirred at 80°C for 5 minutes. The mixture was subjected to solid-liquid separation by suction filtration, and then water was added over the copper powder remaining on the filter and sucked, resulting in washing and solid-liquid separation of the copper powder. The copper powder after solid-liquid separation was crushed and dried with hot air at 60°C for 1 hour. The copper powder was then finely crushed in a mortar and used as copper powder samples (Examples 1 to 11 and Comparative Example 2). An untreated copper powder sample was used as Comparative Example 1.

(Storage test under high temperature and humidity conditions)
The copper powder samples (Examples 1 to 11 and Comparative Examples 1 and 2) were stored for 120 hours in a thermo-hygrostat LHL-114 (manufactured by Espec Corporation) set at a temperature of 85°C and a relative humidity (RH) of 85%, and then allowed to cool to room temperature in a desiccator.

(Evaluation of oxidation resistance of copper powder samples)
To evaluate the oxidation resistance of the copper powder samples, the electrical conductivity of the copper powder samples (Examples 1 to 11 and Comparative Examples 1 and 2) was evaluated before and after a storage test under high temperature and high humidity. Specifically, 5.0 g of the copper powder sample was placed in the probe unit of a powder resistivity measurement system (manufactured by Mitsubishi Chemical Analytech), and the volume resistivity was measured when a pressure of 20 MPa was applied. The volume resistivity/Ωcm values were ranked according to the following criteria to evaluate the electrical conductivity of the copper powder samples. The results are shown in Table 4. Conductivity evaluation results of ◎, ◯, and △ were considered to be pass, and × was considered to be fail.

<Evaluation criteria>
◎: Volume resistivity is less than 2.00×10 ¹ Ωcm ○: Volume resistivity is 2.00×10 ¹ Ωcm or more and less than 5.00×10 ³ Ωcm △: Volume resistivity is 5.00×10 ³ Ωcm or more and less than 1.00×10 ⁵ Ωcm ×: Volume resistivity is 1.00×10 ⁵ Ωcm or more

Claims (2)

Copper powder having a coating layer on the surface thereof, the coating layer comprising benzotriazole and its derivatives and a polyol or monosaccharide having a number average molecular weight of 20,000 or less, wherein the mass ratio of the benzotriazole and its derivatives to the polyol or monosaccharide is 40:5 to 5:40 . A method for producing copper powder having a coating layer on the surface thereof, comprising a mixing step of mixing copper powder with a coating composition comprising benzotriazole and its derivatives, a polyol or monosaccharide having a number average molecular weight of 20,000 or less, and a solvent, wherein the mass ratio of the benzotriazole and its derivatives to the polyol or monosaccharide is 40:5 to 5:40 .