JP5847439B2 - Method for producing silver-containing nanoparticles, silver-containing nanoparticles, and silver coating composition - Google Patents

Description

  The present invention relates to a method for producing silver-containing nanoparticles and silver-containing nanoparticles. Moreover, this invention relates to the silver coating composition containing the said silver containing nanoparticle.

  Silver nanoparticles can be sintered even at low temperatures. Utilizing this property, in the production of various electronic devices, silver coating compositions containing silver nanoparticles are used to form electrodes and conductive circuit patterns on a substrate. Silver nanoparticles are usually dispersed in an organic solvent. Silver nanoparticles have an average primary particle diameter of about several nanometers to several tens of nanometers, and the surface thereof is usually coated with an organic stabilizer (protective agent). When the substrate is a plastic film or sheet, it is necessary to sinter the silver nanoparticles at a low temperature (for example, 200 ° C. or less) lower than the heat resistance temperature of the plastic substrate.

  For example, Japanese Patent Application Laid-Open No. 2006-104576 includes a hydrazine compound containing a silver compound in the presence of a thermally removable stabilizer in a reaction mixture containing a silver compound, a reducing agent, a stabilizer, and a solvent. A method of producing silver nanoparticles is disclosed that includes reacting with a reducing agent to form silver nanoparticles having stabilizer molecules on the surface. As the stabilizer, various organic amine compounds have been mentioned ([0025] to [0027]).

  JP 2010-43355 A discloses a step of forming a mixture containing a silver compound, a carboxylic acid, an amine compound, and a solvent, a step of heating the mixture, a step of adding a hydrazine compound to the mixture, A method of producing silver nanoparticles is disclosed that includes a step of reacting a mixture to form silver nanoparticles. Various organic amine compounds are mentioned as stabilizers ([0019] to [0020], [0040] to [0042]).

Japanese Patent Application Laid-Open No. 2007-297665 discloses a carbodihydrazide H ₂ NHN—CO—NHNH ₂ or polybasic acid polyhydrazide R— (CO—NHNH ₂ ) n after a metal salt compound of a fatty acid is dispersed in a liquid medium. A method for producing a metal fine particle dispersion in which the metal salt compound is reduced using [R is an n-valent polybasic acid residue] is disclosed. Various organic amine compounds are listed as compounds having a dispersion stabilizing function ([0035] to [0036]).

  Japanese Patent Application Laid-Open No. 2011-58092 discloses that in a substantially solvent-free reaction mixture containing a metal compound, a reducing agent, and a stabilizer, the metal compound is reacted with the reducing agent in the presence of the stabilizer. Disclosed is a method for producing metal nanoparticles comprising forming metal-containing nanoparticles having the stabilizer molecules on a surface by a solvent-free reduction process. As the stabilizer, various organic amine compounds are mentioned ([0026] to [0027]).

JP 2006-104576 A JP 2010-43355 A JP 2007-297665 A JP 2011-58092 A

  However, in any of the above patent documents, only a linear aliphatic group in an organic amine compound as a stabilizer is disclosed.

  Silver nanoparticles have an average primary particle diameter of about several nanometers to several tens of nanometers, and are more easily aggregated than micron (μm) size particles. Therefore, the reduction reaction of the silver compound is performed in the presence of the organic stabilizer so that the surface of the obtained silver nanoparticles is coated with the organic stabilizer (protective agent). Conventionally, in order to ensure the space between individual silver nanoparticles, a relatively long chain (for example, having 8 or more carbon atoms) linear alkylamine compound has been used as an organic stabilizer.

  On the other hand, the silver nanoparticles are a silver coating composition (silver ink, silver paste) containing the particles in an organic solvent. In order to develop conductivity, it is necessary to remove the organic stabilizer and sinter the silver particles at the time of firing after coating on the substrate. If the firing temperature is low, the organic stabilizer is difficult to remove. If the degree of sintering of the silver particles is not sufficient, a low resistance value cannot be obtained. That is, the organic stabilizer present on the surface of the silver nanoparticles contributes to the stabilization of the silver nanoparticles, but prevents the silver nanoparticles from being sintered (particularly, sintering at low temperature firing). The more organic stabilizer present on the surface of the silver nanoparticles, the more hindered the sintering of the silver nanoparticles.

  Thus, the stabilization of silver nanoparticles and the expression of a low resistance value at low temperature firing are in a trade-off relationship.

  Then, the objective of this invention is providing the silver nanoparticle which is excellent in stability, and the electroconductivity (low resistance value) expressed by low-temperature baking of 200 degrees C or less, and its manufacturing method. Moreover, the objective of this invention is providing the silver coating composition containing the said silver nanoparticle.

  When the present inventors use a branched aliphatic amine compound as a stabilizer, it is possible to obtain silver nanoparticles that are excellent in stability and exhibit excellent conductivity (low resistance value) by low-temperature firing at 200 ° C. or lower. I found.

The present invention includes the following inventions.
(1) A method for producing silver-containing nanoparticles,
A silver compound and a branched aliphatic amine compound as a stabilizer are mixed to obtain a mixture,
A reducing agent is added to the mixture;
In a solvent-free reaction system, the silver compound is reacted with the reducing agent to form an aggregate of silver-containing nanoparticles.
Look at including it,
The branched aliphatic amine compound is a branched aliphatic primary amine compound having 3 to 16 carbon atoms,
The reducing agent is represented by the general formula (I):
RCO-NHNH ₂ (I)
(Here, R represents H or a saturated aliphatic hydrocarbon group having 1 to 4 carbon atoms)
The manufacturing method of the silver containing nanoparticle aggregate which is the acyl monohydrazide compound represented by these .

(2) The acyl mono hydrazide compounds, formic hydrazide HCO-NHNH _2, acethydrazide CH ₃ CO-NHNH _2, propanohydrazide _{CH 3 CH 2 CO-NHNH 2} , butanoate hydrazide CH ₃ (CH _{2) 2} CO- NHNH _2, 2-methyl propanohydrazide _{(CH 3) 2 CHCO-NHNH} 2, pentanoate hydrazide _{CH 3 (CH 2) 3 CO} -NHNH 2, 3- methylbutanoate hydrazide _{(CH 3) 2 CHCH 2 CO} -NHNH ₂ and 2,2-dimethylpropanohydrazide (CH ₃ ) _{3 The} method for producing a silver-containing nanoparticle aggregate according to (1) , selected from the group consisting of CHCO—NHNH ₂ .

(3) The method for producing a silver-containing nanoparticle aggregate according to (1) or (2) above, wherein 1 to 10 moles of the branched aliphatic amine compound is used per 1 mole of silver atoms of the silver compound.

(4) The silver-containing nanoparticle aggregate according to any one of (1) to (3) above, wherein 0.4 to 2 mol of the hydrazine compound is used per 1 mol of silver atoms of the silver compound. Production method.

(5) A silver-containing nanoparticle aggregate produced by the production method according to any one of (1) to (4 ) above.

(6) A silver coating composition in which silver-containing nanoparticle aggregates produced by the method according to any one of (1) to (4) are dispersed in an organic solvent.

(7) a base material;
On the base material, a silver coating composition in which silver-containing nanoparticle aggregates produced by the method according to any one of the above (1) to (4) are dispersed in an organic solvent is applied, A silver conductive material comprising a sintered silver conductive layer. Firing is performed at a temperature of 200 ° C. or lower.

(8) The silver conductive material according to (7) , wherein the silver conductive layer is patterned.

(9) A silver coating composition in which silver-containing nanoparticle aggregates produced by the method according to any one of (1) to (4) above are dispersed in an organic solvent is applied onto a substrate. And then baking to form a silver conductive layer. Firing is performed at a temperature of 200 ° C. or lower.

(10) The method for producing a silver conductive material according to (9) above, wherein the silver coating composition is applied in a pattern and then baked to form a patterned silver conductive layer.

  In the present invention, when a branched aliphatic amine compound is used as the organic stabilizer, less adhesion to the surface of the silver particle due to a steric factor of the branched aliphatic group than when a linear aliphatic amine compound is used. Larger areas of the silver particle surface can be covered by the amount. Therefore, moderate stabilization of the silver nanoparticles can be obtained with a smaller amount of adhesion on the surface of the silver particles. Since the amount of the organic stabilizer to be removed at the time of firing is small, the organic stabilizer can be removed efficiently even when firing at a low temperature of 200 ° C. or less, and the sintering of silver particles proceeds sufficiently.

  Thus, according to the present invention, there are provided silver nanoparticles that are excellent in stability and exhibit excellent conductivity (low resistance value) by low-temperature firing at 200 ° C. or less, and a method for producing the same. Moreover, according to this invention, the silver coating composition containing the said silver nanoparticle is provided.

4 is a graph showing a TG-DTA measurement result of silver nanoparticles obtained in Example 1. FIG. 2 is a SEM photograph of the dry silver nanoparticle powder obtained in Example 1. 3 is a SEM photograph of the surface of the fired silver film obtained in Example 1. 3 is a graph showing the viscosity measurement results of the silver paste obtained in Example 1. 6 is a graph showing a TG-DTA measurement result of silver nanoparticles obtained in Comparative Example 1. 3 is a SEM photograph of dry silver nanoparticle powder obtained in Comparative Example 1.

In the present invention, a silver compound and a branched aliphatic amine compound as a stabilizer are mixed to obtain a mixture,
A reducing agent is added to the mixture;
In a solvent-free reaction system, the silver compound is reacted with the reducing agent to form silver-containing nanoparticles.
Thus, silver-containing nanoparticles are produced.

  In the present specification, the term “nanoparticle” means that the size of the primary particles (average primary particle diameter) is less than 1000 nm. Further, the size of the particle is intended to be a size excluding the stabilizer existing (coated) on the surface (that is, the size of silver itself). In the present invention, the silver nanoparticles have an average primary particle diameter of, for example, 0.5 nm to 100 nm, preferably 0.5 nm to 50 nm, more preferably 0.5 nm to 25 nm, and still more preferably 0.5 nm to 10 nm. Yes.

  Silver compounds include silver oxide (I), silver oxide (II), silver acetate, silver nitrate, silver acetylacetonate, silver benzoate, silver bromate, silver bromide, silver carbonate, silver chloride, silver citrate, fluorine Silver iodide, silver iodate, silver iodide, silver lactate, silver nitrite, silver perchlorate, silver phosphate, silver sulfate, silver sulfide, silver trifluoroacetate, and the like can be used. Among these, only 1 type may be used and 2 or more types may be used together.

  Further, in order to obtain a composite with silver, other metal compounds other than silver may be used in combination. Examples of other metals include Al, Au, Pt, Pd, Cu, Co, Cr, In, and Ni. Metal salt compounds such as metal acetates, metal trifluoroacetates, metal halides, metal sulfates, metal nitrates, and metal hydrocarbyl sulfonates containing these desired metals can be used. The silver composite is composed of silver and one or more other metals, and examples thereof include Au—Ag, Ag—Cu, Au—Ag—Cu, and Au—Ag—Pd. Based on the total metal, silver accounts for at least 20% by weight, usually 50% by weight, for example 80% by weight.

  In the present invention, a branched aliphatic amine compound is used as the stabilizer. When a branched aliphatic amine compound is used as an organic stabilizer, silver particles can be deposited with a smaller amount of adhesion on the surface of the silver particle due to a steric factor of the branched aliphatic group than when a linear aliphatic amine compound is used. A larger area of the surface can be covered. Therefore, moderate stabilization of the silver nanoparticles can be obtained with a smaller amount of adhesion on the surface of the silver particles. Then, since the amount of the organic stabilizer to be removed at the time of firing is small, the organic stabilizer can be efficiently removed even when firing at a low temperature of 200 ° C. or lower, and the silver particles are sufficiently sintered.

  Examples of branched aliphatic amine compounds include carbon such as isopropylamine, isobutylamine, sec-butylamine, tert-butylamine, isopentylamine, tert-pentylamine, isohexylamine, 2-ethylhexylamine, and tert-octylamine. A primary amine having 3 to 16, preferably 3 to 8 carbon atoms can be used. Cyclohexylamine is also exemplified as a branched aliphatic amine analog.

  Also, secondary amines such as N, N-diisopropylamine, N, N-isobutylamine, N, N-isopentylamine, N, N-isohexylamine, N, N- (2-ethylhexyl) amine and the like can be mentioned. It is done. In addition, tertiary amines such as triisobutylamine, triisopentylamine, triisohexylamine, and tri (2-ethylhexyl) amine can be used.

  Among these, branched aliphatic monoamine compounds having 4 to 6 carbon atoms in the main chain such as isopentylamine, isohexylamine, and 2-ethylhexylamine are preferable. When the main chain has 4 to 6 carbon atoms, appropriate stabilization of the silver nanoparticles is easily obtained. From the viewpoint of the steric factor of the branched aliphatic group, it is effective that the second carbon atom is branched from the N atom side. As a branched aliphatic amine compound, only 1 type may be used and it may be used in combination of 2 or more type.

  The branched aliphatic amine compound may be used in a molar ratio (the branched aliphatic amine compound / silver atom) with respect to the silver atom of the silver compound to be reduced, for example, about 1 to 10 mol. , Preferably about 1.5 to 8 mol, more preferably about 2 to 6 mol. If the amount of the branched aliphatic amine compound is less than the molar ratio 1, the stabilizing effect on the silver particles produced tends to be weak. On the other hand, when the amount of the branched aliphatic amine compound is larger than the molar ratio 10, the coating on the surface of the silver nanoparticles is saturated.

In the present invention, in addition to the branched aliphatic amine compound, a linear aliphatic amine compound may be used in combination as a stabilizer. Examples of linear aliphatic amine compounds include butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine Saturated aliphatic monoamines such as amine, heptadecylamine, octadecylamine; primary amines such as unsaturated aliphatic monoamines such as oleylamine;
N, N-dipropylamine, N, N-dibutylamine, N, N-dipentylamine, N, N-dihexylamine, N, N-dipeptylamine, N, N-dioctylamine, N, N-dinonylamine, N, Secondary such as N-didecylamine, N, N-diundecylamine, N, N-didodecylamine, N-methyl-N-propylamine, N-ethyl-N-propylamine, N-propyl-N-butylamine Amines;
Tertiary amines such as tributylamine and trihexylamine can be mentioned.

  However, when a linear aliphatic amine compound is used, it should be used in an amount that does not impair the effects of the branched aliphatic amine compound. That is, if a large amount of linear aliphatic amine compound is used, a coating effect due to a steric factor cannot be expected, and as a result, the total amount of amine compound adhering to the silver particles increases. Therefore, the amount of the amine compound to be removed during firing increases, which hinders the sintering of silver particles. It is not necessary to use a linear aliphatic amine compound, and if used, the amount should be up to 10 mol%, preferably up to 5 mol%, based on the branched aliphatic amine compound.

  In the present invention, in addition to the branched aliphatic amine compound, an organic carboxylic acid compound may be used in combination as a stabilizer. By using an organic carboxylic acid compound, the stability of silver nanoparticles, particularly the stability in a paint state dispersed in an organic solvent, may be improved.

  As the organic carboxylic acid compound, a saturated or unsaturated aliphatic carboxylic acid is used. For example, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, Examples thereof include saturated aliphatic monocarboxylic acids having 4 or more carbon atoms such as icosanoic acid and eicosenoic acid; unsaturated aliphatic monocarboxylic acids having 8 or more carbon atoms such as oleic acid, elaidic acid, linoleic acid, and palmitoleic acid.

  The organic carboxylic acid compound is represented by a molar ratio (the organic carboxylic acid / silver atom) based on the silver atom of the silver compound to be reduced, depending on the amount of the branched aliphatic amine compound used. For example, about 0.05 to 10 moles may be used, preferably 0.1 to 5 moles, and more preferably 0.5 to 2 moles. When the amount of the organic carboxylic acid is less than the molar ratio 0.05, the effect of improving the stability in a dispersed state by the addition of the carboxylic acid is weak. On the other hand, when the amount of the organic carboxylic acid reaches the molar ratio 10, the effect of improving the stability in the dispersed state is saturated. However, the organic carboxylic acid compound may not be used.

  In the present invention, as the reducing agent, the above-described silver compound, and when used, an appropriate reducing agent that functions as a reducing agent for other metal compounds other than silver can be used. As the reducing agent, for example, boron compounds and hydrazine compounds can be used. Hydrazine compounds include hydrazine, hydrazine derivatives, hydrazine salts and hydrates, and hydrazine derivative salts and hydrates.

  A hydrazine derivative is a compound in which one or both nitrogen atoms of hydrazine are independently mono- or di-substituted with the same or different substituents. Hydrazine derivatives include hydrocarbyl hydrazines such as benzyl hydrazine and phenyl hydrazine; acyl hydrazides; carbazates or hydrazinocarboxylates; sulfonohydrazides and the like.

  In the present invention, an acyl monohydrazide compound that is solid at room temperature (15 ° C. to 25 ° C.) can be used as the reducing agent.

The acyl monohydrazide compound has the general formula (I):
RCO-NHNH ₂ (I)
It is represented by Here, R represents H or a hydrocarbon group. The hydrocarbon group includes an aliphatic hydrocarbon group and an aromatic hydrocarbon group. The acyl monohydrazide compound is synthesized by reacting a corresponding ester of a carboxylic acid with hydrazine hydrate (hydrazine hydrate) or by reacting a corresponding carboxylic acid chloride or carboxylic anhydride with hydrazine. .

  Examples of the aliphatic hydrocarbon group represented by R include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl groups. Examples of the aromatic hydrocarbon group represented by R include a phenyl group. In addition, these aliphatic hydrocarbon groups and aromatic hydrocarbon groups may have a substituent such as a halogen group such as chloro and bromo, and a nitro group. Among the acyl monohydrazide compounds, only one type may be used, or two or more types may be used in combination.

In the present invention, as a preferred reducing agent, the general formula (I):
RCO-NHNH ₂ (I)
The acyl monohydrazide compound represented by these is used. Here, R represents H or a C1-C4 saturated aliphatic hydrocarbon group.

  Said preferred acyl monohydrazide compounds are formic hydrazide, acetohydrazide, propanohydrazide, butanohydrazide, 2-methylpropanohydrazide, pentanohydrazide, 3-methylbutanohydrazide and 2,2-dimethylpropanohydrazide. Choose from the following group. Among the acyl monohydrazide compounds, only one type may be used, or two or more types may be used in combination.

The boiling points of the carboxylic acids corresponding to the preferred acyl monohydrazide compounds are shown below.
・ Formic acid hydrazide HCO-NHNH ₂
Formic acid HCOOH (bp. 100.8 ° C)
Acetohydrazide CH ₃ CO—NHNH ₂
Acetic acid CH ₃ COOH (bp. 118 ° C)
Propanohydrazide CH ₃ CH ₂ CO-NHNH ₂
Propionic acid CH ₃ CH ₂ COOH (bp. 141.1 ° C.)
- butanoate hydrazide _{CH 3 (CH 2) 2 CO} -NHNH 2
Butanoic acid (butyric _{acid) CH 3 (CH 2) 2} COOH (bp. 163.5 ℃)
- 2-methylpropanoate hydrazide _{(CH 3) 2 CHCO-NHNH} 2
Isobutyric acid (CH ₃ ) ₂ CHCOOH (bp. 152-155 ° C.)
・ Pentanohydrazide CH ₃ (CH ₂ ) ₃ CO—NHNH ₂
Pentanoic acid (valeric acid) CH ₃ (CH ₂ ) ₃ COOH (bp. 186-187 ° C.)
- 3-methylbutanoate hydrazide _{(CH 3) 2 CHCH 2 CO} -NHNH 2
Isovaleric acid (CH ₃ ) ₂ CHCH ₂ COOH (bp. 175-177 ° C.)
2,2-dimethyl propanohydrazide _{(CH 3) 3 CHCO-NHNH} 2
Pivalic acid (CH ₃ ) ₃ CHCOOH (bp. 163.8 ° C.)

When the preferable acyl monohydrazide compound (RCONHNH ₂ , R: carbon number of 1 to 4) is used as a reducing agent for the silver compound, the silver compound is reduced and silver nanoparticles are generated. Oxidized acyl monohydrazide compound (chemical species such as RCON = NH) is adsorbed on or near the surface of silver nanoparticles produced by reduction, and used organic stabilizer (branched aliphatic amine). At the same time, it is thought to function as a stabilizer or protective agent for silver nanoparticles. When the silver nanoparticles are fired, the oxidant of the acyl monohydrazide compound is thermally decomposed even at a low temperature of 200 ° C. or less (eg, 100 ° C. to 200 ° C.), and the carboxylic acid (RCOOH) corresponding to the acyl group This produces nitrogen molecules (N ₂ ). At this time, the preferable acyl monohydrazide compound (RCONHNH ₂ , R: carbon number of 1 to 4) is used so that the thermal decomposition of the oxidized form of the acyl monohydrazide compound easily occurs even at a low temperature of 200 ° C. or lower. Is effective. That is, the acyl monohydrazide compound in which the corresponding carboxylic acid has a boiling point of 200 ° C. or less is considered effective. From this, since the thermal decomposition of the oxidized form of the acyl monohydrazide compound easily occurs even when firing at a lower temperature (for example, 100 ° C. to 180 ° C., preferably 150 ° C. to 180 ° C.), the acyl monohydrazide As the compound, formic hydrazide, acetohydrazide, and propanohydrazide are more preferable.

  The corresponding carboxylic acid (RCOOH) liberated by thermal decomposition of the oxidant of the acyl monohydrazide compound destabilizes the presence state of the used organic stabilizer (branched aliphatic amine) on the surface of the silver nanoparticles. Promotes desorption of the organic stabilizer from the surface of the silver nanoparticles.

  For example, when acetohydrazide is used as the reducing agent, acetic acid (bp. 118 ° C.) is obtained by thermal decomposition of the oxidized acetohydrazide in the protective agent coating layer on the surface of the silver nanoparticles in a low temperature baking process of about 150 ° C. to 180 ° C. ) And nitrogen molecules are generated. The generated acetic acid is in a vapor state at the calcination temperature, destabilizes the presence of the organic stabilizer (branched aliphatic amine) forming the protective agent coating layer, and the organic stabilizer from the surface of the silver nanoparticles is destabilized. It is thought that detachment is promoted.

As a result, even in the case of firing at a low temperature of 200 ° C. or lower, it is considered that the protective agent coating layer is removed and the silver particles are sufficiently sintered. Thus, when the preferable acyl monohydrazide compound (RCONHNH ₂ ; R: C number of 1 to 4 ) is used as the reducing agent, the silver nanoparticles obtained in the present invention are excellent in stability and at 200 ° C. or lower. Excellent conductivity is exhibited by low-temperature firing.

  The acyl monohydrazide compound may be used in a molar ratio (said acyl monohydrazide / silver atom) with respect to the silver atom of the silver compound to be reduced. 0.5 to 1.5 mol, more preferably 0.55 to 1.1 mol may be used. If the amount of the acyl monohydrazide compound is less than the molar ratio of 0.4, silver ions cannot be sufficiently reduced, and the yield of silver nanoparticles tends to decrease. On the other hand, if the amount of the acyl monohydrazide compound is larger than the molar ratio 2, an excessively added reducing agent (acyl monohydrazide compound) is wasted, which is not economical, and may be an undesirable side reaction depending on the conditions of the reduction reaction. May occur and the physical properties of the target silver nanoparticles may be impaired.

  In the present invention, first, a silver compound and a branched aliphatic amine compound are mixed without using a solvent to obtain a mixture.

  As a stabilizer, when an organic carboxylic acid compound is used in combination with the organic amine compound, a silver compound and an organic amine compound are mixed, and then the organic carboxylic acid compound is added to the mixture.

  The mixing of the silver compound and the branched aliphatic amine compound is usually performed at room temperature (about 25 ° C.). By stirring after mixing, complex formation occurs, and a uniform solution state is obtained. When using an organic carboxylic acid compound, after mixing the silver compound and the amine compound, the organic carboxylic acid is heated at room temperature (about 25 ° C.) or by heating the mixture to about 25 ° C. to 60 ° C. It may be added.

  Next, a hydrazine compound is added as a reducing agent to the obtained mixture without using a solvent. Phenylhydrazine is liquid at room temperature, but the above-mentioned acyl monohydrazide compound having 1 to 5 carbon atoms (R 1 to 4 carbon atoms) is solid at room temperature. At this time, the acyl monohydrazide compound is added in a powder state. When added in the powder state, there is an advantage that the reduction reaction proceeds mildly and excessive aggregation of silver nanoparticles can be prevented as much as possible. The reason for this is presumed that when a reduction reaction is carried out in a solvent-free system by adding an acyl monohydrazide compound as a reducing agent in a powder state, the reduction reaction of the silver compound gradually proceeds as the powder dissolves. Is done.

  Further, when the acyl monohydrazide compound is added in a powder state and the reduction reaction is performed in a solventless system, there is an advantage that the capacity of the entire reaction system can be reduced as compared with the case of using an organic solvent. Therefore, a high silver nanoparticle yield per reaction volume is obtained.

  After the addition of the hydrazine compound, the silver compound is reacted with the hydrazine compound by stirring the mixture, and optionally stirring with heating at about 25 ° C. to 60 ° C. to form silver nanoparticles. Silver nanoparticles are obtained as an aggregate of particles.

  By this method, a silver nanoparticle composition is formed. Subsequently, sedimentation of silver nanoparticles, decantation / washing operation with an appropriate solvent (water or organic solvent) is performed, and then drying is performed to obtain a stable powder of aggregates of silver nanoparticles.

  For the decantation / cleaning operation, water or an organic solvent is used. As the organic solvent, for example, an alcohol solvent such as methanol, ethanol, propanol, butanol, or a mixed solvent thereof may be used.

  A silver coating composition can be prepared by dispersing the obtained silver nanoparticle powder in a suitable organic solvent (dispersion medium). Examples of the organic solvent for obtaining the silver coating composition include terpene solvents such as Terpionel C for obtaining a silver paste. The amount of the organic solvent may be appropriately determined according to the concentration and viscosity of the desired silver coating composition.

  The silver coating composition containing the silver nanoparticle aggregate obtained by the present invention is excellent in stability. For example, at a silver concentration of 60% by weight, it is stable without causing fusion at room temperature.

  The prepared silver coating composition is applied onto a substrate and then baked at a temperature of 200 ° C. or lower, for example, 100 ° C. to 180 ° C., preferably 150 ° C. to 180 ° C.

  Application is spin coating, inkjet printing, screen printing, dispenser printing, letterpress printing (flexographic printing), sublimation printing, offset printing, laser printer printing (toner printing), intaglio printing (gravure printing), contact printing, microcontact printing It can carry out by well-known methods, such as. When a printing technique is used, a coated layer of a patterned silver coating composition is obtained, and a patterned silver conductive layer is obtained by firing.

  Firing can be performed at a temperature of 200 ° C. or less, for example, 100 ° C. to 180 ° C., preferably 150 ° C. to 180 ° C. The firing time may be appropriately determined in consideration of the coating amount of the silver coating composition, for example, 10 minutes to 2 hours, preferably 15 minutes to 1.5 hours, more preferably 30 minutes to 1 hour. .

  The silver-containing nanoparticles obtained in the present invention have a branched aliphatic amine compound as a stabilizer on the surface thereof. Due to the steric factor, the amount of the branched aliphatic amine compound attached to the surface of the silver particles is small compared to the case where the linear aliphatic amine compound is used. That is, a larger surface area of silver particles is coated with a smaller amount of adhesion. For this reason, the amine compound can be efficiently removed even by such a low-temperature firing step, and the silver particles are sufficiently sintered.

When the above-mentioned preferable acyl monohydrazide compound (RCONHNH ₂ , R: carbon number 1 to 4) is used as the reducing agent for the silver compound, the silver particles are more likely to be sintered by such a low-temperature firing step. As a result, excellent conductivity (low resistance value) is exhibited. A silver conductive layer having a low resistance value (for example, 3 to 10 μΩcm) equivalent to that of bulk silver (bulk silver resistance value: 1.6 μΩcm) is formed.

  Since it can be fired at low temperatures, as a substrate, in addition to a glass substrate, a heat-resistant plastic substrate such as a polyimide film, a polyethylene terephthalate (PET) film, a polyethylene naphthalate (PEN) film, etc. A general-purpose plastic substrate can be suitably used.

  The silver conductive material of the present invention includes an electromagnetic wave control material, a circuit board, an antenna, a heat sink, a liquid crystal display, an organic EL display, a field emission display (FED), an IC card, an IC tag, a solar cell, an LED element, an organic transistor, and a capacitor. (Capacitor), electronic paper, flexible battery, flexible sensor, membrane switch, touch panel, EMI shield, etc.

  The thickness of the silver conductive layer may be appropriately determined according to the intended use. For example, it may be selected from the range of 5 nm to 30 μm, preferably 500 nm to 25 μm, more preferably 1 μm to 20 μm.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. First, each measurement method will be described.

[Content of organic substance and silver in silver nanoparticles]
The obtained silver nanoparticle powder sample was heat-treated from 35 ° C. to 550 ° C. at a rate of temperature increase of 5 ° C./min in an air stream of 50 ml / min. The weight reduction at this time corresponds to the weight of the organic matter.
Weight of silver nanoparticle powder before heat treatment: W ₀ (g)
Weight of silver nanoparticle powder after heat treatment: W ₁ (g)
Then,
Organic content a (wt%) = [(W ₀ −W ₁ ) / W ₀ ] × 100
Silver content b (wt%) = [W ₁ / W ₀ ] × 100
Is calculated as

[Yield in terms of silver in silver nanoparticle synthesis]
From the weight of dry silver nanoparticles obtained in the synthesis of silver nanoparticles: Wy (g), the weight of silver in the starting silver acetate: Ws (g), and the organic content a and the silver content b described above, It is calculated as follows.
Silver conversion yield (%) = {[Wy × b / (a + b)] / Ws} × 100

[TG-DTA (differential thermogravimetric simultaneous analysis)]
The obtained silver nanoparticle powder sample was heated from 35 ° C. to 550 ° C. at a temperature rising rate of 5 ° C./min under an air stream of 50 ml / min using TG / DTA6300 manufactured by SII. Was measured, and the amount of weight loss with respect to the sample at the elevated temperature was determined in%.

[Observation of dry silver nanoparticle powder by scanning electron microscope]
The dried silver nanoparticle powder was observed by a conventional method using a scanning electron microscope (JSM-6700F manufactured by JEOL Ltd.).

[Observation of the cross section of the fired silver film with a scanning electron microscope]
The obtained silver fired film was cut, and the cross section was observed by a conventional method using a scanning electron microscope (JSM-6700F manufactured by JEOL Ltd.).

[Specific resistance value of the fired silver film]
The obtained silver fired film was measured using a four-terminal method (Loresta GP MCP-T610). The measuring range limit of this device is 10 ⁷ Ωcm.

[Viscosity of silver paste]
Measurement was performed using a rotary rheometer MCR301 (manufactured by Anton Paar).

[Example 1]
(Synthesis of silver nanoparticles)
2-ethylhexylamine (23.2 g, 180 mmol) was added to silver acetate (5.0 g, 30 mmol), and the mixture was stirred at 25 ° C. to form a complex mixed solution. To this mixed solution, 1.1 g (15 mmol) of acetohydrazide was added as a powder and reacted with stirring at 25 ° C. for 2 hours. As a result, the reaction solution gradually turned brown and silver nanoparticle aggregates precipitated. did. In this way, a reaction mixture (A) containing silver nanoparticle aggregates was obtained.

  Subsequently, 200 ml of methanol was added to the obtained reaction mixture (A), and excess 2-ethylhexylamine and acetohydrazide were removed by decantation. Thereafter, 200 ml of methanol was added again and decantation was performed. This washing operation of the silver nanoparticles was further repeated once to obtain purified silver nanoparticles from which the reaction solution had been removed and wetted with methanol. Thereafter, the obtained wet purified silver nanoparticles were allowed to stand at 25 ° C. under vacuum for 8 hours to remove volatile components such as methanol, thereby obtaining 3.1 g of dry silver nanoparticle powder.

  When the obtained dry silver nanoparticle powder was subjected to TG-DTA analysis and the organic matter content in the silver nanoparticles was measured, the organic matter content was 2.0%, and the silver equivalent yield was 94%. A measurement chart of TG-DTA is shown in FIG.

  When the obtained dry silver nanoparticle powder was observed with a scanning electron microscope, it was confirmed to be an aggregate of particles having a primary particle diameter of 10 nm to 60 nm. The particle size of the aggregate is observed to be about 400 nm to 1000 nm. A scanning electron microscope (SEM) photograph is shown in FIG.

  Separately, when the reaction mixture (A) was filtered through a 0.2 μm filter, particles that did not pass through the 0.2 μm filter remained on the filter. That is, it was confirmed that silver particles aggregated during the reaction to form silver nanoparticle aggregates.

(Preparation and firing of silver nanopaste)
The dried silver nanoparticle powder obtained above was kneaded with terpineol C (manufactured by Nippon Terpene Chemical Co., Ltd.) so as to have a silver concentration of 60 wt% to prepare a silver nanopaste (B). This paste was applied onto a glass plate by a bar coating method to obtain a coating film.

  The coating film was fired at 150 ° C. for 15 minutes, 30 minutes, and 60 minutes, and at 180 ° C. for 15 minutes and 30 minutes, respectively, to form a 10 μm thick silver fired film. When the specific resistance values of these silver fired films were measured by a four-terminal method, they were 20.2 μΩcm (150 ° C., 15 minutes), 8.5 μΩcm (150 ° C., 30 minutes), 5.5 μΩcm (150 ° C., 60 minutes), respectively. Minutes), 7.8 μΩcm (180 ° C., 15 minutes), and 5.7 μΩcm (180 ° C., 30 minutes).

  When the surface of the silver fired film produced under the firing conditions at 180 ° C. for 15 minutes was observed with a scanning electron microscope, sufficient sintering of the silver nanoparticles was confirmed even when firing at a relatively low temperature for a short time. FIG. 3 shows a scanning electron micrograph of the surface of the silver fired film.

  In addition, when the viscosity of the silver nanopaste (B) was measured separately, it showed the physical property that shear viscosity (Pa * s) falls, so that shear rate (1 / s) becomes large. From this, it confirmed that this silver nano paste (B) was a paste suitable for screen printing. A viscosity measurement chart is shown in FIG.

  In Example 1, silver nanoparticles were directly obtained as aggregates in the reduction reaction system. However, this silver nanoparticle aggregate was stable at the stage of the silver nanopaste (B) and the subsequent coating stage. Therefore, this silver nanoparticle aggregate is suitable for applications used as relatively large secondary particles (aggregates), for example, screen printing applications. When silver nanoparticles are obtained as primary particles, a step for making silver primary particles into secondary particles (aggregates) is required to prepare a screen printing paste. According to this method, since the silver nanoparticle aggregate is directly obtained, a step for obtaining secondary particles (aggregate) for preparing a screen printing paste is omitted.

[Comparative Example 1]
(Synthesis of silver nanoparticles)
2.2 g of dry silver nanoparticle powder was obtained in the same manner as in Example 1 except that 23.2 g (180 mmol) of octylamine was used in place of 2-ethylhexylamine of Example 1.

  When the obtained dry silver nanoparticle powder was subjected to TG-DTA analysis and the organic matter content in the silver nanoparticles was measured, the organic matter content was 4.9% and the silver equivalent yield was 65%. A measurement chart of TG-DTA is shown in FIG.

  When the obtained dry silver nanoparticle powder was observed with a scanning electron microscope, it was confirmed to be an aggregate of particles having a primary particle diameter of 10 nm to 60 nm. A scanning electron microscope (SEM) photograph is shown in FIG.

(Preparation and firing of silver nanopaste)
The dried silver nanoparticle powder obtained above was kneaded with terpineol C (manufactured by Nippon Terpene Chemical Co., Ltd.) so as to have a silver concentration of 60 wt% to prepare a silver nanopaste. This paste was applied onto a glass plate by a bar coating method to obtain a coating film.

  The coating film was fired at 150 ° C. for 15 minutes, 30 minutes, and 60 minutes, respectively, to form a 10 μm thick silver fired film. When the specific resistance values of these fired silver films were measured by the four-terminal method, they were 56.7 μΩcm (150 ° C., 15 minutes), 45.8 μΩcm (150 ° C., 30 minutes), 24.3 μΩcm (150 ° C., 60 minutes), respectively. Minutes). The specific resistance value was inferior as compared with Example 1 using 2-ethylhexylamine having the same carbon number (C8).

Table 1 [Results of specific resistance values]
Specific resistance (μΩcm)
Firing conditions Temperature 150 ° C 150 ° C 150 ° C 180 ° C 180 ° C
Time 15 minutes 30 minutes 60 minutes 15 minutes 30 minutes
[Example 1]
2-Ethylhexylamine 20.2 8.5 5.5 7.8 5.7
[Comparative Example 1]
Octylamine 56.7 45.8 24.3 − −

[Comparative Example 2: Synthesis of silver nanoparticles]
55.6 g (300 mmol) of dodecylamine was added to 5.0 g (30 mmol) of silver acetate, and the mixture was stirred at 55 ° C. to form a complex mixed solution. When 1.78 g (16.5 mol) of phenylhydrazine was added to this mixed solution and reacted with stirring at 55 ° C. for 2 hours, the reaction solution gradually changed color, indicating the formation of silver nanoparticles. In this way, a reaction mixture (C) was obtained.

  When the reaction mixture (C) was filtered through a 0.2 μm filter, few particles remained on the filter. That is, during the reaction, the silver nanoparticles did not aggregate to a size that did not pass through the 0.2 μm filter.

Claims (6)

A method for producing silver-containing nanoparticles comprising:
A silver compound and a branched aliphatic amine compound as a stabilizer are mixed to obtain a mixture,
A reducing agent is added to the mixture;
In a solvent-free reaction system, the silver compound is reacted with the reducing agent to form an aggregate of silver-containing nanoparticles.
Including
The branched aliphatic amine compound is a branched aliphatic primary amine compound having 3 to 16 carbon atoms,
The reducing agent is represented by the general formula (I):
RCO-NHNH ₂ (I)
(Here, R represents H or a saturated aliphatic hydrocarbon group having 1 to 4 carbon atoms)
The manufacturing method of the silver containing nanoparticle aggregate which is the acyl monohydrazide compound represented by these. The acyl mono hydrazide compounds, formic hydrazide HCO-NHNH _2, acethydrazide CH ₃ CO-NHNH _2, propanohydrazide _{CH 3 CH 2 CO-NHNH 2} , butanoate hydrazide _{CH 3 (CH 2) 2 CO} -NHNH 2, 2-methylpropanoate hydrazide _{(CH 3) 2 CHCO-NHNH} 2, pentanoate hydrazide _{CH 3 (CH 2) 3 CO} -NHNH 2, 3- methylbutanoate hydrazide _{(CH 3) 2 CHCH 2 CO} -NHNH 2 and, The method for producing a silver-containing nanoparticle aggregate according to claim 1, which is selected from the group consisting of 2,2-dimethylpropanohydrazide (CH ₃ ) ₃ CHCO—NHNH ₂ .   The manufacturing method of the silver containing nanoparticle aggregate of Claim 1 or 2 using 1-10 mol of said branched aliphatic amine compounds with respect to 1 mol of silver atoms of the said silver compound.   The manufacturing method of the silver containing nanoparticle aggregate in any one of Claims 1-3 which uses 0.4-2 mol of said reducing agents with respect to 1 mol of silver atoms of the said silver compound. To produce a rigging containing nanoparticle aggregates by the method according to any one of claims 1 to 4,
A method for producing a silver coating composition , comprising dispersing the silver-containing nanoparticle aggregate in an organic solvent. A silver-containing nanoparticle aggregate is produced by the method according to any one of claims 1 to 4,
Dispersing the silver-containing nanoparticle aggregate in an organic solvent to produce a silver coating composition,
On a substrate, the silver coating composition was coated, to form a silver conductive layer by firing,
Method for producing a silver conductive material comprising.