JPWO2018190397A1 - Method for producing silver nanoparticles having a broad particle size distribution and silver nanoparticles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining silver nanoparticles having good physical properties by a method in which an emission amount of an amine having a strong irritating odor is suppressed. SOLUTION: A thermally decomposable silver compound (a) is reacted with an amine compound (b) capable of forming a complex with (a) in an organic solvent to form a complex, and the obtained complex is heated. A method for producing silver nanoparticles, which comprises thermally decomposing silver nanoparticles by thermal decomposition, wherein 5 to 20 parts by weight of water is present per 100 parts by weight of the silver compound (a) at the time of complex formation, and A method for producing silver nanoparticles, which comprises reacting an amine compound and a silver atom in a silver compound in a molar ratio of 0.7 to 2.0. Regarding the viscosity behavior of a silver nanoparticle dispersion in which 70 to 95 wt% of silver nanoparticles are contained in an organic solvent, the viscosity (v1) at the time of increasing the shear rate and the shearing rate are in the shear rate range of 2 to 30 s-1. The viscosity ratio (v1 / v2) of the viscosity (v2) at the time of velocity decrease is 2.0 or less, the average particle diameter is 70 to 350 nm, the variation coefficient is 40% to 80%, and the amine compound is bound to the particle surface. Silver nanoparticles. [Selection diagram] None

Description

  The present invention relates to a method for producing silver nanoparticles, which has a large particle size, a wide particle size distribution, and is easily adjusted to a viscous behavior suitable for screen printing, and a silver nanoparticle.

  Since silver nanoparticles sinter even at low temperatures due to the melting point of metal nanoparticles, they are used as electrical wiring on a substrate and as a bonding material for power device semiconductors. However, since the silver nanoparticles are fine, they are easily aggregated, and are easily fused due to a decrease in the melting point. Therefore, an organic layer called a protective agent is present on the surface of the silver nanoparticles. For these organic layers, fatty acids and alkylamines are often used, but silver nanoparticles coated with an alkylamine or an alkyldiamine, in particular, have a protective agent detached at a relatively low temperature and can be fired at a low temperature. (Patent Documents 1 and 2).

  The fired coating film using silver nanoparticles that can be fired at a low temperature is expected to be used as a conductive material for wiring and the like, but in order to ensure the reliability and conductivity of the conductive material for wiring and the like, wiring is required. Is adopted as a thick film. Patent Literature 3 discloses a silver nanoparticle having a primary particle diameter of about several nm to several tens of nanometers as a silver nanoparticle designed for the purpose of increasing the film thickness. A silver paint composition (ink) capable of obtaining a silver coating has been reported. Further, in Patent Document 4, the resistance can be reduced when a sintered body is formed by containing 30% or more of silver particles having a particle size of 100 to 200 nm based on the number of particles. It is described that such silver particles can be obtained by including them in a 100 parts by weight reaction system.

  In these known documents, silver nanoparticles are prepared using a complex formation reaction between a silver compound and an amine compound. Specifically, a complex is formed using silver oxalate and an alkylamine or an alkyldiamine without using any solvent. However, when a complex is formed in the absence of a solvent, it becomes a solid substance having no fluidity, is difficult to stir, lacks uniformity of the system, and is accompanied by a local exothermic reaction, so there is a problem in quality and safety, Difficult to commercialize industrially. Therefore, by conducting a complex formation reaction in an alcohol solvent, the complex reaction is promoted and assisted, the stirring property in the system is increased, the carbon dioxide gas generated rapidly by thermal decomposition is suppressed, and the quality and safety aspects are improved. Are reported (Patent Documents 5 to 7).

  In addition, in the process of thermally decomposing the silver oxalate-alkylamine complex, when a by-product gas (mainly carbon dioxide gas) is generated and discharged, an easily-evaporated alkylamine is also contained and discharged out of the system. In order to avoid such a problem, a production method has been reported in which the complex is continuously introduced into a reaction vessel to control the amount of by-product gas generated during a thermal decomposition reaction (Patent Document 8).

Japanese Patent No. 5574761 JP 2012-162767 A Japanese Patent No. 6001861 Japanese Patent No. 5795096 Japanese Patent No. 5975440 Japanese Patent No. 6026565 JP-A-2006-132825 JP-A-2015-40319

  However, in Patent Document 3, only a coating film having a thickness of less than 8 μm is formed in the examples. Even if a conductive coating film having a thickness of 10 μm or more is formed, since the silver particles are mainly composed of particles having a primary particle diameter of several tens of nm, the amount of the organic protective agent is large, and the volume shrinkage due to the detachment of the protective agent occurs. Low, the possibility of disconnection due to cracks is high.

Even if the amount of by-product gas is controlled as in Patent Literatures 5 to 8, there is no difference in finally discharging carbon dioxide containing alkylamine to the outside of the system.
Furthermore, silver nanoparticle dispersions and coating compositions (inks) are used by being applied to a substrate, and conditions for silver nanoparticles having a viscosity behavior suitable for application to the substrate have been thoroughly studied. I didn't. For this reason, the coating film actually obtained may not have sufficient performance in some cases.
In particular, in screen printing, precise viscosity characteristics are required in order to pass through a screen, but it has been found that using the particles described in Patent Document 4 is not sufficient.

  The present invention solves the above problems, and can be applied to a method for producing silver nanoparticles in consideration of scale-up such as workability, safety, environmental aspects, and various printing methods, particularly screen printing, and a thick film conductive material. It is an object of the present invention to provide silver nanoparticles having a wide particle size distribution range capable of forming a film, and a silver nanoparticle coating composition.

  In order to solve these problems, the present inventors have made intensive studies. As a result, a silver compound and an amine compound are complexed in an organic solvent, and a certain amount of water is present at the time of complex formation. It has been found that the resulting sintered coating film also has excellent performance, and has reached the present invention. Further, by bonding an amine compound having a specific molecular length to the surface of the silver particles, silver particles having a good balance between dispersibility and low-temperature sinterability can be produced, and the silver particles are dispersed in an organic solvent. It was found that the obtained dispersion has a viscosity characteristic particularly suitable for screen printing, and a silver coating composition in which the generation of aggregates can be suppressed can be obtained.

That is, the present invention includes the following inventions.
(1) A silver compound (a) having thermal decomposability is reacted with an amine compound (b) capable of forming a complex with (a) in an organic solvent (c) to form a complex. A method for producing silver nanoparticles which forms silver nanoparticles by heating and thermally decomposing, wherein 5 to 20 parts by weight of water is present relative to 100 parts by weight of silver compound (a) during complex formation. A method for producing silver nanoparticles, wherein the molar ratio of silver atoms in the amine compound (b) and the silver compound (a) is 0.7 or more;
(2) The method for producing silver nanoparticles according to the above (1), wherein (b) is 2-amino-2-methyl-1-propanol.
(3) The method for producing silver nanoparticles according to the above (1) or (2), wherein (a) is silver oxalate,
(4) The method for producing silver nanoparticles according to the above (3), wherein the weight ratio of (c) / (a) is 0.8 to 1.3,
(5) A silver nanoparticle dispersion, comprising: preparing silver nanoparticles by the method according to any one of the above (1) to (4); and dispersing the obtained silver nanoparticles in an organic solvent. Production method,
(6) Silver nanoparticles are produced by the method according to any one of the above (1) to (4), the obtained silver nanoparticles are dispersed in an organic solvent, and an organic binder is further added. , A method for producing a silver paint composition,

(7) The silver nanoparticle dispersion obtained by the method described in the above (5) or the silver coating composition obtained by the method described in the above (6) is applied on a substrate and fired to form a silver conductive layer. A method for producing a silver conductive material, comprising:
(8) The viscosity ratio of the viscosity (v1) at the time of increasing the shear rate and the viscosity (v2) at the time of decreasing the shear rate in the range of the shear rate of 2 to 30 s ^-1 when 78.5% by weight is contained in Texanol. (V1 / v2) is 2.0 or less, the average particle diameter is 70 to 350 nm, the coefficient of variation is 40% to 80%, and silver nanoparticles having an amine compound bonded to the particle surface;
(9) The silver particle according to (8), wherein the length of the molecule of the amine compound bonded to the particle surface is 7 to 8 °;
(10) A silver nanoparticle dispersion, wherein the silver particles according to (8) or (9) are dispersed in an organic solvent.
(11) The silver nanoparticles according to (8) or (9) are contained in an amount of 70 to 95% by weight, and the viscosity (v1) when the shear rate is increased and the viscosity (v1) when the shear rate is decreased in the range of the shear rate of 2 to 30 s ⁻¹ . A silver nanoparticle dispersion, wherein the viscosity ratio (v1 / v2) of the viscosity (v2) is 2.0 or less;
(12) A silver coating composition, wherein the silver nanoparticles according to (8) or (9) are dispersed in an organic solvent, and further containing an organic binder.
(13) A method for producing a silver conductive material, comprising a step of applying the silver nanoparticle dispersion according to the above (10) or (11) on a substrate and baking to form a silver conductive layer;
(14) A method for producing a silver conductive material, comprising a step of applying the silver coating composition according to (12) above on a substrate and firing the composition to form a silver conductive layer.

  According to the present invention, silver particles having a large particle size and a controlled particle size with a wide distribution can be easily obtained. The silver coating composition containing such silver particles can be sintered even in a low temperature range of 150 ° C. or lower, and the resulting sintered body exhibits a low resistance value close to that of bulk silver. The present invention relates to a material capable of forming a silver film having a thickness of several to several tens of micrometers on a relatively heat-resistant plastic substrate such as PET or polypropylene by a printing method represented by screen printing, or a conductive bonding method. It can be expected to be used as a bonding material for electrical equipment handling large currents such as materials and power devices.

  Further, in the synthesis of silver particles in the present invention, even if the amount of the amine compound used is smaller than that of the conventional synthesis method, silver particles having a large particle size and a wide distribution can be obtained, and an alkyl having a high burden on the human body and the environment can be obtained. Since the use of amines can be further reduced, a highly safe production method is provided in scaled-up industrial production.

FIG. 1 is a view showing an SEM photograph of the particles obtained in Example 1. FIG. 2 is a view showing an SEM photograph of the particles obtained in Examples 2 and 3. FIG. 3 is a diagram showing an SEM photograph of the particles obtained in Example 4. FIG. 4 is a diagram showing an SEM photograph of the particles obtained in Example 5. FIG. 5 is a diagram showing an SEM photograph of the particles obtained in Example 6. FIG. 6 is a view showing an SEM photograph of the particles obtained in Example 7. FIG. 7 is a diagram showing SEM photographs of the particles obtained in Examples 8 and 9. FIG. 8 is a diagram showing an SEM photograph of the particles obtained in Comparative Example 1. FIG. 9 is a view showing a STEM photograph of the particles obtained in Comparative Example 2. FIG. 10 is a diagram showing an SEM photograph of the particles obtained in Comparative Example 3. FIG. 11 is a diagram showing an SEM photograph of the particles obtained in Comparative Example 4.

FIG. 12 is a diagram showing an SEM photograph of the particles obtained in Comparative Example 5. FIG. 13 is a STEM photograph of the particles obtained in Comparative Example 6. FIG. 14 is a STEM photograph of the particles obtained in Comparative Example 7. FIG. 15 is a diagram illustrating a particle size distribution histogram of the particles obtained in Example 1. FIG. 16 is a diagram showing a particle size distribution histogram of the particles obtained in Examples 2 and 3. FIG. 17 is a diagram showing a particle size distribution histogram of the particles obtained in Example 4. FIG. 18 is a diagram showing a particle size distribution histogram of the particles obtained in Example 5. FIG. 19 is a diagram showing a particle size distribution histogram of the particles obtained in Example 6. FIG. 20 is a diagram illustrating a particle size distribution histogram of the particles obtained in Example 7. FIG. 21 is a diagram showing a particle size distribution histogram of the particles obtained in Example 8 and Example 9. FIG. 22 is a diagram showing a particle size distribution histogram of the particles obtained in Comparative Example 1. FIG. 23 is a diagram illustrating a particle size distribution histogram of the particles obtained in Comparative Example 2. FIG. 24 is a diagram showing a particle size distribution histogram of the particles obtained in Comparative Example 6. FIG. 25 is a diagram showing a particle size distribution histogram of the particles obtained in Comparative Example 7. FIG. 26 is a diagram showing an SEM photograph of a coating film surface of a paste produced from the particles obtained in Example 8. FIG. 27 is a diagram showing an SEM photograph of the surface of a coating film of a paste produced from the particles obtained in Example 9. FIG. 28 is a diagram showing an SEM photograph of a coating film surface of a paste produced from the particles obtained in Comparative Example 1. FIG. 29 is a diagram showing viscosity comparison data of pastes prepared from the particles obtained in Examples 8 and 9. FIG. 30 is a diagram showing viscosity data of a paste produced from the particles obtained in Comparative Example 1.

The present invention provides a method for producing silver nanoparticles by reacting an amine compound (b) that forms a complex with a thermally decomposable silver compound (a), wherein the complex is formed in an organic solvent, and It is characterized by the presence of a certain amount of water. Thereby, when manufacturing silver nanoparticles having a wide distribution, it is easy to synthesize silver nanoparticles in a large particle size region of 200 to 500 nm, and by using together with a polar solvent, the usage amount of the entire amine compound can be reduced. Can be reduced.
In addition, by binding a specific protective agent to silver particles having a specific particle size and particle size distribution on the surface of the silver particles, it is possible to suppress agglomerates and to produce a silver paint composition having a viscosity behavior particularly suitable for screen printing. To be able to
The details will be described below.

<Explanation of Materials for Silver Nanoparticle Synthesis>
[1. Silver compound (a)]
In the method for producing silver particles of the present invention, first, a silver compound having thermal decomposability is used as a starting material. The thermally decomposable silver compound is a silver compound that is complexed with the component (b) described below and thermally decomposes under heating conditions that can be achieved with ordinary equipment. Specifically, silver oxalate, silver nitrate, silver acetate, silver carbonate, silver oxide, silver nitrite, silver benzoate, silver cyanate, silver citrate, silver lactate, and the like can be used. Among these silver compounds, particularly preferred is silver carbonate or silver oxalate (Ag ₂ C ₂ O ₄ ). More preferably, it is silver oxalate. Silver oxalate can be decomposed at relatively low temperatures without the need for a reducing agent to produce silver particles. In addition, since carbon dioxide generated by decomposition is released as a gas, impurities do not remain in the solution.

[2. Amine compound (b) that forms a complex]
Next, in the present invention, an amine compound capable of forming a complex with a silver compound is used as the component (b). This compound has a function of forming a complex with the silver compound to lower the thermal decomposition temperature of the silver compound and to form silver particles at a low temperature. At the same time, the organic compound of the amine compound has a function of a protective agent that has the effect of dispersion stability of silver particles.
Such an amine compound is not particularly limited as long as it is an amine compound capable of forming a complex with the silver compound. In particular, the number of hydrogen atoms bonded to the amino group of the amine compound is preferably one or two, that is, a primary amine (RNH ₂ ) or a secondary amine (R ₂ NH).

  The formation of silver particles from a silver compound and an amine compound capable of forming a complex with the silver compound is known per se as described as the background art. In the present invention, an aliphatic hydrocarbon amine compound such as an “aliphatic hydrocarbon monoamine” or an “aliphatic hydrocarbon diamine” which has been used in the related art as the amine compound may be used. Specific examples of “aliphatic hydrocarbon monoamine” and “aliphatic hydrocarbon diamine” include alkylamine, alkoxyamine, and alkyletheramine. Among them, examples of the alkylamine include n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, and 2-ethylhexylamine.

However, among these amine compounds, alkylamines have a strong irritating odor, and there is a risk of being emitted at a high temperature together with carbon dioxide gas during the decomposition reaction. Therefore, when it is desired to suppress the irritating odor, an amine compound containing an oxygen atom should be used. Is preferred. Specific examples include alkoxyamines, alkyl ether amines, and amino alcohols.
According to the study by the present inventors, these amine compounds containing oxygen atoms not only have a suppressed irritating odor, but among them, the specific amino alcohols described in particular below have excellent physical properties of the obtained silver particles. found.

(2-1. Amino alcohol (b1))
Amino alcohol having 3 to 4 carbon atoms is particularly preferable as an amine compound containing an oxygen atom, because the effect of increasing the particle size and broadening the particle size distribution can be further enhanced. More preferably, (i) a branched primary amino alcohol having 3 to 4 carbon atoms, (ii) having one amino group and one hydroxyl group, and (iii) via an alkyl chain having 2 carbon atoms , An amino group and a hydroxyl group are bonded, or iv) a linear secondary amino alcohol having 3 carbon atoms. By using such a specific amino alcohol, it is possible to easily obtain particularly large silver particles having a wide particle size distribution.
Here, (i) “branched” means that the skeleton composed of carbon atoms and hetero atoms is not linear but is branched. Further, (ii) those having one or more amino groups and one or more hydroxyl groups are preferred, and one each is particularly preferred. (iii) “An amino group and a hydroxyl group are bonded via an alkyl chain having 2 carbon atoms” means that two adjacent carbon atoms in a skeleton composed of a carbon atom and a hetero atom are each an amino group And a hydroxyl group.
Further, by using an amino alcohol satisfying such (i) to (iii) or iv), complex formation with a silver compound can be promoted, and particles having a large particle size and a wide distribution can be obtained. it can.

  Examples of the amino alcohol having 4 or less carbon atoms satisfying the above conditions include 1-amino-2-butanol, DL-1-amino-2-propanol, and 2-amino-amino alcohol satisfying (i) to (iii). 2-methyl-1-propanol (hereinafter, AMP) and DL-2-amino-1-propanol are exemplified. Moreover, N-methylethanolamine is mentioned as an amino alcohol satisfying (iv).

Among these, AMP, 1-amino-2-butanol, DL-1-amino-2-propanol, and DL-2-amino-1-propanol are particularly easy to handle, and are complex in the presence of a polar solvent such as an alcohol solvent. It is most preferable because formation easily occurs and silver particles having a large particle size and a wide particle size distribution can be easily obtained. Among them, AMP is particularly excellent in the highest effect. Further, by bonding to the silver surface, the effect of increasing the viscosity of the dispersion is excellent.
The above component (b) may be used alone or in combination of two or more.

(2-2. Amine compound (b2) having a molecular length of 5 ° or more)
In the present invention, in order to prevent fusion and aggregation of particles and to obtain a stable dispersion, it is preferable to contain the following amine compounds. That is, an amine compound capable of forming a complex with a silver compound, having a molecular length of 5 ° or more, and atoms constituting the amine compound being N, C and H, or N, C, H and O.

Here, the length of a molecule is a distance between two longest atoms not including a hydrogen atom. The length of this molecule can be determined by calculation. The calculation conditions are density functional theory, function ωB97X-D, basis function 6-31 + G *, environment vacuum energy state ground state, and can be calculated by various molecular calculation software such as SPARTAN`16V1,1,0. When the length of the molecule is 5 ° or more, more preferably 7 ° or more, the function as a protective agent for imparting dispersion stability due to the steric hindrance effect is particularly excellent. Among them, those having a molecular length of 5 to 8 ° are preferable, and those having a molecular length of 7 to 8 ° are more preferable.
Among these amine compounds, an amine compound having a main chain (main skeleton) composed of at least 7 atoms including an amino group is particularly preferable. When the chain is branched, the longest chain is used as the main chain. The number of hydrocarbon groups bonded to the amino group of the amine compound is not limited, but one or two primary amines or secondary amines are preferable because they are particularly easily coordinated with silver.

  Specific examples of such an amine compound having a molecular length of 5 ° or more include, as alkylamines, n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, Ethylhexylamine and the like. Examples of the alkoxyamine include 3-methoxypropylamine and 3-ethoxypropylamine. Examples of the alkyl ether amine include JEFFAMINE M series manufactured by HUNTSMAN, M-600, M-1000, M-2005, and M-2070. Examples of the amino alcohol include 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, and the like. Examples of aminoethoxy include diglycolamine.

More preferred specific examples are those having 7 atoms or more and a molecule length of 7 ° or more, wherein the alkylamine is n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, 2-ethylhexylamine and the like. Examples of the alkoxyamine include 3-methoxypropylamine and 3-ethoxypropylamine. Examples of the amino alcohol include 5-amino-1-pentanol and 6-amino-1-hexanol. Aminoethoxy includes diglycolamine. More preferred are n-hexylamine and 3-ethoxypropylamine.
The above component (b2) can be used alone or in combination of two or more.

(2-3. Ratio of (b1) and (b2))
(B1) when a specific amino alcohol (b1) having 4 or less carbon atoms and an amine compound (b2) having a molecular length of 5 ° or more are used among the amine compounds (component (b)) capable of forming a complex. The molar ratio represented by / [(b1) + (b2)] is preferably 0.3 to 0.8 (molar ratio), preferably 0.4 to 0.8.
This range is most suitable for producing large and highly distributed silver nanoparticles. When the molar ratio is less than 0.3, the amount of the amine compound having a long molecule is increased, the size of the particles is reduced, and the particle size distribution tends to be narrow. Particles are difficult to obtain. On the other hand, when the molar ratio is larger than 0.8, the steric hindrance effect as a protective agent is weakened, and the risk of fusion of silver particles during synthesis increases.

[3. Ratio / addition amount of amine compound (b) and silver compound (a)]
The molar ratio (amine compound / silver compound silver atom) of the silver compound of the silver compound and the amine compound (b) is 0.7 or more. The amount of the amine compound (b) + (d) is adjusted so that it is preferably 0.7 to 2.0, more preferably 0.8 to 1.5, and most preferably 0.8 to 1.3. . By doing so, the particle size varies, and it is easy to obtain silver particles having a target particle size range.

In the above-mentioned various conventional synthesis methods (Patent Documents 1 to 9), the amine compound / silver compound has a silver atom molar ratio of 2.0 or more. On the other hand, in the present invention, silver particles can be obtained with a smaller amount of amine, so that the amount of discharged amine can be reduced. Therefore, it is possible to reduce the risk of human body and environmental load due to amine release from the system. At the same time, according to such a conventional method, particles having a small particle size and a narrow distribution are easily synthesized, whereas in the present invention, silver particles having a large distribution and a large particle size can be obtained. Finally, a thick-film conductive sintered body having excellent low-temperature sinterability and low resistance can be obtained.
On the other hand, when the molar ratio is less than 0.7, flat particles are likely to be formed, easily aggregated, and the dispersion stability of the silver coating composition is lowered.
In addition, under conditions where flat particles are likely to be formed, hysteresis at the shear rate is likely to occur. It is considered that when the particles have a non-uniform shape, the adsorption of the dispersant on the particle surface becomes non-uniform, and the interaction between the particles due to the increase in the contact area between the particles is large. For this reason, particles having a viscosity ratio (v1 / v2) of 1.2 or less of the viscosity (v1) at the time of increasing the shear rate and the viscosity (v2) at the time of decreasing the shear rate in a range of a shear rate of 2 to 30 s ^{−1 which} will be described later. It becomes difficult to obtain.
In particular, the molar ratio of the ratio (b2) of the silver compound to the silver compound (b2) / (silver atom of the silver compound) is preferably 0.2 or more. Particularly preferably, it is 0.2 to 1.4, more preferably 0.4 to 0.9. If the ratio is less than 0.2, the fusion of silver particles tends to occur. It is presumed that the steric hindrance effect as the protective material of the b2 component is reduced. On the other hand, when the ratio exceeds 1.4, it becomes difficult to satisfy the above-mentioned molar ratio of b / silver compound and the preferable ratio of b1 / b2.

[4. Organic solvent (c)]
In the present invention, the complex formation reaction between the silver compound and the amine compound described above is performed in the presence of an organic solvent.
In the present invention, a solvent having a polar functional group is preferred.Specifically, alcohol-based solvents, ketone-based solvents, aldehyde-based solvents, amide-based solvents, S-based solvents, nitrile-based solvents, ether-based solvents, glycols Solvents, glycol ether solvents, glycol ester solvents, and glime solvents are preferred.
Particularly, an alcohol solvent or a glyme solvent is preferable, and among them, an alcohol having 3 to 12 carbon atoms is preferable. For example, n-propanol (bp: 97 ° C), isopropanol (bp: 82 ° C), n-butanol (bp: 117 ° C), isobutanol (bp: 107.89 ° C), sec-butanol (bp: 99. ° C). 5 ° C), tert-butanol (bp: 82.45 ° C), n-pentanol (bp: 136 ° C), n-hexanol (bp: 156 ° C), n-octanol (bp: 194 ° C), 2-octanol (Bp: 174 ° C), n-nonanol (bp: 215 ° C), 5-nonanol (bp: 195 ° C), n-decanol (bp: 232.9 ° C), n-undecanol (bp: 243 ° C), 2 -Undecanol (bp: 131 ° C), n-dodecanol (bp: 259 ° C), 2-dodecanol (bp: 250 ° C) and the like.
Examples of the glyme-based solvent include, for example, monoglyme (bp: 85 ° C), ethyl glyme (bp: 121 ° C), diglyme (bp: 162 ° C), dipropylene glycol dimethyl ether (bp: 171 ° C), ethyl diglyme ( bp: 188 ° C.), triglyme (bp: 216 ° C.), butyl diglyme (bp: 256 ° C.), tetraglyme (bp: 275 ° C.) and the like. Among them, those having a boiling point of 150 ° C. or more are easy to handle.
Among these, n-butanol, n-hexanol, n-decanol, diglyme are considered in consideration of the fact that the temperature of the later-described complex compound pyrolysis step can be increased and the convenience of post-treatment after the formation of silver nanoparticles is taken into consideration. Is preferred. These may be used alone or in combination of two or more.

(4-1. Addition amount of organic solvent)
Further, the organic solvent is used in an amount of 80 to 130 parts by weight (that is, the weight ratio of (c) / (a) is 0.8 to 100 parts by weight with respect to 100 parts by weight of the silver compound (a)) for sufficient stirring operation of each component. (Amount to be 1.3) is preferable. More preferably, the amount is 80 to 125 parts by weight based on 100 parts by weight of (a).

(4-2. Method of adding organic solvent)
In the present invention, the amine compound (b) and the silver compound (a) may take several forms to carry out the complex formation reaction between the silver compound and the amine compound in the presence of an organic solvent.
For example, a solid silver compound and an organic solvent, particularly an alcohol solvent, are mixed to obtain a silver compound-alcohol slurry, and then the amine compound (b) may be added to the obtained silver compound-alcohol slurry. . In the present invention, a slurry refers to a mixture in which a solid silver compound is dispersed in an organic solvent or a mixture of an organic solvent and an amine compound. In order to obtain a slurry, a solid silver compound is charged into a reaction vessel, and an organic solvent or a mixture of an organic solvent and an amine compound is added thereto to obtain a slurry.

Alternatively, a liquid mixture of an organic solvent and an amine compound may be charged into a reaction vessel, and a silver compound may be added thereto.
It has been reported that silver oxalate has explosive properties in a dry state. Therefore, when silver oxalate is used as the silver compound, it is preferable to use a wet one. The reason for this is that the explosive property is significantly reduced by making it in a wet state, and the handling property becomes easy. Therefore, water or the above-mentioned organic solvent may be mixed and used in a wet state.

[5. About aliphatic carboxylic acid)
In order to adjust the particle size and the particle size distribution, an aliphatic carboxylic acid may be used during complex formation. Addition of the aliphatic carboxylic acid tends to reduce the particle size and narrow the particle size distribution. It is desirable to adjust the water content appropriately and use it. The aliphatic carboxylic acid is preferably used together with the amines, and may be added when mixing the silver compound and the amine.
As the aliphatic carboxylic acid, 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, Saturated aliphatic monocarboxylic acids having 4 or more carbon atoms such as icosanoic acid and eicosenoic acid; and unsaturated aliphatic monocarboxylic acids having 8 or more carbon atoms such as oleic acid, elaidic acid, linoleic acid, and palmitoleic acid.

  Among them, saturated or unsaturated aliphatic monocarboxylic acids having 8 to 18 carbon atoms are preferable. When the number of carbon atoms is 8 or more, when the carboxylic acid group is adsorbed on the surface of the silver particles, an interval between the silver particles and other silver particles can be ensured, so that the effect of preventing aggregation of the silver particles is improved. Taking into account the availability and ease of removal during firing, etc., saturated or unsaturated aliphatic monocarboxylic acid compounds having up to 18 carbon atoms are usually preferred. Particularly, octanoic acid, oleic acid and the like are preferably used. One of the aliphatic carboxylic acids may be used alone, or two or more thereof may be used in combination.

(5-1. Addition amount of aliphatic carboxylic acid)
When the aliphatic carboxylic acid is used, it may be used in an amount of, for example, about 0.05 to 10 mol, preferably 0.1 to 5 mol, and more preferably, 1 mol of silver atom of the silver compound as a raw material. It is preferable to use 0.5 to 2 mol. If the amount of the aliphatic carboxylic acid is less than 0.05 mol per 1 mol of the silver atom, the effect of controlling the particle size by adding the aliphatic carboxylic acid is weak. On the other hand, when the amount of the aliphatic carboxylic acid reaches 10 mol, the particle diameter may be too small and uniform, and may be left in the washing or the surface protective agent replacement step. Is difficult to remove. However, an aliphatic carboxylic acid may not be used.

[6. Explanation of water and water content)
The present invention is characterized in that a fixed amount of water is present in the presence of an organic solvent at the time of forming a complex between a silver compound and an amine compound as described above. That is, water is present in an amount of 5 to 20 parts by weight per 100 parts by weight of the silver compound (a). Thus, the present inventors have found that the silver nanoparticles obtained have a relatively large particle size and a wide particle size distribution. The silver nanoparticles having a large particle size and a wide distribution have excellent effects as described later.

Particularly preferably, it is 12 to 18 parts by weight, more preferably 14 to 16 parts by weight.
If the water content is less than 5 parts by weight, the particle size distribution of the obtained silver particles is too uniform, voids are generated in the sintered body, and it is difficult to obtain silver particles with a wide distribution. On the other hand, when the amount exceeds 20 parts by weight, the silver particles become too coarse, and a portion where the particles are fused and united is produced, which is not preferable. As for the water to be used, ion-exchanged water in which metal ion impurities are reduced is preferable. The timing of adding water may be before the heating step, and may be added at any stage before the formation of the silver-amine complex or after the formation of the complex.
Further, the weight ratio of water / organic solvent is preferably 0.03 to 0.3 for the ratio between the above-mentioned organic solvent (c) and water. More preferably, it is 0.1 to 0.25. Particularly in this range, it is easy to obtain silver nanoparticles having the particle size and particle size distribution of the present invention described below.

<Production method of silver nanoparticles>
[7. Mixing of liquid raw materials)
In the present invention, usually, the amine compound that forms the complex is placed in the polar solvent (c) and mixed. If necessary, an aliphatic carboxylic acid and water can be added and mixed to adjust a liquid raw material necessary for the reaction.
When a liquid material has a solid substance at normal temperature, it can be mixed by appropriately heating. The heating temperature is preferably 100 ° C. or lower, more preferably 80 ° C. or lower, and further preferably 60 ° C. or lower. If the temperature is higher than the above temperature range, when mixed with a silver compound to form a slurry, a partial complexation / oxalic acid decomposition reaction will start first, and silver nanoparticles will remain without ensuring uniformity in the system. May be generated.

[8. Preparation of silver compound slurry)
The silver compound (a) is mixed with the liquid raw material to prepare a silver compound slurry. Alternatively, only the polar solvent and the silver compound (a) may be mixed first, and the amine compound may be added later.
A silver compound is mixed with a predetermined amount of an amine mixture, or, if necessary, an aliphatic carboxylic acid and water. The mixing at this time may be carried out while stirring at room temperature or while stirring while appropriately cooling the silver compound to room temperature or lower because the coordination reaction (complexation reaction) with the amines generates heat. Since the mixture of the silver compound and the amine compound is performed in the presence of an organic solvent, stirring and cooling can be performed well. The excess of the organic solvent and the amine compound serves as a reaction medium.

  In addition, the odor of the highly volatile alkylamine has a large adverse effect on the working environment.In the present invention, the amount of the highly volatile alkylamine used in synthesizing silver nanoparticles can be reduced or eliminated. The odor and the exposure to workers can be reduced during the preparation.

[9. About silver amine complex]
Since the formed complex compound generally exhibits a color corresponding to the component, the progress of the complex compound formation reaction can be detected from the change in the color of the reaction mixture. When it is difficult to confirm the change due to the change in color, it is possible to detect the formation state based on a change in the viscosity of the reaction mixture or a change in the temperature. In this way, a silver amine complex is obtained in a medium mainly composed of a polar solvent and an amine compound.

[10. Explanation of heating rate conditions from complexation to decomposition reaction]
In the heating step of the reaction system, since the heating rate affects the particle size of the precipitated silver particles, the particle size of the silver particles can be controlled by adjusting the heating rate in the heating step. Here, it is desirable to adjust the speed of the heating step within the range of 3.0 to 50 ° C./min up to the set decomposition temperature. The slower the temperature rise time, the easier the particle growth occurs and the larger the particle size is likely to be formed. However, if the temperature rise rate is slower than 3.0 ° C./min, the particle growth is easily promoted and the same as the adjacent particles. It is not preferable.

[11. Mechanism of formation of broad distribution silver particles by adding water]
In the reaction mechanism of the silver particle formation by the thermal decomposition as described above, by adding the amount of water defined in the present invention, the particle size of the formed silver nanoparticles varies, and a high distribution of silver particles Is obtained. The mechanism is unknown, but water approaches the silver compound, especially silver oxalate, and when silver amine complex formation or thermal decomposition occurs, it inhibits the amine compound from adsorbing to silver atoms, It is considered that the hindered portion grows as particles. Further, since the amount of water molecules adsorbed on silver oxalate is also uneven (localized), it is considered that an appropriate variation occurs in the particle size. On the other hand, if more than 20 wt% of water is added to the silver compound, the adsorption of the silver atoms of the amine is excessively inhibited, and the silver particles themselves are enlarged, and sintering and coalescence with the adjacent particles are also caused. It is possible that it has been awakened.

[12. Silver particle washing process)
Due to the thermal decomposition of the silver compound, the color varies depending on the particle size of the obtained particles, but a suspension having a color from black-brown to gray is obtained. The removal of the polar solvent and excess amine compound from the suspension, for example, the precipitation of silver nanoparticles, the decantation and washing with an appropriate solvent (water or organic solvent), and the binding of the amine compound. Silver nanoparticles are obtained.

[13. Explanation of washing solvent)
In washing the silver particles, it is preferable to use an alcohol having a boiling point of 150 ° C. or less such as methanol, ethanol, or propanol as a solvent. As a detailed washing method, it is preferable to add a solvent to the solution after the synthesis of the silver particles, stir until the solution is suspended, and then remove the supernatant by decantation. The removal amount of the amine can be controlled by the volume of the solvent to be added and the number of washings. In the case where the above series of operations is performed once, the solvent is preferably washed 1/2 to 3 times with respect to the solution after the silver particle synthesis, and washed 1 to 5 times.

[14. (Protective agent replacement step)
Furthermore, the organic group introduced into the silver nanoparticles by the amine compound during the above complex formation process can be replaced by another amine compound. For example, it can be substituted with an amine compound having a functional group having a greater steric hindrance and a high dispersion stabilizing effect. In addition, it may be replaced with an amine compound suitable for the use of the silver particles. Here, as the amine compound used for substitution, the above-mentioned component (b), particularly the component (b2) or (b1) may be used, or other compounds may be used.
Particularly, an alkylamine having 4 to 8 carbon atoms or an amine compound containing an oxygen atom (alkoxyamine, alkyletheramine, amino alcohol, aminoethoxy) is preferable. The alkylamine and the amine compound containing an oxygen atom can be used alone or in combination of two or more, and the viscosity of the paste can be adjusted depending on the composition.

  In the replacement method, the silver particles after washing are stirred and suspended in an amine compound to be finally replaced for a certain period of time to replace the surface protective agent of the silver particles. At this time, 50 to 100% by weight of the amine compound to be finally substituted is added to the contained pure silver, and the mixture is usually stirred and suspended at room temperature for about 1 hour. Regarding the difference between before and after the surface protective agent replacement step, it is possible to confirm the surface protective agent by a difference in sinterability in DTA measurement, head space GC / MS, or the like. After the above-mentioned step of replacing the surface protective agent, the target silver particles are obtained through a washing step again.

[15. State of Generated Silver Particles (Protective Agent, Particle Size Distribution, Viscosity Hysteresis)] In this way, silver nanoparticles bound with the amine compound are formed. The silver nanoparticles are fine particles which can be produced by the above method and mainly have a silver component and usually have a particle size of about 1 nm to 1000 nm.
The amine compound bonded to the surface of the silver nanoparticles functions as a protective agent for preventing fusion and aggregation of the particles. When the STEM image of the silver nanoparticles of the present invention is confirmed, a layer having a thickness of slightly less than 1 nm to several nm is confirmed on the surface of the particles, which is considered to be an amine compound bonded to the surface of the particles. Here, “bonded to the particle surface” refers to a state in which it is coordinated with a silver atom present on the surface of the silver particle. Due to the coordination bond, it remains even after a washing step for removing an excess amine compound is performed. The difference between the free amine compound and the amine compound bonded to the particle surface can also be confirmed by thermal analysis such as TG / DTA. The bound amine compound tends to have a higher thermal decomposition temperature than the free amine compound. When the amine compound bound as a protective agent is thermally decomposed, sintering of silver particles starts at the same time, and an exothermic peak appears on the DTA chart. The amine compound decomposed near the temperature is a so-called “bonded to the particle surface” amine compound.
The silver nanoparticles contain the amine compound used in the complex formation step and the substitution step described above, and further contain the aliphatic carboxylic acid when used. The content ratio of each of these components in the silver particles is basically determined in consideration of the use ratio in the particle production step and the increase and decrease in the washing step and the protective agent replacement step. Therefore, it is possible to adjust the type and the total amount of the amine compound by the mixing ratio and conditions of these steps.

  The length of the molecule of the amine compound finally bonded to the silver particles is preferably from 2 to 8 °, more preferably from 5 to 8 °. And 7-8 degrees is most preferable. Specific examples of the amine compound satisfying these conditions are as described above as the component (b2). The total amount of the amine compound is preferably 0.3 to 2.0 parts by weight based on 100 parts by weight of the pure silver component. More preferably, it is 0.5 to 1.0 part by weight.

The silver nanoparticles of the present invention usually have a particle size of 1000 nm or less.
Further, the average particle size is 70 to 350 nm, preferably 70 to 300 nm, and more preferably 80 to 200 nm.
The variation coefficient indicating the variation (distribution) of the particle diameter is 40 to 80%, preferably 40 to 70%, and more preferably 50 to 60%.

The average particle size and the variation coefficient are determined as follows. Observe the particle shape of the obtained silver nanoparticles by FE-SEM. Thereafter, using image analysis software SCANDIUM (manufactured by OLYMPUS), the length of 400 or more particle diameters (major diameters) is measured, and the values of the average particle diameter and the standard deviation are determined. Using these values, the coefficient of variation is calculated based on the following formula.
Coefficient of variation (%) = {standard deviation (nm) / average particle diameter (nm)} × 100
The equipment for measuring the particle diameter is not limited as long as the same result as the above method can be obtained.

By having the above average particle diameter and variation coefficient, the thickness of the coating film obtained by applying the silver paint can be increased. Specifically, a film as thick as 10 to 30 μm can be obtained. Further, not only the thickness is increased, but also the volume resistivity of the obtained film can be reduced. Specifically, a thick film having a thickness of 20 μm or more and a small volume resistivity of about 6 to 7 μΩ · cm can be obtained. This is because the particle size distribution is wide, and small particles are closely packed between large particles so that the silver particles are highly filled, and a film with a high content of silver particles is obtained. Guessed.
If the average particle size is less than 70 nm, the amount of the amine compound that protects the surface of the silver particles increases, and the volume resistivity of the obtained coating film cannot be reduced. On the other hand, if the average particle size exceeds 350 nm, the phenomenon of a decrease in the melting point of the silver nanoparticles becomes weak, and sintering at low temperatures becomes difficult, so that also in this case, the volume resistivity of the coating film cannot be reduced.
On the other hand, if the coefficient of variation is less than 30%, the particles are aligned, and the voids between the particles cannot be filled, and the volume resistivity of the coating film cannot be reduced. On the other hand, if the coefficient of variation exceeds 80%, even if there is variation in the particles, the particle sizes are too different, and in this case, it is difficult to fill the voids between the particles. I can't lower it.

By using the silver particles of the present invention having the above average particle diameter and variation, the viscosity can be adjusted to a suitable value as a silver coating composition.
The viscosity of the screen printing ink is preferably in the range of 0.1 to 500 Pa · s (shear speed 5 s- ¹ ). If it is too high, there is no fluidity and printing failure is likely to occur, and if it is too low, the printed ink will sag and the line width will be widened. Therefore, in order to increase the viscosity, an organic binder is usually added in many cases, but the organic binder increases the resistance value of the obtained coating film. On the other hand, the silver particles of the present invention have a relatively high viscosity even when 1 wt% of pure silver is added to Ethocel 45 (manufactured by Nissin Kasei) as an organic binder in a paste having a silver content of about 70 wt%. For example, by adjusting the particle size to an average particle diameter of about 80 nm and a coefficient of variation of about 35%, the viscosity can be adjusted to about 30 to 40 Pa · s. Therefore, even if the amount of the organic binder added is 1% by weight or less based on the pure silver content, the viscosity suitable for the above screen printing can be obtained. As described above, since the viscosity can be controlled by adjusting the particle size, the degree of freedom of the addition amount of the organic binder can be increased and the amount can be reduced.

Further, in the present invention, small particles having a size of 100 nm or less and large particles having a size of 200 nm or more are mixed in an appropriate range.
The silver nanoparticles of the present invention preferably have a particle size of 70% or more based on the number of particles having a particle size other than 100 to 200 nm (the total of (i) particles of 100 nm or less and (ii) 200 nm or more).
The particle diameter here is the particle diameter of each particle obtained by measuring the length of an SEM image by image analysis software in the method described above.
More preferably, the total of particles having a particle diameter of (i) 100 nm or less and (ii) 200 to 500 nm is 70% or more based on the number. More preferably, particles having a size of 100 nm or less account for 60% or more on a number basis.

By including both of these small particles of 100 nm or less and large particles of 200 nm or more, the effect of filling small particles by entering between large particles is particularly high, and the content of high silver particles has a low volume resistivity. Excellent in obtaining a thick coating film at a high rate. In particular, by including the proportion of particles having a size of 100 nm or less at a high content of 60%, an effect of increasing the adhesiveness is also obtained.
The silver nanoparticles of the present invention described above have low-temperature sinterability and electrical conductivity, and the sintered coating (coating obtained by coating on a substrate and sintering) has a thickness of about 20 to 30 μm. It is easy to have This is presumed to be due to the coexistence of the large particle size region and the small particle size region, whereby the silver particles were densely filled when the film was formed, and the voids were reduced.
Further, when the silver nanoparticles of the present invention are contained in Texanol at 78.5% by weight, the viscosity (v1) at the time of increasing the shear rate and the viscosity at the time of decreasing the shear rate in the range of the shear rate of 2 to 30 s ^−1. The viscosity ratio (v1 / v2) of (v2) is 2.0 or less. Preferably it is 1.5 or less, more preferably 1.2 or less.

This means that the difference in viscosity between when the shear rate increases and when the shear rate decreases is small, that is, the hysteresis of the viscosity when the shear rate is changed is small. For example, comparing FIG. 29 showing the change in viscosity in Examples 8 and 9 using the silver nanoparticles of the present invention with FIG. 30 showing the change in viscosity in Comparative Example 1, FIG. While the difference in viscosity at the time of descent is small and (v1 / v2) is 2.0 or less in any range of the shear rate of 2 to 30 s ⁻¹ , there is a portion exceeding 2.0 in FIG. (The viscosity (v1) when the shear rate is increased, the viscosity (v2) when the shear rate is decreased, and their viscosity ratio (v1 / v2) at the speeds ¹ , 2, 3, and 4 s ^-1 are as shown in Table-9.) .
When (v1 / v2) is large, it means that viscosity hysteresis occurs, and that the interaction between particles is large and a pseudo-crosslinked state is formed. From this, it is considered that aggregation is likely to occur, which is supported by the observation of aggregates in FIG. 28 which is a photograph of the coating film surface.
In contrast, the silver nanoparticles of the present invention have a small (v1 / v2) and are less likely to aggregate. For this reason, the smoothness of the coating film surface when formed into a coating film is also excellent.
In addition, since there are few agglomerates, especially in screen printing, the printing accuracy and continuous printability are excellent, and clogging of the screen mesh hardly occurs.

In the production method of the present invention, as described above, the particle size can be controlled by the type of amine used, the type of organic solvent, and the amount of water added. Therefore, it is suitable for industrial production such that silver particles having a large particle size range of 200 to 500 nm and silver particles having a small particle size range of 50 to 200 nm can be synthesized in one batch.
The silver nanoparticles of the present invention thus obtained can contain a large number of silver particles in a large particle diameter region of 200 nm or more. Agglomeration (sintering) is difficult even during the process, and the silver nanoparticle dispersion / silver coating composition can be easily produced without impairing the original characteristics of silver particles. This is also effective when considering scale-up.

<Application>
[16. Silver nanoparticle dispersion, silver coating composition and production method thereof]
Using the silver nanoparticles obtained by the method described above, a silver nanoparticle dispersion can be prepared. Here, the silver nanoparticle dispersion refers to a composition containing at least silver nanoparticles and a dispersion medium. Such silver nanoparticle dispersions can take various forms without limitation. The silver nanoparticle dispersion of the present invention can be obtained by dispersing the silver nanoparticles in a suspension state in an appropriate organic solvent (dispersion medium).
Since the silver nanoparticles of the present invention have excellent dispersibility as described above, they can be stably present in a dispersion medium at a high concentration. For example, the silver nanoparticles in the composition can be contained at a high concentration of 70 to 95 wt%, more preferably 75 to 80 wt%, and can be in a so-called paste state.
Furthermore, it can be set as the silver coating composition containing what is called a binder component other than a silver nanoparticle and a dispersion medium. A silver coating composition containing silver nanoparticles at a high concentration of 70 to 95 wt%, more preferably 75 to 80 wt%, has good printability and is easy to produce a thick conductive film. A composition can be obtained.
That is, the viscosity ratio of the viscosity (v1) when the shear rate is increased and the viscosity (v2) when the shear rate is decreased in the range of the shear rate of 2 to 30 s-1 containing 70 to 95 wt% of the silver nanoparticles of the present invention described above. A silver nanoparticle dispersion or a silver coating composition, wherein (v1 / v2) is 1.2 or less, can be obtained.

(16-1. Dispersion or dispersion medium of coating composition)
Various organic solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, etc. may be used as a dispersion medium for obtaining the silver nanoparticle dispersion or the silver paint composition. Hydrogen solvents; alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; aromatic hydrocarbon solvents such as toluene, xylene and mesitylene; methanol, ethanol, propanol, n-butanol, n-pentanol and n-hexanol; Alcohol solvents such as n-heptanol, n-octanol, n-nonanol, n-decanol, n-dodecanol and the like can be mentioned.

As the organic solvent, among these, an organic solvent having a carbon number of 8 to 16 and having an oxygen atom in the structure and having a boiling point of 280 ° C. or lower is particularly preferable. When the target of the sintering temperature of silver particles is 150 ° C. or less, it is difficult to volatilize and remove a solvent having a boiling point of more than 280 ° C. Preferred examples of this solvent include terpineol (C10, boiling point 220 ° C), dihydroterpineol (C10, boiling point 220 ° C), texanol (C12, boiling point 260 ° C), ethyl carbitol acetate (C8, boiling point 219 ° C), butyl Carbitol acetate (C10, boiling point 247 ° C), 2,4-dimethyl-1,5-pentanediol (C9, boiling point 150 ° C), 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (C16, (Boiling point 280 ° C.). The solvent may be used as a mixture of a plurality of types, or may be used alone.
The type and amount of the organic solvent may be appropriately determined depending on the concentration and viscosity of the desired silver coating composition or silver nanoparticle dispersion.

(16-2. Description of binder of coating composition)
By adding a binder to the silver coating composition, dispersibility of silver particles can be assisted, or adhesion to a substrate can be imparted. The amount of the organic binder to be added is preferably 0.1 to 10% by weight based on the contained silver.
The form in which the binder resin is present in the coating composition may be dissolved in a solvent, or may be an emulsion or a suspension. The binder is not particularly limited, for example, polyester resin, polyurethane resin, polyamide resin, polyvinyl chloride resin, polyacrylamide resin, polyether resin, acrylic resin, melamine resin, vinyl resin, phenol resin, epoxy resin, urea resin , Vinyl acetate resin, polybutadiene resin, vinyl chloride vinyl acetate copolymer resin, fluororesin, silicone resin, rosin, rosin ester, chlorinated polyolefin resin, modified chlorinated polyolefin resin, chlorinated polyurethane resin, cellulose resin, polyethylene glycol , Polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone and the like.
The binder used may be used alone or in combination of two or more.

[17. Printing method and usage with silver paint composition]
Generally, a silver coating composition is applied on a substrate and then fired.
Application is spin coating, inkjet printing, screen printing, dispenser printing, letterpress printing (flexo printing), sublimation printing, offset printing, laser printer printing (toner printing), intaglio printing (gravure printing), contact printing, microcontact printing It can be performed by a known method such as When a printing technique is used, a patterned silver coating composition layer is obtained, and a patterned silver conductive layer is obtained by firing. Further, this silver conductive layer can be applied as a bonding material having excellent conductivity and heat conductivity, and is also useful as a bonding material for electric devices handling large currents such as power devices.

The firing can be performed at a temperature of 200 ° C. or less, for example, room temperature (25 ° C.) to 150 ° C., preferably room temperature (25 ° C.) to 120 ° C. However, in order to complete the sintering of silver by firing in a short time, the sintering may be performed at a temperature of 60 ° C to 200 ° C, for example, 80 ° C to 150 ° C, preferably 90 ° C to 120 ° C. The baking time may be appropriately determined in consideration of the application amount of the silver ink, the baking temperature, and the like, and is, for example, within several hours (for example, 3 hours or 2 hours), preferably within 1 hour, and more preferably within 30 minutes. Good to do.
Since the silver nanoparticles obtained by the present invention have a large particle size and a wide particle size distribution as described above, the sintering of the silver particles sufficiently proceeds even by such a low-temperature and short-time firing step. As a result, excellent conductivity (low resistance value) is exhibited, and a silver conductive layer having a low resistance value (for example, 15 μΩcm or less, a range of 7 to 15 μΩcm) can be formed. The resistance value of bulk silver is 1.6 μΩcm.

[18. Use of silver nanoparticle dispersion and silver coating composition]
Since it can be fired at low temperatures, it can be used as a glass substrate, a heat-resistant plastic substrate such as a polyimide film, or a polyester film such as a polyethylene terephthalate (PET) film or a polyethylene naphthalate (PEN) film. A general-purpose plastic substrate having low heat resistance, such as a film or a polyolefin-based film such as polypropylene, can also be suitably used. Short-time baking reduces the load on these general-purpose plastic substrates having low heat resistance and improves production efficiency.

  The thickness of the silver conductive layer may be appropriately determined depending on the intended use, and particularly when a silver conductive layer having a relatively large thickness is formed by using the silver nanoparticles according to the present invention, high conductivity is obtained. Can be shown. The thickness of the silver conductive layer may be selected, for example, from the range of 100 nm to 30 μm, preferably 1 μm to 20 μm, more preferably 10 μm to 20 μm.

  The silver nanoparticle dispersion and the silver paint composition of the present invention include 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, Applicable to LED elements, organic transistors, capacitors (capacitors), electronic paper, flexible batteries, flexible sensors, membrane switches, touch panels, EMI shields, etc.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
The characteristics of the amine compounds used in Examples and Comparative Examples, such as names and structural formulas, are shown in Tables 1 and 2.

[Example 1]
(Production of silver particles)
In a 2 L flask, 420.00 g (1.38 mol) of a dried product of silver oxalate as a silver compound serving as a raw material and 339.87 g (3.33 mol) of n-hexanol as a polar solvent were stirred to wet silver oxalate. I let it. Thereafter, 128.22 g (1.75 mol) of n-butylamine and 55.83 g (0.55 mol) of n-hexylamine were added, and as an additive for controlling the particle diameter, oleic acid (manufactured by NOF: NAA-35). 4.71 g (0.017 mol) and 21.00 g of ion-exchanged water (15.0 wt% based on silver oxalate) were added. Thereafter, the mixture was stirred for 1 hour to produce a silver-amine complex. Thereafter, the mixture was heated at a heating rate of 3 ° C./min, and at 100 ° C., generation of carbon dioxide, which was considered to have caused a decomposition reaction of silver oxalate, was confirmed. Heating was continued until the generation of carbon dioxide ceased to obtain a liquid in which silver particles were suspended. After the silver particles were precipitated, 900 cc of methanol was added to the reaction solution for washing, followed by centrifugation. This washing and centrifugation were performed three times. Thus, silver nanoparticles were obtained.

(Protective agent replacement treatment)
In order to replace n-butylamine in the obtained silver nanoparticles with n-hexylamine, 71.8 wt% of n-hexylamine and silver nanoparticles were added at room temperature to 71.8 wt% based on the pure silver content of the obtained silver nanoparticles. After stirring for an hour, washing and centrifugation were repeated three times in the same manner as above to obtain silver nanoparticles using hexylamine as a protective agent.

(Confirmation of particle size)
The obtained silver nanoparticles moistened with methanol were suspended in n-hexanol using a vortex mixer, the liquid was dropped on a support such as a collodion film, and the solvent was dried to obtain a sample. In FE-SEM observation, observation and photographing are performed at a magnification of 20000 to 70000 times, and an image having a magnification of 400 or more particles is selected from the images. Thereafter, 400 or more particles were counted using image analysis software SCANDIUM (manufactured by OLYMPUS). When measuring the particle diameter, the long diameter of the particles was measured, and the average particle diameter, particle size distribution, and the like were calculated from the data.
Table 3 shows the particle ratio (%), average particle diameter (nm), and coefficient of variation (%) of particles having a particle size of 100 nm or less, 200 to 500 nm, and more than 500 nm. An FE-SEM photograph is shown in FIG. FIG. 15 shows the particle size distribution histogram.

(Preparation and baking of silver nanoparticle paste and ink)
Next, texanol as a solvent was added to the recovered silver nanoparticles so as to have a silver content of 75 wt%, and mixed. Further, Ethocel 45 (manufactured by Nissin Chemical Co., Ltd.) was added as an organic binder so that the addition amount was 1 wt% with respect to the silver particles, and finally a silver nanoparticle paste ink having a silver content of about 70 wt% was prepared. This paste was cast on a slide glass, and heated at 150 ° C. for 1 hour with a blow dryer. The thickness of the coating film after drying was adjusted to 10 to 30 μm.
The obtained coating film was measured for surface resistance by a four-terminal method, and was multiplied by the thickness of the obtained coating film to obtain a volume resistivity.
Table 3 shows the values of the volume resistivity.

[Examples 2 to 9, Comparative Examples 1 to 7]
(Production of silver particles)
The materials used and the mixing ratio were changed to those shown in Tables 3 to 7, the temperature rising rate after the formation of the silver-amine complex compound was changed to those shown in Tables 3 to 7, and the reaction vessel / heating device was changed to those shown in Tables 3 to 7. Silver particles were produced in the same manner as in (Production of silver particles) of Example 1 except that the silver particles were replaced with those shown in FIG.
As shown in Tables 3 to 4, in Examples 3, 4, 7, and 8, silver particles subjected to (protective agent replacement treatment) were produced in the same manner as in Example 1. In Example 9, silver particles were produced in the same manner as in Example 1, except that n-butylamine was used instead of n-hexylamine in (protective agent substitution treatment).

The obtained silver particles were subjected to the same method as in Example 1 (confirmation of particle diameter). In addition, about Comparative Examples 2, 6, and 7, the particle diameter was confirmed by the STEM image.
In Examples 2 to 7 and Comparative Examples 1 and 2, the obtained particles were used in the same manner as in Example 1 (preparation and baking of silver nanoparticle paste and ink). In Example 3, terpineol C (a mixture of α-, β-, and γ-isomers manufactured by Nippon Terpen Co., Ltd.) was used as the ink solvent.
In Examples 3 and 4, particles (preparation and baking of silver nanoparticle paste and ink) were performed using particles before the protective agent replacement treatment and particles after the protective agent replacement treatment.
In Comparative Examples 6 and 7, as in Patent Documents 1 and 2, the silver content was adjusted to 55 wt% and dispersed in a mixed solvent of isooctane / n-butanol = 4/1 (volume ratio). The silver nanoparticle dispersion thus obtained was applied on glass by spin coating.

  For Examples 2 to 9 and Comparative Examples 1 to 7, the average particle diameter (nm), variation coefficient (%), and particle ratio (%) in each particle diameter range of the obtained particles are shown in Tables 3 to 7. Show. SEM or STEM images are shown in FIGS. 16 to 25 show particle size distribution histograms of Examples 2 to 9 and Comparative Examples 1, 2, 6, and 7. Tables 3 to 7 show the values of the volume resistivity and the film thickness of the sintered coating film in Examples 2 to 9 and Comparative Examples 1, 2, 6, and 7. In the table, “(b) / silver particle mol ratio” indicates the molar ratio of silver particles in (b) / (a).

(Coating observation)
For the Texanol paste having a silver content of 78.5% prepared using the particles described in Example 8, Comparative Example 1, and Example 9, the paste passed through a nylon mesh having an aperture of 20 μm was applied to an aluminum foil with a spatula. An SEM observation was performed on the surface of the coating film obtained by drying the film with a dryer. The coating films observed by SEM are as shown in FIGS.

(Measurement of viscosity of silver paste)
Further, the viscosity of a 78.5% silver content texanol paste prepared using the particles described in Example 8, Comparative Example 1, and Example 9 was measured with a rheometer (HAAKE MARSIII manufactured by Thermo Fisher Scientific). did. The measurement conditions were as follows: measurement mode: hysteresis loop, shear rate: 0.1 s ^-1 → 30 s ^-1 (90 s), 30 s ^-1 → 0.1 s ^-1 (90 s), measurement jig: cone plate (Cone C35 / 1 ° TiL, Lower plate TMP35), gap: 0.052 mm, measurement temperature: 25 ° C. The measured viscosity data is as shown in FIG. 29 for Examples 8 and 9, and is as shown in FIG. 30 for Comparative Example 1.
Further, based on the measured viscosity data, the viscosity value at each shear rate was confirmed by analysis software (HAAKE RheoWin Data Manager manufactured by Thermo Fisher Scientific). In Example 8, Example 9, and Comparative Example 1, the viscosity (v1) when the shear rate was increased and the viscosity (v2) when the shear rate was decreased at a shear rate of ^{1, 2, 3,} 4 s ^-1, and their viscosity ratio (v1) / V2) are shown in Table-9. In Examples 8 and 9 using the silver nanoparticles of the present invention, (v1 / v2) is 2.0 or less at a shear rate of ¹ to 4 s ^-1 . Further, as can be seen from the graph, in the range of 4 to 30 s ⁻¹ , there is no smaller point and no point exceeds 2.0. On the other hand, in Comparative Example 1, the viscosity ratio (v1 / v2) exceeds 1.2 at the points of 2 s ⁻¹ and 3 s ⁻¹ , indicating that the viscosity hysteresis is large.

As described above, according to the present invention, water is present in the range of 5 to 20 parts by weight with respect to 100 parts by weight of the silver compound at the time of complex formation, and the molar ratio of the silver atom in the amine compound to the silver compound is 0.7. By performing the reaction in the range of 2.0 to 2.0, it was confirmed that the amine compound was bonded to the particle surface, and silver particles having an average particle diameter of 70 to 350 nm and a variation coefficient of 40% to 80% were obtained.
Further, these silver particles of the present invention can form a sintered coating film of 20 μm or more, and have a volume resistivity of 50 μΩ · cm or less under firing conditions at 150 ° C. It was confirmed that a film having a property was obtained. Among them, in Examples 2 and 4 in which AMP was used as the amine compound and Texanol was used as the ink solvent, the average particle diameter was as small as about 80 nm, or as large as 260 nm, and the coefficient of variation was 40%. ~ 80% of particles could be obtained, and these particles had excellent low-temperature sintering because the volume resistivity of the coating film at 100 ° C. could be 50 μΩ · cm or less. It has been confirmed that silver nanoparticles having properties can be obtained.

  Further, in Example 3, the same solvent as in Example 2 was used, and the ink solvent was changed to terpineol C. However, by replacing the protective group with n-hexylamine having a molecular length of 7 to 8%, 100% was obtained. It was also confirmed that the volume resistivity of the coating film was significantly reduced under the sintering conditions at a temperature of 0 ° C. as compared with the state without the protective group substitution. Thus, in the silver nanoparticles of the present invention, it can be seen that by adjusting the type of the protective group on the surface of the silver particles, the ink solvent, the sintering conditions, and the like, it is possible to obtain an appropriate silver paint composition and a sintered coating film. .

Regarding the increase in the particle size of silver nanoparticles by using the component (b1), in Examples 5 and 6, N, N-dimethylpropyldiamine and 1-amino- The same mole number of 2-butanol was added, and the size of silver nanoparticles synthesized by synthesizing other raw materials under the same conditions under the same conditions was compared. Comparing Examples 5 and 6, it was confirmed that Example 6 using the component (b1) was easier to synthesize a particle diameter of 200 to 500 nm than Example 5. Also, as in Examples 2 and 3, it can be seen that even when the component (b1) is used, the particle size can be reduced by increasing the proportion of the component (b2).
Furthermore, in Example 7, although diglyme was used instead of n-hexanol as the synthesis solvent, silver nanoparticles having a wide particle size distribution could be formed, and a thick film conductive film of 20 to 30 μm could be obtained. .

On the other hand, in Comparative Examples 1 and 2, water was not added. In this case, the average particle diameter was not only as small as less than 65 nm, but also the coefficient of variation was less than 30% and the variation was small, and 99% or more was 100 nm or less. Has a small particle size. It can be seen that sufficient conductivity cannot be obtained at each sintering temperature unless the film thickness is as small as 10 μm or less for such small particles having little variation. In particular, the volume resistivity is greatly increased under the firing conditions in a low-temperature region having a film thickness of 20 μm or more and 120 ° C. or less.
Further, even when the component (b1) or water was used, too much water was added as in Comparative Example 3, or the component (b2) was too little as in Comparative Example 4, or as in Comparative Example 5. If the rate of temperature rise is too slow, the particles will fuse, and independent silver particles cannot be obtained, indicating that it is difficult to control the particle size.

The particles of Comparative Examples 6 and 7 produced by a method equivalent to the production method of Patent Documents 1 and 2 in which the molar ratio of silver atoms in (b) and (a) is out of the range of the present invention have a small coefficient of variation. Therefore, when the ink is applied, a sintered coating having a thickness of about 0.5 μm is formed, and it is difficult to increase the thickness of the coating.
As can be seen from the above results, in the complex formation reaction of the amine compound and the silver compound in the organic solvent, the ratio of the water and the amine compound is set within the range specified in the present invention, and the ratio of the amine compound and the silver compound is set in the present invention. By the method of the present invention within the range specified in the above, it is possible to obtain the silver nanoparticles of the present invention having an appropriate variation in the particle size distribution, it is easy to obtain a low-resistance thick film conductive silver coating composition It can be seen that can be manufactured. In addition, it can be seen that the silver nanoparticles obtained by using the component (b1) as the amine compound are particularly excellent in the above effects.

The silver pastes of Examples 8 and 9, which show a comparison of the viscosity behavior in FIG. 29, differ only in the length of the molecules of the amine introduced by the protective agent replacement treatment on the particles as described above (Example 8). Example 9 has n-butylamine: 5.004%, whereas n-hexylamine: 7.559%). As shown in Table 9, the dispersion of Example 8 had a viscosity (v1) when the shear rate was increased and a viscosity (v2) when the shear rate was decreased within the range of the shear rate of 2 to 30 s ^-1. Are substantially the same, that is, a pseudoplastic fluid having a viscosity ratio (v1 / v2) of about 1.0, whereas the dispersion of Example 9 has a shear rate in the range of 2 to 4 s ^−1. The viscosity (v2) when the shear rate decreases is lower than the viscosity (v1) when increasing, that is, the viscosity ratio (v1 / v2) is 1.1 to 1.2, and the behavior of the thixotropic fluid is slightly reduced. Tend to show.

  Comparing the photographs of the results of (observation of the coating film) of the silver particle dispersions of Example 8 and Example 9, in Example 8, a smooth coating film was obtained with almost no aggregates. Can confirm the presence of aggregates of several tens of μm. It is presumed that this phenomenon of many agglomerates causes the behavior of the thixotropic fluid of the paste. In Example 9, since the length of the molecule of the amine compound on the particle surface was short, the degree of steric hindrance was relatively low, and the silver particles created a pseudo-crosslinked state, causing aggregation and increasing the viscosity of the paste in a stationary state. Can be inferred. Once the shear is applied, the pseudo-agglomerated state is eliminated, the primary particles are in a dispersed state, and the viscosity of the paste at the time of increasing the viscosity is reduced. However, if left still for a while, a pseudo-crosslinked state is created again, and it is considered that the secondary aggregates and the increase in the viscosity of the paste are reconstructed. Therefore, it can be inferred that the dispersion of Example 8 is superior in continuous printability. Agglomerates may also cause mesh clogging.

Therefore, for the screen printing application, the dispersion of Example 8 in which the length of the molecule of the amine compound is in the range of 7 to 8 ° is more excellent. On the other hand, the dispersion of Example 9 also has excellent electric characteristics in a thick film of 20 μm as shown in Table-8 because the average particle diameter and the coefficient of variation are in the preferable ranges as in the dispersion of Example 8. , 500 μm to several millimeters, and can be suitably used as a bonding material for power semiconductors.
On the other hand, the silver particles of Comparative Example 1 are out of the range of the average particle diameter and the coefficient of variation of the present invention. As can be seen from FIG. 29, even when compared with the particles of Example 9 having the same length of the amine compound on the surface, as shown in Table 9, the shear rate in the range of the shear rate of 2 to 4 s ⁻¹ was obtained. Compared with the viscosity at the time of increase (v1), the viscosity (v2) at the time of decrease in shear rate is lower, that is, the viscosity ratio (v1 / v2) is 1.1 to 2.2, and the viscosity of the thixotropic fluid is lower. Tends to behave. This factor can be inferred from the fact that there are many agglomerates, as shown in FIG. 28, and cracks are liable to occur even when sintering.

  From the above results, like the silver particles of the present invention, the silver particles of the present invention having an appropriate particle diameter and variation can easily produce a thick film exhibiting excellent electric characteristics. Particularly, when a protective agent having an appropriate molecular length (7 to 8 mm) is bonded to the silver surface, a silver coating composition having particularly good dispersibility and having a viscosity behavior suitable for screen printing can be obtained. The printed silver coating composition can provide a thick-film conductive film having good conductivity at low temperature firing.

  According to the present invention, a silver capable of easily forming a thick and highly conductive silver conductive layer having a large particle size and a wide distribution by a method in which the emission amount of an amine having a strong pungent odor is suppressed. A silver paint composition suitable for nanoparticles, especially screen printing, can be obtained.

Claims (14)

  A silver compound (a) having thermal decomposability is reacted with an amine compound (b) capable of forming a complex with (a) in an organic solvent (c) to form a complex, and the obtained complex is heated. A method for producing silver nanoparticles which forms silver nanoparticles by pyrolysis, wherein 5 to 20 parts by weight of water is present with respect to 100 parts by weight of a silver compound (a) at the time of forming a complex, and A method for producing silver nanoparticles, wherein the molar ratio between the compound (b) and the silver atom in the silver compound (a) is 0.7 or more.   The method for producing silver nanoparticles according to claim 1, wherein (b) is 2-amino-2-methyl-1-propanol.   3. The method for producing silver nanoparticles according to claim 1, wherein (a) is silver oxalate.   The method according to claim 3, wherein the weight ratio of (c) / (a) is 0.8 to 1.3.   A method for producing a silver nanoparticle dispersion, comprising producing silver nanoparticles by the method according to any one of claims 1 to 4, and dispersing the obtained silver nanoparticles in an organic solvent.   A silver paint composition comprising: preparing silver nanoparticles by the method according to any one of claims 1 to 4; dispersing the obtained silver nanoparticles in an organic solvent; and further adding an organic binder. Production method.   A silver nanoparticle dispersion obtained by applying a silver nanoparticle dispersion obtained by the method according to claim 5 or a silver coating composition obtained by the method according to claim 6 onto a substrate, followed by firing to form a silver conductive layer. A method for manufacturing a conductive material. When 78.5% by weight is contained in Texanol, the viscosity ratio (v1 / 1) of the viscosity (v1) when the shear rate is increased and the viscosity (v2) when the shear rate is decreased in the range of the shear rate of 2 to 30 s ^−1. v2) is 2.0 or less, the average particle diameter is 70 to 350 nm, the coefficient of variation is 40% to 80%, and silver nanoparticles having an amine compound bonded to the particle surface.   9. The silver nanoparticle according to claim 8, wherein the length of the molecule of the amine compound bonded to the particle surface is 7 to 8 °.   A silver nanoparticle dispersion, wherein the silver particles according to claim 8 or 9 are dispersed in an organic solvent. The viscosity of the viscosity (v1) when the shear rate is increased and the viscosity (v2) when the shear rate is decreased in a range of 2 to 30 s ^-1 containing 70 to 95 wt% of the silver nanoparticles according to claim 8 or 9. A silver nanoparticle dispersion having a ratio (v1 / v2) of 2.0 or less.   A silver paint composition, wherein the silver nanoparticles according to claim 8 or 9 are dispersed in an organic solvent, and further contain an organic binder.   A method for producing a silver conductive material, comprising a step of applying the silver nanoparticle dispersion according to claim 10 or 11 on a substrate and baking to form a silver conductive layer. A method for producing a silver conductive material, comprising a step of applying the silver coating composition according to claim 12 on a substrate and baking to form a silver conductive layer.

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