JP7283703B2 - Method for producing silver nanoparticles with wide particle size distribution and silver nanoparticles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silver particles having a wide particle size distribution and to which a specific amino alcohol having an ether bond is bound as a protective agent, and silver nanoparticles.

Silver nanoparticles can be sintered even at low temperatures due to the melting point depression property of metal nanoparticles, so they are used as electrical wiring on substrates and as a bonding material for power device semiconductors. However, since the silver nanoparticles are fine, they tend to agglomerate and to fuse together due to the depression of the melting point. Fatty acids, alkylamines, and the like are often used for these organic layers. Silver nanoparticles coated with alkylamines or alkyldiamines in particular release protective agents at relatively low temperatures and can be baked at low temperatures. (Patent Documents 1 and 2).

It is expected that the fired coating film using such silver nanoparticles that can be fired at a low temperature can be used as a conductive material such as wiring. is used as a thick film. As silver nanoparticles designed for the purpose of such a thick film, in Patent Document 3, silver nanoparticles having a primary particle diameter of several nanometers to several tens of nanometers are used to achieve a conductivity of 5 to 20 μm. Silver coating compositions (inks) have been reported that provide silver coatings. In addition, in Patent Document 4, it is possible to reduce the resistance when making a sintered body by containing 30% or more of silver particles with 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 100 parts by weight in the reaction system.

In these publications, silver nanoparticles are produced using a complex formation reaction between a silver compound and an amine compound. Specifically, silver oxalate and alkylamine or alkyldiamine are formed into a complex in the absence of a solvent. However, when a complex is formed in the absence of a solvent, it becomes a solid with no fluidity and is difficult to agitate. Industrial practical application is difficult. Therefore, by conducting the complex formation reaction in an alcohol solvent, the complex reaction can be promoted and assisted, the agitation in the system can be improved, the carbon dioxide gas generated rapidly by thermal decomposition can be suppressed, and quality and safety issues can be improved. have been reported (Patent Documents 5 to 7).

In addition, in the process of thermally decomposing the silver oxalate-alkylamine complex, by-product gas (mainly carbon dioxide gas) is generated and discharged. In order to avoid this problem, a production method has been reported in which the complex compound is continuously introduced into a reaction vessel to control the amount of by-product gas generated during the 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 2016-132825 A JP 2015-40319 A JP 2014-152337 A

However, in Patent Document 3, only coating films having a thickness of less than 8 μm are formed in Examples. Even if a conductive coating film with a thickness of 10 μm or more is formed, since the primary particle diameter of the silver particles is mainly several tens of nanometers, the amount of the organic protective agent is large, and volumetric shrinkage occurs due to detachment of the protective agent, resulting in dimensional stability. is low, and there is a high possibility that the phenomenon of disconnection due to cracks will occur.

Even if the amount of by-product gas is controlled as in Patent Documents 5 to 8, carbon dioxide containing alkylamine is finally discharged out of the system.

The present invention solves the above problems and provides a method for producing silver nanoparticles in consideration of workability, safety, environmental aspects, etc., and a method for producing silver nanoparticles having a wide particle size distribution range. The task is to provide

In order to solve these problems, the present inventors have made extensive studies. As a result, by using a specific aminoalcohol having an ether bond as the amine compound capable of forming a complex with the silver compound, the emission of alkylamine can be suppressed and the resulting silver particles are environmentally friendly. The present inventors have arrived at the present invention based on the finding that the sintered coating film obtained has an excellent distribution and excellent performance.

That is, the present invention includes the following inventions.
(1) A thermally decomposable silver compound (a) and an amine compound (b) capable of forming a complex with (a) are reacted in an organic solvent (c) to form a complex, and the resulting complex is A method for producing silver nanoparticles that forms silver nanoparticles by thermal decomposition by heating, wherein (b) is a linear amino alcohol, and amino groups are attached to both ends of the linear molecule. and a hydroxyl group, and an amino alcohol having an ether bond in the linear molecular structure.

(2) The method for producing silver nanoparticles according to (1) above, wherein (b) has 4 or more carbon atoms.
(3) The method for producing silver nanoparticles according to (1) or (2) above, wherein (b) is diglycolamine.
(4) The method for producing silver nanoparticles according to any one of (1) to (3) above, wherein (a) is silver oxalate.
(5) The above (1) to (4) characterized in that 5 to 20 parts by weight of water is present with respect to 100 parts by weight of the silver compound (a) during the complex formation reaction between (a) and (b). ) The method for producing silver nanoparticles according to any one of ).
(6) The method for producing silver nanoparticles according to (5) above, wherein the molar ratio of (b)/[silver atoms contained in (a)] is 0.7 to 2.0.
(7) The method for producing silver nanoparticles according to any one of (1) to (6) above, wherein the weight ratio of (c)/(a) is 0.8 to 1.3.

(8) A silver nanoparticle dispersion characterized by preparing silver nanoparticles by the method according to any one of (1) to (7) above and dispersing the obtained silver nanoparticles in an organic solvent. Production method.
(9) Silver nanoparticles are prepared by the method described in any one of (1) to (8) above, the obtained silver nanoparticles are dispersed in an organic solvent, and an organic binder is added. , a method for producing a silver paint composition.
(10) The silver nanoparticle dispersion obtained by the method described in (8) above or the silver coating composition obtained by the method described in (9) above is coated on a substrate and baked to form a silver conductive layer. A method for producing a silver conductive material, comprising the step of:

The silver paint composition containing silver particles whose particle size is controlled according to the present invention can be sintered even at a low temperature range of 150° C. or less, and the resulting sintered body has a low resistance value close to that of bulk silver. show. The present invention uses a printing method typified by screen printing, on a plastic substrate with relatively low heat resistance such as PET and polypropylene, a material that can form a silver wiring with a thickness of several to several tens of μm, or a conductive bonding It can be expected to be used as a bonding material for electrical equipment that handles large currents such as materials and power devices.

In addition, in the synthesis of silver particles according to the present invention, the amount of amine compound used is smaller than that of the conventional synthesis method, and the specific amine compound having 4 or less carbon atoms that forms a complex with the thermally decomposable silver compound is used. The use of aminoalcohol can further reduce the use of alkylamine, which has a high burden on the human body and the environment, and thus provides a production method with high safety in scaled-up industrial production.

FIG. 1 is an image diagram showing a coordination model of an amine compound to a silver atom and a growth image. In FIG. 1, FIG. 1-1 is a coordination model of diglycolamine to a silver atom (linear type), and FIG. 1-2 is a coordination model of diglycolamine to a silver atom (OH group approaching type). , and FIGS. 1-3 are image diagrams of coordination models of alkylamines to silver atoms. Fig. 1-4 is an image diagram showing an image of linear adsorption and silver particle growth, which is common in alkylamines. Fig. 1-5 is an image diagram showing an image of O atom adsorption type adsorption of aminoalcohol and silver particle growth. -6 is an image diagram showing a realistic adsorption of aminoalcohol and an image of silver particle growth. 2 is a SEM photograph of the particles obtained in Example 1. FIG. 3 is a SEM photograph of the particles obtained in Example 2. FIG. 4 is a SEM photograph of the particles obtained in Example 3. FIG. 5 is a SEM photograph of the particles obtained in Example 4. FIG. 6 is a SEM photograph of the particles obtained in Example 5. FIG. 7 is a SEM photograph of the particles obtained in Example 6. FIG. 8 is a SEM photograph of the particles obtained in Example 7. FIG. 9 is a SEM photograph of the particles obtained in Example 8. FIG. 10 is a SEM photograph of the particles obtained in Comparative Example 1. FIG. 11 is a diagram showing STEM photographs of particles obtained in Comparative Examples 2 and 3. FIG. 12 is a diagram showing an STEM photograph of particles obtained in Comparative Example 4. FIG. 13 is a SEM photograph of the particles obtained in Comparative Example 5. FIG. 14 is a SEM photograph of the particles obtained in Comparative Example 6. FIG. 15 is a SEM photograph of particles obtained in Comparative Example 7. FIG. 16 is a SEM photograph of the particles obtained in Comparative Example 8. FIG. 17 is a SEM photograph of the particles obtained in Comparative Example 9. FIG. 18 is a SEM photograph of the particles obtained in Comparative Example 10. FIG. 19 is a SEM photograph of the particles obtained in Comparative Example 11. FIG. 20 is a SEM photograph of particles obtained in Comparative Example 12. FIG. 21 is a diagram showing a particle size distribution histogram of particles obtained in Example 1. FIG. 22 is a diagram showing a particle size distribution histogram of particles obtained in Example 2. FIG. 23 is a diagram showing a particle size distribution histogram of particles obtained in Example 3. FIG. 24 is a diagram showing a particle size distribution histogram of particles obtained in Example 4. FIG. 25 is a diagram showing a particle size distribution histogram of particles obtained in Example 5. FIG. 26 is a diagram showing a particle size distribution histogram of particles obtained in Example 6. FIG. 27 is a diagram showing a particle size distribution histogram of particles obtained in Example 7. FIG. 28 is a diagram showing a particle size distribution histogram of particles obtained in Example 8. FIG. 29 is a diagram showing a particle size distribution histogram of particles obtained in Comparative Example 1. FIG. 30 is a diagram showing particle size distribution histograms of particles obtained in Comparative Examples 2 and 3. FIG. 31 is a diagram showing a particle size distribution histogram of particles obtained in Comparative Example 4. FIG. 32 is a diagram showing a particle size distribution histogram of particles obtained in Comparative Example 11. FIG. 33 is a diagram showing a particle size distribution histogram of particles obtained in Comparative Example 12. FIG.

The present invention provides a method for producing silver nanoparticles by reacting a thermally decomposable silver compound (a) with an amine compound (b) that forms a complex, wherein the amine compound (i) has a linear structure, , (ii) having one amino group and one hydroxyl group at each end of the linear molecule, and (iii) one or more ether bonds in the linear structure. By using such a specific amino alcohol, it is possible to easily obtain silver nanoparticles with a wide distribution and a relatively large particle size, and in particular, it is easy to synthesize silver nanoparticles with a large particle size range of 200 to 500 nm. Also, it is environmentally friendly because the amount of amine compounds used can be reduced.
A detailed description will be given below.

<Description of materials in synthesis of silver nanoparticles>
[1. Description of silver compound (a)]
In the method for producing silver particles of the present invention, first, a thermally decomposable silver compound is used as a starting material. A thermally decomposable silver compound is a silver compound that forms a complex with the component (b) described later and thermally decomposes under heating conditions that can be carried out in 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 applied. Among these silver compounds, silver carbonate or silver oxalate (Ag ₂ C ₂ O ₄ ) is particularly preferred. Silver oxalate is more preferred. Silver oxalate can decompose at relatively low temperatures to produce silver particles without the need for reducing agents. In addition, since carbon dioxide generated by decomposition is released as gas, impurities do not remain in the solution.

[2. Complex-forming amine compound (b)]
Next, in the present invention, an amine compound capable of forming a complex with a silver compound is used as component (b). This compound has the function of forming a complex with a silver compound to lower the thermal decomposition temperature of the silver compound, thereby enabling the production of silver particles at a low temperature. At the same time, the organic group of the amine compound functions as a protective agent that imparts the effect of stabilizing the dispersion 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 a silver compound. In particular, the number of hydrogen atoms bonded to the amino group of the amine compound is preferably 1 or 2, that is, primary amine (RNH ₂ ) or secondary amine (R ₂ NH).

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 in the background art. Also in the present invention, aliphatic hydrocarbon amine compounds such as "aliphatic hydrocarbon monoamines" and "aliphatic hydrocarbon diamines" that have been used in known techniques may be used as amine compounds. Specific examples of "aliphatic hydrocarbon monoamine" and "aliphatic hydrocarbon diamine" include alkylamines, alkoxyamines, and alkyletheramines. Of these, alkylamines 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 that they will be discharged at a high temperature together with carbon dioxide gas during the decomposition reaction. is preferred. Specifically, they are alkoxyamines, alkyl ether amines and aminoalcohols.
According to studies by the present inventors, these oxygen-containing amine compounds not only suppress irritating odors, but the specific aminoalcohols described below in particular provide excellent physical properties for the obtained silver particles. found.

[2-1. Amino alcohol (b1) with large particle size and wide distribution effect]
Next, the present invention is characterized by using the following as the amine compound capable of forming a complex with the silver compound, which is the component (b). That is, (i) it has a linear structure, (ii) it has one amino group and one hydroxyl group at each end of the linear molecule, and (iii) it has one or more ether bonds in the linear structure. It is characterized by using an amino alcohol (b1) having These amine compounds have the function of lowering the thermal decomposition temperature of the silver compound by forming a complex with the silver compound, making it possible to produce silver particles at a low temperature. Furthermore, in the present invention, the particle size of the silver particles to be obtained can be easily made large and have a wide distribution. That is, by using the above component (b), unexpectedly, the silver nanoparticles obtained have a relatively large particle size and a wide particle size distribution. I did. Silver nanoparticles having a large particle size and a wide distribution have excellent effects as described later.

The class of the amino group of the amine compound (b1) is not limited, and any of primary amine, secondary amine and tertiary amine can be used, but primary or secondary amines are particularly preferred because they readily form complexes.
This amine compound (b1) has (i) a linear structure. Here, the term "straight-chain" means that the carbon atoms and heteroatoms constituting the amine compound are connected in a straight chain and have no branch. Both ends of this linear structure of carbon atoms and heteroatoms have (ii) an amino group and a hydroxyl group, respectively. It has (iii) one or more ether bonds in the linear structure. The number of ether bonds is not limited as long as it is one or more.
By having these characteristics (i) to (iii), it is considered that the excellent effects described above are obtained by the mechanism described later.

Although the number of carbon atoms in the aminoalcohol of component (b1) is not limited, it preferably has 4 or more carbon atoms. It usually has 4 to 7 carbon atoms. Within this range, the excellent effects described above are most excellent. That is, the resulting silver particles have a large particle size and a wide particle size distribution. Presumably, when the number of carbon atoms is 4 or more, the difference in excluded volume due to steric hindrance between the two coordination bond models in the mechanism described later becomes large, so it is speculated that the particles grow large and the particle size distribution widens. .

Examples of amino alcohols satisfying the above conditions include diglycolamine, 3-(3-aminopropoxy)propanol, and 2-[2-(3-aminopropoxy)ethoxy]ethanol. Diglycolamine is preferred. It does not have a strong irritating odor like conventional aliphatic hydrocarbon amine compounds, and is advantageous in terms of safety in handling. In addition, the above (b1) component may be used alone or in combination of two or more.

[2-1. (b1) Mechanism of Large Particle Size Silver Particle Generation by Addition of Component]
The mechanism by which silver nanoparticles having a large particle size and a wide distribution can be obtained by using the amine compound that forms a complex with the silver compound as the component (b1) described above is not completely clear. However, the present inventor presumes as follows.
A complex of an amine compound and a silver compound is formed by coordinating a lone pair of electrons of an amino group of the amine compound to a vacant orbital of a silver atom. Similar to the amino group, the hydroxyl group in the amine compound is also polar and negatively charged. Based on this property, the following model can be considered for the coordination bond state of the silver atoms of the specific aminoalcohol that is the component (b1). i) A model in which the amino group is coordinated to the silver atom and the alkyl chain is oriented linearly to the outside (dispersion medium side) (Fig. 1-1), ii) The amino group is coordinated to the silver atom, and the hydroxyl group and structure In this model (Fig. 1-2), the oxygen atoms of the ether-bonded portion in the middle are also brought closer to the silver atom side and stabilized. Due to the existence of these two coordination bond models, the steric hindrance caused by the amine compound around the silver atom is not uniform. For this reason, it is considered that the produced particle size varies, and a wide range of particle sizes from large to small are formed.

On the other hand, regarding alkylamines that have been conventionally used, only the amino group portion has electron-donating properties, so that the molecules are oriented only linearly, as shown in FIG. 1-3. Therefore, it is difficult for particles to vary. It is believed that this is the reason why only uniform silver particles can be synthesized.

[3. Amino alcohol (b2) that promotes complex formation]
In the present invention, an oxygen atom-containing amine compound, particularly an aminoalcohol having 3 to 4 carbon atoms (b2) can be used in combination with component (b1). Component (b2) is preferable because it can further increase the effect of increasing the particle size and widening the particle size distribution.
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, , in which 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 aminoalcohol, it is possible to easily obtain silver particles having a large particle size and a wide distribution.
Here, (i) "branched type" means that the skeleton composed of carbon atoms and heteroatoms is not linear but branched. (ii) The number is not limited as long as it has one amino group and one hydroxyl group, but usually one each is preferable. (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 consisting of a carbon atom and a heteroatom each have an amino group and hydroxyl groups are bonded.
By using the amino alcohol (b2) satisfying this condition, the complex reaction with the silver compound can be promoted and the particle size distribution is much larger than when the amine compound (b1) is used alone. wide grains can be obtained.

Examples of amino alcohols having 4 or less carbon atoms satisfying the above conditions include 1-amino-2-butanol, DL-1-amino-2-propanol, and 2-amino-, as amino alcohols satisfying (i) to (iii). 2-methyl-1-propanol (hereinafter referred to as AMP) and DL-2-amino-1-propanol. In addition, N-methylethanolamine can be mentioned as an aminoalcohol that satisfies (iv).

Among these, AMP, 1-amino-2-butanol, DL-1-amino-2-propanol, and DL-2-amino-1-propanol, which are amino alcohols satisfying (i) to (iii), are particularly It is most preferable because it is easy to handle, complex formation easily occurs in the presence of a polar solvent such as an alcohol solvent, and silver particles having a large particle size and a wide particle size distribution can be easily obtained. Among these, AMP is particularly excellent because it has the highest effect.
In addition, the above (b2) component may be used alone or in combination of two or more.

[4. Amine compound (b3) having a dispersion stabilizing effect due to steric hindrance]
In the present invention, an amine compound other than the components (b1) and (b2) described above can be present during the complex formation of (a) and (b).
This component has a function of imparting an effect of stabilizing the dispersion of silver particles by a steric hindrance effect.
As the amine compounds other than the components (b1) and (b2), those having a molecular length of 5 Å or more are particularly preferred. That is, the amine compound has a molecular length of 5 Å or more and does not meet the above requirements (b1) and (b2).
Here, the molecular length is the longest distance between two atoms that do not contain a hydrogen atom. The length of this molecule can be obtained by calculation. The calculation conditions are density functional theory, function ωB97X-D, basis function 6-31+G*, environment in vacuum, energy state ground state, and can be calculated with various molecular calculation software such as SPARTAN`16V1,1,0.
The molecular length is preferably greater than or equal to 7 Å. However, if it is too long, the boiling point becomes high and it becomes difficult to remove, so the thickness is preferably 8 Å or less.

In particular, an amine compound having a main chain (main skeleton) composed of 7 or more atoms including an amino group is preferred.
Among them, those in which the atoms constituting the amine compound are N, C and H, or those in which N, C, H and O are preferred.
Although the number of hydrocarbon groups bonded to the amino group of the amine compound is not limited, one or two primary amines or secondary amines are preferable because they are particularly easy to coordinate with silver.
Examples of such component (b3) include aliphatic hydrocarbon monoamines having 4 or more carbon atoms in total.

Aliphatic hydrocarbon monoamines having 4 or more carbon atoms are often used in the method of forming silver nanoparticles by forming a complex with a silver compound as described in the prior art. However, aliphatic hydrocarbon monoamines having 4 or more carbon atoms have a strong irritating odor, and there is a risk that they will be discharged at high temperature together with carbon dioxide gas during the decomposition reaction, so other amine compounds may be used. Specifically, amine compounds containing oxygen atoms (alkoxyamines, alkyl ether amines, amino alcohols) having 4 or more carbon atoms and containing (i) to (iii) or (iv) described above as component (b2) It does not correspond to

Specific examples of the above component (b3) include alkylamines such as n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine and 2-ethylhexylamine. Alkoxyamines include 3-methoxypropylamine, 3-ethoxypropylamine and the like. Examples of alkyl ether amine include JEFFAMINE M series, M-600, M-1000, M-2005, M-2070 manufactured by HUNTSMAN. Amino alcohols include 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol and the like.

More preferred examples of alkylamine include n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, 2-ethylhexylamine and the like. Alkoxyamines include 3-methoxypropylamine, 3-ethoxypropylamine and the like. Amino alcohols include 5-amino-1-pentanol, 6-amino-1-hexanol and the like.
The above component (b3) can be used singly or in combination of two or more.

(3-1. Molar ratio in amine compound (b2)/(b))
(b2)/(b) is preferably 0.3 to 0.8 (molar ratio), preferably 0.4 to 0.8. This range is most suitable for producing silver nanoparticles with large size and high distribution. If the molar ratio is less than 0.3, the amount of the amine compound having a long molecular length increases, and the particles tend to be small overall and the particle size distribution tends to be narrow, which is not preferred. On the other hand, if the molar ratio is more than 0.8, the steric hindrance effect as a protective agent is weakened, increasing the risk of fusion of silver particles during synthesis.

(3-2. Ratio and amount of addition of amine compound (b) and silver oxalate (a))
Regarding the mixing amount of the silver atoms of the silver compound and the amine compound (b), the molar ratio (amine compound/silver atoms of the silver compound) is 0.7 to 2.0. It is desirable to adjust the amount. By doing so, variation in particle size is generated, and it is easy to obtain silver particles having a desired particle size range. More preferably 0.7 to 1.5, still more preferably 0.7 to 1.3, and most preferably 0.7 to 1.3.

In the various conventional synthesis methods described above (Patent Documents 1 to 8), the molar ratio of silver atoms in the amine compound/silver compound is 2.0 or more. In contrast, in the present invention, silver particles can be obtained with a smaller amount of amine, so the amount of amine discharged can be reduced. Therefore, it is possible to reduce the risk to the human body and the environment caused by the release of the amine to the outside of the system. At the same time, the conventional method tends to synthesize silver particles with a small particle size and a narrow distribution, whereas in the present invention, silver particles with a wide 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, if the molar ratio is less than 0.7, flat particles are likely to be formed and aggregate, resulting in low dispersion stability of the silver coating composition.

[4. Description of organic solvent (c)]
In the present invention, the complex formation reaction between the silver compound and the amine compound described above is desirably carried out in the presence of an organic solvent.
Controlling the polarity of these organic solvents is one of the factors that can control the particle size of the silver nanoparticles. For example, by lowering the polarity of the solvent, the amine compound (b) or (d) is more likely to approach the silver atom side, so the size of the synthesized silver nanoparticles tends to be smaller. In the present invention, solvents having a polar functional group are preferred, and specifically, alcohol solvents, ketone solvents, aldehyde solvents, amide solvents, ester solvents, and nitrile solvents are preferred. Alcohol solvents are particularly preferred, and alcohols having 3 to 12 carbon atoms are particularly preferred. For example, n-propanol (boiling point bp: 97°C), isopropanol (bp: 82°C), n-butanol (bp: 117°C), isobutanol (bp: 107.89°C), sec-butanol (bp: 99.0°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.
Among these, n-butanol, n-hexanol, and n-decanol are preferable in consideration of the fact that the temperature of the thermal decomposition step of the complex compound that is performed later can be increased and the convenience of post-treatment after the formation of silver nanoparticles is taken into account. . These may be used alone, or two or more of them may be mixed and used.

(4-1. Regarding the amount of organic solvent added)
In order to sufficiently stir each component, the organic solvent should be 80 to 130 parts by weight with respect to 100 parts by weight of the silver compound (a) (that is, the weight ratio of the organic solvent (c) to the silver compound (a) It is preferable to mix an organic solvent such that (c)/(a)) is 0.8 to 1.3. More preferably, it is 80 to 125 parts by weight per 100 parts by weight of the silver compound.

(4-2. Method for adding organic solvent)
In the present invention, the complex formation reaction between the amine compound (b) or (d) and the silver compound (a) can be carried out in the presence of an organic solvent in several ways.
For example, a solid silver compound and an organic solvent, especially an alcohol solvent are mixed to obtain a silver compound-alcohol slurry, and then the amine compound (b) or (d) is added to the obtained silver compound-alcohol slurry. You may In the present invention, the slurry represents 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, it is preferable to charge a reaction vessel with a solid silver compound and then add an organic solvent or a mixture of an organic solvent and an amine compound to obtain a slurry.

Alternatively, a mixed solution of an organic solvent and an amine compound may be charged into a reaction vessel and a silver compound added thereto.
Silver oxalate has been reported to be explosive in a dry state. Therefore, when silver oxalate is used as a silver compound, it is preferable to use it in a wet state. This is because the wet state significantly lowers the explosiveness and facilitates handling. Therefore, water or the above-described organic solvent may be mixed and used in a wet state.

[5. About aliphatic carboxylic acid]
Also, an aliphatic carboxylic acid may be used during complex formation to adjust the particle size and particle size distribution. Addition of an aliphatic carboxylic acid tends to reduce the particle size and narrow the particle size distribution. It is desirable to adjust the amount of water and use it appropriately. The above-mentioned aliphatic carboxylic acid is preferably used together with the above-mentioned amines, and can also be used by adding when mixing the silver compound and the amine. A saturated or unsaturated aliphatic carboxylic acid is used as the aliphatic carboxylic acid. 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 these, saturated or unsaturated aliphatic monocarboxylic acids having 8 to 18 carbon atoms are preferred. By setting the number of carbon atoms to 8 or more, it is possible to secure a space between the carboxylic acid group and other silver particles when the carboxylic acid group is adsorbed on the surface of the silver particles, thereby improving the effect of preventing aggregation of the silver particles. Saturated or unsaturated aliphatic monocarboxylic acid compounds having up to 18 carbon atoms are generally preferred in consideration of availability, ease of removal during firing, and the like. In particular, octanoic acid, oleic acid and the like are preferably used. Among the aliphatic carboxylic acids, only one type may be used, or two or more types may be used in combination.

(5-2. Addition amount of aliphatic carboxylic acid)
When the aliphatic carboxylic acid is used, it is preferably used in an amount of, for example, about 0.05 to 10 mol, preferably 0.1 to 5 mol, more preferably 0.1 to 5 mol, per 1 mol of the silver atom of the raw silver compound. It is preferable to use 0.5 to 2 mol. If the amount of the aliphatic carboxylic acid is less than 0.05 mol with respect to 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 size may be too small and may remain even in the washing or surface protective agent replacement step, so low-temperature firing is necessary. of the aliphatic carboxylic acid becomes difficult to remove. However, the aliphatic carboxylic acid may not be used.

[6. Description of water/moisture content]
In the present invention, water may be used together with the amine compound as component (b1). The water content of the reaction system is preferably in the range of 5 to 20 parts by weight per 100 parts by weight of the silver compound. Particularly preferably, it is 15 parts by weight or less. Regarding the water content, it depends on the type of amine compound used for complex formation. It may be difficult to achieve the desired effect. On the other hand, if the water content exceeds 20 parts by weight with respect to the silver compound, the silver particles become too coarse, and there are portions where the particles are sintered and coalesced, which is not preferable. As for the water to be used, ion-exchanged water with reduced metal ion impurities is preferable. The timing of adding water may be before the heating step, and may be added at any stage before or after the formation of the silver-amine complex.
As for the ratio between the organic solvent (c) and water, the water/organic solvent weight ratio is preferably 0.03 to 0.3. It is more preferably 0.1 to 0.25. Within this range, it is particularly easy to obtain the effects of the present invention.

(6-1. Mechanism of high-distribution silver grain generation in addition of water)
The presence of water during the reaction of forming silver particles by thermal decomposition, which will be described later, particularly causes variation in the particle size of the formed silver nanoparticles, resulting in highly distributed silver particles. The mechanism is partly unknown, but when water approaches silver compounds, especially silver oxalate, and forms a silver amine complex or thermally decomposes, it inhibits the adsorption of amine compounds to silver atoms. It is considered that grain growth occurs in the portion where the grains are formed. Furthermore, since the amount of water molecules adsorbed on silver oxalate is also biased (localized), it is considered that the particle size is moderately varied. A suitable amount for this is 5 parts by weight or more per 100 parts by weight of the silver compound. Conversely, if more than 20 parts by weight of water is added to 100 parts by weight of the silver compound, the silver particles themselves become enlarged and may sinter and coalesce with neighboring particles. This is presumed to be due to the fact that water inhibits the adsorption of silver atoms by amines, resulting in enlargement of silver particles.

<Method for producing silver nanoparticles>
[7. Mixing of liquid raw materials]
In the present invention, the complex-forming amine compound (b) is usually put into the polar solvent (c) and mixed. If necessary, an aliphatic carboxylic acid and water can be added and mixed to prepare liquid raw materials necessary for the reaction.
If there is a liquid raw material that is solid at room temperature, it can be mixed by appropriately heating it. The heating temperature is preferably 100° C. or lower, preferably 80° C. or lower, more preferably 60° C. or lower, so that the liquid raw material is desirably liquefied. If the temperature is higher than the above temperature range, when it is mixed with a silver compound to form a slurry, a partial complexation/oxalic acid decomposition reaction starts first, and silver nanoparticles are formed without ensuring uniformity in the system. may be generated.

[8. Preparation of silver compound slurry]
The silver compound (a) and the liquid raw material are mixed to prepare a silver compound slurry. Alternatively, the polar solvent and the silver compound (a) alone 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 is preferably carried out while stirring at room temperature, or while stirring after appropriately cooling to room temperature or lower since the coordination reaction (complexing reaction) of the silver compound with amines is accompanied by heat generation. Since the mixed liquid of the silver compound and the amine compound or the like is prepared in the presence of a polar solvent, it can be well stirred and cooled. A polar solvent and an excess of amine compound act as the reaction medium.

In addition, the odor of highly volatile alkylamine has a large adverse effect on the working environment. Reduces odor and worker exposure when preparing

[9. About silver amine complex]
Since the resulting complex compound generally exhibits a color corresponding to its constituent components, the progress of the reaction for producing the complex compound can be detected from the change in the color of the reaction mixture. In addition, when it is difficult to confirm by a change in color, the state of production can be detected by a change in the viscosity of the reaction mixture, a change in temperature, or the like. Thus, a silver amine complex is obtained in a medium based on a polar solvent and an amine compound.

[10. Explanation of temperature rise rate conditions from complexation to decomposition reaction]
In the heating step of the reaction system, the heating rate affects the grain size of the precipitated silver particles, so the grain 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 process in the range of 3.0 to 50° C./min up to the set decomposition temperature. The slower the heating time, the easier it is for particle growth to occur and the larger the particle size to be formed. I don't like it.

[11. Regarding the washing process of silver particles]
The thermal decomposition of the silver compound results in a suspension that varies in color depending on the particle size of the particles obtained, but ranges from dark brown to gray. Removal of polar solvents and excess amine compounds from this suspension, for example, precipitation of silver nanoparticles, decantation and washing with an appropriate solvent (water or organic solvent), to achieve the desired protection Silver nanoparticles to which an amine compound is bound as an agent are obtained.

[12. Explanation of washing solvent]
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 for washing the silver particles. As a detailed washing method, it is preferable to add a solvent to the solution after silver particle synthesis, stir until the mixture is suspended, and then remove the supernatant liquid by decantation. The amount of amine removed can be controlled by the volume of solvent added and the number of washings. When the series of operations described above is performed once, preferably, the solvent is used in a volume that is 1/20 to 3 times the volume of the solution after synthesis of the silver particles, and the washing is performed 1 to 5 times.

[13. Protective agent replacement step]
Furthermore, the above silver nanoparticles are optionally substituted with an amine compound suitable for the application by a step of substituting a surface protective agent with an amine compound having 4 or more carbon atoms (including an oxygen atom). may The amine compound to be finally substituted may be the one used when producing the silver nanoparticles, or may be a new one that has not been used. By stirring and suspending the washed silver particles in the amine compound to be finally replaced for a certain period of time, the surface protective agent of the silver particles is replaced. At that time, 50 to 100 wt % of the amine compound to be finally substituted is added to the contained pure silver, and the mixture is 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 the difference in peaks derived from sintering in DTA measurement, headspace GC/MS, and the like. After the step of replacing the surface protective agent described above, the desired silver particles are obtained through the washing step again.

The amine compound used here is an alkylamine having 4 to 8 carbon atoms or an amine compound containing an oxygen atom (alkoxyamine, alkyletheramine, aminoalcohol). Among them, those with a molecular length of 5 to 8 Å are preferred, and those with a molecular length of 7 to 8 Å are more preferred. The alkylamine and the amine compound containing an oxygen atom can be used singly or in combination of two or more. Depending on the composition, it is possible to adjust the viscosity when processed into a paste.

[14. State of generated silver particles (protective agent, particle size distribution)]
In this way, silver nanoparticles are formed to which the amine compound used is bound as a protective agent. Silver nanoparticles refer to fine particles mainly composed of a silver component and usually having a particle size of 1 to 1000 nm, which can be produced by the following method.

The protective agent, for example, contains the specific amino alcohol (b) having 4 or less carbon atoms, further contains an amine compound (d) having a molecular length of 5 Å or more, and when used, the aliphatic carboxylic acid Contains acid. Their content in the protective agent is the same as their use in the amine mixture. In addition, it is possible to adjust the type and total amount of the protective agent by the washing step and, if necessary, the protective agent replacement step. The length of the molecule of the amine compound finally bound as a protective agent is preferably 2 to 8 Å, more preferably 5 to 8 Å. And 7-8 Å is most preferred. On the other hand, the total amount of protective agent is preferably 0.3 to 2.0 parts by weight per 100 parts by weight of pure silver. Furthermore, it is more preferable if it is 0.5 to 1.0 parts by weight.

The silver nanoparticles of the present invention usually have a particle size of 1000 nm or less.
Also, the average particle size is 70 to 350 nm, preferably 70 to 300 nm, more preferably 80 to 200 nm.
The coefficient of variation that indicates the variation in particle size is 30 to 80%, preferably 40 to 70%, more preferably 50 to 60%.

The average particle size and coefficient of variation are determined as follows. The particle shape of the obtained silver nanoparticles is observed by FE-SEM. After that, using image analysis software SCANDIUM (manufactured by OLYMPUS), the particle diameters of 300 or more particles were measured, and the average particle diameter and standard deviation values were obtained by analysis. Using these values, the coefficient of variation was calculated based on the following formula.
Variation coefficient (%) = {standard deviation (nm) / average particle size (nm)} x 100
The equipment for particle size measurement is not limited as long as it can obtain results equivalent to those of the above method.

By having the above average particle size and distribution (variation), the film 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. In addition to being thick, the volume resistivity of the resulting film can also be low. Specifically, it is possible to obtain a volume resistivity of about 20 to 30 μΩ·cm with a thick film of 20 μm or more. This is because the particle size distribution is wide, and the small particles are packed close together between the large particles, so that the silver particles are highly packed and a film with a high silver particle content is obtained. It is speculated that

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, making it difficult to reduce the volume resistivity of the resulting coating film. On the other hand, if the average particle size exceeds 350 nm, the phenomenon of melting point depression of the silver nanoparticles becomes weak, making it difficult to sinter at low temperatures.
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, making it difficult to lower the volume resistivity of the coating film. 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, so in this case also it becomes difficult to fill the voids between the particles, and in this case also the volume resistivity of the coating film is reduced. difficult to lower.

For this reason, it is preferable to use silver particles having the above average particle size and variation. By using the present invention, such silver particles can be easily obtained. can be adjusted.
The viscosity of the screen printing ink is preferably in the range of 0.1 to 500 Pa·s (at a shear rate of 5 1/sec). If the viscosity is too high, there will be no fluidity and printing defects will tend to occur. Therefore, in order to increase the viscosity, an organic binder is usually added, but the organic binder increases the resistance value of the resulting coating film. On the other hand, the silver particles of the present invention can have a relatively high viscosity even when 1 wt % of Ethocel 45 (manufactured by Nisshin Kasei Co., Ltd.) is added as an organic binder to the pure silver content. By adjusting the viscosity to about 80 nm and the coefficient of variation to 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 wt % or less with respect to the pure silver content, the above viscosity suitable for screen printing can be obtained. In this way, since the viscosity can be controlled by adjusting the particle size, the degree of freedom in the amount of the organic binder to be added is increased, and the amount can be reduced, which is very excellent.

In the production method of the present invention, as described above, the particle size can be controlled by adjusting the type of amine used, the type of organic solvent, the amount of water added, and the like. Therefore, it is suitable for industrial production such that silver particles in the large particle size range of 200 to 500 nm and silver particles in the small particle size range of 50 to 200 nm can be synthesized in one batch.

The silver particles obtained in this way contain silver particles in a large particle size range of 200 nm or more. It is expected to be easy to produce a silver nanoparticle dispersion/silver coating composition without impairing the properties of the original silver particles. This is also effective when considering scale-up.

<Application>
[15. Silver nanoparticle dispersion, silver paint composition, and method for producing the same]
Silver nanoparticles obtained by the method described above can be used to prepare a silver nanoparticle dispersion. 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. For example, a silver nanoparticle dispersion can be obtained by dispersing silver nanoparticles in a suitable organic solvent (dispersion medium) in a suspended state.
Since the silver nanoparticles obtained in the present invention are excellent in dispersibility, they can be stably present in the dispersion medium at a high concentration. For example, the content of silver nanoparticles in the composition can be as high as 70 to 95% by weight, more preferably 75 to 80% by weight, and can be in a so-called paste state.
Furthermore, in addition to silver nanoparticles and a dispersion medium, a silver paint composition containing a so-called binder component can be produced. By containing silver nanoparticles at a high concentration of 70 to 95% by weight, more preferably 75 to 80% by weight, it is possible to obtain a silver coating composition that has good printability and that facilitates the production of a thick conductive film. can.

(15-1. Dispersion medium for dispersion or coating composition)
Various organic solvents such as aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, and tetradecane can be used as dispersion media for obtaining silver nanoparticle dispersions or silver coating compositions. cyclohexane, alicyclic hydrocarbon solvents such as methylcyclohexane; aromatic hydrocarbon solvents such as toluene, xylene, mesitylene, etc.; methanol, ethanol, propanol, n-butanol, n-pentanol, n-hexanol, n- Alcohol solvents such as heptanol, n-octanol, n-nonanol, n-decanol, n-dodecanol and the like are included.

Among these organic solvents, organic solvents having a boiling point of 280° C. or less having 8 to 16 carbon atoms and having an oxygen atom in the structure are particularly preferable. This is because when the target sintering temperature of the silver particles is set to 150° C. or lower, it is difficult to volatilize and remove a solvent having a boiling point exceeding 280° C. Preferred specific examples of this solvent include terpineol (C10, boiling point 219°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). A plurality of solvents may be mixed and used, or may be used singly.
Depending on the desired concentration and viscosity of the silver coating composition or silver nanoparticle dispersion, the type and amount of the organic solvent may be appropriately determined.

(15-2. Description of the organic binder of the coating composition)
An organic binder may be added to the silver coating composition for the purpose of assisting dispersibility of the silver particles or imparting adhesion to the substrate. The amount of the organic binder to be added is preferably 0.1 to 10 parts by weight per 100 parts by weight of silver contained.
The presence form of the binder resin in the conductive ink may be dissolved in a solvent, an emulsion, or a suspension. The binder resin is not particularly limited, but examples include polyester resins, polyurethane resins, polyamide resins, polyvinyl chloride resins, polyacrylamide resins, polyether resins, acrylic resins, melamine resins, vinyl resins, phenol resins, epoxy resins, and urea. Resin, vinyl acetate resin, polybutadiene resin, vinyl chloride vinyl acetate copolymer resin, fluorine resin, 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, polyvinylbutyral, polyvinylpyrrolidone and the like can be mentioned.
The binder resin to be used may be used individually by 1 type, and may be used in combination of 2 or more types.

[16. Printing method and usage with silver paint composition)]
It is common to apply the prepared silver paint composition onto a substrate and then bake it.
Applications include 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, and microcontact printing. It can be carried out by a known method such as. Using a printing technique yields a patterned silver coating composition layer and firing yields a patterned silver conductive layer. In addition, this silver conductive layer can be applied as a bonding material having excellent electrical and thermal conductivity, and is also useful as a bonding material for electrical equipment that handles large currents such as power devices.

Firing can be performed at a temperature of 200° C. or lower, for example room temperature (25° C.) or higher and 150° C. or lower, preferably room temperature (25° C.) or higher and 120° C. or lower. However, in order to complete the sintering of silver by firing in a short time, the temperature should be 60° C. or higher and 200° C. or lower, for example, 80° C. or higher and 150° C. or lower, preferably 90° C. or higher and 120° C. or lower. The firing time may be appropriately determined in consideration of the amount of silver ink applied, the firing temperature, etc. For example, within several hours (eg, 3 hours or 2 hours), preferably within 1 hour, more preferably within 30 minutes. do it.
Since the silver nanoparticles are configured as described above, sintering of the silver particles proceeds sufficiently even in such a low-temperature, short-time firing step. As a result, even if the average particle size exceeds 200 nm, excellent conductivity (low resistance) is exhibited. A silver conductive layer having a low resistance value (eg, 20-30 μΩ·cm) is formed. The resistivity of bulk silver is 1.6 μΩcm.

[17. Applications of Silver Nanoparticle Dispersion and Silver Paint Composition]
Since it can be baked at a low temperature, it can be used as a substrate, in addition to glass substrates and heat-resistant plastic substrates such as polyimide films, as well as polyester substrates such as polyethylene terephthalate (PET) film and polyethylene naphthalate (PEN) film. General-purpose plastic substrates with low heat resistance, such as films and polyolefin films such as polypropylene, can also be suitably used. In addition, the short-time baking reduces the load on these general-purpose plastic substrates with low heat resistance and improves production efficiency.

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

The silver conductive material obtained from the silver nanoparticle dispersion or silver coating composition of the present invention is used as an electromagnetic wave control material, circuit board, antenna, heat sink, liquid crystal display, organic EL display, field emission display (FED), IC card, It can be applied to IC tags, solar cells, LED elements, organic transistors, capacitors, electronic paper, flexible batteries, flexible sensors, membrane switches, touch panels, EMI shields, etc.

EXAMPLES The present invention will now be described in more detail with reference to examples and comparative examples.
The characteristics such as names and structural formulas of the amine compounds used in Examples and Comparative Examples are shown in Tables 1 and 2.

[Example 1]
(Production of silver particles)
7.58 g (24.95 mmol) of dried silver oxalate as a silver compound and 9.21 g (90.14 mmol) of n-hexanol as a polar solvent were stirred in a test tube set in an aluminum block heating stirrer. to wet the silver oxalate. After that, 2.11 g (28.09 mmol) of DL-1-amino-2-propanol and 0.30 g (1.06 mmol) of oleic acid were added. After that, the mixture was stirred for 1 hour to produce a silver-amine complex. After that, the mixture was heated at a temperature increase rate of 3°C/min, and at 100°C, generation of carbon dioxide, which was thought to have occurred due to a decomposition reaction of silver oxalate, was confirmed. Heating was continued until the evolution of carbon dioxide ceased to obtain a liquid in which silver particles were suspended. After the silver particles were precipitated, 20 cc of methanol was added to the reaction solution for washing, followed by centrifugation. This washing and centrifugation was performed three times. Thus, silver nanoparticles were obtained.

(Confirmation of particle size)
The resulting methanol-wet silver nanoparticles were suspended in n-hexanol using a vortex mixer, the liquid was dropped onto a support such as a collodion membrane, and the solvent was dried to obtain a sample. In FE-SEM observation, the sample is observed and photographed at a magnification of 20,000 to 70,000, and an image with a magnification in which 400 or more particles are present is selected. After that, the particle shape was observed by FE-SEM. After that, using image analysis software SCANDIUM (manufactured by OLYMPUS), 400 or more particles were counted, and particle size measurement, average particle size, particle size distribution, etc. were analyzed. When particles have a long diameter and other diameters, the length of the particle diameter was measured by measuring the long diameter.
Table 5 shows the ratio (%) of particles of 100 to 200 nm, the average particle size (nm), and the coefficient of variation (%). An FE-SEM photograph is shown in FIG. A particle size distribution histogram is shown in FIG.

(Silver nanoparticle paste, ink preparation and firing)
Next, Texanol as a solvent was added to the collected silver nanoparticles so that the silver content was 75 wt %, and mixed. Furthermore, Ethocel 45 (manufactured by Nisshin Kasei Co., Ltd.) was added as an organic binder so that the amount added was 1 wt % with respect to the silver particles, and finally a silver nanoparticle paste ink with a silver content of about 70 wt % was produced. This paste was cast on a slide glass and heated at 150° C. for 1 hour in a blower dryer. The coating thickness after drying was adjusted to 10 to 30 μm.
The surface resistance value of the obtained coating film was measured by a four-probe method, and the volume resistivity was obtained by multiplying the thickness of the obtained coating film.
The volume resistivity values are shown in Table-4.

[Examples 2 to 8, Comparative Examples 1 to 12]
(Production of silver particles)
Instead of using the materials and mixing ratios shown in Tables-5 to 12, replacing the temperature rise rate after the generation of the silver-amine complex compound with those shown in Tables-5 to 12, and changing the reaction vessel/heating device to those shown in Tables-5 to 5 Silver particles were produced in the same manner as in Example 1 (production of silver particles), except that the material shown in No. 13 was used.
As shown in Table-7, Example 8 was subjected to (protective agent replacement treatment) described later. The protective agent replacement process is shown below. In order to replace the amine compound in the silver nanoparticles obtained by oxalic acid decomposition reaction of silver oxalate with n-hexylamine, 71.8 wt% n-hexyl relative to the pure silver content of the silver nanoparticles obtained The amine and silver nanoparticles were stirred at room temperature for 1 hour, and washing and centrifugation were repeated three times in the same manner as above to obtain silver nanoparticles using hexylamine as a protective agent.

The obtained silver particles were checked in the same manner as in Example 1 (confirmation of particle size). For Comparative Examples 2 to 4, the particle size was confirmed by STEM images.
In addition, for Examples 2 to 8 and Comparative Examples 1, 2, 11, and 12, the obtained particles were used in the same manner as in Example 1 (silver nanoparticle paste, ink preparation and firing). .
In Example 8, the particles before the protective agent replacement treatment and the particles after the protective agent replacement treatment were used (silver nanoparticle paste, ink preparation and firing).
Further, for Comparative Examples 3 and 4, 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 was applied onto glass by spin coating.

For Examples 2 to 8 and Comparative Examples 1 to 4, 11, and 12, the average particle size (nm), coefficient of variation (%), and particle ratio (%) in each particle size range of the obtained particles are shown. 5-12. SEM or STEM images are shown in Figures 2-20. Particle size distribution histograms of Examples 2-8 and Comparative Examples 1-4, 11 and 12 are shown in FIGS. Tables 5 to 12 show the values of volume resistivity and film thickness of the sintered coating films for Examples 1 to 10 and Comparative Examples 1 to 4.

As described above, according to the present invention, a sintered coating film having a thickness of 20 μm or more can be formed by adding the amine compound as the component (b) during complex formation and using the synthesized silver particles. It was confirmed that the volume resistivity of the coating film was 50 μΩ·cm or less under the baking conditions at 9° C., and that a conductive film was obtained.

In Examples 1 to 3, diglycolamine and the amine compound (b2) are used in combination. Among them, in Example 3, when AMP was used, the coefficient of variation was large and the variation was large, the proportion of particles with small particle diameters was also high, and a sintered film with the lowest volume resistivity was obtained at each sintering temperature.
In Examples 3 and 4, the amount of diglycolamine added was increased or decreased. Moreover, although the average particle diameter increased, the volume resistivity of the sintered coating film at each firing temperature remained almost unchanged.

In Examples 4 to 6, the amine and the short-chain alkylamine or alkyldiamine as the component (b2) were used. A large particle size could be formed. Among them, in Example 4 using AMP, particles with the largest coefficient of variation and dispersion were obtained.
In Examples 7 and 8, AMP and diglycolamine were used, and in Example 8, water was used in combination. As a result, a larger particle size was achieved. Moreover, even when the particle size was increased, the volume resistivity of the sintered coating film at each temperature did not decrease. In Example 8, the volume resistivity of the sintered coating film before and after the hexylamine replacement treatment was evaluated, and the performance was almost the same. Since the polarity of the protective group can be changed, it was possible to synthesize particles with a wide range of dispersibility in various solvents.

In Comparative Example 1, the silver particles were obtained without using diglycolamine or the amine compound of component (b2). of particles were formed. As a result, a thick sintered film having a thickness of about 20 μm resulted in a large increase in the resistance value. Since a small particle size requires a large amount of the protective agent component, it is considered that the protective agent remained in the thick film and became a resistance component.

In addition, in Comparative Example 2 in which the particles of Comparative Examples 2 to 4 were produced by the same method as the production methods of Patent Documents 1 and 2 and were evaluated as Texanol paste, volume shrinkage occurred violently after firing, and cracks occurred throughout the coating film. has occurred. In addition, in Comparative Examples 3 and 4 in which a low-viscosity dispersion state was applied as in Patent Documents 1 and 2, a sintered coating film having a thickness of about 0.5 μm was formed, making it difficult to increase the film thickness.

In Comparative Examples 5 to 10, amine compounds having structures similar to diglycolamine were evaluated. First, in Comparative Examples 5 and 6, 1,5-diaminopentane having an amino group at the terminal end, and in Comparative Example 7, having an amino group and a hydroxyl group at the terminal end and a 2-[ (3-aminopropyl)amino]ethanol, in Comparative Examples 8 and 9, 6-aminohexanoic acid having an amino group and a carboxylic acid at the terminal end, in Comparative Example 10, having an amino group at the terminal end, in the structure 2,2-oxybis(ethylamine) having an ether bond was used. However, no matter which amine compound was used, particles agglomerated during synthesis, and silver particles in a dispersible state could not be obtained. If there are two or more amino groups or carboxylic acids in the molecule, which are strongly adsorbed to the silver particles, they are adsorbed between the particles, which is considered to cause agglomeration. Although the hydroxyl group does not completely adsorb to the silver particles, it has a moderate polarity enough to approach the silver particles. It is thought that the action as a protective agent that can be synthesized without aggregating silver particles can be exhibited.

However, although the aminoalcohol having a molecular length of 5 Å or more, which is not the component (b1), has a performance as a protective agent, as shown in Comparative Examples 11 and 12, the effect of growing silver particles into large particles is not. I think it's extremely low. Presumably, linear coordination, similar to alkylamines, predominates. Since there is no ether bond in the molecule, it is considered that it is difficult to take O-atom-close type coordination only with a hydroxyl group at one end.
As can be seen from the above results, the silver nanoparticles of the present invention easily form particles having an average particle diameter of 200 nm or more by the method of the present invention by using the amine compound, particularly diglycolamine, as component (b1). Thus, it can be seen that it is possible to produce a silver coating composition that facilitates obtaining a thick conductive film with a low resistance by giving an appropriate variation to the particle size distribution.

According to the present invention, a silver conductive layer having a large particle size, a wide distribution, a large thickness, and high conductivity can be easily formed by a method in which the amount of amines with a strong irritating odor is suppressed. Nanoparticles can be obtained.

Claims (9)

A thermally decomposable silver compound (a) and an amine compound (b) capable of forming a complex with (a) are reacted in an organic solvent (c) to form a complex, and the resulting complex is heated. A method for producing silver nanoparticles that forms silver nanoparticles by thermal decomposition, wherein (b) is a linear amino alcohol, and both ends of the linear molecule have an amino group and a hydroxyl group. and an amino alcohol (b1) having an ether bond in the linear molecular structure, wherein the organic solvent (c) has a carbon number of A method for producing silver nanoparticles, characterized in that the alcohol is 3 to 12 . 2. The method for producing silver nanoparticles according to claim 1, wherein (b1) is diglycolamine. 3. The method for producing silver nanoparticles according to claim 1, wherein (a) is silver oxalate. 4. The method according to any one of claims 1 to 3 , wherein 5 to 20 parts by weight of water is present with respect to 100 parts by weight of the silver compound (a) during the complex formation reaction between (a) and (b). method for producing silver nanoparticles. 5. The method for producing silver nanoparticles according to claim 4 , wherein the molar ratio of (b)/[silver atoms contained in (a)] is 0.7 to 2.0. The method for producing silver nanoparticles according to any one of claims 1 to 5, 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 6 and dispersing the obtained silver nanoparticles in an organic solvent. A silver coating composition characterized by producing silver nanoparticles by the method according to any one of claims 1 to 7 , dispersing the obtained silver nanoparticles in an organic solvent, and adding an organic binder. Production method. The silver nanoparticle dispersion obtained by the method according to claim 7 or the silver coating composition obtained by the method according to claim 8 is coated on a substrate and baked to form a silver conductive layer. A method for manufacturing a conductive material.

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