WO2018198810A1 - Method for producing silver nanoparticles having broad particle size distribution, and silver nanoparticles - Google Patents

Abstract

[Problem] To provide a method for producing silver nanoparticles having good physical properties, whereby it becomes possible to reduce the discharge amount of an amine having a very irritating odor. [Solution] A method for producing silver nanoparticles, comprising reacting a silver compound (a) having thermal degradability with an amine compound (b) capable of forming a complex with the component (a) to form a complex and then thermally degrading the complex by heating to form the silver nanoparticles, said method being characterized in that the component (b) is an amino alcohol having 6 or less carbon atoms and also having one primary or secondary amino group and one hydroxyl group. Silver nanoparticles having an average particle diameter of 350 nm or less and a coefficient of variation of 40 to 80%, wherein an amino alcohol having 6 or less carbon atoms and also having one primary or secondary amino group and one hydroxyl group is bonded to the surface of each of the silver particles.

Description

Method for producing silver nanoparticles having wide particle size distribution and silver nanoparticles

The present invention relates to a method for producing silver particles having a relatively large particle size and a wide particle size distribution, silver nanoparticles, and a silver compound-containing composition suitable for producing silver nanoparticles, which can be easily adjusted to a viscosity region suitable for screen printing. About.

Silver nanoparticles are sintered at low temperatures due to the melting point lowering properties of metal nanoparticles, and are therefore used as electrical wiring on a substrate and as a bonding material for power device semiconductors. However, since silver nanoparticles are fine, they tend to agglomerate and are easily fused due to a melting point drop. Has an organic substance layer called a protective agent. In these organic layers, fatty acids, alkylamines, and the like are often used. In particular, silver nanoparticles coated with alkylamine or alkyldiamine are desorbed at a relatively low temperature, and silver nanoparticles that can be fired at a low temperature. (Patent Documents 1 and 2).

It is expected that such a fired coating film using silver nanoparticles that can be fired at a low temperature is used as a conductive material such as wiring. In order to ensure reliability and conductivity as a conductive material such as wiring, wiring The corresponding method is taken with thick film. As silver nanoparticles designed for the purpose of increasing the film thickness, Patent Document 3 uses silver nanoparticles having a primary particle diameter of several nanometers to several tens of nanometers, and has a conductivity of 5 to 20 μm. A silver paint composition (ink) from which a silver coating film can be obtained has been reported. Further, in Patent Document 4, when a sintered body is formed by containing silver particles having a particle diameter of 100 to 200 nm in an amount of 30% or more on the basis of the number of particles, the resistance can be reduced, and the water content is 5 to It is described that such silver particles can be obtained by inclusion in a 100 parts by weight reaction system.

In these known documents, silver nanoparticles are prepared by utilizing a complex formation reaction between a silver compound and an amine compound. Specifically, complex formation is performed in the absence of a solvent using silver oxalate and alkylamine or alkyldiamine. However, complex formation in the absence of a solvent results in a solid material that does not flow, is difficult to stir, lacks system uniformity, and is locally accompanied by an exothermic reaction. There are problems and it is difficult to put it to practical use. Therefore, the complex formation reaction in an alcohol solvent promotes and assists the complex reaction, improves the agitation in the system, suppresses carbon dioxide generated suddenly by thermal decomposition, and improves quality and safety. A silver nanoparticle production method with improved resistance has been reported (Patent Documents 5 to 7).

Also, in the process of thermally decomposing silver oxalate-alkylamine complex, when by-product gas (mainly carbon dioxide) is generated and discharged, it contains alkylamine which is easily volatilized and is discharged out of the system. In order to avoid the problem, a production method in which the complex compound is continuously introduced into a reaction vessel and the amount of by-product gas generated during the thermal decomposition reaction is controlled has been reported (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 Japanese Patent Laying-Open No. 2015-40319

However, in Patent Document 3, only a coating film having a thickness that does not reach 8 μm is produced in the examples. Even if a conductive coating of 10 μm or more is created, silver particles are mainly composed of particles with a primary particle size of several tens of nanometers, so the amount of organic protective agent is large, and volume shrinkage occurs due to removal of the protective agent. It is low, and there is a high possibility of the occurrence of disconnection due to cracks.

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

Furthermore, although the silver nanoparticle dispersion and the coating composition (ink) are used by being applied to a substrate, the conditions of the silver nanoparticles having a viscosity behavior suitable for applying to a substrate are sufficiently studied. It wasn't. For this reason, the actually obtained coating film may not have sufficient performance. In particular, in screen printing, in order to pass through a screen, not only a reduction in particle diameter but also a precise viscosity characteristic is required for the viscosity, so it is necessary to adjust to an appropriate viscosity. To adjust the viscosity, the viscosity can be increased by reducing the particle size or adding an organic binder. However, if the particle size is too small, the content of the surface protection material increases. If it becomes too much, volume shrinkage occurs during sintering, cracks occur, and too much organic binder is added, sintering of silver particles is inhibited, and the conductivity and strength of the sintered body are deteriorated. There is a risk of getting lost.

The present invention solves the above problems, and a method for producing silver nanoparticles in consideration of scale-up such as workability, safety, and environmental aspects, and a method for producing silver nanoparticles having a highly distributed particle size distribution range, and Another object of the present invention is to provide silver nanoparticles that can be easily adjusted to a viscosity suitable for various printing methods, particularly screen printing, and silver nanoparticle coating compositions.

In order to solve these problems, the present inventor has intensively studied. As a result, by using a specific amino alcohol as an amine compound that can form a complex with a silver compound, the emission of alkylamine is suppressed, and it is environmentally friendly. At the same time, the resulting silver particles have excellent particle size and distribution. As a result, the present inventors have found that the obtained sintered coating film also has excellent performance, and reached the present invention. Furthermore, the silver particles having the specific amino alcohol bonded to the surface can surprisingly obtain a dispersion (paste) having a higher viscosity than the silver particles bonded to the conventional alkylamine. The viscosity can be adjusted by changing the type and amount. As a result, it was found that a silver coating composition having a viscosity range particularly suitable for screen printing can be obtained by suppressing the addition amount of an organic binder having a thickening effect.

That is, the present invention includes the following inventions.
(1) A silver compound (a) having thermal decomposability and an amine compound (b) capable of forming a complex with (a) are reacted in an organic solvent (c) to form a complex. A method for producing silver nanoparticles, wherein silver nanoparticles are formed by thermal decomposition by heating, wherein (b) has 6 carbon atoms each having a primary amino group or a secondary amino group and a hydroxyl group. The manufacturing method of the silver nanoparticle characterized by being the following amino alcohols.

(2) (b) is i) a branched primary amino alcohol having 3 to 4 carbon atoms, and (ii) an amine in which an amino group and a hydroxyl group are bonded via an alkyl chain having 2 carbon atoms. The method for producing silver nanoparticles according to (1) above, wherein the compound is (b1) or iii) a linear secondary amino alcohol (b2) having 3 carbon atoms.
(3) The method for producing silver nanoparticles according to the above (1) or (2), wherein (b) is 2-amino-2-methyl-1-propanol.
(4) The method for producing silver nanoparticles according to any one of (1) to (3), wherein (a) is silver oxalate.

(5) In the complex formation reaction of (a) and (b), the amine compound (d) having a molecular length other than (b) having a length of 5 mm or longer is present. ) The method for producing silver nanoparticles according to any one of the above.
(6) Silver nanoparticles according to (5) above, wherein the molar ratio of [(b) + (d)] / [silver atoms contained in (a)] is 0.7 to 2.0 Manufacturing method.
(7) The method for producing silver nanoparticles according to any one of (3) to (6) above, wherein the weight ratio of (c) / (a) is 0.8 to 1.3.
(8) The method for producing silver nanoparticles according to any one of (1) to (7) above, wherein water is present during the complex formation reaction of (a) and (b).
(9) A silver nanoparticle dispersion characterized in that silver nanoparticles are produced by the method according to any one of (1) to (8) above, and the obtained silver nanoparticles are dispersed in an organic solvent. Production method.
(10) Silver nanoparticles are produced by the method according to any one of (1) to (8), the obtained silver nanoparticles are dispersed in an organic solvent, and an organic binder is further added. , A method for producing a silver coating composition.

(11) A silver nanoparticle dispersion obtained by the method described in (9) above or a silver coating composition obtained by the method described in (10) above is applied onto a substrate and baked to form a silver conductive layer. The manufacturing method of the silver electrically-conductive material including the process to do.
(12) A composition comprising a thermally decomposable silver compound (a), an amine compound (b) capable of forming a complex with (a), and an organic solvent (c), wherein b) A silver compound-containing composition, which is an amino alcohol having 6 or less carbon atoms each having a primary amino group or a secondary amino group and a hydroxyl group.
(13) The silver compound containing according to (12) above, wherein [(b) + (d)] / [silver atom contained in (a)] is 0.7 to 2.0 in molar ratio Composition.
(14) The content ratio of the thermally decomposable silver compound (a) and the organic solvent (c) is characterized in that (c) / (a) is 0.8 to 1.3 by weight. The silver compound-containing composition according to (12) or (13) above.

(15) As an amine compound capable of forming a complex with the silver compound (a), an amino alcohol (b) having 6 or less carbon atoms having one primary amino group or one secondary amino group and one hydroxyl group, and other than (b) The amine compound (d) having a molecular length of 5 mm or more and (b) / [(b) + (d)] in a molar ratio of 0.3 to 0.8 (12) The silver compound-containing composition according to any one of (14).
(16) The silver compound-containing composition as described in any of (12) to (15) above, wherein the water content is 5 to 20 parts by weight with respect to 100 parts by weight of the silver compound (a). .
(17) An average particle diameter of 350 nm or less, a coefficient of variation of 30 to 80%, and a primary amino group or an amino alcohol having 6 or less carbon atoms each having a primary amino group and a hydroxyl group bonded to the surface of the silver particle. Silver nanoparticles.
(18) The silver nanoparticle according to (17), wherein i) a branched primary amino alcohol having 3 to 4 carbon atoms, and (ii) an alkyl chain having 2 carbon atoms on the surface of the silver nanoparticle. Via the amine compound (b1) in which an amino group and a hydroxyl group are bonded, or (b1) and iii) a silver nanoparticle in which a linear secondary amino alcohol (b2) having 3 carbon atoms is bonded.

(19) A silver nanoparticle according to (18) above, wherein 2-amino-2-methyl-1-propanol is bound as the amine compound (b1).
(20) The silver nanoparticle according to any one of the above (17) to (19), wherein the silver nanoparticle further binds to an amine compound having a molecular length of 7 to 8 mm other than (b1) and (b2) particle,
(21) A silver nanoparticle dispersion, wherein the silver nanoparticles according to any one of (17) to (20) are dispersed in an organic solvent.
(22) A silver paint composition, wherein the silver nanoparticles according to any one of (17) to (20) are dispersed in an organic solvent and further contain an organic binder.
(23) A method for producing a silver conductive material, comprising: applying a silver nanoparticle dispersion according to (21) above or a silver coating composition according to (22) above onto a substrate and baking to form a silver conductive layer. ,
It is.

The silver coating composition containing silver particles whose particle size is controlled according to the present invention can be sintered even in a low temperature region 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 is a material that can form a silver wiring having a thickness of several to several tens of μm on a plastic substrate having a relatively low heat resistance such as PET or polypropylene by a printing method typified by screen printing, or 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 in the present invention, the amount of amine compound used is less than that of the conventional synthesis method, and as an amine compound that forms a complex with a thermally decomposable silver compound, a specific carbon number of 4 or less. By using amino alcohol, it is possible to further reduce the use of alkylamines that are highly burdened on the human body and the environment. Thus, a highly safe production method is provided in scaled-up industrial production.

Figure 1 is an image of coordination model of aminoalcohol to silver atom (linear type), coordination model of aminoalcohol to silver atom (OH group approaching type), and coordination model of alkylamine to silver atom is there. FIG. 2 is an image diagram of a silver adsorption model and silver particle growth. FIG. 3 is a view showing an SEM photograph of the particles obtained in Example 1. FIG. 4 is a SEM photograph of the particles obtained in Example 2. FIG. 5 is a view showing an SEM photograph of the particles obtained in Example 3. 6 is a SEM photograph of the particles obtained in Example 4. FIG. FIG. 7 is a view showing an SEM photograph of the particles obtained in Example 5. FIG. 8 is a SEM photograph of the particles obtained in Example 6. FIG. 9 is a SEM photograph of the particles obtained in Example 7. FIG. 10 is a view showing an SEM photograph of the particles obtained in Example 8. FIG. 11 is a SEM photograph of the particles obtained in Example 9. 12 is a SEM photograph of the particles obtained in Example 10. FIG. 13 is a SEM photograph of the particles obtained in Example 11. FIG. 14 is a view showing an SEM photograph of particles obtained in Comparative Example 1. FIG. FIG. 15 is a view showing STEM photographs of the particles obtained in Comparative Examples 2 and 3. FIG. FIG. 16 is a view showing an STEM photograph of the particles obtained in Comparative Example 4. FIG. 17 is a diagram showing a particle size distribution histogram of the particles obtained in Example 1. FIG. 18 is a graph showing a particle size distribution histogram of the particles obtained in Example 2. FIG. 19 is a graph showing a particle size distribution histogram of the particles obtained in Example 3. FIG. 20 is a diagram showing a particle size distribution histogram of the particles obtained in Example 4. FIG. 21 is a graph showing a particle size distribution histogram of the particles obtained in Example 5. FIG. 22 is a diagram showing a particle size distribution histogram of the particles obtained in Example 6. FIG. 23 is a graph showing a particle size distribution histogram of the particles obtained in Example 7. FIG. 24 is a diagram showing a particle size distribution histogram of the particles obtained in Example 8. FIG. 25 is a diagram showing a particle size distribution histogram of the particles obtained in Example 9. FIG. 26 is a diagram showing a particle size distribution histogram of the particles obtained in Example 10. FIG. FIG. 27 is a diagram showing a particle size distribution histogram of the particles obtained in Example 11. FIG. FIG. 28 is a diagram showing a particle size distribution histogram of particles obtained in Comparative Example 1. FIG. FIG. 29 is a diagram showing a particle size distribution histogram of the particles obtained in Comparative Examples 2 and 3. FIG. FIG. 30 is a diagram showing a particle size distribution histogram of particles obtained in Comparative Example 4. FIG. 31 is a diagram showing an SEM photograph of the particles obtained in Example 12. 32 is a SEM photograph of the particles obtained in Example 13. FIG. 33 is a SEM photograph of the particles obtained in Example 14. FIG. 34 is a SEM photograph of the particles obtained in Example 15. FIG. FIG. 35 is a view showing an SEM photograph of the particles obtained in Comparative Example 5. FIG. FIG. 36 is a diagram showing an SEM photograph of the particles obtained in Comparative Example 6. FIG. 37 is a view showing an SEM photograph of the coating film surface of a paste prepared from the particles obtained in Example 12. FIG. 38 is a view showing an SEM photograph of the coating film surface of a paste prepared from the particles obtained in Example 13. FIG. 39 is a view showing an SEM photograph of the coating film surface of a paste prepared from the particles obtained in Example 14. 40 is a view showing an SEM photograph of the coating film surface of a paste prepared from the particles obtained in Example 15. FIG. 41 is a view showing an SEM photograph of the coating film surface of a paste prepared from the particles obtained in Comparative Example 5. FIG. FIG. 42 is a view showing an SEM photograph of the coating film surface of a paste prepared from the particles obtained in Comparative Example 6. FIG. 43 is a diagram showing a particle size distribution histogram of the particles obtained in Example 12. FIG. 44 is a graph showing the particle size distribution histogram of the particles obtained in Example 13. 45 is a graph showing the particle size distribution histogram of the particles obtained in Example 14. FIG. FIG. 46 is a diagram showing a particle size distribution histogram of the particles obtained in Example 15. 47 is a diagram showing a particle size distribution histogram of the particles obtained in Comparative Example 5. FIG. FIG. 48 is a diagram showing a particle size distribution histogram of the particles obtained in Comparative Example 6. FIG. 49 is a diagram showing viscosity comparison data of pastes prepared from the particles obtained in Examples 12 to 15 and Comparative Examples 5 and 6.

The present invention relates to a method for producing silver nanoparticles by reacting a thermally decomposable silver compound (a) with an amine compound (b) that forms a complex. As the amine compound (b), a primary amino group or a secondary class is used. It is characterized by the use of an amino alcohol having 6 amino acids and one hydroxyl group.
By using such a specific amino alcohol, it is possible to have two adsorption models for silver particles, and thus easily obtain silver nanoparticles having a wide distribution and a relatively large particle size, Silver nanoparticles having a large particle diameter range of 200 to 500 nm can be easily synthesized, and the amount of the entire amine compound used can be reduced, which is excellent in the environment.
In addition, by using a specific amino alcohol, it is possible to produce a silver paste with a higher viscosity than silver nanoparticles using only conventional alkylamines, and in particular a silver coating composition suitable for the viscosity of screen printing Makes it possible to produce.
Details will be described below.

<Description of materials in silver nanoparticle synthesis>
[1. Description of 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 silver compound having thermal decomposability refers to a silver compound that is complexed with the component (b) described later and thermally decomposes under heating conditions that are possible 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 applied. Of these silver compounds, silver carbonate or silver oxalate (Ag ₂ C ₂ O ₄ ) is particularly preferable. More preferred is silver oxalate. Silver oxalate can be decomposed at a relatively low temperature without a reducing agent to produce silver particles. Further, carbon dioxide generated by the decomposition is released as a gas, so that no impurities remain in the solution.

[2. Amine compound forming complex (b)]
Next, the present invention is characterized in that the following compounds are used as amine compounds capable of forming a complex with the silver compound as component (b). That is, it is a C6 or less amino alcohol having one primary amino group or one secondary amino group and one hydroxyl group.
Since these amine compounds can be dissolved in a polar solvent (especially an alcohol solvent), it is possible to form a complex with a silver compound in the presence of the polar solvent. As a result, it has the function of lowering the thermal decomposition temperature of the silver compound even in a polar solvent and making it possible to produce silver particles at a low temperature.
Amino alcohols having 7 or more carbon atoms or amino alcohols having 2 or more hydroxyl groups are not suitable because many solid substances with low solubility in alcohol solvents are difficult to complex with silver compounds. In addition, amino alcohols having two or more amino groups are too polar, the reduction reaction is stronger than the complex formation reaction, silver particles are likely to precipitate, and the particle size cannot be controlled substantially. It becomes difficult to obtain silver particles.
Furthermore, as will be described later, the component (b) of the present invention is characterized by having two adsorption models for silver particles. For this reason, the particle size of the obtained silver particles can be easily increased and has a wide distribution. It can also be made.
The amine compound (b) may be a primary amino group or an amino alcohol having 6 or less carbon atoms each having a primary amino group or a secondary amino group, and the skeleton may be linear or branched.
Examples of amino alcohol (b) satisfying the above conditions include methanolamine, ethanolamine, 1-amino-2-butanol, DL-1-amino-2-propanol, and 2-amino-2-methyl-1-propanol. (Hereinafter AMP), DL-2-amino-1-propanol, N-methylethanolamine, 3-amino-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino -1-hexanol is mentioned.
Furthermore, in order to further develop the effect of increasing the particle size and the distribution of silver particles, it is particularly preferable to use an amino alcohol having the following characteristics as the component (b). i) an amine compound (b1), which is a branched primary amino alcohol having 3 to 4 carbon atoms, and (ii) an amino group and a hydroxyl group are bonded via an alkyl chain having 2 carbon atoms, or iii) It is a linear secondary amino alcohol (b2) having 3 carbon atoms.
Here, (i) “branched type” means that a skeleton composed of carbon atoms and heteroatoms is branched rather than linear. In addition, (ii) “the amino group and the hydroxyl group are bonded via an alkyl chain having 2 carbon atoms” means that two adjacent carbon atoms in the skeleton composed of carbon atoms and heteroatoms are each amino acids. It means that a group and a hydroxyl group are bonded.

In the case of the amine compound (b1), one amino group and one hydroxyl group are bonded via an alkyl chain having 2 carbon atoms, and the positional relationship between the two functional groups is “a moderate amount capable of complexing with silver oxalate. The polarity of a simple amine compound "and" realization of two adsorption models of silver particles ".
Furthermore, (b2) has the same positional relationship between the amino group and the hydroxyl group as (b1), but since the amino group is secondary, it has a structure with 3 carbon atoms in total, which is similar to (b1). In addition, “appropriate polarity of amine compound capable of complexing with silver oxalate” and “realization of two adsorption models with silver particles” are compatible.
In the case of a secondary amine compound, when the number of carbon atoms is 4 or more, the steric hindrance of the amino group is large, the polarity is lowered as a whole, and complex formation with silver oxalate may hardly occur.

Examples of the amino alcohol (b1) that satisfies the above conditions include 1-amino-2-butanol, DL-1-amino-2-propanol, AMP, and DL-2-amino-1-propanol.
Among these, AMP is most preferable since 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. Furthermore, by bonding to the silver surface, the effect of increasing the viscosity of the dispersion is excellent.
Similarly, (b2) includes, for example, N-methylethanolamine.

The component (b) has no strong irritating odor like the conventionally used aliphatic hydrocarbon amine compounds, and is advantageous in terms of safety in handling.
In addition, the amount of amine compound used is small. Specifically, by using the component (b), in order to promote the complex formation with the silver compound, the short-chain aliphatic hydrocarbon amine compound having 4 to 5 carbon atoms that has been used in the prior art is not used. However, the complex formation reaction with the silver compound can be sufficiently promoted. Therefore, even if an amine compound (d) other than the amino alcohol of component (b) described below is used in combination, the total amount of the aliphatic hydrocarbon amine compound can be reduced or eliminated.
In addition, the above (b) component may use only 1 type, or may mix and use 2 or more types.

(2-1. (B) Formation mechanism of large particle size silver particles by adding component)
The mechanism by which silver nanoparticles having a large particle size and a wide distribution can be obtained by using an amine compound that forms a complex with component (b) described above is not completely clear. However, the present inventor presumes as follows.
The complex formation between the amine compound and the silver compound is such that the amine compound is dissolved in the organic solvent (c), so that it reacts with the silver compound, and the unshared electron pair of the amino group of the amine compound enters the empty orbit of the silver atom. It is formed by coordination. Furthermore, the amine compound used in the present invention is an amino alcohol and has a hydroxyl group. Since this hydroxyl group is also polar and negatively charged like the amino group, it is considered that the hydroxyl group behaves easily toward a silver atom. Based on this property, it is considered that there are the following two models for the coordinate bonding state of the silver atom of the specific amino alcohol used in the present invention as the component (b). i) Similar to alkylamine, a model in which an amino group is coordinated to a silver atom and an alkyl chain is linearly oriented outward (dispersion medium side) (Fig. 1-1), ii) an amino group is coordinated to a silver atom It is a model (Fig. 1-2) in which the hydroxyl group also approaches the silver atom side and stabilizes. Since these two coordination bond models exist, the steric hindrance by the amine compound around the silver atom is not uniform. For this reason, it is considered that the resulting particle diameter varies, and it is widely formed from a large particle diameter to a small particle diameter (FIG. 2).
In addition, the strength of the polarity of the amino group of the amine compound is related to three factors: i) the total number of carbon atoms in the amine compound, ii) the positional relationship between the amino group and the hydroxyl group, and iii) the three-dimensional structure of the amine compound. Conceivable. Specifically, when the number of carbon atoms is too large, complex formation itself hardly occurs (factor (i) above). If the positional relationship between the amino group and the hydroxyl group is too far, the hydroxyl group is difficult to approach the surface of the silver particle (the factors (ii) and (iii) above), and the adsorption model shown in FIG.
For the above reasons, as in the present invention, an amino alcohol having one primary amino group or one secondary amino group and one hydroxyl group and having 6 or less carbon atoms satisfies these three factors, and the above two adsorptions. It is thought that the model can be realized.
Furthermore, i) a branched primary amino alcohol having 3 to 4 carbon atoms and (ii) an amine compound (b1) in which an amino group and a hydroxyl group are bonded via an alkyl chain having 2 carbon atoms, or iii) Since the straight-chain secondary amino alcohol (b2) having 3 carbon atoms is optimal in terms of the above three factors, it is considered that a particularly excellent effect is exhibited.

On the other hand, in the case of alkylamines conventionally used, since only the amino group portion has an electron donating property, it is oriented only linearly, as shown in FIG. 1-3. Therefore, it is considered that this is because there is no variation in particles and only silver particles with uniform particles can be synthesized.
As will be described later, the combined use of the (b) component amino alcohol and water increases the effects of larger particle size and wider distribution.

[3. Amine compound (d) having a dispersion stabilizing effect due to steric hindrance]
In the present invention, an amine compound other than the component (b) can be present when the complex of (a) and (b) is formed. This compound has a molecular length of 5 mm or more, and has a function of giving an effect of dispersion stability of silver particles by a steric hindrance effect. The length of the molecule here is the distance of the longest two atoms that do not contain hydrogen atoms, and the calculation conditions are density functional method, function ωB97X-D, basis function 6-31 + G *, environment vacuum energy State In the ground state, it can be calculated by various molecular calculation software such as Spartan''16V1,1,0.

The length of the molecule is preferably 7 cm or more. However, if it is too long, the boiling point becomes high and it is difficult to remove, so it is preferably 8 mm or less.

In particular, an amine compound having a main chain (main skeleton) composed of 7 or more atoms including an amino group is preferable.
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 preferable are preferable. The number of hydrocarbon groups bonded to the amino group of the amine compound is not limited. However, one or two primary amines or secondary amines are particularly preferable because they easily coordinate with silver.
Examples of such component (d) include aliphatic hydrocarbon monoamines having 4 or more carbon atoms.

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 described in the prior art. However, since aliphatic hydrocarbon monoamines having 4 or more carbon atoms have a strong irritating odor and are at risk of being discharged at a high temperature together with carbon dioxide during the decomposition reaction, other amine compounds may be used. Specifically, it is an amine compound (alkoxyamine, alkyl ether amine, amino alcohol) having 4 or more carbon atoms and containing an oxygen atom. In the present invention, the above-mentioned specific amino alcohol is used as the component (b), and an amine compound containing an oxygen atom as the component (d) is used except for the component (b). At this time, it is possible to produce silver nanoparticles that are excellent in low-temperature sinterability and easily form a thick film conductive sintered body without using any aliphatic hydrocarbon amine compound having a strong irritating odor during the decomposition reaction.

Specific examples of the above component (d) include n-butylamine, 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 alkyl ether amine include JEFFAMINE M series, M-600, M-1000, M-2005, and M-2070 manufactured by HUNTSMAN. Examples of amino alcohols include 4-amino-1-butanol, 5-amino-1-pentanol, and 6-amino-1-hexanol. Other examples include diglycolamine.
More preferable specific examples of the alkylamine include 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 amino alcohols include 5-amino-1-pentanol and 6-amino-1-hexanol. Examples of aminoethoxy include diglycolamine. More preferred are n-hexylamine and 3-ethoxypropylamine.
The above component (d) can be used alone or in combination of two or more.

(3-1. Molar ratio in amine compound (b) / [(b) + (d)])
(B) / [(b) + (d)] 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 particles and high distribution. When the molar ratio is smaller than 0.3, the amount of the amine compound having a long molecular length is increased, the particle becomes small as a whole, and the particle size distribution tends to be narrow, which is not preferable. 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 is increased, which is not preferable.

(3-2. Ratio and addition amount of amine compound (b) (d) and silver compound (a))
Regarding the mixing amount of the silver atom of the silver compound and the amine compound (b) + (d), the molar ratio (amine compound / silver atom of the silver compound) should be 0.7 to 2.0. It is preferable to adjust the amount of (b) + (d). More preferably, it is 0.7 to 1.5, still more preferably 0.7 to 1.3, and most preferably 0.7 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-described various conventional synthesis methods (Patent Documents 1 to 9), the molar ratio of amine atom / silver compound silver atom is 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 amine discharged can be reduced. Therefore, the risk of the human body and environmental burden due to the release of amines outside the system can be reduced. At the same time, in the conventional method, particles having a small particle size and a narrow distribution are easily synthesized, whereas in the present invention, silver particles having a wide distribution and a large particle size can be obtained. Finally, it is possible to obtain a thick film conductive sintered body that is excellent in low-temperature sinterability and has low resistance.

[4. Description of organic solvent (c)]
In the present invention, the above-described complex formation reaction between the silver compound and the amine compound is performed in the presence of an organic solvent.
In the present invention, a solvent having a polar functional group is preferable. Specifically, alcohol solvents, ketone solvents, aldehyde solvents, amide solvents, ester solvents, nitrile solvents, ether solvents, glycols A solvent, a glycol ether solvent, a glycol ester solvent, and a glyme solvent are preferred. In particular, alcohol solvents are preferable, and alcohols having 3 to 12 carbon atoms are particularly preferable. 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. 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.
The use of a glyme-based solvent is also preferable. For example, monoglyme (bp: 85 ° C.), ethyl glyme (bp: 121 ° C.), diglyme (bp: 162 ° C.), dipropylene glycol dimethyl ether (bp: 171 ° C.), ethyl dig Examples include lime (bp: 188 ° C), triglyme (bp: 216 ° C), butyl diglyme (bp: 256 ° C), and tetraglyme (bp: 275 ° C). 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 thermal decomposition step of the complex compound to be performed later can be increased and the convenience in the post-treatment after the formation of the silver nanoparticles. Is preferred. These may be used alone or in combination of two or more.

(4-1. Addition amount of organic solvent)
In addition, the organic solvent has a weight ratio of 80 to 130 parts by weight (that is, a weight ratio of (c) / (a) of 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. What mixed the organic solvent of the quantity which becomes 1.3 is preferable. More preferably, it is 80 to 125 parts by weight.

(4-2. Method for adding organic solvent)
In the present invention, the amine compound (b) or (d) and the silver compound (a) can take several forms in order 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) or (d) is added to the obtained silver compound-alcohol slurry. May be. 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, a solid silver compound is charged into a reaction vessel, and an organic solvent or a mixed solution of an organic solvent and an amine compound is added thereto 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 may be added thereto.
Note that silver oxalate has been reported to be explosive in the dry state. Therefore, when silver oxalate is used as the silver compound, it is preferable to use a wet state. This is because the explosiveness is remarkably lowered and handling is facilitated by making it wet. Therefore, water or the organic solvent described above may be mixed and used in a wet state.

[5. About aliphatic carboxylic acid)
Moreover, you may use aliphatic carboxylic acid at the time of complex formation for adjustment of a particle diameter and a particle size distribution. By adding an aliphatic carboxylic acid, the particle size tends to be small and the particle size distribution tends to be narrow. It is desirable to adjust the water content appropriately and use it. The aliphatic carboxylic acid is preferably used together with the amines, and can be added and used when the silver compound and the amine are mixed. 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, Examples thereof include saturated aliphatic monocarboxylic acids having 4 or more carbon atoms such as icosanoic acid and eicosenoic acid; unsaturated aliphatic monocarboxylic acids having 8 or more carbon atoms such as oleic acid, elaidic acid, linoleic acid, and palmitoleic acid.

Of these, saturated or unsaturated aliphatic monocarboxylic acids having 8 to 18 carbon atoms are preferable. By setting the number of carbon atoms to 8 or more, when the carboxylic acid group is adsorbed on the surface of the silver particle, a space between the silver particle and other silver particles can be secured. In view of availability, easiness of removal during firing, etc., saturated or unsaturated aliphatic monocarboxylic acid compounds having up to 18 carbon atoms are usually preferred. 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 used, the aliphatic carboxylic acid may be used in an amount of, for example, about 0.05 to 10 moles, preferably 0.1 to 5 moles, more preferably, with respect to 1 mole of silver atoms in the starting silver compound. 0.5 to 2 moles may be used. When 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 diameter by adding the aliphatic carboxylic acid is weak. On the other hand, when the amount of the aliphatic carboxylic acid reaches 10 moles, there is a possibility that the particle diameter is too small and uniform, and there is a possibility that it will remain in the washing or surface protection agent replacement step. It is difficult to remove the aliphatic carboxylic acid. However, it is not necessary to use an aliphatic carboxylic acid.

[6. (Description of water and water content)
The water content of the reaction system is preferably within a range of 20 wt% or less with respect to the silver compound. Especially preferably, it is 15 wt% or less. Although the water content depends on the type of amine compound used for complex formation, if the water content is low, the particle size distribution of the resulting silver particles is uniform, and voids in the sintered body are produced, which is expected in the present invention. Effect may be difficult to express. On the other hand, when the water content is 20 wt% or more based on the silver compound, the silver particles become too coarse, and a portion where the particles are sintered and united is produced, which is not preferable. Regarding 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 the formation of the silver-amine complex or after the formation of the complex.
The weight ratio of the organic solvent (c) to water is preferably 0.03 to 0.3 as the weight ratio of water / organic solvent. More preferably, it is 0.1 to 0.25. In this range, it is particularly easy to obtain silver nanoparticles having the particle diameter and particle size distribution of the present invention described later.

(6-1. Mechanism of formation of highly distributed silver particles by adding water)
The presence of water during the reaction of silver particle formation by thermal decomposition described later causes a particular variation in the particle size of the formed silver nanoparticles, and particularly highly distributed silver particles are obtained. Although there is an unknown part about this mechanism, when water approaches silver compounds, especially silver oxalate, silver amine complex formation or thermal decomposition inhibits amine compounds from adsorbing to silver atoms. It is thought that the part that has been made grows grains. Furthermore, since the amount of water molecules adsorbed on silver oxalate is also biased (localized), it is considered that it is easy to cause an appropriate variation in particle size. On the contrary, when an amount of water larger than 20 wt% is added to the silver compound, the silver particles themselves are enlarged, and the adjacent particles are likely to sinter and coalesce. This is presumably because the degree of inhibition of the adsorption of silver atoms of amine is increased, and the silver particles are likely to be enlarged.

<Method for producing silver nanoparticles>
[7. (Mixing of liquid ingredients)
In the present invention, usually, the amine compound (b) that forms the complex and the amine compound (d) that functions as the protective agent are mixed in the polar solvent (c). If necessary, an aliphatic carboxylic acid and water can be added and mixed to prepare a liquid raw material necessary for the reaction. If there is a solid material at room temperature that is a liquid raw material, it can be appropriately heated and mixed. The heating temperature is preferably 100 ° C. or lower, preferably 80 ° C. or lower, and more preferably 60 ° C. or lower. When the temperature is higher than the above temperature range, when mixed with a silver compound and slurried, the complexation and oxalic acid decomposition reaction will start first, and the silver nanoparticles will not be secured without ensuring uniformity in the system. May be generated.

[8. Preparation of silver compound-containing composition (silver compound slurry)]
The silver compound-containing composition of the present invention can be obtained by mixing the silver compound (a) and the liquid raw material. Or only a polar solvent and the said silver compound (a) may be mixed previously, and the said amine compound may be added later. Thus, the manufacturing method of this invention can be implemented using the silver compound containing composition of this invention obtained. The silver compound-containing composition of the present invention is usually prepared in a slurry state.
A silver compound, a predetermined amount of an amine mixed solution, or an aliphatic carboxylic acid and water as necessary are mixed. The mixing at this time is preferably carried out while stirring at room temperature, or while appropriately cooling to room temperature or lower and stirring because the coordination reaction (complexing reaction) with amines to the silver compound involves heat generation. Since the mixed liquid of a silver compound and an amine compound is performed in the presence of a polar solvent, stirring and cooling can be performed satisfactorily. The excess of the polar solvent and the amine compound serves as a reaction medium.

Conventionally, in a thermal decomposition method of a silver amine complex, a liquid alkylamine component is first charged in a reaction vessel, and a powdered silver compound (silver oxalate) is charged therein. The liquid alkylamine component is a flammable substance, and there was a danger in putting the powdery silver compound therein. In other words, there was a risk of ignition due to static electricity due to the introduction of the silver compound of the powder. In addition, there is a risk that the complex formation reaction locally progresses due to the introduction of the silver compound of the powder, and the exothermic reaction is expelled. According to the present invention, such danger can be avoided.

In addition, the odor of the highly volatile alkylamine has a great adverse effect on the working environment. In the present invention, the amount of the highly volatile alkylamine used during the synthesis of the silver nanoparticles can be reduced or eliminated. Odor and exposure to workers can be reduced when charging.

[9. (Silver amine complex)
Since the complex compound to be formed generally exhibits a color corresponding to its constituent components, the progress of the complex compound formation reaction can be detected from the change in the color of the reaction mixture. In addition, when it is difficult to confirm due to a change in color, the generation state can be detected by a change in viscosity of the reaction mixture or a change in temperature. Thus, a silver amine complex is obtained in a medium mainly composed of a polar solvent and an amine compound.

[10. (Explanation of temperature increase rate conditions from complexation to decomposition reaction)
In the heating step of the reaction system, the heating rate affects the particle size of the precipitated silver particles, and therefore the particle size of the silver particles can be controlled by adjusting the heating rate of the heating step. Here, it is desirable to adjust the speed of the heating step in the range of 3.0 to 50 ° C./min up to the set decomposition temperature. If the temperature rise time is slower, particle growth is more likely to occur and a large particle size is likely to be formed. However, if the temperature rise rate is slower than 3.0 ° C./min, particle growth is likely to be promoted and the same as the adjacent particles. This is not preferable.

[11. About washing process of silver particles)
The thermal decomposition of the silver compound results in a suspension exhibiting a color from black-brown to gray, although the color varies depending on the particle size of the obtained particles. From this suspension, removal of polar solvent, excess amine compounds, etc., for example, precipitation of silver nanoparticles, decantation / washing with an appropriate solvent (water or organic solvent), and the desired protection. Silver nanoparticles to which an amine compound is bonded as an agent are obtained.

[12. Explanation of cleaning solvent
The silver particles are preferably washed with an alcohol having a boiling point of 150 ° C. or lower such as methanol, ethanol, propanol or the like as a solvent. And as a detailed method of washing | cleaning, after adding a solvent to the solution after silver particle synthesis | combination and stirring until it suspends, it is preferable to remove a 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 above-described series of operations is performed once, the solvent is preferably used in a volume of 1/20 to 3 times that of the solution after silver particle synthesis, and washed 1 to 5 times.

[13. (Protective agent replacement step)
Furthermore, the above silver nanoparticles may be substituted with an amine compound suitable for the application by replacing the surface protective agent with an amine compound having 4 or more carbon atoms (including those containing oxygen atoms) as necessary. May be. The amine compound finally substituted may be the one used when silver nanoparticles are produced, or a new one not used may be used.

Particularly, it is an alkylamine having 4 to 8 carbon atoms or an amine compound containing an oxygen atom (alkoxyamine, alkyl ether amine, amino alcohol). Among them, those having a molecular length of 5 to 8 mm are preferable, and those having a molecular length of 7 to 8 mm are more 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 can be adjusted when processed into a paste depending on the composition.

The silver particle surface protective agent is replaced by stirring and suspending for a certain period of time in the amine compound to be finally replaced with silver particles after washing. At that time, 50-100 wt% of the amine compound to be finally substituted is added to the pure silver content, and the mixture is stirred and suspended at room temperature for about 1 h. Regarding the difference between before and after the surface protective agent replacement step, the surface protective agent can be confirmed by the difference in peak derived from sintering in DTA measurement, head space GC / MS, pyrolysis GC / MS, or the like. After the surface protective agent replacement step described above, the target silver particles are obtained through the washing step again.
In addition, although the specific amino alcohol itself corresponding to (b) can be almost removed by the washing step, when this remains using other amines, the above substitution step may be appropriately obtained as necessary.
[14. State of generated silver particles (protective agent, particle size distribution)

In this way, silver nanoparticles to which an amine compound is bonded are formed. Silver nanoparticles are fine particles that can be produced by the following method and that have a silver component as a main component and usually have a particle size of 1 to 1000 nm.
Examples of the substance that binds to silver nanoparticles and functions as a protective agent include the specific amino alcohol (b) having 4 or less carbon atoms and / or the amine compound (d) having a molecular length of 5 mm or more, and When used, it contains the aliphatic carboxylic acid. Their content in the protective agent is equivalent to their use in the amine mixture. In addition, the type and total amount of the protective agent can be adjusted by the washing step and, if necessary, the protective agent replacement process. The molecular length of the amine compound finally bonded as a protective agent is preferably 2 to 8 mm, more preferably 5 to 8 mm. 7 to 8 mm is most preferable. On the other hand, the total amount of the protective agent is preferably 0.3 to 2.0 wt% with respect to the pure silver content. Further, 0.5 to 1.0 wt% is more preferable.

The silver nanoparticles of the present invention usually have a particle size of 1000 nm or less.
The average particle diameter is preferably 70 to 350 nm, particularly preferably 70 to 300 nm, and further preferably 80 to 200 nm.
The coefficient of variation indicating the variation in particle diameter is preferably 30 to 80%, particularly preferably 40 to 70%, and further preferably 50 to 60%.

The average particle diameter and coefficient of variation are determined as follows. The obtained silver nanoparticles are observed for particle shape by FE-SEM. Thereafter, using an image analysis software SCANDIUM (manufactured by OLYMPUS), 300 or more particle sizes are measured, and the average particle size and standard deviation are obtained by analysis. Using these values, the coefficient of variation is calculated based on the following formula.
Coefficient of variation (%) = {standard deviation (nm) / average particle size (nm)} × 100
The equipment for measuring the particle size is not limited as long as the same result as the above method can be obtained.

By having the above average particle diameter and coefficient of variation, the thickness of the coating film obtained by applying the silver paint can be increased. Specifically, a thick film having a thickness of 10 to 30 μm can be obtained. Furthermore, not only is it thick, but the volume resistivity of the resulting film can be lowered. 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 packed close to the closest packing between large particles, so that a film with a high silver particle content is obtained because the silver particles are highly packed. It is guessed.
If the average particle diameter exceeds 350 nm, the phenomenon of melting point drop of silver nanoparticles becomes weak and it becomes difficult to sinter at a low temperature, so that the volume resistivity of the coating film cannot be lowered also in this case.
On the other hand, if the coefficient of variation is less than 30%, the particles are aligned, the voids between the particles cannot be filled, and the volume resistivity of the coating film cannot be lowered. On the other hand, if the coefficient of variation exceeds 80%, the particle size is too different even if there is a variation in particles, and in this case too, it becomes difficult to fill the voids between the particles. It cannot be lowered.

If the silver particles of the present invention having the above average particle diameter and variation are used, the viscosity can be adjusted to be suitable as a silver coating composition.
The viscosity of the screen printing ink is preferably in the range of 0.1 to 500 Pa · s (when the shear rate is 5 1 / sec). This is because if it is too high, there is no fluidity and printing failure is liable to occur, and if it is too low, the printed ink will sag and the line width will increase. Thus, 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. In contrast, the silver particles of the present invention can have a viscosity suitable for screen printing even when the amount of the organic binder is relatively small. That is, for example, “Etocel 45” (trade name, manufactured by Nisshin Kasei Co., Ltd.) as an organic binder can be made to have a relatively high viscosity even in a state where 1 wt% is added to the pure silver content. By adjusting to 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 addition amount of the organic binder is 1 wt% or less with respect to the pure silver content, the viscosity suitable for the screen printing can be obtained. As described above, since the viscosity can be controlled by adjusting the particle size, the degree of freedom in the amount of the organic binder added is increased, and the amount can be reduced.

As described above, in the production method of the present invention, the particle size can be controlled by the type of amine used, the type of organic solvent, the amount of water added, and the like. Accordingly, silver particles having a large particle size of 200 to 500 nm and silver particles having a small particle size of 50 to 200 nm can be synthesized in one batch, which is suitable for industrial production.
Since the silver particles of the present invention thus obtained have silver particles in a large particle size region of 200 nm or more, even during the process of cleaning the excess protective agent of silver nanoparticles, protective agent replacement treatment, pasting, etc. It is difficult to agglomerate (sinter), and it can be expected that a silver nanoparticle dispersion / silver coating composition can be easily produced without impairing the characteristics of the original silver particles. This is also effective when considering scale-up.

<Application>
[15. Method for producing silver dispersion / paste (coating composition)]
A silver nanoparticle dispersion corps can be produced using the silver nanoparticles obtained by the method described above. Here, the silver nanoparticle dispersion refers to a composition containing at least silver nanoparticles and a dispersion medium. Such a silver nanoparticle dispersion corps can take various forms without limitation. The silver nanoparticle dispersion of the present invention can be obtained by dispersing silver nanoparticles in a suitable organic solvent (dispersion medium) in a suspended state. Furthermore, a silver coating composition containing a so-called binder component in addition to silver nanoparticles and a dispersion medium can be produced. According to the present invention, a silver coating composition containing 7095% by weight, more preferably 75-80% by weight, of silver nanoparticles can also be prepared.

(15-1. Explanation of Solvent of Silver Nanoparticle Dispersion or Silver Coating Composition)
As a dispersion medium for obtaining a silver nanoparticle dispersion or a silver coating composition, various organic solvents, specifically, fats such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, etc. Aromatic hydrocarbon solvents such as cyclohexane and methylcyclohexane; Aromatic hydrocarbon solvents such as toluene, xylene, mesitylene, etc .; Methanol, ethanol, propanol, n-butanol, n-pentanol, n- Examples include alcohol solvents such as hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-dodecanol and the like.
Among these, an organic solvent having 8 to 16 carbon atoms and an oxygen atom in the structure and having a boiling point of 280 ° C. or lower is particularly preferable. This is because when the target sintering temperature of silver particles is 150 ° C. or lower, it is difficult to volatilize and remove a solvent having a boiling point of 280 ° C. Preferred 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 of 280 ° C.). A plurality of solvents may be used as a mixture or may be used alone.
The type and amount of the organic solvent may be appropriately determined according to the concentration and viscosity of the desired silver coating composition or silver nanoparticle dispersion.

(15-2. Description of Organic Binder of Coating Composition)
By adding an organic binder in the silver coating composition, it is possible to assist the dispersibility of the silver particles or to adhere to the base material. The addition amount of the organic binder is preferably 0.1 to 10 wt% with respect to the contained silver.
The presence form of the binder resin in the conductive ink may be dissolved in a solvent, or may be an emulsion or a suspension. The binder resin 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, fluorine resin, silicone resin, rosin, rosin ester, chlorinated polyolefin resin, modified chlorinated polyolefin resin, chlorinated polyurethane resin, cellulosic resin, polyethylene Examples include glycol, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinyl petital, and polyvinyl pyrrolidone.
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. Explanation of silver paint composition (printing method and usage)]
In general, the prepared silver coating composition is applied onto a substrate and then baked.
Application is spin coating, inkjet printing, screen printing, dispenser printing, letterpress printing (flexographic printing), sublimation printing, offset printing, laser printer printing (toner printing), intaglio printing (gravure printing), contact printing, microcontact printing It can carry out by well-known methods, such as. When a printing technique is used, a patterned silver coating composition layer is obtained, and a patterned silver conductive layer is obtained by firing. In addition, this silver conductive layer can be applied as a bonding material having excellent conductivity and thermal conductivity, and is also useful as a bonding material for electrical equipment that handles a large current such as a power device.

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, it 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 firing time may be appropriately determined in consideration of the amount of silver ink applied, the firing temperature, and the like, for example, within several hours (for example, 3 hours or 2 hours), preferably within 1 hour, more preferably within 30 minutes. Good.
Since the silver nanoparticles are configured as described above, the sintering of the silver particles sufficiently proceeds even by such a firing process at a low temperature and in a short time. As a result, excellent conductivity (low resistance value) is exhibited. A silver conductive layer having a low resistance value (for example, 15 μΩcm or less and in the range of 7 to 15 μΩcm) is formed. The resistance value of bulk silver is 1.6 μΩcm.

[17. (Use of silver nanoparticle dispersion and silver coating composition)
Because it can be fired at low temperatures, the substrate can be a glass substrate, a heat-resistant plastic substrate such as a polyimide film, or a polyester system 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 polyolefin film such as a film or polypropylene can also be suitably used. In addition, short-time firing 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 according to the intended use, and particularly high conductivity even when a silver conductive layer having a relatively large thickness is formed by using the silver nanoparticles according to the present invention. Can show. The thickness of the silver conductive layer may be selected from the range of, for example, 100 nm to 30 μm, preferably 1 μm to 20 μm, more preferably 10 μm to 20 μm.
The silver conductive material of the present invention is an electromagnetic wave control material, circuit board, antenna, heat sink, liquid crystal display, organic EL display, field emission display (FED), IC card, IC tag, solar cell, LED element, organic transistor, capacitor (Capacitor), electronic paper, flexible battery, flexible sensor, membrane switch, touch panel, EMI shield, etc.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
Tables 1 to 3 show characteristics such as names and structural formulas of amine compounds used in Examples and Comparative Examples.

 

[Example 1]
(Manufacture of silver particles)
In a test tube set in an aluminum block type heating stirrer, 7.58 g (24.95 mmol) of a dried silver oxalate product as a raw silver compound and 9.21 g (90.14 mmol) of n-hexanol as a polar solvent are stirred. The silver oxalate was wetted. Thereafter, 2.50 g (25.47 mmol) of AMP and 4.83 g (46.82 mmol) of 3-ethoxypropylamine were added. Thereafter, the mixture was stirred for 1 hour to produce a silver-amine complex. Thereafter, heating was performed at a heating rate of 3 ° C./min, and the generation of carbon dioxide, which was considered to have caused the decomposition reaction of silver oxalate at 100 ° C., was confirmed. Heating was continued until the generation of carbon dioxide stopped to obtain a liquid in which silver particles were suspended. After precipitation of the silver particles, 20 cc of methanol was added to the reaction solution for washing, and this was centrifuged. This washing and centrifugation were performed three times. In this way, silver nanoparticles were obtained.

(Confirmation of particle size)
The obtained silver nanoparticles moistened with methanol were suspended in n-hexanol using a vortex mixer, the solution was dropped onto a support such as a collodion membrane, and the solvent was dried to obtain a sample. In FE-SEM observation, images are observed and photographed at a magnification of 20000 to 70000 times, and an image with a magnification of 400 or more particles is selected in the image. Thereafter, the particle shape was observed with an FE-SEM. Thereafter, using an image analysis software SCANDIUM (manufactured by OLYMPUS), the number of particles of 400 or more was counted, and analysis of particle diameter length measurement, average particle diameter, particle size distribution, etc. was performed.
Table 4 shows the ratio (%), average particle diameter (nm), and coefficient of variation (%) of particles of 100 nm or less, 200 to 500 nm, and more than 500 nm. 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 as to have a silver content of 75 wt% and mixed. Further, Etcel 45 (manufactured by Nisshin Kasei) 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 produced. This paste was cast on a slide glass and heated at 150 ° C. for 1 h in a blow dryer. The coating thickness after drying was adjusted to 10 to 30 μm.
The obtained coating film was measured for surface resistance by the 4-terminal method, and multiplied by the thickness of the obtained coating film to obtain volume resistivity.
Table 4 shows the values of volume resistivity.

[Examples 2 to 15 and Comparative Examples 1 to 6]
(Manufacture of silver particles)
The materials used and the blending ratio were changed to those shown in Tables 4 to 12, the rate of temperature increase after the formation of the silver-amine complex compound was changed to that shown in Tables 4 to 12, and the reaction vessel / heating device was changed to Tables 4 to 4 Silver particles were produced in the same manner as in Example 1 (Production of silver particles) except that the one shown in FIG.
As shown in Tables 6, 7, and 12, Examples 6, 10 and Comparative Example 5 were subjected to (protecting agent replacement treatment) as described below. The protective agent replacement process is shown below. In order to replace the amine compound in the obtained silver nanoparticles with n-hexylamine by the oxalic acid decomposition reaction of silver oxalate, 71.8 wt% of n-hexyl with respect to the pure silver content of the obtained silver nanoparticles 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 subjected to the same method as in Example 1 (confirmation of particle diameter). For Comparative Examples 2 to 4, the particle diameter was confirmed by STEM images.
In Examples 2 to 11 and Comparative Examples 1 and 2, silver nanoparticle pastes and inks were prepared and fired by the same method as in Example 1 using the obtained particles.
In addition, about Example 4, 5, each was carried out using the particle | grains before a protective agent substitution process, and the particle | grains after a protective agent substitution process (preparation and baking of a silver nanoparticle paste and ink).
For Comparative Examples 3 and 4, as in Patent Documents 1 and 2, the silver content is 55 wt% and dispersed in a mixed solvent of isooctane / n-butanol = 4/1 (volume ratio). The silver nanoparticle dispersion was coated on glass by spin coating.
In Examples 12 to 15 and Comparative Examples 5 to 6, using the obtained particles, texanol was added and mixed as a solvent so that the silver content was 78.5%, and a silver nanoparticle paste was prepared. It was.
For Examples 12, 13, 15 and Comparative Example 5, similar to Example 1, silver nanoparticle paste and ink were prepared and fired.

For Examples 2 to 15 and Comparative Examples 1 to 6, the average particle size (nm), coefficient of variation (%), and particle ratio (%) in each particle size range are shown in Tables 4 to 12 Show. SEM or STEM images are shown in FIGS. 4 to 16 and FIGS. 31 to 36. FIG. 17 to 28 and 43 to 48 show the particle size distribution histograms of Examples 2 to 15 and Comparative Examples 1 to 6, respectively. For Examples 1 to 13, 15 and Comparative Examples 1 to 4, the volume resistivity and film thickness values of the sintered coating films are shown in Tables 4 to 12.

(Coating film observation)
For the silver content 78.5% texanol paste prepared using the particles described in Examples 12 to 15 and Comparative Examples 5 to 6, the surface of the coated film obtained by drying a film coated with a spatula on an aluminum foil with a drier was SEM. Observations were made. The coating films observed by SEM are as shown in FIGS.
(Viscosity measurement of silver paste)
Further, in Examples 12 to 15 and Comparative Examples 5 to 6, the viscosity of a 78.5% silver texanol paste prepared using the described particles was measured with a rheometer (HAAKE MARSIII manufactured by Thermo Fisher Scientific). It was measured. Measurement conditions are: 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.
As described above, according to the present invention, it is possible to form a sintered coating having a thickness of 20 μm or more by adding the amine compound of component (b) at the time of complex formation and using synthesized silver particles. It was confirmed that the film had a volume resistivity of 50 μΩ · cm or less and a conductive film could be obtained under the baking conditions at ° C.

In Examples 1 to 5, by utilizing the difference in the amount of the amine compound (b1) added and the polarity of the alcohol solvent used, the particle size can be controlled to a certain degree with a coefficient of variation of 30% or more to control the particle size. It is understood that is possible.
Further, as in Examples 6 to 8, not only the component (b1) but also water may be used in combination in order to increase the particle size and provide variation. Among them, Example 6 using AMP as an amine compound can exhibit a volume resistivity of 10 μΩ · cm or less at 150 ° C. baking, and a thick conductive film with the highest conductivity can be obtained. It was.

Further, as in Example 9, the amine compound of component (b1) and diglycolamine can be used in combination to increase the particle size and distribution, and as in Example 10, diglycolamine and By using water together, the particle size can be increased. In particular, for the silver nanoparticles having an average particle diameter of 258.8 nm of Example 10, a thick film conductive film having a thickness of 50 μΩ · cm can be obtained by firing at 100 to 150 ° C.
Further, as in Example 11, even when the component (b2) amine compound is used, the silver particles can have a large particle size and a wide distribution, and are 40 μm or more and about 30 μΩ · cm thick film conductive film. Could be confirmed.

In contrast, in Comparative Examples 1 and 2, the component (b) amine compound was not added. In this case, not only the average particle size was less than 70 nm, but also the variation coefficient was less than 30% and the variation was small. 99% or more has a small particle size of 100 nm or less. With such small particles with little variation, there are cases where sufficient conductivity cannot be obtained at each firing temperature unless the film thickness is 10 μm or less, or there are cases where cracks occur due to volume shrinkage and there is no conductivity itself. .

Moreover, in the particles of Comparative Examples 3 and 4 produced by the same method as the production method of Patent Documents 1 and 2, when ink is applied, a sintered coating film of about 0.5 μm is formed, and it is difficult to increase the film thickness. It is.
As can be seen from the above results, the silver nanoparticles of the present invention can have an appropriate variation in the particle size distribution in the method of the present invention by using the component (b) within the range defining the amine compound. It can be seen that it is possible to produce a silver paint composition that is easy to obtain a low-resistance thick film conductive film.

As described above, in the present invention, the viscosity of the silver paste is controlled by using silver nanoparticles in which the amine compound of the component (b1) or the amine compound in combination of (b1) and (b2) is bonded to the surface of the silver particles ( It was confirmed that the viscosity was increased.
FIG. 49 shows the viscosity data of Examples 12 to 15 and Comparative Examples 5 to 6. However, in Examples 12 to 14 using AMP as the component (b1), the particle size decreases as the particle size decreases. Example 14 (average particle size 145.9 nm), which has a viscosity but the largest particle size, is a paste comparative example 5 (average particle size) prepared from silver particles whose surface is protected only with a conventional alkylamine. Compared with a diameter of 108.7 nm, the viscosity is high.
Moreover, by using not only the component (b1) but also the component (b2) and adjusting the blending, the viscosity of the silver paste can be adjusted. By reducing the blending amount of the AMP of (b1), the viscosity can be reduced. Tend to be lower. By controlling the blending of the components (b1) and (b2), it is possible to easily adjust the viscosity of a paste prepared from silver nanoparticles having the same particle size. Furthermore, by using an amine compound having a molecular length of 7 to 8 mm, a silver nanoparticle paste excellent in stability and handling can be obtained.

For silver particles whose surface is protected only with conventional alkylamines, it is possible to increase the viscosity by reducing the particle diameter as in Comparative Example 6, but when the dried coating film shown in FIG. It is easy to cause cracks, many irregularities are confirmed on the surface of the coating film, silver nanoparticles are in an aggregated state, and it is a paste from which an excellent conductive film cannot be obtained.

In contrast, the dried coating films of Examples 12 to 15 and Comparative Example 5 have a small amount of agglomerates, so it is considered that a good conductive film is likely to be obtained. As for No. 5, since it has a low viscosity, more organic binder is required to increase the viscosity. Therefore, in high-definition screen printing (with a line width of 50 μm or less), there is a high possibility of impairing the original conductivity. Conceivable.
From the above, the paste made from silver nanoparticles in which the amine compound combined with the component (b1) or the component (b1) (b2) is bonded to the surface of the silver particle is surprisingly a high-viscosity silver paste. In particular, it is possible to provide a silver coating composition that can be easily adjusted to a viscosity suitable for screen printing.

According to the present invention, a silver conductive layer having a large particle size, a wide distribution, a thick film and high conductivity can be easily formed by a method in which the emission amount of a strong pungent amine is suppressed. A silver coating composition having a viscosity suitable for nanoparticles, particularly screen printing, can be obtained.

Claims (23)

1. A silver compound (a) having thermal decomposability 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 by thermally decomposing silver nanoparticles, wherein (b) is an amino acid having 6 or less carbon atoms each having a primary amino group or one secondary amino group and one hydroxyl group. A method for producing silver nanoparticles, which is alcohol.
2. (B) is an amine compound (b1) in which i) a branched primary amino alcohol having 3 to 4 carbon atoms and (ii) an amino group and a hydroxyl group are bonded via an alkyl chain having 2 carbon atoms. Or iii) a linear secondary amino alcohol (b2) having 3 carbon atoms. The method for producing silver nanoparticles according to claim 1, wherein
3. 3. The method for producing silver nanoparticles according to claim 1, wherein (b) is 2-amino-2-methyl-1-propanol.
4. The method for producing silver nanoparticles according to any one of claims 1 to 3, wherein (a) is silver oxalate.
5. 5. The amine compound (d) having a molecular length other than (b) of at least 5 mm during the complex formation reaction between (a) and (b). A method for producing silver nanoparticles.
6. 6. The method for producing silver nanoparticles according to claim 5, wherein the molar ratio of [(b) + (d)] / [silver atoms contained in (a)] is 0.7 to 2.0.
7. The method for producing silver nanoparticles according to any one of claims 3 to 6, wherein the weight ratio of (c) / (a) is 0.7 to 1.3.
8. The method for producing silver nanoparticles according to any one of claims 1 to 7, wherein water is present during the complex formation reaction between (a) and (b).
9. A method for producing a silver nanoparticle dispersion, comprising producing silver nanoparticles by the method according to any one of claims 1 to 8, and dispersing the obtained silver nanoparticles in an organic solvent.
10. A silver coating composition comprising: a silver nanoparticle prepared by the method according to any one of claims 1 to 8; the obtained silver nanoparticle is dispersed in an organic solvent; and an organic binder is further added. Production method.
11. A silver nanoparticle dispersion obtained by the method according to claim 9 or a silver coating composition obtained by the method according to claim 10 is applied on a substrate and baked to form a silver conductive layer. A method for producing a conductive material.
12. A composition comprising a thermally decomposable silver compound (a), an amine compound (b) capable of forming a complex with (a), and an organic solvent (c), wherein b) is a primary amino group Alternatively, a silver compound-containing composition, which is an amino alcohol having 6 or less carbon atoms having one secondary amino group and one hydroxyl group.
13. 13. The silver compound-containing composition according to claim 12, wherein [(b) + (d)] / [silver atoms contained in (a)] is 0.8 to 2.0 in molar ratio.
14. The content ratio of the thermally decomposable silver compound (a) and the organic solvent (c) is such that (c) / (a) is 0.8 to 1.3 by weight. The silver compound containing composition of 12 or 13.
15. As an amine compound capable of forming a complex with the silver compound (a), an amino alcohol (b) having 6 or less carbon atoms having one primary amino group or one secondary amino group and one hydroxyl group, and the length of a molecule other than (b) And (b) / [(b) + (d)] in a molar ratio of 0.3 to 0.8, comprising an amine compound (d) having a thickness of 5% or more. The silver compound containing composition in any one of 14.
16. The silver compound-containing composition according to any one of claims 12 to 15, wherein the water content is 5 to 20 parts by weight with respect to 100 parts by weight of the silver compound (a).
17. Silver nanoparticles having an average particle size of 350 nm or less and a coefficient of variation of 30 to 80%, and having a primary amino group or a secondary amino group and a hydroxyl group having 6 carbon atoms or less bonded to the surface of the silver particle. .
18. 18. The silver nanoparticle according to claim 17, wherein i) a branched primary amino alcohol having 3 to 4 carbon atoms and (ii) an amino chain via an alkyl chain having 2 carbon atoms on the surface of the silver nanoparticle. A silver nanoparticle in which an amine compound (b1) to which a group and a hydroxyl group are bonded, or (b1) and iii) a linear secondary amino alcohol (b2) having 3 carbon atoms is bonded.
19. The silver nanoparticle according to claim 18, wherein 2-amino-2-methyl-1-propanol is bound as the amine compound (b1).
20. 20. The silver nanoparticle according to any one of claims 17 to 19, further comprising an amine compound having a molecular length of 7 to 8 mm other than (b1) and (b2).
21. A silver nanoparticle dispersion, wherein the silver nanoparticles according to any one of claims 17 to 20 are dispersed in an organic solvent.
22. 21. A silver paint composition, wherein the silver nanoparticles according to claim 17 are dispersed in an organic solvent and further contain an organic binder.
23. A method for producing a silver conductive material, comprising: applying a silver nanoparticle dispersion according to claim 21 or a silver coating composition according to claim 22 on a substrate and baking to form a silver conductive layer.

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