JP7474122B2 - Silver nanoparticles and their manufacturing method - Google Patents

Description

The present invention relates to silver nanoparticles and a method for producing the same. The present invention is also applicable to metal nanoparticles containing metals other than silver and a method for producing the same.

Silver nanoparticles can be sintered even at low temperatures. Taking advantage of this property, silver paint compositions containing silver nanoparticles are used to form electrodes and conductive circuit patterns on substrates in the manufacture of various electronic devices. Silver nanoparticles are usually dispersed in an organic solvent. Silver nanoparticles have an average primary particle size of several nm to several tens of nm, and their surfaces are usually coated with an organic stabilizer (protective agent). When the substrate is a plastic film or sheet, it is necessary to sinter the silver nanoparticles at a low temperature (e.g., 200°C or lower) that is lower than the heat resistance temperature of the plastic substrate.

In particular, in recent years, attempts have been made to form fine metal wiring (e.g., silver wiring) not only on heat-resistant polyimide, which is already used as a flexible printed wiring board, but also on various plastic substrates such as PET (polyethylene terephthalate) and polypropylene, which are less heat-resistant than polyimide but are easy to process and inexpensive. When using a plastic substrate with low heat resistance, it is necessary to sinter the metal nanoparticles (e.g., silver nanoparticles) at an even lower temperature.

For example, JP 2008-214695 A discloses a method for producing ultrafine silver particles, which comprises reacting silver oxalate with oleylamine to produce a complex compound containing at least silver, oleylamine, and oxalate ions, and then thermally decomposing the complex compound to produce ultrafine silver particles (claim 1). It also discloses that, in the method, a saturated aliphatic amine having a total carbon number of 1 to 18 is reacted with the silver oxalate and the oleylamine in addition to the complex compound (claims 2 and 3), which makes it possible to easily produce the complex compound, shorten the time required to produce ultrafine silver particles, and produce ultrafine silver particles protected by these amines in a higher yield (paragraph [0011]). It also discloses that the thermal decomposition of the complex compound is preferably carried out at a temperature of about 100°C to 180°C, and particularly preferably at a temperature of about 120°C to 160°C (paragraph [0018]).

JP 2010-265543 A discloses a method for producing coated ultrafine silver particles, which includes a first step of mixing a silver compound that decomposes when heated to produce metallic silver with a medium- or short-chain alkylamine having a boiling point of 100°C to 250°C and a medium- or short-chain alkyldiamine having a boiling point of 100°C to 250°C to prepare a complex compound containing the silver compound, the alkylamine, and the alkyldiamine, and a second step of thermally decomposing the complex compound (Claim 3, paragraphs [0061] and [0062]). It is disclosed that the thermal decomposition of the complex compound is carried out at a temperature of about 80°C to 120°C (paragraph [0043]).

JP 2012-162767 A discloses a method for producing coated metal microparticles, which includes a first step of mixing an amine mixture containing an alkylamine having 6 or more carbon atoms and an alkylamine having 5 or less carbon atoms with a metal compound containing a metal atom to produce a complex compound containing the metal compound and the amine, and a second step of thermally decomposing the complex compound to produce metal microparticles (Claim 1). It also discloses that the coated silver microparticles can be dispersed in an organic solvent, such as an alcohol solvent such as butanol, a non-polar solvent such as octane, or a mixture thereof (Paragraph [0079]). It also discloses that the thermal decomposition of the complex compound was carried out at a temperature of 100°C to 110°C (Paragraph [0094]).

JP 2013-142172 A discloses a method for producing silver nanoparticles, which comprises preparing an amine mixture containing an aliphatic hydrocarbon monoamine (A) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 6 or more, an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms of which is 8 or less, mixing a silver compound with the amine mixture to produce a complex compound containing the silver compound and the amine, and heating the complex compound to cause thermal decomposition, thereby forming silver nanoparticles (Claim 1). It is also disclosed that a silver coating composition, known as silver ink, can be prepared by dispersing the obtained silver nanoparticles in a suspended state in a suitable organic solvent (dispersion medium). Examples of the organic solvent include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, and tetradecane; aromatic hydrocarbon solvents such as toluene, xylene, and mesitylene; and alcohol solvents such as methanol, ethanol, propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, and n-decanol (paragraph [0085]). It is also disclosed that the thermal decomposition of the silver oxalate complex compound is carried out at a temperature of about 80°C to 120°C (paragraph [0080]).

JP 2013-142173 A discloses a method for producing silver nanoparticles, which comprises preparing an amine mixture containing a specific ratio of an aliphatic hydrocarbon monoamine (A) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of the aliphatic hydrocarbon group being 6 or more, and an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of the aliphatic hydrocarbon group being 5 or less, mixing a silver compound with the amine mixture to generate a complex compound containing the silver compound and the amine, and heating the complex compound to cause thermal decomposition to form silver nanoparticles (Claim 1). In addition, as in the above JP 2013-142172 A, it is disclosed that a silver coating composition called a silver ink can be produced by dispersing the obtained silver nanoparticles in a suspension state in an appropriate organic solvent (dispersion medium), and a similar organic solvent is disclosed (paragraph [0076]). It is disclosed that the thermal decomposition of silver oxalate complex compounds is carried out at temperatures of approximately 80°C to 120°C (paragraph [0071]).

JP 2014-034690 A discloses a method for producing silver nanoparticles, which includes: mixing a silver compound with an alcohol-based solvent to obtain a silver compound-alcohol slurry; adding an aliphatic hydrocarbon amine to the obtained silver compound-alcohol slurry to generate a complex compound containing the silver compound and the amine; and heating the complex compound to cause thermal decomposition to form silver nanoparticles.

JP 2015-131991 A discloses a method for producing silver nanoparticles, which includes a complex compound production step of mixing an aliphatic hydrocarbon amine and a silver compound at room temperature to produce a complex compound containing the silver compound and the aliphatic hydrocarbon amine; and a complex compound thermal decomposition step of heating the complex compound to a thermal decomposition temperature of 80 to 120°C at a temperature increase rate of more than 2°C/min to thermally decompose the complex compound, thereby forming silver nanoparticles.

JP 2008-214695 A JP 2010-265543 A JP 2012-162767 A JP 2013-142172 A JP 2013-142173 A JP 2014-034690 A JP 2015-131991 A

Silver nanoparticles have an average primary particle size of several nm to several tens of nm, and are more prone to aggregation than micron (μm) sized particles. Therefore, the reduction reaction of the silver compound (thermal decomposition reaction in the above patent document) is carried out in the presence of an organic stabilizer (a protective agent such as an aliphatic amine or an aliphatic carboxylic acid) so that the surface of the resulting silver nanoparticles is covered with the organic stabilizer.

On the other hand, silver nanoparticles are considered to be a silver paint composition (silver ink, silver paste) containing the particles in an organic solvent. In order to exhibit electrical conductivity, it is necessary that the organic stabilizer covering the silver nanoparticles is removed and the silver particles are sintered during baking after application to a substrate. If the baking temperature is low, the organic stabilizer is difficult to remove. If the silver particles are not sintered to a sufficient degree, a low resistance value cannot be obtained. In other words, the organic stabilizer present on the surface of the silver nanoparticles contributes to the stabilization of the silver nanoparticles, but on the other hand, it hinders the sintering of the silver nanoparticles (especially sintering at low temperatures).

When a relatively long-chain (e.g., carbon number 8 or more) aliphatic amine compounds and/or aliphatic carboxylic acid compounds are used as the organic stabilizer, the silver nanoparticles are more likely to be stabilized because the spacing between the individual silver nanoparticles is more likely to be secured. On the other hand, long-chain aliphatic amine compounds and/or aliphatic carboxylic acid compounds are less likely to be removed if the firing temperature is low.

Thus, there is a trade-off between stabilizing silver nanoparticles and achieving low resistance values when fired at low temperatures.

In the above-mentioned patent documents, the silver complex compound production reaction process and the complex compound thermal decomposition reaction process are carried out in the same reaction tank. In other words, the entire reaction mixture containing the silver complex compound obtained in the production reaction process is heated as is, and the complex compound is subjected to the thermal decomposition reaction process in the same reaction tank. The above-mentioned thermal decomposition reaction is an exothermic reaction, and if the entire reaction mixture containing the silver complex compound is heated as is, there is a drawback in that the thermal decomposition reaction proceeds all at once, making it difficult to control the heat generation. This poses a significant safety risk, especially in scaled-up industrial production.

When the dispersion containing silver nanoparticles is applied to various substrates, it is subjected to a filtration process using a filter. In this filtration process, it is important that the silver nanoparticles in the dispersion have a small average particle diameter, for example, an average particle diameter of 100 nm or less, so that the filter does not become clogged. In addition, from the viewpoint of the homogeneity of the silver coating film after firing, it is also important that the silver nanoparticles in the dispersion have a small average particle diameter, for example, an average particle diameter of 100 nm or less.

Furthermore, when considering inkjet printing, the silver nanoparticle-containing dispersion (silver nanoparticle-containing ink) needs to be one that does not clog the inkjet head.

Therefore, an object of the present invention is to provide a method for producing silver nanoparticles, which produces silver nanoparticles having a small average particle size, using the so-called thermal decomposition method of producing silver nanoparticles by thermal decomposition of a silver-amine complex compound. A further object of the present invention is to provide a method for producing silver nanoparticles, which produces silver nanoparticles that can be sintered at low temperatures and have a small average particle size, using the so-called thermal decomposition method of producing silver nanoparticles by thermal decomposition of a silver-amine complex compound. A further object of the present invention is to provide a method for producing silver nanoparticles, which produces silver nanoparticles having the small average particle size, even in scaled-up industrial production.

A further object of the present invention is to provide silver nanoparticles having a small average particle size. A further object of the present invention is to provide uniform silver nanoparticles that can be sintered at low temperatures and have a small average particle size. These silver nanoparticles can be obtained by the above-mentioned manufacturing method.

As a result of their investigations, the inventors have found that by sequentially introducing the reaction mixture containing the complex compound obtained in the silver complex compound production reaction process into the thermal decomposition reaction process and sequentially thermally decomposing the complex compound, it is possible to control the generation of reaction heat and to facilitate scale-up.

However, it was found that when the reaction mixture containing the silver complex compound obtained in the production reaction process and kept at room temperature was successively added to the thermal decomposition tank, the average particle size of the silver nanoparticles became larger than in the conventional method in which the entire reaction mixture containing the silver complex compound obtained in the production reaction process was heated as is and the complex compound was subjected to a thermal decomposition reaction in the same reaction tank.

The inventors considered that if the generated complex compound is successively added to a pyrolysis tank in the presence of the crystal nuclei of the desired silver nanoparticles and pyrolyzed, the presence of the crystal nuclei may lead to efficient formation of silver nanoparticles.

The inventors have further studied the matter and found that by preheating the reaction mixture containing the complex compound obtained in the silver complex compound production reaction step, and then sequentially introducing the preheated reaction mixture into the thermal decomposition reaction step to sequentially thermally decompose the complex compound, the average particle size of the silver nanoparticles produced becomes smaller than when preheating is not performed. They also found that the silver nanoparticles obtained in this way have two or more peaks in the particle size distribution.

After further intensive research, the inventors have found that by placing pre-prepared silver nanoparticles in a thermal decomposition reaction vessel, sequentially introducing a reaction mixture containing a complex compound obtained in a silver complex compound production reaction step into the thermal decomposition reaction vessel in which the pre-prepared silver nanoparticles are present, and sequentially thermally decomposing the complex compound, the average particle size of the silver nanoparticles produced becomes smaller than when no silver nanoparticles are present in the thermal decomposition reaction vessel. They have also found that the silver nanoparticles obtained in this way have two or more peaks in the particle size distribution.

The present invention includes the following inventions.
(1) Silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine, and which have two or more peaks in their particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more but less than 100 nm.

(2) The aliphatic hydrocarbon amine comprises an aliphatic hydrocarbon monoamine (A) which comprises an aliphatic hydrocarbon group and one amino group, and the total number of carbon atoms in the aliphatic hydrocarbon group is 6 or more,
The silver nanoparticles according to (1) above further contain at least one of an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms in the aliphatic hydrocarbon group being 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms in the aliphatic hydrocarbon group being 8 or less.

(3) The silver nanoparticles described in (2) above, in which the aliphatic hydrocarbon monoamine (A) is at least one selected from the group consisting of linear alkyl monoamines having a linear alkyl group with 6 to 12 carbon atoms and branched alkyl monoamines having a branched alkyl group with 6 to 16 carbon atoms.

(4) The silver nanoparticles according to (2) or (3) above, in which the aliphatic hydrocarbon monoamine (B) is an alkyl monoamine having 2 to 5 carbon atoms.

(5) Silver nanoparticles according to any one of (2) to (4) above, in which the aliphatic hydrocarbon diamine (C) is an alkylenediamine in which one of the two amino groups is a primary amino group and the other is a tertiary amino group.

(6) Silver nanoparticles according to any one of (1) to (5) above, in which the aliphatic hydrocarbon amine is used in a total amount of 1 to 50 moles per mole of silver atoms in the silver nanoparticles.

(7) Silver nanoparticles according to any one of (1) to (6) above, having an average particle diameter of 100 nm or less.

(8) a complex compound generating step of mixing an aliphatic hydrocarbyl amine with a silver compound at room temperature to generate a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
A preheating step of preheating the produced complex compound to a preheating temperature of 60 to 90° C.;
a thermal decomposition step of the complex compound, in which the preheated complex compound is successively added to a thermal decomposition tank having a thermal decomposition temperature of 80 to 120° C., which is higher than the preheating temperature, and thermally decomposed to form silver nanoparticles;
A method for producing silver nanoparticles comprising the steps of:

(9) The method for producing silver nanoparticles described in (8) above, wherein the silver compound is silver oxalate.

(10) The aliphatic hydrocarbon amine comprises an aliphatic hydrocarbon monoamine (A) which comprises an aliphatic hydrocarbon group and one amino group, and the total number of carbon atoms in the aliphatic hydrocarbon group is 6 or more, and further comprises
The method for producing silver nanoparticles according to (8) or (9) above, comprising at least one of an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms in the aliphatic hydrocarbon group being 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms in the aliphatic hydrocarbon group being 8 or less.

(11) The method for producing silver nanoparticles according to any one of (8) to (10) above, wherein in the step of producing the complex compound, the aliphatic hydrocarbon amine and the silver compound are mixed in an alcohol solvent having 3 or more carbon atoms.

(12) The method for producing silver nanoparticles according to any one of (8) to (11) above, wherein the complex compound is heated by a tubular heating device in the preheating step of the complex compound.

(13) The method for producing silver nanoparticles according to any one of (8) to (12) above, wherein in the thermal decomposition step of the complex compound, the thermal decomposition temperature is maintained for 10 to 120 minutes after the addition of the complex compound is completed.

(14) The method for producing silver nanoparticles according to any one of (8) to (13) above, wherein a total of 1 to 50 moles of the aliphatic hydrocarbon amine are used per mole of silver atoms of the silver compound.

(15) a process for producing a complex compound, comprising mixing an aliphatic hydrocarbyl amine with a silver compound at room temperature to produce a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
A thermal decomposition tank preparation step in which silver nanoparticles prepared in advance are present in a thermal decomposition tank for thermally decomposing the generated complex compound;
a thermal decomposition step of the complex compound, in which the generated complex compound is successively added to the thermal decomposition tank having a thermal decomposition temperature of 80 to 120° C. and thermally decomposed to form silver nanoparticles;
A method for producing silver nanoparticles comprising the steps of:

(16) In the method for producing silver nanoparticles described in (15) above, in the step of preparing the pyrolysis tank, the surfaces of the previously prepared silver nanoparticles are coated with a protective agent containing an aliphatic hydrocarbon amine.

(17) The method for producing silver nanoparticles according to (15) or (16) above, wherein the silver compound is silver oxalate.

(18) The aliphatic hydrocarbon amine comprises an aliphatic hydrocarbon monoamine (A) which comprises an aliphatic hydrocarbon group and one amino group, and the total number of carbon atoms in the aliphatic hydrocarbon group is 6 or more,
The method for producing silver nanoparticles according to any one of (15) to (17) above further comprises at least one of an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms in the aliphatic hydrocarbon group being 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms in the aliphatic hydrocarbon group being 8 or less.

(19) The method for producing silver nanoparticles according to any one of (15) to (18) above, wherein in the step of producing the complex compound, the aliphatic hydrocarbon amine and the silver compound are mixed in an alcohol solvent having 3 or more carbon atoms.

(20) The method for producing silver nanoparticles according to any one of (15) to (19) above, wherein in the thermal decomposition step of the complex compound, the thermal decomposition temperature is maintained for 10 to 120 minutes after the addition of the complex compound is completed.

(21) The method for producing silver nanoparticles according to any one of (15) to (20) above, wherein a total of 1 to 50 moles of the aliphatic hydrocarbon amine are used per mole of silver atoms of the silver compound.

(22) A silver particle coating composition comprising the silver nanoparticles described in any one of (1) to (7) above or the silver nanoparticles produced by the method described in any one of (8) to (21) above, and an organic solvent.

The silver particle coating composition according to (22) above, which is used for intaglio offset printing, screen printing, spin coating, or inkjet printing. The intaglio offset printing includes gravure offset printing, etc.

(23) a substrate;
a silver conductive layer formed by coating a silver particle coating composition containing the silver nanoparticles according to any one of (1) to (7) above or the silver nanoparticles produced by the method according to any one of (8) to (21) above and an organic solvent on the substrate, and then baking the composition;
An electronic device having:
The electronic devices include various wiring boards, modules, and the like.

A method for producing an electronic device, comprising: applying a silver particle coating composition containing the silver nanoparticles described in any one of (1) to (7) above or the silver nanoparticles produced by the method described in any one of (8) to (21) above and an organic solvent onto a substrate to form a silver particle-containing coating layer, and then baking the coating layer to form a silver conductive layer.
The firing may be performed at a temperature of 200° C. or less, for example, 150° C. or less, and preferably 120° C. or less, for a time of 2 hours or less, for example, 1 hour or less, preferably 30 minutes or less, and more preferably 15 minutes or less. More specifically, the firing may be performed under conditions of about 90° C. to 120° C., and about 10 minutes to 15 minutes, for example, 120° C., 15 minutes.

The substrate may be selected from a plastic substrate, a ceramic substrate, a glass substrate, and a metal substrate.

(24) An apparatus for producing silver nanoparticles, comprising:
a reaction tank for generating a complex compound for mixing an aliphatic hydrocarbyl amine with a silver compound to generate a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
a thermal decomposition reaction tank for thermally decomposing the complex compound to form silver nanoparticles;
and a tubular passage for sequentially transporting a reaction mixture containing the complex compound produced in the production reaction tank to the pyrolysis reaction tank.

(25) The manufacturing apparatus described in (24) above, in which a preheating device is provided in a portion of the tubular passage.

(26) The manufacturing apparatus according to (24) above, in which the thermal decomposition reaction tank also has a function of mixing an aliphatic hydrocarbon amine with a silver compound to produce a complex compound containing the silver compound and the aliphatic hydrocarbon amine.

(27) a process for producing a complex compound, comprising mixing an aliphatic hydrocarbyl amine with a silver compound at room temperature to produce a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
a thermal decomposition step of the complex compound, in which the generated complex compound is successively added to a thermal decomposition tank set at a thermal decomposition temperature of 80 to 120° C. in a state in which the crystal nuclei of the target silver nanoparticles are present, and thermally decomposed to form silver nanoparticles;
A method for producing silver nanoparticles comprising the steps of:

(28) The method according to (27) above, which produces silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine, and which have two or more peaks in the particle size distribution, including a peak between 1 nm and less than 20 nm and a peak between 20 nm and 100 nm.

(29) a process for producing a complex compound, comprising mixing an aliphatic hydrocarbyl amine with a silver compound at room temperature to produce a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
a thermal decomposition step of the complex compound, in which the generated complex compound is successively added to a thermal decomposition tank set at a thermal decomposition temperature of 80 to 120° C. in a state in which the crystal nuclei of the target silver nanoparticles are present, and thermally decomposed to form silver nanoparticles;
Including,
A method for controlling the particle size of silver nanoparticles, comprising adjusting silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine, the silver nanoparticles having two or more peaks in their particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more but less than 100 nm.

As used herein, "sequential addition" includes both continuous addition and intermittent addition.

The silver nanoparticles of the present invention are silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine, and have two or more peaks in the particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more and 100 nm or less. The silver nanoparticles of the present invention have a small average particle size, for example, an average particle size of 100 nm or less. A dispersion containing silver nanoparticles having a small average particle size (silver nanoparticle-containing ink) does not cause clogging of a filter in a filtration process using a filter. Therefore, the coating process of the silver nanoparticle-containing dispersion on various substrates can be carried out without problems even in industrial production. Furthermore, in consideration of inkjet printing, a dispersion containing silver nanoparticles having a small average particle size (silver nanoparticle-containing ink) does not cause clogging of an inkjet head. In addition, if the silver nanoparticles in the dispersion have a small average particle size, a silver baked film with excellent homogeneity can be obtained from the silver nanoparticle-containing dispersion.

The silver nanoparticles of the present invention have two or more peaks, including a peak of 1 nm or more and less than 20 nm and a peak of 20 nm or more and less than 100 nm, so that particles with a smaller particle diameter (1 nm or more and less than 20 nm) can easily move between particles with a larger particle diameter (20 nm or more and less than 100 nm). It is considered that particles with a smaller particle diameter (1 nm or more and less than 20 nm) improve the flow state of particles with a larger particle diameter (20 nm or more and less than 100 nm), and the good flow state of the dispersion liquid containing silver nanoparticles (silver particle coating composition) is easily maintained. Therefore, the coating suitability of the silver particle coating composition is improved. Furthermore, when the silver particle coating composition is baked, particles with a smaller particle diameter (1 nm or more and less than 20 nm) can move between particles with a larger particle diameter (20 nm or more and less than 100 nm), and it is expected that a dense silver sintered film can be obtained. Therefore, the conductivity of the silver sintered film is improved.

Furthermore, when metal nanoparticles of different particle sizes are produced separately, the compositions of their surface coating agents generally differ. Different coating agents also change the dispersibility of the metal nanoparticles in a solvent. Therefore, it is not easy to uniformly disperse particles of two different particle sizes in the same solvent. The silver nanoparticles of the present invention can be produced from the same reaction system by the method shown in this specification, and therefore have excellent uniform dispersibility in a solvent despite having two or more peaks in the particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more but less than 100 nm. The compositions of their surface coating agents do not differ, and the nanoparticles have excellent uniform dispersibility in a solvent.

In the present invention, when an aliphatic hydrocarbon monoamine (A) having a total carbon number of 6 or more, and at least one of an aliphatic hydrocarbon monoamine (B) having a total carbon number of 5 or less and an aliphatic hydrocarbon diamine (C) having a total carbon number of 8 or less are used as the aliphatic hydrocarbon amine compound that functions as a complexing agent and/or a protective agent, the surface of the formed silver nanoparticles is coated with these aliphatic amine compounds.

The aliphatic hydrocarbon monoamine (B) and the aliphatic hydrocarbon diamine (C) have short carbon chain lengths, and therefore are easily removed from the silver particle surface in a short time of 2 hours or less, for example 1 hour or less, preferably 30 minutes or less, even when fired at a low temperature of 200°C or less, for example 150°C or less, and preferably 120°C or less. Furthermore, due to the presence of the monoamine (B) and/or the diamine (C), the amount of the aliphatic hydrocarbon monoamine (A) adhering to the silver particle surface is small. Therefore, even when fired at the low temperature, these aliphatic amine compounds are easily removed from the silver particle surface in the short time, and the sintering of the silver particles proceeds sufficiently.

In the manufacturing method of the present invention, the silver compound and the complex compound containing an aliphatic hydrocarbon amine generated in the complex compound generation step are successively added to a pyrolysis tank in the presence of the crystal nuclei of the target silver nanoparticles, and pyrolyzed to form silver nanoparticles. This manufacturing method makes it possible to obtain silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine, which have two or more peaks in the particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more but 100 nm, and which have a small average particle size, for example, an average particle size of 100 nm or less. In addition, when the generated complex compound is successively added to a pyrolysis tank in the presence of the crystal nuclei of the target silver nanoparticles, and pyrolyzed, the growth of the crystal nuclei advances due to the presence of the crystal nuclei, and silver nanoparticles with a smaller particle size (1 nm or more but 20 nm or less) are generated.

Furthermore, according to the manufacturing method of the present invention, the particles having a larger particle size (20 nm or more and 100 nm or less) and the particles having a smaller particle size (1 nm or more and less than 20 nm) are both surface-coated with a protective agent containing the same aliphatic hydrocarbon amine, so that the particles have excellent affinity with each other, and it is believed that the particles having a smaller particle size (1 nm or more and less than 20 nm) improve the flow state of the particles having a larger particle size (20 nm or more and 100 nm or less), making it easier to maintain a good flow state of the dispersion liquid containing silver nanoparticles.

According to the manufacturing method of the present invention, the complex compound produced in the complex compound production process is successively added to a pyrolysis tank and pyrolyzed to form silver nanoparticles, so that the heat generated by the pyrolysis reaction can be controlled and safety can be ensured even in scaled-up industrial production.

Furthermore, in the manufacturing method of the present invention, in the step of generating a complex compound containing a silver compound and an aliphatic hydrocarbon amine, a powdered silver compound and an aliphatic hydrocarbon amine are mixed in the presence of an alcohol solvent having 3 or more carbon atoms to generate a complex compound containing the silver compound and the amine. In the step of generating the complex compound, a sufficient stirring operation can be performed, and the reaction heat accompanying the formation of the complex compound can be released outside the system. Therefore, a safe and simple method for manufacturing silver nanoparticles is provided, even in scaled-up industrial production.

In this way, the present invention provides silver nanoparticles that exhibit excellent conductivity (low resistance value) by firing at a low temperature for a short time, and a method for producing the same. The present invention also provides a silver nanoparticle-containing coating composition (silver ink, silver paste) that contains the silver nanoparticles in a stable dispersion state in an organic solvent. The silver nanoparticle-containing ink of the present invention is suitable for inkjet applications.

Furthermore, the present invention is also applicable to a method for producing metal nanoparticles containing metals other than silver and to the production of said metal nanoparticles.

According to the present invention, it is possible to form conductive films and conductive wiring even on various plastic substrates with low heat resistance, such as PET and polypropylene. The silver nanoparticle-containing coating composition of the present invention is suitable for use as elements in various recent electronic devices.

FIG. 1 is a diagram showing a schematic configuration of an example of a silver nanoparticle production apparatus that can be used in the present invention. 1 is a graph showing the measurement results of the particle size distribution of silver nanoparticles in Example 1. The horizontal axis represents particle size (nm) and the vertical axis represents intensity (%). The same applies to the following particle size distribution graphs. 1 is a graph showing the measurement results of the particle size distribution of silver nanoparticles in Example 2. 1 is a graph showing the measurement results of particle size distribution of silver nanoparticles in Comparative Example 1. 1 is a graph showing the measurement results of particle size distribution of silver nanoparticles in Comparative Example 2. 1 is a graph showing the measurement results of particle size distribution of silver nanoparticles in Example 3. 13 is a graph showing the measurement results of particle size distribution of silver nanoparticles in Comparative Example 3.

[Silver nanoparticles]
In the present invention, the silver nanoparticles are silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine, and have two or more peaks in the particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more but 100 nm or less. The silver nanoparticles of the present invention have a small average particle size, for example, an average particle size of 100 nm or less.

In this specification, the average particle size of nanoparticles is the size of primary particles (average primary particle size) determined from the particle size distribution by dynamic light scattering (DLS). The particle size is intended to be the size excluding the protective agent (stabilizer) present (coating) on the surface (i.e., the size of silver itself). In the present invention, the silver nanoparticles have an average primary particle size of, for example, 0.5 nm to 100 nm, preferably 0.5 nm to 70 nm, more preferably 0.5 nm to 60 nm, and even more preferably 0.5 nm to 40 nm or 0.5 nm to 26 nm.

A dispersion containing silver nanoparticles with a small average particle size (silver nanoparticle-containing ink) does not clog the filter during the filtration process using a filter. Therefore, the coating process of the silver nanoparticle-containing dispersion onto various substrates can be carried out without problems even in industrial production. Furthermore, in consideration of inkjet printing, a dispersion containing uniform silver nanoparticles with a small average particle size (silver nanoparticle-containing ink) does not clog the inkjet head. Furthermore, if the silver nanoparticles in the dispersion have a small average particle size, a silver fired film with excellent homogeneity can be obtained from the silver nanoparticle-containing dispersion.

The silver nanoparticles of the present invention have two or more peaks, including a peak of 1 nm or more and less than 20 nm and a peak of 20 nm or more and less than 100 nm, so that particles with a smaller particle diameter (1 nm or more and less than 20 nm) can easily move between particles with a larger particle diameter (20 nm or more and less than 100 nm). It is considered that particles with a smaller particle diameter (1 nm or more and less than 20 nm) improve the flow state of particles with a larger particle diameter (20 nm or more and less than 100 nm), and the good flow state of the dispersion liquid containing silver nanoparticles (silver particle coating composition) is easily maintained. Therefore, the coating suitability of the silver particle coating composition is improved. Furthermore, when the silver particle coating composition is baked, particles with a smaller particle diameter (1 nm or more and less than 20 nm) can move between particles with a larger particle diameter (20 nm or more and less than 100 nm), and it is expected that a dense silver sintered film can be obtained. Therefore, the conductivity of the silver sintered film is improved.

From this perspective, the ratio of particles with smaller particle diameters (1 nm or more and less than 20 nm) to particles with larger particle diameters (20 nm or more and less than 100 nm) is not particularly limited, but for example, the peak intensity in the region of 1 nm or more and less than 20 nm may be 5 to 25%, and the peak intensity in the region of 20 nm or more and less than 100 nm may be 75 to 95%.

In the present invention, the silver nanoparticles may have two or more peaks in the region of 1 nm or more and less than 20 nm, or may have two or more peaks in the region of 20 nm or more and 100 nm or less.

In the silver nanoparticles of the present invention, the aliphatic hydrocarbon amine includes, for example, an aliphatic hydrocarbon monoamine (A) which is composed of an aliphatic hydrocarbon group and one amino group and in which the total number of carbon atoms in the aliphatic hydrocarbon group is 6 or more;
Furthermore, the compound may contain at least one of an aliphatic hydrocarbon monoamine (B) which is composed of an aliphatic hydrocarbon group and one amino group, and the total number of carbon atoms in the aliphatic hydrocarbon group is 5 or less, and an aliphatic hydrocarbon diamine (C) which is composed of an aliphatic hydrocarbon group and two amino groups, and the total number of carbon atoms in the aliphatic hydrocarbon group is 8 or less.

The method for producing silver nanoparticles of the present invention will be described below together with an explanation of the aliphatic hydrocarbon amine that functions as a complexing agent and/or a protective agent.

[Method of manufacturing silver nanoparticles]
The method for producing silver nanoparticles of the present invention includes the steps of: mixing an aliphatic hydrocarbyl amine and a silver compound at room temperature to produce a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
and a thermal decomposition step of the complex compound, in which the produced complex compound is successively added to a thermal decomposition tank set at a thermal decomposition temperature of 80 to 120°C in the presence of crystal nuclei of the target silver nanoparticles, and thermally decomposed to form silver nanoparticles.

Figure 1 shows a schematic diagram of an example of a silver nanoparticle manufacturing device that can be used in the present invention.

Referring to FIG. 1, the silver nanoparticle production apparatus includes a complex compound production reaction tank (10) for mixing an aliphatic hydrocarbylamine and a silver compound in a complex compound production step (I) to produce a complex compound containing the silver compound and the aliphatic hydrocarbylamine;
A thermal decomposition reaction tank (30) for thermally decomposing the complex compound to form silver nanoparticles in a thermal decomposition step (III) of the complex compound;
and a tubular passage (20) for sequentially transferring the reaction mixture containing the complex compound produced in the production reaction tank (10) to the pyrolysis reaction tank (30) in the transfer step (II) of the reaction mixture containing the complex compound.

In the present invention, the silver compound used is one that easily decomposes when heated to produce metallic silver. Examples of such silver compounds include silver carboxylates such as silver formate, silver acetate, silver oxalate, silver malonate, silver benzoate, and silver phthalate; silver halides such as silver fluoride, silver chloride, silver bromide, and silver iodide; and silver sulfate, silver nitrate, and silver carbonate. Silver oxalate is preferably used because it easily produces metallic silver when decomposed and is less likely to produce impurities other than silver. Silver oxalate has the advantage that it has a high silver content, does not require a reducing agent, and metallic silver is obtained directly by thermal decomposition, leaving less impurities derived from the reducing agent.

When producing metal nanoparticles containing metals other than silver, a metal compound that easily decomposes when heated to produce the desired metal is used instead of the silver compound. Such metal compounds include metal salts that correspond to the silver compounds, such as metal carboxylates; metal halides; metal sulfates, metal nitrates, and metal carbonates. Of these, metal oxalates are preferably used because they easily produce metals when decomposed and are less likely to produce impurities other than metals. Examples of other metals include Al, Au, Pt, Pd, Cu, Co, Cr, In, and Ni.

In addition, to obtain a composite with silver, the above silver compound may be used in combination with a compound of a metal other than silver. Examples of the other metal include Al, Au, Pt, Pd, Cu, Co, Cr, In, and Ni. A silver composite is made of silver and one or more other metals, and examples include Au-Ag, Ag-Cu, Au-Ag-Cu, and Au-Ag-Pd. Based on the total metals, silver accounts for at least 20% by weight, usually at least 50% by weight, for example at least 80% by weight.

In the present invention, in the step of producing a complex compound, the aliphatic hydrocarbon amine and the silver compound may be mixed without a solvent, but it is preferable to mix them in the presence of an alcohol solvent having 3 or more carbon atoms to produce a complex compound containing the silver compound and the amine.

As the alcohol solvent, an alcohol having 3 to 10 carbon atoms, preferably an alcohol having 4 to 6 carbon atoms, can be used. Examples include 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), and 2-octanol (bp: 174°C). Among these, butanols and hexanols selected from n-butanol, isobutanol, sec-butanol, and tert-butanol are preferred, taking into consideration the ability to increase the temperature of the subsequent thermal decomposition process of the complex compound and the convenience of post-treatment after the formation of silver nanoparticles. In particular, n-butanol and n-hexanol are preferred.

In order to thoroughly stir the silver compound-alcohol slurry, the alcohol solvent is used in an amount of, for example, 120 parts by weight or more, preferably 130 parts by weight or more, and more preferably 150 parts by weight or more, relative to 100 parts by weight of the silver compound. There is no particular upper limit to the amount of the alcohol solvent, and it is, for example, 1000 parts by weight or less, preferably 800 parts by weight or less, and more preferably 500 parts by weight or less, relative to 100 parts by weight of the silver compound.

In the present invention, the mixing of the aliphatic hydrocarbyl amine and the silver compound in the presence of an alcohol solvent having 3 or more carbon atoms can take several forms.
For example, first, a solid silver compound and an alcohol solvent are mixed to obtain a silver compound-alcohol slurry [slurry formation step], and then an aliphatic hydrocarbon amine may be added to the obtained silver compound-alcohol slurry. The term "slurry" refers to a mixture in which a solid silver compound is dispersed in an alcohol solvent. The solid silver compound may be charged into a reaction vessel, and the alcohol solvent may be added thereto to obtain a slurry.
Alternatively, the aliphatic hydrocarbyl amine and the alcohol solvent may be charged to a reaction vessel, and the silver compound-alcohol slurry may be added thereto.

In the present invention, the aliphatic hydrocarbon amine that functions as a complexing agent and/or a protective agent may include, for example, an aliphatic hydrocarbon monoamine (A) having a total number of carbon atoms in the hydrocarbon group of 6 or more, and may further include at least one of an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms in the aliphatic hydrocarbon group being 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms in the aliphatic hydrocarbon group being 8 or less. These components are usually used as an amine mixture, but the mixing of the amine with the silver compound (or its alcohol slurry) does not necessarily need to be performed using the amines in a mixed state. The amines may be added sequentially to the silver compound (or its alcohol slurry).

In this specification, the term "aliphatic hydrocarbon monoamine" is an established term, but it is a compound consisting of one to three monovalent aliphatic hydrocarbon groups and one amino group. A "hydrocarbon group" is a group consisting only of carbon and hydrogen. However, the aliphatic hydrocarbon monoamine (A) and the aliphatic hydrocarbon monoamine (B) may have a substituent containing a heteroatom (an atom other than carbon and hydrogen) such as an oxygen atom or a nitrogen atom in the hydrocarbon group as necessary. This nitrogen atom does not constitute an amino group.

Furthermore, an "aliphatic hydrocarbon diamine" is a compound consisting of a divalent aliphatic hydrocarbon group (alkylene group), two amino groups interposed between the aliphatic hydrocarbon group, and, in some cases, an aliphatic hydrocarbon group (alkyl group) that replaces the hydrogen atom of the amino group. However, the aliphatic hydrocarbon diamine (C) may have a substituent in the hydrocarbon group that contains a heteroatom (an atom other than carbon and hydrogen) such as an oxygen atom or a nitrogen atom, as necessary. The nitrogen atom does not constitute an amino group.

Aliphatic hydrocarbon monoamines (A) with a total of 6 or more carbon atoms have a high functionality as a protective agent (stabilizer) for the surface of the resulting silver particles due to their hydrocarbon chain.

The aliphatic hydrocarbon monoamine (A) includes primary amines, secondary amines, and tertiary amines. Examples of primary amines include saturated aliphatic hydrocarbon monoamines (i.e., alkyl monoamines) having a linear aliphatic hydrocarbon group having 6 to 18 carbon atoms, such as hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, and octadecylamine. In addition to the linear aliphatic monoamines described above, examples of saturated aliphatic hydrocarbon monoamines include branched aliphatic hydrocarbon monoamines having a branched aliphatic hydrocarbon group having 6 to 16 carbon atoms, preferably 6 to 8 carbon atoms, such as isohexylamine, 2-ethylhexylamine, and tert-octylamine. Cyclohexylamine is also included. Furthermore, unsaturated aliphatic hydrocarbon monoamines (i.e., alkenyl monoamines) such as oleylamine are included.

Examples of secondary amines that are linear include dialkyl monoamines such as N,N-dipropylamine, N,N-dibutylamine, N,N-dipentylamine, N,N-dihexylamine, N,N-diheptylamine, N,N-dioctylamine, N,N-dinonylamine, N,N-didecylamine, N,N-diundecylamine, N,N-didodecylamine, N-methyl-N-propylamine, N-ethyl-N-propylamine, and N-propyl-N-butylamine. Examples of tertiary amines include tributylamine and trihexylamine.

Examples of branched amines include secondary amines such as N,N-diisohexylamine and N,N-di(2-ethylhexyl)amine. Examples of branched amines include tertiary amines such as triisohexylamine and tri(2-ethylhexyl)amine. In the case of N,N-di(2-ethylhexyl)amine, the 2-ethylhexyl group has 8 carbon atoms, but the total number of carbon atoms contained in the amine compound is 16. In the case of tri(2-ethylhexyl)amine, the total number of carbon atoms contained in the amine compound is 24.

Among the monoamines (A), saturated aliphatic hydrocarbon monoamines having 6 or more carbon atoms are preferred in the case of linear monoamines. By making the number of carbon atoms 6 or more, it is possible to secure a distance between the silver particles when the amino group is adsorbed on the surface of the silver particles, improving the effect of preventing aggregation between the silver particles. There is no particular upper limit on the number of carbon atoms, but in consideration of ease of availability and ease of removal during firing, saturated aliphatic monoamines having up to 18 carbon atoms are usually preferred. In particular, alkyl monoamines having 6 to 12 carbon atoms such as hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, and dodecylamine are preferably used. Only one of the linear aliphatic hydrocarbon monoamines may be used, or two or more may be used in combination.

In addition, when a branched aliphatic hydrocarbon monoamine compound is used, a larger area of the silver particle surface can be covered with a smaller amount of adhesion due to the steric factor of the branched aliphatic hydrocarbon group compared to when a straight-chain aliphatic hydrocarbon monoamine compound with the same number of carbon atoms is used. Therefore, appropriate stabilization of the silver nanoparticles can be obtained with a smaller amount of adhesion on the silver particle surface. Since the amount of protective agent (organic stabilizer) to be removed during firing is small, the organic stabilizer can be efficiently removed even when firing at a low temperature of 200°C or less, and sintering of the silver particles proceeds sufficiently.

Among the above branched aliphatic hydrocarbon monoamines, branched alkyl monoamine compounds having 5 to 6 carbon atoms in the main chain, such as isohexylamine and 2-ethylhexylamine, are preferred. When the main chain has 5 to 6 carbon atoms, it is easy to obtain appropriate stabilization of the silver nanoparticles. In addition, from the viewpoint of the steric factor of the branched aliphatic group, it is effective that the branching occurs at the second carbon atom from the N atom side, as in 2-ethylhexylamine. As the branched aliphatic monoamine, only one type may be used, or two or more types may be used in combination.

In the present invention, the linear aliphatic hydrocarbon monoamine and the branched aliphatic hydrocarbon monoamine may be used in combination as the aliphatic hydrocarbon monoamine (A) to obtain the respective advantages.

Aliphatic hydrocarbon monoamines (B) with a total of 5 or less carbon atoms have a shorter carbon chain length than aliphatic monoamines (A) with a total of 6 or more carbon atoms, and therefore are considered to have a low function as a protective agent (stabilizer) in themselves. However, compared to the aliphatic monoamines (A), they have a higher polarity and a higher coordination ability with the silver of the silver compound, and are therefore considered to be effective in promoting complex formation. In addition, because the carbon chain length is short, they can be removed from the silver particle surface in a short time of 30 minutes or less or 20 minutes or less, even at low-temperature firing at, for example, 120°C or less or about 100°C or less, and are therefore effective in low-temperature firing of the obtained silver nanoparticles.

Examples of the aliphatic hydrocarbon monoamine (B) include saturated aliphatic hydrocarbon monoamines having 2 to 5 carbon atoms (i.e., alkyl monoamines), such as ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, pentylamine, isopentylamine, and tert-pentylamine. In addition, examples include dialkyl monoamines, such as N,N-dimethylamine and N,N-diethylamine.

Among these, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, pentylamine, isopentylamine, tert-pentylamine, etc. are preferred, and the above-mentioned butylamines are particularly preferred. Only one of the aliphatic hydrocarbon monoamines (B) may be used, or two or more of them may be used in combination.

Aliphatic hydrocarbon diamines (C) having a total carbon number of 8 or less have a high coordination ability to silver compounds and are effective in promoting the formation of complexes. Aliphatic hydrocarbon diamines generally have a higher polarity than aliphatic hydrocarbon monoamines, and have a higher coordination ability to silver compounds. In addition, the aliphatic hydrocarbon diamines (C) have the effect of promoting thermal decomposition at a lower temperature and in a shorter time in the thermal decomposition process of the complex compound, and can produce silver nanoparticles more efficiently. Furthermore, since the protective coating of the silver particles containing the aliphatic diamines (C) is highly polar, the dispersion stability of the silver particles in a dispersion medium containing a highly polar solvent is improved. Furthermore, since the aliphatic diamines (C) have a short carbon chain length, they can be removed from the silver particle surface in a short time of 30 minutes or less or 20 minutes or less even in low-temperature firing at, for example, 120°C or less or about 100°C or less, and are therefore effective in low-temperature and short-time firing of the obtained silver nanoparticles.

The aliphatic hydrocarbon diamine (C) is not particularly limited, but may be ethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, N,N'-diethylethylenediamine, 1,3-propanediamine, 2,2-dimethyl-1,3-propanediamine, N,N-dimethyl-1,3-propanediamine, N,N'-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine, N,N'-diethyl-1,3-propanediamine, Examples include panediamine, 1,4-butanediamine, N,N-dimethyl-1,4-butanediamine, N,N'-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N'-diethyl-1,4-butanediamine, 1,5-pentanediamine, 1,5-diamino-2-methylpentane, 1,6-hexanediamine, N,N-dimethyl-1,6-hexanediamine, N,N'-dimethyl-1,6-hexanediamine, 1,7-heptanediamine, and 1,8-octanediamine. All of these are alkylenediamines with a total of 8 carbon atoms or less, in which at least one of the two amino groups is a primary amino group or a secondary amino group, and have a high coordination ability with silver compounds and are effective in promoting complex formation.

Among these, preferred are alkylenediamines having a total of 8 or less carbon atoms in which one of the two amino groups is a primary amino group (-NH2) and the other is a tertiary amino group (-NR1R2), such as N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-diethyl- _1,3 -propanediamine, N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, and N, ^N -dimethyl- ^1,6 -hexanediamine. Preferred alkylenediamines are represented by the following structural formula:

^{R1R2N -} R- _NH2
Here, R represents a divalent alkylene group, ^R1 and ^R2 may be the same or different, and represent an alkyl group, provided that the total number of carbon atoms in R, ^R1 and ^R2 is 8 or less. The alkylene group usually does not contain a heteroatom (atom other than carbon and hydrogen) such as an oxygen atom or a nitrogen atom, but may have a substituent containing the heteroatom as necessary. In addition, the alkyl group usually does not contain a heteroatom such as an oxygen atom or a nitrogen atom, but may have a substituent containing the heteroatom as necessary.

When one of the two amino groups is a primary amino group, the silver compound has a high coordination ability with silver, which is advantageous for complex formation, and when the other is a tertiary amino group, the tertiary amino group has poor coordination ability with silver atoms, which prevents the complex formed from having a complex network structure. If the complex has a complex network structure, a high temperature may be required for the thermal decomposition process of the complex. Furthermore, among these, diamines with a total carbon number of 6 or less are preferred, and diamines with a total carbon number of 5 or less are more preferred, from the viewpoint that they can be removed from the silver particle surface in a short time even in low-temperature firing. Of the aliphatic hydrocarbon diamines (C), only one type may be used, or two or more types may be used in combination.

In the present invention, the ratio of the aliphatic hydrocarbon monoamine (A) having a total of 6 or more carbon atoms to either or both of the aliphatic hydrocarbon monoamine (B) having a total of 5 or less carbon atoms and the aliphatic hydrocarbon diamine (C) having a total of 8 or less carbon atoms is not particularly limited. For example, based on the total amines [(A)+(B)+(C)],
The aliphatic monoamine (A): 5 mol% to 65 mol%
Total amount of the aliphatic monoamine (B) and the aliphatic diamine (C): 35 mol% to 95 mol%
It is preferable to set the content of the aliphatic monoamine (A) to 5 mol % to 65 mol %, so that the carbon chain of the component (A) can easily provide a protective and stabilizing function for the surface of the resulting silver particles. If the content of the component (A) is less than 5 mol %, the protective and stabilizing function may be weakly exerted. On the other hand, if the content of the component (A) exceeds 65 mol %, the protective and stabilizing function is sufficient, but the component (A) is difficult to remove by low-temperature firing. When the branched aliphatic monoamine is used as the component (A), it is preferable to set the content of the aliphatic monoamine (A) to 5 mol % to 65 mol %, so as to satisfy the condition of the aliphatic monoamine (A): 5 mol % to 65 mol %.
The branched aliphatic monoamine: 10 mol % to 50 mol %
It would be better to write it as follows.

When the aliphatic monoamine (A) and further both the aliphatic monoamine (B) and the aliphatic diamine (C) are used, the ratio of use thereof is not particularly limited, but may be, for example, based on the total amines [(A)+(B)+(C)],
The aliphatic monoamine (A): 5 mol% to 65 mol%
The aliphatic monoamine (B): 5 mol% to 70 mol%
The aliphatic diamine (C): 5 mol% to 50 mol%
In the case where the branched aliphatic monoamine is used as the component (A), the content of the aliphatic monoamine (A): is preferably 5 mol % to 65 mol %.
The branched aliphatic monoamine: 10 mol % to 50 mol %
It would be better to write it as follows.

In this case, the lower limit of the content of the (A) component is preferably 10 mol% or more, and more preferably 20 mol% or more. The upper limit of the content of the (A) component is preferably 65 mol% or less, and more preferably 60 mol% or less.

By setting the content of the aliphatic monoamine (B) to 5 mol% to 70 mol%, the complex formation promoting effect is easily obtained, and it can contribute to low-temperature and short-time firing by itself, and furthermore, the action of assisting the removal of the aliphatic diamine (C) from the silver particle surface during firing is easily obtained. If the content of the (B) component is less than 5 mol%, the complex formation promoting effect may be weak, or the (C) component may be difficult to remove from the silver particle surface during firing. On the other hand, if the content of the (B) component exceeds 70 mol%, the complex formation promoting effect is obtained, but the content of the aliphatic monoamine (A) is relatively small, and it is difficult to protect and stabilize the surface of the silver particles produced. The lower limit of the content of the (B) component is preferably 10 mol% or more, and more preferably 15 mol% or more. The upper limit of the content of the (B) component is preferably 65 mol% or less, and more preferably 60 mol% or less.

By setting the content of the aliphatic diamine (C) to 5 mol% to 50 mol%, the complex formation promoting effect and the thermal decomposition promoting effect of the complex are easily obtained, and since the protective coating of the silver particles containing the aliphatic diamine (C) has high polarity, the dispersion stability of the silver particles in a dispersion medium containing a highly polar solvent is improved. If the content of the (C) component is less than 5 mol%, the complex formation promoting effect and the thermal decomposition promoting effect of the complex may be weak. On the other hand, if the content of the (C) component exceeds 50 mol%, the complex formation promoting effect and the thermal decomposition promoting effect of the complex are obtained, but the content of the aliphatic monoamine (A) is relatively small, and it is difficult to obtain protection and stabilization of the surface of the generated silver particles. The lower limit of the content of the (C) component is preferably 5 mol% or more, and more preferably 10 mol% or more. The upper limit of the content of the (C) component is preferably 45 mol% or less, and more preferably 40 mol% or less.

When the aliphatic monoamine (A) and the aliphatic monoamine (B) are used (without using the aliphatic diamine (C)), their use ratio is not particularly limited. Taking into consideration the action of each component, the ratio based on the total amines [(A)+(B)] can be, for example,
The aliphatic monoamine (A): 5 mol% to 65 mol%
The aliphatic monoamine (B): 35 mol% to 95 mol%
In the case where the branched aliphatic monoamine is used as the component (A), the content of the aliphatic monoamine (A): is preferably 5 mol % to 65 mol %.
The branched aliphatic monoamine: 10 mol % to 50 mol %
It would be better to write it as follows.

When the aliphatic monoamine (A) and the aliphatic diamine (C) are used (without using the aliphatic monoamine (B)), their use ratio is not particularly limited. Taking into consideration the action of each component, the ratio may be, for example, based on the total amines [(A)+(C)], as follows:
The aliphatic monoamine (A): 5 mol% to 65 mol%
The aliphatic diamine (C): 35 mol% to 95 mol%
In the case where the branched aliphatic monoamine is used as the component (A), the content of the aliphatic monoamine (A): is preferably 5 mol % to 65 mol %.
The branched aliphatic monoamine: 10 mol % to 50 mol %
It would be better to write it as follows.

The above-mentioned proportions of the aliphatic monoamine (A), the aliphatic monoamine (B) and/or the aliphatic diamine (C) are all examples and may be changed in various ways.

In the present invention, when the aliphatic monoamine (B) and/or the aliphatic diamine (C) having a high coordination ability to silver of the silver compound are used, the amount of the aliphatic monoamine (A) having a total carbon number of 6 or more that adheres to the silver particle surface can be reduced depending on the ratio of their use. Therefore, even in the case of firing at a low temperature for a short time, these aliphatic amine compounds are easily removed from the silver particle surface, and the sintering of the silver particles proceeds sufficiently.

In the present invention, the total amount of the aliphatic hydrocarbon amines [e.g., (A), (B) and/or (C)] is not particularly limited, but may be about 1 to 50 moles per mole of silver atoms in the raw silver compound. If the total amount of the amine components [(A), (B) and/or (C)] is less than 1 mole per mole of silver atoms, there is a possibility that silver compounds that are not converted to complex compounds will remain in the complex compound production process, and in the subsequent thermal decomposition process, the uniformity of the silver particles will be impaired, causing particle enlargement, or silver compounds will remain without thermal decomposition. On the other hand, there is thought to be little benefit even if the total amount of the amine components [(A), (B) and/or (C)] exceeds about 50 moles per mole of the silver atoms. In order to prepare a dispersion of silver nanoparticles substantially in a solvent-free environment, the total amount of the amine components may be, for example, about 2 moles or more. By setting the total amount of the amine components to about 2 to 50 moles, the complex compound production process and the thermal decomposition process can be carried out smoothly. The lower limit of the total amount of the amine components is preferably 2 moles or more, more preferably 6 moles or more, per mole of silver atoms of the silver compound. Note that a silver oxalate molecule contains two silver atoms.

In the present invention, in order to further improve the dispersibility of the silver nanoparticles in the dispersion medium, an aliphatic carboxylic acid (D) may be further used as a stabilizer. The aliphatic carboxylic acid (D) may be used together with the amines, and may be used by being included in the amine mixture. By using the aliphatic carboxylic acid (D), the stability of the silver nanoparticles, particularly the stability in the paint state dispersed in an organic solvent, may be improved.

As the aliphatic carboxylic acid (D), a saturated or unsaturated aliphatic carboxylic acid is used. Examples include saturated aliphatic monocarboxylic acids having 4 or more carbon atoms, such as 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, 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 making the number of carbon atoms 8 or more, it is possible to ensure a distance between the silver particles when the carboxylic acid group is adsorbed on the surface of the silver particles, improving the effect of preventing aggregation between the silver particles. In consideration of ease of availability, ease 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, etc. are preferably used. Only one of the aliphatic carboxylic acids (D) may be used, or two or more may be used in combination.

When the aliphatic carboxylic acid (D) is used, it is preferable to use, for example, about 0.05 to 10 moles, preferably 0.1 to 5 moles, and more preferably 0.5 to 2 moles, per mole of silver atoms in the raw silver compound. If the amount of the (D) component is less than 0.05 moles per mole of silver atoms, the effect of improving the stability in the dispersed state by adding the (D) component is weak. On the other hand, if the amount of the (D) component reaches 10 moles, the effect of improving the stability in the dispersed state becomes saturated, and the (D) component becomes difficult to remove by low-temperature firing. However, when the removal of the (D) component by low-temperature firing is taken into consideration, the aliphatic carboxylic acid (D) may not be used.

In the present invention, a mixed solution containing each of the aliphatic hydrocarbon amine components to be used is usually prepared; for example, an amine mixed solution containing the aliphatic monoamine (A) and either or both of the aliphatic monoamine (B) and the aliphatic diamine (C) is prepared [Amine mixed solution preparation process].

The amine mixture can be prepared by stirring the amine (A), (B) and/or (C) components, and the carboxylic acid (D) component, if used, in a predetermined ratio at room temperature.

An aliphatic hydrocarbon amine mixture containing each amine component is added to the silver compound (or its alcohol slurry) to generate a complex compound containing the silver compound and the amine [complex compound generation process]. Each amine component may be added successively to the silver compound (or its alcohol slurry) without forming a mixture.

When producing metal nanoparticles containing a metal other than silver, a metal compound (or an alcohol slurry thereof) containing the desired metal is used instead of the above silver compound (or an alcohol slurry thereof).

Mix the silver compound (or its alcohol slurry) or metal compound (or its alcohol slurry) with a predetermined amount of the amine mixture. Mixing should be done at room temperature. "Room temperature" refers to 5 to 40°C depending on the ambient temperature. For example, 5 to 35°C (JIS Z 8703), 10 to 35°C, or 20 to 30°C. Ordinary room temperature (for example, in the range of 15 to 30°C) may also be used. Mixing at this time may be done with stirring, or, since the coordination reaction of amines with the silver compound (or metal compound) is exothermic, it may be done with stirring after cooling appropriately to the above temperature range, for example, about 5 to 15°C. If the silver compound and the amine mixture are mixed in the presence of an alcohol with 3 or more carbon atoms, stirring and cooling can be performed well. The excess of the alcohol and amines play the role of the reaction medium.

In the conventional thermal decomposition method of silver amine complexes, a liquid aliphatic amine component is first charged into a reaction vessel, and then a powdered silver compound (silver oxalate) is added to it. Liquid aliphatic amine components are flammable substances, and adding a powdered silver compound to them is dangerous. That is, there is a risk of ignition due to static electricity caused by adding the powdered silver compound. In addition, there is a risk that the addition of the powdered silver compound will cause a complex formation reaction to proceed locally, resulting in an explosive exothermic reaction. If the silver compound and the amine mixture are mixed in the presence of the alcohol, such dangers can be avoided. Therefore, it is safe even in scaled-up industrial production.

Since the complex compound formed generally exhibits a color according to its constituent components, the end point of the complex compound formation reaction can be detected by detecting the completion of the color change of the reaction mixture by an appropriate spectroscopy method or the like. In addition, the complex compound formed by silver oxalate is generally colorless (visually observed as white), but even in such cases, the state of formation of the complex compound can be detected based on morphological changes such as changes in the viscosity of the reaction mixture. For example, the time for the complex compound formation reaction is about 30 minutes to 3 hours. In this way, a silver-amine complex (or a metal-amine complex) is obtained in a medium mainly composed of alcohol and amines.

In the present invention, the reaction mixture containing the complex compound obtained in the complex compound production process is sequentially transferred to the thermal decomposition process.

When the reaction mixture containing the complex compound is sequentially transferred to the pyrolysis step, the crystal nuclei of the target silver nanoparticles are present. That is, in the first form, the crystal nuclei of the target silver nanoparticles are present in the reaction mixture containing the complex compound itself, or in the second form, the target silver nanoparticles that have been prepared in advance are present in the pyrolysis tank.

First form:
The production method of the first embodiment includes the steps of producing the above-mentioned complex compound,
a preheating step of preheating the reaction mixture containing the complex compound obtained in the complex compound production step to a preheating temperature of 60 to 90°C;
and a thermal decomposition step of the complex compound, in which the preheated complex compound is successively added to a thermal decomposition tank having a thermal decomposition temperature of 80 to 120° C., which is higher than the preheating temperature, and thermally decomposed to form silver nanoparticles.

An example of a silver nanoparticle production apparatus is shown in Fig. 1. The production apparatus of this example includes a complex compound production reaction tank (10) equipped with a stirring device (M: motor, 11: stirring blade) for mixing an aliphatic hydrocarbylamine and a silver compound in the complex compound production step (I) to produce a complex compound containing the silver compound and the aliphatic hydrocarbylamine;
A thermal decomposition reaction tank (30) for thermally decomposing the complex compound to form silver nanoparticles in the thermal decomposition step (III) of the complex compound, the tank being equipped with an agitation device (M: motor, 31: agitation blade);
and a tubular passage (20) for sequentially transferring the reaction mixture containing the complex compound produced in the production reaction tank (10) to the pyrolysis reaction tank (30) in the transfer step (II) of the complex compound-containing reaction mixture. A tube pump (21) [e.g., a PTFE (polytetrafluoroethylene) tube pump] is provided on the upstream side of the tubular passage (20) extending from the production reaction tank (10) to the pyrolysis reaction tank (30), and a preheating device (22) is provided on the downstream side of the tube pump (21). The tubular passage (20) is composed of a tubular passage (20a) connecting the production reaction tank (10) and the tube pump (21), a tubular passage (20b) connecting the tube pump (21) and the preheating device (22), a tubular passage (20c) located in the preheating device (22), and a tubular passage (20d) connecting the preheating device (22) and the pyrolysis reaction tank (30). The terms "upstream" and "downstream" refer to the flow direction of the complex compound-containing reaction mixture transferred from the production reaction tank (10) to the thermal decomposition reaction tank (30).

In the first embodiment, the reaction mixture containing the complex compound at room temperature in the production reaction tank (10) is transferred downstream through the tubular passage (20) by the tube pump (21), and is preheated to a preheating temperature of 60 to 90°C by the preheating device (22) as the reaction mixture passes through the tubular passage (20c). The preheated reaction mixture containing the complex compound is sequentially added to a pyrolysis tank (30) whose pyrolysis temperature is higher than the preheating temperature and is 80 to 120°C, whereby the complex compound is pyrolyzed to form silver nanoparticles. The configuration of the production apparatus shown in FIG. 1 is one example, and it goes without saying that apparatuses other than this example can be used.

The preheating temperature may vary depending on the type and amount of the aliphatic hydrocarbon amine compound and/or aliphatic carboxylic acid that function as a complexing agent and/or a protective agent, but is set to 60 to 90°C. The thermal decomposition temperature may also vary depending on the type and amount of the aliphatic hydrocarbon amine compound and/or the aliphatic carboxylic acid that form the complex, but is set to a thermal decomposition temperature that is higher than the preheating temperature and is 80 to 120°C. In other words, at the preheating temperature, the target silver amine complex slowly decomposes and the desired crystal nuclei are generated. If the preheating temperature exceeds 90°C, the silver amine complex will rapidly undergo thermal decomposition.

By setting the preheating temperature to, for example, 60 to 90°C, silver nanoparticles with a small average particle size can be obtained in the next thermal decomposition process. Furthermore, the silver nanoparticles obtained in this case have two or more peaks in the particle size distribution, including a peak of 1 nm or more but less than 20 nm and a peak of 20 nm or more but less than 100 nm.

Even if the holding temperature of the pyrolysis tank in the next step is the same, by increasing the preheating temperature and/or by increasing the preheating time, the average particle size of the silver nanoparticles produced tends to become smaller. By setting the preheating temperature at 60 to 90°C, silver nanoparticles having a small average particle size, for example, an average primary particle size of 0.5 nm to 100 nm, preferably 0.5 nm to 70 nm, more preferably 0.5 nm to 60 nm, and even more preferably 0.5 nm to 40 nm or 0.5 nm to 26 nm, can be obtained. There is no particular limit to the lower limit of the average particle size, but it is likely to be, for example, about 5 nm or about 7 nm.

The reason why the average particle size of the silver nanoparticles produced by increasing the preheating temperature or increasing the preheating time is smaller is thought to be as follows. In the process of producing silver nanoparticles, the molecular weight of the silver salt (complex compound) is reduced or dissolved before or simultaneously with the thermal decomposition reaction. By increasing the preheating temperature or increasing the preheating time, the molecular weight of the silver salt (complex compound) is reduced or dissolved more, and as a result, the particle size of the silver nanoparticles produced in the end is smaller. It can also be thought of as follows. In the process of producing silver nanoparticles, there are conditions under which the silver atoms generated with the decomposition of the silver salt (complex compound) form crystal nuclei (supersaturated state), and conditions under which silver atoms accumulate on the crystal nuclei and particles grow (state below saturation concentration). By increasing the preheating temperature or increasing the preheating time, the decomposition of the silver salt in the supersaturated state is more actively caused. As a result, the number of crystal nuclei generated increases, and the number of silver atoms consumed for the subsequent particle growth becomes relatively small. As a result, it is thought that the particle size of the silver nanoparticles produced in the end is smaller. The above theory is consistent with Lamer's rule, which describes the formation of particles.

The preheating temperature is, for example, 60 to 90°C, preferably 70 to 90°C, and more preferably 75 to 85°C. The preheating time is not particularly limited, but from the viewpoint of manufacturing economics, it is preferably 30 seconds to 2 hours, more preferably 1 minute to 1 hour, and even more preferably 1 minute to 30 minutes. The preheating method is not particularly limited, but a method in which a silver complex compound is passed through a tubular passage and then added to a pyrolysis tank, and the inside of the tubular passage is heated to a predetermined temperature, or a method in which a reactor for preheating that can stir the inside is prepared before being transferred to the pyrolysis tank, and a part of the contents of the reactor is added to the pyrolysis tank while adding a silver complex compound to the reactor, etc. are considered. In either case, the sequential addition to the pyrolysis tank may be performed continuously or intermittently. The sequential addition time to the pyrolysis tank is not particularly limited, but from the viewpoint of manufacturing heat removal capacity and economics, it is preferably 5 minutes to 20 hours, more preferably 10 minutes to 10 hours, and even more preferably 20 minutes to 5 hours. The silver nanoparticles obtained in this process have two or more peaks in the particle size distribution. The positions of the peaks vary depending on the reaction conditions, but typically, when measured by dynamic light scattering, they have one peak in the range of 1 nm to less than 20 nm and one peak in the range of 20 nm to 100 nm. They may also have peaks other than the two peaks mentioned above.

When preheating is performed using a tubular passage (20c) (i.e., a tubular heating device) housed in a preheating device (22) as illustrated in FIG. 1, the preheating time is the residence time of the reaction mixture in the tubular passage (20c). The ratio L/D of the inner diameter D (mm) and length L (mm) of the tubular heating device in the tubular passage (20c) portion may be, for example, 10 to 3000, preferably 20 to 2000, and more preferably 30 to 1500. The residence time is appropriately determined based on the transfer speed of the reaction mixture in the tubular passage (20), the inner diameter D (mm), and the length L (mm). The inner diameter D (mm) of the portions other than the tubular passage (20c) (i.e., the portions of the tubular passage (20a), tubular passage (20b), and tubular passage (20d)) may also be substantially the same as that of the tubular passage (20c).

Next, the preheated reaction mixture containing the complex compound is successively added to a pyrolysis tank having a pyrolysis temperature of 80 to 120°C, which is higher than the preheating temperature, to pyrolyze the complex compound and form silver nanoparticles [pyrolysis step of the complex compound]. When a metal compound containing a metal other than silver is used, the desired metal nanoparticles are formed. Silver nanoparticles (metal nanoparticles) are formed without using a reducing agent. However, an appropriate reducing agent may be used as necessary within a range that does not impair the effects of the present invention.

In such metal amine complex decomposition methods, amines generally control the manner in which atomic metals resulting from the decomposition of the metal compound aggregate to form fine particles, and also form a coating on the surface of the formed metal fine particles to prevent re-aggregation between the fine particles. In other words, it is believed that by heating a complex compound of a metal compound and an amine, the metal compound is thermally decomposed to generate atomic metal while maintaining the coordinate bond of the amine to the metal atom, and then the metal atoms coordinated with the amine aggregate to form metal nanoparticles covered with an amine protective film.

The thermal decomposition is carried out by successively adding the complex compound in a reaction medium mainly composed of preheated alcohol (if used) and amines to a thermal decomposition tank maintained at 80 to 120°C (but at a temperature higher than the preheating temperature) and thermally decomposing it to form silver nanoparticles. In this case, it is preferable to carry out the thermal decomposition with stirring.

The thermal decomposition should be carried out within the temperature range in which coated silver nanoparticles (or coated metal nanoparticles) are produced, but it is preferable to carry out the thermal decomposition at a temperature as low as possible within the above temperature range in order to prevent the amine from being removed from the silver particle surface (or metal particle surface). In the case of a silver oxalate complex compound, the temperature can be, for example, about 80°C to 120°C, preferably about 95°C to 115°C, and more specifically, about 100°C to 110°C. In the case of a silver oxalate complex compound, heating to about 100°C causes decomposition and reduction of silver ions, thereby obtaining coated silver nanoparticles. Generally, the thermal decomposition of silver oxalate itself occurs at about 200°C, but the reason why the thermal decomposition temperature drops by about 100°C by forming a silver oxalate-amine complex compound is not clear, but it is presumed that this is because the coordination polymer structure formed by pure silver oxalate is cut when a complex compound of silver oxalate and amine is produced.

In the thermal decomposition step of the complex compound, in order to prevent the detachment of amines from the silver particle surface (or the metal particle surface) during thermal decomposition, it is preferable to have an aliphatic hydrocarbon amine compound and/or an aliphatic carboxylic acid used as a complexing agent and/or a protective agent present in the thermal decomposition tank.

Specifically, it is preferable to have an aliphatic hydrocarbon amine compound and/or an aliphatic carboxylic acid (D) present, which includes at least one of an aliphatic hydrocarbon monoamine (A) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 6 or more, an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms of which is 8 or less. The ratio of each of these compounds may be similar to the ratio described above. The total amount of these aliphatic hydrocarbon amine compounds and/or aliphatic carboxylic acids in the pyrolysis tank is not particularly limited, but may be, for example, about 1/10 to 1/2 of the amount of the complex compound production process.

In the thermal decomposition process of the complex compound, the thermal decomposition temperature is maintained for, for example, 10 to 120 minutes, preferably 30 to 120 minutes. The thermal decomposition process of the complex compound is completed by such a thermal decomposition reaction time.

The thermal decomposition of the complex compound is preferably carried out in an inert gas atmosphere such as argon, but it can also be carried out in air.

Second form:
The second embodiment of the production method includes the steps of producing the complex compound described above,
A thermal decomposition tank preparation step in which silver nanoparticles prepared in advance are present in a thermal decomposition tank for thermally decomposing the generated complex compound;
The method includes a thermal decomposition step of a complex compound, in which the generated complex compound is successively added to the thermal decomposition tank set at a thermal decomposition temperature of 80 to 120° C. and thermally decomposed to form silver nanoparticles.

In the second embodiment, the step of preparing the pyrolysis tank is carried out before the reaction mixture at room temperature containing the complex compound from the step of generating the complex compound is sequentially added to the pyrolysis tank.

In the preparation step of the pyrolysis tank, a form may be adopted in which silver nanoparticles that have been separately prepared in advance are placed in the pyrolysis tank. In this case, it is preferable that the surfaces of the previously prepared silver nanoparticles are coated with a protective agent that contains the target aliphatic hydrocarbon amine. In addition, the average primary particle diameter of the previously prepared silver nanoparticles is not particularly limited, but is preferably 5 to 50 nm.

In addition, in the preparation step of the pyrolysis tank, a form in which silver nanoparticles are prepared in advance in the pyrolysis tank may be adopted. In this case, a complex compound containing a silver compound and an aliphatic hydrocarbon amine may be generated by the same operation as in the above-mentioned complex compound generation step, and then the temperature may be raised to the pyrolysis temperature to pyrolyze the complex compound, thereby forming silver nanoparticles whose surfaces are coated with a protective agent containing an aliphatic hydrocarbon amine. The silver nanoparticles prepared in advance are preferably those whose surfaces are coated with a protective agent containing the target aliphatic hydrocarbon amine. The average primary particle diameter of the silver nanoparticles prepared in advance is not particularly limited, but is preferably 5 to 50 nm. The silver nanoparticles prepared in advance in this case may have one peak of 1 nm or more and 100 nm or less in particle diameter distribution.

In the second embodiment, the amount of silver nanoparticles that are preliminarily present in the pyrolysis tank in the preparation step is not particularly limited, but may be, for example, 0.01 to 100%, or 0.05 to 70%, and preferably 0.1 to 5%, based on the theoretical amount of silver nanoparticles that are generated in the complex compound generation step and successively added to the pyrolysis tank.

After the preparation process, the pyrolysis tank is heated to a pyrolysis temperature of 80 to 120°C.

Next, the complex compound thus produced is successively added to the thermal decomposition tank, which has a thermal decomposition temperature of 80 to 120°C, to thermally decompose the complex compound and form silver nanoparticles [thermal decomposition process of complex compound]. When a metal compound containing a metal other than silver is used, the desired metal nanoparticles are formed. Silver nanoparticles (metal nanoparticles) are formed without using a reducing agent. However, an appropriate reducing agent may be used as necessary within a range that does not impair the effects of the present invention.

In such metal amine complex decomposition methods, amines generally control the manner in which atomic metals resulting from the decomposition of the metal compound aggregate to form fine particles, and also form a coating on the surface of the formed metal fine particles to prevent re-aggregation between the fine particles. In other words, it is believed that by heating a complex compound of a metal compound and an amine, the metal compound is thermally decomposed to generate atomic metal while maintaining the coordinate bond of the amine to the metal atom, and then the metal atoms coordinated with the amine aggregate to form metal nanoparticles covered with an amine protective film.

The thermal decomposition is carried out by successively adding the complex compound in a reaction medium mainly composed of alcohol (if used) and amines to a thermal decomposition tank maintained at 80 to 120°C, and thermally decomposing the complex compound to form silver nanoparticles. It is preferable to carry out the thermal decomposition while stirring.

The thermal decomposition should be carried out within the temperature range in which coated silver nanoparticles (or coated metal nanoparticles) are produced, but it is preferable to carry out the thermal decomposition at a temperature as low as possible within the above temperature range in order to prevent the detachment of amines from the silver particle surface (or metal particle surface). In the case of a silver oxalate complex compound, the temperature can be, for example, about 80°C to 120°C, preferably about 95°C to 115°C, and more specifically, about 100°C to 110°C. In the case of a silver oxalate complex compound, decomposition occurs and silver ions are reduced by heating at about 100°C, and coated silver nanoparticles can be obtained. In general, the thermal decomposition of silver oxalate itself occurs at about 200°C, but the reason why the thermal decomposition temperature drops by about 100°C by forming a silver oxalate-amine complex compound is not clear, but it is presumed that this is because the coordination polymer structure formed by pure silver oxalate is cut when a complex compound of silver oxalate and amine is produced.

In the thermal decomposition step of the complex compound, in order to prevent the detachment of amines from the silver particle surface (or the metal particle surface) during thermal decomposition, it is preferable to have an aliphatic hydrocarbon amine compound and/or an aliphatic carboxylic acid used as a complexing agent and/or a protective agent present in the thermal decomposition tank.

Specifically, it is preferable to have an aliphatic hydrocarbon amine compound and/or an aliphatic carboxylic acid (D) present, which includes at least one of an aliphatic hydrocarbon monoamine (A) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 6 or more, an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms of which is 8 or less. The ratio of each of these compounds may be similar to the ratio described above. The total amount of these aliphatic hydrocarbon amine compounds and/or aliphatic carboxylic acids in the pyrolysis tank is not particularly limited, but may be, for example, about 1/10 to 1/2 of the amount of the complex compound production process.

In the second embodiment, as described above, when a complex compound containing a silver compound and an aliphatic hydrocarbon amine is successively added to a pyrolysis tank and pyrolyzed, previously prepared silver nanoparticles are placed in the pyrolysis tank maintained at 80 to 120°C, and the silver nanoparticles are formed by being successively added to the pyrolysis tank and pyrolyzed. By placing previously prepared silver nanoparticles in the pyrolysis tank, silver nanoparticles having a small average particle size can be obtained. In addition, the silver nanoparticles obtained at this time have two or more peaks in the particle size distribution. By placing previously prepared silver nanoparticles in the pyrolysis tank, silver nanoparticles having a small average particle size, for example, an average primary particle size of 0.5 nm to 100 nm, preferably 0.5 nm to 70 nm, more preferably 0.5 nm to 60 nm, and even more preferably 0.5 nm to 40 nm or 0.5 nm to 26 nm, can be obtained. The lower limit of the average particle size is not particularly limited, but is likely to be, for example, about 5 nm or about 7 nm.

The reason why the average particle size of the silver nanoparticles generated by placing silver nanoparticles prepared in advance in the pyrolysis tank is smaller is thought to be as follows. In the process of generating silver nanoparticles, there are conditions under which the silver atoms generated with the decomposition of the silver salt (complex compound) form crystal nuclei (supersaturated state), and conditions under which silver atoms accumulate on the crystal nuclei and particles grow (state below saturation concentration). By placing silver nanoparticles prepared in advance in the pyrolysis tank, there will be many crystal nuclei that have already been generated. As a result, it is thought that the particle size of the silver nanoparticles that are ultimately generated will be smaller. The above theory is consistent with the particle generation law known as Lamer's rule.

In the thermal decomposition step of the complex compound, the amount of pre-prepared silver nanoparticles to be placed in the thermal decomposition tank when the silver complex compound is successively added to the thermal decomposition tank for thermal decomposition is not particularly limited. From the viewpoint of production economy, the amount is, for example, 0.01 to 100%, or 0.05 to 70%, and preferably about 0.1 to 5%, based on the theoretical amount of silver nanoparticles generated in the complex compound generation step and successively added to the thermal decomposition tank. However, it is not excluded to use an amount exceeding 100%, and it may be, for example, up to 150% or up to 200%. The method of preparing the pre-prepared silver nanoparticles to be placed in the thermal decomposition tank may be by batch method or by successive addition.

The sequential addition to the pyrolysis tank may be performed continuously or intermittently. The time for sequential addition is not particularly limited, but is preferably 5 to 20 hours, more preferably 10 to 10 hours, and even more preferably 20 to 5 hours, in terms of heat removal capacity and economic efficiency in production. The silver nanoparticles obtained in this case have two or more peaks in the particle size distribution. The positions of the peaks vary depending on the reaction conditions, but typically, in measurements by dynamic light scattering, there is one peak at 1 to 20 nm and one peak at 20 to 100 nm. There may also be peaks other than the two peaks.

In the thermal decomposition process of the complex compound, the thermal decomposition temperature is maintained for, for example, 10 to 120 minutes, preferably 30 to 120 minutes. The thermal decomposition process of the complex compound is completed by such a thermal decomposition reaction time.

The thermal decomposition of the complex compound is preferably carried out in an inert gas atmosphere such as argon, but it can also be carried out in air.

In the second embodiment, a manufacturing apparatus as shown in FIG. 1 may be used. In this case, silver nanoparticles are placed in the pyrolysis tank (30) beforehand, and the reaction mixture at room temperature containing the complex compound in the production reaction tank (10) is transferred downstream through the tubular passage (20) by the tube pump (21) without operating the preheating device (22), and is added successively to the pyrolysis tank (30) at a pyrolysis temperature of 80 to 120°C. The complex compound is then pyrolyzed to form silver nanoparticles. The configuration of the manufacturing apparatus shown in FIG. 1 is one example, and it goes without saying that other apparatuses may be used.

[Post-treatment process of silver nanoparticles]
The complex compound is thermally decomposed to give a suspension with a blue luster. From this suspension, the alcohol solvent (if used) and excess amine are removed, for example, by settling the silver nanoparticles (or metal nanoparticles) and decanting and washing with an appropriate solvent (water or organic solvent), to obtain the desired stable coated silver nanoparticles (or coated metal nanoparticles) [post-treatment process of silver nanoparticles]. After the washing operation, the resulting powder of stable coated silver nanoparticles (or coated metal nanoparticles) is obtained by drying. However, wet silver nanoparticles may be used to prepare the silver nanoparticle-containing ink.

Water or an organic solvent is used for the decantation and washing operations. Examples of organic solvents that can be used include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, and tetradecane; alicyclic hydrocarbon solvents such as methylcyclohexane and cyclohexane; aromatic hydrocarbon solvents such as toluene, xylene, and mesitylene; alcohol solvents such as methanol, ethanol, propanol, and butanol; acetonitrile; and mixtures of these.

In the nanoparticle formation process of the present invention, a reducing agent is not required, so there are no by-products derived from the reducing agent, and the coated silver nanoparticles can be easily separated from the reaction system, resulting in high-purity coated silver nanoparticles. However, if necessary, an appropriate reducing agent may be used within a range that does not impair the effects of the present invention.

In this way, silver nanoparticles are formed whose surfaces are coated with the protective agent used. The protective agent contains, for example, the aliphatic monoamine (A), and further contains either one or both of the aliphatic monoamine (B) and the aliphatic diamine (C), and further contains the carboxylic acid (D) when used. The content ratio of these in the protective agent is the same as the usage ratio of these in the amine mixture. The same applies to metal nanoparticles.

[Silver paint composition]
The obtained silver nanoparticles can be used to prepare a silver coating composition. The silver coating composition can take various forms without limitation. For example, a silver coating composition called a silver ink can be prepared by dispersing the silver nanoparticles in a suspension state in a suitable organic solvent (dispersion medium). Alternatively, a silver coating composition called a silver paste can be prepared by dispersing the silver nanoparticles in a kneaded state in an organic solvent.

Examples of organic solvents for obtaining the silver paint composition include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, and tetradecane; alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and decalin; aromatic hydrocarbon solvents such as toluene, xylene, and mesitylene; linear or branched aliphatic alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, n-hexanol, 2-ethylhexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, undecanol, and dodecanol; and cyclic (or cyclic structure-containing) aliphatic alcohol solvents such as cyclopentanol, cyclohexanol, and cyclohexanemethanol. In addition, examples of organic solvents for obtaining a silver paint composition include terpene-based solvents such as terpineol and dihydroterpineol for obtaining a silver paste.

Furthermore, examples of organic solvents for obtaining the silver paint composition include glycol monoethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether (butyl carbitol: BC), propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, diethylene glycol monohexyl ether (hexyl carbitol: HC), and diethylene glycol mono 2-ethylhexyl ether.

Furthermore, glycol monoether monoesters such as ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate (butyl carbitol acetate: BCA), propylene glycol monomethyl ether acetate (PMA; 1-methoxy-2-propyl acetate), and dipropylene glycol monomethyl ether acetate;
Glycol diesters such as ethylene glycol diacetate, diethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, 1,4-butanediol diacetate (1,4-BDDA, boiling point 230° C.), 1,6-hexanediol diacetate (1,6-HDDA, boiling point 260° C.), and 2-ethyl-1,6-hexanediol diacetate;
Examples of glycol ester solvents include:

These solvents may be used alone or in combination of two or more. The type and amount of organic solvent may be appropriately determined depending on the concentration and viscosity of the desired silver paint composition (silver ink, silver paste). The same applies to metal nanoparticles.

The silver nanoparticle powder and silver paint composition obtained by the present invention are highly stable. For example, the silver nanoparticle powder is stable when stored at room temperature for a period of one month or more. The silver paint composition is stable at room temperature for a period of one month or more, for example, at a silver concentration of 50 wt%, without aggregation or fusion.

The prepared silver coating composition is applied onto a substrate and then baked.

Application can be performed by known methods such as spin coating, inkjet printing, screen printing, dispenser printing, letterpress printing (flexographic printing), dye-sublimation printing, offset printing, laser printer printing (toner printing), intaglio printing (gravure printing), contact printing, and microcontact printing. When a printing technique is used, a patterned layer of the silver coating composition is obtained, and when fired, a patterned silver conductive layer is obtained.

Firing can be performed at a temperature of 200°C or less, for example, from room temperature (25°C) to 150°C or less, preferably from room temperature (25°C) to 120°C or less. However, in order to complete the sintering of silver by firing in a short time, it is recommended to perform the firing at a temperature of 60°C to 200°C or less, for example, from 80°C to 150°C or less, preferably from 90°C to 120°C or less. The firing time can be determined appropriately taking into consideration the amount of silver ink applied and the firing temperature, and is, for example, within several hours (for example, 3 hours or 2 hours), preferably within 1 hour, more preferably within 30 minutes, even more preferably 10 to 20 minutes, and more specifically 10 to 15 minutes.

Because the silver nanoparticles are structured as described above, the sintering of the silver particles proceeds sufficiently even with such a low-temperature, short-time firing process. As a result, excellent conductivity (low resistance value) is achieved. A silver conductive layer with low resistance value (for example, 15 μΩcm or less, in the range of 7 to 15 μΩcm) is formed. The resistance value of bulk silver is 1.6 μΩcm.

Because baking at low temperatures is possible, in addition to glass substrates and heat-resistant plastic substrates such as polyimide films, general-purpose plastic substrates with low heat resistance such as polyester films such as polyethylene terephthalate (PET) film and polyethylene naphthalate (PEN) film, and polyolefin films such as polypropylene can also be used suitably as substrates. In addition, baking in a short time reduces the load on these general-purpose plastic substrates with low heat resistance and improves production efficiency.

The silver conductive material of the present invention can be applied to various electronic devices, such as electromagnetic wave control materials, circuit boards, antennas, heat sinks, liquid crystal displays, organic EL displays, field emission displays (FEDs), IC cards, IC tags, solar cells, LED elements, organic transistors, capacitors, electronic paper, flexible batteries, flexible sensors, membrane switches, touch panels, EMI shields, etc.

The thickness of the silver conductive layer can be appropriately determined depending on the intended application, and by using the silver nanoparticles according to the present invention in particular, high conductivity can be exhibited even when a silver conductive layer with a relatively large thickness is formed. The thickness of the silver conductive layer can be selected, for example, from the range of 5 nm to 10 μm, preferably 100 nm to 5 μm, and more preferably 300 nm to 2 μm.

The above explanation has focused mainly on silver nanoparticles, but the present invention can also be applied to the manufacturing method of metal nanoparticles containing metals other than silver and to the metal nanoparticles.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[Average particle size of silver nanoparticles]
The average particle size and particle size distribution were measured by dynamic light scattering (DLS) using a Zetasizer Nano (Malvern Instruments).

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

The following reagents were used in each of the Examples and Comparative Examples.
N,N-Dimethyl-1,3-propanediamine (N,N-dimethylaminopropylamine, MW: 102.18): Reagent manufactured by Tokyo Chemical Industry Co., Ltd. n-Butylamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. n-Hexylamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. n-Octylamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Dodecylamine: Reagent manufactured by Wako Pure Chemical Industries, Ltd. Butanol: Reagent manufactured by Wako Pure Chemical Industries, Ltd. Special grade decalin: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Cyclohexanemethanol: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Silver oxalate (MW: 303.78): Synthesized from silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) and oxalic acid dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.)

[Example 1: With preheating process]
(Formation of Silver Oxalate-Amine Complex)
Referring to FIG. 1, 5.0 g (16.5 mmol) of silver oxalate was charged into a 100 mL flask as a complex compound production reaction tank (10), and 7.5 g (102.5 mmol) of 1-butanol was added thereto to prepare a 1-butanol slurry of silver oxalate. An amine mixture of 14.45 g (197.5 mmol) of n-butylamine, 9.99 g (98.8 mmol), 9.57 g (74.1 mmol) of n-octylamine, 4.58 g (24.7 mmol) of dodecylamine, and 10.09 g (98.8 mmol) of N,N-dimethyl-1,3-propanediamine was added dropwise to the 1-butanol slurry of silver oxalate at 30° C. The mixture was stirred at 30° C. for 2 hours to allow the complex formation reaction between silver oxalate and amine to proceed, forming a white substance (silver oxalate-amine complex). In this way, a reaction liquid containing a silver oxalate-amine complex was obtained.

(Preheating step and pyrolysis step)
A 100 mL flask serving as a thermal decomposition reaction tank (30) for the complex compound was charged with 1.50 g (20.5 mmol) of 1-butanol, 2.89 g (39.5 mmol) of n-butylamine, 2.00 g (19.8 mmol) of n-hexylamine, 1.92 g (14.8 mmol) of n-octylamine, 0.92 g (4.9 mmol) of dodecylamine, and 2.02 g (19.8 mmol) of N,N-dimethyl-1,3-propanediamine, and heated to 100° C.

The 30°C reaction liquid containing the silver oxalate-amine complex was added to the pyrolysis tank (30) set to 100°C over a period of 47 minutes while being preheated through a Teflon® tube ( ^20c ) (outer diameter 4 mm, inner diameter 2 mm, length 3 m, L/D = 1500) immersed in a hot water bath (22) set to 60°C (residence time in the preheated ^Teflon® tube (20c): 2 minutes 50 seconds). After completion of the addition, the mixture was stirred at 100°C for an additional hour to pyrolyze the silver oxalate-amine complex, thereby obtaining a suspension in which dark blue silver nanoparticles were suspended in the amine mixture.

After cooling to room temperature, 60 g of methanol was added to the resulting suspension and stirred, then the silver nanoparticles were precipitated by centrifugation and the supernatant liquid was removed. 18 g of methanol was again added to the silver nanoparticles and stirred, then the silver nanoparticles were precipitated by centrifugation and the supernatant liquid was removed. In this way, wet silver nanoparticles were obtained.

(Silver nanoparticle dispersion)
Next, a cyclohexanemethanol/decalin mixed solvent (weight ratio=80/20) was added as a dispersion solvent to the wet silver nanoparticles so that the silver concentration was 40 wt %, and the mixture was stirred to prepare a silver nanoparticle dispersion.

The average particle size and particle size distribution of the silver nanoparticles in the silver nanoparticle dispersion were measured by dynamic light scattering using a Zetasizer Nano (Malvern Instruments), and found to be 56.1 nm. The peaks in the particle size distribution were 11.2 nm and 78.1 nm. When 6 mL of the dispersion was filtered through a 0.45 μm filter, the entire amount could be filtered without clogging the filter. Figure 2 shows the measurement results of the particle size distribution of the silver nanoparticles in Example 1.

[Example 2: With preheating process]
(Formation of Silver Oxalate-Amine Complex)
In the same manner as in Example 1, a reaction liquid containing a silver oxalate-amine complex was obtained in the complex compound formation reaction tank (10).

(Preheating step and pyrolysis step)
A silver nanoparticle dispersion was prepared in the same manner as in Example 1, except that in the preheating step and the pyrolysis step, the 30° C. reaction solution containing the silver oxalate-amine complex was added to the pyrolysis tank (30) set to 100° C. over a period of 47 minutes while being preheated through a ^Teflon® tube (20c) (outer diameter 4 mm, inner diameter 2 mm, length 3 m) placed in an 85° C. hot water bath (22) (residence time in the preheated ^Teflon® tube (20c): 2 minutes 57 seconds).

The average particle size and particle size distribution of the silver nanoparticles in the silver nanoparticle dispersion were measured by dynamic light scattering using a Zetasizer Nano (Malvern Instruments), and were found to be 39.9 nm. The peaks in the particle size distribution were 5.3 nm and 59.9 nm. When 6 mL of the dispersion was filtered through a 0.45 μm filter, the entire amount could be filtered without clogging the filter. Figure 3 shows the measurement results of the particle size distribution of the silver nanoparticles in Example 2.

This silver nanoparticle dispersion was applied to a non-alkali glass plate by spin coating to form a coating film. After the coating film was formed, it was quickly baked in a fan drying oven at 120°C for 15 minutes to form a baked silver film with a thickness of 0.5 μm. The resistivity of the resulting baked silver film was measured by the four-terminal method, and it showed good conductivity of 10.6 μΩcm.

[Comparative Example 1: No preheating process]
(Formation of Silver Oxalate-Amine Complex)
In the same manner as in Example 1, a reaction liquid containing a silver oxalate-amine complex was obtained in the complex compound formation reaction tank (10).

(Pyrolysis process)
A silver nanoparticle dispersion was prepared in the same manner as in Example 1, except that a pre-heating step was not performed, and in the thermal decomposition step, the reaction liquid containing the silver oxalate-amine complex was added over 50 minutes to the thermal decomposition tank (30) set to 100° C. while passing it through a ^Teflon® tube (20c) (outer diameter 4 mm, inner diameter 2 mm, length 3 m) set to room temperature (25° C.).

The average particle size and particle size distribution of the silver nanoparticles in the silver nanoparticle dispersion were measured by dynamic light scattering using a Zetasizer Nano (Malvern Instruments), and were found to be 63.4 nm. The peak in the particle size distribution was 84.0 nm. When 6 mL of the dispersion was filtered through a 0.45 μm filter, the entire amount could be filtered without clogging the filter. Figure 4 shows the measurement results of the particle size distribution of the silver nanoparticles in Comparative Example 1.

This silver nanoparticle dispersion was applied to a non-alkali glass plate by spin coating to form a coating film. After the coating film was formed, it was promptly baked in a fan drying oven at 120°C for 15 minutes, but there was a lot of repelling and a uniform baked silver film could not be obtained, making it impossible to measure the resistivity.

In this Comparative Example 1, the preheating step was not performed, so the average particle size was larger than in Examples 1 and 2, and only one peak was observed in the particle size distribution.

[Comparative Example 2: No preheating step]
(Formation of Silver Oxalate-Amine Complex)
In the same manner as in Example 1, a reaction liquid containing a silver oxalate-amine complex was obtained in the complex compound formation reaction tank (10).

(Pyrolysis process)
A 100 mL flask serving as a thermal decomposition tank (30) was charged with only 4.50 g (20.5 mmol) of 1-butanol and heated to 100°C.

A silver nanoparticle dispersion was prepared in the same manner as in Example 1, except that a pre-heating step was not performed, and in the thermal decomposition step, the reaction liquid containing the silver oxalate-amine complex was added over 30 minutes to the thermal decomposition tank (30) set to 100° C. while passing it through a ^Teflon® tube (20c) (outer diameter 4 mm, inner diameter 2 mm, length 3 m) set to room temperature (25° C.).

The average particle size and particle size distribution of the silver nanoparticles in the silver nanoparticle dispersion were measured by dynamic light scattering using a Zetasizer Nano (Malvern Instruments), and were found to be 101.3 nm. The peak in the particle size distribution was 108.3 nm. When 6 mL of the dispersion was filtered through a 0.2 μm filter, it became clogged at about 2 mL and could not be filtered. Figure 5 shows the measurement results of the particle size distribution of the silver nanoparticles in Comparative Example 2.

In Comparative Example 2, as in Comparative Example 1, a preheating step was not performed, so the average particle size was larger than in Examples 1 and 2, and only one peak was observed in the particle size distribution. Moreover, in Comparative Example 2, the average particle size was even larger than in Comparative Example 1. This is thought to be because in Comparative Example 2, since only 1-butanol, not an amine component, was present in the pyrolysis tank, when silver particles were generated by pyrolysis, the amine was easily released from the complex, resulting in insufficient amine protective agent on the surface of the silver particles.

[Example 3: Pyrolysis process in the presence of silver nanoparticles without preheating process]
(Formation of Silver Oxalate-Amine Complex)
In the same manner as in Example 1, a reaction liquid containing a silver oxalate-amine complex was obtained in the complex compound formation reaction tank (10).

(Preparation of pyrolysis tank charging liquid)
A 200 mL flask was charged with 3.0 g (9.9 mmol) of silver oxalate, to which 4.5 g (60.7 mmol) of 1-butanol was added to prepare a 1-butanol slurry of silver oxalate. An amine mixture of 8.67 g (118.5 mmol) of n-butylamine, 6.00 g (59.3 mmol) of n-hexylamine, 5.74 g (44.4 mmol) of n-octylamine, 2.75 g (14.8 mmol) of dodecylamine, and 6.05 g (59.3 mmol) of N,N-dimethyl-1,3-propanediamine was added dropwise to the 1-butanol slurry of silver oxalate at 30° C. The mixture was stirred at 30° C. for 2 hours to allow the complex formation reaction between silver oxalate and amine to proceed, forming a white substance (silver oxalate-amine complex). The temperature was raised to 100° C. and the mixture was heated for 1 hour for pyrolysis to prepare a suspension of dark blue silver nanoparticles suspended in the amine mixture. The mixture was then cooled to room temperature. In this manner, the pyrolysis tank (30) was prepared.

(Pyrolysis process)
The solution charged in the pyrolysis tank (30) was heated to 100°C, and the reaction solution containing the silver oxalate-amine complex was added to this pyrolysis tank (30) over a period of 30 minutes while passing it through a ^Teflon® tube (20c) (outer diameter 4 mm, inner diameter 2 mm, length 0.8 m) kept at room temperature (25°C). After completion of the addition, the solution was stirred at 100°C for an additional hour to thermally decompose the silver oxalate-amine complex, thereby obtaining a suspension in which dark blue silver nanoparticles were suspended in the amine mixed solution.

After cooling to room temperature, 80 g of methanol was added to the resulting suspension and stirred, then the silver nanoparticles were precipitated by centrifugation and the supernatant liquid was removed. 24 g of methanol was again added to the silver nanoparticles and stirred, then the silver nanoparticles were precipitated by centrifugation and the supernatant liquid was removed. In this way, wet silver nanoparticles were obtained.

(Silver nanoparticle dispersion)
Next, a cyclohexanemethanol/decalin mixed solvent (weight ratio=80/20) was added as a dispersion solvent to the wet silver nanoparticles so that the silver concentration was 40 wt %, and the mixture was stirred to prepare a silver nanoparticle dispersion.

The average particle size and particle size distribution of the silver nanoparticles in the silver nanoparticle dispersion were measured by dynamic light scattering using a Zetasizer Nano (Malvern Instruments), and were found to be 25.7 nm. The peaks in the particle size distribution were 34.9 nm and 1.6 nm. When 10 mL of the dispersion was filtered through a 0.2 μm filter, the entire amount could be filtered without clogging the filter. Figure 6 shows the measurement results of the particle size distribution of the silver nanoparticles in Example 3.

This silver nanoparticle dispersion was applied to a non-alkali glass plate by spin coating to form a coating film. After the coating film was formed, it was quickly baked in a fan drying oven at 120°C for 15 minutes to form a baked silver film with a thickness of 0.8 μm. The resistivity of the resulting baked silver film was measured by the four-terminal method, and it showed good conductivity of 10 μΩcm or less.

[Comparative Example 3: Complex Compound Formation Reaction and Thermal Decomposition Reaction of the Complex Compound in the Same Reaction Tank]
(Formation of Silver Oxalate-Amine Complex)
A 500 mL flask was charged with 20.0 g (65.8 mmol) of silver oxalate, to which 30.0 g of 1-butanol was added to prepare a 1-butanol slurry of silver oxalate. An amine mixture of 57.8 g (790.1 mmol) of n-butylamine, 40.0 g (395.0 mmol), 38.3 g (296.3 mmol) of n-octylamine, 18.3 g (98.8 mmol) of dodecylamine, and 40.4 g (395.0 mmol) of N,N-dimethyl-1,3-propanediamine was added dropwise to the 1-butanol slurry of silver oxalate at 30° C. The mixture was stirred at 30° C. for 2 hours to allow the complex formation reaction between silver oxalate and amine to proceed, forming a white substance (silver oxalate-amine complex).

(Pyrolysis process)
After the silver oxalate-amine complex was formed, the temperature of the reaction solution was raised from 30°C to 100°C at a rate of 10°C/min, and then heated for 1 hour to thermally decompose the silver oxalate-amine complex, thereby obtaining a suspension of deep blue silver nanoparticles suspended in the amine mixture.

After cooling to room temperature, 200 g of methanol was added to the resulting suspension and stirred, then the silver nanoparticles were precipitated by centrifugation and the supernatant liquid was removed. 60 g of methanol was again added to the silver nanoparticles and stirred, then the silver nanoparticles were precipitated by centrifugation and the supernatant liquid was removed. In this way, wet silver nanoparticles were obtained.

(Silver nanoparticle dispersion)
Next, a cyclohexanemethanol/decalin mixed solvent (weight ratio=80/20) was added as a dispersion solvent to the wet silver nanoparticles so that the silver concentration was 40 wt %, and the mixture was stirred to prepare a silver nanoparticle dispersion.

The average particle size of the silver nanoparticles in the silver nanoparticle dispersion was measured by dynamic light scattering using a Zetasizer Nano (Malvern Instruments) and found to be 26.21 nm. In addition, when 10 mL of the dispersion was filtered through a 0.2 μm filter, the entire amount could be filtered without clogging the filter. Figure 7 shows the measurement results of the particle size distribution of the silver nanoparticles in Comparative Example 3.

At the scale of Comparative Example 3, it was possible to control the temperature of the complex compound formation reaction and the thermal decomposition reaction of the complex compound in the same reaction tank. However, in scaled-up industrial production, there is thought to be a safety risk.

I: Complex compound formation process
II: Transfer step of complex compound-containing reaction mixture
III: Thermal decomposition process of complex compounds
10: Complex compound production reaction tank
M: Motor
11: Stirring blade
20: Tubular tract
21: Tube pump
22: Pre-heating device
30: Pyrolysis reactor
31: Stirring blade

Claims (16)

a complex compound generating step of mixing an aliphatic hydrocarbyl amine and a silver compound at room temperature to generate a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
A preheating step of preheating the produced complex compound to a preheating temperature of 60 to 90° C.;
a thermal decomposition step of the complex compound, in which the preheated complex compound is successively added to a thermal decomposition tank having a thermal decomposition temperature of 80 to 120° C., which is higher than the preheating temperature, and thermally decomposed to form silver nanoparticles;
A method for producing silver nanoparticles comprising the steps of: The method for producing silver nanoparticles according to claim 1 , wherein the silver compound is silver oxalate. The aliphatic hydrocarbon amine includes an aliphatic hydrocarbon monoamine (A) which is composed of an aliphatic hydrocarbon group and one amino group, and the total number of carbon atoms in the aliphatic hydrocarbon group is 6 or more,
3. The method for producing silver nanoparticles according to claim 1 or 2, comprising at least one of an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of the aliphatic hydrocarbon group being 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms of the aliphatic hydrocarbon group being 8 or less. The method for producing silver nanoparticles according to any one of claims 1 to 3 , wherein in the step of producing the complex compound, the aliphatic hydrocarbon amine and the silver compound are mixed in an alcohol solvent having 3 or more carbon atoms. The method for producing silver nanoparticles according to any one of claims 1 to 4 , wherein in the preheating step of the complex compound, the complex compound is heated by a tubular heating device. The method for producing silver nanoparticles according to any one of claims 1 to 5 , wherein in the thermal decomposition step of the complex compound, the thermal decomposition temperature is maintained for 10 to 120 minutes after completion of addition of the complex compound. The method for producing silver nanoparticles according to any one of claims 1 to 6 , wherein the aliphatic hydrocarbon amine is used in a total of 1 to 50 moles per mole of silver atom of the silver compound. a complex compound generating step of mixing an aliphatic hydrocarbyl amine and a silver compound at room temperature to generate a complex compound containing the silver compound and the aliphatic hydrocarbyl amine;
A thermal decomposition tank preparation step in which silver nanoparticles prepared in advance are present in a thermal decomposition tank for thermally decomposing the generated complex compound;
a thermal decomposition step of the complex compound, in which the generated complex compound is successively added to the thermal decomposition tank having a thermal decomposition temperature of 80 to 120° C. and thermally decomposed to form silver nanoparticles;
A method for producing silver nanoparticles comprising the steps of: The method for producing silver nanoparticles according to claim 8 , wherein in the step of preparing the pyrolysis tank, the silver nanoparticles prepared in advance are surface-coated with a protective agent containing an aliphatic hydrocarbon amine. The method for producing silver nanoparticles according to claim 8 or 9 , wherein the silver compound is silver oxalate. The aliphatic hydrocarbon amine comprises an aliphatic hydrocarbon monoamine (A) which comprises an aliphatic hydrocarbon group and one amino group, and the total number of carbon atoms in the aliphatic hydrocarbon group is 6 or more,
The method for producing silver nanoparticles according to any one of claims 8 to 10, further comprising at least one of an aliphatic hydrocarbon monoamine (B) consisting of an aliphatic hydrocarbon group and one amino group, the total number of carbon atoms of which is 5 or less, and an aliphatic hydrocarbon diamine (C) consisting of an aliphatic hydrocarbon group and two amino groups, the total number of carbon atoms of which is 8 or less . The method for producing silver nanoparticles according to any one of claims 8 to 11 , wherein in the step of producing the complex compound, the aliphatic hydrocarbon amine and the silver compound are mixed in an alcohol solvent having 3 or more carbon atoms. The method for producing silver nanoparticles according to any one of claims 8 to 12 , wherein in the thermal decomposition step of the complex compound, the thermal decomposition temperature is maintained for 10 to 120 minutes after completion of addition of the complex compound. The method for producing silver nanoparticles according to any one of claims 8 to 13 , wherein the aliphatic hydrocarbon amine is used in a total of 1 to 50 moles per mole of silver atom of the silver compound. Producing silver nanoparticles by the method according to any one of claims 1 to 14,
A method for producing a silver particle coating composition, comprising dispersing the silver nanoparticles in an organic solvent. 1. A method for manufacturing an electronic device having a substrate and a silver conductive layer on the substrate, comprising the steps of:
Producing silver nanoparticles by the method according to any one of claims 1 to 14,
The silver nanoparticles are dispersed in an organic solvent to prepare a silver particle coating composition;
a silver particle coating composition on a substrate to form a silver particle-containing coating layer, and then baking the silver particle-containing coating layer to form a silver conductive layer.