JP2012140669A - Method for forming metal nanoparticle sintered compact layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for forming a metal nanoparticle sintered compact layer in which low temperature sintering treatment is performed to the coating film of a metal nanoparticle dispersion at temperature of 50-120°C to form a metal nanoparticle sintered compact layer having volume resistivity of at least 3×10Ω cm.SOLUTION: An oxidation-reduction treatment cycle in which an oxidation treatment of blowing a gaseous mixture containing oxygen molecules in the range of 10 to 25 vol.% to the surface of the coating film of a metal nanoparticle dispersion for 5-15 seconds while heating the coating film to 50-120°C to form an oxide film on the surface of each metal nanoparticle is combined with a reduction treatment of blowing a gaseous mixture containing the vapor of an organic compound having an alcoholic hydroxyl group in the range of 10 to 30 vol.% to the surface of the coating film for 120-300 seconds to reduce the oxide film on the surface of each metal nanoparticle is repeated several times, thus the low temperature sintering of each metal nanoparticle is stepwise progressed to form a metal nanoparticle sintered compact layer.

Description

  The present invention relates to a method of forming a metal nanoparticle sintered body layer using a metal nanoparticle dispersion, and in particular, when sintering metal nanoparticles contained in the metal nanoparticle dispersion at a low temperature. The present invention relates to a method for forming a metal nanoparticle sintered body layer by selecting a heating temperature at the time of sintering to be 120 ° C. or lower.

  In recent years related to electronic equipment, miniaturization of wiring patterns to be used is progressing. In addition, regarding a metal thin film layer used for forming various electrode pattern portions, utilization of an extremely thin metal thin film layer is being promoted. For example, when fine wiring formation or thin film formation is achieved by using a screen printing method, a metal fine particle dispersion with a very small particle diameter, especially for ultrafine pattern drawing or thin film coating layer formation, Is intended to be applied to metal nanoparticle dispersions having an average particle size of 100 nm or less. At present, gold and silver nanoparticle dispersions that can be applied to the above-mentioned applications have already been commercialized.

When forming ultrafine wiring patterns using metal nanoparticles, for example, using metal nanoparticles such as gold nanoparticles and silver nanoparticles, sintering the metal nanoparticles at a heating temperature of 150 ° C. or higher A technique for forming a body layer is used. Specifically, by drawing a very fine circuit pattern using a dispersion for ultra fine printing containing metal nanoparticles, and then heating to 150 ° C. or higher to sinter the metal nanoparticles. In the obtained sintered-type wiring layer, it is possible to form a wiring having a wiring width and a space between wirings of 1 to 20 μm and a volume resistivity of 1 × 10 ⁻⁵ Ω · cm or less (see Patent Document 1). .

In addition, when a surface coating layer such as an amine compound that coats the surface of metal nanoparticles having an average particle diameter of 100 nm or less is provided and heated, the coating molecules such as the amine compound can be eluted and detached. A conductive metal nanoparticle paste that is uniformly dispersed in a dispersion solvent containing one or more organic solvents having a boiling point has also been proposed (see Patent Document 2). The conductive metal nanoparticle paste does not contain a binder resin component, and the conductor layer produced using the conductive metal nanoparticle paste is heat-treated at a temperature of 200 ° C. to 300 ° C. Good electrical conductivity is achieved by forming a sintered body layer densely between particles. For example, when a conductive silver paste produced using silver nanoparticles having an average particle diameter of 3 nm is used, the obtained conductor layer has a size of 3 × 10 ⁻⁶ Ω · cm to 3.5 × 10 ⁻⁶ Ω · A volume resistivity of about cm is achieved. The conductive metal nanoparticle paste using metal nanoparticles as the conductive medium, so-called “conductive nanoparticle paste”, is suitable for the production of fine wiring.

  When adopting copper nanoparticles that are susceptible to oxidation as metal nanoparticles used for the production of the sintered body layer, after reducing and removing the surface oxide film formed on the surface of the copper nanoparticles, A technique for performing sintering has also been proposed (see Patent Document 3). In the reduction of the surface oxide film formed on the surface of the copper nanoparticles, the organic compound having the reducing ability is heated to 200 ° C. or more and 300 ° C. or less in a reducing atmosphere containing vapor and gas of the organic compound having the reducing ability. A compound is used as a reducing agent. In addition, once the surface oxide film is reduced, the surface of the copper nanoparticles is oxidized again at a heating temperature of 200 ° C. or more and 300 ° C. or less, and re-reduction is performed using an organic compound having a reducing ability. A technique for performing processing is also used.

JP 2004-247572 A JP 2004-273205 A International Publication No. 2004/103043 Pamphlet

The conventional method for forming a metal fine particle sintered body layer can produce a metal nanoparticle sintered body layer having a volume resistivity of 1 × 10 ⁻⁵ Ω · cm or less with high reproducibility, This is a method of selecting the heating temperature during sintering at least 150 ° C. or higher, usually in the range of 200 ° C. to 300 ° C.

  On the other hand, in order to expand the use of the metal nanoparticle sintered body layer, the heating temperature at the time of sintering is at least 150 ° C., usually in the range of 200 ° C. to 300 ° C., which is employed in the conventional method. Instead, the present inventors have found that it is necessary to develop a new method for forming a metal fine particle sintered body layer that can be selected in a lower temperature range, that is, a temperature range that does not exceed at least 130 ° C.

The present invention solves the newly found problems. That is, an object of the present invention is to perform a heat treatment using a dispersion of metal nanoparticles and form a metal nanoparticle sintered body layer by selecting the heat treatment temperature to be 120 ° C. or less, A novel metal nanoparticle sintered body layer capable of forming a metal fine particle sintered body layer having a specific resistivity of at least 3 × 10 ⁻⁵ Ω · cm or less, preferably 1 × 10 ⁻⁵ Ω · cm or less. It is to provide a forming method.

  In order to solve the above-mentioned problems, the present inventors firstly apply the dispersion liquid on the substrate and then sinter the metal nanoparticles contained in the coating layer in the conventional technique. The phenomenon was examined in detail.

  As a result of the study, it was found that the process of sintering the metal nanoparticles contained in the coating layer can be classified into the following two processes. First, in the first process, a surface coating agent layer is formed on the surface of the metal nanoparticles dispersed in the dispersion, and the surface coating agent layer is removed. In the second process, the metal surface of the metal nanoparticles, in which the surface coating layer is removed, is brought into contact with each other, and the fusion between the metal nanoparticles and the low-temperature sintering are advanced.

  In the conventional method, the removal of the surface coating agent layer in the first process is achieved by elution of the surface coating agent molecules constituting the surface coating agent layer in the dispersion solvent by heating. Therefore, it is necessary to heat to a temperature at which the entire amount of the surface coating agent molecules to be dissolved can be dissolved in the dispersion solvent contained in the coating layer. In the second process, the surface coating agent molecules eluted in the dispersion solvent are selected so that the surface of the metal nanoparticles does not reattach to the metal surface. Mutual fusion and low-temperature sintering are required.

  At that time, when the surface coating molecules eluted in the dispersion solvent are reattached to the metal surface of the metal nanoparticles, the surface migration process of metal atoms on the surface of the metal nanoparticles is inhibited. Fusion and low temperature sintering are hindered. As a result, in some of the metal nanoparticles contained in the coating layer, fusion between the metal nanoparticles and low temperature sintering proceed, but in some cases, the fusion and low temperature sintering are inhibited. As a whole, it is impossible to achieve a state in which the metal nanoparticles are closely fused and sintered at a low temperature.

  In the conventional method, the heat treatment temperature is selected to be at least 150 ° C. or higher, and the solubility of the surface coating molecules in the dispersion solvent is increased, so that the surface coating molecules eluted in the dispersion solvent are removed. The phenomenon of reattaching to the metal surface of the metal nanoparticles was avoided.

  Surface coating agent molecules eluted in the dispersion solvent, such as alkylamines, can evaporate from the surface of the dispersion solvent when they exhibit an equilibrium vapor pressure above a certain level at the heat treatment temperature. In this case, when the boiling point of the surface coating molecule, for example, alkylamine, is significantly lower than the boiling point of the dispersion solvent, the transpiration rate of the surface coating molecule, for example, alkylamine, is the transpiration rate of the dispersion solvent. In comparison, it is relatively high. Therefore, surface coating molecules that elute from the surface of the metal nanoparticles, such as alkylamines, are not concentrated even when the dispersion solvent evaporates, and the surface coating molecules that are once eluted in the dispersion solvent. However, the phenomenon of redeposition to the metal surface of the metal nanoparticles is avoided.

  On the other hand, a long-chain carboxylic acid used as a surface coating agent molecule is bonded to a metal atom on the surface of the metal nanoparticle in the form of a metal salt (R-COOM) of the long-chain carboxylic acid. Therefore, it elutes slightly in the dispersion solvent, and the heat treatment temperature is selected to be at least 150 ° C. or more, so that the long-chain metal salt of carboxylic acid (R-COOM) is degradably reduced. Is caused to remove. Therefore, if the heat treatment temperature is significantly lower than the temperature at which the decomposing reduction reaction proceeds, the long-chain carboxylic acid used as the surface coating agent molecule cannot be removed, and the metal nanoparticles can interact with each other. The fusion and low-temperature sintering are hindered.

  Of course, even surface coating molecules that can be eluted in a dispersion solvent such as alkylamine, when the heat treatment temperature is significantly lower than 150 ° C., the solubility in the dispersion solvent is not sufficient, and the surface of the metal nanoparticles is In this case, surface coating agent molecules such as alkylamine remain with a considerable surface density. For this reason, if the surface density of the remaining surface coating agent molecules such as alkylamine exceeds a certain level, fusion between metal nanoparticles and low-temperature sintering are hindered.

  The present inventors elute the long-chain carboxylic acid bonded to the metal atom on the surface of the metal nanoparticle in the form of a long-chain carboxylic acid metal salt (R-COOM) in the dispersion solvent. We searched for a means to make it. At that time, the solubility of the metal salt of long-chain carboxylic acid (R-COOM) itself in the dispersion solvent is low, but the solubility of the amine complex of the metal salt of long-chain carboxylic acid (R-COOM) in the dispersion solvent is I came up with a much higher price. In addition, when the alkylamine is dissolved in the dispersion solvent, the alkylamine acts on the metal salt of long-chain carboxylic acid (R-COOM) when heated to at least 50 ° C. It was conceived that it is possible to form amine complexes of acid metal salts (R-COOM). The formed amine complex of the long-chain carboxylic acid metal salt (R-COOM) cannot be bonded to the metal atoms on the surface of the metal nanoparticles, and is in a state of being dissolved in the dispersion solvent. At that time, if a large amount of alkylamine is dissolved in the dispersion solvent, the alkylamine binds to the metal atom instead of the detached long-chain metal salt of carboxylic acid (R-COOM). It was also conceived that the surface of the film was converted to an alkylamine-coated state.

  The present inventor further studied, and when a combination of an amine compound such as an alkylamine and a long-chain carboxylic acid as a surface coating molecule for coating the surface of the metal nanoparticles, when heated to at least 50 ° C., A part of an amine compound such as an alkylamine, which coats the surface of the metal nanoparticles, is eluted, and the amine compound such as an alkylamine is eluted with an amine complex of a long-chain metal salt of a carboxylic acid (R-COOM). When forming a metal nanoparticle, a metal salt of a long chain carboxylic acid (R-COOM) is used as an amine complex while avoiding an increase in the concentration of an amine compound such as an alkylamine dissolved in a dispersion solvent. It was found that it can be detached from the surface.

  However, when the liquid temperature of the dispersion solvent is about 50 ° C., for example, only a part of the amine compound covering the surface of the metal nanoparticles, such as alkylamine, is eluted, and a considerable amount of alkylamine, etc. This amine compound remains in a bound state on the surface of the metal nanoparticles. That is, the concentration of the amine compound such as alkylamine dissolved in the dispersion solvent and the surface density of the amine compound such as alkylamine bonded to the metal surface of the surface of the metal nanoparticle are in an equilibrium state. .

  On the other hand, the present inventors have conceived that an amine compound such as an alkylamine can be bonded to a metal atom, but has a much lower bonding ability to a metal oxide.

  Therefore, after leaving an amine compound such as alkylamine and a long-chain carboxylic acid metal salt (R-COOM) from the surface of the metal nanoparticles, the exposed metal surface is oxidized, and only the surface layer is oxidized. When converted to a film, the surface density of amine compounds, such as alkylamines, bound on the metal surface of the surface of the remaining metal nanoparticles is maintained at a level higher than the surface density of the equilibrium state. It was thought that elution of amine compounds such as could be further advanced. Ideally, even when the liquid temperature of the dispersion solvent is about 50 ° C., for example, by using the composite process, the long-chain carboxylic acid that coats the metal surface of the metal nanoparticles is used. It was found that the metal salt (R-COOM) and all amine compounds such as alkylamines can be detached and converted into a state in which a monomolecular oxide film is formed only on the surface layer of the metal nanoparticles. At that time, in the dispersion solvent, an amine complex of a long-chain carboxylic acid metal salt (R-COOM) and an excessive amine compound such as an alkylamine are dissolved. In addition, amine compounds such as long chain carboxylic acid metal salts (R-COOM), long chain carboxylic acid metal salts (R-COOM) and alkylamines dissolved in the dispersion solvent are: Since it is in a dissociation equilibrium state, an extremely slightly long-chain metal salt of carboxylic acid (R-COOM) is produced. A long-chain metal salt of carboxylic acid (R-COOM) can also be bonded to a metal atom, but its bonding ability is much inferior to a metal oxide.

At that time, the oxidation treatment for forming the monomolecular oxide film only on the surface layer of the metal nanoparticles is performed by, for example, dissolving oxygen molecules (O ₂ ) from the surface of the dispersion solvent to convert the oxygen molecules (O ₂ ) into the metal nanoparticles. When acting on metal atoms on the surface, a monomolecular oxide film can be formed only on the surface layer. However, if the oxidation treatment is continued, the oxidation progresses not only to the surface layer but also to the inside of the metal nanoparticles, so the oxidation treatment time needs to be kept within the minimum necessary range.

The solubility of gases such as oxygen molecules (O ₂ ) in the dispersion solvent decreases rapidly as the temperature increases. Therefore, if the content ratio (partial pressure) V _oxygen of oxygen molecules (O ₂ ) in the gas phase is kept constant, the dissolved concentration C (T, O) of oxygen molecules (O ₂ ) dissolved from the gas phase into the dispersion solvent. ₂ ) decreases rapidly as the temperature T _heating increases. On the other hand, the reaction rate constant k _oxidization (T) of the oxidation reaction using oxygen molecules (O ₂ ) increases as the temperature rises. The rate of the oxidation reaction using oxygen molecules (O ₂ ) is proportional to k _oxidization (T) · C (T, O ₂ ), but considering the above two factors, the temperature T _heating is 50 ° C. to 120 ° C. In the range of ° C., the rate of the oxidation reaction using oxygen molecules (O ₂ ) does not increase so much even when the temperature T _heating increases. Therefore, when the temperature T is in the range of 50 ° C. to 120 ° C., the volume ratio V _{oxygen of} oxygen present in the atmosphere is in the range of 10% to 25% by volume, and the oxidation treatment time t ₁ is in the range of 5 seconds to 15 seconds. It was conceived that the surface oxidation can be restricted to a monomolecular layer by selecting to. In particular, after the lapse of oxidation time t _1, when exposed to an atmosphere containing no oxygen molecules (O _2), oxygen molecules dissolved in the dispersion solvent (O ₂₎ in order to evaporate quickly, the oxidation reaction , Can be finished promptly.

  Of course, in the state where the monomolecular oxide film is formed on the surface layer, the metal nanoparticles cannot be fused together and cause low temperature sintering. Therefore, after the metal salt of the long-chain carboxylic acid (R-COOM) and the amine compound such as alkylamine, which had been coated on the metal surface of the metal nanoparticle, have been released, it is formed on the surface layer of the metal nanoparticle. It is necessary to reduce the monomolecular oxide film that has been recovered and restore it to the metal surface, and then fuse the metal nanoparticles to each other to proceed low-temperature sintering.

  The reduction treatment of the monomolecular oxide film formed on the surface layer of the metal nanoparticles can be performed in the presence of a dispersion solvent by using an organic compound having an alcoholic hydroxyl group (> CH—OH) as a reducing agent. I found. Specifically, when a vapor of an organic compound having an alcoholic hydroxyl group (> CH—OH) is supplied to the surface of the dispersion solvent, the organic compound can be dissolved in the dispersion solvent. Reduction treatment can be performed by allowing the dissolved organic compound to act on the monomolecular oxide film formed on the surface layer of the metal nanoparticles.

When the vapor of the organic compound having an alcoholic hydroxyl group (> CH—OH) is contained in the atmosphere at a high volume ratio (partial pressure) in the step of performing the reduction treatment, the organic compound is introduced into the dispersion solvent from the gas phase. The compound dissolves. The concentration C (T,> CH-OH) of the organic compound dissolved in the dispersion solvent is increased to a concentration which is in equilibrium with the volume ratio (partial pressure) V _{reducing-agent} of the vapor of the organic compound present in the gas phase. It is possible to make it. When used for the reduction of monomolecular oxide film formed on the surface layer of metal nanoparticles, ketone compounds (> C = O) derived from organic compounds having alcoholic hydroxyl groups (> CH-OH), An aldehyde compound (—CHO) is formed. Since the boiling point of the ketone compound (> C═O) and then the aldehyde compound (—CHO) is generally lower than that of an organic compound having an alcoholic hydroxyl group (> CH—OH), it evaporates from the surface of the dispersion solvent. Released into the gas phase. In addition, water molecules (H ₂ O) are also generated accompanying the reduction reaction, but in the heated state, the generated water molecules (H ₂ O) are also evaporated from the surface of the dispersion solvent and released into the gas phase. .

  When the metal surface is regenerated on the surface of the metal nanoparticles after reduction, an amine compound such as an alkylamine dissolved in the dispersion solvent and a long-chain carboxylic acid present in a slight amount Since the metal salt (R-COOM) recombines with the metal surface, the fusion between the metal nanoparticles and the low temperature sintering proceed to some extent, but further progress is inhibited.

  However, the amine compound such as alkylamine and the metal salt of long-chain carboxylic acid (R-COOM), which originally constituted the surface coating layer, are mostly metal salt of long-chain carboxylic acid (R-COOM). As the amine complex of) is dissolved in the dispersion solvent, the coverage by the amine compound such as alkylamine and the metal salt of long-chain carboxylic acid (R-COOM) that recombines with the metal surface is reduced. Yes.

  Again, the surface of the exposed metal is oxidized and oxidized to convert only the surface layer into an oxide film. After that, the monomolecular oxide film formed on the surface of the metal nanoparticles is reduced to form a metal. When restored to the surface, it is possible to further promote the fusion of metal nanoparticles and the low temperature sintering. Of course, the amine compound such as alkylamine dissolved in the dispersion solvent and the metal salt (R-COOM) of the long-chain carboxylic acid which is present in a slight amount recombine with the metal surface, and therefore, to some extent. Fusion of metal nanoparticles and low temperature sintering proceed, but further progress is hindered.

  However, by repeating the oxidation treatment and reduction treatment cycles described above, the fusion of metal nanoparticles and low-temperature sintering proceed in stages. We found that it is possible to proceed with termination.

  However, since the long-chain carboxylic acid metal salt (R-COOM) is dissolved in the dispersion solvent as an amine complex of the long-chain carboxylic acid metal salt (R-COOM), the above-described treatment is performed. It cannot be dissolved at a temperature higher than the solubility of the amine complex of the metal salt of long-chain carboxylic acid (R-COOM) in the dispersion solvent.

  When an organic compound having an alcoholic hydroxyl group (> CH—OH) acts on an amine complex of a long-chain carboxylic acid metal salt (R—COOM) dissolved in a dispersion solvent, a reduction reaction proceeds. Thus, it is converted into a metal atom (R) coordinated with a long-chain carboxylic acid (R-COOH) and an amine compound. In the process of the reduction treatment, the long-chain metal salt of carboxylic acid (R-COOM) dissolved in the dispersion solvent is reduced by a reduction reaction using an organic compound having an alcoholic hydroxyl group (> CH—OH). The amine complex is consumed.

  In addition, amine complexes of long-chain carboxylic acid metal salts (R-COOM) can undergo degradative reduction reactions at considerably lower temperatures compared to long-chain carboxylic acid metal salts (R-COOM). I also found out. Specifically, it has been found that, when heated to a temperature of about 80 ° C., a degradative reduction reaction of an amine complex of a long-chain carboxylic acid metal salt (R-COOM) starts. Therefore, when heated to a temperature of 80 ° C. or higher, the amine complex of the long-chain carboxylic acid metal salt (R-COOM) dissolved in the dispersion solvent is consumed even by the decomposing reduction reaction. Therefore, by repeating the cycle of the oxidation treatment and the reduction treatment, the amount of the long-chain carboxylic acid metal salt (R-COOM) that can be reattached to the surface of the metal nanoparticles is reduced stepwise. By utilizing this phenomenon as well, by repeating the above oxidation treatment and reduction treatment cycles, the fusion of metal nanoparticles and low temperature sintering proceed in stages, and finally the target level. It has been found that it is possible to proceed the low-temperature termination of metal nanoparticles.

  Based on the above-described series of findings, the inventors have completed the present invention.

That is, the method for forming a metal nanoparticle sintered body layer according to the present invention,
A method of forming a metal nanoparticle sintered body layer using a metal nanoparticle dispersion,
The metal nanoparticle dispersion liquid includes a metal nanoparticle having an average particle diameter selected in a range of 1 nm to 100 nm, a coating molecule constituting a coating molecule layer formed on the surface of the metal nanoparticle, and a dispersion Containing a solvent,
The metal nanoparticles are metal nanoparticles made of one or more metals selected from the group consisting of gold, silver, platinum, palladium, nickel, or alloys thereof;
The dispersion solvent is selected from the group consisting of hydrocarbon solvents having a boiling point in the range of 180 ° C to 300 ° C;
An aliphatic monocarboxylic acid (R—COOH) having a boiling point in the range of 140 ° C. to 400 ° C. and (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH having a boiling point in the range of 165 ° C. to 250 ° C. ₂ -NH ₂ ) in combination with the coating molecule;
The volume ratio V _{nano-particle} of the metal nanoparticles contained in the metal nanoparticle dispersion is selected in the range of 5 volume% to 25 volume%;
The ratio (N _carboxylate : N _amine ) of the total molecular number N _carboxylate of the aliphatic monocarboxylic acid and the total molecular number N _amine of (dialkylamino) propylamine is in the range of 1: 1.1 to 1: 1.5. Is selected;
And the volume ratio V _carboxylate of the aliphatic monocarboxylic acid to the sum of the volume ratio V _Amine of (dialkylamino) propylamine (V _carboxylate + V _amine), the ratio of the volume ratio V _Solvent of the dispersion solvent {(V _carboxylate + V _amine) : V _solvent } is selected in the range of 1: 1.0 to 1:10,
The process of forming the metal nanoparticle sintered body layer is as follows:
Applying the metal nanoparticle dispersion on the surface of the substrate to form a coating film with a predetermined film thickness, and a coating film forming step,
A low-temperature sintering step in which the coating film of the metal nanoparticle dispersion is heated to a temperature T _heating selected in a range of 50 ° C. to 120 ° C., and the metal nanoparticles included in the coating film are sintered at a low temperature. Including;
The low temperature sintering step includes
In an air stream of an oxygen-containing mixed gas in which oxygen molecules (O ₂ ) are mixed in an inert gas at a volume ratio V _oxygen selected in the range of 10 volume% to 25 volume%, for 5 seconds to 15 seconds. An oxidation treatment sub-step of forming an oxide film on the surface of the metal nanoparticles contained in the coating film by using the oxygen treatment time t ₁ selected in a range, heating to the temperature, and using oxygen molecules as an oxidizing agent; ,
Alcoholic properties that can be converted into an oxo group (> = O) or a formyl group (-CHO) by oxidation at a volume ratio V _{reducing-agent} selected in the range of 10 vol% to 30 vol% in an inert gas In a gas stream of a reducing gas mixture in which vapor of an organic compound having a hydroxyl group (> CH—OH) is mixed, a reduction treatment time t ₂ selected in a range of 120 seconds to 300 seconds is heated to the above temperature. Using the organic compound as a reducing agent to reduce and remove the oxide film on the surface of the metal nanoparticles contained in the coating film,
The oxidation / reduction treatment step, which is a combination of the oxidation treatment substep and the reduction treatment substep, is repeated n times (where n is an integer of 1 or more), and the coating molecular layer covering the surface of the metal nanoparticle is formed. Do the removal,
By selecting the total heat treatment time for repeating the oxidation / reduction treatment step n times, n × (t ₁ + t ₂ ) in the range of 375 seconds to 3150 seconds, the metal nanoparticles contained in the coating film can be obtained. Sintering at low temperature to form a metal nanoparticle sintered body layer;
The boiling point of the organic compound having an alcoholic hydroxyl group (> CH—OH) that can be converted into an oxo group or a formyl group by oxidation is selected in the range of 60 ° C. to 120 ° C. This is a method for forming a particle sintered body layer.

that time,
The metal nanoparticles are preferably metal nanoparticles having an average particle diameter selected in the range of 2 nm to 50 nm.

  The dispersion solvent is preferably selected from the group consisting of chain hydrocarbon solvents having a boiling point in the range of 180 ° C to 300 ° C.

  The aliphatic monocarboxylic acid having a boiling point in the range of 140 ° C. to 400 ° C. is preferably an aliphatic monocarboxylic acid having a total carbon number of 3 to 20.

The alkyl groups R ^1A and R ^2A in the (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ) having a boiling point in the range of 165 ° C. to 250 ° C. have 2 to 4 carbon atoms. It is preferable that it is the alkyl group of the range.

  The organic compound having an alcoholic hydroxyl group (> CH—OH) that can be converted into an oxo group or a formyl group by oxidation is preferably an alkanol having 1 to 6 carbon atoms.

  It is preferable to select the heating temperature in the low-temperature sintering step in the range of 80 ° C to 120 ° C.

  In the low-temperature sintering step, it is preferable to select the number of repetitions n of the oxidation / reduction treatment step in a range of 3 to 10 times.

It is desirable that the volume ratio V _{reducing-agent} is selected in the range of 15 volume% to 25 volume%.

It is desirable to select the volume ratio V _oxygen in the range of 15 volume% to 25 volume%.

After finishing the low-temperature sintering step, it is desirable to have a temperature lowering step of lowering the temperature from the temperature T _heating in the reducing gas mixture.

  The method for forming a metal nanoparticle sintered body layer according to the present invention can be suitably applied when the metal nanoparticles are silver nanoparticles.

  In the method for forming a metal nanoparticle sintered body layer according to the present invention, when the temperature at which the sintering treatment is performed is selected in the range of 50 ° C. to 120 ° C., oxidation treatment is performed for a short time, and then alcoholic hydroxyl groups (> CH The reduction process using the organic compound having —OH) is performed. The oxidation process and the reduction process cycle are used, and the oxidation process and the reduction process are repeated, and the low-temperature sintering of the metal nanoparticles is advanced step by step. be able to. Therefore, the sintered body layer produced by the conventional low-temperature sintering process of metal nanoparticles is inferior to the heating temperature used in the low-temperature sintering process of conventional metal nanoparticles. It is possible to form a sintered body layer of metal nanoparticles exhibiting high conductivity.

  Below, the formation method of the metal nanoparticle sintered compact layer concerning this invention is demonstrated in detail.

When forming the metal nanoparticle sintered body layer by removing the coating agent molecular layer on the metal nanoparticle surface contained in the metal nanoparticle dispersion, the heating temperature T _heating is selected to be 150 ° C. or higher in the conventional method. Then, the technique of removing the coating agent molecular layer is adopted. In the method of forming the metal nanoparticle sintered body layer according to the present invention, the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C. Thus, a method of removing the coating agent molecular layer stepwise by repeating the cycle of oxidation treatment and reduction treatment is adopted. Specifically, when the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., the solubility of the coating molecules in the dispersion solvent is low, and the vapor pressure of the coating molecules is also low. It is difficult to remove the coating material molecule layer on the surface of the metal nanoparticles by elution of the solution into the dispersion solvent and evaporating the eluted coating molecules. Further, when removing the coating molecule capable of decomposing reduction reaction by _heating , when the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., the progress of the decomposing reduction reaction is slow. For this reason, it is difficult to efficiently remove the coating agent molecules. On the other hand, in the method for forming a metal nanoparticle sintered body layer according to the present invention, the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., and then the metal surface of the metal nanoparticles is oxidized. The release of the coating agent molecules is promoted, and then the reduction treatment is performed, whereby the oxide film formed by the oxidation treatment is reduced and removed, thereby promoting the low-temperature sintering of the metal nanoparticles. By repeating the oxidation treatment and reduction treatment cycles described above, the low-temperature sintering of the metal nanoparticles is advanced step by step to finally form a metal nanoparticle sintered body layer exhibiting high conductivity. It is possible.

In the metal nanoparticle dispersion liquid used in the method for forming a metal nanoparticle sintered body layer of the present invention, an aliphatic monocarboxylic acid (R—COOH) and (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ), in particular, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) in combination to form a coating molecular layer on the surface of metal nanoparticles In practice, the aliphatic monocarboxylic acid (R-COOH) is in the form of a metal salt (R-COOM) of the aliphatic monocarboxylic acid in the form of a metal atom ( M) and a metal cation (M ⁺ ) in the metal salt are bonded to the surface of the metal nanoparticle through a metal bond interaction, while (dialkylamino) propylamine (R ^1A R ^2A N-CH ₂ CH ₂ CH ₂ -N H ₂ ), for example, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) uses a lone pair on the nitrogen atom of the amino group (—NH ₂ ). , Coordinated to the metal atom (M) on the surface of the metal nanoparticle.

In the metal nanoparticle dispersion liquid used in the present invention, a hydrocarbon solvent which is a nonpolar solvent is used as a dispersion solvent. Since the solubility of the metal salt of aliphatic monocarboxylic acid (R-COOM) in the hydrocarbon solvent is very low, when the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., the surface of the metal nanoparticles It is difficult to elute a metal salt of an aliphatic monocarboxylic acid into a dispersion solvent. On the other hand, (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ), for example, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH) in the hydrocarbon solvent. ₂ CH ₂ —NH ₂ ) has a relatively high solubility. Therefore, when the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., a part of the (dialkylamino) propylamine on the surface of the metal nanoparticles is a dispersion solvent. It is possible to elute in.

[Process for forming metal nanoparticle sintered body layer]
In the method for forming a metal nanoparticle sintered body layer of the present invention, first, in the coating film forming step, the metal nanoparticle dispersion is applied to the surface of the substrate with a predetermined film thickness to produce a coating film layer. Next, in the low temperature sintering step, the coating film of the metal nanoparticle dispersion is heated to a temperature T _heating selected in the range of 50 ° C. to 120 ° C., and the metal nanoparticles contained in the coating film are sintered at a low temperature. Tie.

  In this low-temperature sintering process, the following oxidation treatment substep and reduction treatment substep are combined and repeated the oxidation / reduction treatment step n times (where n is an integer of 1 or more), and the surface of the metal nanoparticles The coating molecular layer covering the metal is removed, and the low-temperature sintering of the metal nanoparticles is advanced step by step.

(Oxidation sub-step)
When heating is performed, a lone electron pair of an amino group (—NH ₂ ) is utilized on the coating molecule that coats the surface of the metal nanoparticle, in particular, the metal atom (M) on the surface of the metal nanoparticle. (Dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ) having a coordinate bond, for example, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ A portion of (CH ₂ CH ₂ —NH ₂ ) is eluted in a nonpolar hydrocarbon solvent. This (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) is converted to a metal It acts on the metal salt (R-COOM) of the carboxylic acid bonded (adsorbed) on the metal atom (M) on the surface of the nanoparticle, and the metal cation (M ⁺ ) is converted to (dialkylamino) propylamine (R ” ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) An amine complex (R-COOM: (R " ₂ N-CH ₂ CH ₂ CH ₂ -NH ₂ )) of a metal salt of boronic acid (R-COOM) is formed. The amine complex (R-COOM: (R " ₂ N-CH ₂ CH ₂ CH ₂ -NH ₂ )) of the metal carboxylate (R-COOM) is formed on the metal atom (M) on the surface of the metal nanoparticle. It cannot bind and is dissolved in the dispersion solvent.

  In the sub-step of the oxidation treatment, since heating is performed, a part of the coating molecule covering the surface of the metal nanoparticles is eluted in the nonpolar hydrocarbon solvent. Since the surface of the metal nanoparticles is partially exposed, oxygen molecules dissolved in the nonpolar hydrocarbon solvent can be adsorbed and reacted on the metal atoms, and a surface oxide film (MO) is formed on the surface of the metal nanoparticles. ) Is formed.

(Dialkylamino) propylamine (R ″ ₂ N) which has been coordinated on the metal atom (M) on the surface of the metal nanoparticle by utilizing a lone electron pair of an amino group (—NH ₂ ). —CH ₂ CH ₂ CH ₂ —NH ₂ ) cannot recombine on the surface oxide film (MO).

  Further, the metal salt (R-COOM) of the carboxylic acid adsorbed to the metal atom (M) on the surface of the metal nanoparticle through an interaction similar to a metal bond is also applied to the surface oxide film (MO). Cannot rejoin on top.

That is, as a result of the formation of a surface oxide film (MO) on a substantial part of the surface of the metal nanoparticles, recombination of the eluted (dialkylamino) propylamine and the metal salt of carboxylic acid (R-COOM) is suppressed. The On the other hand, the eluted (dialkylamino) propylamine and the metal salt of carboxylic acid (R-COOM) are (dialkylamino) to the metal cation (M ⁺ ) of the metal salt of carboxylic acid (R-COOM). ) by propylamine is coordinated, (amine complexes of R-COOM) (R-COOM : (R "2 N-CH 2 CH 2 CH 2 -NH 2) carboxylic acid metal salt constitutes a). Due to the affinity of the hydrocarbon chain moiety (R-) of the carboxylic acid metal salt (R-COOM) and the alkyl group (R "-) of the (dialkylamino) propylamine to the nonpolar hydrocarbon solvent, the metal carboxylate The amine complex of the salt is dissolved in a nonpolar hydrocarbon solvent.

At that time, the surface oxide film (MO) formed on the surface of the metal nanoparticles shortens the oxidation treatment time t ₁ and the amount of oxidation caused by oxygen molecules (O ₂ ) dissolved in the nonpolar hydrocarbon solvent. By controlling, it is a monomolecular layer. Specifically, the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., preferably in the range of 80 ° C. to 120 ° C., and the volume ratio V _{oxygen of} oxygen present in the atmosphere is 10 vol% to It is desirable to select the range of 25% by volume, preferably 15% by volume to 25% by volume, particularly 20% by volume. In this case, the surface oxidation is kept in the monomolecular layer by selecting the oxidation treatment time t ₁ in the range of 5 seconds to 15 seconds, particularly 10 seconds.

(Reduction processing sub-step)
In the reduction treatment sub-step, the surface oxide film (MO) formed on the surface of the metal nanoparticle is converted into an organic compound having a reducing ability, that is, an oxo group (> = O) or a formyl group (—CHO) by oxidation. Using an organic compound having an alcoholic hydroxyl group (> CH—OH) that can be converted into a metal atom (M), the compound is reduced to a metal atom (M).

  The organic compound having an alcoholic hydroxyl group (> CH—OH) on the surface of the surface oxide film (MO) is composed of an oxygen atom of the metal oxide (MO) and a hydrogen atom of the hydroxyl group (> CH—OH). It adsorbs once through a hydrogen bond.

  Thereafter, reduction of the metal oxide (MO) and oxidation of the organic compound having an alcoholic hydroxyl group (> CH—OH) proceed.

MO + (> CH—OH) → M + H ₂ O + (> C═O)

At that time, by-product water molecules (H ₂ O) are evaporated. On the other hand, the boiling point of a ketone compound (> = O) or an aldehyde compound (-CHO) produced by oxidation of an organic compound having an alcoholic hydroxyl group (> CH-OH) is usually an alcoholic hydroxyl group (> CH--). Considerably lower than the boiling point of organic compounds with OH). Further, the resulting ketone compound (> = O) or aldehyde compound (-CHO) has poor adsorptivity to the metal surface. For this reason, the resulting ketone compound (> = O) or aldehyde compound (-CHO) also evaporates quickly.

An organic compound having an alcoholic hydroxyl group (> CH—OH) has an alcoholic hydroxyl group (> CH—OH) having a lone pair capable of coordinative bonding to a metal atom. However, since the boiling point is 120 ° C. or less, it is difficult to stably adsorb onto the metal atoms on the surface of the metal nanoparticles at the heating temperature T _heating . Therefore, the density of molecules attached to the metal surface of the metal nanoparticle from which the surface oxide film has been removed by the reduction treatment is significantly reduced.

The dispersion solvent, and eluted metal salts of carboxylic acids (R-COOM), (dialkylamino) propylamine ^{(R 1A R 2A N-CH} 2 CH 2 CH 2 -NH 2), for example, (dialkylamino) propylamine _{(R "2 N-CH 2} CH 2 CH 2 -NH 2) consisting of a carboxylic acid metal salt-amine complex (R-COOM: (R" 2 N-CH 2 CH 2 CH 2 -NH 2)) Is dissolved. The carboxylic acid metal salt / amine complex is presumed to have the following structure.

For example, when a carboxylic acid metal salt / amine complex undergoes reduction using an organic compound having an alcoholic hydroxyl group (> CH—OH), the metal atom coordinated by the amine (M: (R ″ ₂ N— _{CH 2 CH 2 CH 2 -NH 2} )) to be converted into a carboxylic acid (R-COOH).
_{2R-COOM: (R "2} N-CH 2 CH 2 CH 2 -NH 2) + (> CH-OH)
→ 2 (M: (R " 2 N-CH 2 CH 2 CH 2 -NH 2)) + 2R-COOH + (> C = O)
In the reduction reaction, an organic compound having an alcoholic hydroxyl group (> CH—OH) and the carboxylic acid metal salt / amine complex form an aggregate through a hydrogen bond, and then an alcoholic hydroxyl group (> It is speculated that the process proceeds from the CH—OH) to the carboxylate anion species (R—COO ⁻ ) due to the donation of a hydrogen atom. As a result, the alcoholic hydroxyl group (> CH—OH) is oxidized to an oxo group (> C═O).

A metal atom coordinated by an amine (M: (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ )) is deposited on the metal surface of the metal nanoparticle. As a result, the metal atom is coordinated. The (dialkylamino) propylamine thus formed is again in a coordinated bond with the metal atom on the surface of the metal nanoparticle, while the free carboxylic acid (R-COOH) is a nonpolar hydrocarbon. In a solvent, it associates with a hydrogen bond to form a dimer (R-COOH: HOCO-R), or a liberated carboxylic acid (R-COOH) and (dialkylamino) propylamine associate with each other by a hydrogen bond. Thus, a carboxylic acid / amine complex (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ : HOCO-R) is formed. The carboxylic acid dimer and the carboxylic acid / amine complex are dissolved in a non-polar hydrocarbon solvent, and are gradually vaporized and evaporated. On the other hand, the resulting ketone compound (> = O) or aldehyde compound (-CHO) produced by oxidation of an organic compound having an alcoholic hydroxyl group (> CH-OH) is once in a nonpolar hydrocarbon solvent. Dissolves but eventually vaporizes and evaporates.

Furthermore, in the carboxylic acid metal salt / amine complex, the following decomposition process may proceed depending on the type of the carboxylic acid metal salt.
R ₄ —CH ₂ —CH ₂ —COOM: (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ )
→ R ₄ —CH═CH ₂ + (HCOM: (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ))
Thereafter, when the metal formate / amine complex produced undergoes reduction using an organic compound having an alcoholic hydroxyl group (> CH—OH), the metal atom coordinated by the amine (M: (R ″ ₂ N -CH ₂ CH ₂ CH ₂ -NH ₂ )) and formic acid (HCOOH).
2HCOOM: (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) + (> CH—OH)
→ 2 (M: (R " 2 N-CH 2 CH 2 CH 2 -NH 2)) + 2HCOOH + (> C = O)
The liberated formic acid (HCOOH) associates with a hydrogen bond in a nonpolar hydrocarbon solvent to form a dimer (HCOOH: HOCOH)). The boiling point of the dimer of formic acid (HCOOH: HOCOH) is 100.8 ° C. and can be evaporated. Further, water molecules (H ₂ O) generated by reduction of the surface oxide film and formic acid (HCOOH) may associate with each other through hydrogen bonds to form a molecular compound (HCOOH: H ₂ O). The boiling point of the azeotrope composed of formic acid and water is 107 ° C., and the molecular compound (HCOOH: H ₂ O) can also be evaporated.

  In general, the boiling point of a ketone compound (> = O) or an aldehyde compound (—CHO) generated by oxidation of alcohol is lower than that of alcohol. Therefore, the resulting ketone compound (> = O) or aldehyde compound (-CHO) produced by oxidation of an organic compound having an alcoholic hydroxyl group (> CH-OH) is once in a nonpolar hydrocarbon solvent. Dissolves but eventually vaporizes and evaporates.

On the other hand, the metal atom coordinated by the amine (M: (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ )) adheres to the metal surface of the metal nanoparticle. The coordinated (dialkylamino) propylamine is again in a coordinated bond with the metal atom on the surface of the metal nanoparticle.

Note that the reduction treatment time t ₂ in the reduction treatment substep is set so that removal of the surface oxide film formed in the oxidation treatment substep is achieved according to the reduction treatment condition, as will be described later.

  As a result, by performing a cycle of oxidation treatment and reduction treatment, a substantial portion of the metal salt of carboxylic acid (R-COOM) that has covered the surface of the metal nanoparticles is reduced to metal atoms (M). Removed. In addition, since the (dialkylamino) propylamine that coats the surface of the metal nanoparticles is once released, a part of the (dialkylamino) propylamine is evaporated. Removed.

  During the above reduction treatment sub-steps, fusion between metal nanoparticles and low-temperature sintering proceed at a site where the metal surfaces of the reduced metal nanoparticles contact each other.

  In the first cycle, when the sub-step of the reduction treatment is completed, the density of the metal salt of carboxylic acid (R-COOM) and the density of (dialkylamino) propylamine covering the surface of the metal nanoparticles are as follows: Compared to the original density, it is considerably reduced.

  When the second cycle of oxidation treatment and reduction treatment is performed, the density of the metal salt of carboxylic acid (R-COOM) covering the surface of the metal nanoparticles at the time when the substep of the reduction treatment is completed, (dialkyl The density of amino) propylamine is further reduced. Meanwhile, during the reduction treatment sub-step, the fusion of metal nanoparticles and the low temperature sintering further progress. That is, when the cycle of the oxidation treatment and the reduction treatment is repeated, the density of the metal salt of carboxylic acid (R-COOM) and the density of (dialkylamino) propylamine covering the surface of the metal nanoparticles are gradually reduced. The At the same time, during each cycle, during the reduction process sub-steps, the fusion of the metal nanoparticles and the low-temperature sintering proceed in stages at the site where the metal surfaces of the reduced metal nanoparticles contact each other.

In the above reduction treatment sub-step, in the reaction of reducing the metal salt of the carboxylic acid (R-COOM) released from the surface, the (dialkylamino) propylamine released from the metal nanoparticles is a bidentate ligand. It is used as. Therefore, when the heating temperature T _heating is high, the amount of (dialkylamino) propylamine released from the metal nanoparticles in the dispersion solvent increases, so that the metal salt of carboxylic acid released from the surface (R-COOM) can be efficiently used. Thus, it can be converted into an amine complex to carry out a reduction reaction. Therefore, the reaction rate of the reduction reaction via the amine complex formation is increased. Therefore, as the heating temperature T _heating increases, the ratio of the density of the metal salt of carboxylic acid (R-COOM) and the density of (dialkylamino) propylamine that covers the surface of the metal nanoparticles in each cycle is reduced. Increases, and the progress of fusion between metal nanoparticles and low-temperature sintering increases.

Therefore, in the method of the present invention, when the heating temperature T _heating is increased from 50 ° C. to 120 ° C., the progress rate of the sintering of the metal nanoparticles increases. However, when the heating temperature T _heating is increased from 50 ° C. to 120 ° C., the liquid phase of an organic compound having an alcoholic hydroxyl group (> CH—OH) dissolved from the gas phase into the liquid phase (dispersion solvent) ( The dissolution rate in the dispersion solvent) gradually decreases. Therefore, the rate of increase in the rate of the reaction for reducing the released carboxylic acid metal salt (R-COOM) becomes small when the heating temperature T _heating exceeds 100 ° C.

In the reduction treatment sub-step, the reduction of the surface oxide film (MO) formed on the surface of the metal nanoparticles during the oxidation treatment sub-step and the metal salt of carboxylic acid (R-COOM) released from the surface. It is necessary to carry out reduction. Therefore, the reduction treatment conditions are selected so that at least the reduction of the surface oxide film (MO) formed on the surface of the metal nanoparticles during the oxidation treatment sub-step is sufficiently achieved. Specifically, the heating temperature T _heating is selected in the range of 50 ° C. to 120 ° C., preferably in the range of 80 ° C. to 120 ° C. The volume ratio (partial pressure) V _{reducing-agent} of an organic compound having an alcoholic hydroxyl group (> CH—OH) present in the atmosphere at the heating temperature T _heating is 10 vol% to 30 vol% (0 0.1 × 1013 hPa to 0.3 × 1013 hPa), preferably 15% to 25% by volume (0.15 × 1013 hPa to 0.25 × 1013 hPa), for example, 20% by volume (0.2 × It is desirable to select 1013 hPa). Further, the reduction treatment time t ₂ is desirably selected in the range of 120 seconds to 300 seconds, preferably in the range of 150 seconds to 300 seconds.

In an organic compound having an alcoholic hydroxyl group (> CH—OH) used in the reduction treatment, the alcoholic hydroxyl group (> CH—OH) is converted into an oxo group (> ═O) or a formyl group by oxidation. Converted to (-CHO). Further, in order to set the volume ratio (partial pressure) V _{reducing-agent} of the gas of the organic compound having an alcoholic hydroxyl group (> CH—OH) contained in the atmosphere within the above range, the heating temperature T _heating The liquid having an equilibrium vapor pressure of 0.3 × 10 13 hPa or more is used.

Therefore, the boiling point of the organic compound having an alcoholic hydroxyl group (> CH—OH) that can be converted into an oxo group or a formyl group by the oxidation is within a range of 60 ° C. to 120 ° C. with respect to the _heating temperature T _heating . It is desirable to choose. For example, it is desirable to select a primary alcohol or a secondary alcohol having a boiling point in the range of 64 ° C to 120 ° C.

  As an organic compound having an alcoholic hydroxyl group (> CH—OH) having a boiling point in the above range and convertible to an oxo group or a formyl group by oxidation, an aliphatic monoalcohol having a boiling point of 120 ° C. or less, preferably An alkanol having 1 to 6 carbon atoms, more preferably an alkanol having 1 to 5 carbon atoms can be used.

Preferable examples of the organic compound having an alcoholic hydroxyl group (> CH—OH) that can be used in the present invention include an aliphatic alcohol having a boiling point of 120 ° C. or lower. For example, as an aliphatic monoalcohol having a boiling point of 120 ° C. or less, methanol (boiling point 64.65 ° C.), ethanol (boiling point 78.32 ° C.), 1-propanol (boiling point 96.15 ° C.), 2-propanol (boiling point 82.82 ° C.). 4 ° C), 2-butanol (boiling point 99.50 ° C), 1-butanol (boiling point 117-118 ° C), 2-methyl-1-propanol (boiling point 107.89 ° C), 2-pentanol (boiling point 119.85) Primary alkanols or secondary alkanols such as C.). In addition, alkyloxyalkanol having a boiling point of 120 ° C. or lower (R ¹ —O—R ² —OH) or alkylene glycol monoalkyl ether such as 1-methoxy-2-propanol (boiling point 118 to 119 ° C.) is used. You can also

The vapor of the organic compound having the alcoholic hydroxyl group (> CH—OH) is mixed with an inert gas such as nitrogen gas (N ₂ ) or a rare gas (He, Ar, Ne), and the heating temperature T _heating And heated on the surface of the coating film of the metal nanoparticle dispersion. As a result, the organic compound having the alcoholic hydroxyl group (> CH—OH) supplied from the gas phase is dissolved in the nonpolar hydrocarbon solvent contained in the coating film. The concentration C _{reducing-agent} of the organic compound having the alcoholic hydroxyl group (> CH—OH) dissolved in the nonpolar hydrocarbon solvent is an organic compound having the alcoholic hydroxyl group (> CH—OH) in the gas phase. The volume ratio (partial pressure) of the compound gas is proportional to V _{reducing-agent} . When the heating temperature T _heating is increased, the concentration C (T,> CH—OH) of the organic compound having the alcoholic hydroxyl group (> CH—OH) to be dissolved is relatively decreased. On the other hand, when the heating temperature T _heating increases, the rate constant k _reduction (T) of the _reduction reaction increases. Since the rate of the reduction reaction is proportional to k _reduction (T) · C (T,> CH—OH), the above two factors are taken into consideration, and the temperature T _heating is in the range of 50 ° C. to 120 ° C. The rate of the reduction reaction using an organic compound having a hydroxyl group (> CH—OH) does not increase so much even when the temperature T _heating increases.

Therefore, in the low temperature sintering step, when the temperature T _heating is in the range of 50 ° C to 120 ° C,
The oxidation treatment time t ₁ in the oxidation treatment substep is selected in the range of 5 seconds to 15 seconds, preferably in the range of 10 seconds to 15 seconds,
The reduction treatment time t ₂ in the reduction treatment substep is selected in the range of 120 seconds to 300 seconds, preferably in the range of 150 seconds to 300 seconds,
The oxidation / reduction treatment step combining the oxidation treatment sub-step and the reduction treatment sub-step is repeated n times (where n is an integer of 1 or more).
The total heat treatment time during the low-temperature sintering step, n × (t ₁ + t ₂ ), ranges from 375 seconds (eg, 3 × (5 + 120) seconds) to 3150 seconds (eg, 10 × (15 + 300) seconds) Preferably, it is desirable to select a range of 450 seconds (for example, 3 × 150 seconds) to 2000 seconds (for example, 10 × 200 seconds).

The low-temperature sintering proceeds stepwise by repeating the oxidation / reduction treatment step. However, when the number of repetitions exceeds a certain level, the low-temperature sintering substantially does not proceed further. Therefore, it is preferable to select the number of repetitions n of the oxidation / reduction treatment step within a range of 3 to 10 while keeping the total heat treatment time, n × (t ₁ + t ₂ ) within the above range.

After finishing the low temperature sintering step, the temperature is lowered. At that time, it is desirable to have a temperature lowering step of lowering the temperature from the temperature T _heating in the flow of the reducing gas mixture used in the reduction processing sub-step. That is, it is desirable to prevent oxidation of the low-temperature sintered body of the formed metal nanoparticles by supplying vapor of an organic compound having an alcoholic hydroxyl group (> CH—OH) even during the temperature drop.

[Metal nanoparticle dispersion]
The metal nanoparticle dispersion used in the method for forming a metal nanoparticle sintered body layer of the present invention is formed on the surface of the metal nanoparticle having an average particle diameter selected in the range of 1 nm to 100 nm and the metal nanoparticle. The coating material molecule | numerator which comprises the coating material molecule | numerator layer to be formed, and the dispersion solvent are included.

  In that case, the said metal nanoparticle is a metal nanoparticle which consists of 1 or more types of metals selected from the group which consists of gold | metal | money, silver, platinum, palladium, nickel, or its alloy. At that time, the average particle diameter of the metal nanoparticles is selected in the range of 1 nm to 100 nm, preferably in the range of 2 nm to 50 nm, more preferably in the range of 5 nm to 30 nm.

  On the other hand, the dispersion solvent is selected from the group consisting of hydrocarbon solvents having a boiling point in the range of 180 ° C. to 300 ° C., preferably in the range of 190 ° C. to 290 ° C. For example, the dispersion solvent is desirably selected from the group consisting of chain hydrocarbon solvents having a boiling point in the range of 180 ° C to 300 ° C. Examples of the dispersing solvent that can be used include chain hydrocarbon solvents having 11 to 16 carbon atoms, for example, alkanes having 11 to 16 carbon atoms. Specific examples include tetradecane (boiling point 253.57 ° C.), undecane (boiling point 195 ° C.), hexadecane (boiling point 287 ° C.), and the like.

In order to disperse the metal nanoparticles uniformly in the dispersion solvent, a coating agent molecular layer is formed on the surface of the metal nanoparticles. The coating molecule forming the coating molecule layer is an aliphatic monocarboxylic acid (R-COOH) having a boiling point in the range of 140 ° C to 400 ° C, preferably in the range of 140 ° C to 380 ° C, and a boiling point of 165 ° C. (Dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ) in the range of ˜250 ° C., preferably in the range of 169 ° C. to 240 ° C., for example (dialkylamino) propylamine ( R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) are used in combination.

The aliphatic monocarboxylic acid (R-COOH) having a boiling point in the above-mentioned range, which is used for the coating molecule, is, for example, an aliphatic monocarboxylic acid having a total carbon number of 3 to 20, more preferably It is desirable to select from aliphatic monocarboxylic acids having a total carbon number of 3-18. For example, oleic acid (CH ₃ (CH ₂ ) ₇ CH═CH (CH ₂ ) ₇ COOH, boiling point: 360 ° C.), propanoic acid (CH ₃ CH ₂ COOH, boiling point 140 ° C.) and the like can be suitably used.

In addition, the alkyl groups R ^1A and R ^2A in (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ) having the boiling point in the above range have ² to 4 carbon atoms. It is desirable to select a range of alkyl groups. For example, when the alkyl groups R ^1A and R ^2A are the same (R ^1A = R ^2A = R ″), that is, in (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) It is desirable to select an alkyl group having 2 to 4 carbon atoms as the alkyl group R ″. For example, dibutylaminopropylamine ((C ₄ H ₉ ) ₂ N (CH ₂ ) ₃ NH ₂ , boiling point: 238 ° C.), diethylaminopropylamine (boiling point 169 to 171 ° C.) in which an ethyl group is selected as the alkyl group R ″ can be suitably used.

In practice, the aliphatic monocarboxylic acid (R-COOH) is in the form of a metal salt of the aliphatic monocarboxylic acid (R-COOM), and the metal atom (M) on the surface of the metal nanoparticle and the metal salt in the metal salt. It is bound to the surface of the metal nanoparticle through a metal binding interaction between the metal cations (M ⁺ ). On the other hand, (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ), for example, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) Uses a lone electron pair on the nitrogen atom of the amino group (—NH ₂ ) to form a coordinate bond to the metal atom (M) on the surface of the metal nanoparticle.

The metal salt of an aliphatic monocarboxylic acid (R-COOM) itself does not dissolve in a hydrocarbon solvent, which is a nonpolar solvent, but binds to the surface of the metal nanoparticle through a metal-bonding interaction. In this state, the hydrocarbon group (R-) of the metal salt of aliphatic monocarboxylic acid (R-COOM) exhibits affinity for the hydrocarbon solvent. In addition, (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ), eg, (dialkyl), which is bonded to the surface of the metal nanoparticle through a coordinate bond. Amino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) is a hydrocarbon solvent of (dialkylamino) propyl group (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —) The metal nanoparticles have a coating molecule layer formed on the surface because the coating molecules that coat the surface of the metal nanoparticles show affinity to the hydrocarbon solvent. The metal nanoparticles are in a state of being uniformly dispersed in the hydrocarbon solvent.

(Dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ), for example, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) It can be dissolved in a hydrocarbon solvent, so that (dialkylamino) propylamine dissolved in the hydrocarbon solvent is bonded to the surface of the metal nanoparticle via a coordinate bond (dialkylamino). ) Propylamine is in dissociation equilibrium.

On the other hand, (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ), for example, (dialkylamino) propylamine (R ″ ₂ N—CH ₂ CH ₂ CH ₂ —NH ₂ ) Is capable of bidentate coordination with the metal cation (M ⁺ ) by utilizing its amino group (—NH ₂ ) and dialkylamino group (R ″ ₂ N—). When heated, (dialkylamino) propylamine acts on the aliphatic monocarboxylic acid metal salt (R-COOM) to release the aliphatic monocarboxylic acid metal salt (R-COOM). COOM) can be converted to amine complexes. The amine complex of a metal salt of an aliphatic monocarboxylic acid (R-COOM) includes a hydrocarbon group (R-) derived from an aliphatic monocarboxylic acid and an alkyl group (R "-derived from (dialkylamino) propylamine. ) Exhibits an affinity for hydrocarbon solvents and can be dissolved in hydrocarbon solvents.

The ratio (N _carboxylate : N _amine ) of the total molecular number N _carboxylate of the aliphatic monocarboxylic acid and the total molecular number N _amine of (dialkylamino) propylamine contained in the metal nanoparticle dispersion is 1: 1. It is selected in the range of 1-1: 1.5, preferably in the range of 1: 1.2-1: 1.5. That is, an amount of (dialkylamino) sufficient to form an amine complex (R-COOM: (R " ₂ N-CH ₂ CH ₂ CH ₂ -NH ₂ )) of a metal salt of an aliphatic monocarboxylic acid (R-COOM). ) Contains propylamine.

Further, the volume ratio V _carboxylate of aliphatic monocarboxylic acid and the volume ratio V amine of (dialkylamino) propylamine V _amine contained in the dispersion (V _carboxylate + V _amine ) and the volume ratio V _solvent of the dispersion solvent The ratio {(V _carboxylate + V _amine ): V _solvent } is selected in the range of 1: 1.0 to 1:10, preferably in the range of 1: 1.2 to 1: 5. That is, when heated, (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ) eluted from the surface of the metal nanoparticles in the dispersion solvent and the metal of the aliphatic monocarboxylic acid When the amine complex of the salt (R-COOM) is dissolved, the volume ratio of the dispersion solvent is selected so that these solute molecules contain a sufficient amount of the dispersion solvent to achieve a state surrounded by the dispersion solvent. Yes.

On the other hand, the volume ratio V _{nano-particle} of the metal nanoparticles contained in the metal nanoparticle dispersion is selected in the range of 5 vol% to 25 vol%, preferably in the range of 7 vol% to 20 vol%. Has been.

At that time, is contained in the dispersion, the volume ratio V _{nano-particle} and the volume ratio V _carboxylate of aliphatic monocarboxylic acids and (dialkylamino) propyl sum of the volume ratio V _Amine amine of the metal nanoparticles (V _carboxylate + V _amine ) ratio, {V _{nano-particle} : (V _carboxylate + V _amine )} is in the range of 1: 1.0 to 1: 4.0, preferably 1: 1.1 to 1: 3.0. It is desirable to select a range.

  For example, an inkjet printing method can be applied to the application of the metal nanoparticle dispersion. When using the inkjet printing method, the viscosity of the metal nanoparticle dispersion is preferably selected in the range of 5 mPa · s to 30 mPa · s (25 ° C.), preferably in the range of 7 mPa · s to 30 mPa · s. .

  A screen printing method can also be used for applying the metal nanoparticle dispersion. When using the screen printing method, the viscosity of the metal nanoparticle dispersion is selected in the range of 50 Pa · s to 200 Pa · s (25 ° C.), preferably in the range of 60 Pa · s to 180 Pa · s. Is desirable.

When the method for forming a metal nanoparticle sintered body layer of the present invention is used, for example, the volume ratio V _{nano-particle of} the metal nanoparticles is 25% by volume. The average thickness of the coating film of the liquid is desirably selected in the range of 5 μm to 30 μm, preferably in the range of 8 μm to 25 μm. At that time, the average film thickness of the low-temperature sintered body layer of the metal nanoparticles to be produced is desirably selected in the range of 1.8 μm to 11 μm, preferably in the range of 2.9 μm to 9.5 μm.

  Hereinafter, the present invention will be described more specifically with reference to examples. These examples are examples of the best mode according to the present invention, but the present invention is not limited to the embodiments described in these examples.

Example 1
In Example 1, a silver nanoparticle sintered body layer is formed using the following silver nanoparticle dispersion.

  The silver nanoparticle dispersion used is a commercially available nanopaste: NPS-J (HP type). The composition thereof is Ag: 64.3% by mass, dibutylaminopropylamine: 5.8% by mass, oleic acid: 5.0% by mass, and tetradecane: 24.9% by mass.

The average particle diameter of the silver nanoparticles contained in the silver nanoparticle dispersion is 5 nm. As a surface coating agent for silver nanoparticles, oleic acid (CH ₃ (CH ₂ ) ₇ CH═CH (CH ₂ ) ₇ COOH, molecular weight 282.5, boiling point: 360 ° C.), and dibutylaminopropylamine ((C ₄ H ₉ ) ₂ N (CH ₂ ) ₃ NH ₂ , molecular weight 186.34, boiling point: 238 ° C.). Tetradecane (boiling point: 253.57 ° C.) is used as a dispersion solvent. On the surface of the silver nanoparticles, a coating agent molecular layer composed of oleic acid and dibutylaminopropylamine is formed. When the silver nanoparticle dispersion liquid is stored, the coating agent molecular layer has a function of a dispersant for dispersing silver nanoparticles in a dispersion solvent while preventing aggregation of silver nanoparticles.

Oleic acid, in the form of silver oleate _{(CH 3 (CH 2) 7} CH = CH (CH 2) 7 COOAg (I)), is adsorbed on the metal surface of the silver nanoparticles. On the other hand, dibutylaminopropylamine uses the amino group (—NH ₂ ) to coordinately bond to silver atoms on the surface of the silver nanoparticles.

Silver oleate itself has low solubility in tetradecane, which is a nonpolar hydrocarbon solvent. However, the hydrocarbon group in the silver oleate _{(CH 3 (CH 2) 7} CH = CH (CH 2) 7 -) moiety are the hydrophobic hydrocarbon group, affinity for tetradecane nonpolar hydrocarbon solvent Therefore, the silver oleate has a function of improving the dispersibility of the silver nanoparticles. On the other hand, dibutylaminopropylamine has a certain degree of solubility in tetradecane, which is a nonpolar hydrocarbon solvent. In addition, since the (C ₄ H ₉ ) ₂ N (CH ₂ ) ₃ -moiety in dibutylaminopropylamine has affinity for tetradecane, which is a nonpolar hydrocarbon solvent, dibutylaminopropylamine is also a silver nanoparticle. Has the function to improve dispersibility.

Metal silver density 10.49 g / cm ³ (20 ° C.), dibutylaminopropylamine density 0.826 g / cm ³ (20 ° C.), oleic acid density 0.895 g / cm ³ (20 ° C.), tetradecane density When 0.7645 g / cm ³ (20 ° C.) is used, the average density ρ of the dispersion is 1.9 g / cm ³ . In the dispersion, the volume ratio of silver nanoparticles is 11.95% by volume, the volume ratio of dibutylaminopropylamine is 13.68% by volume, the volume ratio of oleic acid is 10.89% by volume, and tetradecane The volume ratio corresponds to 63.48% by volume. The viscosity of the silver nanoparticle dispersion is 9 mPa · s, which is suitable for forming fine droplets by the ink jet method.

  Using the silver nanoparticle dispersion, a sintered layer of silver nanoparticles was produced under the following conditions. The volume resistivity of the produced silver nanoparticle sintered body layer was measured, and the aggregation state of silver nanoparticles in the silver nanoparticle sintered body layer was evaluated.

[Conditions for producing silver nanoparticle sintered body layer]
A glass slide is used as a substrate, and the silver nanoparticle dispersion is applied on the surface with a width of 1 cm, a length of 5 cm, and an average coating layer thickness of 10 μm to form a strip-shaped coating layer.

  It heats to 100 degreeC and oxidizes, spraying dry air from the surface for 10 seconds.

  Next, instead of dry air, a methanol vapor / nitrogen gas mixed gas is blown from the surface, and a reduction treatment is performed by holding at 100 ° C. for 2 minutes and 50 seconds in an atmosphere containing methanol vapor having a reducing ability.

  The oxidation treatment and reduction treatment cycle (10 seconds + 2 minutes 50 seconds = 3 minutes) is repeated a total of 5 times, and then the mixture is allowed to cool to room temperature while a mixed gas of methanol vapor / nitrogen gas is blown from the surface.

  In the methanol vapor / nitrogen gas mixture used in Example 1, the content ratio of methanol vapor is 20% by volume. Methanol (boiling point: 64.65 ° C.) is heated to the boiling point, and the generated methanol vapor is transported by nitrogen gas as a carrier gas and supplied as a mixed gas at a temperature of 100 ° C. Therefore, the partial pressure of gaseous methanol in the mixed gas sprayed during the reduction treatment corresponds to 0.2 atm (0.2 × 10 13 hPa).

  Dry air containing 20% by volume of oxygen molecules and 80% by volume of nitrogen molecules from which moisture has been removed in advance is used.

  By performing the above heat treatment, a sintered body layer having an average film thickness of 2 μm was formed from a coating layer having an average coating layer thickness of 10 μm.

  The volume ratio of silver nanoparticles in the dispersion corresponds to 11.95% by volume, and the ratio of metallic silver in the produced sintered body layer is 10 μm × (11.95% by volume) / 2 μm. = 59.8% by volume. Therefore, considering the resistivity of metallic silver of 1.59 μΩ · cm (20 ° C.), the volume resistivity of the produced sintered body layer is usually (1.59 / 0.598) μΩ · cm≈2. 66 μΩ · cm or more.

[Measurement of volume resistivity of sintered body layer]
About the produced sintered compact layer, sheet resistance was measured and the volume resistivity was computed as a uniform thin film layer which has a planar shape of width 1cm, length 5cm, and an average film thickness of 5 micrometers. The calculated volume resistivity was 3.6 μΩ · cm.

[Evaluation of Aggregation of Silver Nanoparticles in Sintered Layer]
About the produced sintered compact layer, the presence or absence of the silver nanoparticle which peels off easily from the surface is observed, and the aggregation state between silver nanoparticles is evaluated. Specifically, the surface of the produced sintered body layer is observed for the presence or absence of silver nanoparticles that fall off when the surface is rubbed with a finger wearing a latex glove.

  In the sintered body layer produced under the conditions of Example 1, no silver nanoparticles were removed from the surface by the friction treatment.

(Example 2 to Example 4)
In Example 2 to Example 4, a strip-shaped coating layer was formed using the dispersion of silver nanoparticles described in Example 1, and the heating temperature in the subsequent heat treatment was 50 ° C. and 80 ° C. The temperature was changed to 120 ° C., and other conditions were selected in the same manner as in Example 1 to produce a sintered body layer.

  The temperature at which the equilibrium vapor pressure of methanol is 200 mmHg is 34.03 ° C., and at a temperature of 50 ° C., the gaseous methanol partial pressure of 0.2 atm is much lower than the equilibrium vapor pressure of methanol. Accordingly, gaseous methanol having a partial pressure of 0.2 atm contained in the mixed gas does not aggregate (liquefy) at a temperature of 50 ° C.

  Table 1 also shows the production conditions of the sintered body layers in Example 1 and Examples 2 to 4 and the evaluation results of the produced sintered body layers.

  Comparing the results shown in Table 1, in the produced sintered body layer, there are no silver nanoparticles to be peeled off, and the sintering is completed. The resistivity of the produced sintered body layer decreases as the heating temperature is increased from 50 ° C. to 120 ° C. At that time, when the heating temperature is 100 ° C. or higher, the resistivity is slightly reduced even when the heating temperature is increased.

  At least the cycle of the oxidation treatment and the reduction treatment is selected as the oxidation treatment time of 10 seconds and the reduction treatment time of 2 minutes and 50 seconds, and the heating temperature is 50 ° C. to 120 ° C. Good conductivity has been achieved.

(Example 5, Example 6, Reference Example 7)
In Example 5, Example 6, and Reference Example 7, a strip-shaped coating layer was formed using the silver nanoparticle dispersion described in Example 1, and the heating temperature in the subsequent heat treatment was 100 ° C. The number of repetitions of the oxidation treatment and reduction treatment cycles was set to 10, 3, and 1, and the other conditions were selected in the same manner as in Example 1 to produce a sintered body layer. Yes.

  Table 2 also shows the production conditions of the sintered body layers in Example 1, Example 5, Example 6, and Reference Example 7, and the evaluation results of the produced sintered body layers.

  Comparing the results shown in Table 2, when the number of cycles of the oxidation treatment and the reduction treatment is one, there remains a portion where the sintering is insufficient, but as the number of repetitions increases, the sintering progresses step by step. You can see that Specifically, the resistivity of the produced sintered body layer decreases as the number of repetitions increases. However, when the number of repetitions is 5 times or more, the resistivity of the produced sintered body layer is slightly reduced thereafter.

(Example 8, Example 9)
In Example 8 and Example 9, using the silver nanoparticle dispersion described in Example 1, a strip-shaped coating layer is formed, and a compound having a reducing ability is used in the subsequent heat treatment. Instead of methanol, ethanol (CH ₃ CH ₂ OH, boiling point: 78.32 ° C.) and isopropanol ((CH ₃ ) ₂ CHOH, boiling point: 82.4 ° C.) were used. The sintered body layer is produced by selecting the same as the above.

  In addition, since the temperature of 100 degreeC is higher than the boiling point of ethanol and the boiling point of isopropanol, aggregation (liquefaction) of gaseous ethanol and isopropanol contained in the mixed gas and having a partial pressure of 0.2 atm does not occur.

  Table 3 also shows the conditions for producing the sintered body layers in Example 1, Example 8 and Example 9, and the evaluation results of the produced sintered body layers.

  Comparing the results shown in Table 3, when adopting the conditions where the heating temperature is 100 ° C. and the cycle number of the oxidation treatment and the reduction treatment is 5 times, methanol, ethanol, and isopropanol are used as the compounds having reducing ability. The resistivity of the produced sintered body layer is 4 μΩ · cm or less.

  As shown in Table 3, as with methanol, when ethanol and isopropanol are used as compounds having a reducing ability, the volume resistivity is on the order of 3 μΩ · cm and good conductivity is achieved. It was confirmed that the effects of repeatedly performing oxidation treatment and reduction treatment can be achieved to the same extent in a wide range of types of compounds having reducing ability to be used.

(Comparative Example 1)
Using the paste-like dispersion prepared in Example 1, a strip-shaped coating layer is formed, and in the subsequent heat treatment, the heat treatment is maintained in a nitrogen atmosphere for 15 minutes instead of repeating the oxidation treatment and the reduction treatment. With respect to the sintered body layer obtained from the coating layer having an average coating layer thickness of 10 μm subjected to the sintering treatment, the other conditions were selected in the same manner as in Example 1, and the length was 1 cm. The volume resistivity was measured as a uniform thin film layer having a planar shape of 5 cm and an average film thickness of 2 μm. The measured volume resistivity was 2.3 × 10 ² μΩ · cm.

  INDUSTRIAL APPLICABILITY The present invention can be used for forming a metal nanoparticle sintered body layer having good conductivity applicable to fine wiring formation.

Claims (12)

A method of forming a metal nanoparticle sintered body layer using a metal nanoparticle dispersion,
The metal nanoparticle dispersion liquid includes a metal nanoparticle having an average particle diameter selected in a range of 1 nm to 100 nm, a coating molecule constituting a coating molecule layer formed on the surface of the metal nanoparticle, and a dispersion Containing a solvent,
The metal nanoparticles are metal nanoparticles made of one or more metals selected from the group consisting of gold, silver, platinum, palladium, nickel, or alloys thereof;
The dispersion solvent is selected from the group consisting of hydrocarbon solvents having a boiling point in the range of 180 ° C to 300 ° C;
An aliphatic monocarboxylic acid (R—COOH) having a boiling point in the range of 140 ° C. to 400 ° C. and (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH having a boiling point in the range of 165 ° C. to 250 ° C. ₂ -NH ₂ ) in combination with the coating molecule;
The volume ratio V _{nano-particle} of the metal nanoparticles contained in the metal nanoparticle dispersion is selected in the range of 5 volume% to 25 volume%;
The ratio (N _carboxylate : N _amine ) of the total molecular number N _carboxylate of the aliphatic monocarboxylic acid and the total molecular number N _amine of (dialkylamino) propylamine is in the range of 1: 1.1 to 1: 1.5. Is selected;
And the volume ratio V _carboxylate of the aliphatic monocarboxylic acid to the sum of the volume ratio V _Amine of (dialkylamino) propylamine (V _carboxylate + V _amine), the ratio of the volume ratio V _Solvent of the dispersion solvent {(V _carboxylate + V _amine) : V _solvent } is selected in the range of 1: 1.0 to 1:10,
The process of forming the metal nanoparticle sintered body layer is as follows:
Applying the metal nanoparticle dispersion on the surface of the substrate to form a coating film with a predetermined film thickness, and a coating film forming step,
A low-temperature sintering step in which the coating film of the metal nanoparticle dispersion is heated to a temperature T _heating selected in a range of 50 ° C. to 120 ° C., and the metal nanoparticles included in the coating film are sintered at a low temperature. Including;
The low temperature sintering step includes
In an air stream of an oxygen-containing mixed gas in which oxygen molecules (O ₂ ) are mixed in an inert gas at a volume ratio V _oxygen selected in the range of 10 volume% to 25 volume%, for 5 seconds to 15 seconds. An oxidation treatment sub-step of forming an oxide film on the surface of the metal nanoparticles contained in the coating film by using the oxygen treatment time t ₁ selected in a range, heating to the temperature, and using oxygen molecules as an oxidizing agent; ,
Alcoholic properties that can be converted into an oxo group (> = O) or a formyl group (-CHO) by oxidation at a volume ratio V _{reducing-agent} selected in the range of 10 vol% to 30 vol% in an inert gas In a gas stream of a reducing gas mixture in which vapor of an organic compound having a hydroxyl group (> CH—OH) is mixed, a reduction treatment time t ₂ selected in a range of 120 seconds to 300 seconds is heated to the above temperature. Using the organic compound as a reducing agent to reduce and remove the oxide film on the surface of the metal nanoparticles contained in the coating film,
The oxidation / reduction treatment step, which is a combination of the oxidation treatment substep and the reduction treatment substep, is repeated n times (where n is an integer of 1 or more), and the coating molecular layer covering the surface of the metal nanoparticle is formed. Do the removal,
By selecting the total heat treatment time for repeating the oxidation / reduction treatment step n times, n × (t ₁ + t ₂ ) in the range of 375 seconds to 3150 seconds, the metal nanoparticles contained in the coating film can be obtained. Sintering at low temperature to form a metal nanoparticle sintered body layer;
The boiling point of the organic compound having an alcoholic hydroxyl group (> CH—OH) that can be converted into an oxo group or a formyl group by oxidation is selected in the range of 60 ° C. to 120 ° C. A method for forming a particle sintered body layer. 2. The method of forming a metal nanoparticle sintered body layer according to claim 1, wherein the metal nanoparticles are metal nanoparticles having an average particle diameter selected in a range of 2 nm to 50 nm. 3. The metal nanoparticle sintered body layer according to claim 1 or 2, wherein the dispersion solvent is selected from the group consisting of chain hydrocarbon solvents having a boiling point in the range of 180C to 300C. Method. The aliphatic monocarboxylic acid having a boiling point in the range of 140 ° C to 400 ° C is an aliphatic monocarboxylic acid having a total carbon number of 3 to 20, according to any one of claims 1 to 3. The formation method of the metal nanoparticle sintered compact layer of description. The alkyl groups R ^1A and R ^2A in the (dialkylamino) propylamine (R ^1A R ^2A N—CH ₂ CH ₂ CH ₂ —NH ₂ ) having a boiling point in the range of 165 ° C. to 250 ° C. have 2 to 4 carbon atoms. 5. The method for forming a metal nanoparticle sintered body layer according to claim 1, wherein the metal nanoparticle sintered body layer is an alkyl group in the range of 5 to 10. The organic compound having an alcoholic hydroxyl group (> CH-OH) that can be converted into an oxo group or a formyl group by the oxidation is an alkanol having 1 to 6 carbon atoms. The method for forming a metal nanoparticle sintered body layer according to any one of claims 5 to 6. The method for forming a metal nanoparticle sintered body layer according to any one of claims 1 to 6, wherein a heating temperature in the low-temperature sintering step is selected in a range of 80 ° C to 120 ° C. The number of repetitions n of the oxidation / reduction treatment step in the low-temperature sintering step is selected in the range of 3 to 10 times, and the metal nanoparticle firing according to any one of claims 1 to 7, A method for forming a bonded layer. The method for forming a metal nanoparticle sintered body layer according to any one of claims 1 to 8, wherein the volume ratio V _{reducing-agent} is selected in the range of 15 vol% to 25 vol%. . The method for forming a metal nanoparticle sintered body layer according to any one of claims 1 to 9, wherein the volume ratio V _oxygen is selected in a range of 15 vol% to 25 vol%. 11. The method according to claim 1, further comprising a temperature lowering step of lowering the temperature from the temperature T _heating in the air stream of the reducing gas mixture after the low temperature sintering step. The formation method of the metal nanoparticle sintered compact layer of description. The said metal nanoparticle is a silver nanoparticle, The formation method of the metal nanoparticle sintered compact layer as described in any one of Claims 1-11 characterized by the above-mentioned.