JP5139846B2 - Silver fine powder and silver ink excellent in affinity with ketone - Google Patents

Description

  The present invention relates to a silver fine powder composed of silver nanoparticles coated with an organic substance, and particularly to a silver fine powder excellent in affinity with a substance having a relatively high boiling point among ketones. The present invention also relates to a silver ink in which the silver fine powder is dispersed in a ketone solvent having a relatively high boiling point. In the present specification, particles having a particle diameter of 40 nm or less are referred to as “nanoparticles”, and a powder composed of nanoparticles is referred to as “fine powder”.

  Silver nanoparticles have been attracting attention as a patterning material for materials with low heat resistance because of their high activity and sintering at low temperatures. In recent years, in particular, due to advances in nanotechnology, it has become possible to manufacture single nanoclass particles relatively easily.

  Patent Document 1 discloses a method for synthesizing a large amount of silver nanoparticles using an amine compound using silver oxide as a starting material. Patent Document 2 discloses a method of synthesizing silver nanoparticles by mixing and melting an amine and a silver compound raw material. Non-Patent Document 1 describes making a paste using silver nanoparticles. Patent Document 4 discloses a technique for producing silver nanoparticles having extremely good dispersibility in a liquid. On the other hand, Patent Document 3 discloses a polar solvent in which an organic protective material B having a functional group such as a mercapto group having a good affinity for metal particles is dissolved in a nonpolar solvent in which metal nanoparticles protected by the organic protective material A are present. Is added, and a method of exchanging the protective material for metal nanoparticles from A to B by stirring and mixing is disclosed.

JP 2006-219893 A International Publication No. 04/012884 Pamphlet JP 2006-89786 A JP 2007-39718 A Nakami Masami et al., “Application of Silver Nanoparticles to Conductive Pastes”, Chemical Industry, Chemical Industry, October 2005, p.749-754

  The surface of the silver nanoparticles is usually covered with an organic protective material. This protective material has a role of separating the particles from each other during the silver particle synthesis reaction. Therefore, it is advantageous to select one having a molecular weight that is somewhat large. If the molecular weight is small, the distance between particles becomes narrow, and in a wet synthesis reaction, sintering may progress during the reaction. If it becomes so, a particle will become coarse and manufacture of a silver fine powder will become difficult.

  On the other hand, when using silver particles as ink, it is desirable to select an appropriate organic medium according to the application. For example, ketone-based organic substances are used as a solvent for silver paste, and have already been used as a solvent for silver conductive coatings. For this reason, many paste viscosity modifiers and thixotropic additives that are highly compatible, such as easy to dissolve and disperse in ketone solvents, as additives for conductive paste, and adjustment of viscosity and thixotropy using them Methods have already been developed and knowledge has been accumulated. When trying to adjust the paste to the desired properties, there is an advantage that these additives and adjustment techniques can be used.

  However, no silver fine powder having a good affinity for ketone organic substances has been known so far. As for silver fine powder, the kind of applicable dispersion medium is largely limited by the kind of protective material (surfactant) covering the particle surface. Conventionally, the degree of freedom in selecting the type of protective material is very small due to manufacturing restrictions and the like, and it is extremely difficult to select an appropriate protective material according to the application.

The present invention has been made in view of such a situation, in particular, among the organic compounds of ketone type, a relatively high boiling point, it is considered to be advantageous for the conductive film formed using silver nanoparticles, isophorone (C ₉ It is intended to provide silver nanoparticles having good affinity (that is, dispersibility) for H ₁₄ O), acetophenone (C ₈ H ₈ O), 2-methylcyclohexanone (C ₇ H ₁₂ O), and the like.

In order to achieve the above object, in the present invention, the amine of silver particles having an amine on the surface is desorbed and 1,4-dihydroxy-2-naphthoic acid (C ₁₁ H ₈ O ₄ ) is adsorbed on the surface. An X-ray crystal particle diameter Dx of 1 to 40 nm and a CV value represented by the following (a): 40% or less of silver particles, which are excellent in at least affinity with acetophenone, are provided.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %).

Further, X-ray crystal particle diameter Dx: 1 to 40 nm obtained by desorbing the amine of silver particles having amine on the surface and adsorbing gallic acid (C ₇ H ₆ O ₅ ) on the surface and represented by (a) above. CV value: Silver fine powder composed of silver particles of 40% or less and excellent in affinity with at least isophorone, acetophenone and 2-methylcyclohexanone is provided.

  1,4-dihydroxy-2-naphthoic acid and gallic acid both have a carboxyl group (hydrophilicity), and are considered to be adsorbed on the surface of the Ag particles at the carboxyl group portion.

In the present invention, the following silver inks (1) to (3) are provided.
(1) X-ray crystal particle diameter Dx formed by desorbing the amine of silver particles having amine on the surface and adsorbing 1,4-dihydroxy-2-naphthoic acid on the surface: 1 to 40 nm, preferably 1 to 15 nm ( looking at the average particle diameter D _TEM, as measured by TEM observation, D _TEM: 3 to 40 nm preferably 4 to 15 nm) and the CV value represented by (a): 40% or less of silver particles, and an amine surface X-ray crystal grain diameter becomes to adsorb gallic acid on the surface together with the desorbing the amine of the silver particles having the Dx: from 1 to 40 nm and preferably viewed in 1-15 nm (average particle diameter D _TEM, D _TEM: 3~ 40 nm, preferably 4 to 15 nm) CV value represented by the above (a): Silver ink in which one or two kinds of silver particles having 40% or less are dispersed in acetophenone.
(2) X-ray crystal particle diameter Dx formed by desorbing the amine of silver particles having amine on the surface and adsorbing gallic acid on the surface: 1 to 40 nm, preferably 1 to 15 nm (average particle diameter D _TEM , D _TEM : 3 to 40 nm, preferably 4 to 15 nm) and silver ink having a CV value represented by (a) of 40% or less dispersed in isophorone.
(3) X-ray crystal grain diameter becomes to adsorb gallic acid on the surface together with the desorbing the amine of the silver particles having an amine on the surface Dx: from 1 to 40 nm and preferably viewed in 1-15 nm (average particle diameter D _TEM , D _TEM : 3 to 40 nm, preferably 4 to 15 nm) and silver ink having a CV value represented by (a) of 40% or less dispersed in 2-methylcyclohexanone.

In the present specification, the ink includes a paste in addition to the liquid ink. In these silver inks (1) to (3), the silver concentration is preferably adjusted to, for example, 10 to 90% by mass. In particular, in the present invention, as a liquid silver ink having extremely good dispersibility, the silver concentration is in the range of 20 to 60% by mass, and when the silver ink is allowed to stand after stirring, the dispersed state is maintained for at least 168 hours. Ink is provided. “Dispersed state” refers to a state in which a transparent supernatant portion is not formed near the liquid surface, and the entire liquid is cloudy due to the presence of silver particles.

  According to the present invention, silver fine powder having a very high affinity for an organic compound having a relatively high boiling point has been clarified specifically among ketones having a proven record as a solvent such as a silver paste. Further, a silver ink is provided in which silver nanoparticles are dispersed at a high concentration in such a ketone solvent, and the dispersibility is very good. Such silver ink has not been a subject of research because it has not existed so far, but its usefulness is considered to be clarified in the future, and application to various uses is expected.

Conventionally, in the production of silver nanoparticles, the type of protective material (surfactant) could not be freely selected due to production limitations. However, according to the method described later, the degree of freedom of selection with respect to the type of protective material can be considerably increased, and various silver nanoparticles that have not existed so far can be obtained. Then, the organic compound becomes adsorbed onto the surface of the X-ray crystal particle diameter having a carboxyl group Dx: from 1 to 40 nm and preferably viewed in an average particle diameter D _TEM, as measured by the 1-15 nm (TEM observation, D _TEM: 3 A novel silver ink was realized in which silver particles (-40 nm, preferably 4-15 nm) were dispersed in a ketone liquid medium such as isophorone, acetophenone, 2-methylcyclohexanone.

  1,4-Dihydroxy-2-naphthoic acid and gallic acid are suitable as a protective material (surfactant) that remarkably improves the dispersibility of silver nanoparticles in acetophenone, and is suitable for isophorone and 2-methylcyclohexanone. In contrast, gallic acid was found to be suitable. These organic compounds have a carboxyl group and have the property of being easily adsorbed on the surface of silver particles.

  Such silver nanoparticles can be obtained through, for example, a “silver particle synthesis step” and a “protective material replacement step”. Hereinafter, the typical method is illustrated.

《Silver particle synthesis process》
Silver nanoparticles having a uniform particle diameter can be synthesized by a wet process as disclosed in Patent Document 4. In this synthesis method, silver particles are precipitated by reducing the silver compound in alcohol or polyol using alcohol or polyol as a reducing agent. However, according to the inventors' subsequent studies, a synthesis method suitable for mass production was found, and the present applicant disclosed in Japanese Patent Application No. 2007-264598. In this method, silver particles are precipitated using a reducing power of 2-octanol by dissolving a silver compound in a mixed solution of a primary amine and 2-octanol and maintaining the temperature at 120 to 180 ° C. . Here, this new synthesis method is illustrated briefly.

Silver compound as the silver ion source (e.g. silver nitrate), (one having a molecular weight of 200 to 400 having an unsaturated bond, for example, oleylamine) a primary amine A as a protective material for precipitated silver particles, and when is a solvent component together reducing agent Prepare 2-octanol, which is also.

A predetermined amount of primary amine A, 2-octanol and a silver compound are mixed to prepare a solution in which a silver compound is dissolved in a mixed solvent of amine A and 2-octanol. The liquid composition at the start of the reduction reaction can usually find suitable conditions in a range satisfying the following (i) to (iii).
(I) Amine A / silver molar ratio: 1 to 10,
(Ii) 2-octanol / silver molar ratio: 0.5-15;
(Iii) 2-octanol / amine A molar ratio: 0.3-2

  The temperature of the liquid is started and maintained in a temperature range of 120 to 180 ° C. At temperatures below 120 ° C., the progress of the reduction reaction is difficult to proceed, so it is difficult to stably obtain a high reduction rate. However, it is important not to greatly exceed the boiling point. The boiling point of 2-octanol is about 178 ° C., and it is acceptable up to about 180 ° C. It is more preferable to set it as the range of 125-178 degreeC. The reaction can be performed under atmospheric pressure, and it is preferable to bring the reaction vessel into a reflux state while purging the gas phase portion with an inert gas such as nitrogen gas. Although silver nanoparticles can be precipitated even if stirring is not carried out very strongly, a certain amount of stirring is required as the size of the reaction vessel increases. In the case of 2-octanol, the degree of freedom of stirring strength is broadened when synthesizing silver particles having a uniform particle diameter as compared with the case of using another alcohol (for example, isobutanol). Note that 2-octanol may be mixed in the necessary amount from the beginning, or may be mixed during or after the temperature increase. You may add (additional addition) 2-octanol suitably after a reduction reaction start. It is desirable to secure a holding time of 0.5 hours or more in the above temperature range, but in the case of a liquid composition satisfying the above (i) to (iii), the reaction is considered to be almost completed in about 1 hour. Even if the holding time is further increased, no significant change is observed in the reduction rate. Usually, it is sufficient to set a holding time of 3 hours or less. When silver particles are precipitated by the progress of the reduction reaction, a slurry in which silver nanoparticles coated with amine A are present is obtained.

  Next, the solid content is recovered from the slurry by decantation or centrifugation. The recovered solid content is mainly composed of silver nanoparticles coated with a protective material containing primary amine A as a component.

  Since impurities are adhering to the above-mentioned solid content, it is preferable to use for washing with methanol or isopropanol.

As described above, X-ray crystal particle diameter Dx coated with primary amine A: 1 to 40 nm, preferably 1 to 15 nm, can be formed. The average particle diameter D _TEM determined by observation of particles using a transmission electron microscope (TEM) is in the range of 3 to 40 nm, preferably about 4 to 15 nm.

《Protective material replacement process》
Next, an operation of changing the protective material adhering to the silver particles from amine A to organic compound B which is the target substance (here, one or more of 1,4-hydroxy-2-naphthoic acid and gallic acid) is performed. The method for producing silver particles of the present invention is characterized in that this step is employed.
An organic compound B having a carboxyl group is applied. The carboxyl group has a property of being easily adsorbed on silver. The above amine A is an amine having an unsaturated bond and a molecular weight of 200 to 400, and it is considered that the adsorbing power for silver is weaker than that of a substance having a carboxyl group. Therefore, if a sufficient amount of organic compound B molecules are present in the vicinity of the surface of the silver particles coated with amine A, the situation is such that amine A is desorbed from the silver surface and organic compound B is easily adsorbed. The replacement proceeds easily.

  However, this substitution proceeds in a solvent. The solvent used in this substitution step is referred to herein as solvent C. As the solvent C, it is necessary to employ a solvent in which the organic compound B is completely dissolved. Specifically, a solvent having good solubility may be selected from solvents such as isopropanol, methanol, ethanol and decalin. In the case of the organic compound B that dissolves well in isopropanol, it is often advantageous to select isopropanol in terms of safety and cost. In the solvent C as described above in which the organic compound B is dissolved, silver nanoparticles coated with the amine A are present and stirred in a temperature range of 30 ° C. or more and the boiling point of the solvent C or less. Substitution is difficult to proceed at a temperature lower than 30 ° C. When isopropanol is used as the solvent C, it is preferably carried out in the range of 35 to 80 ° C. Particles coated with amine A are generally poorly dispersible in solvent C and tend to settle in the liquid, so they must be stirred, but it is not necessary to stir so strongly, and the particles can remain suspended in the liquid. The degree is sufficient.

  The replacement reaction of amine A and organic compound B having a carboxyl group is considered to occur in a relatively short time of about several minutes, but from the viewpoint of supplying an industrially stable quality, it takes 1 hour or more. It is desirable to secure a replacement reaction time for. However, since the further replacement reaction does not proceed much even after 24 hours, it is practical to terminate the replacement reaction within 24 hours. The reaction time required for the substitution is preferably set in the range of 1 to 7 hours.

  Specifically, a liquid in which organic compound B is completely dissolved in solvent C is prepared in advance, and this liquid and silver nanoparticles to which amine A recovered as a solid content is attached are contained in one container. And stirring and mixing. When the organic compound B is liquid at normal temperature, the “solvent C in which the organic compound B is dissolved” as used in this specification means that the organic compound B is uniformly mixed without separation in the solvent C. Means the state. The equivalent B / Ag of the organic compound B to the metal Ag in the particles is preferably 0.1 to 10 equivalents. Here, 1 mol of the organic compound B corresponds to 1 equivalent with respect to 1 mol of silver. The amount of the solvent C may be set within a range in which an amount sufficient for the silver nanoparticles to float in the solution is ensured.

After silver particles formed by adsorbing organic compound B on the surface in this way are formed, solid-liquid separation is performed. For example, “cleaning liquid (for example, methanol or isopropanol) is added to the separated solid component and ultrasonic waves are added. After adding the dispersion, it is preferable to wash and remove the adhering impurities by repeating the operation of “centrifuge the liquid to recover the solid content” several times. The particles after washing are silver nanoparticles having an X-ray crystal particle diameter Dx of 1 to 40 nm, preferably 1 to 15 nm, and an average particle diameter D _TEM measured by TEM observation of 3 to 40 nm, preferably 4 to 15 nm. Has a surfactant formed by adsorbing the organic compound B. A silver ink can be obtained by dispersing the solid content after washing in a target solvent such as isophorone, acetophenone, or 2-methylcyclohexanone.

  Two or more kinds of silver particles having different organic compounds B (protective materials) can be mixed in a solvent in which both are excellent in affinity to produce a silver ink. The silver concentration in the ink is desirably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more. The upper limit of the silver concentration is not particularly limited as long as good dispersibility can be maintained, but may be in the range of approximately 70% by mass or less. In particular, it has been found that a silver ink having extremely good dispersibility can be produced at a high yield, for example, in the range of 50% by mass or less.

Example 1
As a surfactant (a protective material for the surface of the metal Ag particles), oleylamine is used for the primary amine A before substitution, and 1,4-dihydroxy-2-naphthoic acid is used for the organic compound B after substitution. Silver particles were prepared by adsorbing 1,4-dihydroxy-2-naphthoic acid. Then, an attempt was made to create a silver ink having extremely good dispersibility in which the silver particles were dispersed in acetophenone.

[Silver particle synthesis process]
6009.2 g of oleylamine (reagent manufactured by Wako Pure Chemical Industries, Ltd.), 2270.3 g of 2-octanol (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and 1495.6 g of silver nitrate crystal (special grade reagent manufactured by Kanto Chemical Co., Ltd.) were prepared.
2-Octanol, oleylamine, and silver nitrate crystals were mixed to prepare a solution in which silver nitrate was completely dissolved. The formulation is as follows.
・ Mole ratio of oleylamine / silver = 2.5
-Alcohol / silver molar ratio = 2.0
Alcohol / oleylamine molar ratio = 2.0 / 2.5 = 0.8

  Prepare 10 L of the above mixture, transfer to a container equipped with a reflux condenser, place on an oil bath, heat up to 120 ° C. while stirring at 100 rpm with a propeller, 1.0 ° C./min, then heat up to 140 ° C. The temperature was raised at 0.5 ° C./min. Then, it maintained at 140 degreeC for 1 hour, maintaining the said stirring state. At that time, nitrogen gas is supplied to the gas phase portion of the container at a flow rate of 500 mL / min for purging. Thereafter, heating was stopped and cooling was performed.

After the reaction, the slurry was allowed to stand for 3 days, and then the supernatant was removed. At that time, the removal amount of the supernatant was adjusted so that the reduced silver was 20% by mass with respect to the total slurry. 1700 g of isopropanol was mixed with 500 g of the slurry after removing the supernatant, and the mixture was stirred with a propeller at 400 rpm for 1 hour, and then the solid content including silver particles was recovered by centrifugation. Silver particles coated with amine A (oleylamine) are present in the solid content thus washed.
In addition, it is known by measurement separately that about 1 mol of metal Ag is present in 500 g of the slurry before washing.

Separately, a small amount of solid content sample was collected from the washed solid content prepared under the same conditions as above, and the X-ray crystal particle diameter Dx was determined in the following manner. As a result, it was confirmed that Dx of the silver fine powder before substitution was about 7 nm. Moreover, the average particle diameter _DTEM was calculated _| required in the following way. As a result, it was confirmed D _TEM of the silver fine powder before substitution is about 8 nm.
Moreover, the silver fine powder before substitution coated with oleylamine was recovered from the solid content after washing prepared under the same conditions as described above, and TG-DTA measurement was performed at a heating rate of 10 ° C./min. A measurement example of the DTA curve is shown in FIG. In FIG. 1, the large peak between 200 and 300 ° C. and the peak between 300 and 330 ° C. are considered to be attributed to oleylamine, which is amine A.

<Measurement of X-ray crystal particle diameter Dx>
A solid sample of silver particles is applied to a glass cell, set in an X-ray diffractometer, and the diffraction peak of the Ag (111) plane is used to calculate the X-ray crystal grain size D according to Scherrer's formula shown in the following formula (1). _X was determined. Cu-Kα was used for X-rays.
Dx = K · λ / (β · cos θ) (1)
However, K is a Scherrer constant and 0.94 is adopted. λ is the X-ray wavelength of the Cu—Kα ray, β is the half width of the diffraction peak, and θ is the Bragg angle of the diffraction line.

<Measurement of average particle diameter D _TEM >
The silver particle dispersion was observed with a transmission electron microscope (TEM), and the particle diameters of 300 independent silver particles that did not overlap were measured to calculate the average particle diameter.

[Protective material replacement process]
1,4-dihydroxy-2-naphthoic acid (reagent manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 204.18) as the organic compound B, and isopropanol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 60.1) as the polar solvent C. Prepared.
1,4-Hydroxy-2-naphthoic acid 56.8 g and isopropanol 400 g were mixed, the liquid temperature was kept at 40 ° C., and 1,4-dihydroxy-2-naphthoic acid was completely dissolved in isopropanol. To the liquid 456.8 g, the solid content after washing in which silver particles coated with amine A (oleylamine) are present (containing about 1 mol of Ag (about 100 g)) is added, and a propeller is used at 400 rpm. Stir with. While maintaining this stirring state, it was kept at 40 ° C. for 5 hours. In this case, the charge amount of the organic compound B is adjusted so that the amount of the organic compound B with respect to Ag is 0.3 equivalent.

The obtained slurry was subjected to solid-liquid separation by centrifugation at 3000 rpm × 5 min. Thereafter, the operation of “889.7 g of methanol to the solid content (about 30 equivalents with respect to silver) and washing at 400 rpm for 30 minutes and collecting the solid content by centrifugation” was performed twice, and the protective material A silver fine powder sample in which 1,4-dihydroxy-2-naphthoic acid was substituted was obtained.
This sample was subjected to TG-DTA measurement by the method described above. A measurement example of the DTA curve is shown in FIG. From the comparison between FIG. 1 (before substitution) and FIG. 2 (after substitution), almost all of the amine A (oleylamine) was desorbed and replaced with the organic compound B (1,4-dihydroxy-2-naphthoic acid). It is thought that. FIG. 4 shows an example of a TEM photograph of silver particles formed by adsorbing 1,4-dihydroxy-2-naphthoic acid.

This for samples was measured X-ray crystal particle diameter Dx and the average particle diameter D _TEM in the manner described above, Dx is 7.56nm, D _TEM was 8.43Nm.
D particle diameter of each particle used in computing _TEM, the minimum value D _min is 6.59Nm, the maximum value D _max was 13.41Nm. When the standard deviation of the particle diameter is σ _D , the value of “σ _D / D _TEM × 100” is called CV value. The silver fine powder had a CV value of 14.1%. It can be said that the smaller the CV value, the more uniform the particle size of the silver particles. In the use of silver ink, it is desirable that the CV value is 40% or less, and those having a CV value of 15% or less have extremely uniform particle diameters and are extremely suitable for various fine wiring applications.

[Silver ink production process]
The silver fine powder sample obtained as described above (after being washed with methanol and not dried) contains metallic silver, a protective material, and methanol used for washing. The net silver content in the silver fine powder was determined by the following method.

<Silver content in fine silver powder>
[1] The mass W ₀ (g) of the sample taken from the silver fine powder sample is measured.
[2] In order to remove methanol, the sample is treated for 30 minutes at room temperature using a vacuum dryer.
[3] Then, the protective material is volatilized by heating the sample to 700 ° C. at a heating rate of 10 ° C./min in a muffle furnace (manufactured by Yamato Scientific Co., Ltd .; FO100 type), and the mass W ₁ of the sample after volatilization (G) is measured.
[4] silver content in the silver fine powder sample (wt%) is calculated by _{= W 1 / W 0 × 100} .

  Based on the metallic silver content (mass%) in the above-mentioned silver fine powder sample, a silver fine powder sample in which the mass of metallic silver is 10.0 g is weighed, and this is acetophenone (special grade reagent manufactured by Wako Pure Chemical Industries). And a silver particle + acetophenone mixture in which the content of metallic silver in the total amount of metallic silver + protective material + acetophenone was 50% by mass was prepared. This mixture was treated at 40 ° C. or lower for 60 minutes using an ultrasonic cleaner (manufactured by Sharp Corporation; UT606) to disperse silver particles in acetophenone. Subsequently, the process of evacuation for 1 minute and kneading for 2 minutes was repeated with a vacuum kneading defoaming machine (manufactured by EME; Vmini300 type) until no weight loss was observed, and the residual methanol in the liquid was removed. As a result, a silver dispersion (silver ink base solution) having a silver concentration of 50% by mass was obtained.

  Since silver particles that are likely to settle are also present in the silver ink base liquid, it is necessary to remove such particles in order to obtain a silver ink exhibiting excellent dispersibility. Therefore, the silver ink original solution was subjected to centrifugation at 3000 rpm for 30 minutes under a condition of 25 ° C. using a centrifuge (manufactured by Hitachi Koki Co., Ltd .; himacCF7D2 type). Thereafter, the supernatant was recovered to obtain a silver ink in which only particles having excellent dispersibility were dispersed. The silver concentration and ink formation efficiency in the silver ink were determined as follows.

<Silver concentration in silver ink>
[1] The mass W ₂ (g) of the dispersion sample taken from the silver ink is measured.
[2] The dispersion liquid sample is heated to 700 ° C. by a muffle furnace (manufactured by Yamato Scientific Co., Ltd .; FO100 type) at a heating rate of 10 ° C./min to volatilize the protective material, and the mass W of the sample after volatilization ₃ Measure (g).
[3] Silver concentration (mass%) in silver ink = W ₃ / W ₂ × 100
In this example, the silver concentration in the silver ink was 36.62% by mass. This is a high-concentration silver ink that is sufficiently applicable to the formation of a conductive coating film using silver nanoparticles.

<Ink conversion efficiency>
Obtained by the following formula.
Ink conversion efficiency (%) = [Silver concentration in silver ink (% by mass)] / [Silver concentration in silver ink original solution (% by mass)] × 100 = [Silver concentration in silver ink (% by mass)] / 50 (mass%) x 100
The ink conversion efficiency corresponds to the yield of silver when only silver particles having extremely excellent dispersibility are recovered, and the higher the better.
In this example, the ink conversion efficiency is as high as 73.2%, which is a level that can be industrialized sufficiently.

[Standing test]
Next, in order to confirm the dispersion maintainability of the obtained silver ink, after lightly stirring the glass container containing the silver ink, it was uniformly subjected to ultrasonic dispersion treatment for 10 minutes with the ultrasonic cleaner. And allowed to stand at room temperature for 168 hours, and then visually confirmed for the occurrence of turbidity of liquid and precipitation aggregation. As a result, it was confirmed that a transparent supernatant portion was not formed near the liquid surface, the entire liquid was cloudy due to the presence of silver particles, and the dispersed state was maintained. Further, no silver particles deposited on the bottom of the container were confirmed.

Example 2
An experiment similar to Example 1 was performed, except that organic compound B was changed to gallic acid (a reagent manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 170.1). That is, in this example, silver particles formed by adsorbing gallic acid were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in acetophenone.

  Specifically, in the protective material replacement step, 78.83 g of gallic acid and 400 g of isopropanol were mixed, the liquid temperature was kept at 40 ° C., and gallic acid was completely dissolved in isopropanol. Into this liquid 478.83 g was added the solid content after washing in which silver particles coated with amine A (oleylamine) were present (containing about 1 mol of Ag (about 100 g)), and 400 rpm with a propeller. Stir with. While maintaining this stirring state, it was kept at 40 ° C. for 5 hours. In this case, the charge amount of the organic compound B is adjusted so that the amount of the organic compound B with respect to Ag is 0.5 equivalent.

  A measurement example of the DTA curve for the obtained sample is shown in FIG. From the comparison of FIG. 1 (before substitution) and FIG. 3 (after substitution), it is considered that the protective material was almost completely desorbed of amine A (oleylamine) and replaced with organic compound B (gallic acid). FIG. 5 shows an example of a TEM photograph of silver particles formed by adsorbing gallic acid.

Dx for this sample was 6.56 nm and D _TEM was 8.53 nm. Particle diameter of each particle used in computing D _TEM, the minimum value D _min is 3.97Nm, the maximum value D _max is 13.71Nm, CV value of the silver micropowder was 19.7%.

  A silver ink containing acetophenone as a solvent was prepared in the same manner as in Example 1. As a result, the silver concentration in the silver ink was 37.30% by mass. This is a high-concentration silver ink that is sufficiently applicable to the formation of a conductive coating film using silver nanoparticles. Ink conversion efficiency is as high as 74.6%, which is a level that can be industrialized sufficiently. As a result of the static test for 168 hours, it was confirmed that the dispersed state was maintained as in Example 1.

Example 3
An experiment similar to that of Example 2 was performed except that the solvent of the silver ink was changed to isophorone. That is, in this example, silver particles formed by adsorbing gallic acid were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in isophorone.

  Silver particles formed by adsorbing gallic acid were prepared in the same manner as in Example 2, and silver ink using isophorone as a solvent was prepared in the same manner as in Example 1. As a result, silver in silver ink was obtained. The concentration was 36.56% by mass. This is a high-concentration silver ink that is sufficiently applicable to the formation of a conductive coating film using silver nanoparticles. Ink conversion efficiency is as high as 73.1%, which is a level that can be industrialized sufficiently. As a result of the static test for 168 hours, it was confirmed that the dispersed state was maintained as in Example 1.

Example 4
An experiment similar to that of Example 2 was performed except that the solvent of the silver ink was changed to 2-methylcyclohexanone. That is, in this example, silver particles formed by adsorbing gallic acid were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in 2-methylcyclohexanone.

  Silver particles formed by adsorbing gallic acid were prepared in the same manner as in Example 2, and a silver ink using 2-methylcyclohexanone as a solvent was prepared in the same manner as in Example 1. As a result, silver ink was obtained. The silver concentration therein was 44.36% by mass. This is a high-concentration silver ink that is sufficiently applicable to the formation of a conductive coating film using silver nanoparticles. The ink conversion efficiency is as high as 88.7%, which is a level that can be industrialized sufficiently. As a result of the static test for 168 hours, it was confirmed that the dispersed state was maintained as in Example 1.

DTA curve for silver particles before replacement of protective material coated with oleylamine. The DTA curve about the silver particle made to adsorb | suck 1, 4- dihydroxy- 2-naphthoic acid. The DTA curve about the silver particle which makes gallic acid adsorb | suck. A TEM photograph of silver particles formed by adsorbing 1,4-dihydroxy-2-naphthoic acid. TEM photograph of silver particles formed by adsorbing gallic acid.

Claims (8)

X-ray crystal particle diameter Dx: 1 to 40 nm obtained by desorbing the amine of silver particles having amine on the surface and adsorbing 1,4-dihydroxy-2-naphthoic acid on the surface and represented by the following (a) CV value: Silver fine powder composed of silver particles of 40% or less and excellent in at least affinity with acetophenone.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). Silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface : CV value represented by (a): 40% or less Silver fine powder excellent in affinity with at least isophorone, acetophenone and 2-methylcyclohexanone, which is composed of particles.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). X-ray crystal particle diameter Dx: 1 to 40 nm obtained by desorbing the amine of silver particles having amine on the surface and adsorbing 1,4-dihydroxy-2-naphthoic acid on the surface and represented by the following (a) CV value: Silver particles having 40% or less and silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface: 1 to 40 nm and the following (a) CV value represented: Silver ink in which one or two silver particles having a particle size of 40% or less are dispersed in acetophenone.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). Silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface : CV value represented by (a): 40% or less Silver ink in which particles are dispersed in isophorone.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). Silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface : CV value represented by (a): 40% or less Silver ink in which particles are dispersed in 2-methylcyclohexanone.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). X-ray crystal particle diameter Dx: 1 to 40 nm obtained by desorbing the amine of silver particles having amine on the surface and adsorbing 1,4-dihydroxy-2-naphthoic acid on the surface and represented by the following (a) CV value: Silver particles having 40% or less and silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface: 1 to 40 nm and the following (a) CV value represented: A liquid ink in which one or two kinds of silver particles of 40% or less are dispersed in acetophenone at a silver concentration of 20 to 60% by mass, and the liquid ink is allowed to stand after stirring. A silver ink that is maintained in a dispersed state for at least 168 hours.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). Silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface : CV value represented by (a): 40% or less A liquid ink in which particles are dispersed in isophorone at a silver concentration of 20 to 60% by mass, and the dispersed state is maintained for at least 168 hours when the liquid ink is allowed to stand after stirring.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %). Silver particles having amine on the surface X-ray crystal particle diameter Dx formed by desorbing the amine and adsorbing gallic acid on the surface : CV value represented by (a): 40% or less A liquid ink in which particles are dispersed in 2-methylcyclohexanone at a silver concentration of 20 to 60% by mass, and the dispersed state is maintained for at least 168 hours when the liquid ink is allowed to stand after stirring.
(A) In the particle diameter of silver particles measured by TEM observation, when the standard deviation of particle diameter is σ _D and the average particle diameter is D _TEM , the value of “σ _D / D _TEM × 100” is the CV value ( %).