JP2009215502A - Silver ink containing alicyclic and aromatic hydrocarbon as solvent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide new silver ink in which silver nanoparticles are dispersed at relatively high concentration in a liquid medium of alicyclic and aromatic hydrocarbons such as diethylbenzene and decalin. <P>SOLUTION: The silver ink contains silver particles dispersed in a liquid medium of aromatic hydrocarbons at a silver concentration of 20 to 60 mass%, the silver particles adsorbing octyl gallate, dodecyl gallate or castor oil to the surfaces and having a crystal grain diameter Dx by X-ray analysis of 1 to 40 nm, preferably 1 to 15 nm; and when the liquid is left to stand after stirring, the liquid maintains the dispersion state at least for 168 hours. In particular, combinations of diethylbenzene/octyl gallate, diethylbenzene/dodecyl gallate, diethylbenzene/castor oil, decalin/octyl gallate and decalin/dodecyl gallate are preferable. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silver ink with extremely high dispersibility in which silver nanoparticles coated with an organic substance are dispersed in an aromatic hydrocarbon solvent. 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, there is a track record that ketone organic solvents are generally used as the organic medium for the conductive metal paste. However, this ketone-based solvent has a high ability to attack the resin itself when the substrate is an organic substance such as a resin, which may be inappropriate due to a problem that the substrate is eroded by the material of the substrate. Even in the case where the above-mentioned problem occurs when a ketone-based solvent is used, the occurrence of the above-mentioned problem can often be prevented by using a hydrocarbon-based organic solvent. However, among hydrocarbons, aliphatic hydrocarbons are highly oleophilic organic solvents because they are not hydrophilic due to their structure, whereas alicyclic hydrocarbons and aromatic carbons that are cyclic hydrocarbons. Hydrogen has a cyclic structure, and aromatic hydrocarbons have a double bond. It is known that hydrophilicity is imparted by such a structure. For this reason, alicyclic hydrocarbons and aromatic hydrocarbons, which are cyclic hydrocarbons, are characterized by high wettability to substrates with hydrophilic surfaces compared to aliphatic hydrocarbons. It is advantageous. Cycloaliphatic hydrocarbons and aromatic hydrocarbons, which are cyclic hydrocarbons, are highly expected as solvents used in applications such as conductive coatings using silver nanoparticles.

  However, silver fine powder having good affinity with alicyclic hydrocarbons and aromatic hydrocarbons that are cyclic hydrocarbons and protected with a surfactant having a carboxyl group has not been known so far. Until now, amine-based surfactants are often used as protective materials for metal nanoparticles, but they are easily desorbed from the particles because of their weak coordination power to metal. On the other hand, carboxyl groups are characterized by high coordinating power, high dispersion stability, and little change over time. 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.

In view of such a current situation, the present invention is a solvent for cyclic hydrocarbons such as diethylbenzene (C ₁₀ H ₁₄ ) which is an aromatic hydrocarbon and decalin (C ₁₀ H ₁₈ ) which is an alicyclic hydrocarbon. In other words, the present invention aims to provide a silver ink having a very good dispersibility.

  The inventors have examined in detail the type of protective material (surfactant) whether it is possible to impart good dispersibility of silver nanoparticles to various cyclic hydrocarbon solvents. As a result, among the cyclic hydrocarbon solvent / protectant combinations, particularly in the combinations of diethylbenzene / octyl gallate, diethylbenzene / dodecyl gallate, diethylbenzene / castor oil, decalin / octyl gallate, decalin / dodecyl gallate, It has been found that a comparatively high concentration silver nano-ink with extremely high dispersibility can be realized.

Here, octyl gallate and dodecyl gallate are organic compounds having a structure in which H of the carboxyl group of gallic acid is replaced with (CH ₂ ) ₇ CH ₃ and (CH ₂ ) ₁₁ CH ₃ , respectively (FIGS. 1 to 1). 3). Castor oil contains about 90% of triglyceride of ricinoleic acid (C ₁₈ H ₃₄ O ₃ ), and glycerin of oleic acid (C ₁₈ H ₃₄ O ₂ ) and linoleic acid (C ₁₈ H ₃₂ O ₂ ) as other components It is an oil with a small amount of saturated fatty acid glyceride as a component.

In the present invention, the following silver inks (1) and (2) are provided.
(1) X-ray crystal particle diameter Dx formed by adsorbing octyl gallate on the surface: 1 to 40 nm silver particle, X-ray crystal particle diameter Dx formed by adsorbing dodecyl gallate on the surface: silver particle of 1 to 40 nm A silver ink in which one or more silver particles having an X-ray crystal particle diameter Dx of 1 to 40 nm formed by adsorbing castor oil on the surface are dispersed in diethylbenzene.
(2) X-ray crystal particle diameter Dx formed by adsorbing octyl gallate on the surface: 1 to 40 nm silver particles, and X-ray crystal particle diameter Dx formed by adsorbing decyl gallate on the surface: 1 to 40 nm silver A silver ink in which one or more of the particles are dispersed in decalin.

  In the present specification, the ink includes a paste in addition to the liquid ink. In these silver inks (1) and (2), 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, a silver ink having a silver concentration in the range of 20 to 60% by mass and maintaining a dispersed state for at least 168 hours when the liquid is left to stand after stirring. 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 alicyclic hydrocarbons and aromatic hydrocarbons, which are cyclic hydrocarbons used as solvents in various fields, is specifically clarified. It was. Silver nanoparticles were dispersed in a cyclic hydrocarbon solvent such as diethylbenzene and decalin, and a silver ink with extremely good dispersibility was provided. Although such a silver ink that has a practically high silver concentration has not been studied since it has not existed so far, its usefulness is expected to be clarified in the future. It is expected to be applied to other uses.

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. And X-ray crystal particle diameter Dx formed by adsorbing a specific organic compound on the surface: 1 to 40 nm, preferably 1 to 15 nm (in terms of average particle diameter D _TEM measured by TEM observation, D _TEM : 3 to 40 nm A novel silver ink in which silver particles (preferably 4 to 15 nm) are dispersed in a cyclic hydrocarbon liquid medium such as diethylbenzene or decalin has been realized.

  Octyl gallate, dodecyl gallate and castor oil are suitable as protective materials (surfactants) that significantly improve the dispersibility of silver nanoparticles in diethylbenzene, and octyl gallate and gallic acid for decalin. It became clear that dodecyl was suitable.

  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.

  A silver compound (for example, silver nitrate) as a silver ion source, a primary amine A (having a molecular weight of 200 to 400 having an unsaturated bond, for example, oleylamine) as a protective material for precipitated silver particles, and a solvent component as well as a reducing agent A certain 2-octanol is prepared.

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), it is considered that the reaction is 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, the protective material adhering to the silver particles is changed from the amine A to the target organic compound B (here, hexyl gallate, octyl gallate, dodecyl gallate or castor oil). The method for producing silver particles of the present invention is characterized in that this step is employed.
As the organic compound B, one having the property of being easily adsorbed on silver is applied. The above amine A is an amine having an unsaturated bond and a molecular weight of 200 to 400, and the adsorptive power to silver is considered to be weaker than octyl gallate, dodecyl gallate and castor oil. 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.

  Although the substitution reaction of amine A and organic compound B is considered to occur in a relatively short time of about several minutes, the substitution reaction time of 1 hour or more is provided from the viewpoint of supplying industrially stable quality. It is desirable to ensure. 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 the organic compound B is completely dissolved in the solvent C is prepared in advance, and this liquid and silver nanoparticles to which the 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 room 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 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 diethylbenzene or decalin.

  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 approximately 90% by mass or less. In particular, it has been found that a liquid silver ink having extremely good dispersibility can be produced at a high yield, for example, in the range of 60% by mass or less.

Example 1
As a surfactant (protective material for metal Ag particle surface), oleylamine is used for primary amine A before substitution, and octyl gallate is used for organic compound B after substitution, and octyl gallate is adsorbed by the following steps. A silver particle was created. Then, an attempt was made to create a silver ink with extremely good dispersibility in which the silver particles were dispersed in diethylbenzene.

[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. 4, a large peak between 200 and 300 ° C. and a 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]
Octyl gallate (first grade reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared as the organic compound B, and isopropanol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 60.1) was prepared as the solvent C.
138.8 g of octyl gallate was mixed with 400 g of isopropanol, the liquid temperature was kept at 40 ° C., and octyl gallate was completely dissolved in isopropanol. To this liquid, 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)) was added and stirred with a propeller at 400 rpm. . 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.

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 was replaced with octyl gallate 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. 4 (before substitution) and FIG. 5 (after substitution), it is considered that the protective material was almost completely desorbed of amine A (oleylamine) and replaced with organic compound B (octyl gallate).

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 6.53nm, D _TEM was 7.55Nm. D particle diameter of each particle used in computing _TEM, the minimum value D _min is 2.22Nm, the maximum value D _max was 14.21Nm. 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 21%. 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 metal silver content (% by 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 diethylbenzene (special grade reagent manufactured by Wako Pure Chemical Industries). And a silver particle + diethylbenzene mixture in which the content of metallic silver in the total amount of metallic silver + protective material + diethylbenzene was 50 mass%. This mixture was treated at 40 ° C. or lower for 60 minutes using an ultrasonic cleaner (manufactured by Sharp Corporation; UT606), and silver particles were dispersed in metadiethylbenzene. 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.
FIG. 8 shows an example of a TEM photograph of silver particles obtained by adsorbing octyl gallate collected from the silver ink.
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 42.40% 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 84.8%, 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 the organic compound B was changed to dodecyl gallate (first grade reagent manufactured by Tokyo Chemical Industry Co., Ltd.). That is, in this example, silver particles formed by adsorbing dodecyl gallate were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in diethylbenzene. In the protective material replacement step, the amount of organic compound B was adjusted so that the amount of organic compound B (dodecyl gallate) with respect to Ag was 0.5 equivalent.

  About the silver particle sample after substitution, the TG-DTA measurement was performed by the said method. A measurement example of the DTA curve is shown in FIG. From the comparison between FIG. 4 (before substitution) and FIG. 6 (after substitution), it is considered that the protective material was almost completely desorbed from amine A (oleylamine) and replaced with organic compound B (dodecyl gallate).

Dx for this sample was 7.31 nm and D _TEM was 10.36 nm. Particle diameter of each particle used in computing D _TEM, the minimum value D _min is 6.29Nm, the maximum value D _max is 15.2 nm, CV value of the silver micropowder was 20%.

A silver ink using diethylbenzene as a solvent was prepared in the same manner as in Example 1. As a result, the silver concentration in the silver ink was 39.45% 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 78.9%, which is a level that can be industrialized sufficiently.
FIG. 9 shows an example of a TEM photograph of silver particles obtained by adsorbing dodecyl gallate collected from the silver ink.
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 Example 1 was performed except that the organic compound B was changed to castor oil (manufactured by Wako Pure Chemical Industries, Ltd.). That is, in this example, silver particles formed by adsorbing castor oil were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in diethylbenzene. In addition, the mixing amount of the organic compound B (castor oil) was set to 261.77 g with respect to 400 g of isopropanol at the time of preparation of the protective material replacement step.

  About the silver particle sample after substitution, the TG-DTA measurement was performed by the said method. A measurement example of the DTA curve is shown in FIG. From the comparison between FIG. 4 (before substitution) and FIG. 7 (after substitution), it is considered that almost all the amine A (oleylamine) was desorbed and replaced with the organic compound B (castor oil) in the protective material.

Dx for this sample was 8.08 nm and D _TEM was 10.42 nm. Particle diameter of each particle used in computing D _TEM, the minimum value D _min is 4.83Nm, the maximum value D _max is 15.08Nm, CV value of the silver micropowder was 15%.

A silver ink using diethylbenzene as a solvent was prepared in the same manner as in Example 1. As a result, the silver concentration in the silver ink was 40.94% 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 81.9%, which is a level that can be industrialized sufficiently.
FIG. 10 shows an example of a TEM photograph of silver particles obtained by adsorbing castor oil collected from the silver ink.
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
The same experiment as in Example 1 was performed except that the solvent of the silver ink was decalin. In other words, in this example, silver particles formed by adsorbing octyl gallate were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in decalin. The silver particle sample after substitution is the same as that obtained in Example 1.

  A silver ink using decalin as a solvent was prepared in the same manner as in Example 1. As a result, the silver concentration in the silver ink was 45.95% 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 91.9%, 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 5
The same experiment as in Example 2 was performed except that the solvent of the silver ink was decalin. In other words, in this example, silver particles formed by adsorbing dodecyl gallate were prepared, and an attempt was made to produce a silver ink with extremely good dispersibility in which the silver particles were dispersed in decalin. The silver particle sample after substitution is the same as that obtained in Example 2.

  A silver ink containing decalin as a solvent was prepared in the same manner as in Example 1. As a result, the silver concentration in the silver ink was 44.13% 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 88.3%, 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.

The figure showing the structural formula of gallic acid. The figure showing the structural formula of octyl gallate. The figure showing the structural formula of dodecyl gallate. DTA curve for silver particles before replacement of protective material coated with oleylamine. The DTA curve about the silver particle formed by making octyl gallate adsorb | suck. The DTA curve about the silver particle formed by making dodecyl gallate adsorb | suck. The DTA curve about the silver particle which makes castor oil adsorb | suck. TEM photograph of silver particles formed by adsorbing octyl gallate. TEM photograph of silver particles formed by adsorbing dodecyl gallate. A TEM photograph of silver particles obtained by adsorbing castor oil.

Claims (4)

  X-ray crystal particle diameter Dx formed by adsorbing octyl gallate on the surface: 1-40 nm silver particles, X-ray crystal particle diameter Dx formed by adsorbing dodecyl gallate on the surface: silver particles having 1-40 nm, and castor oil A silver ink in which one or more of silver particles having an X-ray crystal particle diameter Dx of 1 to 40 nm are dispersed in diethylbenzene.   X-ray crystal particle diameter Dx formed by adsorbing octyl gallate on the surface: 1 to 40 nm silver particle, and X-ray crystal particle diameter Dx formed by adsorbing dodecyl gallate on the surface: 1 of 1-40 nm silver particle A silver ink in which seeds or two are dispersed in decalin.   X-ray crystal particle diameter Dx formed by adsorbing octyl gallate on the surface: 1-40 nm silver particles, X-ray crystal particle diameter Dx formed by adsorbing dodecyl gallate on the surface: silver particles having 1-40 nm, and castor oil A liquid ink in which one or more of silver particles having an X-ray crystal particle diameter Dx of 1 to 40 nm are dispersed in diethylbenzene at a silver concentration of 20 to 60% by mass. A silver ink that maintains a dispersed state for at least 168 hours when the liquid is allowed to stand after stirring.   X-ray crystal particle diameter Dx formed by adsorbing octyl gallate on the surface: 1 to 40 nm, and X-ray crystal particle diameter Dx formed by adsorbing dodecyl gallate on the surface: 1 of 1-40 nm silver particles A liquid ink in which the seed or two are dispersed in decalin at a silver concentration of 20 to 60% by mass, and the dispersed state is maintained for at least 168 hours when the liquid is allowed to stand after stirring.