JP6247876B2 - Threaded silver powder, silver powder mixture, method for producing the same, and conductive paste - Google Patents

Description

  The present invention relates to a filamentous silver powder, a silver powder mixture, a method for producing the same, and a conductive paste.

Generally, in order to achieve both printability and thinning of the conductive paste, it is necessary to improve the thixotropy of the conductive paste. For example, Patent Document 1 proposes using a mixed powder of atomized silver powder and wet-reduced silver powder to increase the aspect ratio to achieve both printability and thinning, but improves the thixotropy of the conductive paste. The effect to make was not enough.
Therefore, it is highly desired to provide a silver powder capable of achieving a higher thixotropy than conventional silver powder at the time of paste formation and a conductive paste using the same at a low cost flow by only wet reduction without passing through a flaking process. Yes.

JP 2013-105525 A

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention is a thread-like silver powder, a silver powder mixture, a method for producing the same, and a conductive material that can achieve a higher thixotropy than conventional silver powder at the time of paste formation at a low cost flow only by wet reduction without passing through a flaking process. It aims at providing a sex paste.

  The filamentous silver powder of the present invention as a means for solving the above problems has at least one curved portion in the length direction, has an average major axis length of 2 μm to 20 μm, and an average minor axis length. Is 50 nm to 900 nm.

  According to the present invention, the above conventional problems can be solved, and a low cost flow by only wet reduction without passing through a flaking process, and a filamentous shape capable of achieving higher thixotropy than conventional silver powder at the time of pasting Silver powder, a silver powder mixture, a method for producing the same, and a conductive paste can be provided.

1A is an SEM photograph at 2,000 times the silver powder in Example 1. FIG. FIG. 1B is an SEM photograph at 10,000 times the silver powder in Example 1. 2A is an SEM photograph at 2,000 times the silver powder in Example 2. FIG. FIG. 2B is an SEM photograph at 10,000 times the silver powder in Example 2. FIG. 3A is a SEM photograph at 2,000 times the silver powder in Example 3. FIG. 3B is a SEM photograph at 10,000 times the silver powder in Example 3. FIG. 4 is an SEM photograph at 10,000 times the silver powder in Comparative Example 1. FIG. 5 is an SEM photograph at 10,000 times the silver powder in Comparative Example 2. FIG. 6 is an SEM photograph at 10,000 times the silver powder in Comparative Example 3. FIG. 7 is an SEM photograph at 10,000 times the silver powder in Comparative Example 4. FIG. 8 is a graph showing the relationship between the viscosity at a rotation speed of 0.5 rpm and the viscosity ratio (η0.5 / η10). FIG. 9 is a diagram showing a wiring pattern formed in the example.

(Filed silver powder, silver powder mixture and manufacturing method thereof)
The filamentous silver powder of the present invention has at least one curved portion in the length direction, has an average major axis length of 2 μm to 20 μm, and an average minor axis length of 50 nm to 900 nm.
The silver powder mixture of the present invention contains the filamentous silver powder of the present invention, spherical silver powder, flaky silver powder, or both.
In the method for producing a silver powder mixture of the present invention, a reducing agent solution containing L-ascorbic acid and sodium ethylenediaminetetraacetate is added to an aqueous silver nitrate solution.

In the present invention, a thread-like silver powder having a higher thixotropy than conventional silver powder can be obtained at a low cost flow only by wet reduction without passing through a flaking process. The obtained silver-like silver powder has improved thixotropy when it is made into a paste, so that both printability and thinning can be achieved.
By using the filamentous silver powder of the present invention, it has a higher thixo index (ratio of viscosity value to the number of rotations of stirring) than the paste using silver silver powder, flaky silver powder, or both, and after firing Since a conductive paste having a high aspect ratio of the coating film can be obtained, both printability and fine lineability can be improved.

The silver powder mixture of the present invention contains the filamentous silver powder of the present invention, spherical silver powder, flaky silver powder, or both. In the silver powder mixture, since the thread-shaped silver powder and silver powder having different shapes such as a spherical shape and a flake shape are mixed, a conductive paste having high thixotropy can be obtained.
According to the method for producing a silver powder mixture of the present invention, a silver powder having a different shape such as a thread-like silver powder and a spherical silver powder, a flaky silver powder, or both are produced. A conductive paste having high thixotropy can be obtained without mixing. However, in order to obtain arbitrary thixotropy, another silver powder may be mixed to obtain a conductive paste.

<Filed silver powder>
The filamentous silver powder has at least one, preferably 1 to 10 curved portions in the length direction.
Unlike the rod-like or wire-like shape, the yarn-like shape is poor in linearity, is bendable like a yarn, and has at least one bend (curved, Etc., which means a shape having a displacement of a minor axis length or more in the minor axis direction with respect to a straight line. Therefore, it is easy to get entangled with other shapes of silver powder than rod-shaped or wire-shaped, and the effect of improving both printability and fine lineability in a mixed state with different shapes of silver powder can be further extracted. Also, low resistance can be obtained in applications such as a conductive adhesive having a low firing temperature and having conductivity only by point contact.
The filamentous silver powder is preferably a differentiable curve in two-dimensional observation, and the average angle of the curved portion is preferably 5 ° or more and 175 ° or less, more preferably 10 ° or more and 170 ° or less, and further 20 ° or more. 150 degrees or less is more preferable. Here, the average angle of the curved portion can be measured, for example, by observing the filamentous silver powder with a scanning electron microscope (SEM). For example, in the filamentous silver powder observed in the SEM image of 2,000 times Search for a differentiable curved portion having the maximum curvature, and an arbitrary point on the curved line of the curved portion and two points on the curved line 1 μm away from the point (when there are end points and inflection points within 1 μm) Can be obtained by measuring the internal angle (subordinate angle) at the point where the internal angle (inferior angle) of the two sides connecting the end point and the inflection point is the smallest, and the average angle of the curved portion is , Is an average of the angles of the measured curved portions of the ten filamentous silver powders. In addition, each said point shall take the center of short-axis length.

The average major axis length of the filamentous silver powder is 2 μm to 20 μm, preferably 5 μm to 20 μm. When the average major axis length is less than 2 μm, the effect of forming a thread is lost, the viscosity is lowered, and the resistance may be increased. When the average major axis length is more than 20 μm, it is handled in the same manner as ordinary silver powder. It can be difficult.
The average minor axis length is 50 nm to 900 nm, preferably 100 nm to 500 nm. When the average minor axis length is less than 50 nm, it may be difficult to handle in the same manner as ordinary silver powder. When the average minor axis length exceeds 900 nm, the axial ratio is lowered, and resistance is likely to deteriorate. There is.
The average major axis length and the average minor axis length may be observed, for example, by observing the filamentous silver powder with a transmission electron microscope (TEM) and observing the minor axis length with a scanning electron microscope (SEM). The major axis length can be measured and calculated.

The filamentous silver powder has a cumulative 50% powder diameter (D50) in a volume-based powder diameter distribution measured by a laser diffraction particle size distribution measurement method of 0.1 μm to 10 μm, preferably 0.5 μm to 4 μm.
The cumulative 50% powder diameter (D50) can be measured using, for example, a microtrack particle size distribution measuring apparatus [Honeywell-Nikkiso Co., Ltd., 9320HRA (X-100)].

BET specific surface area of the thread silver powder is not particularly limited and may be appropriately selected depending on the intended ^purpose, preferably ^{0.1m 2 / g~5m 2 / g,} 0.7m 2 / g~3m 2 / g is more preferable.
The BET specific surface area can be measured using, for example, a BET specific surface area measuring device [Monosorb (manufactured by Quanta Chrome)].

The tap density of the thread-like silver powder is not particularly limited and may be appropriately selected depending on the intended ^purpose, but is preferably ^{0.5g / cm 3 ~7.0g / cm 3} , 1.0g / cm 3 ~3. 0 g / cm ³ is more preferable.
The tap density can be measured using, for example, a tap density measuring device (Casa specific gravity measuring device SS-DA-2 manufactured by Shibayama Kagaku).

The silver powder mixture of the present invention contains the thread-shaped silver powder of the present invention, spherical silver powder, flaky silver powder, or both.
As the filamentous silver powder of the present invention, those described above can be used.
The spherical or flaky silver powder is not particularly limited and may be appropriately selected depending on the intended purpose.
The content ratio of the filamentous silver powder of the present invention in the silver powder mixture of the present invention is not particularly limited and can be appropriately selected according to the purpose, but is preferably 25% by mass or more, and more preferably 50% by mass or more.

The silver powder mixture is produced by the method for producing the silver powder mixture of the present invention.
In the method for producing a silver powder mixture of the present invention, a reducing agent solution containing L-ascorbic acid and sodium ethylenediaminetetraacetate is added to an aqueous silver nitrate solution.

  It is preferable that the reducing agent solution further contains sodium stearate from the viewpoint of easily obtaining a filamentous silver powder. As for content of the said sodium stearate, 0.5 mass%-10.0 mass% are preferable with respect to silver.

  As the reducing agent solution, it is preferable that copper nitrate trihydrate is further contained from the viewpoint that a filamentous silver powder can be easily obtained. The content of the copper nitrate trihydrate is preferably 0.2% by mass to 5.0% by mass with respect to silver.

(Conductive paste)
The conductive paste of the present invention preferably contains at least a silver powder mixture, and preferably contains a glass frit, a resin, a solvent, and a surfactant, and further contains other components as necessary.
As the silver powder mixture, the silver powder mixture of the present invention is used.
The content of the silver powder mixture is not particularly limited and can be appropriately selected depending on the purpose.

<Glass frit>
The glass frit is not particularly limited and may be appropriately selected depending on the intended purpose. For example, bismuth borosilicate, alkali metal borosilicate, alkaline earth metal borosilicate, zinc borosilicate, borosilicate Lead-based, lead borate-based, lead silicate-based, and the like. These may be used individually by 1 type and may use 2 or more types together. In addition, the thing which does not contain lead from the influence on an environment is preferable.

<Resin>
There is no restriction | limiting in particular as said resin, According to the objective, it can select suitably, For example, an acrylic resin, ethylcellulose, ethylhydroxyethylcellulose, nitrocellulose, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.

<Solvent>
The solvent is not particularly limited and may be appropriately selected depending on the intended purpose. For example, toluene, methyl ethyl ketone, methyl isobutyl ketone, tetradecane, tetralin, propyl alcohol, isopropyl alcohol, terpineol, ethyl carbitol, butyl carbitol , Ethyl carbitol acetate, butyl carbitol acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and the like. These may be used individually by 1 type and may use 2 or more types together.

<Surfactant>
Examples of the surfactant include anionic surfactants such as alkylbenzene sulfonates and polyoxyethylene alkyl ether phosphates, cationic surfactants such as aliphatic quaternary ammonium salts, and amphoteric compounds such as imidazolium betaine. Nonionic surfactants such as surfactants, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters and the like can be mentioned. These may be used individually by 1 type and may use 2 or more types together.

<Other ingredients>
There is no restriction | limiting in particular as said other component, According to the objective, it can select suitably, For example, a dispersing agent, a viscosity modifier, etc. are mentioned.

  The method for producing the conductive paste is not particularly limited and may be appropriately selected depending on the purpose. For example, the silver powder mixture, preferably the glass frit, the resin, the solvent, the surfactant, And other components can be produced by mixing using, for example, an ultrasonic dispersion, a disper, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, a self-revolving stirrer and the like.

  The conductive paste has a viscosity at a rotation speed of 0.5 rpm at 25 ° C. of more than 500 Pa · s, and a viscosity ratio (η0...) Of a viscosity η0.5 at a rotation speed of 0.5 rpm and a viscosity η10 at a rotation speed of 10 rpm. 5 / η10) is preferably 12 or more, more preferably 12-13. When the viscosity ratio (η0.5 / η10) is less than 12, the spread of the conductive paste at the time of electrode formation tends to increase.

  The conductive paste of the present invention can be applied directly on various substrates such as silicon wafers for solar cells, films for touch panels, and glass for EL elements, or on the films provided with a transparent conductive film on these substrates as necessary. In addition, a conductive coating film can be suitably formed by coating or printing. For example, it is suitably used for a current collecting electrode of a solar battery cell, an external electrode of a chip-type electronic component, an RFID, an electromagnetic wave shield, a vibrator adhesion, a membrane switch, an electroluminescence electrode, or an electrical wiring application.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
A silver nitrate aqueous solution (made by DOWA Hitech Co., Ltd.) containing 22.2 g of silver as silver was diluted with pure water to make 250 mL. While stirring this solution, in a beaker maintained at 25 ° C., a reducing agent solution also maintained at 25 ° C. (18.5 g of L-ascorbic acid manufactured by Wako Pure Chemical Industries, Ltd., Wako Pure Chemical Industries, Ltd.) 550 mL of sodium stearate 1.1 g, copper nitrate trihydrate 0.24 g, and 0.15 g of sodium ethylenediaminetetraacetate manufactured by Kirest Co.) were added. Stirring was continued for 3 minutes after the addition of the reducing agent solution, followed by filtration with a Buchner funnel and washing with water. The obtained wet cake was dried with a vacuum dryer set at 75 ° C. Crushing with a coffee mill was performed to obtain a silver powder mixture of Example 1.
About the obtained silver powder mixture of Example 1, powder shape observation, particle size distribution, BET specific surface area, tap density, and coating film evaluation were performed as follows. The results are shown in Tables 1 and 2.

<Observation of powder shape>
The powder shape was observed using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-6100) at 2,000 times and 10,000 times. The obtained SEM photographs are shown in FIGS. 1A and 1B.

<Long axis length of filamentous silver powder, minor axis length, degree of bending, ratio of filamentous silver powder>
The major axis length of the silver powder was measured by measuring ten major axis lengths selected from 2,000 times SEM photographs, and the average was taken as the average major axis length.
The minor axis length of the silver powder was measured by measuring ten minor axis lengths selected from 10,000 times SEM photographs, and taking the average as the average minor axis length.
Of the silver powder mixture of Example 1, the average major axis length of the filamentous silver powder was 17 μm, and the average minor axis length was 230 nm.
In addition, the filamentous silver powder in the silver powder mixture of Example 1 has six curved portions in the length direction as an average of 10 selected from the SEM photograph of 2,000 times, and the average angle of the curved portions is 100. °.
The ratio of the thread-like silver powder was determined by counting the number of the thread-like silver powder from the 10,000 times SEM photograph and the number of all the silver powders including the silver powder of other shapes, and the ratio of the thread-like silver powder was 26%. It was.

<Particle size distribution measurement>
In the wet laser diffraction type particle size distribution measurement, 0.3 g of the obtained silver powder is put into 30 mL of isopropyl alcohol, and dispersed for 5 minutes by an ultrasonic cleaner with an output of 45 W. A microtrack particle size distribution measuring apparatus [Honeywell-Nikkiso Using a 9320HRA (X-100) manufactured by the company, the cumulative 10% powder diameter (D10), the cumulative 50% powder diameter (D50), and the cumulative 90% powder diameter (D90) were measured.

<BET specific surface area>
The BET specific surface area was measured by the BET single point method by nitrogen adsorption using Monosorb (manufactured by Quanta Chrome). In the BET specific surface area measurement, the deaeration conditions before the measurement were 60 ° C. and 10 minutes. did.

<Tap density>
Tap density is measured using a tap density measuring device (Casa specific gravity measuring device SS-DA-2 manufactured by Shibayama Kagaku Co., Ltd.), 15 g of a silver powder sample is weighed, put into a container (20 mL test tube), and 1,000 at a drop of 20 mm. The sample was tapped once and calculated from the tap density = sample weight (15 g) / sample volume after tapping.

<Preparation of conductive paste>
Three roll mills containing 8.3 g of silver powder, 2.0 g of lead-free glass frit, vehicle (mixture of 0.3 g of ethyl cellulose and 1.1 g of butyl carbitol acetate), and 0.1 g of phosphate ester surfactant A conductive paste was prepared by mixing the materials.

  Next, for the obtained conductive paste, a wiring pattern was formed by the following method.

<Formation of wiring pattern>
The obtained conductive paste was formed on a 2-inch square alumina substrate by a screen printing method with a pattern of 500 μm width × 50,000 μm full length, left standing at room temperature for 30 minutes, and then at 150 ° C. in an air dryer. Dried for 10 minutes. The alumina substrate was baked in a muffle furnace at a maximum temperature of 800 ° C. for 60 minutes to obtain a wiring pattern shown in FIG. About the obtained wiring pattern, the aspect-ratio was measured by the method shown below.

<Average aspect ratio (thickness / wiring width)>
The thickness of the wiring pattern and the wiring width were measured at three points with a contact-type surface roughness meter (manufactured by Kosaka Laboratory Ltd.), and the average aspect ratio was calculated from the thickness / wiring width.

(Comparative Example 1)
A silver nitrate aqueous solution (made by DOWA Hitech Co., Ltd.) containing 35.0 g of silver as silver was diluted with pure water to make 600 mL. While stirring this solution, 50 mL of a reducing agent solution (including 10.4 g of anhydrous citric acid) also maintained at 25 ° C. was added to a beaker maintained at 25 ° C., and then the reduction was also maintained at 25 ° C. 150 mL of an agent solution (containing 29.6 g of L-ascorbic acid manufactured by Wako Pure Chemical Industries, Ltd.) was added. Stirring was continued for 3 minutes after addition of the reducing agent solution, followed by filtration with a Buchner funnel and washing with water. The obtained wet cake was dried with a vacuum dryer set at 75 ° C. Crushing with a coffee mill was performed to obtain silver powder of Comparative Example 1.
About the obtained silver powder, it carried out similarly to Example 1, and measured powder shape, particle size distribution, BET specific surface area, and tap density. The results are shown in Tables 1 and 2. The obtained 10,000 times SEM photograph is shown in FIG. From the results of FIG. 4, it was found that the silver powder of Comparative Example 1 was spherical with protrusions.

(Comparative Example 2)
Using the commercially available flake silver powder (1) having the characteristics shown in Table 1, the powder shape, particle size distribution, BET specific surface area, tap density, and coating film evaluation were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2. The obtained 10,000 times SEM photograph is shown in FIG. From the results of FIG. 5, it was found that the silver powder of Comparative Example 2 was flaky.

(Comparative Example 3)
Using the commercially available spherical silver powder (2) having the characteristics shown in Table 1, the obtained silver powder was evaluated in the same manner as in Example 1 for powder shape, particle size distribution, BET specific surface area, tap density, and coating film evaluation. . The results are shown in Tables 1 and 2. The obtained 10,000 times SEM photograph is shown in FIG. From the results of FIG. 6, it was found that the silver powder of Comparative Example 3 was spherical.

(Comparative Example 4)
Using the commercially available spherical silver powder having the characteristics shown in Table 1, the obtained silver powder was evaluated in the same manner as in Example 1 for powder shape, particle size distribution, BET specific surface area, tap density, and coating film evaluation. The results are shown in Tables 1 and 2. The obtained 10,000 times SEM photograph is shown in FIG. From the results of FIG. 7, it was found that the silver powder of Comparative Example 4 was spherical.

* For Comparative Example 1, no coating film evaluation was performed.
From Example 1 and Table 2 and the results of FIGS. 1A and 1B, Example 1 was confirmed to be composed of a mixture of thread-like silver powder and spherical silver powder, flaky silver powder, or both. And the silver powder mixture of Example 1 has a higher viscosity ratio at the same viscosity than Comparative Examples 1 to 4, and since there is little spread of the wiring width from coating to the end of firing, It was found that the aspect ratio was high.

(Example 2)
A silver nitrate aqueous solution (made by DOWA Hitech Co., Ltd.) containing 22.2 g of silver as silver was diluted with pure water to make 250 mL. While stirring this solution, in a beaker maintained at 25 ° C., a reducing agent solution also maintained at 25 ° C. (18.5 g of L-ascorbic acid manufactured by Wako Pure Chemical Industries, Ltd., Wako Pure Chemical Industries, Ltd.) 550 mL) (including 1.1 g sodium stearate and 0.15 g sodium ethylenediaminetetraacetate manufactured by Kyrest) was added. Stirring was continued for 3 minutes after the addition of the reducing agent solution, followed by filtration with a Buchner funnel and washing with water. The obtained wet cake was dried with a vacuum dryer set at 75 ° C. Crushing with a coffee mill was performed to obtain a silver powder mixture of Example 2.
About the obtained silver powder mixture of Example 2, it carried out similarly to Example 1, and measured the powder shape, the particle size distribution, the BET specific surface area, and the tap density. The results are shown in Table 3. The obtained SEM photographs are shown in FIGS. 2A and 2B.
Of the silver powder mixture of Example 2, the average major axis length of the filamentous silver powder was 12 μm and the average minor axis length was 150 nm.
Further, according to the same measurement method as in Example 1, the filamentous silver powder of the silver powder mixture of Example 2 had 10 curved portions in the length direction, and the average angle of the curved portions was 140 °. . The ratio of the thread-like silver powder was 54%.

(Example 3)
A silver nitrate aqueous solution (made by DOWA Hitech Co., Ltd.) containing 22.2 g of silver as silver was diluted with pure water to make 250 mL. While stirring this solution, in a beaker maintained at 25 ° C., a reducing agent solution also maintained at 25 ° C. (Wako Pure Chemical Industries, 18.5 g of L-ascorbic acid, and ethylenediamine manufactured by Kyrest Co., Ltd.) 550 mL) (containing 0.15 g sodium tetraacetate) was added. Stirring was continued for 3 minutes after the addition of the reducing agent solution, followed by filtration with a Buchner funnel and washing with water. The obtained wet cake was dried with a vacuum dryer set at 75 ° C. Crushing with a coffee mill was performed to obtain a silver powder mixture of Example 3.
About the obtained silver powder mixture of Example 3, it carried out similarly to Example 1, and measured the powder shape, the particle size distribution, the BET specific surface area, and the tap density. The results are shown in Table 3. The obtained SEM photographs are shown in FIGS. 3A and 3B.
Of the silver powder mixture of Example 3, the average major axis length of the filamentous silver powder was 7 μm, and the average minor axis length was 270 nm.
Further, according to the same measurement method as in Example 1, among the silver powder mixture of Example 3, the filamentous silver powder had two curved parts in the length direction, and the average angle of the curved parts was 30 °. . The ratio of the thread-like silver powder was 50%.

From the results of Table 3, it was found that if a reducing agent solution containing L-ascorbic acid and sodium ethylenediaminetetraacetate was added to an aqueous silver nitrate solution, silver powder containing filamentous silver powder could be produced.
Moreover, from the result of Table 3, by further including sodium stearate and copper nitrate trihydrate as the reducing agent solution, the yarn of the filamentous silver powder is easily stretched, the average major axis length is increased, and the tap density is increased. I understood that.

<Viscosity evaluation of conductive paste>
Commercially available flake silver powder (1) having the characteristics shown in Table 1 and commercially available spherical silver powder (2) are mixed at a mass ratio (1: 1), and the conductivity of a conventional example corresponding to JP2013-105525A is disclosed. A paste was obtained.
About the obtained electrically conductive paste of the prior art example, the viscosity was measured as follows and viscosity ratio was calculated | required. Further, the conductive paste was prepared by changing the composition ratio of silver powder and vehicle, and the change in viscosity is shown in FIG. 8 with the viscosity at 0.5 rpm as the horizontal axis and the viscosity ratio as the vertical axis.
About the produced electrically conductive paste of Example 1 and Comparative Examples 1-4, the viscosity was measured similarly and the viscosity ratio was calculated | required. The results are shown in Table 4 and FIG.

<Measurement of viscosity of conductive paste>
Measurements were made at 0.5 rpm, 1 rpm, 5 rpm, and 10 rpm at 25 ° C. using an E-type viscometer (Brookfield, DVIII +, cone spindle CP-52).
The measured value of the viscosity at 0.5 rpm was η0.5, the measured value of the viscosity at 10 rpm was η10, and the value of η0.5 / η10 was the viscosity ratio (thixo index).

From the result of FIG. 8, in the conductive paste of the conventional example, in the silver powder obtained by mixing the spherical silver powder and the flaky silver powder, the composition ratio of the silver powder and the vehicle is changed, and the viscosity is adjusted within a range that maintains the conductivity. Even so, it was found that the maximum value of the viscosity ratio was 10, which was less than the viscosity ratio of 12.5 in Example 1.
Moreover, as shown in Table 4 and FIG. 8, the conductive paste of the conventional example changes linearly, but the viscosity ratio including the thread-like silver powder as in Example 1 is far away from the straight line, and the spherical silver powder No matter how the mixing of flake silver powder, spherical silver powder and flaky silver powder was adjusted, it was found that the viscosity ratio of Example 1 containing thread-like silver powder was higher.

Examples of the aspect of the present invention include the following.
<1> It has at least one curved part in the length direction,
A filamentous silver powder having an average major axis length of 2 μm to 20 μm and an average minor axis length of 50 nm to 900 nm.
<2> The filamentous silver powder according to <1>, wherein the average angle of the curved portion is 5 ° or more and 175 ° or less.
<3> A silver powder mixture comprising the filamentous silver powder according to any one of <1> to <2> and a spherical silver powder, a flaky silver powder, or both.
<4> A conductive paste comprising at least the silver powder mixture according to <3>.
<5> A glass frit, a resin, a solvent, and a surfactant are further included. The viscosity at 25 ° C. at a rotation speed of 0.5 rpm is larger than 500 Pa · s, and the viscosity at a rotation speed of 0.5 rpm is η0.5. The conductive paste according to <4>, wherein the viscosity ratio (η0.5 / η10) to the viscosity η10 at a rotation speed of 10 rpm is 12 or more.
<6> The method for producing a silver powder mixture according to <3>,
A method for producing a silver powder mixture comprising adding a reducing agent solution containing L-ascorbic acid and sodium ethylenediaminetetraacetate to an aqueous silver nitrate solution.
<7> The method for producing a silver powder mixture according to <6>, wherein the reducing agent solution further contains sodium stearate.
<8> The method for producing a silver powder mixture according to <6>, wherein the reducing agent solution further contains copper nitrate trihydrate.

Claims (7)

It has a differentiable curve and a curved shape in the length direction,
A filamentous silver powder having an average major axis length of 2 μm to 20 μm and an average minor axis length of 50 nm to 900 nm.   A silver powder mixture comprising the filamentous silver powder according to claim 1 and spherical silver powder, flaky silver powder, or both.   A conductive paste comprising at least the silver powder mixture according to claim 2.   The glass frit, a resin, a solvent, and a surfactant are further included. The viscosity at a rotation speed of 0.5 rpm at 25 ° C. is larger than 500 Pa · s, the viscosity η0.5 at a rotation speed of 0.5 rpm, and the rotation speed. The conductive paste according to claim 3, wherein a viscosity ratio (η0.5 / η10) with a viscosity η10 at 10 rpm is 12 or more. It is a manufacturing method of the silver dust mixture according to claim 2,
A method for producing a silver powder mixture, comprising adding a reducing agent solution containing L-ascorbic acid and sodium ethylenediaminetetraacetate to an aqueous silver nitrate solution.   The method for producing a silver powder mixture according to claim 5, wherein the reducing agent solution further comprises sodium stearate.   The method for producing a silver powder mixture according to claim 5, wherein the reducing agent solution further contains copper nitrate trihydrate.