JPH1088207A - Silver powder and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver powder manufacturing method by which non-reducing reaction does not occur according to the amount of addition, the kind and amount of the dispersing agent are not limited; there problems are caused in the conventional manufacturing method in which the dispersing agent is added to a reaction liquid before reduction; and the silver powder excellent in dispensability is obtained and the silver powder to be obtained thereby. SOLUTION: This silver powder is manufactured by adding an aqueous solution containing a reducing agent to a water-based reaction system containing silver complex salt or silver oxide or both at a rate of >=1 equivalent/min, and either mixing and grinding wet cakes having a water content of 20 to 80% obtained by filtrating and washing slurry containing the silver powder with a mixer or mixing and griding the wet cakes together with the dispersing agent within the mixer after reduced. The silver powder has a characteristic excellent in dispesibility exhibiting a tap density of >=2g/cm<3> , an average particle size by the laser diffraction method of 0.1 to 5μm and a specific surface area of <=5m<2> /g. After this silver powder is pasted, a paste 3 is then piled on a 96% alumina substrate 1, on which a mending tape 2 is stuck for example, is stretched with a glass bar 4, is printed, then the tape is peeled and thereafter a paste coating film 5 is dried, thereby the cahracteristc of a surface roughness Ra of <=2μm and a coating density of >=4.5g/cm<3> is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing silver powder obtained by a reduction precipitation method and a silver powder produced by the method. More specifically, the present invention relates to a method for producing silver powder suitably used for an electronic component such as an internal electrode for a capacitor or a conductor pattern of a circuit board, and a silver powder produced by the method.

[0002]

2. Description of the Related Art Conventionally, a silver paste manufactured by adding silver powder to an organic vehicle together with a glass frit and kneading it for an internal electrode or a circuit conductor pattern of a multilayer capacitor has been used. Silver powder is required to have a suitably small particle size and uniform particle size. In the production of the silver powder, a method of producing silver oxide by adding an alkali to a silver salt-containing aqueous solution to generate silver oxide and further adding a reducing agent, or adding a complexing agent to the silver salt-containing aqueous solution to form a complex And then adding a reducing agent to obtain silver powder.

[0003] However, the silver powder produced by these methods has a problem that the silver powder is so agglomerated that it cannot cope with the thinning of the conductor pattern of fine lines and the internal electrodes of the multilayer ceramic capacitor. Therefore, improvements have been made to make the obtained silver powder less agglomerated, and the results of those studies have been described in, for example, JP-A-49-113754, JP-A-52-54661, and JP-A-54-12.
No. 1270 and Japanese Unexamined Patent Publication No. 61-243105.

[0004] That is, JP-A-49-113754 discloses a method of adding a caustic alkali to a silver salt aqueous solution to generate silver oxide, adding a surfactant to disperse the silver oxide, and then reducing the silver oxide. It is described that when silver oxide is formed, a surfactant can be added to obtain a uniform silver powder with little variation in characteristics. JP-A-52-5466
No. 1 discloses a method of adjusting the specific surface area of silver powder by changing the type and amount of an amine when producing a silver powder by reducing a silver salt solution with hydrazine in the presence of an amine. It is described that the presence thereof has an effect of weakening the strong reducing power of hydrazine and preventing a heterogeneous reaction.

Japanese Patent Application Laid-Open No. 54-212270 discloses that a fatty acid is added to a mixed aqueous solution of a silver nitrate solution and formalin in an amount of 0.1 to 5% by weight based on the amount of precipitated silver, followed by stirring. A method for depositing silver powder is disclosed, and it is described that when silver fine particles are precipitated by a reduction reaction, a fine and dispersed silver powder can be obtained by coating the silver fine particles with a fatty acid. Japanese Patent Application Laid-Open No. 61-243105 discloses a method for producing silver fine particles by reducing an ammoniacal silver nitrate complex solution using a reducing agent in a hydrophobic reaction tank. By adding, a method of obtaining monodispersed silver fine particles is disclosed, and the reason for using a hydrophobic reaction tank is that, in the case of hydrophilicity, the width of the particle size distribution that is aggregated because the precipitation reaction occurs on the wall surface of the container is wide. It states that only silver particles can be obtained. The reason for adding the cationic surfactant to the reaction solution is to reduce the ammoniacal silver nitrate complex solution so that the silver fine particles precipitated in the aqueous solution do not aggregate and remain in a monodispersed state. ing. In the same manner as in this method, JP-A-61-276904 discloses an anionic surfactant, JP-A-61-276905 discloses a nonionic surfactant, and JP-A-61-276906 discloses a nonionic surfactant. Describes a method using an amphoteric surfactant, and JP-A-61-276907 discloses a method using a protective colloid.

[0006]

However, some of such prior arts involve a method of adding a surfactant, a fatty acid, an amine or the like to a reaction solution.
JP-A-9-113754 and JP-A-61-24310
No. 5, JP-A-61-276904 to JP-A-61-276907, the dispersing effect is insufficient due to the pH of the reaction solution or coexisting ions depending on the type of surfactant used. Alternatively, the effect may not be exhibited, the types of surfactants that can be used are limited, and it is difficult to control the strict amount of coating on the surface of silver powder. However, when a large amount of fatty acid is added, an unreduced reaction occurs, or the dispersant is limited to fatty acids.
In the case of Japanese Patent Application Laid-Open No. 2-54661, the specific surface area is adjusted by adding an amine, and there is a problem that silver powder having good dispersibility cannot be obtained. Therefore, the object of the present invention is that, unlike the conventional method for producing a silver powder in which a dispersant is added to a reaction solution before reduction, an unreduction reaction does not occur depending on the amount added, and the type and amount of the dispersant are not limited. Moreover, it is an object of the present invention to provide a method for producing silver powder from which silver powder having excellent dispersibility can be obtained, and a silver powder obtained by the method.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that an aqueous solution or aqueous suspension containing one or both of a silver complex (silver salt) and silver oxide or both. When the aqueous solution containing the reducing agent is added to the aqueous reaction system comprising the mixture of the above, the addition rate of the aqueous solution containing the reducing agent is increased in order to prevent aggregation of the reduced silver particles.
The obtained silver powder-containing slurry was filtered and washed with water to obtain a wet cake having a water content of 20 to 80%, and the wet cake was mixed and disintegrated in a mixer, or The present inventors have found that, if mixed and pulverized together with a dispersant therein, the above-mentioned problem is solved and a silver powder having excellent dispersibility can be obtained, and the present invention has been achieved.

That is, the present invention firstly provides a method for producing silver powder in which an aqueous solution containing a reducing agent is added to an aqueous reaction system containing at least one of a silver salt and silver oxide to reduce and precipitate silver particles. A method for producing silver powder, characterized in that the aqueous reaction system containing precipitated silver particles is filtered to obtain a wet cake, and the wet cake is crushed. Second, the wet cake has a water content of 20 to 80%. 3. The method for producing silver powder according to the first aspect, wherein a dispersant is added to the wet cake. :
Fourth, as the dispersant, any one or more of a fatty acid, a fatty acid salt, a surfactant, an organic metal, and a protective colloid is selectively used, wherein the method for producing silver powder according to the third aspect is as follows: Fifthly, the method for producing silver powder according to any one of the first to fourth aspects, wherein the rate of addition of the reducing agent-containing aqueous solution is 1 equivalent / minute or more with respect to the silver content: , A silver powder produced by the method according to any one of the first to fifth aspects, wherein the silver powder has a tap density of 2 g /
cm ³ or more, laser diffraction method average particle size is 0.1-5μ
and silver powder having a specific surface area of 5 m ² / g or less: Seventh, when the silver powder is pasted, the surface roughness Ra of the coating film printed on the ceramic substrate is 2 μm or less. A film having a coating density of 4.5 g / cm ³ or more, and a fired film obtained by firing the coating in the air, having a surface roughness Ra of 2 μm or less and a fired film density of 10 g / cm ³ or more. Eighth, the silver powder according to the sixth aspect, wherein the silver powder produced by the method according to any one of the first to fifth aspects is coated on a ceramics substrate using a paste and has a surface roughness Ra. Is 2 μm or less, the coating density is 4.5 g / cm ³ or more, and the fired film obtained by firing the coating in the air has a surface roughness Ra of 2 μm or less and a fired film density of 10 g / cm ^3. Characterized by the above Pastes.

[0009]

A feature of the production method of the present invention is that a reducing agent aqueous solution is added at a rate of 1 equivalent / minute or more to an aqueous reaction system containing silver ions (silver salt) or silver oxide in the reduction step. Alternatively, the reduction reaction of silver in the reaction system, that is, the generation reaction of silver powder is completed within about 1 minute.
A wet cake of 0 to 80% is crushed by a mixer without drying, and the addition of a dispersant is to be added at the time of the crushing. In the production method of the present invention,
The form of silver before reduction to silver powder is not particularly limited. Specifically, an aqueous solution containing a silver complex salt is obtained by adding a complexing agent to an aqueous solution of silver nitrate, so that aqueous ammonia, an ammonium salt, a chelate compound or the like can be used as the complexing agent. On the other hand, a silver oxide-containing aqueous suspension can be obtained by adding an alkali such as sodium hydroxide or potassium hydroxide to a silver nitrate aqueous solution. The silver complex salt-containing aqueous solution or the silver oxide-containing aqueous suspension thus obtained may be mixed and then reduced.

The reducing agent is not a problem as long as it is a reducing agent used in a known method for producing silver powder by utilizing an oxidation-reduction reaction in an aqueous solution. Specific examples include hydrazine, hydrazine compounds, formalin, glucose, sodium borohydride, sodium hypophosphite, sulfite, formic acid, sodium formate, anhydrous sodium sulfite, L
(+) Tartaric acid, ammonium formate, Rongalit, L-
Ascorbic acid or a mixture thereof. Among these reducing agents, those in a solid state are used as an aqueous solution. Therefore, a substance which decomposes when used as an aqueous solution at the time of use requires a treatment such as adjusting the solution pH to an alkaline side. About the temperature at the time of reduction
It is desirable to carry out in a temperature range of 80 ° C. Regarding the method of adding the reducing agent, an aqueous solution containing the reducing agent is added at a rate of 1 equivalent / minute or more, or a reaction equivalent of the reducing agent is added within 1 minute to the entire reaction system in order to prevent aggregation of silver powder. To do. As long as the size of the aqueous reaction system to which the reducing agent is added is as large as the size of the reaction tank used in actual operation,
It was confirmed that there was no need to strictly change the addition rate depending on the size of the reaction system, and that the addition at a rate of 1 equivalent / min or more was effective. The reason for this operation is not clear, but by adding the reducing agent in a short time, reductive precipitation on the silver particles occurs at a stroke, and the reduction reaction is completed in a short time, resulting in the aggregation of nuclei generated. It is considered that the dispersibility is difficult to improve. In the case of reduction, the reaction solution is preferably stirred so that the reaction is completed in a shorter time.

The aqueous solution containing silver powder obtained by reduction and precipitation is filtered and washed with water to form a wet cake of silver powder having a water content of 20 to 80%. There is no problem if the method of filtration is a method used for solid-liquid separation. For example, a centrifugal filter,
Filter press, Buchner funnel, etc. The reason why the water content of the wet cake is limited to 20 to 80% is that if the water content is less than 20%, the obtained cake becomes hard and the disintegration in the subsequent step becomes inefficient, and the content exceeds 80%. However, this is because the efficiency of the subsequent disintegration decreases. Silver powder with excellent dispersibility can be obtained by passing it through the step of pulverization by the wet cake mixer thus obtained. The dispersing agent may or may not be added, but by adding and mixing the dispersing agent, the dispersing effect increases, and more preferable results can be obtained.

The mixer used here includes a mixer used for solid-liquid mixing and a mixing pulverizer used for pulverizing solids. As for the kind of the dispersant used here, any kind can be used, but preferably used are fatty acid, fatty acid salt, emulsion of fatty acid or fatty acid salt, cationic surfactant, anionic surfactant ,
One of an amphoteric surfactant, a nonionic surfactant, an organic metal, and a protective colloid, and one or more types can be selected. The amount added is not particularly limited, and may be added in an appropriate amount according to the use of the silver powder. The wet cake pulverized by the mixer is a silver powder-containing slurry having a high concentration, and is further filtered and washed with water to obtain a silver powder wet cake whose surface is coated with a dispersant. As described above, there is no problem in the method of filtration and water washing as long as an apparatus used for ordinary solid-liquid separation is used. The silver powder wet cake thus obtained is converted into silver powder through a drying step.
A known method and equipment may be used for the drying method, and the atmosphere is not particularly limited. The drying temperature is preferably 80 ° C. or lower.

The silver powder produced through these steps is
Top density is 2g / cm^ThreeAbove, flat by laser diffraction method
Uniform particle size: 0.1-5 μm, specific surface area: 5 m^Two/ G or less
It has physical properties. Tap density is JIS K51
By a method according to the tap method of 20.2 of 01-1991.
Measured. The number of tappings is 1,000. Obedience
Silver powder produced by the conventional method has insufficient dispersibility,
Tap density measured by the method of 2 g / cm ^ThreeIs less than
On the other hand, the silver powder obtained by the present invention is closer to monodispersion.
Tap density is 2g / cm^ThreeThat is all. Silver
The average particle size of the powder is measured by the laser diffraction method.
The equipment is a laser diffraction type particle sizer manufactured by Shimadzu Corporation
SALD-1100 was used. The dispersing medium is hexametallic
Sodium salt dissolved in distilled water to make a 0.2% aqueous solution
Used. In addition, at the time of measurement, one drop of
Liquid detergent is added. The refractive index at the time of measurement is A3
You. When measured by this method, the silver obtained by the present invention
While the powder has an average particle size of 0.1 to 5 μm, the conventional method
Silver powder has a value exceeding 5 μm, and dispersibility is poor.
You. The specific surface area was measured by the BET method. Manufactured by the method of the present invention.
Silver powder is 5m^Two/ G or less. Silver powder with the above characteristics
Is evaluated as its main use paste,
You can know the excellent aspect of silver powder.

There is no particular problem for the method of pasting if it is carried out according to a known example. Here, a thick-film silver paste used for forming a conductor pattern such as a hybrid IC is taken as an example. First of all, it is a vehicle used for paste, but in general, various kinds of cellulose, acrylic resin, phenol resin, alkyd resin, etc.
Those dissolved in solvents such as ester, ether, and hydrocarbon are used. In addition, various kinds of inorganic binders are added to the paste in order to bond the conductor pattern to a ceramic substrate such as an alumina substrate. As the inorganic binder, a metal oxide such as copper oxide or bismuth oxide, or a so-called glass frit obtained by finely pulverizing glass is used.

In a test for evaluation, a paste having an extremely general composition was prepared from among many combinations of the above-mentioned paste components, and silver powder was evaluated. As a vehicle, 45 cp of ethyl cellulose was dissolved in terpineol to prepare a 10% solution. The vehicle, GA-8 glass powder and silver powder made by NEC Corporation are weighed to have the following composition. Vehicle: 37.4%, silver powder: 61%, 6A-8 glass powder: 1.6% These paste components are premixed in a beaker, and then dispersed with a three-roll mill to obtain a paste. FIG. 1 is a perspective view showing a printing method after the silver powder is made into a paste. FIG.
FIG. 2B shows the paste coating printed on the substrate in the state of D printing. That is, the paste 3 was placed on a 96% alumina substrate 1 on which a mending tape 2 was stuck in parallel at regular intervals, the paste was stretched and printed with a glass rod 4, and after the tape was peeled off, the paste coating 5 was applied for 10 minutes. After leveling, drying is performed at 150 ° C. for 10 minutes using a hot air circulation dryer.

The dried coating film was evaluated by the following method. Surface roughness can be measured with a stylus-type surface roughness meter,
Here, it measured using Surftest-501 made by Mitutoyo Corporation. The measurement mode is Ra and the measurement range is 8
0 μm, cutoff value 0.3 mm, and measurement section 3 were set.
The coating density was measured by the following method. The thickness of the coating film was measured with a DEKTAKIIA surface roughness meter manufactured by Japan Vacuum Engineering Co., Ltd. However, there is no problem as long as the device has a similar measuring mechanism. The width and length of the coating film were measured with a caliper. The weight of the coating film was determined by measuring the weight of the substrate before printing, measuring the weight of (substrate + coating film) after printing and drying the paste, and determining the difference between them. Then, the coating density was determined by the following equation. D = (w ₂ −w ₁ ) / A × B × T Here, D is the coating density (g / cm ³ ), w ₁ is the weight of the substrate (g), and w ₂ is the weight of the (substrate + coating). Weight (g), A is the width (cm) of the coating, B is the length (cm) of the coating, and T is the thickness (cm) of the coating.

When silver powder was evaluated by these methods, the following was found. The coating film of the paste using the silver powder having excellent dispersibility has a Ra of 2 μm or less, the particularly excellent silver powder has a small value of 0.7 μm or less, and the coating density D
Shows a value of 4.5 g / cm ³ or more, and a dense coating film is obtained. Such a dense and smooth surface coating film can be obtained from silver powder having a tap density of 2 g / cm ³ or more, an average particle diameter of 0.1 to 5 μm by a laser diffraction method, and a specific surface area of 5 m ² / g or less. Needless to say. Further, it has been found that a coating film having such characteristics exhibits excellent characteristics even when formed into a silver conductor pattern by firing. This coating film is fired at 850 ° C. for 7 minutes in a belt furnace in the atmosphere to obtain a fired film. And by the same method as the coating film,
The surface roughness Ra of the fired film and the density of the fired film were measured. As a result, the calcined film Ra was 2 μm or less, and particularly 0.8 μm or less when silver powder having excellent dispersibility was used. Further, a dense film having a fired film density of 10 g / cm ³ or more can be obtained.

As described above, the use of silver powder having a high coating film density and a high fired film density can reduce the contraction rate of the pattern due to the firing or increase the consistency of the contraction rate with various substrates and materials. It is also a feature of the manufacturing method of the present invention that it greatly contributes to the increase in the yield and the improvement of the properties of the applied product obtained as a type, and the type of the dispersant of the silver powder, the shrinkage of the paste coating film can be controlled by the amount added. It is also a characteristic of silver powder. Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited by the following examples.

[0019]

Example 1 150 ml of 25% aqueous ammonia was added to 2000 ml of a 20 g / l silver nitrate aqueous solution as silver ions to obtain a silver ammine complex aqueous solution. This aqueous solution is heated at a liquid temperature of 2
0 ° C, 37% formalin aqueous solution 45m with stirring
1 was added over 40 seconds to precipitate silver powder, thereby obtaining a silver powder-containing slurry. The slurry was filtered and washed with a Buchner funnel to obtain a wet cake having a water content of 55%. GAFACRA-6, a nonionic anionic surfactant manufactured by Toho Chemical Industry Co., Ltd. in an amount of 1% based on the weight of the wet cake and the silver powder.
00 was mixed and disintegrated for about 60 seconds in a tabletop blender mill,
Thereafter, the mixture was filtered again with a Buchner funnel, washed with water, and dried in air at 70 ° C. for 24 hours to obtain silver powder. The obtained silver powder had a tap density of 2.8 g / cm ³ , an average particle size of 3.0 μm by a laser diffraction method, and a specific surface area of 0.7 m ² / g. Further, this powder was made into a paste and evaluated. The method is the method described in the section “Embodiments of the Invention” in the previous section. As a result, the coating density was 4.7 g / cm ³ , and the coating Ra = 1.
7 μm, fired film density 10.5 g / cm ³ , fired film Ra =
At 1.35 μm, good results were obtained in both the coating film density and the fired film density.

[0020]

Example 2 An aqueous silver nitrate solution having a silver ion concentration of 80 g / l in 2000 ml was heated to a temperature of 25 ° C., and then stirred, 800 ml of a 100 g / l aqueous sodium hydroxide solution was stirred.
Was added to obtain a silver oxide slurry. 37% in this slurry
Formalin solution (140 ml) was added for 50 seconds to reduce silver particles, and the obtained silver powder-containing slurry was filtered with a Buchner funnel and washed with water to obtain a wet cake having a water content of 40%.
Then, 1 wt% of Cellosol 920 emulsified with stearic acid manufactured by Chukyo Yushi Co., Ltd. was prepared based on the silver amount, and mixed and pulverized together with the wet cake in a tabletop blender mill for 60 seconds. The mixture thus obtained was filtered through a Buchner funnel, washed with water, and dried in air at 70 ° C. for 24 hours. The obtained silver powder has a tap density of 3.2 g / cm.
^3. Laser diffraction average particle size 1.0 μm, specific surface area 1.
At 5 m ² / g, the dispersibility was excellent. Further, this powder was made into a paste and evaluated. The method is the method described in the section “Embodiments of the Invention” in the previous section. As a result, the coating film density was 5.3 g / cm ³ , the coating film Ra = 0.5 μm, the fired film density was 10.7 g / cm ³ , and the fired film Ra was 0.4 μm.
It was dense and excellent in surface smoothness.

[0021]

COMPARATIVE EXAMPLE A silver oxide slurry was obtained by adding 2,000 ml of an aqueous silver nitrate solution having a silver ion concentration of 60 g / l to a temperature of 25 ° C. and adding 600 ml of 200 g / l sodium hydroxide. 14 ml of 37% formalin solution 140 ml
The silver oxide particles were reduced to silver particles by adding for 10 minutes at an addition rate of / min. Then, the mixture was filtered with a Buchner funnel, washed with water,
Drying was performed at 0 ° C. for 24 hours to obtain silver powder. The silver powder thus obtained had a tap density of 1.0 g / cm ³ , a laser diffraction average particle size of 15.0 μm, and a specific surface area of 0.9 m ² / g, and had poor dispersibility. When this silver powder was pasted and evaluated in the same manner as in the example, the coating density was 3.
0 g / cm ³ , coating Ra = 2.5 μm, fired film density 7.
5 g / cm ³ , the baked film Ra = 2.1 μm, indicating that densification had not progressed.

[0022]

As described above, in the conventional method in which a dispersant is added to a reaction solution before reduction, an unreduced reaction may occur depending on the amount of the dispersant, and the type and amount of the dispersant are limited. On the other hand, according to the method of the present invention, the addition rate of the reducing agent-containing aqueous solution is set to 1 equivalent / min or more, and the obtained silver powder-containing slurry is filtered and washed with water to obtain a wet cake having a water content of 20 to 80%. Is mixed and disintegrated in a mixer, or mixed and disintegrated with a dispersing agent in the mixer, so that silver powder having excellent dispersibility is obtained, and is formed into a paste and is suitable for a conductive pattern or the like of a circuit board. It can be a membrane.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a printing method after a silver powder is made into a paste. FIG. 1a shows a state in which a paste is stretched and printed on a substrate on which a mending tape is attached in parallel at regular intervals.
FIG. 2B is a diagram showing a coating film printed on the substrate.

[Explanation of symbols]

 1 96% alumina substrate 2 Mending tape 3 Paste 4 Glass rod 5 Paste coating

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshimune Itabashi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Chemical Co., Ltd.

Claims (8)

[Claims] 1. A method for producing silver powder in which an aqueous solution containing a reducing agent is added to an aqueous reaction system containing at least one of a silver salt and silver oxide to reduce and deposit silver particles. A method for producing silver powder, comprising filtering an aqueous reaction system into a wet cake, and pulverizing the wet cake. 2. The wet cake according to claim 1, wherein said wet cake has a water content of 20 to 8 or more.
The method for producing silver powder according to claim 1, wherein the content is 0%. 3. The method for producing silver powder according to claim 1, wherein a dispersant is added to the wet cake. 4. As the dispersant, a fatty acid, a fatty acid salt,
4. The method for producing silver powder according to claim 3, wherein at least one of a surfactant, an organic metal, and a protective colloid is selectively used. 5. The method for producing silver powder according to claim 1, wherein the rate of addition of the reducing agent-containing aqueous solution is 1 equivalent / minute or more with respect to the silver content. 6. A silver powder produced by the method according to claim 1, wherein the silver powder has a tap density of 2 g / g.
cm ³ or more, laser diffraction method average particle size is 0.1-5μ
m and a specific surface area of 5 m ² / g or less. 7. When the silver powder is made into a paste, the coating film printed on the ceramic substrate has a surface roughness R.
a is 2 μm or less, the coating density is 4.5 g / cm ³ or more, and the fired film obtained by firing the coating in the air has a surface roughness Ra of 2 μm or less and a fired film density of 10
7. The silver powder according to claim 6, which provides a property of g / cm < ³ > or more. 8. A paste using silver powder produced by the method according to claim 1, wherein the paste has a surface roughness Ra of 2 μm or less in a coating film printed on a ceramic substrate. , The coating density is 4.5 g / cm ³
A paste characterized in that a fired film obtained by firing the coating film in the air has a surface roughness Ra of 2 μm or less and a fired film density of 10 g / cm ³ or more.