KR20060046103A - Spherical silver powder and method for producing same - Google Patents

Abstract

The present invention provides spherical silver powder, which has good dispersibility and is capable of obtaining good sintering degree even when a conductor is formed by firing at a low temperature of 600 ° C. or lower for use in forming a paste. By reducing precipitation of silver particles by adding a reducing agent-containing aqueous solution to an aqueous reaction system containing silver ions, the ratio (Dx / BET) of crystallite diameter Dx (nm) to BET specific surface area (m ² / g) is 5 to 200. A spherical silver powder having a crystallite diameter of 40 nm or less, an average particle diameter of 5 μm or less, a tap density of 2 g / cm ³ or more and a BET specific surface area of 5 m ² / g or less is produced.

Spherical silver powder, conductive paste, firing, dispersibility

Description

Spherical Silver Powder and Method for Producing Same

[Patent Document 1] Japanese Unexamined Patent Publication No. 2000-1706

[Patent Document 2] Japanese Unexamined Patent Publication No. 2000-1707

The present invention relates generally to spherical silver powders and methods for their preparation. More specifically, the present invention relates to spherical silver powder used to form terminal electrodes of electronic components, circuit board patterns, and the like, and methods for producing the same.

In order to form electrodes and circuits, such as an electronic component, the electrically conductive paste which disperse | distributed silver powder in the organic component has been used. In general, the conductive paste is classified into a cermet paste (or calcined paste) and a polymer paste (or resin paste). Cermet pastes and polymeric pastes have different uses and components.

Typical cermet-type pastes include silver powder, vehicles containing ethylcellulose or acrylic resins dissolved in organic solvents, glass frits, inorganic oxides, organic solvents, dispersants, and the like. The cermet paste is formed into a predetermined pattern by dipping or printing, and then fired to form a conductor. Such cermet pastes are used to form electrodes such as hybrid ICs, multilayer ceramic capacitors, chip resistors, and the like.

The firing temperature of the cermet paste depends on its use. Conductors are formed by firing the cermet paste at high temperatures on heat-resistant ceramic substrates such as alumina substrates or glass-ceramic substrates used in hybrid ICs, and by firing the cermet paste on low heat resistant substrates at low temperatures. There is a case.

When baking at the high temperature which is less than melting | fusing point of silver which is 960 degreeC, the resistance value of the sintered compact of silver will fall. However, various problems arise when no silver powder suitable for the firing temperature is used. For example, when the paste is fired at a high temperature on a ceramic substrate, in some cases, problems such as cracking and lamination peeling occur due to shrinkage difference between the sintered body of silver and the ceramic substrate. In order to solve this problem, high crystalline silver powder has been proposed (for example, see Japanese Patent Laid-Open Nos. 2000-1706 and 2000-1707).

On the other hand, typical polymer pastes are used as wiring materials such as through holes or membranes, conductive adhesives, and the like. Such polymeric pastes include silver powder, thermosetting resins such as epoxy resins and urethane resins, curing agents, organic solvents, dispersants and the like. The polymer paste is formed into a predetermined conductive pattern by dispensing or printing, and then cured at a temperature of room temperature to about 250 ° C., thereby obtaining conductivity by bringing silver particles into contact with each other by curing and shrinking of the remaining resin. Therefore, in order to increase the contact area where silver particles come into contact with each other, flaky silver powder obtained by mechanically processing silver powder into scales is generally used. In addition, the resin deteriorates at a temperature above 300 ° C., and the resistance and adhesive strength of the conductor deteriorate.

However, for example, in the case of a plasma display panel (PDP) substrate, the heat resistance of the glass, which is the material of the substrate, is low, and unlike the case of the ceramic substrate, the paste cannot be baked at a high temperature of about 750 to 900 ° C. Therefore, it is necessary to bake the paste at a lower temperature, and in view of the heat resistance of the substrate, it is necessary to form the conductor by firing at a temperature of 600 ° C. or less, in fact, at a low temperature of 500 to 600 ° C. However, it is difficult to lower the resistance of the conductor.

When the paste is baked at a low temperature, the resistance of the conductor can be lowered by adding a glass frit having a softening point lower than the firing temperature to promote sintering. However, in the case of a PDP substrate formed by repeated firing, it is not preferable to use a glass frit having an excessively low softening point because variations in the resistance value of the conductor occur.

In the case where the silver powder is used to form the photosensitive paste, scattering and / or reflection of ultraviolet light occurs when the silver powder is in an amorphous or flaky form, resulting in poor patterning.

In addition, when forming a conductor pattern by another method, for example, the printing method or the transfer method, if the silver powder is irregular or flaky, it is impossible to form a good conductor pattern in view of releasability from the screen plate and transferability. .

Accordingly, an object of the present invention is to provide a spherical silver powder and a method for producing the same, which can obtain a good sintering degree even when conductors are formed by eliminating the above-mentioned problems and firing at a low temperature of 600 ° C. or lower for use in forming a paste. will be. Another object of the present invention is to provide spherical silver powder having good dispersibility and a method for producing the same.

The present inventors have made intensive studies to achieve the above-mentioned and other objects. As a result, spherical silver powder having a ratio (Dx / BET) of crystallite diameter Dx (nm) to BET specific surface area (m ² / g) of 5 to 200, Preferably, when the spherical silver powder having a crystallite diameter of 40 nm or less and an average particle diameter of 5 μm or less is used for baking to form a conductor, a good sintering degree can be obtained even when the firing temperature is lower than 600 ° C. From the paste using spherical silver powder having a dispersibility having a tap density of 2 g / cm ³ or more and a BET specific surface area of 5 m ² / g or less, a good conductor pattern by the photosensitive paste method, printing method or transfer method It was found that can be obtained to complete the present invention.

According to one aspect of the invention, there is provided a spherical silver powder having a ratio (Dx / BET) of crystallite diameter Dx (nm) to BET specific surface area (m ² / g) of 5 to 200. This spherical silver powder has a crystallite diameter of 40 nm or less and an average particle diameter of 5 μm or less. More preferably, the spherical silver powder has a tap density of 2 g / cm ³ or more and a BET specific surface area of 5 m ² / g or less.

According to another aspect of the present invention, there is provided a method for producing the spherical silver powder described above, which produces spherical silver powder by reducing precipitation of silver particles by adding a reducing agent-containing aqueous solution to an aqueous reaction system containing silver ions. In this method, a dispersant is preferably added to the slurry phase reaction system before or after the precipitation of the silver particles. This dispersant is preferably at least one selected from the group consisting of fatty acids, fatty acid salts, surfactants, organometallics, chelate formers and protective colloids. The reducing agent contained in the reducing agent-containing aqueous solution is preferably at least one selected from the group consisting of ascorbic acid, alkanol amines, hydroquinone, hydrazine and formalin. The reducing agent-containing aqueous solution is preferably added at a rate of 1 equivalent / min or more relative to the silver content in the aqueous reaction system containing silver ions. Moreover, Preferably, the surface of spherical silver powder is smoothed by the surface smoothing process which mechanically collides particle | grains. Also, after the surface smoothing step is preferably performed, the silver aggregate is removed by grading.

In a preferred embodiment of the spherical silver powder according to the invention, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) is 5 to 200, preferably the crystallite diameter is 40. It is nm or less and the average particle diameter is 5 micrometers or less. Such a silver powder can be used to form a paste, so that a good sintering degree can be obtained even when fired at a low temperature of 600 ° C. or lower, so that the resistance of the conductor formed can be lowered.

When silver powder is a spherical form, it can be used suitably for performing the photosensitive paste method. In the case where the silver powder is irregular or flake, there is a disadvantage in that the photosensitive characteristics of the silver powder are poor because diffuse reflection and / or scattering of ultraviolet light occur. However, when the silver powder is in spherical form, it is also suitably used for carrying out the printing method or the transferring method.

In a preferred embodiment of the spherical silver powder according to the invention, the tap density is at least 2 g / cm ³ and the BET specific surface area is at most 5 m ² / g. Tap density 2 g / cm ³ If less, the aggregation of the silver powder particles is severe, and even when used in any of the above-described methods, it is difficult to form a precision line. If the BET specific surface area exceeds 5 m ² / g, the viscosity of the paste is too high, resulting in poor workability.

In a preferred embodiment of the method for producing spherical silver powder according to the present invention, silver particles are reduced to precipitate by adding a reducing agent-containing aqueous solution to an aqueous reaction system containing silver ions. It is preferable to add a dispersing agent to the slurry phase reaction system before reduction precipitation of silver particle or after reduction precipitation.

As the aqueous reaction system containing silver ions, an aqueous solution or slurry containing silver nitrate or a silver intermediate can be used. Silver salt complexes can be produced by adding ammonia water, ammonia salts, chelate compounds and the like. Silver intermediates can be produced by adding sodium hydroxide, sodium chloride, sodium carbonate and the like. Among them, in order for the silver powder to have an appropriate particle size and spherical shape, it is preferable to use an ammine complex obtained by adding ammonia water to an aqueous solution of silver nitrate. Since the coordination number of the ammine complex is 2, 2 mol or more of ammonia is added per mol of silver.

The reducing agent is ascorbic acid, sulfite, alkanol amine, hydrogen peroxide, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, sodium borohydride, hydrazine, hydrazine compounds, hydroquinone, pyrogallol, glucose, gallic acid, formalin , Anhydrous sodium sulfate, longgalite. Among them, the reducing agent is preferably at least one selected from the group consisting of ascorbic acid, alkanol amines, hydroquinone, hydrazine and formalin. By using these reducing agents, silver particles of suitable crystallinity and suitable particle size can be obtained.

The reducing agent is preferably added at a rate of 1 equivalent / minute or more in order to prevent aggregation of the silver powder. Although the reason is not clear, it is thought that dispersibility improves when reducing agent is injected in a short time, reduction reduction of silver particle occurs at once, reduction reaction is completed in a short time, and the produced nucleus is hard to aggregate. At the time of reduction, it is preferable to stir the solution to be reacted so that the reaction is completed in a shorter time.

The dispersant is preferably at least one selected from the group consisting of fatty acids, fatty acid salts, surfactants, organometallics, chelate formers and protective colloids. Examples of fatty acids include propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, linoleic acid and arachidonic acid. Examples of fatty acid salts include salts formed by metals and fatty acids such as lithium, sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, lead, zinc, tin, strontium, zirconium, silver, and copper. Can be mentioned. Examples of surfactants include anionic surfactants such as alkylbenzenesulfonates and polyoxyethylene alkyl ether phosphates; Cationic surfactants such as aliphatic quaternary ammonium salts; Amphoteric surfactants such as imidazolinium betaine; And nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters. Examples of the organic metal include acetylacetone tributoxy zirconium, magnesium citrate, diethyl zinc, dibutyl tin oxide, dimethyl zinc, tetra-n-butoxy zirconium, triethyl indium, triethyl gallium, trimethyl indium, trimethyl gallium, Monobutyl tin oxide, tetraisocyanate silane, tetramethylsilane, tetramethoxysilane, polymethoxysiloxane, monomethyl triisocyanate silane, silane coupling agent, titanate coupling agent, aluminum coupling agent. Examples of chelate formers include imidazole, oxazole, thiazole, selenazole, pyrazole, isoxazole, isothiazole, 1H-1,2,3-triazole, 2H-1,2,3-triazole , 1H-1,2,4-triazole, 4H-1,2,4-triazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxa Diazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thia Diazole, 1H-1,2,3,4-tetrazole, 1,2,3,4-oxatriazole, 1,2,3,4-thiatriazole, 2H-1,2,3,4- Tetrazole, 1,2,3,5-oxatriazole, 1,2,3,5-thiatriazole, indazole, benzimidazole, benzotriazole and salts thereof, and oxalic acid, succinic acid, malonic acid, Glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, didodecanoic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, glycolic acid, lactic acid, hydroxybutyric acid, glyceric acid, Tartaric acid, malic acid, tartronic acid, hydracrylic acid, mandelic acid, citric acid There may be mentioned ascorbic acid. Examples of protective colloids include gelatin, albumin, gum arabic, protarbic acid and risalvanic acid.

The spherical silver powder thus obtained can be processed by a surface smoothing process in which particles collide mechanically with each other, and then silver aggregates can be removed from the spherical silver powder by grading. When the spherical silver powder thus obtained is used to form the photosensitive paste, the sensitivity of the thus formed photosensitive paste is good, the linearity of the thus obtained pattern is also very good, and a precise pattern can be obtained. The silver powder thus obtained is excellent in releasability from the printing plate when used for carrying out the printing method and excellent in transferability when used for carrying out the transfer method, so that the silver powder can be suitably used for carrying out various methods.

<Example>

Examples of the spherical silver powder and the method for producing the same according to the present invention will be described in detail below.

<Example 1>

30O mL of industrial ammonia water was added to 3600 mL of an aqueous solution containing 12 g / L of silver nitrate as silver ions to form an aqueous silver ammine complex. The pH of the solution was adjusted by adding 60 g of sodium hydroxide to the silver ammine complex aqueous solution thus formed. Thereafter, 90 mL of industrial formalin functioning as a reducing agent was added to the solution within 10 seconds. Immediately thereafter, 0.5 g of stearic acid emulsion was added to the solution to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water and dried to obtain a silver powder. The surface of the silver powder thus obtained was smoothed by a surface smoothing process using a high speed mixer, and the smoothed silver powder was classified to remove silver aggregates larger than 8 mu m in diameter.

The crystallite diameter of the silver powder thus obtained was calculated. In addition, the BET specific surface area, tap density, and average particle diameter D ₅₀ of the silver powder were measured, and their conductivity was evaluated. In addition, it was confirmed by the scanning electron microscope (SEM) that the silver powder obtained by the Example and the comparative example which were described in this Example and the following is spherical silver powder.

The crystallite diameter of silver powder was calculated | required by the following Scherrer formula.

Dhkl = Kλ / βcosθ

Where Dhkl is the crystallite diameter (size of the crystallite in the direction perpendicular to hkl), λ is the wavelength of the measured X-ray (1.5405 Hz when using a Cu target), and β is an enlargement of the diffraction line based on the size of the crystallite. (rad) (indicated using half-power band width), θ is the Bragg angle of the diffraction angle (angle when the incident angle and the reflection angle are the same, and the angle at the peak top K denotes the Scherrer constant (varies according to the definitions of D and β, and K = 0.94 when using full width as β). In addition, the powder X-ray diffractometer was used for the measurement, and the peak data of the (200) plane was used for calculation.

Evaluation of conductivity was performed as follows. 65 parts by weight of silver powder, 14 parts by weight of an acrylic resin (BR-105 commercially available from Mitsubishi Rayon Co., Ltd.), 21 parts by weight of an organic solvent (diethylene glycol monoethyl ether acetate (reagent)) and a glass frit (Nippon Denki Glass) 1 part by weight of commercially available GA-8) was measured and kneaded with a 3-roll mill to prepare a paste. Then, the paste was printed on the commercially available soda glass substrate, and baked at 550 degreeC for 10 minutes, and the sintered compact was obtained. The electrical conductivity of the sintered compact thus obtained was evaluated. The case where the resistance value of the sintered compact was 3x10 <^-6> ohm * cm or less was stable, and the case where 3x10 <^-6> ohm * cm was exceeded or it was not stable was evaluated as defect.

As a result, the crystallite diameter was 32.4 nm and the BET specific surface area was 0.75 m ² / g. In addition, the tap density was 5.0 g / cm ³ and an average particle diameter D ₅₀ was 1.4 ㎛. In addition, the conductivity was good. In addition, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) was 43.

<Example 2>

180 mL of industrial ammonia water was added to 3600 mL of aqueous solution containing 12 g / L of silver nitrate as silver ions, and the aqueous solution of silver ammine complex was formed. The pH of the solution was adjusted by adding 7 g of sodium hydroxide to the silver ammine complex aqueous solution thus formed. Thereafter, 192 mL of industrial formalin functioning as a reducing agent was added to the solution within 10 seconds. Immediately thereafter, 0.1 g of oleic acid was added to the solution to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water and dried to obtain a silver powder. The silver powder thus obtained was pulverized with a food mixer.

Thus obtained is the crystallite size calculated by the same method as in Example 1 with respect to the powder, and measuring the BET specific surface area, tap density and mean particle diameter D _50, which was evaluated for conductivity. As a result, the crystallite diameter was 29.6 nm and the BET specific surface area was 0.46 m ² / g. In addition, the tap density was 4.7 g / cm ³ , and the average particle diameter D ₅₀ was 2.1 μm. In addition, the conductivity was good. In addition, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) was 64.

<Example 3>

180 mL of industrial ammonia water was added to 3600 mL of aqueous solution containing 12 g / L of silver nitrate as silver ions, to form an aqueous solution of silver ammine complex. 1 g of sodium hydroxide was added to the silver ammine complex aqueous solution thus formed to adjust the pH of the solution. Thereafter, 192 mL of industrial formalin functioning as a reducing agent was added to the solution within 15 seconds. Immediately thereafter, 0.1 g of stearic acid was added to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water and dried to obtain a silver powder. The surface of the silver powder thus obtained was smoothed by a surface smoothing process using a high speed mixer, and the smoothed silver powder was classified to remove silver aggregates larger than 11 μm.

Thus obtained is the crystallite size calculated by the same method as in Example 1 with respect to powder, which was then compared to determine the BET surface area, tap density and mean particle diameter D _50, evaluating the conductivity. As a result, the crystallite diameter was 33.3 nm and the BET specific surface area was 0.28 m ² / g. In addition, the tap density was 5.4 g / cm ³ and an average particle diameter D ₅₀ was 3.1 ㎛. In addition, the conductivity was good. In addition, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) was 119.

<Example 4>

150 mL of industrial ammonia water was added to 360OmL of an aqueous solution containing 12 g / L of silver nitrate as silver ions to form an aqueous solution of silver ammine complex. 13 mL of industrial hydrazine functioning as a reducing agent was added to the silver ammine complex aqueous solution thus formed in 2 seconds. Immediately thereafter, 0.2 g of oleic acid was added to the solution to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water and dried to obtain a silver powder. Then, the surface of the silver powder thus obtained was smoothed by the surface smoothing process using a high speed mixer.

Thus obtained was calculated from the crystallite size by the same method as in Example 1 with respect to the powder, and measuring the BET specific surface area, tap density and mean particle diameter D _50, evaluating the conductivity. As a result, the crystallite diameter was 34.0 nm and the BET specific surface area was 0.86 m ² / g. In addition, the tap density was 4.0 g / cm ³ and an average particle diameter D ₅₀ was 1.7 ㎛. In addition, the conductivity was good. In addition, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) was 39.

Comparative Example 1

50 mL of industrial ammonia water was added to 3600 mL of an aqueous solution containing 6 g / L of silver nitrate as silver ions to form a silver ammine complex aqueous solution. 60 mL of industrial hydrogen peroxide solution functioning as a reducing agent was added to the silver ammine complex aqueous solution thus formed in 15 seconds. Immediately thereafter, 0.1 g of sodium stearate was added to the solution to obtain a silver slurry. The silver slurry thus obtained was filtered, washed with water and dried to obtain a silver powder.

Thus obtained was calculated from the crystallite size by the same method as in Example 1 with respect to the powder, and measuring the BET specific surface area, tap density and mean particle diameter D _50, evaluating the conductivity. As a result, the crystallite diameter was 47.8 nm and the BET specific surface area was 0.15 m ² / g. In addition, the tap density was 5.0 g / cm ³ and an average particle diameter D ₅₀ was 6.5 ㎛. In addition, the conductivity was not good. Further, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) was 318.

Comparative Example 2

Commercially available spraying was performed on the powder (5 μm), the crystallite diameter was calculated by the same method as in Example 1, the BET specific surface area, the tap density and the average particle diameter D ₅₀ were measured, and the conductivity was evaluated. As a result, the crystallite diameter was 42.6 nm and the BET specific surface area was 0.21 m ² / g. In addition, the tap density was 5.2 g / cm ³ and an average particle diameter D ₅₀ was 5.3 ㎛. Also, the conductivity was not good. In addition, the ratio (Dx / BET) of the crystallite diameter Dx (nm) to the BET specific surface area (m ² / g) was 203.

These results are shown in Table 1. In Table 1, the case where the evaluation of electroconductivity was favorable was shown "good", and the case where it was not favorable was shown "bad".

 According to the present invention, spherical silver powder having good dispersibility and capable of obtaining good sintering degree even when a conductor is formed by firing at a low temperature of 600 ° C. or lower, used for forming a paste can be produced.

Claims (10)

Spherical silver powder having a ratio (Dx / BET) of crystallite diameter Dx (nm) to BET specific surface area (m ² / g) of 5 to 200. The spherical silver powder of Claim 1 whose crystallite diameter is 40 nm or less and an average particle diameter is 5 micrometers or less. The spherical silver powder according to claim 1 or 2, wherein the tap density is 2 g / cm ³ or more and the BET specific surface area is 5 m ² / g or less.  The method for producing the spherical silver powder according to any one of claims 1 to 3, wherein spherical silver powder is produced by adding a reducing agent-containing aqueous solution to the aqueous reaction system containing silver ions to reduce precipitation of silver particles. The manufacturing method of the spherical silver powder of Claim 4 which adds a dispersing agent to the slurry phase reaction system before the reduction precipitation of the said silver particle, or after reduction precipitation. The method for producing spherical silver powder according to claim 5, wherein the dispersant is at least one selected from the group consisting of fatty acids, fatty acid salts, surfactants, organometallics, chelate formers and protective colloids.  The method for producing spherical silver powder according to claim 4, wherein the reducing agent contained in the reducing agent-containing aqueous solution is at least one member selected from the group consisting of ascorbic acid, alkanol amine, hydroquinone, hydrazine and formalin. The manufacturing method of the spherical silver powder of Claim 4 which adds the said reducing agent containing aqueous solution at the rate of 1 equivalent / min or more with respect to silver content in the aqueous reaction system containing said silver ion. The manufacturing method of the spherical silver powder of Claim 4 which smoothens the said spherical silver powder by the surface smoothing process which mechanically collides particle | grains. The manufacturing method of the spherical silver powder of Claim 9 which removes silver aggregate by grading after performing the said surface smoothing process.