JP2019053902A - Conductive paste - Google Patents

Abstract

To provide a conductive paste that contains conductive powder composed of aluminum powder, glass frit, and organic vehicle, has a low viscosity and excellent print quality, and a low volume resistivity.SOLUTION: The present invention provides a conductive paste that contains conductive powder composed of aluminum powder, glass frit, and organic vehicle. As the glass frit, used is a silver coated glass powder in which on the surface of glass powder containing bismuth, formed is a coating layer mainly composed of silver (where it contains 30-70 mass% of bismuth and 3-30 mass% of silver and has an average particle size of Dof 0.1-10 μm by laser-diffraction).SELECTED DRAWING: None

Description

  The present invention relates to a conductive paste, and more particularly to a conductive paste using aluminum powder as a conductive powder.

  Conventionally, a conductive paste (aluminum paste) using aluminum powder as the conductive powder is printed on substantially the entire back surface of the solar cell and used to form a back electrode of the solar cell. The conductive paste used for forming the back electrode of such a solar cell needs to be a conductive paste having a low volume resistivity, and the back electrode is efficiently printed to produce a solar cell at a production rate. Therefore, it is desired that the conductive paste has a low viscosity and excellent printability.

  As an aluminum paste used to form the back electrode of a solar cell, a composition in which an aluminum-containing powder, amorphous silicon dioxide, and glass frit are dispersed in an organic medium, or an aluminum-containing powder, amorphous silicon dioxide, glass frit, and Ag are contained. A composition in which powder is dispersed in an organic medium has been proposed (see, for example, Patent Document 1).

JP 2007-128872 A (paragraph numbers 0018-0021)

  However, the conventional aluminum paste has a problem that it is difficult to knead due to poor wetting when it is produced by kneading with three rolls. Further, the conventional aluminum paste has a problem that it has a high viscosity and is difficult to be printed by a screen printer or the like.

  Therefore, in view of such a conventional problem, the present invention includes a conductive powder made of aluminum powder, a glass frit, and an organic vehicle, and has a low viscosity, excellent printability, and low volume resistivity. It aims at providing a sex paste.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have found that a conductive paste comprising an aluminum powder, a glass frit, and an organic vehicle has a surface of the glass powder as a glass frit. In addition, it was found that by using a silver-coated glass powder in which a coating layer containing silver as a main component was formed, a conductive paste having a low viscosity and excellent printability and a low volume resistivity can be provided. The invention has been completed.

  That is, the conductive paste according to the present invention is a conductive paste containing a conductive powder made of aluminum powder, a glass frit, and an organic vehicle. As a glass frit, the conductive paste mainly contains silver on the surface of the glass powder. A silver-coated glass powder having a coating layer formed thereon is used.

In this conductive paste, the silver content in the silver-coated glass powder is preferably 3 to 30% by mass. The glass powder preferably contains bismuth, and the bismuth content in the silver-coated glass powder is preferably 30 to 70% by mass. The silver-coated glass powder may contain one or more selected from the group consisting of boron, barium, silicon, strontium, vanadium, zinc, zirconium, magnesium, and titanium. The average particle diameter _{D 50} of the silver coated glass powder by a laser diffraction method is preferably a 0.1 to 10 [mu] m.

  ADVANTAGE OF THE INVENTION According to this invention, the electroconductive powder which consists of aluminum powder, a glass frit, and an organic vehicle, and can provide the electroconductive paste with low viscosity that is excellent in printability and low volume resistivity.

  In the embodiment of the conductive paste according to the present invention, in the conductive paste containing the conductive powder made of aluminum powder, the glass frit, and the organic vehicle, the glass powder is used as the main component of silver on the surface of the glass powder. A silver-coated glass powder having a coating layer formed thereon is used.

The silver content in the silver-coated glass powder is preferably 3 to 30% by mass, and more preferably 5 to 15% by mass. The glass powder preferably contains bismuth. in this case. The bismuth content in the silver-coated glass powder is preferably 30 to 70% by mass, and more preferably 35 to 50% by mass. Further, the silver-coated glass powder may contain one or more selected from the group consisting of boron, barium, silicon, strontium, vanadium, zinc, zirconium, magnesium, and titanium. The average particle diameter _{D 50} of the silver coated glass powder by a laser diffraction method is preferably from 0.1 to 10 [mu] m, more preferably in the range of 0.5 to 5 [mu] m.

  In the above silver-coated glass powder, the glass powder is immersed in a silver ion-containing solution, a complexing agent or an alkali and a reducing agent are added to the solution, and a coating layer made of precipitated silver is formed on the surface of the glass powder. It can be manufactured by forming.

  The coating layer is obtained by immersing glass powder in a silver ion-containing solution, adding a complexing agent or alkali and a reducing agent to the solution, and then reducing the silver particles by a wet reduction method to deposit the silver powder into the glass powder. It is formed by coating the surface. In the formation of this coating layer, silver particles are added to the surface of the glass powder by adding a complexing agent or an alkali and a reducing agent to the slurry obtained by immersing the glass powder in a silver ion-containing solution while stirring. To precipitate. In the formation of the coating layer, the entire surface of the glass powder may not be completely covered with silver, and a part of the surface of the glass powder may be exposed.

  As the silver ion-containing solution, an aqueous silver nitrate solution or the like can be used. By adding a complexing agent or an alkali to the silver ion-containing solution, an aqueous solution or slurry containing a silver salt complex or a silver intermediate can be produced. As a complexing agent for producing an aqueous solution or slurry containing a silver salt complex, aqueous ammonia, ammonium salt, chelate compound and the like can be used. As an alkali for producing an aqueous solution or slurry containing a silver intermediate, sodium hydroxide, sodium chloride, sodium carbonate or the like can be used. Among these, it is preferable to add aqueous ammonia to an aqueous silver nitrate solution to produce an aqueous silver ammine complex solution. Since the coordination number of ammonia in the ammine complex is 2, the addition amount of ammonia is 2 moles or more per mole of silver. However, if the addition amount of ammonia is too large, the complex is too stabilized and the reduction is difficult to proceed. Therefore, the amount is preferably 8 mol or less per 1 mol of silver. In addition, if adjustment, such as increasing the addition amount of a reducing agent, is performed, even if the addition amount of ammonia exceeds 8 mol, a silver covering glass powder can be obtained.

  As a reducing agent, ascorbic acid, sulfite, alkanolamine, hydrogen peroxide solution, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, sodium borohydride, hydroquinone, hydrazine, hydrazine compound, pyrogallol, One or more of glucose, gallic acid, formalin, anhydrous sodium sulfite, Rongalite and the like can be used. Among these, it is preferable to use one or more selected from the group consisting of ascorbic acid, alkanolamine, sodium borohydride, hydroquinone, hydrazine and formalin, more preferably formalin or hydrazine, Most preferably it is used. The addition amount of the reducing agent is preferably 1 equivalent or more with respect to silver in order to increase the yield of silver. When a reducing agent having a weak reducing power is used, 2 equivalents or more with respect to silver, For example, 10-20 equivalent may be sufficient.

  A conductive paste can be obtained by mixing the silver-coated glass powder, a conductive powder made of aluminum powder, and an organic vehicle and performing a kneading process.

  The organic vehicle preferably contains an organic solvent and an organic resin component. The organic solvent can be appropriately selected according to the purpose of use of the conductive paste. For example, butyl carbitol acetate (BCA), butyl carbitol (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC ), Toluene, methyl ethyl ketone, methyl isobutyl ketone, tetradecane, tetralin, propyl alcohol, isopropyl alcohol, dihydroterpineol, dihydroterpineol acetate, ethyl carbitol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate ( One or more solvents can be selected and used from texanol) and terpineol. The content of the organic solvent is preferably 0 to 20% by mass and more preferably 0 to 18% by mass with respect to the conductive paste. As the organic resin component, one or more of epoxy resin, acrylic resin, polyester resin, polyimide resin, polyurethane resin, phenoxy resin, silicone resin, ethyl cellulose and the like can be used. The content of the organic resin component is preferably 0.02 to 3.0% by mass and more preferably 0.03 to 2.4% by mass with respect to the conductive paste.

  The viscosity of the conductive paste was measured using a viscometer (HBDV-III Ultra manufactured by Brookfield) using a cone plate having a cone radius of 1.2 cm (CPE-52) at 25 ° C. at 1 rpm (5 minutes value) and 5 rpm ( It is preferable that all are 100-500 Pa.s when measured by 1 minute value. If the viscosity of the conductive paste is less than 100 Pa · s, bleeding may occur during printing of the paste. On the other hand, if it exceeds 500 Pa · s, uneven printing may occur, and the printing speed by a screen printer If the speed is increased, the separation of the plate becomes worse and the mesh mark remains, which causes a decrease in yield.

  In order to further improve the printability of the conductive paste, a moisturizer such as a high boiling point solvent such as triethylene glycol butyl methyl ether, a lubricant such as fatty acid amide wax, castor oil, polyethylene wax, stearic acid, etc. A dispersant such as palmitic acid or oleic acid may be added.

  Hereinafter, the Example of the electrically conductive paste by this invention is described in detail.

[Example]
After mixing 3.87 g of a silver nitrate aqueous solution containing 32% by mass of silver with 787 g of pure water being stirred in a 1 L beaker to obtain a silver nitrate aqueous solution containing 1.11 g of silver, this diluted silver nitrate aqueous solution Then, 2.5 g of 28% by mass of ammonia water was added as a complexing agent to obtain a silver ammine complex salt aqueous solution (pH 11). After the liquid temperature of the silver ammine complex salt aqueous solution was set to 30 ° C., 10 g of glass powder containing Bi was added, and immediately after that, 0.3 g of hydrazine as a reducing agent and a TEM particle size of 5 in pure water as a solvent. A solution prepared by mixing 10.3 g of silver colloid and 0.01 g of pure water (containing 0.001 times the amount of silver in an aqueous solution) of 0.01 g of ˜40 nm silver nanoparticles and 20 g of pure water is added. After aging for 5 minutes (so that it does not remain in the liquid) and coating the glass powder with a layer containing silver as a main component, this silver-coated glass powder-containing slurry is suction filtered, and the potential becomes 0.5 mS / m or less. The resulting cake was dried with a vacuum dryer at 75 ° C. for 10 minutes to obtain a silver-coated glass powder (a glass powder coated with a silver-based layer).

With respect to the silver-coated glass powder thus obtained, the volume-based cumulative distribution of the glass powder was determined as a particle size distribution using a laser diffraction / scattering particle size distribution measuring device (MICROTRAC MT3300EXII manufactured by Microtrack Bell Co., Ltd.). However, the cumulative 10% particle size (D ₁₀ ) was 0.9 μm, the cumulative 50% particle size (D ₅₀ ) was 2.3 μm, and the cumulative 90% particle size (D ₉₀ ) was 5.0 μm. The composition analysis of this silver-coated glass powder was performed by high frequency inductively coupled plasma (ICP) emission spectroscopy, and it was found that 9.78 mass% Ag, 6.23 mass% B, and 6.93 mass%. Ba, 42.49 mass% Bi, 0.63 mass% Si, 0.07 mass% Sr, 2.42 mass% V, 0.29 mass% Zn, and the balance As a silver-coated glass powder containing oxygen. In this composition analysis, 0.045 g of silver-coated glass powder was dissolved by heating by adding 5 mL of 61 mass% nitric acid (nitric acid for precision analysis (UGR) manufactured by Kanto Chemical Co., Ltd.) and 10 mL of distilled water, After allowing to cool, the sample is passed through 5C filter paper, the filtrate is made up to a volume of 50 mL, and the measured value obtained by measuring with an ICP emission spectrophotometer (SPS5100 manufactured by Seiko Instruments Inc.) and on the filter paper The residue was transferred into a quartz beaker with distilled water, and 5 mL of 37% by mass nitric acid (nitric acid for precision analysis (UGR) manufactured by Kanto Chemical Co., Ltd.) and 96% by mass nitric acid (for precision analysis manufactured by Kanto Chemical Co., Ltd.) Add nitric acid (2 mL of reagent (UGR)) and dissolve with heating to give white nitric acid smoke to dryness, then add 10 mL of pure water and 5 mL of hydrochloric acid to dissolve with heating, allow to cool, and then adjust to 50 mL. Forgiveness It was performed by summing the measured values obtained by measuring the serial of ICP emission spectrophotometer.

  0.22 parts by weight of the silver-coated glass powder thus obtained, 78 parts by weight of aluminum powder having an average particle size of 4.6 μm, 1.8 parts by weight of ethyl cellulose, 5.0 parts by weight of texanol, butyl carbyl 5.0 parts by weight of tall acetate (BCA), 5.5 parts by weight of terpineol, 1.8 parts by weight of triethylene glycol butyl methyl ether, 2.5 parts by weight of fatty acid amide wax, and 0.2 parts by weight of oleic acid Are mixed (preliminary kneading) with a self-revolving vacuum stirring deaerator (Shinky Co., Ltd. Awatori Nertaro), and then kneaded with three rolls (EXAKT M-80S). Sex paste was obtained.

  The conductive paste thus obtained was subjected to 1 rpm (5 minutes) at 25 ° C. with a viscometer (HBDV-III Ultra manufactured by Brookfield) using a cone plate having a cone radius of 1.2 cm (CPE-52). Value) and 5 rpm (1 minute value) were 381 (Pa · s) and 123 (Pa · s), respectively.

  Next, the obtained conductive paste was applied to a screen printing machine (manufactured by Microtech Co., Ltd.) on the back surface of a substrate obtained by cutting a single crystal silicon wafer for solar cells (105Ω / □) into a substantially square of 1 inch × 1 inch. MT-320T) was printed in a line shape of width 500 μm × length 37.5 mm, dried in air at 200 ° C. for 10 minutes, and then in-out using a high-speed firing IR furnace (manufactured by NGK Corporation). Firing was performed at a peak temperature (firing temperature) of 770 ° C. for 21 seconds.

  When the average thickness of the conductive film thus obtained was measured with a surface roughness / contour shape measuring instrument (Surfcom 480B-12 manufactured by Tokyo Seimitsu Co., Ltd.), the average thickness was 24 μm, and the digital multimeter When the resistance value was measured by (R7451A manufactured by ADC Co., Ltd.), the resistance value was 0.9 μΩ. The volume resistivity of the conductive film was calculated (from this resistance value and the volume obtained from the film thickness, line width, and length) and found to be 30 μΩ · cm.

[Comparative Example 1]
A glass powder containing Bi was prepared, and the particle size distribution was determined by the same method as that for the silver-coated glass powder of Example 1. As a result, the glass powder had a cumulative 10% particle size (D ₁₀ ) of 0.9 μm, a cumulative 50% particle size (D ₅₀ ) of 2.9 μm, and a cumulative 90% particle size (D ₉₀ ) of 6.5 μm. .

  Except that 0.2 parts by weight of this glass powder was used instead of silver-coated glass powder, the conductive paste obtained by the same method as in the example was subjected to 1 rpm (5 rpm) at 25 ° C. by the same method as in the example. The viscosity was measured at 5 minutes (minute value) and 5 rpm (1 minute value) and found to be 572 (Pa · s) and 192 (Pa · s), respectively. In addition, using this conductive paste, for the conductive film obtained by the same method as in the example, the average thickness and resistance value were measured by the same method as in the example, and the volume resistivity was calculated. The thickness was 25 μm, the resistance value was 0.9 μΩ, and the volume resistivity was 31 μΩ · cm.

  From these results, in the conductive paste using the glass powder instead of the silver-coated glass powder of the example, the volume resistivity of the conductive film is increased, the viscosity of the conductive paste is increased, and the printability is deteriorated. I understand that.

[Comparative Example 2]
To 40 g of the conductive paste of Comparative Example 1, 0.0040 g of silver powder (Agglomerated silver powder G-35 (no surface treatment agent) manufactured by DOWA Hightech Co., Ltd., specific surface area 1.11 m ^{2 /} g) was added (of Example 1). The silver powder is added so that the amount of the silver-coated glass powder and silver is the same, that is, the silver powder is added so that the total of the glass powder and the silver powder is 0.22 parts by weight), and the same method as in Example 1 Thus, after mixing (preliminary kneading), kneading gave a conductive paste.

  About the conductive paste thus obtained, the viscosity was measured at 1 rpm (5 minutes value) and 5 rpm (1 minute value) at 25 ° C. by the same method as in the example. 155 (Pa · s). In addition, using this conductive paste, for the conductive film obtained by the same method as in the example, the average thickness and resistance value were measured by the same method as in the example, and the volume resistivity was calculated. The thickness was 25 μm, the resistance value was 0.9 μΩ, and the volume resistivity was 31 μΩ · cm.

  From these results, in the conductive paste added with silver powder using glass powder instead of the silver-coated glass powder of the example, the volume resistivity of the conductive film is high, the viscosity of the conductive paste is also high, It turns out that printability worsens.

  The electrically conductive paste by this invention can be utilized for electronic components, such as a conductor pattern of a circuit board, an electrode of a board | substrate, such as a solar cell, and a circuit.

Claims (6)

In a conductive paste containing conductive powder made of aluminum powder, glass frit, and organic vehicle, silver-coated glass powder in which a coating layer mainly composed of silver is formed on the surface of the glass powder as glass frit A conductive paste, characterized by using. The conductive paste according to claim 1, wherein the silver content in the silver-coated glass powder is 3 to 30% by mass. The conductive paste according to claim 1, wherein the glass powder contains bismuth. The conductive paste according to claim 3, wherein the silver-coated glass powder has a bismuth content of 30 to 70% by mass. The silver-coated glass powder contains one or more selected from the group consisting of boron, barium, silicon, strontium, vanadium, zinc, zirconium, magnesium, and titanium, according to any one of claims 1 to 4. Conductive paste. 6. The conductive paste according to claim 1, wherein the silver-coated glass powder has an average particle diameter D ₅₀ of 0.1 to 10 μm by a laser diffraction method.