JP6681437B2 - Conductive paste - Google Patents

Description

  The present invention relates to a conductive paste, and more particularly to a conductive paste using silver-coated copper powder and silver powder as a conductive metal powder.

  Conventionally, a conductive paste prepared by blending a solvent, a resin, a dispersant and the like with a conductive metal powder such as silver powder or copper powder has been used to form electrodes and wiring of electronic parts by a printing method or the like. There is.

  However, silver powder has a very small volume resistivity and is a good conductive substance, but since it is a powder of a noble metal, the cost is high. On the other hand, copper powder has a low volume resistivity and is a good conductive substance, but it is inferior in storage stability (reliability) to silver powder because it is easily oxidized.

  In order to solve these problems, silver-coated copper powder in which the surface of copper powder is coated with silver has been proposed as the metal powder used in the conductive paste (see, for example, Patent Documents 1 and 2). It has also been proposed to use silver powder and silver-coated copper powder as the metal powder used in the conductive paste (see, for example, Patent Document 3).

  In recent years, as a conductive paste for forming a conductive film such as a bus bar electrode of a solar cell, a conductive paste using silver-coated copper powder, which is cheaper than silver powder, is used instead of the conductive paste using silver powder. However, the use of a conductive paste using silver powder and silver-coated copper powder has also been considered.

  In a general crystalline silicon solar cell, an electrode is formed by firing a firing type conductive paste using silver powder at a high temperature of about 800 ° C. in an air atmosphere. However, copper powder or silver-coated copper powder is used. If you use a conductive paste that uses copper, copper powder or silver-coated copper powder will oxidize when fired at such high temperatures in the atmosphere, so special techniques such as firing in an inert atmosphere Is required, and the cost is high.

  On the other hand, in a HIT (single crystal hybrid type) solar cell or the like, an electrode is generally formed by heating a resin-curable conductive paste using silver powder to about 200 ° C. in an air atmosphere to cure it. Even if heated at such a low temperature in the air atmosphere, copper powder or silver-coated copper powder can withstand oxidation. Therefore, resin-curable conductive paste using silver-coated copper powder or silver powder and silver-coated copper powder can be used. It is possible to use a resin-curable conductive paste that uses powder.

JP, 2010-174311, A (paragraph number 0003) JP, 2010-077495, A (paragraph number 0006) JP-A-11-92739 (paragraph number 0008)

  However, a bus bar electrode formed from a conventional resin-type conductive paste obtained by kneading a resin such as a bisphenol A type epoxy resin using the silver powder and the silver-coated copper powder as described above is soldered to a tab wire. It was found that when the connection was made, the resin of the conductive paste was decomposed at the soldering temperature (about 380 ° C.), the resistance of the bus bar electrode increased, and the conversion efficiency of the solar cell decreased.

  Therefore, in view of such a conventional problem, the present invention can heat a conductive film formed of a resin-type conductive paste using silver powder and silver-coated copper powder to a soldering temperature of about 380 ° C. An object of the present invention is to provide a conductive paste capable of preventing the increase in volume resistivity of the conductive film.

  As a result of earnest research to solve the above problems, the present inventors have conducted a conductive paste containing silver-coated copper powder in which the surface of copper powder is coated with a silver layer, silver powder, and an epoxy resin having a naphthalene skeleton. It was found that the conductive film produced by the method can prevent the increase of the volume resistivity of the conductive film even if the conductive film is heated to a soldering temperature of about 380 ° C., and the present invention has been completed. .

  That is, the conductive paste according to the present invention is characterized by containing silver-coated copper powder in which the surface of copper powder is coated with a silver layer, silver powder, and an epoxy resin having a naphthalene skeleton.

The conductive paste preferably contains dicarboxylic acid. This dicarboxylic acid is preferably attached to silver powder. Further, the dicarboxylic acid is preferably a dicarboxylic acid rational formula is _{HOOC- (CH 2) n -COOH (} n = 1~8), n in this rational formula is in the range of 4-7 More preferable. Further, the amount of dicarboxylic acid in the conductive paste is preferably 0.01 to 0.25 mass% with respect to the silver of the silver layer and silver powder, and 0.1 mass% or less with respect to the conductive paste. Preferably.

  In addition, the conductive paste preferably contains a solvent, and preferably contains a curing agent. The silver-coated copper powder preferably has an average particle size of 1 to 20 μm, and the silver powder preferably has an average particle size of 0.1 to 3 μm. The amount of silver-coated copper powder in the conductive paste is preferably 40 to 94% by mass, the amount of silver powder is preferably 4 to 58% by mass, and the total amount of silver-coated copper powder and silver powder is 75 to 98% by mass. preferable. Further, the amount of the silver layer with respect to the silver-coated copper powder is preferably 5% by mass or more.

In the present specification, the “average particle diameter” means a volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by a laser diffraction type particle size distribution device.

  According to the present invention, even if a conductive film formed of a resin-type conductive paste using silver powder and silver-coated copper powder is heated to a soldering temperature of about 380 ° C., the volume resistivity of the conductive film is increased. A conductive paste that can be prevented can be provided.

  An embodiment of the conductive paste according to the present invention includes silver-coated copper powder in which the surface of copper powder is coated with a silver layer, silver powder, and an epoxy resin having a naphthalene skeleton.

  As the resin having a naphthalene skeleton contained in this conductive paste, an epoxy resin having a naphthalene skeleton as shown in Chemical formula 1 (for example, HP4710 manufactured by Dainippon Ink and Chemicals, Inc.) can be used. The content of the epoxy resin having the naphthalene skeleton is preferably 1 to 20% by mass, and more preferably 3 to 10% by mass with respect to the conductive paste. If the content of the epoxy resin having the naphthalene skeleton is too small, the function of protecting the surface of the silver-coated copper powder from oxidation due to heat becomes insufficient. On the other hand, if too much, the printability when printing on the bus bar electrode shape of the solar cell by the conductive paste, and the adhesive strength of the solder when soldering the bus bar electrode to the tab wire deteriorates, and it is made by the conductive paste. The resistance of the bus bar electrode of the solar cell is increased. Whether or not the epoxy resin has a naphthalene skeleton can be identified by a gas chromatograph mass spectrometer (GC-MS) or C13-NMR.

The conductive paste preferably contains a dicarboxylic acid such as adipic acid, azelaic acid or phthalic acid. This dicarboxylic acid is preferably attached to silver powder. Further, the dicarboxylic acid is preferably rational formula is a dicarboxylic acid of _{HOOC- (CH 2) n -COOH (} n = 1~8), adipic acid, n in rational formula of azelaic acid 4 More preferably, it is a dicarboxylic acid of ~ 7. The amount of dicarboxylic acid in the conductive paste is preferably 0.25% by mass or less (more preferably 0.01 to 0.25% by mass) based on the silver of the silver layer and the silver powder. On the other hand, it is preferably 0.1% by mass or less. The qualitative and quantitative determination of the dicarboxylic acid in the conductive paste is performed, for example, by eluting the dicarboxylic acid with hydrochloric acid and adding methanol (or an esterifying agent) to the hydrochloric acid solution in which the dicarboxylic acid is eluted to form the dicarboxylic acid. It can be methylated (or esterified), and this methylated (or esterified) dicarboxylic acid can be extracted into an organic solvent, and can be carried out by a gas chromatograph mass spectrometer (GC-MS).

  The conductive paste preferably contains a solvent, and this 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, One or more solvents can be selected and used from dihydroterpineol, dihydroterpineol acetate, ethyl carbitol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (texanol) and the like. The content of this solvent is preferably 0 to 20 mass% with respect to the conductive paste, and more preferably 0 to 10 mass%.

  The conductive paste preferably contains a curing agent, and it is preferable to use at least one of imidazole and boron trifluoride amine type curing agent as the curing agent. The content of this curing agent is preferably 0.1 to 10% by mass, and more preferably 0.2 to 6% by mass, based on the epoxy resin.

  Further, the conductive paste may contain other components such as a surfactant, a dispersant, a rheology modifier, a silane coupling agent, and an ion scavenger.

  In the conductive paste, silver-coated copper powder in which the surface of copper powder is coated with a silver layer and silver powder are used as conductors. The shape of the copper powder (silver-coated copper powder) coated with the silver layer may be substantially spherical or flake-shaped. The silver-coated copper powder preferably has an average particle size of 1 to 20 μm, and the silver powder preferably has an average particle size of 0.1 to 3 μm. The amount of silver-coated copper powder in the conductive paste is preferably 40 to 94% by mass, the amount of silver powder is preferably 4 to 58% by mass, and the total amount of silver-coated copper powder and silver powder is 75 to 98% by mass. preferable.

  The silver layer of the silver-coated copper powder is preferably a layer made of silver or a silver compound, and more preferably 90% by mass or more of silver. The amount of silver based on the silver-coated copper powder is preferably 5% by mass or more, more preferably 7 to 50% by mass, further preferably 8 to 40% by mass, and 9 to 20% by mass. Most preferably. When the amount of silver is less than 5% by mass, the conductivity of the silver-coated copper powder is adversely affected, which is not preferable. On the other hand, if it exceeds 50% by mass, the cost increases due to an increase in the amount of silver used, which is not preferable.

  The copper powder used to produce the silver-coated copper powder may be produced by a wet reduction method, an electrolysis method, a vapor phase method, or the like, while melting the copper at a melting temperature or higher and dropping it from the lower part of the tundish. It is preferably produced by a so-called atomizing method (such as a gas atomizing method or a water atomizing method) in which high-pressure gas or high-pressure water is collided and rapidly solidified to obtain fine powder. In particular, spraying high-pressure water, when produced by a so-called water atomization method, it is possible to obtain a copper powder having a small particle size, so when the copper powder is used in a conductive paste, the conductivity of the particles increases due to an increase in contact points between the particles. It is possible to improve.

  As a method of coating the copper powder with a silver layer, it is possible to use a substitution method utilizing a substitution reaction of copper and silver, or a method of depositing silver or a silver compound on the surface of the copper powder by a reduction method using a reducing agent. It is possible to, for example, a method of precipitating silver or a silver compound on the surface of copper powder while stirring a solution containing copper powder and silver or a silver compound in a solvent, or a solution containing copper powder and an organic substance in a solvent and a solvent. A method of mixing silver or a solution containing a silver compound and an organic substance and precipitating silver or a silver compound on the surface of the copper powder while stirring can be used.

  As this solvent, water, an organic solvent, or a mixed solvent thereof can be used. When using a solvent in which water and an organic solvent are mixed, it is necessary to use an organic solvent that becomes a liquid at room temperature (20 to 30 ° C.), but the mixing ratio of water and the organic solvent depends on the organic solvent used. It can be adjusted appropriately. As water used as a solvent, distilled water, ion-exchanged water, industrial water or the like can be used if there is no risk of impurities being mixed in.

  Since silver ions must be present in the solution as a raw material for the silver layer, it is preferable to use silver nitrate, which has high solubility in water and many organic solvents. Further, in order to carry out the reaction of coating the copper powder with the silver layer (silver coating reaction) as uniformly as possible, not a solid silver nitrate but a silver nitrate solution prepared by dissolving silver nitrate in a solvent (water, an organic solvent or a mixture thereof). Is preferably used. The amount of silver nitrate solution, the concentration of silver nitrate in the silver nitrate solution and the amount of organic solvent used can be determined according to the intended amount of the silver layer.

  A chelating agent may be added to the solution in order to form the silver layer more uniformly. As the chelating agent, it is preferable to use a chelating agent having a high complex stability constant with respect to copper ions and the like so that copper ions and the like that are by-produced by the substitution reaction of silver ions and metallic copper do not reprecipitate. . In particular, since the copper powder serving as the core of the silver-coated copper powder contains copper as a main constituent element, it is preferable to select the chelating agent in consideration of the complex stability constant with copper. Specifically, as the chelating agent, a chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine and salts thereof can be used.

  A pH buffer may be added to the solution in order to carry out the silver coating reaction stably and safely. As this pH buffer, ammonium carbonate, ammonium hydrogen carbonate, aqueous ammonia, sodium hydrogen carbonate or the like can be used.

  During the silver coating reaction, before adding the silver salt, the copper powder is put in the solution and stirred, and the solution containing the silver salt is added while the copper powder is sufficiently dispersed in the solution. Is preferred. The reaction temperature in this silver coating reaction is not required to be the temperature at which the reaction solution solidifies or evaporates, but is preferably set in the range of 10 to 40 ° C, more preferably 15 to 35 ° C. The reaction time varies depending on the amount of silver or a silver compound and the reaction temperature, but can be set in the range of 1 minute to 5 hours.

  Hereinafter, examples of the conductive paste according to the present invention will be described in detail.

[Example 1]
Commercially available copper powder manufactured by the atomization method (atomized copper powder SF-Cu 5 μm, manufactured by Japan Atomization Co., Ltd.) was prepared, and the particle size distribution of this copper powder (before silver coating) was determined. The volume-based cumulative 10% particle diameter (D ₁₀ ) was 2.26 μm, the cumulative 50% particle diameter (D ₅₀ ) was 5.20 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 9.32 μm. The particle size distribution of the copper powder is measured by a laser diffraction type particle size distribution device (Microtrac particle size distribution measuring device MT-3300 manufactured by Nikkiso Co., Ltd.), and the volume-based cumulative 10% particle size (D ₁₀ ) is cumulative. The 50% particle size (D ₅₀ ) and the cumulative 90% particle size (D ₉₀ ) were determined.

  Further, a solution of 2.6 kg of ammonium carbonate dissolved in 450 kg of pure water (solution 1), a solution of 319 kg of EDTA-4Na (43%) and 76 kg of ammonium carbonate dissolved in 284 kg of pure water, and silver nitrate containing 16.904 kg of silver nitrate were added. A solution (solution 2) obtained by adding 92 kg of an aqueous solution was prepared.

  Next, in a nitrogen atmosphere, 100 kg of the above copper powder was added to the solution 1, and the temperature was raised to 35 ° C. with stirring. Solution 2 was added to the solution in which the copper powder was dispersed, and the mixture was stirred for 30 minutes, filtered, washed with water, and dried to obtain a copper powder coated with silver (silver-coated copper powder). The washing with water was carried out by pouring pure water on the solid content obtained by filtration until the potential of the liquid after washing became 0.5 mS / m or less.

  5.0 g of the silver-coated copper powder thus obtained was dissolved in 40 mL of an aqueous nitric acid solution having a specific gravity of 1.38 diluted with pure water to a volume ratio of 1: 1 and boiled with a heater to produce silver. After completely dissolving the coated copper powder, a hydrochloric acid aqueous solution having a specific gravity of 1.18 was diluted little by little with pure water to a volume ratio of 1: 1 to this aqueous solution to gradually add silver chloride, The aqueous solution of hydrochloric acid was continuously added until precipitation stopped, and the content of Ag was determined from the obtained silver chloride by a gravimetric method. As a result, the content of Ag in the silver-coated copper powder was 10.14 mass%.

Further, 0.1 g of this silver-coated copper powder was added to 40 mL of isopropyl alcohol and dispersed for 2 minutes with an ultrasonic homogenizer (tip tip diameter 20 mm), and then the particle size distribution of the silver-coated copper powder was measured by laser diffraction / scattering particle size. It was measured by a distribution measuring device (Microtrac MT-3300 EXII manufactured by Microtrac Bell Co., Ltd.). As a result, the volume-based cumulative 10% particle diameter (D ₁₀ ) of the silver-coated copper powder was 2.5 μm, the cumulative 50% particle diameter (D ₅₀ ) was 5.2 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 10. It was 0.1 μm.

The BET specific surface area of this silver-coated copper powder was measured by the BET one-point method using a BET specific surface area measuring device (4Sorb US manufactured by Yuasa Ionics Co., Ltd.). As a result, the BET specific surface area of the silver-coated copper powder was 0.31 m ² / g.

  In addition, 79.0 parts by weight of the obtained silver-coated copper powder, 8.8 parts by weight of silver powder having an average primary particle diameter of 1 μm (Ag-2-1C manufactured by DOWA Electronics Co., Ltd.), and the naphthalene skeleton shown in Chemical formula 1 were used. 6.5 parts by weight of an epoxy resin (HP4710 manufactured by Dainippon Ink and Chemicals, Inc.), 5.3 parts by weight of butyl carbitol acetate (manufactured by Wako Pure Chemical Industries, Ltd.) as a solvent, and imidazole (Shikoku Kasei Kogyo Co., Ltd. 2E4MZ) 0.3 parts by weight and oleic acid (manufactured by Wako Pure Chemical Industries Co., Ltd.) 0.1 part by weight as a dispersant. Manufactured by Awatori Kentaro, and then kneaded by three rolls (EXAKT80S manufactured by Otto Harman Co., Ltd.) (silver-coated copper powder and silver powder in total). Was obtained 7.8 mass% inclusive) conductive paste.

  Next, a conductive paste was printed in a line shape with a width of 500 μm and a length of 37.5 mm on an alumina substrate with a squeegee pressure of 0.18 MPa using a screen printing machine (MT-320T manufactured by Microtec Co., Ltd.), and then air circulation. After being heated at 150 ° C. for 10 minutes by a dryer, it was heated at 200 ° C. for 30 minutes to be dried and cured to form a conductive film. With respect to the conductive film thus formed, the line width was measured using a microscope (Digital Microscope VHK-5000 manufactured by Keyence Corporation), and a surface roughness meter (SE-30D manufactured by Kosaka Laboratory Ltd.) was measured. ) Is used to measure the average thickness, and a digital multimeter (Digital Multimeter R6551 manufactured by Advantest Corporation) is used to measure the resistance of the conductive film by applying terminals to both ends of the line-shaped conductive film. Then, the volume resistivity (initial volume resistivity) was calculated and found to be 85 μΩ · cm. In addition, the soldering iron at 380 ° C. is applied to the conductive film so that the same amount of heat as that at the time of soldering is applied to the conductive film, and the conductive film is moved at a speed of 10 mm / sec. Was measured and the volume resistivity (volume resistivity after heating) was calculated to be 91 μΩ · cm, and the rate of change of the volume resistivity after heating with respect to the initial volume resistivity was 107%.

[Example 2]
50 g of the same silver powder as in Example 1 was put in an electric coffee mill (Select Grind MJ-518 manufactured by Melita Japan Co., Ltd.) and crushed for 10 seconds, and then 10% by mass of adipic acid dissolved in ethanol was obtained. 0.35 g of ethanol solution of adipic acid was added and crushed for 20 seconds to prepare silver powder coated with adipic acid. Example 1 was repeated except that the conductive paste contained 0.006% by mass (0.07% by mass of silver) of adipic acid by using the silver powder coated with adipic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 79 μΩ · cm, the volume resistivity after heating was 86 μΩ · cm, and the rate of change in volume resistivity was 108%.

[Example 3]
By the same method as in Example 1 except that 0.006% by mass of adipic acid (0.07% by mass of adipic acid relative to silver) was added before mixing (preliminary kneading) (with silver-coated copper powder). A conductive paste containing silver powder in total of 87.8 mass% was prepared.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 81 μΩ · cm, the volume resistivity after heating was 87 μΩ · cm, and the change rate of the volume resistivity was 108%.

[Example 4]
Silver powder coated with azelaic acid was produced in the same manner as in Example 2 except that 0.35 g of a 10 mass% ethanolic azelaic acid solution obtained by using azelaic acid instead of adipic acid was added. . Example 1 except that the conductive paste contained 0.006% by mass (0.07% by mass with respect to silver) of azelaic acid using the silver powder coated with azelaic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 71 μΩ · cm, the volume resistivity after heating was 79 μΩ · cm, and the rate of change in volume resistivity was 110%.

[Example 5]
A silver powder coated with phthalic acid was produced in the same manner as in Example 2 except that 0.35 g of a 10 mass% ethanolic phthalate solution obtained by using phthalic acid instead of adipic acid was added. . This example was the same as Example 1 except that the conductive paste contained 0.006% by mass (0.07% by mass with respect to silver) of phthalic acid using the silver powder coated with phthalic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 95 μΩ · cm, the volume resistivity after heating was 98 μΩ · cm, and the rate of change in volume resistivity was 103%.

[Example 6]
Silver powder coated with phthalic anhydride was prepared in the same manner as in Example 2 except that 0.35 g of a 10% by mass ethanolic phthalic acid ethanol solution obtained by using phthalic anhydride instead of adipic acid was added. Was produced. Examples except that 0.006% by mass (0.07% by mass relative to silver) of phthalic anhydride was contained in the conductive paste by using this silver powder coated with phthalic anhydride A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method as in 1.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 87 μΩ · cm, the volume resistivity after heating was 92 μΩ · cm, and the volume resistivity change rate was 106%.

[Example 7]
A conductive paste (containing 87.8 mass% of silver-coated copper powder and silver powder in total) was prepared in the same manner as in Example 1, except that the amounts of silver-coated copper powder and silver powder were each set to 43.9 parts by weight. It was made.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 56 μΩ · cm, the volume resistivity after heating was 55 μΩ · cm, and the change rate of the volume resistivity was 99%.

[Example 8]
A silver powder coated with adipic acid was produced in the same manner as in Example 2 except that the amount of the adipic acid ethanol solution was 0.21 g. Example 7 except that the conductive paste contained 0.018% by mass (0.04% by mass with respect to silver) of adipic acid by using the silver powder coated with adipic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 36 μΩ · cm, the volume resistivity after heating was 36 μΩ · cm, and the rate of change in volume resistivity was 100%.

[Example 9]
A silver powder coated with adipic acid was produced in the same manner as in Example 2 except that the amount of the adipic acid ethanol solution was 0.35 g. Example 7 was repeated except that the conductive paste contained 0.031% by mass (0.07% by mass of silver) of adipic acid by using the silver powder coated with adipic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 37 μΩ · cm, the volume resistivity after heating was 38 μΩ · cm, and the rate of change in volume resistivity was 103%.

[Example 10]
A silver powder coated with adipic acid was produced in the same manner as in Example 2 except that the amount of the adipic acid ethanol solution was 0.49 g. Example 7 was repeated except that the conductive paste contained 0.043% by mass (0.10% by mass with respect to silver) of adipic acid by using the silver powder coated with the adipic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 41 μΩ · cm, the volume resistivity after heating was 42 μΩ · cm, and the volume resistivity change rate was 103%.

[Example 11]
A silver powder coated with adipic acid was produced in the same manner as in Example 2 except that the amount of the ethanol solution of adipic acid was changed to 0.63 g. This example was the same as Example 7 except that the conductive paste contained adipic acid in an amount of 0.055% by mass (0.13% by mass with respect to silver) using the silver powder coated with adipic acid. A conductive paste (containing 87.8% by mass of silver-coated copper powder and silver powder in total) was produced by the same method.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 43 μΩ · cm, the volume resistivity after heating was 45 μΩ · cm, and the volume resistivity change rate was 105%.

[Comparative Example 1]
In place of the epoxy resin having a naphthalene skeleton in the conductive paste 1, a bisphenol F type epoxy resin (EP4901E manufactured by ADEKA Co., Ltd.) shown in Chemical formula 2 was used, and the amount of silver-coated copper powder was 79.9 parts by weight. A conductive paste (containing 88.8% by mass of silver-coated copper powder and silver powder in total) was prepared by the same method as in Example 1 except that the amount of silver powder was 8.9 parts by weight.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 68 μΩ · cm, the volume resistivity after heating was 142 μΩ · cm, and the volume resistivity change rate was 210%.

[Comparative Example 2]
Instead of the epoxy resin having a naphthalene skeleton, a bisphenol F type epoxy resin shown in Chemical formula 2 (EP4901E manufactured by ADEKA Co., Ltd.) is used, the amount of silver-coated copper powder is 79.9 parts by weight, and the amount of silver powder is 8 A conductive paste (containing a total of 88.8% by mass of silver-coated copper powder and silver powder) was prepared by the same method as in Example 2 except that the amount was 1.9 parts by weight.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 49 μΩ · cm, the volume resistivity after heating was 103 μΩ · cm, and the change rate of the volume resistivity was 211%.

[Comparative Example 3]
By the same method as in Example 1 except that the bisphenol A type epoxy resin (JER828 manufactured by Mitsubishi Chemical Corporation) shown in Chemical formula 3 was used instead of the epoxy resin having a naphthalene skeleton (silver-coated copper powder and silver powder Of 87.8 mass% in total) was prepared.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 235 μΩ · cm, the volume resistivity after heating was 510 μΩ · cm, and the volume resistivity change rate was 217%.

[Comparative Example 4]
By the same method as in Example 1 except that an epoxy resin having a biphenyl skeleton shown in Chemical formula 4 (NC-3000-H manufactured by Nippon Kayaku Co., Ltd.) was used instead of the epoxy resin having a naphthalene skeleton, A conductive paste was prepared containing the coated copper powder and the silver powder in total of 87.8 mass%.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 185 μΩ · cm, the volume resistivity after heating was 866 μΩ · cm, and the volume resistivity change rate was 468%.

[Comparative Example 5]
By the same method as in Example 1 except that an epoxy resin having a cyclopentadiene skeleton shown in Chemical formula 5 (XD-1000 manufactured by Nippon Kayaku Co., Ltd.) was used instead of the epoxy resin having a naphthalene skeleton (silver coating A total of 87.8% by mass of copper powder and silver powder was prepared) to prepare a conductive paste.

  Using the conductive paste thus obtained, a conductive film was formed by the same method as in Example 1, the volume resistivity after initial heating and after heating was calculated, and the rate of change in volume resistivity due to heating was calculated. The initial volume resistivity was 183 μΩ · cm, the volume resistivity after heating was 275 μΩ · cm, and the volume resistivity change rate was 150%.

  The results of these Examples and Comparative Examples are shown in Tables 1 and 2.

As can be seen from Tables 1 and 2, when the conductive pastes of Examples 1 to 11 were used to form the conductive film, the conductive films were soldered more than when the conductive pastes of Comparative Examples 1 to 5 were used. Even if heated to the temperature of 1, the increase in volume resistivity of the conductive film can be prevented.
The formation of the conductive film a conductive paste containing a dicarboxylic acid of rational formula, such as adipic acid or azelaic acid _{HOOC- (CH 2) n -COOH (} n = 1~8) as in Examples 2-4 When a conductive paste containing no dicarboxylic acid is used as in Example 1 or when a conductive formula such as phthalic acid or phthalic anhydride is used as in Examples 5 to 6, the rational formula is HOOC- (CH ₂ ). compared with the case of using a conductive paste containing a dicarboxylic acid is not a _n -COOH _(n = _1~8), it is possible to lower the volume resistivity after heating of the conductive film.

  The conductive paste according to the present invention can be used for producing a conductor pattern of a circuit board, electrodes of a substrate such as a solar cell, and electronic parts such as a circuit. For example, it can be used for producing a bus bar electrode of a solar battery, or can be used as an adhesive (bonding electrode) for bonding two solar battery cells used as a roof plate type cell (Shingled-cell).

Claims (15)

A total of 100 mass% of silver-coated copper powder whose surface is coated with a silver layer, silver powder, an epoxy resin having an epoxy resin having a naphthalene skeleton, a solvent, a curing agent, and a dispersant. Characteristic conductive paste. A total of 100 mass of the silver-coated copper powder having the surface of the copper powder coated with a silver layer, the silver powder, the epoxy resin having an epoxy resin having a naphthalene skeleton, the solvent, the curing agent, the dispersant, and the dicarboxylic acid. % Of the conductive paste. The conductive paste according to claim 2, wherein the dicarboxylic acid is attached to the silver powder. The dicarboxylic acid is rational formula is HOOC- _{(CH 2)} n -COOH, wherein the (n = 1 to 8) is a dicarboxylic acid, a conductive paste according to claim 2 or 3. The conductive paste according to claim 4, wherein n in the rational formula is 4 to 7. The conductive paste according to claim 2, wherein the amount of the dicarboxylic acid is 0.01 to 0.25 mass% with respect to the silver of the silver layer and the silver of the silver powder. The amount of the said dicarboxylic acid is 0.1 mass% or less with respect to the said conductive paste, The conductive paste in any one of Claim 2 thru | or 5 characterized by the above-mentioned. The solvent is 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. 4. One or more of alcohol, dihydroterpineol, dihydroterpineol acetate, ethyl carbitol, and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (texanol), characterized in that 8. The conductive paste according to any one of 7 to 7. The conductive paste according to claim 1, wherein the curing agent is at least one of imidazole and a boron trifluoride amine-based curing agent. The conductive paste according to claim 1, wherein the silver-coated copper powder has an average particle diameter of 1 to 20 μm, and the silver powder has an average particle diameter of 0.1 to 3 μm. . The amount of the silver-coated copper powder in the conductive paste is 40 to 94% by mass, the amount of the silver powder is 4 to 58% by mass, and the total amount of the silver-coated copper powder and the silver powder is 75 to 98 % by mass. The conductive paste according to claim 1, wherein the conductive paste is present. The amount of the said silver layer with respect to the said silver coating copper powder is 5 mass% or more, The electroconductive paste in any one of Claim 1 thru | or 11 characterized by the above-mentioned. The conductive paste according to any one of claims 1 to 12, wherein the content of the epoxy resin having the naphthalene skeleton is 1 to 20% by mass based on the conductive paste. Characterized in that said content of the epoxy resin having a naphthalene skeleton is 3 to 10 wt% with respect to the conductive paste, the conductive paste according to any one of claims 1 to 10. The conductive paste was printed in a line shape with a width of 500 μm and a length of 37.5 mm on an alumina substrate with a screen printing machine squeegee pressure of 0.18 MPa, and then heated at 150 ° C. for 10 minutes by an atmospheric circulation dryer and then 200 ° C. By heating for 30 minutes to dry and cure, a conductive film is formed. With respect to this conductive film, the line width is measured using a microscope, and the average thickness is measured using a surface roughness meter. At the same time, the resistance of the conductive film is measured by applying terminals to both ends of the linear conductive film using a digital multimeter, and the volume resistivity (initial volume resistivity) is calculated. When applying a soldering iron of ℃ to the conductive film and moving it at a speed of 10 mm / sec, measuring the resistance of the conductive film after heating and calculating the volume resistivity (volume resistivity after heating), Rate of change of the volume resistivity after heating to the volume resistivity of the period is characterized by a 99 to 110%, the conductive paste according to any one of claims 1 to 14.