JP6796448B2 - Conductive paste and its manufacturing method, and solar cell - Google Patents

Description

The present invention relates to a conductive paste, a method for producing the same, and a solar cell.

Conventionally, a conductive paste in which silver powder is dispersed in an organic component has been used in order to form electrodes and circuits of solar cells, electrodes and circuits of electronic parts, electromagnetic wave shielding films, electromagnetic wave shielding materials, and the like.
As a silver powder for such a conductive paste, a silver powder having a carboxylic acid such as stearic acid or oleic acid on the surface has been proposed in order to obtain one having less aggregation and excellent dispersibility (for example, patent). References 1 and 2 etc.).
Further, a method has been proposed in which a reducing agent is added to an aqueous solution containing silver to reduce and precipitate silver powder, and then a polyvalent carboxylic acid such as succinic acid or adipic acid is added to perform surface treatment (for example, patent). Reference 3).

Japanese Unexamined Patent Publication No. 2006-97086 Japanese Unexamined Patent Publication No. 2006-89768 Japanese Unexamined Patent Publication No. 2011-140714

In recent years, with the thinning of electrodes of solar cells, it has been desired to provide a conductive paste having a lower viscosity. When the viscosity of the conductive paste is low, the viscosity adjustment due to the addition of the solvent can be reduced and the silver content can be increased, so that the conductivity can be increased. If the conductivity of the conductive paste is increased, the efficiency of the solar cell is also improved.
Therefore, it is desired to promptly provide a measure capable of reducing the viscosity and the resistance of the conductive paste.

An object of the present invention is to solve the above-mentioned problems in the past and to achieve the following object. That is, an object of the present invention is to provide a conductive paste having a low viscosity and capable of achieving a low resistance, a method for producing the same, and a solar cell.

As a result of diligent studies by the present inventor in order to solve the above problems, by combining silver powder in which alkenyl succinic anhydride is detected by gas chromatography mass spectrometry with a specific solvent, the viscosity becomes low and the conductivity becomes conductive. It was found that the silver content in the paste can be increased and a low resistance conductive paste can be obtained.

The present invention is based on the above-mentioned findings by the present inventor, and the means for solving the above-mentioned problems are as follows. That is,
<1> Silver powder in which alkenyl succinic anhydride having 13 or more carbon atoms is detected by gas chromatographic mass spectrometry,
It is a conductive paste characterized by containing a solvent containing a compound having a glycol structure.
<2> Silver powder in which alkenyl succinic anhydride having 13 or more carbon atoms is detected by gas chromatographic mass spectrometry,
As the solvent, at least one selected from butyl carbitol acetate (BCA), butyl carbitol (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC) and dipropylene glycol monomethyl ether (DPGE), and It is a conductive paste characterized by containing.
<3> The above <1> or <2>, wherein the content of the filler containing the silver powder is 70% by mass or more and 95% by mass or less, and the content of the solvent is 20% by mass or less. The conductive paste described.
<4> The above-mentioned <1> to <3>, wherein the binder further contains a binder, and the binder is at least one selected from a cellulose derivative, an epoxy resin, and a polyester resin. It is a conductive paste.
<5> A method for producing a conductive paste, which comprises a step of mixing a silver powder in which alkenyl succinic anhydride is detected by gas chromatography mass spectrometry and a solvent containing a compound having a glycol structure.
<6> Silver powder in which alkenyl succinic anhydride is detected by gas chromatography mass spectrometry, butyl carbitol acetate (BCA), butyl carbitol (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC) and A method for producing a conductive paste, which comprises a step of mixing with at least one solvent selected from dipropylene glycol monomethyl ether (DPGE).
<7> In the process of producing silver powder in which alkenyl succinic anhydride having 13 or more carbon atoms is detected by gas chromatography mass spectrometry, a reducing agent is added to an aqueous solution containing silver to reduce and precipitate silver particles. The method for producing a conductive paste according to <5> or <6>, which comprises a step of recovering and washing silver powder after adding alkenyl succinic anhydride having 13 or more carbon atoms.
<8> Production of the conductive paste according to <7>, wherein the amount of alkenyl succinic anhydride added is 0.05% by mass or more and 2.0% by mass or less with respect to the mass of silver. The method.
<9> The solar cell is characterized by having an electrode formed by using the conductive paste according to any one of <1> to <4>.

According to the present invention, it is possible to provide a conductive paste having a low viscosity and a low resistance, a method for producing the same, and a solar cell, which can solve conventional problems.

FIG. 1 is an SEM photograph (10,000 times) of the silver powder produced in Production Example 1. FIG. 2 is an SEM photograph (10,000 times) of the silver powder produced in Comparative Production Example 1. FIG. 3 is a GC-MS analysis profile using the silver powder pyrolyzer (EGA / Py3030D manufactured by Frontier Lab Co., Ltd.) manufactured in Production Example 1. FIG. 4 is a graph showing the relationship between the viscosity of the conductive paste and the type of solvent. FIG. 5 is a graph showing the relationship between the 1 rpm viscosity of the conductive paste and the type of binder. FIG. 6 is a graph showing the relationship between the type of alkenyl succinic anhydride in a conductive paste containing various alkenyl succinic anhydrides having 13 or more carbon atoms and the 1 rpm viscosity of the conductive paste after 24 hours.

(Conductive paste)
The conductive paste of the present invention contains a filler containing silver powder and a solvent, preferably contains a binder, and further contains other components as necessary.

<Silver powder>
The silver powder is a silver powder in which alkenyl succinic anhydride (hereinafter, also referred to as "alkenyl succinic anhydride") is detected by gas chromatographic mass spectrometry.
Here, the silver powder in which alkenyl anhydride succinic acid is detected by the gas chromatography-mass spectrometry (GC / MS) is a pyrolyzer (for example, a multi-shot pyrolyzer EGA / manufactured by Frontier Lab Co., Ltd.). By heating at 300 ° C. using Py3030D) and analyzing using a gas chromatograph mass spectrometer, it means that alkenyl anhydride succinic acid is contained in the component desorbed from the surface of the silver powder.
The reason for measurement by gas chromatography-mass spectrometry (GC / MS) is to mix alkenylsuccinic anhydride and / or silver powder adsorbed with alkenylsuccinic acid with toluene and examine the presence or absence of organic components eluted in toluene. However, alkenylsuccinic anhydride and / or alkenylsuccinic acid is not detected. Since alkenylsuccinic anhydride is detected by GC-MS using a pyrolyzer on the silver powder after the toluene treatment, the adsorption with silver in the silver powder of the present embodiment is not separated by toluene and does not separate by heating. It turns out that it is as strong as it is. From this, it is expected that the acid anhydride portion is cleaved (hydrolyzed) in the adsorbed state and chemisorbed with silver as alkenyl succinic acid, but an attempt was made to identify the adsorbed organic substance by FT-IR or the like. However, there was no evidence to determine if it was alkenyl succinic acid. Therefore, regardless of the form of adsorption with silver, it is certain that alkenyl succinic anhydride is detected by gas chromatographic mass spectrometry. Therefore, the silver powder of the present invention is subjected to gas chromatographic mass spectrometry. It is a silver powder in which alkenyl succinic anhydride is detected.

It is preferable that the silver powder has alkenyl succinic anhydride and / or alkenyl succinic acid on the surface, and further has other components if necessary.

The silver powder is produced by adding alkenyl succinic anhydride to a slurry containing silver particles obtained by a wet reduction method, as described in detail in the method for producing silver powder described later, and as a result, a gas chromatographic mass spectrometry method. It is a silver powder in which alkenyl succinic anhydride is detected by.

-Alkenyl succinic anhydride, alkenyl succinic acid-
The alkenyl succinic anhydride is a succinic anhydride in which one of the hydrogen atoms is substituted with an alkenyl group, and has a structure different from that of succinic anhydride (succinic anhydride). The succinic anhydride is an intramolecular dehydration condensate of succinic acid, and when it comes into contact with water, it hydrolyzes back to succinic acid and reacts with ammonia to form succinic acid imide. On the other hand, the alkenyl succinic anhydride is a succinic anhydride having an alkenyl group (-C _n H _2n-1 ), and is also different from an alkyl group (-C _n H _{2n + 1} ) substituted succinic acid.
Since the succinic anhydride and the alkenyl succinic anhydride have different amounts of adhesion to the surface of the silver powder due to the difference in structure, the storage stability of the silver powder (aggregation and generation of lumps with time) differs. Further, when the succinic anhydride adheres to the surface of the silver powder, it becomes hydrophilic, but when the alkenyl succinic anhydride and / or alkenyl succinic acid adheres to the surface of the silver powder, it becomes hydrophobic.

The alkenyl succinic anhydride is preferably a compound represented by the following general formula (1).
However, in the general formula (1), R ¹ and R ² each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 22 carbon atoms.
R ¹ is preferably a linear alkyl group having 5 to 13 carbon atoms, and more preferably a linear alkyl group having 7 to 11 carbon atoms.
R ² is preferably a hydrogen atom or a linear alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom.
The position of the double bond of the alkenyl group is not limited to the above general formula (1), and may be a different position.

As the alkenyl succinic anhydride, one synthesized appropriately may be used, or a commercially available product may be used. Examples of the commercially available products include DSA and PDSA-DA manufactured by Sanyo Chemical Industry Co., Ltd .; Ricacid DDSA and Ricacid OSA manufactured by New Japan Chemical Co., Ltd .; and products of Tokyo Chemical Industry Co., Ltd.
As a method for synthesizing alkenyl succinic anhydride, for example, olefin and maleic anhydride can be synthesized by heating and stirring.
Examples of the olefin include 1-octene, 1-decene, 1-dodecene, 1-tetradecene, internally isomerized olefins thereof, and mixtures thereof. The internally isomerized olefin is not an α-olefin (an olefin whose double bond position connects carbons at the 1st and 2nd positions of the olefin), but a carbon chain whose double bond is higher than the α-position by some method. Means the olefin present inside the.
The alkenyl succinic anhydride may be a structural isomer thereof or a mixture of branched chain isomers of a fat chain.

Examples of the alkenyl succinic anhydride and / or alkenyl succinic acid include tetrapropenyl succinic acid anhydride, tetradecenyl succinic acid anhydride, dodecenyl succinic acid anhydride, pentadecenyl succinic acid anhydride, and hexadecenyl. Succinic anhydride, octadecenyl succinic anhydride, tetrapropenyl succinic acid, tetradecenyl succinic acid, dodecenyl succinic acid, pentadecenyl succinic acid, hexadecenyl succinic acid, octadecenyl succinic acid, etc. Can be mentioned. These may be used alone or in combination of two or more. From the viewpoint of storage stability and thermal decomposition, it is preferable that the alkenyl succinic anhydride and / or alkenyl succinic acid has more than 12 carbon atoms in the molecule, that is, 13 or more.
If the number of carbon atoms in the molecule of the alkenyl succinic anhydride and / or alkenyl succinic acid is 12 or less, the storage stability deteriorates and aggregation proceeds from the viewpoint of adsorption to the silver powder surface and steric hindrance. This is because the viscosity of the paste becomes high regardless of the above, and it may be difficult to use it as a conductive paste.

Here, the structural formulas of the tetrapropenyl succinic anhydride, tetradecenyl succinic anhydride, dodecenyl succinic anhydride, pentadecenyl succinic anhydride and the like will be specifically described below.

Tetrapropenyl succinic anhydride (“TPSA”, chemical formula: C ₁₆ H ₂₆ O ₃ , molecular weight 266.38)

Tetra decenyl succinic anhydride ( "TDSA", chemical _formula: C _{18 H} 30 _{O 3,} molecular weight: 294.44)

Dodecenyl succinic anhydride (“DSA”, chemical formula: C ₁₆ H ₂₆ O ₃ , molecular weight: 266.368)

-Pentadecenyl succinic anhydride ("PDSA", chemical formula: C ₁₉ H ₂₈ O ₃ , molecular weight: 304.414)

When alkenyl succinic anhydride is detected by gas chromatography-mass spectrometry, for example, silver powder having alkenyl succinic anhydride and / or alkenyl succinic acid on the surface is pyrolyzed by a thermal decomposition apparatus (for example, a mulch manufactured by Frontier Lab Co., Ltd.). It can be desorbed from the silver powder surface by heating at 300 ° C. using a shot pyrolyzer EGA / Py3030D) and analyzed using a GC-MS (gas chromatograph mass spectrometer) or the like. In the case of the above method, the alkenyl succinic acid on the surface of the silver powder is heated to cause intramolecular dehydration condensation, and both alkenyl succinic anhydride and / or alkenyl succinic acid are detected as alkenyl succinic anhydride.
The amount of alkenyl succinic anhydride and / or alkenyl succinic acid adhered to the surface of silver powder is preferably 2.0% by mass or less, more preferably 0.01% by mass or more and 1.0% by mass or less, based on the mass of silver. preferable.
When the amount of alkenyl succinic anhydride and / or alkenyl succinic acid adhered exceeds 2.0% by mass, the conductive film composed of alkenyl succinic anhydride and / or silver powder having alkenyl succinic acid on the surface is formed. Volume resistivity may deteriorate.

The amount of alkenyl succinic anhydride and / or alkenyl succinic anhydride adhering to the surface of the silver powder is such that alkenyl succinic anhydride is separated from the silver powder because there is no elution from the state of adhering to the silver powder to a general organic solvent. Direct quantitative measurement of is difficult.
Therefore, the total carbon content in the silver powder to which the alkenyl succinic anhydride and / or alkenyl succinic acid is adsorbed and the reducing agent or pH adjustment that is taken into the inside of the silver powder or adheres to the surface in the reaction for producing the silver powder. Adsorption of the alkenyl succinic anhydride on the silver powder surface by calculating the difference between the agent-derived carbon atom and the silver powder content and dividing the difference by the carbon content ratio in the added alkenyl succinic anhydride molecule. You can decide the amount. The content of carbon atoms derived from reducing agents and pH adjusters in the silver powder, which is taken into the inside of the silver powder or adheres to the surface in the reaction for producing the silver powder, is determined in the silver powder obtained by not adding a surface treatment agent. It can be obtained by measuring the carbon content.

-Other ingredients-
The component adhering to the surface of the silver powder is not limited to alkenyl succinic anhydride and / or alkenyl succinic acid, and may contain other components. The other components are not particularly limited and may be appropriately selected depending on the intended purpose. For example, fatty acids and fatty acid salts other than alkenyl succinic anhydride and / or alkenyl succinic acid, surfactants, organometallic compounds, etc. Examples include chelating agents and polymer dispersants.

<Manufacturing method of silver powder>
The method for producing silver powder includes at least a step of performing a surface treatment using alkenyl succinic anhydride, and preferably, alkenyl succinic anhydride is obtained by adding a reducing agent to an aqueous solution containing silver to reduce and precipitate silver particles. The surface treatment is performed by adding silver ion dispersion, the silver ion dispersion step, the silver reduction step, the surface treatment step of alkenyl succinic anhydride, the silver powder recovery and cleaning step, and the silver powder drying step. It is preferable to include and, and if necessary, other steps are included. Further, the surface treatment can be performed by using alkenyl succinic acid instead of the alkenyl succinic anhydride.

In the present invention, it is preferable to adsorb alkenylsuccinic anhydride and / or alkenylsuccinic acid on the silver surface in the production of silver powder. In particular, it is preferable that alkenylsuccinic anhydride and / or alkenylsuccinic acid is directly adsorbed on the surface of silver.
A conductive paste using silver powder when surface treatment is performed by adding alkenyl succinic anhydride to a slurry obtained by reducing and precipitating silver particles, and alkenyl succinic anhydride after obtaining silver powder using fatty acid as a surface treatment agent. When a conductive paste using silver powder obtained by dry mixing and a conductive paste using silver powder using a fatty acid as a surface treatment agent are produced, alkenyl succinic anhydride is separately added to the conductive paste. In comparison with, when alkenyl succinic anhydride is added to the slurry in which silver particles are reduced and precipitated based on the case where alkenyl succinic anhydride is not used, the viscosity of the conductive paste is the lowest and the resistance is lowered, and alkenyl succinic anhydride is used. When the acid is dry-mixed, the viscosity decreases to a medium level and the resistance decreases, and when added during the production of the conductive paste, the viscosity decreases but the resistance increases. That is, in the production of silver powder, it is possible to obtain both low viscosity and low resistance of the conductive paste for the first time by using silver powder in which alkenyl succinic anhydride and / or alkenyl succinic acid is adsorbed on the surface of silver in advance. it can.

The most preferable timing for adding alkenyl succinic anhydride is to add alkenyl succinic anhydride to the slurry obtained by reducing and precipitating the silver particles to perform surface treatment. Further, it is preferable to have a silver powder recovery and cleaning step after performing the surface treatment.
In the silver powder that was recovered and washed after adding the alkenyl succinic anhydride of the present embodiment, most of the excess alkenyl succinic anhydride or alkenyl succinic acid that was not adsorbed with silver was removed together with the washing water. Will be done. When alkenyl succinic anhydride was left attached to the silver powder surface by a dry process or the like without going through the recovery and washing steps, or when alkenyl succinic anhydride was added to the conductive paste, it could not be adsorbed on silver. Excessive alkenyl succinic anhydride will be present in the conductive paste, in which case the effect of reducing viscosity will be reduced.

-Silver ion dispersion liquid preparation process-
The liquid preparation step of the silver ion dispersion liquid is a step of preparing the silver ion dispersion liquid.
As the aqueous reaction system containing silver ions, an aqueous solution or slurry containing silver nitrate, a silver complex or a silver intermediate can be used.
The aqueous solution containing the silver complex can be produced by adding aqueous ammonia or an ammonium salt to the aqueous silver nitrate solution or the silver oxide suspension. Among these, in order for the silver powder to have an appropriate particle size and a spherical shape, it is preferable to use a silver ammine complex aqueous solution obtained by adding ammonia water to the silver nitrate aqueous solution.
Since the coordination number of ammonia in the silver ammine complex is 2, 2 mol or more of ammonia is added per 1 mol of silver. Further, if the amount of ammonia added is too large, the complex becomes too stable and reduction does not proceed easily. Therefore, the amount of ammonia added is preferably 8 mol or less per 1 mol of silver. By making adjustments such as increasing the amount of the reducing agent added, it is possible to obtain spherical silver powder having an appropriate particle size even if the amount of ammonia added exceeds 8 mol. Further, a pH adjuster may be added to the aqueous reaction system containing silver ions. The pH adjusting agent is not particularly limited, and general acids and bases can be used, and examples thereof include nitric acid and sodium hydroxide.

-Silver reduction process-
The silver reduction step is a step of reducing and precipitating silver with a reducing agent.
Examples of the reducing agent include ascorbic acid, sulfite, alkanolamine, hydrogen peroxide solution, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, sodium borohydride, hydroquinone, hydrazine, and hydrazine compounds. , Pyrogallol, glucose, formic acid, formic acid, anhydrous sodium sulfite, longalite and the like. These may be used alone or in combination of two or more. Among these, at least one selected from ascorbic acid, alkanolamine, sodium borohydride, hydroquinone, hydrazine and formalin is preferable, and hydrazine and formalin are particularly preferable.

By using the reducing agent, silver powder having an appropriate particle size can be obtained. The content of the reducing agent is preferably 1 equivalent or more with respect to silver in order to increase the reaction yield of silver. When a reducing agent having a weak reducing power is used, it is preferably 2 equivalents or more, more preferably 10 equivalents or more and 20 equivalents or less with respect to silver.
Regarding the method of adding the reducing agent, it is preferable to add the reducing agent at a rate of 1 equivalent / min or more in order to prevent agglutination of silver powder. The reason for this is not clear, but by adding the reducing agent in a short time, the reduction precipitation of silver powder occurs all at once, the reduction reaction is completed in a short time, and the generated nuclei are unlikely to aggregate. It is thought that the dispersibility will improve. Therefore, it is preferable that the addition time of the reducing agent is short. For example, the reducing agent may be added at a rate of 100 equivalents / minute or more, and the reaction may be completed in a shorter time during the reduction. It is preferable to stir the reaction solution. The liquid temperature during the reduction reaction is preferably 5 ° C. or higher and 80 ° C. or lower, and more preferably 15 ° C. or higher and 40 ° C. or lower.

The obtained silver powder is not particularly limited and may be appropriately selected depending on the intended purpose, but spherical or irregularly shaped silver powder is preferable. Here, the spherical shape means that the particle shape is spherical or substantially spherical when the silver powder is observed with a scanning electron microscope (SEM), and the sphericality of 100 particles (sphericity: when the particles are observed in the SEM photograph). (Diameter of the longest diameter part) / (Diameter of the shortest diameter part)) is 1.5 or less. The indefinite shape refers to silver powder whose particle shape is other than the spherical shape when the silver powder is observed by SEM photograph and which does not have the characteristics of a specific particle shape such as a columnar shape, a filamentous shape, a flat shape, and a dendritic shape. Say.

-Succinic anhydride and / or alkenyl succinic acid surface treatment step-
The surface treatment step of alkenyl succinic anhydride is a step of surface-treating silver powder with alkenyl succinic anhydride. The step of adding alkenyl succinic anhydride is not only to add alkenyl succinic anhydride to the slurry obtained in the reduction step, but also to hydrolyze alkenyl succinic anhydride instead of the alkenyl succinic anhydride. It is also possible to use an aqueous solution containing the obtained alkenyl succinic anhydride, alkenyl succinic anhydride and / or alkenyl succinic acid. Both alkenyl succinic anhydride and alkenyl succinic acid may be added, as an emulsion, or as a metal salt of alkenyl succinic acid. By adding a reducing agent to an aqueous solution containing silver to reduce and precipitate silver powder, and then adding the alkenyl succinic anhydride, alkenyl succinic anhydride and / or alkenyl succinic acid can be attached to the surface of the silver powder. The surface treatment step is not limited to the above, and alkenyl succinic anhydride and / or alkenyl succinic acid may be added to the aqueous solution during the reduction precipitation, but it is more preferable to add the silver powder after the reduction precipitation. preferable. By either method, alkenyl succinic anhydride is detected in the obtained silver powder by gas chromatographic mass spectrometry.
The amount of alkenyl succinic anhydride and / or alkenyl succinic acid added is preferably 0.05% by mass or more and 2.0% by mass or less, and 0.1% by mass or more and 1.0% by mass or less, based on the mass of silver. Is more preferable. In the process of adhering alkenyl succinic anhydride to the surface of silver powder, alkenyl succinic anhydride may be partially produced as a derivative of alkenyl succinic anhydride as a result.

-Silver powder recovery and cleaning process-
The silver powder recovery and cleaning step is a step of collecting and cleaning the obtained silver powder.
Since the obtained silver powder contains impurities, it is preferable to wash it.
Pure water is suitable as the cleaning solvent used for the cleaning. The collection and cleaning method is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include decantation and filter press. The end point of the washing can be determined by using the electric conductivity of the water after washing, and it is preferable to carry out the washing until the electric conductivity becomes 0.5 mS / m or less. Excess alkenyl succinic anhydride or alkenyl succinic acid that is not adsorbed with silver is removed with wash water in this step.

-Silver powder drying process-
The step of drying the silver powder is a step of drying the silver powder after the washing.
Since the washed silver powder contains a large amount of water, it is preferable to remove the water before use. Vacuum drying is preferable as the method for removing water. The drying temperature is preferably 100 ° C. or lower. If too much heat is applied, the silver powders will be sintered at the time of drying, which is not preferable.

-Other processes-
The obtained silver powder can be subjected to other steps such as a dry crushing step and a classification step, if necessary. Instead of the dry crushing step, the silver powder is put into a device capable of mechanically fluidizing the silver powder, and the silver powder is mechanically collided with each other to smooth the unevenness and angular portion of the surface of the silver powder. The surface smoothing treatment may be performed. Further, the classification treatment may be performed after the crushing or smoothing treatment. In addition, drying, crushing, and classification may be performed using an integrated device capable of drying, crushing, and classifying (for example, a dry meister or a micron dryer manufactured by Hosokawa Micron Co., Ltd.).

The silver powder having alkenyl succinic anhydride and / or alkenyl succinic acid on the surface obtained by the method for producing silver powder preferably has the following characteristics.

-BET specific surface area of silver powder-
The BET specific surface area of the silver powder can be measured by the BET one-point method by nitrogen adsorption using Maxorb HM-model 1210 (manufactured by MOUNTECH). In the measurement of the BET specific surface area, the degassing condition before the measurement is 60 ° C. for 10 minutes.
The BET specific surface area of the silver powder is preferably 0.1 m ² / g or more and 5.0 m ² / g or less, and more preferably 0.3 m ² / g or more and 2.0 m ² / g or less. If the BET specific surface area is less than 0.1 m ² / g, the size of the silver powder may become large and it may be difficult to draw fine wiring. If it exceeds 5.0 m ² / g, the conductive paste may be formed. When this is done, the viscosity becomes too high, so it is necessary to dilute the conductive paste before use, and the silver concentration in the conductive paste becomes low, which may cause the wiring to break.

-Silver particle size distribution-
The cumulative 50% particle size (D ₅₀ ) in the volume-based particle size distribution measured by the laser diffraction particle size distribution measurement method of the silver powder is preferably 0.05 μm or more and 6.0 μm or less, and more preferably 0.1 μm or more and 4.0 μm or less. preferable.
The ratio of the D _{50 to} the cumulative 90% particle diameter (D ₉₀ ) and the cumulative 10% particle diameter (D ₁₀ ) [(D ₉₀ −D ₁₀ ) / D ₅₀ ] is preferably 3.0 or less, preferably 2.0 or less. Is more preferable.
Similar to the BET specific surface area, if the particle size distribution of the silver powder is too large, it may be difficult to draw fine wiring, and if it is too small, it is difficult to increase the silver concentration in the conductive paste. Further, it is preferable that the silver powder has a narrow peak width of the particle size distribution, a small variation in the particle size, and is uniform.

The particle size distribution of the silver powder can be measured by a wet laser diffraction type particle size distribution measurement. That is, in the wet laser diffraction type particle size distribution measurement, 0.1 g of silver powder is added to 40 mL of isopropyl alcohol and dispersed for 2 minutes by an ultrasonic homogenizer having a chip diameter of 20 mm, and the laser diffraction scattering type particle size distribution measuring device (Microtrack Bell Co., Ltd.) Measured using a company-made MICROTORAC MT3300EXII). Graph the measurement results and obtain the frequency and accumulation of the particle size distribution of silver powder. The cumulative 10% particle size is referred to as D ₁₀ , the cumulative 50% particle size is referred to as D ₅₀ , and the cumulative 90% particle size is referred to as D ₉₀ .

-Ignition loss of silver powder-
The ignition loss of the silver powder is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.02% or more and 1.00% or less.
The ignition loss of the silver powder is carried out by weighing (w1) 2 g of the silver powder sample, putting it in a magnetic crucible, heating it at 800 ° C. for 30 minutes until it becomes constant, cooling it, and weighing it (w2). Can be obtained from.
Ignition loss (%) = [(w1-w2) / w1] x 100

-Filler containing silver powder-
The content of the silver powder in the conductive paste is not particularly limited and may be appropriately selected depending on the intended purpose. In addition to the silver powder, the conductive powder (referred to as a filler) contained in the conductive paste may separately contain a silver powder other than the silver powder or a metal powder such as a silver-coated copper powder. The content of the filler in the conductive paste is preferably 70% by mass or more and 95% by mass or less, and the proportion of the silver powder (silver powder in which alkenyl succinic anhydride is detected) in the filler is half or more. Is preferable.

<Solvent>
As the solvent, a solvent containing a compound having a glycol structure is used.
The compound having a glycol structure is a general term for glycols and esters or ethers of glycols. For example, ethylene glycol is mentioned as glycols, and butyl carbitol acetate (BCA), butyl carbitol (BC), and butyl carbitol (BC) are examples of solvents composed of glycol esters and ethers (also referred to as glycol ester solvents and glycol ether solvents). Typical examples are ethyl carbitol acetate (ECA), ethyl carbitol (EC), and dibutyl carbitol, and dipropylene glycol monomethyl ether (DPGE) and the like can be mentioned. These may be used alone or in combination of two or more.
The solvent is at least selected from butyl carbitol acetate (BCA), butyl carbitol (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC), and dipropylene glycol monomethyl ether (DPGE). By using only one kind, it is possible to realize a low viscosity of the conductive paste.
The compound having the glycol structure is preferably contained in an amount of 10% by mass or more of the components excluding the filler in the conductive paste. As long as the low viscosity of the conductive paste is not impaired, the compound having a glycol structure such as BCA, BC, ECA, EC and DPGE is used in combination with another solvent which is not a compound having a glycol structure. It may be a mixed solvent. When the mixed solvent is used, the proportion of the compound having a glycol structure in the mixed solvent is preferably 30% by mass or more.
Examples of the other solvent include toluene, methyl ethyl ketone, methyl isobutyl ketone, tetradecane, tetralin, propyl alcohol, isopropyl alcohol, dihydroterpineol, dihydroterpineol acetate, ethyl carbitol, 2,2,4-trimethyl-1,3-. Examples thereof include pentandiol monoisobutylate (texanol) and diethylene glycol mono-n-ethyl ether acetate.

<Binder>
The binder is not particularly limited and may be appropriately selected depending on the intended purpose. For example, cellulose derivatives such as methyl cellulose and ethyl cellulose, acrylic resin, alkyd resin, polypropylene resin, polyurethane resin, rosin resin, terpene resin and phenol. Resin, aliphatic petroleum resin, acrylic acid ester resin, xylene resin, kumaron inden resin, styrene resin, dicyclopentadiene resin, polybutene resin, polyether resin, urea resin, melamine resin, vinyl acetate resin, polyisobutyl resin, olefin Examples thereof include based thermoplastic elastomer (TPO), epoxy resin, polyester resin, and the like. These may be used alone or in combination of two or more. Among these, cellulose derivatives, epoxy resins, and polyester resins are preferable from the viewpoint of reducing the viscosity of the conductive paste.

<Other ingredients>
Examples of the other components include surfactants, glass frits, dispersants, viscosity modifiers and the like.

In order to specify the type of solvent or binder used in the conductive paste, for example, (1) 100 mL (solvent amount of about 1 mg / L) of acetone or ethanol is used for 1 mg of the conductive paste. Extract. (2) The extract is heated to 280 ° C. using GC-MS at 10 ° C./min to 20 ° C./min in a He stream. (3) Inject the volatile component into the cavity column. (4) It is possible by performing library collation from the measured molecular weight.

The content of the solvent in the conductive paste is preferably 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less.
The higher the content of the filler, the lower the volume resistivity when the conductive film is formed, but the viscosity increases and it becomes difficult to apply, so that a balance with the solvent is required. In the present invention, since the viscosity of the conductive paste is lowered, the amount of silver powder can be increased to reduce the amount of solvent, the need to reduce the silver concentration in order to reduce the viscosity is small, and the volume resistivity of the conductive film is lowered. be able to.
The contents of the binder and the other components can be appropriately set according to the combination with the solvent.

(Manufacturing method of conductive paste)
The method for producing a conductive paste of the present invention is a solvent containing silver powder in which alkenyl succinic anhydride is detected by gas chromatographic mass spectrometry and a compound having a glycol structure, particularly butyl carbitol acetate (BCA) and butyl carbitol. Includes the step of mixing with at least one solvent selected from (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC) and dipropylene glycol monomethyl ether (DPGE), and if necessary. Includes other steps.

In the process of producing silver powder in which alkenyl succinic anhydride having 13 or more carbon atoms is detected by gas chromatography mass spectrometry, a reducing agent is added to an aqueous solution containing silver to reduce and precipitate silver particles, and the number of carbon atoms is increased. It is preferable to include a step of recovering and washing the silver powder after adding 13 or more alkenyl succinic anhydride.
The amount of alkenyl succinic anhydride added is preferably 0.05% by mass or more and 2.0% by mass or less with respect to the mass of silver.

In the method for producing the conductive paste, silver powder in which alkenyl succinic anhydride is detected by gas chromatographic mass spectrometry, and butyl carbitol acetate (BCA), butyl carbitol (BC), ethyl carbitol acetate (ECA), and ethyl At least one solvent selected from carbitol (EC) and dipropylene glycol monomethyl ether (DPGE), preferably a binder, and optionally other components, such as ultrasonic dispersion, disper, 3-roll mill, and the like. Mix for a predetermined time using a ball mill, a bead mill, a twin-screw kneader, a self-rotating stirrer, or the like.

The viscosity of the conductive paste is preferably 1,000 Pa · s or less, preferably 10 Pa · s or more and 500 Pa · s or less at 25 ° C.
The viscosity of the conductive paste can be measured using, for example, a viscometer (5HBDV-III ULTRA manufactured by Brookfield) at a cone spindle CP-52 and a paste temperature of 25 ° C.

The volume resistivity of the conductive film obtained by using the conductive paste is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 1 × 10 ^-4 Ω · cm or less, and 5 × 10 ^-5 Ω · cm or less is more preferable, and 1 × 10 ^-5 Ω · cm or less is further preferable. When the volume resistivity is 1 × 10 ^-4 Ω · cm or less, a conductive film having an extremely low volume resistivity can be realized. If the volume resistivity exceeds 1 × 10 ^-4 Ω · cm, the conductivity of the conductive film may be insufficient.
For the volume resistivity of the conductive film, for example, a digital multimeter (manufactured by ADVANTEST, R6551) is used to measure the resistance value between two points in the longitudinal direction of the conductive film, and the volume resistivity = resistivity × (conductivity). It can be measured by calculating (thickness of film × width of conductive film ÷ length of conductive film).

The conductive paste of the present invention is a film in which a transparent conductive film is further provided directly on various substrates such as a silicon wafer for a solar cell, a film for a touch panel, and glass for an EL element, or, if necessary, on a substrate. It can be preferably applied or printed on top to form a conductive film.
The conductive film obtained by using the conductive paste of the present invention includes, for example, a current collecting electrode of a solar cell, an external electrode of a chip-type electronic component, an RFID, an electromagnetic wave shield, a vibrator adhesive, a membrane switch, electroluminescence, etc. Suitable for electrodes or electrical wiring applications.
The solar cell of the present invention has an electrode formed by using the conductive paste of the present invention.

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

The methods for measuring the BET specific surface area of silver powder, the tap density of silver powder, the ignition loss of silver powder, and the particle size distribution of silver powder (D ₁₀ , D ₅₀ , and D ₉₀ ) are as shown below.

<Measurement method of BET specific surface area>
The BET specific surface area of the silver powder is Maxorb HM-model 1210 (manufactured by MOUNTECH), using a carrier gas of He: 70% and N ₂ : 30%, and 3 g of silver powder is put into a cell and degassed at 60 ° C. for 10 minutes. After that, the measurement was performed by the BET 1-point method.

<Measurement method of tap density>
For the tap density of silver powder, use a tap density measuring device (manufactured by Shibayama Kagaku Co., Ltd., bulk specific gravity measuring device SS-DA-2), weigh 15 g of silver powder, put it in a container (20 mL test tube), and with a head of 20 mm. It was tapped 1,000 times and calculated from tap density = sample weight (15 g) / (sample volume after tapping).

<Measuring method of particle size distribution (D ₁₀ , D ₅₀ , and D ₉₀ )>
The particle size distribution of silver powder is determined by adding 0.1 g of silver powder to 40 mL of isopropyl alcohol using a laser diffraction / scattering type particle size distribution measuring device (MICROTORAC MT3300EXII, manufactured by Microtrac Bell Co., Ltd.) and using an ultrasonic homogenizer with a chip diameter of 20 mm. The sample was prepared by dispersing for a minute, and the particle size was measured in the total reflection mode. From the volume-based cumulative distribution obtained by the measurement, the values of the cumulative 10% particle size (D ₁₀ ), the cumulative 50% particle size (D ₅₀ ), and the cumulative 90% particle size (D ₉₀ ) were determined.

<Ignition loss of silver powder>
The ignition loss of silver powder is ignited by weighing 2 g of the silver powder sample (w1), putting it in a magnetic crucible, heating it at 800 ° C. for 30 minutes until it becomes constant, cooling it, and weighing it (w2). I asked.
Ignition loss (%) = [(w1-w2) / w1] x 100

<Qualitative analysis of alkenyl succinic anhydride and / or alkenyl succinic acid on the surface of silver powder>
By heating the silver powder at 300 ° C. using a thermal decomposition apparatus (multi-shot pyrolyzer EGA / Py3030D manufactured by Frontier Lab Co., Ltd.), alkenyl succinic anhydride and / or alkenyl succinic acid is desorbed from the surface of the silver powder. , GC-MS (Gas Chromatomass Spectrometer, 7890A / 5975C manufactured by Agilent Technologies, Inc.) was used to perform a qualitative analysis of alkenyl succinic anhydride on the surface of silver powder. In the case of the above method, regardless of whether the added alkenyl succinic anhydride is present on the surface of the silver powder in the state of alkenyl succinic anhydride or in the state of alkenyl succinic acid, the alkenyl succinic acid is heated to be intramolecular. Both are detected as alkenyl succinic anhydride due to dehydration condensation.

(Manufacturing Example 1)
-Making silver powder-
Prepare 3,600 g of a silver nitrate aqueous solution containing 52 g of silver, add 160 g of an ammonia aqueous solution having a concentration of 28 mass% (manufactured by Junsei Chemical Co., Ltd., special grade reagent) to the silver nitrate aqueous solution, and add 4 g of a 20 mass% sodium hydroxide aqueous solution. An aqueous reaction system containing silver nitrate was prepared, and the liquid temperature was set to 28 ° C. 240 g of a 37 mass% formalin aqueous solution (manufactured by Nihon Kasei Corporation) was added as a reducing agent to the aqueous reaction system containing silver ions, and the mixture was sufficiently stirred to obtain a slurry containing silver particles.
Next, 0.1 g (0.19% by mass with respect to silver) of tetrapropenyl succinic anhydride (TPSA, manufactured by Tokyo Chemical Industry Co., Ltd.) was added as a surface treatment agent to the obtained slurry containing silver particles. In addition, it was aged after being sufficiently stirred. The aged slurry was filtered, washed with water, dried and crushed to obtain the silver powder of Production Example 1.
FIG. 1 shows an SEM photograph (10,000 times) of the obtained silver powder of Production Example 1 by a scanning electron microscope (SEM, manufactured by Nippon Denshi Kogyo Co., Ltd., JSM-IT300LV). Table 1 shows the measurement results of the BET specific surface area of the obtained silver powder, the tap density of the silver powder, the ignition loss of the silver powder, and the particle size distribution of the silver powder (D ₁₀ , D ₅₀ , and D ₉₀ ).
As a result of analysis of the silver powder by GC-MS, the tetrapropenyl succinic anhydride was detected, and it was found that tetrapropenyl succinic anhydride and / or tetrapropenyl succinic acid was attached to the surface of the silver powder. FIG. 3 shows a GC-MS analysis profile using a silver powder pyrolyzer (multi-shot pyrolyzer EGA / Py3030D manufactured by Frontier Lab Co., Ltd.). FIG. 3 is a profile extracted with a mass-to-charge ratio (m / z) of 266. This measurement result was referred to the library and identified as tetrapropenyl succinic anhydride.

(Comparative Manufacturing Example 1)
-Making silver powder-
In Production Example 1, 0.1 g of tetrapropenyl succinic anhydride as a surface treatment agent was changed to 0.1 g of stearic acid (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) in the same manner as in Production Example 1. Then, the silver powder of Comparative Production Example 1 was prepared and evaluated in the same manner. The results are shown in Table 1. The SEM photograph (10,000 times) of the obtained silver powder of Comparative Production Example 1 is shown in FIG.
As a result of analysis of silver powder by GC-MS, stearic acid was detected, and it was found that stearic acid was attached to the surface of silver powder.

(Experimental Example 1)
<Selection of solvent for conductive paste>
-Conductive paste No. Preparation of 1-
With respect to 90 parts by mass of the obtained silver powder of Production Example 1, 100 cps of ethyl cellulose (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.8 parts by mass of butyl carbitol acetate (BCA, manufactured by Wako Pure Chemical Industries, Ltd.) 9. Add 2 parts by mass, mix using a propellerless self-rotating stirring and defoaming device (Sinky Co., Ltd., AR-250), and then gradually increase the roll gap using a 3-roll mill (EXAKT, EXAKT80S). Pass through while narrowing to the conductive paste No. I got 1.

-Conductive paste No. Preparation of 2-14-
The conductive paste No. In No. 1, the conductive paste No. 1 was used, except that the type of silver powder and the type of solvent were changed as shown in Table 2. In the same manner as in No. 1, the conductive paste No. 2 to 14 were prepared.

Next, the viscosity of each of the obtained conductive pastes was measured as follows. The results are shown in Table 2 and FIG.

<Viscosity of conductive paste>
The viscosity of each of the obtained conductive pastes was measured using a viscometer (5HBDV-III ULTRA manufactured by Brookfield) at a cone spindle CP-52 and a paste temperature of 25 ° C. The value was measured for 5 minutes at ¹ rpm (slip speed 2 sec ^-1 ).

* BCA: Butylcarbitol acetate (manufactured by Wako Pure Chemical Industries, Ltd., 2- (2-butoxyethoxy) ethyl acetate)
* BC: Butylcarbitol (manufactured by Wako Pure Chemical Industries, Ltd., 2- (2-butoxyethoxy) ethanol)
* ECA: Ethyl carbitol acetate (manufactured by Wako Pure Chemical Industries, Ltd., 2- (2-ethoxyethoxy) ethyl acetate)
* EC: Ethylcarbitol (manufactured by Wako Pure Chemical Industries, Ltd., 2- (2-ethoxyethoxy) ethanol * DPGE: Dipropylene glycol monomethyl ether (manufactured by Wako Pure Chemical Industries, Ltd.)
* TPO: Terpineol (manufactured by Wako Pure Chemical Industries, Ltd., terpineol)
* TEX: Texanol (manufactured by JNC Corporation, CS12)

From the results of Table 2 and FIG. 4, the silver powder of Production Example 1 has a lower viscosity of the conductive paste than the silver powder of Comparative Production Example 1 in the five solvents of BCA, BC, ECA, EC and DPGE. It turns out that it can be achieved. Further, it was found that the effect of reducing the viscosity of the conductive paste was high in the five solvents of BCA, BC, ECA, EC and DPGE, and it was particularly remarkable in ECA. On the other hand, when TPO or TEX was used as the solvent, the silver powder of Production Example 1 tended to have a higher viscosity than the silver powder of Comparative Production Example 1. From this, it was found that a combination of silver powder in which alkenyl succinic anhydride is detected by gas chromatographic mass spectrometry and a solvent of any one of BCA, BC, ECA, EC and DPGE produces a conductive paste having a low viscosity. It was.

(Experimental Example 2)
<Selection of binder for conductive paste>
-Conductive paste No. Preparation of 15-18-
The conductive paste No. 1 and No. In No. 2, the conductive paste No. 2 was used, except that the type of binder was changed to the epoxy resin or polyester resin shown in Table 3 and the paste composition was adjusted. 1 and No. In the same manner as in No. 2, the conductive paste No. 15-18 were made.
The viscosity of each of the obtained conductive pastes was measured in the same manner as in Experimental Example 1. The results are shown in Table 3 and FIG. The values were measured at 1 rpm (sliding speed 2 sec ^-1 ) for 5 minutes and at 5 rpm (sliding speed 10 sec ^-1 ) for 1 minute.

* Ethyl cellulose: Ethyl cellulose 100 cps (manufactured by Wako Pure Chemical Industries, Ltd.)
* Epoxy resin: ADEKA Corporation, EP4901E
* Polyester resin: Toyobo Co., Ltd., Byron 200

From the results of Table 3 and FIG. 5, in BCA, which is one of the solvents whose viscosity was lowered in Table 2, the silver powder of Production Example 1 was compared even when the type of binder was changed from ethyl cellulose to epoxy resin or polyester resin. It was found that the viscosity of the conductive paste could be made lower than that of the silver powder of Production Example 1. The same tendency can be seen in the other four solvents whose viscosities have decreased in Table 2.
In addition, No. 1 and No. Even when the binder is changed from ethyl cellulose to hydroxyethyl cellulose (manufactured by CELLOSIZE QP 09L THE DOWN CHEMICAL COMPANY) and the solvent is changed from BCA to ethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.) for the conductive paste of No. Although it was low, the viscosity of Production Example 1 tended to be lower than that of Comparative Production Example 1.

(Example 1)
-Preparation of conductive paste-
85.8% by mass of the silver powder of Production Example 1 as a conductive powder, 1.95% by mass of solvent A (manufactured by Wako Pure Chemical Industries, Ltd., BCA: butyl carbitol acetate) as a solvent, and solvent B (JNC Co., Ltd.) TEX: Texanol, CS12) 1.95% by mass, ethyl cellulose 10 cps (manufactured by Wako Pure Chemical Industries, Ltd.) as a vehicle, 30% by mass, solvent A (BCA) 35% by mass, solvent B (TEX) 35% by mass. 3.9% by mass dissolved in the mixed solvent of Wako Pure Chemical Industries, Ltd., 0.18% by mass of bismuth oxide (manufactured by DOWA Hightech Industries, Ltd.), 1.59% by mass of glass (ASF-1898B, manufactured by Asahi Glass Co., Ltd.), as other components. Tellurium dioxide 3.9% by mass (manufactured by Wako Pure Chemical Industries, Ltd.), magnesium stearate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.24% by mass and oleic acid (manufactured by Wako Pure Chemical Industries, Ltd.) 0.49% by mass Weighed to%%, mixed (preliminarily kneaded) with a self-revolving stirrer (Sinky Co., Ltd., ARE-250), and then kneaded with three rolls (EXAKT, M-80S). The conductive paste of Example 1 was obtained.
The viscosity of the obtained conductive paste was measured using a CP-52 cone plate on a viscometer (5HBDV-III ULTRA manufactured by Brookfield), and the viscosity at 1 rpm for 5 minutes was 450 ± 30 Pa · s. I confirmed that it would be.

(Comparative Example 1)
-Preparation of conductive paste-
A conductive paste of Comparative Example 1 was prepared in the same manner as in Example 1 except that the silver powder of Comparative Production Example 1 was used.
When the viscosity of the obtained conductive paste was measured, the conductive paste of Comparative Example 1 using the silver powder of Comparative Production Example 1 had a higher viscosity than that of Example 1. A mixed solvent having a mass ratio of BCA and TEX of 1: 1 was additionally added in an amount of 0.83% by mass based on the paste amount according to the viscosity, and CP was added to a viscometer (5HBDV-III ULTRA manufactured by Brookfield). Using a −52 cone plate, the viscosity was adjusted so that the viscosity at 5 minutes at 1 rpm was 450 ± 30 Pa · s.
Due to the addition of the above mixed solvent, the silver concentration in the conductive paste of Comparative Example 1 has been reduced from 85.8% by mass to 85.1% by mass.

-Making a conductive film-
Next, using the obtained conductive paste, a printed pattern film was formed on a Si substrate by screen printing. The screen printing conditions were as follows.
-Printing equipment: MT-320T manufactured by Microtech
・ Plate: Line width 500 μm, routing 37.5 mm, 250 mesh, wire diameter 23 μm
-Printing conditions: squeegee pressure 180 Pa, printing speed 80 mm / s, clearance 1.3 mm

The obtained membrane was heat-treated at 150 ° C. for 10 minutes using an atmospheric circulation dryer. Next, using a high-speed firing furnace, firing was performed at 820 ° C. for 32 seconds to prepare a conductive film for measuring volume resistivity.
The volume resistivity of the conductive film was determined as follows. The results are shown in Table 4.

-Volume resistivity of conductive film-
Using a digital multimeter (R6551 manufactured by ADVANTEST), the resistance value at the position of the length (interval) of each conductive film was measured. The volume of the conductive film was obtained from the size (average thickness, width, length) of each conductive film, and the volume resistivity was obtained from this volume and the measured resistance value.

Next, using each of the obtained conductive pastes, a solar cell was prepared as follows, and the characteristics of the solar cell were evaluated as follows. The results are shown in Table 4.

-Manufacturing of solar cells-
A screen printing machine (Microtech, MT-320T) is used on a silicon substrate for solar cells (80Ω / □), and an aluminum paste (Toyo Aluminum Co., Ltd., Alsolar 14-7021) is used on the back surface of the substrate. A solid pattern of 154 mm □ was formed.
It was dried at 200 ° C. for 10 minutes using a hot air dryer.
A finger electrode having a width of 40 μm and three bus bar electrodes were formed on the surface of the substrate by using each conductive paste.
It was dried at 200 ° C. for 10 minutes using a hot air dryer.
Using a high-speed firing IR furnace (manufactured by NGK Insulators, Ltd.), high-speed heating was performed in-out 21 sec with a peak temperature (firing temperature) of 820 ° C. From the above, a solar cell was manufactured.

-Evaluation of solar cell characteristics-
The characteristics of each of the manufactured solar cells were evaluated using a solar simulator manufactured by WACOM. The results are shown in Table 4.

From the results in Table 4, since the viscosity of Example 1 is lower than that of Comparative Example 1, the necessity of adjusting the viscosity is small. Therefore, there is little need to reduce the silver concentration in order to reduce the viscosity, and the conductive paste of Example 1 can reduce the volume resistivity of the conductive film as compared with Comparative Example 1, and can improve the solar cell characteristics. I understood.

(Experimental Example 3)
-Conductive paste No. Preparation of 19-22-
Next, the results of investigating the difference depending on the timing of addition of alkenyl succinic anhydride will be described.
Since alkenyl succinic anhydride may be used as a curing agent for an epoxy resin as a binder, a general amine-based curing is performed in a conductive paste using an epoxy resin (manufactured by ADEKA Co., Ltd., EP4901E) as a binder. The effect of the present invention was investigated by comparing the case where the agent (BF ₃ NH ₂ Et) was used and the case where tetrapropenyl succinic anhydride (TPSA) was used as the curing agent in the conductive paste as the alkenyl succinic anhydride. .. Butyl carbitol acetate (BCA, manufactured by Wako Pure Chemical Industries, Ltd.) was used as the solvent. The results are shown in Table 5.

(Manufacturing Example 2)
-Preparation of silver powder of Production Example 2-
120 g of silver powder having stearic acid on the surface obtained in Comparative Production Example 1 and 0.216 g of tetrapropenyl succinic anhydride (TPSA, manufactured by Tokyo Chemical Industry Co., Ltd.) were dry-mixed using a crusher to obtain stearic acid. Tetrapropenyl succinic anhydride was further adhered to the surface of the silver powder on the surface to obtain the silver powder of Production Example 2.

Conductive paste No. From the results of 19 to 22, the production method of the present invention, that is, alkenyl succinic anhydride was added to the slurry containing the reduced silver particles, and then the slurry was filtered, washed with water, dried and crushed. It was found that the viscosity of the conductive paste was the lowest and the volume resistivity was the smallest when the silver powder of Production Example 1 was used.
Conductive paste No. When the alkenylsuccinic anhydride is further attached to the silver powder to which the fatty acid (stearic acid) is attached as in No. 21, the effect of reducing the viscosity and the volume resistivity is observed, but it is less than that of Production Example 1. I understood. Then, the conductive paste No. When alkenyl succinic anhydride is added as a curing agent to the conductive paste as in No. 22, although it has the effect of lowering the viscosity, the effect is weaker than that of the silver powder of Production Example 1, and the volume resistivity is greatly deteriorated. I understood. From the above, unless the silver powder to which the alkenyl succinic anhydride is attached in advance, such as the silver powder of Production Example 1 and the silver powder of Production Example 2, the effect of low viscosity and low resistance cannot be obtained, and further, Production Example 2 It was found that the silver powder of Production Example 1 had a greater effect of lowering the viscosity and the resistance than the silver powder of Production Example 1.

(Experimental Example 4)
-Conductive paste No. Preparation of 23-30-
Next, for various alkenyl succinic anhydrides having 12 or more carbon atoms, the binder was ethyl cellulose 100 cps (manufactured by Wako Pure Chemical Industries, Ltd.) and the solvent was butyl carbitol acetate (BCA, manufactured by Wako Pure Chemical Industries, Ltd.). In the case, the initial viscosity and the viscosity after allowing the conductive paste to stand for 24 hours were investigated. The results are shown in Table 6 and FIG.

(Production Examples 3 to 6 and Comparative Production Example 2)
-Preparation of silver powder of Production Examples 3 to 6 and Comparative Production Example 2-
In Production Example 1, as shown in Table 6, silver powders of Production Examples 3 to 6 and Comparative Production Example 2 were produced in the same manner as in Production Example 1 except that the type of alkenyl succinic anhydride as the surface treatment agent was different. .. Comparative Production Example 2 is a silver powder having octenyl succinic anhydride having 12 carbon atoms on its surface.

From the results in Table 6, the conductive paste No. 2 containing silver powder of Comparative Production Example 2 in which octenyl succinic anhydride having 12 carbon atoms was used as a surface treatment agent. In No. 30, the paste viscosity was high and it was difficult to make a paste.
Conductive paste No. 1 containing silver powder using alkenyl succinic anhydride having more than 12 carbon atoms as a surface treatment agent. In Nos. 23 to 27, the conductive paste No. 23 using the silver powder of Comparative Production Example 1 was used. It was found that not only the initial viscosity but also the viscosity after 24 hours tended to be lower than that of 28. Usually, the conductive paste No. As in 28, the viscosity tends to increase with time, and the conductive paste No. 28 Those having a characteristic that the viscosity decreases with time, such as 23 to 27, are also preferable in terms of extending the usable period of the conductive paste.
In addition, the conductive paste No. 1 using the silver powder of Comparative Production Example 1 was used. In contrast to No. 28, the conductive paste No. 28 using the silver powder of Production Example 1. Conductive paste No. 23 using 23 and the silver powder of Production Example 2. Compared with 29, the viscosity of the silver powder of Production Example 2 is lower than that of the case where tetrapropenyl succinic anhydride is not added, but the rate of decrease in viscosity is smaller than that of the silver powder of Production Example 1, and 24 It was also found that the tendency of the viscosity to decrease after time was also different.

The conductive paste of the present invention is suitable for, for example, electrodes for collecting electrodes of solar cells, external electrodes for chip-type electronic components, RFIDs, electromagnetic wave shields, vibrator adhesion, membrane switches, electroluminescence, or other electrodes or electrical wiring applications. Used for.

Claims (8)

It said silver powder carbon atoms 13 or more alkenyl succinic anhydride is detected by a gas chromatography mass spectrometry was heated at 300 ° C. desorbed from silver powder surface measured,
A conductive paste containing a solvent containing a compound having a glycol structure. It said silver powder carbon atoms 13 or more alkenyl succinic anhydride is detected by a gas chromatography mass spectrometry was heated at 300 ° C. desorbed from silver powder surface measured,
As the solvent, at least one selected from butyl carbitol acetate (BCA), butyl carbitol (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC) and dipropylene glycol monomethyl ether (DPGE), and A conductive paste characterized by containing. The conductive paste according to claim 1 or 2, wherein the content of the filler containing the silver powder is 70% by mass or more and 95% by mass or less, and the content of the solvent is 20% by mass or less. The conductive paste according to any one of claims 1 to 3, further comprising a binder, wherein the binder is at least one selected from a cellulose derivative, an epoxy resin, and a polyester resin. Said silver powder by gas chromatography mass spectrometry was heated at 300 ° C. desorbed from silver powder surface measured carbon number 13 or more alkenyl succinic anhydride is found, a solvent containing a compound having a glycol structure, a A method for producing a conductive paste, which comprises a step of mixing. It said silver powder carbon atoms 13 or more alkenyl succinic anhydride is detected by a gas chromatography mass spectrometry was heated at 300 ° C. desorbed from silver powder surface measured, butyl carbitol acetate (BCA), butyl carbitol Conduction comprising the step of mixing with at least one solvent selected from (BC), ethyl carbitol acetate (ECA), ethyl carbitol (EC) and dipropylene glycol monomethyl ether (DPGE). Method for producing sex paste. Manufacturing process of the silver powder carbon atoms by gas chromatography mass spectrometry was heated at 300 ° C. desorbed from silver powder surface measured 13 or more alkenyl succinic anhydride is detected, a reducing agent in an aqueous solution containing silver The fifth or sixth aspect of claim 5 or 6, wherein the slurry is obtained by reducing and precipitating silver particles by adding alkenyl succinic anhydride having 13 or more carbon atoms, and then recovering and washing the silver powder. A method for producing a conductive paste. The method for producing a conductive paste according to claim 7, wherein the amount of alkenyl succinic anhydride added is 0.05% by mass or more and 2.0% by mass or less with respect to the mass of silver.