JP2020132990A - Silver nanowire, production method therefor, silver nanowire-including reaction liquid and silver nanowire dispersing liquid - Google Patents

Abstract

To provide a silver nanowire extremely short in average diameter, advantageous in haze improvement of transparent conductive film in which the silver nanowire is used as a conductive material.SOLUTION: There is provided a silver nanowire having an average diameter of less than 20.0 nm, 100 or more in average aspect ratio Adefined by the expression (1): A=L/D(here, Land Dare the values representing the average length and diameter of the silver nanowire in nm unit, respectively), and 15.0% or less of a diameter variation coefficient CV. A polymer having a vinylpyrrolidone structural unit adheres to the surface of the nanowire. The silver nanowire is obtained by making the nanowire progress a reduction precipitation at a temperature of 50-90°C using an alcohol solvent containing total 40% or more of at least one type of 1,2-alkanediols having the carbon number of 4 to 6.SELECTED DRAWING: Figure 2

Description

The present invention is useful as a conductive material (filler) for a transparent conductive film, a silver nanowire having a small diameter and a small variation in diameter distribution, a method for producing the silver nanowire, and a reaction after completion of the reaction used for the reduction precipitation reaction of the silver nanowire. Regarding liquid. Further, the present invention relates to a silver nanowire dispersion liquid containing the silver nanowires.

In the present specification, a fine metal wire having a thickness of about 200 nm or less is referred to as a “nanowire (s)”.

Silver nanowires are promising as a conductive material for imparting conductivity to a transparent substrate. When a coating liquid containing silver nanowires is applied to a transparent substrate such as glass, PET (polyethylene terephthalate), or PC (polycarbonate) and then the liquid component is removed by evaporation or the like, the silver nanowires come into contact with each other on the substrate. By forming a conductive network, a transparent conductive film can be realized.

A transparent conductive film used for a touch panel or the like of an electronic device is required to have good conductivity and clear visibility with little haze. In order to achieve both conductivity and visibility at a high level in a transparent conductive film using silver nanowires as a conductive material, it is advantageous to apply silver nanowires as thin as possible. However, it is difficult to sufficiently improve the quality of the transparent conductive film simply by reducing the average diameter of the wire. Even if the average diameter value is small, if the amount of thick wires mixed is large, those thick wires hinder the haze reduction effect. In order to stably improve the haze of the transparent conductive film at a high level, in addition to the small average diameter of the silver nanowires, the diameters of the individual wires should be as uniform as possible, that is, the variation in diameter distribution should be small. Is desired. Further, in order to accurately control the sheet resistance of the transparent conductive film within a predetermined range based on the silver concentration in the silver nanowire dispersion liquid for coating, it is advantageous that the variation in diameter distribution is small.

Patent Document 1 shows an example in which fine silver nanowires having an average minor axis diameter of 15.1 nm or 16.4 nm are synthesized (Samples 8 and 10 in FIG. 1). In these examples, an aqueous solvent is used in the seed particle synthesis step (Preparation Examples 8 and 1) and the growth step (Preparation Examples 16 and 17). Silver nanowires synthesized in an aqueous solvent tend to aggregate. Therefore, it is difficult to increase the silver concentration in the reaction solution. It is also necessary to take measures to prevent aggregation, such as adding a large amount of hydrophilic polymer. In fact, in the above preparation examples 16 and 17, a large amount of PVP (polyvinylpyrrolidone) is added. There are many issues to be solved in order to realize industrial mass production by the method of synthesizing silver nanowires using an aqueous solvent. Further, in the examples of Samples 8 and 10 described above, silver nanowires having a coefficient of variation of minor axis diameter of 16 to 17% are obtained. However, in order to meet the high quality improvement (particularly the improvement of haze) required for the transparent conductive film in the future, further improvement regarding the variation in wire diameter is desired.

On the other hand, as a method for synthesizing silver nanowires that is relatively suitable for industrial mass production, a silver compound is dissolved in a polyol solvent such as ethylene glycol or propylene glycol, and in the presence of a halogen compound and an organic protective agent, the polyol that is the solvent is used. A method of precipitating linear metallic silver using reducing power (hereinafter referred to as "alcohol solvent reduction method") is known and has already been put into practical use. However, it has been difficult to stably synthesize extremely fine silver nanowires having an average diameter of less than 20 nm by the alcohol solvent reduction method based on the conventional knowledge.

For example, Patent Document 2 discloses an invention for synthesizing thin metal nanowires having an average diameter of about 10 to 50 nm (paragraph 0007). The synthesis method uses a polyol solvent having 2 to 6 carbon atoms in the alcohol solvent reduction method. Various polyols that can be used are listed, and 1,2-butanediol is also described in them (paragraph 0041). However, the synthetic method specifically shown as an example is a method of reducing and precipitating silver at 150 ° C. using propylene glycol, and the average diameter of the obtained silver nanowires is 32.0 nm even in the thinnest example. (Example 8). In this document, after teaching that it is desirable (paragraph 0006) that a thin film having excellent transparency and conductivity can be formed as the diameter of the metal nanowire is smaller, only an example in which a wire having a thickness exceeding 30 nm is actually synthesized is the only example. From what has been shown, it is considered that it has been difficult in the past to make silver nanowires significantly thinner than these by the alcohol solvent reduction method.

Patent Documents 3 and 4 also describe that metal nanowires are synthesized by an alcohol solvent reduction method using a polyol, and 1,2-butanediol is also described among the listed polyols (Patent Documents). Paragraph 0025 of paragraph 3, paragraph 0027 of Patent Document 4). However, the synthetic method specifically shown as an example in these documents is also a method of reducing and precipitating silver at a temperature of about 150 ° C. using propylene glycol, and the diameters of the obtained silver nanowires are all 30 nm. Beyond. No technique is disclosed for producing silver nanowires significantly thinner than those by the alcohol solvent reduction method.

Japanese Unexamined Patent Publication No. 2013-199691 International Publication No. 2017/05/73726 Japanese Unexamined Patent Publication No. 2017-14621 JP-A-2017-66471

The present invention is to provide silver nanowires having an extremely fine average diameter, which is advantageous for improving the haze of a transparent conductive film using silver nanowires as a conductive material. Further, it is intended to provide a dispersion liquid in which the silver nanowires are dispersed.

The above objectives can be achieved with silver nanowires having an average diameter of less than 20.0 nm and very little diameter variation. Such silver nanowires allow the reduction precipitation of silver to proceed at a temperature of 50 ° C. or higher and 90 ° C. or lower in an alcohol solvent reduction method using 1,2-alkanediol having 4 or more and 6 or less carbon atoms as a solvent. It turned out that it can be manufactured by. The following inventions are disclosed in the present specification.

[1] below average diameter 20.0 nm, the following (1) Average aspect ratio A _M defined by equation 100 or more and 15.0 percent coefficient of variation CV of a diameter, a polymer having vinylpyrrolidone structural unit Is a silver nanowire attached to the surface.
_{A M = L M / D M} ... (1)
Here, L _M represented the average length of silver nanowires in units of nm values, D _M is the value representing the average diameter in nm.
[2] The silver nanowire according to the above [1], wherein the polymer having the vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and another monomer.
[3] The silver nanowire according to the above [1], wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and a diallyldimyldimethylammonium salt monomer.
[4] A reaction solution used for the reduction precipitation reaction of silver nanowires, wherein the silver nanowires according to any one of [1] to [3] above are dispersed in an alcohol-based liquid medium.
[5] In a method for producing silver nanowires, in which silver is reduced and precipitated in the form of a wire in an alcohol solvent in which a silver compound and a polymer having a vinylpyrrolidone structural unit are dissolved.
An alcohol solvent containing at least 40% of one or more 1,2-alkanediols having 4 or more and 6 or less carbon atoms in the mass ratio of the solvent to the alcohol component is used, and the temperature is 50 ° C. or higher and 90 ° C. or lower. A method for producing silver nanowires in which reduction precipitation proceeds at temperature.
[6] The method for producing silver nanowires according to the above [5], wherein the polymer having the vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and another monomer.
[7] The method for producing silver nanowires according to the above [5], wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and a diallyldimyldimethylammonium salt monomer.
[8] The mass ratio "polymer / silver mass ratio" between the amount of the polymer having the vinylpyrrolidone structural unit present in the alcohol solvent and the total amount of silver used for reduction precipitation is 0.5 to 5.0. The method for producing a silver nanowire according to any one of the above [5] to [7].
[9] A silver nanowire dispersion liquid in which the silver nanowires according to any one of [1] to [3] above are dispersed in a liquid medium.
[10] The silver nanowire according to any one of [1] to [3] is a liquid medium having an alcohol mass ratio of 95% or more, a liquid medium having a total mass ratio of alcohol and water of 95% or more. Alternatively, a silver nanowire dispersion liquid dispersed in a liquid medium having a mass ratio of water of 95% or more.

The "alcohol-based" relating to the liquid medium constituting the reaction solution of the above [4] is a term meaning that it is not an "aqueous-based". That is, the "alcohol-based liquid medium" means a liquid medium in which the mass ratio of alcohol to the liquid medium is larger than the mass ratio of water.
The average length, average diameter, and coefficient of variation CV of silver nanowires follow the following definitions.

[Average length]
The trace length from one end to the other end of a silver nanowire on an image observed by a field emission scanning electron microscope (FE-SEM) is defined as the length of the wire. The average length of the individual silver nanowires present on the microscopic image is defined as the average length. In order to calculate the average length, the total number of wires to be measured is 100 or more.

[Average diameter]
On a bright-field observation image by a transmission electron microscope (TEM), the distance between contours on both sides in the thickness direction of a single silver nanowire is defined as the diameter of the wire. Each wire can be considered to have a nearly uniform thickness over its entire length. Therefore, the thickness can be measured by selecting a portion that does not overlap with other wires. In a TEM image showing one field of view, the diameters of all the silver nanowires observed in the image are measured except for the wires that completely overlap with other wires and whose diameter is difficult to measure. The operation is performed on a plurality of randomly selected visual fields, the diameters of a total of 100 or more different silver nanowires are obtained, the average value of the diameters of the individual silver nanowires is calculated, and the value is defined as the average diameter.

[Diameter coefficient of variation CV]
The coefficient of variation CV (%) of the diameter is calculated by the following equation (2) by calculating the standard deviation σ for the diameter value (nm) of a total of 100 or more individual wires used in the above calculation of the average diameter. ..
CV = 100 × σ / D _M … (2)
Here, D _M is the above average diameter (nm).

The silver nanowires according to the present invention have an average diameter of less than 20 nm, which is extremely thin, and the diameter variation is very small. Since the average diameter is extremely thin as described above, it is advantageous in achieving a high level of balance between conductivity and visibility (conductivity-haze balance) in a transparent conductive film using silver nanowires as a conductive material. In addition, the fact that the variation in the average diameter of the wires is very small means that the amount of the wires that are considerably thicker than the average diameter is small. The mixture of thick wires is a factor that increases the haze of the transparent conductive film. Silver nanowires according to the present invention are extremely useful for improving the high haze of transparent conductive films. Further, in the alcohol solvent reduction method of the present invention, the amount of the polymer used for ensuring the dispersibility of the synthesized wire can be significantly reduced as compared with the synthesis method using an aqueous solvent. It is easy to implement industrially in terms of cost. Since the amount of polymer adhering to the synthesized wire is also reduced, it is also advantageous for improving the conductivity of the transparent conductive film. The reaction solution obtained by the alcohol solvent reduction method has significantly reduced agglomeration of the synthesized wires as compared with the reaction solution using an aqueous solvent, and therefore, a silver nanowire dispersion liquid which is a coating liquid after that. It is advantageous in rationally producing.

Structural formula of vinylpyrrolidone structural unit. TEM photograph of silver nanowires obtained in Example 3. TEM photograph of silver nanowires obtained in Example 7. TEM photograph of the compound obtained in Comparative Example 6. TEM photograph of the composite obtained in Comparative Example 7. A graph showing the relationship between the combined temperature and the average diameter. The graph which shows the relationship between the synthesis temperature and the coefficient of variation CV of a diameter.

[Dimensions and shapes of silver nanowires]
The silver nanowires are preferably as thin and long as possible from the viewpoint of forming a transparent conductive coating film having excellent conductivity and visibility. In particular, for improving visibility (reducing haze), it has been found that a very small average diameter and a small amount of thick wires mixed are extremely advantageous. Further, according to the research by the inventors, when the average diameter is reduced to less than 20.0 nm, it becomes easy to adjust the conductivity-haze balance of the transparent conductive film due to the high haze reduction effect, and the conductivity becomes conductive. It was found that increasing the average length of the wire to improve the property became less important. That is, even if the average length of the wire at the time of synthesis is about 2 μm, the conductivity-haze balance is excellent if the length distribution is adjusted by cross-flow filtration or the like before the coating film is prepared. It becomes possible to obtain a transparent conductive film.

In the present invention, the average diameter of silver nanowires less than 20.0 nm, the following (1) Average aspect ratio A _M defined by equation 100 or more, and a point variation coefficient CV of the diameter is less than 15.0% Prescribe. Silver nanowires having such a size and shape have the effect of improving the conductivity-haze balance of the transparent conductive film as compared with those having an average diameter of about 25 nm or about 30 nm that can be produced by a conventionally known alcohol solvent reduction method. Excellent.
_{A M = L M / D M} ... (1)
Here, L _M represented the average length of silver nanowires in units of nm values, D _M is the value representing the average diameter in nm.
The average diameter is more preferably 18.0 nm or less, and even more preferably 16.0 nm or less. The coefficient of variation CV of the diameter is more preferably 12.0% or less, and further preferably 10.0% or less. Further, the value of the average diameter + 3σ is more preferably 22.0 nm or less, and more preferably 20.0 nm or less.
If the average diameter becomes excessively small, it is liable to be damaged such as bending in the process of manufacturing the transparent conductive film, so that more careful handling is required. Usually, the average diameter may be in the range of 10 nm or more. The average aspect ratio is preferably 100 or more and 1000 or less. If the average aspect ratio of the silver nanowires is too small, the probability of contact between the wires in the transparent conductive film becomes low, and the contribution to conductivity becomes insufficient. If the average aspect ratio is excessive, the wires tend to be arranged in a bundle when the silver nanowire dispersion liquid is applied, which may hinder the acquisition of a high-quality transparent conductive film.

[Organic protective agent]
The above-mentioned silver nanowires which are extremely thin and have a small diameter variation can be synthesized by the alcohol solvent reduction method described later. In the alcohol solvent reduction method, the silver precipitation reaction proceeds in the presence of an organic protective agent. The polymer of the organic protective agent used at the time of the reaction adheres to the surface of the synthesized silver nanowires, and the dispersibility in the liquid is ensured. As the organic protective agent, those having a vinylpyrrolidone structural unit can be applied. FIG. 1 shows a vinylpyrrolidone structural unit. Specifically, PVP or a copolymer of vinylpyrrolidone and another monomer can be used.

The above-mentioned copolymer of vinylpyrrolidone and other monomers can improve the dispersibility in an alcohol-added aqueous solvent as compared with PVP. It is important that such copolymers have structural units of hydrophilic monomers. Here, the hydrophilic monomer means a monomer having a property of dissolving 1 g or more in 1000 g of water at 25 ° C. Specific examples thereof include a diallyldimyldimethylammonium salt monomer, an acrylate-based or methacrylate-based monomer, and a maleimide-based monomer. For example, examples of the acrylate-based or methacrylate-based monomer include ethyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate. Examples of maleimide-based monomers include 4-hydroxybutyl acrylate, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, and N-tert-butylmaleimide.

[Manufacturing method of silver nanowires]
As a method for synthesizing silver nanowires, as described above, an "alcohol solvent reduction method" is known in which silver is reduced and precipitated in the form of a wire in an alcohol solvent in which an organic protective agent is dissolved. As a result of detailed research, the inventors have found that in the alcohol solvent reduction method using a polymer having a vinylpyrrolidone structural unit as an organic protective agent,
(I) As the alcohol solvent, use an alcohol solvent containing at least 40% by mass of one or more 1,2-alkanediols having 4 or more and 6 or less carbon atoms in one molecule.
(Ii) Control the temperature at the time of reduction precipitation in the range of 50 to 90 ° C.
As described above, it has been found that it is possible to synthesize silver nanowires having an extremely small average diameter and a very small diameter variation.

In the alcohol solvent reduction method, polymer molecules of the organic protective agent are selectively adsorbed on the {100} plane of the silver nucleus crystal to suppress the growth of the {100} plane, which is the densest plane of the silver crystal {111}. It is believed that the preferential growth of the faces forms a linear structure of metallic silver. It is not clear at this time why silver nanowires having an extremely small average diameter and a very small diameter variation can be stably synthesized by satisfying the reduction conditions of (i) and (ii) above. .. Presumably, in the presence of a polymer having a vinylpyrrolidone structural unit which is an organic protective agent, the reducing power of 1,2-alkanediol having 4 or more and 6 or less carbon atoms is utilized to make it relatively 90 ° C or less. When the reduction reaction of silver is started in a low temperature range, the mechanism is unknown, but it is presumed that a nuclear crystal having a very small particle size, that is, a nuclear crystal having a very small {111} plane size is formed. Then, when the reduction precipitation of silver is further promoted by utilizing the reducing power of 1,2-alkanediol having 4 or more and 6 or less carbon atoms in an environment of 90 ° C. or lower, the {111} plane of the nuclear crystal is small. It is believed that the {111} plane can be grown while maintaining its size, resulting in the synthesis of extremely fine silver nanowires. In this case, since the diameter variation between the individual silver nanowires to be synthesized becomes very small, the reduction precipitation of silver proceeds in the solvent of ethylene glycol or propylene glycol in a temperature range exceeding 90 ° C. Compared with the case of the alcohol solvent reduction method, it is speculated that rapid nuclear formation and growth are suppressed and the reduction reaction proceeds relatively gently. The temperature at the time of reduction precipitation is more preferably 85 ° C. or lower, and further preferably 60 ° C. or lower. On the other hand, if the temperature is too low, the reaction time becomes long, which is uneconomical. As a result of various studies, the temperature at the time of reduction precipitation is set to 50 ° C. or higher. From the viewpoint of reaction time, the temperature is more preferably 53 ° C. or higher. From the viewpoint of stably synthesizing silver nanowires having a particularly small diameter and a particularly small CV value, for example, one or more 1,2-alkanediols having 4 or 5 carbon atoms in one molecule may be used. It is more effective to use an alcohol solvent containing 40% or more in total and to proceed the reduction precipitation at a temperature of 50 ° C. or higher and 60 ° C. or lower.

When synthesizing silver nanowires in a solvent of ethanediol or propanediol having 3 or less carbon atoms at a temperature of 90 ° C. or lower, the average diameter is less than 20.0 nm and the coefficient of variation CV of the diameter is 15.0. It is difficult to stably synthesize silver nanowires having an average diameter of% or less and an extremely small diameter variation. Further, even if the alkanediol has 4 to 6 carbon atoms, the reducing power of only the alkanediol having a hydroxy group other than the 1,2 position such as 1,3-butanediol or 1,4-butanediol is utilized. It is difficult to synthesize thin silver nanowires by the above synthesis. On the other hand, 1,2-alkanediol having 7 or more carbon atoms is often solid at around room temperature, and is inferior in handleability as an alcohol solvent for industrial mass production of silver nanowires.

As 1,2-alkanediol having 4 to 6 carbon atoms, specifically 1,2-butanediol (4 carbon atoms), 1,2-pentanediol (5 carbon atoms), 1,2-hexanediol ( 6) of carbon atoms can be mentioned. One or more of these are used as the alcohol solvent. In the present invention, a mixed alcohol solvent of these 1,2-alkanediols having 4 to 6 carbon atoms and other alcohols can be used, but the number of carbon atoms is 4 or more and 6 in terms of the mass ratio of the solvent to the alcohol component. It is necessary to use an alcohol solvent containing at least 40% of one or more of the following 1,2-alkanediols in total. The content of one or more 1,2-alkanediols having 4 or more and 6 or less carbon atoms in the mass ratio of the solvent to the alcohol component may be controlled to be 80% or more in total or 95% or more in total. Examples of other alcohols include 1,2-propanediol (three carbon atoms).

As the polymer to be present in the alcohol solvent during the synthesis of silver nanowires, the polymer having the vinylpyrrolidone structural unit which is the above-mentioned organic protective agent is applied. The mass ratio "polymer / silver mass ratio" between the amount of the polymer having the vinylpyrrolidone structural unit present in the alcohol solvent and the total amount of silver used for reduction precipitation shall be in the range of 0.5 to 5.0. Is preferable. If an alcohol solvent in which too much polymer is present is used, the amount of polymer adhering to the surface of the synthesized silver nanowires will be excessive. When silver nanowires having an excessive amount of polymer adhered are applied to a transparent conductive film, the contact resistance between the wires becomes large, which is disadvantageous in obtaining a transparent conductive film having high conductivity.

As the silver source used for the synthesis of silver nanowires, a silver compound soluble in an alcohol solvent is used. For example, silver nitrate, silver acetate, silver oxide, silver chloride and the like can be mentioned, but silver nitrate (AgNO ₃ ) is easy to use in consideration of solubility in a solvent and cost. In addition to the silver compound and the polymer having a vinylpyrrolidone structural unit, it is preferable to proceed with the reduction precipitation in an alcohol solvent in which chlorides and bromides are dissolved. Further, it is more preferable to proceed the reduction precipitation in an alcohol solvent in which an alkali metal hydroxide and an aluminum salt are dissolved. Of the above substances, for example, silver compounds, chlorides, bromides, aluminum salts and the like may be added to the reaction vessel in the form of a solution. In that case, as a solvent for preparing a solution of each substance, it is suitable to use a solvent having high polarity and high solubility among alcohol solvents. For example, 1,2-propanediol (propylene glycol) can be mentioned.

In the synthesis of silver nanowires, the total amount of silver used relative to the total amount of alcohol solvent used is preferably in the range of 0.01 to 0.1 mol of silver per liter of alcohol solvent. The total amount of chloride used relative to the total amount of alcohol solvent used is preferably in the range of 0.0001 (1 × 10 ^-5 ) to 0.01 mol as the amount of Cl per 1 L of alcohol solvent, and is 0.0005 (5). More preferably, it is in the range of × 10 ^-5 ) to 0.01 mol. The total amount of bromide used relative to the total amount of alcohol solvent used is preferably in the range of 0.000001 (1 × 10 ^-6 ) to 0.001 (1 × 10 ^-3 ) mol as the amount of Br per 1 L of alcohol solvent. , 0.000005 (5 × 10 ^-6 ) to 0.001 (1 × 10 ^-3 ) mol is more preferable. The total amount of alkali metal hydroxide used relative to the total amount of alcohol solvent used ranges from 0.0001 (1 x 10 ^-4 ) to 0.01 (1 x 10 ^-2 ) mol as the amount of hydroxide per 1 L of alcohol solvent. Is preferable. The total amount of aluminum salt used relative to the total amount of alcohol solvent used is preferably in the range of 0.0001 (1 × 10 ^-5 ) to 0.001 (1 × 10 ^-3 ) mol as the amount of Al per 1 L of solvent. .. Acetic acid ester or water may be contained as a solvent component in a range of 2% or less based on the total mass of the solvent.

[Silver nanowire dispersion]
The "silver nanowire dispersion liquid" synthesized as described above in which silver nanowires with a small diameter and small variation in diameter distribution are dispersed in a liquid medium can be used to construct a transparent conductive film having an excellent conductivity-haze balance. Extremely useful. Here, the "liquid medium" is a liquid portion constituting the silver nanowire dispersion liquid, and when another substance is dissolved in the solvent substance, that substance is also a constituent component of the liquid medium. For example, in a silver nanowire dispersion liquid (which is sometimes called "silver nanowire ink") adjusted to have properties particularly suitable for coating by adding a thickening component or a binder component as necessary, a solvent is used. The thickening component and the binder component dissolved in the liquid medium are also constituent components of the liquid medium.

The solvent used in the silver nanowire dispersion liquid for coating or the silver nanowire dispersion liquid which is an intermediate product for producing the silver nanowire dispersion liquid for coating is an aqueous solvent, a mixed solvent of water and alcohol, and alcohol. It is common to use one of the solvents. The presence of water is advantageous for ensuring the dispersibility of silver nanowires in the liquid, and the presence of alcohol is advantageous for ensuring the wettability of the silver nanowire dispersion with a transparent resin substrate such as PET (polyethylene terephthalate). It becomes. When one or both of water and alcohol are used as the solvent component, the mass ratio of water and alcohol constituting the solvent can be arbitrarily adjusted in the range of 0: 100 to 100: 0 for water: alcohol. Suitable alcohols used as a solvent for the silver nanowire dispersion include monohydric alcohols having 1 to 4 carbon atoms. Specifically, alcohols such as methanol, ethanol, 2-propanol (isopropyl alcohol), 2-methyl-1-propanol, and 1-butanol are suitable targets. These have a moderately high boiling point and are easy to use for coating to form a transparent conductive film. When a plurality of alcohols are mixed and used, it is preferable that one or more of the monohydric alcohols having 1 to 4 carbon atoms is 50% or more based on the total mass of the alcohols used.

In order to obtain a silver nanowire dispersion having a good balance between the dispersibility of silver nanowires in the liquid and the wettability with a substrate such as PET, it is effective to use a mixed solvent of water and alcohol. In that case, the mass ratio of water to alcohol is preferably adjusted in the range of water: alcohol, for example, 95: 5 to 70:30. On the other hand, when the productivity in the coating film drying step is emphasized, it is effective to use an alcohol-based solvent in which water: alcohol is close to 0: 100. At that time, when the organic protective agent attached to the silver nanowire is PVP (polyvinylpyrrolidone) which is generally used in the past, it is necessary to add a surfactant to ensure the dispersibility of the wire in the liquid. It becomes. The use of a large amount of surfactant is a negative factor for the conductivity of the transparent conductive film.

The liquid medium constituting the silver nanowire dispersion liquid may contain a thickening component, a binder component, a surfactant component, and the like in addition to the solvent component. The mass ratio of the solvent component to the liquid medium is preferably 95% or more. For example, when one or both of water and alcohol are used as solvent components, a liquid medium having a mass ratio of alcohol of 95% or more, a liquid medium having a total mass ratio of alcohol and water of 95% or more, and water. It is preferable to apply any of the liquid media having a mass ratio of 95% or more. In the case of a silver nanowire dispersion liquid for coating, the mass ratio of silver nanowires to the total mass of the dispersion liquid is preferably adjusted in the range of, for example, 0.03 to 1.50% in terms of metallic silver.

[Example 1]
At room temperature, 1,2-propanediol (propylene glycol) containing 10% by mass of lithium chloride (manufactured by Aldrich) in 817.6 g of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade). ) Solution 0.399g, potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) content of 1% by mass, 1,2-propanediol solution 0.476g, lithium hydroxide (manufactured by Aldrich) 0.0711g, aluminum nitrate 0.503 g of 1,2-propanediol solution having a nine-hydrate (Kishida Kasei Co., Ltd.) content of 20% by mass, a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (vinylpyrrolidone 99% by mass, vinylpyrrolidone). A copolymer was prepared with 1% by mass of diallyldimethylammonium nitrate, and 8.39 g of a weight average molecular weight of 75,000) was added and dissolved to prepare a solution A.
6.80 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 9.57 g of 1,2-propanediol and 0.80 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 85 ° C. and a reaction time of 24 hours as follows. The above solution A was placed in a 1 L beaker, which is a reaction vessel, and the temperature was raised while stirring from room temperature to 85 ° C., and then the entire amount of solution B was added to solution A over 1 minute. After the addition of Solution B, the containers and pipelines used to add Solution B were co-washed with 4 g of 1,2-propanediol. Then, the liquid in the reaction vessel was kept at 85 ° C. for 24 hours with stirring and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvent used in this example contains 1,2-butanediol present in the above solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the above solution B as alcohol components. .. The mass ratio of each alcohol to all the alcohol components is 98.2% of 1,2-butanediol and 1.8% of 1,2-propanediol. The mass ratio "polymer / silver mass ratio" to the total amount of silver used for reduction precipitation is 1.94.

20 g of the above reaction solution cooled to room temperature was separated into a centrifuge tube, 170 g of pure water was added, and a centrifuge operation was performed at 3000 rpm for 15 minutes. Since the concentrate and the supernatant were observed, the supernatant was removed and the concentrate was recovered. Then, 170 g of pure water was added to the recovered concentrate, and then centrifugation was performed in the same manner as described above to recover the concentrate, which was repeated three times. Then, the recovered concentrate was dispersed in methanol to obtain a silver nanowire dispersion having a solid content (synthesized silver nanowires) of 0.05% by mass.

The average diameter of the obtained silver nanowires was determined as follows. The above dispersion was placed on a grid with a support film for a transmission electron microscope (Cu150 mesh manufactured by Nippon Denshi Co., Ltd.), and the acceleration voltage was 100 kV and the magnification was 40 by using a transmission electron microscope (JEM-1011). A bright-field image is observed at a magnification of 000, an observation image is taken, and the original image taken to measure the diameter accurately is enlarged to twice the size, and then software (Motic Image Plus 2.1S). Was used to measure the average diameter according to the above definition. Further, the standard deviation σ (nm) was obtained based on the diameter values of a total of 100 or more wires used for calculating the average diameter, and the coefficient of variation CV (%) of the diameter was obtained by the above equation (2).

The average length of the obtained silver nanowires was determined as follows. The above dispersion was diluted with a 30% IPA aqueous solution (diluted solution mixed at water: IPA = 70: 30) to a silver concentration of 0.002% by mass to prepare a sample solution, which was used for SEM in a thickness of 200 μm and 3 mm. Take a corner silicon substrate observation table, volatilize water on the observation table, and then observe with a field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation; S-4700) at an acceleration voltage of 3 kV and a magnification of 1,500 times. Was done. For three or more randomly selected visual fields, the average length was measured according to the above definition for all wires whose total length could be confirmed in the visual field. Further, the average aspect ratio _AM was calculated from the average length and the above average diameter by the above equation (1).

The results are shown in Table 1. In this example, silver nanowires having an average diameter of 19.1 nm and a coefficient of variation CV of 9.4%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 2]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 75 ° C. and the reaction time was changed to 72 hours in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 17.8 nm and a coefficient of variation CV of 13.5%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 3]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 65 ° C. and the reaction time was changed to 84 hours in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 17.8 nm and a coefficient of variation CV of 14.6%, which are extremely thin and have very small diameter variations, were synthesized. FIG. 2 illustrates a TEM (transmission electron microscope) photograph of the silver nanowires obtained in this example.

[Example 4]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 55 ° C. and the reaction time was changed to 130 hours in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 15.2 nm and a coefficient of variation CV of 8.6%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 5]
At room temperature, 1,2-propanediol (propylene glycol) containing 10% by mass of lithium chloride (manufactured by Aldrich) in 817.6 g of 1,2-pentanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade). ) Solution 0.399g, potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) content of 1% by mass, 1,2-propanediol solution 0.476g, lithium hydroxide (manufactured by Aldrich) 0.0711g, aluminum nitrate 0.503 g of 1,2-propanediol solution having a nine-hydrate (Kishida Kasei Co., Ltd.) content of 20% by mass, a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (vinylpyrrolidone 99% by mass, vinylpyrrolidone) A copolymer was prepared with 1% by mass of diallyldimethylammonium nitrate, and 8.39 g of a weight average molecular weight of 75,000) was added and dissolved to prepare a solution A.
6.80 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 9.57 g of 1,2-propanediol and 0.80 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 65 ° C. and a reaction time of 72 hours as follows. The above solution A was placed in a 1 L beaker, which is a reaction vessel, and the temperature was raised from room temperature to 65 ° C. with stirring, and then the entire amount of solution B was added to solution A over 1 minute. After the addition of Solution B was completed, the containers and pipelines used for the addition of Solution B were co-washed with 4 g of 1,2-propanediol. Then, the liquid in the reaction vessel was kept at 65 ° C. for 72 hours with stirring and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvent used in this example contains 1,2-pentanediol present in the solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the solution B as alcohol components. .. The mass ratio of each alcohol to the total alcohol component is 98.2% of 1,2-pentanediol and 1.8% of 1,2-propanediol. The mass ratio "polymer / silver mass ratio" to the total amount of silver used for reduction precipitation is 1.94.

The diameter and length of the obtained silver nanowires were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 16.7 nm and a coefficient of variation CV of 13.2%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 6]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 55 ° C. and the reaction time was changed to 130 hours in Example 5. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 15.2 nm and a coefficient of variation CV of 8.6%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 7]
In order to confirm the effect of scaling up the manufacturing apparatus, an experiment was conducted on a scale about 10 times that of Example 3 using a 10 L beaker as a reaction vessel.
At room temperature, 3.986 g of 1,2-propanediol (propylene glycol) solution having a lithium chloride content of 10% by mass, 0.0476 g of potassium bromide, and hydroxide in 811.6.3 g of 1,2-butanediol. 0.711 g of lithium, 4.994 g of 1,2-propanediol solution having an aluminum nitrate nineahydrate content of 20% by mass, a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (99% by mass of vinylpyrrolidone). , A copolymer was prepared with 1% by mass of diallyldimethylammonium nitrate, and 83.875 g of weight average molecular weight (75,000) was added and dissolved to prepare a solution A.
67.96 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 95.70 g of 1,2-propanediol and 8.00 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 65 ° C. and a reaction time of 84 hours as follows. The above solution A is placed in a 10 L beaker, which is a reaction vessel, and the temperature is raised from room temperature to 65 ° C. with stirring at a rotation speed of 225 rpm, and then the entire amount of solution B is poured into solution A over 1 minute from two addition ports. Was added. After the addition of Solution B was completed, the containers and pipelines used for the addition of Solution B were co-washed with 100 g of 1,2-propanediol. Then, the liquid in the reaction vessel was further maintained in a stirred state while being stirred, kept at 65 ° C. for 84 hours, and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvent used in this example contains 1,2-butanediol present in the above solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the above solution B as alcohol components. .. The mass ratio of each alcohol to the total alcohol component is 97.6% of 1,2-butanediol and 2.4% of 1,2-propanediol. The mass ratio "polymer / silver mass ratio" to the total amount of silver used for reduction precipitation is 1.94.

The diameter and length of the obtained silver nanowires were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, extremely fine silver nanowires having an average diameter of 17.9 nm, which is the same as in Example 3, were synthesized. Moreover, the coefficient of variation CV of the diameter was as small as 12.8%. FIG. 3 illustrates a TEM (transmission electron microscope) photograph of the silver nanowires obtained in this example.

[Example 8]
At room temperature, lithium chloride (Aldrich) in a mixed alcohol of 1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 408.8 g and 1,2-propanediol (propylene glycol) 408.8 g. (Manufactured) 0.399 g of 1,2-propanediol (propylene glycol) solution having a content of 10% by mass, and 1,2-propanediol having a potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) content of 1% by mass. 0.476 g of solution, 0.0711 g of lithium hydroxide (manufactured by Aldrich), 0.503 g of 1,2-propanediol solution having an aluminum nitrate nine hydrate (manufactured by Kishida Kasei) content of 20% by mass, vinylpyrrolidone. 8.39 g of a copolymer of diallyldimethlylammonium nitrate (made with 99% by mass of vinylpyrrolidone and 1% by mass of diallyldimethylammonium nitrate, weight average molecular weight 75,000) was added and dissolved, and the solution A was dissolved. And said.
6.80 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 9.57 g of 1,2-propanediol and 0.80 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 55 ° C. and a reaction time of 130 hours as follows. The above solution A was placed in a 1 L beaker, which is a reaction vessel, and the temperature was raised while stirring from room temperature to 55 ° C., and then the entire amount of solution B was added to solution A over 1 minute. After the addition of Solution B was completed, the containers and pipelines used for the addition of Solution B were co-washed with 4 g of 1,2-propanediol. Then, the liquid in the reaction vessel was kept at 55 ° C. for 130 hours with stirring and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvents used in this example are 1,2-hexanediol and 1,2-propanediol (propylene glycol) present in the solution A and a small amount of 1,2-propanediol supplied from the solution B. (Propylene glycol) is contained as an alcohol component. The mass ratio of each alcohol to the total alcohol components is 49.1% 1,2-hexanediol 49.1% and 1,2-propanediol 50.9%. The mass ratio "polymer / silver mass ratio" to the total amount of silver used for reduction precipitation is 1.94.

The diameter and length of the obtained silver nanowires were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 15.9 nm and a coefficient of variation CV of 13.8%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 9]
In a mixed alcohol of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 204.4 g and 1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 613.2 g at room temperature. , Lithium chloride (manufactured by Aldrich) is 10% by mass, 1,2-propanediol (propylene glycol) solution is 0.399 g, and potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) is 1% by mass. 1,2-Propylene diol solution 0.476 g, lithium hydroxide (manufactured by Aldrich) 0.0711 g, aluminum nitrate nine hydrate (manufactured by Kishida Kasei) content of 20 mass% 1,2-propanediol solution Add 8.503 g of a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (copolymerized with 99% by mass of vinylpyrrolidone and 1% by mass of diallyldimethylammonium nitrate, weight average molecular weight 75,000). And dissolved to make solution A.
6.80 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 9.57 g of 1,2-propanediol and 0.80 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 65 ° C. and a reaction time of 84 hours as follows. The above solution A was placed in a 1 L beaker, which is a reaction vessel, and the temperature was raised from room temperature to 65 ° C. with stirring, and then the entire amount of solution B was added to solution A over 1 minute. After the addition of Solution B was completed, the containers and pipelines used for the addition of Solution B were co-washed with 4 g of 1,2-propanediol. Then, the liquid in the reaction vessel was kept at 65 ° C. for 84 hours with stirring and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvents used in this example are 1,2-butanediol and 1,2-hexanediol present in the solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the solution B. Is contained as an alcohol component. The mass ratio of each alcohol to all the alcohol components is 1,2-butanediol 24.5%, 1,2-hexanediol 73.7%, and 1,2-propanediol 1.8%. The mass ratio "polymer / silver mass ratio" to the total amount of silver used for reduction precipitation is 1.94.

The diameter and length of the obtained silver nanowires were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 18.4 nm and a coefficient of variation of diameter of 14.4%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 10]
At room temperature, in a mixed alcohol of 613.2 g of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and 204.4 g of 1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade). , Lithium chloride (manufactured by Aldrich) is 10% by mass, 1,2-propanediol (propylene glycol) solution is 0.399 g, and potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) is 1% by mass. 1,2-Propylene diol solution 0.476 g, lithium hydroxide (manufactured by Aldrich) 0.0711 g, aluminum nitrate nine hydrate (manufactured by Kishida Kasei) content of 20 mass% 1,2-propanediol solution Add 8.503 g of a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (copolymerized with 99% by mass of vinylpyrrolidone and 1% by mass of diallyldimethylammonium nitrate, weight average molecular weight 75,000). And dissolved to make solution A.
6.80 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 9.57 g of 1,2-propanediol and 0.80 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 65 ° C. and a reaction time of 84 hours as follows. The above solution A was placed in a 1 L beaker, which is a reaction vessel, and the temperature was raised from room temperature to 65 ° C. with stirring, and then the entire amount of solution B was added to solution A over 1 minute. After the addition of Solution B was completed, the containers and pipelines used for the addition of Solution B were co-washed with 4 g of 1,2-propanediol. Then, the liquid in the reaction vessel was kept at 65 ° C. for 84 hours with stirring and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvents used in this example are 1,2-butanediol and 1,2-hexanediol present in the solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the solution B. Is contained as an alcohol component. The mass ratio of each alcohol to all the alcohol components is 1,2-butanediol 73.7%, 1,2-hexanediol 24.5%, and 1,2-propanediol 1.8%. The mass ratio "polymer / silver mass ratio" to the total amount of silver used for reduction precipitation is 1.94.

The diameter and length of the obtained silver nanowires were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 17.3 nm and a coefficient of variation CV of 14.7%, which are extremely thin and have very small diameter variations, were synthesized.

[Example 11]
The experiment was carried out under the same conditions as in Example 1 except that the amount of potassium bromide added when preparing the solution A in Example 7 was changed from 0.0476 g to 0.0714 g. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 17.7 nm and a coefficient of variation CV of 13.6% were synthesized, which are extremely thin and have very small diameter variations.

[Example 12]
The experiment was carried out under the same conditions as in Example 1 except that the amount of potassium bromide added when preparing the solution A in Example 7 was changed from 0.0476 g to 0.0952 g. The results are shown in Table 1. In this example, silver nanowires having an average diameter of 17.1 nm and a coefficient of variation of diameter of 14.6%, which are extremely thin and have very small diameter variations, were synthesized.

[Comparative Example 1]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 95 ° C. in Example 1. The results are shown in Table 2. In this example, silver nanowires with an average diameter of 22.7 nm were synthesized. The coefficient of variation CV of the diameter was as small as 11.9%, but since the synthesis temperature was high, an extremely thin wire having an average diameter of less than 20 nm could not be obtained.

[Comparative Example 2]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 105 ° C. in Example 1. The results are shown in Table 2. In this example, silver nanowires with an average diameter of 24.7 nm were synthesized. The coefficient of variation CV of the diameter was as small as 13.4%, but since the synthesis temperature was high, an extremely thin wire having an average diameter of less than 20 nm could not be obtained.

[Comparative Example 3]
The experiment was carried out under the same conditions as in Example 1 except that the synthesis temperature was changed to 115 ° C. in Example 1. The results are shown in Table 2. In this example, silver nanowires with an average diameter of 24.7 nm were synthesized. The coefficient of variation CV of the diameter was as small as 13.4%, but since the synthesis temperature was high, an extremely thin wire having an average diameter of less than 20 nm could not be obtained.

[Comparative Example 4]
At room temperature, 3.986 g of 1,2-propanediol (propylene glycol) solution having a lithium chloride content of 10% by mass, 0.0476 g of potassium bromide, and hydroxide in 811.6.3 g of 1,2-propanediol. 0.711 g of lithium, 4.994 g of 1,2-propanediol solution having an aluminum nitrate nineahydrate content of 20% by mass, a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (99% by mass of vinylpyrrolidone). , A copolymer was prepared with 1% by mass of diallyldimethylammonium nitrate, and 83.875 g of weight average molecular weight (75,000) was added and dissolved to prepare a solution A.
67.96 g of silver nitrate was added to a mixed solvent of alcohol and water consisting of 95.70 g of 1,2-propanediol and 8.00 g of pure water, and the mixture was dissolved by stirring at 35 ° C. to prepare a solution B.

The reduction precipitation reaction of silver was allowed to proceed under the synthesis conditions of a synthesis temperature of 85 ° C. and a reaction time of 24 hours as follows. The above solution A is placed in a 10 L beaker, which is a reaction vessel, and the temperature is raised from room temperature to 65 ° C. with stirring at a rotation speed of 225 rpm. Was added. After the addition of Solution B, the containers and pipelines used to add Solution B were co-washed with 100 g of 1,2-propanediol. Then, while stirring the liquid in the reaction vessel, the vessel and the pipeline used for adding the solution B were co-washed with 100 g of 1,2-propanediol. Then, the liquid in the reaction vessel was kept at 65 ° C. for 24 hours with stirring and then cooled to room temperature to obtain a reaction liquid containing silver nanowires.

The alcohol solvent used in this example is an alcohol containing 1,2-propanediol (propylene glycol) present in the above solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the above solution B. Contains as an ingredient. That is, all of the alcohol components are composed of 1,2-propanediol (propylene glycol).

The diameter and length of the obtained silver nanowires were measured in the same manner as in Example 1. The results are shown in Table 2. In this example, silver nanowires with an average diameter of 25.4 nm and a coefficient of variation CV of 15.6% were synthesized. In the case of 1,2-propanediol (propylene glycol), which is a conventional alcohol solvent for synthesizing silver nanowires, the average diameter is less than 20 nm and the coefficient of variation CV of the diameter is high even if the synthesis temperature is lowered to 90 ° C. or lower. It was not possible to synthesize silver nanowires that are extremely thin, less than 15%, and have very small diameter variations.

[Comparative Example 5]
The experiment was carried out under the same conditions as in Example 4 except that the synthesis temperature was further lowered to 65 ° C. and the reaction time was changed to 72 hours in Comparative Example 4. The results are shown in Table 2. In this example, silver nanowires with an average diameter of 20.6 nm and a coefficient of variation of 22.3% were synthesized. In the case of 1,2-propanediol (propylene glycol), which is a conventional alcohol solvent for synthesizing silver nanowires, it is possible to synthesize silver nanowires having an average diameter of about 20 nm when the synthesis temperature is lowered to 65 ° C. , The variation in diameter (coefficient of variation CV) became large.

[Comparative Example 6]
Synthesis conditions similar to those of Example 1 except that the 1,2-butanediol used in Solution A in Example 1 was changed to 1,4-butanediol having the same mass (manufactured by Wako Pure Chemical Industries, Ltd., special grade). I tried to synthesize silver nanowires.

The alcohol solvent used in this example contains 1,4-butanediol present in the above solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the above solution B as alcohol components. .. The mass ratio of each alcohol to the total alcohol component is 98.2% of 1,4-butanediol and 1.8% of 1,2-propanediol.

The results are shown in Table 2. In this example, 1,4-butanediol was used as the alkanediol having 4 carbon atoms in one molecule, but silver nanowires could not be synthesized. FIG. 4 illustrates a TEM (transmission electron microscope) photograph of the compound obtained in this example.

[Comparative Example 7]
Synthesis conditions similar to those of Example 1 except that the 1,2-butanediol used in Solution A in Example 1 was changed to 1,3-butanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) having the same mass. I tried to synthesize silver nanowires.

The alcohol solvent used in this example contains 1,3-butanediol present in the above solution A and a small amount of 1,2-propanediol (propylene glycol) supplied from the above solution B as alcohol components. .. The mass ratio of each alcohol to the total alcohol component is 98.2% of 1,3-butanediol and 1.8% of 1,2-propanediol.

The results are shown in Table 2. In this example, 1,3-butanediol was used as the alkanediol having 4 carbon atoms in one molecule, but most of the obtained metallic silver was granular. FIG. 5 illustrates a TEM (transmission electron microscope) photograph of the compound obtained in this example.

For reference, FIG. 6 shows a graph showing the relationship between the combined temperature and the average diameter, and FIG. 7 shows a graph showing the relationship between the combined temperature and the coefficient of variation CV of the diameter.

[Haze evaluation of transparent conductive film]
Next, using the silver nanowires synthesized in Example 7 and Comparative Example 4, a transparent conductive film was prepared as follows, and the haze was measured.

[Example 7A]
In this example, the silver nanowires obtained in Example 7 were used, and the experiment was carried out according to the following procedure.
(Precipitation process)
To 8400 g of the reaction solution (cooled to room temperature) obtained in Example 7 above, 1890 g of pure water was added and stirred for 10 minutes. Next, 7580 g of acetone was added and stirred for 10 minutes. Next, 8820 g of xylene was added and stirred for 10 minutes. Then, it was allowed to stand for 3 hours. After standing, a concentrate and a supernatant were observed, so the supernatant was removed and the concentrate containing silver nanowires was recovered.

(1st cleaning step)
A copolymer of vinylpyrrolidone and diallyldimethlylammonium nitrate (copolymerized with 99% by mass of vinylpyrrolidone and 1% by mass of diallyldimethylammonium nitrate, weight average molecular weight 75,000) was dissolved in pure water to dissolve the copolymer. A "polymer-containing aqueous solution" having a concentration of 1% by mass was prepared. 160 g of this polymer-containing aqueous solution was added to the concentrate containing the silver nanowires recovered as described above, and the mixture was stirred at 100 rpm for 2.5 hours in a dimmer. Then, 700 g of acetone was added to precipitate the solid content containing the silver nanowires. The supernatant was removed, and 150 g of acetone was further added to remove the supernatant. Next, 1280 g of the above polymer-containing aqueous solution was added, and the mixture was stirred with a stirrer at a rotation speed of 100 rpm for 12 hours to obtain a silver nanowire dispersion liquid having completed the first washing step.

(Second cleaning process)
Next, 4000 g of acetone was added while stirring the silver nanowire dispersion liquid with a stirrer at a rotation speed of 100 rpm, and the stirring was stopped. It was confirmed that a precipitate was formed and the supernatant was turbid. The turbid supernatant contains short silver nanowires with a slow sedimentation rate (short wires mainly composed of wires with an aspect ratio of less than 100). The supernatant was removed, and 1500 g of acetone was added while stirring with a stirrer at a rotation speed of 100 rpm, and the stirring was stopped. After removing the supernatant, 1280 g of the above-mentioned polymer-containing aqueous solution (the above-mentioned copolymer concentration is 1% by mass) was added, and the mixture was stirred with a stirrer at a rotation speed of 100 rpm for 12 hours to complete the second cleaning step. A dispersion was obtained.

(3rd to 6th cleaning steps)
Further, by repeating the same procedure as the second cleaning step four times, the third cleaning step to the sixth cleaning step were performed to obtain a silver nanowire dispersion liquid after completing the sixth cleaning step. The turbidity of the supernatant was reduced with each repetition of the washing process.

(7th cleaning step)
The silver nanowire dispersion liquid after completing the sixth washing step was stirred with a stirrer at a rotation speed of 100 rpm, 4000 g of acetone was added, and the stirring was stopped after 10 minutes. After the precipitate was formed, the supernatant was removed, 1500 g of acetone was added while stirring with a stirrer at a rotation speed of 100 rpm, and the stirring was stopped. After the precipitate was formed, the supernatant was removed, 1280 g of pure water was added, and the mixture was stirred with a stirrer at a rotation speed of 100 rpm for 12 hours to obtain a silver nanowire dispersion liquid after completing the seventh washing step. When the concentration of metallic silver in this dispersion was measured by ICP emission spectroscopy (equipment: ICP emission spectroscopy 720-ES manufactured by Azilent Technology Co., Ltd.), the concentration of silver nanowires was 2.474 mass in terms of metallic silver. %Met.

(Hot water treatment of thickener)
As a thickener, a powder product of HPMC (hydroxypropyl methylcellulose, manufactured by a chemical manufacturer, weight average molecular weight: 840,000) adjusted to 21.5% by mass of methoxy groups and 30.0% by mass of hydroxypropoxy groups. I prepared. The powder was sieved with a mesh size of 200 μm. To 6000 g of pure water heated to 98 ° C. in a SUS tank having a capacity of 15 L, 150 g of the thickener powder passed through the above mesh was added, and a disk turbine blade having a diameter of 135 mm was used at 600 rpm for 30 minutes. Stirring gave a slurry of thickener. This slurry was filtered under reduced pressure with a PFA mesh, and then washed with hot water by pouring 6400 g of boiling pure water into the solid content of the thickener remaining on the mesh. After confirming that the hot water had been filtered, the solid content of the thickener was loosened before cooling to obtain a solid content of the thickener having a size of about 3 cm. The solid content of the thickener was dried at 70 ° C. for 30 minutes, and then granulated so that the particle size was 1 cm or less before returning to room temperature. Then, it was dried at 70 degreeC for 12 hours, and 120 g of the thickener treated with hot water was obtained. The above operation was carried out in two steps to obtain a total of 240 g of the hot water-treated thickener.

(Preparation of thickener aqueous solution)
To dissolve the thickener, a SUS tank having a capacity of 20 L was used, and a disc turbine blade having a diameter of 150 mm was used. By adding 150 g of the above-mentioned hot water-treated thickener to 9850 g of pure water heated to 95 ° C., allowing the mixture to cool to 40 ° C. with stirring at 475 rpm, and then flowing cooling water cooled by a chiller through the jacket of the tank. It was cooled and stirred for 12 hours. The temperature at the end of stirring was 5 ° C. In this way, the thickener was dissolved in water to obtain an aqueous thickener solution. The obtained aqueous thickener solution was pressure-filtered at a set pressure of 0.2 MPa to remove insoluble components. For the pressurized filtration, a depth pleated filter (manufactured by Roki Techno Co., Ltd .; SCP type) having a filter filtration accuracy (opening) of 1 μm was used. The concentration of the thickener component (HPMC) in the thickener aqueous solution after filtration was 1.24% by mass.

(Preparation of silver nanowire dispersion for coating)
313 g of the silver nanowire dispersion liquid, 1920 g of pure water, and 347 g of the filtered thickener aqueous solution that have completed the seventh cleaning step are placed in one container, and six inclined blades having a diameter of 170 mm are used at 150 rpm for 2 hours. Stirred. Then, 1720 g of a 50% aqueous solution of 2-propanol was added and stirred at 150 rpm for 12 hours to obtain a silver nanowire dispersion for coating in which the solvent components in the liquid medium were water and alcohol. When the metallic silver concentration of this silver nanowire dispersion was measured by ICP emission spectroscopic analysis, the silver nanowire content was 0.180 mass% in terms of metallic silver.

(Preparation of transparent conductive film)
A PET film base material (manufactured by Toyobo Co., Ltd., Cosmo Shine (registered trademark) A4100) having a thickness of 100 μm and a size of 100 mm × 150 mm was prepared. The silver nanowire dispersion for coating was applied to the bare surface of the PET film base material with a bar coater (manufactured by Tester Sangyo Co., Ltd., SA-203) having a count of No. 6 to form a coating film. The area of the coating film formed on the substrate was 80 mm × 120 mm. This coating film was dried in the air at 120 ° C. for 1 minute to obtain a transparent conductive film.

(Measurement of haze)
The haze of the transparent conductive film was evaluated based on the haze value (%) measured by a haze meter NDH 5000 manufactured by Nippon Denshoku Kogyo Co., Ltd. Here, in order to eliminate the influence of the PET substrate, the haze evaluation index H determined by the following equation (3) was adopted.
[Haze evaluation index H] = [Haze value of base material + transparent conductive film]-[Haze value of base material only] ... (3)
Here, the "haze value of the base material + transparent conductive film" is the haze value (%) of the object composed of the base film and the transparent conductive film formed on the base film, and the "haze value of only the base material" is transparent. It is the haze value (%) of the base film before forming the conductive film. It is evaluated that the smaller the value of the haze evaluation index H, which is the difference between the two, the smaller the amount of haze generated by the transparent conductive film.
The haze evaluation index H of the transparent conductive film obtained in this example was 0.40. The results are shown in Table 3.

[Example 7B]
In this example, the silver nanowires obtained in Example 7 were used. The above 6th cleaning step was carried out under the same conditions as in Example 7A to obtain a silver nanowire dispersion liquid after completing the 6th cleaning step. This was subjected to the following steps.
(7th cleaning step)
While stirring the silver nanowire dispersion liquid after completing the sixth washing step with a stirrer at a rotation speed of 100 rpm, 4000 g of acetone was added, and the stirring was stopped after 10 minutes. After the precipitate was formed, the supernatant was removed, 1500 g of acetone was added while stirring with a stirrer at a rotation speed of 100 rpm, and the stirring was stopped. After the precipitate is formed, the supernatant is removed, 1280 g of the above-mentioned polymer-containing aqueous solution (the above-mentioned copolymer concentration is 1% by mass) is added, and the mixture is stirred with a stirrer at a rotation speed of 100 rpm for 12 hours to perform the seventh washing. A silver nanowire dispersion having completed the process was obtained.

(Preparation of silver nanowire dispersion for coating)
While stirring 350 g of the silver nanowire dispersion liquid after completing the seventh washing step with a stirrer at a rotation speed of 100 rpm, 1000 g of acetone was added, and the stirring was stopped after 10 minutes. The supernatant was removed, and 375 g of acetone was added while stirring with a stirrer at a rotation speed of 100 rpm to stop the stirring. Next, after removing the supernatant, 777 g of 2-propanol was added, and then dispersion treatment was performed for 24 hours using an automatic disperser (Mixing Man, SKH-40) to convert silver nanowires into 2-propanol. A dispersed alcohol-based silver nanowire dispersion was obtained. This alcohol-based silver nanowire dispersion was dissolved in 60% nitric acid and analyzed by radio frequency inductively coupled plasma (ICP) emission spectroscopic analysis using CP-OES720 manufactured by Azilent Technology Co., Ltd., and the above alcohol-based silver nanowire dispersion was analyzed. The silver concentration inside was calculated. Based on this silver concentration value, the alcohol-based silver nanowire dispersion was diluted with a predetermined amount of 2-propanol to obtain a silver nanowire dispersion for coating having a silver concentration of 0.2% by mass.

(Preparation of transparent conductive film)
A PET film base material (manufactured by Toyobo Co., Ltd., Cosmo Shine (registered trademark) A4100) having a thickness of 100 μm and a size of 100 mm × 150 mm was prepared. The alcohol-based silver nanowire dispersion for coating was applied to the bare surface of the PET film substrate with a bar coater (manufactured by Tester Sangyo Co., Ltd., SA-203) having a count of No. 6 to form a coating film. The area of the coating film formed on the substrate was 80 mm × 120 mm. This coating film was dried in the air at 80 ° C. for 1 minute to obtain a transparent conductive film.

(Measurement of haze)
The haze evaluation index H was determined by the same method as in Example 7A. The haze evaluation index H of the transparent conductive film obtained in this example was 0.38. The results are shown in Table 3.

[Comparative Example 4A]
In this example, the experiment was carried out under the same conditions as in Example 7B except that the silver nanowires obtained in Comparative Example 4 were used and the precipitation step was performed under the following conditions.
(Precipitation process)
To 8400 g of the reaction solution (cooled to room temperature) obtained in Example 4 above, 1050 g of pure water was added and stirred for 10 minutes. Next, 7580 g of acetone was added and stirred for 10 minutes. Next, 6320 g of xylene was added and stirred for 10 minutes. Then, it was allowed to stand for 3 hours. After standing, a concentrate and a supernatant were observed, so the supernatant was removed and the concentrate containing silver nanowires was recovered.

The haze evaluation index H of the transparent conductive film obtained in this example was 0.62. The results are shown in Table 3.

It was confirmed that silver nanowires having an extremely small average diameter and very small diameter variation are extremely useful in reducing the haze of the transparent conductive film.

Claims (10)

Less than the mean diameter of 20.0 nm, the following (1) Average aspect ratio A _M defined by equation 100 or more and 15.0 percent coefficient of variation CV of a diameter, a polymer having vinylpyrrolidone structural unit is a surface Adhering silver nanowires.
_{A M = L M / D M} ... (1)
Here, L _M represented the average length of silver nanowires in units of nm values, D _M is the value representing the average diameter in nm. The silver nanowire according to claim 1, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and another monomer. The silver nanowire according to claim 1, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and a diallyldimyldimethylammonium salt monomer. A reaction solution used for the reduction precipitation reaction of silver nanowires, wherein the silver nanowires according to any one of claims 1 to 3 are dispersed in an alcohol-based liquid medium. In a method for producing silver nanowires, in which silver is reduced and precipitated in the form of a wire in an alcohol solvent in which a silver compound and a polymer having a vinylpyrrolidone structural unit are dissolved.
An alcohol solvent containing at least 40% of one or more 1,2-alkanediols having 4 or more and 6 or less carbon atoms in the mass ratio of the solvent to the alcohol component is used, and the temperature is 50 ° C. or higher and 90 ° C. or lower. A method for producing silver nanowires in which reduction precipitation proceeds at temperature. The method for producing silver nanowires according to claim 5, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and another monomer. The method for producing silver nanowires according to claim 5, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and a diallyldimethylammanium salt monomer. The claim that the mass ratio "polymer / silver mass ratio" between the amount of the polymer having the vinylpyrrolidone structural unit present in the alcohol solvent and the total amount of silver used for reduction precipitation is 0.5 to 5.0. The method for producing a silver nanowire according to any one of 5 to 7. A silver nanowire dispersion liquid in which the silver nanowires according to any one of claims 1 to 3 are dispersed in a liquid medium. The silver nanowire according to any one of claims 1 to 3 is a liquid medium having an alcohol mass ratio of 95% or more, a liquid medium having a total mass ratio of alcohol and water of 95% or more, or a mass of water. A silver nanowire dispersion liquid dispersed in a liquid medium having a ratio of 95% or more.