TW202104602A - Silver nanowire, method for producing the same, reaction liquid containing silver nanowire, and silver nanowire dispersion liquid - Google Patents

Abstract

An objective of the present invention is to provide a silver nanowire having an extremely small average diameter, which is advantageous for improving the haze of a transparent conductive film using a silver nanowire as a conductive material.

As a solution, the silver nanowire of the present invention is a silver nanowire with a polymer having vinylpyrrolidone structural unit attached to the surface, and the average diameter of the silver nanowire is less than 20.0nm, the average aspect ratio AM defined by the following formula (1) is 100 or more, and the variation coefficient CV of the diameter is 15.0% or less. AM = LM/DM...(1). Herein, LM is a value that represents the average length of the silver nanowire in the unit of nm, and DM is a value that represents the average diameter in the unit of nm. This silver nanowire can be obtained by using an alcohol solvent containing at least 40% in total of at least one 1,2-alkanediol having 4 to 6 carbon atoms, and promoting reduction precipitation at a temperature of 50℃ to 90℃.

Description

Silver nanowire, method for producing the same, and reaction solution containing silver nanowire and silver nanowire dispersion liquid

The present invention relates to a silver nanowire with a fine diameter and small diameter distribution variation that is beneficial as a conductive material (filler) of a transparent conductive film, a method for manufacturing the same, and a reaction used in the reduction and precipitation reaction of the silver nanowire The reaction solution after completion. In addition, it also relates to a silver nanowire dispersion containing the silver nanowire.

In this specification, a fine metal wire with a thickness of about 200 nm or less is called "nanowire (s)".

Silver nanowires are expected as a conductive material for imparting conductivity to transparent substrates. When coating liquid containing silver nanowires on transparent substrates such as glass, PET (polyethylene terephthalate), PC (polycarbonate), etc., when the liquid components are removed by evaporation, etc. By making silver nanowires contact each other on the substrate to form a conductive network, a transparent conductive film can be realized.

Transparent conductive films used in touch panels of electronic devices, etc., not only have good conductivity, but also require low haze and clear visibility. Using silver nanowires as conductive materials In order to balance the high level of conductivity and visibility in the transparent conductive film, it is advantageous to apply as fine silver nanowire as possible. However, it is difficult to adequately meet the requirements for further high-quality transparent conductive films by using wires with a thin average diameter. Even if the average diameter value becomes smaller, if the mixing amount of thick wires is large, the thick wires will hinder the haze reduction effect. In order to improve the haze of the transparent conductive film and achieve high quality and stability, in addition to the small average diameter of the silver nanowires, it is also desirable that the diameter of each wire is as consistent as possible, that is, the variation of the diameter distribution is small. In addition, 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 for coating, it is also advantageous to make the variation of the diameter distribution small.

Patent Document 1 discloses an example of synthesizing fine silver nanowires with an average minor axis diameter of 15.1 nm or 16.4 nm (samples 8 and 10 in Fig. 1). In these examples, an aqueous solvent was used in the seed particle synthesis step (Preparation Examples 8, 1) and the growth step (Preparation Examples 16, 17). The silver nanowire synthesized in an aqueous solvent is easy to aggregate. Therefore, it is very difficult to increase the concentration of silver in the reaction solution. It is necessary to take measures to prevent aggregation, such as adding a large amount of hydrophilic polymer. In fact, a large amount of PVP (polyvinylpyrrolidone) was added to the aforementioned Preparation Examples 16 and 17. There are many problems to be solved in order to realize industrial mass production by the synthetic method of silver nanowires using water-based solvents. Moreover, in the examples of samples 8 and 10 above, silver nanowires with a coefficient of variation of the minor axis diameter of 16 to 17% can be obtained. However, in order to cope with the improved high-quality (especially improvement of haze) required for transparent conductive films in the future, it is more desirable to improve the variation of the wire diameter.

On the other hand, in terms of the synthesis method of silver nanowires that are more suitable for industrial mass production, it is known that silver compounds are dissolved in polyhydric alcohol solvents such as ethylene glycol or propylene glycol, in the presence of halogen compounds and organic protective agents. Next, the method of precipitating linear metallic silver by using the reducing power of the polyhydric alcohol which is a solvent (hereinafter referred to as the "alcohol solvent reduction method") has progressed towards practical use. However, in the alcohol solvent reduction method, it is very difficult to synthesize extremely fine silver nanowires with an average diameter of less than 20 nm stably.

For example, Patent Document 2 discloses an invention that focuses on synthesizing fine metal nanowires (paragraph 0007) with an average diameter of about 10 to 50 nm. This synthesis method uses a polyhydric alcohol solvent with 2 to 6 carbon atoms in the alcohol solvent reduction method. Various polyols considered usable are listed in the literature, and 1,2-butanediol is also described (paragraph 0041). However, the synthesis method specifically disclosed in the examples uses propylene glycol and reduces silver to precipitate at 150°C. The average diameter of the resulting silver nanowires is also 32.0 nm in the smallest example (Example 8) . In this document, it is expected that the thinner the diameter of the metal nanowire, the more excellent the transparency and conductivity of the thin film (paragraph 0006), but in fact only disclosed examples of synthetic wires with a thickness of more than 30nm, so it is believed that, In the past, it was difficult to produce silver nanowires thinner than these diameters by alcohol solvent reduction.

Patent Documents 3 and 4 also describe the synthesis of metal nanowires by the alcohol solvent reduction method using polyhydric alcohols. Among the listed polyols, 1,2-butanediol is also described (paragraph 0025 of Patent Document 3). , Paragraph 0027 of Patent Document 4). However, the synthesis method specifically disclosed in these documents as an example is also a method of using propylene glycol and reducing silver to precipitate at a temperature of about 150°C, and the diameter of any silver nanowire obtained exceeds 30 nm. It does not disclose the technology of producing silver nanowires with finer diameters than these by the alcohol solvent reduction method.

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2013-199691

[Patent Document 2] International Publication No. 2017/057326

[Patent Document 3] Japanese Patent Laid-Open No. 2017-14621

[Patent Document 4] Japanese Patent Laid-Open No. 2017-66471

The present invention intends to provide a silver nanowire with an extremely fine average diameter which is beneficial to improve the haze of a transparent conductive film using silver nanowire as a conductive material. In addition, it is also desired to provide a dispersion in which the silver nanowire is dispersed.

The above-mentioned purpose can be achieved by silver nanowires whose average diameter is smaller than 20.0nm and the diameter variation is very small. It is known that in the alcohol solvent reduction method using 1,2-alkanediol having a carbon number of 4 or more and 6 or less as the solvent, the reduction and precipitation reaction of silver is carried out at a temperature of 50°C or more and 90°C or less to produce such silver Nanowire. The following inventions are disclosed in this specification.

[1] A silver nanowires having an average diameter of less than 20.0 nm, the average aspect ratio of A _M defined by the following equation (1) is 100 or more, the coefficient of variation CV of a diameter of 15.0% or less, and the silver A polymer with vinylpyrrolidone structural unit is attached to the surface of the nanowire.

A _M =L _M /D _M …(1)

Wherein, L _M based an average length of silver nanowires in nm units represented by the value, D _M based the above average diameter expressed in nm of the value.

[2] The silver nanowire according to [1] above, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and other monomers.

[3] The silver nanowire according to the above [1], wherein the polymer having a vinylpyrrolidone structural unit is vinylpyrrolidone and diallyldimethylammonium salt monomer Body of the copolymer.

[4] A reaction liquid used in the reduction and precipitation reaction of silver nanowires, in which the silver nanowires described in any one of [1] to [3] are dispersed in an alcohol-based liquid medium Become.

[5] A method for producing silver nanowires, which is to reduce silver to precipitate linear silver nanowires in an alcohol solvent in which silver compounds and polymers with vinylpyrrolidone structural units are dissolved, and Use an alcohol solvent to perform reduction and precipitation at a temperature above 50°C and below 90°C. The alcohol solvent is based on the mass ratio of the alcohol in the solvent and contains a total of 40% or more of carbon number 4 or more and 6 or less. , 1 or more of 2-alkanediols.

[6] The method for producing silver nanowires as described in [5] above, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and other monomers.

[7] The method for producing silver nanowires as described in [5] above, wherein the polymer having vinylpyrrolidone structural unit is vinylpyrrolidone and diallyldimethylammonium ) Copolymer of salt monomer.

[8] The method for producing silver nanowires as described in any one of [5] to [7] above, wherein the amount of the polymer having vinylpyrrolidone structural unit present in the alcohol solvent and reduction The mass ratio "polymer/silver mass ratio" of the total amount of silver used in precipitation is 0.5 to 5.0.

[9] A silver nanowire dispersion liquid obtained by dispersing the silver nanowire described in any one of [1] to [3] in a liquid medium.

[10] A silver nanowire dispersion, which is a liquid medium in which the silver nanowire described in any one of [1] to [3] is dispersed in an alcohol with a mass ratio of 95% or more, alcohol and water The total mass ratio is 95% or more in the liquid medium, or the water mass ratio is more than 95% in the liquid medium.

The term "alcohol-based" with regard to the liquid medium constituting the reaction liquid in [4] above means non-"aqueous-based". That is, the so-called "alcohol-based liquid medium" means a liquid medium in which the mass ratio of alcohol in the liquid medium is greater than the mass ratio of water.

The average length, average diameter, and variation coefficient of diameter CV of silver nanowires follow the following definitions.

[Average length]

On the observation image obtained by the field emission scanning electron microscope (FE-SEM), the length of the trace from one end to the other end of a certain silver nanowire is defined as the length of the line. The value obtained by averaging the length of each silver nanowire existing on the microscope image is defined as the average length. To calculate the average length, the total number of lines to be measured is set to 100 or more.

[The average diameter]

On the bright-field observation image obtained by a transmission electron microscope (TEM), the distance between the two sides of a silver nanowire in the thickness direction is defined as the diameter of the wire. Each line can be regarded as having an almost uniform thickness over the entire length. Therefore, you can choose the part that does not overlap with other lines to measure the thickness. In the TEM image of one field of view, among the silver nanowires observed in the image, except for the wires that completely overlap with other wires and it is difficult to measure the diameter, the diameters of all wires are measured. This operation is performed on a plurality of arbitrarily selected fields of view to obtain the diameters of more than 100 different silver nanowires in total, calculate the average value of the diameters of each silver nanowire, and define the value as the average diameter.

[Diameter variation coefficient CV]

The diameter variation coefficient CV (%) is calculated by calculating the standard deviation value σ of the diameter (nm) of each line of more than 100 total diameters used to calculate the above average diameter, and then calculated by the following formula (2).

CV=100×σ/D _M …(2)

Here, _DM is the above-mentioned average diameter (nm).

According to the silver nanowires of the present invention, the average diameter is extremely small, less than 20 nm, and the variation of the diameter is very small. Since the average diameter is extremely fine as described above, it is advantageous to have a high-level balance of conductivity and visibility (conductivity-haze balance) in a transparent conductive film using silver nanowire as a conductive material. In addition, the variation of the average diameter of the wire is very small, which means that there is less mixing of wires that are thicker than the average diameter. Mixed with thick lines will increase the haze of the transparent conductive film. The silver nanowire according to the present invention is extremely useful for improving the haze height of the transparent conductive film. In addition, in the alcohol solvent reduction method of the present invention, compared with the synthesis method using an aqueous solvent, the amount of polymer used to ensure the dispersibility of the synthesis line can be greatly reduced, so it is easy to industrialize in terms of cost. Implementation. The amount of polymer adhering to the synthesized thread is also reduced, which also contributes to the improvement of the conductivity of the transparent conductive film. Compared with the reaction solution using an aqueous solvent, the reaction solution obtained by the alcohol solvent reduction method has greatly reduced the aggregation of the synthesized threads, which is beneficial to the subsequent reasonable production of silver nanoparticles belonging to the coating solution. Line dispersion.

Figure 1 is the structural formula of vinylpyrrolidone structural unit.

Figure 2 is a TEM photograph of the silver nanowire obtained in Example 3.

Figure 3 is a TEM photograph of the silver nanowire obtained in Example 7.

Figure 4 is a TEM photograph of the composition obtained in Comparative Example 6.

Fig. 5 is a TEM photograph of the composition obtained in Comparative Example 7.

Figure 6 is a graph showing the relationship between the synthesis temperature and the average diameter.

Fig. 7 is a graph showing the relationship between the synthesis temperature and the variation coefficient CV of the diameter.

[Size and shape of silver nanowire]

From the viewpoint of forming a transparent conductive coating film excellent in conductivity and visibility, the silver nanowire is preferably as long as possible. Especially for the improvement of visibility (reduction of haze), it is known that the average diameter is very small and the amount of thick lines is small. In addition, according to research conducted by the inventors, when the average diameter is as small as less than 20.0 nm, the haze reduction effect becomes higher, which makes it easy to adjust the conductivity-haze balance of the transparent conductive film, and the conductivity is increased to increase The importance of the average length of the line becomes lower. That is, even if the average wire length during synthesis is about 2 μm, if the length distribution is adjusted by lateral flow filtration or the like before the coating liquid is produced, a transparent conductive film with excellent conductivity-haze balance can be obtained.

In the invention, provision is less than the average diameter of silver nanowires 20.0nm, the average aspect ratio of A _M defined by the following equation (1) is 100 or more, and a coefficient of variation of diameter CV of 15.0% or less. Silver nanowires of this size and shape have an improved effect on the conductivity-haze balance of the transparent conductive film compared with those with an average diameter of about 25nm or about 30nm that can be produced by alcohol solvent reduction methods known in the past. Excellent.

A _M =L _M /D _M …(1)

Wherein, L _M based an average length of silver nanowires in nm units represented by the value, D _M based the above average diameter expressed in nm of the value.

The average diameter is more preferably 18.0 nm or less, and even more preferably 16.0 nm or less. It is more preferable that the coefficient of variation of the diameter CV is 12.0% or less, and even more preferably 10.0% or less. In addition, the value of the average diameter +3σ is more preferably 22.0 nm or less, and even more preferably 20.0 nm or less.

When the average diameter is too fine, it is easy to be damaged by bending or the like during the process of manufacturing the transparent conductive film, so it is necessary to be more careful in handling. Usually, the average diameter is more than 10nm The range can be. In addition, 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 contact rate of the wires in the transparent conductive film becomes low, and the contribution to the conductivity is insufficient. When the average aspect ratio is too large, the wires are likely to be arranged in bundles when the silver nanowire dispersion is coated, which may hinder the acquisition of high-quality transparent conductive films.

[Organic Protective Agent]

The silver nanowires, which are very fine and have small diameter variations, can be synthesized by the alcohol solvent reduction method described later. The alcohol solvent reduction method proceeds the precipitation reaction of silver in the presence of an organic protective agent. The polymer of the organic protective agent used in the reaction is attached to the surface of the synthesized silver nanowire to ensure the dispersibility in the solution. The organic protective agent may be those having vinylpyrrolidone structural units. Figure 1 shows the structural units of vinylpyrrolidone. Specifically, PVP or a copolymer of vinylpyrrolidone and other monomers can be used.

The above-mentioned copolymer of vinylpyrrolidone and other monomers can improve the dispersibility in water-based solvents added with alcohol more than that of PVP. For such a copolymer, it is important to have a structural unit of a hydrophilic monomer. Among them, the hydrophilic single system means a monomer having the property of dissolving more than 1 g in 1000 g of water at 25°C. Specifically, for example, diallyldimethylammonium salt monomers, acrylate-based or methacrylic-based monomers, and maleimide-based monomers can be mentioned. Examples of acrylic or methacrylic monomers include ethyl acrylate, 2-hydroxyethyl acrylate, and methacrylic 2-hydroxyacetic acid. In addition, the maleimide-based monomers include, for example, 4-hydroxybutyl acrylate, N-methylmaleimide, N-ethylmaleimide, and N-propylmaleimide. Leimide, N-tertiary butyl maleimide.

[Manufacturing method of silver nanowire]

As mentioned above, the method for synthesizing silver nanowires is known as the "alcohol solvent reduction method" in which silver is reduced and precipitated into a linear shape in an alcohol solvent in which an organic protective agent is dissolved. The results of detailed research by the inventors, In the alcohol solvent reduction method using a polymer having a vinylpyrrolidone structural unit as an organic protective agent, it was found that the following methods (i) and (ii) can be synthesized with extremely fine average diameters as described above. Silver nanowires with very small variations in diameter:

(i) Use as an alcohol solvent containing at least one alcohol solvent containing a total of 40% by mass or more of 1,2-alkanediol having a carbon number of 4 to 6 in a molecule;

(ii) The temperature during reduction and precipitation is controlled within the range of 50 to 90°C.

In the alcohol solvent reduction method, it is believed that the polymer molecules of the organic protective agent selectively adsorb on the {100} face of the silver core crystal to inhibit the growth of the {100} face, and make the {111} the densest face of the silver crystal } The plane grows preferentially, thereby forming a linear structure of metallic silver. The reason why silver nanowires with extremely fine average diameters and very small variations in diameter can be stably synthesized by satisfying the reduction conditions of (i) and (ii) above is currently unclear. It is speculated that it may be because in the presence of a polymer with vinylpyrrolidone structural unit, which is an organic protective agent, the reducing power of 1,2-alkanediol with a carbon number of 4 or more and 6 or less is 90 When the reduction reaction of silver starts in a relatively low temperature range below °C, although the mechanism is not clear, nuclear crystals with very small particle diameters are formed, that is, those with very small size of {111} planes. Then it is believed that the reducing power of 1,2-alkanediol with a carbon number of 4 to 6 can be used to reduce the precipitation reaction of silver in an environment below 90°C, and the {111} plane of the nucleus crystal can be maintained. The size is small and the {111} plane grows at the same time, resulting in the synthesis of extremely fine silver nanowires. In this case, since the diameter variation between the synthesized silver nanowires is very small, it is different from the conventional alcohol solvent reduction in which silver is reduced and precipitated in a solvent of ethylene glycol or propylene glycol at a temperature exceeding 90°C. Compared with the law, it is speculated that the rapid nucleation and growth may be inhibited, and the reduction reaction may proceed more stably. The temperature at the time of reduction and precipitation is more preferably 85°C or less, and even more preferably performed at 60°C or less. On the other hand, when the temperature is too low, the reaction time will be longer, which is not economical. As a result of various reviews, when the temperature at the time of reduction and precipitation is performed at 50°C or higher, it is more preferable to perform it at 53°C or higher from the viewpoint of a small reaction time. In addition, from the viewpoint of stably synthesizing silver nanowires with a particularly fine diameter and a particularly small CV value, for example, a 1,2-alkanediol with a carbon number of 4 or 5 in a molecule containing 40% or more in total is used One or more alcohol solvents are more effective than performing reduction and precipitation reactions at a temperature above 50°C and below 60°C.

When trying to synthesize silver nanowires at a temperature below 90℃ in a solvent of ethylene glycol or propylene glycol with 3 carbons or less, it is difficult to synthesize the average diameter of less than 20.0nm stably and the coefficient of variation CV of the diameter is 15.0% Below, silver nanowires with very fine average diameter and very small variation in diameter. In addition, even if it is an alkanediol with a carbon number of 4 to 6, if only 1,3-butanediol or 1,4-butanediol, such as 1,3-butanediol or 1,4-butanediol, is synthesized using the reducing power of an alkanediol whose hydroxyl group is located outside the 1,2 position , It is also difficult to synthesize fine silver nanowires. On the other hand, 1,2-alkanediols with 7 or more carbons are often solid near room temperature, and they are poor in handling in terms of alcohol solvents used for industrial mass production of silver nanowires. .

For 1,2-alkanediols having 4 to 6 carbon atoms, specific examples include: 1,2-butanediol (carbon number 4), 1,2-pentanediol (carbon number 5), 1 ,2-Hexanediol (carbon number 6). One or two or more of these are used for the alcohol solvent. In the present invention, mixed alcohol solvents of these 1,2-alkanediols with 4 to 6 carbon atoms and other alcohols can also be used, but they must be used based on the mass ratio of the alcohol in the solvent, which contains a total of more than 40% One or more alcohol solvents of 1,2-alkanediol with carbon number of 4 or more and 6 or less. Based on the mass ratio of the alcohol component in the solvent, the content of one or more of 1,2-alkanediols with a carbon number of 4 or more and 6 or less may be controlled to 80% or more in total, or 95% or more in total. Examples of other alcohols include 1,2-propanediol (carbon number 3).

For the polymer pre-existing in the alcohol solvent during the synthesis of silver nanowires, polymers with vinylpyrrolidone structural units belonging to the above-mentioned organic protective agents are applicable. The mass ratio of the amount of the aforementioned polymer having vinylpyrrolidone structural unit in the alcohol solvent to the total amount of silver used in the reduction precipitation "polymer/silver mass ratio" is in the range of 0.5 to 5.0 The surrounding is better. When an alcohol solvent containing too much polymer is used, the amount of polymer attached to the surface of the synthesized silver nanowire becomes too much. When silver nanowires with excessive polymer adhesion are applied to a transparent conductive film, the contact resistance between the wires will increase, which is not conducive to obtaining a transparent conductive film with high conductivity.

As the silver supply source used in the synthesis of silver nanowires, silver compounds soluble in alcohol solvents are used. For example, silver nitrate, silver acetate, silver oxide, silver chloride, etc., if solubility to a solvent or cost is considered, silver nitrate (AgNO ₃ ) is easy to use. In addition to silver compounds and polymers with vinylpyrrolidone structural units, the reduction and precipitation reaction is preferably carried out in an alcohol solvent in which chlorides and bromides are still dissolved. Furthermore, it is better to proceed the reduction precipitation reaction in an alcohol solvent in which alkali metal hydroxides and aluminum salts are dissolved. Among the above-mentioned substances, for example, silver compounds, chlorides, bromides, aluminum salts, etc., can be added to the reaction vessel in a solution state. In this case, it is suitable to use solvents with high polarity and high solubility among alcohol solvents for the solvent used to prepare the solution of each substance. For example, 1,2-propylene glycol (Propylene Glycol).

In the synthesis of silver nanowires, relative to the total amount of alcohol solvent used, the total amount of silver used is preferably in the range of 0.01 to 0.1 mol per 1L of alcohol solvent. Relative to the total amount of alcohol solvent used, the total amount of salt used is preferably in the range of 0.00001 (1×10 ^-5 ) to 0.01 mol per 1L of Cl in the alcohol solvent, 0.00005 (5×10 ^-5 ) To 0.01 mol is more preferable. Relative to the total use amount of the alcohol solvent, the total use amount of bromide is preferably in the range of 0.000001 (1×10 ^-6 ) to 0.001 (1×10 ^-3 ) moles of Br per 1L of the alcohol solvent. The range of 0.000005 (5×10 ^-6 ) to 0.001 (1×10 ^-3 ) mole is more preferable. Relative to the total amount of alcohol solvent used, the total amount of alkali metal hydroxide used is in the range of 0.0001 (1×10 ^-4 ) to 0.01 (1×10 ^-2 ) mole per 1L of alcohol solvent. Better. Relative to the total used amount of the alcohol solvent, the total used amount of the aluminum salt is preferably in the range of 0.00001 (1×10 ^-5 ) to 0.001 (1×10 ^-3 ) mole per 1 L of the solvent. Relative to the total mass of the solvent, it can contain 2% or less of acetate or water as the solvent component.

[Silver Nanowire Dispersion]

The "silver nanowire dispersion", which is synthesized by dispersing silver nanowires with fine diameters and small variations in diameter distribution in a liquid medium as described above, is useful for producing transparent conductive materials with excellent conductivity and haze balance. The membrane is extremely useful. The "liquid medium" refers to the liquid part of the silver nanowire dispersion. When other substances are dissolved in the solvent substance, the substance is also a constituent of the liquid medium. For example, a silver nanowire dispersion (sometimes referred to as "silver nanowire printing ink"), which is adjusted to have properties particularly suitable for coating by adding viscosity-increasing components or adhesive components as necessary, is dissolved in The viscosity-increasing component or binder component in the solvent is also the constituent component of the liquid medium.

For the silver nanowire dispersion for coating, or the intermediate product used to make the silver nanowire dispersion for coating, that is, the solvent used in the silver nanowire dispersion, water solvents and water are generally used. Either a mixed solvent with alcohol and an alcohol solvent. In order to ensure the dispersibility of silver nanowires in the liquid, the presence of water is advantageous. To ensure the wettability of the silver nanowire dispersions on transparent resin substrates such as PET (polyethylene terephthalate), then The presence of alcohol is advantageous. When one or both of water and alcohol are used as the solvent component, the mass ratio of water to alcohol constituting the solvent can be arbitrarily adjusted within the range of water: alcohol from 0:100 to 100:0. Examples of alcohols suitable for use as a solvent for the silver nanowire dispersion include monohydric alcohols with 1 to 4 carbon atoms. Specifically, alcohols such as methanol, ethanol, 2-propanol (isopropanol), 2-methyl-1-propanol, and 1-butanol are suitable objects. These alcohols have a moderately high boiling point and are convenient for coating to form a transparent conductive film. When a plurality of alcohols are mixed and used, it is preferable to set one or two or more of monohydric alcohols having 1 to 4 carbons to 50% or more with respect to the total mass of the alcohols used.

In order to obtain a silver nanowire dispersion that has a good balance between the dispersibility of the silver nanowire in the liquid and the wettability with PET and other substrates, it is effective to use a mixed solvent of water and alcohol. Here In this case, it is better to adjust the mass ratio of water to alcohol to, for example, water:alcohol in the range of 95:5 to 70:30. On the other hand, in the case of attaching importance to the productivity in the coating film drying step, water:alcohol is close to 0:100 and a solvent mainly composed of alcohol is effective. At this time, if the organic protective agent attached to the silver nanowire is PVP (polyvinylpyrrolidone) that is generally used in the past, it is necessary to add a surfactant in order to ensure the liquid dispersibility of the silver wire. A large amount of surfactants will adversely affect the conductivity of the transparent conductive film.

In addition to the solvent component, the liquid medium constituting the silver nanowire dispersion may also contain a thickening component, a binder component, a surfactant component, etc. The mass ratio of the solvent component in the liquid medium is preferably 95% or more. For example, in the case of using one or both of water and alcohol as the solvent component, the mass ratio of the liquid medium with an alcohol mass ratio of 95% or more, the total mass ratio of alcohol and water of 95% or more, and the mass of water are applicable. Any one of liquid media having a ratio of 95% or more is preferable. In the case of the silver nanowire dispersion for coating, the mass ratio of the silver nanowire in the total mass of the dispersion should be adjusted to a range of, for example, 0.03 to 1.50% in terms of metallic silver.

[Example]

[Example 1]

At room temperature, to 817.6 g of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade), 0.399 g of a 1,2-propanediol solution containing 10% by mass of lithium chloride (manufactured by ALDRICH) was added , Potassium bromide (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 nonahydrate (manufactured by KISHIDA CHEMICAL) content It is 0.503 g of a 20% by mass 1,2-propylene glycol solution, a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (based on 99% by mass vinylpyrrolidone, dimethyl A copolymer made of 1% by mass of diallyl ammonium nitrate, with a weight average molecular weight of 75,000) 8.39 g and dissolved to prepare a solution A.

To an alcohol and water mixed solvent composed of 9.57 g of 1,2-propanediol and 0.80 g of pure water, 6.80 g of silver nitrate was added, and the mixture was stirred and dissolved at 35°C to prepare a solution B.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 85°C and a reaction time of 24 hours as follows. The above-mentioned solution A was put in a 1L beaker of the reaction vessel, and the temperature was raised from room temperature to 85°C while stirring, and the total amount of the solution B was added to the solution A in one minute. After solution B is added, the container and pipeline used to add solution B are co-washed with 4g of 1,2-propanediol. After that, the liquid in the reaction vessel was stored at 85°C for 24 hours while 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-mentioned solution A and a small amount of 1,2-propanediol supplied from the above-mentioned solution B as the alcohol component. The mass ratio of various alcohols in all alcohol components is 98.2% for 1,2-butanediol and 1.8% for 1,2-propanediol. The mass ratio "polymer/silver mass ratio" to the total amount of silver used for reduction precipitation was 1.94.

20 g of the above-mentioned reaction solution cooled to room temperature was aliquoted into a centrifuge tube, 170 g of pure water was added, and a centrifugal separation operation was performed at 3000 rpm for 15 minutes by a centrifugal separator. Since the concentrate and the supernatant were observed, the supernatant was removed and the concentrate was recovered. After adding 170 g of pure water to the recovered concentrate, centrifugal separation was performed in the same manner as described above, and the concentrate was recovered. This operation was repeated three times. After that, the recovered concentrate was dispersed in methanol to obtain a silver nanowire dispersion with a solid content (synthesized silver nanowire) content of 0.05% by mass.

The average diameter of the silver nanowires obtained is obtained by the following method. The above dispersion was placed on a grid with a supporting film of a transmission electron microscope (made by Japan Electron Optics Laboratory, Cu150 mesh), and used a transmission electron microscope (made by Japan Electron Optics Laboratory; JEM- 1011). Observe the bright-field image with an acceleration voltage of 100kV and a magnification of 40,000 times and collect the observation image, and enlarge the collected original image into After double the size to measure the diameter correctly, use the software (Motic Image Plus 2.1S) to measure the average diameter according to the above definition. In addition, the standard deviation σ (nm) is obtained from the diameter value of a total of 100 or more wires used to calculate the aforementioned average diameter, and the diameter variation coefficient CV (%) is obtained from the aforementioned equation (2).

Obtain the average length of the silver nanowires obtained in the following way. Dilute the above dispersion with a 30% IPA aqueous solution (diluted solution mixed with water: IPA=70:30) to a silver concentration of 0.002% by mass as a sample solution, and place this in a SEM with a thickness of 200μm and 3mm square On the silicon substrate observation table, after volatilizing water on the observation table, observation was performed with a field emission scanning electron microscope (manufactured by Hitachi High-Technologies Co., Ltd.; S-4700) at an acceleration voltage of 3 kV and a magnification of 1,500 times. In 3 or more selected fields of view, the average length is measured according to the above-mentioned definition with the line that can confirm all the full length in the field of view. And whereby the average length and the average diameter of the above by (1) above Formula A _M average aspect ratio was calculated.

The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 19.1nm and a diameter variation coefficient CV of 9.4% is synthesized, and the diameter variation is very small.

[Example 2]

The experiment was performed under the same conditions as in Example 1, except that the synthesis temperature was changed to 75°C and the reaction hours were changed to 72 hours in Example 1. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 17.8nm, a diameter variation coefficient CV of 13.5%, and a very small variation in diameter was synthesized.

[Example 3]

The experiment was performed under the same conditions as in Example 1, except that the synthesis temperature was changed to 65°C and the reaction hours were changed to 84 hours in Example 1. The results are shown in Table 1. In this example, a very fine diameter with an average diameter of 17.8nm and a coefficient of variation of the diameter CV of 14.6% is synthesized. Silver nanowires with very small variations. An example of a TEM (transmission electron microscope) photograph of the silver nanowire obtained in this example is shown in FIG. 2.

[Example 4]

The experiment was performed under the same conditions as in Example 1, except that the synthesis temperature was changed to 55°C and the reaction hours were changed to 130 hours in Example 1. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 15.2nm and a diameter variation coefficient CV of 8.6% and a very small variation in diameter was synthesized.

[Example 5]

At room temperature, to 817.6 g of 1,2-pentanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade), 0.399 g of a 1,2-propanediol solution containing 10% by mass of lithium chloride (manufactured by ALDRICH) was added , Potassium bromide (Wako Pure Chemical Industries, Ltd.) content of 1% by mass 1,2-propylene glycol solution 0.476g, lithium hydroxide (Aldrich) 0.0711g, aluminum nitrate nonahydrate (KISHIDA CHEMICAL) content 0.503g of 20% by mass 1,2-propylene glycol solution, copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (based on 99% by mass vinylpyrrolidone, methyl A copolymer made of 1% by mass of diallyl ammonium nitrate, with a weight average molecular weight of 75,000) 8.39 g, was dissolved to prepare a solution A.

To an alcohol and water mixed solvent composed of 9.57 g of 1,2-propanediol and 0.80 g of pure water, 6.80 g of silver nitrate was added, and the mixture was stirred and dissolved at 35°C to prepare a solution B.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 65°C and a reaction time of 72 hours in the following manner. The above-mentioned solution A was placed in a 1L beaker of the reaction vessel, and the temperature was raised from room temperature to 65°C while stirring, and the total amount of the solution B was added to the solution A in one minute. After the addition of solution B, the container and pipeline used to add solution B are co-washed with 4g of 1,2-propanediol. After that, the solution in the reaction vessel was stored at 65°C for 72 hours while stirring, and then cooled to room temperature to obtain a reaction solution containing silver nanowires.

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

The diameter and length of the obtained silver nanowire were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 16.7nm and a diameter variation coefficient CV of 13.2% is synthesized, and the diameter variation is very small.

[Example 6]

In Example 5, the experiment was performed under the same conditions as in Example 1, except that the synthesis temperature was changed to 55°C and the reaction hours were changed to 130 hours. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 15.2nm and a diameter variation coefficient CV of 8.6% and a very small variation in diameter was synthesized.

[Example 7]

In order to confirm the effect of increasing the scale of the manufacturing device, a 10L beaker was used as a reaction vessel to conduct an experiment with a scale of approximately 310 times that of Example.

At room temperature, to 8116.3 g of 1,2-butanediol, add 3.986 g of 1,2-propanediol solution containing 10% by mass of lithium chloride, 0.0476 g of potassium bromide, 0.711 g of lithium hydroxide, and aluminum nitrate 4.994 g of a 1,2-propylene glycol solution with a nonahydrate content of 20% by mass, a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (based on vinylpyrrolidone 99 mass %, 1% by mass of dimethyl diallyl ammonium nitrate, a copolymer made with a weight average molecular weight of 75,000) 83.875 g and dissolved to prepare a solution A.

To a mixed solvent of alcohol and water composed of 95.70 g of 1,2-propanediol and 8.00 g of pure water, 67.96 g of silver nitrate was added, and the mixture was stirred and dissolved at 35°C to prepare a solution B.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 65°C and a reaction hour of 84 hours in the following manner. Put the above-mentioned solution A in a 10L beaker of the reaction vessel and stir it at a rotation speed of 225 rpm from room temperature to 65°C, then add the total amount of solution B to the solution from two addition ports in one minute In A. After the addition of solution B, the container and pipeline used to add solution B are co-washed with 100g of 1,2-propanediol. After that, the solution in the reaction vessel was kept stirring while maintaining a stirring state at 65°C for 84 hours and then cooled to room temperature to obtain a reaction solution containing silver nanowires.

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

The diameter and length of the obtained silver nanowire were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, an extremely fine silver nanowire with an average diameter of 17.9 nm equivalent to that of Example 3 was synthesized. In addition, the coefficient of variation of diameter CV is very small, 12.8%. Fig. 3 illustrates a TEM (transmission electron microscope) photograph of the silver nanowire obtained in this example.

[Example 8]

At room temperature, in a mixed alcohol of 408.8 g of 1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and 408.8 g of 1,2-propanediol, the content of lithium chloride (manufactured by ALDRICH) is 10 0.399 g of 1,2-propanediol solution of mass%, 0.476 g of 1,2-propanediol solution of potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) with a content of 1 mass%, lithium hydroxide (manufactured by ALDRICH) 0.0711 g, nitric acid 0.503 g of 1,2-propylene glycol solution containing 20% by mass of aluminum nonahydrate (manufactured by KISHIDA CHEMICAL), vinylpyrrolidone and dimethyldiallylammonium nitrate (diallyldimethylammonium nitrate) copolymer (copolymer made with 99% by mass of vinylpyrrolidone and 1% by mass of dimethyldiallylammonium nitrate, weight average molecular weight 75,000) 8.39g and dissolved to make Solution A.

To a mixed solvent of alcohol and water composed of 9.57 g of 1,2-propanediol and 0.80 g of pure water, 6.80 g of silver nitrate was added, and the mixture was stirred and dissolved at 35°C to prepare a solution B.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 55°C and a reaction hour of 130 hours as follows. The above-mentioned solution A was placed in a 1L beaker of the reaction vessel, and the temperature was raised from room temperature to 55°C while stirring, and the total amount of the solution B was added to the solution A in one minute. After the addition of solution B, the container and pipeline used to add solution B are co-washed with 4g of 1,2-propanediol. After that, the solution in the reaction vessel was stored at 55°C for 130 hours while stirring, and then cooled to room temperature to obtain a reaction solution containing silver nanowires.

The alcohol solvent used in this example contains 1,2-hexanediol and 1,2-propanediol present in the above-mentioned solution A, and a small amount of 1,2-propanediol supplied from the above-mentioned solution B as the alcohol component. The mass ratio of the various alcohols in the total alcohol components is 49.1% for 1,2-hexanediol and 50.9% for 1,2-propanediol. The mass ratio "polymer/silver mass ratio" to the total amount of silver used for reduction precipitation was 1.94.

The diameter and length of the obtained silver nanowire were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 15.9nm, a diameter variation coefficient CV of 13.8%, and a very small variation in diameter was synthesized.

[Example 9]

At room temperature, in a mixed alcohol of 204.4 g of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and 613.2 g of 1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd., special grade), Add 0.399 g of a 1,2-propanediol solution containing 10% by mass of lithium chloride (manufactured by ALDRICH), 0.476 g of a 1,2-propanediol solution containing 1% by mass of potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.), Lithium Hydroxide (Manufactured by ALDRICH) 0.0711 g, aluminum nitrate nonahydrate (manufactured by Kishida Chemical Co., Ltd.), 0.503 g of a 1,2-propylene glycol solution containing 20% by mass, vinylpyrrolidone and dimethyldiallyl nitric acid Copolymer of ammonium (diallyldimethylammonium nitrate) (copolymer made with 99% by mass of vinylpyrrolidone and 1% by mass of dimethyldiallylammonium nitrate, weight average molecular weight 75,000) 8.39g and dissolved For solution A.

To an alcohol and water mixed solvent composed of 9.57 g of 1,2-propanediol and 0.80 g of pure water, 6.80 g of silver nitrate was added, and the mixture was stirred and dissolved at 35°C to prepare a solution B.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 65°C and a reaction hour of 84 hours in the following manner. The above-mentioned solution A was placed in a 1L beaker of the reaction vessel, and the temperature was raised from room temperature to 65°C while stirring, and the total amount of the solution B was added to the solution A in one minute. After the addition of solution B, the container and pipeline used to add solution B are co-washed with 4g of 1,2-propanediol. After that, the solution in the reaction vessel was stored at 65°C for 84 hours while stirring, and then cooled to room temperature to obtain a reaction solution containing silver nanowires.

The alcohol solvent used in this example contains 1,2-butanediol and 1,2-hexanediol present in the above solution A, and a small amount of 1,2-propanediol supplied by the above solution B as the alcohol ingredient. The mass ratio of the various alcohols in the total alcohol components is 24.5% for 1,2-butanediol, 73.7% for 1,2-hexanediol, and 1.8% for 1,2-propanediol. The mass ratio "polymer/silver mass ratio" to the total amount of silver used for reduction precipitation was 1.94.

The diameter and length of the obtained silver nanowire were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 18.4 nm and a diameter variation coefficient CV of 14.4% is synthesized, and the diameter variation is very small.

[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), Added lithium chloride (Manufactured by ALDRICH) 0.399 g of 1,2-propanediol solution with a content of 10% by mass, potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd.), 0.476 g of 1,2-propanediol solution with a content of 1% by mass, lithium hydroxide ( Aldrich Co.) 0.0711 g, aluminum nitrate nonahydrate (Kishida Chemical Co., Ltd.) content of 20% by mass 1,2-propanediol solution 0.503 g, vinylpyrrolidone and dimethyl diallyl ammonium nitrate (diallyldimethylammonium nitrate) nitrate) (copolymer made with 99% by mass of vinylpyrrolidone and 1% by mass of dimethyldiallylammonium nitrate, weight average molecular weight 75,000) 8.39g and dissolved to make solution A .

攪拌使其溶解製作為溶液B。 In a mixed solvent of alcohol and water composed of 9.57g of 1,2-propanediol and 0.80g of pure water, add 6.80g of silver nitrate and heat it at 35°C

The solution B was prepared by stirring and dissolving.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 65°C and a reaction hour of 84 hours in the following manner. The above-mentioned solution A was placed in a 1L beaker of the reaction vessel, and the temperature was raised from room temperature to 65°C while stirring, and the total amount of the solution B was added to the solution A in one minute. After the addition of solution B, the container and pipeline used to add solution B are co-washed with 4g of 1,2-propanediol. After that, the solution in the reaction vessel was stored at 65°C for 84 hours while stirring, and then cooled to room temperature to obtain a reaction solution containing silver nanowires.

The alcohol solvent used in this example contains the 1,2-butanediol and 1,2-hexanediol present in the above solution A, and a small amount of 1,2-propanediol supplied by the above solution B as Alcohol ingredients. The mass ratio of the various alcohols in the total alcohol components is 73.7% for 1,2-butanediol, 24.5% for 1,2-hexanediol, and 1.8% for 1,2-propanediol. The mass ratio "polymer/silver mass ratio" to the total amount of silver used for reduction precipitation was 1.94.

The diameter and length of the obtained silver nanowire were measured in the same manner as in Example 1. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 17.3nm and a coefficient of variation of the diameter CV of 14.7% is synthesized, and the variation of the diameter is very small.

[Example 11]

The experiment was performed under the same conditions as in Example 1, except that the addition amount of potassium bromide when the solution A was produced was changed from 0.0476 g to 0.0714 g in Example 7. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 17.7nm, a diameter variation coefficient CV of 13.6%, and a very small variation in diameter was synthesized.

[Example 12]

The experiment was performed under the same conditions as in Example 1, except that the addition amount of potassium bromide when the solution A was produced was changed from 0.0476 g to 0.0952 g in Example 7. The results are shown in Table 1. In this example, a very fine silver nanowire with an average diameter of 17.1nm and a coefficient of variation of the diameter CV of 14.6% is synthesized, and the variation of the diameter is very small.

[Comparative Example 1]

The experiment was performed 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, a silver nanowire with an average diameter of 22.7nm was synthesized. Although the diameter variation coefficient CV is as small as 11.9%, it is impossible to obtain extremely fine lines with an average diameter of less than 20 nm due to the high synthesis temperature.

[Comparative Example 2]

The experiment was performed 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, a silver nanowire with an average diameter of 24.7nm was synthesized. Although the diameter variation coefficient CV is as small as 13.4%, it is impossible to obtain extremely fine lines with an average diameter of less than 20 nm due to the high synthesis temperature.

[Comparative Example 3]

The experiment was performed 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, a silver nanowire with an average diameter of 24.7 nm was synthesized. Although the diameter variation coefficient CV is as small as 13.4%, it is impossible to obtain extremely fine lines with an average diameter of less than 20 nm due to the high synthesis temperature.

[Comparative Example 4]

At room temperature, to 8116.3 g of 1,2-propanediol, add 3.986 g of 1,2-propanediol solution with a lithium chloride content of 10% by mass, potassium bromide 0.0476g, lithium hydroxide 0.711g, aluminum nitrate nonahydrate Content of 20% by mass in 1,2-propylene glycol solution 4.994g, vinylpyrrolidone and dimethyldiallylammonium nitrate (diallyldimethylammonium nitrate) copolymer (based on vinylpyrrolidone 99% by mass, A copolymer made of 1% by mass of dimethyl diallyl ammonium nitrate, with a weight average molecular weight of 75,000) 83.875 g, was dissolved to prepare a solution A.

To a mixed solvent of alcohol and water composed of 95.70 g of 1,2-propanediol and 8.00 g of pure water, 67.96 g of silver nitrate was added, and the mixture was stirred and dissolved at 35°C to prepare a solution B.

The reduction and precipitation reaction of silver was carried out under the synthesis conditions of a synthesis temperature of 85°C and a reaction time of 24 hours as follows. Put the above-mentioned solution A in a 10L beaker of the reaction vessel and stir it at a rotation speed of 225 rpm from room temperature to 65°C, then add the total amount of solution B to the solution from two addition ports in one minute In A. After solution B is added, the container and pipeline used to add solution B are co-washed with 100g of 1,2-propanediol. After that, while stirring the solution in the reaction vessel, the vessel and pipeline used for adding solution B were co-washed with 100 g of 1,2-propanediol. After that, the solution in the reaction vessel was stored at 65°C for 24 hours while stirring, and then cooled to room temperature to obtain a reaction solution containing silver nanowires.

The alcohol solvent used in this example contains 1,2-propanediol present in the above-mentioned solution A, and a small amount of 1,2-propanediol supplied from the above-mentioned solution B as the alcohol component. That is, all the alcohol components are composed of 1,2-propanediol.

The diameter and length of the obtained silver nanowire were measured in the same manner as in Example 1. The results are shown in Table 2. In this example, a silver nanowire with an average diameter of 25.4nm and a variation coefficient of diameter CV of 15.6% was synthesized. In the case of 1,2-propanediol, which is a conventional alcohol solvent for the synthesis of silver nanowires, even if the synthesis temperature is reduced to below 90°C, it cannot be Synthesize an extremely fine silver nanowire with an average diameter of less than 20nm and a diameter variation coefficient CV of 15% or less, and a very small diameter variation.

[Comparative Example 5]

In Comparative Example 4, the experiment was performed under the same conditions as in Example 4, except that the synthesis temperature was further reduced to 65°C and the reaction hour was changed to 72 hours. The results are shown in Table 2. In this example, a silver nanowire with an average diameter of 20.6nm and a coefficient of variation CV of 22.3% was synthesized. In the case of 1,2-propanediol, which is a conventional alcohol solvent for the synthesis of silver nanowires, even if the synthesis temperature is reduced to 65°C, although silver nanowires with an average diameter of about 20nm can be synthesized, the diameter varies ( The coefficient of variation CV) becomes larger.

[Comparative Example 6]

Except that in Example 1, the 1,2-butanediol used in solution A was changed to 1,4-butanediol of the same quality (manufactured by Wako Pure Chemical Industries, Ltd., special grade). Try to synthesize silver nanowire under the same synthesis conditions.

The alcohol solvent used in this example contains 1,4-butanediol present in the above-mentioned solution A and a small amount of 1,2-propanediol supplied from the above-mentioned solution B as the alcohol component. The mass ratio of various alcohols in the total alcohol components is 98.2% for 1,4-butanediol and 1.8% for 1,2-propanediol.

The results are shown in Table 2. In this example, although 1,4-butanediol is used as an alkanediol with 4 carbon atoms in one molecule, silver nanowires cannot be synthesized. An example of a TEM (transmission electron microscope) photograph of the composite obtained in this example is shown in FIG. 4.

[Comparative Example 7]

Except that in Example 1, the 1,2-butanediol used in solution A was changed to 1,3-butanediol of the same quality (manufactured by Wako Pure Chemical Industries, Ltd., special grade). Try to synthesize silver nanowire under the same synthesis conditions.

The alcohol solvent used in this example contains the 1,3-butanediol present in the above-mentioned solution A and a small amount of 1,2-propanediol supplied from the above-mentioned solution B as the alcohol component. The mass ratio of various alcohols in the total alcohol components is 98.2% for 1,3-butanediol and 1.8% for 1,2-propanediol.

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

[Table 1]

[Table 2]

For reference, FIG. 6 shows a graph showing the relationship between the synthesis temperature and the average diameter, and FIG. 7 shows a graph showing the relationship between the synthesis temperature and the variation coefficient 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 in the following manner, and the haze was measured.

[Example 7A]

In this example, the silver nanowire obtained in Example 7 was used, and the experiment was carried out in the following order.

(Precipitation step)

To 8400 g of the reaction liquid (cooled to room temperature) obtained in the aforementioned Example 7, 1890 g of pure water was added and stirred for 10 minutes. Next, 7,580 g of acetone was added and stirred for 10 minutes. Next, 8820 g of xylene was added and stirred for 10 minutes. After that, let it stand for 3 hours. After standing, since the concentrate and supernatant were observed, the supernatant was partially removed, and the concentrate containing silver nanowires was recovered.

(First washing step)

A copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate (a total of 99% by mass of vinylpyrrolidone and 1% by mass of dimethyldiallylammonium nitrate) The polymer (weight average molecular weight 75,000) was dissolved in pure water to prepare a "polymer-containing aqueous solution" with the concentration of the aforementioned copolymer of 1% by mass. 160 g of this polymer-containing aqueous solution was added to the silver nanowire-containing concentrate recovered as described above, and stirred at 100 rpm for 2.5 hours with an infiltration machine. After that, 700 g of acetone was added to precipitate the solid content containing silver nanowires. The supernatant was removed, 150 g of acetone was further added, and the supernatant was removed. Next, 1280 g of the above-mentioned polymer-containing aqueous solution was added and stirred with a mixer at a rotation speed of 100 rpm for 12 hours to obtain a silver nanowire dispersion liquid that completed the first cleaning step.

(Second washing step)

Next, the above-mentioned silver nanowire dispersion liquid was stirred with a mixer at a rotation speed of 100 rpm while adding 4000 g of acetone, and then the stirring was stopped. Precipitate is formed, confirm the turbidity of the supernatant. The turbid supernatant contains short silver nanowires with a slow sedimentation speed (with an aspect ratio of less than 100). The line is the short line of the main body). The supernatant liquid was removed, and 1500 g of acetone was added while stirring at a rotation speed of 100 rpm using a stirrer, and then the stirring was stopped. After removing the supernatant, 1280 g of the aforementioned polymer-containing aqueous solution (the above-mentioned copolymer concentration is 1% by mass) was added, and stirred with a mixer at 100 rpm for 12 hours to obtain silver nanowires that completed the second cleaning step Dispersions.

(3rd to 6th washing steps)

By further repeating the same procedure as the above-mentioned second cleaning step 4 times, performing the third cleaning step to the sixth cleaning step, and obtaining a silver nanowire dispersion liquid that completed the sixth cleaning step. Each time the washing step is repeated, the turbidity of the supernatant will be reduced.

(Step 7)

Add 4000 g of acetone while stirring the silver nanowire dispersion after the sixth washing step with a mixer at a rotation speed of 100 rpm, and stop stirring after 10 minutes. After the precipitate was formed, the supernatant was removed, and 1500 g of acetone was added while stirring at a rotation speed of 100 rpm using a stirrer, and then the stirring was stopped. After the formation of the precipitate, the supernatant was removed, 1280 g of pure water was added, and the mixture was stirred at a rotation speed of 100 rpm for 12 hours using a mixer to obtain a silver nanowire dispersion liquid that completed the seventh cleaning step. The concentration of metallic silver in this dispersion was measured by ICP emission spectrometry (device: ICP emission spectrophotometer 720-ES manufactured by Agilent Technologies Co., Ltd.), and the concentration of silver nanowires was converted to 2.474 mass in terms of metallic silver. %.

(Hot water treatment of thickener)

Prepare a powder product of HPMC (hydroxypropyl methyl cellulose, manufactured by a chemical manufacturer, weight average molecular weight: 840,000) adjusted to 21.5% by mass of methoxy and 30.0% by mass of hydroxypropyl as a tackifier. Pour this powder into a sieve with a pore size of 200 μm. In a SUS tank with a capacity of 15L, 150g of the powder of the tackifier passing through the sieve is added to 6000g of pure water heated to 98°C, and stirred at 600rpm for 30 minutes with a disc turbine stirring blade with a diameter of 135mm to obtain Tackifier slurry. The slurry was filtered with PFA mesh under reduced pressure, and then, the residual on the mesh The remaining solid content of the tackifier is washed with hot water by pouring 6400 g of boiling pure water. After confirming that the hot water has been filtered, peel off the solid content of the tackifier before it has cooled to obtain a solid content of about 3 cm in size. After the solid content of the tackifier was dried at 70°C for 30 minutes, it was degranulated to a particle size of 1 cm or less before returning to room temperature. After that, it was dried at 70°C for 12 hours to obtain 120 g of a tackifier after hot water treatment. Divide the above operations into 2 times to obtain a total of 240g of tackifier after hot water treatment.

(Production of tackifier aqueous solution)

The dissolution of the tackifier uses a SUS tank with a capacity of 20L and a disc turbine type stirring blade with a diameter of 150mm. Add 150g of the above-mentioned hot water treatment to 9850g of pure water that has been heated to 95°C, and let it cool to 40°C while stirring at 475 rpm, and then cool the tank through a cooler by flowing into the cooling jacket of the tank. It was cooled with water and stirred for 12 hours. The temperature at the end of the stirring was 5°C. In this way, the tackifier is dissolved in water to obtain an aqueous solution of the tackifier. The obtained thickener aqueous solution was pressure-filtered at a set pressure of 0.2 MPa to remove insoluble components. Pressure filtration uses a deep pleated core filter (manufactured by ROKI TECHNO Co., Ltd.; SCP type) with a filter accuracy (pore size) of 1 μm. The concentration of the thickener component (HPMC) in the filtered thickener aqueous solution was 1.24% by mass.

(Production of silver nanowire dispersion for coating)

Put 313 g of the silver nanowire dispersion after the seventh cleaning step, 1920 g of pure water, and 347 g of the filtered tackifier aqueous solution into a container, and stir at 150 rpm using 6 inclined wheels with a diameter of 170 mm 2 hours. After that, 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 component in the liquid medium is water and alcohol. After measuring the metallic silver concentration of this silver nanowire dispersion by ICP emission spectrometry, the silver nanowire content was 0.180% by mass in terms of metallic silver.

(Production of transparent conductive film)

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

(Determination of Haze)

The haze of the above-mentioned transparent conductive film was evaluated based on the haze value (%) measured by Haze Meter NDH 5000 manufactured by Nippon Denshoku Kogyo Co., Ltd. Among them, in order to remove the influence of the PET substrate, the haze evaluation index H defined by the following formula (3) is used.

[Haze evaluation index H]=[substrate + haze value of transparent conductive film]-[haze value of substrate itself]...(3)

Here, [substrate + transparent conductive film haze value] refers to the haze value (%) of an object composed of the substrate film and the transparent conductive film formed on it, "the haze value of the substrate itself "Refers to the haze value (%) of the base film before the transparent conductive film is formed. The difference between the two, that is, the smaller the value of the haze evaluation index H, the less the amount of haze generated due to the transparent conductive film is evaluated.

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 nanowire obtained in Example 7 was used. Prior to the above-mentioned sixth washing step, it was performed under the same conditions as in Example 7A to obtain a silver nanowire dispersion liquid that completed the sixth washing step. Supply this in the following steps.

(Step 7)

After completing the sixth washing step, the silver nanowire dispersion was added with 4000 g of acetone while stirring at a rotation speed of 100 rpm with a stirrer, and stirring was stopped after 10 minutes. Remove the supernatant after the precipitate is formed Liquid, 1500 g of acetone was added while stirring at a rotation speed of 100 rpm using a stirrer, and then the stirring was stopped. After the precipitate is formed, the supernatant is removed, and 1280 g of the aforementioned polymer-containing aqueous solution (the above-mentioned copolymer concentration is 1% by mass) is added, and stirred with a mixer at 100 rpm for 12 hours to complete the seventh cleaning step. The silver nanowire dispersion.

(Production of silver nanowire dispersion for coating)

1000 g of acetone was added to 350 g of the silver nanowire dispersion after the seventh cleaning step was completed using a stirrer at a rotation speed of 100 rpm, and the stirring was stopped after 10 minutes. The supernatant liquid was removed, 375 g of acetone was added while stirring at a rotation speed of 100 rpm using a stirrer, and then the stirring was stopped. Secondly, after removing the supernatant, after adding 777g of 2-propanol, use an automatic disperser (Mazemazeman SKH-40) to carry out a dispersion treatment for 24 hours to obtain a silver nanowire dispersed in 2-propanol alcohol-based silver Nanowire dispersion. This alcohol-based silver nanowire dispersion was dissolved in 60% nitric acid, and analyzed by high-frequency inductively coupled plasma (ICP) emission spectrometry with CP-OES720 manufactured by Agilent Technologies, and the above-mentioned alcohol-based silver nanowires were calculated. The concentration of silver in the rice noodle dispersion. Based on the value of the silver concentration, the alcohol-based silver nanowire dispersion is diluted with a predetermined amount of 2-propanol to obtain a silver nanowire dispersion for coating with a silver concentration of 0.2% by mass.

(Production of transparent conductive film)

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

(Determination of Haze)

The haze evaluation index H was obtained 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 performed under the same conditions as in Example 7B except that the silver nanowire obtained in Comparative Example 4 was used and the precipitation step was performed under the following conditions.

(Precipitation step)

To 8400 g of the reaction liquid (cooled to room temperature) obtained in the foregoing Example 4, 1050 g of pure water was added and stirred for 10 minutes. Next, 7,580 g of acetone was added and stirred for 10 minutes. Next, 6320 g of xylene was added and stirred for 10 minutes, and then left to stand for 3 hours. After standing, since the concentrate and supernatant were observed, the supernatant was partially 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.

[table 3]

It was confirmed that silver nanowires with extremely fine average diameters and very small diameter variations are extremely useful for reducing the haze of the transparent conductive film.

Claims (10)

A silver nanowire with an average diameter of less than 20.0nm, an average aspect ratio A _M defined by the following formula (1) of 100 or more, a diameter variation coefficient CV of 15.0% or less, and the silver nanowire A polymer with vinylpyrrolidone structural unit is attached to the surface; A _M =L _M /D _M …(1) Wherein, L _M based an average length of silver nanowires in nm units represented by the value, D _M based the above average diameter expressed in nm of the value. The silver nanowire according to claim 1, wherein the polymer having a vinylpyrrolidone structural unit is a copolymer of vinylpyrrolidone and other monomers. The silver nanowire according to claim 1, wherein the polymer having vinylpyrrolidone structural unit is a copolymerization of vinylpyrrolidone and diallyldimethylammonium salt monomer Things. A reaction liquid used in the reduction and precipitation reaction of silver nanowires is obtained by dispersing the silver nanowires described in any one of claims 1 to 3 in an alcohol-based liquid medium. A method for producing silver nanowires, in which silver compounds and polymers with vinylpyrrolidone structural units are dissolved in an alcohol solvent to reduce and precipitate silver into linear form. The alcohol solvent is used at a temperature above 50°C. Reduction and precipitation at a temperature below 90°C, where the alcohol solvent is based on the mass ratio of the alcohol in the solvent and contains a total of 40% or more of 1,2-alkanediol with a carbon number of 4 or more and 6 or less. More than species. The method for producing silver nanowires according to claim 5, wherein the polymer having a vinyl pyrrolidone structural unit is a copolymer of vinyl pyrrolidone and other monomers. The method for producing silver nanowires according to claim 5, wherein the polymer having vinylpyrrolidone structural unit is vinylpyrrolidone and diallyldimethylammonium salt monomer The copolymer. The method for producing silver nanowires according to any one of claims 5 to 7, wherein the amount of the polymer having the vinylpyrrolidone structural unit present in the alcohol solvent and the silver used in the reduction precipitation The mass ratio of the total amount of "polymer/silver mass ratio" is 0.5 to 5.0. A silver nanowire dispersion liquid, which is obtained by dispersing the silver nanowire described in any one of claims 1 to 3 in a liquid medium. A silver nanowire dispersion liquid, wherein the silver nanowire described in any one of claims 1 to 3 is dispersed in a liquid medium in which the mass ratio of alcohol is 95% or more, and the total mass ratio of alcohol and water is 95 % Or more of the liquid medium, or the mass ratio of water is more than 95% of the liquid medium.

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