JP2019059977A - Method for producing silver nanowire, silver nanowire, silver nanowire ink and transparent conductive film - Google Patents

Abstract

To stably generate a wire having a high average length in particular and having an average aspect when a fine silver nanowire is synthesized by an alcohol solvent reduction process.SOLUTION: Provided is a method for producing a silver nanowire having a process where silver is subjected to reduction precipitation into a wire shape in an alcohol solvent dissolved with a silver compound and an organic protective agent, wherein a polymer having a vinylpyrrolidone structural unit is used as the organic protective agent and in a state where methyl-t-butyl ether is dissolved at a concentration of 0.3 to 25.0 mmol/L into the alcohol solvent, the reduction precipitation is progressed in the liquid.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing silver nanowires useful as a conductive material (filler) of a transparent conductive film. The present invention also relates to a silver nanowire, a silver nanowire ink, and a transparent conductive film obtained by the production method.

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

  Silver nanowires are considered promising as a conductive material for imparting conductivity to transparent substrates. After the liquid containing silver nanowires (silver nanowire ink) is applied to a transparent substrate such as glass, PET (polyethylene terephthalate), PC (polycarbonate), etc., the liquid component is removed by evaporation or the like, the silver nanowires are on the substrate Since a conductive network is formed by contacting each other, 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 clear visibility with little haze, in addition to good conductivity. 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 that are as thin and long as possible.

  Conventionally, as a synthesis method of silver nanowires, for example, a silver compound is dissolved in a polyol solvent such as ethylene glycol, and in the presence of a halogen compound and an organic protective agent, a linear shape is obtained using the reducing power of the solvent polyol. A method of precipitating metallic silver (hereinafter referred to as "alcohol solvent reduction method") is known. As the organic protective agent, PVP (polyvinyl pyrrolidone) has generally been widely used. PVP is a suitable organic protective agent for depositing thin and long silver nanowires.

  The molecules of the organic protective agent used in the alcohol solvent reduction method adsorb on the surface of the silver nanowire after synthesis, and become a factor governing the dispersibility of the silver nanowire in the liquid medium. Silver nanowires adsorbed with PVP exhibit good dispersibility in water. However, in order to improve the wettability to a substrate such as PET, it is advantageous to apply a silver nanowire ink using a mixed medium of water and an organic solvent (for example, alcohol). In addition, depending on the coating equipment, it may be desirable to apply a silver nanowire ink using a non-aqueous solvent. When considering the dispersibility of silver nanowires in such mixed media and non-aqueous solvents, PVP is not necessarily a satisfactory organic protective agent. Recently, various organic protective agents have been developed which can improve the dispersibility of silver nanowires in liquid media other than water. For example, Patent Document 1 is a copolymer having a polymerization composition of vinyl pyrrolidone and Diallyldimethylammonium salt monomer, Patent Document 2 is a copolymer of vinyl pyrrolidone and an acrylate based or methacrylate based monomer, and Patent Document 3 is Vinyl. Copolymers of pyrrolidone and maleimide based monomers are disclosed, respectively. In the alcohol solvent reduction method using these polymers as organic protective agents, it is possible to synthesize thin and long silver nanowires by optimizing the synthesis conditions, as well as or more than using PVP. is there.

JP, 2015-180772, A JP, 2017-78207, A JP, 2016-135919, A

  As described above, it is advantageous that the silver nanowires used as the conductive material of the transparent conductive coating film have a thin and long form from the viewpoint of achieving both conductivity and visibility at a high level. However, even if thin and long wires can be synthesized, if the wires easily form aggregates in the silver nanowire dispersion liquid, the yield of silver decreases and the handleability in subsequent steps decreases. Not only that, but the aggregates remaining in the final silver nanowire ink cause the reduction in the haze of the transparent conductor and the short circuit in the patterned circuit.

  The present invention is intended to provide a technology that is particularly effective in stably producing long wires when synthesizing thin silver nanowires by alcohol solvent reduction, and highly effective in suppressing aggregation of the synthesized wires. It is a thing.

  The above object is achieved in the alcohol solvent reduction method by advancing a precipitation reaction of silver in an environment in which a predetermined concentration of alkyl ether is present in the solvent. The following invention is disclosed in the present specification.

[1] In a method of producing a silver nanowire, the process of reducing and depositing silver in the form of a wire in an alcohol solvent in which a silver compound and an organic protective agent are dissolved,
Using a polymer having a vinyl pyrrolidone structural unit as the organic protective agent,
The alkyl ether is dissolved in the alcohol solvent at a concentration of 0.3 to 25.0 mol / L, and the reduction deposition is allowed to proceed in the liquid;
A method of producing silver nanowires characterized by
[2] The average length 15μm or more, the average diameter of 35nm or less, and the following (1) to an average aspect ratio A _M is the above-mentioned [1] of silver nanowires according to the silver nanowires to reduction precipitation of 800 or more as defined by the equation Manufacturing method.
A _M = L _M / D _M (1)
Here, L _M is a value representing the average length in nm, and D _M is a value representing the average diameter in nm.
[3] The method for producing silver nanowires according to the above [1] or [2], wherein the alkyl ether is methyl-t-butyl ether.
[4] The method for producing silver nanowires according to any one of the above [1] to [3], wherein the polymer is PVP (polyvinyl pyrrolidone) or a copolymer of vinyl pyrrolidone and a hydrophilic monomer.
[5] The polymer is vinyl pyrrolidone, diallyl dimethyl ammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, N-methyl maleimide, N-ethyl maleimide, N-propyl The above [1] to [3] having a polymerization composition with one or more monomers selected from maleimide, N-tert-butyl maleimide, 2-dimethylaminoethyl methacrylate, and 2-diethylaminoethyl methacrylate The manufacturing method of the silver nanowire in any one of.
[6] The method for producing silver nanowires according to any one of the above [1] to [5], wherein the polymer has a weight average molecular weight Mw of 30,000 to 300,000.
[7] A silver nanowire obtained by the method according to any one of the above [1] to [6].
[8] A silver nanowires ink, wherein the silver nanowires obtained by the method according to any one of the above [1] to [6] are dispersed in a liquid medium.
[9] A transparent conductive film containing, as a conductive material, the silver nanowire obtained by the method according to any one of the above [1] to [6].

The alkyl ether is a compound of the structural formula R-O-R 'type having an ether bond at one position. Here, R and R ′ mean an alkyl group represented by the general formula C _n H _{2n + 1} (n is an integer of 1 or more). This alkyl group is a functional group in the form of removing one hydrogen from an alkane, and is linear or has carbon (tertiary carbon) bonded to the other three carbons. There is. Methyl -t- butyl ether listed above as examples of alkyl ether may also be referred to as TBME (tert-butyl methyl ether), represented by the rational formula (CH _{3) 3} COCH _3.

  In the present specification, the average length, average diameter and average aspect ratio of silver nanowires follow the definitions below.

[Average length L _M ]
The trace length from one end of one silver nanowire to the other end of one silver nanowire is defined as the length of the wire on the image observed with a field emission scanning electron microscope (FE-SEM). A value obtained by averaging the lengths of the individual silver nanowires present on the microscopic image is defined as an average length L _M. In order to calculate the average length, the total number of wires to be measured is set to 100 or more. Here, the average length in the stage in which the silver nanowires recovered from the solution after the reduction reaction were washed (stage before being supplied to the purification step such as cross flow filtration) is evaluated.

[Average diameter D _M ]
On a bright field observation image by a transmission electron microscope (TEM), the distance between contours on both sides in the thickness direction of one silver nanowire is defined as the diameter of the wire. FIG. 4 exemplifies a TEM bright-field observation image (hereinafter referred to as “TEM image”) of silver nanowires according to the present invention. Each wire can be considered to have a substantially even thickness over its entire length. Therefore, thickness measurement can be performed by selecting a portion that does not overlap other wires. In the TEM image of one field of view, among the silver nanowires observed in the image, the diameters of all the wires except for the wires completely overlapping with other wires and whose diameter is difficult to measure are measured. The operation is performed on a plurality of randomly selected fields of view, the diameters of a total of 100 or more different silver nanowires are determined, the average value of the diameters of the individual silver nanowires is calculated, and the value is defined as the average diameter D _M.

[Average aspect ratio]
The average aspect ratio _AM is calculated by substituting the above average diameter D _M and the average length L _M into the following equation (1). However, it is assumed that D _M and L _M to be substituted into the equation (1) are both values expressed in nm.
A _M = L _M / D _M (1)

  According to the present invention, in the case of thin silver nanowires having an average diameter of, for example, 35 nm or less, particularly long silver nanowires having an average length of 15 nm or more and an average aspect ratio of 800 or more can be stably synthesized. Since long silver nanowires with an average length as described above can be obtained at the stage of completion of washing after synthesis, if the purification operation to adjust the wire length distribution by cross flow filtration etc. is performed thereafter, the average length will be Longer, high aspect ratio silver nanowires can be manufactured with high yield. When it is used as a conductive material of a transparent conductive film, a transparent conductive film excellent in visibility with less haze can be realized while maintaining high conductivity.

Structural formula of vinyl pyrrolidone structural unit. SEM photograph of the silver nanowire obtained in Comparative Example 1. SEM photograph of the silver nanowire obtained in Example 5.

  As described above, as a method of synthesizing silver nanowires, a method of precipitating silver in the form of a wire using the reducing power of alcohol as a solvent in an alcohol solvent in which a silver compound and an organic protective agent are dissolved has already been put to practical use It has been This method is called "alcohol solvent reduction method" in the present specification.

  In order to deposit metallic silver in the form of a wire by alcohol solvent reduction method, it is necessary for the polymer molecule of the organic protective agent to be selectively adsorbed on the {100} face of the nucleus crystal that is considered to be multiple twins of silver. It is. Thereby, the growth of the {100} plane is suppressed, the {111} plane which is the closest surface of the silver crystal is preferentially grown, and a linear structure of metallic silver is formed. The selective adsorptivity of polymer molecules is believed to be caused by the interaction between the surface potential of the polymer molecules and the surface potential of the silver crystal face. Homopolymers (PVP) and copolymers having vinyl pyrrolidone structural units are known as polymers excellent in selective adsorption to the silver crystal {100} plane. The structural formula of a vinyl pyrrolidone structural unit is shown in FIG. When the reduction deposition of silver proceeds under the condition that the organic protective agent mainly composed of such a polymer is dissolved in the alcohol solvent, the deposition of silver on the {111} crystal plane preferentially occurs, resulting in a rod shape. Alternatively, a linear metallic silver structure is obtained. However, in order to stably synthesize silver nanowires, it is general to coexist a halide or the like having the function of activating the {111} crystal plane in a solvent.

  The inventors have variously studied a method for improving the average length of the synthesized wire particularly when synthesizing a thin silver nanowire using a polymer having a vinyl pyrrolidone structural unit as an organic protective agent. As a result, it has been found that the addition of an alkyl ether is extremely effective, in addition to the additives such as the halide generally used conventionally. Alkyl ethers have the function of cleaning the {111} crystal face on which silver preferentially precipitates when synthesizing silver nanowires by the alcohol solvent reduction method, that is, the organic protective agent molecules on the {111} crystal face. It is thought that it has an effect of suppressing adsorption and activating the exposed {111} crystal face to promote the deposition of new silver. The action to activate the {111} crystal face is mainly borne by the conventional additives such as halides, but it is presumed that the alkyl ether also acts in a similar manner. The presence of the alkyl ether in addition to the halogen in the vicinity of the previously deposited linear structure of metallic silver increases the effect of the cleaning, and the thickness direction surface of the linear structure ({100} crystal plane) The relative ease of deposition on the lengthwise exposed surface ({111} crystal plane) relative to the ease of deposition of silver on silver is further enhanced, resulting in silver nanowires having a large average aspect ratio. It is considered that the synthesis becomes easy.

  There is a problem in increasing the amount of halide added for the purpose of enhancing the activation action of the {111} crystal face. The organic protective agent which coats the surface of the synthesized silver nanowire is attached with a halogen atom such as chlorine added at the time of synthesis, and the halogen atom is entrained into the transparent conductive film in association with the silver nanowire. . According to the inventor's investigation, it is confirmed that when the concentration of chlorine in the transparent conductive film is high, the deterioration with time of the transparent conductive film is promoted, and a problem that the conductivity is deteriorated early tends to occur. In this respect, in the method of strengthening the cleaning action of the {111} crystal face by the addition of the alkyl ether, the problem of the above-mentioned deterioration of the transparent conductive film with time is avoided.

As a result of various investigations, it is synthesized by proceeding reduction deposition in the state in which alkyl ether is dissolved in alcohol solvent at a concentration of 0.3 mmol / L (= 0.3 × 10 ⁻³ mol / L) or more. The effect of improving the average length of the silver nanowires is remarkable. More preferably, the alkyl ether concentration is 1.0 mmol / L (= 1.0 × 10 ⁻³ mol / L) or more. However, as the alkyl ether concentration increases, the effect of improving the average length of the silver nanowires becomes saturated. The alkyl ether concentration in the solvent may be set in the range of 25.0 mmol / L (= 25.0 × 10 ⁻³ mol / L) or less, and 20.0 mmol / L (= 20.0 × 10 ⁻³ mol / L). L) You may manage as follows.

  The amount ratio of the alkyl ether in the liquid is, for example, 1 mol of the polymer having a vinylpyrrolidone structural unit, which is an organic protective agent, in terms of the quantitative ratio to the organic protective agent present in the alcohol solvent at the time of the reductive deposition reaction. It is preferable to adjust in the range of 003 to 0.30 mol. In addition, the amount of the alkyl ether in the solution can be adjusted in the range of 0.005 to 0.50 mol at the time of reaction disclosure with respect to 1 mol of the total amount of silver used in the reaction, in terms of the amount ratio to silver. preferable.

Examples of the alkyl ether include ethyl methyl ether (CH ₃ CH ₂ OCH ₃ ), methyl-t-butyl ether ((CH ₃ ) ₃ COCH ₃ ) and ethyl isoamyl ether ((CH ₃ ) ₂ CHCH ₂ CH ₂ OC ₂ H ₅ ), ethyl-t-butyl ether ((CH ₃ ) ₃ COC ₂ H ₅ ), diisoamyl ether ((CH ₃ ) ₂ CHCH ₂ CH ₂ OCH ₂ CH ₂ CH (CH ₃ ) ₂ ), diisopropyl ether ((CH ₃ ) ₃ ) ₂ CHOCH (CH ₃ ) ₂ ), diethyl ether (C ₂ H ₅ OC ₂ H ₅ ), dibutyl ether (C ₄ H ₉ OC ₄ H ₉ ), dipropyl ether (C ₃ H ₇ OC ₃ H ₇ ) Dimethyl ether (CH ₃ OCH ₃ ), ethylene glycol monomethyl ether (CH ₃ OCH ₂ CH ₂ OH) and the like. The alkyl ether may be used alone or in combination of two or more.

  As a polymer having a vinylpyrrolidone structural unit used as an organic protective agent, PVP (polyvinylpyrrolidone) or a copolymer of vinylpyrrolidone and a hydrophilic monomer is a suitable target. The latter copolymers include, for example, vinyl pyrrolidone and diallyl dimethyl ammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, N-methyl maleimide, N-ethyl maleimide, N- Copolymers having a polymerization composition with one or more monomers selected from propyl maleimide and N-tert-butyl maleimide may be mentioned. The polymerization composition of the copolymer is preferably 0.1 to 10% by mass of monomers other than vinyl pyrrolidone, with the balance being vinyl pyrrolidone.

  The weight average molecular weight Mw of the polymer used for the organic protective agent is preferably in the range of 30,000 to 300,000, and more preferably in the range of 30,000 to 150,000. Mw can be determined by GPC (gel permeation chromatography).

[Dimensional shape of silver nanowires]
The silver nanowire is preferably as thin and long as possible from the viewpoint of forming a transparent conductive coating film excellent in conductivity and visibility. In the present invention, an object having an average length of 15 μm or more, an average diameter of 35 nm or less, and an average aspect ratio of 800 or more according to the equation (1) is suitable. It is more preferable that the average length is 15 μm or more and the average diameter is 33 nm or less. It is more preferable that the average length is 15 μm or more and the average diameter is 30 nm or less. In the present invention, silver nanowires having a long average length and a large average aspect ratio can be obtained in the synthesis stage, so that the length distribution can be efficiently adjusted at a high yield, for example, by cross flow purification in the subsequent steps. Can.

[Synthesis of silver nanowires]
With the exception of the presence of the alkyl ether in the alcohol solvent, conventionally developed techniques for alcohol solvent reduction can be used. As a kind of alcohol which is a solvent, what has moderate reducing power with respect to silver, and can precipitate metallic silver in a wire form is selected. For example, using an alcohol solvent comprising one or more of ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,3 butanediol, 1,4-butanediol and glycerin it can. These alcohols may be used alone or in combination of two or more. As a silver source, a silver compound soluble in 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 the solubility in a solvent and the cost. In addition to the silver compound, the organic protective agent and the alkyl ether, it is preferable to proceed the reduction deposition in an alcohol solvent in which a chloride or a bromide is dissolved. Furthermore, reduction deposition may be allowed to proceed in an alcohol solvent in which an alkali metal hydroxide or aluminum salt is dissolved. For example, in the method disclosed in Patent Document 1, an alcohol solvent to which an alkyl ether is added can be applied.

Comparative Example 1
(Organic protective agent)
A copolymer powder was prepared by dissolving 1-vinyldipyrrolidone and diallyldimethylammonium nitrate in methyl isobutyl ketone as a solvent, and adding a polymerization initiator to carry out copolymerization. The polymerization composition is 1-vinyldipyrrolidone: diallyldimethylammonium nitrate = 99: 1 in molar ratio.

The 1H NMR spectrum of the copolymer powder was measured by nuclear magnetic resonance spectroscopy (NMR) with JNM-LA400 (400 MHz) manufactured by JEOL Ltd., and the components contained in the powder were examined. As a result, in molar ratio, polymer 95.53%, residual VP (vinyl pyrrolidone): 0.62%, ethyl acetate: 2.79%, methyl t-butyl ether: 0.00%, methyl isobutyl ketone: 1. It was 06%. Here, ethyl acetate uses the integral value of the peak around 4.1 ppm, methyl-t-butyl ether uses the integral value of the peak around 1.2 ppm, and methyl isobutyl ketone uses the integral value of the peak around 0.9 ppm The mole% of each component was calculated. The residual VP amount was determined by the following equation (2).
VP _R (mol%) = [2 × (I ₁ + I ₂ ) / (3 × I ₃ )] × 100 (2)
Here, I ₁ is the integrated value of the peak (7.0-7.2 ppm) derived from the methine proton related to the C = C double bond of the VP monomer, and I ₂ is related to the C = C double bond of the same monomer integral value of peaks derived from the methylene protons (4.3-4.4ppm), I ₃ is the integral value of the peak (3.0-3.4ppm) derived from the methylene protons adjacent to the N atom of the polymer.

Further, the weight average molecular weight Mw of the above copolymer was determined by GPC (gel permeation chromatography) under the following conditions.
・ Device: HLC-8320GPC EcoSEC (made by Tosoh Corporation)
・ Column: TSKgel GMPWXL (× 2) + G2500PWXL
Eluent: 100 mM aqueous sodium nitrate solution / acetonitrile = 80/20
・ Flow rate: 1.0 mL / min
Temperature: 40 ° C
Injection volume: 200 μL
-Multi-angle light scattering detector: DAWN HELEOS II (manufactured by Wyatt Technology)
Refractive index (RI) detector: Optilab T-rEX (manufactured by Wyatt Technology)
As a result, the weight average molecular weight Mw was 89,078.

(Synthesis of silver nanowires)
0.302 g of a propylene glycol solution having a lithium chloride content of 10% by mass in 513.5 g of propylene glycol at normal temperature, 0.893 g of a propylene glycol solution having a potassium bromide content of 1% by mass, lithium hydroxide Solution A was prepared by dissolving 0.0222 g, 0.312 g of a propylene glycol solution having an aluminum nitrate nonahydrate content of 20% by mass, and 5.24 g of the above-mentioned copolymer powder as a source of the organic protective agent. In this example, no alkyl ether is added to solution A. In a separate container, 4.25 g of silver nitrate is added to a mixed solution of 5.98 g of propylene glycol and 0.5 g of pure water, and the solution B containing silver is dissolved by stirring at 35 ° C. Obtained.

The above solution A is put in a reaction vessel and heated from normal temperature to 95 ° C. with stirring at a rotational speed of 250 rpm, and then the whole solution B is added to solution A using a tube pump from two addition ports. Added over a minute. After the addition of solution B, 4 g of a propylene glycol solution is added using a tube pump in order to wash out the inside of the tube to which solution B adheres, and then it is kept stirring at 95 ° C. for 3.5 hours. Cooled to 0 C over 2.0 hours and held at 85 0 C for 19 hours. Then, the silver nanowire was synthesize | combined by cooling a reaction liquid to normal temperature.
The reaction liquid of the stage cooled to normal temperature containing the synthesized silver nanowire is referred to as “post-synthesis reaction liquid” (the same in each of the following examples).

(Average diameter of silver nanowires, average length measurement)
20 g of the post-synthesis reaction solution was separated into a centrifuge tube, 180 g of pure water was added, and centrifugation was performed at 1500 rpm for 15 minutes using a centrifuge. Since the concentrate and the supernatant were observed, the supernatant portion was removed and the concentrate was recovered. This washing operation was repeated several more times to obtain a concentrate. The obtained concentrate was dispersed in pure water. In measuring the length of silver nanowires, the dispersion is placed on an observation table for SEM, water is volatilized on the observation table, and then a field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation; S-4700) The observation was performed at an acceleration voltage of 3 kV and a magnification of 1,500. For three or more randomly selected fields of view, the average length was measured according to the above definition using software (Dr. Kampas) for all wires whose full length can be confirmed within the field of view. In the diameter measurement, the dispersion was placed on an observation table for TEM, and bright field images were observed at an acceleration voltage of 100 kV and a magnification of 40,000 with a transmission electron microscope (manufactured by JEOL Ltd .; JEM-1011). The observation image is taken, and the original image taken to accurately measure the diameter is enlarged to twice the size, and then using software (Motic Image Plus 2.1 S), the average diameter is determined according to the above definition. It was measured. The average aspect ratio was determined by substituting the values of the average length and the average diameter into the equation (1). The average diameter of the silver nanowires was 26.7 nm, and the average length was 20.5 μm. The average aspect ratio was 20500 (nm) /26.7 (nm) ≒ 768. The results are summarized in Table 1 together with other examples and comparative examples.

Example 1
Comparative Example 1 was carried out except that, in addition to the respective substances mixed in Comparative Example 1, 0.0263 g of methyl-t-butyl ether was further mixed and dissolved as solution A when synthesizing silver nanowires. The experiment was performed under the same conditions as in. The concentration of methyl-t-butyl ether in the alcohol solvent at the initiation of the precipitation reaction of silver (ie, the initiation of the addition of solution B) is 0.598 mmol / L. The average diameter of silver nanowires obtained under this condition was 28.4 nm, and the average length was 23.3 μm. The average aspect ratio was 23300 (nm) /28.4 (nm) ≒ 820.

Example 2
Comparative Example 1 was carried out except that, in addition to the respective substances mixed in Comparative Example 1, 0.0798 g of methyl-t-butyl ether was further mixed and dissolved as solution A when synthesizing silver nanowires. The experiment was performed under the same conditions as in. The concentration of methyl-t-butyl ether in the alcohol solvent at the initiation of the precipitation reaction of silver (that is, the initiation of the addition of solution B) is 1.811 mmol / L. The average diameter of the silver nanowire obtained under this condition was 27.8 nm, and the average length was 24.5 μm. The average aspect ratio was 24500 (nm) /27.8 (nm) ≒ 881.

[Example 3]
Comparative Example 1 was carried out except that, in addition to the respective substances mixed in Comparative Example 1, 0.1344 g of methyl-t-butyl ether was further mixed and dissolved as solution A when synthesizing silver nanowires. The experiment was performed under the same conditions as in. The methyl-t-butyl ether concentration in the alcohol solvent at the initiation of the precipitation reaction of silver (that is, the initiation of the addition of the solution B) is 3.049 mmol / L. The average diameter of silver nanowires obtained under this condition was 27.7 nm, and the average length was 22.7 μm. The average aspect ratio was 22700 (nm) /27.7 (nm) ≒ 819.

Example 4
Comparative Example 1 was carried out except that, as the solution A, 0.4250 g of methyl-t-butyl ether was further mixed and dissolved in addition to the respective materials mixed in Comparative Example 1 when synthesizing silver nanowires. The experiment was performed under the same conditions as in. The methyl-t-butyl ether concentration in the alcohol solvent at the initiation of the precipitation reaction of silver (ie, the initiation of the addition of solution B) is 9.643 mmol / L. The average diameter of silver nanowires obtained under this condition was 27.0 nm, and the average length was 24.5 μm. The average aspect ratio was 24500 (nm) /27.0 (nm) 907 907.

[Example 5]
Comparative Example 1 was carried out except that, in addition to the respective substances mixed in Comparative Example 1, 0.5825 g of methyl-t-butyl ether was further mixed and dissolved as solution A when synthesizing silver nanowires. The experiment was performed under the same conditions as in. The concentration of methyl-t-butyl ether in the alcohol solvent at the initiation of the precipitation reaction of silver (that is, the initiation of the addition of solution B) is 13.215 mmol / L. The average diameter of the silver nanowire obtained under this condition was 27.0 nm, and the average length was 26.2 μm. The average aspect ratio was 26200 (nm) /27.0 (nm) 970 970.

  As can be seen from Table 1, the presence of the alkyl ether in the alcohol solvent at the time of silver nanowire synthesis can significantly improve the average length of the synthesized wire and, accordingly, the average aspect ratio of the wire also improves. Do.

  For reference, a SEM photograph of the silver nanowire obtained in Comparative Example 1 is shown in FIG. 2, and a SEM photograph of the silver nanowire obtained in Example 5 is shown in FIG.

<< Measurement of number of aggregates >>
Next, the number of agglomerated particles was examined as follows for some of the above examples (Comparative Example 1, Example 2, and Example 5).
After 500 mL of the reaction liquid after synthesis was taken and transferred to a PFA bottle with a volume of 20 L, 10 kg of acetone was added and stirred for 15 minutes. Then left to stand for 24 hours. After standing, a concentrate and a supernatant were observed, so the supernatant portion was removed to obtain a concentrate. An appropriate amount of 1% by mass PVP (polyvinylpyrrolidone) aqueous solution was added to the obtained concentrate, and the mixture was stirred for 3 hours to confirm that the silver nanowires were redispersed. After stirring, 1 kg of acetone was added and stirred for 10 minutes and then allowed to stand. After standing, a concentrate and a supernatant were newly observed, so the supernatant portion was removed to obtain a concentrate. To the obtained concentrate, 80 g of pure water was added, and stirred for 12 hours to redisperse the silver nanowires. After 1 kg of acetone was added to the redispersed silver nanowire dispersion, the mixture was stirred for 30 minutes and then allowed to stand. After standing, a concentrate and a supernatant were newly observed, so the supernatant portion was removed to obtain a concentrate. An appropriate amount of 0.5 mass% PVP aqueous solution was added to the obtained concentrate, and stirred for 12 hours. The silver nanowires-containing solution after stirring was diluted with pure water so that the content of silver nanowires was adjusted to 0.05% by mass. Thus, a silver nanowire-containing solution after washing was obtained.

  Measurement of the number of particles having a particle diameter of 10 μm or more and 300 μm or less present in the solution after the above-mentioned washing using a flow type particle image analyzer (manufactured by Sysmex, FPIA-3000S) by dark field measurement did. Since the medium of this silver nanowires-containing liquid is water, pure water was used as the sheath liquid in the measurement. The measurement conditions were an LPF measurement mode, a quantitative count mode, and 10 repeated measurements. Moreover, the maximum length limitation range was 10-300 micrometers, and the average luminance value limitation range was 0-40. Ten measured values were integrated, and the number of aggregates per 55 μL of the silver nanowire-containing solution was taken as the number of aggregates counted in the silver nanowire-containing solution. Table 2 shows the results.

  As can be seen from Table 2, the presence of the alkyl ether in the alcohol solvent at the time of silver nanowire synthesis is effective not only to improve the average aspect ratio of the silver nanowires to be synthesized but also to suppress aggregation of the wires.

Claims (9)

In a method of producing a silver nanowire, comprising the step of reducing and precipitating silver in the form of a wire in an alcohol solvent in which a silver compound and an organic protective agent are dissolved,
Using a polymer having a vinyl pyrrolidone structural unit as the organic protective agent,
The alkyl ether is dissolved in the alcohol solvent at a concentration of 0.3 to 25.0 mmol / L, and the reduction deposition is allowed to proceed in the liquid;
A method of producing silver nanowires characterized by Average length 15μm or more, the average diameter of 35nm or less, and the following (1) Silver nanowires method according to claim 1 for the average aspect ratio A _M is precipitated reducing silver nanowires 800 or more defined by the equation.
A _M = L _M / D _M (1)
Here, L _M is a value representing the average length in nm, and D _M is a value representing the average diameter in nm.   The method for producing silver nanowires according to claim 1, wherein the alkyl ether is methyl-t-butyl ether.   The method for producing silver nanowires according to any one of claims 1 to 3, wherein the polymer is PVP (polyvinyl pyrrolidone) or a copolymer of vinyl pyrrolidone and a hydrophilic monomer.   The polymer is selected from vinyl pyrrolidone, diallyl dimethyl ammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, N-methyl maleimide, N-ethyl maleimide, N-propyl maleimide, N The polymer according to any one of claims 1 to 3, which has a polymerization composition with one or more monomers selected from -tert-butylmaleimide, 2-dimethylaminoethyl methacrylate, and 2-diethylaminoethyl methacrylate. The manufacturing method of the silver nanowire as described.   The method for producing silver nanowires according to any one of claims 1 to 5, wherein the polymer has a weight average molecular weight Mw of 30,000 to 300,000.   The silver nanowire obtained by the manufacturing method of any one of Claims 1-6.   The silver nanowire ink which the silver nanowire obtained by the manufacturing method of any one of Claims 1-6 is disperse | distributing in a liquid medium.   The transparent conductive film which contains the silver nanowire obtained by the manufacturing method of any one of Claims 1-6 as a electrically conductive material.