TW201920517A - Method for manufacturing silver nanowire and silver nanowire, silver nanowire ink and transparent conductive film - Google Patents

Abstract

When fine silver nanowires are synthesized by alcohol solvent reduction method, in particular, metal wires with a long average length and large average aspect ratio can be stably produced. A method for manufacturing silver nanowires according to the present invention has a step of reducing and precipitating silver in a wire form in an alcohol solvent in which a silver compound and an organic protective agent are dissolved, wherein a polymer having a vinylpyrrolidone structural unit is used as the organic protective agent, and a state in which an organic acid ester is dissolved in the alcohol solvent at a concentration of 0.1 to 20.0 mmol/L is provided, and the reduction precipitation is performed in the solution.

Description

   Method for manufacturing silver nanowire, silver nanowire, silver nanowire ink and transparent conductive film   

The present invention relates to a method for manufacturing silver nanowires which is used as a conductive material (filler) as a transparent conductive film. The present invention relates to a silver nanowire, a silver nanowire ink, and a transparent conductive film obtained by the manufacturing method.

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

The silver nanowire system is considered to be a promising conductive material for imparting conductivity to a transparent substrate. A silver nanowire-containing liquid (silver nanoline ink) is coated on a transparent substrate such as glass, PET (polyethylene terephthalate), PC (polycarbonate), and the like is evaporated by evaporation or the like When the liquid component is removed, the silver nanowires form a conductive mesh structure by contacting each other on the substrate, so that a transparent conductive film can be realized.

For transparent conductive films used in touch panels of electronic equipment, in addition to good conductivity, clear visibility with low haze is also required. Regarding a transparent conductive film using silver nanowires as a conductive material, it is advantageous to use silver nanowires that are as fine and long as possible to coexist conductivity and visibility at a high level.

Previously, in the synthesis method of silver nanowires, for example, it is known to dissolve a silver compound in a polyhydric alcohol solvent such as ethylene glycol, and reduce the polyhydric alcohol as a solvent in the presence of a halogen compound and an organic protective agent. A method for precipitating metallic silver in a linear shape (hereinafter referred to as "alcohol solvent reduction method"). Regarding this organic protective agent, PVP (polyvinyl pyrrolidone) is usually used in the past. From the viewpoint of precipitating fine and long silver nanowires, PVP is a suitable organic protective agent.

The molecules of the organic protective agent used in the alcohol solvent reduction method are adsorbed on the surface of the synthesized silver nanowires, and become the main reason for controlling the dispersibility of the silver nanowires in the liquid medium. The silver nanowires adsorbed by PVP show good dispersibility to water. However, if it is desired to improve the wettability to a substrate such as PET, it is advantageous to apply a silver nano-line printing ink made of a mixed medium using water and an organic solvent (for example, an alcohol). In addition, depending on the coating equipment, there are cases where silver nano-line printing ink made by using a non-aqueous solvent is preferable. Considering the dispersibility of silver nanowires in such a mixed medium and a non-aqueous solvent, PVP may not necessarily be a satisfactory organic protective agent. Recently, various organic protective agents have been developed which can improve the dispersibility of silver nanowires in a liquid medium other than water. For example, Patent Document 1 discloses a copolymer having a polymer composition composed of vinyl pyrrolidone and a diallyl dimethyl ammonium salt monomer, and Patent Document 2 discloses a copolymer composed of ethylene As a copolymer of a pyrrolidone and an acrylate-based or methacrylate-based monomer, Patent Document 3 discloses a copolymer of a vinylpyrrolidone and a maleimide-based monomer. In the alcohol-solvent reduction method using these polymers as an organic protective agent, it is possible to synthesize fine and long silver nanowires of the same degree or more when using PVP by adjusting the synthesis conditions.

    [Prior technical literature]         [Patent Literature]    

[Patent Document 1] Japanese Patent Laid-Open No. 2015-180772

[Patent Document 2] Japanese Patent Laid-Open No. 2017-78207

[Patent Document 3] Japanese Patent Laid-Open No. 2016-135919

As described above, the silver nanowire used as the conductive material of the transparent conductive coating film is advantageous in that it has a fine and long form from the viewpoint of coexistence of conductivity and visibility at a high level. The present invention provides a technique for stably forming a particularly long metal wire when synthesizing a thinner silver nano wire using an alcohol solvent reduction method.

In view of the above object, in the alcohol solvent reduction method, it is achieved by performing a precipitation reaction of silver in an environment where a predetermined concentration of an organic acid ester is present in a solvent. This specification discloses the following inventions.

[1] A method for producing silver nanowires, comprising: a step of reducing and precipitating silver into a linear form in an alcohol solvent in which a silver compound and an organic protective agent are dissolved; wherein the organic protective agent is a vinylpyrrole A polymer of a pyridone structural unit; a state in which an organic acid ester is dissolved in the alcohol solvent at a concentration of 0.1 to 20.0 mmol / L, and the aforementioned reduction and precipitation are performed in a liquid.

[2] The method for producing a silver nanowire according to the above [1], wherein the average aspect ratio A is set to an average length of 15 μm or more and an average diameter of 35 nm or less as defined by the following formula (1) Reduction and precipitation of silver nanometers with _M above 600, A _M = L _M / D _M … (1)

Here, L _M is a value in which the average length is expressed in nm, and D _M is a value in which the average diameter is expressed in nm.

[3] The method for producing silver nanowires according to the above [1] or [2], wherein the organic acid ester is one of methyl acetate, ethyl acetate, propyl acetate, and butyl acetate, or 2 or more.

[4] The method for producing a silver nanowire according to any one of the above [1] to [3], wherein the polymer is PVP (that is, polyvinylpyrrolidone) or vinylpyrrolidine Copolymer of ketone and hydrophilic monomer.

[5] The method for producing a silver nanowire according to any one of the above [1] to [3], wherein the polymer has a compound consisting of "vinylpyrrolidone" and "selected from diallyl Dimethylammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, N-methylcis butylenediimine, N-ethylcis Butenedifluorene imine, N-propylcis butylenediimide, N-third butylcis butylenediimine, 2-dimethylaminoethyl methacrylate and 2-dimethymethacrylate Polymerization composition of one or more monomers in ethylaminoethyl ".

[6] The method for producing a silver nanowire according to any one of the above [1] to [5], wherein the weight average molecular weight Mw of the polymer is 30,000 to 300,000.

[7] A silver nanowire obtained by the manufacturing method described in any one of the above [1] to [6].

[8] A silver nano-line printing ink obtained by dispersing the silver nano-line obtained by the manufacturing method described in any one of [1] to [6] in a liquid medium.

[9] A transparent conductive film containing a silver nanowire obtained by the manufacturing method according to any one of [1] to [6] as a conductive material.

In this specification, the average length, average diameter, and average aspect ratio of silver nanowires are defined as follows.

[Average length L _M ]

In an observation image obtained by an electric field emission scanning electron microscope (FE-SEM), a track length from one end to the other end of a certain silver nanowire is defined as the length of the metal wire. The average value of the lengths of the silver nanowires present on the microscope image is defined as the average length L _M. To calculate the average length, the total number of metal wires to be measured is set to 100 or more. Here, it refers to the stage after "washing the silver nanowire recovered from the liquid after the reduction reaction is completed (that is, the stage before supplying to purification steps such as cross flow filtration)""To evaluate the average length.

[Average diameter D ^M ]

In a bright-field observation image obtained by a transmission electron microscope (TEM), the distance between wheels on both sides of the thickness direction of a silver nanowire is defined as the diameter of the metal wire. FIG. 4 illustrates a bright-field observation image (hereinafter referred to as a “TEM image”) obtained by the TEM of the silver nanowire of the present invention. Each metal wire system can be regarded as having approximately uniform thickness over the entire length. Therefore, the measurement of the thickness can be performed by selecting a portion that does not overlap with another metal wire. Randomly select a plurality of fields of view, and perform "except for the measurement of TEM images of 1 field of view, among the silver nanowires observed in this image, metal wires that completely overlap with other metal wires and are difficult to measure the diameter are excluded. The operation of "the diameter of all the metal wires" is to obtain the diameters of 100 or more different silver nanowires in total, and calculate the average value of the diameters of the silver nanowires, and define this value as the average diameter D _M.

[Average aspect ratio]

The average aspect ratio A _M is calculated by substituting the above-mentioned average diameter D _M and average length L _M into the following formula (1). However, D _M and L _M substituted into the formula (1) are set to values expressed in nm units.

A _M = L _M / D _M … (1)

According to the present invention, among fine silver nanowires having an average diameter of, for example, 35 nm or less, long silver nanowires having an average length of 15 nm or more and an average aspect ratio of 600 or more can be stably synthesized. Since silver nanowires with a long average length as described above can be obtained at the stage at the end of the washing performed after the synthesis, a purification operation to adjust the length distribution of the metal wires by cross-flow filtration or the like is performed thereafter. In this case, silver nanowires having a longer average length and a high aspect ratio can be produced with good yield. When it is used as a conductive material of a transparent conductive film, a transparent conductive film having excellent visibility and low haze can be realized while maintaining high conductivity.

FIG. 1 is a structural formula of a vinylpyrrolidone structural unit.

FIG. 2 is a SEM photograph of silver nanowires obtained in Comparative Example 1. FIG.

FIG. 3 is a TEM photograph of a silver nanowire obtained in Comparative Example 1. FIG.

FIG. 4 is a SEM photograph of the silver nanowire obtained in Example 3. FIG.

FIG. 5 is a TEM photograph of the silver nanowire obtained in Example 3. FIG.

As described above, in the method for synthesizing silver nanowires, a method of depositing silver into a linear shape using the reducing power of the alcohol as a solvent in an alcohol solvent in which a silver compound and an organic protective agent are dissolved has been put into practical use. This method is called "alcohol solvent reduction method" in this specification.

If the metallic silver is to be precipitated into a linear shape by the alcohol solvent reduction method, the polymer molecules of the organic protective agent must be selectively adsorbed to {100, which is considered to be the core crystal of multiply twinned particles of silver. }surface. This suppresses the growth of the {100} plane, preferentially grows the {111} plane belonging to the close-packed plane of silver crystals, and forms a linear structure of metallic silver. The selective adsorption of the polymer molecules is considered to be caused by the interaction between the surface potential of the polymer molecules and the surface potential of the silver crystal plane. Polymers having excellent selective adsorption for the {100} plane of silver crystals are known, for example, homopolymers (PVP) or copolymers having a vinylpyrrolidone structural unit. FIG. 1 is a structural formula showing a vinylpyrrolidone structural unit. When the organic protective agent mainly composed of such a polymer is dissolved in an alcohol solvent to reduce the precipitation of silver, the precipitation of silver preferentially occurs on the {111} crystal plane, and a rod-shaped or linear metal is obtained. Silver structure. However, if silver nanowires are to be stably synthesized, a halide or the like having a function of activating the {111} crystal plane is usually coexisted in a solvent in advance.

The present inventors have conducted various studies on "methods for particularly increasing the average length of the synthesized metal wires when synthesizing fine silver nanowires using a polymer having a vinylpyrrolidone structural unit as an organic protective agent". As a result, it was found that the addition of organic acid esters is very effective in addition to additives such as halides that have been conventionally used. When synthesizing silver nanowires by the alcohol solvent reduction method, it is considered that the organic acid esters have the effect of cleaning the {111} crystal surface that preferentially precipitates silver, that is, it can inhibit the adsorption of organic protective agent molecules on the {111} crystal At the same time, it also activates the exposed {111} crystal plane and promotes the precipitation of new silver. The effect of activating the {111} crystal plane was previously mainly borne by halides and the like which are common additives, but it is speculated that organic acid esters also have similar effects. In the vicinity of the linear structure of the deposited metallic silver, if an organic acid ester is present in addition to the halogen, it is considered that the above-mentioned cleaning effect can be increased, compared with "the thickness direction of the linear structure". The ease of silver precipitation on the surface ({100} crystal plane) "further improves the" relative ease of silver precipitation on the exposed surface ({111} crystal plane) in the longitudinal direction ". As a result, it is easy to synthesize a large average aspect ratio Silver nanometer.

If the amount of halide added is increased for the purpose of enhancing the activation of the {111} crystal plane, there are problems. A halogen atom such as chlorine added during the synthesis will adhere to the organic protective agent covering the surface of the synthesized silver nanowire, and the halogen atom will enter the transparent conductive film along with the silver nanowire. According to the investigation by the present inventors, it has been confirmed that if the chlorine concentration in the transparent conductive film is high, there is a problem that the degradation of the transparent conductive film with time is promoted and the conductivity is reduced at an early stage. In this regard, if a method of enhancing the cleaning effect of the {111} crystal plane by adding an organic acid ester is used, the problem of deterioration of the transparent conductive film over time as described above can be avoided.

As a result of various studies, if the organic acid ester is reduced and precipitated by dissolving the organic acid ester in an alcohol solvent at a concentration of 0.1 mmol / L (= 0.1 × 10 ^-3 mol / L) or more, it can significantly exert its advantages The effect of increasing the average length of synthetic silver nanowires. More preferably, the organic acid ester concentration is 0.5 mmol / L (= 0.5 × 10 ^-3 mol / L) or more. However, as the concentration of the organic acid ester becomes higher, the effect of increasing the average length of the silver nanowires gradually becomes saturated. The concentration of the organic acid ester in the solvent may be set to a range of 20.0 mmol / L (20.0 × 10 ^-3 mol / L) or less, and may be controlled to 15.0 mmol / L (15.0 × 10 ^-3 mol / L). the following.

In terms of the amount ratio with the "organic protective agent present in the alcohol solvent at the time of reduction and precipitation reaction", for example, compared with 1 mole of the polymer having a vinylpyrrolidone structural unit as an organic protective agent, Preferably, the amount of the organic acid ester in the liquid is adjusted to a range of 0.001 to 0.3 mol. In addition, in terms of the ratio to silver, it is preferable to adjust the amount of organic acid ester present in the liquid at the time of the reaction to 0.001 to 0.5 mol relative to the total amount of silver used in the reaction. Ear range.

Examples of the organic acid esters include diethyl adipate (C ₁₀ H ₁₈ O ₄ ), triethyl acetoacetate (C ₁₄ H ₂₂ O ₈ ), and isoamyl benzoate (C ₁₂ H ₁₆ O ₂ ), ethyl benzoate (C ₉ H ₁₀ O ₂ ), ethyl isovalerate (C ₇ H ₁₄ O ₂ ), ethyl formate (C ₃ H ₆ O ₂ ), butyl formate (C ₅ H ₁₀ O ₂ ), tributyl citrate (C ₁₈ H ₃₂ O ₇ ), diethyl oxalate (C ₆ H ₁₀ O ₄ ), diethyl tartrate (C ₈ H ₁₄ O ₆ ), stearic acid Ethyl ester (C ₂₀ H ₄₀ O ₂ ), ethyl lactate (C ₅ H ₁₀ O ₃ ), diethyl phthalate (C ₁₂ H ₁₄ O ₄ ), ethyl propionate (C ₅ H ₁₀ O ₂ ), Diisopropyl maleate (C ₁₀ H ₁₆ O ₄ ), diethyl malonate (C ₇ H ₁₂ O ₄ ), ethyl butyrate (C ₆ H ₁₂ O ₂ ), methyl acetate (C ₃ H ₆ O ₂ ), ethyl acetate (C ₄ H ₈ O ₂ ), propyl acetate (C ₅ H ₁₀ O ₂ ), butyl acetate (C ₆ H ₁₂ O ₂ ), ethyl acetate (C ₆ H ₁₀ O ₃ ), methyl ethyl acetate (C ₅ H ₈ O ₃ ), amyl acetate (C ₇ H ₁₄ O ₂ ), isobutyl acetate (C ₆ H ₁₂ O ₂ ), benzyl acetate (C ₉ H ₁₀ O ₂ ) and other acetates. One or more organic acid esters can be used.

The polymer having a vinylpyrrolidone structural unit used as an organic protective agent is preferably a PVP (polyvinylpyrrolidone) or a copolymer of a vinylpyrrolidone and a hydrophilic monomer. Thing. As for the latter copolymer, for example, there are compounds having "vinyl pyrrolidone" and "selected from diallyl dimethyl ammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid 2 -Hydroxyethyl ester, 4-Hydroxybutyl acrylate, N-methylcis butylene diimide, N-ethylcis butylene diimide, N-propylcis butylene diimide and N- A copolymer of one or two or more monomers of the third butyl maleimide. The polymerization composition of the copolymer is preferably from 0.1 to 10% by mass of the monomers other than vinylpyrrolidone, and the remainder is vinylpyrrolidone.

The weight average molecular weight Mw of the polymer used as 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. The Mw system can be determined by GPC (gel permeation chromatography).

In the process of polymer synthesis, there are cases where acetate is used as the "organic solvent when the polymer produced by the polymerization is purified". At this time, the acetate is mixed into the polymer powder product as an impurity. However, in the present invention, since the concentration of the organic acid ester in the alcohol solvent is adjusted to the above predetermined range, it is not necessary to supply "the organic acid introduced into the solvent" with "acetate present in the polymer powder". Part of the ester ", therefore, the supply source of the organic protective agent can be" a polymer with vinyl pyrrolidone structural unit of 1 mole, and the amount of acetate compound is, for example, less than 0.002 mole of polymer powder ". At this time, since a small amount of acetate is introduced from the polymer powder into the alcohol solvent, the calculation of the concentration of the organic acid ester in the alcohol solvent can be ignored. The amount of acetate present in the polymer powder can be determined from the NMR (nuclear magnetic resonance) spectrum of the polymer powder.

[Size and shape of silver nanowire]

From the viewpoint of forming a transparent conductive coating film having excellent conductivity and visibility, the silver nanowires are preferably as fine and long as possible. In the present invention, suitable objects are those having an average length of 15 μm or more, an average diameter of 35 nm or less, and an average aspect ratio of 600 or more obtained from the above formula (1). A more suitable object is one having an average length of 15 μm or more and an average diameter of 33 nm or less. Still more suitable objects are those having an average length of 15 μm or more and an average diameter of 30 nm or less. In the present invention, since silver nanowires with a long average length and a large average aspect ratio can be obtained in the synthesis stage, in the subsequent steps, for example, the length can be adjusted in high yield and efficiently by cross-flow purification. distributed.

[Synthesis of silver nanowire]

In addition to the presence of an organic acid ester in an alcohol solvent, a technique of an alcohol solvent reduction method developed in the past can also be used. Regarding the type of the alcohol as a solvent, those having a suitable reducing power for silver and capable of precipitating metallic silver into a linear shape are selected. For example, an alcohol composed of one or more of ethylene glycol, propylene glycol (i.e., 1,2-propylene glycol), 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and glycerol can be used. Solvent. These alcohols may be used individually by 1 type, and may mix and use 2 or more types. The silver source is a silver compound that is soluble in an alcohol solvent. For example, silver nitrate, silver acetate, silver oxide, silver chloride, and the like can be used. However, in consideration of the solubility and cost of the solvent, it is preferable to use silver nitrate (AgNO ₃ ). The reduction and precipitation are preferably performed in an alcohol solvent in which chloride and bromide are dissolved in addition to a silver compound, an organic protective agent, and an organic acid ester. In addition, reduction precipitation may be performed in an alcohol solvent in which an alkali metal hydroxide and an aluminum salt are dissolved. For example, an alcohol solvent to which an organic acid ester is added can be applied to the method disclosed in the aforementioned Patent Document 1.

    [Example]    

[Comparative Example 1]

(Organic protective agent)

A copolymer powder was prepared by dissolving 1-vinyl-2-pyrrolidone and diallyl dimethyl ammonium nitrate in methyl isobutyl ketone as a solvent and polymerizing by addition It is synthesized by a copolymerization method using an initiator. Its polymerization composition was 1-vinyl-2-pyrrolidone: diallyldimethylammonium nitrate = 99: 1 in molar ratio.

With respect to the copolymer powder, a 1H NMR spectrum was measured by JNM-LA400 (400 MHz) manufactured by Japan Electronics Co., Ltd. by nuclear magnetic resonance spectrometry (NMR), and the components contained in the powder were investigated. As a result, the polymer was 97.28% in molar ratio, residual VP (vinylpyrrolidone): 1.07%, ethyl acetate: 0.04%, TBME (third butyl methyl ether): 0.68%, MIBK (methyl isopropyl Butyl ketone): 0.93%. Here, the integrated value of the spectral peak near 4.1 ppm is used for the ethyl acetate system, the integrated value of the spectral peak near 1.2 ppm is used for the TBME system, and the molar% of each component is calculated using the integrated value of the spectral peak near 0.9 ppm for the MIBK system. . The amount of residual VP is determined by the following formula (2).

VP _R (mol%) = [2 × (I ₁ + I ₂ ) / (3 × I ₃ )] × 100… (2)

Here, I ₁ is derived from the integrated value of the peak (7.0-7.2 ppm) of a methine proton related to the C = C double bond of the VP monomer, and I ₂ is derived from the monomer C = C double bond-related methylene proton (4.3-4.4ppm) integrated peak value, I ₃ is derived from the polymer's M atom proton adjacent to the N atom spectrum peak ( 3.0-3.4 ppm).

The weight average molecular weight Mw of the copolymer was determined by GPC (gel permeation chromatography) under the following conditions.

‧Device: HLC-8320GPC EcoSEC (manufactured by TOSOH)

‧Column: TSKgel GMPWXL (× 2) + G2500PWXL

‧Eluent: 100mM sodium nitrate solution / acetonitrile = 80/20

‧Flow rate: 1.0mL / min

‧Temperature: 40 ℃

‧Injection volume: 200μL

‧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 84,000.

(Synthesis of silver nanowire)

At normal temperature, to 513.5 g of propylene glycol, 0.302 g of a propylene glycol solution having a lithium chloride content of 10% by mass, 0.893 g of a propylene glycol solution having a potassium bromide content of 1% by mass, 0.0222 g of lithium hydroxide, and aluminum nitrate nonahydrate 0.312 g of a propylene glycol solution with a content of 20% by mass, and 5.24 g of the copolymer powder as a supply source of an organic protective agent were dissolved to prepare a solution A. In this example, no organic acid ester was added to the solution A. In a separate container, 4.25 g of silver nitrate was added to a mixed solution of 5.98 g of propylene glycol and 0.5 g of pure water, and the mixture was stirred and dissolved at 35 ° C. to obtain a silver-containing solution B.

The solution A was fed into the reaction vessel, and the temperature was raised from normal temperature to 95 ° C while stirring at 250 rpm. Then, the total amount of the solution B was added to the solution A from the two adding ports in 1 minute using a tube pump. in. After the addition of the solution B was completed, 4 g of a propylene glycol solution was added using a tube pump to flush the inside of the tube to which the solution B was adhered, and then maintained at 95 ° C for 3.5 hours while cooling to 85 ° C in 2.0 hours. Hold at 85 ° C for 19 hours. Thereafter, the reaction solution was cooled to room temperature to synthesize silver nanowires.

(Measurement of average diameter and average length of silver nanowires)

20 g of the reaction solution cooled to normal temperature was dispensed into a centrifuge tube, 180 g of pure water was added, and the centrifuge was centrifuged at 1500 rpm for 15 minutes using a centrifuge. The concentrate and supernatant were observed, the supernatant was partially removed, and the concentrate was recovered. This washing operation was repeated several times to obtain a concentrate. The obtained concentrate was dispersed in pure water. When measuring the length of silver nanowires, the dispersion was taken to an observation table for SEM, and water was evaporated on the observation table, and then an electric field emission scanning electron microscope was used (manufactured by Hitachi High Technologies Corporation); The observation was performed under the conditions of an acceleration voltage of 3 kV and a magnification of 1,500 times. For the three or more fields selected at random, all the metal wires whose full length can be confirmed in the field of view are taken as the object, and the average length is measured according to the above definition. When measuring the diameter, the dispersion was taken to an observation stand for TEM, and a bright-field image was obtained using a transmission electron microscope (manufactured by Japan Electronics Co., Ltd .; JEM-1011) under an acceleration voltage of 100 kV and a magnification of 40,000 times. Observe, capture the observation image, and enlarge the captured original image to double the size in order to accurately measure the diameter. Use the software (Motic Image Plus 2.1S) and measure the average diameter according to the above definition. The average aspect ratio is obtained by substituting the values of the average length and the average diameter into the above formula (1). The average diameter of the silver nanowires was 35.8 nm, and the average length was 14.1 μm. The average aspect ratio is 14100 (nm) /35.8 (nm) ≒ 394. The results are summarized in Table 1 together with other examples and comparative examples.

[Example 1]

When synthesizing silver nanowires, solution A was prepared by mixing the materials mixed in Comparative Example 1 with 0.0052 g of ethyl acetate and dissolving it, except that the conditions were the same as those of Comparative Example 1. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 0.119 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 32.6 nm, and the average length was 19.6 μm. The average aspect ratio is 19600 (nm) /32.6 (nm) ≒ 601.

[Example 2]

When synthesizing silver nanowires, the solution A was prepared by mixing the materials mixed in Comparative Example 1 with 0.0131 g of ethyl acetate and dissolving it, and the conditions were the same as those of Comparative Example 1 conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 0.298 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 32.1 nm, and the average length was 19.6 μm. The average aspect ratio is 19600 (nm) /32.1 (nm) ≒ 611.

[Example 3]

When synthesizing silver nanowires, the solution A was prepared under the same conditions as those of Comparative Example 1 except that the substances mixed in Comparative Example 1 were mixed and 0.0263 g of ethyl acetate was further mixed and dissolved. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 0.598 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 28.5 nm, and the average length was 21.8 μm. The average aspect ratio is 21800 (nm) /28.5 (nm) ≒ 765.

[Example 4]

When synthesizing silver nanowires, Solution A was prepared under the same conditions as Comparative Example 1 except that 0.0798 g of ethyl acetate was further mixed and dissolved in each of the substances mixed in Comparative Example 1. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 1.812 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 28.4 nm, and the average length was 23.3 μm. The average aspect ratio is 23300 (nm) /28.4 (nm) ≒ 820.

[Example 5]

When synthesizing silver nanowires, Solution A was prepared under the same conditions as Comparative Example 1 except that the substances mixed in Comparative Example 1 were mixed and 0.1344 g of ethyl acetate was further mixed and dissolved. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 3.051 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 28.8 nm, and the average length was 23.9 μm. The average aspect ratio is 23900 (nm) /28.8 (nm) ≒ 830.

[Example 6]

When synthesizing silver nanowires, the solution A was prepared under the same conditions as those of Comparative Example 1 except that the substances mixed in Comparative Example 1 were mixed and 0.2759 g of ethyl acetate was further mixed and dissolved. conduct experiment. At the time point when the precipitation reaction of silver was started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 6.263 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 28.5 nm, and the average length was 22.2 μm. The average aspect ratio is 22200 (nm) /28.5 (nm) ≒ 779.

[Example 7]

When synthesizing silver nanowires, the solution A was prepared under the same conditions as those of Comparative Example 1 except that the substances mixed in Comparative Example 1 were mixed and 0.3346 g of ethyl acetate was further mixed and dissolved. conduct experiment. At the time point when the precipitation reaction of silver was started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 7.595 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 28.7 nm, and the average length was 22.1 μm. The average aspect ratio is 22100 (nm) /28.7 (nm) ≒ 770.

[Example 8]

When synthesizing silver nanowires, the solution A was prepared under the same conditions as those of Comparative Example 1 except that the substances mixed in Comparative Example 1 were mixed and 0.4250 g of ethyl acetate was further mixed and dissolved. conduct experiment. At the time point when the precipitation reaction of silver was started (that is, the time point when the addition of the solution B was started), the ethyl acetate concentration in the alcohol solvent was 9.648 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 29.4 nm, and the average length was 23.0 μm. The average aspect ratio is 23000 (nm) /29.4 (nm) ≒ 782.

[Example 9]

When synthesizing silver nanowires, solution A was prepared by mixing the substances mixed in Comparative Example 1 with 0.5825 g of ethyl acetate and dissolving it, except that the conditions were the same as those of Comparative Example 1. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when solution B was started to be added), the ethyl acetate concentration in the alcohol solvent was 13.221 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 29.2 nm, and the average length was 24.5 μm. The average aspect ratio is 24500 (nm) /29.2 (nm) ≒ 839.

[Example 10]

When synthesizing silver nanowires, solution A was prepared by mixing the materials mixed in Comparative Example 1 with 0.1052 g of methyl acetate and dissolving it, except that the conditions were the same as those of Comparative Example 1. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when solution B was started to be added), the methyl acetate concentration in the alcohol solvent was 1.812 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 27.7 nm, and the average length was 20.3 μm. The average aspect ratio is 20300 (nm) /27.7 (nm) ≒ 733.

[Example 11]

When synthesizing silver nanowires, solution A was prepared by mixing the materials mixed in Comparative Example 1 with 0.0671 g of propyl acetate and dissolving it, except that the conditions were the same as those of Comparative Example 1. conduct experiment. At the time point when the precipitation reaction of silver was started (that is, the time point when the addition of the solution B was started), the propyl acetate concentration in the alcohol solvent was 1.812 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 28.2 nm, and the average length was 18.2 μm. The average aspect ratio is 18200 (nm) /28.2 (nm) ≒ 645.

[Example 12]

When synthesizing silver nanowires, Solution A was prepared under the same conditions as Comparative Example 1 except that 0.0925 g of butyl acetate was further mixed and dissolved in each of the substances mixed in Comparative Example 1. conduct experiment. At the time point when the precipitation reaction of silver started (that is, the time point when the addition of the solution B was started), the concentration of butyl acetate in the alcohol solvent was 1.812 mmol / L. The average diameter of the silver nanowires obtained under these conditions was 26.6 nm, and the average length was 17.7 μm. The average aspect ratio is 17700 (nm) /26.6 (nm) ≒ 665.

As can be seen from Table 1, when synthesizing silver nanowires, if an organic acid ester is present in an alcohol solvent, the average length of the synthesized metal wires can be significantly increased, and the average aspect ratio of the metal wires also follows this. And promote. In order to fully exert this effect, it is preferable to set the organic acid ester concentration in the alcohol solvent to 0.1 mmol / L or more.

For reference, the SEM photos and TEM photos of the silver nanowires obtained in Comparative Example 1 are shown in Figures 2 and 3, respectively, and the SEM photos and silver nanowires obtained in Example 3 and TEM pictures are shown in Figure 4 and Figure 5, respectively.

Claims (9)

    A method for producing silver nanowires, comprising the steps of reducing and precipitating silver into a linear shape in an alcohol solvent in which a silver compound and an organic protective agent are dissolved; wherein the organic protective agent is a vinylpyrrolidone structure A polymer of a unit; a state in which an organic acid ester is dissolved in the alcohol solvent at a concentration of 0.1 to 20.0 mmol / L, and the aforementioned reduction and precipitation are performed in a liquid.     The method for manufacturing a silver nanowire according to item 1 of the scope of patent application, wherein the average aspect ratio A _M as defined by the following formula (1) is set to an average length of 15 μm or more and an average diameter of 35 nm or less. Silver nanometer lines are reduced and precipitated; A _M = L _M / D _M (1) Here, L _M is a value in which the above average length is expressed in nm units, and D _M is a value in which the above average diameter is expressed in nm units.     The method for manufacturing silver nanowires according to item 1 of the scope of the patent application, wherein the organic acid ester is one or more of methyl acetate, ethyl acetate, propyl acetate, and butyl acetate.         The method for producing silver nanowires according to item 1 of the scope of the patent application, wherein the polymer is polyvinylpyrrolidone (PVP) or a copolymer of vinylpyrrolidone and a hydrophilic monomer Thing.         The method for manufacturing silver nanowires according to item 1 of the scope of the patent application, wherein the polymer has: vinylpyrrolidone and a diallyldimethylammonium salt, ethyl acrylate, acrylic acid 2-Hydroxyethyl ester, 2-Hydroxyethyl methacrylate, 4-Hydroxybutyl acrylate, N-methyl-cis-butenediimide, N-ethyl-cis-butenediimide, N-propyl One of maleimide diimide, N-third butylmaleimide diimide, 2-dimethylaminoethyl methacrylate, and 2-diethylaminoethyl methacrylate Or a polymerization composition of two or more monomers.         The method for manufacturing a silver nanowire according to item 1 of the scope of the patent application, wherein the weight average molecular weight Mw of the aforementioned polymer is 30,000 to 300,000.         A silver nanowire is obtained by the manufacturing method described in item 1 of the scope of patent application.         A silver nano-line printing ink is obtained by dispersing the silver nano-line obtained by the manufacturing method described in the first item of the patent application in a liquid medium.         A transparent conductive film contains silver nanowires obtained by the manufacturing method described in item 1 of the scope of patent application as a conductive material.