WO2021132095A1

WO2021132095A1 - Production method for silver nanowire dispersion

Info

Publication number: WO2021132095A1
Application number: PCT/JP2020/047484
Authority: WO
Inventors: 真尚原; 英樹大籏; 山木　繁; 正彦鳥羽
Original assignee: 昭和電工株式会社
Priority date: 2019-12-27
Filing date: 2020-12-18
Publication date: 2021-07-01
Also published as: TW202138043A; JPWO2021132095A1; CN114302778A; KR20220038762A

Abstract

[Problem] To use cross-flow filtration to purify a crude silver nanowire dispersion that includes silver nanowires and a structure-directing agent and has a silver density of at least 1.0 mass% and produce a high-purity silver nanowire dispersion at high yield. [Solution] A production method for a silver nanowire dispersion that includes: steps (S1–S6) for preparing a crude silver nanowire dispersion that includes silver nanowires that satisfy silver nanowire count/total particle count>90% and a structure-directing agent and has a silver density of at least 1.0 mass%; and a cross-flow filtration step (S7) for purifying the crude silver nanowire dispersion by circulating cross-flow filtration.

Description

Manufacturing method of silver nanowire dispersion liquid

The present invention relates to a method for producing a silver nanowire dispersion liquid.

Silver nanowires are conductive materials made of wire-like (linear) silver with a diameter on the order of nanometers. Since the conductive layer (thin film) formed of silver nanowires has high conductivity and light transmission, it is used as a transparent electrode material for a touch panel, for example.

As a method for producing such silver nanowires, for example, as described in Non-Patent Document 1 below, there is a method of reducing a silver salt in a polyol (glycol solvent) (polyol reduction method).

When silver nanowires are produced by the polyol reduction method, in addition to silver nanowires, a polyol (glycol) solvent, a polymer used as a protective agent, silver nanoparticles produced as by-products, etc. are mixed in the synthetic solution. It is necessary to remove unnecessary substances by filtering (total filtration) or centrifuging, and to isolate only silver nanowires. However, this method has a problem that since the silver nanowires are stressed at the time of isolation, the silver nanowires tend to aggregate and redisperse becomes difficult as the scale of production increases.

Therefore, Patent Documents 1 to 7 below disclose a technique for filtering and purifying a dispersion liquid in which silver nanowires are dispersed by a batch method using cross-flow filtration. When cross-flow filtration is used, agglomeration of silver nanowires can be suppressed.

Patent Document 1 discloses a method for removing a morphological control agent, which is a hydrophilic polymer or an amphipathic molecule, from a silver nanowire dispersion liquid by a membrane separation method using an ultrafiltration membrane. Patent Documents 2 to 5 disclose a method for purifying a dispersion having a dilute silver concentration of 0.4% or less by using cross-flow filtration. In Patent Documents 6 and 7, an excess amount of organic protective agent and silver nanoparticles are removed to some extent by repeating a method (washing step) of adding 20 times the amount of acetone to the reaction solution and decanting after allowing it to stand. A method of further removing a wire having a length of about 1 to 5 μm by performing cross-flow filtration is disclosed.

JP-A-2009-129732 International Publication No. WO2009 / 107694 JP-A-2010-84173 Japanese Unexamined Patent Publication No. 2013-199690 US Publication No. 2018-354039 Japanese Unexamined Patent Publication No. 2017-220453 Japanese Unexamined Patent Publication No. 2016-55283

In the method described in Patent Document 1, a synthetic solution having a dilute silver concentration (about 0.35%) is concentrated until the amount of the solution reaches 15% (silver concentration is about 2.3%), and ethanol is added. This is a method of returning to the initial amount, and the amount of silver that can be purified in one batch is very small, about 1 g. Therefore, in order to increase the yield of silver nanowires, it is necessary to repeat a series of batches a plurality of times, which has a problem of inefficiency. Similarly, Patent Documents 2 to 7 are methods for purifying a dispersion having a dilute silver concentration of 0.4% or less by using cross-flow filtration, and have a problem that the production amount per batch is small.

In order to improve the production volume per batch, it is conceivable to increase the silver concentration of the silver nanowire dispersion liquid to be added to the cross-flow filtration to increase the yield. However, when a silver nanowire dispersion having a high silver concentration is continuously purified by cross-flow filtration, the amount of silver nanowires deposited on the filter increases, so that it is difficult to prevent wire agglomeration even by using the cross-flow filtration method. Therefore, there is a problem that the yield tends to be low.

In Patent Documents 6 and 7, although a dispersion having a silver concentration of 0.8% by mass is obtained as a concentrate after the washing step, the silver concentration becomes 0.08% by mass during cross-flow purification. It is diluted with pure water as described above. It is considered that this is because when the dispersion liquid of 0.8% by mass is cross-flow filtered, the yield is lower than that under the dilute condition of 0.08% by mass. Even if cross-flow filtration is performed under dilute conditions, the isolated yield calculated from the amount of silver charged at the time of synthesis is 34%, which is not a sufficient value for the manufacturing process.

As shown above, it is extremely difficult to purify a dispersion with a high silver concentration in high yield using the cross-flow filtration method, and there is no precedent achieved so far.

An object of the present invention is to purify a crude silver nanowire dispersion liquid containing silver nanowires and a structure-determining agent and having a silver concentration of 1.0% by mass or more by using a cross-flow filtration method to obtain high yield and high purity. It is an object of the present invention to provide a method for producing a silver nanowire dispersion liquid.

As a result of diligent research to solve the above problems, the present inventor purifies a crude dispersion of silver nanoparticles having a silver concentration of 1.0% by mass or more by using a cross-flow filtration method, as a structure-defining agent and silver. It was clarified that the removal of nanoparticles did not proceed. After investigating the cause, it was found that the filtration filter was blocked by silver nanoparticles, which are by-products of silver nanowires.

As a result of further studies based on these findings, the dispersion liquid to be added to the cross-flow filtration step contains a structure-defining agent, and the number of silver nanowires / total number of particles (number of nanowires + number of nanoparticles)> 90%. By using the silver nanowire dispersion liquid, the structure defining agent can be efficiently removed from the silver nanowire coarse dispersion liquid containing silver nanowires and the structure defining agent and having a silver concentration of 1.0% by mass or more, and the silver nanowires can be obtained in high yield. We have found that can be isolated, and have arrived at the present invention.

The present invention includes the following embodiments.

[1] A step of preparing a crude silver nanowire dispersion liquid containing a silver nanowire having a number of silver nanowires / total number of particles> 90% and a structure defining agent and having a silver concentration of 1.0% by mass or more, and the silver nanowire. A method for producing a silver nanowire dispersion, which comprises a cross-flow filtration step of purifying the crude dispersion by a circulating cross-flow filtration method.

[2] The method for producing a silver nanowire dispersion liquid according to [1], wherein in the cross-flow filtration step, the filtration rate per unit filter area and unit time ^{is controlled to 16.0 kg / m 2 · h or less.}

[3] The method for producing a silver nanowire dispersion liquid according to [2], wherein the filtration rate is 1.0 kg / m ^{2 · h or more.}

[4] The method for producing a silver nanowire dispersion liquid according to any one of [1] to [3], wherein the silver nanowire coarse dispersion liquid contains 0.5% by mass or more of a structure-determining agent.

[5] The step of preparing the silver nanowire coarse dispersion liquid includes a silver nanowire coarse dispersion liquid production step of producing a silver nanowire coarse dispersion liquid in which silver nanowires are synthesized and dispersed in a reaction solvent [1] to [4]. ] The method for producing a silver nanowire dispersion liquid according to any one of.

[6] The steps of preparing the silver nanowire coarse dispersion liquid include a sedimentation step of adding a sedimentation solvent to the silver nanowire coarse dispersion liquid in which the silver nanowires are dispersed in the reaction solvent to precipitate the silver nanowires, and by-product nanoparticles. By repeating the supernatant removing step of removing a part of the supernatant of the mixture of the reaction solvent and the settling solvent containing the above and the settling step a plurality of times, by-product nanoparticles are removed, and the number of silver nanowires / total number of particles in the dispersion liquid. The method for producing a silver nanowire dispersion according to [5], further comprising a reprecipitation cleaning step of obtaining a dispersion of> 90% after the silver nanowire coarse dispersion production step.

[7] In the cross-flow filtration step, the amount of the crude silver nanowire dispersion liquid is before filtration by adding a washing solvent so as to supplement the solvent discharged as the filtrate during or after the concentration of the coarse dispersion liquid of silver nanowires. The method for producing a silver nanowire dispersion liquid according to any one of [1] to [6], which maintains 60% or more of the amount of the crude dispersion liquid.

According to the present invention, a crude silver nanowire dispersion liquid containing silver nanowires and a structure-determining agent and having a silver concentration of 1.0% by mass or more is purified by a cross-flow filtration method to obtain a high yield and high yield. A pure silver nanowire dispersion can be produced.

It is a process drawing of the manufacturing method of the silver nanowire dispersion liquid which concerns on embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

FIG. 1 shows a process diagram of a method for producing a silver nanowire dispersion liquid according to an embodiment of the present invention. First, a silver nanowire coarse dispersion liquid in which the silver nanowires are still dispersed in the reaction solvent by synthesis is prepared (S1: silver nanowire coarse dispersion liquid production step). As this step, synthesis of silver nanowires by a conventionally known method or the like can be applied. The crude dispersion obtained by synthesizing silver nanowires contains by-produced silver nanoparticles in addition to the silver nanowires produced by the synthesis, the ionic derivative used in the synthesis, the structure defining agent, and the solvent. The structure-determining agent is contained in the synthetic solvent and adheres to the surface of the generated silver nanowires. In the sedimentation step described later, the by-produced silver nanoparticles are removed, and in the cross-flow filtration step. , The structure defining agent adhering to the surface of the silver nanowire is washed.

The synthetically obtained silver nanowires used herein are metallic silver with a diameter on the order of nanometers and are conductive materials having a linear (including hollow tubular silver nanotubes) shape. .. Further, the metallic silver of the silver nanowires preferably does not contain a metal oxide from the viewpoint of conductive performance, but if air oxidation is unavoidable, a silver oxide may be contained in a part (at least a part of the surface). The length (diameter) of the silver nanowire in the minor axis direction is 10 nm or more and 90 nm or less on average, preferably 10 nm or more and 85 nm or less on average, and the length in the major axis direction is 1 μm or more and 100 μm or less on average, preferably 5 μm or more and 100 μm or less on average. More preferably, the average is 10 μm or more and 80 μm or less. That is, in the present specification, when the length in the major axis direction is a and the length (diameter) in the minor axis direction is b, the aspect ratio represented by a / b exceeds 5. Means things. Further, in the present specification, the “silver nanoparticles” means particles having an aspect ratio of 5 or less, which are by-produced by synthesis, excluding the above-mentioned “silver nanowires”.

The above-mentioned ionic derivative is a component that contributes to the growth of silver wire, and can be applied as long as it is a compound that can be dissolved in a solvent to dissociate halogen ions, and a metal halide is preferable. The halogen ion is preferably at least one of chloride ion, bromine ion, and iodine ion, and more preferably contains a compound capable of dissociating chloride ion.

Examples of the metal halide compound include alkali metal halides, alkaline earth metal halides, and metal halides of Groups 3 to 12 of the Long Periodic Table.

Examples of alkali metal halides include alkali metal chlorides such as lithium chloride, sodium chloride and potassium chloride, alkali metal bromides such as lithium bromide, sodium bromide and potassium bromide, lithium iodide, sodium iodide and potassium iodide. Such as alkali metal iodide and the like. Examples of the alkaline earth metal halide include magnesium chloride and calcium chloride. Examples of Group 3 to Group 12 metal halides in the Long Periodic Table include ferric chloride, ferric chloride, ferric bromide, and cupric bromide. Any one of these may be used alone, or two or more thereof may be used in combination.

Among these, it is particularly preferable to contain a compound that dissociates chloride ions for wire formation. Further, in order to obtain a wire having a small diameter, it is preferable to use a compound that dissociates chloride ions and at least one of a compound that dissociates bromine ions and a compound that dissociates iodine ions in combination. When the total number of moles of chlorine atoms of the compound that dissociates chlorine ions is (A) and the total number of moles of bromine atoms of the compound that dissociates bromine ions and the number of iodine atoms of the compound that dissociates iodine ions is (B), When the molar ratio of A) / (B) becomes large, the wire diameter becomes large, and when it becomes small, the wire diameter becomes small, but when it becomes too small, the by-product rate of spherical powder tends to increase. Therefore, the molar ratio of (A) / (B) is preferably 2 to 8, and more preferably 3 to 6.

The structure-determining agent used in the synthesis is a compound having a function of one-dimensionally defining the growth direction of silver particles at the time of synthesis, and by using the structure-determining agent, the ratio of silver nanowires formed in the particle forming step can be determined. Can be enhanced. In many cases, the structure-determining agent preferentially or selectively adsorbs to a specific crystal plane of the target particle to control the growth direction by suppressing the growth of the adsorption plane. This growth direction can be controlled by adding a structure-determining agent to the polyols described later and adsorbing it on the surface of the silver nanowires to be produced. As the structure-determining agent, a structure-determining agent having a weight average molecular weight of more than 1000 is preferable, a structure-determining agent of 2000 or more is more preferable, and a structure-determining agent of 10,000 or more is further preferable. On the other hand, if the weight average molecular weight of the structure defining agent is too large, there is a high possibility that silver nanowires will aggregate. Therefore, the weight average molecular weight of the structure defining agent is preferably 1.5 million or less, more preferably 1 million or less, and even more preferably 500,000 or less. Examples of the type of the structure-determining agent include poly-N-vinylpyrrolidone (PVP), poly-N-vinylacetamide (PNVA), gelatin, polyvinyl alcohol (PVA), partial alkyl ester of polyacrylic acid, methyl cellulose, and hydroxypropyl. Examples thereof include methyl cellulose, polyalkylene amine, cellulose acetate, acetal resin and the like.

As described above, the structure-determining agent has the effect of controlling the wire-like growth of silver nanowires during the synthesis of silver nanowires and preventing the agglomeration of the produced silver nanowires.

The structure defining agent is preferably contained in the crude silver nanowire dispersion liquid in an amount of 0.5% by mass or more, more preferably 0.7 to 7% by mass, and further preferably 1.0 to 5% by mass. By setting the content to 0.5% by mass or more, agglutination does not occur even when a high-concentration dispersion having a silver concentration of 1.0% or more is handled. Further, if the concentration of the structure-defining agent is too high, the subsequent purification process becomes long and the productivity decreases.

As a method for synthesizing silver nanowires (or silver nanotubes), a known synthesis method can be used. For example, silver nanowires can be synthesized by reducing silver nitrate in the presence of poly-N-vinylpyrrolidone using the Poly-ol method (see Chem. Mater., 2002, 14, 4736). ..

The reaction solvent used in the above polyol method is polyols used as reducing agents, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, 1, Examples thereof include 2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, glycerin and the like, and at least one selected from the group consisting of these. preferable. After the synthesis reaction, the silver nanowire coarse dispersion liquid contains impurities such as silver nanoparticles generated during the synthesis together with the target silver nanowires.

If the amount of the polyol in the crude silver nanowire dispersion is too large, the amount of the poor solvent to be described later increases. Therefore, if necessary, the polyol may be distilled off to concentrate the silver nanowires to some extent (S2 :). Concentration step). However, if it is distilled off at an excessively high temperature, it may aggregate, so it is preferable to distill off at a pressure of 100 mmHg or less and a temperature of 150 ° C. or less. In this case, it is preferable to reduce the amount of the silver nanowire coarse dispersion liquid from 20% by mass to 80% by mass of the original amount. The step S2 is not essential and may be omitted.

Next, a sedimentation solvent is added to the silver nanowire coarse dispersion liquid (if necessary, the silver nanowire coarse dispersion liquid concentrated in S2 above) to precipitate the silver nanowires (S3: sedimentation step).

The precipitation solvent is a poor solvent having low solubility of the structure-determining agent, and examples thereof include a ketone solvent and an ester solvent. Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, benzophenone and the like. Examples of the ester solvent include ethyl acetate, -n-propyl acetate, isopropyl acetate, allyl acetate, -n-butyl acetate, ethyl propionate, propylene glycol monomethyl ether acetate and the like. Among them, the precipitation property of silver nanowires and polyols From the viewpoint of solubility in, acetone, ethyl acetate, acetic acid-n-propyl acetate, isopropyl acetate, acetic acid-n-butyl, and propylene glycol monomethyl ether acetate are preferable. The amount used is preferably 50 parts by mass to 2000 parts by mass, and more preferably 70 parts by mass to 600 parts by mass with respect to 100 parts by mass of the used polyols (after concentration in S2 above). ..

A dispersant (a dispersant that dissolves in the poor solvent among the polymer dispersants) may be added to the poor solvent. As a result, the dispersant is added not only to the initial silver nanowire dispersion liquid but also to the poor solvent, so that the aggregation of silver nanowires can be further suppressed.

After the silver nanowires are precipitated (S3) by adding a poor solvent, the mixture of the reaction solvent and the precipitation solvent, which is the supernatant containing the silver nanoparticles produced as a by-product during the synthesis of the silver nanowires, is removed (S4: supernatant removing step). The method for removing the supernatant is not particularly limited. For example, it can be removed by decantation treatment, or it can be removed by suction with a pump.

As described above, a dispersion solvent different from the reaction solvent is added to the residual liquid containing the precipitate of the silver nanowires from which the reaction solvent and the sedimentation solvent have been removed as the supernatant, and then the sedimentation solvent is added again to precipitate the silver nanowires ( S5: Re-sediment cleaning step). At this time, when the structure defining agent is equal to or less than the threshold value, the silver nanoparticles are well dispersed in the supernatant even after the precipitation solvent is added, so that the silver nanoparticles and the silver nanowires can be separated.

The dispersion solvent used in the reprecipitation washing step is a good solvent having a solubility of the structure defining agent, and examples thereof include water, an alcohol solvent, a nitrile solvent, and a lactone solvent. Of these, water, acetonitrile, and γ-butyrolactone are preferable from the viewpoint of sedimentation of silver nanowires and dispersibility of silver nanoparticles. The amount used is 25 to 400 parts by mass, preferably 30 to 300 parts by mass, and 50 to 200 parts by mass with respect to 1 part by mass of silver in the residual liquid containing the precipitated silver nanowires. More preferred. If it is less than 25 parts by mass, the concentration of silver nanowires is too high and it is difficult to uniformly redisperse it. If it exceeds 400 parts by mass, the amount of solvent required for sedimentation becomes very large. Is required.

The precipitation solvent may be any of the poor solvents mentioned in the precipitation step (S3). The amount used is preferably 50 parts by mass to 500 parts by mass, and more preferably 70 parts by mass to 300 parts by mass with respect to 100 parts by mass of the good solvent used.

By repeating the reprecipitation cleaning step (S5) a plurality of times, it is possible to more effectively separate the silver nanoparticles and the silver nanowires. Repeat until the ratio of silver nanowires contained in the dispersion, that is, the number of silver nanowires / (total number of particles (= number of silver nanowires + number of silver nanoparticles))> 90%, which is advantageous for the purification step described later. ..

As described above, the filtration solvent used for the cross-flow filtration in the next step is added to the residual liquid containing the sediment of the silver nanowires from which the silver nanoparticles and the sedimentation solvent have been removed as the supernatant, and the silver nanowires are redispersed (S6: Redispersion process). The amount of the filtration solvent added is 10 to 100 parts by mass, preferably 25 to 100 parts by mass, and 50 to 100 parts by mass with respect to 1 part by mass of silver in the residual liquid containing the precipitated silver nanowires. Is more preferable. If it is less than 10 parts by mass, the concentration of silver nanowires is too high and it is difficult to uniformly redistribute it. If it exceeds 100 parts by mass, the concentration of silver nanowires is low. Will be performed multiple times, which requires a great deal of labor.

As the filtration solvent, it can be used without particular limitation as long as the silver nanowires do not aggregate. In particular, it is preferable that the solvent is a solvent in which the silver nanoparticles to be removed, the inorganic impurities, the structure defining agent, the silver nanowire manufacturing process, and the excess dispersant added in the sedimentation step are dissolved. As the filtering solvent, in addition to water, alcohols such as methanol, ethanol, isopropyl alcohol and n-propyl alcohol and a mixture of water and alcohol can be used, but water is used from the viewpoint of handleability (safety). It is preferable to use it.

By the steps S1 to S6 above, a silver nanowire coarse dispersion liquid to be cross-flow filtered in the purification step (S7) described later is prepared.

Next, the silver nanowire redispersion liquid (coarse dispersion liquid) obtained in S6 was poured into a filter to perform cross-flow filtration, and the silver nanoparticles and sedimentation solvent coexisting without being completely removed in the reprecipitation cleaning step (S5). The polyol and inorganic impurities present in the synthetic solution of silver nanowires and the structure defining agent used to generate the silver nanowires are removed, and the silver nanowires are purified to obtain a purified silver nanowire aqueous dispersion (S7: Purification step). ). Here, the concentration of silver (including silver nanowires and silver nanoparticles) in the redispersion liquid (coarse dispersion liquid) to be cross-flow filtered is 1.0% by mass or more, and 1.1 to 10.0% by mass. Is preferable, and more preferably 1.2% by mass to 5.0% by mass. Further, a silver nanowire dispersion liquid in which the ratio of silver nanowires contained in the redispersion liquid (coarse dispersion liquid), that is, the number of silver nanowires / (total number of particles (= number of silver nanowires + number of silver nanoparticles))> 90% is used. Use. The silver nanowire ratio is preferably 92% or more, more preferably 95% or more, still more preferably 97% or more. Further, in the cross-flow filtration step, it is preferable to control the filtration rate per unit filter area and unit time (supply rate of coarse dispersion liquid) to 16.0 kg / m ^{2 · h or less.} When the crude dispersion of silver nanowires is purified by the cross-flow filtration method, the higher the silver concentration in the crude dispersion, the more the filtration filter is blocked by silver nanoparticles, which are by-products of the silver nanowires, and the silver nanos. Problems that prevent the removal of particles from progressing are likely to occur. Further, when the filtration speed is increased, a metallic silver film is formed on the filter due to the aggregation of silver nanowires, and a problem that the removal of the polymer (structure-determining agent) does not proceed easily occurs. By controlling the filtration rate, the occurrence of these problems can be remarkably suppressed. Since the productivity is low when the filtration rate is slow, the more preferable filtration rate is 1.0 to 16.0 kg / m ² · h, and the more preferable filtration rate is 2.0 to 15.0 kg / m ² · h. Is. The pressure difference between the front and back of the filter is preferably in the range of 0.01 MPa to 1.0 MPa, more preferably 0.015 to 0.9 MPa, and even more preferably 0.02 to 0.8 MPa. By cross-flow filtration under the above conditions, the structure-defining agent can be efficiently removed while suppressing wire aggregation during filtration, and silver nanowires can be isolated in high yield.

In the above purification step, after concentrating the silver nanowire redispersion liquid, silver is added to the storage tank from an additional line in an amount equivalent to the total amount of the solvent (redispersion liquid) discharged as a filtrate to the outside of the filter. The amount of the coarse dispersion liquid of the nanowire may be maintained at 60% or more of the amount of the coarse dispersion liquid before filtration, and the silver nanowire redispersion liquid may be purified. The cleaning solvent can be used without particular limitation as long as the silver nanowires do not aggregate. In particular, it is preferable that the cleaning solvent dissolves the silver nanoparticles to be removed, the inorganic impurities, the structure defining agent, the surplus dispersant added in the manufacturing process of the silver nanowires, and the sedimentation step. As the cleaning solvent, in addition to water, alcohols such as methanol, ethanol, isopropyl alcohol and n-propyl alcohol and a mixture of water and alcohol can be used, but water is used from the viewpoint of handleability (safety). It is preferable to use it. The cross-flow temperature is not particularly limited, but the time required for filtration can be shortened when the solvent is carried out at a high temperature because the viscosity of the solvent is lowered. It is usually in the range of 10 to 80 ° C, preferably 15 to 70 ° C, and more preferably 20 to 60 ° C.

The material of the filter is not limited as long as it can perform cross-flow filtration, but for example, a ceramic film, a hollow fiber membrane, or the like can be used. As the hollow fiber membrane, a polymer material selected from cellulosic type, polyether sulfonic acid type, PTFE (polytetrafluoroethylene) and the like can be used. Further, as the ceramic film, a porous ceramic material can be used. The average pore size of the ceramic film is preferably 0.01 to 5.0 μm in order to improve the separation efficiency between the solvent and the silver nanowires. If the pore size of the ceramic film is too small, the filtration time will be too long, and if it is too large, not only silver nanoparticles but also a part of silver nanowires will pass through. More preferably, the average is 1.0 to 3.0 μm.

The end timing of purification in the above purification step (S7) can be determined without particular limitation. For example, when the concentration ratio of silver nanowires to the structure-determining agent (silver nanowire / structure-determining agent (mass ratio)) is 10 or more, preferably 15 or more, more preferably 20 or more, or cleaning in a circulating filtrate. The end point may be when the solvent concentration reaches 95% or more, preferably 98% or more. To determine the end point, the masses of the structure-defining agent, silver nanowires, and solvent may be simply measured using an analytical method such as thermogravimetric analysis or gas chromatography.

The dispersion medium of the silver nanowire dispersion liquid obtained by the above method is used as it is, or if necessary, the solvent is replaced with a solvent suitable for printing, and then a binder resin or the like is added as necessary to add silver nanowires. Ink (hereinafter, may be referred to as ink) can be produced. In the present embodiment, since the solvent-substituted silver nanowire dispersion liquid can be obtained without agglomeration, the binder component can be easily added as a subsequent step, and the silver nanowire ink can be easily produced.

A new viscosity adjusting solvent may be added to the silver nanowire ink to adjust the viscosity. Examples of viscosity adjusting solvents include water, alcohols, ketones, esters, ethers, aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents. From the viewpoint of satisfactorily dispersing each component in silver nanowire ink, water, ethanol, isopropyl alcohol, 1-methoxy-2-propanol (PGME), ethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethylene glycol monomethyl ether , Ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diacetone alcohol, ethylene glycol monobutyl ether, propylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol monopropyl ether, diethylene glycol monobutyl ether, tripropylene glycol, tri Ethylene glycol monoethyl ether, tarpineol, dihydroterpineol, dihydroterpinyl monoacetate, methyl ethyl ketone, cyclohexanone, ethyllactate, propylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether Acetate, dibutyl ether, octane and toluene are preferred. These solvents may be used alone or in combination of two or more.

Binder resin can be further added to the silver nanowire ink. Examples of the binder resin include polyacryloyl compounds such as polymethylmethacrylate, polyacrylate and polyacrylonitrile; polyvinyl alcohol; polyesters such as polyethylene terephthalate and polyethylene naphthalate; polycarbonates; highly conjugated polymers such as novolak; polyimides, polyamideimides and polyethers. Iimides such as imide; polysulfide; polysulfone; polyphenylene; polyphenyl ether; polyurethane; epoxy; aromatic polyolefin such as polystyrene, polyvinyltoluene and polyvinylxylene; aliphatic polyolefin such as polypropylene and polymethylpentene; alicyclic such as polynorbornene Formula Poly-N-vinyl compounds such as olefin, poly-N-vinylpyrrolidone, poly-N-vinylcaprolactam, poly-N-vinylacetamide; acrylonitrile-butadiene-styrene copolymer polymer (ABS); hydroxypropylmethylcellulose (HPMC) , Nitrocellulose and other celluloses; Silicone resin; Polyacetate; Synthetic rubber; Polyvinyl chloride, Chlorinated polyethylene, Chlorinated polypropylene and other chlorinated polymers; Polyfluorovinylidene, Polytetrafluoroethylene, Polyhexafluoropropylene, Fluoroolefin -Examples include fluoropolymers such as copolymer polymers of hydrocarbon olefins.

In addition to the above components, known optional components contained in the conductive ink, such as corrosion inhibitors, adhesion promoters, and surfactants, may be contained. Examples of the corrosion inhibitor include benzotriazole and the like, the adhesion accelerator includes 2-hydroxymethyl cellulose and the like, and the surfactant includes the trade name F-472SF (manufactured by DIC Corporation). The transparent conductive ink can be produced by appropriately selecting the above-mentioned components by a known method such as stirring, mixing, heating, cooling, dissolving, and dispersing.

Hereinafter, examples of the present invention will be specifically described. The following examples are for facilitating the understanding of the present invention, and the present invention is not limited to these examples.

Example 1
<Manufacturing of crude silver nanowire dispersion>
Weigh 667 g of propylene glycol (manufactured by AGC Inc.) in a 1 L plastic container, add 22.5 g (0.13 mol) of silver nitrate (manufactured by Toyo Kagaku Kogyo Co., Ltd.) as a silver salt, and stir for 2 hours under room temperature shading. A silver nitrate solution (second solution) was prepared.

In a 5L four-neck separable flask equipped with a mechanical stirrer, a metering pump, a reflux tube, a thermometer, and a nitrogen gas introduction tube, 3000 g of propylene glycol and 0.28 g of sodium chloride as an ionic derivative (4. 8 mmol) (manufactured by Manac Co., Ltd.) and sodium bromide 0.12 g (1.2 mmol) (manufactured by Manac Co., Ltd.), 72.1 g of polyvinylpyrrolidone K-90 (PVP) as a structure-determining agent (BASF, Sokalan K90) Was charged, and the mixture was completely dissolved by stirring at 150 ° C. for 1 hour at a rotation speed of 200 rpm to obtain a first solution. The silver nitrate solution (second solution) prepared above is connected to a metering pump and added dropwise to the first solution at a temperature of 150 ° C. over 2.5 hours to synthesize silver nanowires, and another 30 minutes after the completion of the dropping. The reaction was completed by continuing heating and stirring to obtain a crude silver nanowire dispersion.

The silver concentration of the obtained crude silver nanowire dispersion was measured by the titration method and found to be 0.4% by mass. Further, the shape of the contained silver nanowires was arbitrarily observed at 100 points using SEM (JSM-7000F manufactured by JEOL Ltd.), and the average diameter was 26 nm and the average length was 13 μm.

<Manufacturing of high-concentration silver nanowire dispersion liquid>
The above operation was repeated twice to obtain 7.2 kg of a crude dispersion liquid containing 0.4% by mass of silver nanowires.

6.3 kg of the obtained crude dispersion was placed in a 15 L PFA (perfluoroalkoxy alkane-tetrafluoroethylene copolymer) coated SUS container, and butyl acetate (Fuji Film) was stirred at 150 rpm using a mechanical stirrer. 6.6 kg (manufactured by Wako Pure Chemical Industries, Ltd.) was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 9.0 kg of the supernatant was removed by a decantation operation.

2.3 kg of acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the residual liquid containing the precipitate, and stirring was continued for 10 minutes to redistribute the precipitate, and then 4.5 kg of butyl acetate was added over 10 minutes. did. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (7.5 kg) of the total amount of the supernatant was removed by a decantation operation. Acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) 2.3 kg The operation after the addition was repeated 11 times to remove the nanoparticles produced as by-products.

Add 3.0 kg of acetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to 2.9 kg of the residual liquid containing the precipitate, continue stirring for 10 minutes, stop stirring, and let stand for 10 minutes to make the supernatant liquid. And the precipitate were separated. Then, 80% (4.7 kg) of the total amount of the supernatant was removed by a decantation operation. The residual liquid containing the precipitate was transferred to a 3 L plastic container, ion-exchanged water was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / water dispersion (silver nanowire redispersion) was measured by the titration method and found to be 1.2% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.8% by mass.

The method of measuring the silver concentration is as follows.

The silver concentration is determined using the Forhard method. Weigh about 1 g of the sample into a beaker and add 4 mL of nitric acid (1 + 1) and 20 mL of pure water. Cover the beaker with a watch glass and heat on a hot plate to 150 ° C. to dissolve the solids. After confirming the dissolution, stop heating and allow to cool, and wash the inner surface of the watch glass and the wall surface of the beaker with pure water to make the amount of liquid about 50 mL. To this solution, 5 mL of nitric acid (1 + 1) and 3 mL of ammonium iron (III) sulfate (3% nitric acid acidity) are added, and titration is performed with an aqueous 0.01 mol / L ammonium thiocyanate solution. At this time, the end point is the point where the solution is colored from colorless to light brown.

Based on the titration result, the silver concentration is calculated according to the following formula.
Silver concentration (wt%) = {(V × c) × 107.9 / 1000} / m
m: Sample weight (g)
V: Amount of ammonium thiocyanate aqueous solution consumed for titration to the end point (mL)
c: Concentration of aqueous ammonium thiocyanate solution (0.01 mol / L)
Nitric acid (1 + 1), ammonium iron (III) sulfate, and ammonium thiocyanate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) all used reagents manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. As the ammonium iron (III) sulfate (3% nitric acid acidity), a mixture of 5.17 g of ammonium iron (III) sulfate, 170 g of pure water and 2.00 g of nitric acid was used. As the 0.01 mol / L ammonium thiocyanate aqueous solution, pure water was added to 38.06 mg of ammonium thiocyanate to prepare a total volume of 50 mL.

The PVP concentration measurement by GPC is as follows.

Gel permeation chromatography (hereinafter abbreviated as GPC) was used to measure the polyvinylpyrrolidone (PVP) concentration, and PVP standard aqueous solution (0.05%, 0.10%, 0.25%, 0.50%, 1.00%) was measured and obtained from the calibration curve prepared.
The measurement conditions of GPC are as follows.
Device name: HPLC unit column manufactured by JASCO Corporation Column: Shodex column OHPAK SB-806M HQ
Mobile phase: 0.01M NaCl aqueous solution / methanol = 90:10
Flow velocity: 1.0 mL / min
Detector: RI-2031Plus manufactured by JASCO Corporation
Temperature: 40.0 ° C
Sample volume: Sample loop 100 μliter Sample concentration: Prepared by centrifuging the stock solution to 3-fold diluted solution and then passing the supernatant through a 0.22 μm filter.

The obtained silver nanowire / aqueous dispersion was diluted 300-fold with methanol to prepare a dilute silver nanowire solution. A drop of the silver nanowire dilute solution was dropped on a clean glass plate and dried on a hot plate at 90 ° C. The glass plate was observed using a laser microscope (Keyence VK-X200) at a magnification of 3000 (measurement field of view: 260 μm × 200 μm), and the number of silver nanowires and the number of silver nanoparticles were measured. The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated to be 97%.

<Cross flow filtration>
Pour 2.1 kg of the obtained silver nanowire / water dispersion into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration (corresponding to the first filtration in Examples 6, 11, 12, 15 and 16 performed up to the second filtration) at a circulation flow velocity of 4 L / min, a dispersion liquid temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. Carried out. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 10 g / min, and 100 g of ion-exchanged water was added to the system by backwashing every 100 g of the filtrate (solvent retention rate 95%). Washing pressure 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 18.6 hours, and the filtration rate per unit time and unit filtration area was 7.5 kg / m ² · h.

1.6 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.1 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.2% by mass (yield 76%). Moreover, when the concentration of PVP was measured by GPC, it was 0.07% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 97%. ..

Example 2
The same synthesis method as in Example 1 was repeated three times to obtain 9.7 kg of a crude dispersion liquid containing 0.4% by mass of silver nanowires. The obtained crude dispersion was placed in a 25 L PFA-coated SUS container, and 10.2 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 13.9 kg of the supernatant was removed by a decantation operation.

3.3 kg of acetonitrile was re-added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redisperse the precipitate, and then 6.6 kg of butyl acetate was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (11.1 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 11 times, the nanoparticles produced as by-products were removed.

3.0 kg of acetone was added to 4.3 kg of the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (5.8 kg) of the total amount of the supernatant was removed by a decantation operation. After repeating this operation once more, the residual liquid containing the precipitate was transferred to a 3 L plastic container, ion-exchanged water was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by the titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.7% by mass.

The obtained silver nanowire / aqueous dispersion was diluted 500-fold with methanol to prepare a dilute silver nanowire solution. A drop of the silver nanowire dilute solution was dropped on a clean glass plate and dried on a hot plate at 90 ° C. The glass plate was observed with a laser microscope (VK-X200 manufactured by KEYENCE CORPORATION) at a magnification of 3000 times, and the number of silver nanowires and the number of silver nanoparticles were measured. The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated to be 97%.

The obtained silver nanowire / aqueous dispersion was purified by cross-flow filtration in the same manner as in Example 1. The total filtration time was 29.1 hours, and the filtration rate per unit time and unit filtration area was 4.8 kg / m ² · h. The dispersion liquid after cross-flow filtration was passed through a 355 mesh nylon filter to remove aggregates, thereby obtaining 1.4 kg of a silver nanowire purified liquid. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.02 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 69%). Moreover, when the concentration of PVP was measured by GPC, it was 0.09% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 98%. ..

Example 3
2.1 kg of silver nanowire / water dispersion was obtained in the same manner as in Example 2. The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by a titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.7% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 2 and found to be 97%.

2.1 kg of the obtained silver nanowire / water dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 4 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was about 10 g / min, and 200 g of ion-exchanged water was added to the system by backwashing every time 200 g of the filtrate was obtained (solvent retention rate 90%). Backwash pressure 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 24.7 hours, and the filtration rate per unit time and unit filtration area was 5.7 kg / m ² · h.

1.4 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.01 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.7% by mass (yield 66%). Moreover, when the concentration of PVP was measured by GPC, it was 0.07% by mass.

Example 4
2.1 kg of silver nanowire / water dispersion was obtained in the same manner as in Example 2. The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by a titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.2% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 2 and found to be 95%.

2.1 kg of the obtained silver nanowire / water dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 4 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was about 10 g / min, and 400 g of ion-exchanged water was added to the system by backwash every time 400 g of the filtrate was obtained (solvent retention rate 80%). Backwash pressure 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 24.2 hours, and the filtration rate per unit time and unit filtration area was 5.8 kg / m ² · h.

1.5 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.01 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 72%). Moreover, when the concentration of PVP was measured by GPC, it was 0.06% by mass.

Example 5
2.1 kg of silver nanowire / water dispersion was obtained in the same manner as in Example 2. The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by a titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.0% by mass.

2.1 kg of the obtained silver nanowire / water dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 4 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was about 10 g / min, and 700 g of ion-exchanged water was added to the system by backwashing every 700 g of the filtrate (solvent retention rate 67%). Backwash pressure 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 24.8 hours, and the filtration rate per unit time and unit filtration area was 5.7 kg / m ² · h.

1.9 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.02 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 88%). Moreover, when the concentration of PVP was measured by GPC, it was 0.04% by mass.

Example 6
2.1 kg of silver nanowire / water dispersion was obtained in the same manner as in Example 2. The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by a titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.7% by mass.

2.1 kg of the obtained silver nanowire / water dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration (first filtration) was performed at a circulation flow rate of 4 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was about 10 g / min, and 100 g of ion-exchanged water was added to the system by backwashing every 100 g of the filtrate (solvent retention rate 95%). Backwash pressure 0.15 MPa). When a total of 5600 g of the filtrate was obtained, the solvent added to the system by backwashing was changed from ion-exchanged water to ethanol, and cross-flow filtration (second filtration) was continued at a filtration differential pressure of 0.03 MPa. Cross-flow filtration was terminated when an additional 2800 g of filtrate was obtained. The total first filtration time using ion-exchanged water was 20.9 hours, and the filtration rate per unit time and unit filtration area was 4.6 kg / m ² · h. The total second filtration time using ethanol was 11.7 hours, and the filtration rate per unit time and unit filtration area was 4.0 kg / m ² · h.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 70%). Moreover, when the concentration of PVP was measured by GPC, it was 0.12% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, ethanol was calculated to be 72.0%, and the water ratio was calculated to be 28.0%.

Example 7
The same synthesis method as in Example 1 was repeated 4 times to obtain 14.4 kg of a crude silver nanowire dispersion. 13.2 kg of the obtained crude dispersion was placed in a 35 L ETFE (ethylene-tetrafluoroethylene copolymer) coated SUS container, and 13.8 kg of butyl acetate was added for 10 minutes while stirring at 150 rpm using a mechanical stirrer. It was added over. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 18.8 kg of the supernatant was removed by a decantation operation.

4.5 kg of acetonitrile was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redisperse the precipitate, and then 9.0 kg of butyl acetate was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (15.1 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 11 times, the nanoparticles produced as by-products were removed.

5.0 kg of acetone was added to the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (8.6 kg) of the total amount of the supernatant was removed by a decantation operation. After repeating this operation once more, the residual liquid containing the precipitate was transferred to a 3 L plastic container, ion-exchanged water was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by the titration method and found to be 2.5% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 3.8% by mass.

The obtained silver nanowire / aqueous dispersion was diluted 700-fold with methanol to prepare a dilute silver nanowire solution. A drop of the silver nanowire dilute solution was dropped on a clean glass plate and dried on a hot plate at 90 ° C. The glass plate was observed with a laser microscope (Keyence VK-X200) at a magnification of 3000 times, and the number of silver nanowires and the number of silver nanoparticles were measured. The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated to be 95%.

The silver nanowire / water dispersion was purified by cross-flow filtration in the same manner as in Example 1 except that the filtration differential pressure was 0.04 MPa. The total filtration time was 35.0 hours, and the filtration rate per unit time and unit filtration area was 4.0 kg / m ² · h. The dispersion liquid after cross-flow filtration was passed through a 355 mesh nylon filter to remove aggregates, thereby obtaining 1.4 kg of a silver nanowire purified liquid. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.1 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 2.5% by mass (yield 72%). Moreover, when the concentration of PVP was measured by GPC, it was 0.18% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 96%. ..

Example 8
The same synthesis method as in Example 1 was repeated twice to obtain 7.2 kg of a crude silver nanowire dispersion. 5.3 kg of the obtained crude dispersion was placed in a 15 L PFA-coated SUS container, and 5.6 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 7.6 kg of the supernatant was removed by a decantation operation.

2.3 kg of acetonitrile was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redisperse the precipitate, and then 4.5 kg of butyl acetate was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (7.0 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 11 times, the nanoparticles produced as by-products were removed.

3.0 kg of acetone was added to the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (4.7 kg) of the total amount of the supernatant was removed by a decantation operation. After repeating this operation once more, the residual liquid containing the precipitate was transferred to a 3 L plastic container, methanol was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / methanol dispersion was measured by the titration method and found to be 1.0% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.4% by mass.

The obtained silver nanowire / methanol dispersion was diluted 300-fold with methanol to prepare a dilute silver nanowire solution. A drop of the silver nanowire dilute solution was dropped on a clean glass plate and dried on a hot plate at 90 ° C. The glass plate was observed with a laser microscope (Keyence VK-X200) at a magnification of 3000 times, and the number of silver nanowires and the number of silver nanoparticles were measured. The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated to be 92%.

2.1 kg of the obtained silver nanowire / methanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 10 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.06 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 12 g / min, and 100 g of methanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%) (backwash pressure). 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 12.7 hours, and the filtration rate per unit time and unit filtration area was 11.0 kg / m ² · h.

1.5 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.04 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.0% by mass (yield 75%). Moreover, when the concentration of PVP was measured by GPC, it was 0.07% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that methanol was 88.1% and water ratio was 11.9%.

Example 9
2.1 kg of silver nanowire / methanol dispersion was obtained in the same manner as in Example 8. The silver concentration of the obtained silver nanowire / methanol dispersion was measured by a titration method and found to be 1.0% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.2% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 8 and found to be 95%.

2.1 kg of the obtained silver nanowire / methanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 14 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.07 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 17 g / min, and 100 g of methanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%) (backwash pressure). 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 8.8 hours, and the filtration rate per unit time and unit filtration area was 16.0 kg / m ² · h.

1.3 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.25 g, and the amount of agglomerates generated by the cross-flow filtration was small.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.0% by mass (yield 65%). Moreover, when the concentration of PVP was measured by GPC, it was 0.09% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 92%. ..

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that methanol was 85.6% and water ratio was 14.4%.

Example 10
2.1 kg of silver nanowire / methanol dispersion was obtained in the same manner as in Example 8. The silver concentration of the obtained silver nanowire / methanol dispersion was measured by a titration method and found to be 1.0% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.5% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 8 and found to be 97%.

2.1 kg of the obtained silver nanowire / methanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 14 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.07 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 17 g / min, and 100 g of methanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%) (backwash pressure). 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 7.0 hours, and the filtration rate per unit time and unit filtration area was 20.0 kg / m ² · h.

1.4 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 30 μm depth filter to remove aggregates. When the weight change of the depth filter was measured before and after passing the dispersion liquid, the increase was 0.9 g, and the amount of agglomerates generated by the cross-flow filtration was small.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 0.9% by mass (yield 61%). Moreover, when the concentration of PVP was measured by GPC, it was 0.18% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that methanol was 86.9% and water ratio was 13.1%.

Example 11
The same operation as in Example 1 was repeated twice to obtain 7.2 kg of a crude silver nanowire dispersion liquid. 6.3 kg of the obtained crude dispersion was placed in a 15 L PFA-coated SUS container, and 6.6 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 9.0 kg of the supernatant was removed by a decantation operation.

2.3 kg of acetonitrile was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redisperse the precipitate, and then 4.5 kg of butyl acetate was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (7.5 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 11 times, the nanoparticles produced as by-products were removed.

3.0 kg of acetone was added to the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (4.7 kg) of the total amount of the supernatant was removed by a decantation operation. The residual liquid containing the precipitate was transferred to a 3 L plastic container, methanol was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / methanol dispersion was measured by the titration method and found to be 1.2% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.1% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in the examples, and it was 96%.

2.1 kg of the obtained silver nanowire / methanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration (first filtration) was performed at a circulation flow rate of 10 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 10 g / min, and 100 g of methanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%) (backwash pressure). 0.15 MPa). When a total of 7,000 g of the filtrate was obtained, the solvent added to the system by backwashing was changed from methanol to ethanol, and cross-flow filtration (second filtration) was continued at a filtration differential pressure of 0.02 MPa. Cross-flow filtration was completed when 1400 g of the filtrate was obtained. The total first filtration time using methanol was 16.7 hours, and the filtration rate per unit time and unit filtration area was 7.0 kg / m ² · h. The total second filtration time using ethanol was 3.0 hours, and the filtration rate per unit time and unit filtration area was 7.8 g / m ² · h.

1.5 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.17 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.2% by mass (yield 76%). Moreover, when the concentration of PVP was measured by GPC, it was 0.10% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured by gas chromatography, it was calculated that methanol was 46.5%, ethanol was 38.0%, and water ratio was 15.5%.

Example 12
2.1 kg of silver nanowire / methanol dispersion was obtained in the same manner as in Example 11. The silver concentration of the obtained silver nanowire dispersion was measured by the titration method and found to be 1.2% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.4% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 11 and found to be 96%.

2.1 kg of the obtained silver nanowire / methanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration (first filtration) was performed at a circulation flow rate of 10 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.02 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 10 g / min, and 100 g of methanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%) (backwash pressure). 0.15 MPa). When a total of 6300 g of the filtrate was obtained, the solvent added to the system by backwashing was changed from methanol to ethanol, and cross-flow filtration (second filtration) was continued at a filtration differential pressure of 0.02 MPa. Cross-flow filtration was terminated when an additional 2100 g of filtrate was obtained. The total first filtration time using methanol was 21.2 hours, and the filtration rate per unit time and unit filtration area was 5.0 kg / m ² · h. The total second filtration time using ethanol was 4.2 hours, and the filtration rate per unit time and unit filtration area was 8.3 kg / m ² · h.

1.4 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.18 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.2% by mass (yield 71%). Moreover, when the concentration of PVP was measured by GPC, it was 0.11% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured by gas chromatography, it was calculated that methanol was 38.1%, ethanol was 50.0%, and water ratio was 11.9%.

Example 13
2.1 kg of silver nanowire / methanol dispersion was obtained in the same manner as in Example 2 except that methanol was used instead of ion-exchanged water. The silver concentration of the obtained silver nanowire / methanol dispersion was measured by a titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.6% by mass.

2.1 kg of the obtained silver nanowire / methanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 10 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.06 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was 10 g / min, and 100 g of methanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%) (backwash pressure). 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 15.4 hours, and the filtration rate per unit time and unit filtration area was 9.1 kg / m ² · h.

1.5 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.2 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 75%). Moreover, when the concentration of PVP was measured by GPC, it was 0.06% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that methanol was 79.1% and water ratio was 20.9%.

Example 14
2.1 kg of silver nanowire / ethanol dispersion was obtained in the same manner as in Example 2 except that ethanol was used instead of the ion-exchanged water. The silver concentration of the obtained silver nanowire / ethanol dispersion was measured by a titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.7% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 13 and found to be 92%.

2.1 kg of the obtained silver nanowire / ethanol dispersion was poured into a small desktop testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.06 m ² , pore diameter 2.0 μm, size Φ30 mm × 250 mm). Cross-flow filtration was performed at a circulation flow rate of 12 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.03 MPa. The opening and closing of the permeation valve was adjusted so that the permeation rate of the filtrate was about 5 g / min, and 100 g of ethanol was added to the system by backwash every time 100 g of the filtrate was obtained (solvent retention rate 95%). Pressure 0.15 MPa). Cross-flow filtration was completed when a total of 8400 g of filtrate was obtained. The total filtration time was 40.1 hours, and the filtration rate was calculated to be 3.5 kg / m ² · h.

1.4 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 355 mesh nylon filter to remove aggregates. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.2 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 71%). Moreover, when the concentration of PVP was measured by GPC, it was 0.11% by mass.

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that ethanol was 89.8% and water ratio was 10.2%.

Example 15
The same synthesis method as in Example 1 was repeated 27 times to obtain 97.2 kg of a crude silver nanowire dispersion.

15.4 kg of the above silver nanowire coarse dispersion was placed in a 65 L PFA-coated SUS container, and 16.1 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 22.1 kg of the supernatant was removed by a decantation operation. A further 16.9 kg of a crude silver nanowire dispersion was added, and stirring was continued at 150 rpm for 10 minutes to disperse. 17.8 kg of butyl acetate was added over 10 minutes, stirring was continued for 10 minutes, then the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 31.0 kg of the supernatant was removed by a decantation operation.

7.6 kg of acetonitrile was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redisperse the precipitate, and then 16.0 kg of butyl acetate was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (23.0 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 11 times, the nanoparticles produced as by-products were removed.

7.0 kg of acetone was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes, then the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (11.9 kg) of the total amount of the supernatant was removed by a decantation operation. After repeating this operation once more, the residual liquid containing the precipitate was transferred to a 10 L plastic container, ion-exchanged water was added until the internal liquid reached 7.0 kg, and the mixture was completely dispersed by shaking and stirring.

The above reprecipitation operation was repeated twice more to obtain a total of 21.0 kg of silver nanowire / aqueous dispersion.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 2 and found to be 93%.

<Cross flow filtration>
21.0 kg of the obtained silver nanowire / aqueous dispersion is poured into a standard testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.24 m ² , pore diameter 2.0 μm, size Φ30 mm × 1000 mm) and circulated. Cross-flow filtration (first filtration) was performed at a flow velocity of 7 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.07 MPa. The opening and closing of the permeation valve is adjusted so that the permeation rate of the filtrate is about 40 g / min, and 1.0 kg of ion-exchanged water is backwashed every time 1.0 kg of filtrate is obtained (solvent retention rate 95%). (Backwash pressure 0.15 MPa). When a total of 140 kg of filtrate was obtained, the solvent added to the system by backwashing was changed from ion-exchanged water to ethanol, and cross-flow filtration (second filtration) was continued at a filtration differential pressure of 0.07 MPa. Cross-flow filtration was terminated when an additional 10 kg of filtrate was obtained. The total first filtration time using ion-exchanged water was 82.9 hours, and the filtration rate per unit time and unit filtration area was 7.0 kg / m ² · h. The total second filtration time using ethanol was 7.1 hours, and the filtration rate per unit time and unit filtration area was 5.9 kg / m ² · h.

16.4 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 30 μm depth filter to remove aggregates. When the weight change of the depth filter was measured before and after passing through the dispersion liquid, the increase was 1.6 g, and the agglomerates generated by the cross-flow filtration were very small with respect to the theoretical yield (378 g) of the silver nanowires.

The silver concentration of the silver nanowire purified solution passed through the depth filter was measured by the titration method and found to be 1.8% by mass (yield 78%). Moreover, when the concentration of PVP was measured by GPC, it was 0.09% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the depth filter was calculated by the same method as before, it was 97%. ..

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that ethanol was 43.3% and water ratio was 56.7%.

Example 16
The same synthesis method as in Example 1 was repeated 27 times to obtain 97.2 kg of a crude dispersion liquid containing 0.4% by mass of silver nanowires.

29.0 kg of the obtained crude dispersion was placed in a 65 L PFA-coated SUS container, and 30.5 kg of butyl acetate was added over 20 minutes while stirring at 200 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 41.6 kg of the supernatant was removed by a decantation operation.

23.0 kg of the crude dispersion was added again to the residual liquid containing the precipitate, and stirring was continued for 20 minutes to redisperse the precipitate, and then 24.2 kg of butyl acetate was added over 20 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 45.5 kg of the supernatant was removed by a decantation operation. A further 23.0 kg of the crude dispersion was added again, stirring was continued for 20 minutes to redistribute the precipitate, and then 24.2 kg of butyl acetate was added over 20 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 46.7 kg of the supernatant was removed by a decantation operation. A further 21.9 kg of the crude dispersion was added again, stirring was continued for 20 minutes to redistribute the precipitate, and then 23.0 kg of butyl acetate was added over 20 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 45.4 kg of the supernatant was removed by a decantation operation.

9.0 kg of ion-exchanged water was added to the residual liquid containing the precipitate, stirring was continued for 20 minutes to redisperse the precipitate, and then 20.1 kg of acetone was added over 20 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (29.1 kg) of the total amount of the supernatant was removed by a decantation operation. The by-produced nanoparticles were removed by repeating the operation after the addition of 9.0 kg of ion-exchanged water 30 times.

7.0 kg of acetone was added to 19.4 kg of the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (13.7 kg) of the total amount of the supernatant was removed by a decantation operation. Ion-exchanged water was added to the residual liquid containing the precipitate until the amount of the liquid reached 21.0 kg, and the mixture was completely dispersed by stirring.

The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by the titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 2.5% by mass.

<Cross flow filtration>
21.0 kg of the obtained silver nanowire / aqueous dispersion is poured into a standard testing machine (manufactured by Nippon Gaishi Co., Ltd., using ceramic membrane filter Sepilt, membrane area 0.24 m ² , pore diameter 2.0 μm, size Φ30 mm × 1000 mm) and circulated. Cross-flow filtration (first filtration) was performed at a flow velocity of 7 L / min, a dispersion temperature of 25 ° C., and a filtration differential pressure of 0.08 MPa. The opening and closing of the permeation valve is adjusted so that the permeation rate of the filtrate is about 40 g / min, and 2.0 kg of ion-exchanged water is backwashed every time 2.0 kg of filtrate is obtained (solvent retention rate 90%). (Backwash pressure 0.15 MPa). When a total of 168 kg of filtrate was obtained, the solvent added to the system by backwashing was changed from ion-exchanged water to ethanol, and cross-flow filtration (second filtration) was continued with a filtration differential pressure of 0.08 MPa. Cross-flow filtration was terminated when an additional 14 kg of filtrate was obtained. The total first filtration time using ion-exchanged water was 96.4 hours, and the filtration rate per unit time and unit filtration area was 7.3 kg / m ² · h. The total second filtration time using ethanol was 8.3 hours, and the filtration rate per unit time and unit filtration area was 5.0 kg / m ² · h.

14.7 kg of silver nanowire purified liquid was obtained by passing the dispersion liquid after cross-flow filtration through a 30 μm depth filter to remove aggregates. The weight change of the depth filter was measured before and after passing through the dispersion liquid, and the increase was 1.3 g, and the agglomerates generated by the cross-flow filtration were very small with respect to the theoretical yield (378 g) of the silver nanowires.

The silver concentration of the silver nanowire purified solution passed through the depth filter was measured by the titration method and found to be 1.8% by mass (yield 70%). Moreover, when the concentration of PVP was measured by GPC, it was 0.15% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the depth filter was calculated by the same method as before, it was 96%. ..

When the solvent ratio in the silver nanowire purified liquid was measured using gas chromatography, it was calculated that ethanol was 48.7% and water ratio was 51.3%.

Example 17
The same synthesis method as in Example 1 was repeated three times to obtain 9.7 kg of a crude dispersion liquid containing 0.4% by mass of silver nanowires. The obtained crude dispersion was placed in a 25 L PFA-coated SUS container, and 10.2 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 13.9 kg of the supernatant was removed by a decantation operation.

5.0 kg of acetonitrile was added to the residual liquid containing the precipitate, and stirring was continued for 30 minutes to redistribute the precipitate. The supernatant and the precipitate were separated by centrifuging at 2000 rpm for 30 minutes using a high-speed cooling centrifuge (CR22N, 1.5 L × 4) manufactured by Hitachi Koki Co., Ltd. Then, 80% of the total amount of the supernatant was removed by a decantation operation. The by-produced nanoparticles were removed by repeating the operation after the addition of 5.0 kg of acetonitrile three times.

3.0 kg of acetone was added to 1.3 kg of the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (3.4 kg) of the total amount of the supernatant was removed by a decantation operation. The residual liquid containing the precipitate was transferred to a 3 L plastic container, ion-exchanged water was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by the titration method and found to be 1.7% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 1.8% by mass.

The obtained silver nanowire / aqueous dispersion was diluted 500-fold with methanol to prepare a dilute silver nanowire solution. A drop of the silver nanowire dilute solution was dropped on a clean glass plate and dried on a hot plate at 90 ° C. The glass plate was observed with a laser microscope (Keyence VK-X200) at a magnification of 3000 times, and the number of silver nanowires and the number of silver nanoparticles were measured. The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated to be 92%.

The obtained silver nanowire / aqueous dispersion was purified by cross-flow filtration in the same manner as in Example 1. The total filtration time was 18.8 hours, and the filtration rate per unit time and unit filtration area was 7.4 kg / m ² · h. The dispersion liquid after cross-flow filtration was passed through a 355 mesh nylon filter to remove aggregates, thereby obtaining 1.4 kg of a silver nanowire purified liquid. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.15 g, and there was almost no agglomerate generated by the cross-flow filtration.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.7% by mass (yield 68%). Moreover, when the concentration of PVP was measured by GPC, it was 0.06% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 95%. ..

Comparative Example 1
The same synthesis method as in Example 1 was repeated three times to obtain 9.7 kg of a crude silver nanowire dispersion. The obtained crude dispersion was placed in a 25 L PFA-coated SUS container, and 10.2 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 13.9 kg of the supernatant was removed by a decantation operation.

3.0 kg of acetone was added to the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (7.2 kg) of the total amount of the supernatant was removed by a decantation operation. After repeating this operation once more, the residual liquid containing the precipitate was transferred to a 3 L plastic container, ion-exchanged water was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The silver concentration of the obtained silver nanowire / aqueous dispersion was measured by the titration method and found to be 1.8% by mass. Moreover, when the concentration of PVP was measured by GPC, it was 5.9% by mass.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 2 and found to be 26%.

The silver nanowire concentrate was purified by cross-flow filtration in the same manner as in Example 2. The total filtration time was 40.0 hours, and the filtration rate per unit time and unit filtration area was 3.5 kg / m ² · h. The dispersion liquid after cross-flow filtration was passed through a 355 mesh nylon filter to remove aggregates, thereby obtaining 1.5 kg of a silver nanowire purified liquid. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.1 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified solution passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 74%). Moreover, when the concentration of PVP was measured by GPC, it was 0.22% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 33%. Little progress has been made in removing nanoparticles.

Comparative Example 2
The same synthesis method as in Example 1 was repeated three times to obtain 9.7 kg of a crude silver nanowire dispersion. The obtained crude dispersion was placed in a 25 L PFA-coated SUS container, and 10.2 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 13.9 kg of the supernatant was removed by a decantation operation.

3.3 kg of acetonitrile was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redisperse the precipitate, and then 6.6 kg of butyl acetate was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (11.1 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 6 times, some of the nanoparticles produced as by-products were removed.

3.0 kg of acetone was added to the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 80% (5.8 kg) of the total amount of the supernatant was removed by a decantation operation. After repeating this operation once more, the residual liquid containing the precipitate was transferred to a 3 L plastic container, ion-exchanged water was added until the internal liquid became 2.1 kg, and the mixture was completely dispersed by shaking and stirring.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 2 and found to be 78%.

The silver nanowire concentrate was purified in the same manner as in Example 2 except that cross-flow filtration was continued until a total of 14 kg of filtrate was obtained. The total filtration time was 38.4 hours, and the filtration rate per unit time and unit filtration area was 6.1 kg / m ² · h. The dispersion liquid after cross-flow filtration was passed through a 355 mesh nylon filter to remove aggregates, thereby obtaining 1.4 kg of a silver nanowire purified liquid. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.2 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 67%). Moreover, when the concentration of PVP was measured by GPC, it was 0.15% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 88%. Although the number of cross-flow filtrations was increased as compared with Example 2, the removal of nanoparticles was hardly advanced.

Comparative Example 3
The same synthesis method as in Example 1 was repeated three times to obtain 9.7 kg of a crude silver nanowire dispersion. The obtained crude dispersion was placed in a 25 L PFA-coated SUS container, and 10.2 kg of butyl acetate was added over 10 minutes while stirring at 150 rpm using a mechanical stirrer. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 13.9 kg of the supernatant was removed by a decantation operation.

2.1 kg of ion-exchanged water was added to the residual liquid containing the precipitate, stirring was continued for 10 minutes to redistribute the precipitate, and then 4.4 kg of acetone was added over 10 minutes. After continuing the stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. Then, 70% (8.7 kg) of the total amount of the supernatant was removed by a decantation operation. By repeating this operation 8 times, a part of the nanoparticles produced as a by-product was removed.

3.0 kg of acetone was added to the residual liquid containing the precipitate, and after continuing stirring for 10 minutes, the stirring was stopped and the mixture was allowed to stand for 10 minutes to separate the supernatant and the precipitate. After removing 80% (4.6 kg) of the total liquid volume by decantation operation, transfer the residual liquid containing the precipitate to a 3 L plastic container, and add ion-exchanged water until the internal liquid reaches 2.1 kg. It was completely dispersed by shaking and stirring.

The ratio of silver nanowires in the dispersion (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) was calculated by the same method as in Example 2 and found to be 85%.

The silver nanowire concentrate was purified in the same manner as in Example 2 except that cross-flow filtration was continued until a total of 14 kg of filtrate was obtained. The total filtration time was 35.0 hours, and the filtration rate per unit time and unit filtration area was 5.0 kg / m ² · h. The dispersion liquid after cross-flow filtration was passed through a 355 mesh nylon filter to remove aggregates, thereby obtaining 1.3 kg of a silver nanowire purified liquid. When the weight change of the nylon filter was measured before and after passing the dispersion liquid, the increase was 0.2 g, and the agglomerates generated by the cross-flow filtration were very small.

The silver concentration of the silver nanowire purified liquid passed through the nylon filter was measured by the titration method and found to be 1.8% by mass (yield 65%). Moreover, when the concentration of PVP was measured by GPC, it was 0.18% by mass.

When the silver nanowire ratio (number of silver nanowires / (number of silver nanowires + number of silver nanoparticles)) in the silver nanowire purification solution passed through the nylon filter was calculated by the same method as before, it was 88%. Little progress has been made in removing nanoparticles.

The above results are shown in Table 1. By purifying the silver nanowire coarse dispersion having a silver concentration of 1.0% by mass or more by using a cross-flow filtration method, a high-purity silver nanowire dispersion can be produced in high yield.

From the results of Comparative Examples 1 to 3, when a dispersion having a silver concentration of 1.0% or more and a silver nanowire ratio of 90% or less was purified by cross-flow filtration, the silver nanowire ratio was significantly improved even if the number of cross-flow filtrations was increased. You can see that it doesn't. It is considered that this is because the filter is blocked by the nanoparticles. Since a dispersion liquid having a silver nanowire ratio of 90% or less has a large yellowness due to absorption derived from nanoparticles, if it is used as an ink and applied to produce a transparent conductive film, its optical characteristics become insufficient.

On the other hand, in Examples 1 to 17 in which the dispersion liquid having a silver nanowire ratio of more than 90% was purified by cross-flow filtration, the structure defining agent could be efficiently removed without clogging of the filter, and the solvent retention rate was improved. Even if it is lowered, there is little aggregation.

Claims

A step of preparing a silver nanowire coarse dispersion liquid containing silver nanowires having a number of silver nanowires / total number of particles> 90% and a structure-determining agent and having a silver concentration of 1.0% by mass or more.
A cross-flow filtration step of purifying the silver nanowire coarse dispersion liquid by a circulation type cross-flow filtration method, and
A method for producing a silver nanowire dispersion liquid, which comprises.
The method for producing a silver nanowire dispersion liquid according to claim 1, wherein in the cross-flow filtration step, the filtration rate per unit filter area and unit time is controlled to 16.0 kg / m 2 · h or less.
The method for producing a silver nanowire dispersion liquid according to claim 2 , wherein the filtration rate is 1.0 kg / m 2 · h or more.
The method for producing a silver nanowire dispersion liquid according to any one of claims 1 to 3, wherein the structure-defining agent is contained in a crude silver nanowire dispersion liquid in an amount of 0.5% by mass or more.
Any one of claims 1 to 4, wherein the step of preparing the silver nanowire coarse dispersion liquid includes a silver nanowire coarse dispersion liquid production step of producing a silver nanowire coarse dispersion liquid in which silver nanowires are synthetically dispersed in a reaction solvent. The method for producing a silver nanowire dispersion liquid according to the section.
The step of preparing the silver nanowire coarse dispersion liquid is
A sedimentation step of adding a sedimentation solvent to a crude dispersion of silver nanowires in which the silver nanowires are dispersed in the reaction solvent to precipitate the silver nanowires.
A supernatant removing step of removing a part of the supernatant of the mixture of the reaction solvent and the precipitation solvent containing by-product nanoparticles, and
A re-sedimentation cleaning step of removing by-product nanoparticles by repeating the sedimentation step multiple times to obtain a dispersion liquid in which the number of silver nanowires / total number of particles> 90% in the dispersion liquid is obtained.
The method for producing a silver nanowire dispersion liquid according to claim 5, further comprising after the silver nanowire coarse dispersion liquid production step.
In the cross-flow filtration step, the amount of the silver nanowire coarse dispersion liquid is coarsely dispersed before filtration by adding a washing solvent so as to supplement the solvent discharged as the filtrate during or after the concentration of the silver nanowire coarse dispersion liquid. The method for producing a silver nanowire dispersion liquid according to any one of claims 1 to 6, which is maintained at 60% or more of the liquid amount.