JP2017078207A - Silver nanowire and manufacturing method thereof as well as fluid dispersion and ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slender and long shape silver nanowire that exhibits excellent dispersibility in an aqueous solvent added with alcohol or an alcoholic solvent.SOLUTION: A silver nanowire covered with a copolymer of an acrylate-based monomer and vinylpyrrolidone and having an average diameter of 50 nm or smaller and an average length of 10 μm or longer. The silver nanowire can be manufactured by a method in which, in a manufacturing method of a silver nanowire in which silver is reduced and precipitated in wire in an alcohol solvent in which a silver compound is dissolved, in a state where the copolymer of the acrylate-based monomer and vinylpyrrolidone is dissolved in the solvent, the precipitation is proceeded.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a silver nanowire useful as a material for forming a transparent conductor, and a method for producing the same. The present invention also relates to a silver nanowire ink using the silver nanowire.

  In this specification, a collection of fine metal wires having a thickness of about 200 nm or less is referred to as “nanowires”. In the case of powder, each wire corresponds to “particles” constituting the powder, and nanowires corresponds to “powder” that is a collection of particles.

Silver nanowires are promising as conductive materials for imparting conductivity to transparent substrates. When a liquid containing silver nanowire (silver nanowire ink) is coated on a transparent substrate such as glass, PET (polyethylene terephthalate), PC (polycarbonate), etc., and then the liquid component is removed by evaporation or the like, the silver nanowire becomes the substrate. Since a conductive network is formed by contacting each other above, a transparent conductor can be realized. Conventionally, as a transparent conductive material, a metal oxide film typified by ITO is mainly used for applications such as a transparent electrode. However, the metal oxide film has drawbacks such as high film formation cost and weakness against bending, which hinders flexibility of the final product. In addition, high transparency and high conductivity are required for the conductive film of the touch panel sensor, which is one of the main uses of the transparent conductor, but recently, the demand for visibility has become more severe. In the conventional ITO film, it is necessary to increase the thickness of the ITO layer in order to obtain conductivity, but the increase in thickness causes a decrease in transparency and does not improve the visibility.
Silver nanowires are promising in overcoming the above-described drawbacks inherent in metal oxide films represented by ITO.

  As a method for producing silver nanowires, a silver compound is dissolved in a polyol solvent such as ethylene glycol, and in the presence of a halogen compound and PVP (polyvinylpyrrolidone), which is an organic protective agent, linearity is obtained using the reducing power of the solvent polyol. Techniques for depositing shaped metallic silver are known (Patent Documents 1 and 2, Non-Patent Document 1). PVP is an extremely effective substance as an organic protective agent for synthesizing silver nanowires with high yield.

US2005 / 0056118 Publication US2008 / 0003130 Publication

J. et al. of Solid State Chem. 1992, 100, 272-280

  In order to produce a transparent conductor using silver nanowires, a process of applying “silver nanowire ink” on a transparent substrate is indispensable. Since conventional silver nanowires coated with PVP exhibit good dispersibility in water, they are usually provided as silver nanowire inks using an aqueous liquid medium. However, since it is necessary to improve wettability with PET (polyethylene terephthalate), which is frequently used for transparent substrates, alcohols such as ethanol, 2-propanol, and ethylene glycol are added to the aqueous solvent of the silver nanowire ink. In general. As the amount of alcohol added increases, the wettability with the PET substrate improves. However, the addition of this alcohol has a problem in that the dispersibility of PNP-coated silver nanowires in liquid is lowered. That is, when the amount of alcohol added to the aqueous solvent increases, the silver nanowires coated with PVP tend to aggregate in the liquid, making it difficult to provide a silver nanowire ink having good dispersibility. There is also a need to use a silver nanowire dispersion liquid using an alcohol solvent (for example, a solvent containing 100% alcohol) depending on applications. In the conventional silver nanowire coated with PVP, good dispersion stability in an alcohol solvent cannot be expected.

  On the other hand, the silver nanowire has a smaller diameter and a longer length, which is more advantageous for achieving both high transparency and high conductivity. Conventional silver nanowires synthesized using PVP are not necessarily in consideration of the required characteristics (coexistence of transparency and conductivity at a higher level) that are expected to become more severe in the future for applications such as touch panel sensors. It is not satisfactory.

  As one method for improving the dispersibility of silver nanowires in an aqueous solvent to which alcohol has been added, it is considered effective to apply “alkylated PVP” with reduced hydrophilicity of PVP as an organic protective agent. It is done. However, it is difficult to synthesize thin and long wires by the silver nanowire synthesis method using alkylated PVP as an organic protective agent.

  As described above, a technology that satisfies the need to obtain silver nanowires that exhibit superior dispersibility compared with conventional PVP-coated silver nanowires in an aqueous solvent to which alcohol is added or in an alcohol-based solvent has not yet been established. . In particular, it is even more difficult to reconcile with another need to obtain thinner and longer wires. An object of this invention is to provide the silver nanowire which can respond to these needs.

  As a result of research, the inventors have found that when silver is reduced and deposited in the form of a wire in an alcohol solvent in the presence of an organic protective agent, the organic protective agent is not a PVP, but a “structure derived from an acrylate or methacrylate monomer. It has been found that the use of the “polymer having a unit” can improve the dispersibility in an aqueous solvent to which an alcohol has been added, and can synthesize a thin and long wire.

  The object is to provide silver having an average diameter of 100 nm or less and an average length of 5 μm or more coated with a polymer having a structural unit of an acrylate or methacrylate monomer, more preferably a copolymer of an acrylate or methacrylate monomer and a water-soluble monomer. Achieved by nanowires. Here, the water-soluble monomer means a monomer having a property of dissolving 1 g or more in 1000 g of water at 25 ° C.

  Those having an average diameter of 50 nm or less and an average length of 10 μm or more are more suitable objects, and those having an average diameter of less than 40 nm and an average length of 10 μm or more are more suitable objects. When the ratio of the average length (nm) to the average diameter (nm) is called the average aspect ratio, it is particularly preferable that the average aspect ratio is 250 or more. The average diameter of the silver nanowires is almost determined at the time of synthesis, but the average length and average aspect ratio can be further improved by devising a purification method. For example, silver nanowires having an average aspect ratio of 400 or more can be obtained by cross flow filtration. Here, the average diameter, average length, and average aspect ratio conform to the following definitions.

[Average diameter]
On a microscopic image (for example, FE-SEM image), in a projection image of a single metal wire, the average value of the diameters when the diameter of the inscribed circle in contact with the contours on both sides in the thickness direction is measured over the entire length of the wire. , Defined as the diameter of the wire. And the value which averaged the diameter of each wire which comprises nanowire (nanowires) is defined as the average diameter of the said nanowire. In order to calculate the average diameter, the total number of wires to be measured is set to 100 or more. However, a wire-like product or a granular product having a length (described later) of less than 0.5 μm is excluded from the measurement target.

[Average length]
On a microscopic image similar to the above, in a projected image of a single metal wire, the length from one end of the wire to the other end of the line passing through the center of the thickness of the wire (that is, the center of the inscribed circle) This is defined as the length of the wire. And the value which averaged the length of each wire which comprises nanowire (nanowires) is defined as the average length of the said nanowire. In order to calculate the average length, the total number of wires to be measured is set to 100 or more. However, wire-like products having a length of less than 0.5 μm and granular products are excluded from the measurement target.
The silver nanowire according to the present invention is composed of a very elongated wire. For this reason, the collected silver nanowires often have a curved string shape rather than a straight rod shape. The inventors have created software for efficiently measuring the above-described wire length on an image for such a curved wire and uses it for data processing.

[Average aspect ratio]
The average aspect ratio is calculated by substituting the above average diameter and average length into the following formula (1).
[Average aspect ratio] = [Average length (nm)] / [Average diameter (nm)] (1)

  An acrylate monomer is a monomer having an acryloyl group. A methacrylate monomer is a monomer having a methacryloyl group. The molecular weight of these monomers is, for example, 85 to 300. Specific examples of the monomer corresponding to the “acrylate or methacrylate monomer” include ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, butyl acrylate, 4-hydroxybutyl acrylate and the like.

  As a method for producing a silver nanowire coated with the above polymer, a structure derived from an acrylate-based or methacrylate-based monomer in a method for producing a silver nanowire in which silver is reduced and precipitated in a wire shape in an alcohol solvent in which a silver compound is dissolved A silver nanowire manufacturing method is provided in which the precipitation proceeds in a state where a polymer having units is dissolved in the solvent. When silver nanowires are synthesized by this method, silver nanowires coated with “polymer having a structural unit of acrylate or methacrylate monomer” which is an organic protective agent are obtained. Examples of such a polymer include a copolymer of an acrylate or methacrylate monomer and a water-soluble monomer such as vinyl pyrrolidone as described above.

  In this case, in particular, in order to synthesize a thin and long wire, it is possible to advance the precipitation in a state where the polymer, chloride, bromide, alkali metal hydroxide and aluminum salt are dissolved in the solvent. Is more effective. Examples of the acrylate or methacrylate monomers include the aforementioned ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, butyl acrylate, 4-hydroxybutyl acrylate and the like. As the copolymer of an acrylate or methacrylate monomer and vinyl pyrrolidone, for example, a copolymer having a structure in which 0.1 to 25 parts by mass of an acrylate or methacrylate monomer and 100 parts by mass of vinyl pyrrolidone are polymerized can be applied. A polyol is applicable as the alcohol as the solvent. It is more effective to cause the silver reduction precipitation to proceed in a temperature range of 60 ° C. or higher and lower than the boiling point of the solvent alcohol used.

  Moreover, in this invention, the silver nanowire dispersion liquid in which the silver nanowire coat | covered with the said polymer is disperse | distributing in isopropyl alcohol is provided. Moreover, the silver nanowire ink which contains 0.02-5.0 mass% of silver nanowires coat | covered with the said polymer in a liquid medium is provided.

  In the present invention, a silver nanowire coated with a polymer having a structural unit derived from an acrylate-based or methacrylate-based monomer is disclosed. This new type of organic protective agent exhibits an effect different from that of PVP in terms of improving dispersibility in an aqueous solvent to which an alcohol is added or in an alcohol solvent. By adjusting the blending ratio of the acrylate or methacrylate monomer in the polymer, the hydrophilicity and hydrophobicity of the organic protective agent can be changed, so that the dispersibility according to the type of silver nanoink liquid medium can be changed. Easy to optimize. Therefore, the present invention is extremely useful for obtaining a silver nanowire ink having improved wettability with a PET substrate or the like by adding alcohol or the like. In the case of using a copolymer of an acrylate or methacrylate monomer and vinyl pyrrolidone as an organic protective agent, for example, an average diameter of 50 nm or less, preferably less than 40 nm, an average length of 10 μm or more, an average aspect ratio of 200 or more, preferably 250 or more, It is possible to synthesize thin, long silver nanowires. Thin and long silver nanowires are extremely effective in improving the conductivity and visibility (haze resistance) of transparent conductors.

  As described above, the present invention simultaneously realizes (i) synthesis of thin and long silver nanowires, (ii) improvement of dispersibility of silver nanowire ink, and (iii) improvement of wettability of silver nanowire ink to a transparent substrate. It can be.

Structural formula of ethyl acrylate. Structural formula of 2-hydroxyethyl acrylate. Structural formula of 2-hydroxyethyl methacrylate. Structural formula of 4-hydroxybutyl acrylate. Structural formula of vinylpyrrolidone-ethyl acrylate copolymer. 2 is an SEM photograph of the silver nanowire obtained in Example 1. FIG. 4 is an SEM photograph of silver nanowires obtained in Example 2. FIG. 4 is an SEM photograph of silver nanowires obtained in Example 3. FIG. NMR spectrum of the vinylpyrrolidone-2-hydroxyethyl acrylate copolymer obtained in Example 4. 4 is a SEM photograph of silver nanowires obtained in Example 4. FIG. 4 is an SEM photograph of silver nanowires obtained in Example 5. FIG. 4 is an SEM photograph of silver nanowires obtained in Example 6. FIG. 3 is an SEM photograph of silver nanowires obtained in Comparative Example 1. 3 is an SEM photograph of the product obtained in Comparative Example 2. The drawing substitute photograph showing the mode after leaving still for 3 days of the IPA (isopropyl alcohol) dispersion liquid of the silver nanowire obtained in Example 1 and Comparative Example 3. FIG.

<Synthesis of silver nanowires>
The silver nanowire according to the present invention is coated with an organic protective agent “polymer having a structural unit derived from an acrylate-based or methacrylate-based monomer”. This silver nanowire can be synthesized by a technique of reducing and precipitating silver into a wire shape in the presence of an organic protective agent in an alcohol solvent by using the reducing power of the solvent alcohol. The method will be described below.

[Alcohol solvent]
As the kind of alcohol to be applied, one having an appropriate reducing power for silver and capable of depositing metallic silver in a wire shape is selected. At present, polyols typified by ethylene glycol are considered to be relatively suitable for the production of silver nanowires, but future studies will confirm many applicable alcohols. The inventors have already in an alcohol solvent comprising one or more of ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,3 butanediol, 1,4-butanediol, and glycerin. So, we have succeeded in synthesizing thin and long silver nanowires with a practically practical yield. These alcohols may be used alone or in combination of two or more.

[Organic protective agent]
An organic protective agent has the effect | action which covers the surface of the silver nanowire which precipitated in the reduction reaction, and suppresses coarse growth. Moreover, the organic protective agent which exists in the surface of the obtained silver nanowire has the effect | action which ensures the dispersibility to a liquid medium. PVP (polyvinyl pyrrolidone) is known as an effective organic protective agent for synthesizing silver nanowires by preferentially causing silver precipitation in only one direction. However, with silver nanowires synthesized using PVP, it is difficult to obtain a silver nanowire ink with good dispersion stability. When silver nanowire ink is applied to a transparent substrate typified by a PET substrate, the wettability of the ink with respect to the substrate must be good. Since PVP is highly hydrophilic, an aqueous solvent is usually used for the silver nanowire ink. In this case, in order to ensure wettability with a substrate such as PET, an alcohol is generally added to the aqueous solvent. The addition of alcohol improves the wettability with the substrate, but the dispersibility of the silver nanowires coated with PVP in the aqueous solvent is greatly reduced. That is, it is easy to precipitate when silver nanowires are converted into ink. As described above, in the case of silver nanowires synthesized using PVP, there are severe restrictions on improving the dispersion stability of the silver nanowire ink.

The inventors used a polymer having a structural unit of an acrylate or methacrylate monomer instead of PVP as an organic protective agent, thereby synthesizing a thin and long silver nanowire and a silver nanowire for an aqueous solvent to which an alcohol was added. It has been found that the improvement of dispersibility can be achieved. In particular, it is preferable to apply a copolymer of an acrylate or methacrylate monomer and another water-soluble monomer.
The water-soluble monomer means a monomer having a property of dissolving 1 g or more in 1000 g of water at 25 ° C. Specific examples of such water-soluble monomers include vinylpyrrolidone, vinylacetamide, vinyl alcohol, ethyleneimine, acrylamide, vinylpyridine, vinylcaprolactam, vinylformamide, acrylonitrile, diallyldimethylammonium salt, 2- (dimethylamino) methacrylate Examples include ethyl.
Examples of acrylate or methacrylate monomers include those having a molecular weight of 85-300. For example, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, butyl acrylate, 4-hydroxybutyl acrylate, and the like can be used. The solubility / dispersibility in an aqueous solvent to which an alcohol is added can be adjusted depending on the difference in the number of carbon atoms of the acrylate or methacrylate monomer used and the presence or absence of various substituents.

  The affinity for an aqueous solvent to which an organic substance such as alcohol is added can be adjusted by the polymerization composition of an acrylate or methacrylate monomer and another monomer. For example, when vinylpyrrolidone is used as a polymerization partner with an acrylate or methacrylate monomer, in a copolymer having a composition in which 0.1 to 25 parts by mass of an acrylate or methacrylate monomer and 100 parts by mass of vinylpyrrolidone are polymerized. It is easy to optimize the balance between the ease of synthesis of thin and long silver nanowires and the dispersibility of silver nanowires in an aqueous solvent containing alcohol. Even if the blending ratio of the acrylate or methacrylate monomer to 100 parts by mass of vinylpyrrolidone is as small as 0.1 part by mass, the dispersibility is greatly improved as compared with PVP. On the other hand, if the blending ratio of the acrylate or methacrylate monomer is excessive, it becomes difficult to synthesize thin and long silver nanowires. The range of the blending ratio of the acrylate or methacrylate monomer to 100 parts by mass of vinylpyrrolidone is more preferably 0.1 to 10 parts by mass.

  The polymer used as the organic protective agent preferably has a weight average molecular weight in the range of 30,000 to 3,000,000. When the weight average molecular weight is less than 30,000, silver particles are easily generated, and the yield of silver nanowires is reduced. When the weight average molecular weight exceeds 3,000,000, the diameter of the obtained silver nanowire tends to increase, and it becomes difficult to obtain a thin silver nanowire suitable for a transparent conductive material.

[Silver compound]
A silver compound that is soluble in a solvent is used as a silver source for reducing and depositing silver nanowires. For example, silver nitrate, silver acetate, silver oxide, silver chloride and the like can be mentioned, but silver nitrate (AgNO ₃ ) is easy to use in consideration of solubility in solvents and cost. The amount of Ag added to the total amount of alcohol solvent used is preferably in the range of 0.001 to 0.1 mol of Ag per liter of solvent, and more preferably in the range of 0.025 to 0.080 mol.

〔chloride〕
In order to reduce and precipitate metallic silver in the form of a wire in an alcohol solvent, it is effective to make chloride ions having an effect of providing anisotropy in the growth direction of the precipitation. Chloride ions are considered to have an effect of promptly etching a specific crystal plane of nucleated metallic silver to promote the formation of multiple twins, thereby increasing the abundance of nuclei serving as wires. Various chloride ion sources are applicable as long as they are soluble in alcohol as a solvent. TBAC (tetrabutylammonium chloride; (CH ₃ CH ₂ CH ₂ CH ₂ ) ₄ NCl) which is an organic chlorine compound is also a target. Sodium chloride (NaCl), potassium chloride (KCl), hydrogen chloride (HCl), lithium chloride (LiCl), and the like that are industrially available and inexpensive are suitable targets. Further, copper (II) chloride (CuCl ₂ ) soluble in an alcohol solvent may be used. The amount of chloride added relative to the total amount of alcohol solvent used is preferably in the range of 0.00001 (1 × 10 ⁻⁵ ) to 0.01 mol as the amount of Cl per liter of solvent, and is 0.000005 (5 × 10 5 ^-5 ) to 0.01 mol is more preferable.

[Bromide]
Bromide ions also have the effect of imparting anisotropy in the direction of metal silver precipitation. As a result of various studies, it is possible to obtain thin and long silver nanowires having an average diameter of 50 nm or less, preferably less than 40 nm, and an average length of 10 μm or more by adding bromide ions in addition to the above-described chloride ions in an alcohol solvent. It was found to be extremely effective above. Various bromide ion sources are applicable as long as they are bromides that dissolve in alcohol as a solvent. CTAB (cetyltrimethylammonium bromide; (C ₁₆ H ₃₃ ) N (CH ₃ ) ₃ Br), which is an organic bromine compound, is also an object. Sodium bromide (NaBr), potassium bromide (KBr), hydrogen bromide (HBr), lithium bromide (LiBr) and the like that are industrially available and inexpensive are suitable targets. Although the amount of bromide added is extremely small, it is an extremely effective additive for imparting anisotropy. The amount of bromide added relative to the total amount of alcohol solvent used is preferably in the range of 0.000001 (1 × 10 ⁻⁶ ) to 0.001 (1 × 10 ⁻³ ) mol as Br amount per liter of solvent. A range of 0.0005 (5 × 10 ⁻⁶ ) to 0.001 (1 × 10 ⁻³ ) mol is more preferable.

[Aluminum salt and alkali metal hydroxide]
According to the inventors' research, it is possible to effectively synthesize silver nanowires having a large aspect ratio by dissolving an aluminum salt and an alkali metal hydroxide in a predetermined ratio in a solvent for depositing silver. It is extremely effective. The mechanism of this phenomenon is currently unknown, but it is speculated that aluminum ions may have the effect of activating the crystal plane for silver to grow into a wire shape and improving the reduction rate. Such an action is considered to be exhibited in the proper presence of hydroxide ions.
In addition, the presence of Al is confirmed in the silver nanowire synthesized in the solvent containing the aluminum salt. According to the investigation by the inventors, among metal components, metal nanowires containing 100 to 1000 ppm of Al had a high uniformity of diameter, and although they were thin and long, there was a tendency for local bending and bending to be difficult to occur. . Such silver nanowires are excellent in handleability in the operation of making an ink and the operation of coating on a substrate. Those having an A1 content of 200 ppm or more are more suitable targets.

  In this specification, the molar ratio between the total amount of Al of the aluminum salt dissolved in the solvent and the total amount of hydroxide ions of the alkali metal hydroxide is expressed as “Al / OH”. Sometimes referred to as “OH molar ratio”. As a result of detailed studies, thin and long silver nanowires can be synthesized by setting the Al / OH molar ratio to 0.01 to 0.40. If the Al / OH molar ratio is too high, the reducing power due to the alcohol solvent decreases, and silver ions or silver complexes dissolved in the solvent cannot be reduced to metallic silver. If the Al / OH molar ratio is too low, it becomes difficult to synthesize a long wire having a large average aspect ratio.

  However, even if the Al / OH molar ratio is within an appropriate range, if the amount of alkali hydroxide relative to silver is too large, a composite composed mainly of silver oxide is formed, and the wire cannot be synthesized. Conversely, if the amount of alkali hydroxide relative to silver is too small, the silver reduction reaction is difficult to occur. In the present specification, the molar ratio between the total amount of hydroxide ions of the alkali metal hydroxide dissolved in the solvent and the total amount of Ag of the silver compound is expressed as “OH / Ag”. It may be referred to as “Ag molar ratio”. As a result of detailed studies, the OH / Ag molar ratio is preferably in the range of 0.005 to 0.50.

As the alkali metal hydroxide, industrially, for example, one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferably used.
As the aluminum salt, aluminum nitrate and aluminum chloride are applicable. Aluminum nitrate may be added as aluminum nitrate nonahydrate Al (NO ₃ ) ₃ · 9H ₂ O. When aluminum chloride is used, it can also serve as the above chloride.

[Example of silver nanowire synthesis procedure]
Conventionally, a technique for obtaining silver nanowires by reducing power of alcohol as a solvent in an alcohol solvent in which a silver compound is dissolved in the presence of a halogen compound and an organic protective agent is known. In this case, PVP is considered suitable as an organic protective agent for depositing metallic silver into a wire shape. Also in the present invention, silver nanowires are generated using the reducing power of such an alcohol solvent. However, as described above, in the present invention, a polymer having a structural unit of an acrylate or methacrylate monomer is used as the organic protective agent, not PVP.

  The temperature at which the silver reductive precipitation reaction proceeds can be set in the range of 60 ° C. or higher and the boiling point of the solvent or lower. The boiling point is the boiling point at the pressure of the gas phase space where the liquid level of the solvent in the reaction vessel contacts. When a plurality of types of alcohols are mixed to form a solvent, the temperature may be set to a temperature equal to or lower than the boiling point of the lowest boiling alcohol. However, from the viewpoint of allowing the reaction to proceed gently, it is preferable to avoid boiling and control the temperature below the boiling point. For example, when ethylene glycol is used as a solvent and the reaction is allowed to proceed under atmospheric pressure, the boiling point of ethylene glycol is about 197 ° C., but the reaction is preferably allowed to proceed at 60 to 185 ° C., and 80 to 175 ° C. It is more preferable. What is necessary is just to set reaction time, for example in the range of 10 minutes-100 hours.

  As a procedure, each substance other than the silver compound is dissolved in an alcohol solvent, and after the temperature of the solvent (hereinafter referred to as “solution A”) reaches a predetermined reaction temperature, the silver compound is dissolved in the solution A. It is desirable to add. The silver compound can be added by a method in which the silver compound solution (referred to as “solution B”) is mixed in the solution A after being previously dissolved in an alcohol solvent of the same type as the solvent in another container. It is desirable that the solution B before being mixed with the solution A has a temperature around room temperature (for example, 15 to 40 ° C.). If the temperature of the solution B is too low, it takes time to dissolve the silver compound, and if it is too high, a silver reduction reaction is likely to occur in the stage before mixing with the solution A due to the reducing power of the alcohol solvent in the solution B. A silver compound that is easily soluble in an alcohol solvent, such as silver nitrate, may be added to the solution A as a solid. For the addition of the silver compound, a method of adding the whole amount at once, or a method of adding it intermittently or continuously within a fixed time can be adopted. The liquid is continuously stirred while the reaction is in progress. Further, the gas phase atmosphere in contact with the liquid surface of the solution A during the progress of the reaction can be air or nitrogen.

After the silver precipitation reaction is completed, the slurry containing silver nanowires is solid-liquid separated using means such as centrifugation or decantation to recover the solid content. Decantation may be performed for about 2 to 2 weeks with standing, or at least one solvent with low polarity such as acetone, toluene, hexane, kerosene, etc. is added to the slurry to increase the sedimentation rate. And may be concentrated. In the case of centrifugation, the slurry after the reaction may be directly applied to a centrifuge to concentrate the silver nanowires.
After concentration, the supernatant is removed. Thereafter, a highly polar solvent such as water or alcohol is added to re-disperse the silver nanowires, and further solid-liquid separation is performed using means such as centrifugation or decantation to recover the solid content. It is preferable to repeat this redispersion and concentration step (washing).

[Purification of silver nanowires]
When silver nanowires are synthesized, in addition to sufficiently long silver nanowires, silver nanoparticles and short silver nanowires are also generated. The operation of removing products belonging to impurities (hereinafter referred to as “product impurities”) such as particles and short wires as much as possible and separating and collecting useful long silver nanowires is called “purification”.

  In refining, a phenomenon in which silver nanowires with a large volume are preferentially settled is used. After the silver nanowire-containing solids recovered after synthesis are dispersed in water, the produced impurities are clarified by centrifugation, decantation, etc. And can be removed. In order to increase the sedimentation rate, a solvent having a small polarity may be added.

  Generated impurities such as nanoparticles and short wires are highly cohesive and may be difficult to adhere to and separate from long nanowires. As a countermeasure in such a case, the inventors added a dispersant or a surfactant when dispersing the silver nanowire-containing solid content (concentrate) in water, thereby producing a better dispersion state. It has been found that the separation of impurities is promoted. A suitable dispersant includes PVP.

  In addition, when filtering using a filter with a small pore size such as a membrane filter or nylon filter, the silver nanowires to be collected are trapped without passing through the filter because they are longer than the filter diameter, and separated from the generated impurities passing through the filter. Can do. In addition, it is effective to apply a cross flow filtration method. In particular, cross flow filtration using a ceramic filter can recover silver nanowires having an average aspect ratio of, for example, 400 or more.

  The solid content after washing is mainly composed of silver nanowires having an organic protective agent on the surface. This silver nanowire can be stored as a dispersion liquid dispersed in an appropriate liquid medium according to the purpose. When applied to a method for producing silver nanowire ink, a viscosity modifier and a binder component are added to the silver nanowire dispersion liquid in which the solid content after washing is dispersed in water, alcohol, etc. Let

《Silver nanowire ink》
In order to produce a silver nanowire ink, a silver nanowire dispersion liquid purified as described above is prepared, and a viscosity modifier and a binder component are added to adjust to a predetermined property. Here, a preferable additive substance, composition, property, dispersion stability, and the like of the ink will be described below by taking as an example an ink in which an alcohol effective for improving wettability with a PET base material is added to an aqueous solvent.

[Viscosity modifier]
The viscosity modifier applied to the present invention needs to be dissolved in water + alcohol as a solvent. Various water-soluble polymers conventionally used in various fields can be used as the thickener. For example, as natural systems and derivatives thereof, there are CMC (carboxymethylcellulose) and MC (methylcellulose) in the cellulose fiber and derivatives, and albumin (egg white component) and casein (included in milk) in the protein system. Etc.). In addition, alginic acid, agar, starch, polysaccharides and the like can also be used as water-soluble thickeners. Examples of the synthetic system include polymers such as a vinyl compound, a polyester compound, a polyvinyl alcohol compound, and a polyalkylene oxide compound.

〔binder〕
The adhesion between individual silver nanowires and the adhesion between the silver nanowires and the substrate in the transparent conductive coating obtained by applying silver nanowire ink to the substrate and drying is a yield in producing a transparent conductive film. Is very important. In order to ensure this adhesion, it is necessary to add a binder component having the role of “glue”. In the present specification, a transparent coating film obtained by applying a silver nanowire ink to a substrate and drying it, wherein individual wires are integrated to exhibit conductivity, a transparent conductive coating film I'm calling.

  The conductivity of the transparent conductive film (the bonded structure of the film-like base material and the transparent conductive coating on the surface thereof) is manifested by the silver nanowire metals constituting the transparent conductive coating being in contact with each other. If a binder component is added to the silver nanowire ink, metal contact between the wires may be hindered and sufficient conduction may not be obtained. For this reason, conventionally, a silver nanoink that does not contain a strong binder component is applied onto a substrate and dried to obtain a reliable contact state between the wires, and then an overcoat containing an adhesive component (overcoat) In many cases, a method of applying a coating agent) to ensure adhesion of the transparent conductive coating film is employed.

  However, even in the above-described overcoating method, the film on which the silver nanowire ink is first applied generally passes through the turning point by the roll in the furnace many times in order to increase the drying time. Since bending is applied to the base material at the roll passing point in the line, stress is also applied to the coating film, and there is a possibility that conductivity due to contact between the wires may deteriorate. In order to maintain good continuity, it is difficult to operate at an increased line speed, and improvement in productivity cannot be expected. Further, in many cases, a procedure is taken in which the coil is once wound up in a coil shape to be sent to the next process and is then unwound again in the overcoating process. In this case as well, stress may be applied to the surface of the coating film of the base material at the time of winding / unwinding, which may cause a decrease in conductivity and peeling from the base material. Therefore, even when overcoating is performed, it is indispensable to improve productivity by adding some binder component to the silver nanowire ink and improving the adhesion between the wires and the adhesion between the substrate and the coating film. It becomes. Hereinafter, unless otherwise specified, “adhesion” means both adhesion between wires and adhesion between a substrate and a coating film.

  The binder added to the silver nanowire ink is required to have excellent conductivity, optical performance (high light transmission and low haze), and adhesion. However, it is not easy to meet these requirements to a high degree. Since the binder is basically an adhesive, if the selection is wrong, the adhesive may be interposed between the contact points of the silver nanowires, and the conductivity may be significantly inhibited. Moreover, since it is an adhesive agent, there also exists a problem that silver nanowires will adhere in an ink and aggregation will occur easily. A water-soluble acrylic-urethane copolymer resin can be illustrated as a suitable binder component. Hereinafter, the composition to which the water-soluble acrylic-urethane copolymer resin is applied will be described as an example.

[Ink composition]
The content of the silver nanowire is preferably 0.02 to 1.0% by mass in the mass ratio of the total amount of the silver nanowire ink, and the addition amount of the viscosity modifier is 0.01 to 1.0% by mass. It is preferable that the addition amount of a component is 0.01-2.0 mass% of the addition amount of the water-soluble acrylic-urethane copolymer resin which is an active ingredient. The solvent is preferably a mixture of water and alcohol, and is preferably 5 to 40% by mass of alcohol and the balance water. As the alcohol, those having a solubility parameter (SP value) of 10 or more are preferable. For example, low boiling point alcohols such as methanol, ethanol, isopropyl alcohol (2-propanol) can be preferably used. The SP values are: water: 23.4, methanol: 14.5, ethanol: 12.7, and isopropyl alcohol are 11.5.

[Viscosity and surface tension]
The silver nanowire ink has excellent coating properties when the viscosity is 1 to 100 mPa · s and the surface tension is 20 to 80 mN / m at a shear rate of 300 (1 / s) measured by a rotary viscometer.
The viscosity can be measured using, for example, a thermo-scientific rotational viscometer, HAAKE Rheo Stress 600 (measuring cone: Cone C60 / 1 ° Ti, D = 60 mm, plate: Meas. Plate cover MPC60).
The surface tension can be measured using a fully automatic surface tension meter (for example, a fully automatic surface tension meter manufactured by Kyowa Interface Science Co., Ltd., CBVP-Z).

[Dispersion stability of silver nanowire ink]
Dispersion stability is determined by preparing a silver nanowire ink, then allowing the container containing the ink to stand, and applying the silver nanowire ink to a substrate immediately after the ink is created and after a predetermined time has elapsed to form a dry coating film. Can be evaluated by measuring the sheet resistance. Ink with good dispersion stability of silver nanowires, the sheet resistance values obtained by applying the respective inks immediately after production, after 4 hours, after 8 hours, and after 24 hours remain almost unchanged. Ink with poor dispersion stability decreases the concentration of silver nanowires dispersed in the ink liquid due to the precipitation of silver nanowires, and the ink has a long elapsed time of 4 hours, 8 hours, 24 hours, etc. The formed coating film has a higher sheet resistance value. When such an ink with poor dispersion stability is visually observed in the container, it can be confirmed that the supernatant is transparent after a long time (after 8 hours or 24 hours).

  This dispersion stability is extremely important for the production of transparent conductors. One important application of silver nanowires is in transparent conductive films. In the production process, silver nanoink is continuously coated on a PET film, which is a transparent substrate, in a roll-to-roll manner by a coating apparatus, and the continuous coating time is as long as half a day. In the meantime, the silver nanowire ink is stored in the ink tank of the coating device. However, if the dispersion stability of the silver nanowire is poor, the silver nanowire will precipitate and agglomerate in this ink tank, resulting in stable quality. It becomes difficult to form a coating layer.

[Example 1]
<Creation of a copolymer of ethyl acrylate and vinyl pyrrolidone>
In a 100 mL glass container that can be sealed with a lid, 45 g of 1,4-dioxane as a solvent, 10.014 g of 1-vinyl-2-pyrrolidone, 0.113 g of ethyl acrylate (FIG. 1, molecular weight 100.1), and a polymerization initiator 0.576 g of a certain 2,2′-azobis (isobutyronitrile) was added and stirred using a magnetic stirrer to dissolve each substance in the solvent. Nitrogen gas was blown in for 10 minutes while stirring the solution after dissolution, and then the container was sealed with a lid so that a nitrogen atmosphere could be maintained. This solution was kept at 60 ° C. for 24 hours while stirring at 500 rpm with a magnetic stirrer. After 24 hours, in order to stop the reaction, a container was placed in ice water and rapidly cooled.

The following washing operation was performed for the purpose of removing unreacted monomers and polymerization initiators.
The solution kept for 24 hours was dropped into 500 mL of diethyl ether in a stirred state using a burette. By dripping, a vinylpyrrolidone-ethyl acrylate copolymer precipitates. The precipitated vinylpyrrolidone-ethyl acrylate copolymer was collected by filtration through a membrane filter, and dried at room temperature under vacuum for 30 minutes to obtain a vinylpyrrolidone-ethyl acrylate copolymer solid (end of the first washing step).

  The solid of the vinyl pyrrolidone-ethyl acrylate copolymer that completed the first washing step was dissolved in 100 mL of chloroform. This solution was added dropwise to 500 mL of diethyl ether with stirring using a burette. By dripping, a vinylpyrrolidone-ethyl acrylate copolymer precipitates. The precipitated vinyl pyrrolidone-ethyl acrylate copolymer was recovered by filtration through a membrane filter, and dried at room temperature under vacuum for 30 minutes to obtain a vinyl pyrrolidone-ethyl acrylate copolymer solid (end of the second washing step).

  The solid of the vinyl pyrrolidone-ethyl acrylate copolymer which finished the second washing step was dissolved again in 100 mL of chloroform. This solution was added dropwise to 500 mL of diethyl ether with stirring using a burette. By dripping, a vinylpyrrolidone-ethyl acrylate copolymer precipitates. The precipitated vinylpyrrolidone-ethyl acrylate copolymer was recovered by filtration through a membrane filter, and this was dried by vacuum drying at 60 ° C. for 24 hours to obtain a dried product of vinyl pyrrolidone-ethyl acrylate copolymer (end of the third washing step). .

  Through the above washing operation, a dried product of vinylpyrrolidone-ethyl acrylate copolymer having a structure in which 1.128 parts by mass of an acrylate monomer and 100 parts by mass of vinylpyrrolidone were polymerized was prepared. When the amount of each monomer charged is converted to mass%, ethyl acrylate is 1 mass% and vinylpyrrolidone is 99 mass%. FIG. 5 shows the structural formula of the vinylpyrrolidone-ethyl acrylate copolymer.

<Creation of silver nanowires>
At room temperature, 26 g of propylene glycol (1,2-propanediol) was taken in a 50 mL vial, and 0.402 g of the vinylpyrrolidone-ethyl acrylate copolymer obtained above was contained therein, and the lithium chloride content was 1% by mass. 0.151 g of a 1,2-propanediol solution, 0.150 g of a 1,2-propanediol solution having a lithium hydroxide content of 1% by mass, 1,0.1% having a potassium bromide content of 0.25% by mass A solution A was prepared by adding 0.166 g of a 2-propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2 mass%. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Thereafter, the reaction solution was cooled to room temperature.

  To the reaction solution after cooling, 10 times the amount of acetone was added, and after stirring for 10 minutes, the reaction solution was allowed to stand for 24 hours. Since the concentrate and the supernatant were observed after standing, the supernatant was carefully removed with a pipette to obtain a concentrate. 25 g of pure water was added to the obtained concentrate and stirred for 10 minutes to disperse the concentrate, then 10 times the amount of acetone was added, and the mixture was further allowed to stand for 24 hours after stirring. Since the concentrate and the supernatant were newly observed after standing, the supernatant was carefully removed with a pipette. Since the excessive organic protective agent is unnecessary for obtaining good conductivity, this washing operation was repeated to sufficiently wash the solid content.

  Pure water was added to the solid content after washing to obtain a dispersion of this solid content. The dispersion was collected, and the pure water of the solvent was volatilized on the observation table and then observed with a high resolution FE-SEM (high resolution field emission scanning electron microscope). As a result, the solid content was a silver nanowire. confirmed. FIG. 6 illustrates an SEM photograph of the silver nanowire.

In SEM observation, the average diameter and the average length were determined according to the above-mentioned definition using all the silver nanowires observed in five randomly selected fields as the measurement target. The total number of wires to be measured is 100 or more. The diameter measurement was performed using an SEM image at a magnification of 150,000 times, and the length measurement was performed using an SEM image at a high resolution SEM magnification of 2,500 times.
As a result, the average diameter of the silver nanowire obtained in this example was 32 nm, the average length was 11.1 μm, and the average aspect ratio was 11100 nm / 32 nm≈347.

  The solid content (silver nanowires) after the washing was dispersed in an IPA (isopropyl alcohol) 100% alcohol solvent to obtain a silver nanowire dispersion. The silver concentration in the dispersion was adjusted to 0.2% by mass. About 40 mL of this silver nanowire dispersion was dispensed into a vial, and then the vial was allowed to stand. The state of the liquid after 3 days has elapsed after the start of standing is shown in the photograph of FIG. In the figure, examples of PVP-coated silver nanowires (Comparative Example 3 described later) are shown side by side. It was confirmed that the silver nanowires of this example coated with vinylpyrrolidone-ethyl acrylate copolymer did not precipitate even after 3 days and exhibited excellent dispersion stability in alcohol solvents.

  Moreover, the solid content (silver nanowire) after the washing was dispersed in a mixed solvent of 80% by mass of pure water and 20% by mass of IPA (isopropyl alcohol) to obtain a silver nanowire dispersion. The silver concentration in the dispersion was adjusted to 0.2% by mass. About 40 mL of this silver nanowire dispersion was dispensed into a vial, and then the vial was allowed to stand. No settling of silver nanowires was observed even after 1 day from the start of standing, and the silver nanowires of this example coated with vinylpyrrolidone-ethyl acrylate copolymer had excellent dispersion stability in an aqueous solvent to which alcohol was added. It was confirmed that

[Example 2]
<Preparation of copolymer of 2-hydroxyethyl acrylate and vinyl pyrrolidone>
The copolymer was prepared under the same conditions as in Example 1, except that 0.113 g of 2-hydroxyethyl acrylate (FIG. 2, molecular weight 116.1) was added instead of 0.113 g of ethyl acrylate in the preparation of the copolymer in Example 1. It was created. The obtained copolymer is a vinylpyrrolidone-2-hydroxyethyl acrylate copolymer having a structure in which 1.128 parts by mass of an acrylate monomer and 100 parts by mass of vinylpyrrolidone are polymerized, and the charge amount of each monomer is converted to mass%. As a result, 1% by mass of 2-hydroxyethyl acrylate and 99% by mass of vinylpyrrolidone are obtained.

<Creation of silver nanowires>
At room temperature, 26 g of propylene glycol (1,2-propanediol) is taken into a 50 mL vial, and 0.472 g of the vinylpyrrolidone-2-hydroxyethyl acrylate copolymer obtained above is contained therein, and the content of lithium chloride is 0.151 g of a 1,2-propanediol solution that is 1% by mass, 0.107 g of a 1,2-propanediol solution that has a lithium hydroxide content of 1% by mass, and a potassium bromide content of 0.25% by mass. 0.166 g of a certain 1,2-propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2% by mass were added and mixed to obtain a solution A. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire. FIG. 7 illustrates an SEM photograph of the silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 34 nm, the average length was 12.0 μm, and the average aspect ratio was 12000 nm / 34 nm≈353.

  The washed silver nanowire was dispersed in a mixed solvent of 80% by mass of pure water and 20% by mass of IPA (isopropyl alcohol), and the dispersion stability was examined in the same manner as in Example 1. As a result, after the start of standing, the silver nanowires were not precipitated even after 1 day, and the silver nanowires of this example coated with vinylpyrrolidone-2-hydroxyethyl acrylate copolymer were in an aqueous solvent to which alcohol was added. It was confirmed that it exhibited excellent dispersion stability.

Example 3
<Preparation of copolymer of 2-hydroxyethyl acrylate and vinyl pyrrolidone>
The copolymer was prepared under the same conditions as in Example 1 except that 0.557 g of 2-hydroxyethyl acrylate (FIG. 2, molecular weight 116.1) was added in place of 0.113 g of ethyl acrylate in the preparation of the copolymer in Example 1. It was created. The obtained copolymer is a vinyl pyrrolidone-2-hydroxyethyl acrylate copolymer having a structure in which 5.263 parts by mass of an acrylate monomer and 100 parts by mass of vinyl pyrrolidone are polymerized. Then, it becomes 5 mass% of 2-hydroxyethyl acrylate, and 95 mass% of vinyl pyrrolidone.

<Creation of silver nanowires>
At room temperature, 26 g of propylene glycol (1,2-propanediol) is taken into a 50 mL vial, and 0.472 g of the vinylpyrrolidone-2-hydroxyethyl acrylate copolymer obtained above is contained therein, and the content of lithium chloride is 0.151 g of a 1,2-propanediol solution that is 1% by mass, 0.150 g of a 1,2-propanediol solution that has a lithium hydroxide content of 1% by mass, and a potassium bromide content of 0.25% by mass. 0.166 g of a certain 1,2-propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2% by mass were added and mixed to obtain a solution A. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire. FIG. 8 illustrates an SEM photograph of the silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 39 nm, the average length was 10.7 μm, and the average aspect ratio was 10700 nm / 39 nm≈274.

  The washed silver nanowire was dispersed in a mixed solvent of 80% by mass of pure water and 20% by mass of IPA (isopropyl alcohol), and the dispersion stability was examined in the same manner as in Example 1. As a result, after the start of standing, the silver nanowires were not precipitated even after 1 day, and the silver nanowires of this example coated with vinylpyrrolidone-2-hydroxyethyl acrylate copolymer were in an aqueous solvent to which alcohol was added. It was confirmed that it exhibited excellent dispersion stability.

Example 4
<Preparation of copolymer of 2-hydroxyethyl acrylate and vinyl pyrrolidone>
The copolymer was prepared under the same conditions as in Example 1 except that 2.226 g of 2-hydroxyethyl acrylate (FIG. 2, molecular weight 116.1) was added instead of 0.113 g of ethyl acrylate in the preparation of the copolymer in Example 1. It was created. The obtained copolymer is a vinylpyrrolidone-2-hydroxyethyl acrylate copolymer having a structure in which 25.00 parts by mass of an acrylate monomer and 100 parts by mass of vinylpyrrolidone are polymerized, and the charged amount of each monomer is converted to mass%. Then, 20% by mass of 2-hydroxyethyl acrylate and 80% by mass of vinyl pyrrolidone are obtained.

NMR (nuclear magnetic resonance) spectrum was measured for the obtained vinylpyrrolidone-2-hydroxyethyl acrylate copolymer. FIG. 9 shows the NMR spectrum. In the measured NMR spectrum, a peak considered to correspond to the position of the alphabet symbol described in the copolymer structural formula shown in FIG. 9 was observed. That is, it has been confirmed that the vinylpyrrolidone-2-hydroxyethyl acrylate copolymer prepared by the above method has a structural portion derived from 2-hydroxyethyl acrylate. In FIG. 9, “TMS” represents tetramethylsilane (0PPM) contained in deuterated chloroform as a standard substance. A peak of CHCl ₃ contained in a trace amount in the solvent is also shown.

<Creation of silver nanowires>
At room temperature, take 50 g of propylene glycol (1,2-propanediol) in a 50 mL vial, and in that, 0.402 g of the vinylpyrrolidone-2-hydroxyethyl acrylate copolymer obtained above has a lithium chloride content. 0.151 g of a 1,2-propanediol solution that is 1% by mass, 0.150 g of a 1,2-propanediol solution that has a lithium hydroxide content of 1% by mass, and a potassium bromide content of 0.25% by mass. 0.166 g of a certain 1,2-propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2% by mass were added and mixed to obtain a solution A. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire. FIG. 10 illustrates an SEM photograph of the silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 33 nm, the average length was 8.5 μm, and the average aspect ratio was 8500 nm / 33 nm≈258.

  The washed silver nanowire was dispersed in a mixed solvent of 80% by mass of pure water and 20% by mass of IPA (isopropyl alcohol), and the dispersion stability was examined in the same manner as in Example 1. As a result, after the start of standing, the silver nanowires were not precipitated even after 1 day, and the silver nanowires of this example coated with vinylpyrrolidone-2-hydroxyethyl acrylate copolymer were in an aqueous solvent to which alcohol was added. It was confirmed that it exhibited excellent dispersion stability.

Example 5
<Preparation of copolymer of 2-hydroxyethyl methacrylate and vinyl pyrrolidone>
The copolymer was prepared under the same conditions as in Example 1 except that 0.113 g of 2-hydroxyethyl methacrylate (FIG. 3, molecular weight 130.1) was added instead of 0.113 g of ethyl acrylate in preparation of the copolymer in Example 1. It was created. The obtained copolymer is a vinylpyrrolidone-2-hydroxyethyl methacrylate copolymer having a structure in which 1.128 parts by mass of an acrylate monomer and 100 parts by mass of vinylpyrrolidone are polymerized, and the charge amount of each monomer is converted to mass%. Then, it becomes 1 mass% of 2-hydroxyethyl methacrylate and 99 mass% of vinyl pyrrolidone.

<Creation of silver nanowires>
At room temperature, 26 g of propylene glycol (1,2-propanediol) was taken into a 50 mL vial, and 0.472 g of the vinylpyrrolidone-2-hydroxyethyl methacrylate copolymer obtained above was contained therein, and the lithium chloride content was 0.151 g of a 1,2-propanediol solution that is 1% by mass, 0.150 g of a 1,2-propanediol solution that has a lithium hydroxide content of 1% by mass, and a potassium bromide content of 0.25% by mass. 0.166 g of a certain 1,2-propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2% by mass were added and mixed to obtain a solution A. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire. FIG. 11 illustrates an SEM photograph of the silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 34 nm, the average length was 10.1 μm, and the average aspect ratio was 10100 nm / 34 nm≈297.

  The washed silver nanowire was dispersed in a mixed solvent of 80% by mass of pure water and 20% by mass of IPA (isopropyl alcohol), and the dispersion stability was examined in the same manner as in Example 1. As a result, the silver nanowires of this example coated with vinylpyrrolidone-2-hydroxyethyl methacrylate copolymer were not found in the aqueous solvent to which alcohol was added, even after one day had elapsed after the start of standing. It was confirmed that it exhibited excellent dispersion stability.

Example 6
<Preparation of copolymer of 4-hydroxybutyl acrylate and vinyl pyrrolidone>
The copolymer was prepared under the same conditions as in Example 1 except that 0.113 g of 4-hydroxybutyl acrylate (FIG. 4, molecular weight 144.2) was added instead of 0.113 g of ethyl acrylate in the preparation of the copolymer in Example 1. It was created. The obtained copolymer is a vinylpyrrolidone-4-hydroxybutyl acrylate copolymer having a structure in which 1.128 parts by mass of an acrylate monomer and 100 parts by mass of vinylpyrrolidone are polymerized, and the charge amount of each monomer is converted to mass%. As a result, 1% by mass of 4-hydroxybutyl acrylate and 99% by mass of vinylpyrrolidone are obtained.

<Creation of silver nanowires>
At room temperature, 26 g of propylene glycol (1,2-propanediol) is taken into a 50 mL vial, and 0.402 g of the vinylpyrrolidone-4-hydroxybutyl acrylate copolymer obtained above is contained therein, and the content of lithium chloride is 0.151 g of a 1,2-propanediol solution that is 1% by mass, 0.150 g of a 1,2-propanediol solution that has a lithium hydroxide content of 1% by mass, and a potassium bromide content of 0.25% by mass. 0.166 g of a certain 1,2-propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2% by mass were added and mixed to obtain a solution A. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire. FIG. 12 illustrates an SEM photograph of the silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 34 nm, the average length was 8.2 μm, and the average aspect ratio was 7600 nm / 38 nm≈241. The average length of the silver nanowires measured here was less than 10 μm. However, since this silver nanowire contains many wires having a length exceeding 10 μm, the average length is 10.0 μm by further purification. It is possible to collect the above silver nanowires.

  The washed silver nanowire was dispersed in a mixed solvent of 80% by mass of pure water and 20% by mass of IPA (isopropyl alcohol), and the dispersion stability was examined in the same manner as in Example 1. As a result, after the start of standing, the silver nanowires were not precipitated even after 1 day, and the silver nanowires of this example coated with vinylpyrrolidone-4-hydroxybutyl acrylate copolymer were in an aqueous solvent to which alcohol was added. It was confirmed that it exhibited excellent dispersion stability.

[Comparative Example 1]
As the organic protective agent, commercially available alkylated PVP (manufactured by ISP, Antaron V-904LC) was used. This is a copolymer of vinyl pyrrolidone and 10% by weight of an alkylated vinyl pyrrolidone.

<Creation of silver nanowires>
At room temperature, 20.8 g of propylene glycol (1,2-propanediol) is taken into a 50 mL vial, and the alkylated PVP is 0.56 g and the lithium chloride content is 0.5% by mass. 0.14 g of 1,2-propanediol solution, 0.150 g of 1,2-propanediol solution having a lithium hydroxide content of 1% by mass, 1,2% having an aluminum nitrate nonahydrate content of 2% by mass -0.14 g of propanediol solution was added and mixed to obtain Solution A. A solution B was prepared by dissolving 0.17 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire. FIG. 13 illustrates an SEM photograph of the silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 75 nm, the average length was 3.7 μm, and the average aspect ratio was 3700/75 nm≈49. Although this silver nanowire is coated with alkylated PVP, dispersibility in an aqueous solvent added with alcohol is improved, but a thin and long silver nanowire is synthesized using this type of organic protective agent. Is difficult.

[Comparative Example 2]
<Creation of copolymer of acrylamide and vinylpyrrolidone>
A copolymer was prepared under the same conditions as in Example 1 except that 0.113 g of acrylamide (molecular weight 71.1) was added instead of 0.113 g of ethyl acrylate in the preparation of the copolymer in Example 1. The obtained copolymer is a vinyl pyrrolidone-acrylamide copolymer having a structure in which 1.128 parts by mass of acrylamide and 100 parts by mass of vinyl pyrrolidone are polymerized. The vinyl pyrrolidone is 99% by mass.

<Creation of silver nanowires>
At room temperature, 26 g of propylene glycol (1,2-propanediol) is taken into a 50 mL vial, and 0.442 g of vinylpyrrolidone-acrylamide obtained above is contained therein, and the lithium chloride content is 1% by mass. 0.151 g of a 1,2-propanediol solution, 0.150 g of a 1,2-propanediol solution with a lithium hydroxide content of 1% by mass, 1,2- with a potassium bromide content of 0.25% by mass A solution A was prepared by adding 0.166 g of a propanediol solution and 0.104 g of a 1,2-propanediol solution having an aluminum nitrate nonahydrate content of 2% by mass. A solution B was prepared by dissolving 0.212 g of silver nitrate in 2 g of 1,2-propanediol.

  The total amount of the solution A was raised from room temperature to 115 ° C., and then stirred at 300 rpm for 20 minutes. After stirring time of 20 minutes, the solution B was added to the solution A at 115 ° C. over 1 minute with a tube pump, and the stirring state was maintained and maintained at 115 ° C. for 12 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained the reaction product. FIG. 14 illustrates an SEM photograph of the reaction product.

  The reaction product was only a granular material, and silver nanowires were not confirmed.

[Comparative Example 3]
Commercially available PVP (weight average molecular weight 55,000) was used as the organic protective agent.

<Creation of silver nanowires>
At room temperature, 500 g of propylene glycol (1,2-propanediol) is taken in a 1 L beaker, and 5.240 g of the above PVP and 1,2-propanediol solution 0 having a lithium chloride content of 10% by mass are contained therein. .300 g, 0.110 g of a 1,2-propanediol solution having a lithium hydroxide content of 10% by mass, 0.260 g of a 1,2-propanediol solution having a potassium bromide content of 2% by mass, aluminum nitrate nine 0.780 g of a 1,2-propanediol solution having a hydrate content of 8% by mass was added and mixed to obtain Solution A. A solution B was prepared by dissolving 4.250 g of silver nitrate in 20 g of 1,2-propanediol.

  The whole amount of the solution A was heated from room temperature to 90 ° C., and then stirred at 250 rpm for 20 minutes. After 20 minutes of stirring time, the solution B was added to the solution A at 90 ° C. over 1 minute with a tube pump, and the stirring state was maintained and kept at 90 ° C. for 24 hours. A reaction solution in which the precipitation reaction was completed was obtained. Then, it wash | cleaned by the method similar to Example 1, and obtained silver nanowire.

  The obtained silver nanowire was measured in the same manner as in Example 1. As a result, the average diameter of the silver nanowire was 55 nm, the average length was 9.8 μm, and the average aspect ratio was 9800/55 nm≈178.

  The silver nanowires after washing were dispersed in an IPA (isopropyl alcohol) 100% alcohol solvent, and the dispersion stability was examined in the same manner as in Example 1. The state of the liquid after 3 days has elapsed after the start of standing is shown in the photograph of FIG. In the PVP-coated silver nanowire of this example, precipitation occurs, and the dispersion stability in an alcohol solvent is greatly inferior to that of Example 1.

Claims (20)

  A silver nanowire having an average diameter of 100 nm or less and an average length of 5 μm or more coated with a polymer having a structural unit of an acrylate or methacrylate monomer.   A silver nanowire having an average diameter of 100 nm or less and an average length of 5 μm or more, coated with a copolymer of an acrylate or methacrylate monomer and a water-soluble monomer.   A silver nanowire having an average diameter of 100 nm or less and an average length of 5 μm or more coated with a copolymer of an acrylate or methacrylate monomer and vinylpyrrolidone.   The silver nanowire according to any one of claims 1 to 3, which has an average diameter of 50 nm or less and an average length of 10 µm or more.   The silver nanowire according to any one of claims 1 to 3, wherein the molecular weight of the acrylate or methacrylate monomer is 85 to 300.   The acrylate-based or methacrylate-based monomer is one or more of ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and 4-hydroxybutyl acrylate. Silver nanowire.   The silver nanowire according to claim 3, wherein the copolymer of the acrylate or methacrylate monomer and vinyl pyrrolidone has a polymerization composition of 0.1 to 25 parts by mass of the acrylate or methacrylate monomer and 100 parts by mass of vinyl pyrrolidone.   In the method for producing a silver nanowire in which silver is reduced and deposited in a wire form in an alcohol solvent in which a silver compound is dissolved, the polymer having a structural unit of an acrylate-based or methacrylate-based monomer is dissolved in the solvent. A method for producing silver nanowires that promotes precipitation.   The method for producing silver nanowires according to claim 8, wherein the precipitation proceeds in a state where the polymer, chloride, bromide, alkali metal hydroxide and aluminum salt are dissolved in the solvent.   In the method for producing a silver nanowire in which silver is reduced and precipitated in an alcohol solvent in which a silver compound is dissolved, a copolymer of an acrylate-based or methacrylate-based monomer and a water-soluble monomer is dissolved in the solvent. A method for producing silver nanowires, wherein the precipitation proceeds.   The method for producing silver nanowires according to claim 10, wherein the precipitation proceeds in a state where the copolymer, chloride, bromide, alkali metal hydroxide and aluminum salt are dissolved in the solvent.   In the method for producing a silver nanowire in which silver is reduced and deposited in a wire form in an alcohol solvent in which a silver compound is dissolved, the copolymer of an acrylate-based or methacrylate-based monomer and vinylpyrrolidone is dissolved in the solvent. A method for producing silver nanowires that promotes precipitation.   The method for producing silver nanowires according to claim 12, wherein the precipitation proceeds in a state where the copolymer, chloride, bromide, alkali metal hydroxide and aluminum salt are dissolved in the solvent.   The method for producing a silver nanowire according to any one of claims 8 to 13, wherein the molecular weight of the acrylate or methacrylate monomer is 85 to 300.   The acrylate-based or methacrylate-based monomer is one or more of ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and 4-hydroxybutyl acrylate. A method for producing silver nanowires.   The method for producing silver nanowires according to any one of claims 8 to 13, wherein the alcohol as a solvent is a polyol.   The method for producing silver nanowires according to any one of claims 8 to 13, wherein the reduction precipitation of silver proceeds in a temperature range of 60 ° C or higher and lower than the boiling point of a solvent alcohol to be used.   14. The copolymer of an acrylate or methacrylate monomer and vinyl pyrrolidone has a structure in which 0.1 to 25 parts by mass of an acrylate or methacrylate monomer and 100 parts by mass of vinyl pyrrolidone are polymerized. The manufacturing method of silver nanowire of description.   The silver nanowire dispersion liquid in which the silver nanowire of any one of Claims 1-3 is disperse | distributing in isopropyl alcohol.   The silver nanowire ink which contains the silver nanowire of any one of Claims 1-3 in 0.02-5.0 mass% in a liquid medium.