JP2019206738A - Silver nanowire ink, transparent conductive film producing method and transparent conductive film - Google Patents

Abstract

To provide a silver nanowire ink adapted to realize a silver nanowire conductive film having a high bonding strength to a resin based on acrylic resin.SOLUTION: A silver nanowire ink has, in an aqueous solvent, water-soluble cellulose ether having a methoxy group and a hydroxypropoxy group and a silver nanowire, in which the total of a mass ratio of the methoxy group and a mass ratio of the hydroxypropoxy group to the water-soluble cellulose ether is greater than 35.0 mass%. A transparent conductive film can be produced through a process of applying the silver nanowire onto the resin surface of a material whose surface is made up of a resin based on acrylic resin.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a silver nanowire ink useful as a material for forming a transparent conductive circuit. Moreover, it is related with the manufacturing method and transparent conductive film of the transparent conductive film.

  In the present specification, a fine metal wire having a thickness of about 200 nm or less is referred to as “nanowire (s). In particular, silver nanowires are promising as a conductive material for forming a transparent conductive circuit. A liquid in which silver nanowires are dispersed, and in particular, a liquid in which a thickening component is blended in consideration of application on a substrate is referred to as “silver nanowire ink.” Adding a thickening component or the like to a liquid that has a predetermined property is referred to as “inking.” A conductive film formed by applying silver nanowire ink is referred to as a “silver nanowire conductive film”.

  When manufacturing a transparent conductive circuit using silver nanowires, a silver nanowire conductive film is formed on a transparent substrate typified by PET (polyethylene terephthalate), PC (polycarbonate), etc., and further transparent protection is provided thereon. It is common to form a film. In Patent Document 1, a silver nanowire conductive film is formed on a PET film as a transparent substrate, and a transparent protective film is formed thereon by applying an alcohol solution in which an ultraviolet curable acrylate resin is dissolved. Examples are disclosed (paragraphs 0086-0088).

  When forming a silver nanowire conductive film using a PET film as a base material as in Patent Document 1, it is common to apply a silver nanowire ink on a PET film having an adhesive layer formed on the surface thereof. Is. This is because the silver nanowire conductive film is difficult to adhere directly to the PET surface due to its properties, and it is necessary to ensure the bonding force between the silver nanowire conductive film and the PET film via the adhesive layer. However, it has been found that the interposition of the adhesive layer becomes a factor that increases the haze of the silver nanowire conductive film formed on the substrate.

  Patent Documents 2 and 3 propose that a resin layer such as an acrylic resin or an epoxy resin is provided on a substrate such as a PET film, and a silver nanowire conductive layer is provided on the resin layer. In this case, since the resin layer is in contact with the PET, the bonding force between the PET film and the resin layer thereon is ensured. Therefore, it is not necessary to interpose an adhesive layer, and haze reduction due to the adhesive layer is avoided.

JP 2013-202911 A Japanese Patent Application Laid-Open No. 2006-066606 JP, 2006-104908, A

  As described above, when a resin layer such as an acrylic resin is provided on the upper surface of a substrate such as PET, “delamination” between the substrate and the resin layer immediately above the substrate can be sufficiently suppressed. However, according to the study by the inventors, the bonding force between the resin layer and the silver nanowire conductive film on the resin layer is not always satisfactory, and the “interlayer between the resin layer and the silver nanowire conductive film” It has been newly found that “peeling” can be a problem. Also, a transparent protective layer is often provided on the upper surface of the silver nanowire conductive film, but due to the weak bonding force between the underlying resin layer and the silver nanowire conductive film, the transparent protective layer is formed before the transparent protective layer is formed. There may be a problem that the silver nanowire conductive film is peeled off from the underlying resin layer. Patent Document 2 employs a technique in which a resin layer is further provided on the silver nanowire conductive film. However, depending on the manufacturing process, the silver nanowire conductive film is a base resin before the resin layer on the upper surface is formed. May peel from the layer.

  An object of this invention is to implement | achieve the silver nanowire electrically conductive film with high joining force with resin which has acrylic resin as a main component.

According to the study by the inventors, the above-mentioned problem can be achieved by applying a water-soluble cellulose ether to be blended as a constituent component of the silver nanowire ink, in which the abundance of a specific functional group is regulated within a specific range. I found out.
The present invention specifically discloses the following inventions.

[1] A water-soluble cellulose ether having a methoxy group and a hydroxypropoxy group in a water-based solvent, and silver nanowires, and the total of the mass ratio of the methoxy group and the hydroxypropoxy group in the water-soluble cellulose ether is Silver nanowire ink greater than 35.0% by weight.
[2] The silver nanowire ink according to the above [1], wherein the silver nanowire has a copolymer of vinylpyrrolidone and another monomer attached to the surface.
[3] The silver nanowire ink according to [1], wherein the silver nanowire has a copolymer of vinylpyrrolidone and a cationic monomer attached to the surface.
[4] The silver nanowire ink according to the above [1], wherein the silver nanowire has a copolymer of vinylpyrrolidone and a diallyldimethylammonium salt monomer attached to the surface.
[5] The silver nanowire ink according to any one of the above [1] to [4], wherein the content of the water-soluble cellulose ether is 0.02 to 5.0 parts by mass with respect to 1.0 part by mass of silver.
[6] A step of applying the silver nanowire ink according to any one of the above [1] to [5] on the resin surface of a material composed of a resin whose main component is an acrylic resin. A method for producing a transparent conductive film.
[7] The method for producing a transparent conductive film according to [6], wherein the silver nanowire ink is applied so that the wet thickness is 10 μm or more in the application.
[8] A transparent conductive film containing silver nanowires, the surface of which is made of a resin composed mainly of an acrylic resin and containing silver nanowires, JIS K5600-5-6: 1999 After forming a lattice pattern having 100 square squares with a side of 1 mm and a cut number of 11 in each direction with a single blade cutting tool by a cross-cut method based on (ISO 2409: 1992), it follows JIS Z1522: 2009 When the peel test is performed with a cellophane pressure-sensitive adhesive tape, the adhesiveness is such that the number of squares remaining in the portion of 50% or more of the square area (1 mm ² ) without peeling off the transparent conductive film is 40 or more out of 100. The transparent conductive film adhering to the resin surface.

  According to the present invention, in a transparent conductor in which a silver nanowire conductive film is formed directly on a resin whose main component is an acrylic resin, the bonding force between the resin and the silver nanowire conductive film can be stably improved. . Therefore, since a transparent conductive circuit excellent in adhesion can be stably and easily manufactured using a base material such as PET without an adhesive layer, the present invention is a construction of a transparent conductive film with less haze. Is extremely effective.

The typical laminated structure of the material which formed the transparent conductive film according to this invention. The graph which shows the relationship of the sum total of the mass ratio of the methoxy group which occupies for the water-soluble cellulose ether used for silver nanowire ink, and the mass ratio of a hydroxypropoxy group, and the number of remaining squares in an adhesive test.

[Silver nanowire ink]
The silver nanowire ink according to the present invention has a water-soluble cellulose ether having a methoxy group and a hydroxypropoxy group and a silver nanowire in an aqueous solvent. Hereinafter, the components will be described.

(Aqueous solvent)
“Aqueous solvent” refers to a solvent composed of water or a mixed solution of water and a water-soluble substance, wherein the proportion of water in the substance constituting the solvent is 30% by mass or more. The water-soluble cellulose ether described below used as a thickening component has high solubility in water, and in the case of a mixed solvent such as water and alcohol, it can be industrially implemented by setting the blending ratio of water to 30% by mass or more. Good solubility. Therefore, here, a solvent in which the mixing ratio of water is 30% by mass or more is referred to as an “aqueous solvent”. The mixing ratio of water in the aqueous solvent may be 50% by mass or more.

  Conventionally, PVP (polyvinyl pyrrolidone) has been frequently used as an organic protective agent used in the production of silver nanowires, and recently, examples using a copolymer of vinyl pyrrolidone and other monomers are also known. Since silver nanowires to which these organic protective agents are attached have good dispersibility in water, many use water as a solvent for the silver nanowire ink. In order to improve wettability with a transparent substrate such as PET, it is preferable to use a solvent in which alcohol is dissolved in water. Silver nanowires using PVP (polyvinyl pyrrolidone) as an organic protective agent have a low dispersibility in an aqueous liquid medium to which alcohol is added, and are likely to cause aggregation. Silver nanowires using a copolymer of vinyl pyrrolidone and another monomer as an organic protective agent have an advantage that it is easy to ensure dispersibility even in an aqueous liquid medium to which alcohol is added. In the present invention, a silver nanowire ink using such an aqueous solvent is an object.

  When the aqueous solvent is a mixed solvent of water and alcohol, the alcohol preferably has a polarity having a solubility parameter (SP value) of 10 or more. For example, low boiling point alcohols such as methanol, ethanol, 2-propanol (isopropyl alcohol) can be preferably used. The SP values are: water: 23.4, methanol: 14.5, ethanol: 12.7, and 2-propanol: 11.5. The SP value described here is a value defined by regular solution theory introduced by Hildebrand. When a mixed solvent of water and alcohol is applied, it is more preferable that the alcohol content in the ink is adjusted to a range of 1.0 to 35.0% by mass.

(Water-soluble cellulose ether)
In order to make the silver nanowire ink using an aqueous solvent suitable for application to a substrate, it is common to add a thickening component. In the present invention, a water-soluble cellulose ether having a methoxy group (—OCH ₃ ) and a hydroxypropoxy group (—OCH ₂ CHOHCH ₃ ) is used as the thickening component. The water-soluble cellulose ether is cellulose that has been given water-solubility by replacing the OH group of cellulose with a substituent. A water-soluble cellulose ether having a methoxy group and a hydroxypropoxy group as substituents is called HPMC (hydroxypropylmethylcellulose).

  As a result of detailed studies, the inventors have found that when a silver nanowire ink containing HPMC in which the total of the mass proportion of methoxy groups and hydroxypropoxy groups in the water-soluble cellulose ether is greater than 35.0 mass% is used, acrylic It has been found that the bonding force of the silver nanowire conductive film to the resin containing the resin as a main component can be remarkably improved. As HPMC which can be manufactured industrially, it is thought that the mass ratio of a methoxy group can be adjusted in the range of about 16-30 mass%, and the mass ratio of a hydroxypropoxy group can be adjusted in the range of about 4-32 mass%. However, it is not possible to improve the adhesion with a resin containing an acrylic resin as a main component only by increasing the ratio of only one of these substituents. It is important that the total amount of the methoxy group and the hydroxypropoxy group is greater than 35.0% by mass. The upper limit of the total mass ratio may be adjusted within a range of 62.0% by mass or less, which is considered to be industrially possible, for example. Preferably, you may manage to 40.0 mass% or less.

  The water-soluble cellulose ether having a large mass ratio of methoxy group and hydroxypropoxy group as described above has lower hydrophilicity (higher hydrophobicity) than other water-soluble cellulose ethers. By including such a low-hydrophilic (highly hydrophobic) water-soluble cellulose ether in the ink, the wettability of the ink with respect to a resin mainly composed of a highly hydrophobic acrylic resin is improved. The adhesion between the silver nanowire conductive layer and the resin layer is improved.

  The mass ratio of the methoxy group and hydroxypropoxy group in the water-soluble cellulose ether can be measured by a gas chromatography test based on the hydroxypropylmethylcellulose quantitative method described in the 17th revised Japanese pharmacopoeia.

  The content of the water-soluble cellulose ether in the ink is preferably adjusted so that the blending ratio of the water-soluble cellulose ether is 0.02 to 5.0 parts by mass with respect to 1.0 part by mass of silver. In the silver nanowire ink as the coating liquid, the mass ratio of the water-soluble cellulose ether in the ink can be adjusted, for example, in the range of 0.02 to 1.0 mass%.

(Silver nanowires)
The silver nanowire used in the silver nanowire ink of the present invention preferably has a shape as long as possible from the viewpoint of forming a transparent conductive film excellent in conductivity, and also has a transparent conductive circuit excellent in visibility (characteristic with low haze). From the viewpoint of forming a film, it is preferably as thin as possible. Specifically, the average length is preferably 10 μm or more and the average diameter is 50 nm or less. More preferably, the average length is 10 μm or more and the average diameter is 30 nm or less. The average aspect ratio is preferably 200 or more, and more preferably 450 or more. Here, the average length, average diameter, and average aspect ratio of the silver nanowires conform to the following definitions.

(Average length L _M )
The trace length from one end to the other end of one silver nanowire on the observation image by a field emission scanning electron microscope (FE-SEM) is defined as the length of the wire. The value obtained by averaging the lengths of the individual silver nanowires present on the microscope image, is defined as the average length L _M. In order to calculate the average length, the total number of wires to be measured is set to 100 or more.

(Average diameter D _M )
The distance between contours on both sides in the thickness direction of a single silver nanowire on a bright-field observation image obtained by a transmission electron microscope (TEM) is defined as the diameter of the wire. Each wire can be considered to have a substantially uniform thickness over its entire length. Therefore, the thickness can be measured by selecting a portion not overlapping with another wire. In a TEM image showing one field of view, the diameters of all of the silver nanowires observed in the image, except for the wires that completely overlap with other wires and whose diameter is difficult to measure, are measured. operation performed for a plurality of field chosen randomly determines the diameter of a total of 100 or more different silver nanowires, it calculates the average value of the individual silver nanowires diameter, defining its value and the average diameter D _M.

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

(Synthesis of silver nanowires)
The silver nanowire used in the silver nanowire ink of the present invention can be obtained by a technique (alcohol solvent reduction method) in which silver is precipitated in a wire form in an alcohol solvent in the presence of an organic protective agent. As the type of alcohol, 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 it is expected that many alcohols that can be applied will be confirmed by future research. For example, an alcohol solvent composed of one or more of ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,3 butanediol, 1,4-butanediol, and glycerin is used. The method disclosed in Japanese Patent Laid-Open No. 2015-180772 can be applied. As the organic protective agent, PVP, vinylpyrrolidone and other copolymers can be used. Silver nanowires distributed as industrial products or dispersions thereof may be obtained and used.

  When “copolymer of vinylpyrrolidone and another monomer” is used as the organic protective agent, the dispersibility of the silver nanowires in the aqueous solvent to which alcohol is added can be improved as compared with the case where PVP is used. As such a copolymer, one having a structural unit of a hydrophilic monomer can be applied. Here, the hydrophilic monomer is a monomer having a property of dissolving 1 g or more in 1000 g of water at 25 ° C. Specific examples include diallyldimethylammonium salt monomers, acrylate or methacrylate monomers, and maleimide monomers. For example, acrylate-based or methacrylate-based monomers include ethyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate. Examples of the maleimide monomer include 4-hydroxybutyl acrylate, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, and N-tert-butylmaleimide.

  In general, cationic polymers are likely to adsorb on silver. In the case of a copolymer of vinylpyrrolidone and a cationic monomer, the specific adsorption force on the (100) plane of silver can be controlled by adjusting the amount of the cationic monomer. Therefore, when a copolymer of vinylpyrrolidone and a cationic monomer is used as an organic protective agent during the synthesis of silver nanowires, it is advantageous for the synthesis of silver nanowires having a higher aspect ratio. Examples of the cationic monomer include diallyldimethylammonium salt monomer (a specific example of the salt includes nitrate).

  It is desirable that the silver nanowires used for ink-making have a length distribution optimized by a technique such as cross-flow filtration. In addition, when cross flow filtration is performed, a part of organic protective agent adhering to the silver nanowire surface may desorb | suck, and the dispersibility of the silver nanowire in a liquid may fall. In order to prevent excessive desorption, a polymer having a vinylpyrrolidone structural unit is added to an aqueous liquid medium circulated by crossflow filtration so that the polymer concentration in the liquid is within a predetermined range (for example, 5 to 2000 ppm). It is preferable to perform cross flow filtration while controlling. In the silver nanowire at the stage of forming an ink, the adhesion amount of the organic protective agent is preferably adjusted to 1.5 to 8.0% by mass with respect to the total amount of the organic protective agent and silver. When the adhesion amount of the organic protective agent is too small, the dispersibility in the ink is lowered and aggregates increase. On the other hand, when the amount of the organic protective agent attached is too large, the contact resistance between the wires increases.

[Transparent conductive film]
The conductive film according to the present invention is a silver nanowire conductive film formed on the resin surface of a material whose surface is composed of a resin mainly composed of an acrylic resin. FIG. 1 schematically illustrates a typical laminated structure of a material on which a transparent conductive film according to the present invention is formed. A resin layer 11 mainly composed of an acrylic resin is formed on the surface of a substrate 10 such as PET. Since the resin layer 11 has an excellent bonding force to the base material 10 such as PET, there is usually no need to worry about “delamination” between the base material 10 and the resin layer 11. On the upper surface of the resin layer 11, a silver nanowire conductive film 12 using the silver nanowire ink according to the present invention is formed. Since the silver nanowire conductive film 12 is formed using an ink in which HPMC adjusted to have a total mass ratio of methoxy group and hydroxypropoxy group adjusted to a value larger than 35.0 mass% is blended. The bonding strength with the resin layer 11 is improved. Therefore, the resistance to “delamination” between the resin layer 11 and the silver nanowire conductive film 12 is also strong, and a transparent conductive circuit with high adhesion to the substrate can be realized with a structure in which no adhesive layer is interposed. A known transparent protective film can be formed on the upper surface of the silver nanowire conductive film 12 as necessary. Moreover, between the base material 10 and the resin layer 11, if necessary, one or more additional layers can be interposed as long as sufficient bonding strength at the interface is ensured.

  The silver nanowire conductive film 12 contains water-soluble cellulose ether and silver nanowire, but may contain a binder component and other additive components as long as the effects of the present invention are not impaired. What is necessary is just to adjust the average thickness of a silver nanowire electrically conductive film in the range of 10-30 micrometers in wet thickness, for example. By setting the wet thickness to 10 μm or more, it is further advantageous for improving the adhesion of the transparent conductive film.

  The resin constituting the resin layer 11 is targeted for an acrylic resin as a main component. “Main component” means that the mass ratio of the acrylic resin in the resin is 50% by mass or more. This type of resin is extremely suitable for achieving both high transparency and high strength. As the acrylic resin, known resins such as an acrylic ester resin, a methacrylic ester resin, and a resin having a structure obtained by polymerizing a monomer that is a derivative of acrylic acid or methacrylic acid can be used. Known materials such as acrylic acid esters, acrylamide, acrylic acid, and styrene derivatives can be used. You may make this resin which has an acrylic resin the main component contain well-known additives, such as a photoinitiator. What is necessary is just to adjust the average thickness of the resin layer 11 in the range of 20-200 micrometers, for example.

  Examples of the substrate 10 include a resin film, a glass plate, and a ceramic plate. When a transparent substrate is applied, it is preferable that the total visible light transmittance is 70% or more. Examples of resins include polyesters, polyolefins, vinyl resins, polysulfones, polyethersulfones, polycarbonates, polyamides, acrylic resins, and the like. Among them, transparency, heat resistance, ease of handling, price From the viewpoint, polyethylene terephthalate is preferable. The thickness of this resin film is usually in the range of 5 to 300 μm. When the thickness of the resin film is too thin, the handleability is deteriorated, and when it is too thick, the visible light transmittance tends to be lowered. Therefore, it can be set within the above range according to the use of the transparent conductive circuit.

  The bonding strength between the resin layer 11 and the silver nanowire conductive film 12 can be evaluated by a cross-cut method based on JIS K5600-5-6: 1999 (ISO 2409: 1992). Here, after forming 100 lattice patterns having 100 square squares with a side of 1 mm and a cut number of 11 in each direction with a single blade cutting tool, a peel test is performed with a cellophane adhesive tape according to JIS Z1522: 2009. When performed, the number of cells remaining on the surface of the resin layer 11 without being peeled off by the silver nanowire conductive film 12 with an area ratio of 50% or more (hereinafter sometimes referred to as “the number of remaining cells”). To determine the bonding force. When the silver nanowire conductive film 12 adheres to the surface of the resin layer 11 with the adhesiveness that the remaining number of cells is 40 or more out of 100, the adhesive layer is not formed on the resin layer 11 without an adhesive layer. In the laminated structure in which the silver nanowire conductive film 12 is directly formed, it can be determined that the bonding force is remarkably improved as compared with the conventional structure. According to the examination by the inventors, it is possible to obtain a very excellent adhesion improving effect in which the number of remaining cells in this test is 70 or more out of 100.

[Method for producing transparent conductive film]
On the resin surface of the material whose surface is composed of a resin mainly composed of an acrylic resin (for example, a material in which a resin layer mainly composed of an acrylic resin is formed on a base material such as PET) It can be manufactured through the step of applying the silver nanowire ink. The silver nanowire can be applied by a known coating method such as a bar coater method or a die coater method. After coating, the coating film can be dried at a temperature of about 100 ° C. to obtain a predetermined transparent conductive film.

[Example 1]
(Manufacture of silver nanowires)
Propylene glycol (1,2-propanediol), silver nitrate, lithium chloride, potassium bromide, aluminum nitrate nonahydrate, lithium hydroxide, and a copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate were prepared. . Here, the copolymer of vinylpyrrolidone and diallyldimethylammonium nitrate was prepared using 99 parts by weight of vinylpyrrolidone and 1 part by weight of diallyldimethylammonium nitrate, and the weight average molecular weight was 75,000 g. / Mol.

  At room temperature, in propylene glycol 816.3 g, 4.84 g of propylene glycol solution having a lithium chloride content of 10 mass%, potassium bromide 0.1037 g, lithium hydroxide 0.426 g, aluminum nitrate nonahydrate A solution A was prepared by dissolving 4.994 g of a propylene glycol solution having an amount of 20% by mass and 83.875 g of the above-mentioned polymer A powder as an organic protective agent. In a separate container, 67.96 g of silver nitrate is added to a mixed solution of 95.70 g of propylene glycol and 8.00 g of pure water, and stirred at 35 ° C. to dissolve, and solution B containing silver is added. Obtained. The solution A was put in a reaction vessel and heated from room temperature to 90 ° C. with stirring at a rotation speed of 175 rpm, and then the entire amount of the solution B was added into the solution A from two addition ports over 1 minute. . After completion of the addition of the solution B, the stirring state was further maintained and maintained at 90 ° C. for 24 hours. Then, silver nanowire was synthesize | combined by cooling a reaction liquid to normal temperature.

(Washing)
A 20-fold amount of acetone was added to the reaction solution cooled to room temperature and stirred for 15 minutes. Thereafter, it was allowed to stand for 24 hours. Since the concentrate and the supernatant were observed after standing, the supernatant was removed and the concentrate was recovered. 1280 g of pure water was added to the concentrate, and after stirring for 12 hours, acetone was added in an amount 20 times the total mass of the concentrate and 1280 g of pure water, and allowed to stand for 24 hours after stirring for 10 minutes. Since the concentrate and the supernatant were observed after standing, the supernatant was removed and the concentrate was recovered. The pure water dispersion, acetone addition, standing, and supernatant removal operations were carried out twice to obtain a concentrate. This concentrate is called “concentrate after washing”.

(Preprocessing)
Re-dispersion using a water solvent in which a copolymer of vinylpyrrolidone having a weight average molecular weight of 75,000 and diallyldimethylammonium nitrate is dissolved in pure water as a pretreatment for performing cross-flow circulation washing Treated. That is, an aqueous solvent having a copolymer concentration of 0.5% by mass is prepared, and the aqueous solvent and the concentrate after washing are mixed to obtain a metallic silver concentration (silver concentration in liquid containing silver nanowires and impurity silver nanoparticles). ) Prepared a silver nanowire dispersion liquid of 0.8 mass%.

  The obtained silver nanowire dispersion was diluted with pure water so that the silver concentration would be 0.08% by mass to obtain about 52 kg of silver nanowire dispersion. This dispersion is referred to as a “cross flow original solution”.

(Cross flow circulation cleaning)
The crossflow original solution subjected to the above pretreatment was accommodated in a tank, and subjected to crossflow filtration by a method of continuously circulating the path connecting the tank, the pump, and the crossflow filtration filter with a pipe. As the cross-flow filtration filter, a filter in which nine tubular filters having a length of 500 mm, an outer diameter of 12 mm, and an inner diameter of 9 mm, in which a tube wall is formed of porous ceramics, was arranged in parallel was used. The material of the ceramic was SiC (silicon carbide), and the average pore diameter by a mercury intrusion method using a mercury porosimeter manufactured by Micromeritics was 5.9 μm.
Detailed conditions of the pore distribution measurement by the mercury intrusion method are as follows.
・ Measuring device: Autopore IV9510 type ・ Measuring range: φ440 to 0.003 μm,
-Mercury contact angle: 130 °
Mercury surface tension: 485 dyne / cm,
・ Pretreatment: 300 ℃ × 1h (in air)
・ Measurement sample mass: 3.5 g
In order to ensure sufficient measurement accuracy, 80 points of measurement data were collected in the measurement range of 1 to 100 μm. The average pore diameter here is the median diameter.

  Circulation was performed while supplying a new liquid medium to the tank. The flow rate of the liquid introduced per one of the nine tubular filters arranged in parallel was circulated at 13 L / min. The flow rate of the liquid introduced into the tubular filter was 3490 mm / s. The pressure in the pipe line on the inlet side of the tubular filter was 0.025 MPa. The liquid medium to be replenished was an aqueous solvent to which a copolymer of vinylpyrrolidone having a weight average molecular weight of 75,000 and diallyldimethylammonium nitrate was added. The copolymer concentration (mass ratio) in the aqueous solvent was 50 ppm. The tank is a tank with a jacket, and by flowing cooling water through the jacket, an increase in the liquid temperature during circulation was suppressed. The pure water to be replenished was cooled and cooled pure water having a temperature of 10 to 15 ° C. was used. As a result, the liquid temperature during circulation was in the range of 20 to 30 ° C. Thus, the cross flow circulation washing | cleaning for 5 hours was performed.

(Cross flow concentration)
Following the cross-flow circulation cleaning for 5 hours, circulation by cross-flow filtration is performed with the liquid medium stopped, and the concentration of the silver nanowire dispersion is reduced by utilizing the fact that the liquid volume decreases as the filtrate is discharged. Went. Circulation for about 5 hours was performed to obtain a silver nanowire dispersion liquid in which 0.4% by mass of silver nanowires in terms of metallic silver concentration was dispersed in an aqueous solvent.

(Measurement of organic protective agent adhesion)
From the concentrated silver nanowire dispersion liquid, an amount of liquid containing silver nanowires corresponding to 20 mg of silver was collected, and a high-speed centrifugal cooling centrifuge CR21N (rotor: R8S, centrifuge tube: 50 mL) manufactured by Hitachi Koki Co., Ltd. ) Was centrifuged at 8000 rpm for 45 minutes, and the supernatant was removed and dried at 120 ° C. for 12 hours to obtain a dried silver nanowire. TG-DTA measurement in an air atmosphere was performed on 15 mg of this dried product sample using STA7200 manufactured by Hitachi High-Tech Science Co., Ltd. The temperature was raised at a rate of 10 ° C./min, and the change in weight from 40 ° C. to 700 ° C. was measured. For the measurement, a platinum sample pan (φ5.2 mm, height 5 mm) was used. In the TG-DTA curve, the amount of weight loss at 150 ° C. is regarded as the amount Ws (mass%) of the liquid medium component (specifically water or alcohol having 1 to 4 carbon atoms) remaining in the dry sample, The weight change from 150 ° C. to 600 ° C. was defined as the amount of organic protective agent Wp (mass%) adhering to the silver nanowires. The mass ratio P (mass%) of the organic protective agent with respect to the total amount of the organic protective agent and silver was determined by the following formula (3).
P = 100 × [Wp / (100−Ws)] (3)
here,
P: Mass ratio of organic protective agent to the total amount of organic protective agent and silver (% by mass)
Wp: amount of organic protective agent adhering to the wire (% by mass)
Ws: Amount of liquid medium component remaining in dry sample (% by mass)
As a result, the organic protective agent adhesion amount P of the silver nanowire obtained in this example was 6.2% by mass with respect to the total amount of the organic protective agent and silver.

(Measurement of average length and average diameter of silver nanowires)
The concentrate after the above washing is dispersed in pure water, the dispersion is placed on an observation table for SEM, water is volatilized on the observation table, and then a field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation). S-4700), and observed at an acceleration voltage of 3 kV and a magnification of 1,500 times. For three or more fields selected at random, the average length was measured according to the above definition using software (Doctor Canvas) for all the wires whose total length could be confirmed in the field. In the diameter measurement, the above dispersion is placed on a TEM observation stand, and a bright-field image is observed at an accelerating voltage of 100 kV and a magnification of 40,000 times with a transmission electron microscope (manufactured by JEOL Ltd .; JEM-1011). In order to accurately measure the diameter of the observed image, the original image collected was enlarged to twice the size, and the average diameter was calculated according to the above definition using the software (Motic Image Plus 2.1S). It was measured. The average aspect ratio was determined by substituting the values of the average length and average diameter into the equation (1). As a result, the average length of the silver nanowires was 18.2 μm, the average diameter was 26.9 nm, and the average aspect ratio was 18200 / 26.9≈677.

(Ink)
As water-soluble cellulose ether, HPMC (hydroxypropylmethylcellulose; manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to a water content of 0.5 mass%, a methoxy group of 28.8 mass%, and a hydroxypropoxy group of 6.3 mass% was prepared. The mass ratio of the methoxy group and the mass ratio of the hydroxypropoxy group in the water-soluble cellulose ether and the total value thereof are shown in Table 1 (the same applies in the following examples). In this example, the total value of the mass ratio of the methoxy group and the hydroxypropoxy group in the water-soluble cellulose ether is 35.1%. The HPMC powder was put into hot water that had been vigorously stirred with a stirrer, and then naturally cooled to 40 ° C. while continuing strong stirring, and then cooled to 10 ° C. or lower using a chiller. The solution after stirring was filtered through a metal mesh having an opening of 100 μm to remove gel-like insoluble components, thereby obtaining an aqueous solution in which HPMC was dissolved.

  In a container with a lid, put the silver nanowire dispersion liquid obtained by the crossflow filtration (the medium is water), the aqueous HPMC solution, and 2-propanol (isopropyl alcohol), and close the lid. The container was stirred and mixed by a method of shaking up and down 100 times to obtain a silver nanowire ink. The content (ink composition) of each substance in the ink is 10.0% by mass of 2-propanol, 0.09% by mass of silver, 0.135% by mass of a thickener (HPMC), and the balance is water. . An organic protective agent is attached to the surface of the silver nanowires, but the content of the organic protective agent in the ink is very small compared to the above components, so that the ink composition can be ignored.

(Formation of resin layer)
A PET film substrate (Toyobo Co., Ltd., Cosmo Shine (registered trademark) A4100) having a thickness of 100 μm and dimensions of 150 mm × 200 mm was prepared. As a coating material for forming the resin layer, a material having a content ratio of 46% by mass of acrylic acid ester, 46% by mass of PGME (propylene glycol monomethyl ether), and 8% by mass of a photopolymerization initiator is diluted with methyl isobutyl ketone to obtain a resin. The coating liquid prepared so that the solid content concentration of the mixture was 0.8% by mass was obtained. This coating solution was applied to one side of the PET film substrate by a die coater coating machine (manufactured by Daimon Co., Ltd., New Table Die S-100) to form a coating film having an area of 100 mm × 100 mm. The coating conditions were wet thickness: 13 μm, gap: 80 μm, speed: 50 mm / s, timer: 1.5 s, coating length: 100 mm. After the application, it was dried at 80 ° C. for 1 minute to obtain a transparent resin layer.

(UV curing treatment of resin layer)
The PET film on which the resin layer was formed was subjected to N ₂ substitution with an inert box (ETC-QN-G) manufactured by Heraeus under conditions of 10 kPa and 2 min, and then applied to a UV irradiation device (LC6B) manufactured by Heraeus. The UV curing treatment was performed under the conditions of a conveyor speed of 4.8 m / min, an irradiation intensity of 500 mW / cm ² , and an integrated intensity of 400 mJ / cm ² .

(Formation of transparent conductive film)
On the resin layer after the UV curing treatment, a coating film having an area of 100 mm × 50 mm was formed from the above silver nanowire ink using a bar coater having a winding diameter of 10 mil (about 254 μm). After application, the film was dried at 120 ° C. for 1 minute to obtain a transparent conductive film (silver nanowire conductive film).

(Adhesion test by cross-cut method)
In order to evaluate the bonding strength with respect to the resin layer of the transparent conductive film on the PET substrate obtained by the above procedure, adhesion by a cross-cut method based on JIS K5600-5-6: 1999 (ISO 2409: 1992). The test was conducted as follows.
Cut lines with an interval of 1 mm were formed with a cutter blade on the surface of the transparent conductive film formed on the PET substrate. However, the number of cut lines was eleven. Next, 11 cut lines were further formed so as to be orthogonal to the 11 cut lines. When forming a score line, a cross-cut guide manufactured by Cortec Co., Ltd. was used. In this way, a lattice pattern having 100 square squares with a side of 1 mm was formed. Prepare cellophane adhesive tape according to JIS Z1522: 2009, and apply the cellophane adhesive tape to cover the lattice pattern consisting of 100 squares according to JIS K5600-5-6: 1999, and then peel off. The surface of the sample after the adhesive tape was peeled off was observed with a 3D microscope, and the number of cells in which the transparent conductive film remained on the surface of the resin layer with an area ratio of 50% or more (hereinafter referred to as “number of remaining cells”) And the number of remaining squares in 100 squares was determined. In this test, if the number of remaining squares is 40 or more out of 100, it can be evaluated that the silver nanowire conductive layer has excellent adhesion. The results are shown in Table 1 (same in the following examples). In this example, the remaining number of cells was 81 out of 100. In addition, Nichiban Co., Ltd. CT405AP-24 (width 24mm) was used as said cellophane adhesive tape.

[Example 2]
Except for using HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to a water content of 1.0% by mass, a methoxy group of 22.8% by mass, and a hydroxypropoxy group of 12.8% by mass as a water-soluble cellulose ether. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 35.6%. The number of remaining cells was 77 out of 100.

Example 3
Except for using HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to water content 0.8% by mass, methoxy group 28.9% by mass, and hydroxypropoxy group 8.8% by mass as water-soluble cellulose ether. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 37.7%. The remaining number of cells was 99 out of 100.

Example 4
Except that HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to a water content of 0.6% by mass, a methoxy group of 21.5% by mass and a hydroxypropoxy group of 30.0% by mass was used as the water-soluble cellulose ether. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 51.5%. The number of remaining cells was 84 out of 100.

[Comparative Example 1]
Except that HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to water content of 0.6% by mass, methoxy group of 28.8% by mass, and hydroxypropoxy group of 4.4% by mass was used as the water-soluble cellulose ether in ink production. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 33.2%. The number of remaining cells was 23 out of 100.

[Comparative Example 2]
Except that HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to a water content of 0.3% by mass, a methoxy group of 23.2% by mass and a hydroxypropoxy group of 7.8% by mass was used as the water-soluble cellulose ether. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 31.1%. The number of remaining cells was 20 out of 100.

[Comparative Example 3]
In ink preparation, MC (methylcellulose; manufactured by Shin-Etsu Chemical Co., Ltd.) having a water content of 0.9% by mass and a methoxy group of 29.5% by mass and containing no hydroxypropoxy group was used as the water-soluble cellulose ether. Except for, an experiment was conducted in the same manner as in Example 1, and an adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 29.5%. The number of remaining cells was 1 in 100.

[Comparative Example 4]
Except that HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to water content 3.3% by mass, methoxy group 19.6% by mass, and hydroxypropoxy group 8.4% by mass was used as the water-soluble cellulose ether in ink production. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 28.0%. The number of remaining cells was 2 out of 100.

[Comparative Example 5]
Except for using HPMC (manufactured by Shin-Etsu Chemical Co., Ltd.) adjusted to a water content of 4.2 mass%, a methoxy group of 19.9 mass%, and a hydroxypropoxy group of 4.5 mass% as a water-soluble cellulose ether. The experiment was conducted in the same manner as in Example 1, and the adhesion test was conducted. The total value of the mass proportion of the methoxy group and the mass proportion of the hydroxypropoxy group is 24.4%. The number of remaining cells was 7 out of 100.

  FIG. 2 shows the relationship between the total mass ratio of methoxy groups and hydroxypropoxy groups in the water-soluble cellulose ether used in the silver nanowire ink, and the number of residual cells in the adhesion test.

  When the total of the mass proportion of methoxy groups and hydroxypropoxy groups in the water-soluble cellulose ether is greater than 35.0%, a transparent conductive film (silver nanowire conductive film) for a resin mainly composed of an acrylic resin It can be seen that the adhesion of the film) can be dramatically improved.

10 Substrate 11 Resin layer 12 Silver nanowire conductive film

Claims (8)

  The aqueous solvent has a water-soluble cellulose ether having a methoxy group and a hydroxypropoxy group, and silver nanowires, and the total of the mass ratio of the methoxy group and the hydroxypropoxy group in the water-soluble cellulose ether is 35.0. Silver nanowire ink larger than mass%.   The silver nanowire ink according to claim 1, wherein the silver nanowire has a copolymer of vinylpyrrolidone and another monomer attached to the surface.   The silver nanowire ink according to claim 1, wherein the silver nanowire has a copolymer of vinylpyrrolidone and a cationic monomer attached to the surface.   The silver nanowire ink according to claim 1, wherein the silver nanowire has a copolymer of vinylpyrrolidone and diallyldimethylammonium salt monomer attached to the surface.   The silver nanowire ink according to any one of claims 1 to 4, wherein the content of the water-soluble cellulose ether is 0.02 to 5.0 parts by mass with respect to 1.0 part by mass of silver.   A transparent conductive film comprising a step of applying the silver nanowire ink according to any one of claims 1 to 5 on the resin surface of a material composed of a resin whose main component is an acrylic resin. Production method.   The manufacturing method of the transparent conductive film of Claim 6 which apply | coats silver nanowire ink so that the wet thickness may be 10 micrometers or more in the said application | coating. A transparent conductive film containing silver nanowires, the surface of which is formed on a resin surface composed of a resin whose main component is an acrylic resin, and is JIS K5600-5-6: 1999 (ISO 2409) : A cellophane adhesive tape according to JIS Z1522: 2009 after forming a lattice pattern having 100 square grids with a side of 1 mm and a cut number of 11 in each direction with a single blade cutting tool by a cross-cut method based on 1992) When the peel test is performed, the adhesiveness in which the transparent conductive film does not peel off in a portion of 50% or more of the area (1 mm ² ) of the square is 40 or more of 100 squares, A transparent conductive film adhering to the resin surface.

Images