WO2019082997A1

WO2019082997A1 - Water-soluble cellulose ether solution, viscosity modifier and method for producing silver nanowire ink

Info

Publication number: WO2019082997A1
Application number: PCT/JP2018/039787
Authority: WO
Inventors: 宏敏齋藤; 王高佐藤
Original assignee: Ｄｏｗａエレクトロニクス株式会社
Priority date: 2017-10-27
Filing date: 2018-10-25
Publication date: 2019-05-02
Also published as: CN110997786A; JP2019081889A; TW201922892A

Abstract

[Problem] To provide a water-soluble cellulose ether solution that is unlikely to form coarse electrically conductive filler aggregates when an electrically conductive coating material is prepared or coated. [Solution] A water-soluble cellulose ether solution which contains a water-soluble cellulose ether at a content of 0.05 mass% or more in an aqueous medium, and in which the number of particles having diameters of 10 µm or more, as measured using a light-shielding type in-liquid-particle counter, is 20 particles/mL or less. Examples of the water-soluble cellulose ether include HEMC (hydroxyethylmethyl cellulose) and HPMC (hydroxypropylmethyl cellulose).

Description

Water-soluble cellulose ether solution and viscosity modifier and method for producing silver nanowire ink

The present invention relates to a water-soluble cellulose ether solution having a small content of coarse gel particles, which is useful as a viscosity modifier of a conductive paint, and a viscosity modifier using the same. The present invention also relates to a method of producing a silver nanowires ink using the viscosity modifier.

In the present specification, a fine metal wire having a thickness of about 200 nm or less is referred to as “nanowire (s).” A coating for forming a conductive coating film, which contains a conductive filler such as metal nanowires or metal fine particles. The processing solution is called “conductive paint.” A conductive paint containing silver nanowires as a conductive filler, or a silver nanowire dispersion in which the dispersibility and silver concentration of silver nanowires are adjusted to produce the conductive paint, The operation of obtaining a silver nanowire ink having a predetermined property by adding a binder component, a viscosity modifier, and the like to a solution in which silver nanowires are dispersed is referred to as “inking”.

Silver nanowires are considered promising as a conductive filler to form a transparent conductive film. After the liquid containing silver nanowires (silver nanowire ink) is coated on a transparent substrate such as glass, PET (polyethylene terephthalate), PC (polycarbonate), etc., the liquid component is removed by evaporation or the like, and the silver nanowires become the substrate A transparent conductive film can be realized because the conductive network is formed by contacting each other on top. In recent years, studies on technology for producing thin and long silver nanowires are in progress, and the conductivity and optical properties of transparent conductive films using silver nanowires are being improved.

Usually, a viscosity modifier (thickener) suitable for the application is added to the paint. In the case of a paint using an aqueous solvent, water-soluble cellulose ether can be mentioned as one of the representative substances for viscosity adjustment. For example, silver nanowire inks using HPMC (hydroxypropyl methyl cellulose), which is a kind of water-soluble cellulose ether, as a thickener are known (Patent Documents 1 to 3).

JP, 2015-174922, A JP, 2015-180772, A Japanese Patent Application Publication No. 2009-505358

The conductive paint contains a conductive filler such as metal particles or metal nanowires. The conductive filler is ideally uniformly distributed in the paint. However, in practice, when preparing a conductive paint by mixing a thickener or a binder component with the dispersion of the conductive filler (when making the ink), or when applying the produced conductive paint, part of the conductive filler An event occurs in which the particles aggregate to form an aggregate (hereinafter referred to as "conductive filler aggregate"). Among such conductive filler assemblies, coarse ones cause a short circuit in the circuit of the transparent conductive coating film, and cause deterioration of the appearance as white spot-like foreign matter. In particular, when the filler is a nanowire, it is easy to form a bundle-like aggregate, and the above-mentioned problems due to coarse foreign substances are likely to be manifested. In order to avoid such a foreign matter problem, it is desirable to construct a conductive paint (ink) in which a coarse conductive filler aggregate is not easily formed.

According to the inventors' investigations, it is clear that the "properties" of the thickening substance added at the time of ink formation are largely involved as a factor for the formation of coarse conductive filler aggregates in the conductive paint. became. The present invention provides a solution using a water-soluble cellulose ether which is useful as a viscosity regulator such as a conductive paint, which is unlikely to cause formation of a coarse conductive filler aggregate at the time of preparation or coating of the conductive paint. With the goal.

In order to achieve the above object, the following invention is disclosed herein.
[1] A water-soluble solvent contains water-soluble cellulose ether at a content of 0.05% by mass or more, and the amount of particles with a particle diameter of 10 μm or more measured by a liquid shielding particle counter is 20 / Water-soluble cellulose ether solution which is less than mL.
[2] The water-soluble cellulose ether solution according to the above [1], wherein the content of the water-soluble cellulose ether is 0.05 to 10.0% by mass.
[3] The water-soluble cellulose ether solution according to the above [1], wherein the content of the water-soluble cellulose ether is 0.05 to 5.0% by mass.
[4] The water-soluble cellulose ether solution according to the above [1], wherein the content of the water-soluble cellulose ether is 0.1 to 2.0% by mass.
[5] The water-soluble cellulose ether solution according to any one of the above [1] to [4], which contains one or more selected from HEMC (hydroxyethyl methylcellulose) and HPMC (hydroxypropyl methyl cellulose) as the water-soluble cellulose ether. .
[6] A viscosity modifier for a conductive paint, using the water-soluble cellulose ether solution according to any one of the above [1] to [5].
[7] A viscosity modifier for a silver nanowires ink using the water-soluble cellulose ether solution according to any one of the above [1] to [5].
[8] A method for producing a silver nanowires ink, comprising a step of mixing a viscosity modifier with a silver nanowire dispersion using an aqueous solvent, wherein the viscosity modifier as described in any one of the above [1] to [5] A method for producing a silver nanowires ink, wherein a water-soluble cellulose ether solution is used to adjust the water-soluble cellulose ether content in the ink in the range of 0.01 to 1.0 mass.

The aqueous solvent solution of the water-soluble cellulose ether according to the present invention has a very small amount of coarse gel-like particles. When this water-soluble cellulose ether solution is used for preparation of a conductive paint, it is possible to remarkably suppress the formation of a coarse "conductive filler aggregate" starting from the gel-like particles while exhibiting an appropriate thickening action. it can. Therefore, the water-soluble cellulose ether solution according to the present invention is extremely useful for construction of a transparent conductive circuit free from shorts between adjacent wires and excellent in surface appearance.

The SEM photograph of the electrically conductive coating film which image | photographed the part in which the coarse wire aggregate was observed.

[Water-soluble cellulose ether]
The water-soluble cellulose ether is one that is rendered water-soluble by substituting many of the hydrogen atoms of OH groups possessed by cellulose with a substituent. For example, substitution of a hydrogen atom of an OH group with a methyl group (-CH ₃ ) forms a methoxy group (-OCH ₃ ), and substitution with a hydroxypropyl group (-CH ₂ CHOHCH ₃ ) results in a hydroxypropoxy group (-OCH ₂ CHOHCH ₃ ) is formed and substituted with a hydroxyethyl group (-CH ₂ CH ₂ OH) to form a hydroxyethoxy group (-OCH ₂ CH ₂ OH). In the part having these substituents, the hydrogen bond between the cellulose molecules is eliminated, thereby allowing water molecules to enter between the cellulose molecules and exhibiting water solubility. As the substituent, those obtained by introducing a methoxy group (-OCH ₃₎ and hydroxypropoxy groups _(-OCH 2 CHOHCH ₃₎ is HPMC (hydroxypropyl methylcellulose), a methoxy group and a hydroxyethoxy group _(-OCH 2 _CH 2 OH It is HEMC (hydroxyethyl methyl cellulose) which introduce | transduced. In addition, MC (methylcellulose) is one in which only a methoxy group (-OCH ₃ ) is introduced, and HEC (hydroxyethylcellulose) is one in which only a hydroxyethoxy group (-OCH ₂ CH ₂ OH) is introduced. HPMC, HEMC, MC, HEC, etc. are usually supplied to the market as industrial materials in the form of dried powder. When applied to silver nanowire ink applications, it is more preferable to use, for example, HPMC or HEMC having a weight average molecular weight of 200,000 to 1,500,000. Those having a weight average molecular weight of 300,000 to 1,400,000 are more preferable.

The water-soluble cellulose ether tends to form gel-like particles when the powder product is dissolved in an aqueous solvent. Only some of the particles constituting the powder are wetted with the aqueous solvent in the surface layer portion, and remain in the form of gel particles while leaving undissolved portions in the particles. In the case of a water-soluble cellulose ether which does not dissolve in high temperature water such as HPMC, fine particles of hot water mixed with powder (for example, water of 85 to 100 ° C., preferably 90 to 99 ° C.) After a slurry in which the powder particles are dispersed is prepared, the slurry can be uniformly dissolved by a method of cooling the slurry. As a method of strong stirring, for example, in the case of using a reaction vessel with a capacity of 10 to 100 L provided with a baffle, it is possible to apply a method of stirring at 400 rpm or more with turbine blades. However, even in this case, it is difficult to completely prevent the formation of gel-like particles. In the case of a water-soluble cellulose ether that has the property of being soluble in hot water, such as HEMC, the above-mentioned method of producing a uniform slurry in hot water can not be applied. Measures are required.

The water-soluble cellulose ether solution according to the present invention with very few coarse gel particles utilizes the technique of dissolving the powder in the aqueous solvent as uniformly as possible and filtering through a filter, as exemplified in the following examples. Can be obtained.

[Water based solvent]
As used herein, the term "aqueous solvent" refers to a solvent comprising water or a mixed solution of water and a water-soluble substance, wherein the proportion of water is at least 30% by mass. Water-soluble cellulose ether represented by HPMC and HEMC dissolves well in water, and in the case of a mixed solvent of water and alcohol, it can usually be industrially implemented if the mixing ratio of water is in the range of 30% by mass or more It exhibits solubility. Therefore, a solvent in which the mixing ratio of water is 30 to 100% by mass here is applied as the "aqueous solvent". You may manage so that the mixing | blending ratio of water may apply 50 mass% or more, or the aqueous solvent which is 75 mass% or more.

A water-soluble cellulose ether solution using an aqueous solvent can be used as a viscosity modifier for producing a conductive paint (ink) using an aqueous solvent. In the case of applying an aqueous solvent comprising a mixed solution of water and a water-soluble substance other than water in the conductive paint, the solvent of the water-soluble cellulose ether solution to be added at the time of ink formation also has the same water solubility as the above. It is preferable to use a mixed solution using a substance. For example, the wettability to a substrate such as PET can be improved by making the solvent of the conductive paint "a mixed solvent of water and alcohol". In this case, the “mixed solvent of water and alcohol” using the same alcohol as the conductive paint may be applied to the solvent of the water-soluble cellulose ether solution used for the preparation of the conductive paint. When “a mixed solvent of water and alcohol” is used, as the alcohol, one having a polarity of solubility parameter (SP value) of 10 or more is preferable. For example, low boiling point alcohols such as methanol, ethanol and 2-propanol (isopropyl alcohol) can be suitably used. In addition, it is supposed that SP value is water: 23.4, methanol: 14.5, ethanol: 12.7, and 2-propanol is 11.5. When a mixed solvent of water and alcohol is applied, it is preferable to use an ink whose alcohol content in the ink is adjusted in the range of 1.0 to 25.0% by mass. The SP values described here are the values defined by the regular solution theory introduced by Hildebrand.

[Water-soluble cellulose ether content]
The present invention is directed to a water-soluble cellulose ether solution having a water-soluble cellulose ether content of 0.05% by mass or more in an aqueous solvent. When the content of the water-soluble cellulose ether is too low, it is difficult to obtain a sufficient viscosity control effect at the time of ink formation. It is more preferable to set it as 0.1 mass% or more, and it is more preferable to set it as 0.5 mass% or more. When the water-soluble cellulose ether content is excessive, the amount of gel-like particles tends to be large. For example, in a solution having a water-soluble cellulose ether content of 10.0% by mass or less, the number of gel-like particles having a particle diameter of 10 μm or more can be easily suppressed as described later. The water-soluble cellulose ether content is more preferably 5.0% by mass or less, and still more preferably 2.5% by mass or less. You may manage to 2.0 mass% or less or 1.5 mass% or less. The water-soluble cellulose ether content is the total of the water-soluble cellulose ether dissolved in the solvent and the water-soluble cellulose ether present as gel-like particles. It can be grasped by measuring the amount of water-soluble cellulose ether.

[Amount of coarse particles in solution]
According to the study of the inventors, among the gel-like particles present in the conductive paint, those having a large particle diameter of 10 μm or more tend to be the origin of formation of the conductive filler aggregate, and particularly in the metal nanowire ink, the particle diameter is 10 μm or more It has been found that the reduction of the number of gel-like particles is extremely effective in preventing a short circuit when forming a transparent conductive circuit and preventing visible white spots. As a result of detailed investigation, in the water-soluble cellulose ether solution for use in viscosity control of the conductive paint, the amount of particles having a particle diameter of 10 μm or more measured by a liquid shielding particle counter is 20 particles / mL or less Is desirable, and 10 or less is more desirable. According to the light shielding type liquid particle counter, it is possible to detect the presence of translucent gel-like particles, and to obtain the particle size distribution thereof.

[Preparation of water-soluble cellulose ether solution]
As described above, the water-soluble cellulose ether solution according to the present invention can be prepared using a technique of dissolving the powder in the aqueous solvent as uniformly as possible and then filtering it with a filter. Usually, it is very difficult to industrially efficiently remove such gel-like particles by passing a highly viscous solution used as a thickener through a filter. Such gel-like particles tend to slip through the filter by deformation. It is possible to obtain high capturing power by applying a filter with a small opening. However, in this case, once some particles are trapped, clogging occurs and premature filtration becomes impossible. On the other hand, filters (for example, SCP type shown in the below-mentioned example etc.) which considered the trappability of gel-like particles are also marketed. However, by simply using such a filter, a water-soluble cellulose ether solution (viscosity modifier) suitable for preparing a conductive paint (ink) excellent in the generation inhibiting performance of the conductive filler aggregate can be stably obtained. I can not get it. As a factor, the particle size distribution of gel-like particles in the solution after filtration may be variously changed depending on conditions such as pressure, viscosity of the solution to be subjected to filtration, and amount of gel-like particles present in the solution to be filtered. It can be mentioned.

As described above, the inventors reduced the number of gel-like particles having a particle diameter of 10 μm or more in order to suppress the formation of a coarse “conductive filler assembly” that adversely affects formation of a transparent conductive circuit. Was found to be extremely effective. Heretofore, in a situation where such a knowledge has not been obtained, it has not been found that the number of gel particles having a particle diameter of 10 μm or more is controlled in a water-soluble cellulose ether solution (viscosity modifier). Therefore, an aqueous solvent solution of a water-soluble cellulose ether adjusted to the present form of gel-like particles as specified in the present invention has not been realized until now.

As a result of conducting detailed investigations, the inventors satisfy all the following conditions (i) to (iii) as a water-soluble cellulose ether solution (hereinafter sometimes referred to as "solution before filtration") to be subjected to filtration. By preparing a water-soluble cellulose ether solution in advance, the amount of particles having a particle diameter of 10 μm or more measured by a light shielding type liquid particle counter is 20 using a filter selected from among commercially available products. It has been found that it is possible to industrially relatively efficiently produce the above-mentioned predetermined water-soluble cellulose ether solution which is less than 10 / mL.
(Solution before filtration)
(I) The solvent is water or a solvent comprising a mixed solution of water and a water-soluble substance, and the blending ratio of water is 30% by mass or more.
(Ii) The content of the water-soluble cellulose ether (including the water-soluble cellulose ether present as gel-like particles) in the solvent is more than 0.05% by mass.
(Iii) The amount of particles having a particle diameter of 10 μm or more measured by a light shielding type liquid particle counter should be 3000 particles / mL or less.
Here, in order to clear the above condition (iii), it is necessary to carefully carry out an operation of dissolving the water-soluble cellulose ether in a solvent. When it is difficult to clear the above condition (iii) only by the dissolution operation, after the dissolution operation, for example, "pre-filtration" is performed with a metal mesh filter having a large opening to obtain gel-like particles having a large particle diameter. It is necessary to apply techniques such as removing parts.

More preferably, the viscosity of the solution before filtration is adjusted in the range of 0.005 to 100 Pa · s at 25 ° C. and a shear rate of 3.1 (1 / s). If the viscosity of the solution before filtration is too low, it will be difficult to produce a silver nanowires ink having a viscosity suitable for coating. If the viscosity of the solution before filtration is too high, filtration for trapping gelled particles becomes difficult.

[Example of conductive paint]
A silver nanowire ink is illustrated below as a preferable example of the conductive paint prepared using the above-mentioned water-soluble cellulose ether solution.

(Silver nanowire)
From the viewpoint of forming a transparent conductive coating film excellent in conductivity and visibility, the silver nanowire used in the silver nanowire ink is preferably as thin as possible in a long shape. For example, it is desirable that the average diameter is 50 nm or less and the average length is 10 μm or more. It is more preferable to use one having an average diameter of 30 nm or less and an average length of 10 μm or more. The average aspect ratio is preferably 200 or more, and more preferably 450 or more. Here, the average length, the average diameter, the average ask and the ratio of the silver nanowires follow the following definitions.

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

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

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

Such thin and long silver nanowires can be obtained by a known method (alcohol solvent reduction method) in which silver is deposited on a wire by using the reducing power of alcohol which is a solvent in an alcohol solvent in the presence of an organic protective agent. Can. As the organic protective agent, PVP or a copolymer of vinyl pyrrolidone and another monomer can be used. Usually, the organic protective agent used at the time of synthesis adheres to the surface of the silver nanowire, and the organic protective agent is responsible for the in-liquid dispersibility.

In the copolymer of vinyl pyrrolidone and other monomers described above, the dispersibility in an aqueous solvent to which alcohol is added can be improved more than PVP. For that purpose, it is important that the copolymer has a structural unit of a hydrophilic monomer. Here, the hydrophilic monomer means a monomer having a property of dissolving 1 g or more in 1000 g of water at 25 ° C. Specific examples thereof include diallyldimethylammonium salt monomers, acrylate or methacrylate monomers, and maleimide monomers. For example, monomers of acrylate type or methacrylate type include ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate. Further, as the maleimide-based monomer, 4-hydroxybutyl acrylate, N-methyl maleimide, N-ethyl maleimide, N-propyl maleimide, N-tert-butyl maleimide may be mentioned.

(Ink composition)
The silver nanowire ink targeted here contains the water-soluble cellulose ether supplied from the water-soluble cellulose ether solution according to the present invention in the liquid medium constituting the ink, and is adjusted to a desired viscosity. Water-soluble cellulose ethers such as HEMC (hydroxyethyl methylcellulose) and HPMC (hydroxypropyl methyl cellulose) do not have a ligand that coordinates to silver, such as a carboxyl group. According to the inventors' investigations, when "silver nanowires coated with a copolymer of vinyl pyrrolidone and a hydrophilic monomer" and "a viscosity modifier containing HEMC or HPMC as a main component" are combined, they are coated with PVP. In the case of an ink using an aqueous solvent containing an alcohol in particular, the surface activity of a fluorine-based, nonionic-based, cationic-based, etc. is compared with the case of combining the silver nanowires with “h, vi” and “viscosity modifiers based on HEMC and HPMC”. The dispersibility of silver nanowires in the applied conductive coating can be improved without resorting to the addition of agents.

The liquid medium (portion other than the solid substance) constituting the silver nanowire ink includes the component of the aqueous solvent and the water-soluble cellulose ether. In the silver nanowires ink to which an organic substance other than the water-soluble cellulose ether (for example, an organic substance having a binder function) is added, the organic substance also becomes a component of the liquid medium. The proportion of the liquid medium in the silver nanowires ink is preferably 95% by mass or more, and may be controlled to 98% by mass or more.

The water-soluble cellulose ether content (content ratio of water-soluble cellulose ether to the total mass of the ink including silver nanowires) in the ink is, for example, in the range of 0.01 to 1.0% by mass according to the desired viscosity. You can adjust it. In addition, the weight average molecular weight of the water-soluble cellulose ether to be used can be, for example, in the range of 200,000 to 1,500,000. It may be managed in the range of 300,000 to 1,400,000. The weight average molecular weight can be confirmed, for example, by the GPC-MALS method.

Comparative Example 1
(Dissolution operation)
A powder product of HEMC (hydroxyethyl methyl cellulose) having a weight average molecular weight of 910,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. The solvent was placed in a reaction vessel with a capacity of 20 L provided with a baffle and was kept in a state of being vigorously stirred at 500 rpm by turbine blades while maintaining at 95 ° C. An amount of the above-mentioned water-soluble cellulose ether powder to be 1.50% by mass was charged into this solution, and strong stirring was continued as it is at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid. Hereinafter, the mass ratio of the water-soluble cellulose ether (including the portion present as gel-like particles) in the solution in the total mass of the solution is referred to as the “in-liquid content” of the water-soluble cellulose ether. The content of the water-soluble cellulose ether in the solution obtained in the present example is 1.50% by mass. The solution which has not yet been subjected to the filtration operation at the stage where this dissolution operation has been completed is referred to as "solution before filtration".

(Measurement of number of particles in solution before filtration by particle counter)
A 20 mL sample of the water-soluble cellulose ether solution was taken, and the particle size distribution of the particles present in the liquid was measured by a light shielding type liquid particle counter (manufactured by Rion, KS-42D). As a result, the amount of particles with a particle diameter of 10 μm or more in the solution at the stage of completion of the above-mentioned dissolution operation (solution before filtration) was 2490 particles / mL. Most of the particles counted here are considered to be gel-like particles of water-soluble cellulose ether.

(Viscosity of solution before filtration)
The viscosity of the aqueous solution of cellulose ether (solution before filtration) was determined with a rheometer (viscoelasticity measuring device) (HAAKE RheoStress 600 manufactured by Thermo, cone diameter 35 mm, cone angle 2 ° cone angle). As a result, the viscosity at 25 ° C. and shear rate 3.1 (1 / s) was 9.85 (Pa · s).

(Preparation of silver nanowires)
0.484 g of lithium chloride, 0.1037 g of potassium bromide, 0.426 g of lithium hydroxide, and 4.994 g of a propylene glycol solution having a content of aluminum nitrate nonahydrate of 20 mass% in 7800 g of propylene glycol at normal temperature Then, 83.875 g of a copolymer of vinyl pyrrolidone and diallyldimethyl ammonium nitrate was added and dissolved to obtain solution A. In a separate container, 67.96 g of silver nitrate was added into 320 g of propylene glycol and stirred at room temperature to dissolve, thereby obtaining a solution B containing silver.

The solution A was placed in a reaction vessel, and the temperature was raised while stirring from normal temperature to 90 ° C., and then the whole solution B was added to the solution A over 1 minute. After the addition of solution B was completed, stirring was further maintained and maintained at 90 ° C. for 24 hours. Thereafter, the reaction solution was cooled to room temperature. Thus, silver nanowires were synthesized by the synthesis method (alcohol solvent reduction method) using the reducing power of the alcohol solvent.

The reaction liquid (liquid containing the synthesized silver nanowire) cooled to normal temperature was separated into 1 L, transferred to a PFA bottle with a capacity of 35 L, and then 20 kg of acetone was added and stirred for 15 minutes. Then left to stand for 24 hours. After standing, a concentrate and a supernatant were observed, so the supernatant portion was removed to obtain a concentrate. An appropriate amount of 1% by mass PVP aqueous solution was added to the obtained concentrate, and the mixture was stirred for 3 hours to confirm that the silver nanowires were redispersed. After stirring, 2 kg of acetone was added and stirred for 10 minutes and then allowed to stand. After standing, a concentrate and a supernatant were newly observed, so the supernatant portion was removed to obtain a concentrate. 160 g of pure water was added to the obtained concentrate to redisperse the silver nanowires. After adding 2 kg of acetone with respect to the silver nanowire dispersion liquid after re-dispersion, it stood still after stirring for 30 minutes. After standing, a concentrate and a supernatant were newly observed, so the supernatant portion was removed to obtain a concentrate. An appropriate amount of 0.5% by mass PVP aqueous solution was added to the obtained concentrate, and the mixture was stirred for 12 hours to obtain a silver nanowire dispersion.

The silver nanowire dispersion obtained by the above washing was diluted with pure water to a silver nanowire concentration of 0.07% by mass to make the solution volume 52 L, and subjected to cross flow filtration using a tube of a porous ceramic filter. Cross-flow filtration was performed in a circulating system in which the liquid in the tank was returned to the tank via a pump and a filter. The material of the filter is SiC (silicon carbide), and the size of the tube is 12 mm in outer diameter, 9 mm in inner diameter, and 500 mm in length. The average pore diameter (median diameter) by mercury porosimetry using a mercury porosimeter manufactured by Micromeritics was 5.9 μm. The flow rate was set to 150 L / min, and circulation was performed for 12 hours while supplying pure water equivalent to the amount of liquid discharged as filtrate to the tank. After that, cross flow filtration was continued for 12 hours in a state in which the supply of pure water was stopped, and concentration of the silver nanowires dispersion was performed using the fact that the amount of liquid decreased due to discharge of the filtrate.

About the silver nanowire sample collect | recovered from the silver nanowire dispersion liquid after cross flow filtration, average length L _{M according} to the definition of the above, average diameter D _M , and average aspect ratio were calculated | required. As a result, the average length of the silver nanowires was 17.6 μm and the average diameter was 26.4 nm, and the average aspect ratio was 17600 / 26.4 ≒ 667.

(Ink)
A water soluble cellulose ether solution was used as a thickener to prepare a silver nanowire ink in the following manner. In this example, the liquid at the stage obtained by the above dissolution operation (solution before filtration) was used as a water-soluble cellulose ether solution. Also, water-soluble acrylic as a binder - urethane copolymer resin emulsion (DSM Co., ^NeoPac TM E-125) was used.
In one covered container, the silver nanowire dispersion obtained by the above cross flow filtration (the medium is water), the above water soluble cellulose ether solution, the above water soluble acrylic-urethane copolymer resin emulsion, and isopropyl alcohol After putting in and closing the lid, the container was stirred and mixed in a manner of shaking the container up and down 100 times. In the composition of the mixture, 0.30 mass% of water-soluble cellulose ether component, 0.15 mass% of water-soluble acrylic-urethane copolymer resin component, silver, with respect to the total weight of all mixtures, 80/20 of water / isopropyl alcohol The mixing amount of each substance was adjusted so as to be 0.15 mass% of metallic silver of the nanowires. Thus, a silver nanowire ink was obtained.

(Preparation of conductive coating)
Using the silver nanowire ink described above, a conductive coating was produced as follows.
The surface of a PET film substrate (Lumirror U48, manufactured by Toray Industries, Inc., with a thickness of 100 μm and a size of 150 mm × 200 mm, using a silver coater) using a die coater (Dymon Co., New platform die S-100) To form a coating of 100 mm × 100 mm in area. The coating conditions were: wet thickness: 11 μm, gap: 21 μm, speed: 10 mm / s, timer: 2.2 s, coating length: 100 mm. After coating, it was dried at 120 ° C. for 1 minute to obtain a transparent conductive coating.

In die coater coating, when the nanowires rapidly approach each other in the nozzle, a “wire aggregate”, which is a conductive filler aggregate in which the wires are aggregated in a bundle, is easily formed. When the size of the wire aggregate is large or the number is large, they are accumulated more often to form a coarse wire aggregate. A coarse wire assembly causes a short circuit in the circuit of the transparent conductive coating film and causes deterioration of the appearance as a white spot-like foreign matter. Then, the performance regarding the conductive filler aggregation property of silver nanowire ink was evaluated by how large a coarse wire aggregate is formed in the said conductive coating film formed by die-coater coating. Specifically, the above conductive coating is observed by a scanning electron microscope (SEM), and both a major axis and a minor axis are 10 μm or more in a region of 1 mm ² or more in total of randomly selected fields of view. The case where the presence of the wire assembly was not recognized was evaluated as ○, and the others were evaluated as x. Here, "long diameter" is defined as the length of the longest line segment (hereinafter referred to as "long axis") among line segments connecting any two points on the outline of the wire assembly on the image. As defined, "minor axis" is defined as the length of the longest part of the wire assembly measured in the direction perpendicular to the long axis on the image. According to the inventors' investigation, for example, in the case of an ink using thin and long silver nanowires having an average diameter of 30 nm or less and an average length of 15 μm or more, the ink evaluated as ○ by this observation method is a conductive filler It can be determined that the aggregate generation suppression performance is excellent. Therefore, as evaluation of silver nanowire ink, ○ evaluation was accepted, and × evaluation was rejected.

Tables 1A and 1B show the experimental results together with each example described later. In this comparative example 1, the ink evaluation was a failure (× evaluation). The SEM photograph of the part in which the coarse wire aggregate was observed is illustrated in FIG. 1 about the electrically conductive coating film produced by the comparative example 1. FIG. What appears white is a wire aggregate, and the portion formed by bringing together the above wire aggregates with a portion appearing dark as a core is a coarse wire aggregate. The portion of the core is considered to be mainly attributable to the gel-like particles of the thickening substance. Two coarse wire aggregates can be seen in this image.

Comparative Example 2
The following filtration operation was performed on the water-soluble cellulose ether solution (solution before filtration) produced in Comparative Example 1.
(Filtration operation)
The solution before filtration is put into a pressure filtration device, and a pressure filtration force of 0.2 MPa is applied with nitrogen gas using a 25 μm thread-wound filter (Roki Techno Co .; DIAII) with a filter filtration accuracy (aperture), and pressure filtration is performed. went. The water-soluble cellulose ether solution recovered after filtration is referred to as "solution after filtration" (same in each of the following examples).

(Measurement of water-soluble cellulose ether content of solution after filtration)
After filtration, 100 g of a sample separated from the solution is heated to 120 ° C. in the atmosphere to remove water as a solvent by evaporation to dryness, and measure the mass of the remaining solid content (water-soluble cellulose ether component) After filtration, the content of the water-soluble cellulose ether in the solution was determined. As a result, the solution content of the water-soluble cellulose ether in the solution after this filtration was 1.35% by mass.

(Measurement of number of particles in solution after filtration by particle counter)
With respect to the solution after filtration, the particle size distribution of particles present in the liquid was measured by the particle counting method using the particle counter similar to the solution before filtration described above. As a result, the amount of particles with a particle diameter of 10 μm or more in the solution after filtration was 307 particles / mL.

A conductive coating was prepared under the same conditions as Comparative Example 1 except that the solution after filtration of the water-soluble cellulose ether obtained above was used as a thickener for silver nanowire ink, and the above-mentioned coarse wire was observed by SEM observation. The presence of the aggregates was examined to evaluate the silver nanowire ink. The evaluation method is also the same as in Comparative Example 1. As a result, in the above-mentioned filtration, the removal of gel-like particles having a particle diameter of 10 μm or more was insufficient, and the ink evaluation was rejection (× evaluation).

Comparative Example 3
In the filtration operation, an experiment was conducted under the same conditions as in Comparative Example 2 except that pressure filtration was carried out at a pressure of 0.2 MPa using a 10 μm filter wound filter (Roki Techno Co .; DIAII) with a filter filtration accuracy (aperture). Did. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.33% by mass, and the amount of particles with a particle diameter of 10 μm or more was 134 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink, and a conductive coating film was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation failed ( X).

Comparative Example 4
In the filtration operation, an experiment was conducted under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.05 MPa using a 10-μm filter-wound filter (Roki Techno; DIAII) with a filter filtration accuracy (aperture). Did. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.40% by mass, and the amount of particles with a particle diameter of 10 μm or more was 38 particles / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink, and a conductive coating film was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation failed ( X).

Comparative Example 5
In the filtration operation, an experiment was conducted under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a 5 μm filter wound filter (Roki Techno Co .; DIAII) with a filter filtration accuracy (aperture). Did. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.34% by mass, and the amount of particles with a particle diameter of 10 μm or more was 140 particles / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink, and a conductive coating film was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation failed ( X).

Example 1
In the filtration operation, the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co .; SCP type) with a filter filtration accuracy (aperture) of 3 μm. The experiment was conducted at The obtained solution after filtration had a water-soluble cellulose ether content of 1.19% by mass, and the amount of particles with a particle diameter of 10 μm or more was 6 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Example 2
In the filtration operation, the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co., Ltd .; SCP type) with a filter filtration accuracy (aperture) of 1 μm. The experiment was conducted at As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.07% by mass, and the amount of particles having a particle diameter of 10 μm or more was 4 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 3]
In the filtration operation, the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co., Ltd .; SCP type) with a filter filtration accuracy (aperture) of 5 μm. The experiment was conducted at As for the solution after filtration obtained, the content of the water-soluble cellulose ether in the solution was 0.80% by mass, and the amount of particles with a particle diameter of 10 μm or more was 3 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Example 4
The same conditions as in Comparative Example 2 except that, in the filtration operation, pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 15 μm. The experiment was conducted at As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.36% by mass, and the amount of particles having a particle diameter of 10 μm or more was 3 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 5]
The same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) having a filter filtration accuracy (aperture) of 10 μm in the filtration operation. The experiment was conducted at As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.31% by mass, and the amount of particles with a particle diameter of 10 μm or more was 2 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 6]
The same conditions as in Comparative Example 2 except that in the filtration operation, pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 5 μm. The experiment was conducted at The obtained solution after filtration had a water-soluble cellulose ether content of 1.18% by mass, and the amount of particles with a particle diameter of 10 μm or more was 3 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 7]
In the filtration operation, under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a pleated filter (Roki Techno Co., Ltd .; MPX type) with a filter filtration accuracy (aperture) of 15 μm. I did an experiment. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.36% by mass, and the amount of particles with a particle diameter of 10 μm or more was 2 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Example 8
In the filtration operation, under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a pleated filter (Roki Techno Co., Ltd .; MPX type) with a filter filtration accuracy (aperture) of 10 μm. I did an experiment. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.31% by mass, and the amount of particles with a particle diameter of 10 μm or more was 5 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 9]
In the filtration operation, it is the same as Comparative Example 2 except that pressure filtration is performed at a pressure of 0.2 MPa using a pleated filter (Roki Techno Co., Ltd .; MPX type) having a filter filtration accuracy (aperture) of 4.5 μm. The experiment was conducted under the conditions. The resultant solution after filtration had a water-soluble cellulose ether content of 0.66% by mass, and the amount of particles with a particle diameter of 10 μm or more was 6 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 10]
The same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Roki Techno Co., Ltd .; L1P type) having a filter filtration accuracy (aperture) of 10 μm in the filtration operation. The experiment was conducted at As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.33% by mass, and the amount of particles having a particle diameter of 10 μm or more was 4 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 11]
The same conditions as in Comparative Example 2 except that, in the filtration operation, pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (manufactured by Roki Techno; L1P type) with a filter filtration accuracy (aperture) of 5 μm. The experiment was conducted at As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.31% by mass, and the amount of particles having a particle diameter of 10 μm or more was 4 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 12]
The same conditions as in Comparative Example 2 except that in the filtration operation, pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (manufactured by Roki Techno; L1P type) with a filter filtration accuracy (aperture) of 3 μm. The experiment was conducted at The resultant solution after filtration had a water-soluble cellulose ether content of 1.44% by mass, and the presence of particles having a particle diameter of 10 μm or more was not observed. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 13]
In the filtration operation, the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (Asahi Kasei Co., Ltd .; KNA type) having a filter filtration accuracy (aperture) of 2 μm. The experiment was conducted at The obtained solution after filtration had a water-soluble cellulose ether content of 0.69% by mass, and the amount of particles with a particle diameter of 10 μm or more was 8 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Example 14
In the filtration operation, the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (manufactured by Asahi Kasei Corporation; KNA type) having a filter filtration accuracy (aperture) of 1 μm. The experiment was conducted at As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 0.53% by mass, and the amount of particles having a particle diameter of 10 μm or more was 5 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 15]
In the filtration operation, under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a pleated filter (Asahi Kasei Corporation; KNP type) with a filter filtration accuracy (aperture) of 5 μm. I did an experiment. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.35% by mass, and the amount of particles having a particle diameter of 10 μm or more was 2 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 16]
In the filtration operation, under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a pleated filter (Asahi Kasei Co., Ltd .; KNP type) with a filter filtration accuracy (aperture) of 3 μm. I did an experiment. The resulting solution after filtration had a water-soluble cellulose ether content of 1.35% by mass, and the presence of particles having a particle diameter of 10 μm or more was not observed. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 17]
In the filtration operation, under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a pleated filter (Asahi Kasei Co., Ltd .; KMZ type) with a filter filtration accuracy (aperture) of 5 μm. I did an experiment. As for the solution after filtration obtained, the content of the water-soluble cellulose ether in the solution was 1.28% by mass, and the amount of particles with a particle diameter of 10 μm or more was 1 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

[Example 18]
In the filtration operation, under the same conditions as in Comparative Example 2 except that pressure filtration was performed at a pressure of 0.2 MPa using a pleated filter (Asahi Kasei Co., Ltd .; KMZ type) with a filter filtration accuracy (aperture) of 3 μm. I did an experiment. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.26% by mass, and the amount of particles having a particle diameter of 10 μm or more was 2 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Comparative Example 6
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 350,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 95 degreeC. An amount of the above-mentioned water-soluble cellulose ether powder to be 1.50% by mass was charged into this solution, and strong stirring was continued as it is at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of water-soluble cellulose ether in the liquid was 1.50% by mass, and the amount of particles with a particle diameter of 10 μm or more was 364 particles / mL. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 0.91 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

[Example 19]
The water-soluble cellulose ether solution prepared in Comparative Example 6 was used as the solution before filtration, and in the filtration operation, using a pleated filter (Roki Techno Co., Ltd .; MPX type) with a filter filtration accuracy (aperture) of 10 μm, no pressure was applied. The experiment was performed under the same conditions as Comparative Example 2 except that pressure filtration was performed at 2 MPa. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.33% by mass, and the amount of particles having a particle diameter of 10 μm or more was 6 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Example 20
A dissolution operation is performed in the same manner as Comparative Example 6 except that a powder product of HPMC (hydroxypropyl methyl cellulose) having a weight average molecular weight of 660,000 is used as a water soluble cellulose ether, and a water soluble cellulose ether solution (before filtration Solution) was prepared. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 4.96 (Pa · s). The solution before this filtration was used, and in the filtration operation, pressure filtration was performed at a pressure of 0.2 MPa using a depth pleated filter (manufactured by Loki Techno; L1P type) with a filter filtration accuracy (aperture) of 3 μm. The experiment was performed under the same conditions as in Comparative Example 2 except for. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 1.40% by mass, and the amount of particles having a particle diameter of 10 μm or more was 2 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Comparative Example 7
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 840,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 95 degreeC. An amount of the above-mentioned water-soluble cellulose ether powder to be 2.25% by mass was charged into this solution, and strong stirring was continued as it is at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of water-soluble cellulose ether in the solution was 2.25% by mass, and the amount of particles with a particle diameter of 10 μm or more was 1505 particles / mL. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 63.27 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

[Example 21]
The water-soluble cellulose ether solution prepared in Comparative Example 7 was used as the solution before filtration, and in the filtration operation, using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 10 μm The experiment was performed under the same conditions as Comparative Example 2 except that pressure filtration was performed at 0.35 MPa. As for the solution after filtration obtained, the content of the water-soluble cellulose ether in the solution was 2.03% by mass, and the amount of particles with a particle diameter of 10 μm or more was 9 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Comparative Example 8
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 840,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 95 degreeC. An amount of the above-mentioned water-soluble cellulose ether powder to be 2.75% by mass was charged into this solution, and strong stirring was continued as it is at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of the water-soluble cellulose ether in the liquid was 2.75% by mass, and the amount of particles with a particle diameter of 10 μm or more was 5509 particles / mL. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 107.30 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

Comparative Example 9
The water-soluble cellulose ether solution prepared in Comparative Example 8 as a solution before filtration was subjected to pressure filtration at a pressure of 0.40 MPa using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 10 μm. I tried. However, because of the high viscosity of the water-soluble cellulose ether solution (solution before filtration), filtration under the above conditions was impossible. Therefore, the subsequent experiments were discontinued.

Comparative Example 10
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 660,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 95 degreeC. An amount of the above-mentioned water-soluble cellulose ether powder to be 2.50% by mass was charged into this solution, and strong stirring was continued as it is at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of the water-soluble cellulose ether in the liquid was 2.50% by mass, and the amount of particles with a particle diameter of 10 μm or more was 2804 particles / mL. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 34.38 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

[Example 22]
The water-soluble cellulose ether solution prepared in Comparative Example 10 was used as the solution before filtration, and in the filtration operation, using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 10 μm The experiment was performed under the same conditions as Comparative Example 2 except that pressure filtration was performed at 0.35 MPa. The resultant solution after filtration had a water-soluble cellulose ether content of 2.34% by mass, and the amount of particles having a particle diameter of 10 μm or more was 7 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Comparative Example 11
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 840,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 95 degreeC. A portion of the water-soluble cellulose ether powder in an amount of 0.60% by mass was charged into this solution, and strong stirring was continued at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of water-soluble cellulose ether in the solution was 0.60% by mass, and the amount of particles with a particle diameter of 10 μm or more was 1029 particles / mL. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 2.00 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

[Example 23]
The water-soluble cellulose ether solution prepared in Comparative Example 11 was used as the solution before filtration, and in the filtration operation, using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 10 μm The experiment was performed under the same conditions as Comparative Example 2 except that pressure filtration was performed at 0.20 MPa. As for the solution after filtration, the content of the water-soluble cellulose ether in the solution was 0.56% by mass, and the amount of particles having a particle diameter of 10 μm or more was 5 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Comparative Example 12
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 840,000 was prepared as a water-soluble cellulose ether. As a solvent, 70% by mass of pure water and 30% by mass of 2-propanol (isopropyl alcohol: IPA) were prepared. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 75 degreeC. An amount of the above-mentioned water-soluble cellulose ether powder to be 1.25% by mass was charged into this solution, and strong stirring was continued at 75 ° C. for 1 hour. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of water-soluble cellulose ether in the solution was 1.25% by mass, and the amount of particles with a particle diameter of 10 μm or more was 745 particles / mL. The viscosity of the solution before filtration was measured by the same method as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 11.08 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

[Example 24]
The water-soluble cellulose ether solution prepared in Comparative Example 12 was used as the solution before filtration, and in the filtration operation, using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 10 μm The experiment was performed under the same conditions as Comparative Example 2 except that pressure filtration was performed at 0.20 MPa. The resultant solution after filtration had a water-soluble cellulose ether content of 1.10% by mass, and the amount of particles having a particle diameter of 10 μm or more was 3 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

Comparative Example 13
(Dissolution operation)
A powder product of HPMC (hydroxypropyl methylcellulose) having a weight average molecular weight of 350,000 was prepared as a water-soluble cellulose ether. Pure water was prepared as a solvent. It was set as the state currently stirred strongly by the method similar to the comparative example 1, maintaining the said solvent at 95 degreeC. An amount of the above-mentioned water-soluble cellulose ether powder to be 4.50% by mass was charged into this solution, and strong stirring was continued as it is at 95 ° C. for 24 hours. Then, it cooled to 10 degreeC, continuing strong stirring. Thus, the "water-soluble cellulose ether solution" in which the water-soluble cellulose ether is dissolved in the aqueous solvent was obtained. The solution contains gel-like particles of a water-soluble cellulose ether which is not completely dissolved and remains as a solid.

The experiment was conducted under the same conditions as in Comparative Example 1 except that the "solution before filtration" obtained by the above-described dissolution operation was used. In the solution before filtration, the content of water-soluble cellulose ether in the solution was 4.50% by mass, and the amount of particles having a particle diameter of 10 μm or more was 1408 particles / mL. The viscosity of the solution before filtration was measured in the same manner as in Comparative Example 1. As a result, the viscosity at a shear rate of 3.1 (1 / s) at 25 ° C. was 56.75 (Pa · s). Using this water-soluble cellulose ether solution (solution before filtration) as a thickener for silver nanowire ink, a conductive coating was prepared, and the presence of coarse wire aggregates was examined by SEM observation. As a result, the ink evaluation was not good. It passed (x evaluation).

[Example 25]
The water-soluble cellulose ether solution prepared in Comparative Example 13 was used as the solution before filtration, and in the filtration operation, using a depth pleated filter (Roki Techno Co., Ltd .; SHP type) with a filter filtration accuracy (aperture) of 10 μm The experiment was performed under the same conditions as Comparative Example 2 except that pressure filtration was performed at 0.35 MPa. The resultant solution after filtration had a water-soluble cellulose ether content of 4.19% by mass, and the amount of particles with a particle diameter of 10 μm or more was 9 / mL. The solution after filtration of this water-soluble cellulose ether was used as a thickener for silver nanowire ink to prepare a conductive coating film, and the presence of a coarse wire aggregate was examined by SEM observation. As a result, the ink evaluation passed (○ Evaluation).

As can be seen from Tables 1A and 1B, a silver nanowire ink using a water-soluble cellulose ether solution having a very small amount of particles with a particle diameter of 10 μm or more measured by a light shielding type liquid particle counter as a thickener Are extremely useful for preventing the formation of coarse wire aggregates in the conductive coating.

Claims

Water-soluble cellulose ether is contained at a content of 0.05% by mass or more in an aqueous solvent, and the amount of particles with a particle diameter of 10 μm or more measured by a liquid shielding particle counter is 20 / mL or less There is a water soluble cellulose ether solution.
The water-soluble cellulose ether solution according to claim 1, wherein the content of the water-soluble cellulose ether is 0.05 to 10.0% by mass.
The water-soluble cellulose ether solution according to claim 1, wherein the content of the water-soluble cellulose ether is 0.05 to 5.0% by mass.
The water-soluble cellulose ether solution according to claim 1, wherein the content of the water-soluble cellulose ether is 0.1 to 2.0% by mass.
The water-soluble cellulose ether solution according to claim 1, containing one or more selected from HEMC (hydroxyethyl methyl cellulose) and HPMC (hydroxypropyl methyl cellulose) as the water-soluble cellulose ether.
A viscosity modifier for a conductive paint using the water-soluble cellulose ether solution according to claim 1.
A viscosity modifier for silver nanowires ink using the water-soluble cellulose ether solution according to claim 1.
In a method of producing a silver nanowires ink, comprising mixing a viscosity modifier with a silver nanowire dispersion using an aqueous solvent, the water-soluble cellulose ether solution according to claim 1 is used as the viscosity modifier in an ink. A method of producing a silver nanowires ink, wherein the water-soluble cellulose ether content of the above is adjusted in the range of 0.01 to 1.0 mass.