JP7725124B2 - Method for producing a silver nanowire-containing conductive laminate - Google Patents

Description

The present invention relates to a method for producing a conductive laminate containing silver nanowires.

In recent years, the use of display devices such as liquid crystal displays and organic light-emitting diode (OLED) displays, input sensors such as touch panels, and perovskite solar cells has increased, leading to increased demand for transparent conductive films, which are essential components for these devices.

Traditionally, indium tin oxide (hereinafter sometimes abbreviated as ITO) has been the primary material used for these transparent conductive films. While thin films using ITO offer high transparency and high conductivity, they are typically produced using sputtering or vapor deposition equipment, posing problems in terms of production speed and manufacturing costs. Furthermore, ITO is hard and brittle, limiting its use in applications requiring flexibility. This has led to a demand for the development of a transparent conductive film material to replace ITO.

Silver nanowires are one material that is gaining attention as an alternative to ITO for transparent conductive films. Silver nanowires not only possess the high conductivity and flexibility inherent in silver, but also have high optical transparency in the visible light range due to their small diameter, making them a promising material for transparent conductive films.

In transparent conductive films using silver nanowires, the smaller the diameter of the silver nanowires, the less light scattering there is, and the optical properties of the film are generally improved. For this reason, methods for producing thinner silver nanowires are being investigated. For example, Patent Document 1 reports a method for producing silver nanowires with an average diameter of less than 30 nm and a low-haze transparent conductor using such nanowires.

However, due to their nano-sized diameter, silver nanowires are less stable. For example, it is known that when a transparent conductive film using silver nanowires is exposed to high-temperature, high-humidity conditions, its conductivity gradually decreases. Therefore, methods to solve this problem have been investigated. For example, Patent Document 2 reports that the use of a weather resistance improver that combines specific compounds can suppress the deterioration of silver nanowires under high-temperature, high-humidity conditions and prolonged exposure to sunlight.

However, the silver nanowires obtained in Patent Document 1 have a very small diameter, which further reduces their stability. It has been found that conventional methods for stabilizing silver nanowires are unable to sufficiently prevent the deterioration of silver nanowires under high-temperature, high-humidity conditions, and a method to solve this problem has been sought.

Special Publication No. 2013-517603 Retable No. 2018-116501

In view of the problems with the conventional technology described above, the present invention aims to provide a method for manufacturing a silver nanowire-containing conductive laminate that has a smaller rate of change in resistance value under high-temperature and high-humidity conditions than conventional methods.

As a result of intensive research to solve the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by applying a specific weather resistance-imparting composition to a transparent conductive film using silver nanowires and then heat-treating it under specific conditions, thereby completing the present invention.

That is, the present invention provides:
<1> A method for producing a conductive laminate having a substrate and a silver nanowire-containing conductive layer, comprising:
(A) applying a silver nanowire dispersion to form a silver nanowire-containing conductive layer;
(B) applying a weather resistance-imparting composition containing a compound having a molecular weight of 80 to 400 and having 1 to 3 mercapto groups or a 2-aminothiazole derivative as a weather resistance-imparting agent;
A method for producing a conductive laminate, comprising the step (A) followed by the step (B),
After step (B),
(C) a method for producing a conductive laminate, comprising a step of heat treating the laminate at a temperature of 40°C to 120°C for 30 minutes or more;
<2> The method for producing a conductive laminate according to <1>, wherein the weather resistance-imparting composition contains a polymerizable monomer and/or a macromonomer and a photopolymerization initiator, and the method includes a step of curing the polymerizable monomer and/or the macromonomer between the steps (B) and (C).
<3> The method for producing a conductive laminate according to <2>, wherein the proportion of the weather resistance imparting agent contained in the weather resistance imparting composition in the solute is 0.02% to 1.5%.
<4> The method for producing a conductive laminate according to any one of <1> to <3>, wherein the silver nanowires have a diameter of 10 nm to 30 nm.
<5> The method for producing a conductive laminate according to any one of <1> to <3>, wherein the value of the following formula α, which is represented by the temperature T (°C) and the time t (minutes) of the heat treatment in the step (C), is 500 or more:
α=t×e ^0.08×(T-40)
<6> The method for producing a conductive laminate according to any one of <1> to <3>, wherein the weather resistance imparting agent is an alkanethiol having 8 to 20 carbon atoms.
<7> The method for producing a conductive laminate according to any one of <1> to <3>, wherein the weather resistance imparting agent is 2-aminothiazole or 2-aminobenzothiazole.
<8> The method for producing a conductive laminate according to any one of <1> to <3>, wherein the weather resistance imparting agent is either a compound having a heterocyclic structure selected from imidazole, 2-imidazoline, thiazole, 2-thiazoline, 1,3,4-thiadiazole, pyrimidine, and 1,3,5-triazine, in which a mercapto group is bonded to at least the 2-position, or a compound having a tetrazole structure in which a mercapto group is bonded to the 5-position, in which all of the mercapto groups in the molecule are bonded to carbon atoms having unsaturated bonds in the same heterocyclic ring, and the unsaturated carbon to which the mercapto group is bonded is bonded only to a sulfur or nitrogen atom;
is.

According to the present invention, by applying a specific weather resistance-imparting composition and then heat-treating the film under specific conditions, the deterioration of the conductivity of a silver nanowire-containing conductive film under high-temperature, high-humidity conditions can be suppressed more effectively than with conventional methods.

The present invention is described in detail below.

[substrate]
The substrate may be selected appropriately depending on the application, and may be rigid or flexible. It may also be colored. The substrate in the present invention can be any substrate obtained by a known method or commercially available, and there is no particular limitation. Specific examples of substrate materials include glass, polyimide, polycarbonate, polyethersulfone, polyacrylate, polyester, polyethylene terephthalate, polyethylene naphthalate, polyolefin, and polyvinyl chloride. Organic functional materials and inorganic functional materials may also be formed on the substrate. Multiple substrates may also be laminated.

[Silver nanowires]
In the present invention, the term "silver nanowire" refers to a silver structure having a diameter of less than 1 μm and an aspect ratio (major axis length/diameter) of 10 or more.

[Silver nanowire diameter]
When silver nanowires are used in transparent conductive films, a small average wire diameter is advantageous and preferable in order to enhance transparency. In the present invention, the "diameter of silver nanowires" refers to the diameter measured using a scanning electron microscope (SEM; JSM-5610LV, manufactured by JEOL Ltd.). Furthermore, the "average diameter of silver nanowires" refers to the average diameter measured by observing 100 silver nanowires. In the present invention, the average diameter of silver nanowires is preferably 100 nm or less, more preferably 40 nm or less, even more preferably 30 nm or less, and particularly preferably 25 nm or less. On the other hand, since a larger average diameter of silver nanowires increases durability under high-temperature and high-humidity conditions, the average diameter of silver nanowires is preferably 10 nm or more, and more preferably 15 nm or more.

[Major axis length of silver nanowires]
Transparent conductive films containing silver nanowires exhibit conductivity due to the silver nanowires contacting each other and forming a three-dimensional conductive network structure that is spatially widely distributed. Therefore, from the viewpoint of conductivity, a longer average major axis length of the nanowires is preferable. On the other hand, nanowires that are too long tend to become tangled, so shorter nanowires are preferable from the viewpoint of dispersion stability. In the present invention, the "major axis length of silver nanowires" refers to a value calculated by photographing silver nanowires using a dark-field microscope (product name: BX51, manufactured by Olympus Corporation) and using image processing software (product name: Image-Pro Premier, manufactured by Media Cybernetics, Inc.). Furthermore, the "average major axis length of silver nanowires" refers to the average value of the major axis lengths measured by observing 1,000 silver nanowires. In the present invention, the average major axis length of silver nanowires is preferably 1 to 100 μm, more preferably 3 to 30 μm, and even more preferably 7 to 20 μm.

[Method of manufacturing silver nanowires]
The method for producing the silver nanowires used in the present invention is not particularly limited, and those obtained by known production methods can be used. Among them, it is preferable to use a production method in which silver nanowires are obtained by reducing a silver salt in a polyol in the presence of a growth inhibitor and a halide salt.

[Polyol]
The polyol is not particularly limited as long as it is a compound capable of reducing silver ions, and at least one type can be appropriately selected from compounds having two or more hydroxyl groups depending on the purpose. In particular, from the viewpoints of being liquid and facilitating the dissolution of the growth regulator, saturated hydrocarbon diols having 1 to 5 carbon atoms and saturated hydrocarbon triols having 1 to 5 carbon atoms are preferred. Among these, ethylene glycol, 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,3-butanediol, and glycerin are more preferred, and propylene glycol is even more preferred.

[Growth Regulators]
The growth regulator is not particularly limited, and at least one polymer can be appropriately selected depending on the purpose. Among them, polyvinylpyrrolidone, poly(N-substituted (meth)acrylamide), or copolymers thereof are particularly preferred, and polyvinylpyrrolidone is even more preferred.

[Halide salts]
The halide salt is not particularly limited as long as it is a compound that dissociates halide ions by dissolving an inorganic or organic salt in a polar solvent, and at least one type can be appropriately selected depending on the purpose. The use of chloride salts is particularly preferred because the yield of silver nanowires increases. The use of bromide salts results in silver nanowires with smaller diameters, so it is more preferred to use both chloride salts and bromide salts. Preferred chloride salts include lithium chloride, sodium chloride, potassium chloride, zirconium oxychloride, ammonium chloride, and benzyltriethylammonium chloride, with sodium chloride being more preferred. Preferred bromide salts include sodium bromide, potassium bromide, ammonium bromide, and tetrabutylammonium bromide, with sodium bromide being more preferred.

[Silver halide]
The silver salt is not particularly limited as long as it is a silver compound that can be reduced by a polyol, and at least one type can be appropriately selected depending on the purpose. Among them, silver nitrate is preferably used from the viewpoints of solubility in polyol and ease of availability. The halide salt and silver salt may be used in combination as the same substance. Examples of such compounds include silver chloride and silver bromide.

[Purification of silver nanowires]
The silver nanowires obtained by the above-described method for producing silver nanowires are preferably purified by a conventionally known method such as centrifugation, filtration, decantation, elutriation, or precipitation in a solvent followed by redispersion treatment, and then a dispersion solvent is used to form a silver nanowire dispersion.

[(A) Step of applying a silver nanowire dispersion to form a silver nanowire-containing conductive layer]
The method for producing a conductive laminate having a silver nanowire-containing conductive layer of the present invention includes a step of forming a silver nanowire-containing conductive layer by applying a silver nanowire dispersion onto a substrate. Specific examples of the application method include spin coating, slit coating, dip coating, blade coating, bar coating, spraying, letterpress printing, intaglio printing, screen printing, lithographic printing, dispensing, and inkjet printing. These application methods may also be used to apply the silver nanowire-containing conductive layer multiple times.

[Silver nanowire dispersion]
The silver nanowire dispersion of the present invention is one in which silver nanowires are dispersed in a dispersion solvent. Various additives can be added to this silver nanowire dispersion as needed, provided that the effects of the present invention are not impaired. Specific examples of additives include surfactants and polymer compounds.

[Concentration of Silver Nanowires in Silver Nanowire Dispersion]
The silver nanowire concentration of the silver nanowire dispersion used in the present invention can be set arbitrarily, but from the viewpoint of dispersion stability, it is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. Furthermore, if the silver nanowire concentration is extremely low, in order to achieve the target resistance value during coating, the coating thickness must be increased or multiple coatings must be performed, which increases the effort required during use. Therefore, from the viewpoint of productivity, it is preferably 0.01% by mass or more, and more preferably 0.03% by mass or more.

[Dispersion solvent]
The dispersion solvent used in the present invention may be any compound that can disperse silver nanowires and dissolve various additives contained in the silver nanowire dispersion, such as polymer compounds. Furthermore, since the silver nanowire dispersion is also used to prepare a silver nanowire-containing conductive layer, the dispersion solvent is preferably a compound that forms a uniform coating film by evaporating during film formation of the conductive layer containing silver nanowires. Specific examples include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, and diacetone alcohol; polyols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, and 1,4-butanediol; glycol ethers such as ethylene glycol monomethyl ether and propylene glycol monomethyl ether; glymes such as ethylene glycol dimethyl ether; glycol ether esters such as ethylene glycol monomethyl ether acetate; esters such as ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatics such as toluene; and solvents consisting of two or more of these. Among these, from the viewpoint of the drying property of the solvent during film formation and the dispersibility of the silver nanowires, water and compounds having one or two hydroxyl groups and a boiling point of less than 250°C are preferred, and it is more preferred to use water, alcohols having 1 to 4 carbon atoms, diols having 2 to 4 carbon atoms, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether, diacetone alcohol, and solvents consisting of two or more of these.

[Polymer compound]
It is preferable to add a polymer compound to the silver nanowire dispersion of the present invention for the purpose of improving the dispersion stability of the silver nanowires and improving the coating suitability. Specific examples of the polymer compound include polysaccharides and derivatives thereof, such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, carboxymethyl cellulose, nitrocellulose, cellulose acetate, guar gum, xanthan gum, tamarind seed gum, psyllium seed gum, ghatti gum, locust bean gum, hydroxyethyl guar gum, and hydroxypropyl guar gum; poly(meth)acrylic resins, polyurethane resins, polyester resins, alkyd resins, epoxy resins, ethylene vinyl acetate resins, and polyvinylpyrrolidone; poly(meth)acrylamide, poly(N-substituted (meth)acrylamide), polyvinyl alcohol, and derivatives thereof. Among these, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, poly(N-substituted (meth)acrylamide), and polyvinylpyrrolidone are preferred, with hydroxypropyl methylcellulose and polyvinylpyrrolidone being more preferred.

[Concentration of polymer compound in silver nanowire dispersion]
From the viewpoint of improving the dispersibility of silver nanowires and coating suitability, the concentration of the polymer compound contained in the silver nanowire dispersion is preferably 0.005% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.05% by mass or more. From the viewpoint of the conductivity of the coating film, the content of the polymer compound is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.4% by mass or less.

[Sheet resistance of silver nanowire-containing conductive layer]
The sheet resistance of the silver nanowire-containing conductive layer is used as an indicator of the conductivity of the silver nanowire-containing conductive laminate. The sheet resistance of the silver nanowire-containing conductive layer can be set arbitrarily depending on the intended use by changing the amount of silver nanowires contained in the conductive layer. A preferred usable range of sheet resistance is 0.5 Ω/□ to 1000 Ω/□, more preferably 1 Ω/□ to 300 Ω/□.

[(B) Step of applying a weather resistance imparting composition containing a specific weather resistance imparting agent]
The method for producing a conductive laminate having a silver nanowire-containing conductive layer of the present invention includes a step of applying a weather resistance-imparting composition containing a specific weather resistance-imparting agent described below. A known application method can be used to apply the weather resistance-imparting composition. Specific examples of application methods include spin coating, slit coating, dip coating, blade coating, bar coating, spraying, letterpress printing, intaglio printing, screen printing, lithographic printing, dispensing, and inkjet printing. These application methods may also be used to apply multiple coats.

[Production of silver nanowire-containing conductive laminate]
The silver nanowire-containing conductive laminate is a laminate having a substrate and a silver nanowire-containing conductive layer, and is obtained by further applying a weather resistance-imparting composition. Because the weather resistance-imparting composition can maximize the effects of the present invention by contacting the silver nanowire-containing conductive film, it is preferable to apply the weather resistance-imparting composition after step (A) and then directly onto the silver nanowire-containing conductive film. As long as the effects of the conductive laminate obtained by the present invention are not impaired, the weather resistance-imparting composition may be applied after applying another composition onto the silver nanowire-containing conductive film.

[Weather resistance imparting composition]
The weather resistance-imparting composition is a composition containing a specific weather resistance-imparting agent, which will be described later. The weather resistance-imparting composition may further contain a solvent, a resin, and other additives, as necessary. It is believed that the weather resistance-imparting agent of the present invention exerts its effect by interacting with the silver nanowires, and therefore it is believed that a small amount of transition metal complex or transition metal ion is preferable. Therefore, the concentration of transition metal complex or transition metal ion contained in the weather resistance-imparting composition is preferably less than 0.01%, more preferably less than 0.0001%, and even more preferably substantially free. "Substantially free" means that no transition metal complex or transition metal ion has been added. The present invention includes a step of applying the weather resistance-imparting composition to a conductive laminate including a substrate and a silver nanowire-containing conductive layer.

[Weather resistance additive]
The weather resistance imparting agent is primarily used for the purpose of chemically protecting the silver nanowire-containing conductive layer. The weather resistance imparting agent used in the present invention is a compound having 1 to 3 mercapto groups or a 2-aminothiazole derivative, and has a molecular weight in the range of 80 to 400. Among compounds having 1 to 3 mercapto groups and a molecular weight of 80 to 400, alkanethiols having 8 to 20 carbon atoms, compounds having a heterocyclic structure with a mercapto group bonded to at least the second position and selected from imidazole, 2-imidazoline, thiazole, 2-thiazoline, 1,3,4-thiadiazole, pyrimidine, and 1,3,5-triazine, and compounds having a tetrazole structure with a mercapto group bonded to the fifth position are more preferably used.

Alkanethiols with 8 to 20 carbon atoms are compounds in which one mercapto group is bonded to an alkyl group that does not contain unsaturated bonds or functional groups containing heteroatoms, and can be used without restriction as weather resistance additives. It is believed that alkanethiols impart weather resistance by the mercapto group in the molecule coordinating with silver, so primary alkanethiols that are not sterically crowded around the mercapto group are more preferred, and straight-chain alkanethiols are even more preferred.

Compounds with a heterocyclic structure selected from imidazole, 2-imidazoline, thiazole, 2-thiazoline, 1,3,4-thiadiazole, pyrimidine, and 1,3,5-triazine, each having a mercapto group bonded to at least the second position, or compounds with a heterocyclic structure selected from tetrazole and having a mercapto group bonded to the fifth position, can be used without restriction as weather resistance additives, as long as they have a molecular weight in the range of 80 to 400 and contain one to three mercapto groups in the molecule. The mercapto group may be in the form of a tautomer, a thiocarbonyl structure. Among these, compounds in which all mercapto groups in the molecule are bonded to carbon atoms with unsaturated bonds in the same heterocyclic ring are preferred, and compounds in which the unsaturated carbon atoms to which mercapto groups are bonded are bonded only to sulfur or nitrogen atoms are even more preferred. Specific examples include 2-mercapto-1-methylimidazole, 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, 2-imidazolinethione, 2-mercaptothiazole, rhodanine, 2-mercaptobenzothiazole, 5-chloro-2-mercaptobenzothiazole, 2-mercaptothiazoline, 5-methyl-1,3,4-thiadiazole-2-thiol, 2-mercaptopyrimidine, 2-thiouracil, 6-methyl-2-thiouracil, 2-thiobarbituric acid, thiocyanuric acid, 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, and 5-mercapto-1-phenyl-1H-tetrazole. Among these, compounds having only substituents selected from hydrogen, an alkyl group, a phenyl group, a hydroxyl group, an alkoxyl group, an amino group, a (di)alkylamino group, a nitro group, an alkoxycarbonyl group, a fluoro group, a chloro group, and a mercapto group on a heterocycle can be more preferably used.

The 2-aminothiazole derivative of the present invention can be used without limitation as a weather resistance additive, as long as it has a molecular weight in the range of 80 to 400, a 2-aminothiazole skeleton, and a primary amino group at the 2-position. Specific examples include 2-aminothiazole, 2-amino-4-methylthiazole, 2-amino-5-methylthiazole, 2-amino-5-nitrothiazole, 2-aminothiazole-4-methylcarboxylate, 2-aminobenzothiazole, and 2-amino-6-methoxybenzothiazole. Among these, 2-aminothiazole or a 2-aminothiazole derivative having only a substituent selected from hydrogen, an alkyl group, a phenyl group, a hydroxyl group, an alkoxyl group, an amino group, a (di)alkylamino group, a nitro group, an alkoxycarbonyl group, a fluoro group, or a chloro group on the aromatic ring of 2-aminobenzothiazole is preferred, with 2-aminothiazole or 2-aminobenzothiazole being more preferred, and 2-aminothiazole being even more preferred.

[Molecular weight of weather resistance agent]
The molecular weight of the weather resistance imparting agent of the present invention is in the range of 80 to 400. It is considered that the smaller the molecular weight, the greater the number of molecules per unit weight, and therefore the smaller the necessary amount to be added can be, and therefore the molecular weight of the weather resistance imparting agent is more preferably 350 or less, and even more preferably 300 or less.

The weather resistance-imparting composition preferably contains a solvent from the perspective of improving the coatability of the weather resistance-imparting composition and dissolving the components in the composition. The solvent may be any compound that dissolves the other components in the composition and forms a uniform coating film by evaporating during film formation. Specific examples of solvents include water, methanol, ethanol, 1-propanol, 2-propanol, acetone, methyl ethyl ketone, toluene, n-hexane, 1-butanol, diacetone alcohol, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol diethyl ether, 1,3-butylene glycol diacetate, cyclohexanol acetate, propylene glycol diacetate, and tetrahydrofuran. Among these, it is preferable to use methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, diacetone alcohol, propylene glycol monomethyl ether, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, toluene, tetrahydrofuran, etc. These can be used alone or in combination of two or more.

The weather resistance-imparting composition may further contain a resin. Including a resin in the weather resistance-imparting composition is preferable because it can provide the weather resistance-imparting composition with the physical protection function of the silver nanowire-containing laminate. Any resin can be used as long as it dissolves in the solvent of the weather resistance-imparting composition and does not impair the effects of the present invention. Specific examples of resins include polysaccharides such as ethyl cellulose and their derivatives, poly(meth)acrylic resins, polyurethane resins, polyester resins, epoxy resins, poly-N-vinyl compounds such as polyvinylpyrrolidone, polyvinyl alcohol and its derivatives, etc. Among these, water-insoluble polymers are preferred from the perspective of water resistance, such as water-insoluble poly(meth)acrylic resins, polyurethane resins, polyester resins, ethyl cellulose, and polyvinyl acetal. These can be used alone or in combination of two or more.

The weather resistance-imparting composition may further contain a polymerizable monomer and/or a macromonomer. This is preferable because the weather resistance-imparting composition contains a polymerizable monomer and/or a macromonomer and is then subjected to the curing process described below, thereby providing the silver nanowire-containing laminate with a physical protective function. When the weather resistance-imparting composition contains a polymerizable monomer and/or a macromonomer, it is preferable that the weather resistance-imparting composition further contains a photopolymerization initiator.

[Photopolymerization initiator]
The photopolymerization initiator is not particularly limited, and can be obtained by a known method, or a commercially available photopolymerization initiator can be used. Specific examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoylbenzoic acid, methyl benzoylbenzoate, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, xanthone, anthraquinone, and 2-methylanthraquinone. These can be used alone or in combination of two or more.

[Polymerizable Monomers and Macromonomers]
The polymerizable monomers and macromonomers that can be used are not particularly limited as long as they undergo a polymerization reaction when irradiated with visible light or ionizing radiation such as ultraviolet light or electron beams, either directly or through the action of an initiator. Specific examples of polymerizable monomers having one polymerizable unsaturated group per molecule include (meth)acrylic acid esters such as (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, phenoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, methoxy-diethylene glycol (meth)acrylate, and methoxy-triethylene glycol (meth)acrylate; (meth)allyl compounds such as (meth)allyl alcohol and glycerol mono(meth)allyl ether; aromatic vinyls such as styrene, methylstyrene, and butylstyrene; carboxylic acid vinyl esters such as vinyl acetate; and (meth)acrylamides such as (meth)acrylamide, N-cyclohexyl(meth)acrylamide, N-phenyl(meth)acrylamide, and N-(2-hydroxyethyl)(meth)acrylamide. Specific examples of polymerizable monomers having two or more polymerizable unsaturated groups in one molecule include polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkyl-modified dipentaerythritol (meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, and ethylene oxide-modified isocyanuric acid tri(meth)acrylate. Specific examples of macromonomers that can be used include polymerizable urethane acrylate resins, polymerizable polyurethane resins, polymerizable acrylic resins, polymerizable epoxy resins, and polymerizable polyester resins, each of which has an average of one or more polymerizable unsaturated groups per molecule, and these can be used alone or in combination of two or more.

[Content of weather resistance imparting agent in weather resistance imparting composition]
The content of the weather resistance-imparting agent in the weather resistance-imparting composition used in the present invention can be set as desired, but when the weather resistance-imparting composition contains a resin, a polymerizable monomer, and/or a macromonomer, from the viewpoints of the physical protection function for the silver nanowire-containing conductive film and the improvement of high-temperature, high-humidity resistance by the weather resistance-imparting agent, the proportion of the weather resistance-imparting agent in the solutes in the weather resistance-imparting composition is preferably 0.001% to 5%, more preferably 0.01% to 3%, and even more preferably 0.02% to 1.5%. The proportion of the weather resistance-imparting agent in the solutes in the weather resistance-imparting composition can be determined from the mass of the weather resistance-imparting agent relative to the mass of all solutes in the weather resistance-imparting composition.

[Other additives]
Various additives may be added to the weather resistance-imparting composition within the range that does not impair the effects of the present invention. Examples of additives that can be used include organic fine particles, flame retardants, flame retardant assistants, oxidation stabilizers, leveling agents, slip enhancers, antistatic agents, dyes, and fillers.

[Step of curing polymerizable monomer and/or macromonomer]
When the weather resistance-imparting composition contains a polymerizable monomer and/or a macromonomer, the method includes a step of curing the polymerizable monomer and/or macromonomer after applying the weather resistance-imparting composition. The step of curing the polymerizable monomer and/or macromonomer is carried out by applying the weather resistance-imparting composition containing the polymerizable monomer and/or macromonomer and then irradiating it with light, and a known method can be used for this. In particular, photocuring using ultraviolet light is preferred. The light source for irradiating light can be selected as desired depending on the type of photopolymerization initiator, and examples include a high-pressure mercury lamp, a xenon lamp, a metal halide lamp, and an LED.

[(C) Step of Heat-treating the Conductive Laminate]
In the present invention, the silver nanowire-containing conductive laminate can be provided with good high-temperature, high-humidity resistance by heat treatment under the conditions described below after application of the weathering resistance-imparting composition. The timing of the heat treatment can be set arbitrarily as long as it is performed after application of the weathering resistance-imparting composition. However, if the weathering resistance-imparting composition contains a polymerizable monomer and/or a macromonomer, it is preferable to include a step of curing the polymerizable monomer and/or macromonomer between steps (B) and (C). Furthermore, from the viewpoint of quickly enhancing the protective function of the silver nanowire-containing conductive layer, it is preferable to perform the heat treatment before patterning the silver nanowire-containing conductive layer by etching. After application of the weathering resistance-imparting composition or after the step of curing the polymerizable monomer and/or macromonomer, it is also possible to laminate multiple layers other than the silver nanowire-containing conductive layer and the layer of the weathering resistance-imparting composition, such as an additional metal layer other than the silver nanowires described below. In this case, it is preferable to perform the heat treatment before forming the metal layer other than the silver nanowires, and it is even more preferable to perform the heat treatment before forming any additional layers.

[Metal layer]
The silver nanowire-containing conductive laminate can be provided with a metal layer different from the silver nanowire-containing conductive layer. The metal layer can be used, for example, as an electrode portion for electrically connecting the silver nanowire-containing conductive layer to a circuit. In this case, the metal layer can be formed after forming the silver nanowire-containing conductive layer on the substrate. When forming the metal layer after forming the silver nanowire-containing conductive layer, it is preferable to form the metal layer after applying the weather resistance-imparting composition and after the heat treatment of the present invention. Examples of metals that can be suitably used for the metal layer include metals and alloy materials such as copper, silver, gold, and nickel.

[Heat treatment conditions for conductive laminate]
In the present invention, in order to impart good high-temperature, high-humidity resistance to the silver nanowire-containing conductive laminate, it is necessary to perform heat treatment for 30 minutes or more at a temperature ranging from 40°C to 120°C. Heat treatment temperatures lower than 40°C do not provide good high-temperature, high-humidity resistance, while heat treatment temperatures higher than 120°C may result in deterioration of the substrate and the silver nanowire conductive layer. Furthermore, since better high-temperature, high-humidity resistance can be obtained by performing heat treatment at a high temperature for a long time, in addition to the above conditions, conditions are preferably such that the value of α defined by the following formula (1) is 100 or more, more preferably 500 or more, and even more preferably 1500 or more. On the other hand, a smaller α value for heat treatment is advantageous in terms of preventing deterioration of components contained in the conductive laminate, such as the substrate, and saving energy, so the value of α is preferably 1,000,000 or less, more preferably 100,000 or less.
α=t×e ^0.08×(T-40) … (1)
t: heat treatment time (min)
T: Heat treatment temperature (°C)
As can be seen from formula (1), a higher heat treatment temperature allows the preferable α value to be satisfied in a shorter heat treatment time, so the heat treatment temperature is preferably 50°C or higher, and more preferably 60°C or higher. On the other hand, a lower heat treatment temperature allows the use of materials with low heat resistance for the substrate and other layers contained in the silver nanowire-containing conductive laminate, so the heat treatment temperature is preferably 100°C or lower, and more preferably 80°C or lower. Furthermore, if the heat treatment is performed under high-humidity conditions, the product will be exposed to high-temperature, high-humidity conditions before the high-temperature, high-humidity resistance provided by the heat treatment can be imparted, so heat treatment under high-humidity conditions should be avoided. For this reason, the absolute humidity under the heat treatment conditions is preferably 200 g/ ^m³ or lower, more preferably 100 g/ ^m³ or lower, and even more preferably 50 g/ ^m³ or lower.

The manufacturing method of the present invention can provide a conductive laminate in which deterioration of conductivity under high-temperature, high-humidity conditions is suppressed compared to conventional laminates. In the present invention, the change in conductivity of the conductive laminate can be evaluated by calculating the resistance change rate (%) given by the following formula (2). The lower the resistance change rate (%), the more suppressed the deterioration of conductivity under high-temperature, high-humidity conditions is, and the higher the performance of the conductive laminate is. The sheet resistance change rate is preferably less than 35%, more preferably less than 25%, even more preferably less than 15%, and particularly preferably less than 10%. The sheet resistance of the conductive laminate can be measured using a non-contact surface resistivity meter EC-80P (manufactured by Napson Corporation) or the like.
(r2-r1)/r1×100 (%) … (2)
r1: average sheet resistance of the conductive laminate before high-temperature, high-humidity test r2: average sheet resistance of the conductive laminate after high-temperature, high-humidity test

The silver nanowire-containing conductive laminate obtained by the manufacturing method of the present invention can be widely used in various devices, such as electrode materials for liquid crystal displays, electrode materials for organic EL displays, electrode materials for electronic paper, electrode materials for touch panels, electrode materials for dye-sensitized solar cells, electrode materials for perovskite solar cells, electromagnetic wave shielding materials, and antistatic materials.

The present invention will be explained in detail below based on examples, but the present invention is not limited to these examples.

<Creating silver nanowires>
(Synthesis Example 1)
A stirrer, a thermometer, and a four-neck flask equipped with a nitrogen inlet tube were charged with nitrogen and 666.97 parts by mass of a 1.0% by mass polyvinylpyrrolidone (BASF, Sokalan (registered trademark) K90P) propylene glycol solution, 5.35 parts by mass of a 1.5% by mass sodium chloride propylene glycol solution, 1.87 parts by mass of a 2.2% by mass sodium bromide propylene glycol solution, and 162.95 parts by mass of propylene glycol were added and stirred at room temperature for 30 minutes. The internal temperature was then raised to 145 ° C., and a solution of 1.06 parts by mass of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, 4.80 parts by mass of ion-exchanged water, and 30 parts by mass of propylene glycol was added and stirred for 10 minutes. Thereafter, 127 parts by mass of a propylene glycol solution of silver nitrate with a concentration of 5.5% by mass was added over 90 minutes while maintaining the internal temperature at 145° C., and the mixture was stirred for an additional 30 minutes. The resulting solution was then cooled to obtain a reaction solution containing silver nanowires.

[Preparation of silver nanowire dispersion]
1000 parts by mass of the reaction solution containing silver nanowires was diluted with 3000 parts by mass of water and then suction filtered through a membrane filter. Water was then added to the residue, and suction filtration was repeated five times. Water was then added again to obtain a 0.15% by mass crude silver nanowire dispersion. The obtained crude silver nanowire dispersion was centrifuged at 2000 rpm for 10 minutes, and the remaining supernatant was collected to remove silver nanowires with relatively large diameters. The obtained supernatant was concentrated using a membrane filter to prepare a 0.7% by mass silver nanowire dispersion (a). The obtained silver nanowires had an average major axis length of 12 μm and an average diameter of 25 nm. A plastic container was charged with 8.57 parts by mass of a 0.7% by mass silver nanowire dispersion (a), 2.40 parts by mass of a 0.5% by mass aqueous solution of hydroxypropylmethylcellulose (Methocel 311, manufactured by The Dow Chemical Company), 0.06 parts by mass of a 0.1% by mass aqueous solution of 1,10-phenanthroline monohydrate, 8.89 parts by mass of ion-exchanged water, and 0.08 parts by mass of 1-propanol, and the container was then closed with the lid and mixed for 5 minutes on a shaker to prepare a silver nanowire dispersion (b) with a silver nanowire concentration of 0.3% by mass.

Example 1
[(A) Step of applying a silver nanowire dispersion to form a silver nanowire-containing conductive layer]
The silver nanowire dispersion liquid (b) was uniformly applied onto a 100 μm-thick polyethylene terephthalate film (PET film, manufactured by Toray Industries, Inc., product name "Lumirror (registered trademark) U403") using a No. 7 wire bar, and the applied film was dried for 2 minutes in a hot air convection dryer at 120°C to form a silver nanowire-containing conductive layer.

A four-neck flask was charged with 57.1 parts by mass of dipentaerythritol hexaacrylate and 14.3 parts by mass of trimethylolpropane triacrylate as polymerizable monomers and macromonomers, 3.6 parts by mass of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, and 25 parts by mass of diacetone alcohol as a solvent, and the mixture was stirred until a homogeneous solution was obtained, thereby preparing composition (c) containing polymerizable monomers and/or macromonomers.

[Preparation of Weather Resistance Imparting Composition]
A plastic container was charged with 1.32 parts by mass of the composition (c), 1.2 parts by mass of a 1% by mass solution of 2-mercaptothiazoline in diacetone alcohol as a weather resistance imparting agent, and 17.48 parts by mass of 1-butanol as a solvent, and the mixture was stirred until a uniform solution was obtained, thereby preparing a weather resistance imparting composition (d).

[(B) Step of applying a weather resistance imparting composition containing a specific weather resistance imparting agent]
The weather resistance-imparting composition (d) was uniformly applied to the silver nanowire-containing conductive layer prepared as described above by spin coating (3000 rpm for 30 seconds) and dried for 2 minutes in a hot air convection dryer at 70° C. Thereafter, the PET substrate was irradiated with UV light from above at 500 mJ/ ^cm2 using an ultraviolet irradiation device UV1501C-SZ (manufactured by Sen Engineering Co., Ltd.), thereby curing the polymerizable monomer and/or macromonomer, and a conductive laminate (e) was obtained.

[(C) Step of Heat-treating the Conductive Laminate]
Conductive laminate (e) was heat-treated for 30 minutes in a hot air convection dryer at 80°C to obtain conductive laminate (f). This heat treatment was not performed with humidification, and the saturated water vapor amount at 30°C or below was 50 g/ ^m³ or less, so the heat treatment conditions were an absolute humidity of 50 g/ ^m³ or less.

(Examples 2 to 18, Comparative Examples 1 to 5)
A weather resistance imparting composition (d) was prepared as shown in Table 1, and a silver nanowire-containing conductive laminate was prepared in the same manner as in Example 1, except that the heat treatment conditions were changed as shown in Table 2.

Example 19
A 0.1% by mass solution of 2-mercaptothiazoline in 1-butanol was uniformly applied by spin coating (3000 rpm for 30 seconds) onto the same silver nanowire-containing conductive layer as that prepared in step (A) of Example 1, and then dried for 2 minutes in a hot air convection dryer at 70°C to obtain a conductive laminate. Thereafter, a silver nanowire-containing conductive laminate was prepared in the same manner as in Example 1, except that the heat treatment conditions were changed as shown in Table 2.

(Example 20)
A silver nanowire-containing conductive laminate was prepared in the same manner as in Example 19, except that the 0.1 mass% 1-butanol solution of 2-mercaptothiazoline used in Example 19 was changed to a 1 mass% 1-butanol solution of 2-aminothiazole.

(Example 21)
A weather resistance-imparting composition was prepared by charging a plastic container with 9.9 parts by mass of a 7:3 solution of 10% by mass ethyl cellulose (Aqualon EC N-10, manufactured by Ashland) as a water-insoluble polymer, 1.0 part by mass of a 1% by mass solution of 2-mercaptothiazoline in 1-butanol as a weather resistance-imparting agent, and 7.0 parts by mass of toluene and 3.0 parts by mass of 1-butanol as a solvent, and stirring until a uniform solution was obtained. A silver nanowire-containing conductive laminate was produced in the same manner as in Example 19, except that this weather resistance-imparting composition was used instead of the 0.1% by mass solution of 2-mercaptothiazoline in 1-butanol used in Example 19.

Example 22
A weather resistance-imparting composition was prepared by charging a plastic container with 1.98 parts by mass of a 50% by mass acrylic resin solution (manufactured by DIC Corporation, Acrydic WXU-880-BA) as a water-insoluble polymer, 1.0 part by mass of a 1% by mass solution of 2-mercaptothiazoline in butyl acetate as a weather resistance-imparting agent, and 17.02 parts by mass of butyl acetate as a solvent, and then stirring until a homogeneous solution was obtained. A silver nanowire-containing conductive laminate was produced in the same manner as in Example 19, except that this weather resistance-imparting composition was used instead of the 0.1% by mass solution of 2-mercaptothiazoline in 1-butanol used in Example 19.

The conductive laminates produced in Examples 1 to 22 and Comparative Examples 1 to 5 were subjected to a high-temperature, high-humidity test by the following method, and the calculated results of the rate of change in resistance value before and after the high-temperature, high-humidity test are also shown in Table 2.
[High temperature and humidity test]
The conductive laminate (f) was cut into a size of 3 cm length x 10 cm width. Subsequently, the separator on one side of a glass substrate (a soda glass slide glass made by AS ONE Corporation) to which an optically elastic resin (manufactured by 3M Corporation, product name 8146-2, film thickness 50 μm) had been peeled off was peeled off, and the conductive laminate was bonded so that the optically elastic resin was disposed on the side opposite the PET substrate. The portion of the conductive laminate that protruded from the glass substrate was cut off with a cutter, yielding a sample piece in which a silver nanowire-containing conductive layer was disposed between the PET film and the glass. Thereafter, a high-temperature, high-humidity test was performed by leaving the sample standing for 1,000 hours in an environment of 85°C and 85% RH using a thermo-hygrostat tester (manufactured by Isuzu Motors, TPAV-48-20).
[Calculation of Resistance Change Rate]
The sheet resistance (Ω/□) was measured at five different locations on the PET film side of the sample piece before and after the high-temperature, high-humidity test, and the average sheet resistance of the conductive laminate before and after the high-temperature, high-humidity test and the rate of change in resistance given by the following formula (2) were calculated from the arithmetic mean value. A non-contact surface resistivity meter EC-80P (manufactured by Napson Co., Ltd.) was used to measure the sheet resistance.
(r2-r1)/r1×100 (%) … (2)
r1: average sheet resistance of the conductive laminate before high-temperature, high-humidity test; r2: average sheet resistance of the conductive laminate after high-temperature, high-humidity test. In the present invention, the rate of change in sheet resistance is required to be at least less than 35%, more preferably less than 25%, even more preferably less than 15%, and particularly preferably less than 10%.

In Examples 1 to 22, a weather resistance-imparting composition containing the weather resistance-imparting agent specified in the present invention was applied and the heat treatment conditions specified in the present invention were applied. Therefore, it can be seen that the rate of change in resistance value after high-temperature, high-humidity testing of the resulting conductive laminate was reduced compared to Comparative Example 1, in which the weather resistance-imparting composition specified in the present invention was not applied, Comparative Examples 2, 3, and 4, in which the heat treatment conditions specified in the present invention were not applied, and Comparative Examples 4 and 5, in which the weather resistance-imparting agent specified in the present invention was not used.

Compared to Example 3, Examples 1, 2, 4 to 6 have a heat treatment condition α value that is in a more preferred range, so the rate of change in resistance of the resulting conductive laminate after high-temperature, high-humidity testing is more effectively suppressed. Compared to Examples 1 and 5, Examples 2, 4 and 6 have an even more preferred α value range, so the rate of change in resistance of the resulting conductive laminate after high-temperature, high-humidity testing is even more effectively suppressed.

Compared to Example 16, Example 9 has a more preferable range of the proportion of the weather resistance agent in the solute, and therefore it can be seen that the rate of change in resistance of the resulting conductive laminate after high-temperature, high-humidity testing is more suppressed.

Bencott (registered trademark) M-1 (manufactured by Asahi Kasei Corporation) was reciprocated five times while applying a load of 100 g to the surface of the conductive laminate (f) prepared in Examples 9, 21, and 22 opposite the PET substrate, and the surface of the conductive laminate was then visually inspected to check for peeling. No peeling was observed in the conductive laminates prepared in Examples 9, 21, and 22. It can be seen that the conductive laminates prepared in Examples 9, 21, and 22, which contain a resin, polymerizable monomer, and/or macromonomer, exhibit sufficient abrasion resistance.

Claims (7)

A method for manufacturing a conductive laminate having a substrate and a silver nanowire-containing conductive layer, comprising:
(A) applying a silver nanowire dispersion to form a silver nanowire-containing conductive layer;
(B) applying a weather resistance-imparting composition containing a compound having a molecular weight of 80 to 400 and having 1 to 3 mercapto groups or a 2-aminothiazole derivative as a weather resistance-imparting agent;
A method for producing a conductive laminate, comprising step (A) followed by step (B),
After step (B),
(C) A method for producing a conductive laminate, comprising a step of heat treating at a temperature of 40°C to 120°C for 30 minutes or longer, and satisfying the following condition (A):
(a) The value α defined by the following formula (1) expressed by the temperature T (° C.) and time t (minutes) of the heat treatment in the step C is 500 or more and 100,000 or less.
α=t×e ^0.08×(T-40) …(1) The method for producing a conductive laminate according to claim 1, wherein the weather resistance-imparting composition contains a polymerizable monomer and/or macromonomer and a photopolymerization initiator, and the method includes a step of curing the polymerizable monomer and/or macromonomer between steps (B) and (C). The method for producing a conductive laminate according to claim 1, wherein the proportion of the weather resistance imparting agent in the solute contained in the weather resistance imparting composition is 0.02% to 1.5%. A method for manufacturing a conductive laminate according to any one of claims 1 to 3, wherein the diameter of the silver nanowires is 10 nm to 30 nm. A method for producing a conductive laminate according to any one of claims 1 to 3, wherein the weather resistance imparting agent is an alkanethiol having 8 to 20 carbon atoms. The method for producing a conductive laminate according to any one of claims 1 to 3, wherein the weather resistance imparting agent is 2-aminothiazole or 2-aminobenzothiazole. The method for producing a conductive laminate according to any one of claims 1 to 3, wherein the weather resistance imparting agent is either a compound having a heterocyclic structure selected from imidazole, 2-imidazoline, thiazole, 2-thiazoline, 1,3,4-thiadiazole, pyrimidine, and 1,3,5-triazine, with a mercapto group bonded to at least the second position, or a compound having a tetrazole structure with a mercapto group bonded to the fifth position, in which all mercapto groups in the molecule are bonded to carbon atoms having unsaturated bonds in the same heterocyclic ring, and the unsaturated carbons to which the mercapto groups are bonded are bonded only to sulfur or nitrogen atoms.