Sheet and production method for sheet

Abstract

The present invention addresses the problem of providing: a sheet that, when subjected to a hot press treatment at a temperature equal to or higher than a curing temperature of a thermosetting compound, is capable of forming a thermally conductive sheet having excellent thermal conductivity; and a method for manufacturing the sheet. This sheet comprises a metal nanowire and a thermosetting compound, wherein the porosity of the sheet is 20.0% or less.

Description

Sheet and method for manufacturing the sheet

[0001] The present invention relates to a sheet and a method for manufacturing the sheet.

[0002] Electronic devices using semiconductor elements are rapidly becoming more functional and smaller. Accordingly, the amount of heat generated by semiconductor elements in electronic devices is increasing, and there is a growing need to dissipate the generated heat to the outside. One method for dissipating heat generated inside an electronic device to the outside is to connect the device to a cooling mechanism (e.g., a heat sink and a container capable of introducing a refrigerant) via a thermally conductive sheet. Patent Document 1, for example, discloses a metal fiber sheet containing copper fibers as such a thermally conductive sheet.

[0003] Patent No. 6678701

[0004] A method for producing a thermally conductive sheet may involve drying a composition containing a thermally conductive material, a thermosetting compound, and a solvent to obtain a sheet, and then performing a heat press treatment at a temperature equal to or higher than the curing temperature of the thermosetting compound to cure the thermosetting compound contained in the sheet. The present inventors obtained a thermally conductive sheet by drying a composition containing a thermosetting compound, a solvent, and a fibrous metal material as described in Patent Document 1 to obtain a sheet, and then performing a heat press treatment at a temperature equal to or higher than the curing temperature of the thermosetting compound. However, they found that the thermal conductivity of the thermally conductive sheet was sometimes insufficient, leaving room for improvement.

[0005] Therefore, an object of the present invention is to provide a sheet that can be formed into a thermally conductive sheet having excellent thermal conductivity when subjected to a heat press treatment at a temperature equal to or higher than the curing temperature of the thermosetting compound, and a method for manufacturing the sheet.

[0006] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following configuration.

[0007] [1] A sheet comprising metal nanowires and a thermosetting compound, wherein the porosity of the sheet is 20.0% or less. [2] The sheet according to [1], wherein the oxidation rate of the metal nanowires is 5.0% or less. [3] The sheet according to [1] or [2], wherein the surface exposure rate of the metal nanowires is 20.0% or more. [4] The sheet according to any of [1] to [3], wherein the metal constituting the metal nanowires is copper. [5] The sheet according to any of [1] to [4], wherein the content of the metal nanowires is 30 to 80 volume % with respect to the total volume of the sheet. [6] The sheet according to any of [1] to [5], wherein the thickness of the sheet is 20 to 200 μm. [7] The sheet according to any of [1] to [6], wherein the thermosetting compound includes an epoxy compound and a phenol compound. [8] The sheet according to any of [1] to [7], wherein the molecular weight of the thermosetting compound is 1,000 or less. [9] A method for producing a sheet, comprising: drying a composition containing metal nanowires, a thermosetting compound, and a solvent to obtain a sheet; wherein the viscosity of the composition at 25°C is 100 mPa·s or less; where T is the drying temperature of the composition, Tx is the curing temperature of the thermosetting compound, and Ty is the boiling point of the solvent; the value obtained by subtracting T from Tx is 10°C or more; and the value obtained by subtracting T from Ty is -60°C or more.

[0008] According to the present invention, it is possible to provide a sheet that can be formed into a thermally conductive sheet having excellent thermal conductivity when subjected to a heat press treatment at a temperature equal to or higher than the curing temperature of a thermosetting compound, and a method for manufacturing the sheet.

[0009] FIG. 1 is a schematic cross-sectional view of a valve metal substrate before an anodization process in the procedure of an example of a method for producing metal nanowires; FIG. 2 is a schematic cross-sectional view of a structure after an anodization process in the procedure of an example of a method for producing metal nanowires; FIG. 3 is a schematic cross-sectional view of a structure after a metal filling process in the procedure of an example of a method for producing metal nanowires; FIG. 4 is a schematic cross-sectional view of a structure after an isolation process in the procedure of an example of a method for producing metal nanowires; and FIG. 5 is a schematic cross-sectional view of a structure (metal nanowires) after a crushing process in the procedure of an example of a method for producing metal nanowires.

[0010] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0011] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Furthermore, in this specification, when two or more types of a certain component are present, the "content" of that component means the total content of those two or more components. In this specification, in a numerical range described in stages, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in a numerical range described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0012] The term "step" in this specification includes not only an independent step, but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0013] In this specification, unless otherwise specified, the boiling point means the boiling point under normal pressure (1 atmosphere, 760 mmHg).

[0014] [Sheet] The sheet of the present invention (hereinafter also referred to as "the sheet") comprises metal nanowires and a thermosetting compound, and has a porosity of 20.0% or less. A thermally conductive sheet obtained by subjecting the sheet to a heat press treatment at a temperature equal to or higher than the curing temperature of the thermosetting compound exhibits excellent thermal conductivity. While the details of this reason are unclear, it is generally assumed as follows. That is, since the thermal conductivity of the voids in the sheet is low, a high porosity of the sheet reduces the thermal conductivity of the thermally conductive sheet obtained using the sheet. Furthermore, a high porosity of the sheet increases the contact area of ​​the metal nanowires with the voids (air), oxidizing the surfaces of the metal nanowires and reducing the thermal conductivity of the thermally conductive sheet obtained using the sheet. Furthermore, a high porosity of the sheet results in insufficient fusion between the metal nanowires during the heat press treatment, reducing the thermal conductivity of the thermally conductive sheet obtained using the sheet. In response to such problems, the porosity of the present sheet is 20.0% or less, which makes the above problems less likely to occur, and it is thought that this is why the thermally conductive sheet obtained after the heat press treatment has excellent thermal conductivity. In this specification, when the term "heat press treatment" is used simply, it refers to a heat press treatment performed at a temperature equal to or higher than the curing temperature of the thermosetting compound contained in the sheet, unless otherwise specified.

[0015] The porosity of the present sheet is 20.0% or less, and from the viewpoint of better effects of the present invention, it is preferably 15.0% or less, more preferably 10.0% or less, and even more preferably 5.0% or less. The lower limit of the porosity of the present sheet is 0%. The porosity of the present sheet means the ratio (%) of the area of ​​voids in the cross section of the present sheet to the sum of the area of ​​voids and the area of ​​the portion other than the voids in the cross section of the present sheet (i.e., the area of ​​the cross section of the present sheet). The porosity is determined based on the data obtained by cutting the present sheet along the thickness direction, coating the exposed cross section with platinum, and further processing it with a focused ion beam (FIB), photographing the cross section with a field emission scanning electron microscope (FE-SEM), and processing the photographed image with image processing software (ImageJ). Specific measurement methods are described in the examples below.

[0016] The thickness of the present sheet is preferably 20 to 200 μm, more preferably 50 to 170 μm, and even more preferably 80 to 120 μm, in order to obtain better effects of the present invention. The thickness of the present sheet is determined by observing the cross section of the present sheet with a scanning electron microscope (SEM) and measuring the thicknesses at any 10 points, and then calculating the arithmetic average value of the measured thicknesses.

[0017] The sheet is preferably in a B-stage state, as described in JIS K6900:1944.

[0018] This sheet is suitable for use in the manufacture of thermally conductive sheets. Thermally conductive sheets are used by directly or indirectly contacting a contacted object (e.g., a heat generating object or a heat sink) to efficiently conduct heat from the contacted object and release it to the outside. Examples of contacted objects include circuit boards, integrated circuits, power semiconductor circuits, heat spreaders, lead frames, heat sinks, copper foil, and dicing / die bonding integrated films. The thermally conductive sheet is preferably in the C-stage. The C-stage is as described in JIS K6900:1944. The thermally conductive sheet can be obtained by heat-pressing this sheet at a temperature equal to or higher than the curing temperature (described below) of the thermosetting compound contained in this sheet. The heat-pressing method is not particularly limited, and known methods can be used.

[0019] [Metal Nanowires] The present sheet contains metal nanowires. "Metal nanowires" refer to conductive materials made of metal, shaped like needles or threads, and having a diameter on the order of nanometers. Metal nanowires may be linear or curved. The material of the metal nanowires is not particularly limited as long as it contains a metal, and may contain a non-metallic component in addition to the metal. The metal nanowires may exist as aggregates (metal nanowire aggregates) in the present sheet.

[0020] In the present invention, the metal constituting the metal nanowire is not particularly limited, but it is preferable that the metal has an electrical resistivity of 10 ３It is preferable that the material has a resistivity of Ω cm or less, and specific examples thereof include gold (Au), silver (Ag), copper (Cu), aluminum (Al), titanium (Ti), nickel (Ni), and cobalt (Co), etc. Among these, from the viewpoint of thermal conductivity, Ag or Cu is preferable, and Cu is more preferable.

[0021] The diameter (arithmetic mean value) of the metal nanowires is preferably 10 to 200 nm, more preferably 10 to 100 nm, and even more preferably 10 to 50 nm. The length (arithmetic mean value) of the metal nanowires is preferably 0.3 to 300 μm, more preferably 0.5 to 200 μm, and even more preferably 1 μm to 100 μm. Here, the diameter and length of the metal nanowires can be determined, for example, by observing SEM images at 100 to 500 times magnification using a field emission scanning electron microscope (FE-SEM). Specifically, the diameter and length of the metal nanowires are determined by observing 10 metal nanowires randomly selected from SEM images taken at 100 to 500 times magnification, measuring their diameters and lengths, and performing this measurement in 10 fields of view, to determine the arithmetic mean value of the diameters and lengths of a total of 100 metal nanowires.

[0022] The ratio of the length to the diameter (length / diameter) of the metal nanowire (hereinafter also referred to as "aspect ratio") is preferably 10 or more, and more preferably 100-1000.

[0023] The oxidation rate of the metal nanowires is preferably less than 7.0%, more preferably 5.0% or less, even more preferably 4.0% or less, particularly preferably 3.0% or less, and even more preferably 2.0% or less, and more preferably 1.0% or less, in order to obtain better effects of the present invention. The lower limit of the oxidation rate of the metal nanowires is 0%. The oxidation rate of the metal nanowires can be determined based on a diffraction chart obtained by analyzing the surface of the sheet using an X-ray diffraction device. Specifically, the ratio (%) of the area of ​​the peaks derived from the metal oxide to the area of ​​the peaks derived from the metal is determined from the diffraction chart, and this value is taken as the oxidation rate of the metal nanowires. Specific measurement methods are described in the Examples below.

[0024] The surface exposure rate of the metal nanowires is preferably 15.0% or more, more preferably 20.0% or more, even more preferably 25.0% or more, and particularly preferably 30.0% or more, from the viewpoint of superior effects of the present invention. The upper limit of the surface exposure rate of the metal nanowires is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less, from the viewpoint of adhesiveness. The surface exposure rate of the metal nanowires refers to the ratio (%) of the area of ​​the metal nanowires exposed on the surface of the present sheet to the sum of the area of ​​the metal nanowires exposed on the surface of the present sheet and the area of ​​the portions other than the metal nanowires exposed on the surface of the present sheet (i.e., the area of ​​the present sheet surface). The surface exposure rate of the metal nanowires is determined based on the data obtained by photographing an image of the surface of the present sheet under magnification observation with an optical microscope and processing the photographed image using image processing software (ImageJ). Specific measurement methods are described in the Examples below.

[0025] The metal nanowire content is preferably 30 to 80 volume %, more preferably 35 to 75 volume %, and even more preferably 40 to 70 volume %, relative to the total volume of the sheet. When the metal nanowire content is 30 volume % or more, the effects of the present invention are more excellent. Furthermore, when the metal nanowire content is 80 volume % or less, the sheet exhibits good adhesion when bonded to an object. The metal nanowire content may be determined from the amount of metal nanowires used in preparing the sheet, or from a cross-sectional image of the sheet. The method for determining the metal nanowire content (volume %) from the amount of metal nanowires used in preparing the sheet is as follows: The weight (solid content) of each component used in producing the sheet is divided by the theoretical specific gravity of each component to determine the volume of each component (solid content) in the sheet. The volume occupied by the metal nanowires is then divided by the sum of the volumes of each component (solid content) in the sheet to obtain the metal nanowire content (vol %). The method for determining the metal nanowire content from a cross-sectional image of the sheet is as follows: The sheet is cut along the thickness direction, the exposed cross-section is photographed with a scanning electron microscope (SEM), and the photographed image is processed with image processing software (ImageJ) to obtain data. In this case, the metal nanowire content is calculated as the ratio (%) of the area of ​​the metal nanowires in the cross-section of the sheet to the area of ​​the cross-section of the sheet, and is considered to be a volumetric percentage (volume %).

[0026] The content of the metal nanowires is preferably 75 to 95 mass %, more preferably 80 to 95 mass %, and even more preferably 85 to 95 mass %, based on the total mass of the sheet. When the content of the metal nanowires is 75 mass % or more, the effects of the present invention are more excellent. Furthermore, when the content of the metal nanowires is 95 mass % or less, the strength of the sheet is more excellent.

[0027] <Metal Nanowire Manufacturing Method> One example of a metal nanowire manufacturing method includes an anodizing step of forming a porous anodized film on the surface of a valve metal substrate, a metal filling step of filling the pores with metal, an isolation step of isolating the filled metal from the anodized film and the valve metal substrate, and a crushing step of crushing the isolated metal (hereinafter also abbreviated as "isolated metal") to obtain metal nanowires. When metal nanowires obtained by this method are used to manufacture the present sheet, the effects of the present invention are more excellent.

[0028] Next, an outline of each step in the method for producing metal nanowires will be described using FIGS. 1A to 1E, and then each processing step will be described in detail.

[0029] As shown in Figures 1A and 1B, in the anodizing step, an anodizing treatment is performed on the surface of a valve metal substrate 1, and an anodized film 3 having pores (micropores) 2 is formed on the surface of the valve metal substrate 1. Next, as shown in Figure 1C, in the metal filling step, a metal 4 is filled into the pores 2. Next, as shown in Figure 1D, in the isolation step, the filled metal 4 is isolated from the anodized film 3 and the valve metal substrate 1. Note that the embodiment shown in Figure 1D shows the state in which the isolated metal 5 obtained in the isolation step has been collected (a state in which part of the isolated metal is adhered). Next, as shown in Figure 1E, in the crushing step, metal nanowires 10 in which the isolated metal 5 has been crushed can be obtained.

[0030] (Valve Metal Substrate) The valve metal substrate used in the method for producing metal nanowires is not particularly limited as long as it is a substrate containing a valve metal. Specific examples of valve metals include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Among these, aluminum is preferred because it has good dimensional stability and is relatively inexpensive. Therefore, in the method for producing metal nanowires, it is preferred to use a substrate containing aluminum (hereinafter abbreviated as "aluminum substrate") as the valve metal substrate.

[0031] The aluminum substrate is not particularly limited, and specific examples thereof include a pure aluminum plate; an alloy plate containing aluminum as the main component and trace amounts of other elements; a substrate in which high-purity aluminum is vapor-deposited onto low-purity aluminum (for example, recycled material); a substrate in which the surface of a silicon wafer, quartz, glass, or the like is coated with high-purity aluminum by a method such as vapor deposition or sputtering; and a resin substrate laminated with aluminum.

[0032] In the valve metal substrate, the surface to be anodized in the anodizing step described below preferably has a valve metal purity of 99.5% by mass or more, more preferably 99.9% by mass or more, and even more preferably 99.99% by mass or more. When the valve metal purity is within the above range, the arrangement of the through-holes becomes sufficiently regular.

[0033] In addition, the surface of the valve metal substrate that is to be anodized in the anodizing step described below is preferably subjected to heat treatment, degreasing treatment, and mirror finish treatment in advance. Here, the heat treatment, degreasing treatment, and mirror finish treatment can be the same as the treatments described in paragraphs

[0044] to

[0054] of JP 2008-270158 A.

[0034] (Anodizing Step) The anodizing step is a step of forming a porous anodic oxide film on the surface of the valve metal base by anodizing the surface of the valve metal base.

[0035] The anodizing treatment performed in the anodizing step can be a conventionally known method, but it is preferable to use a self-ordering method or constant voltage treatment because it allows the filled metal to be isolated with little variation in diameter in the isolation step described below. Here, the self-ordering method and constant voltage treatment in the anodizing treatment can be the same as the treatments described in paragraphs

[0056] to

[0108] and [Figure 3] of JP2008-270158A.

[0036] For example, anodizing treatment can be performed by passing a current through a solution having an acid concentration of 1 to 10% by mass, using the valve metal substrate as the anode. The solution used for anodizing treatment is preferably an acid solution, more preferably sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid, glycolic acid, tartaric acid, malic acid, or citric acid, even more preferably sulfuric acid, phosphoric acid, or oxalic acid, and particularly preferably oxalic acid. These acids can be used alone or in combination of two or more.

[0037] The conditions for the anodizing treatment cannot be determined in general because they vary depending on the electrolyte used, but generally, the electrolyte concentration is 0.1 to 20 mass%, the solution temperature is −10 to 30° C., and the current density is 0.01 to 20 A / dm ２ The voltage is preferably 3 to 300 V, the electrolysis time is preferably 0.5 to 30 hours, the electrolyte concentration is 0.5 to 15 mass %, the solution temperature is −5 to 25° C., and the current density is 0.05 to 15 A / dm ２ , the voltage is 5 to 250 V, the electrolysis time is 1 to 25 hours, the electrolyte concentration is 1 to 10 mass%, the solution temperature is 0 to 20°C, and the current density is 0.1 to 10 A / dm ２ More preferably, the voltage is 10 to 200 V and the electrolysis time is 2 to 20 hours.

[0038] The treatment time for the anodizing treatment is preferably 0.5 minutes to 16 hours, more preferably 1 minute to 12 hours, and even more preferably 2 minutes to 8 hours.

[0039] The thickness of the anodic oxide film formed by the anodization step is not particularly limited, but from the viewpoint of adjusting the length of the metal nanowires, it is preferably 0.3 to 300 μm, more preferably 0.5 to 120 μm, and even more preferably 0.5 to 100 μm. The thickness of the anodic oxide film can be calculated by cutting the anodic oxide film in the thickness direction with a focused ion beam (FIB), taking surface photographs (magnification 50,000 times) of the cross section with a field emission scanning electron microscope (FE-SEM), and averaging the measurements at 10 points.

[0040] The density of the pores formed by the anodization process is not particularly limited, but is preferably 2 million / mm２ It is preferable that the density is 10 million / mm or more. ２ More preferably, it is 50 million particles / mm or more. ２ More preferably, it is 100 million particles / mm ２ The density of the porous layer can be measured and calculated by the method described in paragraphs

[0168] and

[0169] of JP-A-2008-270158.

[0041] The average opening diameter of the pores formed by the anodization step is not particularly limited, but from the viewpoint of adjusting the diameter of the metal nanowires, it is preferably 5 to 500 nm, more preferably 20 to 400 nm, even more preferably 40 to 200 nm, and particularly preferably 50 to 100 nm. The average opening diameter of the pores can be calculated by taking a surface photograph (magnification 50,000 times) with an FE-SEM and measuring 50 points, and averaging the results.

[0042] (Metal Filling Step) The metal filling step is a step of filling the interior of the pores with metal after the anodizing step.

[0043] Metal Examples of the metal include the same metals as those described as the metals constituting the metal nanowires.

[0044] Filling Method Examples of a method for filling the interior of the porous structure with the metal include the methods described in paragraphs

[0123] to

[0126] and [FIG. 4] of JP-A-2008-270158.

[0045] In the method for producing metal nanowires, the metal filling step preferably includes a plating step, because this reduces the likelihood of voids being included in the resulting metal nanowires. Specifically, electrolytic plating is preferably used as a method for filling the interior of the pores with the metal. For example, electrolytic plating or electroless plating can be used. Here, conventional electrolytic plating methods used for coloring and the like have difficulty selectively depositing (growing) metal in pores with a high aspect ratio. This is thought to be because the deposited metal is consumed within the pores, preventing plating growth even after electrolysis for a certain period of time. Therefore, in the method for producing metal nanowires, when filling metal using electrolytic plating, a rest period must be provided between pulse electrolysis and constant-potential electrolysis. The rest period must be at least 10 seconds, preferably 30 to 60 seconds. Ultrasonic application is also desirable to promote stirring of the electrolyte. Furthermore, the electrolysis voltage is typically 20 V or less, preferably 10 V or less. However, it is preferable to measure the deposition potential of the target metal in the electrolyte in advance and perform constant-potential electrolysis within +1 V of that potential. When performing constant potential electrolysis, it is desirable to use a device that can also be used with cyclic voltammetry, and potentiostat devices such as those manufactured by Solartron, BAS, Hokuto Denko, and IVIUM can be used.

[0046] A conventionally known plating solution can be used. Specifically, when depositing copper, an aqueous copper sulfate solution is generally used, with the copper sulfate concentration preferably being 1 to 300 g / L, and more preferably being 100 to 200 g / L. The addition of hydrochloric acid to the electrolytic solution can also promote deposition. In this case, the hydrochloric acid concentration is preferably 10 to 20 g / L. When depositing gold, it is desirable to use a sulfuric acid solution of gold tetrachloride and perform plating using AC electrolysis.

[0047] In electroless plating, it takes a long time to completely fill the pores of high aspect ratio porous material with metal, so in the method for producing metal nanowires, it is desirable to fill the metal by electrolytic plating.

[0048] In the method for producing metal nanowires, it is preferable to use a processing method that combines AC electroplating and DC electroplating in this order as the electroplating processing method. Here, in AC electroplating, for example, a voltage is applied that is modulated into a sine wave at a predetermined frequency. Note that the waveform when modulating the voltage is not limited to a sine wave, and can also be, for example, a square wave, a triangular wave, a sawtooth wave, or an inverted sawtooth wave. In addition, in DC electroplating, the processing method in the electroplating method described above can be used as appropriate.

[0049] In the method for manufacturing metal nanowires, it is preferable that the metal filling in the metal filling step be a process performed on the region from the bottom of the hole to halfway through the opening, out of the entire region from the bottom of the hole to the opening, as shown in Figure 1C, in order to shorten the time required to manufacture the metal nanowires.

[0050] (Isolation process) The isolation process is a process of isolating the filled metal from the anodized film and the valve metal base material after the metal filling process. Here, the method of isolating the filled metal from the anodized film and the valve metal base material is not particularly limited, and for example, a method of removing (for example, dissolving, peeling, etc.) the anodized film and the valve metal base material and isolating the filled metal can be preferably mentioned. Therefore, the embodiment after the isolation process also includes, for example, an embodiment in which the filled metal is dispersed in an isolated state in the treatment liquid used in the dissolution process (dissolution treatment) described later.

[0051] In the method for producing metal nanowires, the method for removing the anodic oxide film and the valve metal substrate is not particularly limited, and may be, for example, removal by polishing. However, in order to ensure that the length of the produced metal nanowires is uniform, it is preferable that the isolation process includes a dissolution process, i.e., that at least a portion of the anodic oxide film and the valve metal substrate is removed by dissolution treatment.

[0052] In the method for producing metal nanowires, in order to maintain the shape and size of the produced metal nanowires, it is preferable that the isolation step includes a single-step removal step of removing the anodic oxide film and the valve metal substrate, and it is more preferable that the anodic oxide film is removed by a dissolution treatment. Also, for the same reason, the isolation step may include a two-step removal step of removing the valve metal substrate and then removing the anodic oxide film, and in this case, it is more preferable that both of the two removal steps are removed by a dissolution treatment.

[0053] Removal of the valve metal substrate: The removal of the valve metal substrate is preferably a dissolution treatment using a treatment liquid that is less likely to dissolve the anodized film but is more likely to dissolve the valve metal. The dissolution rate of such a treatment liquid for the valve metal is preferably 1 μm / min or more, more preferably 3 μm / min or more, and even more preferably 5 μm / min or more. Similarly, the dissolution rate for the anodized film is preferably 0.1 nm / min or less, more preferably 0.05 nm / min or less, and even more preferably 0.01 nm / min or less. Specifically, the treatment liquid preferably contains at least one metal compound with a lower ionization tendency than the valve metal, and has a pH of 4 or less or 8 or more, more preferably 3 or less or 9 or more, and even more preferably 2 or less or 10 or more.

[0054] Such treatment solutions are preferably based on an acid or alkaline aqueous solution and contain, for example, compounds of manganese, zinc, chromium, iron, cadmium, cobalt, nickel, tin, lead, antimony, bismuth, copper, mercury, silver, palladium, platinum, and gold (e.g., chloroplatinic acid), fluorides thereof, and chlorides thereof. Among these, an acid aqueous solution base is preferred, and blending of chlorides is preferable. In particular, treatment solutions blended with mercury chloride in an aqueous hydrochloric acid solution (hydrochloric acid / mercury chloride) and treatment solutions blended with copper chloride in an aqueous hydrochloric acid solution (hydrochloric acid / copper chloride) are preferred from the viewpoint of treatment latitude. The composition of such treatment solutions is not particularly limited, and examples that can be used include a bromine / methanol mixture, a bromine / ethanol mixture, and aqua regia.

[0055] The acid or alkali concentration of such a treatment solution is preferably 0.01 to 10 mol / L, more preferably 0.05 to 5 mol / L. Furthermore, the treatment temperature using such a treatment solution is preferably −10° C. to 80° C., more preferably 0° C. to 60° C.

[0056] The valve metal substrate is removed by contacting the valve metal substrate after the metal filling step with the treatment solution. The contact method is not particularly limited, and examples thereof include immersion and spraying. Of these, the immersion method is preferred. The contact time is preferably 10 seconds to 5 hours, more preferably 1 minute to 3 hours.

[0057] Removal of the anodic oxide film The anodic oxide film can be removed using a solvent that does not dissolve the metal filled in the pores but selectively dissolves the anodic oxide film, and either an alkaline aqueous solution or an acid aqueous solution can be used.

[0058] When an alkaline aqueous solution is used, it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and it is more preferable to use an aqueous solution of potassium hydroxide. The concentration of the alkaline aqueous solution is preferably 1 to 30% by mass. The temperature of the alkaline aqueous solution is preferably 10 to 60°C, more preferably 20 to 60°C, and even more preferably 30 to 60°C. On the other hand, when an acid aqueous solution is used, it is preferable to use an aqueous solution of an inorganic acid such as chromic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, or oxalic acid, or a mixture thereof, and it is more preferable to use an aqueous solution of chromic acid. The concentration of the acid aqueous solution is preferably 1 to 30% by mass. The temperature of the acid aqueous solution is preferably 15 to 80°C, more preferably 20 to 60°C, and even more preferably 30 to 50°C.

[0059] The anodic oxide film is removed by contacting the substrate with the alkaline aqueous solution and the acid aqueous solution described above after the metal filling step (preferably after the valve metal substrate is removed). The contacting method is not particularly limited, and examples thereof include immersion and spraying. Of these, the immersion method is preferred. The immersion time in the alkaline aqueous solution and the acid aqueous solution is preferably 1 to 120 minutes, more preferably 2 to 90 minutes, even more preferably 3 to 60 minutes, and particularly preferably 3 to 30 minutes. Of these, 3 to 20 minutes is preferred, and 3 to 10 minutes is more preferred.

[0060] (Crushing Step) The crushing step is a step of crushing the isolated metal after the isolation step. The method for crushing the isolated metal is not particularly limited, but a suitable example is a method of crushing the isolated metal by impacting it in a liquid. The liquid (solvent) used for crushing is not particularly limited as long as it does not alter or dissolve the isolated metal. Examples include water, ethanol, methanol, acetone, methyl ethyl ketone, butanol, ethyl acetate, butyl acetate, tetrahydrofuran, toluene, dimethylformamide, cyclohexane, and cyclohexanone. Among these, water is preferred from the perspective of safety. Furthermore, the crushing step is preferably performed in water or an aqueous solution with an alkali or acid concentration of less than 1% by mass, from the perspective of producing metal nanowires with high bonding strength upon bonding. Examples of crushing treatments include a crushing treatment using cavitation and a crushing treatment using ceramic balls. Devices such as an ultrasonic cleaner, an ultrasonic homogenizer, a jet mill, and a wet atomizer can be used. Among these, the crushing treatment using cavitation or the crushing treatment using ceramic balls is preferred, and the crushing treatment using cavitation is more preferred.

[0061] In the present invention, the concentration of the isolated metal in the liquid during pressure-disintegration in the liquid is preferably 0.1 to 50 mass%, because this results in uniform treatment and improved productivity. Furthermore, the concentration of the isolated metal in the liquid during pressure-disintegration in the liquid is more preferably 0.5 to 30 mass%, and even more preferably 1 to 10 mass%, because this allows metal nanowires with higher bonding strength to be obtained upon bonding.

[0062] (Drying Step) The method for producing metal nanowires preferably further includes a drying step of drying the isolated metal between the isolation step and the crushing step. Here, the method for drying the isolated metal is not particularly limited, but after removing the anodized film and the valve metal substrate, the isolated metal can be recovered and dried by performing a separation operation such as filtration using a filter or centrifugation.

[0063] (Protective Layer Forming Step) The method for producing metal nanowires preferably further includes, after the isolation step (or after the drying step if the method includes the drying step), a step of forming a protective layer on the isolated metal (metal nanowires) using at least one agent selected from the group consisting of a corrosion inhibitor and a silane coupling agent, in order to reduce the oxidation rate of the metal nanowires. The protective layer forming step is preferably carried out after the "reducing or removing step" described below.

[0064] Corrosion Inhibitor The corrosion inhibitor is not particularly limited, and known corrosion inhibitors can be used. Examples of corrosion inhibitors include compounds containing at least one of a nitrogen atom, an oxygen atom, and a sulfur atom. From the viewpoint of durability, the corrosion inhibitor is preferably a heterocyclic compound containing at least one of a nitrogen atom and an oxygen atom, more preferably a compound containing a five-membered ring structure containing one or more nitrogen atoms, and particularly preferably at least one compound selected from the group consisting of compounds containing an imidazole structure, compounds containing a triazole structure, compounds containing a tetrazole structure, compounds containing a benzimidazole structure, and compounds containing a thiadiazole structure. The five-membered ring structure containing one or more nitrogen atoms may be a monocyclic structure or a partial structure constituting a fused ring.

[0065] Furthermore, the corrosion inhibitor is preferably a compound containing at least one of a polar group-containing acid and a polar group-containing base, because this facilitates adsorption to the surface of the isolated metal. Examples of the polar group contained in the polar group-containing acid and the polar group-containing base include a carboxylic acid group (carboxy group), a sulfonic acid group (sulfo group), a phosphonic acid group, a phosphate group, a primary to quaternary ammonium base, a carboxylate group, a sulfonate group, a phosphonate group, and a phosphate group.

[0066] Furthermore, the corrosion inhibitor is preferably a compound containing a carboxy group, since it bonds with metal ions to form complex ions, which facilitates protection of the surface of the isolated metal.

[0067] Specific examples of the corrosion inhibitor include imidazole, benzimidazole, 1,2,4-triazole, benzotriazole (BTA), tolyltriazole (TTA), butylbenzyltriazole, alkyldithiothiadiazole, alkylthiol, 2-aminopyrimidine, 5,6-dimethylbenzimidazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole (DMTDA), 2-mercaptopyrimidine, 2-mercaptobenzoxazole, 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole.

[0068] Other specific examples of the corrosion inhibitor include aliphatic carboxylic acids such as acetic acid, propionic acid, palmitic acid, stearic acid, lauric acid, arachidic acid, terephthalic acid, and oleic acid; carboxylic acids such as glycolic acid, lactic acid, oxalic acid, malic acid, tartaric acid, and citric acid; aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), ethylenediaminediacetic acid (EDDA), and ethylene glycol diethyl ether diaminetetraacetic acid (GEDA); uric acid; gallic acid; and thiourea.

[0069] The corrosion inhibitor may be used alone or in combination of two or more. In order to improve stability over time, the corrosion inhibitor preferably contains a compound containing a nitrogen atom (nitrogen-containing compound), more preferably a nitrogen-containing compound, and even more preferably a heterocyclic compound containing at least one of a nitrogen atom and a sulfur atom.

[0070] Among these, the corrosion inhibitor is preferably at least one selected from the group consisting of a compound containing an imidazole structure, a compound containing a triazole structure, a compound containing a tetrazole structure, and thiourea, in terms of better effects of the present invention.

[0071] Silane Coupling Agents The silane coupling agent is not particularly limited, and examples thereof include dimethyldimethoxysilane, dimethyldiethoxysilane, methylethyldimethoxysilane, methylethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, decyltrimethoxysilane, phenyltriethoxysilane, p-styryltrimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 2-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3 ... Examples of suitable silane coupling agents include N-acryloxypropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-(3,4-epoxycyclohexyl), N-2(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-ureidopropyltrialkoxysilanetris-(trimethoxysilylpropyl)isocyanurate, and methyltriisocyanatosilane. These silane coupling agents may be used alone or in combination of two or more. Among these, silane coupling agents having an epoxy group are preferred because they can further reduce the oxidation rate of the metal nanowires.

[0072] As the silane coupling agent, commercially available products can be used, for example, KA-1003, KBM-1003, KBE-1003, KBM-303, KBM-402, KBM-403, KBE-402, KBE-403, KBM-1403, KBM-502, KBM-503, KBE-502, KBE-503, KBM-5103, KBM-602, KBM-603, KBE-603, KBM-903, KBE-903, K BE-9103, KBM-573, KBM-575, KBM-6123, KBE-585, KBM-703, KBM-802, KBM-803, KBE-846, KBE-9007, KBM-04, KBE-04, KBM-13, KBE-13, KBE-22, KBE-103, HMDS-3, KBM-3063, KBM-3103C, KPN-3504 and KF-99 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0073] The method for forming such a protective layer is not particularly limited, and examples thereof include a method in which the isolated metal recovered in the drying step is added to an aqueous solution containing a corrosion inhibitor and / or a silane coupling agent and stirred; a method in which a corrosion inhibitor and / or a silane coupling agent is added to a washing solvent used to wash the isolated metal recovered in the drying step; and a method in which a composition containing at least one selected from the group consisting of a corrosion inhibitor and a silane coupling agent (see the sheet manufacturing method described below) is used to manufacture the sheet.

[0074] (Reduction or Removal Step) In order to reduce the oxidation rate of the metal nanowires contained in the sheet, the method for producing metal nanowires preferably further includes a step of reducing or removing the surface oxide layer of the isolated metal (metal nanowires) between the isolation step and the crushing step (or before the drying step if the drying step is included). Examples of the reduction or removal step include a step of performing an immersion treatment using an aqueous alkaline solution or an aqueous acid solution, as described in the above-mentioned treatment for removing an anodic oxide film. Furthermore, the aqueous acid solution used in this step may be a citric acid solution in addition to the aqueous acid solutions described in the above-mentioned treatment for removing an anodic oxide film.

[0075] [Thermosetting Compound] The present sheet contains a thermosetting compound. The thermosetting compound is a compound that begins to cure when heated at a curing temperature or higher, and preferably has a curable group. Examples of the curable group include an epoxy group (oxiranyl group) and an active hydrogen group (described below). The thermosetting compound may be either a polymer or a monomer.

[0076] The molecular weight of the thermosetting compound is preferably 1,000 or less, more preferably 750 or less, and even more preferably 500 or less, from the viewpoint of achieving better effects of the present invention. The lower limit of the molecular weight of the thermosetting compound is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more, from the viewpoint of viscosity. When two or more types of thermosetting compounds are used, it is preferable that the molecular weights of all types of thermosetting compounds satisfy the above value, from the viewpoint of achieving better effects of the present invention.

[0077] Examples of thermosetting compounds include epoxy compounds, oxetane compounds, acrylic compounds, methacrylic compounds, benzoguanamine compounds, rosin-modified maleic acid compounds, rosin-modified fumaric acid compounds, melamine compounds, urea compounds, and active hydrogen group-containing compounds. Only one type of thermosetting compound may be contained, or two or more types may be contained. Among these, in order to achieve better effects of the present invention, it is preferable that the thermosetting compound contains at least one type selected from the group consisting of epoxy compounds and active hydrogen group-containing compounds (e.g., phenolic compounds), and it is preferable that the thermosetting compound contains both an epoxy compound and a phenolic compound.

[0078] The curing temperature of the thermosetting compound (corresponding to the curing temperature Tx described below) is preferably 80 to 220° C., more preferably 100 to 200° C., and even more preferably 120 to 180° C. Here, the curing temperature of the thermosetting compound is the temperature at which curing of the thermosetting compound begins, and specifically means the temperature at which an exothermic peak due to curing rises in differential scanning calorimetry (DSC) of the thermosetting compound.

[0079] The content of the thermosetting compound is preferably 5 to 25% by mass, more preferably 5 to 20% by mass, and even more preferably 5 to 15% by mass, relative to the total mass of the sheet. When the content of the thermosetting compound is 5% by mass or more, the strength of the sheet is superior. Furthermore, when the content of the thermosetting compound is 25% by mass or less, the effects of the present invention are superior. While the mass-based thermosetting compound content (mass%) is shown, the volume-based thermosetting compound content (volume%) can be calculated as follows. The charged weight (solid content) of each component used in producing the sheet is divided by the theoretical specific gravity of each component to determine the volume of each component (solid content) in the sheet. The volume occupied by the thermosetting compound is then divided by the sum of the volumes of each component (solid content) in the sheet to obtain the thermosetting compound content (volume%).

[0080] <Epoxy Compound> An epoxy compound is a compound having one or more epoxy groups. However, in this specification, compounds having a silyl group and an epoxy group are not classified as epoxy compounds, but are classified as the above-mentioned silane coupling agents. An epoxy group is a group formed by removing one or more hydrogen atoms (preferably one hydrogen atom) from an oxirane ring. If possible, the epoxy group may further have a substituent. Examples of the substituent include a linear or branched alkyl group having 1 to 5 carbon atoms and an aromatic ring group such as an aromatic hydrocarbon ring group. The number of epoxy groups in the epoxy compound is preferably 2 or more, more preferably 2 to 40, even more preferably 2 to 10, and particularly preferably 2.

[0081] The epoxy compound may be either liquid crystalline or non-liquid crystalline, that is, the epoxy compound may be a liquid crystalline compound having an epoxy group.

[0082] The epoxy compound is preferably a polyhydroxy aromatic ring-type glycidyl ether (a polyhydroxy aromatic ring-type epoxy compound). A polyhydroxy aromatic ring-type glycidyl ether is a compound having a structure in which an aromatic ring having two or more (preferably 2 to 6, more preferably 2 or 3, and even more preferably 2) hydroxy groups as substituents has been glycidyl-etherified at the two or more hydroxy groups. The aromatic ring may be either an aromatic hydrocarbon ring or an aromatic heterocycle, with an aromatic hydrocarbon ring being preferred. The aromatic ring may be either a monocyclic or polycyclic ring. The aromatic ring preferably has 5 to 15 ring members, more preferably 6 to 12, and even more preferably 6. The aromatic ring may have a substituent other than a hydroxy group. An example of the polyhydroxy aromatic ring-type glycidyl ether is 1,3-phenylenebis(glycidyl ether).

[0083] Examples of the epoxy compound include a compound having a partially rod-like structure (rod-like compound) and a discotic compound having a partially discotic structure.

[0084] The epoxy compound may be a commercially available product, and examples thereof include bisphenol F type epoxy compounds such as EPICLON (registered trademark) EXA-830CRP, EXA-830LVP, and EXA-835LV (all of which are trade names manufactured by DIC Corporation). The epoxy compounds may be used alone or in combination of two or more.

[0085] From the viewpoint of achieving superior effects of the present invention, the molecular weight of the epoxy compound is preferably 1,000 or less, more preferably 750 or less, and even more preferably 500 or less. From the viewpoint of viscosity, the lower limit of the molecular weight of the epoxy compound is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more.

[0086] The epoxy equivalent of the epoxy compound is preferably 100 to 250 g / eq, more preferably 120 to 220 g / eq, and even more preferably 140 to 190 g / eq. The epoxy equivalent is the mass of the epoxy compound per equivalent of epoxy groups and can be measured in accordance with JIS K7236 (2009).

[0087] The content of the epoxy compound is preferably 3 to 17% by mass, more preferably 3 to 13% by mass, and even more preferably 3 to 10% by mass, based on the total mass of the sheet. If the content of the epoxy compound is 3% by mass or more, the strength of the sheet is superior. Furthermore, if the content of the epoxy compound is 17% by mass or less, the effects of the present invention are superior.

[0088] <Active Hydrogen Group-Containing Compound> The active hydrogen group-containing compound is a compound having one or more (preferably two or more, more preferably 2 to 10) groups having active hydrogen (active hydrogen groups). Examples of the active hydrogen group include a hydroxy group, a primary amino group, a secondary amino group, and a mercapto group, with a hydroxy group being preferred. The active hydrogen group-containing compound is preferably a polyol having two or more (preferably three or more, more preferably 3 to 6) hydroxy groups.

[0089] When the sheet contains an epoxy compound and an active hydrogen group-containing compound, the active hydrogen group-containing compound is preferably a phenolic compound having one or more (preferably two or more, more preferably three or more, and even more preferably three to six) phenolic hydroxyl groups.

[0090] The phenol compound preferably has a triazine skeleton. The phenol compound "having a triazine skeleton" means that the phenol compound has one or more (preferably 1 to 5) triazine ring groups.

[0091] Examples of the active hydrogen group-containing compound include benzene polyols such as benzenetriol, biphenyl aralkyl phenol resins, phenol novolac resins, cresol novolac resins, aromatic hydrocarbon formaldehyde resin-modified phenol resins, dicyclopentadiene phenol addition resins, phenol aralkyl resins, polyhydric phenol novolac resins synthesized from polyhydric hydroxy compounds and formaldehyde, naphthol aralkyl resins, trimethylolmethane resins, tetraphenylolethane resins, naphthol novolac resins, naphtholphenol co-condensed novolac resins, naphthol-cresol co-condensed novolac resins, biphenyl-modified phenol resins, biphenyl-modified naphthol resins, aminotriazine-modified phenol resins, and alkoxy group-containing aromatic ring-modified novolac resins.

[0092] The active hydrogen group-containing compound may be a commercially available product, and examples thereof include BIR-PC (a phenolic compound manufactured by Asahi Organic Chemicals Co., Ltd.) and phenolic resin manufactured by Sumitomo Bakelite Co., Ltd. The active hydrogen group-containing compound may be used alone or in combination of two or more types.

[0093] The hydroxy group content of the active hydrogen group-containing compound is preferably 3.0 mmol / g or more, more preferably 4.0 mmol / g or more. The upper limit is preferably 25.0 mmol / g or less, more preferably 20.0 mmol / g or less. The hydroxy group content refers to the number of moles of hydroxy groups (preferably phenolic hydroxyl groups) contained in 1 g of the active hydrogen group-containing compound. In addition to hydroxy groups, the active hydrogen group-containing compound may also have an active hydrogen-containing group (e.g., a carboxy group) capable of polymerizing with an epoxy compound. The active hydrogen content (the total content of hydrogen atoms in hydroxy groups and carboxy groups) of the active hydrogen group-containing compound is preferably 3.0 mmol / g or more, more preferably 4.0 mmol / g or more. The upper limit is preferably 25.0 mmol / g or less, more preferably 20.0 mmol / g or less. The active hydrogen content refers to the number of moles of active hydrogen atoms contained in 1 g of the active hydrogen group-containing compound.

[0094] From the viewpoint of achieving superior effects of the present invention, the molecular weight of the active hydrogen group-containing compound (preferably a phenol compound) is preferably 1,000 or less, more preferably 750 or less, and even more preferably 500 or less. From the viewpoint of viscosity, the lower limit of the molecular weight of the active hydrogen group-containing compound (preferably a phenol compound) is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more.

[0095] The content of the active hydrogen group-containing compound (preferably a phenol compound) is preferably 2 to 8 mass %, more preferably 2 to 7 mass %, and even more preferably 2 to 5 mass %, based on the total mass of the sheet. If the content of the active hydrogen group-containing compound is 2 mass % or more, the strength of the sheet is superior. Furthermore, if the content of the active hydrogen group-containing compound is 8 mass % or less, the effects of the present invention are superior.

[0096] When the thermosetting compound contains an epoxy compound and an active hydrogen group-containing compound (preferably a phenolic compound), the epoxy compound and the active hydrogen group-containing compound are preferably contained in the sheet so that the epoxy groups of the epoxy compound react with the active hydrogen groups of the active hydrogen group-containing compound in equivalent amounts. For example, when the epoxy compound contains two epoxy groups and the active hydrogen group-containing compound contains five active hydrogen groups, the epoxy compound and the active hydrogen group-containing compound are preferably contained in the sheet so that the molar ratio of epoxy compound to active hydrogen group-containing compound is 5:2. When the thermosetting compound contains an epoxy compound and an active hydrogen group-containing compound (preferably a phenolic compound), the total content of the epoxy compound and the active hydrogen group-containing compound is preferably 20 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 90 to 100% by mass, based on the total mass of the thermosetting compound.

[0097] [Other Components] The present sheet may contain components other than those described above (hereinafter also referred to as "other components"). Specific examples of other components include the various components that may be contained in the present composition described below, their decomposition products, and their reaction products. The other components may be used alone or in combination of two or more.

[0098] [Method for Manufacturing Sheet] The sheet manufacturing method of the present invention (hereinafter also referred to as "this manufacturing method") includes a step of drying a composition containing metal nanowires, a thermosetting compound, and a solvent (hereinafter also referred to as "this composition") to obtain a sheet (hereinafter also referred to as "drying step"), wherein the viscosity of this composition at 25°C is 100 mPa·s or less, and where T is the drying temperature of the composition, Tx is the curing temperature of the thermosetting compound, and Ty is the boiling point of the solvent, the value obtained by subtracting T from Tx is 10°C or more, and the value obtained by subtracting T from Ty is -60°C or more. This manufacturing method is an example of a suitable embodiment of the method for manufacturing the above-mentioned present sheet. According to this manufacturing method, the above-mentioned present sheet can be easily obtained.

[0099] [Present Composition] The present composition contains metal nanowires, a thermosetting compound, and a solvent, and preferably further contains at least one selected from the group consisting of a corrosion inhibitor and a silane coupling agent.

[0100] <Metal Nanowires> The metal nanowires contained in the present composition are the same as the metal nanowires contained in the present sheet described above, including preferred embodiments. In particular, the metal nanowires contained in the present composition are preferably metal nanowires obtained by the above-mentioned "reduction or removal step," since the present sheet can be easily obtained. The content (mass %) of the metal nanowires relative to the total solid content of the present composition is the same as the content (mass %) of the metal nanowires relative to the total mass of the present sheet described above, including preferred embodiments.

[0101] <Thermosetting Compound> The thermosetting compound contained in the composition is the same as the thermosetting compound contained in the sheet described above, including preferred embodiments. The content (mass %) of the thermosetting compound relative to the total solid content of the composition is the same as the content (mass %) of the thermosetting compound relative to the total mass of the sheet described above, including preferred embodiments.

[0102] <Solvent> The solvent contained in the present composition is preferably an organic solvent. The boiling point of the solvent (corresponding to the boiling point Ty described below) is preferably 130°C or lower, more preferably 100°C or lower, and even more preferably 80°C or lower. If the boiling point of the solvent is 130°C or lower, the thermal curing of the thermosetting compound in the film during the drying process can be suppressed, and the occurrence of voids in the present sheet can be suppressed. The lower limit of the boiling point of the solvent (corresponding to the boiling point Ty described below) is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher, from the viewpoint of preventing volatilization other than during heating.

[0103] Specific examples of organic solvents include cyclohexanone (boiling point 156°C), ethyl acetate (boiling point 77.1°C), methyl ethyl ketone (boiling point 79.64°C), dichloromethane (boiling point 39.6°C), and tetrahydrofuran (boiling point 66°C). Among these, methyl ethyl ketone and ethyl acetate are preferred, and methyl ethyl ketone is more preferred, as they can suppress thermal curing of the thermosetting compound in the film during the drying process and prevent voids from forming in the sheet. The solvents may be used alone or in combination of two or more.

[0104] <Corrosion inhibitor and silane coupling agent> The present composition preferably contains at least one selected from the group consisting of a corrosion inhibitor and a silane coupling agent, in order to further reduce the oxidation rate of the metal nanowires contained in the present sheet. The corrosion inhibitor and silane coupling agent are the same as the corrosion inhibitor and silane coupling agent described in the protective layer formation step of the above-mentioned method for producing metal nanowires, including preferred embodiments. When the present composition contains a corrosion inhibitor, the content of the corrosion inhibitor is preferably 0.01 to 10 mass%, more preferably 0.05 to 5 mass%, and even more preferably 0.1 to 1 mass%, relative to the total mass of the present composition. When the present composition contains a silane coupling agent, the content of the silane coupling agent is preferably 0.01 to 10 mass%, more preferably 0.05 to 5 mass%, and even more preferably 0.1 to 1 mass%, relative to the total mass of the present composition.

[0105] <Other Components> The present composition may contain components other than those described above (hereinafter also referred to as "other components"). Examples of other components include dispersants, catalysts, and curing accelerators (for example, the curing accelerators described in JP 2023-125309 A). When the present composition contains other components, the content of the other components is preferably 1 to 0.001% by mass, more preferably 0.5 to 0.005% by mass, and even more preferably 0.1 to 0.01% by mass, relative to the total mass of the present composition.

[0106] The solid content of the composition is preferably 20 to 60% by mass, more preferably 25 to 55% by mass, and even more preferably 30 to 50% by mass. When the solid content of the composition is 20% by mass or more, it becomes easy to keep the surface exposure rate of the metal nanowires within the above-mentioned range. Furthermore, when the solid content of the composition is 60% by mass or less, the composition has excellent handleability. The "solid content" of the composition refers to the components that form the film formed using the composition. Typically, it refers to all components excluding the solvent. Furthermore, liquid components that form a film are also considered to be solids.

[0107] The viscosity of this composition at 25°C is 100 mPa·s or less, preferably 90 mPa·s or less, and more preferably 80 mPa·s or less. If the viscosity is 100 mPa·s or less, voids generated due to evaporation of the solvent during the drying process are easily filled with components such as thermosetting compounds. This makes it possible to further suppress the generation of voids in the resulting sheet, thereby improving the effects of the present invention. From the viewpoint of an appropriate film thickness, the lower limit of the viscosity of this composition at 25°C is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, and even more preferably 20 mPa·s or more. The viscosity of this composition is measured at 25°C using an E-type viscometer.

[0108] The method for producing the composition is not particularly limited, and examples thereof include a method in which the above-mentioned various components are mixed by a known method.

[0109] [Drying Process] The drying process is a process in which the present composition is dried to obtain a sheet. The drying process volatilizes the solvent in the present composition. Note that, since the drying temperature of the present composition in the drying process is lower than the curing temperature of the thermosetting compound, the thermosetting compound does not cure during the drying process. The drying process may be a process of drying a coating film obtained by applying the present composition, or a process of drying the present composition poured into a container such as a mold. The method for applying the present composition is not particularly limited, and examples thereof include printing, spraying, roll coating, bar coating, curtain coating, spin coating, and die coating (slit coating).

[0110] If the drying temperature of the composition during the drying process is T, the curing temperature of the thermosetting compound is Tx, and the boiling point of the solvent is Ty, the value obtained by subtracting T from Tx (Tx-T) is 10°C or higher, and the value obtained by subtracting T from Ty (Ty-T) is -60°C or higher. By satisfying these drying conditions, the solvent volatilizes slowly, making it easier for components such as the thermosetting compound to fill voids that arise as the solvent volatilizes. This reduces the porosity of the sheet. When two or more solvents are used, the boiling point of the solvent with the highest boiling point is used as the boiling point Ty.

[0111] Tx-T is 10°C or higher, and is preferably 40°C or higher, more preferably 70°C or higher, from the viewpoint of reducing the porosity of the present sheet. The upper limit of Tx-T is preferably 220°C or lower, more preferably 190°C or lower, and even more preferably 160°C or lower, from the viewpoint of drying efficiency. Ty-T is -60°C or higher, and is preferably 0°C or higher, more preferably 20°C or higher, from the viewpoint of reducing the porosity of the present sheet. The upper limit of Ty-T is preferably 60°C or lower, more preferably 50°C or lower, and even more preferably 40°C or lower, from the viewpoint of drying efficiency.

[0112] The drying temperature T is preferably 30 to 130° C., more preferably 40 to 100° C., and even more preferably 50 to 80° C. The preferred ranges of the curing temperature Tx of the thermosetting compound and the preferred ranges of the boiling point Ty of the solvent are as described above.

[0113] The drying time in the drying step is preferably 1 to 40 minutes, more preferably 5 to 20 minutes.

[0114] The state of the sheet obtained through the drying step is preferably B-stage, as described above.

[0115] [Pressing Step] The present manufacturing method may include a pressing step in which the sheet after the drying step is subjected to a pressure treatment. By including the pressing step, the voids in the sheet can be reduced, thereby further reducing the porosity of the sheet. The pressure in the pressing step is preferably 5 to 70 MPa, more preferably 20 to 50 MPa.

[0116] The pressing step may be accompanied by a heat treatment, and the heating temperature of the heat treatment is preferably lower than the curing temperature Tx of the thermosetting compound. Specifically, the heating temperature of the heat treatment is preferably 130° C. or lower, more preferably 100° C. or lower, and is preferably 30° C. or higher, more preferably 40° C. or higher.

[0117] The pressing step may be carried out under either normal pressure or reduced pressure. Examples of the press machine used in the pressing step include a plate press machine and a roll press machine.

[0118] The state of the sheet obtained through the pressing step is preferably B-stage, as described above.

[0119] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0120] [Production of Metal Nanowires 1] <Preparation of Aluminum Substrate> A molten aluminum alloy containing 0.06% by mass of Si, 0.30% by mass of Fe, 0.005% by mass of Cu, 0.001% by mass of Mn, 0.001% by mass of Mg, 0.001% by mass of Zn, and 0.03% by mass of Ti, with the remainder being Al and unavoidable impurities, was prepared. The molten aluminum alloy was then treated and filtered, and an ingot 500 mm thick and 1200 mm wide was produced by DC (Direct Chill) casting. The surface was then scraped off to an average thickness of 10 mm using a facing mill, and the ingot was then soaked at 550°C for approximately 5 hours. When the temperature was lowered to 400°C, it was rolled into a 2.7 mm thick plate using a hot rolling mill. Further, the aluminum substrate was subjected to heat treatment at 500°C using a continuous annealing machine, and then finished to a thickness of 1.0 mm by cold rolling, thereby obtaining an aluminum substrate conforming to JIS (Japanese Industrial Standards) 1050. The aluminum substrate was formed into a wafer having a diameter of 200 mm (8 inches), and then subjected to the following treatments.

[0121] <Electrolytic Polishing Treatment> The above-mentioned aluminum substrate was subjected to electrolytic polishing treatment using an electrolytic polishing solution having the following composition under conditions of a voltage of 25 V, a solution temperature of 65°C, and a solution flow rate of 3.0 m / min. A carbon electrode was used as the cathode, and a GP0110-30R (manufactured by Takasago Machinery Co., Ltd.) was used as the power source. The flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation). (Electrolytic Polishing Solution Composition) 85% by mass phosphoric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 660 mL Pure water 160 mL Sulfuric acid 150 mL Ethylene glycol 30 mL

[0122] <Anodizing step> Next, the aluminum substrate after electrolytic polishing was subjected to anodizing treatment by a self-ordering method according to the procedure described in JP 2007-204802 A. The aluminum substrate after electrolytic polishing was subjected to a 5-hour pre-anodizing treatment in a 0.50 mol / L oxalic acid electrolyte solution under conditions of a voltage of 40 V, a liquid temperature of 16 ° C, and a liquid flow rate of 3.0 m / min. Thereafter, the aluminum substrate after pre-anodizing treatment was subjected to a film removal treatment by immersing it in a mixed aqueous solution of 0.2 mol / L chromic anhydride and 0.6 mol / L phosphoric acid (liquid temperature: 50 ° C) for 12 hours. Thereafter, a 5-hour re-anodizing treatment was performed in a 0.50 mol / L oxalic acid electrolyte solution under conditions of a voltage of 40 V, a liquid temperature of 16 ° C, and a liquid flow rate of 3.0 m / min, to obtain an anodized film with a film thickness of 40 μm. In both the pre-anodizing treatment and the re-anodizing treatment, a stainless steel electrode was used as the cathode, and a GP0110-30R power supply (manufactured by Takasago Machinery Co., Ltd.) was used. A NeoCool BD36 (manufactured by Yamato Scientific Co., Ltd.) was used as the cooling device, and a Pair Stirrer PS-100 (manufactured by EYELA Tokyo Rikakikai Co., Ltd.) was used as the stirring / heating device. Furthermore, the flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation).

[0123] <Metal Filling Step> Next, electrolytic plating was performed using the aluminum substrate as the cathode and platinum as the cathode. Specifically, a copper plating solution having the composition shown below was used, and constant-current electrolysis was performed to produce a metal-filled microstructure in which copper was filled into the porous (micropore) interior. Here, constant-current electrolysis was performed using a plating device manufactured by Yamamoto Plating Tester Co., Ltd. and a power supply (HZ-3000) manufactured by Hokuto Denko Corporation. After confirming the deposition potential by performing cyclic voltammetry in the plating solution, the process was performed under the conditions shown below. (Copper Plating Solution Composition and Conditions) Copper sulfate 100 g / L Sulfuric acid 50 g / L Hydrochloric acid 15 g / L Temperature 25°C Current density 10 A / dm ２

[0124] The surface of the anodized film after filling the pores with metal was observed with an FE-SEM, and the presence or absence of sealing with metal in 1,000 pores was observed, and the sealing rate (number of sealed pores / 1,000) was calculated to be 96%. In addition, the anodized film after filling the pores with metal was cut in the thickness direction with an FIB, and the surface of the cross section was photographed (magnification 50,000 times) with an FE-SEM to check the inside of the pores. It was found that the filling height from the bottom of the sealed pores was 35 μm.

[0125] <Isolation step> The filled metal was isolated from the anodized film and aluminum substrate by immersing the substrate for 300 seconds in an aqueous potassium hydroxide solution (concentration: 5 mol / L) at 60°C. Specifically, the anodized film was dissolved by immersing the substrate for 300 seconds in an aqueous potassium hydroxide solution (concentration: 5 mol / L) at 60°C, and the aluminum substrate was peeled off simultaneously with the dissolution of the anodized film (after 300 seconds), thereby isolating the filled metal.

[0126] <Drying Step> Next, the isolated metal was recovered by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore), and the isolated metal was dried.

[0127] <Reduction or Removal Step> Next, the isolated metal recovered on the membrane was immersed in an aqueous solution containing 1% by mass of citric acid at room temperature (23°C, the same applies below) for 3 hours. Thereafter, the isolated metal on the membrane was recovered.

[0128] <Crushing Step> Next, the recovered isolated metal was added to water at 1% by mass, and subjected to a single cavitation crushing treatment (pressure: 50 MPa) using a Starburst Mini manufactured by Sugino Machine Co., Ltd. Thereafter, the crushed isolated metal was recovered by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore), and dried under reduced pressure at 50° C. for 12 hours to produce metal nanowires 1.

[0129] [Production of Metal Nanowires 2] Metal nanowires 2 were obtained in the same manner as in the production of metal nanowires 1, except that the above-mentioned "reduction or removal step" was not carried out.

[0130] Example 1 Production of Composition 19 g of epoxy compound 1 (EPICLON (registered trademark) EXA-830LVP, manufactured by DIC Corporation, thermosetting compound, molecular weight: 310), 9 g of phenol compound 1 (BIR-PC, manufactured by Asahi Organic Chemicals Co., Ltd., thermosetting compound, molecular weight: 352), 0.1 g of silane coupling agent (KBM-403, manufactured by Shin-Etsu Silicones Co., Ltd., silane coupling agent having an epoxy group), and 18 g of methyl ethyl ketone (MEK, boiling point Ty: 79.64°C) were added to a container and stirred at room temperature for 3 hours to obtain mixture A. The curing temperature Tx of the above composition was found to be 140°C by DSC measurement. Metal nanowires 2, mixture A, and MEK were added to a container and stirred at room temperature for 1 hour to obtain composition A. At this time, the amount of each component added was adjusted so that the solid content (mass %) of composition A was 42 mass % and the content of metal nanowires 2 relative to the total content of metal nanowires 2 and thermosetting compound was 90 mass %. The viscosity of composition A at 25°C measured using an E-type viscometer was 50 mPa s.

[0131] <Production of Sheet> Composition A was poured into a silicone rubber mold at room temperature under atmospheric pressure, and then the mold containing composition A was placed in an explosion-proof oven connected to an exhaust system, where composition A was dried under atmospheric pressure at 130°C (drying temperature T) for 30 minutes to volatilize the MEK (drying step). After the drying step, the mold was removed to obtain a sheet. The sheet was pressed under atmospheric pressure using a press at 50°C and 40 MPa (pressing step) to obtain Sheet 1 of Example 1 (thickness: 100 μm).

[0132] [Examples 2 to 4] Sheets 2 to 4 (each thickness: 102 μm) of Examples 2 to 4 were obtained in the same manner as in Example 1, except that the drying temperature T in the drying step was set as shown in Table 1.

[0133] Examples 5 to 6 Composition B was obtained in the same manner as in the production of the composition of Example 1, except that metal nanowires 1 were used instead of metal nanowires 2. The viscosity of composition B at 25°C, measured using an E-type viscometer, was 51 mPa·s. Sheets 5 to 6 of Examples 5 to 6 (each thickness: 101 μm) were obtained in the same manner as in the production of the sheet of Example 1, except that composition B was used instead of composition A and the drying temperature T in the drying step was set as shown in Table 1.

[0134] Examples 7 to 8 Composition C was obtained in the same manner as in the production of the composition of Example 1, except that the solids concentration of the composition was adjusted to be as shown in Table 1. The viscosity of Composition C at 25°C, measured using an E-type viscometer, was 28 mPa s. Sheets 7 to 8 of Examples 7 to 8 (all thickness: 95 µm) were obtained in the same manner as in the production of the sheet of Example 1, except that Composition C was used instead of Composition A and the drying temperature T in the drying step was set to be as shown in Table 1.

[0135] [Examples 9 to 11] Sheets 9 to 11 (each thickness: 101 μm) of Examples 9 to 11 were obtained in the same manner as in the production of the sheet of Example 1, except that the above-mentioned composition B was used instead of composition A and the drying temperature T in the drying step was set as shown in Table 1.

[0136] Comparative Examples 1 to 3 Composition D was obtained in the same manner as in the production of the composition of Example 1, except that epoxy compound 2 (EPICLON (registered trademark) 830, manufactured by DIC Corporation, thermosetting compound) was used instead of epoxy compound 1. The curing temperature Tx of the above composition was 145°C as measured by DSC. The viscosity of composition D at 25°C, measured using an E-type viscometer, was 108 mPa s. Sheets H1 to H3 of Comparative Examples 1 to 3 (each thickness: 116 μm) were obtained in the same manner as in the production of the sheet of Example 1, except that composition D was used instead of composition A and the drying temperature T in the drying step was set as shown in Table 1.

[0137] [Porosity] The porosity of sheets 1 to 11 and H1 to H3 was measured using the following method. Each sheet was cleaved along the thickness direction. The exposed cross section of the sheet was coated with platinum and then processed with a focused ion beam (FIB). Then, using a field emission scanning electron microscope (FE-SEM) (manufactured by Thermo Fisher Scientific), images of 10 different fields of view of the cross section of the sheet were taken at an acceleration voltage of 2 kV and a magnification of 1000x. In the captured images, voids were displayed in black. The captured images were binarized using the image processing software "ImageJ" to separate the images into dark and light areas, and image processing data was obtained. In the binarized image processing data, the dark areas correspond to the voids in the sheet, and the light areas correspond to the areas other than the voids (metal nanowires and thermosetting compound). The area of ​​the dark areas was automatically detected and measured from the binarized image processing data, and the area of ​​the voids and the area of ​​the areas other than the voids (bright areas) were calculated from the obtained measurements, and the porosity was calculated for each image processing data according to the following formula. The arithmetic mean of the 10 values ​​calculated in this way was taken as the porosity (%) of the sheet. The results are shown in Table 1. Porosity (%) = 100 x [area of ​​voids / (area of ​​voids + area of ​​areas other than voids)]

[0138] [Oxidation Rate] The oxidation rates of the metal nanowires contained in Sheets 1 to 11 and H1 to H3 were measured by the following method. The surface of each sheet was analyzed using an X-ray diffractometer (manufactured by RIGAKU Corporation) under conditions of 40 kV and 30 mA with a Cu radiation source, and a diffraction chart was obtained. For the obtained diffraction chart, the main peaks of MOx and M (where M represents a metal atom and x represents an integer) were identified using the Inorganic Crystal Structure Database (ICSD), and the ratio (%) of the area of ​​the peak derived from the metal and the area of ​​the peak derived from the metal oxide was calculated, and the oxidation rate of the metal nanowires was calculated according to the following formula. The results are shown in Table 1. Oxidation Rate (%) = 100 × [area of ​​peak derived from metal oxide / area of ​​peak derived from metal] For example, when the above M (metal atom) is Cu, identification was performed based on the value of the main peak below, and the ratio of the area of ​​the Cu peak to the area of ​​the Cu peak was calculated. ２The ratio of the total peak area of ​​O to the peak area of ​​CuO (i.e., oxidation rate, unit %) was calculated. ２ Main peak of O: Around 2θ = 37° Main peak of CuO: Around 2θ = 39° Main peak of Cu: Around 2θ = 43°

[0139] [Surface Exposure Rate] The surface exposure rate of the metal nanowires in Sheets 1 to 11 and H1 to H3 was measured by the following method. Using an optical microscope (manufactured by Keyence Corporation), images were taken of 10 different fields of view on the surface of each sheet, observed at 100x magnification. Note that, because the density of the metal nanowires was high, the metal nanowires exposed from the surface appeared white in the taken images. The taken images were binarized using the image processing software "ImageJ" to divide the images into dark and light areas, and image processing data was obtained. In the binarized image processing data, the light areas correspond to the metal nanowires exposed from the sheet surface, and the dark areas correspond to the areas other than the metal nanowires exposed from the sheet surface (the thermosetting compound and the metal nanowires buried in the thermosetting compound). The area of ​​bright areas was automatically detected and measured from the binarized image processing data, and the area of ​​the metal nanowires exposed from the sheet surface and the area of ​​the parts other than the metal nanowires exposed from the sheet surface were calculated from the obtained measurements, and the surface exposure rate was calculated for each image processing data according to the following formula. The arithmetic mean of the 10 values ​​calculated in this way was taken as the surface exposure rate (%) of the metal nanowires for each sheet. The results are shown in Table 1. Surface exposure rate (%) = 100 x [area of ​​metal nanowires exposed from the sheet surface / (area of ​​metal nanowires exposed from the sheet surface + area of ​​parts other than the metal nanowires exposed from the sheet surface)]

[0140] [Metal Nanowire Content] The metal nanowire content (volume %) was calculated from the amount of each component charged during sheet production. Specifically, the charged weight (solid content) of each component used during sheet production was divided by the theoretical specific gravity of each component to determine the volume of each component (solid content) in the sheet. The volume occupied by the metal nanowires was then divided by the sum of the volumes of each component (solid content) in the sheet to calculate the metal nanowire content (volume %).

[0141] [Relative thermal conductivity] Sheets 1 to 11 and H1 to H3 were subjected to a heat press treatment under conditions of 180°C and 10 MPa using a press machine in a nitrogen atmosphere. The thermal conductivity of each sheet (thermally conductive sheet) after the heat press treatment was calculated based on the following formula. The results were expressed as a ratio (relative thermal conductivity) to the thermal conductivity value of the thermally conductive sheet in Comparative Example 1, converted to "1.0". The results are shown in Table 1. Thermal conductivity (W / m K) = specific gravity (g / cm ３ ) × specific heat (kJ / kg K) × thermal diffusivity (mm ２ / s) Here, the specific gravity was measured by Archimedes' method, the specific heat was calculated by differential scanning calorimetry (DSC), and the thermal diffusivity was measured by the laser flash method.

[0142] For sheets 9 to 11 in Examples 9 to 11, the porosity, oxidation rate, and surface exposure rate were determined by the above-mentioned method using the heat-pressed sheets (thermal conductive sheets) used in the thermal conductivity measurement. The results are shown in Table 1.

[0143]

[0144] As shown in Table 1, when a sheet with a porosity of 20.0% or less was heat-pressed at a temperature equal to or higher than the curing temperature of the thermosetting compound, the resulting thermally conductive sheet exhibited excellent thermal conductivity (Examples 1 to 11). On the other hand, when a sheet with a porosity of more than 20.0% was heat-pressed at a temperature equal to or higher than the curing temperature of the thermosetting compound, the resulting thermally conductive sheet exhibited poor thermal conductivity (Comparative Examples 1 to 3). Comparisons between Examples 3 and 5, and between Examples 4 and 6, showed that the thermal conductivity of the resulting thermally conductive sheet was superior when a sheet containing metal nanowires with a low oxidation rate was used. Comparisons between Examples 3 and 7, and between Examples 4 and 8, showed that the thermal conductivity of the resulting thermally conductive sheet was superior when a sheet with a high surface exposure rate of metal nanowires was used.

[0145] 1 Valve metal substrate 2 Porous (micropore) 3 Anodic oxide film 4 Metal 5 Isolated metal 10 Metal nanowire

Claims

1. A sheet comprising metal nanowires and a thermosetting compound, wherein the porosity of the sheet is 20.0% or less.

2. The sheet according to claim 1, wherein the oxidation rate of the metal nanowires is 5.0% or less.

3. The sheet according to claim 1 or 2, wherein the surface exposure rate of the metal nanowires is 20.0% or more.

4. The sheet according to claim 1 or 2, wherein the metal constituting the metal nanowires is copper.

5. The sheet according to claim 1 or 2, wherein the content of the metal nanowires is 30 to 80% by volume relative to the total volume of the sheet.

6. The sheet according to claim 1 or 2, wherein the thickness of the sheet is 20 to 200 μm.

7. The sheet according to claim 1 or 2, wherein the thermosetting compound comprises an epoxy compound and a phenolic compound.

8. The sheet according to claim 1 or 2, wherein the molecular weight of the thermosetting compound is 1,000 or less.

9. A method for manufacturing a sheet, comprising the step of drying a composition containing metal nanowires, a thermosetting compound, and a solvent to obtain a sheet, wherein the viscosity of the composition at 25°C is 100 mPa·s or less, and where T is the drying temperature of the composition, Tx is the curing temperature of the thermosetting compound, and Ty is the boiling point of the solvent, the value obtained by subtracting T from Tx is 10°C or more, and the value obtained by subtracting T from Ty is -60°C or more.

Images