JP6956706B2 - Substrate with metal nanowire layer formed and its manufacturing method - Google Patents

Description

The present invention relates to a base material on which a metal nanowire layer is formed and a method for producing the same.

Metal nanowires are not only materials that can form transparent conductors that are more transparent and conductive than conventional transparent conductive materials such as ITO, but also have mechanical durability such as bending and expansion and contraction. Since it is excellent, it is used for forming a transparent conductive film using a flexible film base material or the like. For example, Patent Document 1 below discloses a method for producing a conductive pattern using metal nanowires.

However, when metal nanowires made of silver, copper, or the like are used as the transparent conductive film material, the transparent conductive film may deteriorate due to migration, sulfide, oxidation, or the like. Therefore, in order to improve the durability of the metal nanowires, graphene or a polymer has been coated on the entire surface of the transparent conductive film, but high durability has not been ensured.

In recent years, a technique of plating silver nanowires to improve durability has been proposed. For example, Patent Document 2 below discloses a configuration in which a metal other than silver is plated on the surface of silver nanowires.

Further, Patent Document 3 below describes that in a conductive film in which linear metal nanowires are joined to each other at intersections to form a mesh, the joining is performed by crimping or plating.

However, in the plating technique in the above-mentioned conventional technique, the metal nanowires are easily peeled off from the substrate, and a stable plating process cannot be performed. Further, it is not possible to obtain high mechanical strength against bending and expansion / contraction simply by forming a transparent conductive film made of metal nanowires on a substrate.

International Publication No. 2014/175163 Pamphlet Japanese Unexamined Patent Publication No. 2013-151752 International Publication No. 2009/035059 Pamphlet

An object of the present invention is to provide a base material on which a metal nanowire layer having high durability against migration, sulfurization, oxidation and the like and high mechanical strength is formed, and a method for producing the same.

In order to achieve the above object, the present invention has the following embodiments.

[1] A base material on which a metal nanowire layer is formed, in which a part of the metal nanowire is embedded in the base material, and a part or all of the exposed metal nanowire is plated. A base material on which a characteristic metal nanowire layer is formed.

[2] The base material on which the metal nanowire layer according to [1] is formed, in which at least a part of the metal nanowires is connected.

[3] Any of the group consisting of polyurethane, silicone resin, saturated polyester, polycarbonate, polyparaxylylene (parylene (registered trademark)), thermoplastic polyimide, polyether sulfone, acrylic resin, polyolefin, and polyvinyl chloride. The base material on which the metal nanowire layer according to [1] or [2] is formed.

[4] The base material on which the metal nanowire layer according to any one of [1] to [3] is formed, wherein the metal constituting the metal nanowire is silver or copper.

[5] The step of forming the metal nanowire layer on the base material, the step of applying external energy to the substrate on which the metal nanowire layer is formed, and the step of embedding a part of the metal nanowire in the base material, and the exposed parts. A method for producing a base material on which a metal nanowire layer is formed, comprising a step of plating a part or all of the metal nanowires.

[6] The method for producing a base material on which a metal nanowire layer is formed, which further comprises a step of connecting at least a part of the metal nanowires before or after the step of plating.

[7] Any of the group consisting of polyurethane, silicone resin, saturated polyester, polycarbonate, polyparaxylylene (parylene (registered trademark)), thermoplastic polyimide, polyether sulfone, acrylic resin, polyolefin, and polyvinyl chloride. The method for producing a base material on which a metal nanowire layer is formed according to [5] or [6].

[8] The method for producing a base material on which a metal nanowire layer is formed according to any one of [5] to [7], wherein the metal constituting the metal nanowire is silver or copper.

[9] A sensor or functional element provided with a base material on which the metal nanowire layer according to any one of [1] to [4] above is formed.

According to the present invention, it is possible to provide a base material on which a metal nanowire layer having high durability against migration, sulfurization / oxidation and the like and high mechanical strength is formed, and a method for producing the same.

It is explanatory drawing of the manufacturing process example of the base material which formed the metal nanowire layer which concerns on embodiment. It is a figure which shows the SEM photograph of the electroless nickel / gold-plated silver nanowire / polyurethane base material which concerns on Example 1. FIG. It is a figure which shows the cross-sectional TEM photograph of the silver nanowire which was electroless nickel / gold-plated which concerns on Example 1. FIG. It is a figure which shows the SEM photograph of the silver nanowire / polyurethane base material which was electroplatinum-plated which concerns on Example 5. FIG. It is a figure which shows the cross-sectional TEM photograph of the silver nanowire which was electroplatinum-plated according to Example 5.

Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described.

The base material on which the metal nanowire layer according to the embodiment is formed is characterized in that a part of the metal nanowire is embedded in the base material and a part or all of the exposed metal nanowire is plated. And.

The metal nanowire is a metal having a diameter on the order of nanometers, and is a conductive material having a wire-like shape. In this embodiment, metal nanotubes, which are conductive materials having a porous or non-porous tubular shape, may be used together with (mixed with) the metal nanowires or instead of the metal nanowires. In the present specification, both "wire-like" and "tube-like" are linear, but the former is intended to have a hollow center and the latter to be hollow in the center. The properties may be flexible or rigid. Hereinafter, when "metal nanowires" and "metal nanotubes" are not described in succession in the present specification, "metal nanowires" are used in the sense of including metal nanowires and metal nanotubes.

As a method for producing metal nanowires or metal nanotubes, a known production method can be used. For example, silver nanowires can be synthesized by reducing silver nitrate in the presence of polyvinylpyrrolidone using the Poly-ol method (see Chem. Matter., 2002, 14, 4736). Gold nanowires can also be similarly synthesized by reducing chloroauric acid hydrate in the presence of polyvinylpyrrolidone (see J. Am. Chem. Soc., 2007, 129, 1733). The techniques for large-scale synthesis and purification of silver nanowires and gold nanowires are described in detail in International Publication No. 2008/073143 and International Publication No. 2008/046058. Gold nanotubes having a porous structure can be synthesized by reducing a gold chloride solution using silver nanowires as a template. Here, the silver nanowires used in the template dissolve in the solution by a redox reaction with chloroauric acid, resulting in gold nanotubes having a porous structure (JAm. Chem. Soc., 2004, 126, 3892). See -3901).

The average diameter of the metal nanowires and the metal nanotubes is preferably 1 to 500 nm, more preferably 5 to 200 nm, further preferably 5 to 100 nm, and particularly preferably 10 to 100 nm. The average length of the major axis of the metal nanowire and the metal nanotube is preferably 1 to 100 μm, more preferably 1 to 80 μm, further preferably 2 to 70 μm, and particularly preferably 5 to 50 μm. For metal nanowires and metal nanotubes, the average diameter thickness and the average length of the major axis satisfy the above range, and the average aspect ratio is preferably larger than 5, more preferably 10 or more, and 100. The above is more preferable, and 200 or more is particularly preferable. Here, the aspect ratio is a value obtained by a / b when the average diameter of the diameters of the metal nanowires and the metal nanotubes is approximated to b and the average length of the major axis is approximated to a. a and b can be measured using a scanning electron microscope (SEM) and an optical microscope. Specifically, the diameter of 10 or more metal nanowires is measured by SEM (FE-SEM SU8020 manufactured by Hitachi High-Technologies Co., Ltd.), and the length of 100 or more metal nanowires is measured by an optical microscope (VHX-600 manufactured by Keyence Co., Ltd.). ), And the average diameter and average length can be obtained from their additive average values.

The material for such metal nanowires is not particularly limited as long as the material itself has some difficulty in durability against migration, sulfurization, oxidation, etc. and needs to be improved, but silver and copper are high in conductivity. Etc. are suitable.

Further, the base material is preferably a thermoplastic resin material. The thermoplastic resin may be colored, but it is preferable that the thermoplastic resin has high transparency due to visible light. For example, polyurethane, silicone resin, saturated polyester (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc.), polycarbonate, polyparaxylylene (parylene (registered trademark)), thermoplastic polyimide, polyether sulfone, acrylic resin, polyolefin. , Polyvinyl chloride and the like. Among these, polyurethane, polyethylene terephthalate (PET), and polyparaxylylene (Parylene (registered trademark)) are preferable from the viewpoint of adhesion of the metal nanowire to the base material and elasticity of the base material.

A part of the metal nanowire is embedded in a base material. The part of the metal nanowire is a part of any one of the longitudinal directions of the metal nanowire, and examples thereof include one or both of both end portions, a portion between both end portions, and the like. Since a part of the metal nanowires is embedded in the base material, the metal nanowire layer formed on the base material can obtain high mechanical strength against bending and expansion and contraction of the base material. The metal nanowires embedded in the substrate preferably have 5 to 95% of their surface area exposed. There may be metal nanowires completely embedded in the substrate. It may also contain metal nanowires that do not have a portion embedded in the substrate. In that case, the metal nanowires having no portion embedded in the base material are preferably 5% or more and 95% or less, more preferably 10% or more and 85% or less, and 15% or more and 75% or less. The following is more preferable.

Further, the metal nanowires are plated with a part or all of a portion exposed from the base material, that is, a part not embedded in the base material. In particular, in the electroless plating step, by performing heat treatment after immersion in the catalyst solution, the plating layer formed on the metal nanowires is stabilized, and a plating layer having excellent durability such as improved peeling resistance can be obtained. Therefore, it is possible to suppress the occurrence of migration and deterioration due to sulfide / oxidation. The heat treatment conditions are not unconditionally determined because they depend on the heat resistant temperature of the base material, but are preferably 0 ° C. to 200 ° C., more preferably 20 ° C. to 150 ° C. within the heat resistant temperature range of the base material. The range is preferred. Further, the treatment time is not restricted as long as the solvent of the catalyst solution volatilizes within a range that does not damage the substrate, but is preferably 1 second to 1 hour, more preferably 30 seconds to 30 minutes. Is the range of.

It is preferable that at least a part of the metal nanowires constituting the metal nanowire layer is connected. The term "connection" as used herein means that the metal nanowires are not simply in contact with each other at the intersection, but are fused and integrated at the intersection. The connection method will be described later.

The base material on which the metal nanowire layer according to the present embodiment described above is formed is required to have reliability inside or outside a member that comes into contact with a solution (water, saline solution, etc.) that promotes metal migration, for example. It can be applied to conductive members, such as transparent conductive films formed on flexible substrates in devices that come into contact with moisture, water, etc., wearable devices that come into contact with sweat, biological fluids, etc. It can be used as a sensor member such as an embedded sensor, a chemical sensor, a microchannel device, an infrastructure exposed to rain or seawater, or a sensor for agriculture and forestry. In addition to sensors, it can be used for conductive members of functional elements that require migration resistance, for example, conductive members such as solar cells, LEDs, and transistors using organic or inorganic semiconductors.

1 (a), (b), and (c) show explanatory views of a manufacturing process example of a base material on which the metal nanowire layer according to the embodiment is formed. In FIG. 1A, a dispersion liquid of metal nanowires is applied onto a flexible base material 10 to form a metal nanowire layer 12 (metal nanowire layer forming step).

Next, in FIG. 1B, external energy is applied to the base material 10 on which the metal nanowire layer 12 is formed, and a part of the metal nanowires is embedded in the base material 10 (embedding step). Here, examples of the method of applying external energy include light irradiation, heating by electromagnetic waves such as dielectric heating and induction heating, and heating by an oven, a hot plate, or the like. When external energy is applied, the surface layer of the base material 10 is melted, and a part of the metal nanowires contained in the metal nanowire layer 12 formed on the surface of the base material 10 is inside the surface layer of the melted base material 10. invade. As a result, as shown in FIG. 1B, a part of the metal nanowires is embedded in the base material 10. Further, in the step of applying external energy, the adhesive area between the metal nanowire and the base material is increased due to physical changes such as expansion or contraction caused by the residual stress of the base material, and the adhesion is improved. As described above, a part of the metal nanowire is at least one of both end portions, a portion between both end portions, and the like. The amount of external energy to be applied differs depending on the base material, but the glass transition point (Tg) of the base material is applied in both cases where electromagnetic waves such as light irradiation, dielectric heating, and induction heating are applied, and when heating by an oven, hot plate, etc. is applied. ) Or above or above the softening point is adopted, and the conditions and temperature are appropriately selected depending on the substrate to be used.

In the method for producing a base material on which the metal nanowire layer is formed as described above, after the metal nanowire layer 12 is formed on the base material 10, a part of the metal nanowire is applied to the base material 10 by applying external energy. The coating layer is not formed so as to cover at least a part of the metal nanowire layer 12 after the metal nanowire layer 12 is formed on the base material 10. That is, a part of the metal nanowires is embedded in the base material 10 itself, and the structure is not embedded only in the coating layer.

Since a part of the metal nanowires constituting the metal nanowire layer 12 is embedded in the base material 10, it is possible to prevent the metal nanowires from peeling off from the base material 10 in the subsequent plating step, and the plating process is stable. Can be done.

Then, as shown in FIG. 1 (c), a part or all of the metal nanowires exposed from the base material forming the metal nanowire layer 12 are plated (plating step). As a plating method, a known technique can be applied. For example, chemical reduction plating typified by electroless plating, replacement plating, electrolytic plating and the like are suitable, and a commercially available plating solution can be used. This plating covers the skeleton of the metal nanowires, and new structural reinforcement can be achieved. Examples of the metal to be plated include gold, nickel / gold, platinum and the like. The plating thickness is not limited as long as it can exhibit the effect of improving durability by plating, but is, for example, 1 nm to 100 nm, preferably 3 nm to 70 nm, and more preferably 5 nm to 50 nm. The plating layer may be formed as a single layer, but it is preferable that a plurality of layers of 2 to 4 are laminated. When the number of layers is five or more, the plating layer forming step becomes complicated from an industrial point of view, and the optical characteristics are sacrificed in terms of the characteristics as a transparent conductive film.

A step of connecting at least a part of the metal nanowires constituting the metal nanowire layer 12 may be provided before or after the plating step. Here, the step of connecting at least a part of the metal nanowires means a step of melting and integrating at least a part of a plurality of intersections of the metal nanowires existing on the surface layer of the substrate. The method of connecting is not limited as long as the energy required for connecting the metal nanowires to each other can be applied without melting and cutting, and heating of an oven or the like, microwave irradiation, and pulsed light irradiation are preferable. ..

Pulsed light irradiation is light irradiation with a short light irradiation time (irradiation time), and when light irradiation is repeated a plurality of times, light is irradiated between the first irradiation time and the second irradiation time. Means light irradiation with a period of non-existence. The light intensity may change within the light irradiation time. The pulsed light is emitted from a light source including a flash lamp such as a xenon flash lamp.

As the pulsed light, an electromagnetic wave having a wavelength range of 1 pm to 1 m can be used, preferably an electromagnetic wave having a wavelength range of 10 nm to 1000 μm, and more preferably an electromagnetic wave having a wavelength range of 100 nm to 2000 nm can be used. Examples of such electromagnetic waves include gamma rays, X-rays, ultraviolet rays, visible light, infrared rays, microwaves, electromagnetic waves on the longer wavelength side than microwaves, and the like. Considering the conversion to thermal energy, if the wavelength is too short, the damage to the resin substrate is large, which is not preferable. Further, if the wavelength is too long, it cannot be efficiently absorbed and generate heat, which is not preferable. Among the above-mentioned wavelengths, the wavelength range is particularly preferably ultraviolet to infrared, and more preferably 100 nm to 2000 nm. There is no particular limitation on the atmosphere in which the pulsed light is irradiated. It can be carried out in an air atmosphere. If necessary, it can be carried out in an inert atmosphere.

The duration of one irradiation of pulsed light depends on the light intensity, but is preferably in the range of 20 microseconds to 50 milliseconds. If it is shorter than 20 microseconds, it is difficult to proceed with sintering of metal nanowires, and if it is longer than 50 milliseconds, photodegradation and thermal deterioration may adversely affect the substrate. More preferably, it is 40 microseconds to 10 milliseconds.

Although it is effective to irradiate the pulsed light in a single shot, it can be repeated as described above. When repeated, the irradiation interval is preferably in the range of 20 microseconds to 5 seconds, more preferably in the range of 2 milliseconds to 2 seconds, in consideration of productivity. If it is shorter than 20 microseconds, it becomes close to continuous light, and since it is irradiated shortly after being allowed to cool after one irradiation, the substrate may be heated and the temperature may rise, resulting in deterioration. If it is longer than 5 seconds, the process time will be long.

The microwave used for microwave heating is an electromagnetic wave having a wavelength range of 1 m to 1 mm (frequency is 300 MHz to 300 GHz). Microwave irradiation is performed in a state where the surface of the substrate on which the metal nanowire layer is formed is maintained substantially parallel to the direction of the electric lines of force (direction of the electric field) of the microwave. Here, substantially parallel means a state in which the surface of the substrate and the direction of the electric lines of force of the microwave are parallel or maintain an angle within 30 degrees with respect to the direction of the electric lines of force. The angle within 30 degrees means a state in which the normal line standing on the surface of the substrate and the direction of the electric lines of force form an angle of 60 degrees or more. As a result, the number of electric lines of force penetrating the metal nanowire layer (printed pattern or solid pattern) formed on the substrate is limited, and the generation of sparks can be suppressed. There is no particular limitation on the atmosphere of irradiating microwaves. It can be carried out in an air atmosphere. If necessary, it can be carried out in an inert atmosphere.

Further, the metal nanowires may be plated first, and the metal nanowires after plating may be used to carry out the metal nanowire layer forming step and the embedding step.

Hereinafter, examples of the present invention will be specifically described. The following examples are for facilitating the understanding of the present invention, and the present invention is not limited to these examples.

Example 1.
Silver nanowires were obtained by chemical synthesis to reduce silver nitrate in an ethylene glycol (EG) solvent in which polyvinylpyrrolidone (PVP) and chloride ions were dissolved.

First, a PVP solution was prepared by mixing PVP (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 360,000 (catalog value)) with an EG solvent. Silver nitrate and iron (III) chloride solution (600 μmol / L, solvent is EG) were added in order to the PVP solution to prepare a mixed solution before the reaction at room temperature. The mixed solution contains 0.006% by mass of PVP, 0.006% by mass of silver nitrate, and 0.1% by mass of iron (III) chloride. Silver nanowires were synthesized by holding the mixture at 110 ° C. for 12 hours without stirring. After the synthesis, the mixture was centrifuged to remove the upper part, ethanol was added and the solvent was replaced, and the silver nanowires were dispersed in ethanol so that the concentration of silver nanowires was 0.1% by mass. The average diameter of the obtained silver nanowires was 90 nm, and the average length was 44 μm. The average diameter of silver nanowires is measured by measuring 10 silver nanowires using a scanning electron microscope (FE-SEM SU8020, manufactured by Hitachi High-Technologies), and the average length is an optical microscope (VHX-600, manufactured by Keyence). ) Was used to measure the length of 200 silver nanowires, and the additive average value was obtained for each.

The obtained silver nanowire / ethanol dispersion is spray-coated on a polyurethane base material (MG90, length 120 mm, width 50 mm, thickness 50 μm, manufactured by Takeda Sangyo) as a flexible base material (PEACE 3, Airtex). A glass substrate with a thickness of 1 mm is placed so as to cover the entire surface of the coating, and heat-treated in a hot air circulation type oven at 100 ° C. for 2 minutes, and a part of silver nanowires is embedded in the substrate. A polyurethane substrate was obtained. In the following Examples and Comparative Examples, the coating amount is arbitrarily adjusted so that the ^{amount of silver nanowires on the substrate is in the range of 0.0001 to 100 μg per 1 cm 2} so as to obtain the desired initial sheet resistance. changed. The polyurethane substrate was treated with dilute sulfuric acid prepared to 0.1 regulation for 10 seconds, and a mixture of a predetermined amount of Pd catalyst solution (KG-529 manufactured by JX Nippon Mining & Metals Co., Ltd.) and dilute hydrochloric acid prepared to 0.1 regulation was used. Minute treatment, then heat treatment in a hot air circulation oven at 100 ° C for 5 minutes, treatment with 80 ° C electroless Ni-P plating solution (KG-531 and KG-531H manufactured by JX Nippon Mining & Metals Co., Ltd.) for 10 seconds, 80 ° C. A nickel layer (about 10 to 30 nm) was formed on the surface of the silver nanowire by treating with a mixture of a predetermined amount of non-cyan-based Au plating solution (CF-500SS manufactured by JX Nippon Mining & Metals Co., Ltd.) and an aqueous solution of gold sodium sulfite for 1 minute. And a gold layer (about 1 to 30 nm) was formed without electrolytic plating.

The appearance (diameter and length) of the sample is observed with a scanning electron microscope (FE-SEM SU8020, manufactured by Hitachi High-Technologies Corporation), and the thickness of the plating layer is measured with an atomic resolution analysis electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.). Was used.

FIG. 2 shows an SEM photograph of a polyurethane base material in which electroless nickel / gold-plated silver nanowires according to Example 1 are embedded in the base material. In FIG. 2, it can be confirmed that a part of the silver nanowires does not have a plating film formed and is embedded in the base material by external energy (heat treatment in Example 1) (white line enclosed portion). It can also be confirmed from the figure that the plating film is formed only on the silver nanowires exposed on the surface layer.

Further, FIG. 3 shows a cross-sectional TEM photograph of the electroless nickel / gold-plated silver nanowires according to Example 1. In FIG. 3, it can be seen that nickel is plated on the outer layer of the silver nanowire having a pentagonal cross section to a thickness of about 10 to 30 nm, and a gold plating layer is further formed on the outer layer. (Each layer is distinguished by the shade of the TEM image.)

Example 2.
Silver nanowires were prepared in the same manner as in Example 1 except that the holding temperature of the mixed solution was changed to 150 ° C., and the base material was a PET base material (Lumilar® S, width 30 mm, length 50 mm, thickness 100 μm, Toray. A silver nanowire layer was formed on the entire surface of the substrate in the same manner except for the change to (manufactured by the company), and then a pattern of silver nanowires having a width of 10 mm and a length of 50 mm was formed by laser etching.

This base material was treated with dilute sulfuric acid prepared to 0.1 regulation for 10 seconds, and a mixture of a predetermined amount of Pd catalyst solution (KG-529 manufactured by JX Nippon Mining & Metals Co., Ltd.) and dilute hydrochloric acid prepared to 0.1 regulation was used. Treatment for 1 minute, then heat treatment in a hot air circulation type oven at 100 ° C for 5 minutes, treatment with electroless Ni-P plating solution (KG-531 and KG-531H manufactured by JX Nippon Mining & Shoji Co., Ltd.) at 80 ° C for 10 seconds, and a predetermined amount. By treating with a mixed solution of a cyan-based Au plating solution (KG-545Y manufactured by JX Nippon Mining & Trading Co., Ltd.) and KAu (CN) ₂ prepared in a concentration range of 0.1 to 1 g / L at 80 ° C. for 1 minute. , Electroless plating was performed to form a nickel layer (15 nm) and a gold layer (15 nm).

As a bending test, both ends (width side) of the above sample are attached to the upper and lower chuck parts of a desktop tensile tester (EZ-TEST, manufactured by Shimadzu Corporation, between chucks 15 mm), and the bent part has a semicircular shape with a radius of approximately 2.5 mm. It was moved up and down until (the silver nanowire layer was on the outside of the bent portion), and this was repeated with a cycle time of 13.2 seconds. The resistance value was measured at predetermined times via the terminals attached to both ends.

Comparative example 1.
A PET base material coated with silver nanowires was prepared by the same treatment as in Example 2 except that it was not plated, and a bending test evaluation was carried out.

Table 1 shows the bending test evaluation results of Example 2 and Comparative Example 1. In Comparative Example 1, the resistance value increases as the number of bendings increases, whereas in Example 2, the low resistance value is maintained even during the bending test, and it can be seen that the mechanical strength is improved.

Example 3.
Dix (registered trademark) -SR (manufactured by KISCO) was deposited on a glass substrate having a thickness of 30 mm × 30 mm × 1 mm by chemical vapor deposition under vacuum to obtain a coating film of parylene (registered trademark) having a thickness of 3 μm. Using parylene (registered trademark) formed on the glass substrate as a base material, silver was treated in the same manner as in Example 1 except that electroless gold plating (about 5 nm) was performed without electroless nickel plating. A base material obtained by electroless plating a silver nanowire layer in which a part of nanowires was embedded in a coating film of Parylene (registered trademark) was obtained.

Next, wiring (width 0.5 mm, length 4 mm) was formed by laser-etching the electroless-plated nanowire layer on the substrate. In order to accelerate the migration of silver, drop one drop of distilled water on the gold-plated silver nanowire wiring to the center of the wiring, cover the 0.5 mm long wiring with water droplets, and then energize for 20 minutes at a current value of 1 mA. The current value was gradually increased to 20 minutes at 10 mA, 20 minutes at 20 mA, 20 minutes at 30 mA, and 20 minutes at 40 mA, and the change in wiring resistance value during the process was continuously measured. The device used for measuring the wiring resistance was B2900A (manufactured by Keysight), and the resistance value measured before the test was measured using LorestaGP T610 manufactured by Mitsubishi Analytech. The initial resistance value of the wiring was 150Ω. Table 2 shows the migration resistance test results.

Example 4.
A parylene (registered trademark) base material formed on a glass substrate treated in the same manner as in Example 3 except that the coating amount of silver nanowires was changed was prepared. The initial resistance value of the wiring was 35Ω. Table 2 shows the migration resistance test results. Gold is plated on the outside of silver nanowires with a pentagonal cross section to a thickness of 5 nm or less.

Comparative example 2.
A parylene (registered trademark) substrate formed on a glass substrate treated in the same manner as in Example 3 except that electroless gold plating was not performed was prepared, and a migration resistance test was carried out. The initial resistance value of the wiring was 140Ω. Table 2 shows the migration resistance test results.

As shown in Table 2, the wiring of Comparative Example 2 was disconnected as soon as the current value was increased to 10 mA after passing a constant current (1 mA) for 20 minutes. On the other hand, the wiring of Example 3 was not broken while a constant current of 10 mA was passed for 20 minutes, and was broken after the current value was increased to 20 mA. We are evaluating the phenomenon that part of the wiring melts as the migration progresses, causing disconnection between the terminals. It is considered that this has the effect of suppressing the migration of silver by plating, and the migration resistance characteristics of the silver nanowires are improved. It can be seen that the wiring prepared in Example 4, which has a lower initial resistance value, does not show any disconnection even when the current value is increased to 40 mA, and the characteristics are further improved.

Example 5.
The same treatment as in Example 1 was carried out except that the plating method was different, to prepare a polyurethane base material in which silver nanowires were partially embedded in the base material.

A polyurethane base material on which silver nanowires are formed is treated with an Ag discoloration remover (EETOREX 70 manufactured by Nippon Electroplating Engineers (EEJA)) for 10 seconds, treated with 0.1-specified dilute sulfuric acid for 10 seconds, at 70 ° C. A Pt plating layer was formed by treating with a Pt plating solution (PRECIOUSFAB Pt3000 manufactured by EEJA). During Pt plating, a current of about ^{1.0 A / dm 2} is applied to the object to be plated with respect to the counter electrode for about 10 seconds. As a result, an electrolytic plating layer of a Pt layer (about 1 to 100 nm) was formed on the surface of the silver nanowires.

The samples were observed using a scanning electron microscope (FE-SEM SU8020, manufactured by Hitachi High-Technologies Corporation) and an atomic resolution analysis electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.).

FIG. 4 shows an SEM photograph of a polyurethane base material in which Pt-plated silver nanowires according to Example 5 are embedded in the base material. FIG. 4 is a photograph taken using the scanning electron microscope (FE-SEM SU8020, manufactured by Hitachi High-Technologies Corporation). In FIG. 4, it can be confirmed that a part of the silver nanowires does not have a plating film formed and is embedded in the base material by external energy (heat treatment similar to Example 1). It can also be confirmed from the figure that the plating film is formed only on the silver nanowires exposed on the surface layer.

Further, FIG. 5 shows a cross-sectional TEM photograph of the Pt-plated silver nanowires according to Example 5. FIG. 5 is a photograph taken using the atomic resolution analysis electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.). In FIG. 5, it can be seen that Pt is plated on the outer layer of the silver nanowire having a pentagonal cross section with an average thickness of about 30 nm. (Each layer is distinguished by the shade of the TEM image.)

Next, wiring (width 0.5 mm, length 4 mm) was formed by laser etching as in Example 3. In order to accelerate the migration of silver, drop one drop of physiological saline on the platinum-plated silver nanowire wiring, cover the wiring 0.5 mm length with water droplets, apply a voltage at a constant voltage of 1 V for 20 minutes, and wire in the middle. The change in resistance value was continuously measured. The device used for measuring the wiring resistance is B2900A (manufactured by Keysight), and the migration resistance test results are shown in Table 3.

Comparative example 3.
The same evaluation as in Example 5 was performed except that a polyurethane base material of silver nanowires not subjected to electroplating was used. Table 3 shows the migration resistance test results.

As shown in Table 3, in the wiring of Comparative Example 3, when a constant voltage (1V) was applied for 5 minutes, the wiring was broken, whereas in the wiring of Example 5, a constant voltage of 1V was applied for 5 minutes. No disconnection was observed during the period, and no disconnection was observed even when the same voltage was additionally applied for 20 minutes. It is considered that plating has the effect of suppressing the migration of silver, and the migration resistance characteristics of silver nanowires are improved.

Example 6.
Similar to Example 1, an electroless gold-plated silver nanowire / polyurethane substrate was prepared. This base material was irradiated with pulsed light in a single shot under the conditions of 655 V and 50 msec under an atmosphere of air temperature and room temperature using a pulsed light irradiating device PulseForge 3300 (manufactured by Novacentrix).

A sample (a silver nanowire layer is formed on the entire surface of a substrate having a width of 15 mm and a length of 30 mm) is subjected to a desktop tensile tester (EZ-test, manufactured by Shimadzu Corporation, test speed: 15-60 mm / min, chuck interval: It was attached to 12 mm, load: 0% -20% strain), repeated expansion and contraction tests were performed, and the resistance value of the sample was measured at a terminal attached to a jig with 34410A multimeter and 11059A (manufactured by Agilent Technologies). The results of the expansion and contraction test are shown in Table 4.

Comparative example 4.
The same evaluation as in Example 6 was performed except that a polyurethane base material of silver nanowires which was not electroless plated and was not irradiated with pulsed light (connection treatment of metal nanowires) was used. The results of the expansion and contraction test are shown in Table 4.

In Comparative Example 4, the wire was broken in 20 expansion and contraction tests, whereas in Example 6 after plating and pulsed light irradiation (metal nanowire connection treatment), the initial resistance value was larger than that in Comparative Example 4. However, the resistance value can be measured even after 100 times, and it can be seen that the stretch resistance is improved.

Example 7.
A silver nanowire / polyurethane base material was prepared in the same manner as in Example 1 except that the coating amount of the silver nanowire / ethanol dispersion was changed, and the electroless gold plating described in Example 2 (the electroless Ni-P plating treatment was performed. Instead, a cyan-based Au plating solution (KG-545Y manufactured by JX Metal Trading Co., Ltd.) and KAu (CN) ₂ were directly subjected to electroless gold plating. The wiring resistance before and after plating was measured using B2900A (manufactured by Keysight). The results are shown in Table 5.

Comparative example 5.
Similar to Example 7 except that both the heat treatment after coating the silver nanowire / ethanol dispersion on the substrate (100 ° C., 2 minutes) and the oven heat treatment after Pd catalyst treatment (100 ° C., 5 minutes) were omitted. A silver nanowire / polyurethane base material was prepared, electroless gold-plated, and resistance was evaluated in the same manner as in Example 7. The results are shown in Table 5.

From Table 5, it can be seen that the silver nanowires were embedded in the base material by the heat treatment after the application of the silver nanowires / ethanol dispersion, and the subsequent gold plating on the silver nanowires was stably performed.

Example 8.
An electroless gold-plated silver nanowire / polyurethane substrate was prepared in the same manner as in Example 7. Table 6 shows the initial resistance value before plating and the resistance value after being left in the air for 8000 hours.

Comparative example 6.
A silver nanowire / polyurethane base material not subjected to electroless gold plating was prepared in the same manner as in Example 7 except that electroless gold plating was omitted. Table 6 shows the initial resistance value and the resistance value after being left in the atmosphere for 8000 hours.

From Table 6, it can be seen that the base material after plating has no change in resistance value even when stored in the atmosphere, and thus has durability that is not affected by oxidation and sulfurization due to being left in the atmosphere.

10 substrates, 12 metal nanowire layers.

Claims (9)

A base material on which a metal nanowire layer having intersections of a plurality of metal nanowires is formed, in which a part of the metal nanowires is embedded in the base material and the other part is exposed from the base material.
A substrate on which a metal nanowire layer is formed, characterized in that only a portion of the exposed metal nanowire is plated on part or all of the side surface of the metal nanowire. The base material on which the metal nanowire layer according to claim 1 is formed, in which at least a part of the metal nanowires is connected. The base material is any one of the group consisting of polyurethane, silicone resin, saturated polyester, polycarbonate, polyparaxylylene (parylene (registered trademark)), thermoplastic polyimide, polyether sulfone, acrylic resin, polyolefin, and polyvinyl chloride. A base material on which the metal nanowire layer according to claim 1 or 2 is formed. The base material on which the metal nanowire layer according to any one of claims 1 to 3 is formed, wherein the metal constituting the metal nanowire is silver or copper. A step of forming a metal nanowire layer having intersections of a plurality of metal nanowires on a base material, and applying external energy to the substrate on which the metal nanowire layers are formed to embed a part of the metal nanowires in the base material, and the like. The process of leaving the part exposed from the base material,
A method for producing a base material on which a metal nanowire layer is formed, which comprises a step of plating a part or all of a side surface of the metal nanowire only on an exposed portion of the metal nanowire. The method for producing a base material on which a metal nanowire layer is formed according to claim 5, further comprising a step of connecting at least a part of the metal nanowires before or after the step of plating. The base material is any one of the group consisting of polyurethane, silicone resin, saturated polyester, polycarbonate, polyparaxylylene (parylene (registered trademark)), thermoplastic polyimide, polyether sulfone, acrylic resin, polyolefin, and polyvinyl chloride. The method for producing a base material on which a metal nanowire layer is formed according to claim 5 or 6. The method for producing a base material on which a metal nanowire layer is formed according to any one of claims 5 to 7, wherein the metal constituting the metal nanowire is silver or copper. A sensor or functional element provided with a base material on which the metal nanowire layer according to any one of claims 1 to 4 is formed.

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