JP2010186642A - Transparent conductive sheet and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent conductive sheet which can form a transparent conductive film without damaging a transparent substrate when forming the transparent conductive film on the transparent substrate by application and has good conductivity and transparency. <P>SOLUTION: The transparent conductive sheet 10 includes: the transparent substrate 11; and the transparent conductive film 12 formed on the transparent conductive film 11. The transparent conductive film 12 includes a transparent conductive layer 12b including transparent conductive particles, and a transparent high refractive index layer 12a including particles having a refractive index higher than that of the transparent conductive particles. The transparent conductive layer 12b is formed on the transparent high refractive index layer 12a, and the transparent high refractive index layer 12a is arranged at a transparent substrate 11 side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transparent conductive sheet in which a transparent conductive film is provided on a transparent substrate and a method for producing the same.

  Conventionally, as materials for transparent conductive films and transparent conductive inks, tin oxide particles, antimony-containing tin oxide particles (ATO), tin-containing indium oxide particles (ITO), aluminum-containing zinc oxide particles (AZO), gallium-containing zinc oxide Particles (GZO) and the like are known. In particular, tin-containing indium oxide particles in which tin is contained in indium oxide are cathode ray tubes for office automation (OA) equipment that are required to have anti-static and electromagnetic shielding because of their high transparency to visible light and high conductivity. (CRT) panel surfaces, liquid crystal display (LCD) surfaces, etc. are used by coating. Furthermore, the transparent conductive film produced by applying a coating liquid (ink) containing tin-containing indium oxide particles is expected to be applied to fields that require higher translucency and conductivity, such as touch panels. Yes.

  In addition, the film forming method of the transparent conductive film that is mainly used at present is a physical method such as a vacuum evaporation method or a sputtering method, but with the increase in size of the substrate on which the film is formed, the manufacturing apparatus becomes large, There is a problem that the cost becomes high.

  From the viewpoint of cost and simplicity, the formation of a transparent conductive film by a coating method has been studied. For example, using an ink in which conductive particles such as a silica sol liquid containing ITO fine particles (see Patent Document 1) and a coating liquid composed of ITO fine particles, a silicate for binder and a polar solvent (see Patent Document 2) are dispersed, A manufacturing method is known in which an ITO transparent conductive film is formed on a substrate such as glass by spin coating, spray coating, dip coating, or the like by applying, drying, and baking. However, in the method of forming a transparent conductive film by applying an ink in which conductive particles are dispersed on a transparent substrate, the contact between the conductive particles is hindered by a binder that is usually insulative, so that the film is formed. There is a problem that the sheet resistance value of the transparent conductive film becomes two orders of magnitude higher than that of the transparent conductive film formed by sputtering. Therefore, in the process of forming the transparent conductive film, in order to obtain a practical sheet resistance value, it is necessary to sinter the transparent conductive sheet at a high temperature to enhance the contact between the conductive particles. As a method for sintering the transparent conductive sheet at a high temperature, there is usually a method of firing in an electric furnace or a high-temperature bath. When the transparent conductive sheet is sintered at a high temperature in this way, the substrate, particularly polyethylene terephthalate is used. There is a risk of damaging a flexible substrate made of a synthetic resin such as a (PET) film.

  In Patent Document 3, tin-containing indium oxide particles having a particle diameter of 40 nm are used, the volume content of particles in the coating film is set to 60 to 80%, and a dry coating film having a film thickness of 3 μm is prepared, and then a steel roll. Has proposed a method of performing a rolling process. However, when only a temperature of about 80 ° C. can be applied and the total light transmittance is about 70%, the sheet resistance is 500 Ω / square or less, but the case where the total light transmittance is as high as about 80% is maintained. However, there is a problem that the sheet resistance value becomes high because it is necessary to reduce the coating film thickness.

  Patent Document 4 proposes obtaining a transparent conductive film having a low resistance value by irradiating the transparent conductive film with microwaves. Further, Patent Document 5 proposes forming a film having low resistance and high visible light transmittance by irradiating the transparent conductive film with plasma or electromagnetic waves. However, in any case, there is a risk of damaging the substrate.

Japanese Patent Laid-Open No. 2-312136 JP-A-8-176794 JP-A-4-237908 JP 2000-123658 A JP 2006-49107 A

  Thus, when forming a transparent conductive film on a board | substrate by application | coating, conventionally, it was difficult to obtain the transparent conductive sheet which did not give a damage to a board | substrate and had favorable electroconductivity and transparency.

  The present invention solves the above-mentioned problem. When a transparent conductive film is formed on a substrate by coating, the transparent conductive film is formed without damaging the substrate, and has both good conductivity and transparency. It provides a sex sheet.

  The transparent conductive sheet of the present invention is a transparent conductive sheet including a transparent substrate and a transparent conductive film formed on the transparent substrate, and the transparent conductive film includes a transparent conductive particle including transparent conductive particles. A transparent high refractive index layer including particles having a higher refractive index than the transparent conductive particles, and the transparent conductive layer is formed on the transparent high refractive index layer, the transparent high refractive index The rate layer is arranged on the transparent substrate side.

  Moreover, the manufacturing method of the transparent conductive sheet of this invention is a manufacturing method of the transparent conductive sheet containing a transparent substrate and the transparent conductive film formed on the said transparent substrate, Comprising: On the said transparent substrate A step of applying a first coating liquid to form a transparent high refractive index layer, a step of applying a second coating liquid on the transparent high refractive index layer to form a transparent conductive layer, and the transparent conductive layer A step of selectively heat-treating only the film, wherein the second coating liquid contains transparent conductive particles, and the first coating liquid contains particles having a higher refractive index than the transparent conductive particles. It is characterized by including.

  Since the transparent conductive sheet of the present invention has both good conductivity and transparency, it can be applied to transparent electrodes such as electronic paper, flat panel display (FPD) and solar cells. Further, according to the method for producing a transparent conductive sheet of the present invention, a transparent conductive film is formed on the substrate without damaging the substrate, and a transparent conductive sheet having both good conductivity and transparency is obtained. It is done.

It is a schematic sectional drawing which shows an example of the transparent conductive sheet of this invention.

  As a result of intensive studies to achieve the above object, the inventors have damaged the substrate by selectively heating only the transparent conductive film after forming the transparent conductive film on the transparent substrate by coating. The inventors have found that a transparent conductive sheet having excellent conductivity and transparency can be obtained, and have completed the present invention. Embodiments of the present invention will be described below.

(Embodiment 1)
First, an embodiment of the transparent conductive sheet of the present invention will be described. The transparent conductive sheet of the present invention includes at least a transparent substrate and a transparent conductive film formed on the transparent substrate. The transparent conductive film includes a transparent conductive layer containing transparent conductive particles and a transparent high refractive index layer containing particles having a higher refractive index than the transparent conductive particles (hereinafter also referred to as high refractive index particles). At least. The transparent conductive layer is formed on the transparent high refractive index layer, and the transparent high refractive index layer is disposed on the transparent substrate side.

  In addition, since the transparent high refractive index layer includes particles having a higher refractive index than the transparent conductive particles contained in the transparent conductive layer, the refractive index of the transparent high refractive index layer is higher than the refractive index of the transparent conductive layer. Get higher.

  Since the transparent conductive sheet of the present invention includes a transparent conductive film having a transparent conductive layer and a transparent high refractive index layer, it can exhibit good conductivity and transparency. In addition, since the transparent high refractive index layer of the transparent conductive film is disposed between the transparent substrate and the transparent conductive layer, even when the transparent conductive film side is heated when forming the transparent conductive film, Is absorbed by the transparent high refractive index layer, does not conduct to the transparent substrate, and does not damage the transparent substrate. In addition, when the heating is performed by flash lamp annealing, the transparent high refractive index layer exhibits the function of a light reflector, so that heat does not conduct to the transparent substrate and may damage the transparent substrate. Absent.

  In the transparent conductive sheet of this invention, the transparent heat insulation layer containing the particle | grains which have heat insulation can also be further arrange | positioned between a transparent substrate and a transparent conductive layer. Thereby, since heat conduction to the transparent substrate can be more effectively prevented, damage to the transparent substrate can be more reliably prevented. The particles having heat insulation properties are not particularly limited, and for example, silsesquioxane or hollow silica particles can be used.

  The volume content of the high refractive index particles in the transparent high refractive index layer and the volume content of the transparent conductive particles in the transparent conductive layer are not particularly limited, and the refractive index of the transparent high refractive index layer is transparent What is necessary is just to adjust the volume content rate of the particle | grains of each layer so that it may become higher than the refractive index of a layer.

  Next, the transparent conductive sheet of this invention is demonstrated based on drawing. FIG. 1 is a schematic cross-sectional view showing an example of the transparent conductive sheet of the present invention. In FIG. 1, a transparent conductive sheet 10 of the present invention includes a transparent substrate 11 and a transparent conductive film 12 on one main surface of the transparent substrate 11. The transparent conductive film 12 includes a transparent high refractive index layer 12a and a transparent conductive layer 12b from the transparent substrate 11 side.

  The transparent substrate 11 is not particularly limited as long as it is made of a transparent material. For example, a film or sheet made of materials such as polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide can be used. . The thickness of the transparent substrate 11 is usually 3 to 300 μm. The transparent substrate 11 may be a hard substrate such as a glass plate or may be flexible.

  The transparent substrate 11 may be added with additives such as an antioxidant, a flame retardant, a heat resistance inhibitor, an ultraviolet absorber, an easy lubricant, and an antistatic agent. Furthermore, in order to improve the adhesiveness with the film | membrane provided on it, you may provide an easily bonding layer (for example, primer layer) on the substrate surface, and surface treatments, such as a corona treatment and a plasma treatment, may be performed.

  The sheet resistance of the transparent conductive sheet of the present invention is preferably 100 Ω / square or less, more preferably 70 Ω / square or less, and particularly preferably 60 Ω / square or less. The said sheet resistance shows the electroconductivity of a transparent conductive sheet, and it shows that electroconductivity is so high that a value is low. In this specification, the sheet resistance refers to the sheet resistance of the transparent conductive film measured after being stored in a desiccator for 1 week after the production of the transparent conductive sheet. This is because immediately after the production of the transparent conductive sheet, the value of the sheet resistance may not be stable, and is stabilized after about one week.

  The total light transmittance in the wavelength region of 380 to 780 nm of the transparent conductive sheet is preferably 80% or more, and more preferably 85% or more. The said total light transmittance shows transparency of a transparent conductive sheet, and it shows that transparency is so high that a value is high.

(Embodiment 2)
Next, an embodiment of a method for producing a transparent conductive sheet of the present invention will be described. The manufacturing method of the transparent conductive sheet of this invention is a manufacturing method of the transparent conductive sheet containing a transparent substrate and the transparent conductive film formed on the said transparent substrate, Comprising: 1st on the said transparent substrate. A step of forming a transparent high refractive index layer by applying the coating liquid, a step of forming a transparent conductive layer by applying a second coating liquid on the transparent high refractive index layer, and only the transparent conductive film And a step of selectively heat-treating. Further, the second coating liquid contains transparent conductive particles, and the first coating liquid contains particles having a higher refractive index than the transparent conductive particles.

  Since the transparent high refractive index layer of the transparent conductive film is disposed between the transparent substrate and the transparent conductive layer, the heat is transparent even if the transparent conductive film side is heated when forming the transparent conductive film. It is absorbed by the high refractive index layer and does not conduct to the transparent substrate, and only the transparent conductive film can be selectively heated, and the transparent substrate is not damaged. In addition, when the heating is performed by flash lamp annealing, the transparent high refractive index layer exhibits the function of a light reflector, so that heat is not conducted to the transparent substrate, and only the transparent conductive film is selectively used. It can be heated and does not damage the transparent substrate.

  Hereinafter, an example of an embodiment of a method for producing a transparent conductive sheet of the present invention will be described in detail. However, description of the part which overlaps with the matter demonstrated in Embodiment 1 may be abbreviate | omitted.

<Preparation of transparent high refractive index layer>
In the production method of the present invention, first, a first coating liquid is applied on the transparent substrate to form a transparent high refractive index layer. The first coating liquid contains particles having a refractive index higher than that of transparent conductive particles contained in the second coating liquid described later, a dispersant, and a solvent.

  The high refractive index particles are not particularly limited as long as the particles have a higher refractive index than the transparent conductive particles described later, and examples thereof include zirconium oxide (refractive index: 2.4), titanium oxide (refractive index). : 2.52), cadmium oxide (refractive index: 2.49), barium titanate (refractive index: 2.4), and the like can be used. Among these, zirconium oxide is particularly preferable because it is excellent in transparency and light resistance (characteristic that particles can exist stably without causing a reaction by energy of light irradiation).

  The primary particle diameter of the high refractive index particles is preferably 5 to 50 nm. When the primary particle diameter is less than 5 nm, it tends to be difficult to increase the refractive index of the transparent high refractive index layer, and when the primary particle diameter is larger than 50 nm, the transparency tends to decrease. In the present specification, the primary particle diameter means an average of the particle diameters of at least 20 particles after observing and measuring the particle diameters of individual particles separated by grain boundaries using a transmission electron microscope (TEM). Average particle diameter.

  The dispersant is not particularly limited, and for example, a known dispersant such as a comb copolymer having a basic functional group as a particle adsorption site can be used.

  Examples of the solvent include aromatic solvents such as benzene, toluene, and xylene; ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone; acetate solvents such as ethyl acetate and butyl acetate; dimethyl carbonate, diethyl carbonate, and the like Carbonate ester solvents; alcohol solvents such as ethanol and isopropanol; and organic solvents such as hexane, tetrahydrofuran and dimethylformamide.

  The content of the high refractive index particles in the first coating liquid is preferably 1 to 50% by weight with respect to the total weight of the first coating liquid. This is because the viscosity of the first coating liquid falls within a range suitable for the coating process within this range. Moreover, it is preferable that content of the dispersing agent in said 1st coating liquid shall be 0.01-5 weight% with respect to the total weight of a 1st coating liquid. This is because within this range, the dispersibility of the high refractive index particles in the first coating solution can be improved.

  Further, in order to improve the coating film hardness and the adhesiveness with the transparent substrate, the first coating liquid may contain a binder. The binder is not particularly limited. For example, vinyl chloride resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, chloride Vinyl-hydroxyl group-containing alkyl acrylate copolymers, nitrocellulose, polyester resins, polyurethane resins, thermosetting resins, UV curable resins, and the like can be used. These binders may be used alone or in combination of two or more. An acrylic resin is preferable from the viewpoint of good optical properties and dispersibility. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

  The binder content in the first coating solution is preferably 0.03 to 15% by weight with respect to the total weight of the first coating solution. This is because within this range, the coating film hardness can be improved and the adhesion between the transparent substrate and the transparent high refractive index layer can be improved.

  A transparent high refractive index layer is formed by apply | coating the said 1st coating liquid to one main surface on a transparent substrate. The coating method is not particularly limited, and for example, coating methods such as roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, and gravure coating, or printing such as gravure printing, screen printing, offset printing, and ink jet printing. The method etc. can be used.

  The film thickness of the transparent high refractive index layer formed by the coating is not particularly limited, but in order to show high translucency and protect the transparent substrate, it is finally 0.1 to 6 μm. It is preferable to set so that. When the film thickness of the transparent high refractive index layer is less than 0.1 μm, the transparency is excellent, but the ability to protect the transparent substrate tends to decrease. Moreover, when the film thickness of the transparent high refractive index layer exceeds 6 μm, high transparency tends to be difficult to obtain.

  The first coating liquid applied to the transparent substrate is heat-treated to remove the dispersant and the solvent, thereby forming a transparent high refractive index layer composed of high refractive index particles. However, the transparent high refractive index layer may contain a dispersant, and a trace amount of solvent may remain. The heating temperature may be a temperature at which the transparent substrate is not thermally damaged, and may be 550 ° C. or lower when the transparent substrate is a glass substrate, and 150 ° C. or lower when the transparent substrate is a resin substrate.

  You may perform a press work process and a calendar process with respect to the transparent high refractive index layer after the said heat processing. By performing press processing or calendaring, the particles in the coating layer are highly filled, and as a result, the average porosity in the transparent high refractive index layer is reduced and the optical properties are improved. In particular, by reducing the scattered light due to the voids between the particles, the haze value, which is a value representing the light scattering intensity, is remarkably reduced, and the transparency becomes high.

<Preparation of transparent conductive layer>
Next, in the manufacturing method of this invention, a 2nd coating liquid is apply | coated on the said transparent high refractive index layer, and a transparent conductive layer is formed. The second coating liquid contains transparent conductive particles, a dispersant, and a solvent.

  The transparent conductive particles are not particularly limited as long as the particles have both transparency and conductivity. For example, conductive metal oxide particles and conductive nitride particles can be used. Examples of the conductive metal oxide particles include metal oxide particles such as indium oxide, tin oxide, zinc oxide, and cadmium oxide. In addition, conductive metal oxide particles doped with tin, antimony, aluminum, gallium, with one or more metal oxides selected from the group consisting of indium oxide, tin oxide, zinc oxide and cadmium oxide as main components, For example, antimony-containing tin oxide particles (ATO), tin-containing indium oxide particles (ITO), aluminum-containing zinc oxide particles (AZO), gallium-containing zinc oxide particles (GZO), conductive metal oxide particles obtained by replacing ITO with aluminum, etc. Is mentioned. Among these, ITO is particularly preferable because it is excellent in transparency, conductivity, and chemical characteristics. In the present invention, the main component is a metal oxide serving as a crystal matrix.

  The primary particle diameter of the transparent conductive particles is preferably 5 to 150 nm. If the primary particle size is less than 5 nm, it tends to be difficult to obtain particles with good crystallinity. On the other hand, if the primary particle size is larger than 150 nm, the transparency tends to decrease.

  The dispersant and the solvent are not particularly limited, and for example, the same dispersants as those used in the first coating liquid can be used.

  The content of the transparent conductive particles in the second coating solution is preferably 1 to 50% by weight with respect to the total weight of the second coating solution. This is because the viscosity of the second coating solution is in a range suitable for the coating process if it is within this range. The content of the dispersant in the second coating solution is preferably 0.01 to 5% by weight with respect to the total weight of the second coating solution. This is because within this range, the dispersibility of the transparent conductive particles in the second coating solution can be improved.

Further, in order to improve the coating film hardness and the adhesiveness with the transparent high refractive index layer, the second coating liquid may contain a binder. The binder is not particularly limited, and for example, the same one as that used for the first coating liquid described above can be used.
The binder content in the second coating solution is preferably 0.03 to 15% by weight with respect to the total weight of the second coating solution. This is because within this range, the coating film hardness is improved and the adhesion between the transparent conductive layer and the transparent high refractive index layer is improved.

  A transparent conductive layer is formed by applying the second coating liquid on the transparent high refractive index layer. The coating method is not particularly limited, and for example, the same coating method as that for the first coating liquid described above can be used.

  The film thickness of the transparent conductive layer formed by the coating is preferably set so as to be finally 0.1 to 6 μm. When the film thickness of the transparent conductive layer is less than 0.1 μm, the transparency is excellent, but high conductivity tends to be difficult to obtain. Moreover, when the film thickness of the transparent conductive layer exceeds 6 μm, high transparency tends to be difficult to obtain.

  The second coating liquid applied to the transparent high refractive index layer may be heat-treated to remove the dispersant and the solvent. Thereby, the transparent conductive layer which consists of transparent conductive particles is formed. However, the transparent conductive layer may contain a dispersant, and a trace amount of solvent may remain. The heating temperature may be a temperature at which the transparent substrate is not thermally damaged, and may be 550 ° C. or lower when the transparent substrate is a glass substrate, and 150 ° C. or lower when the transparent substrate is a resin substrate.

  You may perform a press work process and a calendar process with respect to the transparent conductive layer after the said heat processing. By performing press processing or calendaring, the particles in the coating layer are highly filled. As a result, the average porosity in the transparent conductive layer is reduced, and the optical characteristics and conductivity are improved. In the optical characteristics, the haze value, which is a value representing the light scattering intensity, is remarkably reduced by reducing the scattered light due to the voids between the particles, and the transparency becomes high.

  Subsequently, only the transparent conductive film is selectively heat-treated. By selectively heat-treating the transparent conductive film, a transparent conductive sheet having good conductivity and transparency can be obtained without damaging the transparent substrate. This is presumably because, by selectively heat-treating the transparent conductive film, the bondability between the transparent conductive particles in the transparent conductive layer is increased, so that the conductivity of the transparent conductive layer is improved.

  The selective heat treatment is not particularly limited as long as only the transparent conductive film is selectively heated. The heating temperature is not particularly limited as long as only the transparent conductive film can be heated, heat is not conducted to the transparent substrate, and the sheet resistance of the transparent conductive sheet can be reduced. For example, a short lamp annealing treatment from the transparent conductive film side, a hot air surface layer annealing treatment in which the transparent conductive film side is subjected to hot air treatment while the substrate side is subjected to a cold air treatment, a flash lamp annealing treatment from the transparent conductive film side, and the like. Among these, the flash lamp annealing treatment is preferable because it can impart superior conductivity and transparency without damaging the substrate.

In the flash lamp annealing treatment, the irradiation energy density and the irradiation time are not particularly limited as long as the sheet resistance of the transparent conductive sheet can be reduced. Although depending on the film thickness of the transparent conductive layer, the irradiation energy density is preferably in the range of 0.5 to ¹⁰ J / cm ^{2 in} the final film thickness range of 0.1 to 6 μm. In the present invention, the total energy applied to the unit area of the sample substrate in one pulse, that is, one irradiation process is referred to as irradiation energy per unit area, and 1 cm ² of the sample substrate in one irradiation process. The total energy irradiated to the unit area is called irradiation energy density. The irradiation time is preferably in the range from 10 μs to 10 ms, more preferably in the range from 50 μs to 1 ms, and particularly preferably in the range from 50 μs to 1 ms. If the irradiation time is shorter than 10 μs, uneven irradiation tends to occur. On the other hand, if it exceeds 10 ms, the transparent substrate tends to be deformed or the transparent conductive layer tends to crack.

  The transparent conductive sheet of the present invention produced as described above can achieve both excellent conductivity and transparency without damaging the substrate.

  Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples.

Example 1
<Preparation of coating liquid for forming a transparent high refractive index layer (first coating liquid)>
Zirconium oxide particles (refractive index: 2.4, primary particle size: 10 nm) 5.4 g, Japan Lubrizol Corporation "Solspers 32550" (trade name) 0.6 g, methyl ethyl ketone, toluene equimolar each In addition to 14 g of the mixed organic solvent, the mixture was mixed and then dispersed with a paint conditioner using zirconia beads for dispersion to prepare a coating solution for forming a transparent high refractive index layer.

<Preparation of coating liquid for forming transparent conductive layer (second coating liquid)>
5.4 g of ITO particles (refractive index: 2.1, primary particle size: 30 nm) and 0.6 g of a dispersant “Solspers32550” (trade name) manufactured by Nippon Lubrizol Co., Ltd., and equimolar amounts of methyl ethyl ketone and toluene, respectively. After mixing in addition to 14 g of the mixed organic solvent, dispersion treatment was performed with a paint conditioner using zirconia beads for dispersion to prepare a coating liquid for forming a transparent conductive layer.

<Formation of transparent high refractive index layer>
First, an alkali-free glass plate having a width of 50 mm, a length of 50 mm, and a thickness of 0.8 mm was prepared as a transparent substrate. Next, the prepared coating liquid for forming a transparent high refractive index layer was applied on the glass substrate with a spin coater for 10 seconds under the condition of a rotation speed of 1500 rpm, thereby forming a transparent high refractive index layer. Subsequently, heat treatment was performed at 300 ° C. in an electric furnace in an air atmosphere.

<Formation of transparent conductive layer>
The prepared coating liquid for forming a transparent conductive layer was applied on the transparent high refractive index layer with a spin coater for 10 seconds under the condition of a rotational speed of 1500 rpm to form a transparent conductive layer. Subsequently, heat treatment was performed at 300 ° C. in an electric furnace in an air atmosphere. Further, from the transparent conductive film side, only the transparent conductive film was subjected to flash lamp annealing treatment (hereinafter also referred to as FLA treatment) at an irradiation energy density of 4.25 J / cm ² and an irradiation time of 200 μs. 1 transparent conductive sheet was obtained.

(Example 2)
In the coating liquid for forming a transparent high refractive index layer, the amount of zirconium oxide particles used was 5.16 g, and the amount of dispersant used was 0.84 g. A transparent conductive sheet was obtained.

(Example 3)
The transparent conductive material of Example 3 was the same as Example 1 except that the particles contained in the coating liquid for forming a transparent high refractive index layer were changed to titanium oxide (refractive index: 2.52, primary particle diameter: 10 nm). Sex sheet was obtained.

(Comparative Example 1)
A transparent conductive sheet of Comparative Example 1 was obtained in the same manner as in Example 1 except that the transparent high refractive index layer was not formed.

(Comparative Example 2)
A transparent conductive sheet of Comparative Example 2 was obtained in the same manner as Comparative Example 1 except that the flash lamp annealing treatment was not performed.

(Comparative Example 3)
The entire transparent conductive sheet of Comparative Example 2 that was not subjected to the flash lamp annealing treatment was heat-treated at 550 ° C. in an electric furnace in an air atmosphere to obtain a transparent conductive sheet of Comparative Example 3.

(Comparative Example 4)
The entire transparent conductive sheet of Comparative Example 2 that was not subjected to the flash lamp annealing treatment was heat-treated at 650 ° C. in an electric furnace in an air atmosphere to obtain a transparent conductive sheet of Comparative Example 4.

(Comparative Example 5)
The transparent conductive material of Comparative Example 5 was the same as Example 1 except that the particles contained in the coating liquid for forming a transparent high refractive index layer were changed to silicon oxide (refractive index: 1.45, primary particle size: 20 nm). Sex sheet was obtained.

  About the transparent conductive sheets of Examples 1 to 3 and Comparative Examples 1 to 5, the sheet resistance, the total light transmittance, the surface property, the substrate damage, the refractive index of the transparent conductive layer, and the transparent high refractive index layer are as follows. The refractive index was measured and evaluated, and the results are shown in Table 1.

<Sheet resistance>
Using a resistivity measuring apparatus “Loresta AP MCP-T400” (manufactured by Mitsubishi Chemical Co., Ltd.), the sheet resistance of the transparent conductive sheet after being stored in a desiccator for 1 week was measured.

<Total light transmittance>
An ultraviolet-visible near-infrared spectrophotometer “V-570” (manufactured by JASCO Corporation) was used to measure the total light transmittance in a wavelength region of 380 to 780 nm of the transparent conductive sheet.

<Surface property>
The surface on the transparent conductive film side was visually observed, and A with no cracks and B with cracks were evaluated.

<Board damage>
The transparent substrate side of the transparent conductive sheet was visually observed and judged as follows.
A: When there was no change in shape, it was determined that there was no damage to the transparent substrate.
B: When there was any deformation or when it was burnt, it was determined that the transparent substrate was damaged.

<Refractive index of layer>
The refractive index of the mixture, that is, the refractive index of the layer was determined by the following formula of Lorentz-Lorenz.

Refractive index of layer = Σv × (n ² −1) / (n ² +2)

  In the above formula, v is the volume content of the particles contained in the layer, and n is the refractive index of the particles contained in the layer. Specifically, it is assumed that no voids are included when forming the layer, and the heat treatment is performed to decompose and remove all of the dispersant, and the refraction of the layer assuming that the volume of the dispersant becomes voids. The ratio was calculated assuming that the specific gravity of the dispersant was 1.2, the specific gravity of ITO was 7.1, the specific gravity of zirconium oxide was 6.0, the specific gravity of titanium oxide was 4.0, and the specific gravity of silicon oxide was 2.2.

  Table 1 shows the following.

  From the comparison of Examples 1 to 3 and Comparative Example 1, by forming a transparent high refractive index layer on the transparent conductive film, when only the transparent conductive film is selectively heat-treated, for example, when flash lamp annealing is performed, It was found that sheet resistance can be further reduced while maintaining high transparency and good surface properties.

  From the comparison of Comparative Examples 1 to 3, in the heat treatment of the entire transparent conductive sheet by an electric furnace, unlike the case of selective heat treatment, for example, flash lamp annealing treatment, it is possible to obtain a low sheet resistance of 100Ω / square or less. I found it difficult. Moreover, in the comparative example 4, since the heating temperature was too high, it resulted in a glass substrate cracking.

  From comparison between Examples 1 to 3 and Comparative Example 5, it is preferable that the refractive index of the particles contained in the transparent high refractive index layer is higher than the refractive index of the transparent conductive particles contained in the transparent conductive layer. It was found that the sheet resistance can be reduced while maintaining.

  The present invention forms a transparent high-refractive index layer on a transparent substrate, and further forms a transparent conductive film having a two or more layer structure in which a transparent conductive layer is formed on the transparent high-refractive index layer, By selectively heat-treating only the transparent conductive film, a resistance comparable to that of the sputtering film can be realized, and a transparent electrode of a display element such as a flat panel display (FPD) or electronic paper that requires low resistance, a solar cell The use of transparent electrodes and the like is conceivable and the substrate is not damaged, so that it can be applied to a flexible substrate, and a wide range of uses can be expected.

DESCRIPTION OF SYMBOLS 10 Transparent conductive sheet 11 Transparent substrate 12 Transparent conductive film 12a Transparent high refractive index layer 12b Transparent conductive layer

Claims (10)

A transparent conductive sheet comprising a transparent substrate and a transparent conductive film formed on the transparent substrate,
The transparent conductive film includes a transparent conductive layer containing transparent conductive particles, and a transparent high refractive index layer containing particles having a higher refractive index than the transparent conductive particles,
The transparent conductive layer is formed on the transparent high refractive index layer,
The transparent conductive sheet, wherein the transparent high refractive index layer is disposed on the transparent substrate side.   The transparent conductive sheet according to claim 1, wherein a refractive index of the transparent high refractive index layer is higher than a refractive index of the transparent conductive layer.   The transparent conductive particles are conductive metal oxide particles, and the conductive metal oxide particles are at least one metal oxide particle selected from the group consisting of indium oxide, tin oxide, zinc oxide, and cadmium oxide. The transparent conductive sheet according to claim 1 or 2.   The transparent conductive sheet according to claim 3, wherein the conductive metal oxide particles are further doped with at least one element selected from the group consisting of tin, antimony, aluminum, and gallium.   The sheet resistance of the said transparent conductive sheet is 100 ohms / square or less, The transparent conductive sheet of any one of Claims 1-4.   The transparent conductive sheet according to any one of claims 1 to 5, wherein a total light transmittance in a wavelength region of 380 to 780 nm of the transparent conductive sheet is 80% or more. A method for producing a transparent conductive sheet comprising a transparent substrate and a transparent conductive film formed on the transparent substrate,
Applying a first coating solution on the transparent substrate to form a transparent high refractive index layer;
Applying a second coating liquid on the transparent high refractive index layer to form a transparent conductive layer;
And selectively heat-treating only the transparent conductive film,
The second coating liquid contains transparent conductive particles,
The method for producing a transparent conductive sheet, wherein the first coating liquid contains particles having a higher refractive index than the transparent conductive particles.   The method for producing a transparent conductive sheet according to claim 7, wherein the heat treatment is performed by any one selected from the group consisting of a lamp annealing treatment, a hot air surface layer annealing treatment, and a flash lamp annealing treatment.   The transparent conductive particles are conductive metal oxide particles, and the conductive metal oxide particles are at least one metal oxide particle selected from the group consisting of indium oxide, tin oxide, zinc oxide, and cadmium oxide. The method for producing a transparent conductive sheet according to claim 7 or 8.   The method for producing a transparent conductive sheet according to claim 9, wherein the conductive metal oxide particles are further doped with at least one element selected from the group consisting of tin, antimony, aluminum, and gallium.

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