JP2005209350A - Transparent conductive film and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a transparent conductive film easily forming network structure of noble metal fine particles more uniformly and developed more than existing one with a coating solution for forming a transparent conductive layer applying the noble metal fine particles, and to provide the transparent conductive film manufactured by this method, and having high transmission factor and high conductivity. <P>SOLUTION: A coating solution for forming a silica sol- containing transparent under coat layer is applied onto a transparent substrate, a coating solution for forming a noble metal fine particle-containing transparent conductive film is applied onto the undercoat layer, and they are baked to form two layered film comprising the transparent conductive layer and the undercoat layer. In the two layered film comprising the transparent conductive layer and the transparent undercoat layer, the transparent conductive film has a thickness of 50 nm or less, and the two layer film has a surface resistance of 100 kΩ/sq. or less, and only the two layer film not containing the transparent substrate has a visible ray transmission factor of 80% or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transparent conductive film formed by a coating method on a transparent substrate, in particular, a transparent conductive film applied to a front panel of a display device such as a cathode ray tube, a plasma display panel, a fluorescent display tube, or a liquid crystal display, and the like It relates to a manufacturing method.

  In a display device such as a cathode ray tube (CRT: also called a cathode ray tube), a plasma display panel (PDP), a fluorescent display tube (VFD), a liquid crystal display (LCD) used as a computer display, etc., the display screen is easy to see and visual fatigue It is necessary not to feel it.

Furthermore, recently, there are concerns about the adverse effects of low-frequency electromagnetic waves generated from CRT and the like on the human body, and it is desired that such electromagnetic waves do not leak to the outside. Such leakage electromagnetic waves can be prevented by forming a transparent conductive layer on the front plate surface of the display. For example, for preventing leakage electromagnetic waves (electric field shield) of CRT, the surface resistance is at least 10 ⁶ Ω / □ or less, preferably 5 × 10 ³ Ω / □ or less, more preferably 10 ³ Ω / □ or less. It is required to form a transparent conductive layer.

  As a low resistance transparent conductive layer for such a CRT electric field shield, several proposals have been made so far. For example, conductive oxide fine particles such as indium tin oxide (ITO) or metal fine particles are dispersed in a solvent. There is a method in which a transparent conductive layer forming coating solution is applied and dried on a CRT front glass (front plate) by spin coating or the like, and then baked at a temperature of about 200 ° C. to form a transparent conductive layer. The formation of the transparent conductive layer by this coating method is a very advantageous method because it is much simpler and less expensive to manufacture than the method of forming by a CVD method or a sputtering method.

However, in the transparent conductive layer formed using this coating liquid for forming a transparent conductive layer, when using conductive oxide fine particles such as indium tin oxide (ITO), the surface resistance of the obtained transparent conductive layer is 10 ^{It was as high as 4} to 10 ⁶ Ω / □, which was not sufficient to shield the leakage electric field. On the other hand, the transparent conductive layer forming coating liquid to which the metal fine particles are applied has a low resistance of 10 ² to 10 ³ Ω / □, although the transmittance of the obtained film is lower than that of the coating liquid using ITO. Since a transparent conductive layer can be obtained, it will continue to be a promising method.

  As the metal fine particles applied to the coating liquid for forming the transparent conductive layer, noble metals that are not easily oxidized in air, for example, silver, gold, platinum, palladium, rhodium, ruthenium, and the like have been proposed (JP-A-8-77832). No., JP-A-9-55175). In the above publication, it is described that metal fine particles other than noble metals, such as iron, nickel, cobalt, etc. are applicable, but in actuality, these metal fine particles are coated with an oxide film on the surface in an air atmosphere. Therefore, it is difficult to obtain good conductivity as the transparent conductive layer.

  Further, when comparing the specific resistances of noble metals such as silver, gold, platinum, rhodium, ruthenium, and palladium, the specific resistances of platinum, rhodium, ruthenium, and palladium are respectively 10.6, 4.51, 7.6, 10, and 10. 0.8 μΩ · cm, which is higher than the specific resistances of 1.62 and 2.2 μΩ · cm of silver and gold. Therefore, since it is more advantageous to apply silver fine particles or gold fine particles to form a transparent conductive layer having a low surface resistance, silver fine particles or gold fine particles have been conventionally used as noble metal fine particles used in coating solutions for forming transparent conductive layers. It is mainly used.

  However, the silver fine particles are limited in their use from the standpoint of being inferior in weather resistance because they are easily deteriorated by sulfurization or saline. On the other hand, fine particles such as gold, platinum, rhodium, ruthenium, and palladium do not have the above-mentioned weather resistance problem, but are not necessarily optimal in view of cost. Therefore, recently, noble metal-coated silver fine particles in which the surface of silver fine particles is coated with gold or platinum alone or a composite of gold and platinum, or a noble metal alloy composed of one or more kinds of noble metals other than gold and gold (for example, silver). Fine particles and the like have been proposed (see JP-A-11-228872 and JP-A-2000-268639).

Further, in a display device such as a CRT, in order to make the display screen easy to see, the surface of the front plate is subjected to an antiglare treatment to suppress the reflection of the screen. As this anti-glare treatment, a transparent two-layer film comprising a transparent conductive layer having a high refractive index and a transparent coating layer having a low refractive index is provided so that the reflected light causes destructive interference with the incident light. In general, an antiglare treatment by an interference method for controlling the film thickness is performed. In addition, in the metal, among the optical constants (n−ik, n: refractive index, i ² = −1, k: extinction coefficient), the value of n (refractive index) is small, but the value of k is large. For this reason, even when a transparent conductive layer made of metal fine particles is used, an antireflection effect due to light interference can be obtained in the transparent two-layer film.

  By the way, in the case of a transparent conductive layer formed by a coating method using a coating liquid for forming a transparent conductive layer, since a metal is essentially not transparent to visible light, in order to achieve both high transmittance and low resistance. It is desirable that as little metal fine particles as possible form a conductive path efficiently in the transparent conductive layer. That is, as a structure of a transparent conductive layer obtained by applying a general coating liquid for forming a transparent conductive layer mainly composed of a solvent and metal fine particles on a substrate and drying it, fine pores are formed in the metal fine particle layer. It is necessary to have an introduced structure, a so-called network (network-like) structure.

  By forming such a network structure of metal fine particles, a transparent conductive layer having a low resistance and a high transmittance can be obtained. This is thought to be because the mesh portion made of metal fine particles functions as a conductive path, while the hole portion formed in the mesh structure functions to improve the transmittance.

And as a method of forming such a network (network-like) structure of metal fine particles, the following two methods are roughly classified.
(1) A method of forming a network structure by agglomerating metal fine particles in a film forming process of applying and drying a coating liquid for forming a transparent conductive layer.
(2) A method of forming a network structure of metal fine particles by using a coating liquid for forming a transparent conductive layer in which metal fine particle aggregates in which a plurality of metal fine particles are aggregated are dispersed and applying and drying the same.

  As the method of (1) above, for example, by utilizing the fact that metal fine particles are more likely to aggregate than oxide fine particles and the like, by appropriately selecting the solvent composition and the like of the coating liquid for forming a transparent conductive layer, A network structure can be obtained by agglomerating a certain amount of metal fine particles inevitably in the dry film formation process (see JP-A-9-115438).

  In addition, an aggregation inducer, an aggregation promoting high boiling point solvent, or the like can be added to the coating liquid for forming a transparent conductive layer to actively promote aggregation between metal fine particles (see JP-A-10-110123). Further, an aggregation promoting layer made of inorganic oxide fine particles is previously provided on the lower side of the metal fine particle layer, and when the metal fine particle solution is applied, the solvent is mainly selected into pores formed by the lower inorganic oxide fine particles. It is possible to promote the aggregation of the metal fine particles by permeating into (see JP 2003-77340 A).

  As the method (2), for example, as a coating liquid for forming a transparent conductive layer, primary particles are not uniformly dispersed, but are dispersed in a state of secondary particles in which primary particles are aggregated in a form having small pores. There is a method using a dispersion of fine metal particles ("Industrial Materials", Vol. 44, No. 9, 1996, p68-71). Furthermore, a method using a coating liquid for forming a transparent conductive layer in which metal fine particle groups in which metal fine particles are aggregated in a chain form is dispersed (see Japanese Patent Application Laid-Open No. 2000-124662) is also known.

  Comparing the methods (1) and (2) described above, the method (2) is because the aggregates of metal fine particles are preliminarily completed in the coating liquid for forming a transparent conductive layer. This has the advantage that the structure can be easily formed.

JP-A-8-77832 JP-A-9-55175 JP-A-11-228872 JP 2000-268639 A JP-A-9-115438 JP-A-10-110123 JP 2003-77340 A JP 2000-124662 A “Industrial Materials”, Vol. 44, No. 9, 1996, p.

  Conventionally, even with a general coating liquid for forming a transparent conductive layer, it has been possible to form a transparent conductive layer having a certain degree of network structure by using the above-described method. However, networking of noble metal fine particles in the film forming process of the coating liquid for forming a transparent conductive layer is often difficult because many conditions actually affect each other. For this reason, the contact resistance between the noble metal particles is likely to increase, or the network is likely to be partially cut, resulting in a decrease in the conductivity of the transparent conductive layer.

  For example, as described in JP-A No. 2000-124662, the method using a coating liquid for forming a transparent conductive layer containing noble metal fine particles aggregated in advance in a chain form can also be used for the noble metal fine particles contained in the coating liquid. When the absolute number is small, that is, when the concentration of the noble metal fine particles is low, it is difficult to form a sufficient conductive path because the aggregates are difficult to join when applying and drying the coating solution. In addition, in the coating liquid for forming a transparent conductive layer subjected to excessive aggregation treatment, even if a sufficient conductive path is obtained, the dispersion stability of the fine particles is poor, so that the storage stability and coating properties of the coating liquid are reduced. Serious problems often occurred.

  Further, as proposed in the above Japanese Patent Application Laid-Open No. 2003-77340, in the method of providing an aggregation promoting layer composed of inorganic oxide fine particles having a predetermined particle diameter on a transparent substrate in advance, noble metal-coated silver fine particles In the case of such a coating liquid for forming a transparent conductive layer to which noble metal fine particles are applied, the conductivity of the transparent conductive film is not improved at all regardless of the particle diameter of the inorganic oxide fine particles. In addition, local noble metal fine particles are aggregated due to the influence of electrolyte ions and the like eluted from the aggregation promoting layer, which often causes problems in the coating properties of the coating liquid for forming a transparent conductive layer.

  The present invention has been made by paying attention to such a conventional problem, and by using a coating liquid for forming a transparent conductive layer to which noble metal fine particles are applied, a network structure of noble metal fine particles that is more uniform and developed than before is provided. To provide a method for producing a transparent conductive film that can be easily formed, and to provide a transparent conductive film that is manufactured by the method and that has low resistance and excellent conductivity while maintaining high transmittance. Objective.

  As a result of intensive studies to solve the above-described conventional problems, the present inventor has previously made a transparent base material when forming a transparent conductive layer using a coating liquid for forming a transparent conductive layer to which noble metal fine particles are applied. The inventors have found that a transparent conductive film excellent in conductivity can be obtained while maintaining a high transmittance just by applying an extremely dilute silica sol solution on the surface, and the present invention has been completed. .

  That is, the transparent conductive film according to claim 1 provided by the present invention is a transparent conductive film formed on a transparent substrate, and a transparent undercoat mainly composed of silicon oxide formed on the transparent substrate. And a transparent conductive layer containing noble metal fine particles formed on the transparent undercoat layer.

  A transparent conductive film according to a second aspect of the present invention is the transparent conductive film according to the first aspect, wherein the thickness of the transparent undercoat layer is in the range of 10 to 100 nm. A transparent conductive film according to a third aspect of the present invention is the transparent conductive film according to the first or second aspect, wherein the noble metal fine particles have at least the surface of silver fine particles selected from gold, platinum, palladium, rhodium and ruthenium. It is a noble metal-coated silver fine particle coated with one kind of noble metal.

  A transparent conductive film according to a fourth aspect of the present invention is the transparent conductive film according to any one of the first to third aspects, wherein the transparent conductive layer has a thickness of 50 nm or less. From the transparent conductive layer and the transparent undercoat layer, The two-layer film is characterized in that the surface resistance is 100 kΩ / □ or less, and the visible light transmittance of only the two-layer film not including the transparent substrate is 80% or more.

  Moreover, the manufacturing method of the transparent conductive film concerning Claim 5 which this invention provides is a method of forming a transparent conductive film on a transparent base material, Comprising: The transparent undercoat layer containing a silica sol on a transparent base material A coating liquid for forming is applied, a coating liquid for forming a transparent conductive layer containing noble metal fine particles is applied on the coating layer, and then fired.

  The method for producing a transparent conductive film according to claim 6 of the present invention is the method for producing a transparent conductive film according to claim 5, wherein the silica sol of the coating liquid for forming the transparent undercoat layer is an alkyl silicate and / or a polymer thereof. It is characterized by being. The method for producing a transparent conductive film according to claim 7 according to the present invention is the method for producing a transparent conductive film according to claim 5 or 6, wherein the degree of polymerization of the silica sol is 500 or more in weight average molecular weight. .

  The method for producing a transparent conductive film according to claim 8 of the present invention is the method for producing a transparent conductive film according to any one of claims 5 to 7, wherein the concentration of the noble metal-coated silver fine particles in the coating liquid for forming the transparent conductive layer is used. Is in the range of 0.05 to 0.2% by weight.

  According to the present invention, when a transparent conductive layer mainly composed of noble metal-coated silver fine particles is formed by a coating method, it is only necessary to provide a transparent undercoat layer in which a silica sol solution is previously coated on the surface of a transparent substrate. A transparent conductive layer having a network structure of noble metal fine particles that is more uniform and developed than before can be easily formed. As a result, a transparent conductive film having high transmittance and low surface resistance can be easily and stably formed.

  Moreover, according to the method of the present invention, the coating solution for forming a transparent conductive layer can stably obtain a uniform and developed network structure even when the concentration of noble metal fine particles, which is the main solid content, is dilute compared to the conventional one. Therefore, the manufacturing cost of the transparent conductive layer exhibiting sufficient conductivity can be reduced.

  In the present invention, in order to form a transparent conductive film, first, a coating solution for forming a transparent undercoat layer is applied on a transparent substrate, dried at room temperature as necessary, and further a transparent conductive layer is formed on the coating layer. Apply the coating solution. As a coating method of the coating solution for forming the transparent undercoat layer and the coating solution for forming the transparent conductive layer, a coating method such as spray coating, spin coating, wire bar coating, doctor blade coating, or the like can be used. Next, after coating and laminating the two coating layers as described above, the coating layer is cured by, for example, heating and baking at a temperature of about 50 to 350 ° C., and a transparent undercoat layer and a transparent conductive layer are formed. A conductive film is formed.

  In addition, on the transparent conductive layer of the obtained transparent conductive film of this invention, a transparent overcoat layer can be formed as needed. Also, when a transparent undercoat layer-forming coating solution is applied and cured in this state by heating and baking treatment, and then a transparent conductive layer and a transparent overcoat layer are formed thereon, a baked transparent undercoat This is not preferable because the coating property of the coating liquid for forming a transparent conductive layer on the layer is deteriorated and the surface resistance of the transparent conductive layer to be obtained is increased.

  The coating liquid for forming the transparent undercoat layer contains silica sol. The silica sol is preferably an alkyl silicate and / or a polymer thereof. Specific examples of the silica sol include, for example, a polymer obtained by adding water or an acid catalyst to an alkyl silicate, hydrolyzing it, and dehydrating polycondensation, or a commercially available alkyl silicate solution that has already been polymerized to a tetramer to pentamer. Further, a polymer obtained by further hydrolysis and dehydration condensation polymerization can be used. These alkyl silicate hydrolyzed polymers almost complete the dehydration condensation polymerization reaction during heating and baking, and form a hard silicate film (film mainly composed of silicon oxide) having high surface smoothness.

  Regarding the degree of polymerization of the silica sol used in the coating liquid for forming the transparent undercoat layer, it is preferable that the weight average molecular weight is 500 or more. When the weight average molecular weight is less than 500, it is difficult to obtain a uniform and developed network structure of noble metal fine particles in the transparent conductive layer formed on the transparent undercoat layer, and sufficient conductivity cannot be obtained. In addition, in the case of silica sol in which dehydration condensation polymerization has proceeded excessively, not only sufficient conductivity of the transparent conductive layer cannot be obtained, but also the viscosity of the coating liquid for forming the transparent undercoat layer increases and the coating property deteriorates. Therefore, it is necessary to adjust the degree of dehydration condensation polymerization below the upper limit viscosity that can be applied on the transparent substrate. Therefore, in consideration of the film characteristics of the transparent conductive layer, the applicability of the coating solution for forming the transparent undercoat layer, storage stability, and the like, the polymerization degree of the silica sol is more preferably about 1500 to 3000 in terms of weight average molecular weight.

  By interposing a transparent undercoat layer between the transparent substrate and the transparent conductive layer, the transparent conductive layer forming coating liquid to which the noble metal fine particles are applied can be used even if the noble metal fine particle concentration in the coating liquid is low. The noble metal fine particles of the conductive layer are uniformly connected without being localized, and the developed network structure can be stably formed. That is, even when the concentration of the noble metal fine particles in the coating liquid for forming the transparent conductive layer is extremely dilute, for example, the concentration of the noble metal fine particles is less than 0.3% by weight, more preferably about 0.05 to 0.2% by weight. However, a transparent conductive layer having a sufficiently low surface resistance necessary for preventing leakage electromagnetic waves can be obtained. On the other hand, when a transparent conductive layer is directly formed on a transparent substrate as in the past, in a coating solution with a low concentration of noble metal fine particles, the connection of noble metal fine particles does not proceed and a developed network structure can be stably obtained. Therefore, the surface resistance of the transparent conductive layer becomes high, and the effect of preventing leakage electromagnetic waves cannot be obtained.

  The mechanism by which the uniform and developed network structure of the noble metal fine particles is stably formed in the transparent conductive layer formed thereon by the transparent undercoat layer is not clear. However, it is known that the surface energy of the coating surface of the coating liquid for forming the transparent conductive layer varies greatly depending on the presence of the transparent undercoat layer, and the non-uniform aggregation of the noble metal fine particles is suppressed due to its wettability. It is thought to be for this purpose. In addition, the presence of the transparent undercoat layer significantly increases the internal stress of the film at the time of drying shrinkage. Therefore, it is estimated that the contact between the noble metal fine particles is promoted.

  The transparent conductive film of the present invention thus formed is composed of a transparent undercoat layer formed on a transparent substrate and a transparent conductive layer containing noble metal fine particles formed on the transparent undercoat layer. The For the transparent conductive layer, as described above, even when formed using a coating solution for forming a transparent conductive layer with a very dilute noble metal fine particle concentration, good conductivity can be obtained. Therefore, high transmittance can be achieved.

  The transparent undercoat layer is a silicate layer formed by dehydration condensation polymerization of a silica sol in a coating solution for forming a transparent undercoat layer applied on a transparent substrate during heating and baking, that is, silicon oxide as a main component. It is a layer to do. If the thickness of the transparent undercoat layer is less than 10 nm, a sufficiently conductive transparent conductive film cannot be obtained, and if it exceeds 100 nm, sufficient conductivity cannot be obtained, and film strength and applicability are reduced. Since it connects, it is preferable to set it as the range of 10-100 nm.

  The transparent conductive film comprising the transparent undercoat layer and the transparent conductive layer of the present invention can easily form a uniform and developed noble metal fine particle network structure in the transparent conductive layer as described above, while maintaining high transmittance, At the same time, a transparent conductive film having low resistance and excellent conductivity is obtained. That is, when the thickness of the transparent conductive layer is 50 nm or less, the surface resistance of the two-layer film composed of the transparent conductive layer and the transparent undercoat layer is 100 kΩ / □ or less, and only the above-mentioned two-layer film not including the transparent substrate transmits visible light. A transparent conductive film having a rate of 80% or more can be obtained.

  The transparent base material used in the present invention is not limited to a glass base material such as a CRT face panel, but can be conveniently selected from known transparent plastic films and sheets such as polyethylene, polycarbonate, and acrylic. Can be used.

  Further, as the noble metal fine particles of the transparent conductive layer forming coating liquid and the transparent conductive layer, the noble metal coated silver fine particles obtained by coating the surface of the silver fine particles with at least one kind of noble metal selected from gold, platinum, palladium, rhodium and ruthenium. Is preferred. By coating the surface of the silver fine particles with gold, platinum, palladium, rhodium, or ruthenium, the weather resistance of the silver fine particles can be improved. In addition to the above-mentioned noble metal-coated silver fine particles, noble metal simple particles of gold, platinum, palladium, rhodium and ruthenium, or noble metal alloy fine particles of these noble metals and silver can also be used as the noble metal fine particles in the present invention.

  Next, a method for producing a coating liquid for forming a transparent conductive layer containing noble metal-coated silver fine particles in the present invention will be described by taking an example in which the noble metal fine particles are gold-coated silver fine particles. First, a colloidal dispersion of silver fine particles is prepared by a known method [for example, Carey-Lea method: see Am. J. Sci., 37, 38, 47 (1889)]. Specifically, a mixed solution of an iron (II) sulfate aqueous solution and an aqueous sodium citrate solution is added to a silver nitrate aqueous solution to react, and after the precipitate is filtered and washed, pure water is added to obtain a colloidal dispersion of silver fine particles. can get. Next, a dispersion solution of gold-coated silver fine particles is obtained by adding a reducing agent solution such as hydrazine and a gold salt solution to the silver fine particle colloid dispersion.

  If necessary, a small amount of a dispersant may be added to one or both of the colloidal dispersion of silver fine particles and the gold salt solution in the gold coating step. The silver fine particle colloid dispersion and the gold coated silver fine particle dispersion may be prepared by any method as long as a dispersion of gold coated silver fine particles having an average particle diameter of 1 to 100 nm is finally obtained. It is not limited.

  It is preferable to lower the electrolyte concentration in the dispersion of the obtained gold-coated silver fine particle dispersion by a method such as dialysis, electrodialysis, ion exchange, or ultrafiltration. This is because colloids generally aggregate in the electrolyte unless the electrolyte concentration is lowered, and this phenomenon is known as the Schulze-Hardy law. The gold-coated silver fine particle dispersion having a reduced electrolyte concentration is concentrated by a method such as a vacuum evaporator or ultrafiltration to obtain a gold-coated silver fine particle dispersion. Furthermore, component adjustment (fine particle concentration, water concentration, etc.) by addition of an organic solvent or the like is performed to prepare a dispersion concentrate of gold-coated silver fine particles.

  Here, preferably, the gold-coated silver fine particles are aggregated in advance in a chain form. That is, while stirring the dispersion concentrate of gold-coated silver fine particles, a hydrazine solution is added little by little. For example, the gold-coated silver fine particles are agglomerated in chains by holding at room temperature for several minutes to several hours. By adding a solution to decompose hydrazine, a dispersion (concentration) solution of chain-aggregated gold-coated silver fine particles can be obtained.

  An organic solvent or the like is added to the obtained chain-aggregated gold-coated silver fine particle dispersion (concentration) liquid to adjust the components such as the fine particle concentration, water concentration, and high-boiling organic solvent concentration. Let it be a coating liquid for forming a transparent conductive layer. Further, in order to improve the dispersion stability of the gold-coated silver fine particles and extend the pot life of the final coating liquid for forming a transparent conductive layer, a polymer resin or the like can be added. However, when adding a polymer resin, the strength and weather resistance of the resulting transparent conductive film tend to be slightly deteriorated, so care should be taken.

  In addition, although the manufacturing method of the coating liquid for transparent conductive layer formation whose noble metal fine particles are gold coat silver fine particles was demonstrated here, noble metals other than gold, ie, noble metals coated with noble metals such as platinum, palladium, rhodium, ruthenium, etc. Also in the case of coated silver fine particles, a coating liquid for forming a transparent conductive layer can be produced in the same manner as described above. Moreover, the coating liquid for forming a transparent conductive layer to which noble metal fine particles other than the noble metal-coated silver fine particles are applied can be adjusted in the same manner as described above except for the coating step with noble metal.

  There is no restriction | limiting in particular as an organic solvent used for the coating liquid for transparent conductive layer formation, According to the coating method and film forming conditions, it selects suitably. For example, alcohol solvents such as methanol (MA), ethanol (EA), 1-propanol (NPA), isopropanol (IPA), butanol, pentanol, benzyl alcohol, diacetone alcohol, acetone, methyl ethyl ketone (MEK), methylpropyl Ketone solvents such as ketone, methyl isobutyl ketone (MIBK), cyclohexanone, isophorone, ethylene glycol monomethyl ether (MCS), ethylene glycol monoethyl ether (ECS), ethylene glycol isopropyl ether (IPC), propylene glycol methyl ether (PGM) , Propylene glycol ethyl ether (PE), propylene glycol methyl ether acetate (PGM-AC), propylene glycol ethyl ether Glycol derivatives such as acetate (PE-AC), formamide (FA), N-methylformamide, dimethylformamide (DMF), dimethylacetamide, dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), etc. Although it is mentioned, it is not limited to these.

  In addition, the coating liquid for forming the transparent conductive layer may contain a binder and / or a binder precursor monomer as other components from the viewpoint of improving coating suitability and coating strength. Examples of binders and binder precursor monomers include alkylsilane monomers, polymers obtained by dehydration condensation polymerization thereof, water-soluble polymers such as polyvinyl alcohol and polyethylene glycol, thermosetting resins and photocurable resins, and precursor monomers thereof. However, it is not limited to these. In addition, the binder and binder precursor monomer in the coating liquid for forming the transparent conductive layer are excessively impeded, the contact between the noble metal fine particles is hindered and the conductivity is lowered. Therefore, the range of 1 to 100 parts by weight with respect to 100 parts by weight of the noble metal fine particles is preferable, and the range of 2 to 20 parts by weight is more preferable.

  Furthermore, the transparent conductive film formed on the transparent substrate in the present invention can be composed of a transparent three-layer film including a transparent undercoat layer and a transparent conductive layer, and a transparent overcoat layer further laminated thereon. . The transparent overcoat layer is already known as a protective function and an antireflection function, and the thickness can be appropriately selected according to the purpose. In particular, in the case of a transparent conductive layer formed using a coating solution for forming a transparent conductive layer that does not contain or has a small amount of a binder component, the protective function of the transparent overcoat layer is useful. The transparent overcoat layer is composed of a hard silicate film (a film containing silicon oxide as a main component), like the transparent undercoat layer.

  This transparent overcoat layer is formed by a coating method using a coating liquid for forming a transparent overcoat layer containing silica sol. Specifically, as described above, a transparent undercoat layer-forming coating solution and a transparent conductive layer-forming coating solution are sequentially applied onto a transparent substrate, and after drying as necessary, spray coating, spin coating, Apply a coating solution for forming a transparent overcoat layer by wire bar coating, doctor blade coating, etc., and then heat and bake at a temperature of, for example, about 50 to 350 ° C. to cure the coating layer to form a transparent three-layer film. Form.

  As a coating liquid for forming a transparent overcoat layer, a solution of alkyl silicate and / or a silica sol that is a polymer thereof is used. Specific examples of the silica sol include, for example, a polymer obtained by hydrolyzing an alkyl silicate by adding water or an acid catalyst to promote dehydration condensation polymerization, or a commercially available alkyl silicate that has already been polymerized to a tetramer to a pentamer. A polymer obtained by further hydrolysis and dehydration condensation polymerization of the solution can be used. The degree of dehydration condensation polymerization needs to be adjusted below the upper limit viscosity that can be applied on the transparent substrate, and is preferably about 1000 to 3000 in terms of weight average molecular weight in consideration of film strength, weather resistance and the like.

  For example, in the case of a coating solution for forming a transparent conductive layer that does not contain a binder component or has a small amount, a noble metal fine particle forms a network structure on the transparent undercoat layer at the coating / drying stage, and has high mutual adhesion. It is laminated in a state that does not have the property. When the coating solution for forming the transparent overcoat layer is continuously applied thereon, a part of the coating solution for forming the transparent overcoat layer passes through the hole portion of the network (network-like) structure formed of noble metal fine particles, and becomes conductive. The layer reaches the surface of the transparent undercoat layer while impregnating the layer, and the surplus portion is overcoated on the surface. A three-layer structure of transparent undercoat layer / transparent conductive layer / transparent overcoat layer is formed by the subsequent heating and baking treatment. As a result, the conductivity of the transparent conductive layer is improved, and the contact area between the transparent substrate and the binder matrix such as silicon oxide is increased through the hole portion of the network structure. Improvement is also achieved.

  Further, in the transparent two-layer film of the transparent overcoat layer and the transparent conductive layer, an antireflection effect can be obtained by an interference method that controls the refractive index and the film thickness. The transparent conductive layer containing the noble metal fine particles has an optical constant (n-ik) whose refractive index n is not so large but extinction coefficient k is large. Therefore, the entire transparent conductive film is formed by a laminated structure with the transparent overcoat layer. The reflectance can be greatly reduced. When the transparent substrate is glass, the refractive index of the transparent undercoat layer mainly composed of silicon oxide is the same level as that of the substrate. Therefore, for antireflection, it consists of a normal transparent overcoat layer and a transparent conductive layer. It can be handled in the same manner as the transparent two-layer film.

  The transparent conductive film of the present invention has an excellent electric field shielding effect and high visible light transmittance, and can have a good antireflection effect as required. Therefore, a cathode ray tube (CRT), a plasma display panel ( It is suitable as a front plate of a display device such as a PDP), a fluorescent display tube (VFD), and a liquid crystal display (LCD).

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples. Further, “%” in the text indicates “% by weight” excluding (%) of transmittance, reflectance, and haze value, and “part” indicates “part by weight”.

[Example 1]
First, the coating liquid for forming a transparent undercoat layer was prepared as follows. That is, the polymerization product as methyl silicate 51 (Colcoat Co., Ltd. trade name) 19.6 parts alkyl silicate, ethanol 57.8 parts, 7.9 parts of a 1% aqueous solution of nitric acid, with pure water 14.7 parts SiO ₂ (Silicon oxide) A silica sol solution having a solid content concentration of 10% and a weight average molecular weight of 1850 was prepared, and isopropyl alcohol (IPA) and n-butanol were finally adjusted to have a SiO ₂ solid content concentration of 0.1%. After dilution with a mixture of (NBA) (IPA / NBA = 3/1), the mixture was filtered through a filter having a filtration accuracy (pore size) of 5 μm to obtain a coating solution for forming a transparent undercoat layer of Example 1.

  Next, the coating liquid for forming a transparent conductive layer was prepared as follows. First, a colloidal dispersion of silver fine particles was prepared by the Carey-Lea method. Specifically, a mixture of 390 g of a 23% iron (II) sulfate aqueous solution and 480 g of a 37.5% sodium citrate aqueous solution was added to 330 g of a 9% silver nitrate aqueous solution, reacted, and the precipitate was filtered and washed. Water was added to prepare a colloidal dispersion of silver fine particles (Ag: 0.15%) (solution A). When this colloidal dispersion (liquid A) of silver fine particles was observed with a transmission electron microscope, the average particle diameter of the silver fine particles was 4.8 nm.

80.0 g of a 1% aqueous solution of hydrazine monohydrate (N ₂ H ₄ .H ₂ O) is added to 600 g of this silver fine particle colloid dispersion (liquid A), and potassium metal hydrate [KAu (OH) ₄ is added with stirring. A mixed solution of 4800 g of an aqueous solution (Au: 0.075%) and 2.0 g of a 1% polymer dispersant aqueous solution was added to obtain a colloidal dispersion of gold-coated silver fine particles in which the surface of the silver fine particles was coated with simple gold.

  The gold-coated silver fine particle colloidal dispersion was desalted with an ion exchange resin (trade name: Diaion SK1B, SA20AP, manufactured by Mitsubishi Chemical Corporation), and then ultrafiltered to concentrate the gold-coated silver fine particles. Ethanol (EA) was added to the resulting liquid, and gold-coated silver fine particle dispersion (concentrated) liquid (Ag-Au: 1.6%, water: 20.0%, EA: 78.4%) (liquid B ) When this gold-coated silver fine particle dispersion (concentration) liquid (liquid B) was observed with a transmission electron microscope, the average particle size of the gold-coated silver fine particles was 6.2 nm.

While stirring 60 g of this gold-coated silver fine particle dispersion (concentration) liquid (B liquid), 0.8 g of 0.75% hydrazine aqueous solution (N ₂ H ₄ .H ₂ O :) (1.6% Ag-Au dispersion) After adding 100 ppm to the liquid over 1 minute, the mixture was kept at room temperature for 15 minutes to aggregate the gold-coated silver fine particles in a chain. Next, 0.6 g of 1.5% aqueous hydrogen peroxide solution (H ₂ O ₂ ) is added over 1 minute to decompose hydrazine, and chain-aggregated gold-coated silver fine particle dispersion (concentration) solution (solution C) Got. As a result of observing this chain-aggregated gold-coated silver fine particle dispersion (concentration) liquid (liquid C) with a transmission electron microscope, the gold-coated silver fine particles are arranged in a bead shape and partially branched (length: 20 to 100 μm [individual]. The maximum length of the aggregated gold-coated silver fine particles]).

  In addition, the dispersion | distribution (concentration) liquid of the gold coat silver fine particle which carried out the aggregation fall of the gold coat silver fine particle at the time of adding a hydrazine solution to the dispersion | distribution (concentration) liquid (B liquid) of the said gold coat silver fine particle The stability improvement when the hydrogen peroxide solution was added to (C solution) could be scientifically confirmed from the measured zeta potential of these dispersion (concentrated) solutions.

  Ethanol (EA), propylene glycol monomethyl ether (PGM), diacetone alcohol (DAA), formamide (FA) are added to this chain-aggregated gold-coated silver fine particle dispersion (concentration) liquid (liquid C), and filtration accuracy (pore size) ) Filtration through a 5 μm filter, and transparent conductive layer forming coating solution (Au-coated Ag fine particles: 0.15%, water: 4.79%, PGM: 20.00%, DAA: 10.00%, FA: 0) 0.1%, EA: 64.96%).

Furthermore, the coating liquid for forming a transparent overcoat layer of Example 1 was prepared as follows. That is, 19.6 parts of methyl silicate 51 (trade name, manufactured by Colcoat Co.), 57.8 parts of ethanol, 7.9 parts of 1% nitric acid aqueous solution, and 14.7 parts of pure water were used to obtain SiO ₂ (silicon oxide) solid content. A silica sol solution having a concentration of 10% and a weight average molecular weight of 1,050 was prepared, and finally a mixture of isopropyl alcohol (IPA) and n-butanol (NBA) so that the SiO ₂ solid content concentration was 0.8%. The solution was diluted with (IPA / NBA = 3/1) to obtain a coating liquid for forming a transparent overcoat layer.

  The transparent undercoat layer forming coating solution is spin-coated (150 rpm for 60 seconds) on a glass substrate (3 mm thick soda lime glass) heated to 35 ° C., and then the transparent conductive film forming coating solution. Was spin-coated (at 90 rpm for 10 seconds, and subsequently at 130 rpm for 80 seconds), and then the above-mentioned coating solution for forming a transparent overcoat layer was spin-coated (at 150 rpm for 60 seconds). The glass substrate was polished with a cerium oxide-based abrasive before use, washed with pure water and dried, and then heated to 35 ° C. for use. After that, it is heated and fired at 180 ° C. for 20 minutes to be cured, and a transparent undercoat layer mainly composed of silicon oxide, a transparent conductive layer containing gold-coated silver fine particles as an upper layer, and a silicon oxide as a further upper layer are mainly formed. A glass substrate with a transparent three-layer film composed of a transparent overcoat layer as a component, that is, a transparent conductive substrate of Example 1 was obtained.

Table 1 below shows the weight average molecular weight of the silica sol and the silicon oxide (SiO ₂ ) equivalent concentration in the coating liquid for forming the transparent undercoat layer of Example 1, and the transparent undercoat layer after the formation of the transparent conductive film (three layers). The thicknesses of the transparent conductive layer and the transparent overcoat layer are shown. Table 2 below shows film characteristics of the transparent three-layer film in the transparent conductive substrate of Example 1, that is, surface resistance, visible light transmittance, haze value, bottom reflectance / bottom wavelength.

  The transmittance in the present invention is a visible light transmittance of only a transparent conductive film (transparent three-layer film) that does not contain a transparent substrate unless otherwise specified. In addition, the visible light transmittance | permeability of only the transparent conductive film which does not contain the transparent base material (glass substrate) shown in following Table 2 can be calculated | required with the following formula. That is, the transmittance (%) of only the transparent conductive film not containing the transparent substrate = [(transmittance measured for each transparent substrate) / (transmittance of the transparent substrate)] × 100

The surface resistance of the transparent conductive film was measured using a surface resistance meter Loresta AP (MCP-T400) manufactured by Mitsubishi Chemical Corporation. The visible light transmittance and haze value were measured using a haze meter (HR-200) manufactured by Murakami Color Research Laboratory. The reflectance was measured using a spectrophotometer (U-4000) manufactured by Hitachi, Ltd. The weight average molecular weight of the silica sol was measured by gel permeation chromatography (GPC method) using a high performance liquid chromatograph (LC-10A) manufactured by Shimadzu Corporation. Column used at this time is from Waters Ultra Styler Gel 10 ⁴ and Shodex manufactured KF-801.

[Example 2]
The coating liquid for forming the transparent undercoat layer of Example 2 was prepared as follows. That is, 19.6 parts of methyl silicate 51 (trade name, manufactured by Colcoat Co.), 57.8 parts of ethanol, 7.9 parts of 1% nitric acid aqueous solution, and 14.7 parts of pure water were used to obtain SiO ₂ (silicon oxide) solid content. A silica sol solution having a concentration of 10% and a weight average molecular weight of 1850 was prepared, and finally a mixture of isopropyl alcohol (IPA) and n-butanol (NBA) so that the SiO ₂ solid content concentration was 0.05% ( After dilution with IPA / NBA = 3/1), the solution was filtered through a filter having a filtration accuracy (pore size) of 5 μm to obtain a coating liquid for forming a transparent undercoat layer of Example 2.

  A transparent undercoat layer containing silicon oxide as a main component and a transparent conductive layer containing gold-coated silver fine particles as an upper layer in the same manner as in Example 1 except that this coating solution for forming a transparent undercoat layer was used. Furthermore, a glass substrate with a transparent three-layer film composed of a transparent overcoat layer mainly composed of silicon oxide as an upper layer, that is, a transparent conductive substrate of Example 2 was obtained.

Table 1 below shows the weight average molecular weight of silica sol and the equivalent concentration of silicon oxide (SiO ₂ ) in the coating solution for forming the transparent undercoat layer of Example 2, and the transparent undercoat layer after forming the transparent conductive film (three layers). The thicknesses of the transparent conductive layer and the transparent overcoat layer are shown. In Table 2, the film characteristics of the transparent three-layer film in the transparent conductive substrate of Example 2 were evaluated and shown in the same manner as in Example 1.

[Example 3]
The coating liquid for forming the transparent undercoat layer of Example 3 was prepared as follows. That is, 19.6 parts of methyl silicate 51 (trade name, manufactured by Colcoat Co.), 57.8 parts of ethanol, 7.9 parts of 1% nitric acid aqueous solution, and 14.7 parts of pure water were used to obtain SiO ₂ (silicon oxide) solid content. A silica sol solution having a concentration of 10% and a weight average molecular weight of 500 was prepared, and finally a mixture of isopropyl alcohol (IPA) and n-butanol (NBA) so that the SiO ₂ solid content concentration was 0.1% ( After dilution with IPA / NBA = 3/1), the solution was filtered through a filter having a filtration accuracy (pore size) of 5 μm to obtain a coating liquid for forming a transparent undercoat layer of Example 3.

  A transparent undercoat layer containing silicon oxide as a main component and a transparent conductive layer containing gold-coated silver fine particles as an upper layer in the same manner as in Example 1 except that this coating solution for forming a transparent undercoat layer was used. Furthermore, a glass substrate with a transparent three-layer film composed of a transparent overcoat layer mainly composed of silicon oxide as an upper layer, that is, a transparent conductive substrate of Example 3 was obtained.

Table 1 below shows the weight average molecular weight of silica sol and the silicon oxide (SiO ₂ ) equivalent concentration in the coating liquid for forming the transparent undercoat layer of Example 3, and the transparent undercoat layer after the formation of the transparent conductive film (three layers). The thicknesses of the transparent conductive layer and the transparent overcoat layer are shown. In Table 2 below, the film properties of the transparent three-layer film in the transparent conductive substrate of Example 3 were evaluated and shown in the same manner as in Example 1.

[Example 4]
The coating solution for forming the transparent undercoat layer of Example 4 was prepared as follows. That is, 19.6 parts of methyl silicate 51 (trade name, manufactured by Colcoat Co.), 57.8 parts of ethanol, 7.9 parts of 1% nitric acid aqueous solution, and 14.7 parts of pure water were used to obtain SiO ₂ (silicon oxide) solid content. A silica sol solution having a concentration of 10% and a weight average molecular weight of 470 was prepared, and finally a mixture of isopropyl alcohol (IPA) and n-butanol (NBA) so that the SiO ₂ solid content concentration was 0.1% ( After dilution with IPA / NBA = 3/1), the solution was filtered through a filter having a filtration accuracy (pore size) of 5 μm to obtain a coating liquid for forming a transparent undercoat layer of Example 4.

  A transparent undercoat layer containing silicon oxide as a main component and a transparent conductive layer containing gold-coated silver fine particles as an upper layer in the same manner as in Example 1 except that this coating solution for forming a transparent undercoat layer was used. Furthermore, a glass substrate with a transparent three-layer film composed of a transparent overcoat layer mainly composed of silicon oxide as an upper layer, that is, a transparent conductive substrate of Example 4 was obtained.

Table 1 below shows the weight average molecular weight of the silica sol and the silicon oxide (SiO ₂ ) equivalent concentration in the coating liquid for forming the transparent undercoat layer of Example 4, and the transparent undercoat layer after the formation of the transparent conductive film (three layers). The thicknesses of the transparent conductive layer and the transparent overcoat layer are shown. In Table 2 below, the film characteristics of the transparent three-layer film in the transparent conductive substrate of Example 4 were evaluated and shown in the same manner as in Example 1.

[Example 5]
In the chain-aggregated gold-coated silver fine particle dispersion (concentration) liquid (C liquid) obtained in Example 1, ethanol (EA), propylene glycol monomethyl ether (PGM), diacetone alcohol (DAA), formamide (FA), Then, methyltrimethoxysilane is added as a binder component, and the mixture is filtered through a filter having a filtration accuracy (pore size) of 5 μm. A coating solution for forming a transparent conductive layer (Au-coated Ag fine particles: 0.15%, water: 4.79%, PGM: 20.00%, DAA: 10.00%, FA: 0.1%, methyltrimethoxysilane: 0.015%, EA: 64.945%).

  Next, the transparent undercoat layer-forming coating solution obtained in Example 1 was spin-coated (150 rpm for 60 seconds) on a glass substrate (3 mm thick soda lime glass) heated to 35 ° C., and continued. The transparent conductive film forming coating solution was spin-coated (at 90 rpm for 10 seconds, and subsequently at 130 rpm for 80 seconds). Thereafter, it is cured by heating and baking at 180 ° C. for 20 minutes, and a transparent two-layer film comprising a transparent undercoat layer mainly composed of silicon oxide and a transparent conductive layer containing gold-coated silver fine particles as an upper layer is provided. A transparent conductive substrate of Example 5 was obtained.

Table 1 below shows the weight average molecular weight of silica sol and the equivalent concentration of silicon oxide (SiO ₂ ) in the coating solution for forming the transparent undercoat layer of Example 5, and the transparent undercoat layer after forming the transparent conductive film (two layers). And the thickness of the transparent conductive layer. In Table 2, the film characteristics of the transparent two-layer film in the transparent conductive substrate of Example 5 were evaluated and shown in the same manner as in Example 1.

[Reference Example 1]
The coating solution for forming the transparent undercoat layer of Reference Example 1 was prepared as follows. That is, 19.6 parts of methyl silicate 51 (trade name, manufactured by Colcoat Co.), 57.8 parts of ethanol, 7.9 parts of 1% nitric acid aqueous solution, and 14.7 parts of pure water were used to obtain SiO ₂ (silicon oxide) solid content. A silica sol solution having a concentration of 10% and a weight average molecular weight of 1850 was prepared, and finally a mixture of isopropyl alcohol (IPA) and n-butanol (NBA) so that the SiO ₂ solid content concentration was 0.9% ( After dilution with IPA / NBA = 3/1), the solution was filtered through a filter having a filtration accuracy (pore size) of 5 μm to obtain a coating liquid for forming a transparent undercoat layer of Reference Example 1.

A transparent undercoat layer containing silicon oxide as a main component and a transparent conductive layer containing gold-coated silver fine particles as an upper layer in the same manner as in Example 1 except that this coating solution for forming a transparent undercoat layer was used. Furthermore, a glass substrate with a transparent three-layer film composed of a transparent overcoat layer mainly composed of silicon oxide as an upper layer, that is, a transparent conductive substrate of Reference Example 1 was obtained. Also for this Reference Example 1, the following Table 1 shows the weight average molecular weight of silica sol and the equivalent concentration of silicon oxide (SiO ₂ ) in the coating solution for forming the transparent undercoat layer, and the transparent after the formation of the transparent conductive film (three layers). The thicknesses of the undercoat layer, the transparent conductive layer and the transparent overcoat layer are shown. In Table 2, the film characteristics of the transparent three-layer film in the transparent conductive substrate of Reference Example 1 were evaluated and shown in the same manner as in Example 1.

[Reference Example 2]
The coating solution for forming the transparent undercoat layer prepared in Example 1 is spin-coated (150 rpm for 60 seconds) on a glass substrate (3 mm thick soda lime glass) heated to 35 ° C., and then at 180 ° C. for 20 minutes. It was cured by heating and baking. Then, after cooling to 35 ° C., the transparent conductive film-forming coating solution of Example 1 was spin coated (90 rpm for 10 seconds, then 130 rpm for 80 seconds), and then the transparent overcoat layer of Example 1 was formed. The coating solution was spin coated (at 150 rpm for 60 seconds). After that, it is cured by heating and baking again at 180 ° C. for 20 minutes, and a transparent undercoat layer mainly composed of silicon oxide, a transparent conductive layer containing gold-coated silver fine particles as an upper layer, and further an upper layer of silicon oxide are obtained. A glass substrate with a transparent three-layer film composed of a transparent overcoat layer as a main component, that is, a transparent conductive substrate of Reference Example 2 was obtained.

Table 1 below shows the weight average molecular weight of silica sol and the equivalent concentration of silicon oxide (SiO ₂ ) in the coating liquid for forming the transparent undercoat layer of Reference Example 2, and the transparent undercoat layer after the formation of the transparent conductive film (three layers). The thicknesses of the transparent conductive layer and the transparent overcoat layer are shown. In Table 2, the film characteristics of the transparent three-layer film in the transparent conductive substrate of Reference Example 2 were evaluated and shown in the same manner as in Example 1.

[Comparative Example 1]
The coating liquid for forming a transparent conductive layer prepared in Example 1 was spin-coated on a glass substrate (3 mm thick soda lime glass) heated to 35 ° C. (90 rpm for 10 seconds, then 130 rpm for 80 seconds), Subsequently, the coating liquid for forming the transparent overcoat layer of Example 1 was spin-coated (at 150 rpm for 60 seconds). Thereafter, a transparent two-layer film comprising a transparent conductive layer containing gold-coated silver fine particles and a transparent overcoat layer mainly composed of silicon oxide as an upper layer is cured by heating and baking at 180 ° C. for 20 minutes. A transparent glass substrate with a glass substrate, that is, Comparative Example 1, was obtained.

  Regarding Comparative Example 1, the thickness of each layer is shown in Table 1 below, and the film characteristics of the transparent two-layer film in the transparent conductive substrate are evaluated and shown in Table 2 below in the same manner as in Example 1.

[Comparative Example 2]
The coating liquid for forming the transparent undercoat layer of Comparative Example 2 was prepared as follows. That is, colloidal silica (trade name Snowtex O, SiO ₂ min 20%, colloidal silica particle size 10 to 20 nm) 0.5 part, ethanol 59.5 parts, isopropyl alcohol (IPA) 30 manufactured by Nissan Chemical Industries, Ltd. Part, n-butanol (NBA) 10 parts, mixed so that the solid content concentration of SiO ₂ is 0.1%, stirred for 30 minutes, and then filtered with a filter having a filtration accuracy (pore size) of 5 μm. A coating solution for forming a transparent undercoat layer 2 was obtained.

  A transparent undercoat layer containing silicon oxide as a main component and a transparent conductive layer containing gold-coated silver fine particles as an upper layer in the same manner as in Example 1 except that this coating solution for forming a transparent undercoat layer was used. Further, a glass substrate with a transparent three-layer film composed of a transparent overcoat layer mainly composed of silicon oxide as an upper layer, that is, a transparent conductive substrate of Comparative Example 2 was obtained.

Regarding Comparative Example 2, the following Table 1 shows the silicon oxide (SiO ₂ ) equivalent concentration in the transparent undercoat layer forming coating solution and the thickness of each layer, and Table 2 below shows the transparent three-layer film of the transparent conductive substrate. The film characteristics were evaluated and shown in the same manner as in Example 1.

[Comparative Example 3]
The coating solution for forming the transparent undercoat layer of Comparative Example 3 was prepared as follows. That is, using 0.5 parts of alumina sol 520 (Al ₂ O ₃ min 20%) manufactured by Nissan Chemical Industries, 59.5 parts of ethanol, 30 parts of isopropyl alcohol (IPA), 10 parts of n-butanol (NBA), Al _The mixture was mixed so that the ₂ O ₃ solid content concentration was 0.1%, stirred for 30 minutes, and then filtered through a filter having a filtration accuracy (pore size) of 5 μm to obtain a coating solution for forming a transparent undercoat layer of Comparative Example 3. .

  Except for using this coating liquid for forming the transparent undercoat layer, in the same manner as in Example 1 above, a transparent undercoat layer mainly composed of alumina, and a transparent conductive layer containing gold-coated silver fine particles thereon, Further, a glass substrate with a transparent three-layer film composed of a transparent overcoat layer mainly composed of silicon oxide as an upper layer, that is, a transparent conductive substrate of Comparative Example 3 was obtained.

Regarding Comparative Example 3, the following Table 1 shows the alumina concentration (Al ₂ O ₃ ) equivalent concentration in the coating liquid for forming the transparent undercoat layer and the thickness of each layer, and Table 2 below shows the transparent three layers in the transparent conductive substrate. The film properties of the film were evaluated and shown in the same manner as in Example 1.

  From the results of Table 1 and Table 2, the following can be seen. First, while the surface resistance of the transparent two-layer film of Comparative Example 1 having no conventional transparent undercoat layer is remarkably high, the transparent three-layer films of Examples 1 to 3 having the transparent undercoat layer are The resistance is as low as 1.8 to 7.5 kΩ / □, the visible light transmittance is as high as 90.2 to 92.1%, and both high transmittance and high conductivity are compatible. From this, it can be seen that when the transparent three-layer film according to Examples 1 to 3 is applied to a display device such as a cathode ray tube, the electromagnetic wave shielding characteristics superior to the conventional one can be obtained without impairing the luminance.

  However, in Example 4, since the weight average molecular weight of the silica sol in the used coating solution for forming the transparent undercoat layer was less than 500, the surface resistance of the transparent three-layer film increased to 13.6 kΩ / □. Further, in Example 5, the transparent conductive layer does not have a transparent overcoat layer in place of containing the binder component, but Examples 1 to 3 except that the visible light transmittance is slightly lowered and the haze value is slightly increased. The film characteristics almost the same as those of the transparent three-layer film were obtained.

  Further, as in Reference Example 1, when the thickness of the transparent undercoat layer exceeds 100 nm, the surface resistance of the obtained transparent three-layer film increases rapidly. As in Reference Example 2, when the applied coating solution for forming the transparent undercoat layer is once cured by heating and baking treatment, and then the transparent conductive layer and the transparent overcoat layer are formed thereon, the coatability deteriorates. Further, it can be seen that the surface resistance of the obtained transparent three-layer film tends to increase. Further, as in Comparative Examples 2 to 3, when a dispersion solution mainly composed of an oxide sol having a particle shape is used as a coating liquid for forming a transparent undercoat layer, a conventional transparent undercoat layer is provided. It can be seen that the surface resistance is remarkably increased as in the case of the transparent two-layer film according to Comparative Example 1 that is not present.

  In each of the above examples, a coating liquid for forming a transparent conductive layer using gold-coated silver fine particles has been described. However, one or two kinds of noble metals other than gold, that is, platinum, palladium, rhodium, and ruthenium are described. A coating solution for forming a transparent conductive layer using noble metal-coated silver fine particles coated as described above, and noble metal simple particles of gold, platinum, palladium, rhodium, ruthenium, or noble metal alloy fine particles of these noble metals and silver were used. Also in the case of the coating liquid for forming a transparent conductive layer, a transparent three-layer film excellent in visible light transmittance and conductivity could be obtained as in the above examples.

Claims (8)

A transparent conductive film formed on a transparent substrate, comprising a transparent undercoat layer mainly composed of silicon oxide formed on the transparent substrate, and noble metal fine particles formed on the transparent undercoat layer And a transparent conductive layer. The transparent conductive film according to claim 1, wherein the thickness of the transparent undercoat layer is in the range of 10 to 100 nm. The noble metal fine particles are noble metal coated silver fine particles obtained by coating the surface of silver fine particles with at least one kind of noble metal selected from gold, platinum, palladium, rhodium and ruthenium. The transparent conductive film as described. The transparent conductive layer has a thickness of 50 nm or less, and the two-layer film composed of the transparent conductive layer and the transparent undercoat layer has a surface resistance of 100 kΩ / □ or less and is only visible as a two-layer film not including a transparent substrate. The transparent conductive film according to claim 1, wherein the light transmittance is 80% or more. A method of forming a transparent conductive film on a transparent substrate, wherein a transparent undercoat layer-forming coating solution containing silica sol is applied on the transparent substrate, and the transparent conductive material containing noble metal fine particles on the coating layer A method for producing a transparent conductive film, comprising applying a layer-forming coating solution, followed by firing. The method for producing a transparent conductive film according to claim 5, wherein the silica sol of the coating liquid for forming the transparent undercoat layer is an alkyl silicate and / or a polymer thereof. The method for producing a transparent conductive film according to claim 5 or 6, wherein the degree of polymerization of the silica sol is 500 or more in terms of weight average molecular weight. The production of a transparent conductive film according to any one of claims 5 to 7, wherein the concentration of the noble metal fine particles in the coating liquid for forming the transparent conductive layer is in the range of 0.05 to 0.2% by weight. Method.