Coating composition, coating film manufacturing method, and transparent conductive film

Abstract

To provide a technique for more easily and efficiently obtaining a carbon nanotube-containing transparent conductive film.SOLUTION: A coating composition for forming a transparent conductive film contains carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid. The content of the carbon nanotubes is 0.4 mass% or less. The sulfonic acid-based dispersant is a polymer compound having a monomer unit containing an aromatic ring. The content of the sulfonic acid-based dispersant is 50-2,000 pts.mass based on 100 pts.mass of the carbon nanotubes.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a coating composition, a method for producing a coating film, and a transparent conductive film. [Background technology]

[0002] In recent years, low-resistance transparent conductive films have been used in a variety of fields, including touch panels, organic electroluminescence (EL) displays, solar cells, and transparent electrodes. Various materials have been reported to be used as transparent conductive materials, including metal materials such as ITO, conductive polymers such as PEDOT, and carbon materials such as carbon nanotubes. Currently, the transparent conductive material used in low-resistance transparent conductive films at the practical level is almost always ITO. However, ITO films have the disadvantages of being hard and lacking in flexibility.

[0003] Carbon nanotubes are less expensive and more durable than other transparent conductive materials, and are expected to be applied to products requiring flexibility. However, carbon nanotubes have a relatively high resistance compared to other conductive materials, so when used in transparent conductive films, they are subjected to a resistance-reducing treatment. A typical technique known is to reduce the resistance of a carbon nanotube coating film by immersing the film in an acid solution after forming the film (Patent Document 1). However, the technique of Patent Document 1 has problems such as being cumbersome and dangerous because it uses a large amount of acid solution. Other resistance-reducing techniques also have problems such as being cumbersome and dangerous. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-207116 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a technique for obtaining a carbon nanotube-containing transparent conductive film more simply and efficiently. [Means for solving the problem]

[0006] In the course of research, the present inventors considered incorporating an acid into a paint for forming a carbon nanotube coating film, thereby eliminating the need for acid treatment after coating film formation. However, they found that incorporating an acid into a paint causes problems with the paint appearance, coating film appearance, coating film adhesion, and the like. As a result of further research, the present inventors found that the types of dispersant, binder, acid, and the like used in the paint were the cause of these problems. Based on this finding, the present inventors conducted extensive research and found that the above problems could be solved by using a paint composition containing carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid. That is, the present invention encompasses the following aspects.

[0007] Item 1. A coating composition containing carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid.

[0008] Item 2. The coating composition according to Item 1, wherein the carbon nanotube content is 0.4 mass% or less.

[0009] Item 3. The coating composition according to Item 1 or 2, wherein the sulfonic acid dispersant is a polymer compound having a monomer unit containing an aromatic ring.

[0010] Item 4. The coating composition according to any one of Items 1 to 3, wherein the content of the sulfonic acid dispersant is 50 to 2000 parts by mass per 100 parts by mass of the carbon nanotubes.

[0011] Item 5. The coating composition according to any one of Items 1 to 4, wherein the silicon compound binder is a silicate or colloidal silica.

[0012] Item 6. The coating composition according to any one of Items 1 to 5, wherein the content of the silicon compound binder is 10 to 1000 parts by mass per 100 parts by mass of the carbon nanotubes.

[0013] Item 7. The coating composition according to any one of Items 1 to 6, wherein the inorganic acid is a strong acid.

[0014] Item 8. The coating composition according to any one of Items 1 to 7, wherein the content of the inorganic acid is 0.1 to 5 mass %.

[0015] Item 9. The coating composition according to any one of Items 1 to 8, which is used to form a transparent conductive film.

[0016] Item 10. (a) A method for producing a coating film, comprising a step of applying the coating composition according to any one of items 1 to 9 onto a substrate.

[0017] Item 11. The manufacturing method according to Item 10, further comprising (b) a step of washing the coating film obtained in step (a) with water.

[0018] Item 12. A transparent conductive film containing carbon nanotubes, sulfur atoms, and silicon atoms, and having a surface resistivity of 500 Ω / □ or less.

[0019] Item 13. The transparent conductive film according to Item 12, having a surface resistivity of 300 Ω / □ or less.

[0020] Item 14. The transparent conductive film according to item 12 or 13, which has a resistance change rate of 20% or less after 20 days from film formation under a light-shielded condition at 20°C. [Effects of the Invention]

[0021] According to the present invention, a technique for more simply and efficiently obtaining a transparent conductive film containing carbon nanotubes can be provided, and a carbon nanotube-containing transparent conductive film having a more stable surface resistance can be provided. [Brief explanation of the drawings]

[0022] [Figure 1]The coating film was left standing at 20°C under light-shielded conditions, and the change in surface resistivity over time was measured. The water treatment indicates the case where the coating film was washed with water only, and the acid treatment indicates the case where the film was washed by immersion in acid. The horizontal axis indicates the number of days since film formation, and the vertical axis indicates the rate of change in resistance (= [(surface resistivity after the number of days on the horizontal axis - surface resistivity immediately after film formation) / surface resistivity immediately after film formation] × 100 (%)). [Figure 2] The XPS analysis results for the coating are shown below. The silicon peak at 103-104 ev indicates that the silicon element is present in the form of silica. The carbon peak at 284-285 ev indicates that the element is in the form of carbon. The sulfur peak at 168-170 ev indicates that the element is in the form of sulfone. DETAILED DESCRIPTION OF THE INVENTION

[0023] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0024] 1.Paint In one aspect, the present invention relates to a coating composition (sometimes referred to herein as the "coating composition of the present invention") containing carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid. This is described below.

[0025] The carbon nanotubes are not particularly limited, and carbon nanotubes manufactured by arc discharge, laser evaporation, chemical vapor deposition (CVD), etc. can be used. More specifically, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and mixtures thereof can be used. In view of excellent conductivity, it is preferable to contain at least single-walled carbon nanotubes.

[0026] The length of the carbon nanotubes is preferably 1 to 2000 μm, more preferably 5 to 1000 μm, and even more preferably 5 to 500 μm. When the length of the carbon nanotubes is within the above range, the conductive layer has excellent conductivity and transparency.

[0027] The diameter of the carbon nanotubes is preferably 0.5 to 20 nm, more preferably 1 to 10 nm, in the case of single-walled carbon nanotubes. When the diameter of the carbon nanotubes is within the above range, the conductive layer has excellent conductivity and transparency.

[0028] The BET specific surface area of ​​carbon nanotubes is, for example, 100 to 5000 m 2 / g, preferably 500 to 3000 m 2 / g, more preferably 700 to 2000 m 2 / g.

[0029] The carbon nanotubes may be of one type alone or may be of two or more types in combination.

[0030] The carbon nanotube content in the coating composition of the present invention is not particularly limited as long as the dispersibility of the carbon nanotubes is not significantly impaired and a transparent conductive film can be formed, and the content is, for example, 0.4 mass% or less, preferably 0.01 to 0.4 mass%, more preferably 0.02 to 0.3 mass%, even more preferably 0.04 to 0.2 mass%, and still more preferably 0.07 to 0.15 mass%.

[0031] The sulfonic acid dispersant is not particularly limited as long as it contains a sulfo group (—SO3H) as a partial structure. Preferred examples of the sulfonic acid dispersant include polymer compounds having a monomer unit containing an aromatic ring.

[0032] Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a triazine ring. Examples of the monomer unit containing an aromatic ring include one or more monomer units selected from a monomer unit containing a benzene ring, a monomer unit containing a naphthalene ring, a monomer unit containing an anthracene ring, and a monomer unit containing a triazine ring.

[0033] The weight-average molecular weight of the polymer compound having a monomer unit containing an aromatic ring is, for example, 1,000 to 2,000,000, preferably 5,000 to 1,500,000, more preferably 20,000 to 1,000,000, even more preferably 50,000 to 700,000, still more preferably 100,000 to 500,000, and particularly preferably 150,000 to 300,000.

[0034] Here, "monomer unit" refers to a "repeating unit" in a polymer compound. For example, in the case of a sodium naphthalenesulfonate formalin condensate, a "repeating unit" such as that shown in the following formula is called a monomer unit. In the formula, n represents the number of repeating units.

[0035] [ka]

[0036] Specific examples of polymeric compounds having a monomer unit containing an aromatic ring include polystyrene sulfonic acid, naphthalene sulfonic acid-formalin condensates, and salts thereof. Among these, polystyrene sulfonic acid or a salt thereof is preferred. In one embodiment of the present invention, the sulfonic acid-based dispersant is preferably in the form of a salt.

[0037] The sulfonic acid dispersant in the form of a salt is not particularly limited, and examples thereof include sodium salts and potassium salts.

[0038] As the sulfonic acid dispersant, in addition to the polymer compounds described above, for example, alkylbenzenesulfonic acids such as branched alkylbenzenesulfonic acids and linear alkylbenzenesulfonic acids, or salts thereof can be used.

[0039] The sulfonic acid dispersant may be one type alone or a combination of two or more types.

[0040] The content of the sulfonic acid dispersant in the coating composition of the present invention is not particularly limited as long as the dispersibility of carbon nanotubes is not significantly impaired and a transparent conductive film can be formed. The content (converted to solid content) is, for example, 50 to 2000 parts by mass, preferably 100 to 1500 parts by mass, more preferably 200 to 1000 parts by mass, even more preferably 300 to 700 parts by mass, and still more preferably 400 to 600 parts by mass, relative to 100 parts by mass of carbon nanotubes.

[0041] The silicon compound binder is a colloidal dispersion, solution, or emulsion of a silicon compound, which contains a solid or liquid silicon compound in an aqueous dispersion medium. Examples of the silicon compound binder include silicates such as silicate; colloidal silica; silane, siloxane hydrolyzate emulsion; silicone resin emulsion; emulsions of copolymers of silicone resin and other resins, such as silicone-acrylic resin copolymer and silicone-urethane resin copolymer. Among these, silicates or colloidal silica are preferred as the silicon compound binder, and silicates are more preferred.

[0042] Examples of silicates include lithium salts, sodium salts, potassium salts, etc. Among these, lithium salts are particularly preferred.

[0043] The silicon compound binder may be used alone or in combination of two or more kinds.

[0044] The content of the silicon compound binder in the coating composition of the present invention is not particularly limited, as long as the dispersibility of the carbon nanotubes is not significantly impaired and a transparent conductive film can be formed. The content (converted to solid content) is, for example, 10 to 1000 parts by mass, preferably 20 to 700 parts by mass, more preferably 50 to 500 parts by mass, even more preferably 100 to 400 parts by mass, and still more preferably 150 to 300 parts by mass, relative to 100 parts by mass of the carbon nanotubes.

[0045] The inorganic acid is an acid made of an inorganic compound, and is not particularly limited thereto. Examples of inorganic acids include strong acids such as nitric acid, sulfuric acid, and hydrochloric acid; and weak acids such as phosphoric acid and boric acid. Among these, strong acids are preferred, and nitric acid and sulfuric acid are particularly preferred. From the viewpoint of the stability of the surface resistance of the coating film, sulfuric acid is particularly preferred.

[0046] The inorganic acid may be one kind alone or two or more kinds in combination.

[0047] The content of the inorganic acid in the coating composition of the present invention is not particularly limited as long as the dispersibility of the carbon nanotubes is not significantly impaired and a transparent conductive film can be formed, and the content is, for example, 0.1 to 5 mass%, preferably 0.2 to 4 mass%, more preferably 0.5 to 3 mass%, and even more preferably 1 to 2 mass%.

[0048] The coating composition of the present invention usually contains a solvent. The main solvent is water. It is also possible to use an organic solvent or a mixture of water and an organic solvent. Examples of organic solvents include alcohols such as methanol, ethanol, 2-propanol, and 1-propanol; ethylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol diethyl ether, and diethylene glycol dimethyl ether; glycol ether acetates such as ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate; propylene glycols such as propylene glycol, dipropylene glycol, and tripropylene glycol; and propylene glycols such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, propylene glycol dimethyl ether, and propylene glycol diethyl ether. ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, etc.; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.; hydrocarbons such as toluene, xylene (o-, m-, or p-xylene), hexane, heptane, etc.; esters such as ethyl acetate, butyl acetate, ethyl acetoacetate, methyl orthoacetate, ethyl orthoformate, etc.; amide compounds such as N-methylformamide, N,N-dimethylformamide, γ-butyrolactone, N-methylpyrrolidone, etc.; hydroxyl group-containing compounds such as trimethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, catechol, cyclohexanediol, cyclohexanedimethanol, glycerin, etc.; and compounds having a sulfo group such as dimethyl sulfoxide.

[0049] The coating composition of the present invention may contain other components in addition to those described above. When other components include a dispersant other than a sulfonic acid-based dispersant and a binder other than a silicon compound-based binder, the content of these components is preferably as small as possible.

[0050] When the coating composition of the present invention contains a dispersant other than a sulfonic acid dispersant (another dispersant), the content of the sulfonic acid dispersant is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 99% by mass or more, relative to 100% by mass of the dispersant (total of the sulfonic acid dispersant and the other dispersant).

[0051] When the coating composition of the present invention contains a binder (other binder) other than the silicon compound-based binder, the content of the silicon compound-based binder is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 99% by mass or more, relative to 100% by mass of the binder (total of the silicon compound-based binder and other binder).

[0052] The coating composition of the present invention can be obtained by mixing the respective components. From the viewpoint of dispersibility of carbon nanotubes, it is preferable to prepare a carbon nanotube dispersion solution containing carbon nanotubes and a dispersant in advance, and then mix the solution with a binder and an inorganic acid to obtain the coating composition of the present invention. After mixing, filtration can be performed as necessary.

[0053] The coating composition of the present invention has fewer problems with aggregation or gelation, and by using it, it is possible to more easily and efficiently obtain a carbon nanotube-containing transparent conductive film that has good coating film appearance and coating film adhesion and a certain degree of low resistance.

[0054] 2. Coating production method In one aspect, the present invention relates to (a) a method for producing a coating film (sometimes referred to herein as the "production method of the present invention"), which comprises the step of applying the coating composition of the present invention onto a substrate. This method will be described below.

[0055] The substrate is not particularly limited as long as it contains a resin (substrate resin) that can be used as a substrate for a transparent conductive film.

[0056] The substrate may contain components other than the substrate resin as long as the effects of the present invention are not significantly impaired. In such cases, the total amount of the substrate resin in the substrate is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, but less than 100% by mass.

[0057] The resin for the substrate is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate, and modified polyester, polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, polystyrene resin, and cyclic olefin resin, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polyvinyl acetal resins such as polyvinyl butyral (PVB), polyether ether ketone (PEEK) resin, polysulfone (PSF) resin, polyethersulfone (PES) resin, polycarbonate (PC) resin, polyamide resin, polyimide resin, acrylic resin, triacetyl cellulose (TAC) resin, etc. Among these, from the viewpoint of transparency, etc., preferred are polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polycarbonate, etc., and more preferred is polyethylene terephthalate.

[0058] The resin for the substrate may be one type alone or a combination of two or more types.

[0059] The thickness of the substrate is not particularly limited as long as transparency and strength appropriate for the intended use are ensured, and is, for example, 2 to 500 μm, preferably 10 to 400 μm, more preferably 20 to 300 μm, even more preferably 50 to 200 μm, and still more preferably 70 to 150 μm.

[0060] The layer structure of the substrate is not particularly limited. The substrate may be composed of a single type of substrate, or may be a combination of two or more types of substrates having the same or different compositions.

[0061] The substrate may be subjected to various surface treatments, such as corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, laser treatment, and other surface activation treatments.

[0062] The coating method is not particularly limited, and any conventionally known coating method can be used, such as gravure coating, reverse roll coating, die coating, air doctor coating, blade coating, rod coating, bar coating, curtain coating, knife coating, transfer roll coating, squeeze coating, impregnation coating, kiss coating, spray coating, calendar coating, and extrusion coating.

[0063] After coating, it is preferable to dry the coating. The drying temperature is, for example, 50 to 200° C., preferably 70 to 170° C., and more preferably 90 to 150° C. The drying time may vary depending on the drying temperature, but is, for example, 30 seconds to 15 minutes, preferably 1 to 10 minutes, and more preferably 2 to 5 minutes.

[0064] The production method of the present invention preferably includes the step (b) of washing the coating film obtained in step (a) with water, which can further reduce the surface resistance of the coating film.

[0065] The washing method is not particularly limited, and various methods for bringing water into contact with the coating surface can be used. Typically, washing can be performed by directing running water at the coating surface. The washing time can be, for example, about 1 to 30 seconds.

[0066] After washing, it is preferable to dry the coated film at a drying temperature of, for example, 50 to 200° C., preferably 70 to 170° C., and more preferably 90 to 150° C. The drying time may vary depending on the drying temperature, but is, for example, 30 seconds to 15 minutes, preferably 1 to 10 minutes, and more preferably 2 to 5 minutes.

[0067] The coating film obtained by the production method of the present invention has good coating appearance and coating adhesion, and can exhibit a certain degree of low resistance and transparency, so that the coating film can be used as a transparent conductive film.

[0068] 3.Transparent conductive film In one aspect, the present invention relates to a transparent conductive film (sometimes referred to as "the transparent conductive film of the present invention" in this specification) that contains carbon nanotubes, sulfur atoms, and silicon atoms and has a surface resistivity of 500 Ω / □ or less. This will be described below.

[0069] The transparent conductive film of the present invention can be obtained by the manufacturing method of the present invention. Therefore, the transparent conductive film of the present invention contains elements (sulfur element and silicon element) derived from the dispersant and binder used in the coating composition of the present invention. The presence or absence of these elements is determined by X-ray photoelectron spectroscopy (XPS) (sample angle 75°, measuring instrument: ULVAC-PHI Inc. Model 5400 or equivalent).

[0070] In an XPS graph (horizontal axis: binding energy, vertical axis: electron intensity), a sulfur peak of 168 to 170 eV indicates that the sulfur element is in a sulfone state. Therefore, the transparent conductive film of the present invention preferably exhibits a sulfur peak of 168 to 170 eV in an XPS graph.

[0071] In the XPS graph, a silicon peak at 103 to 104 eV indicates that the silicon exists in the form of silica. Furthermore, in the XPS graph, a silicon peak at 102 to 103 eV indicates that the silicon exists in the form of silicate. Therefore, it is preferable that the transparent conductive film of the present invention exhibits a silicon peak at 103 to 104 eV and / or a silicon peak at 102 to 103 eV in the XPS graph.

[0072] The surface resistivity is measured using a low resistivity meter (Loresta-GP MCP-T610, manufactured by Mitsubishi Chemical Analytech).

[0073] The surface resistivity of the transparent conductive film of the present invention is preferably 400 Ω / □ or less, more preferably 300 Ω / □ or less. The lower limit of the surface resistivity is not particularly limited and is, for example, 10 Ω / □, 20 Ω / □, or 40 Ω / □.

[0074] The transparent conductive film of the present invention preferably has a surface resistivity that is stable over time. For example, the transparent conductive film of the present invention preferably has a resistance change rate (=[(surface resistivity after 20 days - surface resistivity immediately after film formation) / surface resistivity immediately after film formation] x 100 (%)) of 20% or less (preferably 15% or less) 20 days after film formation under a light-shielded condition at 20°C. Furthermore, the transparent conductive film of the present invention preferably has a resistance change rate (=[(surface resistivity after 30 days - surface resistivity immediately after film formation) / surface resistivity immediately after film formation] x 100 (%)) of 30% or less (preferably 25% or less, more preferably 20% or less) 30 days after film formation under a light-shielded condition at 20°C. The transparent conductive film of the present invention preferably has a resistance change rate (=[(surface resistivity after 40 days - surface resistivity immediately after film formation) / surface resistivity immediately after film formation] x 100 (%)) of 30% or less (preferably 25% or less, more preferably 20% or less) 40 days after film formation under a light-shielded condition at 20°C. The transparent conductive film of the present invention preferably has a resistance change rate (=[(surface resistivity after 60 days - surface resistivity immediately after film formation) / surface resistivity immediately after film formation] x 100 (%)) of 30% or less (preferably 25% or less) 60 days after film formation under a light-shielded condition at 20°C.

[0075] The transparent conductive film of the present invention preferably has high adhesion to a substrate. For example, when the transparent conductive film of the present invention formed on a substrate is evaluated by a cross-cut test (JIS K5400, 2 mm square), the ratio of the number of squares that did not peel off to the total number of squares is preferably 95 or more / 100, and more preferably 100 / 100.

[0076] The visible light transmittance of the transparent conductive film of the present invention is, for example, 40% or more, preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. The visible light transmittance is a value measured with an ultraviolet-visible-near-infrared spectrophotometer. Specifically, it is measured and calculated according to the method described in "(4-5) Measurement of visible light transmittance" in the Examples.

[0077] 4.Applications The transparent conductive film of the present invention can be used in various applications requiring transparency and conductivity, such as transparent electrodes in touch panels and display elements of various electronic devices such as televisions of various display types such as liquid crystal, plasma, and field emission, and mobile phones; transparent electrodes in solar cells, electromagnetic wave shielding materials, electronic paper, electroluminescence dimming elements, etc.; electrolytic plating primers; and transparent planar heating elements. [Example]

[0078] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0079] (1) Material The materials used in the preparation of the following paints are listed below.

[0080] [Single-walled carbon nanotubes (CNTs)] Details of the single-walled CNTs used are shown in Table 1.

[0081] [Table 1]

[0082] [Dispersant] Details of the dispersants used are shown in Table 2.

[0083] [Table 2]

[0084] [binder] Details of the binders used are shown in Table 3.

[0085] [Table 3]

[0086] [Acids and bases] Details of the acids and bases used are shown in Table 4.

[0087] [Table 4]

[0088] (2) Preparation of paint Paints were prepared in Examples 1 to 30 and Comparative Examples 1 to 17. The preparation methods are shown below. The dispersants, binders, acids, and bases used in each Example and Comparative Example are shown in Tables 5 to 7 below.

[0089] The dispersant was weighed out and placed in a container, and ion-exchanged water was added to dissolve it. Single-walled CNT powder was added to the resulting dispersant solution. The solids ratio of single-walled CNT / dispersant was adjusted to 100 / 500, and the single-walled CNT solids content was adjusted to 0.1%. Using a dispersing device, the single-walled CNTs were uniformly dispersed in water. The resulting single-walled CNT dispersion was added with binder, isopropyl alcohol (IPA), and inorganic acid, and stirred. The weight ratio of single-walled CNT / binder was adjusted to 1 / 3, and the weight ratio of single-walled CNT dispersion / IPA / inorganic acid (1 mol / L) was adjusted to 100 / 2 / 2. The resulting solution was filtered through a 200-mesh filter to obtain a coating material.

[0090] (3) Preparation of CNT coating film CNT coating films were produced using the coating materials of Examples 1 to 30 and Comparative Examples 1 to 17. The production methods are described below.

[0091] A 100 μm thick PET film (visible light transmittance 90%) was bar coated using a coating bar of any bar diameter (0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.5 mm). The resulting coated film was dried in a hot air dryer at 120°C for 3 minutes. The coated surface of the dried coated film was washed with ion-exchanged water (running water) (water treatment). During this process, the running water was applied to the entire coated surface. The washing time was approximately several to 10 seconds. The washing water on the coating film was gently shaken off, and the film was dried in a hot air dryer at 120°C for 5 minutes until the washing water on the coating film was completely dried, yielding a CNT coating film.

[0092] (4) Measurement and evaluation of paint and coating properties (4-1) Evaluation of paint appearance The appearance of the paint was visually inspected. Specifically, the presence and amount of aggregates in the paint, and the presence or absence of gelation of the paint were checked. Evaluation was made according to the following evaluation criteria. <Evaluation criteria for paint appearance> ○: No visible aggregates (or very little) ×: Aggregates were visually observed, and the paint gelled.

[0093] (4-2) Evaluation of the appearance of the coating film after water treatment The appearance of the coating film was visually inspected for any change before and after the water treatment and evaluated according to the following criteria. <Evaluation criteria for the appearance of the coating film after water treatment> 〇: No change before and after treatment △: CNT aggregation due to coating flow ×: Coating peeled off due to running water.

[0094] (4-3) Evaluation of coating adhesion The adhesion of the coating film was evaluated by the cross-cut method (cross-cut test (JIS K5400), 2 mm square). Evaluation was based on the value of the number of squares that did not peel off / total number of squares, according to the following evaluation criteria. <Evaluation criteria for coating adhesion> 〇:100 / 100 △:50~99 / 100 ×: Less than 50 / 100.

[0095] (4-4) Measurement of surface resistivity The surface resistivity of the coating film before and after the water treatment was measured using a low resistivity meter (Loresta-GP MCP-T610, manufactured by Mitsubishi Chemical Analytech).

[0096] (4-5) Measurement of visible light transmittance After the water treatment, the visible light transmittance of the laminate (PET film + coating film) was measured using a UV-Vis-NIR spectrophotometer (V-770 Spectrophotometer, manufactured by JASCO Corporation). The measured value and the visible light transmittance (90%) of the PET film alone were substituted into formula (1): (Visible light transmittance of laminate (PET film + coating film) / Visible light transmittance of PET film alone) × 100 = Visible light transmittance of coating film alone (1) to calculate the visible light transmittance of the coating film alone.

[0097] (4-6)Result The results are shown in Tables 5 to 7. In the tables, "-" indicates that the measurement was not performed.

[0098] [Table 5]

[0099] [Table 6]

[0100] [Table 7]

[0101] (5) Resistance stability measurement A coating material was prepared using the same materials as in Examples 5 to 9. The composition was as follows: CNT dispersion (TL125) / lithium silicate 35 / IPA / H2SO4 = 10 / 0.1 / 0.2 / 0.2 (weight ratio). Using the obtained coating material, a coating film was prepared in the same manner as in "(3) Preparation of CNT coating film" above. In this case, a sample was also prepared in which the coating film was obtained by acid treatment (immersion in 1 mol / L nitric acid for 2 minutes, followed by washing with running water) instead of water treatment. The obtained coating film was left to stand at 20°C under light-shielded conditions, and the change in surface resistivity over time was measured.

[0102] The results are shown in Figure 1. As shown in Figure 1, it was found that the surface resistance was more stable in the case of water treatment.

[0103] (6) Analysis of the coating surface A coating film was prepared in the same manner as in "(3) Preparation of CNT coating film" above using the paint of Example 8. The surface of the obtained coating film was analyzed by X-ray photoelectron spectroscopy (XPS) (sample angle 75°, measuring device: Model 5400 manufactured by ULVAC-PHI, Inc.).

[0104] The results are shown in Figure 2. It was found that elements (Si and S) derived from the dispersant and binder used in the paint were present.

Claims

1. A coating composition comprising carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid, the sulfonic acid dispersant is polystyrene sulfonic acid, a naphthalene sulfonic acid-formalin condensate, or a salt thereof; the silicon compound binder is a silicate or colloidal silica, the inorganic acid is nitric acid, sulfuric acid, or hydrochloric acid; The carbon nanotube content is 0.4% by mass or less, the content of the sulfonic acid-based dispersant is 50 to 2000 parts by mass relative to 100 parts by mass of the carbon nanotubes; the content of the silicon compound binder is 10 to 1000 parts by mass relative to 100 parts by mass of the carbon nanotubes; The content of the inorganic acid is 1 to 5% by mass. Paint composition.

2. The coating composition according to claim 1, which is used to form a transparent conductive film.

3. A method for producing a coating film, comprising the step of: (a) applying the coating composition according to claim 1 or 2 onto a substrate.

4. The method according to claim 3, further comprising the step (b) of washing the coating film obtained in the step (a) with water.

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