JP2023018187A - Coating composition, method for producing coating film, and transparent conductive film - Google Patents

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 The present invention relates to a coating composition, a method for producing a coating film, and a transparent conductive film.

In recent years, low-resistance transparent conductive films have been used in various fields such as touch panels, organic EL displays, solar cells, and transparent electrodes. It has been reported that various materials such as metal materials such as ITO, conductive polymers such as PEDOT, and carbon materials such as carbon nanotubes are used as transparent conductive materials. At present, most transparent conductive materials used for low-resistance transparent conductive films are ITO at the practical level. However, the ITO film has the drawback of being stiff and having poor flexibility.

Carbon nanotubes are less expensive and more durable than other transparent conductive materials, and are expected to be applied to products that require flexibility. However, since carbon nanotubes have a relatively high resistance compared to other conductive materials, they are subjected to resistance reduction treatment when used in transparent conductive films. Typically, a technique for reducing the resistance of a film by forming a carbon nanotube coating film and then immersing the film in an acid solution is known (Patent Document 1). However, the technique of Patent Literature 1 uses a large amount of acid solution, and thus has problems such as being complicated and highly dangerous. Other low-resistance techniques also have problems such as complexity and danger.

Japanese Patent Application Laid-Open No. 2014-207116

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

In the course of research, the present inventors have considered adding an acid to the coating material for forming the carbon nanotube coating film and omitting the acid treatment after the coating film is formed. However, it has been found that when an acid is added to a paint, problems arise in paint appearance, paint film appearance, paint film adhesion, and the like. As a result of further research, the inventors of the present invention have found that the types of dispersants, binders, acids, etc. used in paints are the cause of the above problems. As a result of intensive research based on this knowledge, the present inventors have solved the above problems by using a coating composition containing carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid. I found a solution. That is, the present invention includes the following aspects.

Section 1. A coating composition comprising carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid.

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

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

Section 4. Item 4. The coating composition according to any one of Items 1 to 3, wherein the content of the sulfonic acid-based dispersant is 50 to 2000 parts by mass with respect to 100 parts by mass of the carbon nanotubes.

Item 5. 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.

Item 6. 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 with respect to 100 parts by mass of the carbon nanotubes.

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

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

Item 9. Item 9. The coating composition according to any one of Items 1 to 8, which is for forming a transparent conductive film.

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

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

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

Item 13. Item 13. The transparent conductive film according to Item 12, which has a surface resistivity of 300Ω/□ or less.

Item 14. 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 the film formation under a light-shielding condition at 20°C.

ADVANTAGE OF THE INVENTION According to this invention, the technique which can obtain the transparent conductive film containing a carbon nanotube more simply and efficiently can be provided. According to the present invention, it is possible to provide a carbon nanotube-containing transparent conductive film with more stable surface resistance.

The coating film was allowed to stand at 20°C under light-shielding conditions, and the change in surface resistivity over time was measured. Water treatment indicates the case where only water was used for washing during coating film formation, and acid treatment indicates the case where acid immersion was conducted during washing. The horizontal axis indicates the number of days elapsed since the film formation, and the vertical axis indicates the resistance change rate (= [(surface resistivity after the number of days on the horizontal axis - surface resistivity immediately after film formation) / surface resistivity immediately after film formation]. × 100 (%)). shows the XPS analysis results of the coating film. The 103-104ev peak of the silicon element indicates that the state of existence of the silicon element is silica. The 284-285ev peak of the carbon element indicates that it is in the state of carbon. The 168-170ev peak of elemental sulfur indicates that elemental sulfur is in the form of sulfone.

As used herein, the expressions "contain" and "include" include the concepts "contain", "include", "consist essentially of" and "consist only of".

1. In one aspect of the paint present invention, a paint composition containing carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid (herein referred to as the "coating composition of the present invention") There are also things.), related to. This will be explained below.

Carbon nanotubes are not particularly limited, and carbon nanotubes produced by an arc discharge method, a laser vaporization method, a chemical vapor deposition method (CVD method) or the like can be used. More specifically, single-walled carbon nanotubes, Both double-walled carbon nanotubes, multi-walled carbon nanotubes and mixtures thereof can be used. It preferably contains at least single-walled carbon nanotubes from the viewpoint of excellent conductivity.

The length of the carbon nanotube is preferably 1-2000 μm, more preferably 5-1000 μm, and still more preferably 5-500 μm. When the length of the carbon nanotube is within the above range, the conductivity and transparency of the conductive layer are excellent.

The diameter of the carbon nanotube 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 nanotube is within the above range, the conductivity and transparency of the conductive layer are excellent.

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

Carbon nanotubes can be of one type alone or can be a combination of two or more types.

The content of carbon nanotubes 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 is, for example, 0.4 mass % or less, preferably 0.01 to 0.4 mass %, more preferably 0.02 to 0.3 mass %, still more preferably 0.04 to 0.2 mass %, still more preferably 0.07 to 0.15 mass %.

The sulfonic acid-based dispersant is not particularly limited as long as it contains a sulfo group (--SO ₃ H) as a partial structure. The sulfonic acid-based dispersant preferably includes a polymer compound having a monomer unit containing an aromatic ring.

Aromatic rings include benzene, naphthalene, anthracene and triazine rings. The aromatic ring-containing monomer units include one or more monomer units selected from benzene ring-containing monomer units, naphthalene ring-containing monomer units, anthracene ring-containing monomer units, and triazine ring-containing monomer units.

The weight-average molecular weight of the polymer compound having monomer units containing aromatic rings is, for example, 1,000 to 2,000,000. The weight average molecular weight is preferably 5,000 to 1,500,000, more preferably 20,000 to 1,000,000, even more preferably 50,000 to 700,000, even more preferably 100,000 to 500,000, and most preferably 150,000 to 300,000.

Here, "monomer unit" means a "repeating unit" in a polymer compound. For example, in the case of a sodium naphthalenesulfonate formalin condensate, a "repeating unit" such as the following formula is called a monomer unit. In the following formula, n indicates the number of repeating units.

Specific examples of polymer compounds having monomer units containing aromatic rings include polystyrenesulfonic acid, naphthalenesulfonic acid-formalin condensates, salts thereof, and the like. Among these, polystyrene sulfonic acid or salts thereof are preferred. Moreover, in one aspect of the present invention, the sulfonic acid-based dispersant is preferably in the form of a salt.

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

As the sulfonic acid-based dispersant, alkylbenzenesulfonic acids such as branched alkylbenzenesulfonic acid and linear alkylbenzenesulfonic acid, or salts thereof can be used in addition to the above-described polymer compounds.

The sulfonic acid-based dispersant can be used singly or in combination of two or more.

The content of the sulfonic acid-based 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 (in terms of 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, and still more preferably 300 to 700 parts by mass with respect to 100 parts by mass of carbon nanotubes. parts, more preferably 400 to 600 parts by mass.

A silicon compound binder is a colloidal dispersion, solution, or emulsion of a silicon compound containing a solid or liquid silicon compound in an aqueous dispersion medium. Silicon compound binders include, for example, silicates such as silicates; colloidal silica; silane, siloxane hydrolyzate emulsions; silicone resin emulsions; silicone resins such as silicone-acrylic resin copolymers and silicone-urethane resin copolymers. and emulsions of copolymers with other resins. Among these, silicates or colloidal silica are preferable as the silicon compound-based binder, and silicates are more preferable.

Examples of silicates include lithium salts, sodium salts, potassium salts and the like. Among these, lithium salts are particularly preferred.

The silicon compound-based binder can be used alone or in combination of two or more.

The content of the silicon compound-based binder 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 (in terms of 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, and still more preferably 100 to 400 parts by mass with respect to 100 parts by mass of carbon nanotubes. parts, more preferably 150 to 300 parts by mass.

The inorganic acid is an acid composed of an inorganic compound, and is not particularly limited in this respect. 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 preferable, and nitric acid and sulfuric acid are particularly preferable. Sulfuric acid is particularly preferred from the viewpoint of the stability of the surface resistance of the coating film.

The inorganic acid can be one type alone, or can be a combination of two or more types.

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. The content is, for example, 0.1 to 5% by mass, preferably 0.2 to 4% by mass, more preferably 0.5 to 3% by mass, still more preferably 1 to 2% by mass.

The coating composition of the present invention usually contains a solvent. Solvents mainly include water. As the solvent, it is also possible to use an organic solvent or a mixed solvent 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; ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, Glycol ethers such as 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 such as propylene glycol, dipropylene glycol and tripropylene glycol Glycols; Propylene glycol ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether; Propylene glycol ether acetates such as propylene glycol monomethyl ether acetate; Diethyl ether Ethers such as , diisopropyl ether, methyl-t-butyl ether, and tetrahydrofuran; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; Toluene, xylene (o-, m-, or p-xylene), hexane, heptane, etc. Hydrocarbons: Esters such as ethyl acetate, butyl acetate, ethyl acetoacetate, methyl orthoacetate, and ethyl orthoformate: Amides such as N-methylformamide, N,N-dimethylformamide, γ-butyrolactone, and N-methylpyrrolidone Compound; hydroxyl group-containing compounds such as trimethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, catechol, cyclohexanediol, cyclohexanedimethanol, glycerin; dimethyl Examples thereof include compounds having a sulfo group such as sulfoxide.

The coating composition of the present invention may contain other components than those mentioned above. When a dispersant other than a sulfonic acid-based dispersant and a binder other than a silicon compound-based binder are included as other components, the content thereof is preferably as small as possible.

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

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

The coating composition of the present invention can be obtained by mixing each component. From the viewpoint of the dispersibility of carbon nanotubes, the coating composition of the present invention can be obtained by preparing in advance a carbon nanotube dispersion solution containing carbon nanotubes and a dispersant, and mixing the solution with a binder and an inorganic acid. preferable. Filtration can be performed after mixing, if necessary.

The coating composition of the present invention has little problem of aggregation or gelation, and by using it, the coating film appearance and coating film adhesion are good, and the carbon nanotube-containing transparent conductive material having a certain degree of low resistance Membranes can be obtained more easily and efficiently.

2. Method for producing a coating film In one aspect of the present invention, a method for producing a coating film (herein referred to as "the (also referred to as “manufacturing method”). This will be explained below.

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

The base material may contain components other than the base material resin as long as the effects of the present invention are not significantly impaired. In that case, the total amount of the base resin in the base is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more, and 100% by mass. is less than

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

The substrate resin may be used alone or in combination of two or more.

The thickness of the substrate is not particularly limited as long as the transparency and strength suitable for the application are ensured. The thickness of the substrate 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, still more preferably 70 to 150 μm.

The layer structure of the substrate is not particularly limited. The base material may be composed of a single type of base material, or may be a combination of two or more types of base materials having the same or different compositions.

The substrate may be subjected to various surface treatments. Examples of the surface treatment include corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, surface activation treatment such as laser treatment, and the like.

The coating method is not particularly limited. For example, 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, extrusion coating. etc., a conventionally known coating method can be used.

It is preferable to dry after coating. The drying temperature is, for example, 50-200°C, preferably 70-170°C, more preferably 90-150°C. The drying time may vary depending on the drying temperature, but is, for example, 30 seconds to 15 minutes, preferably 1 minute to 10 minutes, more preferably 2 minutes to 5 minutes.

The production method of the present invention preferably includes a step (b) of washing the coating film obtained in step (a) with water. Thereby, the surface resistance of the coating film can be further lowered.

The washing method is not particularly limited, and various methods of contacting the coating film surface with water can be employed. Typically, it can be cleaned by directing running water against the coating surface. The washing time can be, for example, about 1 to 30 seconds.

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

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

3. In one aspect of the transparent conductive film of the present invention, a transparent conductive film containing carbon nanotubes, sulfur atoms, and silicon atoms and having a surface resistivity of 500 Ω/□ or less (herein referred to as the “transparent conductive film of the present invention (also referred to as “conductive film”). This will be explained below.

The transparent conductive film of the invention can be obtained by the production method of the 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 the element is determined by X-ray photoelectron spectroscopy (XPS) (specimen angle 75°, measuring instrument: ULVAC-PHI model 5400 or equivalent).

In the XPS graph (horizontal axis: binding energy, vertical axis: electron intensity), the 168-170ev peak of the sulfur element indicates that the sulfur element is in the sulfone state. For this reason, the transparent conductive film of the present invention preferably exhibits a peak of elemental sulfur at 168 to 170 ev in the XPS graph.

In the XPS graph, the 103-104ev peak of the silicon element indicates that the silicon element exists in silica. In addition, in the XPS graph, the 102-103ev peak of the silicon element indicates that the silicon element exists in a silicate. Therefore, the transparent conductive film of the present invention preferably exhibits a peak of silicon element at 103-104ev and/or a peak at 102-103ev in the XPS graph.

The surface resistivity is measured using a low resistivity meter (Loresta-GP MCP-T610, manufactured by Mitsubishi Chemical Analytic Tech).

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

The transparent conductive film of the present invention preferably has a stable surface resistivity over time. For example, the transparent conductive film of the present invention has a rate of change in resistance after 20 days from film formation under a light-shielding condition of 20° C. (=[(surface resistivity after 20 days)−surface resistivity immediately after film formation) Surface resistivity immediately after film]×100 (%)) is preferably 20% or less (preferably 15% or less). In addition, the transparent conductive film of the present invention has a resistance change rate 30 days after film formation under a light-shielding condition of 20°C (= [(surface resistivity after 30 days - surface resistivity immediately after film formation) / Surface resistivity immediately after film]×100 (%)) is preferably 30% or less (preferably 25% or less, more preferably 20% or less). In addition, the transparent conductive film of the present invention has a rate of change in resistance after 40 days from film formation under a light-shielding condition of 20°C (= [(surface resistivity after 40 days - surface resistivity immediately after film formation) / Surface resistivity immediately after film]×100 (%)) is preferably 30% or less (preferably 25% or less, more preferably 20% or less). In addition, the transparent conductive film of the present invention has a resistance change rate after 60 days from the film formation under a light-shielding condition of 20° C. Surface resistivity immediately after film]×100 (%)) is preferably 30% or less (preferably 25% or less).

The transparent conductive film of the present invention preferably has high adhesion to the substrate. For example, when the transparent conductive film of the present invention formed on a base material is evaluated by a cross-cut method (cross-cut test (JIS K5400), 2 mm square), the number of unpeeled squares/the total number of squares is 95. It is preferably greater than or equal to /100, more preferably 100/100.

The visible light transmittance of the transparent conductive film of the present invention is, for example, 40% or higher, preferably 50% or higher, more preferably 60% or higher, even more preferably 70% or higher, and even more preferably 80% or higher. 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 Examples.

Four. Uses The transparent conductive film of the present invention can be used in various applications requiring its transparency and conductivity, such as televisions with various display systems such as liquid crystal, plasma, and field emission, and touch panels and display elements of various electronic devices such as mobile phones. Transparent electrodes; Transparent electrodes in solar cells, electromagnetic wave shielding materials, electronic paper, electroluminescence light control devices, etc.; Electroplating primers; Transparent planar heating elements.

EXAMPLES The present invention will be described in detail below based on examples, but the present invention is not limited by these examples.

(1) Materials Show the materials used in the preparation of the following paints.

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

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

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

[Acid/base]
Details of the acids and bases used are shown in Table 4.

(2) Preparation of Paint Paints of Examples 1-30 and Comparative Examples 1-17 were prepared. The manufacturing method is shown below. Dispersants, binders, acids and bases used in Examples and Comparative Examples are shown in Tables 5 to 7 below.

A dispersant was weighed into a container, and ion-exchanged water was added to dissolve the dispersant. Single-walled CNT powder was added to the resulting dispersant solution. At this time, the single-walled CNT/dispersant ratio was 100/500 (solid content ratio), and the single-walled CNT solid content was adjusted to 0.1%. Single-walled CNTs were uniformly dispersed in water using a dispersion device. A binder, isopropyl alcohol (IPA), and an inorganic acid were added to the obtained single-walled CNT dispersion and stirred. At this time, single-walled CNT/binder = 1/3 (solid content ratio) and single-walled CNT dispersion/IPA/inorganic acid (1 mol/L) = 100/2/2 (weight ratio). The resulting solution was filtered through a 200-mesh filter to obtain a paint.

(3) Fabrication of CNT Coating Films Using the paints of Examples 1-30 and Comparative Examples 1-17, CNT coating films were prepared. The manufacturing method is shown below.

A 100 μm-thick PET film (visible light transmittance 90%) was coated with a bar coater using a coating bar having an arbitrary 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). At this time, running water was applied to the entire coated surface. The cleaning time was about several seconds to ten seconds. The washing water on the coating film was lightly 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 to obtain a CNT coating film.

(4) Measurement and evaluation of physical properties of paints and coating films
(4-1) Evaluation of Paint Appearance The appearance of the paint was visually confirmed. Specifically, the presence and amount of aggregates in the paint and the presence or absence of gelling of the paint were confirmed. It was evaluated according to the following evaluation criteria.
<Evaluation criteria for paint appearance>
〇: Visually no aggregates (or extremely small amount)
x: Aggregates were visually observed, and the paint was gelled.

(4-2) Evaluation of Appearance of Coating Film after Water Treatment The presence or absence of a change in the appearance of the coating film before and after water treatment was visually confirmed. It was evaluated according to the following evaluation criteria.
<Evaluation criteria for appearance of coating film after water treatment>
◯: No change before and after treatment △: CNT aggregation due to coating film flow ×: Coating film peeling due to running water.

(4-3) Evaluation of Coating Film Adhesion The coating film adhesion was evaluated by a crosscut method (cross-cut test (JIS K5400), 2 mm square). Evaluation was made according to the following evaluation criteria based on the value of the number of unpeeled squares/the total number of squares.
<Evaluation Criteria for Coating Adhesion Evaluation Criteria>
○: 100/100
△: 50 to 99/100
x: less than 50/100.

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

(4-5) Measurement of visible light transmittance After water treatment, the visible light transmittance of the laminate (PET film + coating film) was measured using a UV-visible near-infrared spectrophotometer (V-770 Spectrophotometer, manufactured by JASCO Corporation). was measured using The obtained measurement value and the visible light transmittance (90%) of the PET film alone are expressed by the formula (1): (visible light transmittance of the laminate (PET film + coating film) / visible light transmittance of the PET film only) × 100 = Visible light transmittance of the coating film only (1) was substituted to calculate the visible light transmittance of the coating film only.

(4-6) Results The results are shown in Tables 5-7. In the table, "-" indicates unmeasured.

(5) Measurement of resistance stability Using the same materials as in Examples 5 to 9, paints were prepared. The composition is as follows: CNT dispersion (TL125)/lithium silicate 35/IPA/H2SO4 _{= 10} /0.1/0.2/0.2 (weight ratio). Using the obtained paint, a coating film was produced in the same manner as in "(3) Preparation of CNT coating film" above. At this time, instead of water treatment, acid treatment (immersion in 1 mol/L nitric acid for 2 minutes→washing with running water) was also performed to obtain a coating film. The resulting coating film was allowed to stand at 20° C. under light-shielding conditions, and changes in surface resistivity over time were measured.

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

(6) Analysis of Coating Film Surface Using the paint of Example 8, a coating film was prepared in the same manner as in “(3) Preparation of CNT coating film” above. The obtained coating film surface was analyzed by X-ray photoelectron spectroscopy (XPS) (specimen angle 75°, measuring instrument: model 5400 manufactured by ULVAC-PHI).

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

Claims (14)

A coating composition comprising carbon nanotubes, a sulfonic acid-based dispersant, a silicon compound-based binder, and an inorganic acid. The coating composition according to claim 1, wherein the carbon nanotube content is 0.4% by mass or less. The coating composition according to claim 1 or 2, wherein the sulfonic acid-based dispersant is a polymer compound having a monomer unit containing an aromatic ring. The coating composition according to any one of claims 1 to 3, wherein the content of the sulfonic acid-based dispersant is 50 to 2000 parts by mass with respect to 100 parts by mass of the carbon nanotubes. The coating composition according to any one of claims 1 to 4, wherein the silicon compound binder is a silicate or colloidal silica. The coating composition according to any one of claims 1 to 5, wherein the content of the silicon compound binder is 10 to 1000 parts by mass with respect to 100 parts by mass of the carbon nanotubes. A coating composition according to any one of claims 1 to 6, wherein said inorganic acid is a strong acid. The coating composition according to any one of claims 1 to 7, wherein the inorganic acid content is 0.1 to 5% by mass. The coating composition according to any one of claims 1 to 8, which is for forming a transparent conductive film. (a) A method for producing a coating film, comprising the step of applying the coating composition according to any one of claims 1 to 9 onto a substrate. 11. The manufacturing method according to claim 10, comprising the step of (b) washing the coating film obtained in step (a) with water. A transparent conductive film containing carbon nanotubes, sulfur atoms, and silicon atoms, and having a surface resistivity of 500Ω/□ or less. 13. The transparent conductive film according to claim 12, which has a surface resistivity of 300Ω/□ or less. 14. The transparent conductive film according to claim 12 or 13, which has a resistance change rate of 20% or less after 20 days from the film formation under light shielding conditions at 20°C.

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