JP7230928B2 - Carbon nanobrush antistatic paint - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coating film containing fibrous carbon nanohorn aggregates and a method for producing an antistatic coating film.

Conductive paints have been developed to prevent the generation of static electricity. Carbon materials with excellent conductivity such as carbon nanotubes are being studied as a conductive component to be added to paints. For example, Patent Document 1 discloses a coating composition containing carbon nanotubes.

WO2012/060292

Since carbon nanotubes are poor in dispersibility, there is a problem that a coating film having sufficient antistatic performance cannot be formed. An object of the present invention is to provide a coating film having high antistatic performance.

The coating film of the present invention is characterized by containing a conductive component containing fibrous carbon nanohorn aggregates in which single-layer carbon nanohorns are radially aggregated and connected in a fibrous form.

ADVANTAGE OF THE INVENTION According to this invention, the coating film which has high antistatic performance can be provided.

<Fibrous carbon nanohorn aggregate>
The coating film according to this embodiment contains fibrous carbon nanohorn aggregates. A fibrous carbon nanohorn aggregate is also called a carbon nanobrush (CNB), and has a structure in which single-layer carbon nanohorns are radially aggregated and connected in a fibrous manner. A fibrous carbon nanohorn aggregate is different from a single-layered carbon nanohorn aggregate that looks fibrous, and can maintain its fibrous shape even after centrifugation, ultrasonic dispersion, or the like. A single-layer carbon nanohorn is a conical carbon structure with a diameter of 1 nm to 5 nm and a length of 30 nm to 100 nm. is. Here, the carbon structure is a structure mainly containing carbon, and may contain light elements and catalyst metals. A fibrous carbon nanohorn aggregate is a fibrous carbon structure generally having a diameter of 30 nm to 200 nm and a length of 1 μm to 100 μm, eg, 2 μm to 30 μm. The aspect ratio (length/diameter) of the fibrous carbon nanohorn aggregates is generally 4-4000, for example 5-3500. The surface of the fibrous carbon nanohorn aggregate has single-layer carbon nanohorn protrusions with a diameter of 1 nm to 5 nm and a length of 30 nm to 100 nm. Since single-layer carbon nanohorns with high conductivity are connected in a fibrous form and have a long conductive path, the fibrous carbon nanohorn aggregate has high conductivity. Furthermore, the fibrous carbon nanohorn aggregates also have high dispersibility and are highly effective in imparting electrical conductivity.

The fibrous carbon nanohorn aggregates are generally formed by connecting seed-type, bud-type, dahlia-type, petal-dahlia-type, and petal-type (graphene sheet structures) carbon nanohorn aggregates. That is, one type or a plurality of these carbon nanohorn aggregates are contained in the fibrous structure. Seed type is a shape with few or no angular projections on the surface of the aggregate, bud type is a shape with some angular projections on the surface of the aggregate, dahlia type is the surface of the aggregate The petal type is a shape in which petal-like protrusions are seen on the surface of the aggregate. The petal structure has a width of 50 nm to 200 nm, a thickness of 0.34 nm to 10 nm, and 2 to 30 graphene sheets. The petal-dahlia type is an intermediate structure between the dahlia type and the petal type. The produced carbon nanohorn aggregates vary in shape and particle size depending on the type and flow rate of the gas.

Fibrous carbon nanohorn aggregates are also described in detail in WO2016/147909. Transmission micrographs of fibrous carbon nanohorn aggregates are disclosed in FIGS. 1 and 2 of WO2016/147909. In the fibrous carbon nanohorn aggregate shown in this transmission micrograph, radially aggregated single-layer carbon nanohorns (carbon nanohorn aggregates) are connected in a fibrous manner. The entire disclosure of WO2016/147909 is incorporated herein by reference.

In the method for producing fibrous carbon nanohorn aggregates, carbon containing a catalyst is used as a target (referred to as a catalyst-containing carbon target). , carbon dioxide, or a mixed atmosphere by laser ablation to heat the target to vaporize the target. Fibrous carbon nanohorn aggregates are obtained in the process of cooling the evaporated carbon and the catalyst. In addition to the laser ablation method described above, an arc discharge method or a resistance heating method can be used. However, the laser ablation method is more preferable from the viewpoint of continuous production at room temperature and atmospheric pressure.

In the laser ablation method applied in the present invention, a target is irradiated with a laser beam in a pulsed or continuous manner, and when the irradiation intensity exceeds a threshold value, the target converts energy, as a result, a plume is generated, and a product is deposited on a substrate provided downstream of the target, or generated in a space within the apparatus, and recovered in a recovery chamber.

CO ₂ laser, YAG laser, excimer laser, semiconductor laser, etc. can be used for laser ablation, and CO ₂ laser, which can be easily increased in output, is most suitable. A CO ₂ laser can be used with an output of 1 kW/cm ² to 1000 kW/cm ² , and can perform continuous irradiation and pulse irradiation. Continuous irradiation is preferable for the production of fibrous carbon nanohorn aggregates. A laser beam is condensed by a ZnSe lens or the like and irradiated. Also, by rotating the target, it is possible to synthesize continuously. Although the target rotation speed can be set arbitrarily, 0.1 rpm to 6 rpm is particularly preferable. If it is 0.1 rpm or more, graphitization can be suppressed, and if it is 6 rpm or less, an increase in amorphous carbon can be suppressed. At this time, the laser output is preferably 15 kW/cm ² or more, and most effectively 30 kW/cm ² to 300 kW/cm ² . If the laser output is 15 kW/cm ² or more, the target will evaporate appropriately and the fibrous carbon nanohorn aggregates will be easily produced. Also, if the laser output is 300 kW/cm ² or less, an increase in amorphous carbon can be suppressed. The pressure in the container (chamber) can be used at 13332.2 hPa (10000 Torr) or less, but the closer the pressure is to vacuum, the more easily carbon nanotubes are generated, making it impossible to obtain fibrous carbon nanohorn aggregates. The pressure in the container (chamber) is preferably 666.61 hPa (500 Torr) to 1266.56 hPa (950 Torr), more preferably around normal pressure (1013 hPa (1 atm ≈ 760 Torr)) for mass synthesis and cost reduction. is also suitable for The irradiation area can also be controlled by the laser output and the degree of condensing by the lens, and 0.005 cm ² to 1 cm ² can be used.

As the catalyst, Fe, Ni, and Co can be used singly or in combination. Although the concentration of the catalyst can be selected as appropriate, it is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 5% by mass, relative to carbon. When it is 0.1% by mass or more, the production of fibrous carbon nanohorn aggregates is ensured. Moreover, in the case of 10% by mass or less, an increase in target cost can be suppressed.

The inside of the container can be used at any temperature, preferably 0° C. to 100° C., more preferably room temperature, which is suitable for mass synthesis and cost reduction.

Nitrogen gas, inert gas, hydrogen gas, _CO2 gas, or the like is introduced into the container alone or in combination to create the above atmosphere. From the viewpoint of cost, nitrogen gas and Ar gas are preferable. These gases are circulated in the reaction vessel, and the substances produced can be recovered by this gas flow. Any amount can be used as the atmosphere gas flow rate, but a range of 0.5 L/min to 100 L/min is preferable. The gas flow rate is kept constant during the process of vaporizing the target.

The fibrous carbon nanohorn aggregates obtained as described above are usually obtained together with the spherical carbon nanohorn aggregates. Hereinafter, a mixture of fibrous carbon nanohorn aggregates and spherical carbon nanohorn aggregates is also simply referred to as carbon nanohorn aggregates. A spherical carbon nanohorn aggregate is a spherical carbon structure in which single-walled carbon nanohorns are radially aggregated. The spherical carbon nanohorn aggregates have a diameter of about 30 nm to 200 nm and a substantially uniform size. Also, in the fibrous carbon nanohorn aggregates and the spherical carbon nanohorn aggregates obtained, part of the carbon skeleton may be substituted with a catalytic metal element, nitrogen atom, or the like. Fibrous carbon nanohorn aggregates may be isolated and used. The fibrous carbon nanohorn aggregates may be used together with other carbon materials such as spherical carbon nanohorn aggregates. It should be noted that the fibrous carbon nanohorn aggregates and the spherical carbon nanohorn aggregates can be separated by the difference in size. Furthermore, if impurities other than carbon nanohorn aggregates are contained, they can be removed by centrifugation, sedimentation speed difference, size separation, or the like. Also, by changing the production conditions, it is possible to change the ratio of the fibrous carbon nanohorn aggregates and the spherical carbon nanohorn aggregates.

When forming fine holes (opening) in the aggregate of carbon nanohorns, oxidation treatment can be carried out. By this oxidation treatment, surface functional groups containing oxygen are formed in the openings. Moreover, the oxidation treatment can use a vapor phase process and a liquid phase process. In the case of a vapor phase process, heat treatment is performed in an atmosphere gas containing oxygen such as air, oxygen, or carbon dioxide. Among them, air is suitable from the viewpoint of cost. Also, the temperature may be in the range of 300°C to 650°C, more preferably 400°C to 550°C. If the temperature is 300° C. or higher, the carbon is burned and pores can be reliably formed. Moreover, at 650° C. or less, it is possible to prevent the entire carbon nanohorn aggregate from burning. In the case of the liquid phase process, it is carried out in a liquid containing oxidizing substances such as nitric acid, sulfuric acid, hydrogen peroxide and the like. Nitric acid can be used in the temperature range from room temperature to 120°C. If the temperature is 120° C. or less, it will not be oxidized more than necessary. In the case of hydrogen peroxide, it can be used in the temperature range of room temperature to 100°C, preferably 40°C or higher. In the temperature range of 40° C. to 100° C., the oxidizing power works efficiently, and pores can be formed efficiently. Also, in the liquid phase process, it is more effective to use light irradiation together.

The catalyst metal contained during the production of carbon nanohorn aggregates can be removed as necessary. Catalyst metals dissolve in nitric acid, sulfuric acid, and hydrochloric acid and can be removed. From the point of view of ease of use, hydrochloric acid is suitable. Although the temperature for dissolving the catalyst can be selected as appropriate, it is desirable to heat the catalyst to 70° C. or higher to sufficiently remove the catalyst. When nitric acid or sulfuric acid is used, catalyst removal and pore formation can be performed simultaneously or continuously. In addition, since the catalyst may be covered with a carbon coating during the production of carbon nanohorn aggregates, pretreatment is desirable to remove the carbon coating. It is desirable that the pretreatment be performed by heating in the air at a temperature of about 250°C to 450°C. At 300° C. or higher, partial openings may be formed as described above. Carbon nanohorn aggregates are easier to remove catalyst metal than carbon nanotubes. In the present embodiment, by using aggregates of carbon nanohorns from which catalytic metals have been removed, it is possible to form coating films that do not substantially contain metals and do not elute metals. Thereby, metal elution from the coating film can be prevented.

The carbon nanohorn aggregate can be heat-treated in a non-oxidizing atmosphere such as inert gas, hydrogen, or vacuum to improve crystallinity. The heat treatment temperature can be 800°C to 2000°C, preferably 1000°C to 1500°C. After the pore-opening treatment, surface functional groups containing oxygen are formed in the pore-forming portions, but these can be removed by heat treatment. A heat treatment temperature of 150° C. to 2000° C. can be used. A temperature of 150° C. to 600° C. is desirable for removing surface functional groups such as carboxyl groups and hydroxyl groups. A temperature of 600° C. or higher is desirable for removing carbonyl groups, which are surface functional groups. Surface functional groups can also be removed by reduction in a gas or liquid atmosphere. Hydrogen can be used for the reduction in a gaseous atmosphere, and can also be used for improving the crystallinity. Hydrazine or the like can be used in a liquid atmosphere.

<Paint>
The paint according to the present embodiment contains a conductive component containing aggregates of fibrous carbon nanohorns. Examples of conductive components other than fibrous carbon nanohorn aggregates include carbon materials such as spherical carbon nanohorn aggregates, carbon nanotubes, and graphite. The conductive component is a component composed of a conductive material, and may contain various other conductive materials. The conductive component may include, for example, conductive metal particles, a conductive polymer, etc., in addition to the carbon material. In one embodiment, the conductive material is a material with a volume resistivity (20° C.) of about 10 ⁻³ Ω·cm or less.

The base material of the paint is not particularly limited, and may be a material generally used for paint, such as a resin capable of forming a coating film on the base material, or a polymerizable monomer. Examples of resins include alkyd resins, unsaturated polyester resins, melamine resins, phenol resins, epoxy resins, vinyl chloride resins, acrylic resins, acrylic urethane resins, urethane resins, silicone resins, acrylic silicone resins, fluorine resins, and the like. . Polymerizable monomers include, for example, styrene, methyl methacrylate, 2-hydroxyethyl acrylate, methacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, o- and p-styrenesulfonates, divinylbenzene, ethylene diacrylate, N,N-methylenebisacrylamide and the like.

The paint may contain water and/or organic solvents. Examples of organic solvents include alcohols such as methanol, ethanol and isopropanol, glycols such as ethylene glycol, ketones, and ethers.

The coating may contain a curing agent suitable for the matrix (especially the polymerizable monomer). In addition, conventionally known additives such as leveling agents, slip agents, plasticizers, thickeners, desiccants, antifoaming agents, pigments and dyes can be arbitrarily added to the paint.

<Coating film>
A coating film can be formed by applying a coating material to a substrate. If necessary, the coating film may be further dried to remove volatile components such as water and organic solvents. If necessary, the coating film may be further cured. The method of curing the coating film is appropriately determined according to the type of the base material, particularly the polymerizable monomer. For example, heat curing, light curing, or the like can be used. Although the thickness of the coating film is not particularly limited, it is, for example, in the range of 1 μm to 50 μm.

The amount of fibrous carbon nanohorn aggregates contained in the coating film is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and still more preferably 0.003% by mass or more. When the amount of fibrous carbon nanohorn aggregates is within this range, the electrical conductivity of the coating film can be enhanced. The amount of fibrous carbon nanohorn aggregates contained in the coating film is preferably 1% by mass or less, more preferably 0.1% by mass or less, still more preferably 0.01% by mass or less, and particularly preferably 0.005% by mass. It is below. When the amount of the fibrous carbon nanohorn aggregates is within this range, the fibrous carbon nanohorn aggregates hardly affect the color of the coating film, and a transparent coating film can be formed. The total amount of conductive components or carbon materials contained in the coating film is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and still more preferably 0.01% by mass or more. The total amount of conductive components or carbon materials contained in the coating film is preferably 1% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.08% by mass or less.

In order to further increase the conductivity of the coating film, a release sheet may be attached to the surface of the formed coating film. By peeling the release sheet from the coating film, the surface of the coating film can be fluffed. On the surface of the fluffed coating film, the tips of the fibrous carbon nanohorn aggregates are exposed, increasing the conductivity of the coating film.

The release sheet is preferably an easily peelable adhesive sheet having an adhesive layer containing an adhesive component. Examples of the adhesive component used in the adhesive layer of the easily peelable adhesive sheet include rubber-based resins, acrylic resins, silicone resins, urethane resins, vinyl ether resins, and the like. In particular, commercially available dicing tapes and masking tapes can be preferably used as the easily peelable pressure-sensitive adhesive sheet.

The adhesive surface of the easily peelable adhesive sheet preferably has a highly adhesive portion (adhesive portion) and a low adhesive portion (non-adhesive portion). By providing an adhesive part and a non-adhesive part, the easily peelable adhesive sheet expands and contracts when the easily peelable adhesive sheet is peeled off, increasing the number of fibrous carbon nanohorn aggregates exposed from the surface of the coating film. can. A release component such as a silicone release agent or a long-chain alkyl release agent can be used in the non-adhesive portion. Adhesive components such as rubber-based resins, acrylic resins, silicone resins, urethane resins, and vinyl ether resins can be used for the adhesive portion. A release agent layer may be provided on a base material, and an adhesive layer may be provided on a part thereof to form an adhesive portion and a non-adhesive portion. Alternatively, a pressure-sensitive adhesive layer may be provided on the base material, and a release agent layer may be provided on a part thereof to form an adhesive portion and a non-adhesive portion. The shape of the adhesive portion or the non-adhesive portion is not particularly limited, and examples thereof include lattice, dot, perforated, and striped shapes. The area ratio of the adhesive portion to the non-adhesive portion on the adhesive surface of the easily peelable adhesive sheet may be, for example, 1:10 to 10:1, preferably 1:3 to 3:1.

In order to expose the fibrous carbon nanohorn aggregates on the surface of the coating film, it is preferable that the peeling adhesive force between the coating film and the release sheet is within a predetermined range. The peel adhesive strength between the coating film and the release sheet is preferably 0.1 N/cm or more, more preferably 1 N/cm or more, and still more preferably 2 N/cm or more. The peel adhesive strength between the coating film and the release sheet is preferably 10 N/cm or less, more preferably 8 N/cm or less, and even more preferably 4 N/cm or less. The peel adhesive strength is measured according to JIS Z 0237 (a test method in which a release liner is peeled off from the adhesive surface of a tape or sheet at 180°). In JIS Z 0237, the peel adhesive strength is measured by a tensile tester, and the peeling speed of the tensile tester is 5.0±0.2 mm/s.

The coating film according to the present embodiment has high conductivity even when the content of the conductive component is small as described above. The surface resistivity of the coating film is generally 1×10 ¹⁴ Ω/□ or less, preferably 1×10 ¹¹ Ω/□ or less, more preferably 1×10 ¹⁰ Ω/□ or less, further preferably 1×10 Ω/□ or less. ⁹ Ω/□ or less. The surface resistivity of the coating film is generally 1×10 ⁵ Ω/□ or more. Surface resistivity can be measured according to JIS K6911. In one embodiment, the amount of conductive materials other than carbon materials in the conductive component (excluding metals derived from catalysts for producing fibrous carbon nanohorn aggregates) is preferably 1% by mass or less, more preferably 0.5% by mass or less. It is 1% by mass or less, more preferably 0.001% by mass or less. In one embodiment, the coating film does not contain conductive materials other than carbon materials (excluding metals derived from catalysts for producing fibrous carbon nanohorn aggregates) other than conductive components. In one embodiment, the amount of carbon material in the conductive component is preferably 50 wt% or more, more preferably 80 wt% or more, and may be 100 wt%.

<CNB product>
A carbon material mixture containing fibrous carbon nanohorn aggregates (hereinafter referred to as a CNB product) was produced by CO ₂ laser ablation of a carbon target containing iron in a chamber under a nitrogen atmosphere. Specifically, a carbon target containing 1% by weight of iron was rotated at 2 rpm and was continuously irradiated with a CO ₂ laser. The energy density of the _CO2 laser was 50 kW/ ^cm2 . The temperature in the chamber was room temperature, and the flow rate of nitrogen supplied into the chamber was adjusted to 10 L/min. The pressure inside the chamber was controlled at 933.254 hPa to 1266.559 hPa (700 Torr to 950 Torr).

SEM observation of the CNB product revealed fibrous substances (fibrous carbon nanohorn aggregates), spherical substances (spherical carbon nanohorn aggregates), and graphite. The fibrous carbon nanohorn aggregates had a diameter of about 30 nm to 100 nm and a length of several μm to several tens of μm. Most of the spherical carbon nanohorn aggregates had a diameter of about 30 nm to 200 nm and had a substantially uniform size. The graphite had a size of 1 μm to several tens of μm.

Thermogravimetric analysis and particle size distribution measurement by a dynamic light scattering method revealed that the CNB product consisted of 4% by mass of fibrous carbon nanohorn aggregates, 62% by mass of spherical carbon nanohorn aggregates, 21% by mass of graphite, and 13% by mass of iron oxide. was confirmed to contain

<Example 1>
0.05 parts by mass of the CNB product was added to 100 parts by mass of a silicone resin emulsion (Asahi Kasei SILRES (registered trademark), containing 60% by mass of non-volatile components) and kneaded in a three-roll mill. The water-diluted paint was applied to the substrate with a roller and cured at 200° C. for 1 hour. The surface resistivity of this coating film was measured at 25° C. using a semiconductor parameter analyzer (trade name: Agilent 4155C, manufactured by Agilent Technologies) using a four-probe method. It was 2×10 ¹⁰ Ω/□.

<Example 2>
A dicing tape (Hitachi Kasei HAE-1503L) was attached to the surface of the coating film obtained in Example 1 and then peeled off. The surface resistivity of the coating film was 3×10 ⁸ Ω/□.

<Comparative Example 1>
0.05 parts by mass of carbon nanotubes was added to 100 parts by mass of a silicone resin emulsion (Asahi Kasei SILRES (registered trademark), containing 60% by mass of non-volatile components), and kneaded in a three-roll mill. The water-diluted paint was applied to the substrate with a roller and cured at 200° C. for 1 hour. The surface resistivity of the coating film was 5×10 ¹² Ω/□.

<Comparative Example 2>
A dicing tape was attached to the surface of the coating film obtained in Comparative Example 1 and then peeled off. The surface resistivity of the coating was 2×10 ¹² Ω/square, indicating less effect of the surface treatment compared to the coating containing the CNB product. Since the fibrous carbon nanohorn aggregates have an uneven shape, there are many portions that are adhered to the dicing tape, and it is thought that the effect of the surface treatment is enhanced.

This application claims priority based on Japanese Patent Application No. 2019-005018 filed on January 16, 2019, and the entire disclosure thereof is incorporated herein.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims (3)

A method for producing an antistatic coating film containing a conductive component containing fibrous carbon nanohorn aggregates,
a step of applying a coating material containing a conductive component containing fibrous carbon nanohorn aggregates to the base material to form a coating film;
A method for producing an antistatic coating film, comprising a step of laminating an easily peelable adhesive sheet to the coating film, and a step of peeling the easily peelable adhesive sheet from the coating film. 2. The method for producing an antistatic coating according to claim 1 , wherein the amount of fibrous carbon nanohorn aggregates in the antistatic coating is 0.001% by mass or more and 0.1% by mass or less. The charging according to claim 1 or 2 , wherein the amount of the conductive component in the antistatic coating is 0.1% by mass or less, and the surface resistivity of the antistatic coating is 1 × 10 ¹⁰ Ω/□ or less. A method for producing a protective coating.