Structure having layer for preventing lightning damage

Abstract

To provide a novel technique for preventing lightning damage to a structure for outdoor use.SOLUTION: A structure has, on an inner surface of an insulating base material, layers for preventing lightning damage that include the following layers (A) and (B). The layers for preventing lightning damage have a surface resistivity of 1.00×102 to 1.00×104 Ω / sq. (A) A coating layer of a carbon nanotube dispersion, which includes carbon nanotubes and a polymeric acid as a dispersant therefor, the coating layer being formed on the inner surface. (B) An overcoat resin layer formed on the side of the layer (A) opposite from the inner surface.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a structure having a lightning strike damage prevention layer.

Background Art

[0002] As one of the renewable energies, wind power generation has been attracting attention. However, there is a problem that the damage caused by lightning strikes to wind turbine blades is increasing due to the increase in the number and height of installed wind turbines.

[0003] As a lightning protection measure, in order to discharge lightning current to the ground, generally a metal receptacle, which is a lightning receiving part, is installed at the tip of the blade. Despite such measures, lightning strike accidents have been reported where lightning discharge hits a location other than the receptacle and penetrates the blade.

[0004] As a lightning protection measure, generally, it has been studied to impart conductivity to the surface of an insulating base material where there is concern about damage caused by lightning discharge in a structure to discharge electricity, but there is little specific verification at present. Conventionally, studies have been reported on subjecting a polyethylene terephthalate (PET) film coated on only one side to reduce the surface resistivity to airborne discharge (Non-Patent Documents 1 to 3). Even when a coating surface is provided on the grounded side of the inner surface where there are few concerns such as damage and heat generation of the coating surface due to a large current due to being directly exposed to lightning, surface discharge occurs on the film surface and it becomes difficult for the discharge to penetrate the film, and it has been clarified that the lightning resistance performance can be improved. In these studies, a silicone resin added with a conductive polymer or carbon is coated on the surface of an insulating PET film base material. However, there is still room for improvement in the lightning resistance performance based on the penetration probability. In addition, the former has problems in various durability such as strength and weather resistance due to being an organic film, and there are concerns such as damage due to discharge at the weakened part. The latter has the same concerns as the former due to being unsuitable for a thin film thickness, being black-colored, and containing resin.

[0005] Although carbon nanotubes are conductive materials, inks produced by common dispersion methods of carbon nanotubes do not necessarily sufficiently reduce the surface resistivity when the film thickness is thin, and it is difficult to ensure the required conductivity. Carbon nanotube ink using polyacrylic acid as a dispersant can reduce the surface resistivity even when the film thickness is reduced because polyacrylic acid exhibits a doping effect on carbon nanotubes (Patent Documents 1 and 2). Conventionally, this carbon nanotube ink has been suggested for applications as a transparent conductive film material, an electromagnetic wave shielding film, and a flexible electrode material, focusing on transparency and the like due to its thin film thickness, and its application to electrostatic suppression during the transportation of electronic components has also been studied, but no specific study has been conducted on preventing lightning strike damage.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non - Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the above circumstances, the present invention has been made, and an object thereof is to provide a novel technology for preventing damage caused by lightning strikes to structures used outdoors.

Means for Solving the Problems

[0009] To solve the above problems, the present inventors conducted intensive studies. When a conductive layer is provided on an insulating base material where lightning strike damage in the structure is a concern, and the surface resistance and the capacitance between the grounding part are regarded as an RC series circuit connected in series, the time constant of the circuit including the insulating base material can be obtained by multiplying these values. Since the time constant changes depending on the surface resistivity, it was considered that the probability of lightning strike damage such as penetration might change. If the time constant is smaller than the rise time of the applied voltage due to a lightning strike, it is considered that discharge is less likely to penetrate the insulating base material. To verify these considerations, a coating layer was provided on the insulating base material using a carbon nanotube dispersion liquid containing carbon nanotubes and a polymer acid as its dispersant. As a result, it was found that even when a thin coating layer such as 100 nm or less was used, when the surface resistivity was within a specific range, the change in the discharge propagation process and the decrease in the penetration probability occurred critically. Furthermore, it was found that an overcoat resin layer such as a coating of a binder resin can be provided as a protective layer to prevent the scattering of the thin carbon nanotube layer due to discharge, and such an effect can be obtained, thus completing the present invention. Negative polarity lightning impulse discharge is considered to reach spark discharge when a negative polarity leader generated from the high voltage side meets a positive polarity leader generated from the grounding side, and the surface discharge by the negative polarity leader meets the positive polarity leader at the end of the base material and reaches spark discharge. Even when a protective layer is provided to prevent the scattering of the thin carbon nanotube layer due to discharge, in the base material with a reduced surface resistivity, the penetration probability due to discharge is significantly reduced. The negative polarity leader generated from the high voltage side is shielded by the base material with a reduced surface resistivity. On the other hand, the protective layer suppresses the scattering, peeling, etc. of the coating even due to surface discharge on the surface of the base material or the lightning strike of the discharge generated by the positive polarity leader generated from the grounding side, and suppresses the damage due to the discharge of the vulnerable part.

[0010] That is, the structure of the present invention has a lightning strike damage prevention layer including the following layers (A) and (B) on the inner surface of the insulating base material, and the surface resistivity of the lightning strike damage prevention layer is 1.00×10 2 ~1.00×10 4 Ω / □. (A) A coating layer of a carbon nanotube dispersion liquid formed on the inner surface, containing carbon nanotubes and a polymer acid as a dispersant thereof (B) An overcoat resin layer formed on the surface opposite to the inner surface of the layer (A)

Advantages of the Invention

[0011] According to the present invention, damage caused by lightning strikes to structures used outdoors can be prevented.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

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Figure 7

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention will be specifically described. In the structure of the present invention, the (A) layer of the lightning strike damage prevention layer is a coating layer of a carbon nanotube dispersion liquid containing carbon nanotubes and a polymer acid which is a dispersant thereof (in the following description, "carbon nanotubes" are also referred to as "CNT").). The (A) layer imparts lightning strike damage prevention performance due to its conductivity.

[0014] The type of CNT is not particularly limited, and conventionally known ones can be used. For example, any of single-walled CNT (SWNT), double-walled CNT (DWNT), multi-walled CNT (MWNT), rope-like CNT, and ribbon-like CNT can be used. Also, metallic CNT or semiconducting CNT obtained through a separation process of semiconducting CNT can be used alone. The length and diameter of the CNT are not particularly limited, but in order to obtain a highly conductive CNT film, a diameter of 0.4 nm to 2.0 nm and a length of 0.5 μm to 20 μm are preferable. Among these, single-walled CNT is preferable in terms of obtaining a thin film thickness and a low surface resistivity.

[0015] The concentration of CNT in the CNT dispersion liquid is not particularly limited, but considering points such as being able to ensure the required conductivity even when reducing the film thickness, 0.005% by mass or more is preferable, 0.05% by mass or more is more preferable, 0.1% by mass or more is further preferable, and 0.25% by mass or more is particularly preferable. Also, 1% by mass or less is preferable, 0.9% by mass or less is more preferable, 0.75% by mass or less is further preferable, and 0.6% by mass or less is particularly preferable.

[0016] Examples of the polymer acid include (co)polymers obtained by (co)polymerizing raw material monomers including monomers having acidic groups such as monomers having a carboxylic acid group, monomers having a sulfonic acid group, and monomers having a phosphoric acid group. Among these, monomers having a carboxylic acid group are preferable. The monomers having an acidic group may be used alone or in combination of two or more.

[0017] Examples of the monomer having a carboxylic acid group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethyl succinic acid, and the like. These may be used alone or in combination of two or more.

[0018] Examples of the monomer having a sulfonic acid group include styrene sulfonic acids such as p-styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-hydroxy-3-allyloxy-1-propane sulfonic acid, isoprene sulfonic acid, and the like. These may be used alone or in combination of two or more.

[0019] As the polymer acid, polymer carboxylic acids such as polyacrylic acid and polymethacrylic acid, and polymer sulfonic acids such as poly(p-styrene sulfonic acid) are preferable, polymer carboxylic acids are more preferable, and polyacrylic acid is still more preferable.

[0020] Polyacrylic acid exhibits a doping effect on CNTs and can achieve a lower resistance value. In existing coating technologies, it is required to perform the dispersion of CNTs and the doping of CNTs separately, and it is necessary to remove the insulating dispersant after film formation. Therefore, the process is numerous and the process is complicated, and the substrates on which films can be formed are also limited. However, due to the composite structure in which polyacrylic acid wraps around CNTs in a helical shape, a small amount of CNTs can be uniformly dispersed, and at the same time, it becomes a dispersion liquid for doping CNTs. After the formation of the CNT film, high conductivity can be obtained without removing polyacrylic acid, which is a polymer acid. The doping is a charge transfer type doping in which the carboxyl group of polyacrylic acid extracts electrons from CNTs. Since the polymer acid, which is a dispersant, itself functions as a doping agent for CNTs and the polymer acid itself exhibits a doping effect, there is no need to add a separate dopant. In addition, since the polymer acid is stable and non-volatile, a conductive film showing stable conductivity over a long period of time can be obtained. Since the surface of carbon nanotubes has few polar groups, it is necessary to introduce many adsorption groups into the dispersant molecule or a dispersant expecting π-electron interaction. It is known that importance is attached to increasing the adsorptivity among wetting dispersants and that viscosity reduction, that is, stabilization is also required. However, in the CNT composition using polyacrylic acid as a dispersant, the electrical contact between CNTs, the electrical contact between bundles, and the electrical contact between the bundle of CNTs and CNTs are less likely to be hindered by the dispersant. The polymer acid adsorbs so as to cover the periphery of CNTs or CNT bundles, and a low-viscosity dispersion liquid with good dispersion of CNTs even at a high concentration can be obtained, which is suitable for reducing the film thickness. On the other hand, since the polymer acid cannot completely cover the surface of CNTs or CNT bundles, there are portions where CNTs or CNT bundles are exposed. Therefore, since the electrical contact between CNTs or between CNT bundles is not hindered, the coating film exhibits good conductivity. That is, since the electrical connection in the CNT network is improved and the electrical performance is excellent, the required conductivity can be ensured even when the film thickness is reduced.

[0021] The weight-average molecular weight of the high molecular acid is not particularly limited. However, a high molecular acid with a larger molecular weight can better disperse CNTs, shorten the dispersion time, and improve the coating film strength. A shorter dispersion time is advantageous in terms of cost in mass production. From the perspective of suppressing scattering due to lightning strike discharge, etc., it is desirable for the coating film strength to be higher. On the other hand, a high molecular acid with a smaller molecular weight tends to have a greater doping effect, and a smaller molecular weight is more desirable for achieving high conductivity. From the perspective of balancing these properties, the weight-average molecular weight of the high molecular acid (especially polyacrylic acid) is preferably 500 or more, more preferably 1,000 or more, still more preferably 2,000 or more, particularly preferably 4,000 or more, especially preferably 10,000 or more, and most preferably 20,000 or more. Also, it is preferably 500,000 or less, more preferably 250,000 or less, still more preferably 100,000 or less, particularly preferably 50,000 or less, and most preferably 30,000 or less.

[0022] In addition, for the above weight-average molecular weight, the value in terms of a standard polymer (for example, standard polyacrylic acid) by gel permeation chromatography (GPC method) is referred to. Here, as the standard polymer, a polymer with a narrow molecular weight distribution and a known molecular weight having the same or an approximate structure as the measurement target is referred to.

[0023] The concentration of the high molecular acid in the CNT dispersion is not particularly limited. However, considering that the required conductivity can be ensured even when the film thickness is reduced, etc., it is preferably 0.005 mass% or more, more preferably 0.075 mass% or more, still more preferably 0.15 mass% or more, and particularly preferably 0.4 mass% or more. Also, it is preferably 5 mass% or less, more preferably 4.5 mass% or less, still more preferably 3 mass% or less, and particularly preferably 1 mass% or less.

[0024] Considering points such as ensuring the necessary conductivity even when reducing the film thickness, the mass ratio of CNT to the polymer acid is preferably 1:0.8 or more, more preferably 1:1 or more. Also, it is preferably 1:5 or less, preferably 1:4 or less, and even more preferably 1:3 or less. When the mass ratio of the polymer acid to CNT is within this range, the electrical contact between CNTs, the electrical contact between bundles, and the electrical contact between CNTs and CNT bundles are less likely to be hindered by the polymer acid. Within this range, the polymer acid adsorbs to cover the periphery of the CNT or CNT bundle, dispersing the CNT well, but the polymer acid cannot completely cover the surface of the CNT or CNT bundle, resulting in exposed portions of the CNT or CNT bundle. Therefore, since the electrical contact between CNTs or between CNT bundles is not hindered, the CNT composite film exhibits good conductivity.

[0025] The solvent for dispersing the polymer acid and CNT is not particularly limited, but water or an organic solvent can be used. Examples of the organic solvent include alcohol-based organic solvents (e.g., methanol, ethanol, 2-propanol, glycerin, ethylene glycol, etc.), ketone-based organic solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), ether-based organic solvents (e.g., diethyl ether, THF, etc.), ester-based organic solvents (methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate, etc.), hydrocarbon-based organic solvents (toluene, methylcyclohexane, etc.). These can be used alone or in combination of two or more. Among them, considering dispersibility, response to environmental problems, printing suitability and drying properties of the ink, etc., water, alcohol-based organic solvents or a mixed solvent thereof are preferred, for example, water, methanol, ethanol, 2-propanol, glycerin, ethylene glycol, a mixed solution of water and ethanol, a mixed solution of ethanol and 2-propanol, etc.

[0026] In addition to the CNTs, polymer acids, and solvents described above, other components can be blended in the CNT dispersion as long as the effects of the present invention are not impaired. Further, by appropriately selecting a predoping step, a pre-dispersion step, a main dispersion step, etc. as the manufacturing process of the CNT dispersion, it is possible to obtain a layer (A) that has good electrical connection in the CNT network and is excellent in conductivity even when the film thickness is small.

[0027] In the structure of the present invention, the layer (B) of the lightning strike damage prevention layer is an overcoat resin layer. The overcoat resin layer is not particularly limited, but a coating layer of a binder resin is preferable from the viewpoint of effectively functioning as a protective layer for preventing scattering due to discharge during a lightning strike. The coating layer of the binder resin also improves the adhesion, abrasion resistance, solvent resistance, water resistance, and scratch resistance, which are difficult to achieve with only the layer (A), which is the coating layer of the CNT dispersion. Furthermore, by adjusting the film thickness, it is possible to obtain a sheet that has excellent transparency without a decrease in the conductivity of the surface of the lightning strike damage prevention layer.

[0028] The binder resin is coated as an ink using water, a solvent, or the like as a solvent, and is bound to the layer (A) by drying. The binder resin is not particularly limited, and examples thereof include polyester resins, polyacrylic resins, polyurethane resins, epoxy resins, olefin resins, etc. that are water-based or solvent-based.

[0029] More specifically, examples of the binder resin include solvent-based polyacrylic resins, water-based acrylic-modified polyester resins, water-based polyester resins, etc.

[0030] Among the above binder resins, water-based or solvent-based polyacrylic resins and water-based or solvent-based polyester resins are preferable.

[0031] The solvent for the binder resin is not particularly limited, and water or an organic solvent can be used. These are mainly used in a dilution amount that provides an appropriate viscosity during coating. The solvent for the aqueous binder resin must include water, and may also be a mixed solvent of water and an organic solvent compatible with water, such as alcohol-based organic solvents (e.g., methanol, ethanol, 2-propanol, glycerin, ethylene glycol, etc.). The solvent for the solvent-based binder resin is not particularly limited, and examples include alcohol-based organic solvents (e.g., methanol, ethanol, 2-propanol, glycerin, ethylene glycol, etc.), ketone-based organic solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), ether-based organic solvents (e.g., diethyl ether, THF, etc.), ester-based organic solvents (methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate, etc.), hydrocarbon-based organic solvents (toluene, methyl cyclohexane, etc.). These may be used alone or in combination of two or more.

[0032] Other components can be incorporated into the ink of the binder resin within a range that does not impair the effects of the present invention. Examples of other components include additives such as crosslinking agents, waxes, leveling agents, surface modifiers, and defoaming agents. These may be used alone or in combination of two or more. The amount of the additive is not particularly limited, but is, for example, about 1 to 10% by mass depending on the type and the like.

[0033] The structure of the present invention can be produced, for example, by applying and drying a CNT dispersion liquid serving as layer (A) on the inner surface of the structure, specifically, the inner surface of the insulating base material in the structure to form a coating layer, and then applying and drying a binder resin serving as layer (B) on the surface thereof to form a coating layer.

[0034] (A) layer is a CNT dispersion liquid, and the method for applying (B) layer which is a binder resin is not particularly limited. For example, spray coating method, gravure printing, screen printing, casting method, dip coating method, spin coating method, bar coating method, blade coating method, die coating method, inkjet method, etc. can be mentioned. Among these, in terms of being suitable for application to a large-area insulating substrate such as a blade of a wind turbine where lightning strike damage prevention is particularly required, the spray coating method is preferred. Gravure printing is preferred in terms of being able to print at high speed and the CNT dispersion liquid using a polymer acid as a dispersant can ensure the required conductivity even with a small film thickness.

[0035] (A) layer's film thickness is not particularly limited. However, considering conductivity for lightning strike damage prevention etc., the film thickness after drying is preferably 20~1000nm, more preferably 20~300nm.

[0036] (B) layer's film thickness, in terms of effectively functioning as a protective layer for preventing scattering due to discharge during lightning strike of (A) layer which is the coating layer of the CNT dispersion liquid, and further considering improving adhesion, abrasion resistance, solvent resistance, water resistance, scratch resistance which are difficult with (A) layer alone, etc., the film thickness after drying is preferably 0.1~10μm, more preferably 0.5~5μm.

[0037] The structure of the present invention has a lightning strike damage prevention layer including (A) layer and (B) layer on the inner surface of the insulating substrate. Fig. 1(A) is a schematic side view showing an example of the structure of the present invention, Fig. 1(B) is a longitudinal sectional view showing its lightning strike damage prevention layer, and Fig. 1(C) is an inner surface view. The structure 1 has a lightning strike damage prevention layer 3 on the inner surface of the insulating substrate 2. The lightning strike damage prevention layer 3 has a coating layer (A) of a carbon nanotube dispersion liquid formed on the inner surface of the insulating substrate 2 and an overcoat resin layer (B) formed on the surface of (A) layer opposite to the inner surface. Also, a grounding part 4 is provided opposite to the lightning strike damage prevention layer 3.

[0038] The structure 1 of the present invention is not particularly limited, and examples include a wind turbine, an aircraft, etc. that are used outdoors. The structure mainly targets relatively large-scale structures that are concerned about damage caused by lightning strikes. As the insulating base material 2, examples include members whose at least a part of one side faces the outdoors. The shape of the insulating base material 2 is not particularly limited, but from the viewpoint of preventing damage such as penetration by lightning strikes, a planar shape or a curved surface shape is preferable, and particularly, those having a large-area surface are preferable. The lightning strike damage prevention layer 3 is formed on the inner surface opposite to the side facing the outdoors of the insulating base material 2. In a wind turbine, the lightning strike damage prevention layer 3 is formed on the inner surface of the blade which is the insulating base material 2.

[0039] The insulating base material 2 is not particularly limited as long as it has insulation properties that are concerned about lightning strike damage, and it may be either an organic material or an inorganic material. Examples of the organic material include resins. Examples of the inorganic material include ceramics, glass, etc. Also, a composite material of an organic material and an inorganic material may be used. Among these, from the viewpoint that the lightning strike damage prevention layer 3 can effectively prevent damage caused by lightning strikes, a material containing resin is preferable. The material containing resin is not particularly limited, and for example, it may be a conventionally known material as a molding material, a material mainly composed of a synthetic resin or a natural resin, or a material obtained by adding an inorganic filler or fiber (such as glass fiber, organic fiber) thereto, and for example, it may be a fiber reinforced plastic (FRP). Examples of the synthetic resin include thermoplastic resins and thermosetting resins. Examples of the thermoplastic resin include polyester resins, polyolefin resins, polystyrene resins, polyamide resins, polyvinyl chloride resins, polycarbonate resins, etc. Examples of the thermosetting resin include epoxy resins, phenol resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, silicone resins, polyurethanes, thermosetting polyimides, etc. Known additives and the like that are usually blended may be added to the material containing resin.

[0040] The thickness of the insulating base material 2 is not particularly limited, but for the purpose of preventing lightning strike damage, it is preferably thicker than 5 mm. Assuming a wind turbine blade, the tip of the blade where the capacitance C between the down conductor inside the blade and the lightning strike damage prevention layer increases becomes a location under severe conditions, so the capacitance at that point is considered. At the blade tip, the thickness d1 of the insulating base material 2 (blade) is assumed to be about 5 mm to about 10 mm, and the distance d2 from the down conductor is assumed to be several tens of mm. From this, the capacitance C is obtained as shown in the following formula. Since d1 << d2, c1 >> c2, the influence of the thickness of the insulating base material 2 is considered to be about several to ten-odd percent.

Number

[0041] In the structure 1 of the present invention, the surface resistivity of the lightning strike damage prevention layer 3 is 1.00×10 2 ~1.00×10 4 Ω / □. In the experiment in the following examples, the threshold value at which the penetration probability of the CNT-coated film with a protective layer changes when a lightning impulse discharge with a peak value of -520 kV is applied is between 8.10×10 3 ~4.16×10 4 Ω / □, and the penetration probability changes dramatically from 0% to 100%. The upper limit of the surface resistivity is preferably 4.00×10 4 Ω / □ or less, more preferably 1.00×10 4 Ω / □ or less, still more preferably 5.00×10 3 Ω / □ or less, particularly preferably 1.00×10 3 Ω / □ or less. The lower limit of the surface resistivity is not particularly limited, but considering the film thickness, cost balance, etc., it is preferably 1.00×10 1 Ω / □ or more, more preferably 5.00×10 1 Ω / □ or more, still more preferably 1.00×10 2 Ω / □ or more.

[0042] The grounding part 4 is provided to face the lightning strike damage prevention layer 3. The configuration of the grounding part 4 is not particularly limited, and it may be a member that is part of the structure 1, or it may be, for example, the ground that does not constitute the structure 1 itself, and can be defined according to the structure of the structure 1. As the grounding part 4, in particular, since it is greatly involved in the rise of the lightning surge generated by lightning strikes and the difference from the time constant τ of the RC circuit between the lightning strike damage prevention layer 3 and the grounding part 4, a part with a particularly large capacitance defined between it and the lightning strike damage prevention layer 3 is targeted.

[0043] FIG. 2(A) is a perspective view schematically showing an example of the structure of the present invention, which is a wind turbine, and FIG. 2(B) is a longitudinal sectional view showing its blade. The wind turbine 1A has blades 2A, a hub 5, a nacelle 6, and a tower 7. By receiving wind on the rotor composed of a plurality of blades 2A, lift is generated on the windmill, and the hub 5 rotates by the lift, and the rotational force is transmitted by the main shaft. Inside the nacelle 6, a speed increaser, a generator, blade pitch control equipment, yaw control equipment, etc. are housed, and on the upper part of the nacelle 6, a wind direction meter and a wind speed meter for control are installed. If necessary, it is changed to high-speed rotation by a speed increaser to rotate the generator for power generation. The generated electricity is stepped up by a transformer and sent to the transmission line of the power company, and is consumed in factories, homes, etc.

[0044] As shown in FIG. 2(B), a receptor 9, which serves as a lightning receiving part for safely flowing the lightning strike current to the ground as a lightning protection measure, is attached to the tip of the blade 2A. Examples of the receptor 9 include a block-shaped chip receptor, a disk receptor in which a circular metal is embedded, and a rod receptor in which a metal rod is further embedded toward the tip. The receptor 9 is connected to a down conductor 8, which is a pulling-down conductor for flowing the lightning strike current to the ground. A lightning strike damage prevention layer 3 is formed on the inner surface of the blade 2A, which is an insulating base material. The grounding part 4 in FIG. 1(A) is (1) the ground, (2) the down conductor 8, (3) the components of the windmill (such as the nacelle 6 and the tower 7), but it is considered that the degree of influence on the capacitance with the blade 2A is in the order of (2), (1), (3) from large to small.

[0045] The rise of a lightning surge caused by lightning strikes is about 1 μs, and in the following examples, lightning impulse voltages with a similar wavefront length are applied for experiments. The wavefront length t f is, at the rise of the applied impulse waveform, the time t max when the magnitudes are 30% and 90% of the maximum value V 30 and t 90 and is defined by the following formula. t f = (t 90 - t 30 ) / 0.6) Therefore, considering protection from lightning strikes, it is considered that a protection effect will appear if the time constant of the film is set to 1.2 μs or less. Since this value is the value at which the penetration / non-penetration probability begins to change, it is necessary to have a certain margin in the time constant in order not to completely penetrate. However, since the capacitance that determines the time constant varies depending on the actual device and situation, it is preferable to design such that the time constant τ of the RC series circuit including the lightning strike damage prevention layer 3 and the grounding portion 4 is 1.2 μs or less. The time constant τ of the RC series circuit including the lightning strike damage prevention layer 3 and the grounding portion 4 is preferably 1.2 μs or less, more preferably 0.6 μs or less, still more preferably 0.3 μs or less, and particularly preferably 0.12 μs or less. It is considered that the penetration probability can be reduced if the time constant is 1.2 μs or less, which is the voltage rise time due to a general lightning strike. However, in order to more surely obtain the reduction effect, it is necessary to be sufficiently smaller than the rise time of the lightning strike, so a time constant of one digit smaller, 0.12 μs (120 ns) or less, is considered to be a particularly preferable time constant.

[0046] The idea of linking the protection of the actual structure 1 from lightning strikes with the theory of the time constant is as follows. Since the lightning strike damage prevention layer 3 is coated on the inner surface of the insulating base material 2, when considering the time constant of this coating surface, the capacitance that affects the time constant τ of the coating surface is C = εS / d (ε: permittivity, S: area, d: distance). In Fig. (A), the distance d and in Fig. 1(C), the area S are shown as examples. Assuming the permittivity of vacuum ε0 is 8.854×10 -12 (F / m) and the relative permittivity of air is 1, the permittivity ε is 8.854×10 -12 (F / m).

[0047] In the structure 1 of the present invention, the configuration of the time constant can be simply modeled. Assuming an RC series circuit of the surface resistivity of the lightning strike damage prevention layer 3 and the capacitance between the lightning strike damage prevention layer 3 and the grounding portion 4, the time constant τ is calculated as follows. τ = R×C Here, R [Ω] is the product of the surface resistivity of the lightning strike damage prevention layer 3 and the area S, and C [F] is the capacitance between the lightning strike damage prevention layer 3 and the grounding portion 4.

[0048] When the time constant τ is larger than the rise time of the applied voltage, the propagation speed of the potential is slower in the lightning strike damage prevention layer 3. On the other hand, when the time constant τ is smaller than the rise time of the applied voltage, the propagation speed of the potential is faster in the lightning strike damage prevention layer 3. In the following examples, when R is without the lightning strike damage prevention layer 3, it is >10 11 Ω / □, and in Example 1 with the lightning strike damage prevention layer 3, it is 3.00×10 2 Ω / □, and C is 3.32×10 -12 F in both cases, so the time constant is calculated to be 0.5 ms for the untreated film and 0.015 ps for the coating film. When the lightning strike damage prevention layer 3 is provided, since the time constant τ is small and the potential propagation is fast, it is considered that the electric field does not increase locally and surface discharge occurs. That is, due to the influence of the time constant τ, the smaller the surface resistivity, the less likely the electric field is to penetrate into the insulating base material 2. In the propagation process without the lightning strike damage prevention layer 3, it is considered that discharge progresses from the position near the high-voltage source in the insulating base material 2 toward the grounding portion 4, and double leader discharges occur from the insulating base material 2 and the grounding portion 4. On the other hand, in the propagation process when the lightning strike damage prevention layer 3 is provided, it is considered that discharge progresses from the tip of the high-voltage source toward the edge of the lightning strike damage prevention layer 3, and double leader discharges occur from the edge and the grounding portion 4. When the surface resistivity of the lightning strike damage prevention layer 3 is low, the discharge path is thin. On the other hand, when the surface resistivity of the lightning strike damage prevention layer 3 is high, a strongly charged region spreads and penetrates so as to surround the thin discharge path.

[0049] Taking the wind turbine 1A in Fig. 2 as an example, a lightning strike damage prevention layer 3 is coated on the inner surface of the hollow blade 2A. When considering the time constant τ of this coating surface, the capacitances that affect the time constant τ of the coating surface are (1) between the ground and the coating, (2) between the down conductor and the coating, and (3) between the windmill (structures such as the nacelle and tower) and the coating. The degree of influence is considered to be large in the order of (2), (1), and (3). Furthermore, since the capacitance is C = εS / d (ε: dielectric constant, S: area, d: distance), in (2), the capacitance C is larger at the tip of the blade 2A of the windmill than at the root, so the influence is considered to be large. Therefore, it is considered that a protective effect can be obtained by coating with an inclination such that the surface resistivity of the tip side of the blade 2A is decreased and the surface resistivity of the root side of the blade 2A is increased. That is, the distances between the down conductor 8 and the coating surface of the lightning strike damage prevention layer 3 are different at the tip and the root portions. Since the distance is shorter at the tip and the capacitance becomes larger, in order to make the time constant τ = RC of the coating surface constant, it is necessary to lower the surface resistivity at the tip compared to the root.

Example

[0050] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples. 1. Discharge test A CNT-coated film with a protective layer in which a CNT layer and a protective layer were coated on only one side of a 50-μm-thick and 800-mm-wide PET film was used in the central 640-mm width. In this experiment, a sample was cut out with a width of 300 mm and a length of 500 mm from a portion with few dents and scratches inside the roll-shaped film. In this film, a protective layer of polyester resin is provided on the CNT coat so that the CNT does not scatter due to discharge.

[0051] The surface resistivity of the sample film was measured by a method of bringing a probe into contact with the protective layer using a high resistivity meter (MCP-HT450, manufactured by Mitsubishi Chemical Corporation), a URS probe (MCP-HTP14, manufactured by Mitsubishi Chemical Corporation), a low resistivity meter (MCP-T600, manufactured by Mitsubishi Chemical Corporation), and an APS probe (MCP-TP03P, manufactured by Mitsubishi Chemical Corporation).

[0052] Example 1 (Preparation of CNT Dispersion) 17.5 g of PAA (polyacrylic acid, weight average molecular weight 5000, manufactured by Fujifilm Wako Pure Chemical Corporation) was weighed and dissolved in 3500 ml of a 9:1 mixed solution of 2-propanol and ethanol. Then, 11.7 g of SWCNT (Oxaial TUBALL CNT 93%) was added and mixed. This mixed solution was pre-dispersed (stirred) with a stirrer for 30 min. Thereafter, ultrasonic dispersion was performed for 300 min while maintaining the treatment temperature at around 5°C to prepare a uniform CNT dispersion. (Preparation of CNT Coated Sheet) To improve the adhesion and abrasion resistance of the CNT dispersion to A-PET, 20 g / m of the uniform CNT dispersion prepared by the above method was wet-coated on a PET film (A-PET: thickness 50 μm) by gravure printing. 2 · After wet coating and film formation, additives were added to an aqueous acrylic-modified polyester resin as an overcoat layer, stirred, diluted with a 1:1 mixed solution of IPA and water, and wet-coated at 4 g / m with a gravure printing machine. 2 · wet-coated. In this way, a CNT-coated film with a surface resistivity of 3.00×10 2 Ω / □ was prepared.

[0053] Example 2 Coating was performed in the same manner as in Example 1 except that the CNT dispersion was wet-coated at 4 g / m by gravure printing, and a CNT-coated film with a surface resistivity of 8.10×10 2 Ω / □ was prepared. 3 Ω / □ was prepared.

[0054] Comparative Example 1 The CNT dispersion was diluted 1.5-fold with 2-propanol and wet-coated at 4 g / m by gravure printing. Coating was performed in the same manner as in Example 1 except for this, and a CNT-coated film with a surface resistivity of 4.16×10 2 Ω / □ was prepared. 4 Ω / □ was prepared.

[0055] Comparative Example 2 The CNT dispersion was diluted 3.0 times with 2-propanol and gravure printed at 4 g / m 2 ·Coating was performed in the same manner as in Example 1 except that it was made into a wet coating, and a CNT-coated film with a surface resistivity of 1.69 ×× 10 5 Ω / □ was produced.

[0056] The contents of the examples and comparative examples are shown in Table 1. The coating amount indicates the coating amount before drying (wet), and the film thickness indicates the film thickness after drying (dry). The film thickness was calculated from the ink coating amount and the solid content.

[0057]

Table 1

[0058] The surface resistivity is on the GND (ground) side, and on the HV (sky) side, it is >10 11 Ω / □. The thickness of the protective layer (polyester resin) is all 0.7 μm. The sample size is 300 mm × 500 mm for all samples, and the thickness of the PET film is 50 μm.

[0059] As sample films, a CNT-coated film with a protective layer and an uncoated film were arranged with the low-resistance surface facing the ground side. Figure 3(A) is a top view (upper) and a side view (lower) showing the schematic of the experimental configuration. Using a fixing base with a frame provided at the part that becomes the side of the rectangular parallelepiped, the sample was fixed to the fixing base with curing tape. Figure 3(B) is a top view showing the method of fixing the sample film to the fixing base. Near the tape fixing location of the sample, a cutout hole with a width of about 7 mm (=10 mm / √2) and a length of about 77 mm (=55 mm × √2) was provided in consideration of preventing discharge through the curing tape. A rod-shaped electrode was used for the high-voltage electrode and a plate-shaped electrode was used for the ground electrode. The high-voltage electrode was arranged above the fixing base, the fixing base was arranged on the ground electrode, and the distance between the electrodes and the distance between the sample film and the ground electrode were as shown in Figure 3(A). In the case of the CNT-coated film with a protective layer, it was fixed with the coated surface of the CNT-coated film with a protective layer facing the plate electrode side.

[0060] An impulse voltage generator was used to apply a negative lightning impulse voltage between the electrodes to surely generate a spark discharge, and the voltage was applied once per film. After the spark discharge occurred, the penetration probability was determined from the presence or absence of holes in the film by visual inspection. Test conditions High-voltage electrode: Brass rod (tip SR10, φ20) Ground electrode: Copper flat plate (φ5000, thickness 0.1 mm) Negative-polarity lightning impulse voltage (1.8 / 49 μs) Peak value of applied voltage: -520 kV Number of samples: 5 for each Voltage was applied only once per sheet.

[0061] The number of penetrated samples in the CNT-coated film and the uncoated film is shown in Table 2. The penetration probability of the film with a surface resistivity of 10 3 Ω / □ or less was 0% (0 / 5), while the penetration probability of the film with a surface resistivity of 10 4 Ω / □ or less was 100% (5 / 5).

[0062]

Table 2

[0063] Figure 4 is a graph showing the relationship between the surface resistivity on the ground side and the penetration probability in the sample film. From these results, it was found that the surface resistance threshold value that dramatically changes the penetration probability in the PET film with a thickness of 50 μm exists between 8.10×10 3 Ω / □ and 4.16×10 4 Ω / □.

[0064] Figure 5 is a photograph during the test in which a high voltage was applied to the sample film. (A) is a sample film with a low surface resistivity (2.50×10 2When using (B) [unit not clear in the original, assumed as surface resistivity unit], it shows the case of using a sample film with a high surface resistivity (Figure 5(A)). While applying voltage, a single-lens reflex camera was continuously exposed to capture the light emission of the spark discharge. It can be seen that the discharge does not penetrate the sample but crawls on the surface and bends, and flashes between the electrodes. In the case of a sample film with a low surface resistivity (Figure 5(B)), it can be seen that the light emission discharge due to the discharge penetrated the sample and flashed between the electrodes.

[0065] Regarding the charge distribution of the sample after voltage application, the charge distribution on the surface of the high-voltage electrode side of the film was measured by the dust figure method (Figure 6). The dust figure method is a technique that can qualitatively measure the polarity and amount of charge on the sample surface by sprinkling two types of powder particles, each charged positively and negatively, on the sample surface. In this experiment, since powders of carbon and sulfur were used, carbon (black) adhered to the negatively charged surface as shown in Figure 6(A), while sulfur (yellow) adhered to the positively charged surface. The sample before sprinkling the powder was transparent, and there were no easily visible discharge marks as shown in Figure 6(A).

[0066] Figure 6(B) shows the case of using a sample film with a low surface resistivity (2.50×10 2 Ω / □), and Figure 6(C) is a photograph showing the measurement results in the case of using a sample film with a high surface resistivity (1.69×10 5 Ω / □). When the surface resistivity is low (Figure 6(B)), the discharge path is thin. On the other hand, when the surface resistivity is high (Figure 6(C)), the strongly charged region (the area surrounded by the lines in the figure) that surrounds the thin discharge path spreads and penetrates.

[0067] The following results were obtained from this experiment. The threshold value at which the penetration probability of the CNT-coated film with a protective layer changes when a lightning impulse discharge with a peak value of -520 kV is applied is between 8.10×10 3 Ω / □ and 4.16×10 4 Ω / □, and the penetration probability changed dramatically from 0% to 100%. The effect of reducing the penetration probability by lowering the surface resistance occurred in the same way as when there was no protective layer, even when an insulating protective layer was provided on top of the conductive layer. It was found that when the surface resistance increases, the strongly charged region around the discharge path spreads.

[0068] It is considered that the discharge hardly penetrated the sample film with a low surface resistivity due to the time constant τ of the experimental configuration. The experimental configuration can be simply modeled as described above. Assuming an RC series circuit of the surface resistance of the sample film and the capacitance between the film and the ground, when the time constant τ is larger than the rise time of the applied voltage, the propagation speed of the potential is slower in the sample film. On the other hand, when the time constant τ is smaller than the rise time of the applied voltage, the propagation speed of the potential becomes faster than that of the sample film. In the sample film with a low surface resistivity, since the time constant τ was small and the potential propagation was fast, it is considered that the electric field did not increase locally and the creeping discharge occurred.

[0069] 2. Control of Resistance Value by Spray Coating Considering coating the CNT ink on the wind turbine blade, a test was conducted to see if the same surface resistivity as the film used in the experiment could be obtained by spray coating. When the CNT ink was spray-coated with the same coating amount as in Example 1 that did not penetrate in the discharge test, the surface resistivity became almost the same value as when coated by gravure printing, and it was found that the surface resistivity could be controlled by the coating amount regardless of the coating method. Coating amount of 20 g / m of Example 1 2 Coating amount of 4 g / m of Example 2 2 The same coating amounts including 4 g / m 2 15 g / m 2 20 g / m 2 25 g / m 2 The CNT ink was spray-coated on an A-PET plate with a thickness of 2 mm five times for each coating amount, and the surface resistivity was measured. The results are shown in Table 3 and Figure 7.

[0070]

Table 3

[0071] When coated with the same coating amount, no significant difference in surface resistivity was observed between gravure printing and spray coating, and a correlation was confirmed between the coating amount and the surface resistance value.

Explanation of symbols

[0072] 1 Structure 2 Insulating base material 3 Lightning strike damage prevention layer 3A Coating layer (A) of carbon nanotube dispersion 3B Overcoat resin layer (B) 4 Grounding part 1A Wind turbine 2A Blade 5 Hub 6 Nacelle 7 Tower 8 Downconductor 9 Receptor

Claims

1. On the inner surface of the insulating substrate, there is a lightning strike damage prevention layer including the following layers (A) and (B), and the surface resistivity of the lightning strike damage prevention layer is 1.00×10 2 ~1.00×10 4 Ω / sq. The structure. (A)A coating layer of a carbon nanotube dispersion liquid formed on the inner surface and containing carbon nanotubes and a polymer acid as a dispersant thereof (B)An overcoat resin layer formed on the surface opposite to the inner surface of the layer (A)

2. The structure according to claim 1, wherein the time constant τ of the RC series circuit including the lightning strike damage prevention layer and the grounding portion is 1.2 μs or less.

3. The structure according to claim 1 or 2, which is a wind power generator having the lightning strike damage prevention layer on the inner surface of the blade.

Images