JP2004253796A - Electromagnetic wave shielding structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding structure that exhibits electromagnetic wave shielding performance even if an amount of ultra-fine fibers such as carbon nanotube contained in a conductive layer is decreased; in addition, an electromagnetic wave shield material having a conductive layer having improved transparency by reducing the thickness of the layer while maintaining the electromagnetic wave shielding performance. <P>SOLUTION: The electromagnetic wave shielding structure has a transparent conductive layer 2 containing ultra-fine conductive fibers 3 that is formed on at least one side of a base 1. The fibers 3 are dispersed and contacted with each together without aggregation, or in a separated condition for each fiber, or in a separated condition of bundles formed by gathering several fibers for each bundle, thereby the conductive layer has surface resistivity of ≤10<SP>5</SP>Ω/square. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an electromagnetic wave shield used for a casing of an electric device that generates an electromagnetic wave and a viewing window therefor.

A typical example of a conventional transparent electromagnetic wave shielding body is one in which a metal oxide deposited film such as ITO is formed on a surface of a transparent base material.
Further, a coating composition in which a carbon nanotube and / or a carbon microcoil is blended as a film forming component is applied to a methacrylic resin base material and cured to have a thickness of 100 μm and a surface resistivity of about 3 × 10 ³ Ω /. It is known to form a methacrylic resin plate having electromagnetic wave shielding performance by forming a coating film of □ (see Patent Document 1).
JP 2000-26760 A

However, the electromagnetic wave shielding plate on which the metal oxide vapor-deposited film is formed has a problem that the metal oxide vapor-deposited film has a light yellow color, and when the substrate is a thermoplastic resin plate or the like that cannot withstand heat during metal vapor deposition. In addition, there is a problem that it is difficult to form a metal oxide deposited film. In addition, there is also a problem that the metal oxide deposited film is broken by processing such as bending or stretching, the surface resistivity increases, and the electromagnetic wave shielding performance is not exhibited. On the other hand, the methacrylic resin plate having the electromagnetic wave shielding performance of Patent Document 1 has a thick coating film and contains a large amount of carbon nanotubes and the like, so that the coating film becomes dark and the transparency is extremely reduced, There is a problem that it is difficult to use for applications requiring transparency.
If the thickness of the coating film is reduced to solve this problem, the amount of carbon nanotubes contained in the coating film is reduced, so that the surface resistivity required for electromagnetic wave shielding cannot be obtained.

The present invention has been made to address the above-described problems, and an object of the present invention is to provide an electromagnetic wave shielding body that exhibits electromagnetic wave shielding performance even when the amount of ultrafine fibers such as carbon nanotubes contained in the conductive layer is reduced. The task is to provide.
Another object of the present invention is to provide an electromagnetic wave shield having a conductive layer in which the thickness of the conductive layer is reduced and the transparency is improved while maintaining the electromagnetic wave shielding performance.
Another object of the present invention is to provide an inexpensive and economical electromagnetic wave shield having a transparent conductive layer.

In order to achieve the above object, the electromagnetic wave shield of the present invention is an electromagnetic wave shield in which a transparent conductive layer containing a fine conductive fiber is formed on at least one surface of a substrate, wherein the fine conductive fiber aggregates. The conductive layer has a surface resistivity of 10 ⁵ Ω / □ or less.
Further, another electromagnetic wave shielding body of the present invention is an electromagnetic wave shielding body in which a transparent conductive layer containing a fine conductive fiber is formed on at least one surface of a substrate, and the fine conductive fibers are separated one by one. The conductive layer has a surface resistivity of 10 ⁵ Ω / □ or less in a state where a plurality of bundles are collected and bundled and separated and contact each other in a separated state. It is assumed that.

In the above invention, the ultrafine conductive fibers are carbon fibers, and the ultrafine conductive fibers are preferably carbon nanotubes.
Further, the ultrafine conductive fibers are multi-walled carbon nanotubes and are separated from each other in a dispersed state and are in contact with each other. Alternatively, the ultrafine conductive fibers are single-walled carbon nanotubes and a plurality of carbon nanotubes are gathered and bundled. The fine conductive fibers are dispersed and in contact with each other in a bundle, or the ultrafine conductive fibers are 2-3 carbon nanotubes. It is also preferable that the bundles are separated from each other and in contact with each other.
Further, it is also preferable that the base material is a transparent electromagnetic wave shielding body formed of a transparent resin, and the total light transmittance when the thickness is approximately 2 mm is 75% or more and the haze is 5% or less.
It is also preferable that the conductive layer contains ultrafine fibers in an amount of 30 to 450 mg / m ² and the thickness of the conductive layer is 5 to 500 nm.

Further, still another electromagnetic wave shielding body of the present invention is an electromagnetic wave shielding body in which a transparent conductive layer made of a thermoplastic resin containing carbon nanotubes is formed on at least one surface of a transparent base material, In a state in which the conductive layers are separated one by one, or in a state in which a plurality of bundles are separated into bundles, the conductive layers are dispersed in the thermoplastic resin and come into contact with each other. It is characterized by having a surface resistivity of ⁴ Ω / □ or less.

  In each of the above-mentioned present inventions, “without aggregation” is a term meaning that there is no lump having an average diameter of 0.5 μm or more when the surface of the conductive layer is observed with an optical microscope. Further, the term “contact” is a term meaning both the case where the ultrafine conductive fibers are actually in contact with and the case where the ultrafine conductive fibers are close to each other with a small gap that allows conduction.

The first electromagnetic wave shielding body of the present invention is in contact with each other because the ultrafine conductive fibers contained in the conductive layer are dispersed without agglomeration. Since sufficient mutual conduction can be ensured, good conductivity can be obtained. Therefore, even if the amount of the ultrafine conductive fibers is reduced, a surface resistivity of 10 ⁵ Ω / □ or less can be obtained, and an electromagnetic wave shield can be obtained.

Then, the transparency can be improved by the reduced amount of the ultrafine conductive fibers, and the thickness of the conductive layer can be reduced. On the other hand, when the amount of the fine conductive fibers is the same as the conventional amount, the number of the fine conductive fibers contributing to conduction increases as much as the fine conductive fibers are unraveled and the cohesion disappears, and it is possible to obtain better conductivity than ever. Thus, an excellent electromagnetic wave shielding body can be obtained. When the ultrafine conductive fibers are carbon nanotubes, the carbon nanotubes are thin and long, so that the mutual contact can be more preferably ensured, and the surface resistivity can be easily controlled to 10 ⁵ Ω / □ or less. High transparency can be ensured, and it becomes extremely easy to provide an electromagnetic wave shield having transparency.

The second electromagnetic wave shield of the present invention is in a state where the ultrafine conductive fibers are separated one by one, or a plurality of bundles are collected and bundled and separated one by one and are in contact with each other. Therefore, the chance of contact between the dispersed one or one bundle of ultrafine conductive fibers is increased, and sufficient conductivity can be ensured, and good conductivity can be obtained. Therefore, even if the amount of the ultrafine conductive fibers is reduced, a surface resistivity of 10 ⁵ Ω / □ or less can be obtained, and an electromagnetic wave shield can be obtained. In addition, since the surface resistivity of 10 ⁵ Ω / □ or less can be obtained even if the thickness of the conductive layer is reduced, the transparency can be improved accordingly. For example, when the thickness of the shield body is approximately 2 mm, In some cases, the total light transmittance can be greater than 75% and the haze can be less than 5%. On the other hand, if the amount of the ultrafine conductive fiber is the same as the conventional one, the chance of contact of the ultrafine conductive fiber increases more than before, and excellent conductivity can be obtained, and the surface resistivity of 10 ⁵ Ω / □ or less can be easily obtained. Obtainable. When carbon nanotubes are used as the ultrafine conductive fibers, the above-mentioned contact opportunities are further increased, and a highly transparent electromagnetic wave shield can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing one embodiment of a plate-shaped electromagnetic wave shield of the present invention, FIG. 2A is a schematic cross-sectional view showing a state of dispersion of ultrafine conductive fibers inside a conductive layer, and FIG. 3) is a schematic cross-sectional view showing the dispersion state of the ultrafine conductive fibers on the surface of the conductive layer, and FIG. 3 is a schematic plan view showing the dispersion state of the ultrafine conductive fibers when the conductive layer is viewed from a plane.

  This electromagnetic wave shield P is formed by laminating a conductive layer 2 containing ultrafine conductive fibers 3 on one surface of a base material 1 made of synthetic resin, glass, ceramic, inorganic material or the like. The conductive layer 2 may be formed not only on one side of the substrate 1 but also on both sides of the substrate 1.

As the substrate 1, a thermoplastic resin, a curable resin which is cured by heat, ultraviolet rays, an electron beam, radiation, or the like, glass, ceramic, an inorganic material, or the like is used as described above. Among these, a transparent thermoplastic resin, a curable resin, or glass is preferably used in order to obtain a shield body P having transparency. As the transparent thermoplastic resin, for example, polyethylene, polypropylene, olefinic resins such as cyclic polyolefins, polyvinyl chloride, polymethyl methacrylate, vinyl resins such as polystyrene, nitrocellulose, cellulose resins such as triacetyl cellulose, polycarbonate, Ester resins such as polyethylene terephthalate, polydimethylcyclohexane terephthalate, and aromatic polyester, ABS resins, copolymer resins of these resins, and mixed resins of these resins are used. As the transparent curable resin, for example, epoxy resin Resin, polyimide resin, acrylic resin and the like are used.
Further, the substrate 1 does not necessarily have to be flat, but may be of an irregular shape.

  When the thickness of the substrate 1 is 2 mm, a resin having a total light transmittance of 80% or more, preferably 85% or more, and a haze of 4% or less is particularly preferably used. Examples of such a resin include a cyclic polyolefin, polyvinyl chloride, polymethyl methacrylate, polystyrene, triacetyl cellulose, polycarbonate, polyethylene terephthalate, polydimethylcyclohexane terephthalate or a copolymer resin thereof, a mixed resin thereof, and a curable acrylic resin. Used. In addition, glass has a very high total light transmittance of 95% or more in transparency, and is therefore preferably used for obtaining a transparent electromagnetic wave shield P. When such a resin or glass is used for the substrate 1, the total light transmittance of the shield having a thickness of 2 mm can be 75% or more and the haze can be 5% or less.

A plasticizer, a stabilizer, an ultraviolet absorber and the like are appropriately compounded in the synthetic resin base material 1 to improve moldability, heat stability, weather resistance, and the like. Furthermore, pigments or dyes may be added to these base materials 1 to make them opaque or translucent. In this case, an opaque molded product or a translucent molded product is obtained. Therefore, the color tone is not impaired.
The thickness of the substrate 1 may be a thickness according to the application, but usually, the substrate 1 having a thickness of about 0.03 to 10 mm is used.

  The conductive layer 2 formed on one surface of the substrate 1 is a transparent layer containing ultrafine conductive fibers, and the ultrafine conductive fibers are dispersed without agglomeration and are in contact with each other. In other words, in a state where the ultrafine conductive fibers are separated one by one without being entangled, or in a state where a plurality of bundles are collected and separated one by one, they are in contact with each other in a dispersed manner. When the conductive layer 2 is mainly formed of ultrafine conductive fibers and a transparent binder, as shown in FIG. 2A, the ultrafine conductive fibers are dispersed in the binder in the above-described dispersion state and come into contact with each other. Or, as shown in FIG. 2 (B), a part of the ultrafine fibers enter the binder and the other part protrudes or is exposed from the binder surface and is dispersed in the above-mentioned dispersed state and is in contact with each other; Is that a part of the ultrafine conductive fiber is dispersed inside the binder as shown in FIG. 2 (A), and the other ultrafine conductive fiber is projected or exposed from the surface as shown in FIG. 2 (B). It becomes.

FIG. 3 schematically shows the dispersion state of these ultrafine conductive fibers 3 as viewed from the plane. As can be understood from FIG. 3, the ultrafine conductive fibers 3 are slightly bent, but are separated one by one or one by one, and are not entangled with each other in a complicated manner. It is dispersed inside or on the surface of layer 2 and is in contact at each intersection. When dispersed in this way, the fibers are unraveled and present in a wide area as compared with the case where the fibers are aggregated, so that the chance of contact between these fibers is remarkably increased. Can be significantly increased. For example, in order to obtain the same conductivity of 10 ³ Ω / □ as in the conventional patent document 1, it is only necessary to make the contact point (conduction density) the same as the conventional one. Thus, even if the amount of the ultrafine conductive fiber is reduced, the same contact opportunity can be obtained, and accordingly, the amount of the ultrafine conductive fiber can be reduced. As a result, the transparency is improved as much as the amount of the ultrafine conductive fibers that hinder the transparency is reduced, and the conductive layer 2 can be made thinner, so that the transparency can be further improved.

In such a dispersed state, even if the shield body P is bent, the bent portion of the ultrafine conductive fiber can be extended, so that the fiber is not cut, the conductivity can be secured, and the surface resistivity is lowered. I will not let you.
It is not necessary that the ultrafine conductive fibers 3 are completely separated and dispersed one by one or one bundle, and a small agglomerate may be partially entangled. It is preferably not more than 0.5 μm.

On the other hand, when the same amount of the ultrafine conductive fibers 3 as in the related art is included in the conductive layer 2, by making the dispersion state described above, it is possible to obtain more opportunities for contact between the fibers than in the related art. Therefore, the conductivity can be remarkably improved, so that conductivity of 10 ⁵ Ω / □ or less, preferably 10 ⁴ Ω / □ or less can be easily obtained, and good electromagnetic wave shielding performance can be exhibited. .
Further, when the ultrafine conductive fibers 3 are included in the conductive layer 2 and the thickness of the conductive layer 2 is reduced to 5 to 500 nm, the ultrafine conductive fibers 3 dispersed in the thickness direction are concentrated, and the chance of contact with each other is reduced. As the number increases, the conductivity can be further increased. Therefore, it is preferable to reduce the thickness of the conductive layer 2 within the above range, and it is more preferable that the thickness be 10 to 400 nm.

  Examples of the ultrafine conductive fibers 3 used for the conductive layer 2 include ultrafine carbon fibers such as carbon nanotubes, carbon nanohorns, carbon nanowires, carbon nanofibers, and graphite fibrils; metal nanotubes such as platinum, gold, silver, nickel, and silicon; Ultrafine metal fibers such as nanowires, metal oxide nanotubes such as zinc oxide, ultrafine metal oxide fibers such as nanowires, etc., having a diameter of 0.3 to 100 nm and a length of 0.1 to 20 μm, preferably a length Is preferably 0.1 to 10 μm.

These ultra fine conductive fibers 3, which by the one to one by or one bundle by one dispersed without aggregation, the light transmittance when the surface resistivity of the conductive layer 2 is 10 ⁰ ~10 ¹ Ω / □ Is obtained when the surface resistivity is 10 ² to 10 ⁵ Ω / □, and the light transmittance is 75% or more. Among these ultrafine conductive fibers, carbon nanotubes are extremely thin and have a diameter of 0.3 to 80 nm, so that the carbon nanotubes are less likely to hinder light transmission by being dispersed one by one or one bundle at a time, It is particularly preferable to obtain a transparent conductive layer 2 having a light transmittance of 75% or more.

These ultrafine conductive fibers 3 are dispersed one by one or a plurality of bundles without being agglomerated inside or on the surface of the conductive layer 2, and contact with each other to provide conductivity. Have secured. Therefore, by including the basis weight of 30~450mg / ^{m 2} to the conductive layer 2 the ultra Hososhirube conductive fibers, the surface resistivity can be freely controlled by ¹⁰ 0 ^{~10 5 Ω} / □ in the range of. The basis weight is determined by observing the surface of the conductive layer 2 with an electron microscope, measuring the area ratio of the fine conductive fibers to the surface area, and determining the thickness and the specific gravity of the fine conductive fibers (when the fine conductive fibers are carbon nanotubes). Is a value calculated by multiplying the average value of graphite literature values 2.1 to 2.3 by 2.2.

  Here, as not being agglomerated, as described above, the conductive layer is observed with an optical microscope, and if there is an agglomerated mass, its major axis and minor axis are measured, and the average value is 0.5 μm This is a term meaning that there is no such lump.

  The carbon nanotube includes a multi-walled carbon nanotube concentrically provided with a plurality of cylindrically closed carbon walls having different diameters around the central axis, and a single cylindrically closed carbon wall around the central axis. Single-walled carbon nanotubes.

  The former multi-walled carbon nanotube has a structure in which a plurality of tubes each formed of a plurality of cylindrically closed carbon walls having different diameters as described above are superposed in multiple layers around a central axis, and this carbon wall is formed of a carbon hexagonal mesh. It is formed with a structure. In addition, there is also a structure in which the carbon wall is formed in a spiral multilayer. A preferred multi-walled carbon nanotube has two to thirty carbon walls, more preferably two to fifteen layers, and if the layers overlap in this range, the number of carbon walls is small and the light transmittance and haze are further reduced. Can be good. Most of the multi-walled carbon nanotubes are dispersed in a state of being separated one by one, but the two- or three-walled carbon nanotubes may be dispersed in a bundle.

  On the other hand, the latter single-walled carbon nanotube is composed of a single-walled carbon wall closed cylindrically around the central axis as described above, and this carbon wall is also formed by a hexagonal mesh structure of carbon. . Such single-walled carbon nanotubes do not exist alone, but exist in a state in which two or more bundles are bundled, and the bundles are separated one by one without being complicatedly entangled with each other. In an intersecting state, it is dispersed inside or on the surface of the conductive layer, and is in contact at each intersection. Preferably, a bundle of 10 to 50 single-walled carbon nanotubes collected and used is used.

As described above, when the ultrafine conductive fibers 3 are dispersed in the conductive layer 2 without being entangled without being entangled and are in contact with each other, sufficient conduction between the carbon nanotubes is ensured even when the thickness of the conductive layer 2 is reduced. Therefore, even if the basis weight of the ultrafine conductive fibers 3 is 30 to 450 mg / m ² and the thickness of the conductive layer 2 is as thin as 5 to 500 nm, sufficient conduction between the carbon nanotubes is secured because the carbon nanotubes are loosened. In addition, it is easy to make the surface resistivity not more than 10 ⁵ Ω / □, good conductivity can be exhibited, and electromagnetic wave shielding performance can be exhibited. Then, since the ultrafine conductive fibers are unwound and no agglomerates are formed and the light transmission is not hindered, the transparency is improved, and the transparency is improved by reducing the thickness of the conductive layer 2 and reducing the basis weight of the carbon nanotubes. Become like Therefore, when the thickness of the transparent substrate 1 is 2 mm, a transparent shield having a total light transmittance of 75% or more and a haze of 5% or less can be obtained. A more preferred transparent shield has a total light transmittance of 80% or more and a haze of 2% or less.

When the basis weight of the carbon nanotube is about 30 to 250 mg / m ² , a highly transparent (light transmittance of 75 to 88%) conductive layer 2 having a surface resistivity of 10 ² to 10 ⁵ Ω / □ is obtained. be able to. Therefore, when a transparent resin is used for the substrate 1, a transparent body capable of shielding electromagnetic waves can be obtained. For example, when a transparent polycarbonate resin is used for the substrate 1, a highly transparent electromagnetic shielding polycarbonate body having a total light transmittance of 70% or more and a haze of 4% or less when the thickness of the substrate 1 is 2 mm is obtained.
On the other hand, when the order of 250~450mg / ^{m 2} by increasing the basis weight of the carbon ^nanotubes, 10 0 ^{~10 1 Ω} / □ conductive performance on top that can be made excellent, conductive layer 2 of transparent ( (A light transmittance of 50 to 75%), and a transparent electromagnetic wave shield can be obtained by using a transparent resin for the substrate 1. For example, when a transparent polycarbonate resin is used for the substrate 1, a transparent electromagnetic wave shielding polycarbonate body having a total light transmittance of 45% or more and a haze of 5% or less when the thickness of the substrate 1 is 2 mm is obtained.
The light transmittance of the conductive layer 2 can be obtained by using a spectrophotometer for measurement and correcting the light transmittance of the shield at a wavelength of 550 nm with the light transmittance of only the substrate 1. Further, the total light transmittance and the haze are values measured in accordance with ASTM D1003.

In order to contain a large amount of the fine conductive fiber 3 in the conductive layer 2 and to exhibit better electromagnetic wave shielding performance and transparency, the dispersibility of the fine conductive fiber 3 is increased, and the viscosity of the prepared coating liquid is further reduced. It is important to improve the leveling property of the coating liquid and to form a thin conductive layer, and for that purpose, it is important to use a dispersant together. As such a dispersant, a polymer dispersant such as an alkylammonium salt solution of an acidic polymer, a tertiary amine-modified acrylic copolymer or a polyoxyethylene-polyoxypropylene copolymer, or a coupling agent is preferably used. Can be
In addition, additives such as an ultraviolet absorber, a surface modifier, and a stabilizer may be appropriately added to the conductive layer 2 to improve weather resistance and other physical properties.

  Examples of the transparent binder used for the conductive layer 2 include the transparent thermoplastic resin used for the above-described base material 1, particularly, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, nitrocellulose, chlorinated polyethylene. , Chlorinated polypropylene, vinylidene fluoride, and transparent curable resins that are cured by heat, ultraviolet rays, electron beams, radiation, etc., especially silicone resins such as melamine acrylate, urethane acrylate, epoxy resin, polyimide resin, and acrylic-modified silicate Is used so that the conductive layer 2 composed of these binders and the ultrafine conductive fibers becomes a transparent layer. In addition, an inorganic material such as colloidal silica may be added to these binders.

  If the substrate 1 is formed of a transparent thermoplastic resin, the same type of transparent thermoplastic resin or a different kind of transparent thermoplastic resin having compatibility has excellent lamination properties with each other, and a transparent electromagnetic wave shield. It is preferably used for obtaining body. When a binder containing a curable resin or colloidal silica is used as the binder, a shield P excellent in abrasion resistance and the like can be obtained. As described above, since the conductive layer 2 is formed on the surface of the substrate 1, it is desirable to select and use a binder suitable for required weather resistance, surface hardness, wear resistance, and the like.

As described above, the basis weight of the ultrafine fibers in the conductive layer 2 is 30 to 450 mg / m ^2, and the thickness of the conductive layer 2 is reduced to 5 to 500 nm. By dispersing one bundle at a time, good conductivity and transparency having a surface resistivity of 10 ⁵ Ω / □ or less, preferably 10 ⁴ Ω / □ or less are exhibited. The more preferable weight of the ultrafine fiber is 40 to 400 mg / m ² , and the thickness of the conductive layer 2 is 10 to 400 nm. In addition, a conductive metal oxide powder may be contained in an amount of about 30 to 50% by mass in addition to the carbon nanotubes.

  The above-described electromagnetic wave shield can be efficiently mass-produced by, for example, the following method. One method is to uniformly disperse the ultrafine conductive fibers in a solution in which the binder for forming a conductive layer is dissolved in a volatile solvent to prepare a coating solution, and apply and solidify the coating solution on one surface of the substrate 1. This is a method for manufacturing the electromagnetic wave shield P by forming the conductive layer 2 by using the method. Another method is to apply a coating liquid on one surface of a thermoplastic resin film of the same kind as the base material 1 or a thermoplastic resin film of a different kind having compatibility, and solidify the conductive film in which the conductive layer 2 is formed. This is a method of manufacturing the electromagnetic wave shielding body P by forming the conductive film on one surface of the substrate 1 and thermocompression-bonding with a hot press or a roll press. Still another method is to apply the above coating material to a release film such as polyethylene terephthalate and solidify to form a conductive layer 2, and if necessary, further form an adhesive layer to prepare a transfer film. The electromagnetic wave shielding body P can be manufactured by transferring the conductive layer 2 or the adhesive layer and the conductive layer 2 by overlapping and pressing on one surface of the material 1. Needless to say, it is also manufactured by other known manufacturing methods.

When manufacturing the electromagnetic wave shielding body P by the first method, the conductive layer 2 is vertically compressed by hot pressing at the end, and the vertical spacing of the fine conductive fibers dispersed in the conductive layer 2 is reduced to make the conductive layer 2 finer. It is preferable to increase the frequency of contact between the conductive fibers and to reduce the conductive minute gap. This has the advantage that the surface resistivity is further reduced. In the case of manufacturing by the latter laminating method or transfer method, since the conductive layer is compressed at the time of thermocompression bonding or transfer, the last press can be omitted.
Further, if the conductivity obtained after forming the conductive layer matches the purpose, hot pressing is not necessarily required.

  Next, more specific examples of the present invention will be described.

[Example 1]
Single-walled carbon nanotubes (synthesized based on Chemical Physics Letters, 323 (2000) P580-585, diameter 1.3 to 1.8 nm) in an isopropyl alcohol / water mixture (mixing ratio 3: 1) as a solvent. A polyoxyethylene-polyoxypropylene copolymer as a dispersant was added and uniformly mixed and dispersed to prepare a coating liquid containing 0.003% by mass of single-walled carbon nanotubes and 0.05% by mass of a dispersant.
This coating solution is applied to the surface of a commercially available 100 μm-thick polyethylene terephthalate film (total light transmittance 94.5%, haze 1.5%), dried, and further reduced to 1/600 with methyl isobutyl ketone. A conductive layer was formed by applying a diluted thermosetting urethane acrylate solution and drying to obtain a transparent polyethylene terephthalate film.

The surface resistivity of this transparent polyethylene terephthalate film was measured with a Lorester manufactured by Mitsubishi Chemical Corporation. As shown in Table 1, the surface resistivity was about 8.7 × 10 ¹ Ω / □.
Further, the total light transmittance and haze of this film were measured with a direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. in accordance with ASTM D1003. 44.9% and haze were 4.7%.
Further, the basis weight of the single-walled carbon nanotube in the conductive layer of this film was measured and found to be 274 mg / m ² .

Furthermore, when the conductive layer of this film was observed with an optical microscope, no aggregate of 0.5 μ or more was present, and the single-walled carbon nanotubes were sufficiently dispersed. And it turned out that many carbon nanotubes are uniformly disperse | distributed in the state isolate | separated by 1 bundle, and contacted in the state which intersected simply.
Further, the electric field shielding performance was measured by the KEC method (MA8602B, manufactured by Anritsu Corporation), and the results of the electric field shielding performance are shown in Table 1 as the electric field shielding ratio and are graphically shown in FIG. Note that the electric field shielding ratio is a value in which the reflected electric field intensity is represented by% when the incident electric field intensity is 1 (100%).

[Example 2]
The conductive layer was formed by applying the coating liquid used in Example 1 to the surface of the polyethylene terephthalate film used in Example 1 and drying the same, and the basis weight of carbon nanotubes in the conductive layer was 94 mg / m ^2. Was obtained as a transparent polyethylene terephthalate film.
The surface resistivity of this transparent polyethylene terephthalate film was measured in the same manner as in Example 1. As shown in Table 1, the surface resistivity was about 3.6 × 10 ² Ω / □.
The total light transmittance and haze of this film were measured in the same manner as in Example 1. As shown in Table 1, the total light transmittance was 78.4% and the haze was 1.6%. there were.
Further, the results of measuring the electric field shielding performance of this film in the same manner as in Example 1 are also shown in Table 1 and FIG.

[Example 3]
The conductive layer was formed by applying the coating liquid used in Example 1 to the surface of the polyethylene terephthalate film used in Example 1 and drying it, and the basis weight of carbon nanotubes in the conductive layer was 50 mg / m ^2. Was obtained as a transparent polyethylene terephthalate film.
The surface resistivity, total light transmittance, haze, and electric field shielding performance of this film were measured in the same manner as in Example 1, and the results are shown in Table 1 and FIG.

[Example 4]
1.17% by mass of vinyl chloride resin powder as a thermoplastic resin was added to and dissolved in cyclohexanone as a solvent. Into this solution, multi-walled carbon nanotubes (Tinfana Fine Nano-Powder Commercialization Engineering Center Co., Ltd., 0.7-2 nm in diameter) and an alkylammonium salt solution of an acidic polymer as a dispersant are added, and they are uniformly mixed and dispersed. A coating liquid containing 0.3% by mass of a carbon nanotube and 0.3% by mass of a dispersant was prepared.
This coating solution was applied to the surface of a commercially available acrylic film having a thickness of 100 μm and dried to obtain a laminate film. This laminate film was superimposed on the surface of a vinyl chloride resin plate having a thickness of 0.7 mm, and pressed at a temperature of 170 ° C. and a pressure of 50 kg / cm ² to obtain a vinyl chloride resin plate.

  The surface resistivity, total light transmittance, haze, and electric field shielding performance of this resin plate were measured in the same manner as in Example 1, and the results are shown in Table 1 and FIG.

As can be seen from Table 1, all the surface resistivity of Examples 1 to 4 showed a numerical value of 10 ⁵ Ω / □ or less, and had a surface resistivity having sufficient electromagnetic wave shielding performance. From the surface resistivity of Examples 1 to 3, it is understood that the larger the basis weight of the carbon nanotube, the lower the surface resistivity.

Further, as can be seen from Table 1 and FIG. 3, the film having a surface resistivity of about 8.7 × 10 ¹ Ω / □ in Example 1 has an electric field shielding ratio of 95% or more at 1 to 100 MHz, From 100 MHz to 1 GHz, it can be seen that the electric field shielding ratio is 75% or more. The film having a surface resistivity of about 4 × 10 ² Ω / □ in Example 2 has an electric field shielding rate of 80% or more at 1 to 100 MHz, and an electric field shielding rate of 50% or more at 100 MHz to 1 GHz. Further, the film having a surface resistivity of about 1 × 10 ³ Ω / □ in Example 3 has an electric field shielding rate of 60% or more at 1 to 100 MHz and 20% or more at 100 MHz to 1 GHz. It turns out that it has an electric field shielding rate.

From these facts, the films of Examples 1 to 3 have sufficient electromagnetic wave shielding performance, and Examples 1 and 2 having a surface resistivity of 5 × 10 ² Ω / □ or less are more than sufficient. Had good shielding performance. Since it is also understood that the surface resistivity is proportional to the basis weight of the carbon nanotubes contained in the conductive layer, it is understood that the basis weight may be adjusted in order to obtain the required electromagnetic wave shielding performance.

On the other hand, the vinyl chloride resin plate of Example 4 having a surface resistivity of about 1 × 10 ⁴ Ω / □ has an electric field shielding ratio of 60% or more at 1 to 10 MHz and an electric field shielding of 20% or more at 10 MHz to 1 GHz. It turns out that it has a shielding rate. Although the vinyl chloride resin plate is inferior in transparency, it has an electric field shielding ratio, and it can be seen that the vinyl chloride resin plate can be used as an electromagnetic wave shielding plate in applications that do not require much transparency.

As is clear from the above description and Examples, the electromagnetic wave shielding body of the present invention can exhibit good electromagnetic wave shielding performance since the dispersibility of carbon nanotubes in the conductive layer is good. Further, even if the thickness of the conductive layer is reduced, an electromagnetic wave shielding body having a surface resistivity of 10 ⁵ Ω / □ or less and having electromagnetic wave shielding performance can be obtained.

It is sectional drawing which shows one Embodiment of the electromagnetic wave shielding body which concerns on this invention. (A) is a schematic cross-sectional view showing the state of dispersion of microfibers inside the conductive layer of the present invention, and (B) is a schematic cross-sectional view showing the state of dispersion of microfibers on the surface of the conductive layer of the present invention. FIG. 2 is a schematic plan view showing a dispersion state of microfibers when the conductive layer of the present invention is viewed from a plane. 4 is a graph showing electric field shielding characteristics of the electromagnetic wave shielding plate according to the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Base material 2 Conductive layer 3 Multi-walled carbon nanotube P Electromagnetic wave shield

Claims (10)

On at least one surface of a substrate, a ultra fine conductive fibers laden transparent conductive layer electromagnetic shield formed, and dispersed without the ultra fine conductive fibers are agglomerated into contact with one another, the conductive layer is 10 ⁵ An electromagnetic wave shield having a surface resistivity of Ω / □ or less. An electromagnetic wave shielding body in which a transparent conductive layer containing ultrafine conductive fibers is formed on at least one surface of a base material, wherein the ultrafine conductive fibers are separated from each other, or a plurality of the conductive fibers are bundled together. An electromagnetic wave shield, wherein the conductive layers have a surface resistivity of 10 ⁵ Ω / □ or less, and the conductive layers have a surface resistivity of 10 ⁵ Ω / □ or less.   3. The electromagnetic wave shield according to claim 1, wherein the ultrafine conductive fibers are ultrafine carbon fibers.   The electromagnetic wave shield according to claim 3, wherein the ultrafine carbon fibers are carbon nanotubes.   The electromagnetic wave shield according to any one of claims 1 to 4, wherein the ultrafine conductive fibers are multi-walled carbon nanotubes, and the fibers are dispersed one by one and are in contact with each other.   The electromagnetic wave shield according to any one of claims 1 to 4, wherein the ultrafine conductive fibers are single-walled carbon nanotubes, and a plurality of the fibers are dispersed and contacted with each other in a bundled state. .   The electromagnetic wave according to any one of claims 1 to 4, wherein the ultrafine conductive fibers are two to three-walled carbon nanotubes, and a plurality of the conductive fibers are dispersed in a bundled state and are in contact with each other. Shield body.   8. A transparent electromagnetic wave shielding body whose base material is formed of a transparent resin, wherein the total light transmittance when the thickness is approximately 2 mm is 75% or more and the haze is 5% or less. An electromagnetic wave shield according to any of the claims. The conductive layer includes 30~450mg / ^{m 2} The ultra fine conductive fibers, electromagnetic wave shielding body according to any one of claims 1 to 8 the thickness of the conductive layer is 5 to 500 nm. An electromagnetic wave shielding body having a transparent conductive layer made of a thermoplastic resin containing carbon nanotubes formed on at least one surface of a transparent base material, wherein the carbon nanotubes are separated one by one, or a plurality thereof. In a state in which the bundles gathered are separated one by one, they are dispersed in the thermoplastic resin of the conductive layer and come into contact with each other, and the conductive layer has a surface resistivity of 10 ⁴ Ω / □ or less. An electromagnetic wave shield, characterized in that:

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