Electromagnetic shielding sheet

Abstract

To provide an electromagnetic shielding sheet that takes advantage of the electrical conductivity, heat conductive properties, and other characteristics of a CNT.SOLUTION: The electromagnetic shielding sheet has a structure in which a conductive layer including a sheet CNT continuum is sandwiched by insulating layers. A unit CNT usage, which is the amount of CNTs used per 1 cm2, is 0.3 mg or less. The unit CNT usage maybe 0.02 mg or more and 0.15 mg or less. The CNTs included in the sheet CNT continuum may have a structure extending along an in-plane direction of the sheet CNT continuum.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The present invention relates to an electromagnetic shielding sheet. [Background technology]

[0002] In recent years, with the increase in data communication fees, wireless communication frequencies have become higher, for example, wireless LAN (2-6 GHz), Bluetooth (registered trademark) (2.4 GHz), and mobile phones (0.8-3 GHz). In order to prevent electronic devices from malfunctioning (electromagnetic interference, EMI) due to these high-frequency electromagnetic waves, electromagnetic wave shielding technology within electronic devices has become important.

[0003] Conventionally, electromagnetic wave shielding has been generally achieved by using metal plates, but metal plates have problems such as being heavy, inflexible, and susceptible to corrosion, and are also difficult to incorporate into small electronic devices. In addition, metal plates have a high reflectivity and low absorption rate for electromagnetic waves, which can cause other problems when the electromagnetic waves are reflected by the metal plate.

[0004] Non-metallic materials have come to be used to solve the electromagnetic wave shielding problems of metal plates, and the development of composite materials that combine resin materials with conductive fillers (carbon-based materials) is being actively pursued. Electromagnetic wave shielding using carbon-based fillers is less effective than that of metal plates, but it has the advantage of being easier to make small and flexible.

[0005] Carbon nanotubes (CNTs) have high electrical and thermal conductivity in the long axis direction and also have excellent mechanical properties, but CNTs that are generally available commercially are powdered materials. When using powdered CNTs, they are generally dispersed in a liquid medium and applied (e.g., Patent Document 1), or mixed into resin and molded. Non-Patent Documents 1 to 5 disclose the results of measurements of the magnetic shielding effect in the far field (EMI-SE) of electromagnetic shielding sheets in which CNTs are dispersed in resin.

[0006] In this specification, "CNT forest" refers to a type of synthetic structure of multiple CNTs (hereinafter, the individual shape of the CNTs that gives such a synthetic structure is referred to as the "primary structure", and the above synthetic structure is also referred to as the "secondary structure"), and refers to an aggregate of CNTs that have grown so that multiple CNTs are oriented in a certain direction (a specific example is a direction approximately parallel to the normal to one of the surfaces of the substrate) for at least a portion of their longitudinal direction.

[0007] In addition, in this specification, a structure in which multiple CNTs are connected to each other, formed by continuously drawing out multiple CNTs from a CNT forest by pinching some CNTs in the CNT forest and pulling the CNTs away from the CNT forest (in this specification, this operation is also referred to as "spinning" following the operation of producing yarn from fibers in the prior art), is referred to as a "CNT continuum." Patent Document 2 discloses a secondary structure in which multiple CNTs are connected to each other and have a web-like overall shape (in this specification, this secondary structure is referred to as a "CNT web"). The CNTs that make up the CNT web are oriented along one of the in-plane directions of the CNT web (corresponding to the spinning direction). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2013-82610 A [Patent Document 2] Patent No. 5664832 [Non-patent literature]

[0009] [Non-Patent Document 1] M H Al-Saleh, W H Saadeh, U Sundararaj, EMI shielding effectiveness of carbon based nanostructured polymeric materials: a comparative study, Carbon N. Y. 60 (2013) 146?156, doi:10.1016 / j.carbon.2013.04.008. [Non-Patent Document 2] Z Liu, G Bai, Y Huang, Y Ma, F Du, F Li, T Guo, Y Chen, Reflection and absorption contributions to the electromagnetic interference shielding of single-walled carbon nanotube / polyurethane composites, Carbon N. Y 45 (2007) 821?827, doi:10.1016 / j.carbon.2006.11.020. [Non-Patent Document 3] W C Yu, J Z Xu, Z G Wang, Y F Huang, H M Yin, L Xu, Y W Chen, D X Yan, Z M Li, Constructing highly oriented segregated structure towards high-strength carbon nanotube / ultrahigh-molecular-weight polyethylene composites for electromagnetic interference shielding, Compos. Part A Appl. Sci. Manuf. 110 (2018) 237?245, doi:10.1016 / j.compositesa.2018.05.004. [Non-Patent Document 4] WC Yu, GQ Zhang, YH Liu, L Xu, DX Yan, HD Huang, JH Tang, JZ Xu, ZM Li, Selective electromagnetic interference shielding performance and superior mechanical strength of conductive polymer composites with oriented segregated conductive networks, Chem. Eng. J. 373 (2019) 556564, doi:10.1016 / j.cej.2019.05.074. [Non-Patent Document 5] S Teotia, BP Singh, I Elizabeth, VN Singh, R Ravikumar, AP Singh, S Gopukumar, SK Dhawan, A Srivastava, RB Mathur, Multifunctional, robust, light-weight, free-standing MWCNT / phenolic composite paper as anodes for lithium ion batteries and EMI shielding material, RSC Adv. 4 (2014) 33168?33174, doi:10.1039 / c4ra04183f. Summary of the Invention [Problem to be solved by the invention]

[0010] When CNTs are dispersed in a liquid medium or mixed into a resin as in Patent Document 1, the CNTs are randomly oriented in the liquid or resin, making it difficult to align them in a fixed direction, which poses the problem of reducing the excellent properties of CNTs, such as their high electrical conductivity and thermal conductivity.

[0011] An object of the present invention is to provide an electromagnetic shielding sheet that makes use of the characteristics of CNTs, such as electrical conductivity and thermal conductivity. [Means for solving the problem]

[0012] In order to solve the above problems, an electromagnetic shielding sheet having a structure in which a conductive layer having a sheet-shaped CNT continuous body is sandwiched between insulating layers (hereinafter, an electromagnetic shielding sheet having this structure may be referred to as a "sandwich electromagnetic shielding sheet") is provided, which is 1 cm 2 The electromagnetic shielding sheet is characterized in that the amount of CNT used per unit is 0.3 mg or less. The sandwich electromagnetic shielding sheet having a sheet-like CNT continuum can have an area with a high CNT density, and therefore can have high electromagnetic shielding ability without increasing the amount of CNT used per unit.

[0013] Here, if the amount of CNT used in the conductive layer of the sandwich electromagnetic shielding sheet is excessively high, the conductive layer behaves in the same manner as a metal plate. That is, a sandwich electromagnetic shielding sheet made of a sheet-shaped CNT continuum and having a unit CNT usage amount exceeding 0.3 mg has high reflection characteristics similar to a sandwich electromagnetic shielding sheet made by sandwiching a metal plate between insulating layers. For this reason, the electromagnetic wave absorption characteristics are rather difficult to improve. This tendency is remarkable in the high frequency band of 3 GHz or more. Therefore, in the sandwich electromagnetic shielding sheet provided with the sheet-shaped CNT continuum according to the present invention, the electromagnetic wave absorption characteristics can be improved by setting the unit CNT usage amount to 0.3 mg or less.

[0014] In a sandwich electromagnetic shielding sheet comprising a sheet-like CNT continuum, by setting the amount of CNT used per unit to 0.02 mg or more, it is possible to more stably improve the electromagnetic wave absorption characteristics in the high frequency band of 1 GHz or more, and this tendency becomes even more pronounced in the band of 2 GHz or more.

[0015] In a sandwich electromagnetic shielding sheet comprising a sheet-like CNT continuous body, by setting the amount of CNT used per unit to 0.15 mg or less, it is possible to more stably improve the electromagnetic wave absorption characteristics in the high frequency band of 3 GHz or more.

[0016] In some cases, it is preferable that the CNTs contained in the sheet-shaped CNT continuous body have a structure extending along the in-plane direction of the sheet-shaped CNT continuous body. In this case, it is preferable that the length of the CNTs in the major axis direction is longer than the thickness of the conductive layer. Effect of the Invention

[0017] The present invention provides an electromagnetic shielding sheet having improved electromagnetic shielding capability (particularly electromagnetic wave absorption characteristics in the high frequency band of 1 GHz or higher). [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing a schematic configuration of an electromagnetic shielding sheet according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an explanatory diagram of a manufacturing device for an electromagnetic shielding sheet. [Diagram 3] (a) An external view of a CNT web being spun from the end of a CNT forest, and (b) an enlarged view of the spun end, showing the CNTs detaching from the end of the CNT forest. [Figure 4] FIG. 2 is an external view of an example of an electromagnetic shielding sheet. [Diagram 5] FIG. 2 is an observational view of a cross section of an electromagnetic shielding sheet including a sheet-shaped CNT continuous body with one layer of CNT web, cut along the extending direction of the CNTs. [Figure 6] FIG. 6 is a partial enlarged view of a region in the cross section observed in FIG. 5 where a CNT web is displayed. [Figure 7] FIG. 2 is an observational view of a cross section of an electromagnetic shielding sheet including a sheet-shaped CNT continuous body with two layers of CNT webs, cut along the extending direction of the CNTs. [Figure 8] FIG. 8 is a partial enlarged view of a region in the cross section observed in FIG. 7 where a CNT web is displayed. [Figure 9] FIG. 2 is an observational view of a cross section of an electromagnetic shielding sheet including a sheet-shaped CNT continuous body having 10 layers of CNT webs, cut along the extending direction of the CNTs. [Figure 10] FIG. 2 is an observational view of a cross section of an electromagnetic shielding sheet including a sheet-shaped CNT continuous body having 20 layers of CNT webs, cut along the extending direction of the CNTs. [Figure 11] FIG. 1 is a diagram showing the shape of a sample for measuring far-field EMI shielding characteristics. [Figure 12] FIG. 1 illustrates a system for measuring far-field EMI shielding properties. [Figure 13] 4 is a graph showing the measurement results of the far-field EMI shielding characteristics (EMI-SE) of the electromagnetic shielding sheet according to the embodiment. [Figure 14] 4 is a graph showing the measurement results of the reflection characteristics of the electromagnetic shielding sheet according to the example. [Figure 15] 4 is a graph showing the measurement results of the transmission characteristics of an electromagnetic shielding sheet according to an example. [Figure 16] 4 is a graph showing the measurement results of the absorption characteristics of the electromagnetic shielding sheet according to the example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described.

[0020] FIG. 1 is a diagram showing a schematic configuration of an electromagnetic shielding sheet according to an embodiment of the present invention. As shown in FIG. 1, electromagnetic shielding sheet 10 has a structure in which conductive layer 11 comprising a sheet-shaped CNT continuum is sandwiched between two insulating layers 12, 13 (sandwich electromagnetic shielding sheet). By having a structure in which a conductive layer is sandwiched between insulating layers in this way, it is easy to provide areas in electromagnetic shielding sheet 10 where the conductive material (CNTs in electromagnetic shielding sheet 10) is present at a high density, and even if the amount of conductive material used is relatively small, the electromagnetic shielding ability, in particular the electromagnetic wave absorption characteristics, can be improved. In electromagnetic shielding sheet 10, 2When the CNT usage per unit is 0.01 mg or more, high electromagnetic shielding ability is obtained, and when the CNT usage per unit is 0.02 mg or more, high electromagnetic wave absorption characteristics are obtained. This tendency is prominent in the high frequency band of electromagnetic waves above 1 GHz, and is particularly prominent in the band of 2 GHz or more.

[0021] As described above, the sandwich electromagnetic shielding sheet is likely to have excellent electromagnetic shielding ability, but if the density of the conductive material in the conductive layer 11 becomes excessively high, the conductive layer 11 is likely to behave in the same way as when it includes a metal plate. When the conductive layer 11 includes a metal plate, the conductive layer 11 functions as a reflector of electromagnetic waves. In this case, it can be said that the sheet has electromagnetic shielding ability, but the reflected electromagnetic waves may become a new interference factor, and as a result, it may become difficult to reduce electromagnetic interference (EMI). Therefore, it is preferable that the electromagnetic shielding sheet has a high ability to absorb electromagnetic waves (absorption characteristics).

[0022] From this viewpoint, the amount of CNT used per unit in the conductive layer 11 of the electromagnetic shielding sheet 10 is set to 0.3 mg or less. Since the amount of CNT used per unit in the conductive layer 11 is appropriately suppressed, the conductive layer 11 functions appropriately as an absorber of electromagnetic waves. That is, a part of the electromagnetic waves irradiated to the conductive layer 11 penetrates into the conductive layer 11 without being reflected, and interacts with the CNTs of the conductive layer 11 to convert the electromagnetic waves into thermal vibrations. Since CNTs have high thermal conductivity, and the CNTs in the conductive layer 11 exist as a sheet-like CNT continuum, the heat generated by conversion from the electromagnetic waves is quickly diffused in the in-plane direction of the conductive layer 11. Therefore, the electromagnetic shielding sheet 10 can stably maintain excellent absorption characteristics.

[0023] As described later, the absorption characteristics of the electromagnetic shielding sheet 10 increase as the frequency of the irradiated electromagnetic wave increases, but if the amount of unit CNT used exceeds 0.3 mg, the absorption characteristics are unlikely to increase even if the frequency of the irradiated electromagnetic wave increases, and the absorption characteristics may actually decrease relatively at high frequencies. For this reason, the effect of increasing the absorption characteristics of the electromagnetic shielding sheet 10 by setting the amount of unit CNT used to 0.3 mg or less becomes more pronounced as the frequency of the irradiated electromagnetic wave increases (specifically, in the band of 3 GHz or more). From the viewpoint of stably increasing the absorption characteristics of the electromagnetic shielding sheet 10 against electromagnetic waves in the band of 3 GHz or more, the amount of unit CNT used in the conductive layer 11 is preferably 0.15 mg or less, and more preferably 0.10 mg or less.

[0024] The sheet-shaped CNT continuous body of the conductive layer 11 is a structure having a sheet-like overall shape and including a plurality of continuous CNTs, and adjacent CNTs interact with each other by van der Waals forces to maintain the overall shape. In this embodiment, the CNTs included in the sheet-shaped CNT continuous body have a structure extending along the in-plane direction of the sheet-shaped CNT continuous body. Due to this structure, the sheet-shaped CNT continuous body has excellent electrical conductivity and thermal conductivity in the in-plane direction.

[0025] When the sheet-shaped CNT continuous body is manufactured by the method disclosed in Patent Document 2, the sheet-shaped CNT continuous body is made of a CNT web or a laminate of CNT webs, and in a preferred embodiment, the length in the long axis direction of the CNTs constituting the sheet-shaped CNT continuous body is longer than the thickness of the conductive layer 11. In this case, the conductive layer 11 has particularly high orientation in the in-plane direction of electrical conductivity and thermal conductivity. Therefore, the CNTs in the conductive layer 11 tend to interact with electromagnetic waves incident so as to intersect with the electromagnetic shielding sheet 10, and the conductive layer 11 tends to absorb electromagnetic waves. In addition, since heat generated in the CNTs by interacting with the electromagnetic waves tends to diffuse along the extension direction of the CNTs, the absorption characteristics of the conductive layer 11 are unlikely to decrease even if the electromagnetic waves are continuously irradiated.

[0026] When the conductive layer 11 comprises a sheet-shaped CNT continuous body made of a CNT web produced by the method disclosed in Patent Document 2, the amount of CNT used per unit of the conductive layer 11 can be controlled by the number of stacked CNT webs in the sheet-shaped CNT continuous body.

[0027] The conductive layer 11 may be composed of only the sheet-shaped CNT continuous body, but from the viewpoint of enhancing structural stability, it is preferable that the conductive layer 11 has a structure in which the sheet-shaped CNT continuous body is dispersed in a resin material that serves as a matrix, in other words, a structure in which the sheet-shaped CNT continuous body is impregnated with a resin material. The type of resin material impregnated into the sheet-shaped CNT continuous body is not limited. In terms of ease of manufacture, it may be preferable that the resin material is the same as that constituting the insulating layers 12 and 13 located on both sides of the conductive layer 11.

[0028] The thickness of the conductive layer 11 is set according to the thickness of the sheet-shaped CNT continuous body. As a non-limiting example, the thickness of the conductive layer 11 is in the range of about 1 μm to about 30 μm. The volume ratio of CNTs in the conductive layer 11 varies depending on the structure of the sheet-shaped CNT continuous body. When the sheet-shaped CNT continuous body is formed from a CNT web, it is in the range of about 3 vol % to about 15 vol %.

[0029] There are no limitations on the material constituting the insulating layers 12 and 13 as long as it has appropriate insulating properties. From the viewpoints of facilitating the thinning of the overall thickness of the electromagnetic shielding sheet 10 and providing excellent controllability of physical properties, it may be preferable that the material constituting the insulating layers 12 and 13 be a resin-based material that contains a resin material.

[0030] The resin-based material may be composed of a resin material, or may be a resin material in which a non-resin material, such as a glass filler or an inorganic substance such as alumina, is dispersed. Such a non-resin material may be used from the viewpoint of improving the mechanical properties of the insulating layers 12 and 13 and from the viewpoint of improving the flame retardancy of the insulating layers 12 and 13.

[0031] Examples of resin materials include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyamide resins such as nylon 6, 6, thermoplastic resins such as acrylic resins and vinyl chloride resins, and thermosetting resins such as epoxy resins and phenolic resins. Elastomers such as thermoplastic polyurethane and ethylene-propylene rubber are also exemplified as a type of resin material. The resin material may be composed of one type of resin or multiple types of resins.

[0032] There is no particular limitation on the method for producing the electromagnetic shielding sheet 10. Hereinafter, as an example of the production method, a method for producing the electromagnetic shielding sheet 10 using a CNT web produced by the method shown in Patent Document 2 will be described.

[0033] 2 is an explanatory diagram of a manufacturing device for an electromagnetic shielding sheet. The manufacturing device 30 is capable of pressure molding while heating using two back plates 33 and 34 each equipped with a heater (heater 31, heater 32). A laminate 40 is disposed between the heaters 31 and 32. The laminate 40 is composed of a sheet-like CNT continuous body 41 formed by laminating one or more CNT webs, and two resin sheets 42 and 43 positioned so as to sandwich the sheet.

[0034] In this state, the two heaters 31, 32 are heated to a predetermined temperature, and the laminate 40 is heated by the two back plates 33, 34 while being pressed in the lamination direction (indicated by the outlined arrow in FIG. 2 ). As a result, the resin material constituting the resin sheets 42, 43 is impregnated into the gaps in the sheet-like CNT continuous body 41, and an electromagnetic shielding sheet 10 is obtained ( FIG. 1 ) having a structure in which the conductive layer 11, having a structure in which the sheet-like CNT continuous body 41 is dispersed in a matrix made of a resin material, is sandwiched between insulating layers 12, 13 made of a resin material.

[0035] The above-described embodiments are described for the purpose of facilitating understanding of the present invention, and are not described for the purpose of limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. EXAMPLES

[0036] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0037] The electromagnetic shielding sheet shown in FIG. 1 was produced using the production apparatus shown in FIG.

[0038] A CNT forest with a growth height of 1 mm was obtained by the manufacturing method described in Patent Document 2. The diameter of the CNTs constituting the CNT forest was 30 nm to 40 nm. The surface density on the substrate was 5×10 9 cm -2 The crystallinity of the CNTs that make up the CNT forest was evaluated by Raman scattering measurement, and the ratio of the G peak intensity of the graphene in-plane vibration mode to the D peak intensity due to its disorder vibration, I G / I D was 2.5 to 3.

[0039] The CNT forest was spun to obtain a web-like CNT continuous body (CNT web). Figure 3 shows how the CNT web is spun. Figure 3(a) is an external view of the CNT web being spun from the end of the CNT forest, and Figure 3(b) is an enlarged view of the spun end, showing how the CNTs are detached from the end of the CNT forest. The obtained CNT web was wound up on a drum to obtain four types of sheet-like CNT continuous bodies with different numbers of layers in the CNT web (number of layers: 1, 2, 10, 20).

[0040] The obtained sheet-like CNT continuous body was sandwiched between two resin sheets (low-density polyethylene films having a thickness of 25 μm) to form a laminate. These laminates were heated and pressurized using the device shown in FIG. 2. Specifically, the heater was first heated to 100° C. with a pressure of 10 MPa, and this state was maintained for 30 minutes. Thereafter, the heater was heated to 140° C., and the pressure was adjusted to 0.5 MPa to 1 MPa. In this state, heating was continued for another 10 minutes, and then the pressure was terminated and the sheet was naturally cooled to room temperature to obtain an electromagnetic shielding sheet having a thickness of 50 μm (Examples 1 to 4). FIG. 4 is an external view of an example of the electromagnetic shielding sheet thus obtained. The sheet-like CNT continuous body included in the electromagnetic shielding sheet shown in FIG. 4 was a laminate of two CNT webs.

[0041] FIG. 5 is an observational view of a cross section of an electromagnetic shielding sheet having a sheet-shaped CNT continuous body with one layer of CNT web cut along the CNT extension direction. FIG. 6 is a partial enlarged view of a region where the CNT web is displayed in the cross section observed in FIG. 5. FIG. 7 is an observational view of a cross section of an electromagnetic shielding sheet having a sheet-shaped CNT continuous body with two layers of CNT web cut along the CNT extension direction. FIG. 8 is a partial enlarged view of a region where the CNT web is displayed in the cross section observed in FIG. 7. FIG. 9 is an observational view of a cross section of an electromagnetic shielding sheet having a sheet-shaped CNT continuous body with 10 layers of CNT web cut along the CNT extension direction. FIG. 10 is an observational view of a cross section of an electromagnetic shielding sheet having a sheet-shaped CNT continuous body with 20 layers of CNT web cut along the CNT extension direction. In FIG. 5, FIG. 7, FIG. 9, and FIG. 10, the region between two horizontally extending white dashed lines corresponds to the conductive layer.

[0042] 5 to 10, the interior of the sheet-like CNT continuous body was impregnated with polyethylene resin constituting the insulating layer, and the conductive layer had a structure in which the sheet-like CNT continuous body was dispersed in a matrix made of polyethylene resin. When the electrical conductivity of the conductive layer of the electromagnetic shielding sheet (Example 3) including the sheet-like CNT continuous body with 10 laminations of CNT webs was measured along the extension direction of the CNTs, it was 400 S / cm.

[0043] The mass of the sheet-like CNT continuous body and the mass of the resin sheet were measured in advance to determine the CNT weight percentage (unit: wt%) in the laminate, which was used as the CNT weight percentage (unit: wt%) of the electromagnetic shielding sheet formed from the laminate. In addition, the thickness of each sheet was measured by observing the cross section of the electromagnetic shielding sheet. The measurement results are shown in Table 1.

[0044] [Table 1]

[0045] Table 1 shows, as reference examples, information on the electromagnetic shielding sheets disclosed in Non-Patent Documents 1 to 5. It is confirmed that the electromagnetic shielding sheets according to Examples 1 to 4 are thinner than the electromagnetic shielding sheets according to Reference Examples 1 to 5. As such, the electromagnetic shielding sheets according to Examples 1 to 4 are thin, and therefore have excellent flexibility and are easy to handle.

[0046] From the measurement results for the electromagnetic shielding sheets according to Examples 1 to 4, the CNT volume ratio (unit: vol%) of the electromagnetic shielding sheet and the CNT volume ratio (unit: vol%) of the conductive layer were determined. The results are shown in Table 1. As shown in Table 1, the CNT volume ratio of the conductive layer was approximately 2 vol% to 8 vol%. This value is considerably higher (several times to several tens of times) than the CNT volume ratio of the electromagnetic shielding sheet converted from the CNT weight ratio, and it can be said that CNTs are present at a high density in the conductive layer in the electromagnetic shielding sheets according to the examples.

[0047] On the other hand, the electromagnetic shielding sheets according to Reference Examples 1 to 5 have CNTs dispersed throughout the thickness direction, and therefore do not have an insulating layer / conductive layer / insulating layer structure like the electromagnetic shielding sheets according to Examples 1 to 4. Therefore, the thickness of the electromagnetic shielding sheet is the same as the thickness of the conductive layer. Therefore, as shown in Table 1, the CNT volume ratio of the conductive layer of the electromagnetic shielding sheets according to Reference Examples 1 to 5 is the CNT volume ratio of the electromagnetic shielding sheet.

[0048] The obtained electromagnetic shielding sheets were processed into a doughnut shape as shown in Fig. 11 and placed in a coaxial tube as shown in Fig. 12 to measure the far-field EMI shielding characteristics (EMI-SE, unit: dB). The measurement results are shown in Fig. 13. It was confirmed that, as a basic trend, the more the number of layers of the CNT web increases, the higher the EMI-SE becomes (upward on the vertical axis), and the greater the electromagnetic shielding effect becomes.

[0049] The reflection characteristics, transmission characteristics, and absorption characteristics of the electromagnetic shielding sheet constituting the EMI-SE measurement shown in Fig. 13 are shown in Fig. 14, Fig. 15, and Fig. 16, respectively. As shown in Fig. 14, the electromagnetic shielding sheets of Examples 1 and 2, in which the number of layers of the CNT web is 1 or 2, had extremely low reflectance, and the attenuation of electromagnetic waves by these electromagnetic shielding sheets was mainly absorption. As shown in Fig. 15, the electromagnetic shielding sheets of Examples 3 and 4, in which the number of layers of the CNT web is 10 or 20, showed a significant decrease in transmittance at high frequencies of 2 GHz or more compared to the electromagnetic shielding sheets of Examples 1 and 2.

[0050] 16, the basic tendency is that the more the number of layers of the CNT web increases, the higher the absorptivity becomes, and the higher the frequency becomes, the higher the absorptivity also becomes. However, in a relative comparison, the absorptivity of the electromagnetic shielding sheet of Example 4 is lower at high frequencies, and in particular in the band of 3 GHz or higher, the absorptivity is not significantly different from that of the electromagnetic shielding sheet of Example 1.

[0051] The measurement results of the shape, EMI-SE, etc. of the electromagnetic shielding sheet according to this example are shown in Table 1 so as to be comparable with the measurement results of the electromagnetic shielding sheet according to the reference example. As shown in Table 1, the electromagnetic shielding sheet according to this example had excellent electromagnetic shielding ability, despite using a much smaller amount of CNT per unit compared to the electromagnetic shielding sheet according to the reference example. [Explanation of symbols]

[0052] 10: Electromagnetic shielding sheet 11: Conductive layer 12, 13: Insulating layer 30: Manufacturing equipment 31, 32: Heater 33, 34: Back plate 40: Laminate 41: Sheet-shaped CNT continuous body 42, 43: Resin sheet

Claims

1. An electromagnetic shielding sheet having a structure in which a conductive layer having a sheet-shaped CNT continuous body is sandwiched between insulating layers, the sheet having a thickness of 1 cm 2 The electromagnetic shielding sheet is characterized in that the unit CNT usage amount, which is the amount of CNT used per unit, is 0.05 mg or more and 0.08 mg or less.

2. The electromagnetic shielding sheet according to claim 1 , wherein the CNTs contained in the sheet-shaped CNT continuous body are entirely covered with the insulating layer.

3. 3. The electromagnetic shielding sheet according to claim 1, wherein the CNTs contained in the sheet-shaped CNT continuous body have a structure extending along an in-plane direction of the sheet-shaped CNT continuous body.

4. The electromagnetic shielding sheet according to claim 3 , wherein a length in a major axis direction of the CNTs contained in the sheet-shaped CNT continuous body is longer than a thickness of the conductive layer.

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