Electromagnetic noise suppression sheet

Abstract

To provide an electromagnetic wave noise suppression sheet which has the high suppression performance of the electromagnetic wave noise.SOLUTION: An electromagnetic wave noise suppression sheet 100 according to the present invention comprises a first layer 10 which has a carbon fiber and a non-conductive fiber. The orientation intensity of the carbon fiber obtained by Fourier image analysis is equal to or greater than 1.3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Electromagnetic noise suppression sheets that suppress electromagnetic noise have been known in the past. These electromagnetic noise suppression sheets are used, for example, in offices, laboratories, hospitals, etc. to suppress electromagnetic noise emitted from electronic components such as wireless local area networks (LANs).

[0003] For example, Patent Document 1 describes an electromagnetic wave absorber constructed by laminating multiple fiber sheets containing carbon fiber and heat-fusing them together. Electromagnetic noise suppression sheets are required to have improved electromagnetic noise suppression performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-247720 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of some aspects of the present invention is to provide an electromagnetic noise suppression sheet that has high electromagnetic noise suppression performance. [Means for solving the problem]

[0006] One aspect of the electromagnetic noise suppression sheet according to the present invention is a first layer having carbon fibers and non-conductive fibers; The orientation strength of the carbon fibers determined by Fourier image analysis is 1.3 or more.

[0007] In one embodiment of the electromagnetic noise suppression sheet, The carbon fibers may have an orientation strength of 1.8 or more.

[0008] In any one of the above-described electromagnetic noise suppression sheets, The carbon fibers may have an orientation strength of 2.3 or more.

[0009] In any one of the above-described electromagnetic noise suppression sheets, The content of the carbon fiber in the first layer may be 0.1% by mass or more and 20% by mass or less.

[0010] In any one of the above-described electromagnetic noise suppression sheets, The content of the carbon fiber in the first layer may be 0.5% by mass or more and 10% by mass or less.

[0011] In any one of the above-described electromagnetic noise suppression sheets, The carbon fibers may have an average fiber length of 0.04 mm or more and 25 mm or less.

[0012] In any one of the above-described electromagnetic noise suppression sheets, The carbon fibers may have an average fiber length of 1 mm or more and 15 mm or less.

[0013] In any one of the above-described electromagnetic noise suppression sheets, The basis weight of the first layer is 20 g / m 2 More than 650g / m 2 below may be.

[0014] In any one of the above-described electromagnetic noise suppression sheets, The basis weight of the first layer is 23 g / m 2 More than 200g / m 2 below may be.

[0015] In any one of the above-described electromagnetic noise suppression sheets, The non-conductive fibers may be cellulosic fibers.

[0016] In any one of the above-described electromagnetic noise suppression sheets, a second layer disposed on the first layer; the second layer includes carbon fibers and non-conductive fibers; the orientation strength of the carbon fibers contained in the second layer determined by Fourier image analysis is 1.3 or more; The orientation direction of the carbon fibers contained in the first layer and the orientation direction of the carbon fibers contained in the second layer may intersect with each other.

[0017] In any one of the above-described electromagnetic noise suppression sheets, The orientation direction of the carbon fibers contained in the first layer and the orientation direction of the carbon fibers contained in the second layer may intersect with each other at an angle of 45° or more and 90° or less. [Effects of the Invention]

[0018] The electromagnetic noise suppression sheet according to the present invention includes a first layer having carbon fibers and non-conductive fibers, and has a carbon fiber orientation strength of 1.3 or more as determined by Fourier image analysis, thereby providing high electromagnetic noise suppression performance. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram for explaining a method for determining the orientation strength of carbon fibers by Fourier image analysis. [Figure 3] FIG. 1 is a diagram for explaining a method for determining the orientation strength of carbon fibers by Fourier image analysis. [Figure 4] FIG. 1 is a diagram for explaining a method for determining the orientation strength of carbon fibers by Fourier image analysis. [Figure 5] FIG. 1 is a diagram for explaining a method for determining the orientation strength of carbon fibers by Fourier image analysis. [Figure 6] FIG. 1 is a diagram for explaining a method for determining the orientation strength of carbon fibers by Fourier image analysis. [Figure 7] FIG. 3 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet according to a first modified example of the present embodiment. [Figure 8] FIG. 10 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet according to a second modified example of the present embodiment. [Figure 9] FIG. 10 is a diagram for explaining a method for evaluating electromagnetic wave noise suppression performance. [Figure 10] A table showing the carbon fiber orientation strength and Rtp of mixed paper. [Figure 11] A table showing the carbon fiber orientation strength and Rtp of mixed paper. [Figure 12] Graph showing Rtp versus frequency for mixed paper. [Figure 13] Graph showing Rtp versus frequency for mixed paper. [Figure 14] Graph showing Rtp versus frequency for mixed paper. [Figure 15] Graph showing Rtp versus frequency for mixed paper. [Figure 16] Graph showing Rtp versus frequency for mixed paper. [Figure 17] Graph showing Rtp versus frequency for mixed paper. [Figure 18] A table showing the carbon fiber orientation strength and Rtp of mixed paper. [Figure 19] Graph showing Rtp versus frequency for mixed paper. [Figure 20] Graph showing Rtp versus frequency for mixed paper. [Figure 21] A table showing the carbon fiber orientation strength and Rtp of mixed paper. [Figure 22] Graph showing Rtp versus frequency for mixed paper. [Figure 23] Graph showing Rtp versus frequency for mixed paper. DETAILED DESCRIPTION OF THE INVENTION

[0020] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

[0021] 1. Electromagnetic noise suppression sheet 1.1. Overall structure First, the electromagnetic noise suppression sheet according to this embodiment will be described with reference to the drawings. Fig. 1 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet 100 according to this embodiment.

[0022] As shown in FIG. 1, the electromagnetic noise suppression sheet 100 includes a first layer 10 having carbon fibers and non-conductive fibers.

[0023] Carbon fiber The carbon fiber contained in the first layer 10 is a fiber produced by carbonizing organic fibers such as polyacrylonitrile (PAN) fiber or pitch (a by-product of petroleum, coal, coal tar, etc.) fiber at high temperature. Carbon fiber is a conductive fiber that has electrical conductivity.

[0024] The carbon fiber content in the first layer 10 is not particularly limited, but is, for example, 0.1% by mass to 20% by mass, preferably 0.5% by mass to 10% by mass, and more preferably 2% by mass to 5% by mass. If the carbon fiber content is 0.1% by mass or more, electromagnetic noise suppression performance can be improved. If the carbon fiber content is 20% by mass or less, variation in the carbon fiber content can be reduced. The carbon fiber content in the first layer 10 can be measured by a sulfuric acid decomposition method based on "JIS K 7075."

[0025] The carbon fiber may be chopped fiber or milled fiber. However, considering the variation in fiber length of carbon fiber, chopped fiber is preferable. Chopped fiber is carbon fiber that has been bundled with a sizing agent and cut to a uniform length. Milled fiber is produced by pulverizing chopped fiber.

[0026] The average fiber length of the carbon fibers contained in the first layer 10 is not particularly limited, but is, for example, 0.04 mm to 25 mm, and preferably 1 mm to 15 mm. If the average fiber length of the carbon fibers is 0.04 mm or more, electromagnetic noise suppression performance can be improved. If the average fiber length of the carbon fibers is 25 mm or less, a highly uniform slurry can be prepared. The electromagnetic noise suppression sheet 100 is produced by dispersing carbon fibers and non-conductive fibers in water to prepare a slurry, and then sheeting the slurry. The average fiber length of the carbon fibers can be determined by reading the fiber lengths of 100 carbon fibers using a digital microscope and calculating the number average of the fiber lengths of the 100 fibers. Examples of digital microscopes include For example, we use the "VHX-1000" manufactured by Keyence Corporation.

[0027] The average fiber width of the carbon fibers contained in the first layer 10 is not particularly limited, but is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 20 μm or less, and even more preferably 4 μm or more and 10 μm or less. The fiber width is the size in the direction perpendicular to the fiber length. The fiber width can be determined basically by the same method as the fiber length.

[0028] 1.1.2. Non-conductive fibers The non-conductive fibers contained in the first layer 10 are insulators. The non-conductive fibers are, for example, cellulose fibers.

[0029] Cellulose fibers are fibers made from cellulose. They are extracted from cotton or pulp. Examples of pulp include chemical pulps such as LBKP (bleached hardwood kraft pulp) and NBKP (bleached softwood kraft pulp), dissolving pulps such as NBSP (bleached softwood sulfite pulp), mechanical pulps such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemi-mechanical pulp), and CGP (chemi-ground pulp), wood pulps such as DIP (deinked pulp), and non-wood pulps such as kenaf, bagasse, bamboo, and cotton. These pulps may be used alone or in combination of two or more in any proportion.

[0030] The first layer 10 preferably contains LBKP. The LBKP content in the first layer 10 is, for example, 70 mass % or more, and preferably 90 mass % or more. When the LBKP content is 70 mass % or more, distortion of the first layer 10 can be reduced.

[0031] The first layer 10 has a basis weight of 40g / m 2 In the following cases, the first layer 10 preferably contains NBKP. The content of NBKP in the first layer 10 is, for example, 30% by mass or less. If the content of NBKP is 30% by mass or less, the smoothness and strength of the first layer 10 can be maintained.

[0032] The cellulose fibers contained in the first layer 10 may be fine cellulose fibers (for example, cellulose nanofibers). Fine cellulose fibers are minute fibers obtained by nano-processing plant-derived cellulose fibers. Examples of nano-processing include mechanical fiber defibration and catalytic oxidation using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical). The average fiber length of the fine cellulose fibers is several hundred nanometers. The average fiber width of the fine cellulose fibers is several nanometers to several tens of nanometers. The use of fine cellulose fibers can achieve transparency, light weight, and high elasticity.

[0033] The non-conductive fibers contained in the first layer 10 may be chemically synthetic fibers. Chemically synthetic fibers are made by spinning synthetic polymer compounds made from petroleum or other raw materials into fibers using various methods. Examples of chemically synthetic fibers include nylon fibers, polyethylene fibers, polyester fibers, aramid fibers, acrylic fibers, polyvinyl alcohol fibers, polypropylene fibers, polyethylene terephthalate fibers, ethylene vinyl acetate fibers, and urethane fibers. These may be used alone or in combination of two or more types in any desired ratio.

[0034] The non-conductive fibers contained in the first layer 10 may be glass fibers. Glass fibers are made by melting and pulling glass to form fibers. Examples of glass fibers include E-glass (electrical non-alkali glass), C-glass (chemical alkali-containing glass), A-glass (acid-resistant glass), and S-glass (high-strength glass), which are made from silica glass or borosilicate glass. The glass fiber may be glass fiber (long fiber) or glass wool (short fiber). These may be used alone or in a mixture of two or more kinds in any ratio.

[0035] The non-conductive fibers contained in the first layer 10 may be a mixture of two or more types of the above-mentioned cellulose fibers, chemically synthesized fibers, and glass fibers in any ratio.

[0036] The content of the non-conductive fibers in the first layer 10 is not particularly limited, but is, for example, 70% by mass or more and 99.5% by mass or less, preferably 75% by mass or more and 97% by mass or less, and more preferably 80% by mass or more and 93% by mass or less.

[0037] The average fiber length of the non-conductive fibers contained in the first layer 10 is not particularly limited, but is, for example, 1 nm or more and 30 mm or less, preferably 0.1 mm or more and 15 mm or less, and more preferably 0.2 mm or more and 7 mm or less.

[0038] 1.1.3. Additives The first layer 10 may further contain various additives as needed, such as fillers, paper strength agents, sizing agents, bulking agents, retention aids, drainage aids, aluminum sulfate, wet strength agents, coloring dyes, coloring pigments, fluorescent brighteners, pitch control agents, thickeners, preservatives, pH adjusters, etc. Furthermore, the first layer 10 may be coated with a paint such as a CNT dispersion in which carbon nanotubes (CNTs) are dispersed.

[0039] 1.2. Shape etc. The first layer 10 is in the form of a sheet whose size in the direction perpendicular to the thickness direction is sufficiently large relative to its thickness. The thickness of the first layer 10 is not particularly limited, but is, for example, 20 μm to 5 mm, and preferably 40 μm to 3 mm. If the thickness of the first layer 10 is 20 μm or more, the electromagnetic noise suppression performance can be improved. If the thickness of the first layer 10 is 5 mm or less, the electromagnetic noise suppression sheet 100 can be easily produced. The thickness of the first layer 10 can be measured in accordance with "JIS P 8118."

[0040] The basis weight of the first layer 10 is not particularly limited, but is, for example, 20 g / m 2 More than 650g / m 2 or less, preferably 23 g / m 2 More than 200g / m 2 The basis weight of the first layer 10 is 20 g / m 2 If the weight is equal to or greater than this, the strength of the first layer 10 can be increased. 2 If the weight is below this, the formation can be made good. The basis weight of the first layer 10 can be measured based on "JIS P 8124".

[0041] The density of the first layer 10 is not particularly limited, but is, for example, 0.1 g / cm 3 More than 2g / cm 3 or more, preferably 0.2 g / cm 3 More than 1g / cm 3 The density of the first layer 10 is 0.1 g / cm 3If the density of the first layer 10 is 2 g / m or more, the strength of the first layer 10 can be increased. 3 If the density is below this, good formation can be achieved. The density of the first layer 10 can be measured based on "JIS P 8118".

[0042] In the illustrated example, the electromagnetic noise suppression sheet 100 is composed of a single first layer 10. Although not illustrated, the electromagnetic noise suppression sheet 100 may be composed of a plurality of stacked first layers 10. In this case, the number of the plurality of first layers 10 is not particularly limited.

[0043] 1.3. Orientation strength The orientation strength of the carbon fibers contained in the first layer 10 is 1.3 or more, preferably 1.8 or more, more preferably 2.0 or more, even more preferably 2.3 or more, and even more preferably 2.5 or more. The intensity is, for example, 5 or less.

[0044] The orientation strength of the carbon fibers contained in the first layer 10 is determined by Fourier image analysis. Figures 2 to 6 are diagrams illustrating a method for determining the orientation strength of the carbon fibers by Fourier image analysis. In Figures 2 to 4, the upper side shows an example where the orientation strength is 1.1, and the lower side shows an example where the orientation strength is 2.4.

[0045] In order to determine the orientation strength of the carbon fibers by Fourier image analysis, first, a digital microscope is used to photograph the surface of the first layer 10 at 100x magnification. As the digital microscope, for example, a "VHX-1000" manufactured by Keyence Corporation is used.

[0046] Next, an arbitrary 1024 x 1024 pixel portion of the captured image is cut out, and a binarized image is obtained by dynamic binarization, as shown in Figure 2. In the binarized image, the carbon fibers are reflected as black lines.

[0047] Next, the acquired binarized image is subjected to a Fourier transform to obtain a power spectrum as shown in FIG.

[0048] Next, based on the acquired power spectrum, the angular distribution of amplitude is calculated as shown in Figure 4. Specifically, the angle between 0° and 180° is divided into 2048 equal parts, and the average amplitude of the Fourier coefficients for distances (distance from the center) r = 2 to 511 is calculated for each of the 2048 angles from 0 to 2047 × 180 / 2048°. However, since the x and y coordinates cannot be completely converted to polar coordinates, the calculation is performed using values ​​proportionally divided by the distance from the amplitudes of the four surrounding points.

[0049] Specifically, as shown in Figure 5, if the spectral intensity P(x,y) is at a point θ° counterclockwise from the positive x-axis direction and a distance r from the center in the radial direction, then as shown in Figure 6, the P(x n ,y n ), P(x n+1 ,y n ), P(x n ,y n+1 ), P(x n+1 ,y n+1 ) and the distance d along the x-axis and y-axis to the desired point. x , d y The value calculated from the above using the following formula (1) is used as the spectral intensity at that point, and the average of the amplitudes (average spectral value) is calculated.

[0050]

number

[0051] Next, an elliptical approximation is performed from the obtained average spectrum values, as shown in Figure 4. The elliptical function is expressed by the following formula (2) consisting of three coefficient values ​​a, b, and c. For the three coefficient values ​​a, b, and c, the least squares method is used, and the sum of squares of deviations from the elliptical function is set as the objective function. Furthermore, the inequality constraint condition of the following formula (3) is satisfied, and the optimal solution is found by convergence using the gradient method for a nonlinear optimization problem (the following formula (4)) that minimizes this.

[0052]

number

[0053] Next, the minor axis radius L of the approximate ellipse is calculated from the following equations (5) and (6). a and the semimajor axis radius L b and calculate the minor axis radius L a and the semimajor axis radius L b Relative to L b / L a Then, the ratio L is calculated from the above-mentioned photograph of the surface of the first layer 10. b / L a The series of steps up to the calculation of L were repeated two more times, and the three calculated ratios L b / L a The average of these is taken as the orientation strength.

[0054]

number

[0055] The angle θ is calculated by the following formula (7).

[0056]

number

[0057] 1.4. Electromagnetic noise suppression performance The electromagnetic noise suppression sheet 100 has electromagnetic noise suppression performance, which suppresses electromagnetic noise. The electromagnetic noise suppression performance is evaluated by measuring the transmission attenuation rate Rtp [dB] using the microstrip line method. The larger the Rtp, the higher the electromagnetic noise suppression performance. The electromagnetic noise suppression sheet 100 is used by being attached to, for example, electronic components, walls, floors, etc.

[0058] 1.5. Effects The electromagnetic noise suppression sheet 100 includes a first layer containing carbon fibers and non-conductive fibers. The carbon fiber orientation strength determined by Fourier image analysis is 1.3 or higher, preferably 1.8 or higher, and more preferably 2.3 or higher. Therefore, the electromagnetic noise suppression sheet 100 has high electromagnetic noise suppression performance. Specifically, the electromagnetic noise suppression sheet 100 has high electromagnetic noise suppression performance for electromagnetic waves traveling in a predetermined direction. More specifically, as in the experimental example described below, by arranging the electromagnetic noise suppression sheet 100 so that the carbon fiber orientation direction is approximately perpendicular to the transmission line in the microstrip line method, the electromagnetic noise suppression sheet 100 has higher electromagnetic noise suppression performance. The carbon fiber orientation direction is the direction of the major axis of the approximate ellipse obtained as described above (the direction in which the major axis extends).

[0059] 2. Manufacturing method for electromagnetic noise suppression sheet Next, a method for manufacturing the electromagnetic noise suppression sheet 100 according to this embodiment will be described.

[0060] First, a slurry is prepared for producing the first layer 10. The slurry for producing the first layer 10 has a Canadian Standard Freeness (CSF) of, for example, 200 ml or more and 550 ml or less, preferably 250 ml or more and 500 ml or less. The CSF can be determined by the method described in "JIS P 81821-2."

[0061] Next, the prepared slurry is made into paper using an orientation papermaking machine to form the first layer 10. The orientation papermaking machine sprays the slurry from a nozzle onto a rotating papermaking wire gauze with a water wall, forming a paper layer on the wire on the inner wall of the drum. The orientation strength of the carbon fibers in the first layer 10 can be controlled by the rotation speed of the papermaking wire gauze. The rotation speed of the papermaking wire gauze is, for example, 300 m / min or more and 3000 m / min or less, preferably 500 m / min or more and 2500 m / min or less, and more preferably 650 m / min or more and 2000 m / min or less. If the rotation speed of the papermaking wire gauze is 300 m / min or more, the orientation strength of the carbon fibers contained in the first layer 10 can be increased. If the rotation speed of the papermaking wire gauze is 3000 m / min or less, energy conservation can be achieved.

[0062] Through the above steps, the electromagnetic noise suppression sheet 100 can be manufactured.

[0063] 3. Modified electromagnetic noise suppression sheet 3.1. First Variant Next, an electromagnetic noise suppression sheet according to a first modification of this embodiment will be described with reference to the drawings. Fig. 7 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet 200 according to a first modification of this embodiment.

[0064] Hereinafter, in the electromagnetic noise suppression sheet 200 according to the first modified example of this embodiment, components having the same functions as the components of the electromagnetic noise suppression sheet 100 according to this embodiment described above will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0065] As shown in FIG. 7, the electromagnetic noise suppression sheet 200 differs from the above-described electromagnetic noise suppression sheet 100 in that it includes a second layer 20.

[0066] The second layer 20 is provided on the first layer 10. The second layer 20 is laminated on the first layer 10. Although not shown, the second layer 20 may be provided on the first layer 10 via another layer such as an adhesive layer.

[0067] The second layer 20 contains carbon fibers and non-conductive fibers, similar to the first layer 10. The carbon fibers and non-conductive fibers of the second layer 20 can be applied to the carbon fibers and non-conductive fibers of the first layer 10.

[0068] The orientation direction of the carbon fibers in the first layer 10 and the orientation direction of the carbon fibers in the second layer 20 intersect with each other. The orientation direction of the carbon fibers in the first layer 10 and the orientation direction of the carbon fibers in the second layer 20 intersect with each other at an angle of preferably 45° or more and 90° or less, more preferably 60° or more and 90° or less. The orientation direction of the carbon fibers in the first layer 10 and the orientation direction of the carbon fibers in the second layer 20 may intersect with each other at an angle of 90°. The θ of the carbon fibers in the first layer 10 (θ calculated by formula (7)) and the θ of the carbon fibers in the second layer 20 are different from each other.

[0069] The bonding between the first layer 10 and the second layer 20 is not particularly limited, and an adhesive may be used. This may be achieved by swelling and gelatinizing layer 10 and second layer 20 .

[0070] In the electromagnetic noise suppression sheet 200, the orientation direction of the carbon fibers contained in the first layer 10 and the orientation direction of the carbon fibers contained in the second layer 20 intersect with each other, preferably at an angle of 45° to 90°. Therefore, compared to, for example, the electromagnetic noise suppression sheet 100, the electromagnetic noise suppression sheet 200 can have higher electromagnetic noise suppression performance for electromagnetic waves traveling in various directions.

[0071] Although the above description has been given of an example having the first layer 10 and the second layer 20, the electromagnetic noise suppression sheet 200 may further have, for example, a third layer containing carbon fibers and non-conductive fibers, and the orientation direction of the carbon fibers contained in the third layer may intersect with the orientation direction of the carbon fibers contained in the first layer 10 and the orientation direction of the carbon fibers contained in the second layer 20. There is no particular limitation on the number of layers (layers containing carbon fibers and non-conductive fibers) contained in the electromagnetic noise suppression sheet 200, as long as it is two or more layers.

[0072] 3.2. Second Variant Next, an electromagnetic noise suppression sheet according to a second modification of this embodiment will be described with reference to the drawings. Fig. 8 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet 300 according to the second modification of this embodiment.

[0073] Hereinafter, in the electromagnetic noise suppression sheet 300 according to the second modified example of this embodiment, components having the same functions as the components of the electromagnetic noise suppression sheet 100 according to this embodiment described above will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0074] As shown in FIG. 8, an electromagnetic noise suppression sheet 300 differs from the above-described electromagnetic noise suppression sheet 100 in that it includes a first protective layer 30 and a second protective layer 32.

[0075] The first layer 10 is sandwiched between the first protective layer 30 and the second protective layer 32. The first layer 10 is provided between the first protective layer 30 and the second protective layer 32. In the example shown in the figure, the first protective layer 30 is provided on the first layer 10, and the second protective layer 32 is provided below the first layer 10. The protective layers 30 and 32 contain non-conductive fibers. The above description of the non-conductive fibers of the first layer 10 can be applied to the non-conductive fibers of the protective layers 30 and 32.

[0076] The first protective layer 30 and the second protective layer 32 protect the first layer 10. The protective layers 30, 32 do not contain carbon fiber. Because the electromagnetic noise suppression sheet 300 has the first layer 10 sandwiched between the first protective layer 30 and the second protective layer 32, which do not contain carbon fiber, there is little chance of stiff carbon fibers protruding from the surface of the electromagnetic noise suppression sheet 300, and the sheet feels pleasant to the touch.

[0077] The adhesion between the first layer 10 and the first protective layer 30, and the adhesion between the first layer 10 and the second protective layer 32 are not particularly limited, and may be achieved using an adhesive or by swelling and gelatinizing the first layer 10 and the protective layers 30, 32.

[0078] Although not shown, the electromagnetic noise suppression sheet 200 may be provided with a first protective layer 30 and a second protective layer 32. That is, the first layer 10 and the second layer 20 may be provided between the first protective layer 30 and the second protective layer 32.

[0079] 4. Experimental Example The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to these examples.

[0080] 4.1. First experimental example 4.1.1. Preparation of mixed paper A slurry containing cationic starch (Neotack 40T manufactured by Nihon Shokuhin Kako Co., Ltd.) was added as a paper strength agent at 0.5% by mass based on the solid content to a slurry containing LBKP as cellulose fiber and carbon fiber to prepare a slurry containing cationic starch. The CSF of the LBKP was adjusted to 300 ml. Chopped fiber manufactured by Mitsubishi Chemical Corporation with an average fiber length of 3 mm was used as the carbon fiber. LBKP was a product manufactured at the Niigata Plant of Hokuetsu Corporation.

[0081] The prepared slurry was made into a mixed paper using an orientation paper machine. The orientation paper machine used was an "experimental orientation paper machine" manufactured by Kumagai Riki Kogyo Co., Ltd. The rotation speed of the papermaking wire mesh of the orientation paper machine was set to 650 m / min and 1700 m / min.

[0082] The prepared slurry was used to prepare mixed paper on a hand-made machine according to the TAPPI standard papermaking method.

[0083] The carbon fiber content of the mixed paper was varied by adjusting the amount of carbon fiber in the slurry, and the basis weight of the mixed paper was varied by adjusting the amount of slurry fed into the paper machine.

[0084] Evaluation Method For the prepared mixed paper, an approximate ellipse was determined based on the above-mentioned "1.3. Orientation strength", and the orientation strength of the carbon fibers was calculated from the ratio of the major axis to the minor axis.

[0085] Furthermore, the electromagnetic noise suppression performance of the mixed paper was evaluated. The electromagnetic noise suppression performance was evaluated by measuring the transmission attenuation rate Rtp (dB) using the microstrip line method. The measuring equipment used was a network analyzer "ZVA67" manufactured by ROHDE & SCHWARZ, connected to a test fixture "TF-18C" manufactured by KEYCOM. The measurement was carried out in accordance with "IEC62333". The measurement frequency was 500MHz to 18GHz.

[0086] In the microstrip line method, as shown in Fig. 9, evaluation was performed in two states: one in which the mixed paper was arranged so that the major axis of the approximate ellipse obtained in "1.3. Orientation strength" above was perpendicular to the extension direction of the transmission line T (state A shown in Fig. 9), and the other in which the mixed paper was arranged so that the major axis of the approximate ellipse was parallel to it (state B shown in Fig. 9). Note that Fig. 9 is a diagram for explaining the evaluation method for electromagnetic noise suppression performance, and the direction of the electromagnetic field is indicated by an arrow.

[0087] Furthermore, the basis weight, thickness and density of the prepared mixed paper were measured. The thickness and density were measured in accordance with JIS P 8118.

[0088] 4.1.3. Evaluation Results Fig. 10 is a table showing the orientation strength of carbon fibers (hereinafter simply referred to as "orientation strength of mixed paper") and Rtp of mixed paper with a carbon fiber content of 2% by mass. Fig. 11 is a table showing the orientation strength and Rtp of mixed paper with a carbon fiber content of 5% by mass.

[0089] 10 and 11, "MSL direction" indicates the relationship between the transmission line in the microstrip line method and the major axis of the approximation ellipse. "Perpendicular" refers to the state in which the major axis of the approximation ellipse is perpendicular to the transmission line (state A in FIG. 9). "Parallel" refers to the state in which the major axis of the approximation ellipse is parallel to the transmission line (state B in FIG. 9). Furthermore, "difference in maximum Rtp value" refers to the difference between the maximum value of Rtp in the perpendicular state and the maximum value of Rtp in the parallel state. be.

[0090] 12 to 14 show the results for a sample with a carbon fiber content of 2% by mass and a basis weight of 25 g / cm 2 10 is a graph showing the Rtp versus frequency of mixed papers of about 1700 m / min. FIG. 12 is a graph of mixed papers made under the condition that the rotation speed of the papermaking wire gauze of the orientation papermaking machine is 1700 m / min. FIG. 13 is a graph of mixed papers made under the condition that the rotation speed of the papermaking wire gauze of the orientation papermaking machine is 650 m / min. FIG. 14 is a graph of mixed papers made on a hand-made papermaking machine. The values ​​in FIG. 10 are taken from the values ​​in FIGS. 12 to 14.

[0091] 15 to 17 show the results for a sample with a carbon fiber content of 5% by mass and a basis weight of 25 g / cm 2 11 is a graph showing the Rtp versus frequency of mixed papers of about 1000 rpm. FIG. 15 is a graph of mixed papers made under the condition that the rotation speed of the papermaking wire gauze of the orientation papermaking machine is 1700 m / min. FIG. 16 is a graph of mixed papers made under the condition that the rotation speed of the papermaking wire gauze of the orientation papermaking machine is 650 m / min. FIG. 17 is a graph of mixed papers made with a hand-made papermaking machine. The values ​​in FIG. 11 are taken from the values ​​in FIGS. 15 to 17.

[0092] As shown in Figures 10 and 11, the orientation strength of the mixed paper produced at a rotation speed of 1700 m / min was 2.3 or higher. The orientation strength of the mixed paper produced at a rotation speed of 650 m / min was 1.8 or higher. In the mixed paper produced on a handsheet, the carbon fibers are randomly arranged, and the carbon fiber orientation strength is close to 1.0 and less than 1.2. In Figures 10 and 11, the orientation strength of the mixed paper produced on a handsheet is indicated by "-".

[0093] As shown in Figures 10 and 11, for blended papers with the same carbon fiber content and similar basis weight, the Rtp of the blended paper made on the orientation paper machine in the "perpendicular" orientation was greater than the Rtp of the blended paper made on the orientation paper machine in the "parallel" orientation, the Rtp of the blended paper made on the handsheet machine in the "perpendicular" orientation, and the Rtp of the blended paper made on the handsheet machine in the "parallel" orientation, for blended papers with the same carbon fiber content and basis weight. This indicates that blended papers with a carbon fiber orientation strength of 1.8 or higher, as determined by Fourier image analysis, have high electromagnetic noise suppression performance when the carbon fiber orientation is perpendicular to the transmission line in the microstrip line method.

[0094] As shown in Figures 10 and 11, the greater the orientation strength, the greater the "difference in maximum Rtp value." In the mixed paper with a carbon fiber content of 2% by mass, the greater the basis weight, the greater the "maximum Rtp value."

[0095] 4.2. Second experimental example 4.2.1. Preparation of mixed paper The mixed papers were prepared in the same manner as in the first experimental example described above, except that the basis weight was changed.

[0096] Evaluation Method As in the first experimental example, an approximate ellipse was determined, and the orientation strength of the carbon fibers was calculated from the ratio of the major axis to the minor axis. Then, Rtp was measured in three states: when the mixed paper was arranged so that the major axis of the approximate ellipse was perpendicular to the extension direction of the transmission line; when the mixed paper was arranged so that the major axis of the approximate ellipse was parallel to the extension direction of the transmission line; and when the mixed paper was arranged so that the major axis of the approximate ellipse was at 45° to the extension direction of the transmission line.

[0097] 4.2.3. Evaluation Results Fig. 18 is a table showing the orientation strength and Rtp of mixed paper. Fig. 19 is a graph showing Rtp versus frequency for mixed paper with an orientation strength of 2.7. Fig. 20 is a graph showing Rtp versus frequency for mixed paper with an orientation strength of 2.8. 18 is a graph showing Rtp versus frequency for mixed paper. The values ​​in FIG. 18 are taken from the values ​​in FIG. 19 and FIG. 20.

[0098] As shown in Figures 18 to 20, the Rtp when the MSL direction is 45° is larger than the Rtp when it is "parallel" and smaller than the Rtp when it is "perpendicular." This shows that the closer the orientation direction to the extension direction of the transmission line is to 90°, the smaller the Rtp of the electromagnetic wave. noise Furthermore, by adjusting the angle of the orientation direction relative to the extension direction of the transmission line, the electromagnetic wave suppression performance of the mixed paper can be improved. noise It was found that the suppression performance could be controlled.

[0099] 4.3. Third Experimental Example 4.3.1. Preparation of mixed paper The mixed papers were prepared in the same manner as in the first experimental example described above, except that the carbon fiber content and basis weight were changed and the mixed papers were made using a Fourdrinier paper machine. Evaluation Method As in the first experimental example described above, the orientation strength and Rtp of the mixed paper were evaluated.

[0100] 4.3.3. Evaluation Results Figure 21 is a table showing the orientation strength and Rtp of mixed paper. Figure 22 is a graph showing Rtp versus frequency for mixed paper with an orientation strength of 1.2. Figure 23 is a graph showing Rtp versus frequency for mixed paper with an orientation strength of 1.3.

[0101] As shown in Figures 21 to 23, the mixed paper with an orientation strength of 1.3 had a larger RTP in the "perpendicular" state than the mixed paper with an orientation strength of 1.2, and the "difference in maximum RTP" was 10 dB or more. The "difference in maximum RTP" for the mixed paper with an orientation strength of 1.2 was 6.4 dB, which was similar to the mixed paper made with the handsheet machine in the first experimental example described above. This shows that mixed papers with a carbon fiber orientation strength of 1.3 or more have higher electromagnetic wave noise suppression performance in the "perpendicular" state than mixed papers with a carbon fiber orientation strength of less than 1.3.

[0102] The above-described embodiment and modifications are merely examples, and the present invention is not limited to these. For example, the embodiments and modifications can be combined as appropriate.

[0103] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments. A substantially identical configuration means, for example, a configuration that has the same function, method, and result, or a configuration that has the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects or purposes as the configurations described in the embodiments. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments. [Explanation of symbols]

[0104] 10...first layer, 20...second layer, 30...first protective layer, 32...second protective layer, 100, 200, 300...electromagnetic noise suppression sheet

Claims

1. a first layer having carbon fibers and cellulose fibers; a second layer disposed on the first layer; Including, the orientation strength of the carbon fibers contained in the first layer determined by Fourier image analysis is 1.3 or more; the first layer is in sheet form and not in a corrugated form; the second layer includes carbon fibers and non-conductive fibers; the orientation strength of the carbon fibers contained in the second layer determined by Fourier image analysis is 1.3 or more; an orientation direction of the carbon fibers contained in the first layer and an orientation direction of the carbon fibers contained in the second layer intersect with each other.

2. An electromagnetic noise suppression sheet as described in Claim 1, wherein the orientation strength of the carbon fibers contained in the first layer is 1.8 or more.

3. An electromagnetic noise suppression sheet as described in claim 1 or 2, wherein the orientation strength of the carbon fibers contained in the first layer is 2.3 or more.

4. 4. The electromagnetic noise suppression sheet according to claim 1, wherein the content of the carbon fibers in the first layer is 0.1% by mass or more and 20% by mass or less.

5. 5. The electromagnetic noise suppression sheet according to claim 1, wherein the content of the carbon fibers in the first layer is 0.5% by mass or more and 10% by mass or less.

6. An electromagnetic noise suppression sheet described in any one of claims 1 to 5, wherein the average fiber length of the carbon fibers contained in the first layer is 0.04 mm or more and 25 mm or less.

7. An electromagnetic noise suppression sheet described in any one of claims 1 to 6, wherein the average fiber length of the carbon fibers contained in the first layer is 1 mm or more and 15 mm or less.

8. The basis weight of the first layer is 20 g / m ２ 650g / m or more ２ 8. The electromagnetic noise suppression sheet according to claim 1, wherein:

9. The basis weight of the first layer is 23 g / m ２ More than 200g / m ２ 9. The electromagnetic noise suppression sheet according to claim 1, wherein:

10. 10. The electromagnetic noise suppression sheet according to claim 1, wherein an orientation direction of the carbon fibers contained in the first layer and an orientation direction of the carbon fibers contained in the second layer intersect with each other at an angle of 45° to 90°.

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