Electromagnetic wave shielding material and electromagnetic wave shielding structure

Abstract

In electromagnetic wave shielding materials, this prevents tears and pinholes caused by bending, thereby maintaining electromagnetic wave shielding properties. [Solution] An electromagnetic wave shielding material (2) is made of an expanded graphite sheet (1) having a surface treatment structure at least in the portion to be folded that facilitates folding and prevents breakage. The surface treatment structure is a roughened structure with minute irregularities formed on one or both sides.

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave shielding material and an electromagnetic wave shielding structure made of an expanded graphite sheet, and in particular to the structure of the folded portion thereof. [Background technology]

[0002] Conventionally, as disclosed in Patent Documents 1 to 3, it is known that an expanded graphite sheet is used as an electromagnetic wave shielding material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-165470 [Patent Document 2] Special Publication No. 7-19995 [Patent Document 3] International Publication No. 1999-10598 Summary of the Invention [Problem to be solved by the invention]

[0004] The electromagnetic wave shielding material made of an expanded graphite sheet needs to be folded to fit the shape of the device that requires electromagnetic wave shielding.

[0005] However, due to the characteristics of electromagnetic wave shielding materials, when they are bent, cracks tend to occur at the bent points, and electromagnetic waves can pass through tears or pinholes that originate from the cracks, which can easily reduce the electromagnetic wave shielding performance.

[0006] The present invention has been made in view of the above points, and its object is to prevent tears and pinholes caused by bending and maintain electromagnetic wave shielding properties. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a surface treatment structure that makes bending easy and prevents breakage.

[0008] Specifically, in the first invention, the expanded graphite sheet has a surface treatment structure at least in the portion to be folded that makes folding easy and prevents breakage, The surface treatment structure is a roughened structure with minute irregularities formed on one or both sides.

[0009] According to the above configuration, a roughened structure with minute irregularities formed by blasting or the like is formed on one or both sides of the portion to be folded as a surface treatment structure that facilitates folding and prevents breakage, so that the surface is moderately uneven, the occurrence of cracks due to tension at the folding points is suppressed, tears due to cracks and the occurrence of pinholes can be prevented, and electromagnetic wave shielding performance is maintained. When a roughened structure with minute irregularities is formed on both sides, there is an advantage that tears are less likely to occur, particularly in both mountain and valley folds.

[0010] In the second invention, in the first invention, Corrugated plate structures arranged at predetermined intervals in one direction are further formed at least in the portion to be folded.

[0011] According to the above configuration, by aligning the direction in which the corrugated plate structure is arranged with the folding lines, cracks are even less likely to occur at the folding points, and tears and pinholes do not occur.

[0012] In the third invention, in the first invention, Corrugated plate structures arranged at predetermined intervals in two directions intersecting perpendicularly are further formed at least on the portion to be folded.

[0013] According to the above configuration, by aligning the perpendicularly intersecting portions of the electromagnetic wave shielding material with the corners of the equipment requiring electromagnetic wave shielding, cracks are less likely to occur at the bending points, and the occurrence of tears and pinholes is suppressed.

[0014] In a fourth aspect of the present invention, in the third aspect of the present invention, Corrugated plate structures arranged at predetermined intervals in the diagonal direction in addition to the two perpendicularly intersecting directions are further formed at least in the portion to be folded.

[0015] According to the above-mentioned configuration, the sheet is easily bendable in three directions, so that cracks are less likely to occur at the bends even if the bends do not strictly follow the unevenness of the corrugated sheet structure, and the occurrence of tears and pinholes is suppressed.

[0016] The electromagnetic wave shielding structure of the fifth invention is configured such that the electromagnetic wave shielding material of any one of the first to fourth inventions is folded, and there are no cracks or holes on the surface of the folded portion.

[0017] According to the above-mentioned configuration, no tears or pinholes occur, and high electromagnetic wave shielding performance can be obtained. [Effects of the Invention]

[0018] As described above, according to the present invention, by forming a roughened structure with minute irregularities on one or both sides, it is possible to make the film moderately easy to bend, prevent tears and pinholes caused by bending, and maintain electromagnetic wave shielding properties. [Brief explanation of the drawings]

[0019] [Figure 1] 1A and 1B show the flat electromagnetic shielding material that is the raw material, where (a) is a plan view and (b) is a front view. [Figure 2] FIG. 1 is a cross-sectional view showing an example of an electromagnetic wave shielding structure. [Figure 3] 1A and 1B show a photograph of the electromagnetic shielding material of Example 1, in which (a) is a plan view and (b) is a front view. [Figure 4] 1A and 1B show a photograph of the electromagnetic shielding material of Example 2, in which (a) is a plan view and (b) is a front view. [Figure 5] 1A and 1B show a photograph of the electromagnetic shielding material of Example 3, in which (a) is a plan view and (b) is a front view. [Figure 6] 1 is a graph showing the results of a tensile test. [Figure 7] FIG. 1 is a front view showing an outline of a testing machine for a bending test. [Figure 8] 10 is a graph showing the results of a bending test. [Figure 9] 10A and 10B show an electromagnetic wave shielding material according to another embodiment, in which (a) is a photograph showing a plan view of an electromagnetic wave shielding material having a corrugated structure also added in an oblique direction, and (b) is a plan view of an electromagnetic wave shielding material having a corrugated structure added at a position rotated by another 90°. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] 1 shows an expanded graphite sheet 1 used in an electromagnetic wave shielding material 2 according to an embodiment of the present invention. This expanded graphite sheet 1 is made by treating natural graphite particles with acid, expanding them to at least 25 times their original volume, opening the spaces between overlapping carbon laminations, and molding the resulting material into a sheet without using any adhesives or additives. Essentially, neither side of the expanded graphite sheet 1 is covered with a plastic film, paper, or metal foil.

[0022] A feature of this embodiment is that the electromagnetic wave shielding material 2 is made of an expanded graphite sheet 1 having a surface treatment structure at least in the portion to be folded that makes folding easy and prevents breakage.

[0023] 2 shows an electromagnetic shielding structure 3 formed by folding the electromagnetic shielding material 2 of this embodiment. The electromagnetic shielding structure 3 may have a relatively complex shape to match the shape of the device 4 to be protected or the shape of the housing 5 that covers the device 4 to be protected, but is characterized by the absence of cracks or holes on the surface of the folded portions.

[0024] Example 1 As shown in Figure 3, in Example 1, a blast treatment is performed as a surface treatment structure, which is an example of a roughened structure in which minute irregularities are formed on one side. For example, the blast treatment may use media such as silicon carbide (SiC) of 10 to 100 μm, glass beads, iron powder, walnut powder, plastic beads, etc. The irradiation distance is 150 mm and the spray pressure is 2 kg / cm. 2 This is the extent, but is not limited to this.

[0025] In Example 1, one side of the portion to be folded is subjected to blast treatment 11 as a surface treatment structure that facilitates folding and prevents breakage, so that the appropriate unevenness makes it easier to fold, suppresses the occurrence of cracks due to tension at the folding point, prevents breakage due to cracks and the occurrence of pinholes, and maintains electromagnetic wave shielding performance. Note that it is desirable to have the surface-treated side be the tension side when folding.

[0026] Example 2 As shown in FIG. 4, in Example 2, a blast treatment 11 is applied to both surfaces as a surface treatment structure.

[0027] In Example 2, a blast treatment is applied to both sides of the portion to be folded as a surface treatment structure that facilitates folding and prevents breakage, making it moderately easy to fold on both sides, suppressing the occurrence of cracks due to tension at the folding points, preventing tears and pinholes due to cracks, and maintaining electromagnetic wave shielding performance. In particular, Example 2 has the advantage that tears are less likely to occur in both mountain and valley folds, and there is no need to consider the front and back sides when folding.

[0028] Example 3 As shown in Fig. 5, the electromagnetic wave shielding material 2 of Example 3 is blasted on both sides in the same manner as in Example 2, and further has a corrugated structure 12 formed at least in the portion to be folded, arranged at a predetermined interval in two perpendicularly intersecting directions. As shown in Fig. 5(b), the corrugated structure 12 has curved convex portions formed on the upper and lower sides in side view, and can be formed by, for example, pressing in one direction using a press machine for a predetermined corrugated shape, and then rotating the material 90° and pressing again.

[0029] In Example 3, by aligning the perpendicular intersecting portions of the corrugated plate structure 12 of the electromagnetic wave shielding material 2 with the corners of the equipment 4 that require electromagnetic wave shielding, cracks are less likely to occur at the bending points, and the occurrence of tears and pinholes is suppressed.

[0030] When the electromagnetic shielding structure 3 shown in Fig. 2 is constructed using the electromagnetic shielding materials 2 of Examples 1 to 3, no cracks or holes are generated on the surface of the folded portions of the electromagnetic shielding material 2. Therefore, the electromagnetic shielding structure 3 of this embodiment does not generate tears or pinholes, and high electromagnetic shielding performance is achieved.

[0031] -Evaluation test method- Next, the evaluation methods for Examples 1 to 3 and Comparative Example 1 will be described.

[0032] As Comparative Example 1, a flat electromagnetic shielding material without blasting or corrugated structure, as shown in FIG. 1, was prepared.

[0033] (1) Tensile test A tensile test was conducted to confirm the effect of surface treatment on elongation. The chuck distance of the tensile tester was 100 mm, the head speed was 200 mm / min, and the number of tests was 3.

[0034] 6, in Example 1, the elongation was 1.37 times that of Comparative Example 1, and in Example 2, the elongation was 1.48 times that of Comparative Example 1. In Example 3, the elongation was 4.15 times that of Comparative Example 1.

[0035] (2) Bending test A bending test was performed using a bending tester 6, the outline of which is shown in Figure 7. A recess 8 was formed in a base mold 7 with a bending angle of 90°, a bending radius of R5, and a maximum depth of 10 mm. The maximum depth was set to 4.5 mm x 2 times or more the maximum height of a commercially available inductor (the tallest component on the board). A test specimen 10 was placed so as to cover the recess 8, and a press mold 9 corresponding to the shape of the recess 8 was lowered from above, while the specimen was observed for damage.

[0036] The criterion for a pass product was that the formed sheet had no tears or pinholes.

[0037] As shown in Figure 8, in Comparative Example 1, tears occurred at a forming depth of 5.5 mm. In Example 1, tears occurred at a forming depth of 7.0 mm, and in Example 2, tears occurred at a forming depth of 7.5 mm. It was found that both Examples 1 and 2 had increased bending strength compared to Comparative Example 1. Furthermore, in Example 3, no tears or pinholes occurred even at a maximum forming depth of 10.0 mm. In other words, it was found that bending strength was significantly improved not only by double-sided blasting but also by forming a corrugated structure that intersects vertically and horizontally.

[0038] (3) Shield test A shielding test was conducted to confirm the effect of surface treatment on shielding performance. Similar to the case of Comparative Example 1, which was not surface treated, which had a shielding effect of 60 dB or more, all of Examples 1 to 3 had a shielding effect of 60 dB or more.

[0039] In other words, it was found that the shielding effect was not reduced even if the material was subjected to blasting treatment or made into a corrugated structure to make it easier to bend.

[0040] These evaluation tests showed that the elongation and bendability were improved in Examples 1 and 2, which were subjected to blasting treatment, and the shielding effect was not reduced, but that the improvement in elongation and bendability was particularly significant in Example 3.

[0041] As explained above, according to the present invention, by applying blast treatment 11 to one or both sides, the sheet can be made moderately easy to bend, preventing tears and pinholes caused by bending, and maintaining electromagnetic wave shielding properties. Furthermore, by using a corrugated plate structure 12, tears and pinholes caused by bending can be prevented more effectively.

[0042] (Other embodiments) The present invention may be configured as follows in relation to the above embodiment.

[0043] That is, although not shown, in the blasted electromagnetic shielding material 2 of Example 1 or Example 2, a corrugated structure arranged at a predetermined interval in only one direction, rather than in two directions, vertically and horizontally, may be formed at least in the portion to be folded. In this case, even if corrugated structures are not formed vertically and horizontally, by aligning the direction in which the corrugated structure is arranged in one direction with the folding line, cracks are even less likely to occur at the folding point, and tears and pinholes do not occur.

[0044] In the above embodiment, the blast treatment 11 and the corrugated plate structure 12 are provided on the entire electromagnetic wave shielding material 2, but the unfolded portions may be formed flat.

[0045] Furthermore, as shown in Figure 9(a), the electromagnetic shielding material 2 may further have a corrugated plate structure 12 formed at least in the portion to be folded, with the corrugated plate structure 12 arranged at a predetermined interval in a diagonal direction in addition to the two perpendicularly intersecting directions. This configuration allows for easy folding in three directions, making it even less likely for cracks to occur at the folding points, even if the folding does not strictly follow the corrugations of the corrugated plate structure, and thus suppressing the occurrence of tears and pinholes. Furthermore, the diagonal processing may be performed at a position rotated by another 90°, as shown in Figure 9(b).

[0046] In addition, in the above embodiment, the expanded graphite sheet 1 is basically not covered on either side with a plastic film, paper, or metal foil, but it may be covered with a plastic film, paper, or metal foil after surface treatment, or may be subjected to a painting treatment.

[0047] Although blasting has been exemplified as a roughened structure having minute irregularities, the present invention is not limited to this, and other roughening treatments such as chemical roughening may also be used.

[0048] It should be noted that the above-described embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or uses. [Explanation of symbols]

[0049] 1. Expanded graphite sheet 2. Electromagnetic wave shielding materials 3. Electromagnetic wave shielding structure 4 Protected Equipment 5. Cabinet 6. Bending tester 7 bottom type 8 recess 9 Press mold 10 Test specimen 11 Blasting 12 Corrugated sheet structure

Claims

1. The sheet is made of an expanded graphite sheet having a surface treatment structure at least in the portion to be folded, which facilitates folding and prevents breakage, The surface treatment structure is a roughened structure in which minute irregularities are formed on one or both sides. Electromagnetic wave shielding material characterized by:

2. A corrugated plate structure arranged at predetermined intervals in one direction is further formed at least in the portion to be folded.

2. The electromagnetic wave shielding material according to claim 1.

3. Corrugated plate structures arranged at predetermined intervals in two directions intersecting perpendicularly are further formed at least in the portion to be folded.

2. The electromagnetic wave shielding material according to claim 1.

4. In addition to the two perpendicularly intersecting directions, a corrugated plate structure is also formed at a predetermined interval in the diagonal direction at least in the portion to be folded.

2. The electromagnetic wave shielding material according to claim 1.

5. The electromagnetic wave shielding material according to any one of claims 1 to 4 is folded, and the surface of the folded portion is free from cracks and holes. Electromagnetic wave shielding structure characterized by:

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