Electromagnetic wave shielding material and production method therefor
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2024-03-22
- Publication Date
- 2026-06-15
Abstract
Description
Electromagnetic wave shielding material and its manufacturing method
[0001] The present invention relates to an electromagnetic wave shielding material and a method for producing the same.
[0002] Recent advances in microelectronics technology have led to the widespread use of a wide variety of electronic devices, including personal computers and mobile phones. In these environments, the impact of electromagnetic noise caused by unwanted electromagnetic waves on electronic devices has been noted. Furthermore, measures are required for in-vehicle radars and radars for speed measurement, etc., to receive only the electromagnetic waves necessary for measurement and to block unwanted electromagnetic waves. Therefore, there is a demand for devices to prevent malfunctions and breakdowns, suppress the radiation of unwanted electromagnetic waves, and provide sufficient resistance to external electromagnetic waves.
[0003] Countermeasures against electromagnetic waves can be broadly divided into methods that reflect electromagnetic waves and methods that absorb them. For example, metals are commonly used as electromagnetic shields that reflect electromagnetic waves. On the other hand, to prevent malfunctions of equipment due to electromagnetic waves generated by the equipment itself, electromagnetic wave absorbers are required rather than reflectors. Rubber or plastics with ferrite kneaded into them are the mainstream for such products.
[0004] For example, Patent Document 1 proposes an electromagnetic wave absorber for the GHz band consisting of a three-dimensional network-like carbon fiber structure composed of carbon fibers with outer diameters of 15 to 100 nm. Patent Document 2 proposes an electromagnetic wave absorber composed of two or more laminated conductive fiber sheets, each of which has a fiber sheet substrate coated with a conductive polymer. Patent Document 3 proposes an electromagnetic wave absorber composed of a laminate having multiple first layers containing pulp and carbon fiber and a second layer containing pulp but not carbon fiber, with the second layer being disposed between the two first layers in the laminate. Non-Patent Document 1 investigates the electromagnetic wave shielding effect of bamboo charcoal, reporting that bamboo charcoal carbonized at 750°C or higher is effective in reflecting 4 GHz electromagnetic waves.
[0005] US2009 / 0135042A1 US2011 / 0168440A1 JP2021-158175A
[0006] "Study on the Electrical Properties and Electromagnetic Wave Shielding Effect of Bamboo Charcoal", Kagoshima Prefectural Industrial Technology Center Research Report No. 12, 1998
[0007] With technological advances, the wavelength range of electromagnetic waves used in various fields has expanded to a wide range, and there is a demand for materials that can shield with sufficient attenuation from relatively long wavelengths to short wavelengths such as millimeter waves. In particular, there is a demand for shielding materials for short wavelengths of 1 GHz or more. Therefore, an object of the present invention is to provide an electromagnetic wave shielding material that has a high attenuation effect over a wide frequency range, and a method for manufacturing the same.
[0008] The present invention provides an electromagnetic wave shielding material comprising a fabric containing fibers made of a sintered body of rayon-based fibers or silk fibers, the material having an electromagnetic wave shielding ability of 5 dB or more in the frequency range of 500 MHz to 18 GHz, as measured by the coaxial tube method.
[0009] The present invention also provides an electromagnetic wave shielding material comprising a fabric containing fibers made of a sintered body of rayon-based fibers or silk fibers, and having an electromagnetic wave absorption capacity of 10% or more of the irradiated electromagnetic waves in the frequency range of 500 MHz to 18 GHz, as measured by the coaxial tube method.
[0010] The present invention also provides a method for producing an electromagnetic wave absorbing material, which comprises baking a raw fabric containing rayon fibers or silk fibers at a temperature of 300° C. to 2000° C. in vacuum.
[0011] The present invention further provides an electromagnetic wave shielding member comprising a substrate and an electromagnetic wave shielding layer deposited on the substrate, wherein the electromagnetic wave shielding layer is made of fine pieces obtained by cutting the electromagnetic wave shielding material or powder obtained by pulverizing the electromagnetic wave shielding material.
[0012] The present invention further provides a heat-generating fabric that is made of a fabric containing fibers made of a sintered body of rayon-based fibers or silk fibers, has an electromagnetic wave absorption capacity measured by a coaxial tube method in the frequency range of 500 MHz to 18 GHz of 10% or more of the irradiated electromagnetic waves, and is capable of generating heat when irradiated with electromagnetic waves.
[0013] Figures 1(a) and 1(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 1. Figures 2(a) and 2(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 2. Figures 3(a) and 3(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 4. Figures 4(a) and 4(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 5. Figures 5(a) and 5(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 6. Figures 6(a) and 6(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 7. FIGS. 7(a) and 7(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 8. FIGS. 8(a) and 8(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Comparative Example 1. FIG. 9 is a graph showing the results of Raman spectroscopy measured for the electromagnetic shielding material obtained in Example 1. FIG. 10 is a graph showing the results of Raman spectroscopy measured for the electromagnetic shielding material obtained in Example 2. FIG. 11 is a graph showing the results of the near-infrared transmittance measured for the electromagnetic shielding material obtained in Example 1. FIG. 12 is a graph showing the results of the near-infrared transmittance measured for the electromagnetic shielding material obtained in Example 2. FIG. 13 is a graph showing the results of the near-infrared transmittance measured for the electromagnetic shielding material obtained in Example 3. FIG. 14 is a graph showing the results of the near-infrared reflectance measured for the electromagnetic shielding material obtained in Example 1. Fig. 15 is a graph showing the results of measuring the near-infrared reflectance of the electromagnetic wave shielding material obtained in Example 2. Fig. 16 is a graph showing the results of measuring the near-infrared reflectance of the electromagnetic wave shielding material obtained in Example 3.Figures 17(a) to 17(d) are thermographs showing the temperature rise when near-infrared light was irradiated on the electromagnetic wave shielding materials obtained in Examples 1 to 3 and Comparative Example 1, respectively. Figures 18(a) and 18(b) are graphs showing the results of electromagnetic wave shielding ability and electromagnetic wave absorption ability measured for an electromagnetic wave shielding member obtained using the electromagnetic wave shielding material obtained in Example 1. Figures 19(a) and 19(b) are graphs showing the results of electromagnetic wave shielding ability and electromagnetic wave absorption ability measured for an electromagnetic wave shielding member obtained using the electromagnetic wave shielding material obtained in Example 2. Figures 20(a) and 20(b) are graphs showing the results of electromagnetic wave shielding ability and electromagnetic wave absorption ability measured for an electromagnetic wave shielding member obtained using the electromagnetic wave shielding material obtained in Example 4. Figures 21(a) and 21(b) are graphs showing the results of electromagnetic wave shielding ability and electromagnetic wave absorption ability measured for an electromagnetic wave shielding member obtained using the electromagnetic wave shielding material obtained in Example 5. Figures 22(a) and 22(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 9. Figures 23(a) and 23(b) are graphs showing the results of the electromagnetic shielding ability and electromagnetic wave absorption ability measured for the electromagnetic shielding material obtained in Example 10. Figure 24 is an X-ray diffraction diagram of the electromagnetic shielding material obtained in Example 2. Figure 25 is an X-ray diffraction diagram of the electromagnetic shielding materials obtained in Examples 9 and 10. Figure 26 is an infrared absorption spectrum of the electromagnetic shielding material obtained in Example 2. Figure 27 is an infrared absorption spectrum of the electromagnetic shielding material obtained in Example 10.
[0014] The present invention will be described below based on its preferred embodiments. In this specification, "electromagnetic wave shielding" refers to the phenomenon of absorbing or reflecting electromagnetic waves. In the following description, "electromagnetic wave shielding" refers to absorbing electromagnetic waves, reflecting electromagnetic waves, or both absorbing and reflecting electromagnetic waves, depending on the context. Furthermore, in the present invention, "electromagnetic wave shielding material" refers to a material that has the ability to absorb or reflect electromagnetic waves.
[0015] The electromagnetic wave shielding material of the present invention is made of a fabric. In this specification, "fabric" refers to a sheet-like article made of a fiber material. The fabric is made of a woven fabric, knitted fabric, or nonwoven fabric made of a fiber material, or a sheet formed by laminating any of these. Depending on the specific application of the present invention, the fabric may be made of only a sheet formed of a fiber material, or may be a laminate of a sheet formed of a fiber material and a sheet formed of a material other than a fiber material. Examples of sheet formed of a material other than a fiber material include resin films and metal films.
[0016] The electromagnetic wave shielding material of the present invention comprises a fabric containing fibers made of a sintered rayon-based fiber. The use of a fabric containing fibers made of a sintered rayon-based fiber in the present invention is advantageous in that it enhances the electromagnetic wave shielding effect over a wide frequency range, particularly the electromagnetic wave absorption effect in the GHz frequency range and above, while also improving flexibility and lightness. Furthermore, because the rayon-based fiber is a naturally derived material, it also has the advantage of being environmentally friendly.
[0017] From the viewpoint of improving electromagnetic wave shielding, the fabric preferably contains 50% by mass or more of fibers made of sintered rayon-based fibers, more preferably 60% by mass or more, even more preferably 80% by mass or more, particularly preferably 95% by mass or more, or may contain 98% by mass or more, or may contain 99% by mass or more, and most preferably 100% by mass.
[0018] Rayon-based fibers are produced by chemically modifying natural cellulose fibers to dissociate the intermolecular hydrogen bonds, forming a colloidal solution, which is then reconstituted into cellulose molecules, resulting in the reassembly of the polymers and regenerating the fibers. Examples of raw materials include wood pulp, bamboo, and cotton. Rayon-based fibers include rayon (viscose rayon), cuprammonium rayon (cupro), polynosic, lyocell (Tencel), modal, acetate, triacetate, and refined cellulose. Rayon-based fibers may also be regenerated cellulose fibers that have been crosslinked with a crosslinking agent.
[0019] Among the rayon-based fibers mentioned above, rayon-based fibers made from wood pulp or bamboo are preferred because of their high electromagnetic wave shielding effect over a wide frequency range, particularly in the frequency range above 1 GHz, and rayon-based fibers made from bamboo (hereinafter also referred to as "bamboo rayon fibers") are particularly suitable. In particular, the inventors believe that twisting bamboo rayon fibers results in large surface irregularities, which in turn create irregularities on the surface of the fibers obtained by burning these fibers (hereinafter also referred to as "carbonized fibers"), and that these irregularities may contribute to excellent electromagnetic wave absorption and reflection properties. Among bamboo rayon fibers, viscose rayon fibers made from bamboo and produced by the viscose process are particularly preferred because of their extremely high electromagnetic wave shielding effect over a wide frequency range, particularly in the frequency range above 1 GHz, and because bamboo rayon fibers are readily available.
[0020] Bamboo rayon fiber is preferably produced using pulp derived from bamboo, or using pulp derived from bamboo and general wood pulp other than bamboo, in the production of rayon. In order to obtain the excellent properties derived from bamboo, it is preferable that 50% by mass or more of the total cellulose raw material is derived from bamboo, more preferably 70% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass is derived from bamboo.
[0021] In fabrics containing fibers made of sintered rayon-based fibers, the shape of the single yarn made of the sintered fiber can be confirmed using a scanning electron microscope. The cross-sectional shape of the single yarn can be selected from various shapes depending on the shape of the spinneret, and may be, for example, circular, flat, or sawtooth.
[0022] From the viewpoint of improving the drapeability of the electromagnetic wave shielding material, the fiber made of the sintered rayon fiber preferably has a diameter of 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. From the same viewpoint, the diameter in the cross section is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. The fiber diameter can be measured by observing the fiber using a Keyence Corporation digital microscope VHX at a magnification of 20x to 2000x. Measurements are performed on 10 or more samples, and the average value is taken as the fiber diameter.
[0023] In the present invention, instead of the fabric containing fibers made of the above-mentioned sintered rayon-based fibers, a fabric containing fibers made of sintered silk fibers can be used. This fabric contains fibers obtained by using silk material as a raw material and sintering it. The use of a fabric containing fibers made of sintered silk fibers in the present invention is advantageous in that it improves the electromagnetic wave shielding effect over a wide frequency range, particularly the electromagnetic wave absorption effect in the frequency range above GHz, while also improving flexibility and lightness.
[0024] From the viewpoint of improving electromagnetic wave shielding, the fabric preferably contains 50% by mass or more of fibers made of burned silk fibers, more preferably 60% by mass or more, even more preferably 80% by mass or more, particularly preferably 95% by mass or more, or may contain 98% by mass or more, or may contain 99% by mass or more, and most preferably 100% by mass.
[0025] The inventors speculate that twisting silk fibers into yarns increases the unevenness, which in turn creates unevenness on the surface of the carbonized fiber obtained by baking it, and that this unevenness may contribute to excellent electromagnetic wave absorption and electromagnetic wave reflection properties.
[0026] From the viewpoint of improving the drapeability of the electromagnetic wave shielding material, the fibers made of burned silk fibers preferably have a diameter of 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. From the same viewpoint, the diameter is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 9 μm or less. The fiber diameter can be measured by observing the fibers using a Keyence Corporation digital microscope VHX at a magnification of 20x to 2000x. Measurements are made on 10 or more samples, and the average value is taken as the fiber diameter.
[0027] Whether the fibers constituting the electromagnetic wave shielding material are made of sintered rayon-based fibers or sintered silk fibers, it is preferable that the electromagnetic wave shielding material be a woven fabric made from yarns that are thickened by twisting multiple single yarns, as this has a high shielding effect against electromagnetic waves over a wide frequency range, and in particular a high electromagnetic wave absorption effect in the frequency range of 1 GHz or higher.
[0028] When the electromagnetic wave shielding material is a woven fabric containing fibers of the fired body, examples of the woven fabric include plain weave, twill, tussah, satin, honeycomb weave, layered weaves such as single double weave and double double weave, and pile weaves such as corduroy and velvet. Of these, it is preferable to use at least one selected from plain weave, twill, and tussah, as this makes it easier to obtain a flexible and lightweight electromagnetic wave shielding material, and plain weave is particularly preferable.
[0029] The electromagnetic shielding effectiveness SE of an electromagnetic shielding material is expressed by the following Schelkunoff formula (1): SE = R + A + B (1) In the formula, R represents the reflection loss on the surface of the electromagnetic shielding material, A represents the attenuation loss within the electromagnetic shielding material, and B represents the multiple reflection effect within the electromagnetic shielding material. The influence of the term B in the Schelkunoff formula is small except under special conditions where the term A is small (for example, when the electromagnetic shielding material is extremely thin), and therefore can generally be ignored and can be approximated by the following formula (1'): SE = R + A (1') The electromagnetic shielding effectiveness SE of the electromagnetic shielding material of the present invention, measured by the coaxial tube method in the frequency range of 500 MHz to 18 GHz, is preferably 5 dB or more, more preferably 8 dB or more, even more preferably 10 dB or more, even more preferably 20 dB or more, particularly preferably 25 dB or more, particularly preferably 30 dB or more, and most preferably 35 dB or more. In the present invention, the electromagnetic wave shielding effectiveness SE is expressed in decibels as the electric field strength ratio at the level surpassed by the electromagnetic wave shielding material, as expressed by the following formula (2): Electromagnetic wave shielding effectiveness SE (dB) = 20 log １０ (E ０ / E １ ) (2) In the formula, E ０ represents the electric field strength (V / m) when there is no electromagnetic wave shielding material, and E １ represents the electric field strength (V / m) of the electromagnetic wave transmitted through the electromagnetic wave shielding material.
[0030] The electromagnetic wave shielding material of the present invention preferably has an electromagnetic wave absorption capacity, measured by the coaxial tube method, of 10% or more of the irradiated electromagnetic wave in the frequency range of 500 MHz to 18 GHz, more preferably 15% or more, even more preferably 20% or more, even more preferably 25% or more, and particularly preferably 30% or more. In the present invention, the electromagnetic wave absorption capacity corresponds to term A in the Schelkunoff equation expressed by the above-mentioned formula (1), and corresponds to the loss caused by the induced current generated by the electromagnetic wave incident on the electromagnetic wave shielding material. The output (power) of the irradiated electromagnetic wave when measuring the electromagnetic wave absorption capacity is 0.1 mW.
[0031] The electromagnetic wave shielding material of the present invention preferably has an electromagnetic wave shielding efficiency SE of 5 dB or more, more preferably 10 dB or more, even more preferably 15 dB or more, even more preferably 20 dB or more, particularly preferably 25 dB or more, especially preferably 30 dB or more, and most preferably 35 dB or more, even in a frequency range above 18 GHz. Furthermore, the electromagnetic wave shielding material of the present invention preferably has an electromagnetic wave absorption efficiency SE of 10% or more, more preferably 15% or more, even more preferably 20% or more, even more preferably 25% or more, and especially preferably 30% or more, of the irradiated electromagnetic waves, even in a frequency range above 18 GHz.
[0032] The electromagnetic wave shielding material of the present invention is suitable in that, when subjected to Raman spectroscopy, a peak is observed in a specific wave number region, thereby enhancing the electromagnetic wave shielding effect over a wide frequency range, particularly enhancing the electromagnetic wave absorption effect in the frequency range of GHz or higher, while also being flexible and lightweight. Specifically, the electromagnetic wave shielding material of the present invention exhibits a peak of 1600±50 cm in Raman spectroscopy. －１ and 1350±50 cm －１ It is preferable that a peak is observed in the wave number region of 1580±50 cm －１ In the wave number region (hereinafter also referred to as the "first wave number region"), it is preferable that at least one peak is observed, and two or more peaks may be observed. －１ In this wave number region (hereinafter also referred to as the "second wave number region"), it is preferable that at least one peak is observed, and two or more peaks may be observed.
[0033] The intensity of the highest peak among the peaks observed in the first wavenumber region is designated as I １ The intensity of the peak with the highest intensity among the peaks observed in the second wave number region is I ２ When I １ / I ２It is preferable that the value of I is 1 or more, particularly 2 or more, and especially 2.5 or more, from the viewpoint of improving the absorption of electromagnetic waves. １ / I ２ The value of is preferably 10 or less, particularly 9 or less, and especially 8 or less. １ and I ２ represents the integrated intensity of the peak.
[0034] From the viewpoint of enhancing the electromagnetic wave shielding effect over a wide frequency range, particularly enhancing the electromagnetic wave absorption effect in a frequency range of 1 GHz or higher, the electromagnetic wave shielding material of the present invention preferably has a volume resistivity of 1.5 Ω cm or less, more preferably 1.3 Ω cm or less, and even more preferably 1.2 Ω cm or less. The volume resistivity can be measured by the method described in the examples below.
[0035] The fired fiber contained in the electromagnetic shielding material of the present invention, i.e., the carbonized fiber, is a material different from carbon fiber. While carbon fiber is composed almost entirely of carbon, the carbonized fiber constituting the electromagnetic shielding material of the present invention has a lower carbon content than carbon fiber. The inventors believe that this contributes to the electromagnetic shielding material of the present invention exhibiting a high electromagnetic wave shielding effect over a wide frequency range, particularly a high electromagnetic wave absorption effect in the frequency range of 1 GHz or higher. From the viewpoint of achieving a sufficient electromagnetic wave shielding effect, particularly an electromagnetic wave absorption effect, the carbon content of the carbonized fiber contained in the electromagnetic shielding material of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. From the same viewpoint, the carbon content of the carbonized fiber is preferably 95% by mass or less, more preferably 94% by mass or less. The carbon content of the carbonized fiber can be measured by the method described in the Examples below.
[0036] When conventional carbon fibers are measured by X-ray diffraction, diffraction peaks attributable to the crystalline structure of graphite are observed. In contrast, when the burned fibers included in the electromagnetic shielding material of the present invention, particularly carbonized fibers obtained by burning bamboo rayon fibers, are measured by X-ray diffraction, diffraction peaks attributable to the crystalline structure of graphite are not observed. In this respect, the carbonized fibers obtained by burning bamboo rayon fibers are clearly distinguishable from carbon fibers in terms of their crystalline structure. Furthermore, when the carbonized fibers are measured by X-ray diffraction, no diffraction peaks are observed. For example, in X-ray diffraction measurement using Cu Kα radiation as a radiation source, no diffraction peaks are observed in the range of 2θ = 10° to 60°. In other words, the carbonized fibers are amorphous. The inventors believe that the electromagnetic shielding material of the present invention has high electromagnetic shielding ability because it is made of a fabric containing the carbonized fibers having these characteristics.
[0037] The burned fiber contained in the electromagnetic wave shielding material of the present invention, the carbonized fiber obtained by burning bamboo rayon fiber, has a wavelength of 800 cm when measured by infrared spectroscopy. －１ From 2000 cm －１ No absorption peak is observed in the wave number range up to 1110 cm. This wave number range is due to the cellulose structure, e.g., glucose stretching (1110 cm). －１ ) and C-O stretching (1055 cm －１ , 1030 cm －１ ), but no peak due to this absorption is observed in the carbonized fiber obtained by burning bamboo rayon fiber. This means that the molecular structure of cellulose is lost by burning. In particular, when the carbonized fiber obtained by burning bamboo rayon fiber is measured by infrared spectroscopy, the peak at 800 cm －１ From 4000 cm －１ The present inventors believe that the electromagnetic shielding material of the present invention has a high electromagnetic wave shielding ability because it is made of a fabric containing the carbonized fiber having such characteristics.
[0038] The carbonized fiber, which is the fiber of the fired body contained in the electromagnetic shielding material of the present invention, is mainly composed of carbon element and may additionally contain other elements. In particular, when the carbonized fiber contains silicon element, the electromagnetic shielding material has a higher electromagnetic wave shielding effect over a wide frequency range, and particularly a higher electromagnetic wave absorption effect in the frequency range of GHz or higher. From the viewpoint of making this advantage more pronounced, the proportion of silicon element in the carbonized fiber contained in the electromagnetic shielding material of the present invention is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.7 mass% or more. From the same viewpoint, the proportion of silicon element in the carbonized fiber is preferably 3 mass% or less, more preferably 2.5 mass% or less, and even more preferably 1.8 mass% or less. The proportion of silicon element in the carbonized fiber can be measured by the method described in the Examples below.
[0039] In order to incorporate silicon element into the electromagnetic wave shielding material of the present invention, a method can be employed in which an appropriate amount of a silicon-containing compound such as silicone oil is applied to the raw sheet before firing.
[0040] The electromagnetic shielding material of the present invention is preferably lightweight and has high drapeability. From this viewpoint, the electromagnetic shielding material of the present invention is preferably one in which the (002) reflection peak of graphite is not observed in X-ray diffraction measurement. In other words, it is preferable that the electromagnetic shielding material is substantially free of a graphite structure. The reason for this is that the electromagnetic shielding material of the present invention is obtained by carbonizing the raw material rayon fibers or silk fibers through baking, and if carbonization proceeds too far and graphite is produced, the rigidity of the electromagnetic shielding material increases, and its drapeability is likely to decrease.
[0041] The electromagnetic wave shielding material of the present invention is a fabric, and from the viewpoint of a balance between high electromagnetic wave shielding ability and high flexibility and light weight, the thickness of the fabric is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 60 μm or more. From the same viewpoint, the thickness of the fabric is preferably 400 μm or less, more preferably 320 μm or less, and even more preferably 280 μm or less.
[0042] In relation to the thickness of the fabric described above, the basis weight of the fabric is set to 5 g / m from the viewpoint of a balance between high electromagnetic wave shielding ability, high flexibility, and light weight. ２ It is preferable that the content is 8 g / m or more. ２ More preferably, it is 13 g / m or more. ２ From the same viewpoint, the basis weight of the fabric is more preferably 100 g / m or more. ２ It is preferable that the weight is 90 g / m or less. ２ More preferably, it is 80 g / m or less. ２ It is even more preferred that:
[0043] The electromagnetic shielding material of the present invention is also characterized by its low bending rigidity. The smaller the bending rigidity, the easier it is to bend. In other words, the electromagnetic shielding material of the present invention has high drapeability. In particular, when the electromagnetic shielding material of the present invention contains a fabric made of a woven or knitted fabric of carbonized fiber obtained by burning bamboo rayon fiber (hereinafter, this fabric will also be referred to as "burned bamboo fabric"), the drapeability of the electromagnetic shielding material will be even higher. Specifically, the bending rigidity value is 1 gf cm ２ / cm or less, and preferably 0.5 gf cm ２ / cm or less, and more preferably 0.1 gf cm ２ / cm or less, and more preferably 0.05 gf cm ２ / cm or less, and even more preferably 0.04 gf cm ２ It is particularly preferable that the bending stiffness is 0.0001 gf cm or less. There is no particular limit to the lower limit of the bending stiffness, and the lower the value, the more improved the drapeability.２ / cm, especially 0.003 gf cm ２ / cm, sufficient drapeability is exhibited. The bending stiffness is measured using a bending tester KES-FB2 manufactured by Kato Tech. The measurement piece is a rectangle measuring 20 cm x 20 cm. The maximum curvature is ±2.5 cm. －１ The deformation speed is 0.5 cm －１ The bending rigidity may be different in the machine direction MD and the width direction CD of the fabric constituting the electromagnetic wave shielding material, but in such cases, the average value of both values is defined as the bending rigidity value in the present invention.
[0044] The fabric constituting the electromagnetic wave shielding material of the present invention is porous. This fabric is preferably a bamboo-burned fabric made from a woven or knitted fabric of carbonized fiber obtained by burning bamboo rayon fiber. The porosity of the bamboo-burned fabric is preferably 30% or more, thereby improving flexibility and lightness. From this perspective, the porosity is more preferably 32% or more, even more preferably 40% or more, and particularly preferably 43% or more. Since excessively high porosity tends to reduce the electromagnetic wave shielding ability, the porosity of the bamboo-burned fabric is preferably 80% or less, more preferably 70% or less, even more preferably 65% or less, and particularly preferably 50% or less.
[0045] In relation to the porosity described above, the average pore size of the fabric constituting the electromagnetic shielding material of the present invention, particularly the average pore size of the bamboo-burning fabric, is preferably 100 μm or more, more preferably 150 μm or more, and even more preferably 220 μm or more, from the viewpoint of enhancing the flexibility and lightness of the electromagnetic shielding material. Since an excessively large average pore size tends to reduce the electromagnetic shielding ability, the average pore size of the bamboo-burning fabric is preferably 900 μm or less, more preferably 750 μm or less, even more preferably 500 μm or less, even more preferably 350 μm or less, and particularly preferably 280 μm or less.
[0046] The porosity and average pore size are measured by the following method. The surface of the electromagnetic shielding material is observed using an FE-SEM (Hitachi High-Technologies Corporation, S-4100). The electromagnetic shielding material is cut to a predetermined size with a cutter knife and fixed to a sample stage, and the electromagnetic shielding material is photographed using the FE-SEM at a magnification of 50x and an acceleration voltage of 5 kV. The photographed image is binarized using the image processing software Image-J. For the binarization process, the Adjust → Color Thereshold setting is selected in the menu bar of Image-J (the threshold Brightness is set to AUTO). The area of the voids is determined by the binarization process, and this value is used as the average pore size. In addition, the area ratio of the voids is determined, and this value is used as the porosity (%). The average pore size and porosity are measured at three different locations for one electromagnetic shielding material, and the average values are calculated.
[0047] The above description concerns the case where the electromagnetic shielding material of the present invention is made of a fabric. The fabric can be used in the form of fine pieces cut from the fabric or in the form of a powder obtained by pulverizing the fabric. This provides an electromagnetic shielding member according to the present invention. The electromagnetic shielding member of the present invention comprises a substrate and an electromagnetic shielding layer deposited on the substrate, and the electromagnetic shielding layer is made of fine pieces cut from the electromagnetic shielding material made of the above-mentioned fabric or a powder obtained by pulverizing the electromagnetic shielding material.
[0048] The substrate used in the electromagnetic wave shielding member of the present invention can be either a metal material or a non-metal material. Metal materials include, for example, aluminum, copper, iron, and stainless steel. Non-metal materials include, for example, organic polymer materials such as thermoplastic resins and thermosetting resins, and inorganic materials such as silica and alumina. When an electromagnetic wave shielding material made of fabric is cut into small pieces for use, the area of the small pieces should be 0.01 mm or less. ２ More than 5mm ２ From the viewpoint of high electromagnetic wave shielding properties, it is preferable that the average particle size of the powder is 1 μm or more and 300 μm or less.
[0049] In the electromagnetic wave shielding layer, the fine pieces obtained by cutting the electromagnetic wave shielding material or the powder obtained by pulverizing the electromagnetic wave shielding material can be fixed using, for example, a binder, such as a carbon coating spray.
[0050] Next, a preferred method for producing the electromagnetic wave shielding material of the present invention will be described. This method comprises the steps of twisting a plurality of single yarns of rayon or silk fibers to form a weaving yarn, producing a woven fabric using the weaving yarn, and sintering the woven fabric under vacuum.
[0051] One of the features of the present invention is that raw fabric containing rayon or silk fibers is baked under vacuum conditions. By baking under vacuum conditions, an electromagnetic shielding material having a high electromagnetic wave shielding effect over a wide frequency range, particularly an electromagnetic wave shielding material having a high electromagnetic wave absorption effect in the frequency range of GHz or higher, can be easily obtained. From this perspective, the degree of vacuum during baking is preferably within the range of -0.001 kPaG to -85 kPaG in gauge pressure.
[0052] During firing, the pressure inside a firing furnace containing a raw sheet of electromagnetic shielding material is reduced, and after a predetermined vacuum level is reached, the firing furnace is heated. The firing temperature is preferably 300°C or higher and 2000°C or lower, more preferably 600°C or higher and 1900°C or lower, even more preferably 700°C or higher and 1700°C or lower, and even more preferably 750°C or higher and 1600°C or lower. The time from the start of heating (usually room temperature) until the target firing temperature is reached is preferably 200 minutes or higher, particularly 300 minutes or higher. Furthermore, the time from the start of heating until the target firing temperature is reached is preferably 1000 minutes or shorter, particularly 800 minutes or shorter.
[0053] It is preferable to carry out the heating in two or more stages, from the viewpoint of successfully obtaining an electromagnetic shielding material that has a high electromagnetic wave shielding effect over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect in the frequency range of GHz or higher. The multi-stage firing includes at least two firing stages: first firing and second firing. It is preferable not to perform a temperature-lowering operation during the multi-stage firing, from the viewpoint of successfully obtaining an electromagnetic wave shielding material that has the desired electromagnetic wave shielding effect.
[0054] In the first firing in the multi-stage firing, it is preferable to raise the temperature of the raw web at a slow rate. Specifically, it is preferable to set the first temperature rise rate from room temperature to the first firing temperature to 0.4°C / min or more, particularly 0.5°C / min or more. It is also preferable to set the first temperature rise rate to 3.0°C / min or less, particularly 2.0°C / min or less. The temperature rise in the first firing may be performed linearly over time, stepwise, or along a predetermined curve.
[0055] From the viewpoint of successfully obtaining an electromagnetic wave shielding material that has a high shielding effect against electromagnetic waves over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect in a frequency range of GHz or higher, the first firing temperature is preferably set to 300°C or higher and 600°C or lower, and more preferably set to 350°C or higher and 500°C or lower.
[0056] Once the first baking temperature is reached, it is preferable to maintain that temperature for 60 minutes or more and 180 minutes or less, from the viewpoint of successfully obtaining an electromagnetic wave shielding material that has a high electromagnetic wave shielding effect over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect in a frequency range of GHz or more. To further enhance this advantage, once the first baking temperature is reached, it is even more preferable to maintain that temperature for 80 minutes or more and 150 minutes or less.
[0057] After the first firing is completed, the inside of the firing furnace is further heated to perform the second firing, which raises the temperature from the first firing temperature to the second firing temperature, i.e., the desired firing temperature (hereinafter also referred to as the "target temperature"). In the second firing, the second heating rate, which is the heating rate, is preferably 0.15°C / min or more, particularly 0.2°C / min or more. Furthermore, the second heating rate is preferably 7.0°C / min or less, particularly 6.0°C / min or less. The temperature rise in the second firing may be linear over time, stepwise, or may be performed in a predetermined curve.
[0058] From the viewpoint of successfully obtaining an electromagnetic wave shielding material that has a high shielding effect against electromagnetic waves over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect in a frequency range of GHz or higher, the target temperature is preferably set to 750°C or higher and 1700°C or lower, more preferably 1100°C or higher and 1700°C or lower, and even more preferably 1100°C or higher and 1600°C or lower.
[0059] Once the target temperature is reached, it is preferable to maintain that temperature for 60 minutes or more and 200 minutes or less, from the viewpoint of successfully obtaining an electromagnetic wave shielding material that has a high electromagnetic wave shielding effect over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect in the frequency range of GHz or more. To further enhance this advantage, once the target temperature is reached, it is even more preferable to maintain that temperature for 70 minutes or more and 190 minutes or less.
[0060] The degree of vacuum in the firing furnace may be the same or different between the first firing and the second firing. From the viewpoint of successfully obtaining an electromagnetic wave shielding material that has a high electromagnetic wave shielding effect over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect over a frequency range of GHz or higher, it is preferable that the degree of vacuum in the second firing be higher than that in the first firing.
[0061] After the second firing is completed, the firing furnace is cooled. Cooling may be natural or forced. The cooling rate is preferably 2.0 to 15°C / min, and more preferably 2.8 to 10°C / min, from the viewpoint of successfully obtaining an electromagnetic shielding material that has a high electromagnetic wave shielding effect over a wide frequency range, particularly a high electromagnetic wave absorption effect over a frequency range of GHz or higher.
[0062] In this manufacturing method, an intermediate firing may be performed between the first firing and the second firing. By performing the intermediate firing, it is possible to more successfully obtain an electromagnetic wave shielding material that has a high electromagnetic wave shielding effect over a wide frequency range, particularly an electromagnetic wave absorbing effect over a frequency range of GHz or higher.
[0063] In the intermediate baking, the intermediate temperature rise rate from the first baking temperature to the intermediate baking temperature is preferably 0.4°C / min or more, particularly 0.5°C / min or more. Furthermore, the intermediate temperature rise rate is preferably 20°C / min or less, particularly 10°C / min or less. The temperature rise in the intermediate baking may be linear or stepwise over time, or may be along a predetermined curve.
[0064] From the viewpoint of more successfully obtaining an electromagnetic wave shielding material that has a high shielding effect against electromagnetic waves over a wide frequency range, particularly an electromagnetic wave shielding material that has a high electromagnetic wave absorption effect in a frequency range of GHz or higher, the intermediate firing temperature is preferably set to 650°C or higher and 1050°C or lower, and more preferably set to 700°C or higher and 1000°C or lower.
[0065] When intermediate firing is employed in this manufacturing method, the second firing may be omitted and the intermediate firing may be used as the final firing.
[0066] The electromagnetic shielding material of the present invention, which is made of a fabric containing carbonized fibers and which is obtained in this manner, can be used as is. Alternatively, the electromagnetic shielding material can be folded and used. Alternatively, multiple sheets of unfolded electromagnetic shielding material can be stacked and used. Alternatively, multiple sheets of folded electromagnetic shielding material can be stacked and used. Furthermore, the electromagnetic shielding material of the present invention, which is made of a fabric containing carbonized fibers, can be cut into a predetermined shape and used. Alternatively, the electromagnetic shielding material of the present invention can be impregnated with a resin to form a composite material.
[0067] The electromagnetic wave shielding material of the present invention can be used in a variety of fields where electromagnetic wave shielding is desired. For example, the electromagnetic wave shielding material of the present invention can be applied to clothing such as underwear for protecting reproductive organs, maternity wear for protecting the fetus and mother, and various outerwear and innerwear such as dress shirts, T-shirts, and pants. Alternatively, the electromagnetic wave shielding material of the present invention can be applied to medical workwear such as surgical gowns and radiation-shielding clothing. Furthermore, by utilizing the fact that the electromagnetic wave shielding material of the present invention generates heat as a result of absorbing electromagnetic waves, the electromagnetic wave shielding material of the present invention can also be used as a heat-generating fabric that generates heat when irradiated with electromagnetic waves. This heat-generating material can be used as heat-generating clothing, such as heat-generating underwear.
[0068] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."
[0069] Example 1: Bamboo rayon fiber (obtained by the viscose rayon method, with bamboo as the cellulose raw material at 90% by mass or more) was used, consisting of two 80-count single yarns (indicated by British cotton count) twisted together. Several of these yarns were bundled together to form a 5.8 μm diameter yarn bundle, which was then twisted to form a twisted yarn with a diameter of approximately 150 μm, forming a plain weave fabric. The fabric was subjected to a two-stage baking process consisting of a first baking and an intermediate baking in a baking oven under vacuum. In the first baking, the temperature was raised from room temperature (25°C) to the first baking temperature (300°C) at a rate of 2°C / min, and the first baking temperature was maintained for 120 minutes. The vacuum level in the baking oven was set to -0.01 kPaG. During the intermediate firing, the temperature was increased from the first firing temperature (300°C) to the intermediate firing temperature (800°C) at a temperature increase rate of 10°C / min, and the intermediate firing temperature was maintained for 120 minutes. The degree of vacuum inside the firing furnace was set to -0.01 kPaG. After the intermediate firing was completed, the furnace was cooled at a temperature decrease rate of 10°C / min, and after cooling to room temperature, the desired electromagnetic wave shielding material was removed from the firing furnace.
[0070] Example 2 In Example 1, the intermediate firing was followed by the second firing. In the second firing, the temperature was increased from the intermediate firing temperature (800°C) to the second firing temperature (1200°C) at a rate of 4°C / min, and the second firing temperature was maintained for 150 minutes. The degree of vacuum in the firing furnace was set to -0.01 kPaG.
[0071] Example 3 In Example 1, a second firing was performed after the intermediate firing. In the second firing, the temperature was increased from the intermediate firing temperature (800°C) to the second firing temperature (1500°C) at a temperature increase rate of 4°C / min, and the second firing temperature was maintained for 150 minutes. The degree of vacuum in the firing furnace was set to -0.01 kPaG.
[0072] Example 4: Bamboo rayon fiber (obtained by the viscose rayon method, containing at least 90% by mass of bamboo as the cellulose raw material) was used, consisting of two twisted 80-count single yarns (indicated by British cotton count). Several of these yarns were bundled together to form a 5.8 μm diameter yarn bundle, which was then twisted to form a twisted yarn with a diameter of approximately 150 μm, forming a dobby woven fabric. The fabric was subjected to a two-stage baking process consisting of a first baking and an intermediate baking in a baking oven under vacuum. In the first baking, the temperature was raised from room temperature (25°C) to the first baking temperature (300°C) at a rate of 2°C / min, and the first baking temperature was maintained for 120 minutes. The vacuum level in the baking oven was set to -0.01 kPaG. During the intermediate firing, the temperature was increased from the first firing temperature (300°C) to the intermediate firing temperature (800°C) at a temperature increase rate of 10°C / min, and the intermediate firing temperature was maintained for 120 minutes. The degree of vacuum inside the firing furnace was set to -0.01 kPaG. After the intermediate firing was completed, the furnace was cooled at a temperature decrease rate of 10°C / min, and after cooling to room temperature, the desired electromagnetic wave shielding material was removed from the firing furnace.
[0073] Example 5 In Example 4, the intermediate firing was followed by the second firing. In the second firing, the temperature was increased from the intermediate firing temperature (800°C) to the second firing temperature (1200°C) at a temperature increase rate of 4°C / min, and the second firing temperature was maintained for 150 minutes. The degree of vacuum in the firing furnace was set to -0.01 kPaG.
[0074] [Example 6] Silk fiber 15 g / m ２Habutae fabric was used. This fabric was subjected to a three-stage baking process under vacuum using a baking furnace, consisting of a first baking, an intermediate baking, and a second baking. In the first baking, the temperature was increased from room temperature (25°C) to the first baking temperature (300°C) at a temperature increase rate of 2°C / min, and the first baking temperature was maintained for 120 minutes. The degree of vacuum in the baking furnace was -0.01 kPaG. In the intermediate baking, the temperature was increased from the first baking temperature (300°C) to the intermediate baking temperature (800°C) at a temperature increase rate of 10°C / min, and the intermediate baking temperature was maintained for 120 minutes. The degree of vacuum in the baking furnace was -0.01 kPaG. In the second baking, the temperature was increased from the intermediate baking temperature (800°C) to the second baking temperature (1200°C) at a temperature increase rate of 4°C / min, and the second baking temperature was maintained for 150 minutes. The degree of vacuum inside the firing furnace was set to −0.01 kPa G. After the second firing was completed, the inside of the firing furnace was cooled at a temperature decreasing rate of 10° C. / min to room temperature, and then the target electromagnetic wave shielding material was taken out from the firing furnace.
[0075] Example 7: A nonwoven fabric made of silk fibers was used. This fabric was subjected to a three-stage baking process under vacuum in a baking furnace: first baking, intermediate baking, and second baking. In the first baking, the temperature was increased from room temperature (25°C) to the first baking temperature (300°C) at a heating rate of 2°C / min and maintained at the first baking temperature for 120 minutes. The vacuum in the baking furnace was -0.01 kPaG. In the intermediate baking, the temperature was increased from the first baking temperature (300°C) to the intermediate baking temperature (800°C) at a heating rate of 10°C / min and maintained at the intermediate baking temperature for 120 minutes. The vacuum in the baking furnace was -0.01 kPaG. In the second baking, the temperature was increased from the intermediate baking temperature (800°C) to the second baking temperature (1200°C) at a heating rate of 4°C / min and maintained at the second baking temperature for 150 minutes. The degree of vacuum inside the firing furnace was set to −0.01 kPa G. After the second firing was completed, the inside of the firing furnace was cooled at a temperature decreasing rate of 10° C. / min to room temperature, and then the target electromagnetic wave shielding material was taken out from the firing furnace.
[0076] [Example 8] In the second firing of Example 7, the temperature was increased from the intermediate firing temperature (800°C) to the second firing temperature (1500°C) at a temperature increase rate of 4°C / min, and the second firing temperature was maintained for 150 minutes. The degree of vacuum in the firing furnace was set to -0.01 kPaG. Other than this, an electromagnetic wave shielding material was obtained in the same manner as in Example 7.
[0077] Example 9: A satin weave fabric made of bamboo rayon fiber (obtained by the viscose rayon method, containing at least 90% by mass of bamboo as the cellulose raw material, with a fiber diameter of 19 μm and a twisted yarn diameter of 196 μm) was used, which was different from those used in Examples 1 and 2. This fabric was subjected to a two-stage baking process consisting of a first baking and an intermediate baking in a baking furnace under vacuum. In the first baking, the temperature was increased from room temperature (25°C) to the first baking temperature (300°C) at a heating rate of 2°C / min and maintained at the first baking temperature for 120 minutes. The vacuum level in the baking furnace was -0.01 kPaG. In the intermediate baking, the temperature was increased from the first baking temperature (300°C) to the intermediate baking temperature (800°C) at a heating rate of 10°C / min and maintained at the intermediate baking temperature for 120 minutes. The vacuum level in the baking furnace was -0.01 kPaG. After the intermediate firing was completed, the inside of the firing furnace was cooled at a temperature decreasing rate of 10°C / min to room temperature, and then the target electromagnetic wave shielding material was taken out of the firing furnace. The basis weight of the obtained electromagnetic wave shielding material was 100.7 g / m ２ It was.
[0078] Example 10 In Example 9, a second firing was performed after the intermediate firing. In the second firing, the temperature was increased from the intermediate firing temperature (800°C) to the second firing temperature (1200°C) at a temperature increase rate of 4°C / min, and the second firing temperature was maintained for 150 minutes. The degree of vacuum in the firing furnace was set to -0.01 kPaG. The basis weight of the obtained electromagnetic wave shielding material was 89.0 g / m ２ It was.
[0079] Comparative Example 1 In Example 1, only the first baking was carried out at 290° C. The other steps were the same as in Example 1, and the desired electromagnetic wave shielding material was obtained.
[0080] [Evaluation 1] The fiber diameters of the electromagnetic shielding materials obtained in Examples 1 to 8 and Comparative Example 1 were measured using the method described above. The electromagnetic shielding ability and electromagnetic absorption ability of the electromagnetic shielding materials obtained in Examples 1 to 10 and Comparative Example 1 were measured in the frequency range of 500 MHz to 18 GHz using the methods described below. The measurement results for each Example are shown in Figures 1 to 8, 22, and 23. Furthermore, Raman spectroscopy was performed using the method described below to measure peak positions and peak intensities. The measurement results for Example 1 are shown in Figures 9 and 10. Furthermore, volume resistivity and the proportions of carbon and silicon elements were measured using the method described below. Furthermore, XRD measurement was performed using the method described below to determine the presence or absence of graphite. Furthermore, the thickness and basis weight of the electromagnetic shielding materials were measured using the method described below. Furthermore, the porosity, average pore size, and bending rigidity of the electromagnetic shielding materials obtained in Examples 1 to 5 were measured using the methods described above. The results are shown in Table 1 below. XRD patterns for the electromagnetic shielding materials obtained in Examples 2, 9, and 10 are shown in Figures 24 and 25. The infrared absorption spectra of the electromagnetic wave shielding materials obtained in Examples 2 and 10 are shown in FIGS.
[0081] [Measurement of electromagnetic wave shielding ability and electromagnetic wave absorption ability] The electromagnetic wave shielding ability and electromagnetic wave absorption ability were measured using the coaxial tube method in the frequency range of 500 MHz to 18 GHz. A network analyzer, ZVA67, manufactured by Rohde & Schwarz was used for the measurements. An S-GPC7 manufactured by Keycom Corporation was used as an evaluation device for the electromagnetic wave shielding ability.
[0082] [Raman Spectroscopic Measurement] Measurement was carried out using a laser Raman spectrophotometer NRS-3100, a microscopic laser Raman spectrometer manufactured by JASCO Corporation.
[0083] [Measurement of Volume Resistivity] Measurement was carried out using a resistivity meter MCP-360 manufactured by Nitto Seiko Analytic Co., Ltd.
[0084] [Ratio of Carbon and Silicon Elements] Quantitative analysis was carried out using an energy dispersive X-ray analyzer (EDS), employing the ZAF correction method.
[0085] [XRD Measurement] Measurement was carried out using a build-up type multi-function X-ray diffractometer RINT-Ultima III manufactured by Rigaku Corporation.
[0086] [Thickness and basis weight of electromagnetic wave shielding material] The thickness was measured using an Smgda digital thickness gauge. The basis weight was determined by measuring the mass of the electromagnetic wave shielding material cut into a 5 cm x 5 cm square with a precision balance and multiplying the mass by 25 cm ２ It was calculated by dividing by
[0087]
[0088] As is clear from the results shown in Table 1 and Figures 1 to 8, the electromagnetic wave shielding materials obtained in each Example are lightweight and have excellent drapeability, and have high electromagnetic wave shielding and electromagnetic wave absorbing capabilities.
[0089] [Evaluation 2] The near-infrared transmittance and reflectance of the electromagnetic shielding materials obtained in Examples 1 to 3 were measured by the following method. The results are shown in FIGS. 11 to 16. A UV-3600Plus ultraviolet / visible / near-infrared spectrophotometer manufactured by Shimadzu Corporation and an ISR-1503 integrating sphere accessory (inner diameter: 150 mm) were used. The scan speed was set to medium, the sampling pitch was set to 2 nm, and the measurement wavelength range was set to 200 nm or more and 2500 nm or less (frequency: 120 THz or more and 1500 THz or less). As is clear from the results shown in FIGS. 11 to 16, near-infrared light with a frequency of 120 THz or more and 1500 THz or less was neither transmitted nor reflected, and therefore, it is considered that the electromagnetic shielding materials obtained in Examples 1 to 3 absorb near-infrared light in this frequency range.
[0090] [Evaluation 3] The electromagnetic shielding materials obtained in Examples 1 to 3 and Comparative Example 1 were irradiated with near-infrared light having a frequency of 150 THz or more and 300 THz or less, and the degree of temperature rise after 5 minutes was measured using thermography. The results are shown in Figures 17(a) to 17(d). As is clear from the results shown in Figures 17(a) to 17(d), the electromagnetic shielding materials of each Example exhibited a higher degree of temperature rise due to near-infrared light irradiation than the electromagnetic shielding material of the Comparative Example. This means that the electromagnetic shielding materials of each Example have excellent near-infrared light absorption ability.
[0091] Example 11 The electromagnetic wave shielding material obtained in Example 1 was cut into small pieces measuring 1 to 2 mm in length and 1 to 2 mm in width. These small pieces were deposited on aluminum foil (20 μm thick) to obtain a deposit. A carbon coating spray was sprayed onto this deposit to form an electromagnetic wave shielding layer. In this way, an electromagnetic wave shielding member was obtained.
[0092] Examples 12 to 14 Electromagnetic shielding members were obtained in the same manner as in Example 11, except that the electromagnetic shielding materials obtained in Examples 2, 4, and 5 were used. The electromagnetic shielding ability and electromagnetic wave absorption ability of the obtained electromagnetic shielding members were measured using the methods described above. The results are shown in Figures 18 to 21.
[0093] According to the present invention, an electromagnetic wave shielding material having a high attenuation effect over a wide frequency range, particularly in the frequency range of GHz or higher, and a method for manufacturing the same are provided.
Claims
1. A fabric comprising fibers made from a fired body of bamboo rayon-based fibers, The bending stiffness value is 0.0001 gf·cm² / cm or more and 1 gf·cm² / cm or less. An electromagnetic shielding material having an electromagnetic shielding capacity of 5 dB or more, measured by the coaxial tube method, in the frequency range of 500 MHz to 18 GHz.
2. A fabric comprising fibers made of a fired body of bamboo rayon fibers, Including woven or knitted fabrics of the aforementioned fibers, The porosity of the woven or knitted fabric of the aforementioned fibers is 30% or more and 50% or less. The average pore size of the woven or knitted fabric of the aforementioned fibers is 100 μm or more and 900 μm or less. An electromagnetic shielding material having an electromagnetic shielding capacity of 5 dB or more, measured by the coaxial tube method, in the frequency range of 500 MHz to 18 GHz.
3. A fabric comprising fibers made from a fired body of bamboo rayon-based fibers, The bending stiffness value is 0.0001 gf·cm² / cm or more and 1 gf·cm² / cm or less. An electromagnetic shielding material having an electromagnetic wave absorption capacity of 10% or more of the irradiated electromagnetic wave, as measured by the coaxial tube method, in the frequency range of 500 MHz to 18 GHz.
4. A fabric comprising fibers made of a fired body of bamboo rayon-based fibers, Including woven or knitted fabrics of the aforementioned fibers, The porosity of the woven or knitted fabric of the aforementioned fibers is 30% or more and 50% or less. The average pore size of the woven or knitted fabric of the aforementioned fibers is 100 μm or more and 900 μm or less. An electromagnetic shielding material having an electromagnetic wave absorption capacity of 10% or more of the irradiated electromagnetic wave, as measured by the coaxial tube method, in the frequency range of 500 MHz to 18 GHz.
5. An electromagnetic wave shielding material according to any one of claims 1 to 4, wherein the volume resistivity is 1.5 Ω·cm or less.
6. An electromagnetic shielding material according to any one of claims 1 to 4, wherein no diffraction peaks attributable to the crystal structure of graphite are observed by X-ray diffraction measurement.
7. An electromagnetic wave shielding material according to any one of claims 1 to 4, wherein the material is amorphous.
8. Infrared spectroscopy revealed 800 cm －１ From 2000cm －１ An electromagnetic shielding material according to any one of claims 1 to 4, wherein no absorption peak is observed in the wavenumber range up to .
9. Infrared spectroscopy revealed 800 cm －１ From 4000cm －１ An electromagnetic shielding material according to any one of claims 1 to 4, wherein no absorption peak is observed in the wavenumber range up to [a certain frequency].
10. In Raman spectroscopy, 1580 ± 50 cm⁻¹ －１ and 1360 ± 50 cm －１ An electromagnetic shielding material according to any one of claims 1 to 4, wherein a peak is observed in the wavenumber region.
11. It comprises a substrate and an electromagnetic wave shielding layer deposited on the substrate, An electromagnetic wave shielding member wherein the electromagnetic wave shielding layer consists of fine fragments obtained by cutting the electromagnetic wave shielding material described in any one of claims 1 to 4, or powder obtained by crushing the electromagnetic wave shielding material.
12. A fabric comprising fibers made from a fired body of bamboo rayon-based fibers, The bending stiffness value is 0.0001 gf·cm² / cm or more and 1 gf·cm² / cm or less. In the frequency range of 500 MHz to 18 GHz, the electromagnetic wave absorption capacity measured by the coaxial tube method is 10% or more of the irradiated electromagnetic wave. A heat-generating fabric that can generate heat when exposed to electromagnetic waves.
13. A fabric comprising fibers made from a fired body of bamboo rayon-based fibers, Including woven or knitted fabrics of the aforementioned fibers, The porosity of the woven or knitted fabric of the aforementioned fibers is 30% or more and 50% or less. The average pore size of the woven or knitted fabric of the aforementioned fibers is 100 μm or more and 900 μm or less. In the frequency range of 500 MHz to 18 GHz, the electromagnetic wave absorption capacity measured by the coaxial tube method is 10% or more of the irradiated electromagnetic wave. A heat-generating fabric that can generate heat when exposed to electromagnetic waves.