Electromagnetic wave absorption body, composition for electromagnetic wave absorption body molding, and composite filler for electromagnetic wave absorption body molding

Abstract

To provide an electromagnetic wave absorption body capable of obtaining satisfactory electromagnetic wave absorption characteristics in "Low / Mid bands", a composition for electromagnetic wave absorption body molding for forming the same, and a composite filler for electromagnetic wave absorption body molding.SOLUTION: Disclosed is a composition for electromagnetic wave absorption body molding including: a polymer containing at least an acrylic acid ester copolymer as a main component; and a composite filler comprising a conductive filler which is coated with silicon oxide, consequently, formed with a an insulating membrane, wherein the conductive filler is kneaded in the polymer into a dispersion state and contains at least one kind of carbon material selected from among a carbon micro coil, a carbon nano fiber, a carbon nano tube and active carbon. Further disclosed is an electromagnetic wave absorption body which is made of the composition for electromagnetic wave absorption body molding through molding and hardening in a state where the composite filler is dispersed in the polymer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave absorber, an electromagnetic wave absorber molding composition for constituting the electromagnetic wave absorber, and a composite filler for molding the electromagnetic wave absorber that is mixed in when molding the electromagnetic wave absorber. [Background technology]

[0002] Generally, in fifth-generation mobile communication systems, the 3.7GHz / 4.5GHz band, known as "Sub-6," and the 28GHz band, known as "millimeter wave (mmW)," are allocated to fulfill three roles: high speed, large capacity, ultra-low latency, and multiple simultaneous connections. Furthermore, with the 6th generation mobile communication system, it is expected that bands that overlap with 5G, called "Low / Mid-band," and bands that are much higher than 5G, called "High-band," will be used. In such mobile communication systems, various electronic devices used are constructed using electromagnetic wave absorbing materials in order to suppress the effects of malfunctions and the like caused by electromagnetic waves generated during communication.

[0003] Conventionally, examples of such electromagnetic wave absorbing materials include porous electromagnetic wave absorbers containing conductive fillers such as carbon microcoils (see, for example, Patent Document 1), and coating agents containing conductive fillers such as carbon microcoils, which are applied and dried to form a coating layer capable of absorbing electromagnetic waves (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-23142 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-172152 Summary of the Invention [Problem to be solved by the invention]

[0005] However, among the above-mentioned conventional electromagnetic wave absorbing materials, the porous electromagnetic wave absorber described in Patent Document 1 exhibits good electromagnetic wave absorption properties in the 7 to 18 GHz range, which is the "low / mid-band" being considered for the sixth-generation mobile communication system. However, because the electromagnetic wave absorber must be porous, it cannot be used for applications such as constructing the housings of various communication devices that require strength. Therefore, while it is possible to form the absorber into a sheet and attach it to the housing, this would require additional space for electromagnetic wave absorption in communication devices that are designed to be compact in millimeters, such as mobile phones. Furthermore, even if the absorber is made into a sheet, when used in the housings of such electronic devices, the porous electromagnetic wave absorber described in Patent Document 1 easily allows dust and dirt to enter the voids, easily causing contamination problems.

[0006] Furthermore, in the case of the electromagnetic wave absorbing material disclosed in Patent Document 2, good electromagnetic wave absorption properties are not obtained in the "low / mid-band" range of 7 to 18 GHz, which is the target of consideration for the sixth generation mobile communication system.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an electromagnetic wave absorber that can obtain good electromagnetic wave absorption properties in the "low / mid-band" and can be suitably used in various electronic devices, as well as an electromagnetic wave absorber molding composition for forming the same, and a composite filler for molding an electromagnetic wave absorber. [Means for solving the problem]

[0008] The electromagnetic wave absorber molding composition of the present invention, which solves the above-mentioned problems, comprises a polymer made of a thermoplastic resin, and a composite filler in which an insulating coating is formed by coating a conductive filler containing at least one carbon material selected from carbon microcoils, carbon nanofibers, carbon nanotubes, and activated carbon with silicon oxide.

[0009] The composition for molding an electromagnetic wave absorber may be such that the carbon material is carbon microcoils and the mass of silicon oxide in the composite filler is 4.19 to 54.22%.

[0010] The composition for molding an electromagnetic wave absorber may be such that the carbon material is carbon nanofiber and the mass of silicon oxide in the composite filler is 4.18 to 55.17%.

[0011] The electromagnetic wave absorber molding composition may be one in which the carbon material is activated carbon and the mass of silicon oxide in the composite filler is 44.25 to 57.54%.

[0012] In the electromagnetic wave absorber molding composition, the conductive filler may consist solely of a carbon material.

[0013] In the electromagnetic wave absorber molding composition, the conductive filler may be a carbon material whose surface is coated with aluminum.

[0014] The electromagnetic wave absorber molding composition may be composed of 20% by mass of a composite filler and 80% by mass of a polymer.

[0015] The electromagnetic wave absorber according to the present invention, which solves the above-mentioned problems, comprises a polymer made of a thermoplastic resin, and a composite filler in which a conductive filler containing at least one carbon material selected from carbon microcoils, carbon nanofibers, carbon nanotubes, and activated carbon is coated with silicon oxide to form an insulating coating, and the two are kneaded together, and then molded and cured in a state in which the composite filler is dispersed in the polymer.

[0016] The electromagnetic wave absorber may be one in which the carbon material is carbon microcoils and the mass of silicon oxide in the composite filler is 4.19 to 54.22%.

[0017] The electromagnetic wave absorber may be one in which the carbon material is carbon nanofiber and the mass of silicon oxide in the composite filler is 4.18 to 55.17%.

[0018] The electromagnetic wave absorber may be one in which the carbon material is activated carbon and the mass of silicon oxide in the composite filler is 44.25 to 57.54%.

[0019] In the electromagnetic wave absorber, the conductive filler may consist solely of a carbon material.

[0020] In the above-mentioned claim 8, the conductive filler may be a carbon material whose surface is coated with aluminum.

[0021] The electromagnetic wave absorber may be composed of 20% by mass of a composite filler and 80% by mass of a polymer.

[0022] The electromagnetic wave absorber may have an absorption characteristic of −13.26 dB or more in the range of 7 to 18 GHz.

[0023] The electromagnetic wave absorber may have a real part of a complex relative permittivity in the range of 7 to 18 GHz of 7.01 to 21.70.

[0024] The electromagnetic wave absorber may have a dielectric loss tangent of 0.12 to 0.64 at 7 to 18 GHz.

[0025] The electromagnetic wave absorber may have a volume resistivity of 3.96 to 1450.08 Ω·m.

[0026] The electromagnetic wave absorber may be one in which the carbon material is in the form of carbon microcoils and has a thickness of 1.30 to 2.15 mm.

[0027] The carbon material of the electromagnetic wave absorber may be carbon nanofiber, and the thickness may be 1.20 to 1.75 mm.

[0028] The carbon material of the electromagnetic wave absorber may be activated carbon, and the thickness may be 1.55 to 2.06 mm.

[0029] The composite filler for an electromagnetic wave absorber of the present invention, which solves the above-mentioned problems, is a filler that is kneaded into a polymer made of a thermoplastic resin, and is configured to form an electromagnetic wave absorber by molding and curing the polymer in a dispersed state in the polymer, and is a filler for an electromagnetic wave absorber in which an insulating coating is formed by coating a conductive filler containing at least one carbon material selected from carbon microcoils, carbon nanofibers, carbon nanotubes, and activated carbon with silicon oxide.

[0030] The composite filler for an electromagnetic wave absorber may be such that the carbon material is carbon microcoils and the mass of silicon oxide in the composite filler is 4.19 to 54.22%.

[0031] The composite filler for an electromagnetic wave absorber may be one in which the carbon material is carbon nanofiber, and the mass of silicon oxide in the composite filler is 4.18 to 55.17%.

[0032] The composite filler for an electromagnetic wave absorber may be one in which the carbon material is activated carbon and the mass of silicon oxide in the composite filler is 44.25 to 57.54%.

[0033] In the composite filler for an electromagnetic wave absorber, the conductive filler may consist of only a carbon material.

[0034] In the composite filler for an electromagnetic wave absorber, the conductive filler may be a carbon material whose surface is coated with aluminum.

[0035] The electromagnetic wave absorber molding composition is composed of a polymer and a composite filler.

[0036] Examples of the polymer include various thermoplastic resins such as polymethyl methacrylate (PMMA), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), acrylonitrile butadiene styrene resin (ABS), etc. These polymers may be in the form of powder, a solution in a solvent, or a polymer emulsion.

[0037] The composite filler is constructed by coating the surface of a conductive filler with silicon oxide to form an insulating film.

[0038] As the conductive filler, a carbon material or a carbon material whose surface is coated with aluminum can be used.

[0039] The carbon material can be formed into various shapes such as carbon microcoils, carbon nanotubes, carbon nanofibers, activated carbon, etc. The size is preferably 1 to 100 μm.

[0040] Silicon oxide is coated on the surface of the conductive filler so as to form an insulating coating of silicon oxide. This insulating coating can be formed by vapor-depositing silicon oxide on the surface of the conductive filler. A specific vapor deposition method for forming the insulating coating of silicon oxide involves, for example, placing tetraethoxysilane (hereinafter referred to as "TEOS") in an open-topped container, sealing the container together with the conductive filler in a sealed container, heating the sealed container to a temperature above the boiling point of TEOS, filling the sealed container with saturated TEOS vapor, and then cooling to form an insulating coating of silicon oxide on the surface of the conductive filler. This process of forming the insulating coating of silicon oxide may be performed once, or may be performed multiple times by repeating the process two to four times. The amount of silicon oxide coated on the surface of the conductive filler can be calculated by measuring the increase in the amount of conductive filler. The amount of silicon oxide coating is not particularly limited, but it has been confirmed that when the carbon material constituting the conductive filler is carbon microcoils, good results are obtained when the amount is 4.19% by mass to 54.22% by mass. Also, when the carbon material constituting the conductive filler is carbon nanofibers, good results are obtained when the amount is 4.18% by mass to 55.17% by mass. Furthermore, when the carbon material constituting the conductive filler is activated carbon, good results are obtained when the amount is 44.25% by mass to 57.54% by mass.

[0041] Another vapor deposition method for forming an insulating coating of silicon oxide may involve placing a conductive filler in the above-mentioned sealed container, dropping TEOS directly into it, sealing the container, and then heating the sealed container to a temperature equal to or higher than the boiling point of TEOS, filling the sealed container with saturated vapor of TEOS, and leaving it to stand, followed by cooling to form an insulating coating of silicon oxide on the surface of the conductive filler. This vapor deposition method can form a large amount of insulating coating of silicon oxide in a single treatment, but the former vapor deposition method can vapor-deposit a larger amount of silicon oxide.

[0042] When the surface of a carbon material is coated with aluminum as the conductive filler, an insulating film of silicon oxide can be formed by treating the surface of the carbon material in the same manner with this conductive filler.

[0043] The electromagnetic wave absorber molding composition is formed by mixing the polymer and the composite filler. The mixing ratio of the polymer and the composite filler is not particularly limited, but a ratio of 80% by mass of polymer to 20% by mass of composite filler is most preferred, and it is preferable to keep the ratio within a range of ±10% by mass from this range. If the polymer content exceeds this range, the composite filler's full effect cannot be obtained, while if the polymer content is too low, it becomes difficult to mold a thin electromagnetic wave absorber in order to control the effect of the composite filler. The electromagnetic wave absorber molding composition may be provided in a powder state in which a pulverized polymer and the composite filler are mixed together; in a paste state in which the polymer is dissolved in a solvent and the composite filler is thoroughly mixed with the polymer; or in a polymer emulsion in which the composite filler is added and mixed. Alternatively, the composition may be provided in the form of pellets of the polymer and the composite filler. However, in the case of a pelletized polymer, it is necessary to thoroughly knead the heat-molten polymer and the composite filler during heat molding to bring the composite filler into a sufficiently dispersed state. This electromagnetic wave absorber molding composition can be processed into the desired shape of an electromagnetic wave absorber by heat molding.

[0044] The electromagnetic wave absorber is formed into a desired shape, but the shape is not particularly limited and may be one that constitutes the housing of various electronic devices. It may also be formed into a film that can be attached to the inside of such a housing. In particular, when the thickness and strength of the housing are specified, these may not be achieved simply by constructing the housing with an electromagnetic wave absorber, so it is preferable to attach it in the form of a film. In particular, when considering the function as an electromagnetic wave absorber, performance is adjusted by thickness, so it is easier to adjust performance by forming it into a film and attaching it separately from the housing. In addition, to achieve absorption performance, a metal must be installed on the backside, but the thickness is not limited, and it can be a metal plate or metal foil.

[0045] The electromagnetic wave absorber constructed in this manner can achieve absorption characteristics of -13.26 dB or more in the low mid-band of 7 to 18 GHz. In this case, the electromagnetic wave absorber has a real part of the complex relative permittivity of 7.01 to 21.70, a dielectric dissipation factor of 0.12 to 0.64, and a volume resistivity of 3.96 to 1450.08 Ω m in the low mid-band of 7 to 18 GHz.

[0046] Furthermore, the frequency at which the absorption characteristics are best exhibited in the low-mid band can be adjusted by changing the thickness of the electromagnetic wave absorber. For example, if the carbon material constituting the conductive filler is carbon microcoil, the thickness is preferably 1.3 to 2.15 mm, if it is carbon nanofiber, the thickness is preferably 1.2 to 1.75 mm, and if it is activated carbon, the thickness is preferably 1.55 to 2.06 mm.

[0047] The electromagnetic wave absorber molding composition thus formed can be suitably used in the sixth generation mobile communication system. [Brief explanation of the drawings]

[0048] [Figure 1]1 is a graph showing the relationship between the thickness of the electromagnetic wave absorber according to the present invention and the maximum absorption frequency, where (a) and (b) are those using carbon microcoils as the carbon material constituting the conductive filler, (c) is one using carbon nanofibers, and (d) is one using activated carbon. [Figure 2] Graphs (a) and (b) show the relationship between the real part of the complex relative permittivity and frequency and the relationship between the dielectric loss tangent and frequency for the electromagnetic wave absorber according to Example 26, (c) and (d) show the same graphs for the electromagnetic wave absorber according to Example 28, and (e) and (f) show the same graphs for the electromagnetic wave absorber according to Example 29. [Figure 3] Graphs (a) and (b) show the relationship between the real part of the complex relative permittivity and frequency and the relationship between the dielectric loss tangent and frequency for the electromagnetic wave absorber according to Example 30, (c) and (d) show the same graphs for the electromagnetic wave absorber according to Example 31, and (e) and (f) show the same graphs for the electromagnetic wave absorber according to Example 32. [Figure 4] Graphs (a) and (b) show the relationship between the real part of the complex relative permittivity and frequency and the relationship between the dielectric loss tangent and frequency for the electromagnetic wave absorber according to Example 33, (c) and (d) show the same graphs for the electromagnetic wave absorber according to Example 34, and (e) and (f) show the same graphs for the electromagnetic wave absorber according to Example 35. [Figure 5] 10(a) and 10(b) are graphs showing the relationship between the real part of the complex relative permittivity and frequency and the relationship between the dielectric loss tangent and frequency of the electromagnetic wave absorber according to Example 36. [Figure 6] Graphs (a) and (b) show the relationship between the real part of the complex relative permittivity and frequency and the relationship between the dielectric loss tangent and frequency for the electromagnetic wave absorber according to Example 37, (c) and (d) show the same graphs for the electromagnetic wave absorber according to Example 38, and (e) and (f) show the same graphs for the electromagnetic wave absorber according to Example 39. [Figure 7] Graphs (a) and (b) show the relationship between the real part of the complex relative permittivity and frequency and the relationship between the dielectric loss tangent and frequency for the electromagnetic wave absorber according to Example 40, (c) and (d) show the same graphs for the electromagnetic wave absorber according to Example 41, and (e) and (f) show the same graphs for the electromagnetic wave absorber according to Example 42. [Figure 8] Graph (a) shows the relationship between the difference tb-ta of each optimum thickness calculated from the real and imaginary parts of the complex dielectric constant of Example 26 and frequency, graph (b) shows the same for Example 34, graph (c) shows the same for Example 36, graph (d) shows the same for Example 37, and graph (e) shows the same for Example 41. DETAILED DESCRIPTION OF THE INVENTION

[0049] [Preparation of composite filler] -Examples 1 to 7- A 50 ml capacity hydrothermal synthesis vessel (HU-50 manufactured by San-Ai Scientific Co., Ltd.) was prepared, and 0.1 g of carbon microcoil (carbon microcoil manufactured by Microphase Co., Ltd., coil diameter 1 to 4 μm, length 10 to 100 μm) was placed as a carbon material into the PTFE sample vessel of the hydrothermal synthesis vessel. 600 μml of TEOS (manufactured by Nacalai Tesque, Inc.: tetraethyl orthosilicate (grade EP (Nacalai standard first class), purity 95%) was placed in a 6 ml glass container (Labolan screw tube (without lid)), and the glass container containing this TEOS was placed in the PTFE sample container containing the carbon material, and the PTFE sample container was then capped. The PTFE sample container was placed in the stainless steel outer cylinder of a hydrothermal synthesis vessel, and the stainless steel outer cylinder was sealed with a lid. The hydrothermal synthesis vessel in which the sample had been set was placed in a thermostatic chamber and heated. The heating conditions in the thermostatic chamber were as follows: the temperature was raised at a rate that reached 220°C in 22 minutes, followed by heating for 3 hours, and then natural cooling, followed by a single heating treatment, to obtain a composite filler for an electromagnetic wave absorber according to Example 1. This treatment was carried out once to four times to obtain composite fillers for electromagnetic wave absorbers according to Examples 1 to 7. When the treatment was performed two or more times, after each treatment, the lid was opened, the glass container inside the PTFE sample container was removed, and a new glass container containing 600 μml of TEOS was replaced, which was then sealed and the heat treatment was repeated in the same manner as above.

[0050] -Examples 8 to 11- Instead of putting 600 μml of TEOS into a glass container, instead of using a glass container, 600 μml of TEOS was dropped directly onto 0.1 g of carbon microcoil, the container was sealed, and the temperature was raised to 220°C as described above, followed by heating for 3 hours and natural cooling to obtain a composite filler for an electromagnetic wave absorber according to Example 8. The composite fillers for electromagnetic wave absorbers according to Examples 9, 10 and 11 were obtained in the same manner as in Example 8, except that the amount of TEOS dropped was 1800 μml, 3000 μml and 4800 μml.

[0051] -Examples 12 to 17- Except for changing the carbon microcoils of Example 1 to carbon nanofibers (reinforcing carbon nanofibers manufactured by Almedio Co., Ltd., average fiber length: 1 to 15 μm, average fiber diameter: 0.2 to 0.8 μm), the same treatment as in Example 1 was carried out once to three times to obtain composite fillers for electromagnetic wave absorbers according to Examples 12 to 17.

[0052] -Examples 18 to 22- The carbon microcoils of Example 1 were replaced with carbon nanofibers (reinforcing carbon nanofibers manufactured by Almedio Co., Ltd., average fiber length: 1 to 15 μm, average fiber diameter: 0.2 to 0.8 μm) and the amount of TEOS dropped was changed to 600 μml, 1200 μml, 1800 μml, 2400 μml, and 3000 μml, but the same treatment as in Example 8 was carried out to obtain composite fillers for electromagnetic wave absorbers according to Examples 18 to 22.

[0053] -Examples 23 to 25- Except for changing the carbon nanocoils in Example 1 to activated carbon (manufactured by Kuraray Co., Ltd.: average particle diameter 4.7 μm), the same treatment as in Examples 3 and 4 was carried out twice to obtain composite fillers for electromagnetic wave absorbers according to Examples 23 to 25.

[0054] [Analysis of composite fillers] For each of the composite fillers for electromagnetic wave absorbers obtained above, SEM images were measured using a scanning electron microscope and EDS analysis was also performed. This measurement was performed using a scanning electron microscope (JEOL Ltd.: JSM-6010LA) at an acceleration voltage of 15 kV in secondary electron mode. As a result, in addition to carbon, silicon and oxygen peaks were confirmed, confirming that the surface of the carbon material was coated with SiO2. The weights before and after treatment were measured, and the amount of SiO2 coating was calculated from the weight increase. The results are shown in Tables 1 to 3.

[0055] [Table 1]

[0056] [Table 2]

[0057] [Table 3]

[0058] [Preparation of electromagnetic wave absorber test specimens] -Examples 26 to 42, Comparative Examples 1 and 2- Polymethyl methacrylate (manufactured by Nacalai Tesque, Inc.) was dissolved in acetone, and the two were kneaded in a mortar for 15 minutes so that the ratio of the polymethyl methacrylate to the composite filler obtained in Example 1 was 80% by mass and 20% by mass, respectively. This kneaded composition was placed in a mold and molded into a disk shape of φ7 by a heat press to prepare an electromagnetic wave absorber test piece. In addition to the above-mentioned Example 1, the preparation of this electromagnetic wave absorber test piece was also carried out using each of the composite fillers of Examples 2, 3-6, 9, 11, 12, 14, 16, 23, 24, and 25. Furthermore, for some Examples, a plurality of disk-shaped electromagnetic wave absorber test pieces with different thicknesses were prepared. For comparison, an electromagnetic wave absorber test piece was prepared using only polymethyl methacrylate without using any composite filler as Comparative Example 1, and an electromagnetic wave absorber test piece was prepared using only carbon microcoils at a ratio of 20 mass % instead of the composite filler as Comparative Example 2.

[0059] [Volume resistivity measurement] Each of the electromagnetic wave absorber test pieces obtained above was sandwiched between a pair of electrodes on both sides, and the resistance value was measured by the two-terminal method, and the volume resistivity was calculated from the measured value. The resistance value was measured using a digital multimeter (Agilent Technologies 34401A). The volume resistivity (Pv) was calculated from Pv = Rv × (S / L) [Ω·m], where Rv is the volume resistivity, S is the cross-sectional area, and L is the length.

[0060] [Measurement of return loss] A hole of φ3.04 was drilled in the center of the electromagnetic wave absorber test piece obtained above, and the piece was machined into a doughnut shape to obtain an electromagnetic wave absorber test piece for measuring return loss. The electromagnetic wave absorber test piece thus obtained was set in a coaxial tube sample holder (CSF-APC7 manufactured by EM Lab), and the return loss was measured using a vector network analyzer (P5024A manufactured by Keysight Technologies). The measurement frequency was 500 MHz to 18 GHz, and the measurement points were 401. The return loss was measured by placing a metal on the back surface of the sample so that all the incident signal was reflected. From the measurement results, the maximum reflection attenuation and its frequency were determined.

[0061] [Measurement of dielectric constant] The dielectric constant was measured by connecting to port 2 instead of shorting with metal in the return loss measurement above, measuring the reflected and transmitted waves, and calculating the value using software. The software used was Keysight Materials Measurement Suite N1500A, and the measurement model was the NIST Precision model.

[0062] [Relationship between maximum absorption of return loss and thickness] Various electromagnetic wave absorber test pieces with different thicknesses were created, and the maximum absorption of their return loss was measured to investigate the relationship with thickness. The results are shown in Table 4 and Figures 1(a) to 1(d). Note that in Table 4, there were some locations where data could not be collected due to measurement errors, and those locations are left blank.

[0063] [Table 4]

[0064] From the results in Table 4 and Figures 1(a) to 1(d), it was confirmed that each electromagnetic wave absorber test piece according to the examples has excellent absorption properties. Furthermore, the maximum absorption amount of the return loss is correlated with the thickness for each carbon material, and the thicker the thickness, the lower the frequency at which maximum absorption occurs, and the thinner the thickness, the higher the frequency at which maximum absorption occurs. It was therefore confirmed that by adjusting the thickness, absorption properties can be obtained at a desired frequency.

[0065] [Volume resistivity] The volume resistivity of each of the electromagnetic wave absorber test pieces selected from the above examples was measured, and the results are shown in Table 4 above. From the results in Table 4, it was confirmed that excellent absorption characteristics can be obtained when the volume resistivity is in the range of 3.96 to 1450.08 Ω·m.

[0066] [Complex relative permittivity] For each of the electromagnetic wave absorber test pieces selected from the above examples, the minimum value of the real part of the complex relative permittivity and the minimum and maximum values ​​of the dielectric loss tangent were also measured. The results are shown in Table 4 above and in Figures 2 to 7.

[0067] From the results in Table 4, it was confirmed that excellent absorption characteristics could be obtained when the real part of the complex relative permittivity had a minimum value in the range of 8.31 to 21.70.

[0068] [Calculation of optimal thickness from the non-reflection curve condition equation]

[0069]

number

[0070]

number

[0071]

number

[0072] [Table 5]

[0073] From the results in Table 5, it can be seen that when this difference is small, the balance between the real part and the imaginary part of the complex relative permittivity is good, and in the examples according to the present invention, excellent values ​​of 0.01 to 1.1 mm were obtained.

[0074] Furthermore, for some examples (Examples 26, 34, 36, 37, and 41), the change in the difference tb-ta of the optimum thickness at each frequency up to 18 GHz was plotted as a graph, and the results are shown in FIG. As a result, it was confirmed that stable values ​​were obtained in all frequency ranges. This confirmed that if a thickness close to the range of the optimum thickness ta to the optimum thickness tb is prepared, excellent frequency absorption characteristics can be obtained in all frequency ranges up to 18 GHz. As for this thickness, a thickness close to the range of the optimum thickness ta to the optimum thickness tb is sufficient, but a thickness close to the ta side is particularly preferable, and a thickness in the range of ta ± 0.17 mm is more preferable.

[0075] It should be noted that the present invention can be embodied in various other forms without departing from its spirit or essential features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited in any way by the text of the specification. Furthermore, all modifications and variations that fall within the scope of the claims are within the scope of the present invention.

Claims

1. a polymer made of a thermoplastic resin; a composite filler in which an insulating coating is formed by coating a conductive filler containing at least one carbon material selected from carbon microcoils, carbon nanofibers, carbon nanotubes, and activated carbon with silicon oxide; A composition for molding an electromagnetic wave absorber, comprising:

2. 2. The electromagnetic wave absorber molding composition according to claim 1, wherein the carbon material is carbon microcoils, and the mass of silicon oxide in the composite filler is 4.19 to 54.22%.

3. 2. The electromagnetic wave absorber molding composition according to claim 1, wherein the carbon material is carbon nanofiber, and the mass of silicon oxide in the composite filler is 4.18 to 55.17%.

4. 2. The electromagnetic wave absorber molding composition according to claim 1, wherein the carbon material is activated carbon, and the mass of silicon oxide in the composite filler is 44.25 to 57.54%.

5. 5. The electromagnetic wave absorber molding composition according to claim 1, wherein the conductive filler consists solely of a carbon material.

6. 5. The electromagnetic wave absorber molding composition according to claim 1, wherein the conductive filler is a carbon material whose surface is coated with aluminum.

7. 5. The electromagnetic wave absorber molding composition according to claim 1, which comprises 20% by mass of the composite filler and 80% by mass of the polymer.

8. a polymer made of a thermoplastic resin; a composite filler in which an insulating coating is formed by coating a conductive filler containing at least one carbon material selected from carbon microcoils, carbon nanofibers, carbon nanotubes, and activated carbon with silicon oxide; Equipped with The electromagnetic wave absorber is characterized in that it is obtained by kneading the two together, and molding and curing the mixture in a state in which the composite filler is dispersed in the polymer.

9. 9. The electromagnetic wave absorber according to claim 8, wherein the carbon material is carbon microcoils, and the mass of silicon oxide in the composite filler is 4.19 to 54.22%.

10. 9. The electromagnetic wave absorber according to claim 8, wherein the carbon material is carbon nanofiber, and the mass of silicon oxide in the composite filler is 4.18 to 55.17%.

11. 9. The electromagnetic wave absorber according to claim 8, wherein the carbon material is activated carbon, and the mass of silicon oxide in the composite filler is 44.25 to 57.54%.

12. 12. The electromagnetic wave absorber according to claim 8, wherein the conductive filler consists solely of a carbon material.

13. 12. The electromagnetic wave absorber according to claim 8, wherein the conductive filler is a carbon material whose surface is coated with aluminum.

14. 12. The electromagnetic wave absorber according to claim 8, which comprises 20% by mass of the composite filler and 80% by mass of the polymer.

15. 12. The electromagnetic wave absorber according to claim 8, which has an absorption characteristic of −13.26 dB or more in the range of 7 to 18 GHz.

16. 12. The electromagnetic wave absorber according to claim 8, wherein the real part of the complex relative permittivity in the range of 7 to 18 GHz is 7.01 to 21.

70.

17. 12. The electromagnetic wave absorber according to claim 8, wherein the dielectric loss tangent at 7 to 18 GHz is 0.12 to 0.

64.

18. 12. The electromagnetic wave absorber according to claim 8, which has a volume resistivity of 3.96 to 1450.08 Ω·m.

19. 10. The electromagnetic wave absorber according to claim 9, wherein the carbon material is in the form of carbon microcoils and has a thickness of 1.30 to 2.15 mm.

20. 11. The electromagnetic wave absorber according to claim 10, wherein the carbon material is carbon nanofiber and the thickness is 1.20 to 1.75 mm.

21. 12. The electromagnetic wave absorber according to claim 11, wherein the carbon material is activated carbon and the thickness is 1.55 to 2.06 mm.

22. A filler to be kneaded into a polymer made of a thermoplastic resin, The filler for an electromagnetic wave absorber is dispersed in the polymer and the polymer is molded and cured to form the electromagnetic wave absorber, A composite filler for an electromagnetic wave absorber, characterized in that an electrically conductive filler containing at least one carbon material selected from carbon microcoils, carbon nanofibers, carbon nanotubes, and activated carbon is coated with silicon oxide to form an insulating coating.

23. 23. The composite filler for an electromagnetic wave absorber according to claim 22, wherein the carbon material is carbon microcoils, and the mass of silicon oxide in the composite filler is 4.19 to 54.22%.

24. 23. The composite filler for an electromagnetic wave absorber according to claim 22, wherein the carbon material is carbon nanofiber, and the mass of silicon oxide in the composite filler is 4.18 to 55.17%.

25. 23. The composite filler for an electromagnetic wave absorber according to claim 22, wherein the carbon material is activated carbon, and the mass of silicon oxide in the composite filler is 44.25 to 57.54%.

26. 26. The composite filler for an electromagnetic wave absorber according to any one of claims 22 to 25, wherein the conductive filler consists solely of a carbon material.

27. 26. The composite filler for an electromagnetic wave absorber according to claim 22, wherein the conductive filler is a carbon material whose surface is coated with aluminum.

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