JP5720358B2 - Radio wave suppression sheet, electronic device including the sheet, and radio wave suppression component - Google Patents

Description

  The present invention relates to a radio wave suppression sheet that exhibits excellent radio wave absorption performance and radio wave blocking performance with respect to low-frequency microwaves, an electronic device including the sheet, and a radio wave suppression component.

In recent years, electronic devices such as personal computers, mobile phones, personal digital assistants, road information systems, wireless LANs, etc. that use microwaves of relatively low frequency have been widely used. Malfunctions of other electronic devices caused by electromagnetic waves radiated from the devices and effects on the human body have been a problem.
For this reason, it is required that electromagnetic waves be not emitted as much as possible so that they do not affect other electronic devices and the human body, and that they do not malfunction even when receiving external electromagnetic waves. Many radio wave suppression sheets have been developed that can provide blocking performance (hereinafter referred to as radio wave shielding performance).

  For example, as shown in Patent Document 1, a radio wave suppression sheet in which a ferromagnetic material such as an iron alloy or ferrite is vapor-deposited on a substrate surface layer made of an organic polymer such as a polyolefin resin or an organic polymer made of rubber, or a patent As shown in Document 2, a radio wave suppression sheet containing a resin and a nanosize carbon raw material has been proposed.

  Recently, the electronic devices have been further miniaturized and densified, and thinner radio wave suppression sheets have been required for use by bonding and the like. However, since the radio wave shielding performance tends to decrease as the thickness of the sheet is reduced, a film-like sheet has not yet been put into practical use.

On the other hand, one of the evaluations of the radio wave shielding performance is a transmission attenuation factor (Rtp) by a microstrip method. It is said that this transmission attenuation rate (Rtp) is equivalent to absorbing radio waves of 99% at 20 dB, 99.9% at 30 dB, and 99.99% at 40 dB. It has been set to 20 dB.
However, the frequency and time of use of electronic devices tend to increase, and there has been a demand for the development of a radio wave suppression sheet with higher radio wave absorption capability that has less malfunction of electronic devices and less influence on the human body. In particular, electronic devices such as mobile phones, microwave ovens, wireless runs, and various remote controllers use relatively low frequency microwaves with a frequency of 5 GHz or less, but conventional radio wave suppression sheets have a frequency of 5 GHz or less. None of them was capable of absorbing microwaves at a rate of 99.99% (a transmission attenuation factor exceeding 40 dB). Therefore, it has been strongly desired to develop a radio wave suppression sheet that can absorb relatively low frequency microwaves having a frequency of 5 GHz or less.

JP 2005-101474 A JP 2003-158395 A

  The present invention solves the above-mentioned problems, and can cut down relatively low frequency microwaves having a frequency of 5 GHz or less with high absorption capability, thereby reducing malfunctions of electronic devices and effects on the human body. In addition, since it is a film-like sheet that is light and not bulky, it provides a radio wave suppression sheet that can cope with further miniaturization and high density of electronic devices, an electronic device equipped with this sheet, and radio wave suppression components It was completed for the purpose of doing.

The radio wave suppression sheet of the present invention made to solve the above-mentioned problem is obtained by dispersing carbon nanotubes in silicone rubber at a ratio of 15% by mass or more, and forming the film into a film having a thickness of 300 μm or less , In addition, a transmission attenuation factor by a microstrip method with respect to a microwave having a frequency of 5.0 GHz or less has a portion of 40 dB or more .

Furthermore, for wave suppression, characterized in that the invention according an electronic apparatus characterized by comprising a radio wave suppression sheet according to claim 1 to claim 2, equipped with a radio wave suppression sheet according to claim 1 The component is an invention according to claim 3 .

  In the invention according to claim 1, since the carbon nanotubes are dispersed in the silicone rubber and formed into a film having a thickness of 300 μm or less, the carbon nanotubes exhibit high radio wave shielding performance, and the carbon nanotubes are fine. Therefore, even if the film is formed into a film having a thickness of 300 μm or less, high radio wave shielding performance can be exhibited.

Moreover, since the content of the carbon nanotube is set to 15% by mass or more, high radio wave shielding performance can be exhibited.

Moreover, since the transmission attenuation rate by the microstrip method for microwaves having a frequency of 5.0 GHz or less has a portion of 40 dB or more, relatively low frequency microwaves can be absorbed with high capability, It is possible to minimize the malfunction of electronic devices and the influence on the human body as much as possible.

Moreover, in the invention which concerns on Claim 2 and Claim 3 , high electromagnetic wave shielding performance can be exhibited as an electronic device and a component for electromagnetic wave suppression.

It is a graph which shows the relationship between the frequency (GHz) and transmission attenuation factor (dB) in Example 1 of this invention. It is a graph which shows the relationship between the frequency (GHz) and transmission attenuation factor (dB) in Example 2 of this invention. It is a graph which shows the relationship between the frequency (GHz) and transmission attenuation factor (dB) in Example 3 of this invention. It is a graph which shows the relationship between the frequency (GHz) and transmission attenuation factor (dB) in Example 4 of this invention. It is a graph which shows the relationship between the frequency (GHz) and transmission attenuation factor (dB) in Example 5 of this invention. It is a graph which shows the relationship between the frequency (GHz) and transmission attenuation factor (dB) in Example 6 of this invention. It is a graph which shows the relationship between the frequency (GHz) of the electromagnetic wave suppression sheet | seat of a prior art example, and a transmission attenuation factor (dB).

Hereinafter, preferred embodiments of the present invention will be described.
The radio wave suppression sheet of the present invention is characterized in that carbon nanotubes are dispersed in silicone rubber and formed into a film having a thickness of 300 μm or less.
In the present invention, silicone rubber is used as a base material for forming the sheet. Conventionally, it has been usual to use a resin-based material such as natural rubber, ethylene-propylene rubber, polyolefin resin, or polyamide resin as a sheet base material. However, according to the inventor's research, it has been confirmed that it is difficult to disperse the electromagnetic wave absorbing material and form a thin film with a thickness of 300 μm or less by using a conventional resin material. Is due to the finding that silicone rubber is optimal.
The sheet of the present invention is in the form of a film having a thickness of 300 μm or less. In the case of a sheet made of a conventional resin material, the sheet is formed as a sheet body having a thickness of 600 μm or more by press molding, whereas the present invention is formed as a thin film having a thickness of 300 μm or less by an extrusion inflation method or the like. Yes. Although there is no restriction on the lower limit, it is 10 μm or more considering the film forming technique.

In the present invention, carbon nanotubes are used as the electromagnetic wave absorbing material in place of the conventional mixture of carbon fiber and carbon black.
This carbon nanotube is composed of a single layer or multiple layers, has a diameter of 1 to 100 nm, a length of 30 μm or less, and is a finer material than conventional carbon fibers and carbon black. Further, it has excellent dispersibility in silicone rubber and exhibits high radio wave shielding performance.

  The content of the carbon nanotube in the sheet is preferably 15% by mass or more. This is because if it is less than 15% by mass, the desired radio wave shielding performance may not be obtained. The upper limit is in the range of 40% by mass or less, preferably 30% by mass or less considering the molding of the thin film and the molding cost.

The sheet of the present invention having the above-described configuration has a portion with a transmission attenuation factor of 40 dB or more by a microstrip method with respect to a microwave having a frequency of 5.0 GHz or less. And high radio wave absorption performance and radio wave shielding performance (radio wave shielding performance) for electronic devices such as various remote controls.
The transmission attenuation rate (Rtp) by the microstrip method is one of the methods for evaluating the noise suppression of the radio wave suppression sheet, and represents how much the conduction noise transmitted through the transmission line is attenuated when the sheet is mounted. Briefly explaining the measurement method, a measurement sample is placed on the microstrip line, a load of 500 g is applied from above, a high frequency signal is incident, and how much the signal is attenuated by the measurement sample (radio wave suppression sheet). To evaluate. The transmission attenuation factor (Rtp) can be obtained by taking the difference between incidence and reflection and calculating the ratio between the value and the amount of transmission, and this value is an index indicating how much signal the measurement sample has attenuated (absorbed). Become.

  As an embodiment of the present invention, an electronic apparatus including the radio wave suppression sheet can be provided. Specific examples include a case of an electronic device, a circuit board, a printed wiring board, an electronic element, an LSI, an IC chip, a cable, and the like. The electronic device of the present invention is equipped with the radio wave suppression sheet in the electronic device. -Obtained by wearing.

  As an embodiment of the present invention, a radio wave suppression component including the radio wave suppression sheet can be provided. Radio wave suppression components are substrates, storage containers, lids, packaging, etc. that are used to suppress radio waves generated by mounting and mounting on the electronic equipment. Specific examples include circuit boards and printed wiring. It is used as a board, storage container, lid, packaging, etc. for electronic devices such as plates, electronic elements, LSIs, IC chips, and cables.

Next, examples of the present invention will be described.
Carbon nanotubes were dispersed in corn rubber to form a film having a thickness of 100 to 300 μm. The thickness of the film and the content of carbon nanotubes were changed as in Examples 1 to 6 as follows, and the transmission attenuation rate (Rtp) of the obtained radio wave suppression sheet by the microstrip method was measured.
Example 1 (film thickness: 300 μm, carbon nanotube content: 15 mass%)
Example 2 (film thickness: 300 μm, carbon nanotube content: 30% by mass)
Example 3 (film thickness: 200 μm, carbon nanotube content: 15% by mass)
Example 4 (film thickness: 200 μm, carbon nanotube content: 30% by mass)
Example 5 (film thickness: 100 μm, carbon nanotube content: 15% by mass)
Example 6 (film thickness: 100 μm, carbon nanotube content: 30% by mass)
The measurement results of Examples 1 to 6 are shown in FIGS. From these graphs, it was confirmed that in Example 1, a microwave having a frequency of about 2.3 GHz or more can be absorbed with a transmission attenuation rate of 40 dB or more (absorption rate of 99.99% or more). In Example 2, the frequency is about 1.8 GHz or more, in Example 3, the frequency is about 2.8 GHz or more, in Example 4, the frequency is about 1.7 GHz or more, and in Example 5, the frequency is about 4.2 GHz or more. In Example 6, it was confirmed that microwaves having a frequency of about 1.8 GHz or more can be absorbed at a transmission attenuation rate of 40 dB or more.

On the other hand, as a comparative example, a radio wave suppression sheet having a film thickness of 600 μm and a carbon nanotube content of 10% by mass was formed, and the result of measuring the transmission attenuation factor (Rtp) by the microstrip method is shown in FIG.
From the graph of FIG. 7, the sheet of the comparative example has a transmission attenuation factor of 40 dB or less by a microstrip method for a microwave having a frequency of 5.0 GHz or less, and cannot exhibit the high radio wave shielding performance as in the present invention. I was able to confirm.

Claims (3)

Transmission attenuation by a microstrip method for microwaves having a carbon nanotube content dispersed in silicone rubber at a rate of 15% by mass or more , molded into a film with a thickness of 300 μm or less , and a frequency of 5.0 GHz or less A radio wave suppression sheet having a portion with a rate of 40 dB or more .   An electronic apparatus comprising the radio wave suppression sheet according to claim 1.   A radio wave suppression component comprising the radio wave suppression sheet according to claim 1.

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