JP2009060060A - Electromagnetic wave absorbing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber capable of dealing with absorption of electromagnetic waves of several GHz to several dozens of GHz. <P>SOLUTION: An electromagnetic wave absorbing sheet contains a carbon nano-coil and a resin, wherein (1) the carbon nano-coil has an average coil length of ≥1 μm and <100 μm, an average coil diameter of ≥1 nm and <1 μm and an average coil pitch of ≥1 nm and <1 μm and (2) the carbon nano-coil is contained in a ratio of 1 to 10 pts.wt. based on 100 pts.wt. of the resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel electromagnetic wave absorbing sheet using carbon nanocoils.

  2. Description of the Related Art In recent years, various electromagnetic wave absorbing sheets that absorb electromagnetic waves corresponding to each have been provided due to the increase and diversification of communication devices such as mobile phones (Patent Document 1, etc.). For example, for electromagnetic wave absorption, an electromagnetic wave absorber using ferrite or the like, an electromagnetic wave absorber using carbon black or the like has been proposed.

However, these electromagnetic wave absorbers only absorb in a specific absorption wavelength range and cannot cope with a wide wavelength range. For example, an electromagnetic wave absorber using ferrite or the like absorbs a band of several GHz but cannot absorb a band of several tens of GHz. On the other hand, an electromagnetic wave absorber using carbon black or the like can absorb at several tens of GHz, but is not suitable for absorption in a band of several GHz.
JP 2004-140335 A

  Therefore, it is desired to provide an electromagnetic wave absorber that can cope with absorption of electromagnetic waves of several GHz to several tens GHz.

  As a result of intensive studies in view of the above prior art, the present inventors have found that the above problem can be solved by containing a specific amount of carbon nanocoils having a specific structure in the electromagnetic wave absorber, thereby completing the present invention. It came to do. That is, this invention concerns on the manufacturing method of the following electromagnetic wave absorption sheet and electromagnetic wave absorption sheet.

Item 1. An electromagnetic wave absorbing sheet containing carbon nanocoils and a resin,
(1) The carbon nanocoil has an average coil length of 1 μm to less than 100 μm, an average coil diameter of 1 nm to less than 1 μm, and an average coil pitch of 1 nm to less than 1 μm,
(2) The carbon nanocoil is contained in a ratio of 1 to 10 parts by weight with respect to 100 parts by weight of the resin.
An electromagnetic wave absorbing sheet.

  Item 2. Item 2. The electromagnetic wave absorbing sheet according to Item 1, wherein the carbon nanocoil has an average coil length of 10 µm to 40 µm, an average coil diameter of 1 nm to less than 1 µm, and an average coil pitch of 1 nm to less than 1 µm.

  Item 3. Item 2. The electromagnetic wave absorbing sheet according to Item 1, wherein the carbon nanocoil has an average coil length of 20 μm to 40 μm, an average coil diameter of 400 nm to less than 800 nm, and an average coil pitch of 400 nm to 800 nm.

  Item 4. Item 4. The electromagnetic wave absorbing sheet according to any one of Items 1 to 3, wherein the electromagnetic wave absorbing sheet has a thickness of 1 µm to 10 mm.

  Item 5. Item 5. The electromagnetic wave absorbing sheet according to any one of Items 1 to 4, wherein the carbon nanocoil is oriented in a surface direction of the electromagnetic wave absorbing sheet.

  Item 6. The electromagnetic wave absorbing sheet according to any one of Items 1 to 5, having an absorption band in which reflection loss is 10 dB or more in a frequency band of 6.1 GHz to 100 GHz.

  Item 7. Item 7. The electromagnetic wave absorbing sheet according to any one of Items 1 to 6, wherein a metal plate is laminated on one surface.

Item 8. A method for producing an electromagnetic wave absorbing sheet containing carbon nanocoils and a resin,
A step of mixing carbon nanocoils having an average coil length of 1 μm or more and less than 100 μm, an average coil diameter of 1 nm or more and less than 1 μm, and an average coil pitch of 1 nm or more and less than 1 μm with an organic solvent in which the resin is dissolved, and then evaporating the organic solvent;
The manufacturing method of the electromagnetic wave absorption sheet | seat provided with.

Electromagnetic wave absorbing sheet The electromagnetic wave absorbing sheet of the present invention is (1) the carbon nanocoil has an average coil length of 1 μm or more and less than 100 μm, an average coil diameter of 1 nm or more and less than 1 μm, and an average coil pitch of 1 nm or more and less than 1 μm, (2) The carbon nanocoil is contained in a ratio of 1 to 10 parts by weight with respect to 100 parts by weight of the resin.

  The carbon nanocoil contained in the electromagnetic wave absorbing sheet of the present invention has an average coil length of 1 μm or more and less than 100 μm, an average coil diameter of 1 nm or more and less than 1 μm, and an average coil pitch of 1 nm or more and less than 1 μm. Preferably, the average coil length is 10 μm to 40 μm, the average coil diameter is 1 nm to less than 1 μm, and the average coil pitch is 1 nm or more and less than 1 μm. Most preferably, the average coil length is 20 μm to 40 μm, the average coil diameter is 400 nm to less than 800 nm, and the average coil pitch is 400 nm to 800 nm. By setting it as this range, more electromagnetic waves can be absorbed and the electromagnetic wave absorption characteristic excellent with respect to the electromagnetic waves of the wide wavelength range of 1 GHz-100 GHz can be obtained. The electromagnetic wave absorption characteristics in the present invention are evaluated based on the return loss.

  The fiber diameter of the carbon nanocoil is not limited, but is usually about 1 nm to 500 nm, preferably about 50 nm to 300 nm.

  As for the average coil length of the carbon nanocoils of the present invention, 100 carbon nanocoils are arbitrarily selected, and 100 carbon nanocoils are imaged at a magnification of 2000 times with a scanning electron microscope (SEM). The average value of 100 when the coil length is measured visually. The average coil diameter, the average coil pitch, and the average fiber diameter are average values when observed with an SEM image (2000 times) of 100 carbon nanocoils arbitrarily selected in the same manner as the average coil length.

  The compounding amount of the carbon nanocoil in the electromagnetic wave absorbing sheet of the present invention is about 1 to 10 parts by weight, preferably about 3 to 5 parts by weight with respect to 100 parts by weight of the resin. When the amount is less than 1 part by weight, the electromagnetic wave is not sufficiently absorbed. On the other hand, when the amount exceeds 10 parts by weight, the electromagnetic wave is reflected without being absorbed.

  In the present invention, in the electromagnetic wave absorbing sheet, the carbon nanocoils are preferably oriented (plane orientation) in the plane direction of the electromagnetic absorbing sheet. For example, as shown in the left figure of FIG. 1, it is preferable that the axial direction (straight line) of the carbon nanocoil is present on the plane (XY plane) of the electromagnetic wave absorbing sheet. More specifically, the number of carbon nanocoils in which the angle formed between the axial direction of the carbon nanocoils and the plane of the electromagnetic wave absorbing sheet is 10 ° or less is 50% of the total number of carbon nanocoils included in the electromagnetic wave absorbing sheet. It is preferable that it is above (especially 80% or more). In addition, as long as it is orientating in the plane direction (XY plane) like the left figure of FIG. 1, it does not necessarily need to orient (uniaxial orientation) to one direction.

  Resin used for the said electromagnetic wave absorption sheet is not limited, For example, either a thermoplastic resin and a thermosetting resin may be sufficient, and the elastomer which is an elastic material may be sufficient. Among these, a thermoplastic resin that is particularly soluble in an organic solvent is preferable. Specifically, for example, polyvinyl alcohol (PVA), polyethylene (PE), polycarbonate (PC), polypropylene (PP), etc., in addition to styrene resin, acrylic resin, and urethane resin. Of these, styrene resins and urethane resins are particularly preferable.

  In addition, the electromagnetic wave absorbing sheet of the present invention may contain additives such as carbon black, carbon nanotubes, carbon materials such as VGCF, and magnetic materials such as ferrite, if necessary.

  The thickness of the electromagnetic wave absorbing sheet is usually 25 mm or less, preferably 10 mm or less, more preferably about 5 mm or less. This makes it possible to reduce the weight and size. The lower limit is not limited, but may be about 1 μm, for example.

  In addition, as for the electromagnetic absorption sheet of this invention, the metal plate may be laminated | stacked on one surface of the sheet | seat surface as needed. The kind of metal is not limited, and a known or commercially available metal can be used. Examples thereof include aluminum, iron, copper, nickel, and alloys and metal compounds thereof. The thickness of the metal plate is not limited, and can be set widely depending on the use application of the electromagnetic wave and the sheet, but it is usually about 1 μm to 10 mm.

  The electromagnetic wave absorbing sheet of the present invention has at least a part of a high absorption band with a reflection loss of 10 dB or more (particularly 20 dB or more) in an absorption wavelength region of 1 GHz to 100 GHz. In particular, the high absorption band can have a width of about 1 Hz to 10 GHz (particularly 1 GHz to 10 GHz).

  Further, the electromagnetic wave absorbing sheet of the present invention can have the desired absorption band by easily changing the above-described desired absorption band by appropriately changing the thickness of the electromagnetic wave absorbing sheet by, for example, an adjusting method described later.

Production Method The electromagnetic wave absorbing sheet of the present invention can be produced , for example, by mixing carbon nanocoils in an organic solvent in which a resin is dissolved, and then evaporating the organic solvent.

  For the carbon nanocoil of the present invention, a known or commercially available carbon nanocoil may be used. For example, an alumina substrate carrying a catalyst for carbon nanocoil (hereinafter referred to as “alumina substrate with catalyst”) at 100 to 1000 ° C. ( It is preferably applied by a thermal CVD (Chemical Vapor Deposition) method in which a heated gas is heated to about 500 to 800 ° C. and a mixed gas of a hydrocarbon such as acetylene and an inert gas is sprayed onto the heated alumina substrate with catalyst. Can be manufactured.

For the carbon nanocoil catalyst, for example, an indium / tin / iron catalyst is preferably used. Examples of such indium / tin / iron-based catalysts include metal hydrochlorides, and specific examples include iron chloride such as iron trichloride (FeCl ₃ ), indium chloride such as indium trichloride (InCl ₃ ), A mixed oxide obtained by calcining a precipitate produced by a coprecipitation method from a mixed solution with tin chloride such as tin chloride (SnCl ₂ ) at 300 to 1000 ° C. (preferably 500 to 900 ° C.) is preferably used. Further, as the indium / tin / iron-based catalyst, metal nitrate, metal sulfate, or metal organic acid salt may be used in addition to the metal hydrochloride described above. In addition, powders, such as metal oxides, such as iron oxide, an indium oxide, and a tin oxide, may be mixed with such a catalyst, for example. Further, as a catalyst for carbon nanocoil, in addition to the above-mentioned indium / tin / iron-based ternary catalyst, a catalyst not containing indium oxide, for example, a tin / iron-based binary catalyst, specifically, A binary catalyst of iron oxide and tin oxide may be used.

  Examples of the solvent of the mixed solution include water, isopropyl alcohol (IPA), and alcohols such as ethanol.

  Examples of the inert gas include helium and argon.

  The carbon nanocoil coil is controlled by controlling the composition, growth time, heating temperature of the alumina substrate with the catalyst, hydrocarbon type, hydrocarbon concentration and flow rate, etc., when producing the catalyst by the thermal CVD method. The length, coil diameter, coil pitch, etc. can be appropriately controlled.

  In addition, for example, by irradiating the carbon nanocoil with ultrasonic waves or the like, it is possible to shorten the coil length or the like and change the properties of the carbon nanocoil.

  Examples of the carbon nanocoil and the resin include those described above. The organic solvent is not limited as long as it dissolves the resin, and is appropriately determined according to the type of the resin. Examples thereof include chloroform, methyl ethyl ketone (MEK), toluene, and tetrahydrofuran (THF). Among these, chloroform and the like are preferable from the viewpoint of ease of dissolution of the resin and suppression of bubble generation during evaporation.

  The resin content (resin solid content) in the organic solvent is not limited. For example, it is 1 to 25 parts by weight, preferably about 1 to 10 parts by weight with respect to 100 parts by weight of the total amount of the organic solvent and the resin. do it.

  What is necessary is just to carry out so that content of a carbon nanocoil may become the compounding quantity of the electromagnetic wave absorption sheet mentioned above.

  The organic solvent is preferably evaporated by natural evaporation, that is, by standing in an air atmosphere (for example, about 10 to 30 ° C.). Thereby, since the organic solvent is gradually evaporated, the carbon nanocoils in the electromagnetic wave absorbing sheet obtained by solidifying the resin by evaporation can easily lie on the horizontal plane, and thus can be easily oriented in the plane direction.

  The standing time is appropriately determined according to the type, concentration, and the like of the organic solvent, but is usually determined from a wide range of about 1 to 24 hours.

  In addition, the electromagnetic wave absorbing sheet of the present invention includes various other known means such as a solution mixing method, a heat-kneading method, a method of curing after forming a prepreg, and a method of dispersing the coil in a resin emulsion or suspension and drying it. Can be used by dispersing the carbon nanocoil in a resin.

Adjusting method of thickness The adjusting method of the electromagnetic wave absorbing sheet thickness of the present invention is represented by the following formula (1).

(Where λ represents the wavelength of the incident electromagnetic wave, ε _γ represents the complex dielectric constant, d represents the thickness of the electromagnetic wave and the sheet, and j represents the imaginary unit.)
Alternatively, by using an expression derived from the expression (1), two curves (a curve indicating a real part (ε _γ ′) of a complex relative dielectric constant and an imaginary part (ε _γ ″) of a complex relative dielectric constant) The curve d) is displayed on the same graph, and then the thickness d at the intersection of the two curves is obtained, and the electromagnetic wave absorbing sheet is adjusted so as to be the obtained thickness d. As a result, the relationship between the thickness of the electromagnetic wave absorbing sheet and the frequency (absorption peak) of the electromagnetic wave that the sheet absorbs most efficiently can be easily determined from the graph, and thus an electromagnetic wave absorbing sheet having excellent electromagnetic wave absorption characteristics can be obtained. It can be easily manufactured. Hereinafter, the thickness adjusting method will be described in detail below.

  In FIG. 2, the thickness is d and the complex dielectric constant is

Where ε _γ ′ represents the real part of the complex relative dielectric constant, ε _γ ″ represents the imaginary part of the complex relative dielectric constant, and j represents the imaginary unit. The metal plate backed by the absorption sheet is shown. In the thickness adjusting method of the present invention and the measurement related thereto, the metal plate may be laminated (backed) or may not be laminated.

  When electromagnetic waves are perpendicularly incident on the radio wave absorbing sheet as shown in FIG. 2, the condition that the electromagnetic wave absorbing sheet is non-reflective is the following formula (2)

Where λ is the wavelength of the incident electromagnetic wave, ε _γ is the complex dielectric constant, d is the thickness of the electromagnetic wave and sheet (not including the metal plate), and j is the imaginary unit. The
There are an infinite number of complex dielectric constants ε _γ that satisfy the above equation (2). Of these, ε _γ that gives the smallest thickness d can be approximately given by the following equation (1).

(Where λ indicates the wavelength of the incident electromagnetic wave, ε _γ indicates the complex dielectric constant, d indicates the thickness of the electromagnetic wave and the sheet (not including the metal plate), and j indicates the imaginary unit.)
The relationship between the solution by this approximate expression (this is referred to as “approximate solution”) and the exact solution (generally a solution using an expression showing the relationship between the thickness of the electromagnetic wave absorbing sheet and the absorption frequency range) is shown in FIG. 3 shows. From FIG. 3, both solutions show good agreement.

  Here, by transforming the formula (1), the following two formulas that give the thickness d of the electromagnetic wave absorbing sheet can be derived.

(However, Co represents the speed of light in a vacuum (= 2.99979458 × 10 ⁸ m / s), and f represents frequency (Hz).)

Specifically, as the thickness adjustment method, the real part ε _γ ′ of the complex relative permittivity and the imaginary part ε _γ ′ of the complex relative permittivity of the target electromagnetic wave absorbing sheet are known, for example, the intercoaxial method, the free space method, etc. Ε _γ ′ and ε _γ ″ are substituted into the above formulas (3a) and (3b), then the frequency f is plotted on the horizontal axis and the thickness d of the electromagnetic wave absorbing sheet is plotted on the vertical axis. The substituted equations (3a) and (3b) may be plotted on the same graph. This plotted graph is obtained, for example, as a graph as shown in FIG. In FIG. 4, curve a is a plot of equation (3a) and curve b is a plot of equation (3b).

  In FIG. 4, when d given by the expression (3a) and d given by the expression (3b) coincide, that is, when the curve a and the curve b in FIG. 4 intersect (or substantially touch each other), the expression (1 The approximate non-reflective condition given in (1) is satisfied and has a good absorption peak.

  Specifically, for example, in FIG. 4, the curve a and the curve b intersect at a point in the vicinity of 5 to 6 GHz and a thickness of about 5 mm. This means that the non-reflection condition is satisfied in the vicinity of this point, that is, if this material is processed into a flat plate with a thickness of 5 mm and lined with a metal plate as necessary, an absorption peak is observed in the vicinity of 5 to 6 GHz. This means that an electromagnetic wave absorbing sheet is obtained.

  In addition, the method of adjusting the electromagnetic wave absorbing sheet to a desired thickness may be molded by adjusting the amount of resin in advance at the time of manufacture so that the desired thickness is obtained. You may adjust by compressing by.

  According to the present invention, an electromagnetic wave having a specific frequency can be absorbed with high efficiency in a frequency range of 1 GHz to 100 GHz, for example, by simply changing the thickness. Further, since the electromagnetic wave can be absorbed with a sheet thickness of 10 mm or less, it is excellent in terms of weight reduction. Furthermore, since the blending ratio of the carbon nanocoil is a small content of 10 parts by weight or less with respect to the resin as the base material, the content is smaller than that of the electromagnetic wave absorbing sheet using the conventional carbon black, and also in terms of cost. Are better.

  Specifically, in the electromagnetic wave absorbing sheet according to claim 1 of the present invention, a carbon nanocoil having an average coil length of 1 μm or more and less than 100 μm, an average coil diameter of 1 nm or more and less than 1 μm, and an average coil pitch of 1 nm or more and less than 1 μm is 100 parts by weight of resin. 1-10 parts by weight with respect to an electromagnetic wave having a reflection loss of 10 dB or more if the thickness is changed in a desired thickness range (preferably 1 μm to 10 mm) in a frequency band of 1 GHz to 100 GHz. An absorber can be produced, and an electromagnetic wave absorbing sheet can be provided in accordance with a frequency band desired by the market. Moreover, in the absorber area | region of the produced absorption sheet, the width | variety of the absorption range exceeding 10 dB is wide, and it is excellent also as an electromagnetic wave absorption sheet for broadband.

  In the electromagnetic wave absorbing sheet according to claim 2 of the present invention, the carbon nanocoil having an average coil length of 10 μm to less than 40 μm, an average coil diameter of 400 nm to less than 800 nm, and an average coil pitch of 400 nm to 800 nm is 1 to 10 wt. Therefore, it is possible to produce a better electromagnetic wave absorber in the frequency band of 1 GHz to 100 GHz, and it is possible to provide an electromagnetic wave absorbing sheet that matches the frequency band desired by the market. Moreover, in the absorber area | region of the produced absorption sheet, the width | variety of the absorption range exceeding 10 dB is wide, and it is excellent also as an electromagnetic wave absorption sheet for broadband.

  The electromagnetic wave absorbing sheet according to claim 3 of the present invention is 1 to 10 parts by weight of carbon nanocoils having an average coil length of 20 μm to 40 μm, an average coil diameter of 400 nm to 800 nm, and an average coil pitch of 400 nm to 800 nm with respect to 100 parts by weight of the resin. Since it contains, the electromagnetic wave absorption characteristic especially excellent with respect to the frequency of 1 GHz-100 GHz (especially 1 GHz-20 GHz) is shown.

  More specifically, the amount of carbon nanocoil mixed in the electromagnetic wave absorbing sheet according to claim 3, wherein carbon nanocoils having an average coil length of 20 μm to 40 μm, an average coil diameter of 400 nm to 800 nm, and an average coil pitch of 400 nm to 800 nm are used. 1 to 10 parts by weight with respect to 100 parts by weight of the resin and the thickness of the electromagnetic wave absorbing sheet of 1 mm to 10 mm shows excellent electromagnetic wave absorption characteristics such that the electromagnetic wave absorption amount is 20 dB or more with respect to the frequency of 1 to 20 GHz. In addition, since the reflection loss is excellent even with a small amount of carbon nanocoil added, the cost increase due to the carbon nanocoil can be suppressed, and at the same time, the sheet thickness is particularly thin, so that the size can be greatly reduced. This can be seen from FIG. 13 showing the electromagnetic wave absorption characteristics in Example 9 because the frequency showing the absorption peak is 20 GHz when the thickness is 1.6 mm.

  The electromagnetic wave absorbing sheet according to claim 3, wherein carbon nanocoils having an average coil length of 20 μm to 40 μm, an average coil diameter of 400 nm to 800 nm, and an average coil pitch of 400 nm to 800 nm are used. 1 to 10 parts by weight with respect to the part, and the electromagnetic wave absorbing sheet having a thickness of 500 μm to 3 mm exhibit excellent electromagnetic wave absorption characteristics such that the electromagnetic wave absorption amount is 20 dB or more with respect to the frequency of 20 to 60 GHz. In addition, since the reflection loss is excellent even with a small amount of carbon nanocoil added, the cost increase due to the carbon nanocoil can be suppressed, and at the same time, the sheet thickness is particularly thin, so that the size can be greatly reduced. This can be seen from FIG. 13 showing the amount of electromagnetic wave absorption in Example 8 because the frequency showing the absorption peak is 60 GHz when the thickness is 500 μm.

  Furthermore, in the electromagnetic wave absorbing sheet according to claim 3, wherein carbon nanocoils having an average coil length of 20 μm to 40 μm, an average coil diameter of 400 nm to 800 nm, and an average coil pitch of 400 nm to 800 nm are used, When the thickness of the electromagnetic wave absorbing sheet is 1 μm to 2 mm with respect to the part, the electromagnetic wave absorption amount is 20 dB or more with respect to the frequency of 60 to 100 GHz. In addition, since the reflection loss is excellent even with a small amount of carbon nanocoil added, the cost increase due to the carbon nanocoil can be suppressed, and at the same time, the sheet thickness is particularly thin, so that the size can be greatly reduced. This can be seen from FIG. 13 showing the amount of electromagnetic wave absorption in Example 9 because the frequency showing the absorption peak is 100 GHz when the thickness is 1.6 mm.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to the following Example.

Example 1
A chloroform solution in which the resin was dissolved was prepared by adding and stirring a styrene resin (styrene elastomer; manufactured by Shell Chemical Co., Ltd., “Clayton”) so that the resin solid content was about 25 wt%.

  Next, carbon nanocoils (average coil length 20 μm, average coil diameter 440 nm, average coil pitch 560 nm, average fiber diameter 150 nm) are added to the prepared solution so as to be 5 parts by weight with respect to 100 parts by weight of the dissolved resin. After the addition and stirring, the mixture was allowed to stand for about half a day, whereby chloroform was gradually evaporated to produce the electromagnetic wave absorbing sheet (thickness: 200 μm) of Example 1.

Example 2
Instead of the carbon nanocoil (average coil length 20 μm, average coil diameter 440 nm, average coil pitch 560 nm, average fiber diameter 150 nm), the carbon nanocoil was subjected to ultrasonication with an ultrasonic homogenizer (manufactured by SMT Co., 50 W, 20 kHz). Implementation was performed in the same manner as in Example 1 except that carbon nanocoils (average coil length 10 μm, average coil diameter 440 nm, average coil pitch 560 nm, average fiber diameter 150 nm) cut by shortening the coil length by irradiation for minutes were used. The electromagnetic wave absorbing sheet of Example 2 (thickness: 200 μm) was produced.

Measurement of electromagnetic wave absorption characteristics (coaxial tube method)
The complex relative dielectric constant of the electromagnetic wave absorbing sheets of Examples 1 and 2 was measured by the coaxial tube method using the following measuring instrument. The measurement results are shown in FIG. 5 (the left figure is Example 1 and the right figure is Example 2).
Dielectric constant measuring jig: coaxial tube (outer diameter 7 mm, inner diameter 3.04 m; manufactured by Kanto Electronics Application Development Co., Ltd., “CSH2-APC7”),
Network analyzer: Agilent Technologies E8361A (10MHz-67GHz)
Software: Agilent Technologies 85071 Version E1.01
("Precision model" is used as the calculation model)
From FIG. 5, the electromagnetic wave absorption amount (reflection attenuation amount) when the thickness of the electromagnetic wave absorbing sheet was 2 mm, 2.5 mm, and 3 mm was calculated. The calculation results are shown in FIG. 6 (the left figure is Example 1 and the right figure is Example 2).

Measurement test of plane orientation The surface of the electromagnetic wave absorbing sheet of Example 1 was ashed with oxygen plasma, and an image was taken at a magnification of 5000 times with a scanning electron microscope (JEOL, JSM7401F). 100 arbitrarily selected from the carbon nanocoils photographed in the image, and the angle formed between the axial direction of the carbon nanocoils and the electromagnetic wave absorbing sheet was measured. As a result, 90 or more carbon nanocoils had an angle of 10 It was less than °.

Example 3
Carbon nanocoil (average coil length 20 μm, average coil diameter 440 nm, average coil pitch 560 nm, average fiber diameter 150 nm) was added to 100 parts by weight of resin so as to be 4 parts by weight instead of 5 parts by weight. Produced the electromagnetic wave absorbing sheet of Example 3 (thickness: 500 μm) in the same manner as in Example 1.

Example 4
Instead of carbon nanocoils (average coil length 20 μm, average coil diameter 440 nm, average coil pitch 560 nm, average fiber diameter 150 nm), carbon nanocoils (average coil length 26 μm, average coil diameter 920 nm, average coil pitch 670 nm, average fiber diameter) The electromagnetic wave absorbing sheet (thickness: 500 μm) of Example 4 of the present application was produced in the same manner as Example 3 except that 200 nm) was used.

<Measurement of electromagnetic wave absorption characteristics (coaxial tube method)>
The electromagnetic wave absorption characteristics of the electromagnetic wave absorbing sheets of Examples 3 and 4 were determined in the same manner as in Example 1. FIG. 7 shows the measurement results of the complex dielectric constant of the electromagnetic wave absorbing sheets of Examples 3 and 4 (the left figure is Example 3 and the right figure is Example 4). FIG. 8 shows the results of calculation of the amount of electromagnetic wave absorption when the thickness of the electromagnetic wave absorbing sheet is 2 mm, 2.5 mm and 3 mm in Example 3 and 5 mm, 10 mm and 20 mm in Example 4 (the left figure is Example 3 and the right figure are shown in Example 4).

Example 5
Instead of carbon nanocoils (average coil length 20 μm, average coil pitch 560 nm, average fiber diameter 150 nm, average coil diameter 440 nm), carbon nanocoils (average coil length 28 μm, average coil diameter 440 nm, average coil pitch 960 nm, average fiber diameter) The electromagnetic wave absorbing sheet (thickness: 500 μm) of Example 5 was manufactured in the same manner as Example 1 except that 220 nm) was used.

<Measurement of electromagnetic wave absorption characteristics (coaxial tube method)>
The electromagnetic wave absorption characteristics of the electromagnetic wave absorbing sheet of Example 5 were determined in the same manner as in Example 1. In FIG. 9, the measurement result of the complex dielectric constant of the electromagnetic wave absorption sheet of Example 5 is shown. FIG. 10 shows the calculation results of the electromagnetic wave absorption when the thickness of the electromagnetic wave absorbing sheet is 3 mm, 6 mm, 12 mm, and 24 mm.

Example 6
Instead of styrene resin, urethane resin (manufactured by DIC Bayer Polymer, “Pandex”) is used, and carbon nanocoil (average coil length 20 μm, average coil diameter 440 nm, average coil pitch 560 nm, average The electromagnetic wave absorbing sheet (thickness) of Example 6 was the same as Example 1 except that the fiber diameter was 150 nm) added to 4 parts by weight instead of 5 parts by weight with respect to 100 parts by weight of the resin. 500 μm) was manufactured.

Example 7
Carbon nanocoil (average coil length 20 μm, average coil diameter 440 nm, average coil pitch 560 nm, average fiber diameter 150 nm) was added to 100 parts by weight of resin so that the amount was 3 parts by weight instead of 4 parts by weight. Produced the electromagnetic wave absorbing sheet of Example 7 (thickness: 500 μm) in the same manner as in Example 6.

<Measurement of electromagnetic wave absorption characteristics (coaxial tube method)>
The electromagnetic wave absorption characteristics of the electromagnetic wave absorbing sheets of Examples 6 and 7 were determined in the same manner as in Example 1. FIG. 11 shows the measurement results of the complex relative permittivity of the electromagnetic wave absorbing sheets of Examples 6 and 7 (the left figure is Example 6 and the right figure is Example 7). FIG. 12 shows the calculation results of the electromagnetic wave absorption when the thickness of the electromagnetic wave absorbing sheet is 2 mm, 2.5 mm, and 3 mm (the left figure is Example 6 and the right figure is Example 7).

Examples 8 and 9
Example 8 (thickness 500 μm, 10 cm × 10 cm) and Example 9 (thickness 1.6 mm) were the same as Example 1 except that the thickness of the obtained electromagnetic wave absorbing sheet was 500 μm and 1.6 mm, respectively. A 10 cm × 10 cm) electromagnetic wave absorbing sheet was produced.

<Consideration of Example 1 and Example 2 (Influence of Coil Length)>
Comparing the electromagnetic wave absorption amount of FIG. 6 obtained from Example 1 and Example 2, the direction of Example 1 has an electromagnetic wave absorption amount of 30 dB or more at any thickness, whereas in Example 2, it is around 20 dB. Thus, it can be seen that the coil length of Example 1 having a coil length of 20 μm is much superior in electromagnetic wave absorption characteristics than Example 2 having a coil length of 10 μm. From the results of this example, the average coil length of the carbon nanocoil added to the electromagnetic wave absorbing sheet is most preferably 20 μm to 40 μm.

<Consideration of Example 3 and Example 4 (Influence of Coil Diameter)>
Comparing the electromagnetic wave absorption amount of FIG. 8 obtained from Example 3 and Example 4, the direction of Example 3 has an electromagnetic wave absorption amount of 30 dB or more at any thickness, whereas in Example 4, it is around 10 dB. Thus, it can be seen that the electromagnetic coil absorption characteristics of Example 3 having an average coil diameter of 440 nm are much better than those of Example 4 having an average coil diameter of 920 nm. From the results of this example, the average coil diameter of the carbon nanocoil added to the electromagnetic wave absorbing sheet is most preferably 400 nm to 800 nm.

<Consideration of Example 1 and Example 5 (Influence of Coil Pitch)>
6 (left) obtained from Example 1 and Example 5 and the electromagnetic wave absorption amount of FIG. 10 are compared, Example 1 has an electromagnetic wave absorption amount of 30 dB or more at any thickness. In Example 5, it is about 10 dB, and it can be seen that the average coil pitch of Example 3 is 560 nm and the electromagnetic wave absorption characteristics are much better than Example 5 where the average coil diameter is 960 nm. From the results of this example, the average coil pitch of the carbon nanocoils added to the electromagnetic wave absorbing sheet is most preferably 400 nm to 800 nm.

<Measurement of electromagnetic wave absorption characteristics (free space method)>
Using the electromagnetic wave absorbing sheets of Examples 8 and 9, the electromagnetic wave absorption amount in the millimeter wave band was measured by the free space method. The measurement results are shown in FIG.

  As a measuring instrument, an electromagnetic wave absorption measuring apparatus (network analyzer; manufactured by Agilent Technologies; model 8510XF, horn antenna; manufactured by HVS Technologies, Inc .; model FSS-07) installed at the Fine Ceramics Center was used.

  From FIG. 13, it was found that the electromagnetic wave absorbing sheet of the present invention can absorb electromagnetic waves even in a high frequency band of 18 GHz or higher.

<Consideration of Example 8 and Example 9>
From FIG. 13, it can be seen that when the thickness is 1.6 mm, the frequency has an absorption peak with an electromagnetic wave absorption of 20 dB or more near 20 GHz, and when the thickness is 500 μm, the electromagnetic wave absorption amount is around 60 GHz. It turns out that it has an absorption peak of 20 dB or more.

<Measurement of absorption characteristics by approximate solution>
For the electromagnetic wave absorbing sheet of Example 6, two curves (the real part (ε _γ ′) of the complex relative dielectric constant) are shown based on the above (3a) and (3b) derived using the above equation (1). The curve and the imaginary part (ε _γ ″) of the complex dielectric constant were expressed in the same graph. This is shown in FIG. As is apparent from FIG. 14, the curve of the real part (ε _γ ′) and the curve of the imaginary part (ε _γ ″) substantially coincide with each other in the vicinity of the frequency of 700 MHz to 18 GHz. It can be seen that the sheet can adjust an electromagnetic wave absorbing sheet that can absorb a wide band of 700 MHz to 18 GHz.

FIG. 1 shows a conceptual diagram when carbon nanocoils in the electromagnetic wave absorbing sheet of the present invention are plane-oriented and when they are not plane-oriented. FIG. 2 shows an electromagnetic wave absorbing sheet in which metal plates are laminated. FIG. 3 is a graph showing the consistency between the exact solution and the approximate solution. FIG. 4 is an example of a graph used in the thickness adjustment method of the present invention. FIG. 5 shows the measurement results of the complex relative dielectric constant of the electromagnetic wave absorbing sheets of Examples 1 and 2 of the present application. FIG. 6 shows the measurement results of the electromagnetic wave absorption amount of the electromagnetic wave absorbing sheets of Examples 1 and 2 of the present application. FIG. 7 shows the measurement results of the complex relative dielectric constant of the electromagnetic wave absorbing sheets of Examples 3 and 4 of the present application. FIG. 8 shows the measurement results of the electromagnetic wave absorption amount of the electromagnetic wave absorbing sheets of Examples 3 and 4 of the present application. FIG. 9 shows the measurement result of the complex dielectric constant of the electromagnetic wave absorbing sheet of Example 5 of the present application. FIG. 10 shows the measurement results of the electromagnetic wave absorption amount of the electromagnetic wave absorbing sheet of Example 5 of the present application. FIG. 11 shows the measurement results of the complex relative dielectric constant of the electromagnetic wave absorbing sheets of Examples 6 and 7 of the present application. FIG. 12 shows the measurement results of the electromagnetic wave absorption amount of the electromagnetic wave absorbing sheets of Examples 6 and 7 of the present application. FIG. 13 shows the measurement results of the electromagnetic wave absorption amount of the electromagnetic wave absorbing sheets of Examples 8 and 9 of the present application. FIG. 14 is a graph showing the relationship between thickness and absorption frequency for the electromagnetic wave absorbing sheet of Example 6.

Claims (8)

An electromagnetic wave absorbing sheet containing carbon nanocoils and a resin,
(1) The carbon nanocoil has an average coil length of 1 μm to less than 100 μm, an average coil diameter of 1 nm to less than 1 μm, and an average coil pitch of 1 nm to less than 1 μm,
(2) The carbon nanocoil is contained in a ratio of 1 to 10 parts by weight with respect to 100 parts by weight of the resin.
An electromagnetic wave absorbing sheet.   The electromagnetic wave absorbing sheet according to claim 1, wherein the carbon nanocoil has an average coil length of 10 μm to 40 μm, an average coil diameter of 1 nm to less than 1 μm, and an average coil pitch of 1 nm to less than 1 μm.   The electromagnetic wave absorbing sheet according to claim 1, wherein the carbon nanocoil has an average coil length of 20 μm to 40 μm, an average coil diameter of 400 nm to less than 800 nm, and an average coil pitch of 400 nm to 800 nm.   The electromagnetic wave absorbing sheet according to claim 1, wherein the electromagnetic wave absorbing sheet has a thickness of 1 μm to 10 mm.   The electromagnetic wave absorbing sheet according to claim 1, wherein the carbon nanocoil is oriented in a surface direction of the electromagnetic wave absorbing sheet.   The electromagnetic wave absorbing sheet according to any one of claims 1 to 5, which has an absorption band in which a reflection loss is 10 dB or more in a frequency band of 1 GHz to 100 GHz.   The electromagnetic wave absorbing sheet according to claim 1, wherein a metal plate is laminated on one surface. A method for producing an electromagnetic wave absorbing sheet containing carbon nanocoils and a resin,
A step of mixing carbon nanocoils having an average coil length of 1 μm or more and less than 100 μm, an average coil diameter of 1 nm or more and less than 1 μm, and an average coil pitch of 1 nm or more and less than 1 μm with an organic solvent in which the resin is dissolved, and then evaporating the organic solvent;
The manufacturing method of the electromagnetic wave absorption sheet | seat provided with.

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