Electromagnetic wave suppressing material

Abstract

To provide an electromagnetic wave suppressing material having superior electromagnetic wave absorption performance and having enhanced performance in reducing electromagnetic interference, an electronic component sealed with the electromagnetic wave suppressing material, and a cured product of the electromagnetic wave suppressing material.SOLUTION: An electromagnetic wave suppressing material comprises: (A) a thermosetting resin; (B) an inorganic filler; (C) cellulose nanofibers; and (D) a silicone compound. In an infrared absorption spectrum of the (C) cellulose nanofibers determined using attenuated total reflectance (ATR) in Fourier transform infrared spectroscopy (FT-IR), a ratio of absorbance (I) at 1730 cm-1 to absorbance (II) at 1050 cm-1 (absorbance (I) / absorbance (II)) is 0.4 or less. The (D) silicone compound has three or more alkoxy groups per molecule. The mass ratio ((D) / (C)) of the (D) silicone compound to the (C) cellulose nanofibers is from 0.1 to 1.5.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an electromagnetic wave suppression material.

Background Art

[0002] In recent years, various measures have been taken for the purpose of reducing electromagnetic interference such as malfunction of devices due to electromagnetic noise, information leakage, and reduction of information communication speed due to interference. As means for reducing electromagnetic interference, methods of blocking electromagnetic waves by reflection and methods of absorbing electromagnetic waves have been proposed.

[0003] For example, Patent Document 1 proposes an electromagnetic wave absorption sheet containing microfibrous cellulose as an insulating filler and carbon black as a conductive filler. Further, Patent Document 2 proposes an electromagnetic wave absorption sheet containing an organic component mainly composed of micro carbon fibers and cellulose fibers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The electromagnetic wave absorption performance of the electromagnetic wave absorption sheets described in Patent Documents 1 and 2 is mainly due to conductive materials such as carbon. On the one hand, cellulose nanofibers such as microfibrillar cellulose and cellulose fibers have a large number of hydroxyl groups in the molecule. Since the hydroxyl groups are polarized, they have electromagnetic wave absorption performance, and cellulose nanofibers having a large number of hydroxyl groups are considered to have electromagnetic wave absorption performance. However, cellulose nanofibers tend to aggregate due to the interaction of the hydroxyl groups they possess and are difficult to disperse in the matrix (base material), so it has been difficult to effectively exhibit the electromagnetic wave absorption effect that cellulose nanofibers are considered to have.

[0006] Also, by subjecting cellulose nanofibers to TEMPO treatment, aggregation of cellulose nanofibers in the matrix can be suppressed and dispersibility can be improved. However, when subjected to TEMPO treatment, the hydroxyl groups possessed by cellulose nanofibers are substituted, and the electromagnetic wave absorption effect cannot be obtained.

[0007] The present disclosure has been made in view of such circumstances, and an electromagnetic wave suppression material having good electromagnetic wave absorption performance, better electromagnetic interference reduction performance, and high insulation in a high-frequency band, an electronic component sealed using the electromagnetic wave suppression material, and a cured product of the electromagnetic wave suppression material are provided.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that an electromagnetic wave suppression material containing a predetermined (C) cellulose nanofiber and a (D) silicone compound having three or more alkoxy groups in one molecule, and having a mass ratio ((D) / (C)) of the (D) silicone compound to the (C) cellulose nanofiber being a predetermined value has good electromagnetic wave absorption performance, better electromagnetic interference reduction performance, and high insulation.

[0009] That is, the present disclosure relates to the following. <Electromagnetic Wave Suppression Material> [1] It contains (A) a thermosetting resin, (B) an inorganic filler, (C) cellulose nanofibers, and (D) a silicone compound. In the infrared absorption spectrum of the said (C) cellulose nanofibers obtained by using the total reflection measurement method (ATR) of the Fourier transform infrared absorption spectroscopy (FT-IR), the ratio of the absorbance (I) at 1730 cm -1 to the absorbance (II) at 1050 cm -1 (absorbance (I) / absorbance (II)) is 0.4 or less. The said (D) silicone compound has 3 or more alkoxy groups in one molecule, and the mass ratio of the said (D) silicone compound to the said (C) cellulose nanofibers ((D) / (C)) is 0.1 to 1.5. An electromagnetic wave suppression material. [2] The electromagnetic wave suppression material according to [1], wherein the said (A) thermosetting resin contains an epoxy resin. [3] The electromagnetic wave suppression material according to [2], wherein the said epoxy resin has a polyoxyalkylene structure. [4] The electromagnetic wave suppression material according to any one of [1] to [3], wherein the mass ratio of the alkoxy group in one molecule of the said (D) silicone compound is 10 to 80% by mass. [5] The electromagnetic wave suppression material according to any one of [1] to [4], wherein the said (D) silicone compound is an alkoxysilane compound. <Electronic component> [6] An electronic component encapsulated with the electromagnetic wave suppression material according to any one of [1] to [5]. <Cured product> [7] A cured product of the electromagnetic wave suppression material according to any one of [1] to [5].

Advantages of the Invention

[0010] According to the present disclosure, there is provided an electromagnetic wave suppression material that has good electromagnetic wave absorption performance in the high-frequency band, has better electromagnetic interference reduction performance, and has high insulation. Also, according to the present disclosure, there are provided an electronic component encapsulated with the said electromagnetic wave suppression material and a cured product of the said electromagnetic wave suppression material.

Modes for Carrying Out the Invention

[0011] Hereinafter, the present disclosure will be described in detail with reference to one embodiment. In this specification, for numerical ranges (for example, ranges such as content), the lower limit value and the upper limit value described step by step can be combined independently. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0012] [Electromagnetic wave suppression material] The electromagnetic wave suppression material of the present disclosure contains (A) a thermosetting resin, (B) an inorganic filler, (C) cellulose nanofibers, and (D) a silicone compound. And in the infrared absorption spectrum of the (C) cellulose nanofibers obtained by using the total reflection measurement method (ATR) of the Fourier transform infrared absorption spectrum method (FT-IR), the absorbance (I) at 1730 cm -1 and the absorbance (II) at 1050 cm -1 The ratio of (absorbance (I) / absorbance (II)) is 0.4 or less, the (D) silicone compound has 3 or more alkoxy groups in one molecule, and the mass ratio of the (D) silicone compound to the (C) cellulose nanofibers ((D) / (C)) is 0.1 to 1.5. By having the above configuration, the electromagnetic wave suppression material has good electromagnetic wave absorption performance, better electromagnetic interference reduction performance, and high insulation. The reason is not clear, but it is considered as follows. The alkoxy group of the (D) silicone contained in the electromagnetic wave suppression material interacts with the hydroxyl group of the (C) cellulose nanofibers, so that the (D) silicone becomes a spacer for the (C) cellulose nanofibers. As a result, it is presumed that the aggregation of the (C) cellulose nanofibers can be suppressed without substituting the hydroxyl group of the (C) cellulose nanofibers, and the (C) cellulose nanofibers can be dispersed in the (A) thermosetting resin, and the electromagnetic wave absorption effect of the (C) cellulose nanofibers can be effectively exerted. In addition, since the (A) thermosetting resin, (B) inorganic filler, (C) cellulose nanofiber, and (D) silicone compound contained in the electromagnetic wave suppressing material of the present disclosure are insulating, the electromagnetic wave suppressing material has high insulation.

[0013] From the viewpoint of electromagnetic wave absorption performance, the mass ratio ((D) / (C)) of the (D) silicone compound to the (C) cellulose nanofiber in the electromagnetic wave suppressing material may be 0.15 or more, may be 0.20 or more, may be 0.22 or more, and from the viewpoint of moldability, it may be 1.2 or less, may be 1.0 or less, or may be 0.8 or less.

[0014] <(A) thermosetting resin> Examples of the (A) thermosetting resin of the present disclosure include epoxy resins, phenolic resins, imide resins, and the like. The (A) thermosetting resin may be an epoxy resin or an imide resin from the viewpoints of electrical insulation and heat resistance. (A) The thermosetting resin may be used alone or in combination of two or more.

[0015] The epoxy resin has two or more epoxy groups in one molecule, and its molecular structure, molecular weight, etc. are not particularly limited as long as it is generally used in electronic components. Examples of the epoxy resin include phenolic novolak type epoxy resins, cresol novolak type epoxy resins, aliphatic epoxy resins such as dicyclopentadiene derivatives, aromatic epoxy resins such as biphenyl type, biphenyl aralkyl type, naphthyl type, and bisphenol type. These epoxy resins may be used alone or in combination of two or more. The properties are not particularly limited, and it may be liquid or solid at room temperature (25°C). For example, the epoxy resin may be a bisphenol type epoxy resin, and specifically, bisphenol A type and bisphenol F type may be mentioned. Bisphenol A type epoxy resin can be obtained as a commercial product, and examples include Epomic (registered trademark) R140 (manufactured by Mitsui Chemicals, Inc.).

[0016] From the perspective of thermomechanical properties, the epoxy equivalent of the epoxy resin may be 140 or more. From the perspective of electromagnetic wave absorption performance, it may be 200 or more, and may be 250 or more. As the upper limit value of the epoxy equivalent, from the perspective of thermomechanical properties, it may be 400 or less, and may be 380 or less.

[0017] The epoxy resin may be an epoxy resin having a polyoxyalkylene structure represented by (R 1 O)m and a polyoxyalkylene structure represented by (R 2 O)n. By including an epoxy resin having a polyoxyalkylene structure in the electromagnetic wave suppression material of the present disclosure, the resulting molded body exhibits better electromagnetic wave suppression ability. Here, R 1 and R 2 each independently represent an alkylene group having 1 or more carbon atoms. m + n may be 2 or more and 50 or less, and may be 2 or more and 20 or less. Also, m may be 1 or more and 49 or less, and may be 1 or more and 19 or less. n may be 1 or more and 50 or less, and may be 1 or more and 20 or less.

[0018] R 1 and R 2 Examples of the alkylene group represented by include an alkylene group having 1 or more and 6 or less carbon atoms. Specifically, a methylene group, an ethylene group, a trimethylene group, a propylene group, a tetramethylene group, a hexamethylene group, etc. may be mentioned. From the perspective of electromagnetic wave absorption performance, the alkylene group may be a methylene group or an ethylene group. In the m R 1 O groups, the plurality of R 1 may be the same alkylene group as each other, or may be alkylene groups having different carbon numbers. Also, in the n R 2 O groups, the plurality of R 2 may be the same alkylene group as each other, or may be alkylene groups having different carbon numbers.

[0019] Examples of the epoxy resin having the polyoxyalkylene structure include an epoxy resin having a bisphenol A skeleton, polyethylene glycol diglycidyl ether, etc. Examples of commercially available epoxy resins having a bisphenol A skeleton include Likarezine BEO-60E (manufactured by Shin Nippon Rika Co., Ltd.) represented by the following general formula (1), and examples of commercially available polyethylene glycol diglycidyl ether include Epolite 400E (manufactured by Kyoeisha Chemical Co., Ltd.) mainly composed of the compound represented by the following general formula (2).

[0020]

Chemical formula

[0021]

Chemical formula

[0022] Examples of the imide resin include bisallylnadicimide. Bisallylnadicimide can be obtained as a commercially available product, and examples thereof include BANI-M (manufactured by Maruzen Petrochemical Co., Ltd.), BANI-X (manufactured by Maruzen Petrochemical Co., Ltd.), etc.

[0023] (A) The content of the thermosetting resin may be 5% by mass or more and 60% by mass or less, 10% by mass or more and 50% by mass or less, or 12% by mass or more and 45% by mass or less with respect to the total amount of the electromagnetic wave suppressing material of the present disclosure. When the content of the (A) thermosetting resin is 5% by mass or more, suitable thermomechanical properties can be obtained, and when it is 60% by mass or less, appropriate fluidity can be maintained.

[0024] (B) Inorganic filler The (B) inorganic filler of the present disclosure is not particularly limited as long as it is used in electronic components, and it may be an inorganic filler having a high dielectric constant and a high dielectric loss tangent. For example, silica, alumina, titanium oxide, barium titanate, silicon nitride, aluminum nitride, silicon carbide, etc. may be mentioned. These may be used alone or in combination of two or more. The (B) inorganic filler may be at least one selected from silica, alumina, and silicon carbide, or may be silica and silicon carbide, from the viewpoint of improving the electromagnetic wave absorption performance in the high-frequency band of the obtained molded body.

[0025] The shape of the (B) inorganic filler is not particularly limited, and examples include spherical and fibrous shapes. The shape of the (B) inorganic filler may be powdery or spherical.

[0026] The average particle diameter of the (B) inorganic filler is not particularly limited, but it may be 0.1 μm or more and 100 μm or less, may be 0.2 μm or more and 75 μm or less, or may be 0.2 μm or more and 50 μm or less. Further, considering the application to the thin-wall molding material, the maximum particle diameter of the (B) inorganic filler may be 150 μm or less, or may be 100 μm or less. When the average particle diameter of the (B) inorganic filler is 0.1 μm or more, appropriate fluidity can be maintained, and when it is 100 μm or less, molding defects such as unfilled parts can be reduced. In this specification, the average particle diameter means the volume average particle diameter, and the average particle diameter of the (B) inorganic filler can be calculated as the average value of the major axis lengths of the particles measured using a laser diffraction particle size distribution measuring device.

[0027] The content of the (B) inorganic filler may be 30% by mass or more and 90% by mass or less, may be 35% by mass or more and 85% by mass or less, may be 40% by mass or more and 80% by mass or less, or may be 75% by mass or less, based on the total amount of the electromagnetic wave suppression material of the present disclosure. When the content of the (B) inorganic filler is 30% by mass or more, the electromagnetic wave absorption performance of the obtained cured product can be further improved, and when it is 90% by mass or less, appropriate fluidity can be obtained.

[0028] <(C) Cellulose nanofiber> The (C) cellulose nanofiber of the present disclosure means a fibrous material having a fiber diameter of 500 nm or less, which is produced by defibrating plant fibers to the nanolevel. Also, in the infrared absorption spectrum of the (C) cellulose nanofiber obtained by using the attenuated total reflection method (ATR) of the Fourier transform infrared absorption spectroscopy (FT-IR), at 1730 cm -1 the absorbance (I) and at 1050 cm -1 the ratio of the absorbance (II) (absorbance (I) / absorbance (II)) is 0.4 or less.

[0029] For the purpose of suppressing the aggregation of cellulose nanofibers, etc., when the cellulose nanofibers are surface-treated such as TEMPO treatment, the hydroxyl groups of the cellulose nanofibers are substituted with acetyl groups. When the infrared absorption spectrum of such surface-treated cellulose nanofibers is measured using the attenuated total reflection method (ATR method) of the Fourier transform infrared absorption spectroscopy (FT-IR), an absorption (absorbance (I)) derived from the acetyl group appears at 1730 cm -1 On the other hand, since cellulose nanofibers have a glucopyranose ring, when the infrared absorption spectrum is measured in the same manner as the surface-treated cellulose nanofibers described above, an absorption (absorbance (II)) derived from the glucopyranose ring appears at 1050 cm -1 -1 Accordingly, the presence or absence and degree of the surface treatment of the cellulose nanofibers can be understood from the ratio of the absorbance (I) and the absorbance (II). Note that the absorbance (I) / absorbance (II) being 0.4 or less means that no surface treatment has been performed, or that although surface treatment has been performed, only a part of the hydroxyl groups of the cellulose nanofibers have been substituted with acetyl groups (for example, the substitution rate of the hydroxyl groups is 25% or less), and many hydroxyl groups have not been substituted with acetyl groups. The absorbance (I) / absorbance (II) may be 0.2 or less from the viewpoints of the electromagnetic wave absorption performance and the electromagnetic interference reduction performance, and the lower limit is not particularly limited as long as it is 0 or more. ​In this specification, the infrared absorption spectrum of (C) cellulose nanofibers is the spectrum measured under the following conditions using a Fourier transform infrared spectrophotometer and adopting the total reflection measurement method of the Fourier transform infrared absorption spectroscopy method for dry (C) cellulose nanofibers. Measurement wavelength range: 650 - 4000 cm -1 Resolution: 4 cm -1 Incident angle: 45 degrees Number of integrations: 100 times Specifically, it can be obtained by the method described in the examples.

[0030] (C) Cellulose nanofibers may not be surface-treated with TEMPO (2,2,6,6 - tetramethylpiperidine - 1 - oxyl radical) or the like. When using (C) cellulose nanofibers without surface treatment, it becomes possible to more effectively exhibit the electromagnetic wave absorption performance inherent in (C) cellulose nanofibers.

[0031] General cellulose nanofibers have three replaceable hydroxyl groups per unit structure, and the theoretical maximum value of the degree of substitution is 3. By coexisting a (D) silicone compound having three or more alkoxy groups capable of reacting with or having a strong interaction with the hydroxyl group in the electromagnetic wave suppressing material, it becomes possible to effectively exhibit the electromagnetic wave absorption performance inherent in (C) cellulose nanofibers.

[0032] (C) Cellulose nanofibers may be dispersed in a liquid such as water or a thermosetting resin oligomer. (C) The average fiber length of cellulose nanofibers is not particularly limited, but from the viewpoints of workability and fluidity, it may be 1 μm or more and 100 μm or less, or may be 5 μm or more and 50 μm or less. Further, the average fiber diameter of the (C) cellulose nanofiber is not particularly limited, but from the viewpoint of the moldability of the electromagnetic wave suppressing material, it may be 1 nm or more and 1000 nm or less, including aggregates, and may be 4 nm or more and 500 nm or less. The average fiber diameter and average fiber length of the (C) cellulose nanofiber are determined by arithmetically averaging the fiber diameter and fiber length obtained from the results of observing each fiber using an atomic force microscope (AFM).

[0033] The average aspect ratio of the (C) cellulose nanofiber is usually 50 or more. The upper limit is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula (1). Aspect ratio = average fiber length / average fiber diameter (1)

[0034] The raw material of the (C) cellulose nanofiber is not particularly limited, and examples thereof include wood; bamboo; hemp; jute; kenaf; agricultural waste residues, cloth; softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, pulp such as waste paper, and the like. The cellulose raw material may be used alone or in combination of two or more.

[0035] The content of the (C) cellulose nanofiber may be 0.1% by mass or more and 20% by mass or less, 0.2% by mass or more and 10% by mass or less, or 0.3% by mass or more and 5% by mass or less with respect to the total amount of the electromagnetic wave suppressing material of the present disclosure. When the content of the (C) cellulose nanofiber is 0.1% by mass or more with respect to the total amount of the electromagnetic wave suppressing material of the present disclosure, the electromagnetic wave absorption performance is further improved, and when it is 20% by mass or less, molding defects such as non-filling can be reduced.

[0036] <(D) silicone compound> The (D) silicone compound of the present disclosure has three or more alkoxy groups in one molecule. The (D) silicone compound may have a functional group other than an alkoxy group. Examples of the (D) silicone compound include silane compounds and silicone oligomers. Examples of the (D) silicone compound include alkoxysilane compounds such as methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, phenyltrimethoxysilane, phenylaminopropyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, and phenyltriethoxysilane; silane coupling agents such as aminosilane, isocyanatosilane, epoxysilane, vinylsilane, methacryl silane, mercapto silane, acrylic silane, and ureidosilane; and oligomers of these silane compounds and silane coupling agents. From the viewpoint of further improving the electromagnetic wave absorption performance, three alkoxy groups may be directly bonded to the silicon atom in the (D) silicone compound. From the same viewpoint, the mass ratio of the alkoxy group in one molecule of the (D) silicone compound may be 10 to 80% by mass, may be 13 to 60% by mass, or may be 15 to 50% by mass.

[0037] The content of the (D) silicone compound may be 0.01% by mass or more and 10% by mass or less, may be 0.05% by mass or more and 7% by mass or less, or may be 0.1% by mass or more and 5% by mass or less with respect to the total amount of the electromagnetic wave suppressing material of the present disclosure. When the content of the (D) silicone compound is 0.01% by mass or more, the electromagnetic wave absorption performance of the obtained cured product can be further improved, and when it is 10% by mass or less, it can be processed without impairing the moldability.

[0038] <Hardener> The electromagnetic wave suppressing material of the present disclosure may further contain a hardener. Examples of the hardener include aliphatic amines, aromatic amines, dicyandiamide, dihydrazide compounds, acid anhydrides, phenolic resins, and the like. These may be used alone or in combination of two or more. When the electromagnetic wave suppression material of the present disclosure contains a hardener, the content may be 1% by mass or more and 20% by mass or less, 2% by mass or more and 18% by mass or less, or 3% by mass or more and 15% by mass or less based on the total amount of the electromagnetic wave suppression material.

[0039] <Hardening accelerator> The electromagnetic wave suppression material of the present disclosure may further contain a hardening accelerator. Examples of the hardening accelerator include organic peroxides such as dicumyl peroxide and dibutyl peroxide; imidazole compounds such as 2-methylimidazole and 2-ethylimidazole. These may be used alone or in combination of two or more. When the electromagnetic wave suppression material of the present disclosure contains a hardening accelerator, the content may be 0.1% by mass or more and 10% by mass or less, 0.2% by mass or more and 8% by mass or less, or 0.3% by mass or more and 5% by mass or less based on the total amount of the electromagnetic wave suppression material.

[0040] <Dispersion aid> The electromagnetic wave suppression material of the present disclosure may further contain a dispersion aid. The dispersion aid may be any material for stably and highly dispersing inorganic fillers, cellulose nanofibers, and other components in the (A) thermosetting resin.

[0041] When the dispersion aid is contained in the electromagnetic wave suppression material of the present disclosure, the content may be 0.1% by mass or more and 30% by mass or less, 0.2% by mass or more and 10% by mass or less, or 0.3% by mass or more and 5% by mass or less based on the total amount of the electromagnetic wave suppression material from the viewpoints of dispersibility and maintaining thermomechanical properties.

[0042] <Magnetic material> The electromagnetic wave suppression material of the present disclosure may or may not contain a magnetic material. The magnetic body is not particularly limited as long as it is a magnetic body made of a magnetic material generally used for electromagnetic wave reduction. Examples of the magnetic material include soft magnetic materials such as amorphous magnetic metal alloys, Ni-Fe based alloys, pure iron, mild steel, silicon steel (Fe-Si alloys), Fe-Al alloys, Fe-Si-Al alloys, Co-Fe based alloys, carbonyl iron, and ferrites. These may be used alone or in combination of two or more.

[0043] When the electromagnetic wave suppression material of the present disclosure is used as a sealing material for semiconductors, metal foreign matter removal is performed in the process of manufacturing the semiconductor sealing material. When the metal foreign matter removal is performed using a magnet, the magnetic body is regarded as a foreign matter and is removed, resulting in poor yield. From such a viewpoint, when the magnetic body is included in the electromagnetic wave suppression material of the present disclosure, the content thereof may be 1% by mass or less, 0.5% by mass or less, or even 0% by mass with respect to the total amount of the electromagnetic wave suppression material. Also, since the magnetic body has a large specific gravity, the content of the magnetic body may be below the above value from the viewpoint of reducing the weight of the obtained molded body.

[0044] <Other additives> In addition to the above components, the electromagnetic wave suppression material of the present disclosure may contain, within the scope not departing from the gist of the present disclosure, mold release agents such as synthetic wax, natural wax, higher fatty acids, esters of higher fatty acids, etc., which are generally blended in this type of electromagnetic wave suppression material; colorants such as cobalt blue; modifiers such as silicone oil and silicone rubber; hydrotalcites; ion scavengers; other additives such as charge control agents, as needed. Each of these other additives may be used alone or in combination of two or more.

[0045] In the electromagnetic wave suppression material of the present disclosure, the content of each of these other additives may be 0.05% by mass or more and 5% by mass or less, or 0.1% by mass or more and 3% by mass or less, for each other additive and as the total amount of the additives, with respect to the total amount of the electromagnetic wave suppression material.

[0046] [Manufacturing method of electromagnetic wave suppression material] The electromagnetic wave suppression material of the present disclosure may be obtained by sufficiently and uniformly mixing (A) a thermosetting resin, (B) an inorganic filler, (C) cellulose nanofibers, (D) a silicone compound, and other components that are blended as necessary, using a mixer or the like, and then performing a kneading process using a disperser, a kneader, a three-roll mill, a biaxial heating roll, a biaxial heating extrusion kneading device, or the like. The kneading process may be performed with heating. The temperature at that time may be 70°C or higher and 150°C or lower, or may be 75°C or higher and 120°C or lower.

[0047] For example, after the kneading process, the electromagnetic wave suppression material of the present disclosure may be cooled and solidified, and then ground to an appropriate size using a cutting mill, a ball mill, a cyclone mill, a hammer mill, a vibration mill, a cutter mill, a grinder mill, a speed mill, or the like, and used.

[0048] Alternatively, the mixture obtained after the kneading process may be pressed into a sheet shape under the conditions of a temperature of 50°C or higher and 100°C or lower and a pressure of 0.5 MPa or higher and 1.5 MPa or lower using a cold roll, a molding machine, or the like.

[0049] The electromagnetic wave suppression material of the present disclosure can be used as a radio wave absorber, a noise suppression sheet, a semiconductor encapsulant, a sealing sheet, a coating material for electric wires, or the like. As one embodiment of the present disclosure, the electromagnetic wave suppression material formed into a sheet shape may be formed and used at a temperature of 120°C to 200°C. It may be formed under atmospheric pressure, or may be press-formed under the condition of a pressure of 20 MPa or lower.

[0050] As one embodiment of the present disclosure, for example, a semiconductor element fixed on a substrate can be encapsulated with a semiconductor element encapsulant containing the electromagnetic wave suppression material of the present disclosure to obtain a resin-encapsulated electronic component. Note that, to obtain an electronic component, a known molding method is used without particular limitation. The most common molding method is low-pressure transfer molding, but molding by injection molding, casting molding, compression molding, or the like is also possible.

[0051] For example, in the case of the transfer molding method, heat treatment is performed in a molding die by a transfer molding machine at a temperature of 150°C or higher and 200°C or lower for a time of 20 seconds or longer and 200 seconds or shorter. The heat treatment for taking out the molded product from the molding die and completing curing may be performed at a temperature of 150°C or higher and 200°C or lower for 2 hours or longer and 12 hours or shorter.

[0052] Also, in the case of the compression molding method, first, a substrate on which a semiconductor element is mounted is supplied to the upper mold of the molding die, and the electromagnetic wave suppressing material of the present disclosure is supplied into the cavity of the lower mold. Next, by clamping the upper and lower molds with a required clamping pressure, the substrate on which the semiconductor element is mounted is immersed in the electromagnetic wave suppressing material heated and melted in the lower mold cavity. Then, the heated and melted electromagnetic wave suppressing material in the lower mold cavity is pressed by the cavity bottom member, and a required pressure is applied under reduced pressure to perform compression molding. The molding conditions may be a temperature of 120°C or higher and 200°C or lower and a pressure of 2 MPa or higher and 20 MPa or lower.

Example

[0053] Next, the present disclosure will be specifically described by way of examples, but the present disclosure is not limited in any way by these examples.

[0054] [Manufacture of Electromagnetic Wave Suppressing Material] The compounds used for the manufacture of the electromagnetic wave suppressing materials in each example and comparative example are as follows. <(A) Thermosetting Resin> · Licaresin BEO-60E: Bisphenol A bis(triethylene glycol glycidyl ether) ether (main component, epoxy resin); manufactured by Shin Nippon Rika Co., Ltd. · EPICLON N670: Cresol novolak type epoxy resin; manufactured by DIC Corporation <(B) Inorganic Filler> · Denka fused silica FB-940: manufactured by Denka Co., Ltd.; d50 = 15 μm, specific surface area = 2.6 m 2 / g · Denka fused silica FB-105: manufactured by Denka Co., Ltd.; d50 = 12 μm, specific surface area = 4.5 m 2 / g <(C) Cellulose nanofiber> · ELLEX-S: Manufactured by Oji Paper Co., Ltd.; average fiber diameter = 20 - 200 nm, absorbance (I) / absorbance (II) = 0.1 <TEMPO-treated cellulose nanofiber> The TEMPO-treated cellulose nanofiber obtained by the following method was used. To 700 mL of an aqueous solution containing 2% by mass of the above-mentioned ELLEX-S which is (C) cellulose nanofiber, 20 mL of an aqueous solution containing 0.8% by mass of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and 20 mL of an aqueous solution containing 0.8% by mass of sodium bromide were added. An aqueous sodium hypochlorite solution adjusted to a Cl concentration of 8% by mass was slowly added to the resulting mixed solution to cause a TEMPO oxidation reaction. An aqueous sodium hydroxide solution was added thereto to adjust the pH to 10.5, followed by washing with pure water and drying at room temperature to obtain TEMPO-treated cellulose nanofiber (surface-treated cellulose nanofiber). <(D) Silicone compound> · GLYMO: Trimethoxyepoxysilane; manufactured by Evonik Japan Co., Ltd. · DOWSIL TM Z-6883 Silane: Phenylaminopropyltrimethoxysilane; manufactured by Dow Corning Toray Co., Ltd. · KR-516: Silicone oligomer; manufactured by Shin-Etsu Chemical Co., Ltd. <Other silicone compounds> · KBM-402: 3-Glycidoxypropylmethyldimethoxysilane; manufactured by Shin-Etsu Chemical Co., Ltd. <Hardener> · MEH-7500: Triphenylmethane type phenol resin; manufactured by Meiwa Kasei Co., Ltd. · BRG556: Phenol novolac resin; manufactured by Aica Kogyo Co., Ltd. <Hardening accelerator> · 1,2-DMZ: Imidazole compound; Shikoku Kasei Kogyo Co., Ltd. · 2P4MHZ-PW: Imidazole compound; Shikoku Kasei Kogyo Co., Ltd. <Release agent> · Carnauba No. 1: Carnauba wax; manufactured by Nikko Rica Co., Ltd.

[0055] (C) The ratio of the absorbance (I) to the absorbance (II) of cellulose nanofibers and TEMPO-treated cellulose nanofibers (absorbance (I) / absorbance (II)) was calculated by the following method. The dry (C) cellulose nanofibers and TEMPO-treated cellulose nanofibers were measured under the following conditions using the total reflection measurement method (ATR method) to obtain an infrared absorption spectrum. Measuring device: Manufactured by JASCO Corporation, product name: FT / IR-4000 Measuring wavelength range: 650 - 4000 cm -1 Resolution: 4 cm -1 Incident angle: 45 degrees Number of integrations: 100 times The absorbance (I) at a wavelength of 1730 cm of the obtained infrared absorption spectrum and -1 the absorbance (II) at a wavelength of 1050 cm -1 were read, and the ratio of absorbance (I) to absorbance (II) was calculated.

[0056] (Examples 1 - 4 and Comparative Examples 1 - 5) After mixing each component of the type and blending amount described in Table 1 with a universal mixer, it was put into a twin-screw roll kneading device heated to 110°C, and a heat-kneading operation was performed until it became uniform. Next, the obtained heat-kneaded product was put into a cold roll, stretched into a sheet shape, and then molded to obtain a sheet-shaped electromagnetic wave suppression material. The obtained electromagnetic wave suppression material was compression-molded (temperature: 175°C, pressure: 10 MPa) into a sheet-shaped molded body with a thickness of 0.5 mm or 1.0 mm to obtain test pieces.

[0057] (Examples 5 - 9 and Comparative Examples 6 - 8) Each component of the type and compounding quantity described in Table 2 was put into a Henschel mixer and mixed. After that, it was put into a twin-screw roll kneading device heated to 110°C, and a heating and kneading operation was performed until it became uniform. Next, the obtained heat-kneaded product was put into a cold roll, stretched into a sheet shape, and then pulverized to obtain an electromagnetic interference suppression material composition. The obtained electromagnetic interference suppression material composition was compression molded (temperature: 175°C, pressure: 10 MPa) into a sheet-shaped molded body with a thickness of 0.5 mm or 1.0 mm to obtain a test piece.

[0058] [Measurement and Evaluation of Electromagnetic Wave Suppression Material] Regarding the electromagnetic wave suppression materials manufactured in the examples and comparative examples, the following measurements and evaluations were carried out. The evaluation results are shown in Tables 1 and 2.

[0059] (Moldability) The obtained test pieces were visually evaluated according to the following criteria. OK: No generation of nests, unfilled parts, and cracks is observed (no abnormalities are observed). NG: At least one of the generation of nests, unfilled parts, and cracks is observed.

[0060] (Electromagnetic Wave Absorption Performance) A molded body with a thickness of 0.5 mm was installed between a high-frequency oscillation device and a receiving antenna, and the electromagnetic wave intensity when generating electromagnetic waves with a frequency of 10 GHz was measured with and without the molded body, and the ratio (electromagnetic wave intensity absorbed by the molded body / electromagnetic wave intensity when there is no molded body) was taken as the electromagnetic wave absorption performance in dB units. Note that the electromagnetic wave intensity was measured according to "Transactions of the Institute of Electronics, Information and Communication Engineers B Vol. J97-B No. 3 pp. 279-285".

[0061] (Volume Resistivity) Using a molded body with a thickness of 1.0 mm, the volume resistivity at 150°C was measured according to JIS K-6911:2006. Note that the larger the value of the volume resistivity, the higher the insulation.

[0062] (Coefficient of Thermal Expansion) By the TMA method, using a thermal analyzer (manufactured by Seiko Instruments Inc., product name: TMA / SS-150), the temperature was raised at a rate of 10 °C / min, and from the obtained TMA chart, the slope of the portion closest to a straight line between 25 and 60 °C was taken as the linear expansion coefficient.

[0063] [Table 1]

[0064] [Table 2]

[0065] Unfilled portions were observed in the test pieces obtained in Comparative Examples 2, 3, and 7. Further, the electromagnetic wave suppression material obtained in Comparative Example 5 could not be formed into a test piece, and the measurement of the electromagnetic wave absorption performance could not be carried out. As shown in Tables 1 and 2, the electromagnetic wave suppression material of the present disclosure had good electromagnetic wave absorption performance in the high-frequency band, was more excellent in the electromagnetic interference reduction performance, and had high insulation.

Claims

1. (A) a thermosetting resin; (B) an inorganic filler; (C) cellulose nanofibers; (D) a silicone compound; comprising, In the infrared absorption spectrum of the (C) cellulose nanofiber obtained by using the total reflection measurement method (ATR) of the Fourier transform infrared absorption spectroscopy (FT-IR), the absorbance (I) at 1730 cm －１ and the absorbance (II) at 1050 cm －１ The ratio of (absorbance (I) / absorbance (II)) is 0.4 or less, wherein the (D) silicone compound has 3 or more alkoxy groups in one molecule, and the mass ratio ((D) / (C)) of the (D) silicone compound to the (C) cellulose nanofibers is 0.1 to 1.5, an electromagnetic wave suppression material.

2. The electromagnetic wave suppression material according to Claim 1, wherein the (A) thermosetting resin contains an epoxy resin.

3. The electromagnetic wave suppression material according to Claim 2, wherein the epoxy resin has a polyoxyalkylene structure.

4. The electromagnetic wave suppression material according to Claim 1 or 2, wherein the (D) silicone compound has a mass ratio of alkoxy groups in one molecule of 10 to 80% by mass.

5. The electromagnetic wave suppression material according to Claim 1 or 2, wherein the (D) silicone compound is an alkoxysilane compound.

6. An electronic component encapsulated with the electromagnetic wave suppression material according to Claim 1 or 2.

7. A cured product of the electromagnetic wave suppression material according to Claim 1 or 2.

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