Insert-molded housing and method for manufacturing an insert-molded housing

Abstract

An insert-molded housing is provided in which the electromagnetic wave absorbing sheet is less likely to peel off without the use of adhesive, and which can attenuate electromagnetic waves in the high-frequency band. [Solution] The insert-molded housing of the present disclosure comprises an electromagnetic wave absorbing sheet having an electromagnetic wave absorbing layer and an electromagnetic wave shielding layer, and a resin housing. The insert-molded housing has a flat plate portion. The flat plate portion is formed by laminating the electromagnetic wave shielding layer, the electromagnetic wave absorbing layer, and a resin layer which is part of the resin housing in this order. The electromagnetic wave absorbing layer contains a dielectric material. The ratio of the dielectric material to the total amount of the electromagnetic wave absorbing layer is 3% by mass to 10% by mass. The electromagnetic wave shielding layer is a specific metal foil. The reflection attenuation of the flat plate portion for electromagnetic waves in the frequency band from 60 GHz to 90 GHz is less than -15 dB. The adhesive strength between the resin layer and the electromagnetic wave absorbing layer is 1 N / cm or more. The flat plate portion satisfies the following formula (a). JPEG2026088719000009.jpg18149

Description

Technical Field

[0001] The present disclosure relates to an insert molding housing and a method for manufacturing an insert molding housing.

Background Art

[0002] In recent years, due to the high integration of electronic devices (e.g., semiconductor components), the operating frequency of electronic components has increased to a high frequency, and malfunction of electronic devices caused by radiated electromagnetic waves has become a problem. Conventionally, an electromagnetic shielding sheet has been used as a countermeasure against electromagnetic waves of electronic devices.

[0003] As an electromagnetic shielding sheet, Patent Document 1 discloses a resonance-type electromagnetic wave absorption sheet (hereinafter, also referred to as an "electromagnetic wave absorption sheet"). The electromagnetic wave absorption sheet is formed by laminating an electromagnetic wave absorption sheet via an adhesive layer on one side of a metal layer. The electromagnetic wave absorption sheet contains single-walled carbon nanotubes, a titanium compound, and a resin component.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The electromagnetic wave absorption sheet of Patent Document 1 is usually attached to a resin housing of an electronic device using an adhesive. However, for example, when the electromagnetic wave absorption sheet is manually attached to the resin housing, the thickness of the adhesive layer made of the adhesive may vary. Therefore, the electromagnetic wave absorption sheet attached to the resin housing may not be able to attenuate electromagnetic waves in a high-frequency band (e.g., 60 GHz to 90 GHz). That is, there is a risk of inferior quality stability.

[0006] On the other hand, insert molding is a method for integrating an electromagnetic wave absorbing sheet and a resin housing without using adhesives. In insert molding, an insert-molded housing is obtained in which the electromagnetic wave absorbing sheet and the resin housing are integrated by inserting the electromagnetic wave absorbing sheet into an injection molding die and then injection molding it. Therefore, there is a need for an insert-molded housing in which the electromagnetic wave absorbing sheet is less likely to peel off without the use of adhesives and which can attenuate electromagnetic waves in the high-frequency band (for example, 60 GHz to 90 GHz).

[0007] An object of one aspect of this disclosure is to provide an insert-molded housing and a method for manufacturing an insert-molded housing in which the electromagnetic wave absorbing sheet is less likely to peel off without the use of adhesive and which can attenuate electromagnetic waves in the high-frequency band (e.g., 60 GHz to 90 GHz). [Means for solving the problem]

[0008] The following embodiments are included as means for solving the above problems. <1> An insert-molded housing comprising an electromagnetic wave absorbing sheet (A) and a resin housing (B) integrally formed with the electromagnetic wave absorbing sheet (A) on one main surface side of the electromagnetic wave absorbing sheet (A), The electromagnetic wave absorbing sheet (A) has an electromagnetic wave absorbing layer (A1) that is in contact with the resin housing (B), and an electromagnetic wave shielding layer (A2) disposed on the electromagnetic wave absorbing layer (A1). The electromagnetic wave absorbing layer (A1) contains a dielectric material and a first thermoplastic resin, The content ratio of the dielectric material to the total amount of the electromagnetic wave absorbing layer (A1) is 3% by mass to 10% by mass. The electromagnetic wave shielding layer (A2) is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron. The resin housing (B) includes a second thermoplastic resin, The aforementioned insert-molded housing has a flat plate portion, The flat plate portion is formed by laminating the electromagnetic wave shielding layer (A2), the electromagnetic wave absorbing layer (A1), and a resin layer (B1) which is part of the resin housing (B) in this order. The adhesive strength between the resin layer (B1) and the electromagnetic wave absorbing layer (A1) is 1 N / cm or more. The reflection attenuation of the flat plate portion for electromagnetic waves in the frequency band from 60 GHz to 90 GHz is less than -15 dB. An insert-molded housing in which the aforementioned flat plate portion satisfies the following formula (a).

[0009]

number

[0010] (In equation (a), X represents the frequency (Hz) of the electromagnetic wave incident on the flat plate portion. c is 3.0 × 10 8 (This value is shown in m / s.) dA represents the thickness (μm) of the resin layer (B1). εA represents the relative permittivity of the resin layer (B1). dB represents the thickness (μm) of the electromagnetic wave absorbing layer (A1). εB represents the relative permittivity of the electromagnetic wave absorbing layer (A1). <2> The dielectric material includes at least one selected from the group consisting of carbon nanotubes, carbon black, and carbon nanofibers. <1> Insert-molded housing as described above. <3> The first thermoplastic resin comprises at least one of polypropylene and polyethylene. <1> or <2> Insert-molded housing as described above. <4> The content of the first thermoplastic resin is 50% to 97% by mass relative to the total amount of the electromagnetic wave absorbing layer (A1), <3> Insert-molded housing as described above. <5> The first thermoplastic resin further comprises a modified polyolefin resin, <1> ~ <4> An insert-molded housing as described in any one of the following. <6> The content of the modified polyolefin resin is 1% to 30% by mass relative to the total amount of the electromagnetic wave absorbing layer (A1). <5> Insert-molded housing as described above. <7> The thickness of the electromagnetic wave shielding layer (A2) is 100 μm or less. <1> ~ <6> An insert-molded housing as described in any one of the following. <8> By injection molding, the above <1> ~ <7> A method for manufacturing an insert-molded housing as described in any one of the following: The electromagnetic wave absorbing sheet (A) mentioned above is prepared, The electromagnetic wave shielding layer (A2) of the electromagnetic wave absorbing sheet (A) is attached to the cavity wall that constitutes the cavity of the injection molding die. The process involves filling the cavity of the injection mold to which the electromagnetic wave absorbing sheet (A) is attached with molten material for the resin housing (B) to manufacture the resin housing (B), A method for manufacturing an insert-molded housing, including [the specified component]. <9> In preparing the electromagnetic wave absorbing sheet (A), the electromagnetic wave absorbing sheet (A) is manufactured by an extrusion lamination method. <8> A method for manufacturing an insert-molded housing as described above. <10> In manufacturing the resin housing (B), the temperature of the injection mold is higher than 110°C lower than the melting point of the first thermoplastic resin, and lower than the melting point of the first thermoplastic resin. <8> or <9> A method for manufacturing an insert-molded housing as described above. <11> The injection molding die has at least one side gate on the cavity wall that does not face either of the main surfaces of the electromagnetic wave absorbing sheet (A) placed within the cavity, In installing the electromagnetic wave absorbing sheet (A), the electromagnetic wave absorbing sheet (A) is installed in the cavity such that the distance is 5 cm or more. The aforementioned distance represents the shortest distance between the electromagnetic wave absorbing sheet (A) and at least one of the side gates when viewed from a direction perpendicular to the main surface of the electromagnetic wave absorbing sheet (A). <8> ~ <10> A method for manufacturing an insert-molded housing as described in any one of the following. [Effects of the Invention]

[0011] According to one aspect of the present disclosure, there are provided an insert molding housing in which an electromagnetic wave absorbing sheet is difficult to peel off without using an adhesive and can attenuate electromagnetic waves in a high-frequency band (for example, 60 GHz to 90 GHz), and a method for manufacturing the insert molding housing.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is an external perspective view of an insert molding housing according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1. [Figure 3] FIG. 3 is a diagram for explaining a method for manufacturing an insert molding housing according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a photograph showing a surface on the electromagnetic wave shielding layer (A2) side of a flat plate portion in a state where the electromagnetic wave absorbing sheet (A) has melted and spread. [Figure 5] FIG. 5 is a photograph showing a surface on the resin layer (B1) side of a flat plate portion in a state where the electromagnetic wave absorbing sheet (A) has melted and spread. [Figure 6] FIG. 6 is a photograph showing a surface on the electromagnetic wave shielding layer (A2) side of a flat plate portion in a state where the electromagnetic wave absorbing sheet (A) has not melted and spread. [Figure 7] FIG. 7 is a photograph showing a surface on the resin layer (B1) side of a flat plate portion in a state where the electromagnetic wave absorbing sheet (A) has not melted and spread.

Embodiments for Carrying Out the Invention

[0013] In the present disclosure, a numerical range indicated using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions, or may be replaced with the values shown in the examples. In this disclosure, the amount of each component in the material means the total amount of multiple substances present in the material, unless otherwise specified, if there are multiple substances corresponding to each component in the material. In this disclosure, when embodiments are described with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. The sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto.

[0014] (1) Insert-molded housing The insert-molded housing of this disclosure (hereinafter also simply referred to as "insert-molded housing") comprises an electromagnetic wave absorbing sheet (A) and a resin housing (B) integrally formed with the electromagnetic wave absorbing sheet (A) on one main surface side of the electromagnetic wave absorbing sheet (A). The electromagnetic wave absorbing sheet (A) has an electromagnetic wave absorbing layer (A1) in contact with the resin housing (B) and an electromagnetic wave shielding layer (A2) disposed on the electromagnetic wave absorbing layer (A1). The electromagnetic wave absorbing layer (A1) contains a dielectric material and a first thermoplastic resin. The content ratio of the dielectric material to the total amount of the electromagnetic wave absorbing layer (A1) (hereinafter also simply referred to as "content ratio of dielectric material") is 3% by mass to 10% by mass. The electromagnetic wave shielding layer (A2) is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron. The resin housing (B) contains a second thermoplastic resin. The insert-molded housing has a flat plate portion. The flat plate portion is formed by laminating the electromagnetic wave shielding layer (A2), the electromagnetic wave absorbing layer (A1), and a resin layer (B1) which is part of the resin housing (B) in this order. The adhesive strength between the resin layer (B1) and the electromagnetic wave absorbing layer (A1) (hereinafter also simply referred to as "adhesive strength") is 1 N / cm or more. The reflection loss of the flat plate portion with respect to electromagnetic waves in the frequency band from 60 GHz to 90 GHz (hereinafter also simply referred to as "reflection loss of the flat plate portion") is less than -15 dB. The flat plate portion satisfies the following formula (a).

[0015]

number

[0016] In equation (a), X represents the frequency (Hz) of the electromagnetic wave incident on the flat plate portion. c is 3.0 × 10 8 The value is shown in m / s. dA represents the thickness (μm) of the resin layer (B1). εA represents the relative permittivity of the resin layer (B1). dB represents the thickness (μm) of the electromagnetic wave absorbing layer (A1). εB represents the relative permittivity of the electromagnetic wave absorbing layer (A1).

[0017] In this disclosure, "insert-molded housing" refers to a molded product formed by inserting an electromagnetic wave absorbing sheet (A) into an injection molding die and then injection molding the resin housing material. No adhesive layer is interposed between the electromagnetic wave absorbing sheet (A) and the resin housing (B). "Resin housing" refers to a container or part thereof that houses electronic equipment that emits electromagnetic waves. A "dielectric material" is a material that possesses dielectric properties. "Possessing dielectric properties" means that the real part of the complex relative permittivity is 10 or greater at 25°C and at any of the following GHz ranges: 10 GHz to 100 GHz. An "electromagnetic wave absorption layer" primarily refers to a layer that converts at least a portion of the energy of electromagnetic waves introduced into the layer into thermal energy (i.e., a layer that absorbs at least a portion of the energy of electromagnetic waves introduced into the layer). An "electromagnetic wave shielding layer" primarily refers to a layer that reflects electromagnetic waves. A "flat plate portion" refers to a flat plate-shaped portion.

[0018] Equation (a) shows the relationship for attenuation of electromagnetic waves introduced into the interior of a flat plate section. If the flat plate section satisfies equation (a), it indicates that electromagnetic waves are attenuated. If the flat plate section does not satisfy equation (a), it indicates that electromagnetic waves are not attenuated. Equation (a) is an optimized equation obtained by combining the following equation (Y) (see Non-Patent Document 1) and experimental data. Non-patent document 1: Osamu Hashimoto, "Fundamentals of Radio Wave Absorption Technology", [online], IEICE APMC Domestic Committee, Internet,<URL:https: / / apmc-mwe.org / mwe2007 / 05tutorial.html>

[0019] Equation (Y) is the theoretical formula for the input impedance of a λ / 4 type absorber using transmission line theory. In transmission line theory, the incident wave is a plane wave. A λ / 4 type absorber is constructed by stacking a resistive film, a spacer, and a metal plate in that order. In the stacking direction, the resistive film is positioned at a distance of λ / 4 from the metal plate. The spacer has a dielectric constant ε r It consists of a dielectric material. In equation (Y), equation (Y1) below represents the input impedance. Equation (Y2) below represents the wave impedance of a plane wave in free space. Equation (Y3) below represents the dielectric constant of the spacer. Equation (Y4) below represents the thickness of the spacer in the stacking direction (i.e., λ / 4). Equation (Y5) below represents the wavelength within the spacer.

[0020]

number

[0021] In equation (a), c represents the speed of light. Equation (a1) in equation (a) represents the optical path length of electromagnetic waves introduced into the flat plate portion. Equation (a2) in equation (a) represents the optical path length of electromagnetic waves inside the resin layer (B1) among the optical path lengths of electromagnetic waves introduced into the flat plate portion. Equation (a3) ​​in equation (a) represents the optical path length of electromagnetic waves inside the electromagnetic wave absorbing layer (A1) among the optical path lengths of electromagnetic waves introduced into the flat plate portion.

[0022]

number

[0023] Because the insert-molded housing of this disclosure has the above configuration, the electromagnetic wave absorbing sheet is less likely to peel off even without using adhesive, and electromagnetic waves in the high-frequency band (e.g., 60 GHz to 90 GHz) can be attenuated. The reasons why this disclosure is effective are not entirely clear, but they are presumed to be as follows: One of the reasons for the electromagnetic wave attenuation effect of the electromagnetic wave absorbing sheet (A) is the destructive interference of wavelengths of electromagnetic waves originating from the optical path between the incident surface of the electromagnetic wave absorbing sheet (A) (i.e., the surface of the electromagnetic wave absorbing layer (A1)) and the reflective surface (i.e., the interface between the electromagnetic wave absorbing layer (A1) and the electromagnetic wave shielding layer (A2)). The dielectric constant of the resin layer (B1) of the insert molded housing is different from that of air. In other words, the optical path length of electromagnetic waves propagating inside the resin layer (B1) is different from the optical path length of radio waves propagating through the air. As a result, if the insert molded housing is designed assuming that the resin layer (B1) is air, the optical path length of the electromagnetic waves will be shifted by the optical path length inside the resin layer (B1). Consequently, at frequencies in which the electromagnetic wave absorbing sheet exhibits an excellent electromagnetic wave attenuation effect, the insert molded housing will not exhibit a sufficient electromagnetic wave attenuation effect. To improve the adhesion between the electromagnetic wave absorbing layer (A1) and the resin layer (B1) of the electromagnetic wave absorbing sheet, it is necessary to adjust the molding conditions of the insert molding (e.g., temperature, resin composition, etc.). For example, if the temperature of the molten resin layer (B1) is too high, the electromagnetic wave absorbing layer (A1) will dissolve and become thinner. Therefore, even if the adhesion between the electromagnetic wave absorbing layer (A1) and the resin layer (B1) is good, the excellent electromagnetic wave attenuation effect of the insert-molded housing cannot be expected. If the temperature of the molten resin layer (B1) is too low, the molten resin layer (B1) will not fuse to the electromagnetic wave absorbing layer (A1). As a result, even if the insert-molded housing generates an excellent electromagnetic wave attenuation effect, good adhesion between the electromagnetic wave absorbing layer (A1) and the resin layer (B1) cannot be expected.

[0024] Insert-molded enclosures are preferably used as part of or as part of a container for housing electronic equipment. The insert-molded enclosure attenuates high-frequency electromagnetic waves (e.g., 60 GHz to 90 GHz) emitted from the housed electronic equipment. In addition, the electromagnetic shielding layer (A2) of the insert-molded enclosure reflects electromagnetic waves emitted from the housed electronic equipment. As a result, the insert-molded enclosure prevents electromagnetic waves emitted from the housed electronic equipment from being released outside the enclosure.

[0025] The shape of the insert-molded enclosure is not particularly limited as long as it has a flat plate portion, and can be appropriately selected according to the electronic equipment to be housed. The shape of the insert-molded enclosure may be container-like. A container shape has a bottom wall and a peripheral wall protruding from the periphery of the bottom wall. The flat plate portion may be a part of at least one of the bottom wall and the peripheral wall. The size of the insert-molded enclosure can be appropriately selected according to the type of electronic equipment to be housed.

[0026] (1.1) Flat plate part The insert-molded housing has a flat plate portion. The flat plate portion is formed by laminating an electromagnetic wave shielding layer (A2), an electromagnetic wave absorbing layer (A1), and a resin layer (B1) which is part of the resin housing (B) in that order. The flat plate portion satisfies the following formula (a).

[0027]

number

[0028] The shape of the flat plate portion is not particularly limited and may be cubic, rectangular, or irregular in shape. The size of the flat plate portion is appropriately selected according to the type of electronic equipment to be housed. The length of one side of the flat plate portion may be, for example, 1 cm to 10 cm. The thickness of the flat plate portion may be 500 μm to 3000 μm, 800 μm to 2000 μm, or 1000 μm to 1500 μm.

[0029] (1.1.1) Equation (a) The frequency (Hz) of the electromagnetic wave represented by "X" is not particularly limited and may be any frequency band that the electromagnetic wave is absorbed in, and may be a high-frequency band (for example, 60 GHz to 90 GHz).

[0030] The thickness (μm) of the resin layer (B1) represented by "dA" is not particularly limited and is appropriately selected according to the size of the insert molded housing, etc. The thickness of the resin layer (B1) may be 500 μm to 3000 μm, 800 μm to 2000 μm, or 900 μm to 1500 μm. Details of the resin housing (B) will be described later.

[0031] The relative permittivity of the resin layer (B1), represented by "εA", is not particularly limited and may be between 1.5 and 7, between 1.8 and 5, or between 2 and 4. The relative permittivity of the resin layer (B1) is adjusted by the material of the resin housing (B).

[0032] The thickness (μm) of the electromagnetic wave absorbing layer (A1), expressed in "dB," is not particularly limited and is appropriately selected according to the frequency band of electromagnetic waves to be absorbed. From the viewpoint of further improving the absorption performance of electromagnetic waves in the high frequency band (e.g., 60 GHz to 90 GHz), the thickness of the electromagnetic wave absorbing layer (A1) is preferably 800 μm or less, more preferably 500 μm or less. From the viewpoint of further improving the absorption performance of electromagnetic waves in the high frequency band (e.g., 60 GHz to 90 GHz), the thickness of the electromagnetic wave absorbing layer (A1) is preferably 200 μm or more, more preferably 300 μm or more. The thickness (μm) of the electromagnetic wave absorbing layer (A1) may be 200 μm to 800 μm. Details of the electromagnetic wave absorbing layer (A1) will be described later.

[0033] The relative permittivity of the electromagnetic wave absorbing layer (A1), represented by "εB", is not particularly limited and may be 3 to 20, 4 to 18, or 5 to 15. The relative permittivity of the electromagnetic wave absorbing layer (A1) is adjusted by the material of the electromagnetic wave absorbing layer (A1). Details of the electromagnetic wave absorbing layer (A1) will be described later.

[0034] (1.1.2) Reflection loss The return loss of the flat plate portion for electromagnetic waves in the frequency band from 60 GHz to 90 GHz is less than -15 dB. A return loss of less than -15 dB for the flat plate portion indicates that the flat plate portion attenuates electromagnetic waves in the high frequency band (e.g., 60 GHz to 90 GHz). The return loss of the flat plate portion may be less than -15 dB, less than -20 dB, -50 dB or more, or -40 dB or more. The return loss of the flat plate portion may be -50 dB or more and less than -15 dB. The method for measuring the return loss of the flat plate portion is the same as the method described in the examples.

[0035] Methods for adjusting the reflection loss of the flat plate portion to less than -15 dB include: (i) adjusting the dielectric properties to the optimal level that satisfies the formula by changing the content of fillers and matrix contained in the electromagnetic wave absorbing layer (A1); (ii) setting the thickness of the electromagnetic wave absorbing layer (A1) to the optimal thickness that satisfies formula (a) and the aforementioned dielectric properties; and (iii) adjusting the thickness of the electromagnetic wave shielding layer (A2) to a sufficient thickness (for example, 5 μm or more).

[0036] (1.1.3) Adhesive strength The adhesive strength between the resin layer (B1) and the electromagnetic wave absorbing layer (A1) is 1 N / cm or more. An adhesive strength of 1 N / cm or more indicates that the electromagnetic wave absorbing sheet (A) is unlikely to peel off the resin housing (B) even without the use of adhesive. The adhesive strength may be 1 N / cm or more, 2 N / cm or more, 20 N / cm or less, or 15 N / cm or less. The adhesive strength may be between 1 N / cm and 20 N / cm. The method for measuring the adhesive strength is the same as that described in the examples.

[0037] Methods for adjusting the adhesive strength to 1 N / cm or higher include adding a modified polyolefin resin (described later) to the first thermoplastic resin and increasing the content of the modified polyolefin resin relative to the total amount of the electromagnetic wave absorbing layer (A1), as well as adjusting the temperature of the molten resin housing during insert molding, the temperature of the injection mold, and the injection pressure.

[0038] (1.2) Electromagnetic wave absorbing sheet (A) The insert-molded housing is equipped with an electromagnetic wave absorbing sheet (A).

[0039] The electromagnetic wave absorbing sheet (A) has an electromagnetic wave absorbing layer (A1) and an electromagnetic wave shielding layer (A2). The electromagnetic wave absorbing sheet (A) may consist of an electromagnetic wave absorbing layer (A1) and an electromagnetic wave shielding layer (A2).

[0040] The portion of the electromagnetic wave absorbing sheet (A) corresponding to the flat portion may be the entire electromagnetic wave absorbing sheet (A) or a part of the electromagnetic wave absorbing sheet (A). If the portion of the electromagnetic wave absorbing sheet (A) corresponding to the flat portion is a part of the electromagnetic wave absorbing sheet (A), the shape of the portion that is different from the part of the electromagnetic wave absorbing sheet (A) may be flat or not.

[0041] The size of the electromagnetic wave absorbing sheet (A) is not particularly limited and can be appropriately selected depending on the type of electronic equipment to be housed in the insert-molded enclosure. The thickness of the electromagnetic wave absorbing sheet (A) may be 200 μm to 800 μm, or 300 μm to 500 μm.

[0042] (1.2.1) Electromagnetic wave absorption layer (A1) The electromagnetic wave absorbing layer (A1) primarily functions to absorb at least a portion of the energy of the electromagnetic waves introduced into it.

[0043] The thickness of the electromagnetic wave absorbing layer (A1) is sufficient as long as it satisfies equation (a), and is within the range described above.

[0044] (1.2.1.1) Dielectric materials The electromagnetic wave absorbing layer (A1) contains a dielectric material. As a result, the electromagnetic wave absorbing layer (A1) has the ability to absorb electromagnetic waves.

[0045] Dielectric materials are not particularly limited as long as they possess dielectric properties. Examples of dielectric materials include carbon materials (e.g., carbon nanotubes (hereinafter also referred to as "CNT"), carbon black, carbon nanofibers, and graphite), titanium compounds (e.g., barium titanate, strontium titanate, and calcium titanate), potassium compounds (e.g., potassium dihydrogen phosphate, potassium fluoride, potassium carbonate, and potassium bicarbonate), metal niobates (e.g., lithium niobate, lead niobate, and strontium barium niobate), tartaric acid derivatives (e.g., potassium sodium tartrate, potassium bitartrate, and sodium bitartrate), metal oxides (e.g., titanium oxide, aluminum oxide, and silicon oxide), and organic substances (e.g., thiourea and triglyceride sulfate). Dielectric materials may be used individually or in combination of two or more types.

[0046] In particular, the dielectric material preferably includes at least one selected from the group consisting of carbon black, carbon nanofibers, and carbon nanotubes. Metals have difficulty absorbing electromagnetic waves (especially high-frequency electromagnetic waves) due to the snake limit. By including at least one of the above-mentioned dielectric materials, the electromagnetic wave absorbing layer (A1) can be expected to absorb high-frequency electromagnetic waves (e.g., 60 GHz to 90 GHz) even at relatively high frequencies due to its dielectric properties. The dielectric material more preferably contains carbon nanotubes (CNTs). The inclusion of CNTs in the dielectric material improves the absorption properties of the electromagnetic wave absorber. Details about CNTs will be described later.

[0047] The shape of the dielectric material is not particularly limited and can be spherical, needle-shaped, rod-shaped, fibrous, flat, flaky, or plate-shaped. The size of the dielectric material is not particularly limited and can be appropriately selected depending on the type of dielectric material. When the dielectric material is spherical, needle-shaped, rod-shaped, or fibrous, the diameter of the dielectric material is preferably 7 nm to 50 nm. When the dielectric material is needle-shaped, rod-shaped, or fibrous, the aspect ratio is preferably 100 to 1500, more preferably 200 to 1500. When the dielectric material is flat, flaky, or plate-shaped, the thickness of the dielectric material is preferably 7 nm to 50 nm.

[0048] The dielectric material content relative to the total amount of the electromagnetic wave absorbing layer (A1) is between 3% and 10% by mass. If the dielectric material content exceeds 10% by mass, the dielectric material may reflect electromagnetic waves due to the percolation phenomenon, potentially significantly reducing the electromagnetic wave absorption performance of the electromagnetic wave absorbing layer (A1). If the dielectric material content is less than 3% by mass, the electromagnetic wave absorption performance of the electromagnetic wave absorbing layer (A1) may be insufficient. The content of the dielectric material may be 14% by mass or less, 12% by mass or less, 1% by mass or more, or 3% by mass or more.

[0049] (1.2.1.1.1) Carbon nanotubes CNTs have a shape in which graphene sheets are rolled into a single-layer or multi-layered tubular structure. The CNTs preferably contain at least one of single-walled carbon nanotubes (hereinafter also referred to as "single-walled CNTs") and multi-walled carbon nanotubes (hereinafter also referred to as "multi-walled CNTs"), more preferably contain multi-walled CNTs, and even more preferably contain multi-walled CNTs. By containing at least one of single-walled CNTs and multi-walled CNTs, the absorption performance of the electromagnetic wave absorbing layer (A1) is better even with a small amount of added CNTs. By containing multi-walled CNTs, the raw material for the electromagnetic wave absorbing layer (A1) has a lower viscosity than that of single-walled CNTs. Therefore, the manufacturing process for the electromagnetic wave absorbing layer (A1) can be simplified. Furthermore, multi-walled CNTs are more cost-effective than single-walled CNTs. Moreover, multi-walled CNTs have a capacitor-like structure. Therefore, it is presumed that the electromagnetic wave absorption performance of the electromagnetic wave absorbing layer (A1) is even better.

[0050] "Single-walled carbon nanotubes" refer to carbon nanotubes in which a single layer of graphene sheet is rolled into a cylindrical shape. "Multi-walled carbon nanotubes" refer to carbon nanotubes in which a multi-layered structure of graphene sheet is rolled into a cylindrical shape.

[0051] The average diameter of the CNTs is preferably 7 nm to 50 nm, more preferably 10 nm to 50 nm, and even more preferably 20 nm to 40 nm. If the average diameter of the CNTs is within the above range, aggregation of CNTs in the thermoplastic resin can be effectively suppressed. The average length of the CNTs is preferably 1000 nm to 10000 nm, more preferably 2000 nm to 5000 nm. The aspect ratio is preferably 100 to 1500, more preferably 200 to 1500. If the average length of the CNTs is within the above range, aggregation of CNTs in the thermoplastic resin (A) can be effectively suppressed. The average diameter and average length of carbon nanotubes (CNTs) can be determined, for example, by measuring the diameter and length of a randomly selected group (n=10) of CNTs during observation using an electron microscope, and then calculating their arithmetic mean.

[0052] It is preferable that the CNTs are dispersed within the electromagnetic wave absorbing layer (A1). In other words, it is preferable that the CNTs are not aggregated within the electromagnetic wave absorbing layer (A1). Dispersed carbon nanotubes (CNTs) tend to generate less eddy current electromotive force in response to electromagnetic waves compared to when CNTs are aggregated. As a result, CNTs dispersed within the electromagnetic wave absorption layer (A1) can efficiently convert high-frequency electromagnetic waves (e.g., 60 GHz to 90 GHz) into heat. The method for dispersing CNTs in the first thermoplastic resin is not particularly limited and includes physical dispersion methods and chemical dispersion methods. Physical dispersion methods use dispersants, which will be described later. Chemical dispersion methods introduce functional groups to the surface of the CNTs. More specifically, chemical dispersion methods use surface modifiers, which will be described later.

[0053] From the viewpoint of improving the electromagnetic wave absorption performance of the electromagnetic wave absorption layer (A1), the CNT content is preferably 0.3% to 9% by mass, more preferably 0.4% to 8% by mass, and even more preferably 0.5% to 7% by mass, relative to the total amount of the electromagnetic wave absorption layer (A1).

[0054] CNTs may be commercially available. Examples of commercially available CNTs include Nanocyl's "NC7000," Seena Nanotechnology Co., Ltd.'s "FLOTUBE9000," and OCSiAl's "Tubal."

[0055] (1.2.1.2) First thermoplastic resin The electromagnetic wave absorbing layer (A1) contains a first thermoplastic resin. This allows the electromagnetic wave absorbing sheet (A) and the resin housing (B) to be integrated by insert molding. Furthermore, the first thermoplastic resin also functions as a binder for the dielectric material.

[0056] Examples of the first thermoplastic resin include polypropylene, polyethylene, polyamide, hydrogenated styrene-based thermoplastic elastomer (SEBS), ethylene-propylene copolymer, ethylene-butene copolymer, propylene-butene copolymer, ethylene-methacrylate copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ionomer resin, polybutene, 4-methylpentene-1 resin, cyclic polyolefin resin, ethylene-styrene copolymer, styrene resin, styrene-ethylene-butylene-styrene block copolymer, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyacetal, polyphenylene oxide, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, cellulose acetate, polyester, polyimide, fluororesin, polysulfone, polyethersulfone, polyarylate, polyetheretherketone, liquid crystal polymer, thermoplastic polyurethane, thermoplastic elastomer, and biodegradable polymer. These resins may be used individually or in combination of two or more types.

[0057] Polypropylene is, for example, a homopolymer of propylene (homopropylene) or a propylene-α-olefin copolymer. Polypropylene may contain several different isotactic polypropylenes. The α-olefin is not particularly limited, but preferably includes ethylene and α-olefins having 4 to 20 carbon atoms. These α-olefins may be one or more.

[0058] The first thermoplastic resin preferably contains at least one of polypropylene and polyethylene. This allows for the appropriate dispersion of dielectric material while maintaining relatively low mechanical strength and heat resistance of the electromagnetic wave absorbing sheet (A). The first thermoplastic resin preferably contains polypropylene, and more preferably is polypropylene, from the viewpoint of mechanical strength, heat resistance, and injection moldability.

[0059] The melting point of the first thermoplastic resin is not particularly limited and may be 90°C to 300°C, 120°C to 270°C, or 150°C to 250°C.

[0060] The content of the first thermoplastic resin is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, relative to the total amount of the electromagnetic wave absorbing layer (A1), from the viewpoint of mechanical strength, heat resistance, and moldability. The content of the first thermoplastic resin is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less, relative to the total amount of the electromagnetic wave absorbing layer (A1), from the viewpoint of mechanical strength, heat resistance, and moldability. The content of the first thermoplastic resin may be 50% by mass to 99% by mass, relative to the total amount of the electromagnetic wave absorbing layer (A1).

[0061] (1.1.2.1.3) Modified polyolefin resins The first thermoplastic resin preferably further contains a modified polyolefin resin. This improves the adhesion performance between the electromagnetic wave absorbing layer (A1) and the electromagnetic wave shielding layer (A2), as well as the adhesion performance between the electromagnetic wave absorbing layer (A1) and the resin housing (B).

[0062] The modified polyolefin resin is a resin in which at least a portion of the propylene-based polymer has been modified, and it is preferable that at least a portion of the propylene-based polymer is graft-modified with an unsaturated carboxylic acid or its derivative (hereinafter also referred to as "graft monomer").

[0063] The propylene polymer may be isotactic polypropylene or syndiotactic polypropylene. The propylene polymer may be homopolypropylene, a random copolymer of propylene and α-olefins having 2 to 20 carbon atoms (excluding propylene), or a block copolymer. The α-olefin may be used alone or in combination of two or more types.

[0064] Examples of graft monomers include acid anhydrides, esters, amides, imides, and metal salts of unsaturated carboxylic acids. Examples of graft monomers include maleic anhydride, citraconic anhydride, itaconic anhydride; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, monoethyl maleate, diethyl maleate; meth)acrylamide, monoamide maleate, diamide maleate, N-monoethyl maleate; maleimide, N-butylmaleimide, N-phenylmaleimide; sodium (meth)acrylate, and potassium (meth)acrylate. These graft monomers may be used individually or in combination of two or more.

[0065] The amount of graft modification in 100% by mass of propylene polymer is preferably 0.05% to 10% by mass, more preferably 0.10% to 8% by mass, and even more preferably 0.15% to 5% by mass. The amount of graft modification can be easily controlled, for example, by appropriately selecting the grafting conditions. The amount of structural units derived from unsaturated carboxylic acids and / or their derivatives (graft modification amount) can be determined by infrared absorption spectroscopy by the peak derived from the structural units (1790 cm⁻¹ in the case of maleic anhydride). -1 The intensity of the substance is measured and quantified using a pre-prepared calibration curve.

[0066] The method for grafting graft monomers onto a propylene polymer is not particularly limited and any known method is acceptable.

[0067] Modified polyolefin resins may be commercially available products.

[0068] The content of the modified polyolefin resin is preferably 0% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to the total amount of the magnetic wave absorbing layer (A1), from the viewpoint of mechanical strength, heat resistance, and moldability. The content of the modified thermoplastic resin is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, relative to the total amount of the electromagnetic wave absorbing layer (A1), from the viewpoint of mechanical strength, heat resistance, and moldability. The content of the modified polyolefin resin may be 0% to 30% by mass, and may be 1% to 30% by mass, relative to the total amount of the electromagnetic wave absorbing layer (A1).

[0069] (1.1.2.1.4) Additives The electromagnetic wave absorbing layer (A1) may further contain additives.

[0070] Examples of additives include surface modifiers, colorants, antioxidants, light stabilizers, metal deactivators, flame retardants, and antistatic agents.

[0071] (1.2.2) Electromagnetic shielding layer (A2) The electromagnetic shielding layer (A2) primarily functions to reflect electromagnetic waves. In the insert-molded housing, the electromagnetic shielding layer (A2) is exposed. In other words, the electromagnetic shielding layer (A2) constitutes a part of the surface of the insert-molded housing.

[0072] The thickness of the electromagnetic shielding layer (A2) is preferably 100 μm or less. A thickness of 100 μm or less improves the conformability to the injection molding die during insert molding and the productivity of winding the electromagnetic wave absorbing sheet (A). The thickness of the electromagnetic shielding layer (A2) is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of exhibiting the function of reflecting electromagnetic waves. The thickness of the electromagnetic shielding layer (A2) is more preferably 50 μm or less from the viewpoint of flexibility during handling. The thickness of the electromagnetic shielding layer (A2) may be 5 μm to 100 μm.

[0073] The electromagnetic shielding layer (A2) is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron. When the electromagnetic shielding layer (A2) is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron, most electromagnetic waves are reflected without passing through the electromagnetic shielding layer (A2) (i.e., the electromagnetic shielding layer (A2) can shield almost all electromagnetic waves). The electromagnetic shielding layer (A2) may be aluminum foil.

[0074] (1.3) Resin housing (B) The insert-molded housing comprises a resin housing (B). The resin housing (B) functions as a container or part thereof for housing electronic equipment.

[0075] The resin housing (B) is an injection-molded product. The resin housing (B) is welded to the electromagnetic wave absorbing layer (A1) of the electromagnetic wave absorbing sheet (A).

[0076] The shape of the resin housing (B) is the same as the shape exemplified for the insert-molded housing. The size of the resin housing (B) is appropriately selected according to the type of electronic device to be housed.

[0077] The resin housing (B) includes a second thermoplastic resin. The second thermoplastic resin is not particularly limited as long as it is a resin that can be welded to the first thermoplastic resin, and is appropriately selected depending on the type of first thermoplastic resin. Examples of the second thermoplastic resin are the same as those exemplified as the first thermoplastic resin. The second thermoplastic resin may be the same as or different from the first thermoplastic resin.

[0078] The second thermoplastic resin preferably further contains a modified polyolefin resin. This improves the adhesion performance between the magnetic wave absorption layer (A1) and the resin housing (B). Examples of the modified polyolefin resin include those exemplified as the modified polyolefin resin of the first thermoplastic resin. The modified polyolefin resin of the second thermoplastic resin may be the same as or different from the modified polyolefin resin of the first thermoplastic resin.

[0079] The melting point of the second thermoplastic resin is not particularly limited and may be 100°C to 230°C, 120°C to 200°C, or 140°C to 180°C.

[0080] The resin housing (B) may further contain additives. Examples of additives are the same as those exemplified as additives for the electromagnetic wave absorbing layer (A1).

[0081] (1.4)Electronic equipment The electronic devices housed in the insert-molded enclosure are not particularly limited and include, for example, ADAS (Advanced Driver-Assistance Systems), electronic control units, secondary batteries, power converters for motor drive in electric vehicles, desktop personal computers, laptop personal computers, tablet personal computers, mobile phones, smartphones, digital cameras, portable music players, electronic game devices, medical devices, and televisions. An electronic control unit is an electronic control circuit whose main component is a microcomputer. The microcomputer includes a CPU, RAM (Random Access Memory), ROM (Read Only Memory), non-volatile memory, and an interface (I / F). The CPU performs various functions by executing programs stored in the ROM. For example, in an electronic control unit for an electric vehicle, the CPU controls the vehicle's movement or overall operation. Examples of rechargeable batteries include lithium-ion batteries, lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries.

[0082] (1.5) Example of an insert-molded housing An embodiment of the insert-molded housing of this disclosure will be described with reference to Figures 1 and 2.

[0083] The insert-molded housing 1 is a container for housing electronic equipment. As shown in Figure 1, the insert-molded housing 1 comprises an electromagnetic wave absorbing sheet (A) 10 and a resin housing (B) 20. The resin housing (B) 20 is integrally formed with the electromagnetic wave absorbing sheet (A) 10 on one main surface S10A (see Figure 2) side of the electromagnetic wave absorbing sheet (A) 10. The electromagnetic wave absorbing sheet (A) 10 is a square-shaped sheet.

[0084] Hereinafter, the direction in which one pair of sides of the electromagnetic wave absorbing sheet (A) 10 extends is defined as the "X-axis direction". The direction in which the other pair of sides of the electromagnetic wave absorbing sheet (A) 10 extends is defined as the "Y-axis direction". The thickness direction of the electromagnetic wave absorbing sheet (A) 10 is defined as the "Z-axis direction". The X-axis, Y-axis, and Z-axis are all orthogonal to each other. These orientations do not limit the orientation of the insert molded housing when used in this disclosure.

[0085] (1.5.1) Electromagnetic wave absorbing sheet (A) The electromagnetic wave absorbing sheet (A) 10 is a sheet-like material. The electromagnetic wave absorbing sheet (A) 10 has an electromagnetic wave absorbing layer (A1) 11 and an electromagnetic wave shielding layer (A2) 12. The electromagnetic wave absorbing layer (A1) 11 is in contact with the resin housing (B) 20. The electromagnetic wave shielding layer (A2) 12 is placed on the electromagnetic wave absorbing layer (A1).

[0086] The electromagnetic wave absorbing layer (A1) 11 contains a dielectric material and a first thermoplastic resin. The content of the dielectric material is 3% to 10% by mass. The electromagnetic wave shielding layer (A2) 12 is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron. The thickness L12 of the electromagnetic wave shielding layer (A2) 12 (see Figure 2) is preferably 100 μm or less.

[0087] (1.5.2) Resin housing (B) The resin housing (B) 20 is an injection-molded product. The resin housing (B) 20 is a container-shaped object. The resin housing (B) 20 has a square-shaped bottom wall portion 21 and four wall portions 22-24 that protrude from the periphery of the bottom wall portion 21. The four wall portions 22-24 constitute the peripheral wall. The bottom wall portion 21 and the wall portions 22-24 are integrally formed. The resin housing (B) 20 contains a second thermoplastic resin.

[0088] (1.5.3) Flat plate part The insert-molded housing 1 has a flat plate portion R1 (see Figures 1 and 2). The flat plate portion R1 is formed in part of the bottom wall portion 21. The flat plate portion R1 is formed by laminating an electromagnetic wave shielding layer (A2) 12, an electromagnetic wave absorption layer (A1) 11, and a resin layer (B1) 210 which is part of the resin housing (B) 20 in that order.

[0089] The adhesive strength between the resin layer (B1) 210 and the electromagnetic wave absorbing layer (A1) 11 is 1 N / cm or more. The reflection loss of the flat plate portion R1 for electromagnetic waves in the frequency band from 60 GHz to 90 GHz is less than -15 dB. The flat plate portion R1 satisfies the following equation (a).

[0090]

number

[0091] In equation (a), X represents the frequency (Hz) of the electromagnetic wave incident on the flat plate portion R1. c is 3.0 × 10⁻⁶ 8 The value is shown in m / s. dA represents the thickness L210 (μm) of the resin layer (B1) 210 (see Figure 2). εA represents the relative permittivity of the resin layer (B1) 210. dB represents the thickness L11 (μm) of the electromagnetic wave absorbing layer (A1) 11 (see Figure 2). εB represents the relative permittivity of the electromagnetic wave absorbing layer (A1) 11.

[0092] (1.5.4) Effects As described with reference to Figures 1 and 2, the insert-molded housing 1 comprises an electromagnetic wave absorbing sheet (A) 10 and a resin housing (B) 20. The electromagnetic wave absorbing sheet (A) 10 has an electromagnetic wave absorbing layer (A1) 11 and an electromagnetic wave shielding layer (A2) 12. The electromagnetic wave absorbing layer (A1) 11 contains a dielectric material and a first thermoplastic resin. The content of the dielectric material is 3% to 10% by mass. The electromagnetic wave shielding layer (A2) 12 is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron. The resin housing (B) 20 contains a second thermoplastic resin. The insert-molded housing 1 has a flat plate portion R1. The flat plate portion R1 is formed by laminating the electromagnetic wave shielding layer (A2) 12, the electromagnetic wave absorbing layer (A1) 11, and the resin layer (B1) 210 in this order. The adhesive strength between the resin layer (B1) 210 and the electromagnetic wave absorbing layer (A1) 11 is 1 N / cm or more. The reflection loss of the flat plate portion R1 for electromagnetic waves in the frequency band from 60 GHz to 90 GHz is less than -15 dB. The flat plate portion R1 satisfies the following equation (a). As a result, the insert-molded housing 1 is less likely to have the electromagnetic wave absorbing sheet peel off without the use of adhesive, and can attenuate electromagnetic waves in the high-frequency band (e.g., 60 GHz to 90 GHz).

[0093] As explained with reference to Figures 1 and 2, the dielectric material preferably includes at least one selected from the group consisting of carbon nanotubes, carbon black, and carbon nanofibers. This allows the electromagnetic wave absorbing layer (A1) 11 to absorb electromagnetic waves in the high-frequency band (e.g., 60 GHz to 90 GHz) even at relatively high frequencies due to its dielectric properties.

[0094] As explained with reference to Figures 1 and 2, the first thermoplastic resin preferably contains at least one of polypropylene and polyethylene. This allows for the appropriate dispersion of dielectric material while maintaining relatively low mechanical strength and heat resistance of the electromagnetic wave absorbing sheet (A) 11.

[0095] As explained with reference to Figures 1 and 2, the content of the first thermoplastic resin is preferably 50% to 97% by mass relative to the total amount of the electromagnetic wave absorbing layer (A1) 11.

[0096] As explained with reference to Figures 1 and 2, the first thermoplastic resin preferably further contains a modified polyolefin resin. This improves the adhesion performance between the electromagnetic wave absorbing layer (A1) 11 and the electromagnetic wave shielding layer (A2) 12, as well as the adhesion performance between the electromagnetic wave absorbing layer (A1) 11 and the resin housing (B) 20.

[0097] As explained with reference to Figures 1 and 2, the content of the modified polyolefin resin is preferably 1% to 30% by mass relative to the total amount of the electromagnetic wave absorbing layer (A1) 11.

[0098] As explained with reference to Figures 1 and 2, the thickness L12 of the electromagnetic wave shielding layer (A2) 12 is preferably 100 μm or less.

[0099] (2) Method for manufacturing insert molded housing The method for manufacturing an insert-molded housing according to the present disclosure is a method for manufacturing an insert-molded housing according to the present disclosure by injection molding. The method for manufacturing an insert-molded housing according to the present disclosure includes preparing the electromagnetic wave absorbing sheet (A) (hereinafter also referred to as the "preparation step"), attaching the electromagnetic wave shielding layer (A2) of the electromagnetic wave absorbing sheet (A) to the cavity wall constituting the cavity of an injection molding die (hereinafter also referred to as the "attachment step"), and filling the cavity of the injection molding die to which the electromagnetic wave absorbing sheet (A) is attached with molten material for the resin housing (B) (hereinafter also referred to as the "molten material") to manufacture the resin housing (B) (hereinafter also referred to as the "injection molding step"). The preparation step, the attachment step, and the injection molding step are carried out in this order.

[0100] Since the method for manufacturing an insert-molded housing according to this disclosure has the above configuration, it is possible to manufacture the insert-molded housing according to this disclosure.

[0101] (2.1) Preparation process In the preparation step, prepare the electromagnetic wave absorbing sheet (A).

[0102] The method for preparing the electromagnetic wave absorbing sheet (A) is not particularly limited. Examples of methods for manufacturing the electromagnetic wave absorbing sheet (A) include extrusion lamination, plating (e.g., electroless plating), pressing (e.g., a method of bonding the electromagnetic wave shielding layer (A2) and the electromagnetic wave absorbing layer (A1) by pressing), and spraying (e.g., a method of spraying a metallic spray onto the electromagnetic wave absorbing layer (A1)).

[0103] In preparing the electromagnetic wave absorbing sheet (A) (i.e., the preparation step), it is preferable to manufacture the electromagnetic wave absorbing sheet (A) by an extrusion lamination method. This allows for the continuous production of large-area electromagnetic wave absorbing sheets (A) in a short time, thus improving productivity.

[0104] (2.2) Installation process In the installation process, the electromagnetic wave shielding layer (A2) of the electromagnetic wave absorbing sheet (A) is attached to the cavity wall that constitutes the cavity of the injection molding die. This allows the molten material of the resin housing (B) to come into contact with the electromagnetic wave absorbing layer (A1) during the injection molding process.

[0105] The method for attaching the electromagnetic wave shielding layer (A2) of the electromagnetic wave absorbing sheet (A) to the cavity wall is not particularly limited. Examples include using double-sided tape, using temporary adhesive, and setting the injection molding die so that the inner surface of the bottom wall of the injection molding die is horizontal to gravity, and then placing the electromagnetic wave absorbing sheet (A) on the inner surface of the bottom wall. The position of the electromagnetic wave absorbing sheet (A) on the cavity wall is not particularly limited.

[0106] The injection molding die has at least one side gate on the cavity wall that does not face either of the main surfaces of the electromagnetic wave absorbing sheet (A) placed within the cavity, In the process of installing the electromagnetic wave absorbing sheet (A) (i.e., the "installation process"), it is preferable to install the electromagnetic wave absorbing sheet (A) in the cavity such that the distance (hereinafter also referred to as the "insert distance") is 5 cm or more. The aforementioned distance represents the shortest distance between the electromagnetic wave absorbing sheet (A) and at least one of the side gates, when viewed from a direction perpendicular to the main surface of the electromagnetic wave absorbing sheet (A). In the injection molding process, the temperature of the molten material near the side gate is higher than the temperature of the molten material further away from the side gate. Therefore, if the insert distance is less than 5 cm, the electromagnetic wave absorbing layer (A1) of the electromagnetic wave absorbing sheet (A) may melt due to the heat of the molten material. In other words, the electromagnetic wave absorbing layer (A1) may not maintain its shape during the injection molding process. As a result, the electromagnetic wave absorption performance of the resulting insert-molded housing will differ from the electromagnetic wave absorption performance designed for it. Consequently, the insert-molded housing may not be able to attenuate electromagnetic waves in the frequency band to be absorbed. On the other hand, in the installation process, by arranging the electromagnetic wave absorbing sheet (A) in the cavity such that the insert distance is 5 cm or more, the electromagnetic wave absorbing layer (A1) of the electromagnetic wave absorbing sheet (A) is less likely to melt due to the heat of the molten material. As a result, the insert-molded housing can attenuate electromagnetic waves in the frequency band to be absorbed.

[0107] Figure 3 is a diagram illustrating the distance between the electromagnetic wave absorbing sheet (A) and the side gate. In Figure 3, reference numeral 90 indicates an injection mold for manufacturing the insert molded housing 1. Reference numeral 91 indicates a side gate. Reference numeral R90 indicates a cavity. Reference numeral 92 indicates a cavity wall. The injection mold 90 has one side gate 91. An electromagnetic wave absorbing sheet (A) 10 is attached to the cavity wall 92. When viewed from the Z direction (i.e., when viewed from a direction perpendicular to the main surface S10A of the electromagnetic wave absorbing sheet (A) 10), the shortest distance L90 between the electromagnetic wave absorbing sheet (A) 10 and the side gate 91 is 5 cm or more.

[0108] The insert distance is preferably 4 cm to 20 cm, more preferably 5 cm to 18 cm, and even more preferably 6 cm to 15 cm, from the viewpoint of adhesion and electromagnetic wave characteristics.

[0109] The number of side gates is selected appropriately according to the size of the insert-molded housing 1, etc.

[0110] (2.3) Injection molding process In the injection molding process, molten material for the resin housing (B) is filled into the cavity of the injection molding die to which the electromagnetic wave absorbing sheet (A) is attached, thereby producing the resin housing (B). This yields the insert-molded housing of the present disclosure.

[0111] In manufacturing the resin housing (B) (i.e., the injection molding process), it is preferable that the temperature of the injection molding die is higher than 110°C lower than the melting point of the first thermoplastic resin, and lower than the melting point of the first thermoplastic resin. In the injection molding process, if the temperature of the injection mold is higher than the melting point of the first thermoplastic resin, the electromagnetic wave absorbing layer (A1) of the electromagnetic wave absorbing sheet (A) may melt due to the heat of the injection mold. In other words, the electromagnetic wave absorbing layer (A1) may not maintain its shape during the injection molding process. As a result, the electromagnetic wave absorption performance of the resulting insert-molded housing will differ from the electromagnetic wave absorption performance designed for it. Consequently, the insert-molded housing may not be able to attenuate electromagnetic waves in the frequency band to be absorbed. If the temperature of the injection molding die is lower than 110°C lower than the melting point of the first thermoplastic resin, the molten material may solidify easily, making it impossible to form a resin housing (B) of the desired shape. On the other hand, in the injection molding process, if the temperature of the injection mold is higher than 110°C lower than the melting point of the first thermoplastic resin, and lower than the melting point of the first thermoplastic resin, the electromagnetic wave absorbing layer (A1) of the electromagnetic wave absorbing sheet (A) is less likely to melt due to the heat of the injection mold. Furthermore, a resin housing (B) of the desired shape is easily formed. As a result, the insert-molded housing can attenuate electromagnetic waves in the frequency band to be absorbed.

[0112] The temperature of the injection molding die is preferably above the first temperature (i.e., the melting point T℃ of the first thermoplastic resin (hereinafter also simply referred to as "melting point T℃") - 110℃), more preferably above the second temperature (i.e., the melting point T℃ - 100℃), and even more preferably above the third temperature (i.e., the melting point T℃ - 90℃). The temperature of the injection molding die is preferably below the fourth temperature (i.e., the melting point T - 10℃), more preferably below the fifth temperature (i.e., the melting point T℃ - 20℃), and even more preferably below the sixth temperature (i.e., the melting point T℃ - 30℃). When the melting point of the first thermoplastic resin is 160°C, the temperature of the injection mold is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. When the melting point of the first thermoplastic resin is 160°C, the temperature of the injection mold is preferably 150°C or lower, 140°C or lower, and more preferably 130°C. [Examples]

[0113] The embodiments relating to this disclosure will be described in detail below with reference to the examples. However, this disclosure is not limited in any way to the descriptions of these examples.

[0114] [1] Example 1 [1.1] Preparation process The components used in the examples and comparative examples are as follows:

[0115] [1.1.1] Material [1.1.1.1] Materials for the electromagnetic wave absorption layer (A1) <First thermoplastic resin> • PP: "F704NP" (Manufacturer: Prime Polymer Co., Ltd., Composition material: Homo PP, MFR: 7g / 10min (2.16kg, 230℃)) • Modified PP: Commercial product (Constituent material: Isotactic homopolypropylene graft-modified with maleic anhydride, MFR: 100g / 10min, Density: 0.90g / cm³) 3 Graft amount of maleic anhydride: 3.0% by mass <Dielectric materials> • CNT: "NC7000" (Manufacturer: Nanocyl, Composition: Carbon nanotubes, Average diameter: 9.5 nm, Average length: 1.5 μm, Form: Powder, Layer structure: Multilayer)

[0116] [1.1.1.2] Materials for the electromagnetic shielding layer (A2) <Metal foil> • Aluminum foil: Commercially available product (thickness: 15μm)

[0117] [1.1.1.3] Materials for the resin housing (B) <Second thermoplastic resin> • PP: "F704NP" (Manufacturer: Prime Polymer Co., Ltd., Composition material: Homo PP, MFR: 7g / 10min (2.16kg, 230℃)) • PPGF: "V7100" (Manufacturer: Prime Polymer Co., Ltd., Composition: Glass fiber reinforced polypropylene, MFR: 7g / 10min (2.16kg, 230℃), Glass fiber: Short fibers (fiber length 1mm or less), Glass fiber ratio: 20% by mass)

[0118] [1.1.2] Preparation of the masterbatch 15 parts by mass of carbon nanotubes (CNTs) and 85 parts by mass of polypropylene (PP) were placed in an FM mixer (FM10C / I, manufactured by Nippon Coke Industries Co., Ltd., capacity: 9L) and stirred and mixed. The stirring temperature was 140°C, the stirring time was 60 minutes, and the screw rotation speed was 1000 rpm. A masterbatch was obtained. The ratio of the mass of CNTs to the total volume of the masterbatch was 15% by mass.

[0119] [1.1.3] Pellet preparation A dry blend was obtained by mixing 6 parts by mass of masterbatch, 89 parts by mass of modified PP (modified polyolefin resin), and 5 parts by mass of PP (polypropylene). A twin-screw extruder (Toshiba Machine Co., Ltd. "TEM-35B", screw diameter: 35 mm, L / D: 32, vented type) was prepared. A die with a 3 mm diameter hole for strand removal was attached to the outlet of the twin-screw extruder. The dry blend was fed into the twin-screw extruder, melted and kneaded, and extruded through the die to obtain strand-like material. The kneading temperature was 230°C and the screw rotation speed was 100 rpm. The strand-like material was cooled in a water bath and cut with a strand cutter. This obtained pellets.

[0120] [1.1.4] Fabrication of electromagnetic wave absorbing sheet (A) A compounding extruder (Technovel Co., Ltd. "KZW-15TW", screw diameter: 15 mmφ) equipped with a 400 mm wide T-die was prepared. The pellets were fed into the compounding extruder, and an electromagnetic wave absorbing layer (A1) was formed on aluminum foil (electromagnetic wave shielding layer (A2)) by an extrusion lamination method. This resulted in the production of an electromagnetic wave absorbing sheet (A). The electromagnetic wave absorbing sheet (A) consists of aluminum foil (electromagnetic wave shielding layer (A2)) and an electromagnetic wave absorbing layer (A1) laminated on the aluminum foil. The thickness of the electromagnetic wave absorbing sheet (A) can be adjusted by adjusting the feeding speed and take-up speed.

[0121] [1.2] Installation process An injection molding die 90, as shown in Figure 2, was prepared. The injection molding die 90 has one side gate 91. The shape of the cavity R90 of the injection molding die 90 was container-shaped. The size of the cavity bottom wall 92 constituting the cavity R90 was 12 cm × 12 cm.

[0122] The aluminum foil of the electromagnetic wave absorbing sheet (A) 10 was attached to the cavity bottom wall 92 using double-sided tape (Kapton Tape P-223 manufactured by Nitto Denko America). The insert distance L90 was 10 cm.

[0123] [1.3] Injection molding process An injection mold 90 was mounted on an injection molding machine (a fully automatic injection molding machine "EC-SXIII" manufactured by Shibaura Machine Co., Ltd.). The injection position of the upper mold (convex side mold) was adjusted so that the thickness H210 of the resin layer (B1) 210 was 935 μm. Molten PP (second thermoplastic resin) was filled into the cavity R90 of the injection mold 90 to produce a resin housing (B) 20. The temperature of the injection mold 90 was 60°C. In other words, the temperature of the injection mold 90 was 100°C lower than the melting point (160°C) of the first thermoplastic resin. As a result, the insert molded housing 1 shown in Figure 1 was obtained.

[0124] The insert-molded housing 1 has a flat plate portion R1 (see Figures 1 and 2). The flat plate portion R1 was formed in part of the bottom wall portion 21. The flat plate portion R1 is made up of an electromagnetic wave shielding layer (A2) 12, an electromagnetic wave absorbing layer (A1) 11, and a resin layer (B1) 210 which is part of the resin housing (B) 20, laminated in this order.

[0125] [2] Examples 2 to 5 and Comparative Examples 1 to 6 Except for the changes in materials as shown in Table 1, insert-molded enclosures were manufactured in the same manner as in Example 1. In Comparative Example 4 only, modified PP (modified polyolefin resin) was incorporated during the preparation of the masterbatch.

[0126] [3]Measurement method The physical properties of insert-molded enclosures and the like were measured as follows.

[0127] [3.1] Relative permittivity and relative permittivity loss [3.1.1] Relative permittivity and relative permittivity loss of electromagnetic wave absorbing layer (A1) The sample was obtained by peeling off the electromagnetic wave absorbing layer (A1) 11 from the electromagnetic wave absorbing sheet (A) 10. The relative permittivity and relative permittivity loss of the sample were measured using the nicloson-loss method with a network analyzer (Keysight Technologies "5290A"). The measured values ​​were referred to as "relative permittivity and relative permittivity loss of electromagnetic wave absorbing layer (A1)".

[0128] [3.1.2] Relative permittivity and relative permittivity loss of resin housing (B) The sample was obtained by peeling off the resin housing (B) 20 from the insert-molded housing 1. The relative permittivity and relative permittivity loss of the sample were measured using the nicloson-loss method with a network analyzer (Keysight Technologies "5290A"). The measured values ​​were referred to as "Relative permittivity and relative permittivity loss of resin housing (B)".

[0129] [3.2] Electromagnetic wave reflection attenuation A sample was obtained by cutting a 10 cm square from the flat plate portion R1 of the insert-molded housing 1. The sample consisted of an electromagnetic wave shielding layer (A2) 12, an electromagnetic wave absorbing layer (A1) 11, and a resin layer (B1) 210, all laminated in that order. The sample was fixed in place between a transmitting antenna and a receiving antenna facing each other. The resin layer (B1) of the sample faced the transmitting antenna. The S-parameters were measured using the free-space method under the following measurement conditions. The return loss of S11 was defined as the "electromagnetic wave return loss".

[0130] [3.2.1] Measurement conditions Network analyzer: Keysight Technologies "5290A" Millimeter-wave controller: Keysight Technologies' "N5250CX10" Transceiver antenna: Keycom millimeter-wave measurement horn antenna Coaxial cable: Gore 2.4mm connector cable assembly Distance between transmitting and receiving antennas: 300mm Measurement frequency: 60-90 GHz (main peaks are 60 GHz and 76 GHz)

[0131] [3.3] Adhesive strength A sample was obtained by cutting a strip from the flat plate portion R1 of the insert-molded housing 1. The size of the strip-shaped sample was 15 mm wide and 12 cm long. The sample consisted of an electromagnetic wave shielding layer (A2) 12, an electromagnetic wave absorbing layer (A1) 11, and a resin layer (B1) 210 laminated in this order. The adhesive strength was measured according to the method in accordance with JIS K6854-3 "T-type peel". Values ​​exceeding the effective measurement limit of the apparatus, 10 N / cm, were indicated as "<10". The measurement conditions were a temperature of 23°C, a peeling speed of 300 mm / min, and a test section of 10 mm to 70 mm. In Comparative Example 5, the sample fractured. The fracture interface of the sample in Comparative Example 5 was the interface between the resin layer (B1) and the electromagnetic wave absorbing layer (A1).

[0132] [3.4] Adhesion The flat plate portion R1 of the insert-molded housing 1 was cut with scissors, and the appearance was observed to evaluate the adhesion. Specifically, those in which the electromagnetic wave absorbing sheet (A) 10 and the resin housing (B) 20 clearly lifted and peeled off, or where a gap was observed as shown in the figure when the cross-section was observed using an SEM (Hitachi FlexSEM1000), were evaluated as "B1". Those that were not evaluated as "B1" were evaluated as "A1".

[0133] [3.5] Appearance The appearance of the flat plate portion R1 of the insert molded housing 1 was visually observed and evaluated. Specifically, as shown in Figures 4 and 5, those in which the electromagnetic wave absorbing sheet (A) 10 melted and spread were evaluated as "B2". As shown in Figures 6 and 7, those in which the electromagnetic wave absorbing sheet (A) 10 did not melt and spread were evaluated as "A2".

[0134] [3.6] Melting point The melting point (Tm) was determined in accordance with JIS K7121 using a differential scanning calorimeter (Hitachi High-Tech DSC200). Approximately 5 mg of the sample was placed in an aluminum pan for measurement and heated to 270°C at a heating rate of 10°C / min. The temperature of the largest melting peak among the measured melting peaks was defined as the "melting point."

[0135] [Table 1]

[0136] In Table 1, the "melting point" for "electromagnetic wave absorbing layer (A1)" refers to the melting point of the first thermoplastic resin (i.e., the pellet). The "temperature difference" refers to the value obtained by subtracting the temperature of the injection mold from the temperature of the electromagnetic wave absorbing layer (A1).

[0137] [4] Results In Comparative Examples 1 to 3, equation (a) was not satisfied. In Comparative Examples 1 to 4 and 6, the reflection attenuation of the flat plate portion for electromagnetic waves in the frequency band from 60 GHz to 90 GHz was not less than -15 dB. In Comparative Example 4, the content ratio of the dielectric material to the total amount of the electromagnetic wave absorbing layer (A1) was not 3 mass% to 10 mass%. In Comparative Example 5, the adhesive strength between the resin layer (B1) and the electromagnetic wave absorbing layer (A1) was not 1 N / cm or more. As a result of these findings, it was found that the insert-molded housings of Comparative Examples 1 to 6 are not "insert-molded housings in which the electromagnetic wave absorbing sheet is difficult to peel off without the use of adhesive, and which can attenuate electromagnetic waves in the high-frequency band (e.g., 60 GHz to 90 GHz)."

[0138] In Examples 1 to 5, the adhesive strength between the resin layer (B1) and the electromagnetic wave absorbing layer (A1) was 1 N / cm or more. The reflection attenuation of the flat plate portion for electromagnetic waves in the frequency band from 60 GHz to 90 GHz was less than -15 dB. The flat plate portion satisfied the following formula (a). As a result of these findings, it was found that the insert-molded housings of Examples 1 to 5 are "insert-molded housings in which the electromagnetic wave absorbing sheet is less likely to peel off without the use of adhesive, and which can attenuate electromagnetic waves in the high-frequency band (e.g., 60 GHz to 90 GHz)." [Explanation of symbols]

[0139] 1: Insert-molded housing 10: Electromagnetic wave absorbing sheet (A) 11: Electromagnetic wave absorption layer (A1) 12: Electromagnetic wave shielding layer (A2) 20: Resin housing (B) 210: Resin layer (B1) R1: Flat plate section

Claims

1. An insert-molded housing comprising an electromagnetic wave absorbing sheet (A) and a resin housing (B) integrally formed with the electromagnetic wave absorbing sheet (A) on one main surface side of the electromagnetic wave absorbing sheet (A), The electromagnetic wave absorbing sheet (A) has an electromagnetic wave absorbing layer (A1) that is in contact with the resin housing (B), and an electromagnetic wave shielding layer (A2) disposed on the electromagnetic wave absorbing layer (A1). The electromagnetic wave absorbing layer (A1) contains a dielectric material and a first thermoplastic resin, The content ratio of the dielectric material to the total amount of the electromagnetic wave absorbing layer (A1) is 3% by mass to 10% by mass. The electromagnetic wave shielding layer (A2) is a metal foil containing at least one selected from the group consisting of aluminum, copper, and iron. The resin housing (B) includes a second thermoplastic resin, The aforementioned insert-molded housing has a flat plate portion, The flat plate portion is formed by laminating the electromagnetic wave shielding layer (A2), the electromagnetic wave absorbing layer (A1), and a resin layer (B1) which is part of the resin housing (B) in this order. The adhesive strength between the resin layer (B1) and the electromagnetic wave absorbing layer (A1) is 1 N / cm or more. The reflection attenuation of the flat plate portion for electromagnetic waves in the frequency band from 60 GHz to 90 GHz is less than -15 dB. An insert-molded housing in which the aforementioned flat plate portion satisfies the following formula (a). [Math 1] (In equation (a), X represents the frequency (Hz) of the electromagnetic wave incident on the flat plate portion. c is 3.0 × 10 ８ (The value is shown in m / s.) dA represents the thickness (μm) of the resin layer (B1). εA represents the relative permittivity of the resin layer (B1). dB represents the thickness (μm) of the electromagnetic wave absorbing layer (A1). εB represents the relative permittivity of the electromagnetic wave absorbing layer (A1).

2. The insert-molded housing according to claim 1, wherein the dielectric material comprises at least one selected from the group consisting of carbon nanotubes, carbon black, and carbon nanofibers.

3. The insert-molded housing according to claim 1 or claim 2, wherein the first thermoplastic resin comprises at least one of polypropylene and polyethylene.

4. The insert-molded housing according to claim 3, wherein the content of the first thermoplastic resin is 50% by mass to 97% by mass relative to the total amount of the electromagnetic wave absorbing layer (A1).

5. The insert molded housing according to claim 1 or claim 2, wherein the first thermoplastic resin further comprises a modified polyolefin resin.

6. The insert-molded housing according to claim 5, wherein the content of the modified polyolefin resin is 1% by mass to 30% by mass relative to the total amount of the electromagnetic wave absorbing layer (A1).

7. The insert-molded housing according to claim 1 or claim 2, wherein the thickness of the electromagnetic wave shielding layer (A2) is 100 μm or less.

8. A method for manufacturing an insert-molded housing according to claim 1 or claim 2 by injection molding, The electromagnetic wave absorbing sheet (A) is prepared, The electromagnetic wave shielding layer (A2) of the electromagnetic wave absorbing sheet (A) is attached to the cavity wall that constitutes the cavity of the injection molding die. The process involves filling the cavity of the injection mold to which the electromagnetic wave absorbing sheet (A) is attached with molten material for the resin housing (B) to manufacture the resin housing (B), A method for manufacturing an insert-molded housing, including [the specified component].

9. The method for manufacturing an insert-molded housing according to claim 8, wherein the electromagnetic wave absorbing sheet (A) is prepared by an extrusion lamination method.

10. The method for manufacturing an insert molded housing according to claim 8, wherein, in manufacturing the resin housing (B), the temperature of the injection mold is higher than a temperature 110°C lower than the melting point of the first thermoplastic resin, and lower than the melting point of the first thermoplastic resin.

11. The injection molding die has at least one side gate on the cavity wall that does not face either of the main surfaces of the electromagnetic wave absorbing sheet (A) placed within the cavity, In installing the electromagnetic wave absorbing sheet (A), the electromagnetic wave absorbing sheet (A) is installed in the cavity such that the distance is 5 cm or more. The method for manufacturing an insert-molded housing according to claim 8, wherein the distance is the shortest distance between the electromagnetic wave absorbing sheet (A) and at least one of the side gates when viewed from a direction perpendicular to the main surface of the electromagnetic wave absorbing sheet (A).

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