JP2021136540A - Cover and antenna device - Google Patents

Abstract

To provide a cover and an antenna device, capable of suppressing a change of an electric wave transmissivity by a skin thickness fluctuation.SOLUTION: A cover 1 is a resin cover used for an electronic apparatus 10 that performs a communication by using an electric wave with a high frequency band, comprising: a surface layer 2 of which one part is exposed from the electronic apparatus; and an auxiliary layer 3 that contains foam having a density smaller than that of the surface layer, and is arranged in an inner part of the electronic apparatus so as to be contacted to the surface layer. In the cover 1, the minimum value ABS calculated by using a wavelength λ0 in air of the electric wave, a thickness d of the surface layer, N of the magnitude of a complex refractive index of the surface layer, and one or more larger integer number k may be 0.73 or smaller.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to covers and antenna devices.

In recent years, communication technology using radio waves in high frequency bands has been actively developed. For example, in the fields of mobile phones, autonomous driving, weather radar, etc., the use of radio waves in the high frequency band is expanding, and for example, the use of radio waves in the 1 to 100 GHz band is being considered.

For example, a mobile phone base station device uses radio waves in a high frequency band. Patent Document 1 shows a radome that is provided so as to surround a base station apparatus and forms an appearance. The radome acts as a cover that protects the internal equipment from the external environment.

Special Table 2019-508939

Here, it is known that radio waves are more likely to be attenuated as the frequency becomes higher. Therefore, it is important to use a cover having a large radio wave transmittance in an electronic device that uses radio waves in the 1 to 100 GHz band. In a flat cover as in Patent Document 1, radio waves are reflected on the front surface and the back surface. Therefore, when the thickness of the cover fluctuates, the transmittance of radio waves changes, resulting in poor manufacturing stability. Further, when the cover has a specific thickness, the reflected waves on the front surface and the back surface may interfere with each other to increase the reflection, and the transmittance of the radio wave may be reduced.

The present disclosure has been made in view of the above circumstances, and an object of the present invention is to provide a cover and an antenna device capable of suppressing a change in radio wave transmittance due to a change in skin thickness.

The cover according to an embodiment of the present disclosure is
A resin cover used in electronic devices that communicate using radio waves in the high frequency band.
The surface layer that is partially exposed from the electronic device,
It contains a foam having a density lower than that of the surface layer, and includes an auxiliary layer that is arranged inside the electronic device in contact with the surface layer.

The antenna device according to the embodiment of the present disclosure includes the above-mentioned cover.

According to the present disclosure, it is possible to provide a cover and an antenna device capable of suppressing a change in radio wave transmittance due to a change in skin thickness.

FIG. 1 is a diagram showing a configuration example of a cover according to an embodiment. FIG. 2 is a diagram illustrating an antenna device including a cover according to an embodiment. FIG. 3 is a diagram illustrating a reflected wave in the cover according to the embodiment. FIG. 4 is a diagram showing a configuration example of the intermediate layer. FIG. 5 is a diagram showing another configuration example of the intermediate layer. FIG. 6 is a diagram comparing the transmittances of radio waves of a plurality of covers. FIG. 7 is an image (magnification: 400 times) of a cross section of the foam cut in the thickness direction observed with a scanning electron microscope (SEM). FIG. 8 is a diagram illustrating a reflected wave in a cover of a conventional example.

(Cover configuration)
FIG. 1 is a diagram showing a configuration example of a cover 1 according to an embodiment of the present disclosure. The cover 1 is used in an electronic device 10 that communicates using radio waves in a high frequency band. The cover 1 is made of resin. The high frequency band is, for example, a frequency band of 1 to 100 GHz, but is not limited thereto. As another example, the high frequency band may be 300 MHz or higher. Further, as another example, the high frequency band may be 6 GHz or more.

The cover 1 transmits radio waves to and from the outside of the electronic device 10 so that transmission and reception can be performed by the antenna 6 provided inside the electronic device 10. For example, of the radio waves R ₀ from the outside of the electronic device 10, a part of the radio waves R ₂ is reflected by the cover 1, but the radio waves R ₁ pass through the cover 1 and are received by the antenna 6. Further, the cover 1 protects a device such as an antenna 6 provided inside the electronic device 10 from the external environment.

The cover 1 includes a surface layer 2 and an auxiliary layer 3. The auxiliary layer 3 may include a back layer 4 and an intermediate layer 5. The configuration of the cover 1 is not limited to this example. As another example, the auxiliary layer 3 may include only the back layer 4.

Here, as shown in FIG. 1, the orthogonal coordinates are set so that at least a part of the surface 21 of the surface layer 2 is parallel to the yz plane. The x-axis direction is the direction perpendicular to the surface 21. Further, the x-axis direction corresponds to the thickness direction of the surface layer 2, the intermediate layer 5, and the back layer 4, and the stacking direction thereof. For example, the thickness d of the surface layer 2 is the length in the x-axis direction.

The surface layer 2 is provided so that a part of the surface layer 2 is exposed from the electronic device 10. For example, the surface 21 of the surface layer 2 may be exposed from the electronic device 10, and other parts may be inside the electronic device 10. Further, the back surface 22 is a surface opposite to the front surface 21 on the surface layer 2. The front surface layer 2 is in contact with the auxiliary layer 3 on the back surface 22. The surface layer 2 may be made of a resin having a density of 0.9 g / cm ^{3 or more.} Further, the surface layer 2 may be appropriately subjected to surface treatment such as painting.

The auxiliary layer 3 contains a foam having a density lower than that of the surface layer 2, and is arranged inside the electronic device 10 in contact with the surface layer 2. The maximum bubble diameter of the foam contained in the auxiliary layer 3 may be 1500 μm or less as an example from the viewpoint of suppressing the scattering of radio waves. In the present embodiment, the auxiliary layer 3 includes a back layer 4 and an intermediate layer 5 made of a foam. As shown in FIG. 1, the intermediate layer 5 is arranged between the surface layer 2 and the back layer 4. The average density of the intermediate layer 5 is smaller than that of the surface layer 2 and larger than that of the back layer 4. The density of the cover 1 decreases from the surface layer 2 to the back layer 4. Further, the thickness of the intermediate layer 5 may be 0.1 mm or more and 50 mm or less as an example. A detailed description of the foam will be described later. The method of laminating the surface layer 2 and the auxiliary layer 3 is not particularly limited, but a method of heating one side of the foam to melt the surface to prepare (laminate) the surface layer and the auxiliary layer, and foams and skins having different densities. There is a method of laminating by laminating with an adhesive, an adhesive or the like having a very thin thickness (for example, one-fifth or less of the wavelength λ of the radio wave in the surface layer). In the case of laminating by bonding using an adhesive or an adhesive, it is preferable that the thickness of the adhesive and the adhesive layer is sufficiently small in order to reduce the influence on the radio wave transmittance.

(Electronics)
FIG. 2 is a diagram illustrating an antenna device which is an example of an electronic device 10 provided with a cover 1. The antenna device is, for example, a base station device for a mobile phone. As shown in FIG. 2, the antenna device may be composed of one base station unit. Further, the antenna device may be composed of a plurality of base station units. The base station unit has at least one antenna 6 inside. The base station unit uses the cover 1 in order to protect the internal equipment including the antenna 6 from wind and rain and to enable communication using radio waves in a high frequency band. The base station unit has, for example, a cover 1 in a part of the housing, and exposes the surface layer 2 to the outside. Here, the antenna device is not limited to the base station device of the mobile phone, and may be any device having a function of communicating using radio waves, for example, a meteorological radar device, satellite broadcasting equipment, artificial satellite, radar, voice communication. It may be equipment, a mobile phone, another device such as a wireless LAN, or the like. Here, the function of communicating using radio waves is a function of transmitting, receiving, or transmitting and receiving radio waves. Further, the electronic device 10 is not limited to the antenna device, and may be another device such as an in-vehicle device for measuring the inter-vehicle distance or automatic driving or a mobile terminal.

Here, when used in an electronic device 10 that communicates using radio waves in a high frequency band, a part of the cover 1 is provided inside the electronic device 10. The inside of the electronic device 10 can become hot due to heat dissipation of the device, for example. From the viewpoint of improving reliability, the cover 1 preferably has high heat resistance. For example, the back layer 4 that can be arranged near the device inside the electronic device 10 preferably has a deflection temperature under load of 100 ° C. or higher. Further, the resin constituting the cover 1 preferably satisfies the UL94 standard V-0.

(Interference of reflected waves)
Here, FIG. 8 is a diagram illustrating a reflected wave in the cover 101, which is a conventional example. The cover 101 of the conventional example does not include the auxiliary layer 3 in the present embodiment. That is, the cover 101 includes only the surface layer 2 which is a plate-shaped resin. In the example of FIG. 8, the cover 101 is used for the housing of the electronic device 110 having the antenna 6 inside, and the thickness d of the surface layer 2 satisfies (2k-1) × λ / 4. Here, "k" is an integer of 1 or more. “Λ” is a wavelength on the surface layer 2 of the radio wave communicated by the electronic device 110, and is obtained by _{λ 0 / N.} “Λ ₀ ” is the wavelength of radio waves in the air. Further, "N" is the magnitude of the complex refractive index of the surface layer 2. The cover 101 is arranged in the air, and the difference in the refractive index from the air causes reflection of radio waves on the front surface 21 and the back surface 22.

As shown in FIG. 8, the incident wave A of the radio wave from the outside of the electronic device 110 is reflected at the fixed end on the surface 21 of the surface layer 2. The reflected wave A propagates in the opposite direction of the x-axis positive direction, which is the propagation direction of the incident wave A, that is, in the x-axis negative direction. Further, the incident wave B of the radio wave from the outside of the electronic device 110 is reflected at the free end on the back surface 22 of the surface layer 2. The reflected wave B propagates in the opposite direction of the x-axis positive direction, which is the propagation direction of the incident wave B, that is, in the x-axis negative direction. When the thickness d of the surface layer 2 satisfies (2k-1) × λ / 4, the phase of the reflected wave A and the phase of the reflected wave B are aligned and strengthened. In the following, it is said that the strengthening condition is satisfied when the thickness d of the surface layer 2 satisfies (2k-1) × λ / 4. The reflected wave becomes large when the strengthening condition is satisfied. Therefore, among the radio waves from the outside of the electronic device 110, the radio waves that pass through the cover 101 and reach the antenna 6 are reduced. That is, when the strengthening condition is satisfied, the transmittance of the radio wave becomes small. Here, the case where the strengthening condition is just satisfied is regarded as the peak of the decrease in transmittance, and the transmittance becomes small even in the vicinity of the thickness d where the strengthening condition is satisfied. Here, the radio wave transmittance is indicated by T1 / T2, where T1 is the radio wave intensity immediately after the radio wave has passed through the cover 1 or the cover 101, and T2 is the radio wave intensity immediately before the radio wave is incident on the cover 1 or the cover 101. ..

The above-mentioned peak of transmittance decrease occurs every λ / 2. For example, when the electronic device 110 uses a radio wave of 100 GHz, λ / 2 is about 1.5 mm. Determining the thickness d of the surface layer 2 while avoiding a specific value of about 1.5 mm so as not to satisfy the strengthening condition can be a major design constraint. Further, even when the design avoids the strengthening condition, the thickness d of the surface layer 2 may satisfy the strengthening condition due to, for example, thermal expansion, deformation due to an external force, or aging. Therefore, there has been a demand for a configuration capable of suppressing fluctuations in the transmittance of radio waves when fluctuations in thickness occur.

FIG. 3 is a diagram illustrating a reflected wave in the cover 1 according to the present embodiment. Similar to the conventional example, the thickness d of the surface layer 2 of the cover 1 satisfies (2k-1) × λ / 4. Further, as in the conventional example, the incident wave A of the radio wave from the outside of the electronic device 110 is reflected at the fixed end on the surface 21 of the surface layer 2, and the reflected wave A is generated. Further, the incident wave B of the radio wave from the outside of the electronic device 110 is reflected at the free end on the back surface 22 of the surface layer 2, and the reflected wave B is generated. Here, in the cover 1 according to the present embodiment, the back surface 22 of the surface layer 2 is in contact with the auxiliary layer 3 containing the foam. Both the surface layer 2 and the auxiliary layer 3 are made of resin, and the difference in the refractive index between the surface layer 2 and the auxiliary layer 3 is smaller than the difference in the refractive index between the surface layer 2 and the air. Since the reflectance decreases as the difference in the refractive index decreases, the reflected wave B on the back surface 22 is suppressed as compared with the case of the conventional example. Therefore, the cover 1 according to the present embodiment can increase the transmittance of radio waves as compared with the conventional example even when the strengthening condition is satisfied.

Here, even if radio waves are reflected at the interface between the intermediate layer 5 and the back layer 4, both the intermediate layer 5 and the back layer 4 are made of resin, and the refractive indexes of the intermediate layer 5 and the back layer 4 are different. The difference is small. Therefore, it is considered that the reflection at the interface between the intermediate layer 5 and the back layer 4 does not affect the strengthening of the reflected waves. Further, as described above, the back layer 4 is composed of a foam having a lower density than the surface layer 2. Since the dielectric constant of the back layer 4 is smaller than the dielectric constant of the surface layer 2, the refractive index of the back layer 4 is smaller than the refractive index of the surface layer 2. Therefore, the reflectance at the interface between the back layer 4 and air is smaller than the reflectance at the interface between the surface layer 2 and air. Further, when the radio wave propagates through the cover 1, the radio wave is attenuated due to the dielectric loss. The dielectric constant described in the present specification refers to a relative permittivity.

Here, the intermediate layer 5 may have the same density uniformly, but it is preferable to have a density gradient in order to further increase the transmittance of radio waves. As shown in FIG. 4, the intermediate layer 5 may include a plurality of layers 5a, 5b, 5c, and 5d having different densities. Then, the density of the intermediate layer 5 may gradually decrease from the surface layer 2 side to the back layer 4 side. That is, the density of the layer 5a, the density of the layer 5b, the density of the layer 5c, and the density of the layer 5d may gradually decrease in this order. Here, the number of the plurality of layers included in the intermediate layer 5 is not limited to four. The number of multiple layers included in the intermediate layer 5 can be one, two, three, or five or more. Here, in order to reduce the difference in refractive index between adjacent layers, it is preferable that the number of the plurality of layers included in the intermediate layer 5 is large. Further, as shown in FIG. 5, it is more preferable that the density of the intermediate layer 5 gradually decreases from the surface layer 2 side to the back layer 4 side. By gently changing the density from the surface layer 2 to the back layer 4, it is possible to suppress the reflection of radio waves inside the cover 1.

FIG. 6 is a diagram comparing the transmittances of radio waves of a plurality of covers having different configurations. The horizontal axis represents the thickness d of the surface layer 2. The vertical axis shows the transmittance of radio waves. _{The characteristic curve TR 0} shown by the solid line shows the relationship between the thickness d of the cover 101 of the conventional example and the transmittance of the radio wave when a certain high frequency radio wave is used. Some high frequencies are, for example, 79 GHz. _{Further, the characteristic curves TR 1} , TR ₂ and TR ₃ shown by the broken line or the chain line are the thickness d of the cover 1 according to the present embodiment and the transmittance of the radio wave when the same high frequency radio wave is used. Show the relationship. The characteristic curve TR ₁ shows a case where only the back layer 4 is provided as the auxiliary layer 3. Further, the characteristic curve TR ₂ shows a case where the thickness of the intermediate layer 5 is 0.5 mm and the total thickness is 10 mm. Further, the characteristic curve TR ₃ shows a case where the thickness of the intermediate layer 5 is 2 mm and the total thickness is 10 mm.

In the example of FIG. 6, in the case of only the surface layer, the wavelength λ of the light in the surface layer is used, and the thickness of the surface layer fluctuates between λ / 8 and λ × 3/4, so that the maximum value and the minimum value of the transmittance are obtained. The difference between the values is about 16%. On the other hand, when the surface layer and the back layer (foam) are laminated, the transmittance fluctuation (difference between the maximum value and the minimum value) can be suppressed to 14% within the fluctuation range of the same thickness of the surface layer. The effect becomes even more remarkable when there is an auxiliary layer between the surface layer and the back layer (foam). That is, even if the surface layer thickness fluctuates within the range, the fluctuation in the radio wave transmittance of the obtained cover becomes small, so that the manufacturing stability can be improved. Further, when the thickness d of the surface layer 2 is, for example, d ₁ and d ₂ , the strengthening condition is satisfied. The strengthening condition is satisfied every λ / 2. For example, _{the difference between d 1} and d ₂ is λ / 2. As shown in the characteristic curve TR ₀ , the transmittance of the radio wave of the cover 101 of the conventional example becomes smaller even in the vicinity of the thickness d where the strengthening condition is satisfied, with the peak of decrease when the strengthening condition is just satisfied.

As in the characteristic curve TR _1, the cover 1 according to the present embodiment does not reduce the transmittance of radio waves even when the strengthening condition is just satisfied by the above configuration. Therefore, when the thickness d of the surface layer 2 takes a value that satisfies the strengthening condition and a value in the vicinity thereof, the transmittance of the radio wave in the cover 1 is greatly improved as compared with the cover 101. The range of the thickness d in which the transmittance of radio waves is greatly improved will be described later.

As described above, the cover 1 according to the present embodiment can suppress the change in the radio wave transmittance due to the change in the skin thickness. Therefore, it is not necessary to design the cover 1 while avoiding the strengthening condition, and the cover 1 can be freely designed even when it is used in the electronic device 10 that communicates using radio waves in a high frequency band. Further, by providing the auxiliary layer 3 which is a foam, the cover 1 can increase the length in the x-axis direction, that is, the thickness without increasing the weight so much. Therefore, the cover 1 has increased strength and is not easily deformed.

Regarding the cover 1 according to the present embodiment, the wavelength λ ₀ of the radio wave used for communication in the air, the thickness d of the surface layer 2, and the magnitude of the complex refractive index of the surface layer 2 are set to N and an integer k of 1 or more. The value ABS represented by the following formula (A) is obtained. The value ABS indicates how far the thickness d of the surface layer 2 of the cover 1 according to the present embodiment is from the value satisfied by the discretely existing strengthening conditions. The values satisfied by the discretely existing strengthening conditions are, for example, d ₁ and d ₂ in FIG. The “minimum value ABS” refers to the smallest value ABS among a plurality of value ABSs having different values of the integer k. When the ABS is 0, the thickness of the surface layer d has the greatest influence of the strengthening, and when the ABS is 1, the thickness of the surface layer d has the least influence of the strengthening. Here, as the ABS value, the smaller it is 0.73 or less, the greater the effect of improving the transmittance, but it is preferably 0.68 or less, and more preferably 0.63 or less.

(Foam)
Hereinafter, the specific configuration of the foam will be described. The foam contained in the auxiliary layer 3 contains a thermoplastic resin or a thermosetting resin as the base resin. The foam may be obtained by foaming a resin composition containing such a base resin and optionally further containing an additive such as a flame retardant. Examples of the foam include an extruded foam, an injection foam, a bead foam, a stretched foam, and a solvent-extracted foam. These refer to foams produced by the extrusion foaming method, the injection foaming method, the bead foaming method, the stretch foaming method, and the solvent extraction foaming method, which will be described later, respectively. Here, the bead foam is a foam composed of foam particles.

The content of the base resin is preferably 20% by mass or more, more preferably 40% by mass or more, still more preferably 60% by mass or more, and particularly preferably 60% by mass or more, assuming that the resin composition is 100% by mass. It is preferably 70% by mass or more, preferably 100% or less, and more preferably 95% or less. In order to reduce the dielectric constant and the dielectric loss tangent, the base resin is preferably made of a resin having low polarity.

The thermoplastic resin includes polyphenylene ether resin, polystyrene resin, polyethylene resin, polyamide resin, polypropylene resin, ABS resin, vinyl chloride resin, acrylic resin, methyl methacrylate resin, nylon resin, and fluorine resin. Examples thereof include resins, polycarbonate resins, polyurethane resins, polyester resins, etc. From the viewpoints of heat resistance, economy, and foamability, polyphenylene ether resins, polystyrene resins, polyethylene resins, polyamide resins, polypropylene resins, etc. , Acrylic resin and polycarbonate resin are preferable. In particular, as the base resin suitable for the foam of the present disclosure, a resin having a low polarity and a resin having a low density are preferable, and for example, a polyethylene resin, a polypropylene resin, a polycarbonate resin, a polystyrene resin, and a polyphenylene ether resin are used. , Fluorine-based resin and the like. These may be used alone or in combination of two or more.

The polyphenylene ether (PPE) -based resin may be a polymer represented by the following general formula (1). Here, in the formula (1), R ¹ , R ² , R ³ and R ⁴ are independently represented by a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a phenyl group, or a halogen and the general formula (1). A haloalkyl group or a haloalkoxy group having at least two carbon atoms between the benzene ring and the benzene ring inside, which does not contain the 3α-carbon atom. Further, in the formula (1), n is an integer representing the degree of polymerization.

Examples of polyphenylene ether-based resins include poly (2,6-dimethyl-1,4-phenylene) ether, poly (2,6-diethyl-1,4-phenylene) ether, and poly (2-methyl-6-ethyl). -1,4-phenylene) ether, poly (2-methyl-6-propyl-1,4-phenylene) ether, poly (2,6-dipropyl-1,4-phenylene) ether, poly (2-ethyl-6) -Propyl-1,4-phenylene) ether, poly (2,6-dibutyl-1,4-phenylene) ether, poly (2,6-dilauryl-1,4-phenylene) ether, poly (2,6-diphenyl) -1,4-diphenylene) ether, poly (2,6-dimethoxy-1,4-phenylene) ether, poly (2,6-diethoxy-1,4-phenylene) ether, poly (2-methoxy-6-ethoxy) ether -1,4-phenylene) ether, poly (2-ethyl-6-stearyloxy-1,4-phenylene) ether, poly (2,6-dichloro-1,4-phenylene) ether, poly (2-methyl- 6-Phenyl-1,4-phenylene) ether, poly (2,6-dibenzyl-1,4-phenylene) ether, poly (2-ethoxy-1,4-phenylene) ether, poly (2-chloro-1,2, Examples thereof include, but are not limited to, 4-phenylene) ether and poly (2,6-dibromo-1,4-phenylene) ether. Among these, it is particularly preferable that R ¹ and R ² are alkyl groups having 1 to 4 carbon atoms, and R ³ and R ⁴ are hydrogen or alkyl groups having 1 to 4 carbon atoms. These may be used alone or in combination of two or more.

The content of the polyphenylene ether-based resin in the present embodiment is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and further preferably 35 to 50% by mass with respect to 100% by mass of the base resin. It is 60% by mass. When the content of the PPE-based resin is 20% by mass or more, excellent heat resistance and flame retardancy can be easily obtained, and the dielectric constant (εr) and dielectric loss tangent (tan δ) can be easily reduced. Further, when the content of the PPE resin is 80% by mass or less, excellent processability can be easily obtained.

The weight average molecular weight (Mw) of the polyphenylene ether resin is preferably 20,000 to 60,000. Here, the weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC) on the resin, and the molecular weight of the peak of the chromatogram is a calibration curve (standard polystyrene) obtained from the measurement on commercially available standard polystyrene. It refers to the weight average molecular weight obtained by using (created using the peak molecular weight of).

The polystyrene-based resin refers to a homopolymer of styrene and a styrene derivative, and a copolymer containing styrene and a styrene derivative as main components (components contained in the polystyrene-based resin in an amount of 50% by mass or more). Examples of the styrene derivative include o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene, α-methylstyrene, β-methylstyrene, diphenylethylene, chlorostyrene, bromostyrene and the like.

Examples of the polystyrene-based resin of the homopolymer include polystyrene, polyα-methylstyrene, polychlorostyrene and the like. Examples of the polystyrene-based resin of the copolymer include styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, styrene-maleimide copolymer, and styrene-. N-phenylmaleimide copolymer, styrene-N-alkylmaleimide copolymer, styrene-N-alkyl substituted phenylmaleimide copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methylacrylate Dual copolymers such as copolymers, styrene-methylmethacrylate copolymers, styrene-n-alkylacrylate copolymers, styrene-n-alkylmethacrylate copolymers, ethylvinylbenzene-divinylbenzene copolymers; ABS , A ternary copolymer such as butadiene-acrylonitrile-α-methylbenzene copolymer; grafts such as styrene graft polyethylene, styrene graft ethylene-vinyl acetate copolymer, (styrene-acrylic acid) graft polyethylene, styrene graft polyamide, etc. Polymer; etc. These may be used alone or in combination of two or more.

Examples of the polyethylene-based resin include resins such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, a copolymer of ethylene and α-olefin, and a propylene-ethylene copolymer. These may be used alone or in combination of two or more. Further, these polyethylene-based resins may have a crosslinked structure as appropriate with a crosslinking agent or the like.

Examples of the polyamide-based resin include polyamides, polyamide copolymers, and mixtures thereof. The polyamide-based resin may contain a polymer obtained by self-condensation of aminocarboxylic acid, ring-opening polymerization of lactam, and polycondensation of diamine and dicarboxylic acid. Examples of the polyamide include nylon 66, nylon 610, nylon 612, nylon 46, nylon 1212 and the like obtained by polycondensation of diamine and dicarboxylic acid, and nylon 6 and nylon 12 obtained by ring-opening polymerization of lactam. Examples of the polyamide copolymer include nylon 6/66, nylon 66/6, nylon 66/610, nylon 66/612, nylon 66 / 6T (T represents a terephthalic acid component), and nylon 66 / 6I (I). Represents an isophthalic acid component), nylon 6T / 6I, and the like. Examples of these mixtures include a mixture of nylon 66 and nylon 6, a mixture of nylon 66 and nylon 612, a mixture of nylon 66 and nylon 610, a mixture of nylon 66 and nylon 6I, and nylon 66 and nylon 6T. Examples thereof include a mixture of. These may be used alone or in combination of two or more.

In the present embodiment, the content of the thermoplastic resin other than the PPE resin is preferably 10 to 100% by mass with respect to 100% by mass of the base resin from the viewpoint of processability of the foam. It is preferably 20 to 80% by mass.

Examples of the thermosetting resin include phenol resin, epoxy resin, unsaturated polyester resin, polyurethane, melamine resin and the like, and among them, phenol resin and melamine resin are preferable. These may be used alone or in combination of two or more.

Additives include flame retardants, flame retardants, heat stabilizers, antioxidants, antistatic agents, inorganic fillers, anti-dripping agents, UV absorbers, light absorbers, plasticizers, mold release agents, dye pigments. , Rubber components, resins other than the above-mentioned base resin, and the like can be added as long as the effects of the present disclosure are not impaired.

The content of the additive is preferably 0 to 40 parts by mass, more preferably 5 to 30 parts by mass, with 100 parts by mass of the base resin.

Here, the flame retardant is not particularly limited, and examples thereof include an organic flame retardant and an inorganic flame retardant. Examples of the organic flame retardant include halogen-based compounds typified by bromine compounds, phosphorus-based compounds, non-halogen-based compounds typified by silicone-based compounds, and the like. Examples of the inorganic flame retardant include aluminum hydroxide, metal hydroxide typified by magnesium hydroxide, antimony trioxide, and antimony compounds typified by antimony pentoxide. These may be used alone or in combination of two or more.

Among the above flame retardants, non-halogen flame retardants, which are organic flame retardants, are preferable, and phosphorus flame retardants and silicone flame retardants are more preferable, from the viewpoint of environmental friendliness.

As the phosphorus-based flame retardant, one containing phosphorus or a phosphorus compound can be used. Examples of phosphorus include red phosphorus. Further, examples of the phosphorus compound include a phosphoric acid ester and a phosphazene compound having a bond between a phosphorus atom and a nitrogen atom in the main chain. Examples of the phosphoric acid ester include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate and cresildiphenyl. Examples thereof include phosphate, dicredylphenyl phosphate, dimethylethyl phosphate, methyldibutyl phosphate, ethyldipropyl phosphate, hydroxyphenyldiphenyl phosphate, resorcinol bisdiphenyl phosphate, etc., and these are modified with various substituents to form a phosphate ester. Compounds and various condensation-type phosphate ester compounds are also included. Among these, triphenylphosphate and condensation type phosphoric acid ester compounds are preferable from the viewpoint of heat resistance, flame retardancy, and foamability. These may be used alone or in combination of two or more.

Examples of the silicone flame retardant include (mono or poly) organosiloxane. Examples of the (mono or poly) organosiloxane include monoorganosiloxanes such as dimethylsiloxane and phenylmethylsiloxane; polydimethylsiloxanes and polyphenylmethylsiloxanes obtained by polymerizing these; organopolysiloxanes such as copolymers thereof. And so on. In the case of organopolysiloxane, the bonding groups of the main chain and the branched side chains are hydrogen, alkyl group and phenyl group, preferably phenyl group, methyl group, ethyl group and propyl group, but are not limited thereto. The terminal bonding group may be a hydroxyl group, an alkoxy group, an alkyl group, or a phenyl group. The shape of the silicones is not particularly limited, and any silicones such as oil, gum, varnish, powder, and pellets can be used. These may be used alone or in combination of two or more.

The content of the flame retardant may be within the range of the content of the additive, but the base resin is 100 parts by mass, preferably 0 to 30 parts by mass, and more preferably 5 to 25 parts by mass. be. The more the flame retardant added, the easier it is to obtain the effect of improving the flame retardancy of the foam, but in general, the addition of the flame retardant tends to increase the dielectric constant and the dielectric loss tangent.

Further, examples of the rubber component include, but are not limited to, butadiene, isoprene, 1,3-pentadiene and the like. These are preferably those dispersed in the form of particles in a continuous phase made of a polystyrene-based resin. As a method of adding these rubber components, the rubber component itself may be added, or a resin such as a styrene-based elastomer and a styrene-butadiene copolymer may be used as a rubber component supply source. When the rubber component is added, the content of the rubber component may be within the range of the content of the additive, but the base resin is 100 parts by mass, preferably 0.3 to 15 parts by mass, and 0.5 to 8 parts by mass. Parts by mass are more preferable, and parts by mass of 1 to 5 are even more preferable. When it is 0.3 parts by mass or more, the flexibility and elongation of the resin are excellent, the foamed cell film is less likely to break during foaming, and a foam having excellent molding processability and mechanical strength can be easily obtained.

(Maximum cell diameter of foam)
FIG. 7 is an image obtained by observing a cross section of an example of a foam when cut in the thickness direction with a scanning electron microscope (SEM). In FIG. 7, the bubbles are present throughout the foam. For example, the bubble 12 has a part of its contour line coincident with the line 11 indicating the surface of the foam and exists near the surface of the foam. Further, the bubbles 13 are present inside the foam, apart from the surface of the foam.

Here, the measurement of the bubble diameter is the longest of the lengths of the line segments connecting the two points on the contour line of the bubbles when the cross section of the foam cut in the thickness direction is observed with a scanning electron microscope (SEM). The long line segment is measured as the diameter of the bubble. The "maximum bubble diameter" of a bubble in the foam is a surface in which a cross section of the foam is observed using SEM or the like, and a part of the outline of the bubble such as the bubble 12 shows the surface of the foam. At least 15 points or more are measured for each of the air bubbles in contact and the air bubbles existing inside away from the surface of the foam such as air bubbles 13, and the value is set to the largest value among all the measured values. For specific measurement examples, the contents described in the examples can be referred to.

Here, the smaller the maximum bubble diameter with respect to the wavelength of the radio wave, the less likely it is that the radio wave is scattered. From the above viewpoint, for example, when radio waves in the 1 to 100 GHz band are used, the maximum bubble diameter of the bubbles in the foam is preferably 1500 μm or less. It is more preferable that the foam has a maximum cell diameter of 1300 μm or less. It is more preferable that the foam has a maximum cell diameter of 1000 μm or less.

As a method of controlling the maximum bubble diameter of the foam within the above range, for example, in the case of bead foam, the time from the completion of releasing the impregnation pressure of the gas into the base resin to the start of heating (foaming) is shortened. Can be mentioned. As a result, uneven impregnation of gas in the foamed particles at the start of heating at the time of foaming can be reduced, the bubble diameter of the foam can be made uniform, and an increase in the bubble diameter can be prevented. In general, as a method of reducing the maximum bubble diameter of the foam, for example, increasing the concentration of the foaming agent in the base resin in the foaming step, or using a nucleating agent for generating bubbles in the base resin during foaming. When the foaming agent is a gas, the pressure of the gas impregnated in the base resin is increased or lowered in the impregnation step, the foaming temperature in the foaming step is adjusted, and the base material is added. Examples include adjusting the surface tension of the resin and adjusting the glass transition temperature of the base resin.

(Deflection temperature under load of foam)
The foam of the present embodiment preferably has a deflection temperature under load (HDT) of 60 ° C. or higher, more preferably 80 ° C. or higher, and further 100 ° C. or higher, as measured in accordance with ISO75-1 and 75-2. preferable. The deflection temperature under load of the foam can be changed at the time of manufacture depending on the magnitude of the foaming ratio. When the deflection temperature under load of the foam is 60 ° C. or higher, a cover having excellent heat resistance and structural stability can be obtained. The deflection temperature under load also changes depending on the type of resin. Therefore, the deflection temperature under load of the foam can be improved by selecting a resin (generally a resin having a high glass transition temperature) that tends to have a high deflection temperature under load. Further, when a resin having a high deflection temperature under load is used as the base resin of the foam, the bubble diameter tends to be small in general, although it depends on the heating conditions at the time of molding and the above-mentioned gas impregnation conditions. .. Here, the deflection temperature under load can be specifically measured by the method described in Examples.

(Flame retardancy of foam)
The foam of the present embodiment preferably has a flame retardancy of V-2 or higher, more preferably V-1 or higher, and has a flame retardancy of V-0 according to the UL94 standard. Is more preferable. The flame retardancy can be changed depending on the type of resin used at the time of manufacture and the type and content of flame retardant used together with the resin. Since the foam has high flame retardancy, even if combustion occurs due to a short circuit, an explosion, or the like in the electrical equipment, it is possible to suppress the spread of combustion. Here, the flame retardancy according to the UL94 standard can be specifically measured by the method described in the examples.

(Hydrocarbon gas content of foam)
The content of the hydrocarbon gas contained in the foam of the present embodiment is preferably 1% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.1% by mass. % Or less. When the content of the hydrocarbon gas is 1% by mass or less, flame retardancy can be easily maintained and expansion (back blistering) after foam molding can be suppressed, so that the dimensional stability of the foam is stable. It is possible to improve the uniformity of bubbles, reduce the maximum bubble diameter. Here, the hydrocarbon gas content can be measured by gas chromatography.

(Manufacturing method of foam)
The method for producing the foam of the present embodiment is not particularly limited, and examples thereof include an extrusion foaming method, an injection foaming method, a bead foaming method (in-mold foaming method), a stretch foaming method, and a solvent extraction foaming method. In the extrusion foaming method, an organic or inorganic foaming agent is press-fitted into a molten resin using an extruder, and the pressure is released at the outlet of the extruder to have a certain cross-sectional shape, such as a plate shape, a sheet shape, or a columnar shape. It is a method of obtaining the foam of. The injection foaming method is a method of obtaining a foam having pores by injection molding a foamable resin and foaming it in a mold. The bead foaming method or the in-mold foaming method is a method of obtaining a foam by filling the mold with foamed particles and heating them with steam or the like to expand the foamed particles and at the same time heat-sealing the foamed particles to each other. .. The stretch foaming method is a method in which an additive such as a filler is kneaded in a resin in advance and the resin is stretched to generate microvoids to form a foam. The solvent extraction foaming method is a method in which an additive that dissolves in a predetermined solvent is added to a resin, and a molded product is immersed in a predetermined solvent to extract the additive to produce a foam.

In the case of extrusion foaming, the obtained foam is in the form of a plate, a sheet, or the like, and in order to process this, a punching step of cutting into a desired shape, a heat pasting step of laminating the cut parts, and the like are required. On the other hand, in the case of the bead foaming method, since a mold having a desired shape is created and foamed particles are filled therein for molding, the foam can be molded into a complicated shape. Even in the case of the injection foaming method, it is possible to mold the foam into a complicated shape, but in the case of bead foaming, it is easy to increase the foaming ratio of the foam, and it is easy to develop flexibility in addition to heat insulation. ..

The foaming agent is not particularly limited, and a commonly used gas can be used. Examples are inorganic gases such as air, carbon dioxide, nitrogen gas, oxygen gas, ammonia gas, hydrogen gas, argon gas, helium gas, neon gas; trichlorofluoromethane (R11), dichlorodifluoromethane (R12), chlorodifluoromethane. Fluorocarbons such as (R22), tetrachlorodifluoroether (R112) dichlorofluoroethane (R141b) chlorodifluoroethane (R142b), difluoroethane (R152a), HFC-245fa, HFC-236ea, HFC-245ca, HFC-225ca; Saturated hydrocarbons such as butane, i-butane, n-pentane, i-pentane, neopentane; dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, furfural, 2-methylfuran, tetrahydrofuran , Ethers such as tetrahydropyran; dimethyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, ethyl Ketones such as n-butylketone; alcohols such as methanol, ethanol, propyl alcohol, i-propyl alcohol, butyl alcohol, i-butyl alcohol, t-butyl alcohol; methyl formic acid ester, ethyl formic acid ester, propyl ester formic acid, formic acid Carboxylic acid esters such as butyl ester, amyl ester of acid, methyl propionic acid ester, ethyl propionic acid ester; chlorinated hydrocarbons such as methyl chloride and ethyl chloride; and the like can be mentioned. These may be used alone or in combination of two or more.

From the viewpoint of flame retardancy, the foaming agent is preferably flammable and has no or little flammability, and from the viewpoint of gas safety, an inorganic gas is more preferable. In addition, the inorganic gas is less soluble in the resin than the organic gas such as hydrocarbons, and the gas is easily released from the resin after the foaming step or the molding step, so that the foam after molding has an advantage that the dimensional stability of the foam over time is more excellent. There is also. Further, when an inorganic gas is used, plasticization of the resin due to the residual gas is unlikely to occur. Therefore, there is an advantage that excellent heat resistance can be easily exhibited from an earlier stage without going through a process such as aging. Among the inorganic gases, carbon dioxide is preferable from the viewpoint of solubility in resin and ease of handling. In addition, hydrocarbon-based organic gases are generally highly flammable, and when they remain in the foam, their flame retardancy tends to deteriorate.

The foamed particles used in the bead foaming method can be obtained by impregnating (impregnating) the base resin with a foaming agent to cause foaming. Specifically, a base resin (pellet, bead, etc.) is housed in a pressure-resistant container, the gas in the container is replaced with dry air, and then a foaming agent (gas) is press-fitted into the base resin. After impregnating with (gas), the pressure is released to transfer the base resin pellets from the pressure vessel to the foaming furnace, and the base resin pellets are heated by pressurized steam while rotating the stirring blades in the foaming furnace. Examples thereof include a method of producing foamed particles by foaming. The conditions for impregnating the base resin with the foaming agent (gas) are not particularly limited, and from the viewpoint of more efficiently impregnating the base resin with the foaming agent (gas), for example, It is preferable that the impregnation pressure is 0.3 to 30 MPa, the impregnation temperature is -20 to 100 ° C., and the impregnation time is 10 minutes to 96 hours. Further, the maximum vapor pressure of the pressurized steam in the foaming furnace is preferably 30 to 700 kPa · G from the viewpoint of easily obtaining a desired magnification and improving the appearance. In the above method for producing foamed particles, the time from the completion of releasing pressure in the pressure-resistant container (release of impregnation pressure) to the start of heating with pressurized steam in the foaming furnace is preferably less than 600 seconds. , 300 seconds or less, more preferably 120 seconds or less, and particularly preferably 60 seconds or less. When the time is within the above range, it is possible to suppress the non-uniform diffusion of the gas impregnated in the base resin, so that the bubble diameter can be made uniform and the increase in the bubble diameter can be prevented. ..

The method for molding the foam using the foamed particles is not particularly limited, but for example, the foamed particles are filled in the cavity of the molding die and heated to cause expansion, and at the same time, the foamed particles are heated with each other. Examples thereof include a method in which the product is solidified by cooling after being fused and molded. The method for filling the foamed particles is not particularly limited, and a known method can be used. Before filling the cavity of the molding die with the foamed particles, it is preferable to pressurize the foamed particles with a gas. By applying a constant gas pressure to the bubbles of the foamed particles, the foamed particles constituting the obtained foam can be firmly fused to each other, and the rigidity and appearance of the molded product can be improved. The gas used for the pressurizing treatment is not particularly limited, but air and an inorganic gas are preferable from the viewpoint of ease of handling and economy. The method of the pressurizing treatment is not particularly limited, but after filling the foamed particles in the pressurized container, a pressurized gas is introduced and the pressure is increased to a maximum pressure of 0.1 to 20 MPa over 10 minutes to 96 hours. Therefore, a method of supplying gas into the pressurized container can be mentioned. Examples of the heating method for forming the foamed particles include heating using a heat medium such as steam, heating with a heater such as an IR heater, and heating using microwaves. When heating using a heat medium, it may be a general-purpose heat medium, and steam is preferable from the viewpoint of efficiently heating the resin.

In the present embodiment, the method of processing the foam into a desired shape is not particularly limited, but is limited to a method of filling a mold with foamed particles or molten resin to form the foam, and cutting with a cutting tool such as a saw blade and a die-cutting blade. A method of cutting with a mill, a method of adhering a plurality of foams with heat and an adhesive, and the like.

The foam of the present embodiment may be used alone or in combination with an unfoamed resin or the like. At that time, each molded product may be adhered or integrally molded.

The shape, size, thickness, etc. of the foam of the present embodiment are not particularly limited, and may be appropriately determined according to the shape, size, thickness, etc. of the cover 1.

Hereinafter, the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited to the following examples.

(1) Maximum Bubble Diameter of Foam The foams obtained in Examples and Comparative Examples are cut in the thickness direction, and the cross section thereof is cut at a magnification of 30 to 30 using a 3D real surface view microscope VE-9800 manufactured by KEYENCE CORPORATION. The maximum cell diameter of the foam was determined by observing in the range of 400 times. The magnification at the time of cross-section measurement was set so that at least 5 bubbles to be measured when the bubble diameter was rapidly formed, which will be described later, were included in one screen. Here, when measuring the bubble diameter, only the bubble whose entire shape can be clearly observed from the cross-sectional image is the measurement target, and the longest line segment among the lengths of the line segments connecting the two points on the contour line of the bubble. Was measured as the diameter of the bubble. In addition, 30 or more bubbles in contact with the surface of the foam and 30 or more bubbles contained in the range of 20 to 80% in the thickness direction from the surface of the foam were measured, and the maximum value was measured from all the measured values. The maximum bubble diameter was defined as.

(2) ABS
For cover 1 of Examples and Comparative Examples, the wavelength λ ₀ of the radio wave used for communication in the air, the thickness d of the surface layer 2, and the magnitude of the complex refractive index of the surface layer 2 are N and an integer k of 1 or more. , The value ABS represented by the following formula (A) is obtained. The value ABS indicates how far the thickness d of the cover 1 surface layer 2 of Examples and Comparative Examples is from the value satisfied by the discretely existing strengthening conditions. The values satisfied by the discretely existing strengthening conditions are, for example, d ₁ and d ₂ in FIG. The “minimum value ABS” refers to the smallest value ABS among a plurality of value ABSs having different values of the integer k. When the ABS is 0, the thickness of the surface layer d has the greatest influence of the strengthening, and when the ABS is 1, the thickness of the surface layer d has the least influence of the strengthening.

(3) Density of foam A sample is cut out from the foams obtained in Examples and Comparative Examples described later with a thickness of 30 mm square and 10 mm as a guide, and the mass W [g] of the sample is measured to measure the sample volume V. The density was calculated by dividing [cm ^{3] by mass.} Here, when the above cutting out is difficult, the same materials as in each Example and each Comparative Example are prepared, the sample mass is measured, the volume is measured by the submersion method, and the density is calculated using each value. May be good. The method for measuring the density distribution in the thickness direction of the auxiliary layer, the back layer, the intermediate layer, etc. is not particularly limited. Can be calculated.

(4) Deflection temperature under load (HDT) of foam
The deflection temperature under load of the foams obtained in Examples and Comparative Examples described later was measured as described below in accordance with ISO75-1 and 75-2.
First, a sample having a length of 80 mm, a width of 13 mm, and a thickness of 10 mm was cut out from the foams obtained in Examples and Comparative Examples described later. The obtained sample was set in an HDT test device machine test (model 3M-2) manufactured by Toyo Seiki Seisakusho Co., Ltd. so that the distance between fulcrums was 64 mm. A pushing jig was set with respect to the central portion of the set sample, and the sample was immersed in an oil bath with a force of 0.45 MPa applied. Then, while raising the temperature at a rate of 120 ° C./hour, the sample temperature at the time when the pushing jig was moved until the bending threshold was 0.34 mm was defined as the deflection temperature under load (° C.).

(5) Flame Retardantity of Foam The foams obtained in Examples and Comparative Examples described later are tested in accordance with the UL-94 vertical method (20 mm vertical combustion test) of the US UL standard, and are flame retardant. Evaluation was performed.
The details of the measurement method are shown below.
Five test pieces having a length of 125 mm, a width of 13 mm, and a thickness of 5 mm cut out from the foam were used. The test piece was attached vertically to the clamp, and indirect flame for 10 seconds with a 20 mm flame was performed twice, and V-0, V-1, and V-2 were judged based on the combustion behavior.
V-0: The flame combustion duration of the first and second times is within 10 seconds, the total of the flame combustion duration and non-flame combustion time of the second time is within 30 seconds, and the flames of 5 test pieces are further. The total burning time is within 50 seconds, there is no sample that burns to the position of the fixing clamp, and there is no cotton ignition due to burning fallen objects.
V-1: The flame burning duration for both the 1st and 2nd times is within 30 seconds, the total of the 2nd flame burning duration and the non-flame burning time is within 60 seconds, and 5 test pieces are inflamed. The total burning time is within 250 seconds, there is no sample that burns to the position of the fixing clamp, and there is no cotton ignition due to burning fallen objects.
V-2: The flame combustion duration for both the first and second times is within 30 seconds, the total of the flame combustion duration and non-flame combustion time for the second time is within 60 seconds, and five more test pieces are inflamed. The total burning time is within 250 seconds, there is no sample that burns to the position of the fixing clamp, and there is cotton ignition due to burning fallen objects.
Those that do not correspond to any of the above V-0, V-1, and V-2 are marked as nonconforming (x).

(6) Dielectric constant εr and dielectric loss tangent tan δ of epidermis / foam
With reference to the methods described in Examples and Comparative Examples, a 450 mm × 450 mm × 3 mm resin plate made of the same material as the surface layer and a foam having a thickness of 450 mm × 450 mm × 10 mm made of the same material as the back layer were prepared.
Subsequently, the sample was set in a transmission attenuation measuring jig with a dielectric lens of the frequency change method dielectric constant / dielectric loss tangent measuring device DPS10-02 manufactured by KEYCOM, and at room temperature (temperature 26 ° C., humidity 60%). The amount of transmission attenuation and the amount of phase change were measured. Based on the obtained result and the thickness of the sample, the calculated value of the transmission attenuation amount and the phase change amount and the measured value are fitted, and the permittivity and the dielectric loss tangent at the time of the best fitting are obtained. The measured values of rate and dielectric loss tangent were used. The dielectric constant and the dielectric loss tangent can also be measured by the capacitance method (parallel electrode method), the cavity resonator method, the split post dielectric resonator method, the free space method, or the like. Further, if the dielectric properties of the unfoamed resin material and the foam having a certain magnification are known, the dielectric properties of the foam having an arbitrary magnification can be predicted by Wagner's theory or the like, and the value can be applied. Here, the complex permittivity Er is expressed by the following equation.
Er = εr + εr ”, tan δ = εr” / εr
Er: Complex permittivity εr: Permittivity (real part of complex permittivity)
εr ”: Imaginary part of complex permittivity

(7) Complex Refractive Index The complex refractive index of the surface layer 2 of Examples and Comparative Examples described later can be calculated as follows using the dielectric constant and the dielectric loss tangent measured according to the above method.
N ² = Er
N: complex refractive index, Er: complex permittivity

(8) Calculation of radio wave transmittance The calculation of the radio wave transmittance described in Examples and Comparative Examples is performed for each layer calculated or measured by the above method after confirming in advance that the measured values and the calculated values are substantially the same. It was carried out by the characteristic Marix method using the dielectric constant, the dielectric loss tangent of each layer, the complex refractive index of each layer, the composition of each layer, the thickness of each layer, and the radio frequency.

(9) Calculation of Radio Transmittance Fluctuation Amount Generated by Thickness Fluctuation of Surface Layer 2 In the examples and comparative examples described later, the calculation of the radio wave transmittance fluctuation amount generated by the thickness fluctuation of the surface layer 2 was carried out as follows. First, in consideration of the influence of the above-mentioned interference, the thickness fluctuation range of the surface layer 2 is set to the range of the thickness from λ / 8 to λ × 3/4. Here, the wavelength of the radio wave in the surface layer is defined as λ. Next, using the dielectric constant and dielectric loss tangent confirmed by the above method, radio wave transmission when the thickness of the surface layer fluctuates according to the configurations described in Examples and Comparative Examples (the total thickness and the thickness of the intermediate layer are constant). The rate was calculated. From the obtained results, the difference between the maximum transmittance value and the minimum transmittance value when the thickness of the surface layer was changed within the above range was defined as the amount of fluctuation in the transmittance caused by the change in the thickness of the surface layer 2.

(Example 1)
Preparation of foam for auxiliary layer:
60% by mass of GP685 (manufactured by PS Japan Corporation) as a polystyrene resin (PS) and 40% by mass of S201A (manufactured by Asahi Kasei Corporation) as a polyphenylene ether resin (PPE) are heated, melted and kneaded by an extruder. After that, it was extruded to prepare a base resin pellet. Next, according to the method described in Example 1 of JP-A-4-372630, the base resin pellets are housed in a pressure-resistant container, the gas in the container is replaced with dry air, and then carbon dioxide (carbon dioxide) is used as a foaming agent. Gas) is injected, and the base resin pellets are impregnated with carbon dioxide for 3 hours under the conditions of a pressure of 3.0 MPa and a temperature of 10 ° C., and then the base resin pellets are immediately transferred after being taken out from the pressure vessel. Then, the base resin pellet was foamed by pressurized steam of a maximum of 330 kPa · G while rotating the stirring blade at 77 rpm in the foaming furnace to obtain foamed particles. At this time, the time from the time when the impregnation was completed and the pressure release was completed to the start of introduction of the pressurized steam was 10 seconds. The hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and was below the detection limit (0.01% by mass).

Then, the foamed particles were placed in a container, and pressurized air was introduced (pressurized to 0.4 MPa over 4 hours and then held at 0.4 MPa for 16 hours) to perform a pressurizing treatment. This is filled in an in-mold molding die having steam holes, heated with steam to expand and fuse the foamed particles to each other, cooled, taken out from the molding mold, and assisted by the foamed particles. A foam for the layer was obtained.

Fabrication of resin plate for surface layer:
60% by mass of GP685 (manufactured by PS Japan Corporation) as a polystyrene resin (PS) and 40% by mass of S201A (manufactured by Asahi Kasei Corporation) as a polyphenylene ether resin (PPE) are heated, melted and kneaded by an extruder. After that, it was extruded to prepare a base resin pellet. The obtained base resin pellets were spread in a mold to prepare a resin plate for a surface layer having a thickness of 0.5 mm by a hot press method at a temperature of 270 ° C.

Preparation of laminated body of surface layer and auxiliary layer:
In the heat press machine, the temperature of the lower surface is set to 270 ° C. and the temperature of the upper surface is set to 30 ° C., the resin plate for the surface layer is placed on the lower surface, and a frame made of SU304 is installed around the resin plate during pressing. The board was pushed open so that the thickness did not fluctuate. Subsequently, the foam for the auxiliary layer is placed on the resin plate for the surface layer, and pressed until the distance between the upper surface and the lower surface of the heat press machine is smaller than the total thickness of the resin plate and the foam by 2 mm. Then, by holding in that state for 1 minute, a laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained. Table 1 shows the results of evaluating the obtained laminate.

(Example 2)
In the step of producing the laminated body of the surface layer and the auxiliary layer, the laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 1 except that the holding time at the time of hot pressing was changed to 3 minutes. .. Table 1 shows the results of evaluating the obtained laminate.

(Example 3)
The same as in Example 1 except that the distance between the upper surface and the lower surface of the press machine was pressed to be 5 mm smaller than the total thickness of the resin plate and the foam in the step of producing the laminated body of the surface layer and the auxiliary layer. By the method, a laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained. Table 1 shows the results of evaluating the obtained laminate.

(Example 4)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 1 except that the thickness of the resin plate for the surface layer was changed to 1 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 5)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 2 except that the thickness of the resin plate for the surface layer was changed to 1 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 6)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 1 except that the thickness of the resin plate for the surface layer was changed to 2 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 7)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 2 except that the thickness of the resin plate for the surface layer was changed to 2 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 8)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 3 except that the thickness of the resin plate for the surface layer was changed to 2 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 9)
With reference to Example 6, a resin plate for the surface layer and a foam having a foaming ratio of 10.0 cm ³ / g as an auxiliary layer were prepared, and the surface layer and the auxiliary layer were bonded together with an adhesive to obtain a laminate. .. Table 1 shows the results of evaluating the obtained laminate.

(Examples 10 to 14)
A laminate of the surface layer and the auxiliary layer was obtained in the same manner as in Examples 1 to 9. Table 1 shows the results of evaluating the obtained laminate.

(Example 15)
Preparation of foam for auxiliary layer:
60% by mass of S201A (manufactured by Asahi Kasei Co., Ltd.) as a polyphenylene ether resin (PPE), 15% by mass of bisphenol A-bis (diphenyl phosphate) (BBP) as a non-halogen flame retardant, and 6% by mass of rubber concentration. 10% by mass of impact-resistant polystyrene resin (HIPS) and 15% by mass of GP685 (manufactured by PS Japan Co., Ltd.) as general-purpose polystyrene resin (PS), extruded after heat-melt kneading with an extruder. Base resin pellets were prepared.

According to the method described in Example 1 of JP-A-4-372630, the base resin pellets are housed in a pressure-resistant container, the gas in the container is replaced with dry air, and then carbon dioxide (gas) is used as a foaming agent. After injecting and impregnating the base resin pellets with carbon dioxide under the conditions of a pressure of 3.0 MPa and a temperature of 10 ° C. for 3 hours, the base resin pellets were immediately transferred from the pressure vessel and transferred to the base resin pellets. The material resin pellets were foamed with pressurized steam of a maximum of 330 kPa · G while rotating the stirring blade at 77 rpm in a foaming furnace to obtain foamed particles. At this time, the time from the time when the impregnation was completed and the pressure release was completed to the start of introduction of the pressurized steam was 10 seconds. The hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and was below the detection limit (0.01% by mass).

Then, the foamed particles were placed in a container, and pressurized air was introduced (pressurized to 0.4 MPa over 4 hours and then held at 0.4 MPa for 16 hours) to perform a pressurizing treatment. This is filled in an in-mold molding die having steam holes, heated with steam to expand and fuse the foamed particles to each other, cooled, taken out from the molding mold, and assisted by the foamed particles. A foam for the layer was obtained.

Fabrication of resin plate for surface layer:
60% by mass of S201A (manufactured by Asahi Kasei Co., Ltd.) as a polyphenylene ether resin (PPE), 15% by mass of bisphenol A-bis (diphenyl phosphate) (BBP) as a non-halogen flame retardant, and 6% by mass of rubber concentration. 10% by mass of impact-resistant polystyrene resin (HIPS) and 15% by mass of GP685 (manufactured by PS Japan Co., Ltd.) as general-purpose polystyrene resin (PS), extruded after heat-melt kneading with an extruder. Base resin pellets were prepared. The obtained base resin pellets were spread in a mold to prepare a resin plate for a surface layer having a thickness of 3 mm by a hot press method at a temperature of 270 ° C.

Preparation of laminated body of surface layer and auxiliary layer:
In the heat press machine, the temperature of the lower surface is set to 250 ° C. and the temperature of the upper surface is set to 30 ° C., the resin plate for the surface layer is placed on the lower surface, and a frame made of SU304 is installed around the resin plate during pressing. The board was pushed open so that the thickness did not fluctuate. Subsequently, the foam for the auxiliary layer is placed on the resin plate for the surface layer, and pressed until the distance between the upper surface and the lower surface of the heat press machine is smaller than the total thickness of the resin plate and the foam by 2 mm. Then, by holding in that state for 3 minutes, a laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained. Table 1 shows the results of evaluating the obtained laminate.

(Example 16)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 15 except that the thickness of the resin plate for the surface layer was changed to 2 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 17)
Example 15 except that the thickness of the resin plate for the surface layer was changed to 0.5 mm and the holding time during hot pressing was changed from 3 minutes to 1 minute in the step of producing the laminated body of the surface layer and the auxiliary layer. A laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained by the same method as in the above. Table 1 shows the results of evaluating the obtained laminate.

(Example 18)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 15 except that the thickness of the resin plate for the surface layer was changed to 0.5 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 19)
The thickness of the resin plate for the surface layer was changed to 0.5 mm, and in the process of manufacturing the laminated body of the surface layer and the auxiliary layer, the distance between the upper surface and the lower surface of the press machine was 5 mm more than the total thickness of the resin plate and the foam. A laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained in the same manner as in Example 15 except that the sheets were pressed until they became as small as possible. Table 1 shows the results of evaluating the obtained laminate.

(Example 20)
A laminated body of the surface layer, the intermediate layer, and the auxiliary layer was obtained by the same method as in Example 15 except that the thickness of the resin plate for the surface layer was changed to 1.0 mm. Table 1 shows the results of evaluating the obtained laminate.

(Example 21)
A laminate of the surface layer and the auxiliary layer was obtained by the same method as in Example 16. Table 1 shows the results of evaluating the obtained laminate.

(Example 22)
By preparing a resin plate for the surface layer with reference to Example 16 and further changing the pressurized vapor pressure when producing the foamed particles, a foam having a foaming ratio of 3.0 cm ³ / g and a back layer as an intermediate layer. A foam having a foaming ratio of 10.0 cm ³ / g was prepared, and the surface layer, the intermediate layer, and the back layer were bonded together with an adhesive to obtain a laminated body. Table 1 shows the results of evaluating the obtained laminate.

(Example 23)
Preparation of foam for auxiliary layer:
100% by mass of GP685 (manufactured by PS Japan Corporation), which is a polystyrene resin (PS), was extruded by heating, melting and kneading with an extruder to prepare a base resin pellet. Next, according to the method described in Example 1 of JP-A-4-372630, the base resin pellets are housed in a pressure-resistant container, the gas in the container is replaced with dry air, and then carbon dioxide (carbon dioxide) is used as a foaming agent. Gas) is injected, and the base resin pellets are impregnated with carbon dioxide for 3 hours under the conditions of a pressure of 3.0 MPa and a temperature of 10 ° C., and then the base resin pellets are immediately transferred after being taken out from the pressure vessel. Then, the base resin pellet was foamed by pressurized steam of a maximum of 70 kPa · G while rotating the stirring blade at 77 rpm in the foaming furnace to obtain foamed particles. At this time, the time from the time when the impregnation was completed and the pressure release was completed to the start of introduction of the pressurized steam was 10 seconds. The hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and was below the detection limit (0.01% by mass).

Then, the foamed particles were placed in a container, and pressurized air was introduced (pressurized to 0.4 MPa over 4 hours and then held at 0.4 MPa for 16 hours) to perform a pressurizing treatment. This is filled in an in-mold molding die having steam holes, heated with steam to expand and fuse the foamed particles to each other, cooled, taken out from the molding mold, and assisted by the foamed particles. A foam for the layer was obtained.

Fabrication of resin plate for surface layer:
100% by mass of GP685 (manufactured by PS Japan Corporation), which is a polystyrene resin (PS), was extruded by heating, melting and kneading with an extruder to prepare a base resin pellet. The obtained base material resin pellets were spread in a mold, and a resin plate for a surface layer having a thickness of 1.0 mm was prepared by a heat pressing method at a temperature of 200 ° C.

Preparation of laminated body of surface layer and auxiliary layer:
In the heat press machine, the temperature of the lower surface is set to 150 ° C. and the temperature of the upper surface is set to 30 ° C., the resin plate for the surface layer is placed on the lower surface, and a frame made of SU304 is installed around the resin plate during pressing. The board was pushed open so that the thickness did not fluctuate. Subsequently, the foam for the auxiliary layer is placed on the resin plate for the surface layer, and pressed until the distance between the upper surface and the lower surface of the heat press machine is smaller than the total thickness of the resin plate and the foam by 2 mm. Then, by holding in that state for 3 minutes, a laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained. Table 1 shows the results of evaluating the obtained laminate.

(Example 24)
Preparation of foam for auxiliary layer:
Foamed particles (tertiary foamed particles) were obtained by the same method as described in Examples of JP-A-4-372630. The hydrocarbon gas content of the obtained foamed particles (tertiary foamed particles) was measured immediately after foaming, and was below the detection limit (0.01% by mass).

Then, the foamed particles were placed in a container, and pressurized air was introduced (pressurized to 0.4 MPa over 4 hours and then held at 0.4 MPa for 16 hours) to perform a pressurizing treatment. This is filled in an in-mold molding die having steam holes, heated with steam to expand and fuse the foamed particles to each other, cooled, taken out from the molding mold, and assisted by the foamed particles. A foam for the layer was obtained.

Fabrication of resin plate for surface layer:
100% by mass of low-density polyethylene (PE) (density 922 kg / m ³ , MI = 7.0 g / 10 minutes) was extruded by heating, melting and kneading with an extruder to prepare a base resin pellet. The obtained base material resin pellets were spread in a mold, and a resin plate for a surface layer having a thickness of 1.0 mm was prepared by a heat pressing method at a temperature of 200 ° C.

Preparation of laminated body of surface layer and auxiliary layer:
In the heat press machine, the temperature of the lower surface is set to 150 ° C. and the temperature of the upper surface is set to 30 ° C., the resin plate for the surface layer is placed on the lower surface, and a frame made of SU304 is installed around the resin plate during pressing. The board was pushed open so that the thickness did not fluctuate. Subsequently, the foam for the auxiliary layer is placed on the resin plate for the surface layer, and pressed until the distance between the upper surface and the lower surface of the heat press machine is smaller than the total thickness of the resin plate and the foam by 2 mm. Then, by holding in that state for 3 minutes, a laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained. Table 1 shows the results of evaluating the obtained laminate.

(Example 25)
Preparation of foam for auxiliary layer:
A foam was prepared by the following procedure with reference to JP-A-2006-07728.

^{First, low-density polyethylene (PE) (density 922 kg / m 3} , MI = 7.0 g / 10 minutes) was applied to the supply area of a screw extruder having a barrel inner diameter of 150 mm at a rate of 900 kg / hour. It was supplied together with 1.2 parts by mass of talc powder (particle size 8.0 μm) and 0.8 parts by mass of a gas permeation adjuster (stearic acid monoglyceride) as a bubble nucleating agent with respect to 100 parts by mass. The barrel temperature of the extruder is adjusted to 190 to 210 ° C., and 3 parts by mass of a foaming agent consisting of 100% by mass of n-butane is press-fitted into 100 parts by mass of this resin from a foaming agent injection port attached to the tip of the extruder. , Was mixed with the molten resin composition to obtain an effervescent melt mixture.

This effervescent melt mixture is cooled to 108 ° C. by a cooling device attached to the outlet of the extruder, and then at room temperature and atmospheric pressure from an orifice plate having an average thickness of about 4.0 mm and an opening shape of about 226 mm width. The resin foam was continuously extruded into the atmosphere and foamed, and molded while adjusting the take-up speed of the resin foam to obtain a plate-shaped foam having a thickness of 52 mm, a width of 560 mm, a length of 1000 mm, and a density of 100 kg / m ^3. The content of the hydrocarbon gas contained in this resin foam was 2.4% by mass. It was stored in an environment of 40 ° C. for 3 months, and it was confirmed that the content of hydrocarbon gas was below the lower limit of detection (0.01% by mass). The obtained foam was used as a foam for the auxiliary layer.

Fabrication of resin plate for surface layer:
100% by mass of low-density polyethylene (PE) (density 922 kg / m ³ , MI = 7.0 g / 10 minutes) was extruded by heating, melting and kneading with an extruder to prepare a base resin pellet. The obtained base material resin pellets were spread in a mold, and a resin plate for a surface layer having a thickness of 1.0 mm was prepared by a heat pressing method at a temperature of 200 ° C.

Preparation of laminated body of surface layer and auxiliary layer:
In the heat press machine, the temperature of the lower surface is set to 150 ° C. and the temperature of the upper surface is set to 30 ° C., the resin plate for the surface layer is placed on the lower surface, and a frame made of SU304 is installed around the resin plate during pressing. The board was pushed open so that the thickness did not fluctuate. Subsequently, the foam for the auxiliary layer is placed on the resin plate for the surface layer, and pressed until the distance between the upper surface and the lower surface of the heat press machine is smaller than the total thickness of the resin plate and the foam by 2 mm. Then, by holding in that state for 3 minutes, a laminated body of a surface layer, an intermediate layer, and an auxiliary layer was obtained. Table 1 shows the results of evaluating the obtained laminate.

(Example 26)
A laminate of the surface layer and the auxiliary layer was obtained by the same method as in Example 11. Table 1 shows the results of evaluating the obtained laminate.

(Comparative Examples 1 to 15)
With reference to Examples 1 to 26, only a resin plate for the surface layer was produced. Table 2 shows the results of evaluating the obtained resin plate for the surface layer.

(Reference example 1)
Similar to Example 21 except that the time from the completion of releasing the impregnation pressure to the start of heating (introduction of pressurized steam) was changed to 600 seconds when producing the foamed particles from the base resin pellets. A laminated body of a surface layer and an auxiliary layer was obtained by the method of. Table 2 shows the results of evaluating the obtained laminate.

The configurations of Examples and Comparative Examples are as shown in Tables 1 and 2. The above evaluation was performed on these examples and comparative examples. As shown in Tables 1 and 2, it was found that the presence of the surface layer and the auxiliary layer can reduce the amount of fluctuation in the radio wave transmittance generated by the fluctuation in the thickness of the surface layer. In addition, as shown in the increase amount in Table 1, in most of the examples, the increase amount was improved as compared with the case where only the skin material was used.

According to the above examination, by laminating the surface layer and the back layer, the change in the transmittance caused by the change in the thickness of the surface layer can be suppressed, so that the stability of production is improved. Further, when the minimum value ABS represented by the above formula (A) is 0.73 or less, the transmittance of radio waves is improved.

According to the present disclosure, it is possible to provide a cover 1 that is used in an electronic device 10 that communicates using radio waves in a high frequency band and can suppress a change in radio wave transmittance due to a change in skin thickness.

1 Cover 2 Surface 3 Auxiliary layer 4 Back layer 5 Intermediate layer 6 Antenna 10 Electronic device 21 Front surface 22 Back surface 101 Cover 110 Electronic device

Claims (10)

A resin cover used in electronic devices that communicate using radio waves in the high frequency band.
The surface layer that is partially exposed from the electronic device,
A cover including an auxiliary layer containing a foam having a density lower than that of the surface layer and arranged inside the electronic device in contact with the surface layer. _{Using N and an integer k of 1 or more for the wavelength λ 0} of the radio wave in the air, the thickness d of the surface layer, and the magnitude of the complex refractive index of the surface layer, the value ABS represented by the following formula (A). The cover of claim 1, wherein the minimum is 0.73 or less.

The cover according to claim 1 or 2, wherein the surface layer has a density of 0.90 g / cm ^{3 or more.} The cover according to any one of claims 1 to 3, wherein the maximum bubble diameter of the foam in the cut cross section is 1500 μm or less. The auxiliary layer includes a back layer and an intermediate layer composed of the foam.
The intermediate layer is arranged between the surface layer and the back layer.
The cover according to any one of claims 1 to 4, wherein the average density of the intermediate layer is smaller than the density of the surface layer and larger than the density of the back layer. The cover according to claim 5, wherein the density of the intermediate layer gradually decreases from the surface layer side to the back layer side. The cover according to claim 5, wherein the density of the intermediate layer asymptotically decreases from the surface layer side to the back layer side. The cover according to any one of claims 5 to 7, wherein the back layer has a deflection temperature under load of 100 ° C. or higher. The cover according to any one of claims 1 to 8, wherein the resin satisfies UL94 standard V-0. An antenna device comprising the cover according to any one of claims 1 to 9.

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