Waveguide

Abstract

The present disclosure relates to a waveguide having a transmission layer for transmitting an electromagnetic wave and a coating layer for coating a surface of this transmission layer and provides a waveguide high in transmission efficiency and excellent in heat resistance and adhesion between the transmission layer and the coating layer 3. The present disclosure is a waveguide having a transmission layer for transmitting electromagnetic waves and a coating layer for coating the surface of the transmission layer, wherein the transmission layer contains an aromatic polyether ketone and the coating layer is a layer of a foam body containing an aromatic polyether ketone.

Description

Waveguide

[0001] The present disclosure relates to waveguides.

[0002] Resin waveguides are widely used because they are lighter and more flexible than metal waveguides. Known examples of resin waveguides include electromagnetic wave transmission cables having two layers: a hollow waveguide layer made of a cylindrical hollow dielectric layer of polytetrafluoroethylene, and a foamed polystyrene resin layer that covers the surface of the dielectric layer and surrounds the outer periphery of the hollow waveguide over a predetermined length in the longitudinal direction of the hollow waveguide (see, for example, Patent Document 1).

[0003] Patent No. 6667666

[0004] Waveguides may be required to have high transmission efficiency. In particular, waveguides used in next-generation mobile communication systems (e.g., fifth-generation mobile communication systems (5G), sixth-generation mobile communication systems (6G), etc.) may be required to have higher transmission efficiency than ever before. Waveguides may also be arranged and used inside automobiles, for example, near the engine compartment of a gasoline-powered automobile, or near the power module or motor of an electric vehicle. Because these environments can be hot, waveguides may be required to have excellent heat resistance. Furthermore, a waveguide having a transmission layer that transmits electromagnetic waves and a coating layer that coats the surface of the transmission layer may be required to have excellent adhesion between the transmission layer and the coating layer. Waveguides other than those used inside automobiles may also be required to have high transmission efficiency, heat resistance, and excellent adhesion between the transmission layer and the coating layer. However, a waveguide with high transmission efficiency, heat resistance, and excellent adhesion between the transmission layer and the coating layer has not been sufficiently studied to date.

[0005] Therefore, the present disclosure relates to a waveguide having a transmission layer that transmits electromagnetic waves and a coating layer that coats the surface of the transmission layer, and aims to provide a waveguide that has high transmission efficiency, heat resistance, and excellent adhesion between the transmission layer and the coating layer.

[0006] As a result of intensive research, the present inventors have found that by incorporating aromatic polyether ketone, which is a resin with excellent heat resistance, into a transmission layer that transmits electromagnetic waves and a foam layer that serves as a coating layer that coats the surface of the transmission layer, the waveguide has high transmission efficiency, excellent heat resistance, and excellent adhesion between the transmission layer and the coating layer.

[0007] That is, the present disclosure relates to a waveguide having a transmission layer that transmits electromagnetic waves and a covering layer that covers the surface of the transmission layer, wherein the transmission layer contains aromatic polyether ketone, and the covering layer is a layer of foam containing aromatic polyether ketone.

[0008] According to the present disclosure, a waveguide having a transmission layer that transmits electromagnetic waves and a coating layer that coats the surface of the transmission layer can be provided, which has high transmission efficiency, heat resistance, and excellent adhesion between the transmission layer and the coating layer.

[0009] Fig. 1 is a schematic perspective view of a waveguide according to the present embodiment; Fig. 2 is a schematic cross-sectional view of a waveguide-equipped substrate according to another embodiment; Fig. 3 is a schematic cross-sectional view of a core-equipped substrate; Fig. 4 is a cross-sectional photograph of a foamed film of Test Example 7; Fig. 5 is a graph of propagation loss due to a waveguide versus frequency;

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the accompanying drawings.

[0011] Note that the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate without departing from the spirit of the present disclosure. The present disclosure is not limited by the embodiments, but is limited only by the scope of the claims. Furthermore, each aspect disclosed in this specification can be combined with any other feature disclosed in this specification.

[0012] 1 , a waveguide 1 according to this embodiment includes a transmission layer 2 that transmits electromagnetic waves and a covering layer 3 that covers the surface of the transmission layer 2. The transmission layer 2 contains aromatic polyether ketone. The covering layer 3 is a foam layer containing aromatic polyether ketone.

[0013] Aromatic polyether ketone is a resin with excellent heat resistance. By including aromatic polyether ketone (PAEK) in the transmission layer 2 and the covering layer 3, the waveguide 1 according to this embodiment has excellent heat resistance. Furthermore, the present inventors have conducted extensive research and found that by including aromatic polyether ketone (PAEK) in the transmission layer 2 and the covering layer 3, the waveguide 1 according to this embodiment has high transmission efficiency. Furthermore, by including aromatic polyether ketone (PAEK) in both the transmission layer 2 and the covering layer 3, the waveguide 1 according to this embodiment has excellent adhesion between the transmission layer 2 and the covering layer 3. Therefore, the waveguide 1 according to this embodiment has high transmission efficiency, heat resistance, and excellent adhesion between the transmission layer 2 and the covering layer 3.

[0014] The frequency of the electromagnetic waves transmitted by the waveguide 1 according to this embodiment is not particularly limited, but the waveguide 1 according to this embodiment is particularly suitable for transmitting electromagnetic waves in the high frequency band (e.g., 1 GHz to 3000 GHz, specifically 50 GHz to 1000 GHz, more specifically 150 GHz to 500 GHz).

[0015] (Transmission Layer) The transmission layer 2 is a layer that transmits electromagnetic waves and contains aromatic polyether ketone (PAEK). By containing aromatic polyether ketone (PAEK), the transmission layer 2 has excellent heat resistance and high transmission efficiency. Furthermore, since aromatic polyether ketone (PAEK) has low moisture absorption, by containing aromatic polyether ketone (PAEK), it is possible to suppress deterioration of the insulation properties of the transmission layer 2 due to moisture.

[0016] Examples of the aromatic polyetherketone (PAEK) include polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), polyetherketoneetherketoneketone (PEKEKK), etc. From the viewpoint of improving the heat resistance and transmission efficiency of the transmission layer 2, the aromatic polyetherketone (PAEK) of the transmission layer 2 preferably contains polyetheretherketone (PEEK).

[0017] The polyether ether ketone (PEEK) may be, for example, one represented by the following formula (1): where n is a positive integer of 2 or more.

[0018]

[0019] The number-average molecular weight of the aromatic polyether ketone (PAEK) is not particularly limited as long as it allows the transmission layer 2 to be formed in the desired shape. For example, it is 5,000 or more (e.g., 5,000 to 1,000,000), preferably 8,000 or more (e.g., 10,000 to 500,000), and more preferably 15,000 or more (e.g., 20,000 to 100,000). In this embodiment, this refers to a value measured from the polystyrene-equivalent molecular weight distribution using gel permeation chromatography (GPC) with a chloroform eluent. A column suitable for measuring the molecular weight may be used for the GPC. For example, the weight-average molecular weight (Mw) can be determined by setting the column temperature to 40°C, injecting 10 μl of a solution of 3 mg of the target substance in 2 ml of chloroform, and setting the flow rate of the chloroform eluent (mobile phase) to 1.0 ml / min. The GPC device used may be a high-speed GPC device "HLC-8220GPC" (manufactured by Tosoh Corporation), and the column used may be a GPCK-806M (manufactured by Showa Denko KK).

[0020] The melt volume flow rate (MVR) of the aromatic polyether ketone (PAEK) (temperature: 380°C, load: 5 kg) is preferably 5 to 200 cm ３ / 10 min, more preferably 10 to 30 cm ３ In this embodiment, the melt volume flow rate (MVR) is measured in accordance with ISO1133.

[0021] The transmission layer 2 may contain a polymer other than aromatic polyetherketone (PAEK) within the scope that does not impair the effects of the present disclosure. Examples of other polymers include thermoplastic polyimide-based materials, polyarylketone (PAK), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), polyamideimide (PAI), wholly aromatic polyester (PE), polysulfone (PSF), polyacrylate (PA), polyethersulfone (PES), polycarbonate (PC), modified polyphenylene ether (modified PPE), and polyphenylsulfone (PPSU).

[0022] Examples of the thermoplastic polyimide-based material include polyetherimide (PEI), polyamideimide, etc. Commercially available thermoplastic polyimide-based materials include Aurum manufactured by Mitsui Chemicals and Vespel TP-8000 series manufactured by DuPont.

[0023] The polyetherimide (PEI) may be, for example, one represented by the following formula (2): where m is a positive integer of 2 or more.

[0024]

[0025] The transmission layer 2 may also contain additives within a range that does not impair the effects of the present disclosure. Examples of the additives include inorganic fillers, heat stabilizers, UV absorbers, light stabilizers, nucleating agents, colorants, lubricants, and flame retardants. Examples of the inorganic fillers include talc, mica, clay, glass, alumina, silica, aluminum nitride, and silicon nitride.

[0026] The transmission layer 2 contains preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more of aromatic polyether ketone (PAEK). When the transmission layer 2 contains a large amount of aromatic polyether ketone (PAEK), the crystallinity of the transmission layer 2 is increased, which has the advantage of further improving the heat resistance of the waveguide according to this embodiment.

[0027] The glass transition temperature (Tg) of the transmission layer 2 is preferably 140 to 200°C, more preferably 150 to 180°C. Having a glass transition temperature (Tg) of 140°C or higher (more preferably 150°C or higher) of the transmission layer 2 has the advantage of further improving the heat resistance of the waveguide according to this embodiment. By adding polyetherimide (PEI) to aromatic polyetherketone (PAEK) (e.g., polyetheretherketone (PEEK)), the glass transition temperature (Tg) of the transmission layer 2 can be increased because polyetherimide (PEI) is compatible with aromatic polyetherketone (PAEK) and has a higher glass transition temperature (Tg) than aromatic polyetherketone (PAEK).

[0028] In this embodiment, the glass transition temperature (Tg) refers to the midpoint glass transition temperature measured using a differential scanning calorimeter (DSC). The midpoint glass transition temperature can be determined based on the method described in JIS K7121-1987, "Method for Measuring Transition Temperature of Plastics." That is, first, approximately 5 mg of a sample for measuring the midpoint glass transition temperature is prepared, and two metal (e.g., aluminum) containers of the same shape and weight are prepared. Next, the sample is placed in one of the two containers, while the other container is left empty. Then, the container containing the sample and an empty reference container are placed in a DSC, and the midpoint glass transition temperature can be determined from the DSC curve obtained when the sample is heated at a heating rate of 10°C / min while flowing nitrogen gas.

[0029] The average value of the relative dielectric constant of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably 4.5 or less, more preferably 3.5 or less. When the average value of the relative dielectric constant of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz is 4.5 or less, the transmission efficiency is further improved. The average value of the relative dielectric constant of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably small, but is, for example, 1.0 or more, specifically 1.8 or more.

[0030] The average dielectric loss tangent of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably 0.045 or less, more preferably 0.035 or less. When the average dielectric loss tangent of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz is 0.045 or less, the transmission efficiency is further improved. The average dielectric loss tangent of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably small, and is, for example, 0.0001 or more, specifically 0.00015 or more.

[0031] The average value of the relative dielectric constant and the average value of the dielectric loss tangent of the transmission layer 2 for electromagnetic waves with frequencies from 200 GHz to 3 THz can be measured by the method described in the Examples section below.

[0032] The relative dielectric constant of the transmission layer 2 for electromagnetic waves with a frequency of 1 MHz is preferably 4.0 or less, more preferably 3.5 or less. When the relative dielectric constant of the transmission layer 2 for electromagnetic waves with a frequency of 1 MHz is 4.0 or less, the transmission efficiency is further improved. The relative dielectric constant of the transmission layer 2 for electromagnetic waves with a frequency of 1 MHz is preferably small, but is, for example, 1.0 or more, specifically 1.8 or more.

[0033] The dielectric loss tangent of the transmission layer 2 for electromagnetic waves at a frequency of 1 MHz is preferably 0.009 or less, more preferably 0.007 or less. When the dielectric loss tangent of the transmission layer 2 for electromagnetic waves at a frequency of 1 MHz is 0.009 or less, the transmission efficiency is further improved. The dielectric loss tangent of the transmission layer 2 for electromagnetic waves at a frequency of 1 MHz is preferably small, and is, for example, 0.0001 or more, specifically 0.00015 or more.

[0034] The relative dielectric constant and dielectric loss tangent of the coating layer 2 in an electromagnetic wave with a frequency of 1 MHz can be measured by the method described later in the Examples.

[0035] The transmission layer 2 is preferably fibrous. Examples of the outer shape of the cross section (cross section perpendicular to the longitudinal direction of the waveguide) of the transmission layer 2 include a circle, an ellipse, a polygon (e.g., a square), and a semicircle (a concept including a semicircular cross section). The outer shape of the cross section of the transmission layer 2 is preferably a circle.

[0036] The transmission layer 2 may be a solid layer or a hollow layer. In other words, the transmission layer 2 may be a solid tubular shape or a hollow tubular shape. The transmission layer 2 is preferably a solid layer, as shown in FIG. 1 . When the transmission layer 2 is a solid layer, the hollow portion is less likely to be crushed when the waveguide is bent, compared to when the transmission layer 2 is a hollow layer, and the cross-sectional area of ​​the transmission layer 2 can be prevented from becoming smaller, which is advantageous in that transmission loss is less likely to occur.

[0037] When the wavelength of the electromagnetic wave transmitted by the transmission layer 2 is Λ, the diameter of the transmission layer 2 is preferably 1.5Λ to 4.5Λ, and more preferably 2.0Λ to 4.0Λ. When the diameter of the transmission layer 2 is 1.5Λ to 4.5Λ, the transmission efficiency is likely to be further improved.

[0038] The wavelength Λ of the electromagnetic wave transmitted through the transmission layer 2 can be calculated from the following formula (3): Λ = v / f (3) where v is the transmission speed of the electromagnetic wave transmitted through the transmission layer 2, and f is the frequency of the electromagnetic wave transmitted through the transmission layer 2. Furthermore, the transmission speed v of the electromagnetic wave transmitted through the transmission layer 2 can be calculated from the following formula (4): v = v ０ / n (4) where v ０ is the transmission speed of electromagnetic waves in a vacuum, and n is the refractive index of the medium of the transmission layer 2 in the frequency band of interest.

[0039] The diameter of the transmission layer 2 can be determined as follows. First, a cross section of the waveguide (a cross section perpendicular to the longitudinal direction of the waveguide) is photographed using a scanning electron microscope (SEM) or an optical microscope. Next, the area of ​​the transmission layer 2 in the cross section is determined. Then, from the area, the diameter of the transmission layer 2 is calculated assuming that the outer shape of the cross section of the transmission layer 2 is circular. Note that if the outer shape of the cross section of the transmission layer 2 is circular, the cross section of the waveguide may be photographed using a scanning electron microscope (SEM) or an optical microscope, and the diameter may be determined directly without determining the area. As the scanning electron microscope (SEM), for example, an S-4500 manufactured by Hitachi, Ltd. may be used. Furthermore, the area of ​​each bubble may be determined using, for example, image processing software. As the image processing software, for example, Image-Pro Plus manufactured by Japan Visual Science Co., Ltd. may be used.

[0040] Furthermore, when the wavelength of the electromagnetic waves transmitted by the transmission layer 2 is Λ, the length of the cross section of the transmission layer 2 in the amplitude direction of the electric field of the electromagnetic waves (height in the amplitude direction) is preferably 1.5Λ to 4.5Λ, and more preferably 2.0Λ to 4.0Λ. In particular, when the outer shape of the cross section of the transmission layer 2 is rectangular (a concept that includes a square shape) or semicircular (a concept that includes a semicircular cross section), when the wavelength of the electromagnetic waves transmitted by the transmission layer 2 is Λ, the length of the cross section of the transmission layer 2 in the amplitude direction of the electric field of the electromagnetic waves (height in the amplitude direction) is preferably 1.5Λ to 4.5Λ, and more preferably 2.0Λ to 4.0Λ. Having the length of the cross section of the transmission layer 2 in the amplitude direction of the electric field of the electromagnetic waves (height in the amplitude direction) of 1.5Λ to 4.5Λ tends to further improve the transmission efficiency. The cross-sectional length of the transmission layer 2 in the amplitude direction of the electric field of the electromagnetic wave (height in the amplitude direction) can be determined by photographing the cross section of the waveguide with a scanning electron microscope (SEM) or an optical microscope.

[0041] The refractive index of the electromagnetic wave in the transmission layer 2 is higher than the refractive index of the electromagnetic wave in the covering layer 3. The transmission layer 2 may be a non-foam layer or a foam layer. From the viewpoint of making the refractive index of the electromagnetic wave in the transmission layer 2 higher than the refractive index of the electromagnetic wave in the covering layer 3 to prevent the electromagnetic wave transmitted by the transmission layer 2 from leaking into the covering layer 3, from the viewpoint of facilitating the fabrication of the waveguide according to this embodiment, and from the viewpoint of reducing the weight of the waveguide according to this embodiment, it is preferable that the transmission layer 2 is a non-foam layer. From the viewpoint of preventing the electromagnetic wave transmitted by the transmission layer 2 from leaking into the covering layer 3, when the transmission layer 2 is a foam layer, it is preferable that the expansion ratio of the foam of the transmission layer 2 is smaller than the expansion ratio of the foam of the covering layer 3. A method for measuring the expansion ratio will be described later.

[0042] (Covering Layer) The covering layer 3 is a layer that covers the surface of the transmission layer 2 and is a foam layer containing aromatic polyether ketone (PAEK). The covering layer 3 is a layer that covers the surface of the transmission layer 2 in a cross section of the waveguide (a cross section perpendicular to the longitudinal direction of the waveguide).

[0043] The coating layer 3 contains aromatic polyether ketone (PAEK), which provides excellent heat resistance and high transmission efficiency. Furthermore, since aromatic polyether ketone (PAEK) has low moisture absorption, the coating layer 3 contains aromatic polyether ketone (PAEK), which can prevent the insulation of the coating layer 3 from being reduced by moisture.

[0044] Furthermore, since the covering layer 3 is a foam layer, it is possible to prevent the electromagnetic waves transmitted by the transmission layer 2 from leaking to the covering layer 3. Since air has a lower dielectric constant than polymer components, the covering layer 3 has a lower dielectric constant when it is made of a foam layer. As a result, it is possible to prevent the electromagnetic waves transmitted by the transmission layer 2 from leaking to the covering layer 3.

[0045] Examples of the aromatic polyetherketone (PAEK) in the coating layer 3 include the aromatic polyetherketone (PAEK) described in the description of the transmission layer 2. The aromatic polyetherketone (PAEK) contained in the coating layer 3 may be the same as or different from the aromatic polyetherketone (PAEK) contained in the transmission layer 2. From the viewpoint of improving the heat resistance and transmission efficiency of the coating layer 3, the aromatic polyetherketone (PAEK) in the coating layer 3 preferably contains polyetheretherketone (PEEK).

[0046] The covering layer 3 may contain a polymer other than aromatic polyether ketone (PAEK). Examples of the other polymer in the covering layer 3 include the other polymers described in the description of the transmission layer 2.

[0047] Preferably, the covering layer 3 further contains a thermoplastic polyimide-based material, which is the other polymer. Including a thermoplastic polyimide-based material in the covering layer 3 facilitates an increase in the foaming ratio of the foam in the covering layer 3 when a foamable polymer layer (described later) is foamed to obtain a foam layer serving as the covering layer 3, thereby lowering the dielectric constant of the covering layer 3. As a result, there is an advantage in that the leakage of electromagnetic waves transmitted through the transmission layer 2 to the covering layer 3 can be further suppressed. This is believed to be due to the following: The melting point of aromatic polyether ketone (PAEK) is higher than the glass transition temperature of thermoplastic polyimide-based materials. Heating a foamable polymer layer containing aromatic polyether ketone (PAEK) and a thermoplastic polyimide-based material tends to soften the foamable polymer layer, making it easier to foam. Furthermore, the excellent compatibility between thermoplastic polyimide-based materials and aromatic polyether ketone (PAEK) also facilitates foaming of the foamable polymer layer, resulting in a higher foaming ratio for the resulting foam in the covering layer 3. As a result, the dielectric constant of the covering layer 3 becomes low.

[0048] From the viewpoint of making it easier to increase the expansion ratio of the foam of the covering layer 3, the thermoplastic polyimide-based material preferably contains polyetherimide (PEI).

[0049] The coating layer 3 may contain an additive within a range that does not impair the effects of the present disclosure. Examples of the additive in the coating layer 3 include the additives described in the description of the transmission layer 2.

[0050] The coating layer 3 contains, in total, preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more of aromatic polyether ketone (PAEK) and an optional thermoplastic polyimide-based material.

[0051] The mass ratio of the aromatic polyether ketone (PAEK) to the thermoplastic polyimide-based material is preferably 50 / 50 to 87 / 13, more preferably 60 / 40 to 85 / 15, and even more preferably 70 / 30 to 80 / 20.

[0052] The expansion ratio of the foam of the coating layer 3 is preferably 1.30 or more, more preferably 1.40 or more. The larger the expansion ratio of the foam of the coating layer 3, the more preferable it is, but it is, for example, 10 or less, specifically 6.0 or less.

[0053] The expansion ratio of a foam is the value obtained by dividing the "specific gravity of the polymer body in a state before foaming, which will be described later" by the "specific gravity of the foam in a state after foaming." The specific gravities (densities) of foams and polymer bodies can be determined in accordance with Method A (underwater displacement method) of JIS K7112:1999 "Method for measuring density and specific gravity of plastics - non-foamed plastics." The specific gravity of the polymer body may be measured using the polymer body in a state before the foam is obtained, or, if only the foamed foam is available, the foam may be hot-pressed to produce a polymer body, and the measurement may be performed using this polymer body.

[0054] The glass transition temperature (Tg) of the coating layer 3 is preferably 140 to 200° C., more preferably 150 to 180° C. When the glass transition temperature (Tg) of the coating layer 3 is 140° C. or higher, the waveguide according to this embodiment has the advantage of having even more excellent heat resistance.

[0055] The average value of the dielectric constant of the coating layer 3 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably 3.5 or less, more preferably 2.5 or less. When the average value of the dielectric constant of the coating layer 3 for electromagnetic waves with frequencies from 200 GHz to 3 THz is 3.5 or less, transmission efficiency is further improved. The average value of the dielectric constant of the coating layer 3 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably small, but is, for example, 1.0 or more, specifically 1.5 or more.

[0056] The average dielectric loss tangent of the coating layer 3 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably 0.045 or less, more preferably 0.035 or less. When the average dielectric loss tangent of the coating layer 3 for electromagnetic waves with frequencies from 200 GHz to 3 THz is 0.045 or less, transmission efficiency is further improved. The average dielectric loss tangent of the coating layer 3 for electromagnetic waves with frequencies from 200 GHz to 3 THz is preferably small, and is, for example, 0.0001 or more, specifically 0.00015 or more.

[0057] The average value of the relative dielectric constant and the average value of the dielectric loss tangent of the coating layer 3 in the electromagnetic wave having a frequency of 200 GHz to 3 THz can be measured by the method described later in the examples.

[0058] The dielectric constant of the coating layer 3 for electromagnetic waves with a frequency of 1 MHz is preferably 3.5 or less, more preferably 3.0 or less. When the dielectric constant of the coating layer 3 for electromagnetic waves with a frequency of 1 MHz is 3.5 or less, transmission efficiency is further improved. The dielectric constant of the coating layer 3 for electromagnetic waves with a frequency of 1 MHz is preferably small, and is, for example, 1.0 or more, specifically 1.6 or more.

[0059] The dielectric loss tangent of the coating layer 3 for electromagnetic waves with a frequency of 1 MHz is preferably 0.009 or less, more preferably 0.007 or less. When the dielectric loss tangent of the coating layer 3 for electromagnetic waves with a frequency of 1 MHz is 0.009 or less, transmission efficiency is further improved. The dielectric loss tangent of the coating layer 3 for electromagnetic waves with a frequency of 1 MHz is preferably small, and is, for example, 0.0001 or more, specifically 0.00015 or more.

[0060] The relative dielectric constant and dielectric loss tangent of the coating layer 3 in an electromagnetic wave with a frequency of 1 MHz can be measured by the method described later in the examples.

[0061] In the embodiment of FIG. 1, the covering layer 3 covers the entire surface of the transmission layer 2 in a cross section of the waveguide (a cross section perpendicular to the longitudinal direction of the waveguide).

[0062] Examples of the outer shape of the cross section (cross section perpendicular to the longitudinal direction of the waveguide) of the coating layer 3 include a circle, an ellipse, a polygon, etc. The outer shape of the cross section of the coating layer 3 is preferably a circle. Furthermore, from the viewpoint of making it easier to make the thickness of the coating layer 3 relatively uniform, the outer shape of the cross section of the coating layer 3 is preferably a shape similar to the outer shape of the cross section of the transmission layer 2.

[0063] When the wavelength of the electromagnetic wave transmitted by the transmission layer 2 is Λ, the thickness of the coating layer 3 is preferably (1 / 4)Λ or more, more preferably (1 / 2)Λ or more, and even more preferably (4 / 5)Λ or more. The thickness of the coating layer 3 is preferably larger, but is, for example, 6.0Λ or less, specifically 3.0Λ or less, and more specifically Λ or less. When the thickness of the coating layer 3 is (1 / 2)Λ or more, the transmission efficiency is more likely to be improved.

[0064] The thickness of the coating layer 3 can be determined as follows. First, a cross section of the waveguide (a cross section perpendicular to the longitudinal direction of the waveguide) is photographed using a scanning electron microscope (SEM) or an optical microscope. Then, the thickness of the coating layer 3 in the cross section is determined. As the scanning electron microscope (SEM), for example, an S-4500 manufactured by Hitachi, Ltd. can be used. Furthermore, when determining the area of ​​each bubble, for example, image processing software can be used. As the image processing software, for example, Image-Pro Plus manufactured by Nippon Visual Science Co., Ltd. can be used.

[0065] <Method for Manufacturing Waveguide> The waveguide according to this embodiment is configured as described above. Next, a method for manufacturing the waveguide according to this embodiment will be described using a method for manufacturing a fiber-shaped waveguide as an example.

[0066] In the method for manufacturing a waveguide according to this embodiment, a fiber-shaped waveguide can be manufactured using a co-extrusion molding method.

[0067] First, the material for the transmission layer 2 is put into a first extruder, melted by heating, and melt-kneaded to obtain a molten first resin composition, and then the material for the covering layer 3 is put into a second extruder, melted by heating, and melt-kneaded to obtain a molten second resin composition.

[0068] Next, the molten first resin composition and the molten second resin composition are co-extruded to obtain a molded article having a fiber-like transmission layer 2 formed from the first resin composition and a polymer layer formed from the second resin composition and covering the surface of the transmission layer 2. The molding temperature of the first resin composition in the co-extrusion molding method is equal to or higher than the flow initiation temperature of the first resin composition, preferably in the range of "the flow initiation temperature of the first resin composition + 20°C" to 430°C. Furthermore, the molding temperature of the second resin composition in the co-extrusion molding method is equal to or higher than the flow initiation temperature of the second resin composition, preferably in the range of "the flow initiation temperature of the second resin composition + 20°C" to 430°C.

[0069] A foamable polymer body is then obtained by impregnating the polymer body with a pressurized gas or supercritical fluid.

[0070] Examples of pressurized gases or supercritical fluids include carbon dioxide, nitrogen (N ２ ), helium, argon, nitrous oxide, ethylene, ethane, tetrafluoroethylene, perfluoroethane, tetrafluoromethane, trifluoromethane, 1,1-difluoroethylene, trifluoroamide oxide, cis-difluorodiamine, trans-difluorodiamine, nitrogen difluoride chloride, phosphorus tritide, dinitrogen tetrafluoride, ozone, phosphine, nitrosyl fluoride, nitrogen trifluoride, deuterium chloride, xenon, sulfur hexafluoride, fluoromethane, pentafluoroethane, 1,1-difluoroethene, diborane, water, tetrafluorohydrazine, silane, silicon tetrafluoride, germanium tetrahydride, boron trifluoride, carbonyl fluoride, chlorotrifluoromethane, bromotrifluoromethane, vinyl fluoride, and the like. The pressurized gas or supercritical fluid is preferably carbon dioxide, nitrogen, nitrous oxide, ethylene, ethane, tetrafluoroethylene, perfluoroethane, tetrafluoromethane, trifluoromethane, or 1,1-difluoroethylene. The pressurized gas or supercritical fluid is particularly preferably carbon dioxide, nitrogen, helium, or argon.

[0071] From the viewpoint of suppressing deformation of the polymer body, the temperature at which the pressurized gas or supercritical fluid is impregnated into the polymer body is preferably equal to or lower than the glass transition temperature of the polymer body.

[0072] The time for impregnating the polymer body with the pressurized gas or supercritical fluid depends on the thickness of the polymer body, etc., but is preferably 5 minutes or more, more preferably 30 minutes or more. From the viewpoint of productivity, the time for impregnating the polymer body with the pressurized gas or supercritical fluid is preferably 48 hours or less, more preferably 24 hours or less, and even more preferably 12 hours or less.

[0073] The foamable polymer body is then heated to vaporize the impregnated pressurized gas or supercritical fluid, thereby obtaining a foam. That is, a waveguide having a transmission layer 2 and a covering layer 3, which is a foam layer, is obtained. The heating is carried out under no pressure. Examples of equipment used for the heating include a hot air circulation heat treatment furnace, a heat press, an oil bath, and a salt bath. The heating temperature is preferably 150°C to 350°C, more preferably 170°C to 250°C. The heating time may be set to a time required for foaming to be completed.

[0074] It is preferable to obtain a foam by vaporizing the pressurized gas or supercritical fluid impregnated in the polymer body and then cooling the foamed foamable polymer body to about room temperature. It is also preferable to obtain a foam by cooling the foamed foamable polymer body to about room temperature and then heating the foamable polymer body to crystallize it.

[0075] The waveguide according to the present disclosure can be modified in various ways without departing from the gist of the present disclosure.

[0076] For example, the waveguide manufacturing method according to this embodiment uses a co-extrusion molding method, but in other embodiments, when the transmission layer 2 and the covering layer 3 are formed of the same material, extrusion molding may be used. That is, in other embodiments, the materials for the transmission layer 2 and the covering layer 3 are fed into an extruder, melted by heating, and melt-kneaded to obtain a molten resin composition. The molten resin composition is then extruded to obtain a fibrous molded article made of a polymer body. The molding temperature for the resin composition in the extrusion molding method is equal to or higher than the flow initiation temperature of the resin composition, preferably in the range of "the flow initiation temperature of the resin composition + 20°C" to 430°C. A foamable polymer body is then obtained by impregnating the polymer body on the surface side of the molded article with a pressurized gas or supercritical fluid. The foamable polymer body is then heated to vaporize the impregnated pressurized gas or supercritical fluid, thereby obtaining a foam. That is, a waveguide having the transmission layer 2, which is a polymer body layer, and the covering layer 3, which is a foam layer, is obtained.

[0077] 1, in the cross section of the waveguide (cross section perpendicular to the longitudinal direction of the waveguide), the covering layer 3 covers the entire surface of the transmission layer 2 in the waveguide 1 according to this embodiment, but as shown in Fig. 2, in the waveguide 1 according to another embodiment, it may be provided on a substrate 4, and a part of the surface of the transmission layer 2 may be covered by the substrate 4, and another part of the surface of the transmission layer 2 may be covered by the covering layer 3. In other words, the waveguide-equipped substrate according to another embodiment may include a substrate 4 and a waveguide 1 provided on the substrate 4.

[0078] In another embodiment of the method for manufacturing a waveguide-equipped substrate, as shown in FIG. 3 , a core 5 formed of a polymer body is first provided on a substrate 4. The core 5 can be provided on the substrate 4 by a conventionally known method, such as physical etching (RIE), direct light exposure (UV curing), photobleaching (UV modification), self-forming, embossing, or stamping (molding) (see, for example, "Soichi Kobayashi, 'Expectations for Polymer Optical Waveguides and the Materials Technology Supporting Them,' Optics, Vol. 37, No. 2 (2008), pp. 74-81"). A foamed polymer body is then obtained by impregnating the polymer body on the surface side of the core with a pressurized gas or supercritical fluid. The foamed polymer body is then heated to vaporize the impregnated pressurized gas or supercritical fluid, thereby obtaining a foam. That is, a waveguide 1 is obtained, which has a transmission layer 2, which is a polymer body layer, and a covering layer 3, which is a foam layer. This results in a waveguide-equipped substrate comprising the substrate 4 and the waveguide 1 provided on the substrate 4. Conventionally, to form a waveguide on a substrate, it is necessary to cover the core with a cladding material. However, in the method for manufacturing a waveguide-equipped substrate according to another embodiment, foaming the surface portion of the core eliminates the need to cover the core with a cladding material, and the waveguide can be easily formed on the substrate. In other words, when the transmission layer 2 and the covering layer 3 are formed of the same material, a waveguide-equipped substrate can be easily formed.

[0079] Disclosure Items Each of the following items is a disclosure of a preferred embodiment.

[0080] [Item 1] A waveguide having a transmission layer that transmits electromagnetic waves and a coating layer that coats the surface of the transmission layer, wherein the transmission layer contains aromatic polyether ketone, and the coating layer is a layer of foam containing aromatic polyether ketone. [Item 2] The waveguide according to item 1, wherein the foam in the coating layer has an expansion ratio of 1.30 or more. [Item 3] The waveguide according to item 1 or 2, which is in the form of a fiber. [Item 4] The waveguide according to item 3, wherein, when the wavelength of the electromagnetic waves is Λ, the diameter of the transmission layer is 1.5Λ to 4.5Λ and the thickness of the coating layer is (½)Λ or more. [Item 5] The waveguide according to any one of items 1 to 4, wherein the glass transition temperature of the transmission layer is 140 to 200°C, and the glass transition temperature of the coating layer is 140 to 200°C. [Item 6] The waveguide according to any one of items 1 to 5, wherein the transmission layer is a solid layer. [Item 7] The waveguide according to any one of items 1 to 6, wherein the covering layer further comprises a thermoplastic polyimide-based material. [Item 8] The waveguide according to any one of items 1 to 7, wherein the aromatic polyetherketone of the transmission layer comprises polyetheretherketone. [Item 9] The waveguide according to any one of items 1 to 8, wherein the aromatic polyetherketone of the covering layer comprises polyetheretherketone. [Item 10] A waveguide-equipped substrate comprising a substrate and a waveguide provided on the substrate, wherein the waveguide is the waveguide according to any one of items 1 to 9.

[0081] Next, the present disclosure will be described in more detail with reference to test examples, although the present disclosure is not limited to these test examples.

[0082] The following materials were prepared: PEEK: polyetheretherketone (VESTAKEEP (registered trademark) 3300G manufactured by Daicel-Evonik) PEI: polyetherimide (ULTEM1000 manufactured by SABIC) The melt volume flow rate (MVR) of polyetheretherketone (PEEK) is as follows: VESTAKEEP (registered trademark) 3300G: 20 cm ３ / 10 min

[0083] (Test Examples 1 to 8: Foam) PEEK and PEI were premixed in the ratios (parts by mass) shown in Table 1 below, and melt-kneaded using a twin-screw extruder (φ: 25 mm, L / D: 40) under conditions of a cylinder temperature of 380°C and a screw rotation speed of 200 rpm to obtain a resin composition. The resin composition was compression-molded using a heat press under conditions of 380°C and 60 MPa to produce a polymer film having a thickness shown in Table 1 below. The polymer film was placed in a pressure vessel (set temperature: 100°C), and the pressure vessel was evacuated with carbon dioxide (CO ２ ) for 1 to 2 hours, and carbon dioxide in a supercritical fluid state (CO ２ ) was impregnated into the foamed polymer film. The pressure (gauge pressure) during pressurization was set to 20 MPa. The leak valve of the pressure vessel was then fully opened, the pressure in the pressure vessel was released at a decompression rate of 1 MPa / sec, and the foamed polymer film was removed from the pressure vessel. The foamed polymer film was then heated for 1 minute using a hot plate set to a predetermined temperature (foaming temperature: the temperature listed in Table 1 below) to foam it. The surface of the foamed foamed polymer film was then cooled to obtain a foamed film. The foamed film of Test Example 7 was cut, and the cut surface was photographed with a scanning electron microscope (SEM). A cross-sectional photograph of the foamed film of Test Example 7 is shown in Figure 4.

[0084] Test Example 9: Non-foamed article PEEK and PEI were premixed in the ratios (parts by mass) shown in Table 2 below, and melt-kneaded using a twin-screw extruder (φ: 25 mm, L / D: 40) under conditions of a cylinder temperature of 380°C and a screw rotation speed of 200 rpm to obtain a resin composition. The resin composition was compression-molded using a heat press under conditions of 380°C and 60 MPa to produce a polymer film as a non-foamed article having a thickness shown in Table 2 below.

[0085] (Expansion Ratio) The expansion ratio of the foamed film of the example was determined by the method described above. The measured values ​​are shown in Table 1 below.

[0086] (Relative permittivity and dielectric loss tangent in electromagnetic waves of 1 MHz frequency) The relative permittivity and dielectric loss tangent in electromagnetic waves of 1 MHz frequency were measured for the foamed films of Test Examples 1 to 8. The relative permittivity and dielectric loss tangent in electromagnetic waves of 1 MHz frequency were measured at 1 MHz by a non-contact electrode method in accordance with ASTM D150 "Standard Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation". Specifically, the dielectric constant and dielectric loss tangent in an electromagnetic wave with a frequency of 1 MHz were measured at 1 MHz by a non-contact electrode method using an LCR meter ("E4980A" manufactured by Keysight Technologies) equipped with a dielectric test fixture ("16451B" manufactured by Keysight Technologies). The dielectric constant and dielectric loss tangent in an electromagnetic wave with a frequency of 1 MHz are shown in Table 1 below.

[0087] (Average Values ​​of Relative Permittivity and Dielectric Loss Tangent in Electromagnetic Waves with Frequencies from 200 GHz to 3 THz) The average values ​​of relative permittivity and dielectric loss tangent in electromagnetic waves with frequencies from 200 GHz to 3 THz were determined for the foamed films of Test Examples 1 to 8 and the non-foamed polymer film of Test Example 9. Specifically, a terahertz time-domain spectroscopy (THz-TDS) system manufactured by Advantest Corporation (model number: TAS7500TS) was used, with an oscillation frequency-synchronized fiber laser (λ=1.55 μm, pulse width≦∧50 fs, pulse repetition rate=50 MHz) on the emitter side and a fiber pigtail photoconductive antenna on the detector side, and the film to be measured was mounted on an aperture (diameter φ: 10 mm) to measure the dielectric properties. The transmitted pulse of the electromagnetic wave passing through the aperture was measured and Fourier transformed to simultaneously obtain both the amplitude spectrum and the phase spectrum, and the complex refractive index (refractive index = n, extinction coefficient = k) and complex dielectric constant (real part and imaginary part) of the film to be measured were calculated. The relative dielectric constant and dielectric loss tangent of the film to be measured were then calculated. The relative dielectric constant and dielectric loss tangent were determined for electromagnetic waves with frequencies from 200 GHz to 3 THz, and from these values, the average values ​​of the relative dielectric constant (arithmetic mean value) and the average values ​​of the dielectric loss tangent (arithmetic mean value) were calculated. The average values ​​of the relative dielectric constant and the average values ​​of the dielectric loss tangent are shown in Tables 1 and 2 below.

[0088]

[0089]

[0090] (Calculated Value of Transmission Loss Through Waveguide) Using software, the transmission loss (also referred to as "propagation loss") [dB / cm] of electromagnetic waves (frequency: 220 to 325 GHz) through a fiber-like waveguide was calculated. The transmission layer of the waveguide had a regular dodecagonal cross section perpendicular to the longitudinal direction of the waveguide, a diameter of 3 mm, and was formed from the non-foamed material of Test Example 9 (relative dielectric constant (ε): 3.10, dielectric loss tangent (tan δ): 0.029). The covering layer of the waveguide was formed from the foamed material of Test Example 7 (relative dielectric constant (ε): 1.60, dielectric loss tangent (tan δ): 0.014), covering the entire periphery of the surface of the transmission layer in the cross section perpendicular to the longitudinal direction of the waveguide, with a thickness of 1 mm. The transmission loss [dB / cm] was calculated using electromagnetic field simulation software (CST Studio Suite 2021) from Dassault Systèmes. Specifically, the finite integral method was used, the mesh inside the fiber was set to one-tenth of the wavelength of the electromagnetic wave, the boundary condition between the fiber-like waveguide and the atmosphere was set to a PML (Perfectly Matched Layer) absorbing boundary condition, and the permittivity and permeability of the atmosphere were each set to 1 [-]. The simulation was performed, and the transmission loss [dB / cm] was calculated. The results are shown in Figure 5.

[0091] As shown in FIG. 5 , even in the high frequency band (frequency: 220 to 325 GHz), the transmission loss was within a range of approximately 10 to 16 dB / cm, and the transmission efficiency of the waveguide was high. This demonstrates that incorporating aromatic polyether ketone into the transmission layer 2 and the covering layer 3 results in a waveguide with high transmission efficiency. Furthermore, aromatic polyether ketone is a resin with excellent heat resistance. Furthermore, by incorporating aromatic polyether ketone into both the transmission layer and the covering layer, the waveguide exhibits excellent adhesion between the transmission layer and the covering layer. Therefore, the present disclosure provides a waveguide having a transmission layer that transmits electromagnetic waves and a covering layer that covers the surface of the transmission layer, which exhibits high transmission efficiency, heat resistance, and excellent adhesion between the transmission layer and the covering layer.

[0092] 1: Waveguide, 2: Transmission layer, 3: Covering layer, 4: Substrate, 5: Substrate with waveguide, 6: Core

Claims

1. A waveguide having a transmission layer that transmits electromagnetic waves and a covering layer that covers a surface of the transmission layer, the transmission layer containing aromatic polyether ketone, and the covering layer being a layer of foam containing aromatic polyether ketone.

2. The waveguide according to claim 1, wherein the foam of said covering layer has an expansion ratio of 1.30 or more.

3. A waveguide according to claim 1 or 2, which is in the form of a fiber.

4. The waveguide according to claim 3, wherein, when the wavelength of the electromagnetic wave is Λ, the diameter of the transmission layer is 1.5Λ to 4.5Λ, and the thickness of the covering layer is (1 / 2)Λ or more.

5. A waveguide according to claim 1 or 2, wherein the glass transition temperature of said transmission layer is 140 to 200°C, and the glass transition temperature of said covering layer is 140 to 200°C.

6. A waveguide according to claim 1 or 2, wherein the transmission layer is a solid layer.

7. The waveguide of claim 1 or 2, wherein said covering layer further comprises a thermoplastic polyimide-based material.

8. The waveguide of claim 1 or 2, wherein the aromatic polyetherketone of the transmission layer comprises polyetheretherketone.

9. The waveguide of claim 1 or 2, wherein the aromatic polyetherketone of the cladding layer comprises polyetheretherketone.

10. A substrate with a waveguide, comprising: a substrate; and a waveguide provided on the substrate, the waveguide being the waveguide according to claim 1 or 2.

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