Hollow structure film, circuit board, antenna equipment, and method for manufacturing a hollow structure film

Abstract

This invention provides a method for adjusting the CTE (coefficient of thermal expansion) of a film with a low dielectric constant. [Solution] The hollow structure film 1 having a hollow structure comprises a main body 1c having a sheet-like first base portion 11, a sheet-like second base portion 12 overlapping the first base portion 11, and a plurality of support portions 20 provided between the first base portion 11 and the second base portion 12. The first base portion 11 has a first opposing surface 11a facing the second base portion 12. The second base portion 12 has a second opposing surface 12a facing the first base portion 11. At least a portion of the plurality of support portions 20 constitute a continuous support portion 23 extending from the first opposing surface 11a to the second opposing surface 12a. The main body 1c includes an insulating inorganic material member 70. The maximum width of the inorganic material member 70 is three times or more the minimum width of the inorganic material member 70.

Description

[Technical Field]

[0001] This disclosure relates to a hollow structure film, a circuit board, antenna equipment, and a method for manufacturing a hollow structure film. [Background technology]

[0002] In recent years, there has been a growing demand for high-speed transmission and reception of large amounts of data in information and communication equipment. Against this backdrop, increasing the frequency of electrical signals is being explored.

[0003] In particular, when using a communication standard corresponding to 5G in a communication system defined by the International Telecommunication Union (ITU), in Japan, higher frequency bands such as the 4.5GHz band and 28GHz band, which are higher than the 3.7GHz band allocated to communication standards prior to 4G, are allocated to telecommunications carriers.

[0004] In contrast, conventional circuit boards, primarily designed for communication utilizing low-frequency bands, sometimes have relatively high dielectric constants. A higher dielectric constant leads to greater electrical signal propagation delay. Therefore, a lower dielectric constant is preferable to increase the electrical signal propagation speed and enable high-speed calculations. For these reasons, in order to enable high-capacity, high-speed communication using circuit boards in high-frequency bands, it is necessary to lower the dielectric constant of circuit boards compared to conventional designs.

[0005] Furthermore, a high dielectric constant of a circuit board tends to result in greater transmission loss of high-frequency currents generated on the circuit. Therefore, when attempting communication using the same current, circuit boards with higher dielectric constants experience greater radio wave loss, resulting in weaker radio waves usable for communication. This can lead to problems such as shorter communication ranges with circuit boards that have higher dielectric constants.

[0006] As a sheet with a dielectric constant lower than conventional sheets that can be used in circuit boards and the like, a sheet manufactured by forming a resin foam containing air bubbles is known, such as the low dielectric sheet for two-dimensional communication disclosed in Patent Document 1. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5976714 [Overview of the project] [Problems that the invention aims to solve]

[0008] There was a need to adjust the CTE (coefficient of thermal expansion) of low dielectric films used in circuit boards.

[0009] This disclosure has been made in consideration of the above points and aims to adjust the CTE of a film with a low dielectric constant. [Means for solving the problem]

[0010] Embodiments of this disclosure relate to the following [1] to

[17] .

[0011] [1] In a hollow structure film having a hollow structure, The main body comprises a sheet-like first base, a sheet-like second base overlapping the first base, and a plurality of support columns provided between the first base and the second base. The first base portion has a first opposing surface that faces the second base portion, The second base portion has a second opposing surface that faces the first base portion, At least a portion of the multiple support columns constitute a continuous support column extending from the first opposing surface to the second opposing surface. The main body includes an insulating inorganic material member, A hollow structure film in which the maximum width of the inorganic material member is at least three times the minimum width of the inorganic material member.

[0012] [2] The inorganic material member is included in at least one of the first base portion and the second base portion, and the hollow structure film according to [1].

[0013] [3] The inorganic material member is included in a part of at least a plurality of the support portions, and the hollow structure film according to [1] or [2].

[0014] [4] The main body portion further has a sheet-like central portion located between the first opposing surface and the second opposing surface. The plurality of support portions are the hollow structure films according to any one of [1] to [3], which are located on the first opposing surface side and the second opposing surface side of the central portion.

[0015] [5] The inorganic material member is included in at least the central portion, and the hollow structure film according to [4].

[0016] [6] The inorganic material member contains glass, and the hollow structure film according to any one of [1] to [5].

[0017] [7] The hollow structure film according to any one of [1] to [6], in which the maximum width of the inorganic material member is 10 μm or more.

[0018] [8] The main body portion contains polyolefin, and the hollow structure film according to any one of [1] to [7].

[0019] [9] The hollow structure film according to any one of [1] to [8], having a thickness of 50 μm or more and 1000 μm or less.

[0020]

[10] A hollow structured film as described in any of [1] to [9], having a void ratio of 20% or more.

[0021]

[11] The hollow structure film has a first surface and a second surface located on the opposite side of the first surface. A hollow structure film according to any one of [1] to

[10] , further comprising a metal layer constituting at least a portion of at least one of the first surface and the second surface.

[0022]

[12] The metal layer further comprises a metal adjacent layer that joins at least one of the first base and the second base, The hollow structure film according to

[11] , wherein the material of the adjacent metal layer is different from the material of the first base and the second base.

[0023]

[13] The metal layer further comprises a metal adjacent layer that joins at least one of the first base and the second base, The hollow structure film according to

[11] or

[12] , wherein the material of the metal adjacent layer is an adhesive.

[0024]

[14] A hollow structure film according to any one of

[11] to

[13] , further comprising an ionomer layer or an ethylene (meth)acrylic acid copolymer polymer layer that joins the metal layer to at least one of the first base and the second base.

[0025]

[15] A hollow structure film according to any one of [1] to

[10] , having a first surface and a second surface located on the opposite side of the first surface, A circuit board comprising a wiring pattern provided on at least one of the first surface and the second surface.

[0026]

[16]

[15] The circuit board described above, An antenna device comprising an antenna element connected to the aforementioned circuit board.

[0027]

[17] In a method for manufacturing a hollow structure film having a hollow structure, A step of producing a pair of single-sided molded bodies containing an insulating inorganic material member, each having a sheet-like base and a plurality of protrusions formed on one side of the base, using a mold. The process includes overlapping a pair of the fabricated single-sided molded bodies such that at least some of the protrusions face each other, and then heating and pressing them together, A method for manufacturing a hollow structure film, wherein the maximum width of the inorganic material member is three times or more the minimum width of the inorganic material member. [Effects of the Invention]

[0028] According to embodiments of this disclosure, the CTE of a film with a low dielectric constant can be adjusted. [Brief explanation of the drawing]

[0029] [Figure 1A] Figure 1A is a cross-sectional view showing an example of a hollow structure film according to one embodiment. [Figure 1B] Figure 1B is a cross-sectional view showing an example of a hollow structure film according to one embodiment. [Figure 2] Figure 2 is a plan view showing the base of a hollow structure film according to one embodiment. [Figure 3] Figure 3 shows an example of a cross-sectional image of a film having a hollow structure. [Figure 4] Figure 4 is a cross-sectional view showing a hollow structure film according to one embodiment. [Figure 5] Figure 5 is a cross-sectional view showing a hollow structure film according to one embodiment. [Figure 6A] Figure 6A is a perspective view showing a hollow structure film on which the transmission loss of electrical signals is measured. [Figure 6B] Figure 6B shows a method for measuring the transmission loss of electrical signals in a hollow structure film. [Figure 6C] Figure 6C is a perspective view showing antenna equipment according to one embodiment. [Figure 7A] Figure 7A shows a method for manufacturing a hollow structure film according to one embodiment. [Figure 7B] Figure 7B shows a method for manufacturing a hollow structure film according to one embodiment. [Figure 8A] Figure 8A shows a method for manufacturing a hollow structure film according to one embodiment. [Figure 8B] Figure 8B shows a method for manufacturing a hollow structure film according to one embodiment. [Figure 8C] Figure 8C shows a method for manufacturing a hollow structure film according to one embodiment. [Figure 8D] Figure 8D shows a method for manufacturing a hollow structure film according to one embodiment. [Figure 8E] Figure 8E shows a diagram illustrating a method for manufacturing a hollow structure film according to one embodiment. [Figure 9] Figure 9 is a plan view showing the base of the hollow structure film according to Modification 1. [Figure 10] Figure 10 is a cross-sectional view showing a hollow structure film according to Modification 2. [Figure 11] Figure 11 shows a method for manufacturing a hollow structure film according to Modification 3. [Figure 12] Figure 12 is a cross-sectional view showing a hollow structure film according to Modification 3. [Figure 13] Figure 13 shows a method for manufacturing a hollow structure film according to Modification 4. [Figure 14] Figure 14 is a cross-sectional view showing a hollow structure film according to Modification 4. [Figure 15] Figure 15 shows a method for manufacturing a hollow structure film according to Modification 5. [Figure 16] Figure 16 is a cross-sectional view showing a hollow structure film according to Modification 5. [Figure 17A] Figure 17A is a plan view showing a hollow structure film according to Modification 6. [Figure 17B] Figure 17B is a perspective view showing a one-sided form according to Modification 6. [Figure 18A] Figure 18A is a plan view showing a hollow structure film according to Modification 6. [Figure 18B] Figure 18B is a plan view showing a hollow structure film according to Modification 6. [Figure 18C] Figure 18C is a plan view showing a hollow structure film according to Modification 6. [Figure 18D] Figure 18D is a perspective view showing a one-sided form according to Modification 6. [Figure 19A] Figure 19A is a plan view showing a hollow structure film according to Modification 7. [Figure 19B] Figure 19B is a plan view showing a hollow structure film according to Modification 7. [Figure 19C] Figure 19C is a plan view showing a hollow structure film according to Modification 7. [Figure 19D] Figure 19D is a perspective view showing a one-sided form according to Modification 7. [Figure 19E] Figure 19E is a perspective view showing a one-sided form according to Modification 7. [Figure 19F] Figure 19F is a perspective view showing a one-sided form according to Modification 7. [Figure 20] Figure 20 shows the method for measuring CTE. [Modes for carrying out the invention]

[0030] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that, for the sake of illustration and ease of understanding, the scale and aspect ratios of the drawings attached to this specification have been appropriately altered and exaggerated from those of the actual objects.

[0031] In this specification, terms used to describe shapes and geometric conditions, as well as terms that specify their degree, such as "parallel," "perpendicular," and "identical," and values ​​of length and angle, shall not be strictly interpreted, but shall be interpreted to include a range that allows for the expectation of similar functionality.

[0032] In this specification, terms such as "film," "sheet," and "plate" are not distinguished from each other solely on the basis of differences in pronunciation.

[0033] In this specification, if multiple upper limit candidates and multiple lower limit candidates are given for a certain parameter, the numerical range of that parameter may be constructed by combining any one upper limit candidate and any one lower limit candidate. As an example, consider the statement, "Parameter B may be A1 or greater, A2 or greater, A3 or greater. Parameter B may be A4 or less, A5 or less, A6 or less." In this example, the numerical range of parameter B may be A1 or greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, and A3 or greater and A6 or less.

[0034] In this specification, "suppression" means to restrain or prevent the realization or occurrence of something. "Suppression" means not only to completely prevent the realization or occurrence of something, but also to reduce the possibility of it happening or to make it less likely to happen.

[0035] <Hollow structure film> Figures 1A to 8E show one embodiment. Figure 1A is a cross-sectional view of an example of the hollow structure film 1 of this embodiment, cut in a section parallel to the thickness direction of the hollow structure film 1. Figure 1B is a cross-sectional view of a different example of the hollow structure film 1 of this embodiment, cut in a section parallel to the thickness direction of the hollow structure film 1. The hollow structure film 1 has a hollow structure. As shown in Figures 1A and 1B, the hollow structure film 1 comprises a pair of sheet-like bases 10. The hollow structure film 1 comprises a sheet-like first base 11 and a sheet-like second base 12 that overlaps the first base 11 as a pair of bases 10. Furthermore, the hollow structure film 1 comprises a plurality of support columns 20 provided between the first base 11 and the second base 12. The hollow structure film 1 comprises a main body 1c. In particular, the hollow structure film 1 shown in Figures 1A and 1B consists of a main body 1c. The main body portion 1c has a first base portion 11, a second base portion 12, and a plurality of support portions 20. Thus, the hollow structure film 1 comprises the first base portion 11, the second base portion 12, and the plurality of support portions 20 as part of the main body portion 1c. The first base portion 11 has a first opposing surface 11a facing the second base portion 12. The second base portion 12 has a second opposing surface 12a facing the first base portion 11. At least a portion of the plurality of support portions 20 extends from the first opposing surface 11a to the second opposing surface 12a. In the example shown in Figures 1A and 1B, the hollow structure film 1 further comprises a sheet-like central portion 30 that overlaps the first base portion 11 and the second base portion 12. In the example shown in Figures 1A and 1B, the main body portion 1c further comprises the central portion 30. As a result, the hollow structure film 1 further comprises a central portion 30 as part of the main body portion 1c. The central portion 30 is located between the first opposing surface 11a and the second opposing surface 12a.

[0036] In other words, the main body 1c has a first base 11, a second base 12, a plurality of support columns 20, and a sheet-like central portion 30 located between the first opposing surface 11a and the second opposing surface 12a. The plurality of support columns 20 are located on the first opposing surface 11a side and the second opposing surface 12a side of the central portion 30.

[0037] Multiple support columns 20 are provided between the first base portion 11 and the second base portion 12, thereby connecting the first base portion 11 and the second base portion 12 via the support columns 20. Furthermore, the space between the first base portion 11 and the second base portion 12 is partitioned by the multiple support columns 20, forming multiple hollow portions B between the first base portion 11 and the second base portion 12. This forms the hollow structure of the hollow structure film 1. Because the hollow structure film 1 has a hollow structure, the dielectric constant of the hollow structure film 1 is low. For this reason, it is possible to provide a hollow structure film 1 with a low dielectric constant while being less restricted by the material of the hollow structure film 1. In particular, it is possible to provide a hollow structure film 1 with a low dielectric constant without having to use a specific material with a low dielectric constant for the material of the hollow structure film 1.

[0038] The hollow structure film 1 has a first surface 1a and a second surface 1b located on the opposite side of the first surface 1a. In the example shown in Figures 1A and 1B, the first base portion 11 constitutes the first surface 1a, and the second base portion 12 constitutes the second surface 1b. The first base portion 11 and the second base portion 12 overlap in the thickness direction of the hollow structure film 1.

[0039] Multiple support columns 20 are provided between a pair of bases 10, that is, between the first base 11 and the second base 12. In the example shown in Figures 1A and 1B, the multiple support columns 20 extend in the thickness direction of the hollow structure film 1. At least a portion of the multiple support columns 20 extends from the first opposing surface 11a to the second opposing surface 12a. In the example shown in Figures 1A and 1B, at least a portion of the multiple support columns 20 extends in the thickness direction of the hollow structure film 1 from the first opposing surface 11a to the second opposing surface 12a. The portion of the multiple support columns 20 extending from the first opposing surface 11a to the second opposing surface 12a is referred to as the continuous support column 23. At least a portion of the multiple support columns 20 constitutes the continuous support column 23 extending from the first opposing surface 11a to the second opposing surface 12a. If a straight line L1 can be drawn on a cross section obtained by cutting the hollow structure film 1 with a plane parallel to the thickness direction, extending from the first opposing surface 11a to the second opposing surface 12a without extending beyond the hollow structure film 1, then the support portion 20 through which the straight line L1 passes is considered to be a continuous support portion 23. If there is one or more cross sections in the hollow structure film 1 where a continuous support portion 23 appears, then at least a portion of the multiple support portions 20 in the hollow structure film 1 is considered to extend from the first opposing surface 11a to the second opposing surface 12a. The continuous support portion 23 extends from the first opposing surface 11a to the second opposing surface 12a. The multiple support portions 20 may include portions that do not extend from the first opposing surface 11a to the second opposing surface 12a. In the examples shown in Figures 1A and 1B, each of the multiple support columns 20 has a first portion 21 that extends from the first opposing surface 11a to the first central surface 30a of the central portion 30, which will be described later, as a portion that does not extend from the first opposing surface 11a to the second opposing surface 12a. Each of the multiple support columns 20 also has a second portion 22 that extends from the second base 12 to the second central surface 30b of the central portion 30, which will be described later, as a portion that does not extend from one of the pair of base portions 10 to the other.

[0040] Figure 2 is a plan view showing one of the pair of bases 10 (first base 11) of the hollow structure film 1 shown in Figures 1A and 1B, as observed from the thickness direction of the hollow structure film 1. The portion of the base 10 connected to the support portion 20 is referred to as the connecting portion 24. The dashed line labeled 20a in Figure 2 shows the contour of the connecting portion 24 of the first base 11 connected to the support portion 20. In the example shown in Figure 2, multiple connecting portions 24 extend in a first direction d1 perpendicular to the thickness direction of the hollow structure film 1. For this reason, multiple support portions 20 extend in a first direction d1 perpendicular to the thickness direction of the hollow structure film 1. In the example shown in Figure 2, the first base 11 does not have connecting portions 24 extending in directions other than the first direction d1. For this reason, the hollow structure film 1 does not have support portions 20 extending in directions other than the first direction d1.

[0041] In the example shown in Figure 2, the connecting portions 24 of the first base 11 are arranged at equal intervals in the thickness direction of the hollow structure film 1 and in the second direction d2 perpendicular to the first direction d1. That is, in the example shown in Figure 2, the spacing w1 between the connecting portions 24 in the second direction d2 is the same. Although not shown in the figure, the spacing w1 between the connecting portions 24 in the second direction d2 does not have to be the same.

[0042] As an example, the connecting portion 24 of the second base 12 extends in the same direction as the connecting portion 24 of the first base 11, i.e., in the first direction d1. In this embodiment, the shape of the second base 12 and the portion of the multiple support portions 20 located on the second base 12 side of the central portion 30 is the same as the shape of the first base 11 and the portion of the multiple support portions 20 located on the first base 11 side of the central portion 30. The connecting portion 24 of the second base 12 may extend in a direction different from the direction in which the connecting portion 24 of the first base 11 extends. The shape of the second base 12 and the portion of the multiple support portions 20 located on the second base 12 side of the central portion 30 is different from the shape of the first base 11 and the portion of the multiple support portions 20 located on the first base 11 side of the central portion 30. In this specification, unless otherwise specified, a hollow structure film 1 is described in which the connecting portion 24 of the second base 12 extends in the same direction as the connecting portion 24 of the first base 11. In this specification, unless otherwise specified, a hollow structure film 1 is described in which the shape of the second base 12 and the portion of the plurality of support portions 20 located on the second base 12 side of the central portion 30 is the same as the shape of the first base 11 and the portion of the plurality of support portions 20 located on the first base 11 side of the central portion 30.

[0043] The hollow structure film 1 further comprises a sheet-like central portion 30 that overlaps the first base portion 11 and the second base portion 12 and is located between the first opposing surface 11a and the second opposing surface 12a. The central portion 30 has a first central surface 30a facing the first base portion 11 and a second central surface 30b facing the second base portion 12. The central portion 30 constitutes a part of the portion of a plurality of support columns 20 that extends from one of a pair of base portions 10 to the other. Even when the hollow structure film 1 comprises a central portion 30 as shown in Figures 1A and 1B, if a straight line L1 extending from the first opposing surface 11a to the second opposing surface 12a can be drawn on a cross section obtained by cutting the hollow structure film 1 with a plane parallel to the thickness direction, the support column 20 through which the straight line L1 passes is considered a continuous support column 23.

[0044] In the example shown in Figures 1A and 1B, the first portion 21 of the support column 20 extends from the first opposing surface 11a of the first base portion 11 to the first central surface 30a of the central portion 30. That is, the first portion 21 of the support column 20 is connected to the central portion 30. Furthermore, the second portion 22 of the support column 20 extends from the second opposing surface 12a of the second base portion 12 to the second central surface 30b of the central portion 30. That is, the second portion 22 of the support column 20 is connected to the central portion 30.

[0045] The hollow structure film 1 can be made stronger by having a central portion 30. In particular, the strength of the hollow structure film 1 can be made stronger by having the first portion 21 of the support portion 20 connected to the central portion 30 and the second portion 22 of the support portion 20 connected to the central portion 30.

[0046] In this embodiment, the hollow structure film 1 contains polyolefin. In particular, the main body portion 1c of the hollow structure film 1 contains polyolefin. In this embodiment, each of the pair of base portions 10, the plurality of support portions 20, and the central portion 30 contains resin. The resin contained in each of the pair of base portions 10, the plurality of support portions 20, and the central portion 30 may be polyolefin. In this case, polyethylene, polypropylene, and polymethylpentene may be used as the polyolefin. Each of the pair of base portions 10, the plurality of support portions 20, and the central portion 30 may contain polyethylene. Furthermore, these resins may have a partially modified structure. The hollow structure film 1 may contain multiple types of resin. Each of the pair of base portions 10, the plurality of support portions 20, and the central portion 30 may contain multiple resins with different molecular weights and branching structures in the polymer. A specific example of a partially modified polymer is a polymer obtained by copolymerizing ethylene and acrylic acid (ethylene acrylic acid copolymer). An example of a material containing multiple resins with different molecular weights is one in which both general high-density polyethylene (HDPE) and low-density polyethylene (LDPE) are included. The material of the main body portion 1c of the hollow structure film 1 may be a material that can be molded using the mold 90 described later at a heating temperature of less than 330°C. This allows for the production of a single-sided formwork 80 described later by heating the material using a general heating device and molding using the mold 90, and then producing the main body portion 1c from the single-sided formwork 80.

[0047] The case where the hollow structure film 1 contains multiple types of resin will be explained in more detail. 3 A first resin material with a higher density, and 925 kg / m³ 3 It may also contain a second resin material having the following density: 940 kg / m³ 3 Examples of first resin materials with higher density include high-density polyethylene (HDPE). 925 kg / m 3The second resin material having the following densities includes, for example, low-density polyethylene (LDPE). The density of the resin is measured according to the items described in section 3.5.2 "Density" of JIS K6922-1:2018. At least one of the first base 11, the second base 12, and the support column 20 may contain both the first and second resin materials. At least one of the first base 11, the second base 12, and the support column 20 may be formed from a mixture of the first and second resin materials.

[0048] Examples of polyethylene products include Hyzex® (HDPE), Neozex® (C4-LLDPE), and Ultzex® (C6-LLDPE) manufactured by Prime Polymer Co., Ltd.; Dowlex® (2045.11G (C8 copolymer)) (LLDPE) manufactured by Dow Chemical Company; Novatec® HD (HDPE) and Novatec® LL (LLDPE) manufactured by Nippon Polyethylene Co., Ltd.; and Suntec® HD (HDPE) and Suntec® LD (LDPE) manufactured by Asahi Kasei Corporation. Examples of polypropylene products include Prime Polypro® (registered trademark) manufactured by Prime Polymer Co., Ltd. and Novatec® PP manufactured by Nippon Polypropylene Co., Ltd. Examples of polymethylpentene products include TPX® manufactured by Mitsui Chemicals, Inc.

[0049] In the hollow structure film 1, the parts of the multiple support parts 20 that are not composed of the central part 30, along with the pair of base parts 10, are collectively referred to as the form-forming part 13. The resin contained in the form-forming part 13 and the resin contained in the central part 30 may be different. In this case, the form-forming part 13 may contain a first resin material and the central part 30 may contain a second resin material. Alternatively, the form-forming part 13 may contain a second resin material and the central part 30 may contain a first resin material. In this case, the boundary between the part of the multiple support parts 20 composed of the central part 30 and the part not composed of the central part 30 is considered to be at the positions of a virtual surface F1 extended from the first central surface 30a of the central part 30 and a virtual surface F2 extended from the second central surface 30b of the central part 30.

[0050] The resin contained in the central portion 30 may have a lower melting point than the resin contained in the excipient-compatible portion 13. In this case, the resin contained in the central portion 30 may be linear low-density polyethylene (LLDPE). The resin contained in the excipient-compatible portion 13 may be high-density polyethylene (HDPE).

[0051] The hollow structure film 1 of this embodiment has a hollow structure. This makes it possible to lower the dielectric constant of the hollow structure film 1 without having to use a specific material with a low dielectric constant for the material of the hollow structure film 1. For this reason, even when polyolefin is used as the material for each of the pair of base parts 10, the multiple support parts 20, and the central part 30, the dielectric constant of the hollow structure film 1 can be lowered. When polyolefin is used as the resin contained in a film that can be used as a material for a circuit board, such as the hollow structure film 1 described later, the following effects can be obtained compared to, for example, when polyimide is used as the resin contained in the film. Generally, polyolefin is cheaper as a material than polyimide, so the cost required to manufacture the film and the circuit board can be reduced. In addition, as will be described later, when a metal layer 40 is bonded to the surface of the part of the film formed by the resin, the metal layer 40 can be adhered more firmly to the surface of the resin. Furthermore, generally, materials with a low dielectric constant, such as polyimide, often have high melting points and are difficult to process. In contrast, in the hollow structure film 1 of this embodiment, it is not necessary to use a specific material with a low dielectric constant for the material of the hollow structure film 1. This allows for the selection of materials that can be processed using simple methods.

[0052] The hollow structure film 1 of this embodiment may contain a compound having a double bond that is active to radiation or thermal radical initiators.

[0053] In particular, the hollow structure film 1 of this embodiment may contain a compound having a double bond that is active to radiation. A compound having a double bond that is active to radiation is, for example, an electron beam crosslinking agent. In this case, the compound is dispersed in the resin that is the material of the hollow structure film 1. The compound is contained in the resin-containing portion of the hollow structure film 1. At least one of the excipient-compatible portion 13 and the central portion 30 may contain the compound. Both the excipient-compatible portion 13 and the central portion 30 may contain the compound. The hollow structure film 1 containing the compound is manufactured by a method for manufacturing a hollow structure film having a crosslinking step described later. With such a hollow structure film 1, the heat resistance of the hollow structure film 1 can be greatly increased. In particular, when the hollow structure film 1 is used in a circuit board 100, the hollow structure film 1 may be required to have heat resistance that can withstand the temperature during soldering. With the above-described hollow structure film 1, the heat resistance of the hollow structure film 1 can be greatly increased to the extent that it can withstand the temperature during soldering.

[0054] The hollow structure film 1 may contain an ionizing radiation-curable compound as a compound having a double bond that is active to radiation. An ionizing radiation-curable compound means a compound that crosslinks and hardens when irradiated with ionizing radiation, and has an ionizing radiation-curable functional group. An ionizing radiation-curable functional group is a group that crosslinks when irradiated with ionizing radiation, and examples include functional groups (ethylenically unsaturated groups) having an ethylenically double bond, such as (meth)acryloyl groups, vinyl groups, and allyl groups. Ionizing radiation means electromagnetic waves or charged particle beams that have energy quanta that can polymerize or crosslink molecules. Examples of ionizing radiation include electron beams (EB) and ultraviolet rays (UV), as well as electromagnetic waves such as X-rays and gamma rays; and charged particle beams such as alpha rays and ion beams. An ionizing radiation-curable compound that crosslinks and hardens when irradiated with an electron beam corresponds to the electron beam crosslinking agent described above.

[0055] Examples of ionizing radiation-curable compounds include polymerizable monomers and polymerizable oligomers that have been conventionally used as ionizing radiation-curable compounds. As polymerizable monomers, (meth)acrylate monomers having (meth)acryloyl groups in the molecule are preferred, and polyfunctional (meth)acrylate monomers having two or more (meth)acryloyl groups in the molecule are more preferred. The number of (meth)acryloyl groups in the polyfunctional (meth)acrylate monomer is two or more, preferably eight or less, and more preferably six or less.

[0056] Examples of polymerizable monomers include difunctional (meth)acrylates such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, bisphenol A tetraethoxy di(meth)acrylate and bisphenol A tetrapropoxy di(meth)acrylate; trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, Examples include trifunctional or more (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; and ethylene oxide modified, propylene oxide modified, caprolactone modified, isocyanuric acid modified, or propionic acid modified versions of these (meth)acrylates.

[0057] Examples of polymerizable oligomers include (meth)acrylate oligomers having two or more (meth)acryloyl groups in the molecule. Examples of (meth)acrylate oligomers include urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, polycarbonate (meth)acrylate, polycaprolactone urethane (meth)acrylate, polycaprolactone diol urethane (meth)acrylate, and acrylic (meth)acrylate. The number of (meth)acryloyl groups in the polymerizable oligomer is two or more, preferably eight or less, and more preferably six or less.

[0058] Other polymerizable oligomers include highly hydrophobic polybutadiene (meth)acrylate oligomers having (meth)acryloyl groups in the side chains of polybutadiene oligomers, and silicone (meth)acrylate oligomers having polysiloxane bonds in the main chain.

[0059] The weight-average molecular weight of the polymerizable oligomer may be 500 or more, 1,000 or more, 2,000 or more, 10,000 or less, 8,000 or less, or 6,000 or less. The weight-average molecular weight is measured by gel permeation chromatography (GPC) analysis and is the average molecular weight converted to standard polystyrene.

[0060] As ionizing radiation-curable compounds, monofunctional (meth)acrylates may be used in combination with polyfunctional (meth)acrylates as appropriate, for purposes such as reducing the viscosity of the curable composition during coating. Examples of monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isobornyl (meth)acrylate.

[0061] As described above, the ionizing radiation-curable compound may have an allyl group. The ionizing radiation-curable compound having an allyl group may be trialyl cyanurate or trialyl citrate 1,3,5-benzenetricarboxylic acid trialyl.

[0062] The hollow structure film 1 may contain a thermal radical initiator. When the hollow structure film 1 contains a thermal radical initiator, a crosslinking reaction occurs due to the heat generated when the excipient-compatible portion 13 is heated during processing, such as in the manufacturing method of the hollow structure film 1 described later. This crosslinking reaction significantly increases the heat resistance of the hollow structure film 1. In particular, when the hollow structure film 1 is used in a circuit board 100, the hollow structure film 1 may be required to withstand the temperatures during soldering. The hollow structure film 1 containing a thermal radical initiator can increase the heat resistance of the hollow structure film 1 to a level sufficient to withstand the temperatures during soldering. The thermal radical initiator contained in the hollow structure film 1 is not particularly limited, but azo compounds such as 2,2-azobis(isobutyronitrile) and 2,2'-azobis(2-methylpropionic acid)dimethyl, as well as peroxide compounds such as di-tert-butyl peroxide, can be suitably used.

[0063] The thermal radical initiator may also be used as a thermal radical polymerization initiator. That is, the hollow structure film 1 of this embodiment may contain compounds generally known as thermal radical polymerization initiators (crosslinking agents that, when heated, chemically crosslink between molecules such as polyethylene). When the hollow structure film 1 contains a thermal radical polymerization initiator, the following effects can be obtained. As will be described later, in the process of molding the material for the excipient-compatible part 13 in the manufacturing method of the hollow structure film 1, the resin in the mixture that is the material for the excipient-compatible part 13 is melted while the mixture is molded. At this time, because the thermal radical polymerization initiator is included, bonds can be formed between the molecules of the resin by the heat generated when the resin is melted. This makes it possible to more reliably ensure the heat resistance required when the hollow structure film 1 is used in a circuit board 100.

[0064] If the hollow structure film 1 of this embodiment contains the above-mentioned thermal radical polymerization initiator, it may also contain a silane coupling agent in addition to the thermal radical polymerization initiator. In this case, the following effects can be obtained. As will be described later, in the manufacturing method of the hollow structure film 1, in the step of molding the material of the excipient-compatible part 13, the resin in the mixture that is the material of the excipient-compatible part 13 is melted while the mixture is molded. At this time, because the thermal radical polymerization initiator and the silane coupling agent are included, a crosslinking reaction occurs between the resin and the silane coupling agent due to the reaction caused by the heat when the resin is melted. Furthermore, in a step after the step of molding the material of the excipient-compatible part 13, the hollow structure film 1 may be stored in a high-temperature, high-humidity environment. In this case, the silane coupling agents react with each other when the hollow structure film 1 is stored in a high-temperature, high-humidity environment. These reactions make it possible to more reliably ensure the heat resistance required when the hollow structure film 1 is used in a circuit board 100.

[0065] Examples of thermal radical polymerization initiators include di-t-butyl peroxide and dicumyl peroxide 2,2'-azobis(2,4-dimethylvaleronitrile).

[0066] The width of the connecting portion 24, which is the part of the base 10 connected to the support portion 20 in the second direction d2, is defined as width w2. In this case, it is preferable that the spacing w1 between the connecting portions 24 in the second direction d2 is 0.5 times or more and 20 times or less the width w2. By having a spacing w1 of 0.5 times or more the width w2, the size of the hollow portion B can be made particularly large, and the dielectric constant of the hollow structure film 1 can be made particularly low. By having a spacing w1 of 20 times or less the width w2, the strength of the hollow structure film 1 can be made particularly large.

[0067] In the hollow structure film 1 having a central portion 30 as shown in Figures 1A and 1B, the distance between the base portion 10 and the central portion 30 is defined as distance w3. If the distance between the base portion 10 and the central portion 30 is not constant, the distance between the connecting portion 24 of the base portion 10 and the central portion 30 is defined as distance w3. In this case, it is preferable that distance w3 is between 1 and 10 times the width w2. By having distance w3 be 1 or more times the width w2, the size of the hollow portion B can be made particularly large, and the dielectric constant of the hollow structure film 1 can be made particularly low. By having distance w3 be 10 times or less the width w2, the strength of the hollow structure film 1 can be made particularly large.

[0068] The cross-sectional views of the hollow structure film 1 shown in Figures 1A and 1B correspond to diagrams showing a cross-section obtained by cutting the hollow structure film 1, in which a plurality of support columns 20 extend in a first direction d1, through a plane that passes through the plurality of support columns 20 and is perpendicular to the first direction d1. In the cross-sections shown in Figures 1A and 1B, the angle θ1 between the first opposing surface 11a and the portion of the surface 20b of the support column 20 that is in contact with the hollow section B and connected to the first base 11 is between 90° and 150°. In addition, in the cross-sections shown in Figures 1A and 1B, the angle θ2 between the second opposing surface 12a and the portion of the surface 20b of the support column 20 that is in contact with the hollow section B and connected to the second base 12 is between 90° and 150°. By having angles θ1 and θ2 be between 90° and 150°, the size of the hollow portion B can be secured, lowering the dielectric constant of the hollow structure film 1 while ensuring the strength of the hollow structure film 1.

[0069] In the examples shown in Figures 1A and 1B, the surface 20b of the support portion 20 in contact with the hollow portion B is a plane. Therefore, in the cross-sectional view of the hollow structure film 1 shown in Figures 1A and 1B, the surface 20b appears as a straight line. Although not shown, the surface 20b does not have to be a plane. The surface 20b may be a curved surface. If the surface 20b is not a plane, it may appear as a curved surface or a broken line in the cross-sectional view of the hollow structure film 1. In this case, the angle between the tangent line of the surface 20b shown in the cross-sectional view of the hollow structure film 1 at the portion connected to the first base portion 11 and the first opposing surface 11a is considered to be angle θ1. Furthermore, the angle between the tangent line of the surface 20b shown in the cross-sectional view of the hollow structure film 1 at the portion connected to the second base portion 12 and the second opposing surface 12a is considered to be angle θ2.

[0070] As an example, the porosity of the hollow structure film 1 is 10% or more, more preferably 20% or more. By having a porosity of 20% or more of the hollow structure film 1, the size of the hollow portion B can be made particularly large, and the dielectric constant of the hollow structure film 1 can be made particularly low. It is preferable that the porosity of the hollow structure film 1 is 70% or less. By having a porosity of 70% or less of the hollow structure film 1, the decrease in the strength of the film due to a decrease in the amount of resin contained in the hollow structure film 1 can be suppressed. The porosity of the hollow structure film 1 is measured by the following method. Observe the cross-section obtained by cutting the hollow structure film 1 through a plane that passes through a plurality of support portions 20 and is perpendicular to the first direction d1, as shown in Figures 1A and 1B. In the cross-section, draw a straight line L2 that passes through the center in the second direction d2 of one of the plurality of connection portions 24 of one of the pair of base portions 10 (first base portion 11) and is parallel to the thickness direction of the hollow structure film 1. Furthermore, one of the multiple connection portions 24 of one of the pair of base portions 10 (first base portion 11), and the connection portion 24 adjacent to the connection portion 24 on which the straight line L2 is drawn, in the second direction d2, is identified. A straight line L3 is drawn through the center of the said connection portion 24 in the second direction d2 and parallel to the thickness direction of the hollow structure film 1. Next, the ratio of the area of ​​the hollow portion B to the total area of ​​the hollow structure film 1 including the hollow portion B, between the straight line L2 and the straight line L3, is calculated. This ratio is calculated at 10 different locations in the cross-section. By averaging the ratios calculated at these 10 different locations, the porosity of the hollow structure film 1 is obtained. More specifically, the cross-section obtained by cutting the hollow structure film 1 through a plane passing through multiple support portions 20 and perpendicular to the first direction d1 is observed using a scanning electron microscope (SEM) or an optical microscope, and an image of the cross-section is obtained. The magnification of the acquired image can be 100 times or more. Figure 3 shows an example of a cross-sectional image of film 1i obtained by scanning electron microscope (SEM). Figure 3 shows a cross-sectional image of film 1i that has a hollow structure similar to the hollow structure film 1 of this embodiment, but the main body portion 1c does not include the inorganic material member 70 described later. As shown in Figure 3, by drawing straight lines L2 and L3 on the acquired image, the porosity of a film having a hollow structure like the hollow structure film 1 can be obtained from the image.

[0071] The main body portion 1c of the hollow structure film 1 includes an insulating inorganic material member 70. The maximum width of the inorganic material member 70 is at least three times the minimum width of the inorganic material member 70.

[0072] The inorganic material member 70 includes, for example, glass or a metal oxide. The inorganic material member 70 may include glass. The inorganic material member 70 may include a metal oxide. The metal oxide contained in the inorganic material member 70 is, for example, aluminum oxide. The inorganic material member 70 may include boehmite. The inorganic material member 70 may include a ceramic material. When the inorganic material member 70 includes a ceramic material, the ceramic material used is one with a sufficiently small dielectric constant and dielectric loss tangent, taking into consideration the need to sufficiently lower the dielectric constant and dielectric loss tangent of the entire hollow structure film 1.

[0073] The inorganic material member 70 may be included in at least one of the first base portion 11 and the second base portion 12. The inorganic material member 70 may be included in both the first base portion 11 and the second base portion 12. The inorganic material member 70 may be included in at least a portion of the support portion 20. The inorganic material member 70 may be included in all of the support portion 20. When the main body portion 1c has a central portion 30, the inorganic material member 70 may be included in at least the central portion 30. In the example shown in Figure 1A, the inorganic material member 70 is included in both the first base portion 11 and the second base portion 12. In the example shown in Figure 1B, the inorganic material member 70 is included in the first base portion 11, the second base portion 12, all of the support portion 20, and the central portion 30.

[0074] The inorganic material member 70 may be a sheet-like member as shown in Figure 1A. The sheet-like inorganic material member 70 is, for example, a woven fabric made from fibrous glass, which is called glass cloth.

[0075] If the inorganic material member 70 is a sheet-like member, the minimum width of the inorganic material member 70 is the thickness of the sheet-like inorganic material member 70. If the thickness of the sheet-like inorganic material member 70 is not constant, the minimum width of the inorganic material member 70 is the minimum value of the thickness of the sheet-like inorganic material member 70 measured at 10 locations. If the inorganic material member 70 is a sheet-like member, the maximum width of the inorganic material member 70 is the maximum value of the dimension of the inorganic material member 70 in a direction parallel to the surface of the sheet-like inorganic material member 70.

[0076] In the example shown in Figure 1A, a sheet-like inorganic material member 70 is included in both the first base 11 and the second base 12. The surface of the first base 11 opposite to the first opposing surface 11a is referred to as the first outer surface 11b. The sheet-like inorganic material member 70 included in the first base 11 is located between the first opposing surface 11a and the first outer surface 11b. The thickness direction of the sheet-like inorganic material member 70 is oriented in the same direction as the thickness direction of the first base 11. The surface of the second base 12 opposite to the second opposing surface 12a is referred to as the second outer surface 12b. The sheet-like inorganic material member 70 included in the second base 12 is located between the second opposing surface 12a and the second outer surface 12b. The thickness direction of the sheet-like inorganic material member 70 is oriented in the same direction as the thickness direction of the second base 12.

[0077] Although not shown in the figures, if the main body portion 1c has a central portion 30, a sheet-like inorganic material member 70 may be included in the central portion 30. In this case, the sheet-like inorganic material member 70 may be located between the first central surface 30a and the second central surface 30b. The thickness direction of the sheet-like inorganic material member 70 may be oriented in the same direction as the thickness direction of the central portion 30.

[0078] The inorganic material members 70 may be a plurality of rod-shaped members, as shown in Figure 1B. The plurality of rod-shaped inorganic material members 70 may be fibrous glass, such as glass fiber. In the example shown in Figure 1B, the plurality of rod-shaped inorganic material members 70 are dispersed inside the main body 1c. The plurality of rod-shaped inorganic material members 70 are oriented in different directions from each other. The maximum width of the rod-shaped inorganic material members 70 is, for example, 100 μm. In the example shown in Figure 1B, the plurality of rod-shaped inorganic material members 70 are included in the first base 11, the second base 12, all of the plurality of support columns 20, and the central part 30.

[0079] If the inorganic material member 70 is a rod-shaped member, the maximum width of the inorganic material member 70 is the dimension of the inorganic material member 70 in the direction in which the rod-shaped inorganic material member 70 extends. If the inorganic material member 70 is a rod-shaped member, the minimum width of the inorganic material member 70 is the minimum dimension of the inorganic material member 70 in the direction perpendicular to the direction in which the rod-shaped inorganic material member 70 extends.

[0080] Although not shown in the figures, the inorganic material member 70 may be a plurality of flake-shaped members. The plurality of flake-shaped inorganic material members 70 may be, for example, glass flakes (registered trademark) manufactured by Nippon Sheet Glass Co., Ltd. The plurality of flake-shaped inorganic material members 70 may be fine flakes (registered trademark) manufactured by Nippon Sheet Glass Co., Ltd. The plurality of flake-shaped inorganic material members 70 may be dispersed inside the main body 1c. The plurality of flake-shaped inorganic material members 70 may be oriented in different directions from each other.

[0081] If the inorganic material member 70 is a flake-shaped member, the minimum width of the inorganic material member 70 is the thickness of the flake-shaped inorganic material member 70. The maximum width of the inorganic material member 70 is the maximum dimension of the inorganic material member 70 in a direction perpendicular to the thickness direction of the flake-shaped inorganic material member 70.

[0082] The maximum width of the flake-shaped inorganic material member 70 is, for example, 200 μm. The minimum width (thickness) of the flake-shaped inorganic material member 70 is, for example, 0.3 μm or more and 6 μm or less. When the inorganic material member 70 consists of multiple flake-shaped members, the material of the inorganic material member 70 can be the same as the material of the inorganic material member 70 described above. The inorganic material member 70 consisting of multiple flake-shaped members may contain glass. The inorganic material member 70 consisting of multiple flake-shaped members may contain aluminum oxide. The inorganic material member 70 consisting of multiple flake-shaped members may contain boehmite.

[0083] Although not shown in the illustration, the main body 1c may include two or more inorganic material members 70 selected from the group consisting of sheet-like members, multiple rod-shaped members, and multiple scale-like members.

[0084] Although not shown in the diagram, the inorganic material member 70 may have shapes other than sheet, rod, and scale. In this case, the maximum and minimum widths of the inorganic material member 70 are defined by the following method. Consider the direction da in which the dimensions of the inorganic material member 70 are maximized when the dimensions of the inorganic material member 70 are measured in all directions. The maximum width of the inorganic material member 70 is defined as the dimensions of the inorganic material member 70 in direction da. The minimum width of the inorganic material member 70 is defined as the minimum value of the dimensions of the inorganic material member 70 in the direction perpendicular to direction da.

[0085] The hollow structure film 1 may further include a metal layer 40. In this case, the circuit board 100 described later can be manufactured by forming wiring 41, described later, from at least a portion of the metal layer 40. The hollow structure film 1 may further include a metal adjacent layer 60. The metal adjacent layer 60 allows the metal layer 40 to be bonded more firmly to the base 10. Figure 4 is a cross-sectional view showing an example of a hollow structure film 1 comprising a metal layer 40 and a metal adjacent layer 60. In Figure 4, and in Figures 5, 7A to 8C, and 10 to 16 described later, the inorganic material member 70 is not shown. The hollow structure film 1 shown in Figure 4 corresponds to the hollow structure film 1 shown in Figures 1A and 1B, in which the metal adjacent layer 60 and the metal layer 40 are laminated in that order on the first surface 1a. Figure 5 is a cross-sectional view showing a different example of a hollow structure film 1 comprising a metal layer 40 and a metal adjacent layer 60 from Figure 4. The hollow structure film 1 shown in Figure 5 corresponds to the hollow structure film 1 shown in Figures 1A and 1B, in which the adjacent metal layer 60 and the metal layer 40 are laminated in that order on the first surface 1a and the second surface 1b, respectively.

[0086] The hollow structure film 1 shown in Figures 4 and 5 has a first surface 1a and a second surface 1b located opposite to the first surface 1a. The metal layer 40 constitutes at least a part of at least one of the first surface 1a and the second surface 1b. In the example shown in Figure 4, the metal layer 40 constitutes the first surface 1a. In this case, the metal layer 40 may constitute the entire first surface 1a or a part of the first surface 1a. In the example shown in Figure 5, the metal layer 40 constitutes both the first surface 1a and the second surface 1b. In this case, the metal layer 40 may constitute the entire first surface 1a or a part of the first surface 1a. Furthermore, the metal layer 40 may constitute the entire second surface 1b or a part of the second surface 1b.

[0087] The material of the metal layer 40 is not particularly limited, as long as the wiring 41 of the circuit board 100, described later, can be formed from at least a portion of the metal layer 40. The material of the metal layer 40 is, for example, copper. The metal layer 40 can be formed by joining a metal foil to the base 10. A metal layer 40 made of copper can be formed by joining a copper foil to the base 10. The thickness of the metal layer 40 is, for example, 0.1 μm or more and 100 μm or less. The thickness of the metal layer 40 may be 2 μm or more and 20 μm or less.

[0088] The metal layer 40 may be formed by methods other than joining metal foils such as copper foil. The metal layer 40 may be formed by processing such as plating or sputtering. When the metal layer 40 is formed by plating, a commonly known seed layer may be formed. When the metal layer 40 is formed by processing such as plating or sputtering, a plasma treatment known as glow treatment or reverse sputtering may be applied to the surface of the base 10 on which the metal layer 40 is formed before the metal layer 40 is formed. Such treatment can improve the adhesion between the base 10 and the metal layer 40.

[0089] The metal adjoining layer 60 is a layer that joins the metal layer 40 and the base 10. The metal adjoining layer 60 joins the metal layer 40 to at least one of the first base 11 and the second base 12. The material of the metal adjoining layer 60 is different from the material of the base 10. The material of the metal adjoining layer 60 is different from the material of the first base 11 and the second base 12. The metal adjoining layer 60 is a layer of resin that has good adhesion to metal and can be heat-welded to polyolefin. By joining the metal layer 40 and the base 10 with the metal adjoining layer 60, the metal layer 40 can be joined to the base 10 more firmly. The metal adjoining layer 60 may be an ionomer layer, i.e., a layer of ionomer resin. If the metal adjoining layer 60 is an ionomer layer, the material of the metal adjoining layer 60 is, for example, a carboxylic acid copolymer polyethylene containing metal ions. The metal-adjacent layer 60 may be an ethylene (meth)acrylic acid copolymer polymer layer. That is, the hollow structure film 1 may further comprise an ionomer layer or an ethylene (meth)acrylic acid copolymer polymer layer that joins the metal layer 40 and the base 10. The hollow structure film 1 may further comprise an ionomer layer or an ethylene (meth)acrylic acid copolymer polymer layer that joins the metal layer 40 and at least one of the first base 11 and the second base 12. This allows the metal layer 40 to be bonded more firmly to the base 10. The thickness of the metal-adjacent layer 60 is, for example, 20 μm or less.

[0090] A specific example of an ionomer is Hymiran® ​​manufactured by Mitsui Dow Polychemical Co., Ltd. A specific example of an ethylene acrylic acid copolymer is Nucrel® manufactured by Mitsui Dow Polychemical Co., Ltd. The material of the metal-adjacent layer 60 is not limited to the resins described above. Resins having the same functions as the resins described above can be suitably used as the material of the metal-adjacent layer 60.

[0091] The metal-adjacent layer 60 is not limited to the examples described above. Any resin that exhibits the function of adhering to metal can be suitably used as the metal-adjacent layer 60.

[0092] The material of the metal adjacent layer 60 may be an adhesive. The metal adjacent layer 60 may also be a layer formed by coating a varnish, which is formed by dissolving a resin, and then drying it. In the above-described form of the metal adjacent layer 60, an adhesive may be used as the resin used to form the varnish.

[0093] The adjacent metal layer 60 may be a bonding sheet available in sheet form, for example, a commercially available bonding sheet in sheet form.

[0094] Because the hollow structure film 1 of this embodiment has a hollow structure, it is possible to increase the thickness while keeping the dielectric constant low. For this reason, the thickness of the hollow structure film 1 of this embodiment can vary. For example, the thickness of the hollow structure film 1 is 50 μm or more and 1000 μm or less. Thus, the hollow structure film 1 of this embodiment allows for a wide range of values ​​in which the thickness of the hollow structure film 1 can be adopted.

[0095] The storage modulus of the hollow structure film 1 in this embodiment is, for example, 1.0 × 10⁻⁶. 5 The storage modulus of the hollow structure film 1 is 1.0 × 10⁻¹⁰. The hollow structure film 1 contains an electron beam crosslinking agent, and as described later, in the manufacturing method of the hollow structure film 1, the electron beam crosslinking agent is irradiated with an electron beam, thereby increasing the storage modulus of the hollow structure film 1 to 1.0 × 10⁻¹⁰. 5 It can be made to be Pa or higher. By keeping the storage modulus below the above lower limit, the hollow structure film 1 becomes less prone to deformation during short-time high-temperature processing. Specifically, it becomes sufficiently resistant to deformation when soldering the hollow structure film 1 using the solder reflow process. The storage modulus of the hollow structure film 1 is determined using a dynamic viscoelasticity (DMA) measuring device. In measuring the storage modulus of the hollow structure film 1, the measurement mode of the dynamic viscoelasticity measuring device is set to tensile mode, and the storage modulus is measured when the temperature of the hollow structure film 1 is 280°C. As a method for measuring the storage modulus of the hollow structure film 1, the storage modulus measurement method described in the examples below can be adopted.

[0096] In this embodiment, in the hollow structure film 1 comprising a metal layer 40, at least one of the following conditions is satisfied: the transmission loss of an electrical signal with a frequency of 10 GHz applied to a linear wiring 43 formed from the metal layer 40 is greater than -0.30 dB / 3.5 cm; the transmission loss of an electrical signal with a frequency of 20 GHz applied to the linear wiring 43 is greater than -0.60 dB / 3.5 cm; the transmission loss of an electrical signal with a frequency of 30 GHz applied to the linear wiring 43 is greater than -0.90 dB / 3.5 cm; the transmission loss of an electrical signal with a frequency of 40 GHz applied to the linear wiring 43 is greater than -1.30 dB / 3.5 cm; the transmission loss of an electrical signal with a frequency of 50 GHz applied to the linear wiring 43 is greater than -1.80 dB / 3.5 cm; or the transmission loss of an electrical signal with a frequency of 60 GHz applied to the linear wiring 43 is greater than -3.00 dB / 3.5 cm. The value of the electrical signal transmission loss is negative. The closer the transmission loss value of the electrical signal is to zero, the smaller the attenuation of the electrical signal applied to the linear wiring 43. For example, a transmission loss value greater than -0.30 dB / 3.5 cm (closer to zero) means that the attenuation of the applied electrical signal is smaller than when the transmission loss value is -0.30 dB / 3.5 cm. "Large transmission loss value" means that the transmission loss value, if negative, is close to zero. "Small transmission loss value" means that the transmission loss value, if negative, is far from zero. Simply saying "small transmission loss" means that the absolute value of the transmission loss value, if negative, is small. Simply saying "large transmission loss" means that the absolute value of the transmission loss value, if negative, is large.

[0097] In a hollow structure film 1 having a metal layer 40, the transmission loss of an electrical signal with a frequency of 10 GHz applied to a linear wiring 43 formed from the metal layer 40 may be greater than -0.30 dB / 3.5 cm, the transmission loss of an electrical signal with a frequency of 20 GHz applied to the linear wiring 43 may be greater than -0.60 dB / 3.5 cm, the transmission loss of an electrical signal with a frequency of 30 GHz applied to the linear wiring 43 may be greater than -0.90 dB / 3.5 cm, the transmission loss of an electrical signal with a frequency of 40 GHz applied to the linear wiring 43 may be greater than -1.30 dB / 3.5 cm, the transmission loss of an electrical signal with a frequency of 50 GHz applied to the linear wiring 43 may be greater than -1.80 dB / 3.5 cm, and the transmission loss of an electrical signal with a frequency of 60 GHz applied to the linear wiring 43 may be greater than -3.00 dB / 3.5 cm. With such a hollow structure film 1, even when electrical signals of various frequencies are applied to wiring formed from the metal layer 40, the transmission loss can be increased (approaching zero).

[0098] The transmission loss of an electrical signal applied to a linear wiring 43 in a hollow structure film 1 having a metal layer 40 is measured by the following method. First, as shown in Figure 6A, a linear wiring 43 is formed from the metal layer 40 of the hollow structure film 1. Figure 6A is a perspective view showing a hollow structure film 1 having a linear wiring 43 used for measuring the transmission loss of an electrical signal. In Figure 6A and Figure 6C, which will be described later, the details of the structure of the main body 1c of the hollow structure film 1 are omitted from the illustration, and only the general shape of the main body 1c is shown. In Figure 6A and Figure 6C, which will be described later, the illustration of the adjacent metal layer 60 is omitted.

[0099] The hollow structure film 1 shown in Figure 6A has metal layers 40 on the first surface 1a side and the second surface 1b side. In the hollow structure film 1 shown in Figure 6A, linear wiring 43 is formed from the metal layer 40 on the first surface 1a side. The hollow structure film 1 shown in Figure 6A is made from a hollow structure film 1 that includes a metal layer 40 constituting at least a part of the first surface 1a and a metal layer 40 constituting at least a part of the second surface 1b, as shown in Figure 5. The hollow structure film 1 shown in Figure 6A can be made by forming linear wiring 43 from the metal layer 40 constituting at least a part of the first surface 1a of the hollow structure film 1 as shown in Figure 5. The method for forming linear wiring 43 from the metal layer 40 can be the same as the method for forming a wiring pattern from the metal layer 40 in the manufacturing method of the circuit board 100 described later.

[0100] The length w5 of the linear wiring 43 (the dimension of the linear wiring 43 in the direction in which it extends) is 3.5 cm or more. The width w6 of the linear wiring 43 (the dimension of the linear wiring 43 in a direction perpendicular to the direction in which it extends and parallel to the first surface 1a) is 0.75 mm. The thickness w11 of the insulating portion of the film is 0.25 mm. The thickness w11 of the insulating portion of the film corresponds to the distance between the metal layer 40 on the first surface 1a side and the metal layer 40 on the second surface 1b side. In the hollow structure film 1 of this embodiment, the thickness w11 of the insulating portion corresponds to the thickness of the main body portion 1c. The film structure shown in Figure 6A and described above is generally called a microstrip line. The width w6 of the linear wiring 43 is adjusted so that the characteristic impedance of the microstrip line present on the particular film is 50 Ω. The formula used to adjust the characteristic impedance of the linear wiring 43 is as follows. In other words, the width w6 of the straight wiring 43 is adjusted so that the characteristic impedance value calculated from the following formula becomes 50Ω. r " represents the dielectric constant, "Z0" represents the characteristic impedance, "h" represents the thickness w11, "w" represents the width w6 of the straight wiring 43, and "t" represents the thickness w12 of the straight wiring 43.

number

[0101] In measuring the transmission loss of an electrical signal applied to a linear wiring 43, first, the hollow structure film 1, which includes the linear wiring 43, is fixed to a jig 93 as shown in Figure 6B. A probe 94, connected to a network analyzer via a coaxial cable, is attached to the jig 93. By fixing the hollow structure film 1 to the jig 93, the probe 94 comes into contact with the linear wiring 43, as shown in Figure 6B. Next, an AC electrical signal is applied from the network analyzer to both ends of the linear wiring 43 via the probe 94 attached to the jig 93, and the transmission loss of the electrical signal is measured. The measurement of the electrical signal transmission loss is performed under the following conditions: The electrical signal is applied to a 5.0 cm section of the linear wiring 43. During measurement, de-embedded processing is performed to remove the influence of the jig 93 from the measurement results. In the de-embedded processing, the transmission loss of an electrical signal in a 1.5 cm section of a sample having the same wiring configuration as the linear wiring 43 is measured first. Subsequently, de-embedded processing is performed based on the measurement results of the transmission loss of the sample. This allows us to calculate a value equivalent to the transmission loss measured when applying an electrical signal to a 3.5 cm section of the straight wiring 43, by removing the effects of transmission loss at both ends of the straight wiring 43 and the jig 93 from the transmission loss measured when applying an electrical signal to a 5.0 cm section of the straight wiring 43.

[0102] The effects of including an inorganic material member 70 in the main body portion 1c of the hollow structure film 1 of this embodiment will be explained. Consider the case where the metal layer 40 is joined to a part that constitutes at least a part of the main body portion 1c (such as the base portion 10, the single-sided formwork 80, and the resin sheet 32 ​​described later). In this case, the difference in CTE (coefficient of thermal expansion) between the main body portion 1c and the metal layer 40 may cause the metal layer 40 to peel off from the main body portion 1c or wrinkles to form in the metal layer 40. In particular, when heat is applied to the metal layer 40 and the main body portion 1c during joining, the difference in CTE between the main body portion 1c and the metal layer 40 may cause the metal layer 40 to peel off from the main body portion 1c or wrinkles to form in the metal layer 40. In particular, when the metal layer 40 is formed from copper foil and the main body portion 1c contains polyolefin, the difference in CTE between the main body portion 1c and the metal layer 40 may become large. In this case, the CTE of the metal layer 40 may be smaller than that of the main body 1c. In this case, the metal layer 40 may peel off from the main body 1c, or wrinkles may form on the metal layer 40.

[0103] In contrast, the CTE of the main body 1c can be adjusted by including the inorganic material member 70 in the main body 1c. This allows for adjustment of the CTE of the hollow structure film 1, whose dielectric constant is kept low due to its hollow structure. In particular, by including the inorganic material member 70 in the main body 1c of the hollow structure film 1, the CTE of the main body 1c can be adjusted so that the difference in CTE between the main body 1c and the metal layer 40 becomes small. Specifically, by including the inorganic material member 70 in the main body 1c, the CTE of the main body 1c can be reduced. For example, by including the inorganic material member 70 in the main body 1c, the CTE of the main body 1c can be reduced to 120 ppm / °C or less. By including glass or a metal oxide in the inorganic material member 70, particularly glass, the CTE of the main body 1c can be adjusted so that the difference in CTE between the main body 1c and the metal layer 40 becomes small. In particular, when the main body 1c contains a polyolefin, the CTE of the main body 1c can be further reduced by including the inorganic material member 70 in the main body 1c. As described above, by including the inorganic material member 70 in the main body 1c, the difference in CTE between the main body 1c and the metal layer 40 can be reduced by adjusting the CTE of the main body 1c, making it difficult for the metal layer 40 to peel off from the main body 1c and reducing the likelihood of wrinkles forming in the metal layer 40. In particular, when the metal layer 40 is formed from copper foil and the main body 1c contains polyolefin, the metal layer 40 can be made less likely to peel off from the main body 1c and less likely to wrinkle in the metal layer 40. Furthermore, by reducing the difference in CTE between the main body 1c and the metal layer 40, the hollow structure film 1 is less likely to warp due to the difference in CTE between the main body 1c and the metal layer 40. This ensures the ease of processing the hollow structure film 1.

[0104] <Circuit board> Next, the circuit board 100 of this embodiment will be described. The circuit board 100 of this embodiment comprises the hollow structure film 1 of this embodiment. The circuit board 100 of this embodiment further comprises a wiring pattern provided on at least one of the first surface 1a and the second surface 1b. In a hollow structure film 1 having a metal layer 40 as shown in Figures 4 and 5, a circuit board 100 comprising the hollow structure film 1 and a wiring pattern of wiring 41 can be manufactured by forming wiring 41 from at least a part of the metal layer 40. The circuit board 100 manufactured by the above method can be considered to be a circuit board 100 comprising a hollow structure film 1 including a main body portion 1c (hollow structure film 1 shown in Figures 1A and 1B) and a wiring pattern of wiring 41.

[0105] When manufacturing a circuit board 100 from the hollow structure film 1 shown in Figure 4, the wiring pattern of the wiring 41 can be formed from the metal layer 40 constituting the first surface 1a of the hollow structure film 1. When manufacturing a circuit board 100 from the hollow structure film 1 shown in Figure 5, the wiring pattern of the wiring 41 may be formed from either the metal layer 40 constituting the first surface 1a or the metal layer 40 constituting the second surface 1b of the hollow structure film 1. When manufacturing a circuit board 100 from the hollow structure film 1 shown in Figure 5, the wiring pattern of the wiring 41 may be formed from both the metal layer 40 constituting the first surface 1a and the metal layer 40 constituting the second surface 1b.

[0106] When manufacturing a circuit board 100 from the hollow structure film 1 shown in Figure 5, the wiring pattern for the wiring 41 may be formed from the metal layer 40 constituting the first surface 1a of the hollow structure film 1, but it is not necessary to form the wiring pattern for the wiring 41 from the metal layer 40 constituting the second surface 1b of the hollow structure film 1. The circuit board 100 manufactured by this method can be considered to be a circuit board 100 comprising a hollow structure film 1 including a main body portion 1c (hollow structure film 1 shown in Figures 1A and 1B), a wiring pattern for the wiring 41 provided on the first surface 1a of the hollow structure film 1, and a metal layer 40 on the second surface 1b of the hollow structure film 1 that does not have a wiring pattern formed on it. By having a metal layer 40 on the second surface 1b that does not have a wiring pattern formed on it, along with the wiring pattern for the wiring 41 provided on the first surface 1a, unwanted noise is less likely to occur when transmitting electrical signals via the wiring 41. The following reasons can be considered for why the metal layer 40 on the second surface 1b, which does not have a wiring pattern formed on it, makes it less likely for unwanted noise to be generated. When current flows through the wiring 41 formed on the first surface 1a side, a current is generated on the second surface 1b side in the opposite direction to the current flowing through the wiring 41, according to Ampere's law. In particular, when the wiring 41 formed on the first surface 1a side is powered by a high frequency and operated, a current is generated on the second surface 1b side in the opposite direction to the current flowing through the wiring 41, according to Ampere's law. This current is called a feedback current. The feedback current functions as a signal ground. In particular, when an antenna loop is formed between the wiring 41 and the ground plane, the feedback current functions effectively as a signal ground by reducing the size of the antenna loop formed. This makes it less likely for unwanted noise to be generated.

[0107] <Antenna Equipment> Next, the antenna equipment 101 of this embodiment will be described. The antenna equipment 101 comprises the circuit board 100 described above and an antenna element 102 connected to the circuit board 100. The antenna equipment 101 of this embodiment may also be called an antenna substrate, and the terms "equipment" and "substrate" used herein will not be bound by strict meanings, but will be interpreted to include a range that can be expected to perform similar functions. The antenna equipment 101 is, for example, a patch antenna. When the antenna equipment 101 is a patch antenna, the circuit board 100 functions as a dielectric substrate for the patch antenna. When the antenna equipment 101 is a patch antenna, the wiring 41 of the patch antenna may be formed to extend to the feed point in order to conduct current, especially high-frequency current. When the antenna equipment 101 is a patch antenna, the patch antenna may employ a method of feeding by electromagnetic coupling. In this case, the wiring 41 of the patch antenna does not have to be directly connected to the feed point.

[0108] Figure 6C is a perspective view showing an example of the antenna equipment 101 of this embodiment. The antenna equipment 101 shown in Figure 6C comprises the circuit board 100 described above and an antenna element 102 connected to the circuit board 100. The antenna element 102 is connected to the wiring 41 that forms the wiring pattern of the circuit board 100. In the example shown in Figure 6C, the wiring 41 of the circuit board 100 and the antenna element 102 are integrated. In the example shown in Figure 6C, the antenna equipment 101 comprises a hollow structure film 1 (hollow structure film 1 shown in Figures 1A and 1B) including a main body portion 1c, a wiring pattern of the wiring 41, and the antenna element 102. The wiring pattern of the wiring 41 and the antenna element 102 are provided on the first surface 1a of the hollow structure film 1. In the example shown in Figure 6C, the antenna equipment 101 comprises a hollow structure film 1, a wiring pattern for wiring 41 provided on the first surface 1a of the hollow structure film 1, and a metal layer 40 on the second surface 1b of the hollow structure film 1 where no wiring pattern is formed. By providing the metal layer 40 on the second surface 1b where no wiring pattern is formed, the antenna equipment 101 is less likely to generate unwanted noise when transmitting electrical signals through the wiring 41. The reason why the metal layer 40 on the second surface 1b where no wiring pattern is formed is less likely to generate unwanted noise is as follows: When current flows through the wiring 41 formed on the first surface 1a side, a current in the opposite direction to the current flowing through the wiring 41 (the feedback current described above) is generated on the second surface 1b side according to Ampere's law. In particular, when the wiring 41 formed on the first surface 1a side is powered by a high frequency, a feedback current is generated on the second surface 1b side. The feedback current functions as a signal ground. In particular, the feedback current effectively functions as a signal ground by reducing the size of the antenna loop formed when the wiring 41 and ground plane form an antenna loop. This reduces the generation of unwanted noise.

[0109] The antenna element 102 shown in Figure 6C has a rectangular shape when viewed from the thickness direction of the hollow structure film 1. In the example shown in Figure 6C, the wiring 41 extends from one side of the antenna element 102 to the end side of the antenna equipment 101.

[0110] The antenna equipment 101 shown in Figure 6C can be manufactured from the hollow structure film 1 shown in Figure 5. Specifically, the antenna equipment 101 shown in Figure 6C can be manufactured by forming the wiring pattern of the wiring 41 and the antenna element 102 from the metal layer 40 that constitutes the first surface 1a of the hollow structure film 1 shown in Figure 5.

[0111] <Method for manufacturing hollow structure film> A method for manufacturing the hollow structure film 1 of this embodiment will be described. Unless otherwise specified, the method for manufacturing the hollow structure film 1 of this embodiment will be described as a method for manufacturing the hollow structure film 1 in which the metal layer 40 constitutes the first surface 1a and the second surface 1b, as shown in Figure 5. The method for manufacturing the hollow structure film having a hollow structure of this embodiment comprises the steps of: using a mold 90 to produce a pair of single-sided shaped bodies 80 having a sheet-like base 81 and a plurality of protrusions 82 formed on one surface of the base 81; and overlapping the produced pair of single-sided shaped bodies 80 such that the plurality of protrusions 82 face each other in at least a portion, and then heating and pressing them together. The method for manufacturing the hollow structure film of this embodiment further comprises a crosslinking step in which a compound having a double bond that is active to radiation, contained in the single-sided shaped body 80, is reacted with a resin. When the compound having a double bond that is active to radiation is an electron beam crosslinking agent, in the crosslinking step, an electron beam is irradiated onto the electron beam crosslinking agent contained in the single-sided shaped body 80 to react the compound with the resin. Even without containing an electron beam crosslinking agent, the hollow structure film 1 may exhibit desirable physical properties by undergoing electron beam irradiation during the manufacturing process. For example, even without containing an electron beam crosslinking agent, the heat resistance of the hollow structure film 1 can be significantly improved by undergoing electron beam irradiation during the manufacturing process. In this case, the hollow structure film 1 does not need to contain an electron beam crosslinking agent.

[0112] In the process of manufacturing the single-sided formwork 80, a pair of single-sided formwork 80 is manufactured using a mold 90. At this time, a metal foil 42 to be used as the material for the metal layer 40 is prepared. Furthermore, the material for the formwork corresponding portion 13 is prepared. Furthermore, the material for the adjacent metal layer 60 is prepared. In this embodiment, the formwork corresponding portion 13 of the manufactured hollow structure film 1 contains resin. In this case, for example, raw material pellets of the corresponding resin are prepared as the material for the formwork corresponding portion 13. If the formwork corresponding portion 13 of the manufactured hollow structure film 1 contains polyethylene, polyethylene raw material pellets are prepared as the material for the formwork corresponding portion 13. If the formwork corresponding portion 13 of the manufactured hollow structure film 1 contains a compound having a double bond that is active to radiation, the compound is prepared as the material for the formwork corresponding portion 13. If the formwork corresponding portion 13 contains multiple materials, the multiple materials are mixed to create a mixture. If the excipient-corresponding portion 13 of the manufactured hollow structure film 1 contains a resin and a compound having a double bond that is active to radiation, a mixture of the resin and the compound is prepared.

[0113] Next, as shown in Figure 7A, the material for the formwork corresponding portion 13 is molded using the mold 90. If the formwork corresponding portion 13 of the hollow structure film 1 to be manufactured contains a resin and a compound having a double bond that is active to radiation, the mixture of the resin and the compound is molded using the mold 90. The molding of the mixture is carried out while melting the resin contained in the mixture. The mold 90 has a surface 90a with a shape corresponding to the shape of the single-sided formwork 80 to be manufactured. In particular, the surface 90a of the mold 90 has a shape corresponding to the shape of the surface of the single-sided formwork 80 to be manufactured on which the multiple protrusions 82 are formed. By molding the material for the formwork corresponding portion 13 using such a mold 90, a single-sided formwork 80 having a sheet-like base portion 81 and multiple protrusions 82 formed on one surface of the base portion 81 is manufactured from the material for the formwork corresponding portion 13. In this embodiment, the material for the formwork corresponding portion 13 and the material for the adjacent metal layer 60 are formed on the metal foil 42 using a mold 90 by co-extrusion molding. As a result, the adjacent metal layer 60 is made on the metal foil 42, which is the metal layer 40, from the material for the adjacent metal layer 60, and the single-sided formwork 80 is made on the adjacent metal layer 60 from the material for the formwork corresponding portion 13. In this way, a laminate 83 is made in which the metal layer 40, the adjacent metal layer 60, and the single-sided formwork 80 are stacked in this order. Furthermore, another single-sided formwork 80 is made by the same method as the method for making the first single-sided formwork 80 described above. In this embodiment, another laminate 83 is made by the same method as the method for making the first laminate 83 described above.

[0114] When manufacturing a hollow structure film 1 in which the first surface 1a and the second surface 1b are not composed of a metal layer 40, as shown in Figures 1A, 1B, and 4, the single-sided formwork 80, or a laminate of the metal adjacent layer 60 and the single-sided formwork 80, may be manufactured by the following method. Instead of the metal foil 42, a laminate of the material for the formwork corresponding portion 13, or the material for the formwork corresponding portion 13 and the material for the metal adjacent layer 60, is formed on a peelable substrate. After that, the substrate is peeled off. In this case, for example, a polyimide film can be used as the peelable substrate. In particular, Kapton® manufactured by Toray DuPont Co., Ltd. can be used as the peelable substrate. When a peelable substrate is used, the substrate may be peeled off before the step of heat-pressing the pair of single-sided formwork 80, or after the step of heat-pressing the pair of single-sided formwork 80. When a peelable substrate is used, the substrate may be peeled off before the crosslinking step, or after the crosslinking step. Other peelable substrates that can be used include PET (polyethylene terephthalate) film. Specific examples of peelable PET films include CosmoShine® and CosmoPeel® manufactured by Toyobo Co., Ltd.

[0115] Next, a step of heat-pressing the pair of single-sided shaped bodies 80 is performed. In this step, as shown in Figure 7B, the pair of single-sided shaped bodies 80 are superimposed such that the multiple protrusions 82 face each other in at least some areas. The pair of single-sided shaped bodies 80 are superimposed such that the surfaces on which the multiple protrusions 82 are formed face each other. In this embodiment, a pair of laminates 83 including the single-sided shaped bodies 80 are superimposed such that the multiple protrusions 82 of the pair of single-sided shaped bodies 80 face each other in at least some areas.

[0116] The hollow structure film 1 shown in Figure 5 includes a sheet-like central portion 30 that overlaps the first base portion 11 and the second base portion 12 and is located between the first opposing surface 11a and the second opposing surface 12a. When manufacturing such a hollow structure film 1, the material for the central portion 30 is prepared before the step of heat-pressing the pair of single-sided formwork 80. In this embodiment, the central portion 30 of the manufactured hollow structure film 1 contains a resin. Furthermore, the central portion 30 of the manufactured hollow structure film 1 contains a compound having a double bond that is active to radiation. In this case, a resin sheet 32, in which the compound is dispersed in a resin and formed into a sheet, can be used as the material for the central portion 30. As an example, the resin contained in the central portion 30 has a lower melting point than the resin contained in the formwork corresponding portion 13. When manufacturing the hollow structure film 1 with the central portion 30, as shown in Figure 7B, the resin sheet 32 ​​is placed between the pair of single-sided formwork 80 when the pair of single-sided formwork 80 are overlapped.

[0117] Next, as shown in Figure 8A, the pair of single-sided shaped bodies 80 are heat-pressed together. This joins the pair of single-sided shaped bodies 80 to each other. As shown in Figure 7B, when a resin sheet 32 ​​is placed between the pair of single-sided shaped bodies 80, the pair of single-sided shaped bodies 80 are joined to the resin sheet 32 ​​at multiple protrusions 82 by heat-pressing them together as shown in Figure 8A. This joins the pair of single-sided shaped bodies 80 via the resin sheet 32. At this time, in the portion of the pair of single-sided shaped bodies 80 where the multiple protrusions 82 face each other and overlap, portions of the support columns 20 extending from the first opposing surface 11a to the second opposing surface 12a are formed. In particular, in the portion of the pair of single-sided shaped bodies 80 where the multiple protrusions 82 face each other and overlap, a continuous support column 23 is formed. This forms a shaped body corresponding portion 13 from the pair of single-sided shaped bodies 80. Furthermore, the central portion 30 is formed from the resin sheet 32. In addition, a pair of base portions 10 (first base portion 11 and second base portion 12) are formed from the base portion 81 of the single-sided molded body 80.

[0118] The heating temperature when heat-pressing the pair of single-sided formwork 80 is greater than the Vicat softening point temperature of the resin contained in the central portion 30. In particular, as described above, when the resin contained in the central portion 30 is linear low-density polyethylene, the heating temperature when heat-pressing the pair of single-sided formwork 80 is greater than the Vicat softening point temperature of linear low-density polyethylene. This allows the resin sheet 32 ​​to be softened by heat-pressing, and the pair of single-sided formwork 80 to be joined to the resin sheet 32. In this case, as described above, since the resin contained in the central portion 30 has a lower melting point than the resin contained in the formwork corresponding portion 13, when the resin contained in the central portion 30 is heated to a temperature greater than the Vicat softening point temperature, it is possible to suppress large deformation of the single-sided formwork 80 due to heating. The heating temperature when heat-pressing the pair of single-sided formwork 80 can be set to be below the Vicat softening point temperature of the resin contained in the single-sided formwork 80. When heat-pressing a pair of single-sided forms 80, a spacer 92 as shown in Figure 8A may be used. The spacer 92 controls the position of the pair of single-sided forms 80 so that they do not come closer to each other than a certain distance when the pair of single-sided forms 80 are brought close to each other during heat-pressing. The thickness of the hollow structure film 1 produced can be adjusted by the spacer 92.

[0119] In the process of heat-pressing a pair of single-sided shaped bodies 80, instead of the method using the spacer 92 described above, the pair of single-sided shaped bodies 80 may be heat-pressed by the following method. First, the pair of single-sided shaped bodies 80 are processed into a film shape having a certain length or longer. Next, the pair of single-sided shaped bodies 80 are overlapped so that at least some of the protrusions 82 face each other. Next, the pair of single-sided shaped bodies 80, overlapped, are passed between two heated rolls. In this case, when manufacturing a hollow structure film 1 having a central portion 30, a resin sheet 32 ​​having a certain length or longer is prepared and sandwiched between the overlapped pair of single-sided shaped bodies 80. In this state, the pair of single-sided shaped bodies 80 and the resin sheet 32 ​​are passed between two heated rolls. The pair of single-sided shaped bodies 80 may be heat-pressed by the above method. When this method using two rolls is adopted, instead of using a spacer 92, the thickness of the hollow structure film 1 produced can be adjusted to a suitable thickness by adjusting the distance between the two rolls.

[0120] Next, a crosslinking step is performed in which a compound having a radiation-active double bond contained in the single-sided excipient 80 is reacted with the resin. If the compound having a radiation-active double bond contained in the single-sided excipient 80 is an electron beam crosslinking agent, in the crosslinking step, the electron beam crosslinking agent is irradiated with an electron beam to react the compound with the resin. In this case, the conditions of the electron beam irradiated in the crosslinking step are, for example, as follows: The electron beam irradiation dose is, for example, 5 kGy or more and 500 kGy or less (0.5 Mrad or more and 50 Mrad or less), preferably 10 kGy or more and 300 kGy or less (1 Mrad or more and 30 Mrad or less). The electron beam irradiation dose is, for example, 200 kGy (20 Mrad). The electron beam acceleration voltage is, for example, 165 kV. If a resin sheet 32, which is formed into a sheet shape in which a compound having a radiation-active double bond is dispersed in the resin, is used as the material for the central portion 30, the compound contained in the resin sheet 32 ​​may be reacted with the resin in the crosslinking process. In this case, the method of reacting the compound contained in the resin sheet 32 ​​with the resin is the same as the method of reacting the compound contained in the one-sided excipient 80 with the resin. As a result, the hollow structure film 1 shown in Figure 5 is manufactured.

[0121] In particular, in the manufacturing method of the hollow structure film 1, in which the main body portion 1c includes an inorganic material member 70, as shown in Figures 1A and 1B, in the step of manufacturing a pair of single-sided molded bodies 80, a single-sided molded body 80 including an insulating inorganic material member 70 is manufactured. At this time, at least one of the pair of single-sided molded bodies 80 may include the inorganic material member 70. Both of the pair of single-sided molded bodies 80 may include the inorganic material member 70. The inorganic material member 70 may be included in the base portion 81 of the single-sided molded body 80. The inorganic material member 70 may be included in at least a portion of a plurality of protrusions 82. The inorganic material member 70 may be included in all of the plurality of protrusions 82. When a resin sheet 32 ​​is used in the manufacture of the hollow structure film 1, the inorganic material member 70 may be included in the resin sheet 32.

[0122] The hollow structure film 1 shown in Figure 1A can be manufactured from a pair of single-sided molded bodies 80, each containing a sheet-like inorganic material member 70 in its base portion 81, as shown in Figure 8D, and a resin sheet 32. The hollow structure film 1 shown in Figure 1B can be manufactured from a pair of single-sided molded bodies 80, each containing a rod-shaped inorganic material member 70 in its base portion 81 and all of its multiple protrusions 82, as shown in Figure 8E, and a resin sheet 32 ​​containing the rod-shaped inorganic material member 70.

[0123] A circuit board 100 comprising a hollow structure film 1 and a wiring pattern, as described above, can be manufactured, for example, by the following method. The metal layer 40 is formed such that the entire surface of the hollow structure film 1 on which the wiring pattern is to be formed is covered by the metal layer 40. For example, when manufacturing a laminate 83 in which the metal layer 40 and a single-sided form 80 are laminated together, as shown in Figure 7A, the laminate 83 is manufactured such that the entire surface of the single-sided form 80 on which the multiple protrusions 82 are not formed is covered by the metal layer 40. By manufacturing the hollow structure film 1 using this laminate 83, the entire surface of the hollow structure film 1 on which the wiring pattern is to be formed is covered by the metal layer 40. For example, a layer of copper can be formed as the metal layer 40. As an example, the metal layer 40 is joined to the single-sided form 80 via an adjacent metal layer 60. By covering the thus formed metal layer 40 with a mask layer and then etching it, a wiring pattern can be formed from at least a part of the metal layer 40. More specifically, a wiring pattern can be formed from at least a portion of the metal layer 40 by etching the metal layer 40 using, for example, a patterned dry film resist (DFR) as a mask. This makes it possible to manufacture a circuit board 100 comprising a hollow structure film 1 and a wiring pattern.

[0124] A circuit board 100 comprising a hollow structure film 1 and a wiring pattern may be manufactured by the following method. First, as shown in Figure 8B, a single-sided form 80 is formed. The pair of single-sided form 80 shown in Figure 8B have the same shape as the single-sided form 80 included in the laminate 83 shown in Figure 7A. Next, a step of heat-pressing the pair of single-sided form 80 is performed. In this step, as an example, as shown in Figure 8B, a resin sheet 32 ​​is placed between the pair of single-sided form 80. Next, as shown in Figure 8C, the pair of single-sided form 80 is heat-pressed. This joins the pair of single-sided form 80 to each other. Next, a metal layer 40 is formed so as to cover the entire surface of the single-sided form 80 where no multiple protrusions 82 are formed. As an example, the metal layer 40 is joined to the single-sided form 80 via an adjacent metal layer 60. By etching the metal layer 40 formed in this way using the method described above, a wiring pattern can be formed from at least a part of the metal layer 40. This makes it possible to manufacture a circuit board 100 having a hollow structure film 1 and a wiring pattern, as described above.

[0125] The wiring pattern may be formed by attaching pre-formed copper wiring to the base 10. The wiring pattern may also be formed by forming a pattern for the plating seed layer by printing, including inkjet printing, and then plating it up.

[0126] The antenna equipment 101 shown in Figure 6C can be manufactured by forming wiring 41 and antenna elements 102 from a metal layer 40 that constitutes at least a part of the first surface 1a of the hollow structure film 1 shown in Figure 5. The method for forming wiring 41 and antenna elements 102 from the metal layer 40 can be the same as the method for forming wiring patterns from the metal layer 40 in the manufacturing method of the circuit board 100 described above.

[0127] The wiring pattern may be formed by printing using conductive ink. Alternatively, the wiring pattern may be formed by processing with a metal 3D printer.

[0128] The hollow-structured film 1 of this embodiment includes a sheet-like first base portion 11, a sheet-like second base portion 12 overlapping the first base portion 11, and a plurality of support portions 20 provided between the first base portion 11 and the second base portion 12. The first base portion 11 has a first facing surface 11a facing the second base portion 12. The second base portion 12 has a second facing surface 12a facing the first base portion 11. At least a part of the plurality of support portions 20 constitutes a continuous support portion 23 extending from the first facing surface 11a to the second facing surface 12a. As a result, a plurality of hollow portions B are formed between the first base portion 11 and the second base portion 12. For this reason, the hollow-structured film 1 has a hollow structure. According to such a hollow-structured film 1, while being less likely to be restricted by the material of the hollow-structured film 1, the dielectric constant of the hollow-structured film 1 can be lowered. Furthermore, according to such a hollow-structured film 1, the dielectric tangent of the hollow-structured film 1 can be lowered by the hollow structure. The dielectric tangent indicates the amount by which an electrical signal propagating through a dielectric is converted into heat and lost. The lower the value of the dielectric tangent of the hollow-structured film 1, the more the signal loss can be reduced and the transmission rate of the electrical signal can be improved when the hollow-structured film 1 is used for a circuit board designed on the premise of communication.

[0129] The effects of the low values of the dielectric constant and dielectric tangent of the hollow-structured film 1 will be described in more detail. There is a demand for higher frequencies of electrical signals handled in information communication devices such as smartphones and tablet terminals. Along with this increase in the frequency of the electrical signal, the transmission loss in a circuit board designed on the premise of communication increases (the value of the transmission loss with a negative value moves away from zero). On the other hand, it is known that transmission loss, particularly dielectric loss, can be reduced (the value of the transmission loss with a negative value approaches zero) by lowering the values of the dielectric constant and dielectric tangent of the circuit board. Dielectric loss is represented by the following formula (1). In formula (1), α d is the dielectric loss, K is a proportionality constant, f is the frequency, ε γ is the relative permittivity, and tanδ is the dielectric tangent. The relative permittivity ε γ is the ratio of the dielectric constant of an object such as a circuit board to the dielectric constant of a vacuum.

Equation

[0130] From equation (1), it can be understood that dielectric loss can be reduced by lowering the dielectric constant and dielectric loss tangent values ​​of the circuit board. In particular, even when the frequency value is high, i.e., when the electrical signal is high frequency, it can be understood that dielectric loss can be reduced by lowering the dielectric constant and dielectric loss tangent values ​​of the circuit board. Therefore, by using the hollow structure film 1 of this embodiment in circuit boards designed for communication, signal loss can be reduced and the transmission rate of electrical signals can be improved. In particular, in circuit boards that handle high-frequency electrical signals, it is required to lower the dielectric constant and dielectric loss tangent values. For this reason, the hollow structure film 1 of this embodiment is suitably used in circuit boards that handle high-frequency electrical signals. The hollow structure film 1 of this embodiment is suitably used, for example, in circuit boards that handle electrical signals with frequencies of 6 GHz or higher, particularly 26 GHz or higher, and particularly 60 GHz or higher. The hollow structure film 1 of this embodiment may also be used in circuit boards that handle electrical signals with frequencies of 6 GHz to 39 GHz, particularly 26 GHz to 39 GHz. The hollow structure film 1 of this embodiment may be used in a circuit board that handles electrical signals with a frequency of 60 GHz or more and 80 GHz or less.

[0131] As sheets with low dielectric constants, there are also known sheets manufactured by forming a resin foam containing air bubbles, such as the low dielectric sheet for two-dimensional communication disclosed in Japanese Patent No. 5976714. Examples of sheets that are resin foams containing air bubbles include Softlon manufactured by Sekisui Chemical Co., Ltd. and SKYBOND® FOAM manufactured by I.S.T. Corporation. However, the hollow structure film 1 of this embodiment is clearly different from a resin foam sheet in that it has a plurality of support columns 20, and in particular, at least a portion of the plurality of support columns 20 constitutes a continuous support column 23. The hollow structure film 1 of this embodiment has greater hardness than a resin foam sheet due to the presence of a plurality of support columns 20. In particular, the hollow structure film 1 of this embodiment has greater indentation hardness than a resin foam sheet. Thus, the hollow structure film 1 of this embodiment is clearly different from a resin foam sheet in terms of physical properties such as hardness. Because sheets made of resin foam are flexible and easily bent, it is considered difficult to use them to form circuit boards 100 such as antenna equipment 101.

[0132] The hollow structure film 1 of this embodiment comprises a main body 1c having a sheet-like first base portion 11, a sheet-like second base portion 12 overlapping the first base portion 11, and a plurality of support portions 20 provided between the first base portion 11 and the second base portion 12. The first base portion 11 has a first opposing surface 11a facing the second base portion 12. The second base portion 12 has a second opposing surface 12a facing the first base portion 11. At least a portion of the plurality of support portions 20 constitute a continuous support portion 23 extending from the first opposing surface 11a to the second opposing surface 12a. The main body 1c includes an insulating inorganic material member 70. The maximum width of the inorganic material member 70 is three times or more the minimum width of the inorganic material member 70. This makes it difficult for the metal layer 40 to peel off from the main body 1c and makes it difficult for wrinkles to form in the metal layer 40.

[0133] In the hollow structure film 1 of this embodiment, the inorganic material member 70 may be included in at least one of the first base portion 11 and the second base portion 12. This allows the CTE of the base portion 10 to be adjusted so that the difference in CTE between the base portion 10 and the metal layer 40 is small when the base portion 10 and the metal layer 40 are joined together. This makes it difficult for the metal layer 40 to peel off from the base portion 10 and makes it difficult for wrinkles to form in the metal layer 40 joined to the base portion 10.

[0134] In the hollow structure film 1 of this embodiment, the inorganic material member 70 may be included in at least a portion of the support portion 20. This also allows the CTE of the main body portion 1c to be adjusted so that the difference in CTE between the main body portion 1c and the metal layer 40 is small. This makes it difficult for the metal layer 40 to peel off from the main body portion 1c and makes it difficult for wrinkles to form in the metal layer 40.

[0135] The hollow structure film 1 of this embodiment further has a sheet-like central portion 30 located between the first opposing surface 11a and the second opposing surface 12a. The multiple support portions 20 are located on the first opposing surface 11a side and the second opposing surface 12a side of the central portion 30. This makes it possible to further increase the strength of the hollow structure film 1.

[0136] In the hollow structure film 1 of this embodiment, if the main body portion 1c further has a central portion 30, the inorganic material member 70 may be included in at least the central portion 30. This also allows the CTE of the main body portion 1c to be adjusted so that the difference in CTE between the main body portion 1c and the metal layer 40 is small. This makes it difficult for the metal layer 40 to peel off from the main body portion 1c and makes it difficult for wrinkles to form in the metal layer 40.

[0137] In the hollow structure film 1 of this embodiment, the inorganic material member 70 may include glass. This allows the CTE of the main body 1c to be adjusted more effectively using the inorganic material member 70 so that the difference in CTE between the main body 1c and the metal layer 40 is reduced.

[0138] The maximum width of the inorganic material member 70 may be 10 μm or more. This allows the CTE of the main body 1c to be adjusted more effectively using the inorganic material member 70 so that the difference in CTE between the main body 1c and the metal layer 40 is reduced.

[0139] The hollow structure film 1 of this embodiment has a first surface 1a and a second surface 1b located on the opposite side of the first surface 1a. The hollow structure film 1 of this embodiment further comprises a metal layer 40 which constitutes at least a portion of at least one of the first surface 1a and the second surface 1b. This allows wiring 41 to be formed from the metal layer 40 by forming a wiring pattern on the metal layer 40.

[0140] The hollow structure film 1 of this embodiment further includes a metal adjacent layer 60 that joins the metal layer 40 and the base 10. This allows the metal layer 40 to be more firmly bonded to the base 10.

[0141] The circuit board 100 of this embodiment comprises the hollow structure film 1 described above, having a first surface 1a and a second surface 1b located opposite to the first surface 1a, and a wiring pattern provided on at least one of the first surface 1a and the second surface 1b. This makes it possible to lower the dielectric constant of the circuit board 100.

[0142] The antenna equipment 101 of this embodiment comprises the circuit board 100 described above and an antenna element connected to the circuit board 100. This allows the dielectric constant of the circuit board 100 to be lowered. As a result, the transmission loss in the circuit board can be reduced (the transmission loss value, which has a negative value, can be brought close to zero).

[0143] The manufacturing method for the hollow structure film 1 of this embodiment comprises the steps of: using a mold 90 to produce a pair of single-sided shaped bodies 80 having a sheet-like base portion 81 and a plurality of protrusions 82 formed on one side of the base portion 81, and including an insulating inorganic material member 70; and overlapping the produced pair of single-sided shaped bodies 80 such that the plurality of protrusions 82 face each other in at least a portion of the area, and then heating and pressing them together. The maximum width of the inorganic material member 70 is three times or more the minimum width of the inorganic material member 70. By this manufacturing method, a hollow structure film 1 in which the main body portion 1c includes the inorganic material member 70 can be manufactured.

[0144] <Variation> Next, various modifications of this embodiment will be described with reference to Figures 9 to 12. In Figures 9 to 12, the same reference numerals are used for parts that are the same as those shown in Figures 1A to 8E, and detailed descriptions are omitted.

[0145] <Example 1> In the embodiments described above, a hollow structure film 1 was described in which the base portion 10 has a plurality of connecting portions 24 extending in a first direction d1, as shown in Figure 2, and does not have connecting portions 24 extending in directions other than the first direction d1. Furthermore, a hollow structure film 1 was described in which it has a plurality of support portions 20 extending in the first direction d1, and does not have support portions 20 extending in directions other than the first direction d1. However, the direction in which the connecting portions 24 and support portions 20 extend is not limited to the examples described above. Figure 9 is a plan view showing the base portion 10 of Modified Example 1 as observed from the thickness direction of the hollow structure film 1, and corresponds to Figure 2. In the example shown in Figure 9, the base portion 10 has a plurality of connecting portions 24, which are first connecting portions 24a extending in the first direction d1. In addition, in the example shown in Figure 9, the base 10 has a second connecting portion 24b as a plurality of connecting portions 24, which extends in a third direction d3 that is perpendicular to the thickness direction of the hollow structure film 1 and different from the first direction d1. In the example shown in Figure 9, the third direction d3 is perpendicular to the first direction d1. In other words, the third direction d3 coincides with the second direction d2. Because the base 10 has a first connecting portion 24a and a second connecting portion 24b as a plurality of connecting portions 24, the hollow structure film 1 of the modified example 1 has a plurality of support portions 20 extending in the first direction d1 and a plurality of support portions 20 extending in the third direction d3. Even with a base 10 having such connecting portions 24 and a hollow structure film 1 having such support portions 20, a hollow structure can be formed and the dielectric constant can be kept low.

[0146] The hollow structure film 1 of the modified example 1 has a plurality of support portions 20 extending in a first direction d1, and a plurality of support portions 20 extending in a third direction d3. In such a hollow structure film 1, the angles θ1, θ2, and porosity described above are measured based on the portion of the cross section obtained by cutting through a plane passing through the plurality of support portions 20 and perpendicular to the first direction d1, where the plurality of support portions 20 extending in the third direction d3 are not visible.

[0147] <Modification 2> In the embodiments described above, a hollow structure film 1 having a central portion 30, as shown in Figures 1A and 1B, was described. However, the hollow structure film 1 does not have to have a central portion 30. Figure 10 is a cross-sectional view of the hollow structure film 1 of Modification 2, cut in a cross section parallel to the thickness direction of the hollow structure film 1, and corresponds to Figures 1A and 1B. In the example shown in Figure 10, the hollow structure film 1 does not have a central portion 30. In the example shown in Figure 10, at least a portion of the plurality of support portions 20 extends in the thickness direction of the hollow structure film 1 from the first opposing surface 11a to the second opposing surface 12a. In the example shown in Figure 10, a portion of the plurality of support portions 20 constitutes a continuous support portion 23. The portion of the plurality of support portions 20 that does not constitute a continuous support portion 23 constitutes a convex portion 25 that protrudes from the first opposing surface 11a toward the second opposing surface 12a, or from the second opposing surface 12a toward the first opposing surface 11a.

[0148] In the hollow structure film 1 shown in Figure 10, where a portion of the multiple support columns 20 constitutes a protrusion 25, the height of the protrusion 25 (the dimension of the protrusion 25 in the thickness direction of the hollow structure film 1) is defined as height w4. In this case, it is preferable that height w4 is 0.5 times or more and 10 times or less the width w2 of the connecting portion 24 in the second direction d2. By having height w4 at least 0.5 times the width w2, the size of the hollow portion B can be made particularly large, and the dielectric constant of the hollow structure film 1 can be made particularly low. By having height w4 at least 10 times the width w2, the strength of the hollow structure film 1 can be made particularly large.

[0149] A hollow structure film 1 without a central portion 30, as shown in Figure 10, can be manufactured by the same method as the manufacturing method for the hollow structure film 1 with a central portion 30 in the above-described embodiment, except for the points described below. In the step of heat-pressing a pair of single-sided shaped bodies 80, the pair of single-sided shaped bodies 80 are overlapped without placing a resin sheet 32 ​​between them. Then, the pair of single-sided shaped bodies 80 are heat-pressed together. This joins the opposing protrusions 82 of the pair of single-sided shaped bodies 80 together. The joining of the opposing protrusions 82 forms a continuous support column 23. This directly joins the pair of single-sided shaped bodies 80 together. One protrusion 82 of the pair of single-sided shaped bodies 80 that does not face the other protrusion 82 of the pair of single-sided shaped bodies 80 when the pair of single-sided shaped bodies 80 are overlapped constitutes a protrusion 25 in the manufactured hollow structure film 1. The heating temperature when heat-pressing a pair of single-sided molded bodies 80 is adjusted to a temperature that softens the single-sided molded bodies 80, allowing the pair of single-sided molded bodies 80 to be directly joined together.

[0150] The hollow structure film 1 in the modified example 2 also forms a hollow structure, thereby keeping the dielectric constant low.

[0151] <Variation 3> When manufacturing a hollow structure film 1 that does not have a central portion 30, the hollow structure film 1 may be manufactured using a pair of single-sided shaped bodies 80 described below. Figure 11 shows a single-sided shaped body 80 used in the manufacturing method of the hollow structure film of Modification 3. In the example shown in Figure 11, the single-sided shaped body 80 comprises a first layer 84 containing a first resin and a second layer 85 overlapping the first layer 84 and containing a second resin. In the example shown in Figure 11, the surface of the single-sided shaped body 80 on which the plurality of protrusions 82 are formed is composed of the first layer 84. The thickness of the first layer 84 is constant. The second layer 85 constitutes the portion of the plurality of protrusions 82 not composed of the first layer 84, and the base portion 81. The first resin contained in the first layer 84 has a lower melting point than the second resin contained in the second layer 85. With this configuration, when a pair of single-sided molded bodies 80 are heat-pressed together, the first layer 84 can be sufficiently melted while maintaining the shape of the second layer 85. This makes it possible to join a pair of single-sided molded bodies 80 together while minimizing deformation of the overall shape of the single-sided molded bodies 80. The first resin in Modification 3 is, for example, the same as the resin contained in the central part 30 in the above-described embodiment. The material of the first layer 84 in Modification 3 may be the same as the material of the central part 30 in the above-described embodiment. The first layer 84 may contain a compound having a radiation-active double bond, which may be contained in the central part 30 in the above-described embodiment. The second resin in Modification 3 is, for example, the same as the resin contained in the molded body corresponding part 13 in the above-described embodiment.

[0152] The single-sided formwork 80 shown in Figure 11 can be manufactured by co-extrusion molding, using a mold similar to the mold 90 shown in Figure 7A, to form the material for the second layer 85 containing the second resin and the material for the first layer 84 containing the first resin on a metal foil 42.

[0153] By using a pair of single-sided formwork 80 shown in Figure 11, a hollow structure film 1 without a central portion 30, as shown in Figure 12, can be manufactured. In this case, the manufacturing method of the hollow structure film 1 can be the same as the manufacturing method of the hollow structure film 1 without a central portion 30 described in Modification 2 above, except for the points described below. The heating temperature when the pair of single-sided formwork 80 are heat-pressed together is adjusted to a temperature that softens the first layer 84 of the single-sided formwork 80, allowing the pair of single-sided formwork 80 to be directly joined together. For example, the heating temperature when the pair of single-sided formwork 80 are heat-pressed together is greater than the Vicat softening point temperature of the first resin contained in the first layer 84. This allows the first layer 84 to be softened by heat-pressing, and the opposing protrusions 82 of the pair of single-sided formwork 80 to be joined together. In particular, the portions of the opposing protrusions 82 of the pair of single-sided formwork 80 that are composed of the first layer 84 can be joined together. In this case, as described above, because the first resin has a lower melting point than the second resin, when the first layer 84 is heated to a temperature above the Vicat softening point of the first resin, it is possible to suppress the large deformation of the second layer 85 due to heating.

[0154] <Modification 4> In the embodiments and modifications described above, examples were given of manufacturing a hollow structure film 1 using two single-sided formants 80. However, the method for manufacturing the hollow structure film 1 is not limited to this. The hollow structure film 1 may also be manufactured using one single-sided formant 80. Figure 13 shows the method for manufacturing a hollow structure film of Modification 4. Figure 14 shows the hollow structure film 1 manufactured by the method for manufacturing a hollow structure film of Modification 4.

[0155] In the example shown in Figure 13, the resin sheet 32 ​​is positioned opposite the surface of a single-sided formwork 80 on which multiple protrusions 82 are formed. The manufacturing method for the hollow structure film of the modified example 4 includes a step of heat-pressing the single-sided formwork 80 and the resin sheet 32, which are positioned as shown in Figure 13. This makes it possible to manufacture a hollow structure film 1 having a pair of bases 10 and multiple support columns 20, as shown in Figure 14. At this time, the multiple support columns 20 are formed from the multiple protrusions 82 of the single-sided formwork 80. In the example shown in Figure 14, the first base 11 is formed from the base 81 of the single-sided formwork 80. In the example shown in Figure 14, the second base 12 is formed from the resin sheet 32. Although not shown, the second base 12 may be formed from the base 81 of the single-sided formwork 80 and the first base 11 may be formed from the resin sheet 32.

[0156] When heat-pressing the single-sided formwork 80 and the resin sheet 32, a spacer 92 as shown in Figure 13 may be used. The spacer 92 controls the position of the single-sided formwork 80 and the resin sheet 32 ​​so that they do not come closer than a certain distance when they are brought close to each other during heat-pressing. The thickness of the manufactured hollow structure film 1 can be adjusted by using the spacer 92.

[0157] As shown in Figure 14, the hollow structure film 1 of Modified Example 4 may include a metal layer 40 that constitutes at least a part of at least one of the first surface 1a and the second surface 1b of the hollow structure film 1. As shown in Figure 14, the hollow structure film 1 of Modified Example 4 may also include a metal adjacent layer 60 that joins the metal layer 40 to the base 10. In this case, the metal layer 40 may be joined to the single-sided form 80 or the resin sheet 32 ​​via the metal adjacent layer 60 before the step of heat-pressing the single-sided form 80 and the resin sheet 32, or it may be joined to the base 10 via the metal adjacent layer 60 after the step of heat-pressing the single-sided form 80 and the resin sheet 32.

[0158] According to the method for manufacturing a hollow structure film and the hollow structure film 1 of Modification 4, it is possible to provide a hollow structure film 1 with a particularly small thickness.

[0159] <Modification 5> In the embodiments and modifications described above, examples of manufacturing a hollow structure film 1 using two or fewer single-sided formants 80 have been explained. However, the method for manufacturing the hollow structure film 1 is not limited to this. A hollow structure film 1 may be manufactured using three or more single-sided formants 80. Figure 15 shows the components used in the manufacturing method of the hollow structure film of Modification 5, arranged in the order in which they are stacked when manufacturing the hollow structure film 1. Figure 16 shows the hollow structure film 1 manufactured by the manufacturing method of Modification 5.

[0160] In the example shown in Figure 15, the components used in the manufacturing method of the hollow structure film include four single-sided shaped bodies 80. The four single-sided shaped bodies 80 are stacked in the thickness direction of the base portion 81. The components used in the manufacturing method of the hollow structure film further include three resin sheets 32. The four single-sided shaped bodies 80 and the three resin sheets 32 are stacked so as to be alternately arranged in the thickness direction of the base portion 81. The manufacturing method of the hollow structure film in the modified example 4 includes a step of heat-pressing the single-sided shaped bodies 80 and the resin sheets 32 arranged as shown in Figure 15. This makes it possible to manufacture a hollow structure film 1 having a pair of base portions 10 and a plurality of support portions 20, as shown in Figure 16. At this time, the plurality of support portions 20 are formed from the plurality of protrusions 82 of the plurality of single-sided shaped bodies 80. In particular, in the portion where multiple protrusions 82 of multiple single-sided forms 80 are overlapped so as to face each other, a continuous support portion 23 is formed, extending from the first opposing surface 11a to the second opposing surface 12a of multiple support portions 20. A pair of base portions 10 are formed from the base portions 81 of a pair of single-sided forms 80 located on the outermost side in the thickness direction of the base portion 81.

[0161] In the process of heat-pressing the single-sided formwork 80 and the resin sheet 32, the order in which the multiple single-sided formwork 80 and the multiple resin sheets 32 are heat-pressed is not particularly limited. The hollow structure film 1 may be manufactured by simultaneously heat-pressing all of the multiple single-sided formwork 80 and the multiple resin sheets 32. The hollow structure film 1 may also be manufactured by repeatedly heat-pressing adjacent single-sided formwork 80 and resin sheets 32. The hollow structure film 1 shown in Figure 16 may be manufactured by the following method: The first single-sided formwork 80a and the second single-sided formwork 80b shown in Figure 15 are joined via the first resin sheet 32a. Furthermore, the third single-sided formwork 80c and the fourth single-sided formwork 80d shown in Figure 15 are joined via the second resin sheet 32b. Subsequently, the second single-sided formwork 80b and the third single-sided formwork 80c are joined together via the third resin sheet 32c.

[0162] As shown in Figure 16, the hollow structure film 1 of Modified Example 5 may include a metal layer 40 that constitutes at least a part of at least one of the first surface 1a and the second surface 1b of the hollow structure film 1. As shown in Figure 16, the hollow structure film 1 of Modified Example 5 may also include a metal adjacent layer 60 that joins the metal layer 40 to the base 10. In this case, the metal layer 40 may be joined to one of the single-sided shaped bodies 80 via the metal adjacent layer 60 before the step of heat-pressing the single-sided shaped bodies 80 and the resin sheet 32, or it may be joined to the base 10 via the metal adjacent layer 60 after the step of heat-pressing the single-sided shaped bodies 80 and the resin sheet 32.

[0163] According to the method for manufacturing a hollow structure film and the hollow structure film 1 of Modification 5, it is possible to provide a hollow structure film 1 with a particularly large thickness.

[0164] <Variation 6> The shapes of the connecting portion 24 and the support portion 20 are not limited to the examples described in the above embodiments and their respective modifications. The hollow structure film 1 has a first end portion 1d and a second end portion 1e as ends in the first direction d1. In the hollow structure film 1, the connecting portion 24 and the support portion 20 do not necessarily extend from the first end portion 1d to the second end portion 1e.

[0165] In the example shown in Figure 2 above, the base 10 has a plurality of connecting portions 24 extending in the first direction d1, and no connecting portions 24 extending in directions other than the first direction d1. Furthermore, in the example shown in Figure 2 above, the hollow structure film 1 has a plurality of support portions 20 extending in the first direction d1, and no support portions 20 extending in directions other than the first direction d1. In the example shown in Figure 2 above, the connecting portions 24 and support portions 20 extend from the first end portion 1d to the second end portion 1e. However, with respect to the hollow structure film 1 that does not have connecting portions 24 and support portions 20 extending in directions other than the first direction d1, the form of the connecting portions 24 and support portions 20 is not limited to this. Figure 17A is a plan view showing an example of the hollow structure film 1 of modified example 6 as observed from the thickness direction of the hollow structure film 1, and corresponds to Figure 2. In other words, Figure 17A is a plan view showing one of a pair of bases 10 (first base 11) in an example of a hollow structure film 1, as observed from the thickness direction of the hollow structure film 1, using the same representation as in Figure 2. As shown in Figure 17A, the connecting portion 24 and the support portion 20 do not necessarily extend from the first end 1d to the second end 1e. In the example shown in Figure 17A, the connecting portion 24 and the support portion 20 are not located at the first end 1d. Furthermore, in the example shown in Figure 17A, the connecting portion 24 and the support portion 20 are not located at the second end 1e.

[0166] Figure 17B is a perspective view showing a single-sided formwork 80 used in the manufacture of the hollow structure film 1 shown in Figure 17A. In figures showing the single-sided formwork 80, including Figure 17B, the direction that becomes the first direction d1 when the hollow structure film 1 is manufactured using the single-sided formwork 80 is indicated as the first direction d1. Furthermore, the direction that becomes the second direction d2 when the hollow structure film 1 is manufactured using the single-sided formwork 80 is indicated as the second direction d2. The hollow structure film 1 shown in Figure 17A can be manufactured using the single-sided formwork 80 shown in Figure 17B. The single-sided formwork 80 has a first end 801 and a second end 802 as ends in the first direction d1. In the example shown in Figure 17B, the protrusion 82 does not extend from the first end 801 to the second end 802. In the example shown in Figure 17B, the protrusion 82 is not located at the first end 801. Furthermore, in the example shown in Figure 17B, the protrusion 82 is not located at the second end 802.

[0167] In the example shown in Figure 9 above, the hollow structure film 1 has a third end 1f and a fourth end 1g as ends in the third direction d3. In the example shown in Figure 9 above, the base 10 has a plurality of connecting portions 24, a first connecting portion 24a extending in the first direction d1 and a second connecting portion 24b extending in the third direction d3. Furthermore, in the example shown in Figure 9 above, the hollow structure film 1 has a plurality of support portions 20 extending in the first direction d1 and a plurality of support portions 20 extending in the third direction d3. In the example shown in Figure 9 above, the first connecting portion 24a and the support portion 20 extending in the first direction d1 extend from the first end 1d to the second end 1e. In the example shown in Figure 9 above, the second connecting portion 24b and the support portion 20 extending in the third direction d3 extend from the third end 1f to the fourth end 1g. However, with respect to a hollow structure film 1 in which the base 10 has a first connecting portion 24a and a second connecting portion 24b, and a support portion 20 extending in a first direction d1 and a support portion 20 extending in a third direction d3, the form of the connecting portion 24 and the support portion 20 is not limited thereto. Figures 18A, 18B, and 18C are plan views showing an example of the hollow structure film 1 of modified example 6 as observed from the thickness direction of the hollow structure film 1, and correspond to Figure 2. As shown in Figures 18A, 18B, and 18C, the first connecting portion 24a and the support portion 20 extending in the first direction d1 do not have to extend from the first end 1d to the second end 1e. As shown in Figures 18A, 18B, and 18C, the second connecting portion 24b and the support portion 20 extending in the third direction d3 do not have to extend from the third end 1f to the fourth end 1g. In the examples shown in Figures 18A, 18B, and 18C, the connecting portion 24 and the support portion 20 are not located at the first end 1d. In the examples shown in Figures 18A, 18B, and 18C, the connecting portion 24 and the support portion 20 are not located at the second end 1e. In the examples shown in Figures 18A, 18B, and 18C, the connecting portion 24 and the support portion 20 are not located at the third end 1f. Furthermore, in the examples shown in Figures 18A, 18B, and 18C, the connecting portion 24 and the support portion 20 are not located at the fourth end 1g.

[0168] As shown in Figure 18A, the first connecting portion 24a and the second connecting portion 24b may be spaced apart from each other. The support portion 20 extending in the first direction d1 and the support portion 20 extending in the third direction d3 may be spaced apart from each other.

[0169] As shown in Figures 18B and 18C, the first connecting portion 24a and the second connecting portion 24b may be connected to each other. The support portion 20 extending in the first direction d1 and the support portion 20 extending in the third direction d3 may be connected to each other. In this case, as shown in Figure 18B, a "+" shape may be formed by connecting the first connecting portion 24a and the second connecting portion 24b to each other. A "+" shape may be formed by connecting the support portion 20 extending in the first direction d1 and the support portion 20 extending in the third direction d3 to each other. As shown in Figure 18C, an L-shape may be formed by connecting the first connecting portion 24a and the second connecting portion 24b to each other. An L-shape may be formed by connecting the support portion 20 extending in the first direction d1 and the support portion 20 extending in the third direction d3 to each other.

[0170] The hollow structure film 1 shown in Figures 18A, 18B, and 18C can be manufactured using a single-sided formwork 80 having a corresponding shape. As an example, the single-sided formwork 80 used in the manufacture of the hollow structure film 1 shown in Figure 18A will be described. Figure 18D is a perspective view showing the single-sided formwork 80 used in the manufacture of the hollow structure film 1 shown in Figure 18A. In Figure 18D, the direction that becomes the third direction d3 when the hollow structure film 1 is manufactured using the single-sided formwork 80 is shown as the third direction d3. The single-sided formwork 80 has a first end 801 and a second end 802 as ends in the first direction d1. The single-sided formwork 80 has a third end 803 and a fourth end 804 as ends in the third direction d3. In the example shown in Figure 18D, the single-sided form 80 includes a convex portion 82 extending in a first direction d1 and a convex portion 82 extending in a third direction d3. In the example shown in Figure 18D, the convex portion 82 extending in the first direction d1 does not extend from the first end 801 to the second end 802. In the example shown in Figure 18D, the convex portion 82 extending in the third direction d3 does not extend from the third end 803 to the fourth end 804. In the example shown in Figure 18D, the convex portion 82 is not located at the first end 801. In the example shown in Figure 18D, the convex portion 82 is not located at the second end 802. In the example shown in Figure 18D, the convex portion 82 is not located at the third end 803. Furthermore, in the example shown in Figure 18D, the convex portion 82 is not located at the fourth end 804.

[0171] The hollow structure film 1 in the modified example 6 also forms a hollow structure, thereby keeping the dielectric constant low.

[0172] <Example 7> The shapes of the connecting portion 24 and the support portion 20 are not limited to the examples described in the above embodiments and each modified example. The contour shape of the connecting portion 24 and the support portion 20, as observed from the thickness direction of the hollow structure film 1, may be a shape other than a rectangle having a short side and a long side. Figures 19A, 19B, and 19C are plan views showing an example of the hollow structure film 1 of Modified Example 7 as observed from the thickness direction of the hollow structure film 1, and correspond to Figure 2. In the example shown in Figure 19A, the contour shape of the connecting portion 24 and the support portion 20, as observed from the thickness direction of the hollow structure film 1, is a square. In the examples shown in Figures 19B and 19C, the contour shape of the connecting portion 24 and the support portion 20, as observed from the thickness direction of the hollow structure film 1, is circular. Although not shown, the contour shape of the connecting portion 24 and the support portion 20, as observed from the thickness direction of the hollow structure film 1, may also be elliptical. In the hollow structure film 1, the connecting portion 24 and the support portion 20 do not necessarily have to extend in the first direction d1.

[0173] Furthermore, the method of arranging the connecting portion 24 and the support portion 20 is not particularly limited as long as it can form a continuous support portion 23. In the examples shown in Figures 19A, 19B, and 19C, the connecting portion 24 and the support portion 20 are arranged regularly. In the examples shown in Figures 19A, 19B, and 19C, the connecting portion 24 and the support portion 20 are arranged at equal intervals. Although not shown, the connecting portion 24 and the support portion 20 may be arranged randomly. The hollow structure film 1 may have regions in which the connecting portion 24 and the support portion 20 are arranged regularly, and regions in which the connecting portion 24 and the support portion 20 are arranged randomly.

[0174] As shown in Figures 19A and 19B, the connecting portion 24 and the support portion 20 may be arranged along a fourth direction d4, which is the direction in which one of the end sides 1h of the hollow structure film 1 extends, and a fifth direction d5 that intersects the fourth direction d4. In the example shown in Figures 19A and 19B, the fourth direction d4 and the fifth direction d5 are orthogonal.

[0175] As shown in Figure 19C, the connecting portion 24 and the support portion 20 may be arranged along the sixth direction d6 and the seventh direction d7 which intersects the sixth direction d6. The sixth direction d6 is a direction nonparallel to the direction in which the end edge 1h of the hollow structure film 1 extends. The seventh direction d7 is a direction nonparallel to the direction in which the end edge 1h of the hollow structure film 1 extends and is also nonparallel to the sixth direction d6. In the example shown in Figure 19C, the sixth direction d6 and the seventh direction d7 are orthogonal.

[0176] The hollow structure film 1 shown in Figures 19A, 19B, and 19C can be manufactured using a single-sided formwork 80 having a corresponding shape. Figure 18D is a perspective view showing a single-sided formwork 80 used in the manufacture of the hollow structure film 1 shown in Figure 19A. Figure 19E is a perspective view showing a single-sided formwork 80 used in the manufacture of the hollow structure film 1 shown in Figure 19B. Figure 19F is a perspective view showing a single-sided formwork 80 used in the manufacture of the hollow structure film 1 shown in Figure 19C. In the example shown in Figure 19D, the convex portion 82 has the shape of a truncated square pyramid, particularly a regular truncated square pyramid. In the examples shown in Figures 19E and 19F, the convex portion 82 has the shape of a truncated cone.

[0177] In the examples shown in Figures 19D and 19E, the protrusions 82 are arranged along the eighth direction d8, which is the direction in which one of the edges 805 of the single-sided formwork 80 extends, and the ninth direction d9, which intersects the eighth direction d8. In the examples shown in Figures 19D and 19E, the eighth direction d8 and the ninth direction d9 are orthogonal.

[0178] In the example shown in Figure 19F, the protrusions 82 are arranged along the 10th direction d10 and the 11th direction d11 which intersects the 10th direction d10. The 10th direction d10 is a direction nonparallel to the direction in which the edge 805 of the single-sided formwork 80 extends. The 11th direction d11 is a direction nonparallel to the direction in which the edge 805 of the single-sided formwork 80 extends, and also nonparallel to the 10th direction d10. In the example shown in Figure 19F, the 10th direction d10 and the 11th direction d11 are orthogonal.

[0179] The hollow structure film 1 in the modified example 7 also forms a hollow structure, thereby keeping the dielectric constant low. [Examples]

[0180] Next, specific examples of the embodiments and their respective modifications described above will be presented. In order to evaluate the porosity, dielectric constant, dielectric loss tangent, CTE of the main body portion 1c, and the ease with which the copper foil peels off from the main body portion 1c when the copper foil is joined to the main body portion 1c of the hollow structure film 1 in which the main body portion 1c contains an inorganic material member 70, the hollow structure film 1 of Examples 1 to 3 and the film of Comparative Example 1 were prepared.

[0181] (Example 1) A hollow structure film 1 similar to the hollow structure film 1 shown in Figure 1A was manufactured. First, a pair of single-sided formwork 80 were produced using a mold 90. At this time, Kapton® manufactured by Toray DuPont Co., Ltd. was prepared as a peelable substrate. Furthermore, a mixture of resin and electron beam crosslinking agent was prepared as the material for the formwork corresponding part 13. High-density polyethylene raw material pellets (product name "Hyzex® 5000SR", manufactured by Prime Polymer Co., Ltd.) were used as the resin. This resin corresponds to high-density polyethylene (HDPE). TAIC® (manufactured by Shinryo Co., Ltd.) was used as the electron beam crosslinking agent. The ratio of the mass of the resin to the total mass of the resin and electron beam crosslinking agent was 98% by mass. The ratio of the mass of the electron beam crosslinking agent to the total mass of the resin and electron beam crosslinking agent was 2% by mass.

[0182] Next, using a mold 90 having a surface 90a with a shape corresponding to the shape of the single-sided formwork 80 to be manufactured, the material for the formwork-compatible part 13 was molded onto a peelable substrate. This produced a pair of single-sided formwork 80 from the material for the formwork-compatible part 13. When molding the material for the formwork-compatible part 13, a sheet-like inorganic material member 70 was placed on top of the mixture of resin and electron beam crosslinking agent before molding. During molding, the mixture of resin and electron beam crosslinking agent and the inorganic material member 70 were press-formed. This press-formed process caused some of the material originating from the mixture of resin and electron beam crosslinking agent to move through the interior of the inorganic material member 70 to the upper side of the inorganic material member 70. This resulted in the production of a pair of single-sided formwork 80, as shown in Figure 8D, in which the base portion 81 includes a sheet-like inorganic material member 70. In particular, a pair of single-sided molded bodies 80 were fabricated, each having a base 81 comprising a sheet-like inorganic material member 70 and a material derived from a mixture of resin and an electron beam crosslinking agent surrounding the inorganic material member 70. Glass cloth (product name "LU1017:L01Z (vinylsilane-based treatment)", manufactured by Unitika Ltd.) was used as the sheet-like inorganic material member 70. The fabricated pair of single-sided molded bodies 80 had a sheet-like base 81 and a plurality of protrusions 82 formed on one surface of the base 81. The thickness of the single-sided molded body 80 (the sum of the thickness of the base 81 and the dimensions of the protrusions 82 in the thickness direction of the base 81) was 150 μm.

[0183] Furthermore, a resin sheet 32 ​​was prepared to be used as the material for the central part 30. A resin sheet 32, in which the resin material was molded into a sheet, was used. The resin material contained in the resin sheet 32 ​​was linear low-density polyethylene raw material pellets (product name "DOWLEX(registered trademark): 2045.11G (C8 copolymer)", manufactured by Dow Chemical). This resin corresponds to linear low-density polyethylene (LLDPE). The thickness of the resin sheet 32 ​​was set to 50 μm.

[0184] Next, a pair of laminates, each containing a single-sided molded body 80 and a peelable substrate, were stacked on top of each other such that some of the protrusions 82 of the pair of single-sided molded bodies 80 faced each other. In this way, the pair of single-sided molded bodies 80 were stacked so that some of the protrusions 82 faced each other. At this time, a resin sheet 32 ​​was placed between the pair of single-sided molded bodies 80.

[0185] Next, the pair of single-sided molded bodies 80 were heat-pressed together. In particular, by heat-pressing the pair of single-sided molded bodies 80 together, the pair of single-sided molded bodies 80 were joined to the resin sheet 32 ​​at multiple protrusions 82. In this way, the pair of single-sided molded bodies 80 were joined via the resin sheet 32. The heating temperature when heat-pressing the pair of single-sided molded bodies 80 together was set higher than the Vicat softening point of the resin contained in the central portion 30.

[0186] Next, the peelable substrate was peeled off from the pair of single-sided molded bodies 80.

[0187] Next, a crosslinking process was performed in which the electron beam crosslinking agent and the resin contained in the single-sided formwork 80 were irradiated with an electron beam to react the electron beam crosslinking agent and the resin. The electron beam used for irradiation was an electron beam with an acceleration voltage of 200kV, a current of 5mA, and an irradiation dose of 289kGy. Furthermore, in the crosslinking process, the resin contained in the resin sheet 32 ​​was irradiated with an electron beam to react the resin. More specifically, in the crosslinking process, the electron beam crosslinking agent and resin contained in the single-sided formwork 80, and the resin contained in the resin sheet 32 ​​were simultaneously irradiated with an electron beam. As a result, the electron beam crosslinking agent and the resin reacted in the single-sided formwork 80, and at the same time, the resin reacted in the resin sheet 32. This produced the hollow structure film 1 shown in Figure 1A. The ratio of the width w2 to the spacing w1 of the hollow structure film 1 was set to 1:3.

[0188] (Example 2) Except for the following points, the hollow structure film 1 was manufactured in the same manner as in Example 1. In Example 2, the hollow structure film 1 was manufactured in the same manner as the hollow structure film 1 shown in Figure 1B. In Example 2, when molding the material for the formwork corresponding part 13, the sheet-like inorganic material member 70 was not placed inside the mixture of resin and electron beam crosslinking agent. In Example 2, when molding the material for the formwork corresponding part 13, a plurality of rod-shaped inorganic material members 70 were placed inside the mixture of resin and electron beam crosslinking agent before molding. When producing a pair of single-sided formwork 80, the amount of rod-shaped inorganic material member 70 added was 30% by mass in terms of the mass ratio to the total mass of the resin, electron beam crosslinking agent and inorganic material member 70. As a result, a pair of single-sided formwork 80 was produced in which the base portion 81 and a plurality of protrusions 82 all contain rod-shaped inorganic material members 70, as shown in Figure 8E. In Example 2, when forming the resin sheet 32 ​​into a sheet, a plurality of rod-shaped inorganic material members 70 were placed inside the mixture of resin and electron beam crosslinking agent, which are the materials of the resin sheet 32, before forming. The amount of rod-shaped inorganic material members 70 added when producing the resin sheet 32 ​​was 30% by mass, in terms of the mass ratio to the total mass of the resin, electron beam crosslinking agent, and inorganic material members 70. Glass fiber (product name "SS05DE-413SP", manufactured by Nitto Boseki Co., Ltd.) was used as the rod-shaped inorganic material members 70. As a result, a resin sheet 32 ​​containing rod-shaped inorganic material members 70 was produced as shown in Figure 8E. Using the pair of single-sided formwork 80 and the resin sheet 32 ​​produced as described above, a hollow structure film 1 shown in Figure 1B was manufactured.

[0189] (Example 3) A hollow structure film 1 was manufactured in the same manner as in Example 2, except for the following points. In Example 3, a plurality of flake-shaped inorganic material members 70 were used as the inorganic material member 70. With respect to the mixture of resin and electron beam crosslinking agent used as the material for the formwork corresponding part 13, the ratio of the mass of the resin to the total mass of the resin and electron beam crosslinking agent was set to 60% by mass. When producing a pair of single-sided formwork 80, the amount of flake-shaped inorganic material member 70 added was set to 40% by mass in terms of the mass ratio to the total mass of the resin, electron beam crosslinking agent and inorganic material member 70. The product name "REF015A" (manufactured by Nippon Sheet Glass Co., Ltd.) was used as the flake-shaped inorganic material member 70.

[0190] (Comparative Example 1) A film was prepared by dispersing an electron beam crosslinking agent in a resin and forming it into a sheet, which was designated as the film of Comparative Example 1. The resin material used in the film of Comparative Example 1 was high-density polyethylene raw material pellets (product name "Hyzex (registered trademark) 5000SR", manufactured by Prime Polymer Co., Ltd.). This resin is high-density polyethylene (HDPE). The electron beam crosslinking agent used in the film of Comparative Example 1 was TAIC (registered trademark) (manufactured by Shinryo Co., Ltd.). The ratio of the mass of the resin to the total mass of the resin and electron beam crosslinking agent was 95% by mass. The ratio of the mass of the electron beam crosslinking agent to the total mass of the resin and electron beam crosslinking agent was 5% by mass. The thickness of the film of Comparative Example 1 was 350 μm.

[0191] (1) Measurement test of porosity Next, porosity measurement tests were conducted on the hollow structure film 1 of Examples 1 to 3. In the porosity measurement tests, images of cross-sections of the hollow structure film 1, obtained by cutting through a plane passing through multiple support portions 20 and perpendicular to the first direction d1, were acquired using a scanning electron microscope (SEM). On the acquired images, the aforementioned straight lines L2 and L3 were drawn. Subsequently, the ratio of the area of ​​the hollow portion B to the total area of ​​the hollow structure film 1 including the hollow portion B, between straight lines L2 and L3, was calculated. This ratio was calculated at 10 different locations on the cross-section. The porosity of the hollow structure film 1 was obtained by averaging the ratios calculated at these 10 different locations. The porosity of Comparative Example 1, which does not have a hollow portion B, was set to 0.

[0192] (2) Measurement test of dielectric constant and dielectric loss tangent Next, dielectric constant and dielectric loss tangent measurements were performed on the hollow structure film 1 of Examples 1 to 3 and the film of Comparative Example 1. In the dielectric constant and dielectric loss tangent measurement tests, a cavity resonance method measuring device (product name "S-parameter network analyzer 8722ES", manufactured by Agilent Technologies, Inc.), a cavity resonator, and the program CPMA-V2 installed on a notebook PC were used as the measuring device, and the dielectric constant and dielectric loss tangent were measured by the following method. Rectangular samples with a short side of 2 mm and a long side of 100 mm were cut from the hollow structure film 1 of each example and the film of the comparative example. Subsequently, the measuring device was started up. Then, the sample was inserted into the cavity of the cavity resonator of the measuring device from one of its short sides, and the dielectric constant and dielectric loss tangent of the sample were measured. The dielectric constant and dielectric loss tangent of the same sample were measured three times, and the average value of the three measurement results was used as the measured value of dielectric constant and dielectric loss tangent. Furthermore, as an index value for comparing the magnitude of transmission loss (also called the "transmission loss coefficient"), we calculated the product of the square root of the relative permittivity calculated from the measured permittivity and the measured dielectric loss tangent.

[0193] (3) Measurement test of CTE Next, CTE measurement tests were performed on the hollow structure film 1 of Examples 1 to 3 and the film of Comparative Example 1. In the CTE measurement tests, the CTE of the main body portion 1c of the hollow structure film 1 of Examples 1 to 3 and the film of Comparative Example 1 were measured. The CTE was measured by the following method. A thermomechanical analyzer (product name "TMA-60", manufactured by Shimadzu Corporation) was used as the measuring device. First, rectangular samples 97, with a short side 972 of 5 mm and a long side 971 of 14 mm, as shown in Figure 20, were cut from the hollow structure film 1 of Examples 12 to 14 and the film of Comparative Example 7. The region of sample 97 with a width w15 of 2 mm in the direction in which the long side 971 extends, with the short side 972 as one end, is called the chucking region 98. Sample 97 has a pair of chucking regions 98, a first chucking region 981 and a second chucking region 982. An intermediate region 99 is formed between the first chucking region 981 and the second chucking region 982, with a width w16 of 10 mm in the direction in which the long side 971 extends. For the CTE measurement, the first chucking region 981 was fixed to the first fixture by sandwiching the entire first chucking region 981 with the first fixture. Furthermore, the second chucking region 982 was fixed to the second fixture by sandwiching the entire second chucking region 982 with the second fixture. Subsequently, a load of 3.0 g was applied to the intermediate region 99 of the sample 97 located between the first and second fixtures via the first and second fixtures. With the intermediate region 99 thus loaded with a load of 3.0 g, the sample 97, the first fixture, and the second fixture were placed inside the temperature-controlled chamber. Subsequently, the temperature inside the temperature-controlled chamber was set to 10°C. Subsequently, the temperature inside the temperature-controlled chamber was increased at a rate of 10°C / min, and the elongation of the intermediate region 99 of sample 97 in the direction of extension of the long side 971 was measured. In particular, the width w16 of the intermediate region 99 was measured when the temperature inside the temperature-controlled chamber reached 25°C, and when the temperature inside the temperature-controlled chamber reached 75°C. From the above measurement results, the elongation rate of the width w16 of the intermediate region 99 when the temperature inside the temperature-controlled chamber was increased from 25°C to 75°C was calculated in parts per million (ppm).Dividing this elongation rate by 50°C gives the equivalent elongation rate of sample 97 when the temperature is increased by 1°C. This value was calculated as the CTE (ppm / °C) value.

[0194] (4) Evaluation test of the ease with which copper foil can be peeled off Next, an evaluation test was conducted on the ease with which the copper foil could be peeled off the hollow structure film 1 of Examples 1 to 3 and the film of Comparative Example 1. In the evaluation test of the ease with which the copper foil could be peeled off, rectangular samples with a long side of 50 mm and a short side of 10 mm were cut from the main body 1c of the hollow structure film 1 of each example and from the film of the comparative example. On these samples, the metal adjacent layer material (30 μm thick, product name "Nucrel (registered trademark) AN4233C", manufactured by Mitsui Dow Polychemical Co., Ltd.) and copper foil (10 μm thick, product name "CF-LB9-10", purchased from Hosen Co., Ltd.) were laminated in this order so as to cover the entire sample. Subsequently, the overlapping parts of the sample, the metal adjacent layer material, and the copper foil were heated and pressed together at 100°C. The pressed area was formed over the entire sample. Subsequently, the pressed area was left in a room at room temperature of 25°C for 48 hours. We observed whether the copper foil peeled off the sample during heat bonding or when left at room temperature.

[0195] Table 3 shows the results of the porosity measurement tests for the hollow structure film 1 of Examples 1 to 3. In addition, Table 1 shows the results of the dielectric constant and dielectric loss tangent measurement tests, the CTE measurement test, and the evaluation test of the ease of peeling of the copper foil for the hollow structure film 1 of Examples 1 to 3 and the film of Comparative Example 1.

[0196] [Table 1]

[0197] From the results shown in Table 1, it was found that the dielectric constant of all three Examples 1 to 3 was lower than that of Comparative Example 1. It was also found that the CTE of all three Examples 1 to 3 was lower than that of Comparative Example 1. Furthermore, it was found that the CTE of all three Examples 1 to 3 was 120 ppm / °C or less. In addition, in the evaluation test of the ease of peeling of the copper foil, no peeling of the copper foil from the sample occurred.

[0198] The multiple components disclosed in the above embodiments and each of the variations can be combined as needed. Alternatively, some components may be removed from all the components shown in the above embodiments and each of the variations. [Explanation of Symbols]

[0199] 1. Hollow structure film 1a 1st page 1b 2nd side 10 base 20 Support section 30 Central part 40 metal layer 60 Metal adjacent layer 70 Inorganic material components 80 Single-sided form 81 Base 82 Convex part 90 molds 100 circuit boards 101 Antenna Equipment

Claims

1. In a hollow structure film having a hollow structure, The main body comprises a sheet-like first base, a sheet-like second base overlapping the first base, and a plurality of support columns provided between the first base and the second base. The first base portion has a first opposing surface that faces the second base portion, The second base portion has a second opposing surface that faces the first base portion, At least a portion of the multiple support columns constitute a continuous support column extending from the first opposing surface to the second opposing surface. The main body includes an insulating inorganic material member, A hollow structured film in which the maximum width of the inorganic material member is three times or more the minimum width of the inorganic material member.

2. The hollow structure film according to claim 1, wherein the inorganic material member is included in at least one of the first base and the second base.

3. The hollow structure film according to claim 1, wherein the inorganic material member is included in at least a portion of the support column portion.

4. The main body further has a sheet-like central portion located between the first opposing surface and the second opposing surface, The hollow structure film according to claim 1, wherein the plurality of support columns are located on the first opposing surface side and the second opposing surface side of the central portion.

5. The hollow structure film according to claim 4, wherein the inorganic material member is included in at least the central portion.

6. The hollow structure film according to claim 1, wherein the inorganic material member includes glass.

7. The hollow structure film according to claim 1, wherein the maximum width of the inorganic material member is 10 μm or more.

8. The hollow structure film according to claim 1, wherein the main body portion contains a polyolefin.

9. The hollow structure film according to claim 1, wherein the thickness is 50 μm or more and 1000 μm or less.

10. The hollow structure film according to claim 1, wherein the porosity is 20% or more.

11. The hollow structure film has a first surface and a second surface located on the opposite side of the first surface. The hollow structure film according to claim 1, further comprising a metal layer constituting at least a portion of at least one of the first surface and the second surface.

12. The metal layer further comprises a metal adjacent layer that joins at least one of the first base and the second base, The hollow structure film according to claim 11, wherein the material of the adjacent metal layer is different from the material of the first base and the second base.

13. The metal layer further comprises a metal adjacent layer that joins at least one of the first base and the second base, The hollow structure film according to claim 11, wherein the material of the adjacent metal layer is an adhesive.

14. The hollow structure film according to claim 11, further comprising an ionomer layer or an ethylene (meth)acrylic acid copolymer layer that joins the metal layer to at least one of the first base and the second base.

15. A hollow structured film according to any one of claims 1 to 10, the hollow structured film having a first surface and a second surface located on the opposite side of the first surface, A circuit board comprising: a wiring pattern provided on at least one of the first surface and the second surface.

16. The circuit board according to claim 15, An antenna device comprising an antenna element connected to the aforementioned circuit board.

17. In a method for manufacturing a hollow structure film having a hollow structure, A step of producing a pair of single-sided molded bodies containing an insulating inorganic material member, each having a sheet-like base and a plurality of protrusions formed on one side of the base, using a mold. The process includes overlapping a pair of the fabricated single-sided molded bodies such that at least some of the protrusions face each other, and then heating and pressing them together, A method for manufacturing a hollow structure film, wherein the maximum width of the inorganic material member is three times or more the minimum width of the inorganic material member.

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