Formed body

Abstract

This formed body includes a binder and a conductive coil, and the average ratio of the longest side to the shortest side in a minimum cuboid surrounding the conductive coil is 1 to 2, inclusive.

Description

Molded body

[0001] The present invention relates to a molded article.

[0002] Communication devices such as mobile phones and smartphones enable wireless communication using electromagnetic waves, and with technological advances in this field, the frequency bands of the electromagnetic waves used have been expanding. Specifically, wireless communication systems complying with the IMT-Advanced standard established by the International Telecommunication Union (ITU) are specified, and the frequency band of first-generation mobile communication systems (1G), which was approximately 800 MHz, has been expanded to approximately 3 GHz in fourth-generation mobile communication systems (4G). Furthermore, the currently adopted fifth-generation mobile communication systems (5G) have expanded their frequency bands to the 28 GHz band in order to achieve higher speeds, larger capacity, lower latency, and multiple connections. Furthermore, development of sixth-generation mobile communication systems (6G), which use frequency bands of 100 GHz or higher, is currently underway as the next-generation communication system. While the use of electromagnetic waves in high frequency bands has attracted attention, the increasing frequency of electromagnetic waves increases the likelihood of electronic device malfunctions, communication disruptions, information leaks, and health problems, necessitating the control of electromagnetic noise (EMC). Specifically, there is a demand for the development of new materials capable of suppressing both EMI (the cause of the problem) and EMS (the cause of the problem of immunity). One approach to solving this problem is the use of electromagnetic wave control materials that can reduce the effects of electromagnetic waves from the surrounding environment. Electromagnetic wave control materials are available in a variety of forms, including semiconductor packages / modules, housings for electrical / electronic devices, adhesives for semiconductor mounting boards or cables, wallpaper for buildings such as server rooms, and clothing such as aprons for protecting the human body.

[0003] There are various types of electromagnetic wave control materials, and extensive research is underway. Examples include reflective materials that reflect electromagnetic waves by using large metal plates, and absorptive materials that absorb electromagnetic waves by using materials in which conductive materials are mixed with organic materials such as resins and rubbers. For example, research on absorptive materials has shown that using substances with structures one order of magnitude smaller than the wavelength of the electromagnetic waves to be shielded is effective, and materials containing small fillers are being developed as a means of forming such structures. Patent Document 1 discloses a sheet that has excellent electromagnetic wave shielding properties at a frequency of 1 GHz, and is made of a composite having an insulating layer and a conductive layer in which a binder resin contains flaky silver powder with a specific particle size and bulk density. Patent Document 2 also discloses a sheet that can shield electromagnetic waves in the frequency range of 1 MHz to 1 GHz, and is made of a composite in which a binder resin contains ferrite particles that are single-crystal and spherical in shape and have a specific average particle size. Furthermore, Patent Document 3 discloses a sheet made of a composite in which a binder resin contains a specific amount or more of nickel nanowires, which has excellent handleability and flexibility and can shield electromagnetic waves in the frequency band of 18.0 to 26.5 GHz.

[0004] On the other hand, the sheets disclosed in Patent Documents 1 to 3 have a problem in that they cannot handle electromagnetic waves in the frequency band of next-generation wireless communication systems, which is an order of magnitude or more greater than the frequency band used in conventional wireless communication systems. To solve this problem, a sheet using a coil-shaped conductive member is being developed, as disclosed in Patent Document 4.

[0005] JP 2011-86930 A, WO 2017 / 212997 A, JP 2019-67997 A, WO 2022 / 009960 A

[0006] Although the sheet disclosed in Patent Document 4 has excellent electromagnetic wave shielding performance, little consideration has been given to the electrical resistance, which can vary depending on the degree of contact between conductive members, leaving room for improvement. For example, when a molded body such as a sheet having electromagnetic wave shielding performance is used as a case to protect elements such as semiconductor elements, a module can be manufactured in which the molded body is provided on a substrate so as to cover semiconductor elements that are susceptible to electromagnetic waves or that easily emit electromagnetic waves, thereby suppressing the penetration of electromagnetic waves into the case and the leakage of electromagnetic waves to the outside of the case. When such a case is used, the terminals of each semiconductor element are generally exposed, and if the case has high conductivity, i.e., a low electrical resistivity, there is a risk of short circuits occurring between the terminals, making it difficult to save space.

[0007] Therefore, an object of the present invention is to provide a sheet that can shield electromagnetic waves in the high frequency band while maintaining high electrical resistivity.

[0008] As a result of extensive research, the present inventors have found that the above problems can be solved by using a binder and a special type of conductive coil, and have arrived at the present invention.

[0009] That is, the present invention has the following features. [1] A molded body comprising a binder and a plurality of conductive coils, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coils is 1 or more and 2 or less. [2] The molded body according to [1], wherein the binder comprises cellulose nanofibers. [3] The molded body according to [1] or [2], wherein the average number of turns of the conductive coils is 1.2 or more and 50 or less. [4] The molded body according to any one of [1] to [3], wherein the conductive member constituting the conductive coils is spiral-shaped. [5] The molded body according to any one of [1] to [3], wherein the content of the conductive coils in the molded body is 0.02 g / cm ３ Above, 5.00g / cm ３The molded article according to any one of [1] to [4], wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less. [6] The molded article according to any one of [1] to [5], which is an electromagnetic wave shielding sheet. [7] A liquid composition comprising a binder and a conductive coil, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less. [8] A molded article which is a cured product of the liquid composition according to [7]. [9] The molded article according to [8], which is an electromagnetic wave shielding sheet.

[10] An electromagnetic wave shield comprising the molded article according to [6] or [9].

[11] A semiconductor module comprising the molded article according to any one of [1] to [6], [8], and [9].

[12] An electronic device comprising the molded article according to any one of [1] to [6], [8], and [9].

[13] An automotive device comprising the molded article according to any one of [1] to [6], [8], and [9].

[14] A consumer electronic device comprising the molded article according to any one of [1] to [6], [8], and [9].

[15] A medical device having the molded article according to any one of [1] to [6], [8] and [9].

[16] An aerospace device having the molded article according to any one of [1] to [6], [8] and [9].

[17] A system having the molded article according to any one of [1] to [6], [8] and [9].

[18] A method for producing a molded article, comprising: a composition preparation step of obtaining a liquid composition containing a binder and a conductive coil; a freezing step of freezing the liquid composition to obtain a frozen body; and a compression step of compressing the frozen body under load to obtain a molded article, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less.

[19] A method for producing the molded article according to

[18] , comprising, between the freezing step and the compressing step, an immersion step of immersing the frozen body in a liquid containing a component that crosslinks the binder.

[20] The method for producing a molded body according to

[19] , wherein the immersion step includes a process of removing a liquid containing a component that crosslinks the binder, and then immersing the frozen body in a liquid other than the liquid.

[0010] According to the present invention, it is possible to provide a lightweight sheet that can shield electromagnetic waves in the high frequency band.

[0011] FIG. 1 is a diagram schematically showing one embodiment of a conductive coil. FIG. 2 is a diagram for explaining the configuration of a conductive coil. FIG. 3 is a diagram schematically showing one embodiment of a conductive coil. FIG. 4 is a scanning electron microscope image of a conductive coil (photograph as a substitute for a drawing). FIG. 5 is a diagram for explaining the configuration of a conductive coil. FIG. 6 is a diagram schematically showing an experimental device for evaluating electromagnetic wave shielding properties. FIG. 7 is a diagram showing the results of the characteristic evaluation of sheets in Example 1 and Comparative Example 1. FIG. 8 is a diagram showing the results of the characteristic evaluation of sheets in Examples 1 to 3. FIG. 9 is a diagram showing the results of the characteristic evaluation of sheets in Examples 4 to 6. FIG. 10 is a diagram showing the results of the characteristic evaluation of sheets in Examples 7 to 11.

[0012] The following describes embodiments of the present invention in detail. However, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope of the present invention. The present disclosure is not limited by the embodiments, but is limited only by the scope of the claims. In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, and "A to B" means A or greater and B or less. Furthermore, when a numerical range expressed as "A to B" or "A or greater and B or less" is stated in stages (e.g., in order of preference), the upper and lower limits of each numerical range can be arbitrarily combined. Furthermore, although multiple embodiments are described in this disclosure, various conditions in each embodiment may be applied to each other to the extent applicable. Furthermore, in this disclosure, the expression "A or B" can be interpreted as "at least one selected from the group consisting of A and B." Furthermore, in this disclosure, "multiple" means "two or more." The dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are merely examples. Furthermore, this embodiment will be described using drawings as appropriate, but the dimensions in the drawings are also examples. Furthermore, when "average" is used in a parameter of a conductive coil, it refers to a value calculated as the average value of multiple conductive coils. For example, the average outer diameter of a conductive coil is a value calculated by measuring the outer diameters of each of multiple conductive coils and averaging them. The number of measurement targets for calculating the average value is not particularly limited, and does not need to be the total number; for example, it may be 10 arbitrarily selected targets, or it may be 50 arbitrarily selected targets. The number of conductive coils in the molded body may be less than 10.

[0013] <Configuration of Molded Body> A molded body (also simply referred to as "molded body") according to one embodiment of the present disclosure is a molded body that includes a binder and a plurality of conductive coils, and in the smallest rectangular parallelepiped that encloses the conductive coils, the average ratio of the longest side to the shortest side is 1 or more and 2 or less.

[0014] The inventors have focused on developing a conductive coil with a central axis as a structure capable of absorbing strong electromagnetic waves in the terahertz region. The coil shape can be considered as a series of connected pseudo-C-shaped plane structures, and by considering these as a circuit, it has been found that an electromagnetic wave absorption effect can be achieved through LC resonance, with the coil shape itself as inductance L and the gap as capacitance C. It has also been found that absorption can be achieved through the resonance effect of a magnetic field entering the coil.

[0015] In the technical field, when a molded article including a conductive coil having a central axis is used as a molded article for electromagnetic wave shielding, a conductive coil whose length in the central axis direction is longer than its outer diameter has conventionally been used. The present inventors speculate that this is because coil shapes with a longer central axis direction are generally used, and it was believed that the longer the conductive coil's length in the central axis direction, the better the electromagnetic wave shielding performance. Furthermore, the inventors speculate that the use of a conductive coil with a longer central axis direction increases the volume of the conductive coil, thereby increasing the density of the conductive coil in the molded article, thereby improving the electromagnetic wave shielding performance. However, when a conductive coil with a longer central axis direction is used, the probability of contact between the conductive coils increases. Contact between the conductive coils decreases the electrical resistivity of the molded article. For example, when the molded article is used in a module (semiconductor module) in which the molded article is mounted on a substrate to cover semiconductor elements, the terminals of the semiconductor elements are generally exposed. Therefore, if the molded article has high conductivity, i.e., low electrical resistivity, there is a risk of short circuits occurring between the terminals. Furthermore, if contact occurs between the conductive coils, current flows between the conductive coils, making it difficult to obtain the LC resonance effect, which tends to reduce the electromagnetic wave shielding performance. Therefore, the inventors conducted extensive research and produced a molded body according to the above embodiment. In this molded body, the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coils is in the range of 1 to 2, making it less likely for the conductive coils to come into contact with each other than in conventional molded bodies, and thus less likely to cause the above problem.

[0016] Furthermore, when conventional conductive coils are used, if the conductive coils are arranged in a random direction without considering the orientation of the conductive coils, the above-mentioned current conduction is likely to occur, and therefore a process of aligning the conductive coils in a fixed direction is often performed. Such a process is time-consuming and problematic from the perspective of manufacturing costs. On the other hand, with the molded body according to the above embodiment, such current conduction problems are unlikely to occur, and therefore it is possible to arrange the conductive coils in a random direction without considering the orientation of the conductive coils, which is advantageous from the perspective of manufacturing costs.

[0017] Furthermore, in the above-described embodiment, a lightweight material such as a polymeric material can be used as the binder, making it easier to reduce the weight compared to conventional embodiments using a metal plate. Furthermore, one of the roles of an electromagnetic wave shielding member is to prevent the reflection of electromagnetic waves incident from the side where the product to be shielded is located. However, when a metal plate is used, it is difficult to prevent reflection because electromagnetic waves are generally reflected by the metal surface. On the other hand, in the above-described embodiment, a polymeric material or the like that easily prevents the reflection of electromagnetic waves and also easily absorbs electromagnetic waves can be used as the binder, making it superior in terms of electromagnetic wave shielding performance.

[0018] Conventionally, metal cases, primarily stainless steel cases, have been used as electromagnetic wave shields in semiconductor modules. Such stainless steel cases can shield external electromagnetic waves by reflecting them. While reflection can block the entry and exit of electromagnetic waves, the presence of multiple semiconductor elements within the case raises the risk of diffused reflection of electromagnetic waves emitted from the semiconductor elements, potentially causing malfunctions in adjacent semiconductor elements. Furthermore, stainless steel cases are conductive, and in order to prevent the aforementioned short circuit, they must be installed so as not to come into contact with exposed terminals, limiting their space-saving potential. When a conventional stainless steel case is replaced with the molded article according to the present embodiment, the absorber is less likely to cause diffused reflection within the case, reducing the risk of malfunction. Furthermore, due to its high resistance, it can be used in contact with exposed terminals, facilitating space savings. Furthermore, the molded article according to the present embodiment can be molded by coating or spraying, allowing it to adhere closely to multiple semiconductor elements, including their terminals, thereby achieving extreme space savings while maintaining its absorber performance.

[0019] The use of the above-mentioned molded article is not particularly limited, but it is suitably used as an electromagnetic wave shielding sheet, etc. In the following explanation, the molded article in the form of a sheet, particularly an electromagnetic wave shielding sheet, will be specifically described. Hereinafter, the term "sheet" can be interchangeably referred to as "molded article."

[0020] [Conductive Coil] (Configuration of Conductive Coil) The conductive coil has a coil shape (spiral shape) having a central axis. In the present disclosure, a coil shape refers to a shape consisting of a structure surrounding the central axis and a structure extending in the direction of the central axis, or a shape consisting of a structure surrounding the central axis and extending in the direction of the central axis. This structure surrounding the central axis may be a structure having a circular circumferential shape or a structure having a polygonal circumferential shape. Specific examples of the coil shape include a spiral shape having a central axis as shown in FIG. 1( a). Note that the conductive coil need not only have a straight central axis, but may also have a central axis that can approximate a straight line. When the central axis can approximate a straight line, the approximated straight line serves as the central axis. Furthermore, the winding direction of the coil shape is not particularly limited, and a mixture of right-handed and left-handed windings may be used, but it is preferable that the winding direction be consistent with one of the two.

[0021] The cross-sectional shape of the wire that constitutes the coil shape is not particularly limited and may be, for example, circular or polygonal such as triangular or rectangular, but from the standpoint of ease of availability and ease of manufacture, circular is preferable.

[0022] The average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil (also simply referred to as the "average rectangular parallelepiped ratio") is not particularly limited as long as it is 1 or more and 2 or less, from the viewpoint of easily preventing current flow between each conductive coil, but is preferably 1.7 or less, more preferably 1.5 or less, even more preferably 1.2 or less, particularly preferably 1.1 or less, and most particularly preferably 1.05 or less. The smaller the average ratio, the more preferable it is, and the lower limit may be 1 or more. The smallest rectangular parallelepiped enclosing the conductive coil is the rectangular parallelepiped indicated by the dotted line in Figure 1(b).

[0023] The shortest and longest sides of the smallest rectangular parallelepiped surrounding the conductive coil can be measured by observing the sheet with a microscope such as an optical microscope. In particular, if the cross section of the conductive coil is circular, the size of the rectangular parallelepiped can be determined from the length of the conductive coil in the central axis direction and the diameter of the circle. Furthermore, if the conductive coil contained in the sheet cannot be observed, the conductive coil may be removed from the sheet and directly observed. In particular, if the binder can be dissolved, the conductive coil can be removed and directly observed.

[0024] The type of material for the conductive coil is not particularly limited as long as it is conductive, and examples thereof include carbon materials such as carbon, copper (Cu), aluminum (Al), iron (Fe), gold (Au), silver (Ag), platinum (Pt), magnesium (Mg), zinc (Zn), tungsten (W), titanium (Ti), nickel (Ni), or manganese (Mn), alloys of combinations of these metal elements, or metal-containing compounds such as oxides, halides, or sulfides of these metal elements or alloys. Copper (Cu), iron (Fe), or tungsten (W) are preferred, and tungsten (W) is particularly preferred, from the viewpoint that the elastic modulus is suitable for coil processing, and when contained in a binder, the corrosion resistance is good and the linear expansion coefficient is small, resulting in good durability of the sheet.

[0025] The content of the conductive coil in the sheet is not particularly limited, and the preferred range varies depending on the material of the conductive coil. However, from the viewpoint of improving the electromagnetic wave shielding property, the content per volume of the sheet is usually 0.01 g / cm. ３ or more, and 0.02 g / cm ３ It is preferable that the density is 0.15 g / cm or more. ３ More preferably, it is 0.2 g / cm or more. ３ More preferably, it is 0.3 g / cm or more. ３ It is particularly preferable that the concentration is 0.5 g / cm or more. ３ It is most preferable that the thickness is 5.00 g / cm or more. From the viewpoint of preventing contact between the coils as much as possible, it is usually 5.00 g / cm ３or less, or 5.00 g / cm ３ less than 4.00 g / cm ３ Preferably, it is 3.00 g / cm or less. ３ More preferably, it is 2.00 g / cm or less. ３ More preferably, it is 1.50 g / cm or less. ３ More preferably, it is 0.90 g / cm or less. ３ It is even more preferable that:

[0026] The arrangement of the conductive coils is not particularly limited and may be randomly arranged, preferably arranged to form a metamaterial structure. In the present disclosure, a metamaterial structure refers to an arrangement in which the conductive coils are aligned in a sheet, more specifically, an arrangement in which the conductive coils are periodically arranged in a binder. The arrangement is not particularly limited and may include an arrangement in which the conductive coils are aligned to form a circle or a polygon such as a triangle or a square. This aligned arrangement may be configured in one layer or in two or more layers. In addition, when a sheet is formed by stacking multiple layers, the arrangement of the conductive coils in each layer can be set arbitrarily. For example, the arrangement of the conductive coils in all layers may be random, or the arrangement of the conductive coils in all layers may be configured to form a metamaterial structure, or a laminate may be formed by combining these arrangements.

[0027] One embodiment of a conductive coil is shown in Figure 2. The upper view in Figure 2 is a view of the conductive coil observed from the direction of the central axis of the coil, and the lower view in Figure 2 is a view of the conductive coil observed from a direction at an angle of 90° to the central axis. In Figure 2, l is the average outer diameter, m is the average winding pitch width, and n is the average length of the conductive coil in the direction of the central axis. These parameters can be measured by internal observation using CT-X-rays.

[0028] The average outer diameter 1 of the conductive coil (also simply referred to as the "outer diameter of the coil shape") is not particularly limited as long as it is selected so as to maintain the average ratio of the rectangular parallelepiped described above, and may be 10 μm or more, 30 μm or more, 100 μm or more, or 300 μm or more. On the other hand, from the viewpoint of being able to make the molded body thin and from the viewpoint that the molded body of this embodiment easily absorbs electromagnetic waves in a wide frequency band, the average outer diameter 1 is preferably small, and is usually 10,000 μm or less, preferably 1,000 μm or less, more preferably 800 μm or less, even more preferably 750 μm or less, particularly preferably 600 μm or less, and most preferably 500 μm or less.

[0029] The average winding pitch width m of the coil shape (also simply referred to as "winding pitch width of the coil shape") is not particularly limited as long as it is selected so as to maintain the average ratio of the rectangular parallelepiped described above, and its lower limit may be equal to or greater than the lower limit value of the average strand diameter p described below. Furthermore, from the viewpoint of preventing the strand portions from becoming sparse and reducing the electromagnetic wave shielding performance, its upper limit is usually 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 70 μm or less.

[0030] The average length n of the coil-shaped portion of the conductive coil in the central axis direction (also simply referred to as "the length of the coil-shaped portion in the central axis direction of the coil shape") is not particularly limited as long as it is selected so as to maintain the average ratio of the rectangular parallelepiped described above, and may be 20 μm or more, 35 μm or more, 50 μm or more, 100 μm or more, or 300 μm or more. On the other hand, from the viewpoint of being able to make the molded body thin and from the viewpoint that the molded body of this embodiment easily absorbs electromagnetic waves in a wide frequency band, the average length n is preferably small, and is usually 10,000 μm or less, preferably 1,000 μm or less, more preferably 800 μm or less, even more preferably 750 μm or less, particularly preferably 600 μm or less, and most preferably 500 μm or less.

[0031] The average wire diameter p of the conductive coil (also simply referred to as "wire diameter of the coil shape") is not particularly limited, but from the viewpoint of improving rigidity and making it less likely to deform during molding by injection molding or the like, it is usually more than 1 μm (larger than 1 μm), preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, and may be one-third or less of the average outer diameter l. Furthermore, from the viewpoint of reducing weight, the average wire diameter p is usually 75 μm or less, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less.

[0032] The average length of the wires per conductive coil (also simply referred to as "wire length") is not particularly limited, but from the viewpoint of improving shielding performance, it is preferably 1,000 μm or more, more preferably 10,000 μm or more, even more preferably 40,000 μm or more, and particularly preferably 100,000 μm or more; and from the viewpoint of increasing the coil size per coil and making it difficult to make the molded body thin, it is preferably 1,000,000 μm or less, more preferably 800,000 μm or less, even more preferably 500,000 μm or less, and particularly preferably 300,000 μm or less.

[0033] The total wire length of the entire coil contained per unit volume of the sheet (also simply referred to as the "total wire length of the entire coil") is not particularly limited, but from the viewpoint of improving shielding performance, it is preferable that the total wire length be 10 m / cm ３ It is preferable that the thickness is 20 m / cm or more. ３ More preferably, it is 30 m / cm or more. ３ More preferably, it is 50 m / cm or more. ３ It is particularly preferable that the thickness is 2,000 m / cm or more, and from the viewpoint of preventing contact between the coils, ３ Preferably, it is 1,000 m / cm or less. ３ More preferably, it is 500 m / cm or less. ３ It is even more preferable that:

[0034] The average number of turns of the conductive coil (also simply referred to as "number of turns") is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 1 or more, preferably 1.2 or more, more preferably 1.5 or more, and even more preferably 3 or more, and is usually 100 or less, preferably 50 or less, more preferably 30 or less, and even more preferably 20 or less.

[0035] (Double Coil) As shown in Figures 3 and 4, the conductive member constituting the conductive coil may be spiral. In the present disclosure, such a conductive coil is referred to as a "double coil," while a normal conductive coil without such a spiral shape is referred to as a "single coil." A double coil can be manufactured by a known method (e.g., a method of spiraling a single coil), and commercially available products may be used. Furthermore, "the conductive member constituting the conductive coil is spiral" can also be expressed as meaning that a spiral conductive coil further forms a spiral, or that the central axis of the spiral conductive coil is formed to form a spiral, or that the wire forming the conductive coil is spiral.

[0036] FIG. 3 is a schematic diagram of one embodiment of a double coil, and FIG. 4 is a scanning electron microscope image of the double coil. Hereinafter, in a double coil, the helix forming the same helical shape as a single coil is referred to as the "major helix," and the helix formed on the line forming the major helix is ​​referred to as the "minor helix." In a double coil, the central axis of the above-described coil shape corresponds to the central axis of the major helix. In FIG. 3, G represents the central axis of the major helix, and H represents the central axis of the minor helix. In the electromagnetic wave shielding sheet according to this embodiment, when electromagnetic waves pass through the interior of the major helix, the effect of absorbing the electromagnetic waves is exerted by the LC resonance derived from the major helix. Furthermore, when electromagnetic waves pass through the interior of the minor helix, the effect of absorbing the electromagnetic waves is also exerted by the LC resonance derived from the minor helix. This allows electromagnetic waves incident from various directions to be absorbed regardless of the orientation of the coil. By using a coil having such a structure, the electromagnetic wave shielding sheet according to this embodiment can ensure sufficient shielding against electromagnetic waves in the high-frequency band.

[0037] The central axis of the double-coil large helix need not necessarily be a straight line, but may be one that can approximate a straight line. In cases where the central axis is one that can approximate a straight line, that approximate line becomes the central axis.

[0038] The above-mentioned conditions for the coil structure can be applied regardless of whether the coil is a single coil or a double coil, but the following are structural conditions that are particularly preferably applicable to double coils.

[0039] The content of the double coil in the sheet is not particularly limited, and the preferred range varies depending on the material of the conductive coil. From the viewpoint of improving the electromagnetic wave shielding property, the content per volume of the sheet is usually 0.02 g / cm. ３ or more, and ３ It is preferable that the density is 0.15 g / cm or more. ３ More preferably, it is 0.2 g / cm or more. ３ More preferably, it is 0.3 g / cm or more. ３ It is particularly preferable that the concentration is 0.5 g / cm or more. ３It is most preferable that the thickness is 5.00 g / cm or more. From the viewpoint of preventing contact between the coils as much as possible, it is usually 5.00 g / cm ３ or less, or 5.00 g / cm ３ less than 4.00 g / cm ３ Preferably, it is 3.00 g / cm or less. ３ More preferably, it is 2.00 g / cm or less. ３ More preferably, it is 1.50 g / cm or less. ３ More preferably, it is 0.90 g / cm or less. ３ It is even more preferable that:

[0040] The electromagnetic shielding sheet of this embodiment uses a double coil, which has better electromagnetic shielding properties per coil than a single coil, so when trying to achieve the same level of electromagnetic shielding properties, the electromagnetic shielding sheet of this embodiment can use a smaller amount of conductive coil than an electromagnetic shielding sheet manufactured using a single coil.Since conductive coils are usually more expensive per volume than binders, the electromagnetic shielding sheet of this embodiment has lower material costs than an electromagnetic shielding sheet manufactured using a single coil.

[0041] One embodiment of a double coil is shown in Figure 5. The upper diagram in Figure 5 is a diagram of the double coil observed from the direction of the central axis of the major helix of the double coil, and the lower diagram is a diagram of the double coil observed from a direction 90° to the central axis. In Figure 5, l' is the average outer diameter of the major helix, m' is the average winding pitch width of the major helix, n' is the average length of the double coil in the direction of the central axis of the major helix, p' is the average outer diameter of the minor helix, q' is the average winding pitch width of the minor helix, and r' is the average strand diameter. These parameters can be measured by internal observation using CT-X-rays.

[0042] The average outer diameter l' of the major helix (also simply referred to as "outer diameter of the major helix") is not particularly limited as long as it is selected so as to maintain the average ratio of the rectangular parallelepipeds described above, and may be 10 μm or more, 30 μm or more, 100 μm or more, or 300 μm or more. On the other hand, from the viewpoint of being able to make the molded body thin and from the viewpoint that the molded body of this embodiment easily absorbs electromagnetic waves over a wide frequency band, the average outer diameter l' is preferably small, and is typically 10,000 μm or less, preferably 1,000 μm or less, more preferably 800 μm or less, even more preferably 750 μm or less, particularly preferably 600 μm or less, and most preferably 500 μm or less.

[0043] The average winding pitch width m' of the large spiral (also simply referred to as "winding pitch width of the large spiral") is not particularly limited as long as it is selected so as to maintain the average ratio of the rectangular parallelepipeds described above, and its lower limit may be equal to or greater than the lower limit value of the average outer diameter p' of the small spirals described below. Furthermore, from the viewpoint of preventing the strand portions from becoming coarse and reducing the electromagnetic shielding performance, its upper limit is usually 560 μm or less, preferably 490 μm or less, more preferably 420 μm or less, and even more preferably 350 μm or less.

[0044] The average length n' of the double coil (coil-shaped portion) in the direction of the central axis of the large helix (also simply referred to as "the length of the double coil in the direction of the central axis of the large helix") is not particularly limited as long as it is selected so as to maintain the average ratio of the rectangular parallelepipeds described above, and may be 20 μm or more, 35 μm or more, 50 μm or more, 100 μm or more, or 300 μm or more. On the other hand, from the viewpoint of being able to make the molded body thin and from the viewpoint that the molded body of this embodiment easily absorbs electromagnetic waves in a wide frequency band, the average length n' is preferably small, and is typically 10,000 μm or less, preferably 1,000 μm or less, more preferably 800 μm or less, even more preferably 750 μm or less, particularly preferably 600 μm or less, and most preferably 500 μm or less.

[0045] The average outer diameter p' of the minor spiral (also simply referred to as "outer diameter of the minor spiral") is not particularly limited, and may be greater than 3.5 μm (may be greater than 3.5 μm), 35 μm or more, 70 μm or more, 105 μm or more, 490 μm or less, 455 μm or less, 350 μm or less, or 175 μm or less.

[0046] The average winding pitch width q' of the small spiral (also simply referred to as the "winding pitch width of the small spiral") is not particularly limited, and its lower limit may be equal to or greater than the lower limit value of the average strand diameter r' described below. Furthermore, from the viewpoint of preventing the strand portion from becoming sparse and reducing the electromagnetic wave shielding performance, its upper limit is typically 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 70 μm or less.

[0047] The average strand diameter r' (also simply referred to as "strand diameter") is not particularly limited, but from the viewpoint of improving rigidity and reducing deformation during molding by injection molding, etc., it is usually greater than 1 μm (larger than 1 μm), preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more, and may be one-third or less of the average outer diameter p'. Furthermore, from the viewpoint of reducing weight, the average strand diameter r' is usually 140 μm or less, preferably 130 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0048] The average length of the small spirals per conductive coil (also simply referred to as "small spiral length") is not particularly limited, but from the viewpoint of improving shielding performance, it is preferably 1,000 μm or more, more preferably 10,000 μm or more, even more preferably 40,000 μm or more, and particularly preferably 100,000 μm or more. Also, from the viewpoint of increasing the coil size per coil and making it difficult to make the molded body thinner, it is preferably 1,000,000 μm or less, more preferably 800,000 μm or less, even more preferably 500,000 μm or less, and particularly preferably 300,000 μm or less. The small spiral length refers to the length of the double coil when it is stretched linearly while maintaining the shape of the small spiral, i.e., the length of the central axis of the small spiral.

[0049] The total wire length of the entire double coil contained per unit volume of the sheet (also simply referred to as the "total wire length of the entire double coil") is not particularly limited, but from the viewpoint of improving shielding performance, it is preferable that the total wire length be 10 m / cm ３ It is preferable that the thickness is 20 m / cm or more. ３ More preferably, it is 30 m / cm or more. ３ More preferably, it is 50 m / cm or more. ３ It is particularly preferable that the thickness is 2,000 m / cm or more, and from the viewpoint of preventing contact between the coils, ３ Preferably, it is 1,000 m / cm or less. ３ More preferably, it is 500 m / cm or less. ３ It is even more preferable that:

[0050] The average number of turns in the major helix (also simply referred to as "number of turns in the major helix") is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 4 or more, preferably 5 or more, and more preferably 6 or more, and is usually less than 14, preferably 11 or less, more preferably 10 or less, and even more preferably 8 or less. In particular, the fewer the number of turns in the major helix, the wider the frequency band of electromagnetic waves that can be effectively shielded, and the easier it is to shift the frequency band to high frequencies of 100 GHz or more.

[0051] The average number of turns of the small spiral (also simply referred to as the "number of turns of the small spiral") is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 24 or more, preferably 36 or more, more preferably 63 or more, and even more preferably 108 or more, and is usually 942 or less, preferably 603 or less, more preferably 419 or less, and even more preferably 308 or less.

[0052] The wires of the conductive coil may be made of a single metal or alloy, or may have a plated coating on their surfaces. To minimize short circuits between the conductive coils, the wires may be coated with insulating resin, or an oxide coating may be formed on the surface. For example, the oxide coating can be formed by subjecting the conductive coil to high-temperature heat treatment.

[0053] (Characteristics of the Conductive Coil) Volume Resistivity The volume resistivity of the conductive coil is not particularly limited, as long as it is a value that allows a small current to flow. The inventors conducted research and found that there was almost no change in the resonant frequency between copper, which has a volume resistivity of 1.55 μΩcm (0°C), and tungsten, which has a volume resistivity of 4.9 μΩcm (0°C). An example of a value that allows a small current to flow is a volume resistivity of 3352.8 μΩcm (20°C) when using carbon (graphite).

[0054] Thermal Conductivity The thermal conductivity of the conductive coil is not particularly limited. The inventors have conducted research and confirmed that there is almost no change in the resonant frequency between copper, which has a thermal conductivity of 394 W / m·K, and tungsten, which has a thermal conductivity of 174.3 W / m·K.

[0055] [Binder] (Configuration of Binder) The binder can bond multiple conductive coils and is non-conductive. Examples include organic materials such as polymers and inorganic materials such as glass. From the viewpoint of ease of molding, organic materials are preferred, and polymer materials are more preferred. The binder form is not particularly limited. It may be a molten thermoplastic resin cured by cooling into a sheet, a thermosetting resin or photocurable resin obtained by polymerizing a low-molecular-weight monomer through heating or light irradiation and molded into a sheet, or a sheet of fibers such as nanofibers. In the case of a thermoplastic resin cured by cooling, a thermosetting resin cured by heating, or a low-molecular-weight monomer cured by polymerization, the conductive coils tend to be unevenly distributed downward due to their own weight during the curing process. On the other hand, in the case of a fiber such as nanofibers cured into a specific shape, uneven distribution of the conductive coils during the curing process is less likely to occur, making it less likely for the conductive coils to come into contact with each other, and making it easier to achieve the desired electromagnetic wave shielding performance and insulation. Furthermore, since a large relative dielectric constant shortens the apparent wavelength, inorganic materials are preferred from the viewpoint of enabling shielding of higher frequencies, and specific examples include glass and ceramics.

[0056] When a resin is used, it may be a thermosetting resin or a thermoplastic resin, but a thermosetting resin is preferred because the electromagnetic wave shielding sheet may be exposed to high temperatures depending on its intended use. Examples of thermosetting resins include thermosetting resins and photocurable resins. Examples of thermosetting resins include thermosetting acrylic resins, unsaturated polyester resins, epoxy resins, melamine resins, phenolic resins, silicone resins, polyimide resins, and urethane resins. Examples of photocurable resins include photocurable epoxy resins, photocurable polyesters, photocurable vinyl compounds, photocurable epoxy (meth)acrylates, and photocurable urethane (meth)acrylates. Among these, unsaturated polyester resins, photocurable polyesters, epoxy resins, and photocurable epoxy resins are preferred, and epoxy resins and photocurable epoxy resins are particularly preferred from the viewpoint of heat resistance. These resins may be used alone or in combination of two or more types in any type and ratio.

[0057] The type of nanofiber material is not particularly limited, and examples thereof include cellulose, polypropylene, polyethylene terephthalate, chitin, chitosan, aramid, etc. From the viewpoints of easily ensuring insulation and easily suppressing the sedimentation of the coil, which has a higher specific gravity than the binder, cellulose nanofiber, polypropylene nanofiber, or polyethylene terephthalate nanofiber is preferred, and cellulose nanofiber is particularly preferred.

[0058] The binder is preferably a biodegradable material from the viewpoint of preventing environmental pollution, etc. Examples of biodegradable materials include cellulose, and cellulose is preferred.

[0059] The content of the binder in the sheet is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 15% by mass or more, preferably 20% by mass or more, more preferably 22% by mass or more, and usually 99% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less. In particular, when nanofibers are used as the binder, the content of the binder in the sheet is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 15% by mass or more, preferably 20% by mass or more, more preferably 22% by mass or more, and usually 40% by mass or less, preferably 35% by mass or less, and more preferably 30% by mass or less. Furthermore, particularly when a resin other than nanofiber is used as the binder, the content of the binder in the sheet is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 40% by mass or more, preferably 50% by mass or more, and more preferably 55% by mass or more, and is usually 99% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less.

[0060] When fibers are used as the binder, the fibers may be crosslinked. That is, the binder may contain crosslinked fibers or may be crosslinked fibers. The type of crosslinking is not particularly limited, and examples thereof include crosslinking by covalent bonds and crosslinking by ionic bonds.

[0061] The conductive coil may be completely embedded in the binder, or may not be completely embedded (only partially embedded), i.e., part of the conductive coil may be exposed to the outside air.

[0062] (Characteristics of Binder) Refractive Index The refractive index of the binder is not particularly limited, but from the viewpoint of improving electromagnetic wave shielding properties, it is usually 1.35 or more and 1.76 or less, and preferably 1.55 or more and 1.61 or less, which is the refractive index of an epoxy resin. The refractive index can be measured by a known method.

[0063] The volume resistivity of the binder is not particularly limited, but from the viewpoint of ensuring insulation, the larger the volume resistivity, the better. For example, ６ The upper limit of the volume resistivity is not particularly limited, but it is preferably 10 ２０ Ω cm or less, １８ The volume resistivity of the resin can be measured after preparing a sheet of the resin in a sheet form in the same manner as in the measurement of the volume resistivity of a sheet described below.

[0064] [Sheet] (Sheet Configuration) The shape of the sheet is not particularly limited as long as it can be recognized as a sheet, and can be appropriately changed depending on the location where the sheet is to be installed. The sheet may be a single-layer sheet or a laminated sheet. When a laminated sheet is used, it may be a laminated sheet in which multiple sheets according to this embodiment are stacked, or in which other sheets are stacked to impart various functions. The thickness of the sheet is not particularly limited, and from the viewpoint of the miniaturization, lightness, and thinning of electronic devices such as mobile phones, smartphones, and tablets in recent years, it is usually 10 μm or more, preferably 20 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more. It is also usually 10 mm or less, preferably 5 mm or less, more preferably 3 mm or less, and even more preferably 1.5 mm or less. The shape of the sheet is flat, but it may have an uneven shape within a range that can be approximately regarded as flat, or it may be partially curved. Furthermore, the shape of the sheet observed from the surface may be circular or polygonal, such as triangular or rectangular.

[0065] The sheet may be a bulk body in which the binder, conductive coil, and any other components are densely packed, or may be a porous body such as a foam.

[0066] The number of conductive coils in the sheet is not particularly limited, but from the viewpoint of ensuring sufficient electromagnetic wave shielding properties, it is usually 50 coils / cm ３ or more, and 100 particles / cm ３ It is preferable that the number of particles is 200 or more per cm. ３More preferably, it is 300 particles / cm or more. ３ More preferably, it is 10,000 particles / cm or more. ３ or less, and ３ Preferably, the number of particles is 3000 or less per cm ３ More preferably, it is 1000 particles / cm or less. ３ It is more preferable that the number of conductive coils is equal to or less than 1. The number of conductive coils can be measured by internal observation using CT-X-rays.

[0067] The sheet may contain materials (other materials) other than the conductive coil and binder described above, such as inorganic fillers other than the conductive coils or resin fillers. For example, the addition of an inorganic filler not only suppresses contact between the conductive material coils but also adjusts the linear expansion coefficient of the sheet, making it easier to prevent warping, sagging, undulation, etc. of the sheet. The content of inorganic fillers other than the conductive coils in the sheet is not particularly limited and may be contained at any level within a range that achieves the effects of this embodiment. Furthermore, the sheet may contain air, i.e., have voids, or may be a foam. By using a foam, weight reduction can be achieved.

[0068] (Sheet characteristics) Electromagnetic wave shielding property In the present disclosure, the electromagnetic wave shielding property is evaluated by evaluating the power transmittance T(ω) using the following method. This evaluation method is based on the terahertz time-domain spectroscopy used in the transmittance measurement experiment. A schematic diagram of a terahertz time-domain spectroscopy device is shown in Figure 6. In terahertz time-domain spectroscopy, the output from one or two femtosecond lasers is generally used as pump light and probe light. The pump light acts as light that excites the terahertz wave. The probe light synchronizes the timing for measuring the terahertz wave. The electric field component of the terahertz wave in the time domain is measured by changing the arrival times of the pump light and the probe light. The electric field E after the terahertz wave has passed through the sample is ｓａｍ (t) and the electric field E after passing through air without a sample. ｒｅｆ(t) are detected. Using these values, the complex refractive index, complex dielectric constant, transmittance, power spectrum, etc. are derived. The transmittance is derived from the data obtained from the above measurements by Fourier transform. The obtained electric field waveform E ｓａｍ (t), E ｒｅｆ (t) are Fourier transformed to E ｓａｍ (ω), E ｒｅｆ Using these, the power transmittance T(ω) is expressed by the following formula (A).

[0069]

[0070] The transmittance can be measured using a terahertz spectroscopy system (for example, TAS7500TSH manufactured by Advantest Corporation).

[0071] The shielding performance L (dB) can be calculated from the power transmittance T (ω) and the following formula (B): L = 10 × Log １０ (T(ω)) (B) The shielding performance L is not particularly limited, but is usually −10 dB or less, preferably −15 dB or less, and from the viewpoint of preventing malfunction of electronic devices such as computers, it is preferably −20 dB or less, more preferably −30 dB or less, even more preferably −40 dB or less, particularly preferably −60 dB or less, and most particularly preferably −80 dB or less, and although there is no need to set a lower limit, it is usually −90 dB or more. The electromagnetic wave shielding performance is expressed as −20 dB (shielding factor: 90%) when the electromagnetic wave is reduced to 1 / 10, −40 dB (shielding factor: 99%) when it is reduced to 1 / 100, −60 dB (shielding factor: 99.9%) when it is reduced to 1 / 1000, and −80 dB (shielding factor: 99.99%) when it is reduced to 1 / 10,000.

[0072] Volume Resistivity The volume resistivity of the sheet is measured by a resistivity meter (for example, Hiresta UX MCP-HT800 manufactured by Nitto Seiko Analytech Co., Ltd.) using a double ring electrode method (two-terminal method), that is, by sandwiching the molded body between a counter electrode and a double ring electrode.

[0073] The volume resistivity of the sheet that can be measured by the above method is not particularly limited. However, as described above, it is preferable that no current flows between the conductive coils. ４ It is preferable that the resistance is Ω·cm or more, and 10 ６ It is preferable that the resistance is 10 Ω cm or more. ８ It is more preferable that the resistance is 10 Ω cm or more. １０ It is particularly preferable that the volume resistivity is Ω·cm or more. There is no particular need to set an upper limit for the volume resistivity. ２０ Ω cm or less, １８ It may be Ω·cm or less.

[0074] <Method for manufacturing a molded body> Hereinafter, various embodiments relating to the manufacturing method of a molded body will be described, but the manufacturing method of the above-mentioned molded body is not limited to these manufacturing methods. In addition, manufacturing conditions that can be mutually applied in each embodiment can be mutually applied. In addition, the conditions for the above-mentioned molded body can be applied to the conditions of the manufacturing method below to the extent applicable.

[0075] <First Manufacturing Method> A first manufacturing method for a molded body, which is another embodiment of the present disclosure (also simply referred to as the "first manufacturing method" in the description of this embodiment), is a manufacturing method for a molded body, including: a composition preparation step of obtaining a liquid composition containing a binder and a conductive coil; and a curing step including a treatment of curing the liquid composition, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less. The first manufacturing method may include steps other than the composition preparation step and the curing step. Furthermore, the first manufacturing method is a method that can be preferably adopted particularly when a thermoplastic resin, a thermosetting resin, or a photocurable resin is used as the binder.

[0076] [Composition Preparation Step] The first manufacturing method includes a composition preparation step of obtaining a liquid composition containing the binder and conductive coil described above. The method of obtaining the liquid composition containing the binder and conductive coil is not particularly limited, and examples thereof include a method of mixing a liquid binder and a conductive coil, or a method of dissolving the binder in a solvent to obtain a solution and then mixing the solution with the conductive coil. The mixing method is not particularly limited, and any known method can be used.

[0077] When a solvent is used, the type of solvent is not particularly limited as long as it can dissolve the binder and other materials that need to be dissolved. If molding is possible without using a solvent, a solvent need not be used. A curing agent may be added depending on the type of binder used, and known curing agents may be used appropriately depending on the binder. The content of the curing agent in the composition may be, for example, 0.05 to 15% by mass. A polymerization initiator may also be added depending on the type of binder used. For example, a thermal radical generator such as a peroxide, e.g., benzoyl peroxide, may be used as the thermal polymerization initiator, and a photoradical generator, photocation generator, or photoanion generator may be used as the photopolymerization initiator.

[0078] A liquid composition according to another embodiment of the present invention comprises a binder and a conductive coil, and the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less. The method for producing the liquid composition is not particularly limited, but it can be obtained by the method described in the liquid composition production process. A molded product according to yet another embodiment of the present invention is a cured product of the liquid composition. The conditions for the molded product described above can be applied in the same manner.

[0079] [Curing Step] The first manufacturing method includes a curing step that includes a treatment for curing the liquid composition. The curing method is not particularly limited and can be changed appropriately depending on the type of binder. For example, a method of curing using heat or light such as ultraviolet light can be mentioned. Furthermore, when the binder used is a thermoplastic resin and the composition is prepared in a melted state by applying heat, the curing method may be a treatment such as leaving it to stand or cooling. The curing temperature and time vary depending on the materials used, and are not particularly limited as long as they are a temperature and time that can cure the composition.

[0080] <Second Manufacturing Method> A second manufacturing method of a molded body, which is another embodiment of the present disclosure (also simply referred to as the "first manufacturing method" in the description of this embodiment), is a manufacturing method of a molded body, including: a composition preparation step of obtaining a liquid composition containing a binder and a conductive coil; a freezing step of freezing the liquid composition to obtain a frozen body; and a compression step of compressing the frozen body under load to obtain a molded body, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less. The second manufacturing method may include steps other than the composition preparation step, freezing step, and compression step. Furthermore, the second manufacturing method is particularly suitable when fibers such as nanofibers are used as the binder. In this case, the obtained molded body may not be a bulk body, but may be a porous body such as a foam.

[0081] [Composition Preparation Step] The second manufacturing method includes a composition preparation step of obtaining a liquid composition containing the binder and a conductive coil. The conditions for the composition preparation step in the second manufacturing method can be applied to this composition preparation step in the same way. However, when fibers are used as the binder, the fibers need to be dissolved in a solvent, and therefore the use of a solvent is essential.

[0082] [Freezing step] The second manufacturing method includes a freezing step of freezing the liquid composition to obtain a frozen body. This step is intended to efficiently obtain a porous body. In the present disclosure, the frozen body refers to a substance derived from the composition after undergoing a freezing process. Therefore, even a substance derived from the composition in an unfrozen state after thawing is referred to as a frozen body. The method for freezing the liquid composition is not particularly limited, and examples include placing a container containing the liquid composition in a freezer.

[0083] The shape of the frozen body is not particularly limited, but from the viewpoint of being able to perform compression safely and efficiently in the compression step described below, a cylindrical shape or a polygonal prism such as a square prism, a pentagonal prism, or a hexagonal prism is preferred.

[0084] The freezing temperature is not particularly limited as long as it is a temperature at which the liquid composition can be frozen, and may be, for example, −196 to 0° C., −100 to −20° C., or −60 to −30° C. The freezing time is not particularly limited as long as it is a temperature at which the liquid composition can be frozen, and may be, for example, 1 hour or more, 5 hours or more, or 10 hours or more, or 168 hours or less, 72 hours or less, or 24 hours or less.

[0085] [Immersion step] The second manufacturing method may include an immersion step between the freezing step and the compression step described below, in which the frozen body is immersed in a liquid containing a component that cross-links the binder. This step aims to reduce volumetric shrinkage of the frozen body in steps before or after the compression step described below. The method for immersing the frozen body in a liquid containing a component that cross-links the binder is not particularly limited, and examples include a method in which the frozen body is placed in a container containing a liquid containing a component that cross-links the binder, or a method in which a liquid containing a component that cross-links the binder is placed in a container containing the frozen body.

[0086] The type of liquid containing a component that crosslinks the binder is not particularly limited as long as it can crosslink the binder. The type of crosslinking is also not particularly limited, and examples include crosslinking by covalent bonds and crosslinking by ionic bonds. Specific examples of the type of liquid containing a component that crosslinks the binder include polyvalent metal ion-containing liquids and acidic liquids, and more specific examples include aluminum ion-containing liquids such as aluminum nitrate, aluminum nitrate, aluminum sulfate, aluminum acetate, or aluminum chloride, copper nitrate aqueous solution, iron nitrate aqueous solution, hydrochloric acid, and acetic acid. In particular, when the binder is cellulose nanofibers, an acidic liquid is preferred, and aluminum nitrate is more preferred.

[0087] Furthermore, the immersion step may include removing a liquid (first liquid) containing a component that crosslinks the binder, and then immersing the frozen body in a liquid other than the first liquid (second liquid). This treatment is intended to prevent undesired volumetric shrinkage, which may occur if the frozen body is compressed or dried while the liquid containing the component that crosslinks the binder is attached. The method for removing the first liquid is not particularly limited, and examples include removing the first solution from a container containing the first liquid and the frozen body, or removing the frozen body from a container containing the first liquid and the frozen body. The method for immersing the frozen body in the second liquid is not particularly limited, and examples include pouring the frozen body into a container containing the second liquid, or pouring the second liquid into a container containing the frozen body.

[0088] The type of second liquid is not particularly limited as long as it is a liquid compatible with the first liquid, but examples include organic solvents with a surface tension lower than that of water, such as ethanol, acetone, hexane, or pentane. In particular, when the binder is cellulose nanofibers, a liquid such as ethanol can be used. For example, when the first liquid is water, ethanol or acetone, which are compatible with water, can be used, but hexane, which is not compatible with water, cannot be used. The replacement process with the second liquid may be performed two or more times. In this case, the replacement must be performed with a liquid that is compatible with the liquid used in the previous process. For example, when replacing water with hexane, this can be performed in two steps, such as water → ethanol → hexane.

[0089] [Thawing step] The second manufacturing method may include a step of thawing the frozen body. The thawing step may be included between the freezing step and the compression step, and may be performed simultaneously with the immersion step. It is preferable to perform the thawing step after immersing the frozen body in a liquid containing a component that crosslinks the binder, and it is also preferable to perform the thawing step before immersing the frozen body in the second liquid. The thawing method is not particularly limited, and examples include a heating method and a method of natural thawing by leaving it.

[0090] The thawing temperature and thawing time are not particularly limited as long as they can thaw the frozen body, and can be set appropriately depending on the type of composition.

[0091] [Compression step] The second manufacturing method includes a compression step in which a load is applied to the frozen body to compress it to obtain a molded body. This step is intended to mold the frozen body into a desired shape, particularly a sheet shape. The compression method is not particularly limited, and known methods can be used, such as a method of compressing using a press, a method of placing a plate on the frozen body and then placing a weight such as a weight on top of that, and the like.

[0092] The compression pressure is not particularly limited as long as the frozen body can be formed into the desired shape, and may be, for example, 1 to 10 MPa, 1.5 to 7 MPa, or 2 to 5 MPa. The compression temperature is not particularly limited, and may be room temperature or a temperature higher than room temperature.

[0093] [Drying step] The second manufacturing method may include a drying step of drying the molded body after the compression step. This step is intended to remove volatile components contained in the molded body, and, when the above-mentioned immersion step is employed, to promote crosslinking of the component that crosslinks the binder. The drying method is not particularly limited, and known methods can be used, such as a method in which the molded body is placed in a dryer and dried.

[0094] As long as it is possible to describe the volatile components to be removed, and in the case of employing the above-mentioned immersion step, as long as it is possible to promote crosslinking of the components that crosslink the binder, the drying temperature and time are not particularly limited. For example, the drying temperature may be 5 to 150°C, 10 to 100°C, or 15 to 50°C, and the drying time may be 1 hour or more, 5 hours or more, or 10 hours or more, and may be 168 hours or less, 72 hours or less, or 24 hours or less.

[0095] From the viewpoint of improving the efficiency of the manufacturing process, the drying step may be carried out simultaneously with the above-mentioned compression step. That is, the drying treatment by heating or the like may be carried out while compressing the frozen processed body.

[0096] <Uses of Molded Article> Uses of the above-described molded article include electromagnetic wave shielding, and another embodiment of the present invention is an electromagnetic wave shield having the above-described molded article.

[0097] Other embodiments of the present invention include: a semiconductor module having a semiconductor device (e.g., a module in which a semiconductor element is covered with a molded article and packaged, such as in an SOP, QFP, QFN, or BGA package); an electronic device or telecommunications device such as a smartphone, tablet, smart watch, smart security device, monitoring device, or smart home appliance; an automotive device such as a safety system, mobile media, communication, wireless headset, battery-powered, electric, or hybrid powertrain, or high-voltage battery system; a consumer electronic device such as a computer circuit, a wireless transmitter (including a smartphone), an electric motor, a flat panel display, or a liquid crystal display (LCD); a medical device such as a smart bed, a ventilator, a CT scan machine, or a transducer that must acquire information such as pulse rate or blood pressure and convert it into an electronic signal; an aerospace device such as an aircraft, a vehicle, an elastomeric gasket, a conductive paint, or an EMI shielding display; a system such as a railway system, a mass transit system, a high-voltage contact switching system, a signal transmission system, or a control system; or other equipment (equipment other than those described above that may have the molded article); The use of the molded article in each of the above embodiments is not particularly limited as long as the molded article is included as a component. Furthermore, each embodiment is particularly preferably used as an electromagnetic wave shielding sheet.

[0098] In particular, when used as an electromagnetic wave shielding sheet, it can be used in any application that shields electromagnetic waves. For example, by placing the electromagnetic wave shielding sheet so as to surround electronic devices that may malfunction due to electromagnetic waves, such malfunctions can be suppressed. In particular, the above-mentioned electromagnetic wave shielding sheet is superior to conventional electromagnetic wave shielding sheets in shielding electromagnetic waves in the high-frequency band, and therefore can be applied to a wider range of fields than conventional electromagnetic wave shielding sheets in that it can shield against electromagnetic waves originating from communication devices such as mobile phones and smartphones, which are being deployed at higher frequencies, particularly high frequency bands of 100 GHz or higher, in order to achieve higher speeds, larger capacities, and lower latency. Note that the above-mentioned sheet achieves a particularly strong electromagnetic wave shielding effect when the plane of the sheet is perpendicular to the direction in which electromagnetic waves arrive from outside.

[0099] The present disclosure will be described in more detail below with reference to examples, but the present disclosure should not be construed as being limited to the following examples.

[0100] <Materials Used> [Binders] Binder 1: Epoxy resin (a mixture of cold mounting resin JP-21111001 (polyester resin, refractive index at 500 GHz: 1.69) manufactured by Struers Corporation and a hardener (M agent) manufactured by Struers Corporation; the mixing ratio of cold mounting resin:hardener was 100 ml:1.5 ml, and the hardening time was 40 minutes at room temperature.) Binder 2: Cellulose nanofiber (cellulose nanofiber / aqueous dispersion (cellulose nanofiber content: 1% by mass), Rheocrysta I-2SX manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., length exceeding 100 μm and 3 mm or less, fiber diameter 3 nm Binder 3: Photocurable resin (Clear Resin V4 manufactured by Formlab) [Conductive Coil] Single coil: As the single coil in each example, a tungsten single coil (cross-sectional shape of element wire: circular, circumferential shape of spiral: circular) of the shape shown in each table below was used. Double coil: In each example, a tungsten double coil (cross-sectional shape of wire: circular, circumferential shape of large spiral: circular, circumferential shape of small spiral: circular) was used as the double coil.

[0101] In the tables below, "total length" refers to the "average length of the coil-shaped portion in the direction of the central axis of the conductive coil" for single coils, and to the "average length of the double coil in the direction of the central axis of the large spiral" for double coils. Furthermore, "average ratio of rectangular parallelepiped" in the tables below refers to the "average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped that encloses the conductive coil." Furthermore, the numerical values ​​of the parameters related to the shape of the conductive coil in the tables below all indicate average values.

[0102] The wire length per coil in each table described below can be calculated as follows. In the case of a single coil, it is the value obtained by multiplying the outer diameter of the coil by pi and then multiplying that value by the number of turns in the coil. In the case of a double coil, it is the value obtained by multiplying the outer diameter of the minor spiral by pi and then multiplying that value by the number of turns in the minor spiral. The number of turns in the minor spiral is the value obtained by multiplying the outer diameter of the major spiral by pi and then multiplying that value by the number of turns in the major spiral, then dividing that value by the winding pitch of the minor spiral. The wire length can also be mathematically calculated in the same way for triple coils, in which a double coil is further formed into a coil shape, or for coils with special shapes. The total wire length of the coils per unit volume is the value obtained by multiplying the wire length per coil by the number density of the coils per unit volume. The number density of the coils per unit volume can be calculated by dividing the number of coils in the molded body by the volume. The number density of the coils per unit volume may also be the average number density of the coils at any location in the molded body.

[0103] <Characteristics Evaluation> [Electromagnetic Shielding Performance] The electromagnetic shielding performance was evaluated by measuring the power transmittance T(ω) using a terahertz spectroscopy system (TAS7500TSH manufactured by Advantest Corporation). An aperture with a diameter of 5 mm was used. The samples to be measured were obtained by cutting each of the above sheets into a rectangular parallelepiped with a side length of 30 mm and a thickness of 1 mm. Next, the shielding performance L (dB) was calculated from the power transmittance T(ω) obtained by measurement according to the following formula (B): L = 10 × Log １０ (T(ω)) (B) The evaluation results of the electromagnetic wave shielding performance L of each sheet are shown in each table. Note that the shielding performance L shown in each table is a value evaluated at a frequency of 300 GHz.

[0104] [Volume Resistivity] The volume resistivity of the sheet was measured using a resistivity meter (Hiresta UX MCP-HT800 manufactured by Nitto Seiko Analytech Co., Ltd., upper measurement limit 10 １１ The measurement was carried out by using a double ring electrode method (two-terminal method) using a resistivity (Ω·cm) by sandwiching the molded body between an opposing electrode (registration table) and a double ring electrode (URSS probe).

[0105] [Shape of Conductive Coil] The shape of the conductive coil was evaluated using an optical microscope and a scanning electron microscope. At least 10 conductive coils were measured.

[0106] Experiment A: Study of the Average Ratio of the Longest Side to the Shortest Side of the Smallest Rectangular Parallelepiped Surrounding a Conductive Coil. [Sheet Preparation] A double coil was placed into an acrylic mold having a circular hole with a diameter of 20 mm and a thickness of approximately 1 mm, and then Binder 1 was filled in such that the double coil and binder contents were as shown in Table 1-2. The double coil was then held at room temperature for 40 minutes to harden, and the hardened sheet (20 mm in diameter, sample thickness shown in Table 1-2) was removed from the mold to obtain sheet samples for evaluation in Example 1 and Comparative Example 1. The evaluation results for electromagnetic shielding performance and volume resistivity are shown in Table 1-2. FIG. 7 shows a graph obtained by evaluating electromagnetic shielding performance. In the graph of FIG. 7, the reflectance (%), transmittance (%), and absorptance (%) are plotted in the area above 0 on the vertical axis, and the shielding performance (dB) is plotted in the area below 0. Reflectance (%), transmittance (%), and absorptance (%) are expressed as 0% or greater, and shielding performance is expressed as 0 dB or less. This also applies to FIGS.

[0107]

[0108]

[0109] From Tables 1-1 and 1-2, it can be seen that by using a conductive coil in which the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped surrounding the conductive coil is 2 or less, a sheet with excellent electromagnetic wave shielding performance and insulation can be produced.

[0110] <Experiment B: Investigation of Conductive Coil Content> [Sheet Production] Sheet samples for evaluation in Examples 2 and 3 were obtained in the same manner as in Example 1 above, except that the conditions for Binder 1 and the conductive coil were changed to those shown in Tables 2-1 and 2-2. The evaluation results for electromagnetic wave shielding performance and volume resistivity are shown in Table 2-2. The graph obtained from the evaluation of electromagnetic wave shielding performance is shown in FIG.

[0111]

[0112]

[0113] From Tables 2-1 and 2-2, it can be seen that as the content of the conductive coil increases, the electromagnetic wave shielding performance improves while maintaining the insulation performance.

[0114] Experiment C: Study of Binder 2 [Sheet Preparation] Binder 2 and a conductive coil were weighed out at the masses shown in Table 3-2 and mixed to obtain a mixed aqueous dispersion. The 0.1 g mass of binder shown in Table 3-2 corresponds to the mass of cellulose nanofibers, and the weighed mass of the cellulose nanofiber / aqueous dispersion was 10 g. The mixed aqueous dispersion was then filled into a cylindrical plastic container with an inner diameter of 20 mm and a height of 50 mm and frozen at -45°C for 2 hours to obtain a frozen product. The frozen product was then thawed in a 0.1 mol / L aqueous aluminum nitrate solution to prepare a hydrogel in which the cellulose nanofibers were crosslinked with aluminum ions. The obtained hydrogel was washed with distilled water to remove the aluminum nitrate. The hydrogel was then immersed in 99% by mass ethanol, and the water was replaced with the ethanol solvent to obtain an alcogel. The resulting alcogel was dried for 24 hours at 20°C under normal pressure with a load of 3.2 kPa applied, to prepare foams with the thicknesses shown in Table 3-2, and sheet samples for evaluation in Examples 4 to 6 were obtained. The evaluation results for electromagnetic wave shielding performance and volume resistivity are shown in Table 3-2. The graph obtained from the evaluation of electromagnetic wave shielding performance is shown in Figure 9.

[0115]

[0116]

[0117] Tables 3-1 and 3-2 show that excellent electromagnetic shielding performance can be obtained while maintaining insulation, even when binder 2 is used. In particular, when nanofibers are used as the binder, the nanofibers are interposed between the conductive coils, making it easier to suppress contact between the conductive coils compared to when a binder other than nanofibers is used, and the orientation rate of the conductive coils can be increased while maintaining insulation.

[0118] <Experiment D> [Sheet Preparation] A conductive coil was placed into an acrylic mold having a circular hole with a diameter of 20 mm and a thickness of approximately 1 mm, and then Binder 3 was filled in such that the conductive coil and binder contents were as shown in Table 4-2. The mold was then irradiated with ultraviolet light for 1 hour using an ultraviolet irradiation device (Form Cure, manufactured by Formlab) to harden the binder 3, thereby obtaining a first layer (Layer 1, diameter 20 mm, thickness 1 mm). A conductive coil was then placed on Layer 1 in the same amount as the conductive coil and binder 3 in Layer 1, and Binder 3 was filled in. The mold was then irradiated with ultraviolet light for 1 hour using an ultraviolet irradiation device (Form Cure, manufactured by Formlab) to harden the binder 3, thereby obtaining a second layer (Layer 2, diameter 20 mm, thickness 1 mm). A third layer (Layer 3, diameter 20 mm, thickness 1 mm) was then formed on Layer 2 using the same method as for forming Layer 2, thereby obtaining a laminated sheet. Thereafter, the laminate sheet (diameter 20 mm, thickness as shown in Table 4-2) was removed from the mold to obtain laminate sheet samples for evaluation in Examples 7 to 11. The evaluation results for electromagnetic wave shielding performance and volume resistivity are shown in Table 4-2. A graph obtained from the evaluation of electromagnetic wave shielding performance is shown in Figure 10. In Table 4-1, for Example 11, which used a single coil, the outer diameter of the single coil is shown in the small spiral outer diameter column, and the winding pitch width of the single coil is shown in the small spiral winding pitch width column.

[0119]

[0120]

[0121] Tables 4-1 and 4-2 show that excellent electromagnetic shielding performance can be obtained while maintaining insulation whether binder 3 is used or a single coil is used. It is also clear that the longer the total wire length (coil) and total wire length (volume), the better the electromagnetic shielding performance.

[0122] l Average outer diameter m Average winding pitch width n Average length in the central axis direction p Average wire diameter l' Average outer diameter of the major spiral m' Average winding pitch width of the major spiral n' Average length in the central axis direction of the major spiral p' Average outer diameter of the minor spiral q' Average winding pitch width of the minor spiral r' Average wire diameter G Central axis of the major spiral H Central axis of the minor spiral

Claims

1. A molded body comprising a binder and a plurality of conductive coils, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coils is 1 or more and 2 or less.

2. The molded body according to claim 1, wherein the binder comprises cellulose nanofibers.

3. The molded article according to claim 1 or 2, wherein the average number of turns of the conductive coil is 1.2 or more and 50 or less.

4. The molded article according to claim 1 or 2, wherein the conductive member constituting the conductive coil is spirally shaped.

5. The content of the conductive coil in the molded body is 0.02 g / cm ３ Above, 5.00g / cm ３ The molded article according to claim 1 or 2, wherein the molecular weight is less than 1000.

6. The molded article according to claim 1 or 2, which is an electromagnetic wave shielding sheet.

7. A liquid composition comprising a binder and a conductive coil, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less.

8. A molded article which is a cured product of the liquid composition according to claim 7.

9. The molded article according to claim 8, which is an electromagnetic wave shielding sheet.

10. An electromagnetic wave shield comprising the molded article according to claim 6.

11. A semiconductor module comprising the molded article according to claim 1 or 2.

12. An electronic device comprising the molded article according to claim 1 or 2.

13. An automotive device comprising the molded article according to claim 1 or 2.

14. A consumer electronic device comprising the molded article according to claim 1 or 2.

15. A medical device comprising the molded article according to claim 1 or 2.

16. An aerospace device comprising the molded article according to claim 1 or 2.

17. A system comprising the molded body according to claim 1 or 2.

18. A method for producing a molded body, comprising: a composition preparation step of obtaining a liquid composition containing a binder and a conductive coil; a freezing step of freezing the liquid composition to obtain a frozen body; and a compression step of compressing the frozen body under load to obtain a molded body, wherein the average ratio of the longest side to the shortest side of the smallest rectangular parallelepiped enclosing the conductive coil is 1 or more and 2 or less.

19. The method for producing a molded body according to claim 18, further comprising, between the freezing step and the compressing step, a dipping step of dipping the frozen body in a liquid containing a component that crosslinks the binder.

20. The method for producing a molded body according to claim 19, wherein the immersion step includes a process of immersing the frozen body in a liquid other than a liquid that contains a component that crosslinks the binder, after removing the liquid.

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