Composite sheet

Abstract

To provide a composite sheet of a fluorine resin exhibiting electromagnetic wave shielding property.SOLUTION: A composite sheet includes a core material containing a woven fabric of heat-resistant fibers, and a resin layer provided on at least one main surface of the core material. The woven fabric is a carbon fiber woven fabric. The resin layer contains a fluorine resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite sheet. [Background technology]

[0002] In recent years, various electromagnetic waves have been flying around both indoors and outdoors, not only from radio and television broadcast waves but also from wireless communications with the Internet and small devices. From the perspective of security and measures to prevent electromagnetic noise from damaging devices, there is a demand for building materials that have electromagnetic wave shielding properties.

[0003] Known membrane materials used in buildings include, for example, membrane materials in which fluororesin is laminated on both sides of a sheet-like woven fabric made of glass fiber. Glass fiber fabrics have excellent tear strength because they are made of tightly woven glass fibers. Fluororesin is a resin that has excellent heat resistance, chemical resistance, and non-stick properties. Such membrane materials are also used in buildings with large spaces because they are lightweight and have excellent weather resistance and stain resistance. For example, Patent Document 1 discloses membrane structures used in construction applications such as exterior walls, roofing materials, and medium- to large-sized tents. However, such membrane materials do not have electromagnetic wave shielding properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-105211 [Patent Document 2] Patent Publication No. 2021-79595 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a fluororesin composite sheet that exhibits electromagnetic wave shielding properties. [Means for solving the problem]

[0006] A composite sheet is provided, which includes a core material including a woven fabric of heat-resistant fibers and a resin layer provided on at least one main surface of the core material. The woven fabric is a carbon fiber fabric. The resin layer includes a fluororesin. [Effects of the Invention]

[0007] It is possible to provide a composite sheet that exhibits electromagnetic wave shielding properties despite being a fluororesin composite sheet. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a composite sheet according to an embodiment. [Figure 2] 2 is a graph showing the electromagnetic wave shielding performance of the composite sheet of Example 1 measured by the Dual Focus Flat Cavity method. DETAILED DESCRIPTION OF THE INVENTION

[0009] Composite sheets made by impregnating woven fabrics such as glass cloth with fluororesin are used in a wide range of fields, including construction, chemistry, machinery, electricity, and communications. However, the insulation resistance of fluororesin itself is very high, and such fluororesin composite sheets do not have the conductivity required to achieve electromagnetic wave shielding.

[0010] The following describes the embodiments with reference to the drawings as appropriate. Note that common components throughout the embodiments are designated by the same reference numerals, and redundant explanations will be omitted. The drawings are schematic diagrams for explaining and facilitating understanding of the embodiments, and the shapes, dimensions, ratios, etc. may differ from those of actual devices. However, these may be appropriately modified in design, taking into consideration the following explanation and known techniques.

[0011] According to an embodiment of the present invention, there is provided a composite sheet. The composite sheet includes a core material including a heat-resistant fiber woven fabric and a resin layer provided on at least one main surface of the core material. The woven fabric is a carbon fiber woven fabric. The resin layer includes a fluororesin.

[0012] In this composite sheet, the fluororesin itself is positioned as a surface layer protection application, and the core material is made conductive, resulting in a fluororesin composite sheet with electromagnetic wave shielding properties. The function of the fluororesin to protect the surface layer is mainly due to the weather resistance and stain resistance of the fluororesin. To make the core material conductive, the woven fabric material is changed from glass or aramid fiber to a conductive material.

[0013] By including a carbon fiber fabric as a conductive core material, a composite sheet suitable for construction applications can be obtained. That is, such a composite sheet can be used for architectural membrane structures and architectural components with electromagnetic wave shielding properties. Carbon fiber fabrics have excellent flexibility and elongation properties, making them easy to install and more suitable for construction applications than composite materials that use a metal mesh as a core material.

[0014] Hereinafter, embodiments of the present invention will be described in detail.

[0015] The core material may be a woven fabric containing carbon fibers as single fibers. Because carbon fibers have high electrical conductivity, the use of a carbon fiber woven fabric as the core material can provide a fluororesin composite sheet that exhibits electromagnetic wave shielding properties.

[0016] Typically, metallic materials exhibit high electrical conductivity. However, not all materials containing metals are necessarily capable of providing electromagnetic shielding properties. Not only electrical conductivity but also the magnetic permeability of a material determines its electromagnetic shielding properties. Materials with high electrical conductivity and low magnetic permeability have a high amount of electromagnetic wave reflection loss, resulting in high shielding performance. Materials with high electrical conductivity and high magnetic permeability, or materials with slightly low electrical conductivity but high magnetic permeability, have a high amount of electromagnetic wave absorption loss, resulting in high shielding performance. Even materials containing metals, such as stainless steel, have low electrical conductivity and magnetic permeability and do not exhibit electromagnetic shielding properties.

[0017] The diameter of the single fiber is preferably in the range of 3 μm to 13 μm, and the thickness of the yarn formed by the single fiber bundle is preferably in the range of 1.7 tex to 4080 tex, which can further improve the flexibility and strength of the woven fabric.

[0018] The weaving method of the woven fabric is not particularly limited, but may be, for example, plain weave, twill weave, satin weave, leno weave, or moss weave. The thickness of the woven fabric is, for example, 27 μm or more and 1440 μm or less.

[0019] The resin layer is provided on at least one main surface of the base fabric. Preferably, the resin layer is provided on both main surfaces of the base fabric. At least a portion of the resin layer is located on the outermost surface of the composite sheet. Preferably, at least one main surface of the composite sheet is defined by the main surface of the resin layer. When the composite sheet comes into contact with an object, the resin layer is arranged so as to be in direct contact with the object.

[0020] The fluororesin contained in the resin layer is, for example, at least one selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE). The type of fluororesin contained in the resin layer may be one type, or two or more types may be mixed. Among these, it is preferable that the resin layer contains PTFE as the fluororesin because it has excellent heat resistance as well as high chemical resistance. The fluororesin contained in the resin layer may be PTFE alone.

[0021] The resin layer may further contain silicon dioxide (SiO2) in addition to the fluororesin. A resin layer containing silicon dioxide is less likely to crack. This can alleviate stress concentration on the fibers that make up the core material, and can delay the decrease in strength of the single fibers when repeated bending stress is applied. Therefore, the addition of silicon dioxide can improve strength against bending stress. The resin layer can be in the form of a film made of fluororesin or a sintered body of fluororesin with silicon dioxide particles dispersed therein.

[0022] The thickness of the resin layer on each side of the core material is, for example, in the range of 15 μm to 250 μm.

[0023] The resin layer can be formed on the core material by, for example, impregnating the core material with an aqueous dispersion of fluororesin fine particles, followed by drying, baking, and the like.

[0024] Specific examples of applications of the composite sheet to buildings include installation of rooms that shield electromagnetic waves indoors, such as sheets for ceilings and floors, and wallpaper, and installation of spaces that shield electromagnetic waves outdoors, such as outer membranes for tents.

[0025] 1 is a cross-sectional view schematically illustrating an example of a composite sheet according to an embodiment. The composite sheet 1 shown in the figure includes a carbon fiber fabric 10 as a core material and resin layers 11 provided on both main surfaces of the carbon fiber fabric 10. The main surfaces of the resin layers 11 are exposed on the surface of the composite sheet 1. [Example]

[0026] Example 1 A composite sheet was fabricated using a carbon cloth as a core material. Specifically, the core material was impregnated with an aqueous dispersion of tetrafluoroethylene (PTFE) resin particles to coat the PTFE on the core material, followed by drying to remove water and subsequent firing. This impregnation, drying, and firing process was repeated multiple times to form a PTFE layer as a resin layer on the core material, yielding a composite sheet.

[0027] The electromagnetic wave shielding performance of the obtained composite sheet was measured using the Dual Focus Flat Cavity (DFFC) method. The measurement results are shown in Figure 2. As the graph shows, the sheet exhibited a shielding effect of approximately 40 dB against electromagnetic waves over a wide range of wavelengths, and an even higher shielding effect against electromagnetic waves around 11 GHz.

[0028] (Comparative Example 1) A composite cloth was produced by sputtering stainless steel (SUS) onto a glass cloth. A composite sheet was produced using the obtained composite cloth as a core material. When the obtained composite sheet was measured by the DFFC method, it did not exhibit electromagnetic wave shielding properties, unlike the composite sheet obtained in Example 1, which used a carbon cloth as a core material.

[0029] The present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in appropriate combinations, in which case the combined effects can be obtained. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by combining selected elements from the disclosed elements. For example, if the problem can be solved and the desired effect can be obtained even if some elements are deleted from all elements shown in the embodiments, the configuration from which these elements are deleted can be extracted as an invention. [Explanation of symbols]

[0030] 1...composite sheet, 10...carbon fiber fabric, 11...resin layer.

Claims

1. A composite sheet comprising a core material including a heat-resistant fiber woven fabric and a resin layer provided on at least one main surface of the core material, the fabric is a carbon fiber fabric, The resin layer is a composite sheet containing a fluororesin.

2. 2. The composite sheet according to claim 1, wherein the fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxyalkane, perfluoroethylenepropene copolymer, and ethylene-tetrafluoroethylene copolymer.

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