Composite materials for electromagnetic radiation shielding

Abstract

The present invention relates to a composite material for shielding electromagnetic radiation, comprising a mechanically bonded nonwoven fabric, wherein the mechanically bonded nonwoven fabric has a metal coating applied by electroplating on one side and does not have a metal coating on the side opposite to the metal coating applied by electroplating.

Description

Technology Field

[0001] The present invention relates to a composite material for shielding electromagnetic radiation, a method for manufacturing said composite material, and an use of said composite material. The present invention also relates to a composite material-component assembly, and a method for shielding a component from electromagnetic radiation at least partially using the composite material. Background Technology

[0002] Electromagnetic waves consist of electric and magnetic field components. Electromagnetic waves emitted by electronic components can cause mutual electromagnetic interference (EMI). Due to the rapid advancement of semiconductor technology, electronic components have become increasingly miniaturized, and the density of electronic components within electronic devices has increased significantly. For example, as the complexity of electronic systems increases in fields such as electric mobility, aerospace technology, or medical technology, significant challenges regarding the electromagnetic compatibility of individual components are being raised. For instance, in electric vehicles, high-output electric drive systems are integrated into very confined spaces and controlled by electronic components, and these individual components must not interfere with each other in any way. To achieve electromagnetic compatibility, it is known that electromagnetic interference is attenuated by shielding housings. The term Electromagnetic Compatibility (EMC), according to, for example, DIN VDE 0870, is defined as the ability of an electrical device to function satisfactorily in its surrounding environment, which may include other devices, without causing unacceptable effects to that environment. Therefore, EMC must satisfy two conditions: shielding of emitted radiation and immunity to interference from other electromagnetic radiation. In many countries, such devices must comply with statutory regulations. According to DIN VDE 0870, electromagnetic interference (EMI) is defined as the effect of electromagnetic waves on electrical circuits, devices, systems, or living organisms. Such effects can cause not only acceptable but also unacceptable damage to the affected objects, such as degradation of device functionality or danger to humans. In such cases, corresponding protective measures must be taken. The frequency range associated with EMI shielding is generally 100 Hz to 100 GHz.The attenuation achieved by shielding irradiated electromagnetic waves generally consists of reflection and absorption in all shielding principles. Upon absorption, electromagnetic waves lose energy, which is converted into heat energy; absorption depends on the wall thickness of the shielding material. On the other hand, reflection is independent of the material thickness depending on the frequency range and can occur on both the front and back surfaces of the material, as well as within the material.

[0003] In the intermediate frequency range, the electrical conductivity behavior of materials can generally be used directly to evaluate shielding. In the low frequency range, relative permeability can be used to evaluate shielding, and in the high frequency range, reflection and vibration absorption can also be used.

[0004] It is known that plastic composites (composite materials, compounds) are used to manufacture electromagnetic shields, and these composites have a matrix composed of at least one polymer component and at least one filler having shielding properties. They can be used in the form of coatings, insulating tapes, molded articles, etc. To manufacture conductive composites, for example, electrically conductive fillers can be dispersed in a matrix composed of at least one non-conductive polymer. A disadvantage of this is that electrically conductive additives, such as metal powders, are very expensive. Additionally, a high degree of filler is required to overcome the percolation threshold. Furthermore, as wall thickness increases, the absolute amount of additive required to maintain a constant relative content also increases.

[0005] S. Geetha et al. provide an overview of methods and materials for electromagnetic radiation shielding in the Journal of Applied Polymer Science, Vol. 112, pp. 2073–2086 (2009). Various plastic composites based on non-conductive polymers with various conductive fillers are discussed. As an alternative, the use of conductive polymers, particularly polyaniline and polypyrrole, is discussed. A disadvantage of these materials is their low aging resistance. Additionally, they are difficult to handle, require subsequent application, and are costly.

[0006] In addition, it is known that metal housings, for example made of aluminum, are used for electromagnetic radiation shielding. Good shielding attenuation is achieved due to the high conductivity of metals. However, the use of pure metal shields entails various disadvantages, such as cumbersome manufacturing involving punching, bending, and anti-corrosion treatment, which is very costly. In the case of metal materials, the degree of design freedom is also very limited.

[0007] The use of composite materials, such as nonwoven fabrics, with metal coatings on both sides is also known. For example, polyamide spunbond nonwoven fabrics coated with copper on both sides are commercially available. However, due to the double-sided metal coating, these composite materials exhibit high conductivity in both planar and perpendicular directions. This is disadvantageous as it can lead to short circuits and corrosion. For this reason, the surface of the material is electrically insulated by an additional coating, which requires an additional processing step. Furthermore, these composite materials have a relatively high metal content, which further increases production costs.

[0008] EP 0 835 915 A2 discloses the use of spunbond nonwoven fabric as a substrate for electrically conductive transfer bands, wherein the fabric is electroplated by coating with at least one metal layer and an adhesive coating is provided on both sides or on only one side, wherein the average thickness of the fabric is greater than or equal to the total thickness of the adhesive coating(s). Spunbond nonwoven fabrics typically comprise continuous filaments (long fibers) that are thermally and / or chemically bonded to one another. This is disadvantageous because, under load, the thermal or chemical bonding of the fibers of the nonwoven fabric is broken, and cracks are formed in the coating.

[0009] DE 101 45 750 A1 discloses a method for manufacturing a metal layer on a carrier body, wherein in a first step, conductive particles are applied to the surface of a carrier body so as to be fixed on the carrier body, and in a second step, the carrier body having said particles is metallized chemically or by electroplating in a metallization bath to form a metal layer. A fabric, in particular, may be used as the carrier body.

[0010] The objective of the present invention is to provide a material capable of at least partially overcoming the aforementioned disadvantages.

[0011] This objective is achieved by a composite material for shielding electromagnetic radiation comprising a mechanically bonded nonwoven fabric, wherein the mechanically bonded nonwoven fabric has a metal coating applied by electroplating on one side and does not have a metal coating on the side opposite to the metal coating applied by electroplating.

[0012] According to the present invention, a mechanically bonded nonwoven fabric has a metal coating applied by electroplating on only one side. On the opposite side, in contrast, the nonwoven fabric does not have a metal coating. Therefore, the mechanically bonded nonwoven fabric has a metal coating on exactly one side.

[0013] Nonwoven fabrics are sheet-like structures that have a substantially two-dimensional area (base area) and a thickness that is relatively small. Nonwoven fabrics are described in the standard DIN EN ISO 9092:2011. An orthogonal coordinate system may be used to describe nonwoven fabrics, wherein the base area of ​​the nonwoven fabric lies on the plane formed by the x-axis and y-axis (also called the x,y-plane). The z-axis, which is orthogonal to this, may be used to describe the thickness of the material. By convention, "plane" is understood to mean the base area of ​​the nonwoven fabric.

[0014] Compared to nonwoven fabrics with metal coatings on both sides known in the prior art, the composite material according to the present invention has the advantage of being usable without an additional insulation layer. When applied to a component through the metal-coated side, the nonwoven fabric side that is not metal-coated is located on the outside. As a result, conductivity in the resulting composite material-component assembly is generated only internally and not externally, so an additional insulation layer is not required. Furthermore, inherent corrosion protection can also be achieved through this. An additional advantage of this application is that the internal metal coating is well protected from mechanical stress.

[0015] An additional advantage is that high layer thicknesses can be achieved with a relatively small amount of metal because only one side is coated. Furthermore, the uncoated side of the composite material enables better adhesion to parts than the metal-coated surfaces. Equally advantageous is that there is no need to increase the amount of metal as the thickness of the composite material increases, as the metal is used as a coating rather than a filler.

[0016] According to the present invention, the composite material comprises a mechanically bonded nonwoven fabric (hereinafter also simply referred to as nonwoven fabric). This is advantageous compared to woven fabrics because nonwoven fabrics have a significantly higher tensile elongation at break than woven fabrics and do not have regular structures. This is again advantageous because it prevents the formation of interference patterns. Furthermore, the sliding of the fibers of the nonwoven fabric is not hindered at all or hardly by the mechanical bonding. As a result, the conductive coating remains undamaged under load and no cracks are formed.

[0017] In a preferred embodiment, the nonwoven fabric is bonded only mechanically. That is, the nonwoven fabric does not have additional bonding by, for example, binders or binder fibers. In this case, the nonwoven fabric is preferably not chemically bonded by chemical binders and is not thermally bonded by binder fibers. The nonwoven fabric is particularly preferably a needle-punched nonwoven fabric and / or a hydroentangled nonwoven fabric. This allows for particularly good fluidity (mobility) of the fibers of the nonwoven fabric to be obtained.

[0018] In a further preferred embodiment, the nonwoven fabric comprises staple fibers, preferably having a staple fiber length of 10 mm to 90 mm, more preferably 20 mm to 90 mm, and particularly 38 mm to 90 mm. In this case, the proportion of staple fibers based on the total weight of the nonwoven fabric is preferably at least 70 weight%, preferably 80 weight% to 100 weight%, and more preferably 90 weight% to 100 weight%. The advantage of staple fibers is that they impart high flexibility to the nonwoven fabric. In the case of spunbond nonwoven fabrics composed of continuous filaments, the filaments break upon high elongation, whereas staple fibers can slide past each other upon elongation, thereby preventing damage to the metal coating.

[0019] According to the present invention, the fibers of the nonwoven fabric are preferably at least partially synthetic polymer fibers and / or glass fibers. The nonwoven fabric comprises, particularly preferably, at least 50 weight%, more preferably at least 80 weight%, and particularly at least 90 weight% of polyester, polyamide, and / or glass based on the total weight of the nonwoven fabric.

[0020] The nonwoven fabric preferably has a tensile elongation at break parallel to the machine direction (MD), measured according to DIN ISO 9073-3:2023-09, greater than 15%, for example, from 15% to 100%, preferably from 25% to 90%, particularly from 35% to 80%. The nonwoven fabric preferably has a tensile elongation at break in the cross direction (CD), perpendicular to the machine direction, greater than 15%, for example, from 15% to 100%, preferably from 25% to 90%, particularly from 35% to 80%, measured according to DIN ISO 9073-3:2023-09.

[0021] Additionally, the nonwoven fabric preferably has low elastic modulus values ​​parallel to the machine direction, measured according to DIN ISO 9073-3 2023-09. At 10% elongation, the nonwoven fabric preferably has a strength measured according to DIN ISO 9073-3 2023-09 of 50 N / 5cm to 150 N / 5cm, more preferably 70 N / 5cm to 130 N / 5cm, particularly 80 N / 5cm to 110 N / 5cm. At 20% elongation, the nonwoven fabric preferably has a strength measured according to DIN ISO 9073-3 2023-09 of 100 N / 5cm to 160 N / 5cm, more preferably 110 N / 5cm to 150 N / 5cm, particularly 120 N / 5cm to 140 N / 5cm.

[0022] Additionally, the nonwoven fabric preferably has low elastic modulus values ​​orthogonal to the machine direction as measured according to DIN ISO 9073-3 2023-09. At 10% elongation, the nonwoven fabric preferably has a strength as measured according to DIN ISO 9073-3 2023-09 of 20 N / 5cm to 75 N / 5cm, more preferably 25 N / 5cm to 65 N / 5cm, particularly 30 N / 5cm to 50 N / 5cm. At 20% elongation, the nonwoven fabric preferably has a strength of 30 N / 5cm to 100 N / 5cm, more preferably 40 N / 5cm to 90 N / 5cm, particularly 50 N / 5cm to 80 N / 5cm.

[0023] In addition, the nonwoven fabric preferably has a weight per unit area measured according to DIN ISO 9073-1 2023-09 of 20 g / m² to 200 g / m², preferably 40 g / m² to 170 g / m², particularly 50 g / m² to 120 g / m².

[0024] According to the present invention, a composite material has a metal coating applied by electroplating on one side. The metal coating may include various metals. Suitable examples are copper, nickel, silver, aluminum, and / or tin. The metal coating preferably includes copper and / or nickel because they have good conductivity. The metal coating particularly preferably includes copper and / or nickel in a proportion of at least 80 weight percent based on the total weight of the metal coating.

[0025] The metal coating comprises copper and nickel, particularly preferably with a Cu to Ni ratio of 30 wt% to 70 wt% to 5 wt% to 95 wt% based on the total weight of the metal coating.

[0026] In addition, the metal coating preferably has an average thickness determined by scanning electron microscopy of 0.1 μm to 10 μm, preferably 0.1 μm to 2.5 μm, more preferably 0.1 μm to 1.5 μm, particularly 0.1 μm to 0.75 μm.

[0027] According to the present invention, a metal coating is applied by electroplating. "Applied by electroplating" means applied by electroplating technology (also called electroplating). Electroplating technology refers to the electrochemical deposition of metallic films, i.e., coating layers, onto substrates (workpieces) in an electrolytic cell.

[0028] In electroplating, an electric current, preferably direct current, flows through an electrolytic cell. A metal, such as copper or nickel, is located at the anode and is dissolved and transferred to the cathode. Metal ions dissolved in the electrolytic cell are electrically connected to the cathode by reduction and deposited onto the workpiece, which functions as the cathode. Alternatively, the metal ions may already be contained in the electrolyte in the form of a solution. The metal ions are deposited uniformly onto the workpiece at the cathode, and the layer thickness increases over time.

[0029] High layer thicknesses can be achieved simply by the electroplating process. Additionally, the fibers of the nonwoven fabric can be coated across the entire surface. In contrast, PVD processes generally result in only partial coating of the fibers.

[0030] The following table shows the shielding values ​​of the composite material according to the present invention, measured according to ASTM D 4935:2010, and indicates the case without mechanical load and when mechanical load is applied (20% elongation).

[0031] Frequency 30 kHz 450 MHz 900 MHz 1800 MHz 2450 MHz Shielding attenuation 69 dB 65 dB 61 dB 57 dB 53 dB Mechanical load post-shielding damping 68 dB 64 dB 59 dB 54 dB 48 dB

[0032] It is shown that high shielding damping can be achieved despite mechanical loads.

[0033] According to the present invention, the fact that the coating is present on only one side of the nonwoven fabric can be achieved by making one side conductive before the nonwoven fabric is coated by electroplating. To this end, an adhesion promoter, preferably nickel, may be provided on one side of the nonwoven fabric. The adhesion promoter may be applied by a PVD (physical vapor deposition) process.

[0034] Subsequently, a metal coating can be applied to the nonwoven fabric by electroplating on the side provided with an adhesion promoter.

[0035] An additional object of the present invention is a composite material-part assembly comprising a part and a composite material according to the present invention.

[0036] Preferably, in a composite material-part assembly, the part is connected to the composite material through a metal-coated surface of the composite material. The advantage of this is that the metal coating located inside is well protected from mechanical stress. This prevents the metal coating from peeling off, which is particularly advantageous for use in electronic devices.

[0037] Further subject of the present invention is a method for manufacturing a composite material, preferably a method for manufacturing a composite material as described above and below, wherein the method comprises:

[0038] - A step of providing a mechanically bonded nonwoven fabric;

[0039] - A step of applying an adhesion promoter, preferably nickel, to only one side of a mechanically bonded nonwoven fabric;

[0040] - Includes the step of applying an electroplated metal coating to the surface of a mechanically bonded nonwoven fabric provided with an adhesion promoter.

[0041] Preferred embodiments of the method according to the present invention include preferred embodiments of the composite material according to the present invention by making necessary modifications.

[0042] An additional object of the present invention is the use of the composite material according to the present invention for shielding electromagnetic radiation at least partially. Preferred embodiments of the use according to the present invention include preferred embodiments of the composite material according to the present invention with necessary modifications.

[0043] Further subject of the present invention is a method for shielding a component at least partially from electromagnetic radiation, wherein a composite material according to the present invention is applied to at least a portion of the surface of the component. Preferred embodiments of the method according to the present invention include preferred embodiments of the composite material according to the present invention with necessary modifications.

[0044] The part preferably comprises fiber composite materials, for example, SMC (sheet-mould compounds), BMC (bulk-mould compounds), or injection molding materials.

[0045] In a preferred embodiment, the composite material is applied to the surface of a part through a metal-coated side. As a result, the uncoated side of the composite material faces outward.

[0046] The present invention is described in more detail below with reference to non-limiting examples. Specific details for implementing the invention

[0047] Example 1 according to the present invention:

[0048] The composite material according to the present invention is manufactured as follows:

[0049] A needle-punched nonwoven fabric made of polyester fibers with a weight per unit area of ​​70 g / m² is used as a mechanically bonded nonwoven fabric. The fibers are entangled with each other only mechanically by needle punching. The fibers are not bonded to each other thermally or chemically. A tensile elongation at break of approximately 50% in both directions is set by needle punching. Nickel is applied to one side of the nonwoven fabric as an adhesion promoter. The adhesion promoter is applied by a PVD (Physical Vapor Deposition) process. Subsequently, a metal coating (copper and nickel) is applied to the side of the nonwoven fabric with the adhesion promoter by electroplating. The metal coating has a thickness of approximately 0.3 μm. The composite material is measured according to ASTM D 4935:2010. The shielding values ​​shown in Table 1 above are obtained.

[0050] Comparative Example 2:

[0051] A comparative composite material is prepared by manufacturing, coating, and testing a spunbond nonwoven fabric (PES continuous filaments / thermally bonded) in a manner similar to Example 1. The following results are obtained.

[0052] Frequency 30 kHz 450 MHz 900 MHz 1800 MHz 2450 MHz Shielding attenuation 65 dB 62 dB 59 dB 58 dB 52 dB Mechanical load post-shielding damping 0 0 0 0 0

[0053] It is shown that shielding performance can no longer be achieved after a 20% elongation.

Claims

Claim 1 A composite material for shielding electromagnetic radiation, comprising a mechanically bonded nonwoven fabric, wherein the mechanically bonded nonwoven fabric has a metal coating applied by electroplating on one side and does not have a metal coating on the side opposite to the metal coating applied by electroplating. Claim 2 A composite material according to claim 1, characterized in that the nonwoven fabric is mechanically bonded only. Claim 3 A composite material according to claim 1 or 2, characterized in that the nonwoven fabric comprises at least 50 weight%, more preferably at least 80 weight%, and particularly at least 90 weight% of polyester, polyamide, and / or glass based on the total weight of the nonwoven fabric. Claim 4 A composite material according to any one of claims 1 to 3, wherein the nonwoven fabric is characterized by one or more of the following: a tensile elongation at break measured parallel to the machine direction according to DIN ISO 9073-3:2023-09 of greater than 15%, preferably 25% to 90%, particularly 35% to 80%; and a tensile elongation at break measured in a direction orthogonal to the machine direction according to DIN ISO 9073-3:2023-09 of greater than 15%, preferably 25% to 90%, particularly 35% to 80%. Claim 5 A composite material according to any one of claims 1 to 4, wherein the nonwoven fabric has a weight per unit area measured according to DIN ISO 9073-1 2023-09 of 20 g / m² to 200 g / m², preferably 40 g / m² to 170 g / m², particularly 50 g / m² to 120 g / m². Claim 6 A composite material according to any one of claims 1 to 5, wherein the metal coating comprises copper and / or nickel in a ratio of at least 80 weight percent based on the total weight of the metal coating. Claim 7 A composite material according to any one of claims 1 to 6, wherein the metal coating has an average thickness determined by a scanning electron microscope of 0.1 μm to 10 μm, preferably 0.1 μm to 2.5 μm, more preferably 0.1 μm to 1.5 μm, and particularly 0.1 μm to 0.75 μm. Claim 8 A composite material-part assembly comprising a part and a composite material according to any one of claims 1 to 7. Claim 9 A composite material-part assembly according to claim 8, characterized in that the part is connected to the composite material through a metal-coated surface of the composite material. Claim 10 A method for manufacturing a composite material according to any one of claims 1 to 8, comprising: providing a mechanically bonded nonwoven fabric; applying an adhesion promoter, preferably nickel, to only one side of the mechanically bonded nonwoven fabric; and applying an electroplated metal coating to the side of the mechanically bonded nonwoven fabric to which the adhesion promoter is provided. Claim 11 Use of a composite material according to any one of claims 1 to 8 for shielding at least partially electromagnetic radiation. Claim 12 A method for shielding a part from electromagnetic radiation at least partially, characterized in that a composite material according to any one of claims 1 to 8 is applied to at least a portion of the surface of said part. Claim 13 A method according to claim 12, characterized in that the composite material is applied to the surface of the part through a metal-coated surface.