Composite material for shielding against electromagnetic radiation

Abstract

The invention relates to a composite material for shielding against electromagnetic radiation, comprising a mechanically solidified non-woven fabric, said mechanically solidified non-woven fabric having a galvanically applied metal coating on one side and having no metal coating on the side facing away from the galvanically applied metal coating.

Description

[0001] Applicant: Carl Freudenberg KG, 69469 Weinheim

[0002] Composite material for shielding electromagnetic radiation

[0003] Description

[0004] The present invention relates to a composite material for shielding electromagnetic radiation, a method for its production, and its use. The invention further relates to a composite material-component assembly and a method for at least partially shielding a component from electromagnetic radiation using the composite material.

[0005] STATE OF THE ART

[0006] Electromagnetic waves have both an electric and a magnetic field component. Waves emitted by electronic components can lead to mutual electromagnetic interference (EMI). Due to enormous advances in semiconductor technology, electronic components have become increasingly smaller, and their density within electronic devices has increased significantly. The growing complexity of electronic systems, for example in fields such as electromobility, aerospace engineering, and medical technology, poses a significant challenge to the electromagnetic compatibility of individual components. For instance, in electric vehicles, high-power electric drives are integrated into extremely confined spaces and controlled by electronic components, and these individual components must not interfere with each other.To achieve electromagnetic compatibility, it is common practice to attenuate electromagnetic interference using shielding enclosures. The term electromagnetic compatibility (EMC) is defined, for example, according to DIN VDE 0870, as the ability of an electrical device to function satisfactorily in its environment without unduly affecting that environment, which may also include other devices. Therefore, EMC must fulfill two conditions: the shielding of emitted radiation and immunity to interference from other electromagnetic radiation. In many countries, the corresponding devices must comply with legal regulations. According to DIN VDE 0870, electromagnetic interference (EMI) is the effect of electromagnetic waves on electrical circuits, devices, systems, or living beings.Such exposure can lead to acceptable or unacceptable impairments of the affected objects, such as impaired functionality of equipment or endangering people. In such cases, appropriate protective measures must be taken. The frequency range relevant for EMI shielding generally lies between 100 Hz and 100 GHz. The attenuation achieved by shielding an incident electromagnetic wave typically consists of reflection and absorption, regardless of the shielding principle. During absorption, the electromagnetic wave loses energy, which is converted into heat energy. Absorption depends on the thickness of the shielding material. Reflection, on the other hand, is independent of the material thickness, depending on the frequency range, and can occur on the front, back, and within the material itself.

[0007] In the mid-frequency range, the electrical conductivity of the materials can generally be used directly to assess shielding effectiveness. In the lower frequency range, relative permeability can be used to assess shielding effectiveness, and in the upper frequency range, reflection and vibration absorption can be used.

[0008] It is known to use plastic composites (composites, compounds) for the production of electromagnetic shielding. These composites have a matrix consisting of at least one polymer component and at least one filler with shielding properties. They can be used in the form of coatings, insulating tapes, molded parts, etc. For example, electrically conductive fillers can be dispersed in a matrix of at least one non-conductive polymer to produce conductive composites. A disadvantage of this method is that electrically conductive additives such as metal powders are very expensive. Furthermore, a high filler density is required to overcome the percolation threshold. With increasing wall thickness, the absolute amount of additive required to maintain a constant relative concentration also increases.

[0009] S. Geetha et al. provide an overview of methods and materials for shielding electromagnetic radiation in the Journal of Applied Polymer Science, Vol. 112, 2073–2086 (2009). They mention various plastic composites based on non-conductive polymers with a wide variety of conductive fillers. As an alternative, they discuss the use of conductive polymers, specifically polyaniline and polypyrrole. A disadvantage of these materials is their low aging resistance. Furthermore, they are difficult to handle, must be applied after the fact, and are expensive.

[0010] It is also known to use metallic housings, for example made of aluminum, to shield electromagnetic radiation. Due to the high conductivity of metals, good shielding attenuation is achieved. However, the use of purely metallic shielding is associated with several disadvantages, such as the complex manufacturing process involving stamping, bending, and the application of corrosion protection, which is very expensive. Furthermore, the design freedom is very limited with metallic materials.

[0011] The use of composite materials is also well-known, in which textile materials, such as nonwovens, are coated with metal on both sides. For example, polyamide spunbond nonwovens coated with copper on both sides are available. However, due to their double-sided metallic coating, such composite materials exhibit high conductivity both across their surface and perpendicular to it. This is disadvantageous, as it can lead to short circuits and corrosion. For this reason, the surface of the material is made electrically insulating by an additional coating, which necessitates a further processing step. Furthermore, composite materials have a relatively high metal content, which further increases manufacturing costs.

[0012] From EP0835915 A2, the use of spunbond nonwovens as a base material for electrically conductive transfer belts is known, wherein the fabric is electroplated by coating with at least one metal layer and provided with an adhesive coating on both sides or only one side, wherein the average thickness of the fabric is at least as great as the total thickness of the adhesive coating(s). Spunbond nonwovens typically contain continuous filaments that are thermally and / or chemically bonded together. This is disadvantageous because, under stress, the rigid thermal or chemical bond of the fibers of the nonwoven breaks down, thereby forming cracks in the coating.

[0013] From DE10145750 A1, a method for producing a metal layer on a substrate is known, in which, in a first step, conductive particles are applied to a surface of the substrate so that they are fixed to the substrate, and in a second step, the substrate with the particles is chemically or electroplated metallized in a metallization bath to form the metal layer. A textile, among other materials, can be used as the substrate.

[0014] The invention is based on the objective of providing a material with which the aforementioned disadvantages can be at least partially eliminated.

[0015] This problem is solved by a composite material for shielding electromagnetic radiation comprising a mechanically bonded nonwoven fabric, wherein the mechanically bonded nonwoven fabric has an electroplated metal coating on one side and no metal coating on the side facing away from the electroplated metal coating.

[0016] According to the invention, the mechanically bonded nonwoven fabric has a galvanically applied metal coating on only one side. On the opposite side, the nonwoven fabric has no metal coating. The mechanically bonded nonwoven fabric therefore has a metal coating on precisely one side.

[0017] A nonwoven fabric is a sheet-like structure with a predominantly two-dimensional extent (base area) and a comparatively small thickness. Nonwoven fabrics are described in the standard DIN EN ISO 9092:2011. An orthogonal coordinate system can be used to describe nonwoven fabrics, where the base area of ​​the nonwoven lies in the plane spanned by the x-axis and the y-axis (also referred to as the x,y-plane). The z-axis, which is orthogonal to this plane, can be used to describe the material thickness. As is common usage, "side" refers to a base area of ​​the nonwoven fabric.

[0018] Compared to nonwovens known in the prior art that are coated on both sides with metal, the composite material according to the invention has the advantage that it allows for use even without an additional insulating layer. When applied to a component via the metal-coated side, the non-metal-coated side of the nonwoven is on the outside. This means that in the resulting composite material-component assembly, conductivity is generated only on the inside and not on the outside, so that no additional insulating layer is required. Furthermore, inherent corrosion protection can also be achieved in this way. Another advantage of this application is that the inner metal coating is well protected against mechanical stress.

[0019] Another advantage is that relatively little metal can be used to achieve high layer thicknesses, since only one side is coated. Furthermore, the uncoated side of the composite material offers better adhesion to components than metal-coated surfaces. It is also advantageous that increasing the thickness of the composite material does not require an increase in the amount of metal, as the metal is used as a coating and not as a filler.

[0020] According to the 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, since nonwoven fabrics have a significantly higher elongation at break than woven fabrics and do not have regular structures. This, in turn, is advantageous because it prevents the formation of interference patterns. In addition, the mechanical bonding prevents the fibers of the nonwoven fabric from sliding apart, or only to a very limited extent. As a result, the conductive coating remains intact even under load, and no cracks form.

[0021] In a preferred embodiment, the nonwoven fabric is only mechanically bonded. That is, the nonwoven fabric has no additional bonding, for example, by binders or bonding fibers. Preferably, the nonwoven fabric is neither chemically bonded by chemical binders nor thermally bonded by bonding fibers. Particularly preferred is the nonwoven fabric being a needle-punched nonwoven and / or a hydroentangled nonwoven. This allows for particularly good fiber mobility of the nonwoven fabric.

[0022] In a further preferred embodiment, the nonwoven fabric comprises staple fibers, preferably with a staple length of 10 mm to 90 mm, more preferably of 20 mm to 90 mm, and particularly of 38 mm to 90 mm. The proportion of staple fibers based on the total weight of the nonwoven fabric is preferably at least 70 wt.%, more preferably of 80 wt.% to 100 wt.%, and more preferably of 90 wt.% to 100 wt.%. An advantage of staple fibers is that they impart high flexibility to the nonwoven fabric. While in spunbond nonwovens consisting of continuous filaments the filaments break under high elongation, the staple fibers can slide past each other under tension, thus preventing damage to the metallic coating.

[0023] According to the invention, the fibers of the nonwoven fabric preferably consist at least partially of synthetic polymer fibers and / or glass fibers. Particularly preferably, the nonwoven fabric contains at least 50 wt.%, more preferably at least 80 wt.%, and especially at least 90 wt.%, polyester, polyamide, and / or glass, based on the total weight of the nonwoven fabric. Preferably, the nonwoven fabric has an elongation at break, measured parallel to the manufacturing direction according to DIN ISO 9073-3:2023-09, of more than 15%, for example, from 15% to 100%, preferably from 25% to 90%, and especially from 35% to 80%. Orthogonal to the manufacturing direction, the nonwoven fabric preferably has an elongation at break measured according to DIN ISO 9073-3:2023-09 of more than 15%, for example from 15% to 100%, preferably from 25% to 90% and particularly from 35% to 80%.

[0024] The nonwoven fabric preferably exhibits low modulus values ​​measured parallel to the manufacturing direction according to DIN ISO 9073-3 2023-09. At an elongation of 10%, the nonwoven fabric preferably has a tensile strength, measured according to DIN ISO 9073-3 2023-09, of 50 N / 5cm to 150 N / 5cm, more preferably of 70 N / 5cm to 130 N / 5cm, and particularly of 80 N / 5cm to 110 N / 5cm. At an elongation of 20%, the nonwoven fabric preferably has a tensile strength, measured according to DIN ISO 9073-3 2023-09, of 100 N / 5cm to 160 N / 5cm, more preferably of 110 N / 5cm to 150 N / 5cm, and particularly of 120 N / 5cm to 140 N / 5cm.

[0025] The nonwoven fabric preferably exhibits low modulus values ​​measured orthogonally to the manufacturing direction according to DIN ISO 9073-3 2023-09. At an elongation of 10%, the nonwoven fabric preferably exhibits a tensile strength measured according to DIN ISO 9073-3 2023-09 of 20 N / 5cm to 75 N / 5cm, more preferably of 25 N / 5cm to 65 N / 5cm, and particularly of 30 N / 5cm to 50 N / 5cm. At an elongation of 20%, the nonwoven fabric preferably exhibits a tensile strength of 30 N / 5cm to 100 N / 5cm, more preferably of 40 N / 5cm to 90 N / 5cm, and particularly of 50 N / 5cm to 80 N / 5cm.

[0026] Preferably, the nonwoven fabric has a basis weight measured according to DIN ISO 9073-1 2023-09 of 20 g / m². 2 up to 200 g / m² 2 , preferably 40 g / m² 2 up to 170 g / m² 2 especially of 50 g / m² 2 up to 120 g / m² 2According to the invention, the composite material has an electroplated metal coating on one side. The metal coating can contain a wide variety of metals. Suitable metals include, for example, copper, nickel, silver, aluminum, and / or tin. Preferably, the metal coating contains copper and / or nickel because these metals have good conductivity. Particularly preferably, the metal coating contains copper and / or nickel in a proportion of at least 80% by weight, based on the total weight of the metal coating.

[0027] Particularly preferably, the metal coating contains copper and nickel in 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.

[0028] The metal coating preferably has an average thickness determined by scanning electron microscopy of 0.1 pm to 10 pm, preferably of 0.1 pm to 2.5 pm, even more preferably of 0.1 pm to 1.5 pm, in particular of 0.1 pm to 0.75 pm.

[0029] According to the invention, the metal coating is applied electroplated. Electroplated means applied using electroplating technology (also called electroplating). Electroplating technology refers to the electrochemical deposition of metallic deposits, i.e., coatings, onto substrates (workpieces) in an electrolytic bath.

[0030] In electroplating, an electric current, preferably direct current, is passed through an electrolytic bath. At the positive terminal (anode) is a metal such as copper or nickel, which is dissolved and transferred to the negative terminal (cathode). The metal ions dissolved in the electrolytic bath are deposited onto a workpiece by reduction. This workpiece is electrically connected to the negative terminal and thus serves as the cathode. Alternatively, the metal ions can already be present in the electrolyte as a solution. The metal ions are deposited evenly on the workpiece at the negative terminal, and the layer thickness increases over time.

[0031] The electroplating process allows for the simple achievement of high layer thicknesses. Furthermore, the fibers of the nonwoven fabric can be completely coated. In contrast, PVD processes typically result in only partial coating of the fibers.

[0032] The following table shows shielding values ​​of a composite material according to the invention, measured according to ASTM D 4935:2010 without and with mechanical stress (elongation by 20%).

[0033] Table 1

[0034] It turns out that high shielding attenuation can be achieved despite mechanical stress.

[0035] According to the invention, the coating being applied only to one side of the nonwoven fabric can be achieved by making the nonwoven fabric conductive on one side before it is electroplated. For this purpose, the nonwoven fabric can be coated on one side with an adhesion promoter, preferably nickel. The adhesion promoter can be applied using a PVD (Physical Vapor Deposition) process.

[0036] Subsequently, the nonwoven fabric can be electroplated with a metal coating on the side treated with the adhesion promoter.

[0037] Another object of the present invention is a composite material-component assembly comprising a component and a composite material according to the invention.

[0038] Preferably, in the composite material-component assembly, the component is connected to the composite material via the metal-coated side of the composite material. An advantage of this is that the internal metal coating is well protected against mechanical stress. This prevents the metal coating from peeling off, which is particularly advantageous for applications in electronic devices.

[0039] A further object of the present invention is a method for producing a composite material, preferably a composite material as described above and below, comprising the following steps: a) providing a mechanically bonded nonwoven fabric; b) applying an adhesion promoter, preferably nickel, to only one side of the mechanically bonded nonwoven fabric; c) applying an electroplated metal coating to the side of the mechanically bonded nonwoven fabric provided with the adhesion promoter. Preferred embodiments of the method according to the invention include preferred embodiments of the composite material according to the invention, mutatis mutandis.

[0040] A further aspect of the present invention is the use of the composite material according to the invention for at least partial shielding of electromagnetic radiation. Preferred embodiments of the use according to the invention include preferred embodiments of the composite material according to the invention, mutatis mutandis.

[0041] A further object of the present invention is a method for at least partially shielding a component from electromagnetic radiation, in which a composite material according to the invention is applied to at least parts of the surface of the component. Preferred embodiments of the method according to the invention include preferred embodiments of the composite material according to the invention, mutatis mutandis.

[0042] Preferably, the component incorporates fiber composite materials, for example SMC (Sheet-Mould-Compounds), BMC (Bulk-Mould-Compounds), or injection molded materials.

[0043] In a preferred embodiment, the composite material is applied to the surface of the component via the metal-coated side. This means that the uncoated side of the composite material faces outwards.

[0044] The invention is explained in more detail below using non-limiting examples. Example 1 according to the invention:

[0045] A composite material according to the invention is produced as follows: A needle-punched nonwoven fabric made of polyester fibers with a basis weight of 70 g / m² is used as the mechanically bonded nonwoven fabric. 2The fibers are interlocked mechanically by needling. They are not thermally or chemically bonded. The needling process establishes an elongation at break of approximately 50% in both directions. One side of the nonwoven fabric is coated with nickel as an adhesion promoter. The adhesion promoter is applied using a PVD (Physical Vapor Deposition) process. Subsequently, the side of the nonwoven fabric coated with the adhesion promoter is electroplated with a metal coating (copper and nickel). 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.

[0046] Comparative example 2:

[0047] A comparative composite material is produced by coating and testing a spunbond nonwoven fabric (continuous PES filaments / thermally bonded) analogously to Example 1. The following results are obtained. Table 2

[0048] It turns out that after 20% stretching, no shielding performance can be achieved anymore.

Claims

Patent claims 1. Composite material for shielding electromagnetic radiation comprising a mechanically bonded nonwoven fabric, characterized in that the mechanically bonded nonwoven fabric has an electroplated metal coating on one side and no metal coating on the side facing away from the electroplated metal coating.

2. Composite material according to claim 1, characterized in that the composite material is only mechanically strengthened.

3. Composite material according to claim 1 or 2, characterized in that the nonwoven fabric contains at least 50 wt.%, more preferably at least 80 wt.%, in particular at least 90 wt.%, based on the total weight of the nonwoven fabric, polyester, polyamide and / or glass.

4. Composite material according to one or more of the preceding claims, characterized in that the nonwoven fabric has an elongation at break measured parallel to the manufacturing direction according to DIN ISO 9073-3:2023-09 of more than 15%, preferably of 25% to 90% and in particular of 35% to 80% and / or an elongation at break measured orthogonally to the manufacturing direction according to DIN ISO 9073-3:2023-09 of more than 15%, preferably of 25% to 90% and in particular of 35% to 80%.

5. Composite material according to one or more of the preceding claims, characterized in that the nonwoven fabric has a basis weight measured according to DIN ISO 9073-1 2023-09 of 20 g / m² 2 up to 200 g / m² 2 , preferably 40 g / m² 2 up to 170 g / m² 2 , especially of 50 g / m² 2 up to 120 g / m² 2 exhibits.

6. Composite material according to one or more of the preceding claims, characterized in that the metal coating contains copper and / or nickel in a proportion of at least 80 wt.%, based on the total weight of the metal coating.

7. Composite material according to one or more of the preceding claims, characterized in that the metal coating has an average thickness determined by scanning electron microscopy of 0.1 pm to 10 pm, preferably of 0.1 pm to 2.5 pm, more preferably of 0.1 pm to 1.5 pm, and in particular of 0.1 pm to 0.75 pm.

8. Composite material-component assembly comprising a component and a composite material according to one or more of the preceding claims.

9. Composite material-component composite, characterized in that the component is connected to the composite material via the metal-coated side of the composite material.

10. A method for producing a composite material according to one or more of claims 1 to 8, comprising the following steps: a) providing a mechanically bonded nonwoven fabric; b) applying an adhesion promoter, preferably nickel, to only one side of the mechanically bonded nonwoven fabric; c) applying an electroplated metal coating to the side of the mechanically bonded nonwoven fabric provided with the adhesion promoter.

11. Use of a composite material according to one or more of claims 1 to 8 for at least partial shielding of electromagnetic radiation.

12. Method for at least partially shielding a component from electromagnetic radiation, characterized in that a composite material according to one or more of claims 1 to 8 is applied to at least parts of the surface of the component.

13. Method according to claim 12, characterized in that the composite material is applied to the surface of the component via the metal-coated side.

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