Electromagnetic wave shielding material

Abstract

This invention provides an electromagnetic wave shielding material that is a laminate of metal layers and insulating layers, which can improve the electromagnetic wave shielding effect and suppress the cracking of the metal layer caused by molding and processing. The electromagnetic wave shielding material is a laminate obtained by alternately laminating N (where N is an integer greater than or equal to 1) shielding metal layers and N+1 insulating layers with an adhesive layer sandwiched between them. The outermost layer of the laminate also includes a grounding metal layer. Only one surface of the grounding metal layer is sandwiched between the adhesive layer and the insulating layer. When the thickness of the adhesive layer on that surface is denoted as d1 and its Young's modulus as ε1, the thickness of the grounding metal layer is denoted as d2 and its Young's modulus as ε2, and the combined Young's modulus of the adhesive layer and the grounding metal layer on that surface is denoted as ε3, the following relationship is satisfied: ε3 / ε2 > 0.60, where ε3 = ε1(d1 / (d1+d2)) + ε2(d2 / (d1+d2)).

Description

Technical Field

[0001] This invention relates to an electromagnetic wave shielding material. In particular, this invention relates to an electrical or electronic device and its covering or outer packaging material. Background Technology

[0002] In recent years, global concern for environmental issues has been rising, and environmentally friendly vehicles equipped with secondary batteries, such as electric vehicles and hybrid vehicles, are becoming increasingly popular. These vehicles typically employ the following method: the direct current generated by the installed secondary battery is converted into alternating current by an inverter, and the required power is supplied to the AC motor to obtain driving force. The inverter's conversion operation generates electromagnetic waves. These electromagnetic waves can interfere with the signal reception of in-vehicle audio equipment, wireless devices, etc. Therefore, conventional methods have involved shielding the inverter or housing the battery, motor, and other components together in a metal casing to shield against electromagnetic waves (Patent Document 1: Japanese Patent Application Publication No. 2003-285002).

[0003] Furthermore, not limited to automobiles, various electrical and electronic devices, including communication equipment, displays, and medical devices, also emit electromagnetic waves. Electromagnetic waves can potentially cause malfunctions in precision equipment and may also affect the human body. Therefore, various technologies for using electromagnetic wave shielding materials to mitigate the effects of electromagnetic waves are constantly being developed. For example, a copper foil composite (laminated body) formed by stacked copper foil and a resin film is used as an electromagnetic wave shielding material (Patent Document 2: Japanese Patent Application Publication No. 7-290449). The metal foil has electromagnetic wave shielding properties, and the resin film is stacked to reinforce the metal foil. Additionally, an electromagnetic wave shielding structure obtained by stacking metal layers on the inner and outer sides of an intermediate layer formed of insulating material is known (Patent Document 3: Patent No. 4602680). In addition, an optical component for electromagnetic wave isolation is known, comprising: a substrate, and a stacked component formed on one surface of the substrate, the stacked component being composed of a multilayer repeating unit film including a metal layer and a high refractive index layer (niobium pentoxide) (Patent Document 4: Japanese Patent Application Publication No. 2008-21979).

[0004] The metal foils (metal layers) such as copper foil used in electromagnetic wave shielding materials are typically several μm to tens of μm thick, making them prone to cracking when molded together with resin films into laminates. Therefore, avoiding cracking and improving formability are very important.

[0005] Previously, moldable metal laminates were known to be used in food applications and battery packaging. Due to hygiene concerns regarding food safety and to ensure heat-sealing, a resin film was bonded to both surfaces of the metal foil. However, in such laminates, because both surfaces of the metal foil are covered by the resin film, it is difficult to ground the metal foil. When such laminates are used as electromagnetic wave shielding materials, the current component in the electromagnetic waves can cause resonance and other issues, resulting in a deterioration in shielding effectiveness. In other words, there is a technical problem where poor grounding makes it difficult to further improve the shielding effect.

[0006] Furthermore, while techniques like those described in Japanese Patent No. 6278922 (Patent Document 5) exist to significantly improve shielding, these techniques require a multi-layer structure with at least three metal foils, further degrading grounding performance. Shielding materials that are multi-layered and bonded together with resin films of low conductivity require grounding. Therefore, Japanese Patent Application Publication No. 2010-278119 (Patent Document 6) discloses a technique that intermittently leaves the conductive layers used for grounding the laminated body exposed. Additionally, Japanese Patent Application Publication No. 2012-53234 (Patent Document 7) discloses a technique that uses through-holes in the laminated body to achieve grounding.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2003-285002

[0010] Patent Document 2: Japanese Patent Application Publication No. 7-290449

[0011] Patent Document 3: Japanese Patent No. 4602680

[0012] Patent Document 4: Japanese Patent Application Publication No. 2008-21979

[0013] Patent Document 5: Japanese Patent No. 6278922

[0014] Patent Document 6: Japanese Patent Application Publication No. 2010-278119

[0015] Patent Document 7: Japanese Patent Application Publication No. 2012-53234 Summary of the Invention

[0016] The technical problem that the invention aims to solve

[0017] As with Japanese Patent Application Publication Nos. 2010-278119 and 2012-53234, through holes or peeling sections must be provided, which complicates the manufacturing process. In addition, the structure disclosed in Japanese Patent Application Publication No. 2010-278119 has low design freedom and cannot handle various types of molding.

[0018] In view of the above circumstances, the present invention addresses the technical problem of providing an electromagnetic wave shielding material in one embodiment, which is a laminate of a metal layer and an insulating layer, thereby improving the electromagnetic wave shielding effect and suppressing the cracking of the metal layer caused by the molding process.

[0019] Methods for solving technical problems

[0020] The inventors conducted in-depth research and discovered that by placing the grounding metal layer on the outside of the laminate and exposing it (i.e., without covering it with an insulating layer), resonance can be reduced and sufficient shielding effect can be ensured. However, although exposing the metal layer makes grounding easier than providing through holes or peel-off sections, the exposed metal layer is prone to cracking, resulting in a significant reduction in formability.

[0021] Further in-depth research by the inventors revealed that if the composite Young's modulus, which considers both the Young's modulus of the adhesive layer between the grounding metal layer and the adjacent insulating layer, and the Young's modulus of the grounding metal layer, is controlled such that the composite Young's modulus satisfies certain conditions relative to the Young's modulus of the grounding metal layer, then even when molding is performed with the grounding metal layer exposed, cracking can be effectively suppressed. This invention is based on the above insights, and the following solutions are examples: [1]

[0023] An electromagnetic wave shielding material is a laminate obtained by alternately stacking N (where N is an integer greater than or equal to 1) shielding metal layers with N+1 insulating layers sandwiching adhesive layers, and the outermost layer of the laminate also includes a grounding metal layer.

[0024] An adhesive layer is laminated onto the insulating layer on only one surface of the grounding metal layer. When the thickness of the adhesive layer on that one surface is denoted as d1 and the Young's modulus as ε1, the thickness of the grounding metal layer is denoted as d2 and the Young's modulus as ε2, and the combined Young's modulus of the adhesive layer and the grounding metal layer on that one surface is denoted as ε3, the following relationship is satisfied:

[0025] ε3 / ε2>0.60

[0026] Where, ε3=ε1(d1 / (d1+d2))+ε2(d2 / (d1+d2)). [2]

[0028] The electromagnetic wave shielding material described in [1] satisfies the relationship ε3 / ε2≥0.70. [3]

[0030] The electromagnetic wave shielding material described in [1] satisfies the relationship ε3 / ε2≥0.80. [4]

[0032] The electromagnetic wave shielding material as described in any one of [1] to [3], wherein the composite Young's modulus ε3 is 25000 to 45000 MPa. [5]

[0034] The electromagnetic wave shielding material as described in any one of [1] to [4], wherein the thickness of each metal layer is 4 to 100 μm. [6]

[0036] The electromagnetic wave shielding material as described in any one of [1] to [5], wherein the thickness of each insulating layer is 4 to 600 μm. [7]

[0038] The electromagnetic wave shielding material as described in any one of [1] to [6], wherein the total thickness of the shielding metal layer and the grounding metal layer is 15 to 150 μm. [8]

[0040] A covering material or outer packaging material for electrical or electronic equipment, comprising an electromagnetic wave shielding material as described in any one of [1] to [7]. [9]

[0042] An electrical or electronic device having a covering material or outer packaging material as described in [8].

[0043] The effects of the invention

[0044] According to one embodiment of the present invention, an electromagnetic wave shielding material can be provided, which can improve the electromagnetic wave shielding effect and suppress the cracking of the metal layer caused by molding process. Attached Figure Description

[0045] Figure 1 These are photographs of laminate test pieces from some embodiments, processed under specified conditions for evaluating the formability of laminates.

[0046] Figure 2These are photographs of some comparative laminate test pieces processed under specified conditions for evaluating the formability of laminates. Detailed Implementation

[0047] The embodiments of the present invention will now be described in detail. It should be understood that the present invention is not limited to the following embodiments, and appropriate design changes and improvements can be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0048] (1. Shielding metal layer)

[0049] The material used for the shielding metal layer constituting the electromagnetic wave shielding material in one embodiment of the present invention is not particularly limited. However, based on the viewpoint of improving the shielding characteristics against alternating magnetic and electric fields, a metal material with excellent conductivity is preferred. Specifically, a conductivity of 1.0 × 10⁻⁶ is preferred. 6 When a metal with a conductivity of S / m (value at 20°C, the same applies below) or higher is formed, the conductivity of the metal is more preferably 10.0 × 10⁻⁶. 6 S / m or higher, and more preferably 30.0×10 6 S / m or higher, with the optimal value being 50.0 × 10⁻⁶. 6 Amounts above S / m. For example, a metal with a conductivity of approximately 9.9 × 10⁻⁶ can be cited. 6 Iron with a conductivity of S / m has a conductivity of approximately 14.5 × 10⁻⁶. 6 Nickel with a conductivity of S / m has a conductivity of approximately 33.0 × 10⁻⁶. 6 Aluminum with a conductivity of S / m has a conductivity of approximately 58.0 × 10⁻⁶. 6 Copper with a conductivity of S / m and a conductivity of approximately 61.4 × 10⁻⁶. 6 Silver with a conductivity of S / m. When considering both conductivity and cost, aluminum or copper are preferred for practicality. In one embodiment of the present invention, the shielding metal layers constituting the electromagnetic wave shielding material can be entirely of the same metal, or each layer can use a different metal. Furthermore, alloys containing the aforementioned metals can also be used.

[0050] Various surface treatment layers can be formed on the shielding metal surface to promote bonding, environmental resistance, heat resistance, and rust prevention. For example, to improve the environmental resistance and heat resistance required when the metal surface is the outermost layer, Au plating, Ag plating, Sn plating, Ni plating, Zn plating, Sn alloy plating (Sn-Ag, Sn-Ni, Sn-Cu, etc.), chromate treatment, etc., can be performed. These treatments can also be combined. From a cost perspective, Sn plating or Sn alloy plating is preferred. In addition, to improve the adhesion between the shielding metal layer and the insulating layer, chromate plating, roughening treatment, Ni plating, etc., can be performed. These treatments can also be combined. Roughening treatment easily achieves good adhesion and is preferred. Furthermore, to improve the shielding effect against DC magnetic fields, a metal plating layer with high specific permeability can be provided. Examples of metal plating layers with high specific permeability include Fe-Ni alloy plating and Ni plating.

[0051] When using copper foil, high-purity copper foil is preferred for the purpose of improving shielding performance, with a purity preferably of 99.5% by mass or more, and more preferably 99.8% by mass or more. As copper foil, rolled copper foil, electrolytic copper foil, and copper foil formed by metal sputtering can be used, with rolled copper foil having excellent flexibility and formability (formability includes deep drawing; the same applies below) being preferred. When adding alloying elements to copper foil to form copper alloy foil, the total content of these elements and unavoidable impurities is preferably less than 0.5% by mass. In particular, when the copper foil contains at least one of Sn, Mn, Cr, Zn, Zr, Mg, Ni, Si, and Ag in total of 200 to 2000 ppm by mass, and / or contains 10 to 50 ppm by mass of P, the elongation is improved compared to pure copper foil of the same thickness, and is therefore preferred.

[0052] In one embodiment of the present invention, the thickness of the shielding metal layer constituting the electromagnetic wave shielding material is preferably 4 μm or more per sheet. If the thickness is 4 μm or more, the problem of increased processing difficulty can be avoided, and the significant reduction in the ductility of the shielding metal layer and insufficient processability of the laminate can be prevented. Furthermore, when the thickness of each foil sheet is less than 4 μm, multiple shielding metal layers must be laminated to obtain excellent electromagnetic wave shielding effect, thus increasing manufacturing costs. Based on this viewpoint, the thickness of each shielding metal layer is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, further preferably 25 μm or more, and even more preferably 30 μm or more. On the other hand, when the thickness of each foil sheet exceeds 100 μm, the processability deteriorates; therefore, the thickness of each foil sheet is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 45 μm or less, and even more preferably 40 μm or less.

[0053] While a single metal layer can constitute an electromagnetic wave shielding material, it is preferable to stack multiple metal layers with an insulating layer sandwiched between them, based on the viewpoint of improving formability and shielding performance. Furthermore, it is more preferable to stack two or more metal layers with an insulating layer sandwiched between them, based on the viewpoint of achieving a thinner total thickness of the electromagnetic wave shielding material and ensuring excellent electromagnetic wave shielding characteristics. By stacking two or more metal layers with an insulating layer sandwiched between them, even if the total thickness of the metal layers is the same, the shielding effect is significantly improved compared to a single metal layer or directly stacking two metal layers without an insulating layer sandwiched between them. If the metal layers are directly overlapped, although the shielding effect is improved by increasing the total thickness of the metal layers, a significant improvement cannot be achieved. In other words, when multiple metal layers constituting a laminate are stacked with an insulating layer sandwiched between them, the total thickness of the metal layers required to achieve the same electromagnetic wave shielding effect can be reduced, thus simultaneously achieving both lightweight design and effective electromagnetic wave shielding.

[0054] The reason for this is that, since the resin layer exists between the shielding metal layers, the number of electromagnetic wave reflections increases and the electromagnetic wave attenuation occurs. However, although the more layers of shielding metal are stacked, the better the electromagnetic wave shielding characteristics, the more stacking steps are also increased, which leads to higher manufacturing costs. In addition, the shielding improvement effect tends to saturate. Therefore, the shielding metal layers constituting the stack are preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.

[0055] In one embodiment of the present invention, when multiple shielding metal layers are formed, all shielding metal layers may be made of the same material, or each layer may use a different material. Furthermore, all shielding metal layers may have the same thickness, or each layer may have a different thickness.

[0056] Therefore, in the electromagnetic wave shielding material of one embodiment of the present invention, the total thickness of all metal layers can be 15 to 150 μm, or less than 100 μm, or less than 80 μm, or less than 60 μm. It should be noted that, as described below, the grounding metal layer, whose surface on one side is not covered by an insulating layer and is therefore easily grounded, is called a grounding metal layer. However, in terms of providing electromagnetic wave shielding effect, it is the same as the shielding metal layer. Therefore, the total thickness here refers to the combined thickness of all shielding metal layers and the grounding metal layer.

[0057] To ensure the electromagnetic wave shielding material achieves sufficient strength, the shielding metal layer must possess strength. However, excessive strength reduces the ductility of the shielding metal layer, making it prone to cracking. Therefore, the Young's modulus of the shielding metal layer is preferably 50 MPa to 200 MPa, more preferably 50 MPa to 150 MPa, and even more preferably 50 MPa to 100 MPa. The method for determining the Young's modulus of the shielding metal layer and the grounding metal layer described below is explained below.

[0058] (2. Grounding metal layer)

[0059] In one embodiment of the present invention, a grounding metal layer is provided on the outermost layer of the laminate of the shielding metal layer and the insulating layer. The grounding metal layer is laminated to the insulating layer with an adhesive layer sandwiched on only one side of its surface. That is, the other side of the grounding metal layer is exposed, forming part of the outer surface of the electromagnetic wave shielding material.

[0060] The grounding metal layer is called a grounding metal layer because it is easy to ground, but it is the same as the shielding metal layer in that it has the same electromagnetic wave shielding effect. Therefore, the composition, surface treatment, thickness, and other characteristics described for the shielding metal layer can also be applied to the grounding metal layer. In one embodiment, in the electromagnetic wave shielding material, the grounding metal layer can be a metal layer with the same composition and thickness as the shielding metal layer. Therefore, in this specification, when the term "each metal layer" is used, or when only the term "metal layer" is used, both the shielding metal layer and the grounding metal layer refer to the same object.

[0061] One surface of the grounding metal layer is exposed as part of the outer surface of the electromagnetic wave shielding material, thus forming a grounding current path. This facilitates grounding, reduces resonance, and significantly improves the electromagnetic wave shielding effect of the electromagnetic wave shielding material. Furthermore, when the casing of the electrical or electronic equipment to which the electromagnetic wave shielding material is applied is metal, grounding can be achieved simply by configuring the electromagnetic wave shielding material such that the grounding metal layer is in contact with the casing of the electrical or electronic equipment, even without forming an additional current path.

[0062] Therefore, with the structure described in this embodiment, grounding can be easily achieved without the need for through holes and stripping portions as in the prior art, and an improvement in electromagnetic wave shielding effect can be expected. However, even if through holes or stripping portions are additionally used, as long as grounding can be achieved, it will not hinder the effect of this embodiment. Therefore, this embodiment does not exclude the possibility of adding other grounding methods.

[0063] Furthermore, in this embodiment, as described above, the grounding metal layer differs from other metal layers in that its surface on one side is not covered by an insulating layer, making it easy to ground. Therefore, the names "shielding metal layer" and "grounding metal layer" are merely for ease of distinction. As long as the grounding metal layer is a metal layer, it has an electromagnetic wave shielding effect; conversely, a grounding structure can also be provided for the shielding metal layer. However, the shielding metal layer is not easily grounded because both its surfaces are covered by an insulating layer. As a structure to ground the shielding metal layer, through holes and stripping portions, as in the prior art, can be considered, but it is not limited to these.

[0064] (3. Insulation layer)

[0065] In an embodiment of the electromagnetic wave shielding material of the present invention, the significant improvement in electromagnetic wave shielding effect obtained by stacking multiple shielding metal layers is achieved by interleaving an insulating layer between the shielding metal layers. If the shielding metal layers are directly overlapped, although the total thickness of the shielding metal layers increases and the shielding effect improves, a significant improvement cannot be obtained. This can be attributed to the fact that, due to the presence of an insulating layer between the shielding metal layers, the number of electromagnetic wave reflections increases, and electromagnetic wave attenuation occurs.

[0066] As an insulating layer, the greater the impedance difference between the insulating layer and the metal layer, the better the magnetic wave shielding effect, and therefore it is preferred. To generate a large impedance difference, the relative permittivity of the insulating layer needs to be relatively low, specifically, preferably 10 (value at 20°C, the same applies below), more preferably 5.0 or less, and even more preferably 3.5 or less. In principle, the relative permittivity should not be less than 1.0. Commercially available materials typically have a minimum permittivity of around 2.0; if it is further lower than 1.0, the improvement in shielding effect is limited, and the materials themselves are expensive due to their special properties. Considering the balance between cost and effect, the relative permittivity is preferably 2.0 or higher, more preferably 2.2 or higher.

[0067] Specifically, materials constituting the insulating layer include glass, metal oxides, paper, natural resins, and synthetic resins. From a processability perspective, resins are preferred, and synthetic resins are particularly preferred. Therefore, in one embodiment of the present invention, the insulating layer is a resin layer. Among these materials, fiber-reinforcing materials such as carbon fibers, glass fibers, and aramid fibers can be mixed in. From the viewpoints of ease of purchase and processability, examples of synthetic resins include polyesters such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), and PBT (polybutylene terephthalate); olefin resins such as polyethylene and polypropylene; polyamides; polyimides; liquid crystal polymers; polyacetals; fluoropolymers; polyurethanes; acrylic resins; epoxy resins; silicone resins; phenolic resins; melamine resins; ABS resins; polyvinyl alcohol; urea resins; polyvinyl chloride; polycarbonate; polystyrene; and styrene-butadiene rubber. From the perspectives of processability and cost, PET, PEN, polyamides, and polyimides are preferred. The synthetic resin can be an elastomer such as urethane rubber, chloroprene rubber, silicone rubber, fluororubber, styrene-based, olefin-based, chlorinated, urethane-based, or amide-based elastomer. In one embodiment of the electromagnetic wave shielding material of the present invention, the insulating layer can be composed entirely of the same resin material, or different resin materials can be used for each layer.

[0068] The resin material can be laminated in the form of a film or fibers. Alternatively, an uncured resin composition can be coated onto the shielding metal layer and then cured to form a resin layer. A resin film that can be adhered to the metal layer is preferred due to its ease of manufacture. In particular, PET film is preferred. Specifically, using a 2-axis stretched PET film can improve the strength of the shielding material.

[0069] There is no particular limitation on the thickness of the insulating layer, but when the thickness of each layer is less than 4 μm, there is a tendency for the elongation at break of the shielding material to decrease. Therefore, the thickness of each insulating layer is preferably 4 μm or more, more preferably 7 μm or more, even more preferably 9 μm or more, further preferably 10 μm or more, even more preferably 20 μm or more, even more preferably 40 μm or more, even more preferably 80 μm or more, and even more preferably 100 μm or more. On the other hand, when the thickness of each layer is greater than 600 μm, there is also a tendency for the elongation at break of the shielding material to decrease. Therefore, the thickness of each insulating layer is preferably 600 μm or less, more preferably 500 μm or less, even more preferably 400 μm or less, even more preferably 250 μm or less, and even more preferably 200 μm or less. In one embodiment of the present invention, all insulating layers may be of the same thickness, or each layer may have a different thickness.

[0070] In one embodiment of the present invention, the insulating layer is a resin layer. Generally, resin layers have better ductility than metal layers. Therefore, by using resin layers to support both sides of each shielding metal layer, the ductility of the shielding metal layers is significantly improved, and the processability of the laminate is significantly improved. If the shielding metal layers are directly overlapped, the improved processability cannot be achieved.

[0071] Various surface treatments can be applied to the surface of the resin layer to improve adhesion to the metal layer. For example, applying a primer coating or corona discharge treatment to the surface of the resin layer that is bonded to the shielding metal layer can improve adhesion to the shielding metal layer.

[0072] (4. Adhesive layer)

[0073] In one embodiment of the present invention, an adhesive layer is laminated between a shielding metal layer and an insulating layer. There are no particular limitations on the adhesive, but acrylic resins, epoxy resins, urethane resins, polyester resins, silicone resins, vinyl acetate resins, styrene-butadiene rubbers, nitrile rubbers, phenolic resins, and cyanoacrylate resins are preferred. For ease of manufacture and cost reasons, urethane resins, polyester resins, and vinyl acetate resins are preferred. In one embodiment of the present invention, when forming multiple adhesive layers, all adhesive layers may be made of the same material, or each layer may use a different material.

[0074] In another embodiment of the present invention, an adhesive layer is also sandwiched between the grounding metal layer and the insulating layer during lamination. The adhesive between the grounding metal layer and the insulating layer may be different from or the same as the adhesive between the shielding metal layer and the insulating layer; from a productivity point of view, it is preferable that they are the same.

[0075] Adhesives generally have lower strength compared to resin and metal layers. Therefore, when the adhesive layer is too thick, it tends to hinder the improvement of the ductility of the metal layer formed by laminating resin layers. On the other hand, when the adhesive layer is too thin, it is difficult to apply the adhesive to all interfaces between the metal and resin layers, resulting in unbonded areas. Therefore, the thickness d1 of the adhesive layer is preferably 1 μm or more and 20 μm or less, more preferably 1.5 μm or more and 15 μm or less, and even more preferably 2 μm or more and 10 μm or less. It should be noted that the method for measuring the thickness d1 of the adhesive layer will be described below.

[0076] To avoid hindering the improvement of the ductility of the metal layer obtained by laminating insulating layers, the strength of the adhesive layer can be increased. However, if the strength is too high, the ductility of the adhesive layer tends to decrease, which in turn hinders the improvement of ductility. On the other hand, if the adhesive layer is too soft, it will hinder the improvement of ductility even within the aforementioned thickness range. The Young's modulus ε1 of the adhesive layer is preferably 1 MPa to 1500 MPa, more preferably 3 MPa to 1000 MPa, and even more preferably 5 MPa to 800 MPa. The method for measuring the Young's modulus ε1 of the adhesive layer will be described below. The Young's modulus of the adhesive layer can be adjusted, for example, by adjusting the amount of hardener in the adhesive composition.

[0077] (5. Electromagnetic wave shielding materials)

[0078] In one embodiment of the present invention, an electromagnetic wave shielding material is provided, which is a laminate obtained by alternately stacking N (where N is an integer greater than or equal to 1) shielding metal layers with N+1 insulating layers sandwiching adhesive layers, and the outermost layer of the laminate also includes a grounding metal layer.

[0079] An adhesive layer is laminated onto the insulating layer on only one surface of the grounding metal layer. When the thickness of the adhesive layer on that one surface is denoted as d1 and the Young's modulus as ε1, the thickness of the grounding metal layer is denoted as d2 and the Young's modulus as ε2, and the combined Young's modulus of the adhesive layer and the grounding metal layer on that one surface is denoted as ε3, the following relationship is satisfied:

[0080] ε3 / ε2>0.60

[0081] Where, ε3=ε1(d1 / (d1+d2))+ε2(d2 / (d1+d2)).

[0082] N can be any integer greater than or equal to 1, with no particular restrictions. Increasing N can result in a higher level of electromagnetic shielding. However, as mentioned above, N is typically 1, 2, 3, 4, or 5.

[0083] In one embodiment of the present invention, when the thickness of the adhesive layer on the surface between the adhesive layer and the insulating layer of the two surfaces of the grounding metal layer is denoted as d1 and the Young's modulus is denoted as ε1, and the thickness of the grounding metal layer is denoted as d2 and the Young's modulus is denoted as ε2, and the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer is calculated by the formula ε3=ε1(d1 / (d1+d2))+ε2(d2 / (d1+d2)), the relationship ε3 / ε2>0.60 is satisfied.

[0084] By ensuring that the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer satisfies the aforementioned relationship with the Young's modulus ε2 of the grounding metal layer, cracking of the grounding metal layer can be effectively avoided during forming processes such as punching and deep drawing of the laminate. While not intended to limit the invention theoretically, it can be inferred that, due to the satisfaction of the aforementioned relationship, the difference in deformation between the grounding metal layer and the adhesive layer is unlikely to occur, thereby suppressing localized shrinkage in the grounding metal layer and / or the metal layer, resulting in a low likelihood of cracking.

[0085] Based on this viewpoint, in a preferred embodiment of the present invention, the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer satisfies the relationship ε3 / ε2≥0.70; in a more preferred embodiment, the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer satisfies the relationship ε3 / ε2≥0.80; in a further preferred embodiment, the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer satisfies the relationship ε3 / ε2≥0.85; and in an even more preferred embodiment, the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer satisfies the relationship ε3 / ε2≥0.90. The upper limit of the ratio ε3 / ε2 of the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer is not particularly limited. Based on technical difficulties and practical necessity, it can typically be 0.95 or less, or 0.90 or less, or 0.86 or less, or 0.80 or less.

[0086] In addition, in order to make the ratio ε3 / ε2 of the composite Young's modulus ε3 of the adhesive layer and the grounding metal layer fall within the above-mentioned range, the composite Young's modulus ε3 is preferably in the range of 25,000 to 45,000 MPa, more preferably in the range of 26,500 to 45,000 MPa, and even more preferably in the range of 29,000 to 45,000 MPa.

[0087] The electromagnetic wave shielding materials of various embodiments of the present invention are, in particular, applicable as covering materials or outer packaging materials for electrical or electronic equipment (e.g., inverters, communicators, resonators, electron tubes / discharge lamps, electric heating equipment, motors, generators, electronic components, printed circuits, medical devices, etc.), covering materials for wire harnesses and communication cables connected to electrical or electronic equipment, electromagnetic wave shielding sheets, electromagnetic wave shielding plates, electromagnetic wave shielding bags, electromagnetic wave shielding boxes, electromagnetic wave shielding rooms, and various other electromagnetic wave shielding applications.

[0088] Example

[0089] Embodiments of the invention are shown below together with comparative examples, but they are provided to better understand the invention and its advantages, and are not intended to limit the invention.

[0090] Prepare the metal layers and insulating layers listed in Table 1 to manufacture electromagnetic wave shielding materials for the examples and comparative examples. The markings listed in Table 1 are shown below.

[0091] Cu: Rolled copper foil (conductivity at 20℃: 58.0 × 10⁻⁶) 6 S / m)

[0092] Al: Aluminum foil (conductivity at 20℃: 33.0 × 10⁻⁶) 6 S / m)

[0093] PET: Polyethylene terephthalate film (relative permittivity at 20°C: 3.0)

[0094] M: Metal layer (referring to the metal layer in each example)

[0095] As an adhesive, a urethane-based adhesive is prepared, and a hardener is appropriately added to produce an adhesive having Young's modulus ε1 as shown in Table 1.

[0096] Using the metal foil and resin film described above, various laminates with the laminated structures listed in Table 1 were fabricated. The order of materials listed in the "Structure" column of Table 1 corresponds to the actual order of the laminates. The metal layer and the insulating layer were laminated in a manner that ensured the bonding surfaces were of equal area and did not protrude from each other. A specified amount of adhesive was applied to the bonding surface of the insulating layer using a controlled coater (manufactured by Imoto Manufacturing Co., Ltd.). The coating speed was 50 mm / min. Next, the laminates were pressed using a vacuum heating press at 80°C for 30 minutes, and then kept in a constant temperature bath at 40°C for 7 days to promote the curing reaction, thus tightly bonding the metal layer and the insulating layer.

[0097] (Determination of the thickness d1 of the adhesive layer)

[0098] Using a controlled coater (manufactured by Imoto Manufacturing Co., Ltd.) on a benchtop coater, a urethane-based adhesive with the aforementioned hardener was coated onto a Cu foil, and the reaction was carried out for 7 days in a constant temperature bath heated to 40°C. Afterwards, the Cu foil was divided into four sections along its width, and measurements were taken every 10 mm along its length using a micrometer. The average value of the five measurements was subtracted from the Cu foil thickness to calculate the average value in all length and width directions, and this average value was used as the measured thickness of the adhesive layer. This measured value was then used as the thickness d1 of the adhesive layer in a laminate formed under the same conditions.

[0099] (Determination of Young's modulus ε1 of the adhesive layer)

[0100] A urethane-based adhesive with the aforementioned hardener was coated to a thickness of 50 μm onto a Teflon (registered trademark) sheet and cured in a drying oven at 40°C for 7 days. Tensile tests were then performed based on JIS K7127. The test piece was 12.7 mm wide, and the distance between the chucks was 100 mm. The tensile speed was 50 mm / min. The Young's modulus obtained from this tensile test was used as the measured value of the Young's modulus of the adhesive layer. This measured value was then used as the Young's modulus ε1 of the adhesive layer in a laminate formed using an adhesive of the same composition.

[0101] (Determination of the thickness d2 of the grounding metal layer)

[0102] The thickness d2 of the grounding metal layer is determined by dividing the metal layer into four parts along its width and measuring it five times along its length at 10mm intervals using a micrometer. The average value of the five measurements is calculated for all length and width directions, and this average value is taken as the measured value of the grounding metal layer thickness d2.

[0103] (Determination of Young's modulus ε2 of the grounding metal layer)

[0104] For each example of the grounding metal layer (a metal layer in which only one side of the surface is laminated with the insulation layer), a test piece with a width of 12.7 mm was cut out, the distance between the clamps was set to 100 mm, the tensile speed was set to 50 mm / min, and a tensile test was performed based on JIS K7127 to measure the Young's modulus.

[0105] (Evaluation of moldability)

[0106] The molding limits were evaluated using a die for the FLD (Folding Limit Diagram). The die was designed by reducing the size of the die described in ISO-12004-2-2008 by 25%. The punch dimensions were: d = 22.5 mm, and the punch shoulder was R6 mm. The die pressing pressure was an initial pressure of 4000 N, which was sufficient to press the metal-resin composite test piece. For each example laminate, a circular test piece with a diameter of φ60 mm was cut out, and the punching depth was set to 1 mm to 8 mm to form each test piece. By visually observing each test piece, if a crack was observed penetrating the grounding metal layer in the same foil, it was considered to have cracked and evaluated as "×" (refer to...). Figure 2 If no through-grounding metal layer is observed, it is considered normal and rated as "0" (refer to...). Figure 1 ).

[0107] (Evaluation of electromagnetic wave shielding effectiveness)

[0108] Each example of the laminate was placed in an electromagnetic wave shielding effectiveness evaluation device (TSES-KEC, Japan Technical Science & Technology Corporation), with a frequency of 1MHz, and the electromagnetic wave shielding effectiveness was evaluated using the KEC method at 20°C. The evaluation criteria are as follows:

[0109] 〇: This shows a higher value compared to the ideal magnetic field shielding effect under the total thickness of the foils used in the laminate.

[0110] ×: This shows a lower value compared to the ideal magnetic field shielding effect under the total thickness of the foils used in the laminate.

[0111] It should be noted that the ideal magnetic field shielding effect SE (dB) is calculated using the Schelkunoff formula.

[0112] First, when the incident wave, reflected wave, and transmitted wave are denoted as the incident wave (E), the reflected wave (E), and the transmitted wave (E), respectively, the electric field and magnetic field are denoted as the incident wave (E). xi H yi ), reflected wave (E) xr H yr ), transmitted waves (E) xt H yt When ), the electromagnetic field (E) on the incident side x1 H y1 ) and the electromagnetic field on the transmission side (E x2 H y2 As shown in the following formula.

[0113] E x1 =E xi +E xr ··· (1)

[0114] H y1 =H yi +H yr =(E xi +E xr ) / Z0··· (2)

[0115] E x2 =E xt ··· (3)

[0116] H y2 =H yt =E xt / Z0··· (4)

[0117] In the formula, Z0 is the wave impedance of vacuum.

[0118] In addition, the propagation constant γ of the electromagnetic wave shielding material 10 and the wave impedance Z of the electromagnetic wave shielding material 10 are also specified. c As shown in the following formula.

[0119]

[0120] In the formula, j is the imaginary unit, ω is the angular frequency (ω=2πf, f is the frequency), μ is the permeability, σ is the conductivity, and ε is the dielectric constant.

[0121] At this time, the electromagnetic field (E) on the incident side x1 H y1 ), as shown below with the electromagnetic field (E) on the transmission side x2 H y2 Based on this, it is represented using a four-terminal matrix called the transmission F matrix.

[0122]

[0123] In the formula, A is Cosh(γ·d), and B is Z. c ·sinh(γ·d), C is sinh(γ·d) / Z c D is Cosh(γ·d), and d is the thickness of the electromagnetic wave shielding material 10.

[0124] Substituting equations (1) to (4) into equation (5), we can eliminate E. xi and E xt Other than these variables, the electric field intensity E of the incident wave can be obtained. xi With the electric field intensity E of the transmitted wave xt The shielding effect SE(dB), which is the transmission loss, can be calculated using the following formula.

[0125]

[0126] Table 1

[0127]

[0128] (Inspection)

[0129] According to Table 1, when the ratio of the composite Young's modulus ε3 to ε2 of the adhesive layer and the grounding metal layer, ε3 / ε2, satisfies the relationship ε3 / ε2>0.60, not only can a good electromagnetic wave shielding effect be obtained, but also no cracking through the grounding metal layer caused by molding process will occur, and the formability is good.

Claims

1. An electromagnetic wave shielding material, characterized in that, The electromagnetic wave shielding material is a laminate obtained by alternately stacking N shielding metal layers and N+1 insulating layers sandwiching adhesive layers, and the outermost layer of the laminate also includes a grounding metal layer, wherein N is an integer greater than or equal to 1. An adhesive layer is laminated onto the insulating layer on only one surface of the grounding metal layer. When the thickness of the adhesive layer on that one surface is denoted as d1 and the Young's modulus as ε1, the thickness of the grounding metal layer is denoted as d2 and the Young's modulus as ε2, and the combined Young's modulus of the adhesive layer and the grounding metal layer on that one surface is denoted as ε3, the following relationship is satisfied: ε3 / ε2>0.60 Where, ε3=ε1(d1 / (d1+d2))+ε2(d2 / (d1+d2)).

2. The electromagnetic wave shielding material as described in claim 1, wherein, The relationship satisfies ε3 / ε2≥0.

70.

3. The electromagnetic wave shielding material as described in claim 1, wherein, The relationship ε3 / ε2≥0.80 is satisfied.

4. The electromagnetic wave shielding material according to any one of claims 1 to 3, wherein, The composite Young's modulus ε3 is 25000~45000MPa.

5. The electromagnetic wave shielding material according to any one of claims 1 to 4, wherein, The thickness of each metal layer is 4–100 μm.

6. The electromagnetic wave shielding material according to any one of claims 1 to 5, wherein, The thickness of each insulating layer is 4–600 μm.

7. The electromagnetic wave shielding material according to any one of claims 1 to 6, wherein, The combined thickness of the shielding metal layer and the grounding metal layer is 15–150 μm.

8. A covering material or outer packaging material for electrical or electronic equipment, comprising an electromagnetic wave shielding material as described in any one of claims 1 to 7.

9. An electrical or electronic device comprising the covering material or outer packaging material as described in claim 8.

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