JP7692385B2 - Electromagnetic wave shielding laminate, covering material or exterior material, electric/electronic device, and method for producing electromagnetic wave shielding laminate - Google Patents

Description

The present invention relates to an electromagnetic wave shielding laminate, a covering material or exterior material, an electric/electronic device, and a method for manufacturing an electromagnetic wave shielding laminate.

In environmentally friendly automobiles equipped with secondary batteries, such as electric vehicles and hybrid vehicles, the DC current generated by the secondary batteries is converted to AC current via an inverter, and the necessary power is then supplied to an AC motor to obtain driving force. This generates electromagnetic waves due to the switching operation of the inverter. Since electromagnetic waves can cause reception interference for on-board audio equipment and wireless devices, measures are taken to house the inverter and other components in a metal casing to shield them from electromagnetic waves.

However, although metal housings have good electromagnetic wave shielding properties, they are heavy, which reduces fuel efficiency and increases costs. Therefore, there is a need to develop electromagnetic wave shielding housings that can replace metal housings.

Electromagnetic waves are emitted not only from automobiles, but also from many electric and electronic devices, including communication devices, displays, and medical devices. Electromagnetic waves can cause precision devices to malfunction, and there are also concerns about their effects on the human body. For this reason, various technologies have been developed to reduce the effects of electromagnetic waves using electromagnetic shielding materials. For example, Patent Document 1 describes the use of a copper foil composite formed by laminating copper foil and a resin film as an electromagnetic shielding material. Patent Document 2 describes an electromagnetic shielding material having a structure in which at least two metal foils are laminated with a solid insulating layer interposed therebetween, and at least two of the two or more metal foils laminated with the insulating layer interposed therebetween are electrically connected.

Publication No. Heisei 7-290449 JP 2017-45810 A

However, in Patent Document 1, the thickness of the electromagnetic shielding material required to obtain excellent shielding properties must be significantly increased, and sufficient weight reduction cannot be achieved from the perspective of improving fuel efficiency in automobiles.

In addition, Patent Document 2 describes an electrically connected form in which the length of the metal foil is longer than the length of the insulating layer between the metal foils, and the metal foils are in contact with each other (see paragraph 0073 and FIG. 4 of Patent Document 2). This not only reduces the weight of the electromagnetic shielding material itself, but also improves the shielding properties. However, in the production of the electromagnetic shielding material, it is necessary to make the length of the metal foil longer than the length of the insulating layer between the metal foils, so that the electromagnetic shielding material is not suitable for mass production of electromagnetic shielding materials of desired sizes by slitting a roll-shaped electromagnetic shielding material in which a metal foil and an insulating layer are laminated together by lamination or the like.
Therefore, there is still room for improvement in the electromagnetic shielding materials described in Patent Documents 1 and 2.

Therefore, in one embodiment of the present invention, it is an object of the present invention to provide an electromagnetic wave shielding laminate with good shielding properties. In a further embodiment of the present invention, it is an object of the present invention to provide a method for producing an electromagnetic wave shielding laminate that can be produced relatively easily.

That is, in one aspect, the present invention provides an electromagnetic shielding laminate that includes at least two metal layers and an insulating layer, the metal layers and the insulating layers being alternately stacked, the electromagnetic shielding laminate has tapered portions at the ends of which the thickness varies, the distance A between adjacent metal layers at the tip of each tapered portion in the thickness direction, with the insulating layer interposed between them, is shorter than the distance B between adjacent metal layers at the center of the flat portion other than the tapered portion, and none of the metal layers are in contact with each other.

In one embodiment of the electromagnetic shielding laminate of the present invention, the ratio L1/T of the length L1 of each tapered portion to the thickness T of the flat portion of the electromagnetic shielding laminate is 2000% or less.

In one embodiment of the electromagnetic wave shielding laminate according to the present invention, the ratio A/B of the distance A to the distance B is 75% or less.

In one embodiment of the electromagnetic shielding laminate of the present invention, the top and bottom layers of the electromagnetic shielding laminate are metal layers.

In one embodiment of the electromagnetic shielding laminate according to the present invention, the insulating layer between adjacent metal layers has a protruding portion that protrudes outward beyond the tip of the metal layer.

In one embodiment of the electromagnetic shielding laminate of the present invention, none of the metal layers are electrically connected to each other.

In another aspect, the present invention is a covering or exterior material for electrical/electronic devices that includes any one of the electromagnetic shielding laminates described above.

In another aspect, the present invention is an electric/electronic device equipped with the above-mentioned covering material or exterior material.

Furthermore, in another aspect, the present invention is a method for producing an electromagnetic wave shielding laminate described above, which includes the steps of forming a notch in an intermediate laminate in which at least two metal layers and insulating layers are alternately laminated, from the outermost layer side of the intermediate laminate using a notch processing punch having a protruding portion, and, after forming the notch, punching the intermediate laminate in the thickness direction so as to cut a part of the notch to obtain an electromagnetic wave shielding laminate.

According to one embodiment of the present invention, it is possible to provide an electromagnetic wave shielding laminate having good shielding properties. Furthermore, according to a further embodiment of the present invention, it is possible to provide a method for producing an electromagnetic wave shielding laminate that can be produced relatively easily.

FIG. 2 is a flow diagram for explaining an example of a method for producing an electromagnetic wave shielding laminate according to the present invention. FIG. 1 is a flow diagram for explaining an example of a conventional method for producing an electromagnetic wave shielding laminate. 1 is an enlarged photograph of the electromagnetic wave shielding laminate obtained in Test Example 1 taken with a microscope. 1 is an enlarged photograph of the electromagnetic wave shielding laminate obtained in Test Example 2 taken with a microscope. 1 is a schematic front view of an electromagnetic wave shielding laminate obtained in Example 1. FIG. FIG. 2 is a schematic front view of the electromagnetic wave shielding laminate obtained in Comparative Example 1. FIG. 2 is a schematic front view of the electromagnetic wave shielding laminate obtained in Comparative Example 2.

The present invention is not limited to the following embodiments, and the components can be modified without departing from the spirit of the invention. In addition, various inventions can be formed by appropriately combining the components disclosed in the embodiments.
In this specification, the "tapered portion" has a ratio L1/L0 of the horizontal length L1 of each tapered portion to the horizontal length L0 from the tip e of the metal layer to the center of gravity c of the metal layer (see FIG. 4 ). Also, the "non-tapered portion" refers to a flat portion where the thickness of the electromagnetic shielding laminate does not change substantially.

[1. Electromagnetic wave shielding laminate]
One embodiment of the electromagnetic shielding laminate according to the present invention includes at least two metal layers and an insulating layer, and the metal layers and the insulating layers are alternately laminated. In one embodiment, the electromagnetic shielding laminate has a tapered portion whose thickness changes at the end, and it is essential that the distance A between adjacent metal layers with an insulating layer interposed therebetween at the tip (tip surface) of each tapered portion is shorter than the distance B between adjacent metal layers with an insulating layer interposed therebetween at the central portion of the flat portion other than the tapered portion, and none of the metal layers are in contact with each other. In one embodiment, the shielding characteristics are good.
In the present invention, the metal layers are not in contact with each other, and therefore are not electrically connected to each other.

Conventionally, metal foils and insulating layers have been laminated alternately as electromagnetic wave shielding materials, as in the laminate described in Patent Document 1. In order to improve the shielding properties, efforts were made to reduce the overall thickness of the insulating layer in order to narrow the distance between adjacent metal foils separated by one insulating layer. However, the shielding properties at 1 MHz did not improve, and sometimes even decreased. The reason for this is believed to be that the electromagnetic wave attenuation effect decreased as a result of the reduction in the overall thickness of the insulating layer.

Therefore, the present inventors have conducted intensive studies in consideration of the above circumstances, and have found that an electromagnetic wave shielding property is good by providing at least two metal layers and an insulating layer, the metal layers and the insulating layers being alternately stacked, the laminate having a tapered portion whose thickness changes at the end thereof, the distance A between adjacent metal layers at the end of the tapered portion in the thickness direction via an insulating layer being shorter than the distance B between adjacent metal layers at the center of the flat portion in the thickness direction via an insulating layer, and the metal layers not being in contact with each other. Moreover, unlike Patent Document 2, such an electromagnetic wave shielding laminate can be manufactured relatively easily without making the length of the metal layers longer than the length of the insulating layers in the direction perpendicular to the thickness direction.
Preferred embodiments of the present invention will now be described.

In one embodiment, it can be manufactured by alternately laminating metal layers and insulating layers, and has a structure in which at least two metal layers are laminated via an insulating layer. From the viewpoint of electromagnetic shielding properties, the electromagnetic shielding laminate according to the present invention may be, for example, as follows. Layers in parentheses indicate that they may be added as appropriate. From the viewpoint of electromagnetic shielding properties, it is preferable that at least one of the uppermost layer and the lowermost layer as the outermost layer of the electromagnetic shielding laminate is a metal layer, and it is preferable that both the uppermost layer and the lowermost layer of the electromagnetic shielding laminate are metal layers.
(1) (insulating layer)/metal layer/insulating layer/metal layer/(insulating layer)
(2) (insulating layer)/metal layer/insulating layer/metal layer/insulating layer/metal layer/(insulating layer)
(3) (insulating layer)/metal layer/insulating layer/metal layer/insulating layer/metal layer/insulating layer/metal layer/(insulating layer)
In (1) to (3), one "metal layer" can be formed by stacking multiple metal layers without an insulating layer therebetween, and one "insulating layer" can be formed by stacking multiple insulating layers without an insulating layer therebetween. In other words, multiple metal layers stacked without an insulating layer can be regarded as one metal layer, and multiple insulating layers stacked without a metal layer can be regarded as one insulating layer. In addition, layers other than insulating layers and metal layers can be provided.

In this way, by alternately stacking metal layers and insulating layers, a significant improvement in the electromagnetic shielding properties is observed, but the electromagnetic shielding laminate has tapered portions where the thickness of the ends changes, and the distance A between adjacent metal layers with an insulating layer at the tip (tip surface) of each tapered portion in the thickness direction is shorter than the distance B between adjacent metal layers with an insulating layer at the center of the flat portion other than the tapered portion, and none of the metal layers are in contact with each other, which can further improve the electromagnetic shielding properties. Although it is not intended to limit the present invention by theory, this is believed to be due to the following reasons. That is, it is believed that the shielding effect is improved by shortening the distance between the metal layers, which reduces the amount of electromagnetic waves leaking out from the insulating layer and weakens the strength of the electromagnetic waves that wrap around the receiving antenna.

(Distance A, Distance B)
In one embodiment, from the viewpoint of shortening the distance between adjacent metal layers with an insulating layer interposed therebetween, the ratio A/B of the distance A to the distance B is preferably 75% or less as an upper limit, more preferably 50% or less, and even more preferably 40% or less as an upper limit, while the ratio A/B is typically 8% or more, and more typically 10% or more as a lower limit.
More specifically, the upper limit of the distance A is, for example, 250 μm or less, or, for example, 150 μm or less, while the lower limit is, for example, 1.5 μm or more, or, for example, 2.0 μm or more. The lower limit of the distance B is, for example, 20 μm or more, or, for example, 25 μm or more, while the upper limit is, for example, 300 μm or less, or, for example, 250 μm or less.
An example of a method for measuring the distances A and B will be described below.
The distances can be measured by cutting the electromagnetic shielding laminate in the thickness direction and observing the cut surface with a microscope (optical microscope), etc. That is, distance A and distance B each mean the perpendicular distance between the metal layers in the thickness direction.

(Tapered section length)
From the viewpoint of ease of processing, it is preferable that the ratio L1/T of the horizontal length L1 of each tapered portion to the thickness T of the flat portion of the electromagnetic shielding laminate is 2000% or less (see FIG. 4). If the ratio exceeds this ratio, an additional taper processing step will be required after punching. On the other hand, the lower limit of the ratio L1/T is typically 30% or more, and more typically 50% or more.
The length of the tapered portion can be measured using a microscope, similar to the method for measuring the distances A and B described above.

(metal layer)
In one embodiment, the material of the metal layer to be used is not particularly limited, but from the viewpoint of improving the shielding properties against AC magnetic fields and AC electric fields, it is preferable to use a metal material with excellent conductivity. Specifically, it is preferable to form it with a metal having a conductivity of 1.0×10 ⁶ S/m (value at 20° C.; the same applies below), and it is more preferable that the metal has a conductivity of 10.0×10 ⁶ S/m or more, even more preferable that the metal has a conductivity of 30.0×10 ⁶ S/m or more, and most preferable that the metal has a conductivity of 50.0×10 ⁶ S/m or more. Examples of such metals include Fe with a conductivity of about 9.9×10 ⁶ S/m, Ni with a conductivity of about 14.5×10 ⁶ S/m, Al with a conductivity of about 39.6×10 ⁶ S/m, Cu with a conductivity of about 58.0×10 ⁶ S/m, and Ag with a conductivity of about 61.4×10 ⁶ S/m. Considering both the electrical conductivity and the cost, it is practically preferable to use Al or Cu. All the metal layers used in the electromagnetic shielding laminate according to the present invention may be made of the same metal, or different metals may be used for each layer. Alloys of the above-mentioned metals may also be used. Various surface treatment layers may be formed on the surface of the metal layer for the purposes of adhesion promotion, environmental resistance, heat resistance, rust prevention, etc.

For example, in order to improve the environmental resistance and heat resistance required when the metal layer 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. may be applied. These treatments may also be combined. From the viewpoint of cost, Sn plating or Sn alloy plating is preferred.

In order to improve the adhesion between the metal layer and the insulating layer, chromate treatment, roughening treatment, Ni plating, etc. can be performed. These treatments may also be combined. Roughening treatment is preferred as it is easier to obtain adhesion.

In addition, a metal layer with high relative magnetic permeability can be provided to improve the shielding properties against DC magnetic fields. Examples of metal layers with high relative magnetic permeability include Fe-Ni alloy plating and Ni plating.

When using copper foil as the metal layer, it is preferable to use one with high purity, since it improves shielding properties, and the purity is preferably 99.5% by mass or more, more preferably 99.8% by mass or more. As the copper foil, rolled copper foil, electrolytic copper foil, metallized copper foil, etc. can be used, but rolled copper foil, which has excellent flexibility and formability, is preferable. When alloy elements are added to the copper foil to make a copper alloy foil, the total content of these elements and unavoidable impurities should be less than 0.5% by mass. In particular, it is preferable to contain at least one selected from Sn, Mn, Cr, Zn, Zr, Mg, Ni, Si, and Ag in a total of 50 to 2000 ppm by mass, and/or P in a total of 10 to 50 ppm by mass, since this improves elongation compared to pure copper foil of the same thickness.

In one embodiment, the thickness of the metal layer used is preferably 4 μm or more per layer. If it is less than 4 μm, the ductility of the metal layer may be significantly reduced, and the moldability of the electromagnetic wave shielding laminate may be insufficient. In addition, if the thickness of each layer is less than 4 μm, it becomes necessary to stack a large number of metal layers in order to obtain excellent electromagnetic wave shielding properties, which causes a problem of increased manufacturing costs. From this perspective, the thickness of the metal layer is more preferably 10 μm or more per layer, even more preferably 15 μm or more, even more preferably 20 μm or more, even more preferably 25 μm or more, and even more preferably 30 μm or more. On the other hand, even if the thickness of the metal layer per layer exceeds 100 μm, the moldability is deteriorated, so the thickness of the metal layer is preferably 100 μm or less per layer, more preferably 50 μm or less, even more preferably 45 μm or less, and particularly preferably 40 μm or less.

Since an insulating layer is interposed between the metal layers, the effect of the present invention can be achieved as long as there are at least two metal layers. However, although the shielding properties improve with a larger number of metal layers, increasing the number of layers increases the number of stacking steps, leading to increased manufacturing costs, and the effect of improving the shielding properties tends to saturate, so the number of metal layers in the electromagnetic shielding laminate may be five or less, and may be four or less. When there are three or more metal layers, the ratio A/B of the distance A to the distance B between at least one of the outermost metal layers or the metal layer adjacent to the outermost layer and the metal layer adjacent to the outermost layer via an insulating layer may be 75% or less.

That is, in one embodiment, the total thickness of the metal layers can be 15 to 150 μm, or can be 100 μm or less, 80 μm or less, or 60 μm or less.

(Insulating layer)
A significant improvement in the electromagnetic shielding properties of laminated metal layers can be achieved by placing an insulating layer between the metal layers. Directly stacking metal layers on top of each other does not result in a significant improvement, although the shielding properties improve as the total thickness of the metal layers increases. This is thought to be because the presence of an insulating layer between the metal layers increases the number of times that electromagnetic waves are reflected, resulting in the attenuation of the electromagnetic waves.

For the insulating layer, a layer with a large impedance difference from the metal layer is preferable in terms of obtaining excellent electromagnetic shielding properties. To produce a large impedance difference, the dielectric constant of the insulating layer must be small, and specifically, it is preferably 10 (value at 20°C; the same applies below) or less, more preferably 5.0 or less, and even more preferably 3.5 or less. In principle, the dielectric constant cannot be smaller than 1.0. For commonly available materials, the dielectric constant is at most about 2.0, and even if it is lowered further to approach 1.0, the increase in shielding properties is limited, while the material itself becomes specialized and expensive. Considering the balance between cost and function, the dielectric constant is preferably 2.0 or more, and more preferably 2.2 or more.

Specifically, the materials constituting the insulating layer include glass, metal oxides, paper, natural resins, and synthetic resins, with synthetic resins being preferred from the viewpoint of processability. These materials can also be mixed with fiber reinforcements such as carbon fiber, glass fiber, and aramid fiber. 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, polyacetal, fluororesins, polyurethanes, acrylic resins, epoxy resins, silicone resins, phenolic resins, melamine resins, ABS resins, polyvinyl alcohol, urea resins, polyvinyl chloride, PC (polycarbonate), polystyrene, and styrene butadiene rubber, and among these, PET, PEN, polyamides, and polyimides are preferred for reasons of processability and cost. Synthetic resins can also be elastomers such as urethane rubber, chloroprene rubber, silicone rubber, fluororubber, styrene-based, olefin-based, PVC-based, urethane-based, and amide-based. Furthermore, the synthetic resin itself may act as an adhesive, in which case the metal layer is laminated via the adhesive. There are no particular limitations on the adhesive, but examples include acrylic resins, epoxy resins, urethanes, polyesters, silicone resins, vinyl acetates, styrene butadiene rubbers, nitrile rubbers, phenolic resins, and cyanoacrylates. For reasons of ease of manufacture and cost, urethanes, polyesters, and vinyl acetates are preferred.

The resin material can be laminated in the form of a film or fiber. The resin layer may be formed by applying an uncured resin composition to the metal layer and then curing it, but it is preferable to use a resin film that can be attached to the metal layer for the reason of ease of production. In particular, a PET film can be preferably used. In particular, by using a biaxially stretched film as the PET film, the strength of the shielding material can be increased.

The thickness of the insulating layer is not particularly limited, but it is preferable that the thickness of one insulating layer in the tapered portion is thinner than the thickness of one insulating layer in the central portion of the flat portion. The upper limit of the thickness of one insulating layer in the tapered portion is, for example, 250 μm or less, and, for example, 150 μm or less. On the other hand, the lower limit of the thickness of one insulating layer in the tapered portion is, for example, 1.5 μm or more, and, for example, 2.0 μm or more.
The lower limit of the thickness of the single insulating layer in the central portion of the flat portion is, for example, 20 μm or more, and for example, 25 μm or more. Meanwhile, the upper limit of the thickness of the single insulating layer in the central portion of the flat portion is, for example, 300 μm or less, and for example, 250 μm or less. In an electromagnetic wave shielding laminate in which the outermost layer is an insulating layer, the thickness of the outermost insulating layer may be equal to the thickness of the single insulating layer in the central portion of the flat portion.

(Protruding part)
In one embodiment, an insulating layer interposed between adjacent metal layers may have a protruding portion that protrudes outward beyond the tip of the metal layer.

The lamination method for laminating the insulating layer and the metal layer may be to use an adhesive between the insulating layer and the metal layer, or to thermocompress the insulating layer to the metal layer without using an adhesive. Although a method of simply stacking without using an adhesive is also acceptable, in consideration of the integrity of the electromagnetic wave shielding laminate, it is preferable to bond at least the ends (for example, each side when the shielding material is rectangular) with an adhesive or by thermocompression. However, it is preferable to use an adhesive from the viewpoint of not applying excess heat to the insulating layer. The adhesive is the same as that described above and is not particularly limited, but examples include acrylic resin, epoxy resin, urethane, polyester, silicone resin, vinyl acetate, styrene butadiene rubber, nitrile rubber, phenolic resin, and cyanoacrylate, and urethane, polyester, and vinyl acetate are preferred for ease of manufacture and cost reasons.

The thickness of the adhesive layer is preferably 6 μm or less. If the thickness of the adhesive layer exceeds 6 μm, the metal layer alone will be prone to breakage after the insulating layer is laminated onto the metal layer. However, in cases where the adhesive layer also serves as the insulating layer as described above, this is not the case, and the thickness can be as described in the explanation of the insulating layer.

In one embodiment, the thickness of the electromagnetic shielding laminate at the tip of the tapered portion is, as an upper limit, for example, 400 μm or less, for example, 300 μm or less, while the thickness of the electromagnetic shielding laminate at the tip of the tapered portion is, as a lower limit, for example, 8 μm or more, for example, 10 μm or more.
The upper limit of the thickness of the electromagnetic shielding laminate at the center of the flat portion is, for example, 500 μm or less, e.g., 400 μm or less, whereas the lower limit of the thickness of the electromagnetic shielding laminate is, for example, 100 μm or more, e.g., 150 μm or more.

According to one embodiment, the magnetic shielding characteristic (how much the signal is attenuated on the receiving side) can be 36 dB or more at 1 MHz, preferably 40 dB or more, more preferably 50 dB or more, even more preferably 60 dB or more, and particularly preferably 70 dB or more, for example, 36 to 90 dB. In the present invention, the magnetic shielding characteristic is measured by the KEC method. The KEC method refers to the "electromagnetic shielding characteristic measurement method" of the Kansai Electronics Industry Development Center.

(Application)
In one embodiment, the electromagnetic wave shielding laminate can be used for various electromagnetic wave shielding applications, particularly as a covering or exterior material for electric/electronic devices (e.g., inverters, communication devices, resonators, electron tubes/discharge lamps, electric heating devices, electric motors, generators, electronic components, printed circuits, medical devices, etc.), a covering material for harnesses and communication cables connected to electric/electronic devices, an electromagnetic wave shielding sheet, an electromagnetic wave shielding panel, an electromagnetic wave shielding bag, an electromagnetic wave shielding box, an electromagnetic wave shielding room, and the like.

[2. Manufacturing method of electromagnetic wave shielding laminate]
In one embodiment of the method for producing an electromagnetic wave shielding laminate according to the present invention, the above-mentioned electromagnetic wave shielding laminate is produced by, for example, forming a notch and punching in this order. Note that any explanation that overlaps with the above-mentioned explanation will be omitted.

(Notch formation)
As shown in Figures 1 (A) and (B), at least two metal layers and insulating layers are used, and a notch is formed in the intermediate laminate (hereinafter, the laminate before notching is called the intermediate laminate) in which the metal layers and the insulating layers are alternately stacked, from the outermost layer side (e.g., the bottom layer side) of the intermediate laminate using a notch processing punch having a convex portion. Each metal layer may be made of the same or different materials and may have the same or different thicknesses. Also, each insulating layer may be made of the same or different materials and may have the same or different thicknesses. The angle of the tip of the notch, the radius of curvature R, the pressing load (or pressing amount) of the notch, etc. can be set variously depending on the thickness and material of each metal layer and each insulating layer.
The outermost layer of the intermediate laminate in which the notch is formed is preferably a metal layer, since this layer has a small amount of deformation after processing and is less susceptible to springback.

When the outer surface of the top layer of the intermediate laminate is pressed with a notch processing die and the convex part of the notch processing punch is pressed against the outer surface of the bottom layer of the intermediate laminate, a notch is formed in the outer surface of the bottom layer of the intermediate laminate.

(Punching)
After forming the notch, as shown in Fig. 1(C), the intermediate laminate is punched in the thickness direction so as to cut a part of the notch, to obtain an electromagnetic shielding laminate. More specifically, the intermediate laminate is placed on a die, and the intermediate laminate is punched in the thickness direction with the punch so that the punch hits the apex of the notch. As a result, a tapered portion is formed in which the width of each end of the metal layers adjacent to each other through an insulating layer narrows toward the tip, and the distance A between the metal layers adjacent to each other through an insulating layer at the tip of each tapered portion is shorter than the distance B between the metal layers adjacent to each other through an insulating layer at the central portion of the flat portion other than the tapered portion, thereby obtaining an electromagnetic shielding laminate in which none of the metal layers are in contact with each other. In addition, no sagging or the like occurs on the entire fracture surface (tip) after punching.
2A and 2B, if the intermediate laminate is punched out without forming a notch in the intermediate laminate in the above-mentioned embedding step, the metal layers of the intermediate laminate after cutting are not in contact with each other, but the metal layers and insulating layers are pulled during punching, which may cause sagging across the entire fracture surface. It is presumed that such sagging reduces the shielding properties of the electromagnetic shielding laminate.

The appropriate clearance between the punch and die is, for example, 2 to 8% of the total thickness of the electromagnetic shielding laminate in order to prevent sagging of the fracture surface.

In addition, in one embodiment of the method for producing an electromagnetic shielding laminate according to the present invention, if the metal layer and the insulating layer are not bonded with an adhesive, thermocompression bonding, or the like during the production of the intermediate laminate, the method may include a step of fixing the ends of the above-mentioned punched electromagnetic shielding laminate (for example, if the laminate has a rectangular shape when viewed from above, the four ends) with tape to prevent misalignment.

The present invention will be specifically explained based on test examples, examples, and comparative examples. The following examples and comparative examples are merely specific examples intended to facilitate understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these specific examples.

[Study on the production of electromagnetic wave shielding laminate]
(Test Examples 1 and 2)
As shown in Table 1, a copper foil (width: 50 mm, depth: 40 mm, thickness: 18 to 21 μm) and a PET film (width: 50 mm, depth: 40 mm, thickness: 99 to 100 μm) were prepared as Test Example 1, and a copper foil (width: 50 mm, depth: 40 mm, thickness: 35 to 36 μm) and a PC film (width: 50 mm, depth: 40 mm, thickness: 100 μm) were prepared as Test Example 2. According to the configuration shown in Table 1, an intermediate laminate was produced by bonding the PET film or PC film and the copper foil with an adhesive (see FIG. 1(A)).
Next, a notch was formed in the intermediate laminate using a notch processing punch having a protruding portion from the bottom layer side of the intermediate laminate (see FIG. 1(B)). Next, the intermediate laminate was placed on a die, and the intermediate laminate was punched in the thickness direction with the punch so that the punch hit the apex of the notch, thereby obtaining an electromagnetic wave shielding laminate having a tapered portion and a flat portion other than the tapered portion (see FIG. 1(C)). At this time, the clearance between the die and the punch was set to 0.01 mm.

<Evaluation method>
(Observation after punching)
The electromagnetic wave shielding laminate was observed under the following observation conditions and evaluated based on the following criteria. The results are shown in Table 1 and Figure 3A (Test Example 1) and Figure 3B (Test Example 2).
Observation conditions Measurement equipment: Microscope (Keyence VHX-6000)
Measurement location: Cross-sectional shape of the end of the laminate (The laminate was cut and embedded in resin, and the cross-sectional shape of the cut laminate was then polished.)
Observation magnification: 20x Evaluation criteria: In the obtained electromagnetic shielding laminate, if the ratio A/B of the distance A between adjacent metal layers at the tip of the tapered portion with an insulating layer interposed therebetween to the distance B between adjacent metal layers at the central part of the flat portion other than each tapered portion, was 75% or less, it was indicated as "good." Note that the distances A and B in Test Example 1 mean the vertical distances in the thickness direction between the lowermost metal layer in which the notch is formed and the adjacent metal layer with an insulating layer interposed therebetween.

(Consideration 1)
In Test Examples 1 and 2, at least two metal layers, copper foil and an insulating layer, were used, and a notch was formed in the intermediate laminate in which the metal layers and the insulating layers were alternately laminated, from the bottom layer side of the intermediate laminate with a notch processing punch having a convex portion, and the intermediate laminate was then punched in the thickness direction so as to cut off a part of the notch. As a result, an electromagnetic shielding laminate was obtained in which the thickness of the end portion changes, and the distance A between adjacent metal layers at the tip of each tapered portion in the thickness direction, with an insulating layer interposed therebetween, is shorter than the distance B between adjacent metal layers at the central portion of the flat portion other than the tapered portion, and none of the metal layers are in contact with each other (see Figures 3A and B).

[Electromagnetic wave shielding laminate]
Example 1
In Example 1, the electromagnetic shielding laminate 100 shown in Fig. 4 was produced as follows. First, two sheets of copper foil 110, 112 (width: 60 mm, depth: 60 mm, thickness: 17 µm) were prepared as metal layers, and two sheets of PET film 120, 124 (width: 50 mm, depth: 50 mm, thickness: 100 µm) and one sheet of PET film 122 (width: 70 mm, depth: 70 mm, thickness: 25 µm) were prepared as insulating layers. The PET film 120, the PET film 122, the PET film 124, and the copper foil 112 were laminated in this order on the copper foil 110 to obtain an intermediate laminate without using any adhesive.

In order to form a tapered portion and a flat portion other than the tapered portion of the intermediate laminate, the copper foils 110, 112 were folded along the step between the edge of the PET film 120, 124 and the PET film 122. Next, the four sides of the laminate were taped to fix the position of each component, and the electromagnetic shielding laminate 100 shown in Figure 4 was obtained. Note that the width and depth of the PET film 122 were both greater than the copper foils 110, 112, so the obtained electromagnetic shielding laminate 100 had a protruding portion 123.

(Electromagnetic wave shielding characteristic evaluation)
In order to prevent the copper foils 110, 112 and the PET films 120, 122, 124 constituting the electromagnetic shielding laminate 100 from shifting during measurement, the outer periphery of the electromagnetic shielding laminate 100 was fixed with tape, and the electromagnetic shielding laminate 100 was placed in a magnetic field shielding property evaluation device (Model T SES-KEC, manufactured by Techno Science Japan) and the magnetic field shielding property was evaluated by the KEC method under room temperature (25°C) conditions. The frequency was then changed from 0.1 MHz to 10 MHz to investigate the transition of the magnetic field shielding property with respect to the change in frequency. Table 2 shows the magnetic field shielding property at 1 MHz.

(Distance A, distance B, tapered section length)
The distance A between the adjacent copper foils 110, 112 at the tip of the tapered portion 115 with the PET film 122 interposed therebetween corresponds to the thickness of the PET film 122 measured with a height gauge (manufactured by Toyo Seiki Seisakusho), which is shown in Table 2. The distance B between the adjacent copper foils 110, 112 at the center of the flat portion 116 with the PET films 120, 122, 124 interposed therebetween corresponds to the total value of the thicknesses of the PET films 120, 122, 124 measured with a height gauge, which is shown in Table 2.
The horizontal length L1 of each tapered portion is approximately 5 mm, the ratios L1/L0 of the horizontal length L1 of the tapered portion to the horizontal length L0 from the tip e of the copper foils 110, 112 to the center of gravity c are each 20% or less, and the ratios L1/T of the horizontal length L1 of each tapered portion to the thickness T of the central portion of the flat portion of the electromagnetic shielding laminate 100 are each reliably kept to 2000% or less.

<Comparative Example 1>
In Comparative Example 1, the electromagnetic shielding laminate 200 shown in Fig. 5 was produced as follows. First, two sheets of copper foil 210, 212 (width: 60 mm, depth: 60 mm, thickness: 17 μm) were prepared as metal layers, and two sheets of PET film 220, 224 (width: 50 mm, depth: 50 mm, thickness: 100 μm) and one sheet of PET film 222 (width: 70 mm, depth: 70 mm, thickness: 25 μm) were prepared as insulating layers. The PET film 220, the PET film 222, the PET film 224, and the copper foil 212 were laminated in this order on the copper foil 210 to obtain an intermediate laminate. The electromagnetic shielding laminate 200 was produced in the same manner as in Example 1, except that the ends of the metal layers were not tapered. As for the distance C between the adjacent copper foils 210, 212 with the PET films 220, 222, 224 interposed therebetween, the total value of the thicknesses of the PET films 220, 222, 224 is shown in Table 3.
The magnetic field shielding properties of the obtained electromagnetic wave shielding laminate 200 were evaluated by the KEC method. The results are shown in Table 3.

<Comparative Example 2>
In Comparative Example 2, the electromagnetic shielding laminate 300 shown in FIG. 6 was prepared as follows. Two sheets of copper foil 310, 312 (width: 60 mm, depth: 60 mm, thickness: 17 μm) were prepared as metal layers, and one sheet of PET film 322 (width: 60 mm, depth: 60 mm, thickness: 25 μm) was prepared as an insulating layer. The PET film 322 and the copper foil 312 were laminated in this order on the copper foil 310 to obtain an intermediate laminate. The electromagnetic shielding laminate 300 was prepared in the same manner as in Example 1, except that the ends of the metal layers were not tapered. As for the distance D between the copper foils 310, 312 adjacent to each other via the PET film 322, the thickness of the PET film 322 is shown in Table 3.
The magnetic field shielding characteristics of the obtained electromagnetic wave shielding laminate 300 were evaluated by the KEC method. The results are shown in Table 3.

(Consideration 2)
In Example 1, there was a tapered portion with a varying thickness at the end, and the distance A between adjacent metal layers, interposing an insulating layer, at the tip of each tapered portion in the thickness direction was shorter than the distance B between adjacent metal layers, interposing an insulating layer, at the central portion of the flat portion other than the tapered portion, and none of the metal layers were in contact with each other, resulting in an electromagnetic wave shielding laminate with good shielding properties.
On the other hand, in Comparative Examples 1 and 2, since no tapered processing was performed, the distances C and D between adjacent metal layers at the tip with an insulating layer interposed therebetween were equivalent to the distances C and D between adjacent metal layers at the center with an insulating layer interposed therebetween, and therefore the shielding characteristics were inferior to Example 1. In particular, in Comparative Example 2, the distance D was shorter than the distance B, even though it was equivalent to the distance A, compared to Example 1, and therefore the shielding characteristics were inferior.
In addition, taking Example 1 into consideration, it is presumed that in Test Examples 1 and 2, electromagnetic shielding laminates with good shielding properties were obtained.

100, 200, 300 Electromagnetic wave shielding laminate 110, 112, 210, 212, 310, 312 Copper foil 115 Tapered portion 120, 122, 124, 220, 222, 224, 320 PET film 123 Protruding portions A to D Distance L0, L1 Horizontal length T Thickness c Center of gravity e Tip

Claims (9)

An electromagnetic wave shielding laminate comprising at least two metal layers and an insulating layer, the metal layers and the insulating layers being alternately laminated,
The electromagnetic wave shielding laminate has a tapered portion at an end thereof where the thickness changes,
a distance A between adjacent metal layers with an insulating layer interposed therebetween at the tip of each tapered portion in the thickness direction is shorter than a distance B between adjacent metal layers with an insulating layer interposed therebetween at a central portion of a flat portion other than the tapered portion;
An electromagnetic wave shielding laminate in which none of the metal layers are in contact with each other. The electromagnetic shielding laminate according to claim 1, in which the ratio L1/T of the length L1 of each tapered portion to the thickness T of the flat portion of the electromagnetic shielding laminate is 2000% or less. The electromagnetic shielding laminate according to claim 1 or 2, wherein the ratio A/B of the distance A to the distance B is 75% or less. The electromagnetic shielding laminate according to claim 1 or 2, wherein the top and bottom layers of the electromagnetic shielding laminate are metal layers. The electromagnetic shielding laminate according to claim 1 or 2, in which the insulating layer between adjacent metal layers has a protruding portion that protrudes outward beyond the tip of the metal layer. The electromagnetic shielding laminate according to claim 1 or 2, in which none of the metal layers are electrically connected to each other. A covering or exterior material for electrical/electronic devices comprising the electromagnetic shielding laminate according to claim 1 or 2. An electric/electronic device equipped with the covering material or exterior material according to claim 7. A method for producing the electromagnetic shielding laminate according to claim 1 or 2, comprising the steps of:
a step of forming a notch in an intermediate laminate, in which at least two metal layers and an insulating layer are alternately laminated, from the outermost layer side of the intermediate laminate by using a notch processing punch having a protruding portion;
and after forming the notch, punching out the intermediate laminate in a thickness direction so as to cut a portion of the notch to obtain an electromagnetic wave shielding laminate.