Electromagnetic wave shielding film

Abstract

The purpose of the present invention is to provide an electromagnetic wave shielding film in which a protective layer surface has a sufficiently high scratch resistance. An electromagnetic wave shielding film according to the present invention comprises: a protective layer having a first main surface and a second main surface opposite the first main surface; and a shield layer disposed on the second main surface side of the protective layer. The L* value of the first main surface is 29 or greater, and the fastest decay auto-correlation rate (Sal) of the first main surface is 3 μm or greater.

Description

Electromagnetic wave shielding film

[0001] The present invention relates to an electromagnetic wave shielding film.

[0002] Conventionally, an electromagnetic wave shielding film has been attached to a printed wiring board such as a flexible printed wiring board (FPC) to shield external electromagnetic waves. As a method for shielding a printed wiring board, a method is known in which an electromagnetic wave shielding film having a protective layer and a shielding layer is attached to the printed wiring board by heating and pressing to form a shielded printed wiring board.

[0003] When placing an electromagnetic wave shielding film on a printed wiring board or when placing a shielded printed wiring board with an electromagnetic wave shielding film on an electronic device, a sensor may be used to measure the position of the electromagnetic wave shielding film, etc. In this case, if the surface of the electromagnetic wave shielding film has a high gloss, reflected light may cause the sensor to malfunction.

[0004] As an electromagnetic wave shielding film for preventing malfunction of a sensor due to such reflected light, Patent Document 1 discloses an electromagnetic wave shielding film having an insulating resin layer, a conductive layer adjacent to the insulating resin layer, and a carrier film adjacent to the insulating resin layer on the side opposite to the conductive layer, wherein the arithmetic mean roughness Ra of the surface of the carrier film on the insulating resin layer side is 0.2 μm or more and 2.5 μm or less, and the arithmetic mean roughness Ra and the average length Rsm of the roughness curve element of the surface of the carrier film on the insulating resin layer side satisfy the following relationship: Ra / Rsm=3.0×10 －３ Above 50.0 x 10 －３ An electromagnetic wave shielding film that satisfies the following relationship is disclosed.

[0005] Japanese Patent Application Laid-Open No. 2018-129472

[0006] In Patent Document 1, the gloss level is reduced by adjusting the surface roughness of the protective layer of the electromagnetic wave shielding film. However, in order to obtain an electromagnetic wave shielding film with a more excellent appearance, it is necessary to reduce the gloss level of the protective layer of the electromagnetic wave shielding film. To reduce the gloss level, the surface roughness is generally adjusted to be rougher. However, this inevitably leads to a problem of reduced scratch resistance of the surface of the protective layer (insulating resin layer) of the electromagnetic wave shielding film.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide an electromagnetic wave shielding film having a protective layer surface with sufficiently high scratch resistance.

[0008] The electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface facing the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, wherein the L of the first main surface ＊ The present invention is characterized in that the value of the minimum autocorrelation length Sal of the first principal surface is 29 or more, and the minimum autocorrelation length Sal of the first principal surface is 3 μm or more.

[0009] In the electromagnetic wave shielding film of the present invention, the minimum autocorrelation length Sal of the first main surface of the protective layer is 3 μm or more, and therefore the gloss of the first main surface of the protective layer is sufficiently low.

[0010] Generally, when the protective layer of an electromagnetic wave shielding film is scratched, a white mark appears. In the electromagnetic wave shielding film of the present invention, the L of the first main surface of the protective layer ＊ Since the value is 29 or more, the film is relatively bright and the white marks are not easily noticeable. Therefore, in the electromagnetic wave shielding film of the present invention, the scratch resistance of the first main surface of the protective layer is sufficiently high. In this specification, "high scratch resistance" means both that the first main surface of the protective layer is not easily scratched and that even if the first main surface of the protective layer is scratched, the scratch is not easily noticeable.

[0011] In the electromagnetic wave shielding film of the present invention, the minimum autocorrelation length Sal of the first main surface may be 8 μm or more. In this case, the first main surface of the protective layer is less susceptible to scratches. Therefore, the scratch resistance of the first main surface of the protective layer is further improved.

[0012] Another aspect of the present invention provides an electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface facing the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, wherein the L of the first main surface ＊ The present invention is characterized in that the value of the developed area ratio Sdr of the interface of the first main surface is 29 or more, and the developed area ratio Sdr of the interface of the first main surface is 35% or less.

[0013] In the electromagnetic wave shielding film of the present invention, the developed area ratio Sdr of the interface of the protective layer is 35% or less, and therefore the glossiness of the first main surface of the protective layer is sufficiently low.

[0014] Generally, when the protective layer of an electromagnetic wave shielding film is scratched, a white mark appears. In the electromagnetic wave shielding film of the present invention, the L of the first main surface of the protective layer ＊ Since the value is 29 or more, the image is relatively bright and the white marks are not easily noticeable. Therefore, in the electromagnetic wave shielding film of the present invention, the scratch resistance of the first main surface of the protective layer is sufficiently high.

[0015] In the electromagnetic wave shielding film of the present invention, the developed area ratio Sdr of the interface of the first main surface may be 10% or less. In this case, the first main surface of the protective layer is less susceptible to scratches. Therefore, the scratch resistance of the first main surface of the protective layer is further improved.

[0016] In the electromagnetic wave shielding film of the present invention, the root-mean-square slope Sdq of the first main surface is preferably 0.3 to 1.4. If the root-mean-square slope Sdq of the first main surface is less than 0.3, the gloss level tends to increase. If the root-mean-square slope Sdq of the first main surface is more than 1.4, the technical difficulty increases. Furthermore, the first main surface tends to be easily scratched.

[0017] In the electromagnetic wave shielding film of the present invention, the 60° gloss of the first main surface is preferably 15% or less. In the electromagnetic wave shielding film of the present invention, when the 60° gloss is 15% or less, the appearance of the first main surface of the protective layer is good. In this specification, "good appearance" means that the second main surface of the protective layer is not easily visible through the film.

[0018] According to the present invention, it is possible to provide an electromagnetic wave shielding film having a protective layer surface with sufficiently high scratch resistance.

[0019] FIG. 1 is a cross-sectional view schematically showing an example of a cross section of an electromagnetic wave shielding film according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a cross section of another aspect of an electromagnetic wave shielding film according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing an example of a cross section of an electromagnetic wave shielding film according to a first embodiment of the present invention, the electromagnetic wave shielding film having a mat layer and a base film. FIG. 4A is a cross-sectional view schematically showing an example of a state in which the electromagnetic wave shielding film according to the first embodiment of the present invention is attached to a printed wiring board. FIG. 4B is a cross-sectional view schematically showing an example of a cross section of a shielded printed wiring board using the electromagnetic wave shielding film according to the first embodiment of the present invention. FIG. 5 is a process diagram schematically showing an example of a mat layer forming step in the method for producing the electromagnetic wave shielding film according to the first embodiment of the present invention. FIG. 6 is a process diagram schematically showing an example of a protective layer forming step in the method for producing the electromagnetic wave shielding film according to the first embodiment of the present invention. FIG. 7 is a process diagram schematically showing an example of a metal layer forming step in the method for producing the electromagnetic wave shielding film according to the first embodiment of the present invention. FIG. 8 is a process diagram schematically showing an example of a conductive adhesive layer forming step in the method for producing the electromagnetic wave shielding film according to the first embodiment of the present invention. Fig. 9A is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for a rating of 6 in the evaluation of scratch resistance. Fig. 9B is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for a rating of 5 in the evaluation of scratch resistance. Fig. 9C is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for a rating of 4 in the evaluation of scratch resistance. Fig. 9D is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for a rating of 3 in the evaluation of scratch resistance. Fig. 9E is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for a rating of 2 in the evaluation of scratch resistance. Fig. 9F is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for a rating of 1 in the evaluation of scratch resistance.

[0020] The electromagnetic wave shielding film of the present invention will be specifically described below. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0021] First Embodiment Fig. 1 is a cross-sectional view schematically illustrating an example of a cross section of an electromagnetic wave shielding film according to a first embodiment of the present invention. The electromagnetic wave shielding film 1 shown in Fig. 1 includes a protective layer 10 having a first main surface 10a and a second main surface 10b facing the first main surface 10a, and a shielding layer 20 disposed on the second main surface 10b of the protective layer 10. In the electromagnetic wave shielding film 1, the shielding layer 20 is made of a metal layer, and a conductive adhesive layer 30 is disposed on the main surface of the metal layer opposite to the main surface in contact with the protective layer 10.

[0022] In the electromagnetic wave shielding film 1, unevenness 11 is formed on the first main surface 10a of the protective layer 10, and the minimum autocorrelation length Sal of the first main surface 10a of the protective layer 10 is 3 μm or more. The "minimum autocorrelation length Sal" represents the horizontal distance in the direction in which the autocorrelation function decays most rapidly to a specific value s (0.2 by default). Furthermore, the "minimum autocorrelation length Sal" quantifies the density of the unevenness in units of length, so the smaller the value, the finer the texture.

[0023] When the minimum autocorrelation length Sal of the first main surface 10a of the protective layer 10 is 3 μm or more, the irregularities 11 on the first main surface 10a of the protective layer 10 have an appropriate fineness. Therefore, the glossiness of the first main surface 10a of the protective layer 10 is sufficiently low.

[0024] The minimum autocorrelation length Sal of the first main surface 10a of the protective layer 10 may be 3 μm or more and less than 8 μm, and is preferably 6 to 8 μm. In this case, the first main surface 10a of the protective layer 10 is relatively easily scratched. However, as will be described later, the L of the first main surface 10a of the protective layer 10 ＊Since the value is 29 or more, the image is bright and scratches are less noticeable. Therefore, it can be said that the scratch resistance of the first main surface 10a of the protective layer 10 is sufficiently high. Furthermore, it is relatively easy to set the minimum autocorrelation length Sal of the first main surface 10a of the protective layer 10 to 3 μm or more and less than 8 μm. However, if the minimum autocorrelation length Sal of the first main surface of the protective layer is set to less than 3 μm, it is necessary to make the unevenness of the first main surface of the protective layer finer, which increases the technical difficulty.

[0025] The minimum autocorrelation length Sal of the first major surface 10a of the protective layer 10 may be 8 μm or more, and is preferably 8 to 20 μm. In this case, the first major surface 10a of the protective layer 10 is less susceptible to scratches. This further improves the scratch resistance of the first major surface 10a of the protective layer 10. Furthermore, it becomes easier to maintain a low gloss level on the first major surface 10a of the protective layer 10.

[0026] In this specification, the surface texture of the first main surface of the protective layer (the above-mentioned Sal, and the later-described Sdr, Sdq, etc.) is a value measured based on ISO 25178-6:2010, and a specific measurement method will be described in the examples.

[0027] In the electromagnetic wave shielding film 1, the L ＊ The value is 29 or more. ＊ The value is more preferably 33 to 95. ＊ The values ​​are measured in accordance with JIS Z 8781-4 (2013). Generally, scratches on the protective layer of an electromagnetic wave shielding film leave white marks. However, in the electromagnetic wave shielding film 1, the L ＊ Since the value is 29 or more, the image is relatively bright and the white marks are not easily noticeable. Therefore, in the electromagnetic wave shielding film 1, the scratch resistance of the first main surface 10a of the protective layer 10 is sufficiently high.

[0028] In the electromagnetic wave shielding film 1, the L of the first main surface 10a ＊ A method for adjusting the value is to add a pigment or dye to the protective layer.

[0029] The pigment added to the protective layer may be a white pigment or a black pigment. Examples of white pigments include titanium oxide, zinc oxide, zinc sulfide, barium carbonate, barium sulfate, aluminum hydroxide, tin oxide, aluminum silicate, calcium silicate, calcium carbonate, and silica. Examples of black pigments include carbon black, aniline black, titanium black, triiron tetroxide, a composite oxide of iron and manganese, a composite oxide of iron, cobalt, and chromium, a composite oxide of copper and chromium, a composite oxide of copper, chromium, and zinc, and a composite oxide of copper, chromium, and manganese.

[0030] The weight ratio of the pigment contained in the protective layer is determined based on the desired L ＊ The content may be appropriately set to obtain a desired value, but a range of 5 to 80 wt % is preferred, for example.

[0031] In the electromagnetic wave shielding film 1, the root-mean-square slope Sdq of the first main surface 10a of the protective layer 10 is preferably 0.3 to 1.4, more preferably 0.4 to 1.0. The "root-mean-square slope Sdq" is a parameter calculated from the root-mean-square of the slope at all points in a defined region. When the root-mean-square slope Sdq of the first main surface 10a is 0.3 to 1.4, the distance from the bottom to the top of the irregularities 11 on the first main surface 10a and the density of the irregularities 11 fall within appropriate ranges. This improves the scratch resistance of the first main surface 10a of the protective layer 10. When the root-mean-square slope Sdq of the first main surface is less than 0.3, the gloss level tends to increase. When the root-mean-square slope Sdq of the first main surface is greater than 1.4, the technical difficulty increases. Furthermore, the first main surface is more susceptible to scratches.

[0032] In the electromagnetic wave shielding film 1, the 60° gloss of the first main surface 10a is preferably 15% or less, and more preferably 0.1 to 10%. In the electromagnetic wave shielding film of the present invention, when the 60° gloss of the first main surface 10a is 15% or less, the appearance of the first main surface of the protective layer is good.

[0033] Furthermore, the 85° gloss of the first main surface 10a of the electromagnetic wave shielding film 1 is preferably 60% or less, and more preferably 5 to 50%. When the 85° gloss of the electromagnetic wave shielding film 1 is 60% or less, the appearance of the first main surface of the protective layer is good.

[0034] In this specification, the terms "60° gloss" and "85° gloss" refer to values ​​measured using a BYK Gardner Micro-Gloss (portable gloss meter).

[0035] Each component of the electromagnetic wave shielding film 1 will be described in detail below.

[0036] (Protective Layer) The protective layer 10 is preferably made of a resin material, has insulating properties, and satisfies predetermined mechanical strength, chemical resistance, and heat resistance.

[0037] The resin material constituting the protective layer 10 is not particularly limited as long as it has sufficient insulating properties, but for example, a thermoplastic resin composition, a thermosetting resin composition, and an active energy ray curable composition can be used.

[0038] The thermoplastic resin composition is not particularly limited, but examples thereof include styrene-based resin compositions, vinyl acetate-based resin compositions, polyester-based resin compositions, polyethylene-based resin compositions, polypropylene-based resin compositions, imide-based resin compositions, and acrylic-based resin compositions. The thermosetting resin composition is not particularly limited, but examples thereof include phenol-based resin compositions, epoxy-based resin compositions, urethane-based resin compositions, melamine-based resin compositions, and alkyd-based resin compositions. The active energy ray-curable composition is not particularly limited, but examples thereof include polymerizable compounds having at least two (meth)acryloyloxy groups in the molecule. These compositions may be used alone or in combination of two or more.

[0039] The protective layer 10 may contain, as needed, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, a viscosity adjuster, an antiblocking agent, and the like.

[0040] The protective layer 10 has irregularities 11 on its first main surface 10a. The method for forming the irregularities 11 is not particularly limited, and the irregularities 11 can be formed by, for example, the following methods. A method in which a matte layer having irregularities is formed on a substrate film, a resin for forming the protective layer 10 is applied to the surface of the matte layer, and the resin is dried to transfer the irregularities of the matte layer to the protective layer 10. A method in which a resin for forming the protective layer is applied to the shield layer (metal layer) 20, a mold having irregularities is pressed against the resin, and the resin is then cured to transfer the irregularities of the mold to the protective layer. A method in which particles for forming irregularities are added to the protective layer 10. A method in which the first main surface 10a of the protective layer 10 is subjected to a blasting treatment to form the irregularities 11.

[0041] Among the above methods, a preferred method is to form a matte layer having irregularities on a base film, then apply a resin to the surface of the matte layer to form protective layer 10, and dry the resin to transfer the irregularities of the matte layer to protective layer 10.

[0042] When the irregularities 11 are formed by adding irregularity-forming particles to the protective layer 10, the irregularity-forming particles can be, for example, resin fine particles or inorganic fine particles. Examples of resin fine particles that can be used include acrylic resin fine particles, polyacrylonitrile fine particles, polyurethane fine particles, polyamide fine particles, and polyimide fine particles. Examples of inorganic fine particles that can be used include calcium carbonate fine particles, calcium silicate fine particles, clay, kaolin, talc, silica fine particles, glass fine particles, diatomaceous earth, mica powder, alumina fine particles, magnesium oxide fine particles, zinc oxide fine particles, barium sulfate fine particles, aluminum sulfate fine particles, calcium sulfate fine particles, and magnesium carbonate fine particles. These resin fine particles and inorganic fine particles can be used alone or in combination. From the viewpoint of improving the scratch resistance of the protective layer, inorganic fine particles are preferred.

[0043] The thickness of the protective layer 10 is not particularly limited and can be set appropriately as needed, but is preferably 1 to 20 μm, and more preferably 4 to 10 μm. If the thickness of the protective layer is less than 1 μm, the strength of the protective layer will be low and it will be difficult to protect the shielding layer (metal layer). If the thickness of the protective layer exceeds 20 μm, the flexibility of the electromagnetic wave shielding film will be reduced.

[0044] (Metal Layer) The material of the metal layer is not particularly limited, but examples thereof include nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, and alloys containing two or more of these metals.

[0045] The material and thickness of the metal layer may be appropriately selected depending on the required electromagnetic wave shielding effect and resistance to repeated bending and sliding. For example, from the viewpoint of obtaining a sufficient electromagnetic wave shielding effect, the thickness of the metal layer is preferably 0.1 μm or more. From the viewpoints of productivity, flexibility, etc., the thickness is preferably 8 μm or less.

[0046] The metal layer can be formed by electrolytic plating, electroless plating, sputtering, electron beam evaporation, vacuum evaporation, CVD, metal organic, etc. The metal layer can also be formed from metal foil, metal nanoparticles, scale-like metal particles, etc.

[0047] (Conductive Adhesive Layer) In the electromagnetic wave shielding film 1, the conductive adhesive layer 30 may have isotropic conductivity or anisotropic conductivity. As described below, the conductive adhesive layer 30 is disposed on a printed wiring board. In such a case, when the conductive adhesive layer 30, which has either isotropic conductivity or anisotropic conductivity, is brought into contact with the ground wiring of the printed wiring board, the ground wiring of the printed wiring board can be electrically connected to the shielding layer (metal layer) 20 of the electromagnetic wave shielding film 1 via the conductive adhesive layer 30. This allows the electromagnetic wave shielding film 1 to suitably shield electromagnetic waves.

[0048] When the conductive adhesive layer 30 has anisotropic conductivity, the transmission characteristics of high frequency signals transmitted through the signal circuits of the printed wiring board are improved compared to when the conductive adhesive layer 30 has isotropic conductivity.

[0049] The conductive adhesive layer 30 contains a conductive filler and an adhesive resin.

[0050] The conductive filler of the conductive adhesive layer 30 is not particularly limited, but may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by silver-plating copper powder, fine particles of polymer fine particles or glass beads coated with metal, etc. Among these, from an economical standpoint, copper powder or silver-coated copper powder, which are inexpensively available, is preferable.

[0051] The shape of the conductive filler is not particularly limited, and can be appropriately selected from spherical, flake, scale, dendritic, rod-like, fibrous, and other shapes. Among these, flake and dendritic shapes are preferred. If the conductive filler is a flake-shaped conductive filler, when the electromagnetic wave shielding film 1 is bent, the conductive filler also bends, making it easier to maintain contact between the conductive filler particles. As a result, the conductivity of the conductive adhesive layer is less likely to decrease.

[0052] The average major axis of the conductive filler is not particularly limited, but is preferably 0.5 to 15.0 μm, and more preferably 5.0 to 13.0 μm. When the average major axis of the conductive filler is 0.5 μm or more, the conductivity of the conductive adhesive layer is good. When the average major axis of the conductive filler is 15.0 μm or less, the conductive adhesive layer can be made thinner. In this specification, the average major axis of the conductive filler refers to a value measured by the following method. A scanning electron microscope (SEM) image of a cross section of the conductive adhesive layer is obtained. The average major axis of the conductive filler refers to the average value of the major axes of any five conductive fillers in the SEM image.

[0053] The weight percentage of the conductive filler contained in the conductive adhesive layer 30 is preferably 10 to 80% by weight. When the conductive adhesive layer 30 has anisotropic conductivity, the weight percentage of the conductive filler contained in the conductive adhesive layer 30 is preferably 10 to 40% by weight, and more preferably 15 to 35% by weight.

[0054] The thickness of the conductive adhesive layer 30 is not particularly limited and can be set appropriately as needed, but is preferably 0.5 to 30.0 μm. If the thickness of the conductive adhesive layer is less than 0.5 μm, it becomes difficult to obtain good conductivity. If the thickness of the conductive adhesive layer exceeds 30.0 μm, the entire electromagnetic wave shielding film becomes thick and difficult to handle.

[0055] The material of the adhesive resin contained in the conductive adhesive layer 30 is not particularly limited, but may be a thermoplastic resin such as a styrene-based resin, a vinyl acetate-based resin, a polyester-based resin, a polyethylene-based resin, a polypropylene-based resin, an imide-based resin, an amide-based resin, or an acrylic-based resin, or a thermosetting resin such as a phenol-based resin, an epoxy-based resin, a urethane-based resin, a melamine-based resin, or an alkyd-based resin. The adhesive resin material of the conductive adhesive layer 30 may be one of these alone or a combination of two or more of them.

[0056] Next, another aspect of the electromagnetic wave shielding film according to the first embodiment of the present invention will be described. Fig. 2 is a cross-sectional view schematically showing an example of a cross section of another aspect of the electromagnetic wave shielding film according to the first embodiment of the present invention.

[0057] 2 includes a protective layer 10 having a first main surface 10a and a second main surface 10b facing the first main surface 10a, and a shielding layer 120 disposed on the second main surface 10b of the protective layer 10. The shielding layer 120 is made of a conductive adhesive layer. Note that the conductive adhesive layer must be an isotropically conductive adhesive layer in order to function as a shielding layer.

[0058] That is, the electromagnetic wave shielding film 101 has the same configuration as the electromagnetic wave shielding film 1 except that the metal layer and the conductive adhesive layer are a shielding layer (conductive adhesive layer) 120 .

[0059] The electromagnetic wave shielding film according to the first embodiment of the present invention may have a substrate film on which a matte layer is formed. Such an embodiment will be described with reference to the drawings.

[0060] 3 is a cross-sectional view schematically illustrating an example of an electromagnetic wave shielding film according to a first embodiment of the present invention, the electromagnetic wave shielding film including a matte layer and a substrate film. In FIG. 3, the electromagnetic wave shielding film 1 includes a matte layer 40 disposed on a first main surface 10a of the protective layer 10, and a substrate film 50 disposed on a main surface 40b of the matte layer 40 opposite to the main surface 40a in contact with the protective layer 10.

[0061] When producing the electromagnetic wave shielding film 1, the irregularities 41 formed in the matte layer 40 are transferred to the first main surface 10a of the protective layer 10, thereby forming irregularities 11 on the first main surface 10a of the protective layer 10. Therefore, by adjusting the irregularities 41 of the matte layer 40, it is possible to achieve desired surface properties, such as the minimum autocorrelation length Sal, on the first main surface 10a of the protective layer 10. Furthermore, when the base film 50 is disposed on the electromagnetic wave shielding film 1, the first main surface 10a of the protective layer 10 can be protected from impacts and the like. Therefore, it is possible to prevent the protective layer 10 from being damaged when the electromagnetic wave shielding film 1 or the electromagnetic wave shielding film 101 is transported.

[0062] Note that preferred materials for the matte layer 40 and the base film 50 will be described in detail later in the description of the method for producing an electromagnetic wave shielding film according to the first embodiment of the present invention.

[0063] The electromagnetic wave shielding film 101 may also have a base film on which a matte layer is formed.

[0064] Next, the use of the electromagnetic wave shielding film according to the first embodiment of the present invention will be described. The electromagnetic wave shielding film according to the first embodiment of the present invention is attached to a printed wiring board. A method for attaching the electromagnetic wave shielding film according to the first embodiment of the present invention will be described below with reference to the drawings.

[0065] Fig. 4A is a cross-sectional view schematically showing an example of a state in which the electromagnetic wave shielding film according to the first embodiment of the present invention is attached to a printed wiring board, and Fig. 4B is a cross-sectional view schematically showing an example of a cross-section of a shielded printed wiring board using the electromagnetic wave shielding film according to the first embodiment of the present invention.

[0066] As shown in FIG. 4A, the electromagnetic wave shielding film 1 having the base film 50 on which the mat layer 40 is formed is attached to the printed wiring board 60 so that the conductive adhesive layer 30 comes into contact with the printed wiring board 60.

[0067] The printed wiring board 60 is made up of a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62. An opening 63a is formed in the coverlay 63 to expose the ground circuit 62a.

[0068] When the electromagnetic wave shielding film 1 is attached to the printed wiring board 60, the conductive adhesive layer 30 of the electromagnetic wave shielding film 1 fills the opening 63a in the coverlay 63 and contacts the ground circuit 62a. In this manner, the ground circuit 62a of the printed wiring board 60 is electrically connected to the conductive adhesive layer 30 and the shielding layer (metal layer) 20 of the electromagnetic wave shielding film 1. This allows the electromagnetic wave shielding film 1 to effectively shield electromagnetic waves.

[0069] In the printed wiring board 60, the base film 61 and the coverlay 63 are preferably both made of engineering plastics, such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide (PPS).

[0070] In the printed wiring board 60, the printed circuit 62 can be made of a common circuit material such as copper.

[0071] The base film 61 and the printed circuit 62 may be bonded with an adhesive, or may be bonded without adhesive, similar to a so-called adhesiveless copper-clad laminate. The coverlay 63 may be formed by bonding multiple flexible insulating films with an adhesive, or may be formed by a series of methods such as coating a photosensitive insulating resin, drying, exposing, developing, and heat treating.

[0072] A conventionally known method can be used to attach the electromagnetic wave shielding film 1 to the printed wiring board 60. For example, it is preferable to place the electromagnetic wave shielding film 1 on the printed wiring board 60 so that the conductive adhesive layer 30 of the electromagnetic wave shielding film 1 contacts the coverlay 63 of the printed wiring board 60, and then perform thermocompression bonding under conditions of 150 to 200°C, 2 to 5 MPa, and 1 to 60 minutes.

[0073] Thereafter, as shown in FIG. 4B, the base film 50 on which the mat layer 40 has been formed is peeled off from the electromagnetic wave shielding film 1, thereby forming the shielded printed wiring board 70.

[0074] Next, a method for producing the electromagnetic wave shielding film 1 will be described. The method for producing the electromagnetic wave shielding film 1 includes (1) a matte layer forming step, (2) a protective layer forming step, (3) a metal layer forming step, and (4) a conductive adhesive layer forming step. Each step will be described in detail below.

[0075] (1) Matte Layer Forming Step Fig. 5 is a process diagram schematically illustrating an example of the matte layer forming step in the method for producing the electromagnetic wave shielding film according to the first embodiment of the present invention. When producing the electromagnetic wave shielding film of the present invention, a base film 50 is prepared as shown in Fig. 5. Then, a resin composition containing roughness-forming particles is applied to the main surface of the base film 50, and the applied resin composition is dried to form a matte layer 40 having roughness 41.

[0076] The material of the base film 50 is not particularly limited, but examples thereof include plastic sheets such as polyethylene terephthalate, polyethylene naphthalate, polyvinyl fluoride, polyvinylidene fluoride, rigid polyvinyl chloride, polyvinylidene chloride, nylon, polyimide, polystyrene, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polycarbonate, polyacrylonitrile, polybutene, flexible polyvinyl chloride, polyvinylidene fluoride, polyethylene, polypropylene, polyurethane, ethylene-vinyl acetate copolymer, and polyvinyl acetate; papers such as glassine paper, fine paper, kraft paper, and coated paper; various nonwoven fabrics; synthetic paper; metal foil; and composite films combining these.

[0077] The roughness-forming particles constituting the mat layer 40 are not particularly limited, and resin fine particles or inorganic fine particles can be used. Examples of resin fine particles that can be used include acrylic resin fine particles, polyacrylonitrile fine particles, polyurethane fine particles, polyamide fine particles, and polyimide fine particles. Examples of inorganic fine particles that can be used include calcium carbonate fine particles, calcium silicate fine particles, clay, kaolin, talc, silica fine particles, glass fine particles, diatomaceous earth, mica powder, alumina fine particles, magnesium oxide fine particles, zinc oxide fine particles, barium sulfate fine particles, aluminum sulfate fine particles, calcium sulfate fine particles, and magnesium carbonate fine particles. These resin fine particles and inorganic fine particles can be used alone or in combination.

[0078] The resin component constituting the mat layer 40 is not particularly limited, but polyester-based resin compositions, acrylic-based resin compositions, phenol-based resin compositions, epoxy-based resin compositions, urethane-based resin compositions, silicone-based resin compositions, melamine-based resin compositions, and alkyd-based resin compositions can be used.

[0079] The properties of the irregularities 41 of the matte layer 40 can be made to be as desired by adjusting the type, size, and amount of the irregularity-forming particles used, and the type of resin component.

[0080] (2) Protective Layer Forming Step Fig. 6 is a process diagram schematically illustrating an example of the protective layer forming step in the manufacturing method for the electromagnetic wave shielding film according to the first embodiment of the present invention. Next, as shown in Fig. 6, the protective layer 10 is formed on the main surface of the mat layer 40 on which the irregularities 41 have been formed. As a result, the irregularities 41 of the mat layer 40 are transferred to the protective layer 10, and the irregularities 11 of the protective layer 10 are formed. A conventionally known method can be used to form the protective layer 10.

[0081] (3) Metal Layer Forming Step Figure 7 is a process diagram schematically illustrating an example of the metal layer forming step in the manufacturing method of the electromagnetic wave shielding film according to the first embodiment of the present invention. Next, as shown in Figure 7, a shielding layer (metal layer) 20 is formed on the second main surface 10b of the protective layer 10. The method for forming the metal layer is not particularly limited, and may include a method of laminating a metal foil formed to a predetermined thickness onto the protective layer 10, or a method of forming a metal layer on the surface of the protective layer 10 by vapor deposition, plating, or the like.

[0082] (4) Conductive Adhesive Layer Forming Step Figure 8 is a process diagram schematically illustrating an example of the conductive adhesive layer forming step in the manufacturing method for the electromagnetic wave shielding film according to the first embodiment of the present invention. Next, as shown in Figure 8, a conductive adhesive layer 30 is formed on the shielding layer (metal layer) 20. The method for forming the conductive adhesive layer 30 is not particularly limited, and can be performed by applying a conductive adhesive layer composition containing the materials that constitute the conductive adhesive layer 30. Examples of the application method include conventionally known coating methods, such as gravure coating, kiss coating, die coating, lip coating, comma coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, and dip coating.

[0083] The above steps can be used to manufacture the electromagnetic wave shielding film 1. Note that when the electromagnetic wave shielding film 1 shown in Fig. 8 is rotated 180°, it becomes the electromagnetic wave shielding film 1 having the base film 50 on which the matte layer 40 shown in Fig. 3 is formed.

[0084] In addition, when manufacturing the electromagnetic wave shielding film 101, the electromagnetic wave shielding film 101 can be manufactured by not performing the "(3) metal layer formation process" but by forming a conductive adhesive layer having isotropic conductivity on the second main surface of the protective layer in the "(4) conductive adhesive layer formation process."

[0085] Furthermore, in the above-mentioned "(1) matte layer forming step," the matte layer 40 is formed by applying a resin composition containing roughness-forming particles to the base film 50, but when producing the electromagnetic wave shield according to the first embodiment of the present invention, the base film 50 may be embossed to form a part of the base film 50 into the matte layer 40, or the base film 50 may be blasted to form a part of the base film 50 into the matte layer 40. The properties of the roughness 41 of the matte layer 40 can be controlled by adjusting the embossing conditions and the blasting conditions.

[0086] (Second Embodiment) An electromagnetic wave shielding film according to a second embodiment of the present invention has the same configuration as the electromagnetic wave shielding film according to the first embodiment of the present invention, except that the essential constituent requirement is that the minimum autocorrelation length Sal of the first main surface is 3 μm or more and that the developed area ratio Sdr of the interface of the first main surface is 35% or less. That is, the electromagnetic wave shielding film according to the second embodiment of the present invention is an electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface facing the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, ＊ The "interface developed area ratio Sdr" is a numerical value that indicates how much the developed area (surface area) of a defined region has increased relative to the area of ​​the defined region.

[0087] In the electromagnetic wave shielding film according to the second embodiment of the present invention, the developed interface area ratio Sdr of the first main surface of the protective layer is 35% or less, so that the glossiness of the first main surface of the protective layer is sufficiently low.

[0088] In the electromagnetic wave shielding film according to the second embodiment of the present invention, the developed area ratio Sdr of the interface of the first main surface of the protective layer may be more than 10% and not more than 35%, and more preferably more than 10% and not more than 30%. In this case, the first main surface of the protective layer is relatively easily scratched. However, in the electromagnetic wave shielding film according to the second embodiment of the present invention, the L of the first main surface of the protective layer ＊Since the value is 29 or higher, the image is bright and scratches are less noticeable. Therefore, it can be said that the scratch resistance of the first main surface of the protective layer is sufficiently high. Furthermore, it is relatively easy to make the developed area ratio Sdr of the interface of the first main surface of the protective layer exceed 10% and not exceed 35%. However, if the developed area ratio Sdr of the interface of the first main surface of the protective layer is to exceed 35%, it is necessary to increase the number of irregularities on the first main surface of the protective layer and make the irregularities larger, which increases the technical difficulty.

[0089] In the electromagnetic wave shielding film according to the second embodiment of the present invention, the developed area ratio Sdr of the interface of the first main surface may be 10% or less, and preferably 5 to 10%. In this case, the first main surface of the protective layer is less susceptible to scratches. Therefore, the scratch resistance of the first main surface of the protective layer is further improved. Note that when the developed area ratio Sdr of the interface of the first main surface of the protective layer is less than 5%, the gloss of the first main surface of the protective layer is less likely to decrease.

[0090] In all other respects, the preferred configuration of the electromagnetic wave shielding film according to the second embodiment of the present invention is the same as the preferred configuration of the electromagnetic wave shielding film according to the first embodiment of the present invention.

[0091] Other Embodiments In the electromagnetic wave shielding film of the present invention, the first main surface may have a minimum autocorrelation length Sal of 3 μm or more and a developed area ratio Sdr of the interface of 35% or less.

[0092] In the electromagnetic wave shielding film of the present invention, when the shielding layer is a metal layer, a non-conductive adhesive layer may be disposed on the main surface of the metal layer opposite the main surface in contact with the protective layer. In this embodiment of the electromagnetic wave shielding film of the present invention, the metal layer can provide sufficient electromagnetic wave shielding. The material for the non-conductive adhesive layer is not particularly limited, but examples include thermoplastic resins such as styrene-based resins, vinyl acetate-based resins, polyester-based resins, polyethylene-based resins, polypropylene-based resins, imide-based resins, amide-based resins, and acrylic-based resins, and thermosetting resins such as phenol-based resins, epoxy-based resins, urethane-based resins, melamine-based resins, and alkyd-based resins.

[0093] This specification describes the following inventions:

[0094] The present invention (1) provides an electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface opposite to the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, wherein the L of the first main surface ＊ value is 29 or more, and the minimum autocorrelation length Sal of the first main surface is 3 μm or more.

[0095] The present invention (2) is the electromagnetic wave shielding film according to the present invention (1), wherein the minimum autocorrelation length Sal of the first main surface is 8 μm or more.

[0096] The present invention (3) is an electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface opposite to the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, wherein the L of the first main surface ＊ value is 29 or more, and the developed area ratio Sdr of the interface of the first main surface is 35% or less.

[0097] The present invention (4) is the electromagnetic wave shielding film according to the present invention (3), wherein the developed area ratio Sdr of the interface of the first main surface is 10% or less.

[0098] The present invention (5) is the electromagnetic wave shielding film according to any one of the present inventions (1) to (4), wherein the root mean square slope Sdq of the first main surface is 0.3 to 1.4.

[0099] The present invention (6) is the electromagnetic wave shielding film according to any one of the present inventions (1) to (5), wherein the 60° gloss of the first main surface is 15% or less.

[0100] Examples will be given below to explain the present invention more specifically, but the present invention is not limited to these examples.

[0101] (Examples 1 to 7) and (Comparative Examples 1 to 6) (1) Matte Layer Formation Step A polyethylene terephthalate film was prepared as a base film. Next, an epoxy resin containing roughness-forming particles was applied to the main surface of the polyethylene terephthalate film to a thickness of 4.0 μm to form a matte layer having roughness. In this process, the type, size, and amount of roughness-forming particles were adjusted so that the surface properties of the first main surface of the protective layer of the electromagnetic wave shielding films produced according to Examples 1 to 7 and Comparative Examples 1 to 6 would be as shown in Tables 1 and 2.

[0102] (2) Protective layer forming step Next, titanium oxide was mixed as a white pigment into the epoxy resin to prepare a protective layer composition. ＊ Carbon black was added so that the values ​​became the values ​​shown in Tables 1 and 2. Next, the prepared protective layer composition was applied to the matte layer and heated at 100°C for 2 minutes using an electric oven to prepare a protective layer with a thickness of 5 µm. As a result, the irregularities of the matte layer were transferred to the first main surface of the protective layer.

[0103] (3) Metal Layer Formation Step: A 0.1 μm thick silver layer was then formed on the protective layer by vapor deposition. This silver layer served as a shielding layer.

[0104] (4) Conductive adhesive layer formation step Next, 100 parts by mass of bisphenol A type epoxy resin, 0.1 parts by mass of a curing agent (Mitsubishi Chemical, ST14), and 25 parts by mass of dendritic silver-coated copper powder (average particle size 13 μm) were added to toluene so that the solid content was 20 mass%, and the mixture was stirred and mixed to prepare a conductive adhesive layer composition. The obtained conductive adhesive layer composition was applied to the silver layer to form a conductive adhesive layer with a thickness of 15 μm.

[0105] Through the above steps, the electromagnetic wave shielding films according to Examples 1 to 7 and Comparative Examples 1 to 6 were produced.

[0106] (Examples 8) to (Example 11) and (Comparative Example 7) Electromagnetic wave shielding films according to Examples 8 to 11 and Comparative Example 7 were produced in the same manner as described above, except that the following "(1') sandblasting step" and "(2') protective layer forming step" were carried out instead of the above "(1) matte layer forming step" and "(2) protective layer forming step".

[0107] (1') Sandblasting Step A polyethylene terephthalate film was prepared as a base film. Next, the surface of the polyethylene terephthalate film was sandblasted to form irregularities. At this time, the sandblasting conditions were adjusted so that the surface properties of the first main surface of the protective layer of the electromagnetic wave shielding films according to Examples 8 to 11 and Comparative Example 7 to be produced would have the values ​​shown in Tables 1 and 2.

[0108] (2') Protective layer forming step Next, titanium oxide was mixed as a white pigment into the epoxy resin to prepare a protective layer composition. ＊ Carbon black was added so that the values ​​became the values ​​shown in Tables 1 and 2. Next, the prepared protective layer composition was applied to the surface of the polyethylene terephthalate film on which the irregularities had been formed, and heated at 100°C for 2 minutes using an electric oven to prepare a protective layer with a thickness of 5 µm. In this way, the irregularities were transferred to the first main surface of the protective layer.

[0109] [Evaluation of Electromagnetic Wave Shielding Film] A 25 μm thick polyimide film was prepared as a model adherend, and the electromagnetic wave shielding film according to each Example and Comparative Example was arranged so that the conductive adhesive layer was in contact with the polyimide film, and the films were bonded together by heating and pressing using a press under conditions of 170° C., 3 minutes, and 2.0 MPa, and further heating for 1 hour at 150° C. Thereafter, the substrate film on which the matte layer had been formed was peeled off, and the properties of the first main surface of the protective layer of the electromagnetic wave shielding film according to each Example and Comparative Example were measured and evaluated as follows.

[0110] [Measurement of Surface Texture of Protective Layer] Using a confocal microscope (OPTELICS HYBRID, manufactured by Lasertec, objective lens 50x), five arbitrary locations on the surface of the protective layer of each Example and Comparative Example were measured, and then the surface tilt was corrected using data analysis software (LMeye7), and the surface texture was measured in accordance with ISO 25178-6:2010. The cutoff wavelength of the S filter was 0.0025 mm, and the cutoff wavelength of the L filter was 0.8 mm. The results are shown in Tables 1 and 2.

[0111] [Gloss Measurement] The 60° gloss and 85° gloss of the surface of the protective layer of each of the electromagnetic wave shielding films according to each Example and Comparative Example were measured using a BYK Gardner Micro-Gloss (portable gloss meter). The results are shown in Tables 1 and 2.

[0112] [L ＊ Measurement of L value] The L value of the surface of the protective layer of the electromagnetic wave shielding film according to each example and each comparative example was measured using an integrating sphere spectrophotometer (X-Rite, Ci64, tungsten light source). ＊ The values ​​were measured. ＊ value and b ＊ The results are shown in Tables 1 and 2.

[0113] [Evaluation of Scratch Resistance] The protective layer of the electromagnetic wave shielding film according to each Example and Comparative Example was scratched with a fingernail at a load of 0.5 to 0.8 N. The protective layer of the electromagnetic wave shielding film according to each Example and Comparative Example was then visually inspected and evaluated for scratch resistance on a scale of 1 to 6. Note that in this evaluation, a higher score indicates higher scratch resistance. The evaluation results are shown in Tables 1 and 2. The criteria for the ratings are shown in Figures 9A to 9F. Figure 9A is a photograph showing the surface condition of the protective layer of the electromagnetic wave shielding film, which serves as the basis for a rating of 6 in the scratch resistance evaluation. Figure 9B is a photograph showing the surface condition of the protective layer of the electromagnetic wave shielding film, which serves as the basis for a rating of 5 in the scratch resistance evaluation. Figure 9C is a photograph showing the surface condition of the protective layer of the electromagnetic wave shielding film, which serves as the basis for a rating of 4 in the scratch resistance evaluation. Figure 9D is a photograph showing the surface condition of the protective layer of the electromagnetic wave shielding film, which serves as the basis for a rating of 3 in the scratch resistance evaluation. Fig. 9E is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for rating 2 in the evaluation of scratch resistance. Fig. 9F is a photograph showing the surface condition of the protective layer of an electromagnetic wave shielding film, which serves as the basis for rating 1 in the evaluation of scratch resistance.

[0114]

[0115]

[0116] As shown in Tables 1 and 2, the L of the first main surface of the protective layer ＊ When the value is 29 or more and the minimum autocorrelation length Sal of the first main surface is 3 μm or more, or when the L ＊ It was found that when the value is 29 or more and the developed area ratio Sdr of the interface of the first main surface is 35% or less, the scratch resistance is high.

[0117] In particular, it was found that in Examples 1 to 3 and 8 to 11, the minimum autocorrelation length Sal of the first main surface of the protective layer was less than 8 μm, but the scratch resistance was sufficiently high. Also, it was found that in Examples 1 to 5 and 8 to 11, the developed area ratio Sdr of the interface of the first main surface of the protective layer was more than 10%, but the scratch resistance was sufficiently high.

[0118] REFERENCE SIGNS LIST 1, 101 Electromagnetic wave shielding film 10 Protective layer 10a First main surface of protective layer 10b Second main surface of protective layer 11 Concave and convex of protective layer 20, 120 Shielding layer 30 Conductive adhesive layer 40 Matte layer 40a, 40b Main surface of matte layer 41 Concave and convex of matte layer 50 Substrate film 60 Printed wiring board 61 Base film 62 Printed circuit 62a Ground circuit 63 Coverlay 63a Opening 70 Shielded printed wiring board

Claims

1. An electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface opposite to the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, ＊ a minimum autocorrelation length Sal of the first main surface is 3 μm or more.

2. The electromagnetic wave shielding film according to claim 1, wherein the minimum autocorrelation length Sal of the first main surface is 8 μm or more.

3. An electromagnetic wave shielding film comprising: a protective layer having a first main surface and a second main surface opposite to the first main surface; and a shielding layer disposed on the second main surface side of the protective layer, ＊ a value of 29 or more, and a developed area ratio Sdr of the interface of the first main surface is 35% or less.

4. The electromagnetic wave shielding film according to claim 3, wherein the developed area ratio Sdr of the interface of the first main surface is 10% or less.

5. The electromagnetic wave shielding film according to any one of claims 1 to 4, wherein the root mean square slope Sdq of the first main surface is 0.3 to 1.

4.

6. An electromagnetic wave shielding film according to any one of claims 1 to 5, wherein the 60° gloss of the first main surface is 15% or less.

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