Electromagnetic wave shielding film

Abstract

Provided is an electromagnetic wave shielding film having excellent blackness regardless of the constituent components of a black layer. An electromagnetic wave shielding film 1 has a protective layer 2 on a surface, the protective layer 2 having a black protective layer 21, the surface of the protective layer 2 having a minimum autocorrelation length Sal of 10 μm or less, an interface expansion area ratio Sdr of 200% or more, and a ratio [Sdr / Sal] of the aforementioned Sdr to the aforementioned Sal of 50 or more. The brightness L of the protective layer 2 side * 24 or less is preferable.

Description

Technical Field

[0001] This disclosure relates to electromagnetic wave shielding films. Background Technology

[0002] For a long time, in portable devices such as smartphones and tablets, flexible printed circuit boards (FPCs) with electromagnetic wave shielding films have been used to block electromagnetic waves generated internally and electromagnetic waves invading from the outside.

[0003] Electromagnetic wave shielding films (hereinafter sometimes simply referred to as "shielding films") are used in shielded printed circuit boards. For example, a shielding film used to bond to a printed circuit board has: a shielding layer such as a metal layer, a conductive adhesive sheet disposed on the surface of the shielding layer, and a protective layer for protecting the shielding layer.

[0004] For example, electromagnetic wave shielding films used in display devices equipped with plasma display panels (PDP), liquid crystal displays (LCD), organic EL displays, etc., are required to have light-shielding properties.

[0005] In recent years, there has been a tendency to seek electromagnetic wave shielding films with superior light-shielding properties from the perspective of visibility, etc. Patent documents 1 and 2 disclose electromagnetic wave shields that have improved blackness by having a black layer.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2009-76824

[0009] Patent Document 2: Japanese Patent Application Publication No. 2004-288972 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] However, the electromagnetic wave shields disclosed in Patent Documents 1 and 2 improve blackness by specifying the type of colorant in the black layer. In such methods that limit the composition of the black layer by specifying the type of colorant, even if the blackness is improved, the shielding film and the properties that the layers constituting the shielding film should have in the past are poor, and other properties are sometimes deteriorated.

[0012] Therefore, the purpose of this disclosure is to provide an electromagnetic wave shielding film with excellent blackness regardless of the composition of the black layer.

[0013] Solution for solving the problem

[0014] The inventors of this disclosure conducted in-depth research to achieve the aforementioned objectives and discovered that by having a protective layer containing a black layer on the surface of the electromagnetic wave shielding film, and by making the surface of the protective layer have a specific shape, the blackness is excellent regardless of the composition of the black layer. This disclosure is based on these insights.

[0015] This disclosure provides an electromagnetic wave shielding film having a protective layer on its surface.

[0016] The aforementioned protective layer has a black protective layer.

[0017] The minimum autocorrelation length Sal on the surface of the aforementioned protective layer is less than 10 μm, and the interface expansion area ratio Sdr is greater than 200%.

[0018] The ratio of Sdr to Sal [Sdr / Sal] is 50 or higher.

[0019] The aforementioned protective layer may include: a black protective layer located inside the electromagnetic wave shielding film, and a transparent or black protective layer located on the surface of the electromagnetic wave shielding film.

[0020] The aforementioned black protective layer can be located on the surface of the aforementioned electromagnetic wave shielding film.

[0021] The brightness L on the protective layer side mentioned above * Preferably below 24.

[0022] The root mean square slope Sdq of the above-mentioned protective layer surface is preferably 2.0 or higher.

[0023] The gloss level of the 85° side of the above-mentioned protective layer is preferably 25 or less.

[0024] The effects of the invention

[0025] The electromagnetic wave shielding film disclosed herein exhibits excellent blackness regardless of the composition of the black layer. Therefore, the performance of the shielding film can be maintained while ensuring excellent blackness without altering the composition of the black layer. Furthermore, due to the excellent blackness, it also provides excellent light-blocking properties, resulting in superior aesthetics of the printed circuit board, improved visibility of prints on the protective layer of the shielding film, and excellent coverage of the circuit patterns on the printed circuit board when the shielding film is adhered to it. Attached Figure Description

[0026] Figure 1 A cross-sectional schematic diagram is shown for illustrating one embodiment of the electromagnetic wave shielding film of this disclosure.

[0027] Figure 2 A cross-sectional schematic diagram illustrating another embodiment of the electromagnetic wave shielding film of this disclosure.

[0028] Figure 3 A cross-sectional schematic diagram illustrating another further embodiment of the electromagnetic wave shielding film of this disclosure. Detailed Implementation

[0029] Electromagnetic wave shielding film

[0030] The electromagnetic wave shielding film disclosed herein has at least a protective layer. The protective layer is provided on the surface of the electromagnetic wave shielding film. The electromagnetic wave shielding film may have other layers besides the protective layer. Examples of these other layers include an electromagnetic wave shielding layer that provides electromagnetic wave shielding, a conductive adhesive layer, etc. Each layer constituting the electromagnetic wave shielding film may be a single layer or multiple layers.

[0031] (protective layer)

[0032] The aforementioned protective layer functions to protect the internal layers of the electromagnetic wave shielding layer within the aforementioned electromagnetic wave shielding film. The aforementioned protective layer includes at least a black-colored protective layer (black protective layer). The aforementioned protective layer may also be an insulating layer (insulating protective layer).

[0033] The aforementioned protective layer can be a single layer or multiple layers. In the case of multiple layers, for example, it can be a laminate of two or more layers with different physical properties such as material, hardness, or elastic modulus. For example, the outer layer of a laminate with a low-hardness outer layer and a high-hardness inner layer has a buffering effect, thus mitigating the pressure exerted on the electromagnetic wave shielding layer, such as the metal layer, during the process of heating and pressurizing the electromagnetic wave shielding film onto the printed circuit board. Therefore, the height difference on the printed circuit board can be used to suppress damage to the electromagnetic wave shielding layer.

[0034] When the protective layer is a single layer, it is the black protective layer located on the surface of the electromagnetic wave shielding film. When the protective layer is multi-layered, at least one of the protective layers is the black protective layer. Furthermore, when the protective layer is multi-layered, it is preferable to have at least one black protective layer inside the electromagnetic wave shielding film (i.e., outside the surface). Moreover, when the protective layer is multi-layered, it is more preferable that the protective layer located on the surface of the electromagnetic wave shielding film is a transparent protective layer or a black protective layer. In this case, the protective layer on the surface can exhibit functions different from those of the black protective layer located inside, such as superior surface hardness. Furthermore, when the protective layer is multi-layered and has multiple black protective layers, these multiple black protective layers can be layers with the same composition (colorant content, etc.) and thickness, or they can be different layers.

[0035] In one embodiment of the aforementioned electromagnetic wave shielding film, using Figures 1-3 Please provide an explanation. Figures 1-3These are cross-sectional schematic diagrams showing one embodiment of the electromagnetic wave shielding film described above.

[0036] Figure 1 The electromagnetic wave shielding film 1 shown includes: a conductive adhesive layer 4, an electromagnetic wave shielding layer 3 disposed adjacent to one side of the conductive adhesive layer 4, and a protective layer 2 disposed on the surface of the electromagnetic wave shielding layer 3 (the surface opposite to the conductive adhesive layer 4). The protective layer 2 is composed of a single black protective layer 21. In other words, the electromagnetic wave shielding film 1 sequentially includes: a conductive adhesive layer 4, an electromagnetic wave shielding layer 3, and a black protective layer 21. It should be noted that the electromagnetic wave shielding layer 3 may be omitted.

[0037] Figure 2 The electromagnetic wave shielding film 1 shown differs from the other films in that the protective layer 2 is composed of two layers: a black protective layer 21 and a transparent protective layer 22. Figure 1 The electromagnetic wave shielding film 1 is shown. The transparent protective layer 22 is located on the surface of the electromagnetic wave shielding film 1. Figure 3 The electromagnetic wave shielding film 1 shown differs from others in that the protective layer on its surface is a black protective layer 23 instead of a transparent protective layer 22. Figure 2 The electromagnetic wave shielding film 1 shown.

[0038] The surface of the aforementioned protective layer (e.g.) Figures 1-3 The minimum autocorrelation length Sal shown in 2a) is 10 μm or less, preferably 9.7 μm or less, and more preferably 6.0 μm or less. The smaller the Sal, the smaller the height of each unevenness on the surface. The Sal is, for example, 1 μm or more, preferably 2 μm or more.

[0039] The interface expansion area ratio Sdr of the aforementioned protective layer surface is 200% or more, preferably 250% or more, and more preferably 300% or more. Sdr represents how much the expanded area (surface area) of the defined region increases relative to the area of ​​the defined region; for a completely flat surface, Sdr is 0%.

[0040] The ratio of Sdr (%) to Sal (μm) on the surface of the above-mentioned protective layer [Sdr / Sal] is 50 or more, preferably 53 or more, and more preferably 60 or more.

[0041] In the aforementioned electromagnetic wave shielding film, the Sal, Sdr, and [Sdr / Sal] are all within the aforementioned ranges, resulting in small unevenness on the surface of the protective layer and a large extended surface area. This reduces the reflectivity of visible light incident on the surface of the protective layer. Therefore, as long as the shape of the protective layer surface is within the aforementioned range, regardless of the composition of the black protective layer, the blackness is superior compared to cases where the shape of the protective layer surface is not within the aforementioned range. Furthermore, by keeping the Sal and Sdr of the protective layer surface within specific ranges, the aforementioned electromagnetic wave shielding film avoids increasing the height of the unevenness on the protective layer surface. Therefore, it is unnecessary to provide thicker embedding layers such as the release layer for embedding particles into the protective layer and the transfer film described later. Therefore, compared to conventional electromagnetic wave shielding films, the production efficiency, curl resistance, and particle shedding resistance of the electromagnetic wave shielding film are not reduced.

[0042] The root mean square slope Sdq of the protective layer surface is preferably 2.0 or higher, more preferably 3.0 or higher, and even more preferably 3.5 or higher. If Sdq is 2.0 or higher, there is a tendency for the blackness of the protective layer surface to increase.

[0043] The arithmetic mean height Sa of the protective layer surface is preferably 0.4–2.0 μm, more preferably 0.5–1.5 μm. A height Sa within this range is preferred in terms of the balance between gloss and productivity. The maximum peak height Sp of the protective layer surface is preferably 2.5–9.0 μm, more preferably 3.0–7.0 μm. A maximum peak height Sp within this range is preferred in terms of the balance between gloss and productivity. The maximum valley depth Sv of the protective layer surface is preferably 2.0–7.0 μm, more preferably 3.0–7.0 μm. A maximum valley depth Sv within this range is preferred in terms of the balance between gloss and productivity. The maximum height Sz of the protective layer surface is preferably 6.0–20.0 μm, more preferably 6.5–15.0 μm. A maximum height Sz within this range is preferred in terms of the balance between gloss and productivity.

[0044] Each layer constituting the above-mentioned protective layer preferably includes an adhesive component. Examples of such adhesive components include thermoplastic resins, thermosetting resins, and active energy radiation-curable compounds. Only one type of adhesive component may be used, or two or more may be used.

[0045] Examples of the aforementioned thermoplastic resins include polystyrene-based resins, vinyl acetate-based resins, polyester-based resins, polyolefin-based resins (e.g., polyethylene-based resins, polypropylene-based resin compositions, etc.), polyimide-based resins, and acrylic resins. Only one of these thermoplastic resins may be used, or two or more may be used.

[0046] Examples of thermosetting resins include both thermosetting resins and resins obtained by curing the aforementioned thermosetting resins. Examples of thermosetting resins include phenolic resins, epoxy resins, urethane resins, melamine resins, and alkyd resins. Only one type of thermosetting resin may be used, or two or more types may be used.

[0047] Examples of epoxy resins mentioned above include bisphenol type epoxy resins, spirocyclic epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, terpene type epoxy resins, glycidyl ether type epoxy resins, glycidyl amine type epoxy resins, and phenolic varnish type epoxy resins.

[0048] Examples of bisphenol-type epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, and tetrabromobisphenol A type epoxy resin. Examples of glycidyl ether type epoxy resins include tris(glycidyloxyphenyl)methane and tetra(glycidyloxyphenyl)ethane. Examples of glycidylamine type epoxy resins include tetraglycidyldiaminodiphenylmethane. Examples of phenolic varnish type epoxy resins include cresol phenolic varnish type epoxy resin, phenolic varnish type epoxy resin, α-naphthol phenolic varnish type epoxy resin, and brominated phenolic varnish type epoxy resin.

[0049] Examples of the aforementioned active energy ray-curable compounds include both compounds that can be cured by irradiation with active energy rays (active energy ray-curable compounds) and compounds obtained by curing the aforementioned active energy ray-curable compounds. There are no particular limitations on the active energy ray-curable compound; examples include polymeric compounds having one or more (preferably two or more) free radical reactive groups (e.g., (meth)acryloyl) in their molecules. Only one of the aforementioned active energy ray-curable compounds may be used, or two or more may be used.

[0050] The aforementioned black protective layer preferably includes a colorant. As the colorant, a black-based colorant is preferred. As the black-based colorant, known or commonly used colorants (pigments, dyes, etc.) for producing black can be used, such as carbon black (furnace black, channel black, acetylene black, thermal cracking black, lampblack, pine soot, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanide black, activated carbon, ferrites (non-magnetic ferrites, magnetic ferrites, etc.), magnets, chromium oxide, iron oxide, molybdenum disulfide, chromium complexes, anthraquinone-based colorants, zirconium nitride, etc. Only one black-based colorant may be used, or two or more may be used. Alternatively, colorants that produce colors other than black can be mixed and blended to function as a black-based colorant.

[0051] The protective layer may also contain other components besides those listed above, without impairing the effectiveness of this disclosure. Examples of such other components include curing agents, curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, other colorants, leveling agents, coupling agents, ultraviolet absorbers, tackifying resins, and anti-blocking agents. Only one of these other components may be used, or two or more may be used.

[0052] The thickness of the aforementioned protective layer is not particularly limited and can be appropriately set as needed, preferably 1–20 μm, more preferably 2–15 μm, and even more preferably 3–10 μm. A thickness of 1 μm or more provides more adequate protection for the inner layer. A thickness of 20 μm or less offers excellent flexibility and bendability, and is also economical.

[0053] When the aforementioned protective layer is multilayered, the thickness of the protective layer (e.g., a transparent protective layer) located on the surface of the electromagnetic wave shielding film is preferably 0.1–10 μm, more preferably 0.5–5 μm. Furthermore, the thickness of the black protective layer located inside the electromagnetic wave shielding film is preferably 0.5–15 μm, more preferably 1–10 μm.

[0054] (Electromagnetic wave shielding layer)

[0055] As the aforementioned electromagnetic wave shielding layer, any known or commonly used shielding layer with electromagnetic wave shielding properties can be used. Preferably, the electromagnetic wave shielding layer includes a metal layer. The electromagnetic wave shielding layer can be a single layer or multiple layers, either is acceptable.

[0056] Examples of metals constituting the aforementioned metal layer include gold, silver, copper, aluminum, nickel, tin, palladium, chromium, titanium, zinc, or alloys thereof. Metal plates or foils are preferred as the aforementioned metal layer. Specifically, copper plates (copper foils) and silver plates (silver foils) are preferred as the aforementioned metal layer.

[0057] The thickness of the electromagnetic wave shielding layer is preferably 0.01 to 10 μm. A thickness of 0.01 μm or more provides more adequate shielding performance. A thickness of 10 μm or less provides better flexibility.

[0058] (Conductive adhesive layer)

[0059] The aforementioned conductive adhesive layer, for example, possesses adhesiveness and conductivity for bonding the aforementioned electromagnetic wave shielding film to a printed circuit board. The conductive adhesive layer is preferably formed adjacent to the electromagnetic wave shielding layer. The conductive adhesive layer can be a single layer or multiple layers, either is acceptable.

[0060] The aforementioned conductive adhesive layer preferably comprises: an adhesive component that functions as an adhesive, and conductive particles. Examples of the adhesive component include thermoplastic resins, thermosetting resins, and active energy radiation-curable compounds. Examples of the thermoplastic resins, thermosetting resins, and active energy radiation-curable compounds that can be included as adhesive components in the aforementioned protective layer can be specified. Only one adhesive component may be used, or two or more may be used.

[0061] As the adhesive component described above, a thermosetting resin is preferred. In this case, after the electromagnetic wave shielding film is placed on the printed circuit board, the adhesive component can be cured by applying pressure and heating, resulting in better adhesion.

[0062] When the adhesive composition includes a thermosetting resin, it may also include a curing agent to promote the thermosetting reaction. The curing agent can be appropriately selected depending on the type of thermosetting resin. Only one type of curing agent may be used, or two or more types may be used.

[0063] The content ratio of the adhesive component in the aforementioned conductive adhesive layer is not particularly limited, but relative to 100% by mass, it is preferably 40-98% by mass, more preferably 50-97% by mass, further preferably 60-96% by mass, even more preferably 70-95.5% by mass, and particularly preferably 75-95% by mass. If the content ratio is 40% by mass or more, the adhesion to the printed circuit board is superior. If the content ratio is 98% by mass or less, it can sufficiently contain conductive particles.

[0064] Examples of conductive particles include metal particles, metal-coated resin particles, metal fibers, carbon fibers, and carbon nanotubes. Only one type of conductive particle may be used, or two or more may be used.

[0065] Examples of metals constituting the metal particles and the covering portion of the metal-coated resin particles include gold, silver, copper, nickel, and zinc. Only one of these metals may be used, or two or more may be used.

[0066] Examples of the aforementioned metal particles include, for instance, copper particles, silver particles, nickel particles, silver-plated copper particles, gold-plated copper particles, silver-plated nickel particles, gold-plated nickel particles, and silver-plated alloy particles. Examples of silver-plated alloy particles include, for instance, copper alloy particles (e.g., copper alloy particles formed from an alloy of copper, nickel, and zinc) coated with silver, and silver-plated copper alloy particles. These metal particles can be manufactured using electrolysis, atomization, reduction, or similar methods.

[0067] Among the aforementioned metal particles, silver particles, silver-copper coated particles, and silver-copper alloy coated particles are preferred. From the viewpoints of excellent conductivity, suppression of oxidation and aggregation of metal particles, and reduction of metal particle cost, silver-copper coated particles and silver-copper alloy coated particles are particularly preferred.

[0068] Examples of the shapes of the aforementioned conductive particles include spherical, flake-like, dendritic, fibrous, and amorphous (polyhedral).

[0069] The median particle size (D50) of the aforementioned conductive particles is preferably 1–50 μm, more preferably 3–40 μm. If the median particle size is 1 μm or more, the conductive particles exhibit good dispersibility, suppress aggregation, and are less prone to oxidation. If the average particle size is 50 μm or less, conductivity becomes good. The median particle size can be determined based on the particle size distribution on a volume basis.

[0070] The percentage of conductive particles in the conductive adhesive layer is not particularly limited, but is preferably 2-80% by mass, more preferably 5-60% by mass, and even more preferably 10-40% by mass, relative to 100% of the total conductive adhesive layer. If the percentage is 2% by mass or more, the conductivity is better. If the percentage is 80% by mass or less, it sufficiently contains adhesive components, resulting in better adhesion to the printed circuit board.

[0071] The conductive adhesive layer described above can be formed to have isotropic or anisotropic conductivity as needed. When the conductive adhesive layer has anisotropic conductivity, the electromagnetic wave shielding film preferably has the structure of the electromagnetic wave shielding layer (e.g., [protective layer / electromagnetic wave shielding layer / conductive adhesive layer]). When the conductive adhesive layer has isotropic conductivity, the electromagnetic wave shielding film may also be configured without the electromagnetic wave shielding layer (e.g., [protective layer / conductive adhesive layer]).

[0072] The conductive adhesive layer described above may also contain other components besides those listed above, without impairing the effects of this disclosure. Examples of these other components include those found in known or commonly used adhesive layers. Examples of these other components include curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, colorants, leveling agents, coupling agents, UV absorbers, tackifying resins, and anti-blocking agents. Only one of these other components may be used, or two or more may be used.

[0073] The thickness of the conductive adhesive layer is preferably 1 to 40 μm, more preferably 5 to 30 μm. A thickness of 1 μm or more results in better adhesion to the adhered objects. A thickness of 40 μm or less helps to control costs and allows for the design of products with the conductive adhesive layer to be thinner. It should be noted that the thickness of the conductive adhesive layer when the adhesive component (adhesive component) forming the conductive adhesive layer flows and penetrates into the opening formed in the adhered objects through heating or the like, is the thickness of the adhesive layer in the area that does not penetrate into the opening.

[0074] The aforementioned electromagnetic wave shielding film may also include a separator (release film) on the protective layer side and / or the conductive adhesive layer side. The separator is laminated in a manner that allows it to be peeled off from the aforementioned electromagnetic wave shielding film. The separator is an element used to cover the protective layer and conductive adhesive layer for protection, and is peeled off when the electromagnetic wave shielding film is used.

[0075] Examples of such diaphragms include: polyethylene terephthalate (PET) film, polyethylene film, polypropylene film, plastic film and paper obtained by surface coating with release agents such as fluorinated release agents and long-chain alkyl acrylate release agents.

[0076] The thickness of the aforementioned diaphragm is preferably 10–200 μm, more preferably 15–150 μm. A thickness of 10 μm or more provides superior protective performance. A thickness of 200 μm or less makes the diaphragm easier to peel off during use.

[0077] The aforementioned electromagnetic wave shielding film can further form an anchor coating between the protective layer and the electromagnetic wave shielding layer. With this configuration, the adhesion between the electromagnetic wave shielding layer and the protective layer becomes better.

[0078] Examples of materials that can form the aforementioned anchor coating include urethane resins, acrylic resins, core-shell composite resins with urethane resin as the shell and acrylic resin as the core, epoxy resins, polyimide resins, polyamide resins, melamine resins, phenolic resins, urea-formaldehyde resins, end-capped isocyanates obtained by reacting polyisocyanates with end-capping agents such as phenol, polyvinyl alcohol, and polyvinylpyrrolidone. Only one of these materials may be used, or two or more may be used.

[0079] The brightness L on the protective layer side of the aforementioned electromagnetic wave shielding film * Preferably below 24. The above brightness L * It is L * a * b * The luminance specified in the colorimetric system. The aforementioned luminance L... *The value is measured from the protective layer side of the electromagnetic wave shielding film, with the protective layer as the outermost surface. In the case of a diaphragm, the measurement is performed by peeling off the diaphragm. It should be noted that, in the laminated structure composed of the protective layer and the conductive adhesive layer, the brightness L measured from the protective layer side is particularly preferred. * Within the above range. The above brightness L * If the value is below 24, the black level is high, and the coverage is superior. The brightness L mentioned above... * It can be determined based on JIS Z8722 (2009).

[0080] The gloss level at 85° on the protective layer side of the aforementioned electromagnetic wave shielding film is preferably 25 or less, more preferably 22 or less. If the gloss level at 85° is 25 or less, the coverage of the circuit pattern on the printed circuit board with the shielding film attached is even better. It should be noted that, in the laminated structure composed of the aforementioned protective layer and the aforementioned conductive adhesive layer, it is particularly preferable that the gloss level at 85° measured from the protective layer side is within the aforementioned range.

[0081] The gloss level at 60° on the protective layer side of the aforementioned electromagnetic wave shielding film is preferably 2.0 or less, more preferably 1.5 or less. If the gloss level at 60° is 2.0 or less, the printed circuit board exhibits better aesthetics and print visibility when printed on the surface of the protective layer of the shielding film, provided the shielding film is adhered to it. It should be noted that, in the laminated structure composed of the aforementioned protective layer and the aforementioned conductive adhesive layer, a gloss level at 60° measured from the protective layer side within the aforementioned range is particularly preferred.

[0082] The gloss level described above is a value measured from the protective layer side of the electromagnetic wave shielding film, with the protective layer as the outermost surface. In the case of a diaphragm, the gloss level is measured by peeling off the diaphragm. The gloss level described above can be measured according to the method in JIS Z8741.

[0083] The reflectance of light with a wavelength of 450 nm on the protective layer side of the aforementioned electromagnetic wave shielding film is preferably 5.0% or less, more preferably 4.0% or less. If the reflectance is 5.0% or less, the blackness becomes higher. It should be noted that in the laminated structure composed of the aforementioned protective layer and the aforementioned conductive adhesive layer, the reflectance measured from the protective layer side is particularly preferred to be within the aforementioned range.

[0084] The reflectance of light with a wavelength of 550 nm on the protective layer side of the aforementioned electromagnetic wave shielding film is preferably 5.0% or less, more preferably 4.0% or less. If the reflectance is 5.0% or less, the blackness becomes higher. It should be noted that in the laminated structure composed of the aforementioned protective layer and the aforementioned conductive adhesive layer, the reflectance measured from the protective layer side is particularly preferred to be within the aforementioned range.

[0085] The reflectance of light with a wavelength of 650 nm on the protective layer side of the aforementioned electromagnetic wave shielding film is preferably 5.0% or less, more preferably 4.0% or less. If the reflectance is 5.0% or less, the blackness becomes higher. It should be noted that in the laminated structure composed of the aforementioned protective layer and the aforementioned conductive adhesive layer, the reflectance measured from the protective layer side is particularly preferred to be within the aforementioned range.

[0086] The aforementioned reflectivity is a value measured from the protective layer side of the electromagnetic wave shielding film, with the protective layer as the outermost surface. In the case of a diaphragm, the reflectivity is measured by peeling off the diaphragm. The aforementioned reflectivity can be measured according to the method in JIS Z8722.

[0087] The aforementioned electromagnetic wave shielding film is preferably used for printed circuit boards, and particularly preferably for flexible printed circuit boards (FPCs).

[0088] (Manufacturing method of electromagnetic wave shielding film)

[0089] One embodiment of the method for manufacturing the electromagnetic wave shielding film described above will be described. Figure 1 In the fabrication of the electromagnetic wave shielding film 1 shown, firstly, a laminate of the protective layer 2 and the electromagnetic wave shielding layer 3, and a conductive adhesive layer 4 are fabricated separately. Then, the separately fabricated laminate is bonded to the conductive adhesive layer 4 (laminarization). It should be noted that for electromagnetic wave shielding films without an electromagnetic wave shielding layer 3, the protective layer 2 and the conductive adhesive layer 4 are fabricated separately, and then the protective layer 2 is bonded to the conductive adhesive layer 4.

[0090] The protective layer 2 can be formed, for example, by coating (applying) a resin composition for forming the protective layer 2 onto a transfer film such as a diaphragm, and then desolvating and / or partially curing it as needed. An uneven shape can be formed on the surface of the transfer film where the resin composition is applied. By forming the protective layer in this way, the shape derived from the uneven shape is transferred to the surface of the protective layer. The uneven shape on the surface of the transfer film can be produced by known or commonly used methods such as sandblasting or embedding particles into the layers constituting the transfer film in a manner that protrudes from the surface of the transfer film. Then, by appropriately adjusting the sandblasting conditions and the size of the embedded particles, the uneven shape formed on the surface of the transfer film can be designed, thereby adjusting the surface parameters such as Sal and Sdr of the protective layer surface. Afterwards, the transfer film can also be used as a diaphragm in the electromagnetic wave shielding film.

[0091] A release layer can also be provided on the surface of the transfer film having an uneven shape. Examples of release layers include those formed by surface treatment with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, and molybdenum sulfide. It should be noted that when a release layer is provided, its thickness and shape are appropriately set such that the uneven shape of the surface does not disappear, i.e., the transfer film has the aforementioned uneven shape.

[0092] The resin composition forming the above-mentioned protective layer may contain a solvent in addition to the components included in the protective layer. Examples of solvents include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide. The concentration of solid components in the resin composition is appropriately set according to the thickness of the formed protective layer.

[0093] The coating of the above-mentioned resin composition can be carried out using known coating methods. For example, gravure roller coating machines, reverse roller coating machines, licking roller coating machines, lip coating machines, dip roller coating machines, bar coating machines, doctor blade coating machines, spray coating machines, comma coating machines, direct coating machines, slot die coating machines, and other coating machines can be used.

[0094] Next, an electromagnetic wave shielding layer 3 is formed on the surface of the protective layer 2 formed on the transfer film. The electromagnetic wave shielding layer 3 is preferably formed by vapor deposition or sputtering. The aforementioned vapor deposition and sputtering methods can be known or commonly used. Thus, a laminate of the protective layer 2 and the electromagnetic wave shielding layer 3 is fabricated.

[0095] On the other hand, when making the conductive adhesive layer 4, the conductive adhesive layer 4 can be formed, for example, by applying (coating) an adhesive composition for forming the conductive adhesive layer 4 onto a temporary substrate or substrate such as a separation film, and desolvating and / or partially curing as needed, thereby forming the conductive adhesive layer 4.

[0096] The adhesive composition described above, for example, includes a solvent in addition to the components contained in the conductive adhesive layer. Examples of solvents that can be included in the resin composition can be given. The concentration of the solid components in the adhesive composition is appropriately set according to the thickness of the formed conductive adhesive layer, etc.

[0097] The coating of the above-described adhesive composition can be performed using known coating methods. For example, a coating machine used in the coating of the above-described resin composition can be cited as an example.

[0098] Next, the exposed surface (electromagnetic wave shielding layer 3 side) of the separately prepared laminates is bonded to the conductive adhesive layer 4 to form an electromagnetic wave shielding film 1.

[0099] The electromagnetic wave shielding film 1 can also be manufactured by a method other than the lamination method described above, where layers are sequentially stacked (direct coating method). For example... Figure 1 The electromagnetic wave shielding film 1 shown can be manufactured as follows: an adhesive composition for forming a conductive adhesive layer 4 is coated (applied) on the surface of the electromagnetic wave shielding layer 3 of the above-mentioned laminate, and the solvent is removed and / or partially cured as needed to form the conductive adhesive layer 4, thereby manufacturing it.

[0100] The aforementioned electromagnetic wave shielding film can be used to fabricate shielded printed circuit boards. For example, by attaching the conductive adhesive layer of the electromagnetic wave shielding film to a printed circuit board (e.g., a cover layer), a shielded printed circuit board with the electromagnetic wave shielding film attached to it can be obtained. In the aforementioned shielded printed circuit board, the conductive adhesive layer can also be thermosetting, for example, through subsequent heat and pressure treatment.

[0101] Example

[0102] Hereinafter, based on embodiments, one embodiment of the electromagnetic wave shielding film of the present disclosure will be described in more detail, but the electromagnetic wave shielding film of the present disclosure is not limited to these embodiments.

[0103] Examples 1-3 and Comparative Examples 1-3

[0104] (Formation of the protective layer)

[0105] A transparent protective layer is formed by coating a resin solution (solid content: 35% by mass) containing a polyester resin and an amino resin as a curing agent onto the release treatment surface of a transfer film made in such a way that the surface of the protective layer has the surface parameters shown in Table 1, and then removing the solvent by heating.

[0106] Next, a resin solution containing carbon black mixed in epoxy resin (solid content: 20% by mass) is coated onto the surface of the transparent protective layer, and the solvent is removed by heating to form a black protective layer. This process creates a protective layer on the transfer film by sequentially stacking a transparent protective layer (1 μm thick) and a black protective layer (3 μm thick).

[0107] (Formation of a conductive adhesive layer)

[0108] An adhesive composition (solid content: 30% by mass) containing copper powder in epoxy resin is applied to the release surface of a PET film that has undergone a release treatment. The solvent is removed by heating, thereby forming a conductive adhesive layer (10 μm thick).

[0109] (Fabrication of electromagnetic wave shielding film)

[0110] The conductive adhesive layer is bonded to the black protective layer of the protective layer to create an electromagnetic wave shielding film composed of a conductive adhesive layer, a black protective layer, and a transparent protective layer.

[0111] (evaluate)

[0112] The electromagnetic wave shielding films obtained in the examples and comparative examples were evaluated as follows. The evaluation results are recorded in Table 1.

[0113] (1) Surface parameters of the protective layer

[0114] Using a confocal microscope (trade name "OPTELICS HYBRID", Lasertec, 100x objective lens), according to ISO 25178, the transfer film was peeled off from the electromagnetic wave shielding film. For the unevenness formed at any 5 points on the exposed transparent protective layer surface, the arithmetic mean height Sa, maximum peak height Sp, maximum valley depth Sv, maximum height Sz, minimum autocorrelation length Sal, root mean square slope Sdq, and interface expansion area ratio Sdr were measured. It should be noted that the cutoff wavelength of the S-filter was set to 0.0025 mm, and the cutoff wavelength of the L-filter was set to 0.8 mm.

[0115] (2) Gloss

[0116] Using a portable gloss meter (trade name "Gardner Micro-Gloss", manufactured by BYK), the transfer film was peeled off from the electromagnetic wave shielding film, and the 60° and 85° gloss of the unevenness formed on the exposed transparent protective layer surface were measured.

[0117] (3) Reflectivity

[0118] Using a spectrophotometer (trade name "CM-26d", manufactured by Konica Minolta, Inc.), in accordance with JIS Z8722 (condition c), the transfer film was peeled off from the electromagnetic wave shielding film, and the reflectance of light at wavelengths of 450 nm, 550 nm, and 650 nm was measured on the exposed transparent protective layer surface.

[0119] (4) Brightness L *

[0120] Using a spectrophotometer (trade name "Ci64UV", manufactured by X-rite), the transfer film was peeled off from the electromagnetic wave shielding film, and the luminance L of the exposed transparent protective layer surface was measured. * .

[0121] [Table 1]

[0122] (Table 1)

[0123]

[0124] As shown in Table 1, the electromagnetic wave shielding film of the embodiment has lower brightness and better blackness compared with electromagnetic wave shielding films (Comparative Examples 1-3) in which at least one of Sal, Sdr and [Sdr / Sal] is not within a specific range. Therefore, based on this embodiment, it has been confirmed that regardless of the composition of the black layer, the blackness is improved by having a protective layer with a specific surface shape.

[0125] Industrial availability

[0126] The electromagnetic wave shielding film of the present invention is suitable for use in portable devices and image display devices.

[0127] Explanation of reference numerals in the attached figures

[0128] 1 Electromagnetic wave shielding film

[0129] 2 Protective layer

[0130] 2a Protective layer surface

[0131] 21 Black protective layer

[0132] 22 Transparent protective layer

[0133] 23 Black protective layer

[0134] 3 Electromagnetic wave shielding layer

[0135] 4. Conductive adhesive layer

Claims

1. An electromagnetic wave shielding film, having a protective layer on its surface, The protective layer has a black protective layer. The minimum autocorrelation length Sal of the protective layer surface is less than 10 μm, and the interface expansion area ratio Sdr of the protective layer surface is greater than 200%. The ratio of Sdr to Sal [Sdr / Sal] is 60 or higher. The root mean square slope Sdq of the protective layer surface is greater than 2.

0. The arithmetic mean height Sa of the surface of the protective layer is 0.4~0.62μm.

2. The electromagnetic wave shielding film according to claim 1, wherein, The protective layer comprises: a black protective layer located inside the electromagnetic wave shielding film, and a transparent or black protective layer located on the surface of the electromagnetic wave shielding film.

3. The electromagnetic wave shielding film according to claim 1, wherein, The black protective layer is located on the surface of the electromagnetic wave shielding film.

4. The electromagnetic wave shielding film according to any one of claims 1 to 3, wherein, The brightness L on the protective layer side * It is below 24.

5. The electromagnetic wave shielding film according to any one of claims 1 to 3, wherein, The gloss level at 85° on the protective layer side is below 25.

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