JP7566151B2 - Electromagnetic wave shielding film - Google Patents

Description

This disclosure relates to an electromagnetic wave shielding film.

Traditionally, mobile devices such as smartphones and tablet terminals have used flexible printed circuit boards (FPCs) with an electromagnetic wave shielding film attached to them to block electromagnetic waves generated from within and electromagnetic waves entering from the outside.

Shielded printed wiring boards use electromagnetic wave shielding films (hereinafter sometimes simply referred to as "shielding films"). For example, a shielding film that is adhered to a printed wiring board has a shielding layer such as a metal layer, a conductive adhesive sheet provided on the surface of the shielding layer, and a protective layer to protect the shielding layer.

For example, electromagnetic wave shielding films used in screen display devices equipped with plasma display panels (PDPs), liquid crystal displays (LCDs), organic EL displays, etc., are required to have light-blocking properties.

In recent years, there has been a demand for electromagnetic wave shielding films with better light-shielding properties from the standpoint of visibility, etc. Patent documents 1 and 2 disclose electromagnetic wave shielding bodies that have a black layer and have an increased degree of blackness.

JP 2009-76824 A JP 2004-288972 A

However, in both of the electromagnetic shields disclosed in Patent Documents 1 and 2, the blackness is improved by specifying the type of colorant in the black layer. In this way, even if the blackness is improved by limiting the composition of the black layer, such as by specifying the type of colorant, other performance may be deteriorated, such as the performance that the shielding film and each layer that constitutes the shielding film should traditionally have being inferior.

Therefore, the object of the present disclosure is to provide an electromagnetic wave shielding film that has excellent blackness regardless of the composition of the black layer.

As a result of intensive research into achieving the above object, the inventors of the present disclosure have discovered that by providing a protective layer including a black layer on the surface of an electromagnetic wave shielding film and by specifying the shape of the protective layer surface, excellent blackness can be achieved regardless of the composition of the black layer. The present disclosure has been completed based on these findings.

The present disclosure relates to an electromagnetic wave shielding film having a protective layer on a surface thereof,
The protective layer has a black protective layer,
the minimum autocorrelation length Sal of the protective layer surface is 10 μm or less, and the developed area ratio Sdr of the interface is 200% or more;
The electromagnetic wave shielding film has a ratio of the Sdr to the Sal, [Sdr/Sal], of 50 or more.

The protective layer may include a black protective layer located inside the electromagnetic wave shielding film and a transparent protective layer or a black protective layer located on the surface of the electromagnetic wave shielding film.

The black protective layer may be located on the surface of the electromagnetic wave shielding film.

The lightness L ^* of the protective layer side is preferably 24 or less.

It is preferable that the root mean square slope Sdq of the protective layer surface is 2.0 or more.

It is preferable that the 85° gloss of the protective layer side is 25 or less.

The electromagnetic wave shielding film of the present disclosure has excellent blackness regardless of the composition of the black layer. Therefore, it is possible to obtain an excellent blackness while maintaining the performance of the shielding film without changing the composition of the black layer. In addition, because of its excellent blackness, it has excellent light-shielding properties, and when the shielding film is attached to a printed wiring board, it has excellent aesthetics of the printed wiring board, visibility of printing when printed on the surface of the protective layer of the shielding film, and concealment of the circuit pattern of the printed wiring board.

1 is a cross-sectional schematic diagram showing one embodiment of an electromagnetic wave shielding film of the present disclosure. FIG. 2 is a cross-sectional schematic diagram showing another embodiment of the electromagnetic wave shielding film of the present disclosure. FIG. 2 is a schematic cross-sectional view showing still another embodiment of the electromagnetic wave shielding film of the present disclosure.

[Electromagnetic wave shielding film]
The electromagnetic wave shielding film of the present disclosure includes 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 include layers other than the protective layer. Examples of the other layers include an electromagnetic wave shielding layer that exhibits electromagnetic wave shielding properties, a conductive adhesive layer, and the like. Each layer constituting the electromagnetic wave shielding film may be a single layer or multiple layers.

(Protective Layer)
The protective layer has a function of protecting each inner layer, such as the electromagnetic shielding layer, in the electromagnetic shielding film. The protective layer includes at least a protective layer exhibiting a black color (black protective layer). The protective layer may be a layer having insulating properties (insulating protective layer).

The protective layer may be a single layer or multiple layers. When the protective layer is multiple layers, it may be, for example, a laminate of two or more layers having different materials or physical properties such as hardness or elastic modulus. For example, in a laminate of an outer layer with low hardness and an inner layer with high hardness, the outer layer has a cushioning effect, so that the pressure applied to the electromagnetic shielding layer such as a metal layer can be reduced in the process of heating and pressing the electromagnetic shielding film to the printed wiring board. This makes it possible to prevent the electromagnetic shielding layer from being destroyed by steps provided on the printed wiring board.

When the protective layer is a single layer, the single layer is the black protective layer, and the black protective layer is located on the surface of the electromagnetic wave shielding film. When the protective layer is a multi-layer, at least one layer of the protective layer is the black protective layer. When the protective layer is a multi-layer, it is preferable that the electromagnetic wave shielding film has at least one black protective layer inside (i.e., other than the surface). When the protective layer is a multi-layer, 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 located on the surface can exhibit a function different from that of the black protective layer located inside, such as excellent surface hardness. When the protective layer is a multi-layer and has multiple black protective layers, the multiple black protective layers may be layers having the same composition (colorant content, etc.) and thickness, or may be different layers.

One embodiment of the electromagnetic wave shielding film will be described with reference to Figures 1 to 3. Figures 1 to 3 are each a schematic cross-sectional view showing one embodiment of the electromagnetic wave shielding film.

The electromagnetic wave shielding film 1 shown in Figure 1 comprises a conductive adhesive layer 4, an electromagnetic wave shielding layer 3 provided adjacent to one side of the conductive adhesive layer 4, and a protective layer 2 provided on the surface of the electromagnetic wave shielding layer 3 (the surface opposite 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 comprises the conductive adhesive layer 4, the electromagnetic wave shielding layer 3, and the black protective layer 21 in this order. Note that the electromagnetic wave shielding layer 3 does not necessarily have to be provided.

The electromagnetic wave shielding film 1 shown in Figure 2 differs from the electromagnetic wave shielding film 1 shown in Figure 1 in that the protective layer 2 is composed of two layers, a black protective layer 21 and a transparent protective layer 22. The transparent protective layer 22 is located on the surface of the electromagnetic wave shielding film 1. The electromagnetic wave shielding film 1 shown in Figure 3 differs from the electromagnetic wave shielding film 1 shown in Figure 2 in that the protective layer located on its surface is a black protective layer 23 rather than a transparent protective layer 22.

The minimum autocorrelation length Sal of the protective layer surface (e.g., 2a shown in Figures 1 to 3) 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, and preferably 2 μm or more.

The developed area ratio Sdr of the interface of the protective layer surface is 200% or more, preferably 250% or more, and more preferably 300% or more. The Sdr indicates how much the developed area (surface area) of the defined area has increased relative to the area of the defined area, and the Sdr of a completely flat surface is 0%.

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

In the electromagnetic wave shielding film, the Sal, the Sdr, and the ratio [Sdr/Sal] are each within the above-mentioned ranges, so that the individual unevenness of the protective layer surface is small and the developed surface area is large. This reduces the reflectance of visible light incident on the protective layer surface. Therefore, if the shape of the protective layer surface is within the above-mentioned range, the blackness is superior to when the shape of the protective layer surface is not within the above-mentioned range, regardless of the composition of the black protective layer. In addition, the electromagnetic wave shielding film has Sal and Sdr of the protective layer surface in a specific range, and does not aim to increase the height of the uneven shape of the protective layer surface, so there is no need to provide a thick protective layer or an embedding layer such as a release treatment layer for embedding particles in a transfer film described later. Therefore, compared to conventional electromagnetic wave shielding films, the productivity, curl resistance, and particle drop-off resistance of the electromagnetic wave shielding film are not reduced.

The root mean square slope Sdq of the protective layer surface is preferably 2.0 or more, more preferably 3.0 or more, and even more preferably 3.5 or more. When the Sdq is 2.0 or more, the blackness of the protective layer surface tends to be high.

The arithmetic mean height Sa of the protective layer surface is preferably 0.4 to 2.0 μm, more preferably 0.5 to 1.5 μm. If the arithmetic mean height Sa is within the above range, it is preferable in terms of the balance between glossiness and productivity. The maximum peak height Sp of the protective layer surface is preferably 2.5 to 9.0 μm, more preferably 3.0 to 7.0 μm. If the maximum peak height Sp is within the above range, it is preferable in terms of the balance between glossiness and productivity. The maximum valley depth Sv of the protective layer surface is preferably 2.0 to 7.0 μm, more preferably 3.0 to 7.0 μm. If the maximum valley depth Sv is within the above range, it is preferable in terms of the balance between glossiness and productivity. The maximum height Sz of the protective layer surface is preferably 6.0 to 20.0 μm, more preferably 6.5 to 15.0 μm. If the maximum height Sz is within the above range, it is preferable in terms of the balance between glossiness and productivity.

Each layer constituting the protective layer preferably contains a binder component. Examples of the binder component include a thermoplastic resin, a thermosetting resin, and an active energy ray-curable compound. Only one type of the binder component may be used, or two or more types may be used.

Examples of the thermoplastic resin include polystyrene resin, vinyl acetate resin, polyester resin, polyolefin resin (e.g., polyethylene resin, polypropylene resin composition, etc.), polyimide resin, acrylic resin, etc. Only one type of the thermoplastic resin may be used, or two or more types may be used.

The thermosetting resin includes both a resin having thermosetting properties (thermosetting resin) and a resin obtained by curing the thermosetting resin. Examples of the thermosetting resin include phenolic resin, epoxy resin, urethane resin, melamine resin, alkyd resin, etc. The thermosetting resin may be used alone or in combination of two or more kinds.

Examples of the epoxy resins include bisphenol type epoxy resins, spirocyclic type 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 novolac type epoxy resins.

Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, and tetrabromobisphenol A type epoxy resin. Examples of the glycidyl ether type epoxy resin include tris(glycidyloxyphenyl)methane and tetrakis(glycidyloxyphenyl)ethane. Examples of the glycidylamine type epoxy resin include tetraglycidyldiaminodiphenylmethane. Examples of the novolac type epoxy resin include cresol novolac type epoxy resin, phenol novolac type epoxy resin, α-naphthol novolac type epoxy resin, and brominated phenol novolac type epoxy resin.

The active energy ray curable compound includes both a compound that can be cured by irradiation with active energy rays (active energy ray curable compound) and a compound obtained by curing the active energy ray curable compound. The active energy ray curable compound is not particularly limited, but examples thereof include polymerizable compounds having one or more (preferably two or more) radical reactive groups (e.g., (meth)acryloyl groups) in the molecule. Only one type of the active energy ray curable compound may be used, or two or more types may be used.

The black protective layer preferably contains a colorant. The colorant is preferably a black colorant. As the black colorant, a known or conventional colorant (pigment, dye, etc.) for providing a black color can be used, such as carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, pine smoke, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite (non-magnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, anthraquinone colorant, zirconium nitride, etc. Only one type of black colorant may be used, or two or more types may be used. In addition, a colorant that functions as a black colorant may be used by combining and blending colorants that provide a color other than black.

The protective layer may contain other components in addition to the above-mentioned components, within the scope of the present disclosure, without impairing the effects of the present disclosure. Examples of the 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, UV absorbers, tackifier resins, and anti-blocking agents. Only one type of the other components may be used, or two or more types may be used.

The thickness of the protective layer is not particularly limited and can be set appropriately as needed, but is preferably 1 to 20 μm, more preferably 2 to 15 μm, and even more preferably 3 to 10 μm. If the thickness is 1 μm or more, the inner layer can be protected more sufficiently. If the thickness is 20 μm or less, the flexibility and bendability are excellent, and it is also economically advantageous.

When the protective layer is a multi-layered layer, 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 to 10 μm, more preferably 0.5 to 5 μm. The thickness of the black protective layer located inside the electromagnetic wave shielding film is preferably 0.5 to 15 μm, more preferably 1 to 10 μm.

(Electromagnetic wave shielding layer)
As the electromagnetic wave shielding layer, a known or commonly used shielding layer having electromagnetic wave shielding properties can be used. The electromagnetic wave shielding layer preferably includes a metal layer. The electromagnetic wave shielding layer may be a single layer or a multi-layer.

Examples of metals constituting the metal layer include gold, silver, copper, aluminum, nickel, tin, palladium, chromium, titanium, zinc, and alloys thereof. The metal layer is preferably a metal plate or metal foil. That is, the metal layer is preferably a copper plate (copper foil) or a silver plate (silver foil).

The thickness of the electromagnetic wave shielding layer is preferably 0.01 to 10 μm. If the thickness is 0.01 μm or more, more sufficient shielding performance can be obtained. If the thickness is 10 μm or less, the flexibility is better.

(Conductive adhesive layer)
The conductive adhesive layer has adhesiveness and electrical conductivity for adhering the electromagnetic wave shielding film to a printed wiring board, for example. The conductive adhesive layer is preferably formed adjacent to the electromagnetic wave shielding layer. The conductive adhesive layer may be a single layer or multiple layers.

The conductive adhesive layer preferably contains a binder component capable of functioning as an adhesive and conductive particles. Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray curable compounds. Examples of the thermoplastic resins, thermosetting resins, and active energy ray curable compounds include those exemplified as binder components that may be contained in the protective layer described above. Only one type of binder component may be used, or two or more types may be used.

Of the above binder components, thermosetting resins are preferred. In this case, after the electromagnetic shielding film is placed on the printed wiring board, the binder components can be cured by applying pressure and heat, resulting in better adhesion.

When the binder component contains a thermosetting resin, the binder component may contain a curing agent for accelerating the thermosetting reaction. The curing agent may be appropriately selected depending on the type of the thermosetting resin. Only one type of curing agent may be used, or two or more types may be used.

The content ratio of the binder component in the conductive adhesive layer is not particularly limited, but is preferably 40 to 98 mass%, more preferably 50 to 97 mass%, even more preferably 60 to 96 mass%, even more preferably 70 to 95.5 mass%, and particularly preferably 75 to 95 mass%, relative to 100 mass% of the total amount of the conductive adhesive layer. If the content ratio is 40 mass% or more, the adhesion to the printed wiring board is superior. If the content ratio is 98 mass% or less, the conductive particles can be sufficiently contained.

Examples of the conductive particles include metal particles, metal-coated resin particles, metal fibers, carbon fillers, carbon nanotubes, etc. The conductive particles may be used alone or in combination of two or more kinds.

Examples of metals constituting the coating portion of the metal particles and the metal-coated resin particles include gold, silver, copper, nickel, zinc, etc. Only one type of the above metals may be used, or two or more types may be used.

Specific examples of the metal particles include copper particles, silver particles, nickel particles, silver-coated copper particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, and silver-coated alloy particles. Examples of the silver-coated alloy particles include silver-coated copper alloy particles in which alloy particles containing copper (e.g., copper alloy particles made of an alloy of copper, nickel, and zinc) are coated with silver. The metal particles can be produced by electrolysis, atomization, reduction, or the like.

Among the above metal particles, silver particles, silver-coated copper particles, and silver-coated copper alloy particles are preferred. Silver-coated copper particles and silver-coated copper alloy particles are particularly preferred from the viewpoints of excellent electrical conductivity, suppression of oxidation and aggregation of metal particles, and reduction of the cost of metal particles.

The shapes of the above conductive particles include spherical, flake (scale-like), dendritic, fibrous, and irregular (polyhedral) shapes.

The median diameter (D50) of the conductive particles is preferably 1 to 50 μm, and more preferably 3 to 40 μm. If the median diameter is 1 μm or more, the conductive particles have good dispersibility, aggregation can be suppressed, and they are less likely to be oxidized. If the average particle size is 50 μm or less, the conductivity is good. The median diameter can be measured from the volume-based particle size distribution.

The content of the conductive particles in the conductive adhesive layer is not particularly limited, but is preferably 2 to 80% by mass, more preferably 5 to 60% by mass, and even more preferably 10 to 40% by mass, relative to 100% by mass of the total amount of the conductive adhesive layer. If the content is 2% by mass or more, the conductivity will be better. If the content is 80% by mass or less, the binder component can be sufficiently contained, resulting in better adhesion to the printed wiring board.

The conductive adhesive layer can be a layer having isotropic conductivity or anisotropic conductivity as required. When the conductive adhesive layer has anisotropic conductivity, it is preferable that the electromagnetic shielding film has the electromagnetic shielding layer (e.g., [protective layer/electromagnetic shielding layer/conductive adhesive layer]). When the conductive adhesive layer has isotropic conductivity, the electromagnetic shielding film may have a configuration not having the electromagnetic shielding layer (e.g., [protective layer/conductive adhesive layer]).

The conductive adhesive layer may contain other components in addition to the above-mentioned components, within the range that does not impair the effects of the present disclosure. Examples of the other components include components contained in publicly known or conventional adhesive layers. Examples of the other components include curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, colorants, leveling agents, coupling agents, UV absorbers, tackifier resins, and anti-blocking agents. Only one type of the other components may be used, or two or more types may be used.

The thickness of the conductive adhesive layer is preferably 1 to 40 μm, and more preferably 5 to 30 μm. If the thickness is 1 μm or more, the adhesion strength to the adherend is better. If the thickness is 40 μm or less, costs can be reduced and products equipped with the conductive adhesive layer can be designed to be thin. Note that the thickness of the conductive adhesive layer in cases where the adhesive components (binder components) constituting the conductive adhesive layer flow due to heating or the like and infiltrate into an opening formed in the adherend is the thickness of the adhesive layer in the area that does not infiltrate into the opening.

The electromagnetic shielding film may have a separator (peeling film) on the protective layer side and/or the conductive adhesive layer side. The separator is laminated so as to be peelable from the electromagnetic shielding film. The separator is an element for covering and protecting the protective layer and the conductive adhesive layer, and is peeled off when the electromagnetic shielding film is used.

Examples of the separator include polyethylene terephthalate (PET) film, polyethylene film, polypropylene film, plastic films and papers whose surfaces are coated with a release agent such as a fluorine-based release agent or a long-chain alkyl acrylate release agent.

The thickness of the separator is preferably 10 to 200 μm, and more preferably 15 to 150 μm. If the thickness is 10 μm or more, the protective performance is superior. If the thickness is 200 μm or less, the separator is easily peeled off during use.

The electromagnetic shielding film may further include an anchor coat layer formed between the protective layer and the electromagnetic shielding layer. With such a configuration, the adhesion between the electromagnetic shielding layer and the protective layer is improved.

Materials for forming the anchor coat layer 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, blocked isocyanates obtained by reacting polyisocyanates with blocking agents such as phenol, polyvinyl alcohol, polyvinylpyrrolidone, etc. Only one of the above materials may be used, or two or more may be used.

The lightness L ^* of the protective layer side of the electromagnetic shielding film is preferably 24 or less. The lightness L ^* is a lightness defined by the L ^* a ^* b ^* color system. The lightness L ^* is a value measured from the protective layer side of the electromagnetic shielding film in which the protective layer is the outermost surface, and if a separator is present, the value is measured by peeling off the separator. In addition, in a laminate structure composed of the protective layer and the conductive adhesive layer, it is particularly preferable that the lightness L ^* measured from the protective layer side is within the above range. When the lightness L ^* is 24 or less, the blackness is high and the concealment is excellent. The lightness L ^* can be measured based on JIS Z8722 (2009).

The 85° gloss of the protective layer side of the electromagnetic wave shielding film is preferably 25 or less, more preferably 22 or less. When the 85° gloss is 25 or less, the concealment of the circuit pattern of the printed wiring board is superior when the shielding film is attached to the printed wiring board. In addition, in a laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly preferable that the 85° gloss measured from the protective layer side is within the above range.

The 60° gloss of the protective layer side of the electromagnetic shielding film is preferably 2.0 or less, and more preferably 1.5 or less. If the 60° gloss is 2.0 or less, when the shielding film is attached to the printed wiring board, the aesthetics of the printed wiring board and the visibility of the printing when printed on the surface of the protective layer of the shielding film are excellent. Note that in a laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly preferable that the 60° gloss measured from the protective layer side is within the above range.

The gloss level is a value measured from the protective layer side of the electromagnetic shielding film in which the protective layer is the outermost surface, and if a separator is present, the separator is peeled off and the gloss level is measured. The gloss level can be measured by a method conforming to JIS Z8741.

The reflectance of light with a wavelength of 450 nm on the protective layer side of the electromagnetic wave shielding film is preferably 5.0% or less, and more preferably 4.0% or less. If the reflectance is 5.0% or less, the blackness becomes higher. In addition, in a laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly preferable that the reflectance measured from the protective layer side is within the above range.

The reflectance of light with a wavelength of 550 nm on the protective layer side of the electromagnetic wave shielding film is preferably 5.0% or less, and more preferably 4.0% or less. If the reflectance is 5.0% or less, the blackness becomes higher. In addition, in a laminate structure composed of the protective layer and the conductive adhesive layer, it is particularly preferable that the reflectance measured from the protective layer side is within the above range.

The reflectance of light having a wavelength of 650 nm on the protective layer side of the electromagnetic wave shielding film is preferably 5.0% or less, and more preferably 4.0% or less. If the reflectance is 5.0% or less, the degree of blackness will be higher. In addition, in a laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly preferable that the reflectance measured from the protective layer side is within the above range.

The reflectance is a value measured from the protective layer side of the electromagnetic shielding film in which the protective layer is the outermost surface, and if a separator is present, the separator is peeled off and the reflectance is measured. The reflectance can be measured by a method conforming to JIS Z8722.

The above electromagnetic wave shielding film is preferably used for printed wiring boards, and particularly preferably for flexible printed wiring boards (FPCs).

(Method of manufacturing electromagnetic wave shielding film)
An embodiment of a method for producing the electromagnetic shielding film will be described. In producing the electromagnetic shielding film 1 shown in Fig. 1, first, a laminate of the protective layer 2 and the electromagnetic shielding layer 3 and a conductive adhesive layer 4 are separately produced. Then, the separately produced laminates and the conductive adhesive layer 4 are bonded together (lamination method). For an electromagnetic shielding film that does not have the electromagnetic shielding layer 3, the protective layer 2 and the conductive adhesive layer 4 are separately produced, and then the protective layer 2 and the conductive adhesive layer 4 are bonded together.

The protective layer 2 can be formed, for example, by applying (coating) a resin composition for forming the protective layer 2 onto a transfer film such as a separator, and, if necessary, removing the solvent and/or partially curing the resin composition. The surface of the transfer film to which the resin composition is applied is formed with an uneven shape. By forming the protective layer in this manner, a shape derived from the uneven shape is transferred to the surface of the protective layer. The uneven shape of the transfer film surface can be produced by a known or conventional method such as sandblasting or a method of embedding particles in each layer constituting the transfer film so that the particles protrude from the transfer film surface. Then, the surface parameters such as Sal and Sdr of the protective layer surface can be adjusted by appropriately adjusting the sandblasting conditions and the size of the embedded particles to design the uneven shape formed on the transfer film surface. The transfer film may then be used as a separator in the electromagnetic wave shielding film.

A release treatment layer may be provided on the uneven surface of the transfer film. Examples of the release treatment layer include layers formed by surface treatment with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide release agent. When a release treatment layer is provided, the thickness and shape of the release treatment layer are appropriately set so that the uneven surface shape does not disappear, that is, so that the transfer film has the uneven shape.

The resin composition forming the protective layer contains, for example, a solvent in addition to the components contained in the protective layer described above. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide. The solid content concentration of the resin composition is appropriately set according to the thickness of the protective layer to be formed.

A known coating method may be used to apply the resin composition. For example, a coater such as a gravure roll coater, reverse roll coater, kiss roll coater, lip coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, direct coater, or slot die coater may be used.

Next, the electromagnetic shielding layer 3 is formed on the surface of the protective layer 2 formed on the transfer film. The electromagnetic shielding layer 3 is preferably formed by a vapor deposition method or a sputtering method. The vapor deposition method and sputtering method may be any known or commonly used method. In this manner, a laminate of the protective layer 2/electromagnetic shielding layer 3 is produced.

On the other hand, when preparing the conductive adhesive layer 4, the conductive adhesive layer 4 can be formed, for example, by applying (spraying) the adhesive composition for forming the conductive adhesive layer 4 onto a temporary substrate or substrate such as a separate film, and, if necessary, removing the solvent and/or partially curing the same.

The adhesive composition contains, for example, a solvent in addition to the components contained in the conductive adhesive layer described above. Examples of the solvent include those exemplified as solvents that may be contained in the resin composition described above. The solid content concentration of the adhesive composition is appropriately set according to the thickness of the conductive adhesive layer to be formed, etc.

A known coating method may be used to apply the adhesive composition. For example, the coater exemplified above for applying the resin composition may be used.

Next, the exposed surface (electromagnetic wave shielding layer 3 side) of each of the laminates produced is bonded to a conductive adhesive layer 4 to produce the electromagnetic wave shielding film 1.

The electromagnetic shielding film 1 may be produced by a method of sequentially stacking each layer (direct coating method) in addition to the above-mentioned lamination method. For example, the electromagnetic shielding film 1 shown in FIG. 1 can be produced by applying (coating) an adhesive composition for forming the conductive adhesive layer 4 to the surface of the electromagnetic shielding layer 3 of the laminate described above, and removing the solvent and/or partially curing the adhesive composition as necessary to form the conductive adhesive layer 4.

A shielded printed wiring board can be produced using the electromagnetic shielding film. For example, a shielded printed wiring board in which the electromagnetic shielding film is bonded to a printed wiring board can be obtained by bonding the conductive adhesive layer of the electromagnetic shielding film to a printed wiring board (e.g., a coverlay). In the shielded printed wiring board, the conductive adhesive layer may be thermally cured, for example, by a subsequent heating and pressure treatment.

Below, one embodiment of the electromagnetic shielding film of the present disclosure is described in more detail based on examples, but the electromagnetic shielding film of the present disclosure is not limited to these examples.

Examples 1 to 3 and Comparative Examples 1 to 3
(Formation of protective layer)
A resin solution (solid content: 35% by mass) containing a polyester resin and an amino resin as a curing agent was applied to the release-treated surface of a transfer film prepared so that the protective layer surface had a shape having the surface parameters shown in Table 1, and the solvent was removed by heating to form a transparent protective layer.

Next, a resin solution (solid content: 20% by mass) made by mixing epoxy resin with carbon black was applied to the surface of the transparent protective layer, and the solvent was removed by heating to form a black protective layer. In this way, a protective layer was produced in which a transparent protective layer (thickness 1 μm) and a black protective layer (thickness 3 μm) were laminated in this order on the transfer film.

(Formation of conductive adhesive layer)
An adhesive composition (solid content: 30 mass%) made by mixing copper powder with an epoxy resin was applied to the release-treated surface of a PET film whose surface had been release-treated, and the solvent was removed by heating to form a conductive adhesive layer (thickness: 10 μm).

(Preparation of electromagnetic wave shielding film)
The obtained conductive adhesive layer was attached to the black protective layer surface of the protective layer to prepare an electromagnetic wave shielding film having a conductive adhesive layer/black protective layer/transparent protective layer structure.

(evaluation)
The electromagnetic wave shielding films obtained in the Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Table 1.

(1) Surface parameters of protective layer Using a confocal microscope (product name "OPTELICS HYBRID", manufactured by Lasertec, objective lens 100x), in accordance with ISO25178, the transfer film was peeled off from the electromagnetic shielding film, and 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 development area ratio Sdr were measured for the uneven shapes formed at any five points on the exposed transparent protective layer surface. The cutoff wavelength of the S filter was 0.0025 mm, and the cutoff wavelength of the L filter was 0.8 mm.

(2) Glossiness Using a portable glossmeter (product name "Gardner Micro-Gloss", manufactured by BYK Corporation), the transfer film was peeled off from the electromagnetic wave shielding film, and the 60° glossiness and 85° glossiness of the uneven shape formed on the exposed surface of the transparent protective layer were measured.

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

(4) Lightness L ^*
The transfer film was peeled off from the electromagnetic wave shielding film, and the lightness L ^* of the exposed transparent protective layer surface was measured using a spectrophotometer (product name "Ci64UV", manufactured by X-rite Corporation).

As can be seen from Table 1, the electromagnetic shielding films of the examples had lower brightness and better blackness than the electromagnetic shielding films (Comparative Examples 1 to 3) in which at least one of Sal, Sdr, and [Sdr/Sal] was not within the specific range. Therefore, based on this example, it was confirmed that blackness is improved by providing a protective layer with a specific surface shape, regardless of the composition of the black layer.

The electromagnetic wave shielding film of the present invention can be suitably used in mobile devices and image display devices.

Reference Signs List 1 Electromagnetic wave shielding film 2 Protective layer 2a Protective layer surface 21 Black protective layer 22 Transparent protective layer 23 Black protective layer 3 Electromagnetic wave shielding layer 4 Conductive adhesive layer

Claims (6)

This is an electromagnetic wave shielding film with a protective layer on the surface.
The protective layer comprises a black protective layer,
the minimum autocorrelation length Sal of the protective layer surface is 10 μm or less, and the developed area ratio Sdr of the interface is 200% or more;
The ratio of the Sdr to the Sal, [Sdr/Sal], is 50 or more. The electromagnetic wave shielding film of claim 1, wherein the protective layer comprises a black protective layer located inside the electromagnetic wave shielding film and a transparent protective layer or a black protective layer located on the surface of the electromagnetic wave shielding film. The electromagnetic wave shielding film described in 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 claim 1, wherein the lightness L ^* of the protective layer side is 24 or less. An electromagnetic wave shielding film described in any one of claims 1 to 4, wherein the root mean square slope Sdq of the protective layer surface is 2.0 or more. An electromagnetic wave shielding film described in any one of claims 1 to 5, wherein the 85° gloss of the protective layer side is 25 or less.

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