TWI869660B - Electromagnetic wave shielding film - Google Patents

Abstract

The present invention provides an electromagnetic wave shielding film having excellent blackness regardless of the structure and composition of the black layer. The electromagnetic wave shielding film 1 of the present invention has a protective layer 2 on the surface, and the protective layer 2 has a black protective layer 21, the minimum self-correlation length Sal of the surface of the protective layer 2 is less than 10 μm, the interface development area ratio Sdr is more than 200%, and the ratio of the aforementioned Sdr to the aforementioned Sal [Sdr/Sal] is more than 50. The lightness L ^* of the protective layer 2 side is preferably less than 24.

Description

Electromagnetic wave shielding film

Field of the invention The present invention relates to an electromagnetic wave shielding film.

Background technology Until now, in mobile devices such as smartphones and tablet terminals, flexible printed circuit boards (FPCs) with electromagnetic wave shielding films attached have been used to block electromagnetic waves generated from the inside or intruding from the outside.

An electromagnetic wave shielding film (hereinafter, sometimes simply referred to as "shielding film") is used to shield a printed wiring board. For example, a shielding film used in contact with 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 for protecting the shielding layer.

For example, image display devices equipped with plasma display panels (PDP), liquid crystal displays (LCD), organic EL displays, etc. require light-shielding properties for the electromagnetic wave shielding films used therein.

In recent years, there is a trend of demanding electromagnetic wave shielding films with better light shielding properties from the viewpoint of visibility, etc. Patent Documents 1 and 2 disclose electromagnetic wave shielding bodies having a black layer and improved blackness.

Prior art documents Patent documents Patent document 1: Japanese Patent Publication No. 2009-76824 Patent document 2: Japanese Patent Publication No. 2004-288972

Summary of the invention Problems to be solved by the invention However, the electromagnetic wave shielding bodies disclosed in Patent Documents 1 and 2 all improve the blackness by specifying the type of colorant in the black layer. Such a method of limiting the composition of the black layer by specifying the type of colorant may cause the shielding film or the layers constituting the shielding film to deteriorate in other aspects of performance, such as the deterioration of performance that should have been possessed in the past, even if the blackness is improved.

Therefore, the object of the present invention is to provide an electromagnetic wave shielding film having excellent blackness regardless of the structural composition of the black layer.

Means for solving the problem The inventors of the present invention have made careful studies to achieve the above-mentioned purpose, and found that by providing a protective layer including a black layer on the surface of the electromagnetic wave shielding film, and making the shape of the surface of the protective layer a specific shape, it is possible to have excellent blackness regardless of the structural composition of the black layer. The present invention is completed based on these insights.

The present invention provides an electromagnetic wave shielding film having a protective layer on its surface, wherein the protective layer has a black protective layer, the minimum self-correlation length Sal of the protective layer surface is less than 10 μm, the interface development area ratio Sdr is greater than 200%, and the ratio of the Sdr to the Sal [Sdr/Sal] is greater than 50.

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.

The root mean square slope Sdq of the protective layer surface should preferably be greater than 2.0.

The 85° glossiness of the protective layer side should be less than 25.

Effect of the invention The electromagnetic wave shielding film disclosed in the present invention has excellent blackness regardless of the structural composition of the black layer. Therefore, the performance of the shielding film can be maintained without changing the structural composition of the black layer and the blackness is excellent. In addition, due to the excellent blackness, the light shielding property is excellent. When the shielding film is attached to the printed wiring board, the beauty of the printed wiring board or the visibility of the printed text when printing on the protective layer surface of the shielding film and the concealment of the circuit pattern of the printed wiring board are excellent.

Forms for implementing the invention [Electromagnetic wave shielding film] The electromagnetic wave shielding film disclosed in the present invention 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 also have other layers other than the protective layer. The other layers may include an electromagnetic wave shielding layer that can exert electromagnetic wave shielding properties, a conductive adhesive layer, etc. The layers constituting the electromagnetic wave shielding film may be single layers or multiple layers.

(Protective layer) The protective layer has the function of protecting the internal layers such as the electromagnetic wave shielding layer in the electromagnetic wave shielding film. The protective layer at least has a black protective layer (black protective layer). The protective layer may also be an insulating layer (insulating protective layer).

The protective layer may be a single layer or a multilayer. When the protective layer is a multilayer, it may be a laminate of two or more layers having different physical properties such as material, 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 buffering effect, so when the electromagnetic wave shielding film is heated and pressurized on the printed wiring board, the pressure applied to the electromagnetic wave shielding layer such as the metal layer can be relieved. Therefore, the electromagnetic wave shielding layer can be prevented from being damaged due to the height difference of 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 of the protective layers is the black protective layer. Furthermore, 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., outside the surface). Furthermore, when the protective layer is a multi-layer, it is more desirable 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 exert functions different from those of the black protective layer located inside, such as excellent surface hardness. Furthermore, when the protective layer is a multi-layer, when there are multiple black protective layers, the multiple black protective layers may be layers having the same composition (colorant content, etc.) or thickness, or may be different layers.

One embodiment of the electromagnetic wave shielding film will be described using Figures 1 to 3. Figures 1 to 3 are schematic cross-sectional views showing one embodiment of the electromagnetic wave shielding film.

The electromagnetic wave shielding film 1 shown in FIG1 comprises: a conductive adhesive layer 4; an electromagnetic wave shielding layer 3, which is disposed adjacent to one surface of the conductive adhesive layer 4; and a protective layer 2, which is 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 layer of a 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 sequence. In addition, the electromagnetic wave shielding layer 3 may not be provided.

The electromagnetic wave shielding film 1 shown in FIG2 has a protective layer 2 composed of two layers, a black protective layer 21 and a transparent protective layer 22, which is different from the electromagnetic wave shielding film 1 shown in FIG1. 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 FIG3 has a protective layer located on its surface, not the transparent protective layer 22, but a black protective layer 23, which is different from the electromagnetic wave shielding film 1 shown in FIG2.

The minimum self-correlation length Sal of the protective layer surface (e.g., 2a shown in FIG. 1 to FIG. 3) is less than 10 μm, preferably less than 9.7 μm, and more preferably less than 6.0 μm. The smaller the above Sal, the smaller the height of each concave and convex surface. The above Sal is, for example, greater than 1 μm, preferably greater than 2 μm.

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

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

In the electromagnetic wave shielding film, by making the above-mentioned Sal, the above-mentioned Sdr and the above-mentioned ratio [Sdr/Sal] within the above-mentioned ranges, the various concavities and convexities on the surface of the protective layer are small and the developed surface area is large. Thereby, the reflectivity of visible light incident on the surface of the protective layer can be reduced. Therefore, as long as the shape of the surface of the protective layer is set within the above-mentioned range, regardless of the structural composition of the black protective layer, it will have a better blackness than the case where the shape of the surface of the protective layer is not set within the above-mentioned range. Furthermore, the electromagnetic wave shielding film sets the Sal and Sdr of the protective layer surface within a specific range, and does not intend to increase the height of the concavo-convex shape of the protective layer surface. Therefore, there is no need to provide a thick protective layer or to provide an embedding layer such as a release treatment layer for embedding particles on the transfer film described later. Therefore, compared with the conventional electromagnetic wave shielding film, the productivity, anti-curling property, and particle fall-off resistance of the electromagnetic wave shielding film are not reduced.

The root mean square slope Sdq of the protective layer surface is preferably greater than 2.0, more preferably greater than 3.0, and more preferably greater than 3.5. If the above Sdq is greater than 2.0, the blackness of the protective layer surface tends to increase.

The arithmetic mean height Sa of the surface of the protective layer should preferably be 0.4~2.0μm, preferably 0.5~1.5μm. If the arithmetic mean height Sa is within the above range, it is ideal from the perspective of a balance between gloss and productivity. The maximum peak height Sp of the surface of the protective layer should preferably be 2.5~9.0μm, preferably 3.0~7.0μm. If the maximum peak height Sp is within the above range, it is ideal from the perspective of a balance between gloss and productivity. The maximum trough depth Sv of the surface of the protective layer should preferably be 2.0~7.0μm, preferably 3.0~7.0μm. If the maximum trough depth Sv is within the above range, it is ideal from the perspective of a 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. If the maximum height Sz is within the above range, it is ideal from the perspective of balancing glossiness and productivity.

Each layer constituting the protective layer preferably contains a binder component. The binder component may include thermoplastic resins, thermosetting resins, active energy ray-hardening compounds, etc. The binder component may be used alone or in combination of two or more.

Examples of the thermoplastic resin include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (e.g. polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, acrylic resins, etc. The thermoplastic resins may be used alone or in combination of two or more.

The thermosetting resins include resins having thermosetting properties (thermosetting resins) and resins obtained by hardening the thermosetting resins. Examples of the thermosetting resins include phenolic resins, epoxy resins, urethane resins, melamine resins, alkyd resins, etc. The thermosetting resins may be used alone or in combination of two or more.

Examples of the epoxy resin include bisphenol epoxy resins, spirocyclic epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, terpene epoxy resins, glycidyl ether epoxy resins, glycidyl amine epoxy resins, and novolac 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, tetrabromobisphenol A type epoxy resin, etc. Examples of the glycidyl ether type epoxy resin include tris(glycidoxyphenyl)methane, tetrakis(glycidoxyphenyl)ethane, etc. Examples of the glycidyl amine type epoxy resin include tetraglycidyl diamino diphenylmethane, etc. Examples of the novolac epoxy resin include cresol novolac epoxy resin, phenol novolac epoxy resin, α-naphthol novolac epoxy resin, brominated phenol novolac epoxy resin, and the like.

The active energy ray-hardening compound can be exemplified by compounds that can be hardened by irradiation with active energy rays (active energy ray-hardening compounds) and compounds obtained by hardening the active energy ray-hardening compounds. The active energy ray-hardening compound is not particularly limited, and examples thereof include polymerizable compounds having one or more (preferably two or more) free radical reactive groups (e.g., (meth)acryloyl groups) in the molecule. The active energy ray-hardening compound can be used alone or in combination of two or more.

The black protective layer preferably contains a colorant. The colorant is preferably a black colorant. The black colorant may be a known or commonly used colorant (pigment, dye, etc.) for presenting black, for example: 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, granulated iron (non-magnetic granulated iron, magnetic granulated iron, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, anthraquinone colorant, zirconium nitride, etc. Only one black colorant may be used, or two or more may be used. Furthermore, a coloring agent having the function of a black coloring agent by combining or mixing a coloring agent that exhibits a color other than black may be used.

The protective layer may contain other components other than the above components without prejudice to the effects of the present invention. Examples of the above other components include hardeners, hardening accelerators, plasticizers, flame retardants, defoamers, viscosity regulators, antioxidants, diluents, anti-settling agents, fillers, other colorants, levelers, coupling agents, ultraviolet absorbers, adhesive resins, anti-caking agents, etc. The above other components may be used alone or in combination of two or more.

The thickness of the protective layer is not particularly limited and can be appropriately set as needed, preferably 1-20 μm, preferably 2-15 μm, and more preferably 3-10 μm. If the thickness is above 1 μm, the inner layer can be more fully protected. If the thickness is below 20 μm, the softness and flexibility are excellent, and it is also economically advantageous.

When the protective layer is a multilayer, the thickness of the protective layer (e.g., transparent protective layer) on the surface of the electromagnetic wave shielding film is preferably 0.1-10 μm, preferably 0.5-5 μm. Moreover, the thickness of the black protective layer inside the electromagnetic wave shielding film is preferably 0.5-15 μm, preferably 1-10 μm.

(Electromagnetic wave shielding layer) The electromagnetic wave shielding layer may be a known or commonly used shielding layer having electromagnetic wave shielding properties. The electromagnetic wave shielding layer preferably contains a metal layer. The electromagnetic wave shielding layer may be a single layer or a multi-layer.

The metal constituting the metal layer may be, for example, gold, silver, copper, aluminum, nickel, tin, palladium, chromium, titanium, zinc or alloys thereof. The metal layer is preferably a metal plate or a 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 above 0.01 μm, a more adequate shielding performance can be obtained. If the thickness is below 10 μm, the flexibility will become better.

(Conductive adhesive layer) The conductive adhesive layer has adhesiveness and conductivity for bonding 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 a multi-layer.

The conductive adhesive layer preferably contains a binder component and conductive particles that can function as an adhesive. The binder component may include thermoplastic resins, thermosetting resins, active energy ray-curing compounds, etc. The thermoplastic resins, thermosetting resins, and active energy ray-curing compounds may be exemplified as the binder components that may be contained in the protective layer. The binder component may be used alone or in combination of two or more.

Among them, the above-mentioned adhesive component is preferably a thermosetting resin. In this case, after the electromagnetic wave shielding film is arranged on the printed wiring board, the adhesive component can be hardened by applying pressure and heat, and the adhesion will become better.

When the binder component contains a thermosetting resin, the components constituting the binder component may also contain a hardener for promoting a thermosetting reaction. The hardener may be appropriately selected according to the type of the thermosetting resin. The hardener may be used alone or in combination of two or more.

The content ratio of the binder component in the conductive adhesive layer is not particularly limited. Relative to the total amount of the conductive adhesive layer (100 mass%), it is preferably 40-98 mass%, preferably 50-97 mass%, more preferably 60-96 mass%, still more preferably 70-95.5 mass%, and particularly preferably 75-95 mass%. If the content ratio is above 40 mass%, the adhesion to the printed wiring board will be better. If the content ratio is below 98 mass%, the conductive particles can be contained in sufficient amount.

Examples of the conductive particles include metal particles, metal-coated resin particles, metal fibers, carbon fillers, carbon nanotubes, etc. Only one type of conductive particles may be used, or two or more types may be used.

The metal particles and the metal forming the coating of the metal-coated resin particles may be, for example, gold, silver, copper, nickel, zinc, etc. Only one kind of the metal may be used, or two or more kinds may be used.

Specifically, the metal particles include, for example, 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. The silver-coated alloy particles include, for example, copper-containing alloy particles (e.g., copper alloy particles composed of an alloy of copper, nickel, and zinc) and silver-coated copper alloy particles. The metal particles may be produced by electrolysis, atomization, reduction, and the like.

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

The shapes of the conductive particles include spherical, flake (scale), branch-like, fiber-like, amorphous (polyhedral), etc.

The median diameter (D50) of the conductive particles is preferably 1 to 50 μm, more preferably 3 to 40 μm. If the median diameter is greater than 1 μm, the conductive particles have good dispersibility and can suppress aggregation, and are not easily oxidized. If the average particle diameter is less than 50 μm, the conductivity will be good. The median diameter can be measured by a particle size distribution based on volume.

The content ratio of the conductive particles in the conductive adhesive layer is not particularly limited. It is preferably 2-80 mass%, preferably 5-60 mass%, and more preferably 10-40 mass%, relative to the total amount of the conductive adhesive layer (100 mass%). If the content ratio is above 2 mass%, the conductivity will be better. If the content ratio is below 80 mass%, the adhesive component can be contained in sufficient amount, and the adhesion to the printed wiring board will be better.

The conductive adhesive layer can be a layer with isotropic conductivity or anisotropic conductivity as required. When the conductive adhesive layer has anisotropic conductivity, the electromagnetic wave shielding film should preferably have a 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 be a structure without the electromagnetic wave shielding layer (e.g., [protective layer/conductive adhesive layer]).

The conductive adhesive layer may contain other components other than the above components without prejudice to the effects of the present invention. The other components may be components contained in known or commonly used adhesive layers. The other components may include, for example, hardening accelerators, plasticizers, flame retardants, defoamers, viscosity regulators, antioxidants, diluents, anti-settling agents, fillers, colorants, leveling agents, coupling agents, ultraviolet absorbers, adhesive resins, anti-caking agents, etc. The other components may be used alone or in combination of two or more.

The thickness of the conductive adhesive layer is preferably 1 to 40 μm, preferably 5 to 30 μm. If the thickness is above 1 μm, the adhesion strength to the adherend will be better. If the thickness is below 40 μm, the cost can be suppressed, and the product having the conductive adhesive layer can be designed to be thin and light. In addition, in the case where the adhesive component (binder component) constituting the conductive adhesive layer begins to flow due to heating and penetrates into the opening formed in the adherend, the thickness of the conductive adhesive layer at this time is the thickness of the adhesive layer in the area that has not penetrated into the opening.

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

The above-mentioned separating member can be, for example, a polyethylene terephthalate (PET) film, a polyethylene film, a polypropylene film, a plastic film or paper coated with a stripping agent such as a fluorine-based stripping agent or a long-chain alkyl acrylate-based stripping agent, etc.

The thickness of the separation piece is preferably 10-200 μm, preferably 15-150 μm. If the thickness is above 10 μm, the protective performance will be better. If the thickness is below 200 μm, the separation piece is easy to peel off during use.

The electromagnetic wave shielding film may further include an anchor coating layer formed between the protective layer and the electromagnetic wave shielding layer. With such a structure, the adhesion between the electromagnetic wave shielding layer and the protective layer will be further improved.

The materials forming the anchor coating layer include urethane resins, acrylic resins, core-shell composite resins with urethane resins as shells and acrylic resins as cores, epoxy resins, polyimide resins, polyamide resins, melamine resins, phenol resins, urea-formaldehyde resins, blocked isocyanates obtained by reacting a blocking agent such as phenol with polyisocyanate, polyvinyl alcohol, polyvinyl pyrrolidone, etc. Only one of the above materials may be used, or two or more of them may be used.

The lightness L ^* of the protective layer side of the electromagnetic wave shielding film is preferably 24 or less. The lightness L ^* is the lightness specified in the L ^* a ^* b ^* colorimetric system. The lightness L ^* is a value measured from the protective layer side of the electromagnetic wave shielding film on the outermost surface of the protective layer. When there is a separation piece, the separation piece is peeled off and then measured. In addition, in the laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly ideal that the lightness L ^* measured from the protective layer side is within the above range. If the lightness L ^* is below 24, the blackness is high and the concealment is more excellent. The lightness L ^* can be measured based on JIS Z8722 (2009).

The 85° glossiness of the protective layer side of the electromagnetic wave shielding film is preferably 25 or less, and more preferably 22 or less. If the 85° glossiness is 25 or less, the circuit pattern of the printed wiring board will be more concealed when the shielding film is attached to the printed wiring board. In addition, in the laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly ideal that the 85° glossiness measured from the protective layer side is within the above range.

The 60° gloss on the protective layer side of the electromagnetic wave 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 appearance of the printed wiring board or the visibility of the printed text on the protective layer surface of the shielding film will be better. In addition, in the laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly ideal that the 60° gloss measured from the protective layer side is within the above range.

The glossiness is a value measured from the side of the protective layer with respect to the electromagnetic wave shielding film on the outermost surface of the protective layer. If there is a separation member, the separation member is peeled off before measurement. The glossiness can be measured by a method in accordance with JIS Z8741.

The reflectivity of light at 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 reflectivity is below 5.0%, the blackness will be further improved. In addition, in the laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly ideal that the reflectivity measured from the protective layer side is within the above range.

The reflectivity of the light at 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 reflectivity is below 5.0%, the blackness will be further improved. In addition, in the laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly ideal that the reflectivity measured from the protective layer side is within the above range.

The reflectivity of light at 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 reflectivity is below 5.0%, the blackness will be further improved. In addition, in the laminated structure composed of the protective layer and the conductive adhesive layer, it is particularly ideal that the reflectivity measured from the protective layer side is within the above range.

The reflectivity is a value measured from the protective layer side of the electromagnetic wave shielding film on the outermost surface of the protective layer. If there is a separator, the separator is peeled off before measurement. The reflectivity can be measured by a method in accordance with JIS Z8722.

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

(Method for manufacturing electromagnetic wave shielding film) One embodiment of the method for manufacturing the electromagnetic wave shielding film described above is described. When manufacturing the electromagnetic wave shielding film 1 shown in FIG. 1, first, a laminate of the protective layer 2 and the electromagnetic wave shielding layer 3 and the conductive adhesive layer 4 are individually manufactured. Then, the individually manufactured laminate and the conductive adhesive layer 4 are bonded together (lamination method). In addition, for an electromagnetic wave shielding film without the electromagnetic wave shielding layer 3, the protective layer 2 and the conductive adhesive layer 4 are individually manufactured, 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 on a transfer film such as a separator, and removing the solvent and/or partially hardening it as needed. A concave-convex shape is formed on the surface of the transfer film on which the resin composition is applied. By forming the protective layer in this way, a shape derived from the concave-convex shape can be transferred to the surface of the protective layer. The concave-convex shape on the surface of the transfer film can be produced using known or conventional methods, such as sandblasting, embedding particles in the layers constituting the transfer film so that they protrude from the surface of the transfer film, etc. Furthermore, by properly adjusting the sandblasting conditions or the size of the embedded particles to design the concave and convex shapes formed on the transfer film surface, the surface parameters such as Sal and Sdr of the protective layer surface can be adjusted. Then, the transfer film can be used as a separator in the electromagnetic wave shielding film.

A release treatment layer may also be provided on the surface of the transfer film having the concavo-convex shape. The release treatment layer may be, for example, a layer formed by surface treatment using a polysilicone-based, long-chain alkyl-based, fluorine-based, molybdenum sulfide or other peeling treatment agent. In addition, when there is a release treatment layer, the thickness or shape of the release treatment layer may be appropriately set so that the concavo-convex shape of the surface does not disappear, that is, the transfer film has the concavo-convex shape.

The resin composition forming the protective layer includes, in addition to the components contained in the protective layer, a solvent. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, dimethylformamide, etc. The solid content concentration of the resin composition can be appropriately set according to the thickness of the protective layer to be formed.

The resin composition can be applied by a known coating method. For example, a coating machine such as a gravure roll coater, a reverse roll coater, a contact roll coater, a die lip coater, a dip roll coater, a rod coater, a knife coater, a spray coater, a notched wheel coater, a direct coater, a slot die coater, etc. can be used.

Next, an electromagnetic wave shielding layer 3 is formed on the surface of the protective layer 2 formed on the transfer film. The formation of the electromagnetic wave shielding layer 3 is preferably performed by evaporation or sputtering. The evaporation and sputtering methods can be known or conventional methods. In this way, a laminate of the protective layer 2/electromagnetic wave shielding layer 3 is produced.

On the other hand, when preparing the conductive adhesive layer 4, for example, the adhesive composition used to form the conductive adhesive layer 4 can be applied (coated) on a temporary substrate or substrate such as a separation film, and the conductive adhesive layer 4 can be formed by removing the solvent and/or partially hardening as needed.

The adhesive composition includes, for example, the components contained in the conductive adhesive layer, and also includes a solvent. Examples of the solvent include the solvents that may be contained in the resin composition. The solid component concentration of the adhesive composition may be appropriately set according to the thickness of the conductive adhesive layer to be formed.

The adhesive composition can be applied by a known coating method, such as the coating machine used for coating the resin composition.

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

As another aspect other than the above-mentioned lamination method, the electromagnetic wave shielding film 1 can also be manufactured by a method of sequentially laminating each layer (direct coating method). For example, the electromagnetic wave shielding film 1 shown in FIG. 1 can be manufactured as follows: an adhesive composition for forming a conductive adhesive layer 4 is coated (coated) on the surface of the electromagnetic wave shielding layer 3 of the above-mentioned laminate, and the conductive adhesive layer 4 is formed by removing the solvent and/or partially hardening as needed.

The electromagnetic wave shielding film can be used to produce a shielded printed wiring board. For example, by laminating the conductive adhesive layer of the electromagnetic wave shielding film to a printed wiring board (e.g., a cover layer), a shielded printed wiring board having the electromagnetic wave shielding film laminated to the printed wiring board can be produced. In the shielded printed wiring board, the conductive adhesive layer can be thermally cured by, for example, a subsequent heating and pressure treatment.

Embodiments Below, based on the embodiments, an embodiment of the electromagnetic wave shielding film of the present invention is described in more detail, but the electromagnetic wave shielding film of the present invention is not limited to the embodiments.

Examples 1-3 and Comparative Examples 1-3 (Forming a protective layer) A resin solution (solid content: 35% by mass) containing a polyester resin and an amino resin as a hardener is applied to the release-treated surface of a transfer film, wherein the transfer film is formed such that the protective layer surface has a shape having the surface parameters shown in Table 1, and the solvent is removed by heating to form a transparent protective layer.

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

(Forming a conductive adhesive layer) An adhesive composition (solid content: 30% by mass) in which copper powder is mixed in epoxy resin is applied to the release-treated surface of a PET film, and the solvent is removed by heating to form a conductive adhesive layer (thickness 10 μm).

(Preparation of electromagnetic wave shielding film) The above-prepared conductive adhesive layer is bonded to the black protective layer of the above-mentioned protective layer to produce an electromagnetic wave shielding film composed of a conductive adhesive layer/black protective layer/transparent protective layer structure.

(Evaluation) Each electromagnetic wave shielding film produced in the embodiment and the comparative example was evaluated as follows. The evaluation results are shown in Table 1.

(1) Surface parameters of protective layer Using a confocal microscope (trade name "OPTELICS HYBRID", manufactured by Lasertec, objective lens 100 times), in compliance with ISO25178, the surface of the transparent protective layer exposed by peeling off the transfer film from the electromagnetic wave shielding film was measured for the arithmetic mean height Sa, maximum peak height Sp, maximum trough depth Sv, maximum height Sz, minimum autocorrelation length Sal, root mean square slope Sdq and interface development area ratio Sdr of the concave and convex shapes formed at any five locations on the surface of the transparent protective layer. In addition, 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.

(2) Gloss Using a portable gloss meter (trade name "Gardner micro gloss", manufactured by BYK), the 60° gloss and 85° gloss of the concave and convex shapes formed on the surface of the transparent protective layer exposed after the transfer film was peeled off from the electromagnetic wave shielding film were measured.

(3) Reflectivity Using a spectrophotometer (trade name "CM-26d", manufactured by Konica Minolta Co., Ltd.), in compliance with JIS Z8722 (condition c), the light reflectivity at wavelengths of 450nm, 550nm, and 650nm was measured for the surface of the transparent protective layer exposed after the transfer film was peeled off from the electromagnetic wave shielding film.

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

[Table 1]

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

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

FIG1 is a schematic cross-sectional view showing one embodiment of the electromagnetic wave shielding film of the present invention. FIG2 is a schematic cross-sectional view showing another embodiment of the electromagnetic wave shielding film of the present invention. FIG3 is a schematic cross-sectional view showing yet another embodiment of the electromagnetic wave shielding film of the present invention.

1:Electromagnetic wave shielding film

2: Protective layer

2a: Protective layer surface

3: Electromagnetic wave shielding layer

4: Conductive adhesive layer

21: Black protective layer

Claims (9)

An electromagnetic wave shielding film having a protective layer on the surface, wherein the protective layer has a black protective layer, the minimum self-correlation length Sal of the surface of the protective layer is less than 10 μm, the interface development area ratio Sdr is greater than 200%, and the ratio of the Sdr to the Sal [Sdr/Sal] is greater than 50. As in claim 1, the electromagnetic wave shielding film, wherein the aforementioned protective layer comprises: a black protective layer located inside the aforementioned electromagnetic wave shielding film; and a transparent protective layer or a black protective layer located on the surface of the aforementioned electromagnetic wave shielding film. As in claim 1, the electromagnetic wave shielding film, wherein the aforementioned black protective layer is located on the surface of the aforementioned electromagnetic wave shielding film. The electromagnetic wave shielding film of claim 1, wherein the lightness L ^* of the protective layer side is 24 or less. The electromagnetic wave shielding film of claim 2, wherein the lightness L ^* of the protective layer side is 24 or less. The electromagnetic wave shielding film of claim 3, wherein the lightness L ^* of the protective layer side is 24 or less. An electromagnetic wave shielding film as claimed in any one of claims 1 to 6, wherein the root mean square slope Sdq of the surface of the protective layer is greater than 2.0. The electromagnetic wave shielding film of any one of claims 1 to 6, wherein the 85° glossiness of the protective layer side is less than 25. The electromagnetic wave shielding film of claim 7, wherein the 85° glossiness of the protective layer side is less than 25.