Electromagnetic wave shielding film

Abstract

The present invention provides an electromagnetic wave shielding film that can be easily bonded to a bonded object, has excellent electrical connection stability, and is also excellent in transparency, shielding performance, and environmental resistance. In the electromagnetic wave shielding film of the present invention, a first insulating layer, a transparent metal layer, a second insulating layer, and a conductive adhesive layer are laminated in sequence, the thickness of the second insulating layer is 10 to 500 nm, the conductive adhesive layer contains a binder component and spherical conductive particles, the median diameter of the spherical conductive particles is 3 to 50 μm, and the content ratio of the spherical conductive particles is 5 to 20% by mass relative to 100% by mass of the conductive adhesive layer.

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave shielding film. More specifically, the present invention relates to an electromagnetic wave shielding film for a printed wiring board. Background Art

[0002] Printed circuit boards are often used to assemble circuits into mechanisms in electronic devices such as mobile phones, cameras, and notebook personal computers. In addition, printed circuit boards are also used to connect movable parts such as print heads with control parts. For the above electronic devices, electromagnetic wave shielding measures are essential, and shielded printed circuit boards that implement electromagnetic wave shielding measures are also used for printed circuit boards used in devices.

[0003] Electromagnetic wave shielding films (hereinafter sometimes referred to as "shielding films") are used in shielded printed wiring boards. For example, shielding films used in conjunction with printed wiring boards include a shielding layer such as a metal layer and a conductive bonding sheet provided on the surface of the shielding layer.

[0004] Regarding the shielding film containing a conductive bonding sheet, for example, the shielding films disclosed in Patent Documents 1 and 2 are known. The shielding film is used by bonding the exposed surface of the conductive bonding sheet to the surface of the printed circuit board, specifically, to the surface of the covering film provided on the surface of the printed circuit board. Usually, thermocompression bonding is performed under high temperature and high pressure conditions so that the conductive bonding sheet is bonded to the printed circuit board and laminated to the printed circuit board. The shielding film configured on the printed circuit board as described above exerts the performance of shielding electromagnetic waves from outside the printed circuit board (shielding performance).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-110769;

[0008] Patent document 2: Japanese Patent Application Laid-Open No. 2012-28334. Summary of the invention

[0009] Technical problem to be solved by the invention

[0010] In recent years, shielding films are sometimes required to have the performance of being easy to position when attached to a printed circuit board. Therefore, the shielding film tends to be required to be transparent. As a method to improve transparency, thinning the metal layer in the shielding film can be considered. However, although this method improves transparency, there are the following problems: in a high temperature and high humidity environment or in an environment with electrolytes, the transparent metal layer deteriorates and becomes turbid, which impairs transparency and reduces shielding performance, that is, poor environmental resistance.

[0011] In addition, in recent years, there has been a tendency to pursue a shielding film containing a conductive adhesive layer that can be bonded to a printed circuit board under relatively mild conditions rather than high temperature and high pressure conditions. However, when using the conventional anisotropic conductive adhesive sheet as the conductive adhesive layer in the shielding film, there is a problem of unstable electrical connection with the external ground. In order to improve the stability of the electrical connection, a method of increasing the amount of conductive particles compounded in the conventional anisotropic conductive adhesive sheet can be considered. In this case, the connection stability can be improved, but it cannot compensate for the reduced environmental resistance caused by the thin filmization of the metal layer, and the transparency is reduced.

[0012] In view of the above, an object of the present invention is to provide an electromagnetic wave shielding film that can be easily bonded to an object to be bonded, has excellent electrical connection stability, and is also excellent in transparency, shielding performance, and environmental resistance.

[0013] Technical means to solve technical problems

[0014] The inventors of the present invention have made intensive research to achieve the above-mentioned purpose and have found that an electromagnetic wave shielding film having a specific layer structure and using a specific conductive adhesive layer can be easily bonded to a bonded object, has excellent electrical connection stability, and is also excellent in transparency, shielding performance, and environmental resistance. The present invention was completed based on the above-mentioned knowledge.

[0015] That is, the present invention provides an electromagnetic wave shielding film in which a first insulating layer, a transparent metal layer, a second insulating layer and a conductive adhesive layer are laminated in this order.

[0016] The thickness of the second insulating layer is 10 to 500 nm.

[0017] The conductive adhesive layer contains a binder component and spherical conductive particles.

[0018] The median diameter of the spherical conductive particles is 3 to 50 μm.

[0019] The content ratio of the spherical conductive particles is 5 to 20% by mass relative to 100% by mass of the conductive adhesive layer.

[0020] It is preferable that the second insulating layer and the transparent metal layer are directly laminated.

[0021] It is preferable that the second insulating layer includes an inorganic layer formed of an inorganic substance.

[0022] It is preferred that the inorganic layer and the transparent metal layer be directly laminated.

[0023] It is preferable that the second insulating layer has a laminated structure including an inorganic layer formed of an inorganic substance and a resin layer formed of a resin.

[0024] It is preferred that the resin layer and the conductive adhesive layer are directly laminated, and the inorganic layer and the transparent metal layer are directly laminated.

[0025] It is preferable that a third insulating layer is included between the first insulating layer and the transparent metal layer.

[0026] It is preferred that the total light transmittance of the electromagnetic wave shielding film is 62% or more.

[0027] In addition, the present invention provides a shielding printed circuit board including the above-mentioned electromagnetic wave shielding film.

[0028] Effects of the Invention

[0029] The electromagnetic wave shielding film of the present invention can be easily bonded to an object to be bonded, and has excellent electrical connection stability, transparency, shielding performance and environmental resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030]

Figure 1

[0031]

Figure 2

[0032]

Figure 3

[0033]

Figure 4

[0034] [Shielding film]

[0035] The shielding film of the present invention has a layer structure in which a first insulating layer, a transparent metal layer, a second insulating layer and a conductive adhesive layer are laminated in this order.

[0036] One embodiment of the shielding film of the present invention is described below. Figure 1 It is a schematic cross-sectional view of one embodiment of the electromagnetic wave shielding film of the present invention. Figure 1 The shielding film 1 of the present invention shown includes a first insulating layer 11, a transparent metal layer 12, a second insulating layer 13, and a conductive adhesive layer 14 in this order.

[0037] (1st insulation layer)

[0038] The first insulating layer is a transparent substrate that functions as a support in the shielding film of the present invention. Examples of the first insulating layer include a plastic substrate (especially a plastic film), a glass plate, etc. The first insulating layer may be a single layer or a laminate of the same or different types.

[0039] Examples of the resin constituting the plastic substrate include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homopolypropylene, polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate (random, alternating) copolymer, ethylene-butene copolymer, ethylene-hexene copolymer and other polyolefin resins; polyurethane; polyethylene terephthalate (PET); Polyesters such as polyethylene naphthalate (ET), polyethylene naphthalate, and polybutylene terephthalate (PBT); polycarbonate (PC); polyimide (PI); polyetheretherketone (PEEK); polyetherimide; polyamides such as aromatic polyamide and wholly aromatic polyamide; polyphenylene sulfide; polysulfone (PS); polyethersulfone (PES); acrylic resins such as polymethyl methacrylate (PMMA); acrylonitrile-butadiene-styrene copolymer (ABS); fluororesin; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as triacetyl cellulose (TAC); silicone resin, etc. The above resins may be used alone or in combination of two or more. Among the above resins, polyester and cellulose resins are preferred from the perspective of superior transparency, and polyethylene terephthalate and triacetyl cellulose are more preferred.

[0040] For the purpose of improving the close adhesion and placement performance with adjacent layers such as the transparent metal layer, for example, the surface of the first insulating layer (especially the surface on the transparent metal layer side) may be subjected to the following surface treatments: physical treatments such as corona discharge treatment, plasma treatment, sandblasting treatment, ozone exposure treatment, flame exposure treatment, high voltage electric shock exposure treatment, ionizing radiation treatment, etc.; chemical treatments such as chromic acid treatment; easy bonding treatment by a coating agent (primer), etc. The surface treatment for improving close adhesion is preferably applied to the entire surface of the transparent metal layer side of the first insulating layer.

[0041] The thickness of the first insulating layer is not particularly limited, but is preferably 1 to 15 μm, and more preferably 3 to 10 μm. If the thickness is greater than 1 μm, the shielding film and the protective transparent metal layer can be more fully supported. If the thickness is less than 15 μm, the transparency and flexibility are excellent, and it is also economically advantageous. In addition, when the first insulating layer is a multilayer structure, the thickness of the first insulating layer is the sum of the thicknesses of all layers.

[0042] (Transparent metal layer)

[0043] In the shielding film of the present invention, the transparent metal layer is an element that functions as a shielding layer. The transparent metal layer may be a single layer or a laminate of the same or different types of metal layers.

[0044] Examples of the metal constituting the transparent metal layer include gold, silver, copper, aluminum, lithium, nickel, tin, palladium, chromium, titanium, zinc, or alloys of the above metals. Examples of the alloys include silver / copper alloys, magnesium / copper alloys, magnesium / silver alloys, magnesium / aluminum alloys, magnesium / indium alloys, lithium / aluminum alloys, and ITO (Indium Tin Oxide). Among the above metals, copper and silver are preferred from the perspective of superior electromagnetic wave shielding performance, and silver / copper alloys are preferred from the perspective of superior migration resistance and sulfidation resistance.

[0045] The method for forming the transparent metal layer is not particularly limited, and examples thereof include electrolysis, vapor deposition (e.g., vacuum vapor deposition), sputtering, CVD, metal organic (MO), plating, and rolling processing, etc. Among them, a transparent metal layer formed by vapor deposition or sputtering is preferred from the perspective of ease of production.

[0046] The thickness of the transparent metal layer is preferably 10 to 100 nm, more preferably 10 to 50 nm. If the thickness is above 10 nm, the shielding performance is more excellent. If the thickness is below 100 nm, the transparency is excellent. In addition, when the transparent metal layer is a multilayer structure, the thickness of the transparent metal layer is the sum of the thicknesses of all layers.

[0047] (Second insulation layer)

[0048] The second insulating layer is a transparent layer that protects the transparent metal layer. By having the second insulating layer between the transparent metal layer and the conductive adhesive layer, environmental resistance can be improved, and the reduction in transparency and connection stability can be suppressed. The reduction in transparency and connection stability is presumed to be caused by the degradation of the transparent metal layer caused by electrolytes such as water, acidic components or salts contained in sweat in the conductive adhesive layer. The second insulating layer can be a single layer or multiple layers.

[0049] The second insulating layer can be a resin layer mainly formed of a resin or an inorganic layer formed of an inorganic substance. When the second insulating layer is an inorganic layer, it can protect the transparent metal layer and inhibit the degradation of the transparent metal layer in a high temperature and high humidity environment and an environment where an electrolyte exists, thereby reducing the transparency and shielding performance, that is, it has excellent environmental resistance. On the other hand, when the second insulating layer is a resin layer, it has excellent environmental resistance as when it is an inorganic layer, and has better flexibility than an inorganic layer, so it has excellent embedding properties in small diameter holes and better connection stability.

[0050] As the resin forming the above-mentioned resin layer, a thermoplastic resin, a thermosetting resin or an active energy ray curing compound is preferred. For the above-mentioned thermoplastic resin, thermosetting resin and active energy ray curing compound, the examples of the binder components that can be contained in the conductive adhesive layer described later can be listed respectively. The above-mentioned resins can be used alone or in combination of two or more.

[0051] Examples of the inorganic material forming the inorganic material layer include inorganic transparent pigments such as glass, clay, mica, talc, kaolinite, halloysite, zeolite, acid clay, activated clay, boehmite, pseudoboehmite, inorganic oxides, and metal salts [e.g., alkaline earth metal salts, etc.]; organic transparent pigments such as resin pigments such as styrene resins, polydivinylbenzene, and polytetrafluoroethylene; and transparent particles such as hollow particles composed of the above organic transparent pigments and containing a hollow structure (air-filled structure). The above transparent particles may be transparent particles subjected to a well-known or even customary surface treatment.

[0052] Examples of the inorganic oxides include aluminum oxide, magnesium oxide, antimony oxide, titanium oxide, zirconium oxide, zinc oxide, and silicon oxide. Examples of the alkaline earth metal salts include carbonates, silicates, sulfates, and fluorides such as magnesium carbonate, calcium carbonate, barium carbonate, magnesium silicate, calcium silicate, magnesium hydroxide, magnesium phosphate, magnesium hydrogen phosphate, magnesium sulfate, calcium sulfate, barium sulfate, magnesium fluoride, and calcium fluoride. Examples of metal salts other than alkaline earth metal salts include aluminum silicate, aluminum hydroxide, and zinc sulfide.

[0053] Among them, from the viewpoint of transparency and economic efficiency, the inorganic oxide is preferably aluminum oxide, magnesium oxide, titanium oxide, or silicon oxide, and more preferably titanium oxide.

[0054] When the second insulating layer is an inorganic layer, its formation method can include electrolysis, vapor deposition (such as vacuum vapor deposition), sputtering, CVD method, metal organic (MO), plating and rolling processing. Among them, from the perspective of ease of manufacturing, an inorganic layer formed by vapor deposition or sputtering is preferred. When the second insulating layer is a resin layer, its formation method can adopt a well-known method such as coating.

[0055] In the range that the technical effect of the present invention is not impaired, in addition to the resin forming the above-mentioned resin layer and the inorganic substance forming the inorganic substance layer, the second insulating layer may contain other components. As the above-mentioned other components, for example, curing agent, curing accelerator, plasticizer, flame retardant, defoaming agent, viscosity modifier, antioxidant, diluent, anti-settling agent, filler, leveling agent, coupling agent, ultraviolet absorber, tackifying resin and anti-adhesion agent can be listed. The above-mentioned other components can be used alone or in combination of two or more.

[0056] The thickness of the second insulating layer is 10 to 500 nm, preferably 10 to 300 nm. When the thickness is above 10 nm, the connection stability is excellent and the environmental resistance is excellent. When the thickness is below 500 nm, the connection stability is excellent even when it is joined to the printed wiring board under relatively mild conditions. In addition, when the second insulating layer is a multilayer structure, the thickness of the second insulating layer is the sum of the thicknesses of all layers.

[0057] From the viewpoint of protecting the transparent metal layer, it is preferred that the second insulating layer is directly laminated on the transparent metal layer. In particular, from the viewpoint of improving environmental resistance, it is preferred that the inorganic layer is directly laminated on the transparent metal layer.

[0058] In addition, from the perspective of transparency, connection stability and environmental resistance, it is preferred that the second insulating layer has a laminated structure including the resin layer and the inorganic layer. At this time, from the perspective of the protection performance of the transparent metal layer based on environmental resistance and the protection performance against damage caused by the conductive adhesive layer, it is preferred that the inorganic layer is on the transparent metal layer side and the resin layer is on the conductive adhesive layer side. Furthermore, it is preferred that the conductive adhesive layer and the resin layer are directly laminated, and the transparent metal layer and the inorganic layer are directly laminated.

[0059] For example, Figure 2 In the shielding film 2 shown, the second insulating layer includes a laminated structure including an inorganic layer 13a and a resin layer 13b, and the second insulating layer is composed of the laminated structure. The inorganic layer 13a is arranged on the transparent metal layer 12 side and the resin layer 13b is arranged on the conductive adhesive layer 14 side. The inorganic layer 13a is directly laminated with the transparent metal layer 12, and the resin layer 13b is directly laminated with the conductive adhesive layer 14.

[0060] (Conductive adhesive layer)

[0061] The conductive adhesive layer has, for example, bonding properties for bonding the shielding film of the present invention to a printed circuit board and conductivity for electrical connection to the transparent metal layer. In addition, the conductive adhesive layer also functions as a shielding layer that exerts shielding properties together with the transparent metal layer. The conductive adhesive layer may be a single layer or multiple layers.

[0062] The conductive adhesive layer contains a binder component and spherical conductive particles. From the perspective of connection stability, the conductive particles used in the conductive adhesive layer of the shielding film generally use dendritic (dendritic) conductive particles, while the shielding film of the present invention uses spherical conductive particles. Therefore, compared with the case of using dendritic conductive particles, the transparency is superior.

[0063] As the above-mentioned binder component, thermoplastic resins, thermosetting resins, active energy ray curing compounds, etc. can be listed. The above-mentioned binder component can be used alone or in combination. As the above-mentioned thermosetting resin, both resins with thermosetting properties (thermosetting resins) and resins obtained by curing the above-mentioned thermosetting resins can be listed. As the above-mentioned thermoplastic resin, for example, polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (for example, polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, and acrylic resins can be listed. The above-mentioned thermoplastic resins can be used alone or in combination.

[0064] Examples of the thermosetting resin include phenolic resins, epoxy resins, polyurethane resins, polyurethane urea resins, melamine resins, and alkyd resins. The thermosetting resins may be used alone or in combination of two or more.

[0065] Examples of the epoxy resin include bisphenol epoxy resins, spirocycle epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, terpene epoxy resins, glycidyl ether epoxy resins, glycidyl amine epoxy resins, and novolac epoxy resins.

[0066] Examples of the bisphenol epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, and tetrabromobisphenol A epoxy resins. Examples of the glycidyl ether epoxy resins include tris(glycidyloxyphenyl)methane and tetra(glycidyloxyphenyl)ethane. Examples of the glycidylamine epoxy resins include tetra(glycidyldiaminodiphenyl)methane. Examples of the (linear) novolac epoxy resins include cresol (linear) novolac epoxy resins, phenol (linear) novolac epoxy resins, α-naphthol (linear) novolac epoxy resins, and brominated phenol (linear) novolac epoxy resins.

[0067] The active energy ray-curable compound includes compounds that can be cured by irradiation with active energy rays (active energy ray-curable compounds) and compounds obtained by curing the active energy ray-curable compounds. The active energy ray-curable compound is not particularly limited, and examples thereof include polymerizable compounds having at least two free radical reactive groups (e.g., (meth)acryloyl groups) in the molecule. The active energy ray-curable compound may be used alone or in combination of two or more.

[0068] Among them, thermosetting resin is preferably used as the adhesive component. In this case, after the shielding film of the present invention is placed on a printed wiring board for bonding with the printed wiring board, the adhesive component can be cured by applying pressure and heat, thereby achieving good bonding with the printed wiring board.

[0069] When the binder component includes a thermosetting resin, a curing agent for promoting a thermosetting reaction may also be included as a component constituting the binder component. The curing agent may be appropriately selected according to the type of the thermosetting resin. Only one type of curing agent may be used, or two or more types of curing agents may be used.

[0070] The content of the binder component in the conductive adhesive layer is not particularly limited, and is preferably 5 to 95% by mass, more preferably 40 to 95% by mass, and further preferably 60 to 95% by mass relative to the total amount of the conductive adhesive layer (100% by mass). If the content is 5% by mass or more, the close adhesion to the printed wiring board is more excellent. If the content is 95% by mass or less, the conductive particles can be fully contained.

[0071] Examples of the spherical conductive particles include metal particles, metal-coated resin particles, and carbon-based fillers. The spherical conductive particles may be used alone or in combination of two or more.

[0072] Examples of the metal constituting the coating portion of the metal particles and the metal-coated resin particles include gold, silver, copper, nickel, zinc, etc. The metals may be used alone or in combination of two or more.

[0073] Specifically, 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 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 can be produced by electrolysis, atomization, reduction, and the like.

[0074] Among them, silver particles, silver-coated copper particles, and silver-coated copper alloy particles are preferred as the metal particles. Silver-coated copper particles and silver-coated copper alloy particles are particularly preferred from the perspectives of excellent conductivity, suppression of oxidation and coagulation of metal particles, and reduction of metal particle costs.

[0075] The median diameter (D50) of the spherical conductive particles is 3 to 50 μm, preferably 5 to 30 μm. The median diameter is the median diameter of all spherical conductive particles in the conductive adhesive layer, and refers to the particle size at the cumulative value of 50% in the particle size distribution obtained by laser diffraction scattering. By making the median diameter within the above range, the connection stability of the present invention using spherical conductive particles is excellent. For example, the median diameter can be measured by a laser diffraction particle size analyzer (trade name "SALD-2200", manufactured by Shimadzu Corporation).

[0076] The content of the spherical conductive particles in the conductive adhesive layer is 5 to 20% by mass, preferably 5 to 15% by mass, relative to 100% by mass of the conductive adhesive layer. By making the spherical conductive particles having a specific median diameter within the above range, the transparency is excellent and the connection resistance value is excellent. If the above content exceeds 20% by mass, the connection resistance value is high. It is speculated that this is due to the excessive conductive particles causing the above transparent metal layer to be damaged.

[0077] The content of the spherical conductive particles in the conductive adhesive layer is not particularly limited, but is preferably 1 to 30 parts by mass, more preferably 5 to 20 parts by mass, relative to 100 parts by mass of the binder component in the conductive adhesive layer. If the content is within the above range, there is a tendency for excellent transparency and excellent connection stability.

[0078] In the range that the technical effect of the present invention is not impaired, the above-mentioned conductive adhesive layer may contain other ingredients except the above-mentioned components. The above-mentioned other ingredients can list well-known and even conventional adhesive layer components. The above-mentioned other ingredients can, for example, list curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, leveling agents, coupling agents, ultraviolet absorbers, tackifying resins and anti-adhesion agents, etc. The above-mentioned other ingredients can be used only one, or two or more. In addition, relative to 100 parts by mass of spherical conductive particles, the content of conductive particles other than the spherical conductive particles is, for example, less than 10 parts by mass, preferably less than 5 parts by mass, and more preferably less than 1 part by mass.

[0079] The thickness of the conductive adhesive layer is not particularly limited, but is preferably 3 to 20 μm, more preferably 5 to 15 μm. If the thickness is 3 μm or more, shielding performance is more excellent. If the thickness is 20 μm or less, the surface of the spherical conductive particles tends to be closer to the layer surface or exposed from the surface, and connection stability is more excellent.

[0080] The ratio of the thickness of the conductive adhesive layer to the D50 of the spherical conductive particles [adhesive layer thickness / D50] is not particularly limited, and is preferably 0.5 to 1.2, and more preferably 0.8 to 1.0. If the above ratio is greater than 0.5, the bonding property with the bonded object such as a printed wiring board is better. If the above ratio is less than 1.2, the amount of spherical conductive particles exposed from the surface of the conductive adhesive layer is large, and the connection stability is more excellent.

[0081] like Figure 3 As shown, the shielding film of the present invention may include a third insulating layer 15 between the first insulating layer 11 and the transparent metal layer 12 .

[0082] By including the third insulating layer, the connection stability is improved when bonding to a printed wiring board under relatively mild conditions, and the transparent metal layer is protected from the first insulating layer side, thereby achieving better environmental resistance. The third insulating layer may be a single layer or multiple layers.

[0083] The third insulating layer can be a resin layer mainly formed of a resin or an inorganic layer formed of an inorganic substance. The above-mentioned resin can be a thermoplastic resin, a thermosetting resin, an active energy ray-curable compound, etc. For the above-mentioned thermoplastic resin, thermosetting resin and active energy ray-curable compound, the above-mentioned things as examples of binder components that can be contained in the above-mentioned conductive adhesive layer can be listed respectively. The above-mentioned resin can be used alone or in combination of two or more.

[0084] The third insulating layer is preferably an inorganic layer. When it is an inorganic layer, it can protect the transparent metal layer and make the environmental resistance better, and further improve the transparency. For the inorganic material forming the above-mentioned inorganic layer, the inorganic material that can be contained in the above-mentioned second insulating layer can be listed as an example and description. Among them, from the perspective of transparency and economy, inorganic oxides are preferred, and titanium oxide is more preferred. The above-mentioned inorganic material can be used only one, or two or more. In addition, when the third insulating layer is multilayer, the third insulating layer, which is preferably an inorganic layer, is on the side of the above-mentioned transparent metal layer (especially directly laminated with the above-mentioned transparent metal layer).

[0085] In the range that does not impair the technical effect of the present invention, in addition to the resin forming the above-mentioned resin layer and the inorganic substance forming the above-mentioned inorganic substance layer, the third insulating layer may contain other components. As the above-mentioned other components, for example, curing agent, curing accelerator, plasticizer, flame retardant, defoaming agent, viscosity modifier, antioxidant, diluent, anti-settling agent, filler, leveling agent, coupling agent, ultraviolet absorber, tackifying resin and anti-adhesion agent can be listed. The above-mentioned other components can be used alone or in combination of two or more.

[0086] The thickness of the third insulating layer is not particularly limited, and is preferably 10 to 500 nm, and more preferably 10 to 300 nm. If the thickness is above 10 nm, the connection stability and environmental resistance are more excellent. If the thickness is below 500 nm, the connection stability is excellent even when it is joined to the printed wiring board under relatively mild conditions. In addition, when the third insulating layer is a multilayer structure, the thickness of the third insulating layer is the sum of the thicknesses of all layers.

[0087] Figure 4 Shown is yet another embodiment of the shielding film of the present invention. Figure 4 In the shielding film 4 shown, the second insulating layer contains Figure 2 The second insulating layer of the shielding film 2 shown in FIG. 1 has the same structure as that of the second insulating layer, that is, a structure composed of a laminated structure including an inorganic layer 13a and a resin layer 13b. Figure 3 The shielding film 3 shown in FIG. 1 includes a third insulating layer 15 between the first insulating layer 11 and the transparent metal layer 12. The third insulating layer 15 is preferably an inorganic layer. Figure 4 As shown, the transparent metal layer 12 is sandwiched between the inorganic layers to protect both sides of the transparent metal layer 12, and the shielding film 4 has an exceptionally excellent environmental resistance, and the presence of the resin layer 13b suppresses damage to the transparent metal layer 14. Therefore, even when the shielding film 4 is bonded to the printed circuit board under relatively mild conditions, the connection stability is exceptionally good.

[0088] The shielding film of the present invention may contain a separator (peeling film) on the conductive adhesive layer side. The separator is laminated so as to be peelable from the shielding film of the present invention. The separator is an element used to cover the conductive adhesive layer for protection and is peeled off when the shielding film of the present invention is used.

[0089] Examples of the separator include polyethylene terephthalate (PET) films, polyethylene films, polypropylene films, and 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-based release agent.

[0090] The thickness of the separator is preferably 10 to 200 μm, more preferably 15 to 150 μm. If the thickness is greater than 10 μm, the protective performance is better. If the thickness is less than 200 μm, the separator is easy to peel off during use.

[0091] In addition to the first insulating layer, the transparent metal layer, the second insulating layer, the conductive adhesive layer and the third insulating layer, the shielding film of the present invention may contain other layers. Examples of the other layers include other insulating layers, antireflection layers, antiglare layers, antifouling layers, hard coating layers, ultraviolet absorbing layers and anti-Newton ring layers.

[0092] The shielding film of the present invention has excellent transparency. The total light transmittance of the shielding film of the present invention is preferably above 62%, more preferably above 65%, and particularly preferably above 67%. The above total light transmittance can be measured using a well-known spectrophotometer. In addition, the above total light transmittance is measured for a laminate having the first insulating layer and the above conductive adhesive layer as the two end layers.

[0093] The shielding film of the present invention is preferably used for printed circuit boards, and is particularly preferably used for flexible printed circuit boards (FPCs). The shielding film of the present invention can be easily joined to the object to be joined, and has excellent electrical connection stability and excellent shielding performance. In addition, it has excellent transparency and is easy to position on the printed circuit board. Therefore, the shielding film of the present invention can be preferably used as an electromagnetic wave shielding film for a flexible printed circuit board.

[0094] (Method for producing electromagnetic wave shielding film)

[0095] An embodiment of the method for producing a shielding film of the present invention will be described.

[0096] exist Figure 1 In the production of the shielding film 1 of the present invention, a transparent metal layer 12 is first formed on the first insulating layer 11. The transparent metal layer 12 is preferably formed by a vapor deposition method or a sputtering method. The vapor deposition method and the sputtering method can adopt a well-known or even conventional method. In this way, by forming the transparent metal layer 12 by the vapor deposition method or the sputtering method, a metal layer with a suitable thickness and transparency can be easily manufactured.

[0097] Next, for example, a composition for forming the second insulating layer 13 may be applied (spread) on the surface of the formed transparent metal layer 12 , and the second insulating layer 13 may be formed by removing the solvent and / or partially curing the composition as needed.

[0098] For example, in addition to the components contained in the second insulating layer, the composition further includes a solvent (solvent). Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide. The solid content concentration of the composition is appropriately set according to the thickness of the second insulating layer to be formed.

[0099] The composition can be applied by a well-known coating method, for example, a coating machine such as a gravure roll coater, a reverse roll coater, an oiling roll coater, a lip coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, a direct coater, or a slit coater can be used.

[0100] Next, the adhesive composition for forming the conductive adhesive layer 14 may be applied (spread) on the surface of the formed second insulating layer 13 , and the conductive adhesive layer 14 may be formed by removing the solvent and / or partially curing the adhesive composition as needed.

[0101] For example, in addition to the components contained in the conductive adhesive layer, the adhesive composition further includes a solvent (solvent). The solvent can be exemplified as a solvent that can be contained in the composition for forming the second insulating layer. The solid content concentration of the adhesive composition is appropriately set according to the thickness of the conductive adhesive layer to be formed, etc.

[0102] The adhesive composition can be applied by a known coating method. For example, a coating machine can be used for applying the composition.

[0103] In addition, Figure 2 In the production of the shielding film 2 of the present invention, it is possible to Figure 1 The surface of the transparent metal layer 12 formed in the same manner as the shielding film 1 shown in the figure is coated (applied) with a composition for forming an inorganic layer 13a, and the solvent is removed as needed to form the inorganic layer 13a. Next, the surface of the formed inorganic layer 13a can be coated (applied) with a resin composition for forming a resin layer 13b, and the solvent is removed and / or partially cured as needed to form the resin layer 13b. For example, in addition to the various components contained in the above-mentioned inorganic layer or resin layer, the above-mentioned compositions also contain a solvent (solvent). For the solvent, examples of solvents that can be contained in the above-mentioned composition can be listed. The solid content concentration of the above-mentioned composition is appropriately set according to the thickness of the formed inorganic layer or resin layer, etc. The coating of the above-mentioned composition can be applied using a well-known coating method. For example, an example of a coating machine for coating the above-mentioned composition can be listed. Thereafter, a conductive adhesive layer 14 is formed on the surface of the formed resin layer 13b. Other methods and Figure 1 The manufacturing method of the shielding film 1 of the present invention is the same.

[0104] In addition, Figure 3 In the preparation of the shielding film 3 of the present invention shown in the figure, before forming the transparent metal layer 12, the third insulating layer 15 is first formed on the first insulating layer 11. For example, the composition for forming the third insulating layer 15 can be applied (smeared), and the solvent can be removed and / or partially cured as needed to form the third insulating layer 15. For example, in addition to the various components contained in the third insulating layer, the composition also contains a solvent (solvent). For the solvent, examples of solvents that can be contained in the composition can be listed. The solid content concentration of the composition is appropriately set according to the thickness of the third insulating layer to be formed, etc. The composition can be applied using a well-known coating method. For example, an example of a coating machine for applying the composition can be listed. Thereafter, a transparent metal layer 12 is formed on the surface of the formed third insulating layer 15. Other methods and Figure 1 The manufacturing method of the shielding film 1 of the present invention is the same.

[0105] In addition, it is possible to appropriately combine Figure 2 The shielding film 2 and Figure 3 The method for making the shielding film 3 is to make Figure 4 The shielding film 4 of the present invention is shown.

[0106] In addition, in the above-mentioned manufacturing method, a method of forming each layer in sequence for production (direct coating method) is described, but it is not limited to this method. For example, it can be produced by laminating each layer formed separately on a temporary substrate such as a release film or a substrate and sequentially bonding them (lamination method).

[0107] The shielding film of the present invention can be used to make a printed circuit board. For example, by laminating the conductive adhesive layer of the shielding film of the present invention to a printed circuit board (e.g., a cover film), a shielded printed circuit board in which the shielding film of the present invention is laminated to the printed circuit board can be obtained. In the above-mentioned shielded printed circuit board, the above-mentioned conductive adhesive layer can be thermally cured. Example

[0108] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples. In addition, the blending amounts described in Table 1 are relative blending amounts (pure amounts) of each component, and are expressed in "parts by mass" unless otherwise specified.

[0109] Example 1

[0110] A toluene solution of epoxy resin (epoxy resin concentration: 23.6 mass%) was applied to the surface of a PET film (thickness 6 μm) using a wire rod, and heated at 100°C for 3 minutes to form an epoxy resin insulating film (thickness 100 nm). Next, a silver / copper alloy foil (thickness 10 nm) was formed on the surface of the epoxy resin insulating film by sputtering. Next, a polyester resin composition was applied to the surface of the alloy foil using a wire rod, and heated at 100°C for 3 minutes to form a polyester insulating film (thickness 100 nm). Subsequently, a bonding agent composition obtained by mixing the epoxy resin toluene solution and silver-coated copper powder (spherical, median diameter 6 μm) in the amounts shown in Table 1 was applied to the surface of the polyester insulating film using a wire rod, and heated at 100°C for 3 minutes to form a conductive adhesive layer (thickness 5 μm). The shielding film of Example 1 was prepared as described above.

[0111] Examples 2 to 3 and Comparative Examples 1 to 2

[0112] Each shielding film was produced in the same manner as in Example 1 except that the adhesive composition used was changed to the composition shown in Table 1.

[0113] Examples 4 to 5 and Comparative Examples 3 to 4

[0114] Each shielding film was produced in the same manner as in Example 1 except that the thickness of the polyester insulating film (second insulating layer) was changed to that shown in Table 1.

[0115] Comparative Example 5

[0116] A shielding film was prepared in the same manner as in Example 1 except that silver-coated copper powder (spherical, median diameter 2 μm) was used instead of silver-coated copper powder (spherical, median diameter 6 μm).

[0117] Comparative Example 6

[0118] A shielding film was prepared in the same manner as in Example 1 except that silver-coated copper powder (spherical, median diameter 55 μm) was used instead of silver-coated copper powder (spherical, median diameter 6 μm).

[0119] Comparative Example 7

[0120] A shielding film was prepared in the same manner as in Example 1 except that silver-coated copper powder (dendritic, median diameter 6 μm) was used instead of silver-coated copper powder (spherical, median diameter 6 μm).

[0121] (evaluate)

[0122] The shielding films obtained in Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in the table.

[0123] (1) Connection resistance value measurement

[0124] Two electrodes with a width of 10 mm and a length of 30 mm were arranged at an interval of 100 mm on a polyimide film with a thickness of 25 μm. Subsequently, the shielding films obtained in the examples and comparative examples were punched out into a width of 10 mm and a length of 130 mm, and a conductive adhesive layer was attached to the arrangement surface of the electrodes by reciprocating a 2 kg roller once to connect the electrodes. After attaching the conductive adhesive layer, the resistance value between the two electrodes was measured using a four-terminal tester (trade name "RM3542", manufactured by Hioki Electric Co., Ltd.).

[0125] (2) Salt water resistance

[0126] The shielding films obtained in the examples and comparative examples were sprayed with salt water according to the conditions specified in JIS Z2371, and the silver / copper alloy foil of the shielding film was visually observed to see whether it changed from colorless and transparent to turbid. Then, if no turbidity was observed with the naked eye, it was evaluated as ○, and if turbidity was observed with the naked eye, it was evaluated as ×.

[0127] (3) Total light transmittance

[0128] The shielding films obtained in Examples and Comparative Examples were measured by irradiating measurement light using a turbidity meter (trade name “NDH4000”, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7361-1 with the PET film surface facing the integrating sphere side.

[0129]

[0130] It can be seen that the shielding film of the present invention has a high total light transmittance and excellent transparency, a low connection resistance value and excellent shielding performance, and further, good salt water resistance and excellent environmental resistance. On the other hand, when the adhesive layer does not contain conductive particles, the connection resistance value is high and the shielding property is poor (Comparative Example 1). In addition, when the content ratio of conductive particles is excessive, the connection resistance value is also high and the shielding property is poor (Comparative Example 2). When the thickness of the second insulating layer is thin, the salt water resistance is poor and the environmental resistance is poor (Comparative Example 3). When the thickness of the second insulating layer is thick (Comparative Example 4) and the median diameter of the conductive particles is small (Comparative Example 5), the connection resistance value is high and the shielding property is poor. When the median diameter of the conductive particles is large (Comparative Example 6) and the shape of the conductive particles is dendritic (Comparative Example 7), the total light transmittance is low and the transparency is low.

[0131] Number Description

[0132] 1~4 Shielding film

[0133] 11. First insulation layer

[0134] 12 Transparent Metal Layer

[0135] 13 Second insulation layer

[0136] 13a Inorganic layer

[0137] 13b Resin layer

[0138] 14 Conductive adhesive layer

[0139] 15 Third insulation layer

Claims

1. An electromagnetic wave shielding film, wherein: A first insulating layer, a transparent metal layer, a second insulating layer and a conductive adhesive layer are laminated in sequence; in, The first insulating layer is a transparent substrate, The second insulating layer is a transparent layer, and the thickness of the second insulating layer is 10 to 500 nm; The conductive adhesive layer comprises a binder component and spherical conductive particles; The median diameter D50 of the spherical conductive particles is 3 to 50 μm; The content ratio of the spherical conductive particles is 5 to 20% by mass based on 100% by mass of the conductive adhesive layer. The ratio of the thickness of the conductive adhesive layer to the median diameter D50 of the spherical conductive particles [adhesive layer thickness / D50] is 0.5 to 1.

2.

2. The electromagnetic wave shielding film according to claim 1, characterized in that: The second insulating layer is directly laminated on the transparent metal layer.

3. The electromagnetic wave shielding film according to claim 1, characterized in that: The second insulating layer includes an inorganic layer formed of an inorganic substance.

4. The electromagnetic wave shielding film according to claim 3, characterized in that: The inorganic layer is directly laminated with the transparent metal layer.

5. The electromagnetic wave shielding film according to claim 1, characterized in that: The second insulating layer has a laminated structure including an inorganic layer formed of an inorganic substance and a resin layer formed of a resin.

6. The electromagnetic wave shielding film according to claim 5, characterized in that: The resin layer is directly laminated on the conductive adhesive layer, and the inorganic layer is directly laminated on the transparent metal layer.

7. The electromagnetic wave shielding film according to claim 1, characterized in that: A transparent third insulating layer is included between the first insulating layer and the transparent metal layer.

8. The electromagnetic wave shielding film according to any one of claims 1 to 7, characterized in that: The total light transmittance of the electromagnetic wave shielding film is above 62%.

9. A shielding printed wiring board comprising the electromagnetic wave shielding film according to any one of claims 1 to 8.

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