Electromagnetic wave shielding film

Abstract

The present invention provides an electromagnetic wave shielding film having excellent transparency and low connection resistance even when a conductive adhesive layer is mixed with a large amount of conductive particles. In the electromagnetic wave shielding film of the present invention, a first insulating layer, a transparent conductive layer, a second insulating layer and a conductive adhesive layer are stacked in this order, the transparent conductive layer is a metal layer composed of gold, silver, copper, palladium, nickel, aluminum or an alloy of the above metals and having a thickness of 5 to 100 nm, the thickness of the second insulating layer is 50 to 1000 nm, the conductive adhesive layer contains a binder component and spherical or dendritic conductive particles, and the content ratio of the conductive particles is 1 to 80% 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 used in a printed wiring board. Background Art

[0002] Printed circuit boards are widely used to integrate circuits in electronic devices such as mobile phones, cameras, and notebook personal computers. They are also used to connect movable parts such as print heads with control parts. In these electronic devices, electromagnetic wave shielding measures are necessary, and even printed circuit boards used in devices use shielded printed circuit boards that implement electromagnetic wave shielding measures.

[0003] In shielded printed circuit boards, an electromagnetic wave shielding film (hereinafter sometimes referred to as "shielding film") is used to achieve electromagnetic wave shielding measures. For example, a shielding film used in conjunction with a printed circuit board contains a shielding layer such as a metal layer and a conductive bonding sheet provided on the surface of the shielding layer.

[0004] For shielding films containing conductive bonding sheets, for example, those disclosed in Patent Documents 1 and 2 are known. The shielding film is used by adhering 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. The conductive bonding sheet is usually bonded and laminated to the printed circuit board by thermocompression bonding under high temperature and high pressure conditions. The shielding film arranged on the printed circuit board as 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 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 align when attached to a printed circuit board. Therefore, there is a tendency to require shielding films to have transparency. Methods for improving transparency include, for example, using a thin transparent conductive layer as the conductive layer in the shielding film.

[0011] However, in conventional shielding films, the conductivity increases as the amount of conductive particles added to the conductive adhesive layer increases. In contrast, in shielding films using a transparent conductive layer, if a large amount of conductive particles is added to the conductive adhesive layer, there is a problem that the electrical connection resistance value increases and the conductivity decreases.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electromagnetic wave shielding film having excellent transparency and low electrical connection resistance even when a large amount of conductive particles is blended in a conductive adhesive layer.

[0013] Technical means to solve technical problems

[0014] The inventors of the present invention have made intensive studies to achieve the above-mentioned object and have found that an electromagnetic wave shielding film having a specific layer structure can have excellent transparency and low electrical connection resistance even when a large amount of conductive particles are blended in the conductive adhesive layer. The present invention has been completed based on this finding.

[0015] That is, the present invention provides an electromagnetic wave shielding film, in which a first insulating layer, a transparent conductive layer, a second insulating layer and a conductive adhesive layer are stacked in this order, the transparent conductive layer is a metal layer with a thickness of 5 to 100 nm and is composed of gold, silver, copper, palladium, nickel, aluminum or an alloy including one or more of the above metals, the thickness of the second insulating layer is 50 to 1000 nm, and the conductive adhesive layer includes a binder component and spherical or dendritic conductive particles, and the content ratio of the conductive particles is 1 to 80 mass% relative to 100 mass% of the conductive adhesive layer.

[0016] Preferably, the second insulating layer and the conductive adhesive layer are directly laminated.

[0017] Preferably, the second insulating layer is directly laminated on one surface and the conductive adhesive layer, and is directly laminated on the other surface and the transparent conductive layer.

[0018] Preferably, the content ratio of the conductive particles is 30 to 80% by mass relative to 100% by mass of the conductive adhesive layer.

[0019] Preferably, the electromagnetic wave shielding film has a total light transmittance of 10% or more in a measurement method in accordance with JIS K 7361-1.

[0020] In addition, the present invention provides a shielding printed wiring board including the electromagnetic wave shielding film.

[0021] Effects of the Invention

[0022] The electromagnetic wave shielding film of the present invention has excellent transparency and low electrical connection resistance value regardless of whether a small amount of conductive particles are blended in the conductive adhesive layer or a large amount of conductive particles are blended. BRIEF DESCRIPTION OF THE DRAWINGS

[0023]

Figure 1

[0024] [Shielding film]

[0025] The shielding film of the present invention has a layer structure in which a first insulating layer, a transparent conductive layer, a second insulating layer, and a conductive adhesive layer are stacked in this order.

[0026] An embodiment of the shielding film of the present invention will be described below. Figure 1 It is a schematic cross-sectional view of one embodiment of the shielding film of the present invention. Figure 1 The shielding film 1 of the present invention shown in the figure comprises a first insulating layer 11, a transparent conductive layer 12, a second insulating layer 13, and a conductive adhesive layer 14 in the following order.

[0027] (1st insulation layer)

[0028] In the shielding film of the present invention, the first insulating layer is a transparent substrate that functions as a protection for the transparent conductive layer and a support for the transparent conductive layer. 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.

[0029] The resin constituting the above-mentioned plastic substrate can be listed, for example, as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homopolymer polypropylene, 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 (PE T), polyesters such as 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); fluorocarbon resin; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as triacetate cellulose (TAC); silicone resin, etc. The above resins can be used alone or in combination. From the perspective of superior transparency, polyesters and cellulose resins are preferred among the above resins, and polyethylene terephthalate and triacetate cellulose are more preferred.

[0030] For the purpose of improving the close adhesion and retention performance with adjacent layers such as the transparent conductive layer, the surface of the first insulating layer (especially the transparent conductive layer side surface) may be subjected to the following surface treatments, for example: 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 using a coating agent (primer), etc. The surface treatment for improving close adhesion is preferably applied to the entire surface of the transparent conductive layer side of the first insulating layer.

[0031] 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 1 μm or more, the shielding film and the transparent conductive layer can be more fully supported. If the thickness is 15 μm or less, the transparency and flexibility are excellent, and it is also economically advantageous. 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.

[0032] (Transparent conductive layer)

[0033] The transparent conductive layer is an element that functions as a shielding layer in the shielding film of the present invention. The transparent conductive layer may be a single layer or a laminate of the same or different layers.

[0034] The transparent conductive layer is made of gold, silver, copper, palladium, nickel, aluminum or an alloy of one or more of the above metals. The transparent conductive layer has shielding properties and excellent transparency.

[0035] Examples of the alloys include silver / copper alloys, silver / zinc alloys, silver / tin alloys, silver / palladium alloys, silver / nickel alloys, silver / aluminum alloys, silver / bismuth alloys, silver / germanium alloys, silver / yttrium alloys, silver / neodymium alloys, silver / scandium alloys, silver / indium alloys, silver / antimony alloys, and silver / gallium alloys. Among the metals, copper and silver are preferred from the viewpoint of superior electromagnetic wave shielding performance, and silver / copper alloys are preferred from the viewpoint of suppressing silver from being sulfurized by sulfur components or corroded by chlorine contained in sweat during solder reflow or when using a shielding film in a high temperature and high humidity environment.

[0036] The thickness of the transparent conductive layer is 5 to 100 nm, preferably 10 to 50 nm. By making the thickness above 5 nm or more, the shielding performance can be maintained. By making the thickness below 100 nm, the transparency of the shielding film is excellent. When the transparent conductive layer is a multilayer structure, the thickness of the transparent conductive layer is the sum of the thicknesses of all layers. The thickness of the transparent conductive layer can be calculated by measuring the cross section of the transparent conductive layer using a transmission electron microscope (TEM).

[0037] The method for forming the transparent conductive 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 conductive layer formed by vapor deposition or sputtering is preferred from the viewpoint of ease of production.

[0038] (Second insulation layer)

[0039] The second insulating layer is a transparent layer that protects the transparent conductive layer. By placing the second insulating layer between the transparent conductive layer and the conductive adhesive layer, it is possible to suppress the reduction in transparency and connection stability. It is speculated that the above-mentioned reduction in transparency and connection stability is caused by the transparent conductive layer being damaged due to friction with the conductive particles in the conductive adhesive layer. The second insulating layer can be a single layer or multiple layers.

[0040] The second insulating layer preferably contains a binder component. Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray-curable compounds. Examples of the thermoplastic resins, thermosetting resins, and active energy ray-curable compounds include those exemplified as binder components that may be contained in the conductive adhesive layer described later. Only one type of the binder component may be used, or two or more types may be used.

[0041] The content of the binder component in the second insulating layer is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, and more preferably 90% by mass or more relative to 100% by mass of the second insulating layer. If the content is 70% by mass or more, the flexibility is better, the embedding property in the small diameter hole is better, and the connection stability is better.

[0042] The second insulating layer may contain other components other than the above-mentioned binder component within the scope of not damaging the effect of the present invention. The above-mentioned other components can be listed, for example, as 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, etc. The above-mentioned other components can be used alone or in combination of two or more.

[0043] The thickness of the second insulating layer is 50 to 1000 nm, preferably 100 to 300 nm. When the thickness is 50 nm or more, shielding performance and connection stability are excellent. When the thickness is 1000 nm or less, transparency and connection stability are excellent. When the second insulating layer is a multi-layer structure, the thickness of the second insulating layer is the sum of the thicknesses of all layers.

[0044] From the viewpoint of protecting the transparent conductive layer, the second insulating layer is preferably directly laminated on the conductive adhesive layer, and particularly preferably directly laminated on one surface with the conductive adhesive layer and directly laminated on the other surface with the transparent conductive layer.

[0045] (Conductive adhesive layer)

[0046] 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 electrically connecting to the transparent conductive layer. Furthermore, the conductive adhesive layer functions together with the transparent conductive layer as a shielding layer that exerts shielding properties. The conductive adhesive layer may be a single layer or multiple layers.

[0047] The conductive adhesive layer contains a binder component and spherical or dendritic (dendrite-like) conductive particles.

[0048] Examples of the binder component include thermoplastic resins, thermosetting resins, active energy ray-curable compounds, etc. The binder component may be used alone or in combination of two or more.

[0049] 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, and acrylic resins. The thermoplastic resins may be used alone or in combination of two or more.

[0050] The thermosetting resin includes both thermosetting resins (thermosetting resins) and resins obtained by curing the thermosetting resins. Examples of the thermosetting resins include phenolic resins, epoxy resins, polyurethane resins, polyurethane urea resins, melamine resins, alkyd resins, and the like. The thermosetting resins may be used alone or in combination of two or more.

[0051] 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.

[0052] 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 tetraglycidyldiaminodiphenylmethane. 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.

[0053] The active energy ray curable compound can include 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 can be used alone or in combination of two or more.

[0054] The adhesive component is preferably a thermosetting resin. In this case, after the shielding film of the present invention is placed on a printed wiring board for bonding to the printed wiring board, the adhesive component can be cured by applying pressure and heat, thereby achieving good bonding to the printed wiring board.

[0055] When the adhesive component includes a thermoplastic resin, a monomer component of the thermoplastic resin may be included as a component constituting the adhesive component. When the adhesive component includes a monomer component, temporary adhesiveness, reworkability, and close adhesion after hot pressing to the object to be bonded are good.

[0056] 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.

[0057] In the conductive adhesive layer, the content of the binder component is not particularly limited, and is preferably 20 to 99% by mass, more preferably 30 to 80% by mass, and further preferably 40 to 70% by mass relative to the total amount 100% by mass of the conductive adhesive layer. If the content is 20% by mass or more, the close adhesion to the printed wiring board is more excellent. If the content is 99% by mass or less, the conductive particles can be fully contained.

[0058] The conductive particles may be spherical conductive particles and / or dendritic conductive particles. The use of the spherical or dendritic conductive particles provides excellent transparency and connection stability even when a large amount of conductive particles are added. The use of spherical conductive particles provides even better transparency.

[0059] Examples of the conductive particles include metal particles, metal-coated resin particles, and carbon-based fillers. The conductive particles may be used alone or in combination of two or more.

[0060] 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.

[0061] 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, silver-coated alloy particles, etc. The silver-coated alloy particles include, for example, silver-coated copper alloy particles obtained by coating copper-containing alloy particles (for example, copper alloy particles composed of an alloy of copper, nickel, and zinc) with silver, etc. The metal particles can be produced by electrolysis, atomization, reduction, etc.

[0062] Among them, the 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 viewpoint of being able to provide excellent conductivity, suppressing oxidation and coagulation of the metal particles, and reducing the cost of the metal particles.

[0063] The median diameter (D50) of the conductive particles is not particularly limited, but is preferably 5 to 15 μm, and more preferably 5 to 10 μm. The median diameter is the median diameter of all spherical conductive particles and / or dendritic conductive particles in the conductive adhesive layer, and refers to the particle size at 50% of the cumulative value in the particle size distribution obtained by the laser diffraction / scattering method. By making the median diameter within the above range, the connection stability of the present invention using conductive particles is superior. The median diameter can be measured, for example, by a laser diffraction particle size analyzer (trade name "SALD-2200", manufactured by Shimadzu Corporation).

[0064] In the conductive adhesive layer, the content of the conductive particles is 1 to 80% by mass, preferably 20 to 70% by mass, and more preferably 30 to 60% by mass, relative to 100% by mass of the conductive adhesive layer. In the shielding film of the present invention, the conductive adhesive layer has a low connection resistance value and excellent connection stability regardless of whether it includes a small amount of the conductive particles of about 1% by mass or a large amount of the conductive particles of up to 80% by mass.

[0065] In the range that does not impair the effect of the present invention, the conductive adhesive layer may also contain other ingredients other than the above-mentioned components. The above-mentioned other ingredients can list well-known and even commonly used 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, levelers, coupling agents, ultraviolet absorbers, colorants and anti-adhesion agents. The above-mentioned other ingredients can be used only one, or two or more. And relative to 100 parts by mass of spherical conductive particles and / or dendritic conductive particles, the content of conductive particles other than spherical conductive particles and dendritic 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.

[0066] 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 conductive particles tends to be closer to the layer surface or exposed from the surface, and connection stability is more excellent.

[0067] The ratio of the thickness of the conductive adhesive layer to the D50 of the conductive particles [adhesive layer thickness / D50] is not particularly limited, but is preferably 0.2 to 1.5, and more preferably 0.5 to 1.0. If the ratio is 0.2 or more, the bonding property with the bonded object such as a printed wiring board is better. If the ratio is 1.5 or less, the amount of conductive particles exposed from the surface of the conductive adhesive layer is large, and the connection stability is more excellent.

[0068] The shielding film of the present invention may also contain a separator (peeling film) on the conductive adhesive layer side. The separator is laminated in a manner that allows it to be peeled off from the shielding film of the present invention. The separator is an element for covering and protecting the conductive adhesive layer and is peeled off when the shielding film of the present invention is used.

[0069] Examples of the separator include polyethylene terephthalate (PET) films, polyethylene films, polypropylene films, and plastic films or 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.

[0070] The thickness of the separator is preferably 10 to 200 μm, more preferably 15 to 150 μm. If the thickness is 10 μm or more, the protective performance is better. If the thickness is 200 μm or less, the separator is easy to peel off during use.

[0071] The shielding film of the present invention may also contain other layers besides the first insulating layer, the transparent conductive layer, the second insulating layer and the conductive adhesive layer. Examples of the other layers include other insulating layers, antireflection layers, antiglare layers, antifouling layers, hard coating layers, ultraviolet absorbing layers, anti-Newton ring layers, and the like.

[0072] The shielding film of the present invention has excellent transparency. In the measurement method according to JIS K 7361-1, the total light transmittance of the shielding film of the present invention is preferably 10% or more, more preferably 20% or more, further preferably 50% or more, and particularly preferably 65% ​​or more. The total light transmittance can be measured using a well-known spectrophotometer. The measurement of the total light transmittance is performed on a laminate having the first insulating layer and the conductive adhesive layer as the two end layers.

[0073] In the measurement method according to JIS K 7361-1, the haze value of the shielding film of the present invention is preferably 95% or less, more preferably 92% or less, and further preferably 90% or less. The above haze value can be measured using a well-known spectrophotometer. The above haze value is measured for a laminate having the first insulating layer and the above conductive adhesive layer as the end layers.

[0074] The shielding film of the present invention is preferably used for a printed circuit board or for a wireless power transmission system, and is particularly preferably used for a flexible printed circuit board (FPC) or for an electromagnetic induction wireless power transmission system. Regardless of whether a small amount of conductive particles are mixed in the conductive adhesive layer or a large amount of conductive particles are mixed, the shielding film of the present invention has a low electrical connection resistance value. In addition, the shielding film of the present invention has excellent transparency and is easy to align on the bonded objects such as the power supply or transmission coil in the printed circuit board and the wireless power transmission system. Therefore, the shielding film of the present invention is preferably used as an electromagnetic wave shielding film for a flexible printed circuit board.

[0075] (Method for producing electromagnetic wave shielding film)

[0076] The method for producing the shielding film of the present invention is described below.

[0077] exist Figure 1 In the production of the shielding film 1 of the present invention, a transparent conductive layer 12 is first formed on the first insulating layer 11. The transparent conductive layer 12 is preferably formed by a vapor deposition method or a sputtering method. The above-mentioned vapor deposition method and sputtering method can adopt a well-known or even commonly used method. In this way, by forming the transparent conductive layer by the vapor deposition method or the sputtering method, a conductive layer with a suitable thickness and transparency can be easily manufactured.

[0078] Next, the second insulating layer 13 can be formed by, for example, applying (coating) the resin composition for forming the second insulating layer 13 on the surface of the formed transparent conductive layer 12 , and removing the solvent and / or partially curing the resin composition as necessary.

[0079] For example, in addition to the components contained in the second insulating layer, the resin composition further includes a solvent (solvent). Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, ethyl acetate, propyl acetate, butyl acetate, dimethylformamide, etc. The solid content concentration of the resin composition is appropriately set according to the thickness of the second insulating layer to be formed, etc.

[0080] The resin 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.

[0081] Next, the adhesive composition for forming the conductive adhesive layer 14 may be applied (coated) on the surface of the formed second insulating layer, and the conductive adhesive layer 14 may be formed by removing the solvent and / or partially curing the adhesive composition as needed.

[0082] For example, in addition to the components contained in the conductive adhesive layer, the adhesive composition further includes a solvent (solvent). The solvent can include the solvents exemplified as the solvents that can be contained in the resin composition. The solid content concentration of the adhesive composition is appropriately set according to the thickness of the conductive adhesive layer to be formed.

[0083] The adhesive composition can be applied by a known coating method, for example, a coating machine exemplified as a coating machine used for coating the resin composition can be used.

[0084] In the above-mentioned manufacturing method, a method of sequentially forming each layer (direct coating method) is described, but the present invention is not limited to the above-mentioned method. For example, it can be produced by stacking each layer formed individually on a temporary substrate such as a peeling film or a substrate and sequentially bonding them (stacking method).

[0085] The shielding film of the present invention can be used to make a printed circuit board. For example, the conductive adhesive layer of the shielding film of the present invention is bonded to a printed circuit board (such as a cover film), thereby obtaining a shielded printed circuit board in which the shielding film of the present invention is bonded to the printed circuit board. In the above-mentioned shielded printed circuit board, the above-mentioned conductive adhesive layer can also be thermally cured. Example

[0086] The present invention will be described in further detail below based on examples, but the present invention is not limited to these examples. The conductive particle content ratio in the table indicates the ratio in the conductive adhesive layer.

[0087] Comparative Example 1

[0088] A silver / copper alloy layer (10 nm thick) was formed on the surface of a PET film (6 μm thick) by sputtering. Then, an adhesive composition obtained by mixing an epoxy resin solution and conductive particles A (silver-coated copper powder, spherical, median diameter 5 μm) was applied to the surface of the alloy layer using a wire rod, and heated at 120°C for 1 minute to form a conductive adhesive layer (5 μm thick). The shielding film of Comparative Example 1 was prepared as above. The epoxy resin solution and conductive particles A were mixed in an amount such that the proportion of epoxy resin in the conductive adhesive layer was 70% by mass and the proportion of conductive particles A was 30% by mass.

[0089] Comparative Examples 2 to 4

[0090] Each barrier film was produced in the same manner as in Comparative Example 1 except that the type and content ratio of the conductive particles were changed as shown in Table 1. The conductive particles B were silver-coated copper powder (dendritic, median diameter 5 μm).

[0091] Example 1

[0092] A silver / copper alloy layer (10 nm thick) was formed on the surface of a PET film (6 μm thick) by sputtering. Next, a polyester resin composition was applied to the surface of the alloy layer using a wire rod, and heated at 100°C for 1 minute, thereby forming a resin layer (50 nm thick). Then, an adhesive composition obtained by mixing an epoxy resin solution and conductive particles A was applied to the surface of the resin layer using a wire rod, and heated at 120°C for 1 minute, thereby forming a conductive adhesive layer (5 μm thick). The shielding film of Example 1 was prepared as above. The mixing amount of the epoxy resin solution and the conductive particles A was such that the proportion of the epoxy resin in the conductive adhesive layer was 70% by mass and the proportion of the conductive particles A was 30% by mass.

[0093] Examples 2 to 4 and Comparative Examples 5 and 6

[0094] Each shielding film was produced in the same manner as in Example 1 except that the thickness of the resin layer was changed as shown in Table 1.

[0095] Example 5

[0096] Except having changed the content ratio of the electroconductive particles as shown in Table 1, it carried out similarly to Example 1, and produced the shielding film.

[0097] Examples 6 to 8 and Comparative Examples 7 and 8

[0098] Each shielding film was produced in the same manner as in Example 5 except that the thickness of the resin layer was changed as shown in Table 1.

[0099] Example 9

[0100] Except having changed the kind of electroconductive particle as shown in Table 1, it carried out similarly to Example 1, and produced the shielding film.

[0101] Examples 10 to 12 and Comparative Examples 9 and 10

[0102] Each shielding film was produced in the same manner as in Example 9 except that the thickness of the resin layer was changed as shown in Table 1.

[0103] (evaluate)

[0104] The shielding films obtained in the examples and comparative examples were evaluated as follows. The evaluation results are shown in the table. Only the PET film (thickness 6 μm) was used as the evaluation object of reference example 1. In addition, "OL" in the table indicates a value exceeding the measurement limit of 100Ω due to overload.

[0105] (1) Connection resistance value

[0106] The following printed circuit substrate is prepared: two copper foil patterns (4 mm wide and 1 mm apart) similar to the ground pattern are formed on a base component composed of a polyimide film, and a covering film (insulating film) composed of an insulating adhesive layer and a polyimide film is formed thereon. A gold plating layer is provided on the surface of the copper foil pattern as a surface layer. A circular opening with a diameter of 0.8 mm is formed on the covering film to simulate the ground connection portion. The shielding film and the printed circuit substrate made in each embodiment and comparative example are joined using a pressing machine at a temperature of 170°C, a time of 30 minutes, and a pressure of 2 to 3 MPa. After joining the shielding film, the resistance value between the two copper foil patterns is measured with a resistance meter, and the connectivity between the copper foil pattern and the conductive bonding sheet is evaluated as the connection resistance value.

[0107] (2) Total light transmittance

[0108] The shielding films obtained in Examples and Comparative Examples were measured using a haze meter (trade name “NDH4000”, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7361-1, with the PET film surface on the integrating sphere side being irradiated with measuring light.

[0109]

[0110] When a silver / copper alloy layer with a thickness of 10 nm is used as a transparent conductive layer, the shielding film of the present invention can achieve high total light transmittance, excellent transparency, low connection resistance and excellent connection stability even when a large amount of conductive particles is mixed as much as 30 to 50% by mass (Examples 1 to 12). In addition, compared with the case of using dendritic conductive particles (Examples 9 to 12), there is a tendency for high total light transmittance and excellent transparency when spherical conductive particles are used (Examples 1 to 4). On the other hand, as shown in the results, when there is no resin layer between the silver / copper alloy layer and the conductive adhesive layer (Comparative Examples 1 to 4), the connection resistance value is high under the condition of a large amount of mixing of more than 30% by mass. When the thickness of the resin layer is more than 2000nm, the connection resistance value is also high (Comparative Examples 5 to 10).

[0111] Number Description

[0112] 1 Shielding film

[0113] 111st insulation layer

[0114] 12Transparent conductive layer

[0115] 13 Second insulation layer

[0116] 14 Conductive adhesive layer

Claims

1. An electromagnetic wave shielding film, characterized in that: In the electromagnetic wave shielding film, a first insulating layer, a transparent conductive layer, a second insulating layer and a conductive adhesive layer are stacked in this order; in, The first insulating layer is a transparent substrate, The transparent conductive layer is a metal layer composed of gold, silver, copper, palladium, nickel, aluminum or an alloy of one or more of the above metals, with a thickness of 5 to 100 nm; The second insulating layer is a transparent layer, and the thickness of the second insulating layer is 50 to 1000 nm; The conductive adhesive layer comprises a binder component and spherical or dendritic conductive particles; The content ratio of the conductive particles is 1 to 80% by mass relative to 100% by mass of the conductive adhesive layer.

2. The electromagnetic wave shielding film according to claim 1, characterized in that: The second insulating layer and the conductive adhesive layer are directly laminated.

3. The electromagnetic wave shielding film according to claim 1, characterized in that: The second insulating layer has one surface directly laminated on the conductive adhesive layer, and the other surface directly laminated on the transparent conductive layer.

4. The electromagnetic wave shielding film according to claim 1, characterized in that: The content ratio of the conductive particles is 30 to 80% by mass relative to 100% by mass of the conductive adhesive layer.

5. The electromagnetic wave shielding film according to any one of claims 1 to 4, characterized in that: The electromagnetic wave shielding film has a total light transmittance of 10% or more in a measurement method in accordance with JIS K 7361-1.

6. A shielded printed circuit board, characterized in that: The shielding printed circuit board comprises the electromagnetic wave shielding film according to any one of claims 1 to 5.

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