TWI842957B - Electromagnetic wave shielding film - Google Patents

Abstract

The present invention provides an electromagnetic wave shielding film, which has excellent transparency and low electrical connection resistance even when a large amount of conductive particles are mixed in the conductive adhesive layer. The electromagnetic wave shielding film of the present invention is sequentially laminated with a first insulating layer, a nanosilver wire layer, a second insulating layer and a conductive adhesive layer; the thickness of the second insulating layer is 50-500 nm; the conductive adhesive layer contains: a binder component and spherical or branch-shaped conductive particles; the content ratio of the conductive particles is 1-80 mass % relative to 100 mass % of the conductive adhesive layer.

Description

Electromagnetic wave shielding film

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 Technology

In electronic devices such as mobile phones, cameras, and laptops, printed wiring boards are mostly used to integrate circuits into the mechanism. They are also used to connect the movable parts such as the print head of a printer and the control part. In these electronic devices, electromagnetic wave shielding measures are required, and even the printed wiring boards used in the devices use shielded printed wiring boards that implement electromagnetic wave shielding measures.

In a shielded printed wiring board, an electromagnetic wave shielding film (hereinafter sometimes referred to as "shielding film") is used for the purpose of electromagnetic wave shielding. For example, the shielding film used in conjunction with the printed wiring board has a shielding layer such as a metal layer and a conductive adhesive sheet provided on the surface of the shielding layer.

As for the shielding film with a conductive adhesive sheet, for example, those disclosed in Patent Documents 1 and 2 are known. The shielding film is used by bonding the exposed surface of the conductive adhesive sheet to the surface of the printed wiring board, specifically, the surface of the covering film provided on the surface of the printed wiring board. Such conductive adhesive sheets are usually bonded and laminated on the printed wiring board by heat pressing under high temperature/high pressure conditions. Thus, the shielding film disposed on the printed wiring board can exert the performance of shielding electromagnetic waves from outside the printed wiring board (shielding performance). Prior Art Documents Patent Documents

[Patent Document 1] Japanese Patent Publication No. 2015-110769 [Patent Document 2] Japanese Patent Publication No. 2012-28334

Summary of invention Problem to be solved by the invention

In recent years, there is a demand for shielding films to be easily aligned when attached to a printed wiring board. Therefore, there is a tendency to demand transparency for shielding films. As a method of improving transparency, for example, it is considered to use a thin transparent conductive layer as the conductive layer of the shielding film.

However, in conventional shielding films, the conductivity increases as the amount of conductive particles in the conductive adhesive layer increases. In contrast, in shielding films using a transparent conductive layer, when a large amount of conductive particles is mixed in the conductive adhesive layer, there is a problem of increased electrical connection resistance and decreased conductivity.

The present invention is completed in view of the above, and the purpose of the present invention is to provide an electromagnetic wave shielding film, which has excellent transparency and low electrical connection resistance even when a large amount of conductive particles are mixed in the conductive adhesive layer. Means for solving the problem

The inventors of the present invention have devoted themselves to research to achieve the above-mentioned purpose and have found that an electromagnetic wave shielding film having a specific layer structure has excellent transparency and low electrical connection resistance even when a large amount of conductive particles are mixed in the conductive adhesive layer. The present invention is completed based on the above-mentioned findings.

That is, the present invention provides an electromagnetic wave shielding film, which is sequentially laminated with a first insulating layer, a nanosilver wire layer, a second insulating layer and a conductive adhesive layer; The thickness of the second insulating layer is 50-500 nm; The conductive adhesive layer contains: a binder component and spherical or branch-shaped conductive particles; The content ratio of the conductive particles is 1-80% by mass relative to 100% by mass of the conductive adhesive layer.

The second insulating layer and the conductive adhesive layer are preferably directly laminated.

The second insulating layer is preferably directly laminated with the conductive adhesive layer on one side and directly laminated with the silver nanowire layer on the other side.

The content ratio of the conductive particles is preferably 30-80 mass % relative to 100 mass % of the conductive adhesive layer.

The total light transmittance of the electromagnetic wave shielding film is preferably 10% or more according to the measurement method of JIS K 7361-1.

Furthermore, the present invention provides a shielded printed wiring board having the above-mentioned electromagnetic wave shielding film. Effect of the invention

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 mixed in the conductive adhesive layer or a large amount of conductive particles are mixed in the conductive adhesive layer.

The form used to implement the invention

[Shielding film] The shielding film of the present invention has the following layer structure: a first insulating layer, a nanosilver wire layer, a second insulating layer and a conductive adhesive layer are sequentially layered.

The following is a description of an embodiment of the shielding film of the present invention. Fig. 1 is a cross-sectional schematic diagram showing an embodiment of the shielding film of the present invention. The shielding film 1 of the present invention shown in Fig. 1 has a first insulating layer 11, a nanosilver wire layer 12, a second insulating layer 13 and a conductive adhesive layer 14 in sequence.

(First insulating layer) The first insulating layer is a transparent substrate and plays the role of protecting the nanosilver wire layer and serving as a support for the nanosilver wire 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 type or different types.

The resin constituting the above-mentioned plastic substrate may be, for example, 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), ionic polymer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate (random, alternating) copolymer, ethylene-butene copolymer, ethylene-hexene copolymer and other polyolefin resins; polyurethane; polyethylene terephthalate Polyesters such as PET, polyethylene naphthalate, and polybutylene terephthalate (PBT); polycarbonate (PC); polyimide (PI); polyetheretherketone (PEEK); polyetherimide; polyamides such as polyarylamide 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 triacetate (TAC); silicone resins, etc. Only one type of the above resins may be used, or two or more types may be used. Among the above resins, polyester and cellulose resins are preferred from the viewpoint of having better transparency, and polyethylene terephthalate and cellulose triacetate are more preferred.

For the purpose of improving the adhesion and retention of the adjacent layers such as the nanosilver wire layer, the surface of the first insulating layer (especially the side surface of the nanosilver wire layer) can also be subjected to 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; and surface treatments such as easy-to-adhesion treatment using a coating agent (primer). The surface treatment for improving adhesion is preferably applied to the entire surface of the side surface of the nanosilver wire layer in the first insulating layer.

The thickness of the first insulating layer is not particularly limited, and 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 protective nanosilver wire 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. Furthermore, when the first insulating layer is a multi-layer structure, the thickness of the first insulating layer is the total thickness of all layers.

(Nanosilver wire layer) The above-mentioned nanosilver wire layer is a necessary element for functioning as a shielding layer in the shielding film of the present invention. The above-mentioned nanosilver wire layer may be a single layer or a laminate of the same type or different types.

The thickness of the nanosilver wire layer is preferably 20-500nm, preferably 50-150nm. If the thickness is 20nm or more, high shielding performance can be maintained. If the thickness is 500nm or less, the transparency of the shielding film is excellent. Furthermore, when the nanosilver wire layer is a multi-layer structure, the thickness of the nanosilver wire layer is the total thickness of all layers.

(Second insulating layer) The second insulating layer is a transparent layer that protects the nanosilver wire layer. By interposing the second insulating layer between the nanosilver wire layer and the conductive adhesive layer, the decrease in transparency and connection stability can be suppressed. The above-mentioned decrease in transparency and connection stability is presumed to be caused by the nanosilver wire layer being damaged by friction with the conductive particles in the conductive adhesive layer. The second insulating layer can be a single layer or multiple layers.

The second insulating layer preferably contains a binder component. The above-mentioned binder component may include thermoplastic resins, thermosetting resins, active energy ray-curable compounds, etc. The above-mentioned thermoplastic resins, thermosetting resins, and active energy ray-curable compounds may include the binder components that can be included in the conductive adhesive layer as described below. The above-mentioned binder component may be used alone or in combination of two or more.

The content of the above-mentioned 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 above-mentioned content is 70% by mass or more, the flexibility is better, the filling property of small diameter holes is better, and the connection stability is better.

The second insulating layer may also contain other components other than the above-mentioned binder component within the scope of not impairing the effect of the present invention. The above-mentioned other components include, for example: hardener, hardening accelerator, plasticizer, flame retardant, defoamer, viscosity adjuster, antioxidant, diluent, anti-settling agent, filler, leveler, coupling agent, ultraviolet absorber, adhesion imparting resin, anti-caking agent, etc. The above-mentioned other components may be used alone or in combination of two or more.

The thickness of the second insulating layer is 50-500nm, preferably 100-300nm. When the thickness is 50nm or more, the shielding performance and connection stability are excellent. When the thickness is 500nm or less, the transparency and connection stability are excellent. Furthermore, when the second insulating layer is a multi-layer structure, the thickness of the second insulating layer is the total thickness of all layers.

From the viewpoint of protecting the silver nanowire layer, the second insulating layer is preferably directly laminated with the conductive adhesive layer, and more preferably, one side of the second insulating layer is directly laminated with the conductive adhesive layer, and the other side of the second insulating layer is directly laminated with the silver nanowire layer.

(Conductive adhesive layer) The conductive adhesive layer has the properties of bonding the shielding film of the present invention to a printed wiring board, and the conductivity of being electrically connected to the nanosilver wire layer. In addition, the conductive adhesive layer also functions as a shielding layer that exhibits shielding properties together with the nanosilver wire layer. The conductive adhesive layer may be a single layer or multiple layers.

The conductive adhesive layer contains a binder component and spherical or branch-shaped (dendrite) conductive particles.

The above-mentioned binder components include thermoplastic resins, thermosetting resins, active energy ray-hardening compounds, etc. The above-mentioned thermoplastic resins include, for example, polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (such as polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, acrylic resins, etc. The above-mentioned thermoplastic resins may be used alone or in combination of two or more.

Examples of the thermosetting resin include phenolic resins, epoxy resins, urethane resins, urethane urea resins, melamine resins, alkyd resins, etc. The thermosetting resins may be used alone or in combination of two or more.

Examples of the epoxy resins include bisphenol epoxy resins, spiro epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, terpene epoxy resins, glycidyl ether epoxy resins, glycidyl amine epoxy resins, and phenolic epoxy resins.

Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, and tetrabromobisphenol A type epoxy resin. Examples of the glycidyl ether type epoxy resin include tris(glycidoxyphenyl)methane and tetrakis(glycidoxyphenyl)ethane. Examples of the glycidyl amine type epoxy resin include tetraglycidyl diaminodiphenylmethane. Examples of the novolac epoxy resin include cresol novolac epoxy resin, phenol novolac epoxy resin, α-naphthol novolac epoxy resin, brominated phenol novolac epoxy resin, and the like.

The active energy ray-curable compound is not particularly limited, and examples thereof include polymerizable compounds having at least two radical reactive groups (such as (meth)acryloyl groups) in the molecule. The active energy ray-curable compound may be used alone or in combination of two or more.

The adhesive component is preferably a thermosetting resin. In order to bond to a printed wiring board, the shielding film of the present invention can be placed on the printed wiring board and then cured by applying pressure and heat to improve the bonding property with the printed wiring board.

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

The content ratio of the binder component in the conductive adhesive layer is not particularly limited, but is preferably 20-99 mass%, preferably 30-80 mass%, and more preferably 40-70 mass%, relative to 100 mass% of the total amount of the conductive adhesive layer. If the content ratio is 20 mass% or more, the adhesion to the printed wiring board is better. If the content ratio is 99 mass% or less, the conductive particles can be sufficiently contained.

The conductive particles are spherical conductive particles and/or dendrite conductive particles. By using the spherical or dendrite conductive particles, even when a large amount is prepared, the transparency is excellent and the connection stability is excellent. Regarding the conductive particles, the conductive particles are preferably dendrite conductive particles from the viewpoint of having a better connection stability. In addition, from the viewpoint of having an excellent transparency of the shielding film, the conductive particles are preferably spherical conductive particles.

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

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

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

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 viewpoints of excellent electrical conductivity, suppression of oxidation and aggregation of metal particles, and reduction of metal particle costs.

The median particle size (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 particle size refers to the median particle size of all spherical conductive particles and/or dendrite-shaped conductive particles in the conductive adhesive layer, and is the particle size of 50% of the cumulative value in the particle size distribution obtained by the laser diffraction scattering method. When the median particle size is within the above range, the connection stability is better in the present invention using conductive particles. The median particle size can be measured, for example, by a laser diffraction particle size distribution measuring device (trade name "SALD-2200", manufactured by Shimadzu Corporation).

The content ratio of the conductive particles in the conductive adhesive layer is 1-80 mass%, preferably 20-70 mass%, and more preferably 30-60 mass%, relative to 100 mass% of the conductive adhesive layer. In the shielding film of the present invention, whether the conductive adhesive layer contains a small amount of the conductive particles of about 1 mass% or a large amount of the conductive particles of 80 mass%, the connection resistance value is low and the connection stability is excellent.

The conductive adhesive layer may contain other components other than the above components within the scope of not impairing the effect of the present invention. As for the above other components, the components contained in the known or even conventional adhesive layer can be cited. As for the above other components, for example, hardening accelerators, plasticizers, flame retardants, defoaming agents, viscosity regulators, antioxidants, diluents, anti-settling agents, fillers, leveling agents, coupling agents, ultraviolet absorbers, adhesion-imparting resins, anti-caking agents, etc. The above other components may be used alone or in combination of two or more. The content of the conductive particles other than the spherical conductive particles and the dendrite-shaped 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, based on 100 parts by mass of the spherical conductive particles and/or the dendrite-shaped conductive particles.

The thickness of the conductive adhesive layer is not particularly limited, but is preferably 3 to 20 μm, preferably 5 to 15 μm. If the thickness is 3 μm or more, the shielding performance is better. 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 the connection stability is better.

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, more preferably 0.5 to 1.0. If the ratio is 0.2 or more, the adhesion to the adherend 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 increases, and the connection stability is better.

The shielding film of the present invention may also have a separator (peeling film) on the conductive adhesive layer side. The separator is laminated in a manner that it can be peeled off from the shielding film of the present invention. The separator is a component for covering and protecting the conductive adhesive layer and is peeled off when the shielding film of the present invention is used.

Examples of the above-mentioned separation material include polyethylene terephthalate (PET) films, polyethylene films, polypropylene films, plastic films or papers coated with a stripping agent such as a fluorine-based stripping agent or a long-chain alkyl acrylate-based stripping agent, etc.

The thickness of the separation piece is preferably 10-200 μm, preferably 15-150 μm. If the thickness is 10 μm or more, the protective performance is more excellent. If the thickness is 200 μm or less, the separation piece is easy to peel off during use.

The shielding film of the present invention may also have other layers besides the first insulating layer, the nanosilver wire layer, the second insulating layer and the conductive adhesive layer. The other layers include, for example: other insulating layers, anti-reflection layers, anti-glare layers, anti-fouling layers, hard coating layers, ultraviolet absorption layers, anti-Newton ring layers, etc.

The shielding film of the present invention has excellent transparency. The total light transmittance of the shielding film of the present invention according to the measurement method of JIS K 7361-1 is preferably 10% or more, preferably 20% or more, more preferably 50% or more, and particularly preferably 65% or more. The above total light transmittance can be measured using a known spectrometer. Furthermore, 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.

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

The shielding film of the present invention is suitable for use in printed wiring boards, and is particularly suitable for use in flexible printed wiring boards (FPCs). The shielding film of the present invention has a low electrical connection resistance value 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. In addition, the shielding film has excellent transparency and is easy to align on the printed wiring board. Therefore, the shielding film of the present invention can be suitably used as an electromagnetic wave shielding film for flexible printed wiring boards.

(Method for manufacturing electromagnetic wave shielding film) The method for manufacturing the shielding film of the present invention is described.

In the manufacturing of the shielding film 1 of the present invention shown in FIG1 , the nanosilver wire layer 12 is first formed on the first insulating layer 11 . The nanosilver wire layer 12 can be formed by laminating the nanosilver wire layer 12 on the surface of the first insulating layer 11 .

Next, the second insulating layer 13 may be formed by, for example, coating (applying) a resin composition for forming the second insulating layer 13 on the surface of the formed nanosilver wire layer 12, and removing the solvent and/or partially hardening the resin composition as necessary.

The resin composition, for example, includes a solvent in addition to the components included in the second insulating layer. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, ethyl acetate, propyl acetate, butyl acetate, and dimethylformamide. The solid component concentration of the resin composition is appropriately set according to the thickness of the second insulating layer to be formed.

When applying the resin composition, a known coating method may be used, such as a gravure roll coater, a reverse roll coater, a contact roll coater, a lip coater, a dip roll coater, a rod coater, a knife coater, a spray coater, a notch wheel coater, a direct coater, a slot die coater, and the like.

Next, the conductive adhesive layer 14 may be formed by coating (applying) an adhesive composition on the surface of the formed second insulating layer, and removing the solvent and/or partially curing the adhesive composition as necessary.

The adhesive composition may include, for example, a solvent in addition to the components included in the conductive adhesive layer. The solvent may be the solvents that can be included in the resin composition. The solid component concentration of the adhesive composition may be appropriately set according to the thickness of the conductive adhesive layer to be formed.

When applying the adhesive composition, a known coating method may be used. For example, the coating machine described above for applying the resin composition may be cited.

Furthermore, in the above-mentioned manufacturing method, although the method of forming each layer in sequence (direct coating method) is described, it is not limited to the above-mentioned method. For example, it can also be manufactured by a method of forming each layer individually on a temporary substrate such as a release film or a substrate, and then laminating the aforementioned layers and bonding them in sequence (lamination method).

The shielding film of the present invention can be used to manufacture a printed wiring board. For example, by laminating the conductive adhesive layer of the shielding film of the present invention to a printed wiring board (e.g., a cover film), a shielded printed wiring board having the shielding film of the present invention laminated to the printed wiring board can be obtained. In the above-mentioned shielded printed wiring board, the above-mentioned conductive adhesive layer can also be heat-cured.

[Examples] The present invention is described in more detail below based on examples, but the present invention is not limited to these examples. In addition, the content ratio of the conductive particles in the table represents the ratio in the conductive adhesive layer.

Comparative Example 1 A nanosilver wire layer (wire diameter 30nm, wire length 20μm, thickness about 70nm) was laminated on the surface of a PET film (thickness 6μm). Then, a wire rod was used to apply an adhesive composition obtained by mixing an epoxy resin solution and conductive particles A on the surface of the nanosilver wire layer, and heated at 120°C for 1 minute to form a conductive adhesive layer (thickness 5μm). The shielding film of Comparative Example 1 was prepared as above. In addition, the mixing amount of the epoxy resin solution and the conductive particles A was set to: the ratio of the epoxy resin in the conductive adhesive layer was 70% by mass, and the ratio of the conductive particles A was 30% by mass.

Comparative Examples 2 and 3 Except for changing the type and content ratio of the conductive particles as shown in Table 1, the same procedures as in Comparative Example 1 were followed to produce shielding films.

Example 1 A nanosilver wire layer (wire diameter 30nm, wire length 20μm, thickness about 70nm) is laminated on the surface of a PET film (thickness 6μm). Then, a polyester resin composition is applied to the surface of the nanosilver wire layer using a wire rod, and heated at 100°C for 1 minute to form a resin layer (thickness 50nm). Then, an adhesive composition obtained by mixing an epoxy resin solution and conductive particles A is applied to the surface of the above resin layer using a wire rod, and heated at 120°C for 1 minute to form a conductive adhesive layer (thickness 5μm). The shielding film of Example 1 is prepared as above. The mixing amounts of the epoxy resin solution and the conductive particles A were set such that the ratio of the epoxy resin in the conductive adhesive layer was 70% by mass and the ratio of the conductive particles A was 30% by mass.

Examples 2, 3 and Comparative Example 4 Except for changing the thickness of the resin layer as shown in Table 1, each shielding film was produced in the same manner as Example 1.

Example 4 Except for changing the content ratio of the conductive particles as shown in Table 1, a shielding film was prepared in the same manner as Example 11.

Examples 5, 6 and Comparative Example 5 Except for changing the thickness of the resin layer as shown in Table 1, each shielding film was produced in the same manner as Example 4.

Example 7 Except for changing the type of conductive particles as shown in Table 1, a shielding film was prepared in the same manner as Example 1.

Examples 8, 9 and Comparative Example 6 Except for changing the thickness of the resin layer as shown in Table 1, each shielding film was produced in the same manner as Example 4.

(Evaluation) Each shielding film obtained in the embodiment and the comparative example was evaluated as follows. The evaluation results are recorded in the table. In addition, only PET film (thickness 6μm) was used as the evaluation object of reference example 1. In addition, "OL" in the table indicates a value exceeding 100Ω, which is the measurement limit, due to overload.

(1) Connection resistance value The following printed wiring board was prepared: a substrate member composed of a polyimide film was formed with two copper foil patterns (4 mm wide, 1 mm spacing) simulating a ground pattern, and a covering film (insulating film) composed of an insulating adhesive layer and a polyimide film was formed thereon. A gold-plated layer was provided on the surface of the copper foil pattern as a surface layer. Furthermore, a circular opening portion simulating a ground connection portion with a diameter of 0.8 mm was formed on the covering film. Using a press, the shielding film and the printed wiring board prepared in each embodiment and comparative example were connected under the conditions of temperature: 170°C, time: 30 minutes, and pressure: 2~3MPa. After the shielding film is applied, the resistance between the two copper foil patterns is measured with a resistance meter to evaluate the connectivity between the copper foil pattern and the conductive adhesive sheet as the connection resistance value.

(2) Total light transmittance For the shielding films obtained in the embodiments and comparative examples, the light transmittance was measured by irradiating the PET film surface with the integrating sphere side using a haze meter (trade name "NDH4000", manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7361-1.

[Table 1] Resin layer thickness [nm] Conductive particles Total light transmittance[%] Connection resistance [Ω] Type Shape Content ratio [mass %] Comparison Example 1 - Conductive particles A Spherical 30 82.4 OL Comparison Example 2 - Conductive particles A Spherical 50 75.5 OL Comparison Example 3 - Conductive particles B Branch 30 76.1 15.0 Embodiment 1 50 Conductive particles A Spherical 30 82.9 25.7 Embodiment 2 100 Conductive particles A Spherical 30 83.4 26.1 Embodiment 3 200 Conductive particles A Spherical 30 80.8 28.0 Comparison Example 4 1000 Conductive particles A Spherical 30 80.6 OL Embodiment 4 50 Conductive particles A Spherical 50 75.5 27.3 Embodiment 5 100 Conductive particles A Spherical 50 74.4 22.9 Embodiment 6 200 Conductive particles A Spherical 50 77.2 23.4 Comparison Example 5 1000 Conductive particles A Spherical 50 73.4 OL Embodiment 7 50 Conductive particles B Branch 30 67.1 13.6 Embodiment 8 100 Conductive particles B Branch 30 70.1 14.5 Embodiment 9 200 Conductive particles B Branch 30 66.2 13.8 Comparative Example 6 1000 Conductive particles B Branch 30 65.7 OL Reference Example 1 - - - - 82.3 OL

When the nanosilver wire layer is used as the transparent conductive layer, the shielding film of the present invention has a high total light transmittance and excellent transparency, a low connection resistance and excellent connection stability even when the conductive particles are mixed in a large amount of 30-50 mass % (Examples 1-9). In addition, in the case of using spherical conductive particles (Examples 1-6), there is a tendency for the total light transmittance to be high and the transparency to be excellent compared to the case of using dendrite-shaped conductive particles (Examples 7-9). On the other hand, in the case of using dendrite-shaped conductive particles (Examples 7-9), there is a tendency for the connection resistance to be low and the connection stability to be excellent compared to the case of using spherical conductive particles (Examples 1-6). Furthermore, under the condition of a large amount of 30 mass % or more, when there is no resin layer between the nanosilver wire layer and the conductive adhesive layer (Comparative Examples 1-3), the connection resistance value becomes higher compared to the case where the same type of conductive particles are used at the same ratio (Examples 1-9).

1: Shielding film 11: 1st insulating layer 12: Nanosilver wire layer 13: 2nd insulating layer 14: Conductive adhesive layer

FIG. 1 is a schematic cross-sectional view showing an embodiment of the electromagnetic wave shielding film of the present invention.

1: Shielding film

11: First insulating layer

12: Nanosilver wire layer

13: Second insulation layer

14: Conductive adhesive layer

Claims (7)

An electromagnetic wave shielding film is sequentially laminated with a first insulating layer, a nanosilver wire layer, a second insulating layer and a conductive adhesive layer; the thickness of the second insulating layer is 50-500nm; the conductive adhesive layer comprises: a binder component and spherical or branch-shaped conductive particles; the content ratio of the conductive particles is 1-80% by mass relative to 100% by mass of the conductive adhesive layer. The electromagnetic wave shielding film of claim 1, wherein the second insulating layer and the conductive adhesive layer are directly laminated. As in claim 1, the electromagnetic wave shielding film, wherein the second insulating layer is directly laminated with the conductive adhesive layer on one side and directly laminated with the nanosilver wire layer on the other side. An electromagnetic wave shielding film as claimed in any one of claims 1 to 3, wherein the content ratio of the conductive particles is 30-80% by mass relative to 100% by mass of the conductive adhesive layer. For the electromagnetic wave shielding film of any one of claim items 1 to 3, the total light transmittance thereof is 10% or more in accordance with the measurement method of JIS K 7361-1. For example, the electromagnetic wave shielding film in claim 4 has a total light transmittance of 10% or more in accordance with the measurement method of JIS K 7361-1. A shielded printed wiring board having an electromagnetic wave shielding film as described in any one of claims 1 to 6.