WO2022255438A1

WO2022255438A1 - Electromagnetic wave shield film

Info

Publication number: WO2022255438A1
Application number: PCT/JP2022/022433
Authority: WO
Inventors: 茂樹竹下; 晃司高見; 正博渡辺
Original assignee: タツタ電線株式会社
Priority date: 2021-06-02
Filing date: 2022-06-02
Publication date: 2022-12-08
Also published as: JPWO2022255438A1; TW202315510A; CN117397379A

Abstract

Provided is an electromagnetic wave shield film which can be easily bonded to an adherend, has excellent adhesion properties and electrical connection stability, and also has excellent environmental resistance. An electromagnetic wave shield film 1 obtained by layering a metal layer 3, a first inorganic layer 4 and a conductive adhesive layer 5 in this order, wherein the thickness of the first inorganic layer 4 is 0.1-100nm, the conductive adhesive layer 5 contains a binder component and conductive particles, and the ratio of the thickness of the conductive adhesive layer 5 to the median diameter of the conductive particles is 0.2-3.5.

Description

electromagnetic wave shielding film

The present invention relates to an electromagnetic wave shielding film. More particularly, the present invention relates to electromagnetic wave shielding films used in printed wiring boards.

Printed wiring boards are often used to incorporate circuits into the mechanisms of electronic devices such as mobile phones, video cameras, and laptop computers. It is also used to connect a movable part such as a printer head and a control part. These electronic devices require measures to shield against electromagnetic waves, and the printed wiring boards used in the devices also use shield printed wiring boards that take measures to shield against electromagnetic waves.

An electromagnetic wave shielding film (hereinafter sometimes simply referred to as "shielding film") is used for the shield printed wiring board. For example, a shield film that is used by adhering to a printed wiring board has a shield layer such as a metal layer and a conductive adhesive sheet provided on the surface of the shield layer.

As a shield film having a conductive adhesive sheet, for example, those disclosed in

Patent Documents

1 and 2 are known. The above-mentioned shield film is used by laminating such that the surface where the conductive adhesive sheet is exposed is adhered to the surface of the printed wiring board, specifically the surface of the coverlay provided on the surface of the printed wiring board. These conductive adhesive sheets are usually adhered and laminated on a printed wiring board by thermocompression bonding under high temperature and high pressure conditions. The shielding film arranged on the printed wiring board in this way exhibits the performance (shielding performance) of shielding electromagnetic waves from the outside of the printed wiring board.

JP 2015-110769 A JP 2012-28334 A

　Conventionally, the shield film is used by bonding it to the substrate under high temperature and high pressure conditions. However, depending on the type of substrates to be bonded together, there are cases where high temperature and high pressure conditions cannot be applied. For this reason, there is a tendency to demand a shielding film that can be adhered to a printed wiring board under relatively gentle conditions rather than under high temperature and high pressure conditions. However, conventional shielding films have the problem of being inferior in adhesion strength and electrical connection stability when bonded to a substrate under relatively mild conditions.

Also, in recent years, conventional shielding films have had the problem that the metal layer deteriorates in a high-temperature, high-humidity environment and the shielding performance deteriorates, that is, the environmental resistance is poor.

The present invention has been made in view of the above, and an object of the present invention is to provide an electromagnetic wave shielding film that can be easily adhered to an adherend, has excellent adhesion and electrical connection stability, and has excellent environmental resistance. to provide.

As a result of intensive studies to achieve the above object, the present inventors have found that an electromagnetic wave shielding film having a specific layer structure can be easily adhered to an adherend and has excellent adhesion and electrical connection stability. It was found to be excellent in environmental resistance. The present invention has been completed based on these findings.

That is, in the present invention, a metal layer, a first inorganic layer, and a conductive adhesive layer are laminated in this order,
The thickness of the first inorganic layer is 0.1 to 100 nm,
The conductive adhesive layer contains a binder component and conductive particles,
Provided is an electromagnetic wave shielding film, wherein the ratio of the thickness of the conductive adhesive layer to the median diameter of the conductive particles is 0.2 to 3.5.

It is preferable that an insulating protective layer is directly laminated on the surface of the metal layer opposite to the first inorganic layer.

It is preferable to have a second inorganic layer directly laminated with the metal layer as the insulating protective layer.

The thickness of the second inorganic layer is preferably 0.1 to 100 nm.

The second inorganic layer is preferably made of metal oxide.

It is preferable to have a resin layer as the insulating protective layer.

The first inorganic layer is preferably made of metal oxide.

The first inorganic layer is preferably laminated directly with the metal layer.

The conductive adhesive layer is preferably laminated directly with the first inorganic layer.

The present invention also provides a shield printed wiring board comprising the electromagnetic wave shielding film.

The electromagnetic wave shielding film of the present invention can be easily adhered to an adherend, yet has excellent adhesion to the adherend, excellent electrical connection stability, and excellent environmental resistance. Therefore, the electromagnetic wave shielding film of the present invention can be used even for substrates having poor resistance to high temperatures and high pressures. Moreover, it can be used in an environment where environmental resistance is required.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows one Embodiment of the electromagnetic wave shielding film of this invention. It is a cross-sectional schematic diagram which shows other embodiment of the electromagnetic wave shielding film of this invention.

[Shielding film]
The electromagnetic wave shielding film (shielding film) of the present invention has a layer structure in which a metal layer, a first inorganic layer, and a conductive adhesive layer are laminated in this order.

From the viewpoint of more sufficiently protecting the surface of the metal layer on which the conductive adhesive layer is provided and having better environmental resistance, it is preferable that the first inorganic layer is directly laminated with the metal layer. In addition, from the viewpoint of excellent connection stability even when adhered to a printed wiring board under relatively mild conditions, the conductive adhesive layer is preferably laminated directly with the first inorganic layer. preferable.

In addition, from the viewpoint of sufficiently protecting the surface of the metal layer opposite to the side provided with the conductive adhesive layer and improving environmental resistance, the metal layer on the side opposite to the first inorganic layer It is preferable to provide an insulating protective layer on the surface. It is preferable that the insulating protective layer is directly laminated on the metal layer.

An embodiment of the shielding film of the present invention will be described below. FIG. 1 is a schematic cross-sectional view showing one embodiment of the shielding film of the present invention. The shield film 1 shown in FIG. 1 has an insulating protective layer 2, a metal layer 3, a first inorganic layer 4, and a conductive adhesive layer 5 in this order. In the shield film 1, the insulating protective layer 2, the metal layer 3, the first inorganic layer 4, and the conductive adhesive layer 5 are directly laminated to adjacent layers.

(Conductive adhesive layer)
The conductive adhesive layer has, for example, adhesiveness and adhesiveness for adhering the shield film of the present invention to a printed wiring board, and electrical conductivity for electrically connecting with the metal layer. In addition, it can function as a shield layer exhibiting shielding performance together with the metal layer. The conductive adhesive layer may be a single layer or multiple layers.

The conductive adhesive layer contains a binder component and conductive particles.

Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray-curable compounds. Only one type of the binder component may be used, or two or more types may be used.

Examples of the thermoplastic resin include polystyrene-based resin, vinyl acetate-based resin, polyester-based resin, polyolefin-based resin (polyethylene-based resin, polypropylene-based resin, etc.), polyamide-based resin, rubber-based resin, acrylic-based resin, silicone-based resin, etc. is mentioned. Only one type of the thermoplastic resin may be used, or two or more types may be used.

Examples of the thermosetting resin include both resins having thermosetting properties (thermosetting resins) and resins obtained by curing the above thermosetting resins. Examples of the thermosetting resin include phenol-based resins, epoxy-based resins, urethane-based resins, melamine-based resins, alkyd-based resins, acrylic-based resins, and the like. Only one kind of the thermosetting resin may be used, or two or more kinds thereof may be used.

Examples of the epoxy resin include bisphenol type epoxy resin, spirocyclic epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, terpene type epoxy resin, glycidyl ether type epoxy resin, glycidyl amine type Epoxy-based resins, novolak-type epoxy-based resins, and the like are included.

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

The active energy ray-curable compounds include both 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, but for example, a polymerizable compound having one or more (preferably two or more) radical reactive groups (e.g., (meth)acryloyl groups) in the molecule. mentioned. Only 1 type may be used for the said active-energy-ray-curable compound, and 2 or more types may be used for it.

Among them, a thermoplastic resin is preferable as the binder component. In this case, the conductive adhesive layer has tackiness, and when the shield film of the present invention is used by being attached to an adherend such as a printed wiring board, it can be easily attached without being subjected to high temperature and high pressure conditions. can be matched.

When the binder component contains a thermosetting resin, it may contain a curing agent for accelerating the thermosetting reaction as a constituent component of the binder component. The curing agent can be appropriately selected according to the type of the thermosetting resin. Only one kind of the curing agent may be used, or two or more kinds thereof may be used.

Examples of the conductive particles include metal particles, metal-coated resin particles, metal fibers, carbon fillers, and carbon nanotubes.

Examples of metals constituting the coating portion of the metal particles and the metal-coated resin particles include gold, silver, copper, nickel, zinc, indium, tin, lead, bismuth, and alloys containing two or more of these. . Only one kind of the above metals may be used, or two or more kinds thereof may be used.

Specific examples of the metal particles include copper particles, silver particles, nickel particles, silver-coated copper particles, indium particles, tin particles, lead particles, bismuth particles, gold-coated copper particles, silver-coated nickel particles, gold coated nickel particles, indium-coated copper particles, tin-coated copper particles, lead-coated copper particles, bismuth-coated copper particles, indium-coated nickel particles, tin-coated nickel particles, bismuth-coated nickel particles, silver-coated alloy particles, and the like. Examples of the silver-coated alloy particles include silver-coated copper alloy particles in which alloy particles containing copper (for example, copper alloy particles made of an alloy of copper, nickel and zinc) are coated with silver. The metal particles can be produced by an electrolysis method, an atomization method, a reduction method, or the like.

Among the metal particles, silver particles, silver-coated copper particles, silver-coated copper alloy particles, nickel particles, and silver-coated nickel particles are preferable. Silver-coated copper particles and silver-coated copper alloy particles are particularly preferred from the viewpoints of excellent conductivity, suppression of oxidation and agglomeration of the metal particles, and reduction in the cost of the metal particles.

Specific examples of the metal-coated resin particles include silver-coated resin particles, gold-coated resin particles, indium-coated resin particles, tin-coated resin particles, lead-coated resin particles, and bismuth-coated resin particles.

Examples of the shape of the conductive particles include spherical, flake-like (scale-like), dendritic (dendrite-like), fibrous (filament-like), amorphous (polyhedral), and spike-like shapes.

The median diameter (D50) of the conductive particles is preferably 1-50 μm, more preferably 3-40 μm. When the median diameter is 1 μm or more, the dispersibility of the conductive particles is good and aggregation can be suppressed. When the average particle size is 50 µm or less, the conductivity becomes good. The median diameter is the median diameter of all the conductive particles in the conductive adhesive layer, and refers to the particle size at 50% of the integrated value in the particle size distribution determined by the laser diffraction/scattering method. When the median diameter is within the above range, the connection stability is more excellent. The median diameter can be measured, for example, with a laser diffraction particle size distribution analyzer (trade name “SALD-2200”, manufactured by Shimadzu Corporation).

The conductive adhesive layer can be a layer having isotropic conductivity or anisotropic conductivity depending on the application.

The content of the conductive particles in the conductive adhesive layer is preferably 3 to 95% by mass, more preferably 5 to 90% by mass, with respect to 100% by mass of the total amount of the conductive adhesive layer. be. In the case of forming an isotropically conductive conductive adhesive layer, it can be 40 to 95% by mass. In the case of forming an anisotropically conductive conductive adhesive layer, it can be 3 to 40% by mass.

The conductive adhesive layer may contain components other than the components described above within a range that does not impair the effects of the present invention. Examples of the above-mentioned other components include components contained in known or commonly used adhesive layers. Examples of the above other components include curing accelerators, plasticizers, flame retardants, defoaming agents, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, leveling agents, coupling agents, and UV absorbers. agents, tackifying resins, antiblocking agents, and the like. Only one kind of the other components may be used, or two or more kinds thereof may be used.

Although the thickness of the conductive adhesive layer is not particularly limited, it is preferably 3-20 μm, more preferably 5-18 μm. When the thickness is 3 μm or more, the adhesiveness to the adherend is more excellent. Moreover, it is superior in environmental resistance. When the thickness is 20 μm or less, the connection stability is excellent even when adhered to a printed wiring board under relatively mild conditions.

The ratio of the thickness of the conductive adhesive layer to the D50 of the conductive particles [adhesive layer thickness/D50] is 0.2 to 3.5, preferably 0.3 to 3.0. . When the above ratio is 0.2 or more, the adhesion to adherends such as printed wiring boards becomes better. When the above ratio is 3.5 or less, the amount of conductive particles exposed from the surface of the conductive adhesive layer is increased, and connection stability is ensured even when adhered to a printed wiring board under relatively mild conditions. better than

(First inorganic layer)
The first inorganic layer is a layer that protects the metal layer. By interposing the first inorganic layer between the metal layer and the conductive adhesive layer, the surface of the metal layer on the side provided with the conductive adhesive layer is protected, and in a high-temperature and high-humidity environment, the above-mentioned It is possible to suppress deterioration of the connection stability due to deterioration of the metal layer, that is, excellent environmental resistance. It is presumed that the deterioration of the connection stability is caused by the deterioration of the metal layer due to the moisture or the like in the conductive adhesive layer. The first inorganic layer may be a single layer or multiple layers.

Examples of inorganic substances that constitute the first inorganic layer include metal oxides and other inorganic oxides. Only one kind of the inorganic substance may be used, or two or more kinds thereof may be used.

Examples of the inorganic oxide include aluminum oxide (alumina), magnesium oxide, antimony oxide, titanium oxide, chromium oxide, zirconium oxide, zinc oxide, nickel oxide, palladium oxide, tungsten oxide, indium oxide, and ITO (Indium Tin Oxide). ; indium tin oxide) and silicon oxide. Examples of the alkaline earth metal salt include fluoride salts such as magnesium fluoride and calcium fluoride. Examples of metal salts other than alkaline earth metal salts include aluminum silicate, aluminum hydroxide, and zinc sulfide.

Among these inorganic substances, inorganic oxides are preferable, and metal oxides are more preferable, and titanium oxide, chromium oxide, and zirconium oxide are more preferable from the viewpoint of superior environmental resistance and economic efficiency.

Examples of methods for forming the first inorganic layer include electrolysis, vapor deposition (eg, vacuum vapor deposition), sputtering, CVD, metal organic (MO), plating, and rolling. Among them, an inorganic layer formed by vapor deposition, sputtering, or plating is preferable from the viewpoint of ease of manufacture.

The thickness of the first inorganic layer is 0.1 to 100 nm, preferably 0.1 to 20 nm, more preferably 0.1 to 10 nm, still more preferably 0.1 to 5 nm, particularly preferably 0.1 ~2.2 nm. When the thickness is 0.1 nm or more, the environmental resistance is excellent. When the thickness is 100 nm or less, the connection stability is excellent even when the adhesive is adhered to the printed wiring board under relatively mild conditions. When the first inorganic layer has a multilayer structure, the thickness of the first inorganic layer is the total thickness of all layers.

(metal layer)
The metal layer is an element that functions as a shield layer in the shield film of the present invention. The metal layer may be a single layer or a laminate of the same or different types.

Examples of metals forming the metal layer include gold, silver, copper, aluminum, lithium, nickel, tin, palladium, chromium, titanium, zinc, and alloys thereof. Examples of the alloy include silver/copper alloy, magnesium/copper alloy, magnesium/silver alloy, magnesium/aluminum alloy, magnesium/indium alloy, lithium/aluminum alloy, ITO (Indium Tin Oxide; indium tin oxide), and the like. mentioned. Among these metals, copper and silver are preferable from the viewpoint of excellent electromagnetic wave shielding performance, and silver/copper alloy is preferable from the viewpoint of excellent migration resistance and sulfurization resistance.

The method of forming the metal layer is not particularly limited, and examples include electrolysis, vapor deposition (eg, vacuum vapor deposition), sputtering, CVD, metal organic (MO), plating, and rolling. Among them, a metal layer formed by vapor deposition, plating, or sputtering is preferable from the viewpoint of ease of manufacture.

Although the thickness of the metal layer is not particularly limited, it is, for example, 5 nm to 15 μm, preferably 5 nm to 13 μm. When the metal layer has a multi-layer structure, the thickness of the metal layer is the sum of all layer thicknesses.

(insulating protective layer)
The insulating protective layer has insulating properties and protects the inner layers of the shield film of the present invention. By providing the insulating protective layer, it is possible to improve the environmental resistance of the surface of the metal layer on which the first inorganic layer is not provided, and to further suppress the deterioration of the connection stability. The insulating protective layer may be a single layer or multiple layers.

Examples of the insulating protective layer include a resin layer formed mainly from a resin, or an inorganic layer formed from an inorganic substance. When the insulating protective layer is an inorganic layer, the environmental resistance is further improved. When the insulating protective layer is a resin layer, it functions as a support in the shield film of the present invention. The insulating protective layer may be a single layer or a laminate of the same or different types.

The insulating protective layer preferably has a resin layer and an inorganic layer. In this case, the inorganic layer is preferably on the metal layer side. In this specification, the inorganic layer that can be included in the insulating protective layer may be referred to as a "second inorganic layer". The second inorganic layer is preferably laminated directly on the metal layer from the viewpoint of better environmental resistance.

FIG. 2 shows an embodiment of the shield film of the present invention in which the insulating protective layer comprises a resin layer and a second inorganic layer. In the shielding film 1 shown in FIG. 2, the insulating protective layer 2 has a laminate structure of a resin layer 21 and a second inorganic layer 22, and is composed of the laminate structure. The second inorganic layer 22 is arranged on the metal layer 3 side and the resin layer 21 is arranged on the outermost surface, and the second inorganic layer 22 is directly laminated on the metal layer 3 .

Examples of the resin constituting the resin layer in the insulating protective layer include thermoplastic resins, thermosetting resins, and active energy ray compounds. It is preferably a type compound. Only one kind of the above resin may be used, or two or more kinds thereof may be used.

Examples of the thermoplastic resin 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, poly Methylpentene, ethylene-vinyl acetate copolymer (EVA), ionomer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester (random, alternating) copolymer, ethylene-butene copolymer , Polyolefin resins such as ethylene-hexene copolymer; polyurethane; polyester such as polyethylene terephthalate (PET), polyethylene naphthalate, polybutylene terephthalate (PBT); polycarbonate (PC); polyimide (PI); ); Polyetherimide; Aramid, polyamide such as wholly aromatic polyamide; Polyamideimide; Polyphenyl sulfide; Polysulfone (PS); Polyethersulfone (PES); styrene copolymer (ABS); fluorine resin; polyvinyl chloride; polyvinylidene chloride; cellulose resin such as triacetyl cellulose (TAC); Only one type of the thermoplastic resin may be used, or two or more types may be used. From the viewpoint of excellent transparency, the thermoplastic resin is preferably polyester or cellulose resin, and more preferably polyethylene terephthalate or triacetyl cellulose.

Examples of the thermosetting resin include both resins having thermosetting properties (thermosetting resins) and resins obtained by curing the above thermosetting resins. Examples of the thermosetting resin include phenol-based resins, epoxy-based resins, urethane-based resins, melamine-based resins, alkyd-based resins, imide-based resins, amide-based resins, polyamideimide-based resins, polyphenylsulfide-based resins, liquid crystals, Examples include polymers (LCP) and acrylic resins. Only one kind of the thermosetting resin may be used, or two or more kinds thereof may be used.

The surface of the resin layer (especially the surface on the side of the metal layer) may be subjected to, for example, corona discharge treatment, plasma treatment, sand mat treatment, and the like, for the purpose of enhancing adhesion and retention with adjacent layers such as the metal layer. Physical treatment such as ozone exposure treatment, flame exposure treatment, high voltage shock exposure treatment, ionizing radiation treatment; chemical treatment such as chromic acid treatment; surface treatment such as easy adhesion treatment with coating agent (undercoat). good too. It is preferable that the surface treatment for enhancing adhesion is applied to the entire surface of the resin layer on the metal layer side.

Although the thickness of the resin layer is not particularly limited, it is preferably 1 to 20 μm, more preferably 1 to 4 μm. When the thickness is 1 μm or more, the shield film can be more sufficiently supported and the metal layer can be protected. When the thickness is 20 µm or less, the transparency and flexibility are excellent, and economically advantageous. In addition, when the said resin layer is a multilayer structure, the thickness of the said resin layer is the total thickness of all the layers.

Examples of the inorganic substance forming the second inorganic layer include those exemplified and explained as the inorganic substance forming the first inorganic layer. Only one kind of the inorganic substance may be used, or two or more kinds thereof may be used.

Examples of methods for forming the second inorganic layer include electrolysis, deposition (eg, vacuum deposition), sputtering, CVD, metal organic (MO), plating, and rolling. Among them, an inorganic layer formed by vapor deposition, plating, or sputtering is preferable from the viewpoint of ease of manufacture.

The thickness of the second inorganic layer is 0.1 to 100 nm, preferably 0.1 to 20 nm, more preferably 0.1 to 10 nm, still more preferably 0.1 to 5 nm, particularly preferably 0.1 ~2.2 nm. When the thickness is 0.1 nm or more, the environmental resistance is excellent. When the thickness is 100 nm or less, the connection stability to the outside is excellent. When the second inorganic layer has a multilayer structure, the thickness of the second inorganic layer is the total thickness of all layers.

The shield film of the present invention may have a separator (release film) on the side of the conductive adhesive layer. The separator is laminated so as to be peelable from the shield film of the present invention. A separator is an element for covering and protecting the conductive adhesive layer, and is peeled off when using the shield film of the present invention.

Examples of the separator include polyethylene terephthalate (PET) film, polyethylene film, polypropylene film, plastic film and paper surface-coated with a release agent such as a fluorine-based release agent and a long-chain alkyl acrylate release agent. .

The thickness of the separator is preferably 10-200 μm, more preferably 15-150 μm. When the thickness is 10 µm or more, the protective performance is excellent. When the thickness is 200 μm or less, the separator is easily peeled off during use.

The shielding film of the present invention may have layers other than the layers described above. Examples of the other layers include other insulating layers, antireflection layers, antiglare layers, antifouling layers, hard coat layers, ultraviolet absorption layers, anti-Newton ring layers, and the like.

The shielding film of the present invention can be easily adhered to an adherend, yet has excellent adhesion to the adherend, excellent electrical connection stability, and excellent environmental resistance. Therefore, the electromagnetic wave shielding film of the present invention can be used even for substrates having poor resistance to high temperatures and high pressures. Moreover, it can be used in an environment where environmental resistance is required.

The shielding film of the present invention is preferably used for printed wiring boards, and particularly preferably for flexible printed wiring boards (FPC).

In addition, the shielding film of the present invention has excellent environmental resistance. Therefore, it can be preferably used in a high-temperature and high-humidity environment, for example, inside a vehicle such as an automobile.

(Manufacturing method of electromagnetic wave shielding film)
One embodiment of the method for manufacturing the shielding film of the present invention will be described with reference to FIGS. 1 and 2. FIG. In producing the shield film 1 shown in FIG. 1, first, the metal layer 3 is formed on the insulating protective layer 2 . Formation of the metal layer 3 can be performed by the various methods described above.

In the production of the shield film 1 shown in FIG. 2, the insulating protective layer 2 can be formed by forming the second inorganic layer 22 on the resin layer 21 by vacuum deposition, sputtering, or the like. Next, a metal layer 3 is formed on the insulating protective layer 2 by vacuum deposition, sputtering, plating, or the like.

Next, the first inorganic layer 4 can be formed on the surface of the formed metal layer 3 by vacuum deposition, sputtering, or the like.

Next, the adhesive composition for forming the conductive adhesive layer 5 is applied (coated) to the surface of the formed first inorganic layer 4, and if necessary, the solvent is removed and / or partially cured. can be formed. The adhesive composition contains, for example, a solvent (solvent) in addition to the components contained in the conductive adhesive layer. Examples of the solvent include those exemplified as solvents that can be contained in the composition for forming the insulating protective layer. The solid content concentration of the adhesive composition is appropriately set according to the thickness of the conductive adhesive layer to be formed.

A known coating method may be used to apply each of the above compositions. For example, coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, lip coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, direct coaters and slot die coaters may be used.

In the above-described manufacturing method, a method of sequentially forming each layer (direct coating method) was mainly described, but it is not limited to such a method. It may also be produced by a method (lamination method) in which each layer separately formed on a material is laminated and successively adhered.

A printed wiring board can be produced using the shielding film of the present invention. For example, by bonding the conductive adhesive layer of the shield film of the present invention to a printed wiring board (for example, a coverlay), a shield printed wiring board in which the shield film of the present invention is bonded to the printed wiring board can be obtained. can. In the shield printed wiring board, the conductive adhesive layer may be thermoset.

The present invention will be described in more detail below based on examples, but the present invention is not limited only to these examples.

Example 1
A TiO ₂ film (thickness: 2 nm) was formed as a second inorganic layer by sputtering on the surface of a PET film (thickness: 6 μm), which was a resin layer, to prepare an insulating protective layer. Next, a silver thin film (10 nm thick) was formed as a metal layer on the surface of the TiO ₂ film by vacuum deposition. Next, a TiO ₂ film (thickness: 1.5 nm) was formed on the surface of the silver thin film by sputtering as a first inorganic layer. Then, as a conductive adhesive layer, 95 parts by mass of thermoplastic acrylic resin, 5 parts by mass of silver-coated copper powder (spherical, median diameter 5 μm), and 400 parts by mass of toluene (solid content: 20% by mass) are blended. The adhesive composition obtained by mixing is applied to the surface of a polyester film whose surface has been subjected to release treatment using a wire bar, and is heated at 100° C. for 3 minutes to form a conductive adhesive layer (thickness: 5 μm). was formed and attached to the TiO ₂ film side as the first inorganic layer. As described above, the shield film of Example 1 was produced.

Examples 2-4
An electromagnetic wave shielding film of each example was produced in the same manner as in Example 1, except that the thickness of the first inorganic layer was changed as shown in Table 1.

Example 5
The epoxy resin composition was applied to a PET film substrate whose surface had been subjected to mold release treatment, and cured by heating at 100° C. for 3 minutes to form a resin layer of epoxy resin having a thickness of 5 μm. Chromium oxide (thickness: 0.2 nm) was formed by plating on both side surfaces of a rolled copper foil having a thickness of 6 μm to obtain a laminate consisting of the second inorganic layer/metal layer/first inorganic layer. Next, the second inorganic layer surface of the laminate was attached to the surface of the resin layer by heat lamination. Next, on the surface of the first inorganic layer, 95 parts by mass of thermoplastic acrylic resin as a conductive adhesive layer, 5 parts by mass of nickel particles (filament shape, median diameter 20 μm), and 400 parts by mass of toluene (solid content is 20% by mass), the adhesive composition obtained by mixing is applied using a wire bar and heated at 100 ° C. for 3 minutes to form a conductive adhesive layer (thickness 13 μm). Thus, an electromagnetic wave shielding film of Example 5 was obtained.

Examples 6-8
An electromagnetic wave shielding film of each example was prepared in the same manner as in Example 5 except that the thickness of the first inorganic layer, the thickness of the second inorganic layer, and the type of conductive particles were changed as shown in Table 1. made.

Comparative example 1
An electromagnetic wave shielding film of Comparative Example 1 was produced in the same manner as in Example 1, except that the metal layer and the conductive adhesive layer were directly bonded together without producing the first inorganic layer.

Comparative example 2
An electromagnetic wave shielding film of Comparative Example 2 was produced in the same manner as in Example 3, except that the thickness of the first inorganic layer was 150 nm.

Comparative example 3
An electromagnetic wave shielding film of Comparative Example 3 was produced in the same manner as in Example 3, except that the thickness of the conductive adhesive layer was 1 μm, the silver-coated copper powder was spherical, and the median diameter was 7 μm.

Comparative example 4
An electromagnetic wave shielding film of Comparative Example 4 was produced in the same manner as in Example 3, except that instead of the silver-coated copper powder of Example 1, spherical silver-coated copper powder having a median diameter of 1 μm was used.

[evaluation]
Each shield film obtained in Examples and Comparative Examples was evaluated as follows. The evaluation results are shown in the table. Items that were not used and items that could not be accurately measured are indicated as "-" in the table.

(connection resistance value measurement)
Two electrodes each having a width of 5 mm and a length of 10 mm were placed on a glass epoxy substrate having a thickness of 2 mm with a spacing of 100 mm. Then, the shielding film obtained in the example was punched out on the electrode arrangement surface to a width of 5 mm and a length of 130 mm, and under normal temperature and pressure conditions, a 2 kg roller was reciprocated once to connect the electrodes to conductive adhesion. The agent layer surfaces were pasted together. After laminating the conductive adhesive layer surfaces, the resistance value between the two electrodes was measured using a 4-terminal method tester (trade name "RM3542", manufactured by Hioki Electric Co., Ltd.) immediately after the electromagnetic shielding film was produced and at 65 ° C. Each was measured after storage for 72 hours in an environment of 90% RH.

It was confirmed that the shielding films of the present invention (Examples 1 to 8) have low connection resistance values and excellent shielding performance even when laminated under mild conditions that are not high temperature and high pressure conditions. On the other hand, when the first inorganic layer was not provided, the environmental resistance was poor (Comparative Example 1), and when the first inorganic layer was too thick, the connection stability was poor (Comparative Example 2). Further, when the ratio of the thickness of the conductive adhesive layer to the median diameter of the conductive particles is too small, the adhesiveness cannot be exhibited, resulting in the resistance value being unmeasurable (Comparative Example 3). When the ratio of the thickness of the conductive adhesive layer to the median diameter of the particles was too large, the connection stability was poor (Comparative Example 4).

The electromagnetic wave shielding film of the present invention can be suitably used for printed wiring boards.

REFERENCE SIGNS LIST 1 shield film 2 insulating protective layer 21 resin layer 22 second inorganic layer 3 metal layer 4 first inorganic layer 5 conductive adhesive layer

Claims

A metal layer, a first inorganic layer, and a conductive adhesive layer are laminated in this order,
The thickness of the first inorganic layer is 0.1 to 100 nm,
The conductive adhesive layer contains a binder component and conductive particles,
An electromagnetic wave shielding film, wherein the ratio of the thickness of the conductive adhesive layer to the median diameter of the conductive particles is 0.2 to 3.5.
The electromagnetic wave shielding film according to claim 1, wherein an insulating protective layer is directly laminated on the surface of the metal layer opposite to the first inorganic layer.
The electromagnetic wave shielding film according to claim 2, which has a second inorganic layer directly laminated with the metal layer as the insulating protective layer.
The electromagnetic wave shielding film according to claim 3, wherein the second inorganic layer has a thickness of 0.1 to 100 nm.
The electromagnetic wave shielding film according to claim 3 or 4, wherein the second inorganic layer is composed of a metal oxide.
The electromagnetic wave shielding film according to any one of claims 2 to 5, which has a resin layer as the insulating protective layer.
The electromagnetic wave shielding film according to any one of claims 1 to 6, wherein the first inorganic layer is composed of a metal oxide.
The electromagnetic wave shielding film according to any one of claims 1 to 7, wherein the first inorganic layer is directly laminated with the metal layer.
The electromagnetic wave shielding film according to any one of claims 1 to 8, wherein the conductive adhesive layer is directly laminated with the first inorganic layer.
A shield printed wiring board comprising the electromagnetic wave shielding film according to any one of claims 1 to 9.