CN115004875A - Electromagnetic wave shielding film - Google Patents

Electromagnetic wave shielding film Download PDF

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Publication number
CN115004875A
CN115004875A CN202180012297.1A CN202180012297A CN115004875A CN 115004875 A CN115004875 A CN 115004875A CN 202180012297 A CN202180012297 A CN 202180012297A CN 115004875 A CN115004875 A CN 115004875A
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CN
China
Prior art keywords
layer
shielding film
adhesive layer
conductive adhesive
insulating layer
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Pending
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CN202180012297.1A
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Chinese (zh)
Inventor
梅村滋和
矶部修
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Tatsuta Electric Wire and Cable Co Ltd
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Tatsuta Electric Wire and Cable Co Ltd
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Publication of CN115004875A publication Critical patent/CN115004875A/en
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0073—Shielding materials
    • H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
    • H05K9/0086—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising a single discontinuous metallic layer on an electrically insulating supporting structure, e.g. metal grid, perforated metal foil, film, aggregated flakes, sintering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/02—Layer formed of wires, e.g. mesh
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form
    • B32B3/26—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer
    • B32B3/266—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer characterised by an apertured layer, the apertures going through the whole thickness of the layer, e.g. expanded metal, perforated layer, slit layer regular cells B32B3/12
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/02—Non-macromolecular additives
    • C09J11/04—Non-macromolecular additives inorganic
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/20—Adhesives in the form of films or foils characterised by their carriers
    • C09J7/29—Laminated material
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J9/00—Adhesives characterised by their physical nature or the effects produced, e.g. glue sticks
    • C09J9/02—Electrically-conducting adhesives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B5/00—Non-insulated conductors or conductive bodies characterised by their form
    • H01B5/14—Non-insulated conductors or conductive bodies characterised by their form comprising conductive layers or films on insulating-supports
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/03—Use of materials for the substrate
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
    • B32B2307/212—Electromagnetic interference shielding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2311/00—Metals, their alloys or their compounds
    • B32B2311/02—Noble metals
    • B32B2311/08—Silver
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2457/00—Electrical equipment
    • B32B2457/08—PCBs, i.e. printed circuit boards
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J201/00—Adhesives based on unspecified macromolecular compounds

Abstract

The invention provides an electromagnetic wave shielding film which has excellent transparency and low connection resistance value even if a conductive adhesive layer is mixed with a large amount of conductive particles. In the electromagnetic wave shielding film of the present invention, a 1 st insulating layer, a silver nanowire layer, a 2 nd insulating layer, and a conductive adhesive layer are laminated in this order, the thickness of the 2 nd insulating layer is 50 to 500nm, 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% by mass with respect to 100% by mass of the conductive adhesive layer.

Description

Electromagnetic wave shielding film
Technical Field
The present invention relates to an electromagnetic wave shielding film. More particularly, the present invention relates to an electromagnetic wave shielding film used in a printed wiring board.
Background
Printed wiring boards are widely used for incorporating circuits into mechanisms in electronic devices such as mobile phones, video cameras, and notebook-size personal computers. And is also used to connect a movable portion of the print head and a control portion. In these electronic devices, electromagnetic wave shielding measures are essential, and even printed wiring boards used in the devices are shielded printed wiring boards on which the electromagnetic wave shielding measures are implemented.
For the purpose of electromagnetic wave shielding measures, electromagnetic wave shielding films (hereinafter also simply referred to as "shielding films") are used in shielded printed wiring boards. For example, a shielding film used for bonding to a printed wiring board includes a shielding layer such as a metal layer and a conductive bonding sheet provided on the surface of the shielding layer.
As a shielding film including a conductive bonding sheet, for example, shielding films disclosed in patent documents 1 and 2 are known. The shielding film is used by attaching the exposed surface of the conductive bonding sheet to the surface of the printed wiring board, specifically, to the surface of a cover film provided on the surface of the printed wiring board. The conductive bonding pad is usually subjected to hot pressing under high temperature/high pressure conditions to bond and laminate with a printed wiring board. The shielding film thus disposed on the printed wiring board exhibits a performance of shielding electromagnetic waves from the outside of the printed wiring board (shielding performance).
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2015-110769;
patent document 2: japanese patent laid-open No. 2012-28334.
Disclosure of Invention
Technical problems to be solved by the invention
In recent years, when the shielding film is attached to a printed wiring board, it is sometimes required to have a performance of facilitating alignment. Therefore, the shielding film tends to require transparency. As a method for improving the transparency, a transparent conductive layer having a small layer thickness is used as a conductive layer in a shielding film.
However, in the conventional shielding film, the conductivity is improved as the amount of the conductive particles in the conductive adhesive layer is increased, and in the shielding film using the transparent conductive layer, the connection resistance value is increased and the conductivity is decreased as the amount of the conductive particles in the conductive adhesive layer is increased.
In view of the above problems, an object of the present invention is to provide an electromagnetic wave shielding film having excellent transparency and a low connection resistance value even when a large amount of conductive particles are mixed in a conductive adhesive layer.
Means for solving the problems
The present inventors have conducted extensive studies to achieve the above object and have found that: an electromagnetic wave shielding film having a specific layer structure is excellent in transparency and low in connection resistance even when a large amount of conductive particles are mixed in a conductive adhesive layer. The present invention has been completed based on this finding.
That is, the present invention provides an electromagnetic wave shielding film in which a 1 st insulating layer, a silver nanowire layer, a 2 nd insulating layer, and a conductive adhesive layer are laminated in this order.
The thickness of the 2 nd insulating layer is 50 to 500nm,
the conductive adhesive layer includes a binder component and spherical or dendritic conductive particles,
the content ratio of the conductive particles is 1 to 80% by mass with respect to 100% by mass of the conductive adhesive layer.
Preferably: the 2 nd insulating layer and the conductive adhesive layer are directly laminated.
Preferably, the following components are used: the 2 nd insulating layer is directly laminated on one surface with the conductive adhesive layer and directly laminated on the other surface with the silver nanowire layer.
Preferably: the content of the conductive particles is 30 to 80% by mass with respect to 100% by mass of the conductive adhesive layer.
Preferably: the electromagnetic wave shielding film has a total light transmittance of 10% or more in a measurement method according to JIS K7361-1.
In addition, the present invention provides a shielded printed wiring board comprising the electromagnetic wave shielding film.
Effects of the invention
The electromagnetic wave shielding film of the present invention has excellent transparency and low connection resistance, regardless of whether a small amount of conductive particles or a large amount of conductive particles are blended in the conductive adhesive layer.
Drawings
Fig. 1 is a schematic cross-sectional view of an embodiment of an electromagnetic wave shielding film according to the present invention.
Detailed Description
[ Shielding film ]
The shielding film of the present invention has a layer structure in which a 1 st insulating layer, a silver nanowire layer, a 2 nd insulating layer, and a conductive adhesive layer are laminated in this order.
An embodiment of the shielding film of the present invention will be described below. Fig. 1 is a schematic cross-sectional view of an embodiment of a shielding film of the present invention. The shielding film 1 of the present invention shown in fig. 1 includes a 1 st insulating layer 11, a silver nanowire layer 12, a 2 nd insulating layer 13, and a conductive adhesive layer 14 in this order.
(insulating layer 1)
The 1 st insulating layer is a transparent substrate that functions as a protection of the silver nanowire layer and a support of the silver nanowire layer in the shielding film of the present invention. Examples of the 1 st insulating layer include a plastic substrate (particularly, a plastic film), a glass plate, and the like. The 1 st insulating layer may be a single layer or a laminate of the same or different types.
Examples of the resin constituting the plastic substrate include: polyolefin resins such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homo polypropylene, polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomer, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid ester (random, alternating) copolymer, ethylene-butene copolymer, and ethylene-hexene copolymer; a polyurethane; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate, and polybutylene terephthalate (PBT); polycarbonate (PC); polyimide (PI); polyetheretherketone (PEEK); a polyetherimide; polyamides such as aromatic polyamides and wholly aromatic polyamides; polyphenylene sulfide; polysulfone (PS); polyethersulfone (PES); acrylic resins such as polymethyl methacrylate (PMMA); acrylonitrile-butadiene-styrene copolymer (ABS); a fluorocarbon resin; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as triacetyl cellulose (TAC); silicone, and the like. The resin may be used alone or in combination of two or more. Among these resins, polyester and cellulose resins are preferable, and polyethylene terephthalate and triacetyl cellulose are more preferable from the viewpoint of better transparency.
For the purpose of improving close adhesiveness, retainability, and the like with an adjacent layer such as a silver nanowire layer, the surface of the 1 st insulating layer (particularly, the silver nanowire layer-side surface) may be subjected to physical treatment such as corona discharge treatment, plasma treatment, sand blast processing treatment, ozone exposure treatment, flame exposure treatment, high-voltage shock exposure treatment, ionizing radiation treatment, and the like; chemical treatments such as chromic acid treatment; surface treatment such as easy-to-bond treatment using a coating agent (primer). The surface treatment for improving the close adhesiveness is preferably applied to the entire surface of the silver nanowire layer side in the 1 st insulating layer.
The thickness of the 1 st insulating layer is not particularly limited, but is preferably 1 to 15 μm, more preferably 3 to 10 μm. If the thickness is 1 μm or more, the silver nanowire layer can be protected while supporting the shielding film more sufficiently. When the thickness is 15 μm or less, the transparency and flexibility are excellent, and the cost efficiency is also favorable. In the case where the 1 st insulating layer has a multi-layer structure, the thickness of the 1 st insulating layer is the sum of all the layer thicknesses.
(silver nanowire layer)
The silver nanowire layer is an element that functions as a shielding layer in the shielding film of the present invention. The silver nanowire layer may be a single layer, or a laminate of the same or different types.
The thickness of the silver nanowire layer is preferably 20 to 500nm, and more preferably 50 to 150 nm. When the thickness is 20nm or more, high shielding performance can be maintained. When the thickness is 500nm or less, the transparency of the shielding film is excellent. When the silver nanowire layer has a structure of plural layers, the thickness of the silver nanowire layer is the sum of all the layer thicknesses.
(insulating layer 2)
The 2 nd insulating layer is a transparent layer protecting the silver nanowire layer. By providing the 2 nd insulating layer between the silver nanowire layer and the conductive adhesive layer, it is possible to suppress a decrease in transparency and connection stability. The decrease in transparency and connection stability is presumed to be due to damage to the silver nanowire layer caused by friction with the conductive particles in the conductive adhesive layer. The 2 nd insulating layer may be a single layer or a plurality of layers.
The 2 nd insulating layer preferably includes a binder component. Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray-curable compounds. The thermoplastic resin, the thermosetting resin, and the active energy ray-curable compound are exemplified by the case where the conductive adhesive layer described later may contain a binder component. The binder component may be used alone or in combination of two or more.
The content of the binder component in the 2 nd insulating layer is not particularly limited, and is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more with respect to 100% by mass of the 2 nd insulating layer. When the content is 70% by mass or more, the flexibility is more excellent, the insertion property into a small-diameter hole is excellent, and the connection stability is more excellent.
The 2 nd insulating layer may contain other components than the above binder component within a range not to impair the effects of the present invention. Examples of the other components include a curing agent, a curing accelerator, a plasticizer, a flame retardant, an antifoaming agent, a viscosity adjuster, an antioxidant, a diluent, an anti-settling agent, a filler, a leveling agent, a coupling agent, an ultraviolet absorber, a tackifying resin, and an anti-blocking agent. The other components may be used alone or in combination of two or more.
The thickness of the 2 nd insulating layer is 50 to 500nm, preferably 100 to 300 nm. By making the thickness 50nm or more, the shielding performance and the connection stability are superior. When the thickness is 500nm or less, the transparency and the connection stability are excellent. If the 2 nd insulating layer has a multi-layer structure, the thickness of the 2 nd insulating layer is the sum of all the layer thicknesses.
From the viewpoint of protecting the silver nanowire layer, the 2 nd insulating layer is preferably directly laminated with the conductive adhesive layer, and particularly preferably directly laminated with the conductive adhesive layer on one surface and directly laminated with the silver nanowire layer on the other surface.
(conductive adhesive layer)
The conductive adhesive layer has, for example, adhesiveness for bonding the shielding film of the present invention to a printed wiring board and conductivity for electrically connecting to the silver nanowire layer. And also functions as a shielding layer that exhibits shielding performance together with the silver nanowire layer. The conductive adhesive layer may be a single layer or a plurality of layers.
The conductive adhesive layer contains a binder component and spherical or dendritic conductive particles.
Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray-curable compounds. The binder component may be used alone or in combination of two or more.
Examples of the thermoplastic resin include polystyrene resin, vinyl acetate resin, polyester resin, polyolefin resin (e.g., polyethylene resin, polypropylene resin composition, etc.), polyimide resin, and acrylic resin. The thermoplastic resin may be used alone, or two or more kinds thereof may be used.
Examples of the thermosetting resin include both a resin having thermosetting properties (thermosetting resin) and a resin obtained by curing the thermosetting resin. Examples of the thermosetting resin include phenol resins, epoxy resins, polyurethane urea resins, melamine resins, alkyd resins, and the like. The thermosetting resin may be used alone or in combination of two or more.
Examples of the epoxy resin include bisphenol epoxy resins, spiro (spirocyclic) epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, terpene epoxy resins, glycidyl ether epoxy resins, glycidyl amine epoxy resins, and (novolac) epoxy resins.
Examples of the bisphenol epoxy resin include bisphenol a epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, tetrabromobisphenol a epoxy resin, and the like. Examples of the glycidyl ether type epoxy resin include tris (glycidyl ether oxyphenyl) methane and tetrakis (glycidyl ether oxyphenyl) ethane. Examples of the glycidyl amine type epoxy resin include tetraglycidyl diaminodiphenylmethane and the like. Examples of the (novolac) type epoxy resin include cresol (novolac) type epoxy resin, phenol (novolac) type epoxy resin, α -naphthol (novolac) type epoxy resin, and brominated phenol (novolac) type epoxy resin.
Examples of the active energy ray-curable compound include both a compound curable by irradiation with an active energy ray (active energy ray-curable compound) and a compound obtained by curing the active energy ray-curable compound. The active energy ray-curable compound is not particularly limited, and examples thereof include polymerizable compounds having at least 2 radical-reactive groups (e.g., (meth) acryloyl groups) in the molecule. The active energy ray-curable compound may be used alone or in combination of two or more.
Among them, the binder component is preferably a thermosetting resin. In this case, after the shielding film of the present invention is disposed on a printed wiring board for bonding to the printed wiring board, the adhesive component can be cured by applying pressure and heat, and the bonding property to the printed wiring board is good.
When the binder component includes a thermosetting resin, a curing agent for promoting a thermosetting reaction may be included as a component constituting the binder component. The curing agent can be appropriately selected according to the kind of the thermosetting resin. The curing agent may be used alone or in combination of two or more.
The content of the binder component in the conductive adhesive layer is not particularly limited, and is preferably 20 to 99 mass%, more preferably 30 to 80 mass%, and further preferably 40 to 70 mass% with respect to 100 mass% of the total amount of the conductive adhesive layer. When the content is 20% by mass or more, the adhesiveness to a printed wiring board is more excellent. When the content ratio is 99% by mass or less, the conductive particles can be sufficiently contained.
Spherical conductive particles and/or dendritic conductive particles are used as the conductive particles. By using the spherical or dendritic conductive particles, excellent transparency and excellent connection stability can be obtained even when a large amount of the particles is mixed. Among the conductive particles, the conductive particles are preferably dendritic conductive particles from the viewpoint of better connection stability. In addition, the conductive particles are preferably spherical conductive particles from the viewpoint of excellent transparency of the shielding film.
Examples of the conductive particles include metal particles, metal-coated resin particles, and carbon-based fillers. The conductive particles may be used alone, or two or more kinds thereof may be used.
Examples of the metal constituting the coating portion of the metal particles and the metal-coated resin particles include gold, silver, copper, nickel, and zinc. The metal may be used alone or in combination of two or more.
Specifically, examples of the metal particles include copper particles, silver particles, nickel particles, silver-coated copper particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, and silver-coated alloy particles. Examples of the silver-coated alloy particles include 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 electrolytic method, an atomization method, a reduction method, or the like.
Among them, the metal particles are preferably silver particles, silver-coated copper particles, or silver-coated copper alloy particles. Silver-coated copper particles and silver-coated copper alloy particles are particularly preferable from the viewpoint of excellent conductivity, suppression of oxidation and coagulation of metal particles, and reduction in cost of metal particles.
The median diameter (D50) of the conductive particles is not particularly limited, but is preferably 5 to 15 μm, more preferably 5 to 10 μm. The median diameter is a median diameter of all spherical conductive particles and/or dendritic conductive particles in the conductive adhesive layer, and refers to a particle diameter at a cumulative value of 50% in a particle size distribution obtained by a laser diffraction/seed scattering method. By making the median diameter within the above range, the connection stability in the present invention using the conductive particles is more excellent. The median diameter can be measured, for example, by a laser diffraction particle size analyzer (trade name "SALD-2200", manufactured by Shimadzu corporation).
The content of the conductive particles in the conductive adhesive layer is 1 to 80 mass%, preferably 20 to 70 mass%, and more preferably 30 to 60 mass% with respect to 100 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 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 up to 80 mass%.
The conductive adhesive layer may contain other components than the above components within a range not to impair the effects of the present invention. The other components include those contained in a known or commonly used adhesive layer. Examples of the other components include a curing accelerator, a plasticizer, a flame retardant, an antifoaming agent, a viscosity adjuster, an antioxidant, a diluent, an anti-settling agent, a filler, a leveling agent, a coupling agent, an ultraviolet absorber, a tackifying resin, and an anti-blocking agent. The other components may be used alone or in combination of two or more. On the other hand, the content of the conductive particles other than the spherical conductive particles and the 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, based on 100 parts by mass of the spherical conductive particles and/or the dendritic conductive particles.
The thickness of the conductive adhesive layer is not particularly limited, but is preferably 3 to 20 μm, and more preferably 5 to 15 μm. When the thickness is 3 μm or more, the shielding performance is more excellent. When the thickness is 20 μm or less, the surface of the conductive particles tends to be closer to the surface of the layer or exposed from the surface, and the connection stability is more excellent.
The ratio [ adhesive layer thickness/D50 ] of the thickness of the conductive adhesive layer to the D50 of the conductive particles is not particularly limited, but is preferably 0.2 to 1.5, and more preferably 0.5 to 1.0. When the ratio is 0.2 or more, the bondability to the object to be bonded such as a printed wiring board is further improved. When the ratio is 1.5 or less, the amount of the conductive particles exposed from the surface of the conductive adhesive layer is large, and the connection stability is more excellent.
The shielding film of the present invention may contain a separator (release film) on the conductive adhesive layer side. The separator is laminated so as to be peelable from the shielding film of the present invention. The separator is an element 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 separator include a polyethylene terephthalate (PET) film, a polyethylene film, a polypropylene film, a plastic film coated with a release agent such as a fluorine-based release agent or a long-chain alkyl acrylate-based release agent, and paper.
The thickness of the separator is preferably 10 to 200 μm, more preferably 15 to 150 μm. When the thickness is 10 μm or more, the protective property is more excellent. When the thickness is 200 μm or less, the separator is easily peeled off at the time of use.
The shielding film of the present invention may contain other layers than the 1 st insulating layer, the silver nanowire layer, the 2 nd insulating layer, and the conductive adhesive layer. Examples of the other layer include other insulating layers, antireflection layers, antiglare layers, antifouling layers, hard coat layers, ultraviolet absorbing layers, and anti-newton ring layers.
The shielding film of the present invention is excellent in transparency. The total light transmittance of the shielding film of the present invention in a measurement method according to JIS K7361-1 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 known spectrophotometer. The total light transmittance was measured for a laminate having the 1 st insulating layer and the conductive adhesive layer as both end layers.
The haze value of the shielding film of the present invention in the measurement method according to JIS K7361-1 is preferably 95% or less, more preferably 92% or less, and further preferably 90% or less. The haze value can be measured using a well-known spectrophotometer. The haze value was measured for a laminate having the insulating layer 1 and the conductive adhesive layer as both end layers.
The shielding film of the present invention is preferably used for a printed wiring board, and particularly preferably used for a flexible printed wiring board (FPC). The shielding film of the present invention can reduce the connection resistance value even when a small amount of conductive particles or a large amount of conductive particles are mixed in the conductive adhesive layer. And the transparency is excellent, and the contraposition on the printed circuit board is easy. Therefore, the shielding film of the present invention can be suitably used as an electromagnetic wave shielding film for a flexible printed wiring board.
(method for producing electromagnetic wave shielding film)
A method for producing a shielding film of the present invention will be described.
In the operation of manufacturing the shielding film 1 of the present invention shown in fig. 1, first, the silver nanowire layer 12 is formed on the 1 st insulating layer 11. The silver nanowire layer 12 can be formed by laminating the silver nanowire layer 12 on the surface of the 1 st insulating layer 11.
Next, the surface of the formed silver nanowire layer 12 can be formed by, for example, applying (coating) a resin composition for forming the 2 nd insulating layer 13, and removing the solvent and/or partially curing it as necessary.
The resin composition may contain a solvent (solvent) in addition to the components contained in the insulating layer 2. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, ethyl acetate, propyl acetate, butyl acetate, and dimethylformamide. The solid content concentration of the resin composition is appropriately set according to the thickness of the 2 nd insulating layer to be formed.
The resin composition can be applied by a known coating method. For example, a gravure roll coater, a reverse roll coater, an oil feed roll coater, a lip coater dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, a direct coater, a slit coater, or the like can be used.
Next, an adhesive composition for forming the conductive adhesive layer 14 can be applied (coated) on the surface of the insulating layer 2 to be formed, and the composition can be formed by removing the solvent and/or partially curing the composition as necessary.
The adhesive composition may contain a solvent (solvent) in addition to the components contained in the conductive adhesive layer. Examples of the solvent include those exemplified as the solvent which can be contained in the resin composition. The solid content concentration of the adhesive composition is appropriately set in accordance with the thickness of the conductive adhesive layer to be formed, and the like.
The adhesive composition can be applied by a known coating method. Examples thereof include coaters used for coating the resin composition.
In the above-described manufacturing method, a method (direct coating method) of forming each layer in sequence has been described, but the method is not limited to the above-described method, and for example, the method (lamination method) of laminating each layer formed separately on a temporary substrate such as a release film or a substrate and bonding the layers in sequence may be used.
The shielding film of the present invention can be used to manufacture a printed wiring board. For example, a shielded printed wiring board in which the shielding film of the present invention is bonded to a printed wiring board (for example, a cover film) can be obtained by bonding the conductive adhesive layer of the shielding film of the present invention to the printed wiring board. In the shielded printed wiring board, the conductive adhesive layer may be thermally cured.
Examples
The present invention will be described in further detail below with reference to examples, but the present invention is not limited to these examples. The content ratio of the conductive particles in the table indicates the ratio in the conductive adhesive layer.
Comparative example 1
A silver nanowire layer (wire diameter 30nm, wire length 20 μm, thickness about 70 nm) was laminated on the surface of a PET film (thickness 6 μm). Then, an adhesive composition obtained by mixing an epoxy resin solution and conductive particles a was applied to the surface of the silver nanowire layer using a wire bar, and the mixture was heated at 120 ℃ for 1 minute to form a conductive adhesive layer (thickness 5 μm). The shielding film of comparative example 1 was produced as described above. The amount of the epoxy resin solution and the conductive particles a was set to an amount such that the ratio of the epoxy resin in the conductive adhesive layer was 70 mass% and the ratio of the conductive particles a was 30 mass%.
Comparative examples 2 and 3
Each shielding film was produced in the same manner as in comparative example 1 except that the kind and content ratio of the conductive particles were changed as shown in table 1.
Example 1
A silver nanowire layer (wire diameter 30nm, wire length 20 μm, thickness about 70 nm) was laminated on the surface of a PET film (thickness 6 μm). Next, a polyester resin composition was applied to the surface of the silver nanowire layer using a wire bar, and heated at 100 ℃ for 1 minute, thereby forming a resin layer (thickness 50 nm). Then, an adhesive composition obtained by mixing and mixing an epoxy resin solution and conductive particles a was applied to the surface of the resin layer by wire bar coating, and heated at 120 ℃ for 1 minute to form a conductive adhesive layer (thickness 5 μm). The shielding film of example 1 was produced as above. The amount of the epoxy resin solution and the conductive particles a was set to 70 mass% of the epoxy resin and 30 mass% of the conductive particles a in the conductive adhesive layer.
Examples 2 and 3 and comparative example 4
Each of the shielding films 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.
Example 4
A shielding film was produced in the same manner as in example 11 except that the content ratio of the conductive particles was changed as shown in table 1.
Examples 5 and 6 and comparative example 5
Each of the shielding films was produced in the same manner as in example 4 except that the thickness of the resin layer was changed as shown in table 1.
Example 7
A shielding film was produced in the same manner as in example 1 except that the types of conductive particles were changed as shown in table 1.
Examples 8 and 9 and comparative example 6
Each of the shielding films was produced in the same manner as in example 4 except that the thickness of the resin layer was changed as shown in table 1.
(evaluation)
Each of the shielding films obtained in examples and comparative examples was evaluated as follows. The evaluation results are set forth in the table. Only a PET film (thickness: 6 μm) was used as an evaluation object in reference example 1. Further, "OL" in the table is represented as a value exceeding the measurement limit of 100 Ω due to overload.
(1) Connection resistance value
Preparing the following printed circuit base materials: on a base member made of a polyimide film, 2 copper foil patterns (4 mm wide and 1mm pitch) similar to a ground pattern were formed, and a cover film (insulating film) made of an insulating adhesive layer and a polyimide film was formed thereon. And a gold plating layer is arranged on the surface of the copper foil pattern to be used as a surface layer. And a circular opening portion simulating a ground connection portion having a diameter of 0.8mm is formed in the cover film. Using a press at temperature: 170 ℃ and time: 30 minutes, pressure: the shielding films and the printed wiring substrates produced in the examples and comparative examples were bonded under a pressure of 2 to 3 MPa. After the shield film was bonded, the resistance values between 2 copper foil patterns were measured by a resistance meter, and the connectivity between the copper foil patterns and the conductive bonding sheet was evaluated as a connection resistance value.
(2) Total light transmittance
The shielding films obtained in examples and comparative examples were measured by irradiating measurement light with the PET film surface as an integrating sphere side in accordance with JIS K7361-1 using a nephelometer apparatus (trade name "NDH 4000", manufactured by japan electrochrome industries, ltd.).
[ Table 1]
Figure 357571DEST_PATH_IMAGE002
When a silver nanowire layer 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 value, and excellent connection stability even when a large amount of conductive particles is added up to 30 to 50 mass% (examples 1 to 9). In addition, compared with the use of dendritic conductive particles (examples 7 to 9), in the use of spherical conductive particles (examples 1 to 6) in the total light transmittance high, transparency tendency. On the other hand, when dendritic conductive particles are used (examples 7 to 9), the connection resistance value tends to be low and the connection stability tends to be excellent, as compared with the case where spherical conductive particles are used (examples 1 to 6). On the other hand, in the case where no resin layer was present between the silver nanowire layer and the conductive adhesive layer (comparative examples 1 to 3), the connection resistance value was high in the case where the same kind of conductive particles were used at the same ratio under the condition of a large amount of blending of 30 mass% or more (examples 1 to 9).
Description of the numbering
1 Shielding film
11 the 1 st insulating layer
12 silver nanowire layer
13 nd 2 nd insulating layer
14 conductive adhesive layer.

Claims (6)

1. An electromagnetic wave shielding film, characterized in that:
a 1 st insulating layer, a silver nanowire layer, a 2 nd insulating layer, and a conductive adhesive layer are laminated in this order;
the thickness of the 2 nd insulating layer is 50-500 nm;
the conductive adhesive layer includes a binder component and spherical or dendritic conductive particles;
the content ratio of the conductive particles is 1-80% 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 2 nd insulating layer and the conductive adhesive layer are directly laminated.
3. The electromagnetic wave-shielding film according to claim 1, wherein:
the 2 nd insulating layer is directly laminated on one surface of the conductive adhesive layer and directly laminated on the other surface of the silver nanowire layer.
4. The electromagnetic wave shielding film according to any one of claims 1 to 3, characterized in that:
the content ratio of the conductive particles is 30-80% 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 total light transmittance in the measurement method according to JIS K7361-1 was 10% or more.
6. A shielded printed wiring board characterized in that:
the shielding printed wiring board includes the electromagnetic wave shielding film according to any one of claims 1 to 5.
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