TWI807242B - Electromagnetic wave shielding film and shielding printed wiring board - 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 prepared in a conductive adhesive layer.

The electromagnetic shielding film of the present invention is laminated with a first insulating layer, a transparent conductive layer, a second insulating layer and a conductive adhesive layer in sequence; the aforementioned transparent conductive layer is a metal layer with a thickness of 5-100 nm and is made of gold, silver, copper, palladium, nickel, aluminum or an alloy thereof; the thickness of the aforementioned second insulating layer is 50-1000 nm; the aforementioned conductive adhesive layer includes a binder component and spherical or dendritic conductive particles; The adhesive agent layer is 100 mass % and 1-80 mass %.

Description

Electromagnetic wave shielding film and shielding printed wiring board

The present invention relates to an electromagnetic wave shielding film. More specifically, this invention relates to the electromagnetic wave shielding film used for a printed wiring board.

Background technique

Printed wiring boards are widely used in electronic devices such as mobile phones, cameras, and notebook computers to incorporate circuits in mechanisms. In addition, it is also used in the connection between the movable part and the control part of the print head of the printer. Electromagnetic wave shielding measures are required in such electronic equipment, and shielded printed wiring boards with electromagnetic wave shielding measures are also used for printed wiring boards used in devices.

In shielding printed wiring boards, in order to achieve electromagnetic wave shielding measures, an electromagnetic wave shielding film (hereinafter sometimes simply referred to as "shielding film") is used. For example, a shielding film to be used next to a 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.

Regarding shielding films having conductive adhesive sheets, for example, those disclosed in Patent Documents 1 and 2 are known. The above-mentioned shielding film is used by bonding the exposed surface of the conductive adhesive sheet to the surface of the printed wiring board. Specifically, the shielding film is used by bonding the exposed surface of the conductive adhesive sheet to the surface of the cover film provided on the surface of the printed wiring board. These conductive bonding sheets are usually thermocompressed under high temperature/high pressure conditions, and then bonded and laminated on the printed wiring board. Thereby, the shielding film arrange|positioned on a printed wiring board can exhibit the performance (shielding performance) of shielding the electromagnetic wave from the outside of a printed wiring board.

Prior art literature patent documents

[Patent Document 1] Japanese Patent Laid-Open No. 2015-110769

[Patent Document 2] Japanese Unexamined Patent Publication No. 2012-28334

Summary of the invention

In recent years, shielding films have sometimes been required to perform alignment easily when sticking to printed wiring boards. Therefore, transparency tends to be required for a barrier film. As a method of improving the transparency, for example, using a thin transparent conductive layer as the conductive layer of the shielding film is considered.

However, in conventional shielding films, the more the amount of conductive particles blended in the conductive adhesive layer increases, the higher the conductivity will be. On the contrary, in the shielding film that has used a transparent conductive layer, if a large amount of conductive particles are blended in the conductive adhesive layer, there will be a problem that the electrical connection resistance value will increase and the conductivity will decrease.

The present invention was made in view of the above, and an object of the present invention is to provide an electromagnetic wave shielding film that has excellent transparency and low electrical connection resistance even when a large amount of conductive particles are blended in a conductive adhesive layer.

The inventors of the present invention conducted repeated studies to achieve the above object, and 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 is prepared in a conductive adhesive layer. This invention is completed based on the said knowledge.

That is, the present invention provides an electromagnetic wave shielding film, which is sequentially laminated with a first insulating layer, a transparent conductive layer, a second insulating layer and a conductive adhesive layer; the above-mentioned transparent conductive layer is a metal layer with a thickness of 5-100 nm and is composed of gold, silver, copper, palladium, nickel, aluminum or an alloy containing more than one of these metals; the thickness of the above-mentioned second insulating layer is 50-1000 nm; 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 relative to 100% by mass of the conductive adhesive layer.

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

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

It is preferable that the content ratio of the said electroconductive particle is 30-80 mass % with respect to 100 mass % of the said electroconductive adhesive agent layers.

The total light transmittance of the above-mentioned electromagnetic wave shielding film in accordance with the measuring method of JIS K 7361-1 is preferably more than 10%.

Moreover, this invention provides the shielded printed wiring board provided with the said electromagnetic wave shielding film.

The electromagnetic shielding film of the present invention has excellent transparency and low electrical 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.

1: shielding film

11: The first insulating layer

12: Transparent conductive layer

13: The second 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.

form for carrying out the invention

[shielding film]

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

One embodiment of the shielding film of the present invention will be described below. FIG. 1 is a schematic cross-sectional view showing an embodiment of the shielding film of the present invention. The shielding film 1 of the present invention shown in Fig. 1 has sequentially The first insulating layer 11 , the transparent conductive layer 12 , the second insulating layer 13 and the conductive adhesive layer 14 .

(1st insulating layer)

The first insulating layer is a transparent substrate that protects the transparent conductive layer and functions as a support for the transparent conductive layer in the shielding film of the present invention. As for a 1st insulating layer, a plastic base material (especially a plastic film), a glass plate, etc. are mentioned, for example. The first insulating layer may be a single layer or a laminate of the same type or different types.

As for the resin constituting the above-mentioned plastic substrate, for example, 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, 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, etc.; Formic esters; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate, and polybutylene terephthalate (PBT); polycarbonate (PC); polyimide (PI); polyetheretherketone (PEEK); Acrylic resins such as polymethyl methacrylate (PMMA); acrylonitrile-butadiene-styrene copolymer (ABS); fluororesins; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as cellulose triacetate (TAC); silicone resins, etc. The above-mentioned resins may be used alone or in combination of two or more. From the standpoint of more excellent transparency, among the above-mentioned resins, polyester and cellulose resins are preferable, and polyethylene terephthalate and cellulose triacetate are more preferable.

For the purpose of improving the adhesion and retention of the adjacent layers such as the transparent conductive layer, the surface of the first insulating layer (especially the side surface of the transparent conductive 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 exposure treatment, and ionizing radiation treatment; chemical treatments such as chromic acid treatment; Surface treatment for improving adhesion is preferably performed on the entire surface of the first insulating layer on the side of the transparent conductive layer.

The thickness of the first insulating layer is not particularly limited, but is preferably 1-15 μm, preferably 3-10 μm. If the above-mentioned thickness is 1 μm or more, the shielding film and the protection of the transparent conductive layer can be more fully supported. When the said thickness is 15 micrometers or less, transparency and flexibility are excellent, and it is also economically advantageous. Furthermore, when the first insulating layer has a multi-layer structure, the thickness of the first insulating layer is the sum of the thicknesses of all the layers.

(transparent conductive layer)

The above-mentioned transparent conductive layer is a requirement for functioning as a shielding layer in the shielding film of the present invention. The above-mentioned transparent conductive layer may be a single layer or a laminate of the same type or different types.

The above-mentioned transparent conductive layer is composed of gold, silver, copper, palladium, nickel, aluminum or an alloy containing one or more of these metals. Such a transparent conductive layer has shielding performance without losing excellent transparency.

Examples of the above alloys include silver/copper alloys, silver/zinc alloys, silver/tin alloys, silver/palladium alloys, silver/nickel alloys, silver/aluminum alloys, silver/bismuth alloys, silver/germanium alloys, silver/yttrium alloys, silver/neodymium alloys, silver/scandium alloys, silver/indium alloys, silver/antimony alloys, and silver/gallium alloys. Among the above metals, copper and silver are preferable from the standpoint of better electromagnetic wave shielding performance, and silver/copper alloys are preferable from the standpoint of preventing silver from being vulcanized by sulfur components or corroded by chlorine contained in sweat, etc. during solder reflow or when using a shielding film in a high-temperature and high-humidity environment.

The thickness of the above-mentioned transparent conductive layer is preferably 5-100 nm, preferably 10-50 nm. When the above-mentioned thickness is 5 nm or more, shielding performance can be maintained. When the said thickness is 100 nm or less, the transparency of a shielding film is excellent. Furthermore, when the transparent conductive layer has a multi-layer structure, the thickness of the transparent conductive layer is the sum of the thicknesses of all the layers. In addition, the thickness of the transparent conductive layer can be calculated by measuring the cross section of the transparent conductive layer with a transmission electron microscope (TEM).

The method for forming the above-mentioned transparent conductive layer is not particularly limited, for example, electrolysis, evaporation (such as vacuum evaporation), sputtering, CVD, metal-organic (MO), plating, calendering, etc. can be mentioned. Among them, from the viewpoint of ease of manufacture, a transparent conductive layer formed by vapor deposition or sputtering is preferable.

(2nd insulating layer)

The second insulating layer is a transparent layer for protecting the transparent conductive layer. By interposing the second insulating layer between the transparent conductive layer and the conductive adhesive layer, it is possible to suppress a decrease in transparency and connection stability. The decrease in the above-mentioned transparency and connection stability is presumed to be because the transparent conductive layer is damaged by friction with the conductive particles in the conductive adhesive layer. The second insulating layer may be a single layer or a plurality of layers.

The second insulating layer preferably contains a binder component. Examples of the binder component include thermoplastic resins, thermosetting resins, active energy ray-curable compounds, and the like. Regarding the above-mentioned thermoplastic resin, thermosetting resin, and active energy ray-curable compound, respectively, those exemplified as adhesive components that can be contained in the conductive adhesive layer described later are mentioned. The said binder component may use only 1 type, and may use 2 or more types.

The content of the binder component in the second insulating layer is not particularly limited, but is preferably at least 70% by mass, preferably at least 80% by mass, more preferably at least 90% by mass, relative to 100% by mass of the second insulating layer. When the above-mentioned content is 70% by mass or more, the flexibility will be more excellent, the filling property into small-diameter holes will be better, and the connection stability will be more excellent.

The second insulating layer may contain components other than the above-mentioned binder components within the range that does not impair the effects of the present invention. Regarding the above-mentioned other components, for example, hardeners, hardening accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, thinners, anti-settling agents, fillers, leveling agents, coupling agents, ultraviolet absorbers, tackifying resins, anti-blocking agents, etc. can be mentioned. The above-mentioned other components may be used alone or in combination of two or more.

The thickness of the second insulating layer is 50-1000 nm, preferably 100-300 nm. When the above-mentioned thickness is 50 nm or more, shielding performance and connection stability are excellent. When the said thickness is 1000 nm or less, transparency and connection stability are excellent. Furthermore, when the second insulating layer has a multi-layer structure, the thickness of the second insulating layer is the sum of the thicknesses of all the layers.

From the viewpoint of protecting the above-mentioned transparent conductive layer, the second insulating layer is preferably directly laminated with the above-mentioned conductive adhesive layer, and it is especially preferable to directly laminate with the above-mentioned conductive adhesive layer on one side, and on the other side and the upper layer. The above-mentioned transparent conductive layer is directly laminated.

(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 transparent conductive layer. Moreover, it can also function as a shielding layer exhibiting shielding performance together with the above-mentioned transparent conductive layer. The above-mentioned conductive adhesive layer may be any of a single layer or a plurality of layers.

The above-mentioned conductive adhesive layer contains a binder component and spherical or dendritic (dendrite) conductive particles.

Examples of the binder component include thermoplastic resins, thermosetting resins, active energy ray-curable compounds, and the like. The said binder component may use only 1 type, and may use 2 or more types.

Regarding the aforementioned thermoplastic resins, for example, polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (such as polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, acrylic resins, etc. can be cited. The above-mentioned thermoplastic resins may be used alone or in combination of two or more.

Examples of the above-mentioned thermosetting resin include both resins having thermosetting properties (thermosetting resins) and resins obtained by curing the above-mentioned thermosetting resins. As for the said thermosetting resin, a phenol resin, an epoxy resin, a urethane resin, a urethane urea resin, a melamine resin, an alkyd resin, etc. are mentioned, for example. The above-mentioned 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, glycidylamine 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, and tetrabromobisphenol A epoxy resin. about As said glycidyl ether type epoxy-type resin, ginseng (glycidoxy phenyl) methane, tetrakis (glycidoxy phenyl) ethane, etc. are mentioned, for example. Tetraglycidyldiaminodiphenylmethane etc. are mentioned about the said glycidylamine type epoxy resin. Examples of the novolac epoxy resin include cresol novolak epoxy resins, phenol novolac epoxy resins, α-naphthol novolac epoxy resins, and brominated phenol novolak epoxy resins.

Examples of the active energy ray-curable compound include both compounds curable by irradiation with active energy rays (active energy ray-curable compounds) and compounds obtained by curing the above-mentioned active energy ray-curable compounds. The active energy ray-curing compound is not particularly limited, but examples thereof include polymerizable compounds having at least two radical reactive groups (for example, (meth)acryl groups) in the molecule. The above-mentioned active energy ray-curing compound may be used alone, or two or more kinds may be used.

Among the above-mentioned binder components, a thermosetting resin is preferable. At this time, in order to adhere to the printed wiring board, the shielding film of the present invention can be placed on the printed wiring board, and then the adhesive component is hardened by pressing and heating, so that the adhesiveness with the printed wiring board becomes good.

When the said binder component contains a thermoplastic resin, the monomer component of a thermoplastic resin may also be contained about the component which comprises the said binder component. When the adhesive component contains a monomer component, temporary adhesiveness, reworkability, and adhesion after heat and pressure are applied to the adherend become good.

When the above-mentioned binder component contains a thermosetting resin, a curing agent for promoting a thermosetting reaction may be included with respect to the components constituting the above-mentioned binder component. The said hardening|curing agent can be selected suitably according to the kind of the said thermosetting resin. The above curing agents may be used alone or in combination of two or more.

The content ratio of the adhesive component in the conductive adhesive layer is not particularly limited, but is preferably 20 to 99% by mass, preferably 30 to 80% by mass, more preferably 40 to 70% by mass, based on 100% by mass of the total amount of the conductive adhesive layer. When the said content rate is 20 mass % or more, the adhesiveness with respect to a printed wiring board will become more excellent. Electroconductive particle can be fully contained as the said content rate is 99 mass % or less.

Spherical electroconductive particle and/or dendritic electroconductive particle are used for the said electroconductive particle. By using the said spherical or dendritic electroconductive particle, even when it mix|blends a large amount, it is excellent in transparency, and it is excellent in connection stability. When spherical electroconductive particle is used, transparency is more excellent.

As said electroconductive particle, a metal particle, a metal-coated resin particle, a carbon filler, etc. are mentioned, for example. The said electroconductive particle may use only 1 type, and may use 2 or more types.

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 above-mentioned metals may be used alone or in combination of two or more.

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 (for example, copper alloy particles made of an alloy of copper, nickel, and zinc) are coated with silver. The above-mentioned metal particles can be produced by electrolysis, atomization, reduction or the like.

Among them, silver particles, silver-coated copper particles, and silver-coated copper alloy particles are preferable as the above-mentioned metal particles. Silver-coated copper particles and silver-coated copper alloy particles are preferable from the viewpoint of excellent electrical conductivity, suppression of oxidation and aggregation of metal particles, and cost reduction of metal particles.

The median diameter (D50) of the conductive particles is not particularly limited, but is preferably 5-15 μm, more preferably 5-10 μm. The above-mentioned median particle size is the median particle size of all the spherical conductive particles and/or dendritic conductive particles in the above-mentioned conductive adhesive layer, and refers to the particle size of 50% of the cumulative value in the particle size distribution obtained by the laser diffraction/scattering method. When the said median diameter exists in the said range, in this invention which uses electroconductive particle, connection stability becomes more excellent. The above-mentioned median diameter can be measured by, for example, a laser diffraction particle size distribution analyzer (trade name "SALD-2200", manufactured by Shimadzu Corporation).

The content rate of the said electroconductive particle in the said electroconductive adhesive layer is preferably 1-80 mass % with respect to 100 mass % of electroconductive adhesive layer, Preferably it is 20-70 mass %, More preferably, it is 30-60 mass %. In the shielding film of the present invention, whether the conductive adhesive layer contains a small amount of about 1% by mass In the case of the above-mentioned electroconductive particles, even in the case of including as much as 80% by mass of the above-mentioned electroconductive particles, the connection resistance value is low and the connection stability is also excellent.

In the range which does not impair the effect of this invention, the said electroconductive adhesive agent layer may contain other components other than the said each component. About the said other component, the component contained in the well-known or usual adhesive agent layer can be mentioned. Examples of the above-mentioned other components include hardening accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, thinners, anti-settling agents, fillers, leveling agents, coupling agents, ultraviolet absorbers, colorants, anti-blocking agents, and the like. The above-mentioned other components may be used alone or in combination of two or more. Furthermore, the content of conductive particles other than spherical conductive particles and dendritic conductive particles is, for example, less than 10 parts by mass, preferably less than 5 parts by mass, more preferably less than 1 part by mass relative to 100 parts by mass of spherical conductive particles and/or dendritic conductive particles.

The thickness of the conductive adhesive layer is not particularly limited, but is preferably 3-20 μm, preferably 5-15 μm. When the said thickness is 3 micrometers or more, shielding performance will be more excellent. When the said thickness is 20 micrometers or less, the surface of electroconductive particle exists in the tendency for the surface of a layer to come closer or to be exposed from the surface, and connection stability will become more excellent.

The ratio [adhesive layer thickness/D50] of the conductive adhesive layer thickness to D50 of the conductive particles is not particularly limited, but is preferably 0.2-1.5, preferably 0.5-1.0. When the said ratio is 0.2 or more, the adhesiveness with respect to to-be-adhered bodies, such as a printed wiring board, becomes more favorable. If the said ratio is 1.5 or less, the quantity of the electroconductive particle exposed from the surface of an electroconductive adhesive layer will increase, and connection stability will become more excellent.

The shielding film of the present invention may have a separator (peeling film) on the conductive adhesive layer side. The separator is laminated so as to be peelable from the masking film of the present invention. The separator is a requirement 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: polyethylene terephthalate (PET) film, polyethylene film, polypropylene film, fluorine-based release agent, or plastic film or paper coated with a release agent such as a long-chain alkyl acrylate release agent.

The thickness of the above separator is preferably 10-200 μm, preferably 15-150 μm. When the said thickness is 10 micrometers or more, protection performance is more excellent. When the said thickness is 200 micrometers or less, it becomes easy to peel off a separator at the time of use.

The shielding film of the present invention may have layers other than the first insulating layer, the transparent conductive layer, the second insulating layer, and the conductive adhesive layer. Examples of the above-mentioned other layers include other insulating layers, antireflection layers, antiglare layers, antifouling layers, hard coat layers, ultraviolet absorbing layers, and anti-Newton ring layers.

The masking film of the present invention is excellent in transparency. The total light transmittance of the shielding film of the present invention is preferably at least 10%, preferably at least 20%, more preferably at least 50%, and most preferably at least 65% under the measurement method of JIS K 7361-1. The above-mentioned total light transmittance can be measured using a known spectrometer. In addition, the said total light transmittance was measured about the laminated body which used the 1st insulating layer and the said conductive adhesive layer as both end layers.

The haze value of the shielding film of the present invention is preferably 95% or less, preferably 92% or less, more preferably 90% or less in accordance with the measurement method of JIS K 7361-1. The said haze value can be measured using a well-known spectrometer. In addition, the said haze value was measured about the laminated body which used the 1st insulating layer and the said electroconductive adhesive layer as both end layers.

The shielding film of the present invention is suitable for use in printed wiring boards or wireless power transmission systems, especially for flexible printed wiring boards (FPC) or electromagnetic induction wireless power transmission systems. The shielding film of the present invention has low electrical connection resistance regardless of whether a small amount of conductive particles or a large amount of conductive particles are mixed in the conductive adhesive layer. In addition, it is excellent in transparency, and it is easy to align on a printed wiring board or an adherend such as a coil for power supply or power transmission in a wireless power transmission system. Therefore, the shielding film of this invention can be used suitably as the electromagnetic wave shielding film for flexible printed wiring boards.

(Manufacturing method of electromagnetic wave shielding film)

The manufacturing method of the masking film of this invention is demonstrated.

In the manufacture of the shielding film 1 of the present invention shown in FIG. 1, at first the first insulating layer 11 is formed into a transparent conductive layer 12. The formation of the transparent conductive layer 12 is preferably performed by evaporation or sputtering. The above-mentioned vapor deposition method and sputtering method can employ known or commonly used methods. Thus, by forming a transparent conductive layer by vapor deposition method or sputtering method, the conductive layer which has moderate thickness and transparency can be manufactured easily.

Next, for example, a resin composition for forming the second insulating layer 13 may be coated (coated) on the surface of the formed transparent conductive layer 12, and the solvent may be removed and/or a part thereof may be cured as necessary.

The resin composition includes, for example, a solvent (vehicle) in addition to the components contained in the second insulating layer. As a solvent, for example, toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, ethyl acetate, propyl acetate, butyl acetate, dimethylformamide, etc. are mentioned. The solid content concentration of the above-mentioned resin composition is appropriately set according to the thickness of the second insulating layer to be formed, and the like.

When coating the above-mentioned resin composition, a known coating method can also be used. For example, coating machines such as a gravure roll coater, reverse roll coater, touch roll coater, die coater, dip roll coater, bar coater, knife coater, spray coater, chip coater, direct coater, slot die coater, etc. can be used.

Next, the adhesive composition for forming the conductive adhesive layer 14 can be coated (coated) on the surface of the formed second insulating layer, and the solvent can be removed and/or a part of it can be cured as necessary.

The above-mentioned adhesive composition contains, for example, a solvent (vehicle) in addition to each component contained in the above-mentioned conductive adhesive layer. As for the solvent, those exemplified as solvents that can be contained in the above-mentioned resin composition can be mentioned. The solid content concentration of the said adhesive composition can be set suitably according to the thickness etc. of the electroconductive adhesive layer to be formed.

A well-known coating method can also be used when coating the said adhesive composition. For example, the coater used for coating of the said resin composition mentioned above is mentioned as an example.

In addition, in the above-mentioned production method, the method of sequentially forming each layer (direct coating method) was described, but it is not limited to this method. For example, it can also be produced by laminating and sequentially laminating each layer formed on a temporary base material such as a separation membrane or a base material (lamination method).

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 shielding film of the present invention to a printed wiring board (for example, a cover film), a shielded printed wiring board having the shielding film of the present invention bonded to the printed wiring board can be obtained. In the said shielded printed wiring board, the said electroconductive adhesive layer can also be heat-cured.

[Example]

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the content ratio of the electroconductive particle in a table shows the ratio in a conductive adhesive agent layer.

Comparative example 1

A silver/copper alloy layer (thickness 10 nm) was formed on the surface of the PET film (thickness 6 μm) by sputtering. Then, use a wire bar to coat the adhesive composition obtained by mixing epoxy resin solution and conductive particles A (silver-coated copper powder, spherical shape, median diameter 5 μm) on the surface of the alloy layer, and heat at 120° C. for 1 minute to form a conductive adhesive layer (thickness 5 μm). As mentioned above, the masking film of the comparative example 1 was produced. Moreover, the compounding quantity of the epoxy resin solution and electroconductive particle A was set to the quantity which made the ratio of the epoxy resin in the electroconductive adhesive layer 70 mass %, and the ratio of electroconductive particle A was 30 mass %.

Comparative example 2~4

Except having changed the kind and content ratio of electroconductive particle as shown in Table 1, it carried out similarly to the comparative example 1, and produced each masking film. Moreover, electroconductive particle B is a silver-coated copper powder (dendritic shape, median diameter 5 micrometers).

Example 1

A silver/copper alloy layer (thickness 10 nm) was formed on the surface of the PET film (thickness 6 μm) by sputtering. Next, a polyester resin composition was coated on the surface of the alloy layer using a wire bar, and heated at 100° C. for 1 minute to form a resin layer (thickness: 50 nm). Then, the adhesive composition obtained by mixing the epoxy resin solution and conductive particles A was coated on the surface of the resin layer using a wire bar, and heated at 120° C. for 1 minute to form a conductive adhesive layer (thickness 5 μm). As described above, the masking film of Example 1 was produced. Also, epoxy resin The compounding quantity of liquid and electroconductive particle A was set so that the ratio of the epoxy resin in the electroconductive adhesive layer may be 70 mass %, and the ratio of electroconductive particle A shall be 30 mass %.

Embodiment 2～4 and comparative example 5,6

Except having changed the thickness of the resin layer as shown in Table 1, it carried out similarly to Example 1, and each masking film was produced.

Example 5

Except having changed the content ratio of electroconductive particle as shown in Table 1, it carried out similarly to Example 1, and produced the masking film.

Embodiment 6～8 and comparative example 7,8

Except having changed the thickness of the resin layer as shown in Table 1, it carried out similarly to Example 5, and each masking film was produced.

Example 9

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

Embodiment 10～12 and comparative example 9,10

Except having changed the thickness of the resin layer as shown in Table 1, it carried out similarly to Example 9, and each masking film was produced.

(evaluate)

Each masking film obtained by the Example and the comparative example was evaluated as follows. The evaluation results are shown in the table. In addition, only the PET film (thickness 6 micrometers) was used as the evaluation object of the reference example 1. In addition, "OL" in the table represents the value exceeding 100Ω which is the measurement limit due to overload.

(1) Connection resistance value

Prepare the printed wiring board as follows: 2 copper foil patterns (4 mm wide, 1 mm pitch) for simulating grounding patterns are formed on the base member made of polyimide film, and an insulating adhesive layer and poly Covering film (insulating film) made of imide film. A gold-plated layer is provided on the surface of the copper foil pattern as a surface layer. Furthermore, a circular opening simulating a ground connection portion with a diameter of 0.8 mm was formed in the cover film. The masking film and the printed wiring board prepared in each example and comparative example were bonded under the conditions of temperature 170° C., time 30 minutes, and pressure: 2 to 3 MPa using a press machine. After the shielding film is applied, the resistance value between the two copper foil patterns is measured with a resistance meter, and the connection between the copper foil pattern and the conductive adhesive sheet is evaluated as the connection resistance value.

(2) Total light transmittance

The masking films obtained in Examples and Comparative Examples were measured by irradiating measurement light with the PET film surface facing 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] (Table 1)

When a silver/copper alloy layer with a thickness of 10nm is used as the transparent conductive layer, the shielding film of the present invention still has high total light transmittance, excellent transparency, low connection resistance, and excellent connection stability even when a large amount of conductive particles is prepared in an amount of 30-50% by mass (Examples 1-12). Moreover, the case of using spherical electroconductive particle (Examples 1-4) tended to have a high total light transmittance and excellent transparency compared with the case of using dendritic electroconductive particle (Example 9-12). On the other hand, in the case where there is no resin layer between the silver/copper alloy layer and the conductive adhesive layer (Comparative Examples 1-4), and under the conditions of a large amount of 30% by mass or more, The result is a higher connection resistance value. In addition, the case where the thickness of the resin layer was 2000 nm or more was the same, and as a result, the connection resistance value was high (comparative examples 5 to 10).

1: shielding film

11: The first insulating layer

12: Transparent conductive layer

13: The second insulating layer

14: Conductive adhesive layer

Claims (6)

An electromagnetic wave shielding film, which is sequentially laminated with a first insulating layer, a transparent conductive layer, a second insulating layer, and a conductive adhesive layer; the aforementioned transparent conductive layer is a metal layer with a thickness of 5-100 nm and is composed of gold, silver, copper, palladium, nickel, aluminum, or an alloy containing more than one of these metals; the thickness of the aforementioned second insulating layer is 50-1000 nm; the aforementioned conductive adhesive layer includes a binder component and spherical or dendritic conductive particles; The content rate is 1-80 mass % with respect to 100 mass % of said electroconductive adhesive layer. The electromagnetic shielding film according to claim 1, wherein the second insulating layer and the conductive adhesive layer are directly laminated. The electromagnetic wave shielding film according to claim 1, wherein the second insulating layer is directly laminated on one side with the aforementioned conductive adhesive layer, and is directly laminated with the aforementioned transparent conductive layer on the other side. The electromagnetic shielding film according to any one of claims 1 to 3, wherein the content ratio of the conductive particles is 30 to 80% by mass relative to 100% by mass of the conductive adhesive layer. The electromagnetic wave shielding film according to any one of claims 1 to 3, which has a total light transmittance of 10% or more in accordance with the measuring method of JIS K 7361-1. A shielded printed wiring board, comprising the electromagnetic wave shielding film according to any one of Claims 1 to 5.